Intercellular Movements Research Articles

A genetic algorithm for multiple objective dealing with exceptional elements in cellular manufacturing

Cellular Manufacturing (CM) is an important application of Group Technology (GT) in which families of parts are produced in manufacturing cells or a group of various machines, which are physically close together and can entirely process a part family. The manufacturing system established based on such an idea is called Cellular Manufacturing System (CMS). A major problem associated with many CMSs is the existence of Exceptional Elements (EEs), i.e. bottleneck machines and exceptional parts. These are machines/parts that cannot be exclusively assigned to a machine cell/part family. In this paper a new model is presented for dealing with the EEs in the form of a Multi-objective Optimization Problem (MOP). This model aims to minimize: (1) intercellular parts movements, (2) total cost needed for machine duplication and part subcontracting, (3) the system's under-utilization, and (4) deviations among the cells' utilization. Attaining an ideal solution, which is optimal to all of the objectives is prohibited, as they conflict with each other. Hence, a Multi-Objective Genetic Algorithm (MOGA) is developed to provide the decision-maker with a set of non-dominated or Pareto-optimal solutions. Comparisons between the developed MOGA and three other MOGAs show its viability in three performance aspects, namely: quality, diversity and CPU time.

Modified fuzzy C-means algorithm for cellular manufacturing

Several studies have used the fuzzy C-means (FCM) algorithm for part–machine grouping in cellular manufacturing. However, the application of the standard FCM algorithm to this problem has a number of drawbacks. This paper proposes a modified FCM (MFCM) algorithm that groups components and machines in parallel and through an annealing process with the weighting exponent arrives at a crisp solution and an objective function value which can be interpreted in terms of the number of voids and intercellular movements of the part–machine grouping obtained. Computational experiences show that although MFCM may sometimes require slightly more computing time than other methods, not only is it able to find better solutions but also it has higher discriminating power for determining the number of cells.

A transiently chaotic neural network approach to the design of cellular manufacturing

The design of Cellular Manufacturing Systems (CMS) has attained the significant attention of academicians and practitioners over the last three decades. Minimizing intercellular movements while maximizing utilization of machines are the main objectives of interest in designing CMS and are considered in present research. In this paper, the drawbacks of former neural networks-based approaches to cell formation are discussed. The standard version of cell formation problem is formulated and a 'Transiently Chaotic Neural Network' (TCNN) with supplementary procedures is introduced as a powerful rival. A simplified network is constructed. After developing the related equations the approach is tested using the proposed algorithm with 18 problems selected from literature. The results are compared with various other approaches including ART1, Extended-ART1, Ortho-Synapse Hopfield Neural Network (OSHN), etc. The main advantages of our proposed method are: (1) the ability to avoid the local optima trap, (2) the ability to solve problems of different sizes with the same set of values for parameters, and (3) the less computation time. The results also indicate considerable improvement in grouping efficiency through the proposed approach.

Machine grouping using sequence-based similarity coefficients and neural networks

Most neural network approaches to the cell formation problem do not use information on the sequence of operations on part types. They only use as input the binary part-machine incidence matrix. In this paper we investigate two sequence-based neural network approaches for cell formation. The objective function considered is the minimization of transportation costs (including both intracellular and intercellular movements). Constraints on the minimum and maximum number of machines per cell can be imposed. The problem is formulated mathematically and shown to be equivalent to a quadratic programming integer program that uses symmetric, sequence-based similarity coefficients between each pair of machines. Of the two energy-based neural network approaches investigated, namely Hopfield model and Potts Mean Field Annealing, the latter seems to give better and faster solutions, although not as good as a Tabu Search algorithm used for benchmarking.

A genetic algorithm approach to cellular manufacturing systems

A genetic algorithm (GA) metaheuristic-based cell formation procedure is presented in this paper. The cell formation problem solved here is to simultaneously group machines and part-families into cells so that intercellular movements are minimized. An option for considering the minimization of cell load variation is included and another, which combines minimization of intercellular movements and cell load-variation, exists. The algorithm solves this problem through improving a cell configuration using the GA metaheuristic. The designer is allowed to specify the number of cells required a priori and impose lower and upper bounds on cell size. This makes the GA scheme flexible for solving the cell formation problems. The solution procedure was found to perform well on tested large-scale problems and published data sets. Moreover, the proposed procedure compares very favorably to a well-known algorithm, and another TSP-based heuristic available in the literature. The results of computational tests presented are very encouraging.

Gap junctions and ion channels: relevance to erectile dysfunction.

The corporal myocyte is a critical determinant of erectile capacity whose functional integrity, in the vast majority of impotent patients, is sufficient to guarantee its relevance as a therapeutic target. As with numerous other smooth muscle cell types, ion channels are important modulators of corporal smooth muscle tone/contractility. As such, the transmembrane flow of ions (ie Ca(2+), K(+) and Cl(-)) plays an important role in modulating membrane potential and contractile status in individual human corporal smooth muscle cells, while intercellular ion flow ensures the functionality of myocyte cellular networks. The integral membrane proteins that selectively regulate many aspects of these critical transmembrane (eg K(+) and Ca(2+) channels) and intercellular (eg gap junctions) ionic movements have been identified. To date, the large conductance calcium-sensitive K(+) channel (ie K(Ca)), the metabolically regulated K+ channel (ie K(ATP)), and the L-type voltage-dependent Ca(2+) channel appear to be the most physiologically relevant nonjunctional ion channels. With respect to intercellular ionic/solute/second messenger movement, connexin43-derived gap junction channels are widely recognized as an obligatory component to normal integrative erectile biology. The presence of an intercellular pathway ensures that individual cellular alterations are carefully orchestrated in the rapid and syncytial fashion required for normal erectile function. This report reviews the known details concerning junctional and nonjunctional ion channels in human corporal tissue, and illustrates how one particular application of this knowledge, that is, preclinical studies utilizing low efficacy gene therapy (ie low transfection efficiency) with the K(Ca) channel has further confirmed the physiological relevance and therapeutic potential of gap junctions and ion channels to erectile physiology/dysfunction. International Journal of Impotence Research (2000) 12, Suppl 4, S15-S25.

Cellular manufacturing systems design using Tabu search

Several techniques have appeared in the literature for the cell formation problem. However, most of these heuristics have the disadvantages that they cannot solve real-life problems typical of manufacturing firms in reasonable computational time, and deal with the part family formation and cell grouping problems separately. The Tabu search meta-heuristic is presented for resolving these problems. The minimization of intercellular movements as an objective function is demonstrated, although minimization of cell load variation and the multiobjective function option exist in the procedure developed. The results discussed for some problems taken from the literature show that the Tabu search is a promising technique for solving the cellular manufacturing systems design problem for both medium and large problem instances.

A tabu search approach to cellular manufacturing systems

A tabu search metaheuristic-based cell formation procedure is presented in this paper. The cell formation problem solved here is to group machines and part-families simultaneously into cells so that intercellular movements are minimized. An option for considering the minimization of cell load variation is included and another which combines minimization of intercellular movements and cell load variation exists. The algorithm solves this problem through improving a cell configuration using the tabu search metaheuristic. The designer is allowed to specify the number of cells required a priori and impose lower and upper bounds on cell size. This makes the tabu search scheme flexible for solving the cell formation problems. The solution procedure was found to perform well on tested large-scale problems and published data sets. The results of computational tests presented are very encouraging.

A cost-based algorithm for design of Cellular Manufacturing Systems

This paper describes a cost-based algorithm that deals with the design problems of Cellular Manufacturing Systems (CMS) associated exceptional parts and bottleneck machines. The developed algorithm employes explicitly the main elements of manufacturing costs, such as the fixed machine cost, the production cost, the setup cost, and the material handling cost. The algorithm is based on the minimization of sum of these costs, and considers three alternatives to solve exceptional issues. The first alternative is to try to eliminate the maximum number of intercellular movements from the presently configured manufacturing system by buying and installing extra bottleneck machines into the appropriate cells. The second alternative considers the alternative process plans available and tries to complete the job using the overtime basis in the small machine cells. The third alternative considers the possibility of subcontracting the processing operations of exceptional part(s) to outside vendors to reduce the overall cost for the manufacturing system. The total costs of the three cases are compared and the best alternative for any given problem is identified. In order to illustrate performance of the algorithm developed, a test example is provided.

Forming minimum-cost machine cells with exceptional parts using zero-one integer programming

The value of forming machine cells for efficient job shop operations is well recognized. In practice, machine cells have often been formed based on intuitive guidelines driven by business objectives. For example, the cell design may seek to match the required skills of operator teams to available personnel, simplify material flow patterns, relieve congested areas around key equipment, and minimize the effect of undesirable environmental factors (noise, vibration, heat, and so on). Traditional methods of cell design often use heuristic rules that involve production flow analysis, similarity coefficients, rank-order clustering, or graph-theoretic methods. A more academic approach is to describe the problem as minimizing a constrained objective function written in terms of cost. The cost-minimizing approach has an advantage in that its importance is naturally understood by upper management. However, this approach generally involves using zero-one integer programming (IP) and thus has had limited usage because the IP approach is computationally demanding and relatively inflexible because it does not allow a controlled number of intercellular movements. Recent studies have shown how to reduce the computational demands. This leaves the inflexibility of the IP approach as its major obstacle. The motivation for this research is to show a method for increasing the zero-one IP method's flexibility by removing its prohibition on intercellular operations while minimizing overall operating costs.

A heuristic workload-based model to form cells by minimizing intercellular movements

Abstract A common problem of cellular manufacturing systems is the formation of part families and machine cells. The total number of inter- and intracellular movements have to be minimized because both contribute to lower productivity. Nevertheless, we show here that intracellular movements are not so important compared with the intercellular movements. We give an efficient algorithm based on minimizing the total intercellular movements, pointing out the importance of being very careful in the selection of the key workstation of each cell. The algorithm has been tested with problems selected from the literature. The results show that in all cases we get a higher utilization rate and lower central processing unit times that other algorithms published in the past.

Minimizing intercellular part movements in manufacturing cell formation

Abstract When using the machine grouping approach for designing cellular manufacturing cells, improper machine assignment commonly arises resulting in higher intercellular movement of parts. The objective of this paper is therefore to examine the cause of such a problem and to propose a workable optimal solution for it. A machine grouping algorithm that is based in the new machine unit concept is developed and the solution is proven to be optimal at each stage. A comparison of the proposed model with two existing algorithms is presented, followed by a discussion on the behaviour of machine cell formation.

A goal programming approach to the cell formation problem

AbstractCellular manufacturing is employed to achieve efficiencies in production by exploiting similarities inherent in the production of parts. Specifically, parts with similar processing requirements are identified and the equipment necessary to process these groups of parts is identified and located together. Several important design objectives associated with cellular manufacturing are to: 1) reduce setup times, 2) produce parts cell complete, i.e., minimize intercellular movements of parts, 3) minimize investment in new equipment, and 4) maintain acceptable machine utilization levels.The goal of this research was to develop a cell formation procedure that directly addressed these design objectives. To achieve this, three goal programming models were developed corresponding to three unique situations: (1) setting up an entirely new system and purchasing all new equipment, (2) reorganizing the system using only existing equipment, and (3) reorganizing the system using existing equipment and some new equipment.Several assumptions were made in the development of the goal programming models. First, it was assumed that each part had a fixed routing. Also, it was assumed that the processing times for the parts at each machine, the demand for each part, and the capacity and cost of each machine were known. In addition it was assumed that a given machine type could be placed in more than one cell and that the sequence in which the parts are processed affects setup times. Finally, it was assumed that a batch of each part is produced every production cycle and that only one batch of parts is processed in a particular cell at any given time.Clearly defining the objectives and constraints associated with the cell formation problem is the major contribution of the three formulations. Correct identification of the problem and the relationships inherent to cellular manufacturing is a necessary first step in the decision process that heretofore has not received adequate attention. However, because of the large number of 0/1 variables contained in the goal programming formulations they are very difficult to solve for realistically‐sized problems. Thus, a heuristic solution procedure is presented. The heuristic solution procedure involved partitioning the goal programming formulations into two Subproblems and solving them in successive stages. A numerical example is presented that illustrates the two‐stage heuristic procedure.

A network approach to cell formation in cellular manufacturing

SUMMARY Formation of machine cells often results in some intercellular movements between the cells. These movements cause lack of segregation among the cells. This is in conflict with the main objective of group technology which aims at independently operating cells. This paper presents a non-heuristic network approach to form manufacturing cells with minimum intercellular interactions. The machine-part matrix containing machining times is represented as a network which is subsequently partitioned by using a modified Gomory-Hu algorithm to find a minimum intercellular interaction. The modified algorithm improves the computational efficiency.

Identification of icsA, a plasmid locus of Shigella flexneri that governs bacterial intra- and intercellular spread through interaction with F-actin.

The capacity of Shigella to spread within the cytosol of infected epithelial cells and to infect adjacent cells is critical for the development of infection foci, which lead to mucosal abscesses. Shigella is a nonmotile microorganism that appears to utilize host cell microfilaments to generate intra- as well as intercellular movements, since this movement was inhibited by cytochalasin D and involvement of F-actin was demonstrated by direct labeling of infected cells with the specific dye N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)phallacidin. Such movements led to the formation of extracellular protrusions, which may explain cell to cell spread. icsA, a locus necessary for intra- and intercellular spread, was identified on the Shigella flexneri virulence plasmid pWR100. This locus was cloned and shown to express a 120-kDa outer membrane protein, which plays an important role in the interactions established between host cell microfilaments and the bacterial surface, thus leading to intracellular movement.

Development of spermatozoa in the rhea.

We have examined the ultrastructural changes that take place during spermiogenesis in the rhea. Spermatozoa are characterized by a curved head and a midpiece. A thin rod extends from the anterior tip of the spermatozoon through the center of the nucleus. A 3-mu-long distal centriole occupies the entire midpiece. The principal piece is characterized by a small fibrous sheath and tiny dense fibers that are only observed in the region of the principal piece, which is immediately behind the annulus. During development a circular manchette surrounds the nucleus of young spermatids. Later the microtubules of the circular manchette become reorganized into a longitudinal manchette. A long distal and short proximal centriole are observed in early round spermatids. The distal centriole becomes associated with the plasma membrane. Later the proximal centriole is observed in association with the nucleus. The area around the centriole pair then accumulates dense material, which is associated with either the centrioles or the circular manchette. The longitudinal manchette forms and then disappears and mitochondria subsequently associate with the distal centriole. The long centriole of the rhea enables this species to develop a midpiece similar to the midpiece of mammalian sperm without the complex intercellular movements that characterize mammalian spermiogenesis.

Occurrence of microtubules in the hyphae of Schizophyllum commune during intercellular nuclear migration.

During the intercellular nuclear migration of the basidiomycete Schizophyllum commune cytoplasmic microtubules were frequently observed scattered in the hyphae around interphase nuclei and connected with a semiglobular structure at the poles of mitotic and postmitotic nuclei. Thus it seems possible that microtubules, which have been demonstrated to participate in the intracellular nuclear movements in the dikaryotic hyphae of the basidiomycetes, are also involved in the intercellular nuclear movements of these fungi. During hyphal fusion microtubules close to an interphase nucleus were connected with electron-dense structures. It is suggested that these structures are centers for the assembly of microtubules necessary for nuclear movements not associated with nuclear divisions.