34,601 research outputs found
Optical Dipole Trapping beyond Rotating Wave Approximation: The case of Large Detuning
We show that the inclusion of counter-rotating terms, usually dropped in
evaluations of interaction of an electric dipole of a two level atom with the
electromagnetic field, leads to significant modifications of trapping potential
in the case of large detuning. The results are shown to be in excellent
numerical agreement with recent experimental findings, for the case of modes of
Laguerre-Gauss spatial profile.Comment: 13 pages, 2 figure
Surface optical vortices
It is shown how the total internal reflection of orbital-angular-momentum-endowed light can lead to the generation of evanescent light possessing rotational properties in which the intensity distribution is firmly localized in the vicinity of the surface. The characteristics of these surface optical vortices depend on the form of the incident light and on the dielectric mismatch of the two media. The interference of surface optical vortices is shown to give rise to interesting phenomena, including pattern rotation akin to a surface optical Ferris wheel. Applications are envisaged to be in atom lithography, optical surface tweezers, and spanners
Study of ball bearing torque under elastohydrodynamic lubrication
Spinning and rolling torques were measured in an angular-contact ball bearing with and without a cage under several lubrication regimes in a modified NASA spinning torque apparatus. Two lubricants were used, a di-2 ethylhexyl sebacate and a synthetic paraffinic oil, at shaft speeds of 1000, 2000, and 3000 rpm and bearing loads from 10 lbs to 90 lbs. An analytical model was developed from previous spinning friction models to include rolling with spinning under lubrication regimes from thin film to flooded conditions. The bearing torque values have a wide variation, under any condition of speed and load, depending on the amount of lubricant present in the bearing. The analytical model compared favorably with experimental results under several lubrication regimes
New generalized rheological model for lubrication of a ball spinning in a nonconforming groove
The elastohydrodynamic theory for predicting the spinning friction of a ball in a nonconforming groove was modified to incorporate a rheological model. The rheological model is based on the exponential pressure viscosity relation for low shear stresses, but at high shear rates and pressures, the relation is altered to one in which the shear stress is porportional to the normal stress. The model was fitted to experimental spinning torques for four different lubricants: a synthetic paraffinic lubricant, di-2-ethylhexyl sebacate, a super-refined naphthenic mineral oil, and a polyphenyl ether (5P4E). Good agreement between the model and experiment was found
Role of three-body interactions in formation of bulk viscosity in liquid argon
With the aim of locating the origin of discrepancy between experimental and
computer simulation results on bulk viscosity of liquid argon, a molecular
dynamic simulation of argon interacting via ab initio pair potential and
triple-dipole three-body potential has been undertaken. Bulk viscosity,
obtained using Green-Kubo formula, is different from the values obtained from
modeling argon using Lennard-Jones potential, the former being closer to the
experimental data. The conclusion is made that many-body inter-atomic
interaction plays a significant role in formation of bulk viscosity.Comment: 4 pages, 3 figure
Electronic thermal conductivity at high temperatures: Violation of the Wiedemann-Franz law in narrow band metals
We study the electronic part of the thermal conductivity kappa of metals. We
present two methods for calculating kappa, a quantum Monte-Carlo (QMC) method
and a method where the phonons but not the electrons are treated
semiclassically (SC). We compare the two methods for a model of alkali-doped
C60, A3C60, and show that they agree well. We then mainly use the SC method,
which is simpler and easier to interpret. We perform SC calculations for Nb for
large temperatures T and find that kappa increases with T as kappa(T)=a+bT,
where a and b are constants, consistent with a saturation of the mean free
path, l, and in good agreement with experiment. In contrast, we find that for
A3C60, kappa(T) decreases with T for very large T. We discuss the reason for
this qualitatively in the limit of large T. We give a quantum-mechanical
explanation of the saturation of l for Nb and derive the Wiedemann-Franz law in
the limit of T much smaller than W, where W is the band width. In contrast, due
to the small W of A3C60, the assumption T much smaller than W can be violated.
We show that this leads to kappa(T) \sim T^{-3/2} for very large T and a strong
violation of the Wiedemann-Franz law.Comment: 8 pages, 4 figure
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AMERICA'S FORGOTTEN PEOPLE AND PLACES: ENDING THE LEGACY OF POVERTY IN THE RURAL SOUTH
This study focuses on the longstanding impoverishment of the rural South and three of its subregions-Appalachia, the Mississippi Delta, and the Black Belt. The poor quality of life in rural Appalachia and along the Mississippi Delta has been publically acknowledged by programs and commissions for improving conditions. However, the more comprehensive Black Belt subregion that links parts of Southern Appalachia and the Southern Delta has not received such regional policy attention. While the South as a whole is more rural and impoverished than other U.S. regions, this is largely due to the poor conditions in the Black Belt. In addition to region and rurality, a third feature of the pattern is race. It is in the Black Belt that the South's poor socioeconomic conditions are most concentrated. Policy and program attention are needed for regional solutions that take rurality and race into account along with demographic and other subregional characteristics.Appalachia, Black Belt, Mississippi Delta, policy, poverty, quality of life, rural, South, Community/Rural/Urban Development,
Effect of surface roughness on rate-dependent slip in simple fluids
Molecular dynamics simulations are used to investigate the influence of
molecular-scale surface roughness on the slip behavior in thin liquid films.
The slip length increases almost linearly with the shear rate for atomically
smooth rigid walls and incommensurate structures of the liquid/solid interface.
The thermal fluctuations of the wall atoms lead to an effective surface
roughness, which makes the slip length weakly dependent on the shear rate. With
increasing the elastic stiffness of the wall, the surface roughness smoothes
out and the strong rate dependence is restored again. Both periodically and
randomly corrugated rigid surfaces reduce the slip length and its shear rate
dependence.Comment: 15 pages, 5 figures; submitted to J. Chem. Phy
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