16,845 research outputs found
A Reverse-Shock Model for the Early Afterglow of GRB 050525A
The prompt localization of gamma-ray burst (GRB) 050525A by {\em Swift}
allowed the rapid follow-up of the afterglow. The observations revealed that
the optical afterglow had a major rebrightening starting at days
and ending at days, which was followed by an initial power-law
decay. Here we show that this early emission feature can be interpreted as the
reverse shock emission superposed by the forward shock emission in an
interstellar medium environment. By fitting the observed data, we further
constrain some parameters of the standard fireball-shock model: the initial
Lorentz factor of the ejecta , the magnetic energy fraction
, and the medium density . These
limits are consistent with those from the other very-early optical afterglows
observed so far. In principle, a wind environment for GRB 050525A is
disfavored.Comment: 11 pages, 1 figure, accepted for publication in Ap
Strategic Asset Seeking and Innovation Performance: The Role of Innovation Capabilities and Host Country Institutions
fals
First principles calculation of lithium-phosphorus co-doped diamond
We calculate the density of states (DOS) and the Mulliken population of the
diamond and the co-doped diamonds with different concentrations of lithium (Li)
and phosphorus (P) by the method of the density functional theory, and analyze
the bonding situations of the Li-P co-doped diamond thin films and the impacts
of the Li-P co-doping on the diamond conductivities. The results show that the
Li-P atoms can promote the split of the diamond energy band near the Fermi
level, and improve the electron conductivities of the Li-P co-doped diamond
thin films, or even make the Li-P co-doped diamond from semiconductor to
conductor. The effect of Li-P co-doping concentration on the orbital charge
distributions, bond lengths and bond populations is analyzed. The Li atom may
promote the split of the energy band near the Fermi level as well as may
favorably regulate the diamond lattice distortion and expansion caused by the P
atom.Comment: 14 pages, 11 figure
Bridging Atomistic/Continuum Scales in Solids with Moving Dislocations
We propose a multiscale method for simulating solids with moving dislocations. Away from atomistic subdomains where the atomistic dynamics are fully resolved, a dislocation is represented by a localized jump profile, superposed on a defect-free field. We assign a thin relay zone around an atomistic subdomain to detect the dislocation profile and its propagation speed at a selected relay time. The detection technique utilizes a lattice time history integral treatment. After the relay, an atomistic computation is performed only for the defect-free field. The method allows one to effectively absorb the fine scale fluctuations and the dynamic dislocations at the interface between the atomistic and continuum domains. In the surrounding region, a coarse grid computation is adequate
Behavior of X-Ray Dust Scattering and Implications for X-Ray Afterglows of Gamma-Ray Bursts
The afterglows of gamma-ray bursts (GRBs) have commonly been assumed to be
due to shocks sweeping up the circum-stellar medium. However, most GRBs have
been found in dense star-forming regions where a significant fraction of the
prompt X-ray emission can be scattered by dust grains. Here we revisit the
behavior of dust scattering of X-rays in GRBs. We find that the features of
some X-ray afterglows from minutes to days after the gamma-ray triggers are
consistent with the scattering of prompt X-ray emission from GRBs off host dust
grains. This implies that some of the observed X-ray afterglows (especially
those without sharp rising and decaying flares) could be understood with a
dust-scattering--driven emission model.Comment: ApJ, in pres
Photographic observations of 10 artificial meteors
Photographic observation of artificial meteo
Lost City meteorite - It's recovery and a comparison with other fireballs
Photographic and trajectory data for Lost City meteor and establishment of calibration of mass scale of other meteor
Hadron-quark phase transition in asymmetric matter with dynamical quark masses
The two-Equation of State (EoS) model is used to describe the hadron-quark
phase transition in asymmetric matter formed at high density in heavy-ion
collisions. For the quark phase, the three-flavor Nambu--Jona-Lasinio (NJL)
effective theory is used to investigate the influence of dynamical quark mass
effects on the phase transition. At variance to the MIT-Bag results, with fixed
current quark masses, the main important effect of the chiral dynamics is the
appearance of an End-Point for the coexistence zone. We show that a first order
hadron-quark phase transition may take place in the region T=(50-80)MeV and
\rho_B=(2-4)\rho_0, which is possible to be probed in the new planned
facilities, such as FAIR at GSI-Darmstadt and NICA at JINR-Dubna. From isospin
properties of the mixed phase somepossible signals are suggested. The
importance of chiral symmetry and dynamical quark mass on the hadron-quark
phase transition is stressed. The difficulty of an exact location of
Critical-End-Point comes from its appearance in a region of competition between
chiral symmetry breaking and confinement, where our knowledge of effective QCD
theories is still rather uncertain.Comment: 13 pages, 16 figures (revtex
Influence of vector interactions on the hadron-quark/gluon phase transition
The hadron-quark/gluon phase transition is studied in the two-phase model. As
a further study of our previous work, both the isoscalar and isovector vector
interactions are included in the Polyakov loop modified Nambu--Jona-Lasinio
model (PNJL) for the quark phase. The relevance of the exchange (Fock) terms is
stressed and suitably accounted for. The calculation shows that the isovector
vector interaction delays the phase transition to higher densities and the
range of the mixed phase correspondingly shrinks. Meanwhile the asymmetry
parameter of quark matter in the mixed phase decreases with the strengthening
of this interaction channel. This leads to some possible observation signals
being weakened, although still present. We show that these can be rather
general effects of a repulsion in the quark phase due to the symmetry energy.
This is also confirmed by a simpler calculation with the MIT--Bag model.
However, the asymmetry parameter of quark matter is slightly enhanced with the
inclusion of the isoscalar vector interaction, but the phase transition will be
moved to higher densities. The largest uncertainty on the phase transition lies
in the undetermined coupling constants of the vector interactions. In this
respect new data on the mixed phase obtained from Heavy Ion Collisions at
Intermediate Energies appear very important.Comment: submitted to Phys. Rev.
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