21,782 research outputs found
Triple Products and Yang-Baxter Equation (II): Orthogonal and Symplectic Ternary Systems
We generalize the result of the preceeding paper and solve the Yang-Baxter
equation in terms of triple systems called orthogonal and symplectic ternary
systems. In this way, we found several other new solutions.Comment: 38 page
Integration of visual stimuli by the crayfish central nervous system
For the crayfish, properties of visually reacting interneurone types in the optic nerve are described on the basis of single-unit analysis.
Sustaining fibres show: (a) âsurroundâ inhibition over the whole retina, including the excitatory field; (b) âonâ and âoffâ effects at field boundaries; (c) a dark discharge in deteriorated preparations; (d) an increase in adapted firing rate and response to flashes in an âexcited stateâ of the preparation; (e) increased overall impulse frequency to fast-moving shadows at frequencies of 2-10/sec. which elicit short bursts.
Dimming fibres, having mainly reversed properties, show: (a) bursts followed by adaptation to a lower ferquency level of spikes on light dimming; (b) total inhibition by illumination for times proportional to light intensity; (c) responsiveness to quickly moving shadows.
'Jitteryâ movement fibres lack directional sensitivity. For them: (a) total illumination and contrast have, within a wide range, no effect on discharges to moving targets; (b) large, dark cards moved at constant speed are seen only near their visual field boundary; (c) the less predictable the movement of a small dark object is, the longer its excitatory effect lasts; (d) responsiveness of field parts exposed is decreased for long durations; (e) no firing is caused by active or passive eye motions.
Space-constant fibres show changed location and size of their excitatory fields with eye position. Their potential visual fields below the horizontal plane are unresponsive, due to inhibition caused mainly by statocyst input.
Two eye muscle motor fibres, also under statocyst control, are influenced by light on the limited sensory fields of two pairs of identifiable sustaining fibres. The two motor fibres, which innervate antagonistic muscles, are reversely excited and inhibited by these fields
Quantum Condensates in Nuclear Matter: Problems
In connection with the contribution "Quantum Condensates in Nuclear Matter"
some problems are given to become more familiar with the techniques of
many-particle physics.Comment: 8 pages, 1 figur
Nonclassical Imaging for a quantum search of trapped ions
We discuss a simple search problem which can be pursued with different
methods, either on a classical or on a quantum basis. The system is represented
by a chain of trapped ions. The ion to be searched is a member of that chain,
consists, however, of an isotopic species different to the others. It is shown
that the classical imaging may lead as fast to the final result as the quantum
imaging. However, for the discussed case the quantum method gives more
flexibility and higher precision when the number of ions considered in the
chain is increasing. In addition, interferences are observable even when the
distances between the ions is smaller than half a wavelength of the incident
light.Comment: 5 pages, 5 figure
Non-equilibrium Goldstone phenomenon in tachyonic preheating
The dominance of the direct production of elementary Goldstone waves is
demonstrated in tachyonic preheating by numerically determining the evolution
of the dispersion relation, the equation of state and the kinetic power spectra
for the angular degree of freedom of the complex matter field. The importance
of the domain structure in the order parameter distribution for the
quantitative understanding of the excitation mechanism is emphasized. Evidence
is presented for the very early decoupling of the low-momentum Goldstone modes.Comment: 14 LaTeX pages, 5 figures, version published in Phys. Rev.
Large Magnetic Moments of Arsenic-Doped Mn Clusters and their Relevance to Mn-Doped III-V Semiconductor Ferromagnetism
We report electronic and magnetic structure of arsenic-doped manganese
clusters from density-functional theory using generalized gradient
approximation for the exchange-correlation energy. We find that arsenic
stabilizes manganese clusters, though the ferromagnetic coupling between Mn
atoms are found only in MnAs and MnAs clusters with magnetic moments 9
and 17 , respectively. For all other sizes, 3, 5-10,
MnAs clusters show ferrimagnetic coupling. It is suggested that, if grown
during the low temperature MBE, the giant magnetic moments due to ferromagnetic
coupling in MnAs and MnAs clusters could play a role on the
ferromagnetism and on the variation observed in the Curie temperature of
Mn-doped III-V semiconductors.Comment: 4 Pages, 3 Figures[1 EPS and 2 JPG files], RevTeX
Density wave instability in a 2D dipolar Fermi gas
We consider a uniform dipolar Fermi gas in two-dimensions (2D) where the
dipole moments of fermions are aligned by an orientable external field. We
obtain the ground state of the gas in Hartree-Fock approximation and
investigate RPA stability against density fluctuations of finite momentum. It
is shown that the density wave instability takes place in a broad region where
the system is stable against collapse. We also find that the critical
temperature can be a significant fraction of Fermi temperature for a realistic
system of polar molecules.Comment: 10 figure
Scaling property and peculiar velocity of global monopoles
We investigate the scaling property of global monopoles in the expanding
universe. By directly solving the equations of motion for scalar fields, we
follow the time development of the number density of global monopoles in the
radiation dominated (RD) universe and the matter dominated (MD) universe. It is
confirmed that the global monopole network relaxes into the scaling regime and
the number per hubble volume is a constant irrespective of the cosmic time. The
number density of global monopoles is given by during the RD era and during the MD era. We also examine the peculiar velocity of global
monopoles. For this purpose, we establish a method to measure the peculiar
velocity by use of only the local quantities of the scalar fields. It is found
that during the RD era and during
the MD era. By use of it, a more accurate analytic estimate for the number
density of global monopoles is obtained.Comment: 17 pages, 8 figures, to appear in Phys. Rev.
More on Gribov copies and propagators in Landau-gauge Yang-Mills theory
Fixing a gauge in the non-perturbative domain of Yang-Mills theory is a
non-trivial problem due to the presence of Gribov copies. In particular, there
are different gauges in the non-perturbative regime which all correspond to the
same definition of a gauge in the perturbative domain. Gauge-dependent
correlation functions may differ in these gauges. Two such gauges are the
minimal and absolute Landau gauge, both corresponding to the perturbative
Landau gauge. These, and their numerical implementation, are described and
presented in detail. Other choices will also be discussed.
This investigation is performed, using numerical lattice gauge theory
calculations, by comparing the propagators of gluons and ghosts for the minimal
Landau gauge and the absolute Landau gauge in SU(2) Yang-Mills theory. It is
found that the propagators are different in the far infrared and even at energy
scales of the order of half a GeV. In particular, also the finite-volume
effects are modified. This is observed in two and three dimensions. Some
remarks on the four-dimensional case are provided as well.Comment: 23 pages, 16 figures, 6 tables; various changes throughout most of
the paper; extended discussion on different possibilities to define the
Landau gauge and connection to existing scenarios; in v3: Minor changes,
error in eq. (3) & (4) corrected, version to appear in PR
New D-term chaotic inflation in supergravity and leptogenesis
We present a new model of D-term dominated chaotic inflation in supergravity.
The F-flat direction present in this model is lifted by the dominant D-term,
which leads to chaotic inflation and subsequent reheating. No cosmic string is
formed after inflation because the U(1) gauge symmetry is broken during
inflation. The leptogenesis scenario via the inflaton decay in our D-term
chaotic inflation scenario is also discussed.Comment: 14 pages, no figure, to appear in Phys. Rev.
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