Smart Geodesic Tracing in GRworkbench

We have developed a new tool for numerical work in General Relativity: GRworkbench. We discuss how GRworkbench's implementation of a numerically-amenable analogue to Differential Geometry facilitates the development of robust and chart-independent numerical algorithms. We consider, as an example, geodesic tracing on two charts covering the exterior Schwarzschild space-time.     

Acrylamide analysis: assessment of results from six rounds of Food Analysis Performance Assessment Scheme (FAPAS) proficiency testing

Six proficiency tests have now been completed in an ongoing program of the UK Food Analysis Performance Assessment Scheme (FAPAS) for the analysis of acrylamide in a range of food matrixes. Homogeneous test material samples were requested by laboratories throughout the world, with 29 to 45 submitting results for each test. Results were analyzed by appropriate statistical procedures, and z-scores were awarded for reported values. In the absence of both legislation and collaborative trial data, the target standard deviation was derived from the Horwitz equation, although it is acknowledged that there is a need to establish a "fit for purpose" target standard deviation specifically for acrylamide analysis. Participants were encouraged to use the analytical method routinely used in their own laboratory and to provide details of their procedure. Close examination of the data submitted indicates that performance is generally acceptable in terms of accuracy. There is no significant difference between results submitted by gas chromatography and liquid chromatography (GC and LC) methods, and no method dependency on the use of internal standards or sample size. However, choice of extraction solvent may be important, with indications that plain water is an acceptable extraction method. There is evidence from the most recent test that direct (underivatized) GC methodology may present problems, but more data are required and this aspect will be monitored in the continuing proficiency testing program.     

Determination of pyrethrin and pyrethroid pesticides in urine and water matrixes by liquid chromatography with diode array detection

The following pyrethrin and pyrethroid pesticides were determined in urine and water matrixes by liquid chromatography with diode array detection (LC-DAD): pyrethrin I, pyrethrin II, tetramethrin, baythroid, bifenthrin, fenvalerate, phenothrin, allethrin, resmethrin, cis-permethrin, and trans-permethrin. In addition, 3-phenoxybenzyl alcohol, a metabolite of various pyrethroids, was also successfully determined by the analytical method. The matrix extraction was simple, inexpensive, and fast, using only sodium chloride and acetonitrile. The acetonitrile extract was filtered and analyzed by LC-DAD. The method detection limits for the pyrethrin pesticides in 5 mL urine were determined to range from 0.002 to 0.04 microg/mL, depending on the individual pyrethrin. Recoveries from spiked tap water ranged from 77 to 96%; recoveries from urine ranged from 80 to 117%. This method is especially well-suited to clinical investigations, in which rapid analysis of forensic samples is often required.     

Stabilised phosphorus(I) and arsenic(I) iodide: readily-synthesised reagents for low oxidation state main group chemistry

Herein we report a surprisingly facile and clean synthesis of base-stabilised phosphorus(I) and arsenic(I) iodide salts, which are reagents that provide convenient access to new low oxidation state main group compounds.     

Electronic structure and properties of isoreticular metal-organic frameworks: the case of M-IRMOF1 (M = Zn, Cd, Be, Mg, and Ca)

We investigate the possibility of tailoring the electronic properties of isoreticular metal-organic materials by replacing the metal atom in the metal-organic cluster and by doping. The electronic structure of M-IRMOF1, where IRMOF1 stands for isoreticular metal-organic framework 1 and M = Be, Mg, Ca, Zn, and Cd, was examined using density-functional theory. The results show that these materials have similar band gaps (ca. 3.5 eV) and a conduction band that is split into two bands, the lower of which has a width that varies with metal substitution. This variation prompted us to investigate whether doping with Al or Li could be used to tailor the electronic properties of the Zn-IRMOF1 and Be-IRMOF1 materials. It is shown that replacing one metal atom with Al can effectively be used to create IRMOFs with different metallic properties. On the other hand, adding Li produces structural changes that render this approach less suitable.     

Continuum formulation of the Scheutjens-Fleer lattice statistical theory for homopolymer adsorption from solution

Homopolymer adsorption from a dilute solution on an interacting (attractive) surface under static equilibrium conditions is studied in the framework of a Hamiltonian model. The model makes use of the density of chain ends n(1,e) and utilizes the concept of the propagator G describing conformational probabilities to locally define the polymer segment density or volume fraction phi; both n(1,e) and phi enter into the expression for the system free energy. The propagator G obeys the Edwards diffusion equation for walks in a self-consistent potential field. The equilibrium distribution of chain ends and, consequently, of chain conformational probabilities is found by minimizing the system free energy. This results in a set of model equations that constitute the exact continuum-space analog of the Scheutjens-Fleer (SF) lattice statistical theory for the adsorption of interacting chains. Since for distances too close to the surface the continuum formulation breaks down, the continuum model is here employed to describe the probability of chain configurations only for distances z greater than 2l, where l denotes the segment length, from the surface; instead, for distances z < or = 2l, the SF lattice model is utilized. Through this novel formulation, the lattice solution at z = 2l provides the boundary condition for the continuum model. The resulting hybrid (lattice for distances z < or = 2l, continuum for distances z > 2l) model is solved numerically through an efficient implementation of the pseudospectral collocation method. Representative results obtained with the new model and a direct application of the SF lattice model are extensively compared with each other and, in all cases studied, are found to be practically identical.     

AN ACTION SPECTRUM FOR LETHAL PHOTOSENSITIZATION OF Candida albicans BY 8-MOP AFTER LOW-DOSE BROAD-BAND UV-A IRRADIATION; AN ACTION SPECTRUM FOR 8-MOP 4′,5′- MONOADDUCTS?

An action spectrum was obtained for lethal photosensitization of Candida albicans that had been pre-irradiated with a sub-lethal low dose of broad-band UV-A after incubation with 8-methoxypsoralen and then washed to remove any non-photobound 8-methoxypsoralen. The resultant spectrum with a peak in the 320-335 nm region was similar to that obtained by a conventional method (single irradiation only) and also to the absorption spectrum of the 4',5'-monoadduct. These data support the hypothesis that the chromophore for lethal photosensitization by 8-methoxypsoralen is the 8-methoxypsoralen/DNA 4',5'-monoadduct rather than 8-methoxypsoralen itself.     

Bounds for the generalized Marcum function of the second kind

The Ramanujan Journal - This paper provides elementary proofs for several types of congruences involving multipartitions and self-convolutions of the divisor function. Our computations use...