Front propagation in stochastic neural fields

We analyse the effects of extrinsic multiplicative noise on front propagation in a scalar neural field with excitatory connections. Using a separation of time scales, we represent the fluctuating front in terms of a diffusive–like displacement (wandering) of the front from its uniformly translating position at long time scales, and fluctuations in the front profile around its instantaneous position at short time scales. One major result of our analysis is a comparison between freely propagating fronts and fronts locked to an externally moving stimulus. We show that the latter are much more robust to noise, since the stochastic wandering of the mean front profile is described by an Ornstein–Uhlenbeck process rather than a Wiener process, so that the variance in front position saturates in the long time limit rather than increasing linearly with time. Finally, we consider a stochastic neural field that supports a pulled front in the deterministic limit, and show that the wandering of such a front is now subdiffusive

The effects of noise on binocular rivalry waves: a stochastic neural field model

We analyse the effects of extrinsic noise on traveling waves of visual perception in a competitive neural field model of binocular rivalry. The model consists of two one-dimensional excitatory neural fields, whose activity variables represent the responses to left-eye and right-eye stimuli, respectively. The two networks mutually inhibit each other, and slow adaptation is incorporated into the model by taking the network connections to exhibit synaptic depression. We first show how, in the absence of any noise, the system supports a propagating composite wave consisting of an invading activity front in one network co-moving with a retreating front in the other network. Using a separation of time scales and perturbation methods previously developed for stochastic reaction-diffusion equations, we then show how multiplicative noise in the activity variables leads to a diffusive–like displacement (wandering) of the composite wave from its uniformly translating position at long time scales, and fluctuations in the wave profile around its instantaneous position at short time scales. The multiplicative noise also renormalizes the mean speed of the wave. We use our analysis to calculate the first passage time distribution for a stochastic rivalry wave to travel a fixed distance, which we find to be given by an inverse Gaussian. Finally, we investigate the effects of noise in the depression variables, which under an adiabatic approximation leads to quenched disorder in the neural fields during propagation of a wave

Neural field model of binocular rivalry waves

We present a neural field model of binocular rivalry waves in visual cortex. For each eye we consider a one–dimensional network of neurons that respond maximally to a particular feature of the corresponding image such as the orientation of a grating stimulus. Recurrent connections within each one-dimensional network are assumed to be excitatory, whereas connections between the two networks are inhibitory (cross-inhibition). Slow adaptation is incorporated into the model by taking the network connections to exhibit synaptic depression. We derive an analytical expression for the speed of a binocular rivalry wave as a function of various neurophysiological parameters, and show how properties of the wave are consistent with the wave–like propagation of perceptual dominance observed in recent psychophysical experiments. In addition to providing an analytical framework for studying binocular rivalry waves, we show how neural field methods provide insights into the mechanisms underlying the generation of the waves. In particular, we highlight the important role of slow adaptation in providing a “symmetry breaking mechanism” that allows waves to propagate

Temporal variations of the anomalous oxygen component

Data from the cosmic ray experiment on Voyagers 1 and 2 was used to examine anomalous oxygen in the time period from launch in 1977 to the end of 1981. Several time periods were found where large periodic (typically 26 day) temporal variations of the oxygen intensity between approximately 5 - 15 MeV/nuc are present. Variations in intensity by up to a factor of 10 are observed during these periods. Several characteristics of these variations indicate that they are not higher energy extensions of the low energy particle (approximately 1 MeV/nuc) increases found in many corotating interaction regions (CIR's). Many of these periodic temporal variations are correlated with similar, but much smaller, recurrent variations in the 75 MeV proton rate. Voyager 1 and Voyager 2 counting rates were compared to estimate the local radial gradient for both the protons and the oxygen. The proton gradients during periods of both maximum and minumum fluxes are consistent with the overall positive radial gradients reported by others from Pioneer and near-Earth observations, supporting the view that these variations are due to local modulation of a source outside the radial range of project measurements. In contrast, the oxygen gradients during periods of maximum proton flux differ in sign from those during minimum proton fluxes, suggesting that the origin of the oxygen variations is different from that of the protons

Technology and Urban Management. Semiannual Report, October 1, 1967 through March 31, 1968

The projects under Technology and Urban Management (TAUM) have continued during the last few months with considerable success. The individual studies conducted in the City of Oakland and the progress made are described in this report

Voyager measurements of the energy spectrum, charge composition, and long term temporal variations of the anomalous components in 1977-1982

The large collecting area and wide energy range of the cosmic ray experiment on Voyager 1 and 2 was used to examine the energy spectra, charge composition, and long term temporal variations of the anomalous components in 1977-1982. Individual energy spectra are obtained for 17 separate quiet time periods during the time interval. The composite spectra of anomalous He, N, O, and Ne are obtained to a new level of precision. This includes the spectral shape and the relative abundance. Essentially, the spectral shape of N, O, and Ne appear to be similar. The ratios of anomalous N and Ne to O are found to be different from both the solar cosmic ray and galactic cosmic ray source composition. Some evidence is found for the enhancement of Ar as well. In the case of elements such as C, Mg, S, and Fe it is difficult to separate a possible lower intensity anomalous component from a quasi-steady interplanetary component that appears to be present at the lowest energies. The long term temporal variations of the anomalous He and O components were studied from 1977-82, a period from minimum to maximum in the modulation cycle. The tracking between these anomalous component intensities and the integral intensity of 75 MeV protons is striking; however, the intensity decrease of the anomalous components is much greater

The UK geography of the E-Society: a national classification

It is simplistic to think of the impacts of new information and communication technologies (ICTs) in terms of a single, or even small number of, 'digital divides'. As developments in what has been termed the ?e-society? reach wider and more generalisedaudiences, so it becomes appropriate to think of digital media as having wider-ranging but differentiated impacts upon consumer transactions, information gathering and citizen participation. This paper describes the development of a detailed, nationwide household classification based on levels of awareness of different ICTs; levels of use of ICTs; andtheir perceived impacts upon human capital formation and the quality of life. It discusses how geodemographic classification makes it possible to provide context for detailed case studies, and hence identify how policy might best improve both the quality and degree ofsociety?s access to ICTs. The primary focus of the paper is methodological, but it alsoillustrates how the classification may be used to investigate a range of regional and subregional policy issues. This paper illustrates the potential contribution of bespoke classifications to evidence-based policy, and the likely benefits of combining the most appropriate methods, techniques, datasets and practices that are used in the public and private sectors. It is simplistic to think of the impacts of new information and communication technologies (ICTs) in terms of a single, or even small number of, 'digital divides'. As developments in what has been termed the ?e-society? reach wider and more generalisedaudiences, so it becomes appropriate to think of digital media as having wider-rangingbut differentiated impacts upon consumer transactions, information gathering and citizen participation. This paper describes the development of a detailed, nationwide household classification based on levels of awareness of different ICTs; levels of use of ICTs; and their perceived impacts upon human capital formation and the quality of life. It discusses how geodemographic classification makes it possible to provide context for detailed case studies, and hence identify how policy might best improve both the quality and degree of society?s access to ICTs. The primary focus of the paper is methodological, but it also illustrates how the classification may be used to investigate a range of regional and subregional policy issues. This paper illustrates the potential contribution of bespoke classifications to evidence-based policy, and the likely benefits of combining the most appropriate methods, techniques, datasets and practices that are used in the public and private sectors

Measurements of the fragmentation of (40)Ar, (28)Si and (12)C in CH2C and H targets between 300 and 1500 MeV/nuc at the Bevalac

Studies of the fragmentation of various nuclei in CH2 and C targets were continued with the objective of obtaining cross sections in hydrogen for use in the cosmic ray propagation problem. New measurements include Fe-56. Measurements were made at 6 energies between 300 and 1700 MeV/nuc. C-12 measurements were made at six energies. Si-28 measurements were made at three energies and measurements were made at two energies. New data on C.-12 Si-28 and AR-44 nuclei are given. The data are compare it with the earlier semi-empirical predictions

Can switching fuels save water? A life cycle quantification of freshwater consumption for Texas coal-and natural gas-fired electricity

Thermal electricity generation is a major consumer of freshwater for cooling, fuel extraction and air emissions controls, but the life cycle water impacts of different fossil fuel cycles are not well understood. Much of the existing literature relies on decades-old estimates for water intensity, particularly regarding water consumed for fuel extraction. This work uses contemporary data from specific resource basins and power plants in Texas to evaluate water intensity at three major stages of coal and natural gas fuel cycles: fuel extraction, power plant cooling and power plant emissions controls. In particular, the water intensity of fuel extraction is quantified for Texas lignite, conventional natural gas and 11 unconventional natural gas basins in Texas, including major second-order impacts associated with multi-stage hydraulic fracturing. Despite the rise of this water-intensive natural gas extraction method, natural gas extraction appears to consume less freshwater than coal per unit of energy extracted in Texas because of the high water intensity of Texas lignite extraction. This work uses new resource basin and power plant level water intensity data to estimate the potential effects of coal to natural gas fuel switching in Texas’ power sector, a shift under consideration due to potential environmental benefits and very low natural gas prices. Replacing Texas’ coal-fired power plants with natural gas combined cycle plants (NGCCs) would reduce annual freshwater consumption in the state by an estimated 53 billion gallons per year, or 60% of Texas coal power’s water footprint, largely due to the higher efficiency of NGCCs.Mechanical Engineerin