309 research outputs found
Genetic and memetic algorithms for scheduling railway maintenance activities
Nowadays railway companies are confronted with high infrastructure maintenance costs. Therefore good strategies are needed to carry out these maintenance activities in a most cost effective way. In this paper we solve the preventive maintenance scheduling problem (PMSP) using genetic algorithms, memetic algorithms and a two-phase heuristic based on opportunities. The aim of the PMSP is to schedule the (short) routine activities and (long) unique projects for one link in the rail network for a certain planning period such that the overall cost is minimized. To reduce costs and inconvenience for the travellers and operators, these maintenance works are clustered as much as possible in the same time period. The performance of the algorithms presented in this paper are compared with the performance of the methods from an earlier work, Budai et al. (2006), using some randomly generated instances.genetic algorithm;heuristics;opportunities;maintenance optimization;memetic algorithm
Re-scheduling in railways: the rolling stock balancing problem
This paper addresses the Rolling Stock Balancing Problem (RSBP). This problem arises at a passenger railway operator when the rolling stock has to be re-scheduled due to changing circumstances. These problems arise both in the planning process and during operations. The RSBP has as input a timetable and a rolling stock schedule where the allocation of the rolling stock among the stations does not fit to the allocation before and after the planning period. The problem is then to correct these off-balances, leading to a modified schedule that can be implemented in practice.For practical usage of solution approaches for the RSBP, it is important to solve the problem quickly. Therefore, the focus is on heuristic approaches. In this paper, we describe two heuristics and compare them with each other on some (variants of) real-life instances of NS, the main Dutch passenger railway operator. Finally, to get some insight in the quality of the proposed heuristics, we also compare their outcomes with optimal solutions obtained by solving existing rolling stock circulation models.heuristics;railway planning;integer linear programming;rolling stock re-scheduling
Assessing a Knowledge Management (KM) Project Selection Framework
Knowledge management (KM) is becoming recognized as a valuable tool for establishing and maintaining competitive advantage. Decision superiority, the ultimate goal of KM, is only possible through the effective and efficient use of knowledge. But, to effectively and efficiently create and use KM, it is important to carefully select KM projects. This research assesses the usefulness of a KM project selection framework that was developed by U.S. Air Force Captain William Bower (2001) and refined by 1st Lt Jeffrey Phillips (2003) referred to here as the Bower-Phillips decision framework. To assess the usability of the framework, a case study was undertaken at an Air Force organization to identify and address potential knowledge management opportunities. The framework was found to be useful in identifying possible KM projects
Quasi-linear analysis of the extraordinary electron wave destabilized by runaway electrons
Runaway electrons with strongly anisotropic distributions present in
post-disruption tokamak plasmas can destabilize the extraordinary electron
(EXEL) wave. The present work investigates the dynamics of the quasi-linear
evolution of the EXEL instability for a range of different plasma parameters
using a model runaway distribution function valid for highly relativistic
runaway electron beams produced primarily by the avalanche process. Simulations
show a rapid pitch-angle scattering of the runaway electrons in the high energy
tail on the time scale. Due to the wave-particle
interaction, a modification to the synchrotron radiation spectrum emitted by
the runaway electron population is foreseen, exposing a possible experimental
detection method for such an interaction
Scheduling preventive railway maintenance activities
A railway system needs a substantial amount of maintenance. To
prevent unexpected breakdowns as much as possible, preventive
maintenance is required. In this paper we discuss the Preventive
Maintenance Scheduling Problem (PMSP), where (short) routine
activities and (long) unique projects have to be scheduled in a
certain period. To reduce costs and inconvenience for the
travellers and operators, these activities have to be scheduled as
much as possible together. We present a mathematical formulation
for this problem and some greedy heuristics to solve it fast.
Moreover, we compare the performance of these heuristics with the
optimal solution using some randomly generated instances
Genetic and memetic algorithms for scheduling railway maintenance activities
Nowadays railway companies are confronted with high infrastructure maintenance costs. Therefore good strategies are needed to carry out these maintenance activities in a most cost effective way. In this paper we solve the preventive maintenance scheduling problem (PMSP) using genetic algorithms, memetic algorithms and a two-phase heuristic based on opportunities. The aim of the PMSP is to schedule the (short) routine activities and (long) unique projects for one link in the rail network for a certain planning period such that the overall cost is minimized. To reduce costs and inconvenience for the travellers and operators, these maintenance works are clustered as much as possible in the same time period. The performance of the algorithms presented in this paper are compared with the performance of the methods from an earlier work, Budai et al. (2006), usin
Operations Research Models for Scheduling Railway Infrastructure Maintenance
In the last decades, maintenance of technical systems has become increasingly impor-
tant in many industries. Such systems are transport systems (rail, bus, airplane), civil
engineering systems (roads, buildings, bridges), health care (hospitals), communication
systems, manufacturing plants, etc. Failures of these systems may cause expensive pro-
duction losses and can have a negative e®ect on the environment and safety. For example,
a train accident, crash of an airplane, collapse of a building, computer breakdown in an
hospital, may cause large societal costs. Substantial environmental damage may result
from a failure i
Re-scheduling in railways: the rolling stock balancing problem
This paper addresses the Rolling Stock Balancing Problem (RSBP). This problem arises at a passenger railway operator when the rolling stock has to be re-scheduled due to changing circumstances. These problems arise both in the planning process and during operations.
The RSBP has as input a timetable and a rolling stock schedule where the allocation of the rolling stock among the stations does not fit to the allocation before and after the planning period. The problem is then to correct these off-balances, leading to a modified schedule that can be implemented in practice.
For practical usage of solution approaches for the RSBP, it is important to solve the problem quickly. Therefore, the focus is on heuristic approaches. In this paper, we describe two heuristics and compare them with each other on some (variants of) real-life instances of NS, the main Dutch passenger railway operator. Finally, to get some insight in the quality of the proposed heuristics, we also compare their outcomes with optimal solutions obtained by solving existing rolling stock circulation models
Spatially Resolved Mapping of Local Polarization Dynamics in an Ergodic Phase of Ferroelectric Relaxor
Spatial variability of polarization relaxation kinetics in relaxor
ferroelectric 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 is studied using time-resolved
Piezoresponse Force Microscopy. Local relaxation attributed to the
reorientation of polar nanoregions is shown to follow stretched exponential
dependence, exp(-(t/tau)^beta), with beta~~0.4, much larger than the
macroscopic value determined from dielectric spectra (beta~~0.09). The spatial
inhomogeneity of relaxation time distributions with the presence of 100-200 nm
"fast" and "slow" regions is observed. The results are analyzed to map the
Vogel-Fulcher temperatures on the nanoscale.Comment: 23 pages, 4 figures, supplementary materials attached; to be
submitted to Phys. Rev. Let
Wachstumsminderung
X-ray absorption near edge structure (XANES) analysis in combination with synchrotron radiation induced total reflection X-ray fluorescence (SR-TXRF) acquisition was used to determine the oxidation state of Fe in human cancer cells and simultaneously their elemental composition by applying a simple sample preparation procedure consisting of pipetting the cell suspension onto the quartz reflectors.
XANES spectra of several inorganic and organic iron compounds were recorded and compared to that of different cell lines. The XANES spectra of cells, independently from the phase of cell growth and cell type were very similar to that of ferritin, the main Fe store within the cell. The spectra obtained after CoCl2 or NiCl2 treatment, which could mimic a hypoxic state of cells, did not differ noticeably from that of the ferritin standard. After 5-fluorouracil administration, which could also induce an oxidative-stress in cells, the absorption edge position was shifted toward higher energies representing a higher oxidation state of Fe. Intense treatment with antimycin A, which inhibits electron transfer in the respiratory chain, resulted in minor changes in the spectrum, resembling rather the N-donor Fe-,′-dipyridyl complex at the oxidation energy of Fe(III), than ferritin. The incorporation of Co and Ni in the cells was followed by SR-TXRF measurements
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