5,614 research outputs found
Domain Size Distribution in Segregating Binary Superfluids
Domain size distribution in phase separating binary Bose--Einstein
condensates is studied theoretically by numerically solving the
Gross--Pitaevskii equations at zero temperature. We show that the size
distribution in the domain patterns arising from the dynamic instability obeys
a power law in a scaling regime according to the dynamic scaling analysis based
on the percolation theory. The scaling behavior is kept during the relaxation
development until the characteristic domain size becomes comparable to the
linear size of the system, consistent with the dynamic scaling hypothesis of
the phase-ordering kinetics. Our numerical experiments indicate the existence
of a different scaling regime in the size distribution function, which can be
caused by the so-called coreless vortices.Comment: 7 pages, 2 figure
Domain-area distribution anomaly in segregating multicomponent superfluids
The domain-area distribution in the phase transition dynamics of
symmetry breaking is studied theoretically and numerically for segregating
binary Bose--Einstein condensates in quasi-two-dimensional systems. Due to the
dynamic scaling law of the phase ordering kinetics, the domain-area
distribution is described by a universal function of the domain area, rescaled
by the mean distance between domain walls. The scaling theory for general
coarsening dynamics in two dimensions hypothesizes that the distribution during
the coarsening dynamics has a hierarchy with the two scaling regimes, the
microscopic and macroscopic regimes with distinct power-law exponents. The
power law in the macroscopic regime, where the domain size is larger than the
mean distance, is universally represented with the Fisher's exponent of the
percolation theory in two dimensions. On the other hand, the power-law exponent
in the microscopic regime is sensitive to the microscopic dynamics of the
system. This conjecture is confirmed by large-scale numerical simulations of
the coupled Gross--Pitaevskii equation for binary condensates. In the numerical
experiments of the superfluid system, the exponent in the microscopic regime
anomalously reaches to its theoretical upper limit of the general scaling
theory. The anomaly comes from the quantum-fluid effect in the presence of
circular vortex sheets, described by the hydrodynamic approximation neglecting
the fluid compressibility. It is also found that the distribution of superfluid
circulation along vortex sheets obeys a dynamic scaling law with different
power-law exponents in the two regimes. An analogy to quantum turbulence on the
hierarchy of vorticity distribution and the applicability to chiral superfluid
He in a slab are also discussed.Comment: 9 pages, 5 figure
Quantum and thermal phase transitions in the Bechgaard salts and their analogs
In order to investigate quantum and thermal phase transitions in the
Bechgaard salts and their sulfur analogs, we perform finite-temperature
Hartree-Fock calculations in one dimension with particular emphasis on the
interplay between charge ordering and lattice instability. The coexisting
charge- and spin-density-wave state as well as its precursor fluctuations in
(TMTSF)2PF6 and the lattice tetramerization in (TMTTF)2ReO4 are well
interpreted.Comment: 2 pages, 3 figures embedded, submitted to Synth. Me
Type III Dyson Sphere of Highly Advanced Civilizations around a Super Massive Black Hole
We describe a new system for a society of highly advanced civilizations
around a super massive black hole (SMBH), as an advanced Type III "Dyson
Sphere", pointing out an efficient usage of energy for the advanced
civilizations. SMBH also works as a sink for waste materials. Here we assume
that Type III civilisations of Kardashev classification [1] form a galactic
club [2] in a galaxy, and the energy from the SMBH will be delivered to the
club members, forming an energy control system similar to power grids in our
present society. The energy is probably transmitted by a sharp beam with
coherent electro-magnetic waves, which provide a new concept for the search for
extraterrestrial intelligence (SETI) via detection of such energy transmission
signals. This expands the search window for other intelligences within the
Universe.Comment: 4 pages, 1 color pag
Nambu-Goldstone modes in segregated Bose-Einstein condensates
Nambu-Goldstone modes in immiscible two-component Bose-Einstein condensates
are studied theoretically. In a uniform system, a flat domain wall is
stabilized and then the translational invariance normal to the wall is
spontaneously broken in addition to the breaking of two U(1) symmetries in the
presence of two complex order parameters. We clarify properties of the
low-energy excitations and identify that there exist two Nambu-Goldstone modes:
in-phase phonon with a linear dispersion and ripplon with a fractional
dispersion. The signature of the characteristic dispersion can be verified in
segregated condensates in a harmonic potential.Comment: 5 pages, 3 figure
Rabi-coupled Countersuperflow in Binary Bose-Einstein Condensates
We show theoretically that periodic density patterns are stabilized in two
counter-propagating Bose-Einstein condensates of atoms in different hyperfine
states under Rabi coupling. In the presence of coupling, the relative velocity
between two components is localized around density depressions in
quasi-one-dimensional systems. When the relative velocity is sufficiently
small, the periodic pattern reduces to a periodic array of topological solitons
as kinks of relative phase. According to our variational and numerical
analyses, the soliton solution is well characterized by the soliton width and
density depression. We demonstrate the dependence of the depression and width
on the Rabi frequency and the coupling constant of inter-component
density-density interactions. The periodic pattern of the relative phase
transforms continuously from a soliton array to a sinusoidal pattern as the
period becomes smaller than the soliton width. These patterns become unstable
when the localized relative velocity exceeds a critical value. The
stability-phase diagram of this system is evaluated with a stability analysis
of countersuperflow, by taking into account the finite-size-effect owing to the
density depression.Comment: 9 pages, 8 figure
PAKE-based mutual HTTP authentication for preventing phishing attacks
This paper describes a new password-based mutual authentication protocol for
Web systems which prevents various kinds of phishing attacks. This protocol
provides a protection of user's passwords against any phishers even if
dictionary attack is employed, and prevents phishers from imitating a false
sense of successful authentication to users. The protocol is designed
considering interoperability with many recent Web applications which requires
many features which current HTTP authentication does not provide. The protocol
is proposed as an Internet Draft submitted to IETF, and implemented in both
server side (as an Apache extension) and client side (as a Mozilla-based
browser and an IE-based one). The paper also proposes a new user-interface for
this protocol which is always distinguishable from fake dialogs provided by
phishers
Counterflow Quantum Turbulence and the Instability in Two-component Bose-Einstein Condensates
We theoretically study the nonlinear dynamics of the instability of
counter-superflow in two miscible Bose-Einstein condensates. The condensates
become unstable when the relative velocity exceeds a critical value, which is
called counter-superflow instability. We reveal that the counter-superflow
instability can lead to quantum turbulence by numerically solving the coupled
Gross-Pitaevskii equations. The modes amplified by the instability grow into
solitons and decay into quantized vortices.Eventually, the vortices become
tangled and quantum turbulence of two superfluids. We show that this process
may occur in experiments by investigating the dynamics in a 2D trapped system.Comment: 7 pages, 5 figures, submitted to Journal of Low Temperature Physic
Is a doubly quantized vortex dynamically unstable in uniform superfluids?
We revisit the fundamental problem of the splitting instability of a doubly
quantized vortex in uniform single-component superfluids at zero temperature.
We analyze the system-size dependence of the excitation frequency of a doubly
quantized vortex through large-scale simulations of the Bogoliubov--de Gennes
equation, and find that the system remains dynamically unstable even in the
infinite-system-size limit. Perturbation and semi-classical theories reveal
that the splitting instability radiates a damped oscillatory phonon as an
opposite counterpart of a quasi-normal mode.Comment: 8 pages, 6 figure
Phase ordering percolation and an infinite domain wall in segregating binary Bose-Einstein condensates
Percolation theory is applied to the phase-transition dynamics of domain
pattern formation in segregating binary Bose--Einstein condensates in
quasi-two-dimensional systems. Our finite-size-scaling analysis shows that the
percolation threshold of the initial domain pattern emerging from the dynamic
instability is close to 0.5 for strongly repulsive condensates. The percolation
probability is universally described with a scaling function when the
probability is rescaled by the characteristic domain size in the dynamic
scaling regime of the phase-ordering kinetics, independent of the
intercomponent interaction. It is revealed that an infinite domain wall
sandwiched between percolating domains in the two condensates has an noninteger
fractal dimension and keeps the scaling behavior during the dynamic scaling
regime. This result seems to be in contrast to the argument that the dynamic
scale invariance is violated in the presence of an infinite topological defect
in numerical cosmology.Comment: 8 pages, 4 figure
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