Viscosity of gauge theory plasma with a chemical potential from AdS/CFT correspondence

We compute the strong coupling limit of the shear viscosity for the N=4 super-Yang-Mill theory with a chemical potential. We use the five-dimensional Reissner-Nordstrom-anti-deSitter black hole, so the chemical potential is the one for the R-charges U(1)_R^3. We compute the quasinormal frequencies of the gravitational and electromagnetic vector perturbations in the background numerically. This enables one to explicitly locate the diffusion pole for the shear viscosity. The ratio of the shear viscosity eta to the entropy density s is eta/s=1/(4pi) within numerical errors, which is the same result as the one without chemical potential.Comment: 11 pages, 5 figures, ReVTeX4; v2: minor improvements; v3: explanations added and improved; v4: version to appear in PR

Gas Enrichment at Liquid-Wall Interfaces

Molecular dynamics simulations of Lennard-Jones systems are performed to study the effects of dissolved gas on liquid-wall and liquid-gas interfaces. Gas enrichment at walls is observed which for hydrophobic walls can exceed more than two orders of magnitude when compared to the gas density in the bulk liquid. As a consequence, the liquid structure close to the wall is considerably modified, leading to an enhanced wall slip. At liquid-gas interfaces gas enrichment is found which reduces the surface tension.Comment: main changes compared to version 1: flow simulations are included as well as different types of gase

Robust and Scalable Scheme to Generate Large-Scale Entanglement Webs

We propose a robust and scalable scheme to generate an $N$-qubit $W$ state among separated quantum nodes (cavity-QED systems) by using linear optics and postselections. The present scheme inherits the robustness of the Barrett-Kok scheme [Phys. Rev. A {\bf 71}, 060310(R) (2005)]. The scalability is also ensured in the sense that an arbitrarily large $N$-qubit $W$ state can be generated with a quasi-polynomial overhead $\sim 2^{O[(\log_2 N)^2]}$. The process to breed the $W$ states, which we introduce to achieve the scalability, is quite simple and efficient, and can be applied for other physical systems.Comment: 5 pages, 3 figure

Radiation from an accelerated quark via AdS/CFT

In this paper we investigate radiation by an accelerated quark in a strongly coupled gauge theory via AdS/CFT correspondence. According to AdS/CFT dictionary, we can read off energy density or energy flux of the radiation from asymptotic gravitational field in AdS bulk sourced by an accelerated string trailing behind the quark. In the case of an oscillating quark with frequency $\Omega$, we show that the time averaged energy density is asymptotically isotropic and it falls off as $(g_{\text{YM}}^2 N)^{1/2} \Omega^4/R^{2}$ with distance $R$ from the source. In a toy model of a scattered quark by an external field, we simply estimate Poynting vector by the bremsstrahlung radiation and show that the energy flux is anisotropic outgoing radiation. Based on these investigations, we discuss the properties of strongly coupled gauge theory radiation in comparison with electromagnetic radiation.Comment: 16 pages, no figures, accepted for publication in Phys. Rev.

Nebular Spectra of SN 1998bw Revisited: Detailed Study by One and Two Dimensional Models

Refined one- and two-dimensional models for the nebular spectra of the hyper-energetic Type Ic supernova (SN) 1998bw, associated with the gamma-ray burst GRB980425, from 125 to 376 days after B-band maximum are presented. One dimensional, spherically symmetric spectrum synthesis calculations show that reproducing features in the observed spectra, i.e., the sharply peaked [OI] 6300\AA doublet and MgI] 4570\AA emission, and the broad [FeII] blend around 5200\AA, requires the existence of a high-density O-rich core expanding at low velocities (\lsim 8,000 km s$^{-1}$) and of Fe-rich material moving faster than the O-rich material. Synthetic spectra at late phases from aspherical (bipolar) explosion models are also computed with a two-dimensional spectrum synthesis code. The above features are naturally explained by the aspherical model if the explosion is viewed from a direction close to the axis of symmetry ($\sim 30^{\rm o}$), since the aspherical model yields a high-density O-rich region confined along the equatorial axis. By examining a large parameter space (in energy and mass), our best model gives following physical quantities: the kinetic energy $E_{51} \equiv E_{\rm K}/10^{51}$ ergs \gsim 8 - 12 and the main-sequence mass of the progenitor star M_{\rm ms} \gsim 30 - 35 \Msun. The temporal spectral evolution of SN 1998bw also indicates mixing among Fe-, O-, and C-rich regions, and highly clumpy structure.Comment: 38 pages, 22 figures. ApJ, 640 (01 April 2006 issue), in pres

Exact Analysis of ESR Shift in the Spin-1/2 Heisenberg Antiferromagnetic Chain

A systematic perturbation theory is developed for the ESR shift and is applied to the spin-1/2 Heisenberg chain. Using the Bethe ansatz technique, we exactly analyze the resonance shift in the first order of perturbative expansion with respect to an anisotropic exchange interaction. Exact result for the whole range of temperature and magnetic field, as well as asymptotic behavior in the low-temperature limit are presented. The obtained g-shift strongly depends on magnetic fields at low temperature, showing a significant deviation from the previous classical result.Comment: 4 pages, 3 figures,to be published in Phys. Rev. Let

Efeito da mistura de lodo celulósico com cinza de biomassa de madeira no desenvolvimento de Pinus taeda L.

Editores técnicos: Marcílio José Thomazini, Elenice Fritzsons, Patrícia Raquel Silva, Guilherme Schnell e Schuhli, Denise Jeton Cardoso, Luziane Franciscon. EVINCI. Resumos

Collision of Domain Walls and Reheating of the Brane Universe

We study a particle production at the collision of two domain walls in 5-dimensional Minkowski spacetime. This may provide the reheating mechanism of an ekpyrotic (or cyclic) brane universe, in which two BPS branes collide and evolve into a hot big bang universe. We evaluate a production rate of particles confined to the domain wall. The energy density of created particles is given as $\rho \approx 20 \bar{g}^4 N_b ~m_\eta^4$ where $\bar{g}$ is a coupling constant of particles to a domain-wall scalar field, $N_b$ is the number of bounces at the collision and $m_\eta$ is a fundamental mass scale of the domain wall. It does not depend on the width $d$ of the domain wall, although the typical energy scale of created particles is given by $\omega\sim 1/d$. The reheating temperature is evaluated as $T_{\rm R}\approx 0.88 ~ \bar{g} ~ N_b^{1/4}$. In order to have the baryogenesis at the electro-weak energy scale, the fundamental mass scale is constrained as m_\eta \gsim 1.1\times 10^7 GeV for $\bar{g}\sim 10^{-5}$.Comment: 10 pages, 12 figure

The effect of electromechanical coupling on the strain in AlGaN/GaN heterojunction field effect transistors

The strain in AlGaN/GaN heterojunction field-effect transistors (HFETs) is examined theoretically in the context of the fully-coupled equation of state for piezoelectric materials. Using a simple analytical model, it is shown that, in the absence of a two-dimensional electron gas (2DEG), the out-of-plane strain obtained without electromechanical coupling is in error by about 30% for an Al fraction of 0.3. This result has consequences for the calculation of quantities that depend directly on the strain tensor. These quantities include the eigenstates and electrostatic potential in AlGaN/GaN heterostructures. It is shown that for an HFET, the electromechanical coupling is screened by the 2DEG. Results for the electromechanical model, including the 2DEG, indicate that the standard (decoupled) strain model is a reasonable approximation for HFET calculataions. The analytical results are supported by a self-consistent Schr\"odinger-Poisson calculation that includes the fully-coupled equation of state together with the charge-balance equation.Comment: 6 figures, revte

On two pieces of folklore in the AdS/CFT duality

In the AdS/CFT duality, it is often said that a local symmetry in a bulk theory corresponds to a global symmetry in the corresponding boundary theory, but the global symmetry can become local when one couples with an external source. As a result, the GKP-Witten relation gives a response function instead of a Green function. We explore this point in details using the example of holographic superconductors. We point out that these points play a crucial role to interpret the holographic London equation properly.Comment: 11 pages, ReVTeX4.1; v2: added discussio