Direct Detection of Galactic Halo Dark Matter

The Milky Way Galaxy contains a large, spherical component which is believed to harbor a substantial amount of unseen matter. Recent observations indirectly suggest that as much as half of this ``dark matter'' may be in the form of old, very cool white dwarfs, the remnants of an ancient population of stars as old as the Galaxy itself. We conducted a survey to find faint, cool white dwarfs with large space velocities, indicative of their membership in the Galaxy's spherical halo component. The survey reveals a substantial, directly observed population of old white dwarfs, too faint to be seen in previous surveys. This newly discovered population accounts for at least 2% of the halo dark matter. It provides a natural explanation for the indirect observations, and represents a direct detection of Galactic halo dark matter.Comment: 13 pages, 4 figures, 1 table. Note added after Science Express online publication: This text reflects the correction of a few typographical errors in the online version of the table. It also includes the new constraint on the calculation of d_max which accounts for the fact that the survey could not have detected stars with proper motions below 0.33 arcseconds per year. Published online at ScienceExpress www.sciencemag.org 22 March 2001; 10.1126/science.1059954; To appear in Science 27 April 200

Pressure dependence of the sound velocity in a 2D lattice of Hertz-Mindlin balls: a mean field description

We study the dependence on the external pressure $P$ of the velocities $v_{L,T}$ of long wavelength sound waves in a confined 2D h.c.p. lattice of 3D elastic frictional balls interacting via one-sided Hertz-Mindlin contact forces, whose diameters exhibit mild dispersion. The presence of an underlying long range order enables us to build an effective medium description which incorporates the radial fluctuations of the contact forces acting on a single site. Due to the non linearity of Hertz elasticity, self-consistency results in a highly non-linear differential equation for the "equation of state" linking the effective stiffness of the array with the applied pressure, from which sound velocities are then obtained. The results are in excellent agreement with existing experimental results and simulations in the high and intermediate pressure regimes. It emerges from the analysis that the departure of $v_{L}(P)$ from the ideal $P^{1/6}$ Hertz behavior must be attributed primarily to the fluctuations of the stress field, rather than to the pressure dependence of the number of contacts

Psychosis in autism: comparison of the features of both conditions in a dually affected cohort.

BackgroundThere is limited information on the presentation and characteristics of psychotic illness experienced by people with autism spectrum disorder (ASD).AimsTo describe autistic and psychotic phenomenology in a group of individuals with comorbid ASD and psychosis (ASD-P) and compare this group with populations affected by either, alone.MethodWe studied 116 individuals with ASD-P. We compared features of their ASD with people with ASD and no comorbid psychosis (ASD-NP), and clinical characteristics of psychosis in ASD-P with people with psychosis only.ResultsIndividuals with ASD-P had more diagnoses of atypical psychosis and fewer of schizophrenia compared with individuals with psychosis only. People with ASD-P had fewer stereotyped interests/behaviours compared with those with ASD-NP.ConclusionsOur data show there may be a specific subtype of ASD linked to comorbid psychosis. The results support findings that psychosis in people with ASD is often atypical, particularly regarding affective disturbance.Medical Research Council (PhD studentship, Autism Imaging Multicentre Study (MRC AIMS) Consortium), Baily Thomas Charitable Trust, Health Foundation, University of Cambridge (William Binks Autism Neuroscience Fellowship), Child and Youth Mental Health Collaborative at the Centre for Addiction and Mental Health and The Hospital for Sick Children, Toronto (O’Brien Scholars Program), Autism Research Trust, National Institute for Health Research (NIHR) Collaboration for Leadership in Applied Health Research and Care East of England at the Cambridgeshire & Peterborough NHS Foundation TrustThis is the final version of the article. It first appeared from The Royal College of Psychiatrists via https://doi.org/10.1192/bjp.bp.116.18768

TBI lesion segmentation in head CT: impact of preprocessing and data augmentation

Automatic segmentation of lesions in head CT provides keyinformation for patient management, prognosis and disease monitoring.Despite its clinical importance, method development has mostly focusedon multi-parametric MRI. Analysis of the brain in CT is challengingdue to limited soft tissue contrast and its mono-modal nature. We studythe under-explored problem of fine-grained CT segmentation of multiplelesion types (core, blood, oedema) in traumatic brain injury (TBI). Weobserve that preprocessing and data augmentation choices greatly impactthe segmentation accuracy of a neural network, yet these factors arerarely thoroughly assessed in prior work. We design an empirical studythat extensively evaluates the impact of different data preprocessing andaugmentation methods. We show that these choices can have an impactof up to 18% DSC. We conclude that resampling to isotropic resolutionyields improved performance, skull-stripping can be replaced by using theright intensity window, and affine-to-atlas registration is not necessaryif we use sufficient spatial augmentation. Since both skull-stripping andaffine-to-atlas registration are susceptible to failure, we recommend theiralternatives to be used in practice. We believe this is the first work toreport results for fine-grained multi-class segmentation of TBI in CT. Ourfindings may inform further research in this under-explored yet clinicallyimportant task of automatic head CT lesion segmentation

Thermoregulation of foraging honeybees on flowering plants: seasonal variability and influence of radiative heat gain

1. During nectar and pollen foraging in a temperate climate, honeybees are exposed to a broad range of ambient temperatures, challenging their thermoregulatory ability. The body temperature that the bees exhibit results from endothermic heat production, exogenous heat gain from solar radiation, and heat loss. In addition to profitability of foraging, season was suggested to have a considerable influence on thermoregulation. To assess the relative importance of these factors, the thermoregulatory behaviour of foragers on 33 flowering plants in dependence on season and environmental factors was investigated

The Lyot project: toward exoplanet imaging and spectroscopy

Among the adaptive optics systems available to astronomers, the US Air Force Advanced Electro-Optical System (AEOS) is unique because it delivers very high order wave front correction. The Lyot Project includes the construction and installation of the world’s first diffraction-limited, optimized coronagraph that exploits the full astronomical potential of AEOS and represents a critical step toward the long-term goal of directly imaging and studying extrasolar planets (a.k.a. “exoplanets”). We provide an update on the Project, whose coronagraph saw first light in March 2004. The coronagraph is operating at least as well as predicted by simulations, and a survey of nearby stars has begun