Comparative study of push and pull systems considering quality performance in a cell-based job shop environment

Simulation experiments were used to investigate the influences of quality performance on the performance difference between push and pull systems in a cell-based job shop environment. Quality performance was represented by two factors, i.e. mean magnitude of step shifts (MMSS) and mean frequency of step shifts (MFSS). Shop performance was based on the average and standard deviation of flow time. Results show that push systems are superior to pull systems, regardless of quality performance and set-up time reduction (STR) effected by cellular manufacturing. Therefore, to justify the adoption of pull systems, their potentials beyond material flow control (e.g. in promoting continuous improvement) need to be realized. In addition, the larger the STR, the more effective the quality performance improvement. With a large STR (of 80%), reduction of MMSS or (and) MFSS can improve the average (standard deviation) of flow time. In particular, reduction of MFSS tends to be more effective for a pull system with a larger STR. Accordingly, for a pull system in a cell-based job shop environment, substantial set-up time reduction is critical not only for efficient process operations, but also for effective quality performance improvement.     

Technical note The performance of push and pull systems: a corrected analysis

In a recent article, Sarker and Fitzsimmons (1989) compare the effects of push and pull tactics in a serial production line with identical stations. As part of their work, they present data on the relationship between the throughput of the line and the coefficient of variation of processing times. We take issue with their distinction between push and pull, and we provide evidence that their numerical estimates are flawed.     

Comparison of push and pull systems with transporters: A metamodelling approach

This paper analyses push and pull systems with transportation consideration. A multiproduct, multiline, multistage production system was used to compare the two systems. The effects of four factors (processing time variation, demand variation, transporters, batch size) on throughput rate, average waiting time in the system and machine utilization were studied. The study uses metamodels to compare the two systems. They serve a dual purpose of expressing system performance measures in the form of a simple equation and reducing computational time when comparing the two systems. Research shows that the number of transporters used and the batch size have a significant effect on the performance measures of both systems.     

Simulation-based comparison of push and pull systems in a job-shop environment considering the context of JIT implementation

An investigation of the effects of adopting a pull system in a job-shop environment in contrast to a push system is presented considering the implementation of Just-in-Time production. Implementation of pull systems in job-shop environments should be coordinated with a set of core supporting Just-in-Time concepts, i.e. cellular manufacturing, one-piece production and conveyance, and adaptive material-handling performance. A simulation experiment was carried out to compare the effects of applying these core Just-in-Time concepts on the performances of push and pull systems. The results show that to avoid adverse effects, it is essential that a suitable shop layout and part flow type are adopted for either a push or a pull system based on the extent of set-up time reduction effected by cellular manufacturing. Suitable material-handling equipment can then be employed accordingly to achieve better production performance. In addition, although a push system was always superior to a pull system in the simulated job-shop environment, the performance difference between the two systems was small. This finding implies that pull systems can be expected to bring about greater improvement in production performance than push systems as long as the potential of pull systems in shaping production environments is effectively realized.     

A comparative study of research performance in computer science

The paper compares the research performance in computer science of four major Western countries, India and China, based on the data abstracted from INSPEC database during the period 1993–2002. A total of 9,632 computer science papers recorded in INSPEC database were used for the comparison. The findings indicate that, on the one hand, the number of papers produced in China has considerably increased in the past few years. Particularly, in recent years, China occupies a remarkable high position in terms of counts of papers indexed by the INSPEC database. On the other hand, Chinese scientists preferred to publish in domestic journals and proceedings and shares of SCI-papers to the total journal papers for China have still remained the lowest. This indicates that the research activities of Chinese scientists in computer science are still rather “local” and suffer from a low international visibility. Various scientometric indicators, such as Normalized Impact Factor, ratio of papers in high quality journals are further adopted to analyze research performance and diverse finding are obtained. Nevertheless, for these surrogate indicators, China has optimistically achieved great progress, characterized with “low level of beginning and high speed of developing”. The policy implication of the findings lies in that China, as well as other less developed countries in science, can earn relative competitive advantages in some new emerging or younger disciplines such as computer science by properly using catch-up strategy. This revised version was published online in June 2006 with corrections to the Cover Date.     

Vaccine R&D in Brazil: The effectiveness of push and pull regulations

Government regulations can guide the technological progress, investment in research and development (R&D), and institutional organization of a specific sector. In this context, using patent data, this study aimed to analyze the effectiveness of three laws that pertain to R&D in Brazilian pharmaceutical market for vaccines. The results reveal an increasing international interest in the Brazilian market since the promulgation of the Industrial Property Law. Despite its limitations, this study reveals significant efforts and promising results in Brazil with respect to ensuring that technological and industrial policies and strategies incorporate innovation in vaccine R&D and change the economy's competitive circumstances.     

A comparative study of cell formation in cellular manufacturing systems

This paper analyses and evaluates six of the promising cell formation techniques by comparing and contrasting them in relation to the scores of efficiency indices of the exceptional elements and inner-cell densities, work-load balance, and under-utilizations in different scenarios. Accordingly, all six are more or less altered with proper extensions to realize a broader capability. Effectiveness of the suggested efficiency measures in the evaluation is also illustrated. Each technique seems to have a favourite operating area of its own considering a variety of factors.     

A comparative study on the performance of meshless approximations and their integration

The goal of this research is to study the performance of meshless approximations and their integration. Two diffuse shape functions, namely the moving least-squares and local maximum-entropy function, and a linear triangular interpolation are compared using Gaussian integration and the stabilized conforming nodal integration scheme. The shape functions and integration schemes are tested on two elastic problems, an elasto-plastic problem and the inf-sup test. The elastic computation shows a somewhat lower accuracy for the linear triangular interpolation than for the two diffuse functions with the same number of nodes. However, the computational effort for this interpolation is considerably lower. The accuracy of the calculations in elasto-plasticity depends to great extend on the used integration scheme. All shape functions, and even the linear triangular interpolation, perform very well with the nodal integration scheme and locking-free behavior is shown in the inf-sup test.     

Comparison of push and pull control strategies for supply network management in a make-to-stock environment

The performance differences of ‘push’ and ‘pull’ strategies for operational planning and control of a make-to-stock supply network under different environmental conditions (forecast error and initial levels of inventory) were explored. Results suggest that control strategy, forecast error and levels of inventory buffer all significantly affect each of the performance measures studied. Under all combinations of different conditions of inventory buffer level and forecast error, push outperforms pull in terms of customer service level and throughput, while pull outperforms push in term of total inventory. In terms of throughput and customer service level, push is more sensitive to forecast error but less sensitive to levels of inventory buffer than pull.     

A comparative study of bibliometric past performance analysis and peer judgement

A comparison is made between two types of research past performance analysis: the results of bibliometric-indicators and the results of peer judgement. This paper focuses on two case studies: the work of Dutch National Survey Committees on Chemistry and on Biology, both compared with our bibliometric results for research groups in these disciplines at the University of Leiden. The comparison reveals a serious lack of agreement between the two types of past performance analysis. This important, science-policy relevant observation is discussed in this paper.     

Risks and performance in supply chain: the push effect

A risk, when it occurs, causes negative effects on outputs. Typically risks are not independent, as multiple risks occur simultaneously. These risks have links, creating a ‘push’ effect, thus increasing the severity of each and all risk(s) on outputs. This paper aims to verify the mechanism of the push effect that is a new approach in the supply chain risk management literature. In this study, two models were compared: (1) only exists in direct effects of risks on supply chain performance, i.e. the competitive model. The other, (2), contains relationships among risks that show the mechanism of the push effect, i.e. the hypothesised model. Empirical evidence found in the Vietnam construction sector proved that the hypothesised model is better suited and has greater effect on supply chain performance in terms of each and all risk(s). Comparing 55% variance of the competitive model, the hypothesised one can explain up to 73% variance of supply chain performance. These results confirm our hypotheses of the push effect. Furthermore, findings achieved from this research can be used as ‘a guideline’ for reducing the impact of this mechanism.     

A comparative thermodynamic study of sorption systems: second law analysis

As a consequence of the phasing out of CFCs, sorption systems appear to be potential candidates to replace vapour compression systems. Amongst sorption systems there exists a choice between several systems, such as liquid absorption, solid adsorption and chemical reaction heat pumps. Nevertheless, few comparative studies between these systems have been undertaken so far. It is the aim of this paper to present such a study based on combined first and second law thermodynamical analysis of the different cycles. Simple entropy generation processes explain why the basic cycles for these systems yield performances much lower than the Carnot efficiency. The possibility of operating regenerative cycles with internal heat recovery and higher efficiencies has also been considered for typical common base conditions. Different entropy generation considerations have been visualised, such as thermal coupling (external/internal), non-uniform temperature component entropy production and other irreversible processes for the COP degradation in these systems. It is found that thermal coupling irreversibilities in solid sorption systems and other internal irreversibilities in liquid sorption systems with solution heat exchanger are dominant in the actual COP degradation with respect to the reversible Carnot COP.     

Workload balancing capability of pull systems in MTO production

Pull systems focusing on throughput time control and applicable in situations with high variety and customisation are scarce. This paper compares three unit-based pull systems that can cope with such situations: POLCA, CONWIP and m-CONWIP. These systems control the shop floor throughput time of orders by limiting the number of orders on the shop floor. However, their effectiveness in terms of reducing total throughput time is questioned. Theory states that an improvement in the average total throughput time will be due to the workload balancing capability of a pull system, but that many pull systems lack this capability. This paper shows that this workload balancing capability exists for POLCA and m-CONWIP, but not for CONWIP. The magnitude of the effect differs strongly, depending on the configuration of the system, the order arrival pattern and the variability of the processing time of the orders.     

A comparative study of ion exchange kinetics in zinc/lead-modified zeolite-clinoptilolite systems

The kinetics of zinc and lead ions removal by modified zeolite-clinoptilolite has been investigated. The rate of the ion exchange process for lead ions is faster than for zinc ions, as well as the time needed to reach the equilibrium. The ion exchange capacity of zeolite of lead ions is doubly higher than that of zinc ions. Diffusion models according to the Vermeulen's approximation, the parabolic diffusion model and the homogeneous diffusion model have been tested with the experimental data of ion exchange for zinc and lead. For both systems examined, the best fit of the models proposed with the experimental data was shown by the Vermeulen's approximation and the homogeneous diffusion model with t-->t(infinity). The diffusion coefficients are calculated from kinetic models of lead ions they are of the order of 10(-6)cm(2)/min, constant for all examined initial concentrations and not dependent on time. The diffusion coefficients in the system of zinc ions is of the order of 10(-8)cm(2)/min, also independent of initial concentrations, but decreasing with time from the beginning of ion exchange to the equilibrium.     

A comparative study of the reported performance of ab initio protein structure prediction algorithms

Protein structure prediction is one of the major challenges in bioinformatics today. Throughout the past five decades, many different algorithmic approaches have been attempted, and although progress has been made the problem remains unsolvable even for many small proteins. While the general objective is to predict the three-dimensional structure from primary sequence, our current knowledge and computational power are simply insufficient to solve a problem of such high complexity.Some prediction algorithms do, however, appear to perform better than others, although it is not always obvious which ones they are and it is perhaps even less obvious why that is. In this review, the reported performance results from 18 different recently published prediction algorithms are compared. Furthermore, the general algorithmic settings most likely responsible for the difference in the reported performance are identified, and the specific settings of each of the 18 prediction algorithms are also compared.The average normalized r.m.s.d. scores reported range from 11.17 to 3.48. With a performance measure including both r.m.s.d. scores and CPU time, the currently best-performing prediction algorithm is identified to be the I-TASSER algorithm. Two of the algorithmic settings--protein representation and fragment assembly--were found to have definite positive influence on the running time and the predicted structures, respectively. There thus appears to be a clear benefit from incorporating this knowledge in the design of new prediction algorithms.     

Average BER performance of FSO SIM-QAM systems in the presence of atmospheric turbulence and pointing errors

This paper presents the exact average bit error rate (BER) analysis of the free-space optical system employing subcarrier intensity modulation (SIM) with Gray-coded quadrature amplitude modulation (QAM). The intensity fluctuations of the received optical signal are caused by the path loss, atmospheric turbulence and pointing errors. The exact closed-form analytical expressions for the average BER are derived assuming the SIM-QAM with arbitrary constellation size in the presence of the Gamma–Gamma scintillation. The simple approximate average BER expressions are also provided, considering only the dominant term in the finite summations of obtained expressions. Derived expressions are reduced to the special case when optical signal transmission is affected only by the atmospheric turbulence. Numerical results are presented in order to illustrate usefulness of the derived expressions and also to give insights into the effects of different modulation, channel and receiver parameters on the average BER performance. The results show that the misalignment between the transmitter laser and receiver detector has the strong effect on the average BER value, especially in the range of the high values of the average electrical signal-to-noise ratio.     

A comparative study of the difference in research performance in biomedical fields among selected Western and Asian countries

In this study, a series of relative indicators are used to compare the difference in research performance in biomedical fields between ten selected Western and Asian countries. Based on Thomson’s Essential Science Indicators (ESI) 1996–2006, the output of papers and their citations in ten biomedical fields are compared at multiple levels using relative indicators. Chart diagrams and hierarchical clustering are applied to represent the data. The results confirm that there are many differences in intra- and interdisciplinary scientific activities between the West and the East. In most biomedical fields Asian countries perform below world average.     

On the performance of Mindlin plate elements in modelling plate-elastic medium interaction: A comparative study

This paper discusses the finite element analysis of the flexural interaction between an elastic plate and an elastic half-space. The applicability of certain Mindlin-type plate elements, based on reduced integration techniques, to this class of interaction problem is investigated. A series of numerical computations reveal that those elements which possess spurious zero-energy modes are deficient in modelling properly the interaction phenomenon. It is also found that the ‘heterosis’ plate element reported in the literature is capable of modelling the plate-elastic medium interaction very efficiently.