Impact of basic angle variations on the parallax zero point for a scanning astrometric satellite

Determination of absolute parallaxes by means of a scanning astrometric satellite such as Hipparcos or Gaia relies on the short-term stability of the so-called basic angle between the two viewing directions. Uncalibrated variations of the basic angle may produce systematic errors in the computed parallaxes. We examine the coupling between a global parallax shift and specific variations of the basic angle, namely those related to the satellite attitude with respect to the Sun. The changes in observables produced by small perturbations of the basic angle, attitude, and parallaxes are calculated analytically. We then look for a combination of perturbations that has no net effect on the observables. In the approximation of infinitely small fields of view, it is shown that certain perturbations of the basic angle are observationally indistinguishable from a global shift of the parallaxes. If such perturbations exist, they cannot be calibrated from the astrometric observations but will produce a global parallax bias. Numerical simulations of the astrometric solution, using both direct and iterative methods, confirm this theoretical result. For a given amplitude of the basic angle perturbation, the parallax bias is smaller for a larger basic angle and a larger solar aspect angle. In both these respects Gaia has a more favourable geometry than Hipparcos. In the case of Gaia, internal metrology is used to monitor basic angle variations. Additionally, Gaia has the advantage of detecting numerous quasars, which can be used to verify the parallax zero point.Comment: 8 pages, 2 figures; Accepted for publication in Astronomy & Astrophysic

A sequential dynamic Bayesian network for pore pressure estimation with uncertainty quantification

Pore-pressure estimation is an important part of oil-well drilling, since drilling into unexpected highly pressured fluids can be costly and dangerous. However, standard estimation methods rarely account for the many sources of uncertainty, or for the multivariate nature of the system. We propose the pore pressure sequential dynamic Bayesian network (PP SDBN) as an appropriate solution to both these issues. The PP SDBN models the relationships between quantities in the pore pressure system, such as pressures, porosity, lithology and wireline log data, using conditional probability distributions based on geophysical relationships to capture our uncertainty about these variables and the relationships between them. When wireline log data is given to the PP SDBN, the probability distributions are updated, providing an estimate of pore pressure along with a probabilistic measure of uncertainty that reflects the data acquired and our understanding of the system. This is the advantage of a Bayesian approach. Our model provides a coherent statistical framework for modelling the pore pressure system. The specific geophysical relationships used can be changed to better suit a particular setting, or reflect geoscientists’ knowledge. We demonstrate the PP SDBN on an offshore well from West Africa. We also perform a sensitivity analysis, demonstrating how this can be used to better understand the working of the model and which parameters are the most influential. The dynamic nature of the model makes it suitable for real time estimation during logging while drilling. The PP SDBN models shale pore pressure in shale rich formations with mechanical compaction as the overriding source of overpressure. The PP SDBN improves on existing methods since it produces a probabilistic estimate that reflects the many sources of uncertainty present

Raloxifene Enhances Material-Level Mechanical Properties of Femoral Cortical and Trabecular Bone

We have previously documented that raloxifene enhances the mechanical properties of dog vertebrae independent of changes in bone mass, suggesting a positive effect of raloxifene on material-level mechanical properties. The goal of this study was to determine the separate effects of raloxifene on the material-level mechanical properties of trabecular and cortical bone from the femur of beagle dogs. Skeletally mature female beagles (n = 12 per group) were treated daily for 1 yr with oral doses of vehicle or raloxifene (0.50 mg/kg d). Trabecular bone mechanical properties were measured at the femoral neck using reduced platen compression, a method that allows the trabecular bone to be tested without coring specimens. Cortical bone properties were assessed on prismatic beam specimens machined from the femoral diaphysis using both monotonic and dynamic (cyclic relaxation) four-point bending tests. Trabecular bone from raloxifene-treated animals had significantly higher ultimate stress (+130%), modulus (+89%), and toughness (+152%) compared with vehicle-treated animals. Cortical bone from raloxifene-treated animals had significantly greater toughness (+62%) compared with vehicle, primarily as a function of increased postyield displacement (+100%). There was no significant difference between groups in the percentage of stiffness loss during cortical bone cyclic relaxation tests. These results are consistent with previous data from the vertebrae of these same animals, showing raloxifene has positive effects on biomechanical properties independent of changes in bone volume/density. This may help explain how raloxifene reduces osteoporotic fractures despite modest changes in bone mass.This work was supported by National Institutes of Health Grants AR047838 and AR007581 and a research grant from Lilly Research Laboratories. This investigation used an animal facility constructed with support from Research Facilities Improvement Program Grant Number C06 RR10601-01 from the National Center for Research Resources, National Institutes of Health. Disclosure Summary: M.R.A. has research contracts from Eli Lilly and the Alliance for Better Bone Health. D.B.B. has research contracts from Eli Lilly, the Alliance for Better Bone Health, and Amgen; owns stock in Amgen, Eli Lilly, Pfizer, and Glaxo SmithKline; and is a speaker/consultant for Merck, Eli Lilly, the Alliance for Better Bone Health, and Amgen. A.S.K. and M.C.K. have a family member employed by Eli Lilly. H.A.H. and W.A.H. have nothing to declare

An ASCA Study of the Heavy Element Distribution in Clusters of Galaxies

We perform a spatially resolved X-ray spectroscopic study of a set of 11 relaxed clusters of galaxies observed by the ROSAT/PSPC and ASCA/SIS. Using a method which corrects for the energy dependent effects of the ASCA PSF based on ROSAT images, we constrain the spatial distribution of Ne, Si, S and Fe in each cluster. Theoretical prescriptions for the chemical yields of Type Ia and II supernovae, then allow determination of the Fe enrichment from both types of supernovae as a function of radius within each cluster. Using optical measurements from the literature, we also determine the iron mass-to-light ratio (IMLR) separately for Fe synthesized in both types of supernovae. For clusters with the best photon statistics, we find that the total Fe abundance decreases significantly with radius, while the Si abundance is either flat or decreases less rapidly, resulting in an increasing Si/Fe ratio with radius. This result indicates a greater predominance of Type II SNe enrichment at large radii in clusters. We suggest that the high Si/Fe ratios in the outskirts of rich clusters may arise from enrichment by Type II SNe released to ICM via galactic star burst driven winds. Abridged.Comment: 17 pages, ApJ in press (Nov. 2000), a study of systematics is adde

Drawing Trees with Perfect Angular Resolution and Polynomial Area

We study methods for drawing trees with perfect angular resolution, i.e., with angles at each node v equal to 2{\pi}/d(v). We show: 1. Any unordered tree has a crossing-free straight-line drawing with perfect angular resolution and polynomial area. 2. There are ordered trees that require exponential area for any crossing-free straight-line drawing having perfect angular resolution. 3. Any ordered tree has a crossing-free Lombardi-style drawing (where each edge is represented by a circular arc) with perfect angular resolution and polynomial area. Thus, our results explore what is achievable with straight-line drawings and what more is achievable with Lombardi-style drawings, with respect to drawings of trees with perfect angular resolution.Comment: 30 pages, 17 figure

Borderline Personality Disorder Symptom Severity and Sexually Transmitted Infection and HIV Risk in African American Incarcerated Men

Sexually transmitted infections (STI)/HIV rates are disproportionately high among men involved in the criminal justice system. Mental health disorders, including personality disorders, are also elevated among inmates. Borderline personality disorder (BPD) may be an important risk factor for STI/HIV, yet remains relatively understudied, particularly among inmates

Validation of the Cepheid GeneXpert for Detecting Ebola Virus in Semen

Background: Ebola virus (EBOV) RNA persistence in semen, reported sexual transmission, and sporadic clusters at the end of the 2013-2016 epidemic have prompted recommendations that male survivors refrain from unprotected sex unless their semen is confirmed to be EBOV free. However, there is no fully validated assay for EBOV detection in fluids other than blood. Methods: The Cepheid Xpert Ebola assay for EBOV RNA detection was validated for whole semen and blood using samples obtained from uninfected donors and spiked with inactivated EBOV. The validation procedure incorporated standards from Clinical and Laboratory Standards Institute and Good Clinical Laboratory Practices guidelines for evaluating molecular devices for use in infectious disease testing. Results: The assay produced limits of detection of 1000 copies/mL in semen and 275 copies/mL in blood. Limits of detection for both semen and blood increased with longer intervals between collection and testing, with acceptable results obtained up to 72 hours after specimen collection. Conclusions: The Cepheid Xpert Ebola assay is accurate and precise for detecting EBOV in whole semen. A validated assay for EBOV RNA detection in semen informs the care of male survivors of Ebola, as well as recommendations for public health

Reviews

Tolkien, Race and Cultural History: From Fairies to Hobbits. Dimitra Fimi. Reviewed by Jason Fisher. Charles Williams and his Contemporaries. Suzanne Bray and Richard Sturch, eds. Reviewed by Joe R. Christopher. In the Land of Invented Languages: Esperanto Rock Stars, Klingon Poets, Loglan Lovers, and the Mad Dreamers who Tried to Build a Perfect Language. Arika Okrent. Reviewed by Harley J. Sims. Millennial Mythmaking: Essays on the Power of Science Fiction and Fantasy Literature, Films and Games. John Perlich & David Whitt, eds. Reviewed by Priscilla Hobbs Middle-earth Minstrel: Essays on Music in Tolkien. Bradford Lee Eden, ed. Reviewed by Emily A. Moniz. Harry Potter & Imagination: The Way Between Two Worlds. Travis Prinzi. Reviewed by David D. Oberhelman. Fastitocalon: Studies in Fantasticism Ancient to Modern: Immortals and the Undead. Eds. Thomas Honneger and Fanfan Chen. Reviewed by Janet Brennan Croft. Theodor Seuss Geisel [sic]. Donald E. Pease. Reviewed by Joe R. Christopher