Michigan State University

About: Michigan State University is a education organization based out in East Lansing, Michigan, United States. It is known for research contribution in the topics: Population & Poison control. The organization has 60109 authors who have published 137074 publications receiving 5633022 citations. The organization is also known as: MSU & Michigan State.

When the Problem Is Not the Question and the Solution Is Not the Answer: Mathematical Knowing and Teaching

Abstract: This paper describes a research and development project in teaching designed to examine whether and how it might be possible to bring the practice of knowing mathematics in school closer too what it means to know mathematics within the discipline by deliberately altering the roles and responsibilities of teacher and students in classroom discourse. The project was carried out as a regular feature of lessons in fifth-grade mathematics in a public school. A case of teaching and learning about exponents derived from lessons taught in the project is described and interpreted from mathematical, pedagogical, and sociolinguistic perspectives. To change the meaning of knowing and learning in school, the teacher initiated and supported social interactions appropriate to making mathematical arguments in response to students’ conjectures. The activities students engaged in as they asserted and examined hypotheses about the mathematical structures that underlie their solutions to problems are contrasted with the conv...

Stream denitrification across biomes and its response to anthropogenic nitrate loading

Abstract: About a quarter of the nitrogen added to the biosphere is exported from rivers to the ocean or inland basins, indicating substantial sinks for nitrogen must exist in the landscape. Data from nitrogen stable isotope tracer experiments across 72 streams suggests that the total uptake of nitrate is related to ecosystem photosynthesis, and that denitrification is related to ecosystem respiration. A stream network model demonstrates that excess nitrate in streams elicits a disproportionate increase in the fraction of nitrate that is exported to receiving waters and reduces the relative role of small versus large streams as nitrate sinks. Anthropogenic addition of bioavailable nitrogen to the biosphere is increasing1,2 and terrestrial ecosystems are becoming increasingly nitrogen-saturated3, causing more bioavailable nitrogen to enter groundwater and surface waters4,5,6. Large-scale nitrogen budgets show that an average of about 20–25 per cent of the nitrogen added to the biosphere is exported from rivers to the ocean or inland basins7,8, indicating that substantial sinks for nitrogen must exist in the landscape9. Streams and rivers may themselves be important sinks for bioavailable nitrogen owing to their hydrological connections with terrestrial systems, high rates of biological activity, and streambed sediment environments that favour microbial denitrification6,10,11. Here we present data from nitrogen stable isotope tracer experiments across 72 streams and 8 regions representing several biomes. We show that total biotic uptake and denitrification of nitrate increase with stream nitrate concentration, but that the efficiency of biotic uptake and denitrification declines as concentration increases, reducing the proportion of in-stream nitrate that is removed from transport. Our data suggest that the total uptake of nitrate is related to ecosystem photosynthesis and that denitrification is related to ecosystem respiration. In addition, we use a stream network model to demonstrate that excess nitrate in streams elicits a disproportionate increase in the fraction of nitrate that is exported to receiving waters and reduces the relative role of small versus large streams as nitrate sinks.

First stars V - abundance patterns from C to Zn and supernova yields in the early galaxy

Abstract: In the framework of the ESO Large Programme "First Stars", very high-quality spectra of some 70 very metal-poor dwarfs and giants were obtained with the ESO VLT and UVES spectrograph. These stars are likely to have descended from the first generation(s) of stars formed after the Big Bang, and their detailed composition provides constraints on issues such as the nature of the first supernovae, the efficiency of mixing processes in the early Galaxy, the formation and evolution of the halo of the Galaxy, and the possible sources of reionization of the Universe. This paper presents the abundance analysis of an homogeneous sample of 35 giants selected from the HK survey of Beers et al. (1992, 1999), emphasizing stars of extremely low metallicity: 30 of our 35 stars are in the range −4.1 < (Fe/H) < −2. 7, and 22 stars have (Fe/H) < −3.0. Our new VLT/UVES spectra, at a resolving power of R ∼ 45 000 and with signal-to-noise ratios of 100-200 per pixel over the wavelength range 330-1000 nm, are greatly superior to those of the classic studies of McWilliam et al. (1995) and Ryan et al. (1996). The immediate objective of the work is to determine precise, comprehensive, and homogeneous element abundances for this large sample of the most metal-poor giants presently known. In the analysis we combine the spectral line modeling code "Turbospectrum" with OSMARCS model atmospheres, which treat continuum scattering correctly and thus allow proper inter- pretation of the blue regions of the spectra, where scattering becomes important relative to continuous absorption ( λ< 400 nm). We obtain detailed information on the trends of elemental abundance ratios and the star-to-star scatter around those trends, en- abling us to separate the relative contributions of cosmic scatter and observational/analysis errors. Abundances of 17 elements from C to Zn have been measured in all stars, including K and Zn, which have not previously been detected in stars with (Fe/H) < −3.0. Among the key results, we discuss the oxygen abundance (from the forbidden (OI) line), the different and sometimes complex trends of the abundance ratios with metallicity, the very tight relationship between the abundances of certain elements (e.g., Fe and Cr), and the high (Zn/Fe) ratio in the most metal-poor stars. Within the error bars, the trends of the abundance ratios with metallicity are consistent with those found in earlier literature, but in many cases the scatter around the average trends is much smaller than found in earlier studies, which were limited to lower-quality spectra. We find that the cosmic scatter in several element ratios may be as low as 0.05 dex. The evolution of the abundance trends and scatter with declining metallicity provides strong constraints on the yields of the first supernovae and their mixing into the early ISM. The abundance ratios found in our sample do not match the predicted yields from pair-instability hypernovae, but are consistent with element production by super- novae with progenitor masses up to 100 M� . Moreover, the composition of the ejecta that have enriched the matter

Psychiatric Disorders and Drug Use Among Human Immunodeficiency Virus–Infected Adults in the United States

Abstract: Background: There have been no previous nationally representative estimates of the prevalence of mental disorders and drug use among adults receiving care for human immunodeficiency virus (HIV) disease in the United States. It is also not known which clinical and sociodemographic factors are associated with these disorders. Subjects and Methods: We enrolled a nationally representative probability sample of 2864 adults receiving care for HIV in the United States in 1996. Participants were administered a brief structured psychiatric instrument that screened for psychiatric disorders (major depression, dysthymia, generalized anxiety disorders, and panic attacks) and drug use during the previous 12 months. Sociodemographic and clinical factors associated with screening positive for any psychiatric disorder and drug dependence were examined in multivariate logistic regression analyses. Results: Nearly half of the sample screened positive for a psychiatric disorder, nearly 40% reported using an illicit drug other than marijuana, and more than 12% screened positive for drug dependence during the previous 12 months. Factors independently associated with screening positive for a psychiatric disorder included number of HIV-related symptoms, illicit drug use, drug dependence, heavy alcohol use, and being unemployed or disabled. Factors independently associated with screening positive for drug dependence included having many HIV-related symptoms, being younger, being heterosexual, having frequent heavy alcohol use, and screening positive for a psychiatric disorder. Conclusions: Many people infected with HIV may also have psychiatric and/or drug dependence disorders. Clinicians may need to actively identify those at risk and work with policymakers to ensure the availability of appropriate care for these treatable disorders.