3,779 research outputs found
Student-Athletes\u27 Perceptions of Athletic Trainers
The purpose of this study is to look at the perceptions student-athletes at Southern Illinois University have about their athletic trainers. Data was collected from 86 student-athletes at a NCAA Division I, mid-major university. The participants were administered an 11-question perception questionnaire. The perceptions scores of student-athletes with a full-time athletic trainer were compared to student-athletes with a graduate assistant athletic trainer. The results showed that both groups had a high mean perception score with no significant difference. The mean perception score for all 86 student-athletes was 28.14 (SD = 2.49) out of a total score of 33. Student-athletes with a full-time athletic trainer averaged 28.95 (SD = 2.45) while student-athletes with a graduate assistant athletic trainer averaged 27.53 (SD = 2.36). This study can lead to futher investigation of student-athletes perceptions of athletic trainers especially the differences between full-time and graduate assistant athletic trainers
Response Surface Modeling of Rim Phase Shift Masks
The use of statistically designed experiments provide an efficient method of investigating a lithographic process. Lithographic simulators have also been used as a tool in the investigation of these processes. This paper provides a general methodology for conducting designed experiments in which a computer simulator is the tool used as the data collection device. The rim shifter is a phase shifting technique that was investigated. Response surfaces measuring depth of focus were generated from simulated data. The resolution and depth of focus capabilities of this phase shift technique were also measured by both experimental and simulated data
XROMM analysis of tooth occlusion and temporomandibular joint kinematics during feeding in juvenile miniature pigs
Like humans, domestic pigs are omnivorous and thus are a common model for human masticatory function. Prior attempts to characterize food–tooth interactions and jaw movements associated with mastication have been limited to aspects of the oral apparatus that are visible externally (with videography) and/or to 2D movements of oral structures (with monoplanar videofluoroscopy). We used XROMM, a 3D technique that combines CT-based morphology with biplanar videofluoroscopy, to quantify mandibular kinematics, tooth occlusion and mandibular condylar displacements within the temporomandibular joint (TMJ) during feeding. We observed that the pig TMJ moved detectably in only three of six possible degrees of freedom during mastication: two rotations, pitch and yaw; and one translation, protraction–retraction. Asymmetrical yaw around a dorsoventral axis produced the observed alternating left–right chewing cycles responsible for food reduction. Furthermore, the relative motions of the upper and lower premolars contained a substantial mesiodistal component in addition to the buccolingual component, resulting in an oblique (rather than a strictly transverse) power stroke. This research demonstrates the capacity of XROMM to explore the kinematic underpinnings of key masticatory movements, such as the occlusal power stroke, by integrating tooth, joint and rigid body jaw movements. XROMM also allowed us to test kinematic hypotheses based on skeletal anatomy with actual kinematics observed during naturalistic feeding behaviors. We observed that the soft tissue structures of the TMJ appear to play a significant role in limiting the range of motion of a joint, and thus analyses based solely on osseous morphology may over-estimate joint mobility
The Fourth BATSE Gamma-Ray Burst Catalog (Revised)
The Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray
Observatory (CGRO) has triggered on 1637 cosmic gamma-ray bursts between 1991
April 19 and 1996 August 29. These events constitute the Fourth BATSE burst
catalog. The current version (4Br) has been revised from the version first
circulated on CD-ROM in September 1997 (4B) to include improved locations for a
subset of bursts that have been reprocssed using additional data. A significant
difference from previous BATSE catalogs is the inclusion of bursts from periods
when the trigger energy range differed from the nominal 50-300 keV. We present
tables of the burst occurrence times, locations, peak fluxes, fluences, and
durations. In general, results from previous BATSE catalogs are confirmed here
with greater statistical significance.Comment: 45 pages, 12 Postscript figures, accepted for publication in Ap. J.
Supp
The Opacity of Nearby Galaxies from Counts of Background Galaxies: II. Limits of the Synthetic Field Method
Recently, we have developed and calibrated the Synthetic Field Method (SFM)
to derive the total extinction through disk galaxies. The method is based on
the number counts and colors of distant background field galaxies that can be
seen through the foreground object, and has been successfully applied to NGC
4536 and NGC 3664, two late-type galaxies located, respectively, at 16 and 11
Mpc. Here, we study the applicability of the SFM to HST images of galaxies in
the Local Group, and show that background galaxies cannot be easily identified
through these nearby objects, even with the best resolution available today. In
the case of M 31, each pixel in the HST images contains 50 to 100 stars, and
the background galaxies cannot be seen because of the intrinsic granularity due
to strong surface brightness fluctuations. In the LMC, on the other hand, there
is only about one star every six linear pixels, and the lack of detectable
background galaxies results from a ``secondary'' granularity, introduced by
structure in the wings of the point spread function. The success of the SFM in
NGC 4536 and NGC 3664 is a natural consequence of the reduction of the
intensity of surface brightness fluctuations with distance. When the dominant
confusion factor is structure in the PSF wings, as is the case of HST images of
the LMC, and would happen in M 31 images obtained with a 10-m diffraction-
limited optical telescope, it becomes in principle possible to improve the
detectability of background galaxies by subtracting the stars in the foreground
object. However, a much better characterization of optical PSFs than is
currently available would be required for an adequate subtraction of the wings.
Given the importance of determining the dust content of Local Group galaxies,
efforts should be made in that direction.Comment: 45 pages, 10 Postscript figure
Luminous Satellites of Early-Type Galaxies I: Spatial Distribution
We study the spatial distribution of faint satellites of intermediate
redshift (0.1<z<0.8), early-type galaxies, selected from the GOODS fields. We
combine high resolution HST images and state-of-the-art host subtraction
techniques to detect satellites of unprecedented faintness and proximity to
intermediate redshift host galaxies (up to 5.5 magnitudes fainter and as close
as 0."5/2.5 kpc to the host centers). We model the spatial distribution of
objects near the hosts as a combination of an isotropic, homogenous
background/foreground population and a satellite population with a power law
radial profile and an elliptical angular distribution. We detect a significant
population of satellites, Ns =1.7 (+0.9,-0.8) that is comparable to the number
of Milky Way satellites with similar host-satellite contrast.The average
projected radial profile of the satellite distribution is isothermal, gamma_p=
-1.0(+0.3,-0.4), which is consistent with the observed central mass density
profile of massive early-type galaxies. Furthermore, the satellite distribution
is highly anisotropic (isotropy is ruled out at a >99.99% confidence level).
Defining phi to be the offset between the major axis of the satellite spatial
distribution and the major axis of the host light profile, we find a maximum
posterior probability of phi = 0 and |phi| less than 42 degrees at the 68%
confidence level. The alignment of the satellite distribution with the light of
the host is consistent with simulations, assuming that light traces mass for
the host galaxy as observed for lens galaxies. The anisotropy of the satellite
population enhances its ability to produce the flux ratio anomalies observed in
gravitationally lensed quasars.Comment: 21 pages, 16 figures, Accepted for publication in Ap
The non-Gaussian tail of cosmic-shear statistics
Due to gravitational instability, an initially Gaussian density field
develops non-Gaussian features as the Universe evolves. The most prominent
non-Gaussian features are massive haloes, visible as clusters of galaxies. The
distortion of high-redshift galaxy images due to the tidal gravitational field
of the large-scale matter distribution, called cosmic shear, can be used to
investigate the statistical properties of the LSS. In particular, non-Gaussian
properties of the LSS will lead to a non-Gaussian distribution of cosmic-shear
statistics. The aperture mass () statistics, recently introduced as
a measure for cosmic shear, is particularly well suited for measuring these
non-Gaussian properties. In this paper we calculate the highly non-Gaussian
tail of the aperture mass probability distribution, assuming Press-Schechter
theory for the halo abundance and the `universal' density profile of haloes as
obtained from numerical simulations. We find that for values of
much larger than its dispersion, this probability distribution is closely
approximated by an exponential, rather than a Gaussian. We determine the
amplitude and shape of this exponential for various cosmological models and
aperture sizes, and show that wide-field imaging surveys can be used to
distinguish between some of the currently most popular cosmogonies. Our study
here is complementary to earlier cosmic-shear investigations which focussed
more on two-point statistical properties.Comment: 9 pages, 5 figures, submitted to MNRA
Unstable states in QED of strong magnetic fields
We question the use of stable asymptotic scattering states in QED of strong
magnetic fields. To correctly describe excited Landau states and photons above
the pair creation threshold the asymptotic fields are chosen as generalized
Licht fields. In this way the off-shell behavior of unstable particles is
automatically taken into account, and the resonant divergences that occur in
scattering cross sections in the presence of a strong external magnetic field
are avoided. While in a limiting case the conventional electron propagator with
Breit-Wigner form is obtained, in this formalism it is also possible to
calculate -matrix elements with external unstable particles.Comment: Revtex, 7 pages. To appear in Phys. Rev. D53(2
Confirmation of Two Cyclotron Lines in Vela X-1
We present pulse phase-resolved X-ray spectra of the high mass X-ray binary
Vela X-1 using the Rossi X-ray Timing Explorer. We observed Vela X-1 in 1998
and 2000 with a total observation time of ~90 ksec. We find an absorption
feature at 23.3 +1.3 -0.6 kev in the main pulse, that we interpret as the
fundamental cyclotron resonant scattering feature (CRSF). The feature is
deepest in the rise of the main pulse where it has a width of 7.6 +4.4 -2.2 kev
and an optical depth of 0.33 +0.06 -0.13. This CRSF is also clearly detected in
the secondary pulse, but it is far less significant or undetected during the
pulse minima. We conclude that the well known CRSF at 50.9 +0.6 -0.7 kev, which
is clearly visible even in phase-averaged spectra, is the first harmonic and
not the fundamental. Thus we infer a magnetic field strength of B=2.6 x 10^12
G.Comment: 12 pages, LaTeX, 15 Figures, accepted by A&
GaBoDS: The Garching-Bonn Deep Survey -- I. Anatomy of galaxy clusters in the background of NGC 300
The Garching-Bonn Deep Survey (GaBoDS) is a virtual 12 square degree cosmic
shear and cluster lensing survey, conducted with the [email protected] MPG/ESO telescope
at La Silla. It consists of shallow, medium and deep random fields taken in
R-band in subarcsecond seeing conditions at high galactic latitude. A
substantial amount of the data was taken from the ESO archive, by means of a
dedicated ASTROVIRTEL program.
In the present work we describe the main characteristics and scientific goals
of GaBoDS. Our strategy for mining the ESO data archive is introduced, and we
comment on the Wide Field Imager data reduction as well. In the second half of
the paper we report on clusters of galaxies found in the background of NGC 300,
a random archival field. We use weak gravitational lensing and the red cluster
sequence method for the selection of these objects. Two of the clusters found
were previously known and already confirmed by spectroscopy. Based on the
available data we show that there is significant evidence for substructure in
one of the clusters, and an increasing fraction of blue galaxies towards larger
cluster radii. Two other mass peaks detected by our weak lensing technique
coincide with red clumps of galaxies. We estimate their redshifts and masses.Comment: 20 pages, 16 figures, gzipped. An online postscript version with
higher quality figures (3.3 MBytes) can be downloaded from
http://www.mpa-garching.mpg.de/~mischa/ngc300/ngc300.ps.gz . Submitted to A&
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