ANALYTICAL APPROXIMATIONS FOR KITTING SYSTEMS WITH MULTIPLE INPUTS

2008 ◽  
Vol 25 (02) ◽  
pp. 187-216 ◽  
Author(s):  
RAM RAMAKRISHNAN ◽  
ANANTH KRISHNAMURTHY

This research analyzes a kitting system where multiple components are grouped to form a predefined kit prior to assembly. The kitting system is modeled as a fork/join synchronization station and component supply is assumed to be from fabrication facilities operating under a kanban control policy. Exact analysis of these systems is computationally intensive even under Markovian assumptions. To evaluate the impact of input parameters on kitting system performance, several easily computable bounds on system throughput are first identified. Using these bounds, closed form approximate expressions for system throughput are derived. The throughput estimate is used to compute other performance measures of interest such as mean queue length and mean waiting time in the system. The accuracy of the approximations is validated using numerical experiments and some performance insights are given.

2020 ◽  
Vol 12 (6) ◽  
pp. 2343
Author(s):  
Doo Il Choi ◽  
Dae-Eun Lim

This study analyzes the performance of a queue length-dependent overload control policy using a leaky bucket (LB) scheme. This queueing model is applied to the operation of a battery swapping and charging station for electric vehicles (EVs). In addition to the LB scheme, we propose two congestion control policies based on EV queue length thresholds. With these policies, the model determines both EV-arrival and battery-supply intervals, and these depend on the number of EVs waiting in the queue. The queue length distributions, including those at arbitrary epochs, are derived using embedded Markov chain and supplementary variable methods. Performance measures such as blocking probability and mean waiting time are investigated using numerical examples. We study the characteristics of the system using numerical examples and use a cost analysis to investigate situations in which the application of each congestion control policy is advantageous.


2018 ◽  
Vol 52 (2) ◽  
pp. 439-452 ◽  
Author(s):  
Qing-Qing Ma ◽  
Ji-Hong Li ◽  
Wei-Qi Liu

This paper deals with the N-policy M/M/1 queueing system with working vacations. Once the system becomes empty, the server begins a working vacation and works at a lower service rate. The server resumes regular service when there are N or more customers in the system. By solving the balance equations, the stationary probability distribution and the mean queue length under observable and unobservable cases are obtained. Based on the reward-cost structure and the theory of Markov process, the social welfare function is constructed. Finally, the impact of several parameters and information levels on the mean queue length and social welfare is illustrated via numerical examples, comparison work shows that queues with working vacations(WV) and N-policy have advantage in controlling the queue length and improving the social welfare.


2015 ◽  
Vol 10 (S318) ◽  
pp. 221-230
Author(s):  
D. Farnocchia

AbstractWe review the most standard impact monitoring techniques. Linear methods are the fastest approach but their applicability regime is limited because of the chaotic dynamics of near-Earth asteroids. Among nonlinear methods, Monte Carlo algorithms are the most reliable ones but also most computationally intensive and so unpractical for routine impact monitoring. In the last 15 years, the Line of Variations method has been the most successful technique thanks to its computational efficiency and capability of detecting low probability events deep in the nonlinear regime. We also present some more recent techniques developed to deal with the new challenges arising in the impact hazard assessment problem. In particular, we describe keyhole maps as a tool to go beyond strongly scattering encounters and how to account for nongravitational perturbations, especially the Yarkovsky effect, when their contribution is the main source of prediction uncertainty. Finally, we discuss systematic ranging to deal with the short-term hazard assessment problem for newly discovered asteroids, when only a short observed arc is available thus leading to severe degeneracies in the orbit estimation process.


2010 ◽  
Vol 20-23 ◽  
pp. 236-242 ◽  
Author(s):  
Zhi Gang Zeng ◽  
Guo Hua Chen

A wave motion compensating platform has the function of compensating the ship’s generalized heave motion (a coupling result of roll, pitch and heave). It can decrease the impact of ship motion on some sea works and equipments. The hydraulic mechanism of platform system has the characteristics of nonlinear and big inertia. In order to compensate generalized heave motion effectively, an adaptive predictive control policy is used for controlling the hydraulic mechanism. Based on equal-dimension and new information, an automation regressive model can get adaptive multi-step prediction. The model parameter estimation based on the least square algorithm is easy to blow up and be unstable when the system has random noise. To improve the problem solution, a damped recursive least square algorithm is proposed to estimate the parameters on line. For the short regulation time, strong anti-disturbance ability and great robustness, a nonlinear PID controller whose gain parameters vary with errors is suitable for controlling the hydraulic mechanism. Using the collected experimental data, the simulations suggest that adopting the above adaptive predictive control policy to control hydraulic mechanism is able to decrease the generalized heave amplitude of wave motion compensating platform.


2016 ◽  
Vol 9 (2) ◽  
pp. 181 ◽  
Author(s):  
Rajeev Kumar Singh ◽  
Helmut Yabar ◽  
Rie Murakami-Suzuki ◽  
Noriko Nozaki ◽  
Randeep Rakwal

<p>Environmental policies are designed to deal with externalities either by internalizing environmental costs or imposing specific standards for environmental pollution. This study aims to examine the impact of environmental regulations related to End-of-Life Vehicles (ELV) on innovation in Japan. We determined whether there is any statistical difference in patent activity comparing the periods before and after the regulations were enacted. In order to control for exogenous factors such as business cycles, we also analyzed the ratios of ELV and total environmental patents during the same periods. Results showed that environmental regulations drive innovations and the number of ELV-related patents were larger even after controlling for such exogenous factors. We concluded that environmental policy for ELV in Japan was effective in inducing innovation. However, we also found that the weakness in these types of command and control policy is the lack of incentives for further innovation.</p>


2016 ◽  
Vol 11 (1) ◽  
pp. 203 ◽  
Author(s):  
Dio Putera Hasian

Bureau of mining heavy equipment maintenance at PT. Semen Padang have task in maintenance mine heavy equipment with preventive maintenance although breakdown maintenance. Part inventory is needed to make this activity work properly. If stockout happened will have the impact to PT.Semen Padang mining and production activity. To solve this problem, minimum-maximum inventory control policy is used to give an optimum value of inventory mine heavy equipment. This research is focused in filter and lubricant inventory because they have high demand rate. Data consumption filter and lubricant from January until December 2010 is used in this research. The service level that used is 95%. The result is quantity optimum inventory mine heavy equipment at filter and lubricant with application part inventory of mine heavy equipment. Because it can keep stockout although excess inventory.Keywords: stockout, optimum, inventory


2020 ◽  
Vol 8 (6) ◽  
pp. 1-140
Author(s):  
Timea R Partos ◽  
Rosemary Hiscock ◽  
Anna B Gilmore ◽  
J Robert Branston ◽  
Sara Hitchman ◽  
...  

Background Increasing tobacco prices through taxation is very effective for reducing smoking prevalence and inequalities. For optimum effect, understanding how the tobacco industry and smokers respond is essential. Tobacco taxation changes occurred in the UK over the study period, including annual increases, a shift in structure from ad valorem to specific taxation and relatively higher increases on roll-your-own tobacco than on factory-made cigarettes. Objectives Understanding tobacco industry pricing strategies in response to tax changes and the impact of tax on smokers’ behaviour, including tax evasion and avoidance, as well as the effect on smoking inequalities. Synthesising findings to inform how taxation can be improved as a public health intervention. Design Qualitative analysis and evidence synthesis (commercial and Nielsen data) and longitudinal and aggregate cross-sectional analyses (International Tobacco Control Policy Evaluation Project data). Setting The UK, from 2002 to 2016. Data sources and participants Data were from the tobacco industry commercial literature and retail tobacco sales data (Nielsen, New York, NY, USA). Participants were a longitudinal cohort (with replenishment) of smokers and ex-smokers from 10 surveys of the International Tobacco Control Policy Evaluation Project (around 1500 participants per survey). Main outcome measures (1) Tobacco industry pricing strategies, (2) sales volumes and prices by segments over time and (3) smokers’ behaviours, including products purchased, sources, brands, consumption, quit attempts, success and sociodemographic differences. Review methods Tobacco industry commercial literature was searched for mentions of tobacco products and price segments, with 517 articles extracted. Results The tobacco industry increased prices on top of tax increases (overshifting), particularly on premium products, and, recently, the tobacco industry overshifted more on cheap roll-your-own tobacco than on factory-made cigarettes. Increasingly, price rises were from industry revenue generation rather than tax. The tobacco industry raised prices gradually to soften impact; this was less possible with larger tax increases. Budget measures to reduce cheap product availability failed due to new cheap factory-made products, price marking and small packs. In 2014, smokers could buy factory-made (roll-your-own tobacco) cigarettes at real prices similar to 2002. Exclusive roll-your-own tobacco and mixed factory-made cigarettes and roll-your-own tobacco use increased, whereas exclusive factory-made cigarette use decreased, alongside increased cheap product use, rather than quitting. Quitting behaviours were associated with higher taxes. Smokers consumed fewer factory-made cigarettes and reduced roll-your-own tobacco weight over time. Apparent illicit purchasing did not increase. Disadvantaged and dependent smokers struggled with tobacco affordability and were more likely to smoke cheaper products, but disadvantage did not affect quit success. Limitations Different for each data set; triangulation increased confidence. Conclusions The tobacco industry overshifted taxes and increased revenues, even when tax increases were high. Therefore, tobacco taxes can be further increased to reduce price differentials and recoup public health costs. Government strategies on illicit tobacco appear effective. Large, sudden tax increases would reduce the industry’s ability to manipulate prices, decrease affordability and increase quitting behaviours. More disadvantaged, and dependent, smokers need more help with quitting. Future work Assessing the impact of tax changes made since 2014; changing how tax changes are introduced (e.g. sudden intermittent or smaller continuous); and tax changes on tobacco initiation. Funding This project was funded by the National Institute for Health Research (NIHR) Public Health Research programme and will be published in full in Public Health Research; Vol. 8, No. 6. See the NIHR Journals Library website for further project information.


2021 ◽  
Author(s):  
Marcel Thielmann ◽  
Gregor Golabek ◽  
Hauke Marquardt

&lt;p&gt;The rheology of the Earth&amp;#8217;s lower mantle is poorly constrained due to a lack of knowledge of the rheological behaviour of its constituent minerals. In addition, the lower mantle does not consist of only a single, but of multiple mineral phases with differing deformation behaviour. The rheology of Earth&amp;#8217;s lower mantle is thus not only controlled by the rheology of its individual constituents (bridgmanite and ferropericlase), but also by their interplay during deformation. This is particularly important when the viscosity contrast between the different minerals is large. Experimental studies have shown that ferropericlase may be significantly weaker than bridgmanite and may thus exert a strong control on lower mantle rheology.&lt;/p&gt;&lt;p&gt;Here, we thus explore the impact of phase morphology on the rheology of a ferropericlase-bridgmanite mixture using numerical models. We find that elongated ferropericlase structures within the bridgmanite matrix significantly lower the effective viscosity, even in cases where no interconnected network of weak ferropericlase layers has been formed. In addition to the weakening, elongated ferropericlase layers result in a strong viscous anisotropy. Both of these effects may have a strong impact on lower mantle dynamics, which makes is necessary to develop upscaling methods to include them in large-scale mantle convection models. We develop a numerical-statistial approach to link the statistical properties of a ferropericlase-bridgmanite mixture to its effective viscosity tensor. With this approach, both effects are captured by analytical approximations that have been derived to describe the evolution of the effective viscosity (and its anisotropy) of a two-phase medium with aligned elliptical inclusions, thus allowing to include these microscale processes in large-scale mantle convection models.&lt;/p&gt;


Author(s):  
Yoel Tenne

Modern engineering often uses computer simulations as a partial substitute to real-world experiments. As such simulations are often computationally intensive, metamodels, which are numerical approximations of the simulation, are often used. Optimization frameworks which use metamodels require an initial sample of points to initiate the main optimization process. Two main approaches for generating the initial sample are the ‘design of experiments' method which is statistically based, and the more recent metaheuristic-based sampling which uses a metaheuristic or a computational intelligence algorithm. Since the initial sample can have a strong impact on the overall optimization search and since the two sampling approaches operate based only widely different mechanisms this study analyzes the impact of these two approaches on the overall search effectiveness in an extensive set of numerical experiments which covers a wide variety of scenarios. A detailed analysis is then presented which highlights which method was the most beneficial to the search depending on the problem settings.


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