8,130 research outputs found
A gauge approach to the "pseudogap" phenomenology of the spectral weight in high Tc cuprates
We assume the t-t'-J model to describe the CuO_2 planes of hole-doped
cuprates and we adapt the spin-charge gauge approach, previously developed for
the t-J model, to describe the holes in terms of a spinless fermion carrying
the charge (holon) and a neutral boson carrying spin 1/2 (spinon), coupled by a
slave-particle gauge field. In this framework we consider the effects of a
finite density of incoherent holon pairs in the normal state. Below a crossover
temperature, identified as the experimental "upper pseudogap", the scattering
of the "quanta" of the phase of the holon-pair field against holons reproduces
the phenomenology of Fermi arcs coexisting with gap in the antinodal region. We
thus obtain a microscopic derivation of the main features of the hole spectra
due to pseudogap. This result is obtained through a holon Green function which
follows naturally from the formalism and analytically interpolates between a
Fermi liquid-like and a d-wave superconductor behavior as the coherence length
of the holon pair order parameter increases. By inserting the gauge coupling
with the spinon we construct explicitly the hole Green function and calculate
its spectral weight and the corresponding density of states. So we prove that
the formation of holon pairs induces a depletion of states on the hole Fermi
surface. We compare our results with ARPES and tunneling experimental data. In
our approach the hole preserves a finite Fermi surface until the
superconducting transition, where it reduces to four nodes. Therefore we
propose that the gap seen in the normal phase of cuprates is due to the thermal
broadening of the SC-like peaks masking the Fermi-liquid peak. The Fermi arcs
then correspond to the region of the Fermi surface where the Fermi-liquid peak
is unmasked.Comment: 10 figures, comments and references added, 2 figures change
Phase Equilibrium of Binary Mixtures in Mixed Dimensions
We study the stability of a Bose-Fermi system loaded into an array of coupled
one-dimensional (1D) "tubes", where bosons and fermions experience different
dimensions: Bosons are heavy and strongly localized in the 1D tubes, whereas
fermions are light and can hop between the tubes. Using the 174Yb-6Li system as
a reference, we obtain the equilibrium phase diagram. We find that, for both
attractive and repulsive interspecies interaction, the exact treatment of 1D
bosons via the Bethe ansatz implies that the transitions between pure fermion
and any phase with a finite density of bosons can only be first order and never
continuous, resulting in phase separation in density space. In contrast, the
order of the transition between the pure boson and the mixed phase can either
be second or first order depending on whether fermions are allowed to hop
between the tubes or they also are strictly confined in 1D. We discuss the
implications of our findings for current experiments on 174Yb-6Li mixtures as
well as Fermi-Fermi mixtures of light and heavy atoms in a mixed dimensional
optical lattice system.Comment: 12 pages, 6 figure
Peak effect in twinned superconductors
A sharp maximum in the critical current as a function of temperature
just below the melting point of the Abrikosov flux lattice has recently been
observed in both low and high temperature superconductors. This peak effect is
strongest in twinned crystals for fields aligned with the twin planes. We
propose that this peak signals the breakdown of the collective pinning regime
and the crossover to strong pinning of single vortices on the twin boundaries.
This crossover is very sharp and can account for the steep drop of the
differential resistivity observed in experiments.Comment: 4 pages, revtex 3.0, no figure
Energy Efficient Scheduling for Loss Tolerant IoT Applications with Uninformed Transmitter
In this work we investigate energy efficient packet scheduling problem for
the loss tolerant applications. We consider slow fading channel for a point to
point connection with no channel state information at the transmitter side
(CSIT). In the absence of CSIT, the slow fading channel has an outage
probability associated with every transmit power. As a function of data loss
tolerance parameters and peak power constraints, we formulate an optimization
problem to minimize the average transmit energy for the user equipment (UE).
The optimization problem is not convex and we use stochastic optimization
technique to solve the problem. The numerical results quantify the effect of
different system parameters on average transmit power and show significant
power savings for the loss tolerant applications.Comment: Published in ICC 201
Plasticity in current-driven vortex lattices
We present a theoretical analysis of recent experiments on current-driven
vortex dynamics in the Corbino disk geometry. This geometry introduces
controlled spatial gradients in the driving force and allows the study of the
onset of plasticity and tearing in clean vortex lattices. We describe plastic
slip in terms of the stress-driven unbinding of dislocation pairs, which in
turn contribute to the relaxation of the shear, yielding a nonlinear response.
The steady state density of free dislocations induced by the applied stress is
calculated as a function of the applied current and temperature. A criterion
for the onset of plasticity at a radial location in the disk yields a
temperature-dependent critical current that is in qualitative agreement with
experiments.Comment: 11 pages, 4 figure
Models of plastic depinning of driven disordered systems
Two classes of models of driven disordered systems that exhibit
history-dependent dynamics are discussed. The first class incorporates local
inertia in the dynamics via nonmonotonic stress transfer between adjacent
degrees of freedom. The second class allows for proliferation of topological
defects due to the interplay of strong disorder and drive. In mean field theory
both models exhibit a tricritical point as a function of disorder strength. At
weak disorder depinning is continuous and the sliding state is unique. At
strong disorder depinning is discontinuous and hysteretic.Comment: 3 figures, invited talk at StatPhys 2
The ambitious role of anti angiogenesis molecules: Turning a cold tumor into a hot one
In renal cancer emerging treatment options are becoming available and there is a strong need to combine therapies to reformulate and adjourn clinical practice. We here highlight and discuss the need to take advantage of the common immune targets to design combined strategies to increase clinical responses
Driven depinning of strongly disordered media and anisotropic mean-field limits
Extended systems driven through strong disorder are modeled generically using
coarse-grained degrees of freedom that interact elastically in the directions
parallel to the driving force and that slip along at least one of the
directions transverse to the motion. A realization of such a model is a
collection of elastic channels with transverse viscous couplings. In the
infinite range limit this model has a tricritical point separating a region
where the depinning is continuous, in the universality class of elastic
depinning, from a region where depinning is hysteretic. Many of the collective
transport models discussed in the literature are special cases of the generic
model.Comment: 4 pages, 2 figure
Recovery of White and Gray Isolates of Ceratocystis fagacearum from Red Oaks
Boles of four Erythrobalanus oaks were inoculated with white and gray isolates of Ceratocystis fagacearum at diametrically opposed loci. Bole and branches were sampled in an orderly manner when a tree exhibited moderately severe foliar wilt symptoms. Isolations were made on PDA plates. Of the four red oaks, two yielded only the white isolate; the remaining two yielded both isolates. In no instance were both isolates recovered from the same branch, but all sections from the main trunk yielded both, and in several instances both isolates were observed growing from the same chip. This pilot experiment and the findings of other workers indicate that any factor effecting survival of one isolate of C. fagacearum over others is manifested at the time of germination of inocula, and that mycelia of different isolates have little significant inhibitory effect on each other
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