Symmetry and Condensed Matter Physics – A Computational Approach,by M. El-Batanouny and F. Wooten

The behaviour of positrons below the inelastic collision threshold in rare gases can usually be completely accounted for in terms of the annihilation and elastic scattering cross sections for collisions between a positron and a single gas atom. Determining these cross sections has been the subject of many theoretical and experimental investigations. However the basic premise that the positron interacts with the gas atoms, one at a time, has been recently questioned by the yet unexplained results of some low-temperature experiments. This article discusses the annihilation and elastic scattering cross sections as they relate to the conventional picture of positrons in He, Ne, Ar, Kr and Xe gas; as well as the possibility of bound states for positrons in the gases at low temperatures.     

A new approach to variable selection in least squares problems

The title Lasso has been suggested by Tibshirani (1996) as acolourful name for a technique of variable selection which requiresthe minimization of a sum of squares subject to an l₁ bound on the solution. This forces zero components in the minimizingsolution for small values of . Thus this bound can functionas a selection parameter. This paper makes two contributionsto computational problems associated with implementing the Lasso:(1) a compact descent method for solving the constrained problemfor a particular value of is formulated, and (2) a homotopymethod, in which the constraint bound becomes the homotopyparameter, is developed to completely describe the possibleselection regimes. Both algorithms have a finite terminationproperty. It is suggested that modified Gram-Schmidt orthogonalizationapplied to an augmented design matrix provides an effectivebasis for implementing the algorithms.     

Addition of phenylisocyanate to 3,5-diphenyl-1,2-dithiolium-4-olate gives a thioketone

The Type B mesoionic heterocycle, 3,5-diphenyl-1,2-dithiolium-4-olate, reacts with phenylisocyanate producing a thioketone derivative rather than a pseudo-semi-conjugated heterocyclic mesomeric betaine. The structure of the thioketone product was confirmed by an X-ray crystallographic investigation.     

Differentiable Formation of Chiroptical Lanthanide Heterometallic LnnLn’4-n(L6) (n=0–4) Tetrahedra with C2-Symmetrical Bis(tridentate) Ligands

Construction of lanthanide heterometallic complex is important for engineering multifunction molecular containers. However, it remains a challenge because of the similar ionic radii of lanthanides. Herein we attempt to prepare chiral lanthanide heterometallic tetrahedra. Upon crystallization with a mixture of [Eu₂ L ₃] and [Ln₂ L ₃] (Ln=Gd, Tb and Dy) helicates, a mixture of heterometallic Eu_nLn’_4-n( L ₆) (n=0–4) tetrahedra was prepared. Selective formation of heterometallic tetrahedron was observed as MS deconvolution results deviated from statistical results. The formation of heterometallic tetrahedron was found to be sensitive to ionic radii as well as the ratio of the two helicates used in the crystallization.     

Siderophore-Mediated Iron Uptake Promotes Yeast–Bacterial Symbiosis

In the present study, siderophore produced by the marine yeast Aureobasidium pullulans was characterized as hydroxamate by chemical and bioassays. The hydroxamate assignment was supported by the appearance of peaks at 1,647.21?C1,625.99?cm^?1 and at 1,435.04?cm^?1 in the infrared spectrum. The purified siderophore exhibited specific growth-promoting activity under iron-limited conditions for siderophore auxotrophic probiotic bacteria. Cross-utilization of siderophore indicates a symbiotic relationship between the yeast A. pullulans and the selected probiotic bacterial strains. Statistical optimization of medium components for improved siderophore production in A. pullulans was depicted by response surface methodology. The shift in UV?CVis spectroscopy indicates the photoreactive property and subsequent oxidative cleavage of purified siderophore on exposure to sunlight.     

Flux line lattice symmetries in the borocarbide superconductor LuNi2B2C

We compare the results of small angle neutron scattering on the flux line lattice (FLL) obtained in the borocarbide superconductor LuNi₂B₂C with the applied field along the c- and a-axes. For H‖c the temperature dependence of the FLL structural phase transition from square to hexagonal symmetry was investigated. Above 10 K the transition onset field. H ₂(T), rises sharply, bending away from H _c2(T) in contradiction to theoretical predictions of the two merging. For H‖a a first order FLL reorientation transition is observed at H _tr=3–3.5 kOe. Below H _tr the FLL nearest neighbor direction is parallel to the b-axis, and above H _tr to the c-axis. This transition cannot be explained using nonlocal corrections to the London model.