Electronic properties of low temperature microcrystalline silicon carbide prepared by Hot Wire CVD

Microcrystalline silicon carbide (μc-SiC) was prepared at low substrate temperatures using Hot Wire chemical vapor deposition (HWCVD). High crystalline volume fractions were achieved at high hydrogen dilution and high deposition pressure. Without intentional doping, such material shows high dark conductivity and high optical absorption below the band gap. The material prepared at low deposition pressure or low hydrogen dilution, on the other hand, shows much lower conductivity and sub-gap absorption, but high spin densities up to 5 × 10¹⁹ cm⁻³. This high absorption can be attributed to free carriers, different to μc-Si:H where a correlation between the sub-gap absorption and the spin density is observed.     

Development of microcrystalline silicon carbide window layers by hot-wire CVD and their applications in microcrystalline silicon thin film solar cells

Microcrystalline silicon carbide (μc-SiC:H) thin films in stoichiometric form were deposited from the gas mixture of monomethylsilane (MMS) and hydrogen by Hot-Wire Chemical Vapor Deposition (HWCVD). These films are highly conductive n-type. The optical gap E₀₄ is about 3.0-3.2 eV. Such μc-SiC:H window layers were successfully applied in n-side illuminated n-i-p microcrystalline silicon thin film solar cells. By increasing the absorber layer thickness from 1 to 2.5 μm, the short circuit current density (j_SC) increases from 23 to 26 mA/cm² with Ag back contacts. By applying highly reflective ZnO/Ag back contacts, j_SC = 29.6 mA/cm² and η = 9.6% were achieved in a cell with a 2-μm-thick absorber layer.     

Modelling immunomagnetic cell capture in CFD

The separation of cells from a complex sample by immunomagnetic capture has recently obtained increased attention for microfluidic applications. Here, we present a simulation approach for immunomagnetic separation in a flow-through microfluidic environment that for the first time takes binding kinetics of beads to target cells as well as binding of multiple beads per cell into account. The approach is implemented into a computational fluid dynamics code and facilitates the tailored design of microfluidic magnetophoretic devices with an optimised separation performance. Although the specific computational model under study is constrained to a 2D geometry, appropriate parameter sets that allow for a continuous separation of cell/bead complexes from non-magnetic particles could be derived. In addition, based on magnetophoretic mobilities, a critical threshold value of beads per cell is revealed, where further binding is considerably reduced or the reaction cascade ceases.     

Antioxidant activity of Egyptian Eucalyptus camaldulensisvar. brevirostrisleaf extracts

Leaves from Eucalyptus camaldulensis var. brevirostris trees, planted in the Nile delta in Egypt, were examined for the antioxidant activity of their nonvolatile compounds. The extracts obtained by ethanol digestion and by supercritical fluid extraction (SFE; CO₂ with 15% ethanol) showed the most promising antioxidative activities. In order to identify the most active compounds, both extracts were subjected to a semipreparative reversed‐phase HPLC separation, the main fractions were collected, tested for antioxidative activity and analysed by different chromatographical and spectroscopical methods for identification of the most relevant compounds. Gallic and ellagic acid were found to be the prevailing antioxidants in the ethanolic extract. The main two compounds of the SFE extract with antioxidative activity revealed to be flavones. To a high degree of probability they were identified as 5‐hydroxy‐7,4′‐dimethoxy flavone and 5‐hydroxy‐7,4′‐dimethoxy‐8‐methyl flavone, respectively. The extracts obtained by ethanol digestion were dried and administered to rats for toxicity evaluation (up to 3 g/kg body weight). No mortality was observed which indicates a very low lethality of the tested extract.     

Sensitivity and diagnosticity of the 0.1-Hz component of heart rate variability as an indicator of mental workload

We investigated whether the 0.1-Hz component of heart rate variability (HRV) allows one to discriminate among levels of mental work stress induced by different types of tasks (diagnosticity) as well as among those induced by different levels of difficulty (sensitivity). Our 14 participants were presented 14 tasks of the Advisory Group for Aerospace Research and Development Standardized Tests for Research with Environmental Stressors battery in a repeated-measures design. Sufficient sensitivity was obtained for a discrimination between work and rest, but we found no support for a more fine-grained sensitivity. Concerning diagnosticity, only the grammatical reasoning task could be discriminated from all other tasks, indicating for this task a level of mental strain comparable to rest, which was in contrast with the results both for perceived difficulty and performance. We propose that HRV is an indicator for time pressure or emotional strain, not for mental workload, given that it seems to allow discrimination between tasks with and without pacing. Application of this research argues against using HRV as a measure of mental and especially cognitive workload, particularly where system safety or occupational risks may be at stake (e.g., when evaluating operator tasks or interface design in control room operations).     

Purine alkaloids in seeds ofTheobroma species from the Amazon

Summary The content of purine alkaloids in seeds of fourTheobroma species from the Amazon basin was analized by a reversed phase high-performance liquid chromatographic method.Theobroma grandiflorum was found to contain 0.38% of 1,3,7,9-tetramethyluric acidT. subincanum 0.07% 1,3,7,9-tetramethyluric acid,T. speciosum 0.01% theobromine and 0.04% 1,3,7,9-tetramethyluric acid and finallyT. mariae 2.35% theobromine and 0.12% caffeine. Theophylline could not be detected in any of these species. The results were confirmed qualitatively by thin-layer chromatography.

---

Purinalkaloide in Samen vonTheobroma-Arten aus dem Amazonas-Becken

Zusammenfassung Das Vorkommen von Purin-Alkaloiden in Samen von vierTheobroma-Arten des Amazonasbeckens wurde mit Hilfe einer RP-HPLC-Methode untersucht. In Samen vonTheobroma grandiflorum wurden 0,38% 1,3,7,9-Tetramethylharnsäure (TMU), vonT. subincanum 0,07% TMU, vonT. speciosum 0,01% Theobromin und 0,04% TMU sowie schließlich vonT. mariae 2,35% Theobromin und 0,12% Coffein gefunden. Die Ergebnisse wurden qualitativ dünnschichtchromatographisch bestätigt.

     

Precision time-domain measurement system

For an accurate comparison of two pulse signals on one channel of a sampling system, an alternating pretrigger shift is used. Simultaneously, a quartz-stable c.w. sine gives a precise time reference. A programmable data-acquisition system performs control and output operations. After averaging, the usable dynamic range is 70 dB with noise and drifts below 0.2 mVeff     

Evaporation dynamics of sessile liquid drops in still air with constant contact radius

Evaporation of sessile drops with constant wetting radius is investigated. In contrast to constant contact angle the temporal evaluation of the droplet volume can not be formulated in a closed form. We provide two approximations for initial contact angles below 90° which allow predicting the evaporation dynamics in practice easily. The derived linear approximation is suitable for small initial contact angles with a maximum relative deviation of 1% for contact angles below 30°. Further, we provide a non-linear algebraic approximation with a maximum relative error 0.3% in the entire range of contact angle considered.     

Bemessungshilfen und Konstruktion bei geneigten Querkräften

Design Methods and Detailing for RC Beams with Inclined Shear Forces The shear‐resistant design of reinforced concrete (RC) beams with rectangular cross sections and inclined shear forces (biaxial shear) is presented. Equations for the shear resistances provided by the tensile strut and by the compressive strut are derived according to the design concepts of DIN 1045‐1 and EC 2. They are verified to experimental data and elaborated to gain design charts. Examples show the practical applications. Existing detailing provisions for the anchorage of stirrups and the horizontal displacement in the tensile force of the bending reinforcement can directly be applied to cases of biaxial shear, if the rotations of the neutral axis and of the resultant strut‐and‐tie system are taken into account.