Transient Nucleation near the Mean-Field Spinodal

Nucleation is considered near the pseudospinodal in a one-dimensional $\phi^4$ model with a non-conserved order parameter and long-range interactions. For a sufficiently large system or a system with slow relaxation to metastable equilibrium, there is a non-negligible probability of nucleation occurring before reaching metastable equilibrium. This process is referred to as transient nucleation. The critical droplet is defined to be the configuration of maximum likelihood that is dynamically balanced between the metastable and stable wells. Time-dependent droplet profiles and nucleation rates are derived, and theoretical results are compared to computer simulation. The analysis reveals a distribution of nucleation times with a distinct peak characteristic of a nonstationary nucleation rate. Under the quench conditions employed, transient critical droplets are more compact than the droplets found in metastable equilibrium simulations and theoretical predictions.Comment: 7 Pages, 5 Figure

Comments on "There is no axiomatic system for the quantum theory"

In a recent paper, Nagata [1] claims to derive inconsistencies from quantum mechanics. In this paper, we show that the inconsistencies do not come from quantum mechanics, but from extra assumptions about the reality of observables

Intense CIII] 1907,1909 emission from a strong Lyman continuum emitting galaxy

We have obtained the first complete ultraviolet (UV) spectrum of a strong Lyman continuum(LyC) emitter at low redshift -- the compact, low-metallicity, star-forming galaxy J1154+2443 -- with a Lyman continuum escape fraction of 46% discovered recently. The Space Telescope Imaging Spectrograph spectrum shows strong Lya and CIII] 1909 emission, as well as OIII] 1666. Our observations show that strong LyC emitters can have UV emission lines with a high equivalent width (e.g. EW(CIII])$=11.7 \pm 2.9 \AA$ rest-frame), although their equivalent widths should be reduced due to the loss of ionizing photons. The intrinsic ionizing photon production efficiency of J1154+2443 is high, $\log(\xi_{\rm ion}^0)=25.56$ erg$^{-1}$ Hz, comparable to that of other recently discovered $z \sim 0.3-0.4$ LyC emitters. Combining our measurements and earlier determinations from the literature, we find a trend of increasing $\xi_{\rm ion}^0$ with increasing CIII] 1909 equivalent width, which can be understood by a combination of decreasing stellar population age and metallicity. Simple ionization and density-bounded photoionization models can explain the main observational features including the UV spectrum of J1154+2443.Comment: 5 pages, 4 figures. Accepted for publication in A&A Letter

Local cosmic string in generalised scalar tensor theory

A recent investigation shows that a local gauge string with a phenomenological energy momentum tensor, as prescribed by Vilenkin, is inconsistent in Brans-Dicke theory. In this work it has been shown that such a string is consistent in a more general scalar tensor theory where $\omega$ is function of the scalar field.A set of solutions of full nonlinear Einstein's equations for interior region of such a string are presented.Comment: 7 pages, latex format, minor changes according to referee's suggestions, revised version submitted in Phys.Rev.

Utilização do modelo ZAE/FAO para a estimativa da produtividade do sorgo em Alagoas.

O manejo adequado, como a escolha da época de plantio ou o uso da irrigação, permite o maior aproveitamento dos recursos hídricos disponíveis no ambiente. Pode-se estimar a produtividade agrícola da cultura do sorgo através de modelos, desde que calibrados, permitindo variar os manejos. Dessa forma é possível conhecer a resposta da cultura à disponibilidade hídrica de cada local e sua variação ao longo do ano. Assim o objetivo do trabalho foi calibrar o modelo ZAE, estimar a produtividade e avaliar quais as épocas de plantio com menor risco para a cultura do sorgo no Estado de Alagoas. Para calibração do modelo ZAE/FAO foram utilizados dados provenientes do Programa de Melhoramento Genético de Sorgo do Nordeste na região de Araripina ? PE, após a calibração foram simulados os cenários para as cidades de Água Branca, Arapiraca, Palmeira dos Índios e Porto de Pedras, em Alagoas, baseados na época de plantio (a cada 10 dias) x CAD do solo (30, 40 e 65 mm) X sistema de plantio (sequeiro). O modelo apresentou ótimo ajuste, com R2 = 0,87; índice de Wilmont (d) = 0,94; índice de confiabilidade (IC) de 0,87. As produtividades variaram de 1,8 a 1,9 Mg ha-¹, em Água Branca, de 3,7 a 4,1 Mg ha-¹ em Arapiraca, 1,9 a 2,0 Mg ha-¹ em Palmeira dos Índios, 2,2 a 2,3 Mg ha-¹ em Porto de Pedras, no mês de plantio mais produtivo

Fibrous model for the simulation of the cyclic behaviour of 3D reinforced concrete frames

Relatório 07-DEC/E-04Non-linear finite element analysis has attracted a lot of attention in last few decades, as real life problems dealing with analysis of concrete beams and columns are generally non-linear in nature. This project deals with non-linear analysis of beam and columns, using Timoshenko beam theory. The Timoshenko beam theory is applied to every element, but before applying the theory the element is divided into fibers. The fibers as a whole will govern the behavior of element. The section of each element is divided in “finite elements”. Each finite element is a fiber along the length of element. Each fiber element is independent in terms of the material constitutive laws, which govern the behavior, while at the same time they are associated to each other by the relation of displacements. The material laws of each fiber deals with the stress-strain relation The numerical results are compared with the experimental results, which show a reasonable correlation, and in turn demonstrate the capability of the proposed model to depict the cyclic behavior of concrete elements

Numerical model for CFRP confined concrete elements subject to monotonic and cyclic loadings

Uniaxial cyclic and monotonic compression tests were carried out on partially and fully wrapped concrete cylinders with Carbon Fibre Reinforced Polymer (CFRP) wet lay-up sheets. The influence of the concrete compressive strength, CFRP stiffness, geometric confinement arrangement and loading type on the compressive behaviour of reinforced concrete column elements of circular cross section up to their failure was assessed. A uniaxial stress-strain constitutive model is proposed, and the results obtained from the experimental tests were used to calibrate some of the parameters of this model, and to appraise the model performance. This model allows the simulation of reinforced concrete members by using Timoshenko one-dimensional elements, in the context of the finite element method (fibre model). Good agreement was obtained between numerical simulations and experimental results for both monotonic and cyclic loading tests.The first author acknowledges the support provided by the grant within the ambit of the research program PABERPRO supported by Program POCI 2010 - IDEIA, Project No. 13-05-04-FDR-00007, contract reference ADI/2007/V4.1/0049. The present work was also supported by Program PIDDAC, Project No. PTDC/ECM/74337/2006 by FCT. The authors acknowledge the materials generously supplied by S&P and Degussa Portugal

Design-curves of strain softening and strain hardening fibre reinforced concrete elements subjected to axial load and bending moments

Several structural components made by fibre reinforced concrete (FRC) are submitted to axial load and bending moments. In some cases fibres cannot replace completely the conventional reinforcement, even if strain hardening FRC is used; therefore the optimization of the reinforcement solution for these elements depends on the post-cracking behaviour of the FRC, as well as the percentage of conventional reinforcement to replace. To fully exploit the FRC capabilities, the development of a suitable, comprehensive and design-oriented model of its tensile response is of the utmost importance. To provide a practical tool for the pre-design of FRC-structural-elements subjected to axial load and bending moments, design curves were generated using a computational program capable of simulating the main features of the tensile and compressive behaviour of strain softening and strain hardening FRC’s, and steel bars. The post-cracking tensile behaviour of the FRC is characterized by two parameters that define its residual strength ratio (α) and its corresponding tensile strain ratio (β). To generate these curves, a parametric study is carried out based on the tensile parameters α and β and considering distinct mechanical reinforcement ratios, from 0 to 1 with a step of 0.2. For every reinforcement ratio, four distinct cases in terms of β are considered; additionally, for every case of β, α is divided from strain hardening to strain softening in five distinct residual strength classes. By sequentially varying α and β, the bending capacity of a section is evaluated to provide a design perspective of the effect of ductility and strength. The model used in this study is described, the design curves are presented and analyzed and some practical design examples are provided