Endocrine and fluid metabolism in males and females of different ages after bedrest, acceleration and lower body negative pressure

Space shuttle flight simulations were conducted to determine the effects of weightlessness, lower body negative pressure (LBNP), and acceleration of fluid and electrolyte excretion and the hormones that control it. Measurements were made on male and female subjects of different ages before and after bedrest. After admission to a controlled environment, groups of 6 to 14 subjects in the age ranges 25 to 35, 35 to 45, 45 to 55 to 65 years were exposed to +3 G sub z for 15 minutes (G1) and to LBNP (LBNP1) on different days. On 3 days during this prebedrest period, no tests were conducted. Six days of bedrest followed, and the G sub z (G2) and LBNP (LBNP2) tests were run again. Hormones, electrolytes, and other parameters were measured in 24-hour urine pools throughout the experiment. During bedrest, cortisol and aldosterone excretion increased. Urine volume decreased, and specific gravity and osmolality increased. Urinary electrolytes were statistically unchanged from levels during the non-stress control period. During G2, cortisol increased significantly over its control and bedrest levels. Urine volume, sodium, and chloride were significantly lower; specific gravity and osmolality were higher during the control period or bedrest. The retention of fluids and electrolytes after +G sub z may at least partially explain decreased urine volume and increased osmolality observed during bedrest in this study. There were some who indicated that space flight would not affect the fluid and electrolyte metabolism of females or older males any more severely than it has affected that of male astronauts

Fahrtbericht der "Poseidon"-Reise 101b [POS101/b] in den Nordostatlantik vom 20.6.83 - 24.7.83

Die Fahrt l0lb des FS "Poseidon" fand zwischen dem 20.6. und 24.7.83 im Nordatlantik statt. Es wurden Schnitte gefahren von Lissabon nach Ponta Delgada, von Ponta Delgada bis 54°50'N, 37°28'W und zurück und von Ponta Delgada über OWS "R" zum Englischen Kanal (Abbildung 1.1). Es wurde auch eine Vermessung der Polarfront bei 52°N, 33~ durchgeführt (Abbildung 1.2). Während der ganzen Zeit wurden hydrographische Parameter mit einem geschleppten Fisch-System gemessen. Strömungen an der Meeresoberfläche wurden mit einem elektromagnetischen Log und Strömungen in der Tiefe mit einem akustischen Stromprofiler gemessen. Ein Verzeichnis der gefahrenen Schnitte ist in Anhang 1 gegeben

Ingestion of Small-Bodied Zooplankton by Zebra Mussels (Dreissena polymorpha): Can Cannibalism on Larvae Influence Population Dynamics?

The zebra mussel Dreissena polymorpha established populations in western Lake Erie in 1986 and achieved densities exceeding 3.4 × 105 individuals∙m−2 during 1990. We assessed apparently incidental predation on Lake Erie and Erindale Pond zooplankton by adult mussels. Dreissena larvae and small rotifers (Polyarthra spp., Keratella spp., Trichocerca) sustained moderate to high predatory mortality whereas larger taxa (Bosmina, Scapholeberis) were invulnerable to predation. Larval Dreissena almost always sustain \u3e 99% mortality in European lakes. While mortality has been ascribed primarily to lack of suitable settling substrate and unfavourable environmental conditions, it may be confounded by larval predation by adults. We demonstrate using STELLA™-modelling that with a larval mortality rate of 99%, settled mussel densities observed in western Lake Erie during 1990 would not be achieved until at least 1994. A model that combines a lower rate (70%) of abiotic mortality with larval predation by adult mussels c..., Les populations de dreissena polymorphe (Dreissena polymorpha) déjà établies dans la partie ouest du lac Érié en 1986 atteignaient des densités supérieures à 3,4 × 105 individus par mètre carré au cours de 1990. Nous avons évalué Ta prédation du zooplancton du lac Érié et de l\u27étang Erindale par les dreissenas adultes. Les larves des dreissenas et les petits rotifères (Polyarthra spp., Keratella spp., Trichocerca) présentaient une mortalité par prédation variant de moyenne à élevée tandis que les plus gros taxons (Bosmima, Scapholeberis) résistaient à toute prédation. Les larves de Dreissena des lacs européeens présentent presque toujours un taux de mortalité supérieur à 99%. La mortalité a surtout été attribuée à l\u27absence d\u27un substrat de fixation adéquat et à des conditions environnementales défavorables, mais elle peut être confondue avec celle découlant de la prédation des larves par les adultes. Nous avons montré, à l\u27aide d\u27un modèle STELLAmd, que les densités de dreissenas fixées notées en 1990 n\u27..

Spherically Symmetric Solutions to Fourth-Order Theories of Gravity

Gravitational theories generated from Lagrangians of the form f(R) are considered. The spherically symmetric solutions to these equations are discussed, paying particular attention to features that differ from the standard Schwarzschild solution. The asymptotic form of solutions is described, as is the lack of validity of Birkhoff's theorem. Exact solutions are presented which illustrate these points and their stability and geodesics are investigated.Comment: 10 pages, published versio

Two-subband conduction in a gated high density InAlN/AlN/GaN heterostructure

Magnetotransport measurements on an In0.16Al0.84N/AlN/GaN gated Hall bar sample have been performed at 0.28 K. By the application of a gate voltage we were able to vary the total two-dimensional electron gas density from 1.83×1013 to 2.32×1013 cm−2. Two frequency Shubnikov–de Haas oscillations indicate occupation of two subbands by electrons. The density of electrons in the first and second sublevels are found to increase linearly with gate voltage with a slope of 2.01×1012 cm−2/V and 0.47×1012 cm−2/V, respectively. And the quantum lifetimes for the first and second subbands ranged from 0.55 to 0.95×10−13 s and from 1.2 to 2.1×10−13 s

Analytic Behaviour of Competition among Three Species

We analyse the classical model of competition between three species studied by May and Leonard ({\it SIAM J Appl Math} \textbf{29} (1975) 243-256) with the approaches of singularity analysis and symmetry analysis to identify values of the parameters for which the system is integrable. We observe some striking relations between critical values arising from the approach of dynamical systems and the singularity and symmetry analyses.Comment: 14 pages, to appear in Journal of Nonlinear Mathematical Physic

A dynamical system approach to higher order gravity

The dynamical system approach has recently acquired great importance in the investigation on higher order theories of gravity. In this talk I review the main results and I give brief comments on the perspectives for further developments.Comment: 6 pages, 1 figure, 2 tables, talk given at IRGAC 2006, July 200

Ultrafast decay of hot phonons in an AlGaN/AlN/AlGaN/GaN camelback channel

A bottleneck for heat dissipation from the channel of a GaN-based heterostructure field-effect transistor is treated in terms of the lifetime of nonequilibrium (hot) longitudinal optical phonons, which are responsible for additional scattering of electrons in the voltage-biased quasi-two-dimensional channel. The hot-phonon lifetime is measured for an Al0.33Ga0.67N/AlN/Al0.1Ga0.9N/GaN heterostructure where the mobile electrons are spread in a composite Al0.1Ga0.9N/GaN channel and form a camelback electron density profile at high electric fields. In accordance with plasmon-assisted hot-phonon decay, the parameter of importance for the lifetime is not the total charge in the channel (the electron sheet density) but rather the electron density profile. This is demonstrated by comparing two structures with equal sheet densities (1 × 1013 cm−2), but with different density profiles. The camelback channel profile exhibits a shorter hot-phonon lifetime of ∼270 fs as compared with ∼500 fs reported for a standard Al0.33Ga0.67N/AlN/GaN channel at low supplied power levels. When supplied power is sufficient to heat the electrons \u3e 600 K, ultrafast decay of hot phonons is observed in the case of the composite channel structure. In this case, the electron density profile spreads to form a camelback profile, and hot-phonon lifetime reduces to ∼50 fs