2,446 research outputs found
Unbundling the housing crisis
Problem statement: An unregulated globalized residential mortgage industry imploded upon itself and transformed traditional neighborhood fabrics and ex-urban development tracts into widespread landscapes of mass foreclosures affecting society and our economy across all social strata to a critical point of near institutional financial collapse
General Relativity and Gravitation: A Centennial Perspective
To commemorate the 100th anniversary of general relativity, the International
Society on General Relativity and Gravitation (ISGRG) commissioned a Centennial
Volume, edited by the authors of this article. We jointly wrote introductions
to the four Parts of the Volume which are collected here. Our goal is to
provide a bird's eye view of the advances that have been made especially during
the last 35 years, i.e., since the publication of volumes commemorating
Einstein's 100th birthday. The article also serves as a brief preview of the 12
invited chapters that contain in-depth reviews of these advances. The volume
will be published by Cambridge University Press and released in June 2015 at a
Centennial conference sponsored by ISGRG and the Topical Group of Gravitation
of the American Physical Society.Comment: 37 page
Solar wind turbulent heating by interstellar pickup protons: 2-component model
We apply a recently developed 2-component phenomenology to the turbulent heating of the core solar wind protons as seen at the Voyager 2 spacecraft. We find that this new description improves the model predictions of core temperature and correlation scale of the fluctuations, yielding excellent agreement with the Voyager measurements. However, the model fluctuation intensity substantially exceeds the Voyager measurements in the outer heliosphere, indicating that this picture needs further refinement
Asymptotically Hyperbolic Non Constant Mean Curvature Solutions of the Einstein Constraint Equations
We describe how the iterative technique used by Isenberg and Moncrief to
verify the existence of large sets of non constant mean curvature solutions of
the Einstein constraints on closed manifolds can be adapted to verify the
existence of large sets of asymptotically hyperbolic non constant mean
curvature solutions of the Einstein constraints.Comment: 19 pages, TeX, no figure
How I treat anticoagulant-refractory thrombotic antiphospholipid syndrome
The standard treatment of thrombotic antiphospholipid syndrome (APS) is lifelong oral anticoagulation with a vitamin K antagonist (VKA), generally warfarin. A minority of APS patients re-thrombose despite seemingly adequate anticoagulation. These patients are deemed anticoagulant-refractory. The management of anticoagulant-refractory APS is largely empirical and extrapolated from other clinically similar situations. Further options include increased VKA anticoagulation intensity or alternative antithrombotic strategies, including low-molecular-weight heparin, fondaparinux, the addition of antiplatelet therapy and consideration of vascular options. Anticoagulant-refractory thrombotic APS patients may have APS-associated thrombocytopenia, which necessitates balancing the risk of recurrent thrombosis versus bleeding, to achieve adequate anticoagulation. The multiple mechanisms involved in the generation of the thrombotic phenotype in APS suggest that anticoagulation alone may not control thrombosis. Thus, other modalities, including adjunctive treatment (hydroxychloroquine, statins and vitamin D) for APS-related thrombosis merit consideration, as well as immunomodulatory therapy and complement inhibition. APS patients may have coexistent systemic lupus erythematosus, which adds to the complexity of managing their thromboembolic disease. However, with attention to detail and judicious application of the limited data, it is possible to minimise the morbidity resulting from anticoagulant-refractory thrombotic APS. Multicentre studies are required to guide the sequence of interventions and their comparative efficacy in patients with anticoagulant-refractory thrombotic APS
The constraint equations for the Einstein-scalar field system on compact manifolds
We study the constraint equations for the Einstein-scalar field system on
compact manifolds. Using the conformal method we reformulate these equations as
a determined system of nonlinear partial differential equations. By introducing
a new conformal invariant, which is sensitive to the presence of the initial
data for the scalar field, we are able to divide the set of free conformal data
into subclasses depending on the possible signs for the coefficients of terms
in the resulting Einstein-scalar field Lichnerowicz equation. For many of these
subclasses we determine whether or not a solution exists. In contrast to other
well studied field theories, there are certain cases, depending on the mean
curvature and the potential of the scalar field, for which we are unable to
resolve the question of existence of a solution. We consider this system in
such generality so as to include the vacuum constraint equations with an
arbitrary cosmological constant, the Yamabe equation and even (all cases of)
the prescribed scalar curvature problem as special cases.Comment: Minor changes, final version. To appear: Classical and Quantum
Gravit
Testing Approximations of Thermal Effects in Neutron Star Merger Simulations
We perform three-dimensional relativistic hydrodynamical calculations of
neutron star mergers to assess the reliability of an approximate treatment of
thermal effects in such simulations by combining an ideal-gas component with
zero-temperature, micro-physical equations of state. To this end we compare the
results of simulations that make this approximation to the outcome of models
with a consistent treatment of thermal effects in the equation of state. In
particular we focus on the implications for observable consequences of merger
events like the gravitational-wave signal. It is found that the characteristic
gravitational-wave oscillation frequencies of the post-merger remnant differ by
about 50 to 250 Hz (corresponding to frequency shifts of 2 to 8 per cent)
depending on the equation of state and the choice of the characteristic index
of the ideal-gas component. In addition, the delay time to black hole collapse
of the merger remnant as well as the amount of matter remaining outside the
black hole after its formation are sensitive to the description of thermal
effects.Comment: 10 pages, 6 figures, 9 eps files; revised with minor additions due to
referee comments; accepted by Phys.Rev.
TURBULENT HEATING OF THE DISTANT SOLAR WIND BY INTERSTELLAR PICKUP PROTONS IN A DECELERATING FLOW
Previous models of solar wind heating by interstellar pickup proton-driven turbulence have assumed that the wind speed is a constant in heliocentric radial position. However, the same pickup process, which is taken to provide the turbulent energy, must also decelerate the wind. In this paper, we extend our phenomenological turbulence model to include variable wind speed, and then incorporate the deceleration due to interstellar pickup protons into the model. We compare the model results with plasma and field data from Voyager 2, taking this opportunity to present an extended and improved data set of proton core temperature, magnetic field fluctuation intensity, and correlation length along the Voyager trajectory. A particular motivation for including the solar wind deceleration in this model is the expectation that a slower wind would reduce the resulting proton core temperature in the region beyond ~60 AU, where the previous model predictions were higher than the observed values. However, we find instead that the deceleration of the steady-state wind increases the energy input to the turbulence, causing even higher temperatures in that region. The increased heating is shown to result from the larger values of the ratio of Alfven speed to solar wind speed that develop in the decelerating wind.Jet Propulsion Laboratory (U.S.) (NASA contract 959203)United States. National Aeronautics and Space Administration (NASA grant NNX08A147G)United States. National Aeronautics and Space Administration (NASA Guest Investigator grant NNX07AH75G)United States. National Aeronautics and Space Administration (NASA Guest Investigator grant NNX08AJ19G
A Self-Consistent Marginally Stable State for Parallel Ion Cyclotron Waves
We derive an equation whose solutions describe self-consistent states of
marginal stability for a proton-electron plasma interacting with
parallel-propagating ion cyclotron waves. Ion cyclotron waves propagating
through this marginally stable plasma will neither grow nor damp. The
dispersion relation of these waves, {\omega} (k), smoothly rises from the usual
MHD behavior at small |k| to reach {\omega} = {\Omega}p as k \rightarrow
\pm\infty. The proton distribution function has constant phase-space density
along the characteristic resonant surfaces defined by this dispersion relation.
Our equation contains a free function describing the variation of the proton
phase-space density across these surfaces. Taking this free function to be a
simple "box function", we obtain specific solutions of the marginally stable
state for a range of proton parallel betas. The phase speeds of these waves are
larger than those given by the cold plasma dispersion relation, and the
characteristic surfaces are more sharply peaked in the v\bot direction. The
threshold anisotropy for generation of ion cyclotron waves is also larger than
that given by estimates which assume bi-Maxwellian proton distributions.Comment: in press in Physics of Plasma
- âŠ