A fast heuristic for quay crane scheduling with interference constraints

This paper considers the problem of scheduling quay cranes which are used at sea port container terminals to load and unload containers. This problem is studied intensively in a recent stream of research but still lacks a correct treatment of crane interference constraints. We present a revised optimization model for the scheduling of quay cranes and propose a heuristic solution procedure. At its core a Branch-and-Bound algorithm is applied for searching a subset of above average quality schedules. The heuristic takes advantage from efficient criteria for branching and bounding the search with respect to the impact of crane interference. Although the used techniques are quite standard, the new heuristic produces much better solutions in considerably shorter run times than all algorithms known from the literature.     

Gallium gradients in Cu(In,Ga)Se2 thin‐film solar cells

The gallium gradient in Cu(In,Ga)Se₂ (CIGS) layers, which forms during the two industrially relevant deposition routes, the sequential and co‐evaporation processes, plays a key role in the device performance of CIGS thin‐film modules. In this contribution, we present a comprehensive study on the formation, nature, and consequences of gallium gradients in CIGS solar cells. The formation of gallium gradients is analyzed in real time during a rapid selenization process by in situ X‐ray measurements. In addition, the gallium grading of a CIGS layer grown with an in‐line co‐evaporation process is analyzed by means of depth profiling with mass spectrometry. This gallium gradient of a real solar cell served as input data for device simulations. Depth‐dependent occurrence of lateral inhomogeneities on the µm scale in CIGS deposited by the co‐evaporation process was investigated by highly spatially resolved luminescence measurements on etched CIGS samples, which revealed a dependence of the optical bandgap, the quasi‐Fermi level splitting, transition levels, and the vertical gallium gradient. Transmission electron microscopy analyses of CIGS cross‐sections point to a difference in gallium content in the near surface region of neighboring grains. Migration barriers for a copper‐vacancy‐mediated indium and gallium diffusion in CuInSe₂ and CuGaSe₂ were calculated using density functional theory. The migration barrier for the In_Cu antisite in CuGaSe₂ is significantly lower compared with the Ga_Cu antisite in CuInSe₂, which is in accordance with the experimentally observed Ga gradients in CIGS layers grown by co‐evaporation and selenization processes. Copyright © 2014 John Wiley & Sons, Ltd.     

Production scheduling and rescheduling with genetic algorithms

A general model for job shop scheduling is described which applies to static, dynamic and non-deterministic production environments. Next, a Genetic Algorithm is presented which solves the job shop scheduling problem. This algorithm is tested in a dynamic environment under different workload situations. Thereby, a highly efficient decoding procedure is proposed which strongly improves the quality of schedules. Finally, this technique is tested for scheduling and rescheduling in a non-deterministic environment. It is shown by experiment that conventional methods of production control are clearly outperformed at reasonable run-time costs.     

Sichtbarmachung von Strömungen in Luft

Zusammenfassung Die Sichtbarmachung von Luftstr?mungen h?ngt von Gewicht, Schwebef?higkeit und Leuchkraft des beigemengten Stoffes ab. Als solcher hat sich in neuerer Zeit durch Erhitzen in Flockenform überführtes Metaldehyd recht brauchbar erwiesen. Nachstehend wird über von Str?mungen um K?rper berichtet; die hierbei gewonnenen photographischen Aufanhamen werden gezeigt. VDI VDI     

Rigorous finite-difference analysis of coupled channel waveguideswith arbitrarily varying index profile

A rigorous finite-difference formulation for the hybrid-mode analysis of coupled diffused dielectric channel waveguides is presented. The method includes the two-dimensional continuous index profile variations directly in the finite-difference form of coupled equations and avoids the shortcomings inherent in the usual staircase approximations. The formulation in terms of the wave equation for the transverse components of the magnetic field leads to an eigenvalue problem where the nonphysical, spurious modes do not appear. The analysis includes the complete set of hybrid-modes, takes mode-conversion effects and complex waves into account, if they exist, and allows the calculation of dielectric channel waveguides with large index difference levels. Dispersion characteristic examples are calculated for coupled structures suitable for optical integrated circuits. The theory verified by comparison with results available from other methods     

Electrical characteristics of low temperature-Al0.3Ga0.7As

In this work, we present electrical characterizations of n⁺ GaAs/low temperature (LT)-Al_0.3Ga_0.7As/n⁺ GaAs resistor structures in which the LT layers are grown at nominal substrate temperatures of 250 and 300°C. The resistivity and V_tfl parameters of these LT-Al_0.3Ga_0.7As layers are compared with those of LT-GaAs and Al_0.3Ga_0.7As grown at a normal growth temperature of 720°C. Low-temperature Al_0.3Ga_0.7As layers exhibit resistivities as high as 10¹² ohm-cm, nearly four orders of magnitude higher than that of LT-GaAs, and V_tfl values as high as 45 V, over twice that of LT-GaAs. We also find that the LT-Al_0.3Ga_0.7As materials grown at 250 and 300°C appear to show opposite and contradictory trends with respect to resistivity and V_tfl. We propose that this result can be explained by residual hopping conduction in the 250°C material. Temperature dependent conductivity measurements confirm the presence of a hopping mechanism in LT-Al_0.3Ga_0.7As grown at 250°C and yield activation energies of 0.77 and 0.95 eV for LT-GaAs and LT-Al_0.3Ga_0.7As, respectively.     

Influence of the Impaction Angle on the Triboelectric Charging of Aerosol Nanoparticles

A low pressure impactor is used to measure triboelectric charging behavior of metallic nanoparticles. Ag nanoparticles, produced by spark discharge, were impacted onto Pt sputtered targets. The influence of the impaction angle and impaction velocity on the triboelectric charging was investigated. While for perpendicular impaction the charge transfer behavior of previous work was confirmed, the oblique impaction revealed new phenomena. Additional charge transfer was observable, which increases with obliqueness. The possibility of mass transfer between particle and target due to the high-energy collisions was also investigated. SEM characterization and Auger spectroscopy indicate mass transfer from the particle to the target surface.     

Application of geothermal absorption air-conditioning system: A case study

Possible applications of geothermal energy are increasingly attracting worldwide interest as a low carbon source of energy. Sedimentary basins offer an accessible low grade geothermal heat source to launch energetically efficient air-conditioning systems. The natural temperature, porosity and permeability of these sedimentary basins may be sufficient to provide usable geothermal power for heat-driven sorption air-conditioning system. In the Perth metropolitan region, hot sedimentary aquifers with temperatures between 70 and 100 °C are generally available at around 3 km depth or shallower. This paper outlines the possible application of a large scale geothermal absorption air-conditioning system to provide baseload cooling to the main campus of the University of Western Australia (UWA). The conceptual design of this system is proposed. The design considerations and the performance outcomes are presented. The economic analysis based on the real-time cooling load profile at the UWA and the chiller operation scheme demonstrates the viablity of geothermal absorption air-conditioning system. This paper will help engineers appreciate the opportunities and barriers to geothermal applications, the latest developments and how this technology may help to significantly reduce carbon dioxide emissions.     

CIGS thin-film solar cells on steel substrates

Steel foil is an attractive candidate for use as a flexible substrate material for Cu(In_x,Ga_1 − x)Se₂ solar cells (CIGS). It is stable at the high temperatures involved during CIGS processing and is also commercially available. Stainless chromium (Cr) steel is more expensive than Cr-free steel sheets, but the latter are not stable against corrosion. We processed CIGS solar cells on both types of substrates. The main problem arising here is the diffusion of detrimental elements from the substrate into the CIGS absorber layer. The diffusion of iron (Fe) and other substrate elements into the CIGS layer was investigated by Secondary Ion Mass Spectrometry (SIMS). The influence of the impurities on the solar cell parameters was determined by current voltage (JV) and external quantum efficiency (EQE) measurements. A direct correlation between the Fe content in the CIGS layer and the solar cell efficiency was found. The diffusion of Fe could be strongly reduced by a diffusion barrier layer. Thus we could process CIGS solar cells with a conversion efficiency of 12.8% even on Cr-free steel substrate.