6,461 research outputs found
Collision probabilities of migrating small bodies and dust particles with planets
Probabilities of collisions of migrating small bodies and dust particles
produced by these bodies with planets were studied. Various Jupiter-family
comets, Halley-type comets, long-period comets, trans-Neptunian objects, and
asteroids were considered. The total probability of collisions of any
considered body or particle with all planets did not exceed 0.2. The amount of
water delivered from outside of Jupiter's orbit to the Earth during the
formation of the giant planets could exceed the amount of water in Earth's
oceans. The ratio of the mass of water delivered to a planet by Jupiter-family
comets or Halley-type comets to the mass of the planet can be greater for Mars,
Venus, and Mercury, than that for Earth.Comment: 7 pages (original paper consists of 4 pages, with all sub-figures on
one page). Proceedings of the IAU Symposium 263 "Icy bodies in the Solar
System" (Rio de Janeiro, Brazil, 3-7 August, 2009), ed. by D. Lazzaro, D.
Prialnik, R. Schulz, J.A. Fernandez, submitte
IMPROVING FLOW DISTRIBUTION IN SMALL-SCALE WATER-SUPPLY SYSTEMS THROUGH THE USE OF FLOW-REDUCING DISCS AND METHODS FOR ANALYZING THE EFFECTIVENESS OF SOLAR POWERED PUMPING FOR A DRINKING WATER SUPPLY IN RURAL PANAMA
As continued global funding and coordination are allocated toward the improvement of access to safe sources of drinking water, alternative solutions may be necessary to expand implementation to remote communities.
This report evaluates two technologies used in a small water distribution system in a mountainous region of Panama; solar powered pumping and flow-reducing discs. The two parts of the system function independently, but were both chosen for their ability to mitigate unique issues in the community. The design program NeatWork and flow-reducing discs were evaluated because they are tools taught to Peace Corps Volunteers in Panama.
Even when ample water is available, mountainous terrains affect the pressure available throughout a water distribution system. Since the static head in the system only varies with the height of water in the tank, frictional losses from pipes and fittings must be exploited to balance out the inequalities caused by the uneven terrain. Reducing the maximum allowable flow to connections through the installation of flow-reducing discs can help to retain enough residual pressure in the main distribution lines to provide reliable service to all connections.
NeatWork was calibrated to measured flow rates by changing the orifice coefficient (θ), resulting in a value of 0.68, which is 10-15% higher than typical values for manufactured flow-reducing discs. NeatWork was used to model various system configurations to determine if a single-sized flow-reducing disc could provide equitable flow rates throughout an entire system. There is a strong correlation between the optimum single-sized flow- reducing disc and the average elevation change throughout a water distribution system; the larger the elevation change across the system, the smaller the recommended uniform orifice size.
Renewable energy can jump the infrastructure gap and provide basic services at a fraction of the cost and time required to install transmission lines. Methods for the assessment of solar powered pumping systems as a means for rural water supply are presented and assessed. It was determined that manufacturer provided product specifications can be used to appropriately design a solar pumping system, but care must be taken to ensure that sufficient water can be provided to the system despite variations in solar intensity
New RR Lyrae variables in binary systems
Despite their importance, very few RR Lyrae (RRL) stars have been known to
reside in binary systems. We report on a search for binary RRL in the OGLE-III
Galactic bulge data. Our approach consists in the search for evidence of the
light-travel time effect in so-called observed minus calculated ()
diagrams. Analysis of 1952 well-observed fundamental-mode RRL in the OGLE-III
data revealed an initial sample of 29 candidates. We used the recently released
OGLE-IV data to extend the baselines up to 17 years, leading to a final sample
of 12 firm binary candidates. We provide diagrams and binary parameters
for this final sample, and also discuss the properties of 8 additional
candidate binaries whose parameters cannot be firmly determined at present. We
also estimate that per cent of the RRL reside in binary systems.Comment: MNRAS Letters, in pres
Two-photon E1M1 decay of 2 3P0 states in heavy heliumlike ions
Two-photon E1M1 transition rates are evaluated for heliumlike ions with
nuclear charges in the range Z = 50-94. The two-photon rates modify previously
published lifetimes/transition rates of 2 3P0 states. For isotopes with nuclear
spin I not equal 0, where hyperfine quenching dominates the 2 3P0 decay,
two-photon contributions are significant; for example, in heliumlike 187 Os the
two-photon correction is 3% of the total rate. For isotopes with I= 0, where
the 2 3P0 decay is unquenched, the E1M1 corrections are even more important
reaching 60% for Z=94. Therefore, to aid in the interpretation of experiments
on hyperfine quenching in heliumlike ions and to provide a more complete
database for unquenched transitions, a knowledge of E1M1 rates is important.Comment: 6 pages, 3 figures, 3 table
Nonrelativistic ionization energy for the helium ground state
The helium ground state nonrelativistic energy with 24 significant digits is
presented. The calculations are based on variational expansion with randomly
chosen exponents. This data can be used as a benchmark for other approaches for
many electron and/or three-body systems.Comment: 3 pages, 0 figure
Activation of the phosphosignaling protein CheY. I. Analysis of the phosphorylated conformation by 19F NMR and protein engineering
CheY, the 14-kDa response regulator protein of the Escherichia coli chemotaxis pathway, is activated by phosphorylation of Asp57. In order to probe the structural changes associated with activation, an approach which combines 19F NMR, protein engineering, and the known crystal structure of one conformer has been utilized. This first of two papers examines the effects of Mg(II) binding and phosphorylation on the conformation of CheY. The molecule was selectively labeled at its six phenylalanine positions by incorporation of 4-fluorophenylalanine, which yielded no significant effect on activity. One of these 19F probe positions monitored the vicinity of Lys109, which forms a salt bridge to Asp57 in the apoprotein and has been proposed to act as a structural "switch" in activation. 19F NMR chemical shift studies of the labeled protein revealed that the binding of the cofactor Mg(II) triggered local structural changes in the activation site, but did not perturb the probe of the Lys109 region. The structural changes associated with phosphorylation were then examined, utilizing acetyl phosphate to chemically generate phsopho-CheY during NMR acquisition. Phosphorylation triggered a long-range conformational change extending from the activation site to a cluster of 4 phenylalanine residues at the other end of the molecule. However, phosphorylation did not perturb the probe of Lys109. The observed phosphorylated conformer is proposed to be the first step in the activation of CheY; later steps appear to perturb Lys109, as evidenced in the following paper. Together these results may give insight into the activation of other prokaryotic response regulators
Reduced brain activity during a working memory task in middle-aged apolipoprotein E +4 carriers with overweight/obesity
Objective: The apolipoprotein E +4 (APOE +4) allele and midlife obesity are
independent risk factors for Alzheimer’s disease (AD). Both of these risk factors
are also associated with differences in brain activation, as measured by blood
oxygenation level-dependent (BOLD) responses, in the absence of detectable
cognitive deficits. Although the presence of these risk factors may influence
brain activity during working memory tasks, no study to date has examined
whether the presence of the +4 allele explains variation in working memory
brain activity while matching for levels of overweight/obesity. The primary
aim of this study was to determine whether the presence of the +4 allele is
associated with differences in task-functional magnetic resonance imaging
(fMRI) brain activation in adults with overweight/obesity. We predicted that +4
carriers would have greater brain activation in regions that support working
memory.
Methods: This ancillary study included 48 (n = 24 APOE +4 carriers;
n = 24 APOE +4 non-carriers), sedentary middle-aged adults
(Mean age = 44.63 8.36 years) with overweight/obesity (Mean
BMI = 32.43 4.12 kg/m2) who were matched on demographic
characteristics. Participants were a subsample enrolled in 12-month
randomized clinical trial examining the impact of energy-restricted diet
and exercise on cardiovascular health outcomes. Participants completed
a n-back working memory task with fMRI, which were completed within
one month of the start of the intervention. Participants also underwent
pseudo-continuous arterial spin labeling scans, a MRI measure of cerebral
blood flow (CBF). Results: Compared to non-+4 carriers with overweight/obesity, +4 carriers
with overweight/obesity had lower fMRI brain activity in the middle frontal
gyrus, pre and post central gyrus, supramarginal gyrus, superior temporal
gyrus, lateral occipital cortex, and angular gyrus (z range = 2.52–3.56) during
the n-back working memory task. Differences persisted even when controlling
for CBF in these brain regions.
Conclusion: These results indicate that presence of the APOE +4 allele in
middle-aged adults with overweight/obesity is related to altered brain activity
during a working memory paradigm, which may confer risk for accelerated
neurocognitive decline in late adulthood. Future research is needed to clarify
the clinical implications of these findings in the context of risk for AD.United States Department of Health & Human ServicesNational Institutes of Health (NIH) - USA
University of Pittsburgh Clinical and Translational Science Institute (CTSI) 3R01AG060741-03S1
R01 DK095172
R01-HL103646
UL1 TR00185
Relativistic, QED, and nuclear mass effects in the magnetic shielding of He
The magnetic shielding of He is studied. The complete
relativistic corrections of order , leading QED corrections of
order , and finite nuclear mass effects of order
are calculated with high numerical precision. The resulting
theoretical predictions for are the most
accurate to date among all elements and support the use of He as a NMR
standard.Comment: 10 pages, corrected minor errors in Eqs.(6,7
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