976,597 research outputs found
Renormalized field theory and particle density profile in driven diffusive systems with open boundaries
We investigate the density profile in a driven diffusive system caused by a
plane particle source perpendicular to the driving force. Focussing on the case
of critical bulk density we use a field theoretic renormalization
group approach to calculate the density as a function of the distance
from the particle source at first order in (: spatial
dimension). For we find reasonable agreement with the exact solution
recently obtained for the asymmetric exclusion model. Logarithmic corrections
to the mean field profile are computed for with the result for .Comment: 32 pages, RevTex, 4 Postscript figures, to appear in Phys. Rev.
Shock associated noise reduction from inverted-velocity-profile coannular jets
Acoustic measurements show that the shock noise from the outer stream is virtually eliminated when the inner stream is operated at a Mach number just above unity, regardless of all the other jet operating conditions. At this optimum condition, the coannular jet provides the maximum noise reduction relative to the equivalent single jet. The shock noise reduction can be achieved at inverted-as well as normal-velocity-profile conditions, provided the coannular jet is operated with the inner stream just slightly supersonic. Analytical models for the shock structure and shock noise are developed indicate that a drastic change in the outer stream shock cell structure occurs when the inner stream increases its velocity from subsonic to supersonic. At this point, the almost periodic shock cell structure of the outer stream nearly completely disappears the noise radiated is minimum. Theoretically derive formulae for the peak frequencies and intensity scaling of shock associated noise are compared with the measured results, and good agreement is found for both subsonic and supersonic inner jet flows
Crystal Symmetry, Electron-Phonon Coupling, and Superconducting Tendencies in LiPdB and LiPtB
After theoretical determination of the internal structural coordinates in
LiPdB, we calculate and analyze its electronic structure and obtain the
frequencies of the two phonons (40.6 meV for nearly pure Li mode, 13.0
meV for the strongly mixed Pd-Li mode). Pd can be ascribed a
configuration, but strong 4d character remains up to the Fermi level. Small
regions of flat bands occur at -70 meV at both the and X points.
Comparison of the Fermi level density of states to the linear specific heat
coefficient gives a dynamic mass enhancement of = 0.75. Rough Fermi
surface averages of the deformation potentials of individual Pd and Li
displacements are obtained. While is small, ~ 1.15 eV/\AA
is sizable, and a plausible case exists for its superconductivity at 8 K being
driven primarily by coupling to Pd vibrations. The larger d bandwidth in
LiPtB leads to important differences in the bands near the Fermi
surface. The effect on the band structure of spin-orbit coupling plus lack of
inversion is striking, and is much larger in the Pt compound.Comment: 8 pages and 8embedded figures, to be appeared in PR
A Dewpoint Meter Using Cooling by Expansion of CO2
For use in certain aerodynamical problems a dewpoint meter using the Joule-Thompson effect, with CO2 as cooling agent, has been developed. The instrument described here has some advantages over the common instrument which depends oupon the evaporation of ether. Two slightly different devices have been used successfully
Resonant three-body physics in two spatial dimensions
We discuss the three-body properties of identical bosons exhibiting large
scattering length in two spatial dimensions. Within an effective field theory
for resonant interactions, we calculate the leading non-universal corrections
from the two-body effective range to bound-state and scattering observables. In
particular, we compute the three-body binding energies, the boson-dimer
scattering properties, and the three-body recombination rate for finite
energies. We find significant effective range effects in the vicinity of the
unitary limit. The implications of this result for future experiments are
briefly discussed.Comment: 15 pages, 8 figures, published versio
Surface critical behavior of driven diffusive systems with open boundaries
Using field theoretic renormalization group methods we study the critical
behavior of a driven diffusive system near a boundary perpendicular to the
driving force. The boundary acts as a particle reservoir which is necessary to
maintain the critical particle density in the bulk. The scaling behavior of
correlation and response functions is governed by a new exponent eta_1 which is
related to the anomalous scaling dimension of the chemical potential of the
boundary. The new exponent and a universal amplitude ratio for the density
profile are calculated at first order in epsilon = 5-d. Some of our results are
checked by computer simulations.Comment: 10 pages ReVTeX, 6 figures include
Identification of the dominant diffusing species in silicide formation
Implanted noble gas atoms of Xe have been used as diffusion markers in the growth study of three silicides: Ni2Si, VSi2, and TiSi2. Backscattering of MeV He has been used to determine the displacement of the markers. We found that while Si atoms predominate the diffusion in VSi2 and TiSi2, Ni atoms are the faster moving species in Ni2Si
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