Kinetics of the enzymatic degradation of poly(vinyl acetate) in solution

The enzymatic degradability of poly(vinyl acetate) was investigated in toluene solutions at various temperatures with hog pancreas lipase. The polymer degraded by specific scission to yield oligomeric products with a molecular weight of 700. Continuous distribution kinetics were used to determine the rate coefficients. The variation of the rate coefficients with the temperature indicated an optimum at 55°C. The p‐toluene sulfonic acid catalyzed degradation of poly(vinyl acetate) was also investigated. The degradation mechanism was random chain scission, and the energy of activation for degradation was determined from the variation of the rate coefficients with the temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2579–2582, 2003     

An explicit predictor-corrector solver with application to seismic wave modelling

Wave-equation-based forward modelling using explicit finite-difference methods is a standard technique for calculating synthetic seismograms. The stability criterion restricts the size of the time step. In this paper a predictor–corrector method for solving the wave equation is described which allows the use of a larger time step. A stability analysis of the method is also carried out. Parallel implementation of the algorithm is described for a distributed computing environment which makes use of MPI and PVM message passing calls for communication between processors.     

A new controller for boost dc–dc converters based on a novel sliding surface

ABSTRACT

In this paper, two control schemes for boost converters affected by uncertainties in input voltage and load are proposed. The boost converter dynamics is redefined in terms of new state variables to facilitate the use of a disturbance observer that can estimate matched and unmatched disturbances. A sliding surface, which is new in the context of boost converters, is proposed to enable tracking and regulation of output voltage without requiring measurement of input voltage and load current. The stability of the overall system including the disturbance observer, the sliding variable and the output is proved. The performance of the schemes is assessed for regulation of output voltage and tracking of reference voltage by simulation as well as experimentation in which various types of uncertainties and various types of reference voltages are considered.     

Role of MoS2 morphology on wear and friction under spectrum loading conditions

One of the ways by which grease is evaluated is by using a four‐ball wear test using ASTM D2266. However, actual applications may require bearings to be subjected to spectrum loading conditions. This study focuses on using ball milling to mitigate the wear from sharp edges in the MoS₂ particles. Two different blends of greases were formulated using MoS₂ in the as‐received state (unmilled) and milled MoS₂; they were tested under spectrum loading conditions where the load and frequency of the tests were treated as variables. It was found that ball milling of the MoS₂ significantly reduces the wear under spectrum loading condition both for ramp‐up and ramp‐down conditions. It was also shown that shortening the time step for both the ramp‐up and ramp‐down cycles resulted in larger wear for unmilled MoS₂ particles in comparison with milled MoS₂ particles in grease. The milling process did not play a significant role when frequency of the test was either ramped up or down. Copyright © 2015 John Wiley & Sons, Ltd.     

Robust input–output linearisation using uncertainty and disturbance estimation

This article proposes a new approach to robustify an input–output linearisation controller. The robustification is achieved by estimating the uncertainties and external unmeasurable disturbances using a novel uncertainty and disturbance estimator. A significant feature of the proposed approach is that it does not need any information about the uncertainties. The stability of the system and the estimator is established. Effectiveness of the proposed approach is demonstrated through application to the wing rock motion control problem.     

The large scale electric power system as a distributed continuum

By modeling an electric power system of generators and transmissions lines as a continuum, a nonlinear partial differential equation is written which exhibits the travelling wave behavior that has been observed in experiments with synchronized phasor measurements. The fact that disturbances spread through the interconnected power system with a certain velocity of propagation is reasonable but not quantitatively well understood. The model relates the velocity of propagation to parameters in the distributed model. Numerical simulations of the continuum model are presented     

Managing carbon regulatory risk in utility resource planning: Current practices in the Western United States

Concerns about global climate change have substantially increased the likelihood that future policy will seek to minimize carbon dioxide emissions. As such, even today, electric utilities are making resource planning and investment decisions that consider the possible implications of these future carbon regulations. In this article, we examine the manner in which utilities assess the financial risks associated with future carbon regulations within their long-term resource plans. We base our analysis on a review of the most recent resource plans filed by 15 electric utilities in the Western United States. Virtually all of these utilities made some effort to quantitatively evaluate the potential cost of future carbon regulations when analyzing alternate supply- and demand-side resource options for meeting customer load. Even without federal climate regulation in the US, the prospect of that regulation is already having an impact on utility decision-making and resource choices. That said, the methods and assumptions used by utilities to analyze carbon regulatory risk, and the impact of that analysis on their choice of a particular resource strategy, vary considerably, revealing a number of opportunities for analytic improvement. Though our review focuses on a subset of US electric utilities, this work holds implications for all electric utilities and energy policymakers who are seeking to minimize the compliance costs associated with future carbon regulations.     

An adaptive out-of-step relay [for power system protection]

The paper describes the development of an adaptive out-of-step relay, from the formulation of its concept to its field implementation at the Florida-Georgia interface. Adaptive relaying seeks to make adjustments to the relay characteristics as power system conditions change, thereby making the relay more attuned to the prevailing power system conditions. The work described here began as a theoretical examination of the out-of-step relaying application, its possible shortcomings, and the opportunities to make adaptive improvements. It is shown that for a system that behaves primarily as a two-machine power system, the out-of-step relay could be made more secure by applying the principle of equal area criterion. The paper describes the theory of such a relay, its hardware configuration, and the system as it is installed in the field. The newly developed technology of synchronized phasor measurements plays an important role in the realization of this relay. The paper includes a summary of the field experience gathered over a period of one year     

How many Enrons? Mark-ups in the stated capital cost of independent power producers' (IPPs') power projects in developing countries

I analyze the determinants of the stated capital cost of IPPs' power projects which significantly influences their price of power. I show that IPPs face a strong incentive to overstate their capital cost and argue that effective competition or regulatory scrutiny will limit the extent of the same. I analyze the stated capital costs of combined cycle gas turbine (CCGT) IPP projects in eight developing countries which became operational during 1990–2006 and find that the stated capital cost of projects selected without competitive bidding is 44–56% higher than those selected with competitive bidding, even after controlling for the effect of cost differences among projects. The extent to which the stated capital costs of projects selected without competitive bidding are higher compared those selected with competitive bidding, is a lower bound on the extent to which they are overstated. My results indicate the drawbacks associated with a policy of promoting private sector participation without an adequate focus on improving competition or regulation.