1,356 research outputs found
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
Putting zoo animal cancer into perspective
As part of a comparative research agenda that promises insights that help extend the human lifespan and combat cancer, cancer prevalence in zoo animals has received recent attention. Here, we want to draw attention to a principle of cancer research that was introduced into the zoo world as early on as 1933, but that seems to have gone somewhat forgotten: Cancer is mainly a disease of old age, and therefore studies aiming at identifying taxa that are particularly susceptible or resistant to cancer must control for whether the respective zoo populations are âold.â In a comparative context, âold ageâ cannot be measured in absolute terms (e.g., years), but only in relation to a species' maximum lifespan: Species that achieve, across zoos, a higher mean lifespan as a percent of their maximum lifespan are âolder.â When applying this metric to former as well as more recently published data on cancer prevalence, it appears that those species that become relatively old in zoosâin particular, the carnivoresâhave a relatively high cancer prevalence. Any improvement in animal husbandryâwhich reduces premature deathsâshould, by default, lead to more cancer. Cancer in zoo animals, like any other oldâage condition, might therefore be embraced as a proxy for good husbandry. Rather than following a sensationalist approach that dramatizes disease and death per se, zoos should be clear about what their husbandry goals are, what relative longevities they want to achieve for which species, and what oldâage diseases they should therefore expect: in the end, one has to die of something
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 MĂ€use wurden mit der Reportermauslinie Rosa26R gekreuzt, so dass in doppelt transgenen Nachkommen die Cre AktivitĂ€t durch LacZ-FĂ€rbung analysiert werden konnte. Die Untersuchung von flk-1-Cre/ Rosa26R Embryonen und adulten Tieren zeigte eine spezifische FĂ€rbung der Endothelzellen von BlutgefĂ€Ăen in fast allen Organsystemen. AuĂerdem wurde die Cre Expression in GefĂ€Ăen 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 GefĂ€Ăentwicklung 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 GefĂ€Ăstrukturen gebildet, was auf eine normale Vaskulogenese hinwies. Diese unreifen GefĂ€Ăe 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 AktivitĂ€t 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 groĂer SequenzidentitĂ€t. Im Mausgen enthĂ€lt diese Region (ÂEnhancerÂ) Bindungsstellen fĂŒr Transkriptionsfaktoren und sie ist essentiell fĂŒr die endothelspezifische Expression in vivo. Die Bindungsstellen fĂŒr 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
Chronic Thromboembolic Pulmonary Hypertension - What Have We Learned From Large Animal Models
Chronic thrombo-embolic pulmonary hypertension (CTEPH) develops in a subset of patients after acute pulmonary embolism. In CTEPH, pulmonary vascular resistance, which is initially elevated due to the obstructions in the larger pulmonary arteries, is further increased by pulmonary microvascular remodeling. The increased afterload of the right ventricle (RV) leads to RV dilation and hypertrophy. This RV remodeling predisposes to arrhythmogenesis and RV failure. Yet, mechanisms involved in pulmonary microvascular remodeling, processes underlying the RV structural and functional adaptability in CTEPH as well as determinants of the susceptibility to arrhythmias such as atrial fibrillation in the context of CTEPH remain incompletely understood. Several large animal models with critical clinical features of human CTEPH and subsequent RV remodeling have relatively recently been developed in swine, sheep, and dogs. In this review we will discuss the current knowledge on the processes underlying development and progression of CTEPH, and on how animal models can help enlarge understanding of these processes
Electronic Scattering Effects in Europium-Based Iron Pnictides
In a comprehensive study, we investigate the electronic scattering effects in
EuFe(AsP) by using Fourier-transform infrared
spectroscopy. In spite of the fact that Eu local moments order around
\,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
EuFeAs in the antiferromagnetically ordered state, yielding a
higher Drude weight and lower scattering rate along the crystallographic
-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
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