1,971 research outputs found
Acute Effects Of The Mid-thigh Power Clean On The Advanced Tennis Serve
Post-activation potentiation (PAP) is a phenomenon in which athletic performance is acutely enhanced after a muscle contraction (evoked or voluntary). Most studies have examined isometric maximal voluntary contraction and heavy resistance exercise as PAP inducing protocols, but minimal research exists analyzing Olympic lifting exercises. The purpose of this study was to investigate the acute PAP response of mid-thigh power clean on the tennis serve among NCAA Division I male tennis players. Tennis players (n=6) who were current roster members performed 5 tennis serves before and 4 min after one set of 5 repetitions of the mid-thigh power clean exercise at 60% 1RM. Performance was evaluated by measuring (pre and post) peak velocity [F (1, 57)=1.456, p=.232], peak power [F (1, 57)= 0.799, p=.375], total power output [F (1, 57) = 0.748, p=.391], impulse [F (1, 58) = 3.163, p=.081], and rate of force development [F (1, 58) = 0.531, p=.469]. There were no significant differences in any of the outcomes indicating there was no evidence of a PAP. Further research is needed to study the possible applicability of Olympic lifting to induce PAP effects on tennis players. It appears that the effective application of PAP inducing exercises appears to be highly individualized. Thus, the use of PAP complexes in tennis athletes should consider both the absolute and relative strength of each athlete in conjunction with the length of the rest period when attempting to optimize the PAP response using an Olympic lifting exercise
Absorption in quantum electrodynamics cavities in terms of a quantum jump operator
We describe the absorption by the walls of a quantum electrodynamics cavity
as a process during which the elementary excitations (photons) of an internal
mode of the cavity exit by tunneling through the cavity walls. We estimate by
classical methods the survival time of a photon inside the cavity and the
quality factor of its mirrors
IRIS Observations of Spicules and Structures Near the Solar Limb
We have analyzed IRIS spectral and slit-jaw observations of a quiet region
near the South Pole. In this article we present an overview of the
observations, the corrections, and the absolute calibration of the intensity.
We focus on the average profiles of strong (Mg ii h and k, C ii and Si iv), as
well as of weak spectral lines in the near ultraviolet (NUV) and the far
ultraviolet (FUV), including the Mg ii triplet, thus probing the solar
atmosphere from the low chromosphere to the transition region. We give the
radial variation of bulk spectral parameters as well as line ratios and
turbulent velocities. We present measurements of the formation height in lines
and in the NUV continuum, from which we find a linear relationship between the
position of the limb and the intensity scale height. We also find that low
forming lines, such as the Mg ii triplet, show no temporal variations above the
limb associated with spicules, suggesting that such lines are formed in a
homogeneous atmospheric layer and, possibly, that spicules are formed above the
height of 2 arc sec. We discuss the spatio-temporal structure near the limb
from images of intensity as a function of position and time. In these images,
we identify p-mode oscillations in the cores of lines formed at low heights
above the photosphere, slow moving bright features in O i and fast moving
bright features in C ii. Finally, we compare the Mg ii k and h line profiles,
together with intensity values of the Balmer lines from the literature, with
computations from the PROM57Mg non-LTE model developed at the Institut
d'Astrophysique Spatiale and estimated values of the physical parameters. We
obtain electron temperatures in the range of K at small heights to
K at large heights, electron densities from to
cm and a turbulent velocity of km/s.Comment: Accepted for publication in Solar Physic
Optical determination and identification of organic shells around nanoparticles: application to silver nanoparticles
We present a simple method to prove the presence of an organic shell around
silver nanoparticles. This method is based on the comparison between optical
extinction measurements of isolated nanoparticles and Mie calculations
predicting the expected wavelength of the Localized Surface Plasmon Resonance
of the nanoparticles with and without the presence of an organic layer. This
method was applied to silver nanoparticles which seemed to be well protected
from oxidation. Further experimental characterization via Surface Enhanced
Raman Spectroscopy (SERS) measurements allowed to identify this protective
shell as ethylene glycol. Combining LSPR and SERS measurements could thus give
proof of both presence and identification for other plasmonic nanoparticles
surrounded by organic shells
Nonlinear viscous damping and tuned mass damper design for occupant comfort in flexible tall buildings subjected to wind loading
During wind events, tall buildings may exhibit floor accelerations levels that compromise occupant comfort. The use of energy dissipating devices to reduce peak floor accelerations is a sound strategy to improve building performance. The estimation of mean peak floor accelerations of a steel-frame building subjected to random wind forces and the design procedure of supplemental nonlinear viscous dampers to improve occupant comfort in one-year recurrence wind events are described in this paper. A stochastic wind load model is developed to estimate acceleration performance; drag, lift and torsional moments at each story are defined as random stationary processes by the definition of their cross-spectral density matrix. Wind tunnel results and computational fluid dynamic analyses are used to fine-tune the stochastic load models. Reduced-order structural models of the tower are developed to estimate the frequency response function from floor loadings to floor accelerations at corners points of the buildings. Statistical linearization is used to estimate the performance of the buildings with non-linear viscous dampers installed in different configurations. Floor acceleration reductions achieved with supplemental viscous dampers and a tuned mass damper are evaluated to comply with occupant performance standards.Publicado en: Mecánica Computacional vol. XXXV, no. 12Facultad de IngenierÃ
Nonlinear viscous damping and tuned mass damper design for occupant comfort in flexible tall buildings subjected to wind loading
During wind events, tall buildings may exhibit floor accelerations levels that compromise occupant comfort. The use of energy dissipating devices to reduce peak floor accelerations is a sound strategy to improve building performance. The estimation of mean peak floor accelerations of a steel-frame building subjected to random wind forces and the design procedure of supplemental nonlinear viscous dampers to improve occupant comfort in one-year recurrence wind events are described in this paper. A stochastic wind load model is developed to estimate acceleration performance; drag, lift and torsional moments at each story are defined as random stationary processes by the definition of their cross-spectral density matrix. Wind tunnel results and computational fluid dynamic analyses are used to fine-tune the stochastic load models. Reduced-order structural models of the tower are developed to estimate the frequency response function from floor loadings to floor accelerations at corners points of the buildings. Statistical linearization is used to estimate the performance of the buildings with non-linear viscous dampers installed in different configurations. Floor acceleration reductions achieved with supplemental viscous dampers and a tuned mass damper are evaluated to comply with occupant performance standards.Publicado en: Mecánica Computacional vol. XXXV, no. 12Facultad de IngenierÃ
On the Effect of Adjacent Sector Multiple Access Interference on Space Time Spreading Systems
Space Time Spreading systems are proposed as a method to enhance communications between the Base Station (BS) and Mobile Station (MS) by using multiple transmit antennas at the Base Station. This provides a form of transmit diversity when there are more than one transmitting antennas. Space Time Spreading systems have been shown to be efficient in their use of the limited number of orthogonal spreading sequences and to provide a diversity gain, which in the case of two transmitter antennas at the BS and one receiving antenna at the MS, is of order two. The paper looks at the effect of unsynchronized adjacent cell interference caused by scatterers causing the target MS to experience Multiple Access Interference (MAI) due to misaligned orthogonal codes from adjacent sectors in a sectorised cell (with 120 degree sectorisation). The study finds that adjacent MAI does adversely influence the Bit Error Rate (BER) of the target MS
Nonlinear viscous damping and tuned mass damper design for occupant comfort in flexible tall buildings subjected to wind loading
During wind events, tall buildings may exhibit floor accelerations levels that compromise occupant comfort. The use of energy dissipating devices to reduce peak floor accelerations is a sound strategy to improve building performance. The estimation of mean peak floor accelerations of a steel-frame building subjected to random wind forces and the design procedure of supplemental nonlinear viscous dampers to improve occupant comfort in one-year recurrence wind events are described in this paper. A stochastic wind load model is developed to estimate acceleration performance; drag, lift and torsional moments at each story are defined as random stationary processes by the definition of their cross-spectral density matrix. Wind tunnel results and computational fluid dynamic analyses are used to fine-tune the stochastic load models. Reduced-order structural models of the tower are developed to estimate the frequency response function from floor loadings to floor accelerations at corners points of the buildings. Statistical linearization is used to estimate the performance of the buildings with non-linear viscous dampers installed in different configurations. Floor acceleration reductions achieved with supplemental viscous dampers and a tuned mass damper are evaluated to comply with occupant performance standards.Publicado en: Mecánica Computacional vol. XXXV, no. 12Facultad de IngenierÃ
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