Long-term degradation of optical devices on the moon

Forty years ago, Apollo astronauts placed the first of several retroreflector arrays on the lunar surface. Their continued usefulness for laser-ranging might suggest that the lunar environment does not damage optical devices. However, new laser ranging data reveal that the efficiency of the three Apollo reflector arrays is now diminished by a factor of ten at all lunar phases and by an additional factor of ten when the lunar phase is near full moon. These deficits did not exist in the earliest years of lunar ranging, indicating that the lunar environment damages optical equipment on the timescale of decades. Dust or abrasion on the front faces of the corner-cube prisms may be responsible, reducing their reflectivity and degrading their thermal performance when exposed to face-on sunlight at full moon. These mechanisms can be tested using laboratory simulations and must be understood before designing equipment destined for the moon.Comment: 9 pages; 4 figures; accepted for publication in Icaru

A cross-sectional study of peripartum blood transfusion in the Eastern Cape, South Africa

Background. Obstetric haemorrhage (OH) remains a major contributor to maternal morbidity and mortality. Blood transfusion is critical in OH management; yet, data on peripartum transfusion are lacking. A pilot study reported high rates of peripartum transfusion in a sample of South African (SA) hospitals, which was independently associated with HIV status.Objectives. To assess the incidence of peripartum transfusion in a sample of Eastern Cape, SA hospitals to evaluate generalisability of preceding study findings.Methods. Hospital chart reviews were conducted of all deliveries at three large regional hospitals from February to June 2013. Additional clinical data were collected for patients who sustained OH and/or were transfused.Results. A total of 7 234 women were enrolled in the study; 1 988 (27.5%) were HIV-positive. Of the 767 HIV-positive women with a CD4 count <350 cells/μL, 86.0% were on full antiretroviral therapy and 9.9% received drugs for prevention of mother-to-child transmission. The overall transfusion rate was 3.2%, with significant variability by hospital: Frere Hospital (1.5%), Dora Nginza Hospital (3.8%) and Cecilia Makiwane Hospital (4.6%). The number of red blood cell units per transfused patient and per delivery varied significantly by hospital. Bivariate analysis showed significant association between transfusion and HIV status. In a multivariate analysis, controlling for OH, age, mode of delivery, gestational age, parity and birthweight, this association (odds ratio 1.45; 95% confidence interval 0.78 - 2.71) was no longer significant.Conclusion. These findings confirm high rates of peripartum transfusion in SA. While this can be possibly ascribed to variability in practice and patient profile, variation in care and improvement in HIV treatment should be considered

Pain location and widespread pain in youth with orthopaedic conditions: Exploration of the reliability and validity of a body map

BackgroundPain location and widespread pain are important but underexamined dimensions of paediatric pain. Body map tools to assess pain location in youth have been used for several decades, but few studies have established reliability and validity of these measures. The purpose of this study was to explore the reliability and validity of a pain body map among youth with orthopaedic conditions before surgery.MethodYouth ages 10â 17 years completed the body map and other selfâ reported outcomes at their preoperative clinic visit and at their day of surgery.ResultsMost (91.7%) youth had small discrepancy between body map scores at preoperative clinic visit (baseline) and day of surgery (second assessment), and siteâ toâ site agreement ranged from 78% to 98%. Those with back and lower extremity diagnoses had high correspondence between body map sites and diagnostic sites. Body map scores and widespread pain were associated with other dimensions of pain, as well as other patientâ reported outcomes. Higher pain intensity and widespread pain predicted greater discrepancy between body map scores.ConclusionsThese results support the use of body map tools in further research examining widespread pain among youth by demonstrating adequate reliability, descriptive validity and associative validity.SignificanceThese results contribute to the limited information regarding psychometric properties of paediatric pain body maps, provide novel information about widespread pain among youth undergoing orthopaedic surgeries, and pave the way for improved assessment and treatment of paediatric pain.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/147159/1/ejp1282.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/147159/2/ejp1282_am.pd

Heliospheric Transport of Neutron-Decay Protons

We report on new simulations of the transport of energetic protons originating from the decay of energetic neutrons produced in solar flares. Because the neutrons are fast-moving but insensitive to the solar wind magnetic field, the decay protons are produced over a wide region of space, and they should be detectable by current instruments over a broad range of longitudes for many hours after a sufficiently large gamma-ray flare. Spacecraft closer to the Sun are expected to see orders-of magnitude higher intensities than those at the Earth-Sun distance. The current solar cycle should present an excellent opportunity to observe neutron-decay protons with multiple spacecraft over different heliographic longitudes and distances from the Sun.Comment: 12 pages, 4 figures, to be published in special issue of Solar Physic

Lifetime of Two-Dimensional Electrons Measured by Tunneling Spectroscopy

For electrons tunneling between parallel two-dimensional electron systems, conservation of in-plane momentum produces sharply resonant current-voltage characteristics and provides a uniquely sensitive probe of the underlying electronic spectral functions. We report here the application of this technique to accurate measurements of the temperature dependence of the electron-electron scattering rate in clean two-dimensional systems. Our results are in qualitative agreement with existing calculations.Comment: file in REVTEX format produces 11 pages, 3 figures available from [email protected]

Mott Transition in Degenerate Hubbard Models: Application to Doped Fullerenes

The Mott-Hubbard transition is studied for a Hubbard model with orbital degeneracy N, using a diffusion Monte-Carlo method. Based on general arguments, we conjecture that the Mott-Hubbard transition takes place for U/W \propto \sqrt{N}, where U is the Coulomb interaction and W is the band width. This is supported by exact diagonalization and Monte-Carlo calculations. Realistic parameters for the doped fullerenes lead to the conclusion that stoichiometric A_3 C_60 (A=K, Rb) are near the Mott-Hubbard transition, in a correlated metallic state.Comment: 4 pages, revtex, 1 eps figure included, to be published in Phys.Rev.B Rapid Com

Circulating pancreatic polypeptide concentrations predict visceral and liver fat content

CONTEXT AND OBJECTIVE: No current biomarker can reliably predict visceral and liver fat content, both of which are risk factors for cardiovascular disease. Vagal tone has been suggested to influence regional fat deposition. Pancreatic polypeptide (PP) is secreted from the endocrine pancreas under vagal control. We investigated the utility of PP in predicting visceral and liver fat. PATIENTS AND METHODS: Fasting plasma PP concentrations were measured in 104 overweight and obese subjects (46 men and 58 women). In the same subjects, total and regional adipose tissue, including total visceral adipose tissue (VAT) and total subcutaneous adipose tissue (TSAT), were measured using whole-body magnetic resonance imaging. Intrahepatocellular lipid content (IHCL) was quantified by proton magnetic resonance spectroscopy. RESULTS: Fasting plasma PP concentrations positively and significantly correlated with both VAT (r = 0.57, P < .001) and IHCL (r = 0.51, P < .001), but not with TSAT (r = 0.02, P = .88). Fasting PP concentrations independently predicted VAT after controlling for age and sex. Fasting PP concentrations independently predicted IHCL after controlling for age, sex, body mass index (BMI), waist-to-hip ratio, homeostatic model assessment 2-insulin resistance, (HOMA2-IR) and serum concentrations of triglyceride (TG), total cholesterol (TC), and alanine aminotransferase (ALT). Fasting PP concentrations were associated with serum ALT, TG, TC, low- and high-density lipoprotein cholesterol, and blood pressure (P < .05). These associations were mediated by IHCL and/or VAT. Fasting PP and HOMA2-IR were independently significantly associated with hepatic steatosis (P < .01). CONCLUSIONS: Pancreatic polypeptide is a novel predictor of visceral and liver fat content, and thus a potential biomarker for cardiovascular risk stratification and targeted treatment of patients with ectopic fat deposition

Semiparametric theory and empirical processes in causal inference

In this paper we review important aspects of semiparametric theory and empirical processes that arise in causal inference problems. We begin with a brief introduction to the general problem of causal inference, and go on to discuss estimation and inference for causal effects under semiparametric models, which allow parts of the data-generating process to be unrestricted if they are not of particular interest (i.e., nuisance functions). These models are very useful in causal problems because the outcome process is often complex and difficult to model, and there may only be information available about the treatment process (at best). Semiparametric theory gives a framework for benchmarking efficiency and constructing estimators in such settings. In the second part of the paper we discuss empirical process theory, which provides powerful tools for understanding the asymptotic behavior of semiparametric estimators that depend on flexible nonparametric estimators of nuisance functions. These tools are crucial for incorporating machine learning and other modern methods into causal inference analyses. We conclude by examining related extensions and future directions for work in semiparametric causal inference

Using the past to constrain the future: how the palaeorecord can improve estimates of global warming

Climate sensitivity is defined as the change in global mean equilibrium temperature after a doubling of atmospheric CO2 concentration and provides a simple measure of global warming. An early estimate of climate sensitivity, 1.5-4.5{\deg}C, has changed little subsequently, including the latest assessment by the Intergovernmental Panel on Climate Change. The persistence of such large uncertainties in this simple measure casts doubt on our understanding of the mechanisms of climate change and our ability to predict the response of the climate system to future perturbations. This has motivated continued attempts to constrain the range with climate data, alone or in conjunction with models. The majority of studies use data from the instrumental period (post-1850) but recent work has made use of information about the large climate changes experienced in the geological past. In this review, we first outline approaches that estimate climate sensitivity using instrumental climate observations and then summarise attempts to use the record of climate change on geological timescales. We examine the limitations of these studies and suggest ways in which the power of the palaeoclimate record could be better used to reduce uncertainties in our predictions of climate sensitivity.Comment: The final, definitive version of this paper has been published in Progress in Physical Geography, 31(5), 2007 by SAGE Publications Ltd, All rights reserved. \c{opyright} 2007 Edwards, Crucifix and Harriso