Phase-field modeling of grain-boundary premelting using obstacle potentials.

We investigate the multiorder parameter phase field model of Steinbach and Pezzolla [Physica D 134, 385 (1999)] concerning its ability to describe grain boundary premelting. For a single order parameter situation solid-melt interfaces are always attractive, which allows us to have (unstable) equilibrium solid-melt-solid coexistence above the bulk melting point. The temperature-dependent melt layer thickness and the disjoining potential, which describe the interface interaction, are affected by the choice of the thermal coupling function and the measure to define the amount of the liquid phase. Due to the strictly finite interface thickness the interaction range also is finite. For a multiorder parameter model we find either purely attractive or purely repulsive finite-ranged interactions. The premelting transition is then directly linked to the ratio of the grain boundary and solid-melt interfacial energy.

Solidification in syntectic and monotectic systems.

We present theoretical studies of syntectic and monotectic solidification scenarios. Steady-state solidification along the liquid-liquid interface in a syntectic system is considered by means of a boundary-integral technique developed previously. We study the case of small asymmetry of the pattern and extract from the results the scaling relations in terms of the undercooling and the asymmetry parameter. We also investigate monotectic solidification using the phase-field method. We present two kinds of two-phase fingers, with the solid phase being either the exterior phase or the interior phase, and the pattern corresponding to the growth along the solid-liquid interface. We finally analyze the asymptotic shape of these new morphologies far behind their tip.

Solidification along the interface between demixed liquids in monotectic systems.

The steady-state solidification along the liquid-liquid interface in the monotectic system is discussed. A boundary-integral formulation describing the diffusion in the two liquid phases is given and the corresponding equations for the three interfaces (two solid-liquid interfaces and one liquid-liquid interface) are solved. Scaling relations are extracted from the results and supported by analytic arguments in the limit of small deviation from the monotectic temperature. We present also a complementary phase-field simulation, which proves the stability of the process.

Growth of a two-phase finger in eutectics systems.

We present a theoretical study of the growth of a two-phase finger in eutectic systems. This pattern was observed experimentally by Akamatsu and Faivre [Phys. Rev. E 61, 3757 (2000)]. We study this two-phase finger using a boundary-integral formulation and we complement our investigation by a phase-field validation of the stability of the pattern. The deviations from the eutectic temperature and from the eutectic concentration provide two independent control parameters, leading to very different patterns depending on their relative importance. We propose scaling laws for the velocity and the different length scales of the pattern.

Pattern formation during diffusional transformations in the presence of triple junctions and elastic effects.

We compare different scenarios for dendritic melting of alloys with respect to the front propagation velocity. In contrast to conventional dendritic growth, selection can here be also due to the presence of a grain boundary or coherence strains, and the propagation speed is higher. The most favorable situation is partial melting, where two parabolic fronts, one melting and one solidifying interface, are moving together, since the process is then determined by diffusion in the thin liquid layer. There, and also in phase field simulations of melting in peritectic and eutectic systems, we observe a rotation of the triple junction relative to the growth direction. Finally, we discuss the role of elastic effects due to density and structural differences on solid-state phase transformations, and we find that they significantly alter the selection principles. In particular, we obtain free dendritic growth even with isotropic surface tension. This is investigated by Green's function methods and a phase field approach for growth in a channel and illustrated for the formation of a twin phase.

Theory of dendritic growth in the presence of lattice strain.

We discuss elastic effects due to lattice strain which are a new key ingredient in the theory of dendritic growth for solid-solid transformations. Both thermal and elastic fields are eliminated by Green's function techniques, and a closed nonlinear integro-differential equation for the evolution of the interface is derived. We find dendritic patterns even without the anisotropy of the surface energy required by classical dendritic growth theory. In this sense, elastic effects serve as a new selection mechanism.

Velocity selection problem in the presence of the triple junction.

Melting of a bicrystal along the grain boundary is discussed. A triple junction plays a crucial role in the velocity selection problem in this case. In some range of the parameters an entirely analytical solution of this problem is given. This allows us to present a transparent picture of the structure of the selection theory. We also discuss the selection problem in the case of the growth of a "eutectoid dendrite."

Percutaneous portal vein embolisation in preparation for extended hepatic resection of primary nonresectable liver tumours.

BACKGROUND: In patients with malignant primary and secondary liver tumours or proximal bile duct carcinoma radical surgery is superior to all other therapeutic modalities in terms of survival and quality of life. Radical resection, however, often requires the removal of a large amount of liver parenchyma, resulting in a marked reduction of functional liver tissue with the risk of liver failure. AIM: Preoperative partial portal vein embolisation induces hypertrophy of the controlateral liver and thereby increases the safety of extended liver resections. PATIENTS AND METHODS: Between January 1997 and February 2001 we applied this strategy in 19 patients with primary and secondary nonresectable hepatobiliary malignancies, in whom the estimated amount of the remnant liver was < or =25% of the liver volume. RESULTS: The increase in volume ranged between 7 and 245%. Radical extended liver resection was performed in 13 patients (68%) without mortality. After a mean observation time of 22 months patient survival was 19 months with six tumour-related deaths during the second year after surgery. The remaining seven patients are alive and well with tumour recurrence in one. CONCLUSION: Preoperative partial portal vein embolisation allows more patients with previously unresectable liver tumours to benefit from a potentially curative resection.

Radiologic abnormalities and low back pain in elite skiers.

Lumbar radiographs of 120 adolescent elite skiers were evaluated for radiologic abnormalities by two independent observers. All athletes had no symptoms before the study. Radiographs were taken before enrollment of the students in elite level training. To determine the clinical significance of these abnormalities, all athletes were observed prospectively during the subsequent 2-year period for development of low back pain under high performance training. Anterior end plate lesions, Schmorl's nodes, posterior end plate lesions, spondylolysis, scoliosis, and spina bifida occulta were found. The depth of anterior end plate lesions showed a two-peak distribution, with peaks at 11% and 22% and a valley at 18% vertebral body height. The overall low back pain incidence was 12.5%. Students with severe anterior lesions (greater than 18% vertebral body height, n = 25) had significantly more low back pain (incidence, 32%) than did students without severe anterior lesions (incidence, 7.4%). Accordingly, students with severe anterior lesions had a significantly higher risk of having low back pain develop. Moderate end plate lesions and other abnormalities were not related to an increased incidence of low back pain. Adolescent students of elite sports with severe lumbar anterior end plate lesions have an increased risk of having low back pain develop under high performance training.

[Value of sonography in kidney transplantation]. / Stellenwert der Sonographie in der Nierentransplantation.

Colour coded duplex sonography (CCDS) is the method of choice in diagnostic monitoring of kidney transplants. Lack of radiation exposure, easy accessibility and high resolution have contributed to the fact that CCDS is used to monitor kidneys after transplantation. However, the value of CCDS in diagnosis of rejection is still a matter of debate. CCDS is used to evaluate perfusion of transplanted kidneys, detect renal artery stenosis or real vein thrombosis and arteriovenous fistulas. The value of recent technical advances, such as 3D Sonography, contrast harmonic imaging and tissue harmonic imaging, is currently being tested. This article focuses on indications and limitations of CCDS in the diagnosis of functional impairment of transplanted kidneys.

[A passive sampler for nitrogen dioxide]. / Passivsammler für Stickstoffdioxid.

Passive samplers run without electric power supply, are easy to handle and thus are suitable for exposure measurements in epidemiological studies, to evaluate indoor air quality, to control ambient concentrations etc. Passive sampler values agree with continuous measuring apparatus within 85 to 105% and the lower detection limit is 4 micrograms/m3 for a one week exposure or longer.