The recent rapid development of China’s foreign trade has led to the significant increase in waterway transportation and automated container ports. Automated terminals can significantly improve the loading and unload...The recent rapid development of China’s foreign trade has led to the significant increase in waterway transportation and automated container ports. Automated terminals can significantly improve the loading and unloading efficiency of container terminals. These terminals can also increase the port’s transportation volume while ensuring the quality of cargo loading and unloading, which has become an inevitable trend in the future development of ports. However, the continuous growth of the port’s transportation volume has increased the horizontal transportation pressure on the automated terminal, and the problems of route conflicts and road locks faced by automated guided vehicles (AGV) have become increasingly prominent. Accordingly, this work takes Xiamen Yuanhai automated container terminal as an example. This work focuses on analyzing the interference problem of path conflict in its horizontal transportation AGV scheduling. Results show that path conflict, the most prominent interference factor, will cause AGV scheduling to be unable to execute the original plan. Consequently, the disruption management was used to establish a disturbance recovery model, and the Dijkstra algorithm for combining with time windows is adopted to plan a conflict-free path. Based on the comparison with the rescheduling method, the research obtains that the deviation of the transportation path and the deviation degree of the transportation path under the disruption management method are much lower than those of the rescheduling method. The transportation path deviation degree of the disruption management method is only 5.56%. Meanwhile, the deviation degree of the transportation path under the rescheduling method is 44.44%.展开更多
Due to the effects of the COVID-19 pandemic and the rise of online shopping, the offline sales of IKEA Fuzhou have been declining since 2020. Because the cost of distribution warehouse is a major expense for offline c...Due to the effects of the COVID-19 pandemic and the rise of online shopping, the offline sales of IKEA Fuzhou have been declining since 2020. Because the cost of distribution warehouse is a major expense for offline chain furniture retailers, and the picking process is a key activity in distribution warehouse operations. To reduce the cost of distribution warehouse and alleviate the survival pressure of the offline chain furniture retailers, this paper focuses on optimizing the picking route of the IKEA Fuzhou distribution warehouse. It starts by creating a two-dimensional coordinate system for the storage location of the distribution warehouse using the traditional S-type picking strategy to calculate the distance and time of the sorting route. Then, the problem of optimizing the picking route is then transformed into the travelling salesman problem (TSP), and picking route optimization model is developed using a genetic algorithm to analyze the sorting efficiency and picking route optimization. Results show that the order-picking route using the genetic algorithm strategy is significantly better than the traditional S-type picking strategy, which can improve overall sorting efficiency and operations, reduce costs, and increase efficiency. Thus, this establishes an implementation process for the order-picking path based on genetic algorithm optimization to improve overall sorting efficiency and operations, reduce costs, increase efficiency, and alleviate the survival pressure of pandemic-affected enterprises.展开更多
In the present study a numerical model developed by Lynett and Liu （2002） is modified to include density difference in a stratified two-layer fluid in a three-dimensional internal wave domain. The internal solitary ...In the present study a numerical model developed by Lynett and Liu （2002） is modified to include density difference in a stratified two-layer fluid in a three-dimensional internal wave domain. The internal solitary wave （ISW） in the model is assumed to be weakly nonlinear and weakly dispersive, and the viscosity effects at all boundaries are ignored. The governing equations based on the Navier-Stokes and Euler equations are solved for internal solitary wave propagation over variable seabed topography. Theoretical formulations are established, from which analytical solutions are obtained, in addition to numerical results. Wave profiles from previous experimental studies are compared with the numerical results from the present analytical solutions. Numerical models developed on the basis of the present analytical solutions are better than those developed by Lynett and Liu （2002）. The results of numerical modeling agree well with the experimental data.展开更多
Internal solitary wave propagation over a submarine ridge results in energy dissipation, in which the hydrodynamic interaction between a wave and ridge affects marine environment. This study analyzes the effects of ri...Internal solitary wave propagation over a submarine ridge results in energy dissipation, in which the hydrodynamic interaction between a wave and ridge affects marine environment. This study analyzes the effects of ridge height and potential energy during wave-ridge interaction with a binary and cumulative logistic regression model. In testing the Global Null Hypothesis, all values are p 〈0.001, with three statistical methods, such as Likelihood Ratio, Score, and Wald. While comparing with two kinds of models, tests values obtained by cumulative logistic regression models are better than those by binary logistic regression models. Although this study employed cumulative logistic regression model, three probability functions p^1, p^2 and p^3, are utilized for investigating the weighted influence of factors on wave reflection. Deviance and Pearson tests are applied to cheek the goodness-of-fit of the proposed model. The analytical results demonstrated that both ridge height （X1 ） and potential energy （X2 ） significantly impact （p 〈 0. 0001 ） the amplitude-based refleeted rate; the P-values for the deviance and Pearson are all 〉 0.05 （0.2839, 0.3438, respectively）. That is, the goodness-of-fit between ridge height （ X1 ） and potential energy （X2） can further predict parameters under the scenario of the best parsimonious model. Investigation of 6 predictive powers （ R2, Max-rescaled R^2, Sorners＇ D, Gamma, Tau-a, and c, respectively） indicate that these predictive estimates of the proposed model have better predictive ability than ridge height alone, and are very similar to the interaction of ridge height and potential energy. It can be concluded that the goodness-of-fit and prediction ability of the cumulative logistic regression model are better than that of the binary logistic regression model.展开更多
Fundamental experiments were carried out in a wave flume on internal solitary wave （ISW） of depression-type propagating over a submerged ridge. The seabed ridge included either triangular or semicircular shape - reg...Fundamental experiments were carried out in a wave flume on internal solitary wave （ISW） of depression-type propagating over a submerged ridge. The seabed ridge included either triangular or semicircular shape - regarded as topographic obstacles. Influenced by the submarine ridge, the transmitted waves were found to always consist of a leading pulse （a solitary wave） followed by a dispersive wave train. The wave profile propagating over a triangular ridge was similar to that caused by a semicircular obstacle. Apparently, the smooth face of a semicircular ridge produced time lag of wave propagation. From experimental results available, the reduction in wave energy induced by a semicircular ridge was larger than that by a triangular one. The events of wave distortion, strong breaking, internal bolus, and stratification mixing happened in case that the crest of an ISW was great enough to interact with the topographic obstacle. The reduction in wave energy was induced by strong breaking, and it depended on the ridge height rather than the geometric shape of the ridge.展开更多
The main idea of this study is to provide help to West and Central Africa port logistics authorities in making, evaluating and realizing their decisions on port development/management, all in an effort to guaranty por...The main idea of this study is to provide help to West and Central Africa port logistics authorities in making, evaluating and realizing their decisions on port development/management, all in an effort to guaranty port efficiency and operational brilliance to profit the different ports, their hinterlands and their related clients. Consequently, an examination is made as far as port sector is concerned, with an ever more demanding enhancement in operational efficiency. Moreover, a past research on West and Central Africa Ports, as well as an overview on port logistics was made, making it possible to determine what has been done (prospects) and what is still to be done (ineffectiveness), in prospective of a more reformed and efficient port. One of the principles of this paper is also to confer all the aspects that operate as obstacles to the WCA port’s improvement and development;using thus the evaluation model called EWCA (Evaluation of West and Central Africa Ports), which gives a descriptive analysis of the present situation of the latter’s port logistics, including the aid of multiple regression model to determine an impact of explanatory variables on the study probability. Applying the method of strategic development, this paper thus deals with exploring typical problems and quandaries of West and Central Africa ports. The findings suggested how to fight back or overcome the constrictions and strangulations;enabling West and Central Africa port logistics attain their desired strategic development aims, despite the ineffectiveness. Tremendous efforts were made, giving a vital shoot on African economy and development;even though there is still a lot to do, for the data and variables showed how the port logistics augment and descend frequently without a long period of stability.展开更多
Logit regression analysis is widely applied in scientific studies and laboratory experiments, where skewed observations on a data set are often encountered. A number of problems with this method, for example, oudiers ...Logit regression analysis is widely applied in scientific studies and laboratory experiments, where skewed observations on a data set are often encountered. A number of problems with this method, for example, oudiers and influential observations, can cause overdispersion when a model is fitted. In this study a systematic statistical approach, including the plotting of several indices is used to diagnose the lack-of-fit of a logistic regression model. The outliers and influential observations on data from laboratory experiments are then detected. Specifically we take account of the interaction of an internal sohtary wave （ISW） with an obstacle, i.e., an underwater ridge, and also analyze the effects of the ridge height, the lower layer water depth, and the potential energy on the amplitude-based transmission rate of the ISW. As concluded, the goodness-of-fit of the revised logit regression model is better than that of the model without this approach.展开更多
The study on temperature dependence of exchange bias field and coercivity is crucial to solving the writing/reading dilemma in magnetic recording.Motivated by recent experimental findings,a complete switch between exc...The study on temperature dependence of exchange bias field and coercivity is crucial to solving the writing/reading dilemma in magnetic recording.Motivated by recent experimental findings,a complete switch between exchange bias field and coercivity with temperature is proposed,and the performance,characterized by average switching temperature(T_(S))and switching temperature width(T_(W)),controlled by antiferromagnetic anisotropy(KAF)and exchange coupling(J_(AF))constants is studied based on a MonteCarlo simulation.The results show that a linear relationship between T_(S)and KAFis established when KAFis above a critical value,while T_(S)is weakly influenced by J_(AF).On the contrary,T_(W)is insensitive to KAF,while strongly depends on J_(AF).Besides overcoming thermal energy,the increase of KAFfor a small J_(AF)guarantees the completely frozen states in the antiferromagnetic layers during magnetizing at higher temperature,below which the exchange bias field exists with a negligible coercivity.Otherwise,for a large J_(AF),the uncompensated antiferromagnetic magnetization behavior during the ferromagnetic magnetization reversal becomes complicated,and the switching process in the low temperature range depends on the irreversibility of uncompensated antiferromagnetic magnetization reversal during magnetizing,while in the high temperature range mainly influenced by the field-cooling process,resulting in a large T_(W).This work provides an opportunity to control/optimize the performance of the temperatureinduced switch between unidirectional and uniaxial symmetries through precisely tuning KAFand/or J_(AF)to meet different application demands in the next generation information technology.展开更多
Production prediction is an important factor influencing the realization of an intelligent agricultural supply chain.In an Internet of Things(IoT)environment,accurate yield prediction is one of the prerequisites for a...Production prediction is an important factor influencing the realization of an intelligent agricultural supply chain.In an Internet of Things(IoT)environment,accurate yield prediction is one of the prerequisites for achieving an efficient response in an intelligent agricultural supply chain.As an example,this study applied a conventional prediction method and deep learning prediction model to predict the yield of a characteristic regional fruit(the Shatian pomelo)in a comparative study.The root means square error(RMSE)values of regression analysis,exponential smoothing,grey prediction,grey neural network,support vector regression(SVR),and long short-term memory(LSTM)neural network methods were 53.715,6.707,18.440,1.580,and 1.436,respectively.Among these,the mean square error(MSE)values of the grey neural network,SVR,and LSTM neural network methods were 2.4979,31.652,and 2.0618,respectively;and theirRvalues were 0.99905,0.94,and 0.94501,respectively.The results demonstrated that the RMSE of the deep learning model is generally lower than that of a traditional prediction model,and the prediction results are more accurate.The prediction performance of the grey neural network was shown to be superior to that of SVR,and LSTM neural network,based on the comparison of parameters.展开更多
Shipping industry has become more capital intensive, technically more demanding and subject to major global regulatory reforms. As a consequence, the number of African shipping lines has been severely reduced. Interna...Shipping industry has become more capital intensive, technically more demanding and subject to major global regulatory reforms. As a consequence, the number of African shipping lines has been severely reduced. International trade of the WCA countries remains weak, limited to 30% of their Gross Domestic Product (GDP). The goal of this paper is to provide a comprehensive overview of the port and shipping convey management in the WCA region, and of course to describe what has been achieved since then and what still have to be done to better its infrastructures and port community.展开更多
This study focuses on estimating O-D （origin-destination） trip demand from link traffic flows. Equality relationship among link traffic flow, path flow, and O-D trip matrices are used to establish a linear equation ...This study focuses on estimating O-D （origin-destination） trip demand from link traffic flows. Equality relationship among link traffic flow, path flow, and O-D trip matrices are used to establish a linear equation system. Solution characteristics are analyzed based on the relationship between the rank of the link/path incidence matrix and column variables. And under the solution framework of conditional inverse matrices, a column exchange method and a path flow proportion method have been developed. Network testing results verify that the proposed methods yield good results.展开更多
This paper generalizes the classic resource allocation problem to the resource planning and allocation problem, in which the resource itself is a decision variable and the cost of each activity is uncertain when the r...This paper generalizes the classic resource allocation problem to the resource planning and allocation problem, in which the resource itself is a decision variable and the cost of each activity is uncertain when the resource is determined. The authors formulate this problem as a two-stage stochastic programming. The authors first propose an efficient algorithm for the case with finite states. Then, a sudgradient method is proposed for the general case and it is shown that the simple algorithm for the unique state case can be used to compute the subgradient of the objective function. Numerical experiments are conducted to show the effectiveness of the model.展开更多
It is essential to fully understand master the traffic characteristics of the self-stabilizing control effect and roadcharacteristics to ensure the regular operation of transportation. Traffic flow on curved roads and...It is essential to fully understand master the traffic characteristics of the self-stabilizing control effect and roadcharacteristics to ensure the regular operation of transportation. Traffic flow on curved roads and slopes is irregularand more complicated than that on the straight road. However, most of the research only considers the effect ofself-stabilizing in the straight road. This study attempts to bridge this deficiency from the following three aspects.First, we review the potential influencing factors of traffic flow stability, which are related to the vehicle’s steadyvelocity, history velocity, and the turn radius of the road and the slope of the road. Based on the above review,an extended continuum model accounting for the self-stabilizing effect on a curved road with slope is proposed.Second, the linear stability criterion of the new model is derived by applying linear stability theory, and the neutralstability curve is obtained in detail. The modified KdV equation describing the evolution characteristics of trafficcongestion is derived by using the nonlinear analysis method. Upon the theoretical analysis, the third aspectfocuses on simulating the self-stabilizing effect under different slopes and radius, which demonstrates that theself-stabilizing effect is conducive to reducing congestion of the curved road with slope.展开更多
Stability analysis plays a central role in nonlinear system theory and engineering application. Over the past few years, the stability analysis of fuzzy systems has been proposed and there are many successful applicat...Stability analysis plays a central role in nonlinear system theory and engineering application. Over the past few years, the stability analysis of fuzzy systems has been proposed and there are many successful applications in practical engineering. Therefore, in this paper firstly proposed is the stability analysis on oceanic structure by fuzzy models. In the present study, Takagi-Sugeno （T-S） fuzzy model is proposed for a time delay tension leg platform （TLP） system subjected to an external wave force. In terms of stability analysis, linear matrix inequality （LMI） conditions are derived via Lyapunov theory to guarantee the stability of the TLP system.展开更多
This study proposed a bilevel optimization model for the network signal timing design problem by considering the linkflows reflected by the trip-chain route choice behaviors of road users.The bilevel programming model...This study proposed a bilevel optimization model for the network signal timing design problem by considering the linkflows reflected by the trip-chain route choice behaviors of road users.The bilevel programming model is formulated based on theinteractions between signal timing control and trip-chain behavior,and a solution algorithm by combining variational inequalitysensitivity analysis,the generalized inverse matrix method,and a gradient projection approach revised for trip-chain user equilibriumis developed for the transportation design problem.The performance of the developed model framework was verified throughnumerical analysis under different test scenarios.展开更多
This study developed a user equilibrium traffic assignment model based on trip-chains with flexible activity scheduling order and derived the corresponding optimality conditions. We based on the gradient projection me...This study developed a user equilibrium traffic assignment model based on trip-chains with flexible activity scheduling order and derived the corresponding optimality conditions. We based on the gradient projection method to develop a solution algorithm, the accuracy of which was verified using the test network of UTown. This model could be used to estimate the transportation demands with and without activities scheduling restriction between OD （origin-destination） pairs based on trip-chains, as well as based on trips. Thus, the proposed model is more generalization than conventional trip based or trip-chain based traffic assignment models.展开更多
In recent years,there are many crimes related drug fraud occuring in China and many experts think that the main cause is that China Food and Drug Administration (CFDA)adopts announced inspection (AI).In order to circu...In recent years,there are many crimes related drug fraud occuring in China and many experts think that the main cause is that China Food and Drug Administration (CFDA)adopts announced inspection (AI).In order to circumvent this difficulty,CFDA has exploited unannounced inspection (UI)since 2014.In this paper,the authors study the problem of which one performs better, AI or UI.Specifically,the authors consider a supervisor,which decides the inspection approach,inspection strength and punishment to force the firm to put self-inspection effort to meet the requirements of Good Manufacturing Practice,and a firm,which produces a drug and decides its self-inspection effort. The authors use game theory to model this problem,characterize the equilibrium policies under AI, and compare the effects of the two approaches on preventing drug fraud under complete and incomplete information.The results show that under the complete information,UI performs better if the firm's technical level and the inspection cost are low and AI performs better otherwise.When the supervisor doesn't know the firm's technical level,if the low technical level is high,AI performs better.Otherwise, UI performs better if the inspection cost is low and AI performs better if the inspection cost is high.展开更多
This paper addresses the simultaneous determination of pricing and inventory replenishment strate- gies under a fluctuating environment. Specifically, we analyze the single item, periodic review model. The demand cons...This paper addresses the simultaneous determination of pricing and inventory replenishment strate- gies under a fluctuating environment. Specifically, we analyze the single item, periodic review model. The demand consists of two parts： the deterministic component, which is influenced by the price, and the stochastic component （perturbation）. The distribution of the stochastic component is determined by the current state of an exogenous Markov chain. The price that is charged in any given period can be specified dynamically. A replenishment order may be placed at the beginning of some or all of the periods, and stockouts are fully backlogged. Ordering costs that are lower semicontinuous, and inventory/backlog （or surplus） costs that are continuous with polynomial growth. Finite-horizon and infinite-horizon problems are addressed. Existence of optimal policies is established. Furthermore, optimality of （s,S,p）-type policies is proved when the ordering cost consists of fixed and proportional cost components and the surplus cost （these costs are all state-dependent） is convex.展开更多
The authors analyze a finite horizon,single product,period review model in which pricingand inventory decisions are made simultaneously.Demands in different periods are random variablesthat are independent of each oth...The authors analyze a finite horizon,single product,period review model in which pricingand inventory decisions are made simultaneously.Demands in different periods are random variablesthat are independent of each other and their distributions depend on the product price.Pricing andordering decisions are made at the beginning of each period and all shortage are backlogged.Orderingcost is a convex function of the amount ordered.The objective is to find an inventory and pricing policymaximizing expected discounted profit over the finite horizon.The authors characterize the structure ofthe optimal combined pricing and inventory strategy for this model.Moreover,the authors demonstratehow the profit-to-go function,order up to level,reorder point and optimal price change with respectto state and time.展开更多
文摘The recent rapid development of China’s foreign trade has led to the significant increase in waterway transportation and automated container ports. Automated terminals can significantly improve the loading and unloading efficiency of container terminals. These terminals can also increase the port’s transportation volume while ensuring the quality of cargo loading and unloading, which has become an inevitable trend in the future development of ports. However, the continuous growth of the port’s transportation volume has increased the horizontal transportation pressure on the automated terminal, and the problems of route conflicts and road locks faced by automated guided vehicles (AGV) have become increasingly prominent. Accordingly, this work takes Xiamen Yuanhai automated container terminal as an example. This work focuses on analyzing the interference problem of path conflict in its horizontal transportation AGV scheduling. Results show that path conflict, the most prominent interference factor, will cause AGV scheduling to be unable to execute the original plan. Consequently, the disruption management was used to establish a disturbance recovery model, and the Dijkstra algorithm for combining with time windows is adopted to plan a conflict-free path. Based on the comparison with the rescheduling method, the research obtains that the deviation of the transportation path and the deviation degree of the transportation path under the disruption management method are much lower than those of the rescheduling method. The transportation path deviation degree of the disruption management method is only 5.56%. Meanwhile, the deviation degree of the transportation path under the rescheduling method is 44.44%.
文摘Due to the effects of the COVID-19 pandemic and the rise of online shopping, the offline sales of IKEA Fuzhou have been declining since 2020. Because the cost of distribution warehouse is a major expense for offline chain furniture retailers, and the picking process is a key activity in distribution warehouse operations. To reduce the cost of distribution warehouse and alleviate the survival pressure of the offline chain furniture retailers, this paper focuses on optimizing the picking route of the IKEA Fuzhou distribution warehouse. It starts by creating a two-dimensional coordinate system for the storage location of the distribution warehouse using the traditional S-type picking strategy to calculate the distance and time of the sorting route. Then, the problem of optimizing the picking route is then transformed into the travelling salesman problem (TSP), and picking route optimization model is developed using a genetic algorithm to analyze the sorting efficiency and picking route optimization. Results show that the order-picking route using the genetic algorithm strategy is significantly better than the traditional S-type picking strategy, which can improve overall sorting efficiency and operations, reduce costs, and increase efficiency. Thus, this establishes an implementation process for the order-picking path based on genetic algorithm optimization to improve overall sorting efficiency and operations, reduce costs, increase efficiency, and alleviate the survival pressure of pandemic-affected enterprises.
文摘In the present study a numerical model developed by Lynett and Liu （2002） is modified to include density difference in a stratified two-layer fluid in a three-dimensional internal wave domain. The internal solitary wave （ISW） in the model is assumed to be weakly nonlinear and weakly dispersive, and the viscosity effects at all boundaries are ignored. The governing equations based on the Navier-Stokes and Euler equations are solved for internal solitary wave propagation over variable seabed topography. Theoretical formulations are established, from which analytical solutions are obtained, in addition to numerical results. Wave profiles from previous experimental studies are compared with the numerical results from the present analytical solutions. Numerical models developed on the basis of the present analytical solutions are better than those developed by Lynett and Liu （2002）. The results of numerical modeling agree well with the experimental data.
基金This paper was financially supported by NSC96-2628-E-366-004-MY2 and NSC96-2628-E-132-001-MY2
文摘Internal solitary wave propagation over a submarine ridge results in energy dissipation, in which the hydrodynamic interaction between a wave and ridge affects marine environment. This study analyzes the effects of ridge height and potential energy during wave-ridge interaction with a binary and cumulative logistic regression model. In testing the Global Null Hypothesis, all values are p 〈0.001, with three statistical methods, such as Likelihood Ratio, Score, and Wald. While comparing with two kinds of models, tests values obtained by cumulative logistic regression models are better than those by binary logistic regression models. Although this study employed cumulative logistic regression model, three probability functions p^1, p^2 and p^3, are utilized for investigating the weighted influence of factors on wave reflection. Deviance and Pearson tests are applied to cheek the goodness-of-fit of the proposed model. The analytical results demonstrated that both ridge height （X1 ） and potential energy （X2 ） significantly impact （p 〈 0. 0001 ） the amplitude-based refleeted rate; the P-values for the deviance and Pearson are all 〉 0.05 （0.2839, 0.3438, respectively）. That is, the goodness-of-fit between ridge height （ X1 ） and potential energy （X2） can further predict parameters under the scenario of the best parsimonious model. Investigation of 6 predictive powers （ R2, Max-rescaled R^2, Sorners＇ D, Gamma, Tau-a, and c, respectively） indicate that these predictive estimates of the proposed model have better predictive ability than ridge height alone, and are very similar to the interaction of ridge height and potential energy. It can be concluded that the goodness-of-fit and prediction ability of the cumulative logistic regression model are better than that of the binary logistic regression model.
基金The work was supported by the National Science Council under Grant Nos . NSC 95-2221-E-366-001 and NSC 95-2218-E-132-001 .
文摘Fundamental experiments were carried out in a wave flume on internal solitary wave （ISW） of depression-type propagating over a submerged ridge. The seabed ridge included either triangular or semicircular shape - regarded as topographic obstacles. Influenced by the submarine ridge, the transmitted waves were found to always consist of a leading pulse （a solitary wave） followed by a dispersive wave train. The wave profile propagating over a triangular ridge was similar to that caused by a semicircular obstacle. Apparently, the smooth face of a semicircular ridge produced time lag of wave propagation. From experimental results available, the reduction in wave energy induced by a semicircular ridge was larger than that by a triangular one. The events of wave distortion, strong breaking, internal bolus, and stratification mixing happened in case that the crest of an ISW was great enough to interact with the topographic obstacle. The reduction in wave energy was induced by strong breaking, and it depended on the ridge height rather than the geometric shape of the ridge.
文摘The main idea of this study is to provide help to West and Central Africa port logistics authorities in making, evaluating and realizing their decisions on port development/management, all in an effort to guaranty port efficiency and operational brilliance to profit the different ports, their hinterlands and their related clients. Consequently, an examination is made as far as port sector is concerned, with an ever more demanding enhancement in operational efficiency. Moreover, a past research on West and Central Africa Ports, as well as an overview on port logistics was made, making it possible to determine what has been done (prospects) and what is still to be done (ineffectiveness), in prospective of a more reformed and efficient port. One of the principles of this paper is also to confer all the aspects that operate as obstacles to the WCA port’s improvement and development;using thus the evaluation model called EWCA (Evaluation of West and Central Africa Ports), which gives a descriptive analysis of the present situation of the latter’s port logistics, including the aid of multiple regression model to determine an impact of explanatory variables on the study probability. Applying the method of strategic development, this paper thus deals with exploring typical problems and quandaries of West and Central Africa ports. The findings suggested how to fight back or overcome the constrictions and strangulations;enabling West and Central Africa port logistics attain their desired strategic development aims, despite the ineffectiveness. Tremendous efforts were made, giving a vital shoot on African economy and development;even though there is still a lot to do, for the data and variables showed how the port logistics augment and descend frequently without a long period of stability.
基金Science Council of Taiwan Province under Grant Nos.NSC 96-2628-E-366-004-MY2 and 96-2628-E-132-001-MY2
文摘Logit regression analysis is widely applied in scientific studies and laboratory experiments, where skewed observations on a data set are often encountered. A number of problems with this method, for example, oudiers and influential observations, can cause overdispersion when a model is fitted. In this study a systematic statistical approach, including the plotting of several indices is used to diagnose the lack-of-fit of a logistic regression model. The outliers and influential observations on data from laboratory experiments are then detected. Specifically we take account of the interaction of an internal sohtary wave （ISW） with an obstacle, i.e., an underwater ridge, and also analyze the effects of the ridge height, the lower layer water depth, and the potential energy on the amplitude-based transmission rate of the ISW. As concluded, the goodness-of-fit of the revised logit regression model is better than that of the model without this approach.
基金financially supported by the National Natural Science Foundation of China(No.11774045)the Joint Research Fund Liaoning-Shenyang National Laboratory for Materials Science(No.20180510008)。
文摘The study on temperature dependence of exchange bias field and coercivity is crucial to solving the writing/reading dilemma in magnetic recording.Motivated by recent experimental findings,a complete switch between exchange bias field and coercivity with temperature is proposed,and the performance,characterized by average switching temperature(T_(S))and switching temperature width(T_(W)),controlled by antiferromagnetic anisotropy(KAF)and exchange coupling(J_(AF))constants is studied based on a MonteCarlo simulation.The results show that a linear relationship between T_(S)and KAFis established when KAFis above a critical value,while T_(S)is weakly influenced by J_(AF).On the contrary,T_(W)is insensitive to KAF,while strongly depends on J_(AF).Besides overcoming thermal energy,the increase of KAFfor a small J_(AF)guarantees the completely frozen states in the antiferromagnetic layers during magnetizing at higher temperature,below which the exchange bias field exists with a negligible coercivity.Otherwise,for a large J_(AF),the uncompensated antiferromagnetic magnetization behavior during the ferromagnetic magnetization reversal becomes complicated,and the switching process in the low temperature range depends on the irreversibility of uncompensated antiferromagnetic magnetization reversal during magnetizing,while in the high temperature range mainly influenced by the field-cooling process,resulting in a large T_(W).This work provides an opportunity to control/optimize the performance of the temperatureinduced switch between unidirectional and uniaxial symmetries through precisely tuning KAFand/or J_(AF)to meet different application demands in the next generation information technology.
基金This work was supported by the 2021‘Cultivation plan for thousands of young andmiddle-aged backbone teachers in Guangxi Colleges and universities’by the Project of Humanities and Social Sciences in‘Research on Collaborative Integration of Logistics Service Supply Chain under High-QualityDevelopmentGoals’(2021QGRW044)In addition,the studywas supported by the 2019 National Social Science Project in‘Research on the Integration of Transnational Supply Chains under the Belt and Road Initiative(19BJY184)’This paper was also supported by Guangxi Philosophy and Social Science Planning Office Project:Research on the DynamicMechanism and Model Innovation of the Cross-border Integration Growth of Guangxi Logistics Enterprises(18BGL010).
文摘Production prediction is an important factor influencing the realization of an intelligent agricultural supply chain.In an Internet of Things(IoT)environment,accurate yield prediction is one of the prerequisites for achieving an efficient response in an intelligent agricultural supply chain.As an example,this study applied a conventional prediction method and deep learning prediction model to predict the yield of a characteristic regional fruit(the Shatian pomelo)in a comparative study.The root means square error(RMSE)values of regression analysis,exponential smoothing,grey prediction,grey neural network,support vector regression(SVR),and long short-term memory(LSTM)neural network methods were 53.715,6.707,18.440,1.580,and 1.436,respectively.Among these,the mean square error(MSE)values of the grey neural network,SVR,and LSTM neural network methods were 2.4979,31.652,and 2.0618,respectively;and theirRvalues were 0.99905,0.94,and 0.94501,respectively.The results demonstrated that the RMSE of the deep learning model is generally lower than that of a traditional prediction model,and the prediction results are more accurate.The prediction performance of the grey neural network was shown to be superior to that of SVR,and LSTM neural network,based on the comparison of parameters.
文摘Shipping industry has become more capital intensive, technically more demanding and subject to major global regulatory reforms. As a consequence, the number of African shipping lines has been severely reduced. International trade of the WCA countries remains weak, limited to 30% of their Gross Domestic Product (GDP). The goal of this paper is to provide a comprehensive overview of the port and shipping convey management in the WCA region, and of course to describe what has been achieved since then and what still have to be done to better its infrastructures and port community.
文摘This study focuses on estimating O-D （origin-destination） trip demand from link traffic flows. Equality relationship among link traffic flow, path flow, and O-D trip matrices are used to establish a linear equation system. Solution characteristics are analyzed based on the relationship between the rank of the link/path incidence matrix and column variables. And under the solution framework of conditional inverse matrices, a column exchange method and a path flow proportion method have been developed. Network testing results verify that the proposed methods yield good results.
基金supported by in part by the National Natural Science Foundation of China under Grant Nos.71390334 and 71132008the MOE Project of Key Research Institute of Humanities and Social Sciences at Universities under Grant No.11JJD630004Program for New Century Excellent Talents in University under Grant No.NCET-13-0660
文摘This paper generalizes the classic resource allocation problem to the resource planning and allocation problem, in which the resource itself is a decision variable and the cost of each activity is uncertain when the resource is determined. The authors formulate this problem as a two-stage stochastic programming. The authors first propose an efficient algorithm for the case with finite states. Then, a sudgradient method is proposed for the general case and it is shown that the simple algorithm for the unique state case can be used to compute the subgradient of the objective function. Numerical experiments are conducted to show the effectiveness of the model.
基金supported by the Natural Science Foundation of Zhejiang Province,China(Grant No.LY19A010002).
文摘It is essential to fully understand master the traffic characteristics of the self-stabilizing control effect and roadcharacteristics to ensure the regular operation of transportation. Traffic flow on curved roads and slopes is irregularand more complicated than that on the straight road. However, most of the research only considers the effect ofself-stabilizing in the straight road. This study attempts to bridge this deficiency from the following three aspects.First, we review the potential influencing factors of traffic flow stability, which are related to the vehicle’s steadyvelocity, history velocity, and the turn radius of the road and the slope of the road. Based on the above review,an extended continuum model accounting for the self-stabilizing effect on a curved road with slope is proposed.Second, the linear stability criterion of the new model is derived by applying linear stability theory, and the neutralstability curve is obtained in detail. The modified KdV equation describing the evolution characteristics of trafficcongestion is derived by using the nonlinear analysis method. Upon the theoretical analysis, the third aspectfocuses on simulating the self-stabilizing effect under different slopes and radius, which demonstrates that theself-stabilizing effect is conducive to reducing congestion of the curved road with slope.
基金supported by the Science Council under Contract Nos.NSC 96-2628-E-366-004-MY2 and NSC96-2628-E-132-001-MY2
文摘Stability analysis plays a central role in nonlinear system theory and engineering application. Over the past few years, the stability analysis of fuzzy systems has been proposed and there are many successful applications in practical engineering. Therefore, in this paper firstly proposed is the stability analysis on oceanic structure by fuzzy models. In the present study, Takagi-Sugeno （T-S） fuzzy model is proposed for a time delay tension leg platform （TLP） system subjected to an external wave force. In terms of stability analysis, linear matrix inequality （LMI） conditions are derived via Lyapunov theory to guarantee the stability of the TLP system.
文摘This study proposed a bilevel optimization model for the network signal timing design problem by considering the linkflows reflected by the trip-chain route choice behaviors of road users.The bilevel programming model is formulated based on theinteractions between signal timing control and trip-chain behavior,and a solution algorithm by combining variational inequalitysensitivity analysis,the generalized inverse matrix method,and a gradient projection approach revised for trip-chain user equilibriumis developed for the transportation design problem.The performance of the developed model framework was verified throughnumerical analysis under different test scenarios.
文摘This study developed a user equilibrium traffic assignment model based on trip-chains with flexible activity scheduling order and derived the corresponding optimality conditions. We based on the gradient projection method to develop a solution algorithm, the accuracy of which was verified using the test network of UTown. This model could be used to estimate the transportation demands with and without activities scheduling restriction between OD （origin-destination） pairs based on trip-chains, as well as based on trips. Thus, the proposed model is more generalization than conventional trip based or trip-chain based traffic assignment models.
基金supported by Beijing Logistics Information Research Base,and the National Natural Science Foundation of China under Grant Nos.71390334 and 71661167009
文摘In recent years,there are many crimes related drug fraud occuring in China and many experts think that the main cause is that China Food and Drug Administration (CFDA)adopts announced inspection (AI).In order to circumvent this difficulty,CFDA has exploited unannounced inspection (UI)since 2014.In this paper,the authors study the problem of which one performs better, AI or UI.Specifically,the authors consider a supervisor,which decides the inspection approach,inspection strength and punishment to force the firm to put self-inspection effort to meet the requirements of Good Manufacturing Practice,and a firm,which produces a drug and decides its self-inspection effort. The authors use game theory to model this problem,characterize the equilibrium policies under AI, and compare the effects of the two approaches on preventing drug fraud under complete and incomplete information.The results show that under the complete information,UI performs better if the firm's technical level and the inspection cost are low and AI performs better otherwise.When the supervisor doesn't know the firm's technical level,if the low technical level is high,AI performs better.Otherwise, UI performs better if the inspection cost is low and AI performs better if the inspection cost is high.
基金supported in part by (i) National Natural Science Foundation of China(NSFC), Nos. 70671100, 71072029, and Beijing Philosophy and Social Science, Research Center for Beijing Transportation Development for J.L. Zhang(ii) NSFC Research Fund Nos. 70971069 and 70772052, and the Fok Ying-Tong Education Foundation of China No. 121078, for Y.J. Li
基金Supported by the National Natural Science Foundation of China (No. 70621061,70890082,70671100)Science Foundation of Beijing Jiaotong University (2007RC014)
文摘This paper addresses the simultaneous determination of pricing and inventory replenishment strate- gies under a fluctuating environment. Specifically, we analyze the single item, periodic review model. The demand consists of two parts： the deterministic component, which is influenced by the price, and the stochastic component （perturbation）. The distribution of the stochastic component is determined by the current state of an exogenous Markov chain. The price that is charged in any given period can be specified dynamically. A replenishment order may be placed at the beginning of some or all of the periods, and stockouts are fully backlogged. Ordering costs that are lower semicontinuous, and inventory/backlog （or surplus） costs that are continuous with polynomial growth. Finite-horizon and infinite-horizon problems are addressed. Existence of optimal policies is established. Furthermore, optimality of （s,S,p）-type policies is proved when the ordering cost consists of fixed and proportional cost components and the surplus cost （these costs are all state-dependent） is convex.
基金supported by the National Natural Science Foundation of China under Grant Nos.70621061,70671100,70501014Beijing Philosophy and Social Science, Research Center for Beijing Transportation Development
文摘The authors analyze a finite horizon,single product,period review model in which pricingand inventory decisions are made simultaneously.Demands in different periods are random variablesthat are independent of each other and their distributions depend on the product price.Pricing andordering decisions are made at the beginning of each period and all shortage are backlogged.Orderingcost is a convex function of the amount ordered.The objective is to find an inventory and pricing policymaximizing expected discounted profit over the finite horizon.The authors characterize the structure ofthe optimal combined pricing and inventory strategy for this model.Moreover,the authors demonstratehow the profit-to-go function,order up to level,reorder point and optimal price change with respectto state and time.
