68 research outputs found
Energy of bond defects in quantum spin chains obtained from local approximations and from exact diagonalization
We study the influence of ferromagnetic and antiferromagnetic bond defects on
the ground-state energy of antiferromagnetic spin chains. In the absence of
translational invariance, the energy spectrum of the full Hamiltonian is
obtained numerically, by an iterative modification of the power algorithm. In
parallel, approximate analytical energies are obtained from a local-bond
approximation, proposed here. This approximation results in significant
improvement upon the mean-field approximation, at negligible extra
computational effort.Comment: 3 pages, 2 figures. Manuscript accepted by Journal of Magnetism and
Magnetic Materials, special issue for LAWMMM 2007 conferenc
Estudos sobre a nutrição mineral do arroz: X. marcha de absorção de micronutrientes pela variedade IAC-25
The uptake of micronutrients (B, Cu, Fe, Mn and Zn) by the variety IAC-25 in various phases of its development was studied, the plants being grown in nutrient solution, Main conclusions were the following: (a) only two variables, namely dry matter production an Fe accumulation, showed a tendency to level off as the plants complete their life cycle; (b) indication of internal redistribution was observed in the case of Fe and Mn; (c) maximum rate of uptake, was well as of dry matter production took place in the period which goes from tillering to grain filling.Em condições controladas estudaram-se: acumulação de micronutrientes e produção de materia seca pela variedade de arroz IAC-25. A curva que descreve a produção de matéria seca total em função do tempo apresentou a tendência a sigmóide. Com respeito a acumulação global de micronutrientes, entretanto, o mesmo foi observado somente no caso do ferro
Orchidaceae em um fragmento de Floresta Semidecídua de encosta na região sul do Estado do Espírito Santo, Sudeste do Brasil
Constructing Exactly Solvable Pseudo-hermitian Many-particle Quantum Systems by Isospectral Deformation
A class of non-Dirac-hermitian many-particle quantum systems admitting
entirely real spectra and unitary time-evolution is presented. These quantum
models are isospectral with Dirac-hermitian systems and are exactly solvable.
The general method involves a realization of the basic canonical commutation
relations defining the quantum system in terms of operators those are hermitian
with respect to a pre-determined positive definite metric in the Hilbert space.
Appropriate combinations of these operators result in a large number of
pseudo-hermitian quantum systems admitting entirely real spectra and unitary
time evolution. Examples of a pseudo-hermitian rational Calogero model and XXZ
spin-chain are considered.Comment: To appear in the Special Issue PHHQP 2010, International Journal of
Theoretical Physics; 16 pages, LateX, no figur
Algumas propriedades físicas e hídricas de três solos na Chapada do Apodi, RN, cultivados com melão
Amostragem e variabilidade espacial de atributos físicos de um latossolo vermelho em Mossoró, RN
Efeitos da terra diatomácea sobre Diabrotica speciosa (Germar, 1824) (Coleoptera: Chrysomelidae) em batata inglesa
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