ALBERT — All Library Books, journals and Electronic Records Telegrafenberg

1

Electronic Resource

Tribological properties of chromium implanted silicon nitride ceramics correlated with microstructure (1997)

Brenscheidt, F. ; Wieser, E. ; Matz, W. ; [et al.]

Springer

Applied physics 65 (1997), S. 281-286

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ISSN: 1432-0630

Keywords: PACS: 81.40; 61.80; 62

Source: Springer Online Journal Archives 1860-2000

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

Notes: 3 N4 ceramic after chromium implantation were investigated for the dependence on implantation energy between 200 keV and 3 MeV at a fixed fluence of 1017 ions/cm2. The wear of the modified material is reduced for a load of 2 N independent of ion energy accompanied by a slight increase of the friction coefficient. At higher loads only high-energy implantations result in improved wear behaviour. Structural investigations show the absence of any new phases formed by ion implantation. All energies result in an amorphous layer. For lower energies this amorphous layer reaches up to the surface whereas at higher energies it is covered by still-crystalline but damaged material. The observed wear behaviour can be explained with the amorphization of the near surface region and the stress generated by the volume swelling of the amorphous layer.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s003390050579

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2

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Rapid communicationPhotoelectron emission in femtosecond laser assisted scanning tunneling microscopy (1997)

Pfeiffer, W. ; Sattler, F. ; Vogler, S. ; [et al.]

Springer

Applied physics 64 (1997), S. 265-268

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ISSN: 1432-0649

Keywords: PACS:42.65.Re, 73.40.Gk, 79.60.-i

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Notes: Abstract. Direct illumination of the tunneling gap in an ultrahigh vacuum scanning tunneling microscope with ultrashort pump-probe laser pulses may offer ultimate spatial and temporal resolution in surface experiments. The electronic bandwidth of the tunneling gap ( $〈$ 1 THz) does not limit the time resolution. Our experiments show that multiphoton photoelectron emission from the sample limits the application of this detection scheme at high laser fluence. However, a substrate specific pump-probe effect in the photoelectron yield with femtosecond transients is observed on Tantalum and on GaAs(110) surfaces.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s003400050173

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3

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Neural clustering networks based on global optimisation of prototypes in metric spaces (1997)

Galicki, Miroslaw ; Möller, Ulrich ; Witte, Herbert

Springer

Neural computing & applications 5 (1997), S. 2-13

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ISSN: 1433-3058

Keywords: Global optimisation ; Clustering ; Unsupervised learning ; Neural networks ; Random optimisation ; EEG processing

Source: Springer Online Journal Archives 1860-2000

Topics: Computer Science , Mathematics

Notes: Abstract The utilisation of clustering algorithms based on the optimisation of prototypes in neural networks is demonstrated for unsupervised learning. Stimulated by common clustering methods of this type (learning vector quantisation [LVQ, GLVQ] and K-means) a globally operating algorithm was developed to cope with known shortcomings of existing tools. This algorithm and K-means (for the common methods) were applied to the problem of clustering EEG patterns being pre-processed. It can be shown that the algorithm based on global random optimisation may find an optimal solution repeatedly, whereas K-means provides different sub-optimal solutions with respect to the quality measure defined as objective function. The results are presented. The performance of the algorithms is discussed.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01414098

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4

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Detection of scopolin in the grapefruit (Citrus paradisi Macf.) (1997)

Runkel, Michael ; Moeller, Anja ; Tegtmeier, Martin ; [et al.]

Springer

Fresenius' journal of analytical chemistry 359 (1997), S. 516-520

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ISSN: 1432-1130

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology

Notes: Abstract Ripe fruits of Citrus paradisi Macf. and their juices contain high concentrations of scopolin (β-glucopyranoside of 7-hydroxy-6-methoxycoumarin). The identity of the aglycon being scopoletin was proven analysing extracts of β-glucosidase-treated fruit preparations with TLC, HPLC and GC-MS techniques. The naturally occurring glycoside was identified as the glucoside of scopoletin comparing it with authentic scopolin. The intake of scopolin of either grapefruits or juices thereof leads to a renal excretion of its aglycon as a glucuronide. The excretion is complete within 24 h. An enzymatic hydrolysis of the glucuronide produces scopoletin (i.e. aglycon) which can be quantified by HPLC. Mass spectra revealed that scopoletin releases one methyl- and two carbonyl-groups. The molecule finally breaks into fragments of 51 and 69 atomic mass units.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s002160050623

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5

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Inhibition of complex I by neuroleptics in normal human brain cortex parallels the extrapyramidal toxicity of neuroleptics (1997)

Maurer, Iris ; Möller, Hans-Jürgen

Springer

Molecular and cellular biochemistry 174 (1997), S. 255-259

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ISSN: 1573-4919

Keywords: mitochondria ; neuroleptics ; oxidative phosphorylation ; complex I

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Chemistry and Pharmacology , Medicine

Notes: Abstract There is increasing evidence that a defect of the mitochondrial respiratory chain is implicated in the development of Parkinson disease. Decreased complex I activity of the mitochondrial respiratory chain has been reported in platelets, muscle, and brain of patients with Parkinson disease. Extrapyramidal symptoms (e.g. parkinsonism and dystonic reactions) are major limiting side effects of neuroleptics. Experimental evidence suggests that neuroleptics inhibit complex I in rat brain. There has not been a study of the effects of neuroleptics in human tissue, however. We therefore analyzed the activities of complexes I + III, complexes II + III, succinate dehydrogenase, complex IV (cytochrome c oxidase), and of citrate synthase in normal human brain cortex after the addition of haloperidol and chlorpromazine and the atypical neuroleptics risperidone, zotepine, and clozapine. Activity of complex I was progressively inhibited by all neuroleptics. Half maximal inhibition (IC50) was 0.1 mM fo r haloperidol, 0.4 mM for chlorpromazine, and 0.5 mM for risperidone and zotepine. Clozapine had no effect on enzyme activity at concentrations up to 0.5 mM, followed by a slow decline with a maximum inhibition of 70% at 10 mM. IC50 was at about 2.5 mM. Thus, the concentration of clozapine needed to cause 50% inhibition of the activity of complexes I and III was about 5 times that of zotepine and risperidone, about 6 times that of chlorpromazine, and 25 times that of haloperidol. The inhibition thus paralleled the incidence of extrapyramidal effects caused by the different neuroleptics as they are known from numerous clinical studies. Our data support the hypothesis that neuroleptic-induced extrapyramidal side effects may be due to inhibition of the mitochondrial respiratory chain. (Mol Cell Biochem 174: 255–259, 1997)

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1006872911332

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6

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Seltenerdelement-, Yttrium-Gehalte und Bleiisotope in Thermal- und Mineralwässern des Schwarzwaldes (1997)

Möller, Peter ; Stober, Ingrid ; Dulski, Peter

Springer

Grundwasser 2 (1997), S. 118-132

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ISSN: 1432-1165

Source: Springer Online Journal Archives 1860-2000

Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences

Description / Table of Contents: Abstract In the Black Forest, mineral waters from five wells in crystalline basement (granite and gneisses), their probable source rocks and the experimental leachates were evaluated for rare earth elements (REE), yttrium contents, and lead isotope ratios. The distribution of REE and Y, and the Pb-isotope ratios are powerful tools to identify the most likely type of rock that controls cation contents of the mineral water. Granites and gneisses lead to REE patterns with varying negative europium anomalies in waters; i. e., gneisses have a tendency for positive or only slightly negative europium anomalies in fluids, whereas granites exhibit negative anomalies. The comparison of REE and Y in the leachates and waters shows that these elements are characteristically redistributed during water-rock inter-action between rock-forming and accessory minerals, surface layers and adsorption films. REE and Y are leachable in the aquifer rocks, in which light REE are partially impoverished. REE and Y in samples from surface outcrops show enhanced leachable fractions. In alterated rocks, large fractions of 206 Pb are definitely leached from other solid phases than 207 Pb and 208 Pb.

Notes: Kurzfassung Seltenerdelement(SEE)- und Yttrium(Y)-Gehalte sowie Bleiisotopen-Verhältnisse wurden in den potentiellen Aquifergesteinen, deren experimentellen Laugungslösungen und den Mineralwässern ermittelt. Für diese Studie wurden Mineralwässer aus fünf Bohrungen im kristallinen Grundgebirge (Granit und Gneis) des Schwarzwaldes ausgewählt. Die Verteilung der Lanthaniden, des Yttriums und der Bleiisotope sind geeignete Mittel, um das Gestein zu erkennen, das den Kationengehalt der Mineralwässern dominant prägt. Gneise und Granite führen zu Lanthanidenmustern mit unterschiedlichen Europium-Anomalien; Wässer aus Gneisen sind eher durch positive, aus Graniten häufig durch negative Europium-Anomalien charakterisiert. Der Vergleich der SEE- und Y-Gehalte in den Laugungslösungen mit denen der Wässer zeigt auf, wie sich in den Wasserleitern die Einbindung dieser Elemente in den Mineralen und Akzessorien, ihren Oberflächenzonen und Adsorbatfilmen gegenüber den weniger alterierten Gesteinen der Umgebung verändert hat. SSE und Y sind in den Wasserleitern gut laugbar, teilweise sind diese bereits an den leichten SEE verarmt, während die SEE- und Y-Gehalte in den Gesteinsproben von Oberflächenaufschlüssen insgesamt höher und insbesondere an leichten SEE nicht verarmt sind. 206 Pb wird zu einem erheblichen Teil aus anderen Festphasen als 207 Pb und 208 Pb gelaugt.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s767-1997-8533-0

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7

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Experimental, geochemical, mineralogical and O-isotope constraints on the late-magmatic history of the Fichtelgebirge granites (Germany) (1997)

Irber, W. ; Förster, H.-J. ; Hecht, L. ; [et al.]

Springer

Geologische Rundschau 86 (1997), S. S110

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ISSN: 0016-7835

Keywords: Key words Leaching experiments ; Cation exchange resin ; Zr ; Sr ; Trace element fractionation ; Zr/Hf ; Y/Ho ; Rare earth elements ; Tetrad effect ; Metamictization ; Magmatic-hydrothermal alteration ; Greisenization ; S-type granites ; Variscan granites ; Tin granites

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract Mineralogical, experimental, geochemical and stable-isotope data give evidence for an aqueous late-stage fluid which develops increasingly from the less to the more highly evolved granites of the Fichtelgebirge (G1–G4). In less-evolved granites (particularly G1) only minor chloritization and sericitization, minor hydration and corrosion of zircons, low leachable fractions of Sr and Zr, the nearly chondritic ratios of Zr/Hf and Y/Ho, and rare-earth-element (REE) patterns lacking the tetrad effect provide evidence of a less-differentiated granitic melt system, poor in complexing agents and water, with insignificant late magmatic fluid–rock interaction. The subsequent low-temperature alteration, which is suggested by oxygen-isotope composition of quartz and biotite, did not affect the whole-rock chemical composition. In the highly evolved granites (particularly G4), albitization, sericitization and fluoritization, ubiquitous hydration and corrosion of zircons, high leachable fractions of Sr and Zr, Zr/Hf and Y/Ho ratios very different from the chondritic ratios, and REE patterns showing a marked tetrad effect point to the presence of a highly specialized fluid system, rich in water and complexing agents, such as fluorine, leading to a marked magmatic–hydrothermal alteration. The oxygen isotopes also indicate alteration by high-temperature fluids which were likely exsolved during the final stage of crystallization.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/PL00014647

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8

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Element mobility in paragneisses and metabasites of the Continental Deep Drilling Project (KTB/Germany) (1997)

Möller, P. ; Irber, W. ; Giese, U.

Springer

Geologische Rundschau 86 (1997), S. S184

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ISSN: 0016-7835

Keywords: Key words Leaching experiment ; Cation-exchange resin ; Alteration ; Hydrothermal fluids ; Element transport ; Shear zone ; Factor analysis

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract Leaching experiments (pH=3, T=70 °C) have been performed on paragneisses and metabasites from the KTB drill cores. The experiments yielded the fraction of total element content that is easily available to acidic aqueous fluids. The intensity of mineralogic alteration in the studied samples is expressed in terms of easily leachable fractions of K or Ba. Its reliability is shown by correlation with a petrographically determined alteration index. For the paragneisses, the easily available fractions of Fe, Mg, Mn, Ca, Na, K, Ba, Co, Cr, Ni, Sr, V, and Y together with the variables whole-rock content and depth of samples were subjected to a factor analysis, the results of which are presented as a five-factor model. Correlation plots of easily leachable element fraction and whole-rock content vs an alteration index (percentage of leachable K) reveal the changes in leachability as a function of intensity of alteration. In a cataclastic boundary between paragneisses and metabasites at 1610 m depth, the changes in whole-rock content and leachability of elements are studied in detail and compared with the general trends in alteration. The results point to considerable intercrystalline element redistribution during retrograde metamorphism, with only insignificant element transport on a meter scale. Although considerable fractions of many elements were easily available to acidic fluids (3〈pH〈4) in the experiments, the whole-rock element content was maintained during retrogression, suggesting that water/rock ratio and fluid flow were low. During alteration K, Ba, Fe, Co, Ni, Cr, and V are immobilized in situ, whereas Sr, Ca, and Y become more leachable. Across the studied, strongly altered, lithologic contact, element transport up to 7 m normal to foliation can be traced. Here, Ca, Sr, Mg, Co, Ni, and Cr are slightly enriched, whereas K, Ba, Fe, and Mn are slightly depleted.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/PL00014653

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