22,063 research outputs found
A deductive statistical mechanics approach for granular matter
We introduce a deductive statistical mechanics approach for granular
materials which is formally built from few realistic physical assumptions. The
main finding is an universal behavior for the distribution of the density
fluctuations. Such a distribution is the equivalent of the Maxwell-Boltzmann's
distribution in the kinetic theory of gasses. The comparison with a very
extensive set of experimental and simulation data for packings of monosized
spherical grains, reveals a remarkably good quantitative agreement with the
theoretical predictions for the density fluctuations both at the grain level
and at the global system level. Such agreement is robust over a broad range of
packing fractions and it is observed in several distinct systems prepared by
using different methods. The equilibrium distributions are characterized by
only one parameter () which is a quantity very sensitive to changes in the
structural organization. The thermodynamical equivalent of and its relation
with the `granular temperature' are also discussed.Comment: 15 pages, 6 figure
Statistical Mechanics of Vibration-Induced Compaction of Powders
We propose a theory which describes the density relaxation of loosely packed,
cohesionless granular material under mechanical tapping. Using the compactivity
concept we develope a formalism of statistical mechanics which allows us to
calculate the density of a powder as a function of time and compactivity. A
simple fluctuation-dissipation relation which relates compactivity to the
amplitude and frequency of a tapping is proposed. Experimental data of
E.R.Nowak et al. [{\it Powder Technology} 94, 79 (1997) ] show how density of
initially deposited in a fluffy state powder evolves under carefully controlled
tapping towards a random close packing (RCP) density. Ramping the vibration
amplitude repeatedly up and back down again reveals the existence of reversible
and irreversible branches in the response. In the framework of our approach the
reversible branch (along which the RCP density is obtained) corresponds to the
steady state solution of the Fokker-Planck equation whereas the irreversible
one is represented by a superposition of "excited states" eigenfunctions. These
two regimes of response are analyzed theoretically and a qualitative
explanation of the hysteresis curve is offered.Comment: 11 pages, 2 figures, Latex. Revised tex
A Quantitative Non-radial Oscillation Model for the Subpulses in PSR B0943+10
In this paper, we analyze time series measurements of PSR B0943+10 and fit
them with a non-radial oscillation model. The model we apply was first
developed for total intensity measurements in an earlier paper, and expanded to
encompass linear polarization in a companion paper to this one. We use PSR
B0943+10 for the initial tests of our model because it has a simple geometry,
it has been exhaustively studied in the literature, and its behavior is
well-documented. As prelude to quantitative fitting, we have reanalyzed
previously published archival data of PSR B0943+10 and uncovered subtle but
significant behavior that is difficult to explain in the framework of the
drifting spark model. Our fits of a non-radial oscillation model are able to
successfully reproduce the observed behavior in this pulsar.Comment: 45 pages, 16 figures, accepted Ap
Physical Nucleon Properties from Lattice QCD
We demonstrate that the extremely accurate lattice QCD data for the mass of
the nucleon recently obtained by CP-PACS, combined with modern chiral
extrapolation techniques, leads to a value for the mass of the physical nucleon
which has a systematic error of less than one percent.Comment: 4 pages, 2 figure
Residual Chiral Symmetry Breaking in Domain-Wall Fermions
We study the effective quark mass induced by the finite separation of the
domain walls in the domain-wall formulation of chiral fermion as the function
of the size of the fifth dimension (), the gauge coupling and the
physical volume . We measure the mass by calculating the small eigenvalues
of the hermitian domain-wall Dirac operator ( in the
topologically-nontrivial quenched SU(3) gauge configurations. We find that the
induced quark mass is nearly independent of the physical volume, decays
exponentially as a function of , and has a strong dependence on the size
of quantum fluctuations controlled by . The effect of the choice of the
lattice gluon action is also studied.Comment: 12 pages, 7 figure
Nucleon Generalized Parton Distributions from Full Lattice QCD
We present a comprehensive study of the lowest moments of nucleon generalized
parton distributions in N_f=2+1 lattice QCD using domain wall valence quarks
and improved staggered sea quarks. Our investigation includes helicity
dependent and independent generalized parton distributions for pion masses as
low as 350 MeV and volumes as large as (3.5 fm)^3, for a lattice spacing of
0.124 fm. We use perturbative renormalization at one-loop level with an
improvement based on the non-perturbative renormalization factor for the axial
vector current, and only connected diagrams are included in the isosinglet
channel.Comment: 40 pages, 49 figures; Revised chiral extrapolations in sections A-K,
main conclusions unchange
Ultrasonic inspection and self-healing of Ge and 3C-SiC semiconductor membranes
Knowledge of the mechanical properties and stability of thin film structures is important for device operation. Potential failures related to crack initiation and growth must be identified early, to enable healing through e.g. annealing. Here, three square suspended membranes, formed from a thin layer of cubic silicon carbide (3C-SiC) or germanium (Ge) on a silicon substrate, were characterised by their response to ultrasonic excitation. The resonant frequencies and mode shapes were measured during thermal cycling over a temperature range of 20--100~C. The influence of temperature on the stress was explored by comparison with predictions from a model of thermal expansion of the combined membrane and substrate. For an ideal, non-cracked sample the stress and Q-factor behaved as predicted. In contrast, for a 3C-SiC and a Ge membrane that had undergone vibration and thermal cycling to simulate extended use, measurements of the stress and Q-factor showed the presence of damage, with the 3C-SiC membrane subsequently breaking. However, the damaged Ge sample showed an improvement to the resonant behaviour on subsequent heating. Scanning electron microscopy showed that this was due to a self-healing of sub-micrometer cracks, caused by expansion of the germanium layer to form bridges over the cracked regions, with the effect also observable in the ultrasonic inspection
Diffusion and mixing in gravity-driven dense granular flows
We study the transport properties of particles draining from a silo using
imaging and direct particle tracking. The particle displacements show a
universal transition from super-diffusion to normal diffusion, as a function of
the distance fallen, independent of the flow speed. In the super-diffusive (but
sub-ballistic) regime, which occurs before a particle falls through its
diameter, the displacements have fat-tailed and anisotropic distributions. In
the diffusive regime, we observe very slow cage breaking and Peclet numbers of
order 100, contrary to the only previous microscopic model (based on diffusing
voids). Overall, our experiments show that diffusion and mixing are dominated
by geometry, consistent with fluctuating contact networks but not thermal
collisions, as in normal fluids
Calculation of the nucleon axial charge in lattice QCD
Protons and neutrons have a rich structure in terms of their constituents,
the quarks and gluons. Understanding this structure requires solving Quantum
Chromodynamics (QCD). However QCD is extremely complicated, so we must
numerically solve the equations of QCD using a method known as lattice QCD.
Here we describe a typical lattice QCD calculation by examining our recent
computation of the nucleon axial charge.Comment: Prepared for Scientific Discovery through Advanced Computing (SciDAC
2006), Denver, Colorado, June 25-29 200
Effects of intervention upon precompetition state anxiety in elite junior tennis players: The relevance of the matching hypothesis
Reproduced with permission of publisher from:
Terry, P., Coakley, L., & Karageorghis, C. Effects of intervention upon precompetition state anxiety in elite junior tennis players: the relevance of the matching hypothesis. Perceptual and Motor Skills, 1995, 81, 287-296. © Perceptual and Motor Skills 1995The matching hypothesis proposes that interventions for anxiety should be matched to the modality in which anxiety is experienced. This study investigated the relevance of the matching hypothesis for anxiety interventions in tennis. Elite junior tennis players (N = 100; Age: M = 13.9 yr., SD = 1.8 yr.) completed the Competitive State Anxiety Inventory-2 before and after one of four randomly assigned intervention strategies approximately one hour prior to competition at a National Junior Championship. A two-factor multivariate analysis of variance (group x time) with repeated measures on the time factor gave no significant main effect by group but indicated significant reductions in somatic anxiety and cognitive anxiety and a significant increase in self-confidence following intervention. A significant group by time interaction emerged for self-confidence. The results question the need to match intervention strategy to the mode of anxiety experienced
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