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  • 1
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Mutants of Aspergillus nidulans blocked in the main pathway of cysteine synthesis show an elevated level of the enzymes involved in the synthesis of cysteine from homocysteine i.e. cystathionine β-synthase and γ-cystathionase and a depressed level of homocysteine methyltransferase. This results in a considerable change in the sulfur amino acids pool as compared to the wild type. Upon addition of cysteine to the growth medium the first two enzymes are repressed while the level of the third one increases. These data indicate that the two diverging pathways of homocysteine metabolism are anti-coordinately regulated.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary Wave-organized convective features in the southwest Indian Ocean are described using Hovmoller composites of satellite imagery, OLR anomalies and ECMWF precipitable water departures during the southern summer. Westward movement of large convective elements is noted in the 10–20°S latitude band in about half of the years between 1970 and 1984. A study of 47 convective systems from satellite imagery establishes the climatological features, including zonal propagation speeds for maritime systems in the range −2 to −4 m s−1, wavelengths of 25–35° longitude (3,000 km), lifespans of 10–20 days and convective areas of 7–10° longitude (800 km). Transient convective waves over the tropical SW Indian Ocean are slower and more diverse than their northern hemisphere counterparts. Interannual tendencies in the frequency and mode are studied. Wet summers over SE Africa correspond with an increased frequency of westward moving convective systems, whereas in dry summers convective systems tend to be quasi-stationary. INSAT data composites provide additional insight into the convective structure and show that tropical waves penetrated into southern Africa in February 1988. A more quantitative assessment of transient convective waves is provided by Hovmoller composites of OLR anomalies and precipitable water departures. Both display westward moving systems in 1976 and 1984 and highlight the wide variety and mixed mode character of convective waves. A case study is analyzed which illustrates the deepening of a moist, unstable layer coincident with the westward passage of a convective wave.
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  • 3
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary Differences in the convective potential of troughs passing over the plateau of southern Africa in the early summer are assessed using operational synoptic weather data and radiosonde time-height sections. Wet and dry trough cases are chosen on the basis of the intensity and distribution of rainfall, sharp thermodynamic changes across the plateau and the passage of a geopotential wave. Composite differences are computed and indicate a high-low geopotential anomaly in the east-west direction, and a threefold increase in precipi-table water from 15 mm in dry cases to 28 mm in wet cases. The 500 hPa structure obtained by differencing wet and dry composites is dominated by low geopotentials and cyclonic vorticity over the plateau near 25°S, 25°E, and high geopotentials and anticyclonic vorticity to the south over the oceans near 40°S, 30°E. The dipole anomaly suggests a diffluent tilted baroclinic wave in the subtropical jet stream in convective cases. A double jet streak structure in the wet events enhances upper divergence which contributes to widespread uplift in the mid-troposphere. A case study comparison highlights the importance of pre-frontal moist influx, the kinematic trigger and thermodynamic instability.
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  • 4
    ISSN: 1435-5914
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract The number of partitions of a bi-partite number into at mostj parts is studied. We consider this function,p j (x, y), on the linex+y=2n. Forj≤4, we show that this function is maximized whenx=y. Forj〉4 we provide an explicit formula forn j so that, for alln≥n j ,x=y yields a maximum forp j (x,y).
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  • 5
    ISSN: 1435-5914
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Numbers similar to those of van der Waerden are studied. We consider increasing sequences of positive integers {x 1,x 2,...,x n } that either form an arithmetic progression or for which there exists a polynomialf with integer coefficients and degree exactlyn − 2, andx j+1 =f(x j ). We denote byq(n, k) the least positive integer such that if {1, 2,...,q(n, k)} is partitioned intok classes, then some class must contain a sequence of the type just described. Upper bounds are obtained forq(n, 3), q(n, 4), q(3, k), andq(4, k). A table of several values is also given.
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  • 6
    ISSN: 1573-5133
    Keywords: Cyprinids ; Size structured populations ; Pikeperch ; Smelt ; Feeding efficiency ; Predator-prey-relationships
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Synopsis Most of the lakes in The Netherlands are turbid and without vegetation. This is regarded as the result of increasing eutrophication within the last decades. Under these conditions common bream, roach, and white bream are the most common cyprinids. In six shallow (1–3 m), wind exposed lakes the abundance of common bream and roach was linked to the abundance of pikeperch; bream dominated when pikeperch was abundant, but when the latter species was rare, roach was dominant and the biomass of bream was reduced. The biomass of white bream was always relatively low. In lake Tjeukemeer the distribution of roach 〈 20 cm fork length (FL) and bream was also related to the distribution of pikeperch. Only roach 〉 20 cm FL managed to coexist with pikeperch in the open water area, whereas roach 〈 20 cm was confined to the littoral zone where pikeperch was nearly absent. Bream occurred mainly in the open water and avoided the littoral zone where it competed with roach. White bream occupied an intermediate position, occurring in relatively low density both in the littoral zone and in open water. The importance of predation and competition in determining the distribution and abundance of roach and common bream in the eutrophic lakes of The Netherlands is discussed.
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  • 7
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Observations of a number of helium triplet (λλ 10830, 4713, 4471, 3889, 4026) and hydrogen (Hγ, δ, η, θ) emission line intensities in six quiescent prominences are presented. The regions of prominence and neighboring corona were raster-scanned by the telescope, and all lines were measured concurrently at each point. The instrumental field of view was 5″ × 20″. The results are compared with previous observations and theory. In particular, the intensity of the λ 10830 emission relative to the other triplets is found to differ strongly from the predictions of the recent detailed calculations of Heasley et al. (1974) for model quiescent prominences.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 63 (1979), S. 221-235 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present a cylindrically symmetric model for a sunspot atmosphere using the similarity principle of Schlüter and Temesvary for the magnetic field configuration. The equations of magnetostatic equilibrium are used, augmented by a radial Evershed flow. The LTE radiative transfer equations for the Stokes vector were solved under a variety of conditions for a ray emerging from a typical penumbral point. The contribution from isolated lines to the broadband circular polarization in sunspot penumbrae is evaluated using a more realistic model sunspot atmosphere than has hitherto been considered. Results indicate that the inclusion of a velocity field along B is unable to give a net circular polarization of sufficient magnitude, although the variation with the angle between the line-of-sight and B is in qualitative agreement with observations. The corresponding results for the net linear polarization are satisfactory.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 63 (1979), S. 87-92 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present measurements of the middle Balmer decrement (n = 10–22) in a number of quiescent prominences. The average decrement continues smoothly the trend of the decrement determined in our previous work on the earlier Balmer lines. The range of T ex is found to be 3450–11 000 K, consistent with the generally accepted range of values for T e. In addition, some values for the hydrogen-to-metal (Fe, Ti+) integrated line intensities are given.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 50 (1976), S. 383-394 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Observations of the He λ 10830 line emission in a number of quiescent prominences are presented. The line shapes are analyzed to obtain values for the Doppler widths and optical thicknesses, leading to a determination of the 23 P − 23 S excitation temperature of 4020 K. The results are compared with those of previous observational and theoretical research.
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