Magnetically filtered Faraday probe for measuring the ion current density profile of a Hall thruster

The ability of a magnetically filtered Faraday probe (MFFP) to obtain the ion current density profile of a Hall thruster is investigated. The MFFP is designed to eliminate the collection of low-energy, charge-exchange (CEX) ions by using a variable magnetic field as an ion filter. In this study, a MFFP, Faraday probe with a reduced acceptance angle (BFP), and nude Faraday probe are used to measure the ion current density profile of a 5 kW5kW Hall thruster operating over the range of 300–500 V300–500V and 5–10 mg/s5–10mg∕s. The probes are evaluated on a xenon propellant Hall thruster in the University of Michigan Large Vacuum Test Facility at operating pressures within the range of 4.4×10−4 Pa4.4×10−4Pa Xe (3.3×10−6 Torr3.3×10−6Torr Xe) to 1.1×10−3 Pa1.1×10−3Pa Xe (8.4×10−6 Torr8.4×10−6Torr Xe) in order to study the ability of the Faraday probe designs to filter out CEX ions. Detailed examination of the results shows that the nude probe measures a greater ion current density profile than both the MFFP and BFP over the range of angular positions investigated for each operating condition. The differences between the current density profiles obtained by each probe are attributed to the ion filtering systems employed. Analysis of the results shows that the MFFP, operating at a +5 A+5A solenoid current, provides the best agreement with flight-test data and across operating pressures.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87898/2/013503_1.pd

Improved Cosmological Constraints from Gravitational Lens Statistics

We combine the Cosmic Lens All-Sky Survey (CLASS) with new Sloan Digital Sky Survey (SDSS) data on the local velocity dispersion distribution function of E/S0 galaxies, $\phi(\sigma)$, to derive lens statistics constraints on $\Omega_\Lambda$ and $\Omega_m$. Previous studies of this kind relied on a combination of the E/S0 galaxy luminosity function and the Faber-Jackson relation to characterize the lens galaxy population. However, ignoring dispersion in the Faber-Jackson relation leads to a biased estimate of $\phi(\sigma)$ and therefore biased and overconfident constraints on the cosmological parameters. The measured velocity dispersion function from a large sample of E/S0 galaxies provides a more reliable method for probing cosmology with strong lens statistics. Our new constraints are in good agreement with recent results from the redshift-magnitude relation of Type Ia supernovae. Adopting the traditional assumption that the E/S0 velocity function is constant in comoving units, we find a maximum likelihood estimate of $\Omega_\Lambda = 0.74$--0.78 for a spatially flat unvierse (where the range reflects uncertainty in the number of E/S0 lenses in the CLASS sample), and a 95% confidence upper bound of $\Omega_\Lambda<0.86$. If $\phi(\sigma)$ instead evolves in accord with extended Press-Schechter theory, then the maximum likelihood estimate for $\Omega_\Lambda$ becomes 0.72--0.78, with the 95% confidence upper bound $\Omega_\Lambda<0.89$. Even without assuming flatness, lensing provides independent confirmation of the evidence from Type Ia supernovae for a nonzero dark energy component in the universe.Comment: 35 pages, 15 figures, to be published in Ap

Photoreversible interconversion of a phytochrome photosensory module in the crystalline state.

A major barrier to defining the structural intermediates that arise during the reversible photointerconversion of phytochromes between their biologically inactive and active states has been the lack of crystals that faithfully undergo this transition within the crystal lattice. Here, we describe a crystalline form of the cyclic GMP phosphodiesterases/adenylyl cyclase/FhlA (GAF) domain from the cyanobacteriochrome PixJ in Thermosynechococcus elongatus assembled with phycocyanobilin that permits reversible photoconversion between the blue light-absorbing Pb and green light-absorbing Pg states, as well as thermal reversion of Pg back to Pb. The X-ray crystallographic structure of Pb matches previous models, including autocatalytic conversion of phycocyanobilin to phycoviolobilin upon binding and its tandem thioether linkage to the GAF domain. Cryocrystallography at 150 K, which compared diffraction data from a single crystal as Pb or after irradiation with blue light, detected photoconversion product(s) based on Fobs - Fobs difference maps that were consistent with rotation of the bonds connecting pyrrole rings C and D. Further spectroscopic analyses showed that phycoviolobilin is susceptible to X-ray radiation damage, especially as Pg, during single-crystal X-ray diffraction analyses, which could complicate fine mapping of the various intermediate states. Fortunately, we found that PixJ crystals are amenable to serial femtosecond crystallography (SFX) analyses using X-ray free-electron lasers (XFELs). As proof of principle, we solved by room temperature SFX the GAF domain structure of Pb to 1.55-Å resolution, which was strongly congruent with synchrotron-based models. Analysis of these crystals by SFX should now enable structural characterization of the early events that drive phytochrome photoconversion

Predictors of coronary artery calcium and long-term risks of death, myocardial infarction, and stroke in young adults

Background Coronary artery calcium (CAC) is well-validated for cardiovascular disease risk stratification in middle to older-aged adults; however, the 2019 American College of Cardiology/American Heart Association guidelines state that more data are needed regarding the performance of CAC in low-risk younger adults. Methods and Results We measured CAC in 13 397 patients aged 30 to 49 years without known cardiovascular disease or malignancy between 1997 and 2009. Outcomes of myocardial infarction (MI), stroke, major adverse cardiovascular events (MACE; MI, stroke, or cardiovascular death), and all-cause mortality were assessed using Cox proportional hazard models, controlling for baseline risk factors (including atrial fibrillation for stroke and MACE) and the competing risk of death or noncardiac death as appropriate. The cohort (74% men, mean age 44 years, and 76% with ≤1 cardiovascular disease risk factor) had a 20.6% prevalence of any CAC. CAC was independently predicted by age, male sex, White race, and cardiovascular disease risk factors. Over a mean of 11 years of follow-up, the relative adjusted subhazard ratio of CAC \u3e0 was 2.9 for MI and 1.6 for MACE. CAC \u3e100 was associated with significantly increased hazards of MI (adjusted subhazard ratio, 5.2), MACE (adjusted subhazard ratio, 3.1), stroke (adjusted subhazard ratio, 1.7), and all-cause mortality (hazard ratio, 2.1). CAC significantly improved the prognostic accuracy of risk factors for MACE, MI, and all-cause mortality by the likelihood ratio test

Invited Review: Lessons From The Covid-19 Pandemic For Food Supply Chains

Purpose Some of the biggest economic disruptions from the COVID-19 pandemic were experienced in food supply chains, particularly in the protein sector. This article examines these protein-sector supply-chain shocks, exploring the nature and causes of the market disruptions during the pandemic, evaluating the effects of these shocks from an economic perspective, and discussing potential market and policy responses that could mitigate the adverse effects of similar events in the future. Sources A variety of sources contemporary to the pandemic were surveyed to document pandemic effects on meat and poultry supply chains. The implications of pandemic effects for supply chain participants were explored, drawing from sources in supply chain management, network reliability, and agricultural economics literature. Synthesis Pandemic-related disruptions to meat supply chains and the economic hardship associated with those disruptions have generated tremendous interest in improving supply chain robustness and resilience. Much of that interest focuses on encouraging local and regional processing operations, creating shorter supply chains. At the same time, commercial interests will most likely aggressively pursue further automation to mitigate the effects of labor supply disruption—their major problem during the pandemic. Conclusions and Applications Local and regional processing operations are receiving a significant infusion of pandemic relief funds. Consumers are currently keenly interested in local and regional food options. At the same time, commercial operations will likely become even more efficient due to postpandemic adjustments. Thus, local and regional operations may face an even more challenging competitive environment than before the pandemic

The Sloan Digital Sky Survey Quasar Lens Search. IV. Statistical Lens Sample from the Fifth Data Release

We present the second report of our systematic search for strongly lensed quasars from the data of the Sloan Digital Sky Survey (SDSS). From extensive follow-up observations of 136 candidate objects, we find 36 lenses in the full sample of 77,429 spectroscopically confirmed quasars in the SDSS Data Release 5. We then define a complete sample of 19 lenses, including 11 from our previous search in the SDSS Data Release 3, from the sample of 36,287 quasars with i<19.1 in the redshift range 0.6<z<2.2, where we require the lenses to have image separations of 1"<\theta<20" and i-band magnitude differences between the two images smaller than 1.25 mag. Among the 19 lensed quasars, 3 have quadruple-image configurations, while the remaining 16 show double images. This lens sample constrains the cosmological constant to be \Omega_\Lambda=0.84^{+0.06}_{-0.08}(stat.)^{+0.09}_{-0.07}(syst.) assuming a flat universe, which is in good agreement with other cosmological observations. We also report the discoveries of 7 binary quasars with separations ranging from 1.1" to 16.6", which are identified in the course of our lens survey. This study concludes the construction of our statistical lens sample in the full SDSS-I data set.Comment: 37 pages, 2 figures and 5 tables, accepted to A

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