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

Risk factors and prediction models for incident heart failure with reduced and preserved ejection fraction

Abstract: Aims: This study aims to develop the first race‐specific and sex‐specific risk prediction models for heart failure with preserved (HFpEF) and reduced ejection fraction (HFrEF). Methods and results: We created a cohort of 1.8 million individuals who had an outpatient clinic visit between 2002 and 2007 within the Veterans Affairs (VA) Healthcare System and obtained information on HFpEF, HFrEF, and several risk factors from electronic health records (EHR). Variables were selected for the risk prediction models in a ‘derivation cohort’ that consisted of individuals with baseline date in 2002, 2003, or 2004 using a forward stepwise selection based on a change in C‐index threshold. Discrimination and calibration were assessed in the remaining participants (internal ‘validation cohort’). A total of 66 831 individuals developed HFpEF, and 92 233 developed HFrEF (52 679 and 71 463 in the derivation cohort) over a median of 11.1 years of follow‐up. The HFpEF risk prediction model included age, diabetes, BMI, COPD, previous MI, antihypertensive treatment, SBP, smoking status, atrial fibrillation, and estimated glomerular filtration rate (eGFR), while the HFrEF model additionally included previous CAD. For the HFpEF model, C‐indices were 0.74 (SE = 0.002) for white men, 0.76 (0.005) for black men, 0.79 (0.015) for white women, and 0.77 (0.026) for black women, compared with 0.72 (0.002), 0.72 (0.004), 0.77 (0.017), and 0.75 (0.028), respectively, for the HFrEF model. These risk prediction models were generally well calibrated in each race‐specific and sex‐specific stratum of the validation cohort. Conclusions: Our race‐specific and sex‐specific risk prediction models, which used easily obtainable clinical variables, can be a useful tool to implement preventive strategies or subtype‐specific prevention trials in the nine million users of the VA healthcare system and the general population after external validation

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

Applications of electrified dust and dust devil electrodynamics to Martian atmospheric electricity

Atmospheric transport and suspension of dust frequently brings electrification, which may be substantial. Electric fields of 10 kVm-1 to 100 kVm-1 have been observed at the surface beneath suspended dust in the terrestrial atmosphere, and some electrification has been observed to persist in dust at levels to 5 km, as well as in volcanic plumes. The interaction between individual particles which causes the electrification is incompletely understood, and multiple processes are thought to be acting. A variation in particle charge with particle size, and the effect of gravitational separation explains to, some extent, the charge structures observed in terrestrial dust storms. More extensive flow-based modelling demonstrates that bulk electric fields in excess of 10 kV m-1 can be obtained rapidly (in less than 10 s) from rotating dust systems (dust devils) and that terrestrial breakdown fields can be obtained. Modelled profiles of electrical conductivity in the Martian atmosphere suggest the possibility of dust electrification, and dust devils have been suggested as a mechanism of charge separation able to maintain current flow between one region of the atmosphere and another, through a global circuit. Fundamental new understanding of Martian atmospheric electricity will result from the ExoMars mission, which carries the DREAMS (Dust characterization, Risk Assessment, and Environment Analyser on the Martian Surface)-MicroARES (Atmospheric Radiation and Electricity Sensor) instrumentation to Mars in 2016 for the first in situ measurements

Adiabatic invariants and diagnostic study of climate

The question of using of adiabatic invariants in climate studies and for verification of General Circulation Model is discussed. Main functionals from these invariants, which are slowly transformed only due to the influences of irreversible processes could be convenient indices of climatic changes. Short review of vari- ous diagnostic methods based on the analysis of potential vorticity and potential temperature fields and the functionals from these meteorological parameters in the investigations of weather regimes and climate vari- ability is presented. The example of the use of some of these methods to the analysis of the output data of CPTEC General Circulation Model is given.Pages: 261-27

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

The linkage between POLar air-sea ice-ocean interaction, Arctic climate change and Northern hemisphere weather and climate EXtremes (POLEX).

First results of the POLEX project will be presented. The objectives of our project comprise: 1) An improvement of the representation of atmosphere-sea ice-ocean interaction in climate models by developing and implementing a suite of advanced turbulence parametrizations for polar conditions 2) Performance of present day and future climate change simulations for the 21st century using the new suite of parametrizations 3) Understanding the dynamical linkages between Arctic climate change, mid-latitude atmospheric circulation changes and subsequent changes in extreme events 4) Determination of recent and future changes in extreme events over the Arctic, Middle Europe and Russia and assessment of their impact on Northern Sea route, wildfire and vegetation over the key regions Arctic and Russia Our project will strongly enhance the climate models capability to represent Arctic processes that are known to be critical for simulating linkages between the Arctic and mid-latitudes

Interannual variability of the Arctic summer sea-ice cover

The possible disappearance of the Arctic summer sea ice and its time are currently discussed among climate researchers in view of the rapid decrease of the summer sea-ice cover in recent years. Whether this decrease represents a climate change signal caused by anthropogenic influence or an extreme manifestation of internal climate variabilityis still unclear. By means of a 20-year simulation of a coupled regional pan-Arctic atmosphere-ocean-ice model for the 1980s and 1990s and comparison of the model results with SSM/I satellite-derived sea-ice concentrations, the patterns of maximum amplitude of interannual variability of the Arctic summer sea-ice cover are revealed. They are shown to concentrate beyond an area enclosed by an isopleth of barotropic planetary potential vorticity that marks the edge of the cyclonic rim current around the deep inner Arctic basin. It is argued that the propagation of the interannual variability signal farther into the inner Arctic basin is likely to be possible owing to changes in the oceanic circulation. Such changes could be jointly responsible for the exceptionally strong decrease of the summer sea-ice cover during the last years when sea-ice decay waspromoted by anomalous atmospheric circulation patterns