Optimal search strategies of space-time coupled random walkers with finite lifetimes

We present a simple paradigm for detection of an immobile target by a space-time coupled random walker with a finite lifetime. The motion of the walker is characterized by linear displacements at a fixed speed and exponentially distributed duration, interrupted by random changes in the direction of motion and resumption of motion in the new direction with the same speed. We call these walkers "mortal creepers". A mortal creeper may die at any time during its motion according to an exponential decay law characterized by a finite mean death rate $\omega_m$. While still alive, the creeper has a finite mean frequency $\omega$ of change of the direction of motion. In particular, we consider the efficiency of the target search process, characterized by the probability that the creeper will eventually detect the target. Analytic results confirmed by numerical results show that there is an $\omega_m$-dependent optimal frequency $\omega=\omega_{opt}$ that maximizes the probability of eventual target detection. We work primarily in one-dimensional ($d=1$) domains and examine the role of initial conditions and of finite domain sizes. Numerical results in $d=2$ domains confirm the existence of an optimal frequency of change of direction, thereby suggesting that the observed effects are robust to changes in dimensionality. In the $d=1$ case, explicit expressions for the probability of target detection in the long time limit are given. In the case of an infinite domain, we compute the detection probability for arbitrary times and study its early- and late-time behavior. We further consider the survival probability of the target in the presence of many independent creepers beginning their motion at the same location and at the same time. We also consider a version of the standard "target problem" in which many creepers start at random locations at the same time.Comment: 18 pages, 7 figures. The title has been changed with respect to the one in the previous versio

Critical phenomena of thick branes in warped spacetimes

We have investigated the effects of a generic bulk first-order phase transition on thick Minkowski branes in warped geometries. As occurs in Euclidean space, when the system is brought near the phase transition an interface separating two ordered phases splits into two interfaces with a disordered phase in between. A remarkable and distinctive feature is that the critical temperature of the phase transition is lowered due to pure geometrical effects. We have studied a variety of critical exponents and the evolution of the transverse-traceless sector of the metric fluctuations.Comment: revtex4, 4 pages, 4 figures, some comments added, typos corrected, published in PR

Monte Carlo simulation of SU(2) Yang-Mills theory with light gluinos

In a numerical Monte Carlo simulation of SU(2) Yang-Mills theory with light dynamical gluinos the low energy features of the dynamics as confinement and bound state mass spectrum are investigated. The motivation is supersymmetry at vanishing gluino mass. The performance of the applied two-step multi-bosonic dynamical fermion algorithm is discussed.Comment: latex, 48 pages, 16 figures with epsfi

S wave velocity structure below central Mexico using high-resolution surface wave tomography

Shear wave velocity of the crust below central Mexico is estimated using surface wave dispersion measurements from regional earthquakes recorded on a dense, 500 km long linear seismic network. Vertical components of regional records from 90 well-located earthquakes were used to compute Rayleigh-wave group-velocity dispersion curves. A tomographic inversion, with high resolution in a zone close to the array, obtained for periods between 5 and 50 s reveals significant differences relative to a reference model, especially at larger periods (>30 s). A 2-D S wave velocity model is obtained from the inversion of local dispersion curves that were reconstructed from the tomographic solutions. The results show large differences, especially in the lower crust, among back-arc, volcanic arc, and fore-arc regions; they also show a well-resolved low-velocity zone just below the active part of the Trans Mexican Volcanic Belt (TMVB) suggesting the presence of a mantle wedge. Low densities in the back arc, inferred from the low shear wave velocities, can provide isostatic support for the TMVB

Poynting's theorem and energy conservation in the propagation of light in bounded media

Starting from the Maxwell-Lorentz equations, Poynting's theorem is reconsidered. The energy flux vector is introduced as S_e=(E x B)/mu_0 instead of E x H, because only by this choice the energy dissipation can be related to the balance of the kinetic energy of the matter subsystem. Conservation of the total energy as the sum of kinetic and electromagnetic energy follows. In our discussion, media and their microscopic nature are represented exactly by their susceptibility functions, which do not necessarily have to be known. On this footing, it can be shown that energy conservation in the propagation of light through bounded media is ensured by Maxwell's boundary conditions alone, even for some frequently used approximations. This is demonstrated for approaches using additional boundary conditions and the dielectric approximation in detail, the latter of which suspected to violate energy conservation for decades.Comment: 5 pages, RevTeX4, changes: complete rewrit

Costs Associated with Malaria in Pregnancy in the Brazilian Amazon, a Low Endemic Area Where Plasmodium vivax Predominates.

BACKGROUND: Information on costs associated with malaria in pregnancy (MiP) in low transmission areas where Plasmodium vivax predominates is so far missing. This study estimates health system and patient costs of MiP in the Brazilian Amazon. METHODS/PRINCIPAL FINDINGS: Between January 2011 and March 2012 patient costs for the treatment of MiP were collected through an exit survey at a tertiary referral hospital and at a primary health care centre in the Manaus metropolitan area, Amazonas state. Pregnant and post-partum women diagnosed with malaria were interviewed after an outpatient consultation or at discharge after admission. Seventy-three interviews were included in the analysis. Ninety-six percent of episodes were due to P. vivax and 4% to Plasmodium falciparum. In 2010, the total median costs from the patient perspective were estimated at US $45.91 and US$216.29 for an outpatient consultation and an admission, respectively. When multiple P. vivax infections during the same pregnancy were considered, patient costs increased up to US $335.85, representing the costs of an admission plus an outpatient consultation. Provider direct and overhead cost data were obtained from several sources. The provider cost associated with an outpatient case, which includes several consultations at the tertiary hospital was US$103.51 for a P. vivax malaria episode and US $83.59 for a P. falciparum malaria episode. The cost of an inpatient day and average admission of 3 days was US$118.51 and US $355.53, respectively. Total provider costs for the diagnosis and treatment of all malaria cases reported in pregnant women in Manaus in 2010 (N = 364) were US$17,038.50, of which 92.4% (US$ 15,741.14) due to P. vivax infection. CONCLUSION: Despite being an area of low risk malaria transmission, MiP is responsible for a significant economic burden in Manaus. Especially when multiple infections are considered, costs associated with P. vivax are higher than costs associated with P. falciparum. The information generated may help health policy decisions for the current control and future elimination of malaria in the area

Fundamentos econômicos da formação do preço internacional de açucar e dos preços domésticos de açucar e etanol.

O objetivo deste estudo foi investigar os fatores que afetam o comportamento do etanol no mercado interno e os preços do açúcar nos mercados doméstico e internacional. Três ordens de fatores explicativos são considerados para o preço internacional: (a) índice geral de preços das commodities CRB Spot, (b) macro-fatores (taxa de câmbio, juros, liquidez) (c) fatores idiossincráticos relacionados ao mercado mundial de açúcar. Os fatores explicativos para os preços brasileiros de açúcar e etanol são: (a) preço internacional do açúcar, (b) macro fatores nacionais e internacionais (c) fatores idiossincráticos (clima, produtividade). O preço internacional é previsto principalmente pelo índice CRB e preços do petróleo. Relacionado ao mercado interno, o preço do açúcar foi previsto pelos preços internacionais e taxa de câmbio do real. Os erros de previsão permaneceram na faixa de 20%. No caso dos preços de etanol, os preços internacionais e domésticos do açúcar foram os principais preditores, embora os erros tenham atingido 40%. Como o etanol é commodity menos negociadas no exterior, seus preços são mais sensíveis a fatores idiossincráticos. No entanto, permanece a conclusão geral de que o comportamento dos preços do açúcar e etanol no mercado brasileiro é bastante coerente com o mercado global de commodities

A Educação do Corpo no Projeto Republicano na Cidade de Vitória (1908-1912)

Analisa historicamente a visibilidade dada ao corpo na cena urbana da cidade de Vitória entre 1908 e 1912, no contexto do governo de Jerônimo de Souza Monteiro. Busca compreender a constituição de um novo ethos que deslocaria o pensamento do exercício corpóreo associado tanto ao trabalho quanto às práticas legítimas de engrandecimento do espírito por meio do fortalecimento corporal e da visibilidade que o corpo passa a assumir na cena urbana como prática favorável e confluente aos discursos em prol da modernidade e do progresso. Na esteira dessa proposta, voltamo-nos ao processo de constituição do ensino da ginástica nas instituições escolares e das práticas corporais esportivas em efervescência nos clubes e agremiações, investigando processos que objetivavam produzir a educabilidade dos corpos na cena urbana. Toma como cenário privilegiado de investigação a cidade de Vitória, capital do Espírito Santo que, durante o período analisado, concentrou parte significativa dos investimentos republicanos, constituindo-se como lócus modelar da modernidade e do progresso capixaba. O corpus documental constitui-se de mensagens de governo, relatórios da Secretaria de Instrução, artigos publicados na imprensa periódica local, leis e decretos, fontes bibliográficas e imagens. Para a análise das fontes, parte da compreensão de que a história se constitui em meio a relações de força produzidas no contexto investigado (Ginzburg, 1990, 2002, 2006, 2007). Dialoga com as noções de teatrocracia e drama em Balandier (1976, 1982) para análise de questões que envolvem o processo de espetacularização e encenação dos princípios republicanos vinculados à noção de modernidade. Considera que o governo do Espírito Santo se manteve atento ao debate sobre a valorização e o espraiamento do esporte, da ginástica e do civismo que chegam ao Brasil. À medida que esse espraiamento se expande como prática e prescrição corporal, agregando referências que se alinhavam à civilidade e ao progresso, torna- se mercadoria para consumo e produção de modos de educabilidade para o corpo republicano indícios já observados nos estudos de Moreno (2001), Melo (2001), Linhales (2006) e Vago (1999)