Enhancing CLP branch and bound techniques for scheduling problems

In this paper, we propose a constraint logic programming (CLP) approach to the solution of a job shop scheduling problem in the field of production planning in orthopaedic hospital departments. A pure CLP on finite domain (CLP(FD)) approach to the problem has been developed, leading to disappointing results. In fact, although CLP(FD) has been recognized as a suitable tool for solving combinatorial problems, it presents some drawbacks for optimization problems. The main reason concerns the fact that CLP(FD) solvers do not effectively handle the objective function and cost‐based reasoning through the simple branch and bound scheme they embed. Therefore, we have proposed an improvement of the standard CLP branch and bound algorithm by exploiting some well‐known operations research results. The branch and bound we integrate in a CLP environment is based on the optimal solution of a relaxation of the original problem. In particular, the relaxation used for the job shop scheduling problem considered is the well‐known shifted bottleneck procedure considering single machine problems. The idea is to decompose the original problem into subproblems and solve each of them independently. Clearly, the solutions of each subproblem may violate constraints among different subproblems which are not taken into account. However, these solutions can be exploited in order to improve the pruning of the search space and to guide the search by defining cost‐based heuristics. The resulting algorithm achieves a significant improvement with respect to the pure CLP(FD) approach that enables the solution of problems which are one order of magnitude greater than those solved by a pure CLP(FD) algorithm. In addition, the resulting code is less dependent on the input data configuration. Copyright © 2001 John Wiley & Sons, Ltd.     

Habitat suitability curves for brown trout (Salmo trutta fario L.) in the River Adda,Northern Italy: comparing univariate and multivariate approaches

Habitat suitability of brown trout (Salmo trutta fario) was studied in the upper portion of the Adda River, Northern Italy. Measurements were made for 528 individuals distributed in two life‐stage classes, adult and juvenile, based on body length. In order to provide basic biological information for the physical habitat simulation (PHABSIM) system of the instream flow incremental methodology (IFIM) in the Italian regulated rivers, habitat suitability curves (HSCs) have been developed with respect to several microhabitat riverine parameters. Initially, current velocity, water depth, substrate class size and cover were analysed with an univariate approach, then bivariate habitat suitability models were developed from depth and velocity data. The comparison of experimental univariate HSCs with those from the literature outlined some differences that can essentially be explained by characteristics of the investigated river, confirming the necessity of using site‐specific curves in relation to each experimental study area. To compare the univariate and bivariate approaches, the weighted usable area (WUA)–discharge relationships were calculated using both types of HSCs. Response curves obtained from the two approaches turned out to be quite different. In PHABSIM habitat modelling, HSCs univariate functions need to be aggregated to produce the WUA–discharge relationship. A multiplicative criterion is generally used for the combined suitability factor; by means of this aggregation criterion all variables have equal weight. According to bivariate models, depth is much more important than velocity in defining habitat suitability requirements. Copyright © 2001 John Wiley & Sons, Ltd.     

Enhanced Elastic Migration of Magnesium Cations in alpha-Manganese Dioxide Tunnels Locally Tuned by Aluminium Substitution

The harsh conditions of large hydrated ion radius of Mg²⁺ cations and the strong electrostatic interaction with the host material put forward higher requirements for high-performance aqueous magnesium ion (Mg²⁺) energy storage devices. Herein, substituted aluminium ions (Al³⁺) doped α-MnO₂ materials are prepared. The introduction of Al³⁺ cations adjust the local chemical environment inside the tunnel structure of α-MnO₂ and precisely regulates the diffusion behavior of inserted Mg²⁺ cations. The shortened oxygens’ distance and abundant oxygen defects result in a substantially enhanced elastic migration pattern of Mg²⁺ cations driven by strengthened electrostatic attraction, which brings the lower diffusion energy barrier, improved reaction kinetics, and adaptive volume expansion as evidenced by Climbing Image-Nudged Elastic Band density function theory calculations coupled with experimental confirmation in X-ray photoelectron spectroscopy, electron paramagnetic resonance, and galvanostatic intermittent titration technique. As a result, this rationally designed cathode exhibits a high reversible capacity of 197.02 mAh g^-1 at 0.1 A g^-1 and stable cycle performance of 2500 cycles with 82% retention. These parameters are among the best of Mg-ion capacitors reported to date. This study offers a detailed insight into the local tunnel structure tunning effect and opens up a new path of modification for tunnel-type structural materials.     

Silane-Mediated Expansion of Domains in Si-Doped κ-Ga2O3 Epitaxy and its Impact on the In-Plane Electronic Conduction

Unintentionally doped (001)-oriented orthorhombic κ-Ga₂O₃ epitaxial films on c-plane sapphire substrates are characterized by the presence of ≈ 10 nm wide columnar rotational domains that can severely inhibit in-plane electronic conduction. Comparing the in- and out-of-plane resistance on well-defined sample geometries, it is experimentally proved that the in-plane resistivity is at least ten times higher than the out-of-plane one. The introduction of silane during metal-organic vapor phase epitaxial growth not only allows for n-type Si extrinsic doping, but also results in the increase of more than one order of magnitude in the domain size (up to ≈ 300 nm) and mobility (highest µ ≈ 10 cm²V⁻¹s⁻¹, with corresponding lowest ρ ≈ 0.2 Ωcm). To qualitatively compare the mean domain dimension in κ-Ga₂O₃ epitaxial films, non-destructive experimental procedures are provided based on X-ray diffraction and Raman spectroscopy. The results of this study pave the way to significantly improved in-plane conduction in κ-Ga₂O₃ and its possible breakthrough in new generation electronics. The set of cross-linked experimental techniques and corresponding interpretation here proposed can apply to a wide range of material systems that suffer/benefit from domain-related functional properties.