2,745 research outputs found
Computing the set of Epsilon-efficient solutions in multiobjective space mission design
In this work, we consider multiobjective space mission design problems. We will start from the need, from a practical point of view, to consider in addition to the (Pareto) optimal solutions also nearly optimal ones. In fact, extending the set of solutions for a given mission to those nearly optimal significantly increases the number of options for the decision maker and gives a measure of the size of the launch windows corresponding to each optimal solution, i.e., a measure of its robustness. Whereas the possible loss of such approximate solutions compared to optimal—and possibly even ‘better’—ones is dispensable. For this, we will examine several typical problems in space trajectory design—a biimpulsive transfer from the Earth to the asteroid Apophis and two low-thrust multigravity assist transfers—and demonstrate the possible benefit of the novel approach. Further, we will present a multiobjective evolutionary algorithm which is designed for this purpose
Two-neutrino double electron capture on Xe based on an effective theory and the nuclear shell model
We study the two-neutrino double electron capture on Xe based on an
effective theory (ET) and large-scale shell model calculations, two modern
nuclear structure approaches that have been tested against Gamow-Teller and
double-beta decay data. In the ET, the low-energy constants are fit to electron
capture and transitions around xenon. For the nuclear shell model,
we use an interaction in a large configuration space that reproduces the
spectroscopy of nuclei in this mass region. For the dominant transition to the
Te ground state, we find half-lives y for the ET and y for the shell model. The ET uncertainty leads to
a half-life almost entirely consistent with present experimental limits and
largely within the reach of ongoing experiments. The shell model half-life
range overlaps with the ET, but extends less beyond current limits. Our
findings thus suggest that the two-neutrino double electron capture on
Xe has a good chance to be discovered by ongoing or future experiments.
In addition, we present results for the two-neutrino double electron capture to
excited states of Te.Comment: 5 pages, 2 figure
Ion homeostasis and variation in low temperature performance in the fall and spring field crickets (Orthoptera: Gryllidae)
Low temperature performance affects the geographical distribution of insects. The lower critical temperature limits of chill-susceptible insects are likely determined by failure of ion and water balance at low temperature. I used phenotypic plasticity in the cold tolerance of Gryllus pennsylvanicus, and the naturally higher cold tolerance of Gryllus veletis to test the hypothesis that variation in low temperature performance is accompanied by variation in ion and water homeostasis at low temperatures. Low temperature acclimation and cold adaptation enhanced performance at low temperatures. Groups with higher cold tolerance had an enhanced ability to prevent or mitigate the migration of hemolymph Na+ and water into the digestive system, which ultimately resulted in smaller decreases in K+ equilibrium potentials at the muscle tissue. The ability to maintain ion and water balance as a result of changes in gut membrane permeability increased performance at low temperatures, and reduced the onset of chilling injury
Piecewise Linear Representation Segmentation as a Multiobjective Optimization Problem
Proceedings of: Forth International Workshop on User-Centric Technologies and applications (CONTEXTS 2010). Valencia, September 7-10, 2010Actual time series exhibit huge amounts of data which require an unaffordable computational load to be processed, leading to approximate representations to aid these processes. Segmentation processes deal with this issue dividing time series into a certain number of segments and approximating those segments with a basic function. Among the most extended segmentation approaches, piecewise linear representation is highlighted due to its simplicity. This work presents an approach based on the formalization of the segmentation process as a multiobjetive optimization problem and the resolution of that problem with an evolutionary algorithm.This work was supported in part by Projects CICYT TIN2008-06742-C02-02/TSI, CICYT TEC2008-06732-C02-02/TEC, CAM CONTEXTS (S2009/TIC-1485) and DPS2008-07029-C02-02.Publicad
Spin Filtering and Entanglement Swapping through Coherent Evolution of a Single Quantum Dot
We exploit the non-dissipative dynamics of a pair of electrons in a large
square quantum dot to perform singlet-triplet spin measurement through a single
charge detection and show how this may be used for entanglement swapping and
teleportation. The method is also used to generate the AKLT ground state, a
further resource for quantum computation. We justify, and derive analytic
results for, an effective charge-spin Hamiltonian which is valid over a wide
range of parameters and agrees well with exact numerical results of a realistic
effective-mass model. Our analysis also indicates that the method is robust to
choice of dot-size and initialization errors, as well as decoherence introduced
by the hyperfine interaction.Comment: 5 pages, 3 figure
An Improvement Study of the Decomposition-based Algorithm Global WASF-GA for Evolutionary Multiobjective Optimization
The convergence and the diversity of the decompositionbased evolutionary algorithm Global WASF-GA (GWASF-GA) relies
on a set of weight vectors that determine the search directions for new non-dominated solutions in the objective space. Although using weight vectors whose search directions are widely distributed may lead to a well-diversified approximation of the Pareto front (PF), this may not be enough to obtain a good approximation for complicated PFs (discontinuous, non-convex, etc.). Thus, we propose to dynamically adjust the weight vectors once GWASF-GA has been run for a certain number of generations. This adjustment is aimed at re-calculating some of the weight vectors, so that search directions pointing to overcrowded regions of the PF are redirected toward parts with a lack of solutions that may be hard to be approximated. We test different parameters settings of the dynamic adjustment in optimization problems with three, five, and six objectives, concluding that GWASF-GA performs better when adjusting the weight vectors dynamically than without applying the adjustment.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
About Designing an Observer Pattern-Based Architecture for a Multi-objective Metaheuristic Optimization Framework
Multi-objective optimization with metaheuristics is an active and popular research field which is supported by the availability of
software frameworks providing algorithms, benchmark problems, quality indicators and other related components. Most of these tools follow a monolithic architecture that frequently leads to a lack of flexibility when a user intends to add new features to the included algorithms. In this paper, we explore a different approach by designing a component-based architecture for a multi-objective optimization framework based on the observer pattern. In this architecture, most of the algorithmic components
are observable entities that naturally allows to register a number of observers. This way, a metaheuristic is composed of a set of observable and observer elements, which can be easily extended without requiring to modify the algorithm. We have developed a prototype of this architecture and implemented the NSGA-II evolutionary algorithm on top of it as a case study. Our analysis confirms the improvement of flexibility using this architecture, pointing out the requirements it imposes and how performance is affected when adopting it.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
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