Recent developments in the use of isotope ratio mass spectrometry in sports drug testing

According to the annual report of the World Anti-Doping Agency, steroids are the most frequently detected class of doping agents. Detecting the misuse of endogenously occurring steroids, i.e. steroids such as testosterone that are produced naturally by humans, is one of the most challenging issues in doping control analysis. The established thresholds for urinary concentrations or concentration ratios such as the testosterone/epitestosterone quotient are sometimes inconclusive owing to the large biological variation in these parameters.     

Structural analysis of PTCDA monolayers on epitaxial graphene with ultra-high vacuum scanning tunneling microscopy and high-resolution X-ray reflectivity

Epitaxial graphene, grown by thermal decomposition of the SiC (0001) surface, is a promising material for future applications due to its unique and superlative electronic properties. However, the innate chemical passivity of graphene presents challenges for integration with other materials for device applications. Here, we present structural characterization of epitaxial graphene functionalized by the organic semiconductor perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA). A combination of ultra-high vacuum scanning tunneling microscopy (STM) and high-resolution X-ray reflectivity (XRR) is used to extract lateral and vertical structures of 0, 1, and 2 monolayer (ML) PTCDA on epitaxial graphene. Both Fienup-based phase-retrieval algorithms and model-based least-squares analyses of the XRR data are used to extract an electron density profile that is interpreted in terms of a stacking sequence of molecular layers with specific interlayer spacings. Features in the STM and XRR analysis indicate long-range molecular ordering and weak π–π* interactions binding PTCDA molecules to the graphene surface. The high degree of both lateral and vertical ordering of the self-assembled film demonstrates PTCDA functionalization as a viable route for templating graphene for the growth and deposition of additional materials required for next-generation electronics and sensors.     

Reduction of uranium triiodide to metal by thermal decomposition

Uranium metal was successfully produced from uranium triiodide through thermal decomposition in a tetra-arc crystal furnace. The uranium triiodide was produced by reacting uranium and iodine at 600 °C for 24 h. After the uranium triiodide was heated in the arc furnace, a product was confirmed to be uranium metal through X-ray diffraction, density, and energy-dispersive X-ray spectroscopy measurements. Historically, uranium triiodide has been reduced after passing through a gaseous intermediate of uranium tetraiodide and reduced on a hot filament. This is the first report of directly reducing uranium triiodide to uranium metal, circumventing the uranium tetraiodide intermediary.

     

Minimal-energy splines: I. Plane curves with angle constraints

This is the first in a series of papers on minimal-energy splines. The paper is devoted to plane minimal-energy splines with angle constraints. We first consider minimal-energy spline segments, then general minimal-energy spline curves. We formulate problems for minimal-energy spline segments and curves, prove the existence of solutions, justify the Lagrange multiplier rules, and obtain some nice properties (e.g., the infinite smoothness). Finally, we report our computational experience on minimal-energy splines.     

Temperature distributions and thermal stresses in a partially filled annulus

The problem consists of determining the temperature distribution and the thermal stresses in an annulus partly filled with a cold fluid with free convection in air as the outer thermal-boundary condition. An iterative computer solution provided temperature distributions which were compared to those measured experimentally. Analytical calculations of the stresses using Fourier series expression for the temperature distribution agreed with experimental results by photothermoelasticity. The stress-intensity factors determined by photothermoelasticity for partly filled annuli with a crack extending radially 1/5 of the wall thickness were compared with approximate analytical methods.     

Counting solutions to trinomial Thue equations: a different approach

We consider the problem of counting solutions to a trinomial Thue equation -- that is, an equation

where is an irreducible form in with degree at least three and with three non-zero coefficients. In a 1987 paper J. Mueller and W. Schmidt gave effective bounds for this problem. Their work was based on a series of papers by Bombieri, Bombieri-Mueller and Bombieri-Schmidt, all concerned with the ``Thue-Siegel principle" and its relation to . In this paper we give specific numerical bounds for the number of solutions to by a somewhat different approach, the difference lying in the initial step -- solving a certain diophantine approximation problem. We regard this as a real variable extremal problem, which we then solve by elementary calculus.