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  • 1
    Electronic Resource
    Electronic Resource
    Exploiting early sorting and early partitioning for decision support query processing (2000)
    Springer
    The VLDB journal 9 (2000), S. 190-213 
    Details
    ISSN: 0949-877X
    Keywords: Key words: Decision Support Systems – Query processing and optimization – Early sorting and partitioning – Hash joins and hash teams – Performance evaluation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract. Decision support queries typically involve several joins, a grouping with aggregation, and/or sorting of the result tuples. We propose two new classes of query evaluation algorithms that can be used to speed up the execution of such queries. The algorithms are based on (1) early sorting and (2) early partitioning– or a combination of both. The idea is to push the sorting and/or the partitioning to the leaves, i.e., the base relations, of the query evaluation plans (QEPs) and thereby avoid sorting or partitioning large intermediate results generated by the joins. Both early sorting and early partitioning are used in combination with hash-based algorithms for evaluating the join(s) and the grouping. To enable early sorting, the sort order generated at an early stage of the QEP is retained through an arbitrary number of so-called order-preserving hash joins. To make early partitioning applicable to a large class of decision support queries, we generalize the so-called hash teams proposed by Graefe et al. [GBC98]. Hash teams allow to perform several hash-based operations (join and grouping) on the same attribute in one pass without repartitioning intermediate results. Our generalization consists of indirectly partitioning the input data. Indirect partitioning means partitioning the input data on an attribute that is not directly needed for the next hash-based operation, and it involves the construction of bitmaps to approximate the partitioning for the attribute that is needed in the next hash-based operation. Our performance experiments show that such QEPs based on early sorting, early partitioning, or both in combination perform significantly better than conventional strategies for many common classes of decision support queries.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007780000030
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  • 2
    Electronic Resource
    Electronic Resource
    Übersicht über die Pfeffer-Festschrift (1915)
    Springer
    Naturwissenschaften 3 (1915), S. 131-136 
    Details
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01546012
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  • 3
    Electronic Resource
    Electronic Resource
    Herkunft, Wirkung und Synthese der Ibhaltsstoffe des Haschisch (1966)
    Springer
    Naturwissenschaften 53 (1966), S. 541-546 
    Details
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00602952
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  • 4
    Electronic Resource
    Electronic Resource
    Charged particle erosion of solid rare gases and dilute rare gas alloys (1982)
    Springer
    Applied physics 29 (1982), S. 57-61 
    Details
    ISSN: 1432-0630
    Keywords: 79.20. −m ; 61.80. −x ; 71.35. +z
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract We present the first experimental results on electron-induced erosion of solid neon. The measurements are interpreted qualitatively within a new model invoking excitation transport by free excitons and their subsequent decay at the surface. The model accounts for the magnitude of the observed yield and the energy dependence. A theoretically predicted decrease in the erosion yield due to doping with a heavier rare gas, in casu argon, has been observed experimentally. The strong influence of very small amounts of different types of impurities makes sample purity a crucial problem in investigations of the erosion of solid rare gases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00632426
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  • 5
    Electronic Resource
    Electronic Resource
    Functional-join processing (2000)
    Springer
    The VLDB journal 8 (2000), S. 156-177 
    Details
    ISSN: 0949-877X
    Keywords: Key words:Object identifier – Logical OID – Physical OID – Query processing – Pointer join – Functional join – Order-preserving join
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract. Inter-object references are one of the key concepts of object-relational and object-oriented database systems. In this work, we investigate alternative techniques to implement inter-object references and make the best use of them in query processing, i.e., in evaluating functional joins. We will give a comprehensive overview and performance evaluation of all known techniques for simple (single-valued) as well as multi-valued functional joins. Furthermore, we will describe special order-preserving\/ functional-join techniques that are particularly attractive for decision support queries that require ordered results. While most of the presentation of this paper is focused on object-relational and object-oriented database systems, some of the results can also be applied to plain relational databases because index nested-loop joins\/ along key/foreign-key relationships, as they are frequently found in relational databases, are just one particular way to execute a functional join.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007780050002
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  • 6
    Electronic Resource
    Electronic Resource
    Modeling bio-geophysical feedback in the African and Indian monsoon region (1997)
    Springer
    Climate dynamics 13 (1997), S. 247-257 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract.  An asynchronously coupled global atmosphere-biome model is used to assess the dynamics of deserts and drought in the Sahel, Saudi-Arabia and the Indian subcontinent. Under present-day conditions of solar irradiation and sea-surface temperatures, the model finds two solutions: the first solution yields the present-day distribution of vegetation and deserts and the second shows a northward spread of savanna and xerophytic shrub of some 600 km, particularly in the southwest Sahara. Comparison of atmospheric states associated with these solutions corroborates Charney’s theory of a self-induction of deserts through albedo enhancement in the Sahel. Over the Indian subcontinent, changes in vegetation are mainly caused by a positive feedback between increased soil moisture and stronger summer monsoon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003820050164
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  • 7
    Electronic Resource
    Electronic Resource
    Simulation of the global bio-geophysical interactions during the Last Glacial Maximum (1998)
    Springer
    Climate dynamics 14 (1998), S. 461-471 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract  The bio-geophysical feedbacks during the Last Glacial Maximum (LGM, 21 000 y BP) are investigated by use of an asynchronously coupled global atmosphere-biome model. It is found that the coupled model improves on the results of an atmosphere-only model especially for the Siberian region, where the inclusion of vegetation-snow-albedo interaction leads to a better agreement with geological reconstructions. Furthermore, it is shown that two stable solutions of the coupled model are possible under LGM boundary conditions. The presence of bright sand desert at the beginning of a simulation leads to more extensive subtropical deserts, whereas an initial global vegetation cover with forest, steppe, or dark desert results in a northward spread of vegetation of up to some 1000 km, mainly in the western Sahara. These differences can be explained in the framework of Charney’s theory of a “self-induction” of deserts through albedo enhancement. Moreover, it is found that the tropical easterly jet is strengthened in the case of the “green” Sahara, which in turn leads to a modification of the Indian summer monsoon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003820050234
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  • 8
    Electronic Resource
    Electronic Resource
    Comparison of the last interglacial climate simulated by a coupled global model of intermediate complexity and an AOGCM (2000)
    Springer
    Climate dynamics 16 (2000), S. 799-814 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract  The climate at the Last Interglacial Maximum (125 000 years before present) is investigated with the atmosphere-ocean general circulation model ECHAM-1/LSG and with the climate system model of intermediate complexity CLIMBER-2. Comparison of the results of the two models reveals broad agreement in most large-scale features, but also some discrepancies. The fast turnaround time of CLIMBER-2 permits one to perform a number of sensitivity experiments to (1) investigate the possible reasons for these differences, in particular the impact of different freshwater fluxes to the ocean, (2) analyze the sensitivity of the results to changes in the definition of the modern reference run concerning CO2 levels (preindustrial versus “present”), and (3) estimate the role of vegetation in the changed climate. Interactive vegetation turns out to be capable of modifying the initial climate signals significantly, leading especially to warmer winters in large parts of the Northern Hemisphere, as indicated by various paleodata. Differences due to changes in the atmospheric CO2 content and due to interactive vegetation are shown to be at least of the same order of magnitude as differences between the two completely different models, demonstrating the importance of careful experimental design.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003820000078
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  • 9
    Electronic Resource
    Electronic Resource
    Mid-Holocene greening of the Sahara: first results of the GAIM 6000 year BP Experiment with two asynchronously coupled atmosphere/biome models (2000)
    Springer
    Climate dynamics 16 (2000), S. 643-659 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract  The mid-Holocene `green' Sahara represents the largest anomaly of the atmosphere-biosphere system during the last 12 000 years. Although this anomaly is attributed to precessional forcing leading to a strong enhancement of the African monsoon, no climate model so far has been able to simulate the full extent of vegetation in the Sahara region 6000 years ago. Here two atmospheric general circulation models (LMD 5.3 and ECHAM 3) are asynchronously coupled to an equilibrium biogeography model to give steady-state simulations of climate and vegetation 6000 years ago, including biogeophysical feedback. The two model results are surprisingly different, and neither is fully realistic. ECHAM shows a large northward extension of vegetation in the western part of the Sahara only. LMD shows a much smaller and more zonal vegetation shift. These results are unaffected by the choice of `green' or modern initial conditions. The inability of LMD to sustain a `green' Sahara 6000 years ago is linked to the simulated strength of the tropical summer circulation. During the northern summer monsoon season, the meridional gradient of sea-level pressure and subsidence over the western part of northern Africa are both much weaker in ECHAM than in LMD in the present as well as the mid-Holocene. These features allow the surface moist air flux to penetrate further into northern Africa in ECHAM than in LMD. This comparison illustrates the importance of correct simulation of atmospheric circulation features for the sensitivity of climate models to changes in radiative forcing, particularly for regional climates where atmospheric changes are amplified by biosphere-atmosphere feedbacks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003820000074
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  • 10
    Electronic Resource
    Electronic Resource
    On the momentum forcing of a large-scale sea-ice model (1993)
    Springer
    Climate dynamics 9 (1993), S. 71-80 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A large-scale sea-ice - oceanic mixed-layer model for the Southern Ocean is forced with daily atmospheric fields from operational numerical weather prediction analyses. The strength of the atmospheric forcing is modified considering atmospheric surface-layer physics, which is itself directly dependent on the instantaneous sea-ice condition provided by the sea-ice model. In earlier applications, the atmospheric drag on sea ice was computed from the local momentum transfer over ice. In the present study, this is replaced by a large-scale momentum flux, which is characterized by a large-scale stability function and a large-scale roughness length. The large-scale roughness length depends on the local skin drags and on the form drag, where the latter is given as a function of the ice-plus-snow freeboard and the ice concentration, both provided by the sea-ice model. The thermodynamic part of the calculation is given by the local fluxes, which depend on the local stability of the atmospheric surface layer. This, physically more reasonable, description of the largescale dynamic forcing generally leads to an increase of the momentum transfer via an increase of the roughness length and a decrease of the stability in the atmospheric surface layer. Finally, this yields improved model results, especially in terms of a more dynamic pattern of the ice-thickness distribution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00210010
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