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The paper contains an extended summary of an invited plenary talk given at the Workshop on Active Chaos at the Los Alamos National Laboratory on 29-31 May 2001 by one of us (F.S.R.). (c) 2002 American Institute of Physics.

Laser-Induced Fluorescence is used to tomographically produce volume information of concentration distribution in a turbulent shear flow. Based on Adaptive Least Squares Correlation (ALSC) of grey level distributions in small patches cut out of consecutive tomographically constructed observation volumes, 3-D fields of velocity, vorticity and rate-of-strain are determined with high spatial resolution, satisfactory temporal resolution and high accuracy. This novel technique opens new perspectives for the study of mixing processes.

Stability and convergence analysis of the fractional step $\Theta $-scheme for the Navier–Stokes equations coupled with the finite element approximations is presented. The solutions of the underlying Stokes and Burgers problems are described in detail. The asymptotic solution obtained by the numerical stabilization is compared with the analytical solution of the Lid-driven cavity problem.

The zero-temperature phase diagram is rigorously obtained for a two-dimensional lattice model with four energy parameters. It is shown that the parameter space can be divided into regions, together with their boundaries, such that in each region the ground-state configurations are of one of seven different types. These types include one which is nondegenerate, four which are doubly degenerate, one which is infinitely degenerate but with no residual entropy, and one which is infinitely degenerate and has a nonzero residual entropy. The Pirogov-Sinai extension of the Peierls argument is used to establish the existence at low temperatures of four different types of ordered surface-reconstructed phases.

The videogrammetric Least Square Matching Technique (LSM) presented by A. Grun in Chapter three of this volume can be applied to tomographically obtained threedimensional LIF images as shown by H.-G. Maas in this chapter. The method yields three shift components of a small cuboid and the nine components of the tensor describing its transformation, which is assumed to be affine. Provided a good estimate of it can be made for starting the iteration, no restriction is imposed on the magnitude of the shift by videogrammetry.

Preface. I. Introduction to the Fluid Mechanics of Mesoscale Flow Fields B.W. Atkinson. II. Boundary Conditions and Treatment of Topography in Limited-Area models D.P. Eppel, U. Callies. III. Thermodynamic and Radiative Processes in the Atmosphere M. Beniston, J. Schmetz. IV. Atmospheric Boundary-Layer Processes and Influence of Inhomogeneous Terrain F.T.M. Nieuwstadt. V. Some Topics in Turbulent Diffusion H. van Dop. VI. Modelling Diffusion and Dispersion of Pollutants T. Mikkelsen. VII. Climatology of Cities P.G. Mestayer, S. Anquetin. VIII. Inversion Layers E. Fedorovich. Index.

Laser induced fluorescence (LIF) is used to construct images of passive scalar concentration fields in turbulent flows. This technique was applied by Koochesfahani & Dimotakis (1986) and Dahm & Dimotakis (1990). We developed this technique into a flow tomography to observe three-dimensional turbulent fields of order of the Taylor microscale with a resolution sixteen times smaller than the Kolmogorov length scale.

A problem of asymmetric swirling flow in a pipe has been analyzed by the finite volume numerical simulation of the three-dimensional incompressible Navier-Stokes equations expressed in cylindrical polar coordinates. The swirl is generated by one tangential inlet near the closed base of the duct. Because of the high value of the swirl number, S, a vortex breakdown forms near the base of the cylinder; it is of bubble-like shape. Downstream of the bubble the axial flow is at first wavy and finally tends toward the Poiseuille profile, while the swirl decays exponentially. At high enough axial Reynolds number, Re, the flow becomes time dependent.

The magnetic and electrical properties of new copper arylcarboxylates are presented. Special emphasis on copper(II) terephthalate trihydrate (CuTT) is given, and the magnetic and electrical properties are correlated with the crystal structure, recently determined by us. We have obtained new conductor materials by partial reduction of CuTT. The properties of these new compounds are discussed.

We present a fractal analysis of severe convective storms using data collected during a recent hail suppression experiment ``Grossversuch IV'' in Switzerland. For larger clouds, a fractal shape is observed and from an analysis of the perimeter-to-area relation the fractal (i.e., Hausdorff) dimension is found to be ${\mathrm{D}}_{\mathrm{s}}$=1.36\ifmmode\pm\else\textpm\fi{}0.1 in agreement with the value 1.35 from the theory of relative turbulent diffusion and an earlier analysis of cloud shapes. Moreover, a particle drift, present in strong lateral winds as well as in the center of hail clouds, is presumably responsible for a rather sharp crossover to a smooth behavior (${\mathrm{D}}_{\mathrm{s}}$=1) showing the existence of an apparent characteristic length.

The interface roughening phenomenon is formulated in terms of a statistical model of thermally created atomic steps. The simple case of a length-proportional energy is equivalent to known roughening models featuring an infinite-order roughening phase transition with an exponentially diverging correlation length and interface thickness. If, in addition, a step bending energy is included which is different for up- and down-steps, the sharp roughening transition is destroyed and the correlation length and the interface thickness remain finite Hence, in this case, a roughening or surface melting transition is absent. Some estimates on the observability of this result, which has consequence, e.g. for the structural behaviour of solid surfaces and on the crystal growth mechanism, are made.

A recently developed efficient Monte-Carlo method is used to calculate the critical equilibrium properties of a 2-dimensional system of thermal loops (loop gas) in dependence of the line stiffness energys. With increasing s the critical temperatureT c (defining an Ising-like behaviour fors1,T c increases monotonically withs and defines anon-universal critical behaviour. The critical line is calculated in a phase diagram (i) as aT c -versus-s plot showing a dipT c =0 ats=1 and (ii) in a concentration (c)-versus-s diagram, describing, alternatively, a dilute system of rough polymers. In the latter diagram the critical concentration decreases monotonically withs fors 1.

The occurrence of disordered phases at low temperatures in adsorbed monolayers, as shown recently in a domain wall model, is discussed, the main results are summarized and some relevant experimental systems are mentionned.

On resout un modele statistique de parois domaines lineaires en interaction sur le reseau carre a l'aide de resultats exactes et numeriques d'un modele 8-sommets equivalent

The excluded-volume problem of a system of m flexible polymers with given lengths N(α), (α = 1, …, m) is described by the spin-anisotropic vector model with n·m components upon taking the limit n→0. The anisotropic spin coupling constants J(α) and the components h(α) of the external field are related to N(α) and the total monomer concentration c. An interesting application to the psi-transition of the DNA in biological systems is discussed briefly.

Resultats de mesures thermodynamiques et de diffraction d'electrons de faible energie dans le cas d'azote moleculaire faiblement chimisorbe sur la surface Ni(110), entre 87 et 150 K. La phase commensurable (2×1) se transforme avec les recouvrements croissants en une serie de structures solides incommensurables

Two roughening phenomena are discussed. The kink-driven line roughening of high-indexed surfaces (such as fcc(113), (115) and (117), discussed in various papers recently) is presumably undergoing an Ising-type transition in contrast to the step-driven surface roughening which shows either a Kosterlitz-Thouless-type infinite-order phase transition, or, depending on the step energy parameters, a smooth cross-over only.

Magnetic and transport properties of superconductors with a periodic array of twinning planes (TP's) are studied for the case of an increase of the critical temperature in the neighborhood of a TP. Based on the modified London model, the critical magnetic field Hc1, the barrier field Hs, and the critical current jc(H) are calculated for low temperatures much less than Tc. For “resonant” vortex configurations, a peak in the curve jc(H) is predicted with a peak value which cannot be larger than 106 A/cm2. Furthermore, the interplay of the bulk and surface pinning for T≪Tc as well as the magnetic and transport properties for Tc0

The equilibrium roughening of perfect, clean, crystalline surfaces is described in terms of thermally created atomic steps in the frame of a lattice model (loop gas). If the bending energies for convex and concave step corners are different, the ``particle-hole'' symmetry is destroyed and the sharp infinite-order roughening transition disappears. Instead, a rather smooth crossover from a smooth to a rough surface occurs. A simple model illustrates this result, which is expected to be important for the crystal-growth process and for surface-catalytic reactions.

A recently proposed statistical model for the two-dimensional reconstruction transition of H/Ni(110) is investigated using a suitable fast Monte Carlo formalism. The phase diagram is presented for some range of the parameter values. Various low temperature (LT) non-reconstructed, and homogeneous and pairing-row reconstructed phases are found. Near the phase boundaries the approach to equilibrium is strongly slowed down due to topological constraints. Similar features are reported from experimental studies on the clean Pd(110) surface.

An analysis of recent radar data on hail clouds yields, for larger clouds, a fractal shape with a fractal (Hausdorff) dimension D1, = 1.36 ± 0.1 in agreement with an earlier analysis of cloud shapes by Lovejoy 9 and the theory of relative turbulent diffusion 10 . Moreover, a particle drift, present in strong winds as well as in the center of hail clouds is presumably responsible for a rather sharp cross-over to a smooth behaviour (D1 = 1) showing the existence of an apparent characteristic length.

The present work focuses on the flow characteristics and mixing induced by Sulzer SMRX static mixers. It is obsd. both exptl. and numerically that pressure drop increases linearly with velocity for this mixer type and that, as expected, this effect is amplified when multiple mixers are placed in the flow field. It is further shown numerically that the slope of the pressure drop vs. velocity curve increases for increasing internal mixer tube crossing angles. Moreover, it is found that mixing efficiency is a strong function of the internal tube crossing angle. Finally, anal. of the pressure drop results, particle patterns at the reactor outlet, streamlines, and the intensity of segregation suggests that the optimum configuration of an SMRX mixer is one with a 90 Deg internal tube crossing angle. It also shows to what extent the use of two static mixers provide enhanced mixing compared to one. [on SciFinder (R)]

The use of microcomputers (Personal Computers, Home Computers) for sophisticated scientific calculations is exemplified. A fast Monte Carlo program is applied to simulate a whole class of statistical models on the two-dimensional square lattice in the critical region. Specifically, results on the critical behaviour of the loop gas model order parameter are presented, which show that the model lies in the Ising universality class.

Adsorption along a linear chain of adsorption sites is considered in an Ising model with nearest neighbor interactions. The kinetics are studied in a master equation approach with transition probabilities describing single spin flips to mimic adsorption-desorption processes. Exchange of two spins to account for diffusion can be included as well. Numerical results show that desorption is frequently of fractional (including zero) order. Only at low coverage and high temperature is desorption a first order process. Finite size effects and readsorption are also studied.