4,266 research outputs found
Phase oscillations in superfluid 3He-B weak links
Oscillations in quantum phase about a mean value of , observed across
micropores connecting two \helium baths, are explained in a Ginzburg-Landau
phenomenology. The dynamics arises from the Josephson phase relation,the
interbath continuity equation, and helium boundary conditions. The pores are
shown to act as Josephson tunnel junctions, and the dynamic variables are the
inter bath phase difference and fractional difference in superfluid density at
micropores. The system maps onto a non-rigid, momentum-shortened pendulum, with
inverted-orientation oscillations about a vertical tilt angle , and
other modes are predicted
Quantum versus Semiclassical Description of Selftrapping: Anharmonic Effects
Selftrapping has been traditionally studied on the assumption that
quasiparticles interact with harmonic phonons and that this interaction is
linear in the displacement of the phonon. To complement recent semiclassical
studies of anharmonicity and nonlinearity in this context, we present below a
fully quantum mechanical analysis of a two-site system, where the oscillator is
described by a tunably anharmonic potential, with a square well with infinite
walls and the harmonic potential as its extreme limits, and wherein the
interaction is nonlinear in the oscillator displacement. We find that even
highly anharmonic polarons behave similar to their harmonic counterparts in
that selftrapping is preserved for long times in the limit of strong coupling,
and that the polaronic tunneling time scale depends exponentially on the
polaron binding energy. Further, in agreement, with earlier results related to
harmonic polarons, the semiclassical approximation agrees with the full quantum
result in the massive oscillator limit of small oscillator frequency and strong
quasiparticle-oscillator coupling.Comment: 10 pages, 6 figures, to appear in Phys. Rev.
On the Mass Eigenstate Composition of the 8B Neutrinos from the Sun
The present data of gallium experiments provide indirectly the only
experimental limit on the fraction of mass eigenstate for the B
neutrinos from the Sun. However, if to use the experimental data alone, the
fraction of and, consequently, still is allowed to
be varied within a rather broad range. The further experimental efforts are
needed to clear this point.Comment: 13 pages, 1 figure, 1 table. Corrected version, published in
JCAP04(2007)00
Spectral Properties of Coupled Bose-Einstein Condensates
We investigate the energy spectrum structure of a system of two (identical)
interacting bosonic wells occupied by N bosons within the Schwinger realization
of the angular momentum. This picture enables us to recognize the symmetry
properties of the system Hamiltonian H and to use them for characterizing the
energy eigenstates. Also, it allows for the derivation of the single-boson
picture which is shown to be the background picture naturally involved by the
secular equation for H. After deriving the corresponding eigenvalue equation,
we recast it in a recursive N-dependent form which suggests a way to generate
the level doublets (characterizing the H spectrum) via suitable inner
parameters. Finally, we show how the presence of doublets in the spectrum
allows to recover, in the classical limit, the symmetry breaking effect that
characterizes the system classically.Comment: 8 pages, 3 figures; submitted to Phys. Rev. A. The present extended
form replaces the first version in the letter forma
Oral diabetes medication monotherapy and short-term mortality in individuals with type 2 diabetes and coronary artery disease
Objective To determine whether sulfonylurea use, compared with non-sulfonylurea oral diabetes medication use, was associated with 2-year mortality in individuals with well-controlled diabetes and coronary artery disease (CAD). Research design and methods We studied 5352 US veterans with type 2 diabetes, obstructive CAD on coronary angiography, hemoglobin A1c ≤7.5% at the time of catheterization, and taking zero or one oral diabetes medication (categorized as no medications, non-sulfonylurea medication, or sulfonylurea). We estimated the association between medication category and 2-year mortality using inverse probability of treatment-weighted (IPW) standardized mortality differences and IPW multivariable Cox proportional hazards regression. Results 49%, 35%, and 16% of the participants were on no diabetes medications, non-sulfonylurea medications, and sulfonylureas, respectively. In individuals on no medications, non-sulfonylurea medications, and sulfonylureas, the unadjusted mortality rates were 6.6%, 5.2%, and 11.9%, respectively, and the IPW-standardized mortality rates were 5.9%, 6.5%, and 9.7%, respectively. The standardized absolute 2-year mortality difference between non-sulfonylurea and sulfonylurea groups was 3.2% (95% CI 0.7 to 5.7) (p=0.01). In Cox proportional hazards models, the point estimate suggested that sulfonylurea use might be associated with greater hazard of mortality than non-sulfonylurea medication use, but this finding was not statistically significant (HR 1.38 (95% CI 1.00 to 1.93), p=0.05). We did not observe significant mortality differences between individuals on no diabetes medications and non-sulfonylurea users. Conclusions Sulfonylurea use was common (nearly one-third of those taking medications) and was associated with increased 2-year mortality in individuals with obstructive CAD. The significance of the association between sulfonylurea use and mortality was attenuated in fully adjusted survival models. Caution with sulfonylurea use may be warranted for patients with well-controlled diabetes and CAD, and metformin or newer diabetes medications with cardiovascular safety data could be considered as alternatives when individualizing therapy
Microstructure and residual stress evolution in nanocrystalline Cu–Zr thin films
Grazing incidence X-ray diffraction (GIXRD) and scanning transmission electron microscopy (STEM) combined with energy dispersive X-ray spectroscopy (EDS) were employed to study the microstructure evolution and stress development in the nanocrystalline Cu100−X-ZrX (2.5 at ≤ x ≤ 5.5 at) alloy thin films. Small Zr additions to Cu led to significant lattice parameter anisotropy in the as-deposited Cu-Zr thin films both due to macroscopic lattice strain and stacking faults in the Cu matrix. Strain free lattice parameters obtained after the XRD stress analysis of Cu-Zr thin films confirmed formation of a supersaturated substitutional Cu-Zr solid solution. For the first time, the study of film microstructure by XRD line profile analysis (XLPA) confirmed progressive generation of dislocations and planar faults with increasing Zr composition in Cu-Zr alloy films. These microstructural changes led to the generation of tensile stresses in the thin films along with considerable stress gradients across the films thicknesses which are quantified by the traditional dψhkl−Sin2ψ and GIXRD stress measurement methods. The origin of tensile stresses and stress gradients in the Cu-Zr film are discussed on the basis of film growth and heterogeneous microstructure with changing Zr composition. © 202
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