3,737 research outputs found
Maxillary nerve blocks in horses: an experimental comparison of surface landmark and ultrasound-guided techniques
Diffusion in scale-free networks with annealed disorder
The scale-free (SF) networks that have been studied so far contained quenched
disorder generated by random dilution which does not vary with the time. In
practice, if a SF network is to represent, for example, the worldwide web, then
the links between its various nodes may temporarily be lost, and re-established
again later on. This gives rise to SF networks with annealed disorder. Even if
the disorder is quenched, it may be more realistic to generate it by a
dynamical process that is happening in the network. In this paper, we study
diffusion in SF networks with annealed disorder generated by various scenarios,
as well as in SF networks with quenched disorder which, however, is generated
by the diffusion process itself. Several quantities of the diffusion process
are computed, including the mean number of distinct sites visited, the mean
number of returns to the origin, and the mean number of connected nodes that
are accessible to the random walkers at any given time. The results including,
(1) greatly reduced growth with the time of the mean number of distinct sites
visited; (2) blocking of the random walkers; (3) the existence of a phase
diagram that separates the region in which diffusion is possible from one in
which diffusion is impossible, and (4) a transition in the structure of the
networks at which the mean number of distinct sites visited vanishes, indicate
completely different behavior for the computed quantities than those in SF
networks with quenched disorder generated by simple random dilution.Comment: 18 pages including 8 figure
A generalized spin model of financial markets
We reformulate the Cont-Bouchaud model of financial markets in terms of
classical "super-spins" where the spin value is a measure of the number of
individual traders represented by a portfolio manager of an investment agency.
We then extend this simplified model by switching on interactions among the
super-spins to model the tendency of agencies getting influenced by the opinion
of other managers. We also introduce a fictitious temperature (to model other
random influences), and time-dependent local fields to model slowly changing
optimistic or pessimistic bias of traders. We point out close similarities
between the price variations in our model with super-spins and total
displacements in an -step Levy flight. We demonstrate the phenomena of
natural and artificially created bubbles and subsequent crashes as well as the
occurrence of "fat tails" in the distributions of stock price variations.Comment: 11 pages LATEX, 7 postscript figures; longer text with theoretical
analysis, more accurate numerical data, better terminology, additional
references. Accepted for publication in European Physical Journal
Numerical investigation of novel microwave applicators based on zero-order mode resonance for hyperthermia treatment of cancer
This paper characterizes three novel microwave applicators based on zero-order mode resonators for use in hyperthermia treatment of cancer. The radiation patterns are studied with numerical simulations in muscle tissue-equivalent model at 434 MHz. The relative performance of the applicators is compared in terms of reflection coefficient, current distribution, power deposition (SAR) pattern, effective field size in 2D and 3D tissue volumes, and penetration depth. One particular configuration generated the most uniform SAR pattern, with 25% SAR covering 84 % of the treatment volume extending to 1 cm depth under the aperture, while remaining above 58% coverage as deep as 3 cm under the aperture. Recommendations are made to further optimize this structure
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Gregory Butler. Bach's Clavier-Ubung III: The Making of a Print. With a Companion Study of the Canonic Variations on "Vom Himmel Hoch," BWV 769.
This article discusses Gregory Butler's Bach's Clavier-Ubung III' The Making of a Print and the authors thoughts on Bach. At the conclusion of a round table on post-World War II developments in Bach research, a long session in which the manuscript studies of Alfred Durr, Georg von Dadelsen, and Robert Marshall were discussed in some detail, Mendel quipped, with a wry smile: "And if the original manuscripts have revealed a lot about Bach's working habits, wait until we take a closer look at the original prints!" The remark drew laughter, as Mendel intended, and struck one at the time as facetious, for how could the prints of Bach's works ever show as much about chronology and the compositional process as the manuscripts? The surviving manuscript materials, written by Bach and his copyists, display a wealth of information that can be unraveled through source-critical investigation: revisions, corrections, organizational second thoughts. The prints, by contrast, appear inscrutable. Uniform and definitive in appearance, made by engravers rather than Bach or his assistants, they seem to be closed books, telling little-if any thing about the genesis of the texts they contain
A new model of binary opinion dynamics: coarsening and effect of disorder
We propose a model of binary opinion in which the opinion of the individuals
change according to the state of their neighbouring domains. If the
neighbouring domains have opposite opinions, then the opinion of the domain
with the larger size is followed. Starting from a random configuration, the
system evolves to a homogeneous state. The dynamical evolution show novel
scaling behaviour with the persistence exponent and
dynamic exponent . Introducing disorder through a
parameter called rigidity coefficient (probability that people are
completely rigid and never change their opinion), the transition to a
heterogeneous society at is obtained. Close to , the
equilibrium values of the dynamic variables show power law scaling behaviour
with . We also discuss the effect of having both quenched and annealed
disorder in the system.Comment: 4 pages, 6 figures, Final version of PR
Frequency dependent effective conductivity of two-dimensional metal-dielectric composites
We analyze a random resistor-inductor-capacitor lattice model of
2-dimensional metal-insulator composites. The results are compared with
Bruggeman's and Landauer's Effective Medium Approximations where a discrepancy
was observed for some frequency zones. Such a discrepancy is mainly caused by
the strong conductivity fluctuations. Indeed, a two-branches distribution is
observed for low frequencies. We show also by increasing the system size that
at the so-called Drude peak vanishes; it increases for vanishing losses.Comment: 7 pages including all figures, accepted in Int. J. Mod. Phys.
On Spatial Consensus Formation: Is the Sznajd Model Different from a Voter Model?
In this paper, we investigate the so-called ``Sznajd Model'' (SM) in one
dimension, which is a simple cellular automata approach to consensus formation
among two opposite opinions (described by spin up or down). To elucidate the SM
dynamics, we first provide results of computer simulations for the
spatio-temporal evolution of the opinion distribution , the evolution of
magnetization , the distribution of decision times and
relaxation times . In the main part of the paper, it is shown that the
SM can be completely reformulated in terms of a linear VM, where the transition
rates towards a given opinion are directly proportional to frequency of the
respective opinion of the second-nearest neighbors (no matter what the nearest
neighbors are). So, the SM dynamics can be reduced to one rule, ``Just follow
your second-nearest neighbor''. The equivalence is demonstrated by extensive
computer simulations that show the same behavior between SM and VM in terms of
, , , , and the final attractor statistics. The
reformulation of the SM in terms of a VM involves a new parameter , to
bias between anti- and ferromagnetic decisions in the case of frustration. We
show that plays a crucial role in explaining the phase transition
observed in SM. We further explore the role of synchronous versus asynchronous
update rules on the intermediate dynamics and the final attractors. Compared to
the original SM, we find three additional attractors, two of them related to an
asymmetric coexistence between the opposite opinions.Comment: 22 pages, 20 figures. For related publications see
http://www.ais.fraunhofer.de/~fran
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