10,436 research outputs found
Photoionization models for extreme Ly 1216 and HeII 1640 ratios in quasar halos, and PopIII vs AGN diagnostics
We explore mechanisms to produce extremely high Ly-alpha/HeII flux ratios, or
to enhance the observed number of Ly-alpha photons per incident ionizing
photon, in extended AGN-photoionized nebulae at high-redshift. Using
photoionization models, we explore the impact of ionization parameter, gas
metallicity, ionizing spectrum, electron energy distribution, and cloud viewing
angle on the relative fluxes of Ly-alpha, HeII and other lines, and on the
observed number of Ly-alpha photons per incident ionizing photon. We find that
low ionization parameter, a relatively soft or filtered ionizing spectrum, low
gas metallicity, kappa-distributed electron energies, or reflection of Ly-alpha
photons by HI can all result in significantly enhanced Ly-alpha relative to
other lines (>10%), with log Ly-alpha/HeII reaching values up to 4.6. In the
cases of low gas metallicity, reflection by HI, or a hard or filtered ionizing
spectrum, the observed number of Ly-alpha photons per incident ionizing photon
is itself significantly enhanced above the nominal Case B value of 0.66 due to
collisional excitation, reaching values up to 5.3 in our 'extreme case' model.
At low gas metallicity (e.g. 0.1 x Solar), the production of Ly-alpha is
predominantly via collisional excitation rather than recombination. In
addition, we find that collisional excitation of Ly-alpha becomes more
efficient if the ionizing continuum is pre-filtered through an optically thin
screen of gas closer to the AGN. We also show that Ly-alpha / HeII ratios of
the z~3.5 quasars studied by Borisova et al. (2016) are consistent with
AGN-photoionization of gas with moderate to low metallicity and/or low
ionization parameter, without requiring exotic ionization/excitation mechanisms
such as strong line-transfer effects. We also present UV-optical diagnostic
diagrams to distinguish between photoionization by Pop III stars and AGN
photoionization.Comment: Accepted for publication in A&A. 14 pages, 9 figures. Abstract
slightly shortened to meet arxiv character limi
THE STRUCTURE OF FARMERS' PERCEPTIONS OF GROUND WATER POLLUTION
Data from a 1992 Georgia Farm Practices survey are used to examine the structure of farmers' perceptions of ground water pollution and their support of regulations to protect ground water. Estimates of the influence of farm and farmer characteristics on pollution perceptions and support for pollution control were computed using a multiple-indicator model. Results show that the willingness to change farm practices to protect ground water is positively related to how an operator perceives the seriousness of the pollution problem. Regulatory policies that negatively affect farmers' income are likely to be opposed by farmers.Factor analysis, Latent variable model, Water quality, Environmental Economics and Policy,
A survey of elementary principals, kindergarten teachers, and kindergarten parents focusing on preferences for academic or developmental programming at the kindergarten level
The primary purpose of this study was to determine the preferences regarding instructional practices at the kindergarten level and investigate the relationships of these preferences among elementary principals, kindergarten teachers, and kindergarten parents. A survey of a systematic sample of 217 Iowa public elementary schools provided perceptual data from 148 (68%) of these schools. Elementary principals, kindergarten teachers, and kindergarten parents were asked to complete a questionnaire based on the Hitz 1986 Oregon Department of Education questionnaire which provided insight to their preferences on developmental and academic instructional practices at the kindergarten level. Of the population, 132 principals out of 217 (61%), 137 kindergarten teachers out of 217 (63%), and 524 kindergarten parents out of 1,085 (48%) returned completed survey material.
After completion of descriptive statistics, the investigator applied inferential statistical analysis to complete cross group comparisons on the items 1-12 common to all three questionnaires. These items were designed to elicit responses showing a preference for developmental or academic kindergarten programming. Analysis of variance, F value, was used for these 12 items. In addition, the F test was also used on the summative group mean scores to determine whether the three group means were significantly different from each other at the .05 level. The Scheffe\u27 multiple comparison procedure was then used to determine which pairs of groups had statistically different means.
The analysis of variance of the summative score for items 1-12 indicated a significant difference among group means, F(2,761) = 170.73, p = .001. The Scheffe\u27 multiple comparison procedure indicated that the following pairs of groups were significantly different at the .05 level: (a) principals and parents, and (b) teachers and parents. On the 1-5 Likert scale utilized with the 12 items (1 = strongly disagree, 2 = disagree, 3 = neutral, 4 = agree, 5 strongly agree) elementary principals scored a summative mean of 3.84 (S.D. .46). Kindergarten teachers scored a summative mean of 3.89 (S.D. .49), and kindergarten parents scored a summative mean of 3.19 (S.D. .48). The principal and teacher summative means placed them nearly in the response of agree with developmental instructional practices at the kindergarten level. The parent summative group mean placed them nearly in the response of neutral which does not show strong support for either developmental or academic instructional practices at the kindergarten level
Intraday credit: risk, value, and pricing
An abstract for this article is not availableElectronic funds transfers ; Payment systems ; Overdrafts
The Comparison of a New Constant Temperature Anemometer with Several Laser Anemometer Configurations
This paper covers electronic design advances that have made it possible to adjust the frequency response of a film probe and make it comparable to that of a wire probe. Also, a test setup for the laser anemometer will be presented using the forward scattering technique. Sample data taken in a hydraulic loop will be related to the laser system output. Following the presentation of the anemometer and laser systems, five fluid flow measurement features will be discussed in order to help the experimenter choose the method most suited to his particular application
Liquid Turbulence and Its Measurement
This paper covers several principles which have been successfully developed over the past few years and used in the measurement of liquid flows. In particular, ultrasonics, electro-magnetics, thermal heat transfer and optical light transmission will be discussed. Each concept will be covered by basic definitions and laws, theory of operation and application where measurement parameters will be highlighted, thus allowing the user to choose the best instrument to fit his experimental needs
The Somatic Chromosomes of Cypripedium hirsutum and Six Species of Habenaria
The chromosome numbers of eight species of the Orchidaceae were reported last year. The purpose of this paper is to report seven more species. The material was collected in Minnesota and Massachusetts. The following numbers were found: Cypripedium hirsutum, 2n = 20; Habenaria blephariglottis, 2n = 42; H. clavellata, 2n = 42; H. dilatata, 2n = 42; H. Hookeri, 2n = 42; H. hyperborea, 2n = 42; and H. obtusata, 2n = 42. The size relationships are the same as in the species studied last year. The Cypripedium has very large chromosomes, and the Habenarias relatively very small ones
The Relationship Between Urinary Tract Infections And Mental Status Changes In Elders
The purpose of this study was to explore pregnant women\u27s knowledge of the danger signs of pregnancy, as well as the normal discomforts of pregnancy and those symptoms of pregnancy that could be treated in a primary care clinic
- …