660 research outputs found
Dephasing in Metals by Two-Level Systems in the 2-Channel-Kondo Regime
We point out a novel, non-universal contribution to the dephasing rate
1/\tau_\phi \equiv \gamma_\phi of conduction electrons in metallic systems:
scattering off non-magnetic two-level systems (TLSs) having almost degenerate
Kondo ground states. In the regime \Delta_{ren} < T < T_K (\Delta_{ren} =
renormalized level splitting, T_K = Kondo temperature), such TLSs exhibit
non-Fermi-liquid physics that can cause \gamma_\phi, which generally decreases
with decreasing T, to seemingly saturate in a limited temperature range before
vanishing for T \to 0. This could explain the saturation of dephasing recently
observed in gold wires [Mohanty et al. Phys. Rev. Lett. 78, 3366 (1997)].Comment: Final published version, including minor improvements suggested by
referees. 4 pages, Revtex, 1 figur
Forced Imbibition - a Tool for Determining Laplace Pressure, Drag Force and Slip Length in Capillary Filling Experiments
When a very thin capillary is inserted into a liquid, the liquid is sucked
into it: this imbibition process is controlled by a balance of capillary and
drag forces, which are hard to quantify experimentally, in particularly
considering flow on the nanoscale. By computer experiments using a generic
coarse-grained model, it is shown that an analysis of imbibition forced by a
controllable external pressure quantifies relevant physical parameter such as
the Laplace pressure, Darcy's permeability, effective pore radius, effective
viscosity, dynamic contact angle and slip length of the fluid flowing into the
pore. In determining all these parameters independently, the consistency of our
analysis of such forced imbibition processes is demonstrated.Comment: 4 pages, 5 figure
Disparities in kidney transplantation accessibility among immigrant populations in Europe: A systematic review and meta-analysis
Background and objectives: Disparities in access to healthcare for patients with an immigration background are well-known. The aim of this study was to determine whether disparities among immigrant populations translate into a relative difference in the number of kidney transplants (KT) performed in documented immigrant patients (first and second generation) relative to native-born patients in Europe. Methods: A literature search was performed in PubMed from inception to 11-10-2022. Studies were eligible if: (1) written in English, (2) included immigrant and native-born KT patients, (3) performed in countries registered as Council of Europe members, (4) focused on documented first- and second-generation immigrant populations [1]. Systematic reviews, literature reviews, and case reports or articles about emigration, non-KT, and undocumented immigrants were excluded. The outcome measurement was a relative percentage of KTs to the total population per 100.000 residents. By dividing the immigrant percentages by the native-born resident percentages, the odds ratio (OR) was calculated in a meta-analysis. The risk of bias was assessed; articles with high risk of bias were excluded in a second meta-analysis. Results: Out of 109 articles, 5 were included (n = 24,614). One Italian study (n = 24,174) had a ratio below 1, being 0.910 (95%CI 0.877-0.945). The other four articles (n = 196, n = 283, n = 77, n = 119) had ratios above 1: 1.36 (95%CI 0.980-1.87), 2.04 (95%CI 1.56-2.68), 2.23 (95%CI 1.53-3.25) and 2.64 (95%CI 1.68-4.15). After performing a meta-analysis, the OR did not show a significant difference: 1.68 (95%CI 1.03-2.75). After bias correction, this remained unchanged: 1.78 (95%CI 0.961-3.31). Conclusions: In our meta-analysis we did not find a significant difference in the relative number of KTs performed in immigrant versus native-born populations in Europe. However, a lesser likelihood for immigrants to receive a pre-emptive kidney transplantation was found. Large heterogeneity between studies (e.g. different sample size, patient origins, study duration, adult vs children patients) was a shortcoming to our analysis. Nevertheless, our article is the first review in this understudied topic. As important questions (e.g. on ethnicity, living donor rate) remain, future studies are needed to address them
Erratum: Micromachined Fabry-Pérot Interferometer with Embedded Nanochannels for Nanoscale Fluid Dynamics
In ref 1, the erroneous numbers are not discussed in detail, yet we briefly noted, p 349, the observation of an enhanced lling speed with respect to the Lucas Washburn equation...
Micromachined Fabry-Perot interferometer with embedded nanochannels for nanoscale fluid dynamics
We describe a microfabricated Fabry-Pérot interferometer with nanochannels of various heights between 6 and 20 nm embedded in its cavity. By multiple beam interferometry, the device enables the study of liquid behavior in the nanochannels without using fluorescent substances. During filling studies of ethanol and water, an intriguing filling mode for partially wetting water was observed, tentatively attributed to the entrapment of a large amount of gas inside the channels
Oscillatory Tunnel Splittings in Spin Systems: A Discrete Wentzel-Kramers-Brillouin Approach
Certain spin Hamiltonians that give rise to tunnel splittings that are viewed
in terms of interfering instanton trajectories, are restudied using a discrete
WKB method, that is more elementary, and also yields wavefunctions and
preexponential factors for the splittings. A novel turning point inside the
classically forbidden region is analysed, and a general formula is obtained for
the splittings. The result is appled to the \Fe8 system. A previous result for
the oscillation of the ground state splitting with external magnetic field is
extended to higher levels.Comment: RevTex, one ps figur
Quantum tunneling of two coupled single-molecular magnets
Two single-molecule magnets are coupled antiferromagnetically to form a
supramolecule dimer. We study the coupling effect and tunneling process by
means of the numerical exact diagonalization method, and apply them to the
recently synthesized supramoleculer dimer [Mn4]2 The model parameters are
calculated for the dimer based on the tunneling process. The absence of
tunneling at zero field and sweeping rate effect on the step height in the
hysterisis loops are understood very well in this theory.Comment: 4 pages including 3 figure and 1 tabl
Macroscopic Quantum Tunneling and Dissipation of Domain Wall in Ferromagnetic Metals
The depinning of a domain wall in ferromagentic metal via macroscopic quantum
tunneling is studied based on the Hubbard model. The dynamics of the
magnetization verctor is shown to be governed by an effective action of
Heisenberg model with a term non-local in time that describes the dissipation
due to the conduction electron. Due to the existence of the Fermi surface there
exists Ohmic dissipation even at zero temperature, which is crucially different
from the case of the insulator. Taking into account the effect of pinning and
the external magnetic field the action is rewritten in terms of a collective
coordinate, the position of the wall, . The tunneling rate for is
calculated by use of the instanton method. It is found that the reduction of
the tunneling rate due to the dissipation is very large for a thin domain wall
with thickness of a few times the lattice spacing, but is negligible for a
thick domain wall. Dissipation due to eddy current is shown to be negligible
for a wall of mesoscopic size.Comment: of pages 26, to appear in "Quantum Tunneling of Magnetization, ed. B.
Barbara and L. Gunther (Kluwer Academic Pub.), Figures available by FAX
(81-48-462-4649
Quenched Spin Tunneling and Diabolical Points in Magnetic Molecules: II. Asymmetric Configurations
The perfect quenching of spin tunneling first predicted for a model with
biaxial symmetry, and recently observed in the magnetic molecule Fe_8, is
further studied using the discrete phase integral (or
Wentzel-Kramers-Brillouin) method. The analysis of the previous paper is
extended to the case where the magnetic field has both hard and easy
components, so that the Hamiltonian has no obvious symmetry. Herring's formula
is now inapplicable, so the problem is solved by finding the wavefunction and
using connection formulas at every turning point. A general formula for the
energy surface in the vicinity of the diabolo is obtained in this way. This
formula gives the tunneling apmplitude between two wells unrelated by symmetry
in terms of a small number of action integrals, and appears to be generally
valid, even for problems where the recursion contains more than five terms.
Explicit results are obtained for the diabolical points in the model for Fe_8.
These results exactly parallel the experimental observations. It is found that
the leading semiclassical results for the diabolical points appear to be exact,
and the points themselves lie on a perfect centered rectangular lattice in the
magnetic field space. A variety of evidence in favor of this perfect lattice
hypothesis is presented.Comment: Revtex; 4 ps figures; follow up to cond-mat/000311
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