ARPES studies of the electronic structure of LaOFe(P, As)

We report a comparison study of LaOFeP and LaOFeAs, two parent compounds of recently discovered iron-pnictide superconductors, using angle-resolved photoemission spectroscopy. Both systems exhibit some common features that are very different from well-studied cuprates. In addition, important differences have also been observed between these two ferrooxypnictides. For LaOFeP, quantitative agreement can be found between our photoemission data and the LDA band structure calculations, suggesting that a weak coupling approach based on an itinerant ground state may be more appropriate for understanding this new superconducting compound. In contrast, the agreement between LDA calculations and experiments in LaOFeAs is relatively poor, as highlighted by the unexpected Fermi surface topology around (π, π). Further investigations are required for a comprehensive understanding of the electronic structure of LaOFeAs and related compounds.     

Near-infrared spectroscopic study of selected hydrated hydroxylated phosphates

Near-infrared spectroscopy has been applied to a suite of hydrated hydroxylated phosphate minerals including cacoxenite, hureaulite, planerite, gormanite and wardite. The NIR spectra may be conveniently divided into three regions (a) the first hydroxyl fundamental, (b) the water HOH overtone and (c) the region between 4000 and 4800 cm(-1) where combination bands resulting from the bands in the mid-IR. For each of these regions, the minerals show distinctive spectra which enable their identification and characterisation. NIR spectroscopy is a less used technique which does have great application for the study of minerals, particularly minerals which have hydrogen in the structure either as hydroxyl units or as water bonded to the cation or as zeolitic water as is the case for cacoxenite. The study of minerals on planets is topical and NIR spectroscopy provides a rapid technique for the distinction and identification of minerals.     

Dissimilarity and the Classification of Male Singing Voices

Traditionally, timbre has been defined as that perceptual attribute that differentiates two sounds when pitch and loudness are equal, and thus is a measure of dissimilarity. By such a definition, each voice possesses a set of timbres, and the ability to identify any voice or voice category across different pitch-loudness-vowel combinations must be due to an ability to "link" these timbres by abstracting the "timbre transformation," the manner in which timbre subtly changes across pitch and loudness for a specific voice or voice category. Using stimuli produced across the singing range by singers from different voice categories, this study sought to examine how timbre and pitch interact in the perception of dissimilarity in male singing voices. This study also investigated whether or not listener experience affects the perception of timbre as a function of pitch. The resulting multidimensional scaling (MDS) representations showed that for all stimuli and listeners, dimension 1 correlated with pitch, while dimension 2 correlated with spectral centroid and separated vocal stimuli into the categories baritone and tenor. Dimension 3 appeared highly idiosyncratic depending on the nature of the stimuli and on the experience of the listener. Inexperienced listeners appeared to rely more heavily on pitch in making dissimilarity judgments than did experienced listeners. The resulting MDS representations of dissimilarity across pitch provide a glimpse of the timbre transformation of voice categories across pitch.     

Influence of Achiral Phosphine Ligands on a Synergistic Organo- and Palladium-Catalyzed Asymmetric Allylic Alkylation

An unusual diastereodivergent stereoselective allylation reaction is presented. It consists of a palladium-catalyzed allylation reaction of an organocatalytically generated amino isobenzofulvene, where the diastereoselectivity is controlled by the electronic properties of a monodentate, achiral ligand on palladium. One major diastereoisomer is formed using triarylphosphines substituted with neutral or electron-donating substituents of the aryl group, while those with electron-withdrawing substituents favor the other diastereoisomer. The diastereoselectivity correlates with the Taft inductive parameter of substituents on the triarylphosphine ligand on palladium. The synergistic reaction involves both a catalytic secondary amine catalyst for the indene-aldehyde activation and the monodentate phosphine ligands on palladium, affording a highly enantioselective reaction with up to 98 % enantiomeric excess. Based on computational investigations, the role of the monodentate phosphine ligand on the diastereoselectivity is discussed.     

Hydrodynamic optical alignment for microflow cytometry

A microfabricated flow cytometer has been developed that is capable of detecting nearly all of the microparticles in an aqueous suspension. Current design allows for integrated coupling between an optical fiber-based detection system and the particle stream via hydrodynamic focusing. By adjusting the relative flow-rates at the auxiliary inputs of the focusing manifold, the particle stream can be steered out-of-plane relative to the illuminating laser, and similarly the particle stream can be squeezed or expanded. The microfabricated device was constructed in polydimethylsiloxane with cross-sectional microfluidic dimensions of 125 μm×125 μm. Using the present device and method, fluorescent microparticles in aqueous solution were counted at an absolute counting efficiency of 91±4%. The coefficient of variation of the fluorescence pulse-heights for far-red fluorescent microparticles was 15%. The device exhibited a linear response to fluorescence intensity calibration microparticles as shown by comparison with a commercial cytometer instrument.     

Tracing Compressed Curves in Triangulated Surfaces

A simple path or cycle in a triangulated surface is normal if it intersects any triangle in a finite set of arcs, each crossing from one edge of the triangle to another. A normal curve is a finite set of disjoint normal paths and normal cycles. We describe an algorithm to “trace” a normal curve in $O(\min \{ X, n^2\log X \})$ O ( min { X , n 2 log X } ) time, where $n$ n is the complexity of the surface triangulation and $X$ X is the number of times the curve crosses edges of the triangulation. In particular, our algorithm runs in polynomial time even when the number of crossings is exponential in $n$ n . Our tracing algorithm computes a new cellular decomposition of the surface with complexity $O(n)$ O ( n ) ; the traced curve appears in the 1-skeleton of the new decomposition as a set of simple disjoint paths and cycles. We apply our abstract tracing strategy to two different classes of normal curves: abstract curves represented by normal coordinates, which record the number of intersections with each edge of the surface triangulation, and simple geodesics, represented by a starting point and direction in the local coordinate system of some triangle. Our normal-coordinate algorithms are competitive with and conceptually simpler than earlier algorithms by Schaefer et al. (Proceedings of 8th International Conference Computing and Combinatorics. Lecture Notes in Computer Science, vol. 2387, pp. 370–380. Springer, Berlin 2002; Proceedings of 20th Canadian Conference on Computational Geometry, pp. 111–114, 2008) and by Agol et al. (Trans Am Math Soc 358(9): 3821–3850, 2006).