Configurational entropy of Wigner crystals

We present a theoretical study of classical Wigner crystals in two- and three-dimensional isotropic parabolic traps aiming at understanding and quantifying the configurational uncertainty due to the presence of multiple stable configurations. Strongly interacting systems of classical charged particles confined in traps are known to form regular structures. The number of distinct arrangements grows very rapidly with the number of particles, many of these arrangements have quite low occurrence probabilities and often the lowest-energy structure is not the most probable one. We perform numerical simulations on systems containing up to 100 particles interacting through Coulomb and Yukawa forces, and show that the total number of metastable configurations is not a well defined and representative quantity. Instead, we propose to rely on the configurational entropy as a robust and objective measure of uncertainty. The configurational entropy can be understood as the logarithm of the effective number of states; it is insensitive to the presence of overlooked low-probability states and can be reliably determined even within a limited time of a simulation or an experiment.Comment: 12 pages, 8 figures. This is an author-created, un-copyedited version of an article accepted for publication in J. Phys.: Condens. Matter. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The definitive publisher-authenticated version is available online at 10.1088/0953-8984/23/7/075302.

Formation energy and interaction of point defects in two-dimensional colloidal crystals

The manipulation of individual colloidal particles using optical tweezers has allowed vacancies to be created in two-dimensional (2d) colloidal crystals, with unprecedented possibility of real-time monitoring the dynamics of such defects (Nature {\bf 413}, 147 (2001)). In this Letter, we employ molecular dynamics (MD) simulations to calculate the formation energy of single defects and the binding energy between pairs of defects in a 2d colloidal crystal. In the light of our results, experimental observations of vacancies could be explained and then compared to simulation results for the interstitial defects. We see a remarkable similarity between our results for a 2d colloidal crystal and the 2d Wigner crystal (Phys. Rev. Lett. {\bf 86}, 492 (2001)). The results show that the formation energy to create a single interstitial is $12$ lower than that of the vacancy. Because the pair binding energies of the defects are strongly attractive for short distances, the ground state should correspond to bound pairs with the interstitial bound pairs being the most probable.Comment: 5 pages, 2 figure

Generalized Ladder Operators for Shape-invariant Potentials

A general form for ladder operators is used to construct a method to solve bound-state Schr\"odinger equations. The characteristics of supersymmetry and shape invariance of the system are the start point of the approach. To show the elegance and the utility of the method we use it to obtain energy spectra and eigenfunctions for the one-dimensional harmonic oscillator and Morse potentials and for the radial harmonic oscillator and Coulomb potentials.Comment: in Revte

Obstructive sleep apnea syndrome among obese individuals: A cross-sectional study

sem informaçãoThe obstructive sleep apnea syndrome (OSAS) is a respiratory illness, characterized by recurrent episodes of apnea and hypopnea, leading to reduction or cessation of the airflow. Obesity is one of the major risk factors for the development of OSAS. To hel6310862868sem informaçãosem informaçãosem informaçã

Supersymmetric and Shape-Invariant Generalization for Nonresonant and Intensity-Dependent Jaynes-Cummings Systems

A class of shape-invariant bound-state problems which represent transition in a two-level system introduced earlier are generalized to include arbitrary energy splittings between the two levels as well as intensity-dependent interactions. We show that the couple-channel Hamiltonians obtained correspond to the generalizations of the nonresonant and intensity-dependent nonresonant Jaynes-Cummings Hamiltonians, widely used in quantized theories of laser. In this general context, we determine the eigenstates, eigenvalues, the time evolution matrix and the population inversion matrix factor.Comment: A combined version of quant-ph/0005045 and quant-ph/0005046. 24 pages, LATE

Efeito de diferentes manejo sobre a eficiência de produção líquida de forragem em pasto de capim-tanzânia (Panicum maximum cv. Tanzânia) no Nordeste Brasileiro.

O objetivo do trabalho foi identificar entre tipos de manejo, o mais eficiente na conversão de fatores bióticos e abióticos em produção líquida de forragem de capim-tanzânia, para uso tanto na época seca quanto chuvosa, no Nordeste brasileiro. O pasto recebeu quatro tratamentos: intensivo (resíduo póspastejo de 30cm e adubação com 600 kg N/ha ano), moderado (resíduo pós-p de 45cm, adubação 300 kg N/ha ano), leve (resíduo pós-p 45cm sem adubação) e extensivo (resíduo pós-p 30cm sem adubação). As variáveis analisadas foram a produção total de forragem (PTF), a produção líquida de forragem (PLF) e produção de material morto (PMM). As variáveis analisadas foram afetadas tanto pelo tratamento quanto pela época do ano (p<0,05). A maior produção total e produção líquida de forragem foi obtida no tratamento moderado. O tratamento extensivo foi o menos produtivo. As maiores produções de forragem ocorreram durante a durante a época seca. O tratamento moderado foi o mais eficiente em converter insumos em produção de forragem

Componentes da biomassa pós-pastejo do dossel de capim-tifton 85 submetido a diferentes manejos sob lotação rotativa.

Resumo: Avaliaram-se componentes de biomassa pós-pastejo do capim-tifton 85 submetido a diferentes manejos. Os manejos consistiam em Convencional (altura residual 10 cm e sem adubação), Intensivo (altura residual 10 cm e adubação equivalente a 600 kg de N/ha x ano), Leve (altura residual 20 cm e sem adubação) e Moderado (altura residual 20 cm e adubação equivalente a 300 kg de N/ha x ano). Utilizou-se um delineamento inteiramente casualizado com medidas repetidas no tempo em dois períodos do ano com quatro repetições. Tanto a Massa Seca de Forragem Total residual (MSFTr), quanto a de Forragem Verde residual (MSFVr) e Forragem Morta residual (MSFMr) apresentaram efeito dos manejos e do período do ano, com maiores médias de MSFTr e MSFMr para os manejos Moderado e Leve e para a MSFVr no manejo Moderado. O período seco apresentou os maiores valores de MSFTr, MSFVr e MSFMr com 3674, 2416 e 1258 kg/ha, respectivamente. A relação Material Vivo/Material Morto residual foi maior nos manejos Intensivo e Moderado. A Massa Seca de Lâmina foliar Verde residual (MSLVr) e a de Colmo Verde residual (MSCVr) comportaram-se de forma semelhante com maior média para o manejo Moderado. Na MSCVr houve maior produção de colmo no período seco. A relação Folha/Colmo residual foi menor no manejo Convencional e maior no período chuvoso. Os manejos Moderado e Intensivo apresentam uma maior quantidade de massas de forragem residual que garantem maior vigor na rebrotação da pastagem de capim-tifton 85. [Biomass components Tifton 85 grass canopy post-grazing, under different managements in intermittent stocking]. Abstract: Was evaluated the structural characteristics pos grazing of tifton 85 bermudagrass, subjected to different intensities of management. The management consisted in Extensive (residual height 10 cm and no fertilization), Intensive (residual height 10 cm and equivalent fertilization 600 kg of N/ha x year), Light (residual height 20 cm and no fertilization) e Moderate (residual height 20 cm and equivalent fertilization 300 kg of N/ha x year). We used entirely randomized with repeated measurements over time in two seasons with four replicates. Both residual Dry Mass Total Herbage (DMTHr), as the residual Green Herbage (DMGHr) and residual Dead Herbage (DMDHr) had the effect of the managements and the season of year, with higher average DMTHr and DMDHr for the Moderate and Light managements and for the DMGHr in the Moderate management. The dry season had the higest values of DMTHr, DMGHr and DMDHr with 3674, 2416 e 1258 kg/ha, respectively. The residual Live Material/Dead Material ratio was highest in the Intensive and Moderate management. The residual Dry Mass of Green Leaf (DMGLr) and the residual Green Stems (DMGSr) behaved similarly with highest average for Moderate management. In DMGSr had highest stem production in the rainy season. The residual Leaf/Stem ration was lowest in the Conventional management and the rainy season. The Moderate and Intensive management present a higher amount residual forage mass to ensure greater strength in the pasture regrowth of Tifton 85 grass

Características estruturais pós-pastejo do dossel de capim-tifton 85 submetido a diferentes manejos sob lotação rotativa.

Avaliaram-se as características estruturais pós-pastejo do capim-tifton 85 submetido a diferentes manejos. Os manejos consistiam em Convencional (altura residual 10 cm e sem adubação), Intensivo (altura residual 10 cm e adubação equivalente a 600 kg de N/ha x ano), Leve (altura residual 20 cm e sem adubação) e Moderado (altura residual 20 cm e adubação equivalente a 300 kg de N/ha x ano). Utilizou-se um delineamento inteiramente casualizado com medidas repetidas no tempo em dois períodos do ano com quatro repetições. O Índice de Área Foliar residual (IAFr) foi maior no manejo Moderado, com média de 1,81 e menor nos manejos Convencional e Intensivo, com 0,91 e 0,98, respectivamente. A Interceptação da Radiação Fotossinteticamente Ativa residual (IRFAr) apresentou efeito dos manejos, acompanhando a mesma tendência do IAFr. A Densidade Populacional de Perfilhos residual (DPPr) foi semelhante entre os manejos no período chuvoso, e maior no manejo Intensivo no período seco, com 4915 perfilho/m². A estrutura pós-pastejo no manejo Moderado em capim-tifton 85 condiciona ao pasto uma maior facilidade de rebrotação sem comprometer o perfilhamento. Structural characteristics Tifton 85 grass canopy post-grazing, under different managements in intermittent stocking. Abstract: Was evaluated the structural characteristics pos grazing of tifton 85 bermudagrass, subjected to different intensities of management. The management consisted in Extensive (residual height 10 cm and no fertilization), Intensive (residual height 10 cm and equivalent fertilization 600 kg of N/ha x year), Light (residual height 20 cm and no fertilization) e Moderate (residual height 20 cm and equivalent fertilization 300 kg of N/ha x year). We used entirely randomized with repeated measurements over time in two seasons with four replicates. The residual Leaf Area Index (LAIr) was higher in Moderate management, with an average of 1,81 and lowest in Conventional e Intensive management, with 0,91 and 0,98, respectively. The residual Photosynthetically Radiation Active Interception present effect of managements, following the same trend LAIr. The residual Tiller Density Population (TDPr) was similar between the managements during the rainy season, and the higher in the Intensive management during the dry season, with 4915 tillers/m². The structure post-grazing in tifton 85 grass in the Moderate management conditions an easier regrowth of the pasture without compromising tillering