Bestimmung von Spurenelementen in Staubproben durch Röntgenfluorescenzanalyse mit Radionuklidanregung unter besonderer Berücksichtigung der Matrixeffekte

The analysis of dust samples by X-ray fluorescence using Cd-109 as X-ray source is described. For calibration silica gel standards are used. The correction for matrix effects is carried out by means of the Compton peaks. Besides the elements K, Ca, Ti, Fe, Rb, Sr, Y, Zr, which may be considered to be natural components of the ground, the elements Cr, Mn, Ni, Cu, Zn, Br and Pb are determined in the dust samples.     

Preparation and characterization of standard reference material 1849 infant/adult nutritional formula

Standard Reference Material (SRM) 1849 Infant/Adult Nutritional Formula has been issued by the National Institute of Standards and Technology (NIST) as a replacement for SRM 1846 Infant Formula, issued in 1996. Extraction characteristics of SRM 1846 have changed over time, as have NIST's analytical capabilities. While certified mass fraction values were provided for five constituents in SRM 1846 (four vitamins plus iodine), certified mass fraction values for 43 constituents are provided in SRM 1849 (fatty acids, elements, and vitamins) and reference mass fraction values are provided for an additional 43 constituents including amino acids and nucleotides, making it the most extensively characterized food-matrix SRM available from NIST.     

Feasability study of wall shear stress imaging using microstructured surfaces with flexible micropillars

A new optical sensor technique based on a sensor film with arrays of hair-like flexible micropillars on the surface is presented to measure the temporal and spatial wall shear stress field in boundary layer flows. The sensor principle uses the pillar tip deflection in the viscous sublayer as a direct measure of the wall shear stress. The pillar images are recorded simultaneously as a grid of small bright spots by high-speed imaging of the illuminated sensor film. Two different ways of illumination were tested, one of which uses the fact that the transparent pillars act as optical microfibres, which guide the light to the pillar tips. The other method uses pillar tips which were reflective coated. The tip displacement field of the pillars is measured by image processing with subpixel accuracy. With a typical displacement resolution on the order of 0.2 m, the minimum resolvable wall friction value is _w20 mPa. With smaller pillar structures than those used in this study, one can expect even smaller resolution limits.     

A theoretical description of elastic pillar substrates in biophysical experiments.

Arrays of elastic pillars are used in biophysical experiments as sensors for traction forces. The evaluation of the forces can be complicated if they are coupled to the pillar displacements over large distances. This is the case if many of the pillars are interconnected by elastic linkages as, for example, in fiber networks that are grown on top of pillars. To calculate the traction forces in such a network, we developed a set of nonlinear inhomogeneous equations relating the forces in the linking elements to the resulting pillar deflections. We chose a homogeneous, activated two-dimensional network of cytoskeletal actin filaments to illustrate that a pillar substrate is generally not a force sensor but a force-gradient sensor. In homogeneous networks the forces acting along the filaments can be approximated by analyzing only pillar deflections in the edge zones of the substrate and by integration over the corresponding force gradients.     

Eine neue Form von Trocken-, Absorptions- oder Waschr?hren

Ohne Zusammenfassung     

NAA characterization of the new Bovine Liver SRM

The National Institute of Standards and Technology (NIST) is preparing a freeze-dried powdered bovine liver tissue Standard Reference Material (SRM) to replace SRM 1577b Bovine Liver as the stock of this material was exhausted during 2006. Like the original SRM 1577 issued in 1972, this renewal focuses on the key elements for diagnostic, nutritional, and toxicological measurements that are important to medical, veterinary, and environmental sciences investigations. NIST’s approach for value assignment included extensive characterization by neutron activation analysis (NAA). Difficulties in the determination of some elements present at very low levels were overcome by use of radiochemical separations. Twentyone elements were characterized in SRM 1577c by NAA. The previous materials, SRM 1577 and 1577b, served as quality control.