Analysis of Near Rectilinear Halo Orbit Insertion with a 40-kW Solar Electric Propulsion System

This paper examines low thrust trajectories for delivery of a 40-kW solar electric propulsion spacecraft and potential additional payload to a desired NRHO. One option considered is a trans-lunar injection launch as a co-manifested payload on the Space Launch System. For this option, a reference trajectory is designed and a scan of launch dates is completed to understand the propellant mass sensitivity. A 15-day period cyclical variation in required propellant is observed that is attributed to solar gravity effects. A second option considered is to launch on a smaller commercial launch vehicle to a less energetic elliptical orbit and use SEP to spiral out to NRHO. For this option, analysis is completed to understand the trades between delivered mass to NRHO, total propellant required, time of flight, and solar array degradation. Results show that, while launching to lower altitudes can deliver greater payload mass to NRHO, significant solar array degradation can be observed

Sevelamer attenuates the progression of coronary and aortic calcification in hemodialysis patients

Sevelamer attenuates the progression of coronary and aortic calcification in hemodialysis patients.BackgroundCardiovascular disease is frequent and severe in patients with end-stage renal disease. Disorders of mineral metabolism may contribute by promoting cardiovascular calcification.MethodsWe conducted a randomized clinical trial comparing sevelamer, a non-absorbed polymer, with calcium-based phosphate binders in 200 hemodialysis patients. Study outcomes included the targeted concentrations of serum phosphorus, calcium, and intact parathyroid hormone (PTH), and calcification of the coronary arteries and thoracic aorta using a calcification score derived from electron beam tomography.ResultsSevelamer and calcium provided equivalent control of serum phosphorus (end-of-study values 5.1 ± 1.2 and 5.1 ± 1.4 mg/dL, respectively, P = 0.33). Serum calcium concentration was significantly higher in the calcium-treated group (P = 0.002), and hypercalcemia was more common (16% vs. 5% with sevelamer, P = 0.04). More subjects in the calcium group had end-of-study intact PTH below the target of 150 to 300 pg/mL (57% vs. 30%, P = 0.001). At study completion, the median absolute calcium score in the coronary arteries and aorta increased significantly in the calcium treated subjects but not in the sevelamer-treated subjects (coronary arteries 36.6 vs. 0, P = 0.03 and aorta 75.1 vs. 0, P = 0.01, respectively). The median percent change in coronary artery (25% vs. 6%, P = 0.02) and aortic (28% vs. 5%, P = 0.02) calcium score also was significantly greater with calcium than with sevelamer.ConclusionsCompared with calcium-based phosphate binders, sevelamer is less likely to cause hypercalcemia, low levels of PTH, and progressive coronary and aortic calcification in hemodialysis patients

Hypertension and Smoking Are Associated With Reduced Regional Left Ventricular Function in Asymptomatic Individuals The Multi-Ethnic Study of Atherosclerosis

ObjectivesThis study sought to test the hypothesis that reduced regional left ventricular (LV) function is associated with traditional risk factors including hypertension, hypercholesterolemia, and smoking in asymptomatic individuals.BackgroundCoronary artery disease is the main etiology of congestive heart failure in the U.S. and Europe. However, the relationship between risk factors for coronary artery disease and decreased myocardial function has not been studied systematically in asymptomatic individuals.MethodsThe Multi-Ethnic Study of Atherosclerosis (MESA) is a cohort study designed to investigate the nature of atherosclerosis in asymptomatic individuals. A total of 1,184 participants (45 to 84 years old) underwent tagged cardiac magnetic resonance imaging. Regional LV function was quantified by analyzing peak systolic circumferential strain (Ecc) in regions corresponding to the left anterior descending (LAD), circumflex (LCX), and right coronary (RCA) territories. The association between risk factors and strains was studied using multiple linear regression.ResultsHigher diastolic blood pressure (DBP) was associated with lower Ecc (p ≤ 0.002). The Ecc’s in the LAD territory of participants with DBP <80, 80 to 84, 85 to 89, and ≥90 mm Hg were −15.6%, −14.8%, −14.2%, and −13.7%, respectively (p < 0.001). Similar results were documented in other territories and after multivariable analysis. Smokers had lower Ecc in the LAD and RCA regions compared with nonsmokers. Furthermore, dose response relationship between cigarette consumption measured in pack-years and regional LV dysfunction by Ecc was noted (p ≤ 0.01 in LAD and RCA territories). Finally, combined diastolic hypertension and smoking was associated with a greater reduction of regional LV function.ConclusionsHigher diastolic blood pressure and smoking are associated with decreased regional LV function in asymptomatic individuals

VAST: An ASKAP Survey for Variables and Slow Transients

The Australian Square Kilometre Array Pathfinder (ASKAP) will give us an unprecedented opportunity to investigate the transient sky at radio wavelengths. In this paper we present VAST, an ASKAP survey for Variables and Slow Transients. VAST will exploit the wide-field survey capabilities of ASKAP to enable the discovery and investigation of variable and transient phenomena from the local to the cosmological, including flare stars, intermittent pulsars, X-ray binaries, magnetars, extreme scattering events, interstellar scintillation, radio supernovae and orphan afterglows of gamma ray bursts. In addition, it will allow us to probe unexplored regions of parameter space where new classes of transient sources may be detected. In this paper we review the known radio transient and variable populations and the current results from blind radio surveys. We outline a comprehensive program based on a multi-tiered survey strategy to characterise the radio transient sky through detection and monitoring of transient and variable sources on the ASKAP imaging timescales of five seconds and greater. We also present an analysis of the expected source populations that we will be able to detect with VAST.Comment: 29 pages, 8 figures. Submitted for publication in Pub. Astron. Soc. Australi

Limits on fast radio bursts from four years of the V-FASTR experiment

The V-FASTR experiment on the Very Long Baseline Array was designed to detect dispersed pulses of milliseconds duration, such as fast radio bursts (FRBs). We use all V-FASTR data through February 2015 to report V-FASTR's upper limits on the rates of FRBs, and compare these with re-derived rates from Parkes FRB detection experiments. V-FASTR's operation at lambda=20 cm allows direct comparison with the 20 cm Parkes rate, and we derive a power-law limit of \gamma<-0.4 (95% confidence limit) on the index of FRB source counts, N(>S)\propto S^\gamma. Using the previously measured FRB rate and the unprecedented amount of survey time spent searching for FRBs at a large range of wavelengths (0.3 cm > \lambda > 90 cm), we also place frequency-dependent limits on the spectral distribution of FRBs. The most constraining frequencies place two-point spectral index limits of \alpha_{20cm}^{4cm} < 5.8 and \alpha_{90cm}^{20cm} > -7.6, where fluence F \propto f^\alpha if we assume true the burst rate reported by Champion et al. (2016) of R(F~0.6 Jy ms) = 7 x 10^3 sky^{-1} day^{-1} (for bursts of ~3 ms duration). This upper limit on \alpha suggests that if FRBs are extragalactic but non-cosmological, that on average they are not experiencing excessive free-free absorption due to a medium with high optical depth (assuming temperature ~8,000 K), which excessively invert their low-frequency spectrum. This in turn implies that the dispersion of FRBs arises in either or both of the intergalactic medium or the host galaxy, rather than from the source itself.Comment: Accepted for publication in Ap

A growing global network’s role in outbreak response: AFHSC-GEIS 2008-2009

A cornerstone of effective disease surveillance programs comprises the early identification of infectious threats and the subsequent rapid response to prevent further spread. Effectively identifying, tracking and responding to these threats is often difficult and requires international cooperation due to the rapidity with which diseases cross national borders and spread throughout the global community as a result of travel and migration by humans and animals. From Oct.1, 2008 to Sept. 30, 2009, the United States Department of Defense’s (DoD) Armed Forces Health Surveillance Center Global Emerging Infections Surveillance and Response System (AFHSC-GEIS) identified 76 outbreaks in 53 countries. Emerging infectious disease outbreaks were identified by the global network and included a wide spectrum of support activities in collaboration with host country partners, several of which were in direct support of the World Health Organization’s (WHO) International Health Regulations (IHR) (2005). The network also supported military forces around the world affected by the novel influenza A/H1N1 pandemic of 2009. With IHR (2005) as the guiding framework for action, the AFHSC-GEIS network of international partners and overseas research laboratories continues to develop into a far-reaching system for identifying, analyzing and responding to emerging disease threats

Kepler eclipsing binary stars. VII. the catalogue of eclipsing binaries found in the entire Kepler data set

The primary Kepler Mission provided nearly continuous monitoring of ~200,000 objects with unprecedented photometric precision. We present the final catalog of eclipsing binary systems within the 105 deg2 Kepler field of view. This release incorporates the full extent of the data from the primary mission (Q0-Q17 Data Release). As a result, new systems have been added, additional false positives have been removed, ephemerides and principal parameters have been recomputed, classifications have been revised to rely on analytical models, and eclipse timing variations have been computed for each system. We identify several classes of systems including those that exhibit tertiary eclipse events, systems that show clear evidence of additional bodies, heartbeat systems, systems with changing eclipse depths, and systems exhibiting only one eclipse event over the duration of the mission. We have updated the period and galactic latitude distribution diagrams and included a catalog completeness evaluation. The total number of identified eclipsing and ellipsoidal binary systems in the Kepler field of view has increased to 2878, 1.3% of all observed Kepler targets

A machine learning classifier for fast radio burst detection at the VLBA

Time domain radio astronomy observing campaigns frequently generate large volumes of data. Our goal is to develop automated methods that can identify events of interest buried within the larger data stream. The V-FASTR fast transient system was designed to detect rare fast radio bursts within data collected by the Very Long Baseline Array. The resulting event candidates constitute a significant burden in terms of subsequent human reviewing time. We have trained and deployed a machine learning classifier that marks each candidate detection as a pulse from a known pulsar, an artifact due to radio frequency interference, or a potential new discovery. The classifier maintains high reliability by restricting its predictions to those with at least 90% confidence. We have also implemented several efficiency and usability improvements to the V-FASTR web-based candidate review system. Overall, we found that time spent reviewing decreased and the fraction of interesting candidates increased. The classifier now classifies (and therefore filters) 80%–90% of the candidates, with an accuracy greater than 98%, leaving only the 10%–20% most promising candidates to be reviewed by humans