116 research outputs found
Nonlinear ultrasonic spectroscopy using ESAM and DORT symbiosis
No full textNational audienceCombination of DORT (Décomposition de lOpérateur du Retournement Temporel) and ESAM (Excitation Symmetry Analysis Method) presented as a powerful tool for detection and localization of defects by analysis of their nonlinear signature[1,2]. The third order nonlinear responses are extracted from ESAM eigen-excitations and constitute the multistatic data matrix associated with the singular value decomposition. The symbiosis of ESAM-DORT provides a normalization process of singular values associated with scatterers, validated with simulations and experiments of acoustic propagation[3]. Piezoelectric transducers are used for both excitation and data acquisition. Transmitters consequently emit the excitation signals and corresponding responses are measured by the array of receivers. The amplitude of excitation signals is variable as to separate the nonlinear parts of the measured signal. ESAM signal pre-processing is used for nonlinear parts extraction. Separated signal records form linear and nonlinear multistatic data matrices. DORT method is applied on data matrices to separate echoes of defects in the tested medium. Data obtained from DORT method are used for evaluation of nonlinear parameters corresponding to separated defects and also for their localization. The procedure is completed by visualization of nonlinear signatures of detected defects which is referred to as pseudotomographic imaging. This ESAM-DORT approach improves the performance of the local TR-NEWS methods, which can be applied to the tomography of structural defects [1] C. Prada, S. Manneville, D. Spoliansky, and M. Fink, Decomposition of the time reversal operator: Detection and selective focusing on two scatterers , J. Acoust. Soc. Am., vol. 99, pp. 20672076, 1996. [2] S. Dos Santos and C. Plag, Excitation symmetry analysis method (ESAM) for calculation of higher order nonlinearities, International Journal of Non-Linear Mechanics, vol. 43, pp. 164169, 2008. [3] S. Dos Santos, S. Vejvodova, and Z. Prevorovsky, Local Nonlinear Scatterers Signature using Symbiosis of the Time-Reversal Operator and Symmetry Analysis Signal Processing, J. Acoust. Soc. Am. (2009) in pres
Inflation in Czechoslovakia, 1985-91
No full textThe authors assess inflation in Czechoslovakia between 1985 and 1991 and identify the main causes of inflation through a literature survey and empirical studies. The official prices in centrally planned economies were never perceived by central planners to be fully market clearing. Only by coincidence would the overall price level correspond to the level associated with general equilibrium. What is missing in official price indices in centrally planned economies - including the consumer price index - is suppressed inflation, manifast in queuing for products, forced substitution of demand, and forced savings. Also missing is hidden inflation, associated with practices that disguise price increases behind cosmetic or other change in product quality. The authors argue that inflationary pressures in Czechoslovakia in 1985-89 originated mainly in the investment sector. Even though the investment sector was strictly controlled, making it difficult for open inflation to emerge, the scope for inflationary pressures was great in Czechoslovakia. Such pressures arose from a mixture of factors, including poor investment planning, accommodating government finance, and the high priority given to investments and social consumption. For Czechoslovakia, the official price indices show virtually no inflation between 1985 and 1989, when there were long waiting lists for such products as cars and state and cooperative flats. Trends in these price indices do not seem to depend on the method used for constructing them, according to the sensitivity tests conducted by Czechoslovakia's Federal Statistical Office. Obviously, the official price indices failed to capture the full extent of economic disequilibrium in that period. But the extent to which official price indices understated inflationary pressures was not serious in Czechoslovakia, compared with other centrally planned economies. Estimates of hidden inflation for 1985-89 range from 0.5 percent to 2 percent a year in consumer markets and about 3 percent in the industrial sector. Estimates for suppressed inflation were less than 5 percent. The relatively small inflationary gap is indirectly confirmed by the sharp inflation associated with the recent price liberalization that subsided in a relatively short period, and both suppressed and hidden inflations have virtually disappeared. Estimates of hidden inflation were based on benchmark price comparisons between Czechoslovakia and such market economies as Austria. Those for suppressed inflation were based on disequilibrium econometric models of asset holdings and on conjecture tests.Economic Theory&Research,Environmental Economics&Policies,Markets and Market Access,Access to Markets,Financial Intermediation
Acoustic emission characteristics of surface friction in bio-medical application
No full textThe paper describes the use of acoustic emission (AE) techniques in a study of surface friction properties. All dynamic friction processes generate quasi-continuous AE signal, which can be used to characterize surface friction. The AE signal is produced by stick-slip motion of two materials in contact. Signal intensity depends on contact force, motion velocity, molecular adhesion forces between both materials, and surface properties as roughness, hardness, elastic and plastic properties and surface layer properties (lubrication, dry friction). A series of tests have been performed using a new prototype of friction brush probe combined with tangential force measurement. This probe has been designed for measurement of human skin friction coefficient, but can be applied also to other materials. Measured signals (AE signal, tangential and normal forces) were recorded and analyzed by digital processing analyzer DAKEL-XEDO . Various friction head materials were tested on samples made of different materials. The best results were obtained using carbon-fiber brush friction head. The contact force and motion velocity were optimized to produce maximal AE signal amplitude at a contact force as low as possible. Good correlation was observed between frictional forces and global AE activity parameters
Imaging of human tooth using ultrasound based chirp-coded nonlinear time reversal acoustics
No full textUltrasonographie dentaire par techniques TR-NEWS
No full textNational audienceL'imagerie ultrasonore d'une molaire humaine est abordée expérimentalement par l'utilisation des méthodes TR-NEWS, symbioses des méthodes NEWS (Nonlinear Elastic Wave Spectroscopy) bien connues pour révéler les signatures non linéaires de la dégradation des matériaux solides endommagés d'une part, et des techniques de focalisation par symétries de retournement temporel (TR) et de réciprocité d'autre part. La complexité de la structure interne de la dent (email, structure tubulaire de la dentine, pulpe, distribution de cracks entre les tubules) est explorée via un système d'excitation ultrasonore optimisé par codage fréquentiel en balayage dans la bande 0.1-10 MHz (chirp-coded excitation). La réponse acoustique de la dent étalonnée en vitesse particulaire est mesurée à la surface de celle-ci par vibrométrie laser (sensibilité 125 mm/s/V). La mise en œuvre expérimentale de la technique TR-NEWS utilisant le système TRA de Artann Laboratories ( http://www.artannlabs.com/tra-electronic.html), associé à un traitement du signal symétrisé permet l'obtention d'un B-scan polaire (120°-350°) étalonné en vitesse particulaire et référencé spatialement par rapport à la surface de la dent. L'extraction de la signature non linéaire et de sa localisation seront alors conduites par l'utilisation des propriétés de symétries de la focalisation spatiale et temporelle des ultrasons produites par TR-NEWS
Rent - seeking trade policy : a time series approach
No full textUsing a time-series approach, the author analyzes the relationship between the extent of rent-seeking trade policy and both political and economic variables. For rent-seeking trade policy, the indicator he uses is the number of foreign-trade regulations passed each year for the benefit of a single firm or industry. The author uses data from Uruguay for 1925-83. Uruguay, which experienced an impressive economic decline, is an outstanding example of a rent-seeking society. After being a wealthy economy in midcentury, it suffered almost complete stagnation, which led to social and policital disintegration by the end of the 1960s. Three decades of restrictive regulations on foreign trade had created a nearly closed economy by the end of the 1960s. It was worth analyzing whether policymakers'great receptiveness to demands for protection could account for Uruguay's decline. Over the period 1925-83, the author finds almost 4,000 laws, decrees, and administrative resolutions that create, maintain, or modify a foreign-trade regulation for the benefit of a single firm or industry. About half of them explicitly identify the petitioner - usually a firm or guild. Since the size of the Uruguayan economy changed over the period studied, the author scales the annual number of regulations by output or exports to measure the extent of rent-seeking trade policy. The author shows that the extent of rent-seeking trade policy increased with discretionary policies and under dictatorship. (In the period studied, there were two stages of democracy - until 1932 and from 1943-72 - and two stages of dictatorship.) He also shows that rent-seeking trade restrictions increased under import-substitution strategies and, more unexpectedly, under active export promotion. This suggests that discretionary power leads to wasteful distribution, whether it is used to support inward- or outward-oriented policies. Finally, the author analyzes the correlation between innovations in the trade policy indicator and innovations in the growth rates of output and exports, with a lag of up to 20 years. Surprisingly, he finds a positive correlation with output growth rates after two or three years. But the correlation becomes negative some years later, particularly in the case of exports. The short-run positive impact on growth rates, together with the surprisingly long time lag before the negative impact, may account for policymakers'receptiveness to demands for protection.Trade Policy,Achieving Shared Growth,TF054105-DONOR FUNDED OPERATION ADMINISTRATION FEE INCOME AND EXPENSE ACCOUNT,Economic Theory&Research,Environmental Economics&Policies
Price and quality competitiveness of socialist countries'exports
No full textIn this report the authors have analyzed pricing of the centrally planned economies (CPEs) in the highly competitive export markets of the EC countries in the first half of the 1980s. They found that the CPEs'export prices were lower than prices in both developed and developing countries. Manufactured goods from CPEs were underpriced an average 31 to 45 percent - even more on some commodities. Protection of EC countries doesn't seem to be a factor in CPE underpricing of manufactured goods. This could not be explained either by a deliberate policy of CPEs to penetrate Western markets. The CPEs inability to upgrade manufactured exports that are subject to quotas suggests serious quality constraints on exports of manufactured goods. They appear to underprice their manufactured exports not because of cost advantages that make them more competitive, but because most of their manufactured goods are inferior in quality to their competitors.Environmental Economics&Policies,TF054105-DONOR FUNDED OPERATION ADMINISTRATION FEE INCOME AND EXPENSE ACCOUNT,Economic Theory&Research,Markets and Market Access,Access to Markets
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