Integrable anisotropic spin-ladder model

We present an integrable spin-ladder model, which possesses a free parameter besides the rung coupling J. Wang's system based on the SU(4) symmetry can be obtained as a special case. The model is exactly solvable by means of the Bethe ansatz method. We determine the dependence on the anisotropy parameter of the phase transition between gapped and gapless spin excitations and present the phase diagram. Finally, we show that the model is a special case of a more general Hamiltonian with three free parameters.

Integrable open boundary conditions for the Bariev model of three coupled X Y spin chains

The integrable open-boundary conditions for the Bariev model of three coupled one-dimensional XY spin chains are studied in the framework of the boundary quantum inverse scattering method. Three kinds of diagonal boundary K-matrices leading to nine classes of possible choices of boundary fields are found and the corresponding integrable boundary terms are presented explicitly. The boundary Hamiltonian is solved by using the coordinate Bethe ansatz technique and the Bethe ansatz equations are derived. (C) 2001 Elsevier Science B.V. All rights reserved.

Quantum dynamics of spin polarized optoelectronic processes

We study the quantum dynamics of the emission of multimodal polarized light in light emitting devices (LED) due to spin polarized carriers injection. We present the equations for photon number and carrier numbers, and calculate the polarisation degree of the light generated by LED. (C) 2002 Elsevier Science B.V. All rights reserved.

Characterization of [Fe(AMN3S3sarH)]3+ - a rigorously low-spin iron(II) complex

The iron(II) complex [Fe(AMN(3)S(3)sarH)](ClO4)(3).3H(2)O (AMN(3)S(3)sarH = 8-ammonio-1-methyl-3,13,16-trithia-6,10,19-triazabicyclo[6.6.6]icosane) has been synthesized and characterized by single crystal structure and spectroscopic methods. The Fe(II)-S(thiaether) bond lengths are short, indicative of a large degree of metal-ligand orbital mixing (pi-acceptor character) of the thiaether ligand. The complex is stable to metal centred oxidation. (C) 2002 Elsevier Science Ltd. All rights reserved.

Control of chaotic motion in a dual-spin spacecraft with nutational damping

Control of chaotic vibrations in a dual-spin spacecraft with an axial nutational damper is achieved using two techniques. The control methods are implemented on two realistic spacecraft parameter configurations that have been found to exhibit chaotic instability when a sinusoidally varying torque is applied to the spacecraft for a range of forcing amplitudes and frequencies. Such a torque, in practice, may arise under malfunction of the control system or from an unbalanced rotor. Chaotic instabilities arising from these torques could introduce uncertainties and irregularities into a spacecraft's attitude motion and, consequently, could have disastrous effects on its operation. The two control methods, recursive proportional feedback and continuous delayed feedback, are recently developed techniques for control of chaotic motion in dynamic systems. Each technique is outlined and the effectiveness on this model compared and contrasted. Numerical simulations are performed, and the results are studied by means of time history, phase space, Poincare map, Lyapunov characteristic exponents, and bifurcation diagrams.

Control of chaotic instability in a dual-spin spacecraft with dissipation using energy methods

Control of chaotic instability in a rotating multibody system in the form of a dual-spin spacecraft with an axial nutational damper is achieved using an algorithm derived using energy methods. The control method is implemented on two realistic spacecraft parameter configurations which have been found to exhibit chaotic instability when a sinusoidally varying torque is applied to the spacecraft for a range of forcing amplitudes and frequencies. Such a torque, in practice, may arise under malfunction of the control system or from an unbalanced rotor. Chaotic instabilities arising from these torques could introduce uncertainties and irregularities into a spacecraft's attitude and consequently impair pointing accuracy. The control method is formulated from nutational stability results derived using an energy sink approximation for a dual-spin spacecraft with an asymmetric platform and axisymmetric rotor. The effectiveness of the control method is shown numerically and the results are studied by means of time history, phase space, Poincare map, Lyapunov characteristic exponents and Bifurcation diagrams.

Electron exchange coupling for single-donor solid-state spin qubits

Intervalley interference between degenerate conduction band minima has been shown to lead to oscillations in the exchange energy between neighboring phosphorus donor electron states in silicon [B. Koiller, X. Hu, and S. Das Sarma, Phys. Rev. Lett. 88, 027903 (2002); Phys. Rev. B 66, 115201 (2002)]. These same effects lead to an extreme sensitivity of the exchange energy on the relative orientation of the donor atoms, an issue of crucial importance in the construction of silicon-based spin quantum computers. In this article we calculate the donor electron exchange coupling as a function of donor position incorporating the full Bloch structure of the Kohn-Luttinger electron wave functions. It is found that due to the rapidly oscillating nature of the terms they produce, the periodic part of the Bloch functions can be safely ignored in the Heitler-London integrals as was done by Koiller, Hu, and Das Sarma, significantly reducing the complexity of calculations. We address issues of fabrication and calculate the expected exchange coupling between neighboring donors that have been implanted into the silicon substrate using an 15 keV ion beam in the so-called top down fabrication scheme for a Kane solid-state quantum computer. In addition, we calculate the exchange coupling as a function of the voltage bias on control gates used to manipulate the electron wave functions and implement quantum logic operations in the Kane proposal, and find that these gate biases can be used to both increase and decrease the magnitude of the exchange coupling between neighboring donor electrons. The zero-bias results reconfirm those previously obtained by Koiller, Hu, and Das Sarma.

Integrable impurity spin ladder systems

Two different types of integrable impurities in a spin ladder system are proposed. The impurities are introduced in such a way that the integrability of the models is not violated. The models are solved exactly with the Bethe ansatz equations as well as the energy eigenvalues obtained. We show for both models that a phase transition between gapped and gapless spin excitations occurs at a critical value of the rung coupling J. In addition, the dependence of the impurities on this phase transition is determined explicitly. In one of the models the spin gap decreases by increasing the impurity strength A. Moreover, for a fixed A, a reduction in the spin gap by increasing the impurity concentration is also observed.

Integrable generalized spin ladder models based on the SU(1|3) and SU(3|1) algebras

We present two integrable spin ladder models which possess a general free parameter besides the rung coupling J. The models are exactly solvable by means of the Bethe ansatz method and we present the Bethe ansatz equations. We analyze the elementary excitations of the models which reveal the existence of a gap for both models that depends on the free parameter. (C) 2003 American Institute of Physics.

Integra????o das decis??es e procedimentos dos sistemas produtivo e de gest??o

O Lacen, desde sua cria????o em 1982, acompanha de forma compartilhada os esfor??os da Eletronorte em se tornar uma empresa de excel??ncia mundial. Desta forma mant??m uma cronologia de projetos e programas de trabalhos que objetivam aperfei??oar seus sistemas produtivos e de gest??o. Ap??s implantar em 1997 a gest??o por processos alicer??ada num Sistema da Qualidade - SQ baseados na norma ISO 17025, observou-se que o sistema de trabalho da unidade carecia de integra????o ?? medida que as avalia????es e diagn??sticos se efetuavam. Desta forma, a iniciativa consiste em um s??rie de a????es que visam a integra????o do sistema de trabalho, de forma a otimizar os recursos produtivos e de gest??o

Sistemas de informa????es para o licenciamento ambiental: exemplo de coopera????o interinstitucional para melhoria da gest??o ambiental

Em 1981, com a edi????o da Lei no 6938, foi criado o Sistema Nacional de Meio Ambiente (Sisnama), composto dos ??rg??os federais e estaduais respons??veis pela formula????o e implementa????o das pol??ticas de meio ambiente. No ??mbito federal, integram o Sisnama o Minist??rio do Meio Ambiente (MMA) e o Instituto Brasileiro de Meio Ambiente e Recursos Naturais (Ibama); nos estados s??o integrantes os ??rg??os estaduais de meio ambiente. O licenciamento ambiental de qualquer atividade econ??mica ?? obrigat??rio em todo o pa??s, mas somente seis desses ??rg??os ambientais estaduais possuem sistemas informatizados para acompanhamento da situa????o desses empreendimentos. Essa situa????o conduz a uma s??rie de problemas gerenciais e administrativos entre os empreendedores e o governo, entre o p??blico e o governo e entre os empreendedores e a sociedade. At?? mesmo o Minist??rio P??blico, ao requisitar informa????es sobre a situa????o de determinada atividade econ??mica, n??o recebe dados com a presteza e a confiabilidade necess??rias

Sistemas de protocolo postal da Justi??a do Trabalho 3?? Regi??o

Os advogados/usu??rios da Justi??a do Trabalho em Minas Gerais dispunham de 114 Varas do Trabalho para protocoliza????o de peti????es trabalhistas. Necessitavam se deslocar para as cidades das Varas do Trabalho para efetuarem a protocoliza????o. Tal situa????o em muitas ocasi??es gerava gastos com viagens, di??rias, hospedagens al??m da perda de tempo na locomo????o. A Empresa Brasileira de Correios e Tel??grafos em Minas Gerais, no atendimento comercial ao cliente Tribunal Regional do Trabalho 3?? Regi??o, identificou junto ?? equipe da Diretoria Geral Judici??ria a necessidade de amplia????o dos pontos de atendimento para os advogados/usu??rios agilizarem a remessa das peti????es trabalhistas aos seus destinos

Abrang??ncia, inser????o e impacto transformador dos sistemas de compras eletr??nicas na administra????o p??blica: an??lise do Siasg/Comprasnet

Quais as funcionalidades necess??rias aos sistemas de compras eletr??nicas no ambiente da administra????o p??blica? Que par??metros s??o relevantes para a an??lise e a avalia????o desses sistemas? O trabalho aborda a aplica????o da tecnologia da informa????o ??s compras governamentais, focalizando o caso do Sistema Integrado de Administra????o de Servi??os Gerais (Siasg) e seu portal na Internet, o Comprasnet, desenvolvido pela Administra????o P??blica Federal brasileira. Contextualiza a emerg??ncia do com??rcio eletr??nico e sua aplica????o ?? administra????o p??blica. Sistematiza as fases e os procedimentos do processo de compras e contrata????es na administra????o p??blica brasileira, indicando os componentes e as funcionalidades que devem compor os sistemas de compras eletr??nicas governamentais. Prop??e par??metros de an??lise para a avalia????o desses sistemas: abrang??ncia, inser????o e impacto na transforma????o da gest??o. A aplica????o desses par??metros ao estudo de caso evidencia que o Siasg/Comprasnet apresenta abrang??ncia ainda incompleta, inser????o consolidada e impacto transformador mais acentuado sobre as compras realizadas por meio de modalidades de licita????o eletr??nicas.