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861.
B. Canals D.A. Garanin 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):439-447
Thermodynamic quantities and correlation functions (CFs) of the classical antiferromagnet on the checkerboard lattice are
studied for the exactly solvable infinite-component spin-vector model, D↦∞. In contrast to conventional two-dimensional magnets with continuous symmetry showing extended short-range order at distances
smaller than the correlation length, r
ξ
c∝ exp(T
*/T), correlations in the checkerboard-lattice model decay already at the scale of the lattice spacing due to the strong degeneracy
of the ground state characterized by a macroscopic number of strongly fluctuating local degrees of freedom. At low temperatures,
spin CFs decay as <
>∝ 1/r
2 in the range a
0≪r≪ξ
c∝T
-1/2, where a0 is the lattice spacing. Analytical results for the principal thermodynamic quantities in our model are very similar with
MC simulations, exact and analytical results for the classical Heisenberg model (D = 3) on the pyrochlore lattice. This shows that the ground state of the infinite-component spin vector model on the checkerboard
lattice is a classical spin liquid.
Received 16 November 2001 and Received in final form 12 February 2002 相似文献
862.
We study a one parameter variational wave function to improve the spin density wave ground state of the Hubbard model by inclusion of quantum spin fluctuations. Using a perturbative approach and novel lattice summation techniques we present analytical as well as numerical results for the correlation energies and the staggered magnetizations in one and two dimensions. We find ground state energies which are satisfyingly close to known exact results and are significantly lower than those of existing Gutzwiller and numerical treatments. 相似文献
863.
E. Rastelli A. Tassi 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(3):341-347
Ferromagnetic spin chains of a hexagonal lattice coupled by a weak antiferromagnetic interaction J1 develop a helix arrangement if the intrachain antiferromagnetic NNN exchange J2 is sufficiently large. We show that the classical minimum energy spin configuration is an umbrella when an external magnetic field is applied. The scenario is dramatically changed by quantum fluctuations. Indeed we find
that the zero point motion forces the spins in a plane containing the magnetic field so that classical expectation is deceptive
for our model. Our result is obtained by controlled expansion in the low field-long wavelength modulation limit.
Received: 9 September 1997 / Revised: 15 October 1997 / Accepted: 17 November 1997 相似文献
864.
F. Capraro C. Gros 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(1):35-40
Using the density matrix renormalization group technique, we evaluate the low-energy spectrum (ground state and first excited
states) of the anisotropic antiferromagnetic spin-one-half chain under magnetic fields. We study both homogeneous longitudinal
and transversal fields as well as the influence of a transversal staggered field on the opening of a spin-gap. We find that
only a staggered transversal field opens a substantial gap.
Received 16 April 2002 / Received in final form 4 July 2002 Published online 17 September 2002 相似文献
865.
Ricardo Jimnez 《Solid State Ionics》1996,90(1-4):233-244
The a.c. electrical response of an electrically isotropic solid electrolyte pressed powder pellet, has been calculated using the Percolation Effective Medium Theory (P.E.M.T.) approximation. The pressed powder pellet is represented by a mixture of a conducting phase (solid electrolyte) and an isolation one (air). The physical meaning of the derived results is discussed in reference to a real solid electrolyte pellet response. The pellet response calculated by the P.E.M.T. equation should correspond to the usual ‘bulk’ one. The influence of the microstructure on the pellet response, derived from the model, can be used to improve the ‘bulk’ ionic conductivity, in pressed powder pellets of solid electrolytes with isotropic conductivity, and to obtain its real electrical characteristics. 相似文献
866.
Y. Funaki A. Tohsaki H. Horiuchi P. Schuck G. Röpke 《The European Physical Journal A - Hadrons and Nuclei》2006,28(3):259-263
In order to discuss the spatial extention of the 02
+-state of 12C (Hoyle state), we analyze the inelastic form factor of electron scattering to the Hoyle state, which our 3α-condensate wave
function reproduces very well like previous 3α RGM/GCM models. The analysis is made by varying the size of the Hoyle state
artificially. As a result, we find that only the maximum value of the form factor sensitively depends on its size, while the
positions of maximum and minimum are almost unchanged. This size dependence is found to come from a characteristic feature
of the transition density from the ground state to the Hoyle state. We further show the theoretical predictions of the inelastic
form factor to the 22
+-state of 12C, which was recently observed above the Hoyle state, and of the inelastic form factor to the calculated 03
+-state of 16O, which was conjectured to correspond to the 4α condensed state in previous theoretical work by the present authors. 相似文献
867.
868.
针对城市管线网GIS领域特色,引入图论代数相关理论、改进GIS现有网络结构模型组织与表达,提出城市管线网GIS一体化空间数据模型,并实现该模型支持下的强大的地理计算和空间分析功能,最后在“数字城市”管线网GIS共享集成平台和专业管线GIS系统中实现了模型的功能应用。 相似文献
869.
A bilevel program is a mathematical program involving functions defined implicitly as solutions to another mathematical program. We discuss a method for extracting derivative information on the implicit function, which is especially efficient when the lower-level problem has simple bounds on the variables and/or many inactive constraints. Computational experience on problems with up to 230 variables and 30 constraints is presented.Computational support from Robert Bivins and Myron Stein is gratefully acknowledged. We have also appreciated comments from Jon Bard and an anonymous referee. This work was supported in part by the US Department of Energy through the Los Alamos National Laboratory. 相似文献
870.
K. Singh S. Sihotra S. S. Malik J. Goswamy D. Mehta N. Singh R. Kumar R. P. Singh S. Muralithar E. S. Paul J. A. Sheikh C. R. Praharaj 《The European Physical Journal A - Hadrons and Nuclei》2006,27(3):321-324
The collective band structures of the 125Cs nucleus have been investigated by in-beam γ-ray spectroscopic techniques following the 110Pd ( 19F, 4n) reaction at 75MeV. The previously known level scheme, with rotational bands built on πg7/2, πg9/2 and πh11/2 orbitals, has been extended and evolves into bands involving rotationally aligned ν(h11/2)2 and π(h11/2)2 quasiparticles. A strongly coupled band has been reassigned a high-K πh11/2 ⊗ νg7/2 ⊗ νh11/2 three-quasiparticle configuration and a new side band likely to be its chiral partner has been identified. Configurations
assigned to various bands are discussed in the framework of Principal/Tilted Axis Cranking (PAC/TAC) model calculations. 相似文献