26 Al beam production by a solid state laser ion source at TRIUMF

Many experiments carried out at radioactive beam facilities require the production of intense, isotopically clean and isobar free beams of a particular isotope. At TRIUMF the addition of a resonant ionization laser ion source (TRILIS) enables a multitude of new beams and therefore new experiments to be carried out. ²⁶Al was one of the first radioactive ion beams delivered to an experiment using TRILIS. This paper outlines the development of the ²⁶Al ion beam for nuclear astrophysics.      

Extended X-ray absorption fine structure measurements of laser-shocked V and Ti and crystal phase transformation in Ti

Extended x-ray absorption fine structure (EXAFS), using a laser-imploded target as a source, can yield the properties of laser-shocked metals on a nanosecond time scale. EXAFS measurements of vanadium shocked to approximately 0.4 Mbar yield the compression and temperature in good agreement with hydrodynamic simulations and shock-speed measurements. In laser-shocked titanium at the same pressure, the EXAPS modulation damping is much higher than is warranted by the predicted temperature increase. This is shown to be due to the alpha-Ti to omega-Ti crystal phase transformation, known to occur below approximately 0.1 Mbar for slower shock waves.     

New mechanism for the alpha to omega martensitic transformation in pure titanium

We propose a new direct mechanism for the pressure driven alpha-->omega martensitic transformation in pure titanium. A systematic algorithm enumerates all possible pathways whose energy barriers are evaluated. A new, homogeneous pathway emerges with a barrier at least 4 times lower than other pathways. The pathway is shown to be favorable in any nucleation model.     

A procedure for new product positioning in an attribute space

Planning a preferred position of a new product in an attribute space may be considered as a mixed integer non-linear programming problem. A procedure to solve this problem is described which draws on some special features of the problem. Optimality considerations of the procedure as well as computational experiences with it are reported.     

Synthesis, testing, and characterization of a novel Nafion membrane with superior performance in photoassisted immobilized Fenton catalysis

A new type of Nafion/Fe structured membrane ensuring faster kinetics, higher efficiency, and mechanical properties has been prepared and will be compared in its performance with the Fe-exchanged commercial Dupont 117 Nafion/Fe membrane during the abatement of model organic compounds. During the casting of the laboratory Nafion sample, the iron ions were introduced directly into the Nafion oligomer solution. This novel laboratory Nafion/Fe was tested as an immobilized catalyst in the degradation of several toxic pollutants showing a faster photoassisted degradation kinetics and a wider effective photocatalytic pH range compared to the Fe-exchanged commercial Dupont 117 Nafion/Fe membrane. When carrying out Ar ion sputtering of the 50 topmost catalyst layers, evidence is presented by X-ray photoelectron spectroscopy that Fe ions are found in the inner Nafion layers and seem to be responsible for the immobilized photoassisted Fenton processes leading to the degradation of 4-chorophenol (4-CP) taken as a model organic pollutant for the degradation process reported in this study. In the laboratory sample, the iron oxy/hydroxy Nafion moiety undergoes a transition to a more stable Nafion/Fe species during 4-CP degradation as determined by X-ray diffraction. This more stable form shows a higher iron dispersion and crystallinity compared to the fresh sample and is stabilized by the Nafion matrix avoiding the formation of separate iron phases. By infrared absorption (Fourier transform infrared), evidence is presented for the band of akaganeite-like species at 870 cm(-1) on the laboratory Nafion/Fe sample. This band disappears after 4-CP degradation because of the formation of the more highly dispersed iron species. Sputtering experiments show a decrease of F-containing groups in the laboratory Nafion/Fe samples closer to the catalyst upper layer while the amounts of Fe, C, and in particular O species increase in the topmost layer(s). In particular, the oxygenated species develop in the Nafion/Fe up to approximately 50 A below the catalyst surface. These species remain stable during the long-term Nafion/Fe degradation of 4-CP. Dynamo-mechanical analysis performed on laboratory Nafion/ Fe membrane samples revealed that these membranes possessed a greater mechanical modulus and resistance than the commercial Dupont 117 Nafion membrane.     

Analysis of the Propagation of Sound Waves in Partially Saturated Soils by Means of a Macroscopic Linear Poroelastic Model

In this paper, the propagation of sound waves in partially saturated soils is investigated. A macroscopic linear model that is based on the two-component model of Biot and on the Simple Mixture Model by Wilmanski is used. For the construction of the model by a micro-macro transition, see Albers, Géotechnique, 2007. We investigate a porous medium consisting of a deformable skeleton and two compressible, chemically non-reacting, pore fluids (liquid and gas). The wave analysis of the poroelastic model reveals the number of acoustic waves and the dependence of velocities and attenuations of these waves on the initial saturation and frequency. There appear four body waves: three longitudinal waves, P1, P2, P3, and one shear wave, S. The P2-wave shows a similar feature as in air–water mixtures: from the theory of suspensions, it is well known that the existence of air bubbles in water reveals a minimum in the sonic velocity. This is also the case for the P2 -speed in the unsaturated porous medium. The P1-velocity increases very abruptly for a certain degree of saturation. This provides the hope for the development of a nondestructive testing method.     

Alkyne Addition and Insertion Reactions of [(Me3Si)3Si]2Ge⋅PMe3

Silylated germylene–PMe₃ adducts exchange their phosphane moiety smoothly for an N‐heterocyclic carbene or isocyanide species to form their respective base adducts. Reaction of the silylated germylene–PMe₃ adducts with monosubstituted alkynes produce germylene adducts with the alkyne inserted into a Ge?Si bond. A computational study of this process provides evidence for the initial formation of a germirene, which rearranges to a vinylgermylene species. The thermodynamic driving force for this reaction is provided by subsequent adduct formation with PMe₃. Reaction of the PMe₃ adduct of bis[(trimethylsilyl)silyl]germylene with disubstituted alkynes leads to the formation of stable germirenes, which can be isomerized further to silagermetes.     

Contact geometry of the restricted three‐body problem

We show that the planar circular restricted three‐body problem is of restricted contact type for all energies below the first critical value (action of the first Lagrange point) and for energies slightly above it. This opens up the possibility of using the technology of contact topology to understand this particular dynamical system. © 2011 Wiley Periodicals, Inc.     

Estimation of time-delayed mutual information and bias for irregularly and sparsely sampled time-series

A method to estimate the time-dependent correlation via an empirical bias estimate of the time-delayed mutual information for a time-series is proposed. In particular, the bias of the time-delayed mutual information is shown to often be equivalent to the mutual information between two distributions of points from the same system separated by infinite time. Thus intuitively, estimation of the bias is reduced to estimation of the mutual information between distributions of data points separated by large time intervals. The proposed bias estimation techniques are shown to work for Lorenz equations data and glucose time series data of three patients from the Columbia University Medical Center database.