Chemical ordering beyond the superstructure in long-range ordered systems

To describe chemical ordering in solid solutions systems Warren-Cowley short-range parameters are ordinarily used. However, they are not directly suited for application to long-range ordered systems, as they do not converge to zero for large separations. It is the aim of this paper to generalize the theory to long-range ordered systems and quantitatively discuss chemical short-range order beyond the superstructure arrangements. This is demonstrated on the example of a non-stoichiometric B2-ordered intermetallic alloy. Parameters of interatomic potentials are taken from an embedded atom method (EAM) calculations and the degree of order is simulated by the Monte Carlo method. Both on-lattice and off-lattice methods, where the latter allows individual atoms to deviate from their regular lattice sites, were used, and the resulting effects are discussed

Location of charging stations in electric car sharing systems

Electric vehicles are prime candidates for use within urban car sharing systems, both from economic and environmental perspectives. However, their relatively short range necessitates frequent and rather time-consuming recharging throughout the day. Thus, charging stations must be built throughout the system's operational area where cars can be charged between uses. In this work, we introduce and study an optimization problem that models the task of finding optimal locations and sizes for charging stations, using the number of expected trips that can be accepted (or their resulting revenue) as a gauge of quality. Integer linear programming formulations and construction heuristics are introduced, and the resulting algorithms are tested on grid-graph-based instances, as well as on real-world instances from Vienna. The results of our computational study show that the best-performing exact algorithm solves most of the benchmark instances to optimality and usually provides small optimality gaps for the remaining ones, whereas our heuristics provide high-quality solutions very quickly. Our algorithms also provide better solutions than a sequential approach that considers strategic and operational decisions separately. A cross-validation study analyzes the algorithms' performance in cases where demand is uncertain and shows the advantage of combining individual solutions into a single consensus solution, and a simulation study investigates their behavior in car sharing systems that provide their customers with more flexibility regarding vehicle selection

A polyhedral study of the diameter constrained minimum spanning tree problem

This paper provides a first polyhedral study of the diameter constrained minimum spanning tree problem (DMSTP). We introduce a new set of inequalities, the circular-jump inequalities which strengthen the well-known jump inequalities. These inequalities are further generalized in two ways: either by increasing the number of partitions defining a jump, or by combining jumps with cutsets. Most of the proposed new inequalities are shown to define facets of the DMSTP polytope under very mild conditions. Currently best known lower bounds for the DMSTP are obtained from an extended formulation on a layered graph using the concept of central nodes/edges. A subset of the new families of inequalities is shown to be not implied by this layered graph formulation

Methodisch - technische Aspekte der Muskelbiopsie

Die vorliegende Arbeit befasst sich mit den Möglichkeiten der Probenentnahme aus dem menschlichen Skelettmuskel. Es wird neben einem allgemeinen Überblick über das Verfahren schwerpunktmäßig auf die technischen und methodischen Aspekte der Biopsie eingegangen. Dazu werden der Aufbau und die Funktion unterschiedlicher Instrumente erläutert, wie auch die methodischen Möglichkeiten der Probenentnahme aufgezeigt. Neben der Beschreibung der unterschiedlichen Entnahmetechniken bildet die Nadel - Muskelbiopsie einen Schwerpunkt, da sie für den sportwissenschaftlichen Bereich die größte Bedeutung aufweist. Dabei wird auch die Frage aufgegriffen, wie gut diese Methode ethisch vertretbar ist bzw. wie sie im Vergleich zu den anderen Techniken beurteilt werden kann. Des Weiteren werden unterschiedliche Einsatzmöglichkeiten der Biopsie im Bereich des Sports beschrieben. Als Ergebnis der Arbeit kann die Muskelbiopsie generell als wichtiges Instrument für die Erforschung der Muskulatur von kranken, als auch von gesunden Personen wie z. B. Sportlern angesehen werden, wobei dies vor allem für die Nadeltechnik gilt, die durch die ständige Weiterentwicklung von Instrumenten und Technik immer größere Bedeutung erlangt. Hinsichtlich der Ethikfrage zeigt sich ebenso, dass die Nadelbiopsie als gering invasive und risikoarme Methode mit Sicherheit jenes Verfahren darstellt, das am ehesten jenen Kriterien entspricht, die von entsprechenden Komitees gefordert werden.The present work describes the possibilities of taking samples from the human skeletal muscle. Among a general description of the muscle biopsy, the focus is pointed at technical and methodical aspects of this procedure. For this reason the functional design and function of biopsy instruments are described just as different ways of muscle biopsy. The various technologies to take samples are described, whereas the focal point of interests is directed on the needle muscle biopsy, which plays an important role for the sport science field. The percutaneous needle technique is compared with the other procedures like open and semiopen biopsy and different application possibilities in sports are described. The result of this work is, that the muscle biopsy in general is a very important tool to investigate the muscles both from sick and healthy persons like athletes. Because of the permanent improvement of instruments and techniques, the needle muscle biopsy will become more and more important in comparison with the alternative methods. Furthermore it is a minimal invasive procedure which is far more ethicaly acceptable than the open and semiopen techniques

An Exact Method for (Constrained) Assortment Optimization Problems with Product Costs

We study the problem of optimizing assortment decisions in the presence of product-specific costs when customers choose according to a multinomial logit model. This problem is NP-hard and approximate solutions methods have been proposed in the literature to obtain both lower and upper bounds in a tractable manner. We propose the first exact solution method for this problem and show that provably optimal assortments of instances with up to one thousand products can be found, on average, in about two tenths of a second. In particular, we propose a bounding procedure based on the approximation method of Feldman and Topaloglu (2015a) to provide tight lower and upper bounds at a fraction of their computing times. We show how these bounds can be used to effectively identify an optimal assortment. We also describe how to adapt our approach to handle cardinality or space/resource capacity constraints on the assortment as well as assortment optimization under a mixed-multinomial logit model. In both cases, our solution method provides significant computational boosts compared to exact methods from the literature