118862133
Residual Energy in Weak and Strong MHD Turbulence
Recent numerical and observational studies revealed that spectra of magnetic and velocity fluctuations in MHD turbulence have different scaling indexes. This intriguing feature has been recently explained in the case of weak MHD turbulence, that is, turbulence consisting of weakly interacting Alfven waves. However, astrophysical turbulence is strong in majority of cases. In the present work, we propose a unifying picture that allows one to address weak and strong MHD turbulence on the same footing. We argue that magnetic and kinetic energies are different in both weak and strong MHD turbulence. Their difference, the so-called residual energy, is spontaneously generated by turbulence, it has the Fourier spectrum E_r(k)=E_v(k)-E_b(k) \propto -f_w(k_||/k_perp) k_perp^{-2} in weak turbulence, and E_r(k) \propto -f_s(k_||/k_perp) k_perp^{-3} in strong turbulence. Here f_w,s(x) are functions declining fast for x>C_w,s and not significantly varying for $x<C_w,s$ with some constants C_w,s, and k_|| and k_perp the field-parallel and field-perpendicular wave vectors with respect to the applied strong uniform magnetic field.
119295443
RESIDUAL ENERGY IN MAGNETOHYDRODYNAMIC TURBULENCE
There is mounting evidence in solar wind observations and in numerical simulations that kinetic and magnetic energies are not in equipartition in magnetohydrodynamic (MHD) turbulence. The origin of their mismatch, the residual energy Er = Ev – Eb , is not understood well. In the present work this effect is studied analytically in the regime of weak MHD turbulence. We find that residual energy is spontaneously generated by turbulent dynamics, and it has a negative sign, in good agreement with the observations. We find that the residual energy condenses around k || = 0 with its k ||-spectrum broadening linearly with k ⊥, where k || and k ⊥ are the wavenumbers parallel and perpendicular to the background magnetic field, and the field-perpendicular spectrum of the residual energy has the scaling Er (k ⊥)∝k –1 ⊥ in the inertial interval. These results are found to be in agreement with numerical simulations. We propose that residual energy plays a fundamental role in Alfvenic turbulence and it should be taken into account for the correct interpretation of observational and numerical data.
121593151
Identification of tau decays using a neural network
Abstract A neural network is constructed to identify the decays τ → ρν in the L3 detector at LEP. The same network is used to identify τ → π (K) ν and τ → e ν ν as a cross check. High efficiency in the rho channel is obtained. A major effort has been made to study the systematic errors introduced by the use of a neural network and no obvious bias has been found.
14261978
How Sensitive Are Weak Lensing Statistics to Dark Energy Content
Future weak lensing surveys will directly probe the clustering of dark matter, in addition to providing a test for various cosmological models. Recent studies have provided us with the tools that can be used to construct the complete probability distribution function for convergence fields. It is also possible to construct the bias associated with the hot spots in convergence maps. These techniques can be used in both the quasi-linear and the highly nonlinear regimes using various well-developed numerical methods. We use the results here to study the weak lensing statistics of cosmological models with dark energy. We study how well various classes of dark energy models can be distinguished from models with a cosmological constant. We find that the ratio of the square root of the variance of convergence is complementary to the convergence skewness S3 in probing the dark energy equation of state; it can be used to predict the expected difference in weak lensing statistics between various dark energy models and for choosing optimized smoothing angles to constrain a given class of dark energy models. Our results should be useful for probing dark energy using future weak lensing data with high statistics from galaxy weak lensing surveys and supernova pencil beam surveys.
118163168
Three-dimensional two-layer outer gap model: the third peak of vela pulsar
We extend the two-dimensional two-layer outer gap model to a three-dimensional geometry and use it to study the high-energy emission of the Vela pulsar. We apply this three-dimensional two-layer model to the Vela pulsar and compare the model light curves, the phase-averaged spectrum and the phase-resolved spectra with the recent Fermi observations, which also reveals the existence of the third peak between two main peaks. The phase position of the third peak moves with the photon energy, which cannot be explained by the geometry of magnetic field structure and the caustic effect of the photon propagation. We suggest that the existence of the third peak and its energy dependent movement results from the azimuthal structure of the outer gap.
14364890
Hawking–Moss tunneling in non-commutative eternal inflation
The quantum behavior of non-commutative eternal inflation is quite different from the usual scenario. Unlike the usual eternal inflation, non-commutative eternal inflation has quantum fluctuation suppressed by the Hubble parameter. Because of this, we need to reconsider many conceptions of eternal inflation. In this paper we study the Hawking-Moss tunneling in non-commutative eternal inflation using the stochastic approach. We obtain a brand new form of tunneling probability for this process and find that the Hawking Moss tunneling is more unlikely to take place in the non-commutative case than in the usual one. We also conclude that the lifetime of a metastable de Sitter vacuum in the non-commutative spacetime is longer than that in the commutative case.
55694014
Statistical study of coronal mass ejection source locations: Understanding CMEs viewed in coronagraphs
[1] How to properly understand coronal mass ejections (CMEs) viewed in white light coronagraphs is crucial to many relative researches in solar and space physics. The issue is now particularly addressed in this paper through studying the source locations of all the 1078 Large Angle and Spectrometric Coronagraph (LASCO) CMEs listed in Coordinated Data Analysis Workshop (CDAW) CME catalog during 1997–1998 and their correlation with CMEs' apparent parameters. By manually checking LASCO and Extreme Ultraviolet Imaging Telescope (EIT) movies of these CMEs, we find that, except 231 CMEs whose source locations cannot be identified due to poor data, there are 288 CMEs with location identified on the frontside solar disk, 234 CMEs appearing above solar limb, and 325 CMEs without evident eruptive signatures in the field of view of EIT. On the basis of the statistical results of CMEs' source locations, there are four physical issues: (1) the missing rate of CMEs by SOHO LASCO and EIT, (2) the mass of CMEs, (3) the causes of halo CMEs, and (4) the deflections of CMEs in the corona, are exhaustively analyzed. It is found that (1) about 32% frontside CMEs cannot be recognized by SOHO, (2) the brightness of a CME at any heliocentric distance is roughly positively correlated with its speed, and the CME mass derived from the brightness is probably overestimated, (3) both projection effect and violent eruption are the major causes of halo CMEs, and especially for limb halo CMEs the latter is the primary one, and (4) most CMEs deflected toward equator near the solar minimum; these deflections can be classified into three types: the asymmetrical expansion, the nonradial ejection, and the deflected propagation.