423 research outputs found
An implantable multi-channel temperature transmitter
Implantable multi-channel temperature transmitte
Quantitative measurement by telemetry of ovulation and oviposition in the fowl
Radio telemetry used to determine body temperature cycles in fowl and its relation to ovulation and ovipositio
Circadian, endocrine, and metabolic effects of prolonged bedrest: Two 56-day bedrest studies
Two bedrest studies of 56 days each have been conducted to evaluate the effects of prolonged bedrest on circadian synchrony and endocrine and metabolic function. Measurements included the pituitary-adrenal, thyroid, parathyroid, insulin-glucose-growth hormones, catecholamine excretion, body temperature, and heart rate. The results indicated that a rigorous regimen of exercise did not prevent the endocrine and metabolic effects of prolonged bedrest. Changes in circadian, endocrine, and metabolic functions in bedrest appear to be due to changes in hydrostatic pressure and lack of postural cues rather than to inactivity, confinement, or the bleeding schedule. Prolonged bedrest, particularly beyond 24 days, resulted in rhythm desynchronization in spite of well regulated light/dark cycles, temperature, humidity, activity, and meal times and meal composition and in increased lability of all endocrine parameter measured. It also resulted in an apparent insensitivity of the glucose response to insulin, of cortisol secretion to ACTH, and of growth hormone secretion to hypoglycemia
Element-by-element factorization algorithms for heat conduction
Element-by-element solution strategies are developed for transient heat conduction problems. Results of numerical tests indicate the effectiveness of the procedures proposed. The small database requirements and attractive architectural features of the algorithms suggest considerable potential for solving large scale problems
Space Station Centrifuge: A Requirement for Life Science Research
A centrifuge with the largest diameter that can be accommodated on Space Station Freedom is required to conduct life science research in the microgravity environment of space. (This was one of the findings of a group of life scientists convened at the University of California, Davis, by Ames Research Center.) The centrifuge will be used as a research tool to understand how gravity affects biological processes; to provide an on-orbit one-g control; and to assess the efficacy of using artificial gravity to counteract the deleterious biological effect of space flight. The rationale for the recommendation and examples of using ground-based centrifugation for animal and plant acceleration studies are presented. Included are four appendixes and an extensive bibliography of hypergravity studies
Cells in Space
Discussions and presentations addressed three aspects of cell research in space: the suitability of the cell as a subject in microgravity experiments, the requirements for generic flight hardware to support cell research, and the potential for collaboration between academia, industry, and government to develop these studies in space. Synopses are given for the presentations and follow-on discussions at the conference and papers are presented from which the presentations were based. An Executive Summary outlines the recommendations and conclusions generated at the conference
Photometric Identification of Cool White Dwarfs
We investigate the use of a narrow-band DDO51 filter for photometric
identification of cool white dwarfs. We report photometric observations of 30
known cool white dwarfs with temperatures ranging from 10,000 K down to very
cool temperatures (<3500 K). Follow-up spectroscopic observations of a sample
of objects selected using this filter and our photometric observations show
that DDO51 filter photometry can help select cool white dwarf candidates for
follow-up multi--object spectroscopy by rejecting 65% of main sequence stars
with the same broad--band colors as the cool white dwarfs. This technique is
not selective enough to efficiently feed single--object spectrographs. We
present the white dwarf cooling sequence using this filter. Our observations
show that very cool white dwarfs form a sequence in the r-DDO vs. r-z
color--color diagram and demonstrate that significant improvements are needed
in white dwarf model atmospheres.Comment: Accepted for publication in A
Identification of Cool White Dwarfs in the NOAO Deep Wide-Field Survey
We report our search for the cool white dwarfs belonging to the Galactic disk
by extending the NOAO Deep Wide-Field Survey. Narrow-band DDO51 photometry of
the Deep Wide-Field Survey's northern field was obtained using the 4m-Mayall
Telescope and the MOSAIC imager to separate cool white dwarfs from other
stellar types of similar T_eff. Follow-up spectroscopy of four white dwarf
candidates from our photometric search resulted in the discovery of two new
cool white dwarfs as companions to M dwarfs.Comment: 2 pages, 2 figures, to appear in proceedings of the 13th European
Workshop on White Dwarf
A new look at the pulsating DB white dwarf GD 358:Line-of-sight velocity measurements and constraints on model atmospheres
We report on our findings of the bright, pulsating, helium atmosphere white
dwarf GD 358, based on time-resolved optical spectrophotometry. We identify 5
real pulsation modes and at least 6 combination modes at frequencies consistent
with those found in previous observations. The measured Doppler shifts from our
spectra show variations with amplitudes of up to 5.5 km/s at the frequencies
inferred from the flux variations. We conclude that these are variations in the
line-of-sight velocities associated with the pulsational motion. We use the
observed flux and velocity amplitudes and phases to test theoretical
predictions within the convective driving framework, and compare these with
similar observations of the hydrogen atmosphere white dwarf pulsators (DAVs).
The wavelength dependence of the fractional pulsation amplitudes (chromatic
amplitudes) allows us to conclude that all five real modes share the same
spherical degree, most likely, l=1. This is consistent with previous
identifications based solely on photometry. We find that a high signal-to-noise
mean spectrum on its own is not enough to determine the atmospheric parameters
and that there are small but significant discrepancies between the observations
and model atmospheres. The source of these remains to be identified. While we
infer T_eff=24kK and log g~8.0 from the mean spectrum, the chromatic
amplitudes, which are a measure of the derivative of the flux with respect to
the temperature, unambiguously favour a higher effective temperature, 27kK,
which is more in line with independent determinations from ultra-violet
spectra.Comment: 14 pages, 11 figures; accepted for publication in A&
The Effect of Crystallization on the Pulsations of White Dwarf Stars
We consider the pulsational properties of white dwarf star models with
temperatures appropriate for the ZZ Ceti instability strip and with masses
large enough that they should be substantially crystallized. Our work is
motivated by the existence of a potentially crystallized DAV, BPM 37093, and
the expectation that digital surveys in progress will yield many more such
massive pulsators.
A crystallized core makes possible a new class of oscillations, the torsional
modes, although we expect these modes to couple at most weakly to any motions
in the fluid and therefore to remain unobservable. The p-modes should be
affected at the level of a few percent in period, but are unlikely to be
present with observable amplitudes in crystallizing white dwarfs any more than
they are in the other ZZ Ceti's. Most relevant to the observed light variations
in white dwarfs are the g-modes. We find that the kinetic energy of these modes
is effectively excluded from the crystallized cores of our models. As
increasing crystallization pushes these modes farther out from the center, the
mean period spacing between radial overtones increases substantially with the
crystallized mass fraction. In addition, the degree and structure of mode
trapping is affected. The fact that some periods are strongly affected by
changes in the crystallized mass fraction while others are not suggests that we
may be able to disentangle the effects of crystallization from those due to
different surface layer masses.Comment: 18 pages, 5 figures, accepted on 1999 July 2 for publication in the
Astrophysical Journa
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