Statistical mechanics of voting

Decision procedures aggregating the preferences of multiple agents can produce cycles and hence outcomes which have been described heuristically as `chaotic'. We make this description precise by constructing an explicit dynamical system from the agents' preferences and a voting rule. The dynamics form a one dimensional statistical mechanics model; this suggests the use of the topological entropy to quantify the complexity of the system. We formulate natural political/social questions about the expected complexity of a voting rule and degree of cohesion/diversity among agents in terms of random matrix models---ensembles of statistical mechanics models---and compute quantitative answers in some representative cases.Comment: 9 pages, plain TeX, 2 PostScript figures included with epsf.tex (ignore the under/overfull \vbox error messages

Why is the rate of single parenthood lower in Canada than in the U.S.? A dynamic equilibrium analysis of welfare policies

A critical question in the design of welfare policies is whether totarget aid according to household composition, as was done in the U.S. under the Aid to Families with Dependent Children (AFDC)\ program, or to rely exclusively on means-testing, as in Canada. Restricting aid to single mothers, for instance, has the potential to distort behavior along three demographic margins: marriage, fertility and divorce. We contrast the Canadian and the U.S. policies within an equilibrium model of household formation and human capital investment on children. Policy differences weconsider are: eligibility, dependence of transfers on the number of children, and generosity of transfers. Our simulations indicate that the policy differences can account for the higher rate of single-parenthood in the U.S. They also show that Canadian welfare policy is more effective for fostering human capital accumulation among children from poor families. Interestingly, a majority of agents in our benchmark economy prefers awelfare system that targets single mothers (as the U.S. system does), yet does not (unlike the U.S. system) make transfers dependent on the number of children

Recent Performance of the NPTC Equipment Compared with the Clinical Specifications

The construction of the Northeast Proton Therapy Center (NPTC) at Massachusetts General Hospital is nearing completion. Preliminary beam tests have begun and clinical acceptance testing is soon to follow. Preliminary measurements have been made to determine the properties of the system as compared to the clinical requirements. These results will be discussed. The procedures and instrumentation to be used for testing will also be described