Satisfiability and Optimization in Periodic Traffic Flow Problems

Automatically calculating periodic timetables in public railway transport systems is an NP-complete problem – namely the Periodic Event Scheduling Problem (PESP). The original model is restricted to basic periodic timetabling. Extending the model by decisional transport networks with flows induces new possibilities in the timetabling and planning process. Subsequently, the given flexibility results in a generic model extension of PESP that can be applied in subsets of the timetabling process. The successful utilization of this approach is presented for distinct chain paths, duplicated chain paths and non-connected flow graphs that represent integration of routing and timetabling, planning of periodic rail freight train paths and track allocation, respectively. Furthermore, the encoding of this generic model into a binary propositional formula is introduced and the appropriate usage of several techniques like SAT solving and MaxSAT to calculate and optimize the corresponding instances will be presented accordingly. Computational results for real-world scenarios suggest the practical impact and give promising perspectives for further scientific research

A Local Search Algorithm for Solving Large Scale Conflict Graphs in Freight Railway Timetabling

We consider the problem of planning the annual timetable for all freight trains in Germany simultaneously. That is, for each train, construct a slot through the network such that no two slots of different trains have a conflict. We denote this task by the Train Path Assignment Problem (TPAP) and consider a column generation approach where iteratively, we are given for each train request a growing set of possible slots. In each iteration, we look for a maximum subset without any conflicts. We model this problem as the Maximum Independent Set problem (MIS). Due to the many slots that are constructed, hence variables that are generated, we deal with large scale MIS instances. Therefore, we solve the MIS heuristically and develop a local search algorithm called Conflict Resolving (CR) that is tailored to the specially structured instances from the application. To solve the MIS, CR iteratively perturbs the current solution in order to leave local optima and then repeatedly improves the solution by replacing k-1 solution vertices by k non-solution vertices. These steps are embedded in a simulated annealing framework. In this paper, we present the column generation approach that is solved as an MIS. Furthermore, we introduce the CR algorithm and numerically compare it to both, a MIP solver and Iterated Local Search (ILS), a state-of-the-art heuristics. It turns out that CR performs best for the instances from real-world timetabling, and is also comparable to the ILS on selected MIS benchmark instances

Charge transport through a molecule driven by a high-frequency field

We study the current and the associated noise for the transport through a two-site molecule driven by an external oscillating field. Within a high-frequency approximation, the time-dependent Hamiltonian is mapped to a static one with effective parameters that depend on the driving amplitude and frequency. This analysis allows an intuitive physical picture explaining the nontrivial structure found in the noise properties as a function of the driving amplitude. The presence of dips in the Fano factor permits a control of the noise level by means of an appropriate external driving.Comment: 15 pages, 5 figures, elsart styl

Transport suppression in heterostructures driven by an ac gate voltage

We explore the possibility of inducing in heterostructures driven by an ac gate voltage the coherent current suppression recently found for nanoscale conductors in oscillating fields. The destruction of current is fairly independent of the transport voltage, but can be controlled by the driving amplitude and frequency. Within a tight-binding approximation, we obtain analytical results for the average current in the presence of driving. These results are compared against an exact numerical treatment based on a transfer-matrix approach.Comment: 18 pages, 4 figures, elsart style, corrected proo

Gastight Paperboard Package: A new Step in Food Packaging

Packages made from coated paperboard are currently used in food packaging for frosted or microwave food. These cups are usually deep drawn from flat paperboard blanks. The blanks are pre-creased to control the material overflow that appears during drawing. The resulting wrinkles in the sealing area have to be considered as capillary tubes allowing the gas exchange between the package and the environmental atmosphere. A new technological approach in 3D forming enables the prevention of capillary tubes in the sealing area. The result is a gas-tight sealable paperboard cup which is limited by its coating concerning the degree of gas tightness

Laser controlled molecular switches and transistors

We investigate the possibility of optical current control through single molecules which are weakly coupled to leads. A master equation approach for the transport through a molecule is combined with a Floquet theory for the time-dependent molecule. This yields an efficient numerical approach to the evaluation of the current through time-dependent nano-structures in the presence of a finite external voltage. We propose tunable optical current switching in two- and three-terminal molecular electronic devices driven by properly adjusted laser fields, i.e. a novel class of molecular transistors.Comment: 11 pages, 4 figures, elsart.cls include

Schöneberger Norden

SCHÖNEBERGER NORDEN Schöneberger Norden / Großmann, Ute (Rights reserved) ( -

Small town research in Germany - status quo and recommendations

Urban studies in Germany are traditionally oriented towards large cities. The structures, meanings and functions of small towns are not sufficiently perceived and differentiated in scientific or political debates. Adequate research on small towns requires systematic, comparative, inter- and transdisciplinary approaches. Traditional attributions should be questioned critically and small towns should be examined empirically in their diversity and differentiation. This involves paying attention to external influences and heterogeneous internal structures as well as to regional functions and interdependencies. The availability and generation of statistical data, which also make small-scale analyses possible, are just as necessary as more comprehensive studies, which go beyond limited case studies. Finally, also research funding and academic teaching should address small towns more systematically than it has been the case in the past. This position paper presents recommendations for research, university teaching, official statistics and research funding in the field of small town research. The Ad-hoc Working Group focused on small town research in Germany and German-language literature, respectively