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  • 1
    Electronic Resource
    Electronic Resource
    The spatial relationship between active regions and coronal holes and the occurrence of intense geomagnetic storms throughout the solar activity cycle (1997)
    Springer
    Annales geophysicae 16 (1997), S. 49-54 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We study the annual frequency of occurrence of intense geomagnetic storms (Dst 〈 −100 nT) throughout the solar activity cycle for the last three cycles and find that it shows different structures. In cycles 20 and 22 it peaks during the ascending phase, near sunspot maximum. During cycle 21, however, there is one peak in the ascending phase and a second, higher, peak in the descending phase separated by a minimum of storm occurrence during 1980, the sunspot maximum. We compare the solar cycle distribution of storms with the corresponding evolution of coronal mass ejections and flares. We find that, as the frequency of occurrence of coronal mass ejections seems to follow very closely the evolution of the sunspot number, it does not reproduce the storm profiles. The temporal distribution of flares varies from that of sunspots and is more in agreement with the distribution of intense geomagnetic storms, but flares show a maximum at every sunspot maximum and cannot then explain the small number of intense storms in 1980. In a previous study we demonstrated that, in most cases, the occurrence of intense geomagnetic storms is associated with a flaring event in an active region located near a coronal hole. In this work we study the spatial relationship between active regions and coronal holes for solar cycles 21 and 22 and find that it also shows different temporal evolution in each cycle in accordance with the occurrence of strong geomagnetic storms; although there were many active regions during 1980, most of the time they were far from coronal holes. We analyse in detail the situation for the intense geomagnetic storms in 1980 and show that, in every case, they were associated with a flare in one of the few active regions adjacent to a coronal hole.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-997-0049-7
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  • 2
    Electronic Resource
    Electronic Resource
    The production of xylitol from d-xylose by fermentation with Hansenula polymorpha (1998)
    Springer
    Applied microbiology and biotechnology 50 (1998), S. 608-611 
    Details
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract We have analysed the influence of the initial pH of the medium and the quantity of aeration provided during the batch fermentation of solutions of d-xylose by the yeast Hansenula polymorpha (34438 ATCC). The initial pH was altered between 3.5 and 6.5 whilst aeration varied between 0.0 and 0.3 vvm. The temperature was kept at 30 °C during all the experiments. Hansenula polymorpha is known to produce high quantities of xylitol and low quantities of ethanol. The most favourable conditions for the growth of xylitol turned out to be: an initial pH of between 4.5 and 5.5 and the aeration provided by the stirring vortex alone. Thus, at an initial pH of 5.5, the maximum specific production rate (μm) was 0.41 h−1, the overall biomass yield (Y x/s G) was 0.12 g g−1, the specific d-xylose-consumption rate (q s ) was 0.075 g g−1 h−1 (for t = 75 h), the specific xylitol-production rate (q Xy ) was 0.31 g g−1 h−1 (for t = 30 h) and the overall yields of ethanol (Y E/s G) and xylitol (Y Xy/s G) were 0.017 and 0.61 g g−1 respectively. Both q s and q Xy decreased during the course of the experiments once the exponential growth phase had finished.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002530051343
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  • 3
    Electronic Resource
    Electronic Resource
    Signatures of interplanetary transients behind shocks and their associated near-surface solar activity (1998)
    Springer
    Annales geophysicae 16 (1998), S. 359-369 
    Details
    ISSN: 0992-7689
    Keywords: Interplanetary physics ; Interplanetary shocks ; Solar wind plasma ; Solar physics ; Flares and mass ejections
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Interplanetary transients with particular signatures different from the normal solar wind have been observed behind interplanetary shocks and also without shocks. In this paper we have selected four well-known transient interplanetary signatures, namely: magnetic clouds, helium enhancements and bidirectional electron and ion fluxes, found in the solar wind behind shocks, and undertaken a correlative study between them and the corresponding solar observations. We found that although commonly different signatures appear in a single interplanetary transient event, they are not necessarily simultaneous, that is, they may belong to different plasma regions within the ejecta, which suggests that they may be generated by complex processes involving the ejection of plasma from different solar regions. We also found that more than 90% of these signatures correspond to cases when an Hα flare and the eruption of a filament occurred near solar central meridian between 1 and 4 days before the observation of the disturbance at 1 AU, the highest association being with flares taking place between 2 and 3 days before. The majority of the Hα flares were also accompanied by soft X-ray events. We also studied the longitudinal distribution of the associated solar events and found that between 80% and 90% of the interplanetary ejecta were associated with solar events within a longitudinal band of ±30° from the solar central meridian. An east-west asymmetry in the associated solar events seems to exist for some of the signatures. We also look for coronal holes adjacent to the site of the explosive event and find that they were present almost in every case.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-998-0359-4
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  • 4
    Electronic Resource
    Electronic Resource
    Performance and feeding behavior of Ceratitis capitata: comparison of a wild population and a laboratory population (1998)
    Springer
    Entomologia experimentalis et applicata 87 (1998), S. 67-72 
    Details
    ISSN: 1570-7458
    Keywords: fruit flies ; feeding behavior ; diet nutritional values ; insects ; Diptera ; Tephritidae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Experiments were carried out to test the performance and some aspects of feeding behavior in two populations of Ceratitis capitata (a population reared in the laboratory for 16 years, i.e., approximately 160 generations, and a wild one obtained from infested coffee, Coffea arabica grains). Two types of food were used in the experiment: an artificial yeast diet used for laboratory rearing and papaya (Carica papaya), a natural host of the fly. The performance parameters tested were percent emergence, time to emergence, adult female size, and egg production during the pre-oviposition phase (first five days of adult life). The behavioral aspects tested were food preference by newly hatched larvae, induction, estimated ingestion of the two diets, whether the larvae placed on one diet stayed there or moved to the other diet, and acceptance of food for oviposition. The results indicated that the performance of the wild population was superior when the flies fed on papaya, whereas the performance of the laboratory population was similar with the two diets; the wild population showed a strong preference for papaya in all choice experiments, whereas the laboratory population showed no diet preference; the females of the wild population only oviposited on pieces of papaya that had not been peeled, and did not oviposit in the artificial diet; the females of the laboratory population oviposited indiscriminately on unpeeled and peeled papaya and on the artificial diet.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003211931514
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  • 5
    Electronic Resource
    Electronic Resource
    Variables Aggregation in Time Varying Discrete Systems (1998)
    Springer
    Acta biotheoretica 46 (1998), S. 273-297 
    Details
    ISSN: 1572-8358
    Keywords: Approximate aggregation ; population dynamics ; time scales ; strong ergodicity ; cyclic environment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In this work we extend approximate aggregation methods in time discrete linear models to the case of time varying environments. Approximate aggregation consists in describing some features of the dynamics of a general system involving many coupled variables in terms of the dynamics of a reduced system with a few number of variables. We present a time discrete time varying model in which we distinguish two time scales. By using perturbation methods we transform the system to make the global variables appear and build up the aggregated system. The asymptotic relationships between the general and aggregated systems are explored in the cases of a cyclically varying environment and a changing environment in process of stabilization. We show that under quite general conditions the knowledge of the behavior of the aggregated system characterizes that of the general system. The general method is also applied to aggregate a multiregional time dependent Leslie model showing that the aggregated model has demographic rates depending on the equilibrium proportions of individuals in the different patches.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1001741327984
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  • 6
    Electronic Resource
    Electronic Resource
    Linear discrete models with different time scales (1995)
    Springer
    Acta biotheoretica 43 (1995), S. 465-476 
    Details
    ISSN: 1572-8358
    Keywords: Approximate aggregation of variables ; population dynamics ; perturbations ; time scales ; eigenvalues and eigenvectors analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Aggregation of variables allows to approximate a large scale dynamical system (the micro-system) involving many variables into a reduced system (the macro-system) described by a few number of global variables. Approximate aggregation can be performed when different time scales are involved in the dynamics of the micro-system. Perturbation methods enable to approximate the large micro-system by a macro-system going on at a slow time scale. Aggregation has been performed for systems of ordinary differential equations in which time is a continuous variable. In this contribution, we extend aggregation methods to time-discrete models of population dynamics. Time discrete micro-models with two time scales are presented. We use perturbation methods to obtain a slow macro-model. The asymptotic behaviours of the micro and macro-systems are characterized by the main eigenvalues and the associated eigenvectors. We compare the asymptotic behaviours of both systems which are shown to be similar to a certain order.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00713565
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  • 7
    Electronic Resource
    Electronic Resource
    Coronal hole flux tubes and the problem of relating interplanetary and solar features (1996)
    Springer
    Astrophysics and space science 243 (1996), S. 113-121 
    Details
    ISSN: 1572-946X
    Keywords: Coronal holes ; Solar wind sources
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Coronal flux tubes have in general very large divergence, and the properties of their flow vary greatly inside the flux tube. We present here a general description of the evolution and the characteristics of coronal holes and discuss how these characteristics may lead to erroneous associations, between interplanetary and solar structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00644040
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  • 8
    Electronic Resource
    Electronic Resource
    Consequences of the Collision Between the Gas Ejected in the Collapse of a White Dwarf and a Low-Mass Star (1998)
    Springer
    Astrophysics and space science 263 (1998), S. 287-290 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1002159607585
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  • 9
    Electronic Resource
    Electronic Resource
    SIXE: A Payload for MINISAT-02 (1998)
    Springer
    Astrophysics and space science 263 (1998), S. 389-392 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A description of the X-ray instrument SIXE proposed for the MINISAT-02 mission is presented. The description includes the scientific goals and instrument performances.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1002169619339
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  • 10
    Electronic Resource
    Electronic Resource
    Technical efficiency measures for dairy farms using panel data: A comparison of alternative model specifications (1996)
    Springer
    Journal of productivity analysis 7 (1996), S. 399-415 
    Details
    ISSN: 1573-0441
    Keywords: Production functions ; stochastic frontiers ; fixed effects ; technical efficiency ; panel data
    Source: Springer Online Journal Archives 1860-2000
    Topics: Economics
    Notes: Abstract This article examines the impact of fixed effects production functions vis-à-vis stochastic production frontiers on technical efficiency measures. An unbalanced panel consisting of 96 Vermont dairy farmers for the 1971–1984 period was used in the analysis. The models examined incorporated both time-variant and time-invariant technical efficiency. The major source of variation in efficiency levels across models stemmed from the assumption made concerning the distribution of the one-sided term in the stochastic frontiers. In general, the fixed effects technique was found superior to the stochastic production frontier methodology. Despite the fact that the results of various statistical tests revealed the superiority of some specifications over others, the overall conclusion of the study is that the efficiency analysis was fairly consistent throughout all the models considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00162049
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