Infrared and Raman line shapes of dilute HOD in liquid H2O and D2O from 10 to 90 degrees C

A combined electronic structure/molecular dynamics approach was used to calculate infrared and isotropic Raman spectra for the OH or OD stretches of dilute HOD in D2O or H2O, respectively. The quantities needed to compute the infrared and Raman spectra were obtained from density functional theory calculations performed on clusters, generated from liquid-state configurations, containing an HOD molecule along with 4-9 solvent water molecules. The frequency, transition dipole, and isotropic transition polarizability were each empirically related to the electric field due to the solvent along the OH (or OD) bond, calculated on the H (or D) atom of interest. The frequency and transition dipole moment of the OH (or OD) stretch of the HOD molecule were found to be very sensitive to its instantaneous solvent environment, as opposed to the isotropic transition polarizability, which was found to be relatively insensitive to environment. Infrared and isotropic Raman spectra were computed within a molecular dynamics simulation by using the empirical relationships and semiclassical expressions for the line shapes. The line shapes agree well with experiment over a temperature range from 10 to 90 degrees C.     

Inferring wettability of heterogeneous surfaces by ToF-SIMS

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) has been examined as a possible predictive tool for surface wettability. Heterogeneous surfaces were prepared with hydrophilic and hydrophobic regions of known surface coverage using self-assembled monolayers. The surface coverage of each component was then correlated with ToF-SIMS fragmentation of the hydrophobic and hydrophilic surface groups and static contact angle measurements. From these measurements, a clear relationship between the surface wettability and relative intensity of characteristic secondary ions was identified. Moreover, our results for planar surfaces can be extrapolated to predict the wettability of particulate samples for which direct contact angle measurements are not straightforward. The ability to infer particle wettability by ToF-SIMS is well suited to mineral characterization and in particular, the prediction of mineral flotation efficiencies.     

A mode-coupling theory of vibrational line broadening in near-critical fluids

We present a fully microscopic mode-coupling theory of near-critical line broadening. All the structural and dynamical input required by the theory is calculated directly from intermolecular potentials. We compute vibrational frequency time-correlation functions and line shapes as the critical point is approached along both the critical isochore and the liquid-gas coexistence curve. Theory is shown to be in good agreement with simulation.     

Non-symmetric 2-designs modulo 2

Necessary conditions are obtained for the existence of a 2 – (v, k, ) design, for which the block intersection sizess ₁,s ₂, ...,s _n satisfys ₁ s ₂ ... s _n s (mod 2 ^e ), wheree is odd. These conditions are obtained by combining restrictions on the Smith Normal Form of the incidence matrix of the design with some well known properties of self-orthogonal binary codes with all weights divisible by 4.Research done at AT&T Bell Laboratories.     

A PDMS sheath flow cuvette for high‐sensitivity LIF measurements in CE

A simple method for producing a sheath flow cuvette in PDMS suitable for post‐column detection in CE is described. Two types of cuvette were investigated. In the first, the sheath flow channel had a round cross‐section of approximately 635 μm diameter, whereas the second cuvette had a 300×300 μm² square channel. Both cuvettes produced laminar flows that ensheathed the separation capillary's effluent allowing sensitive fluorescence measurements. The elasticity of the PDMS allowed the 300×300 μm² square sheath flow channel to expand uniformly and accommodate the larger 330–340 μm od round separation capillary, producing a self‐aligning cuvette with robust mechanical properties. With this cuvette, linear calibrations of over five orders of magnitude and 15–30 zmol fluorescein detection limits were obtained for 12 and 50 μm id capillaries.     

Pore size characterization of monolith for electrochromatography via atomic force microscopy studies in air and liquid phase

This paper investigates the use of scanning electron microscopy (SEM) and atomic force microscopy (AFM) for the characterization of monoliths used in capillary electrochromatography (CEC) while focusing on the nature of the information available from both techniques. SEM imaging revealed a compact structure of non-porous micrometer sized particles homogeneously agglomerated. With a simple AFM methodology, we found by direct observation that the same material exhibits mesopores in the nanometer range while SEM showed non-porous surfaces. These results obtained by AFM clearly showed that micrometer sized particles shrank and micrometer sized pores increased in the monolith when wetted. Thus, AFM was capable of demonstrating the morphological differences between wet and dried monolithic materials that are not possible by other imaging methods at micrometer resolution.     

Tracking sperm whales with a towed acoustic vector sensor

Passive acoustic towed linear arrays are increasingly used to detect marine mammal sounds during mobile anthropogenic activities. However, these arrays cannot resolve between signals arriving from the port or starboard without vessel course changes or multiple cable deployments, and their performance is degraded by vessel self-noise and non-acoustic mechanical vibration. In principle acoustic vector sensors can resolve these directional ambiguities, as well as flag the presence of non-acoustic contamination, provided that the vibration-sensitive sensors can be successfully integrated into compact tow modules. Here a vector sensor module attached to the end of a 800 m towed array is used to detect and localize 1813 sperm whale "clicks" off the coast of Sitka, AK. Three methods were used to identify frequency regimes relatively free of non-acoustic noise contamination, and then the active intensity (propagating energy) of the signal was computed between 4-10 kHz along three orthogonal directions, providing unambiguous bearing estimates of two sperm whales over time. These bearing estimates are consistent with those obtained via conventional methods, but the standard deviations of the vector sensor bearing estimates are twice those of the conventionally-derived bearings. The resolved ambiguities of the bearings deduced from vessel course changes match the vector sensor predictions.     

Grain-boundary fluctuations in two-dimensional colloidal crystals

We study grain-boundary fluctuations in two-dimensional colloidal crystals in real space and time using video microscopy. The experimentally obtained static and dynamic correlation functions are very well described by expressions obtained using capillary wave theory. This directly leads to values for the interfacial stiffness and the interface mobility, the key parameters in curvature-driven grain-boundary migration. Furthermore, we show that the average grain-boundary position exhibits a one-dimensional random walk as recently suggested by computer simulations [Z. T. Trautt, M. Upmanyu, and A. Karma, Science 314, 632 (2006)]. The interface mobility determined from the mean-square displacement of the average grain-boundary position is in good agreement with values inferred from grain-boundary fluctuations.