3,815 research outputs found

    Nuclear Equation of State from Observations of Short Gamma-Ray Burst Remnants

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    The favoured progenitor model for short γ\gamma-ray bursts (SGRBs) is the merger of two neutron stars that triggers an explosion with a burst of collimated γ\gamma-rays. Following the initial prompt emission, some SGRBs exhibit a plateau phase in their XX-ray light curves that indicates additional energy injection from a central engine, believed to be a rapidly rotating, highly magnetised neutron star. The collapse of this `protomagnetar' to a black hole is likely to be responsible for a steep decay in XX-ray flux observed at the end of the plateau. In this letter, we show that these observations can be used to effectively constrain the equation of state of dense matter. In particular, we show that the known distribution of masses in binary neutron star systems, together with fits to the XX-ray light curves, provide constraints that exclude the softest and stiffest plausible equations of state. We further illustrate how a future gravitational wave observation with Advanced LIGO/Virgo can place tight constraints on the equation of state, by adding into the picture a measurement of the chirp mass of the SGRB progenitor.Comment: accepted for publication in Phys. Rev.

    Heirs\u27 Property in Virginia: Filling in the Gaps

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    The term heirs’ property refers to land that has been passed down informally for multiple generations through intestate succession. Each generation of intestate succession can drastically increase the number of heirs who own the property as tenants-in-common to the point that many may not even know their heirship status. This clouds the title to the property and makes ownership more fractionalized. Because heirs’ property exists outside of the official estate and title systems, owners are vulnerable both at the community and individual levels for three main reasons. First, and most importantly, heirs’ property is a leading cause of involuntary Black land loss. [...] Second, scholars have found a link between heirs’ property and diminished community vitality. [...] Finally, heirs’ property ownership structures can remove owners’ access to funding and government assistance programs, creating links to poverty at a parcel-by-parcel level. This abstract has been adapted from the authors\u27 opening paragraphs

    Meridional heat transport across the Antarctic Circumpolar Current by the Antarctic Bottom Water overturning cell

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    The heat transported by the lower limb of the Southern Ocean meridional overturning circulation is commonly held to be negligible in comparison with that transported by eddies higher in the water column. We use output from one of the first global high resolution models to have a reasonably realistic export of Antarctic Bottom Water, the OCCAM one twelfth degree model. The heat fluxed southward by the deep overturning cell using the annual mean field for 1994 at 56S is 0.033 PW, but the 5-day mean fields give a larger heat flux (0.048 and 0.061 PW depending on calculation method). This is more than 30% of previous estimates of the total heat flux. Eddies and other transients add considerably to the heat flux. These results imply that this component of meridional heat flux may not be negligible as has been supposed

    Recovery of spermatogenesis following testosterone replacement therapy or anabolic-androgenic steroid use

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    The use of testosterone replacement therapy (TRT) for hypogonadism continues to rise, particularly in younger men who may wish to remain fertile. Concurrently, awareness of a more pervasive use of anabolic-androgenic steroids (AAS) within the general population has been appreciated. Both TRT and AAS can suppress the hypothalamic-pituitary-gonadal (HPG) axis resulting in diminution of spermatogenesis. Therefore, it is important that clinicians recognize previous TRT or AAS use in patients presenting for infertility treatment. Cessation of TRT or AAS use may result in spontaneous recovery of normal spermatogenesis in a reasonable number of patients if allowed sufficient time for recovery. However, some patients may not recover normal spermatogenesis or tolerate waiting for spontaneous recovery. In such cases, clinicians must be aware of the pathophysiologic derangements of the HPG axis related to TRT or AAS use and the pharmacologic agents available to reverse them. The available agents include injectable gonadotropins, selective estrogen receptor modulators, and aromatase inhibitors, but their off-label use is poorly described in the literature, potentially creating a knowledge gap for the clinician. Reviewing their use clinically for the treatment of hypogonadotropic hypogonadism and other HPG axis abnormalities can familiarize the clinician with the manner in which they can be used to recover spermatogenesis after TRT or AAS use

    A redshift - observation-time relation for gamma-ray bursts: evidence of a distinct sub-luminous population

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    We show how the redshift and peak-flux distributions of gamma-ray bursts (GRBs) have an observation time dependence that can be used to discriminate between different burst populations. We demonstrate how observation time relations can be derived from the standard integral distributions and that they can differentiate between GRB populations detected by both the BATSE and \emph{Swift} satellites. Using \emph{Swift} data we show that a redshift--observation-time relation (log\,ZZ\,--\,log\,TT) is consistent with both a peak-flux\,--\,observation time relation (log\,PP\,--\,log\,TT) and a standard log\,NN\,--\,log\,PP brightness distribution. As the method depends only on rarer small-zz events, it is invariant to high-zz selection effects. We use the log\,ZZ\,--\,log\,TT relation to show that sub-luminous GRBs are a distinct population occurring at a higher rate of order 150−90+180Gpc−3yr−1150^{+180}_{-90} \mathrm{Gpc}^{-3}\mathrm{yr}^{-1}. Our analysis suggests that GRB 060505 -- a relatively nearby GRB observed without any associated supernova -- is consistent with a sub-luminous population of bursts. Finally, we suggest that our relations can be used as a consistency test for some of the proposed GRB spectral energy correlations.Comment: Accepted by MNRA

    Cognitive dysfunction in patients with cerebral microbleeds on T2*-weighted gradient-echo MRI.

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    Gradient echo T2*-weighted MRI has high sensitivity in detecting cerebral microbleeds, which appear as small dot-like hypointense lesions. Microbleeds are strongly associated with intracerebral haemorrhage, hypertension, lacunar stroke and ischaemic small vessel disease, and have generated interest as a marker of bleeding-prone microangiopathy. Microbleeds have generally been considered to be clinically silent; however, since they are located in widespread cortical and basal ganglia regions and are histologically characterized by tissue damage, we hypothesized that they would cause cognitive dysfunction. We therefore studied patients with microbleeds (n = 25) and a non-microbleed control group (n = 30) matched for age, gender and intelligence quotient. To avoid the confounding effects of coexisting cerebrovascular disease, the groups were also matched for the extent of MRI-visible white matter changes of presumed ischaemic origin, location of cortical strokes, and for the proportion of patients with different stroke subtypes (including lacunar stroke). A battery of neuropsychological tests was used to assess current intellectual function, verbal and visual memory, naming and perceptual skills, speed and attention and executive function. Microbleeds were most common in the basal ganglia but were also found in frontal, parieto-occipital, temporal and infratentorial regions. There was a striking difference between the groups in the prevalence of executive dysfunction, which was present in 60% of microbleed patients compared with 30% of non-microbleed patients (P = 0.03). Logistic regression confirmed that microbleeds (but not white matter changes) were an independent predictor of executive impairment (adjusted odds ratio = 1.32, 95% confidence interval 1.01-1.70, P = 0.04). Patients with executive dysfunction had more microbleeds in the frontal region (mean count 1.54 versus 0.03; P = 0.002) and in the basal ganglia (mean 1.17 versus 0.32; P = 0.048). There was a modest correlation between the number of microbleeds and the number of cognitive domains impaired (r = 0.44, P = 0.03). This study provides novel evidence that microbleeds are associated with cognitive dysfunction, independent of the extent of white matter changes of presumed ischaemic origin, or the presence of ischaemic stroke. The striking effect of microbleeds on executive dysfunction is likely to result from associated tissue damage in the frontal lobes and basal ganglia. These findings have implications for the diagnosis of stroke patients with cognitive impairment, and for the appropriate use of antihypertensive and antiplatelet treatments in these patients

    Fall back accretion and energy injections in gamma-ray bursts

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    Intense flares that occur at late times relative to the prompt phase have been observed by the SwiftSwift satellite in the X-ray afterglows of gamma-ray bursts (GRBs). Here, we present a detailed analysis on the fall back accretion process to explain the intense flare phase in the very early X-ray afterglow light curves. To reproduce the afterglow at late times, we resort to the external shock by engaging energy injections. By applying our model to GRBs 080810, 081028 and 091029, we show that their X-ray afterglow light curves can be reproduced well. We then apply our model to the ultra-long SwiftSwift GRB 111209A, which is the longest burst ever observed. The very early X-ray afterglow of GRB 111209A showed many interesting features, such as a significant bump observed at around 2000 s after the SwiftSwift/BAT trigger. We assume two constant energy injection processes in our model. These can explain the observed plateau at X-ray wavelength in the relatively early stage (8.0×1038.0\times10^{3} s) and a second X-ray plateau and optical rebrightening at about 10510^{5} s. Our analysis supports the scenario that a significant amount of material may fall back toward the central engine after the prompt phase, causing an enhanced and long lived mass accretion rate powering a Poynting-flux-dominated outflow.Comment: 2 tables, 3 figures, accepted by MNRA

    Through the Looking Glass: An Autoethnographic View of the Perceptions of Race and Institutional Support in the Tenure Process

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    This autoethnography study reflects on the experiences of three assistant professors of different races of the tenure process at a large public research university. The study was framed by social cognitive career theory (SCCT), which is often used to describe career interest and career choice in a variety of professional domains, considering cognitive - personal, environmental, and experiential factors (Lent, 2005; Tang, Pan, & Newmeyer, 2008). Despite the commonality of the journey through the tenure process, everyone’s path looks different. Isolation, collegial relationships, and for some, unusually high service commitments and family responsibilities, whether because of gender or race, have provided a back drop for the lives of women in academe and have, in large part, defined their experiences on the tenure track. The results of the reflections of our experiences identify that environmental variables are important to the success of tenure seeking faculty
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