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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 2327-2337 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Direct and Fowler–Nordheim tunneling currents through oxide and dual layer silicon oxide–silicon nitride dielectrics are investigated for substrate and gate injection. The calculations include depletion effects in the heavily doped (n+) polysilicon gate electrodes as well as quantization effects in the less heavily doped n-type substrates. The Wentzel–Kramers–Brillouin (WKB) effective mass approximation has been compared with exact calculations for the tunneling probability, and based on these comparisons it has been found that the WKB approximation is adequate for single layer dielectrics, but is not for the dual layer dielectrics that are the focus of this article. Using exact tunneling transmission calculations, current-voltage (I–V) characteristics for ultrathin single layer oxides with different thicknesses (1.4, 2.0, and 2.3 nm) have been shown to agree well with recently reported experiments. Extensions of this approach demonstrate that direct tunneling currents in oxide/nitride structures with oxide equivalent thickness of 1.5 and 2.0 nm can be significantly lower than through single layer oxides of the same respective thickness. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 224-226 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Enhanced formation of C54-TiSi2 in high-temperature deposited Ti thin films on preamorphized (001)Si has been investigated by high-resolution transmission electron microscopy in conjunction with autocorrelation function analysis. The increase in the thickness of the amorphous TiSix layer is due to the preamorphization implantation for the most part. The dominant effect of high-temperature sputtering is to increase the density of crystallites in the amorphous TiSix layer. The enhanced formation of C54–TiSi2 in high-temperature deposited samples is attributed to the more extensive presence of silicide crystallites, which serve as nucleation sites, in the amorphous TiSix layer than that in samples deposited at room temperature. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-2145
    Keywords: Key words Nicotiana tabacum ; In vitro fertilization ; Gamete interaction ; Cytology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  In vitro double fertilization in tobacco was carried out with attention to fusion behavior and gamete interaction. Structural and cytological events indicating possible reaction to the fusion of sperm-egg and especially sperm-central cell were recorded by video-enhanced microscopy. Generative cells were fused with the egg cell or central cell as a control system to better understand gamete interaction. As early as adherence of the male cell, the female cell showed response by means of cytoplasm strand formation. After gamete fusion, cytoplasm activation in the egg cell was observed as long distance movement of organelles. In fertilized central cells, however, fusion did not result in notable cytological change within 30 min. Male nuclear movement recorded in the female cell illustrated two different patterns of movement which showed similarity to organelle movement. The dynamics of male and female nuclear fusion after in vitro fertilization was also recorded in the central cell. It revealed that the fusion process requires only a few seconds and is similar to that of gamete fusion in vitro. This may offer a new clue for understanding how female and male nuclei attract, adhere and finally fuse each other.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Plant cell reports 19 (2000), S. 1184-1187 
    ISSN: 1432-203X
    Keywords: Keywords Zygote ; In vitro culture ; Electroporation ; Transformation ; Tobacco ; AbbreviationsNAA: Naphthaleneacetic acid ; ¶BA: 6-Benzyladenine ; GUS: β-Glucuronidase ; ¶GFP: Green fluorescent protein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  We have established a technique for isolating, culturing and transforming tobacco zygotes. Zygotes were isolated by microdissection or enzymatic maceration from fertilized embryo sacs. Viable zygotes cocultured with mesophyll protoplasts underwent first division after 3 days of culture. Zygotes isolated by microdissection underwent a higher frequency of first division (61.2%) than those isolated by enzymatic maceration (30.5%). Globular embryos were formed only from microdissected zygotes, at a frequency of 8.7% after 1–2 weeks in culture. An efficient millicell device for the electroporation of DNA into zygotes was established. The electroporated zygotes divided in vitro at a frequency of 54.6% and developed into proembryos. Introduced GFP gene constructs showed transient expression in about 2.6% of the electroporated tobacco zygotes.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Plant cell reports 19 (2000), S. 321-326 
    ISSN: 1432-203X
    Keywords: Key words Oryza sativa L. ; Egg cell ; Zygote ; Central cell ; Isolation ; Microculture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  All component cells of the embryo-sac before and after fertilization in rice were isolated by manual microdissection under conditions either free of enzymes or combined with a short pulse of enzymatic treatment.In general, the frequency of isolated unfertilized or fertilized egg cells or central cells reached 15–40%. Various component cells of the embryo-sac after isolation were distinguished by their own morphological characteristics. The isolated cells were cultured in a microchamber and fed with dividing rice suspension cells. Both unfertilized and fertilized egg cells and central cells were induced to divide. Among them only the fertilized egg cells (the zygotes) developed into proembryo-like multicellular structures. The frequency of the first zygotic division and the frequency of multicellular structures were higher using the non-enzymatic method than using the enzymatic one.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-2145
    Keywords: Key words Microprojectile bombardment ; Nicotiana tabacum ; De-exined pollen ; β-glucuronidase gene ; Green fluorescent protein gene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Gene constructs containing the β-glucuronidase (GUS) gene or green fluorescent protein (GFP) gene under the control of pollen-specific promoter Zm13-260 from maize were introduced by particle bombardment into de-exined pollen of Nicotiana tabacum. The de-exined pollen exhibited transient expression of the GUS or GFP gene as indicated by histochemical and fluorescent assay, respectively. The frequency of de-exined pollen transformation with the GUS or GFP gene was approximately 6 and 3 times higher, respectively, than that of pollen with intact walls, indicating that pollen deprived of the exine barrier responded better to foreign gene transfer than did the original. Cytological observation of GUS-expressing pollen grains showed that introduced gold particles were visible in the cytoplasm and vegetative nucleus as well as in the generative nucleus. GFP-expressing pollen tubes were observed in the style even after pollination.
    Type of Medium: Electronic Resource
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