Parameterized complexity of machine scheduling: 15 open problems

Machine scheduling problems are a long-time key domain of algorithms and complexity research. A novel approach to machine scheduling problems are fixed-parameter algorithms. To stimulate this thriving research direction, we propose 15 open questions in this area whose resolution we expect to lead to the discovery of new approaches and techniques both in scheduling and parameterized complexity theory.Comment: Version accepted to Computers & Operations Researc

Scheduling reentrant jobs on parallel machines with a remote server

This paper explores a specific combinatorial problem relating to re-entrant jobs on parallel primary machines, with a remote server machine. A middle operation is required by each job on the server before it returns to its primary processing machine. The problem is inspired by the logistics of a semi-automated micro-biology laboratory. The testing programme in the laboratory corresponds roughly to a hybrid flowshop, whose bottleneck stage is the subject of study. We demonstrate the NP-hard nature of the problem, and provide various structural features. A heuristic is developed and tested on randomly generated benchmark data. Results indicate solutions reliably within 1.5% of optimum. We also provide a greedy 2-approximation algorithm. Test on real-life data from the microbiology laboratory indicate a 20% saving relative to current practice, which is more than can be achieved currently with 3 instead of 2 people staffing the primary machines

Development and characterization of treated kaolin filled polypropylene/kaolin nanocomposites

This research work focused on producing modified kaolin filler in polypropylene/kaolin (PP/K) nanocomposite by melt compounding process in order to improve its mechanical and thermal properties for industrial applications. The surface treatments of micron sized Malaysian kaolin were conducted to produce nano sized kaolin by acidification of kaolin fillers with sulphuric acid and planetary milling using urea (mechanochemical milling). Testing on both surface treated kaolin were carried out with the aid of Field Scanning Electron Microscopy (FESEM), Fourier Transform Infrared (FTIR), Brunauer–Emmett–Teller (BET), X-ray Diffraction (XRD) and Particle Size Analyser and results of both treated kaolin were compared. However, the surface treated kaolin using acidification was unsuccessful as shown by XRD, FTIR and BET results. A successful delamination of micron sized into nano sized kaolin was achieved by mechanochemical milling. The additional bands at 3624, 3445 and 3388 cm-1 and illite phase at lower 2θ by FTIR and XRD studies respectively, indicated delamination of kaolin. Surface area increased by 400% from BET results. The PP/K nanocomposite was produced by incorporating low weight (1-7%) percentages of organically modified nanokaolin into PP by melt compounding with polypropylene grafted maleic anhydride (PP-g-MA) as coupling agent. The FTIR and XRD analyses on chemical structure showed successful synthesis of PP/K nanocomposites by the vanishing of characteristic of OH bands and peaks of kaolin respectively. The tensile and impact strength, tan δ, loss modulus and melt flow index of PP/K nanocomposite decreases by 17, 27, 36, 32 and 78% respectively. Conversely, the results show that incorporation of nanokaolin clay into PP causes increase in thermal degradation (200%), crystalinity (17%), nucleation effect (17%), storage modulus (10%), surface roughness (87%), and optical (262%). Whereas, TEM of PP/K nanocomposite exhibit nanokaolin dispersion with nanoscale sizes. Therefore, the PP/K nanocomposites formulated shall be a potential candidate for manufacturing novel new materials of attraction in many sectors

Pool-based electricity market model for Malaysia electricity supply industry considering minimum generation capacity payment

Malaysia is improving its electricity supply industry to become more transparent, productive and competitive with the introduction of the single buyer market model. However, since the electricity demand is lower than the reserved capacity, the implementation of this market model does not provide transparent competition as Tenaga Nasional Berhad (TNB) has suffered massive profit erosion because of monthly capacity payment that should be paid to Independent Power Producers (IPP) regardless of electricity usage. Since 2005, the Malaysia Electricity Supply Industry (MESI) has planned to change to the pool market model as it is recognized as a model which could overcome the shortcomings of the single buyer market model. However, there are a few issues on introducing the pool model such as price fluctuation and market power exercises which could influence the welfare of generators as well as the consumers. Some researchers have developed pool-based market models with the aim to overcome the aforementioned issues, but the efficiency and the energy price offered from the generators are not considered. Therefore, this research developed a model introducing the minimum generation capacity payment involving the efficiency of the generators and base load sharing approaches. The proposed model was tested using the 2, 16 and 24 generator test systems involving IPPs and Tenaga Nasional Berhad Generation (TNBG) around Peninsular Malaysia for an economic analysis to highlight the merits of the proposed model in terms of generation revenue and demand payment. The results have shown that the proposed market model ensures the intermediate value of total generation revenue which decreased from 1.99% to 4.67% and 3% to 9.62% during the weekday and weekend, respectively. The demand payment decreased as it is proportional to the generation revenue. However, this proposed model did not consider market uncertainties. This findings can be applied for MESI and globally, in assisting and creating a new policy to achieve a better electricity market model