1,489 research outputs found
BIOMECHANICAL ANALYSIS OF STANDING LONG JUMP: A 3D STUDY
Many studies had investigated 2D standing long jump, and some indicated that when jump with optimal load, the jumping performance would be improved. But till now, no study reported the 3D kinetic and kinematic data in standing long jump. The purpose of the study was to compare the kinetic and kinematic difference between restricted arm jump, normal jump, and loaded standing long jump
Degravitation, Inflation and the Cosmological Constant as an Afterglow
In this report, we adopt the phenomenological approach of taking the
degravitation paradigm seriously as a consistent modification of gravity in the
IR, and investigate its consequences for various cosmological situations. We
motivate degravitation-- where Netwon's constant is promoted to a scale
dependent filter function-- as arising from either a small (resonant) mass for
the graviton, or as an effect in semi-classical gravity. After addressing how
the Bianchi identities are to be satisfied in such a set up, we turn our
attention towards the cosmological consequences of degravitation. By
considering the example filter function corresponding to a resonantly massive
graviton (with a filter scale larger than the present horizon scale), we show
that slow roll inflation, hybrid inflation and old inflation remain
quantitatively unchanged. We also find that the degravitation mechanism
inherits a memory of past energy densities in the present epoch in such a way
that is likely significant for present cosmological evolution. For example, if
the universe underwent inflation in the past due to it having tunneled out of
some false vacuum, we find that degravitation implies a remnant `afterglow'
cosmological constant, whose scale immediately afterwards is parametrically
suppressed by the filter scale () in Planck units . We discuss circumstances through which this scenario reasonably
yields the presently observed value for . We also
find that in a universe still currently trapped in some false vacuum state,
resonance graviton models of degravitation only degravitate initially Planck or
GUT scale energy densities down to the presently observed value over timescales
comparable to the filter scale.Comment: To appear in JCAP; sections discussing degravitation as a
semi-classical effect and the modified Bianchi identities adde
Magnetic phase diagram in EuLaFeAs single crystals
We have systematically measured resistivity, susceptibility and specific heat
under different magnetic fields (H) in EuLaFeAs single
crystals. It is found that a metamagnetic transition from A-type
antiferromagnetism to ferromagnetism occurs at a critical field for magnetic
sublattice of . The jump of specific heat is suppressed and shifts to
low temperature with increasing H up to the critical value, then shifts to high
temperature with further increasing H. Such behavior supports the metamagnetic
transition. Detailed H-T phase diagrams for x=0 and 0.15 crystals are given,
and possible magnetic structure is proposed. Magnetoresistance measurements
indicate that there exists a strong coupling between local moment of
and charge in Fe-As layer. These results are very significant to understand the
underlying physics of FeAs superconductors.Comment: 5 pages, 4 figure
Loop Corrections to Cosmological Perturbations in Multi-field Inflationary Models
We investigate one-loop quantum corrections to the power spectrum of
adiabatic perturbation from entropy modes/adiabatic mode cross-interactions in
multiple DBI inflationary models. We find that due to the non-canonical kinetic
term in DBI models, the loop corrections are enhanced by slow-varying parameter
and small sound speed . Thus, in general the loop-corrections
in multi-DBI models can be large. Moreover, we find that the loop-corrections
from adiabatic/entropy cross-interaction vertices are IR finite.Comment: 21 pages, 7 figures; v2, typos corrected, ref added; v3 typos
corrected, version for publishing in jca
Thermodynamic Description of the Relaxation of Two-Dimensional Euler Turbulence Using Tsallis Statistics
Euler turbulence has been experimentally observed to relax to a
metaequilibrium state that does not maximize the Boltzmann entropy, but rather
seems to minimize enstrophy. We show that a recent generalization of
thermodynamics and statistics due to Tsallis is capable of explaining this
phenomenon in a natural way. The maximization of the generalized entropy
for this system leads to precisely the same profiles predicted by the
Restricted Minimum Enstrophy theory of Huang and Driscoll. This makes possible
the construction of a comprehensive thermodynamic description of Euler
turbulence.Comment: 15 pages, RevTe
Equilibrium and nonequilibrium fluctuations at the interface between two fluid phases
We have performed small-angle light-scattering measurements of the static
structure factor of a critical binary mixture undergoing diffusive partial
remixing. An uncommon scattering geometry integrates the structure factor over
the sample thickness, allowing different regions of the concentration profile
to be probed simultaneously. Our experiment shows the existence of interface
capillary waves throughout the macroscopic evolution to an equilibrium
interface, and allows to derive the time evolution of surface tension.
Interfacial properties are shown to attain their equilibrium values quickly
compared to the system's macroscopic equilibration time.Comment: 10 pages, 5 figures, submitted to PR
CMB constraints on noncommutative geometry during inflation
We investigate the primordial power spectrum of the density perturbations
based on the assumption that spacetime is noncommutative in the early stage of
inflation. Due to the spacetime noncommutativity, the primordial power spectrum
can lose rotational invariance. Using the k-inflation model and slow-roll
approximation, we show that the deviation from rotational invariance of the
primordial power spectrum depends on the size of noncommutative length scale
L_s but not on sound speed. We constrain the contributions from the spacetime
noncommutativity to the covariance matrix for the harmonic coefficients of the
CMB anisotropies using five-year WMAP CMB maps. We find that the upper bound
for L_s depends on the product of sound speed and slow-roll parameter.
Estimating this product using cosmological parameters from the five-year WMAP
results, the upper bound for L_s is estimated to be less than 10^{-27} cm at
99.7% confidence level.Comment: 8 pages, 1 figure, References added, Accepted for publication in EPJC
(submitted version
On primordial trispectrum from exchanging scalar modes in general multiple field inflationary models
We make an complementary investigation of the primordial trispectrum from
exchanging intermediate scalar modes in multi-field inflation models with
generalized kinetic terms. Together with the calculation of irreducible
contributions to the primordial trispectrum in Ref.[103], we give the full
leading-order primordial trispectrum in generalized multi-field models.Comment: 15 pages, 1 figure; v2 references adde
Franck-Condon Effect in Central Spin System
We study the quantum transitions of a central spin surrounded by a
collective-spin environment. It is found that the influence of the
environmental spins on the absorption spectrum of the central spin can be
explained with the analog of the Franck-Condon (FC) effect in conventional
electron-phonon interaction system. Here, the collective spins of the
environment behave as the vibrational mode, which makes the electron to be
transitioned mainly with the so-called "vertical transitions" in the
conventional FC effect. The "vertical transition" for the central spin in the
spin environment manifests as, the certain collective spin states of the
environment is favored, which corresponds to the minimal change in the average
of the total spin angular momentum.Comment: 8 pages, 8 figure
Anomalous c-axis charge dynamics in copper oxide materials
Within the t-J model, the c-axis charge dynamics of the copper oxide
materials in the underdoped and optimally doped regimes is studied by
considering the incoherent interlayer hopping. It is shown that the c-axis
charge dynamics is mainly governed by the scattering from the in-plane
fluctuation. In the optimally doped regime, the c-axis resistivity is a linear
in temperatures, and shows the metallic-like behavior for all temperatures,
while the c-axis resistivity in the underdoped regime is characterized by a
crossover from the high temperature metallic-like behavior to the low
temperature semiconducting-like behavior, which are consistent with experiments
and numerical simulations.Comment: 6 pages, Latex, Three figures are adde
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