458 research outputs found
Gas levitator having fixed levitation node for containerless processing
A method and apparatus is disclosed for levitating a specimen of material in a containerless environment at a stable nodal position independent of gravity. An elongated levitation tube has a contoured interior in the form of convergent section, constriction, and a divergent section in which the levitation node is created. A gas flow control means prevents separation of flow from the interior walls in the region of a specimen. The apparatus provides for levitating and heating the specimen simultaneously by combustion of a suitable gas mixture combined with an inert gas
Density-matrix spectra for integrable models
The spectra which occur in numerical density-matrix renormalization group
(DMRG) calculations for quantum chains can be obtained analytically for
integrable models via corner transfer matrices. This is shown in detail for the
transverse Ising chain and the uniaxial XXZ Heisenberg model and explains in
particular their exponential character in these cases.Comment: 14 pages, 7 figures, to appear in Ann. Physi
Time-resolved impulse response of the magnetoplasmon resonance in a two-dimensional electron gas
We have used optically excited ultrashort electrical pulses to measure the
magnetoplasmon resonance of a two-dimensional electron gas formed in an
AlGaAs/GaAs heterostructure at frequencies up to 200 gigahertz. This is
accomplished by incorporating the sample into a guided wave probe operating in
a pumped (^{3}He) system. We are able to detect the resonance by launching a
stimulus pulse in the guide, and monitoring the system response in a time
resolved pump-probe arrangement. Data obtained from measurements yield resonant
frequencies that agree with the magnetoplasmon dispersion relation.Comment: 4 pages, 4 figure
Anisotropic dielectric function in polar nano-regions of relaxor ferroelectrics
The paper suggests to treat the infrared reflectivity spectra of single
crystal perovskite relaxors as fine-grained ferroelectric ceramics: locally
frozen polarization makes the dielectric function strongly anisotropic in the
phonon frequency range and the random orientation of the polarization at
nano-scopic scale requires to take into account the inhomogeneous
depolarization field. Employing a simple effective medium approximation
(Bruggeman symmetrical formula) to dielectric function describing the polar
optic modes as damped harmonic oscillators turns out to be sufficient for
reproducing all principal features of room temperature reflectivity of PMN. One
of the reflectivity bands is identified as a geometrical resonance entirely
related to the nanoscale polarization inhomogeneity. The approach provides a
general guide for systematic determination of the polar mode frequencies split
by the inhomogeneous polarization at nanometer scale.Comment: 5 pages, 2 figure
Relativistic Effects in the Motion of the Moon
The main general relativistic effects in the motion of the Moon are briefly
reviewed. The possibility of detection of the solar gravitomagnetic
contributions to the mean motions of the lunar node and perigee is discussed.Comment: LaTeX file, no figures, 13 pages, to appear in: 'Testing relativistic
gravity in space', edited by C. Laemmerzahl, C.W.F. Everitt and F.W. Hehl
(Springer, Berlin 2000
An Exploratory Study of the Effects of Aquatic Walking on Function and Muscle Activity in Knee Osteoarthritis: Part 2
This paper presents Part 2 of a study that investigated the effects of an 8-week (3x/week) underwater treadmill (UT) walking intervention on knee osteoarthritis (KOA) outcomes in 6 adults with KOA (62.7 ± 14.2 years). The Knee Outcome Survey (KOS) for activities of daily living and muscle activity during a 10-m walk and a 20 cm step down were measured before and after the intervention. The following KOS measures improved after the UT walking program (p \u3c 0.05; g \u3e 0.8): stiffness, swelling, weakness, walking, going up stairs, going downstairs, kneeling on the front of the knee, squatting, and sitting with the knee bent. Knee flexion excursion during stance of walking increased after the UT walking intervention (p = .01). Co-activation between the tibialis anterior and medial gastrocnemius decreased during the 20 cm step down (p = .04). The findings of this study support using the WWE as a model for UT walking interventions in KOA
Silicon nanoparticles and interstellar extinction
To examine a recently proposed hypothesis that silicon nanoparticles are the
source of extended red emission (ERE) in the interstellar medium, we performed
a detailed modeling of the mean Galactic extinction in the presence of silicon
nanoparticles. For this goal we used the appropriate optical constants of
nanosized Si, essentially different from those of bulk Si due to quantum
confinement. It was found that a dust mixture of silicon nanoparticles, bare
graphite grains, silicate core-organic refractory mantle grains and three-layer
silicate-water ice-organic refractory grains works well in explaining the
extinction and, in addition, results in the acceptable fractions of UV/visible
photons absorbed by silicon nanoparticles: 0.071-0.081. Since these fractions
barely agree with the fraction of UV/visible photons needed to excite the
observed ERE, we conclude that the intrinsic photon conversion efficiency of
the photoluminescence by silicon nanoparticles must be near 100%, if they are
the source of the ERE.Comment: Latex2e, uses emulateapj.sty (included), multicol.sty, epsf.sty, 6
pages, 3 figures (8 Postscript files), accepted for publication in ApJ
Letters, complete Postscript file is also available at
http://physics.technion.ac.il/~zubko/eb.html#SNP
Создание износостойких покрытий, наплавленных в пучке релятивистских электронов
Работа направлена на формирование на поверхности низкоуглеродистой стали СтЗ износостойких покрытий методом наплавки на ускорители релятивистских электронов ЭЛВ-6.The work is aimed at forming wear-resistant coatings on the surface of low-carbon steel STZ by surfacing on relativistic electron accelerators ELV-6
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