Characterization of solid standards prepared by freeze‐drying

Solid standards prepared by freeze‐drying consistently showed a high degree of homogeneity. The freezing process, completed in fractions of a second, preserves the original homogeneous distribution of the dopants, and the subsequent sublimation step would minimize any disturbance. Compared to those prepared by conventional methods such as blending and spiking, freeze‐dried standards exhibited superior lateral distribution and better uniform depth distribution. There is, however, a concentration constraint for achieving homogeneity. At 5% doping, segregation was observed in both lateral and depth distribution. Many tungsten standards doped with 10–28 elements ranging from 10 to 200 ppm were successfully prepared and used as controls for a number of analytical techniques including glow discharge mass spectrometry (GDMS) and d.c.‐arc optical emission spectroscopy (OES). Copyright © 2009 John Wiley & Sons, Ltd.     

The impact of water column variability on horizontal wave number estimation and mode based geoacoustic inversion results

The influence of water column variability on low-frequency, shallow water geoacoustic inversion results is considered. The data are estimates of modal eigenvalues obtained from measurements of a point source acoustic field using a horizontal aperture array in the water column. The inversion algorithm is based on perturbations to a background waveguide model with seabed properties consistent with the measured eigenvalues. Water column properties in the background model are assumed to be known, as would be obtained from conductivity, temperature, and depth measurements. The scope of this work in addressing the impact of water column variability on inversion is twofold. Range-dependent propagation effects as they pertain to eigenvalue estimation are first considered. It is shown that mode coupling is important even for weak internal waves and can enhance modal eigenvalue estimates. Second, the effect of the choice of background sound speed profile in the water column is considered for its impact on the estimated bottom acoustic properties. It is shown that a range-averaged sound velocity profile yields the best geoacoustic parameter estimates.     

An integrated QCM-based narcotics sensing microsystem

We present the design, fabrication and successful testing of a 14x14x4 mm3 integrated electronic narcotics sensing system which consists of only four parts. The microsystem absorbs airborne narcotics molecules and performs a liquid assay using an integrated quartz crystal microbalance (QCM). A vertically conductive double-sided adhesive foil (VCAF) was used and studied as a novel material for LOC and MEMS applications and provides easy assembly, electrical contacting and liquid containment. The system was tested for measuring cocaine and ecstasy, with successful detection of amounts as small as 100 ng and 200 ng, respectively. These levels are of interest in security activities in customs, prisons and by the police.     

Using mixed integer programming models to synchronously determine production levels and market prices in an integrated market for roundwood and forest biomass

Annals of Operations Research - We study a problem of integrating the supply chain of roundwood with the supply chain of forest biomass. The developed optimization model is a multiperiod,...     

Measurement and prediction of ultralow frequency ocean ambient noise off the eastern U.S. coast

Ultralow frequency (0.02-2 Hz) acoustic ambient noise was monitored from January to April 1991 at six ocean bottom stations off the eastern U.S. coast. The depths of the stations ranged from about 100 m to 2500 m. The measured spectra are in good agreement with predictions made using Cato's theory [J. Acoust. Soc. Am. 89, 1076-1095 (1991)] for noise generation by surface-wave orbital motion after extending the calculations to incorporate horizontally stratified environments. Contributions from both the linear, single-frequency (virtual monopole) and the nonlinear, double-frequency (dipole) mechanisms are clearly recognizable in the data. The predictions make use of directional wave data obtained from surface buoys deployed during the SWADE experiment and an ocean bottom model derived from compressional wave speed data measured during the EDGE deep seismic reflection survey. The results demonstrate conclusively that nonlinear surface-wave interactions are the dominant mechanism for generating deep-ocean ULF noise in the band 0.2-0.7 Hz.     

Applications of surface analytical techniques for study of the interactions between mercury and fluorescent lamp materials

Several surface analytical techniques, including electron spectroscopy for chemical analysis (ESCA)(X-ray photoelectron spectroscopy) and sputtered neutral mass spectrometry (SNMS), were used to study the interaction between Hg and other components of fluorescent lamps, a very critical issue in lighting industries. Active sites, responsible for Hg interaction/deposition, can be successfully identified by comparing the x- y distribution (obtained by ESCA mapping) and depth distribution (available through SNMS) of respective lamp components with that of Hg. A correlation in both depth and x- y distribution is strong evidence of site preference for Hg interaction/deposition. A burial mechanism is, however, proposed when only depth distribution, not x- y, is correlated. Other modes of ESCA (high resolution, angle-resolved, etc.) were also helpful. Information about the valence states of the interacted Hg species would help to define the nature of the interaction.     

A microfluidic device for parallel 3-D cell cultures in asymmetric environments

We demonstrate a concept for how a miniaturized 3-D cell culture in biological extracellular matrix (ECM) or synthetic gels bridges the gap between organ-tissue culture and traditional 2-D cultures. A microfluidic device for 3-D cell culture including microgradient environments has been designed, fabricated, and successfully evaluated. In the presented system stable diffusion gradients can be generated by application of two parallel fluid flows with different composition against opposite sides of a gel plug with embedded cells. Culture for up to two weeks was performed showing cells still viable and proliferating. The cell tracer dye calcein was used to verify gradient formation as the fluorescence intensity in exposed cells was proportional to the position in the chamber. Cellular response to an applied stimulus was demonstrated by use of an adenosine triphosphate gradient where the onset of a stimulated intracellular calcium release also depended on cell position.     

A concept for miniaturized 3-D cell culture using an extracellular matrix gel

This paper presents a novel method to embed, anchor, and cultivate cells in a controlled 3-D flow-through microenvironment. This is realized using an etched silicon pillar flow chamber filled with extracellular matrix (ECM) gel mixed with cells. At 4 degrees C, while in liquid form, ECM gel is mixed with cells and injected into the chamber. Raising the temperature to 37 degrees C results in a gel, with cells embedded. The silicon pillars both stabilize and increase the surface to volume ratio of the gel. During polymerization the gel shrinks, thus creating channels, which enables perfusion through the chip. The pillars increase the mechanical stability of the gel permitting high surface flow rates without surface modifications. Within the structure cells were still viable and proliferating after 6 days of cultivation. Our method thus makes it possible to perform medium- to long-term cultivation of cells in a controlled 3-D environment. This concept opens possibilities to perform studies of cells in a more physiological environment compared to traditional 2-D cultures on flat substrates.     

Bead-based microfluidic toxin sensor integrating evaporative signal amplification

We have devised a microfluidic platform that incorporates substrate-laden silica beads for sensing the proteolytic activity of botulinum neurotoxin type A (BoNT/A)-one of the most poisonous substances known and a significant biological threat. The sensor relies on toxin-mediated cleavage of a fluorophore-tagged peptide substrate specific for only BoNT/A. Peptide immobilized on beads is recognized and cleaved by the toxin, releasing fluorescent fragments into solution that can be concentrated at an isolated port via evaporation and detected using microscopy. Evaporative concentration in combination with a specific channel geometry provides up to a 3-fold signal amplification in 35 min, allowing for detection of low levels of fluorophore-labeled peptide-a task not easily accomplished using traditional channel designs. Our bead-based microfluidic platform can sense BoNT/A down to 10 pg of toxin per mL buffer solution in 3.5 h and can be adapted to sensing other toxins that operate via enzymatic cleavage of a known substrate.