A constraint-based perspective in resource constrained project scheduling

In this study, a new heuristic approach to the resource constrained project scheduling problem is introduced. This approach, which is called local constraint based analysis (LCBA), is more robust than the dispatching rules found in the literature, since it does not depend on an a priori insight as do the dispatching rules. LCBA consists of the application of local essential conditions which respect the current temporal and resource constraints to generate a necessary sequence of activities at a scheduling decision time point in a single-pass parallel scheduling algorithm. LCBA is a time efficient procedure due to the localized aspect with which the activities are handled. Only the activities which are schedulable at the current scheduling time are considered for the application of the essential conditions. LCBA is tested against well-known rules from the literature and some recently developed rules. This testing is done using a set of problems of a special design and also a set of optimally solved problems from a recent benchmark in the literature. It is observed that near optimal time efficient solutions are obtained by LCBA and the procedure's performance is considerably better than that of the dispatching rules.     

Content-Based Recommendations for Sustainable Wardrobes Using Linked Open Data

Mobile Networks and Applications - Textile production industry is one of the biggest industries available and it is known by its negative effects to the environment. Greenhouse gas emissions can...     

Operational strategies for seru production system: a bi-objective optimisation model and solution methods

In recent years, the interest in seru production system (SPS) has increased to enhance the flexibility of production systems. Because the worker resource in an SPS is critical for adapting to changes in demand, this study focuses on workforce-related operational strategies rarely considered for SPS. To this end, for the first time in the literature, a bi-objective workforce scheduling problem is addressed by considering the interseru worker transfer in SPS. A novel optimisation model is proposed to achieve two objectives, that of minimising makespan and reducing workload imbalance among workers. Because it is proved that the problem falls within a non-deterministic polynomial-time hardness (NP-hard) class, non-dominated sorting genetic algorithm-II (NSGA-II) is employed to solve large-sized problems. For small-sized problems, the second version of the augmented ε-constrained (AUGMECON2) method is implemented and Pareto-optimal solutions are obtained. A set of evaluation metrics is considered to compare two different operational strategies in terms of the desired objectives. The computational results indicate that allowing worker transfer leads to better results for all metrics. The main contribution of the present study is to provide a novel optimisation model for the addressed problem to compare two operational strategies by considering the heterogeneity inherent of workers.     

An OWA Operator‐Based Cumulative Belief Degrees Approach for Credit Rating

Credit lenders utilize credit rating approaches to provide a classification system for characterizing credit borrowers. In order to measure the borrowers’ credibility, that is, ability and willingness to repay the debt, there are many financial and non‐financial criteria that should be considered. The basic aim of this study is to propose a multiple‐criteria credit rating approach that integrates different kinds of information and represents the borrowers’ credibility as a distribution among all the credit ratings. The cumulative belief degree approach is proposed for this purpose. Since all the available information is used in the final representation, a distribution‐based credit rating approach is expected to strengthen the lender's inference competency. In order to eliminate subjectivity in the weighting of criteria, an ordered weighted averaging operator is used. Additionally, the credit rating distribution can be transformed into a single credit rating by considering a threshold value. This study proposes a goodness‐of‐fit test to handle the subjectivity and difficulty of setting the threshold value. The applicability of the proposed approach is demonstrated by analyzing the credibility of selected Turkish firms from the stock exchange market of Turkey.     

Dispersion of clusters of nanoscale silica particles using batch rotor-stators

Nanoparticle powders added into a liquid medium form structures which are much larger than the primary particle size (aggregates and agglomerates)-typically of the order of 10’s of microns. An important process step is therefore the deagglomeration of these clusters to achieve as fine a dispersion as possible. This paper reports the findings of a study on the dispersion of hydrophilic fumed silica nanoparticle clusters, Aerosil 200 V, in water using two batch rotor-stators: MICCRA D-9 and VMI. The MICCRA D-9 head consists of a set of teeth for the stator and another for the rotor, whereas the VMI has a stator with slots and a rotor which consists of a 4-bladed impeller attached to an outer set of teeth. The dispersion process, studied at different power input values and over a range of concentrations (1, 5, 10 wt.%), was monitored through the evolution of PSD. Erosion was found to be the dominant breakage mechanism irrespective of operating conditions or rotor-stator type. The smallest attainable size was also found to be independent of the power input or the design of the rotor-stator. Break up kinetics increased upon the increase of power input, and this also depended on the rotor-stator design. With MICCRA D-9 which has smaller openings on both the stator and rotor, the break up rate was faster. Increasing the particle concentration decreased break up kinetics. It could also be shown that operating at high concentrations can still be beneficial as the break up rate is higher when assessed on the basis of specific power input per mass of solids.     

Laser ignition of explosives: Effects of gas pressure on the threshold ignition energy

Abstract

This paper describes a method for measuring the effect of initial gas pressure and the type of gas on the threshold ignition energy of several high explosives. The method is based on a 300 W CW CO₂-laser. An extensive study of these parameters for PETN and RDX is also presented. These high explosives all show a strong decrease in ignition energy/power with increasing initial gas pressure. The gases tested are air and nitrogen. The studied pressures are in the interval 0.1 to 10 MPa. The ignitability of PETN and RDX was tested at a laser pulse width of 1.2 ms. All tested high explosives had a lower ignition energy/power in air than in nitrogen at low pressures (< 2 MPa), whereas RDX and PETN had a lower ignition energy in nitrogen than in air at high pressures (>4 MPa). For TNT the time to ignition, measured as a function of air pressure, decreased with increasing pressure. These results are interpreted as a multiple phase ignition process. The method was also used for obtaining ignition data for TNT, Comp B-3 and Torpex.     

Influence of finite notch root radius and optically determined crack length on the measured fracture toughness of brittle materials

When measuring the fracture toughness of ceramics, for instance with the Single Edge V-Notched Beam (SEVNB) method, a known problem is given by the finite notch root radius. If this radius is larger than a certain small value of a few micrometers, the measured stress intensity factor is higher than the true intrinsic value. Another problem is that due to technical and physical reasons the optically measured crack length at stable crack growth is smaller than the true crack length, which might lead to an underestimation of the fracture toughness. In the given paper an experimental approach is presented to register these effects quantitatively with stable crack advance and to finally obtain the correct fracture toughness. This is achieved by applying a new computer aided automatic control system for stable crack advance and by analyzing the results in force–displacement and crack length–force diagrams. The used material is zirconia-toughened alumina.