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J. E. Colwell, University of Central Florida Orlando, Florida, USA,
J. Blum, Technische Universität Braunschweig Braunschweig, GERMANY,
R. N. Clark, Planetary Science Institute Tucson, Arizona, USA,
S. Kempf, University of Colorado Boulder, Colorado, USA,
R. M. Nelson, Planetary Science Institute Tucson, Arizona, USA
The surface area of Saturn's rings is greater than that of any of the planets in the solar system, yet, aside from dust, we have never observed or sampled an individual ring particle. Rings are unique in the solar system in that they are a complex dynamical system whose individual constituents interact not only with the light that we use to sense them remotely, but also with each other through gravitational and contact forces. These dynamical interactions play as large a role in determining the appearance of the ring system as do the optical properties of the individual ring particles. In this chapter we review the experimental work that has been done to help us understand both aspects of planetary rings: their collective dynamical behavior and their optical properties.
We have a wealth of data on the behavior of ensembles of particles, both dynamically and their optical properties. Laboratory measurements of the behavior of various likely ring particle analogs are a critical link in connecting these bulk observations with the nature of individual ring particles, and understanding the properties of individual ring particles should provide clues to the outstanding unanswered questions about the age and origin of rings.
Images of Saturn's rings and optical depth profiles from occultations show features at a variety of spatial scales, from the resolution limit of tens of meters for occultations up to thousands of kilometers, and including most scales in between (Colwell et al., 2009; Chapter 3). A frustratingly small fraction of these structures is well understood. Many that remain puzzling, such as the large optical depth fluctuations in Saturn's central B ring, the complex structure in the B ring and the inner A ring, the long-wavelength low-amplitude undulations in optical depth in the C ring, and the plateaus in the C ring, are likely linked to either the collective behavior of the ring particles governed in part by their collisional properties (see e.g. Schmidt et al., 2009, for a review) or by ballistic transport of material due to extrinsic micrometeoroid bombardment (Chapter 9). The mechanical properties of individual ring particles are critical in both types of process.
On August 25, 2017, Hurricane Harvey made landfall near Corpus Christi, Texas. The ensuing unprecedented flooding throughout the Texas coastal region affected millions of individuals.1 The statewide response in Texas included the sheltering of thousands of individuals at considerable distances from their homes. The Dallas area established large-scale general population sheltering as the number of evacuees to the area began to amass. Historically, the Dallas area is one familiar with “mega-sheltering,” beginning with the response to Hurricane Katrina in 2005.2 Through continued efforts and development, the Dallas area had been readying a plan for the largest general population shelter in Texas. (Disaster Med Public Health Preparedness. 2019;13:33–37)
Most of the Milky Way's evolved massive stellar population is hidden from view. We can attempt to remedy this situation with near-infrared observations, and in this paper we present our method for detecting Wolf-Rayet stars in highly extincted regions and apply it to the inner Galaxy. Using narrow-band filters at K-band wavelengths, we demonstrate how WR stars can be detected in regions where they are optically obscured. Candidates are selected for spectroscopic follow-up from our relative line and continuum photometry. The final results of applying this method with a near-IR survey in the Galactic plane will provide a more complete knowledge of the structure of the galactic disk, the role of metallicity in massive stellar evolution, and environments of massive star formation. In this paper we briefly describe the survey set-up and report on recent progress. We have discovered four emission-line objects in the inner Galaxy: two with nebular emission lines, and two new WR stars, both of late WC subtype.
We present radial velocities for approximately 40 stars in each of four optically obscured, off-axis fields toward the Galactic bulge. The mean heliocentric radial velocity and velocity dispersion are −75 ± 24 km s–1 and 127 ± 16 km s–1 2 ± 23 km s–1 and 127 ± 14 km s–1, −14 ± 22 km s–1 and 126 ± 14 km s–1, and −31 ± 28 km s–1 and 153 ± 17 km s–1 for fields located at 299, 288, 171, and 160 pc projected radius, respectively. The dispersions generally match Kent's (1992) axisymmetric mass model but may be higher than the model's predictions at small projected radius.
We are measuring Fe abundances of cool, luminous stars within 30 pc of the center of the Milky Way. Our sample contains both AGB stars and M supergiants. Low-resolution (λ/Δλ = 500) H and K band spectra are used to estimate temperatures and gravities. Stellar Fe abundances are determined from high-resolution (λ/Δλ = 40 000) K band spectra obtained on the IRTF using CSHELL. We find that Fe abundances of stars in the Galactic Center are consistent with the solar Fe abundance.
Star formation in the Galactic Center (GC) happens under unusual conditions, which include high gas temperatures, high velocity dispersions, and strong tidal shear (Spergel & Blitz 1992; Blitz et al. 1993). All these conditions may lead to an initial mass function (IMF) dominated by massive stars (Morris & Serabyn 1996). A history of chemical evolution dominated by massive stars is expected to result in enhancements of α-elements (Mg, Si, Ca, Ti) relative to Fe (Wheeler et al. 1989). This argument is the main motivation to study the abundance of Fe and Mg in GC stars.
The United States of America (USA) has the largest international population of any nation in the world. Immigrants from Latin American countries, where intestinal parasites are endemic, comprise more than half of this population. This study aims to determine the prevalence of strongyloidiasis, a potentially deadly parasitic infection, in foreign-born individuals. We conducted a cross-sectional study in Washington, DC, to determine the seroprevalence of Strongyloides stercoralis infection using an NIE-ELISA IgG antibody assay. Multi-parallel quantitative real-time polymerase chain reaction (qPCR) was performed in stool samples of NIE-ELISA-positive patients to investigate possible polyparasitism. The NIE-ELISA assay detected an S. stercoralis prevalence of 4.2% in a group of 119 volunteers. Combining NIE-ELISA and qPCR detected a parasite prevalence of 5.0%. Our results underscore the relevance of systematic testing for gastrointestinal parasites in individuals from endemic regions. It also makes a case for a survey in the USA to identify immigrants' risk for strongyloidiasis and other gastrointestinal parasitic infections.
Giant HII (GHII) regions in our Galaxy are typically initially found by radio observations of their optically thin free-free continuum emission. Most of them are partially or totally obscured in the visible by the absorbing effect of intervening and/or local interstellar dust. We (Blum et al. 1999, 2000) have selected a list of the brightest GHII regions in our Galaxy (from Smith et al. 1978) and have begun a program of JHK imaging and K band spectroscopy to identify and classify the exciting stars. We have obtained near IR imaging of eight GHII regions (and data is available for four others). All of these, aside from W49, show the presence of a stellar cluster in the K band at the radio source position. The K,H — K diagrams are used to select the brightest stars. The J — Kvs. H — K diagrams distinguish those stars along the normal reddening line from those with K band excesses. The former group ought to have normal OB star spectra; the latter will have featureless continua in the K band due to emission from localized warm dust arising in a natal disc (Hanson et al. 1997). A disc geometry can also produce CO emission (or absorption) band features.
Ecological restoration of trees is often constrained by limited knowledge of the biology, propagation and management requirements of individual species. Consequently, restoration initiatives rarely incorporate less well-known species or those that are difficult to source and grow. We describe challenges associated with the restoration of threatened trees in the Araucaria Forest of southern Brazil, and analyse the effectiveness of methods used to define target species, identify seed sources and generate information on the phenology of rare or threatened tree species. A review of secondary data identified 71 rare or threatened taxa as targets for seed collection. We then surveyed 68.7 km of trails in 26 forest remnants, identifying and mapping 1,027 seed-producing trees of 38 species. Surveys confirmed the scarcity of several tree species (including seven species with an abundance of <0.04 individuals per km), and nine species showed no signs of fruiting during 3 years of phenological monitoring. These findings, together with limited knowledge and application of optimal seed collection methods, are significant factors impeding the recovery of these species within their natural habitat. Wider application of the results of this case study could support restoration of the Araucaria Forest with seedlings from a wider diversity of species.
We present a comprehensive survey of various computational methods in CEDRES++ (Couplage Equilibre Diffusion Résistive pour l'Etude des Scénarios) for finding equilibria of toroidal plasma. Our focus is on free-boundary plasma equilibria, where either poloidal field coil currents or the temporal evolution of voltages in poloidal field circuit systems are given data. Centered around a piecewise linear finite element representation of the poloidal flux map, our approach allows in large parts the use of established numerical schemes. The coupling of a finite element method and a boundary element method gives consistent numerical solutions for equilibrium problems in unbounded domains. We formulate a new Newton method for the discretized nonlinear problem to tackle the various nonlinearities, including the free plasma boundary. The Newton method guarantees fast convergence and is the main building block for the inverse equilibrium problems that we can handle in CEDRES++ as well. The inverse problems aim at finding either poloidal field coil currents that ensure a desired shape and position of the plasma or at finding the evolution of the voltages in the poloidal field circuit systems that ensure a prescribed evolution of the plasma shape and position. We provide equilibrium simulations for the tokamaks ITER and WEST to illustrate the performance of CEDRES++ and its application areas.
In view of the complexity of thin-film solar cells, which are comprised of a multitude of layers, interfaces, surfaces, elements, impurities, etc., it is crucial to characterize and understand the chemical and electronic structure of these components. Because of the high complexity of the Cu2ZnSn(S,Se)4 compound semiconductor absorber material alone, this is particularly true for kesterite-based devices. Hence, this paper reviews our recent progress in the characterization of Cu2ZnSnS4 (CZTS) thin films. It is demonstrated that a combination of different soft x-ray spectroscopies is an extraordinarily powerful method for illuminating the chemical and electronic material characteristics from many different perspectives, ultimately resulting in a comprehensive picture of these properties. The focus of the article will be on secondary impurity phases, electronic structure, native oxidation, and the CZTS surface composition.
The aim of our present study was to examine the regulation of xenobiotic- and antioxidant enzymes by phytogenic feed additives in the intestine and the liver of broilers. A total of 240 male Ross-308 broiler chickens (1 d old) were fed a commercial starter diet for 2 weeks. On day 15, the birds were assigned to six treatment groups of forty birds each. The control (Con) group was fed a diet without any additive for 3 weeks. The diet of group sulforaphane (SFN) contained broccoli extract providing 0·075 g/kg SFN, whereas the diets of the other four groups contained 0·15 g/kg essential oils from turmeric (Cuo), oregano (Oo), thyme and rosemary (Ro). Weight gain and feed conversion were slightly impaired by Cuo and Oo. In the jejunum SFN, Cuo and Ro increased the expression of xenobiotic enzymes (epoxide hydrolases 1 and 2 and aflatoxin B1 aldehyde reductase) and of the antioxidant enzyme haeme oxygenase regulated by an ‘antioxidant response element’ (ARE) compared to group Con. In contrast to our expectations in the liver, the expression of these enzymes was decreased by all the additives. Nevertheless, all the additives increased the Trolox equivalent antioxidant capacity of the jejunum and the liver and reduced Fe-induced lipid peroxidation in the liver. We conclude that the up-regulation of ARE genes in the small intestine reduces oxidative stress in the organism and represents a novel mechanism by which phytogenic feed additives improve the health of farm animals.
Modern time-domain surveys have demonstrated that finding variable objects is relatively straightforward. The problem now is one of selecting and following up discoveries. With even larger-scale surveys on the horizon, the magnitude of the problem will inevitably increase. One way to prepare for the coming deluge is to have realistic estimates of the numbers of potential detections so that resources can be developed to meet that need. To that end, astronomers at the National Optical Astronomy Observatory (NOAO) have begun a project to characterize the variable sky in terms of type of objects, distribution on the sky and range of variation.
The composition of Cu2ZnSnS4 thin-film solar cell absorbers was varied to induce the.formation of secondary impurity phases. For their identification, the samples have been investigated by Cu L3 and S L2,3 soft x-ray absorption (XAS) spectroscopy. We find that Cu L3 XAS is especially sensitive to the presence of copper sulfides as well as copper oxides and/or changes in the electron configuration, suggesting a basis for future studies of the surface, defect, and interface characterization of similar samples. Additionally, it is shown that the S L2,3 absorption data can be used as a very sensitive probe of the variations in the prevalence of S-Zn bonds in the near-surface region of the investigated samples.
We sought to determine attitudes toward patients with borderline personality disorder (BPD) among mental health clinicians at nine academic centers in the United States.
A self-report questionnaire was distributed to 706 mental health clinicians, including psychiatrists, psychiatry residents, social workers, nurses, and psychologists.
The study showed that most clinicians consider BPD a valid diagnosis, although nearly half reported that they preferred to avoid these patients. The clinician's occupational subgroup was significantly related to attitude. Staff nurses had the lowest self-ratings on overall caring attitudes, while social workers had the highest. Social workers and psychiatrists had the highest ratings on treatment optimism. Social workers and psychologists were most optimistic about psychotherapy effectiveness, while psychiatrists were most optimistic about medication effectiveness. Staff nurses had the lowest self-ratings on empathy toward patients with BPD and treatment optimism.
Negative attitudes persist among clinicians toward BPD, but differ among occupational subgroups. Overall, caring attitudes, empathy, and treatment optimism were all higher among care providers who had cared for a greater number of BPD patients in the past 12 months.
These findings hold important implications for clinician education and coordination of care for patients with BPD.
We present a technique to synthesize high aspect ratio metallic nanostructures based on the radiolysis method. In our experiments, we use gamma rays to irradiate aqueous solutions containing Ag and Pt ions and a water-soluble polymer. The aspect ratio of the nanoparticles is controlled by varying the radiation dose rate, the type of polymer, and the type of counter ions. Transmission electron microscopy shows that wire-like structures composed of grains with a face centered cubic (fcc) structure can be formed with a length of up to 3.5μm and typical diameters between 5 and 12nm. X-Ray absorption spectroscopy shows that Ag and Pt do not form an alloy, but remain segregated.
The use of preceramic polymers in diverse ceramic applications requires control of a complex set of chemical characteristics to ease processing and develop suitable ceramic properties. The desirable characteristics of a good precursor system are controllable viscosity (preferably without the use of solvents), inhibition of curing during fabrication followed by rapid curing, minimal release of volatiles during curing, high ceramic yield, and controllable final composition and stoichiometry.
This paper describes the use of chemical concepts to synthesize, modify, and manipulate polymeric precursors to silicates and the importance of curing (crosslinking) mechanisms and processing conditions as critical elements in developing ceramic matrix composites.