1,474 research outputs found
Viscoelastic Behavior of Solid He
Over the last five years several experimental groups have reported anomalies
in the temperature dependence of the period and amplitude of a torsional
oscillator containing solid He. We model these experiments by assuming that
He is a viscoelastic solid--a solid with frequency dependent internal
friction. We find that while our model can provide a quantitative account of
the dissipation observed in the torsional oscillator experiments, it only
accounts for about 10% of the observed period shift, leaving open the
possibility that the remaining period shift is due to the onset of
superfluidity in the sample.Comment: 4 pages, 3 figure
Gallium Desorption Behavior At AlGaAs/GaAs Heterointerfaces During High-temperature Molecular Beam Epitaxy
A Monte Carlo simulation study is performed to investigate the Ga desorption behavior during AlGaAs-on-GaAs heterointerface formation by molecular beam epitaxy. The transients in the Ga desorption rate upon opening the Al shutter are shown to be associated with the concurrent reduction in the V/III flux ratio. Monte Carlo simulations employing a constant V/III flux ratio yield a “steplike” variation in the Ga desorption rate with the resulting interfaces closer in abruptness to the ideal AlGaAs-on-GaAs interface. Further details on the stoichiometry of the interface and its relationship with predicted Ga desorption profiles is presented
Subcutaneous Immunoglobulin Replacement Therapy with Hizentra® is Safe and Effective in Children Less Than 5 Years of Age.
BACKGROUND:Hizentra® (IGSC 20%) is a 20% liquid IgG product approved for subcutaneous administration in adults and children 2 years of age and older who have primary immunodeficiency disease (PIDD). There is limited information about the use of IGSC 20 % in very young children including those less than 5 years of age. METHODS:A retrospective chart review involved 88 PIDD infants and children less than 5 years of age who received Hizentra®. RESULTS:The mean age at the start of Hizentra® was 34 months (range 2 to 59 months). IGSC 20 % was administered weekly to 86 infants (two additional infants received twice weekly and three times weekly infusions, respectively) and included an average of 63 infusions (range 6-182) for an observation period up to 45.5 months. Infusion by manual delivery occurred in 15 patients. The mean dose was 674 mg/kg/4 weeks. The mean IgG level was 942 mg/dL while on IGSC 20 %, compared to a mean trough IgG level of 794 mg/dL (p < 0.0001) during intravenous or subcutaneous IgG administration prior to IGSC 20 %. Average infusion time was 47 (range 5-120) minutes, and the median number of infusion sites was 2 (range 1-4). Local reactions were mostly mild and observed in 36/88 (41%) children. No serious adverse events were reported. A significant increase in weight percentile (7 % ± 19.2, p = 0.0012) among subjects was observed during IGSC 20% administration. The rate of serious bacterial infections was 0.067 per patient-year while receiving IGSC 20%, similar to previously reported efficacy studies. CONCLUSIONS:Hizentra® is effective in preventing infections, and is well tolerated in children less than age 5 years
Dynamic transitions between metastable states in a superconducting ring
Applying the time-dependent Ginzburg-Landau equations, transitions between
metastable states of a superconducting ring are investigated in the presence of
an external magnetic field. It is shown that if the ring exhibits several
metastable states at a particular magnetic field, the transition from one
metastable state to another one is governed by both the relaxation time of the
absolute value of the order parameter tau_{|psi|} and the relaxation time of
the phase of the order parameter tau_{phi}. We found that the larger the ratio
tau_{|psi|}tau_{phi} the closer the final state will be to the absolute minimum
of the free energy, i.e. the thermodynamic equilibrium. The transition to the
final state occurs through a subsequent set of single phase slips at a
particular point along the ring.Comment: 7 pages, 6 figures, Revtex 4.0 styl
Hall-Effect Sign Anomaly and Small-Polaronic Conduction in (La_{1-x}Gd_x)_{0.67}Ca_{0.33}MnO_3
The Hall coefficient of Gd-doped La_{2/3}Ca_{1/3}MnO_3 exhibits Arrhenius
behavior over a temperature range from 2T_c to 4T_c, with an activation energy
very close to 2/3 that of the electrical conductivity. Although both the doping
level and thermoelectric coefficient indicate hole-like conduction, the Hall
coefficient is electron-like. This unusual result provides strong evidence in
favor of small-polaronic conduction in the paramagnetic regime of the
manganites.Comment: 11 pages, 4 figures, uses revtex.st
Flux penetration in slab shaped Type-I superconductors
We study the problem of flux penetration into type--I superconductors with
high demagnetization factor (slab geometry).Assuming that the interface between
the normal and superconducting regions is sharp, that flux diffuses rapidly in
the normal regions, and that thermal effects are negligible, we analyze the
process by which flux invades the sample as the applied field is increased
slowly from zero.We find that flux does not penetrate gradually.Rather there is
an instability in the process and the flux penetrates from the boundary in a
series of bursts, accompanied by the formation of isolated droplets of the
normal phase, leading to a multiply connected flux domain structure similar to
that seen in experiments.Comment: 4 pages, 2 figures, Fig 2.(b) available upon request from the
authors, email - [email protected]
Travelling waves in a drifting flux lattice
Starting from the time-dependent Ginzburg-Landau (TDGL) equations for a type
II superconductor, we derive the equations of motion for the displacement field
of a moving vortex lattice without inertia or pinning. We show that it is
linearly stable and, surprisingly, that it supports wavelike long-wavelength
excitations arising not from inertia or elasticity but from the
strain-dependent mobility of the moving lattice. It should be possible to image
these waves, whose speeds are a few \mu m/s, using fast scanning tunnelling
microscopy.Comment: 4 pages, revtex, 2 .eps figures imbedded in paper, title shortened,
minor textual change
Bound states of edge dislocations: The quantum dipole problem in two dimensions
We investigate bound state solutions of the 2D Schr\"odinger equation with a
dipole potential originating from the elastic effects of a single edge
dislocation. The knowledge of these states could be useful for understanding a
wide variety of physical systems, including superfluid behavior along
dislocations in solid He. We present a review of the results obtained by
previous workers together with an improved variational estimate of the ground
state energy. We then numerically solve the eigenvalue problem and calculate
the energy spectrum. In our dimensionless units, we find a ground state energy
of -0.139, which is lower than any previous estimate. We also make successful
contact with the behavior of the energy spectrum as derived from semiclassical
considerations.Comment: 6 pages, 3 figures, submitted to PR
- …