818 research outputs found
The free surface of superfluid 4He at zero temperature
The structure and energetics of the free surface of superfluid He are
studied using the diffusion Monte Carlo method. Extending a previous
calculation by Vall\'es and Schmidt, which used the Green's function Monte
Carlo method, we study the surface of liquid He within a slab geometry
using a larger number of particles in the slab and an updated interatomic
potential. The surface tension is accurately estimated from the energy of slabs
of increasing surface density and its value is close to one of the two existing
experimental values. Results for the density profiles allow for the calculation
of the surface width which shows an overall agreement with recent experimental
data. The dependence on the transverse direction to the surface of other
properties such as the two-body radial distribution function, structure factor,
and one-body density matrix is also studied. The condensate fraction, extracted
from the asymptotic behavior of the one-body density matrix, shows an
unambiguous enhancement when approaching the surface.Comment: RevTex, 11 pages, accepted in Phys. Rev.
Charged Particle Activation Analysis of Some Contaminants in Rare Earth Oxides
開始ページ、終了ページ: 冊子体のページ付
Scaling Properties of Antiferromagnetic Transition in Coupled Spin Ladder Systems Doped with Nonmagnetic Impurities
We study effects of interladder coupling on critical magnetic properties of
spin ladder systems doped with small concentrations of nonmagnetic impurities,
using the scaling theory together with quantum Monte Carlo (QMC) calculations.
Scaling properties in a wide region in the parameter space of the impurity
concentration x and the interladder coupling are governed by the quantum
critical point (QCP) of the undoped system for the transition between
antiferromagnetically ordered and spin-gapped phases. This multi-dimensional
and strong-coupling region has characteristic power-law dependences on x for
magnetic properties such as the N\'eel temperature. The relevance of this
criticality for understanding experimental results of ladder compounds is
stressed.Comment: 4 pages LaTeX including 3 PS figure
Mixed-Spin Ladders and Plaquette Spin Chains
We investigate low-energy properties of a generalized spin ladder model with
both of the spin alternation and the bond alternation, which allows us to
systematically study not only ladder systems but also alternating spin chains.
By exploiting non-linear model techniques we study the model with
particular emphasis on the competition between gapful and gapless states. Our
approach turns out to provide a more consistent semi-classical description of
alternating spin chains than that in the previous work. We also study a closely
related model, i.e., a spin chain with plaquette structure, and show that
frustration causes little effect on its low-energy properties so far as the
strength of frustration is weaker than a certain critical value.Comment: 7 pages, REVTeX, 3 figures, submitted to JPS
Efficacy of lamivudine for preventing hepatocellular carcinoma in chronic hepatitis B: A multicenter retrospective study of 2795 patients
ArticleHEPATOLOGY RESEARCH. 32(3): 173-184 (2005)journal articl
Cavitation of Electrons Bubbles in Liquid Helium Below saturation Pressure
We have used a Hartree-type electron-helium potential together with a density
functional description of liquid He and He to study the explosion of
electron bubbles submitted to a negative pressure. The critical pressure at
which bubbles explode has been determined as a function of temperature. It has
been found that this critical pressure is very close to the pressure at which
liquid helium becomes globally unstable in the presence of electrons. It is
shown that at high temperatures the capillary model overestimates the critical
pressures. We have checked that a commonly used and rather simple
electron-helium interaction yields results very similar to those obtained using
the more accurate Hartree-type interaction. We have estimated that the
crossover temperature for thermal to quantum nucleation of electron bubbles is
very low, of the order of 6 mK for He.Comment: 22 pages, 9 figure
Li Induced Spin and Charge Excitations in a Spin Ladder
A lithium dopant in a cuprate spin ladder acts as a vacant (non-magnetic)
site accompanied by an extra hole bound by a Coulomb potential. We find that,
although the undoped ladder spin gap is not essentially altered by Li doping, a
dopant-magnon bound state appears within the gap. Contrary to the case of
Zn-doped ladders, we predict that, in the Li-doped ladder, the spin liquid
character is very robust against antiferromagnetism. We also predict the
spatial dependence of the density of states in the vicinity of the dopant which
could be measured by local spectroscopic probes.Comment: 4 pages, Submitted to Physical Review Letter
Structural and dynamical properties of superfluid helium: a density functional approach
We present a novel density functional for liquid 4He, properly accounting for
the static response function and the phonon-roton dispersion in the uniform
liquid. The functional is used to study both structural and dynamical
properties of superfluid helium in various geometries. The equilibrium
properties of the free surface, droplets and films at zero temperature are
calculated. Our predictions agree closely to the results of ab initio Monte
Carlo calculations, when available. The introduction of a phenomenological
velocity dependent interaction, which accounts for backflow effects, is
discussed. The spectrum of the elementary excitations of the free surface and
films is studied.Comment: 37 pages, REVTeX 3.0, figures on request at [email protected]
Numerical renormalization-group study of spin correlations in one-dimensional random spin chains
We calculate the ground-state two-spin correlation functions of spin-1/2
quantum Heisenberg chains with random exchange couplings using the real-space
renormalization group scheme. We extend the conventional scheme to take account
of the contribution of local higher multiplet excitations in each decimation
step. This extended scheme can provide highly accurate numerical data for large
systems. The random average of staggered spin correlations of the chains with
random antiferromagnetic (AF) couplings shows algebraic decay like ,
which verifies the Fisher's analytic results. For chains with random
ferromagnetic (FM) and AF couplings, the random average of generalized
staggered correlations is found to decay more slowly than a power-law, in the
form close to . The difference between the distribution functions of
the spin correlations of the random AF chains and of the random FM-AF chains is
also discussed.Comment: 14 pages including 8 figures, REVTeX, submitted to Physical Review
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