Showing papers by "Technical University of Berlin published in 1982"

On the inviscid instability of a circular jet with external flow

Abstract: The influence of an external flow velocity on the instability of a circular jet has been investigated by means of the inviscid linearized stability theory. The instability properties of spatially growing axisymmetric and first-order azimuthal disturbances show that the external flow inhibits the instability of the circular jet, but increases the unstable frequency range. Similarity considerations lead to the result that, in a first approximation, the disturbed flow field is independent of the external flow velocity, if the axial co-ordinate is contracted by a suitably chosen stretching factor and if the disturbance frequency is reduced by the same factor. It is concluded that the large-scale structure of jet turbulence is modified in the same manner by the external flow.

Water in microcrystalline quartz of volcanic origin: Agates

Abstract: Agates of volcanic origin, containing the different quartz species, fibrous, length-fast chalcedony (CH), granular fine quartz (FQ), and fibrous, length-slow, to lepidospheric quartzine (QN), have been investigated to evaluate possible relations between microstructure, i.e. crystallite size and texture, refractive indices, densities, contents of trace elements and of “water”, as well as dehydration behaviour. By means of near infrared spectroscopy, total “water” contents $$c_{({\text{H}}_{\text{2}} {\text{O}}){\text{tot}}} $$ , could be differentiated quantitatively into contents of molecular “water”, $$c_{{\text{(H}}_{\text{2}} {\text{O)mol}}} $$ , and silanole-group “water”, $$c_{{\text{(H}}_{\text{2}} {\text{O)SiOH}}} $$ . Despite the low total “water” contents of the agates studied ( $$c_{({\text{H}}_{\text{2}} {\text{O}}){\text{tot}}} $$ between 1 and 2 wt.%), near infrared spectroscopy results in reliable data on $$c_{{\text{(H}}_{\text{2}} {\text{O)mol}}} $$ and $$c_{{\text{(H}}_{\text{2}} {\text{O)SiOH}}} $$ . Wall-layering CH consists of fibrous quartz crystals and exhibits higher C-ratios, $${{C = c_{{\text{(H}}_{\text{2}} {\text{O)SiOH}}} } \mathord{\left/ {\vphantom {{C = c_{{\text{(H}}_{\text{2}} {\text{O)SiOH}}} } c}} \right. \kern- ulldelimiterspace} c}_{{\text{(H}}_{\text{2}} {\text{O)tot}}} $$ , than horizontally layered FQ which consists predominantly of granular quartz crystals (C CH=0.45±0.11 (N=6), C FQ=0.36±0.10 (N=4). This result is interpreted to be due to analogy with the behaviour of C-ratios in fluid phase-deposited opals-AN (hyalithe) and liquid phase-deposited opals-AG (non-crystalline opal) or -CT (common opal) (Langer and Florke 1974). Translucent layers of CH show mostly lower refractive indices, when measured parallel than when measured perpendicular to the axes of the quartz fibers. The same is true for milky layers of CH. Crystallite sizes are smaller in the latter than in the former. For all samples studied, exists a positive correlation between σ at% (1/2Ca+1/2Mg+Na+K+Li) and σ at% (Al3++Fe3+). This indicates that at least parts of (A13++ Fe3+) substitute for Si in the quartz structure. The charge is balanced by incorporation of di- and mono-valent cations in structural interstices. When the quantity at % H+, as obtained from $$c_{{\text{(H}}_{\text{2}} {\text{O)SiOH}}} $$ , is included into the sum σ at% (1/2 Me2++Me+), the above correlation is destroyed. This result could be indicative for a strong concentration of the Si-OH groups in the surface of the quartz microcrystallites.

A Turbulence Model for Buoyant Flows and Its Application to Vertical Buoyant Jets

Abstract: Publisher Summary Many flows in engineering practice and in the environment are influenced by buoyancy forces arising from density differences or are caused by such forces, like in the case of free-convection flows. Waste fluid discharged into the environment has a density different from the latter, which leads to a buoyancy-induced rise or fall of the discharged fluid. The rise is limited by the presence of a stable stratification in the environment, like inversion layers in the atmosphere or thermoclines in the upper part of oceans, and such stable stratifications have a strong damping effect on the turbulence and inhibit the mixing and the spreading of pollutants; on the other hand, turbulent mixing and pollutant spreading are enhanced under unstably stratified conditions. Density currents driven by some existing density difference might occur in the atmosphere and in oceans and other large water bodies, and free convection flows arise from the presence of heat sources such as heated surfaces or fires and occur frequently in rooms as well as in the atmosphere.

The Berry-Esseen theorem for strongly mixing Harris recurrent Markov chains

Abstract: Let ξ0, ξ1,... be a stationary Harris recurrent Markov chain with state space (E,ℰ), and let f∶ E → IR, X i=f(ξi). It is known that the sequence X i, i≧0, is strongly mixing, i.e. α(n)→>0 where α(n) are the strong (or Rosenblatt) mixing coefficients. If α(n) decreases at a sufficiently fast rate and f is suitable, then a central limit holds for the partial sums $$\sum\limits_{i = 0}^n {X_i } $$ . The present paper gives conditions in order that the convergence rates are O(n −1/2).

Coupling of mixing and microbial kinetics for evaluating the performance of bioreactors

Abstract: The effect of the dynamics of the mixing process in mechanically stirred bioreactors upon their performance has been investigated by using a circulation-model for flow of fluid and a two-environment-model to account for the extent of micromixing in the vessel. With the help of an empirical kinetic model to depict the oxidative and the fermentative growth of bakers' yeast, experimentally observed effects of initial sugar concentrations upon critical dilution rates in continuous cultures of this system could be explained. Effect of different scales of operation upon productivities of fed-batch cultures of bakers' yeast could also be satisfactorily predicted. A discrete simulation procedure was found to be a convenient tool in coupling the two-environment circulation-model of mixing with kinetics of microbial reactions. On a etudie l'effet de la dynamique du processus de melange, dans les bioreacteurs agites mecaniquement, sur leurs performances; on a employe a cette fin un modele de circulation pour l'ecoulement du fluide et un modele comportant deux milieux pour representer le degre de micromelange dans le recipient. On a pu expliquer, grǎce a l'emploi d'un modele cinetique empirique de la croissance de la levure de boulangerie par oxydation et fermentation, les effets observes de la concentration initiale du sucre sur les vitesses de dilution critiques dans les cultures continues du systeme en question. On a pu aussi prevoir d'une maniere satisfaisante l'effet de l'operation a differentes echelles, sur les productivites des cultures de levure de boulangerie alimentees de maniere discontinue. On a trouve qu'une procedure de simulation discrete constituait un moyen approprie pour associer le modele de melange impliquant deux milieux, a la cinetique des reactions microbiennes.

Inequalities for the Angular Derivative of an Analytic Function in the Unit Disk

Abstract: Let $ be a function, analytic in the unit disk, D, that maps the unit disk into itself ((z) ^ 2). In this paper, we present some inequalities for the angular derivative of cj). The more important of these concern the derivative of $ at its fixed points in the closed unit disk. Since (f) and 0' need not be continuous in D we need to clarify the terms \"fixed point\" and \"derivative of ^ at a fixed point\".

Einfluß der Extrusionsparameter auf funktionelle Eigenschaften von Weizenstärke

Abstract: Die funktionellen Eigenschaften nativer Starken konnen unter den Bedingungen der Kochextrusion in Abhangigkeit von den Arbeitsvariablen verandert werden. Mit Hilfe der systemanalytischen Betrachtungsweise last sich der Einflus der Variablen auf die Starkeeigenschaften differenzieren. Dazu wird ein Modell vorgeschlagen, welches die Extrusion nach beeinflussenden und beeinflusten Grosen untergliedert sowie diese in funktionale Beziehungen zueinander stellt. Die systemanalytischen Beziehungen konnten mittels der Ergebnisse des experimentellen Versuchsansatzes quantitativ anhand von Regressionsgleichungen dargestellt werden. Damit ist es moglich, bei Kenntnis der Arbeitsvariablen und der Systemgrosen entweder die sich ergebenden Starkeeigenschaften abzuschatzen oder bei Vorgabe dieser Eigenschaften die erforderlichen Extrusionsbedingungen festzulegen. The Influence of Extrusion Parameters on the Functional Properties of Wheat Starch. The functional properties of native starch can be altered by regulating the technical parameters in the extrusion cooking process. The influence of specific variables on the resultant starch properties can be differentiated by means of system analysis. To make this clear, a model has been put forward which divides individual factors into those which influence the process and those which are influenced by the process, as well as examining their interrelationships. As a result of the experiments, it was possible to use regression analysis to examine the relationships between the various system analysis components. Thus it is possible either to predict the properties of the resultant starch knowing the extrusion and system parameters, or to suggest suitable extrusion conditions in order to obtain a particular starch product.

Negative chemical ionization mass spectrometry of organophosphorus pesticides

Abstract: The negative ion mass spectra of 52 organophosphorus pesticides obtained by chemical ionization with methane under electron capture conditions are presented. The influence of different ionization parameters on the total ion current as well as the relative intensities of the various fragment ions was investigated. In general, the mass spectra show few fragment ions, but these are characteristic for the chemical class of the compound (phosphate, phosphorothionate, phosphorothiolate, phosphorodithioate). The occurrence of the molecular anion is strongly dependent on the structure of the molecule and its ability to stabilize by charge delocalization the radical formed in the primary electron capture reaction. This takes place particularly in the organophosphorus esters of the parathion group which have an aromatic moiety with an electron attracting substituent. The phosphorothionates of the parathion group form a stable thiophenolate fragment which competes in the stability with the molecular anion. The relative intensity of these two ions in the spectrum is dependent on the ion source temperature. Because of the few, but intense fragment ions formed, negative ion mass spectrometry with multiple ion detection is expected to be a valuable tool for residue analysis in food and environmental samples.