Ground-State Analysis for an Exactly Solvable Coupled-Spin Hamiltonian

We introduce a Hamiltonian for two interacting $su(2)$ spins. We use a mean-field analysis and exact Bethe ansatz results to investigate the ground-state properties of the system in the classical limit, defined as the limit of infinite spin (or highest weight). Complementary insights are provided through investigation of the energy gap, ground-state fidelity, and ground-state entanglement, which are numerically computed for particular parameter values. Despite the simplicity of the model, a rich array of ground-state features are uncovered. Finally, we discuss how this model may be seen as an analogue of the exactly solvable $p+ip$ pairing Hamiltonian

Notas sobre a trajetória da questão ambiental e principais temas em debate na conferência Rio + 20

O tema do meio ambiente começou a ser tratado oficialmente pela ONU apenas na década de 1970, destacando-se as questões ambientais e a influência do homem sobre a natureza. Oficialmente, a primeira reunião sobre essa temática realizada pela ONU ocorreu na Suécia, em 1972, quando se organizou a "Conferência das Nações Unidas sobre o Ambiente Humano", momento em que se discutiu, pela primeira vez, a questão dos impactos das ações do homem sobre o planeta. Dez anos depois, em 1982, foi elaborada a "Carta Mundial da Natureza", que afirmava que “a humanidade é parte da natureza e depende do funcionamento ininterrupto de seus sistemas naturais”. No ano de 1992, ocorreu na cidade do Rio de Janeiro a Conferência das Nações Unidas sobre o Meio Ambiente e Desenvolvimento, também conhecida como Rio-92 ou Eco-92. Neste evento, organizado conjuntamente pela ONU e pelo governo brasileiro, pela primeira vez colocou-se a temática ambiental no centro dos debates, ao se estabelecer um conjunto de acordos políticos com metas e objetivos que deveriam ser seguidas nos decênios seguintes por todos os países signatários do documento final da referida conferência.

Semeadura direta de timbaúva (Enterolobium contortisiliquum), canafístula (Peltophorum dubium) e cedro (Cedrela fissilis) em campos abandonados.

The objective of this work was to evaluate species “timbauva” (Enterolobium contortisiliquum), “canafistula” (Peltophorum dubium) and “cedro” (Cedrela fissilis) in direct sowing, in unproductive areas. Efficiency of shelter utilization at the sowing point was tested and compared to initial vegetation cover management by herbicide application at the sowing point, opposed to manual weeding. Sowing was made in points distanced 1 m in 2.5 m spaced rows. The following variables were evaluated: emergence, survival and number of points with at least one plant, until seven month after sowing. Results allowed to conclude that the native species “timbaúva”, “canafístula” and “cedro” have potencial to be used in the direct sowing method in unproductive agricultural áreas. Shelter utilization favors initial establishment of “cedro” plants, especially by contributing to lower inicial mortality. Early weed control by a chemical dessecant, at the sowing date, allows for an initial higher plant population of “timbauva” and “cedro”.Foram avaliadas as espécies timbaúva (Enterolobium contortisiliquum), canafístula (Peltophorum dubium) e cedro (Cedrela fissilis) com semeadura direta em campos abandonados, quanto à eficiência da utilização do laminado de madeira como protetor físico e o manejo inicial da cobertura vegetal, através da aplicação de herbicida ou capina manual em torno da cova de semeadura. A semeadura foi realizada em covas separadas de 1 m na fileira e 2,5 m entre fileiras. Foram avaliadas as variáveis emergência, sobrevivência e número de covas com pelo menos uma planta, até sete meses após a semeadura. Os resultados encontrados possibilitaram concluir que as espécies nativas timbaúva, canafístula e cedro possuem potencial para serem utilizadas no método de regeneração por semeadura direta em campos abandonados. A utilização do laminado como protetor físico favorece o estabelecimetno inicial de plantas de cedro, especialmente por contribuir para uma menor mortalidade inicial. O manejo inicial de plantas daninhas, através da utilização de herbicida dessecante, no momento da semeadura, proporciona condições para a obtenção de maior densidade populacional inicial de plantas de timbaúva e cedro

Obtenção de materiais por resfriamento ultra-rapido

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Quantum phase transitions in Bose–Einstein condensates from a Bethe ansatz perspective

We investigate two solvable models for Bose–Einstein condensates and extract physical information by studying the structure of the solutions of their Bethe ansatz equations. A careful observation of these solutions for the ground state of both models, as we vary some parameters of the Hamiltonian, suggests a connection between the behavior of the roots of the Bethe ansatz equations and the physical behavior of the models. Then, by the use of standard techniques for approaching quantum phase transition – gap, entanglement and fidelity – we find that the change in the scenery in the roots of the Bethe ansatz equations is directly related to a quantum phase transition, thus providing an alternative method for its detection

Examining Different Regimes of Ionization-Induced Damage in GaN Through Atomistic Simulations

Peer reviewe

Emergent quantum phases in a heteronuclear molecular Bose--Einstein condensate model

We study a three-mode Hamiltonian modelling a heteronuclear molecular Bose--Einstein condensate. Two modes are associated with two distinguishable atomic constituents, which can combine to form a molecule represented by the third mode. Beginning with a semi-classical analogue of the model, we conduct an analysis to determine the phase space fixed points of the system. Bifurcations of the fixed points naturally separate the coupling parameter space into different regions. Two distinct scenarios are found, dependent on whether the imbalance between the number operators for the atomic modes is zero or non-zero. This result suggests the ground-state properties of the model exhibit an unusual sensitivity on the atomic imbalance. We then test this finding for the quantum mechanical model. Specifically we use Bethe ansatz methods, ground-state expectation values, the character of the quantum dynamics, and ground-state wavefunction overlaps to clarify the nature of the ground-state phases. The character of the transition is smoothed due to quantum fluctuations, but we may nonetheless identify the emergence of a quantum phase boundary in the limit of zero atomic imbalance.Comment: 23 pages, 10 figure

Opening of the Neo-Tethys Ocean and the Pangea B to Pangea A transformation during the Permian

We studied the stratigraphy, composition, and paleomagnetic properties of lateritic weathering profiles of Permian age from northern Iran and western Karakoram, Pakistan. A limited set of samples deemed representative yielded stable low-inclination paleomagnetic components carried essentially by hematite of chemical origin isolated in massive, fine-grained, and homogeneous ferricrete facies. These laterites originated at equatorial paleolatitudes characterized by intense weathering processes under warm and humid climatic conditions. Paleomagnetic estimates of paleolatitude from Iran, Karakoram, and north Tibet from this study and the literature, albeit sparse, provide testable constraints on the motion of the Cimmerian terranes as the result of the opening of the Neo-Tethys Ocean along the eastern margin of Gondwana during the Permian. We confirm and help refine previous suggestions that the Cimmerian terranes migrated from southern Gondwanan paleolatitudes in the Early Permian to subequatorial paleolatitudes by the Middle Permian – Early Triassic. As a novel conclusion, we find that timing, rates, and geometry of Cimmerian tectonics are broadly compatible with the transformation of Pangea from an Irvingian B to a Wegenerian A-type configuration with Neo-Tethyan opening taking place contemporaneously essentially in the Permian

Unravelling the secrets of the resistance of GaN to strongly ionising radiation

GaN is the most promising upgrade to the traditional Si-based radiation-hard technologies. However, the underlying mechanisms driving its resistance are unclear, especially for strongly ionising radiation. Here, we use swift heavy ions to show that a strong recrystallisation effect induced by the ions is the key mechanism behind the observed resistance. We use atomistic simulations to examine and predict the damage evolution. These show that the recrystallisation lowers the expected damage levels significantly and has strong implications when studying high fluences for which numerous overlaps occur. Moreover, the simulations reveal structures such as point and extended defects, density gradients and voids with excellent agreement between simulation and experiment. We expect that the developed modelling scheme will contribute to improving the design and test of future radiation-resistant GaN-based devices. Gallium nitride is a wide bandgap semiconductor which is generally expected to replace some silicon-based technologies, despite some of its properties still requiring further investigation. Here, using a two-temperature model coupled to molecular dynamics simulations, the authors investigate and predict the effects of strongly ionising radiation in gallium nitride, revealing the mechanism behind its unusual resistance to radiation.Peer reviewe

Graphene-Based Ka Band Tunable Antenna for Nanosatellites Applications

The increase in the number of connected objects and the new commercial possibilities associated with nanosatellites for both remote sensing and data relay require communication systems with small volumes, low consumption, and high capacity of data transmission. This work presents preliminary results for the development of a Ka-band tunable antenna for a nanosatellite software defined communication system