531 research outputs found
We Can Make A Difference [8th grade]
In this unit students will be reading about a variety of injustices that exist both locally and around the world. Students will be uncovering the understanding that justice is not always a black and white issue and often has more than one perspective it can be seen from. Students will also see examples of individuals who have fought against injustice. Students will practice using their reading skills on both fiction and non-fiction pieces on this topic. Students will also participate in shared inquiry discussion and a debate wrestling with the ideas of justice. In the culminating performance task, students choose an injustice that exists in their city to fight against. Students first research their local injustice and then create and implement an action plan appropriate to their chosen issue. For example, if students chose to fight the injustice of homelessness in San Antonio, then they could create a school-wide awareness campaign and clothing drive. They could find creative ways to encourage other students to bring in clothes and/or food and then donate their contributions to a local homeless shelter
Metal-poor dwarf galaxies in the SIGRID galaxy sample. I. HII region observations and chemical abundances
In this paper we present the results of observations of seventeen HII regions
in thirteen galaxies from the SIGRID sample of isolated gas rich irregular
dwarf galaxies. The spectra of all but one of the galaxies exhibit the auroral
[OIII] 4363A line, from which we calculate the electron temperature, Te, and
gas-phase oxygen abundance. Five of the objects are blue compact dwarf (BCD)
galaxies, of which four have not previously been analysed spectroscopically. We
include one unusual galaxy which exhibits no evidence of the [NII]
{\lambda}{\lambda} 6548,6584A lines, suggesting a particularly low metallicity
(< Zsolar/30). We compare the electron temperature based abundances with those
derived using eight of the new strong line diagnostics presented by Dopita et
al. (2013). Using a method derived from first principles for calculating total
oxygen abundance, we show that the discrepancy between the Te-based and strong
line gas-phase abundances have now been reduced to within ~0.07 dex. The
chemical abundances are consistent with what is expected from the
luminosity-metallicity relation. We derive estimates of the electron densities
and find them to be between ~5 and ~100 cm-3. We find no evidence for a
nitrogen plateau for objects in this sample with metallicities 0.5 > Zsolar >
0.15.Comment: 46 pages, 15 figures, 6 tables, 1 appendix. Accepted for publication
in the Astrophysical Journa
Modeling Expert Opinions on Food Healthiness: A Nutrition Metric
Background Research over the last several decades indicates the failure of existing nutritional labels to substantially improve the healthiness of consumers' food and beverage choices. The difficulty for policy-makers is to encapsulate a wide body of scientific knowledge in a labeling scheme that is comprehensible to the average shopper. Here, we describe our method of developing a nutrition metric to fill this void. Methods We asked leading nutrition experts to rate the healthiness of 205 sample foods and beverages, and after verifying the similarity of their responses, we generated a model that calculates the expected average healthiness rating that experts would give to any other product based on its nutrient content. Results The form of the model is a linear regression that places weights on 12 nutritional components (total fat, saturated fat, cholesterol, sodium, total carbohydrate, dietary fiber, sugars, protein, vitamin A, vitamin C, calcium, and iron) to predict the average healthiness rating that experts would give to any food or beverage. We provide sample predictions for other items in our database. Conclusions Major benefits of the model include its basis in expert judgment, its straightforward application, the flexibility of transforming its output ratings to any linear scale, and its ease of interpretation. This metric serves the purpose of distilling expert knowledge into a form usable by consumers so that they are empowered to make healthier decisions.
A physically-based model of the ionizing radiation from active galaxies for photoionization modeling
We present a simplified model of Active Galactic Nucleus (AGN) continuum
emission designed for photoionization modeling. The new model {\sc oxaf}
reproduces the diversity of spectral shapes that arise in physically-based
models. We identify and explain degeneracies in the effects of AGN parameters
on model spectral shapes, with a focus on the complete degeneracy between the
black hole mass and AGN luminosity. Our re-parametrized model {\sc oxaf}
removes these degeneracies and accepts three parameters which directly describe
the output spectral shape: the energy of the peak of the accretion disk
emission , the photon power-law index of the non-thermal
emission , and the proportion of the total flux which is emitted in the
non-thermal component . The parameter is
presented as a function of the black hole mass, AGN luminosity, and `coronal
radius' of the {\sc optxagnf} model upon which {\sc oxaf} is based. We show
that the soft X-ray excess does not significantly affect photoionization
modeling predictions of strong emission lines in Seyfert narrow-line regions.
Despite its simplicity, {\sc oxaf} accounts for opacity effects where the
accretion disk is ionized because it inherits the `color correction' of {\sc
optxagnf}. We use a grid of {\sc mappings} photoionization models with {\sc
oxaf} ionizing spectra to demonstrate how predicted emission-line ratios on
standard optical diagnostic diagrams are sensitive to each of the three {\sc
oxaf} parameters. The {\sc oxaf} code is publicly available in the Astrophysics
Source Code Library.Comment: 14 pages, 9 figures, 1 table. Accepted for publication in Ap
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