Ab initio calculation of the dynamical properties of PPP and PPV

In this work, we have calculated the vibrational modes and frequencies of the crystalline PPP (in both the Pbam and Pnnm symmetries) and PPV (in the P21/c symmetry). Our results are in good agreement with the available experimental data. Also, we have calculated the temperature dependence of their specific heats at constant volume, and of their vibrational entropies. Based on our results, at high temperatures, the PPP is more stable in the Pnnm structure than in the Pbam one.Comment: 5 pages, 7 figures, accepted for publication in Braz. J. Phys., special number, Proceedings of BWSP-12, 12th Brazilian Workshop on Semiconductor Physic

Comparação de homogeneidade e heteroneneidade de variância residual em modelos de regressão aleatória na descrição do crescimento de ovinos Santa Inês.

Resumo: Utilizaram-se 17.767 registros de pesos de cordeiros da raça Santa Inês com o objetivo de comparar modelos de regressão aleatória com diferentes estruturas para modelar a variância residual. As regressões fixas e aleatórias foram ajustadas por meio de polinômios de Legendre de ordens quatro e três, respectivamente. A variância residual foi ajustada por meio de classes e funções de variâncias. O modelo considerando homogeneidade de variâncias residuais mostrou-se inadequado. De acordo com os critérios utilizados, a variância residual contendo sete classes heterogêneas proporcionou melhor ajuste, embora um mais parcimonioso, com cinco classes, poderia ser utilizado. O ajuste de funções de variâncias com qualquer ordem foi melhor que o obtido por meio de classes, sendo que o polinômio ordinário de ordem seis proporcionou melhor ajuste dentre as estruturas testadas. A modelagem do resíduo interferiu nas estimativas dos parâmetros genéticos. Além da alteração da classificação dos reprodutores, constataramse, também, alterações consideráveis na magnitude dos valores genéticos preditos em função do ajuste da variância residual empregado. Portanto, faz-se necessário a utilização de heterogeneidade de variâncias residuais para modelar as variâncias associadas à curva de crescimento dos ovinos Santa Inês em estudo. Comparison of homogeneity and heterogeneity of residual variance in random regression models in the description of the growth of Santa Inês sheep]. Abstract: Data set of 17,767 records of 4,210 Santa Inês lambs were used aiming to compare random regression models with different structures to fit the residual variance. Fixed and random regressions were fitted by Legendre polynomials of orders four and three, respectively. The residual variance was fitted by classes and functions of variances. The model considering homogeneity of residual variances was inadequate. According to the criteria used, the residual variance containing seven heterogeneous classes provided the best fit, although a more parsimonious one, with five classes, could be used. The fit of variances functions with any order was better than that obtained by classes and the ordinary polynomial of order six provided best fit among the tested structures. The modelling of the residue interfered the estimative of the genetic parameters. Beyond the Change in the classification of the reproducers it was verified alterations in the magnitude of the genetic values predicted as function of the fit of the variance residual studied. Therefore, it is necessary the use of residual heterogeneity variances to model the variances associated to the growth curve of Santa Inês sheep in study

Modeling of average growth curve in Santa Ines sheep using random regression models.

Abstract: Polynomial functions of age of different orders were evaluated in the modeling of the average growth trajectory in Santa Ines sheep in random regression models. Initially, the analyses were performed not considering the animal effect. Subsequently, the random regression analyses were performed including the random effects of the animal and its mother (genetic and permanent environment). The linear fit was lower, and the other orders were similar until near 100 days of age. The cubic function provided the closest fit of the observed averages, mainly at the end of the curve. Orders superior to this one tended to present incoherent behavior with the observed weights. The estimated direct heritabilities, considering the linear fit, were higher to those estimated by considering other functions. The changes in animal ranking based on predicted breeding values using linear fit and superior orders were small; however, the difference in magnitude of the predicted breeding values was higher, reaching values 77% higher than those obtained with the cubic function. The cubic polynomial function is efficient in describing the average growth curve. [Modelagem da curva média de crescimento de ovinos Santa Inês em modelos de regressão aleatória]. Resumo: Funções polinomiais da idade de diferentes ordens foram avaliadas na modelagem da trajetória média de crescimento de ovinos Santa Inês em modelos de regressão aleatória. As análises foram executadas inicialmente desconsiderando o efeito de animal. Posteriormente, as análises de regressão aleatória foram realizadas incluindo-se os efeitos aleatórios de animal e da mãe (genético e de ambiente permanente). O ajuste linear foi inferior, e as demais ordens foram semelhantes até próximo dos 100 dias de idade. A função cúbica proporcionou o ajuste mais próximo das médias observadas, principalmente ao final da curva. Ordens superiores a esta tenderam a apresentar comportamento incoerente com os pesos observados. As herdabilidades diretas estimadas considerando ajuste linear foram superiores às estimadas considerando as demais funções. As mudanças no ordenamento dos animais, com base nos valores genéticos preditos empregando ajuste linear e de ordens superiores, foram pequenas, porém, a diferença na magnitude dos valores genéticos preditos foi maior, chegando a valores 77% maiores que os obtidos com a função cúbica. A função polinomial cúbica é eficiente para descrever a curva média de crescimento

Alternate islands of multiple isochronous chains in wave-particle interactions

We analyze the dynamics of a relativistic particle moving in a uniform magnetic field and perturbed by a standing electrostatic wave. We show that a pulsed wave produces an infinite number of perturbative terms with the same winding number, which may generate islands in the same region of phase space. As a consequence, the number of isochronous island chains varies as a function of the wave parameters. We observe that in all the resonances, the number of chains is related to the amplitude of the various resonant terms. We determine analytically the position of the periodic points and the number of island chains as a function of the wave number and wave period. Such information is very important when one is concerned with regular particle acceleration, since it is necessary to adjust the initial conditions of the particle to obtain the maximum acceleration.Comment: Submitte

Modelos de regressão aleatória na avaliação genética do crescimento de ovinos da raça Santa Inês.

Utilizaram-se 17.767 registros de peso de 4.210 cordeiros da raça Santa Inês com o objetivo de comparar modelos de regressão aleatória com diferentes estruturas para modelar a variância residual em estudos genéticos da curva de crescimento. Os efeitos fixos incluídos na análise foram: grupo contemporâneo e idade da ovelha no parto. As regressões fixas e aleatórias foram ajustadas por meio de polinômios de Legendre de ordens 4 e 3, respectivamente. A variância residual foi ajustada por meio de classes heterogêneas e por funções de variância empregando polinômios ordinários e de Legendre de ordens 2 a 8. O modelo considerando homogeneidade de variâncias residuais mostrou-se inadequado. De acordo com os critérios utilizados, a variância residual contendo sete classes heterogêneas proporcionou melhor ajuste, embora um mais parcimonioso, com cinco classes, pudesse ser utilizado sem perdas na qualidade de ajuste da variância nos dados. O ajuste de funções de variância com qualquer ordem foi melhor que o obtido por meio de classes. O polinômio ordinário de ordem 6 proporcionou melhor ajuste entre as estruturas testadas. A modelagem do resíduo interferiu nas estimativas de variâncias e parâmetros genéticos. Além da alteração da classificação dos reprodutores, a magnitude dos valores genéticos preditos apresenta variações significativas, de acordo com o ajuste da variância residual empregado. [Random regression models on genetic evaluation on the growth of Santa Inês breed sheep]. Abstract: It was used 17,767 weight records of 4,210 Santa Inês breed lambs aiming to compare random regression models with different structures to model the residual variance in genetic studies of the growth curve. The fixed effects included in the analysis were contemporary group and age of the ewe at lambing. Fixed and random regressions were fitted through Legendry polynomials of orders 4 and 3, respectively. The residual variance was fitted by heterogeneous classes and by functions of variances employing ordinary polynomials and Legendry polynomials of the orders 2 to 8. The model considering homogeneity of residual variances was inadequate. Accordingly to the used criteria, the residual variance containing seven heterogeneous classes provided the best fit, although a more parsimonious one, with five classes, could be used without losses on the quality of variance fit on the data. The fit of functions of variances with any order was better than that obtained through classes. The ordinary polynomial of order 6 provided the best fit among the tested structures. The modeling of the residue interfered on the estimative of the variances and genetic parameters. In addition to changes in the classification of the reproducers, the magnitude of the predicted genetic values shows significant variations, accordingly to the fitting of the used residual variance

Response to tilted magnetic fields in Bi2Sr2CaCu2O8 with columnar defects: Evidence for transverse Meissner effect

The transverse Meissner effect (TME) in the highly layered superconductor Bi2Sr2CaCu2O(8+y) with columnar defects is investigated by transport measurements. We present detailed evidence for the persistence of the Bose-glass phase when H is tilted at an angle theta < theta_c (T) away from the column direction: (i) the variable-range vortex hopping process for low currents crosses over to the half-loops regime for high currents; (ii) in both regimes near theta_c(T) the energy barriers vanish linearly with tan(theta) ; (iii) the transition temperature is governed by T_{BG}(0) -T_{BG}(theta) sim |tan(theta)|^{1/\nu_{\perp}} with \nu_{\perp}=1.0 +/- 0.1. Furthermore, above the transition as theta->\theta_c+, moving kink chains consistent with a commensurate-incommensurate transition scenario are observed. These results thereby clearly show the existence of the TME for theta < theta_c(T).Comment: 4 pages, RevTeX, 5 EPS figure