Partikelgröße und Permeation

Particle Size and Permeation Using the Tesafilm (adhesive tape)-tear off method and by microscopie evaluation of the resulting films in polarized light the penetration of crystalline particles in the horny skin can be followed. As seen with examples, such as Tolnaftat, Na₂CO₃ · 10 H₂O and KF 224, crystalline particles can permeate upto remarkable depths in the horny skin. These studies indicate that the particle size of the crystals are only of minor significance. Possibly the depth of penetration depends more upon the crystalline form and on the solubility of substances in the components of the horny layer. Such processes can be determining factors for the intensity and duration of action of dermatological agents.     

Microscopic differential cell counts in milk for the evaluation of inflammatory reactions in clinically healthy and subclinically infected bovine mammary glands

Somatic cell count (SCC) is generally regarded as an indicator of udder health. A cut-off value of 100×10(3) cells/ml is currently used in Germany to differentiate between normal and abnormal secretion of quarters. In addition to SCC, differential cell counts (DCC) can be applied for a more detailed analysis of the udder health status. The aim of this study was to differentiate somatic cells in foremilk samples of udder quarters classified as normal secreting by SCC <100×10(3) cells/ml. Twenty cows were selected and 72 normal secreting udder quarters were compared with a control group of six diseased quarters (SCC >100×10(3) cells/ml). In two severely diseased quarters of the control group (SCC of 967×10(3) cells/ml and 1824×10(3) cells/ml) Escherichia coli and Staphylococcus aureus were detected. DCC patterns of milk samples (n = 25) with very low SCC values of ≤6·25×10(3)cells/ml revealed high lymphocyte proportions of up to 92%. Milk cell populations in samples (n = 41) with SCC values of (>6·25 to ≤25)×10(3) cells/ml were also dominated by lymphocytes (mean value 47%), whereas DCC patterns of milk from udder quarters (n = 6) with SCC values (>25 to ≤100)×10(3)cells/ml changed. While in samples (n = 3) with SCC values of (27-33)×10(3) cells/ml macrophages were predominant (35-40%), three milk samples with (43-45)×10(3) cells/ml indicated already inflammatory reactions based on the predominance of polymorphonuclear leucocytes (PMN) (54-63%). In milk samples of diseased quarters PMN were categorically found as dominant cell population with proportions of ≥65%. Macrophages were the second predominant cell population in almost all samples tested in relationship to lymphocytes and PMN. To our knowledge, this is the first study evaluating cell populations in low SCC milk in detail. Udder quarters classified as normal secreting by SCC <100×10(3) cells/ml revealed already inflammatory processes based on DCC.     

Geometrical criteria on the higher order smoothness of composite surfaces

A generalization of a theorem by Pegna and Wolter—called Linkage Curve Theorem—is presented. The new theorem provides a condition for joining two surfaces with high order geometric continuity of arbitrary degree n. It will be shown that the Linkage Curve Theorem can be generalized even for the case when the common boundary curve is only G¹.     

Investigations on indium phosphide grown by chemical beam epitaxy

In this paper, we present a systematic study of the properties of indium phosphide (InP) layers grown by chemical beam epitaxy (CBE). Trimethylindium (TMIn) and phosphine (PH₃) are used as source materials. The relation between the phosphine cracker temperature and the cracking efficiency has been studied by mass spectroscopy during growth. The growth rate and morphology of the layers have been studied by varying the TMIn and phosphine flow rates as well as the substrate temperature. We have found that, under a wide range of growth conditions, the deposition rate is only determined by and proportional to the TMIn flow rate. This is in agreement with literature. Additionally, we observe that the growth rate decreases below a certain phosphine to TMIn flow rate (V/III) ratio and becomes phosphine flow limited. From investigations of the growth rate as a function of temperature, it is concluded that the desorption of indium species from InP starts at a temperature slightly below 540°C. For this desorption process, we have found an activation energy of (217 ± 20) kJ/mol. Further characterization of the InP layers has been carried out by photoluminescence and Hall measurements. From both methods, the optimum growth conditions have been established. Under these conditions, we reproduc-ibly obtain InP layers showing linewidths of the donor-bound exciton transition at 5K around 0.25 meV and a mobility at 77K of about 7.0·10⁴ cm²/Vs. From the analysis of the mobility in the temperature range from 20 to 300K, we conclude that, additionally to shallow donors and acceptors, deep-donor centers with an activation energy of about 150 meV are present in all layers.     

Photo-ionization spectroscopy of traps in AlGaN/GaN high-electron mobility transistors

Four different layer structures are used to study deep-level traps in AlGaN/GaN high-electron mobility transistors (HEMTs) by photo-ionization spectroscopy. The structures grown on sapphire substrates by metal-organic chemical vapor deposition show nearly identical Hall data. However, the direct current (DC) performance of HEMTs with identical geometry is found to differ strongly. In all structures investigated, two distinct defect levels, namely, at 2.84–2.94 eV and 3.24–3.28 eV, were found from the fits of the photo-ionization cross-sectional data. Additionally, different trap concentrations can be deduced. These are in good correlation with the different transconductance and drain current measured. It is assumed that the defect levels observed are related to the AlGaN surface.