827 research outputs found
Measurements of Solid Spheres Bouncing Off Flat Plates
Recent years have seen a substantial increase of interest in the flows of granular materials whose rheology is dominated by the physical contact between particles and between particles and the containing walls. Considerable advances in the theoretical understanding of rapid granular material flows have been made by the application of the statistical methods of molecular gas dynamics (e.g., Jenkins and Savage (1983), Lun et al. (1984)) and by the use of computers simulations of these flows (e.g., Campbell and Brennen (1985), Walton (1984)). Experimental studies aimed at measurements of the fundamental rheology properties are much less numerous and are understandably limited by the great difficulties involved in trying to measure velocity profiles, solid fraction profiles, and fluctuating velocities within a flowing granular material. Nevertheless, it has become clear that one of the most severe problems encountered when trying to compare experimental data with the theoretical models is the uncertainty in the material properties governing particle/particle or particle/wall collisions. Many of the theoretical models and computer simulations assume a constant coefficient of restitution (and, in some cases, a coefficient of friction).
The purpose of the present project was to provide some documentation for particle/wall collisions by means of a set of relatively simple experiments in which solid spheres of various diameters and materials were bounced off plates of various thickness and material. The objective was to provide the kind of information on individual particle/wall collisions needed for the theoretical rheological models and computer simulations of granular material flows: in particular, to help resolve some of the issues associated with the boundary condition at a solid wall. For discussion of the complex issues associated with dynamic elastic or inelastic impact, reference is made to Goldsmith (1960) and the recent text by Johnson (1985)
Counting function for a sphere of anisotropic quartz
We calculate the leading Weyl term of the counting function for a
mono-crystalline quartz sphere. In contrast to other studies of counting
functions, the anisotropy of quartz is a crucial element in our investigation.
Hence, we do not obtain a simple analytical form, but we carry out a numerical
evaluation. To this end we employ the Radon transform representation of the
Green's function. We compare our result to a previously measured unique data
set of several tens of thousands of resonances.Comment: 16 pages, 11 figure
Spectrum of stochastic evolution operators: Local matrix representation approach
A matrix representation of the evolution operator associated with a nonlinear
stochastic flow with additive noise is used to compute its spectrum. In the
weak noise limit a perturbative expansion for the spectrum is formulated in
terms of local matrix representations of the evolution operator centered on
classical periodic orbits. The evaluation of perturbative corrections is easier
to implement in this framework than in the standard Feynman diagram
perturbation theory. The result are perturbative corrections to a stochastic
analog of the Gutzwiller semiclassical spectral determinant computed to several
orders beyond what has so far been attainable in stochastic and
quantum-mechanical applications.Comment: 7 pages, 2 figures, Third approach to a problem we considered in
chao-dyn/9807034 and chao-dyn/981100
A25 COLLAGEN TYPE II DEGRADATION AND FORMATION ASSESSED IN EX VIVO AND IN VIVO IN MODELS OF RA
Experimental Electronic Structure and Interband Nesting in BaVS_3
The correlated 3d sulphide BaVS_3 is a most interesting compound because of
the apparent coexistence of one-dimensional and three-dimensional properties.
Our experiments explain this puzzle and shed new light on its electronic
structure. High-resolution angle-resolved photoemission measurements in a 4eV
wide range below the Fermi level explored the coexistence of weakly correlated
a_1g wide-band and strongly correlated e_g narrow-band d-electrons that is
responsible for the complicated behavior of this material. The most relevant
result is the evidence for a_1g--e_g inter-band nesting condition.Comment: 4 pages, 3 figure
An optimally concentrated Gabor transform for localized time-frequency components
Gabor analysis is one of the most common instances of time-frequency signal
analysis. Choosing a suitable window for the Gabor transform of a signal is
often a challenge for practical applications, in particular in audio signal
processing. Many time-frequency (TF) patterns of different shapes may be
present in a signal and they can not all be sparsely represented in the same
spectrogram. We propose several algorithms, which provide optimal windows for a
user-selected TF pattern with respect to different concentration criteria. We
base our optimization algorithm on -norms as measure of TF spreading. For
a given number of sampling points in the TF plane we also propose optimal
lattices to be used with the obtained windows. We illustrate the potentiality
of the method on selected numerical examples
SU(N) group-theory constraints on color-ordered five-point amplitudes at all loop orders
Color-ordered amplitudes for the scattering of n particles in the adjoint
representation of SU(N) gauge theory satisfy constraints arising solely from
group theory. We derive these constraints for n=5 at all loop orders using an
iterative approach. These constraints generalize well-known tree-level and
one-loop group theory relations.Comment: 16 pages, no figures; v2: minor corrections and clarifications,
published versio
Cartilage degradation is fully reversible in the presence of aggrecanase but not matrix metalloproteinase activity
Multigluon tree amplitudes with a pair of massive fermions
We consider the calculation of n-point multigluon tree amplitudes with a pair
of massive fermions in QCD. We give the explicit transformation rules of this
kind of massive fermion-pair amplitudes with respect to different reference
momenta and check the correctness of them by SUSY Ward identities. Using these
rules and onshell BCFW recursion relation, we calculate the analytic results of
several n-point multigluon amplitudes.Comment: 15page
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