Partial symmetry and existence of least energy solutions to some nonlinear elliptic equations on Riemannian models

We consider least energy solutions to the nonlinear equation $-\Delta_g u=f(r,u)$ posed on a class of Riemannian models $(M,g)$ of dimension $n\ge 2$ which include the classical hyperbolic space $\mathbb H^n$ as well as manifolds with unbounded sectional geometry. Partial symmetry and existence of least energy solutions is proved for quite general nonlinearities $f(r,u)$, where $r$ denotes the geodesic distance from the pole of $M$

Interplane charge dynamics in a valence-bond dynamical mean-field theory of cuprate superconductors

We present calculations of the interplane charge dynamics in the normal state of cuprate superconductors within the valence-bond dynamical mean-field theory. We show that by varying the hole doping, the c-axis optical conductivity and resistivity dramatically change character, going from metallic-like at large doping to insulating-like at low-doping. We establish a clear connection between the behavior of the c-axis optical and transport properties and the destruction of coherent quasiparticles as the pseudogap opens in the antinodal region of the Brillouin zone at low doping. We show that our results are in good agreement with spectroscopic and optical experiments.Comment: 5 pages, 3 figure

Impact of electronic correlations on the equation of state and transport in ϵ\epsilon-Fe

We have obtained the equilibrium volumes, bulk moduli, equations of state of the ferromagnetic cubic $\alpha$ and paramagnetic hexagonal $\epsilon$ phases of iron in close agreement with experiment using an ab initio dynamical mean-field theory approach. The local dynamical correlations are shown to be crucial for a successful description of the ground-state properties of paramagnetic $\epsilon$-Fe. Moreover, they enhance the effective mass of the quasiparticles and reduce their lifetimes across the $\alpha \to \epsilon$ transition leading to a step-wise increase of the resistivity, as observed in experiment. The calculated magnitude of the jump is significantly underestimated, which points to non-local correlations. The implications of our results for the superconductivity and non-Fermi-liquid behavior of $\epsilon$-Fe are discussed.Comment: 6 pages, 3 figure

Photometric and spectroscopic variations of the Be star HD 112999

Be objects are stars of B spectral type showing lines of the Balmer series in emission. The presence of these lines is attributed to the existence of an extended envelope, disk type, around them. Some stars are observed in both the Be and normal B-type spectroscopic states and they are known as transient Be stars. In this paper we show the analysis carried out on a new possible transient Be star, labelled HD 112999, using spectroscopic optical observations and photometric data.Comment: 10 pages, 5 figures, accepted for publication in IBV

Conformal Antenna Array for Millimeter-Wave Communications: Performance Evaluation

In this paper, we study the influence of the radius of a cylindrical supporting structure on radiation properties of a conformal millimeter-wave antenna array. Bent antenna array structures on cylindrical surfaces may have important applications in future mobile devices. Small radii may be needed if the antenna is printed on the edges of mobile devices and in items which human beings are wearing, such as wrist watches, bracelets and rings. The antenna under study consists of four linear series-fed arrays of four patch elements and is operating at 58.8 GHz with linear polarization. The antenna array is fabricated on polytetrafluoroethylene substrate with thickness of 0.127 mm due to its good plasticity properties and low losses. Results for both planar and conformal antenna arrays show rather good agreement between simulation and measurements. The results show that conformal antenna structures allow achieving large angular coverage and may allow beam-steering implementations if switches are used to select between different arrays around a cylindrical supporting structure.Comment: Keywords: conformal antenna, millimeter-wave communications, patch antenna array. 11 pages, 10 figures, 1 tabl

A Web-Based Distributed Virtual Educational Laboratory

Evolution and cost of measurement equipment, continuous training, and distance learning make it difficult to provide a complete set of updated workbenches to every student. For a preliminary familiarization and experimentation with instrumentation and measurement procedures, the use of virtual equipment is often considered more than sufficient from the didactic point of view, while the hands-on approach with real instrumentation and measurement systems still remains necessary to complete and refine the student's practical expertise. Creation and distribution of workbenches in networked computer laboratories therefore becomes attractive and convenient. This paper describes specification and design of a geographically distributed system based on commercially standard components

Short-time dynamics of finite-size mean-field systems

We study the short-time dynamics of a mean-field model with non-conserved order parameter (Curie-Weiss with Glauber dynamics) by solving the associated Fokker-Planck equation. We obtain closed-form expressions for the first moments of the order parameter, near to both the critical and spinodal points, starting from different initial conditions. This allows us to confirm the validity of the short-time dynamical scaling hypothesis in both cases. Although the procedure is illustrated for a particular mean-field model, our results can be straightforwardly extended to generic models with a single order parameter.Comment: accepted for publication in JSTA