Optimization of the Hartmann-Shack microlens array

In this work we propose to optimize the microlens-array geometry for a Hartmann-Shack wavefront sensor. The optimization makes possible that regular microlens arrays with a larger number of microlenses are replaced by arrays with fewer microlenses located at optimal sampling positions, with no increase in the reconstruction error. The goal is to propose a straightforward and widely accessible numerical method to calculate an optimized microlens array for a known aberration statistics. The optimization comprises the minimization of the wavefront reconstruction error and/or the number of necessary microlenses in the array. We numerically generate, sample and reconstruct the wavefront, and use a genetic algorithm to discover the optimal array geometry. Within an ophthalmological context, as a case study, we demonstrate that an array with only 10 suitably located microlenses can be used to produce reconstruction errors as small as those of a 36-microlens regular array. The same optimization procedure can be employed for any application where the wavefront statistics is known.     

Strength of free-standing chemically vapour-deposited diamond measured by a range of techniques

The strength of free-standing chemically vapour-deposited diamond was determined using a bursting-disc test, a three-point bend test and a four-point bend test. The bursting-disc technique has advantages for determining the strength of ceramic materials since the maximum tensile stress is at the centre of the disc. The much smaller stresses near the sample edges are rarely responsible for failure and so edge effects are negligible. However, the bursting-disc test is often impractical for ascertaining the strength of chemically vapour-deposited diamond since the cost of samples is high. A three-point bend test is often employed instead, since it may be performed on smaller samples. However, the area stressed in the three-point bend test is smaller, and so there is less chance of stressing a large flaw, resulting in higher strength values. A further disadvantage is that specimen edges are stressed and, unless the specimen sides are polished, as well as its faces, misleading results may be obtained (although this is not the case for chemically vapour-deposited diamond). A four-point bend test is often used because it stresses a larger volume of material than the three-point bend test and so the results are more reliable. Furthermore, the diamond used in a four-point bend test can be of similar size to those used in a three-point bend test and so the expenditure is comparable. However, ensuring that the four-point bend test is applied correctly is technically more difficult. Strength data are reported for both the growth and the nucleation sides, for difference nucleation densities and for as-received and polished samples.     

Some comments on ring currents in five-membered heterocyclic molecules

An extension of the single excitation MCSCF method to include certain double excitations is described. The wavefunctions are obtained by direct minimization methods after the introduction of a quadratic representation of the CI coefficients. Illustrative calculations on He, Be, N-methylhydroxylamine and water are described. The water results are compared with the results from conventional CI calculations.     

FT-IR,EDXRF and Gamma-Isotopic Analyses of Ashes from Coal Fired Power Plants of Turkey

Abstract

Nine ash samples collected from five coal fired power plants of Turkey have been analysed by FT-IR, EDXRF and γ -isotopic analyses methods. IR spectroscopy together with mineralogical analysis is found to be a useful method for investigating the inorganic chemical composition of the ashes which is an inherently variable material due to differences in the inorganic chemical composition of the source coal and in ash collection. Gamma-isotopic analysis indicated that all samples contained Ra-226, U-238 and Th-232. On the other hand Cs-137 (16.3 pCi/g) was found only in the ash sample collected from the Yata?an coal fired power plant. An ash sample taken from the electro-filter of the Ambarli, a fuel oil fired-power plant of Turkey, was also analysed for comparision and found that it contained least amount of U-238.     

Characterisation of cascade summing effects in gamma spectroscopy using Monte Carlo simulations

A GEANT4 based Monte Carlo simulation has been successfully utilised to calculate peak efficiency characterisations and cascade summing (true coincidence summing) corrections in two source geometries commonly used for environmental monitoring. The cascade summing corrections are compared with values generated using an existing (validated) system, and found to be in excellent agreement for all radionuclides simulated. The calculated correction factors and peak efficiencies were also tested by analysing well defined sources used in the operation of the International Monitoring System, which undertakes radionuclide monitoring for verification of the Comprehensive Nuclear-Test-Ban Treaty. All abundances of the radionuclides measured matched the values that were previously determined using proprietary software. Using GEANT4 in this way, cascade summing corrections can now be extended to complex detector models and source matrices, such as Compton Suppression systems.     

Convenient Synthesis of Vinyldiazomethanes from α-Diazo-β-Keto Esters and Related Systems

A series of vinydiazomethanes were readily prepared by sodium borohydride reduction of a-diazo-p-ketoesters followed by phosphorus oxychloride induced dehydration of the resulting a-diazo-p-hydroxyesters.     

Guide to enantioselective dirhodium(II)-catalyzed cyclopropanation with aryldiazoacetates

Catalytic enantioselective methods for the generation of cyclopropanes have been of long standing pharmaceutical interest. Chiral dirhodium(II) catalysts prove to be an effective means for the generation of diverse cyclopropane libraries. Rh₂(R-DOSP)₄ is generally the most effective catalyst for asymmetric intermolecular cyclopropanation of methyl aryldiazoacetates with styrene. Rh₂(S-PTAD)₄ provides high levels of enantioinduction with ortho-substituted aryldiazoacetates. The less-established Rh₂(R-BNP)₄ plays a complementary role to Rh₂(R-DOSP)₄ and Rh₂(S-PTAD)₄ in catalyzing highly enantioselective cyclopropanation of 3-methoxy substituted aryldiazoacetates. Substitution on the styrene has only moderate influence on the asymmetric induction of the cyclopropanation.     

Engineering Cytochrome‐Modified Silica Nanoparticles To Induce Programmed Cell Death

A low native membrane permeability and ineffective access to the cellular cytosol, together with aggressive proteolytic degradation, often severely hampers the practical application of any therapeutic protein or antibody. Through engineering the charging profile of mesoporous silica nanoparticles, cellular uptake and subsequent subcellular distribution can be controlled. We show herein that programmed cell death can subsequently be induced across a population of cancer cells with remarkable efficacy on conjugating a specific caspase‐cascade‐activating cytochrome to such cytosol‐accessing particles.