Long-Chain Alkane Dehydrogenation over Hierarchically Porous Ti-Doped Pt–Sn–K/TiO2–Al2O3 Catalysts

Kinetics and Catalysis - Hierarchically porous γ-Al2O3, TiO2–Al2O3 composite supports, and Pt–Sn–K/Al2O3 and Pt–Sn–K/TiO2–Al2O3 catalysts were prepared...     

Secondary Metabolites of Mahonia bealei

Chemistry of Natural Compounds -     

The zonal linearization method for multidimensional mass transfer problems in porous media

A number of methods have been proposed in recent years for calculating the combined flows of immiscible and miscible liquids in strata to systems of boreholes. We propose a method which can naturally be called the zonal linearization method [1]. It is more compact than the usual finite-difference method and has high accuracy, in particular, in the neighborhood of a borehole, since it is closely similar to the method of characteristics. The method can be applied to both continuous and discontinuous flows and in principle makes it possible to investigate the formation and breakdown of discontinuities. As distinct from the method of characteristics, it is well suited to programming and implementation on a computer, and it also makes it possible to obtain an approximate analytic solution of the problem in many cases and to estimate the accuracy of the solution. The method is based on the zonal linearization of the equation for mass conservation in the total flow between chosen surfaces or contour lines (lines of equal saturation or concentration). Determination of the dynamics of the contour surfaces leads to a Cauchy problem for a system of integrodifferential equations involving partial derivatives. The zonal linearization method is a development of the scheme described in [2–4], and the method of solving the Cauchy problem is a generalization of the methods described in [4–13]. The essence of the method and its convergence are illustrated by means of two-dimensional problems in two-phase filtration.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 66–80, July–August, 1973.     

An approach to computer control for legged vehicles

Observation of the locomotion of animals and human beings in difficult terrain makes it quite obvious that legged locomotion offers substantial mobility advantages over conventional wheeled or tracked systems. However, effective adaptation of legged locomotion principles to off-road vehicles has to date been frustrated by the complexity of the joint coordination control problem and by the lack of suitable sources of power for individual leg joints. This paper is addressed to the first problem and is intended to show that some of the techniques used in aircraft autopilots can be adapted to legged vehicle control. The main results presented are derived from a computer simulation study of a system in which vehicle speed and direction are determined by a human operator while individual joint commands are generated automatically by a digital computer. Present indications are that such a vehicle might be as easy to control as a conventional wheeled or tracked automotive system.     

Pulsatile flow of an elastico-viscous liquid in a channel of elliptic cross-section

Summary The pulsatile flow of an elastico-viscous liquid through an elliptic tube is considered in this note. The problem is solved as a boundary and initial value problem by using the Laplace Transform method. Explicit expressions for velocity distribution are obtained in the two limiting cases of small and large values of time. The effect of elasticity on the flow is discussed analytically.

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Zusammenfassung In dieser Mitteilung wird die pulsierende Strömung einer viskoelastischen Flüssigkeit durch ein elliptisches Rohr betrachtet. Das Problem wird als Anfangs- und Randwertproblem mit Hilfe der Laplace-Transformation gelöst. Explizite Ausdrücke der Geschwindigkeitsverteilung werden für die beiden Grenzfälle kurzer und langer Zeiten angegeben. Die Wirkung der Elastizität auf die Strömung wird analysiert.

     

Deformation und Stabilität windbeanspruchter Kühlturmschalen

Übersicht Nach der Formulierung des Deformations- und des Stabilitätsproblems auf der Grundlage ursprünglich nicht-konformer, dreiecksförmiger, gekrümmter finiter Elemente wird zunächst das Deformationsproblem für eine ausgeführte Kühlturmschale numerisch gelöst. Die nachfolgende Stabilitätsanalyse dieser Kühlturmschale zeigt gute Übereinstimmung der mittels der Methode der finiten Elemente errechneten Beulsicherheit mit dem aufgrund des Munganschen Beulkriteriums erhaltenen Kleinstwert der Beulsicherheit.

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Summary Following the formulation of the deformation and stability problem on the basis of originally non-conforming triangular curved finite elements with the help of a variational principle with subsidiary conditions, the deformation problem is solved numerically for an existing cooling tower shell. The subsequent stability analysis of this cooling tower shell shows relatively good agreement of the buckling safety computed by means of the finite element method and the minimum of buckling safety obtained with the help of Mungan's stability criterion.

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Diese Arbeit wurde mit Unterstützung der Cooling Tower Division von Zurn Industries, Tampa, Florida, USA, begonnen und mit Unterstützung Seitens des Fonds zur Förderung der wissenschaftlichen Forschung, Wien, zu Ende geführt. Beiden Sponsoren Sei an dieser Stelle aufrichtig gedankt. Der erstgenannte Autor ist darüber hinaus der Max Kade Foundation, New York, N. Y., für die Finanzierung Seines Studienaufenthaltes an der Cornell University, Ithaca, N. Y., im Rahmen dessen er mit der Thematik dieses Aufsatzes konfrontiert wurde, zu Dank verpflichtet. Aus demselben Grund sagt der dritte Autor für ein NATO Fellowship Dank.     

Methods and correlations for the prediction of quenching rates on hot surfaces

A substantial quantity of experimental data on rewetting, much of which has not been previously reported, is analysed using the results of calculations of the two-dimensional conduction processes taking place in the walls of tubes, which have been used to simulate the cladding of nuclear fuel elements. Correlations giving the quenching heat-transfer coefficient and sputtering temperature are proposed as a result of the analysis. These correlations may be combined with the previously reported conduction analysis to predict rewetting rates under a wide range of conditions. The new data include falling film rewetting rates measured for a range of system pressures (1–15 bars), initial wall temperatures (200–650°C), coolant mass flowrates (3–50 g sec^?1) and subcoolings (0–90°C). Measurements have also been made of rewetting rates by bottom flooding of both saturated and subcooled water at atmospheric pressure.     

Development of perturbations in plane shock waves

Investigation of the stability of plane shock waves as regards nonuniform perturbations was first performed by D'yakov [1]. He obtained criteria for stability, and showed that perturbations grow exponentially with time in the case of instability. Iordanskii [2] has shown that in the case of stability, the perturbations are attenuated according to a power law. However, the stability criteria of [2] do not agree with the results of [1], Kontorovich [3] has explained the cause of the apparent discrepancies, and asserts the correctness of the criteria of [2]. A power law for the attenuation of perturbations has also been obtained in [4,5] under a somewhat different formulation of the boundary conditions.The Cauchy problem with perturbations is examined in §1 of this paper, results are obtained for cases of practical interest, and the asymptotic behavior is investigated.In §2 the effect of a low viscosity on the development of perturbations is examined. It is shown that when t the amplitude of perturbations is attenuated mainly as exp(-t), where >0 does not depend on the form of the boundary conditions at the shock wave front. The results of §2 were used in processing the experimental data of [6], which made it possible to determine the viscosity of a number of substances at high pressure.In conclusion, the author expresses his gratitude to A. D. Sakharov for valuable advice, and to A. G. Oleinik and V. N. Mincer for useful discussions. The author also thanks G. I. Barenblatt, L. A. Galin, and others who took part in a seminar at the Institute for Problems in Mechanics, for their interesting discussion and valuable comments.     

Out-of-plane deflections of metallic and composite pin-loaded coupons

The projection shadow moiré technique was employed to determine an out-of-plane contouring history of aluminum, [(+45/–45)]_3S , [(0/90₃,0] _S and [(0/90/+45/–45)]_2S fiberglass epoxy pin-loaded specimens experimentally. The contouring interval was limited to 0.0254 mm by experimental concerns. Qualification of the projection shadow moiré optical arrangement was initially accomplished by the out-of-plane contouring of a clamped, centrally loaded, circular aluminum plate. Experimental results indicate significant out-of-plane displacements in the bearing region of the coupon at load levels well below ultimate. Effects of material anisotropy could be seen in the fiber-oriented shape of the displacement contours. Comparisons with three-dimensional finite-element results indicate that experimental out-of-plane contours were significantly larger than their finite-element counterparts in the region above the pin for the [(+45/–45)]_3S , [(0/90)₃, 0] _S laminates. These deviations increased with increasing pin-load level. These variations could be attributed to linear-elastic through-thickness moduli assumptions as well as through-thickness finite-element mesh coarseness.