1,197 research outputs found
Late-Time Behavior of Stellar Collapse and Explosions: I. Linearized Perturbations
Problem with the figures should be corrected. Apparently a broken uuencoder
was the cause.Comment: 16pp, RevTex, 6 figures (included), NSF-ITP-93-8
Quantum healing of classical singularities in power-law spacetimes
We study a broad class of spacetimes whose metric coefficients reduce to
powers of a radius r in the limit of small r. Among these four-parameter
"power-law" metrics we identify those parameters for which the spacetimes have
classical singularities as r approaches 0. We show that a large set of such
classically singular spacetimes is nevertheless nonsingular quantum
mechanically, in that the Hamiltonian operator is essentially self-adjoint, so
that the evolution of quantum wave packets lacks the ambiguity associated with
scattering off singularities. Using these metrics, the broadest class yet
studied to compare classical with quantum singularities, we explore the
physical reasons why some that are singular classically are "healed" quantum
mechanically, while others are not. We show that most (but not all) of the
remaining quantum-mechanically singular spacetimes can be excluded if either
the weak energy condition or the dominant energy condition is invoked, and we
briefly discuss the effect of this work on the strong cosmic censorship
hypothesis.Comment: 14 pages, 1 figure; extensive revision
Quantum singularity of Levi-Civita spacetimes
Quantum singularities in general relativistic spacetimes are determined by
the behavior of quantum test particles. A static spacetime is quantum
mechanically singular if the spatial portion of the wave operator is not
essentially self-adjoint. Here Weyl's limit point-limit circle criterion is
used to determine whether a wave operator is essentially self-adjoint. This
test is then applied to scalar wave packets in Levi-Civita spacetimes to help
elucidate the physical properties of the spacetimes in terms of their metric
parameters
Neighbors' income, public goods, and wellâbeing
How does neighbors' income affect individual wellâbeing? Our analysis is based on rich U.S. local data from the Behavioral Risk Factor Surveillance System, which contains information on where respondents live and their selfâreported wellâbeing. We find that the effect of neighbors' income on individuals' selfâreported wellâbeing varies with the size of the neighborhood included. In smaller areas such as ZIP codes, we find a positive relationship between median income and individuals' life satisfaction, whereas it is the opposite at the county, MSA, and state levels. We provide evidence that local public goods and local area characteristics such as unemployment, criminality, and poverty rates drive the association between satisfaction and neighbors' income at the ZIP code level. The neighbors' income effects are mainly concentrated among poorer individuals and are as large as one quarter of the effect of own income on selfâreported wellâbeing
BSR Spondyloarthritis Course, 27 February 2020. Spondyloarthritis: pathogenesis, diagnosis and management
High-quality continuous medical education is essential to maintain excellence in health-care delivery, upskilling professionals and improving patient outcomes. This is particularly relevant when addressing rare disease groups, such as the spondyloarthritides, a group of heterogeneous inflammatory conditions that affect joints and other organs, such as the skin, bowel and eye. Professional bodies, such as the British Society for Rheumatology (BSR), are well placed to deliver this type of education. In 2020, the BSR ran a dedicated SpA course aimed at rheumatology health-care professionals wishing to update their basic knowledge of SpA with a review of the latest advances in the field. Here, we summarize the proceedings of the meeting and discuss the value of such an initiative
Performance of composite measures used in a trial of etanercept and methotrexate as monotherapy or in combination in psoriatic arthritis
Objectives:
To examine which composite measures are most sensitive to change when measuring psoriatic arthritis (PsA) disease activity, analyses compared the responsiveness of composite measures used in a 48-week randomized, controlled trial of MTX and etanercept in patients with PsA.
Methods:
The trial randomised 851 patients to receive weekly: MTX (20âmg/week), etanercept (50âmg/week) or MTX plus etanercept. Dichotomous composite measures examined included ACR 20/50/70 responses, minimal disease activity (MDA) and very low disease activity (VLDA). Continuous composite measures examined included Disease Activity Score (28 joints) using CRP (DAS28-CRP), Clinical Disease Activity Index (CDAI), Simplified Disease Activity Index (SDAI), Disease Activity for Psoriatic Arthritis (DAPSA) and Psoriatic Arthritis Disease Activity Score (PASDAS).
Results:
At week 24, etanercept-treated groups were significantly more effective than MTX monotherapy to achieve ACR 20 (primary end point) and MDA (key secondary end point). When examining score changes from baseline at week 24 across the five continuous composite measures, PASDAS demonstrated relatively greater changes in the etanercept-treated groups compared with MTX monotherapy and had the largest effect size and standardized response. Joint count changes drove overall score changes at week 24 from baseline in all the continuous composite measures except for PASDAS, which was driven by the Physician and Patient Global Assessments.
Conclusion:
PASDAS was the most sensitive continuous composite measure examined with results that mirrored the protocol-defined primary and key secondary outcomes. Composite measures with multiple domains, such as PASDAS, may better quantify change in PsA disease burden.
Trail registration:
https://ClinicalTrials.gov, number NCT02376790
Particle Creation If a Cosmic String Snaps
We calculate the Bogolubov coefficients for a metric which describes the
snapping of a cosmic string. If we insist on a matching condition for all times
{\it and} a particle interpretation, we find no particle creation.Comment: 10 pages, MRC.PH.17/9
Algae as nutritional and functional food sources: revisiting our understanding.
Global demand for macroalgal and microalgal foods is growing, and algae are increasingly being consumed for functional benefits beyond the traditional considerations of nutrition and health. There is substantial evidence for the health benefits of algal-derived food products, but there remain considerable challenges in quantifying these benefits, as well as possible adverse effects. First, there is a limited understanding of nutritional composition across algal species, geographical regions, and seasons, all of which can substantially affect their dietary value. The second issue is quantifying which fractions of algal foods are bioavailable to humans, and which factors influence how food constituents are released, ranging from food preparation through genetic differentiation in the gut microbiome. Third is understanding how algal nutritional and functional constituents interact in human metabolism. Superimposed considerations are the effects of harvesting, storage, and food processing techniques that can dramatically influence the potential nutritive value of algal-derived foods. We highlight this rapidly advancing area of algal science with a particular focus on the key research required to assess better the health benefits of an alga or algal product. There are rich opportunities for phycologists in this emerging field, requiring exciting new experimental and collaborative approaches.AGS & KEH thank the Biotechnology and Biological Sciences Research Council (BBSRC BB/1013164/1) of the UK for funding. The University of Dundee is a registered Scottish charity, No. SC015096. PP is supported by IDEALG in the frame of the stimuli program entitled âInvestissements dâavenir, Biotechnologies-Bioressourcesâ (ANR-10-BTBR-04-02). The open access fee was supported by NSF-OCE-1435021 (MLW), DIC project 1823-06 (MEC), Maine Sea Grant (NOAA) 5405971 (SHB), NSF #11A-1355457 to Maine EPSCoR at the University of Maine (SHB), and the listed funding to AGS and PP
Note on the point-splitting procedure to evaluate vacuum fluctuation in certain cylindrically symmetric backgrounds
We revisit two-point function approaches used to study vacuum fluctuation in
wedge-shaped regions and conical backgrounds. Appearance of divergent integrals
is discussed and circumvented. The issue is considered in the context of a
massless scalar field in cosmic string spacetime.Comment: REVTeX file, 7 page
Regularity of Cauchy horizons in S2xS1 Gowdy spacetimes
We study general S2xS1 Gowdy models with a regular past Cauchy horizon and
prove that a second (future) Cauchy horizon exists, provided that a particular
conserved quantity is not zero. We derive an explicit expression for the
metric form on the future Cauchy horizon in terms of the initial data on the
past horizon and conclude the universal relation A\p A\f=(8\pi J)^2 where
A\p and A\f are the areas of past and future Cauchy horizon respectively.Comment: 17 pages, 1 figur
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