3,544 research outputs found
Uniform Decay of Local Energy and the Semi-Linear Wave Equation on Schwarzchild Space
We provide a uniform decay estimate of Morawetz type for the local energy of
general solutions to the inhomogeneous wave equation on a Schwarzchild
background. This estimate is both uniform in space and time, so in particular
it implies a uniform bound on the sup norm of solutions which can be given in
terms of certain inverse powers of the radial and advanced/retarded time
coordinate variables. As a model application, we show these estimates give a
very simple proof small amplitude scattering for nonlinear scalar fields with
higher than cubic interactions.Comment: 24 page
The Government of the Living-The Legacy of the Dead
Akhil Amar has written a stunning book about what he calls the high temple of our constitutional order -the Bill of Rights. The temple metaphor is revealing, for it is evident throughout his book that Professor Amar views the Constitution as a sanctified structure, the use of which is to be determined by a holistic study of the original blueprints and the surviving comments of the long-dead architects. This characterization is complicated but not fundamentally changed by the fact that Amar\u27s story is, as the subtitle of the book proclaims, one of creation and reconstruction. The creation is that of the original Bill of Rights, proposed in 1789 and ratified in 1791. The reconstruction is that wrought by the Fourteenth Amendment, proposed in 1866 and ratified in 1868. The story pretty much stops there. Although Amar criticizes what he terms curiously selective ancestor worship, it turns out that he is merely arguing for a somewhat more inclusive ancestor worship--John Bingham as well as James Madison, and Frederick Douglass as well as Patrick Henry. Worthy ancestors all, but what about their descendants
Maritime Archaeology and Capacity Development in the Global South
The Honor Frost Foundation sponsored a session, ‘Maritime Archaeology, Capacity Building and Training in the Developing World’ at the Sixth International Congress on Underwater Archaeology (IKUWA VI) in Fremantle, Australia, held in Freemantle, Australia, in November 2016, dedicated to capacity development in the context of maritime archaeology. The papers presented in this special issue of this journal represent an attempt to understand different approaches to capacity building and development within the sphere of maritime cultural heritage. This paper, by way of an introduction to the subject, and this special issue, aims to explore the nature of capacity building and development in relation to maritime cultural heritage
Proton radiation damage in bulk n-GaAs
Bulk samples of Te-doped n-type GaAs were irradiated using 10 MeV to 24 MeV protons to fluences between 2 x 10 to the 11th power protons/sq cm and 2 x 10 to the 14th power protons/sq cm. Majority carrier electrical effects were measured using the vanderPauw techniques and it was observed that radiation damage was minimal at the 10 to the 11th power proton/sq cm fluence. For the higher fluences, carrier removal was proportional to Delta E/Delta x for the protons indicating ionization interactions between the protons and atoms. Thermal annealing was observed at 155 C
Toward stronger theory in critical public health: Insights from debates surrounding posthumanism
The “posthumanist turn” in critical theory comprises efforts to recognize and analyze the interdependence of human existence with non-human entities, including other animals, spaces, and technologies. Scholarship aligned to and debating posthumanism pertains to public health, but has yet to be clearly articulated for a public health audience. This commentary and an appended glossary illustrate the relevance of these ideas for enhancing critical theory in public health. Keywords: Social Sciences, Humanities, Technology, Animals, Public HealthCanadian Institutes of Health Researc
Limitations in Predicting Radiation-Induced Pharmaceutical Instability during Long-Duration Spaceflight
As human spaceflight seeks to expand beyond low-Earth orbit, NASA and its
international partners face numerous challenges related to ensuring the safety
of their astronauts, including the need to provide a safe and effective
pharmacy for long-duration spaceflight. Historical missions have relied upon
frequent resupply of onboard pharmaceuticals; as a result, there has been
little study into the effects of long-term exposure of pharmaceuticals to the
space environment. Of particular concern are the long-term effects of space
radiation on drug stability, especially as missions venture away from the
protective proximity of the Earth. Here we highlight the risk of space
radiation to pharmaceuticals during exploration spaceflight, identifying the
limitations of current understanding. We further seek to identify ways in which
these limitations could be addressed through dedicated research efforts aimed
towards the rapid development of an effective pharmacy for future spaceflight
endeavors.Comment: in press, Nature Microgravit
Decay of the Maxwell field on the Schwarzschild manifold
We study solutions of the decoupled Maxwell equations in the exterior region
of a Schwarzschild black hole. In stationary regions, where the Schwarzschild
coordinate ranges over , we obtain a decay rate of
for all components of the Maxwell field. We use vector field methods
and do not require a spherical harmonic decomposition.
In outgoing regions, where the Regge-Wheeler tortoise coordinate is large,
, we obtain decay for the null components with rates of
, , and . Along the event horizon and in ingoing regions, where ,
and when , all components (normalized with respect to an ingoing null
basis) decay at a rate of C \uout^{-1} with \uout=t+r_* in the exterior
region.Comment: 37 pages, 5 figure
Limitations in Predicting the Space Radiation Health Risk for Exploration Astronauts
Despite years of research, understanding of the space radiation environment
and the risk it poses to long-duration astronauts remains limited. There is a
disparity between research results and observed empirical effects seen in human
astronaut crews, likely due to the numerous factors that limit terrestrial
simulation of the complex space environment and extrapolation of human clinical
consequences from varied animal models. Given the intended future of human
spaceflight, with efforts now to rapidly expand capabilities for human missions
to the moon and Mars, there is a pressing need to improve upon the
understanding of the space radiation risk, predict likely clinical outcomes of
interplanetary radiation exposure, and develop appropriate and effective
mitigation strategies for future missions. To achieve this goal, the space
radiation and aerospace community must recognize the historical limitations of
radiation research and how such limitations could be addressed in future
research endeavors. We have sought to highlight the numerous factors that limit
understanding of the risk of space radiation for human crews and to identify
ways in which these limitations could be addressed for improved understanding
and appropriate risk posture regarding future human spaceflight.Comment: Accepted for publication by Nature Microgravity (2018
Comparison Testings between Two High-temperature Strain Measurement Systems
An experimental evaluation was conducted at NASA Lewis Research Center to compare and contrast the performance of a newly developed resistance strain gage, the PdCr temperature-compensated wire strain gage, to that of a conventional high-temperature extensometry. The evaluation of the two strain measurement systems was conducted through the application of various thermal and mechanical loading spectra using a high-temperature thermomechanical uniaxial testing system equipped with quartz lamp heating. The purpose of the testing was not only to compare and contrast the two strain sensors but also to investigate the applicability of the PdCr strain gage to the testing environment typically employed when characterizing the high-temperature mechanical behavior of structural materials. Strain measurement capabilities to 8OO C were investigated with a nickel base superalloy IN100 substrate material, and application to titanium matrix composite (TMC) materials was examined with the SCS-6/Ti-15-3 08 system. PdCr strain gages installed by three attachment techniques, namely, flame spraying, spot welding and rapid infrared joining were investigated
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