9,487 research outputs found
Spatial fluctuations of a surviving particle in the trapping reaction
We consider the trapping reaction, , where and particles
have a diffusive dynamics characterized by diffusion constants and .
The interaction with particles can be formally incorporated in an effective
dynamics for one particle as was recently shown by Bray {\it et al}. [Phys.
Rev. E {\bf 67}, 060102 (2003)]. We use this method to compute, in space
dimension , the asymptotic behaviour of the spatial fluctuation,
, for a surviving particle in the perturbative regime,
, for the case of an initially uniform distribution of
particles. We show that, for , with
. By contrast, the fluctuations of paths constrained to return to
their starting point at time grow with the larger exponent 1/3. Numerical
tests are consistent with these predictions.Comment: 10 pages, 5 figure
Microwave magnetoplasmon absorption by a 2DEG stripe
Microwave absorption by a high mobility 2DEG has been investigated
experimentally using sensitive Electron Paramagnetic Resonance cavity
technique. It is found that MW absorption spectra are chiefly governed by
confined magnetoplasmon excitations in a 2DEG stripe. Spectra of the 2D
magnetoplasmons are studied as a function of magnetic field, MW frequency and
carrier density. The electron concentration is tuned by illumination and
monitored using optical photoluminescence technique.Comment: to be published in International Journal of Modern Physics
Enhanced transmission of slit arrays in an extremely thin metallic film
Horizontal resonances of slit arrays are studied. They can lead to an
enhanced transmission that cannot be explained using the single-mode
approximation. A new type of cavity resonance is found when the slits are
narrow for a wavelength very close to the period. It can be excited for very
low thicknesses. Optimization shows these structures could constitute
interesting monochromatic filters
Higgs boson production via vector-like top-partner decays: diphoton or multilepton plus multijets channels at the LHC
We first build a minimal model of vector-like quarks where the dominant Higgs
boson production process at LHC -- the gluon fusion -- can be significantly
suppressed, being motivated by the recent stringent constraints from the search
for direct Higgs production over a wide Higgs mass range. Within this model,
compatible with the present experimental constraints on direct Higgs searches,
we demonstrate that the Higgs () production via a heavy vector-like
top-partner () decay, , , allows to
discover a Higgs boson at the LHC and measure its mass, through the decay
channels or . We also comment on the recent hint
in LHC data from a possible GeV Higgs scalar, in the presence of
heavy vector-like top quarks.Comment: 14 pages, 8 figure
Cascade time-scales for energy and helicity in homogeneous isotropic turbulence
We extend the Kolmogorov phenomenology for the scaling of energy spectra in
high-Reynolds number turbulence, to explicitly include the effect of helicity.
There exists a time-scale for helicity transfer in homogeneous,
isotropic turbulence with helicity. We arrive at this timescale using the
phenomenological arguments used by Kraichnan to derive the timescale
for energy transfer (J. Fluid Mech. {\bf 47}, 525--535 (1971)). We show that in
general may not be neglected compared to , even for rather low
relative helicity. We then deduce an inertial range joint cascade of energy and
helicity in which the dynamics are dominated by in the low wavenumbers
with both energy and helicity spectra scaling as ; and by at
larger wavenumbers with spectra scaling as . We demonstrate how,
within this phenomenology, the commonly observed ``bottleneck'' in the energy
spectrum might be explained. We derive a wavenumber which is less than
the Kolmogorov dissipation wavenumber, at which both energy and helicity
cascades terminate due to dissipation effects. Data from direct numerical
simulations are used to check our predictions.Comment: 14 pages, 5 figures, accepted to Physical Review
Single particle and collective orientational relaxation in an anisotropic liquid near the isotropic-nematic transition
We report molecular dynamics simulation results for the single particle and collective orientational correlations for Gay-Berne fluid of anisotropy parameters κ = 3 and κ' = 5. The following significant results are reported. (i) The decay of collective orientational relaxation of rank two is found to slow down appreciably while approaching the isotropic-nematic (I-N) transition. It eventually becomes even slower than the single particle orientational relaxation of rank one. Surprisingly, even the latter shows a marked slowing down near the I-N transition. (ii) Analysis of the long-time behavior shows a breakdown of the rank dependence predicted by the Debye law in the same region. (iii) An analysis of the memory functions of the orientational time-correlation functions shows that for the collective relaxation surprisingly approaches a Markovian behavior near the I-N transition
The Lived Experience of an In-Season Concussion Amongst NCAA Division I Student-Athletes
International Journal of Exercise Science 7(1) : 62-74, 2014. The clinical presentation and recovery from a sports-related concussion has been well-documented in the sports medicine literature; however, the post-injury experience of the injured individual has been largely unexplored. Therefore, the purpose of this study was to examine collegiate student-athletesâ lived experiences of an in-season concussion. Four NCAA Division I student-athletes who suffered an in-season concussion were interviewed utilizing an existential phenomenological approach to capture the lived experience of the injury. Five major themes developed from the participantsâ experiences: 1) symptoms and emotional response to injury, 2) experiences of concussion testing, 3) fear of failing to meet teammate expectations, 4) support from friends and family, and 5) effect on school. These results provide documented evidence of multiple clinical concerns and anecdotal reports of student-athletes unwillingness to report concussion symptoms, potential dishonesty in reporting post-injury symptoms, negative effects on academic performance, challenges of concussion assessment, and the need to monitor student-athletes activity levels outside athletics. The results of this study can help sports medicine clinicians improve their understanding of the injured student-athleteâs perceptions following an in-season concussion
Optimal estimation for Large-Eddy Simulation of turbulence and application to the analysis of subgrid models
The tools of optimal estimation are applied to the study of subgrid models
for Large-Eddy Simulation of turbulence. The concept of optimal estimator is
introduced and its properties are analyzed in the context of applications to a
priori tests of subgrid models. Attention is focused on the Cook and Riley
model in the case of a scalar field in isotropic turbulence. Using DNS data,
the relevance of the beta assumption is estimated by computing (i) generalized
optimal estimators and (ii) the error brought by this assumption alone. Optimal
estimators are computed for the subgrid variance using various sets of
variables and various techniques (histograms and neural networks). It is shown
that optimal estimators allow a thorough exploration of models. Neural networks
are proved to be relevant and very efficient in this framework, and further
usages are suggested
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