10,251 research outputs found
Spin-spin Correlation in Some Excited States of Transverse Ising Model
We consider the transverse Ising model in one dimension with
nearest-neighbour interaction and calculate exactly the longitudinal spin-spin
correlation for a class of excited states. These states are known to play an
important role in the perturbative treatment of one-dimensional transverse
Ising model with frustrated second-neighbour interaction. To calculate the
correlation, we follow the earlier procedure of Wu, use Szego's theorem and
also use Fisher-Hartwig conjecture. The result is that the correlation decays
algebraically with distance () as and is oscillatory or
non-oscillatory depending on the magnitude of the transverse field.Comment: 5 pages, 1 figur
A human performance modelling approach to intelligent decision support systems
Manned space operations require that the many automated subsystems of a space platform be controllable by a limited number of personnel. To minimize the interaction required of these operators, artificial intelligence techniques may be applied to embed a human performance model within the automated, or semi-automated, systems, thereby allowing the derivation of operator intent. A similar application has previously been proposed in the domain of fighter piloting, where the demand for pilot intent derivation is primarily a function of limited time and high workload rather than limited operators. The derivation and propagation of pilot intent is presented as it might be applied to some programs
Bailey flows and Bose-Fermi identities for the conformal coset models
We use the recently established higher-level Bailey lemma and Bose-Fermi
polynomial identities for the minimal models to demonstrate the
existence of a Bailey flow from to the coset models
where is a
positive integer and is fractional, and to obtain Bose-Fermi identities
for these models. The fermionic side of these identities is expressed in terms
of the fractional-level Cartan matrix introduced in the study of .
Relations between Bailey and renormalization group flow are discussed.Comment: 28 pages, AMS-Latex, two references adde
Stress relaxation and mechanical properties of RL-1973 and PD-200-16 silicone resin sponge materials
Stress relaxation tests were conducted by loading specimens in double-lap shear to a preselected strain level and monitoring the decay of stress with time. The stress relaxation response characteristics were measured over a temperature range of 100 to 300 K and four strain levels. It is concluded that only a slight amount of stress relaxation was observed, and the stiffness increased approximately two orders of magnitude over the range of temperatures
Are classroom internet use and academic performance higher after government broadband subsidies to primary schools?
This paper combines data from a government programme providing broadband access to primary schools in Ireland with survey microdata on schools’, teachers’ and pupils use of the internet to examine the links between public subsidies, classroom use of the internet and educational performance. Provision of broadband service under a government scheme was associated with more than a doubling of teachers’ use of the internet in class after about a two year lag. Better computing facilities in schools were also associated with higher internet use, but advertised download speed was not statistically significant. A second set of models show that use of the internet in class was associated with significantly higher average mathematics scores on standardised tests. There was also a less robust positive association with reading scores. A set of confounding factors is included, with results broadly in line with previous literature
Finite Temperature and Dynamical Properties of the Random Transverse-Field Ising Spin Chain
We study numerically the paramagnetic phase of the spin-1/2 random
transverse-field Ising chain, using a mapping to non-interacting fermions. We
extend our earlier work, Phys. Rev. 53, 8486 (1996), to finite temperatures and
to dynamical properties. Our results are consistent with the idea that there
are ``Griffiths-McCoy'' singularities in the paramagnetic phase described by a
continuously varying exponent , where measures the
deviation from criticality. There are some discrepancies between the values of
obtained from different quantities, but this may be due to
corrections to scaling. The average on-site time dependent correlation function
decays with a power law in the paramagnetic phase, namely
, where is imaginary time. However, the typical
value decays with a stretched exponential behavior, ,
where may be related to . We also obtain results for the full
probability distribution of time dependent correlation functions at different
points in the paramagnetic phase.Comment: 10 pages, 14 postscript files included. The discussion of the typical
time dependent correlation function has been greatly expanded. Other papers
of APY are available on-line at http://schubert.ucsc.edu/pete
The importance of the Ising model
Understanding the relationship which integrable (solvable) models, all of
which possess very special symmetry properties, have with the generic
non-integrable models that are used to describe real experiments, which do not
have the symmetry properties, is one of the most fundamental open questions in
both statistical mechanics and quantum field theory. The importance of the
two-dimensional Ising model in a magnetic field is that it is the simplest
system where this relationship may be concretely studied. We here review the
advances made in this study, and concentrate on the magnetic susceptibility
which has revealed an unexpected natural boundary phenomenon. When this is
combined with the Fermionic representations of conformal characters, it is
suggested that the scaling theory, which smoothly connects the lattice with the
correlation length scale, may be incomplete for .Comment: 33 page
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