1,037 research outputs found
Localization Lifetime of a Many-Body System with Periodic Constructed Disorder
We show that, in a many-body system, all particles can be strongly confined
to the initially occupied sites for a time that scales as a high power of the
ratio of the bandwidth of site energies to the hopping amplitude. Such
time-domain formulation is complementary to the formulation of the many-body
localization of all stationary states with a large localization length. The
long localization lifetime is achieved by constructing a periodic sequence of
site energies with a large period in a one-dimensional chain. The scaling of
the localization lifetime is independent of the number of particles for a broad
range of the coupling strength. The analytical results are confirmed by
numerical calculations
Comment on "Kinetic theory for a mobile impurity in a degenerate Tonks-Girardeau gas"
In a recent paper, arxiv:1402.6362, Gamayun, Lychkovskiy, and Cheianov
studied the dynamics of a mobile impurity embedded into a one-dimensional
Tonks-Girardeau gas of strongly interacting bosons. Employing the Boltzmann
equation approach, they arrived at the following main conclusions: (i) a light
impurity, being accelerated by a constant force does not exhibit Bloch
oscillations; (ii) a heavy impurity does undergo Bloch oscillations,
accompanied by a drift with the velocity proportional to the square root of
force. In this comment we argue that the result (i) is an artifact of the
classical Boltzmann approximation, which misses the formation of the (quasi)
bound-state between the impurity and a hole. Result (ii), while not valid at
asymptotically small force, indeed reflects an interesting intermediate-force
behavior. Here we clarify its limits of applicability and extend beyond the
Tonks-Girardeau limit.Comment: 2 pages, 1 figur
Composite Topological Excitations in Ferromagnet-Superconductor Heterostructures
We investigate the formation of a new type of composite topological
excitation -- the skyrmion-vortex pair (SVP) -- in hybrid systems consisting of
coupled ferromagnetic and superconducting layers. Spin-orbit interaction in the
superconductor mediates a magnetoelectric coupling between the vortex and the
skyrmion, with a sign (attractive or repulsive) that depends on the topological
indices of the constituents. We determine the conditions under which a bound
SVP is formed, and characterize the range and depth of the effective binding
potential through analytical estimates and numerical simulations. Furthermore,
we develop a semiclassical description of the coupled skyrmion-vortex dynamics
and discuss how SVPs can be controlled by applied spin currents.Comment: Final version accepted by Physical Review Letters; 9 pages, 5 figure
Critical velocity of a mobile impurity in one-dimensional quantum liquids
We study the notion of superfluid critical velocity in one spatial dimension.
It is shown that for heavy impurities with mass exceeding a critical mass
, the dispersion develops periodic metastable branches resulting
in dramatic changes of dynamics in the presence of an external driving force.
In contrast to smooth Bloch Oscillations for , a heavy impurity
climbs metastable branches until it reaches a branch termination point or
undergoes a random tunneling event, both leading to an abrupt change in
velocity and an energy loss. This is predicted to lead to a non-analytic
dependence of the impurity drift velocity on small forces.Comment: 5 pages, 2 figures; New version with Supplemental Material (3 pages,
6 figures); Accepted to PR
Obesity is Associated with More Disability at Presentation and After Treatment in Low Back Pain but Not in Neck Pain: Findings from the OIOC Registry
Background: The influence on the treatment response in patients with low back pain (LBP) and neck pain (NP) is unknown. The aim of the study was to investigate the influence of body weight in patients with low back pain (LBP) and neck pain (NP) on baseline and end of treatment disability.
Methods: Cross-sectional analysis of baseline factors. Longitudinal analysis of prospectively collected patient information at an outpatient physical therapy registry (data from June 2010 to December 2012). WHO-BMI classification was used: underweight, lean, overweight, obesity class I, obesity class II and III. The influence of body weight and a predefined set of confounders was analyzed by multiple regression models.
Results: In LBP, disability increased with increasing BMI [lean = reference, obesity class I Beta 5.41 (95 % CI 0.75; 10.07), obesity class II-III Beta 7.58 (95 % CI 2.13; 13.03)]. Compared to lean patients, disability after treatment improved in overweight subjects [Beta −3.90 (95 % CI −7.4; −0.41)] but not in subjects with obesity class II–III [Beta 3.43 (95 % CI −3.81; 10.68)]. There were insufficient patients in the sample with severe obesity and therefore this trend has to be confirmed. The likelihood for meaningful important change (MID) was similar in all BMI subgroups. For patients with NP, BMI was not associated with baseline disability, and did not predict end of treatment disability or the likelihood of a MID. These findings must be interpreted with caution as BMI subgroups did not meet the required sample size.
Conclusion: Overweight and obesity are associated with higher levels of disability before treatment in LBP patients, but not in NP. In severely obese patients class II–III with LBP the rate of MID was lowest indicating that these patients experienced the least treatment response compared to the other groups. Further studies should address the impact of severe obesity on the prognosis of LBP. In patients with LBP, severe obesity may be an important factor to consider during the physical therapy treatment. In particular, combined treatment strategies combining weight management, cardiovascular fitness, and low back pain rehabilitation should be investigated
Stability of Neutrinos in the Singlet Majoron Model
We show that there is no one-loop enhancement of the rate for a light
neutrino to decay into a lighter neutrino plus a majoron, contrary to a recent
claim. Thus the light neutrinos must satisfy the cosmological bound of having
masses less than 35 eV in the singlet majoron model, or else violate the
constraint imposed by galaxy formation. In the latter case, could
have a mass between 40 and 500 keV, while satisfying all other cosmological
constraints.Comment: 11 pp., latex, UMN-TH-1218-93. Correct nucleosynthesis bound of 500
keV on nu_tau mass is incorporated; one-loop electroweak contribution to
neutrino mass is correcte
Three-dimensional coherent X-ray diffraction imaging of a ceramic nanofoam: determination of structural deformation mechanisms
Ultra-low density polymers, metals, and ceramic nanofoams are valued for
their high strength-to-weight ratio, high surface area and insulating
properties ascribed to their structural geometry. We obtain the labrynthine
internal structure of a tantalum oxide nanofoam by X-ray diffractive imaging.
Finite element analysis from the structure reveals mechanical properties
consistent with bulk samples and with a diffusion limited cluster aggregation
model, while excess mass on the nodes discounts the dangling fragments
hypothesis of percolation theory.Comment: 8 pages, 5 figures, 30 reference
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