2,024 research outputs found
The separate computation of arcs for optimal flight paths with state variable inequality constraints
Computation of arcs for optimal flight paths with state variable inequality constraint
Refractory amorphous metallic (W0.6Re0.4)76B24 coatings on steel substrates
Refractory metallic coatings of (W0.6Re0.4)76B24 (WReB) have been deposited onto glass, quartz, and heat-treated AISI 52100 bearing steel substrates by dc magnetron sputtering. As-deposited WReB films are amorphous, as shown by their diffuse x-ray diffraction patterns; chemically homogeneous, according to secondary ion mass spectrometry (SIMS) analysis; and they exhibit a very high (~1000°C) crystallization temperature. Adhesion strength of these coatings on heat-treated AISI 52100 steel is in excess of ~20, 000 psi and they possess high microhardness (~2400 HV50). Unlubricated wear resistance of such hard and adherent amorphous metallic coatings on AISI 52100 steel is studied using the pin-on-disc method under various loading conditions. Amorphous metallic WReB coatings, about 4 µm thick, exhibit an improvement of more than two and a half orders of magnitude in the unlubricated wear resistance over that of the uncoated AISI 52100 steel
Interior Weyl-type Solutions of the Einstein-Maxwell Field Equations
Static solutions of the electro-gravitational field equations exhibiting a
functional relationship between the electric and gravitational potentials are
studied. General results for these metrics are presented which extend previous
work of Majumdar. In particular, it is shown that for any solution of the field
equations exhibiting such a Weyl-type relationship, there exists a relationship
between the matter density, the electric field density and the charge density.
It is also found that the Majumdar condition can hold for a bounded perfect
fluid only if the matter pressure vanishes (that is, charged dust). By
restricting to spherically symmetric distributions of charged matter, a number
of exact solutions are presented in closed form which generalise the
Schwarzschild interior solution. Some of these solutions exhibit functional
relations between the electric and gravitational potentials different to the
quadratic one of Weyl. All the non-dust solutions are well-behaved and, by
matching them to the Reissner-Nordstr\"{o}m solution, all of the constants of
integration are identified in terms of the total mass, total charge and radius
of the source. This is done in detail for a number of specific examples. These
are also shown to satisfy the weak and strong energy conditions and many other
regularity and energy conditions that may be required of any physically
reasonable matter distribution.Comment: 21 pages, RevTex, to appear in General Relativity and Gravitatio
Strengthening the integration of midwifery in health systems; a leader-to-leader collaboration
Barriers and facilitators for quality midwifery care exist on different levels in the health systems. After decades of challenges and varied degrees of success, a stakeholder leader-to-leader collaboration could provide added value through knowledge sharing on how to integrate the midwifery cadre into an existing health system. Initiated by The Midwifery Society of Nepal, Dalarna University Sweden and MAMTA - Health Institute for Mother and Child India, a research network focusing midwifery has been formed. The background, purpose and activities of this network has been described in this News and Events paper
Connecting Rural Public Libraries to LIS Education and Research: The Case of Health Services, Programs, and Partnerships
In our increasingly interdisciplinary field, health professionals, advocates, and
researchers frequently look to public librarians as partners. This trend may be particularly
important in small and rural communities, where the public library occupies a uniquely important
role given the disinvestment in health infrastructure in those communities. How are both current
and aspiring small and rural public librarians receiving the education, training, and ongoing
support needed to foster and sustain health services and programs with local, regional, and
national partners? This panel draws attention to and discusses these issues in three ways: 1.
Showcasing connections across three Institute of Museum and Library Services funded projects
focused on small and rural public libraries and health; 2. Fostering audience interaction by
soliciting questions and feedback prior to the conference; 3. Engaging in dialogue about how LIS
educators can form and sustain connections to public librarians, particularly in small and rural
communities. Topics the panelists will explore or discuss include, 1. What challenges and
opportunities are associated with forming and sustaining partnerships with small and rural
librarians, particularly in grant funded projects? 2. How can LIS educators learn from the
experiences of rural and small librarians to ensure that LIS graduates have the knowledge and
skills to be successful in their communities? 3. What additional work is needed to understand and
support small and rural public librarians as catalysts of social justice and health justice
Trapped and excited w modes of stars with a phase transition and R>=5M
The trapped -modes of stars with a first order phase transition (a density
discontinuity) are computed and the excitation of some of the modes of these
stars by a perturbing shell is investigated. Attention is restricted to odd
parity (``axial'') -modes. With the radius of the star, its mass,
the radius of the inner core and the mass of such core, it is
shown that stars with can have several trapped -modes, as long
as . Excitation of the least damped -mode is confirmed for
a few models. All of these stars can only exist however, for values of the
ratio between the densities of the two phases, greater than . We also
show that stars with a phase transition and a given value of can have far
more trapped modes than a homogeneous single density star with the same value
of , provided both and are smaller than 3. If the
phase transition is very fast, most of the stars with trapped modes are
unstable to radial oscillations. We compute the time of instability, and find
it to be comparable to the damping of the -mode excited in most cases where
-mode excitation is likely. If on the other hand the phase transition is
slow, all the stars are stable to radial oscillations.Comment: To appear in Physical Review
Hamiltonian dynamics of the two-dimensional lattice phi^4 model
The Hamiltonian dynamics of the classical model on a two-dimensional
square lattice is investigated by means of numerical simulations. The
macroscopic observables are computed as time averages. The results clearly
reveal the presence of the continuous phase transition at a finite energy
density and are consistent both qualitatively and quantitatively with the
predictions of equilibrium statistical mechanics. The Hamiltonian microscopic
dynamics also exhibits critical slowing down close to the transition. Moreover,
the relationship between chaos and the phase transition is considered, and
interpreted in the light of a geometrization of dynamics.Comment: REVTeX, 24 pages with 20 PostScript figure
The Tolman VII solution, trapped null orbits and w - modes
The Tolman VII solution is an exact static spherically symmetric perfect
fluid solution of Einstein's equations that exhibits a surprisingly good
approximation to a neutron star. We show that this solution exhibits trapped
null orbits in a causal region even for a tenuity (total radius to mass ratio)
. In this region the dynamical part of the potential for axial w - modes
dominates over the centrifugal part.Comment: 5 pages revtex. 10 figures png. Further information at
http://grtensor.phy.queensu.ca/tolmanvii
Curvature fluctuations and Lyapunov exponent at Melting
We calculate the maximal Lyapunov exponent in constant-energy molecular
dynamics simulations at the melting transition for finite clusters of 6 to 13
particles (model rare-gas and metallic systems) as well as for bulk rare-gas
solid. For clusters, the Lyapunov exponent generally varies linearly with the
total energy, but the slope changes sharply at the melting transition. In the
bulk system, melting corresponds to a jump in the Lyapunov exponent, and this
corresponds to a singularity in the variance of the curvature of the potential
energy surface. In these systems there are two mechanisms of chaos -- local
instability and parametric instability. We calculate the contribution of the
parametric instability towards the chaoticity of these systems using a recently
proposed formalism. The contribution of parametric instability is a continuous
function of energy in small clusters but not in the bulk where the melting
corresponds to a decrease in this quantity. This implies that the melting in
small clusters does not lead to enhanced local instability.Comment: Revtex with 7 PS figures. To appear in Phys Rev
A First Principles Estimate of Finite Size Effects in Quark-Gluon Plasma Formation
Using lattice simulations of quenched QCD we estimate the finite size effects
present when a gluon plasma equilibrates in a slab geometry, i.e., finite width
but large transverse dimensions. Significant differences are observed in the
free energy density for the slab when compared with bulk behavior. A small
shift in the critical temperature is also seen. The free energy required to
liberate heavy quarks relative to bulk is measured using Polyakov loops; the
additional free energy required is on the order of 30-40 MeV at 2-3 T_c.Comment: 10 pages, 5 figures, RevTeX; revised version includes comparison with
the Bjorken model and various small improvement
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