Adriana Gomes Dickman

THEORY OF THE NO+CO SURFACE-REACTION MODEL

We derive a pair approximation (PA) for the NO+CO model with instantaneous reactions. For both the triangular and square lattices, the PA, derived here using a simpler approach, yields a phase diagram with an active state for CO-fractions y in the interval y(1)<y<y(2), with a continuous (discontinuous) phase transition to a poisoned state at y(1) (y(2)). This is in qualitative agreement with simulation for the triangular lattice, where our theory gives a rather accurate prediction for y(2). To obtain the correct phase diagram for the square lattice, i.e., no active stationary state, we reformulate the PA using sublattices. The (formerly) active regime is then replaced by a poisoned state with broken symmetry (unequal sublattice coverages), as observed recently by Kortlüke et al. [Chem. Phys. Lett. 275, 85 (1997)]. In contrast with their approach, in which the active state persists, although reduced in extent, we report here the qualitatively correct theory of the NO+CO model on the square lattice. Surface diffusion of nitrogen can lead to an active state in this case. In one dimension, the PA predicts that diffusion is required for the existence of an active state.

A globally accurate theory for a class of binary mixture models

The self-consistent Ornstein-Zernike approximation results for the 3D Ising model are used to obtain phase diagrams for binary mixtures described by decorated models, yielding the plait point, binodals, and closed-loop coexistence curves for the models proposed by Widom, Clark, Neece, and Wheeler. The results are in good agreement with series expansions and experiments.

Adapting diagrams from physics textbooks: a way to improve the autonomy of blind students

We devise and test a set of tactile symbols to represent elements frequently used in mechanics diagrams, such as vectors, ropes, pulleys, blocks and surfaces, that can be used to adapt drawings of physics situations in textbooks for blind students. We also investigate how figures are described for blind students in classroom activities and exams, by interviewing three blind students using the oral history method. The symbols were tested at a specialized school for the blind. Our results indicate that, with training, blind students become familiar with the symbols and can identify them in a problem without the need for a spoken description. This educational product can help blind students to achieve the same conditions of autonomy as sighted ones when studying physics.

Computational model of a vector-mediated epidemic

We discuss a lattice model of vector-mediated transmission of a disease to illustrate how simulations can be applied in epidemiology. The population consists of two species, human hosts and vectors, which contract the disease from one another. Hosts are sedentary, while vectors (mosquitoes) diffuse in space. Examples of such diseases are malaria, dengue fever, and Pierces disease in vineyards. The model exhibits a phase transition between an absorbing (infection free) phase and an active one as parameters such as infection rates and vector density are varied.

Website: material de apoio para professores de biofísica aplicada a enfermagem

In this paper we report the elaboration process of a didactic material, in the form of a website, designed to help teachers to prepare biophysics classes in nursing programmes. The material includes compiled texts, exercises, videos, applets, problem-based situations and scientific papers about biophysics applied to nursing. The methodology used to select the discussed topics involves research carried out with teachers and students in nursing programs, in addition to professional nurses. The topics discussed in the material are related to hydrostatics, hydrodynamics, and scaling laws in biology, including instructions suggesting how to approach the contents, based on the problem-based learning (PBL) methodology. Biology and physics teachers indicated, through an evaluation, that the material is appropriate, providing useful information about biophysics considering the professional practice of the future nurses.

Verificando a lei de Boyle em um laboratório didático usando grandezas estritamente mensuráveis

We propose an alternative way to verify Boyles law. Our procedure uses only measurable quantities such as manometric pressure and the variation in the volume of the gas, in a setup consisting of a syringe connected to a manometer. Using simple algebra one can obtain a linear relation between the inverse of these variables. A linear fit of the experimental data provides estimates of the absolute pressure and the total volume (syringe plus hose), quantities that cannot be measured directly in this case. It therefore makes sense to verify the compatibility of the data with the linear expression representing Boyles law, rather than introducing values for the initial absolute pressure and the total volume, which would have to be obtained in separate experiments.

Phase diagram and critical behavior of the pair annihilation model

We study the critical behavior of the pair annihilation model (PAM) with diffusion in one, two and three dimensions, using the pair approximation (PA) and Monte Carlo simulation. Of principal interest is the dependence of the critical creation rate, λc, on the diffusion probability D, in particular, whether survival is possible at arbitrarily small creation rates, for sufficiently rapid diffusion. Whilst the PA predicts that in any spatial dimension d ≥ 1, at some diffusion probability D* 0 for any D < 1. Our simulation results are consistent with this theorem. In two dimensions, the extinction region becomes narrow as D approaches unity. Our results are well described by , with γ = 1.43(2). In three dimensions we find D* = 0.340 53(1). The simulation results confirm that the PAM belongs to the directed percolation universality class.

Transferência de fluido por meio de um sifão vs. aplicação da equação de Bernoulli

A basic physics problem consists in analyzing the transfer of fluid between two containers using a siphon. We show that a careful analysis of this situation, using Bernoullis theorem, leads to conceptual misinterpretations if the fluid viscosity is neglected, as is usually required in the exercises. In this work, besides discussing possible solutions to the problem and identifying the conceptual mistakes involved, we present a model for the correct description of the system, considering energy loss in the siphon.

Transições de fase sem termodinâmica

Phase transitions find application well beyond the context of equilibrium thermodynamics, where they arose. We review one of the prime examples of a phase transition in a system lacking thermodynamics, the contact process (PC), emphasizing mean-field theory methods. We also present mean-field results for a model of transmission of malaria in a population, and discuss the new approaches of quasi-stationary distributions, and the conserved contact process.