A Quantitative 3D Motility Analysis of Trypanosoma brucei by Use of Digital In-line Holographic Microscopy

We present a quantitative 3D analysis of the motility of the blood parasite Trypanosoma brucei. Digital in-line holographic microscopy has been used to track single cells with high temporal and spatial accuracy to obtain quantitative data on their behavior. Comparing bloodstream form and insect form trypanosomes as well as mutant and wildtype cells under varying external conditions we were able to derive a general two-state-run-and-tumble-model for trypanosome motility. Differences in the motility of distinct strains indicate that adaption of the trypanosomes to their natural environments involves a change in their mode of swimming

[Evaluation of the Quantase R Phenylalanine assay and the Millipore Multiscreen Assay System for the neonatal screening on PKU.]

The Quantase R Phenylalanine Assay, an enzymatic/colorimetric method for the determination of phenylalanine (Phe) in dried bloodspots, was evaluated for the neonatal screening on PKU. The within run variation (N=12) for bloodspot samples with 0.15, 0.29 and 0.53 mmol/l was 10%, 5% and 5%, respectively. The between run variation (N=56) for bloodspot samples with 0.38 and 0.96 mmol/l was 9% and 8%, respectively. The mean concentration and standarddeviation in 33630 bloodspot samples was 0.077 +- 0.025 mmol/l (%CV=32%). The measured Phe-concentration was elevated (>=0.24 mmol/l) in 13 samples (0.039%). Reanalysis of these samples, in the same bloodspots, revealed a Phe-concentration of <0.12 mmol/l in 6 samples. These 6 samples were also found to be 'negative' in the Guthrie-test. Therefore, 6 samples (0.018%) were 'false-elevated'. For 5 of these samples no explanation was found. In 5770 bloodspot samples Guthrie test. All 'negative' samples in the Quantase were also 'negative' in the Guthrie. According to the manufacturer the absorbance has to be read at 570 nm. To reduce the number of samples with a 'false-elevated' concentration, we recommend to read the absorbances both at 570 nm and at 690 nm to correct for non-specific absorbance (dual wavelength). We used the Millipore Multiscreen Assay System for the extraction of the phenylalanine from the bloodspots. This system appeared to function well in practive. The special filterplates are rather expensive, but under stringent conditions the plates can be recycled three times. A visual control on the correct transfer of the extracts is necessary

SURFACE FREE-ENERGY COMPONENTS OF GLASS FROM ELLIPSOMETRY AND ZETA-POTENTIAL MEASUREMENTS

Two different experimental approaches based on ellipsometry and zeta potential measurements have been employed to determine the dispersion and polar surface free energy components of glass. From ellipsometry the adsorption isotherms of n-octane and water have been determined, yielding values for the film pressures of n-octane and water and the dispersion and polar surface free energy components of glass. Similarly, zeta potentials in water of glass covered with various amounts of n-octane and n-hexanol have been determined. Next, the film pressures of these liquids and surface free energy components of glass were also calculated. Thus determined values are 32 and 80 mJ/m2 (from ellipsometry) and 25 and 80 mJ/m2 (from zeta potentials) for the dispersion and polar components, respectively. The correspondence between the surface free energies obtained by two completely independent methods gives confidence to the approaches employed

Impact-toughening mechanisms of calcium carbonate-reinforced polypropylene nanocomposite

The impact fracture mechanisms of polypropylene (PP), containing 9.2 vol \% of calcium carbonate (CaCO3) nanoparticles, were investigated using optical microscopy and transmission electron microscopy. The incorporation of CaCO3 nanoparticles reduces the size of spherulites and induces the formation of P-phase crystallites, which leads to a more ductile PP matrix. Double-notch four-point bending (DN-4PB) Charpy impact specimens and notched Izod impact specimens were utilized to study the fracture mechanism(s) responsible for the observed toughening effect. A detailed investigation reveals that the CaCO3 nanoparticles act as stress concentrators to initiate massive crazes, followed by shear banding in PP matrix. These toughening mechanisms are responsible for the observed, improved impact strength. A comparison of the fracture mechanisms observed between DN-4PB Charpy and Izod impact tests is also made to show the effectiveness of DN4PB for investigation of impact fracture mechanisms of polymeric systems. (c) 2006 Wiley Periodicals, Inc