Classical artificial two-dimensional atoms: the Thomson model

The ring configurations for classical two-dimensional atoms are calculated within the Thomson model and compared with the results from `exact' numerical simulations. The influence of the functional form of the confinement potential and the repulsive interaction potential between the particles on the configurations is investigated. We also give exact results on those eigenmodes of the system whose frequency does not depend on the number of particles in the system.Comment: 9 pages, RevTeX, 4 figure

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

Algebraic Nature of Shape-Invariant and Self-Similar Potentials

Self-similar potentials generalize the concept of shape-invariance which was originally introduced to explore exactly-solvable potentials in quantum mechanics. In this article it is shown that previously introduced algebraic approach to the latter can be generalized to the former. The infinite Lie algebras introduced in this context are shown to be closely related to the q-algebras. The associated coherent states are investigated.Comment: 8 page

Barrier Penetration for Supersymmetric Shape-Invariant Potentials

Exact reflection and transmission coefficients for supersymmetric shape-invariant potentials barriers are calculated by an analytical continuation of the asymptotic wave functions obtained via the introduction of new generalized ladder operators. The general form of the wave function is obtained by the use of the F-matrix formalism of Froman and Froman which is related to the evolution of asymptotic wave function coefficients

Comportamento ingestivo de ovinos alimentados com rações contendo quatro níveis de inclusão do farelo de mamona.

Este trabalho foi desenvolvido com o objetivo de observar a influência de quatro níveis de substituição (0; 50; 75 ou 100%) do farelo de soja pelo farelo de mamona destoxificado em rações para ovinos mestiços ½ Morada Nova x ½ SPRD (sem padrão racial definido) sobre o seu comportamento ingestivo. O delineamento utilizado foi o inteiramente casualizado com quatro tratamentos e cinco repetições. Os ovinos eram machos, inteiros, com peso corporal 18,01 ± 1,41 kg e idade média de 7 meses. Foram avaliadas atividades contínuas (tempo de alimentação, ruminação, outras atividades e ócio) e pontuais (consumo de sal, ingestão de água, micção e defecação), como também a eficiência de alimentação (EAL), eficiência de ruminação (ERU), tempo de alimentação (TAL), tempo de ruminação (TRU), tempo de mastigação total (TMT), número de bolos ruminais (BOL), tempo de mastigações merícicas por bolo ruminal (MMtb ) e número de mastigações merícicas por bolo ruminal (MMnb ). As variáveis tempo de alimentação, ruminação, outras atividades, ócio, consumo de sal e ingestão de água foram afetadas (P<0,05), especialmente o MMnb , que foi inferior para os animais alimentados com as rações com 100% de substituição, possivelmente pelo seu menor teor de fibra (oriundo da forragem), sendo possível a substituição total do farelo de soja pelo farelo de mamona destoxificado. Ingestive behavior of sheep fed diets containing four levels of castor meal. Abstract - The aim of this work was to evaluate the effect of the replacement of four levels of a soybean meal by detoxified castor meal in rations fed to seven month-old ½ Morada Nova x ½ WDB (without defined breed) crossbred lambs, average 18 kg BW, on their ingestive behavior. The experiment was conducted in a completely randomized design with four treatments and five replicates. Continuous (feeding time, rumination, other activities and idleness) and punctual (salt consumption, water ingestion, urination and defecation) activities, as well as eating efficiency, rumination efficiency, eating time, rumination time, total chewing time, number of ruminal bolus, time of jaw movements per ruminal bolus and number of jaw movements per ruminal bolus were evaluated. The variables feeding time, rumination, other activities, idleness, salt consumption and water ingestion were influenced (P<0.05) by the replacement, especially the number of jaw movements per ruminal bolus, which was lower for animals fed diets with 100% replacement, possibly due to its lower fiber content. The results showed that it is possible the total replacement of the soybean meal by detoxified castor meal

Pastagens no ecossistema semi-árido brasileiro: atualização e perspectiva futuras.

As regiões áridas e semi-áridas representam 55% das terras do mundo, perfazendo 2/3 da superfície total de 150 países e abrangendo ao redor de 700 milhões de pessoas. As regiões com características de aridez e semi-aridez na América Latina e Caribe estão localizadas na Argentina, Brasil, Chile e México. Todas estas áreas abrangem 313 milhões de hectares e compreendem 80% das áreas tropical e subtropical. No âmbito do Brasil, o Semi-árido abrange 70% da área do Nordeste, mais o norte de Minas Gerais. A região é coberta por solos rasos de baixa fertilidade e caracterizada pela vegetação da Caatinga. Os problemas básicos dessa região são a escassez e a irregularidade de chuvas. Ciclicamente ocorrem estiagens prolongadas, com reflexos danosos na econo,ia e com custos sociais elevados. Em função das características edafo-climáticas, a pecuária tem se constituído, ao longo tempo, na atividade básica das populações rurais distribuídas nos 95 milhões de hectares do Semi-árido. As lavouras tem sido consideradas apenas como um subcomponente na maioria dos sistemas de produção predominantes, pela sua maior vulnerabilidade às limitações ambientais. O rebanho nordestino, embora expressivo (23,89 milhões de bovinos, 8,79 milhões de caprinos e 8,01 milhões de ovinos), apresenta níveis de produtividade bastante baixos (IBGE, 2004). Nessa revisão, enseja-se discorrer acerca das características do Semi-árido brasileiro, mormente de suas pastagens, enfocando alternativas de complementaridade nos sistemas de produão pecuários com vistas à sua sustentabilidade social, econômica e ecológica

Does soil thinning change soil erodibility? An exploration of long-term erosion feedback systems

Soil erosion rates on arable land frequently exceed the pace at which new soil is formed. This imbalance leads to soil thinning (i.e. truncation), whereby subsoil horizons and their underlying parent material become progressively closer to the land surface. As soil erosion is a selective process and subsurface horizons often have contrasting properties to the original topsoil, truncation-induced changes to soil properties might affect erosion rates and runoff formation through a soil erosion feedback system. However, the potential interactions between soil erosion and soil truncation are poorly understood due to a lack of empirical data and the neglection of long-term erodibility dynamics in erosion simulation models. Here, we present a novel model-based exploration of the soil erosion feedback system over a period of 500 years using measured soil properties from a diversified database of 265 agricultural soil profiles in the UK. For this, we adapted the Modified Morgan–Morgan–Finney model (MMMF) to perform a modelling experiment in which topography, climate, land cover, and crop management parameters were held constant throughout the simulation period. As selective soil erosion processes removed topsoil layers, the model gradually mixed subsurface soil horizons into a 0.2 m plough layer and updated soil properties using mass-balance mixing models. Further, we estimated the uncertainty in model simulations with a forward error assessment. We found that modelled erosion rates in 99 % of the soil profiles were sensitive to truncation-induced changes in soil properties. The soil losses in all except one of the truncation-sensitive profiles displayed a decelerating trend, which depicted an exponential decay in erosion rates over the simulation period. This was largely explained by decreasing silt contents in the soil surface due to selective removal of this more erodible particle size fraction and the presence of clayey or sandy substrata. Moreover, the soil profiles displayed an increased residual stone cover, which armoured the land surface and reduced soil detachment. Contrastingly, the soils with siltier subsurface horizons continuously replenished the plough layer with readily erodible material, which prevented the decline of soil loss rates over time. Although our results are limited by the edaphoclimatic conditions represented in our data, as by our modelling assumptions, we have demonstrated how modelled soil losses can be sensitive to erosion-induced changes in soil properties. These findings are likely to affect how we calculate soil lifespans and make long-term projections of land degradation.</p

An Algebraic q-Deformed Form for Shape-Invariant Systems

A quantum deformed theory applicable to all shape-invariant bound-state systems is introduced by defining q-deformed ladder operators. We show these new ladder operators satisfy new q-deformed commutation relations. In this context we construct an alternative q-deformed model that preserve the shape-invariance property presented by primary system. q-deformed generalizations of Morse, Scarf, and Coulomb potentials are given as examples

Capacidade de retenção de água em neossolo quartzarênico sob pastagens nativas no ecossistema Pantanal.

A pecuária é a principal atividade econômica do ecossistema Pantanal, sendo as pastagens nativas a base da alimentação dos bovinos. Assim, o presente estudo teve por objetivo construir a curva de retenção de água para Neossolo Quartzarênico sob três diferentes pastagens nativas (dominadas por Axonopus purpusii, Hymenachne amplexicaulis e Mesosetum chaseae) mantidas sob pastejo contínuo e sem pastejo por quatro anos, no Pantanal Sul-Mato-Grossense. Para a obtenção das curvas de retenção de água do solo, as amostras foram submetidas às tensões de 1, 2, 4, 6, 10 kPa na unidade de sucção e 33, 100, 500 e 1500 kPa no extrator de Richards. Através dos dados obtidos foram ajustadas a curva de retenção de água do solo segundo o modelo de van Genuchten. A pastagem com predominância de H. amplexicaulis apresentou maior amplitude de umidade na curva de retenção de água e maior capacidade de água disponível. O teor de Corg, que está associado à posição da pastagem nativa na paisagem, é preponderante na retenção de água desses solos altamente arenosos. Não há diferenças marcantes entre as pastagens sob pastejo contínuo e sem pastejo por quatro anos, independentemente das gramíneas predominantes