带时间窗口的多式联运模型与算法

以带时间窗的多式联运模型为基础,考虑节点间的运输时间、节点处的运输方式转换时间以及可能发生的货运延迟,以包括运输成本、转运成本和时间偏离惩罚成本在内的总成本最小为目标函数,建立基于满意时间路径的多式联运模型.在算法上,构造了基于K最短路的改进遗传算法,通过3个算例说明多式联运的运输路径与运输方式搭配可以不是唯一的,为多式联运的相关研究工作提供了理论基础.     

基于改进遗传算法的多式联运网络优化

在对多种运输方式比较分析的基础上,从运输成本、换装成本及时间惩罚成本3个角度,建立多式联运网络模型,采用改进遗传算法进行模型求解,在标准遗传算法基础上引入移民算子,保证了种群多样性,避免了局部最优,增强了算法搜索能力.采用MATLAB计算平台对模型进行案例求解,结果表明,采用多式联运网络运作模型的成本降低了45.8%,从而验证了多式联运网络运作模型的有效性和实用性.     

考虑服务效率的无人系统多式联运自适应优化策略北大核心

针对无人系统配送的稳定性,考虑多式联运过程中存在的货运质量变化的情况,以无人车间配送系统满足市场需求的比率度量系统服务效率,构建了由一个生产部门和多个货运部门组成的无人车间配送系统,货运部门之间进行多式联运,将无人系统的库存补货点和联运响应点作为决策变量,以实现多式联运系统的总成本最小化。根据问题和模型的特点设计模拟退火(Simulated Annealing,SA)算法进行求解。数值研究结果验证了模型在成本优化方面的显著性和自适应策略的有效性。研究结果表明,在同等服务效率和同等商品残次率条件下,无人系统允许载人系统参与辅助的多式联运的库存控制方案要优于不允许多式联运库存方案。同时发现,在协同响应方面,所提出的无人系统自适应补货和响应控制策略的系统总成本优于实时更新策略。     

多式联运的最短时间路径-运输费用模型研究

随着经济的迅速发展，单一的运输方式越来越不能满足来自客户的敏捷制造、快速响应市场、物流供应链管理等诸多方面的需求，多式联运为之提供了良好的解决方案；多式联运运输网络考虑了节点间的运输时间、节点处的运输方式转换时间以及可能发生的货运延迟；给出了多式联运下的路径最短时间模型，并根据求得的最短时间路径提供了相应的运输费用模型，为多式联运的相关研究工作提供了理论基础。     

考虑服务效率的无人系统多式联运自适应优化策略

针对无人系统配送的稳定性,考虑多式联运过程中存在的货运质量变化的情况,以无人车间配送系统满足市场需求的比率度量系统服务效率,构建了由一个生产部门和多个货运部门组成的无人车间配送系统,货运部门之间进行多式联运,将无人系统的库存补货点和联运响应点作为决策变量,以实现多式联运系统的总成本最小化。根据问题和模型的特点设计模拟退火(Simu?lated Annealing,SA)算法进行求解。数值研究结果验证了模型在成本优化方面的显著性和自适应策略的有效性。研究结果表明,在同等服务效率和同等商品残次率条件下,无人系统允许载人系统参与辅助的多式联运的库存控制方案要优于不允许多式联运库存方案。同时发现,在协同响应方面,所提出的无人系统自适应补货和响应控制策略的系统总成本优于实时更新策略。     

对我国多式联运发展现状的分析

多式联运作为一种混合式运输方式，缩短了货物运输的在途时间，大大提高了物流运输效率，为节约物流运输成本提供了条件。目前，我国的多式联运还处于起步阶段，明确多式联运在我国的发展现状是发展物流行业的前提。本文通过分析我国多式联运的发展现状，与发达国家的多式联运发展水平进行比较，并分析未来我国多式联运的发展趋势。     

不确定运价下长江集装箱多式联运路径优化

为充分贴合长江集装箱多式联运场景,在分析长江多式联运组织特点的基础上,考虑不确定运价及不同航段航道通航条件影响,以包含运输周转成本、碳排放成本和时间成本在内的总成本最小化为目标,构建不确定条件下长江集装箱多式联运路径优化模型,并设计蒙特卡洛仿真与改进的狼群算法实现模型求解,最后通过算例分析验证改进的狼群算法的有效性。算例分析结果表明,公路运输能有效控制运输的时间成本,铁路与水路运输在运输经济性与绿色性方面更具优势。在长江航道通航能力与最大中转次数限制下,运输任务将选择较高成本运输方案以满足航道与托运人要求。     

考虑高铁时间窗和客户满意度的生鲜品公铁联运路径选择

针对生鲜品小批量、高时效的运输特点,提出将“高速公路+高速铁路”作为一种快速联运方式应用于生鲜品的多式联运中。以总成本最低为目标,以高铁服务时间窗、客户满意度为约束,构建基于模糊需求的生鲜品公铁联运路径选择与运输方式组合模型。以“哈尔滨-昆明”联运网络为例进行算例分析,应用Lingo12.0实现模型求解。结果表明,提出的“高速公路+高速铁路”联运方式在运输总成本和客户满意度方面均优于单一运输方式,且与“高速公路+航空”联运方式相比具有成本优势;采用灵敏度分析法,分别探究了置信水平、客户品质满意度约束值和时间满意度约束值的变化对运输总成本的影响关系,同时验证了模型的有效性,为“高速公路+高速铁路”方式下的生鲜品运输路径选择提供有益参考。     

一种多式联运网络运输方式的组合优化模式

针对我国多式联运目前普遍存在的信息化水平不高,缺乏相应的决策支持系统的现状,首先对多种运输方式的运输特性进行了分析,通过对比,得出了运输方式的选择依据;然后建立了多式联运虚拟运输网络;最后在运输方式选择依据和运输网络的基础上得出了多种运输方式组合优化模型,并给出了求解算法。     

具有模糊时间窗的多模式联运建模及优化

以考虑用户偏好的模糊时间窗多式联运为研究对象,建立了基于图状结构的模糊时间多式联运模型。在分析模型特征的基础上,设计了基于正交试验的混合田口遗传算法实现路径及运输方式的组合优化。通过考虑不同用户偏好的5个任务来考察模型和优化算法的有效性。计算结果表明,该算法能有效求解出满足用户偏好的路径及运输组合方式,为物流企业决策提供依据。     

Impact of finite receiver-aperture size in a non-line-of-sight single-scatter propagation model

In this paper, a single-scatter propagation model is developed that expands the classical model by considering a finite receiver-aperture size for non-line-of-sight communication. The expanded model overcomes some of the difficulties with the classical model, most notably, inaccuracies in scenarios with short range and low elevation angle where significant scattering takes place near the receiver. The developed model does not approximate the receiver aperture as a point, but uses its dimensions for both field-of-view and solid-angle computations. To verify the model, a Monte Carlo simulation of photon transport in a turbid medium is applied. Simulation results for temporal responses and path losses are presented at a wavelength of 260 nm that lies in the solar-blind ultraviolet region.     

Developing a risk/cost framework for routing truck movements of hazardous materials

As the United States continues to increase its dependence on industrial technologies which require hazardous materials and generate hazardous wastes, concern is mounting over the safe transport of hazardous cargo. It is estimated that 1.5 billion tons of hazardous cargo are moved through the nation's transportation systems (excluding pipeline), with truck as the primary mode of transport. Because of the dynamic nature of exposure to the population and environment associated with the transport of hazardous cargo, it is important to develop an accurate representation of this type of transport risk, and to structure a framework for designating a permanent set of shipping routes based on optimizing across risks and costs. This paper describes a methodology which has been developed that incorporates risk and cost into a framework for optimizing the routing of truck movements of hazardous materials. Considerable attention is focused on the risk estimation part of this process, as this is a subject of much uncertainty and of considerable significance to policymakers. The resulting methodology is applied in a regional setting to illustrate its use as an analysis tool. Enhancements to the model structure and extensions beyond the truck routing problem are also discussed.     

Non-equilibrium Thermodynamic Model for the Estimation of the Soret Coefficient in Dilute Polymer Solutions

In the present work a theoretical model based on linear non-equilibrium thermodynamics and the concept of Eyring’s activation energy of viscous flow is developed to estimate the Soret coefficient in dilute polymer solutions. The model is capable of predicting a sign change in the Soret coefficient, when the polymer molecular weight changes. The key part of the model is the way that the net heat of transport of the polymer molecules is simulated. Employing the Mark–Houwink equation, which correlates the polymer solution intrinsic viscosity with its molecular weight, the net heat of transport of the polymer is correlated with the activation energy of viscous flow of the polymer’s monomer in the liquid state, the Mark–Houwink solution parameter, and the polymer molecular weight. The model is evaluated against the experimental data, where qualitative and in some cases quantitative agreement is found.     

Vertical Charge Transport via Small Polaron Hopping within TIPS‐Pentacene Lamellar Single Crystal

A modified liquid method is employed to grow an ultralarge 6,13‐bis(triisopropylsilylethynyl)pentacene crystal, ensuring fabrication and measurements of the two terminal devices. The hole transport mechanism is studied by analyzing the space charge limited currents (SCLCs) at various temperatures. Modified SCLC theory with a small polaron hopping model is developed and employed to successfully simulate the I–V curves. Values of effective hopping distance, transfer integral, and reorganization energy are extracted and reasonably discussed. A scenario is suggested that hopping transport takes place from one molecule to its nearest neighbor along the c‐axis, with every molecule acting as a trapping center.     

Two-dimensional contaminant transport modeling using meshfree point collocation method (PCM)

Groundwater contamination is a severe problem in many parts of the world including India. The complex problem of groundwater flow and contaminant transport is studied generally by solving the governing equations of flow and transport using numerical models such as finite difference method (FDM) or finite element method (FEM). Meshfree (MFree) method is an alternative numerical approach to solve these governing equations in simple and accurate manner. MFree method does not require any grid and only makes the use of a set of scattered collocation points, regardless of the connectivity information between them. Kansa (1990) [9] developed a multi-quadratic (MQ) based MFree method for the solution of partial differential equations. Based on the Kansa’s method, the present study proposes a MFree point collocation method (PCM) with multi-quadric radial basis function (MQ-RBF) for the two-dimensional coupled groundwater flow and transport simulation in unconfined conditions. The accuracy of the developed model is verified with available analytical solutions in literature. The coupled model developed is further applied to a field problem to compute the groundwater head and concentration distribution and the results are compared with available finite element based simulation. The outcomes of the model results showed the applicability of the present approach.     

Electrode material transport and re-deposition in high-intensity arc discharge lamps

A two-dimensional model of sintered electrode activator (in particular, barium) transport in the arc discharge lamp tube volume has been developed, based on a numerical solution of the non-stationary diffusion equation. The dependence of the barium atom flow density at the electrode rod tip on fill gas pressure and electrode dimensions has been calculated. It has been found that the main mechanism of activator transport to the rod tip is evaporation from the sintered body and diffusion through the gas. Evolution of tungsten rod emission characteristics caused by deposition of the evaporated material on its surface has been studied experimentally.     

Numerical modeling of liquid water movement through layered snow based on new measurements of the water retention curve

Liquid water movement in snow is an important aspect of wet snow metamorphism and is vital for forecasting wet snow avalanches. However, despite its importance, liquid water movement is over-simplified in the current version of the numerical model SNOWPACK, yielding an inadequate simulation of the water content profile. In general, estimations of liquid water flux in porous materials are based on hydraulic conductivity and suction. This paper presents a water transport model based on the van Genuchten formulation, with parameters obtained from gravity drainage column experiments. Simulations that try to describe the capillary barrier between layers of different grain sizes lead to long computation times because of the small time increments required. In this study, a new algorithm was developed and incorporated in the water transport model in order to simulate the capillary barrier using relatively long time increments (60 s). The model was then used to simulate water movement between snow layers of different grain size. The results confirm that a water-saturated layer forms at the boundary between fine and underlying very coarse snow, which is consistent with observations.The new water transport model was incorporated in SNOWPACK, which then produced an unstable water-saturated layer at the boundary between different grain sizes. Simulation results from the SNOWPACK model were compared with measurements. The main achievement in this study is that the natural capillary barrier was documented and then reproduced using the modified SNOWPACK model. Nevertheless, much work has still to be done to get fully satisfactory results for the reproducibility of grain size and liquid water content.     

Simulation–optimization model for groundwater contamination remediation using meshfree point collocation method and particle swarm optimization

Remediation of the groundwater contamination problem is a tedious, time consuming and expensive process. Pump and treat (PAT) is one of the commonly used techniques for groundwater remediation in which the contaminated groundwater is pumped, treated and put back to the aquifer system or other sources. Developing simulation-optimization (S/O) model proved to be very useful in the design process of an effective PAT system. Simulation models help in predicting the spatial and temporal variation of the contamination plume while optimization models help in minimizing the cost of pumping. Generally, grid or mesh based models such as Finite Difference Method (FDM) or Finite Element Methods (FEM) is used for the groundwater flow and transport simulation. But it is found that grid/mesh generation is a time consuming process. Therefore, recently Meshfree (MFree) based numerical models are developed to avoid this difficulty of meshing and remeshing. MFree Point Collocation Method (PCM) is a simple meshfree method used for the simulation of coupled groundwater flow and contaminant transport. For groundwater optimization problems, even though number of methods such as linear programming, nonlinear programming, etc. are available, evolutionary algorithm based techniques such as genetic algorithm (GA) and particle swarm optimization (PSO) are found to be very effective. In this paper, a simulation model using MFree PCM for confined groundwater flow and transport and a PSO based single objective optimization model are developed and coupled to get an effective S/O model for groundwater remediation using PAT. The S/O model based on PCM and PSO is applied for a polluted hypothetical confined aquifer and its performance is compared with Finite Element Method?CBinary Coded Genetic Algorithm (FEM?CGA) model. It is found that both the models are in good agreement with each other showing the applicability of the present approach. The PCM?CPSO based S/O model is simple and more effective in groundwater contamination remediation design using PAT.     

Prediction of transport properties of wood below the fiber saturation point - A multiscale homogenization approach and its experimental validation. Part II: Steady state moisture diffusion coefficient

In this publication a multiscale homogenization model for moisture transport in wood is developed and validated. The model aims at prediction of macroscopic transport properties of clear wood samples from their microstructure and the physical properties of a few microscale constituents. In the first part of this two-part paper, the theoretical background and fundamentals of the model were presented, and its specification for the estimation of macroscopic thermal conductivities was shown. In this second part the model is applied to steady state moisture diffusion below the fiber saturation point. The model starts on a scale of about 50 μm, where the wood cells form a honeycomb-like structure. In a first homogenization step the effective moisture transport behavior of the cell structure is determined from moisture diffusion properties of the cell walls and the (moist) air in lumens, respectively. Further homogenization steps account for the larger vessels that exist in hardwood species, the annual rings which are a succession of layers with different densities, and finally wood rays, that form pathways in the radial direction throughout the stem. The model validation rests on experiments as in the case of heat conduction: The macroscopic diffusion coefficients predicted by the multiscale homogenization model for tissue-specific composition data (input data set II) are compared to corresponding experimentally determined tissue-specific diffusion coefficients under steady state conditions (experimental data set). As for thermal conductivity, the good agreement of model predictions and test data underlines the suitability of the presented multiscale model.     

Lipid Bilayers on a Picoliter Microdroplet Array for Rapid Fluorescence Detection of Membrane Transport

This paper describes picoliter‐sized lipid bilayer chambers and their theoretical model for the rapid detection of membrane transport. To prepare the chambers, semispherical aqueous droplets are patterned on a hydrophilic/hydrophobic substrate and then brought into contact with another aqueous droplet in lipid‐dispersed organic solvent, resulting in the formation of the lipid bilayers on the semispherical droplets. The proposed method implements the lipid bilayer chambers with 25‐fold higher ratio of lipid membrane area (S) to chamber volume (V) compared to the previous spherical droplet chambers. Using these chambers, we are able to trace the time‐course of Ca²⁺ influx through α‐hemolysin pores by a fluorescent indicator. Moreover, we confirm that the detection time of the substrate transport is inversely proportional to the S/V ratio of the developed chambers, which is consistent with the simulation results based on the developed model. Our chambers and model might be useful for rapid functional analyses of membrane transport phenomena.