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  • 1
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The morphology of polycrystalline films grown by low-pressure chemical-vapor deposition (LPCVD) is investigated by transmission electron microscopy (TEM) as a function of the film thickness, the deposition pressure, and the level of contamination. An orientation filtering mechanism, due to the growth-velocity competition in the early stage of growth, is responsible for the preferred orientation of the films. The size of the crystallites, the surface roughness, and the type of the structural defects are investigated by combined cross-sectional and plane-view TEM analysis. In polycrystalline silicon thin-film transistors (TFTs), the influence of surface roughness scattering on the mobility is investigated by measuring the effective electron mobility under high effective normal field at 295 and 77 K. Although the surface curvature is increased when the deposition pressure is decreased, the surface roughness scattering is constant in the deposition pressure range from 40 to 0.5 mTorr. By decreasing the deposition pressure from 40 to 10 mTorr, although the grain size increases, the TFT performance degrades due to the following factors: (a) the increase of the grain-boundary trap density which is related to the change of the mode of growth at 10 mTorr; and (b) the increase of impurity contamination in the environment of the LPCVD system with constant silane flow rate at all pressures. At a deposition pressure of 0.5 mTorr the TFT performance is improved indicating that the grain size is the prevailing key factor.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of neuroscience 9 (1997), S. 0 
    ISSN: 1460-9568
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: Recent studies have localized γ-aminobutyric acid (GABA)-containing neurons and identified cells that express subunits of the GABAA receptor in the proliferative zone of the developing cerebral cortex and have demonstrated a role for GABA in cortical neurogenesis. We examined here the interactions between a number of neurotrophic factors, known to be involved in cortical cell proliferation and differentiation, and the GABAergic system (GABA and GABAA receptors) in the regulation of cell production in dissociated cortical cell cultures. We found that basic fibroblast growth factor (bFGF) increased the number of cells labelled for the α1 subunit of the GABAA receptor but not for the α2, α3 or α5 subunits. The α1 subunit was expressed by the majority of proliferating neuroepithelial cells as well as by differentiated neurons. We also found that activation of the GABAA receptor by GABA or muscimol inhibited the proliferative effects of bFGF on cortical progenitors, leading to an increased number of differentiated neurons. These results suggest that bFGF stimulates cell proliferation and GABAA receptor expression in cultured progenitor cells of the developing neocortex, and that GABA regulates cell production by providing a feedback signal that terminates cell division.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 41 (1985), S. 440-445 
    ISSN: 1600-5724
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: A theoretical analysis for the computation of the coincidence site lattice (CSL) symmetry is presented. It is shown that three types of symmetry elements can exist and each one can be found by properly using the CSL's rotation matrix of the smallest-angle description. Thus, from the existence of the subgroup H1, the order of which is directly connected with the number of the different orientations that the sublattice Λ11 can have, a low-symmetry H1 group implies more possibilities for the formation of the corresponding CSL. From the existence of the symmetry elements of the second type, the smallest-angle rotation matrix can be a symmetry element but only of the fourth or sixth order. From the third type of elements a connection between CSLs of different Σvalues can exist. Since the analytical form of this smallest-angle rotation matrix can be deduced for every crystallographic system, the procedure described here is of general use. Thus a new classification of the different CSLs is possible according to their symmetry group. This allows the study of the CSL model from the symmetry point of view.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 41 (1985), S. 445-451 
    ISSN: 1600-5724
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: A combination of analytical expressions and a knowledge of symmetry is employed for the displacement shift complete lattice (DSCL) base computation. The method is of general use and its application to cubic and hexagonal systems is given. Tables containing all the symmetrically equivalent descriptions of one and the same coincidence site lattice (CSL) as a function of one description are given for both cubic and hexagonal systems.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    Anatomy and embryology 176 (1987), S. 65-70 
    ISSN: 1432-0568
    Schlagwort(e): Primary optic fibers ; Insectivores-(3H)-Leucine ; HRP-histochemistry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The retinal projections of the hedgehog were studied using tritiated leucine and horseradish peroxidase as orthograde tracers. In both series of experiments labeling was seen bilaterally in the suprachiasmatic nucleus, the dorsal and the ventral lateral geniculate nucleus, the superior colliculus, and the pretectal area and contralaterally in the terminal nuclei (dorsal, lateral and medial) of the accessory optic system. A retino-intergeniculate leaflet projection is described for the first time in this species, and its significance is discussed.
    Materialart: Digitale Medien
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  • 6
    ISSN: 1432-0568
    Schlagwort(e): Auditory cortex ; Thalamus ; Thalamocortical connections ; Horseradish peroxidase ; Sheep
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The auditory area of the sheep cerebral cortex was studied on the basis of its afferents from the medial geniculate nucleus, traced with the horseradish peroxidase retrograde transport method. The results show that the medial geniculate nucleus projects only to the anterior parts of the posterior ectosylvian gyrus and the posterior sylvian gyrus. A small area of the posterior ectosylvian gyrus receives afferents exclusively from the ventral part of the medial geniculate nucleus, while the anterior part of the posterior sylvian gyrus receives also afferents from the posterior nucleus of the thalamus and the pulvinar. In addition, it was found that the medial part of the medial geniculate nucleus projects in a sparse way to the auditory cortex. The middle part of the posterior ectosylvian gyrus receives afferents from the posterior nucleus of the thalamus, the suprageniculate nucleus and the pulvinar, while the posterior part of the posterior ectosylvian gyrus together with the posteriormost part of the posterior sylvian gyrus receive afferents from the pulvinar. Finally, the area located between the anterior and the posteriormost part of the posterior sylvian gyrus receives afferents from both the posterior nucleus of the thalamus and the pulvinar.
    Materialart: Digitale Medien
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  • 7
    ISSN: 1432-0568
    Schlagwort(e): Cortex ; Brain stem ; Spinal afferents ; Horseradish peroxidase ; Hedgehog
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Cortical and brain stem neurons projecting to the spinal cord in the hedgehog were studied by means of the horseradish peroxidase (HRP) tracing method. HRP injections were placed in the first cervical segments, in the cervical enlargement (C5-T3) and in the lumbar enlargement. Following injections in the first cervical segments and in the cervical enlargement labelled neurons were observed in the somatic motor and somatic sensory cortices, the paraventricular and the dorsomedial hypothalamic nucleus, the lateral hypothalamic area, the nuclei of field H of Forel, the red nucleus, the mesencephalic reticular formation, the deep layers of the superior colliculus, the Edinger-Westphal nucleus, the periaqueductal grey, the mesencephalic trigeminal nucleus, the loci coeruleus and subcoeruleus, the nuclei raphe dorsalis, centralis superior, raphe magnus, raphe pallidus, and raphe obscurus, the rhombencephalic reticular formation, the lateral, medial and caudal vestibular nuclei, the nucleus ambiguus, the nucleus of the solitary tract and the gracile nucleus. After HRP injections in the lumbar enlargement, labelled neurons were not found in the cortex, the dorsomedial hypothalamic nucleus, the nuclei of field H of Forel, the superior colliculus and the mesencephalic trigeminal nucleus. These results show that cortical and brain stem projection to the spinal cord are comparable to those described in other species.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    [s.l.] : Nature Publishing Group
    Nature 362 (1993), S. 489-489 
    ISSN: 1476-4687
    Quelle: Nature Archives 1869 - 2009
    Thema: Biologie , Chemie und Pharmazie , Medizin , Allgemeine Naturwissenschaft , Physik
    Notizen: [Auszug] SIR — I wish to comment on the letter from Emmanuel Papamichael (Nature 360, 704; 1992) on the new university law recently adopted by the Greek parliament. The letter is one-sided and misleading. Before the law was introduced in the Greek parliament, there was an extremely long ...
    Materialart: Digitale Medien
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  • 9
    ISSN: 1432-1106
    Schlagwort(e): Somatostatin ; Visual deprivation ; Cortical areas 17, 18, 18a ; Transience ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The distribution of somatostatin (SRIF)-immunoreactive neurons in the visual cortical areas 17, 18 and 18a of Wistar rats from birth to adulthood was followed in both normal and dark-reared animals. The SRIF neurons show difference in distribution amongst the three cortical areas studied as early as the first postnatal week. Area 17 was distinguished by fewer SRIF cells in the upper layers (I–III), which results in a lower overall density. The SRIF neurons in all areas appeared to increase in numbers up to about 3 weeks and then decline dramatically to adult levels, which were 14–19% of the peak levels. Although this decline was still obvious, it moderated to 25–31% in dark-reared animals. The greatest effect was seen in area 18 where, at 60 days of age, there were twice as many SRIF cells in darkreared as in normal controls. It is suggested that, under conditions of dark rearing, the overall pattern of development of SRIF neurons, being uninfluenced by extrinsic factors, reveals the cells' genetic potential.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials science 16 (1981), S. 733-738 
    ISSN: 1573-4803
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Monoclinic Ga-Te was heated in the electron microscope. At about 800° C decomposition was observed and after cooling down to room temperature, two compounds were identified: the fcc Ga2Te3 and the Ga3Te4, for which a trigonal structure was identified. A relation between the three structures of Ga-Te, Ga3Te4 and Ga2Te3 is put forward.
    Materialart: Digitale Medien
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