The Traveling Repairman Problem is a customer-oriented routing problem in which a repairman is visiting a set of geographically distributed customers. The objective function is to minimize the total waiting times of all customers. The importance of this problem can be found in its applications in the following areas: blood distributing, manufacturing systems, and transportation and logistics. Apart from its importance, research on this problem is very limited. In this paper a new mixed-integer programming FORMULATION is developed, and several properties of model are studied. Additionally, by developing lower and upper bounds, a branch and bound algorithm is developed to solve the problems with up to 30 nodes. According to the computational experiments, the developed model is very competitive.

A novel MATHEMATICAL model has been developed to aid the FORMULATION of emulsion explosives. This MATHEMATICAL model calculated heat of explosion, oxygen balance and raw material cost as a function of explosive ingredients, and the solution of the MATHEMATICAL model was obtained by a MS Excel program. The effects of the different content of NH4NO3, NaNO3, H2O, and span-80 and composite fuel oil on the heat of explosion and the specific volume of emulsion explosive were discussed based on the proposed MATHEMATICAL model. The results show that (1) with the increasing of the content of NH4NO3, the heat of explosion and the specific volume increase. (2) The better content of NaNO3, H2O and Span-80 in the FORMULATION of emulsion explosive are 7%~9%, 9%~10%, 1.5%~2% respectively, and this FORMULATION results in an oxygen balance of zero or close to zero.

In a recent paper, Caserta et al. [M. Caserta, S. Schwarze, and S. Vob\A MATHEMATICAL FORMULATION and complexity considerations for the blocks relocation problem", European Journal of Operational Research, 219, pp.96-104 (2012)] proposed two MATHEMATICAL models for the blocks relocation problem. Because of the complexity of their first model, called BRP-I, they employed a simplifying assumption and introduced a relatively fast model, called BRP-II, to solve medium-sized instances. In this paper, it is first proven that the BRP-II model is incorrect. Then, the corrected and improved FORMULATION of BRP-II, called BRP2c and BRP2ci, respectively, are presented. By correcting a constraint in BRP-II, the reported optimal solution is either corrected or improved in many instances. Also, it is proven that some results of BRP-II reported by Caserta et al. are incorrect. Incorporating some new cut constraints into BRP2ci, the computational time of solving instances is decreased 25 times, on average.

Background and the purpose of the study: This study reports the laboratory optimization for the preparation of salbutamol sulphate-ethyl cellulose micro particles by a non-solvent addition coacervation technique through adjustment of the ratio of salbutamol sulphate to ethyl cellulose. The variation of drug release between the micro particles and tabletted micro particles was also investigated.Methods: In vitro release profiles of developed micro particles and tabletted micro particles were studied using USP XXIV dissolution apparatus I and II, respectively, in 450 ml double distilled water at 50 rpm maintained at 37oC.Results: White microparticles with no definite shape having good entrapment efficiency (96.68 to 97.83%) and production yield (97.48±1.21 to 98.35±1.08%) were obtained. In this investigation, initial burst effect was observed in the drug release behavior. The rate of drug release from microparticles decreased as the concentration of polyisobutylene was increased from 6% to 12% during microencapsulation. The release pattern of tabletted micro particles was affected significantly (p<0.05) by the addition of hydroxy propyl methyl cellulose (HPMC) as excepient and insignificantly (p>0.05) by the type of dissolution media and stirring speed. Tabletted micro particles showed good stability and reproducibility. Ethyl cellulose was found to be compatible with salbutamol sulphate. The drug release from all FORMULATIONs was best fit to Higuchi’s equation and the mechanism of drug release was anomalous diffusion from all FORMULATIONs.Conclusion: The results of this study suggest that by using ethylcellulose it is possible to design a single-unit, sustained-release oral dosage form of salbutamol sulphate for indication of twice a day.

In this research, a multi-objective MATHEMATICAL model is proposed for the airline multi-skilled crew scheduling problem. The multi-skilled crew can be assigned to flights and airplanes according to their skills. The objective functions of the proposed model are: (1) Maximizing the number of leave days planned according to the days announced by the flight crew, and (2) Minimizing the penalty costs associated with violation of minimum and maximum working hours. Several test problems have been designed based on the data acquired by the airline studied in this research. Due to the NP-hard essence of the model, we have employed two meta-heuristics, namely the multi-objective differential evolution (MODE) and Non-dominated Sorting Genetic Algorithm II (NSGA-II). These algorithms are calibrated using the Taguchi method. The algorithms have been compared based on several multi-objective performance measures. Each algorithm has been more successful in terms of some metrics. The comparisons between algorithms and sensitivity analysis show that the proposed model and algorithms can produce appropriate schedules for the airline crew scheduling problem.

An 8 port narrowband Radial Power Combiner (RPC) with excellent combining efficiency is presented. A novel useful criteria for optimal design of the RPC is developed and the design is studied based on it. Also to provide a reliable, tolerant and cost effective mechanical design, the mechanical structure of the combiner is simplified for fabrication and assembly. The designed RPC has standard waveguide ports at inputs, so it can be used in standard high power applications without any adaptors. The physical structure simplicity guarantees the product reliability for industrial high power applications. The optimized RPC design is fabricated and the measurement results are presented. The back-to-back measurement setup using customized through lines and two identical combiners have helped to take into account other efficiency degrading phenomena like port junctions’ discontinuity. It is shown that simulated power combining efficiency of 99% and measured power combining efficiency of 97.7 % is achieved.

In this paper, we address the weighted multi-objective re-entrant flow-shop scheduling problem considering release dates in order to minimize makespan, total completion time, total tardiness, maximum idle time, and number of tardy jobs. Each job is taken into account with deterministic processing times, and release dates. The flow-shop comprised of two workshops in whose jobs are entered to the main workshop and after the first part of the processing, they are transferred to the second workshop and after this stage, the jobs are returned to the main workshop for the last part of the processing. We model the problem by a new mixed integer programming based on formulating sum of idle time as a new concept. Moreover, a hybrid evolutionary algorithm is proposed based on some dispatching rules, ant colony optimization, and genetic algorithm. The performance of the proposed algorithm on some test instances is compared to the mixed integer linear programming model as well as the state-of-the-art algorithms called genetic algorithm, tabu search, bio-geography based optimization, and artificial bee colony. The computational experiments show that our proposed approach outperforms other algorithms and the results indicate efficiency and capability of the proposed algorithm in comparison with the traditional algorithms.