74,275 research outputs found
Broadband lightcurve characteristics of GRBs 980425 and 060218 and comparison with long-lag, wide-pulse GRBs
It has been recently argued that low-luminosity gamma-ray bursts (LL-GRBs)
are likely a unique GRB population. Here, we present systematic analysis of the
lightcurve characteristics from X-ray to gamma-ray energy bands for the two
prototypical LL-GRBs 980425 and 060218. It is found that both the pulse width
() and the ratio of the rising width to the decaying width () of theses
two bursts are energy-dependent over a broad energy band. There exists a
significant trend that the pulses tend to be narrower and more symmetry with
respect to the higher energy bands for the two events. Both the X-rays and the
gamma-rays follow the same and relations. These facts may
indicate that the X-ray emission tracks the gamma-ray emission and both are
likely to be originated from the same physical mechanism. Their light curves
show significant spectral lags. We calculate the three types of lags with the
pulse peaking time (), the pulse centroid time (), and the
cross-correlation function (CCF). The derived and are a
power-law function of energy. The lag calculated by CCF is strongly correlated
with that derived from . But the lag derived from is less
correlated with that derived from and CCF. The energy dependence of
the lags is shallower at higher energy bands. These characteristics are well
consistent with that observed in typical long-lag, wide-pulse GRBs, suggesting
that GRBs 980425 and 060218 may share the similar radiation physics with them.Comment: 26 pages, 10 figures, 3 tables, accepted for publication in Ap
A Codazzi-like equation and the singular set for smooth surfaces in the Heisenberg group
In this paper, we study the structure of the singular set for a
smooth surface in the -dimensional Heisenberg group . We
discover a Codazzi-like equation for the -area element along the
characteristic curves on the surface. Information obtained from this ordinary
differential equation helps us to analyze the local configuration of the
singular set and the characteristic curves. In particular, we can estimate the
size and obtain the regularity of the singular set. We understand the global
structure of the singular set through a Hopf-type index theorem. We also
justify that Codazzi-like equation by proving a fundamental theorem for local
surfaces in .Comment: 64 pages, 17 figure
Hole spin relaxation in semiconductor quantum dots
Hole spin relaxation time due to the hole-acoustic phonon scattering in GaAs
quantum dots confined in quantum wells along (001) and (111) directions is
studied after the exact diagonalization of Luttinger Hamiltonian. Different
effects such as strain, magnetic field, quantum dot diameter, quantum well
width and the temperature on the spin relaxation time are investigated
thoroughly. Many features which are quite different from the electron spin
relaxation in quantum dots and quantum wells are presented with the underlying
physics elaborated.Comment: 10 pages, 10 figure
Boundary effect on CDW: Friedel oscillations, STM image
We study the effect of open boundary condition on charge density waves (CDW).
The electron density oscillates rapidly close to the boundary, and additional
non-oscillating terms (~ln(r)) appear. The Friedel oscillations survive beyond
the CDW coherence length (v_F/Delta), but their amplitude gets heavily
suppressed. The scanning tunneling microscopy image (STM) of CDW shows clear
features of the boundary. The local tunneling conductance becomes asymmetric
with respect to the Fermi energy, and considerable amount of spectral weight is
transferred to the lower gap edge. Also it exhibits additional zeros reflecting
the influence of the boundary.Comment: 7 pages, 6 figure
Radiative Kaon Decays and Direct CP Violation
It is stressed that a measurement of the electric dipole amplitude for direct
photon emission in \kpm decays through its interference with inner
bremsstrahlung is important for differentiating among various models. Effects
of amplitude CP violation in the radiative decays of the charged kaon are
analyzed in the Standard Model in conjunction with the large approach. We
point out that gluon and electromagnetic penguin contributions to the
CP-violating asymmetry between the Dalitz plots of \kpm are of equal weight.
The magnitude of CP asymmetry ranges from to when the photon energy in the kaon rest frame varies from 50 MeV to
170 MeV.Comment: Latex, 11 pages, ITP-SB-93-36, IP-ASTP-22-9
Pair loading in Gamma-Ray Burst Fireball And Prompt Emission From Pair-Rich Reverse Shock
Gamma-ray bursts (GRBs) are believed to originate from ultra-relativistic
winds/fireballs to avoid the "compactness problem". However, the most energetic
photons in GRBs may still suffer from absorption leading to
electron/positron pair production in the winds/fireballs. We show here that in
a wide range of model parameters, the resulting pairs may dominate those
electrons associated with baryons. Later on, the pairs would be carried into a
reverse shock so that a shocked pair-rich fireball may produce a strong flash
at lower frequencies, i.e. in the IR band, in contrast with optical/UV emission
from a pair-poor fireball. The IR emission would show a 5/2 spectral index due
to strong self-absorption. Rapid responses to GRB triggers in the IR band would
detect such strong flashes. The future detections of many IR flashes will infer
that the rarity of prompt optical/UV emissions is in fact due to dust
obscuration in the star formation regions.Comment: 8 pages, 2 figures, ApJ accepte
Journal Staff
Discoba (Excavata) is an ancient group of eukaryotes with great morphological and ecological diversity. Unlike the other major divisions of Discoba (Jakobida and Euglenozoa), little is known about the mitochondrial DNAs(mtDNAs) of Heterolobosea. We have assembled a complete mtDNA genome from the aggregating heterolobosean amoeba, Acrasis kona, which consists of a single circular highly AT-rich (83.3%) molecule of 51.5 kb. Unexpectedly, A. kona mtDNA is missing roughly 40% of the protein-coding genes and nearly half of the transfer RNAs found in the only other sequenced heterolobosean mtDNAs, those of Naegleria spp. Instead, over a quarter of A. kona mtDNA consists of novel open reading frames. Eleven of the 16 protein-coding genes missing from A. kona mtDNA were identified in its nuclear DNA and polyA RNA, and phylogenetic analyses indicate that at least 10 of these 11 putative nuclear-encoded mitochondrial (NcMt) proteins arose by direct transfer from the mitochondrion. Acrasis kona mtDNA also employs C-to-U type RNA editing, and 12 homologs of DYW-type pentatricopeptide repeat (PPR) proteins implicated in plant organellar RNA editing are found in A. kona nuclear DNA. A mapping of mitochondrial gene content onto a consensus phylogeny reveals a sporadic pattern of relative stasis and rampant gene loss in Discoba. Rampant loss occurred independently in the unique common lineage leading to Heterolobosea + Tsukubamonadida and later in the unique lineage leading to Acrasis. Meanwhile, mtDNA gene content appears to be remarkably stable in the Acrasis sister lineage leading to Naegleria and in their distant relatives Jakobida
Chirally symmetric but confining dense and cold matter
The folklore tradition about the QCD phase diagram is that at the chiral
restoration phase transition at finite density hadrons are deconfined and there
appears the quark matter. We address this question within the only known
exactly solvable confining and chirally symmetric model. It is postulated
within this model that there exists linear Coulomb-like confining interaction.
The chiral symmetry breaking and the quark Green function are obtained from the
Schwinger-Dyson (gap) equation while the color-singlet meson spectrum results
from the Bethe-Salpeter equation. We solve this model at T=0 and finite
chemical potential and obtain a clear chiral restoration phase transition
at the critical value \mu_{cr}. Below this value the spectrum is similar to the
previously obtained one at \mu = 0. At \mu > \mu_{cr} the quarks are still
confined and the physical spectrum consists of bound states which are arranged
into a complete set of exact chiral multiplets. This explicitly demonstrates
that a chirally symmetric matter consisting of confined but chirally symmetric
hadrons at finite chemical potential is also possible in QCD. If so, there must
be nontrivial implications for astrophysics.Comment: 7 pp; the paper has been expanded to make some technical details more
clear; 3 new figures have been added. To appear in PR
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