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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant breeding 114 (1995), S. 0 
    ISSN: 1439-0523
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The objectives of this research were to gather hybridization information about crosses between tetraploid and synthetically derived octoploid lines of Avena and their reciprocals, and to study the cytology of the hybrids obtained. When the octoploid plants were used as females, only 2.6% of the pollinated florets set seed, while seed set increased to 39.0% in reciprocal crosses. However, germination was 95.7% for the first group of hybrids and only 18.2% for the reciprocals. These diverse results can be explained by the paternal: maternal endosperm genomic ratios and the hypothesis of polar nuclei activation. The tetraploid-octoploid hybrids did not always contain 42 chromosomes. Octoploid lines derived indirectly from tetraploid (AABB) × hexaploid (AACCDD) crosses were found to retain their A and B genome chromosomes. Univalents in the above hybrids averaged 15.44 in 1990 and 15.15 in 1991, indicating the presence of C and D genome chromosomes inherited from the octoploid lines. Directly synthesized octoploids from diploid (AcAc) × hexaploid (AACCDD) crosses were found to form 20.44 univalents, 5.30 bivalents, and 2.69 trivalents when crossed with AABB tetraploid species. The high number of univalents indicates that chromosomes from at least three genomes, i.e. B, C, and D, remain unpaired, while trivalents are the result of homology between the A and Ac genomes. Hybrids between tetraploid and octoploid lines can be obtained at low frequencies but, regardless of the direction of the cross, these hybrids are highly sterile.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 100 (1990), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The fast Fourier transform (FFT) technique is a very powerful tool for the efficient evaluation of gravity field convolution integrals. It can handle heterogeneous and noisy data, and thus presents a very attractive alternative to the classical, time consuming approaches, provided gridded data are available. This paper reviews the mathematics of the FFT methods as well as their practical problems, and presents examples from physical geodesy where the application of these methods is especially advantageous. The spectral evaluation of Stokes’, Vening Meinesz' and Molodensky's integrals, least-squares collocation in the frequency domain, integrals for terrain reductions and for airborne gravity gradiometry, and the computation of covariance and power spectral density functions are treated in detail. Numerical examples illustrate the efficiency and accuracy of the FFT methods.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-2242
    Keywords: Endosperm development ; Evolution ; Imprinting ; Incompatibility ; Reciprocal crosses
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The Endosperm Balance Number (EBN) and the polar-nuclei activation (PNA) hypotheses have been developed to interpret, explain and predict interspecific and interploidy crossabilities in the Solanums and the Gramineae, respectively. Although these two hypotheses evolved independently, they share a number of common features. Assignment of EBNs and ‘activation/response values’ (AVs/RVs) depend on plumpness, size, and germinability of hybrid seeds. Also, both hypotheses emphasize the importance of a balanced parental genic contribution for the normal development of endosperm. However, in the EBN hypothesis a 2 maternal∶1 paternal EBN ratio is a prerequisite for successful interspecific crossability, while the PNA hypothesis is based on the stimulative strength of the male nuclei to initiate mitotic divisions in the primary endosperm nucleus and is idependent on a 2∶1 ratio between the RV of the polar nuclei and the AV of the male gamete. Differences and similarities betweeen the EBN and PNA hypotheses are summarized and contrasted. It is proposed that EBN and PNA be considered as the same concept.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Euphytica 81 (1995), S. 1-6 
    ISSN: 1573-5060
    Keywords: Avena ; 2n gametes ; binucleate cell ; evolution ; sexual polyploidization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Sexual polyploidization via the action of 2n gametes (gametes with the sporophytic chromosome number) has been identified as the most important evolutionary mode of polyploidization among plant genera. This study was conducted to determine whether 2n gametes are present in the tetraploid level of the genus Avena (2n=4×=28) Twenty tetraploid Avena lines, representing four species and one interspecific hybrid, were screened for pollen grain size in order to differentiate between n and 2n pollen. Avena vaviloviana (Malz.) Mordv. line PI 412767 was observed to contain large pollen grains at a 1.0% frequency. Cytogenetic analyses of pollen mother cells of PI 412767 revealed cells with double the normal chromosome number (i.e., 56 chromosomes at metaphase I and anaphase I). The mode of chromosome doubling was found to be failure of cell wall formation during the last mitotic division that preceded meiosis. The resulting binucleate cells underwent normal meiotic divisions and formed pollen grains with 28 chromosomes. Based on the formation and function of 2n gametes, three models involving diploid and tetraploid oat lines are proposed to describe possible evolutionary pathways for hexaploid oats. If stable synthetic hexaploid oat lines could be developed by utilizing 2n gametes from diploid and tetraploid oat species through bilateral sexual polyploidization, the resulting hexaploids could be used in breeding programs for transferring genes from diploids and tetraploids to cultivated hexaploids.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Euphytica 83 (1995), S. 103-108 
    ISSN: 1573-5060
    Keywords: oat ; Avena sativa ; pollen grain size ; chromosome number
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Pollen grain size in many genera positively correlated with chromosome number. In this study, oat (Avena) pollen grain size was examined in diploids (2×=14, one species, for accessions), tetraploids (4×=28, five species, 20 accessions), hexaploids (6×=42, one species, eight cultivars), and in 10 octoploid (8×=56) accessions. Mature anthers ready to dehisce pollen were sampled from one to six plants per accession, and pollen grains were squeezed out of the anther with tweezers. Oat pollen grains are slightly elliptical, and the length of the major axis was found to be highly correlated with the minor axis width (r=0.94**). Pollen grain length, 39.3 μm for diploids, 41.3 μm for tetraploids, 47.0 μm for hexaploids, and 48.8 μm for octoploids, was positively correlated (r=0.86**) with ploidy level. No genomic or species effects appeared to influence this trait. Only tetraploidAvena vaviloviana accession PI 412767 produced two distinct class sizes of pollen grains, 99% normal (43.0 μm) and 1% large (52.7 μm).
    Type of Medium: Electronic Resource
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  • 6
    Publication Date: 2012-07-25
    Description: The Greenland GPS Network (GNET) uses the Global Positioning System (GPS) to measure the displacement of bedrock exposed near the margins of the Greenland ice sheet. The entire network is uplifting in response to past and present-day changes in ice mass. Crustal displacement is largely accounted for by an annual oscillation superimposed on a sustained trend. The oscillation is driven by earth’s elastic response to seasonal variations in ice mass and air mass (i.e., atmospheric pressure). Observed vertical velocities are higher and often much higher than predicted rates of postglacial rebound (PGR), implying that uplift is usually dominated by the solid earth’s instantaneous elastic response to contemporary losses in ice mass rather than PGR. Superimposed on longer-term trends, an anomalous ‘pulse’ of uplift accumulated at many GNET stations during an approximate six-month period in 2010. This anomalous uplift is spatially correlated with the 2010 melting day anomaly.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 7
    Publication Date: 2017-03-22
    Description: An autism-associated serotonin transporter variant disrupts multisensory processing Translational Psychiatry 7, e1067 (March 2017). doi:10.1038/tp.2017.17 Authors: J K Siemann, C L Muller, C G Forsberg, R D Blakely, J Veenstra-VanderWeele & M T Wallace
    Electronic ISSN: 2158-3188
    Topics: Medicine
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  • 8
    Publication Date: 2021-05-17
    Description: Airborne gravimetry is an important method for measuring gravity over large un- surveyed areas. This technology has been widely applied in Canada, Antarctica and Greenland to map the gravity fields of these regions and in recent years, in the oil industry. In 2005, two tests in the Italian area were performed by ENI in cooperation with the Politecnico di Milano and the Danish National Space Center. To the knowl- edge of the authors, these were the first experiments of this kind in Italy and were performed over the Ionian coasts of Calabria and the Maiella Mountains. The Cal- abria test field is characterized by strong gravity variations due to the geophysical and topographic structure of the area. The ground gravity coverage is also quite dense. It was thus possible to compare airborne gravity with the ground observed values in order to check the precision of the airborne gravimetry. The second campaign was performed in an unsurveyed area centred on the Maiella Mountains, thus filling the data gap of this zone. Comparisons with existing ground data were also carried out in this area. After smoothing, the collected data have an accuracy of 2–3 mgal, as derived by cross-over analysis. Moreover, the collocation method applied to compare and merge ground-based and airborne data proved to be efficient and reliable. The standard de- viation of the discrepancies between airborne data and collocation upward continued gravity is, in both cases, less than 8 mgal. In the Maiella test, the gravity field obtained by merging airborne and ground data using collocation also provides a more detailed description of the high-frequency pattern of the geopotential field in this area.
    Description: Published
    Description: 625–632
    Description: 1T. Struttura della Terra
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 9
    Publication Date: 2020-11-16
    Description: Greenland Ice Sheet surface melting has increased since the 1990s, affecting the rheology and scattering properties of the near‐surface firn. We combine firn cores and modeled firn densities with 7 years of CryoVEx airborne Ku‐band (13.5 GHz) radar profiles to quantify the impact of melting on microwave radar penetration in West Central Greenland. Although annual layers are present in the Ku‐band radar profiles to depths up to 15 m below the ice sheet surface, fluctuations in summer melting strongly affect the degree of radar penetration. The extreme melting in 2012, for example, caused an abrupt 6.2 ± 2.4 m decrease in Ku‐band radar penetration. Nevertheless, retracking the radar echoes mitigates this effect, producing surface heights that agree to within 13.9 cm of coincident airborne laser measurements. We also examine 2 years of Ka‐band (34.5 GHz) airborne radar data and show that the degree of penetration is half that of coincident Ku‐band.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 10
    Publication Date: 2017-10-17
    Description: The Antarctic Digital Magnetic Anomaly Project completed the first international magnetic anomaly compilation of the Antarctic region south of 60
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
    Format: application/pdf
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