13,083 research outputs found
Zirconium, Barium, Lanthanum and Europium Abundances in Open Clusters
We present an analysis of the s-process elements Zr, Ba, and La and the
r-process element Eu in a sample of 50 stars in 19 open clusters. Stellar
abundances of each element are based on measures of a minimum of two lines per
species via both equivalent width and spectrum synthesis techniques. We
investigate cluster mean neutron-capture abundance trends as a function of
cluster age and location in the Milky Way disk and compare them to results
found in other studies in the literature. We find a statistically significant
trend of increasing cluster [Ba/Fe] as a function of decreasing cluster age, in
agreement with recent findings for other open cluster samples, supporting the
increased importance of low-mass asymptotic giant branch stars to the
generation of s-process elements. However, the other s-process elements,
[La/Fe] and [Zr/Fe], do not show similar dependences, in contrast to
theoretical expectations and the limited observational data from other studies.
Conversely, cluster [Eu/Fe] ratios show a slight increase with increasing
cluster age, although with marginal statistical significance. Ratios of
[s/r]-process abundances, [Ba/Eu] and [La/Eu], however, show more clearly the
increasing efficiency of s-process relative to r-process enrichment in open
cluster chemical evolution, with significant increases among younger clusters.
Last, cluster neutron-capture element abundances appear to be independent of
Galactocentric distance. We conclude that a homogeneous analysis of a larger
sample of open clusters is needed to resolve the apparent discrepant
conclusions between different studies regarding s-process element abundance
trends with age to better inform models of galactic chemical evolution.Comment: 24 pages, 13 figures, 10 tables; published in The Astronomical
Journa
Thermionic research and development program Final report, 15 Jul. 1966 - 15 Jan. 1968
Thermionic research and development program - improvement of performance of low emitter temperature cesium vapor thermionic converter
Theoretical and experimental comparison of vapor cavitation in dynamically loaded journal bearings
Vapor cavitation for a submerged journal bearing under dynamically loaded conditions was investigated. The observation of vapor cavitation in the laboratory was done by high-speed photography. It was found that vapor cavitation occurs when the tensile stress applied to the oil exceeded the tensile strength of the oil or the binding of the oil to the surface. The theoretical solution to the Reynolds equation is determined numerically using a moving boundary algorithm. This algorithm conserves mass throughout the computational domain including the region of cavitation and its boundaries. An alternating direction implicit (MDI) method is used to effect the time march. A rotor undergoing circular whirl was studied. Predicted cavitation behavior was analyzed by three-dimensional computer graphic movies. The formation, growth, and collapse of the bubble in response to the dynamic conditions is shown. For the same conditions of dynamic loading, the cavitation bubble was studied in the laboratory using high-speed photography
Mechanics of universal horizons
Modified gravity models such as Ho\v{r}ava-Lifshitz gravity or
Einstein-{\ae}ther theory violate local Lorentz invariance and therefore
destroy the notion of a universal light cone. Despite this, in the infrared
limit both models above possess static, spherically symmetric solutions with
"universal horizons" - hypersurfaces that are causal boundaries between an
interior region and asymptotic spatial infinity. In other words, there still
exist black hole solutions. We construct a Smarr formula (the relationship
between the total energy of the spacetime and the area of the horizon) for such
a horizon in Einstein-{\ae}ther theory. We further show that a slightly
modified first law of black hole mechanics still holds with the relevant area
now a cross-section of the universal horizon. We construct new analytic
solutions for certain Einstein-{\ae}ther Lagrangians and illustrate how our
results work in these exact cases. Our results suggest that holography may be
extended to these theories despite the very different causal structure as long
as the universal horizon remains the unique causal boundary when matter fields
are added.Comment: Minor clarifications. References update
Restoring Health to Health Reform: Integrating Medicine and Public Health to Advance the Population\u27s Wellbeing
The Patient Protection and Affordable Care Act is a major achievement in improving access to health care services. However, evidence indicates that the nation could achieve greater improvements in health outcomes, at a lower cost, by shifting its focus to public health. By focusing nearly exclusively on health care, policy makers have chronically starved public health of adequate and stable funding and political support. The lack of support for public health is exacerbated by the fact that health care and public health are generally conceptualized, organized, and funded as two separate systems. In order to maximize gains in health status and to spend scarce health resources most effectively, health care and public health should be treated as two interactive parts of a single, unified health system.
The core purpose of health reform ought to be the improvement of the population’s health. We propose five criteria that would significantly advance this goal: prevention and wellness, human resources, a strong and sustainable health infrastructure, robust performance measurement, and reduction of health disparities. Although the Patient Protection and Affordable Care Act includes provisions addressing these criteria, population health is not a central focus of the reform.
In order to guide health reform implementation and to inform future health reform efforts, we offer three major policy reforms: changing the environment to incentivize healthy behavioral choices, strengthening the public health infrastructure at the state and local levels, and developing a health-in-all policies strategy that would engage multiple agencies in improving health incomes. Adopting these reforms would facilitate integration and dramatically improve the population’s health, particularly when compared to the health gains likely to be realized from a continued focus on access to health care services
Tribolgy of selected ceramics at temperatures to 900 deg C
Results of fundamental and focused research on the tribological properties of ceramics are discussed. The basic friction and wear characteristics are given for ceramics of interest for use in gas trubine, adiabatic diesel, and Stirling engine applications. The importance of metal oxides in ceramic/metal sliding combinations is illustrated. The formulation and tribological additives are described. Friction and wear date are given for carbide and oxide-based composite coatings for temperatures to at least 900 C
Collapse of Kaluza-Klein Bubbles
Kaluza-Klein theory admits ``bubble" configurations, in which the
circumference of the fifth dimension shrinks to zero on some compact surface. A
three parameter family of such bubble initial data at a moment of time-symmetry
(some including a magnetic field) has been found by Brill and Horowitz,
generalizing the (zero-energy) ``Witten bubble" solution. Some of these data
have negative total energy. We show here that all the negative energy bubble
solutions start out expanding away from the moment of time symmetry, while the
positive energy bubbles can start out either expanding or contracting. Thus it
is unlikely that the negative energy bubbles would collapse and produce a naked
singularity.Comment: 6 pages, plain LaTeX, UMDGR-94-08
On the effects of the Dvali-Gabadadze-Porrati braneworld gravity on the orbital motion of a test particle
In this paper we explicitly work out the secular perturbations induced on all
the Keplerian orbital elements of a test body to order O(e^2) in the
eccentricity e by the weak-field long-range modifications of the usual
Newton-Einstein gravity due to the Dvali-Gabadadze-Porrati (DGP) braneworld
model. The Gauss perturbative scheme is used. It turns out that the argument of
pericentre and the mean anomaly are affected by secular rates which are
independent of the semimajor axis of the orbit of the test particle. The first
nonvaishing eccentricity-dependent corrections are of order O(e^2). For
circular orbits the Lue-Starkman (LS) effect on the pericentre is obtained.
Some observational consequences are discussed for the Solar System planetary
mean longitudes lambda which would undergo a 1.2\cdot 10^-3 arcseconds per
century braneworld secular precession. According to recent data analysis over
92 years for the EPM2004 ephemerides, the 1-sigma formal accuracy in
determining the Martian mean longitude amounts to 3\cdot 10^-3 milliarcseconds,
while the braneworld effect over the same time span would be 1.159
milliarcseconds. The major limiting factor is the 2.6\cdot 10^-3 arcseconds per
century systematic error due to the mismodelling in the Keplerian mean motion
of Mars. A suitable linear combination of the mean longitudes of Mars and Venus
may overcome this problem. The formal, 1-sigma obtainable observational
accuracy would be \sim 7%. The systematic error due to the present-day
uncertainties in the solar quadrupole mass moment, the Keplerian mean motions,
the general relativistic Schwarzschild field and the asteroid ring would amount
to some tens of percent.Comment: LaTex2e, 23 pages, 5 tables, 1 figure, 37 references. Second-order
corrections in eccentricity explicitly added. Typos corrected. References
update
Work function determination of promising electrode materials for thermionic energy converters
The work function determinations of candidate materials for low temperature (1400 K) thermionics through vacuum emission tests are discussed. Two systems, a vacuum emission test vehicle and a thermionic emission microscope are used for emission measurements. Some nickel and cobalt based super alloys were preliminarily examined. High temperature physical properties and corrosion behavior of some super alloy candidates are presented. The corrosion behavior of sodium is of particular interest since topping cycles might use sodium heat transfer loops. A Marchuk tube was designed for plasma discharge studies with the carbide and possibly some super alloy samples. A series of metal carbides and other alloys were fabricated and tested in a special high temperature mass spectrometer. This information coupled with work function determinations was evaluated in an attempt to learn how electron bonding occurs in transition alloys
Defending Public Health Regulations: The Message Is the Medium
The second of five commentaries on “Bloomberg's Health Legacy: Urban Innovator or Meddling Nanny?” from the September‐October 2013 .Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/102670/1/hast243.pd
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