A 3D implementation of ray tracing combined with diffraction on facets: Verification and a potential application

A 3D implementation of a new model of light scattering applicable to dielectric faceted objects is introduced. The model combines standard geometric optics with diffraction on individual facets. It can be applied to any faceted geometry. The model adds no significant computational overheads to classical geometric optics yet provides much improved results. Initial results for long hexagonal columns are compared to SVM and appear favourable. 2D scattering patterns are calculated for a hexagonal column in a fixed orientation and compared to those created by ice analogue crystals in the laboratory with close agreement. The comparison includes the observation of a guided wave propagating along the length of the column. The new model is then applied to a selection of geometries to illustrate how it could be used to aid particle characterization, particularly in the case of cirrus ice.     

Extending the stochastic programming framework for the modeling of several decision makers: pricing and competition in the telecommunication sector

In a previous paper, Gouveia and Magnanti (2003) found diameter-constrained minimal spanning and Steiner tree problems to be more difficult to solve when the tree diameter D is odd. In this paper, we provide an alternate modeling approach that views problems with odd diameters as the superposition of two problems with even diameters. We show how to tighten the resulting formulation to develop a model with a stronger linear programming relaxation. The linear programming gaps for the tightened model are very small, typically less than 0.5–, and are usually one third to one tenth of the gaps of the best previous model described in Gouveia and Magnanti (2003). Moreover, the new model permits us to solve large Euclidean problem instances that are not solvable by prior approaches. Research funded in part by the Research Projects POCTI-ISFL-1-152,POSI/CPS/41459/2001 and POCTI/MAT/139/94 Research funded in part by the Singapore-MITAlliance(SMA)     

Ivory species identification using electrophoresis‐based techniques

Despite continuous conservation efforts by national and international organizations, the populations of the three extant elephant species are still dramatically declining due to the illegal trade in ivory leading to the killing of elephants. A requirement to aid investigations and prosecutions is the accurate identification of the elephant species from which the ivory was removed. We report on the development of the first fully validated multiplex PCR‐electrophoresis assay for ivory DNA analysis that can be used as a screening or confirmatory test. SNPs from the NADH dehydrogenase 5 and cytochrome b gene loci were identified and used in the development of the assay. The three extant elephant species could be identified based on three peaks/bands. Elephas maximus exhibited two distinct PCR fragments at approximate 129 and 381 bp; Loxodonta cyclotis showed two PCR fragments at 89 and 129 bp; and Loxodonta africana showed a single fragment of 129 bp. The assay correctly identified the elephant species using all 113 ivory and blood samples used in this report. We also report on the high sensitivity and specificity of the assay. All single‐blinded samples were correctly classified, which demonstrated the assay's ability to be used for real casework. In addition, the assay could be used in conjunction with the technique of direct amplification. We propose that the test will benefit wildlife forensic laboratories and aid in the transition to the criminal justice system.     

Low solvent consumption gel permeation chromatography method

This study presents the possibility of reducing the volume of solvent necessary for gel permeation chromatography analysis by up to 20 times when using two 2.1-mm internal diameter (ID) columns instead of the traditional three 7.5-mm ID columns. The low solvent consumption method was optimized by evaluating the number of theoretical plates at different flow rates. By injecting a broad polystyrene standard 16 times, good reproducibility and accuracy of weight average molecular weights (M_w) and peak surface areas were obtained for the optimized method.     

Role of 2‐oxo and 2‐thioxo modifications on the proton affinity of histidine and fragmentation reactions of protonated histidine

A combination of electrospray ionisation (ESI), multistage and high‐resolution mass spectrometry experiments was used to compare the gas‐phase chemistry of the amino acids histidine (1), 2‐oxo‐histidine (2), and 2‐thioxo‐histidine (3). Collision‐induced dissociation (CID) of all three different proton‐bound heterodimers of these amino acids led to the relative gas‐phase proton affinity order of: histidine >2‐thioxo‐histidine >2‐oxo‐histidine. Density functional theory (DFT) calculations confirm this order, with the lower proton affinities of the oxidised histidine derivatives arising from their ability to adopt the more stable keto/thioketo tautomeric forms. All protonated amino acids predominately fragment via the combined loss of H₂O and CO to yield a₁ ions. Protonated 2 and 3 also undergo other small molecule losses including NH₃ and the imine HN=CHCO₂H. The observed differences in the fragmentation pathways are rationalised through DFT calculations, which reveal that while modification of histidine via the introduction of the oxygen atom in 2 or the sulfur atom in 3 does not affect the barriers against the loss of H₂O+CO, barriers against the losses of NH₃ and HN=CHCO₂H are lowered relative to protonated histidine. Copyright © 2010 John Wiley & Sons, Ltd.