161 research outputs found

    A large neighbourhood based heuristic for two-echelon routing problems

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    In this paper, we address two optimisation problems arising in the context of city logistics and two-level transportation systems. The two-echelon vehicle routing problem and the two-echelon location routing problem seek to produce vehicle itineraries to deliver goods to customers, with transits through intermediate facilities. To efficiently solve these problems, we propose a hybrid metaheuristic which combines enumerative local searches with destroy-and-repair principles, as well as some tailored operators to optimise the selections of intermediate facilities. We conduct extensive computational experiments to investigate the contribution of these operators to the search performance, and measure the performance of the method on both problem classes. The proposed algorithm finds the current best known solutions, or better ones, for 95% of the two-echelon vehicle routing problem benchmark instances. Overall, for both problems, it achieves high-quality solutions within short computing times. Finally, for future reference, we resolve inconsistencies between different versions of benchmark instances, document their differences, and provide them all online in a unified format


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    Die Heilung von Inzisionswunden nach lokalem Weichteiltrauma : Eine intravitalmikroskopische Untersuchung an der Maus

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    Einfluss der Bodenbearbeitung und des Säverfahrens auf die Spross- und Wurzelleistung unterschiedlicher Zwischenfrucht-Mischungen

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    Zusammenfassung Der Zwischenfruchtbau stellt für den ökologisch wirtschaftenden Betrieb eine wichtige Stellgröße im Management der Bodenfruchtbarkeit dar. Ein hoher Biomasse-Aufwuchs sowie eine intensive Durchwurzelung sind dabei maßgebliche Kenngrößen. Hierbei stellt sich die Frage welches Verfahren zur Bodenbearbeitung und Saat geeignet ist, um einen wirksamen Zwischenfruchtbestand zu etablieren. Im vorliegenden Parzellenversuch wurden sechs verschiedene Zwischenfruchtmischungen mit je zwei unterschiedlichen Bodenbearbeitungs- und Säverfahren kombiniert. Es wurde sowohl der Sprossertrag als auch die Wurzelmasse und -verteilung gemessen. Die Ergebnisse zeigen deutlich, dass die Bestellverfahren einen ertragswirksamen Einfluss auf die Zwischenfrüchte nehmen. Der Sprossertrag wurde maßgeblich vom Säverfahren beeinflusst. Die Grundbodenbearbeitung zeigte keinen signifikanten Effekt auf den Spross- und Wurzelertrag. Die Wurzelverteilung in die Tiefe war dagegen stark von der Bodenbearbeitung abhängig. Wechselwirkungen der Zwischenfruchtmischungen mit dem Bestellverfahren waren erkennbar, ließen sich aber nicht statistisch absichern

    More or Less Political: Findings on a Central Feature of Local Engagement for Refugees in Germany

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    The article is based on research in the region of Heidelberg—the city itself and two small municipalities nearby. It addresses three dimensions of local support movements for refugees: (1) the varying bundles of motives among those engaged, (2) the diversity of organizations concerned and (3) their interaction with the local political administration. A focal point of the study concerns features and processes that give actions and organizations a more or less political character. Our results reveal that, especially among newly engaged helpers and activists, political and apolitical motives coexist. Many people and their local organizations take positions in the country-wide controversial political debates on refugees, but for their practical action on location, moral concerns clearly prevail. Processes of politicization and depoliticization of refugee support largely depend on the ways and degrees to which nationwide political controversies and local developments intermesh. Politicization may take place due to controversies that call for more than a moral attitude, have an impact and build up at the local level. However, resistance to supportive action, be it by changing discourses or the persistence of traditional administrative routines, may also cause depoliticization, where volunteers and initiatives restrict themselves to acting as mere helpers that bring some human touch into an environment that longs to return to normality

    Age-Specific Characteristics and Coupling of Cerebral Arterial Inflow and Cerebrospinal Fluid Dynamics

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    The objective of this work is to quantify age-related differences in the characteristics and coupling of cerebral arterial inflow and cerebrospinal fluid (CSF) dynamics. To this end, 3T phase-contrast magnetic resonance imaging blood and CSF flow data of eleven young ( years) and eleven elderly subjects ( years) with a comparable sex-ratio were acquired. Flow waveforms and their frequency composition, transfer functions from blood to CSF flows and cross-correlations were analyzed. The magnitudes of the frequency components of CSF flow in the aqueduct differ significantly between the two age groups, as do the frequency components of the cervical spinal CSF and the arterial flows. The males' aqueductal CSF stroke volumes and average flow rates are significantly higher than those of the females. Transfer functions and cross-correlations between arterial blood and CSF flow reveal significant age-dependence of phase-shift between these, as do the waveforms of arterial blood, as well as cervical-spinal and aqueductal CSF flows. These findings accentuate the need for age- and sex-matched control groups for the evaluation of cerebral pathologies such as hydrocephalus
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