4,242 research outputs found
Giant Charge Relaxation Resistance in the Anderson Model
We investigate the dynamical charge response of the Anderson model viewed as
a quantum RC circuit. Applying a low-energy effective Fermi liquid theory, a
generalized Korringa-Shiba formula is derived at zero temperature, and the
charge relaxation resistance is expressed solely in terms of static
susceptibilities which are accessible by Bethe ansatz. We identify a giant
charge relaxation resistance at intermediate magnetic fields related to the
destruction of the Kondo singlet. The scaling properties of this peak are
computed analytically in the Kondo regime. We also show that the resistance
peak fades away at the particle-hole symmetric point.Comment: 4 pages, 1 figur
-Kicked Quantum Rotors: Localization and `Critical' Statistics
The quantum dynamics of atoms subjected to pairs of closely-spaced
-kicks from optical potentials are shown to be quite different from the
well-known paradigm of quantum chaos, the singly--kicked system. We
find the unitary matrix has a new oscillating band structure corresponding to a
cellular structure of phase-space and observe a spectral signature of a
localization-delocalization transition from one cell to several. We find that
the eigenstates have localization lengths which scale with a fractional power
and obtain a regime of near-linear spectral variances
which approximate the `critical statistics' relation , where is related to the fractal
classical phase-space structure. The origin of the exponent
is analyzed.Comment: 4 pages, 3 fig
A Supersymmetric U(1)' Model with Multiple Dark Matters
We consider a scenario where a supersymmetric model has multiple dark matter
particles. Adding a U(1)' gauge symmetry is a well-motivated extension of the
Minimal Supersymmetric Standard Model (MSSM). It can cure the problems of the
MSSM such as the mu-problem or the proton decay problem with high-dimensional
lepton number and baryon number violating operators which R-parity allows. An
extra parity (U-parity) may arise as a residual discrete symmetry after U(1)'
gauge symmetry is spontaneously broken. The Lightest U-parity Particle (LUP) is
stable under the new parity becoming a new dark matter candidate. Up to three
massive particles can be stable in the presence of the R-parity and the
U-parity. We numerically illustrate that multiple stable particles in our model
can satisfy both constraints from the relic density and the direct detection,
thus providing a specific scenario where a supersymmetric model has
well-motivated multiple dark matters consistent with experimental constraints.
The scenario provides new possibilities in the present and upcoming dark matter
searches in the direct detection and collider experiments.Comment: 25 pages, 5 figure
Andreev scattering in the asymmetric ladder with preformed bosonic pairs
We discuss the phase coherence which emanates from the ladder-like proximity
effect between a ``weak superconductor'' with preformed bosonic pairs (here, a
single-chain Luther-Emery liquid with superconducting correlations that decay
approximately as ) and a Fermi gas with unpaired fermions. Carefully
studying tunneling mechanism(s), we show that the boson-mediated Cooper pairing
between remaining unpaired electrons results in a quasi long-range
superconductivity: Superconducting correlations decay very slowly as
with . This process is reminiscent of the coupling
of fermions to preformed bosonic pairs introduced in the context of high-Tc
cuprates.Comment: 5 pages, final version (To appear in PRB Rapid Communication
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A quantitative exploration of gastrointestinal bleeding in intensive care unit patients
Background
Quantitative assessments of the severity of bleeding in patients with bleeds within the gastrointestinal tract (GIB) are generally limited to blood tests like the hematocrit. The varied and irregular nature of the data collected during such observations makes it difficult in retrospective data analysis to characterize the complete course of bleeding. We intend to quantify the rate of blood loss over the course of an ICU stay, facilitating more precise analysis of retrospective data, and to use this quantification to examine questions about the effects of GIB.
Methods and findings
A population of 2,445 intensive care admissions across 2,266 patients with a diagnosis of GIB was studied. Using statistical techniques for smoothing data and accepted medical approaches for calculating blood loss, we are able to convert collections of individual laboratory readings that are difficult to understand into a simple, interpretable overview of the patient’s bleeding status over time. To demonstrate this method, we compare patients’ standard vital signs while bleeding heavily to times when they are not bleeding, finding a 3.0 ± 0.5% increase in heart rate, a 1.3 ± 0.4% decrease in systolic blood pressure and a 0.9 ± 0.5% decrease in diastolic blood pressure. After considering the effect of bleeding on standard vital signs, we demonstrate that patients with upper GIB have significantly elevated blood urea nitrogen levels while bleeding heavily, with a mean increase of 11.7 ± 7.2%, while patients with lower GIB do not, with a mean increase of 4.2 ± 6.6%.
Conclusions
This study introduces a novel method of processing retrospective laboratory data to characterize the course of bleeds within the gastrointestinal tract. This method is used to examine the direct effects of bleeding on a patient and can be deployed in future studies of bleeding using retrospective data
Chaotic quantum ratchets and filters with cold atoms in optical lattices: properties of Floquet states
Recently, cesium atoms in optical lattices subjected to cycles of
unequally-spaced pulses have been found to show interesting behavior: they
represent the first experimental demonstration of a Hamiltonian ratchet
mechanism, and they show strong variability of the Dynamical Localization
lengths as a function of initial momentum. The behavior differs qualitatively
from corresponding atomic systems pulsed with equal periods, which are a
textbook implementation of a well-studied quantum chaos paradigm, the quantum
delta-kicked particle (delta-QKP). We investigate here the properties of the
corresponding eigenstates (Floquet states) in the parameter regime of the new
experiments and compare them with those of the eigenstates of the delta-QKP at
similar kicking strengths. We show that, with the properties of the Floquet
states, we can shed light on the form of the observed ratchet current as well
as variations in the Dynamical Localization length.Comment: 9 pages, 9 figure
Double-gap superconducting proximity effect in nanotubes
We theoretically explore the possibility of a superconducting proximity
effect in single-walled metallic carbon nanotubes due to the presence of a
superconducting substrate. An unconventional double-gap situation can arise in
the two bands for nanotubes of large radius wherein the tunneling is (almost)
symmetric in the two sublattices. In such a case, a proximity effect can take
place in the symmetric band below a critical experimentally-accessible Coulomb
interaction strength in the nanotube. Furthermore, due to interactions in the
nanotube, the appearance of a BCS gap in this band stabilizes superconductivity
in the other band at lower temperatures. We also discuss the scenario of highly
asymmetric tunneling and show that this case too supports double-gap
superconductivity.Comment: 4 pages, 2 figure
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