Commensurate Nb2Zr5O15: Accessible Within the Field Nb2ZrxO2x+5 After All

Doped niobium zirconium oxides are applied in field-effect transistors and as special-purpose coatings. Whereas their material properties are sufficiently known, their crystal structures remain widely uncharacterized. Herein, we report on the comparably mild sol–gel synthesis of Nb2Zr5O15 and the elucidation of its commensurately modulated structure via neutron diffraction. We describe the structure using the most appropriate superspace as well as the convenient supercell approach. It is part of an α-PbO2-homeotypic field with the formula Nb2ZrxO2x+5, which has previously been reported only for x ≥ 5.1, and is closely related to the structure of Hf3Ta2O11. The results, supported by X-ray diffraction and additional synthesis experiments, are contextualized within the existing literature. Via the sol–gel route, metastable Nb–Zr–O compounds and their heavier congeners are accessible that shed light on possible structures of these commercially utilized materials.DFG, 198634447, SPP 1613: Regenerativ erzeugte Brennstoffe durch lichtgetriebene Wasserspaltung: Aufklärung der Elementarprozesse und Umsetzungsperspektiven auf technologische KonzepteTU Berlin, Open-Access-Mittel - 201

Multiple Meixner-Pollaczek polynomials and the six-vertex model

We study multiple orthogonal polynomials of Meixner-Pollaczek type with respect to a symmetric system of two orthogonality measures. Our main result is that the limiting distribution of the zeros of these polynomials is one component of the solution to a constrained vector equilibrium problem. We also provide a Rodrigues formula and closed expressions for the recurrence coefficients. The proof of the main result follows from a connection with the eigenvalues of block Toeplitz matrices, for which we provide some general results of independent interest. The motivation for this paper is the study of a model in statistical mechanics, the so-called six-vertex model with domain wall boundary conditions, in a particular regime known as the free fermion line. We show how the multiple Meixner-Pollaczek polynomials arise in an inhomogeneous version of this model.Comment: 32 pages, 4 figures. References adde

Bourdieu, networks, and movements: Using the concepts of habitus, field and capital to understand a network analysis of gender differences in undergraduate physics

Current trends suggest that significant gender disparities exist within Science, Technology, Engineering, and Mathematics (STEM) education at university, with female students being underrepresented in physics, but more equally represented in life sciences (e.g., biology, medicine). To understand these trends, it is important to consider the context in which students make decisions about which university courses to enrol in. The current study seeks to investigate gender differences in STEM through a unique approach that combines network analysis of student enrolment data with an interpretive lens based on the sociological theory of Pierre Bourdieu. We generate a network of courses taken by around 9000 undergraduate physics students (from 2009 to 2014) to quantify Bourdieu's concept of field. We explore the properties of this network to investigate gender differences in transverse movements (between different academic fields) and vertical movements (changes in students' achievement rankings within a field). Our findings indicate that female students are more likely to make transverse movements into life science fields. We also find that university physics does a poor job in attracting high achieving students, and especially high achieving female students. Of the students who do choose to study physics, low achieving female students are less likely to continue than their male counterparts. The results and implications are discussed in the context of Bourdieu's theory, and previous research. We argue that in order to remove constraints on female student's study choices, the field of physics needs to provide a culture in which all students feel like they belong.Comment: 23 pages, 6 figures, 1 tabl

Short-term Response of Holcus lanatus L. (Common Velvetgrass) to Chemical and Manual Control at Yosemite National Park, USA

One of the highest priority invasive species at both Yosemite and Sequoia and Kings Canyon national parks is Holcus lanatus L. (common velvetgrass), a perennial bunchgrass that invades mid-elevation montane meadows. Despite velvetgrass being a high priority species, there is little information available on control techniques. The goal of this project was to evaluate the short-term response of a single application of common chemical and manual velvetgrass control techniques. The study was conducted at three montane sites in Yosemite National Park. Glyphosate spotspray treatments were applied at 0.5, 1.0, 1.5, and 2.0% concentrations, and compared with hand pulling to evaluate effects on cover of common velvetgrass, cover of other plant species, and community species richness. Posttreatment year 1 cover of common velvetgrass was 12.1% 6 1.6 in control plots, 6.3% 6 1.5 averaged over the four chemical treatments (all chemical treatments performed similarly), and 13.6% 6 1.7 for handpulled plots. This represents an approximately 50% reduction in common velvetgrass cover in chemically- treated plots recoded posttreatment year 1 and no statistically significant reduction in hand pulled plots compared with controls. However, there was no treatment effect in posttreatment year 2, and all herbicide application rates performed similarly. In addition, there were no significant treatment effects on nontarget species or species richness. These results suggest that for this level of infestation and habitat type, (1) one year of hand pulling is not an effective control method and (2) glyphosate provides some level of control in the short-term without impact to nontarget plant species, but the effect is temporary as a single year of glyphosate treatment is ineffective over a twoyear period

DEVELOPING AND PRICING PRECIPITATION INSURANCE

Production agriculture and agribusiness are exposed to many weather-related risks. Recent years have seen the emergence of an increased interest in weather-based derivatives as mechanisms for sharing risks due to weather phenomena. In this study, a unique precipitation derivative is proposed that allows the purchaser to specify the parameters of the idemnity function. Pricing methods are presented in the context of a cotton harvest example from Mississippi. Our findings show a potential for weather derivatives to serve niche markets within U.S. agriculture.Risk and Uncertainty,

Dynamic Web Tools for Undergraduate Mathematics

The internet has become widely available, and tools for mathematical computation on the net have now appeared. The authors used webMathematica software to create interactive web pages which allow students and faculty to compute and visualize results directly from a web browser. The nature of the innovation, its significance for instruction, and some implications for student understanding are discussed

Fourier series approximations and low pass filtering: facilitating learning of digital signal processing for biomechanics students

pre-printFiltering raw biomechanical data to remove noise is a key first step that must be performed prior to further biomechanical analysis. Raw biomechanical data are usually filtered to remove noise above a specified cutoff frequency, a process known as "low pass filtering". The concept of frequency content within a signal may be difficult for students to grasp, and authors of biomechanics textbooks often use Fourier series approximations to introduce this concept. To facilitate student learning, we have created an Excel spreadsheet that allows students to observe several orders of Fourier series approximations to a representative set of biomechanical data. In this paper, we provide a short tutorial on Fourier series approximations and instructions for using the Excel spreadsheet. The Fourier series coefficients are determined iteratively with a first-principles approach of minimizing the sum of squared error between the original data and the approximation using the Solver function in Excel. The user can reset these coefficients and run Solver to observe the iterative process. This first-principles approach may be helpful in a broad range of applications because it allows users to perform non-linear regression within an Excel spreadsheet. The Excel spreadsheet also includes a fourth-order zero-lag Butterworth low pass filter with adjustable cutoff frequency so that the effects of filtering can be observed and compared with the Fourier series approximations. We believe this tutorial and Excel spreadsheet will be helpful to those teaching and learning digital signal processing in biomechanics

Introducing evidence based medicine to the journal club, using a structured pre and post test: a cohort study

BACKGROUND: Journal Club at a University-based residency program was restructured to introduce, reinforce and evaluate residents understanding of the concepts of Evidence Based Medicine. METHODS: Over the course of a year structured pre and post-tests were developed for use during each Journal Club. Questions were derived from the articles being reviewed. Performance with the key concepts of Evidence Based Medicine was assessed. Study subjects were 35 PGY2 and PGY3 residents in a University based Family Practice Program. RESULTS: Performance on the pre-test demonstrated a significant improvement from a median of 54.5 % to 78.9 % over the course of the year (F 89.17, p < .001). The post-test results also exhibited a significant increase from 63.6 % to 81.6% (F 85.84, p < .001). CONCLUSIONS: Following organizational revision, the introduction of a pre-test/post-test instrument supported achievement of the learning objectives with a better understanding and utilization of the concepts of Evidence Based Medicine

Single Gate P-N Junctions in Graphene-Ferroelectric Devices

Graphene's linear dispersion relation and the attendant implications for bipolar electronics applications have motivated a range of experimental efforts aimed at producing p-n junctions in graphene. Here we report electrical transport measurements of graphene p-n junctions formed via simple modifications to a PbZr$_{0.2}$Ti$_{0.8}$O$_3$ substrate, combined with a self-assembled layer of ambient environmental dopants. We show that the substrate configuration controls the local doping region, and that the p-n junction behavior can be controlled with a single gate. Finally, we show that the ferroelectric substrate induces a hysteresis in the environmental doping which can be utilized to activate and deactivate the doping, yielding an `on-demand' p-n junction in graphene controlled by a single, universal backgate