Signatures of Electronic Correlations in Optical Properties of LaFeAsO1−x_{1-x}Fx_x

Spectroscopic ellipsometry is used to determine the dielectric function of the superconducting LaFeAsO$_{0.9}$F$_{0.1}$ ($T_c$ = 27 K) and undoped LaFeAsO polycrystalline samples in the wide range 0.01-6.5 eV at temperatures 10 $\leq T \leq$ 350 K. The free charge carrier response in both samples is heavily damped with the effective carrier density as low as 0.040$\pm$0.005 electrons per unit cell. The spectral weight transfer in the undoped LaFeAsO associated with opening of the pseudogap at about 0.65 eV is restricted at energies below 2 eV. The spectra of superconducting LaFeAsO$_{0.9}$F$_{0.1}$ reveal a significant transfer of the spectral weight to a broad optical band above 4 eV with increasing temperature. Our data may imply that the electronic states near the Fermi surface are strongly renormalized due to electron-phonon and/or electron-electron interactions.Comment: 4 pages, 4 figures, units in Fig.2 adde

Use of an Integrated System Dynamics Model for Analyzing Behaviour of the Social-economic-climatic System in Policy Development

Climate change remains one of the most critical issues that humans and the natural world face today. Yet while a strong body of scientific research has identified the risks if mitigation and adaptation measures are not taken, there still remains a policy lag. This leads researchers to pose several questions: is there an identified need by the policy domain for more or different science? Is the science that is conducted made policyrelevant? If not, are there tools to better link science to policy? This report will explain the process of science-policy communication related to the development of an integrated system dynamics model of the social-economic-climatic system at the University of Western Ontario under NSERC strategic grant program funding. It will describe the science-policy interface and outline the main challenge to developing science tools for policy, and will then explain how the UWO research team overcame such challenges. Finally, it explains (a) briefly the proposed model and (b) the process of policy scenarios development. The main objective of the research presented in this report is to bring the model closer to policy makers and emphasize how useful this tool is specifically for the Canadian federal government. The science policy communication process has been established through the set of interviews and workshops. Interviews were used (a) to identify the issues of importance to be incorporated in the model development and (b) to formalize a set of policy scenarios that will provide input for policy making. Workshops were used to communicate science to policy developers and discuss the issues of importance for policy development. The research was fundamentally based on a multi-disciplinary approach that assisted in bridging the research domain to the policy domain. Ultimately, the feedback from the interviews and workshops was embedded in the development of the model and its scenarios, and made it possible to transform policy questions into model scenarios. In other words, by linking science and policy domains, the research team was able to produce a science-based and policy-relevant tool. Limitations to the work mainly reflect the current stage of research and model development. As the strategic research continues on the integrated system dynamics model of the social-economic-climatic system, these limitations are likely to be overcome. The other key limitation is in the selection of the government partners. While the current group of partners has provided valuable insight, further research will aim to expand the group of partners across different departments. This will not only reflect a broader range of interests, but will also more accurately represent a systems view of government. Furthermore, a broader range of disciplinary biases will be consulted, including government policymakers who work more intimately with science and policy research.https://ir.lib.uwo.ca/wrrr/1029/thumbnail.jp

Determinants of low clearances of small solutes during peritoneal dialysis

Peritoneal dialysis plasma clearances of large molecular weight solutes such as inulin (5,200 daltons) usually equal or exceed plasma clearances of such solutes seen with extracorporeal dialyzers, [1–4]. Clearances of smaller solutes such as urea (60 daltons), however, are usually 15% or less of urea clearances with extracorporeal dialysis systems. In Table 1, typical values for clearances of urea and inulin, dialysis solution flow rate (QD), blood flow rate (QB), and surface area are compared for peritoneal and extracorporeal (hemodialysis) techniques. Effective peritoneal capillary blood flow rate is unknown. Gross total anatomical peritoneal surface area is estimated to be approximately equal to body surface area [2, 4]

Importance of In-Plane Anisotropy in the Quasi Two-Dimensional Antiferromagnet BaNi2_{2}V2_{2}O8_{8}

The phase diagram of the quasi two-dimensional antiferromagnet BaNi$_{2}$V$_{2}$O$_{8}$ is studied by specific heat, thermal expansion, magnetostriction, and magnetization for magnetic fields applied perpendicular to $\mathbf{c}$. At $\mu_0H^{*}\simeq1.5$ T, a crossover to a high-field state, where $T_N(H)$ increases linearly, arises from a competition of intrinsic and field-induced in-plane anisotropies. The pressure dependences of $T_N$ and $H^{*}$ are interpreted using the picture of a pressure-induced in-plane anisotropy. Even at zero field and ambient pressure, in-plane anisotropy cannot be neglected, which implies deviations from pure Berezinskii-Kosterlitz-Thouless behavior.Comment: 4 pages, 4 figure

Effect of annealing on the specific heat of optimally doped Ba(Fe0.92_{0.92}Co0.08_{0.08})2_{2}As2_{2}

We report the temperature dependence of the low-temperature specific heat down to 400 mK of the electron-doped Ba(Fe$_{0.92}$Co$_{0.08}$)$_{2}$As$_{2}$ superconductors. We have measured two samples extracted from the same batch: first sample has been measured just after preparation with no additional heat treatment. The sample shows $T_{c}$=20 K, residual specific heat $\gamma_{0}$=3.6 mJ/mol K$^{2}$ and a Schottky-like contribution at low temperatures. A second sample has been annealed at 800 $^{o}C$ for two weeks and shows $T_{c}$ = 25 K and $\gamma_{0}$=1.4 mJ/mol~K$^{2}$. By subtracting the lattice specific heat, from pure BaFe$_{2}$As$_{2}$, the temperature dependence of the electronic specific heat has been obtained and studied. For both samples the temperature dependence of $C_{el}(T)$ clearly indicate the presence of low-energy excitations in the system. Their specific heat data cannot be described by single clean s- or d-wave models and the data requires an anisotropic gap scenario which may or may not have nodesComment: SCES 2010, 5 pages, 2 figure

Dominance of the planktonic diatom Thalassiosira minima in recent summers in the Bahia Blanca Estuary, Argentina

The diatom Thalassiosira minima was first recorded in the Baha Blanca Estuary in 1992. In 19921993 it exhibited a broad seasonal occurrence. A recent survey (20062007) showed a seasonal appearance restricted mainly to summer together with a greater relative abundance within the phytoplankton. A close connection was found with warmer, more saline and highly turbid conditions experienced in recent summers in the estuary. Whether these changes will impact the estuary trophic dynamics remains an open question

Dipole-active optical phonons in YTiO_3: ellipsometry study and lattice-dynamics calculations

The anisotropic complex dielectric response was accurately extracted from spectroscopic ellipsometry measurements at phonon frequencies for the three principal crystallographic directions of an orthorhombic (Pbnm) YTiO_3 single crystal. We identify all twenty five infrared-active phonon modes allowed by symmetry, 7B_1u, 9B_2u, and 9B_3u, polarized along the c-, b-, and a-axis, respectively. From a classical dispersion analysis of the complex dielectric functions \tilde\epsilon(\omega) and their inverses -1/\tilde\epsilon(\omega) we define the resonant frequencies, widths, and oscillator strengths of the transverse (TO) and longitudinal (LO) phonon modes. We calculate eigenfrequencies and eigenvectors of B_1u, B_2u, and B_3u normal modes and suggest assignments of the TO phonon modes observed in our ellipsometry spectra by comparing their frequencies and oscillator strengths with those resulting from the present lattice-dynamics study. Based on these assignments, we estimate dynamical effective charges of the atoms in the YTiO_3 lattice. We find that, in general, the dynamical effective charges in YTiO_3 lattice are typical for a family of perovskite oxides. By contrast to a ferroelectric BaTiO_3, the dynamical effective charge of oxygen related to a displacement along the c-axis does not show the anomalously large value. At the same time, the dynamical effective charges of Y and ab-plane oxygen exhibit anisotropy, indicating strong hybridization along the a-axis.Comment: 8 pages, 7 figure

Large single crystal growth of BaFe1.87Co0.13As2 using a nucleation pole

Co-doped iron arsenic single crystal of BaFe1.87Co0.13As2 with dimension up to 20 x 10 x 2 mm3 were grown by a nucleation pole: an alumina stick served as nucleation center during growth. The high quality of crystalline was illustrated by the measurements of neutron rocking curve and X-ray diffraction pattern. A very sharp superconducting transition temperature Tc~25 K was revealed by both resistivity and susceptibility measurements. A nearly 100% shielding fraction and bulk nature of the superconductivity for the single crystal were confirmed using magnetic susceptibility data.Comment: 4 pages, 5 figure

Superconductivity mediated by a soft phonon mode: specific heat, resistivity, thermal expansion and magnetization of YB6

The superconductor YB6 has the second highest critical temperature Tc among the boride family MBn. We report measurements of the specific heat, resistivity, magnetic susceptibility and thermal expansion from 2 to 300 K, using a single crystal with Tc = 7.2 K. The superconducting gap is characteristic of medium-strong coupling. The specific heat, resistivity and expansivity curves are deconvolved to yield approximations of the phonon density of states, the spectral electron-phonon scattering function and the phonon density of states weighted by the frequency-dependent Grueneisen parameter respectively. Lattice vibrations extend to high frequencies >100 meV, but a dominant Einstein-like mode at ~8 meV, associated with the vibrations of yttrium ions in oversized boron cages, appears to provide most of the superconducting coupling and gives rise to an unusual temperature behavior of several observable quantities. A surface critical field Hc3 is also observed.Comment: 29 pages, 5 tables, 17 figures. Accepted for publication in Phys. Rev.

Genetic diversity of the narrow endemic Astragalus oniciformis (Fabaceae)

Astragalus oniciformis Barneby is a narrow endemic xerophyte of the upper Snake River Plain of central Idaho, USA, where it inhabits stabilized, aeolian sand deposits and previously burned, sandy sites over Quaternary basalt flows. The objective of this study was to determine the levels and distribution of genetic differentiation within and among populations of A. oniciformis. Fifteen individuals from each of eight populations, chosen from throughout the range of the species, were selected based on accessibility, density of individuals, and large population size. Inter-simple sequence repeats were chosen as the marker to assess genetic differentiation. The two primers selected yielded 40 polymorphic loci in A. oniciformis. In an analysis of molecular variance, 88.69% of the variation was significantly attributed to variation within populations. High gene flow (Nm = 3.91–3.93; SD = 0.01) and a low percentage deviation from Hardy-Weinberg equilibrium due to population subdivision (GST = 0.113–0.1134; SD = 0.0002) were found among sampled populations. These results suggest that current threats to this species, including changing fire patterns and habitat loss from grazing disturbance, have not yet affected the genetic diversity of this species. Preservation of large populations and smaller, intervening, dispersed patches will help preserve the genetic integrity and the genetic diversity found in A. oniciformis.Keywords: endemic, conservation, Idaho, USA, genetic diversity, Fabaceae, Astragalus, ISSRGenetic diversity of the narrow endemic… Published version can be found at American Journal of Botany: http://www.amjbot.org/content/vol91/issue12