A mean-field monomer-dimer model with attractive interaction. The exact solution

A mean-field monomer-dimer model which includes an attractive interaction among both monomers and dimers is introduced and its exact solution rigorously derived. The Heilmann-Lieb method for the pure hard-core interacting case is used to compute upper and lower bounds for the pressure. The bounds are shown to coincide in the thermodynamic limit for a suitable choice of the monomer density m. The consistency equation characterising m is studied in the phase space (h, J), where h tunes the monomer potential and J the attractive potential. The critical point and exponents are computed and show that the model is in the mean-field ferromagnetic universality class.Comment: 32 pages, 6 figure

The Spectral Function for Finite Nuclei in the Local Density Approximation

The spectral function for finite nuclei is computed within the framework of the Local Density Approximation, starting from nuclear matter spectral functions obtained with a realistic nucleon-nucleon interaction. The spectral function is decomposed into a single-particle part and a ''correlated'' part; the latter is treated in the local density approximation. As an application momentum distributions, quasi-particle strengths and overlap functions for valence hole states, and the light-cone momentum distribution in finite nuclei are computed.Comment: 21 pages + 9 figures available upon request, RevTex, preprint KVI-108

Classical Rotons in Cold Atomic Traps

We predict the emergence of a roton minimum in the dispersion relation of elementary excitations in cold atomic gases in the presence of diffusive light. In large magneto-topical traps, multiple-scattering of light is responsible for the collective behavior of the system, which is associated to an effective Coulomb-like interaction between the atoms. In optically thick clouds, the re-scattered light undergoes diffusive propagation, which is responsible for a stochastic short-range force acting on the atoms. We show that the dynamical competition between these two forces results on a new polariton mode, which exhibits a roton minimum. Making use of Feynman's formula for the static structure factor, we show that the roton minimum is related to the appearance of long-range order in the system.Comment: 5 pages, 3 figure

An Extended Variational Principle for the SK Spin-Glass Model

The recent proof by F. Guerra that the Parisi ansatz provides a lower bound on the free energy of the SK spin-glass model could have been taken as offering some support to the validity of the purported solution. In this work we present a broader variational principle, in which the lower bound, as well as the actual value, are obtained through an optimization procedure for which ultrametic/hierarchal structures form only a subset of the variational class. The validity of Parisi's ansatz for the SK model is still in question. The new variational principle may be of help in critical review of the issue.Comment: 4 pages, Revtex

General properties of overlap probability distributions in disordered spin systems. Toward Parisi ultrametricity

For a very general class of probability distributions in disordered Ising spin systems, in the thermodynamical limit, we prove the following property for overlaps among real replicas. Consider the overlaps among s replicas. Add one replica s+1. Then, the overlap q(a,s+1) between one of the first s replicas, let us say a, and the added s+1 is either independent of the former ones, or it is identical to one of the overlaps q(a,b), with b running among the first s replicas, excluding a. Each of these cases has equal probability 1/s.Comment: LaTeX2e, 11 pages. Submitted to Journal of Physics A: Mathematical and General. Also available at http://rerumnatura.zool.su.se/stefano/ms/ghigu.p

Cohomology rings of extended powers and free infinite loop spaces

We calculate mod-p cohomology of extended powers, and their group completions which are free infinite loop spaces. We consider the cohomology of all extended powers of a space together and identify a Hopf ring structure with divided powers within which cup product structure is more readily computable than on its own. We build on our previous calculations of cohomology of symmetric groups, which are the cohomology of extended powers of a point, the well-known calculation of homology, and new results on cohomology of symmetric groups with coefficients in the sign representation. We then use this framework to understand cohomology rings of related spaces such as infinite extended powers and free infinite loop spaces.Comment: 37 pages, 1 figur

Designing and Building a Wireless Network Prototype for the Management and Invoicing System of Real-Time Commands, Implemented to Smart Restaurants

This paper proposes a design and construction of a wireless network prototype for the management and invoicing system of real-time commands, which is implemented to smart bar-restaurants. It is mainly made up of three modules that are interlinked through Wi-fi wireless technology. The administration module provides all the information required for commands management and invoices to the user through the management module that uses touch-based devices, this generated information is sent directly to the preparation module. The communication of each module is performed with SQL searches on the database server developed on phpAdmin. An application was developed for each module in the Android Studio and NetBeans programming environments. The applied methodology is based on surveys that determine the prototype needs and requirements. For prototype validation, a series of tests were conducted on the integral operation and wireless communication range of the latter, establishing the maximum operating distance at 33.75 meters, so that the operation did not present malfuncions due to the Location dimensions are within range. Menu query times were verified obtaining that the system optimizes in 86.00% the time used in the traditional way. Significantly reduces command management time by 62.90%. There was no saturation in the network since the traffic generated only represented 2.76% of the router's capacity. It is recommended to hire a remote service to store the data. Keywords: wireless communication, data transmission, bandwidth, command, invoicing, wifi, system, modules. Resumen El presente artículo propone un diseño y construcción de un prototipo de red inalámbrica para la gestión y facturación de comandas en tiempo real, aplicado a la implementación de bares-restaurantes inteligentes. Está constituido por tres módulos que se comunican mediante tecnología Wi-fi. El módulo de administración proporciona la información necesaria para manejo de base de datos y facturas de usuario, el mismo que mediante el módulo de gestión utiliza dispositivos táctiles para generar pedidos, esta información es enviada directamente al módulo de preparación. La comunicación entre módulos se establece mediante consultas SQL para acceder a la base de datos creada en phpMyAdmin. Para cada módulo se desarrolló una aplicación en los entornos de programación Android Studio y NetBeans. La metodología aplicada en base a encuestas facilitó la determinación de necesidades y requerimientos del prototipo. Para la validación del sistema se realizaron pruebas sobre el funcionamiento íntegro y alcance de comunicación inalámbrica de este, estableciendo la distancia máxima de funcionamiento a los 33,75 metros, cumpliendo con las dimensiones del local en el que se implementó. Se verificaron tiempos de consulta de menú obteniendo que el sistema optimiza hasta un 86,00% los tiempos utilizados en la forma tradicional. Reduce notablemente el tiempo de toma de pedido en un 62,90%. No se presentó saturación de red ya que el tráfico generado representa el 2,76% de la capacidad del enrutador. Palabras clave: comunicación inalámbrica, transmisión de datos, ancho de banda, comanda, facturación, wifi, sistema, módulos

Sistema integrado de produção agroecológica: uma experiência de pesquisa em agricultura orgânica.

O sistema integrado de produção agroecológica (SIPA). Alguns resultados de pesquisa no SIPA.bitstream/item/111699/1/CNPAB-Sistema-Integrado-de-Producao-Agroecologica-SIPA-DOC.-169-03.pd

Mechanisms for spin suppression and orbital enhancement in M1 transitions: Critical assessment

9 págs.; 3 figs.; 3 tabs.We discuss different nuclear structure properties that may lead to spin suppression in magnetic dipole excitations (as well as in Gamow-Teller transitions). We especially compare the triaxial and the axial asymptotic deformation limits and show that the summed B(M1) strength can be quite different in the two cases. A connection between triaxial deformation and spin suppression is established. It is known, however, that modern Hartree-Fock calculations yield axially symmetric solutions for several nuclei which were previously thought to be triaxial. We show that taking into account the effects of higher shells can lead to an enhanced orbital contribution to M1 excitations without affecting ground-state magnetic moments. © 1989 The American Physical Society.This work was supported by a NATO Collaborative Research Grant (0702/87) and by the Department of Energy DE-FG05-86ER40299. One of us (E.M.G.) is also indebted to DGICYT (Spain) for partial financial support under Contract No. PB8710311.Peer Reviewe