161,074 research outputs found
X-Ray Spectral Variability in Cygnus X-1
Spectral variability in different energy bands of X-rays from Cyg X-1 in
different states is studied with RXTE observations and time domain approaches.
In the hard tail of energy spectrum above keV, average peak aligned
shots are softer than the average steady emission and the hardness ratio
decreases when the flux increases during a shot for all states. In regard to a
soft band lower keV, the hardness in the soft state varies in an
opposite way: it peaks when the flux of the shot peaks. For the hard and
transition states, the hardness ratio in respect to a soft band during a shot
is in general lower than that of the steady component and a sharp rise is
observed at about the shot peak. For the soft state, the correlation
coefficient between the intensity and hardness ratio in the hard tail is
negative and decreases monotonically as the timescale increases from 0.01 s to
50 s, which is opposite to that in regard to a soft band. For the hard and
transition states, the correlation coefficients are in general negative and
have a trend of decrease with increasing timescale.Comment: 14 pages, 3 figures, accepted by Ap
QED Penguin Contributions To Isospin Splittings of Heavy-Light Quark Systems
Recent experiments show that the isospin-violating mass splitting of the B
mesons is very small, but the best fits with a QCD sum rule analysis give a
splitting of at least 1.0 MeV. The isospin-violating mass splittings of the
charmed mesons, on the other hand, are in agreement with experiment. In this
letter we show that the inclusion of 2 kind QED penguin diagrams can
account for this discrepancy within the errors in the QCD sum rule method.Comment: 9 pages, latex, 2 figure
Temporal variability in early afterglows of short gamma-ray bursts
The shock model has successfully explained the observed behaviors of
afterglows from long gamma-ray bursts (GRBs). Here we use it to investigate the
so-called early afterglows from short GRBs, which arises from blast waves that
are not decelerated considerably by their surrounding medium. We consider a
nearby medium loaded with pairs (Beloborodov 2002). The temporal
behaviors show first a soft-to-hard spectral evolution, from the optical to
hard X-ray, and then a usual hard-to-soft evolution after the blast waves begin
to decelerate. The light curves show variability, and consist of two peaks. The
first peak, due to the pair effect, can be observed in the X-ray, though too
faint and too short in the optical. The second peak will be easily detected by
{\it Swift}. We show that detections of the double-peak structure in the light
curves of early afterglows are very helpful to determine all the shock
parameters of short GRBs, including both the parameters of the relativistic
source and the surroundings. Besides, from the requirement that the
forward-shock emission in short GRBs should be below the BATSE detection
threshold, we give a strong constraint on the shock model parameters. In
particular, the initial Lorentz factor of the source is limited to be no more
than , and the ambient medium density is inferred to be low, n\la
10^{-1} cm.Comment: 5 pages, 1 figure, minor changes to match the publish in MNRA
Critical exponents of the two-layer Ising model
The symmetric two-layer Ising model (TLIM) is studied by the corner transfer
matrix renormalisation group method. The critical points and critical exponents
are calculated. It is found that the TLIM belongs to the same universality
class as the Ising model. The shift exponent is calculated to be 1.773, which
is consistent with the theoretical prediction 1.75 with 1.3% deviation.Comment: 7 pages, with 10 figures include
Highlights of the TEXONO Research Program on Neutrino and Astroparticle Physics
This article reviews the research program and efforts for the TEXONO
Collaboration on neutrino and astro-particle physics. The ``flagship'' program
is on reactor-based neutrino physics at the Kuo-Sheng (KS) Power Plant in
Taiwan. A limit on the neutrino magnetic moment of \munuebar < 1.3 X 10^{-10}
\mub} at 90% confidence level was derived from measurements with a high purity
germanium detector. Other physics topics at KS, as well as the various R&D
program, are discussedComment: 10 pages, 9 figures, Proceedings of the International Symposium on
Neutrino and Dark Matter in Nuclear Physics (NDM03), Nara, Japan, June 9-14,
200
Corrections to the thermodynamics of Schwarzschild-Tangherlini black hole and the generalized uncertainty principle
We investigate the thermodynamics of Schwarzschild-Tangherlini black hole in
the context of the generalized uncertainty principle. The corrections to the
Hawking temperature, entropy and the heat capacity are obtained via the
modified Hamilton-Jacobi equation. These modifications show that the GUP
changes the evolution of Schwarzschild-Tangherlini black hole. Specially, the
GUP effect becomes susceptible when the radius or mass of black hole approach
to the order of Planck scale, it stops radiating and leads to black hole
remnant. Meanwhile, the Planck scale remnant can be confirmed through the
analysis of the heat capacity. Those phenomenons imply that the GUP may give a
way to solve the information paradox. Besides, we also investigate the
possibilities to observe the black hole at LHC, the results demonstrate that
the black hole can not be produced in the recent LHC.Comment: 12 pages, 6 figure
DISCHARGE OXIDE STORAGE CAPACITY AND VOLTAGE LOSS IN LI-AIR BATTERY
Air cathodes, where oxygen reacts with Li ions and electrons with discharge oxide stored in their pore structure, are often considered as the most challenging component in nonaqueous Lithium-air batteries. In non-aqueous electrolytes, discharge oxides are usually insoluble and hence precipitate at local reaction site, raising the oxygen transport resistance in the pore network. Due to their low electric conductivity, their presence causes electrode passivation. This study aims to investigate the air cathode's performance through analytically obtaining oxygen profiles, modeling electrode passivation, evaluating the transport polarization raised by discharge oxide precipitate, and developing analytical formulas for insoluble Li oxides storage capacity. The variations of cathode quantities, including oxygen content and temperature, are evaluated and related to a single dimensionless parameter - the Damköhler Number (Da). An approximate model is developed to predict discharge voltage loss, along with validation against two sets of experimental data. Air cathode properties, including tortuosity, surface coverage factor and the Da number, and their effects on the cathode's capacity of storing Li oxides are formulated and discussed
Quantum state transfer via the ferromagnetic chain in a spatially modulated field
We show that a perfect quantum state transmission can be realized through a
spin chain possessing a commensurate structure of energy spectrum, which is
matched with the corresponding parity. As an exposition of the mirror inversion
symmetry discovered by Albanese et. al (quant-ph/0405029), the parity matched
the commensurability of energy spectra help us to present the novel
pre-engineered spin systems for quantum information transmission. Based on the
these theoretical analysis, we propose a protocol of near-perfect quantum state
transfer by using a ferromagnetic Heisenberg chain with uniform coupling
constant, but an external parabolic magnetic field. The numerical results shows
that the initial Gaussian wave packet in this system with optimal field
distribution can be reshaped near-perfectly over a longer distance.Comment: 5 pages, 2 figure
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