Robust Optimal Risk Sharing and Risk Premia in Expanding Pools

We consider the problem of optimal risk sharing in a pool of cooperative agents. We analyze the asymptotic behavior of the certainty equivalents and risk premia associated with the Pareto optimal risk sharing contract as the pool expands. We first study this problem under expected utility preferences with an objectively or subjectively given probabilistic model. Next, we develop a robust approach by explicitly taking uncertainty about the probabilistic model (ambiguity) into account. The resulting robust certainty equivalents and risk premia compound risk and ambiguity aversion. We provide explicit results on their limits and rates of convergence, induced by Pareto optimal risk sharing in expanding pools

Continuous Gravitational Waves from Isolated Galactic Neutron Stars in the Advanced Detector Era

We consider a simulated population of isolated Galactic neutron stars. The rotational frequency of each neutron star evolves through a combination of electromagnetic and gravitational wave emission. The magnetic field strength dictates the dipolar emission, and the ellipticity (a measure of a neutron star's deformation) dictates the gravitational wave emission. Through both analytic and numerical means, we assess the detectability of the Galactic neutron star population and bound the magnetic field strength and ellipticity parameter space of Galactic neutron stars with or without a direct gravitational wave detection. While our simulated population is primitive, this work establishes a framework by which future efforts can be conducted.Comment: Accepted for publication by Physical Review D, 8 pages, 5 figure

Social work support and unmet social needs in life after stroke: a cross-sectional exploratory study

Background: Stroke patients are often affected by long-term disabilities with needs concerning social issues. There is relatively little consideration of social recovery of patients and the support required to return to work, receive social benefits, participate in daily life activities, maintain contact with family and friends and to organize financial affairs. In our study we aimed to investigate if existing tools record social needs adequately. We analyzed the current provision of social support provided in long-term care after stroke and whether unmet social needs were associated with quality of life, caregiver burden, overall function and degree of disability. Methods: Our analysis is part of the Managing Aftercare of Stroke study (MAS-I), a cross-sectional exploratory study of patient needs 2–3 years after initial stroke. Assessment tools included the Nikolaus-score (social situation), the EuroQoL (quality of life), the German Burden Scale for Family Caregivers (caregiver burden), the modified Rankin Scale (disability / dependence), Stroke Impact Scale (function and degree of disability) and the Stroke Survivor Needs Questionnaire (unmet needs). Results: Overall 57 patients were included in MAS-I, with ten patients classified in urgent need of socio-economic support according to the Nikolaus-score. Patients with lower than normal Nikolaus-score had a higher degree of disability. Thirty percent of all patients had never received professional social support. Social worker contact happened mostly during the stay in acute hospital or rehabilitation institution. Only four patients (11%) reported long-term support after discharge. Apart from social worker contact during acute care, 43% of patients had unmet needs in the long-term aftercare. Forty percent of all patients included in MAS-I were recommended for social work intervention after an in-depth analysis of their situation. Finally, we saw that unmet social needs were associated with lower quality of life and higher caregiver burden. Conclusions: Our data suggest significant unmet needs in social care in long-term stroke patients. Screening tools for unmet social needs such as the Nikolaus-score do not holistically report patients’ needs

Timing of a Young Mildly Recycled Pulsar with a Massive White Dwarf Companion

We report on timing observations of the recently discovered binary pulsar PSR J1952+2630 using the Arecibo Observatory. The mildly recycled 20.7-ms pulsar is in a 9.4-hr orbit with a massive, M_WD > 0.93 M_sun, white dwarf (WD) companion. We present, for the first time, a phase-coherent timing solution, with precise spin, astrometric, and Keplerian orbital parameters. This shows that the characteristic age of PSR J1952+2630 is 77 Myr, younger by one order of magnitude than any other recycled pulsar-massive WD system. We derive an upper limit on the true age of the system of 50 Myr. We investigate the formation of PSR J1952+2630 using detailed modelling of the mass-transfer process from a naked helium star on to the neutron star following a common-envelope phase (Case BB Roche-lobe overflow). From our modelling of the progenitor system, we constrain the accretion efficiency of the neutron star, which suggests a value between 100 and 300% of the Eddington accretion limit. We present numerical models of the chemical structure of a possible oxygen-neon-magnesium WD companion. Furthermore, we calculate the past and the future spin evolution of PSR J1952+2630, until the system merges in about 3.4 Gyr due to gravitational wave emission. Although we detect no relativistic effects in our timing analysis we show that several such effects will become measurable with continued observations over the next 10 years; thus PSR J1952+2630 has potential as a testbed for gravitational theories.Comment: 12 pages, 10 figures, to be published in MNRA

Prospects of observing continuous gravitational waves from known pulsars

Several past searches for gravitational waves from a selection of known pulsars have been performed with data from the science runs of the Laser Inferometer Gravitational-wave Observatory (LIGO) gravitational wave detectors. So far these have lead to no detection, but upper limits on the gravitational wave amplitudes have been set. Here we study our intrinsic ability to detect, and estimate the gravitational wave amplitude for non-accreting pulsars. Using spin-down limits on emission as a guide we examine amplitudes that would be required to observe known pulsars with future detectors (Advanced LIGO, Advanced Virgo and the Einstein Telescope), assuming that they are triaxial stars emitting at precisely twice the known rotation frequency. Maximum allowed amplitudes depend on the stars' equation of state (e.g. a normal neutron star, a quark star, a hybrid star) and the theoretical mass quadrupoles that they can sustain. We study what range of quadrupoles, and therefore equations of state, would be consistent with being able to detect these sources. For globular cluster pulsars, with spin-downs masked by accelerations within the cluster, we examine what spin-down values gravitational wave observations would be able to set. For all pulsars we also alternatively examine what internal magnetic fields they would need to sustain observable ellipticities.Comment: version to be published in Monthly Notices of the Royal Astronomical Societ

Fast Radio Burst Discovered in the Arecibo Pulsar ALFA Survey

Recent work has exploited pulsar survey data to identify temporally isolated, millisecond-duration radio bursts with large dispersion measures (DMs). These bursts have been interpreted as arising from a population of extragalactic sources, in which case they would provide unprecedented opportunities for probing the intergalactic medium; they may also be linked to new source classes. Until now, however, all so-called fast radio bursts (FRBs) have been detected with the Parkes radio telescope and its 13-beam receiver, casting some concern about the astrophysical nature of these signals. Here we present FRB 121102, the first FRB discovery from a geographic location other than Parkes. FRB 121102 was found in the Galactic anti-center region in the 1.4-GHz Pulsar ALFA survey with the Arecibo Observatory with a DM = 557.4 $\pm$ 3 pc cm$^{-3}$, pulse width of $3\; \pm 0.5$ ms, and no evidence of interstellar scattering. The observed delay of the signal arrival time with frequency agrees precisely with the expectation of dispersion through an ionized medium. Despite its low Galactic latitude ($b = -0.2^{\circ}$), the burst has three times the maximum Galactic DM expected along this particular line-of-sight, suggesting an extragalactic origin. A peculiar aspect of the signal is an inverted spectrum; we interpret this as a consequence of being detected in a sidelobe of the ALFA receiver. FRB 121102's brightness, duration, and the inferred event rate are all consistent with the properties of the previously detected Parkes bursts.Comment: 9 pages, 3 figures, submitted to Ap

Social work after stroke: identifying demand for support by recording stroke patients' and carers' needs in different phases after stroke.

BACKGROUND: Previous studies examining social work interventions in stroke often lack information on content, methods and timing over different phases of care including acute hospital, rehabilitation and out-patient care. This limits our ability to evaluate the impact of social work in multidisciplinary stroke care. We aimed to quantify social-work-related support in stroke patients and their carers in terms of timing and content, depending on the different phases of stroke care. METHODS: We prospectively collected and evaluated data derived from a specialized "Stroke-Service-Point" (SSP); a "drop in" center and non-medical stroke assistance service, staffed by social workers and available to all stroke patients, their carers and members of the public in the metropolitan region of Berlin, Germany. RESULTS: Enquiries from 257 consenting participants consulting the SSP between March 2010 and April 2012 related to out-patient and in-patient services, therapeutic services, medical questions, medical rehabilitation, self-help groups and questions around obtaining benefits. Frequency of enquiries for different topics depended on whether patients were located in an in-patient or out-patient setting. The majority of contacts involved information provision. While the proportion of male and female patients with stroke was similar, about two thirds of the carers contacting the SSP were female. CONCLUSION: The social-work-related services provided by a specialized center in a German metropolitan area were diverse in terms of topic and timing depending on the phase of stroke care. Targeting the timing of interventions might be important to increase the impact of social work on patient's outcome

identifying demand for support by recording stroke patients’ and carers’ needs in different phases after stroke

Background Previous studies examining social work interventions in stroke often lack information on content, methods and timing over different phases of care including acute hospital, rehabilitation and out-patient care. This limits our ability to evaluate the impact of social work in multidisciplinary stroke care. We aimed to quantify social-work-related support in stroke patients and their carers in terms of timing and content, depending on the different phases of stroke care. Methods We prospectively collected and evaluated data derived from a specialized “Stroke-Service-Point” (SSP); a “drop in” center and non-medical stroke assistance service, staffed by social workers and available to all stroke patients, their carers and members of the public in the metropolitan region of Berlin, Germany. Results Enquiries from 257 consenting participants consulting the SSP between March 2010 and April 2012 related to out-patient and in-patient services, therapeutic services, medical questions, medical rehabilitation, self-help groups and questions around obtaining benefits. Frequency of enquiries for different topics depended on whether patients were located in an in-patient or out-patient setting. The majority of contacts involved information provision. While the proportion of male and female patients with stroke was similar, about two thirds of the carers contacting the SSP were female. Conclusion The social- work-related services provided by a specialized center in a German metropolitan area were diverse in terms of topic and timing depending on the phase of stroke care. Targeting the timing of interventions might be important to increase the impact of social work on patient’s outcome

Mast cells modulate the pathogenesis of elastase-induced abdominal aortic aneurysms in mice

Abdominal aortic aneurysm (AAA), an inflammatory disease, involves leukocyte recruitment, immune responses, inflammatory cytokine production, vascular remodeling, neovascularization, and vascular cell apoptosis, all of which contribute to aortic dilatation. This study demonstrates that mast cells, key participants in human allergic immunity, participate in AAA pathogenesis in mice. Mast cells were found to accumulate in murine AAA lesions. Mast cell–deficient KitW-sh/KitW-sh mice failed to develop AAA elicited by elastase perfusion or periaortic chemical injury. KitW-sh/KitW-sh mice had reduced aortic expansion and internal elastic lamina degradation; decreased numbers of macrophages, CD3+ T lymphocytes, SMCs, apoptotic cells, and CD31+ microvessels; and decreased levels of aortic tissue IL-6 and IFN-γ. Activation of mast cells in WT mice via C48/80 injection resulted in enhanced AAA growth while mast cell stabilization with disodium cromoglycate diminished AAA formation. Mechanistic studies demonstrated that mast cells participated in angiogenesis, aortic SMC apoptosis, and matrix-degrading protease expression. Reconstitution of KitW-sh/KitW-sh mice with bone marrow–derived mast cells from WT or TNF-α–/– mice, but not from IL-6–/– or IFN-γ–/– mice, caused susceptibility to AAA formation to be regained. These results demonstrate that mast cells participate in AAA pathogenesis in mice by releasing proinflammatory cytokines IL-6 and IFN-γ, which may induce aortic SMC apoptosis, matrix-degrading protease expression, and vascular wall remodeling, important hallmarks of arterial aneurysms

Blandford's Argument: The Strongest Continuous Gravitational Wave Signal

For a uniform population of neutron stars whose spin-down is dominated by the emission of gravitational radiation, an old argument of Blandford states that the expected gravitational-wave amplitude of the nearest source is independent of the deformation and rotation frequency of the objects. Recent work has improved and extended this argument to set upper limits on the expected amplitude from neutron stars that also emit electromagnetic radiation. We restate these arguments in a more general framework, and simulate the evolution of such a population of stars in the gravitational potential of our galaxy. The simulations allow us to test the assumptions of Blandford's argument on a realistic model of our galaxy. We show that the two key assumptions of the argument (two dimensionality of the spatial distribution and a steady-state frequency distribution) are in general not fulfilled. The effective scaling dimension D of the spatial distribution of neutron stars is significantly larger than two, and for frequencies detectable by terrestrial instruments the frequency distribution is not in a steady state unless the ellipticity is unrealistically large. Thus, in the cases of most interest, the maximum expected gravitational-wave amplitude does have a strong dependence on the deformation and rotation frequency of the population. The results strengthen the previous upper limits on the expected gravitational-wave amplitude from neutron stars by a factor of 6 for realistic values of ellipticity.Comment: 12 pages, 6 Figures, published in Phys. Rev. D, v3: final published versio