C o n t e n t s. Monica Nadasan, T. Visan Regarding the optical trapping forces on microparticles 15

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1 U.P.B., Sci. Bull., Series B, Vol. 68, No. 2, C o n t e n t s CHEMISTRY O. RADUCAN, A. WOINAROSCHY, V. LAVRIC Optimal control of a wastewater activated sludge system 3 Monica Nadasan, T. Visan Regarding the optical trapping forces on microparticles 15 Gh. Hubca, Camelia Hodosan, P.O. Stanescu, Iulia Pocsan, M. Dimonie Synthèse de l'alcool polyvinylique au degré d'hydrolyse dirigeable par l'alcoolyse du polyvinylacétate en solution homogène 25 D. Radu, Corina Ibris Correlations mechanical strength - granulometric uniformity degree for portland cement 35 MATERIALS SCIENCE Mirela Tinica, R. Saban Microscopical analysis and creep behaviour examination applied to steam lines in power station equipment 41 Irina Carceanu, Georgeta Cosmeleata Some aspects concerning manufacturing of W-Ni composite powder by mechanical alloying 49 Mirela Sohaciu, Gh. Iorga, A.Nicolae Analysis of quality and economic indicators in steel making involving secondary materials recirculation 57 C.D. Urban The influence of cooling rate on grain refining of 6063 alloy with altic 65

2 U.P.B., 4 Sci. Bull., Series B, Vol. 68, No. 2, 2006 OPTIMAL CONTROL OF A WASTEWATER ACTIVATED SLUDGE SYSTEM O. RADUCAN, A. WOINAROSCHY, V. LAVRIC The biological wastewater cleaning is defined as the metabolic consumption of organic wastes from water (industrial or municipal) by a mixed population of microorganisms (yeasts, fungi etc) known as activated sludge. The process takes place in systems composed of an aerated tank (bioreactor) and filter, which separates the activated sludge recycled to maintain its high concentration from the clean reusable water. A small part of the recycled sludge is removed from the system through a purge, thus controlling the viability of the biomass and the dead cells concentration. Irrespective of the chosen filtering system (crossflow or dead -end), it is intrinsically non-stationary, introducing a specific dynamic for the whole system. The optimal control of the activated sludge system previously defined is aimed to search for the right purge fraction which could maintain the same quality of the clean water throughout the operating time. REGARDING THE OPTICAL TRAPPING FORCES ON MICROPARTICLES Monica NADASAN, T. VISAN Working with a strongly focused laser beam it is possible to trap and manipulate particles (of biological or dielectric material) in a size range from nm to µm. In this paper the case of the trap of silica particles by means of an inverted microscope and a Gaussian laser beam is discussed. In the theoretical part the procedures for measurement of forces acting on a trapped particle are presented. In experiments using optical tweezers the optical efficiencies were in the range of 2-12%, with upper values corresponding to 20x or 40x magnification of microscope. An increase of 24-50% in the laser power was calculated to trap silica particles if the displacement of stage is µm. The difference between trapping forces considering either local speed of the fluid or the boundary speed as well a change of these forces due to the temperature increase are also discussed.

3 U.P.B., Sci. Bull., Series B, Vol. 68, No. 2, SYNTHÈSE DE L'ALCOOL POLYVINYLIQUE AU DEGRÉ D'HYDROLYSE DIRIGEABLE PAR L 'ALCOOLYSE DU POLYVINYLACÉTATE EN SOLUTION HOMOGÈNE GH. HUBCA, Camelia HODOSAN, P.O. STANESCU, Iulia POCSAN, M. DIMONIE Le contrôle de la réaction d'alcoolyse du polyvinyle acétate en solution homogène présente des difficultés à cause de la vitesse de réaction élevée et de la transformation de la masse de réaction dans un gel très consistant avec une grande tendance à la solidification. Vu ces aspects, ce travail a comme but l'étude des possibilités de diriger la réaction d'a lcoolyse du polyvinyle acétate. Ils ont été étudiées deux variantes: a) l'introduction dans le milieux réactionnel d'une quantité strictement contrôlée d'eau (inhibiteur du processus d'alcoolyse) de telle manière que le catalyseur disparaisse du système au moment où le degré d'alcoolyse désiré est atteint; b) le dosage par analyse chromatographique du méthyle acétate (résulté comme produit secondaire) qui existe au moment donné dans le système. Controlling the alcoholysis of polyvinyl acetate in homogeneous solution presents a series of difficulties determined by the high reaction rate and the fo r- mation of a very consistent gel with high tendency towards solidification. The aim of the present study is to assess different reaction control methods. Two ways were considered: a) the alcoholysis in the presence of strictly co ntrolled amount of water (alcoholysis inhibitor) stops at the desired degree of alcoholysis at the moment of the water depletion; b) gas chromatographical determination of methyl acetate (resulted as by-product) present at a certain time in the reaction mixture. CORRELATIONS MECHANICAL STRENGTH - GRANULOMETRIC UNIFORMITY DEGREE FOR PORTLAND CEMENT D. RADU, Corina IBRIS Cement quality, expressed as strength, depends on granulometric uniformity degree. For this reason there is a practical interest in corelating mechanical strength of cement and granulometric uniformity degree. Correlations between mechanical strength and granulometric uniformity degree

4 U.P.B., 6 Sci. Bull., Series B, Vol. 68, No. 2, 2006 are obtained using literature data and also the analysis romanian marks of Portland cement. MICROSCOPICAL ANALYSIS AND CREEP BEHAVIOUR EXAMINATION APPLIED TO STEAM LINES IN POWER STATION EQUIPMENT Mirela TINICA, R. SABAN Applying microscopical examination to the metallic material of which the steam lines in power station equipment is made of represents a useful tool for predicting the life time and for increasing the reliability of components subject to long term creep stresses at high temperature. The specific metallographic methods discussed and applied in this papers have proved to be in good agreement with the results obtained by creep evaluation. SOME ASPECTS CONCERNING MANUFACTURING OF W-Ni COMPOSITE POWDER BY MECHANICAL ALLOYING Irina CARCEANU, Georgeta COSMELEATA This paper presents the preoccupation of author in production of homogenous mixtures of W-Ni powders system by mechanical alloying.the elaboration of these alloys by conventional methods is difficult, resulting products with low mechanical properties, due to their structure unhomogenity. The milling of W and Ni powders respectively to less than 4 µm particle size, for mechanical alloying, was carried out in a vertical axis planetary mill, with no protective atmosphere or lubricant. The milling time was 110 hours. Powder samples were taken every 20 hours during the 110 hour milling time for qualitative and quantitative evaluation by X ray diffraction. The influence of the technological parameters on structurals, physical and mechanical characteristics of the materials thus obtained are also presented.

5 U.P.B., Sci. Bull., Series B, Vol. 68, No. 2, ANALYSIS OF QUALITY AND ECONOMIC INDICATORS IN STEEL MAKING INVOLVING SECONDARY MATERIALS RECIRCULATION Mirela SOHACIU, GH. IORGA, A.NICOLAE The paper tries to define and determine some in dicators, which are proper to the EAF steel making using the recirculation of secondary materials represented by brickets made from EAF dust and scale. The analyzed indicators were: carbon, sulphur, phosphorus at the melting point, zinc content of steel, high quality steel output and iron scrap specific co nsumption. The defined indicators are used to characterize the ecological function and the substitution function for used secondary materials. THE INFLUENCE OF COOLING RATE ON GRAIN REFINING OF 6063 ALLOY WITH ALTIC C.D. Urban In the paper the influence of cooling speed on the finishing granulate degree of 6063 alloy finished with binary master alloy AlTi10 and ternary master alloy Al3Ti0.15C is presented. Microstructures and macrostructures that evid entiated the influence for the dissolved element (Ti - 0,03%) and for the nucleant (TiC) are presented. Testing on the finishing degree were performed on an ALCOA d e- vice by using three different types of molds with different thermal conductivities.