Adaptive Filtering Enhances Information Transmission in Visual Cortex

Sensory neuroscience seeks to understand how the brain encodes natural environments. However, neural coding has largely been studied using simplified stimuli. In order to assess whether the brain's coding strategy depend on the stimulus ensemble, we apply a new information-theoretic method that allows unbiased calculation of neural filters (receptive fields) from responses to natural scenes or other complex signals with strong multipoint correlations. In the cat primary visual cortex we compare responses to natural inputs with those to noise inputs matched for luminance and contrast. We find that neural filters adaptively change with the input ensemble so as to increase the information carried by the neural response about the filtered stimulus. Adaptation affects the spatial frequency composition of the filter, enhancing sensitivity to under-represented frequencies in agreement with optimal encoding arguments. Adaptation occurs over 40 s to many minutes, longer than most previously reported forms of adaptation.Comment: 20 pages, 11 figures, includes supplementary informatio

History and Applications of Dust Devil Studies

Studies of dust devils, and their impact on society, are reviewed. Dust devils have been noted since antiquity, and have been documented in many countries, as well as on the planet Mars. As time-variable vortex entities, they have become a cultural motif. Three major stimuli of dust devil research are identified, nuclear testing, terrestrial climate studies, and perhaps most significantly, Mars research. Dust devils present an occasional safety hazard to light structures and have caused several deaths

Application of the modified ertel's potential vorticity to investigation of south hemisphere circulation

A arbitrariedade que existe em definição geral da vorticidade potencial de Ertel (EPV) é usada para conseguir vorticidade potencial (PV) modificada " optimal ", no sentido de minimizar a rapidez de mudança da PV com tempo devido ao atrito e a aquecimento diabatico. Foi obtido que novo PV modificado e alguns dos seus funcionais são quasi-conservadores em processos climáticos, e podem ser usados com alguma vantagem em investigações de regimes climaticos. Aplicando funcionais tais como a carga do vorticidade, e entropia informativa da distribuição da massa de ar sob vorticidade potencial modificado de Ertel ao estudo de comportamento temporal das estatisticas da circulação para os meses de janeiro e de julho detectamos um crescimento progressivo da diferença da temperatura do ar entre equador e pólo na superfície do Hemisfério Sul durante os 1980s

Application of the modified Estel's potential vorticity to investigation of atmospheric climate variability

It can be shown that the freedom available in Ertel's potential vorticity definition allows one to arrive at a pair of (q, x(8))-variables [q is the modified potential vorticity (MPV), X(8) is the appropriately taken function of potential temperature e which enters MPV-definition], such that the air mass enclosed within solenoids formed by intersection between the families of equiscalar surfaces q=const and x=const is nearly preserved despite the inftuence of diabatic heating and turbulent friction. It is hypothesized and attempted to prove that in (q,X)-co-ordinates the long-term atmospheric climate processes admit a simple statistical description.Pages: 131-13

Atmospheric Circulation Regimes in a Nonlinear Quasi-Geostrophic Model

Atmospheric low-frequency variability and circulation regime behavior are investigated in the context of a quasi-geostrophic (QG) three-level T63 model of the wintertime atmospheric circulation over the Northern Hemisphere (NH). The model generates strong interannual and decadal variability, with the domination of the annular mode of variability. It successfully reproduces a satisfactory model climatology and the most important atmospheric circulation regimes. The positive phase of the Arctic Oscillation is a robust feature of the quasi-geostrophic T63 model. The model results based on QG dynamics underlie atmospheric regime behavior in the extratropical NH and suggest that nonlinear internal processes deliver significant contribution to the atmospheric climate variability on interannual and decadal timescales

Observational evidence for exponential tornado distributions over specific kinetic energy

Observational evidence supports the recent analytical prediction that tornado intensities are exponentially distributed over peak wind speed squared (v 2), or equivalently, Rayleigh-distributed over v. For large USA data samples, exponential tails are found in the tornado intensity distributions over v 2 from about F2 intensity on. Similar results follow for smaller worldwide data samples. For the 1990s data from the USA and Oklahoma, deviations from the Rayleigh distribution for weak tornadoes can be explained by the emergence of a separate, likely non-mesocyclonic tornado mode. These bimodal datasets can be modeled by superposition of two Rayleigh distributions. The change in modal dominance occurs at about the F2 threshold (v ≈ 50 m s−1). In France, likely mainly the mesocyclonic tornado mode has been recorded, while in the UK, only a non-mesocyclonic mode seems to be present