Nonequilibrium Blunt Body Flows in Ionized Gases

The behaviors of electrons and electronically excited atoms in non-equilibrium and partially ionized blunt-body-flows are described. Formulation has been made separately in a shock layer and in a free stream, and then the free stream solution has been connected with the shock layer solution by matching the two solutions at the shock layer edge. The method of this matching is described here. The partially ionized gas is considered to be composed of neutral atoms, ions and electrons. Furthermore, the neutral atoms are divided into atoms in excited levels. Therefore, it is considered that electron energy released due to excitation, and that gained due to de-excitation, contribute to electron energy. Thus, the electron energy equation including these contributions is solved, coupled with the continuity equations of the excited atoms and the electrons. An electron temperature distribution from a free stream to a blunt body wall has been investigated for a case when the electrons are in thermal non-equilibrium with heavy particles in the free stream. In addition, the distributions of the excited atom density are discussed in the present analysis

Diagnostics of Shock Tube Flows by Laser Interferometry

In this paper, the diagnostics of shock tube flows by a laser differential interferometer using Wollaston prisms is described. This method has some advantages. It can apply to a case in which the optical path change is only a small fraction of the wave length, and the influence of vibration and laser ripple can be suppressed whereby excellent resolutions in space and time are obtained. In the present work, this method was applied to the measurements of the density change across a shock generated in a shock tube and a shock Mach number. From the investigations of the incident shock, reflected shock and contact surface, it was concluded that the influence of the boundary layer on the side and end wall becomes large when the initial pressure in the test chamber is less than 1.0 kPa. It was also concluded that a strong interaction of the reflected shock with the side-wall boundary layer is caused for air. Through these experiments, a technique of the density measurement by means of this interferometer has been established. It was confirmed that this method is an excellent way for density measurements in a case where the density change is very small

Experimental and Numerical Investigations of Annular Freejets

The structure of an axisymmetric freejet issuing from an annular orifice is described for the stagnation chamber to ambient pressure ratio of 13. The flowfield is numerically calculated. In the calculations, the physical plane is transformed to the computational one because of taking more grid points in the vicinity of the orifice. For two-dimensional calculations, the operator splitting method is used, and also the two-step Lax-Wendroff scheme is applied to each operator. To verify the computational data, laser interferometry is employed to determine the density in the freejet. The radially resolved densities are determined by means of the Abel inversion. The experimental results show a fairly good agreement with the computational results

Population Density Measurements in a Supersonic Freejet Expansion Flow of an O₂-seeded Ar Plasma

The population densities of O(3p³P) and O(3p⁵P) were measured along the freejet centerline of an O₂-seeded Ar plasma, which was such that oxygen gas was seeded into a pre-ionized argon plasma. The ratio of the measured population densities of the 3p³P and 3p⁵P states was compared with the predicted ratio, which was determined from a steady state population assumption of O(3p⁵P), over the whole region of the freejet. The comparison showed that on the condition Nₑ=1.8×10¹³-1.7×10¹²cm⁻³ Tₑ= 3000-900 K and p＝48-0.19 Pa, the 3p⁵P state is populated by electron-collisional de-excitations of the 3p³P state, rather than by quenching of the 3p³P state by the ground state argon. Further, the 3p⁵P state is de-populated by electron-collisional de-excitations rather than by radiative de-excitations

Design and Performance Tests of a Low Power DC Arcjet Thruster

This paper describes a quasi-one-dimensional flow model which can be used for the design of an arcjet thruster. Owing to the simplicity of the model, the performance characteristics of the thruster can be calculated easily for finding an optimum configuration suitable for various missions. In order to verify adequacy of the model, a thruster was fabricated and its performance characteristics were measured. The experimental results were compared with the calculation predicted with the model. Both are in satisfactory agreement, and it is concluded that this flow model is a useful tool for the design of the arcjet thruster

Electron-Temperature and Ion-Density Measurements in Partially Ionized Boundary Layer on a Flat Plate

Electron temperatures and ion densities have been measured with a cylindrical Langmuir probe in a partially ionized boundary layer flow on a flat plate. The experiments have been carried out in a low density plasma wind tunnel with argon as the test gas at local freestream Mach number of 3.5. The experimental and theoretical results have been compared, and a good agreement has been obtained for the electron temperature profile. For the ion density profile, the experimental results have qualitatively agreed fairly well with the theoretical ones

Evolution of feeding specialization in Tanganyikan scale-eating cichlids: a molecular phylogenetic approach

<p>Abstract</p> <p>Background</p> <p>Cichlid fishes in Lake Tanganyika exhibit remarkable diversity in their feeding habits. Among them, seven species in the genus <it>Perissodus </it>are known for their unique feeding habit of scale eating with specialized feeding morphology and behaviour. Although the origin of the scale-eating habit has long been questioned, its evolutionary process is still unknown. In the present study, we conducted interspecific phylogenetic analyses for all nine known species in the tribe Perissodini (seven <it>Perissodus </it>and two <it>Haplotaxodon </it>species) using amplified fragment length polymorphism (AFLP) analyses of the nuclear DNA. On the basis of the resultant phylogenetic frameworks, the evolution of their feeding habits was traced using data from analyses of stomach contents, habitat depths, and observations of oral jaw tooth morphology.</p> <p>Results</p> <p>AFLP analyses resolved the phylogenetic relationships of the Perissodini, strongly supporting monophyly for each species. The character reconstruction of feeding ecology based on the AFLP tree suggested that scale eating evolved from general carnivorous feeding to highly specialized scale eating. Furthermore, scale eating is suggested to have evolved in deepwater habitats in the lake. Oral jaw tooth shape was also estimated to have diverged in step with specialization for scale eating.</p> <p>Conclusion</p> <p>The present evolutionary analyses of feeding ecology and morphology based on the obtained phylogenetic tree demonstrate for the first time the evolutionary process leading from generalised to highly specialized scale eating, with diversification in feeding morphology and behaviour among species.</p

Electrostatic Probe Measurements in Argon Plasma Boundary Layer

A combined experimental and numerical investigation was conducted in a partially ionized boundary layer flow on a flat plate. The experiments were carried out in a low-density plasma wind tunnel, with argon as the test gas at the local freestream Mach number of 4.4. A cylindrical Langmuir probe was used to measure the ion number density and the electron temperature in the boundary layer. The effect of flush probe size, bias and flow properties were examined. Numerical calculations were made by using the charged species conservation and electron energy equations in the quasineutral region of the boundary layer, except for a thin plasma sheath. Numerical profiles of the ion number density and the electron temperature agreed fairly well with the experimental results. Also, ambipolar diffusion fluxes theoretically predicted agreed very well with the flush probe ion saturation current measured by a flush probe

A PROGRAMMING ENVIRONMENT FOR NOVICES WITH VISUAL BLOCK AND TEXTUAL INTERFACES

Abstract Visual block languages such as Scratc