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61.
Clemens Nothegger Alfred Mayer Andreas Chwatal Günther R. Raidl 《Annals of Operations Research》2012,194(1):325-339
In this work we present a new approach to tackle the problem of Post Enrolment Course Timetabling as specified for the International Timetabling Competition 2007 (ITC2007), competition track 2. The heuristic procedure is
based on Ant Colony Optimization (ACO) where artificial ants successively construct solutions based on pheromones (stigmergy) and local information. The key feature of our algorithm is the use of two distinct but simplified pheromone matrices
in order to improve convergence but still provide enough flexibility for effectively guiding the solution construction process.
We show that by parallelizing the algorithm we can improve the solution quality significantly. We applied our algorithm to
the instances used for the ITC2007. The results document that our approach is among the leading algorithms for this problem;
in all cases the optimal solution could be found. Furthermore we discuss the characteristics of the instances where the algorithm
performs especially well. 相似文献
62.
Anil Arya Clemens Löffler Brian Mittendorf Thomas Pfeiffer 《European Journal of Operational Research》2015
The prevalence of intermediaries (middlemen) in supply chains is often seen as a dying remnant of less efficient times. Despite predictions that supply chains will rapidly “cut out the middleman” as technological advances have eased logistics, middlemen have continued to thrive. In this paper, we demonstrate a transaction role of middlemen that may help clarify their staying power. In a model with self-interested decision-making by both a manufacturer and a retailer, wherein incentive misalignment creates investment and production inefficiencies, we show that the integrated (first-best) outcome can be achieved with simple cost-based contracts if and only if a middleman is present. We further show that the approach of utilizing a middleman to fully coordinate the supply chain is robust in that it can be applied to a variety of circumstances discussed in the literature, including multilateral investment/effort choices, multiple product providers, and logistical investments made by the middleman. 相似文献
63.
We establish a dichotomy theorem characterizing the circumstances under which a treeable Borel equivalence relation E is essentially countable. Under additional topological assumptions on the treeing, we in fact show that E is essentially countable if and only if there is no continuous embedding of E1 into E. Our techniques also yield the first classical proof of the analogous result for hypersmooth equivalence relations, and allow us to show that up to continuous Kakutani embeddability, there is a minimum Borel function which is not essentially countable-to-one. 相似文献
64.
This paper presents results from seven experimental facilities on the co-current flow of air and water in downward sloping pipes. As a function of the air flow rate, pipe diameter and pipe slope, the required water discharge to prevent air accumulation was determined. In case the water discharge was less than the required water discharge, the air accumulation and additional gas pocket head loss were measured. Results show that volumetric air discharge as small as 0.1% of the water discharge accumulate in a downward sloping section. The experimental data cover all four flow regimes of water-driven air transport: stratified, blow-back, plug and dispersed bubble flow. The analysis of the experimental results shows that different dimensionless numbers characterise certain flow regimes. The pipe Froude number determines the transition from blow-back to plug flow. The gas pocket head loss in the blow-back flow regime follows a pipe Weber number scaling. A numerical model for the prediction of the air discharge as a function of the relevant system parameters is proposed. The novelty of this paper is the presentation of experimental data and a numerical model that cover all flow regimes on air transport by flowing water in downward inclined pipes. 相似文献
65.
Synthesis and characterisation of the SrxBa1−xFeO3−y-system and the fluorinated phases SrxBa1−xFeO2F
Oliver Clemens Robert Haberkorn Peter R. Slater Horst Philipp Beck 《Solid State Sciences》2010,12(8):1455-1463
Compounds in the system SrxBa1?xFeO3?y have been prepared under different partial pressures of oxygen. In this system, different perovskite-type structures are found depending highly on the values of x and y. Fluorination using polyvinylidenedifluoride (PVDF) gives oxyfluoride materials of composition SrxBa1?xFeO2F, which normally crystallize in the cubic perovskite structure. Rietveld refinement results provide information about the packing density for oxide and oxyfluoride samples and allow a general comparison between these two different types of materials. Furthermore, the determination of the average iron oxidation state also showed that the oxygen deficiency, y, depends significantly on the value of x and the structure determined by the Sr/Ba ratio. 相似文献
66.
Gary E. Martin R. Thomas Williamson Kirill A. Blinov Clemens G. Anklin Wolfgang Bermel 《Magnetic resonance in chemistry : MRC》2012,50(10):691-695
1,1‐ADEQUATE and the related long‐range 1,n‐ and n,1‐ADEQUATE variants were developed to provide an unequivocal means of establishing 2JCH and the equivalent of nJCH correlations where n = 3,4. Whereas the 1,1‐ and 1,n‐ADEQUATE experiments have two simultaneous evolution periods that refocus the chemical shift and afford net single quantum evolution for the carbon spins, the n,1‐variant has a single evolution period that leaves the carbon spin to be observed at the double quantum frequency. The n,1‐ADEQUATE experiment begins with an HMBC‐type nJCH magnetization transfer, which leads to inherently lower sensitivity than the 1,1‐ and 1,n‐ADEQUATE experiments that begin with a 1JCH transfer. These attributes, in tandem, serve to render the n,1‐ADEQUATE experiment less generally applicable and more difficult to interpret than the 1,n‐ADEQUATE experiment, which can in principle afford the same structural information. Unsymmetrical and generalized indirect covariance processing methods can complement and enhance the structural information encoded in combinations of experiments e.g. HSQC‐1,1‐ or ?1,n‐ADEQUATE. Another benefit is that covariance processing methods offer the possibility of mathematically combining a higher sensitivity 2D NMR spectrum with for example 1,1‐ or 1,n‐ADEQUATE to improve access to the information content of lower sensitivity congeners. The covariance spectrum also provides a significant enhancement in the F1 digital resolution. The combination of HMBC and 1,1‐ADEQUATE spectra is shown here using strychnine as a model compound to derive structural information inherent to an n,1‐ADEQUATE spectrum with higher sensitivity and in a more convenient to interpret single quantum presentation. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
67.
68.
Elisabeth Eidenberger Erich Stergar Harald Leitner Peter Staron Jürgen Spitaler Claudia Ambrosch-Draxl Helmut Clemens 《Applied Physics A: Materials Science & Processing》2009,97(2):331-340
Atom probe tomography (APT) measurements were conducted to analyze nm-sized precipitates in a Fe-25 m% Co-15 m% Mo model alloy.
Calculation of isoconcentration surfaces and application of cluster-search algorithms yielded the chemical compositions of
matrix and precipitates. Small-angle neutron scattering (SANS) was performed in order to calculate the ratio of magnetic to
nuclear scattering. This so-called A-ratio was compared with values calculated from the chemical information derived from the atom probe data. For this, the magnetism
of the precipitates has to be taken into account. Ab-initio studies have been carried out to determine the magnetic moment
of the precipitate phase. The results show that the extremely fine precipitates are ferromagnetic and exhibit near-equilibrium
composition. In the very early stage of decomposition, however, the composition is different from near-equilibrium. The influences
of the magnetism of the precipitates as well as of artifacts from atom probe measurements on the obtained results are discussed. 相似文献
69.
70.
Weisshoff H Preiss A Nehls I Win T Mügge C 《Analytical and bioanalytical chemistry》2002,373(8):810-819
A hyphenated HPLC-(1)H NMR method for the identification and quantification of PAHs in soil samples has been developed and applied to a PAH reference sample provided by the Federal Institute for Materials Research and Testing (BAM, Berlin, Germany). The results were compared with those obtained by HPLC-DAD, HPLC-F, and GC-MS analyses of the same sample. 相似文献