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c638e434-4cb4-4e75-84c5-7a3cd79f334c | c638e434-4cb4-4e75-84c5-7a3cd79f334c | c638e434-4cb4-4e75-84c5-7a3cd79f334c | human | null | null | none | abstracts | Developing the Galactic diffuse emission model for the GLAST Large Area
Telescope | null | Diffuse emission is produced in energetic cosmic ray (CR) interactions, mainly protons and electrons, with the interstellar gas and radiation field and contains the information about particle spectra in distant regions of the Galaxy. It may also contain information about exotic processes such as dark matter annihilation, black hole evaporation etc. A model of the diffuse emission is important for determination of the source positions and spectra. Calculation of the Galactic diffuse continuum gamma-ray emission requires a model for CR propagation as the first step. Such a model is based on theory of particle transport in the interstellar medium as well as on many kinds of data provided by different experiments in Astrophysics and Particle and Nuclear Physics. Such data include: secondary particle and isotopic production cross sections, total interaction nuclear cross sections and lifetimes of radioactive species, gas mass calibrations and gas distribution in the Galaxy (H_2, H I, H II |
994de64b-5b33-4557-ab4f-175650e1bb72 | 994de64b-5b33-4557-ab4f-175650e1bb72 | 994de64b-5b33-4557-ab4f-175650e1bb72 | human | null | null | none | abstracts | Prompt Emission of High Energy Photons from Gamma Ray Bursts | null | Within the internal shock scenario we consider different mechanisms of high energy ($>1$ MeV) photon production inside a Gamma Ray Burst (GRB) fireball and derive the expected high energy photon spectra from individual GRBs during the prompt phase. The photon spectra of leptonic and hadronic origins are compared within different sets of parameter regimes. Our results suggest that the high energy emission is dominated by the leptonic component if fraction of shock energy carried by electrons is not very small (e.g. $\epsilon_e > 10^{-3}$). For very small values of $\epsilon_e$ the hadronic emission component could be comparable to or even exceed the leptonic component in the GeV-TeV regime. However, in this case a much larger energy budget of the fireball is required to account for the same level of the observed sub-MeV spectrum. The fireballs are therefore extremely inefficient in radiation. For a canonical fireball bulk Lorentz factor (e.g. $\Gamma=400$), emissions above $\sim 10$ G |
c942a7b7-92c0-437b-8d94-126e25c0cf7f | c942a7b7-92c0-437b-8d94-126e25c0cf7f | c942a7b7-92c0-437b-8d94-126e25c0cf7f | human | null | null | none | abstracts | Resummation Effects in the Search of SM Higgs Boson at Hadron Colliders | null | We examine the soft-gluon resummation effects, including the exact spin correlations among the final state particles, in the search of the Standard Model Higgs boson, via the process $gg\to H\to WW/ZZ \to 4 leptons, at the Tevatron and the LHC. A comparison between the resummation and the Next-to-Leading order (NLO) calculation is performed after imposing various kinematics cuts suggested in the literature for the Higgs boson search. For the $H\to ZZ$ mode, the resummation effects increase the acceptance of the signal events by about 25%, as compared to the NLO prediction, and dramatically alter various kinematics distributions of the final state leptons. For the $H\to WW$ mode, the acceptance rates of the signal events predicted by the resummation and NLO calculations are almost the same, but some of the predicted kinematical distributions are quite different. Thus, to precisely determine the properties of the Higgs boson at hadron colliders, the soft-gluon resummation effects have |
36f6bb9d-ed3c-4d08-8557-8121d7799880 | 36f6bb9d-ed3c-4d08-8557-8121d7799880 | 36f6bb9d-ed3c-4d08-8557-8121d7799880 | human | null | null | none | abstracts | Prediction of future fifteen solar cycles | null | In the previous study (Hiremath 2006a), the solar cycle is modeled as a forced and damped harmonic oscillator and from all the 22 cycles (1755-1996), long-term amplitudes, frequencies, phases and decay factor are obtained. Using these physical parameters of the previous 22 solar cycles and by an {\em autoregressive model}, we predict the amplitude and period of the future fifteen solar cycles. Predicted amplitude of the present solar cycle (23) matches very well with the observations. The period of the present cycle is found to be 11.73 years. With these encouraging results, we also predict the profiles of future 15 solar cycles. Important predictions are : (i) the period and amplitude of the cycle 24 are 9.34 years and 110 ($\pm 11$), (ii) the period and amplitude of the cycle 25 are 12.49 years and 110 ($\pm$ 11), (iii) during the cycles 26 (2030-2042 AD), 27 (2042-2054 AD), 34 (2118-2127 AD), 37 (2152-2163 AD) and 38 (2163-2176 AD), the sun might experience a very high sunspot act |
64e96a18-1c6e-4ef3-a5cf-8e5fbce521b7 | 64e96a18-1c6e-4ef3-a5cf-8e5fbce521b7 | 64e96a18-1c6e-4ef3-a5cf-8e5fbce521b7 | human | null | null | none | abstracts | Fast recursive filters for simulating nonlinear dynamic systems | null | A fast and accurate computational scheme for simulating nonlinear dynamic systems is presented. The scheme assumes that the system can be represented by a combination of components of only two different types: first-order low-pass filters and static nonlinearities. The parameters of these filters and nonlinearities may depend on system variables, and the topology of the system may be complex, including feedback. Several examples taken from neuroscience are given: phototransduction, photopigment bleaching, and spike generation according to the Hodgkin-Huxley equations. The scheme uses two slightly different forms of autoregressive filters, with an implicit delay of zero for feedforward control and an implicit delay of half a sample distance for feedback control. On a fairly complex model of the macaque retinal horizontal cell it computes, for a given level of accuracy, 1-2 orders of magnitude faster than 4th-order Runge-Kutta. The computational scheme has minimal memory requirements, |
8e953edf-08bc-4c46-81d6-fb1f5d853388 | 8e953edf-08bc-4c46-81d6-fb1f5d853388 | 8e953edf-08bc-4c46-81d6-fb1f5d853388 | human | null | null | none | abstracts | Anisotropy and Magnetic Field Effects on the Genuine Multipartite
Entanglement of Multi-Qubit Heisenberg {\it XY} Chains | null | It has been shown that, for the two-qubit Heisenberg XY model, anisotropy and magnetic field may together be used to produce entanglement for any finite temperature by adjusting the external magnetic field beyond some finite critical strength. This interesting result arises from an analysis employing the Wootters concurrence, a computable measure of entanglement for two-qubit states. Recently, Mintert {\em et al.} proposed generalizations of Wootters concurrence for multipartite states. These MKB concurrences possess a mathematical property that enables one to understand the origin of this characteristic behavior. Here, we first study the effect of anisotropy and magnetic field on the multipartite thermal entanglement of a four-qubit Heisenberg XY chain using the MKB concurrences. We show that this model exhibits characteristic behavior similar to that of the two-qubit model. In addition, we show that this can again be understood using the same mathematical property. Next, we show th |
352225e0-debf-4fd7-83e0-a75cfd2547fd | 352225e0-debf-4fd7-83e0-a75cfd2547fd | 352225e0-debf-4fd7-83e0-a75cfd2547fd | human | null | null | none | abstracts | A Language-Based Approach for Improving the Robustness of Network
Application Protocol Implementations | null | The secure and robust functioning of a network relies on the defect-free implementation of network applications. As network protocols have become increasingly complex, however, hand-writing network message processing code has become increasingly error-prone. In this paper, we present a domain-specific language, Zebu, for describing protocol message formats and related processing constraints. From a Zebu specification, a compiler automatically generates stubs to be used by an application to parse network messages. Zebu is easy to use, as it builds on notations used in RFCs to describe protocol grammars. Zebu is also efficient, as the memory usage is tailored to application needs and message fragments can be specified to be processed on demand. Finally, Zebu-based applications are robust, as the Zebu compiler automatically checks specification consistency and generates parsing stubs that include validation of the message structure. Using a mutation analysis in the context of SIP and RT |
52d5ccd8-9820-4676-92ad-8c96feb85ea1 | 52d5ccd8-9820-4676-92ad-8c96feb85ea1 | 52d5ccd8-9820-4676-92ad-8c96feb85ea1 | human | null | null | none | abstracts | A Panchromatic Study of the Globular Cluster NGC 1904. I: The Blue
Straggler Population | null | By combining high-resolution (HST-WFPC2) and wide-field ground based (2.2m ESO-WFI) and space (GALEX) observations, we have collected a multi-wavelength photometric data base (ranging from the far UV to the near infrared) of the galactic globular cluster NGC1904 (M79). The sample covers the entire cluster extension, from the very central regions up to the tidal radius. In the present paper such a data set is used to study the BSS population and its radial distribution. A total number of 39 bright ($m_{218}\le 19.5$) BSS has been detected, and they have been found to be highly segregated in the cluster core. No significant upturn in the BSS frequency has been observed in the outskirts of NGC 1904, in contrast to other clusters (M 3, 47 Tuc, NGC 6752, M 5) studied with the same technique. Such evidences, coupled with the large radius of avoidance estimated for NGC 1904 ($r_{avoid}\sim 30$ core radii), indicate that the vast majority of the cluster heavy stars (binaries) has already sun |
fee640b1-9e01-467c-b484-3a1c276d4154 | fee640b1-9e01-467c-b484-3a1c276d4154 | fee640b1-9e01-467c-b484-3a1c276d4154 | human | null | null | none | abstracts | What Can be Learned Studying the Distribution of the Biggest Fragment ? | null | In the canonical formalism of statistical physics, a signature of a first order phase transition for finite systems is the bimodal distribution of an order parameter. Previous thermodynamical studies of nuclear sources produced in heavy-ion collisions provide information which support the existence of a phase transition in those finite nuclear systems. Some results suggest that the observable Z1 (charge of the biggest fragment) can be considered as a reliable order parameter of the transition. This talk will show how from peripheral collisions studied with the INDRA detector at GSI we can obtain this bimodal behaviour of Z1. Getting rid of the entrance channel effects and under the constraint of an equiprobable distribution of excitation energy (E*), we use the canonical description of a phase transition to link this bimodal behaviour with the residual convexity of the entropy. Theoretical (with and without phase transition) and experimental Z1-E* correlations are compared. This comp |
d211de25-585c-4f97-9bf1-97d80643a279 | d211de25-585c-4f97-9bf1-97d80643a279 | d211de25-585c-4f97-9bf1-97d80643a279 | human | null | null | none | abstracts | Reconstructing the Intrinsic Triaxial Shape of the Virgo Cluster | null | To use galaxy clusters as a cosmological probe, it is important to account for their triaxiality. Assuming that the triaxial shapes of galaxy clusters are induced by the tidal interaction with the surrounding matter, Lee and Kang recently developed a reconstruction algorithm for the measurement of the axial ratio of a triaxial cluster. We examine the validity of this reconstruction algorithm by performing an observational test of it with the Virgo cluster as a target. We first modify the LK06 algorithm by incorporating the two dimensional projection effect. Then, we analyze the 1275 member galaxies from the Virgo Cluster Catalogue and find the projected direction of the Virgo cluster major axis by measuring the anisotropy in the spatial distribution of the member galaxies in the two dimensional projected plane. Applying the modified reconstruction algorithm to the analyzed data, we find that the axial ratio of the triaxial Virgo cluster is (1: 0.54 : 0.73). This result is consistent |
5d59df5a-7985-48dd-ad9f-9bd7b3316b87 | 5d59df5a-7985-48dd-ad9f-9bd7b3316b87 | 5d59df5a-7985-48dd-ad9f-9bd7b3316b87 | human | null | null | none | abstracts | Dynamic fracture of icosahedral model quasicrystals: A molecular
dynamics study | null | Ebert et al. [Phys. Rev. Lett. 77, 3827 (1996)] have fractured icosahedral Al-Mn-Pd single crystals in ultrahigh vacuum and have investigated the cleavage planes in-situ by scanning tunneling microscopy (STM). Globular patterns in the STM-images were interpreted as clusters of atoms. These are significant structural units of quasicrystals. The experiments of Ebert et al. imply that they are also stable physical entities, a property controversially discussed currently. For a clarification we performed the first large scale fracture simulations on three-dimensional complex binary systems. We studied the propagation of mode I cracks in an icosahedral model quasicrystal by molecular dynamics techniques at low temperature. In particular we examined how the shape of the cleavage plane is influenced by the clusters inherent in the model and how it depends on the plane structure. Brittle fracture with no indication of dislocation activity is observed. The crack surfaces are rough on the scal |
c05e8460-dbb4-4a2c-8464-f4af70ea2384 | c05e8460-dbb4-4a2c-8464-f4af70ea2384 | c05e8460-dbb4-4a2c-8464-f4af70ea2384 | human | null | null | none | abstracts | A unified projection formalism for the Al-Pd-Mn quasicrystal
Xi-approximants and their metadislocations | null | The approximants xi, xi' and xi'_n of the quasicrystal Al-Mn-Pd display most interesting plastic properties as for example phason-induced deformation processes (Klein, H., Audier, M., Boudard, M., de Boissieu, M., Beraha, L., and Duneau, M., 1996, Phil. Mag. A, 73, 309.) or metadislocations (Klein, H., Feuerbacher, M., Schall, P., and Urban, K., 1999, Phys. Rev. Lett., 82, 3468.). Here we demonstrate that the phases and their deformed or defected states can be described by a simple projection formalism in three-dimensional space - not as usual in four to six dimensions. With the method we can interpret microstructures observed with electron microscopy as phasonic phase boundaries. Furthermore we determine the metadislocations of lowest energy and relate them uniquely to experimentally observed ones. Since moving metadislocations in the xi'-phase can create new phason-planes, we suggest a dislocation induced phase transition from xi' to xi'_n. The methods developed in this paper can a |
dc96fce4-fe8c-49fd-ac3c-4b8a0547587b | dc96fce4-fe8c-49fd-ac3c-4b8a0547587b | dc96fce4-fe8c-49fd-ac3c-4b8a0547587b | human | null | null | none | abstracts | The blue plume population in dwarf spheroidal galaxies: genuine blue
stragglers or young stellar population? | null | Abridged... Blue stragglers (BSS) are thought to be the product of either primordial or collisional binary systems. In the context of dwarf spheroidal galaxies it is hard to firmly disentangle a genuine BSS population from young main sequence (MS) stars tracing a ~1-2 Gyr old star forming episode. Assuming that their blue plume populations are made of BSS, we estimate the BSS frequency for 8 Local Group non star-forming dwarf galaxies, using a compilation of ground and space based photometry. Our results can be summarized as follows: (i) The BSS frequency in dwarf galaxies, at any given Mv, is always higher than that in globular clusters of similar luminosities; (ii) the BSS frequency for the lowest luminosity dwarf galaxies is in excellent agreement with that observed in the Milky Way halo; and most interestingly (iii) derive a statistically significant anti-correlation between the BSS frequency and the galaxy Mv. The low density, almost collision-less, environments of our dwarf |
6cb3e00d-e655-4069-8662-db79517913ad | 6cb3e00d-e655-4069-8662-db79517913ad | 6cb3e00d-e655-4069-8662-db79517913ad | human | null | null | none | abstracts | Heisenberg antiferromagnet with anisotropic exchange on the Kagome
lattice: Description of the magnetic properties of volborthite | null | We study the properties of the Heisenberg antiferromagnet with spatially anisotropic nearest-neighbour exchange couplings on the kagome net, i.e. with coupling J in one lattice direction and couplings J' along the other two directions. For J/J' > 1, this model is believed to describe the magnetic properties of the mineral volborthite. In the classical limit, it exhibits two kinds of ground states: a ferrimagnetic state for J/J' < 1/2 and a large manifold of canted spin states for J/J' > 1/2. To include quantum effects self-consistently, we investigate the Sp(N) symmetric generalisation of the original SU(2) symmetric model in the large-N limit. In addition to the dependence on the anisotropy, the Sp(N) symmetric model depends on a parameter kappa that measures the importance of quantum effects. Our numerical calculations reveal that in the kappa-J/J' plane, the system shows a rich phase diagram containing a ferrimagnetic phase, an incommensurate phase, and a decoupled chain phase, th |
2fc841eb-9be8-4ed4-a52d-69b690ef9b43 | 2fc841eb-9be8-4ed4-a52d-69b690ef9b43 | 2fc841eb-9be8-4ed4-a52d-69b690ef9b43 | human | null | null | none | abstracts | Deformed Wigner crystal in a one-dimensional quantum dot | null | The spatial Fourier spectrum of the electron density distribution in a finite 1D system and the distribution function of electrons over single-particle states are studied in detail to show that there are two universal features in their behavior, which characterize the electron ordering and the deformation of Wigner crystal by boundaries. The distribution function has a $\delta$-like singularity at the Fermi momentum $k_F$. The Fourier spectrum of the density has a step-like form at the wavevector $2k_F$, with the harmonics being absent or vanishing above this threshold. These features are found by calculations using exact diagonalization method. They are shown to be caused by Wigner ordering of electrons, affected by the boundaries. However the common Luttinger liquid model with open boundaries fails to capture these features, because it overestimates the deformation of the Wigner crystal. An improvement of the Luttinger liquid model is proposed which allows one to describe the above |
df579248-0b43-4595-90da-d4c07eddb212 | df579248-0b43-4595-90da-d4c07eddb212 | df579248-0b43-4595-90da-d4c07eddb212 | human | null | null | none | abstracts | Structures in the Universe and Origin of Galaxies | null | The analysis of images (of obtained in various ranges of the lengths of waves) of luminous objects in the Universe by means of a method of multilevel dynamic contrasting led author to the conclusions: a) the structures of all observable galaxies represents a complicated constructions which have the tendency to self-similarity and made of separate (basic) blocks, which are a coaxially tubular structures and a cartwheel-like structures; b) the majority of observable objects in the Universe are luminous butt-ends of almost invisible (of almost completely transparent) of filamentary formations which structures are seen only near to their luminous butt-ends; c) the result of analysis of images of cosmic objects show the structure of many pairs of cooperating galaxies point to opportunity of their formation at butt-ends generated in a place of break of the similar filament; d) the interacting galaxies (M 81 and M 82) show they are butt-ends of sawed off of two branches of a treelike filame |
f7e5d13c-b8e7-499a-ae9a-b12c8a1f2e54 | f7e5d13c-b8e7-499a-ae9a-b12c8a1f2e54 | f7e5d13c-b8e7-499a-ae9a-b12c8a1f2e54 | human | null | null | none | abstracts | U B V R I Photometry of Stellar Structures throughout the Disk of the
Barred Galaxy NGC 3367 | null | We report new detailed surface U, B, V, R, and I photometry of 81 stellar structures in the disk of the barred galaxy NGC 3367. The images show many different structures indicating that star formation is going on in the most part of the disk. NGC 3367 is known to have a very high concentration of molecular gas distribution in the central regions of the galaxy and bipolar synchrotron emission from the nucleus with two lobes (at 6 kpc) forming a triple structure similar to a radio galaxy. We have determined the U, B, V, R, and I magnitudes and U - B, B - V, U - V, and V - I colors for the central region (nucleus), a region which includes supernovae 2003 AA, and 79 star associations throughout NGC 3367. Estimation of ages of star associations is very difficult due to several factors, among them: filling factor, metallicity, spatial distribution of each structure and the fact that we estimated the magnitudes with a circular aperture of 16 pixels in diameter, equivalent to $6''.8\sim1.4$ |
d57cb11d-aba6-48de-bbe0-3ea28227e6ff | d57cb11d-aba6-48de-bbe0-3ea28227e6ff | d57cb11d-aba6-48de-bbe0-3ea28227e6ff | human | null | null | none | abstracts | Chaos and Symmetry in String Cosmology | null | We review the recently discovered interplay between chaos and symmetry in the general inhomogeneous solution of many string-related Einstein-matter systems in the vicinity of a cosmological singularity. The Belinsky-Khalatnikov-Lifshitz-type chaotic behaviour is found, for many Einstein-matter models (notably those related to the low-energy limit of superstring theory and M-theory), to be connected with certain (infinite-dimensional) hyperbolic Kac-Moody algebras. In particular, the billiard chambers describing the asymptotic cosmological behaviour of pure Einstein gravity in spacetime dimension d+1, or the metric-three-form system of 11-dimensional supergravity, are found to be identical to the Weyl chambers of the Lorentzian Kac-Moody algebras AE_d, or E_{10}, respectively. This suggests that these Kac-Moody algebras are hidden symmetries of the corresponding models. There even exists some evidence of a hidden equivalence between the general solution of the Einstein-three-form syst |
b294b2d7-cf77-4d40-bc94-42dd6bb1be26 | b294b2d7-cf77-4d40-bc94-42dd6bb1be26 | b294b2d7-cf77-4d40-bc94-42dd6bb1be26 | human | null | null | none | abstracts | Radio Emission from the Intermediate-mass Black Hole in the Globular
Cluster G1 | null | We have used the Very Large Array (VLA) to search for radio emission from the globular cluster G1 (Mayall-II) in M31. G1 has been reported by Gebhardt et al. to contain an intermediate-mass black hole (IMBH) with a mass of ~2 x 10^4 solar masses. Radio emission was detected within an arcsecond of the cluster center with an 8.4 GHz power of 2 x 10^{15} W/Hz. The radio/X-ray ratio of G1 is a few hundred times higher than that expected for a high-mass X-ray binary in the cluster center, but is consistent with the expected value for accretion onto an IMBH with the reported mass. A pulsar wind nebula is also a possible candidate for the radio and X-ray emission from G1; future high-sensitivity VLBI observations might distinguish between this possibility and an IMBH. If the radio source is an IMBH, and similar accretion and outflow processes occur for hypothesized ~ 1000-solar-mass black holes in Milky Way globular clusters, they are within reach of the current VLA and should be detectable |
950912c1-80db-4102-be61-423f967f4cd7 | 950912c1-80db-4102-be61-423f967f4cd7 | 950912c1-80db-4102-be61-423f967f4cd7 | human | null | null | none | abstracts | Landau-Lifshitz sigma-models, fermions and the AdS/CFT correspondence | null | We define Landau-Lifshitz sigma models on general coset space $G/H$, with $H$ a maximal stability sub-group of $G$. These are non-relativistic models that have $G$-valued N\"other charges, local $H$ invariance and are classically integrable. Using this definition, we construct the $PSU(2,2|4)/PS(U(2|2)^2)$ Landau-Lifshitz sigma-model. This sigma model describes the thermodynamic limit of the spin-chain Hamiltonian obtained from the complete one-loop dilatation operator of the N=4 super Yang-Mills (SYM) theory. In the second part of the paper, we identify a number of consistent truncations of the Type IIB Green-Schwarz action on $AdS_5\times S^5$ whose field content consists of two real bosons and 4,8 or 16 real fermions. We show that $\kappa$-symmetry acts trivially in these sub-sectors. In the context of the large spin limit of the AdS/CFT correspondence, we map the Lagrangians of these sub-sectors to corresponding truncations of the $PSU(2,2|4)/PS(U(2|2)^2)$ Landau-Lifshitz sigma-m |
3a7f92a6-3d28-41c0-a317-5d7bb1806639 | 3a7f92a6-3d28-41c0-a317-5d7bb1806639 | 3a7f92a6-3d28-41c0-a317-5d7bb1806639 | human | null | null | none | abstracts | Sparse Estimators and the Oracle Property, or the Return of Hodges'
Estimator | null | We point out some pitfalls related to the concept of an oracle property as used in Fan and Li (2001, 2002, 2004) which are reminiscent of the well-known pitfalls related to Hodges' estimator. The oracle property is often a consequence of sparsity of an estimator. We show that any estimator satisfying a sparsity property has maximal risk that converges to the supremum of the loss function; in particular, the maximal risk diverges to infinity whenever the loss function is unbounded. For ease of presentation the result is set in the framework of a linear regression model, but generalizes far beyond that setting. In a Monte Carlo study we also assess the extent of the problem in finite samples for the smoothly clipped absolute deviation (SCAD) estimator introduced in Fan and Li (2001). We find that this estimator can perform rather poorly in finite samples and that its worst-case performance relative to maximum likelihood deteriorates with increasing sample size when the estimator is tun |
7768d431-5e25-456d-8d29-913400ece506 | 7768d431-5e25-456d-8d29-913400ece506 | 7768d431-5e25-456d-8d29-913400ece506 | human | null | null | none | abstracts | Capillary ordering and layering transitions in two-dimensional hard-rod
fluids | null | In this article we calculate the surface phase diagram of a two-dimensional hard-rod fluid confined between two hard lines. In a first stage we study the semi-infinite system consisting of an isotropic fluid in contact with a single hard line. We have found complete wetting by the columnar phase at the wall-isotropic fluid interface. When the fluid is confined between two hard walls, capillary columnar ordering occurs via a first-order phase transition. For higher chemical potentials the system exhibits layering transitions even for very narrow slits (near the one-dimensional limit). The theoretical model used was a density-functional theory based on the Fundamental-Measure Functional applied to a fluid of hard rectangles in the restricted-orientation approximation (Zwanzig model). The results presented here can be checked experimentally in two-dimensional granular media made of rods, where vertical motions induced by an external source and excluded volume interactions between the gr |
b142dcae-3b1e-42ee-b930-140f5cf94e32 | b142dcae-3b1e-42ee-b930-140f5cf94e32 | b142dcae-3b1e-42ee-b930-140f5cf94e32 | human | null | null | none | abstracts | TeV-scale gravity in Horava-Witten theory on a compact complex
hyperbolic threefold | null | The field equations and boundary conditions of Horava-Witten theory, compactified on a smooth compact spin quotient of CH^3, where CH^3 denotes the hyperbolic cousin of CP^3, are studied in the presence of Casimir energy density terms. If the Casimir energy densities near one boundary result in a certain constant of integration taking a value greater than around 10^5 in units of the d = 11 gravitational length, a form of thick pipe geometry is found that realizes TeV-scale gravity by the ADD mechanism, with that boundary becoming the inner surface of the thick pipe, where we live. Three alternative ways in which the outer surface of the thick pipe might be stabilized consistent with the observed value of the effective d = 4 cosmological constant are considered. In the first alternative, the outer surface is stabilized in the classical region and the constant of integration is fixed at around 10^{13} in units of the d = 11 gravitational length for consistency with the observed cosmolo |
535f5348-e429-41c8-8a00-1199d2e62991 | 535f5348-e429-41c8-8a00-1199d2e62991 | 535f5348-e429-41c8-8a00-1199d2e62991 | human | null | null | none | abstracts | Search for the radiative leptonic decay B+ --> gamma l+ nu | null | We present the results of a search for $B^{+}\to\gamma \ell^{+}\nu_{\ell}$, where $\ell = e, \mu$. We use a sample of 232 million $B\bar{B}$ pairs recorded at the $\Upsilon(4S)$ with the BaBar detector at the PEP-II $B$ Factory. We measure a partial branching fraction $\Delta\mathcal{B}$ in a restricted region of phase space that reduces the effect of theoretical uncertainties, requiring the lepton energy to be between 1.875 and 2.850GeV, the photon energy to be between 0.45 and 2.35GeV, and the cosine of the angle between the lepton and photon momenta to be less than -0.36, with all quantities computed in the $\Upsilon(4S)$ center-of-mass frame. We find $\Delta\mathcal{B}(B^{+}\to\gamma \ell^{+}\nu_{\ell}) = (-0.3^{+1.3}_{-1.5} ({stat}) \pm 0.6 ({syst}) \pm 0.1 ({th})) \times 10^{-6}$, assuming lepton universality. Interpreted as a 90% C.L. Bayesian upper limit, the result corresponds to $1.7\times10^{-6}$ for a prior flat in amplitude, and $2.3\times10^{-6}$ for a prior flat in bra |
c1db1b16-660c-42c9-a96b-1b8a92fee27d | c1db1b16-660c-42c9-a96b-1b8a92fee27d | c1db1b16-660c-42c9-a96b-1b8a92fee27d | human | null | null | none | abstracts | Magnetic structure of Sm2IrIn8 | null | The magnetic structure of the intermetallic antiferromagnet Sm2IrIn8 was determined using x-ray resonant magnetic scattering (XRMS). Below TN = 14.2, Sm2IrIn8 has a commensurate antiferromagnetic structure with a propagation vector (1/2,0,0). The Sm magnetic moments lie in the ab plane and are rotated roughly 18 degrees away from the a axis. The magnetic structure of this compound was obtained by measuring the strong dipolar resonant peak whose enhancement was of over two orders of magnitude at the L2 edge. At the L3 edge both quadrupolar and dipolar features were observed in the energy line shape. The magnetic structure and properties of Sm2IrIn8 are found to be consistent with the general trend already seen for the Nd-, Tb- and the Ce-based compounds from the RmMnIn3m+2n family (R = rare earth; M=Rh or Ir, m = 1, 2; n = 0, 1), where the crystalline electrical field (CEF) effects determine the direction of magnetic moments and the TN evolution in the series. The measured Neel temper |
1c291100-ea74-444a-b7b3-6dddcf796b52 | 1c291100-ea74-444a-b7b3-6dddcf796b52 | 1c291100-ea74-444a-b7b3-6dddcf796b52 | human | null | null | none | abstracts | Deciphering top flavor violation at the LHC with B factories | null | The LHC will have unprecedented sensitivity to flavor-changing neutral current (FCNC) top quark decays, whose observation would be a clear sign of physics beyond the standard model. Although many details of top flavor violation are model dependent, the standard model gauge symmetries relate top FCNCs to other processes, which are strongly constrained by existing data. We study these constraints in a model independent way, using a low energy effective theory from which the new physics is integrated out. We consider the most important operators which contribute to top FCNCs and analyze the current constraints on them. We find that the data rule out top FCNCs at a level observable at the LHC due to most of the operators comprising left-handed first or second generation quark fields, while there remains a substantial window for top decays mediated by operators with right-handed charm or up quarks. If FCNC top decays are observed at the LHC, such an analysis may help decipher the underlyi |
870e0d76-44bf-486f-929b-4ee011c64a96 | 870e0d76-44bf-486f-929b-4ee011c64a96 | 870e0d76-44bf-486f-929b-4ee011c64a96 | human | null | null | none | abstracts | Exploring Infrared Properties of Giant Low Surface Brightness Galaxies | null | Abridged: We present analysis of Spitzer Space Telescope observations of the three low surface brightness (LSB) optical giant galaxies Malin 1, UGC 6614 and UGC 9024. Mid- and far-infrared morphology, spectral energy distributions, and integrated colors are used to derive the dust mass, dust-to-gas mass ratio, total infrared luminosity, and star formation rate (SFR). The 8 micron images indicate that polycyclic aromatic hydrocarbon molecules are present in the central regions of all three metal-poor LSB galaxies. The diffuse optical disks of Malin 1 and UGC 9024 remain undetected at mid- and far-infrared wavelengths. The dustiest of the three LSB galaxies, UGC 6614, has infrared morphology that varies significantly with wavelength. The 8 and 24 micron emission is co-spatial with H\alpha emission previously observed in the outer ring of UGC 6614. The estimated dust-to-gas ratios, from less than 10^{-3} to 10^{-2}, support previous indications that the LSB galaxies are relatively dust |
b04898fd-79e8-4324-b180-8ac25cd9219a | b04898fd-79e8-4324-b180-8ac25cd9219a | b04898fd-79e8-4324-b180-8ac25cd9219a | human | null | null | none | abstracts | Staggered Heavy Baryon Chiral Perturbation Theory | null | Although taste violations significantly affect the results of staggered calculations of pseudoscalar and heavy-light mesonic quantities, those entering staggered calculations of baryonic quantities have not been quantified. Here I develop staggered chiral perturbation theory in the light-quark baryon sector by mapping the Symanzik action into heavy baryon chiral perturbation theory. For 2+1 dynamical quark flavors, the masses of flavor-symmetric nucleons are calculated to third order in partially quenched and fully dynamical staggered chiral perturbation theory. To this order the expansion includes the leading chiral logarithms, which come from loops with virtual decuplet-like states, as well as terms the order of the cubed pion mass, which come from loops with virtual octet-like states. Taste violations enter through the meson propagators in loops and tree-level terms the order of the squared lattice spacing. The pattern of taste symmetry breaking and the resulting degeneracies and |
6375ef97-70a4-4c18-bb7a-e81799e66765 | 6375ef97-70a4-4c18-bb7a-e81799e66765 | 6375ef97-70a4-4c18-bb7a-e81799e66765 | human | null | null | none | abstracts | A Diagrammatic Category for the Representation Theory of U_q(sl_n) | null | This thesis provides a partial answer to a question posed by Greg Kuperberg in q-alg/9712003 and again by Justin Roberts as problem 12.18 in "Problems on invariants of knots and 3-manifolds", math.GT/0406190, essentially: "Can one describe the category of representations of the quantum group U_q(sl_n) (thought of as a spherical category) via generators and relations?" For each n \geq 0, I define a certain tensor category of trivalent graphs, modulo isotopy, and construct a functor from this category onto (a full subcategory of) the category of representations of the quantum group U_q(sl_n). One would like to describe completely the kernel of this functor, by providing generators. The resulting quotient of the diagrammatic category would then be a category equivalent to the representation category of U_q(sl_n). I make significant progress towards this, describing certain generators of the kernel, and some obstructions to further elements. It remains a conjecture that these relatio |
3513ac96-c7d3-4b92-b7a7-34f3165bf6d0 | 3513ac96-c7d3-4b92-b7a7-34f3165bf6d0 | 3513ac96-c7d3-4b92-b7a7-34f3165bf6d0 | human | null | null | none | abstracts | HST/ACS Coronagraphic Observations of the Dust Surrounding HD 100546 | null | We present ACS/HST coronagraphic observations of HD 100546, a B9.5 star, 103 pc away from the sun, taken in the F435W, F606W, and F814W bands. Scattered light is detected up to 14'' from the star. The observations are consistent with the presence of an extended flattened nebula with the same inclination as the inner disk. The well-known ``spiral arms'' are clearly observed and they trail the rotating disk material. Weaker arms never before reported are also seen. The inter-arm space becomes brighter, but the structures become more neutral in color at longer wavelengths, which is not consistent with models that assume that they are due to the effects of a warped disk. Along the major disk axis, the colors of the scattered-light relative to the star are \Delta (F435W-F606W) ~ 0.0--0.2 mags and \Delta (F435W-F814W)~0.5--1 mags. To explain these colors, we explore the role of asymmetric scattering, reddening, and large minimum sizes on ISM-like grains. We conclude each of these hypothese |
e8492d61-5b68-4109-b612-5030f4e0f1ab | e8492d61-5b68-4109-b612-5030f4e0f1ab | e8492d61-5b68-4109-b612-5030f4e0f1ab | human | null | null | none | abstracts | Gauge Invariant Factorisation and Canonical Quantisation of
Topologically Massive Gauge Theories in Any Dimension | null | Abelian topologically massive gauge theories (TMGT) provide a topological mechanism to generate mass for a bosonic p-tensor field in any spacetime dimension. These theories include the 2+1 dimensional Maxwell-Chern-Simons and 3+1 dimensional Cremmer-Scherk actions as particular cases. Within the Hamiltonian formulation, the embedded topological field theory (TFT) sector related to the topological mass term is not manifest in the original phase space. However through an appropriate canonical transformation, a gauge invariant factorisation of phase space into two orthogonal sectors is feasible. The first of these sectors includes canonically conjugate gauge invariant variables with free massive excitations. The second sector, which decouples from the total Hamiltonian, is equivalent to the phase space description of the associated non dynamical pure TFT. Within canonical quantisation, a likewise factorisation of quantum states thus arises for the full spectrum of TMGT in any dimension. |
f7ae5cb8-b453-4d27-9e1f-eb9b993da2fd | f7ae5cb8-b453-4d27-9e1f-eb9b993da2fd | f7ae5cb8-b453-4d27-9e1f-eb9b993da2fd | human | null | null | none | abstracts | Compton Scattering of Fe K alpha Lines in Magnetic Cataclysmic Variables | null | Compton scattering of X-rays in the bulk flow of the accretion column in magnetic cataclysmic variables (mCVs) can significantly shift photon energies. We present Monte Carlo simulations based on a nonlinear algorithm demonstrating the effects of Compton scattering on the H-like, He-like and neutral Fe K alpha lines produced in the post-shock region of the accretion column. The peak line emissivities of the photons in the post-shock flow are taken into consideration and frequency shifts due to Doppler effects are also included. We find that line profiles are most distorted by Compton scattering effects in strongly magnetized mCVs with a low white dwarf mass and high mass accretion rate and which are viewed at an oblique angle with respect to the accretion column. The resulting line profiles are most sensitive to the inclination angle. We have also explored the effects of modifying the accretion column width and using a realistic emissivity profile. We find that these do not have a si |
bbdaf766-145e-4d8f-a95b-900742050954 | bbdaf766-145e-4d8f-a95b-900742050954 | bbdaf766-145e-4d8f-a95b-900742050954 | human | null | null | none | abstracts | Cosmological Shock Waves in the Large Scale Structure of the Universe:
Non-gravitational Effects | null | Cosmological shock waves result from supersonic flow motions induced by hierarchical clustering of nonlinear structures in the universe. These shocks govern the nature of cosmic plasma through thermalization of gas and acceleration of nonthermal, cosmic-ray (CR) particles. We study the statistics and energetics of shocks formed in cosmological simulations of a concordance $\Lambda$CDM universe, with a special emphasis on the effects of non-gravitational processes such as radiative cooling, photoionization/heating, and galactic superwind feedbacks. Adopting an improved model for gas thermalization and CR acceleration efficiencies based on nonlinear diffusive shock acceleration calculations, we then estimate the gas thermal energy and the CR energy dissipated at shocks through the history of the universe. Since shocks can serve as sites for generation of vorticity, we also examine the vorticity that should have been generated mostly at curved shocks in cosmological simulations. We find |
ec57ae69-9bc8-4a2b-ae47-a8b495446f86 | ec57ae69-9bc8-4a2b-ae47-a8b495446f86 | ec57ae69-9bc8-4a2b-ae47-a8b495446f86 | human | null | null | none | abstracts | The orbit, mass, size, albedo, and density of (65489) Ceto/Phorcys: A
tidally-evolved binary Centaur | null | Hubble Space Telescope observations of Uranus- and Neptune-crossing object (65489) Ceto/Phorcys (provisionally designated 2003 FX128) reveal it to be a close binary system. The mutual orbit has a period of 9.554 +/- 0.011 days and a semimajor axis of 1840 +/- 48 km. These values enable computation of a system mass of (5.41 +/- 0.42) 10^18 kg. Spitzer Space Telescope observations of thermal emission at 24 and 70 microns are combined with visible photometry to constrain the system's effective radius (109 +10/-11 km) and geometric albedo (0.084 +0.021/-0.014). We estimate the average bulk density to be 1.37 +0.66/-0.32 g cm^-3, consistent with ice plus rocky and/or carbonaceous materials. This density contrasts with lower densities recently measured with the same technique for three other comparably-sized outer Solar System binaries (617) Patroclus, (26308) 1998 SM165, and (47171) 1999 TC36, and is closer to the density of the saturnian irregular satellite Phoebe. The mutual orbit of Ce |
18e78a04-3046-4736-8e80-37daad6418b8 | 18e78a04-3046-4736-8e80-37daad6418b8 | 18e78a04-3046-4736-8e80-37daad6418b8 | human | null | null | none | abstracts | Critical Current of Type-II Superconductors in a Broken Bose Glass State | null | The tilt modulus of a defective Abrikosov vortex lattice pinned by material line defects is computed using the boson analogy. It tends to infinity at long wavelength, which yields a Bose glass state that is robust to the addition of weak point-pinning centers, and which implies a restoring force per vortex line for rigid translations about mechanical equilibrium that is independent of magnetic field. It also indicates that the Bose glass state breaks into pieces along the direction of the correlated pinning centers if the latter have finite length. The critical current is predicted to crossover from two dimensional to three dimensional behavior as a function of sample thickness along the correlated pinning centers in such case. That crossover notably can occur at a film thickness that is much larger than that expected from point pins of comparable strength. The above is compared to the dependence on thickness shown by the critical current in certain films of high-temperature supercon |
3481949f-c6a7-46f9-9dde-254dd9dea75f | 3481949f-c6a7-46f9-9dde-254dd9dea75f | 3481949f-c6a7-46f9-9dde-254dd9dea75f | human | null | null | none | abstracts | Rounding of first-order phase transitions and optimal cooperation in
scale-free networks | null | We consider the ferromagnetic large-$q$ state Potts model in complex evolving networks, which is equivalent to an optimal cooperation problem, in which the agents try to optimize the total sum of pair cooperation benefits and the supports of independent projects. The agents are found to be typically of two kinds: a fraction of $m$ (being the magnetization of the Potts model) belongs to a large cooperating cluster, whereas the others are isolated one man's projects. It is shown rigorously that the homogeneous model has a strongly first-order phase transition, which turns to second-order for random interactions (benefits), the properties of which are studied numerically on the Barab\'asi-Albert network. The distribution of finite-size transition points is characterized by a shift exponent, $1/\tilde{\nu}'=.26(1)$, and by a different width exponent, $1/\nu'=.18(1)$, whereas the magnetization at the transition point scales with the size of the network, $N$, as: $m\sim N^{-x}$, with $x=.6 |
f4bb666b-7cd3-4c09-af23-2bc4d3e31da6 | f4bb666b-7cd3-4c09-af23-2bc4d3e31da6 | f4bb666b-7cd3-4c09-af23-2bc4d3e31da6 | human | null | null | none | abstracts | Discrete Nonholonomic Lagrangian Systems on Lie Groupoids | null | This paper studies the construction of geometric integrators for nonholonomic systems. We derive the nonholonomic discrete Euler-Lagrange equations in a setting which permits to deduce geometric integrators for continuous nonholonomic systems (reduced or not). The formalism is given in terms of Lie groupoids, specifying a discrete Lagrangian and a constraint submanifold on it. Additionally, it is necessary to fix a vector subbundle of the Lie algebroid associated to the Lie groupoid. We also discuss the existence of nonholonomic evolution operators in terms of the discrete nonholonomic Legendre transformations and in terms of adequate decompositions of the prolongation of the Lie groupoid. The characterization of the reversibility of the evolution operator and the discrete nonholonomic momentum equation are also considered. Finally, we illustrate with several classical examples the wide range of application of the theory (the discrete nonholonomic constrained particle, the Suslov sys |
edc9043b-c1c8-44e0-b783-84557c5eab40 | edc9043b-c1c8-44e0-b783-84557c5eab40 | edc9043b-c1c8-44e0-b783-84557c5eab40 | human | null | null | none | abstracts | The electronic structures, the equilibrium geometries and finite
temperature properties of Na_n (n=39-55) | null | Density-functional theory has been applied to investigate systematics of sodium clusters Na_n in the size range of n= 39-55. A clear evolutionary trend in the growth of their ground-state geometries emerges. The clusters at the beginning of the series (n=39-43) are symmetric and have partial icosahedral (two-shell) structure. The growth then goes through a series of disordered clusters (n=44-52) where the icosahedral core is lost. However, for n>52 a three shell icosahedral structure emerges. This change in the nature of the geometry is abrupt. In addition, density-functional molecular dynamics has been used to calculate the specific heat curves for the representative sizes n= 43, 45, 48 and 52. These results along with already available thermodynamic calculations for n= 40, 50, and 55 enable us to carry out a detailed comparison of the heat capacity curves with their respective geometries for the entire series. Our results clearly bring out strong correlation between the evolution o |
389710bd-e989-410a-a75f-dae1c55dc610 | 389710bd-e989-410a-a75f-dae1c55dc610 | 389710bd-e989-410a-a75f-dae1c55dc610 | human | null | null | none | abstracts | Galaxy evolution in the infra-red: comparison of a hierarchical galaxy
formation model with SPITZER data | null | We present predictions for the evolution of the galaxy luminosity function, number counts and redshift distributions in the IR based on the Lambda-CDM cosmological model. We use the combined GALFORM semi-analytical galaxy formation model and GRASIL spectrophotometric code to compute galaxy SEDs including the reprocessing of radiation by dust. The model, which is the same as that in Baugh et al (2005), assumes two different IMFs: a normal solar neighbourhood IMF for quiescent star formation in disks, and a very top-heavy IMF in starbursts triggered by galaxy mergers. We have shown previously that the top-heavy IMF seems to be necessary to explain the number counts of faint sub-mm galaxies. We compare the model with observational data from the SPITZER Space Telescope, with the model parameters fixed at values chosen before SPITZER data became available. We find that the model matches the observed evolution in the IR remarkably well over the whole range of wavelengths probed by SPITZER. |
ffb4d25e-0962-4e0e-ab7e-8ee7ce3405cd | ffb4d25e-0962-4e0e-ab7e-8ee7ce3405cd | ffb4d25e-0962-4e0e-ab7e-8ee7ce3405cd | human | null | null | none | abstracts | Use of Triangular Elements for Nearly Exact BEM Solutions | null | A library of C functions yielding exact solutions of potential and flux influences due to uniform surface distribution of singularities on flat triangular and rectangular elements has been developed. This library, ISLES, has been used to develop the neBEM solver that is both precise and fast in solving a wide range of problems of scientific and technological interest. Here we present the exact expressions proposed for computing the influence of uniform singularity distributions on triangular elements and illustrate their accuracy. We also present a study concerning the time taken to evaluate these long and complicated expressions \textit{vis a vis} that spent in carrying out simple quadratures. Finally, we solve a classic benchmark problem in electrostatics, namely, estimation of the capacitance of a unit square plate raised to unit volt. For this problem, we present the estimated values of capacitance and compare them successfully with some of the most accurate results available in |
f58b55c4-db60-40fe-b073-ad028039eb78 | f58b55c4-db60-40fe-b073-ad028039eb78 | f58b55c4-db60-40fe-b073-ad028039eb78 | human | null | null | none | abstracts | One-way permutations, computational asymmetry and distortion | null | Computational asymmetry, i.e., the discrepancy between the complexity of transformations and the complexity of their inverses, is at the core of one-way transformations. We introduce a computational asymmetry function that measures the amount of one-wayness of permutations. We also introduce the word-length asymmetry function for groups, which is an algebraic analogue of computational asymmetry. We relate boolean circuits to words in a Thompson monoid, over a fixed generating set, in such a way that circuit size is equal to word-length. Moreover, boolean circuits have a representation in terms of elements of a Thompson group, in such a way that circuit size is polynomially equivalent to word-length. We show that circuits built with gates that are not constrained to have fixed-length inputs and outputs, are at most quadratically more compact than circuits built from traditional gates (with fixed-length inputs and outputs). Finally, we show that the computational asymmetry function is |
9f1acc0d-2a78-4622-864c-024a6ef82de4 | 9f1acc0d-2a78-4622-864c-024a6ef82de4 | 9f1acc0d-2a78-4622-864c-024a6ef82de4 | human | null | null | none | abstracts | A method for the direct determination of the surface gravities of
transiting extrasolar planets | null | We show that the surface gravity of a transiting extrasolar planet can be calculated from only the spectroscopic orbit of its parent star and the analysis of its transit light curve. This does not require additional constraints, such as are often inferred from theoretical stellar models or model atmospheres. The planet's surface gravity can therefore be measured precisely and from only directly observable quantities. We outline the method and apply it to the case of the first known transiting extrasolar planet, HD 209458b. We find a surface gravity of g_p = 9.28 +/- 0.15 m/s, which is an order of magnitude more precise than the best available measurements of its mass, radius and density. This confirms that the planet has a much lower surface gravity that that predicted by published theoretical models of gas giant planets. We apply our method to all fourteen known transiting extrasolar planets and find a significant correlation between surface gravity and orbital period, which is rela |
9ce49892-4e8f-4aa5-8067-9efc3286a04b | 9ce49892-4e8f-4aa5-8067-9efc3286a04b | 9ce49892-4e8f-4aa5-8067-9efc3286a04b | human | null | null | none | abstracts | Optical implementation and entanglement distribution in Gaussian valence
bond states | null | We study Gaussian valence bond states of continuous variable systems, obtained as the outputs of projection operations from an ancillary space of M infinitely entangled bonds connecting neighboring sites, applied at each of $N$ sites of an harmonic chain. The entanglement distribution in Gaussian valence bond states can be controlled by varying the input amount of entanglement engineered in a (2M+1)-mode Gaussian state known as the building block, which is isomorphic to the projector applied at a given site. We show how this mechanism can be interpreted in terms of multiple entanglement swapping from the chain of ancillary bonds, through the building blocks. We provide optical schemes to produce bisymmetric three-mode Gaussian building blocks (which correspond to a single bond, M=1), and study the entanglement structure in the output Gaussian valence bond states. The usefulness of such states for quantum communication protocols with continuous variables, like telecloning and teleport |
c2fa60e9-2e25-476a-9527-d57199a49045 | c2fa60e9-2e25-476a-9527-d57199a49045 | c2fa60e9-2e25-476a-9527-d57199a49045 | human | null | null | none | abstracts | Can One Estimate The Unconditional Distribution of Post-Model-Selection
Estimators? | null | We consider the problem of estimating the unconditional distribution of a post-model-selection estimator. The notion of a post-model-selection estimator here refers to the combined procedure resulting from first selecting a model (e.g., by a model selection criterion like AIC or by a hypothesis testing procedure) and then estimating the parameters in the selected model (e.g., by least-squares or maximum likelihood), all based on the same data set. We show that it is impossible to estimate the unconditional distribution with reasonable accuracy even asymptotically. In particular, we show that no estimator for this distribution can be uniformly consistent (not even locally). This follows as a corollary to (local) minimax lower bounds on the performance of estimators for the distribution; performance is here measured by the probability that the estimation error exceeds a given threshold. These lower bounds are shown to approach 1/2 or even 1 in large samples, depending on the situation |
c26d5449-1485-408d-9fb1-5edf8a36125e | c26d5449-1485-408d-9fb1-5edf8a36125e | c26d5449-1485-408d-9fb1-5edf8a36125e | human | null | null | none | abstracts | Possible X-ray diagnostic for jet/disk dominance in Type 1 AGN | null | Using Rossi X-ray Timing Explorer Seyfert 1 and 1.2 data spanning 9 years, we study correlations between X-ray spectral features. The sample consists of 350 time-resolved spectra from 12 Seyfert 1 and 1.2 galaxies. Each spectrum is fitted to a model with an intrinsic powerlaw X-ray spectrum produced close to the central black hole that is reprocessed and absorbed by material around the black hole. To test the robustness of our results, we performed Monte Carlo simulations of the spectral sample. We find a complex relationship between the iron line equivalent width (EW) and the underlying power law index (Gamma). The data reveal a correlation between Gamma and EW which turns over at Gamma <~ 2, but finds a weak anti-correlation for steeper photon indices. We propose that this relationship is driven by dilution of a disk spectrum (which includes the narrow iron line) by a beamed jet component and, hence, could be used as a diagnostic of jet-dominance. In addition, our sample shows a st |
1e795a73-420f-46e3-9260-4162b8acc093 | 1e795a73-420f-46e3-9260-4162b8acc093 | 1e795a73-420f-46e3-9260-4162b8acc093 | human | null | null | none | abstracts | Flavour-Dependent Type II Leptogenesis | null | We reanalyse leptogenesis via the out-of-equilibrium decay of the lightest right-handed neutrino in type II seesaw scenarios, taking into account flavour-dependent effects. In the type II seesaw mechanism, in addition to the type I seesaw contribution, an additional direct mass term for the light neutrinos is present. We consider type II seesaw scenarios where this additional contribution arises from the vacuum expectation value of a Higgs triplet, and furthermore an effective model-independent approach. We investigate bounds on the flavour-specific decay asymmetries, on the mass of the lightest right-handed neutrino and on the reheat temperature of the early universe, and compare them to the corresponding bounds in the type I seesaw framework. We show that while flavour-dependent thermal type II leptogenesis becomes more efficient for larger mass scale of the light neutrinos, and the bounds become relaxed, the type I seesaw scenario for leptogenesis becomes more constrained. We also |
ffd2f037-7cef-4c6d-9523-56a6527d99ef | ffd2f037-7cef-4c6d-9523-56a6527d99ef | ffd2f037-7cef-4c6d-9523-56a6527d99ef | human | null | null | none | abstracts | The VIMOS VLT Deep Survey. The Assembly History of the Stellar Mass in
Galaxies: from the Young to the Old Universe | null | We present a detailed analysis of the Galaxy Stellar Mass Function of galaxies up to z=2.5 as obtained from the VVDS. We estimate the stellar mass from broad-band photometry using 2 different assumptions on the galaxy star formation history and show that the addition of secondary bursts to a continuous star formation history produces systematically higher (up to 40%) stellar masses. At low redshift (z=0.2) we find a substantial population of low-mass galaxies (<10^9 Msun) composed by faint blue galaxies (M_I-M_K=0.3). In general the stellar mass function evolves slowly up to z=0.9 and more significantly above this redshift. Conversely, a massive tail is present up to z=2.5 and have extremely red colours (M_I-M_K=0.7-0.8). We find a decline with redshift of the overall number density of galaxies for all masses (59+-5% for M>10^8 Msun at z=1), and a mild mass-dependent average evolution (`mass-downsizing'). In particular our data are consistent with mild/negligible (<30%) evolution up |
df859f2c-43bf-4501-8e68-bb5ba25cca66 | df859f2c-43bf-4501-8e68-bb5ba25cca66 | df859f2c-43bf-4501-8e68-bb5ba25cca66 | human | null | null | none | abstracts | Measuring energy dependent polarization in soft gamma-rays using Compton
scattering in PoGOLite | null | Linear polarization in X- and gamma-rays is an important diagnostic of many astrophysical sources, foremost giving information about their geometry, magnetic fields, and radiation mechanisms. However, very few X-ray polarization measurements have been made, and then only mono-energetic detections, whilst several objects are assumed to have energy dependent polarization signatures. In this paper we investigate whether detection of energy dependent polarization from cosmic sources is possible using the Compton technique, in particular with the proposed PoGOLite balloon-experiment, in the 25-100 keV range. We use Geant4 simulations of a PoGOLite model and input photon spectra based on Cygnus X-1 and accreting magnetic pulsars (100 mCrab). Effective observing times of 6 and 35 hours were simulated, corresponding to a standard and a long duration flight respectively. Both smooth and sharp energy variations of the polarization are investigated and compared to constant polarization signals |
c5986474-abab-4672-bf51-833c0052619b | c5986474-abab-4672-bf51-833c0052619b | c5986474-abab-4672-bf51-833c0052619b | human | null | null | none | abstracts | Burgers Turbulence | null | The last decades witnessed a renewal of interest in the Burgers equation. Much activities focused on extensions of the original one-dimensional pressureless model introduced in the thirties by the Dutch scientist J.M. Burgers, and more precisely on the problem of Burgers turbulence, that is the study of the solutions to the one- or multi-dimensional Burgers equation with random initial conditions or random forcing. Such work was frequently motivated by new emerging applications of Burgers model to statistical physics, cosmology, and fluid dynamics. Also Burgers turbulence appeared as one of the simplest instances of a nonlinear system out of equilibrium. The study of random Lagrangian systems, of stochastic partial differential equations and their invariant measures, the theory of dynamical systems, the applications of field theory to the understanding of dissipative anomalies and of multiscaling in hydrodynamic turbulence have benefited significantly from progress in Burgers turbule |
2a80de8e-eed8-4968-b109-3c46a04d713c | 2a80de8e-eed8-4968-b109-3c46a04d713c | 2a80de8e-eed8-4968-b109-3c46a04d713c | human | null | null | none | abstracts | Dynamical Coupled-Channel Model of $\pi N$ Scattering in the W $\leq$ 2
GeV Nucleon Resonance Region | null | As a first step to analyze the electromagnetic meson production reactions in the nucleon resonance region, the parameters of the hadronic interactions of a dynamical coupled-channel model, developed in {\it Physics Reports 439, 193 (2007)}, are determined by fitting the $\pi N$ scattering data. The channels included in the calculations are $\pi N$, $\eta N$ and $\pi\pi N$ which has $\pi\Delta$, $\rho N$, and $\sigma N$ resonant components. The non-resonant meson-baryon interactions of the model are derived from a set of Lagrangians by using a unitary transformation method. One or two bare excited nucleon states in each of $S$, $P$, $D$, and $F$ partial waves are included to generate the resonant amplitudes in the fits. The parameters of the model are first determined by fitting as much as possible the empirical $\pi N$ elastic scattering amplitudes of SAID up to 2 GeV. We then refine and confirm the resulting parameters by directly comparing the predicted differential cross section a |
2424e857-3a2a-42a9-b0c8-5650d6173f2f | 2424e857-3a2a-42a9-b0c8-5650d6173f2f | 2424e857-3a2a-42a9-b0c8-5650d6173f2f | human | null | null | none | abstracts | High-resolution study of a star-forming cluster in the Cep-A HW2 region | null | Due to its relatively small distance (725 pc), the Cepheus A East star-forming region is an ideal laboratory to study massive star formation processes. Based on its morphology, it has been suggested that the flattened molecular gas distribution around the YSO HW2 may be a 350-AU-radius massive protostellar disk. Goal of our work is to ascertain the nature of this structure. We have employed the Plateau de Bure Interferometer to acquire (sub-)arcsecond-resolution imaging of high-density and shock tracers, such as methyl cyanide (CH3CN) and silicon monoxide (SiO), towards the HW2 position. On the 1-arcsecond (about 725 AU) scale, the flattened distribution of molecular gas around HW2 appears to be due to the projected superposition, on the plane of the sky, of at least three protostellar objects, of which at least one is powering a molecular outflow at a small angle with respect to the line of sight. The presence of a protostellar disk around HW2 is not ruled out, but such structure is |
0ca4c1c2-2148-4fac-9b65-a95279c835e4 | 0ca4c1c2-2148-4fac-9b65-a95279c835e4 | 0ca4c1c2-2148-4fac-9b65-a95279c835e4 | human | null | null | none | abstracts | Intramolecular long-range correlations in polymer melts: The segmental
size distribution and its moments | null | Presenting theoretical arguments and numerical results we demonstrate long-range intrachain correlations in concentrated solutions and melts of long flexible polymers which cause a systematic swelling of short chain segments. They can be traced back to the incompressibility of the melt leading to an effective repulsion $u(s) \approx s/\rho R^3(s) \approx ce/\sqrt{s}$ when connecting two segments together where $s$ denotes the curvilinear length of a segment, $R(s)$ its typical size, $ce \approx 1/\rho be^3$ the ``swelling coefficient", $be$ the effective bond length and $\rho$ the monomer density. The relative deviation of the segmental size distribution from the ideal Gaussian chain behavior is found to be proportional to $u(s)$. The analysis of different moments of this distribution allows for a precise determination of the effective bond length $be$ and the swelling coefficient $ce$ of asymptotically long chains. At striking variance to the short-range decay suggested by Flory's i |
c56d4b63-4193-4b86-8bd0-946277be4166 | c56d4b63-4193-4b86-8bd0-946277be4166 | c56d4b63-4193-4b86-8bd0-946277be4166 | human | null | null | none | abstracts | A Systematic Scan for 7-colourings of the Grid | null | We study the mixing time of a systematic scan Markov chain for sampling from the uniform distribution on proper 7-colourings of a finite rectangular sub-grid of the infinite square lattice, the grid. A systematic scan Markov chain cycles through finite-size subsets of vertices in a deterministic order and updates the colours assigned to the vertices of each subset. The systematic scan Markov chain that we present cycles through subsets consisting of 2x2 sub-grids and updates the colours assigned to the vertices using a procedure known as heat-bath. We give a computer-assisted proof that this systematic scan Markov chain mixes in O(log n) scans, where n is the size of the rectangular sub-grid. We make use of a heuristic to compute required couplings of colourings of 2x2 sub-grids. This is the first time the mixing time of a systematic scan Markov chain on the grid has been shown to mix for less than 8 colours. We also give partial results that underline the challenges of proving rapid |
1bc35458-8b6f-4a19-87ff-9bdff1991486 | 1bc35458-8b6f-4a19-87ff-9bdff1991486 | 1bc35458-8b6f-4a19-87ff-9bdff1991486 | human | null | null | none | abstracts | Exciting the Magnetosphere of the Magnetar CXOU J164710.2-455216 in
Westerlund 1 | null | We describe XMM-Newton observations taken 4.3 days prior to and 1.5 days subsequent to two remarkable events that were detected with Swift on 2006 September 21 from the candidate magnetar CXOU J164710.2-455216: (1) a 20 ms burst with an energy of 1e37 erg (15-150 keV), and (2) a rapid spin-down (glitch) with a fractionap period change of 1e-4. We find that the luminosity of the pulsar increased by a factor of 100 in the interval between observations, from 1e33 to 1e35 erg/s (0.5-8.0 keV), and that its spectrum hardened. The pulsed count rate increased by a factor of 10 (0.5-8.0 keV), but the fractional rms amplitude of the pulses decreased from 65 to 11 per cent, and their profile changed from being single-peaked to exhibiting three peaks. Similar changes have been observed from other magnetars in response to outbursts, such as that of 1E 2259+586 in 2002 June. We suggest that a plastic deformation of the neutron star's crust induced a very slight twist in the external magnetic field |
a9c3894d-5a60-45f7-a0f1-deda025b1c48 | a9c3894d-5a60-45f7-a0f1-deda025b1c48 | a9c3894d-5a60-45f7-a0f1-deda025b1c48 | human | null | null | none | abstracts | Further Evidence that the Redshifts of AGN Galaxies May Contain
Intrinsic Components | null | In the decreasing intrinsic redshift (DIR) model galaxies are assumed to be born as compact objects that have been ejected with large intrinsic redshift components, z_(i), out of the nuclei of mature AGN galaxies. As young AGN (quasars) they are initially several magnitudes sub-luminous to mature galaxies but their luminosity gradually increases over 10^8 yrs, as z_(i) decreases and they evolve into mature AGN (Seyferts and radio galaxies). Evidence presented here that low- and intermediate-redshift AGN are unquestionably sub-luminous to radio galaxies is then strong support for this model and makes it likely that the high-redshift AGN (quasars) are also sub-luminous, having simply been pushed above the radio galaxies on a logz-m_(v) plot by the presence of a large intrinsic component in their redshifts. An increase in luminosity below z = 0.06 is also seen. It is associated in the DIR model with an increase in luminosity as the sources mature but, if real, is difficult to interpret |
a91300bd-0f88-4515-9f53-6b822ded5abf | a91300bd-0f88-4515-9f53-6b822ded5abf | a91300bd-0f88-4515-9f53-6b822ded5abf | human | null | null | none | abstracts | Light Curves of Dwarf Plutonian Planets and other Large Kuiper Belt
Objects: Their Rotations, Phase Functions and Absolute Magnitudes | null | (Abridged) I report new light curves and determine the rotations and phase functions of several large Kuiper Belt objects, including the dwarf planet Eris (2003 UB313). (120348) 2004 TY364 shows a light curve which if double-peaked has a period of 11.70+-0.01 hours and peak-to-peak amplitude of 0.22+-0.02 magnitudes. (84922) 2003 VS2 has a well defined double-peaked light curve of 7.41+-0.02 hours with a 0.21+-0.02 magnitude range. (126154) 2001 YH140 shows variability of 0.21+-0.04 magnitudes with a possible 13.25+-0.2 hour single-peaked period. The seven new KBOs in the sample which show no discernible variations within the uncertainties on short rotational time scales are 2001 UQ18, (55565) 2002 AW197, (119979) 2002 WC19, (120132) 2003 FY128, (136108) Eris 2003 UB313, (90482) Orcus 2004 DW, and (90568) 2004 GV9. The three medium to large sized Kuiper Belt objects 2004 TY364, Orcus and 2004 GV9 show fairly steep linear phase curves (~0.18 to 0.26 mags per degree) between phase angl |
6a348c0f-f4c9-4701-9562-0766ee9670d2 | 6a348c0f-f4c9-4701-9562-0766ee9670d2 | 6a348c0f-f4c9-4701-9562-0766ee9670d2 | human | null | null | none | abstracts | Spectral Analysis of the Chandra Comet Survey | null | We present results of the analysis of cometary X-ray spectra with an extended version of our charge exchange emission model (Bodewits et al. 2006). We have applied this model to the sample of 8 comets thus far observed with the Chandra X-ray observatory and ACIS spectrometer in the 300-1000 eV range. The surveyed comets are C/1999 S4 (LINEAR), C/1999 T1 (McNaught-Hartley), C/2000 WM1 (LINEAR), 153P/2002 (Ikeya-Zhang), 2P/2003 (Encke), C/2001 Q4 (NEAT), 9P/2005 (Tempel 1) and 73P/2006-B (Schwassmann-Wachmann 3) and the observations include a broad variety of comets, solar wind environments and observational conditions. The interaction model is based on state selective, velocity dependent charge exchange cross sections and is used to explore how cometary X-ray emission depend on cometary, observational and solar wind characteristics. It is further demonstrated that cometary X-ray spectra mainly reflect the state of the local solar wind. The current sample of Chandra observations was fi |
a04b7f8c-0e56-4f30-974e-fb7fe2b1ec2c | a04b7f8c-0e56-4f30-974e-fb7fe2b1ec2c | a04b7f8c-0e56-4f30-974e-fb7fe2b1ec2c | human | null | null | none | abstracts | Route to Lambda in conformally coupled phantom cosmology | null | In this letter we investigate acceleration in the flat cosmological model with a conformally coupled phantom field and we show that acceleration is its generic feature. We reduce the dynamics of the model to a 3-dimensional dynamical system and analyze it on a invariant 2-dimensional submanifold. Then the concordance FRW model with the cosmological constant $\Lambda$ is a global attractor situated on a 2-dimensional invariant space. We also study the behaviour near this attractor, which can be approximated by the dynamics of the linearized part of the system. We demonstrate that trajectories of the conformally coupled phantom scalar field with a simple quadratic potential crosses the cosmological constant barrier infinitely many times in the phase space. The universal behaviour of the scalar field and its potential is also calculated. We conclude that the phantom scalar field conformally coupled to gravity gives a natural dynamical mechanism of concentration of the equation of state |
3fa11bec-09c2-4a6e-b5ce-9746caeef01c | 3fa11bec-09c2-4a6e-b5ce-9746caeef01c | 3fa11bec-09c2-4a6e-b5ce-9746caeef01c | human | null | null | none | abstracts | The Peculiar Velocities of Local Type Ia Supernovae and their Impact on
Cosmology | null | We quantify the effect of supernova Type Ia peculiar velocities on the derivation of cosmological parameters. The published distant and local Ia SNe used for the Supernova Legacy Survey first-year cosmology report form the sample for this study. While previous work has assumed that the local SNe are at rest in the CMB frame (the No Flow assumption), we test this assumption by applying peculiar velocity corrections to the local SNe using three different flow models. The models are based on the IRAS PSCz galaxy redshift survey, have varying beta = Omega_m^0.6/b, and reproduce the Local Group motion in the CMB frame. These datasets are then fit for w, Omega_m, and Omega_Lambda using flatness or LambdaCDM and a BAO prior. The chi^2 statistic is used to examine the effect of the velocity corrections on the quality of the fits. The most favored model is the beta=0.5 model, which produces a fit significantly better than the No Flow assumption, consistent with previous peculiar velocity stud |
1ba239b9-7a95-4bfb-a670-0d30c7cfba5b | 1ba239b9-7a95-4bfb-a670-0d30c7cfba5b | 1ba239b9-7a95-4bfb-a670-0d30c7cfba5b | human | null | null | none | abstracts | Temperature-driven transition from the Wigner Crystal to the
Bond-Charge-Density Wave in the Quasi-One-Dimensional Quarter-Filled band | null | It is known that within the interacting electron model Hamiltonian for the one-dimensional 1/4-filled band, the singlet ground state is a Wigner crystal only if the nearest neighbor electron-electron repulsion is larger than a critical value. We show that this critical nearest neighbor Coulomb interaction is different for each spin subspace, with the critical value decreasing with increasing spin. As a consequence, with the lowering of temperature, there can occur a transition from a Wigner crystal charge-ordered state to a spin-Peierls state that is a Bond-Charge-Density Wave with charge occupancies different from the Wigner crystal. This transition is possible because spin excitations from the spin-Peierls state in the 1/4-filled band are necessarily accompanied by changes in site charge densities. We apply our theory to the 1/4-filled band quasi-one-dimensional organic charge-transfer solids in general and to 2:1 tetramethyltetrathiafulvalene (TMTTF) and tetramethyltetraselenafulv |
6bd9ac4b-8607-4d7f-9231-56b92b8f3e3b | 6bd9ac4b-8607-4d7f-9231-56b92b8f3e3b | 6bd9ac4b-8607-4d7f-9231-56b92b8f3e3b | human | null | null | none | abstracts | Stochastic fluctuations in metabolic pathways | null | Fluctuations in the abundance of molecules in the living cell may affect its growth and well being. For regulatory molecules (e.g., signaling proteins or transcription factors), fluctuations in their expression can affect the levels of downstream targets in a network. Here, we develop an analytic framework to investigate the phenomenon of noise correlation in molecular networks. Specifically, we focus on the metabolic network, which is highly inter-linked, and noise properties may constrain its structure and function. Motivated by the analogy between the dynamics of a linear metabolic pathway and that of the exactly soluable linear queueing network or, alternatively, a mass transfer system, we derive a plethora of results concerning fluctuations in the abundance of intermediate metabolites in various common motifs of the metabolic network. For all but one case examined, we find the steady-state fluctuation in different nodes of the pathways to be effectively uncorrelated. Consequentl |
d7c28993-fb95-4ec9-903b-8f5e1a2a7176 | d7c28993-fb95-4ec9-903b-8f5e1a2a7176 | d7c28993-fb95-4ec9-903b-8f5e1a2a7176 | human | null | null | none | abstracts | Exploiting Social Annotation for Automatic Resource Discovery | null | Information integration applications, such as mediators or mashups, that require access to information resources currently rely on users manually discovering and integrating them in the application. Manual resource discovery is a slow process, requiring the user to sift through results obtained via keyword-based search. Although search methods have advanced to include evidence from document contents, its metadata and the contents and link structure of the referring pages, they still do not adequately cover information sources -- often called ``the hidden Web''-- that dynamically generate documents in response to a query. The recently popular social bookmarking sites, which allow users to annotate and share metadata about various information sources, provide rich evidence for resource discovery. In this paper, we describe a probabilistic model of the user annotation process in a social bookmarking system del.icio.us. We then use the model to automatically find resources relevant to a |
c54b5b1d-8cd0-4f75-a01f-75afdfe85228 | c54b5b1d-8cd0-4f75-a01f-75afdfe85228 | c54b5b1d-8cd0-4f75-a01f-75afdfe85228 | human | null | null | none | abstracts | Personalizing Image Search Results on Flickr | null | The social media site Flickr allows users to upload their photos, annotate them with tags, submit them to groups, and also to form social networks by adding other users as contacts. Flickr offers multiple ways of browsing or searching it. One option is tag search, which returns all images tagged with a specific keyword. If the keyword is ambiguous, e.g., ``beetle'' could mean an insect or a car, tag search results will include many images that are not relevant to the sense the user had in mind when executing the query. We claim that users express their photography interests through the metadata they add in the form of contacts and image annotations. We show how to exploit this metadata to personalize search results for the user, thereby improving search performance. First, we show that we can significantly improve search precision by filtering tag search results by user's contacts or a larger social network that includes those contact's contacts. Secondly, we describe a probabilistic |
4813f797-36c7-4624-a472-3360cccd1db5 | 4813f797-36c7-4624-a472-3360cccd1db5 | 4813f797-36c7-4624-a472-3360cccd1db5 | human | null | null | none | abstracts | Settling the Complexity of Computing Two-Player Nash Equilibria | null | We settle a long-standing open question in algorithmic game theory. We prove that Bimatrix, the problem of finding a Nash equilibrium in a two-player game, is complete for the complexity class PPAD Polynomial Parity Argument, Directed version) introduced by Papadimitriou in 1991. This is the first of a series of results concerning the complexity of Nash equilibria. In particular, we prove the following theorems: Bimatrix does not have a fully polynomial-time approximation scheme unless every problem in PPAD is solvable in polynomial time. The smoothed complexity of the classic Lemke-Howson algorithm and, in fact, of any algorithm for Bimatrix is not polynomial unless every problem in PPAD is solvable in randomized polynomial time. Our results demonstrate that, even in the simplest form of non-cooperative games, equilibrium computation and approximation are polynomial-time equivalent to fixed point computation. Our results also have two broad complexity implications in mathematica |
a30577e6-4b3e-448d-9738-2e0723100ef9 | a30577e6-4b3e-448d-9738-2e0723100ef9 | a30577e6-4b3e-448d-9738-2e0723100ef9 | human | null | null | none | abstracts | Equation of State in Relativistic Magnetohydrodynamics: variable versus
constant adiabatic index | null | The role of the equation of state for a perfectly conducting, relativistic magnetized fluid is the main subject of this work. The ideal constant $\Gamma$-law equation of state, commonly adopted in a wide range of astrophysical applications, is compared with a more realistic equation of state that better approximates the single-specie relativistic gas. The paper focus on three different topics. First, the influence of a more realistic equation of state on the propagation of fast magneto-sonic shocks is investigated. This calls into question the validity of the constant $\Gamma$-law equation of state in problems where the temperature of the gas substantially changes across hydromagnetic waves. Second, we present a new inversion scheme to recover primitive variables (such as rest-mass density and pressure) from conservative ones that allows for a general equation of state and avoids catastrophic numerical cancellations in the non-relativistic and ultrarelativistic limits. Finally, selec |
8d16f433-5b1c-4360-a3f7-e9648ceb7f62 | 8d16f433-5b1c-4360-a3f7-e9648ceb7f62 | 8d16f433-5b1c-4360-a3f7-e9648ceb7f62 | human | null | null | none | abstracts | Carbon Nanotube Thin Film Field Emitting Diode: Understanding the System
Response Based on Multiphysics Modeling | null | In this paper, we model the evolution and self-assembly of randomly oriented carbon nanotubes (CNTs), grown on a metallic substrate in the form of a thin film for field emission under diode configuration. Despite high output, the current in such a thin film device often decays drastically. The present paper is focused on understanding this problem. A systematic, multiphysics based modelling approach is proposed. First, a nucleation coupled model for degradation of the CNT thin film is derived, where the CNTs are assumed to decay by fragmentation and formation of clusters. The random orientation of the CNTs and the electromechanical interaction are then modeled to explain the self-assembly. The degraded state of the CNTs and the electromechanical force are employed to update the orientation of the CNTs. Field emission current at the device scale is finally obtained by using the Fowler-Nordheim equation and integration over the computational cell surfaces on the anode side. The simulat |
24b62220-00b8-43c2-8ef4-7692ac3e377b | 24b62220-00b8-43c2-8ef4-7692ac3e377b | 24b62220-00b8-43c2-8ef4-7692ac3e377b | human | null | null | none | abstracts | Demographics of Transition Objects | null | The unusual properties of transition objects (young stars with an optically thin inner disc surrounded by an optically thick outer disc) suggest that significant disc evolution has occured in these systems. We explore the nature of these systems by examining their demographics, specifically their stellar accretion rates (Mdot) and disc masses (Mdisc) compared to those of accreting T Tauri stars of comparable age. We find that transition objects in Taurus occupy a restricted region of the Mdot vs. Mdisc plane. Compared to non-transition single stars in Taurus, they have stellar accretion rates that are typically ~10 times lower at the same disc mass and median disc masses ~4 times larger. These properties are anticipated by several proposed planet formation theories and suggest that the formation of Jovian mass planets may play a significant role in explaining the origin of at least some transition objects. Considering transition objects as a distinct demographic group among accreting |
ba674f74-eccb-41bb-ba5e-5df43c3277fa | ba674f74-eccb-41bb-ba5e-5df43c3277fa | ba674f74-eccb-41bb-ba5e-5df43c3277fa | human | null | null | none | abstracts | Two Results on Homogeneous Hessian Nilpotent Polynomials | null | Let $z=(z_1, ..., z_n)$ and $\Delta=\sum_{i=1}^n \frac {\partial^2}{\partial z^2_i}$ the Laplace operator. A formal power series $P(z)$ is said to be {\it Hessian Nilpotent}(HN) if its Hessian matrix $\Hes P(z)=(\frac {\partial^2 P}{\partial z_i\partial z_j})$ is nilpotent. In recent developments in [BE1], [M] and [Z], the Jacobian conjecture has been reduced to the following so-called {\it vanishing conjecture}(VC) of HN polynomials: {\it for any homogeneous HN polynomial $P(z)$ $($of degree $d=4$$)$, we have $\Delta^m P^{m+1}(z)=0$ for any $m>>0$.} In this paper, we first show that, the VC holds for any homogeneous HN polynomial $P(z)$ provided that the projective subvarieties ${\mathcal Z}_P$ and ${\mathcal Z}_{\sigma_2}$ of $\mathbb C P^{n-1}$ determined by the principal ideals generated by $P(z)$ and $\sigma_2(z):=\sum_{i=1}^n z_i^2$, respectively, intersect only at regular points of ${\mathcal Z}_P$. Consequently, the Jacobian conjecture holds for the symmetric polynomial maps |
e27cc405-b78c-4a9f-8796-bcc878e3dfc2 | e27cc405-b78c-4a9f-8796-bcc878e3dfc2 | e27cc405-b78c-4a9f-8796-bcc878e3dfc2 | human | null | null | none | abstracts | A Vanishing Conjecture on Differential Operators with Constant
Coefficients | null | In the recent progress [BE1], [Me] and [Z2], the well-known JC (Jacobian conjecture) ([BCW], [E]) has been reduced to a VC (vanishing conjecture) on the Laplace operators and HN (Hessian nilpotent) polynomials (the polynomials whose Hessian matrix are nilpotent). In this paper, we first show that the vanishing conjecture above, hence also the JC, is equivalent to a vanishing conjecture for all 2nd order homogeneous differential operators $\Lambda$ and $\Lambda$-nilpotent polynomials $P$ (the polynomials $P(z)$ satisfying $\Lambda^m P^m=0$ for all $m\ge 1$). We then transform some results in the literature on the JC, HN polynomials and the VC of the Laplace operators to certain results on $\Lambda$-nilpotent polynomials and the associated VC for 2nd order homogeneous differential operators $\Lambda$. This part of the paper can also be read as a short survey on HN polynomials and the associated VC in the more general setting. Finally, we discuss a still-to-be-understood connection of $ |
ce11f36a-b566-49f8-8ae5-46bb884bdb40 | ce11f36a-b566-49f8-8ae5-46bb884bdb40 | ce11f36a-b566-49f8-8ae5-46bb884bdb40 | human | null | null | none | abstracts | Locally Decodable Codes From Nice Subsets of Finite Fields and Prime
Factors of Mersenne Numbers | null | A k-query Locally Decodable Code (LDC) encodes an n-bit message x as an N-bit codeword C(x), such that one can probabilistically recover any bit x_i of the message by querying only k bits of the codeword C(x), even after some constant fraction of codeword bits has been corrupted. The major goal of LDC related research is to establish the optimal trade-off between length and query complexity of such codes. Recently [Y] introduced a novel technique for constructing locally decodable codes and vastly improved the upper bounds for code length. The technique is based on Mersenne primes. In this paper we extend the work of [Y] and argue that further progress via these methods is tied to progress on an old number theory question regarding the size of the largest prime factors of Mersenne numbers. Specifically, we show that every Mersenne number m=2^t-1 that has a prime factor p>m^\gamma yields a family of k(\gamma)-query locally decodable codes of length Exp(n^{1/t}). Conversely, if for |
39739e17-f11a-4a6e-a07c-9c46e94dd864 | 39739e17-f11a-4a6e-a07c-9c46e94dd864 | 39739e17-f11a-4a6e-a07c-9c46e94dd864 | human | null | null | none | abstracts | Effect of the Spatial Dispersion on the Shape of a Light Pulse in a
Quantum Well | null | Reflectance, transmittance and absorbance of a symmetric light pulse, the carrying frequency of which is close to the frequency of interband transitions in a quantum well, are calculated. Energy levels of the quantum well are assumed discrete, and two closely located excited levels are taken into account. A wide quantum well (the width of which is comparable to the length of the light wave, corresponding to the pulse carrying frequency) is considered, and the dependance of the interband matrix element of the momentum operator on the light wave vector is taken into account. Refractive indices of barriers and quantum well are assumed equal each other. The problem is solved for an arbitrary ratio of radiative and nonradiative lifetimes of electronic excitations. It is shown that the spatial dispersion essentially affects the shapes of reflected and transmitted pulses. The largest changes occur when the radiative broadening is close to the difference of frequencies of interband transitio |
a81e81a2-dc40-4a5c-a35c-9599df099763 | a81e81a2-dc40-4a5c-a35c-9599df099763 | a81e81a2-dc40-4a5c-a35c-9599df099763 | human | null | null | none | abstracts | Dislocation Dynamics in a Crystal Lattice (Peierls-Nabarro) Relief | null | The theory of the dislocation motion in the periodic potential relief of the crystal lattice (the Peierls-Nabarro barriers) is reviewed. On the basis of the kink mechanism the temperature dependence of the flow stress is described for a wide class of materials. The theory of quantum mechanical dislocation tunnelling through the Peierls-Nabarro barriers is extended and compared with experimental data on the plasticity of alkali halides, BCC and HCP metals at low temperatures. The behavior of the flow stress at the range of athermic anomalies is modeled by changing the mechanism of the dislocation motion from the thermally activated hopping over the barriers to the quantum tunnelling through them. Some results of previous calculations are represented in a more explicit convenient for applications form. The pronounced effect of the switching between the normal and the superconducting states on the flow stress of metals is explained on the basis of the change in the dissipative propertie |
3a020859-4a9f-4937-9f7a-2d44ecb3ee11 | 3a020859-4a9f-4937-9f7a-2d44ecb3ee11 | 3a020859-4a9f-4937-9f7a-2d44ecb3ee11 | human | null | null | none | abstracts | Spectrum of cosmic rays, produced in supernova remnants | null | Nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova remnants is employed to calculate CR spectra. The magnetic field in SNRs is assumed to be significantly amplified by the efficiently accelerating nuclear CR component. It is shown that the calculated CR spectra agree in a satisfactory way with the existing measurements up to the energy $10^{17}$ eV. The power law spectrum of protons extends up to the energy $3\times 10^{15}$ eV with a subsequent exponential cutoff. It gives a natural explanation for the observed knee in the Galactic CR spectrum. The maximum energy of the accelerated nuclei is proportional to their charge number $Z$. Therefore the break in the Galactic CR spectrum is the result of the contribution of progressively heavier species in the overall CR spectrum so that at $10^{17}$ eV the CR spectrum is dominated by iron group nuclei. It is shown that this component plus a suitably chosen extragalactic CR component can give a consistent description for t |
ec55fdf4-b073-4acf-9d18-82345a8f9802 | ec55fdf4-b073-4acf-9d18-82345a8f9802 | ec55fdf4-b073-4acf-9d18-82345a8f9802 | human | null | null | none | abstracts | Spheroidal and torsional modes of quasistatic shear oscillations in the
solid globe models of nuclear physics and pulsar astrophysics | null | The past three decades of investigation on nuclear physics and pulsar astrophysics have seen gradual recognition that elastodynamic approach to the continuum mechanics of nuclear matter provides proper account of macroscopic motions of degenerate Fermi-matter constituting interior of the nuclear material objects, the densest of all known today. This paper focuses on one theoretical issue of this development which is concerned with oscillatory behavior of a viscoelastic solid globe in the regime of quasistatic, force-free, non-compressional oscillations less investigated in the literature compared to oscillations in the regime of standing shear waves. We show that in this case the problem of computing frequency and lifetime of spheroidal and torsional modes of non-radial shear vibrations damped by viscosity can be unambiguously resolved by working from the energy balance equation and taking advantage of the Rayleigh's variational method. The efficiency of this method is demonstrated b |
e920de7d-8a0b-4490-ba7d-580b5f44c383 | e920de7d-8a0b-4490-ba7d-580b5f44c383 | e920de7d-8a0b-4490-ba7d-580b5f44c383 | human | null | null | none | abstracts | Detection of a 1258 Hz high-amplitude kilohertz quasi-periodic
oscillation in the ultra-compact X-ray binary 1A 1246-588 | null | We have observed the ultra-compact low-mass X-ray binary (LMXB) 1A 1246-588 with the Rossi X-ray Timing Explorer (RXTE). In this manuscript we report the discovery of a kilohertz quasi-periodic oscillation (QPO) in 1A 1246-588. The kilohertz QPO was only detected when the source was in a soft high-flux state reminiscent of the lower banana branch in atoll sources. Only one kilohertz QPO peak is detected at a relatively high frequency of 1258+-2 Hz and at a single trial significance of more than 7 sigma. Kilohertz QPOs with a higher frequency have only been found on two occasions in 4U 0614+09. Furthermore, the frequency is higher than that found for the lower kilohertz QPO in any source, strongly suggesting that the QPO is the upper of the kilohertz QPO pair often found in LMXBs. The full-width at half maximum is 25+-4 Hz, making the coherence the highest found for an upper kilohertz QPO. From a distance estimate of ~6 kpc from a radius expansion burst we derive that 1A 1246-588 is a |
e73039ed-c130-4c1b-a78d-2ab78f18a3c9 | e73039ed-c130-4c1b-a78d-2ab78f18a3c9 | e73039ed-c130-4c1b-a78d-2ab78f18a3c9 | human | null | null | none | abstracts | Surface gap solitons at a nonlinearity interface | null | We demonstrate existence of waves localized at the interface of two nonlinear periodic media with different coefficients of the cubic nonlinearity via the one-dimensional Gross--Pitaevsky equation. We call these waves the surface gap solitons (SGS). In the case of smooth symmetric periodic potentials, we study analytically bifurcations of SGS's from standard gap solitons and determine numerically the maximal jump of the nonlinearity coefficient allowing for the SGS existence. We show that the maximal jump vanishes near the thresholds of bifurcations of gap solitons. In the case of continuous potentials with a jump in the first derivative at the interface, we develop a homotopy method of continuation of SGS families from the solution obtained via gluing of parts of the standard gap solitons and study existence of SGS's in the photonic band gaps. We explain the termination of the SGS families in the interior points of the band gaps from the bifurcation of linear bound states in the con |
2cfc8339-cf78-417d-9bc7-579fb2004837 | 2cfc8339-cf78-417d-9bc7-579fb2004837 | 2cfc8339-cf78-417d-9bc7-579fb2004837 | human | null | null | none | abstracts | Blazar surveys with WMAP and Swift | null | We present the preliminary results from two new surveys of blazars that have direct implications on the GLAST detection of extragalactic sources from two different perspectives: microwave selection and a combined deep X-ray/radio selection. The first one is a 41 GHz flux-limited sample extracted from the WMAP 3-yr catalog of microwave point sources. This is a statistically well defined sample of about 200 blazars and radio galaxies, most of which are expected to be detected by GLAST. The second one is a new deep survey of Blazars selected among the radio sources that are spatially coincident with serendipitous sources detected in deep X-ray images (0.3-10 keV) centered on the Gamma Ray Bursts (GRB) discovered by the Swift satellite. This sample is particularly interesting from a statistical viewpoint since a) it is unbiased as GRBs explode at random positions in the sky, b) it is very deep in the X-ray band (\fx \simgt $10^{-15}$ \ergs) with a position accuracy of a few arc-seconds, |
670a2b79-f676-4e2d-ac34-718871106cbd | 670a2b79-f676-4e2d-ac34-718871106cbd | 670a2b79-f676-4e2d-ac34-718871106cbd | human | null | null | none | abstracts | Information Theoretic Proofs of Entropy Power Inequalities | null | While most useful information theoretic inequalities can be deduced from the basic properties of entropy or mutual information, up to now Shannon's entropy power inequality (EPI) is an exception: Existing information theoretic proofs of the EPI hinge on representations of differential entropy using either Fisher information or minimum mean-square error (MMSE), which are derived from de Bruijn's identity. In this paper, we first present an unified view of these proofs, showing that they share two essential ingredients: 1) a data processing argument applied to a covariance-preserving linear transformation; 2) an integration over a path of a continuous Gaussian perturbation. Using these ingredients, we develop a new and brief proof of the EPI through a mutual information inequality, which replaces Stam and Blachman's Fisher information inequality (FII) and an inequality for MMSE by Guo, Shamai and Verd\'u used in earlier proofs. The result has the advantage of being very simple in that |
335c4d2c-9395-44ac-88f8-865915f7fb65 | 335c4d2c-9395-44ac-88f8-865915f7fb65 | 335c4d2c-9395-44ac-88f8-865915f7fb65 | human | null | null | none | abstracts | Galaxy Evolution and Environment | null | The properties of galaxies are strongly correlated with their environment, with red galaxies dominating galaxy clusters and blue galaxies dominating the general field. However, not all field galaxies are young: studies of the colors, line strengths, and M/L ratios of massive early-type galaxies at 0<z<1.3 show that the most massive galaxies do not seem to care about their surroundings, and have very similar ages irrespective of their environment. There is good evidence that the growth of these galaxies does continue longer in the field than in clusters, via (nearly) dissipationless mergers of already old galaxies. These results are consistent with predictions of recent galaxy formation models, which incorporate AGN feedback to suppress star formation in the most massive halos. Systematic studies of the relation of galaxies with their environment beyond z=1 are difficult, and still somewhat contradictory. Intriguingly both the DEEP2 and VVDS surveys find that the color-density relatio |
6ef98d8d-66d3-4bcc-930c-d73283934a2d | 6ef98d8d-66d3-4bcc-930c-d73283934a2d | 6ef98d8d-66d3-4bcc-930c-d73283934a2d | human | null | null | none | abstracts | GLSM's for partial flag manifolds | null | In this paper we outline some aspects of nonabelian gauged linear sigma models. First, we review how partial flag manifolds (generalizing Grassmannians) are described physically by nonabelian gauged linear sigma models, paying attention to realizations of tangent bundles and other aspects pertinent to (0,2) models. Second, we review constructions of Calabi-Yau complete intersections within such flag manifolds, and properties of the gauged linear sigma models. We discuss a number of examples of nonabelian GLSM's in which the Kahler phases are not birational, and in which at least one phase is realized in some fashion other than as a complete intersection, extending previous work of Hori-Tong. We also review an example of an abelian GLSM exhibiting the same phenomenon. We tentatively identify the mathematical relationship between such non-birational phases, as examples of Kuznetsov's homological projective duality. Finally, we discuss linear sigma model moduli spaces in these gauged li |
06ee3396-02ae-4423-ac61-3e923165d247 | 06ee3396-02ae-4423-ac61-3e923165d247 | 06ee3396-02ae-4423-ac61-3e923165d247 | human | null | null | none | abstracts | The multiplicity of planet host stars - New low-mass companions to
planet host stars | null | We present new results from our ongoing multiplicity study of exoplanet host stars, carried out with the infrared camera SofI at ESO-NTT. We have identified new low mass companions to the planet host stars HD101930 and HD65216. HD101930AB is a wide binary systems composed of the planet host star HD101930A and its companion HD101930B which is a M0 to M1 dwarf with a mass of about 0.7Msun separated from the primary by ~73arcsec (2200AU projected separation). HD65216 forms a hierarchical triple system, with a projected separation of 253AU (angular separation of about 7arcsec) between the planet host star HD65216A and its close binary companion HD65216BC, whose two components are separated by only ~0.17arcsec (6AU of projected separation). Two VLT-NACO images separated by 3 years confirm that this system is co-moving to the planet host star. The infrared photometry of HD65216B and C is consistent with a M7 to M8 (0.089Msun), and a L2 to L3 dwarf (0.078Msun), respectively, both close to t |
bf677ab4-9aef-4d09-84c9-f55c4f1a87e3 | bf677ab4-9aef-4d09-84c9-f55c4f1a87e3 | bf677ab4-9aef-4d09-84c9-f55c4f1a87e3 | human | null | null | none | abstracts | Satellites of Simulated Galaxies: survival, merging, and their relation
to the dark and stellar halos | null | We study the population of satellite galaxies formed in a suite of N-body/gasdynamical simulations of galaxy formation in a LCDM universe. We find little spatial or kinematic bias between the dark matter and the satellite population. The velocity dispersion of the satellites is a good indicator of the virial velocity of the halo: \sigma_{sat}/V_{vir}=0.9 +/- 0.2. Applied to the Milky Way and M31 this gives V_{vir}^{MW}=109 +/- 22$ km/s and V_{vir}^{M31} = 138 +/- 35 km/s, respectively, substantially lower than the rotation speed of their disk components. The detailed kinematics of simulated satellites and dark matter are also in good agreement. By contrast, the stellar halo of the simulated galaxies is kinematically and spatially distinct from the population of surviving satellites. This is because the survival of a satellite depends on mass and on time of accretion; surviving satellites are biased toward low-mass systems that have been recently accreted by the galaxy. Our results su |
65d0e4b3-20f2-4a6a-9866-a4a0092923e6 | 65d0e4b3-20f2-4a6a-9866-a4a0092923e6 | 65d0e4b3-20f2-4a6a-9866-a4a0092923e6 | human | null | null | none | abstracts | Analysis of the Velocity Field of F and G Dwarfs in the Solar
Neighborhood as a Function of Age | null | The space velocities from the catalog of Nordstrom et al. (2004) are used to trace variations of a number of kinematic parameters of single F and G dwarfs as a function of their age. The vertex deviation of disk stars increases from 7+- 1 to 15+-2 degrees as the mean age decreases from 4.3 to 1.5 Gyr. The two-dimensional velocity distributions in the UV, UW, and VW planes are analyzed. The evolution of the main peaks in the velocity distributions can be followed to an average age of approximately 9 Gyr. We find that: (1) in the distributions of the UV velocity components, stars of different types are concentrated toward several stable peaks (the Hyades, Pleiades, and Sirius Cluster), suggesting that the stars belonging to these formations did not form simultaneously; (2) the peak associated with the Hyades Cluster dominates in all age intervals; and (3) the Hyades peak is strongest for stars with an average age of 1.5 Gyr, suggesting that this peak contains a considerable fraction of |
fe72f80e-6f3b-4a29-9212-02866f671a3c | fe72f80e-6f3b-4a29-9212-02866f671a3c | fe72f80e-6f3b-4a29-9212-02866f671a3c | human | null | null | none | abstracts | Cosmic M\'enage \`a Trois: The Origin of Satellite Galaxies On Extreme
Orbits | null | We examine the orbits of satellite galaxies identified in a suite of N-body/gasdynamical simulations of the formation of $L_*$ galaxies in a LCDM universe. Most satellites follow conventional orbits; after turning around, they accrete into their host halo and settle on orbits whose apocentric radii are steadily eroded by dynamical friction. However, a number of outliers are also present, we find that ~1/3 of satellites identified at $z=0$ are on unorthodox orbits, with apocenters that exceed their turnaround radii. This population of satellites on extreme orbits consists typically of the faint member of a satellite pair that has been ejected onto a highly-energetic orbit during its first approach to the primary. Since the concurrent accretion of multiple satellite systems is a defining feature of hierarchical models of galaxy formation, we speculate that this three-body ejection mechanism may be the origin of (i) some of the newly discovered high-speed satellites around M31 (such as |
e1f1ea87-a8a9-4170-8045-e67ff5dd0def | e1f1ea87-a8a9-4170-8045-e67ff5dd0def | e1f1ea87-a8a9-4170-8045-e67ff5dd0def | human | null | null | none | abstracts | Magnetic and axial-vector transitions of the baryon antidecuplet | null | We report the recent results of the magnetic transitions and axial-vector transitions of the baryon antidecuplet within the framework of the chiral quark-soliton model. The dynamical model parameters are fixed by experimental data for the magnetic moments of the baryon octet, for the hyperon semileptonic decay constants, and for the singlet axial-vector constant. The transition magnetic moments $\mu_{\Lambda\Sigma}$ and $\mu_{N\Delta}$ are well reproduced and other octet-decuplet and octet-antidecuplet transitions are predicted. In particular, the present calculation of $\mu_{\Sigma\Sigma^*}$ is found to be below the upper bound $0.82\mu_N$ that the SELEX collaboration measured very recently. The results explains consistently the recent findings of a new $N^*$ resonance from the GRAAL and Tohoku LNS group. We also obtain the transition axial-vector constants for the $\Theta^+\to KN$ from which the decay width of the $\Theta^{+}$ pentaquark baryon is determined as a function of the pi |
d5d0fc07-8e66-4e3c-99eb-da69018207b9 | d5d0fc07-8e66-4e3c-99eb-da69018207b9 | d5d0fc07-8e66-4e3c-99eb-da69018207b9 | human | null | null | none | abstracts | HS1857+5144: A hot and young pre-cataclysmic variable | null | We report the discovery of a new white dwarf/M dwarf binary, HS1857+5144, identified in the Hamburg Quasar Survey (HQS). Time-resolved optical spectroscopy and photometry were carried out to determine the properties of this new cataclysmic variable progenitor pre-CV). The light curves of HS1857+5144 display a sinusoidal variation with a period of Porb=383.52 min and peak-to-peak amplitudes of 0.7 mag and 1.1 mag in the B-band and R-band, respectively. The large amplitude of the brightness variation results from a reflection effect on the heated inner hemisphere of the companion star, suggesting a very high temperature of the white dwarf. Our radial velocity study confirms the photometric period as the orbital period of the system. A model atmosphere fit to the spectrum of the white dwarf obtained at minimum light provides limits to its mass and temperature of Mwd=~0.6-1.0 Msun and Twd=~70000-100000 K, respectively. The detection of HeII 4686 absorption classifies the primary star of |
8696bb95-34f5-4c6b-a3b2-808f69fd911c | 8696bb95-34f5-4c6b-a3b2-808f69fd911c | 8696bb95-34f5-4c6b-a3b2-808f69fd911c | human | null | null | none | abstracts | Unicast and Multicast Qos Routing with Soft Constraint Logic Programming | null | We present a formal model to represent and solve the unicast/multicast routing problem in networks with Quality of Service (QoS) requirements. To attain this, first we translate the network adapting it to a weighted graph (unicast) or and-or graph (multicast), where the weight on a connector corresponds to the multidimensional cost of sending a packet on the related network link: each component of the weights vector represents a different QoS metric value (e.g. bandwidth, cost, delay, packet loss). The second step consists in writing this graph as a program in Soft Constraint Logic Programming (SCLP): the engine of this framework is then able to find the best paths/trees by optimizing their costs and solving the constraints imposed on them (e.g. delay < 40msec), thus finding a solution to QoS routing problems. Moreover, c-semiring structures are a convenient tool to model QoS metrics. At last, we provide an implementation of the framework over scale-free networks and we suggest how t |
8d164fd8-3735-4a53-93ee-23964d773fc0 | 8d164fd8-3735-4a53-93ee-23964d773fc0 | 8d164fd8-3735-4a53-93ee-23964d773fc0 | human | null | null | none | abstracts | Learning more from the Lorentz transformations | null | Admitting the validity of Lorentz transformations for the space as time coordinates of the same event we derive their differential form in order to underline the correct prerequisites for the application of time and length contraction or dilation effects. Furthermore we quantify the simultaneity error occurring in the relativity theory. Having done this, we analyse the root cause of these effects and identify it with a finite phase velocity associated with the moving frame. We define this phase velocity by analogy to the de Broglie wave associated with a moving particle. Based on this construct we demonstrate that the phase of the de Broglie waves further extended for stationary particles is a relativistic invariant being the same for all corresponding observers. Also the phase of the electromagnetic waves transporting energy at light speed is a relativistic invariant. Therefore the universe and its matter / energy may be seen as a superposition of waves propagating such that their p |
452842f9-9a47-47b5-8148-b0f66d1c9023 | 452842f9-9a47-47b5-8148-b0f66d1c9023 | 452842f9-9a47-47b5-8148-b0f66d1c9023 | human | null | null | none | abstracts | On the Mapping of Time-Dependent Densities onto Potentials in Quantum
Mechanics | null | The mapping of time-dependent densities on potentials in quantum mechanics is critically examined. The issue is of significance ever since Runge and Gross (Phys. Rev. Lett. 52, 997 (1984)) established the uniqueness of the mapping, forming a theoretical basis for time-dependent density functional theory. We argue that besides existence (so called v-representability) and uniqueness there is an important question of stability and chaos. Studying a 2-level system we find innocent, almost constant densities that cannot be constructed from any potential (non-existence). We further show via a Lyapunov analysis that the mapping of densities on potentials has chaotic regions in this case. In real space the situation is more subtle. V-representability is formally assured but the mapping is often chaotic making the actual construction of the potential almost impossible. The chaotic nature of the mapping, studied for the first time here, has serious consequences regarding the possibility of usi |
0ff09bed-68ab-4d3c-a584-437db8fd3508 | 0ff09bed-68ab-4d3c-a584-437db8fd3508 | 0ff09bed-68ab-4d3c-a584-437db8fd3508 | human | null | null | none | abstracts | Chiral Mechanisms Leading to Orbital Quantum Structures in the Nucleon | null | Color confinement and chiral symmetry specify some important territory for the study of hadronic physics. Any hadron can be defined as a color-singlet composite system of qurks and gluons, the fundamental fields of qcd, while the landscape of the hadronic spectrum is dominated by the fact that two quark flavors, u and d, are characterized by masses small compared to the fundamental scale of this theory. Measurements sensitive to the orbital angular momenta of the color constituents of the nucleon display the interplay of chiral dynamics and confinement in a unique manner. This pageant can be explored by an evaluation, within the context of the Georgi-Manohar chiral quark model, of the normalization of the orbital structure functions and the normalization of the Boer-Mulders functions for different quark flavors. The resolution structures in the chiral quark model represent an evaluation of Collins functions for a confined system defined by the quantum numbers of the nucleon in the co |
01981de3-1f2b-4a50-ba87-aa68bcc832bf | 01981de3-1f2b-4a50-ba87-aa68bcc832bf | 01981de3-1f2b-4a50-ba87-aa68bcc832bf | human | null | null | none | abstracts | Intrinsic ripples in graphene | null | The stability of two-dimensional (2D) layers and membranes is subject of a long standing theoretical debate. According to the so called Mermin-Wagner theorem, long wavelength fluctuations destroy the long-range order for 2D crystals. Similarly, 2D membranes embedded in a 3D space have a tendency to be crumpled. These dangerous fluctuations can, however, be suppressed by anharmonic coupling between bending and stretching modes making that a two-dimensional membrane can exist but should present strong height fluctuations. The discovery of graphene, the first truly 2D crystal and the recent experimental observation of ripples in freely hanging graphene makes these issues especially important. Beside the academic interest, understanding the mechanisms of stability of graphene is crucial for understanding electronic transport in this material that is attracting so much interest for its unusual Dirac spectrum and electronic properties. Here we address the nature of these height fluctuation |
31b40a91-ef00-466f-b5cd-816a08af0418 | 31b40a91-ef00-466f-b5cd-816a08af0418 | 31b40a91-ef00-466f-b5cd-816a08af0418 | human | null | null | none | abstracts | A unified shear-thinning treatment of both film thickness and traction
in EHD | null | A conclusive demonstration has been provided that the nature of the shear-thinning, that affects both film thickness and traction in EHL contacts, follows the ordinary power-law rule that has been described by many empirical models of which Carreau is but one example. This was accomplished by accurate measurements in viscometers of the shear response of a PAO that possesses a very low critical stress for shear-thinning and accurate measurements in-contact of film thickness and traction under conditions which accentuate the shear-thinning effect. The in-contact central film thickness and traction were entirely predictable from the rheological properties obtained from viscometers using simple calculations. These data should be invaluable to researchers endeavoring to accurately simulate Hertz zone behavior since the shear-thinning rheology is extensively characterized and accurate in-contact data are available to test. In addition, a new model has been introduced that may be useful for |
f006a958-e7d1-47e2-b23c-a362d1584a97 | f006a958-e7d1-47e2-b23c-a362d1584a97 | f006a958-e7d1-47e2-b23c-a362d1584a97 | human | null | null | none | abstracts | Super Low Traction under EHD and Mixed Lubrication Regimes | null | After the pioneered experimental works on superlubricity by Martin et al. on MoS2 [1], Hirano et al. on tungsten and silicon [2] and the further confirmation by Dienwiebel et al. on graphite [3], many groups around the word investigated the occurrence of near frictionless sliding contacts. This large mobilization of tribologists, material sciences specialists and physicists has lead to emerging solutions involving new materials and coatings, the most promising being carbon based like graphite, diamond, carbon composites or diamond-like-carbons. Some of them are currently used in practical applications. The situation is different especially in EHL: the highest friction coefficients are close to 10% when traction fluids are involved, i.e. fluids that have especially designed to transmit the highest friction, and they vary within 3-6% for the rest of lubricants. The range of variation is consequently very narrow and these typical values are really low compared to those obtained in dry c |
384eff46-3903-402a-866b-6a33f00fe168 | 384eff46-3903-402a-866b-6a33f00fe168 | 384eff46-3903-402a-866b-6a33f00fe168 | human | null | null | none | abstracts | Phenomenology with Massive Neutrinos | null | The current status and some perspectives of the phenomenology of massive neutrinos is reviewed. We start with the phenomenology of neutrino oscillations in vacuum and in matter. We summarize the results of neutrino experiments using solar, atmospheric, reactor and accelerator neutrino beams. We update the leptonic parameters derived from the three-neutrino oscillation interpretation of this data. We describe the method and present results on our understanding of the solar and atmospheric neutrino fluxes by direct extraction from the corresponding neutrino event rates. We present some tests of different forms of new physics which induce new sources of leptonic flavor transitions in vacuum and in matter which can be performed with the present neutrino data. The aim and potential of future neutrino experiments and facilities to further advance in these fronts is also briefly summarized. Last, the implications of the LSND observations are discussed, and the status of extended models whic |
1f049b1b-974b-484f-bec1-4c89845acae8 | 1f049b1b-974b-484f-bec1-4c89845acae8 | 1f049b1b-974b-484f-bec1-4c89845acae8 | human | null | null | none | abstracts | Equation of state of atomic systems beyond s-wave determined by the
lowest order constrained variational method: Large scattering length limit | null | Dilute Fermi systems with large s-wave scattering length a_s exhibit universal properties if the interparticle spacing r_o greatly exceeds the range of the underlying two-body interaction potential. In this regime, r_o is the only relevant length scale and observables such as the energy per particle depend only on r_o (or, equivalently, the energy E_{FG} of the free Fermi gas). This paper investigates Bose and Fermi systems with non-vanishing angular momentum l using the lowest order constrained variational method. We focus on the regime where the generalized scattering length becomes large and determine the relevant length scales. For Bose gases with large generalized scattering lengths, we obtain simple expressions for the energy per particle in terms of a l-dependent length scale \xi_l, which depends on the range of the underlying two-body potential and the average interparticle spacing. We discuss possible implications for dilute two-component Fermi systems with finite l. Further |
ca0eff53-5540-472e-90cc-0afd410c411b | ca0eff53-5540-472e-90cc-0afd410c411b | ca0eff53-5540-472e-90cc-0afd410c411b | human | null | null | none | abstracts | Unifying Evolutionary and Network Dynamics | null | Many important real-world networks manifest "small-world" properties such as scale-free degree distributions, small diameters, and clustering. The most common model of growth for these networks is "preferential attachment", where nodes acquire new links with probability proportional to the number of links they already have. We show that preferential attachment is a special case of the process of molecular evolution. We present a new single-parameter model of network growth that unifies varieties of preferential attachment with the quasispecies equation (which models molecular evolution), and also with the Erdos-Renyi random graph model. We suggest some properties of evolutionary models that might be applied to the study of networks. We also derive the form of the degree distribution resulting from our algorithm, and we show through simulations that the process also models aspects of network growth. The unification allows mathematical machinery developed for evolutionary dynamics to b |
d9bf3197-16ff-4990-8559-6a7d30734a7d | d9bf3197-16ff-4990-8559-6a7d30734a7d | d9bf3197-16ff-4990-8559-6a7d30734a7d | human | null | null | none | abstracts | The LuckyCam Survey for Very Low Mass Binaries II: 13 new M4.5-M6.0
Binaries | null | We present results from a high-angular-resolution survey of 78 very low mass (VLM) binary systems with 6.0 <= V-K colour <= 7.5 and proper motion >= 0.15 arcsec/yr. 21 VLM binaries were detected, 13 of them new discoveries. The new binary systems range in separation between 0.18 arcsec and 1.3 arcsec. The distance-corrected binary fraction is 13.5% (+6.5%/-4%), in agreement with previous results. 9 of the new binary systems have orbital radii > 10 AU, including a new wide VLM binary with 27 AU projected orbital separation. One of the new systems forms two components of a 2300 AU separation triple system. We find that the orbital radius distribution of the binaries with V-K < 6.5 in this survey appears to be different from that of redder (lower-mass) objects, suggesting a possible rapid change in the orbital radius distribution at around the M5 spectral type. The target sample was also selected to investigate X-ray activity among VLM binaries. There is no detectable correlation betwee |
a96fb918-b86c-4ab5-8b6d-e601b5fffa97 | a96fb918-b86c-4ab5-8b6d-e601b5fffa97 | a96fb918-b86c-4ab5-8b6d-e601b5fffa97 | human | null | null | none | abstracts | A Measure of de Sitter Entropy and Eternal Inflation | null | We show that in any model of non-eternal inflation satisfying the null energy condition, the area of the de Sitter horizon increases by at least one Planck unit in each inflationary e-folding. This observation gives an operational meaning to the finiteness of the entropy S_dS of an inflationary de Sitter space eventually exiting into an asymptotically flat region: the asymptotic observer is never able to measure more than e^(S_dS) independent inflationary modes. This suggests a limitation on the amount of de Sitter space outside the horizon that can be consistently described at the semiclassical level, fitting well with other examples of the breakdown of locality in quantum gravity, such as in black hole evaporation. The bound does not hold in models of inflation that violate the null energy condition, such as ghost inflation. This strengthens the case for the thermodynamical interpretation of the bound as conventional black hole thermodynamics also fails in these models, strongly su |
ffbf6b09-b116-4cb1-84dc-7cb78b40da7e | ffbf6b09-b116-4cb1-84dc-7cb78b40da7e | ffbf6b09-b116-4cb1-84dc-7cb78b40da7e | human | null | null | none | abstracts | Redefining the Missing Satellites Problem | null | Numerical simulations of Milky-Way size Cold Dark Matter (CDM) halos predict a steeply rising mass function of small dark matter subhalos and a substructure count that greatly outnumbers the observed satellites of the Milky Way. Several proposed explanations exist, but detailed comparison between theory and observation in terms of the maximum circular velocity (Vmax) of the subhalos is hampered by the fact that Vmax for satellite halos is poorly constrained. We present comprehensive mass models for the well-known Milky Way dwarf satellites, and derive likelihood functions to show that their masses within 0.6 kpc (M_0.6) are strongly constrained by the present data. We show that the M_0.6 mass function of luminous satellite halos is flat between ~ 10^7 and 10^8 M_\odot. We use the ``Via Lactea'' N-body simulation to show that the M_0.6 mass function of CDM subhalos is steeply rising over this range. We rule out the hypothesis that the 11 well-known satellites of the Milky Way are host |
26faba24-c368-4018-b79f-0e88807f3451 | 26faba24-c368-4018-b79f-0e88807f3451 | 26faba24-c368-4018-b79f-0e88807f3451 | human | null | null | none | abstracts | Low-density graph codes that are optimal for source/channel coding and
binning | null | We describe and analyze the joint source/channel coding properties of a class of sparse graphical codes based on compounding a low-density generator matrix (LDGM) code with a low-density parity check (LDPC) code. Our first pair of theorems establish that there exist codes from this ensemble, with all degrees remaining bounded independently of block length, that are simultaneously optimal as both source and channel codes when encoding and decoding are performed optimally. More precisely, in the context of lossy compression, we prove that finite degree constructions can achieve any pair $(R, D)$ on the rate-distortion curve of the binary symmetric source. In the context of channel coding, we prove that finite degree codes can achieve any pair $(C, p)$ on the capacity-noise curve of the binary symmetric channel. Next, we show that our compound construction has a nested structure that can be exploited to achieve the Wyner-Ziv bound for source coding with side information (SCSI), as well |