1,939 research outputs found
Can conventional forces really explain the anomalous acceleration of Pioneer 10/11 ?
A conventional explanation of the correlation between the Pioneer 10/11
anomalous acceleration and spin-rate change is given. First, the rotational
Doppler shift analysis is improved. Finally, a relation between the radio beam
reaction force and the spin-rate change is established. Computations are found
in good agreement with observational data. The relevance of our result to the
main Pioneer 10/11 anomalous acceleration is emphasized. Our analysis leads us
to conclude that the latter may not be merely artificial.Comment: 9 pages, no figur
Axes determination for segmented true-coaxial HPGe detectors
A fast method to determine the crystallographic axes of segmented
true-coaxial high-purity germanium detectors is presented. It is based on the
analysis of segment-occupancy patterns obtained by irradiation with radioactive
sources. The measured patterns are compared to predictions for different axes
orientations. The predictions require a simulation of the trajectories of the
charge carriers taking the transverse anisotropy of their drift into account.Comment: 18 pages, 1 table, 31 figures; included background contribution to
the occupancy patterns and systematic uncertainties, results slightly change
A search for solar-like oscillations in the Am star HD 209625
The goal is to test the structure of hot metallic stars, and in particular
the structure of a near-surface convection zone using asteroseismic
measurements. Indeed, stellar models including a detailed treatement of the
radiative diffusion predict the existence of a near-surface convection zone in
order to correctly reproduce the anomalies in surface abundances that are
observed in Am stars. The Am star HD 209625 was observed with the Harps
spectrograph mounted on the 3.6-m telescope at the ESO La Silla Observatory
(Chile) during 9 nights in August 2005. This observing run allowed us to
collect 1243 radial velocity (RV) measurements, with a standard deviation of
1.35 m/s. The power spectrum associated with these RV measurements does not
present any excess. Therefore, either the structure of the external layers of
this star does not allow excitation of solar-like oscillations, or the
amplitudes of the oscillations remain below 20-30 cm/s (depending on their
frequency range).Comment: 5 pages, 4 figures, A&A accepte
On the photoproduction of jets at HERA
We discuss the inclusive jet production at HERA in the next-to-leading
logarithm approximation. Theoretical uncertainties are considered in some
details. We show the importance of the jet rapidity distribution to constrain
the parton densities in the photon. A comparison is made with the recent H1
data.Comment: 10 + 7 figures included uuencoded tar-compressed
([email protected]) , ENSLAPP-A-484/94, LPTHE Orsay 94-8
The Chromospheric Activity and Ages of M Dwarf Stars in Wide Binary Systems
We investigate the relationship between age and chromospheric activity for
139 M dwarf stars in wide binary systems with white dwarf companions. The age
of each system is determined from the cooling age of its white dwarf component.
The current limit for activity-age relations found for M dwarfs in open
clusters is 4 Gyr. Our unique approach to finding ages for M stars allows for
the exploration of this relationship at ages older than 4 Gyr. The general
trend of stars remaining active for a longer time at later spectral type is
confirmed. However, our larger sample and greater age range reveals additional
complexity in assigning age based on activity alone. We find that M dwarfs in
wide binaries older than 4 Gyr depart from the log-linear relation for clusters
and are found to have activity at magnitudes, colors and masses which are
brighter, bluer and more massive than predicted by the cluster relation. In
addition to our activity-age results, we present the measured radial velocities
and complete space motions for 161 white dwarf stars in wide binaries.Comment: 22 pages including 9 figures and 5 tables. Accepted for publication
in The Astronomical Journa
Sport-Specific Differences in Dynamic Visual Acuity and Gaze Stabilization in Division-I Collegiate Athletes
BACKGROUND: The vestibular-ocular reflex (VOR) integrates the vestibular and ocular systems to maintain gaze during head motion. This reflex is often negatively affected following sport-related concussion. Objective measures of gaze stability, a function mediated by the VOR, such as the computerized dynamic visual acuity test (DVAT) and gaze stabilization test (GST), may have utility in concussion management. However, normative data specific to sport, sex, or concussion history have not been established in collegiate athletes.
OBJECTIVE: The objective of this study was to establish normative values for the DVAT and GST in collegiate athletes and explore the effect of sport, sex, and concussion history on VOR assessments.
METHODS: The DVAT and GST were completed by 124 collegiate athletes (72 male, 52 female, mean±SD, age: 19.71±1.74 years, height: 173.99±13.97 cm, weight: 80.06±26.52 kg) recruited from Division-I athletic teams (football, soccer and cheerleading). The DVAT and GST were performed in the rightward and leftward directions during a single session in a standardized environment. Normative values for DVAT and GST measures were expressed as percentiles. Non-parametric statistics were used to compare differences between groups based on sex, sport, and concussion history. Alpha was set a-priori at 0.05.
RESULTS: Overall, the median LogMAR unit for 124 athletes completing the DVAT was 0 (IQR = 0.17) for both leftward and rightward. The median velocities achieved on the GST were 145 °/sec and 150 °/sec (IQR = 45 and 40) for the leftward and rightward directions respectively. Significant differences were observed between sports (p = 0.001-0.17) for the GST with cheerleading demonstrating higher velocities than the other sports. However, no significant differences were identified based on sex (p≥0.09) or history of concussion (p≥0.15).
CONCLUSIONS: Normative estimates for the DVAT and GST may assist in the clinical interpretation of outcomes when used in post-concussion evaluation for collegiate athletes. Although sex and previous concussion history had no effect on the DVAT or GST, performance on these measures may be influenced by type of sport. Sport-related differences in the GST may reflect VOR adaptations based on individual sport-specific demands
The O-type eclipsing binary SZ Cam revisited
We analyse new spectra of the multiple system SZ Cam because previous studies
found different values of the primary radial velocity amplitude. The older
solutions of light curves also have different ratios of secondary to primary
luminosity as inferred from the observed equivalent widths of spectral lines.
We therefore reanalyse the light curves of the eclipsing pair. Only the light
curve derived by Wesselink has a solution that agrees with the observed
equivalent width ratio. The resulting parameters of the binary are discussed.
Masses of and M, and radii and
R are derived. We point out that radial velocities measured
with the CCF method can be misleading when the method is applied to multiple
systems with complex line blends. New radial velocities are also obtained for
the visual component ADS 2984 A (HD 25639).Comment: Astronomy and Astrophysics, accepte
Large-Mass Ultra-Low Noise Germanium Detectors: Performance and Applications in Neutrino and Astroparticle Physics
A new type of radiation detector, a p-type modified electrode germanium
diode, is presented. The prototype displays, for the first time, a combination
of features (mass, energy threshold and background expectation) required for a
measurement of coherent neutrino-nucleus scattering in a nuclear reactor
experiment. The device hybridizes the mass and energy resolution of a
conventional HPGe coaxial gamma spectrometer with the low electronic noise and
threshold of a small x-ray semiconductor detector, also displaying an intrinsic
ability to distinguish multiple from single-site particle interactions. The
present performance of the prototype and possible further improvements are
discussed, as well as other applications for this new type of device in
neutrino and astroparticle physics (double-beta decay, neutrino magnetic moment
and WIMP searches).Comment: submitted to Phys. Rev.
Signals for Vector Leptoquarks in Hadronic Collisions
We analyze systematically the signatures of vector leptoquarks in hadronic
collisions. We examine their single and pair productions, as well as their
effects on the production of lepton pairs. Our results indicate that a machine
like the CERN Large Hadron Collider (LHC) will be able to unravel the existence
of vector leptoquarks with masses up to the range of -- TeV.Comment: 15 pages and 5 figures (available upon request or through anonymous
ftp), revtex3, IFUSP-P 108
Experimental Evidence for Simple Relations between Unpolarized and Polarized Parton Distributions
The Pauli exclusion principle is advocated for constructing the proton and
neutron deep inelastic structure functions in terms of Fermi-Dirac
distributions that we parametrize with very few parameters. It allows a fair
description of the recent NMC data on and at
, as well as the CCFR neutrino data at and . We
also make some reasonable and simple assumptions to relate unpolarized and
polarized quark parton distributions and we obtain, with no additional free
parameters, the spin dependent structure functions and
. Using the correct evolution, we have checked that they
are in excellent agreement with the very recent SMC proton data at and the SLAC neutron data at .Comment: 17 pages,CPT-94/P.3032,latex,6 fig available on cpt.univ-mrs.fr
directory pub/preprints/94/fundamental-interactions /94-P.303
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