1,720,957 research outputs found
Managing supply chain risks with dual sourcing: Bayesian learning of censored supply capacity
No full textDual sourcing is a common strategy for mitigating supply chain risks, with supply capacity uncertainty being one of the most significant risks. However, firms often have limited knowledge about uncertain supply capacity, and can only observe it when the delivered quantity is less than the ordered amount. This leads to censored supply capacity observations. To investigate how supply capacity learning affects dual-sourcing decisions, we propose a model of a firm sourcing non-storable substitute products from an expensive reliable supplier and an inexpensive unreliable supplier to meet a deterministic time-varying demand over a finite horizon. The unreliable supplier has a random capacity with an unknown parameter. The firm updates its belief about this parameter using Bayesian learning and adapts its sourcing decisions to balance the tradeoff between maximizing current profits based on its current belief (exploitation) and increasing the precision of its belief for future periods (exploration). We use Bayesian dynamic programming to determine the firm's myopic sourcing policy and partially characterize its optimal sourcing policy. We apply a state space reduction technique to Weibull distributed capacity, resulting in an inductively solvable optimization problem. The optimal sourcing policy can be obtained under a condition that ensures splitting the demand between the suppliers is optimal. For exponentially distributed capacity, the optimization problem has a recursive closed-form solution, and the optimal sourcing policy is such that the optimal order quantity from the reliable (unreliable) supplier is smaller (greater) than the myopic quantity. We complement our analytical results with numerical examples and discuss extensions to random demand and inventory carryover
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Markov decision processes with multidimensional action spaces
No full textWe study controlled Markov processes where multiple decisions need to be made for each state. We present conditions on the cost structure and the state transition mechanism of the process under which optimal decisions are restricted to a subset of the decision space. As a result, the numerical computation of the optimal policy may be significantly expedited.Markov processes Dynamic programming Multiple servers
Optimal stochastic scheduling and routing in queueing networks.
No full textQueueing networks are extensively used in the study of systems such as communication, computer, and manufacturing networks. Presently there exists some conceptual understanding of many underlying issues of network performance; yet, there remain fundamental issues that are not well understood and need to be investigated. Such issues are related to efficient network resource utilization and routing under imperfect information. In this dissertation we investigate stochastic scheduling, resource allocation and dynamic routing problems arising in queueing networks. We determine optimal policies or derive qualitative properties of optimal policies for the problems described below. We study the problem of optimally scheduling time-critical tasks in multi-class queueing systems. Two different versions of the problem are considered: (i) If the service of a task does not begin by a certain deadline, the task is lost and a fixed cost is incurred; and (ii) if the service of a task is completed at a time other than a certain due date, a penalty proportional to the earliness or tardiness is incurred. We determine properties of dynamic nonidling strategies that minimize infinite horizon expected costs. Next we consider the problem of optimally scheduling tasks in a multi-server system consisting of two interconnected queues. Tasks incur an instantaneous holding cost during the time they remain in the system. We establish sufficient conditions on the service times, the holding costs, and the interconnection process under which it is possible to explicitly determine the strategy that minimizes the total expected discounted cost. Finally we investigate the following decentralized routing problem. We consider a queueing system consisting of two service stations and two controllers, one in front of each station. Customers arriving at a controller's site are to be routed to one of the two stations. Each controller has perfect knowledge of the queue length in its own station and receives information about the other station's queue length with delay of one time unit. We explicitly determine the controllers' routing strategies that minimize the customers' total flowtime.PhDElectrical Engineering: SystemsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/104185/1/9501012.pdfDescription of 9501012.pdf : Restricted to UM users only
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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