985 research outputs found
Influence of Mg, Ag and Al substitutions on the magnetic excitations in the triangular-lattice antiferromagnet CuCrO2
Magnetic excitations in CuCrO, CuCrMgO,
CuAgCrO, and CuCrAlO have been
studied by powder inelastic neutron scattering to elucidate the element
substitution effects on the spin dynamics in the Heisenberg triangular-lattice
antiferromagnet CuCrO. The magnetic excitations in
CuCrMgO consist of a dispersive component and a flat
component. Though this feature is apparently similar to CuCrO, the energy
structure of the excitation spectrum shows some difference from that in
CuCrO. On the other hand, in CuAgCrO and
CuCrAlO the flat components are much reduced, the
low-energy parts of the excitation spectra become intense, and additional
low-energy diffusive spin fluctuations are induced. We argued the origins of
these changes in the magnetic excitations are ascribed to effects of the doped
holes or change of the dimensionality in the magnetic correlations.Comment: 7 pages, 5 figure
A Two-dimensional Infinte System Density Matrix Renormalization Group Algorithm
It has proved difficult to extend the density matrix renormalization group
technique to large two-dimensional systems. In this Communication I present a
novel approach where the calculation is done directly in two dimensions. This
makes it possible to use an infinite system method, and for the first time the
fixed point in two dimensions is studied. By analyzing several related blocking
schemes I find that there exists an algorithm for which the local energy
decreases monotonically as the system size increases, thereby showing the
potential feasibility of this method.Comment: 5 pages, 6 figure
The critical behaviour of the 2D Ising model in Transverse Field; a Density Matrix Renormalization calculation
We have adjusted the Density Matrix Renormalization method to handle two
dimensional systems of limited width. The key ingredient for this extension is
the incorporation of symmetries in the method. The advantage of our approach is
that we can force certain symmetry properties to the resulting ground state
wave function. Combining the results obtained for system sizes up-to and finite size scaling, we derive the phase transition point and the
critical exponent for the gap in the Ising model in a Transverse Field on a two
dimensional square lattice.Comment: 9 pages, 8 figure
The 1/D Expansion for Classical Magnets: Low-Dimensional Models with Magnetic Field
The field-dependent magnetization m(H,T) of 1- and 2-dimensional classical
magnets described by the -component vector model is calculated analytically
in the whole range of temperature and magnetic fields with the help of the 1/D
expansion. In the 1-st order in 1/D the theory reproduces with a good accuracy
the temperature dependence of the zero-field susceptibility of antiferromagnets
\chi with the maximum at T \lsim |J_0|/D (J_0 is the Fourier component of the
exchange interaction) and describes for the first time the singular behavior of
\chi(H,T) at small temperatures and magnetic fields: \lim_{T\to 0}\lim_{H\to 0}
\chi(H,T)=1/(2|J_0|)(1-1/D) and \lim_{H\to 0}\lim_{T\to 0}
\chi(H,T)=1/(2|J_0|)
A Computation of the Maximal Order Type of the Term Ordering on Finite Multisets
We give a sharpening of a recent result of Aschenbrenner and Pong about the maximal order type of the term ordering on the finite multisets over a wpo. Moreover we discuss an approach to compute maximal order types of well-partial orders which are related to tree embeddings
Physiological hyperinsulinaemia increases intramuscular microvascular reactive hyperaemia and vasomotion in healthy volunteers
A density matrix renormalisation group algorithm for quantum lattice systems with a large number of states per site
A variant of White's density matrix renormalisation group scheme which is
designed to compute low-lying energies of one-dimensional quantum lattice
models with a large number of degrees of freedom per site is described. The
method is tested on two exactly solvable models---the spin-1/2
antiferromagnetic Heisenberg chain and a dimerised XY spin chain. To illustrate
the potential of the method, it is applied to a model of spins interacting with
quantum phonons. It is shown that the method accurately resolves a number of
energy gaps on periodic rings which are sufficiently large to afford an
accurate investigation of critical properties via the use of finite-size
scaling theory.Comment: RevTeX, 8 pages, 2 figure
Tissue-specific expression of high-voltage-activated dihydropyridine-sensitive L-type calcium channels
The cloning of the cDNA for the α1 subunit of L-type calcium channels revealed that at least two genes (CaCh1 and CaCh2) exist which give rise to several splice variants. The expression of mRNA for these α1 subunits and the skeletal muscle α2/δ, β and γ subunits was studied in rabbit tissues and BC3H1 cells. Nucleic-acid-hybridization studies showed that the mRNA of all subunits are expressed in skeletal muscle, brain, heart and aorta. However, the α1-, β- and γ-specific transcripts had different sizes in these tissues. Smooth muscle and heart contain different splice variants of the CaCh2 gene. The α1, β and γ mRNA are expressed together in differentiated but not in proliferating BC3H1 cells. A probe specific for the skeletal muscle α2/δ subunit did not hybridize to poly(A)-rich RNA from BC3H1 cells. These results suggest that different splice variants of the genes for the α1, β and γ subunits exist in tissues containing L-type calcium channels, and that their expression is regulated in a coordinate manner
Noise-induced switching between vortex states with different polarization in classical two-dimensional easy-plane magnets
In the 2-dimensional anisotropic Heisenberg model with XY-symmetry there are
non-planar vortices which exhibit a localized structure of the z-components of
the spins around the vortex center. We study how thermal noise induces a
transition of this structure from one polarization to the opposite one. We
describe the vortex core by a discrete Hamiltonian and consider a stationary
solution of the Fokker-Planck equation. We find a bimodal distribution function
and calculate the transition rate using Langer's instanton theory (1969). The
result is compared with Langevin dynamics simulations for the full many-spin
model.Comment: 15 pages, 4 figures, Phys. Rev. B., in pres
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