3,773 research outputs found
Entropy Change through Rayleigh-B\'enard Convective Transition with Rigid Boundaries
The previous investigation on Rayleigh-B\'enard convection of a dilute
classical gas [T. Kita: J. Phys. Soc. Jpn. {\bf 75} (2006) 124005] is extended
to calculate entropy change of the convective transition with the rigid
boundaries. We obtain results qualitatively similar to those of the stress-free
boundaries. Above the critical Rayleigh number, the roll convection is realized
among possible steady states with periodic structures, carrying the highest
entropy as a function of macroscopic mechanical variables.Comment: 5 pages, 4 figure
Gap Anisotropy and de Haas-van Alphen Effect in Type-II Superconductors
We present a theoretical study on the de Haas-van Alphen (dHvA) oscillation
in the vortex state of type-II superconductors, with a special focus on the
connection between the gap anisotropy and the oscillation damping. Numerical
calculations for three different gap structures clearly indicate that the
average gap along extremal orbits is relevant for the magnitude of the extra
damping, thereby providing a support for experimental efforts to probe gap
anisotropy through the dHvA signal. We also derive an analytic formula for the
extra damping which gives a good fit to the numerical results.Comment: 5 pages, 1 figure, changes in Introductio
Nonbipartite Dulmage-Mendelsohn Decomposition for Berge Duality
The Dulmage-Mendelsohn decomposition is a classical canonical decomposition
in matching theory applicable for bipartite graphs, and is famous not only for
its application in the field of matrix computation, but also for providing a
prototypal structure in matroidal optimization theory. The Dulmage-Mendelsohn
decomposition is stated and proved using the two color classes, and therefore
generalizing this decomposition for nonbipartite graphs has been a difficult
task. In this paper, we obtain a new canonical decomposition that is a
generalization of the Dulmage-Mendelsohn decomposition for arbitrary graphs,
using a recently introduced tool in matching theory, the basilica
decomposition. Our result enables us to understand all known canonical
decompositions in a unified way. Furthermore, we apply our result to derive a
new theorem regarding barriers. The duality theorem for the maximum matching
problem is the celebrated Berge formula, in which dual optimizers are known as
barriers. Several results regarding maximal barriers have been derived by known
canonical decompositions, however no characterization has been known for
general graphs. In this paper, we provide a characterization of the family of
maximal barriers in general graphs, in which the known results are developed
and unified
Unconventional Vortices and Phase Transitions in Rapidly Rotating Superfluid ^{3}He
This paper studies vortex-lattice phases of rapidly rotating superfluid ^3He
based on the Ginzburg-Landau free-energy functional. To identify stable phases
in the p-Omega plane (p: pressure; Omega: angular velocity), the functional is
minimized with the Landau-level expansion method using up to 3000 Landau
levels. This system can sustain various exotic vortices by either (i) shifting
vortex cores among different components or (ii) filling in cores with
components not used in the bulk. In addition, the phase near the upper critical
angular velocity Omega_{c2} is neither the A nor B phases, but the polar state
with the smallest superfluid density as already shown by Schopohl. Thus,
multiple phases are anticipated to exist in the p-Omega plane. Six different
phases are found in the present calculation performed over 0.0001 Omega_{c2} <=
Omega <= Omega_{c2}, where Omega_{c2} is of order (1- T/T_c) times 10^{7}
rad/s. It is shown that the double-core vortex experimentally found in the B
phase originates from the conventional hexagonal lattice of the polar state
near Omega_{c2} via (i) a phase composed of interpenetrating polar and
Scharnberg-Klemm sublattices; (ii) the A-phase mixed-twist lattice with polar
cores; (iii) the normal-core lattice found in the isolated-vortex calculation
by Ohmi, Tsuneto, and Fujita; and (iv) the A-phase-core vortex discovered in
another isolated-vortex calculation by Salomaa and Volovik. It is predicted
that the double-core vortex will disappear completely in the experimental p-T
phase diagram to be replaced by the A-phase-core vortex for Omega >~ 10^{3} ~
10^{4} rad/s. C programs to minimize a single-component Ginzburg-Landau
functional are available at {http://phys.sci.hokudai.ac.jp/~kita/index-e.html}.Comment: 13 pages, 9 figure
Theory of Flux-Flow Resistivity near for s-wave Type-II Superconductors
This paper presents a microscopic calculation of the flux-flow resistivity
for s-wave type-II superconductors with arbitrary impurity
concentrations near the upper critical field . It is found that, as the
mean free path becomes longer, increases gradually from the
dirty-limit result of Thompson [Phys. Rev. B{\bf 1}, 327 (1970)] and Takayama
and Ebisawa [Prog. Theor. Phys. {\bf 44}, 1450 (1970)]. The limiting behaviors
suggest that at low temperatures may change from convex downward
to upward as increases, thus deviating substantially from the linear
dependence predicted by the Bardeen-Stephen theory
[Phys. Rev. {\bf 140}, A1197 (1965)]
Oxygen isotope systematics and Al-Mg chronology of chondrules: Implications to protoplanetary disk evolution
第6回極域科学シンポジウム[OA] 南極隕石11月17日(火) 国立国語研究所 2階 講
Contact resistivity and current flow path at metal/graphene contact
The contact properties between metal and graphene were examined. The
electrical measurement on a multiprobe device with different contact areas
revealed that the current flow preferentially entered graphene at the edge of
the contact metal. The analysis using the cross-bridge Kelvin structure (CBK)
suggested that a transition from the edge conduction to area conduction
occurred for a contact length shorter than the transfer length of ~1 micron.
The contact resistivity for Ni was measured as ~5*10-6 Ohmcm2 using the CBK. A
simple calculation suggests that a contact resistivity less than 10-9 Ohmcm2 is
required for miniaturized graphene field effect transistors
Properties of Nambu-Goldstone Bosons in a Single-Component Bose-Einstein Condensate
We theoretically study the properties of Nambu-Goldstone bosons in an
interacting single-component Bose-Einstein condensate (BEC). We first point out
that the proofs of Goldstone's theorem by Goldstone, et al. [Phys. Rev. {\bf
127} (1962) 965] may be relevant to distinct massless modes of the BEC: whereas
the first proof deals with the poles of the single-particle Green's function
, the second one concerns those of the two-particle Green's function.
Thus, there may be multiple Nambu-Goldstone bosons even in the single-component
BEC with broken U(1) symmetry. The second mode turns out to have an infinite
lifetime in the long-wavelength limit in agreement with the conventional
viewpoint. In contrast, the first mode from , i.e., the Bogoliubov
mode in the weak-coupling regime, is shown to be a "bubbling" mode fluctuating
temporally out of and back into the condensate. The substantial lifetime
originates from an "improper" structure of the self-energy inherent in the BEC,
which has been overlooked so far and will be elucidated here, and removes
various infrared divergences pointed out previously.Comment: 9 pages, 6 gigure
Vertical and meridional distributions of the atmospheric CO2 mixing ratio between northern midlatitudes and southern subtropics
The atmospheric CO2 mixing ratio was measured using a continuous measurement system onboard a Gulfstream-II aircraft between the northern midlatitudes and the southern subtropics during the Biomass Burning and Lightning Experiment Phase A (BIBLE A) campaign in September-October 1998. The vertical distribution Of CO2 over tropical regions was almost constant from the surface to an altitude of 13 km. CO2 enhancements from biomass burning and oceanic release were observed in the tropical boundary layer. Measurements in the upper troposphere indicate interhemispheric exchange was effectively suppressed between 2°N-7°N. Interhemispheric transport of air in the upper troposphere was suppressed effectively in this region. The CO2 mixing ratios in the Northern and Southern Hemispheres were almost constant, with an average value of about 365 parts per million (ppm) and 366 ppm, respectively. The correlation between the CO2 and NOy mixing ratios observed north of 7°N was apparently different from that obtained south of 2°N. This fact strongly supports the result that the north-south boundary in the upper troposphere during BIBLE A was located around 2°N-7°N as the boundary is not necessary a permanent feature
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