Grate Bars Research Articles

Modeling texture-constancy of cortical grating cells

Cortical grating cells respond only and in a contrast-independent way to repetitive bar stimuli (bar gratings), but not to individual bars: their responses behave like the neural correlate of perceptual texture-constancy. We present a recurrent mean-field model for grating response. A first stage consists of idealized simple cell pools with identical preferred orientations, which are coupled by intracortical long-range patchy connections. In the second stage, grating cells sum up the simple cell input. The proposed model shows texture constancy, quantitatively reproduces the responses of macaque monkey grating cells and provides testable predictions of further cellular response properties.

都市ごみ焼却炉における耐熱鋳鋼SCH2製火格子の粒界腐食挙動と機構(FR3 バイオマス・自然エネルギー・廃棄物利用2)

都市ごみ焼却炉における耐熱鋳鋼SCH2製火格子の粒界腐食挙動と機構(FR3 バイオマス・自然エネルギー・廃棄物利用2)

Technical note: Use of ferro wastes in sinter making

A higher bed height - up to 680 mm, including a 30 mm hearth layer of sized return sinter - and high suction below the grate bars up to 1400 mm WG have resulted in increasing productivity to 33 t m-2/day and have reduced the coke rate to a level of 46 kg t-1 sinter. Ferro wastes such as blue dust, flue dust, mill scale, collection from dust catcher and gas cleaning plant, have been successfully added to the charge mix to produce quality sinters. In this paper, work carried out at the Regional Research Laboratory (CSIR) over the last few years is briefly descibed and two case studies are discussed, including the successful development of pan sintering units.

Characterization of municipal solid waste combustion in a grate furnace

The objective of this paper is to evaluate the combustion process of municipal solid waste combustion in a grate furnace both experimentally and numerically by using data of a reference experiment with over-stoichiometric primary air supply. Measurements were carried out inside the combustion chamber of a pilot plant by monitoring temperatures and sampling gaseous combustion products along the bed surface. The data were assessed using elemental and energy balances. Experimental data of the axial temperature profiles of the flue gas, the fuel bed and the grate bars, as well as local gas flows and the flue gas composition measured above the fuel bed along the grate were used to describe the conversion process, including drying and carbon burnout. These data served as input to model the thermo- and fluid dynamic processes of the gas phase above the bed inside the combustion chamber. For this purpose the commercial code FLUENT was employed to carry out the simulations. Thus, the turbulent temperature, flow and species distributions in the combustion chamber of the pilot waste incinerator TAMARA were predicted. The results of the FLUENT modeling showed that under the prevailing conditions the flue gas burnout is almost completed before entering the first flue due to high temperatures, effective mixing and sufficient residence times of the flue gas inside the combustion chamber. This agrees well with the experimental results inside the first flue. On the basis of the above mentioned results, design and parametric studies can be carried out in a more efficient way by saving cost and time.

Determining the profile of textured membranes by the alpha particle energy loss method

Alpha particle energy loss (AEL) spectroscopy was used to characterize a 5 μm pitch grating of silicon bars on a silicon dioxide membrane. Comparison of the data with simulated spectra shows that the angle of nonvertical grating sidewalls are readily quantified by AEL. The potential of AEL for distinguishing undercut and overcut etch profiles is assessed.

The effect of barge and ocean freight price volatility in international grain markets

This paper looks at the potential role of time-varying volatility of Mississippi river barge and ocean freight prices on commodity prices in Illinois, at the US Gulf and in Rotterdam using a Vector Error Correction GARCH-in-Mean model. The model is used to infer the extent to which transportation price risk affects price dynamics in international grain markets. Results from a simulation exercise indicate that both barge and ocean price volatility influence grain prices, but barge price volatility tends to have a greater impact on grain prices and marketing margins than that arising from ocean price volatility. Consistent with most studies that evaluate the role of risk in marketing channels, results here suggest that a reduction in barge rate risk would reduce marketing margins between Illinois and the US Gulf, and between the US Gulf and Rotterdam. The existence of an ocean freight futures contract coupled with the lack of a futures contract for barge rates may be partially responsible for the finding that barge rates have a significant influence on grain prices and contribute most to wide marketing margins found throughout the international grain-marketing system.

The effect of barge and ocean freight price volatility in international grain markets

AbstractThis paper looks at the potential role of time‐varying volatility of Mississippi river barge and ocean freight prices on commodity prices in Illinois, at the US Gulf and in Rotterdam using a Vector Error Correction GARCH‐in‐Mean model. The model is used to infer the extent to which transportation price risk affects price dynamics in international grain markets. Results from a simulation exercise indicate that both barge and ocean price volatility influence grain prices, but barge price volatility tends to have a greater impact on grain prices and marketing margins than that arising from ocean price volatility. Consistent with most studies that evaluate the role of risk in marketing channels, results here suggest that a reduction in barge rate risk would reduce marketing margins between Illinois and the US Gulf, and between the US Gulf and Rotterdam. The existence of an ocean freight futures contract coupled with the lack of a futures contract for barge rates may be partially responsible for the finding that barge rates have a significant influence on grain prices and contribute most to wide marketing margins found throughout the international grain‐marketing system.

A neural network model for the self-organization of cortical grating cells.

A neural network model with incremental Hebbian learning of afferent and lateral synaptic couplings is proposed,which simulates the activity-dependent self-organization of grating cells in upper layers of striate cortex. These cells, found in areas V1 and V2 of the visual cortex of monkeys, respond vigorously and exclusively to bar gratings of a preferred orientation and periodicity. Response behavior to varying contrast and to an increasing number of bars in the grating show threshold and saturation effects. Their location with respect to the underlying orientation map and their nonlinear response behavior are investigated. The number of emerging grating cells is controlled in the model by the range and strength of the lateral coupling structure.

Evaluation of separator grates for reduction of bycatch in the silver hake ( Merluccius bilinearis) otter trawl fishery off Nova Scotia, Canada

The effectiveness of separator grates in reducing bycatches in the small-mesh otter trawl fishery for silver hake on the Scotian Shelf was examined in three experiments aboard a research and two commercial vessels. Different grate bar orientations, bar spacings, grate insertion angles, and guiding mechanisms were tested. The size selection and escapement levels resulting from these grate configurations are described. A grate with vertical bars spaced 40 mm apart inserted at 45–60°, and with a funnel or panel forward of the grate to direct fish to its base, released 85–98% by weight of pollock and haddock, and 48–70% of other species, while retaining 95% of silver hake. Commercial bycatches contained more small haddock than did experimental catches, and it is projected that commercial use of this grate would release 75–80% by weight of haddock encountered, and only 50% by number. Other grate configurations tested displayed poorer species selection characteristics.

Nonlinear operator for oriented texture

Texture is an important part of the visual world of animals and humans and their visual systems successfully detect, discriminate, and segment texture. Relatively recently progress was made concerning structures in the brain that are presumably responsible for texture processing. Neurophysiologists reported on the discovery of a new type of orientation selective neuron in areas V1 and V2 of the visual cortex of monkeys which they called grating cells. Such cells respond vigorously to a grating of bars of appropriate orientation, position and periodicity. In contrast to other orientation selective cells, grating cells respond very weakly or not at all to single bars which do not make part of a grating. Elsewhere we proposed a nonlinear model of this type of cell and demonstrated the advantages of grating cells with respect to the separation of texture and form information. In this paper, we use grating cell operators to obtain features and compare these operators in texture analysis tasks with commonly used feature extracting operators such as Gabor-energy and co-occurrence matrix operators. For a quantitative comparison of the discrimination properties of the concerned operators a new method is proposed which is based on the Fisher (1923) linear discriminant and the Fisher criterion. The operators are also qualitatively compared with respect to their ability to separate texture from form information and their suitability for texture segmentation.

Mid-peripheral pattern electrical retinal responses in normals, glaucoma suspects, and glaucoma patients

AIMSReliance on intraocular pressure, optic nerve cupping changes, nerve fibre layer integrity, and visual field changes may delay treatment of glaucoma since irreversible changes may have already occurred at the...

A neural network model for the emergence of grating cells.

A correlation-based learning (CBL) neural network model is proposed, which simulates the emergence of grating cells as well as some of their response characteristics to periodic pattern stimuli. These cells, found in areas V1 and V2 of the visual cortex of monkeys, respond vigorously and exclusively to bar gratings of a preferred orientation and periodicity. Their non-linear behaviour differentiates grating cells from other orientation-selective cells, which show linear spatial frequency filtering.

Liberation of alkali salts from fluxed iron ore pellets during induration

During the induration of fluxed taconite pellets, alkali salts deposit on the grate support bars, causing severe corrosive degradation of these alloys. To determine the source of these deposits and to understand the mechanism by which the salts are conveyed to the grate bars, a study of the reactions between fluxed pellets and combustion gas was carried out. The study focused on the thermodynamics and kinetics of several processes associated with induration; namely, oxidation of magnetite, calcination of flux, and the formation and gaseous transport of various alkali salt species. Both theoretical and experimental techniques were used. It was concluded that the principal source of alkali salt deposits is alkali chlorides, which are present as contaminants in the flux and/or residue from contaminated washwater. The pathway from pellet to grate bar involves the following steps: evaporation of chloride salts within the pellet; diffusion of salt vapor out of the pellet, aided by the outflow of CO2 from calcination of the flux; convective transport by the combustion gas with concurrent (partial) conversion to alkali sulfates by reaction with residual SOx in the combustion gas; and condensation of salts on the grate bars.

Computational models of visual neurons specialised in the detection of periodic and aperiodic oriented visual stimuli: bar and grating cells.

Computational models of periodic- and aperiodic-pattern selective cells, also called grating and bar cells, respectively, are proposed. Grating cells are found in areas V1 and V2 of the visual cortex of monkeys and respond strongly to bar gratings of a given orientation and periodicity but very weakly or not at all to single bars. This non-linear behaviour, which is quite different from the spatial frequency filtering behaviour exhibited by the other types of orientation-selective neurons such as the simple cells, is incorporated in the proposed computational model by using an AND-type non-linearity to combine the responses of simple cells with symmetric receptive field profiles and opposite polarities. The functional behaviour of bar cells, which are found in the same areas of the visual cortex as grating cells, is less well explored and documented in the literature. In general, these cells respond to single bars and their responses decrease when further bars are added to form a periodic pattern. These properties of bar cells are implemented in a computational model in which the responses of bar cells are computed as thresholded differences of the responses of corresponding complex (or simple) cells and grating cells. Bar and grating cells seem to play complementary roles in resolving the ambiguity with which the responses of simple and complex cells represent oriented visual stimuli, in that bar cells are selective only for form information as present in contours and grating cells only respond to oriented texture information. The proposed model is capable of explaining the results of neurophysiological experiments as well as the psychophysical observation that the perception of texture and the perception of form are complementary processes.

Spatially distributed responses induced by contrast reversal in cat visual cortex.

Field potentials were recorded from cat striate cortex, either between an epidural screw electrode and a cannula-electrode inserted deep in the gray matter (transcortical recording) or with a pair of metal microelectrodes. Electrodes were placed bilaterally near the cortical projection of the area centralis. The horizontal separation of the recording tips was approximately 2 mm and approximately 300 microns, respectively. The area of the visual field providing input to the recording site (receptive field) was determined by measuring the field potentials generated by contrast reversal of high-contrast, achromatic bar gratings. Five-degree-diameter grating patches were presented individually over a large area of the visual field. The gratings were contrast-reversed at 4, 6 or 10 Hz, while also being swept in spatial frequency between 0.56 and 5.24 c/deg. The receptive fields were approximately 20 deg across or more, substantially larger than expected on the basis of cortical retinotopy. Responses were also elicited by stimulation of the hemi-field contralateral to that contributing to the classical receptive field, implicating the presence of a callosal projection. The large, spatially distributed receptive fields consisted of patches of high and low sensitivity. Continuous cortical infusion of either 100 microM tetrodotoxin or 10 mM muscimol at the recording site totally suppressed the transcortically recorded field potentials, proving that the local field potentials were generated postsynaptically. The present findings suggest that a cluster of cortical cells near the projection site of the area centralis receives input from remote cortical regions to an extent that is comparable with that of anatomically demonstrated long-range lateral connections.

Retinotopic and nonretinotopic field potentials in cat visual cortex.

Two types of field potentials were identified in cat visual cortex using contrast reversal of oriented bar gratings: a short-latency fast-local component with a retinotopic organization similar to that seen with single-unit discharges at the same cortical site, and a slow, nonretinotopic component with a longer peak latency. The slow-distributed component had an extensive receptive field mapped by measuring the amplitude of binary kernels and showed strong inhibitory interactions within the receptive field. The peak latency of the slow-local component increased with distance from the retinotopic center, suggesting a possible conduction delay. Both components showed some orientation bias depending on the laminar location, but the bias could be independent of the orientation preferred by single units in the immediate vicinity. The present findings indicate that locally generated field potentials reflect cortical mechanisms for nonlinear integration over wide areas of the visual field.

The role of early mechanisms in motion transparency and coherence

Perceptual dissociation of moving plaid patterns into independently moving bar gratings occurs most readily when the grating signals are combined as if the bars were semi-transparent objects (Ramachandran, V. S. (1990) in: AI and the Eye. Wiley, Chichester, pp. 21-77. Stoner, G. R., Albright, T. D. and Ramachandran, V. S. (1990) Nature 344, 153-155). These and other examples of motion transparency are exploited to constrain the set of viable models for human motion processing. For example, one may exclude any fixed recombination of local motion signals into a plaid motion signal. Broad classes of linear and non-linear mechanisms for tracking blobs, corners, and other unambiguous plaid motion cues can also be ruled out because they fail to reproduce the experimental results even qualitatively. The shifting balance between the 'coherent plaid' and 'sliding gratings' percepts are attributed to processing stages before any integration or combination of local motion signals. The first essential stage is a roughly logarithmic nonlinearity before orientation filtering. In general, the resulting cross-products (at the intersections) code unambiguously for the true plaid motion vector, but these signals will be nulled for multiplicatively combined plaid components. Supporting evidence for this idea is obtained in our measurements of detection thresholds for the 'plaid' and 'sliding' percepts. The essential element of the second stage consists of 'end-stop' cells which detect the nullable intersection signal, and so produce a plaid-motion signal with the required characteristics. Finally, it is argued that the ecological role of the proposed mechanism lies in the ability to handle movement of patterned objects in lighting conditions dominated by complicated cast shadows.

Striate cortical contribution to the surface-recorded pattern-reversal vep in the alert monkey

The striate cortical contribution to the surface pattern-reversal visual evoked potential (VEP) was investigated in awake monkeys during performance of a visual fixation task, by examining laminar profiles of VEP, current source density (CSD) and concomitant multiunit activity (MUA) in Area 17, recorded simultaneously at incremental depths using multicontact electrodes. Stimuli were black/white bar gratings centered on the fixation point. The typical surface pattern-reversal VEP over striate cortex consists of a prominent positivity peaking at 50–70 msec (P60), followed by a large negativity peaking at approx. 80 msec (N80), and then by a late broad positivity, peaking between 120 and 150 msec (P125). P60 is often preceded by a small negativity peaking at 45–55 msec (N50), and on rare occasions a small positivity (P40) is also observed. N50 is generated primarily by current sinks in Lamina 4C. P60 arises from large current sources in the supragranular laminae. N80 and P125 appear to be composite waveforms reflecting complex contributions from local activity and from activity occurring outside of the foveal/immediate parafoveal representation in Area 17. The basic physiologic sequence elicited by patterned stimulation is similar to that elicited by diffuse luminance or by electrical stimulation, but is characterized by more prominent supra- and infragranular activation. It is consistent with the cellular and synaptic anatomy of Area 17: initial activation of the thalamorecipient subdivisions of Lamina 4C, followed by activation of mid/upper Lamina 4 and of supra- and infragranular laminae. Our results suggest the possibility of differentiating synaptic stages and cellular processes reflected in the human VEP, based on homologies with simian VEP components.

The influence of grating characteristics on moiré fringe multiplication

Coherent optical techniques of fringe multiplication can be used to enhance the sensitivity of moire measurements. However, for some coherent optical-processing systems, the significance of the resulting interference pattern is influenced by the characteristics of the gratings being processed. Analysis of one commonly used system for fringe multiplication involving two bar and space amplitude gratings reveals that accuracy of displacements and strains calculated from a fringe pattern is very sensitive to the transmission ratios of the gratings being processed. For variations of the transmission ratio of only 10 percent from the ideal case of 50 percent, the interference patterns produced by optical processing no longer correspond to multiplied moire-fringe patterns.

Reflection of magnetostatic forward volume waves by ion-implanted periodic arrays

Reflection of magnetostatic forward volume waves impinging on 45° oblique incidence ion-implanted periodic arrays has been investigated. Waves propagating in pure yttrium iron garnet (YIG) epilayers are reflected by bars implanted with three kinds of ions (helium, boron, neon) at doses up to 1.5×1017 ions/cm2 and energies spread from 60 to 340 keV. For high doses, the YIG thickness damaged by incident ions was measured versus maximum ion energy. It reaches 1 μm for helium ions at 300 keV. The relative reflection response of 9 bar gratings was experimentally determined versus dose at different energies for a fundamental wavelength of 350 μm at 4 GHz and space harmonics. A saturation effect is observed for every ion type. The reflection coefficient per wave impedance discontinuity at saturation was deduced from measurement results for various implantation conditions. It can be larger than 10% for helium or boron ions at 150 keV. The origins of this reflection effect are discussed.