Compact full ku-band triplexer with improved e-plane power divider

An improved E-plane power divider for compact waveguide triplexers with large separation between channels is presented. The configuration of the divider aims to exploit the different behavior of the device for frequency bands with large separation, leading to a very asymmetric E-plane junction. H-plane filters with inductive windows are used for each channel, in order to obtain reduced insertion losses and lower sensitivity than in metal-insert E-plane filters. The resultant triplexer configuration is very compact, and its design is analyzed and optimized by Mode-Matching. The experimental results of a full Ku-band prototype for communications satellite systems show a very good agreement with the expected simulated response

Phase diagram of the (bosonic) Double-Exchange Model

The phase diagram of the simplest approximation to Double-Exchange systems, the bosonic Double-Exchange model with antiferromagnetic super-exchange coupling, is fully worked out by means of Monte Carlo simulations, large-N expansions and Variational Mean-Field calculations. We find a rich phase diagram, with no first-order phase transitions. The most surprising finding is the existence of a segment like ordered phase at low temperature for intermediate AFM coupling which cannot be detected in neutron-scattering experiments. This is signaled by a maximum (a cusp) in the specific heat. Below the phase-transition, only short-range ordering would be found in neutron-scattering. Researchers looking for a Quantum Critical Point in manganites should be wary of this possibility. Finite-Size Scaling estimates of critical exponents are presented, although large scaling corrections are present in the reachable lattice sizes.Comment: 17 pages, 14 figure

Diseño de filtros de canal elípticos y autoEcualizados en banda Ka implementados en guía rectangular plano H

En esta comunicación se presenta un proceso sistemático de diseño de filtros de canal elípticos y autoecualizados en guía de onda rectangular y configuración plano-H en banda Ka. Se pretende desarrollar una alternativa a la configuración clásica dual-mode en guía de onda circular, con el objetivo de abaratar el coste y simplificar el proceso de producción. Para validar la metodología presentada se ha diseñado, fabricado y medido un filtro de orden seis con dos ceros de transmisión a frecuencias finitas para mejorar el rechazo y dos ceros de ecualización para el retardo de grupo. Los resultados experimentales validan el método propuesto

SUE: A Special Purpose Computer for Spin Glass Models

The use of last generation Programmable Electronic Components makes possible the construction of very powerful and competitive special purpose computers. We have designed, constructed and tested a three-dimensional Spin Glass model dedicated machine, which consists of 12 identical boards. Each single board can simulate 8 different systems, updating all the systems at every clock cycle. The update speed of the whole machine is 217ps/spin with 48 MHz clock frequency. A device devoted to fast random number generation has been developed and included in every board. The on-board reprogrammability permits us to change easily the lattice size, or even the update algorithm or the action. We present here a detailed description of the machine and the first runs using the Heat Bath algorithm.Comment: Submitted to Computer Physics Communications, 19 pages, 5 figures, references adde

Dynamical generation of a gauge symmetry in the Double-Exchange model

It is shown that a bosonic formulation of the double-exchange model, one of the classical models for magnetism, generates dynamically a gauge-invariant phase in a finite region of the phase diagram. We use analytical methods, Monte Carlo simulations and Finite-Size Scaling analysis. We study the transition line between that region and the paramagnetic phase. The numerical results show that this transition line belongs to the Universality Class of the Antiferromagnetic RP(2) model. The fact that one can define a Universality Class for the Antiferromagnetic RP(2) model, different from the one of the O(N) models, is puzzling and somehow contradicts naive expectations about Universality

An in-depth view of the microscopic dynamics of Ising spin glasses at fixed temperature

Using the dedicated computer Janus, we follow the nonequilibrium dynamics of the Ising spin glass in three dimensions for eleven orders of magnitude. The use of integral estimators for the coherence and correlation lengths allows us to study dynamic heterogeneities and the presence of a replicon mode and to obtain safe bounds on the Edwards-Anderson order parameter below the critical temperature. We obtain good agreement with experimental determinations of the temperature-dependent decay exponents for the thermoremanent magnetization. This magnitude is observed to scale with the much harder to measure coherence length, a potentially useful result for experimentalists. The exponents for energy relaxation display a linear dependence on temperature and reasonable extrapolations to the critical point. We conclude examining the time growth of the coherence length, with a comparison of critical and activated dynamics.Comment: 38 pages, 26 figure

Experimental verification of extraordinary transmission without surface plasmons

This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.This letter provides an experimental demonstration of extraordinary transmission in a closed waveguide system loaded with an electrically small diaphragm. This is a situation where the standard surface plasmon polariton SPP theory does not apply. The theoretical explanation is then based on the concept of impedance matching. This concept has previously been applied by some of the authors to account for enhanced transmission in situations where surface plasmon theory can be used: periodic arrays of small holes or slits in flat metal screens. The experiment in this letter supports the impedance matching model, valid for when SPPs are present or not. © 2009 American Institute of PhysicsThe authors would like to acknowledge the support of this research by the Spanish Ministry of Science and Innovation and European Union Feder Funds Grant Nos. TEC2007-65376 and Consolider Ingenio 2010 CSD2008- 00066 and by the Spanish Junta de Andalucía Project No. TIC-25

Ianus: an Adpative FPGA Computer

Dedicated machines designed for specific computational algorithms can outperform conventional computers by several orders of magnitude. In this note we describe {\it Ianus}, a new generation FPGA based machine and its basic features: hardware integration and wide reprogrammability. Our goal is to build a machine that can fully exploit the performance potential of new generation FPGA devices. We also plan a software platform which simplifies its programming, in order to extend its intended range of application to a wide class of interesting and computationally demanding problems. The decision to develop a dedicated processor is a complex one, involving careful assessment of its performance lead, during its expected lifetime, over traditional computers, taking into account their performance increase, as predicted by Moore's law. We discuss this point in detail

Matching microscopic and macroscopic responses in glasses

We first reproduce on the Janus and Janus II computers a milestone experiment that measures the spin-glass coherence length through the lowering of free-energy barriers induced by the Zeeman effect. Secondly we determine the scaling behavior that allows a quantitative analysis of a new experiment reported in the companion Letter [S. Guchhait and R. Orbach, Phys. Rev. Lett. 118, 157203 (2017)]. The value of the coherence length estimated through the analysis of microscopic correlation functions turns out to be quantitatively consistent with its measurement through macroscopic response functions. Further, non-linear susceptibilities, recently measured in glass-forming liquids, scale as powers of the same microscopic length.Comment: 6 pages, 4 figure