Dissipation layers in Rayleigh-Bénard convection: a unifying view.

Boundary layers play an important role in controlling convective heat transfer. Their nature varies considerably between different application areas characterized by different boundary conditions, which hampers a uniform treatment. Here, we argue that, independent of boundary conditions, systematic dissipation measurements in Rayleigh-Bénard convection capture the relevant near-wall structures. By means of direct numerical simulations with varying Prandtl numbers, we demonstrate that such dissipation layers share central characteristics with classical boundary layers, but, in contrast to the latter, can be extended naturally to arbitrary boundary conditions. We validate our approach by explaining differences in scaling behavior observed for no-slip and stress-free boundaries, thus paving the way to an extension of scaling theories developed for laboratory convection to a broad class of natural systems.

Statistical analysis of global wind dynamics in vigorous Rayleigh-Bénard convection.

Experimental and numerical studies of thermal convection have shown that sufficiently vigorous convective flows exhibit a large-scale thermal wind component sweeping along small-scale thermal boundary layer instabilities. A characteristic feature of these flows is an intermittent behavior in the form of irregular reversals in the orientation of the large-scale circulation. There have been several attempts toward a better understanding and description of the phenomenon of flow reversals, but so far most of these models are based on a statistical analysis of few-point measurements or on simplified theoretical assumptions. The analysis of long-term data sets (>5×10(5) turnover times τ(t)=d/u(rms)) obtained by numerical simulations of turbulent two-dimensional Rayleigh-Bénard convection allows us to get a more comprehensive view of the spatio-temporal flow behavior. By means of a global statistical analysis of the characteristic spatial modes of the flow we extract information about the stability of dominant large-scale modes as well as the reversal paths in state subspace. We examine probability density functions and drift vector fields of two-dimensional state subspaces spanned by different large-scale spatial modes. This also provides information about the coexistence of dominant modes.

A profile of deaths in custody in Victoria, 1991-96.

In Victoria, all deaths in custody are investigated and a coronial inquest is held. The findings are entered into a data base held at the Victorian Institute of Forensic Medicine. Utilizing this data base, all listed cases of deaths in custody during the 6-year period, January 1991-December 1996, were reviewed. The deceased's age, sex, cause and mechanism of death and the custodial service under which they were held at the time of death were correlated. During the 6-year period, there was a total of 96 deaths (90 male, six female) ranging in age from 15-77 years. Of all the cases, 45 occurred whilst in police custody, 30 under corrective services and 21 involved non-custodial corrections. There were 31 accidental deaths, 29 suicides, 17 natural deaths, and 18 police shootings. Excluding police shootings, 42 deaths involved the presence of drugs or alcohol, either as a direct cause of death or as a contributory factor. Drug toxicity alone was implicated in 28 deaths. Deaths from unnatural causes remains the major cause of death of persons in custody. An awareness of these causes must assist in developing mechanisms to further reduce fatalities in this setting.

[Bertalanffy-like fluorescence staining with 3-dimethylamino-6-methoxyacridine]. / Uber eine Bertalanffy-analoge Fluorochromierung mit 3-Dimethylamino-6-methoxyacridin.

Three new acridine dyes, 3-dimethylamino-6-methoxyacridine 1, 3-amino-6-methoxyacridine 2 and 3-amino-7-methoxyacridine 3, have been prepared and tested as fluorochromes of LM- and HeLa-cells. The dyes are basic compounds (pKA: 1 8,76; 2 8,01; 3 7,65) and form cations in neutral or acidic aqueous solutions by addition of a proton to the aza-nitrogen atom of the heterocycle. The fluorochromes stain fixed LM- and HeLa-cells at pH = 6. The fluorescence shows metachromasy similar to the staining with acridine orange AO according to the technique of Bertalanffy. But there is less fading of the fluorescence. The dye 1 is the most suitable fluorochrome of the series. It was studied in detail. Using optimized staining conditions the fluorescence of the nucleus is yellow-green that of the cytoplasm and the nucleoli orange or brownish-red. Enzymatic digestion experiments show that the dye cations are bound to DNA in the nucleus and to RNA in the cytoplasm or nucleoli. The absorption and emission spectra of the stained cells have been studied by means of microspectrophotometry. The absorption spectra of the nucleus and the cytoplasm are very similar. The maximum of the long wave length absorption of both occurs at 21400 cm-1 (467 nm) with a shoulder at ca 20100 cm-1 (498 nm). The fluorescence spectra of nucleus and cytoplasm of metachromatically stained cells are different. The emission maximum of the cytoplasm and nucleoli, 16200 cm-1 (617 nm), is red-shifted relative to the maximum of the nucleus, 18200 cm-1 (549 nm). This shift causes the metachromatic fluorescence effect. In addition we studied the concentration dependence of the absorption and fluorescence spectra of the cation 1 in aqueous solution, pH = 6, in the concentration range 6 X 10(-6)-6 X 10(-4) M. Shape and maximum of the long wave length absorption and emission depend only slightly on the concentration: Mean value of absorption maximum ca 21500 cm-1 (465 nm), shoulder at ca 20300 cm-1 (493 nm), fluorescence maximum ca 18300 cm-1 (547 nm). With growing concentration diminishes the molar absorptivity. This decrease in absorptivity and isosbestic points in the absorption spectra indicate the formation of dimers with growing dye concentration. The absorption spectra of the metachromatically stained cells and of the dye in aqueous solution are very similar.(ABSTRACT TRUNCATED AT 400 WORDS)

[Fluorescent staining of chromosomes and nuclear structures in living LM- and HeLa-cells with new acridine dyes]. / Vitalfluorochromierung von Chromosomen und Kernstrukturen in LM- und HeLa-Zellen mit neuen Acridinfarbstoffen.

Fluorescent staining of chromosomes and nuclear structures (nucleolus associated chromatin) in living HeLa- and LM-cells (mouse fibroblasts) with new acridine dyes is reported. The dyes have aminoethylgroups in 9-position with different end groups at this residue (scheme of structures). Dyes without these 9-substituents only induce the formation of lysosomes. An exceptional position on vital staining of chromosomes and nuclear chromatin has the dye 3-amino-6-methoxy-9-(2-hydroxyethylamino)acridine 1. Concentrations of 10(-3) M can be used in vital staining experiments. Measuring the consumption of oxygen we could demonstrate that the dye has no effect on the activity of respiration even at these high dye concentrations. Therefore we conclude that we have really observed vital staining and not postvital staining of chromosomes and nuclear chromatin. Similar properties has the well known vital dye acridine orange.

[The fluorescent staining of mitochondria in living HeLa- and LM-cells with new acridine dyes (author's transl)]. / Uber die Vitalfluorochromierung von Mitochondrien in HeLa- und LM-Zellen mit neuen Acridinfarbstoffen.

The fluorescent staining of mitochondria in living cells with new acridine dyes is reported. The fluorescent dyes used are derivatives of acridine orange (AO) and of 3-amino-6-methoxyacridine (AMA) with various residues in 9- or 10-position (Scheme 1). They are either permanent cationic dyes or cations which are formed by protonation in the culture medium. HeLa cells and mouse fibroblasts (LM cells) have been used for our staining experiments. On favourable conditions we succeeded in staining the mitochondria not only orthochromatically but also metachromatically. Photodynamical effects which have been observed during the exposure of the stained cells in the fluorescence microscope are described. The residues in 9- or 10-position favour the dye accumulation in the mitochondria. Vital staining with the basic compounds AO and AMA however leads to the formation of metachromatically stained lysosomes in the orthochromatically stained cytoplasm. The dye 3-amino-6-methoxy-9-(2-hydroxyethyl)acridine stains the nucleus of living cells.