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  • 1
    ISSN: 1432-1130
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The oxidation behavior of cubic Ti1-xAlxN films was improved by decreasing the Ti/Al ratio from 50/50 in the direction of the phase transition between cubic and hexagonal structure. Metastable, polycrystalline, single-phase Ti1-xAlxN films were deposited on high speed steel (HSS) substrates by reactive magnetron sputtering ion plating (MSIP). The composition of the bulk was determined by electron probe microanalysis (EPMA), the crystallographic structure by thin film X-ray diffraction (XRD). A Ti1-xAlxN film with a Ti/Al atomic ratio of 38/62 was deposited in cubic NaCl structure, whereas a further decrease of the Ti/Al ratio down to 27/73 led to a two-phase film with both cubic and hexagonal constituents. The Ti0.38Al0.62N film was oxidized in synthetic air for 1 h at 800 °C. The oxidic overlayer was analyzed by X-ray photoelectron spectroscopy (XPS) sputter depth profiling, EPMA crater edge linescan analysis, and secondary neutrals mass spectroscopy (SNMS). Scanning electron microscopy (SEM) micrographs of the cross sectional fracture were taken for morphological examination. With higher Ti content, the Ti1-xAlxN formed a TiO2-x rich sublayer beneath an Al2O3 rich toplayer, whereas the oxide layer on the Ti0.38Al0.62N film consisted of pure Al2O3. The thickness of the oxide layer was determined to 60–80 nm, about a quarter of the oxide layer thickness detected on Ti0.5Al0.5N films. The absence of a TiO2-x sublayer was also confirmed by XRD. The results show a distinct improvement of the oxidation resistance of cubic Ti1-xAlxN films by increasing the Al content from x = 0.5 to 0.62, whereas a further increase leads to the hexagonal structure, which is less suitable for tribological applications due to its tendency to form cracks during oxidation.
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  • 2
    ISSN: 1432-1130
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Structural transitions of metastable Ti1–xAlxN coatings on technically relevant substrates were determined as a function of the Ti/Al ratio. Ti1–xAlxN films with different Ti/Al ratios were deposited on high speed steel (HSS) substrates at substrate temperatures of 300 ° and 500 °C by means of reactive magnetron sputtering ion plating (MSIP). A Ti/Al compound target was used as well as a cluster arrangement of one Ti and one Al target for comparison. The composition of the films was determined by electron probe microanalysis (EPMA), the crystallographic structure by thin film X-ray diffraction (XRD). The analyses revealed that films deposited with Ti/Al ratios of 44/56 and 36/64 had grown in cubic NaCl structure, a film with a Ti/Al ratio of 32/68 was two-phase, and a Ti/Al ratio of 25/75 led to a hexagonal film in wurtzite structure. Only small differences of the lattice parameters could be observed in dependence of temperature: At 300 °C the lattice parameters of the cubic structure corresponded exactly to Vegard‘s law, whereas they slightly decreased in the films deposited at 500 °C. The application of a cluster arrangement instead of a compound target resulted in nearly the same lattice parameters and peak shapes.
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  • 3
    ISSN: 1435-1463
    Keywords: Keywords: Alzheimer's disease ; apoptosis ; cytokine ; diabetes ; alcohol ; nerve growth factor (NGF) ; neurodegeneration ; neuropathy ; neuroplasticity ; neurotrophin ; p75 ; trkA.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary. Nerve growth factor (NGF) is the prototype of related neurotrophic proteins, the so-called neurotrophins. NGF is essential for proper development of sympathetic and neural crest-derived sensory neurons of the peripheral nervous system (PNS) as well as of the neurons in the cholinergic basal forebrain (CBF). In the mature peripheral and central nervous system (CNS) NGF is also biologically active; NGF facilitates neuronal plasticity and regulates synaptic transmission and connectivity. Besides this well established neurotrophic function, recent findings suggest a role of NGF in neuroimmune and stress-associated processes, which NGF imparts not only as the classical "target-derived messenger", that is retrogradly transported within NGF-sensitive neurons, but also as para- and autocrine cytokine modulating the function of non-neuronal cells.. Since neurotrophins are produced in very small amounts in vivo, NGF-sensitive cells have to compete for the limited NGF even under physiological conditions, so that normally only less than 10% of NGF receptors (NGFR) are saturated with their endogenous ligand. Consequently, it is feasable that minute changes in NGF concentrations can influence neuronal function in an extensive way. Hence, one plausible pathomechanism of disease(s) may be that a deficiency in NGF leads to malfunction of NGF-sensitive neurons. The change in NGF concentrations in the course of several diseases, namely during alcoholic and diabetic neuropathy as well as in Alzheimer's disease (AD) and several lesion-models of the CBF, indicates that fluctuations of endogenous NGF concentrations in PNS and CNS follow a distinctive pattern. An initial deficit of NGF at the onset of pathological processes is typically followed by its temporary elevation, during which some neuronal deficits may be partially ameliorated. However, if the disease progresses a decrease of NGF is typically observed, which appears to be a "normalization" of formerly elevated NGF concentrations. In our hypothesis we postulate that after acute or chronic injuries NGF is up-regulated as an intrinsic attempt to regenerate NGF-sensitive neurons. After long-term exposure to noxious processes, however, this compensatory increase of NGF cannot be maintained and eventually breaks down. The extent of such a compensatory up-regulation may depend on age and condition of NGF-sensitive neurons as well as on the type of lesion (acute or chronic). Furthermore, we also postulate that an exceeding level of NGF or its chronic elevation could even be detrimental to neuronal functioning under certain conditions.. Thus, endogenous NGF has the capacity to modulate and even to compensate different kinds of harmful processes and in this way it may reinstate the homeostatic equilibrium. In our view, it seems to be a more appropriate app-roach to regard NGF changes as independent of classical constructs of neuropsychiatric diseases. Perhaps our understanding of NGF may even model for a new approach to the aetiology of multifactorial neuropsychiatric disorders.
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  • 4
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The construction and the operation mode of an ultrahigh vacuum PVD system with integrated electron spectroscopic surface analysis is described. It consists of two metal-ion beam sources and a nitrogen radical beam source. High-energy electron diffraction (HEED) with grazing incidence of the electron beam is applied in-situ to determine the crystallographic data, as texture and structure of the growing layer. Chemical composition and bonding states of the components of the layer are determined also in-situ using an Auger electron spectrometer (AES). In-situ is taken to mean that analysis takes place during deposition of the layer. This work shows that the information depth of HEED with grazing incidence of the beam (θ〈 1°) is of the same order of magnitude as the information depthof AES i.e. a few atom layers. This enables constitution and structure of the near-surface region of the growing layer to be directly determined as a function of the PVD parameters. In the initial experiments Cu/Al bilayers, homogeneous Cu3N and heterogeneous Cu/Cu3N layers were deposited. The influence of the Cu-ion energy and of the radical portion in the nitrogen reactive gas on the formation of the homogeneous Cu3N layer was investigated.
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 117 (2002), S. 2068-2075 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A sensitive experimental method for ion spectroscopy and state specific reaction dynamics is described, briefly called laser induced reactions (LIR). The technique is based on (i) trapping ions over a long time in a cold 22-pole rf ion trap followed by mass spectrometric detection, (ii) providing a suitable low density gas environment for collisions, (iii) modifying the low temperature chemical kinetics using selective excitation via a tunable radiation source. In this paper, the H-atom transfer reaction C2H2+ (v3=1,J)+H2→C2H3++H, is used to monitor the infrared excitation of acetylene ions. Rotationally resolved spectra are presented for the antisymmetric C–H stretching vibration. For recording a spectrum, it is sufficient to fill the trap with a few thousand parent ions. Differences with respect to conventional IR spectroscopy are discussed, especially the processes which influence the LIR signal. From the measured intensities and their dependence on parameters such as storage time, laser fluence and target gas density, information on state specific rate coefficients has been obtained at an ambient temperature of 90 K. Based on a model simulating the kinetics, rate coefficients for various inelastic and reactive collisions are derived. Vibrational excitation of C2H2+ (v3=1,J) increases the rate of the title reaction by more than three orders of magnitude, while rotation hinders the reaction. The fine-structure state of the parent ion does not affect its reactivity. Ways are pointed out to apply the method to various classes of molecular ions. © 2002 American Institute of Physics.
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