Use of source apportionment model for designing acid deposition mitigating strategies in Massachusetts

The Commonwealth of Massachusetts promulgated an Act limiting S2 emissions from large sources that burn fuel at a rate greater than or equal to 100 million Btu (MBtu) of fuel input per hour. The Act requires that by 1995 the average emission rate at such facilities be less than or equal to 1.2 lb SO2 per MBtu fuel input. Because of their size, almost all power plants in Massachusetts could be subject to emission reductions. Since the average 1980-1982 annual emission rate of Massachusetts power plants was 1.84 lb S02/MBtu ("base case"), the Act requires the annual average emission rate of power plants to diminish by 35%. We use a source apportionment model to estimate the wet sulfate deposition to typical sensitive Massachusetts receptors from Massachusetts power plants, separately for the summer (April-September) and winter (October-March) half-years. We find that the summer wet deposition is about twice the winter deposition, although summer and winter SO2 emissions are approximately equal. Therefore, to reduce sulfate deposition, t is more effective to reduce emissions in the summer months rather than in winter. Using the seasonal source apportionment model we find that an annual wet deposition reduction equal to that resulting from the Act could be accomplished if only summer emission rates were reduced to 0.86 lb SO /MBtu, with winter emission rates remaining at 1.84 lb S02/MBtu. The resulging annual average emission rate is 1.35 lb SO /MBtu, 27% less than the base value. As 1980-1982 average annual emissions rom power plants amounted to 270,000 tons of SO annually, a summer emission control program would save about 21,000 tons of S emission reduction without sacrificing wet deposition protection. Te summer emission reduction could be acomplished by substituting lower sulfur content fuels, including natural gas, for higher sulfur content fuels.New England Power Company under the Electric Utility Program at the Energy Laborator

Ground-level ozone in eastern North America : its formation and transport

Ozone (Os), a natural component of the troposphere, is augmented by photochemical processes involving manmade emissions of nitrogen oxides (NOx) and volatile organic compounds (VOCs). Sufficiently high concentrations of ozone are detrimental to the respiratory system. Ozone exposure also reduces crop yields and damages forests. This study attempts to explain the underlying factors which contribute to observed ozone levels.Long range transport models of three species - NOx, VOCs and ozone - are developed for eastern North America. The seasonally averaged models include the essential physical and chemical processes in a relatively simple framework. NOx and VOCs are treated as primary species, i.e., they are modeled from their introduction into the atmosphere to their point of removal. Detailed emission inventories serve as input to the precursor models. Ozone is considered a secondary species because it is not directly emitted. Rather, its production is assumed to be a function of ambient NO, and VOCs levels.Measured concentrations, available for NO 2 and ozone, are compared with model predictions and aid in determining adjustable model parameters. Predicted NOx concentrations are consistent with rural observations but underestimate sites influenced by nearby sources at which the long range assumptions break down. Local models which properly treat proximate sources account for the discrepancy. The VOCs model, having no measurements for verification, adopts parameters consistent with the NOx model and known chemical properties. Both biogenic and manmade emissions contribute to ambient VOCs levels. Biogenic emissions are found to be more important over most of ENA; anthropogenic sources of VOCs are dominant only in urban areas.Consistent with empirical patterns, the ozone model predicts small regional gradients and hence a limited dependence on NOx and VOCs precursors. The natural background component is determined to be two-thirds of average ozone levels. Regional transport is significant; ozone lifetimes are estimated to be of the order of a day. The high background level and insensitivity to precursors suggests that significant reductions of average ozone concentrations will be difficult to achieve

Temporal decorrelation of collective oscillations in neural networks with local inhibition and long-range excitation

We consider two neuronal networks coupled by long-range excitatory interactions. Oscillations in the gamma frequency band are generated within each network by local inhibition. When long-range excitation is weak, these oscillations phase-lock with a phase-shift dependent on the strength of local inhibition. Increasing the strength of long-range excitation induces a transition to chaos via period-doubling or quasi-periodic scenarios. In the chaotic regime oscillatory activity undergoes fast temporal decorrelation. The generality of these dynamical properties is assessed in firing-rate models as well as in large networks of conductance-based neurons.Comment: 4 pages, 5 figures. accepted for publication in Physical Review Letter

How well can we estimate the information carried in neuronal responses from limited samples?

It is difficult to extract the information carried by neuronal responses about a set of stimuli because limited data samples result in biased estimates. Recently two improved procedures have been developed to calculate information from experimental results: a binning-and-correcting procedure and a neural network procedure. We have used data produced from a model of the spatiotemporal receptive fields of parvocellular and magnocellular lateral geniculate neurons to study the performance of these methods as a function of the number of trials used. Both procedures yield accurate results for one-dimensional neuronal codes. They can also be used to produce a reasonable estimate of the extra information in a three-dimensional code, in this instance, within 0.05-0.1 bit of the asymptotically calculated value - about 10% of the total transmitted information. We believe that this performance is much more accurate than previous procedures

Shift in critical temperature for random spatial permutations with cycle weights

We examine a phase transition in a model of random spatial permutations which originates in a study of the interacting Bose gas. Permutations are weighted according to point positions; the low-temperature onset of the appearance of arbitrarily long cycles is connected to the phase transition of Bose-Einstein condensates. In our simplified model, point positions are held fixed on the fully occupied cubic lattice and interactions are expressed as Ewens-type weights on cycle lengths of permutations. The critical temperature of the transition to long cycles depends on an interaction-strength parameter $\alpha$. For weak interactions, the shift in critical temperature is expected to be linear in $\alpha$ with constant of linearity $c$. Using Markov chain Monte Carlo methods and finite-size scaling, we find $c = 0.618 \pm 0.086$. This finding matches a similar analytical result of Ueltschi and Betz. We also examine the mean longest cycle length as a fraction of the number of sites in long cycles, recovering an earlier result of Shepp and Lloyd for non-spatial permutations.Comment: v2 incorporated reviewer comments. v3 removed two extraneous figures which appeared at the end of the PDF

A new test for random number generators: Schwinger-Dyson equations for the Ising model

We use a set of Schwinger-Dyson equations for the Ising Model to check several random number generators. For the model in two and three dimensions, it is shown that the equations are sensitive tests of bias originated by the random numbers. The method is almost costless in computer time when added to any simulation.Comment: 6 pages, 3 figure

Mean field approximation of two coupled populations of excitable units

The analysis on stability and bifurcations in the macroscopic dynamics exhibited by the system of two coupled large populations comprised of $N$ stochastic excitable units each is performed by studying an approximate system, obtained by replacing each population with the corresponding mean-field model. In the exact system, one has the units within an ensemble communicating via the time-delayed linear couplings, whereas the inter-ensemble terms involve the nonlinear time-delayed interaction mediated by the appropriate global variables. The aim is to demonstrate that the bifurcations affecting the stability of the stationary state of the original system, governed by a set of 4N stochastic delay-differential equations for the microscopic dynamics, can accurately be reproduced by a flow containing just four deterministic delay-differential equations which describe the evolution of the mean-field based variables. In particular, the considered issues include determining the parameter domains where the stationary state is stable, the scenarios for the onset and the time-delay induced suppression of the collective mode, as well as the parameter domains admitting bistability between the equilibrium and the oscillatory state. We show how analytically tractable bifurcations occurring in the approximate model can be used to identify the characteristic mechanisms by which the stationary state is destabilized under different system configurations, like those with symmetrical or asymmetrical inter-population couplings.Comment: 5 figure

On leaders and condensates in a growing network

The Bianconi-Barabasi model of a growing network is revisited. This model, defined by a preferential attachment rule involving both the degrees of the nodes and their intrinsic fitnesses, has the fundamental property to undergo a phase transition to a condensed phase below some finite critical temperature, for an appropriate choice of the distribution of fitnesses. At high temperature it exhibits a crossover to the Barabasi-Albert model, and at low temperature, where the fitness landscape becomes very rugged, a crossover to the recently introduced record-driven growth process. We first present an analysis of the history of leaders, the leader being defined as the node with largest degree at a given time. In the generic finite-temperature regime, new leaders appear endlessly, albeit on a doubly logarithmic time scale, i.e., extremely slowly. We then give a novel picture for the dynamics in the condensed phase. The latter is characterized by an infinite hierarchy of condensates, whose sizes are non-self-averaging and keep fluctuating forever.Comment: 29 pages, 13 figures, 3 tables. A few minor change

Punctured polygons and polyominoes on the square lattice

We use the finite lattice method to count the number of punctured staircase and self-avoiding polygons with up to three holes on the square lattice. New or radically extended series have been derived for both the perimeter and area generating functions. We show that the critical point is unchanged by a finite number of punctures, and that the critical exponent increases by a fixed amount for each puncture. The increase is 1.5 per puncture when enumerating by perimeter and 1.0 when enumerating by area. A refined estimate of the connective constant for polygons by area is given. A similar set of results is obtained for finitely punctured polyominoes. The exponent increase is proved to be 1.0 per puncture for polyominoes.Comment: 36 pages, 11 figure

Population coding by globally coupled phase oscillators

A system of globally coupled phase oscillators subject to an external input is considered as a simple model of neural circuits coding external stimulus. The information coding efficiency of the system in its asynchronous state is quantified using Fisher information. The effect of coupling and noise on the information coding efficiency in the stationary state is analyzed. The relaxation process of the system after the presentation of an external input is also studied. It is found that the information coding efficiency exhibits a large transient increase before the system relaxes to the final stationary state.Comment: 7 pages, 9 figures, revised version, new figures added, to appear in JPSJ Vol 75, No.