Path finding in the tile assembly model

Swarm robotics, active self-assembly, and amorphous computing are fields that focus on designing systems of large numbers of small, simple components that can cooperate to complete complex tasks. Many of these systems are inspired by biological systems, and all attempt to use the simplest components and environments possible, while still being capable of achieving their goals. The canonical problems for such biologically-inspired systems are shape assembly and path finding. In this paper, we demonstrate path finding in the well-studied tile assembly model, a model of molecular self-assembly that is strictly simpler than other biologically-inspired models. As in related work, our systems function in the presence of obstacles and can be made fault-tolerant. The path-finding systems use Θ(1)$\Theta \left(1\right)$ distinct components and find minimal-length paths in time linear in the length of the path.     

Nondeterministic polynomial time factoring in the tile assembly model

Formalized study of self-assembly has led to the definition of the tile assembly model, Previously I presented ways to compute arithmetic functions, such as addition and multiplication, in the tile assembly model: a highly distributed parallel model of computation that may be implemented using molecules or a large computer network such as the Internet. Here, I present tile assembly model systems that factor numbers nondeterministically using Θ(1)$\Theta \left(1\right)$ distinct components. The computation takes advantage of nondeterminism, but theoretically, each of the nondeterministic paths is executed in parallel, yielding the solution in time linear in the size of the input, with high probability. I describe mechanisms for finding the successful solutions among the many parallel executions and explore bounds on the probability of such a nondeterministic system succeeding and prove that the probability can be made arbitrarily close to 1.     

面向虚拟装配的装配建模及其重构

装配建模是进行虚拟装配的前提和基础,决定着虚拟装配实施的质量和效率。针对虚拟装配中装配建模问题,介绍一种多视图层次化的装配模型,给出了模型的信息组成和信息来源,并很好地解决了在此模型基础上的重构问题。     

Allocation of maintenance resources in mixed model assembly systems

Mixed-model assembly systems (MMASs) have been well recognized for their ability to handle product variety for mass customization. With multiple products to produce, the prioritization of maintenance work-order becomes more crucial and challenging. This paper develops a quantitative method to systematically determine maintenance work-order priorities in an MMAS using on-line production information. The effect of product mix ratio on maintenance decisions is studied in detail. Based on the proposed approach, one can search for an optimal maintenance plan that will lead to improved productivity within the optimization horizon.     

Mixed model assembly line design in a make-to-order environment

Mixed model assembly lines can be found today in many industrial environments. With the growing trend for greater product variability and shorter life cycles, they are replacing the traditional mass production assembly lines. In many cases, these lines follow a ‘make-to-order’ production policy, which reduces the customer lead-time, and is expressed in a random arrival sequence of different model types to the line. Additional common characteristics of such mixed model lines in a make-to-order environment are: small numbers of work stations, a lack of mechanical conveyance, and highly skilled workers. The design problem of mixed model assembly lines in a make-to-order environment is addressed in this paper. A mathematical formulation is presented which considers the differences between our model and traditional models. A heuristic that minimizes the number of stations for a predetermined cycle time is developed consisting of three stages: the balancing of a combined precedence diagram, balancing each model type separately subject to the constraints resulting from the first stage, and a neighborhood search based improvement procedure.     

基于混合模型的虚拟装配关键技术研究

针对虚拟装配中采用多边形网格模型引起的组件定位困难和碰撞检测精度低等问题,提出一种采用精确几何模型及其对应的多边形网格模型的混合模型作为底层数据,支持精确装配的虚拟装配系统构造方法,并基于Parasolid和Vir-tools平台进行了实现。基于混合模型的碰撞检测能根据计算精度和时间要求自适应求解,在速度快的同时,满足高精度碰撞检测要求;基于混合模型的组件装配,采用离散采样点定义装配路径,通过装配几何约束交互式定义限制组件的运动范围,通过自由度规约、装配约束求解实现了零部件精确定位,通过四元数插值实现装配路径中零部件位姿的平滑过渡,能满足高精度的装配要求。该方法已经在开发的多个系统中得到验证和应用。     

HLognGP: A parallel computation model for GPU clusters

Parallel computation model is an abstraction for the performance characteristics of parallel computers, and should evolve with the development of computational infrastructure. The heterogeneous CPU/Graphics Processing Unit (GPU) systems have been and will be important platforms for scientific computing, which introduces an urgent demand for new parallel computation models targeting this kind of supercomputers. In this research, we propose a parallel computation model called HLog_nGP to abstract the computation and communication features of heterogeneous platforms like TH‐1A. All the substantial parameters of HLog_nGP are in vector form and deal with the new features in GPU clusters. A simplified version HLog₃GP of the proposed model is mapped to a specific GPU cluster and verified with two typical benchmarks. Experimental results show that HLog₃GP outperforms the other two evaluated models and can well model the new particularities of GPU clusters. Copyright © 2015 John Wiley & Sons, Ltd.     

Genetic algorithms for sequencing problems in mixed model assembly lines

Mixed model assembly lines are a type of production line where a variety of product models similar in product characteristics are assembled. The effective utilisation of these lines requires that a schedule for assembling the different products be determined. In this paper, the performance of genetic algorithms for sequencing problems in mixed model assembly lines is investigated. The problem first considered is a comparison between a existing heuristic and the proposed genetic algorithm to get the constant usage of every part used by the line considering variation at multi levels (Number of levels fixed as four. level 1—product, level 2—subassembly, level 3—component, level 4—raw-materials) for various test-bed problems. The algorithms proposed by Miltenburg and Sinnamon hereafter referred to as MS 1992 [IIE Trans. 24 (1992) 121] and the proposed genetic algorithm (GA) applied to mixed model assembly line are compared. Results of evaluation indicate that the GA performs better over MS1992 on 25 of the 40 problems investigated.

The other problem solved is a multiple objective sequencing problem in mixed model assembly lines. Three practically important objectives are minimizing total utility work keeping a constant rate of part-usage, minimizing the variability in parts usage and minimizing total setup cost. In this paper, the performance of the selection mechanisms, the Pareto stratum-niche cubicle and the selection based on scalar fitness function value are compared with respect to the objective of minimising variation in part-usage, minimising total utility work and minimising the setup cost. Results of evaluation indicate that the genetic algorithm that uses the Pareto stratum-niche cubicle performs better than the genetic algorithm with the other selection mechanisms.     

一种恶意模型下高效的两方安全计算协议

为了提高恶意参与者模型下两方安全计算协议的效率,文中协议使用了简单的轮换映射,这样不仅可以检测恶意参与方输入的一致性,而且避免了检测一致性时由于图的全连接性带来的复杂度,从而与经典协议相比效率提高了近50%。此外,为了使协议的安全性得到更好的保证,在理想/现实对模型下,本文采用回退的方法,在OT12协议完全可模拟和知识证明等性质的基础上,用现实模型模拟理想模型的方法,给出了协议完整、严格的形式化证明和失败率分析。     

Molecular solutions for minimum and exact cover problems in the tile assembly model

The tile assembly model is a novel biological computing model where information is encoded in DNA tiles. It is an efficient way to solve NP-complete problems due to its scalability and parallelism. In this paper, we apply the tile assembly model to solve the minimum and exact set cover problems, which are well-known NP-complete problems. To solve the minimum set cover problem, we design a MinSetCover system composed of three parts, i.e., the seed configuration subsystem, the nondeterministic choice subsystem, and the detection subsystem. Moreover, we improve the MinSetCover system and propose a MinExactSetCover system for solving the problem of exact cover by 3-sets. Finally we analyze the computation complexity and perform a simulation experiment to verify the effectiveness and correctness of the proposed systems.     

Human gait simulation with a neuromusculoskeletal model and evolutionary computation

This paper describes a human gait animation system with a precise neuromusculoskeletal model and evolutionary computation. The neuromusculoskeletal model incorporates 14 rigid bodies, 19 degrees of freedom, 60 muscular models, 16 pairs of the neural oscillators, and other neuronal systems. By changing the search parameters and the evaluative criteria of the evolutionary search process, we demonstrate various locomotive patterns, such as normal gait, pathological gait, running and ape‐like walking. The proposed simulation system takes not only kinematic data but also in vivo dynamic data such as energy consumption information into consideration, so that the resultant locomotion patterns are natural and valid from a biomechanical point of view. Hence the simulation system can also be used for finding a biologically appropriate physical model to realize a desired gait by simultaneously modifying the body dynamics parameters with the neuronal parameters. This capability creates a novel application of human gait simulation systems, such as rehabilitation tool design and consultation for physically handicapped people. Copyright © 2003 John Wiley & Sons, Ltd.     

A mathematical model and a genetic algorithm for two-sided assembly line balancing

A two-sided assembly line is a type of production line where tasks are performed in parallel at both sides of the line. The line is often found in producing large products such as trucks and buses. This paper presents a mathematical model and a genetic algorithm (GA) for two-sided assembly line balancing (two-ALB). The mathematical model can be used as a foundation for further practical development in the design of two-sided assembly lines. In the GA, we adopt the strategy of localized evolution and steady-state reproduction to promote population diversity and search efficiency. When designing the GA components, including encoding and decoding schemes, procedures of forming the initial population, and genetic operators, we take account of the features specific to two-ALB. Through computational experiments, the performance of the proposed GA is compared with that of a heuristic and an existing GA with various problem instances. The experimental results show that the proposed GA outperforms the heuristic and the compared GA.     

一种新型混合算法在混流装配调度中的应用

针对含有缓冲区的混流装配中同时存在的生产成本和库存成本问题,提出了一种基于遗传算法和差分进化算法的混合框架,并将其用于混流装配调度的实际问题中。通过融合遗传算法有效处理离散变量及差分进化算法有效处理连续变量的优点,在综合考虑降低生产成本和缓冲区库存的同时,兼顾了每个型号产品生产的顺序及数量。计算机仿真结果表明,与传统算法相比,该算法在混流装配调度上具有收敛速度快、优化能力强、算法可靠等优势。该混合算法可以显著改善多参数、高度非线性问题的优化结果,提高计算效率。     

一种人工情绪模型及其电商计算实验应用

针对电子商务顾客购物人工系统的计算实验研究,提出一种基于状态类比假说的人工情绪模型,给出了情绪的产生、增强、衰落和消失过程的描述方法,研究了外部刺激、情感强度和内部驱动力的计算方法,并进行了模拟分析。基于此人工情绪模型,构建了电商顾客购物的情绪行为影响关系模型;将其应用于电商顾客购物的计算实验分析。结果表明,该人工情绪模型能较好地应用于电商复杂人工系统顾客购物的计算实验。     

Analysis of the structure and morphology of fenoxycarb crystals

In this paper, we have explored the relationship between surface structure and crystal growth and morphology of fenoxycarb (FC). Experimental vs. predicted morphologies/face indices of fenoxycarb crystals are presented. Atomic-scale surface structures of the crystalline particles, derived from experimentally indexed single crystals, are also modelled. Single crystals of fenoxycarb exhibit a platelet-like morphology which closely matches predicted morphologies. The solvent choice does not significantly influence either morphology or crystal habit. The crystal morphology is dominated by the {0 0 1} faces, featuring weakly interacting aliphatic or aromatic groups at their surfaces. Two distinct modes of interaction of a FC molecule in the crystal can be observed, which appear to be principal factors governing the microscopic shape of the crystal: the relatively strong collateral and the much weaker perpendicular bonding. Both forcefield-based and quantum-chemical calculations predict that the aromatic and aliphatic terminated {0 0 1} faces have comparably high stability as a consequence of weak intermolecular bonding. Thus we predict that the most developed {0 0 1} surfaces of fenoxycarb crystals should be terminated randomly, favouring neither aliphatic nor aromatic termination.     

Computational relaxed TP model transformation: restricting the computation to subspaces of the dynamic model

The tensor‐product (TP) model transformation is a recently proposed numerical method capable of transforming linear parameter varying state‐space models to the higher order singular value decomposition (HOSVD) based canonical form of polytopic models. It is also capable of generating various types of convex TP models, a type of polytop models, for linear matrix inequality based controller design. The crucial point of the TP model transformation is that its computational load exponentially explodes with the dimensionality of the parameter vector of the parameter‐varying state‐space model. In this paper we propose a modified TP model transformation that leads to considerable reduction of the computation. The key idea of the method is that instead of transforming the whole system matrix at once in the whole parameter space, we decompose the problem and perform the transformation element wise and restrict the computation to the subspace where the given element of the model varies. The modified TP model transformation can readily be executed in higher dimensional cases when the original TP model transformation fails. The effectiveness of the new method is illustrated with numerical examples. Copyright © 2009 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

A new robust model predictive control method I: theory and computation

The success of the single-model MPC (SMPC) controller depends on the accuracy of the process model. Modeling errors cause sub-optimal control performance and may cause the control system to become closed-loop unstable. The goal of this paper is to examine the control performance of the robust MPC (RMPC) method proposed by Wang and Rawlings [34] on several illustrative examples. In this paper, we show the RMPC method successfully controls systems with time-varying uncertainties in the process gain, time constant and time delay and achieves offset-free non-zero set point tracking and non-zero disturbance rejection subject to input and output constraints.