Designing a mixed-model,open-station assembly line using mixed-integer programming

An open-station assembly line that manufactures mixed models of sheet metal cabinets is considered in this research. The problem minimizes the total cost of the idle and utility times incurred in an assembly line with different line parameters (such as launch interval, station length, starting point of work, upstream walk, locus of the operator's movement, etc.) and operation sequences of the mixed models. An open-station system plays a significant controlling role in determining the optimal line parameters that minimize the total cost of idle and utility times in a mixed-model assembly line. Thus, a mixed-integer programming model for an open-station system is developed here to determine line parameters optimally. The model is tested on a three-station mixed-model line, which is a partial representation of a complete long assembly line. This research obtained a set of line parameters that minimize the total cost of idle and utility times optimally. Results indicate that the minimum total cost of idle and utility times in an open-station system decreases with line length. Other results pertinent to the line design are also demonstrated.     

An ordering policy for deteriorating items with allowable shortage and permissible delay in payment

In many inventory situations, the purchaser is allowed a permissible period to pay back the cost of goods bought without paying any interest. Depending on the length of that payment period, the purchaser can earn interest on the sales of the inventory. This paper develops a model to determine an optimal ordering policy for deteriorating items under permissible delay of payment and allowable shortage. Different facets of the permissible delays in payment are discussed, and this generalized model exhibits a set of solutions that reduces to an existing model. Results are discussed and demonstrated with an illustrative example.     

Structural studies and photochromism of mercury(II)-iodo complexes of (arylazo)imidazoles

Neat reaction between HgI2 and 1-methyl-2-(phenylazo)imidazole (Pai-Me) under microwave irradiation has isolated a novel compound whose structure shows intercalated HgI2 in the layers of Pai-Me. They exist independently in interpenetrated arrays. In a solution phase study, the same reaction has synthesized an iodo-bridged azoimidazole-Hg(II) complex, [Hg(RaaiR')(mu-I)(I)]2 (RaaiR' = 1-alkyl-2-(arylazo)imidazole). The structures have been characterized by X-ray diffraction studies. Chloro-bridged Hg(II) complexes of azoimidazoles, [Hg(RaaiR')(mu-Cl)(Cl)]2, are also known. These complexes upon irradiation with UV light show trans-to-cis isomerization. The reverse transformation, cis-to-trans isomerization, is very slow with visible light irradiation. Quantum yields (phi t-->c) of trans-to-cis isomerization are calculated, and the free ligand shows higher phi than their Hg(II) complexes. The cis-to-trans isomerization is a thermally induced process. The activation energy (Ea) of cis-to-trans isomerization is calculated by controlled temperature reaction. The Ea's of free ligands are much higher than that of halo-bridged Hg(II)-azoimidazole complexes. Chloro-bridged Hg(II) complexes show lower Ea's than those of iodo-bridged complexes. DFT calculation has been adopted to rationalize the experimental results.     

Lavandulifolioside B: a new phenylethanoid glycoside from the aerial parts of Stachys lavandulifolia Vahl

Reversed-phase preparative HPLC analyses of the methanol extract of the aerial parts of Stachys lavandulifolia afforded a new phenylethanoid glycoside, 4,3',4'-trimethoxy-lavandulifolioside A, named lavandulifolioside B, together with three other known phenylethanoid glycosides, lavandulifolioside A, verbascoside and leucosceptoside A, and an iridoid glycoside 5-O-β-allopyranosyloxy-aucubin (5-O-β-allopyranosyl-monomelittoside). While the structures of the known compounds, except the iridoid glycoside, were established by direct comparison of their spectroscopic data with respective literature data, lavandulifolioside B and 5-O-β-allopyranosyloxy-aucubin were identified comprehensively by extensive 1D and 2D NMR analyses. The distribution of the isolated compounds within the genus Stachys has been discussed.     

Photochemical eliminations involving zwitterionic intermediates generated via electrocyclic ring closure of benzothiophene carboxanilides

Leaving groups such as carboxylate, thiolate, and phenolate are expelled via zwitterionic intermediates produced upon photochemical electrocyclic ring closure of benzothiophene carboxanilides in the triplet excited state. Chemical yields generally exceed 90%, while quantum yields vary with basicity of the released leaving group.     

Optimization of the conditions for extraction of serine protease from kesinai plant (Streblus asper) leaves using response surface methodology

Response surface methodology (RSM) using a central composite design (CCD) was employed to optimize the conditions for extraction of serine protease from kesinai (Streblus asper) leaves. The effect of independent variables, namely temperature (42.5,47.5, X?), mixing time (2-6 min, X?), buffer content (0-80 mL, X?) and buffer pH (4.5-10.5, X?) on specific activity, storage stability, temperature and oxidizing agent stability of serine protease from kesinai leaves was investigated. The study demonstrated that use of the optimum temperature, mixing time, buffer content and buffer pH conditions protected serine protease during extraction, as demonstrated by low activity loss. It was found that the interaction effect of mixing time and buffer content improved the serine protease stability, and the buffer pH had the most significant effect on the specific activity of the enzyme. The most desirable conditions of 2.5 °C temperature, 4 min mixing time, 40 mL buffer at pH 7.5 was established for serine protease extraction from kesinai leaves.     

Multi-vendor integrated procurement-production system under shared transportation and just-in-time delivery system

Just-in-time (JIT) procurement is one of the important elements of lean production system. Successful implementation of JIT needs vendor-manufacturer cooperation on small lot size delivery and inbound logistics cost reduction. Unlike the most recent literature focusing on single-vendor and single-buyer integrated inventory systems, this paper studies a multi-vendor integrated procurement-production inventory system that incorporates delivery and shared transportation costs. A multi-vendor optimal model is developed here for deciding the batch size of vendor's production, and delivery frequencies of different vendors to the manufacturer. Solution procedures for two special cases—uncapacitated and capacitated models are developed; especially, a new approximate method for capacitated model is devised. Numerical examples demonstrate the solution mechanism for the model. The results highlight cooperation between vendors and manufacturers on JIT procurement practices.     

Handling equality constraints with agent-based memetic algorithms

In addition to inequality constraints, many mathematical models require equality constraints to represent the practical problems appropriately. The existence of equality constraints reduces the size of the feasible space significantly, which makes it difficult to locate feasible and optimal solutions. This paper presents a new equality constraint handling technique which enhances the performance of an agent-based evolutionary algorithm in solving constrained optimization problems with equality constraints. The technique is basically used as an agent learning process in the agent-based evolutionary algorithm. The performance of the proposed algorithm is tested on a set of well-known benchmark problems including seven new problems. The experimental results confirm the improved performance of the proposed technique.     

Differential evolution with multi-constraint consensus methods for constrained optimization

Constrained optimization is an important research topic that assists in quality planning and decision making. To solve such problems, one of the important aspects is to improve upon any constraint violation, and thus bring infeasible individuals to the feasible region. To achieve this goal, different constraint consensus methods have been introduced, but no single method performs well for all types of problems. Hence, in this research, for solving constrained optimization problems, we introduce different variants of the Differential Evolution algorithm, with multiple constraint consensus methods. The proposed algorithms are tested and analyzed by solving a set of well-known bench mark problems. For further improvements, a local search is applied to the best variant. We have compared our algorithms among themselves, as well as with other state of the art algorithms. Those comparisons show similar, if not better performance, while also using significantly lower computational time.