5,951 research outputs found
Application of dispersion relations to low-energy meson-nucleon scattering
Relativistic dispersion relations are used to derive equations for low-energy S-, P-, and D-wave meson-nucleon scattering under the assumption that the (3,3) resonance dominates the dispersion integrals. The P-wave equations so obtained differ only slightly from those of the static fixed-source theory. The conclusions of the static theory are re-examined in the light of their new derivation
Performance analysis of the Malaysian elite youth squash players
This study analysed the frequencies and court locations of squash strokes performed by elite Malaysian youth players before and during a national tournament. One hundred and seventy nine matches participated by six players (three men and three women) were analysed. Data collected via video recordings and coded post match using Studiocode® analysis software. The straight and cross court drives were the most frequent strokes used by both genders, with more on the backhand side. The drop shot and straight drives contributed to most winners for the men and women respectively. Most winners were produced by the players when they occupied the middle areas of the court. The areas that resulted most errors were the four corners of the court for the men whilst the women was on their backhand side areas. Objective feedback on the performance prior to a major competition provided some positive results.Keywords: performance analysis, squash, youth
Electromyography - A Reliable Technique for Muscle Activity Assessment
In recent years, many questions have been raised on the credibility of Electromyography (EMG) as a technique to evaluate muscle activity, particularly by sports and fitness community. This questioning goes farther when it comes to surface electromyography (sEMG). This paper covers an overview of EMG, addresses some basic concepts and provide rudiment for research. Muscle activity assessment through EMG has been reviewed in terms of the type of movements. There are few limitations to EMG but these confines are addressable. The problem rather lies in the interpretation and generalization of that data. Limitations are there in every technology, precautionary measures must be taken to avoid those while using it. Reservations about EMG have been summarized along with their responses. A few techniques to analyze EMG data, and possibilities to extrapolate and interpret, are also provided. Current perspectives and practical applications of EMG and sEMG are also part of this article
Mushroom-Shaped Structures as Tracers of Buoyant Flow in the Galactic Disk
Recent HI emission observations of the Southern Galactic hemisphere have
revealed a mushroom-like structure extending from z=-70 to -450 pc, composed of
a stem and a cap. Similar structures occur in three-dimensional simulations of
a dynamic galactic disk driven by isolated and clustered supernovae. Using
these simulations, we show that hot gas in the Galactic disk that is not
evacuated through chimneys expands into the cooler gas of the thick disk,
forming mushroom-shaped structures. This new class of objects traces buoyant
flow of hot gas into the thick disk.Comment: Accepted for publication in ApJ Letters. Latex manuscript, 3 figures
(4 postsript files
Bound States and Threshold Resonances in Quantum Wires with Circular Bends
We study the solutions to the wave equation in a two-dimensional tube of unit
width comprised of two straight regions connected by a region of constant
curvature. We introduce a numerical method which permits high accuracy at high
curvature. We determine the bound state energies as well as the transmission
and reflection matrices, and and focus on the nature of
the resonances which occur in the vicinity of channel thresholds. We explore
the dependence of these solutions on the curvature of the tube and angle of the
bend and discuss several limiting cases where our numerical results confirm
analytic predictions.Comment: 24 pages, revtex file, one style file and 17 PostScript figures
include
Gate-controlled Guiding of Electrons in Graphene
Ballistic semiconductor structures have allowed the realization of
optics-like phenomena in electronics, including magnetic focusing and lensing.
An extension that appears unique to graphene is to use both n and p carrier
types to create electronic analogs of optical devices having both positive and
negative indices of refraction. Here, we use gate-controlled density with both
p and n carrier types to demonstrate the analog of the fiber-optic guiding in
graphene. Two basic effects are investigated: (1) bipolar p-n junction guiding,
based on the principle of angle-selective transmission though the graphene p-n
interface, and (2) unipolar fiber-optic guiding, using total internal
reflection controlled by carrier density. Modulation of guiding efficiency
through gating is demonstrated and compared to numerical simulations, which
indicates that interface roughness limits guiding performance, with
few-nanometer effective roughness extracted. The development of p-n and
fiber-optic guiding in graphene may lead to electrically reconfigurable wiring
in high-mobility devices.Comment: supplementary materal at
http://marcuslab.harvard.edu/papers/OG_SI.pd
The Multi-Colored Hot Interstellar Medium of "The Antennae" Galaxies (NGC 4038/39)
We report the results of the analysis of the extended soft emission
discovered in the Chandra ACIS pointing at the merging system NGC 4038/39 (the
Antennae). We present a `multi-color' X-ray image that suggests both extensive
absorption by the dust in this system, peaking in the contact region, as well
as variations in the temperature of different emitting regions of the hot
interstellar medium (ISM). Spectral fits to multi-component thermal emission
models confirm this picture and give a first evaluation of the parameters of
the hot plasma. We compare the diffuse X-ray emission with radio continuum
(6cm), HI, CO, and H images to take a first look at the multi-phase ISM
of the Antennae galaxies. We find that the hot (X-ray) and cold (CO) gas have
comparable thermal pressures in the two nuclear regions. We also conclude that
the displacement between the peak of the diffuse X-ray emission in the north of
the galaxy system, towards the inner regions of the northern spiral arm (as
defined by H, radio continuum and HI), could result from ram pressure
of infalling HI clouds.Comment: Accepted by Ap
Multiple Reggeon Exchange from Summing QCD Feynman Diagrams
Multiple reggeon exchange supplies subleading logs that may be used to
restore unitarity to the Low-Nussinov Pomeron, provided it can be proven that
the sum of Feynman diagrams to all orders gives rise to such multiple regge
exchanges. This question cannot be easily tackled in the usual way except for
very low-order diagrams, on account of delicate cancellations present in the
sum which necessitate individual Feynman diagrams to be computed to subleading
orders. Moreover, it is not clear that sums of high-order Feynman diagrams with
complicated criss-crossing of lines can lead to factorization implied by the
multi-regge scenario. Both of these difficulties can be overcome by using the
recently developed nonabelian cut diagrams. We are then able to show that the
sum of -channel-ladder diagrams to all orders does lead to such multiple
reggeon exchanges.Comment: uu-encoded latex file with 11 postscript figures (20 pages
Rap1-mediated nuclear factor-kappaB (NF-κB) activity regulates the paracrine capacity of mesenchymal stem cells in heart repair following infarction
published_or_final_versio
9.7 um Silicate Features in AGNs: New Insights into Unification Models
We describe observations of 9.7 um silicate features in 97 AGNs, exhibiting a
wide range of AGN types and of X-ray extinction toward the central nuclei. We
find that the strength of the silicate feature correlates with the HI column
density estimated from fitting the X-ray data, such that low HI columns
correspond to silicate emission while high columns correspond to silicate
absorption. The behavior is generally consistent with unification models where
the large diversity in AGN properties is caused by viewing-angle-dependent
obscuration of the nucleus. Radio-loud AGNs and radio-quiet quasars follow
roughly the correlation between HI columns and the strength of the silicate
feature defined by Seyfert galaxies. The agreement among AGN types suggests a
high-level unification with similar characteristics for the structure of the
obscuring material. We demonstrate the implications for unification models
qualitatively with a conceptual disk model. The model includes an inner
accretion disk (< 0.1 pc in radius), a middle disk (0.1-10 pc in radius) with a
dense diffuse component and with embedded denser clouds, and an outer clumpy
disk (10-300 pc in radius).Comment: Accepted for publication in ApJ, 14 pages, 5 figures. The on-line
table is available at http://cztsy.as.arizona.edu/~yong/silicate_tab1.pd
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