68 research outputs found
Exact Expressions for Minor Hysteresis Loops in the Random Field Ising Model on a Bethe Lattice at Zero Temperature
We obtain exact expressions for the minor hysteresis loops in the
ferromagnetic random field Ising model on a Bethe lattice at zero temperature
in the case when the driving field is cycled infinitely slowly.Comment: Replaced with the published versio
Zero-temperature Hysteresis in Random-field Ising Model on a Bethe Lattice
We consider the single-spin-flip dynamics of the random-field Ising model on
a Bethe lattice at zero temperature in the presence of a uniform external
field. We determine the average magnetization as the external field is varied
from minus infinity to plus infinity by setting up the self-consistent field
equations, which we show are exact in this case. We find that for a
3-coordinated Bethe lattice, there is no jump discontinuity in magnetization
for arbitrarily small gaussian disorder, but the discontinuity is present for
larger coordination numbers. We have checked our results by Monte Carlo
simulations employing a technique for simulating classical interacting systems
on the Bethe lattice which avoids surface effects altogether.Comment: latex file with 5 eps figures. This version is substantially revised
with new material. Submitted to J. Phys.
Hysteresis in Anti-Ferromagnetic Random-Field Ising Model at Zero Temperature
We study hysteresis in anti-ferromagnetic random-field Ising model at zero
temperature. The external field is cycled adiabatically between - and
. Two different distributions of the random-field are considered, (i) a
uniform distribution of width centered at the origin, and (ii) a
Gaussian distribution with average value zero and standard deviation .
In each case the hysteresis loop is determined exactly in one dimension and
compared with numerical simulations of the model
Analysis of wasp-waisted hysteresis loops in magnetic rocks
The random-field Ising model of hysteresis is generalized to dilute magnets
and solved on a Bethe lattice. Exact expressions for the major and minor
hysteresis loops are obtained. In the strongly dilute limit the model provides
a simple and useful understanding of the shapes of hysteresis loops in magnetic
rock samples.Comment: 11 pages, 4 figure
Critical Hysteresis in Random Field XY and Heisenberg Models
We study zero-temperature hysteresis in random-field XY and Heisenberg models
in the zero-frequency limit of a cyclic driving field. We consider three
distributions of the random field and present exact solutions in the mean field
limit. The results show a strong effect of the form of disorder on critical
hysteresis as well as the shape of hysteresis loops. A discrepancy with an
earlier study based on the renormalization group is resolved.Comment: 10 pages, 6 figures; this is published version (added some text and
references
The magnetization-driven random field Ising model at T=0
We study the hysteretic evolution of the random field Ising model (RFIM) at
T=0 when the magnetization M is controlled externally and the magnetic field H
becomes the output variable. The dynamics is a simple modification of the
single-spin-flip dynamics used in the H-driven situation and consists in
flipping successively the spins with the largest local field. This allows to
perform a detailed comparison between the microscopic trajectories followed by
the system with the two protocols. Simulations are performed on random graphs
with connectivity z=4 (Bethe lattice) and on the 3-D cubic lattice. The same
internal energy U(M)is found with the two protocols when there is no
macroscopic avalanche and it does not depend on whether the microscopic states
are stable or not. On the Bethe lattice, the energy inside the macroscopic
avalanche also coincides with the one that is computed analytically with the
H-driven algorithm along the unstable branch of the hysteresis loop. The output
field, defined here as dU/dM, exhibits very large fluctuations with the
magnetization and is not self-averaging. Relation to the experimental situation
is discussed.Comment: 11 pages, 13 figure
Hysteresis in Random Field XY and Heisenberg Models: Mean Field Theory and Simulations at Zero Temperature
We examine zero temperature hysteresis in random field XY and Heisenberg
models in the zero frequency limit of a cyclic driving field. Exact expressions
for hysteresis loops are obtained in the mean field approximation. These show
rather unusual features. We also perform simulations of the two models on a
simple cubic lattice and compare them with the predictions of the mean field
theory.Comment: replaced by the published versio
Meeting Stakeholder Energy Technology Education Needs Using a Mobile Demonstration
Understanding the impact of workshops that include mobile demonstrations for describing technical applications can be useful when planning an Extension program on new energy technologies. We used a mobile demonstration in a workshop that provided information on small-scale on-farm biodiesel production. Evaluation of the workshop outcomes identified significant increases in attendees\u27 perceptions, awareness, interest, and knowledge related to the topic. On the basis of our process for planning and conducting the workshop and the results of the evaluation, we recommend implementing a well-distributed needs assessment and using a mobile demonstration to present technology that is economically feasible to use. The workshop we describe can be used as a model for other Extension programs
Morphometric analysis of Dactylorhiza hatagirea (D. Don), a critically endangered orchid in cold desert Ladakh region of India
The morphometric study was conducted during 2009 to 2010. About 28 morphological characters were measured under 13 natural populations of Dactylorhiza hatagirea. Geographic variation in morphology reflects phenotypic responses to environmental gradients and evolutionary history of populations and species. At points, beside its broad geographic range (Nubra, Suru and Indus valley) characterization of Dactylorhiza phenotype is normally accomplished by use of morphological descriptors, hence as a first step, phenotype collection and its morphometric analysis was assessed. However, plant height, leaf length, lowermost leaf length, length of second leaf from base and mean length from lowest bract to the top of inflorescence are presented to account for the remarkable variation in morphological characters. Tirith population showed more values of this trait while Skurru showed less value. From this, it is concluded that Tirith showed great morphometric variation as compared to other population. Multivariate morphometric techniques, principal component analysis (PCA), multidimensional scaling (MDS) and cluster analysis were used to determine whether these populations can be reliably morphologically similar or dissimilar. The first two principal components encompass more than 75% variation among population. The results of PCA and MDS analysis were comparable to the cluster analysis, which shows considerable phenotypic variation in morphological and horticultural traits that can be utilized in its genetic improvement. To support this study, further constructive information were provided on the status of the populations of D. hatagirea which may increase the conservation value of this site and resolve the suitable areas with taxonomic and nomenclatural controversies.Keywords: Morphological characters, principal component analysis (PCA), multidimensional scaling (MDS), plant height, leaf length, leaf widt
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