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  • Communications and Radar  (5)
  • Agrobacterium  (2)
  • 1995-1999  (7)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Plant molecular biology 33 (1997), S. 1097-1103 
    ISSN: 1573-5028
    Keywords: Ac ; Agrobacterium ; periclinal chimera ; rolC ; transgenic Populus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The transposable element Ac from maize, in combination with the phenotypic selectable marker rolC, was employed in transformation experiments of a hybrid aspen clone. A number of transgenic clones exhibited light-green sectors on green leaves. In vitro regeneration from leaves showing a high number of light-green spots resulted in R2 plants, which also showed light-green sectored leaves. However, only one out of 385 regenerated plants obtained showed green leaves. Both PCR and northern analysis indicated Ac excision and restoration of rolC expression. In Southern blot analysis of this green plant additional bands were observed as compared to the original R1 plant. The occurrence of these bands and a suggested Ac excision in the non-green L1-epidermal layer leading to periclinal chimerism of this plant is discussed.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-9368
    Keywords: Ac ; Agrobacterium ; aspen ; Populus ; transformation ; transposition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Aspen (Populus tremula) and hybrid aspen (P. tremula × P. tremuloides) were transformed with different gene constructs using two types of promoter. The aim was to determine the influence of the reporter gene rolC, controlled by promoters of viral or plant origin, on genetic and morphologic expression of different transgenic aspen clones. An improved transformation method using leaf discs was developed, by which putative transgenic plantlets were regenerated at high efficiencies (up to 34%) on kanamycin-containing medium. Transgenic aspen carrying the rolC gene from Agrobacterium rhizogenes under control of the cauliflower-35S-promoter are reduced in size with smaller leaves, whereas aspen transgenic for the same rolC gene, but under control of the light inducible rbcS promoter from potato, are only slightly reduced in size compared to untransformed controls. However, all clones carrying 35S-rolC and rbcS-rolC genes revealed light-green colouration of leaves when compared to untransformed aspen. Owing to this special feature, constructs were used in which expression of the rolC gene was inhibited by insertion of a transposable element, Ac, from maize. Transgenic aspen transformed with the 35S-Ac-rolC and rbcS-Ac-rolC genes were morphologically similar to untransformed aspen, but out of 54 independently regenerated 35S-Ac-rolC transgenic aspen clones, 30 clones showed light-green/dark green variegated leaves. In contrast, out of 19 independently transformed rbcS-Ac-rolC aspen clones, only two clones revealed light-green/dark green variegated leaves. The role of bacterial strains in transformation, and molecular genetics of transgenic aspen plants (including the function of the transposable element, Ac, in the aspen genome) are discussed
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  • 3
    Publication Date: 2019-07-13
    Description: The need for high efficiency components has grown significantly due to the expanding role of fiber optic communications for various applications. Integrated optics is in a state of metamorphosis and there are many problems awaiting solutions. One of the main problems being the lack of a simple and efficient method of coupling single-mode fibers to thin-film devices for integrated optics. In this paper, optical coupling between a single-mode fiber and a uniform and tapered thin-film waveguide is theoretically modeled and analyzed. A novel tapered structure presented in this paper is shown to produce perfect match for power transfer.
    Keywords: Communications and Radar
    Type: NASA-CR-200274 , NAS 1.26:200274 , 1995 SBMO/IEEE MTT-S International Microwave and Optoelectronics Conference; Jul 24, 1995 - Jul 27, 1995; Rio de Janeiro; Brazil
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  • 4
    Publication Date: 2019-07-13
    Description: Theoretical derivations, computer analysis and test data are provided to demonstrate that the cavity model is a feasible one to analyze thin-substrate, rectangular-patch microstrip antennas. Seven separate antennas were tested. Most of the antennas were designed to resonate at L-band frequencies (1-2 GHz). One antenna was designed to resonate at an S-band (2-4 GHz) frequency of 2.025 GHz. All dielectric substrates were made of Duroid, and were of varying thicknesses and relative dielectric constant values. Theoretical derivations to calculate radiated free space electromagnetic fields and antenna input impedance were performed. MATHEMATICA 2.2 software was used to generate Smith Chart input impedance plots, normalized relative power radiation plots and to perform other numerical manipulations. Network Analyzer tests were used to verify the data from the computer programming (such as input impedance and VSWR). Finally, tests were performed in an anechoic chamber to measure receive-mode polar power patterns in the E and H planes. Agreement between computer analysis and test data is presented. The antenna with the thickest substrate (e(sub r) = 2.33,62 mils thick) showed the worst match to theoretical impedance data. This is anticipated due to the fact that the cavity model generally loses accuracy when the dielectric substrate thickness exceeds 5% of the antenna's free space wavelength. A method of reducing computer execution time for impedance calculations is also presented.
    Keywords: Communications and Radar
    Type: NASA-CR-203835 , NAS 1.26:203835
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  • 5
    Publication Date: 2019-07-13
    Description: The propagation properties of transverse electric TE(sup pm) modes and their dispersion relations in rectangular waveguides with two conventional and two superconducting walls, derived by using the Meissner boundary conditions on the superconducting walls, are presented. In addition to recovering some previously known results, some novel results have been obtained: the cut-off wavelength of the dominant TE(sup 10) mode is greater than that of the conventional TE(sub 10) mode, and the tangential electric field and normal magnetic field for the dominant mode TE(sup 10) exist on the superconducting surfaces. Expressions for electromagnetic components, surface currents, attenuation coefficient, maximum transmitted power, dispersion and wave impedance are also presented.
    Keywords: Communications and Radar
    Type: NASA-CR-200275 , NAS 1.26:200275 , (ISSN 0020-7217)
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  • 6
    Publication Date: 2019-07-10
    Description: This project was a comprehensive research program for developing techniques for improving the performance of Internet protocols over Asynchronous Transfer Mode (ATM) based satellite networks. Among the service categories provided by ATM networks, the most commonly used category for data traffic is the unspecified bit rate (UBR) service. UBR allows sources to send data into the network without any feedback control. The project resulted in the numerous ATM Forum contributions and papers.
    Keywords: Communications and Radar
    Type: NASA/CR-1999-209158 , E-11718 , NAS 1.26:209158
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  • 7
    Publication Date: 2019-07-10
    Description: This report presents a survey of the traffic management Issues in the design and implementation of satellite Asynchronous Transfer Mode (ATM) networks. The report focuses on the efficient transport of Transmission Control Protocol (TCP) traffic over satellite ATM. First, a reference satellite ATM network architecture is presented along with an overview of the service categories available in ATM networks. A delay model for satellite networks and the major components of delay and delay variation are described. A survey of design options for TCP over Unspecified Bit Rate (UBR), Guaranteed Frame Rate (GFR) and Available Bit Rate (ABR) services in ATM is presented. The main focus is on traffic management issues. Several recommendations on the design options for efficiently carrying data services over satellite ATM networks are presented. Most of the results are based on experiments performed on Geosynchronous (GEO) latencies. Some results for Low Earth Orbits (LEO) and Medium Earth Orbit (MEO) latencies are also provided.
    Keywords: Communications and Radar
    Type: NASA/TM-1999-209196 , E-11711 , NAS 1.15:209196
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