We present a novel concept to process human blood on a spinning polymer disk for the determination of the hematocrit level by simple visual inspection. The microfluidic disk which is spun by a macroscopic drive unit features an upstream metering structure and a downstream blind channel where the centrifugally enforced sedimentation of the blood is performed. The bubble-free priming of the blind channel is governed by centrifugally assisted capillary filling along the sloped hydrophilic side-wall and the lid as well as the special shape of the dead end of the two-layer channel. The hematocrit is indicated at the sharp phase boundary between the plasma and the segregated cellular pellet on a disk-imprinted calibrated scale. This way, we conduct the hematocrit determination of human blood within 5 min at a high degree of linearity (R(2) = 0.999) and at a high accuracy (CV = 4.7%) spanning over the physiological to pathological working range. As all processing steps including the priming, the metering to a defined volume as well as the centrifugation are executed automatically during rotation, the concept is successfully demonstrated in a conventional PC-CDROM drive while delivering the same performance (R(2) = 0.999, CV = 4.3%).

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This work reports on an experimental study of the aging behavior of thin films of different classes of natural ester dielectric liquids. Thin film samples of three different natural ester liquids were prepared for the investigations and the aging experiments were performed in a medium of dry air at different temperatures (23°C and 65°C) and durations (up to around 100 days). The degradation of the samples was then evaluated in terms of changes in the dynamic viscosity of the liquid. Further analyses were also performed on the aged liquids through visual inspection, Infrared (IR) spectroscopy analysis and Oxidative Induction Time (OIT) measurements. Results show that the aging behaviors of natural ester dielectric liquids may greatly vary depending on the base chemistry of the liquid. Based on these results, it is suggested that natural ester dielectric liquids be classified into different categories considering their oleic acid content.

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In high voltage DC applications one of the most critical parameters of insulation materials is the conductivity. It is however challenging to measure conductivity accurately, since it is influenced by composition, morphology, sample thickness, temperature, electric field strength and electrode material. There is no standard electrode material used for electrical characterization of insulation in research. It is known that different electrode materials give rise to different conduction currents and different space charge inside a polymer sample. It is also believed that oxide layers on metal electrodes influence the activation energy of the interface between the polymer sample and the metal electrode. In the present work, a pure nonstabilized LDPE was used to investigate different electrode materials. The following materials were investigated: brass, copper, aluminum, gold, silver and semi conductive polymer. The method of application of the electrodes onto the polymer samples was also varied. The results indicate that the contact material and the method how to connect the material to the polymer sample had an influence on the time behavior of the DC conductivity during 24h of polarization. It could be shown that the applied electrical field influenced the crystal structure of the sample.