1,331 research outputs found
Fermat Potentials for Non-Perturbative Gravitational Lensing
The images of many distant galaxies are displaced, distorted and often
multiplied by the presence of foreground massive galaxies near the line of
sight; the foreground galaxies act as gravitational lenses. Commonly, the lens
equation, which relates the placement and distortion of the images to the real
source position in the thin-lens scenario, is obtained by extremizing the time
of arrival among all the null paths from the source to the observer (Fermat's
principle). We show that the construction of envelopes of certain families of
null surfaces consitutes an alternative variational principle or version of
Fermat's principle that leads naturally to a lens equation in a generic
spacetime with any given metric. We illustrate the construction by deriving the
lens equation for static asymptotically flat thin lens spacetimes. As an
application of the approach, we find the bending angle for moving thin lenses
in terms of the bending angle for the same deflector at rest. Finally we apply
this construction to cosmological spacetimes (FRW) by using the fact they are
all conformally related to Minkowski space.Comment: accepted for publication in Phys. Rev.
Iterative Approach to Gravitational Lensing Theory
We develop an iterative approach to gravitational lensing theory based on
approximate solutions of the null geodesic equations. The approach can be
employed in any space-time which is ``close'' to a space-time in which the null
geodesic equations can be completely integrated, such as Minkowski space-time,
Robertson-Walker cosmologies, or Schwarzschild-Kerr geometries. To illustrate
the method, we construct the iterative gravitational lens equations and time of
arrival equation for a single Schwarzschild lens. This example motivates a
discussion of the relationship between the iterative approach, the standard
thin lens formulation, and an exact formulation of gravitational lensing.Comment: 27 pages, 2 figures, submitted to Phys.Rev.D, minor revisions, new
reference
Structure-activity relationships and molecular modeling of sphingosine kinase inhibitors
The design, synthesis, and evaluation of the potency of new isoform-selective inhibitors of sphingosine kinases 1 and 2 (SK1 and SK2), the enzyme that catalyzes the phosphorylation of d-erythro-sphingosine to produce the key signaling lipid, sphingosine 1-phosphate, are described. Recently, we reported that 1-(4-octylphenethyl)piperidin-4-ol (RB-005) is a selective inhibitor of SK1. Here we report the synthesis of 43 new analogues of RB-005, in which the lipophilic tail, polar headgroup, and linker region were modified to extend the structure-activity relationship profile for this lead compound, which we explain using modeling studies with the recently published crystal structure of SK1. We provide a basis for the key residues targeted by our profiled series and provide further evidence for the ability to discriminate between the two isoforms using pharmacological intervention
From the Field | Field Notes From Jail: How Incarceration and Homelessness Impact Womenâs Health
A multi-disciplinary team explored the journey they took with female inmates to develop a collaborative research strategy among the university, community organizations, and the correctional facility. The team consisted of academic researchers, inner city physicians, social workers, nurses, Aboriginal art therapists, Aboriginal cultural consultants, correctional healthcare administrators, and inner city chaplains from non-profit organizations. This paper describes how the team reflected on the journey to determine the impact of incarceration and/or homelessness on the health of female inmates, as they (the team) patiently waited for ethics boards and administrative approval; negotiated correctional center lockdowns; and became exhausted from trying to reconnect with women who were released from incarceration. The researchers discovered what kept them passionate about helping female inmates work through multiple hurdles that included housing, child custody, employment, probation appointments, and counseling. These administrative and operational challenges strengthened the teamâs resolve to support these vulnerable women
Lactobacillus fermentum (PCCÂź) supplementation and gastrointestinal and respiratory-tract illness symptoms: a randomised control trial in athletes
BACKGROUND Probiotics purportedly reduce symptoms of gastrointestinal and upper respiratory-tract illness by modulating commensal microflora. Preventing and reducing symptoms of respiratory and gastrointestinal illness are the primary reason that dietary supplementation with probiotics are becoming increasingly popular with healthy active individuals. There is a paucity of data regarding the effectiveness of probiotics in this cohort. The aim of this study was to evaluate the effectiveness of a probiotic on faecal microbiology, self-reported illness symptoms and immunity in healthy well trained individuals. METHODS Competitive cyclists (64 males and 35 females; age 35 ± 9 and 36 ± 9 y, VO2max 56 ± 6 and 52 ± 6 ml.kg-1.min-1, mean ± SD) were randomised to either probiotic (minimum 1 Ă 109 Lactobacillus fermentum (PCCÂź) per day) or placebo treatment for 11 weeks in a double-blind, randomised, controlled trial. The outcome measures were faecal L. fermentum counts, self-reported symptoms of illness and serum cytokines. RESULTS Lactobacillus numbers increased 7.7-fold (90% confidence limits 2.1- to 28-fold) more in males on the probiotic, while there was an unclear 2.2-fold (0.2- to 18-fold) increase in females taking the probiotic. The number and duration of mild gastrointestinal symptoms were ~2-fold greater in the probiotic group. However, there was a substantial 0.7 (0.2 to 1.2) of a scale step reduction in the severity of gastrointestinal illness at the mean training load in males, which became more pronounced as training load increased. The load (durationĂseverity) of lower respiratory illness symptoms was less by a factor of 0.31 (99%CI; 0.07 to 0.96) in males taking the probiotic compared with placebo but increased by a factor of 2.2 (0.41 to 27) in females. Differences in use of cold and flu medication mirrored these symptoms. The observed effects on URTI had too much uncertainty for a decisive outcome. There were clear reductions in the magnitude of acute exercise-induced changes in some cytokines. CONCLUSION L. fermentum may be a useful nutritional adjunct for healthy exercising males. However, uncertainty in the effects of supplementation on URTI and on symptoms in females needs to be resolved. TRIAL REGISTRATION The trial was registered in the Australia and New Zealand Clinical Trials Registry (ACTRN12611000006943).The study was funded by Christian Hansen A/S, Probiomics and the Australian Institute of Sport
First evidence of cryptotephra in palaeoenvironmental records associated with Norse occupation sites in Greenland
The Norse/Viking occupation of Greenland is part of a dispersal of communities across the North Atlantic coincident with the supposed Medieval Warm Period of the late 1st millennium AD. The abandonment of the Greenland settlements has been linked to climatic deterioration in the Little Ice Age as well as other possible explanations. There are significant dating uncertainties over the time of European abandonment of Greenland and the potential influence of climatic deterioration. Dating issues largely revolve around radiocarbon chronologies for Norse settlements and associated mire sequences close to settlement sites. Here we show the potential for moving this situation forward by a combination of palynological, radiocarbon and cryptotephra analyses of environmental records close to three âiconicâ Norse sites in the former Eastern Settlement of Greenland â Herjolfsnes, Hvalsey and GarĂ°ar (the modern Igaliku). While much work remains to be undertaken, our results show that palynological evidence can provide a useful marker for both the onset and end of Norse occupation in the region, while the radiocarbon chronologies for these sequences remain difficult. Significantly, we here demonstrate the potential for cryptotephra to become a useful tool in resolving the chronology of Norse occupation, when coupled with palynology. For the first time, we show that cryptotephra are present within palaeoenvironmental sequences located within or close to Norse settlement ruin-groups, with tephra horizons detected at all three sites. While shard concentrations were small at Herjolfsnes, concentrations sufficient for geochemical analyses were detected at Igaliku and Hvalsey. WDS-EPMA analyses of these tephra indicate that, unlike the predominantly Icelandic tephra sources reported in the Greenland ice core records, the tephra associated with the Norse sites correlate more closely with volcanic centres in the Aleutians and Cascades. Recent investigations of cryptotephra dispersal from North American centres, along with our new findings, point to the potential for cryptotephra to facilitate hypothesis testing, providing a key chronological tool for refining the timing of Norse activities in Greenland (e.g. abandonment) and of environmental contexts and drivers (e.g. climate forcing)
Was Sinn FĂ©in dying? A quantitative post-mortem of the party's decline and the emergence of Fianna FĂĄil
This article calls for a reappraisal of the consensus surrounding the split within Sinn FĂ©in in 1926 that led to the foundation of Fianna FĂĄil. It demonstrates that quantitative factors cited to demonstrate Sinn FĂ©inâs âterminalâ decline â finances, cumann numbers, and election results â and to explain de Valeraâs decision to leave Sinn FĂ©in and establish a rival republican organisation, Fianna FĂĄil, do not provide sufficient objective grounds to explain the republican leaderâs actions. This article demonstrates that Sinn FĂ©inâs election results during the period in question (1923-1926) were encouraging and the decline in finances and cumann numbers can be explained by the fact that the base year used to compare progress was 1923, an election year. Moreover, this article compares the performance of Sinn FĂ©in to the first five years of Fianna FĂĄil (1926-1931) to show that what has been interpreted as terminal decline can also be attributed to normal inter-election lulls in party activity. Correspondingly, subjective factors â e.g. personal rivalries, differences in ideology, organisational style and levels of patience in terms of achieving political power â were most likely the determining factors rather than organisational decline
Added value and cascade effects of inflammatory marker tests in UK primary care: A cohort study from the Clinical Practice Research Datalink
This is the final version. Available from Royal College of General Practitioners via the DOI in this record.âŻBackground: Inflammatory markers (C-reactive protein, erythrocyte sedimentation rate, and plasma viscosity) are commonly used in primary care. Though established for specific diagnostic purposes, there is uncertainty around their utility as a non-specific marker to rule out underlying disease in primary care.
Aim: To identify the value of inflammatory marker testing in primary care as a rule-out test, and measure the cascade effects of testing in terms of further blood tests, GP appointments, and referrals.
Design and setting: Cohort study of 160 000 patients with inflammatory marker testing in 2014, and 40 000 untested age, sex, and practice-matched controls, using UK primary care data from the Clinical Practice Research Datalink.
Method: The primary outcome was incidence of relevant disease, including infections, autoimmune conditions, and cancers, among those with raised versus normal inflammatory markers and untested controls. Process outcomes included rates of GP consultations, blood tests, and referrals in the 6 months after testing.
Results: The overall incidence of disease following a raised inflammatory marker was 15%: 6.3% infections, 5.6% autoimmune conditions, 3.7% cancers. Inflammatory markers had an overall sensitivity of <50% for the primary outcome, any relevant disease (defined as any infections, autoimmune conditions, or cancers). For 1000 inflammatory marker tests performed, the authors would anticipate 236 false-positives, resulting in an additional 710 GP appointments, 229 phlebotomy appointments, and 24 referrals in the following 6 months.
Conclusion: Inflammatory markers have poor sensitivity and should not be used as a rule-out test. False-positive results are common and lead to increased rates of follow-on GP consultations, tests, and referrals.National Institute for Health ResearchCancer Research UKNIHR Collaboration for Leadership in Applied Health Research and Care Wes
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