Gasdynamic wave interaction in two spatial dimensions

We examine the interaction of shock waves by studying solutions of the two-dimensional Euler equations about a point. The problem is reduced to linear form by considering local solutions that are constant along each ray and thereby exhibit no length scale at the intersection point. Closed-form solutions are obtained in a unified manner for standard gasdynamics problems including oblique shock waves, Prandtl–Meyer flow and Mach reflection. These canonical gas dynamical problems are shown to reduce to a series of geometrical transformations involving anisotropic coordinate stretching and rotation operations. An entropy condition and a requirement for geometric regularity of the intersection of the incident waves are used to eliminate spurious solutions. Consideration of the downstream boundary conditions leads to a formal determination of the allowable downstream matching criteria. By retaining the time-dependent terms, an approach is suggested for future investigation of the open problem of the stability of shock wave interactions

Simple, adjustable beam splitting element for differential interferometers based on photoelastic birefringence of a prismatic bar

We examine the prototypical Toepler optical arrangement for the visualization of phase objects and consider the effect of different contrast elements placed at the focus of the source. In particular, Wollaston prism beam splitting elements based on the crystallographic birefringence of calcite or quartz find application in differential interferometry systems based on the Toepler arrangement. The focus of the current article is a simple low cost alternative to the Wollaston prism that is realized by inserting a prismatic bar constructed of a photoelastic material into the optical path. It is shown that, under the action of an applied bending moment, the prismatic bar functions as a first-order approximation to a Wollaston prism. Results are derived for the divergence angle of the beam splitter for orthogonally polarized rays. The implementation of a practical device is discussed and representative experimental results are presented, taken from the field of shock wave visualization in supersonic flow

Identification of a CD4+ T cell-stimulating antigen of pathogenic bacteria by expression cloning.

Identifying the immunogenic proteins that elicit pathogen-specific T cell responses is key to rational vaccine design. While several approaches have succeeded in identifying major histocompatibility complex (MHC) class I bound peptides that stimulate CD8+ T cells, these approaches have been difficult to extend to peptides presented by MHC class II molecules that stimulate CD4+ T cells. We describe here a novel strategy for identifying CD4+ T cell-stimulating antigen genes. Using Listeria monocytogenes-specific, lacZ-inducible T cells as single-cell probes, we screened a Listeria monocytogenes genomic library as recombinant Escherichia coli that were fed to macrophages. The antigen gene was isolated from the E. coli clone that, when ingested by the macrophages, allowed generation of the appropriate peptide/MHC class II complex and T cell activation. We show that the antigenic peptide is derived from a previously unknown listeria gene product with characteristics of a membrane-bound protein

Precedence relationship representations of mechanical assembly sequences

Two types of precedence relationship representations for mechanical assembly sequences are presented: precedence relationships between the establishment of one connection between two parts and the establishment of another connection, and precedence relationships between the establishment of one connection and states of the assembly process. Precedence relationship representations have the advantage of being very compact. The problem with these representations was how to guarantee their correctness and completeness. Two theorems are presented each of which leads to the generation of one type of precedence relationship representation guaranteeing its correctness and completeness for a class of assemblies

Spatio-textual indexing for geographical search on the web

Many web documents refer to specific geographic localities and many people include geographic context in queries to web search engines. Standard web search engines treat the geographical terms in the same way as other terms. This can result in failure to find relevant documents that refer to the place of interest using alternative related names, such as those of included or nearby places. This can be overcome by associating text indexing with spatial indexing methods that exploit geo-tagging procedures to categorise documents with respect to geographic space. We describe three methods for spatio-textual indexing based on multiple spatially indexed text indexes, attaching spatial indexes to the document occurrences of a text index, and merging text index access results with results of access to a spatial index of documents. These schemes are compared experimentally with a conventional text index search engine, using a collection of geo-tagged web documents, and are shown to be able to compete in speed and storage performance with pure text indexing

Which User Interaction for Cross-Language Information Retrieval? Design Issues and Reflections

A novel and complex form of information access is cross-language information retrieval: searching for texts written in foreign languages based on native language queries. Although the underlying technology for achieving such a search is relatively well understood, the appropriate interface design is not. This paper presents three user evaluations undertaken during the iterative design of Clarity, a cross-language retrieval system for rare languages, and shows how the user interaction design evolved depending on the results of usability tests. The first test was instrumental to identify weaknesses in both functionalities and interface; the second was run to determine if query translation should be shown or not; the final was a global assessment and focussed on user satisfaction criteria. Lessons were learned at every stage of the process leading to a much more informed view of what a cross-language retrieval system should offer to users

Transient heat flux measurement using a surface junction thermocouple

A new form of surface junction thermocouple sensor has been developed and tested. The novel feature of the design is the use of a tapered fit between two coaxial thermocouple elements to form a thin, robust junction. The gauge has a response time on the order of 1 µs and is suitable for measuring large transient heat fluxes in hypervelocity wind tunnels. Asymptotic analysis is used to demonstrate the operating principles and to assess the errors associated with the finite thickness of the surface junction. Spectral deconvolution methods are used to infer a mean square optimal estimate of the surface heat flux from time resolved surface temperature measurements. This improved signal processing method is applicable to transient heat flux gauges of all types. Potential reducible error sources and other systematic errors are described. Measurements of the heat flux about the forebody of a cylindrical body in a hypervelocity flow demonstrate the functioning of the gauge and are used to obtain statistical estimates of the repeatability of the technique. The measured heat fluxes are compared with established theoretical predictions

Aspects of planar, oblique and interacting shock waves in an ideal dissociating gas

We develop a compact dimensionless framework for the analysis of canonical thermo-chemical nonequilibrium flow fields involving normal, oblique and interacting shock waves. Discontinuous solutions of the conservation equations are coupled with thermodynamic and kinetic models for an ideal dissociating gas. Convenient forms are provided for the variation of the relevant dimensionless parameters across shock waves in dissociating gases. The treatment is carried through in a consistent manner for the pressure–flow deflection angle plane representation of shock wave interaction problems. The contribution of the current paper is a careful nondimensionalization of the problem that yields a tractable formulation and allows results with considerable generality to be obtained

Development of the children's eating behaviour questionnaire

Individual differences in several aspects of eating style have been implicated in the development of weight problems in children and adults, but there are presently no reliable and valid scales that assess a range of dimensions of eating style. This paper describes the development and preliminary validation of a parent-rated instrument to assess eight dimensions of eating style in children; the Children's Eating Behaviour Questionnaire (CEBQ). Constructs for inclusion were derived both from the existing literature on eating behaviour in children and adults, and from interviews with parents. They included reponsiveness to food, enjoyment of food, satiety responsiveness, slowness in eating, fussiness, emotional overeating, emotional undereating, and desire for drinks. A. large pool of items covering each of these: constructs was developed. The number of items was then successively culled through analysis of responses from three samples of families of young children (N = 131; N = 187, N = 218), to produce a 35-item instrument with eight scales which were internally valid and had good test-retest reliability. Investigation of variations by gender and age revealed only minimal gender differences in any aspect of eating style. Satiety responsiveness and slowness in eating diminished from age 3 to 8. Enjoyment of food and food responsiveness increased over this age range. The CEBQ should provide a useful measure of eating style for research into the early precursors of obesity or eating disorders. This is especially important in relation to the growing evidence for the heritability of obesity, where good measurement of the associated behavioural phenotype will be crucial in investigating the contribution of inherited variations in eating behaviour to the process of weight gain