4,388 research outputs found
The Effects of Inter-particle Attractions on Colloidal Sedimentation
We use a mesoscopic simulation technique to study the effect of short-ranged
inter-particle attraction on the steady-state sedimentation of colloidal
suspensions. Attractions increase the average sedimentation velocity
compared to the pure hard-sphere case, and for strong enough attractions, a
non-monotonic dependence on the packing fraction with a maximum velocity
at intermediate is observed. Attractions also strongly enhance
hydrodynamic velocity fluctuations, which show a pronounced maximum size as a
function of . These results are linked to a complex interplay between
hydrodynamics and the formation and break-up of transient many-particle
clusters.Comment: 4 pages 4 figure
Studies in physiological undernourishment in sheep
1. An examination of changes in weight and body composition in
a flock of free -grazing Scottish Blackface ewes indicated
that, during the greater part of pregnancy, these ewes were
undernourished and catabolizing considerable amounts of
body tissue.2. The nutritional states of ewes from two differently managed
Scottish Blackface flocks were characterized during late
pregnancy in terms of circulating concentrations of plasma
free fatty acids and ketones. Marked undernourishment was
evident in both situations.3. Data collected in a variety of situations supported the
hypothesis that the severity of undernourishment during late
pregnancy is determined principally by foetal weight and the
level of food intake. Within a group of pregnant ewes with
comparable intakes, the general degree of undernourishment is
dependent on the level of intake, and the relative severity
of undernourishment in individual animals is determined by
differences in foetal weight.4. The use of certain biochemical parameters as indices of undernourishment was examined in ewes with artificially induced
hypoglycaemia. It was concluded that nutritional state is
best characterized in terms of that parameter which shows the
greatest response per unit change in either nutrient intake
or nutrient requirement.5. Biochemical parameters were used to control the nutritional states of individual animals in an experiment on the effects of undernourishment during pregnancy on lamb
birth- weight. The results of this experiment indicated
that the undernourishment occurring in free- grazing hill
ewes during late pregnancy was likely to reduce the birth - weight of single lambs by 10%, and that of twins by 25%.6. The additional energy requirements during pregnancy were
estimated to be 100g digestible organic matter per kg
foetus
Multiplicity at the Stellar/Substellar Boundary in Upper Scorpius
We present the results of a high-resolution imaging survey of 12 brown dwarfs
and very low mass stars in the closest (~145 pc) young (~5 Myr) OB association,
Upper Scorpius. We obtained images with the Advanced Camera for Surveys/High
Resolution Camera on HST through the F555W (V), F775W (i'), and F850LP (z')
filters. This survey discovered three new binary systems, including one
marginally resolved pair with a projected separation of only 4.9 AU, resulting
in an observed binary fraction of 25+/-14% at separations >4 AU. After
correcting for detection biases assuming a uniform distribution of mass ratios
for q>0.6, the estimated binary fraction is 33+/-17%. The binary fraction is
consistent with that inferred for higher-mass stars in Upper Sco, but the
separation and mass ratio distributions appear to be different. All three
low-mass binary systems in Upper Sco are tight (<18 AU) and of similar mass
(q>0.6), consistent with expectations based on previous multiplicity studies of
brown dwarfs and very low mass stars in the field and in open clusters. The
implication is that the distinct separation and mass ratio distributions of
low-mass systems are set in the formation process or at very young ages, rather
than by dynamical disruption of wide systems at ages >5 Myr. Finally, we
combine the survey detection limits with the models of Burrows et al. (1997) to
show that there are no planets or very low-mass brown dwarfs with masses >10
M_J at projected separations >20 AU, or masses >5 M_J at projected separations
>40 AU orbiting any of the low-mass (0.04-0.10 M_sun) objects in our sample.Comment: Accepted for publication in ApJ; 10 pages, 4 figures in emulateapj
forma
Phase Stability and Segregation in Alloy 22 Base Metal and Weldments
The current design of the waste disposal containers relies heavily on encasement in a multi-layered container, featuring a corrosion barrier of Alloy 22, a Ni-Cr-Mo-W based alloy with excellent corrosion resistance over a wide range of conditions. The fundamental concern from the perspective of the Yucca Mountain Project, however, is the inherent uncertainty in the (very) long-term stability of the base metal and welds. Should the properties of the selected materials change over the long service life of the waste packages, it is conceivable that the desired performance characteristics (such as corrosion reistance) will become compromised, leading to premature failure of the system. To address this, we will study the phase stability and solute segregation characteristics of Alloy 22 base metal and welds. A better understanding of the underlying microstructural evolution tendencies, and their connections with corrosion behavior will (in turn) produce a higher confidence in the extrapolated behavior of the container materials over time periods that are not feasibly tested in a laboratory. Additionally, the knowledge gained here may potentially lead to cost savings through development of safe and realistic design constraints and model assumptions throughout the entire disposal system
Potential for increasing producers' income from wool, fibre and pelts in Central Asia
The systems of livestock production, marketing and research have been profoundly transformed by recent policies in Central Asia since the break up of the Soviet Union. Decollectivisation of state farms has transferred livestock ownership to new private farming units. These receive little or no state support for inputs, or for processing and selling livestock products. Most livestock-keeping families have much-reduced incomes compared to the Soviet period. Live animal sales now constitute the main subsistence income for such families, but may be unsustainable for the majority of families who own small numbers of animals. Poverty is particularly prevalent in the more remote areas distant from urban markets
The Model Underlying SIMSOC
http://deepblue.lib.umich.edu/bitstream/2027.42/50927/1/152.pd
A Long-Lived Accretion Disk Around a Lithium-Depleted Binary T Tauri Star
We present a high dispersion optical spectrum of St 34 and identify the
system as a spectroscopic binary with components of similar luminosity and
temperature (both M3+/-0.5). Based on kinematics, signatures of accretion, and
location on an H-R diagram, we conclude that St 34 is a classical T Tauri star
belonging to the Taurus-Auriga T Association. Surprisingly, however, neither
component of the binary shows LiI 6708 A, absorption, the most universally
accepted criterion for establishing stellar youth. In this uniquely known
instance, the accretion disk appears to have survived longer than the lithium
depletion timescale. We speculate that the long-lived accretion disk is a
consequence of the sub-AU separation companion tidally inhibiting, though not
preventing, circumstellar accretion. Comparisons with pre-main sequence
evolutionary models imply, for each component of St 34, a mass of 0.37+/-0.08
Msun and an isochronal age of 8+/-3 Myr, which is much younger than the
predicted lithium depletion timescale of ~ 25 Myr. Although a distance 38%
closer than that of Taurus-Auriga or a hotter temperature scale could reconcile
this discrepancy at 21-25 Myr, similar discrepancies in other systems and the
implications of an extremely old accreting Taurus-Auriga member suggest instead
a possible problem with evolutionary models. Regardless, the older age implied
by St 34's depleted lithium abundance is the first compelling evidence for a
substantial age spread in this region. Additionally, since St 34's coeval
co-members with early M spectral types would likewise fail the lithium test for
youth, current membership lists may be incomplete.Comment: 4 pages, including 2 figures. Accepted for publication in ApJ Let
Remote sensing applications in forestry. The development of an earth resources information system using aerial photographs and digital computers photographs and digital computers
Remote aerial sensing and automatic mapping for forest resources information syste
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