Gray Walls Research Articles

Bounded, High-Resolution Differencing Schemes Applied to the Discrete Ordinates Method

This paper presents an improved spatial differencing practice for the discrete ordinates form of the radiative transport equation (RTE). Several Bounded, high resolution (HR) schemes are applied to the primitive variable form of the RTE in a finite volume context. These schemes provide high accuracy while removing non-physical oscillations that are characteristic of the diamond difference scheme. A defect correction technique is applied to solve the equations that result from the high-order operators. Predictions from the HR schemes are compared to those of the conventional step and diamond difference schemes for a number of two-dimensional enclosures with gray walls and either absorbing or isotropically scattering media. Accuracy, stability, and effects on convergence are addressed for the different schemes. The HR schemes were found to provide both accuracy and boundedness at modest computational costs.

Locality and Pleasure in Landscape: A Study of Three Nineteenth-Century Scottish Watercolourists

Helensburgh is a Scottish town whose quiet streets lead uphill away from the North Clyde Estuary. A short walk from the waterfront esplanade, almost hidden behind a naval housing estate (1957), an observant tourist can contemplate the stone remains of Ardencaple Castle, parts of which might date to the thirteenth century but more of which dates to the eighteenth century. Walking near the stone wall which runs parallel to the small street, it is difficult to imagine that a large, imposing, perhaps intimidating, building once stood upon vast grounds, housing the chief of the Clan MacAuley (or Macaulay). Recently, I stood with a friend in the warm September sun looking at the grey wall, trying to imagine the visage and the determination of nineteenth-century watercolourist Kate Macaulay as she might have gazed, sketchbook in hand, at the then extant house, once the property of her dispersed clan. She may have turned her eyes and her pencil away from the house toward the river or toward the rolling, treed and rocky terrain that stretched beyond the castle walls toward Loch Lomond. She, after all, preferred to draw and paint land and water more than the buildings sprouting from the stone and the soil. But she did paint ‘MacAuley’ land, recording numbers of scenes in and around Loch Lomond, Gare Loch and Loch Long, sometimes moving beyond clan boundaries to Oban and Skye or to the area around her own ‘Ardencaple House’ in North Wales.

Effect of Ambient Illuminant on Surface Colour Constancy

Generally, we are completely enclosed in a real environment, which may act as an entire view-field or adapting field. But in most studies on colour constancy experiments have been made with spatially restricted stimuli. We built a room with gray (N5) walls inside to measure the effect of ambient illuminant on colour constancy. The room illuminant could change its colour from white (D65) to either blue, orange, green, or purple. The observer sat in this main room and adapted to the illuminant for 5 min before the start of the experiment. The observer was shown a smaller room, which had the same variable-colour illuminant, through an aperture (11 deg × 8 deg) in the left side wall. We set the illuminant for each room independently, but in asymmetric illuminant-colour conditions either was set to white. The observer viewed the central part of a colour CRT monitor, placed behind a small aperture (5 deg × 5 deg) in the front wall, and matched its colour appearance to four OSA colour chips in the smaller room. Under symmetric illuminant conditions, eg blue vs blue, the observers' settings showed a complete match with the physical chromaticities of the colour chips. In asymmetric illuminant conditions, eg white vs blue, matched colours showed systematic deviations from both physical chromaticities and colour constancy. This implies that taking the ambient illuminant as adapting field did not yield perfect colour constancy. We introduce a simple model based on incomplete adaptation to the ambient illuminant and a spatial-interaction mechanism, which accounts for our results.

Analysis of Discrete Ordinates Method with Even Parity Formulation

The even parity formulation (EPF) of the discrete ordinates method (DOM) is used to simulate radiative heat transfer in two-dimensional enclosures containing an absorbing-emitting and scattering medium. The discrete ordinates equations for the EPF are second-order differential equations and they are spatially discretized using a second-order central difference scheme. At the boundary, a higher-order upwind scheme is employed to prevent solution instability and minimize errors. The matrix solver of the discretized equations is based on a preconditioned conjugate gradients method. To investigate the accuracy and efficiency of the EPF of the DOM, several two-dimensional benchmark problems with an absorbing-emitting and scattering medium enclosed by gray walls are considered. By taking an appropriate numerical treatment, the numerical results from the EPF appear to compare favorably with other available solutions. However, the even parity solution usually requires more CPU time and iterations to converge in comparison with the conventional DOM, especially for the case with a small optical thickness.

USE OF THE 2-D COLLAPSED DIMENSION METHOD IN GRAY ENCLOSURES WITH ABSORBING-EMITTING-ISOTROPIC SCATTERING MEDIA IN RADIATIVE EQUILIBRIUM

A Cartesian-based method is proposed for combustion-radiation problems in gray enclosures having one ordinate symmetry and containing absorbing-emitting media with isotropic scattering. This method collapses the 3-D radiative information of the problem into its 2-D solution plane and is shown to be applicable for all ranges of optical thicknesses, including the optically very thin case, while maintaining near-analytic accuracy over most of this range. To accomplish this task, the collapsed dimension method makes use of effective intensity rays, each of which contains the information of the conglomerate of all the conventional intensity rays focused on the same point and contained in a plane that is both inclined at the same angle as the ray and is also normal to the solution plane. This novel procedure thus eliminates the use of solid angles and reduces both the complexity and the computational expense involved in the solution of such problems. The method is shown to be applicable to gray wall problems en...

Radiation heat transfer in dust-loaded systems

The design of radiation heat exchangers in the high-temperature range is influenced by the solid loading of the participating media. In order to obtain data and criteria for a more sophisticated design, emission measurements of different gas-dispersed solids (quartz sand, ash from fluidized bed combustion, corundum) have been carried out in an experimental plant specially designed for this purpose. An equation is derived to describe the particle emission coefficient in a geometry with surrounding grey walls. The experimental data fit this model well. An examination of the composition of the solids has shown the considerable influence of the quartz content on the radiation behaviour.

Comparison of discrete ordinates formulations for radiative heat transfer in multidimensional geometries

This article compares predictions of radiative heat transfer in two-dimension al enclosures for several formulations of the discrete ordinates method. The discrete ordinates equations are formulated for an absorbing, isotropically scattering, and re-emitting medium enclosed by gray walls. Control volume based finite element formulations of the radiative transport equation (RTE) are presented for the primitive variable (PV) and even parity (EP) equations. These formulations are compared to the finite element formulation of the EP equations, to the control volume formulation of the PV radiative transport equation, and to exact solutions. Several test enclosures are modeled, including enclosures with either absorbing or isotropically scattering media. Solution accuracy is investigated for two angular discretization schemes: 1) the Sn discrete ordinates approximation and 2) the piece wise constant angular approximation. The PV formulations of the RTE appear to be more accurate than EP formulations. Nomenclature Eh = emissive power, aT4, W/m2 G = incident energy, J477/ dil, W/m2 G* = nondimensional incident energy, GIEh I = intensity, /(r, ft), W/m2- sr M = total number of discrete ordinate directions N = total number of global nodes NJ = basis function N6 = number of divisions in polar direction Nfi = number of divisions in azimuthal direction n = surface normal Q* = nondimensional net wall heat flux, qlEh q =

Human rights and double standards

Crossing the street from Durant onto Telegraph Avenue heading toward the Berkeley library, I almost missed seeing the man with the matted gray beard as he crouched, leaning diagonally against the gray wall of the bank on the corner. I had been thinking about my friend Vilma, because somehow what had happened to her said something to me about human rights. My memory, like my eyes, was snagged by the still form of the homeless man. There he was, like a rock around which the stream must eddy, and I mused once again about how we all cringe from or blank out the bodies who live on our streets. What was this “passing by” doing to our spirit, this rapid decision to notice or not notice the human beings whose purpose in being on a sidewalk at a given moment is not to get somewhere, like to the Berkeley library to do research on human rights, but to catch up on sleep in the sun, minimally protected by the wall from the still chilly wind of early April.

Finite element formulation of the discrete-ordinates method for multidimensional geometries

Radiative heat transfer in a multidimensional participating medium was predicted using the discrete-ordinates (DO) method. The even parity radiative transfer equation (RTE) is formulated for an absorbing, isotropically scattering, and re-emitting medium enclosed by gray walls. The even parity RTE is spatially discretized with the finite element method. The solution accuracy and convergence are discussed for several element types. Several test enclosures are modeled. Results are compared with the standard DO control volume formulation, exact solutions, and the P3 differential approximation. Solutions are found for enclosures with either absorbing or isotropically scattering media. Results compare well with published results. Also, the use of the method for complex geometries and unstructured grids is discussed. Nomenclature Eh = emissive power, 6T4, W/m2 G = incident energy, J47r / dft, W/m2 G* = nondimensional incident energy, G/Eb I = intensity, 7(r, ft), W/m2-sr L = characteristic length, m M = total number of discrete ordinate directions N = total number of global nodes NJ = basis function n = surface normal Q* = nondimensional net wall heat flux, qlEb q = heat flux, J2ir |rt-ft|7 dft, W/m2

Radiant and convective heat transfer for flow of a radiation gas in a heated/cooled tube with a grey wall

An analytical investigation is presented of the influence of radiative heat transfer on the complex heat exchange problem involving flow of an optically active (radiating) gas inside a tube of diffuse grey properties. The method used is based on Hottel's formulation of zone division, and involves the transformation-zone approach, where radiation gas emission is replaced with an equivalent surface emission. Separable-kernel and surface transformation techniques give a set of non-linear differential equations treated by the Runge-Kutta method with Hamming modification. The solutions are governed by several independent parameters such as the wall and radiation gas emissivities, inlet and exit gas temperatures, length diameter ratio of the tube, uniform and non-uniform heat flux and variable convective heat transfer coefficient at the inner surface. The results apply both to heating and cooling situations.

Parallelization of 3-D Radiative Heat Transfer Analysis in Non-gray Gas.

A parallel computational method is developed for the Monte Carlo analysis of radiative heat transfer in three-dimensional nongray gas enclosed by gray walls. The highly parallel computer AP1000 is used for the analysis. For the nongray gas, a mixture of water vapor and carbon dioxide is chosen as the absorbing-emitting medium. Three types of parallelization are studied: type (1), event parallelization; type (2), combination of event parallelization and algorithm parallelization, and type (3), memory-saving algorithm of type (2). When 512 cells are used, values of the speed-up ratios of 395, 430, and 370 are obtained for types (1), (2), and (3), respectively. The maximum number of elements which can be treated is increased from 1200 for type (1) to 140000 for type (3).

The stepwise gray P-1 approximation for multi-dimensional radiative transfer in molecular-gas—particulate mixtures

The stepwise gray method is the simplest method for incorporating the effects of absorption-emission bands in radiative heat transfer calculations. The non-gray character of the mixture is replaced by an “equivalent” stepwise gray character. A method to obtain this equivalent gray character by utilizing the mean beam length is outlined. This method is coupled with the P-1 approximation, resulting in a simple model to deal with radiation from gas-particulate media in multi-dimensional geometries. To validate the accuracy of the method, it is applied to a few simple 1-D problems, i.e., to isothermal plane-parallel and spherical media as well as to plane-parallel media at radiative equilibrium. Absorption and scattering behavior are studied for both black and gray walls. Results are compared with those obtained from Monte Carlo calculations incorporating the exponential-wide-band model, indicating good accuracy for all conditions studied, within the limitations of the P-1 approximation.

Firing properties of hippocampal neurons in a visually symmetrical environment: contributions of multiple sensory cues and mnemonic processes

The location-specific firing of hippocampal place cells can easily be brought under the control of experimenter-defined cues. Nevertheless, there is evidence that these firing fields are not determined just by immediate sensory input, but also by earlier states of the nervous system (O'Keefe and Speakman, 1987). Here, we report further on the roles of multiple visual cues and mnemonic processes in determining the firing of place cells. Rats were trained to chase food pellets in a cylinder with homogeneous gray walls and 1 white cue card. After a cell's field was recorded in this "standard" condition, probe sessions were conducted in which a second card was placed 180 degrees away from the first. This configuration created a diametrically symmetrical environment in which pairs of locations 180 degrees apart were identical with respect to views of the wall and cards. If place cells are strongly controlled by these immediately available views, firing in the 2-card configuration should be diametrically symmetrical. Alternatively, because the rat moves freely in the cylinder, information is available that pairs of visually identical places are not truly the same. If some mnemonic process stores and updates information about the rat's paths during the session, it is possible that the firing pattern will be different in 2 such places, especially because the original training was conducted in the 1-card, asymmetrical environment. Thirteen of 18 cells had a single, asymmetric firing pattern after the second card was introduced; the field was the same size and shape as in the 1-card configuration and in the same spatial relation to 1 of the 2 cards. The field position during 2-card sessions could be rotated 180 degrees by starting the rat by one card or the other. In further probe sessions in which the cue cards, entry location, and background cues were, in various combinations, rotated in relation to each other, these cells always showed a single field, similar in size and shape to that in the standard, and in the same relationship as in the standard to as many cues as possible. The remaining 5 cells showed complex changes over repeated 2-card sessions, and 3 of these showed paired fields, 180 degrees apart for at least some of the sessions. In one case, the second field disappeared with repeated exposures to 2 cards; in another, the second field persisted when only 1 card was used. We conclude that place cells are influenced both by the immediate sensory configuration and by internal neural states related to earlier experience in the environment.

Three-dimensional radiative heat-transfer solutions by the discrete-ordinates method

Radiative heat transfer in a three-dimensional participating medium was predicted using the discrete-ordinates method. The discrete-ordinates equations are formulated for an absorbing, anisotropically scattering, and re-emitting medium enclosed by gray walls. The solution strategy is discussed and the conditions for computational stability are presented. Several test enclosures are modeled. Results have been obtained for the S2, S4, S6, and S8 approximation s that correspond to 8, 24, 48, and 80 fluxes, respectively, and are compared with the exact-zone solution and the P3 differential approximation. Solutions are found for conditions that simulate absorbing media and isotropically and anisotropically scattering media. Solution accuracy and convergence are discussed for the various flux approximations. The S4, S6, and S8 solutions compare favorably with the other methods and can be used to predict radiant intensity, incident energy, and surface heat flux. A an bn B C E G / L n q r S x y z a /U,,£,TJ p a a © V Nomenclature = north-south areas, m2 = coefficients of a Legendre series = coefficients of a modified Legendre series = east-west areas, m2 = front-back areas, m2 = emissive power ( = aT4), W/m2 = incident energy, /4w/d6, W/m2 = radiant intensity, W/(m2 • Sr) = enclosure dimension, m = unit normal = heat flux, W/m2 = position vector, m = source term, W/m3 = volume of pth control volume, m3 = weight function in a direction - m (fractional area of a unit sphere) = coordinate, m = coordinate, m = coordinate, m — finite-difference weighting factor = extinction coefficient, a -f K,m~l = surface emittance = absorption coefficient, m1 = ordinates p = cos0, £ = sin0 sin , TJ = sinG cos = outgoing direction of radiation = phase function = surface reflectance = scattering coefficient, m1 = Boltzmann's constant, 5.669 X 1(T 8 W/(m2

Landing responses of the tsetse fly Glossina morsitans morsitans Westwood and the stable fly Stomoxys calcitrans (L.) (Diptera: Glossinidae & Muscidae) to black-and-white patterns: a laboratory study

AbstractThe landing preferences of fed males of Glossina morsitans morsitans Westwood and Stomoxys calcitrans (L.) were measured under constant conditions in a two-choice situation. Pairs of black-and-white landing targets were presented on the grey walls of an arena ca 60 cm in diameter. In a simple choice of blackness vs whiteness, G. m. morsitans showed a ninefold greater preference for black; S. calcitrans displayed no preference. G. m. morsitans landed twice as frequently on a 15×30-cm vertical black stripe as on a horizontal one, but S. calcitrans preferred the horizontal one. Comparisons between a vertical stripe (or a horizontal one) and similar stripes sloping at various angles indicated that at about 50° G. m. morsitans distinguished the sloping stripe from the vertical (or the horizontal), but did not well distinguish slopes closer to the vertical (or horizontal). Tests with multiple vertical stripe patterns indicated that G. m. morsitans did not significantly distinguish between a single 15-cm stripe and two- or three-striped targets of the same total black area, but landed significantly less frequently on targets of four or five stripes, implying an angular, behavioural visual ‘resolution' of roughly 17°; S. calcitrans responded similarly. Both species showed a marked preference for landing near the edge of the black on all targets, with G. m. morsitans strongly biassed to the black side of an interface.

Radiative and conductive transfer for a real gas in a cylindrical enclosure with gray walls

The purpose of this study is to examine the interaction of radiative and conductive transfer for a radiatively participating real gas stagnant in a cylindrical enclosure with gray diffuse walls. Consideration of reflecting boundaries represents an extension of previous black wall studies. Examination of radiative transfer was made by the zone method with gas radiative properties furnished by the weighted sum of gray gases model. Directed flux areas are expressed as the weighted sum of gray gas total exchange areas which are evaluated using the matrix formulation method from direct exchange areas. Axial and radial gas temperatures are examined along with wall heat flux or temperature for respective cases of either specified wall temperatures or heat fluxes. Emphasis is placed on examining results to show the effects of wall emittance and duct diameter. Results for heat generation within the gas are also presented.

Coupled Radiative and Conductive Heat Transfer in a Two-Dimensional Rectangular Enclosure With Gray Participating Media Using Finite Elements

A numerical solution of the exact equations of coupled radiative/conductive heat transfer and temperature distribution inside a medium, and of the heat flux distribution at all the gray walls of a two-dimensional rectangular enclosure with the medium having uniform absorbing/emitting properties, using the finite element method, is presented. The medium can also have distributed energy sources. Comparison is made to the results of the P-3 approximation method.

The Road to Paradise: First Notes on Marianne Moore's "An Octopus"

traveler to Seattle who arrives on an overcast day sees a somber but beautiful Puget Sound to the west. To the east, he sees the hills of the city surrounding Lakes Washington and Union, and beyond them to the southeast, nothing at all: a gray wall like any rainy vista in the lowland parts of the country. When the skies clear, however, from that wall of nothingness, the mountain comes out, as the natives say, as if it were a sun. vast, snowy bulk seems to arise from the sea and in its utter hugeness dominates everything east of the Pacific. effect is startling, awesome, unforgettable. Indians called it Tacoma, The Mountain who is God; the English, Mt. Rainier. point of access to its peak, a meadow perched on the side of the great Nisqually Glacier, is called Paradise. Marianne Moore traveled to Paradise Park in July 1922 when she spent two days on the mountain. An Octopus is the record of that trip and of a second journey to the Northwest made the following summer; the poem also includes some of the sights seen on both trips along the route from New York through the Canadian Rockies to Washington. In the following pages, I will sketch the biographical circumstances for the poem, through them examine the method of composition and the poem's organization, and then focus on one major set of images: Mt. Rainier and the references to Greece.' I will consider the first extant

Influences of Potassium, Cultivar, and Season on Tomato Graywall and Blotchy Ripening1

Abstract ‘Healani’, ‘Homestead-24’, ‘Walter’, and ‘Flora-Dade’ tomatoes (Lycopersicon esculentum Mill.) were grown with 0, 93, 186, 372, or 744 kg K/ha during spring and fall to determine the influence of K rate, cultivar, and season on the separate fruit disorders of graywall (GW) and blotchy ripening (BR). Susceptibility to GW was determined by inoculating a GW-inducing type of bacteria, Erwinia herbicola (Dye), into the outer pericarp of immature green fruit. All 4 cultivars developed more GW without added K than with it during the spring season. In both field and greenhouse conditions, ‘Flora-Dade’ and ‘Homestead-24’ were more resistant to GW than ‘Healani’ and ‘Walter’. Natural GW, contrasted to bacterially induced GW, occurred in ‘Healani’ and ‘Homestead-24’ fruit grown with low K concentrations in a sand culture experiment. Both cultivars were free of natural GW with the high-K treatment. ‘Flora-Dade’ was resistant to natural GW under all K treatments. Fruit from all cultivars had significantly less BR with K fertilization in both seasons. External blotchy ripening (EBR) and internal blotchy ripening (IBR) were more severe in the spring than in the fall. ‘Healani’ showed resistance to yellow shoulder, the primary EBR symptom, which was severe during the spring in all other culti vars. ‘Healani’ was generally the most BR-resistant cultivar and ‘Flora-Dade’ the most BR-susceptible. Pericarp K concentration increased with K rate in all cultivars during both seasons, but differences in susceptibility to BR between cultivars were not associated with differences in pericarp K, Ca, Mg, or P content.

The Games they Play (At Siesta Time): Juegos a la hora de siesta

The action takes place on a bright day, siesta time, in the corner of some park or square. In the background there is a high gray wall: centre stage, a park bench. A hammock is suspended from a tree which is to the left of the bench; the hammock should be at a height which makes it appear that the actor is swinging over the orchestra pit. Near the edge of the stage to the right of the bench, is a sandbox. The light is dazzlingly brilliant. The characters, although they are children, are played by adults; a mature restraint rather than a puerile interpretation should characterize these roles. In the interplay of characters the actors should caricaturize ‘miniature adults’, prototypes of their future selves. The properties should be commensurate with the actual size of the actors; therefore they will be larger than is ordinarily the case with children. When the stage is set, a shrill, strident chirping and singing of birds is heard, interrupted ever so often by sounds of children playing at war… rrrrrrrr… tata tatatatat… When the curtain rises, the stage is flooded with sunshine. Diego is playing in the sandbox; he is kneeling and his arms are extended outward in an imitation of a plane in combat; he simulates the march of tanks as well; he mimics bombs falling, explosions, and the roar of motors with his voice. Each time a plane is presumably hit, his body lifts off the ground, then falls, creating a shower of sand which falls over his body and reaches the orchestra pit; he is completely absorbed in the game and lost to the world.