Transatmospheric vehicle research

Research was conducted into the alternatives to the supersonic combustion ramjet (scramjet) engine for hypersonic flight. A new engine concept, the Oblique Detonation Wave Engine (ODWE) was proposed and explored analytically and experimentally. Codes were developed which can couple the fluid dynamics of supersonic flow with strong shock waves, with the finite rate chemistry necessary to model the detonation process. An additional study was conducted which compared the performance of a hypersonic vehicle powered by a scramjet or an ODWE. Engineering models of the overall performances of the two engines are included. This information was fed into a trajectory program which optimized the flight path to orbit. A third code calculated the vehicle size, weight, and aerodynamic characteristics. The experimental work was carried out in the Ames 20MW arc-jet wind tunnel, focusing on mixing and combustion of fuel injected into a supersonic airstream. Several injector designs were evaluated by sampling the stream behind the injectors and analyzing the mixture with an on-line mass spectrometer. In addition, an attempt was made to create a standing oblique detonation wave in the wind tunnel using hydrogen fuel. It appeared that the conditions in the test chamber were marginal for the generation of oblique detonation waves

Analytical and experimental investigations of the oblique detonation wave engine concept

Wave combustors, which include the Oblique Detonation Wave Engine (ODWE), are attractive propulsion concepts for hypersonic flight. These engines utilize oblique shock or detonation waves to rapidly mix, ignite, and combust the air-fuel mixture in thin zones in the combustion chamber. Benefits of these combustion systems include shorter and lighter engines which will require less cooling and can provide thrust at higher Mach numbers than conventional scramjets. The wave combustor's ability to operate at lower combustor inlet pressures may allow the vehicle to operate at lower dynamic pressures which could lessen the heating loads on the airframe. The research program at NASA-Ames includes analytical studies of the ODWE combustor using CFD codes which fully couple finite rate chemistry with fluid dynamics. In addition, experimental proof-of-concept studies are being carried out in an arc heated hypersonic wind tunnel. Several fuel injection designs were studied analytically and experimentally. In-stream strut fuel injectors were chosen to provide good mixing with minimal stagnation pressure losses. Measurements of flow field properties behind the oblique wave are compared to analytical predictions

Perioperative care of a child with tetanus

Tetanus is caused by tetanospasmin, a toxin that is produced by the anaerobic bacterium, Clostridium tetani. Despite widespread vaccination, which limits its incidence in many parts of the world, tetanus may still occur owing to lack of immunisation related to religious tenets, cultural beliefs or inaccessibility to medical care. Of major concern during the perioperative care of such patients is control of the muscle spasms and the propensity for autonomic dysfunction, resulting in blood pressure instability. Ongoing muscle spasms may impair upper airway control or respiratory muscle function, thereby resulting in respiratory failure. Autonomic dysfunction may result in profound hypertension followed by hypotension, bradycardia and asystole. The pathophysiology of tetanus, its clinical manifestations, and current treatment options are discussed. The preoperative implications of tetanus and the care of these patients are reviewed.South Afr J Anaesth Analg, 2011;17(6):380-38

Wave combustors for trans-atmospheric vehicles

The Wave Combustor is an airbreathing hypersonic propulsion system which utilizes shock and detonation waves to enhance fuel-air mixing and combustion in supersonic flow. In this concept, an oblique shock wave in the combustor can act as a flameholder by increasing the pressure and temperature of the air-fuel mixture and thereby decreasing the ignition delay. If the oblique shock is sufficiently strong, then the combustion front and the shock wave can couple into a detonation wave. In this case, combustion occurs almost instantaneously in a thin zone behind the wave front. The result is a shorter, lighter engine compared to the scramjet. This engine, which is called the Oblique Detonation Wave Engine (ODWE), can then be utilized to provide a smaller, lighter vehicle or to provide a higher payload capability for a given vehicle weight. An analysis of the performance of a conceptual trans-atmospheric vehicle powered by an ODWE is given here

Ostracods, rock facies and magnetic susceptibility of the Trois-Fontaines and Terres d’Haurs Formations (Early Givetian) in the Rancennes quarry at the Mont d’Haurs (Givet, France)

About 1,200 ostracods were extracted from 64 samples collected in the upper part of the Trois-Fontaines Formation (Fm) and in the base of the Terres d’Haurs Fm in the Rancennes quarry located along the western rampart of an historic entrenched military camp at the Mont d’Haurs (southern part of the Dinant Synclinorium, Ardennes Department, France). The ostracod richness and diversity are quite variable, and monospecificity prevails in numerous samples. Forty-nine ostracod species are recognised. In the Trois-Fontaines Fm, environments were lagoonal or semi-restricted, and the level containing numerous Leperditicopid ostracods (Herrmannina) indicative of (brackish?) lagoonal environments is 40 m thick. In the Terres d’Haurs Fm the environment was semi-restricted or more frequently shallow marine but the energy of the environment was apparently never very high. The level rich in Leperditicopida (Herrmannina) in the Trois-Fontaines Fm corresponds remarkably to the highest magnetic susceptibility (MS) value. The Rancennes microfacies point to a tidal flat system with various subenvironments such as restricted intertidal, supratidal and channel deposits. The system was bordered by subtidal open marine deposits where former reefal constructions have been destroyed. Frequent oscillations in this low-gradient shallow platform led to the exposure and modification of marginal ponds, floodplain environments or palustrine areas. No evidence of evaporitic environments or sabkha were encountered. The sedimentary system records the evolution of a shallow restricted carbonate platform (Trois-Fontaines Fm) to a carbonate ramp setting (Terres d’Haurs Fm). The evolution of the platfom to a ramp could be related to the cessation of the active role of a reefal barrier possibly as a response to synsedimentary tectonism and block faulting.The magnetic susceptibility curve established for the Rancennes quarry highlights 26 short-term magnetic evolutions that can be grouped into 10 major long-term magnetic sequences characterized by decreasing, increasing or stable magnetic susceptibility fluctuations. Magnetic susceptibility values range between 3.75 x 10-9 and 2.98 x 10-7 m³/kg. There is a general good correspondence between the microfacies and magnetic susceptibility curves, which are clearly mimetic at the smaller scale (i.e., 5th-order parasequences). The magnetic susceptibility curve could thus be interpreted as sea-level oscillations. A part of the magnetic minerals carrying the MS signal must have a detrital origin. Magnetization and coercivity ratios deduced from hysteresis loops indicate the presence of detrital coarse-grained multi-domain magnetite and authigenic mixtures of fine-grained superparamagnetic and single-domain magnetite. The MS signal of the Rancennes quarry seems to be controlled by the ferrimagnetic fraction (magnetite) with minor paramagnetic contribution (clay minerals and pyrite).The Rancennes quarry completes the stratotype of the Terres d’Haurs Fm because the section exposes the boundary with the Trois-Fontaines Fm unlike the previously proposed stratotype located on the south-eastern flank of the Mont d’Haurs entrenched camp

On some singularities of the correlation functions that determine neutrino opacities

Certain perturbation graphs in the calculation of the effects of the medium on neutrino scattering in supernova matter have a nonintegrable singularity in a physical region. A number of papers have addressed the apparent pathology through an ansatz that invokes higher order (rescattering) effects. Taking the Gamow-Teller terms as an example, we display an expression for the spin-spin correlation function that determines the cross-sections. It is clear from the form that there are no pathologies in the order by order perturbation expansion. Explicit formulae are given for a simple case, leading to an answer that is very different from one given by other authors.Comment: 8 page

The Use of Steady and Pulsed Detonations for Propulsion Systems

Objectives of the ODWE concept studies are: demonstrate the feasibility of the oblique detonation wave engine (ODWE) for hypersonic propulsion; demonstrate the existance and stability of an oblique detonation wave in hypersonic wind tunnels; develop engineering codes which predict the performance characteristics of the ODWE including specific impulse and thrust coefficients for various operating conditions; develop multi-dimensional computer codes which can model all aspects of the ODWE including fuel injection, mixing, ignition, combustion and expansion with fully detailed chemical kinetics and turbulence models; and validate the codes with experimental data use the simulations to predict the ODWE performance for conditions not easily obtained in wind tunnels