Acoustic and radar scattering from directional seas

The small-slope approximation is applied to predict acoustic and electromagnetic scattering from directional seas. Results are presented for the scatter of high-frequency fields from fetch-limited seas for which the wavenumber spectrum is isotropic at high wavenumbers but highly directional near the spectral peak. Monostatic backscatter is found to display an upwind-crosswind dependence for a broad range of scattering angles due solely to the directionality of the large-scale waves.     

Attrition-enhanced total resolution leads to homochiral families of amino acid derivatives

The total resolution of five structurally similar racemizable amino acid derivatives, three of which have racemic crystal structures, was performed simultaneously. By enantioselective incorporation in an amino acid derivative that forms a conglomerate the other four were deracemized on attrition-induced grinding. The outcome of the resolution was random (R) or (S), but all compounds had the same absolute configuration and high enantiomeric purities.     

A high voltage asymmetric waveform generator for FAIMS

High field asymmetric waveform ion mobility spectrometry (FAIMS) has been used increasingly in recent years as an additional method of ion separation and selection before mass spectrometry. The FAIMS electrodes are relatively simple to design and fabricate for laboratories wishing to implement their own FAIMS designs. However, construction of the electronics apparatus needed to produce the required high magnitude asymmetric electric field oscillating at a frequency of several hundred kilohertz is not trivial. Here we present an entirely custom-built electronics setup capable of supplying the required waveforms and voltages. The apparatus is relatively simple and inexpensive to implement. We also present data acquired on this system demonstrating the use of FAIMS as a gas-phase ion filter interface to an ion trap mass spectrometer.     

Analysis of salazinic, norstictic, and usnic acids in Xanthoparmelia chlorochroa by ultra-performance liquid chromatography/tandem mass spectrometry

The lichen species Xanthoparmelia chlorochroa is toxic when consumed by domestic sheep, cattle, and Rocky Mountain elk. Clinical signs exhibited by poisoned animals include red urine, ataxia, and muscular weakness that rapidly progresses to recumbency. Elk are unable to recover once becoming recumbent; however, most affected cattle can recover if offered suitable feed shortly following the onset of signs. At present, the pathogenesis and specific toxin(s) are unknown. As part of an effort to elucidate the proximate toxin, a method using ultra-performance LC coupled to MS/MS with negative-ion electrospray ionization has been developed to compare salazinic, norstictic, and usnic acid concentrations in X. chlorochroa collected from locales associated with lichen poisonings. Compounds were extracted from lichen samples with acetone and sonication. The stationary phase was a Waters Acquity UPLCTM BEH Ca18 (50 x 2.1 mm; 1.7 microm particle size) column. The mobile phase consisted of an acetonitrile-water gradient. The precision of the method was confirmed by an SD below 0.4% (n=9) for triplicate samples. LOD values were 200, 100, and 50 ng/mL for salazinic, norstictic, and usnic acids, respectively.     

Nanostructured Macromolecular Metal Containing Materials in Catalysis

Summary: Nanostructured regular materials based on cross-linked polypropylene imine (PPI) dendrimers and silica-gel polyamine composites were used as a support for the synthesis of Pd nanoparticles. The materials were tested as catalysts and displayed a high activity and selectivity for the hydrogenation of conjugated double bonds.     

Modifiable low‐rank approximation to a matrix

A truncated ULV decomposition (TULVD) of an m×n matrix X of rank k is a decomposition of the form X = ULV^T+E, where U and V are left orthogonal matrices, L is a k×k non‐singular lower triangular matrix, and E is an error matrix. Only U,V, L, and ∥E∥_F are stored, but E is not stored. We propose algorithms for updating and downdating the TULVD. To construct these modification algorithms, we also use a refinement algorithm based upon that in (SIAM J. Matrix Anal. Appl. 2005; 27 (1):198–211) that reduces ∥E∥_F, detects rank degeneracy, corrects it, and sharpens the approximation. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopic monitoring of droplet polymerization in a microfluidic device

Microfluidic methodologies are becoming increasingly important for rapid formulation and screening of materials, and development of analytical tools for multiple sample screening is a critical step in achieving a combinatorial 'lab on a chip' approach. This work demonstrates the application of Raman spectroscopy for analysis of monomer composition and degree of conversion of methacrylate-based droplets in a microfluidic device. Droplet formation was conducted by flow focusing on the devices, and a gradient of component composition was created by varying the flow rates of the droplet-phase fluids into the microchannels. Raman data were collected using a fiber optic probe from a stationary array of the droplets/particles on the device, followed by partial least squares (PLS) calibration of the first derivative (1600 cm(-1) to 1550 cm(-1)) allowing successful measurement of monomer composition with a standard error of calibration (SEC) of +/-1.95% by volume. Following photopolymerization, the percentage of double bond conversion of the individual particles was calculated from the depletion of the normalized intensity of the C[double bond, length as m-dash]C stretching vibration at 1605 cm(-1). Raman data allowed accurate measurement of the decrease in double bond conversion as a function of increasing crosslinker concentration. The results from the research demonstrate that Raman spectroscopy is an effective, on-chip analytical tool for screening polymeric materials on the micrometre scale.     

Synthesis of butane-like SiGe hydrides: enabling precursors for CVD of Ge-rich semiconductors

The synthesis of butane-like (GeH(3))(2)(SiH(2))(2) (1), (GeH(3))(2)SiH(SiH(3)) (2), and (GeH(3))(2)(SiH(2)GeH(2)) (3) Si-Ge hydrides with applications in low-temperature synthesis of Ge-rich Si(1-x)Ge(x) optoelectronic alloys has been demonstrated. The compositional, vibrational, structural, and thermochemical properties of these compounds were studied by FTIR, multinuclear NMR, mass spectrometry, Rutherford backscattering, and density functional theory (DFT) simulations. The analyses indicate that the linear (GeH(3))(2)(SiH(2))(2) (1) and (GeH(3))(2)(SiH(2)GeH(2)) (3) compounds exist as a mixture of the classic normal (n) and gauche (g) conformational isomers which do not seem to interconvert at 22 degrees C. The conformational proportions in the samples were determined using a new fitting procedure, which combines calculated molecular spectra to reproduce those observed by varying the global intensity, frequency scale, and admixture coefficients of the individual conformers. The (GeH(3))(2)(SiH(2))(2) (1) species was then utilized to fabricate Si(0.50)Ge(0.50) semiconductor alloys reflecting exactly the Si/Ge content of the precursor. Device quality layers were grown via gas source MBE directly on Si(100) at unprecedented low temperatures 350-450 degrees C and display homogeneous compositional and strain profiles, low threading dislocation densities, and atomically planar surfaces. Low energy electron microscopy (LEEM) analysis has demonstrated that the precursor is highly reactive on Si(100) surfaces, with H(2) desorption kinetics comparable to those of Ge(2)H(6), despite the presence of strong Si-H bonds in the molecular structure.