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Spontaneous Symmetry Breaking for Driven Interacting Particles on Triangular Substrates
For collectively interacting repulsive particles driven on triangular
substrates, we show that for certain directions of drive a spontaneous symmetry
breaking phenomena occurs where the particles can flow in one of two directions
that are not aligned with the external drive, giving rise to a positive or
negative Hall current. Along these directions, the particle flow is highly
ordered, while in the direction of the drive the flow is disordered. We also
find a number of dynamical phase transitions and unusual hysteretic properties
that arise due to the symmetry breaking properties of the flows.Comment: 4 pages, 4 postscript figure
Statics and Dynamics of Yukawa Cluster Crystals on Ordered Substrates
We examine the statics and dynamics of particles with repulsive Yukawa
interactions in the presence of a two-dimensional triangular substrate for
fillings of up to twelve particles per potential minimum. We term the ordered
states Yukawa cluster crystals and show that they are distinct from the
colloidal molecular crystal states found at low fillings. As a function of
substrate and interaction strength at fixed particle density we find a series
of novel crystalline states that we characterize using the structure factor.
For fillings greater than four, shell and ring structures form at each
potential minimum and can exhibit sample-wide orientational order. A disordered
state can appear between ordered states as the substrate strength varies. Under
an external drive, the onsets of different orderings produce clear changes in
the critical depinning force, including a peak effect phenomenon that has
generally only previously been observed in systems with random substrates. We
also find a rich variety of dynamic ordering transitions that can be observed
via changes in the structure factor and features in the velocity-force curves.
The dynamical states encompass a variety of moving structures including
one-dimensional stripes, smectic ordering, polycrystalline states, triangular
lattices, and symmetry locking states. Despite the complexity of the system, we
identify several generic features of the dynamical phase transitions which we
map out in a series of phase diagrams. Our results have implications for the
structure and depinning of colloids on periodic substrates, vortices in
superconductors and Bose-Einstein condensates, Wigner crystals, and dusty
plasmas.Comment: 14 pages, 17 postscript figure
Advanced thin film thermocouples
The fabrication, materials characterization, and performance of thin film platinum rhodium thermocouples on gas turbine alloys was investigated. The materials chosen for the study were the turbine blade alloy systems MAR M200+Hf with NiCoCrAlY and FeCrAlY coatings, and vane alloy systems MAR M509 with FeCrAlY. Research was focussed on making improvements in the problem areas of coating substrate stability, adhesion, and insulation reliability and durability. Diffusion profiles between the substrate and coating with and without barrier coatings of Al2O3 are reported. The relationships between fabrication parameters of thermal oxidation and sputtering of the insulator and its characterization and performance are described. The best thin film thermocouples were fabricated with the NiCoCrAlY coatings which were thermally oxidized and sputter coated with Al2O3
Ordering and Melting in Colloidal Molecular Crystal Mixtures
We show in simulations that a rich variety of novel orderings such as
pinwheel and star states can be realized for colloidal molecular crystal
mixtures at rational ratios of the number of colloids to the number of minima
from an underlying periodic substrate. These states can have multi-step melting
transitions and also show coexistence in which one species disorders while the
other species remains orientationally disordered. For other mixtures, only
partially ordered or frustrated states form.Comment: 4 pages, 4 postscript figure
Uncertainty in Measurements of Distance
Ng and van Dam have argued that quantum theory and general relativity give a
lower bound of L^{1/3} L_P^{2/3} on the uncertainty of any distance, where L is
the distance to be measured and L_P is the Planck length. Their idea is roughly
that to minimize the position uncertainty of a freely falling measuring device
one must increase its mass, but if its mass becomes too large it will collapse
to form a black hole. Here we show that one can go below the Ng-van Dam bound
by attaching the measuring device to a massive elastic rod. Relativistic
limitations on the rod's rigidity, together with the constraint that its length
exceeds its Schwarzschild radius, imply that zero-point fluctuations of the rod
give an uncertainty greater than or equal to L_P.Comment: 5 pages LaTe
Study of an attitude reference system utilizing an electrically suspended gyro final report, 1 aug. 1964 - 31 mar. 1965
Miniature electrically suspended gyroscope for spacecraft attitude reference syste
Effects of infrequent dried distillers grain supplementation on spring-calving cow performance
Feed and supplement costs and the expenses associated with delivery of winter supplements
account for a large proportion of the total operating expenditures for cow-calf
producers. Cattle grazing low-quality dormant native range (<6% crude protein) typically
are unable to consume sufficient protein from the forage base, which limits microbial
activity and forage digestion. Supplemental protein often is required to maintain
cow body weight and body condition score during the last trimester of pregnancy. Low
cow body condition scores at calving are common and may negatively affect lactation,
rebreeding rates, and calf weaning weight. Failure to maintain proper nutritional status
during this period severely affects short-term cow performance, reduces overall herd
productivity, and limits profit potential.
The most effective means of supplying supplemental protein to cows consuming
dormant native range is to provide a small amount of high-protein feedstuff (>30%
crude protein). Dried distillers grains with solubles (DDGS) are a by-product of the
ethanol refining process. Distillers grains supply the recommended 30% crude protein
level, are readily available, and often are favorably priced compared with more traditional
feedstuffs.
With the rising costs of inputs in today’s cow-calf sector, reducing cost is necessary to
maintain viability of the national cowherd. Reducing the frequency of supplementation
results in less labor and fuel use, effectively reducing input costs; however, this is viable
only as long as cow performance is maintained at acceptable levels. Therefore, the objective
of this study was to examine the effects of infrequent supplementation of dried
distillers grains with solubles on cow body weight and body condition score
Colloidal Dynamics on Disordered Substrates
Using Langevin simulations we examine driven colloids interacting with
quenched disorder. For weak substrates the colloids form an ordered state and
depin elastically. For increasing substrate strength we find a sharp crossover
to inhomogeneous depinning and a substantial increase in the depinning force,
analogous to the peak effect in superconductors. The velocity versus driving
force curve shows criticality at depinning, with a change in scaling exponent
occuring at the order to disorder crossover. Upon application of a sudden pulse
of driving force, pronounced transients appear in the disordered regime which
are due to the formation of long-lived colloidal flow channels.Comment: 4 pages, 4 postscript figure
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