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  • 1
    Call number: SR 90.0092(55)
    In: Mitteilungen der geodätischen Institute der Technischen Universität Graz
    Type of Medium: Series available for loan
    Pages: 151 S.
    Series Statement: Mitteilungen der Geodätischen Institute der Technischen Universität Graz 55
    Language: German
    Location: Lower compact magazine
    Branch Library: GFZ Library
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  • 2
    Publication Date: 2023-06-22
    Description: In 2015, the International Association of Geodesy defined the International Height Reference System (IHRS) as the conventional gravity field-related global height system. The IHRS is a geopotential reference system co-rotating with the Earth. Coordinates of points or objects close to or on the Earth’s surface are given by geopotential numbers C(P) referring to an equipotential surface defined by the conventional value W0 = 62,636,853.4 m2 s−2, and geocentric Cartesian coordinates X referring to the International Terrestrial Reference System (ITRS). Current efforts concentrate on an accurate, consistent, and well-defined realisation of the IHRS to provide an international standard for the precise determination of physical coordinates worldwide. Accordingly, this study focuses on the strategy for the realisation of the IHRS; i.e. the establishment of the International Height Reference Frame (IHRF). Four main aspects are considered: (1) methods for the determination of IHRF physical coordinates; (2) standards and conventions needed to ensure consistency between the definition and the realisation of the reference system; (3) criteria for the IHRF reference network design and station selection; and (4) operational infrastructure to guarantee a reliable and long-term sustainability of the IHRF. A highlight of this work is the evaluation of different approaches for the determination and accuracy assessment of IHRF coordinates based on the existing resources, namely (1) global gravity models of high resolution, (2) precise regional gravity field modelling, and (3) vertical datum unification of the local height systems into the IHRF. After a detailed discussion of the advantages, current limitations, and possibilities of improvement in the coordinate determination using these options, we define a strategy for the establishment of the IHRF including data requirements, a set of minimum standards/conventions for the determination of potential coordinates, a first IHRF reference network configuration, and a proposal to create a component of the International Gravity Field Service (IGFS) dedicated to the maintenance and servicing of the IHRS/IHRF.
    Description: https://www.ngs.noaa.gov/GRAV-D/data_ms05.shtml
    Keywords: ddc:526 ; International Height Reference System (IHRS) ; International Height Reference Frame (IHRF) ; World height system ; Global unified vertical reference system ; Geopotential height datum ; Permanent tide ; Tide systems ; The Colorado experiment
    Language: English
    Type: doc-type:article
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  • 3
    ISSN: 1432-1394
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract One year (November 1986 to October 1987) of Geosat altimeter data with improved orbits produced at The Ohio State University has been used to define sea surface heights for 22 ERM and one year averaged Geosat track. All sea surface heights were referenced to the single reference track through the application of geoid gradient corrections. The root mean square (RMS) gradient correction was on the order of ±1 cm although it could reach 20 cm with data points in trench areas. 10 values used to form the mean were considered. Although this study was initially driven by a need for a good reference sea surface for geodetic applications the formation of the reference track yields information on the variability of the ocean surface in the first year of the Geosat ERM. The RMS point variability was ± 12.6 cm with only a very small number of values exceeding 50 cm when a depth editing criteria was used. Global plots of the sea surface variability clearly reveal the major ocean currents and their variations in position in the year. Examination of the 1° × 1° averaged sea surface height variations show average and maximum variability values as follows: Gulf Stream (29 and 50 cm); Kurshio Current (24 and 49 cm); Agulhas Current (24 and 52 cm) and the Gulf of Mexico (18 and 31 cm). These magnitudes may be dependent on the radial orbit correction procedure. To investigate this effect sea slope variations were also computed. These results also showed clear current structures but also high frequency gravity field information despite efforts to average out such information. The data described in the paper is available from the authors for numerous other studies, some of which are suggested in the paper.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd.
    Molecular microbiology 45 (2002), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Here, we report an indispensable role for spindle assembly checkpoint (SAC) component CaMad2p in the survival and virulence of Candida albicans in mice. We hypothesized that cell cycle checkpoint functions, especially those monitoring the integrity of DNA and chromosome segregation, might be required for the pathogen to repair damage caused by host defence. To test this idea, we created SAC-defective mutants by deleting the CaMAD2 gene that encodes a key component of the SAC pathway. The CaMAD2 mutant appears normal in morphology, growth rate and growth mode switch in unperturbed conditions. However, it quickly loses viability when treated with nocodazole, which causes disassembly of mitotic spindles. The mutant also exhibits increased frequency of chromosome loss. The virulence of the mutant is greatly reduced in mice, presumably because of the inability of the mutant cells to stop the cell cycle when the host defence damages cellular components important for chromosome segregation. Supporting this hypothesis, unlike the wild-type cells that can proliferate within and eventually grow out of macrophages, most of the CaMAD2 null mutant cells are unable to survive. This study suggests that SAC is required for survival of C. albicans in the host and could thus be targeted for anti-C. albicans therapies.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 117 (1994), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: A gravimetric geoid undulation, on a 3’ x 3’ grid has been calculated in the Gulf Stream region: 30°≤φ≤ 45°, 278°≤λ≤ 318°. These undulations were calculated using two 360 potential coefficient models, land, ship and altimeter-derived gravity anomalies, and bathymetric data. Least-squares collocation and fast Fourier transform procedures were used with various data selection and gridding procedures. Results from five different undulation computations are described with comparisons made with synthetic geoid undulations along Geosat tracks in the region. the standard deviation of the undulation differences was ±14 cm when a cubic polynomial was used to model long-wavelength errors. A point verification of the geoid undulation at the laser tracking station on Bermuda was also made with a discrepancy (‘ground truth’ minus model undulation) of 40 cm, within the predicted standard deviation. the gravimetric geoid undulation was used to compute dynamic topography along Geosat tracks for comparison with existing estimates based on hydrographic data in the Gulf Stream region. the agreement between these two estimates is on the order of ±15 cm although the discrepancies can reach 60cm. the larger differences are usually associated with a location on a track that passes near a seamount where the gravity data may be inadequate to represent the high-frequency variations in the geoid undulations. This effect will be represented in the undulation standard deviations that have been calculated using the least-squares collocation procedure. the average accuracy is ±16 cm with the range from ±14 to ±48 cm. the dynamic height derived from the gravimetric undulations and altimeter data has been used to calculate characteristics of the Gulf Stream (width, velocity, centre location, height profile) using an implied velocity model for the set. the results are compared with previous estimates with generally good agreement. However, the maximum velocities and the jump function are approximately 30 per cent larger than previous studies that used an average of altimeter tracks to define the geoid undulation. the dynamic topography was calculated for the entire region using a mean sea surface based on Geos-3, Seasat and Geosat data. the results are compared with two hydrographic estimates due to Martel/Wunsch and LeTraon/Mercier. the agreement is at the ±25 cm level with the best correlation coefficient reaching 0.72 with the Martel/Wunsch model.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 49 (2003), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Saccharomyces cerevisiae Spa2p is a component of polarisome that controls cell polarity. Here, we have characterized the role of its homologue, CaSpa2p, in the polarized growth in Candida albicans. During yeast growth, GFP-tagged CaSpa2p localized to distinct growth sites in a cell cycle-dependent manner, while during hyphal growth it persistently localized to hyphal tips throughout the cell cycle. Persistent tip localization of the protein was also observed in Catup1Δ and Canrg1Δ, mutants constitutive for filamentous growth. Caspa2Δ exhibited defects in polarity establishment and maintenance, such as random budding and failure to confine growth to a small surface area leading to round cells with wide, elongated bud necks and markedly thicker hyphae. It was also defective in nuclear positioning, presumably a result of defective interactions between cytoplasmic microtubules with certain polarity determinants. The highly conserved SHD-I and SHD-V domains were found to be important and responsible for different aspects of CaSpa2p function. Caspa2Δ exhibited no virulence in the mouse systemic candidiasis model. Because of the existence of distinct growth forms and the easy control of the switch between them in vitro, C. albicans may serve as a useful model in cell polarity research.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Surveys in geophysics 14 (1993), S. 373-380 
    ISSN: 1573-0956
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Three geopotential models (OSU91A, GEM-T3, and GRIM4-C2), available in 1991, have been compared in several ways. The models have been differenced to find the geoid undulation difference are on the order of 1 m in land areas and 30 cm in ocean areas with extreme differences reaching 6 m. The models were also evaluated, augmented by higher degree terms, when necessary, through comparisons with undulations at Doppler and GPS positioned stations. The undulation difference at the Doppler stations was ± 1.57 m with no significant difference between models. Using 4 GPS test areas, differences were seen between the various models. A final comparison was made between geoid undulations implied by a Geosat 17 day cycle and undulations from the three models. The OSU91A model performed best having a difference standard deviation of ±34 cm.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The titanates derived from α,α,α′,α′-tetraaryl-1,3-dioxolane-4,5-dimethanols (TADDOLs, prepared from tartrate) act as catalysts for enantioselective additions of dialkylzinc compounds to aldehydes. For the standard reaction chosen for this investigation of the mechanism, the addition of diethylzinc to benzaldehyde, there is very little change of selectivity with different aryl substituents on the TADDOLate ligands (Tables 2-4, examples). With 0.02 to 0.2 equiv. of the chiral titanates, selectivities above 90% are observed only in the presence of excess tetraisopropyl titanate! According to NMR measurements (Fig. 2), the chiral bicyclic titanate and the achiral titanate do not react to give new species under these conditions. From experiments with different stoichiometries of the components, and with different achiral or chiral OR groups on the Ti-atom of the seven-membered ring titanate, it is concluded (i) that a single chiral titanate is involved in the product-forming step, (ii) that the bulky TADDOLate ligand renders the Ti-center catalytically more active than that of (i-PrO)4Ti, due to fast dynamics of ligand exchange on the sterically hindered Ti-center (Table 5, Fig. 3), and (iii) that the role of excess (i-PrO)4Ti is to remove - by ligand exchange - the product alkoxides (R*O) from the catalytically active Ti-center (Scheme 4, Table 6). Three new crystal structures of TADDOL derivatives (two clathrates with secondary amines, and a dimethyl ether) have been determined by X-ray diffraction (Figs. 5-7), and are compared with those previously reported. The distances between the C(aryl)2O oxygen atoms in the C2- and C1-symmetrical structures vary from 2.58 to 2.94 Å, depending upon the conformation of their dioxolane rings and the presence or absence of an intramolecular H-bond (Fig. 8). A single-crystal X-ray structure of a spiro-titanate, with two TADDOLate ligands on the Ti-atom, is described (Fig. 9); it contains six different seven-membered titanate-ring conformations in the asymmetric unit (Fig. 10), which suggests a highly flexible solution structure. The structures of Ti TADDOLate complexes are compared with those of C2-symmetrical Ru, Rh, and Pd disphosphine chelates (Table 7). A common topological model is presented for all nucleophilic additions to aldehydes involving Ti TADDOLates (Si attack with (R,R)-derivatives, relative topicity unlike; Fig. 11). Possible structures of complexes containing bidentate substrates for Ti TADDOLate-mediated ene reactions and cycloadditions are proposed (Fig. 12). A simple six-membered ring chair-type arrangement of the atoms involved can be used to describe the result of TADDOLate-mediated nucleophilic additions to aldehydes and ketones, with Ti, Zr, Mg, or Al bearing the chiral ligand (Scheme 6). A proposal is also made for the geometry of the intermediate responsible for enantioselective hydrogenation of N-(acetylamino)cinnamate catalyzed by Rh complexes containing C2-symmetrical diphosphines (Fig. 13).
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Preparation and screening of twenty new ligands, all analogs of α,α,α′,α′-tetraaryl-1,3-dioxolane-4,5-dimethanol (TADDOL), for the Ti-catalyzed asymmetric addition of methyltri(isopropoxy)titanium and diethylzinc to benzaldehyde are described. These ligands have the dioxolane ring of the TADDOL's replaced by cyclobutane, cyclopentane, cyclohexene, cyclohexane, bicyclo[2.2.1]heptene and -heptane and bicyclo[2.2.2]octene and -octane moieties; several have H-atoms or alkyl groups in place of the aryl groups, and nine of them have C2 symmetry. X-Ray crystallography and molecular mechanics are used to analyze the structure of the ligands, and two structural features appear to correlate with selectivity: (i) the torsion angle for the chelating O-atom and the ortho-C-atom of the axial Ph group (a small, ca. 19°, angle is optimum, Fig.8) and (ii) the “degree of perpendicularity” of the axial Ph group (Fig. 9). Competition experiments indicate that TADDOL 1a catalyzes both the methyltitanium and diethylzinc additions ≥ 50 times faster than the related dioxolane analogs 12a, 12c, and 12e (Scheme 7), indicating that both axial and equatorial aryl groups (see Footnote 6) are necessary for ligand-accelerated catalysis of these reactions. A refined mechanistic hypothesis is presented (Fig. 10) to explain the selectivities observed for these new ligands. Our analysis suggests that a combination of structural features appear necessary for good catalytic efficiency and high selectivity. These features, especially the rather subtle conformational effects, appear to be optimized (among the ligands tested) in the TADDOL's.
    Additional Material: 10 Ill.
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  • 10
    ISSN: 0044-8249
    Keywords: Anhydride ; Asymmetrische Synthesen ; Halbester ; TADDOL ; Titanverbindungen ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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