Slack-variable models versus Scheffé's mixture models

Slack-variable models are compared against Scheffé's polynomial model for mixture experiments. The notion of model equivalence and the use of various diagnostic measures provide effective tools in making such comparisons, particularly when the experimental region is highly constrained. It is demonstrated that the choice of the best fitting model, through variable selection, depends on which mixture component is selected as a slack variable, and on the size of the fitted model. In addition, the equivalence of two well-known representations of a complete mixture model is shown to be valid. Two numerical examples are presented.     

Computing maximum likelihood estimates from type II doubly censored exponential data

It is well-known that, under Type II double censoring, the maximum likelihood (ML) estimators of the location and scale parameters, θ and δ, of a twoparameter exponential distribution are linear functions of the order statistics. In contrast, when θ is known, theML estimator of δ does not admit a closed form expression. It is shown, however, that theML estimator of the scale parameter exists and is unique. Moreover, it has good large-sample properties. In addition, sharp lower and upper bounds for this estimator are provided, which can serve as starting points for iterative interpolation methods such as regula falsi. Explicit expressions for the expected Fisher information and Cramér-Rao lower bound are also derived. In the Bayesian context, assuming an inverted gamma prior on δ, the uniqueness, boundedness and asymptotics of the highest posterior density estimator of δ can be deduced in a similar way. Finally, an illustrative example is included.     

Improving flexibility and efficiency by adding parallelism to genetic algorithms

In this paper we develop a study on several types of parallel genetic algorithms (PGAs). Our motivation is to bring some uniformity to the proposal, comparison, and knowledge exchange among the traditionally opposite kinds of serial and parallel GAs. We comparatively analyze the properties of steady-state, generational, and cellular genetic algorithms. Afterwards, this study is extended to consider a distributed model consisting in a ring of GA islands. The analyzed features are the time complexity, selection pressure, schema processing rates, efficacy in finding an optimum, efficiency, speedup, and resistance to scalability. Besides that, we briefly discuss how the migration policy affects the search. Also, some of the search properties of cellular GAs are investigated. The selected benchmark is a representative subset of problems containing real world difficulties. We often conclude that parallel GAs are numerically better and faster than equivalent sequential GAs. Our aim is to shed some light on the advantages and drawbacks of various sequential and parallel GAs to help researchers using them in the very diverse application fields of the evolutionary computation.     

Examining Familial-Based Academic Success Factors in Urban High School Students: The Case of Puerto Rican Female High Achievers

ABSTRACT

This article works to dispel the myth that Puerto Rican female urban high school students living in poverty are not capable of performing at high academic levels. This article attempts to counteract these beliefs by describing the four success factors that seven Puerto Rican female high school students attribute to their high academic achievement. These success factors are: (1) religiosity and extracurricular activities as sources of social capital, (2) affirming and maintaining a Puerto Rican identity, (3) maternal influences on students' academic achievement and, (4) the potential for caring teachers and other school staff to influence high academic achievement. Finally, our findings suggest that opportunities for Latinas and other youth of color are still inequitably structured in large, comprehensive high schools. Hence, we argue that schools must continue to bridge the large gap between themselves and the families/communities they serve and utilize the funds of knowledge and social capital that their students already bring to school.     

Speed in the Internationalization Process of the Firm

While firm internationalization processes have been understood as being dynamic, the dimension of speed has rarely been the main focus of research efforts, which, until a decade ago, focused principally on explaining sequences of entry modes and choices of markets. The emergence of the study of international entrepreneurship has enhanced the role of speed, although this has usually been measured in terms of the time lag between a firm's foundation and its initial international action, with little attempt at defining and explaining the speed of the process once it is under way. This study reviews the concept of speed from an internationalization perspective, describes the multidimensional nature of the concept and sets out the different aspects that link timescales with the types of changes – continuous and discontinuous – that take place during internationalizing processes. The paper concludes with a research agenda as a guide for future work on considering the role of speed in the internationalization process.     

Inter-firm collaborations and supply chain coordination: review of key elements and case study

Considering the effects of globalisation, the increase of production and energy costs, and the introduction of advanced technologies, companies need to change their way of doing business if they want to stay competitive. One way of doing this is to establish collaborations with suppliers, distributors and retailers, in order to exchange products efficiently and create value for customers. Nevertheless, the structure of the collaboration must be designed carefully and some coordination mechanisms must be implemented to support this way of doing business. In this article, we first analyse: why companies work together, how they should build their partnership, and which strategies they can implement to facilitate coordination of supply chain activities. We then report a case study of collaboration in the forest industry that shows the benefits of implementing coordination mechanisms as well as the necessity of using incentives to better share these benefits.     

Waste identification diagrams

Value Stream Mapping (VSM) is a very popular tool in lean environments to represent production flows, mapping value stream of a product or family of products, and helps to identify some types of waste. Although very popular, this tool has some limitations as already described in many publications, especially in terms of restrictions in showing most types of waste as well as in its inability to represent various production routes. The purpose of this study is to introduce the waste identification diagram (WID), a new tool to represent production units with its different forms of waste, which overcomes some VSM limitations. The originality of WID comes from the use of its symbols’ dimensions to convey, in a visual and immediate way, relevant information about a production unit. In this paper, WID is applied on a production unit of a lift manufacturer, for testing its performance and comparing it to VSM. The main findings are that WID is in general more effective than VSM in terms of representation of complex production units and in terms of identification of more forms of waste. WID must however overcome some of its limitations such as the lack of information-flow representation and the links to suppliers and clients.     

Influence diagnostics in the capital asset pricing model under elliptical distributions

In this paper we consider the Capital Asset Pricing Model under Elliptical (symmetric) Distributions. This class of distributions, which contains the normal distribution, t, contaminated normal and power exponential, among others, offers a more flexible framework for modelling asset prices or returns. In order to analyze the sensibility to possible outliers and/or atypical returns of the maximum likelihood estimators, the local influence method was implemented. The results are illustrated by using a set of shares from companies who trade in the Chilean Stock Market. Our main conclusion is that symmetric distributions having heavier tails than those of the normal distribution, especially the t distribution with small degrees of freedom, show a better fit and allow the reduction of the influence of atypical returns in the maximum likelihood estimators.     

The minimal overlap rule revisited

This paper provides an analysis of the Minimal Overlap Rule, a solution for bankruptcy problems introduced by O’Neill (1982). We point out that this rule can be understood as a composition of Ibn Ezra’s proposal and the recommendation given by the Constrained Equal Loss Rule. Following an interpretation of bankruptcy problems in terms of TU games, we show that the Minimal Overlap Value is the unique solution for bankruptcy games which satisfies Anonymity and Core Transition Responsiveness.