A note on scheduling jobs with missing operations in permutation flow shops

Flowshop scheduling problems are usually handled as permutation flowshops because of computational complexity although the technical framework in realworld problems often allows that jobs pass each other. Having a missing operation of a job on a machine, this job passing becomes a natural way to process jobs unless the underlying system is not an inflexible flow-line. However, when scheduling, missing operations are usually handled as zero processing time operations not allowing for any job passing. It is shown that even permitting job passing for missing operations while keeping the permutation constraint improves total completion time only under rather specific circumstances. We propose 'partial permutation flowshop sequencing' to overcome these specific formal requirements with respect to the real-world problem setting.     

Distributed amplifiers as duplexer/low crosstalk bidirectionalelements in S-band

Research into a novel class of distributed amplifiers which have a high isolation bandstop response in the reverse gain direction is described. These devices may be used as duplexer/circulator or bidirectional amplifier elements which, for many applications, can perform the function of ferrite isolator and circulator elements. The authors detail the design of such an amplifier, working in the S-band, and gives measured test data     

Fabrication of multilayer dielectrically loaded antennas using aqueous electrophorectic deposition of polyether ether ketone

The paper presents proof of concept of a viable multilayer technology to enhance the performance of multifilar helix, receive-only satellite antennas. Approximately, 30-μm layers of polyether ether ketone (PEEK) were deposited onto the Cu filars of a single layer dielectrically loaded multifilar helix antenna using aqueous electrophoretic deposition (EPD). The PEEK coating was densified at ~400–420 °C in flowing N₂ to prevent oxidation of the Cu filars. A second Cu metallisation was deposited onto the surface of the PEEK and the resulting antenna characterised. The multilayer antenna revealed a dual band response with peak radiation efficiencies >25 % and ~50 % increase in bandwidth. Multilayered surface architectures fabricated from PEEK using EPD, therefore, show great potential for the development of a broad range of high-performance multiband dielectrically loaded antennas whose peak frequencies may, in principle, be tuned by modifying the thickness of the PEEK layer.     

Sequencing CONWIP flow-shops: Analysis and heuristics

In this paper, we address the backlog sequencing problem in a flow-shop controlled by a CONWIP production control system, with the objective to minimize the makespan. We characterize the problem and analyse its similarities and differences with the unconstrained permutation flow-shop problem. A comparison of some well-known flow-shop heuristics is carried out, and a simple and fast dispatching rule is proposed. Regarding the more simple and faster heuristics, the proposed dispatching rule outperforms those commonly used for the unconstrained permutation flow-shop problem.     

Review and classification of hybrid flow shop scheduling problems from a production system and a solutions procedure perspective

In this paper, an extensive review of recently published papers on hybrid flow shop (HFS) scheduling problems is presented. The papers are classified first according to the HFS characteristics and production limitations considered in the respective papers. This represents a new approach to the classification of papers in the HFS environment. Second, the papers have been classified according to the solution approach proposed. These two classification categories give a comprehensive overview on the state of the art of the problem and can guide the reader with respect to future research work.     

Circularly Polarized Dielectric‐Loaded Antennas: Current Technology and Future Challenges

In the last few years, dielectric loaded antennas (DLAs) have emerged as a viable solution for high‐gain reception at microwave frequencies for handheld devices such as satellite phones, radios, and global positioning systems. This article compares the performance, cost, and volumetric efficiencies of the two dominant designs, namely the dielectrically loaded quadrifilar‐helix and microstrip patch antennas. The current and future material requirements for DLAs are discussed and an example is given of a recently developed castable glass ceramic based on BiNbO₄, which is suitable in terms of properties and glass formability for the single‐step fabrication of net‐shape antenna cores.