125 research outputs found
In-plane deformation of a triangulated surface model with metric degrees of freedom
Using the canonical Monte Carlo simulation technique, we study a Regge
calculus model on triangulated spherical surfaces. The discrete model is
statistical mechanically defined with the variables , and , which
denote the surface position in , the metric on a two-dimensional
surface and the surface density of , respectively. The metric is
defined only by using the deficit angle of the triangles in {}. This is in
sharp contrast to the conventional Regge calculus model, where {} depends
only on the edge length of the triangles. We find that the discrete model in
this paper undergoes a phase transition between the smooth spherical phase at
and the crumpled phase at , where is the bending
rigidity. The transition is of first-order and identified with the one observed
in the conventional model without the variables and . This implies
that the shape transformation transition is not influenced by the metric
degrees of freedom. It is also found that the model undergoes a continuous
transition of in-plane deformation. This continuous transition is reflected in
almost discontinuous changes of the surface area of and that of ,
where the surface area of is conjugate to the density variable .Comment: 13 pages, 7 figure
Finsler geometry modeling and Monte Carlo study of skyrmion shape deformation by uniaxial stress
Skyrmions in chiral magnetic materials are topologically stable and
energetically balanced spin configurations appearing under the presence of
ferromagnetic interaction (FMI) and Dzyaloshinskii-Moriya interaction (DMI).
Much of the current interest has focused on the effects of magneto-elastic
coupling on these interactions under mechanical stimuli, such as uniaxial
stresses for future applications in spintronics devices. Recent studies suggest
that skyrmion shape deformations in thin films are attributed to an anisotropy
in the coefficient of DMI, such that , which makes the
ratio anistropic, where the coefficient of FMI is
isotropic. It is also possible that while
is isotropic for to be anisotropic. In this paper, we study this
problem using a new modeling technique constructed based on Finsler geometry
(FG). Two possible FG models are examined: In the first (second) model, the FG
modeling prescription is applied to the FMI (DMI) Hamiltonian. We find that
these two different FG models' results are consistent with the reported
experimental data for skyrmion deformation. We also study responses of helical
spin orders
under lattice deformations corresponding to uniaxial extension/compression
and find a clear difference between these two models in the stripe phase,
elucidating which interaction of FMI and DMI is deformed to be anisotropic by
uniaxial stresses.Comment: 42 pages, 23 figure
Monte Carlo studies of skyrmion stabilization under geometric confinement and uniaxial strain
Geometric confinement (GC) of skyrmions in nanodomains plays a crucial role
in skyrmion stabilization. This confinement effect decreases the magnetic field
necessary for skyrmion formation and is closely related to the applied
mechanical stresses. However, the mechanism of GC is unclear and remains
controversial. Here, we numerically study the effect of GC on skyrmion
stabilization and find that zero Dzyaloshinskii-Moriya interaction (DMI)
coupling constants imposed on the boundary surfaces of small thin plates cause
confinement effects, stabilizing skyrmions in the low-field region. Moreover,
the confined skyrmions are further stabilized by tensile strains parallel to
the plate, and the skyrmion phase extends to the low-temperature region. This
stabilization occurs due to the bulk anisotropic DMI coupling constant caused
by lattice deformations. Our simulation data are qualitatively consistent with
reported experimental data on skyrmion stabilization induced by tensile strains
applied to a thin plate of the chiral magnet .Comment: 33 pages, 16 figure
Finsler geometry modeling of reverse piezoelectric effect in PVDF
We apply the Finsler geometry (FG) modeling technique to study the electric field-induced strain in ferroelectric polymers. Polyvinylidene difluoride (PVDF) has a negative longitudinal piezoelectric coefficient, which is unusual in ferroelectrics, and therefore the shape changes in this material are hard to predict. We find that the results of Monte Carlo simulations for the FG model are in good agreement with experimental strain-electric field curves of PVDF-based polymers in both longitudinal and transverse directions. This implies that FG modeling is suitable for reproducing the reverse piezoelectric effect in PVDF
Calcium Channel Blockers, More than Diuretics, Enhance Vascular Protective Effects of Angiotensin Receptor Blockers in Salt-Loaded Hypertensive Rats
The combination therapy of an angiotensin receptor blocker (ARB) with a calcium channel blocker (CCB) or with a diuretic is favorably recommended for the treatment of hypertension. However, the difference between these two combination therapies is unclear. The present work was undertaken to examine the possible difference between the two combination therapies in vascular protection. Salt-loaded stroke-prone spontaneously hypertensive rats (SHRSP) were divided into 6 groups, and they were orally administered (1) vehicle, (2) olmesartan, an ARB, (3) azelnidipine, a CCB, (4) hydrochlorothiazide, a diuretic, (5) olmesartan combined with azelnidipine, or (6) olmesartan combined with hydrochlorothiazide. Olmesartan combined with either azelnidipine or hydrochlorothiazide ameliorated vascular endothelial dysfunction and remodeling in SHRSP more than did monotherapy with either agent. However, despite a comparable blood pressure lowering effect between the two treatments, azelnidipine enhanced the amelioration of vascular endothelial dysfunction and remodeling by olmesartan to a greater extent than did hydrochlorothiazide in salt-loaded SHRSP. The increased enhancement by azelnidipine of olmesartan-induced vascular protection than by hydrochlorothiazide was associated with a greater amelioration of vascular nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activation, superoxide, mitogen-activated protein kinase activation, and with a greater activation of the Akt/endothelial nitric oxide synthase (eNOS) pathway. These results provided the first evidence that a CCB potentiates the vascular protective effects of an ARB in salt-sensitive hypertension, compared with a diuretic, and provided a novel rationale explaining the benefit of the combination therapy with an ARB and a CCB
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