Image analysis of oil film interferometry — a method of measuring wall shear stress distributions

A method is described of measuring a wall shear stress distribution that varies in the direction of the flow. Variations in the height of a very thin oil film moving under the boundary layer generate interference fringes, which are recorded and digitised using image processing equipment.The evolution of the film surface in space and time can be reconstructed from the interference fringe patterns and used to calculate the shear stress field. This reconstruction is achieved by comparing the picture data with images that were calculated for prescribed heights that are adjusted iteratively, until the calculated intensities match the data.The method is applied to a flow approaching a step, and the results are compared with pulsed-wire measurements.     

Variational Analysis and Generalized Equations in Electronics

The paper is devoted to the study of the Aubin/Lipschitz-like property and the isolated calmness of a particular non-monotone generalized equation arising in electronics. The variational and non-smooth analysis is applied in the theory of non-regular electrical circuits involving electronic devices like ideal diodes, practical diodes, DIACs, silicon controlled rectifiers (SCR), and transistors. We also discuss the relationship of our results to the ones using classical techniques from (smooth) analysis and provide a simulation for several simple electrical circuits which are chosen in order to cover the most common non-smooth elements in electronics. The simulations of the electrical circuits discussed in this paper are performed by using Xcos (a component of Scilab).     

Towards a General Theory of Quantized Fields on the Anti-de Sitter Space-Time

 We propose a general framework for studying quantum field theory on the anti-de-Sitter space-time, based on the assumption of positivity of the spectrum of the possible energy operators. In this framework we show that the n-point functions are analytic in suitable domains of the complex AdS manifold, that it is possible to Wick rotate to the Euclidean manifold and come back, and that it is meaningful to restrict AdS quantum fields to Poincaré branes. We give also a complete characterization of two-point functions which are the simplest example of our theory. Finally we prove the existence of the AdS-Unruh effect for uniformly accelerated observers on trajectories crossing the boundary of AdS at infinity, while that effect does not exist for all the other uniformly accelerated trajectories. Received: 3 December 2001 / Accepted: 26 July 2002 Published online: 21 October 2002     

A nilregular element property

An element a of a commutative ring R is nilregular if and only if x is nilpotent whenever ax is nilpotent. More generally, an ideal I of R is nilregular if and only if x is nilpotent whenever ax is nilpotent for all a ∈ I . We give a direct proof that if R is Noetherian, then every nilregular ideal contains a nilregular element. In constructive mathematics, this proof can then be seen as an algorithm to produce nilregular elements of nilregular ideals whenever R is coherent, Noetherian, and discrete. As an application, we give a constructive proof of the Eisenbud-Evans-Storch theorem that every algebraic set in n-dimensional affine space is the intersection of n hypersurfaces.Received: 6 September 2004     

Response of plane viscous jet to entrance flow rate perturbation

A two‐dimensional numerical simulation solving unsteady incompressible Navier–Stokes equations is used to study the natural varicose instability of a plane jet in the Reynolds number range of 100–900. A transient train of vortices is observed at the beginning of the computation. It disappears yielding a steady flow. This flow is then used at the basis for forced excitation in order to study the space time development of instability. A Reynolds number dependant behaviour is observed which implies that viscosity directly affects the vortex dynamics. Copyright © 2001 John Wiley & Sons, Ltd.     

Nonorganic Habitual Dysphonia and Autonomic Dysfunction

The present study was designed to test the hypothesis that there is a relation between nonorganic habitual dysphonia and subjective experience of dysfunction of the autonomic nervous system (neurovegetative lability). Eighty-three patients (65 women and 18 men) with a nonorganic voice disorder and a matched control group answered a questionnaire of 46 questions. One question replicated in different terms and six nonrelevant questions point out that the inquiry forms were answered in a consistent way. It appears that female patients in all age categories with a nonorganic habitual dysphonia report significantly more autonomic symptoms and complaints than healthy controls. This hypothesis cannot be confirmed for the male subgroup.     

Energetic Properties of Rocket Propellants Evaluated through the Computational Determination of Heats of Formation of Nitrogen‐Rich Compounds

The use of ab initio and DFT methods to calculate the enthalpies of formation of solid ionic compounds is described. The results obtained from the calculations are then compared with those from experimental measurements on nitrogen‐rich salts of the 2,2‐dimethyltriazanium cation (DMTZ) synthesized in our laboratory and on other nitrogen‐rich ionic compounds. The importance of calculating accurate volumes and lattice enthalpies for the determination of heats of formation is also discussed. Furthermore, the crystal structure and hydrogen‐bonding networks of the nitroformate salt of the DMTZ cation is described in detail. Lastly, the theoretical heats of formation were used to calculate the specific impulses (I_sp) of the salts of the DMTZ cation in view of a prospective application in propellant formulations.