2,452 research outputs found
Shear Thickening and Scaling of the Elastic Modulus in a Fractal Colloidal System with Attractive Interactions
Dilute oil dispersions of fractal carbon black particles with attractive Van
der Waals interactions display continuous shear thickening followed by shear
thinning at high shear rates. The shear thickening transition occurs at
and is driven by hydrodynamic
breakup of clusters. Pre-shearing dispersions at shear rates
produces enhanced-modulus gels where and is directly proportional to the residual stress
in the gel measured at a fixed sample age. The observed data can be accounted
for using a simple scaling model for the breakup of fractal clusters under
shear stress.Comment: 5 pages, 5 figures; v2: treating low shear rate date separately;
edited title; reworked figure
Study of effects of fuel properties in turbine-powered business aircraft
Increased interest in research and technology concerning aviation turbine fuels and their properties was prompted by recent changes in the supply and demand situation of these fuels. The most obvious change is the rapid increase in fuel price. For commercial airplanes, fuel costs now approach 50 percent of the direct operating costs. In addition, there were occasional local supply disruptions and gradual shifts in delivered values of certain fuel properties. Dwindling petroleum reserves and the politically sensitive nature of the major world suppliers make the continuation of these trends likely. A summary of the principal findings, and conclusions are presented. Much of the material, especially the tables and graphs, is considered in greater detail later. The economic analysis and examination of operational considerations are described. Because some of the assumptions on which the economic analysis is founded are not easily verified, the sensitivity of the analysis to alternates for these assumptions is examined. The data base on which the analyses are founded is defined in a set of appendices
Low-emissivity impact craters on Venus
An analysis of 144 impact craters on Venus has shown that 11 of these have floors with average emissivities lower than 0.8. The remaining craters have emissivities between 0.8 and 0.9, independent of the specific backscatter cross section of the crater floors. These 144 impact craters were chosen from a possible 164 craters with diameters greater than 30 km as identified by researchers for 89 percent of the surface of Venus. We have only looked at craters below 6053.5 km altitude because a mineralogical change causes high reflectivity/low emissivity above the altitude. We have also excluded all craters with diameters smaller than 30 km because the emissivity footprint at periapsis is 16 x 24 km and becomes larger at the poles
Maximal Acceleration Corrections to the Lamb Shift of Hydrogen, Deuterium and He
The maximal acceleration corrections to the Lamb shift of one--electron atoms
are calculated in a non--relativistic approximation. They are compatible with
experimental results, are in particularly good agreement with the Lamb
shift in hydrogen and reduce by the experiment--theory discrepancy
for the shift in .Comment: LaTex file, 15 pages, to be published in Phys. Lett.
Avalanche statistics and time-resolved grain dynamics for a driven heap
We probe the dynamics of intermittent avalanches caused by steady addition of
grains to a quasi-two dimensional heap. To characterize the time-dependent
average avalanche flow speed v(t), we image the top free surface. To
characterize the grain fluctuation speed dv(t), we use Speckle-Visibility
Spectroscopy. During an avalanche, we find that the fluctuation speed is
approximately one-tenth the average flow speed, and that these speeds are
largest near the beginning of an event. We also find that the distribution of
event durations is peaked, and that event sizes are correlated with the time
interval since the end of the previous event. At high rates of grain addition,
where successive avalanches merge into smooth continuous flow, the relationship
between average and fluctuation speeds changes to dv Sqrt[v]
Bose-Einstein Condensation in a CO_2-laser Optical Dipole Trap
We report on the achieving of Bose-Einstein condensation of a dilute atomic
gas based on trapping atoms in tightly confining CO_2-laser dipole potentials.
Quantum degeneracy of rubidium atoms is reached by direct evaporative cooling
in both crossed and single beam trapping geometries. At the heart of these
all-optical condensation experiments is the ability to obtain high initial
atomic densities in quasistatic dipole traps by laser cooling techniques.
Finally, we demonstrate the formation of a condensate in a field insensitive
m_F=0 spin projection only. This suppresses fluctuations of the chemical
potential from stray magnetic fields.Comment: 8 pages, 5 figure
Herschel-Bulkley rheology from lattice kinetic theory of soft-glassy materials
We provide a clear evidence that a two species mesoscopic Lattice Boltzmann
(LB) model with competing short-range attractive and mid-range repulsive
interactions supports emergent Herschel-Bulkley (HB) rheology, i.e. a power-law
dependence of the shear-stress as a function of the strain rate, beyond a given
yield-stress threshold. This kinetic formulation supports a seamless transition
from flowing to non-flowing behaviour, through a smooth tuning of the
parameters governing the mesoscopic interactions between the two species. The
present model may become a valuable computational tool for the investigation of
the rheology of soft-glassy materials on scales of experimental interest.Comment: 5 figure
- …