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 $1/4\pi$, 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