Three-dimensional convection of binary mixtures in porous media.

We investigate convection patterns of binary mixtures with a positive separation ratio in porous media. As setup, we choose the Rayleigh-Bénard system of a fluid layer heated from below. Results are obtained by a multimode Galerkin method. Using this method, we compute square and crossroll patterns, and we analyze their structural, bifurcation, and stability properties. Evidence is provided that, for a strong enough Soret effect, both structures exist as stable forms of convection. Some of their properties are found to be similar to square and crossroll convection in the system without porous medium. However, there are also qualitative differences. For example, squares can be destabilized by oscillatory perturbations with square symmetry in porous media, and their velocity isolines are deformed in the so-called Soret regime.

Roll and square convection in binary liquids: a few-mode Galerkin model.

We present a few-mode Galerkin model for convection in binary fluid layers subject to an approximation to realistic horizontal boundary conditions at positive separation ratios. The model exhibits convection patterns in form of rolls and squares. The stable squares at onset develop into stable rolls at higher thermal driving. In between, a regime of a so-called cross roll structure is found. The results of our few-mode model are in good agreement with both experiments and numerical multimode simulations.

Stationary and oscillatory convection of binary fluids in a porous medium.

We investigate numerically stationary convection and traveling wave structures of binary fluid mixtures with negative separation ratio in the Rayleigh-Bénard system filled with a porous medium. The bifurcation behavior of these roll structures is elucidated as well as the properties of the velocity, temperature, and concentration fields. Moreover, we discuss lateral averaged currents of temperature and concentration. Finally, we investigate the influence of the Lewis number, of the separation ratio, and of the normalized porosity on the bifurcation branches.

Thermal convection in mixtures with an inversion of the separation ratio.

We have numerically investigated Rayleigh-Bénard convection in binary mixtures assuming a thermal diffusion ratio that depends on the local temperature and changes its sign within the cell. The stationary instability has been found to precede the oscillatory one for a wide range of negative mean psi values. The bifurcation diagram for stationary rolls turns out to be qualitatively different from that for constant Soret effect. Nevertheless, it can be mapped onto this special case by using a scaling argument, taking into account the fact that for small convection amplitudes the rolls are restricted to parts of the cell where the sign of the Soret coefficient favors instability.

Convection patterns in colloidal solutions.

We investigate the bifurcation properties and pattern selection in Rayleigh-Bénard convecting binary mixtures for parameter combinations that are typical for colloidal fluids using the Galerkin method. In such fluids the typical Lewis numbers and separation ratios differ by orders of magnitude from the values found in molecular mixtures like alcohol/water. We study stationary rolls, square and crossroll patterns for positive separation ratios, and traveling waves for negative separation ratios. Results are compared to those for molecular mixtures.

Magnetization of concentrated polydisperse ferrofluids: cluster expansion.

The equilibrium magnetization of concentrated ferrofluids described by a system of polydisperse dipolar hard spheres is calculated as a function of the internal magnetic field using the Born-Mayer or cluster expansion technique. This paper extends the results of Huke and Lücke [Phys. Rev. E 62, 6875 (2000)] obtained for monodisperse ferrofluids. The magnetization is given as a power series expansion in two parameters related to the volume fraction and the coupling strength of the dipolar interaction, respectively.

Magnetization of ferrofluids with dipolar interactions: A born-mayer expansion

For ferrofluids that are described by a system of hard spheres interacting via dipolar forces we evaluate the magnetization as a function of the internal magnetic field with a Born-Mayer technique and an expansion in the dipolar coupling strength. Two different approximations are presented for the magnetization, considering different contributions to a series expansion in terms of the volume fraction of the particles and the dipolar coupling strength.

[Considerations in a long-term study on progressive cranio-carpo-tarsal osteolysis (author's transl)]. / Uberlegungen bei einer Langzeitstudie über eine progressive kranio-karpo-tarsale Osteolyse.

A long-term study conducted in a female patient who is now 21 years old and who showed a disease pattern similar to cranio-carpo-tarsal dystrophia, investigated thoroughly by Liersch and Hoevels when the girl was 6 years old. It must be stated as a result of this long-term study that in our case, the osteolyses at the wristbone (carpalia) and tarsal bone remained progressive up to the onset of puberty. The radiological changes came to a standstill after puberty had set in; in fact, there was even a certain amount of clinical compensation of the radiologically visible defects during the years that followed. It seems that the disease pattern described here, is limited to the growth period of the patient. It was not possible to classify this disease pattern as belonging to a particular category, and its cause remains largely unknown. The author describes the disease pattern as an "essential" one.

[Hyperextending ruptures of vessels in course of arthroplasties of the hip and knee (author's transl)]. / Der Uberdehnungsriss von Gefässen als Komplikation alloarthroplastischer Operationen

The authors referred specific complications in the course of arthroplasties of the hip and of the knee: hyper-extending-ruptures of vessels in sequence of indirect lesions. Causes of these so far not described complications are extreme passive articulations of hip respectively knee during operation. Clinical symptoms are enumerated, the pathogenetic mechanisms explicated and directions for treatment given. Important are the knowledge of these complications and the measure for their prophylaxis.