1,824 research outputs found
Testing the validity of the effective rate constant approximation for surface reaction with transport
AbstractWhen one incorporates transport effects into a surface-volume reaction, an integrodifferential equation for the bound state concentration occurs. Such a form is inconvenient for data analysis. An effective rate constant approximation for the solution is correct to O(Da2) as the Damköhler number Da → 0. A numerical simulation of the integrodifferential equation is performed which shows that the effective rate constant approximation is useful even outside this regime
KINEMATIC COMPARATIVE ANALYSIS OF THE COORDINATION PATTERN OF THE BASKETBALL FREE THROW
Coordination patterns are an important part of everyday movement. The pattern of intersegmental movement is specific to each task we perform. Hudson (1986) broke down tasks into two basic categories: simultaneous which is used when accuracy is important to the task, and sequential which is used when velocity is the key to the task. The sequential pattern of movement is best defined by the summation of speed principle put forth by Bunn (1972) when he stated that in activities where the highest speed at the moment of release was necessary, the speed was developed when the movement of each segment started at the moment of greatest velocity of the preceding segment. The purpose of this study was to conduct a comparative biomechanical analysis of the system of coordination used in the basketball free throw. Four individuals of different abilities ranging from elite (a professional basketball player) to novice (an eleven year old boy with little basketball experience) participated in this study. The subjects were video taped (60 fps) shooting a free throw on a regulation basketball court in the sagittal plane on the right side (all subjects were right handed). Each performance was digitized and analyzed using the PEAK Performance 2-dimensional movement analysis system interfaced with a Panasonic AG-7350 recorder, Sony PVM-1341 monitor, and Zenith 486 microcomputer. The angular velocity of the shoulder, elbow, and wrist of the shooting arm and the hip, knee, and ankle of the same side were examined. It was found that all subjects exhibited simultaneous movement of all three joints of the leg. The elite performer exhibited sequential movement of the segments of the shooting arm where the novice exhibited complete simultaneous movement. From the results of the study, the free throw was defined as an intermediate task requiring both velocity and accuracy. This research may be used as a coaching tool in improving the performance of the free throw for any basketball player by studying the detailed analysis of the pattern of coordination of a professional player then comparing the player to any subject on the continuum outlined in this study
Electromagnetic field energy density in artificial microwave materials with negative parameters
General relations for the stored reactive field energy density in passive
linear artificial microwave materials are established. These relations account
for dispersion and absorption effects in these materials, and they are valid
also in the regions where the real parts of the material parameters are
negative. These relations always give physically sound positive values for the
energy density in passive metamaterials. The energy density and field solutions
in active metamaterials with non-dispersive negative parameters are also
considered. Basic physical limitations on the frequency dispersion of material
parameters of artificial passive materials with negative real parts of the
effective parameters are discussed. It is shown that field solutions in
hypothetical materials with negative and non-dispersive parameters are
unstable
Neutron matter with a model interaction
An infinite system of neutrons interacting by a model pair potential is
considered. We investigate a case when this potential is sufficiently strong
attractive, so that its scattering length tends to infinity. It appeared, that
if the structure of the potential is simple enough, including no finite
parameters, reliable evidences can be presented that such a system is
completely unstable at any finite density. The incompressibility as a function
of the density is negative, reaching zero value when the density tends to zero.
If the potential contains a sufficiently strong repulsive core then the system
possesses an equilibrium density. The main features of a theory describing such
systems are considered.Comment: 8 pages, LaTeX. In press, Eur. Phys. J.
Many-body approach to proton emission and the role of spectroscopic factors
The process of proton emission from nuclei is studied by utilizing the
two-potential approach of Gurvitz and Kalbermann in the context of the full
many-body problem. A time-dependent approach is used for calculating the decay
width. Starting from an initial many-body quasi-stationary state, we employ the
Feshbach projection operator approach and reduce the formalism to an effective
one-body problem. We show that the decay width can be expressed in terms of a
one-body matrix element multiplied by a normalization factor. We demonstrate
that the traditional interpretation of this normalization as the square root of
a spectroscopic factor is only valid for one particular choice of projection
operator. This causes no problem for the calculation of the decay width in a
consistent microscopic approach, but it leads to ambiguities in the
interpretation of experimental results. In particular, spectroscopic factors
extracted from a comparison of the measured decay width with a calculated
single-particle width may be affected.Comment: 17 pages, Revte
Floc formation reduces the pH stress experienced by microorganisms living in alkaline environments
The survival of microorganisms within a cementitious geological disposal facility for radioactive wastes is heavily dependent on their ability to survive the calcium dominated, hyper-alkaline conditions resulting from the dissolution of the cementitious materials. The present study shows that the formation of flocs, composed of a complex mixture of extracellular polymeric substances (EPS), provides protection against alkaline pH values up to pH 13.0. The flocs were dominated by Alishewanella and Dietzia sp, producing a mannose rich carbohydrate fraction incorporating extracellular DNA, resulting in Ca2+ sequestration. EPS provided a ~10 µm thick layer around the cells within the centre of the flocs, which were capable of growth at pH 11.0 and 11.5, maintaining internal pH values of pH 10.4 and 10.7 respectively. Survival was observed at pH 12.0, where an internal floc pH of 11.6 was observed alongside a reduced associated biomass. Limited floc survival (<2 weeks) was observed at pH 13.0.This study demonstrates that flocs are able to maintain a lower internal pH in response to the hyperalkaline conditions expected to occur within a cementitious, geological disposal facility for radioactive wastes and indicates that floc communities within such a facility would be capable of survival up to a pH of 12.0
Bremsstrahlung radiation by a tunneling particle
We study the bremsstrahlung radiation of a tunneling charged particle in a
time-dependent picture. In particular, we treat the case of bremsstrahlung
during alpha-decay, which has been suggested as a promissing tool to
investigate the problem of tunneling times. We show deviations of the numerical
results from the semiclassical estimates. A standard assumption of a preformed
particle inside the well leads to sharp high-frequency lines in the
bremsstrahlung emission. These lines correspond to "quantum beats" of the
internal part of the wavefunction during tunneling arising from the
interference of the neighboring resonances in the well.Comment: 4 pages, 4 figure
Coherent photon bremsstrahlung and dynamics of heavy-ion collisions: comparison of different models
Differential spectra of coherent photon bremsstrahlung in relativistic heavy
ion collisions are calculated within various schematic models of the
projectile-target stopping. Two versions of the degradation length model, based
on a phenomenological deceleration law, are considered. The simple shock wave
model is studied analytically. The predictions of these models agree in the
soft photon limit, where the spectrum is determined only by the final velocity
distribution of charged particles. The results of these models in the case of
central Au+Au collisions at various bombarding energies are compared with the
predictions of the microscopic transport model UrQMD. It is shown that at the
AGS energy the coherent photon bremsstrahlung exceeds the photon yield from
-decays at photon energies \omega\loo 50 MeV.Comment: 23 pages RevTeX, 9 eps Figure
Background Thermal Contributions in Testing the Unruh Effect
We consider inertial and accelerated Unruh-DeWitt detectors moving in a
background thermal bath and calculate their excitation rates. It is shown that
for fast moving detectors such a thermal bath does not affect substantially the
excitation probability. Our results are discussed in connection with a possible
proposal of testing the Unruh effect in high energy particle accelerators.Comment: 13 pages, (REVTEX 3.0), 3 figures available upon reques
Precise measurements of radio-frequency magnetic susceptibility in (anti)ferromagnetic materials
Dynamic magnetic susceptibility, , was studied in several intermetallic
materials exhibiting ferromagnetic, antiferromagnetic and metamagnetic
transitions. Precise measurements by using a 14 MHz tunnel diode oscillator
(TDO) allow detailed insight into the field and temperature dependence of
. In particular, local moment ferromagnets show a sharp peak in
near the Curie temperature, . The peak amplitude decreases and shifts to
higher temperatures with very small applied dc fields. Anisotropic measurements
of CeVSb show that this peak is present provided the magnetic easy axis is
aligned with the excitation field. In a striking contrast, small moment,
itinerant ferromagnets (i.e., ZrZn) show a broad maximum in that
responds differently to applied field. We believe that TDO measurements provide
a very sensitive way to distinguish between local and itinerant moment magnetic
orders. Local moment antiferromagnets do not show a peak at the N\'eel
temperature, , but only a sharp decrease of below due to the
loss of spin-disorder scattering changing the penetration depth of the ac
excitation field. Furthermore, we show that the TDO is capable of detecting
changes in spin order as well as metamagnetic transitions. Finally, critical
scaling of in the vicinity of is discussed in CeVSb and
CeAgSb
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