1,037 research outputs found
Transport Coefficients from Extremal Gauss-Bonnet Black Holes
We calculate the shear viscosity of strongly coupled field theories dual to
Gauss-Bonnet gravity at zero temperature with nonzero chemical potential. We
find that the ratio of the shear viscosity over the entropy density is
, which is in accordance with the zero temperature limit of the ratio
at nonzero temperatures. We also calculate the DC conductivity for this system
at zero temperature and find that the real part of the DC conductivity vanishes
up to a delta function, which is similar to the result in Einstein gravity. We
show that at zero temperature, we can still have the conclusion that the shear
viscosity is fully determined by the effective coupling of transverse gravitons
in a kind of theories that the effective action of transverse gravitons can be
written into a form of minimally coupled scalars with a deformed effective
coupling.Comment: 23 pages, no figure; v2, refs added; v3, more refs added; v4, version
to appear in JHE
Artificial-Noise-Aided Physical Layer Phase Challenge-Response Authentication for Practical OFDM Transmission
Recently, we have developed a PHYsical layer Phase Challenge-Response
Authentication Scheme (PHY-PCRAS) for independent multicarrier transmission. In
this paper, we make a further step by proposing a novel artificial-noise-aided
PHY-PCRAS (ANA-PHY-PCRAS) for practical orthogonal frequency division
multiplexing (OFDM) transmission, where the Tikhonov-distributed artificial
noise is introduced to interfere with the phase-modulated key for resisting
potential key-recovery attacks whenever a static channel between two legitimate
users is unfortunately encountered. Then, we address various practical issues
for ANA-PHY-PCRAS with OFDM transmission, including correlation among
subchannels, imperfect carrier and timing recoveries. Among them, we show that
the effect of sampling offset is very significant and a search procedure in the
frequency domain should be incorporated for verification. With practical OFDM
transmission, the number of uncorrelated subchannels is often not sufficient.
Hence, we employ a time-separated approach for allocating enough subchannels
and a modified ANA-PHY-PCRAS is proposed to alleviate the discontinuity of
channel phase at far-separated time slots. Finally, the key equivocation is
derived for the worst case scenario. We conclude that the enhanced security of
ANA-PHY-PCRAS comes from the uncertainty of both the wireless channel and
introduced artificial noise, compared to the traditional challenge-response
authentication scheme implemented at the upper layer.Comment: 33 pages, 13 figures, submitted for possible publicatio
Fine-structure transitions of Si and S induced by collisions with atomic hydrogen
Using a quantum-mechanical close-coupling method, we calculate cross sections
for fine structure excitation and relaxation of Si and S atoms in collisions
with atomic hydrogen. Rate coefficients are calculated over a range of
temperatures for astrophysical applications. We determine the
temperature-dependent critical densities for the relaxation of Si and S in
collisions with H and compare these to the critical densities for collisions
with electrons. The present calculation should be useful in modeling
environments exhibiting the [S i] 25 {\mu}m and [S i] 57 {\mu}m far-infrared
emission lines or where cooling of S and Si by collisions with H are of
interest.Comment: Accepted for publication in MNRA
Effect of bupleurum liver-coursing powder on acute gastric ulcer and expressions of gastric mucosal epidermal growth factor and receptor
Purpose: To investigate the ameliorative effect of bupleurum liver-coursing powder on symptoms of acute gastric ulcer (AGU), and on the expressions of gastric mucosal epidermal growth factor (EGF) and EGF receptor (EGFR).Methods: A total of 120 patients were recruited over a 1-year period for this study, and assigned to observation and control groups (60 patients each). The observation group consisted of 31 males and 29 females aged between 23 and 55 years (mean age, 38.77 ± 4.36 years; mean disease history, 7.94 ± 2.49 days). Control group consisted of 33 males and 27 females aged between 26 and 51 years (mean age, 37.68 ± 4.67 years; mean disease history, 8.06 ± 2.31 days). Following 14 days of treatment, clinical symptoms such as gastric swelling and pain, chest distress, belching, and sour regurgitation were recorded and analyzed. Serum levels of C-reactive protein (CRP), IL-6 and TNF-α were assayed using ELISA, while the expressions of EGF and EGFR were determined using immuno-histochemical staining.Results: Total effectiveness (recovery, excellent, effective and ineffective) in observation patients (91.70 %) was significantly higher (p < 0.001) than in control group (65.0 %). Prior to treatment, both groups were comparable with respect to the major symptoms of AGU, and serum levels of CRP, TNF-α and IL-6. However, there were significant reductions in symptoms and serum levels of CRP, TNF-α and IL-6 in bupleurum liver-coursing powder-treated patients, post-treatment (p < 0.05). Similarly, after treatment, there were significant increases in the expressions of EGF and EGFR in the observation patients, relative to control patients (p < 0.05).Conclusion: Bupleurum liver-coursing powder is effective in ameliorating symptoms of AGU, and it enhances the expressions of EGF and EGFR.Keywords: Acute gastric ulcer, Bupleurum liver-coursing powder, Inflammation-related factors, Epithelial growth factor, Recepto
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