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Notizen: We have investigated boron doped Si1−xGex bulk crystals over the composition range 0≤x≤0.13 by photoconductivity, photoluminescence, and temperature-dependent Hall effect measurements. Hall effect measurements yield the relation EI=(44.4–108x) meV for the change of the boron ionization energy EI with alloy composition. The far-infrared photoconductivity onset caused by the shallow acceptor boron does not shift as much to lower energies with increasing Ge content as previously reported. Transitions that involve excited levels of the shallow acceptor boron are recognizable as a redshift of the photoconductivity onset with increasing temperature. Comparison of the Hall effect data with the shift of the photoconductivity spectra and the evaluation of photoluminescence linewidths give experimental evidence for an inhomogeneous distribution of Ge atoms in the alloy. © 1998 American Institute of Physics.

Notizen: We report on the change of shallow donor energy levels with alloy composition in Ge-rich Ge1−xSix bulk crystals. For phosphorus, we find a strong, linear increase of the ionization energy with increasing Si content for 0〈x〈0.1, whereas, for antimony the ionization energy shifts only slightly to higher energies with increasing Si content up to x=0.11. We observe a rapid increase of the antimony ionization energy in the composition range 0.11〈x〈0.16, where the change in the conduction band minimum from Ge- to Si-like occurs. The different behavior of phosphorus and antimony in Ge-rich GeSi reflects the different short range impurity potentials of these donors and, thus, different mixing of bands. © 1999 American Institute of Physics.

Notizen: Abstract: The distribution of myo-inositol, a substance that has been implicated in synaptic transmission, has been mapped within sections of the cat cochlear nucleus as well as some nearby regions. Highest values in the cochlear nucleus were found in regions of granule cells along the periphery of the anteroventral subdivision of the nucleus. Highest values overall were found in the molecular layer of the cerebellar flocculus. A fairly good correlation was found between myo-inositol levels and activities of the enzymes of acetyl-choline metabolism in the cat cochlear nucleus, supporting the possibility that myo-inositol may be involved in cholinergic synaptic transmission. No positive correlation was found between myo-inositol levels and the levels of glutamate, aspartate, glycine, or γ-aminobutyric acid (GABA). The most striking gradient of myo-inositol levels within a region was found in the auditory nerve, where different myo-inositol levels might be related to nerve fibers innervating different parts of the cochlea. The distribution of scyllo-inositol, a stereoisomer of myo-inositol, was also examined, and found to parallel closely the distribution of myo-inositol, with levels 4–5% as high.

Notizen: Abstract: The effects of synthetic β-amyloid (Aβ1–42) on cell viability and cellular Ca2+ homeostasis have been studied in the human neuron-like NT2N cell, which differentiates from a teratocarcinoma cell line, NTera2/C1.D1, by retinoic acid treatment. NT2N viability was measured using morphological criteria and fluorescent live/dead staining and quantified using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide metabolism. Aβ1–42 dose-dependently caused NT2N cell death when it was present in the cell culture for 14 days but had no effect on viability when it was present for 4 days. The lowest effective concentration was 4 µM, and the strongest effect was produced by 40 µM. Control NT2N cells produced spontaneous cytosolic Ca2+ oscillations under basal conditions. These oscillations were inhibited dose-dependently (0.4–40 µM) by Aβ1–42 that was present in the cell culture for 1 or 4 days. Ca2+ wave frequency was decreased from 0.21 ± 0.02 to 0.05 ± 0.02/min, amplitude from 88 ± 8 to 13 ± 4 nM, and average Ca2+ level from 130 ± 8 to 58 ± 3 nM. The Ca2+ responses to 30 mM K+ and 100 µM glutamate were not different between control and Aβ-treated cells. Thus, the results do not support the hypothesis that cytosolic early Ca2+ accumulation mediates Aβ-induced NT2N cell death.

Notizen: The present paper is devoted to the problem of teleology in modern biology. Teleology is restricted to the phenomenon of goal-directedness, whereas goal-intended actions are denied. Thus, only the aspect of seemingly material teleology or teleonomy is required which paraphrases functions of certain value for the self maintenance of a system and is explainable without reference to vitalistic premises.Some aspects of evolution and selection are discussed and subsumed under a systems-theoretically oriented view. Furthermore it is stressed that teleological explanations are compatible with causal (mechanical) ones. The result of these assertions is the possibility of the reconciliation of seemingly irreconcilable positions. This, last not least, means a plea for the re-assessment of an old and venerable problem.〈section xml:id="abs1-2"〉〈title type="main"〉RésuméCet article est consacré au problèm de la finalité dans la biologie moderne, » finalite «étant pris ici dans un sens restreint de »comportement dirigé vers un but«, écartant toute notion d'intention consciente.La finalité matérielle apparente ou téléonomie, qui dénote simplement des fonctions ayant pour effet la conservation de systèmes, suffit donc, sans qu'un recours à des prémisses vitalistes soit nécessaire.Quelques aspects de l'evolution et de la sélection sont discutés dans le cadre de la théorie des systèmes. L'auteur montre aussi que les explications téléologiques n'entrent pas en contradiction avec des explications causales (mécanistes), d'où une synthèse possible de positions apparemment incompatibles. Enfin il plaide pour une réévaluation de ce problème ancien et vénérable.〈section xml:id="abs1-3"〉〈title type="main"〉ZusammenfassungVorliegende Arbeit ist dem Problem der Teleologie in der modernen Biologie gewidmet. Die Teleologie wird dabei auf zielgerichtetes Verhalten eingeschränkt, während zielintendiertes Ver-halten geleugnet wird. Daher genügt der Aspekt der scheinbaren materialen Teleologie oder Teleonomie, die lediglich Funktionen von systemerhaltendem Wert umschreibt und ohne Rückgriff auf vitalistische Pramissen erklart werden kann.Es werden einige Aspekte der Evolution und Selektion diskutiert und unter eine systemtheo-retisch orientierte Betrachtungsweise subsumiert. Ferner wird hervorgehoben, dass teleologische Erklärungen nicht im Widerspruch zu kausalen (mechanischen) Erklärungen stehen, was in einer moglichen Synthese von scheinbar inkompatiblen Positionen resultiert. Dies bedeuted nicht zuletzt ein Plädoyer für die Wieder-(Neu-)bewertung eines altehrwürdigen Problems.

Notizen: In order to study surface disordering of ice at temperatures below the bulk melting point as a function of depth into the bulk, Car–Parrinello molecular-dynamics simulations of a periodic model of the hexagonal ice (0001) surface were carried out. Partial disorder in the uppermost bilayer was observed at a simulation temperature of 190 K, which is ∼30 K below the estimated bulk melting point, qualitatively validating earlier classical molecular-dynamics studies of this phenomenon. Over 0.5 ps, the time scale of a simulation, there were three particularly useful (and complementary) measures of disorder: The pair distribution function g(r), the distance of the oxygen atoms from the bottommost bilayer, and the distribution of angles φ and θ formed by the molecular dipole vector and the Cartesian axes. Our results set the stage for future studies addressing the effect of the disordered ice surface on heterogeneous atmospheric chemistry. © 2000 American Institute of Physics.

Notizen: We have studied Ca2+ homeostasis in a unique model of human neurons, the NT2N cell, which differentiates from a human teratocarcinoma cell line, NTera2/C1.D1 by retinoic acid treatment. When perifused with Krebs–HEPES buffer containing 2.5 mm CaCl2, fura-2 loaded NT2N cells produced spontaneous cytosolic Ca2+ oscillations, or Ca2+ transients. These cytosolic Ca2+ transients were not blocked by antagonists of glutamate (6-cyano-7-nitroquinoxaline-2,3-dione and d(–)-2-amino-5-phosphonopentanoic acid) or muscarinic (atropine) receptors. Omission of extracellular Ca2+ completely abolished Ca2+ oscillations and decreased the average Ca2+ level from 106 ± 14 nm to 59 ± 8 nm. Addition of the L-type Ca2+ channel blocker nifedipine (1 or 10 μm) or of the N-type inhibitor ω-conotoxin GVIA (5 μm) significantly, although incompletely, suppressed Ca2+ oscillations, while ω-conotoxin MVIIC (5 μm), a selective antagonist of P- and Q-channels, had no effect. Ni2+, at 100 μm, a concentration selective for T-type channels, did not inhibit Ca2+ transients. Non-specific blockage of Ca2+ channels by higher concentrations of Ni2+ (2–5 mm) or Co2+ (1 mm) abolished Ca2+ oscillations completely. The endoplasmic reticulum Ca2+-ATPase inhibitor, thapsigargin (1 μm), slightly decreased Ca2+ oscillation frequency, and induced a small transitory increase in the average cytosolic Ca2+ concentration. The mRNAs of L- (α1D subunit) and N-type (α1B subunit) Ca2+ channel were present in NT2N cells, while that of a T-type Ca2+ channel (α1-subunit) was not present in the NT2N cells as shown by reverse transcription–polymerase chain reaction. In conclusion, NT2N neuronal cells generate cytosolic Ca2+ oscillations mainly by influx of extracellular Ca2+ through multiple channels, which include L- and N-type channels, and do not require activation of glutamate or muscarinic receptors.