4,375 research outputs found
Searching for a Supersolid in Cold Atom Optical Lattices
We suggest a technique for the observation of a predicted supersolid phase in
extended Bose-Hubbard models which are potentially realizable in cold atom
optical lattice systems. In particular, we discuss important subtleties arising
from the existence of the trapping potential which leads to an externally
imposed (as opposed to spontaneous) breaking of translational invariance. We
show, by carefully including the trapping potential in our theoretical
formalism, that noise correlations could prove instrumental in identifying the
supersolid and density wave phases. We also find that the noise correlation
peak width scales inversely with the relative size of trapped Mott domains.Comment: 5 pages, 4 figure
Spin Polarization Dependence of Carrier Effective Mass in Semiconductor Structures: Spintronic Effective Mass
We introduce the concept of a spintronic effective mass for spin-polarized
carriers in semiconductor structures, which arises from the strong
spin-polarization dependence of the renormalized effective mass in an
interacting spin-polarized electron system. The majority-spin many-body
effective mass renormalization differs by more than a factor of 2 at rs=5
between the unpolarized and the fully polarized two-dimensional system, whereas
the polarization dependence (~15%) is more modest in three dimensions around
metallic densities (rs~5). The spin-polarization dependence of the carrier
effective mass is of significance in various spintronic applications.Comment: Final versio
Ground-state of graphene in the presence of random charged impurities
We calculate the carrier density dependent ground state properties of
graphene in the presence of random charged impurities in the substrate taking
into account disorder and interaction effects non-perturbatively on an equal
footing in a self-consistent theoretical formalism. We provide detailed
quantitative results on the dependence of the disorder-induced spatially
inhomogeneous two-dimensional carrier density distribution on the external gate
bias, the impurity density, and the impurity location. We find that the
interplay between disorder and interaction is strong, particularly at lower
impurity densities. We show that for the currently available typical graphene
samples, inhomogeneity dominates graphene physics at low (
cm) carrier density with the density fluctuations becoming larger than
the average density.Comment: Final version, accepted for publication in Phys. Rev. Let
An evaluation of physical and biogeochemical processes regulating perennial suboxic conditions in the water column of the Arabian Sea
Monthly oxygen budgets for the subsurface Arabian Sea (100-1000 m) are constructed on the basis of Modular Ocean Model and recently collected oxygen data. The model results are in agreement with the observed pattern. The model results revealed that Oxygen Minimum Zone (OMZ) in the Arabian Sea is regulated largely by physical processes in association with biogeochemical cycling of oxygen. This results in perennial suboxic conditions in the water column with no significant seasonal variability. Maintenance of OMZ during non-monsoon seasons, when oligotrophic conditions prevail in surface layers, occurs through low supply of oxygen by physical pump aided by continued oxygen consumption in the oxidation of organic matter produced during monsoons. On the other hand, formation of anoxic conditions during monsoons, when higher sinking fluxes of carbon occur, is prevented by higher flux of oxygen by the physical pump. Hence, suboxic conditions in the Arabian Sea are maintained by physical pump with moderation from monsoonal biological pump. The residence time of the Arabian Sea intermediate waters (100-1000 m) was computed to be 6.5 years with rapid replacement during monsoons. The oxygen consumption rates are also high during monsoons compared with non-monsoon seasons. The carbon regeneration rates computed based on the water mass-mixing model, bacterial carbon demand, and electron transport system activity in the subsurface layers are in agreement with oxygen consumption rates estimated based on this model
Condensates induced by interband coupling in a double-well lattice
We predict novel inter-band physics for bosons in a double-well lattice. An
intrinsic coupling between the s and px band due to interaction gives rise to
larger Mott regions on the phase diagram at even fillings than the ones at odd
fillings. On the other hand, the ground state can form various types of
condensates, including a mixture of single-particle condensates of both bands,
a mixture of a single-particle condensate of one band and a pair-condensate of
the other band, and a pair-condensate composed of one particle from one band
and one hole from the other band. The predicted phenomena should be observable
in current experiments on double-well optical lattices.Comment: Published versio
Electrical neurostimulation for chronic pain: on selective relay of sensory neural activities in myelinated nerve fibers
Chronic pain affects about 100 million adults in the US. Despite their great
need, neuropharmacology and neurostimulation therapies for chronic pain have
been associated with suboptimal efficacy and limited long-term success, as
their mechanisms of action are unclear. Yet current computational models of
pain transmission suffer from several limitations. In particular, dorsal column
models do not include the fundamental underlying sensory activity traveling in
these nerve fibers. We developed a (simple) simulation test bed of electrical
neurostimulation of myelinated nerve fibers with underlying sensory activity.
This paper reports our findings so far. Interactions between stimulation-evoked
and underlying activities are mainly due to collisions of action potentials and
losses of excitability due to the refractory period following an action
potential. In addition, intuitively, the reliability of sensory activity
decreases as the stimulation frequency increases. This first step opens the
door to a better understanding of pain transmission and its modulation by
neurostimulation therapies
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