Entanglement entropy for the n-sphere

We calculate the entanglement entropy for a sphere and a massless scalar field in any dimensions. The reduced density matrix is expressed in terms of the infinitesimal generator of conformal transformations keeping the sphere fixed. The problem is mapped to the one of a thermal gas in a hyperbolic space and solved by the heat kernel approach. The coefficients of the logarithmic term in the entropy for 2 and 4 spacetime dimensions are in accordance with previous numerical and analytical results. In particular, the four-dimensional result, together with the one reported by Solodukhin, gives support to the Ryu–Takayanagi holographic ansatz. We also find that there is no logarithmic contribution to the entropy for odd spacetime dimensions.     

Interactions of Cu(I) with selenium-containing amino acids determined by NMR, XAS, and DFT studies

Cu(I) coordination by organoselenium compounds was recently reported as a mechanism for their prevention of copper-mediated DNA damage. To establish whether direct Se-Cu coordination may be involved in selenium antioxidant activity, Cu(I) coordination of the selenoamino acids methyl-Se-cysteine (MeSeCys) and selenomethionine (SeMet) was investigated. NMR results in D(2)O indicate that Cu(I) binds to the Se atom of both MeSeCys and SeMet as well as the carboxylic acid oxygen atom(s) or amine nitrogen atoms. X-ray absorption spectroscopy (XAS) and density functional theory (DFT) results confirm Se-Cu coordination, with the identification of a 2.4 ? Se-Cu vector in both the Se- and Cu-EXAFS data. XAS studies also show Cu(I) in an unusual three-coordinate environment with the additional two ligands arising from O/N (2.0 ?). DFT models of 1:1 Cu-selenoamino acid complexes suggest that both selenoamino acids coordinate Cu(I) through the selenium and amino groups, with the third ligand assumed to be water. These compounds represent the first structurally characterized copper(I) complexes with sulfur- or selenium-containing amino acids.     

Effect of phosphomolybdic acid on the catalytic behavior of bifunctional Pt-Cr/nanocrystalline Y zeolite in hydroisomerization of n-octane

In this study, Y zeolite nanocrystals were synthesized without an organic template and were used as a support for bifunctional nanocatalysts in the hydroisomerization of n-octane. Different types of catalysts were synthesized by loading Pt, Cr, and phosphomolybdic acid (HPMo) on Y zeolite nanocrystal supports and were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), field emission scanning electron microscope (FE-SEM), and transmission electron microscope (TEM) analysis. The Cr-Pt/HPMo-Y nanocatalyst with a surface area of approx. 600 m²/g showed the best performance in the hydroisomerization of n-octane. The optimization of n-octane hydroisomerization over bifunctional nanocatalysts supported on nanocrystalline Y zeolite, in the presence of H₂ gas, was applied based on the response surface methodology (RSM) and Box–Behnken design (BBD) template. The effect of three different process variables on the yield of iso-alkanes as the purpose process was determined. Experiments were carried out using a fixed-bed microreactor under different ranges of weight hourly space velocity (WHSV) (A = 0.5–1.5 hr⁻¹), H₂ to n-C₈ molar ratio (B = 1:1–3:1), and reaction temperature (C = 200–300°C). The RSM proved that the temperature variable had the greatest impact on the hydroisomerization reaction yield.     

Un método de captura de choques basado en las funciones de forma para Galerkin discontinuo de alto orden

This article presents a high-order Discontinuous Galerkin method for compressible flow problems, in which is very frequent the formation of shocks. The stabilization is introduced by a new basis functions. This base has the flexibility to vary locally (within each element) between continuous polynomial functions space and a space of piecewise polynomial functions. Thus, the proposed method provides a bridge between the standard methods of high-order Discontinuous Galerkin and classical Finite Volume methods, maintaining the locality and compactness of the scheme. The variation of basis functions is automatically set according to the regularity of the solution and the stabilization is introduced by the jump operator, standard in Discontinuous Galerkin methods. Unlike the classical methods of slope limiting, the strategy here presented is very local, robust, and applies to any order of approximation. Moreover, the proposed method does not require adaptive mesh refinement techniques and it can be used with any temporal integration scheme. Several applications of the Euler equations are shown, demonstrating the validity and effectiveness of the method, especially for high orders of approximation.     

Entropy,information theory,and the approach to equilibrium of coupled harmonic oscillator systems

Finite segments of infinite chains of classical coupled harmonic oscillators are treated as models of thermodynamic systems in contact with a heat bath, i.e., canonical ensembles. The Liouville function for the infinite chain is reduced by integrating over the outside variables to a function _N of the variables of theN-particle segment that is the thermodynamic system. The reduced Liouville function _N which is calculated from the dynamics of the infinite chain and the statistical knowledge of the coordinates and momenta att = 0, is a time-dependent probability density in the 2N-dimensional phase space of the system. A Gibbs entropy defined in terms of _N measures the evolution of knowledge of the system (more accurately, the growth of missing pertinent information) in the sense of information theory. As ¦t ¦ , energy is equipartitioned, the entropy evolves to the value expected from equilibrium statistical mechanics, and _N evolves to an equilibrium distribution function. The simple chain exhibits diffusion in coordinate space, i.e., Brownian motion, and the diffusivity is shown to depend only on the initial distribution of momenta (not of coordinates) in the heat bath. The harmonically bound chain, in the limit of weak coupling, serves as an excellent model for the approach to equilibrium of a canonical ensemble of weakly interacting particles.     

Dynamical encoding by networks of competing neuron groups: winnerless competition

Following studies of olfactory processing in insects and fish, we investigate neural networks whose dynamics in phase space is represented by orbits near the heteroclinic connections between saddle regions (fixed points or limit cycles). These networks encode input information as trajectories along the heteroclinic connections. If there are N neurons in the network, the capacity is approximately e(N-1)!, i.e., much larger than that of most traditional network structures. We show that a small winnerless competition network composed of FitzHugh-Nagumo spiking neurons efficiently transforms input information into a spatiotemporal output.     

Cosmological bounds on a left-right symmetric model

The right-handed neutrino cross sections of the processes ν_L + ? → ν_R + ? and ν_R + ? → ν_R + ?, where ? is a relativistic lepton, are calculated in the SU(2)_L × SU(2)_R × U(1) model. According to a cosmological criterion the parameters of the model are bounded. In particular we obtain the bound $\text{M}{}_{\mathrm{<mtext>W</mtext>}}{}_{\mathrm{<mtext>R</mtext>}}\text{? 30 M}{}_{\mathrm{<mtext>W</mtext>}}{}_{\mathrm{<mtext>L</mtext>}}$, assuming the neutrinos are Dirac four-component particles.     

Finite conductivity and the interchange instability in railgun arcs

A first-order perturbation expansion of the MHD (magnetohydrodynamic) equation is used to describe the onset of the interchange instability due to the high accelerations in railgun plasma-arc armatures. J.D. Powell (1986) considered the problem of perturbing an initial isothermal equilibrium with appropriate distributed current and density profiles, treating the perturbation equations with infinite conductivity. Here, the authors model the arc the same way, but they include the effects of finite conductivity σ. A fourth-order mode equation is derived and solved numerically. The authors find continuous spectra of unstable modes for a nonzero plasma acceleration g, whose growth rates are mostly greater than √kg, depending on the values of k and σ. The resistivity always raises growth rates higher than Powell's especially for large k and large resistivity. The resulting growth rates in typical railgun situations are large enough to permit full development of the instability     

Reproducible sequence generation in random neural ensembles

Little is known about the conditions that neural circuits have to satisfy to generate reproducible sequences. Evidently, the genetic code cannot control all the details of the complex circuits in the brain. In this Letter, we give the conditions on the connectivity degree that lead to reproducible and robust sequences in a neural population of randomly coupled excitatory and inhibitory neurons. In contrast to the traditional theoretical view we show that the sequences do not need to be learned. In the framework proposed here just the averaged characteristics of the random circuits have to be under genetic control. We found that rhythmic sequences can be generated if random networks are in the vicinity of an excitatory-inhibitory synaptic balance. Reproducible transient sequences, on the other hand, are found far from a synaptic balance.     

Magnetically active Ag–Zn nanoferrites synthesized by solution combustion route: physical chemical studies and density functional theory analysis

Nanoparticles with mixed compositions, particularly spinel ferrites with magnetic activity, have arisen as contrast agents for magnetic resonance imaging, magnetic hyperthermia. For such applications, it is desirable to possess specific particle size and physicochemical properties, i.e., magnetic response, porosity, crystallinity, and so on. It is well known that controlling specific variables in the synthetic process has a dramatic effect on final product properties and behavior. Amid preparation techniques reported in the literature, low-temperature solution combustion method has shown the ability to control and direct synthesis simply and efficiently. We are presenting a study about controlling and tuning the magnetic properties and the effect of particle size modified in Ag–Zn nanoferrites with different amounts of Co and Ni as doping metals. Different combinations of Co and Ni within Ag–Zn (Ag_0.25Zn_0.5-xM_xFe_2.25O₄) nanoferrites have been synthesized using the low-temperature solution combustion technique, and this method proved to be efficient and reliable for developing homogenous, fine structured materials. X-ray diffraction confirmed that the atomic structure of prepared nanoferrites is pure and cubic, whereas electron microscopy confirmed a semispherical and monodisperse morphology with particle diameter around 20 nm. The magnetic behavior of bred materials has been explained by analyzing magnetic factors such as saturation magnetization, coercivity, and retentivity, and all experimental findings are matched with theoretical density functional theory (DFT) studies to understand the effect of each material within A and B sites in ferrite crystal cell. The observed magnetic properties highlight the superparamagnetic behavior and the effect of doping metals which is an asset in developing new materials for diagnostic and therapeutic applications. DFT modeling was achieved in an attempt to understand the effect of metal substitution in cubic ferrite cells.