Thermal fluctuations and nanoscale effects in the nucleation of carbonaceous dust grains

We investigate the role of thermal fluctuations and of the finite number of monomers in small clusters of carbon atoms on the nucleation rate of carbonaceous grains. Thermal fluctuations are due to the quantized nature of the energy exchanges between the clusters, the gas, and the radiation field. Nanoscale effects modify the spontaneous detachment of monomers due to the finite amount of internal energy contained in small clusters. We find that both corrections have a big impact on the stability of the clusters and on the rate of nucleation. We implement our model within a Monte Carlo code to derive the new stability conditions for clusters as well as nucleation rates. Due to computing limitations, we can explore the consequences of this approach only at high temperatures, at which particle interactions are not much less frequent than photon interactions. We found that the combined effect of the detachment correction and the temperature fluctuations produces faster nucleation. We also found that the nucleation rate depends on the composition of the gas and not only on the partial pressure of the compound that condensates into grains. This is a unique result of this model that can be used to prove or disprove it.Comment: 10 pages, submitted to MNRAS, comments welcom

Recursive Sustainability: Intertemporal Efficiency and Equity

PV-optimality in a capital-resource economy can imply decreasing utility over some portion of the time horizon. Various criteria have been proposed to maintain intergenerational equity defined as nondeclining utility, but these have some limitations and problems. This paper proposes a new welfare criteria incorporating present value to maintain efficiency, and an equity function with convex costs on declining utility. This criterion is economically efficient, time-consistent and recursive. An extension of dynamic programming to multiple value functions is developed to solve this problem. Increasing the equity weight increasingly eliminates declining portions of utility time paths. Sustainability implies increasing consumption in the early time periods and some intermediate time periods relative to PV-optimality. A surprising result is that sustainability can actually result in increased resource usage in early time periods, followed later by higher levels of resource stocks compared to PV-optimality. The sustainability analysis shows that while conventional benefit-cost and valuation analysis contribute to efficiency, they do not necessarily induce sustainability due to incorrect dynamic GE prices. Similar comments apply to Green NNP analysis. The concepts and extended DP methods developed in this paper extend naturally to uncertainty and can also be applied to generalized consumer and social choice models beyond those typically considered in the literature.growth, environment, intergenerational equity, dynamic programming, Research Methods/ Statistical Methods,

EXHAUSTIBLE RESOURCE ALLOCATION, INTERGENERATIONAL EQUITY, AND SUSTAINABILITY

An OLG model with exhaustible resources and solar energy is developed, and equilibrium time paths are characterized numerically using recursive methods. For the parameter values considered, resource prices increase over time, and extractions, output, and utility decline over time until a steady-state is reached. Decreasing the intertemporal elasticity of substitution or raising consumers' subjective discount rate hastens exhaustion of the resource stock. Market equilibrium can result in much quicker use of the stock than social optimality under a constant discount rate, with consequent higher utility for early generations and lower utility for future generations in contrast to social optimality.Resource /Energy Economics and Policy,

Maverick Examples Of Coset Conformal Field Theories

We present coset conformal field theories whose spectrum is not determined by the identification current method. In these ``maverick'' cosets there is a larger symmetry identifying primary fields than under the identification current. We find an A-D-E classification of these mavericks. }Comment: 16pages , reportSWAT-93-0

INTERNATIONAL TRADE IN THE FOOD SECTOR AND ENVIRONMENTAL QUALITY, HEALTH, AND SAFETY: A SURVEY OF POLICY ISSUES

International Relations/Trade,

Cheap Food Policy: Fact or Rhetoric?

The term "cheap food policy" has frequently been used as a descriptor for U.S. commodity programs by those who contend these payments to farmers ultimately result in lower food costs for consumers. More recently, farm policy has been criticized for contributing to the obesity problem in the U.S. by making large quantities of fattening foods widely available and relatively inexpensive. This paper econometrically evaluates the impact of direct government payments to farmers from 1960-1999 on the proportion of disposable income consumers spend on food. The model finds the payments do not significantly affect the affordability of food.Agricultural and Food Policy,