766 research outputs found
Phase diagram of an exactly solvable t-J ladder model
We study a system of one-dimensional t-J models coupled to a ladder system. A
special choice of the interaction between neighbouring rungs leads to an
integrable model with supersymmetry, which is broken by the presence of rung
interactions. We analyze the spectrum of low-lying excitations and ground state
phase diagram at zero temperature.Comment: LaTeX, 8 pp. incl. 1 figur
Calculation forces from bar movement on parallel bars in gymnastics
Modern artistic gymnastics apparatus have elastic properties, which the gymnast should use. It is important to know how a gymnast can give energy to the apparatus, especially to the bar(s) and how the stored energy can be used by the gymnast. The parallel bars were not included in such questions in the research yet. A static calibration at different positions of one bar was utilized as a precondition for the calculation of the forces during gymnastics exercises. Using synchronized 2D-video-analysis of the bar movement and the gymnasts performance (2 cameras) we calculate the forces based on our calibration. Examples of force-time-curves from parallel bars dismounts from German national gymnastics team will be shown. Using force-time-characteristics for supporting motor learning is a difficult task for the future
Thermodynamics of the (1,1/2) Ferrimagnet in Finite Magnetic Fields
We investigate the specific heat and magnetisation of a ferrimagnet with gS=1
and S=1/2 spins in a finite magnetic field using the transfer matrix DMRG down
to T=0.025J. Ferromagnetic gapless and antiferromagnetic gapped excitations for
H=0 lead to rich thermodynamics for H > 0. While the specific heat is
characterized by a generic double peak structure, magnetisation reveals two
critical fields, Hc1=1.76(1) and Hc2=3.00(1) with square-root behaviour in the
T=0 magnetisation. Simple analytical arguments allow to understand these
experimentally accessible findings.Comment: 5 pages, 7 eps figures, uses RevTeX, submitted to PR
Combined effect of frustration and dimerization in ferrimagnetic chains and square lattice
Within the zero-temperature linear spin-wave theory we have investigated the
effect of frustration and dimerization of a Heisenberg system with alternating
spins and on one- and two-dimensional lattices. The combined
effect most visibly appears in the elementary excitation spectra. In contrast
to the ground state energy that decreases with dimerization and increases with
frustration, the excitation energies are shown to be suppressed in energy by
both dimerization and frustration. The threshold value of frustration that
signals a transition from a classical ferrimagnetic state to a spiral state,
decreases with dimerization, showing that dimerization further helps in the
phase transition. The correlation length and sublattice magnetization decrease
with both dimerization and frustration indicating the destruction of the
long-range classical ferrimagnetic. The linear spin wave theory shows that in
the case of a square lattice, dimerization initially opposes the
frustration-led transition to a spiral magnetic state, but then higher
magnitudes of lattice deformation facilitate the transition. It also shows that
the transition to spiral state is inhibited in a square lattice beyond a
certain value of dimerization.Comment: 8 pages, latex, 12 postscript figure
Геофизические исследования скважин для выявления коллекторов и определения их фильтрационно-емкостных свойств на Вынгаяхинском газо-нефтяном месторождении (Тюменская область)
Объектом исследования является месторождение Вынгаяхинское. Цель работы – проектирование комплекса геофизических методов исследования скважин с целью изучения пластов- коллекторов Вынгаяхинского месторождения (ЯНАО). В процессе исследования проводились сбор и анализ геофизических материалов для обоснования оптимального комплекса. В результате исследования предложен комплекс ГИС для выявления и исследования нефтенасыщенных коллекторов. Область применения: предназначаемый комплекс ГИС может применяться на любых месторождениях нефти с терригенно-поровым типом коллекторов. Экономическая значимость работы определяется необходимостью исследований для подсчетов запасов.The object of this study is to deposit Vyngayakhinskoye. The purpose of the work - design of geophysical methods for wells to examine plastov- collectors Vyngayakhinskoye deposit (Yamalo-Nenets District). The study carried out collection and analysis of geophysical data to support the optimum combination. The study proposed a set of GIS for the detection and investigation of oil-saturated reservoir.
Scope: intended complex GIS can be used on any oil fields with terrigenous pore type reservoirs. The economic significance of the work is determined by the necessity of research for calculation of reserves
Electronic Ladders with SO(5) Symmetry: Phase Diagrams and Correlations at half-filling
We construct a family of electronic ladder models with SO(5) symmetry which
have exact ground states in the form of finitely correlated wave functions.
Extensions for these models preserving this symmetry are studied using these
states in a variational approach. Within this approach, the zero temperature
phase diagram of these electronic ladders at half filling is obtained,
reproducing the known results in the weak coupling (band insulator) and strong
coupling regime, first studied by Scalapino, Zhang and Hanke. Finally, the
compact form of the variational wave functions allows to compute various
correlation functions for these systems.Comment: RevTeX+epsf macros, 23 pp. including figure
Magnetic Properties of a Quantum Ferrimagnet: NiCu(pba)(D_2O)_3 . 2D_2O
We report the results of magnetic measurements on a powder sample of
NiCu(pba)(D_2O)_3 \cdot 2D_2OS\chi\chi TT\chi TJ/k_B=121
K^{2+}^{2+}g_{Ni}g_{Cu}\chi T$ at low temperatures
is reproduced fairly well by the calculation for the same ferrimagnetic model.Comment: 7pages, 4 postscript figures, usues REVTEX. appear in J. Phys. Soc.
Jpn vol 67 No.7 (1998
Elementary excitations in the gapped phase of a frustrated S=1/2 spin ladder: from spinons to the Haldane triplet
We use the variational matrix-product ansatz to study elementary excitations
in the S=1/2 ladder with additional diagonal coupling, equivalent to a single
S=1/2 chain with alternating exchange and next-nearest neighbor interaction. In
absence of alternation the elementary excitation consists of two free S=1/2
particles ("spinons") which are solitons in the dimer order. When the
nearest-neighbor exchange alternates, the "spinons" are confined into one S=1
excitation being a soliton in the generalized string order. Variational results
are found to be in a qualitative agreement with the exact diagonalization data
for 24 spins. We argue that such an approach gives a reasonably good
description in a wide range of the model parameters.Comment: RevTeX, 13 pages, 11 embedded figures, uses psfig and multico
Low Temperature Properties of Quantum Antiferromagnetic Chains with Alternating Spins S=1 and 1/2
We study the low-temperature properties of S=1 and 1/2 alternating spin
chains with antiferromagnetic nearest-neighbor exchange couplings using
analytical techniques as well as a quantum Monte Carlo method. The spin-wave
approach predicts two different low-lying excitations, which are gapped and
gapless, respectively. The structure of low-lying levels is also discussed by
perturbation theory in the strength of the Ising anisotropy. These analytical
findings are compared with the results of quantum Monte Carlo calculations and
it turns out that spin-wave theory well describes the present system. We
conclude that the quantum ferrimagnetic chain exhibits both ferromagnetic and
antiferromagnetic aspects.Comment: 13 pages, RevTeX, six figures, submitted to J. Phys. Cond. Ma
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