Search Results - (Author, Cooperation:Rüssel)

2018-03-31

American Chemical Society (ACS)

1528-7483

1528-7505

Chemistry and Pharmacology

Geosciences

Physics

2018-09-21

MDPI Publishing

1996-1944

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

A theoretical model is developed according to which crystals formed in a glass-forming melt can exhibit a previously unreported growth behavior. After growing very fast in one or two directions, the growth stops due to changes in concentration and turns into dissolution. Along the other direction(s) the growth rate is initially lower; it also slows down but never becomes negative. This is the result of a competition between several processes that take place simultaneously in a nonequilibrium system. Due to direction-dependent growth rates (the latter can vary over a large range), such behavior may result in the first step in the formation of plate or needlelike crystals. After a drop in the concentration of some key compounds (the crystals are consuming the latter), in the second stage the crystals approach their equilibrium shape since relaxation processes prevail. It is demonstrated with an example (mica plates formed from an extruded glass) that such effects in fact can be found experimentally. Although at this initial stage the model is quite simplified it leads to a surprisingly good agreement with the experimental data. It seems that there are many other examples of processes in nonequilibrium systems in which a given parameter is developing, at early stages, far beyond its equilibrium value, and later (when the resources of the system are becoming exhausted and consequently the growth rates slow down) relaxation kinetics dominates. © 1999 American Institute of Physics.

Electronic Resource

1551-2916

Blackwell Publishing Journal Backfiles 1879-2005

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

Nitrogen (via a polymeric AlN precursor) and ZrO2 are introduced into a MgO-CaO-Al2O3-SiO2-glass. Subsequent crystallization of the glass results in a fine-grained oxynitride glass-ceramic. The microstructure of the latter is found to be entirely different for nitrogen concentrations of 4.85 and 9.94 mol%. Not only do the phase contents differ, but also tetragonal zirconia is more effectively stabilized at higher nitrogen concentrations. Partial stabilization of tetragonal zirconia is not due to nitrogen incorporation but is based on an indirect effect: the spherical morphology of tetragonal zirconia precipitated at higher nitrogen contents suppresses the nucleation of the martensitic transformation. The beneficial effects of the introduction of nitrogen and the simultaneous incorporation of zirconia into a glass-ceramic result in overall improved mechanical properties.

Electronic Resource

1600-079X

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

The purpose of the present studies using artificial light was to determine how the timing and duration of exposure influence the light-induced suppression of pineal melatonin levels in hamsters. An 8-min exposure to 0.186 μW/cm2 of cool white fluorescent light caused a continued depression of pineal melatonin even when animals were returned to darkness. In addition, the pineal gland does not appear to change its sensitivity to light throughout the night. A 20-min exposure to 0.019 μW/cm2 of cool white fluorescent light did not significantly suppress pineal melatonin during any time of the melatonin peak, whereas a 20-min exposure to 0.186 μW/cm2was capable of always suppressing melatonin. Furthermore, increasing the duration of 0.019-μW/cm2 exposure to 30, 60, 120, or 180 min does not increase the capacity of this irradiance to depress melatonin.Similar to artifical light, natural light has a variable capacity for suppressing nocturnal levels of pineal melatonin. Twilight irradiances of 0.138 μW/cm2 or less did not suppress nocturnal melatonin whereas twilight irradiances of 3.0 μW/cm2 or greater did suppress pineal melatonin. A few animals did have lower melatonin after a 40-min exposure to full moonlight during July (0.045 μW/cm2) or January (0.240 μW/cm2). However, pineal melatonin levels remained high in the majority of animals exposed to full moonlight.

Electronic Resource

1437-1596

Springer Online Journal Archives 1860-2000

Medicine

Law

Electronic Resource

1439-0361

Springer Online Journal Archives 1860-2000

Biology

Summary α-, β-, γ-HCH, HCB Σ DDT, Dieldrin, Endrin, and Σ PCB were determined in 45 eggs and 8 livers of young Lapwings in 1984 and 1986. High concentrations of Dieldrin were found in eggs while those in livers of young Lapwings were lower. The low residues of the other pesticides and the moderate ones of Σ PCB are in accordance with the low trophic level of the Lapwing. The probable influence of the Dieldrin burden on the decline of Lapwing populations in several regions is discussed briefly.

Zusammenfassung 45 Eier und 8 Kükenlebern des Kiebitzes aus den Jahren 1984 und 1986 wurden auf α-, β-, γ-HCH, HCB, Σ DDT, Dieldrin, Endrin und Σ PCB untersucht. Hohe Konzentrationen an Dieldrin wurden in den Eiern gefunden, während die Lebern von Kiebitzküken geringer belastet waren. Die geringen Konzentrationen der übrigen Pestizide und die mäßige an Σ PCB entsprachen der niedrigen Trophieebene des Kiebitzes. Die Frage, ob die Belastung mit Dieldrin einen Einfluß auf den Rückgang von Kiebitzpopulationen in einigen Gebieten haben könnte, wird kurz diskutiert.

Electronic Resource

1439-0361

Springer Online Journal Archives 1860-2000

Biology

Summary Residues of chlorinated hydrocarbons in eggs and livers of some bird species — Tree Sparrow, House Martin, White Stork, Heron, Rook, Mallard, and further species — are presented. The dependence on place of breeding, food web, and migration is discussed.

Zusammenfassung Rückstände chlorierter Kohlenwasserstoffe in Eiern und Lebern von im Binnenland Niedersachsens brütenden Vogelarten — Feldsperling, Mehlschwalbe, Weißstorch, Graureiher, Saatkrähe, Stockente und andere Arten — werden angegeben und deren Abhängigkeit von Brutort, Nahrung und Zugverhalten diskutiert.

Electronic Resource

1439-0361

Springer Online Journal Archives 1860-2000

Biology

Summary Regional and interspecific differences of mercury residues were investigated in the eggs of seven species breeding at the German North Sea Coast (Tadorna tadorna, Haematopus ostralegus, Charadrius hiaticula, Larus argentatus, L. ridibundus, Sterna hirundo, S. sandvicensis). We found distinct geographical differences in contamination (Fig. 1): In eggs from the Elbe Eastuary (region V) maximum residues of mercury were ascertained. Eggs of Oystercatcher and Common Tern from the Bay of Helgoland (region VI) contained larger quantities than eggs from Northern Frisia (region VII). 353 from 355 eggs examined showed a value exceeding the legal standard value for eggs which is 0,03 mg/kg in Germany. Common Tern and Sandwich Tern eggs had the highest, Shelduck, Oystercatcher and Blackheaded Gull eggs the lowest mercury contamination (Fig. 2, 4.2.). With the exception of Shelduck and Herring Gull, residues in many eggs of the other species — at the river Elbe in all eggs — came up to a range endangering breeding success, especially in Common Terns.

Zusammenfassung Regionale und artliche Unterschiede der Rückstände von Quecksilber in Eiern von sieben Brutvogelarten der deutschen Nordseeküste wurden untersucht. Bei vier Arten stellten wir deutliche geographische Unterschiede in der Kontamination fest (Abb. 1). Höchstgehalte fanden wir in Eiern von der Elbmündung (Region V). Austernfischer- und Flußseeschwalbeneier von der inneren Deutschen Bucht (Region VI) enthielten größere Mengen als solche von Nordfriesland (Region VII). Der gesetzliche Richtwert für Eier (0,03 mg/kg) wurde von 353 der 355 untersuchten Eier überschritten. Fluß- und Brandseeschwalbe waren am stärksten, Brandgans, Austernfischer und Lachmöwe am wenigsten mit Quecksilber kontaminiert (Abb. 2, 4.2.). Mit Ausnahme von Brandgans und Silbermöwe erreichten die Rückstände in vielen Eiern der anderen Arten, an der Elbe sogar in allen Eiern, eine den Bruterfolg gefährdende Größenordnung, insbesondere bei der Flußseeschwalbe.

Electronic Resource

1437-1596

Springer Online Journal Archives 1860-2000

Medicine

Law

Electronic Resource

1437-1596

Springer Online Journal Archives 1860-2000

Medicine

Law

Electronic Resource

1437-1596

Springer Online Journal Archives 1860-2000

Medicine

Law

Electronic Resource

1437-1596

Springer Online Journal Archives 1860-2000

Medicine

Law

Electronic Resource

1437-1596

Springer Online Journal Archives 1860-2000

Medicine

Law

Electronic Resource

1437-1596

Springer Online Journal Archives 1860-2000

Medicine

Law

Electronic Resource

1437-1596

Springer Online Journal Archives 1860-2000

Medicine

Law

Electronic Resource

1437-1596

Springer Online Journal Archives 1860-2000

Medicine

Law

Electronic Resource

1432-0800

Springer Online Journal Archives 1860-2000

Energy, Environment Protection, Nuclear Power Engineering

Medicine

Summary Lead in liver, spleen and kidney of poisoned cattle is bound to substances containing ferric hydroxide. In liver and kidney the smaller amount of lead is sorbed by ferritin, the greater amount by insoluble ferric hydroxide. In the spleen ferritin and insoluble ferric hydroxide contain approximately the same amount of lead. The insoluble ferric hydroxide particles could be concentrated by digestion of insoluble liver proteins with phenol. They were not identical with hemosiderin. The sorption of lead ions and of other metal ions to ferritin and ferric hydroxide was investigated in vitro. Lead sorption is preferred over the sorption of other metal ions. Reaction of metal ions with the protein shell of ferritin occurred only with copper ions. The sorbed metal ions could be split from ferritin by high concentrations of other metal ions and strongly by hydrogen ions. It seems, that lead binding disturbs the storage of iron in tissues in lead poisoning.

Electronic Resource

1430-2772

Springer Online Journal Archives 1860-2000

Psychology

Electronic Resource

1573-4838

Springer Online Journal Archives 1860-2000

Medicine

Technology

Abstract The characterization of plasma spray induced changes become complicated by the formation of amorphous phases.31P magic angle spinning (MAS)-nuclear magnetic resonance (NMR) measurements are suited to detect both crystalline and amorphous calcium phosphates. Therefore, we used31P-MAS-NMR and X-ray diffraction (XRD) to characterize plasma-sprayed hydroxyapatite. Besides small quantities of nearly unchanged crystalline apatite, disordered partly X-ray amorphous apatite was detected. Additionally, a non-stoichiometric amorphous calcium phosphate phase possessing a structure similar to TCP, probably calcium enriched, was observed. No indications of tetracalciumphosphate could be found. The decomposition of apatite during plasma spraying is reversible. An additional annealing procedure of plasma-sprayed hydroxyapatite at suitable temperatures above 500 °C rebuilds crystalline apatite structure.

Electronic Resource