Ant Colony Optimization with Global Pheromone Evaluation for Scheduling a Single Machine

Ant Colony Optimization (ACO) is a metaheuristic that has recently been applied to scheduling problems. We propose an ACO algorithm for the Single Machine Total Weighted Tardiness Problem and compare it to an existing ACO algorithm for the unweighted problem. The proposed algorithm has some novel properties that are of general interest for ACO optimization. A main novelty is that the ants are guided on their way through the decision space by global pheromone information instead of using only local pheromone information. It is also shown that the ACO optimization behaviour can be improved when priority scheduling heuristics are adapted so that they appropriately reflect absolute quality differences between the alternatives before they are used by the ants. Further improvements can be obtained by identifying situations where the ants can perform optimal decisions.     

Non-Classical Electrostriction in Hydrated Acceptor Doped BaZrO3: Proton Trapping and Dopant Size Effect

Point defects such as oxygen vacancies and protonic interstitials are not only essential for ionic conductivity in oxides since they also affect the mechanical and electromechanical properties. These properties of nominally dry and hydrated proton-conducting BaZr_0.85M_0.15O_2.925+δH_2δ (M = Al, Ga, Sc, In, Y, Eu) ceramics are investigated. Doping decreases Young's modulus with increasing ionic radii difference between the dopant and the host. Nominally dry samples show consistently higher Young's moduli than hydrated samples. All samples exhibit large non-classical electrostriction, with a negative electrostriction coefficient M₃₃<0. M₃₃ shows saturation with the field and a non-ideal Debye relaxation with frequency. The low-frequency M₃₃ value for both dry and hydrated samples shows a similar dependence on dopant radius as Young's modulus. For the hydrated samples, the relaxation frequency increases by a factor >100 in the series Ga-Y, emphasizing the importance of proton trapping, with Y-doped samples having minimal trapping energy. This coincides with the fact that the saturation strain for Y-doped samples is also the smallest. In light of these findings, it is concluded that the present data give strong evidence for the existence of defect-related elastic dipoles in acceptor doped barium zirconate and that the non-classical electrostriction originates in their reorientation under electric field.     

Gravure printed flexible small-molecule organic light emitting diodes

Small-molecule based flexible organic light-emitting diodes (SMOLEDs) were fabricated by gravure printing. In order to modify rheological properties of the functional ink, the green emitter was embedded into an ultrahigh molecular weight polystyrene (UHMW-PS) matrix. The viscosity of the ink was characterized as a function of the small molecule:UHMW-PS weight ratio and solvent type. The gravure printed SMOLEDs exhibited a maximum luminance of 850 cd m⁻², a maximum efficiency of up to 7.7 cd A⁻¹, and turn on voltage of ∼3.5 V. The gravure printed SM:UHMW-PS device exhibits ∼67% higher luminance efficiency comparing to the spin-coated pristine SM device.     

Integration of organic semiconductor lasers and single-mode passive waveguides into a PMMA substrate

Efficiently combining active and passive elements in integrated optics is a key ingredient for their successful employment. Here, we present the fabrication of an optimized PMMA substrate structure for improved coupling of laser light generated by organic semiconductor distributed feedback lasers into single-mode deep ultraviolet induced waveguides. For production, electron beam lithography on an oxidized silicon wafer and subsequent reactive ion etching is used to form the feedback grating of the laser. Afterwards, an aligned second electron beam lithography step on top of the grating allows the fabrication of a topographical step of 1.67 μm on the edges of the grating area. Metal is evaporated on this resulting master structure serving as a plating base for electroforming of a Ni tool. The tool is then used for hot embossing of the structure into PMMA bulk material. On a length of 500 μm the imprinted grating lines, having a period of 200 nm, are 100 nm wide and 60 nm high. Aligned deep ultraviolet exposure to induce a passive single- or multi-mode waveguide and co-evaporation of the active material Alq₃:DCM finish the coupling region. This structure optimizes the coupling of laser light generated in the laser structure into the passive waveguide. In combination with microfluidic channels, the laser light can be considered for sensing applications on a PMMA lab-on-chip system.     

Solution-processed polymer–silver nanowire top electrodes for inverted semi-transparent solar cells

We present a transparent, fully solution-processed top anode system comprising a thin, conductive polymer interlayer below a silver nanowire mesh for efficient organic electronic devices. We fabricate inverted semi-transparent polymer solar cells exhibiting power conversion efficiencies that are comparable to devices incorporating an opaque electrode. By means of scanning electron microscopy and light beam induced photocurrent measurements we show that the thin polymer interlayer facilitates charge extraction from the active layer and efficient transport to the metallic nanowire mesh.     

The role of the polymer solid electrolyte molecular weight in light-emitting electrochemical cells

Different molecular weights (M_w) of poly (methyl methacrylate) (PMMA) were used as the base for the polymer solid electrolyte (PSE) in light-emitting electrochemical cells (LECs). The rheological properties of the LECs formulations are influenced by the M_w of PMMA. The M_w of PMMA also influences the PSE ionic conductivity and therefore affects the threshold voltage of the devices. Furthermore, partial segregation of the two polymers is observed, which correlates directly to the PMMA M_w. The device with the best performance was prepared with a PMMA M_w of 350,000 and exhibited an effective maximum luminance ～3000 cd m^?2.     

On solving permutation scheduling problems with ant colony optimization

A new approach for solving permutation scheduling problems with ant colony optimization (ACO) is proposed in this paper. The approach assumes that no precedence constraints between the jobs have to be fulfilled. It is tested with an ACO algorithm for the single-machine total weighted deviation problem. In the new approach the ants allocate the places in the schedule not sequentially, as in the standard approach, but in random order. This leads to a better utilization of the pheromone information. It is shown by experiments that adequate combinations between the standard approach which can profit from list scheduling heuristics and the new approach perform particularly well.