790 research outputs found
IceCube Non-detection of GRBs: Constraints on the Fireball Properties
The increasingly deep limit on the neutrino emission from gamma-ray bursts
(GRBs) with IceCube observations has reached the level that could put useful
constraints on the fireball properties. We first present a revised analytic
calculation of the neutrino flux, which predicts a flux an order of magnitude
lower than that obtained by the IceCube collaboration. For benchmark model
parameters (e.g. the bulk Lorentz factor is \Gamma=10^{2.5}, the observed
variability time for long GRBs is t_v=0.01 s and the ratio between the energy
in accelerated protons and in radiation is \eta_p=10 for every burst) in the
standard internal shock scenario, the predicted neutrino flux from 215 bursts
during the period of the 40-string and 59-string configurations is found to be
a factor of ~3 below the IceCube sensitivity. However, if we accept the
recently found inherent relation between the bulk Lorentz factor and burst
energy, the expected neutrino flux increases significantly and the spectral
peak shifts to lower energy. In this case, the non-detection then implies that
the baryon loading ratio should be \eta_p<10 if the variability time of long
GRBs is fixed to t_v=0.01 s. Instead, if we relax the standard internal shock
scenario but keep to assume \eta_p=10, the non-detection constrains the
dissipation radius to be R>4x10^{12} cm assuming the same dissipation radius
for every burst and benchmark parameters for fireballs. We also calculate the
diffuse neutrino flux from GRBs for different luminosity functions existing in
the literature. The expected flux exceeds the current IceCube limit for some
luminosity functions, and thus the non-detection constrains \eta_p<10 in such
cases when the variability time of long GRBs is fixed to t_v=0.01 s.Comment: Accepted by ApJ, 14 pages, 5 figures, typos corrected, scheduled for
the June 10, 2012, v752 - 1 issu
Deep Variational Free Energy Approach to Dense Hydrogen
We developed a deep generative model-based variational free energy approach
to the equations of state of dense hydrogen. We employ a normalizing flow
network to model the proton Boltzmann distribution and a fermionic neural
network to model the electron wave function at given proton positions. By
jointly optimizing the two neural networks we reached a comparable variational
free energy to the previous coupled electron-ion Monte Carlo calculation. The
predicted equation of state of dense hydrogen under planetary conditions is
denser than the findings of ab initio molecular dynamics calculation and
empirical chemical model. Moreover, direct access to the entropy and free
energy of dense hydrogen opens new opportunities in planetary modeling and
high-pressure physics research.Comment: 7+5 pages, 3+4 figures, code: https://github.com/fermiflow/hydroge
Quantitative analysis of the genes affecting development of the hypopharyngeal gland in honey bees (Apis mellifera L.)
Royal jelly has many important biological functions, however the molecular mechanism of royal jelly secretion in hypopharyngeal gland (HG) is still not well understood. In our previously study, six genes (SV2C, eIF-4E, PDK1, IMP, cell growth-regulating nucleolar protein and TGF-βR1) have been shown to might be associated with royal jelly secretion. In this study, the relative expression levels of these genes were examined in the hypopharyngeal gland of workers at different developmental stages (nurse, forager and reversed nurse stages). The results indicated that the relative expression levels of SV2C, eIF-4E, IMP, cell growth-regulating nucleolar protein and TGF-βR1 were reversed at reversed nurse stage compared to forager stage. We concluded that these genes are possibly candidates related to hypopharyngeal gland development or royal jelly secretion
General bubble expansion at strong coupling
The strongly-coupled system like the quark-hadron transition (if it is of
first order) is becoming an active play-yard for the physics of cosmological
first-order phase transitions. However, the traditional field theoretic
approach to strongly-coupled first-order phase transitions is of great
challenge, driving recent efforts from holographic dual theories with explicit
numerical simulations. These holographic numerical simulations have revealed an
intriguing linear correlation between the phase pressure difference (pressure
difference away from the wall) to the non-relativistic terminal velocity of an
expanding planar wall, which has been reproduced analytically alongside both
cylindrical and spherical walls from perfect-fluid hydrodynamics in our
previous study but only for a bag equation of state. We have also found in our
previous study a universal quadratic correlation between the wall pressure
difference (pressure difference near the bubble wall) to the non-relativistic
terminal wall velocity regardless of wall geometries. In this paper, we will
generalize these analytic relations between the phase/wall pressure difference
and terminal wall velocity into a more realistic equation of state beyond the
simple bag model, providing the most general predictions so far for future
tests from holographic numerical simulations of strongly-coupled first-order
phase transitionsComment: 22 pages, 10 figure
A Data Driven Method for Multi-step Prediction of Ship Roll Motion in High Sea States
Ship roll motion in high sea states has large amplitudes and nonlinear
dynamics, and its prediction is significant for operability, safety, and
survivability. This paper presents a novel data-driven methodology to provide a
multi-step prediction of ship roll motions in high sea states. A hybrid neural
network is proposed that combines long short-term memory (LSTM) and
convolutional neural network (CNN) in parallel. The motivation is to extract
the nonlinear dynamic characteristics and the hydrodynamic memory information
through the advantage of CNN and LSTM, respectively. For the feature selection,
the time histories of motion states and wave heights are selected to involve
sufficient information. Taken a scaled KCS as the study object, the ship
motions in sea state 7 irregular long-crested waves are simulated and used for
the validation. The results show that at least one period of roll motion can be
accurately predicted. Compared with the single LSTM and CNN methods, the
proposed method has better performance in predicting the amplitude of roll
angles. Besides, the comparison results also demonstrate that selecting motion
states and wave heights as feature space improves the prediction accuracy,
verifying the effectiveness of the proposed method
Re-examining the premise of isobaric collisions and a novel method to measure the chiral magnetic effect
In these proceedings we show that the premise of the isobaric and collisions to search for the chiral magnetic effect (CME) may not hold as originally anticipated due to large uncertainties in the isobaric nuclear structures. We demonstrate this using Woods-Saxon densities and the proton and neutron densities calculated by the density functional theory. Furthermore, a novel method is proposed to gauge background and possible CME contributions in the same system, intrinsically better than the isobaric collisions of two different systems. We illustrate the method with Monte Carlo Glauber and AMPT (A Multi-Phase Transport) simulations
Extended dissipaton equation of motion for electronic open quantum systems: Application to the Kondo impurity model
In this paper, we present an extended dissipaton equation of motion for
studying the dynamics of electronic impurity systems. Compared with the
original theoretical formalism, the quadratic couplings are introduced into the
Hamiltonian accounting for the interaction between the impurity and its
surrounding environment. By exploiting the quadratic dissipaton algebra, the
proposed extended dissipaton equation of motion offers a powerful tool for
studying the dynamical behaviors of electronic impurity systems, particularly
in situations where nonequilibrium and strongly correlated effects play
significant roles. Numerical demonstrations are carried out to investigate the
temperature dependence of the Kondo resonance in the Kondo impurity model.Comment: 6 pages, 1 figur
- …