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  • 1
    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.
    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 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.
    Type of Medium: Electronic Resource
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  • 3
    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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  • 4
    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.
    Type of Medium: Electronic Resource
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  • 5
    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.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 26 (1993), S. 296-300 
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 71.10.+x
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Energetics and structures of small aluminum-lithium clusters were investigated using structure-minimization and dynamic simulated annealing on the Born-Oppenheimer surface, calculated via local-spin-density functional method. A transition from atomic-based characteristics forn≤5 to a perturbed delocalized electronic cluster-shell behavior forn≥6, containing an AiLi5 “core”, is suggested.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 26 (1993), S. 119-125 
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 31.20.Sy ; 32.80.Dz ; 71.10.+x
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Theoretical investigations of size evolutionary patterns for multiply charged anionic metal clusters and solvation of sodium in water clusters are discussed. For Na N Z- clusters, energetic stability and electron decay channels are determined. Formation of a “surface Rydberg-like state” in Na(H2O) N , correlating with calculated and measured ionization potentials, is analyzed.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 8187-8195 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The properties of excess hydrated electrons in liquid water, at room temperature, are studied via coupled quantum-classical simulations. In these simulations, the system evolves dynamically on the adiabatic potential energy surface with the electron maintained in the ground state throughout the process. The diffusion constant of the hydrated electron under field-free conditions is found to be the same as that obtained, via the Nernst–Townsend–Einstein relation, from the electron mobility simulated for a system under an electric field of 3.2×106 V/cm, acting on the electron. For larger electric fields, the electron mobility is found to be field dependent. The mode of migration of the excess electron is polaronic in nature and the influence of the intramolecular degrees of freedom of the water molecules on the hydrated electron transport properties is investigated. It is shown that the electron diffusion constant obtained in simulations under field-free conditions with rigid-water molecules [D0e=(3.7±0.7)×10−5 cm2/s] is larger than that obtained from simulations where a flexible-water model potential is employed D0e=(1.9±0.4)×10−5] cm2/s] and smaller than the experimental estimated value obtained from conductivity measurements (4.9×10−5 cm2/s). The difference between the diffusion constants calculated for the two models is correlated with a marked enhancement of the probability of reversal of the direction of motion of the migrating electron in flexible water. The self-diffusion constant of water using the rigid-molecules model [Ds=(3.6±0.4)×10−5 cm2/s] is also larger than that found for the flexible-water molecule model Ds=(2.3±0.2)×10−5] cm2/s], with the latter in agreement with the experimental value (Ds=2.3×10−5 cm2/s). Structural and dynamical aspects of hydrated electron transport are discussed.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 550-560 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Filtration using large pressures is an effective method for removing liquids from a flocculated suspension and creating a high volume fraction filtercake. Recent experimental work exhibits phenomena that are unexplained by previous calculations with nonlinear models. These models are modified and now predict the region of clear liquid and the high concentration of the filtercake observed in filtration at large pressure. The governing equations are based on the assumption that, at sufficiently high volume fractions, a network forms through the aggregation of flocs and possesses a compressive yield stress Py(φ) that depends only on the local volume fraction φ.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 1495-1509 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pressure filtration is an important method for removing liquids from a suspension. Previous work used linear models or applied to stable suspensions. Nonlinear models for flocculated suspensions are studied here. The equations governing the consolidation of flocculated suspensions under the influence of an applied pressure are based on the assumption that when the volume fraction is high enough, the network formed from the aggregation of flocs possesses a compressive yield stress Py(φ) that is a function of local volume fraction φ only. There are two modes of operation of the pressure filter—the fluid flux or the applied pressure is specified—and both of these are studied. The resulting nonlinear partial differential equations involve the time-dependent piston position, and in the case of the suspension being initially unnetworked, another internal moving boundary below which the suspension is networked. The small time behavior of these systems is obtained with an asymptotic method. In general, at later times, the solution can only be found numerically and an algorithm for doing this is discussed. The important parameters and properties of the filter cake are described. The results suggest various ways of controlling the filtration process, which may be useful in the manufacture of ceramics.
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