Certification of standard samples of electrical conductivity

Conclusions The electrical conductivity should be determined for that part of the SS in which the cross-sectional area can be found and the nonuniformity of the material taken into consideration with the necessary degree of accuracy. The value of determined according to (1) corresponds most closely with that part of the SS for which deviates least of all from the arithmetical mean deviation for all sections of the SS. Therefore, this part should be noted and used for checking the instrument.Translated from Izmeritel'naya Tekhnika, No. 3, pp. 40–42, March, 1980.     

Conductivity measurements of various yttria-stabilized zirconia samples

Samples of yttria-stabilized zirconia manufactured by the following fabrication procedures, were obtained from commercial sources: (i) hot isostatic pressing; (ii) tape casting; (iii) vacuum plasma spraying, and (iv) calendering. The ionic conductivities of these samples were measured by (a) impedance spectroscopy; (b) the four-point probe method; (c) the current-interruption technique, and (d) the van der Pauw technique. The tape-cast and hot pressed samples showed good and very reproducible conductivity values. The vacuum plasma sprayed samples showed an anisotropy in their conductivity, with the cross-plane value being several times lower than the in-plane value. A simple model based on the porous microstructure of these samples can explain this observation. Sintering of the plasma sprayed samples minimized the anisotropy and significantly improved their conductivity values. The calendered samples also showed a similar anisotropy in their conductivity data when they were inadequately sintered.     

Limit of detection determination for censored samples

The problem of setting the limit of detection is considered for censored samples and heterogeneous errors. After formal definitions of the critical level and of the method detection limit, we obtain simplified maximum likelihood-type estimators. The estimation problem of the truncation parameter and its uncertainty are reviewed. Upper confidence bounds for the limit of detection are derived and some simulation results are given.     

Microchip-based purification of DNA from biological samples

A microchip solid-phase extraction method for purification of DNA from biological samples, such as blood, is demonstrated. Silica beads were packed into glass microchips and the beads immobilized with sol-gel to provide a stable and reproducible solid phase onto which DNA could be adsorbed. Optimization of the DNA loading conditions established a higher DNA recovery at pH 6.1 than 7.6. This lower pH also allowed for the flow rate to be increased, resulting in a decrease in extraction time from 25 min to less than 15 min. Using this procedure, template genomic DNA from human whole blood was purified on the microchip platform with the only sample preparation being mixing of the blood with load buffer prior to loading on the microchip device. Comparison between the microchip SPE (microchipSPE) procedure and a commercial microcentrifuge method showed comparable amounts of PCR-amplifiable DNA could be isolated from cultures of Salmonella typhimurium. The greatest potential of the microchipSPE device was illustrated by purifying DNA from spores from the vaccine strain of Bacillus anthracis, where eventual integration of SPE, PCR, and separation on a single microdevice could potentially enable complete detection of the infectious agent in less than 30 min.     

Field portable XRF analysis of environmental samples

One of the critical factors for successfully conducting contamination characterization, removal, and remedial operations at hazardous waste sites is rapid and appropriate response to analyze samples in a timely fashion. Turnaround time associated with off-site analysis is often too slow to support efficient utilization of the data. Field portable X-ray fluorescence (FPXRF) techniques provide viable and effective analytical approaches to meet on-site analysis needs for many types of environmental samples. Applications include the in situ analysis of metals in soils and sediments, thin films/particulates, and lead in paint.     

Evaluation of activation energy in sintered samples

The neck curvature obtained in sintering two spherical particles is related to the neck radius of the contact area and the radius of the particles. The radius of the neck curvature, when expressed in terms of the fractional shrinkage, leads to an elegant method of evaluating the activation energy corresponding to the operating mechanism at different stages of sintering. The calculated values of activation energy confirm the diffusion mechanisms operative at different temperatures and different sintering durations.