Principles and application of shock-tubes and shock tunnels

The principles, theoretical flow equations, calculation techniques, limitations and practical performance characteristics of basic and high performance shock tubes and shock tunnels are presented. Selected operating curves are included

Surface roughness during depositional growth and sublimation of ice crystals

Full version of an earlier discussion paper (Chou et al. 2018)Ice surface properties can modify the scattering properties of atmospheric ice crystals and therefore affect the radiative properties of mixed-phase and cirrus clouds. The Ice Roughness Investigation System (IRIS) is a new laboratory setup designed to investigate the conditions under which roughness develops on single ice crystals, based on their size, morphology and growth conditions (relative humidity and temperature). Ice roughness is quantified through the analysis of speckle in 2-D light-scattering patterns. Characterization of the setup shows that a supersaturation of 20 % with respect to ice and a temperature at the sample position as low as-40 °C could be achieved within IRIS. Investigations of the influence of humidity show that higher supersaturations with respect to ice lead to enhanced roughness and irregularities of ice crystal surfaces. Moreover, relative humidity oscillations lead to gradual ratcheting-up of roughness and irregularities, as the crystals undergo repeated growth-sublimation cycles. This memory effect also appears to result in reduced growth rates in later cycles. Thus, growth history, as well as supersaturation and temperature, influences ice crystal growth and properties, and future atmospheric models may benefit from its inclusion in the cloud evolution process and allow more accurate representation of not just roughness but crystal size too, and possibly also electrification properties.Peer reviewe

Untersuchungen zur Funktion endothelialer Transkriptionsfaktoren bei der Angiogenese

Mit Hilfe des Cre-loxP Rekombinationssystems können Gene zelltypspezifisch inaktiviert werden. Hier wurden die genregulatorischen Elemente des flk-1 Gens mit dem Cre Rekombinase Gen fusioniert und transgene Mauslinien etabliert (flk-1-Cre). Diese Mäuse wurden mit der Reportermauslinie Rosa26R gekreuzt, so dass in doppelt transgenen Nachkommen die Cre Aktivität durch LacZ-Färbung analysiert werden konnte. Die Untersuchung von flk-1-Cre/ Rosa26R Embryonen und adulten Tieren zeigte eine spezifische Färbung der Endothelzellen von Blutgefäßen in fast allen Organsystemen. Außerdem wurde die Cre Expression in Gefäßen von experimentellen BFS-1 Tumoren nachgewiesen. Flk-1-Cre Mauslinien können in Zukunft verwendet werden, um gefloxte Zielgene spezifisch in Endothelzellen zu inaktivieren. Die Rolle von Hypoxie-induzierbaren Faktoren (HIF) in der embryonalen Gefäßentwicklung wurde untersucht, indem HIF Signalwege im Endothel blockiert wurden. Dazu wurde eine dominant negative HIF2-alpha Mutante verwendet (HIFdn), die mittels der regulatorischen Elemente des flk-1 Gens spezifisch in Endothelzellen von transgenen Mausembryonen exprimiert wurde. Die HIFdn transgenen Embryonen zeigten eine Wachstumsretardierung und starben an Tag 11,5 der Embryonalentwicklung. In den transgenen Embryonen wurden primitive Gefäßstrukturen gebildet, was auf eine normale Vaskulogenese hinwies. Diese unreifen Gefäße wurden aber nicht remodelliert, da keine sprossende Angiogenese auftrat. In Herzen von HIFdn transgenen Embryonen zeigten sich Defekte in der Bildung von Trabekeln und in der Ausbildung der Herzschleife. Die Analyse der Genexpression zeigte, dass endotheliale Gene wie tie-2, flt-1 und flk-1 in transgenen Embryonen stark reduziert waren. Diese Ergebnisse lassen den Schluss zu, dass endotheliale HIF eine essentielle Rolle in der embryonalen Angiogenese spielen. Die Regulation des humanen VEGF Rezeptor-2 Gens (KDR) wurde untersucht. Es konnte gezeigt werden, dass der Transkriptionsfaktor HIF2-alpha, nicht aber der verwandte HIF1-alpha die Aktivität des KDR Promotors in Reportergenexperimenten stimulierte. Potentielle HIF2 Bindungsstellen im KDR Promotor wurden identifiziert. Durch die Mutation einer dieser Bindungsstellen wurde die Aktivierbarkeit des Promotors stark reduziert. Im Vergleich zum Mausgen, zeigte das 1. Intron des humanen KDR Gens eine Region großer Sequenzidentität. Im Mausgen enthält diese Region („Enhancer“) Bindungsstellen für Transkriptionsfaktoren und sie ist essentiell für die endothelspezifische Expression in vivo. Die Bindungsstellen für diese Transkriptionsfaktoren (SCL/Tal-1, Gata, Ets) sind im 1. Intron des humanen Gens konserviert, so dass sie wahrscheinlich an der Regulation der Genexpression beteiligt sind

Rupture Strength of Several Nickel-base Alloys in Sheet Form

The 100-hour rupture strengths of Inconel X, Inconel 700, Incoloy 901, Refractaloy 26, and R-235 at 1200 and 1350 F. in both the annealed and heat-treated conditions were determined. Inconel 700 had the highest rupture strength at both temperatures; Incoloy 901 was second strongest at 1200 F, and R-235 second strongest at 1350 F. With the exception of Incoloy 901, ductility was low. Photomicrographs show that fractures are through the grain boundaries. Results are compared with published data for other sheet alloys and bar stock

Ka-band study: 1988

The Ka-band study team was chartered in late 1987 to bring together all the planning elements for establishing 32 GHz (Ka-band) as the primary downlink frequency for deep-space operation, and to provide a stable baseline from which to pursue that development. This article summarizes the results of that study at its conclusion in mid-1988, and corresponds to material presented to NASA's Office of Space Operations on July 14, 1988. For a variety of reasons, Ka-band is the right next major step in deep-space communications. It offers improved radio metric accuracy through reduced plasma sensitivity and increased bandwidth. Because of these improvements, it offers the opportunity to reduce costs in the flight radio system or in the DSN by allocating part of the overall benefits of Ka-band to this cost reduction. A mission scenario is being planned that can drive at least two and possibly all three of the DSN subnets to provide a Ka-band downlink capability by the turn of the century. The implementation scenario devised by the study team is believed to be feasible within reasonable resource expectations, and capable of providing the needed upgrade as a natural follow-on to the technology development which is already underway

Electronic Scattering Effects in Europium-Based Iron Pnictides

In a comprehensive study, we investigate the electronic scattering effects in EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ by using Fourier-transform infrared spectroscopy. In spite of the fact that Eu$^{2+}$ local moments order around $T_\text{Eu} \approx 20$\,K, the overall optical response is strikingly similar to the one of the well-known Ba-122 pnictides. The main difference lies within the suppression of the lower spin-density-wave gap feature. By analysing our spectra with a multi-component model, we find that the high-energy feature around 0.7\,eV -- often associated with Hund's rule coupling -- is highly sensitive to the spin-density-wave ordering, this further confirms its direct relationship to the dynamics of itinerant carriers. The same model is also used to investigate the in-plane anisotropy of magnetically detwinned EuFe$_{2}$As$_{2}$ in the antiferromagnetically ordered state, yielding a higher Drude weight and lower scattering rate along the crystallographic $a$-axis. Finally, we analyse the development of the room temperature spectra with isovalent phosphor substitution and highlight changes in the scattering rate of hole-like carriers induced by a Lifshitz transition

RESULTS OF AN EXPERIMENT TO LEAD CRANES ON MIGRATION BEHIND MOTORIZED GROUND VEHICLES

Ten greater sandhill cranes (Grus canadensis tabida) , trained to enter and ride in a specially-equipped truck, were transported at ca 80 days of age from their rearing site at Patuxent Wildlife Research Center (patuxent), Maryland, to a reintroduction site located within the species\u27 former breeding range in northern Arizona. After 5 additional weeks of training, these juvenile cranes were led south ca 600 km to a wintering area on the Arizona/Mexico border. Nine of the 10 survived the trek, 495 km of which were flown, although only a few cranes flew every stage of the route. Their longest flight was 77 lan. Major problems during the migration were powerline collisions (3, 1 fatal), eagle attacks (none fatal), and overheating (when air temperatures exceeded ca 25 C). All cranes that entered training quickly learned to follow the truck, and their tenacity when following under unfavorable conditions (e.g., poor light, extreme dust, or heat) showed that cranes could consistently be led over long distances. We cannot predict if the cranes will retrace their route unassisted when adults, but 2 cranes returned 130 km to the starting point of the migration after the flock was scattered by an eagle during our migration south. Three other cranes were recovered 55 km from the attack site and on course toward the starting point

RESULTS OF AN EXPERIMENT TO LEAD CRANES ON MIGRATION BEHIND MOTORIZED GROUND VEHICLES

Ten greater sandhill cranes (Grus canadensis tabida) , trained to enter and ride in a specially-equipped truck, were transported at ca 80 days of age from their rearing site at Patuxent Wildlife Research Center (patuxent), Maryland, to a reintroduction site located within the species\u27 former breeding range in northern Arizona. After 5 additional weeks of training, these juvenile cranes were led south ca 600 km to a wintering area on the Arizona/Mexico border. Nine of the 10 survived the trek, 495 km of which were flown, although only a few cranes flew every stage of the route. Their longest flight was 77 lan. Major problems during the migration were powerline collisions (3, 1 fatal), eagle attacks (none fatal), and overheating (when air temperatures exceeded ca 25 C). All cranes that entered training quickly learned to follow the truck, and their tenacity when following under unfavorable conditions (e.g., poor light, extreme dust, or heat) showed that cranes could consistently be led over long distances. We cannot predict if the cranes will retrace their route unassisted when adults, but 2 cranes returned 130 km to the starting point of the migration after the flock was scattered by an eagle during our migration south. Three other cranes were recovered 55 km from the attack site and on course toward the starting point