3,048 research outputs found
Oil, the economy, and monetary policy
An examination of the theoretical impact of an oil shortage on the U.S. economy and the problems that such shortages present for monetary policy.Power resources - Prices ; Monetary policy
Reversal-field memory in magnetic hysteresis
We report results demonstrating a singularity in the hysteresis of magnetic
materials, the reversal-field memory effect. This effect creates a
nonanalyticity in the magnetization curves at a particular point related to the
history of the sample. The microscopic origin of the effect is associated with
a local spin-reversal symmetry of the underlying Hamiltonian. We show that the
presence or absence of reversal-field memory distinguishes two widely studied
models of spin glasses (random magnets).Comment: 3 pages, 5 figures. Proceedings of "2002 MMM Conferece", Tampa, F
Reversal-Field Memory in the Hysteresis of Spin Glasses
We report a novel singularity in the hysteresis of spin glasses, the
reversal-field memory effect, which creates a non-analyticity in the
magnetization curves at a particular point related to the history of the
sample. The origin of the effect is due to the existence of a macroscopic
number of "symmetric clusters" of spins associated with a local spin-reversal
symmetry of the Hamiltonian. We use First Order Reversal Curve (FORC) diagrams
to characterize the effect and compare to experimental results on thin magnetic
films. We contrast our results on spin glasses to random magnets and show that
the FORC technique is an effective "magnetic fingerprinting" tool.Comment: 4 pages, 6 figure
Percolation Threshold, Fisher Exponent, and Shortest Path Exponent for 4 and 5 Dimensions
We develop a method of constructing percolation clusters that allows us to
build very large clusters using very little computer memory by limiting the
maximum number of sites for which we maintain state information to a number of
the order of the number of sites in the largest chemical shell of the cluster
being created. The memory required to grow a cluster of mass s is of the order
of bytes where ranges from 0.4 for 2-dimensional lattices
to 0.5 for 6- (or higher)-dimensional lattices. We use this method to estimate
, the exponent relating the minimum path to the
Euclidean distance r, for 4D and 5D hypercubic lattices. Analyzing both site
and bond percolation, we find (4D) and
(5D). In order to determine
to high precision, and without bias, it was necessary to
first find precise values for the percolation threshold, :
(4D) and (5D) for site and
(4D) and (5D) for bond
percolation. We also calculate the Fisher exponent, , determined in the
course of calculating the values of : (4D) and
(5D)
Polaron percolation in diluted magnetic semiconductors
We theoretically study the development of spontaneous magnetization in
diluted magnetic semiconductors as arising from a percolation of bound magnetic
polarons. Within the framework of a generalized percolation theory we derive
analytic expressions for the Curie temperature and the magnetization, obtaining
excellent quantitative agreement with Monte Carlo simulation results and good
qualitative agreement with experimental results.Comment: 5 page
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