12,121 research outputs found
Surface scattering analysis of phonon transport in the quantum limit using an elastic model
We have investigated the effect on phonon energy transport in mesoscopic
systems and the reduction in the thermal conductance in the quantum limit due
to phonon scattering by surface roughness using full 3-dimensional elasticity
theory for an elastic beam with a rectangular cross-section. At low frequencies
we find power laws for the scattering coefficients that are strongly mode
dependent, and different from the dependence, deriving from
Rayleigh scattering of scalar waves, that is often assumed. The scattering
gives contributions to the reduction in thermal conductance with the same power
laws. At higher frequencies the scattering coefficients becomes large at the
onset frequency of each mode due to the flat dispersion here. We use our
results to attempt a quantitative understanding of the suppression of the
thermal conductance from the universal value observed in experiment.Comment: 27 pages, 13 figure
Domain Coarsening in Systems Far from Equilibrium
The growth of domains of stripes evolving from random initial conditions is
studied in numerical simulations of models of systems far from equilibrium such
as Rayleigh-Benard convection. The scaling of the size of the domains deduced
from the inverse width of the Fourier spectrum is studied for both potential
and nonpotential models. The morphology of the domains and the defect
structures are however quite different in the two cases, and evidence is
presented for a second length scale in the nonpotential case.Comment: 11 pages, RevTeX; 3 uufiles encoded postscript figures appende
Designing novel applications for emerging multimedia technology
Current R&D in media technologies such as Multimedia, Semantic Web and Sensor Web technologies are advancing in a fierce rate and will sure to become part of our important regular items in a 'conventional' technology inventory in near future. While the R&D nature of these technologies means their accuracy, reliability and robustness are not sufficient enough to be used in real world yet, we want to envision now the near-future where these technologies will have matured and used in real applications in order to explore and start shaping many possible new ways these novel technologies could be utilised.
In this talk, some of this effort in designing novel applications that incorporate various media technologies as their backend will be presented. Examples include novel scenarios of LifeLogging application that incorporate automatic structuring of millions of photos passively captured from a SenseCam (wearable digital camera that automatically takes photos triggered by environmental sensors) and an interactive TV application incorporating a number of multimedia tools yet extremely simple and easy to use with a remote control in a lean-back position. The talk will conclude with remarks on how the design of novel applications that have no precedence or existing user base should require somewhat different approach from those suggested and practiced in conventional usability engineering methodology
Effect of phonon scattering by surface roughness on the universal thermal conductance
The effect of phonon scattering by surface roughness on the thermal
conductance in mesoscopic systems at low temperatures is calculated using full
elasticity theory. The low frequency behavior of the scattering shows novel
power law dependences arising from the unusual properties of the elastic modes.
This leads to new predictions for the low temperature depression of the thermal
conductance below the ideal universal value. Comparison with the data of Schwab
et al. [Nature 404, 974 (2000)] suggests that surface roughness on a scale of
the width of the thermal pathway is important in the experiment.Comment: 6 pages, 3 figure
Dynamical Properties of Multi-Armed Global Spirals in Rayleigh-Benard Convection
Explicit formulas for the rotation frequency and the long-wavenumber
diffusion coefficients of global spirals with arms in Rayleigh-Benard
convection are obtained. Global spirals and parallel rolls share exactly the
same Eckhaus, zigzag and skewed-varicose instability boundaries. Global spirals
seem not to have a characteristic frequency or a typical size ,
but their product is a constant under given experimental
conditions. The ratio of the radii of any two dislocations (,
) inside a multi-armed spiral is also predicted to be constant. Some of
these results have been tested by our numerical work.Comment: To appear in Phys. Rev. E as Rapid Communication
Sex, Age, and Breed Related Changes in Bovine Testosterone and Intramuscular Collagen
Castration of the male in meat-producing animals has long been a traditional practice in the production of commercial livestock. Numerous research studies have indicated that intact bovine males grow more rapidly, utilize feed more efficiently, and produce a higher yielding carcass than castrates. Even though young bulls have obvious growth and leanness advantages over steers, their meat is usually lower and more variable in tenderness than steers. These differences in tenderness have been attributed to differences in fatness or differences in connective tissue.
Factors influencing the amount and strength of intramuscular collagen have been linked to animal age, sex, and breed. The literature strongly indicates that collagen solubility decreases significantly with animal age and that most of these changes take place from birth to about 2 years of age. Results have illustrated that the age-related changes in tenderness are significantly more pronounced in bulls than in steers and heifers, particularly in muscles high in collagen. These findings suggest that age-related changes in the cross-linking of collagen might be related to the sex of the animals.
Several workers reported an increase in collagen content in young bulls at about 12 months of age. Others have suggested that the increase in collagen content at this age, which was accompanied by an increased solubility, was due to an increase in collagen synthesis related to the hormonal changes occurring during puberty in young bulls.
The objective of this phase of our research was to investigate the influence of animal age, breed, and sex condition (bull vs steer) on the content and solubility of intramuscular collagen using muscle biopsies in the longissimus muscle
Mass spectrometers and atomic oxygen
The likely role of atmospheric atomic oxygen in the recession of spacecraft surfaces and in the shuttle glow has revived interest in the accurate measurement of atomic oxygen densities in the upper atmosphere. The Air Force Geophysics Laboratory is supplying a quadrupole mass spectrometer for a materials interactions flight experiment being planned by the Johnson Space Center. The mass spectrometer will measure the flux of oxygen on test materials and will also identify the products of surface reactions. The instrument will be calibrated at a new facility for producing high energy beams of atomic oxygen at the Los Alamos National Laboratory. The plans for these calibration experiments are summarized
Parametrically excited surface waves in magnetic fluids: observation of domain structures
Observations of parametrically excited surface waves in a magnetic fluid are
presented. Under the influence of a magnetic field these waves have a
non--monotonic dispersion relation, which leads to a richer behavior than in
ordinary liquids. We report observation of three novel effects, namely:
i) domain structures,
ii) oscillating defects and
iii) relaxational phase oscillations.Comment: to be published in Physical Review Letter
The Effect of Surface Roughness on the Universal Thermal Conductance
We explain the reduction of the thermal conductance below the predicted
universal value observed by Schwab et al. in terms of the scattering of thermal
phonons off surface roughness using a scalar model for the elastic waves. Our
analysis shows that the thermal conductance depends on two roughness
parameters: the roughness amplitude and the correlation length .
At sufficiently low temperatures the conductance decrease from the universal
value quadratically with temperature at a rate proportional to .
Values of equal to 0.22 and equal to about 0.75 of the width of
the conduction pathway give a good fit to the data.Comment: 10 pages, 5 figures. Ref. added, typo correcte
Grain boundary motion in layered phases
We study the motion of a grain boundary that separates two sets of mutually
perpendicular rolls in Rayleigh-B\'enard convection above onset. The problem is
treated either analytically from the corresponding amplitude equations, or
numerically by solving the Swift-Hohenberg equation. We find that if the rolls
are curved by a slow transversal modulation, a net translation of the boundary
follows. We show analytically that although this motion is a nonlinear effect,
it occurs in a time scale much shorter than that of the linear relaxation of
the curved rolls. The total distance traveled by the boundary scales as
, where is the reduced Rayleigh number. We obtain
analytical expressions for the relaxation rate of the modulation and for the
time dependent traveling velocity of the boundary, and especially their
dependence on wavenumber. The results agree well with direct numerical
solutions of the Swift-Hohenberg equation. We finally discuss the implications
of our results on the coarsening rate of an ensemble of differently oriented
domains in which grain boundary motion through curved rolls is the dominant
coarsening mechanism.Comment: 16 pages, 5 figure
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