Context-Sensitive Binding by the Laminar Circuits of V1 and V2: A Unified Model of Perceptual Grouping, Attention, and Orientation Contrast

A detailed neural model is presented of how the laminar circuits of visual cortical areas V1 and V2 implement context-sensitive binding processes such as perceptual grouping and attention. The model proposes how specific laminar circuits allow the responses of visual cortical neurons to be determined not only by the stimuli within their classical receptive fields, but also to be strongly influenced by stimuli in the extra-classical surround. This context-sensitive visual processing can greatly enhance the analysis of visual scenes, especially those containing targets that are low contrast, partially occluded, or crowded by distractors. We show how interactions of feedforward, feedback and horizontal circuitry can implement several types of contextual processing simultaneously, using shared laminar circuits. In particular, we present computer simulations which suggest how top-down attention and preattentive perceptual grouping, two processes that are fundamental for visual binding, can interact, with attentional enhancement selectively propagating along groupings of both real and illusory contours, thereby showing how attention can selectively enhance object representations. These simulations also illustrate how attention may have a stronger facilitatory effect on low contrast than on high contrast stimuli, and how pop-out from orientation contrast may occur. The specific functional roles which the model proposes for the cortical layers allow several testable neurophysiological predictions to be made. The results presented here simulate only the boundary grouping system of adult cortical architecture. However we also discuss how this model contributes to a larger neural theory of vision which suggests how intracortical and intercortical feedback help to stabilize development and learning within these cortical circuits. Although feedback plays a key role, fast feedforward processing is possible in response to unambiguous information. Model circuits are capable of synchronizing quickly, but context-sensitive persistence of previous events can influence how synchrony develops. Although these results focus on how the interblob cortical processing stream controls boundary grouping and attention, related modeling of the blob cortical processing stream suggests how visible surfaces are formed, and modeling of the motion stream suggests how transient responses to scenic changes can control long-range apparent motion and also attract spatial attention.Defense Advanced Research Projects agency and the Office of Naval Research (N00014-95-1-0409); National Science Foundation (IRI 94-01659, IRI 97-20333); ONR (N00014-92-J-1309, N00014-95-1-0657

Towards a Theory of the Laminar Architecture of Cerebral Cortex: Computational Clues from the Visual System

One of the most exciting and open research frontiers in neuroscience is that of seeking to understand the functional roles of the layers of cerebral cortex. New experimental techniques for probing the laminar circuitry of cortex have recently been developed, opening up novel opportunities for investigating ho1v its six-layered architecture contributes to perception and cognition. The task of trying to interpret this complex structure can be facilitated by theoretical analyses of the types of computations that cortex is carrying out, and of how these might be implemented in specific cortical circuits. We have recently developed a detailed neural model of how the parvocellular stream of the visual cortex utilizes its feedforward, feedback, and horizontal interactions for purposes of visual filtering, attention, and perceptual grouping. This model, called LAMINART, shows how these perceptual processes relate to the mechanisms which ensure stable development of cortical circuits in the infant, and to the continued stability of learning in the adult. The present article reviews this laminar theory of visual cortex, considers how it may be generalized towards a more comprehensive theory that encompasses other cortical areas and cognitive processes, and shows how its laminar framework generates a variety of testable predictions.Defense Advanced Research Projects Agency and the Office of Naval Research (N00014-95-0409); National Science Foundation (IRI 94-01659); Office of Naval Research (N00014-92-1-1309, N00014-95-1-0657

Acute effect of sumithion on certain blood parameters and mortality rate of fish, Heteropneustes fossilis (Bloch)

The acute toxic effect of the toxicant sumithion (50% E.C.) on mortality rate (after 24, 48, 72, and 96 h), total RBC count and haemoglobin content (after 48 and 72 h) on Heteropneustes fossilis was investigated at four concentrations (9.7, 10.7 and 11.1 ppm). The sumithion treated fishes showed lower RBC and Hb levels than the untreated ones. A gradual decrease in the total RBC counts and Hb contents was recorded with increasing concentration of toxicant after 72 h but the blood showed fluctuating values after 48 h of treatment

Theoretical and Computational Modeling of Contaminant Removal in Porous Water Filters

Contaminant transport in porous media is a well-researched problem across many scientific and engineering disciplines, including soil sciences, groundwater hydrology, chemical engineering, and environmental engineering. In this thesis, we attempt to tackle this multiscale transport problem using the upscaling approach, which leads to the development of macroscale models while considering a porous medium as an averaged continuum system. First, we describe a volume averaging-based method for estimating flow permeability in porous media. This numerical method overcomes several challenges faced during the application of traditional permeability estimation techniques, and is able to accurately provide the complete permeability tensor of a porous sample in a single simulation. Several anisotropic unit cells are created in two- and three-dimensions based on three different parameters: (1) unit-cell size, (2) particle shape, and (3) aspect ratio of the particles inside the unit cells. The results from the volume averaging-based method show good agreement on comparison with the conventional Stokes-Darcy flow technique for the two- and three-dimensional models. We also find that the proposed method provides much faster results than the Stokes-Darcy flow technique for 3D unit-cell geometries. Next, the cartridges used in commercial water filters are mostly created by packing particles or beads that can be assumed to be of mono-modal size distribution and thus create single-scale porous media. In this thesis, we employ the volume averaging method to upscale the phenomenon of solute transport (which include both diffusion and advection) accompanied with adsorption in such homogeneous porous media. Our novel contribution in this research is the development of a micro-macro coupling between the microscopic and macroscopic length scales, which forms the basis of our macroscale models to reflect the macroscopic behaviour of the system. Two versions of the macroscale models are proposed: (a) complete Volume Averaged Model (VAMc) and (b) simplified Volume Averaged Model (VAMs), which involve two effective transfer coefficients, namely, the total dispersion tensor and the adsorption-induced vector. Further, in order to investigate one of the critical design parameters of a porous water filter, the \u27hydraulic detention time\u27 of the polluted water in the filter, we carry out an extensive numerical investigation of the proposed macroscale models. For this, first we nondimensionalize the pore-scale and macroscale models, which leads to surfacing of two important dimensionless numbers, namely, the Damkohler number and the Peclet number. Next, we develop a 2-D geometry of porous media made up of a chain of 100 identical unit cells for testing the above-mentioned models. The numerical simulations corresponding to the dimensionless pore-scale model, which are referred to as the Direct Numerical Simulation (DNS), and the dimensionless macroscale models, which are referred to as the Volume Averaged Model (VAM), are conducted on the chain-of-unit-cells geometry. The intrinsic average concentration predictions from the macroscale models display excellent results on comparison with the pore-scale (or DNS) outcomes. We also assess the importance of large fluid-solid interfacial area inherent in porous adsorbents by varying the porosity and number of particles inside the artificially-prepared porous-media models. The total dispersion tensor coefficient is validated and found to be in excellent agreement with the literature. Our findings reveal that an increase in the interfacial area of the models leads to higher effective transfer coefficient values. Last, we perform adsorption experiments in an effort to evaluate the effectiveness of the proposed macroscale models. For this, three trials of column-flow experiment are conducted using an adsorbent made up of functionalized zeolite material to remove phosphorus from synthetically prepared influent. Micro-CT scans of zeolite material are used to develop a unit-cell representative of the pore space inside the actual adsorbent medium. The numerical simulations on the unit-cell provide realistic effective transfer coefficient values; however, a large difference between the concentration predictions from theory and experimental results is noted. The lack of adherence to the time-scale constraints is assessed to be the primary reason behind this discrepancy. We offer different recommendations in order to improve the experiments and accurately gauge the effectiveness of the macroscale models. Overall, these models have the potential to improve the state-of-the-art technologies for modeling contaminant transport in porous water filters by providing useful recommendations based on numerical simulations, and may be used as a tool for the optimization of the design of porous water filters

Diversifying Agricultural Practices to Meet Fodder Requirements in the NW Himalayas through Improved Land Use Systems

True grasslands formed as climatic climaxes in India are confined to the alpine regions (\u3e 3000 m s l) in the Eastern and Western Himalayas and have been studied for their productivity (Joshi et al.,1988., Ram et al., 1989) and vegetation diversity (Raizada et al., 1998). Other grasslands as they exist are stable sub-climax formations formed as a result of forest degradation and the occurrence of secondary succession in almost all over the Himalayan region. The livelihoods of mountain dwellers is mainly dependent on traditional agriculture and livestock rearing. Animal husbandry is an inseparable component of hill agriculture and the system may be referred to as dairy-manure-draught cattle production system. In the hills, fodder trees, shrubs and open grazing in forest areas is the main source of feed for livestock including agricultural residue. Nearly 66 to75% of the fodder requirement are met from the forest in the mid hills and 26-43% in the lower hills. Summer grazing is practices the alpine regions which are overgrazed. High livestock population and diminishing fodder production have increased fodder demand on the forests which are damaged by extensive lopping and consequent poor regeneration), further contributing to the process of ecological degradation. Land degradation is now a major threat to food production and environmental security in the Himalayan region. Nearly half of the land area in the region is degraded, the major causes being soil erosion due to water, faulty land use practices and the harsh terrain conditions. Available estimates shows that the pressure of livestock grazing on forest and pasture land is 2 to 4 times higher than the normal carrying capacity of grazing areas in some hilly areas (Tiwari, 1997). Given the status of feed-fodder deficiencies and declining per capita land availability, sustaining the livestock sector has become a formidable challenge. The major constraints for supporting livestock is inadequate availability of green forage, particularly in winter, causing deficiency of protein and vitamins, resulting in low productivity. It is therefore necessary to develop and implement suitable land use systems which will provide enough fodder and also maintain environmental security in the fragile Himalayan regions

Existentialism in Arun Joshi’s Novels

Existentialism is a twentieth century’s most influential literary and philosophical movement that focuses on individual existence. It originated in the philosophical and literary works of Sartre and Camus. It focuses on acting on ones conviction in order to arrive at personal truth. Existentialism deals with the problems of the meaning and purpose of life on earth, finding the world as hostile in nature. It is an attitude, an outlook that emphasizes on the purpose and meaning of human existence in this world. Indian form of existentialism as manifested in The Gita and The Upanishads deals with the problems of our existence on earth. The basic theory of existentialism is an insistence on the actual existence of the individual as the basic and important fact, instead of a reliance on the theories of abstractions. The central doctrine is that man is what he makes of himself; he is not predestines by a God or by society, or by biology. Keywords: Existentialism, Alienation, Existence, Technology, loneliness, Rootlessness, Labyrinth, Foreignness

A simpler explanation of the reflective properties of conic sections, by following light rays along local isosceles paths

Ellipses, parabolas and hyperbolas all have beautiful reflective properties. However, an intuitive explanation for why they have those properties has been lacking. There exist many mathematical proofs, but they tend to involve several analytical steps or geometrical constructions, making them unintuitive and hard to understand. Here, a simpler explanation is presented which only requires following the paths of light rays, and examining local paths that move from one point on a conic to a nearby one. First, a light-ray is followed as it runs along one of the legs of an isosceles triangle, and then reflects off a mirror that is parallel to the triangle's base. It bounces back along the path of the triangle's other leg. Next, a path is examined, moving from an arbitrary point on a conic section curve to a nearby point on the same curve. This path consists of two equal-length straight line steps, with each step following one of the constraints that defines the curve. For example, on an ellipse, defined by the sum of the distances to the two foci remaining constant, the path starts at a point on the ellipse, moves a distance delta directly away from one focus, then makes a second equal-length step directly towards the second focus. These two steps form the legs of precisely the sort of isosceles triangle described above, with its base running along the path of the curve. A light ray following the legs of that triangle gets reflected directly from one focus to the other. As the triangle shrinks towards zero, the reflection point converges onto the actual curve. Exactly the same argument also explains the reflections of parabolas and hyperbolas. Surprisingly, this explanation does not seem to have appeared previously in the long history of writings about conics. It is hoped that it will help to make the reflective properties of conic sections easier to understand and to explain.Comment: Minor edits to previous version to improve clarity of text, and added mention of local isosceles paths to the titl

Consciousness and Complexity or Conciousness and Resonance?

Defense Advanced Research Projects Agency and the Office of Naval Research (N00014-95-1-0409); National Science Foundation (IRI 97-20333); Office of Naval Research (N00014-95-1-0657, N00014-92-J-1309

Some new features of electron density irregularities over SHAR during strong spread F

International audienceAn RH-560 rocket flight was conducted from Sriharikota rocket range (SHAR) (14°N, 80°E, dip latitude 5.5°N) to study electron density and electric field irregularities during spread F. The rocket was launched at 2130 local time (LT) and it attained an apogee of 348 km. Results of electron density fluctuations are presented here. Two extremely sharp layers of very high electron density were observed at 105 and 130 km. The electron density increase in these layers was by a factor of 50 in a vertical extent of 10 km. Large depletions in electron density were observed around 175 and 238 km. Both sharp layers as well as depletions were observed also during the descent. The presence of sharp layers and depletions during the ascent and the descent of the rocket as well as an order of magnitude less electron density, in 150-300 km region during the descent, indicate the presence of strong large-scale horizontal gradients in the electron density. Some of the valley region irregularities (165-178 km), in the intermediate scale size range, observed during this flight, show spectral peaks at 2 km and can be interpreted in terms of the image striation theory suggested by Vickrey et al. The irregularities at 176 km do not exhibit any peak at kilometer scales and appear to be of new type. The growth rate of intermediate scale size irregularities, produced through generalized Rayleigh Taylor instability, was calculated for the 200-330 km altitude, using observed values of electron density gradients and an assumed vertically downward wind of 20 ms-1. These growth rate calculations suggest that the observed irregularities could be produced by the gradient drift instability