Dissipation as a mechanism of energy gain

Some properties of the annular billiard under the presence of weak dissipation are studied. We show, in a dissipative system, that the average energy of a particle acquires higher values than its average energy of the conservative case. The creation of attractors, associated with a chaotic dynamics in the conservative regime, both in appropriated regions of the phase space, constitute a generic mechanism to increase the average energy of dynamical systems.

Competition between suppression and production of Fermi acceleration

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Suppressing Fermi acceleration in two-dimensional driven billiards

We consider a dissipative oval-like shaped billiard with a periodically moving boundary. The dissipation considered is proportional to a power of the velocity V of the particle. The three specific types of power laws used are: (i) F proportional to-V; (ii) F proportional to-V-2 and (iii) F proportional to-V-delta with 1 < delta < 2. In the course of the dynamics of the particle, if a large initial velocity is considered, case (i) shows that the decay of the particle's velocity is a linear function of the number of collisions with the boundary. For case (ii), an exponential decay is observed, and for 1 < delta < 2, an powerlike decay is observed. Scaling laws were used to characterize a phase transition from limited to unlimited energy gain for cases (ii) and (iii). The critical exponents obtained for the phase transition in the case (ii) are the same as those obtained for the dissipative bouncer model. Therefore near this phase transition, these two rather different models belong to the same class of universality. For all types of dissipation, the results obtained allow us to conclude that suppression of the unlimited energy growth is indeed observed.

Energy gain induced by boundary crisis

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Stickiness in a bouncer model: A slowing mechanism for Fermi acceleration

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Natural radionuclides in major aquifer systems of the Parana sedimentary basin, Brazil

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

POLIEMBRIONIA em CLONES DE LARANJA 'PÊRA' E VARIEDADES ASSEMELHADAS

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Comparação de diferentes estratégias para a análise de características de crescimento e de carcaça de suínos cruzados: modelos finito e infinitesimal poligênico

Foi utilizada uma análise de segregação com o uso da inferência Bayesiana para estimar componentes de variância e verificar a presença de genes de efeito principal (GEP) influenciando duas características de carcaça: gordura intramuscular (GIM), em %, e espessura de toucinho (ET), em mm; e uma de crescimento, ganho de peso (g/dia) dos 25 aos 90 kg de peso vivo (GP). Para este estudo, foram utilizadas informações de 1.257 animais provenientes de um delineamento de F2, obtidos do cruzamento de suínos machos Meishan e fêmeas Large White e Landrace. No melhoramento genético animal, os modelos poligênicos finitos (MPF) podem ser uma alternativa aos modelos poligênicos infinitesimais (MPI) para avaliação genética de características quantitativas usando pedigrees complexos. MPI, MPF e MPI combinado com MPF foram empiricamente testados para se estimar componentes de variâncias e número de genes no MPF. Para a estimação de médias marginais a posteriori de componentes de variância e de parâmetros, foi utilizada uma metodologia Bayesiana, por meio do uso da Cadeia de Markov, algoritmos de Monte Carlo (MCMC), via Amostrador de Gibbs e Reversible Jump Sampler (Metropolis-Hastings). em função dos resultados obtidos, pode-se evidenciar quatro GEP, sendo dois para GIM e dois para ET. Para ET, o GEP explicou a maior parte da variação genética, enquanto, para GIM, o GEP reduziu significativamente a variação poligênica. Para a variação do GP, não foi possível determinar a influência do GEP. As herdabilidades estimadas ajustando-se MPI para GIM, ET e GP foram de 0,37; 0,24 e 0,37, respectivamente. Estudos futuros com base neste experimento que usem marcadores moleculares para mapear os genes de efeito principal que afetem, principalmente GIM e ET, poderão lograr êxito.

Efeitos do teor de carboidratos solúveis sobre as características da silagem de cana-de-açúcar

Objetivou-se quantificar na cana-de-açúcar o teor de carboidratos solúveis (CHOs) que anula a produção de etanol e avaliar os efeitos desses carboidratos sobre o valor nutritivo e outras características fermentativas da silagem de cana-de-açúcar. Utilizou-se o delineamento inteiramente casualizado com três tratamentos, cada um com quatro repetições. Os tratamentos consistiram da retirada total do caldo da cana-de-açúcar, por meio de prensagem, e de sua reconstituição (0, 50 ou 100%) à cana. No nível de 50% de reconstituição, o caldo foi adicionado à cana juntamente com 50% de água e, no nível 0%, adicionou-se 100% de água à cana. A restituição resultou em concentrações de 41,6; 34,0 e 23,0% de carboidratos solúveis na matéria seca (MS). O material foi ensilado em 12 silos experimentais confeccionados a partir de baldes plásticos. A abertura dos silos foi realizada 85 dias após a ensilagem, quando foram determinados os teores dos ácidos orgânicos e a composição química das silagens. A retirada de carboidratos solúveis da cana-de-açúcar teve efeito linear decrescente sobre os teores de matéria seca, o teor de carboidratos solúveis e a digestibilidade in vitro da matéria seca (DIVMS) das silagens, no entanto, ocasionou aumento dos teores de fibra detergente ácido (FDA), fibra detergente neutro (FDN) e lignina. Observou-se efeito linear decrescente da retirada dos carboidratos solúveis sobre os teores de etanol e ácidos lático e butírico e as perdas de matéria seca das silagens. Não se observaram efeitos de tratamentos sobre os dados de estabilidade aeróbia. A produção de etanol seria nula se a cana-de-açúcar contivesse apenas 12,4% de CHOs com base na matéria seca (MS).

Intercellular pectic protuberances in leaves of some Xyris species (Xyridaceae)

Mature leaves of eight species of Xyris were prepared by standard methods for electron transmission microscopy. Wartlike intercellular pectic protuberances were observed on the surface of inner periclinal walls of epidermal cells in Xyris obcordata, Xyris hymenachne, and Xyris pterygoblephara. In the latter, the protuberances also occur on the surface of parenchymatic mesophyll cells; they frequently project into intercellular spaces and may connect opposing cells. For the genus Xyris, the intercellular pectic protuberances may be considered taxonomically significant at the species level.

Manipulation of anchoring strength in an azo-dye side chain polymer by photoisomerization

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Energy localization in the Phi(4) oscillator chain

We study energy localization in a finite one-dimensional Phi(4) oscillator chain with initial energy in a single oscillator of the chain. We numerically calculate the effective number of degrees of freedom sharing the energy on the lattice as a function of time. We find that for energies smaller than a critical value, energy equipartition among the oscillators is reached in a relatively short time. on the other hand, above the critical energy, a decreasing number of particles sharing the energy is observed. We give an estimate of the effective number of degrees of freedom as a function of the energy. Our results suggest that localization is due to the appearance, above threshold, of a breather-like structure. Analytic arguments are given, based on the averaging theory and the analysis of a discrete nonlinear Schrodinger equation approximating the dynamics, to support and explain the numerical results.

Evidence for a respiratory component, similar to mammalian respiratory sinus arrhythmia, in the heart rate variability signal from the rattlesnake, Crotalus durissus terrificus

Autonomic control of heart rate variability and the central location of vagal preganglionic neurones (VPN) were examined in the rattlesnake ( Crotalus durissus terrificus), in order to determine whether respiratory sinus arrhythmia (RSA) occurred in a similar manner to that described for mammals. Resting ECG signals were recorded in undisturbed snakes using miniature datalogging devices, and the presence of oscillations in heart rate (f(H)) was assessed by power spectral analysis (PSA). This mathematical technique provides a graphical output that enables the estimation of cardiac autonomic control by measuring periodic changes in the heart beat interval. At fH above 19 min(-1) spectra were mainly characterised by low frequency components, reflecting mainly adrenergic tonus on the heart. By contrast, at f(H) below 19 min(-1) spectra typically contained high frequency components, demonstrated to be cholinergic in origin. Snakes with a f(H) > 19 min(-1) may therefore have insufficient cholinergic tonus and/or too high an adrenergic tonus acting upon the heart for respiratory sinus arrhythmia ( RSA) to develop. A parallel study monitored f(Hd) simultaneously with the intraperitoneal pressures associated with lung inflation. Snakes with a fH < 19 min(-1) exhibited a high frequency (HF) peak in the power spectrum, which correlated with ventilation rate (f(V)). Adrenergic blockade by propranolol infusion increased the variability of the ventilation cycle, and the oscillatory component of the f(H) spectrum broadened accordingly. Infusion of atropine to effect cholinergic blockade abolished this HF component, confirming a role for vagal control of the heart in matching f(H) and f(V) in the rattlesnake. A neuroanatomical study of the brainstem revealed two locations for vagal preganglionic neurones (VPN). This is consistent with the suggestion that generation of ventilatory components in the heart rate variability (HRV) signal are dependent on spatially distinct loci for cardiac VPN. Therefore, this study has demonstrated the presence of RSA in the HRV signal and a dual location for VPN in the rattlesnake. We suggest there to be a causal relationship between these two observations.

Energy localization in the Peyrard-Bishop DNA model

We study energy localization on the oscillator chain proposed by Peyrard and Bishop to model DNA. We search numerically for conditions with initial energy in a small subgroup of consecutive oscillators of a finite chain and such that the oscillation amplitude is small outside this subgroup on a long time scale. We use a localization criterion based on the information entropy and verify numerically that such localized excitations exist when the nonlinear dynamics of the subgroup oscillates with a frequency inside the reactive band of the linear chain. We predict a mimium value for the Morse parameter (mu>2.25) (the only parameter of our normalized model), in agreement with the numerical calculations (an estimate for the biological value is mu=6.3). For supercritical masses, we use canonical perturbation theory to expand the frequencies of the subgroup and we calculate an energy threshold in agreement with the numerical calculations.

Experimental model for transanal endorectal pull-through surgery. Technique of de la Torre and Ortega

Background: We describe an experimental model for transanal endorectal pull-through surgery using the method of de]a Torre and Ortega that can be used for training purposes in experimental laboratories.Methods: Ten rabbits were submitted to the transanal endorectal pull-through technique of de la Torre and Ortega. Animals were randomly selected in the Botucatu School of Medicine experimental laboratory. Animals weighted between 2800 and 4400 g. Colons were not prepared, and antibiotic therapy was not used; dipyrone(1) was administered postoperatively for analgesic purposes. We standardized resected segment size, recorded surgical time, and observed Survival and possible complications for 1 month.Results: All animals survived the initial follow-up period without infection. Bowel movements returned quickly, and all animals were evacuating regularly within the first 24 hours. Mean surgical time was 48.6 minutes.Conclusions: the experimental model proposed in this study is very useful for training and improving surgical techniques using the method of de la Torre and Ortega. The rabbit is an excellent animal for this surgery because of its size and postoperative resistance. (c) 2005 Elsevier B.V. All rights reserved.