In-house reference materials of mometasone furoate with traceable assay certified values

Characterization of in-house reference materials (IHRMs) with traceable property values for the mometasone furoate assay is discussed. The traceability of the value carried by the IHRM has been established to the value carried by a higher metrological status United States Pharmacopoeia Reference Standard (USP RS). A comparative approach is used to overcome systematic errors in measurement results, specific to the measurement method and/or to the laboratory developing the IHRM. The traceability chain was realized by the simultaneous analysis of the IHRM and the USP RS test portions under the same conditions.     

Assessment of the parallelization approach of d2_cluster for high-performance sequence clustering

The exponential increase in expressed sequence tag (EST) sequence data amplifies the computational cost of clustering sequences such that new algorithms are required to analyze data at a greater rate. We have parallelized d2_cluster on a SGI Origin 2000 multiprocessor and observed a speedup of approximately 100x on 126 processors when processing a 15,876 EST dataset. The parallelized d2_cluster code is obtainable from the SANBI website (http://www.sanbi.ac.za/CODES).     

Unusual aggregates from the oxidation of alkene self-assembled monolayers: a previously unrecognized mechanism for SAM ozonolysis?

Self-assembled monolayers (SAMs) of vinyl-terminated 3- and 8-carbon compounds were generated on Si substrates and reacted at room temperature with approximately 1 ppm gaseous O(3). A combination of atomic force microscopy (AFM), scanning electron microscopy (SEM), Auger electron spectroscopy (AES) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to study the surface composition and morphology after oxidation. A distribution of large ( approximately 0.1-10 microm) organic aggregates was formed, while the surrounding substrate became depleted of carbon compared to the unreacted SAM. This highly unusual result establishes that the mechanism of ozonolysis of alkene SAMs must have a channel that is unique compared to that in the gas phase or in solution, and may involve polymerization induced by the Criegee intermediate (CI). Oxidation at 60% RH led to the formation of a number of smaller aggregates, suggesting water intercepted the CI in competition with aggregate formation. The uptake of water, measured using transmission FTIR, was not increased upon oxidation of these films. In conjunction with literature reports of polymer formation from VOC-NO(x) photooxidations, these results suggest that formation of aggregates and polymers in the atmosphere is much more widespread than previously thought. The implications for the ozonolysis of alkenes on surfaces, for the transformation of organics in the atmosphere, and for the reactions and stability of unsaturated SAMs, are discussed.     

Finding the projection of a point onto the intersection of convex sets via projections onto half-spaces

We present a modification of Dykstra's algorithm which allows us to avoid projections onto general convex sets. Instead, we calculate projections onto either a half-space or onto the intersection of two half-spaces. Convergence of the algorithm is established and special choices of the half-spaces are proposed.The option to project onto half-spaces instead of general convex sets makes the algorithm more practical. The fact that the half-spaces are quite general enables us to apply the algorithm in a variety of cases and to generalize a number of known projection algorithms.The problem of projecting a point onto the intersection of closed convex sets receives considerable attention in many areas of mathematics and physics as well as in other fields of science and engineering such as image reconstruction from projections.In this work we propose a new class of algorithms which allow projection onto certain super half-spaces, i.e., half-spaces which contain the convex sets. Each one of the algorithms that we present gives the user freedom to choose the specific super half-space from a family of such half-spaces. Since projecting a point onto a half-space is an easy task to perform, the new algorithms may be more useful in practical situations in which the construction of the super half-spaces themselves is not too difficult.     

Density functional calculations for modeling the active site of nickel-iron hydrogenases. 2. Predictions for the unready and ready States and the corresponding activation processes

ZORA relativistic DFT calculations are presented which aim to model the geometric and electronic structure of the active site of NiFe hydrogenases in its EPR-active oxidized states Ni-A (unready state) and Ni-B (ready state). Starting coordinates are taken from the X-ray structure of a mutant of Desulfovibrio fructosovorans hydrogenase refined at 1.81 A resolution. Nine possible candidates for Ni-A and Ni-B are analyzed in terms of their geometric and electronic structure. Comparison of calculated geometric and magnetic resonance parameters with available experimental data indicates that both oxidized states have a micro-hydroxo bridge between the two metal centers. The different electronic structures of both forms can be explained by a modification of a terminal cysteine in Ni-B, best modeled by protonation of the sulfur atom. A possible mechanism for the activation of both oxidized forms is presented.     

Solar Ultraviolet Radiation Exposure and Sun Protection Behaviors and Knowledge Among a High‐Risk and Overlooked Group of Outdoor Workers in South Africa

The exposure of outdoor car guards to solar ultraviolet radiation (UVR), the majority with deeply pigmented skin, to solar UVR was measured for five consecutive days during early spring (September 2017) in South Africa using electronic UVR dosimeters attached to the upper arm of each participant. The exposure of the nape of the neck, forehead, nose, cheek and hand was extrapolated from the measurements. The onsite ambient solar UVR on a flat, horizontal, unshaded surface was measured concurrently. The sun‐related knowledge, behavior and attitudes of the car guards were evaluated using questionnaires. Total personal daily solar UVR exposure as a percentage of the ambient solar UVR exposure was 24%. The exposure of car guards on several body sites was in excess of the occupational threshold limit value. Sleeved shirts and hats were the most commonly used sun protection measures (worn by 70% and 80%, respectively). Considering the high levels of solar UVR reported on most days throughout the year in South Africa, more studies quantifying the personal exposure of outdoor workers in both the informal and formal sectors are necessary.     

Development and validation of an HPLC-DAD analytical procedure for quality control of damiana (Turnera diffusa), using an antioxidant marker isolated from the plant

Damiana is a shrub used as a dietary supplement and as an additive in several foods. This report presents the first validated analytical method for QC of products made from damiana. Through bioassay-guided fractionation, the compound showing the best antioxidant activity, determined using 2,2-diphenyl-1-picryl-hydrazyl assay in TLC, was purified and identified as 8-C-beta-[6-deoxy-2-O-(alpha-1-rhamnopyranosyl)-xylo- hexopyranos-3-uloside] (Cl50 5.56 g/mL). This is the only natural source from which this compound has been reported, and has been found in all native damiana samples analyzed. Therefore, it was used as a biomarker to develop an HPLC-diode-array detection analytical procedure using the first-order derivative of the chromatograms. Separation was achieved using an AccQ Tag C18 150 x 3.9 mm (4 microm) column, with a gradient of methanol and 0.1% trifluoroacetic acid in water. The method was shown to be accurate, sensitive, and reproducible, providing a useful quantitative means to apply QC to damiana products.     

Optimization of gain-assisted waveguiding in metal-dielectric nanowires

We theoretically demonstrate that, for a given diameter of the core-pumped metal-dielectric nanowire, there is an optimum thickness of the metallic cladding that provides the maximum propagation length of the lowest-order surface plasmon polariton (SPP) modes. If the nanowire is fabricated with the optimum cladding thickness, the lowest pumping power is required to fully compensate for the SPP propagation losses. We also show that a strong confinement of SPPs within the nanowire can be achieved, but at the expense of either high optical gains or large nanowire diameters. For example, a gain of 565 cm(-1) would suffice to make up for the decay of SPPs in a 250-nm-thick silver-GaAs nanowire; the confinement of optical power within such nanowires exceeds 90%, which makes them ideal interconnects for nanophotonic circuitry.     

Benchmark policies for utility-carrying queues with impatience

Queueing Systems - Men and jobs alike are characterized by a single trait, which may take on categorical values according to given population frequencies. Men arrive to the system following a...