4,288 research outputs found
The utopian tradition: A comparison of The Republic and Utopia with James Hilton\u27s \u27Lost Horizon
Utopia -- the concept more than the word -- has captured the imagination and fostered the hopes of men through thousands of years of recorded history. Behind the concept, one which various ages have redefined for their own particular situations, lies the nascent belief that humankind, working in harmony and unison, can create a better world and achieve maximum progress towards happiness
Anomalous Spin Dynamics in Doped Quantum Antiferromagnets
Finite-temperature spin dynamics in planar t-J model is studied using the
method based on the Lanczos diagonalization of small systems. Dynamical spin
structure factor at moderate dopings shows the coexistence of free-fermion-like
and spin-fluctuation timescales. At T<J, the low-frequency and static
susceptibility show pronounced T dependence, supporting a scenario, related to
the marginal Fermi-liquid one, for the explanation of neutron-scattering and
NMR-relaxation experiments in cuprates. Calculated NMR relaxation rates
reasonably reproduce experimental ones.Comment: 10 pages + 4 figures, Postscript in uuencoded compressed tar file,
IJS-TP-94/2
Thrombophilia in Systemic Lupus Erythematosus: A Review of Multiple Mechanisms and Resultant Clinical Outcomes
Neutral interstellar He parameters in front of the heliosphere 1994--2007
Analysis of IBEX measurements of neutral interstellar He flux brought the
inflow velocity vector different from the results of earlier analysis of
observations from GAS/Ulysses. Recapitulation of results on the helium inflow
direction from the past ~40 years suggested that the inflow direction may be
changing with time. We reanalyze the old Ulysses data and reprocess them to
increase the accuracy of the instrument pointing to investigate if the GAS
observations support the hypothesis that the interstellar helium inflow
direction is changing. We employ a similar analysis method as in the analysis
of the IBEX data. We seek a parameter set that minimizes reduced chi-squared,
using the Warsaw Test Particle Model for the interstellar He flux at Ulysses
with a state of the art model of neutral He ionization in the heliosphere, and
precisely reproducing the observation conditions. We also propose a
supplementary method of constraining the parameters based on cross-correlations
of parameters obtained from analysis of carefully selected subsets of data. We
find that the ecliptic longitude and speed of interstellar He are in a very
good agreement with the values reported in the original GAS analysis. We find,
however, that the temperature is markedly higher. The 3-seasons optimum
parameter set is lambda = 255.3, beta = 6, v = 26.0 km/s, T = 7500 K. We find
no evidence that it is varying with time, but the uncertainty range is larger
than originally reported. The originally-derived parameters of interstellar He
from GAS are in good agreement with presently derived, except for the
temperature, which seems to be appreciably higher, in good agreement with
interstellar absorption line results. While the results of the present analysis
are in marginal agreement with the earlier reported results from IBEX, the most
likely values from the two analyses differ for reasons that are still not
understood.Comment: submitted for publication in Astronomy & Astrophysic
Spin diffusion of the t-J model
The spin-diffusion constant of the 2D model is calculated for the first
time using an analytical approach at high temperatures and a recently-developed
numerical method based on the Lanczos technique combined with random sampling
in the intermediate temperature regime. A simple relation, ,
between spin conductivity and spin diffusion is established and used to
calculate the latter. In the high-temperature and low-doping limit the
calculated diffusion constant agrees with known results for the Heisenberg
model. At small hole doping, increases approximately linearly with
doping, which leads us to an important conclusion that hopping processes
enhance spin diffusion at high temperatures. At modest hole doping, , diffusion exhibits a nonmonotonic temperature dependence, which
indicates anomalous spin dynamics at small frequencies.Comment: 12 pages with figure
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