Transitions in rapidly rotating convection driven dynamos.

Numerical simulations of dynamos in rotating Rayleigh-Bénard convection in plane layers are presented. Two different types of dynamos exist which obey different scaling laws for the amplitude of the magnetic field. The transition between the two occurs within a hydrodynamically uniform regime which can be classified as rapidly rotating convection.

Experimental determination of zonal winds driven by tides.

We describe a new phenomenon of zonal wind generation by tidal forcing. Following a recent theoretical and numerical analysis [A. Tilgner, Phys. Rev. Lett. 99, 194501 (2007)], we present the first experimental evidence that the nonlinear self-interaction of a tidally forced inertial mode can drive an intense axisymmetric flow in a rotating deformed sphere. Systematic measurements of zonal flows are carried out by an embarked system of particle image velocimetry, allowing the determination of general scaling laws. These results are fully relevant for zonal winds generation in planets and stars, and illustrate a generic mechanism of geostrophic flow generation by periodic forcing.

Heat transport in rotating convection without Ekman layers.

Numerical simulation of rotating convection in plane layers with free slip boundaries show that the convective flows can be classified according to a quantity constructed from the Reynolds, Prandtl, and Ekman numbers. Three different flow regimes appear: laminar flow close to the onset of convection, turbulent flow in which the heat flow approaches the heat flow of nonrotating convection, and an intermediate regime in which the heat flow scales according to a power law independent of thermal diffusivity and kinematic viscosity.

Fast Peroxy Radical Isomerization and OH Recycling in the Reaction of OH Radicals with Dimethyl Sulfide.

Dimethyl sulfide (DMS), produced by marine organisms, represents the most abundant, biogenic sulfur emission into the Earth's atmosphere. The gas-phase degradation of DMS is mainly initiated by the reaction with the OH radical forming first CH3SCH2O2 radicals from the dominant H-abstraction channel. It is experimentally shown that these peroxy radicals undergo a two-step isomerization process finally forming a product consistent with the formula HOOCH2SCHO. The isomerization process is accompanied by OH recycling. The rate-limiting first isomerization step, CH3SCH2O2 → CH2SCH2OOH, followed by O2 addition, proceeds with k = (0.23 ± 0.12) s-1 at 295 ± 2 K. Competing bimolecular CH3SCH2O2 reactions with NO, HO2, or RO2 radicals are less important for trace-gas conditions over the oceans. Results of atmospheric chemistry simulations demonstrate the predominance (≥95%) of CH3SCH2O2 isomerization. The rapid peroxy radical isomerization, not yet considered in models, substantially changes the understanding of DMS's degradation processes in the atmosphere.

Spatial correlation of temperature in turbulent Rayleigh-Bénard convection.

A cubic Rayleigh-Bénard cell is operated at a Rayleigh number of 1.5x10(9) and a Prandtl number of 6.1. The cell is equipped with thermistors placed along the vertical line through the center of the cell. The spatial correlation of temperature is deduced from simultaneous temperature recordings from these thermistors. The correlation function is well fitted by the sum of two exponentials. There is no cascade in the temperature field as only two characteristic length scales appear. The direct measurement of spatial correlations allows us to test the validity of Taylor's hypothesis in this flow.

Onset of dynamo action in an axisymmetric flow.

Peffley, Cawthorne, and Lathrop [Phys. Rev. E 61, 5287 (2000)] have reported on an experiment using liquid sodium, which studies the approach toward a self-generating dynamo. Their results challenge the traditional views of kinematic dynamo theory because (i) the modes of the magnetic field with the smallest decay rates appear to be nearly axisymmetric and (ii) the observed decay rates vary spatially. This report shows how these observations can be reconciled with kinematic dynamo theory.

Coherent structures in boundary layers of Rayleigh-Bénard convection.

A coherent structure is revealed experimentally by a dyeing technique in the boundary layer of Rayleigh-Bénard convection in water. Dye accumulates in streaks aligned with the mean flow. Possible mechanisms for the formation of these streaks are discussed.

Invisible mean field dynamos.

We provide examples of alpha(2) dynamos in spheres which generate magnetic fields that are confined to the conductor and are therefore undetectable in the surrounding vacuum.

[Transcutaneous oxygen partial pressure in the evaluation of circulatory disorders in myocutaneous island flaps in the rat]. / Der transkutane Sauerstoffpartialdruck zur Bewertung von Durchblutungsstörungen in myokutanen Insellappen der Ratte.

In rectus abdominis myocutaneous island flaps (3.0 x 1.5 cm) of 86 rats (Uje: WIST) transcutaneous oxygen tension measurements (tcPO2) were made by a Universal-PO2-Meter MO 10.1 (PRACITRONIC, Dresden, GDR) for monitoring flap viability following blood flow insufficiency produced experimentally. This insufficiency was induced by ligation of the pedicle vessels (superior epigastric artery and vein) on the 3rd, 4th, 5th and 7th day after flap reposition and by occlusion of these vessels with microclips for two hours. Only the tcpO2 differences between the intact skin and the contralateral myocutaneous island flap were used to assess effects on blood flow and not the absolute values. These differences were statistically insignificant between the right and left non-operated abdominal skin (0.24 +/- 0.11 kPa), the non-operated skin and the rectus abdominis myocutaneous island flap with intact pedicle vessels (group 2) (0.59 +/- 0.14 kPa) as well as flaps ligated at 5-days (0.71 +/- 0.18 kPa) in which vascular pedicle ligation were induced following incision of the cranial flap border. In the two-hour-ischemia group, the 3-days, 4-days and 7-days ligation groups the average tcpO2 differences were greater (1.17 +/- 0.40; 1.58 +/- 0.31; 1.24 +/- 0.22; 1.22 +/- 0.28 kPa) and statistically significant (p less than 0.05) in comparison to the myocutaneous flaps of group 2. Transcutaneous oxygen tension monitoring was useless in predicting flap survival in later postoperative blood flow insufficiency and in assessing the neovascularization. Only during the intraoperative manipulations or the early postoperative period (24 h) tcpO2 monitoring was valuable in assessing the blood supply of myocutaneous flaps in rats.

Magnetic energy dissipation and mean magnetic field generation in planar convection-driven dynamos.

A numerical study of dynamos in rotating convecting plane layers is presented which focuses on magnetic energies and dissipation rates and the generation of mean fields (where the mean is taken over horizontal planes). The scaling of the magnetic energy with the flux Rayleigh number is different from the scaling proposed in spherical shells, whereas the same dependence of the magnetic dissipation length on the magnetic Reynolds number is found for the two geometries. Dynamos both with and without mean field exist in rapidly rotating convecting plane layers.

Simulations of the kinematic dynamo onset of spherical Couette flows with smooth and rough boundaries.

We study numerically the dynamo transition of an incompressible electrically conducting fluid filling the gap between two concentric spheres. In a first series of simulations, the fluid is driven by the rotation of a smooth inner sphere through no-slip boundary conditions, whereas the outer sphere is stationary. In a second series a volume force intended to simulate a rough surface drives the fluid next to the inner sphere within a layer of thickness one-tenth of the gap width. We investigate the effect of the boundary layer thickness on the dynamo threshold in the turbulent regime. The simulations show that the boundary forcing simulating the rough surface lowers the necessary rotation rate, which may help to improve spherical dynamo experiments.

Convection in an ideal gas at high Rayleigh numbers.

Numerical simulations of convection in a layer filled with ideal gas are presented. The control parameters are chosen such that there is a significant variation of density of the gas in going from the bottom to the top of the layer. The relations between the Rayleigh, Peclet, and Nusselt numbers depend on the density stratification. It is proposed to use a data reduction which accounts for the variable density by introducing into the scaling laws an effective density. The relevant density is the geometric mean of the maximum and minimum densities in the layer. A good fit to the data is then obtained with power laws with the same exponent as for fluids in the Boussinesq limit. Two relations connect the top and bottom boundary layers: The kinetic energy densities computed from free fall velocities are equal at the top and bottom, and the products of free fall velocities and maximum horizontal velocities are equal for both boundaries.

Atmospheric stability of levoglucosan: a detailed laboratory and modeling study.

Levoglucosan, an important molecular marker for biomass burning, represents an important fraction of the water-soluble organic carbon in atmospheric particles influenced by residential wood burning and wildfires. However, particle phase oxidation processes of levoglucosan by free radicals are not well-known. Hence, detailed kinetic studies on the reactivity of levoglucosan with OH, NO(3), and SO(4)(-) radicals in aqueous solutions were performed to better understand the levoglucosan oxidation in the deliquescent particles. The data obtained were implemented into a parcel model with detailed microphysics and complex multiphase chemistry to investigate the degradation fluxes of levoglucosan in cloud droplets and in deliquescent particles. The model calculations show that levoglucosan can be oxidized readily by OH radicals during daytime with mean degradation fluxes of about 7.2 ng m(-3) h(-1) in summer and 4.7 ng m(-3) h(-1) in winter for a polluted continental plume. This indicates that the oxidation of levoglucosan in atmospheric deliquescent particles is at least as fast as that of other atmospherically relevant organic compounds and levoglucosan may not be as stable as previously thought in the atmosphere, especially under high relative humidity conditions.

Wave-driven dynamo action in spherical magnetohydrodynamic systems.

Hydrodynamic and magnetohydrodynamic numerical studies of a mechanically forced two-vortex flow inside a sphere are reported. The simulations are performed in the intermediate regime between the laminar flow and developed turbulence, where a hydrodynamic instability is found to generate internal waves with a characteristic m=2 zonal wave number. It is shown that this time-periodic flow acts as a dynamo, although snapshots of the flow as well as the mean flow are not dynamos. The magnetic fields' growth rate exhibits resonance effects depending on the wave frequency. Furthermore, a cyclic self-killing and self-recovering dynamo based on the relative alignment of the velocity and magnetic fields is presented. The phenomena are explained in terms of a mixing of nonorthogonal eigenstates of the time-dependent linear operator of the magnetic induction equation. The potential relevance of this mechanism to dynamo experiments is discussed.

Dynamo action with wave motion.

It is shown that time dependent velocity fields in a fluid conductor can act as dynamos even when the same velocity fields frozen in at any particular time cannot. This effect is observed in propagating waves in which the time dependence is simply a steady drift of a fixed velocity pattern. The effect contributes to magnetic field generation in numerical models of planetary dynamos and relies on the property that eigenmodes of the induction equation are not all orthogonal to each other.

Zonal wind driven by inertial modes.

Inertial modes are oscillatory modes in rotating fluids. Shear layers appear in inertial modes in spherical shells that become singularities in the inviscid limit. It is shown here that the nonlinearity in the shear layers drives a zonal flow whose amplitude diverges in the inviscid limit. These results are relevant for the dynamics of planets and stars in which inertial modes are excited by tidal forcing.

[Histopathology of the arterial wall after animal experiment microsurgical operations]. / Histopathologie der Arterienwand nach tierexperimentellen mikrochirurgischen Eingriffen.

Histologic findings on microvessels of laboratory animals are reviewed. Lesions of the microvascular wall may be caused by preparation, microvascular clips and anastomosis. The intensity of the closing pressure of microclips as well as the clipping time influence the extent of the damage. Thrombosis of microarteries was not seen, even after a clipping time of 2 hours. The vascular lesions were reparable. Four different techniques of anastomosis used experimentally and clinically were compared: end-to-end suture anastomosis (absorbable and non-absorbable sutures), telescopic 2-suture anastomosis, sutureless telescopic adhesive anastomosis (fibrinogen, IMMUNO AG Wien), and telescopic 2-suture adhesive anastomosis. The tissue restitution was better in suture anastomosis carried out with absorbable sutures than performed with non-absorbable suture material. The sutureless telescopic adhesive anastomosis is a very gentle method, but the anastomoses are not always stable enough. The advantages of the telescopic 2-suture adhesive anastomosis (absorbable sutures, fibrinogen adhesive) are relatively small lesions of the vascular wall, good restitution and sufficient stability. The patency rate (96%) corresponds to that of the end-to-end suture anastomoses (94%). The clinical application of the telescopic anastomosis is estimated critically, and evidently it is more suitable for microarteries than for microveins.

[Suture and gluing technics in microvascular surgery. Comparative animal-experiment clinical studies]. / Naht-und Klebetechniken in der Mikrogefässchirurgie. Vergleichende tierexperimentelle klinische Untersuchungen.

In 135 femoral vessels of rats (70 arteries, 60 veins) end-to-end anastomoses performed, using 3 different methods (anastomoses with interrupted sutures, two-suture telescopic anastomosis, sutureless telescopic anastomosis with fibrinogen adhesive). The advantages and disadvantages of these methods were investigated and valued by clinical aspects (time of anastomosing, patency rate, complications). The results showed that a combined two-suture-telescopic anastomosis using absorbable suture material and fibrinogen adhesive is very stable and causes minimal lesions of the vessel wall, so that this method will be a nearly ideal anastomosing technique.