Structural integration of tellurium oxide into mixed-network-former glasses: connectivity distribution in the system NaPO(3)-TeO(2).

Sodium phosphate tellurite glasses in the system (NaPO(3))(x)(TeO(2))(1-) (x) were prepared and structurally characterized by thermal analysis, vibrational spectroscopy, X-ray photoelectron spectroscopy (XPS) and a variety of complementary solid-state nuclear magnetic resonance (NMR) techniques. Unlike the situation in other mixed-network-former glasses, the interaction between the two network formers tellurium oxide and phosphorus oxide produces no new structural units, and no sharing of the network modifier Na(2)O takes place. The glass structure can be regarded as a network of interlinked metaphosphate-type P(2) tetrahedral and TeO(4/2) antiprismatic units. The combined interpretation of the O 1s XPS data and the (31)P solid-state NMR spectra presents clear quantitative evidence for a nonstatistical connectivity distribution. Rather, the formation of homoatomic P--O--P and Te--O--Te linkages is favored over mixed P--O--Te connectivities. As a consequence of this chemical segregation effect, the spatial sodium distribution is not random, as also indicated by a detailed analysis of (31)P/(23)Na rotational echo double-resonance (REDOR) experiments.     

How to statistically analyze nano exposure measurement results: using an ARIMA time series approach

Measurement strategies for exposure to nano-sized particles differ from traditional integrated sampling methods for exposure assessment by the use of real-time instruments. The resulting measurement series is a time series, where typically the sequential measurements are not independent from each other but show a pattern of autocorrelation. This article addresses the statistical difficulties when analyzing real-time measurements for exposure assessment to manufactured nano objects. To account for autocorrelation patterns, Autoregressive Integrated Moving Average (ARIMA) models are proposed. A simulation study shows the pitfalls of using a standard t-test and the application of ARIMA models is illustrated with three real-data examples. Some practical suggestions for the data analysis of real-time exposure measurements conclude this article.     

C-terminal processing of yeast Spt7 occurs in the absence of functional SAGA complex

Background  

Spt7 is an integral component of the multi-subunit SAGA complex that is required for the expression of ~10% of yeast genes. Two forms of Spt7 have been identified, the second of which is truncated at its C-terminus and found in the SAGA-like (SLIK) complex.     

Redox effects on resin extraction of herbicides from soil

Relative soil aeration affects the surfaces upon which pesticides adsorb and non-ionic resins offer a means of observing and evaluating this factor. A non-ionic resin extractor, developed for pesticide extraction under reducing conditions, was used to adsorb a fraction of the reversibly adsorbed (active portion) herbicides. The extractor consists of cleaned XAD-2 resin encased in a dialysis membrane composed of regenerated cellulose. Anaerobiosis was achieved by incubating soil suspensions with glucose under a 95% N(2)-5% H(2) environment until the redox potential reached -150 mV. Nine soils with a range of physical and chemical characteristics were examined for atrazine, metribuzin, and alachlor content. Amounts of atrazine, metribuzin, and alachlor extracted from soil ranged to 100, 140, and 75 ng g(-1), respectively. Resin extractions (RE) conducted under aerobic conditions recovered about 25-50% of the pesticide extractable with conventional solid phase solvent extraction at 60 degrees C (SPE(60)). Under anaerobic conditions, equal amounts of atrazine were extracted with RE and SPE(60). Slightly less metribuzin was recovered under anaerobic extraction with the exception of those soils lacking detectable amounts by SPE(60). Larger amounts of alachlor were extracted with resins under anaerobic conditions than under aerobic conditions but the amounts were not correlated with those determined by SPE(60). Large amounts of soil organic matter were solublized under anaerobiosis and smaller molecular weight material was extracted with the herbicides. The nature and amounts of co-extracted organic matter varied among soils. RE directly from soil suspensions enabled simultaneous determination of all three herbicides.     

Structural investigations of tungsten silver phosphate glasses by solid state NMR, vibrational and X-ray absorption near edge spectroscopies

Glasses were prepared in the pseudo-binary system (1 − x)AgPO₃-xWO₃ (0≤ × ≤ 0.6 mol%). The structural evolution of the vitreous network was studied as a function of composition by thermal analysis, Fourier Transform Infrared spectroscopy (FTIR), Raman scattering, high resolution ³¹P solid state NMR and XANES at the W-L₁ absorption edge. For compositions with x ranging from 0 to 0.5 a pronounced increase in the glass transition temperature is observed, suggesting a significant increase in the glass network connectivity. At the same time Raman spectra indicate that tungsten atoms are linked to non-bridging oxygen atoms (W-O- or W=O bonded species) whereas the ³¹P MAS-NMR spectra indicate the successive formation of new P-O-W linkages. The formation of some anionic tungsten sites (if these are revealed by the presence of W-O terminal bonds) implies an increase in the average degree of polymerization of the phosphate network, which is consistent with the compositional evolution of the ³¹P MAS-NMR spectra at low x values. For higher x-values, the Raman spectra indicate the presence of W-O-W linkages. W-L₁ XANES data indicate that at least 90% of tungsten atoms are octahedrally coordinated.     

Characterizing STEM Teacher Education: Affordances and Constraints of Explicit STEM Preparation for Elementary Teachers

Although science, technology, engineering, and mathematics (STEM) education sits at the center of a national conversation, comparatively little attention has been given to growing need for STEM teacher preparation, particularly at the elementary level. This study analyzes the outcomes of a novel, preservice STEM teacher education model. Building on both general and STEM‐specific teacher preparation principles, this program combined two traditional mathematics and science methods courses into one STEM block. Analysis compared preservice teachers in the traditional courses with those enrolled in the STEM block, investigating STEM teaching efficacy, reported and exhibited pedagogical practices, and STEM literacies using a pre‐post survey as well as analysis of lesson planning products. Linear regression models indicated that substantial growth was seen in both approaches but STEM block preservice teachers reported significantly greater gains in STEM teaching efficacy as compared with traditional‐route teachers. Lesson planning artifacts also demonstrated increased facilitation of STEM literacies, with specific attention to content integration, engineering and design, and arts inclusion. Technology and computational thinking emerged as areas for further growth and clarification in STEM teacher education models. Findings contribute to a growing research base on developing the STEM teacher workforce.     

Quasi-monocrystalline silicon for thin-film devices

Thermal crystallization of a double layer porous Si film creates a monocrystalline Si film with a thin separation layer between the Si film and the reusable starting wafer. The process enables transfer of thin monocrystalline Si films to foreign substrates, whereby devices may be formed before or after separation of the film. Sub-micrometer thick films are almost compact, while films with a thickness of several μm contain voids, and are therefore termed “quasi-monocrystalline”. Internal voids strongly enhance optical absorption by light scattering. The hole mobility is 78 cm² V^-1 s^-1 at a p-type starting wafer resistivity of 0.05 Ω cm. Received: 24 March 1999 / Accepted: 29 March 1999 / Published online: 5 May 1999     

Structural studies of AgPO3–MoO3 glasses using solid state NMR and vibrational spectroscopies

Vitreous samples (1-x) AgPO₃–x MoO₃ (0 ≤ x ≤ 0.5) were prepared by conventional melt-quenching and characterized by Differential Scanning Calorimetry (DSC). The structural evolution of the vitreous network was monitored by ³¹P solid state nuclear magnetic resonance and Raman scattering, and assignments were aided by corresponding studies on the model compound AgMoO₂PO₄. The ³¹P MAS-NMR data differentiate between species having two, one, and zero P―O―P linkages (Q⁽²⁾ Q⁽¹⁾, and Q⁽⁰⁾ species), respectively. Interatomic connectivities involving these units are revealed by two-dimensional INADEQUATE data, utilizing the formation of double quantum coherences mediated by indirect ³¹P–³¹P spin–spin interactions via P―O―P linkages. As this method discriminates against isolated P atoms, it also serves as an important spectral editing tool for constraining lineshape fits. ⁹⁵Mo NMR data and Raman spectra suggest that the Mo species are most likely six-coordinate, forming four P―O―Mo linkages and are otherwise invariant with composition, except at MoO₃ contents ≥ 40 mole %, where some Mo―O―Mo bonding and/or clustering is observed.     

Discriminant analysis in the presence of interferences: Combined application of target factor analysis and a Bayesian soft-classifier

A method is described for performing discriminant analysis in the presence of interfering background signal. The method is based on performing target factor analysis on a data set comprised of contributions from analyte(s) and interfering components. A library of data from representative analyte classes is tested for possible contributing factors by performing oblique rotations of the principal factors to obtain the best match, in a least-squares sense, between test and predicted vectors. The degree of match between the test and predicted vectors is measured by the Pearson correlation coefficient, r, and the distribution of r for each class is determined. A Bayesian soft classifier is used to calculate the posterior probability based on the distributions of r for each class, which assist the analyst in assessing the presence of one or more analytes. The method is demonstrated by analyses performed on spectra obtained by laser induced breakdown spectroscopy (LIBS). Single and multiple bullet jacketing transfers to steel and porcelain substrates were analyzed to identify the jacketing materials. Additionally, the metal surrounding bullet holes was analyzed to identify the class of bullet jacketing that passed through a stainless steel plate. Of 36 single sample transfers, the copper jacketed (CJ) and non-jacketed (NJ) class on porcelain had an average posterior probability of the metal deposited on the substrate of 1.0. Metal jacketed (MJ) bullet transfers to steel and porcelain were not detected as successfully. Multiple transfers of CJ/NJ and CJ/MJ on the two substrates resulted in posterior probabilities that reflected the presence of both jacketing materials. The MJ/NJ transfers gave posterior probabilities that reflected the presence of the NJ material, but the MJ component was mistaken for CJ on steel, while non-zero probabilities were obtained for both CJ and MJ on porcelain. Jacketing transfer from a bullet to steel as the projectile passed through the steel also proved difficult to analyze. Over 50% of the samples left insufficient transfer to be identified. Transfer from NJ and CJ jacketing was successfully identified by posterior probabilities greater than 0.8.