Worcester Polytechnic Institute

About: Worcester Polytechnic Institute is a education organization based out in Worcester, Massachusetts, United States. It is known for research contribution in the topics: Computer science & Population. The organization has 6270 authors who have published 12704 publications receiving 332081 citations. The organization is also known as: WPI.

Policy insights from a green supply chain optimisation model

Abstract: This paper introduces a practical supply chain optimisation model that incorporates both economic and carbon emission objectives. The proposed model is implemented to examine the possible economic and environmental trade-offs for various carbon-pricing and fuel-pricing scenarios in an actual case company representing the discrete, durable parts manufacturing sector. Analysis of the numerical results provides important managerial implications and policy insights. For industry practitioners, the findings can assist in identifying the critical activities along the supply chain on which to focus in order to minimise the cost implications of a carbon-pricing regulation. For related policy-makers, the findings provide insights on how carbon should be priced to make meaningful impacts on emissions reduction while matching variations in fuel prices.

Best-performing US mutual fund families from 1993 to 2008: Evidence from a novel two-stage DEA model for efficiency decomposition

Abstract: When analyzing relative performance, especially at the institutional level, the traditional data envelopment analysis (DEA) models do not recognize vastly different and important activities as separate functions and therefore cannot identify which function may be the main source of inefficiency. We propose a novel two-stage DEA model that decomposes the overall efficiency of a decision-making unit into two components and demonstrate its applicability by assessing the relative performance of 66 large mutual fund families in the US over the period 1993–2008. By decomposing the overall efficiency into operational management efficiency and portfolio management efficiency components, we reveal the best performers, the families that deteriorated in performance, and those that improved in their performance over the sample period. We also make frontier projections for poorly performing mutual fund families and highlight how the portfolio managers have managed their funds relative to the others during financial crisis periods.

Studies of Warning Coloration and Mimicry. IV. A. Mathematical Model of Model-Mimic Frequencies

Abstract: One of the principal tenets of the Batesian theory of mimicry is that the effectiveness of pseudaposematic coloration is reduced as the incidence of models decreases in relation to that of the mimics. This is to be expected since learning efficiency of predators will be reduced if models become scarce. Field studies (Carpenter 1932, 1949; Ford 1936) have shown that mimicry is, indeed, less effective where the frequency of models is low. Unfortunately, the following generalization is often assumed: if the model outnumbers the mimic, the pseudaposematic coloration is effective, whereas if the mimic outnumbers the model, the system breaks down. Sometimes the principle is stated qualitatively: the mimic must be rare with respect to the model. However, as pointed out by Sheppard (1959) and. Brower (1960), there is nothing unique about the 50-50% ratio. In studies by Brower using caged starlings as predators and meal worms as artificial models and mimics, it was found that the effectiveness of mimicry in a population containing 60% mimics was of the same order of magnitude as that of one containing only 30%. The effectiveness of aposematic and pseudaposematic coloration depends upon a number of variables in addition to model frequency. One is the ability of the predator to remember the aposematic signal. This in turn depends upon the inherent ability of the predator to learn, the nature of the warning signal, and the intensity of the stimulus that the predator receives upon sampling the model. Sheppard (1958) has called attention to the last factor: "An animal sufficiently obnoxious to make predators avoid its colour pattern, even when having encountered only one, could give protection to a mimetic form as common as, or commoner than, the model." In addition, the effectiveness of pseudaposematic coloration depends on the degree of similarity of the model and mimic. Other variables such as hunger, although influencing behavior strongly, may be considered relatively unimportant since their effects would be averaged out over a large sample. It would be advantageous if a mathematical model could be used to describe the situation obtaining between a model and a mimic. Although it should be possible to construct such a model employing all of the variables mentioned above, a simplified model is less cumbersome to handle, and at our present state of knowledge appears entirely adequate. As more data accumulate, it may become desirable to elaborate the simple model presented here. The following assumptions are made: (1) The effectiveness of the mimic pattern is 100%, i.e., the mimic cannot be distinguished visually from the model. This is patently untrue except in the case of artificial models and mimics analyzed below, but it must be admitted that in many cases of known mimicry this condition is approached closely. (2) The strength of the model's stimulus and the ability of the predator to remember it can be expressed in terms of a single parameter, n. This parameter corresponds to the total number of individuals (including the original model) protected by the predator rejecting the model, remembering the stimulus received from it, and thus avoiding both models and mimics until it forgets and renews sampling.

Consideration of thermodynamic, transport, and mechanical properties in the design of polymer electrolyte membranes for higher temperature fuel cell operation

Abstract: A phenomenological theory is provided for water sorption and proton transport in polymer electrolyte membranes (PEMs) as well as in polymer-inorganic nanocomposite membranes (NCPEMs) that not only serves to rationalize the sorption and conductivity behavior of conventional PEMs such as Nafion but also provides a framework for rational design of improved PEMs and NCPEMs. The thermodynamic model, which considers the effect of osmotic pressure on the activity of free water within the membrane pores, predicts the entire sorption isotherm and provides a plausible explanation for the so-called Schroeder's paradox. The transport model incorporates the various mechanisms of proton transport, namely, surface hopping, Grotthuss diffusion, and en masse diffusion. As the design of alternate PEMs suitable for effective proton transport under hot and dry conditions is a key current technolog- ical goal, the rational design of NCPEMs for this purpose is considered here in detail on the basis of an extension of the transport model to account for the influence of the inclusion of functional additives in NCPEMs. The results also point to the reason that Nafion is an excellent PEM, because the hydrophobic nature of its backbone induces water away from surface into pore bulk where efficient proton diffusion occurs. V C 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2183-2200, 2006