5,748 research outputs found
Monoid automata for displacement context-free languages
In 2007 Kambites presented an algebraic interpretation of
Chomsky-Schutzenberger theorem for context-free languages. We give an
interpretation of the corresponding theorem for the class of displacement
context-free languages which are equivalent to well-nested multiple
context-free languages. We also obtain a characterization of k-displacement
context-free languages in terms of monoid automata and show how such automata
can be simulated on two stacks. We introduce the simultaneous two-stack
automata and compare different variants of its definition. All the definitions
considered are shown to be equivalent basing on the geometric interpretation of
memory operations of these automata.Comment: Revised version for ESSLLI Student Session 2013 selected paper
Enhancement of the Gilbert damping constant due to spin pumping in noncollinear ferromagnet/nonmagnet/ferromagnet trilayer systems
We analyzed the enhancement of the Gilbert damping constant due to spin
pumping in non-collinear ferromagnet / non-magnet / ferromagnet trilayer
systems. We show that the Gilbert damping constant depends both on the
precession angle of the magnetization of the free layer and on the direction of
the magntization of the fixed layer. We find the condition to be satisfied to
realize strong enhancement of the Gilbert damping constant.Comment: 4 pages, 3 figures, to be published in Phys. Rev.
Fano hypersurfaces and Calabi-Yau supermanifolds
In this paper, we study the geometrical interpretations associated with
Sethi's proposed general correspondence between N = 2 Landau-Ginzburg orbifolds
with integral \hat{c} and N = 2 nonlinear sigma models. We focus on the
supervarieties associated with \hat{c} = 3 Gepner models. In the process, we
test a conjecture regarding the superdimension of the singular locus of these
supervarieties. The supervarieties are defined by a hypersurface \widetilde{W}
= 0 in a weighted superprojective space and have vanishing super-first Chern
class. Here, \widetilde{W} is the modified superpotential obtained by adding as
necessary to the Gepner superpotential a boson mass term and/or fermion
bilinears so that the superdimension of the supervariety is equal to \hat{c}.
When Sethi's proposal calls for adding fermion bilinears, setting the bosonic
part of \widetilde{W} (denoted by \widetilde{W}_{bos}) equal to zero defines a
Fano hypersurface embedded in a weighted projective space. In this case, if the
Newton polytope of \widetilde{W}_{bos} admits a nef partition, then the
Landau-Ginzburg orbifold can be given a geometrical interpretation as a
nonlinear sigma model on a complete intersection Calabi-Yau manifold. The
complete intersection Calabi-Yau manifold should be equivalent to the
Calabi-Yau supermanifold prescribed by Sethi's proposal.Comment: 24 pages, uses JHEP3.cls; v2: minor corrections, references adde
Chiral Condensate in Holographic QCD with Baryon Density
We consider the chiral condensate in the baryonic dense medium using the
generalized Sakai-Sugimoto model. It is defined as the vacuum expectation value
of open Wilson line that is proposed to be calculated by use of the area of
world-sheet instanton. We evaluate it in confined as well as deconfined phase.
In both phases, the chiral condensate has a minimum as a function of baryon
density. In the deconfined phase, taking into account the chiral symmetry
restoration, we classify the behavior of chiral condensate into three types.
One can set the parameter of the theory such that the results, in low but
sufficiently higher density, is in agreement with the expectation from QCD.Comment: 23 pages, 8 figure
Viscoelasticity of two-layer-vesicles in solution
The dynamic shape relaxation of the two-layer-vesicle is calculated. In
additional to the undulation relaxation where the two bilayers move in the same
direction, the squeezing mode appears when the gap between the two bilayers is
small. At large gap, the inner vesicle relaxes much faster, whereas the slow
mode is mainly due to the outer layer relaxation. We have calculated the
viscoelasticity of the dilute two-layer-vesicle suspension. It is found that
for small gap, the applied shear drives the undulation mode strongly while the
slow squeezing mode is not much excited. In this limit the complex viscosity is
dominated by the fast mode contribution. On the other hand, the slow mode is
strongly driven by shear for larger gap. We have determined the crossover gap
which depends on the interaction between the two bilayers. For a series of
samples where the gap is changed systematically, it is possible to observe the
two amplitude switchings
Magnon-photon coupling in the noncollinear magnetic insulator Cu 2 OSeO 3
Anticrossing behavior between magnons in the noncollinear chiral magnet Cu2OSeO3 and a two-mode X-band microwave resonator was studied in the temperature range 5–100 K. In the field-induced ferrimagnetic phase, we observed a strong-coupling regime between magnons and two microwave cavity modes with a cooperativity reaching 3600. In the conical phase, cavity modes are dispersively coupled to a fundamental helimagnon mode, and we demonstrate that the magnetic phase diagram of Cu2OSeO3 can be reconstructed from the measurements of the cavity resonance frequency. In the helical phase, a hybridized state of a higher-order helimagnon mode and a cavity mode—a helimagnon polariton—was found. Our results reveal a class of magnetic systems where strong coupling of microwave photons to nontrivial spin textures can be observed
Peristaltic Transport of a Couple Stress Fluid: Some Applications to Hemodynamics
The present paper deals with a theoretical investigation of the peristaltic
transport of a couple stress fluid in a porous channel. The study is motivated
towards the physiological flow of blood in the micro-circulatory system, by
taking account of the particle size effect. The velocity, pressure gradient,
stream function and frictional force of blood are investigated, when the
Reynolds number is small and the wavelength is large, by using appropriate
analytical and numerical methods. Effects of different physical parameters
reflecting porosity, Darcy number, couple stress parameter as well as amplitude
ratio on velocity profiles, pumping action and frictional force, streamlines
pattern and trapping of blood are studied with particular emphasis. The
computational results are presented in graphical form. The results are found to
be in good agreement with those of Shapiro et. al \cite{r25} that was carried
out for a non-porous channel in the absence of couple stress effect. The
present study puts forward an important observation that for peristaltic
transport of a couple stress fluid during free pumping when the couple stress
effect of the fluid/Darcy permeability of the medium, flow reversal can be
controlled to a considerable extent. Also by reducing the permeability it is
possible to avoid the occurrence of trapping phenomenon
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