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Empirical Expression (empirical + expression)

Distribution by Scientific Domains

Engineering	50%
Chemistry	50%

Selected Abstracts

A displacement-based seismic design procedure for RC buildings and comparison with EC8

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 10 2001
T. B. Panagiotakos
Abstract A procedure for displacement-based seismic design (DBD) of reinforced concrete buildings is described and applied to a 4-storey test structure. The essential elements of the design procedure are: (a) proportioning of members for gravity loads; (b) estimation of peak inelastic member deformation demands in the so-designed structure due to the design (,life-safety') earthquake; (c) revision of reinforcement and final detailing of members to meet these inelastic deformation demands; (d) capacity design of members and joints in shear. Additional but non-essential steps between (a) and (b) are: (i) proportioning of members for the ULS against lateral loads, such as wind or a serviceability (,immediate occupancy') earthquake; and (ii) capacity design of columns in flexure at joints. Inelastic deformation demands in step (b) are estimated from an elastic analysis using secant-to-yield member stiffnesses. Empirical expressions for the deformation capacity of RC elements are used for the final proportioning of elements to meet the inelastic deformation demands. The procedure is applied to one side of a 4-storey test structure that includes a coupled wall and a two-bay frame. The other side is designed and detailed according to Eurocode 8. Major differences result in the reinforcement of the two sides, with significant savings on the DBD-side. Pre-test calculations show no major difference in the seismic performance of the two sides of the test structure. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Modelling the response of sprinklers in compartment fires

FIRE AND MATERIALS, Issue 3 2001
A. K. Gupta
Alpert's expressions are used extensively to calculate the maximum temperature and velocity in the ceiling-jet at any distance, r, from the fire axis. These expressions are valid for unconfined ceilings insofar as the environment outside the ceiling-jet is uniform in temperature and is atmospheric ambient. In compartments the outward flow of hot gases is checked by the presence of bounding walls and so a layer of hot gases is formed in the upper portion of the compartment. The environment outside the ceiling-jet is no longer ambient atmospheric. Expressions due to Alpert becomes unsuitable, unless the effects of the accumulated hot layer are included in these expressions. The effect of the upper layer temperature has been taken by assuming that since the ceiling-jet is completely submerged in the upper hot gas layer, the entrained gases are drawn from this layer only instead of the ambient atmospheric air at T,. Thus T, has been replaced by TL in the Alpert's empirical expression for ceiling-jet temperatures. The proposed equation is then used to calculate the response time of sprinklers fitted in compartments of varying sizes. Calculations have been done for identical conditions to those employed by Evans and compared. Comparison has also been made with Cooper's LAVENT model predictions. The study shows that the present model is capable of predicting the maximum, as well as average, temperatures in the ceiling-jets submerged in the hot gas layer. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Kinetics and mechanism of oxidation of the drug mephenesin by bis(hydrogenperiodato)argentate(III) complex anion

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2007
Shigang Shen
Mephenesin is being used as a central-acting skeletal muscle relaxant. Oxidation of mephenesin by bis(hydrogenperiodato)argentate(III) complex anion, [Ag(HIO6)2]5,, has been studied in aqueous alkaline medium. The major oxidation product of mephenesin has been identified as 3-(2-methylphenoxy)-2-ketone-1-propanol by mass spectrometry. An overall second-order kinetics has been observed with first order in [Ag(III)] and [mephenesin]. The effects of [OH,] and periodate concentration on the observed second-order rate constants k, have been analyzed, and accordingly an empirical expression has been deduced: k, = (ka + kb[OH,])K1/{f([OH,])[IO,4]tot + K1}, where [IO,4]tot denotes the total concentration of periodate, ka = (1.35 ± 0.14) × 10,2M,1s,1 and kb = 1.06 ± 0.01 M,2s,1 at 25.0°C, and ionic strength 0.30 M. Activation parameters associated with ka and kb have been calculated. A mechanism has been proposed to involve two pre-equilibria, leading to formation of a periodato-Ag(III)-mephenesin complex. In the subsequent rate-determining steps, this complex undergoes inner-sphere electron transfer from the coordinated drug to the metal center by two paths: one path is independent of OH, whereas the other is facilitated by a hydroxide ion. In the appendix, detailed discussion on the structure of the Ag(III) complex, reactive species, as well as pre-equilibrium regarding the oxidant is provided. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 440,446, 2007 [source]

Packed bed structure: Evaluation of radial particle distribution

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2002
Néstor J. Mariani
Abstract A model describing the radial distribution of monosized spheres in randomly packed beds up to distances of about two particle diameters from the vessel wall is presented here. The model is based on the existence of a highly ordered layer of particles adjacent to the wall followed by a more diffuse, but still identifiable, second layer. Expressions generated from simple geometrical concepts (intersection between a cylindrical surface and a sphere) straightforwardly allow calculating the radial voidage profile given the radial distribution of particle centers and vice versa. These expressions are employed to fit the model to measures of voidage profiles within a wide range of aspect ratios, a = (RT/RP). The model can be used to accurately predict radial voidage profiles, but it is stressed that the identification of particle distribution constitutes more valuable information than an empirical expression for describing voidage variations. On présente ici un modèle décrivant la distribution radiale de sphères monodisperses dans des lits garnis aléatoires jusqu'à des distances d'environ deux diamètres de particules de la paroi du réservoir. Le modèle s'appuie sur l'existence d'une couche très ordonnée de particules adjacentes à la paroi, suivie d'une seconde couche, plus diffuse mais cependant identifiable. Les expressions provenant de concepts géométriques simples (intersection entre une surface cylindrique et une sphère) permettent de calculer directement le profil de vide radial lorsque la distribution radiale des centres de particules est donnée et vice versa. Ces expressions servent à caler le modèle de mesures de profils de vide dans une vaste gamme de paramètres d'élancement, a = (RT/RP. Le modèle peut être utile pour prédire de manière précise les profils de vide radiaux, mais il faut dire que la détermination de la distribution des particules constitue une information plus valable qu'une expression empirique pour décrire les variations de vide. [source]