析之极其精,合之尽其大 --略论朱熹的科学思维

针对过去学术界关于西方重分析、中国重综合的流行看法,从朱熹的“析之极其精而不乱,然后合之尽其大而无余”的治学方法切入,着重探讨朱熹的分析综合思维,层次思维、整体思维和科学分析论证法,并揭示出其科学思维即理论思维能力的培养在于努力学习以往的哲学,掌握了“理一分殊”的辩证法原理.哲学是科学思维之母.朱熹的科学思维方法,过去颇有影响,至今仍有借鉴意义.     

Analysis of ALD-processed thin films by ion-beam techniques

This review introduces the possibilities of ion-beam techniques for the analysis of thin films and thin-film structures processed by atomic layer deposition (ALD). The characteristic features of ALD are also presented. The analytical techniques discussed include RBS, NRA and ERDA with its variants, viz. the TOF-ERDA and HI-ERDA. The thin film examples are taken from flat-panel display technology (TFEL structures) and the semiconductor industry (high-k insulators).Dedicated to the memory of Wilhelm Fresenius     

松弛模型中的液气共存平衡态

对密闭的一维有限长管道里的等温相变．研究了松弛模型中液气共存平衡态的稳定性．使用匹配渐近展开形式上推出了一阶扰动满足的线性系统．理论分析发现．初始小扰动通常会被耗散掉,然而在一些特殊情况下,它们会维持在一定的水平上．数值计算也表明了松弛机制对相变演化具有稳定作用．     

Uniform blow-up profiles and boundary layer for a parabolic system with localized nonlinear reaction terms

This paper deals with the blow-up properties of the solution to a semilin-ear parabolic system with localized nonlinear reaction terms, subject to the null Dirichlet boundary condition. We first give sufficient conditions for that the classical solution blows up in the finite time, secondly give necessary conditions and a sufficient condition for that two components blow up simultaneously, and then obtain the uniform blow-up profiles in the interior. Finally we describe the asymptotic behavior of the blow-up solution in the boundary layer.     

Steady flow generated by the differential rotation of a porous disk of finite thickness

When a body of fluid bounded by a porous disk of finite thickness is disturbed from a state of rigid rotation by an enhanced (or reduced) angular velocity of the disk, a few authors followed Darcys model and observed that the centrifugal pumping occurs through the entire porous layer regarded as a convection zone. The shear stress can develop only at the edge of the porous layer. We use a porous disk of high permeability that allows the fluid in the porous disk to deform in response to the changing angular velocity. Based on the Birkmans model, we solve for the steady non-linear flow and observe that there arises (i) a convection zone of nearly uniform angular velocity at the boundary (within the porous layer) and (ii) a transition zone adjacent to the convection zone which provides a smooth transition to the interior. This makes the model relevant to some astrophysical situations as described by some authors [1, 3]. The two point boundary value problem is solved subject to the boundary conditions, the far field conditions, and the matching conditions at the fluid-porous medium interface. The solution is obtained using a numerical procedure known as the method of Adjoints.Received: June 13, 2002; revised: July 7, 2003     

Beeinflussung der Turbulenzstruktur in der ebenen Mischungsschicht zweier Ströme durch Polymerzusätze

Zusammenfassung Ausgehend von der Frage, ob beim Phänomen der Widerstandsverminderung (Toms-Effekt) die Wirkung der Polymeren nur auf die Strömung in den wandnahen Bereichen beschränkt ist oder eine solche auch in wandferneren Gebieten gefunden werden kann, hat die vorliegende Untersuchung zum Ziel, den Einfluß derartiger Zusätze in der sog. Freien Turbulenz zu analysieren, bei denen also keine Wechselwirkungen mit festen Wänden vorhanden sind. Als besonders einfaches Beispiel einer solchen Strömung wurde diejenige in einer ebenen turbulenten Mischungsschicht ausgewählt, die sich zwischen zwei mit verschiedener Geschwindigkeit bewegten Parallelströmen ausbildet. In derartigen Strömungen existiert eine charakteristische Wirbelstruktur, die von einer turbulenten Mikrostruktur überlagert wird, und es sollte untersucht werden, wie diese Strukturen sich bei Zugabe von widerstandsvermindernden Polymeren ändern.Als Untersuchungsmethode wurde die raum-zeitliche Korrelationsanalyse mittels Laser-Doppler-Anemometern verwendet. Da aber die bekannten Systeme hierfür nur bedingt einsetzbar sind, wurde eine für diesen Zweck besser geeignete optische Anordnung neu entwickelt.Als wichtigstes Ergebnis wurde gefunden, daß durch den Polymerzusatz die Intensität und die Kohärenzlänge der turbulenten Makrostrukturen erheblich anwachsen, wohingegen die turbulenten Mikrostrukturen weitgehend unterdrückt werden. Größe und Abstand der Wirbel werden zwar verkleinert, doch wird ihre Aufeinanderfolge vergleichmäßigt, und ihre Lebensdauer nimmt entsprechend zu. Weiter wurde nachgewiesen, daß die mit der Polymerzugabe verbundene Viskositätserhöhung nicht die Hauptursache für diese Effekte sein kann, da solche bei newtonschen Flüssigkeiten mit vergleichbarer Viskosität längst nicht in so ausgeprägter Weise auftreten.Das ebenfalls beobachtete verringerte Dickenwachstum vor allem im Anfangsbereich der Mischungsschicht in Verbindung mit einer Verstärkung der Intensität der langsameren turbulenten Längsschwankungen legt die Deutung nahe, daß durch die Hauptströmung infolge Entknäuelung und Orientierung der Polymermolekeln eine Fließanisotropie erzeugt wird. Dagegen läßt sich die Verlangsamung des Wirbelwachstums und die Unterdrückung der Mikroturbulenz am ehesten durch die Behinderung lokaler Dehnströmungen infolge einer stark erhöhten Dehnviskosität erklären. Die Vorstellung, daß bei den Austauschvorgängen in einer freien turbulenten Mischungsschicht die Flüssigkeitseigenschaften keine Rolle spielen, ist somit durch diese Untersuchung als zumindest für viskoelastische Flüssigkeiten nicht zutreffend nachgewiesen worden.

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An important question concerning the phenomenon of drag reduction (Toms effect) is whether the influence of polymer additives is restricted to regions near the wall or whether it also extends to the core. Therefore the aim of the present investigation was to analyse the influence of such additives on socalled free turbulence in which there are no interactions with rigid walls. A plane turbulent mixing layer formed between two parallel streams moving with different velocities was chosen as a particularly simple example of such a flow. There exists in these flows a characteristic vortex structure with a superimposed turbulent micro-structure. The influence on these structures of an addition of drag reducing polymers was investigated.Space-time correlation analysis using Laser-Doppler Anemometry was chosen as the technique for investigating the turbulent flow field. Because commercially available systems are not particularly well suited for such measurements, a special optical arrangement was developed.The most important result was that the polymer additive significantly raised the intensity and coherence length of the turbulent macro-structure whereas the turbulent micro-structure was strongly attenuated. The size and separation of the vortices were decreased but their occurrence became more regular and their lifetimes increased. Furthermore it was demonstrated that the viscosity increase associated with the addition of polymer could not be the main reason for these effects, as such effects were far less pronounced in Newtonian liquids of comparable viscosity.The slower growth in the thickness of the mixing layer, observed particularly in the initial region, as well as the increase in the intensity of the slower longitudinal turbulent fluctuations suggest that the main flow induces a flow anisotropy as a result of uncoiling and orientation of the polymer molecules. On the other hand the decrease in the vortex growth rate and the suppression of the micro-turbulence can best be explained by a hindrance of local extensional flows resulting from a strong increase in the extensional viscosity. The notion that fluid properties do not play a role in the process of momentum exchange in a free turbulent mixing layer has been shown by these investigations to be inappropriate at least for viscoelastic liquids.

Von der Abteilung Chemietechnik der Universität Dortmund genehmigte Dissertation; auszugsweise vorgetragen auf der Jahrestagung der Deutschen Rheologischen Gesellschaft in Aachen vom 5.–7. März 1979 und auf dem VIII. Internationalen Rheologie-Kongreß in Neapel vom 1.–5. September 1980.     

Correlation of TLC/densitometry-data with capillary GC-data of some main volatile components of essential oils

The results of the densitometric and the capillary gas chromatographic investigations of numerous lavender oils of different origin and of essential oils of the woody group were correlated. Especially the main components, the monoterpenes linalool (¯1) and linalyl acetate (¯2), were quantified by densitometry with an average standard deviation of 6–7% in the examined oils. The use of TLC in combination with densitometry in the quantification of the main components to essential oils is thus a valuable addition to capillary gas chromatographic investigation. In addition to this, a useful and efficient alternative is given to groups specialized in TLC/densitometry to obtain data on such volatile compounds of essential oils during quantification. The use of TLC/densitometry thus combines the advantage of LC-with detection of also less volatile compounds—and the possibility of the parallel investigation of more samples in one step in a very efficient way.     

Kinetic theory of hydrodynamic flows. I. The generalized normal solution method and its application to the drag on a sphere

We consider the flow of a dilute gas around a macroscopic heavy object. The state of the gas is described by an extended Boltzmann equation where the interactions between the gas molecules and the object are taken into account in computing the rate of change of the distribution function of the gas. We then show that the extended Boltzmann is equivalent to the usual Boltzmann equation, supplemented by boundary conditions imposed on the distribution function at the surface of the object. The remainder of the paper is devoted to a study of the solution of the extended Boltzmann equation in the case that the mean free path of a gas molecule is small compared to some characteristic dimension of the macroscopic object. We show that the Chapman-Enskog normal solution of the ordinary Boltzmann equation is not in general a solution of the extended equation near the surface of the object and must be supplemented by a boundary layer term. We then introduce a projection operator method which allows us to decompose the solution of the extended equation into a normal solution part and a boundary layer part when the gas flow is sufficiently slow. As a specific example of the method we consider the flow around a sphere, and derive the Stokes-Boussinesq form for the frequency-dependent force on the sphere for arbitrary slip coefficient. This derivation is the first one that starts from the Boltzmann equation for a general dilute gas and incorporates the effect of the boundary layer on the drag force.Work supported by the National Science Foundation.     

A unified approach to direct and inverse boundary layer solutions

A unified approach is presented for solving the two-dimensional incompressible boundary layer equations. Solutions are obtained for direct and inverse options using the same equation formulation by a simple interchange of boundary conditions. A modified form of the mechul function scheme obtains inverse solutions with specification of transformed wall shear, skin friction coefficient or displacement thickness distributions. Direct solutions may be obtained without altering the block tridiagonal structure of the system by simply requiring no corrections on the streamwise pressure gradient parameter. Fourth-order spline discretization approximates normal derivatives with two- and three-point backward differences approximating streamwise derivatives, yielding a fully implicit solution method. The resulting spline/finite difference equations are solved by Newton-Raphson iteration together with partial pivoting. The results of the study demonstrate the importance of proper linearization of all equations. The successful use of spline discretization is also tied to the use of strong two-point boundary conditions at the wall for cases involving reversed flow. Numerical solutions are presented for several non-similar flows and compared with published results.