Surrogate-based optimization of a periodic rescheduling algorithm

Periodic rescheduling is an iterative method for real-time decision-making on industrial process operations. The design of such methods involves high-level when-to-schedule and how-to-schedule decisions, the optimal choices of which depend on the operating environment. The evaluation of the choices typically requires computationally costly simulation of the process, which—if not sufficiently efficient—may result in a failure to deploy the system in practice. We propose the continuous control parameter choices, such as the re-optimization frequency and horizon length, to be determined using surrogate-based optimization. We demonstrate the method on real-time rebalancing of a bike sharing system. Our results on three test cases indicate that the method is useful in reducing the computational cost of optimizing an online algorithm in comparison to the full factorial sampling.     

Solving parity games by a reduction to SAT

This paper presents a reduction from the problem of solving parity games to the satisfiability problem in propositional logic (SAT). The reduction is done in two stages, first into difference logic, i.e. SAT combined with the theory of integer differences, an instance of the SAT modulo theories (SMT) framework. In the second stage the integer variables and constraints of the difference logic encoding are replaced with a set of Boolean variables and constraints on them, giving rise to a pure SAT encoding of the problem. The reduction uses Jurdziński?s characterisation of winning strategies via progress measures. The reduction is motivated by the success of SAT solvers in symbolic verification, bounded model checking in particular. The paper reports on prototype implementations of the reductions and presents some experimental results.     

A Microprocessor Controlled System For Photoelectrochemical Measurements

ABSTRACT

An automatic system for measuring photocurrent of electrodes as a function of excitation wavelength and electrode potential is described. Applications to a chemically modified transparent Sn0₂ electrode and an oxide-covered tantalum electrode are shown.     

Stable meshfree methods in fluid mechanics based on Green’s functions

Recently, stable meshfree methods for computational fluid mechanics have attracted rising interest. So far such methods mostly resort to similar strategies as already used for stabilized finite element formulations. In this study, we introduce an information theoretical interpretation of Petrov–Galerkin methods and Green’s functions. As a consequence of such an interpretation, we establish a new class of methods, the so-called information flux methods. These schemes may not be considered as stabilized methods, but rather as methods which are stable by their very nature. Using the example of convection–diffusion problems, we demonstrate these methods’ excellent stability and accuracy, both in one and higher dimensions.     

Zeros of Z-rational functions and D0L equivalence

Effective findability of zeros of Z-rational functions (an open problem at the time of writing) is shown to imply solvability of the equivalence problem as well as the ultimate equivalence problem for HD0L sequences. As a special case, these problems are shown to be solvable for HD0L sequences the morphisms of the generating HD0L systems of which have Parikh matrices with eigenvalues of the form rε where r is a real number and ε is a root of unity.     

Effects of annealing on performance of InP solar cells on GaAs substrates

Effects of annealing on crystal structure and device characteristics of InP solar cells on GaAs substrates were studied. Two different methods, thermally cycled annealing during the growth, and rapid thermal annealing after the growth, were applied. The results obtained for the annealed solar cells were compared with those obtained for nonannealed and homoepitaxial solar cells. The dislocation density was significantly reduced by annealing from that of the non-annealed heteropitaxial solar cells, and most of the device characteristics were improved.     

Distillability of extracted mixed-birch tall oil

Chemical and physical properties of tall oil made in the CSR process and distillation results of three different types of distillation plants are presented. Chemically extracted, mixed-birch, tall oil differs remarkably from the normal Scandinavian crude tall oil. The extracted oil deviates from the normal, unextracted, mixed-birch tall oil with respect to the smaller unsaponifiable amount and the fatty acid esters. The amount of resin acid is small in extracted mixed-birch tall oil. The quantity of fatty acids, especially that of saturated fatty acids, is large. Distillation of extracted mixed-birch tall oil is most successful in a distillation plant where thin film evaporators are used.     

Electrostatic image theory for two anisotropic half-spaces

An image solution for the canonical electrostatic problem of a point charge in an anisotropic half-space bounded by another anisotropic half-space is presented. The image source is obtained in operator form by using Fourier-transformed Maxwell equations and transmission line theory. After applying Heaviside operator calculus the image operator can be interpreted as a combination of a point charge and a sector of planar charge. The new theory is shown to coincide with the previously known image solutions of less general anisotropic media. In addition to being applicable to any physically feasible anisotropic medium of electrostatics, the method can be used for steady-current conductivity problems via a duality transformation.