http://dspace.mit.edu The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. Search the Channel search http://dspace.mit.edu/simple-search http://hdl.handle.net/1721.1/41527 Title: Perfect Implementation of Normal-Form Mechanisms <br/> <br/>Authors: Izmalkov, Sergei; Lepinski, Matt; Micali, Silvio <br/> <br/>Abstract: Privacy and trust affect our strategic thinking, yet they have not been precisely modeled in mechanism design. In settings of incomplete information, traditional implementations of a normal-form mechanism ---by disregarding the players' privacy, or assuming trust in a mediator--- may not be realistic and fail to reach the mechanism's objectives. We thus investigate implementations of a new type.We put forward the notion of a perfect implementation of a normal-form mechanism M: in essence, an extensive-form mechanism exactly preserving all strategic properties of M, WITHOUT relying on a trusted mediator or violating the privacy of the players. We prove that ANY normal-form mechanism can be perfectly implemented by a PUBLIC mediator using envelopes and an envelope-randomizing device (i.e., the same tools used for running fair lotteries or tallying secret votes). Differently from a trusted mediator, a public one only performs prescribed public actions, so that everyone can verify that he is acting properly, and never learns any information that should remain private. Mon, 26 Feb 2007 22:58:59 GMT http://hdl.handle.net/1721.1/41526 Title: Gesture in Automatic Discourse Processing <br/> <br/>Authors: Eisenstein, Jacob <br/> <br/>Abstract: Computers cannot fully understand spoken language without access to the wide range of modalities that accompany speech. This thesis addresses the particularly expressive modality of hand gesture, and focuses on building structured statistical models at the intersection of speech, vision, and meaning.My approach is distinguished in two key respects. First, gestural patterns are leveraged to discover parallel structures in the meaning of the associated speech. This differs from prior work that attempted to interpret individual gestures directly, an approach that was prone to a lack of generality across speakers. Second, I present novel, structured statistical models for multimodal language processing, which enable learning about gesture in its linguistic context, rather than in the abstract.These ideas find successful application in a variety of language processing tasks: resolving ambiguous noun phrases, segmenting speech into topics, and producing keyframe summaries of spoken language. In all three cases, the addition of gestural features -- extracted automatically from video -- yields significantly improved performance over a state-of-the-art text-only alternative. This marks the first demonstration that hand gesture improves automatic discourse processing. Tue, 06 May 2008 22:58:59 GMT http://hdl.handle.net/1721.1/41525 Title: Analysis of U.S. Greenhouse Gas Tax Proposals <br/> <br/>Authors: Metcalf, Gilbert E.; Paltsev, Sergey.; Reilly, John M.; Jacoby, Henry D.; Holak, Jennifer <br/> <br/>Abstract: The U.S. Congress is considering a set of bills designed to limit the nation’s greenhouse gas (GHG) emissions. Several of these proposals call for a cap-and-trade system; others propose an emissions tax. This paper complements the analysis by Paltsev et al. (2007) of cap-and-trade bills and applies the MIT Emissions Prediction and Policy Analysis (EPPA) model to carry out an analysis of the tax proposals. Several lessons emerge from this analysis. First, a low starting tax rate combined with a low rate of growth in the tax rate will not reduce emissions significantly. Second, the costs of GHG reductions are reduced with the inclusion of non-CO2 gases in the carbon tax scheme. The costs of the Larson plan, for example, fall by 20% with inclusion of the other GHGs. Third, welfare costs of the policies can be affected by the rate of growth of the tax, even after controlling for cumulative emissions. Fourth, a carbon tax – like any form of carbon pricing – is regressive. However, general equilibrium considerations suggest that the short-run measured regressivity may be overstated. A portion of the carbon tax is passed back to workers, owners of equity, and resource owners. To the extent that relatively wealthy resource and equity owners bear some fraction of the tax burden, the regressivity will be reduced. Additionally, the regressivity can be offset with a carefully designed rebate of some or all of the revenue. Finally, the carbon tax bills that have been proposed or submitted are for the most part comparable to many of the carbon cap-and-trade proposals that have been suggested. Thus the choice between a carbon tax and cap-and-trade system can be made on the basis of considerations other than their effectiveness at reducing emissions over some control period. Either approach (or some hybrid of the two approaches) can be equally effective at reducing GHG emissions in the United States. <br/> <br/>Description: Abstract in HTML and technical report in PDF available on the MIT Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/). Sat, 29 Mar 2008 22:58:59 GMT http://hdl.handle.net/1721.1/41524 Title: Impact of Sulfur and Carbonaceous Emissions from International Shipping on Aerosol Distributions and Direct Radiative Forcing <br/> <br/>Authors: Wang, Chien.; Kim, Dongchul. <br/> <br/>Abstract: We describe in this report an effort using the MIT/NCAR three-dimensional aerosol-climate model to study the impact of ship emissions on chemical composition and radiative forcing of aerosols. Our results indicate that international shipping can be a non-negligible factor in determining the radiative forcing of aerosols over specific regions with intensive ship activities. These places include the European, eastern Asian, and American coastal regions. The global mean aerosol radiative forcing caused by the ship emissions ranges from -12.5 to -23 mW/m^2, depending on whether the mixing between black carbon and sulfate is included in the model. However, over the aforementioned places, the radiative forcing resulting from ship emissions can be much more important in the total regional aerosol forcing. <br/> <br/>Description: Abstract in HTML and technical report in PDF available on the MIT Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/). Sat, 29 Mar 2008 22:58:59 GMT