1,402 research outputs found
Submicrosecond comparison of international clock synchronization by VLBI and the NTS satellite
The intercontinental clock synchronization capabilities of Very Long Baseline Interferometry (VLBI) and the Navigation Technology Satellite (NTS) were compared using both methods to synchronize the Cesium clocks at the NASA Deep Space Net complexes at Madrid, Spain and Goldstone, California. Verification of the accuracy of both systems was examined. The VLBI experiments used the Wideband VLBI Data Acquisition System developed at the NASA Jet Propulsion Laboratory. The NTS Satellites were designed and built by the Naval Research Laboratory used with NTS Timing Receivers developed by the Goddard Space Flight Center. The two methods agreed at about the one-half microsecond level
Harnessing the senga institution of adolescent sex education for the control of HIV and STDs in rural Uganda.
Senga (father's sister) is a traditional channel of communication about sexual behaviour for adolescent females in rural Uganda. We evaluated a modification of this approach as an intervention for HIV and STDs in a pilot study in two intervention villages and one control village over 12 months. Eleven adult women and three adolescent girls were chosen and trained to become sengas. Adolescent girls were encouraged to visit the sengas for sexual health information. Adult sengas saw an average of 21 clients; adolescent sengas saw five. Adolescent girls made 45% of visits. The expected reasons for attending the sengas accounted for 51% of visits. Knowledge about HIV/AIDS, sexual communication skills, consistent condom use and family planning service use increased in the intervention group of girls over the study period and compared to control girls. Symptomatic STDs decreased in the intervention group. This intervention was readily accepted by the community; members of all ages and both sexes attended for a wider variety of reasons than anticipated. Adolescent girls in the intervention group showed improved knowledge, attitudes and practices related to HIV and STDs. This promising intervention warrants further testing in larger studies and other settings
Health Departments’ Engagement in Emergency Preparedness Activities: The Influence of Health Informatics Capacity
Background: Local health departments (LHDs) operate in a complex and dynamic public health landscape, with changing demands on their emergency response capacities. Informatics capacities might play an instrumental role in aiding LHDs emergency preparedness. This study aimed to explore the extent to which LHDs’ informatics capacities are associated with their activity level in emergency preparedness and to identify which health informatics capacities are associated with improved emergency preparedness. Methods: We used the 2013 National Profile of LHDs study to perform Poisson regression of emergency preparedness activities. Results: Only 38.3% of LHDs participated in full-scale exercises or drills for an emergency in the 12 months period prior to the survey, but a much larger proportion provided emergency preparedness training to staff (84.3%), and/or participated in tabletop exercises (76.4%). Our multivariable analysis showed that after adjusting for several resource-related LHD characteristics, LHDs with more of the 6 information systems still tend to have slightly more preparedness activities. In addition, having a designated emergency preparedness coordinator, and having one or more emergency preparedness staff were among the most significant factors associated with LHDs performing more emergency preparedness activities. Conclusion: LHDs might want to utilize better health information systems and information technology tools to improve their activity level in emergency preparedness, through improved information dissemination, and evidence collection
Gas-cooling by dust during dynamical fragmentation
We suggest that the abrupt switch, from hierarchical clustering on scales
larger than 0.04 pc, to binary (and occasionally higher multiple) systems on
smaller scales, which Larson has deduced from his analysis of the grouping of
pre-Main-Sequence stars in Taurus, arises because pre-protostellar gas becomes
thermally coupled to dust at sufficiently high densities. The resulting change
from gas-cooling by molecular lines at low densities to gas-cooling by dust at
high densities enables the matter to radiate much more efficiently, and hence
to undergo dynamical fragmentation.
We derive the domain where gas-cooling by dust facilitates dynamical
fragmentation. Low-mass (i.e. solar mass) clumps - those supported mainly by
thermal pressure - can probably access this domain spontaneously, albeit rather
quasistatically, provided they exist in a region where external perturbations
are few and far between. More massive clumps probably require an impulsive
external perturbation, for instance a supersonic collision with another clump,
in order for the gas to reach sufficiently high density to couple thermally to
the dust. Impulsive external perturbations should promote fragmentation, by
generating highly non-line ar substructures which can then be amplified by
gravity during the subsequent collapse.Comment: 9 pages, 4 figures, accepted by MNRA
Dynamical Expansion of Ionization and Dissociation Front around a Massive Star. II. On the Generality of Triggered Star Formation
We analyze the dynamical expansion of the HII region, photodissociation
region, and the swept-up shell, solving the UV- and FUV-radiative transfer, the
thermal and chemical processes in the time-dependent hydrodynamics code.
Following our previous paper, we investigate the time evolutions with various
ambient number densities and central stars. Our calculations show that basic
evolution is qualitatively similar among our models with different parameters.
The molecular gas is finally accumulated in the shell, and the gravitational
fragmentation of the shell is generally expected. The quantitative differences
among models are well understood with analytic scaling relations. The detailed
physical and chemical structure of the shell is mainly determined by the
incident FUV flux and the column density of the shell, which also follow the
scaling relations. The time of shell-fragmentation, and the mass of the
gathered molecular gas are sensitive tothe ambient number density. In the case
of the lower number density, the shell-fragmentation occurs over a longer
timescale, and the accumulated molecular gas is more massive. The variations
with different central stars are more moderate. The time of the
shell-fragmentation differs by a factor of several with the various stars of
M_* = 12-101 M_sun. According to our numerical results, we conclude that the
expanding HII region should be an efficient trigger for star formation in
molecular clouds if the mass of the ambient molecular material is large enough.Comment: 49 pages, including 17 figures ; Accepted for publication in Ap
High-intensity exercise in the evening does not disrupt sleep in endurance runners.
PURPOSE: To investigate the effect of early evening exercise training at different intensities on nocturnal sleep and cardiac autonomic activity in endurance-trained runners. METHODS: Eight runners completed three experimental trials in a randomised, counterbalanced order. In the early evening (end of exercise 3.5 h before bedtime), participants performed either: (i) a 1 h high-intensity interval running session (HIGH, 6 × 5 min at 90% VO2peak interspersed with 5 min recovery); (ii) a 1 h low-intensity running session (LOW, 60 min at 45% VO2peak) or (iii) no exercise (CON). Subsequent nocturnal sleep was assessed using polysomnography, wristwatch actigraphy, and subjective sleep quality. A two-lead electrocardiogram recorded nocturnal cardiac autonomic activity. RESULTS: Total sleep time increased after HIGH (477.4 ± 17.7 min, p = 0.022) and LOW (479.6 ± 15.6 min, p = 0.006) compared with CON (462.9 ± 19.0 min). Time awake was lower after HIGH (31.8 ± 18.5 min, p = 0.047) and LOW (30.4 ± 15.7 min, p = 0.008) compared with CON (46.6 ± 20.0 min). There were no differences between conditions for actigraphy and subjective sleep quality (p > 0.05). Nocturnal heart rate variability was not different between conditions, but average nocturnal heart rate increased after HIGH (50 ± 5 beats min-1) compared with LOW (47 ± 5 beats min-1, p = 0.02) and CON (47 ± 5 beats min-1, p = 0.028). CONCLUSION: When performed in the early evening, high-intensity exercise does not disrupt and may even improve subsequent nocturnal sleep in endurance-trained runners, despite increased cardiac autonomic activity. Additionally, low-intensity exercise induced positive changes in sleep behaviour that are comparable to those obtained following high-intensity exercise
2,5-PRODAN Derivatives as Highly Sensitive Sensors of Low Solvent Acidity
Two 5-acyl-2-dimethylaminonaphthalene derivatives, one with a propionyl group and the other with a fused cyclohexanone ring, are investigated as sensors of H-bond-donating ability in protic solvents of low solvent acidity. Their fluorescence is highly quenched in protic solvents, and the quenching order of magnitude is linearly related to the H-bond-donating ability of the solvent as quantified by the solvent acidity (SA) scale. As the solvent acidity increases from 0.15 to 0.40, the fluorescence for both is quenched by more than a factor of ten; thus, they are extremely sensitive sensors of the hydrogen-bond-donating ability in this weakly acidic range. Preferential solvation studies suggest that quenching occurs from a doubly H-bonded excited state
Numerical simulations of protostellar encounters I. Star-disc encounters
It appears that most stars are born in clusters, and that at birth most stars
have circumstellar discs which are comparable in size to the separations
between the stars. Interactions between neighbouring stars and discs are
therefore likely to play a key role in determining disc lifetimes, stellar
masses, and the separations and eccentricities of binary orbits. Such
interactions may also cause fragmentation of the discs, thereby triggering the
formation of additional stars.
We have carried out a series of simulations of disc-star interactions using
an SPH code which treats self-gravity, hydrodynamic and viscous forces. We find
that interactions between discs and stars provide a mechanism for removing
energy from, or adding energy to, the orbits of the stars, and for truncating
the discs. However, capture during such encounters is unlikely to be an
important binary formation mechanism.
A more significant consequence of such encounters is that they can trigger
fragmentation of the disc, via tidally and compressionally induced
gravitational instabilities, leading to the formation of additional stars. When
the disc-spins and stellar orbits are randomly oriented, encounters lead to the
formation of new companions to the original star in 20% of encounters. If most
encounters are prograde and coplanar, as suggested by simulations of
dynamically-triggered star formation, then new companions are formed in
approximately 50% of encounters.Comment: 17 pages, submitted to MNRAS; low resolution figures onl
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