Drosselklappen für hohe Geschwindigkeiten zum Einbau in Grundablässen

Zusammenfassung Für hohe Geschwindigkeiten, z. B. in Grundabl?ssen, ist die übliche linsenf?rmige Drosselklappe wegen der Gefahr der Schwingungen durch Abl?sungswirbel und Kavitation unbrauchbar. Es wurden daher neue Klappenformen entwickelt und durch Modellversuche die Einflüsse der Kavitation auf den Str?mungswiderstand und das Drehmoment untersucht. Eine neue Klappenform erzwingt die Abl?sung der Str?mung und arbeitet daher in jeder Stellung zwischen voll ge?ffnet und geschlossen schwingungsfrei. Vortrag, gehalten auf der Aerodynamik-Tagung in G?ttingen im Juni 1933.     

Beitr?ge zur Fruchtsaft-Statistik

Ohne ZusammenfassungMitteilung aus der Kgl. Untersuchungsanstalt beim Hygienischen Institut der Universität Leipzig.     

Resonant metal-mesh bandpass filters for the far infrared

The spectral performance of freestanding resonant metal-mesh bandpass filters operating with center frequencies ranging from 585 GHz to 2.1 THz is presented. These filters are made up of a 12-μm-thick copper film with an array of cross-shaped apertures that fill a circular area with a 50-mm diameter. The filters exhibit power transmission in the range 97-100% at their respective center frequencies and stop-band rejection in excess of 18 dB. The theoretically predicted nondiffracting properties of the meshes are experimentally verified through high-resolution beam mapping. Scalability of the filter spectra with mesh dimensions is demonstrated over a wide spectral range. Several modeling methods are considered, and results from the models are shown.     

Traumatogenic factors affecting the knees of carpet installers

An ergonomics analysis of carpet installation tasks was performed. The purpose was to identify and quality potential sources of biomechanical trauma that may be responsible for the high rates of knee morbidity found by previous researchers among carpet layers. Nine carpet layers were studied either at an apartment building worksite or at a training school. Results from a job analysis indicated that workers spent approximatately 75% of their time in the kneeling position using a tool called a knee-kicker to stretch and install carpet. Awkward body postures were identified from films of workers installing carpets. At the moment of impact the knee is severely flexed, subtended angles were less than 60 degrees. To obtain measures of impact force on the knee, the kicker-tool was instrumented with a load cell. Workers who executed the hardest kicks with the tool produced impact peak forces that averaged 3019 newtons (N), which is equivalent to about four times body weight. Measures from an accelerometer attached to the worker's knee showed values in ecxess of 120 m/s², which are comparable to those found during vigorous running and jumping exercises. The results imply that repetitive impact of the knee joint from the use of the knee-kicker combined with knee flexion, kneeling and squatting may be responsible for the high level of occupational knee-morbidity found among carpet layers.     

The undercooling of aluminum

An important parameter affecting microstructure development during solidification is the amount of undercooling prior to nucleation. The undercooling potential of aluminum has been assessed by thermal analysis measurements on powder dispersions of the liquid metal. A number of variables have been identified which influence the undercooling of powder Al samples including powder coating, powder size, melt cooling rate, and melt superheat. Surface analysis by Auger electron spectroscopy indicates that changing the medium in which the powders are produced is an effective method of altering the coating chemistry. Factorial design analysis has been employed to quantify the potential of processing variables to increase the undercooling level obtainable in aluminum. The factorial analysis indicates that control of the powder coating through changing the medium in which the powders are produced is most effective in decreasing the nucleation temperature. Additionally, the finest powders produced in the medium which induces the least catalytic coating, when cooled at high rates,T = 500 °C/s, from low superheats,T _s = 710 °C, are found to achieve the deepest undercooling, ΔT = 175 °C. These studies provide the basis for further increases in undercooling and for future investigations into the solidification reactions which produce both stable and metastable structures in aluminum alloys. Formerly Research Assistant in the Department of Metallurgical and Mineral Engineering, University of Wisconsin-Madison     

Cellular automata method for macroscopic surface and friction dynamics in brake systems

The friction dynamics in the boundary layer of a brake system is closely linked with the growth and the destruction of typical structures on the brake pad. These processes are caused by an interaction of friction and wear and determine the (as well measured) time-dependence of global parameters, such as the friction coefficient μ or the temperature. Based on the simulation with a set of differential equations, this equilibrium of flow has also already been described with a cellular-automaton-discretization. This paper will show new results and fundamental conclusions with respect to the surface topography dynamics and the friction behaviour of a brake system.     

Rationale for en bloc vein resection in the treatment of pancreatic adenocarcinoma adherent to the superior mesenteric-portal vein confluence. Pancreatic Tumor Study Group

The enzymatic activity of protein kinase C (PKC) was measured in the cytosol and particulate fraction of parabrachial nucleus, the presumed site of conditioned taste aversion (CTA) engrams. At various time intervals after acquisition of the task (pairing saccharin consumption with subsequent LiCl poisoning) the nucleus was dissected from the frozen coronal sections. An increase (+40%) in the cytosol PKC activity was found 48 h after that pairing in comparison with controls (saline injection instead of LiCl). Particulate enzyme activity virtual did not change (-5%). Thus the total PKC activity increased significantly (21%). Qualitatively similar but less markedly expressed PKC shifts (+18% in cytosol) ere found 24 h following CTA. Twelve hours and 5 days after CTA acquisition the activity and distribution of PKC was similar to that seen in normal rats. The control experiments revealed that 6 h after LiCl injection alone (without previous saccharin consumption) translocation of PKC from the cytosol to the membrane fraction (found previously 1 h after LiCl injection alone) still persisted but did not differ from that found 6 h after its pairing with saccharin drinking (CTA). It is concluded that acquisition of conditioned taste aversion may be followed by synthesis of PKC rather than by its translocation or downregulation.     

Modulated dispersion explains changes in arrhythmia vulnerability during premature stimulation of the heart

BACKGROUND: Previously, we have shown that a premature stimulus can significantly modulate spatial gradients of ventricular repolarization (ie, modulated dispersion), which result from heterogeneous electrophysiological properties between cells. The role modulated dispersion may play in determining electrical instability in the heart is unknown. METHODS AND RESULTS: To determine if premature stimulus-induced changes in repolarization are a mechanism that governs susceptibility to cardiac arrhythmias, optical action potentials were recorded simultaneously from 128 ventricular sites (1 cm2) in 8 Langendorff-perfused guinea pig hearts. After baseline pacing (S1), a single premature stimulus (S2) was introduced over a range of S1S2 coupling intervals. Arrhythmia vulnerability after each premature stimulus was determined by measurement of a modified ventricular fibrillation threshold (VFT) during the T wave of each S2 beat (ie, S2-VFT). As the S1S2 interval was shortened to an intermediate value, spatial gradients of repolarization and vulnerability to fibrillation decreased by 51+/-9% (mean+/-SEM) and 73+/-45%, respectively, compared with baseline levels. As the S1S2 interval was further shortened, repolarization gradients increased above baseline levels by 54+/-30%, which was paralleled by a corresponding increase (37+/-8%) in vulnerability. CONCLUSIONS: These data demonstrate that modulation of repolarization gradients by a single premature stimulus significantly influences vulnerability to ventricular fibrillation. This may represent a novel mechanism for the formation of arrhythmogenic substrates during premature stimulation of the heart.