335 research outputs found
Spin-catalyzed hopping conductivity in disordered strongly interacting quantum wires
In one-dimensional electronic systems with strong repulsive interactions,
charge excitations propagate much faster than spin excitations. Such systems
therefore have an intermediate temperature range [termed the "spin-incoherent
Luttinger liquid'" (SILL) regime] where charge excitations are "cold" (i.e.,
have low entropy) whereas spin excitations are "hot." We explore the effects of
charge-sector disorder in the SILL regime in the absence of external sources of
equilibration. We argue that the disorder localizes all charge-sector
excitations; however, spin excitations are protected against full localization,
and act as a heat bath facilitating charge and energy transport on
asymptotically long timescales. The charge, spin, and energy conductivities are
widely separated from one another. The dominant carriers of energy are neither
charge nor spin excitations, but neutral "phonon" modes, which undergo an
unconventional form of hopping transport that we discuss. We comment on the
applicability of these ideas to experiments and numerical simulations.Comment: 14 pages, 6 figure
Instability of many-body localized systems as a phase transition in a nonstandard thermodynamic limit
The many-body localization (MBL) phase transition is not a conventional
thermodynamic phase transition. Thus to define the phase transition one should
allow the possibility of taking the limit of an infinite system in a way that
is not the conventional thermodynamic limit. We explore this for the so-called
"avalanche" instability due to rare thermalizing regions in the MBL phase for
quenched-random systems in more than one spatial dimension, finding an
unconventional way of scaling the systems so that they do have a type of phase
transition. These arguments suggest that the MBL phase transition in systems
with short-range interactions in more than one dimension is a transition where
entanglement in the eigenstates begins to spread in to some typical regions:
the transition is set by when the avalanches start. Once this entanglement gets
started, the system does thermalize. From this point of view, the much-studied
case of one-dimensional MBL with short-range interactions is a special case
with a different, and in some ways more conventional, type of phase transition.Comment: 10 pages, 2 figure
Weak crystallization theory of metallic alloys
We extend the Weak Crystallization theory to the case of metallic alloys. The
additional ingredient -- itinerant electrons -- generates nontrivial dependence
of free energy on the angles between ordering wave vectors of ionic density.
That leads to stabilization of FCC, Rhombohedral, and icosahedral
quasicrystalline (iQC) phases, which are absent in the generic theory with only
local interactions. The condition for stability of iQC that we find, is
consistent with the Hume-Rothery rules known empirically for majority of stable
iQC; namely, the length of the primary Bragg peak wavevector is approximately
equal to the diameter of the Fermi surface.Comment: 10 pages, 5 figure
Spectral features of a many-body localized system weakly coupled to a heat bath
We study many-body-localized (MBL) systems that are weakly coupled to
thermalizing environments, focusing on the spectral functions of local
operators. We argue that these spectral functions carry signatures of
localization even away from the limit of perfectly isolated systems. We find
that, in the limit of vanishing coupling to a bath, MBL systems come in two
varieties, with either discrete or continuous local spectra. Both varieties of
MBL systems exhibit a "soft gap" at zero frequency in the spatially-averaged
spectral functions of local operators, which serves as a diagnostic for
localization. We estimate the degree to which coupling to a bath broadens these
spectral features, and find that characteristics of incipient localization
survive as long as the system-bath coupling is much weaker than the
characteristic energy scales of the system. Since perfect isolation is
impossible, we expect the ideas discussed in this paper to be relevant for all
experiments on many-body localization.Comment: Expanded discussion of multiple lengthscales and of properties as a
quantum memor
Feedback-dependent control of stochastic synchronization in coupled neural systems
We investigate the synchronization dynamics of two coupled noise-driven
FitzHugh-Nagumo systems, representing two neural populations. For certain
choices of the noise intensities and coupling strength, we find cooperative
stochastic dynamics such as frequency synchronization and phase
synchronization, where the degree of synchronization can be quantified by the
ratio of the interspike interval of the two excitable neural populations and
the phase synchronization index, respectively. The stochastic synchronization
can be either enhanced or suppressed by local time-delayed feedback control,
depending upon the delay time and the coupling strength. The control depends
crucially upon the coupling scheme of the control force, i.e., whether the
control force is generated from the activator or inhibitor signal, and applied
to either component. For inhibitor self-coupling, synchronization is most
strongly enhanced, whereas for activator self-coupling there exist distinct
values of the delay time where the synchronization is strongly suppressed even
in the strong synchronization regime. For cross-coupling strongly modulated
behavior is found
Hydrodynamics of operator spreading and quasiparticle diffusion in interacting integrable systems
We address the hydrodynamics of operator spreading in interacting integrable
lattice models. In these models, operators spread through the ballistic
propagation of quasiparticles, with an operator front whose velocity is locally
set by the fastest quasiparticle velocity. In interacting integrable systems,
this velocity depends on the density of the other quasiparticles, so
equilibrium density fluctuations cause the front to follow a biased random
walk, and therefore to broaden diffusively. Ballistic front propagation and
diffusive front broadening are also generically present in non-integrable
systems in one dimension; thus, although the mechanisms for operator spreading
are distinct in the two cases, these coarse grained measures of the operator
front do not distinguish between the two cases. We present an expression for
the front-broadening rate; we explicitly derive this for a particular
integrable model (the "Floquet-Fredrickson-Andersen" model), and argue on
kinetic grounds that it should apply generally. Our results elucidate the
microscopic mechanism for diffusive corrections to ballistic transport in
interacting integrable models.Comment: Published versio
Quantum Quasicrystals of Spin-Orbit-Coupled Dipolar Bosons
We study quasi-two-dimensional dipolar Bose gases in which the bosons experience a Rashba spin-orbit coupling. We show that the degenerate dispersion minimum due to the spin-orbit coupling, combined with the long-range dipolar interaction, can stabilize a number of quantum crystalline and quasicrystalline ground states. Coupling the bosons to a fermionic species can further stabilize these phases. We estimate that the crystalline and quasicrystalline phases should be detectable in realistic dipolar condensates, e.g., dysprosium, and discuss their symmetries and excitations.Physic
पिंजऱ्याची बांधणी : तत्त्व आणि आराखडा
The culture of finfishes in cages has been practiced for years in countries like
Cambodia, Vietnam, Indonesia, Thailand, Malaysia, Singapore and Hongkong. Cage was first
used as a holding facility for fish. True cage culture was said to have started in 1243 in China.
Use of modern cage materials like synthetic nets, woods and metals started in early 1960’s.
The size and shape of the cages are very important for the growth and production of the
fishes/ shell fishes living inside it. The design will vary depending on the selected site. The
constructed cage must withstand the force of wind and wave while holding the stock safely.
The cage must be safe, secure and easy to manage. Circular cage bags make the most
efficient use of materials, and thus have the lowest costs per unit volume. Shape is likely to
influence effective stocking densities and swimming behaviour, which in turn can influence
production. Fish cages can be constructed from a variety of materials. All materials used for
the cage should be durable, nontoxic, and rustproof
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