Classification of Processes by the Lyapunov exponent

This paper deals with the problem of the discrimination between wellpredictable and not-well-predictable time series. One criterion for the separation is given by the size of the Lyapunov exponent, which was originally defined for deterministic systems. However, the Lyapunov exponent can also be analyzed and used for stochastic time series. Experimental results illustrate the classification between well-predictable and not-well-predictable time series. --

A local defect resonance for linear and nonlinear ultrasonic thermography

An efficient wave-defect interaction is the key to a high thermal response of flaws in ultrasonic thermography. To selectively enhance defect vibrations a concept of local defect resonance is developed and applied to ultrasonic activation of defects. The frequency match between the defect resonance frequency and the probing ultrasonic wave results in a substantial rise of a local defect temperature. The defect resonance is accompanied by depletion of the excitation frequency vibration due to nonlinear frequency conversion to higher harmonics. The local generation of higher frequency components provides a high thermal defect response in such an acoustically nonlinear thermography mode

Turbulent Fluid Flow Over Aerodynamically Rough Surfaces Using Direct Numerical Simulations

Incompressible turbulent fluid flow in aerodynamically rough channels is investigated using direct numerical simulations. A comprehensive database of simulation data for rough surfaces with different topographical properties has been developed for 17 industrially relevant rough surface samples. It includes numerous commonlyseen industrial rough surfaces such as concrete, graphite, carbon-carbon composite and ground, shotblasted and spark-eroded steel. Other surfaces such as cast, filed and gritblasted steel are also studied, along with replicas of ship propeller surfaces eroded by periods of service. The Reynolds number considered is Reτ = 180, for which the flow is in the transitionally rough regime. A study with variable δ/Sq ratio while keeping S + q constant, where Sq is the root mean squared roughness height, is conducted for one of the samples with the mean profiles showing convergence for δ/Sq >≈ 25. A Reynolds number dependence study is conducted for two of the samples with Reτ up to 720 showing a more complete range up to the fully rough flow regime, allowing the equivalent sandgrain roughness height, ks to be computed. A correlation based on the frontal and wetted roughness area is found to be superior to the surface skewness in predicting ∆U + based on the topographic surface parameters

Restructuring and Recovery of Output in Russia

The Economic Transition and Integration (ETI) Project at the International Institute for Applied Systems Analysis (IIASA) has built on the institute's tradition of promoting collaborative research between East and West. The ETI Project's proven ability in dealing with issues pertaining to the transformation from central planning to market economies has been valuable for policy-makers and scientists alike. As a result, the government of the Russian Federation turned in 1992 to the ETI Project to organize a series of seminars and provide reports on topics of concern to the government. The Ford Foundation and Pew Charitable Trusts have generously provided financial support for the seminar series. This report summarizes the contribution of participants at a seminar held at IIASA on 9-11 June 1994, "Restructuring and Recovery of Output in Russia". This workshop had several goals: to understand the root causes and effects of the recent enormous output decline in Russia, to assess the amount of restructuring that has occurred in Russia, and to develop a path of restructuring for recovery of output in Russia. Insights into this broad agenda were made through seminar sections on macroeconomics and public policy, enterprise behavior, unemployment, and domestic and international competition. Under the rubric of these topics, seminar participants presented papers and had discussions ranging from the role of subsidies to measurement problems, from output to employment decline and their relationship to regulation and trade issues. When available, comparisons to the transition experiences of Central European countries were used. This wide array of paper presentations and discussions was moved to greater depth by the intense willingness of workshop participants from Russia, Central and Eastern Europe, and the West to share their experiences and engage each other with provocative thoughts. Through this process, the workshop was able to move toward a better understanding of what has occurred to output decline and restructuring as well as what the best path to further restructuring and output recovery will be for Russia's future

Classification of Processes by the Lyapunov exponent

This paper deals with the problem of the discrimination between well-predictable and not-well-predictable time series. One criterion for the separation is given by the size of the Lyapunov exponent, which was originally defined for deterministic systems. However, the Lyapunov exponent can also be analyzed and used for stochastic time series. Experimental results illustrate the classification between well-predictable and not-well-predictable time series

Comparing Time Series from Experiments with and without Spiralling

In this paper we compare data from BTA deep-hole drilling experiments conducted according to an experimental design, which had to be repeated due to the development of spiralling in all experiments in the first repetition. We compare the time series of the drilling torque and the bending moment with respect to the development of the maximal Lyapunov-Exponent and the overall relevant frequencies and the relevant frequencies on sections of the process. --

Mean flow instabilities of two-dimensional convection in strong magnetic fields

The interaction of magnetic fields with convection is of great importance in astrophysics. Two well-known aspects of the interaction are the tendency of convection cells to become narrow in the perpendicular direction when the imposed field is strong, and the occurrence of streaming instabilities involving horizontal shears. Previous studies have found that the latter instability mechanism operates only when the cells are narrow, and so we investigate the occurrence of the streaming instability for large imposed fields, when the cells are naturally narrow near onset. The basic cellular solution can be treated in the asymptotic limit as a nonlinear eigenvalue problem. In the limit of large imposed field, the instability occurs for asymptotically small Prandtl number. The determination of the stability boundary turns out to be surprisingly complicated. At leading order, the linear stability problem is the linearisation of the same nonlinear eigenvalue problem, and as a result, it is necessary to go to higher order to obtain a stability criterion. We establish that the flow can only be unstable to a horizontal mean flow if the Prandtl number is smaller than order , where B0 is the imposed magnetic field, and that the mean flow is concentrated in a horizontal jet of width in the middle of the layer. The result applies to stress-free or no-slip boundary conditions at the top and bottom of the layer

Employment and Unemployment in Russia from Microeconomic Perspective

The Economic Transition and Integration (ETI) Project at the International Institute for Applied Systems Analysis (IIASA) has built on the institute's tradition of promoting collaborative research between East and West. The ETI Project's proven ability in dealing with issues pertaining to the transformation from central planning to market economies has been valuable for policy-makers and scientists alike. As a result, the government of the Russian Federation turned in 1992 to the ETI Project to organize a series of seminars and provide reports on topics of concern to the government. The Ford Foundation and Pew Charitable Trusts have generously provided financial support for the seminar series. This report summarizes the contribution of participants at a seminar held at IIASA on 23-25 June 1994 "Employment and Unemployment in Russia from a Microeconomic Perspective." This workshop was an attempt to deepen the understanding of and unveil some of the mysteries in Russian employment and unemployment. Topics ranged from the demographics of employment to the lack of unemployment despite severe output declines, and from in-depth studies of certain sectors and industries to comparisons with some Central European employment circumstances. More specifically, seminar participants presented papers and had discussions in five research areas: recent developments in employment and unemployment, adjustments in the use of labor, case studies, the experience of East European countries in unemployment concentrated to regions and sectors, and finally future prospects of employment. This wide array of paper presentations and discussions was enhanced by the willingness of workshop participants from Russia, Central and Eastern Europe, and the West to share their experiences and engage each other with provocative thoughts. Through this iterative process, the workshop was successful in shedding light on the empirical facts of employment and unemployment, better understand some mysteries surrounding facets of this data, and in the end make some valuable speculation about the future of employment and unemployment in Russia

Comparing Time Series from Experiments with and without Spiralling

In this paper we compare data from BTA deep-hole drilling experiments conducted according to an experimental design, which had to be repeated due to the development of spiralling in all experiments in the first repetition. We compare the time series of the drilling torque and the bending moment with respect to the development of the maximal Lyapunov-Exponent and the overall relevant frequencies and the relevant frequencies on sections of the process