121843826
Hubble constant, lensing, and time delay in Te Ve S
Hubble constant can be determined by the time delay of gravitational lensing systems. As data on time delay observation accumulates, it is time to revisit this approach. As in other dynamical phenomena in scales of galaxy and cluster of galaxies, gravitational lensing in these scales is also plagued by the problem of excess acceleration or gravity (a.k.a. missing mass problem). There are always some accelerations unaccounted for by luminous matter. Usually dark matter is introduced to interpret the discrepancy. However, MOdified Newtonian Dynamics (MOND) is more successful in explaining the excess accelerations in galaxy scale. We adopt TeVeS as the relativistic version of MOND to study gravitational lensing phenomena, and we can evaluate the Hubble constant from the derived time-delay formula. To apply our method, we rely on the CASTLE quasar lensing survey and the Sloan Digital Sky Survey (SDSS). Four samples are suitable for our study. Using only the luminous part of the lensing galaxies, the average of the derived Hubble constant is 68.5 km s^-1Mpc^-1
119432484
Open clusters in a dispersing molecular cloud
Star clusters are formed in molecular clouds which are believed to be the birth places of most stars. From recent observational data, Lada & Lada (2003) estimated that only 4 to 7% of the proto-clusters have survived. A possible reason is the dispersion of molecular clouds by UV radiation, stellar winds or supernova explosions. We study the cloud dispersion in the embedded clusters by N-body simulations. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
16205821
Particle propagation in the galactic center and spatial distribution of non-thermal x-rays
We showed that if the non-thermal emission from the galactic center in the range 14–40 keV is due to inverse bremsstrahlung emission of subrelativistic protons, their interactions with hot and cold fractions of the interstellar medium are equally important. Our estimation shows that about 30% of the total non-thermal flux from the GC in the range 14–40 keV is generated in regions of cold gas while the rest is produced by proton interaction with hot plasma. From the spatial distribution of 6.7 keV iron line we concluded the spatial distribution of hot plasma is strongly non-uniform that should be taken into account in analysis of proton propagation in the GC. From the Suzaku data we got independent estimates for the diffusion coefficient of subrelativistic protons in the GC, which was in the range 10 26 –10 27 cm 2 s � 1 .
16308661
Origin of thermal and non-thermal hard X-ray emission from the Galactic center
We analyse new results of Chandra and Suzaku Observatories which found a flux of hard X-ray emission from the compact region around Sgr A � (r � 100 pc). We suppose that this emission is generated by accretion processes onto the central supermassive blackhole when an unbound part of captured stars obtains an additional momentum. As a result a flux of subrelativistic protons is generated near the galactic center which heats the background plasma up to temperatures about 6–10 keV and produces by inverse bremsstrahlung a flux of non-thermal X-ray emission in the energy range above 10 keV.
5224194
3D Magneto-hydrodynamic simulations of Parker instability with cosmic rays
This study investigates Parker instability in an interstellar medium (ISM) near the Galactic plane using three-dimensional magneto-hydrodynamic simulations. Parker instability arises from the presence of a magnetic field in a plasma, wherein the magnetic buoyant pressure expels the gas and cause the gas to move along the field lines. The process is thought to induce the formation of giant molecular clouds in the Galaxy. In this study, the effects of cosmic-ray (CR) diffusion are examined. The ISM at equilibrium is assumed to comprise a plasma fluid and a CR fluid at various temperatures, with a uniform magnetic field passing through it in the azimuthal direction of the Galactic disk. After a small perturbation, the unstable gas aggregates at the footpoint of the magnetic fields and forms dense blobs. The growth rate of the instability increases with the strength of the CR diffusion. The formation of dense clouds is enhanced by the effect of cosmic rays (CRs), whereas the shape of the clouds depends sensitively on the initial conditions of perturbation.
17286551
Indicators for cluster survivability in a dispersing cloud
We use N-body simulations to survey the response of embedded star clusters to the dispersal of their parent molecular cloud. The final stages of the clusters can be divided into three classes: the cluster (1) is destroyed, (2) has a loose structure, and (3) has a compact core. We are interested in three of the governing parameters of the parent cloud: (1) the mass, (2) the size, and (3) the dispersing rate. It is known that the final stage of the cluster is well correlated with the star formation efficiency (SFE) for systems with the same cluster and cloud profile. We deem that the SFE alone is not enough to address systems with clouds of different sizes. Our result shows that the initial cluster-cloud mass ratio at a certain Lagrangian radius and the initial kinetic energy are better indicators for the survivability of embedded clusters.
39436824
J/psi absorption by nucleons in the meson-exchange model
We reinvestigate the $J/\ensuremath{\psi}$ dissociation processes induced by the reactions with nucleons, $J/\ensuremath{\psi}+N\ensuremath{\rightarrow}{\overline{D}}^{(*)}+{\ensuremath{\Lambda}}_{c}$, in the meson-exchange model. Main constraints used in this work are vector-meson dominance and charm vector-current conservation. We show that the cross section for $J/\ensuremath{\psi}+N\ensuremath{\rightarrow}\overline{D}+{\ensuremath{\Lambda}}_{c}$ can be larger than that for $J/\ensuremath{\psi}+N\ensuremath{\rightarrow}{\overline{D}}^{*}+{\ensuremath{\Lambda}}_{c}$ when these constraints are imposed. The dependence of the cross sections on the coupling constants is analyzed in detail, and the comparison with the recent quark-interchange model predictions is also made.
18778142
Determination of the stiffness of the nuclear symmetry energy from isospin diffusion.
With an isospin- and momentum-dependent transport model, we find that the degree of isospin diffusion in heavy-ion collisions at intermediate energies is affected by both the stiffness of the nuclear symmetry energy and the momentum dependence of the nucleon potential. Using a momentum dependence derived from the Gogny effective interaction, recent experimental data from NSCL-MSU on isospin diffusion are shown to be consistent with a nuclear symmetry energy given by E(sym)(rho) approximately 31.6(rho/rho(0))(1.05) at subnormal densities. This leads to a significantly constrained value of about -550 MeV for the isospin-dependent part of the isobaric incompressibility of isospin asymmetric nuclear matter.
16350602
Partonic effects in heavy ion collisions at RHIC
Effects of partonic interactions in heavy ion collisions at RHIC are studied in a multiphase transport model (AMPT) that includes both initial partonic and final hadronic interactions. It is found that a large parton scattering cross section is needed to understand the measured elliptic flow of pions and two-pion correlation function.
11222928
Progress Towards Determining the Density Dependence of the Nuclear Symmetry Energy Using Heavy-Ion Reactions
The latest development in determining the density dependence of the nuclear symmetry energy using heavy-ion collisions is reviewed. Within the IBUU04 version of an isospin- and momentum-dependent transport model using a modified Gogny effective interaction, recent experimental data from NSCL/MSU on isospin diffusion are found to be consistent with a nuclear sym- metry energy of Esym(ρ) ≈ 31.6(ρ/ρ0) 1.05 at subnormal densities. Predictions on several observables sensitive to the density dependence of the symmetry en- ergy at supranormal densities accessible at GSI and the planned Rare Isotope Accelerator (RIA) are also made.
17515511
Partonic effects on anisotropic flows at RHIC
We report recent results from a multiphase transport (AMPT) model on the azimuthal anisotropies of particle momentum distributions in heavy ion collisions at the relativistic heavy ion collider. These include higher-order anisotropic flows and their scaling, the rapidity dependence of anisotropic flows and the elliptic flow of charm quarks.