Organizing product releases in time-driven development processes: a probabilistic analysis

In this paper, the problem is addressed of how to organizea new product development process that is fast on the one handand that provides good-quality results on the other hand. Severalplanning techniques, like PERT and CPM, are available to analysethe completion time or product release time of such complexprocesses. Although these techniques are all well known andare widely used in project management, they do not address theiterative mode of operation that is characteristic for suchuncertain processes. Neither do they offer a tool or guidelinesto ‘design’ a composition of iterative processesbecause they are analytical. In this paper, a quantitative concept is presented for modellingthe release time of a single uncertain iterative activity, asa random variable to deal with the probabilistic aspect in asimple way. From this simple model, the complexity is extendedsystematically to model fundamentally different configurations,that are on the one hand simple enough to be studied analyticallyand on the other hand exhibit their fundamentally differentrelease characteristics, as experienced in real life. From theanalysis, guidelines are formulated for organizing or (re)configuringa complex process configuration. It is demonstrated that organizing uncertain processes fora fast product release requires a balance between the exploitationof the principles of concurrent engineering and the risk ofoverrunning time targets. An important factor in this balanceis the decision structure for the release of intermediate results.The ‘empowerment’ structure, a structure where decisionsare not clustered as milestones but are made without any delay,offers great opportunity in terms of small mean release timesand small variances thereof.     

Genetic algorithm-based multi-criteria project portfolio selection

Project portfolio selection is one of the most important decision-making problems for most organizations in project management and engineering management. Usually project portfolio decisions are very complicated when project interactions in terms of multiple selection criteria and preference information of decision makers (DMs) in terms of the criteria importance are taken into consideration simultaneously. In order to solve this complex decision-making problem, a multi-criteria project portfolio selection problem considering project interactions in terms of multiple selection criteria and DMs?? preferences is first formulated. Then a genetic algorithm (GA)-based nonlinear integer programming (NIP) approach is used to solve the multi-criteria project portfolio selection problem. Finally, two illustrative examples are presented for demonstration and verification purposes. Experimental results obtained indicate that the GA-based NIP approach can be used as a feasible and effective solution to multi-criteria project portfolio selection problems.     

Spurious terms in the three-body problem

The method of hyperharmonics is used to split the central two-body interactions and the Faddeev components of the wave function in a three-body system into physical and spurious terms. The sum of the physical terms of the interactions or of the Faddeev components for all pairs of particles is nonzero, whereas the sums of spurious terms of both the interactions and the Faddeev components over all pairs of particles vanish identically. We establish a criterion for the existence of spurious terms. We show that a sufficient condition for this criterion is equivalent to the conservation law for a certain quantum number. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 125, No. 2, pp 253–271, November, 2000.     

Completely analytic interactions with infinite values

Summary In this note we extend the notion of completely analytic interactions of Gibbs random fields that is known for finite interactions with finite range to interactions that can have infinite values, too. We formulate a set of ten conditions on such interactions in terms of analyticity properties of the partition functions, or correlation decay. The main theorem states that all these conditions are equivalent. Therefore, an interaction is called a completely analytic interaction, if it satisfies one of these conditions.     

Order sequencing on a unidirectional cyclical picking line

A real life order-picking configuration that requires multiple pickers to cyclically move around fixed locations in a single direction is considered. This configuration is not the same, but shows similarities to, unidirectional carousel systems described in literature. The problem of minimising the pickers’ travel distance to pick all orders on this system is a variant of the clustered travelling salesman problem. An integer programming (IP) formulation of this problem cannot be solved in a realistic time frame for real life instances of the problem. A relaxation of this IP formulation is proposed that can be used to determine a lower bound on an optimal solution. It is shown that the solution obtained from this relaxation can always be transformed to a feasible solution for the IP formulation that is, at most, within one pick cycle of the lower bound. The computational results and performance of the proposed methods as well as adapted order sequencing approaches for bidirectional carousel systems from literature are compared to one another by means of real life historical data instances obtained from a retail distribution centre.     

AN AGENT‐BASED EVENT DRIVEN FORAGING MODEL

ABSTRACT. A game‐theoretic foraging model is developed in an agent‐based framework. The animal's environment is described in terms of agents representing prey, predators and the habitat. The animal has two modes of behavior for each agent: tactical mode behaviors alter the outcomes of the events and strategic mode behaviors alter the probability of future events. Possible event outcomes are represented as utilities which have both benefit and cost components. The probabilities of successful behaviors are tracked via short‐term (tactical), intermediate‐term (strategic) and long‐term (reference) memories. Probabilities change continually through the moment‐to‐moment events, and switches in behavior occur when the expected utility of one behavior exceeds that of another. At the switch point, the expected utilities of the behaviors are equivalent; through this property the model parameters can be calibrated from behavioral experiments. A bluegill foraging study on giving‐up time is used to calibrate the model and then habitat foraging is simulated. Problems with interpreting behavioral studies without fully characterizing the multiple scales of interactions with agents are discussed.     

Re-sourcing teachers’ work and interactions: a collective perspective on resources, their use and transformation

This paper reviews the literature on the theme of mathematics teachers’ work and interactions with resources, taking a particular perspective, the so-called ‘collective perspective’ on resources, their use and transformation. The review is presented under three headings: (1) theoretical frameworks commonly used in this area of research; (2) teachers’ interactions with resources in terms of their design and use; and (3) teachers’ interactions with resources in terms of teacher learning and professional development. From the literature, and the collection of papers in this issue, we argue that the collective dimensions play an important role in mathematics teachers’ work with resources and in their professional learning/development. Further empirical investigations are likely to be needed on: how teachers may work in collectives and with resources, and in which ways ‘productive’ collectives may form and work together; which roles particular resources can play in these delicate constellations and how particular resources may support teachers in their work and learning; and which kinds of resources offer opportunities for community building.     

Limiting behaviour of the mean residual life

In survival or reliability studies, the mean residual life or life expectancy is an important characteristic of the model. Here, we study the limiting behaviour of the mean residual life, and derive an asymptotic expansion which can be used to obtain a good approximation for large values of the time variable. The asymptotic expansion is valid for a quite general class of failure rate distributions—perhaps the largest class that can be expected given that the terms depend only on the failure rate and its derivatives.     

Computing availability for redundant flow systems

There are many papers in the literature about computing reliability for binary redundant systems. However in the real world there are many systems, whose economics depend on average availability of flow throughout the life span of the system rather than reliability on one particular threshold level only. Such systems exist in oil and gas redundant flow networks. To best of this author’s knowledge no attempt has been made yet to compute availability of such systems. Computing availability of flow is of utmost importance for the economical planning and design of any industrial flow networks. In this paper an approach is proposed to compute availability of flow in redundant flow systems. The proposed approach is compared with the approach used in the weighted $k$ -out-of- $n$ systems for computing reliability. The results show the better performance of the proposed approach in terms of computational time if the system bears heavier weights. Furthermore proposed scheme has additional advantage of being capable of handling fractional weights.     

Higher order shadow waves and delta shock blow up in the Chaplygin gas

The introductory part of this paper contains an overview of known results about elementary and delta shock solutions to Riemann problem for well known Chaplygin gas model (nowadays used in cosmological theories for dark energy) in terms of entropic shadow waves. Shadow waves are introduced in [17] and they are represented by shocks depending on a small parameter ε with unbounded amplitudes having a distributional limit involving the Dirac delta function. In a search for admissible solutions to all possible cases of mutual interactions of waves arising from double Riemann initial data we found same cases that cannot be resolved with already known types of elementary or shadow wave solutions. These cases are resolved by introducing a sequence of higher order shadow waves depending on integer powers of ε. It is shown that such waves have a distributional limit but only until some finite time T.     

Detecting relevant variables and interactions in supervised classification

The widely used Support Vector Machine (SVM) method has shown to yield good results in Supervised Classification problems. When the interpretability is an important issue, then classification methods such as Classification and Regression Trees (CART) might be more attractive, since they are designed to detect the important predictor variables and, for each predictor variable, the critical values which are most relevant for classification. However, when interactions between variables strongly affect the class membership, CART may yield misleading information. Extending previous work of the authors, in this paper an SVM-based method is introduced. The numerical experiments reported show that our method is competitive against SVM and CART in terms of misclassification rates, and, at the same time, is able to detect critical values and variables interactions which are relevant for classification.     

Discrete vs. continuous time implementation of a ring car following model in which overtaking is allowed

Car following models seek to describe the interactions between individual vehicles as they move along a stretch of road where the behaviour of each vehicle is dependent on the motion of the vehicle directly in front and overtaking is typically not permitted. In this work we study a modified version of the traditional car following model in which the vehicles are travelling on a closed loop and the ‘no overtaking’ restriction has been removed. The resulting model is described firstly in terms of a set of coupled continuous time delay differential equations and then in terms of their discrete time equivalents and both forms of the model are then solved numerically to analyse their post transient behaviour under a periodic perturbation. For certain parameter choices both the continuous and discrete forms of the model can exhibit chaotic behaviour but a comparison of the behaviour of the two models over a wide range of parameter values shows that the discretization can dramatically affect the type of post transient behaviour exhibited. This becomes increasingly evident as the time step used in the discrete time model is increased.     

Estimation of high-order moment-independent importance measures for Shapley value analysis

Moment-independent importance measures are increasingly used by practitioners to understand how output uncertainty may be shared between a set of stochastic inputs. Computing Borgonovo's sensitivity indices for a large group of inputs is still a challenging problem due to the curse of dimensionality and it is addressed in this article. An estimation scheme taking the most of recent developments in copula theory is developed. Furthermore, the concept of Shapley value is used to derive new sensitivity indices, which makes the interpretation of Borgonovo's indices much easier. The resulting importance measure offers a double advantage compared with other existing methods since it allows to quantify the impact exerted by one input variable on the whole output distribution after taking into account all possible dependencies and interactions with other variables. The validity of the proposed methodology is established on several analytical examples and the benefits in terms of computational efficiency are illustrated with real-life test cases such as the study of the water flow through a borehole. In addition, a detailed case study dealing with the atmospheric re-entry of a launcher first stage is completed.     

A Phase Field Approach for Martensitic Transformations in Elastoplastic Materials

A multivariant phase field model for martensitic transformations in elastoplastic materials is introduced which is in mathematical terms the regularization of a sharp interface approach. The evolution of microstructure is assumed to follow a time dependent Ginzburg-Landau equation. The coupled problem of the mechanical balance equation and the evolution equations is solved using finite elements and an implicit time integration scheme. In this work, plasticity is considered for the austenitic phase which influences the martensitic evolution. With aid of the model these interactions are studied in detail. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

利用动态贝叶斯网构建基因调控网络的研究进展

构建基因调控网络是21世纪人类科学所面临的重要挑战之一。基因调控网络是一个基因组内基因相互作用而形成的关系网络,它从全基因组水平上以系统和全局的角度来研究复杂的生命现象及其本质。本文阐述了近几年来此领域的研究进展,着重介绍利用动态贝叶斯网络重构基因调控网络的若干模型,包括加权核l1模型,正则化模型、高斯混合贝叶斯网模型和自回归时间变化模型。     

Two definitions of exponential dichotomy for skew-product semiflow in Banach spaces

In this paper we introduce a concept of exponential dichotomy for linear skew-product semiflows (LSPS) in infinite dimensional Banach spaces, which is an extension of the classical concept of exponential dichotomy for time dependent linear differential equations in Banach spaces. We prove that the concept of exponential dichotomy used by Sacker-Sell and Magalhães in recent years is stronger than this one, but they are equivalent under suitable conditions. Using this concept we where able to find a formula for all the bounded negative continuations. After that, we characterize the stable and unstable subbundles in terms of the boundedness of the corresponding projector along (forward/backward) the LSPS and in terms of the exponential decay of the semiflow. The linear theory presented here provides a foundation for studying the nonlinear theory. Also, this concept can be used to study the existence of exponential dichotomy and the roughness property for LSPS.

     

Representing the mean residual life in terms of the failure rate

In survival or reliability studies, the mean residual life or life expectancy is an important characteristic of the model. Whereas the failure rate can be expressed quite simply in terms of the mean residual life and its derivative, the inverse problem—namely that of expressing the mean residual life in terms of the failure rate—typically involves an integral of a complicated expression. In this paper, we obtain simple expressions for the mean residual life in terms of the failure rate for certain classes of distributions which subsume many of the standard cases. Several results in the literature can be obtained using our approach. Additionally, we develop an expansion for the mean residual life in terms of Gaussian probability functions for a broad class of ultimately increasing failure rate distributions. Some examples are provided to illustrate the procedure.     

Interactions between party members and local party activists: A formal model and its empirical application*

Data taken from two surveys among party members and local party activists are used to test a formal theory of intra‐party interaction at a low regional level. For this purpose a miniature version of legitimation theory is axiomatized according to Joseph D. Sneed's proposals. A possible partial model for this miniature theory is defined, terms theoretical in this theory are introduced to make up a possible model of the theory, and several variants of the model of this theory are discussed together with their empirical claims. The axiomatized theory does not only allow the interpretation of empirical correlations among attitudinal variables as effects of interactions between persons bearing those attitudes, but also compels to consider nonlinear interactions as well.     

A new criterion for the logarithmic Sobolev inequality and two applications

We give a criterion for the logarithmic Sobolev inequality (LSI) on the product space X₁×?×XN. We have in mind an N-site lattice, unbounded continuous spin variables, and Glauber dynamics. The interactions are described by the Hamiltonian H of the Gibbs measure. The criterion for LSI is formulated in terms of the LSI constants of the single-site conditional measures and the size of the off-diagonal entries of the Hessian of H. It is optimal for Gaussians with positive covariance matrix. To illustrate, we give two applications: one with weak interactions and one with strong interactions and a decay of correlations condition.     

A standby system with two types of repair persons

A continuously monitored one‐unit system, backed by an identical standby unit, is perfectly repaired by an in‐house repair person, if achievable within a random or deterministic patience time (DPT), or else by a visiting expert, who repairs one or all failed units before leaving. We study four models in terms of the limiting availability and limiting profit per unit time, using semi‐Markov processes, when all distributions are exponential. We show that a DPT is preferable to a random patience time, and we characterize conditions under which the expert should repair multiple failed units (rather than only one failed unit) during each visit. We also extend the method when life‐ and repair times are non‐exponential. Copyright © 2009 John Wiley & Sons, Ltd.