Computing Cyclic List Structures

It is argued that list structures containing cycles are useful and unobjectionable Lisp entities. If this is so, it is desirable to have a means of computing them less foreign to the equational-definition style characteristic of Lisp than are the list-structure-altering primitives rplaca and rplacd. A notion is developed of a reasonable system of mutually recursive equations, guaranteed to have a unique solution in list structures. The notion is given in terms of the computations invoked by the equations, without reference to the forms of expressions appearing in them. A variety of programming examples are presented, including a curious implementation of the Knuth-Morris-Pratt string matching algorithm. Two methods of implementing the recursive definitions facility are discussed

Combining a renewable portfolio standard with a cap-and-trade policy : a general equilibrium analysis

Thesis (S.M. in Technology and Policy)--Massachusetts Institute of Technology, Engineering Systems Division, Technology and Policy Program, 2009.Includes bibliographical references (p. 68-71).Most economists see incentive-based measures such a cap-and-trade system or a carbon tax as cost effective policy instruments for limiting greenhouse gas emissions. In actuality, many efforts to address GHG emissions combine a cap-and-trade system with other regulatory instruments. This raises an important question: What is the effect of combining a cap-and-trade policy with policies targeting specific technologies? To investigate this question I focus on how a renewable portfolio standard (RPS) interacts with a cap-and-trade policy. An RPS specifies a certain percentage of electricity that must come from renewable sources such as wind, solar, and biomass. I use a computable general equilibrium (CGE) model, the MIT Emissions Prediction and Policy Analysis (EPPA) model, which is able to capture the economy-wide impacts of this combination of policies. I have represented renewables in this model in two ways. At lower penetration levels renewables are an imperfect substitute for other electricity generation technologies because of the variability of resources like wind and solar. At higher levels of penetration renewables are a higher-cost prefect substitute for other generation technologies, assuming that with the extra cost the variability of the resource can be managed through backup capacity, storage, long range transmissions and strong grid connections. To represent an RPS policy, the production of every kilowatt hour of electricity from non-renewable sources requires an input of a fraction of a kilowatt hour of electricity from renewable sources.(cont.) The fraction is equal to the RPS target. I find that adding an RPS requiring 25 percent renewables by 2025 to a cap that reduces emissions by 80% below 1990 levels by 2050 increases the welfare cost of meeting such a cap by 27 percent over the life of the policy, while reducing the CO2-equivalent price by about 8 percent each year.by Jennifer F. Morris.S.M.in Technology and Polic

Electricity generation and emissions reduction decisions under uncertainty : a general equilibrium analysis

Thesis (Ph. D.)--Massachusetts Institute of Technology, Engineering Systems Division, 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 169-183).The electric power sector, which accounts for approximately 40% of U.S. carbon dioxide emissions, will be a critical component of any policy the U.S. government pursues to confront climate change. In the context of uncertainty in future policy limiting emissions and future technology costs, society faces the following question: What should the electricity mix we build in the next decade look like? We can continue to focus on conventional generation or invest in low-carbon technologies. There is no obvious answer without explicitly considering the risks created by uncertainty. This research investigates socially optimal near-term electricity investment decisions under uncertainty in future policy and technology costs. It employs a novel framework that models decision-making under uncertainty with learning in an economy-wide setting that can measure social welfare impacts. Specifically, a computable general equilibrium (CGE) model is formulated as a two-stage stochastic dynamic program focused on decisions in the electric power sector. The new model is applied to investigate a number of factors affecting optimal near-term electricity investments: (1) policy uncertainty, (2) expansion rate limits on low-carbon generation, (3) low-carbon technology cost uncertainty, (4) technological learning (i.e., near-term investment lowers the expected future technology cost), and (5) the inclusion of a safety valve in future policy which allows the emissions cap to be exceeded, but at a cost. In modeling decision-making under uncertainty, an optimal electricity investment hedging strategy is identified. Given the experimental design, the optimal hedging strategy reduces the expected policy costs by over 50% compared to a strategy derived using the expected value for the uncertain parameter; and by 12-400% compared to strategies developed under a perfect foresight or myopic framework. This research also shows that uncertainty has a cost, beyond the cost of meeting a policy. In the experimental design used here, uncertainty in the future policy increases the expected cost of policy by over 45%. If political consensus can be reached and the climate science uncertainties resolved, setting clear, long-term policies can minimize expected policy costs. In addition, this work contributes to the learning-by-doing literature by presenting a stochastic formulation of technological learning in which near-term investments in a technology affect the probability distribution of the future cost of that technology. Results using this formulation demonstrate that learning rates lower than those found in the literature can lead to significant additional near-term investment in low-carbon technology in order to lower the expected future cost of the technology in case a stringent policy is adopted.Ultimately, this dissertation demonstrates that near-term investments in low-carbon technologies should be greater than what would be justified to meet near-term goals alone. Near-term low-carbon investments can lower the expected cost of future policy by developing a less carbon-intensive electricity mix, spreading the burden of emissions reductions over time, helping to overcome technology expansion rate constraints, and reducing the expected future cost of low-carbon technologies-all of which provide future flexibility in meeting a policy. The additional near-term cost of low-carbon investments is justified by the future flexibility that such investments create. The value of this flexibility is only explicitly considered in the context of decision-making under uncertainty.by Jennifer Faye Morris.Ph.D

Risk-taking and inhibitory control in behaviourally inhibited and disinhibited preschool children

The temperament style Behavioural Inhibition (BI) has been implicated as a risk factor for the development of internalising disorders such as anxiety. Of interest is what factors influence the developmental trajectories of both inhibited and disinhibited children and the development of psychopathology. One such factor is risk-taking behaviour. Using the computer based Balloon Analogue Risk Task, we assessed risk taking behaviour in behaviourally inhibited (n = 27) and behaviourally disinhibited (n = 43) children. This is the first study to examine the relationship between BI, executive functioning and risk-taking. The results indicated Behavioural Inhibition was not related to risk-taking but that inhibitory control predicted reward focused results. These findings illustrate how inhibitory control affects risk-taking and risk avoidance in both inhibited and disinhibited children

Analysis of controller bandwidth interactions for vector-controlled VSC connected to very weak AC grids

Stability assessment of conventional vector current control (VCC) of voltage-source converters (VSCs) in weak grids has not been standardized. In this paper, a small signal model is derived to quantify the maximum active power transfer in a very weak grid across a much wider range of controller bandwidths than has previously been investigated. A novel investigation of the VCC-VSC controller bandwidth interactions between inner and outer control loops, including the phase-locked loop (PLL) dynamics, is demonstrated and a stability bubble of safe operating points is established. Robustness of the stability bubble under different SCRs is investigated and dynamic performance considerations are introduced to form a reduced operating region with good transient performance. The controller gains within this region allow rated power transfer in inverting mode and good dynamic performance with no modifications to the conventional VCC structure. For very weak grids, it is recommended that PLL bandwidths between 5 and 30 Hz are avoided. If a slow PLL bandwidth is chosen, the outer loop q-axis should have a fast bandwidth; with a fast PLL, the outer loop q-axis control bandwidth should be reduced. In all cases, the outer loop d-axis should be slowed down to reach the power transfer limit

The Cost of Climate Policy in the United States

We consider the cost of meeting emissions reduction targets consistent with a G8 proposal of a 50 percent global reduction in emissions by 2050, and an Obama Administration proposal of an 80 percent reduction over this period. We apply the MIT Emissions Prediction and Policy Analysis (EPPA), modeling these two policy scenarios if met by applying a national cap-and-trade system, and compare results with an earlier EPPA analysis of reductions of this stringency. We also test results to alternative assumptions about program coverage, banking behavior, and cost of technology in the electric power sector. Two main messages emerge from the exercise. First, technology uncertainties have a huge effect on the generation mix but only a moderate effect on the emissions price and welfare cost of achieving the assumed targets. Measured in terms of changes in economic welfare, the economic cost of 80 percent reduction by 2050 is in the range of 2 to 3% by 2050, with CO2 prices between $48 and$67 in 2015 rising to between $190 and$266 by 2050. Second, implementation matters. When an idealized economy-wide cap-and-trade is replaced by coverage omitting some sectors, or if the credibility of long-term target is weak (limiting banking behavior) prices and welfare costs change substantially.Massachusetts Institute of Technology. Center for Energy and Environmental Policy Research

Observations on Expedited Systems Engineering Practices in Military Rapid Development Projects

This research, conducted in the Systems Engineering Research Center (SERC), examined systems engineering and engineering management practices for military rapid capability and urgent needs programs. Lifecycle of urgent needs programs is driven by “time to market” as opposed to complete satisfaction of static requirements, with delivery expected in months versus years/decades. The processes and practices applied to urgent needs must add value and not require an excessive bureaucratic oversight to implement, while at the same time address, understand, and manage risk such that programs can understand better where to include, truncate, eliminate, tailor, or scale systems engineering practices and processes. Focusing on aspects of the product, process, and people of military rapid organizations, the analysis showed that these organizations have the right team, develop innovative conceptual solutions, quickly prune the design space, and identify appropriate designs that can deliver warfighting capability expeditiously. While these observations may not seem new, they provide the foundation for a broader framework of rapid development, which is the subject of ongoing research

Observations on Expedited Systems Engineering Practices in Military Rapid Development Projects

This research, conducted in the Systems Engineering Research Center (SERC), examined systems engineering and engineering management practices for military rapid capability and urgent needs programs. Lifecycle of urgent needs programs is driven by “time to market” as opposed to complete satisfaction of static requirements, with delivery expected in months versus years/decades. The processes and practices applied to urgent needs must add value and not require an excessive bureaucratic oversight to implement, while at the same time address, understand, and manage risk such that programs can understand better where to include, truncate, eliminate, tailor, or scale systems engineering practices and processes. Focusing on aspects of the product, process, and people of military rapid organizations, the analysis showed that these organizations have the right team, develop innovative conceptual solutions, quickly prune the design space, and identify appropriate designs that can deliver warfighting capability expeditiously. While these observations may not seem new, they provide the foundation for a broader framework of rapid development, which is the subject of ongoing research

Toward Better Training in Peer Assessment: Does Calibration Help?

For peer assessments to be helpful, student reviewers need to submit reviews of good quality. This requires certain training or guidance from teaching staff, lest reviewers read each other\u27s work uncritically, and assign good scores but offer few suggestions. One approach to improving the review quality is calibration. Calibration refers to comparing students\u27 individual reviews to a standard—usually a review done by teaching staff on the same reviewed artifact. In this paper, we categorize two modes of calibration for peer assessment and discuss our experience with both of them in a pilot study with Expertiza system

Stability limits and tuning recommendation of the classical current control providing inertia support

The drastic increase in renewable energy sources in power grids has raised stability concerns. A particular concern exists in the ability of the converters to preserve frequency stability, due to their inherent lack of inertia provision. Grid forming converters have been presented as a solution to this issue, however the control structure for such converters is significantly different from the vector current control structures utilized by most installed control-converter systems. The classical current controller with a Phase Locked Loop (PLL) can be modified to provide inertia by including an additional control loop that injects active power in the case of a frequency event. This paper presents a detailed stability study, using a small signal model, and presents a set of controller tuning recommendations for the classical current controller with inertia emulation capability. The investigation found that the classical current and PLL tuning decreases the power that can be provided using the inertia emulation loop. Reducing the current loop time constant can allow for stable inertia emulation with classical vector current control