On the Distribution and Scaling of Convective Wavespeeds in the Shear Layers of Heated Supersonic Jets

The noise generated by supersonic plumes is of growing concern given the enormous peak noise intensity radiated by tactical aircraft engines. A key component of this noise is the enhanced radiation of mixing noise caused by large scale eddies convecting supersonically relative to the surrounding quiescent medium. As very little data exist for eddy convection in high Reynolds number, supersonic plumes, our current ability to develop concepts that alter compressible eddy convection is limited. Herein we present new experimental data of eddy convective wavespeeds in the developing shear layer of supersonic heated jets. A new scaling of the wavespeed in radial similarity coordinates is proposed which takes into account the influence of the ratio of static densities between the jet and ambient streams. In particular, we observe a structural change in wavespeed spectra at the end of the potential core—in addition to high turbulence levels, the potential core breakdown region can have enhanced eddy wavespeeds, increasing noise radiation efficiency. The results provide a first examination of the interplay of density ratio effects and the dynamic breakdown process of the potential core in supersonic jets—physics integral to the noise generation process.     

Mathematikgeschichte für Lehrer – Gründe und Beispiele

Zusammenfassung. Die folgenden überlegungen beinhalten ein Pl?doyer für die verbindliche Einführung einer Vorlesung über Mathematikgeschichte in die Lehrerbildung. Es wird dargestellt, warum eine solche Veranstaltung n?tig und wünschenswert ist. Dann wird an Beispielen gezeigt, was Inhalte und Botschaft sein k?nnten. In einem dritten Schritt wird eine p?dagogische Konzeption für die Einbeziehung historischer Inhalte in den Mathematikunterricht skizziert. Eingegangen am 15.5.1995 / Angenommen am 30.10.1995     

Light-polarization and intensity dependence of higher-order nonlinearities in excitonic FWM signals

A theory-experiment comparison for the intensity and polarization dependence of spectrally resolved transient four-wave-mixing signals is presented for a ZnSe single quantum well. Results for high intensities deviate from a simple model based on the optical Bloch equations for a five-level system whereas a microscopic theory for coherent excitonic and biexcitonic nonlinearities shows excellent agreement.Received: 8 July 2004, Published online: 14 December 2004PACS: 71.35.-y Excitons and related phenomena - 78.47. + p Time-resolved optical spectroscopies and other ultrafast optical measurements in condensed matter     

Efficient approximations of univariate nonlinearities for linear planning models

Univariate nonlinearities occur either if the variables or parameters of a planning model are nonlinear functions of time, or if linear functions of time are multiplied by each other. Moreover, cost functions or revenue functions consist in most cases of univariate nonlinear terms. These nonlinearities are approximated by several types of piecewise-linear functions either particularly or simultaneously. In the case of linearizing nonlinearities in the decision variables it should be mentioned that the results of the approximation can only be used for linear models, if the convexity of the set of feasible solutions is guaranteed. Since the approximating procedure is based on variable nodes, the fit may be improved by optimizing the positions of these nodes. Therefore, this approach yields a far better fit than an approximation on the basis of equidistant and fixed nodes. As the number of variables and restrictions in linearized models increases according to the number of approximating intervals, the number of nodes determines substantially the size of a LP-model and therefore the expenses of a planning approach. Using the procedure described here, the number of approximating intervals will be minimal at a given goodness of fit and the model's size may be effectively reduced. On the other hand, for a certain number of intervals the most efficient approximation is found.     

Pulsed-field gel electrophoresis analysis of a Pseudomonas aeruginosa pathovar.

This paper presents the genome organization and mobility of Pseudomonas aeruginosa strains that had been isolated in half-year intervals from 30 patients with cystic fibrosis since the onset of colonization over a 2- to 8-year period. The chromosomes were digested with DraI or SpeI, separated by pulsed-field gel electrophoresis, blotted and hybridized with probes encoding housekeeping or virulence genes. Strains were differentiated by relatedness of macrorestriction fingerprints. After some turnover of strains during the first two years of colonization, each patient had acquired a set of strains that diversified during the course of the disease. In the majority of patients, two clonal lineages were found to account for colonization in the air passages but each lung habitat was characterized by some specific signature of bands in the macrorestriction fragment pattern.     

OR at Work in Modern Manufacturing

By describing the industrial assembly of a real product, methodologies and considerations are discussed for the re-alignment of discrete assembly systems in line with modern standards. Poor manufacturing procedures are highlighted, and a number of alternative strategies for system replacement are presented. A decision tree is used to categorize assembly into one of three types, and an integrated solution is proposed. The possible financial benefits, essential to maintain market position, are identified for each stage of an evolutionary cycle of continuous product design and changing manufacturing methods.     

Application of a novel lipophilized fluorescent dye in an optical nitrate sensor

A new lipophilic pH probe (1-hydroxypyrene-3,6,8-tris-octadecylsulfonamide) has been synthesized, and its spectral properties and applications in a solid state nitrate sensor are shown. The sensor is investigated with respect to sensitivity, limits of detection, and selectivity over other anions found in drinking water.Abbreviations used HPTS trisodium-1-hydroxy-pyrene-3,6,8-trisul-fonate - HPTS-TO 1-hydroxypyrene-tris-3,6,8-octadecylsulfonamide - TDMACl tridodecylmethylammonium chloride - PVC poly(vinyl chloride) - DOS bis-(2-ethylhexyl)-sebacate - THF tetrahydrofurane - DMF dimethylformamide