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  • 1
    Electronic Resource
    Electronic Resource
    A model exciter for type III solar radiobursts (1975)
    Springer
    Solar physics 40 (1975), S. 193-216 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In an earlier paper (Harvey and Aubier, 1973) the large scale radial electron density gradient in the corona and solar wind was shown to cause the phase velocity of plasma waves to decrease as they propagate away from the Sun, thus leading to appreciable Landau damping of the plasma waves. It is proposed here that this same phase velocity decrease creates conditions which facilitate the stabilisation of a beam of exciter electrons of finite duration, provided that three conditions are fulfilled. Two of these conditions concern the velocity-time distribution of the exciter electrons at their point of ejection from the Sun, while the third is simply that, above a certain altitude, the coronal electron density decreases with altitude r faster than r −2. The plasma wave source is then associated with the leading edge of the electron stream. The spatial density of the power converted into plasma waves is calculated as a function of position and time, and is shown to be independent of the nature of the stabilisation mechanism. The maximum of this power density is found to move outwards from the Sun at a uniform speed when a simple electron injection model with a Maxwellian velocity distribution is introduced.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00183162
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  • 2
    Electronic Resource
    Electronic Resource
    Type III solar radioburst profiles and the associated electron energy spectra (1976)
    Springer
    Solar physics 46 (1976), S. 509-509 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An attempt is made to explain the observed frequency-time profiles of type III solar radiobursts in terms of a rapid plasma wave decay rate combined with the exciter model recently proposed by the author. The decay rate is assumed to be sufficiently rapid for the plasma wave energy density profile to be similar to the excitor power density time profile; this is consistent with the exciter model, the rapid decay being caused by Landau damping on the electrons of the modified high energy tail of the ambient plasma electron velocity distribution. The model is compared with radio observations by making simple assumptions about the dependence of the radio intensity upon the plasma wave energy. A comparison is made with simultaneous radio and electron observations by further assuming a simple power-law velocity distribution for the electrons at their point of ejection from the Sun.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00149878
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  • 3
    Electronic Resource
    Electronic Resource
    Remnant trees and the conservation of biodiversity in Costa Rican pastures (1998)
    Springer
    Agroforestry systems 44 (1998), S. 37-68 
    Details
    ISSN: 1572-9680
    Keywords: farmer management ; Monteverde ; shade trees ; silvopastoral systems ; timeber trees
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Remnant trees may play an important role in conserving biodiversity within agricultural systems because they provide habitats and resources that are otherwise absent from agricultural landscapes. In order to determine the potential importance of remnant trees for conservation, we surveyed the density and species composition of remnant trees occurring in pastures of 24 dairy farms near Monteverde, Costa Rica. In addition, we conducted interviews with farmers to determine why they leave trees in pastures and how they manage them. In our survey of 237 ha of pastures, we counted 5583 trees of 190 species (mean density of 25 trees/ha). Primary forest trees accounted for 57% of all of the species and 33% of tree individuals. Over 90% of the species are known to provide food for forest birds and other animals. In addition, many of the species are important locally for humans as sources of timber (37%), firewood (36%) or fence posts (20%). Farmers mentioned 19 reasons for leaving trees in pastures. Of these, shade for cattle, timber, fruits for birds and fence posts were most commonly cited. Most farmers were well aware of both the economic and ecological benefits of pasture trees, and were interested in the possibility of increasing tree cover within their pastures. Although the current densities and richness of pasture trees in Monteverde are high, the size distribution indicates that diversity will decrease substantially in future years, both because farmers are harvesting trees and because saplings of primary forest trees are scarce within the pastures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006122211692
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  • 4
    Electronic Resource
    Electronic Resource
    Efficient On-Line Nonparametric Kernel Density Estimation (1999)
    Springer
    Algorithmica 25 (1999), S. 37-57 
    Details
    ISSN: 1432-0541
    Keywords: Key words. On-line fast multiple algorithm, Smoothing, Kernel regression, Nonparametric density estimation.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract. Nonparametric density estimation has broad applications in computational finance especially in cases where high frequency data are available. However, the technique is often intractable, given the run times necessary to evaluate a density. We present a new and efficient algorithm based on multipole techniques. Given the n kernels that estimate the density, current methods take O(n) time directly to sum the kernels to perform a single density query. In an on-line algorithm where points are continually added to the density, the cumulative O(n 2 ) running time for n queries makes it very costly, if not impractical, to compute the density for large n . Our new Multipole-accelerated On-line Density Estimation (MODE) algorithm is general in that it can be applied to any kernel (in arbitrary dimensions) that admits a Taylor series expansion. The running time for a density query reduces to O (logn) or even constant time, depending on the kernel chosen, and, hence, the cumulative running time is reduced to O (n logn) or O(n) , respectively. Our results show that the MODE algorithm provides dramatic advantages over the direct approach to density evaluation. For example, we show using a modest computing platform that on-line density updates and queries for 1 million points and two dimensions take 8 days to compute using the direct approach versus 40 seconds with the MODE approach.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00009282
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  • 5
    Electronic Resource
    Electronic Resource
    Density and magnetic field fluctuations observed by ISEE 1–2 in the quiet magnetosheath (1995)
    Springer
    Annales geophysicae 13 (1995), S. 343-357 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We analyse the fluctuations of the electron density and of the magnetic field in the Earth’s magnetosheath to identify the waves observed below the proton gyrofrequency. We consider two quiet magnetosheath crossings i.e. 2 days characterized by small-amplitude waves, for which the solar wind dynamic pressure was low. On 2 August 1978 the spacecraft were in the outer magnetosheath. We compare the properties of the observed narrow-band waves with those of the unstable linear wave modes calculated for an homogeneous plasma with Maxwellian electron and bi-Maxwellian (anisotropic) proton and alpha particle distributions. The Alfvén ion cyclotron (AIC) mode appears to be dominant in the data, but there are also density fluctuations nearly in phase with the magnetic fluctuations parallel to the magnetic field. Such a phase relation can be explained neither by the presence of a proton or helium AIC mode nor by the presence of a fast mode in a bi-Maxwellian plasma. We invoke the presence of the helium cut-off mode which is marginally stable in a bi-Maxwellian plasma with 〈alpha〉 particles: the observed phase relation could be due to a hybrid mode (proton AIC + helium cut-off) generated by a non-Maxwellian or a non-gyrotropic part of the ion distribution functions in the upstream magnetosheath. On 2 September 1981 the properties of the fluctuations observed in the middle of the magnetosheath can be explained by pure AIC waves generated by protons which have reached a bi-Maxwellian equilibrium. For a given wave mode, the phase difference between B\Vert and the density is sensitive to the shape of the ion and electron distribution functions: it can be a diagnosis tool for natural and simulated plasmas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-995-0343-1
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  • 6
    Electronic Resource
    Electronic Resource
    Density fluctuations measured by ISEE 1–2 in the Earth’s magnetosheath and the resultant scattering of radio waves (1997)
    Springer
    Annales geophysicae 15 (1997), S. 387-396 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Radio waves undergo angular scattering when they propagate through a plasma with fluctuating density. We show how the angular scattering coefficient can be calculated as a function of the frequency spectrum of the local density fluctuations. In the Earth’s magnetosheath, the ISEE 1–2 propagation experiment measured the spectral power of the density fluctuations for periods in the range 300 to 1 s, which produce most of the scattering. The resultant local angular scattering coefficient can then be calculated for the first time with realistic density fluctuation spectra, which are neither Gaussian nor power laws. We present results on the variation of the local angular scattering coefficient during two crossings of the dayside magnetosheath, from the quasi-perpendicular bow shock to the magnetopause. For a radio wave at twice the local electron plasma frequency, the scattering coefficient in the major part of the magnetosheath is b(2fp) ≃ 0.5–4 × 10−9 rad2/m. The scattering coefficient is about ten times stronger in a thin sheet (0.1 to IRE) just downstream of the shock ramp, and close to the magnetopause.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-997-0387-5
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  • 7
    Electronic Resource
    Electronic Resource
    Sex determination in Actinidia. 1. Sex-linked markers and progeny sex ratio in diploid A. chinensis (1997)
    Springer
    Sexual plant reproduction 10 (1997), S. 149-154 
    Details
    ISSN: 1432-2145
    Keywords: Key words Actinidia ; Dioecism ; Sex determination ; Sex markers ; Sex ratios
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  First results from two strategies aimed at elucidating the genetics of sex in the dioecious genus Actinidia Lindl. (Actinidiaceae) support the hypothesis that sex-determining genes are localized in a pair of chromosomes which, although cytologically indistinguishable, function like an XX/XY system with male heterogamety. A. chinensis Planch., a close relative of the kiwifruit [A. deliciosa (A. Chev.) CF Liang et AR Ferguson], has diploid and tetraploid races. Bulk segregant analysis to find sex-linked markers revealed two markers whose inheritance patterns in three diploid families showed X and Y linkage and indicated that the male is the heterogametic sex. Some recombination between the markers and the sex-determining loci was also demonstrated. Sex ratios in 12 progenies from controlled crosses varied around 1:1, as expected for an XX/XY system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004970050082
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  • 8
    Electronic Resource
    Electronic Resource
    Mycoparasitic relationships (1977)
    Springer
    Archives of microbiology 111 (1977), S. 207-224 
    Details
    ISSN: 1432-072X
    Keywords: Host-parasite relationships ; Ultrastructure ; Papillae ; Infection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The mode of attack and the infection structures of the necrotrophic mycoparasite, Pythium acanthicum, as well as the responses of various fungal hosts to parasitism were studied using both electron and light microscopy. Many taxonomically distinct fungal hosts were used, though Phycomyces blakesleeanus, Pythium aphanidermatum, Rhizoctonia solani and a basidiomycete identified as Corticium sensu lato were studied in greatest detail. Parasitism was by direct penetration of the fungal host without appressorium formation by the parasite. The host's cells responded to contact by P. acanthicum by forming papillae. The morphological features of the papillae varied with the particular host. In P. blakesleeanus they were comprised of vesicles and segments of cytoplasm entrapped in a fibrillo-granular matrix, while in R. solani and the Corticium basidiomycete they contained considerable amounts of electron-opaque and electron-translucent material. Evidence for both mechanical and enzymatic penetration of the host fungi by the parasite are presented. Details of host wall and septum penetration by the parasite are presented using time-lapse light microscopy with in vivo systems. Many of these stages of parasitism were examined ultrastructurally. Some comparisons of these mycoparasitic relationships are discussed in relation to what is known from the literature about phytoparasitic interactions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00549358
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  • 9
    Electronic Resource
    Electronic Resource
    Fatigue of aluminium alloy 2024-T351 in humid and dry air (1990)
    Springer
    Journal of materials science 25 (1990), S. 4708-4711 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Reversed bending fatigue tests conducted on specimens of aluminium alloy 2024-T351 in dry and humid air at stress levels of 248, 276, 290, 317 and 359 MPa showed that at low stress amplitude humid air reduces the fatigue life by as much as 21%. Mirco-hardness tests showed that the reduction in fatigue life is primarily attributed to localized hydrogen-induced overageing. SEM analysis and microhardness data were combined with past studies to propose a mechanism for environmentally induced fatigue in aluminium alloy 2024-T351 over a wide range of stress levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01129929
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  • 10
    Electronic Resource
    Electronic Resource
    Effects of Cd++ on short-circuit current across epithelial membranes (1976)
    Springer
    The journal of membrane biology 26 (1976), S. 109-119 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Cadmium ion (Cd++) significantly increased potential difference (PD) and short-circuit current (SCC) across isolated frog skin when added to the outside Ringer's solution at 10−4, 10−3 and 5×10−3 m concentration. Resistance was reduced by 10−4 m Cd++ but not significantly changed by the higher concentrations. When SCC was first stimulated by vasopressin, 10−4 and 10−3 m Cd++ produced additive stimulation which was reversible by washing with Cd++-free Ringer's. If SCC was first stimulated by Cd++, further stimulation by vasopressin was additive with 10−4 m Cd++ but completely inhibited by 10−3 m Cd++. Elevating the calcium ion (Ca++) concentration of the outer Ringer's from 10−3 m to 5×10−3 m or 10−2 m prior to Cd++ treatment did not reduce the magnitude of SCC stimulation by Cd++. Removal of Ca++ from the outside Ringer's with 2×10−3 m EDTA increased SCC as predicted. Subsequent addition of 5×10−3 m Cd++ drastically reduced SCC below control levels while equimolar concentrations of Cd++ and EDTA reduced SCC only to control levels. These results suggest that Cd++ interacts with the components of the apical plasma membranes of epithelial cells which are associated with the stimulation of SCC by vasopressin and Ca++ removal and may be a useful probe for elucidating these components.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868869
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