106,531 research outputs found
Micro-Structured Ferromagnetic Tubes for Spin Wave Excitation
Micron scale ferromagnetic tubes placed on the ends of ferromagnetic CoTaZr
spin waveguides are explored in order to enhance the excitation of Backward
Volume Magnetostatic Spin Waves. The tubes produce a closed magnetic circuit
about the signal line of the coplanar waveguide and are, at the same time,
magnetically contiguous with the spin waveguide. This results in a 10 fold
increase in spin wave amplitude. However, the tube geometry distorts the
magnetic field near the spin waveguide and relatively high biasing magnetic
fields are required to establish well defined spin waves. Only the lowest
(uniform) spin wave mode is excited.Comment: 3 pages, 3 figure
Techniques of replica symmetry breaking and the storage problem of the McCulloch-Pitts neuron
In this article the framework for Parisi's spontaneous replica symmetry
breaking is reviewed, and subsequently applied to the example of the
statistical mechanical description of the storage properties of a
McCulloch-Pitts neuron. The technical details are reviewed extensively, with
regard to the wide range of systems where the method may be applied. Parisi's
partial differential equation and related differential equations are discussed,
and a Green function technique introduced for the calculation of replica
averages, the key to determining the averages of physical quantities. The
ensuing graph rules involve only tree graphs, as appropriate for a
mean-field-like model. The lowest order Ward-Takahashi identity is recovered
analytically and is shown to lead to the Goldstone modes in continuous replica
symmetry breaking phases. The need for a replica symmetry breaking theory in
the storage problem of the neuron has arisen due to the thermodynamical
instability of formerly given solutions. Variational forms for the neuron's
free energy are derived in terms of the order parameter function x(q), for
different prior distribution of synapses. Analytically in the high temperature
limit and numerically in generic cases various phases are identified, among
them one similar to the Parisi phase in the Sherrington-Kirkpatrick model.
Extensive quantities like the error per pattern change slightly with respect to
the known unstable solutions, but there is a significant difference in the
distribution of non-extensive quantities like the synaptic overlaps and the
pattern storage stability parameter. A simulation result is also reviewed and
compared to the prediction of the theory.Comment: 103 Latex pages (with REVTeX 3.0), including 15 figures (ps, epsi,
eepic), accepted for Physics Report
Octet baryon magnetic moments from QCD sum rules
A comprehensive study is made for the magnetic moments of octet baryons in
the method of QCD sum rules. A complete set of QCD sum rules is derived using
the external field method and generalized interpolating fields. For each
member, three sum rules are constructed from three independent tensor
structures. They are analyzed in conjunction with the corresponding mass sum
rules. The performance of each of the sum rules is examined using the criteria
of OPE convergence and ground-state dominance, along with the role of the
transitions in intermediate states. Individual contributions from the u, d and
s quarks are isolated and their implications in the underlying dynamics are
explored. Valid sum rules are identified and their predictions are obtained.
The results are compared with experiment and previous calculations.Comment: 21 pages, 11 figures, 6 figures; added a reference, minor change in
tex
Phenomenology of the Baryon Resonance 70-plet at Large N_c
We examine the multiplet structure and decay channels of baryon resonances in
the large N_c QCD generalization of the N_c = 3 SU(6) spin-flavor 70. We show
that this ``70'', while a construct of large N_c quark models, actually
consists of five model-independent irreducible spin-flavor multiplets in the
large N_c limit. The preferred decay modes for these resonances fundamentally
depend upon which of the five multiplets to which the resonance belongs. For
example, there exists an SU(3) ``8'' of resonances that is eta-philic and
pi-phobic, and an ``8'' that is the reverse. Moreover, resonances with a strong
SU(3) ``1'' component prefer to decay via a K-bar rather than via a pi.
Remarkably, available data appears to bear out these conclusions.Comment: 26 pages, ReVTe
Short-Term Memory in Orthogonal Neural Networks
We study the ability of linear recurrent networks obeying discrete time
dynamics to store long temporal sequences that are retrievable from the
instantaneous state of the network. We calculate this temporal memory capacity
for both distributed shift register and random orthogonal connectivity
matrices. We show that the memory capacity of these networks scales with system
size.Comment: 4 pages, 4 figures, to be published in Phys. Rev. Let
Magnetic polarizability of hadrons from lattice QCD in the background field method
We present a calculation of hadron magnetic polarizability using the
techniques of lattice QCD. This is carried out by introducing a uniform
external magnetic field on the lattice and measuring the quadratic part of a
hadron's mass shift. The calculation is performed on a lattice with
standard Wilson actions at beta=6.0 (spacing fm) and pion mass down to
about 500 MeV. Results are obtained for 30 particles covering the entire baryon
octet (, , , , , , ,
) and decuplet (, , , ,
, , , , ,
), plus selected mesons (, , , , ,
, , , , , , ). The
results are compared with available values from experiments and other
theoretical calculations.Comment: 30 pages, 23 figures, 5 table
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