Measuring helmet sound attenuation characteristics using an acoustic manikin

The sound attenuation characteristics of two military helmets were measured using an acoustic manikin as the test apparatus. The manikin results are compared to the results of attenuation measurements made on human subjects wearing identical helmets. The testing room and instrumentation were the same for both the manikin and human subjects. Procedures in ANSI S3.19-1974 were used in the real-ear attentuation at threshold (REAT) part of this study. The results are encouraging as they suggest that the manikin may be used in place of a panel of human subjects to evaluate the hearing protection characteristics of military head gear.     

Synthesis and solid-state structural characterisation of Pt(II,IV) bromide complexes containing bidentate organothiomethylpyridine heteroleptic ligands

A convenient synthetic method for the preparation of organothiomethylpyridine ligands 2-(RSCH₂)C₅H₄N (R = Ph (L¹), Me (L²)), 2-MeS–6-Me-C₅H₃N (L³), and 2-MeS–4-Me-C₅H₃N (L⁴) via the initial lithiation of substituted 2-picolines followed by the nucleophilic reaction with a diorganyldisulfide is described. The complexes [PtBr₂L] (L = L¹–L⁴) have been prepared in good to high yields as yellow solids with low solubility in organic solvents. The solid state structures of the complexes have been determined, showing the spatial arrangement of the complexes to depend significantly upon varying substituents within the ligand. The complexes undergo oxidation by bromine to form the tetravalent complexes [PtBr₄(L)] (L = L¹–L⁴). The solid state structures of [PtBr₄(L²)] and [PtBr₄(L₄)] have been determined, and shown to be monomeric with the ligand chelating the platinum centre.     

Determination of ampicillin in New Zealand white rabbit plasma using column switching technique and HPLC

Summary The purpose of this study was to develop a simple and fast analytical method for quantitation of ampicillin in rabbit plasma, suitable for analysis of large numbers of samples collected from experimental animals. The concentration of ampicillin in rabbit plasma was determined utilizing ion-pair reverse-phase high performance liquid chromatography (HPLC) with UV detection and a column switching technique. Plasma samples were treated with a perchloric acid solution to precipitate proteins and centrifuged to pellet the precipitated proteins. Cephalexin was used as an internal standard. The C₁₈ precolumn was placed in the injector loop of the Rheodyne injector. Samples were injected with the injector in the load position and the precolumn was washed free from interfering compounds. When the injector was switched to the inject position, the mobile phase was passed through the precolumn taking relatively pure compounds onto the analytical column. The limit of quantitation was established to be 400 ng mL^–1 of plasma. The standard curves were linear over the range of ampicillin concentrations assayed, 400 to 10,000 ng mL^–1 of rabbit plasma, and had a mean regression coefficient of 0.9962 (±0.0043). Intra-day variability was determined using six replicates of controls (low and high) analyzed on a single assay. The percent of relative accuracy for low and high controls were 5.67 and 1.12, respectively. Inter-day variability was determined over a four day period analyzing replicates of each control. The percent of relative accuracy for low and high controls were 4.33 and 1.63, respectively.     

Differential thermal analysis and temperature profile analysis of pyrotechnic delay systems: mixtures of tungsten and potassium dichromate

The self-propagating combustion reaction between tungsten and potassium dichromate has been studied by differential thermal analysis and temperature profile analysis. Two reaction stages have been distinguished in the combustion where the rate of temperature rise is ? 10⁵ K min^?1: in the first potassium dichromate is reduced by tungsten to form potassium chromate and in the second stage the potassium chromate reacts with more tungsten to form potassium tungstate and chromic oxide.     

Supported palladium catalysis using a heteroleptic 2-methylthiomethylpyridine-N,S-donor motif for Mizoroki-Heck and Suzuki-Miyaura coupling, including continuous organic monolith in capillary microscale flow-through mode

Flow-through catalysis utilising (2-methylthiomethylpyridine)palladium(II) chloride species covalently attached to a macroporous continuous organic polymer monolith synthesised within fused silica capillaries of internal diameter 250 μm is described, together with related studies of ground bulk monolith compared with supported catalysis on Merrifield and Wang beads and homogeneous catalysis under identical conditions to bulk supported catalysis. The monolith substrate, poly(chloromethylstyrene-co-divinylbenzene), has a backbone directly related to Merrifield and Wang resins. The homogeneous precatalyst PdCl₂(L²) (L²=4-(4-benzyloxyphenyl)-2-methylthiomethylpyridine) contains the benzyloxyphenyl group on its periphery as a model for the spacer between the ‘PdCl₂(N∼S)’ centre and the polymer substituent of the resins and monolith. Suzuki-Miyaura and Mizoroki-Heck catalysis exhibit anticipated trends in reactivity with variation of aryl halide reagents for each system, and show that supported catalysis on beads and monolith gives higher yields than for homogeneous catalysis. The synthesis of 2-methylthiomethylpyridines is presented, together with crystal structures of 4-bromo-2-bromomethylpyridine hydrobromide, 4-(4-hydroxyphenyl)-2-methylthiomethylpyridine (L¹), PdCl₂(L¹) and PdCl₂(L²). Hydrogen bonding occurs in 4-bromo-2-bromomethylpyridine hydrobromide as N-H?Br interactions, in 4-(4-hydroxyphenyl)-2-methylthiomethylpyridine as O-H?N to form chains, and in PdCl₂(L¹) as O-H?Cl interactions leading to adjacent π-stacked chains oriented in an antiparallel fashion.     

Experiment‐Driven Modeling of Crystalline Phosphorus Nitride P3N5: Wide‐Ranging Implications from a Unique Structure

Nitridophosphates have emerged as advanced materials due to their structural variability and broad technical applicability. Their binary parent compound P₃N₅, a polymeric network of corner‐ and edge‐sharing PN₄ tetrahedra with N 2 and N 3 sites, is a particularly interesting example. We present a study of the band gap and electronic structure of α‐P₃N₅ by using soft X‐ray spectroscopy measurements and DFT calculations. The band gap, which is crucial for all applications, is measured to be 5.87±0.20 eV. This agrees well with the calculated, indirect band gap of 5.21 eV. The density of states are found to show dramatic variation between the nonequivalent N sites and a high degree of covalency. Coupled to these results is what is, to our knowledge, the largest core hole shift reported to date for a soft X‐ray absorption spectrum. We propose an intuitive bonding scheme for α‐P₃N₅ that explains the observed band gap and unique density of states, while providing a framework for predicting these properties in known and yet to be discovered PN compounds. We briefly consider the implications of these results for new low‐dimensional P and PN materials, which alongside graphene, could become important materials for nanoelectronics.     

Dark-matter search with CRESST

The CRESST experiment is looking for non-baryonic particle dark matter via nuclear scattering in CaWO₄. The simultaneous measurement of the heat and the scintillation light generated by an event in a CaWO₄ single crystal is used to discriminate between electron and nuclear recoils thanks to their different light output. This allows an efficient suppression of the electron recoil background. The set-up consists of modules with a 300 g CaWO₄ crystal mounted in a reflective housing together with a light detector. The heat signal is read out using a superconducting transition-edge sensor (TES) made of tungsten evaporated directly on to the crystal that is operated at a few mK. Currently the second phase of the experiment is being set up at the Laboratori Nazionali del Gran Sasso in which it is planned to run 33 detector modules providing a total target mass of 10 kg. First test runs with prototype detectors have been successfully performed. Presented by W. Westphal at the Workshop on calculation of double-beta-decay matrix elements (MEDEX’05), Corfu, Greece, September 26–29, 2005.