1,903 research outputs found
BIOMECHANICAL ANALYSIS OF GYMNASTIC BACK HANDSPRING
The purpose of this study is to compare the kinematics and kinetics of back handspring of skilled and non-skilled performers. Eight gymnasts and eight cheerleaders participted in the study. A JVC 9800 DV camera (60 Hz) was synchronized by using a LED light with a Kistler force platform (600 Hz) to collect the data. The results indicated the peak vertical GRF before take-off for gymnasts and cheerleaders are 2.3 BW and 2.19 BW; and the peak horizontal GRF before take-off are 0.67 BW and 0.53 BW respectively; the gymnasts have greater jump height, take-off center of mass (CM) velocity, horizontal CM velocity at hand push off, hip angle at take-off and longer first phase flight time than the cheerleaders. It suggests that the greater jump height and longer flight time are required for good handspring performance
Gravin orchestrates protein kinase A and 2-adrenergic receptor signaling critical for synaptic plasticity and memory
A kinase-anchoring proteins (AKAPs) organize compartmentalized pools of protein kinase A (PKA) to enable localized signaling events within neurons. However, it is unclear which of the many expressed AKAPs in neurons target PKA to signaling complexes important for long-lasting forms of synaptic plasticity and memory storage. In the forebrain, the anchoring protein gravin recruits a signaling complex containing PKA, PKC, calmodulin, and PDE4D (phosphodiesterase 4D) to the β2-adrenergic receptor. Here, we show that mice lacking the α-isoform of gravin have deficits in PKA-dependent long-lasting forms of hippocampal synaptic plasticity including β2-adrenergic receptor-mediated plasticity, and selective impairments of long-term memory storage. Furthermore, both hippocampal β2-adrenergic receptor phosphorylation by PKA, and learning-induced activation of ERK in the CA1 region of the hippocampus are attenuated in mice lacking gravin-α. We conclude that gravin compartmentalizes a significant pool of PKA that regulates learning-induced β2-adrenergic receptor signaling and ERK activation in the hippocampus in vivo, thereby organizing molecular interactions between glutamatergic and noradrenergic signaling pathways for long-lasting synaptic plasticity, and memory storage
High-resolution x-ray study of the nematic - smectic-A and smectic-A - smectic-C transitions in 8barS5-aerosil gels
The effects of dispersed aerosil nanoparticles on two of the phase
transitions of the thermotropic liquid crystal material
4-n-pentylphenylthiol-4'-n-octyloxybenzoate 8barS5 have been studied using
high-resolution x-ray diffraction techniques. The aerosils hydrogen bond
together to form a gel which imposes a weak quenched disorder on the liquid
crystal. The smectic-A fluctuations are well characterized by a two-component
line shape representing thermal and random-field contributions. An elaboration
on this line shape is required to describe the fluctuations in the smectic-C
phase; specifically the effect of the tilt on the wave-vector dependence of the
thermal fluctuations must be explicitly taken into account. Both the magnitude
and the temperature dependence of the smectic-C tilt order parameter are
observed to be unaffected by the disorder. This may be a consequence of the
large bare smectic correlation length in the direction of modulation for this
transition. These results show that the understanding developed for the nematic
to smectic-A transition for octylcyanobiphenyl (8CB) and octyloxycyanobiphenyl
(8OCB) liquid crystals with quenched disorder can be extended to quite
different materials and transitions.Comment: 7 pages, 8 figure
Effective nonlinear optical properties of composite media of graded spherical particles
We have developed a nonlinear differential effective dipole approximation
(NDEDA), in an attempt to investigate the effective linear and third-order
nonlinear susceptibility of composite media in which graded spherical
inclusions with weak nonlinearity are randomly embedded in a linear host
medium. Alternatively, based on a first-principles approach, we derived exactly
the linear local field inside the graded particles having power-law dielectric
gradation profiles. As a result, we obtain also the effective linear dielectric
constant and third-order nonlinear susceptibility. Excellent agreement between
the two methods is numerically demonstrated. As an application, we apply the
NDEDA to investigate the surface plasma resonant effect on the optical
absorption, optical nonlinearity enhancement, and figure of merit of
metal-dielectric composites. It is found that the presence of gradation in
metal particles yields a broad resonant band in the optical region, and further
enhances the figure of merit.Comment: 20 pages, 5 figure
An Improved Shashlyk Calorimeter
Shashlyk electromagnetic calorimeter modules with an energy resolution of
about 3%/sqrt{E (GeV)} for 50-1000 MeV photons has been developed, and a
prototype tested. Details of these improved modules, including mechanical
construction, selection of wave shifting fibers and photo-detectors, and
development of a new scintillator with improved optical and mechanical
properties are described. How the modules will perform in a large calorimeter
was determined from prototype measurements. The experimentally determined
characteristics of the calorimeter prototype show energy resolution of
sigma_E/E=(1.96+-0.1)% \oplus (2.74+-0.05)%/sqrt{E}, time resolution of sigma_T
= (72+-4)/sqrt{E} \oplus (14+-2)/E (ps), where photon energy E is given in GeV
units and \oplus means a quadratic summation. A punch-through inefficiency of
photon detection was measured to be \epsilon = 5*10^{-5} (\Theta >5 mrad).Comment: 29 pages, 21 figure
Correlations in Ising chains with non-integrable interactions
Two-spin correlations generated by interactions which decay with distance r
as r^{-1-sigma} with -1 <sigma <0 are calculated for periodic Ising chains of
length L. Mean-field theory indicates that the correlations, C(r,L), diminish
in the thermodynamic limit L -> \infty, but they contain a singular structure
for r/L -> 0 which can be observed by introducing magnified correlations,
LC(r,L)-\sum_r C(r,L). The magnified correlations are shown to have a scaling
form F(r/L) and the singular structure of F(x) for x->0 is found to be the same
at all temperatures including the critical point. These conclusions are
supported by the results of Monte Carlo simulations for systems with sigma
=-0.50 and -0.25 both at the critical temperature T=Tc and at T=2Tc.Comment: 13 pages, latex, 5 eps figures in a separate uuencoded file, to
appear in Phys.Rev.
Measuring non-extensitivity parameters in a turbulent Couette-Taylor flow
We investigate probability density functions of velocity differences at
different distances r measured in a Couette-Taylor flow for a range of Reynolds
numbers Re. There is good agreement with the predictions of a theoretical model
based on non-extensive statistical mechanics (where the entropies are
non-additive for independent subsystems). We extract the scale-dependent
non-extensitivity parameter q(r, Re) from the laboratory data.Comment: 8 pages, 5 figure
Variational approach to a class of nonlinear oscillators with several limit cycles
We study limit cycles of nonlinear oscillators described by the equation
. Depending on the nonlinearity this equation
may exhibit different number of limit cycles.
We show that limit cycles correspond to relative extrema of a certain
functional. Analytical results in the limits and are
in agreement with previously known criteria. For intermediate numerical
determination of the limit cycles can be obtained.Comment: 12 pages, 3 figure
Understanding the and with Sum Rules in HQET
In the framework of heavy quark effective theory we use QCD sum rules to
calculate the masses of the and excited
states. The results are consistent with that the states and
observed by BABAR and CLEO are the and states in the
doublet
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