Worst-Case Analysis of Process Flexibility Designs

Theoretical studies of process flexibility designs have mostly focused on expected sales. In this paper, we take a different approach by studying process flexibility designs from the worst-case point of view. To study the worst-case performances, we introduce the plant cover indices (PCIs), defined by bottlenecks in flexibility designs containing a fixed number of products. We prove that given a flexibility design, a general class of worst-case performance measures can be expressed as functions of the design’s PCIs and the given uncertainty set. This result has several major implications. First, it suggests a method to compare the worst-case performances of different flexibility designs without the need to know the specifics of the uncertainty sets. Second, we prove that under symmetric uncertainty sets and a large class of worst-case performance measures, the long chain, a celebrated sparse design, is superior to a large class of sparse flexibility designs, including any design that has a degree of two on each of its product nodes. Third, we show that under stochastic demand, the classical Jordan and Graves (JG) index can be expressed as a function of the PCIs. Furthermore, the PCIs motivate a modified JG index that is shown to be more effective in our numerical study. Finally, the PCIs lead to a heuristic for finding sparse flexibility designs that perform well under expected sales and have lower risk measures in our computational study.National Science Foundation (U.S.) (Grant CMMI-0758069)Masdar Institute of Science and TechnologyFord-MIT AllianceNatural Sciences and Engineering Research Council of Canada (Postgraduate Scholarship

Analyzing process flexibility: A distribution-free approach with partial expectations

We develop a distribution-free model to evaluate the performance of process flexibility structures when only the mean and partial expectation of the demand are known. We characterize the worst-case demand distribution under general concave objective functions, and apply it to derive tight lower bounds for the performance of chaining structures under the balanced systems (systems with the same number of plants and products). We also derive a simple lower bound for chaining-like structures under unbalanced systems with different plant capacities. Keywords: Process flexibility; Distributionally-robust analysis; Chaining; Production system desig

Sparse Signal Processing Concepts for Efficient 5G System Design

As it becomes increasingly apparent that 4G will not be able to meet the emerging demands of future mobile communication systems, the question what could make up a 5G system, what are the crucial challenges and what are the key drivers is part of intensive, ongoing discussions. Partly due to the advent of compressive sensing, methods that can optimally exploit sparsity in signals have received tremendous attention in recent years. In this paper we will describe a variety of scenarios in which signal sparsity arises naturally in 5G wireless systems. Signal sparsity and the associated rich collection of tools and algorithms will thus be a viable source for innovation in 5G wireless system design. We will discribe applications of this sparse signal processing paradigm in MIMO random access, cloud radio access networks, compressive channel-source network coding, and embedded security. We will also emphasize important open problem that may arise in 5G system design, for which sparsity will potentially play a key role in their solution.Comment: 18 pages, 5 figures, accepted for publication in IEEE Acces

Design Performance Measurement in the Construction Sector: A Pilot Study

This paper examines the role and deployment of design performance measurements (DPMs) in the construction industry, focusing on the consulting engineering sector, the design 'heart' of construction. Compared with manufacturing, there has been very little research on the use of DPMs in construction, and firms often struggle to find appropriate performance indicators. Using results from structured questionnaires, the paper shows that the few DPMs which do exist focus mainly on cost. Other measures are needed to address quality, innovative performance and client satisfaction. In contrast to manufacturing, DPMs in construction also need to address the project-based, multi-firm and non-routine nature of construction design, as well as the separation of design from manufacturing, build and operation. Interviews and workshops with industrialists were used to identify recent DPM practices in construction and combine these with lessons from other sectors. The resulting DPM tools provide guidance on how to: (a) integrate design into wider business processes in construction; (b) identify key design indicators, at both project and firm level; and (c) use DPMs to provide a balanced scorecard for design performance.performance indicators, design integration, design indicators, construction industry

Density and Strength of Ties in Innovation Networks: An Analysis of Multi-Media and Biotechnology

In this article we provide an empirical illustration of hypotheses, developed in the literature, on the role of density and strength of ties in innovation networks.We study both exploration and exploitation networks in the Dutch multimedia and pharmaceutical biotechnology industry.We find support for most of our hypotheses but not all.These findings, in line with the mixed results in the literature, seem to indicate that the distinction between exploration versus exploitation, albeit useful, is still too general.There may be a stronger sectoral effect in how exploration and exploitation settle in network structural properties than anticipated thus far.innovation;networks;density;strength of ties;governance;biotechnology;multimedia

Density And Strength Of Ties In Innovation Networks: A Competence And Governance View

This article studies density and strength of ties in innovation networks. It combines issues of ‘competence’ with issues of ‘governance’. It argues that in networks for exploration there are good reasons, counter to the thesis of the ‘strength of weak ties’, for a dense structure of ties that are strong in most dimensions. In exploitation, there are good reasons for structures that are non-dense, with ties that are strong in other dimensions than in networks for exploration. Evidence is presented from two longitudinal empirical studies of the emergence and development of networks in the multimedia and pharmaceutical biotechnology industries.governance;innovation;networks;biotechnology;multi-media;strength of ties