scholarly journals Safe Multi-objective Planning with a Posteriori Preferences

2016 ◽  
Author(s):  
Ralph Eastwood ◽  
Rob Alexander ◽  
Tim Kelly
Keyword(s):  
A Posteriori ◽  
Multi Objective

Multi-Objective Stochastic Optimization Algorithms to Calibrate Microsimulation Models

2019 ◽  
Vol 2673 (4) ◽  
pp. 743-752 ◽  
Author(s):  
Mohammad Karimi ◽  
Maryam Miriestahbanati ◽  
Hamed Esmaeeli ◽  
Ciprian Alecsandru
Keyword(s):  
Particle Swarm Optimization ◽  
Stochastic Optimization ◽  
Simulation Model ◽  
Optimization Algorithm ◽  
Real World ◽  
A Priori ◽  
A Posteriori ◽  
Swarm Optimization ◽  
Calibration Process ◽  
Multi Objective

The calibration process for microscopic models can be automatically undertaken using optimization algorithms. Because of the random nature of this problem, the corresponding objectives are not simple concave functions. Accordingly, such problems cannot easily be solved unless a stochastic optimization algorithm is used. In this study, two different objectives are proposed such that the simulation model reproduces real-world traffic more accurately, both in relation to longitudinal and lateral movements. When several objectives are defined for an optimization problem, one solution method may aggregate the objectives into a single-objective function by assigning weighting coefficients to each objective before running the algorithm (also known as an a priori method). However, this method does not capture the information exchange among the solutions during the calibration process, and may fail to minimize all the objectives at the same time. To address this limitation, an a posteriori method (multi-objective particle swarm optimization, MOPSO) is employed to calibrate a microscopic simulation model in one single step while minimizing the objectives functions simultaneously. A set of traffic data collected by video surveillance is used to simulate a real-world highway in VISSIM. The performance of the a posteriori-based MOPSO in the calibration process is compared with a priori-based optimization methods such as particle swarm optimization, genetic algorithm, and whale optimization algorithm. The optimization methodologies are implemented in MATLAB and connected to VISSIM using its COM interface. Based on the validation results, the a posteriori-based MOPSO leads to the most accurate solutions among the tested algorithms with respect to both objectives.

Optimum Design of a Compliant Uniaxial Accelerometer

2008 ◽  
Author(s):  
Simon Desrochers ◽  
Jorge Angeles ◽  
Damiano Pasini
Keyword(s):  
Optimum Design ◽  
Compliant Mechanism ◽  
Pareto Frontier ◽  
Cad Model ◽  
A Posteriori ◽  
Multi Objective Optimization ◽  
Dynamics Model ◽  
Multi Objective ◽  
Pareto Plot

This work focuses on the multi-objective optimization of a compliant-mechanism accelerometer. The method is used to optimally design an accelerometer with the architecture of a novel version of the Sarrus mechanism. The purpose is to maximize the sensitivity of the accelerometer in its sensing direction, while minimizing its sensitivity in all other directions. The paper starts with a brief description of the dynamics model of the compliant mechanism, followed by the formulation of the a posteriori multi-objective optimization. By using the normalized constrained method, an evenly distribution of the Pareto frontier is found. The paper also provides several optimum solutions on a Pareto plot, as well as the CAD model of the selected solution.

Practical Correction of Three Fold Astigmatism in the Philips CM TEM

1996 ◽  
Vol 54 ◽  
pp. 418-419
Author(s):  
Arno J. Bleeker ◽  
Mark H.F. Overwijk ◽  
Max T. Otten
Keyword(s):  
Optical Properties ◽  
Phase Contrast ◽  
The Other ◽  
Objective Lens ◽  
Symmetric Part ◽  
A Posteriori ◽  
Contrast Transfer Function ◽  
High Brightness ◽  
Rotationally Symmetric ◽  
Brightness Field

With the improvement of the optical properties of the modern TEM objective lenses the point resolution is pushed beyond 0.2 nm. The objective lens of the CM300 UltraTwin combines a Cs of 0. 65 mm with a Cc of 1.4 mm. At 300 kV this results in a point resolution of 0.17 nm. Together with a high-brightness field-emission gun with an energy spread of 0.8 eV the information limit is pushed down to 0.1 nm. The rotationally symmetric part of the phase contrast transfer function (pctf), whose first zero at Scherzer focus determines the point resolution, is mainly determined by the Cs and defocus. Apart from the rotationally symmetric part there is also the non-rotationally symmetric part of the pctf. Here the main contributors are not only two-fold astigmatism and beam tilt but also three-fold astigmatism. The two-fold astigmatism together with the beam tilt can be corrected in a straight-forward way using the coma-free alignment and the objective stigmator. However, this only works well when the coefficient of three-fold astigmatism is negligible compared to the other aberration coefficients. Unfortunately this is not generally the case with the modern high-resolution objective lenses. Measurements done at a CM300 SuperTwin FEG showed a three fold-astigmatism of 1100 nm which is consistent with measurements done by others. A three-fold astigmatism of 1000 nm already sinificantly influences the image at a spatial frequency corresponding to 0.2 nm which is even above the point resolution of the objective lens. In principle it is possible to correct for the three-fold astigmatism a posteriori when through-focus series are taken or when off-axis holography is employed. This is, however not possible for single images. The only possibility is then to correct for the three-fold astigmatism in the microscope by the addition of a hexapole corrector near the objective lens.

Expected A Posteriori Estimation of Multiple Latent Traits

2005 ◽  
Author(s):  
Damon U. Bryant ◽  
Ashley K. Smith ◽  
Sandra G. Alexander ◽  
Kathlea Vaughn ◽  
Kristophor G. Canali
Keyword(s):  
A Posteriori ◽  
Latent Traits ◽  
Posteriori Estimation
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