1,327 research outputs found
Dynamic characteristics and processing of fillers in polyurethane elastomers for vibration damping applications
Polyurethane elastomers have the potential of being used to reduce vibrational noise in many engineering applications. The performance of the elastomer is directly related to matching the nature of the mechanical loss characteristics to the frequency and temperature dependence of the source of the vibration. Materials with a broad frequency response and good mechanical properties are desirable for situations were load bearing and isolation becomes an issue. Because automobile, and other related vehicles operate over a broad temperature range, it is desirable for the damping characteristics of the elastomer to ideally be independent of temperature and frequency. In practice, this is not possible and the creation of materials with a broad spectrum response is desirable. In this paper, the effects of various fillers on the breadth and temperature dependence of the vibration damping characteristics of a filled and crosslinked polyurethane elastomer are explored. The fillers studied are wollastonite, barium sulphate and talc. These materials have different shapes, sizes and surface chemistry and undergo different types of interaction with the matrix. The vibration damping characteristics were further varied by the use of a crosslinking agent. Data presented on the rheological characteristics indicate the strength of the filler-polyol interactions. Dielectric relaxation and dynamic mechanical thermal analysis demonstrate the way in which changes in the type of filler, concentration and amount of crosslinker lead to changes in the location and breadth of the energy dissipation process in these elastomers. The vibration damping characteristics of a selected material are presented to demonstrate the potential of these materials
Spin 1 inversion: a Majorana tensor force for deuteron alpha scattering
We demonstrate, for the first time, successful S-matrix to potential
inversion for spin one projectiles with non-diagonal yielding a
interaction. The method is a generalization of the
iterative-perturbative, IP, method. We present a test case indicating the
degree of uniqueness of the potential. The method is adapted, using established
procedures, into direct observable to potential inversion, fitting ,
, , and for d + alpha scattering over
a range of energies near 10 MeV. The interaction which we find is
very different from that proposed elsewhere, both real and imaginary parts
being very different for odd and even parity channels.Comment: 7 pages Revtex, 4 ps figure
Influence of single-neutron stripping on near-barrier <sup>6</sup>He+<sup>208</sup>Pb and <sup>8</sup>He+<sup>208</sup>Pb elastic scattering
The influence of single-neutron stripping on the near-barrier elastic scattering angular distributions for the 6,8He+208Pb systems is investigated through coupled reaction channels (CRC) calculations fitting recently published data to explore the differences in the absorptive potential found in the scattering of these two neutron-rich nuclei. The inclusion of the coupling reduces the elastic cross section in the Coulomb-nuclear interference region for 8He scattering, whereas for 6He its major impact is on the large-angle elastic scattering. The real and imaginary dynamic polarization potentials are obtained by inverting the CRC elastic scattering S-matrix elements. These show that the main absorptive features occur between 11 and 12 fm for both projectiles, while the attractive features are separated by about 1 fm, with their main structures occurring at 10.5 fm for 6He and 11.5 fm for 8He
Magnetic anisotropy of vicinal (001) fcc Co films: role of crystal splitting and structure relaxation in step-decoration effect
The uniaxial in-plane magnetic anisotropy (UIP-MA) constant is calculated for
a single step on the (001) surface of fcc Co() films. The calculations are
done for both an undecorated step and the step decorated with one or more, up
to 7, Cu wires. Our objective is to explain the mechanisms by which the
decoration decreases the UIP-MA constant, which is the effect observed
experimentally for ultrathin Co films deposited on vicinal (001) Cu surfaces
and can lead to reorientation of magnetization within the film plane.
Theoretical calculations performed with a realistic tight-binding model show
that the step decoration changes the UIP-MA constant significantly only if the
splitting between the on-site energies of various -orbitals is included for
atoms located near the step edge. The local relaxation of atomic structure
around the step is also shown to have a significant effect on the shift of the
UIP-MA constant. The influence of these two relevant factors is analyzed
further by examining individual contributions to the UIP-MA constant from atoms
around the step. The magnitude of the obtained UIP-MA shift agrees well with
experimental data. It is also found that an additional shift due to possible
charge transfer between Cu and Co atoms is very small.Comment: 12 pages,9 figures, RevTeX, submitted to Physical Review B version 3:
additions to content version 2: minor correction
Barrier and internal wave contributions to the quantum probability density and flux in light heavy-ion elastic scattering
We investigate the properties of the optical model wave function for light
heavy-ion systems where absorption is incomplete, such as Ca
and O around 30 MeV incident energy. Strong focusing effects
are predicted to occur well inside the nucleus, where the probability density
can reach values much higher than that of the incident wave. This focusing is
shown to be correlated with the presence at back angles of a strong enhancement
in the elastic cross section, the so-called ALAS (anomalous large angle
scattering) phenomenon; this is substantiated by calculations of the quantum
probability flux and of classical trajectories. To clarify this mechanism, we
decompose the scattering wave function and the associated probability flux into
their barrier and internal wave contributions within a fully quantal
calculation. Finally, a calculation of the divergence of the quantum flux shows
that when absorption is incomplete, the focal region gives a sizeable
contribution to nonelastic processes.Comment: 16 pages, 15 figures. RevTeX file. To appear in Phys. Rev. C. The
figures are only available via anonynous FTP on
ftp://umhsp02.umh.ac.be/pub/ftp_pnt/figscat
Age and Prostate-Specific Antigen Level Prior to Diagnosis Predict Risk of Death from Prostate Cancer.
A single early prostate-specific antigen (PSA) level has been correlated with a higher likelihood of prostate cancer diagnosis and death in younger men. PSA testing in older men has been considered of limited utility. We evaluated prostate cancer death in relation to age and PSA level immediately prior to prostate cancer diagnosis. Using the Veterans Affairs database, we identified 230,081 men aged 50-89 years diagnosed with prostate cancer and at least one prior PSA test between 1999 and 2009. Prostate cancer-specific death over time was calculated for patients stratified by age group (e.g., 50-59 years, through 80-89 years) and PSA range at diagnosis (10 ranges) using Kaplan-Meier methods. Risk of 10-year prostate cancer mortality across age and PSA was compared using log-rank tests with a Bonferroni adjustment for multiple testing. 10.5% of men diagnosed with prostate cancer died of cancer during the 10-year study period (mean follow-up = 3.7 years). Higher PSA values prior to diagnosis predict a higher risk of death in all age groups (p < 0.0001). Within the same PSA range, older age groups are at increased risk for death from prostate cancer (p < 0.0001). For PSA of 7-10 ng/mL, cancer-specific death, 10 years after diagnosis, increased from 7% for age 50-59 years to 51% for age 80-89 years. Men older than 70 years are more likely to die of prostate cancer at any PSA level than younger men, suggesting prostate cancer remains a significant problem among older men (even those aged 80+) and deserves additional study
Velocity distributions in dissipative granular gases
Motivated by recent experiments reporting non-Gaussian velocity distributions
in driven dilute granular materials, we study by numerical simulation the
properties of 2D inelastic gases. We find theoretically that the form of the
observed velocity distribution is governed primarily by the coefficient of
restitution and , the ratio between the average number of
heatings and the average number of collisions in the gas. The differences in
distributions we find between uniform and boundary heating can then be
understood as different limits of , for and
respectively.Comment: 5 figure
n-atic Order and Continuous Shape Changes of Deformable Surfaces of Genus Zero
We consider in mean-field theory the continuous development below a
second-order phase transition of -atic tangent plane order on a deformable
surface of genus zero with order parameter . Tangent plane order expels Gaussian curvature. In addition, the total
vorticity of orientational order on a surface of genus zero is two. Thus, the
ordered phase of an -atic on such a surface will have vortices of
strength , zeros in its order parameter, and a nonspherical
equilibrium shape. Our calculations are based on a phenomenological model with
a gauge-like coupling between and curvature, and our analysis follows
closely the Abrikosov treatment of a type II superconductor just below
.Comment: REVTEX, 12 page
Benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase II from Acinetobacter calcoaceticus. Purification and preliminary characterization
Theoretical Study of Fluid Membranes of Spherical Topology with Internal Degrees of Freedom
A theoretical study of vesicles of topological genus zero is presented. The
bilayer membranes forming the vesicles have various degrees of intrinsic
(tangent-plane) orientational order, ranging from smectic to hexatic,
frustrated by curvature and topology. The field-theoretical model for these
`-atic' surfaces has been studied before in the low temperature (mean-field)
limit. Work presented here includes the effects of thermal fluctuations. Using
the lowest Landau level approximation, the coupling between order and shape is
cast in a simple form, facilitating insights into the behaviour of vesicles.
The order parameter contains vortices, whose effective interaction potential is
found, and renormalized by membrane fluctuations. The shape of the phase space
has a counter-intuitive influence on this potential. A criterion is established
whereby a vesicle of finite rigidity may be burst by its own in-plane order,
and an analogy is drawn with flux exclusion from a type-I superconductor.Comment: 34 pages + 4 Postscript figures. Uses RevTe
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