Biomedical and Chemical EngineeringCopyright (c) 2017 Syracuse University All rights reserved.
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Recent documents in Biomedical and Chemical Engineeringen-usFri, 14 Apr 2017 11:01:48 PDT3600Using the symmetry of false matches to solve the correspondence problem.
http://surface.syr.edu/bce/47
http://surface.syr.edu/bce/47Fri, 14 Apr 2017 11:01:30 PDT
Sensing stereoscopic depth requires that image points be binocularly matched. Therein lies the correspondence problem: how are true matches distinguished from false ones? Conventional algorithms select true matches on the basis of correlated features and adherence to natural statistics, while rejecting false matches as noise. We propose here an alternative that uses the signals present in false matches to delineate the true solution. When visualized in a Keplerian array, binocular matches are symmetrically reflected about an axis that represents a potential solution. Surface properties such as slant and curvature are encoded the transformation that describes how one-half of the matches reflects across the symmetry axis onto the other. To implement this strategy, we convolved left and right images with Gaussian kernels of various standard deviations (spatial frequencies). We then produced Keplerian arrays by comparing filter responses across left and right spatial-frequency combinations. Responses that are minimally different across the eyes gave rise to regions of high symmetry; response position within the Keplerian array gave the location of a solution in space. Solutions possessing natural surface regularities consistently showed minimal differences for one left : right spatial frequency ratio, which is correlated with the local surface slant. As a result, combining responses within particular ratio families can distinguish true matches from false ones. True matches tend to be elongated and smoothly contoured, with symmetry preserved across all members of a ratio family from low to high spatial-frequency combinations. This approach is efficient; preprocessing is minimal since no feature extraction is involved. It can be implemented in machine vision to solve the correspondence problem for depth sensing algorithms. It is robust when tested against perfectly camouflaged surfaces in random dot stereograms and consistent with physiological data showing that false match signals are propagated to higher cortical areas along the dorsal pathway.
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Cherlyn J. Ng et al.Stereoacuity improves after short-term binocular pattern mismatch.
http://surface.syr.edu/bce/46
http://surface.syr.edu/bce/46Fri, 14 Apr 2017 11:01:26 PDT
Monocular deprivation can chronically suppress vision in the deprived eye, if it is applied for sufficient duration early in life. However, it can have a transient effect in the opposite direction if applied briefly (a few hours) to normal adults. This short-term monocular deprivation appears to increase the gain for the deprived eye relative to the undeprived eye, affecting binocular vision by shifting the interocular balance. An interocular gain difference produced by patching a single eye might be expected to lower stereoacuity in normal observers, since raising contrast in just one eye reduces stereoacuity (the ‘contrast paradox’). We hypothesized that alternately depriving each eye in turn might benefit stereoacuity by increasing post‐deprivation gain in both eyes and dampening interocular suppression. We switched a translucent patch between the eyes of visually normal adult observers hourly for 6 hours. The unpatched eye viewed the natural visual environment. Compared to pre-patch performance, post-patch grating stereoacuity, measured during 20 minutes following patch removal, improved by 20% to 33%. In a second experiment, we alternately covered the left and right eyes of two observers with cylinder lenses to determine the existence of orientation-specific gain. Each eye was ‘patched’ with the lens for 45 or 60 minute periods, giving a total through-the-lens viewing of 4 to 6 hours. Unexpectedly, post-patching stereoacuity improved for test gratings with the same orientation as seen through the lens and worsened for orthogonal gratings. This result cannot be explained by monocular orientation adaptation. It implies that the interocular balance has a channel structure that is modulated not specifically by monocular deprivation but rather by interocular pattern mismatch. The post-patching enhancement evident in both experiments indicates that interocular suppression may limit stereoacuity under natural viewing conditions.
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Bart Farell et al.Attention to pattern depth depends on pattern dimensionality
http://surface.syr.edu/bce/45
http://surface.syr.edu/bce/45Fri, 14 Apr 2017 11:01:22 PDT
The perceived stereo depth separating two stimuli usually varies with the horizontal disparity difference between the stimuli. This, however, is not the case when one or both stimuli are one-dimensional. Instead, perceived depth depends on the difference between the disparity vectors of the two stimuli; relative disparity magnitude and direction both matter, interactively (Farell, Chai, Fernandez, Vis. Res., 2009). Here, we compare judgments of the depth of 1-D and 2-D stimuli, asking how attention affects this interaction. Our displays contained a central stimulus whose disparity varied across trials. This stimulus was either 1-D (a grating) or 2-D (a plaid). The stimuli surrounding the center were oblique-disparity plaids, the location of one being designated as relevant. The task was to judge the relative depth of the central stimulus and the relevant plaid; the remaining plaids were irrelevant throughout the block of trials and were to be ignored. Psychometric functions for depth judgments of the grating and the relevant plaid shifted laterally in response to the plaid's disparity direction (parallel or orthogonal to the grating's disparity). Interestingly, the disparities of irrelevant plaids produced exactly the same effect. Thus, attention failed to distinguish relevant and irrelevant stimuli when observers judged a grating-plaid pair. By contrast, when the stimuli being judged were both plaids, psychometric functions were affected neither by the disparities of irrelevant stimuli nor by the disparity direction of relevant stimuli. Attentional filtering of disparity signals thus succeeded only when observers judged the depths of 2-D stimuli. The judged depth of a 1-D stimulus varied with all the disparities in the display, whether relevant or irrelevant, revealing a disparity field that could be useful in transforming ambiguous 1-D component disparities into coherent object depths.
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Bart Farell et al.The Perception of Symmetry in Depth: Effect of Symmetry Plane Orientation
http://surface.syr.edu/bce/44
http://surface.syr.edu/bce/44Fri, 14 Apr 2017 11:01:18 PDT
The visual system is sensitive to symmetries in the frontoparallel plane, and bilateral symmetry about a vertical axis has a particular salience. However, these symmetries represent only a subset of the symmetries realizable in three-dimensional space. The retinal image symmetries formed when viewing natural objects are typically the projections of three-dimensional objects—animals, for example—that have a symmetry in depth. To characterize human sensitivity to depth symmetry, experiments measured observers’ ability to discriminate stereo displays that were symmetrically distributed in depth and those that were asymmetrically distributed. Disparity values were distributed about one of four planes passing through the z-axis and differing in frontoparallel orientation. Asymmetrical patterns were generated by perturbing one of these disparities. Symmetrical-asymmetrical discrimination thresholds were lowest for symmetry about the vertical plane and highest for the horizontal plane. Thresholds for discriminating repetitions and non-repetitions of depth values did not differ across the four planes, whereas discriminations for depth gradients differed from both the symmetry and repetition cases. The heightened sensitivity to symmetry in depth about the vertical plane is a 3-D analog of 2-D mirror-image symmetry performance and could be its source.
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Bart FarellTrue Three-Dimensional Camera
http://surface.syr.edu/bce/43
http://surface.syr.edu/bce/43Fri, 14 Apr 2017 11:01:14 PDT
An imager that can measure the distance from each pixel to the point on the object that is in focus at the pixel is described. This is accomplished by short photo-conducting lightguides at each pixel. In the eye the rods and cones are the fiber-like lightguides. The device uses ambient light that is only coherent in spherical shell-shaped light packets of thickness of one coherence length. Modern semiconductor technology permits the construction of lightguides shorter than a coherence length of ambient light. Each of the frequency components of the broad band light arriving at a pixel has a phase proportional to the distance from an object point to its image pixel. Light frequency components in the packet arriving at a pixel through a convex lens add constructively only if the light comes from the object point in focus at this pixel. The light in packets from all other object points cancels. Thus the pixel receives light from one object point only. The lightguide has contacts along its length. The lightguide charge carriers are generated by the light patterns. These light patterns, and thus the photocurrent, shift in response to the phase of the input signal. Thus, the photocurrent is a function of the distance from the pixel to its object point. Applications include autonomous vehicle navigation and robotic vision. Another application is a crude teleportation system consisting of a camera and a three-dimensional printer at a remote location.
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Philipp Kornreich et al.Thermal stability and decomposition of diesel fuel under subcritical and supercritical conditions
http://surface.syr.edu/bce/42
http://surface.syr.edu/bce/42Fri, 14 Apr 2017 11:01:11 PDT
A novel concept of clean diesel combustion using supercritical fluids is proposed and being investigated to address some key challenges encountered in the fuel and transportation sector. The core of this concept is to inject diesel fuel (DF) in the supercritical state to achieve clean, high-efficient combustion in diesel engines. Among other challenging issues that must be addressed for the implementation of this new concept is the thermal stability of DF and the potential decomposition and solid deposit formation under engine conditions. In this work, thermal stability of DF was experimentally evaluated under subcritical and supercritical conditions in both static (batch system) and dynamic (continuous flow system) thermal stressing systems. The effects of thermal stressing temperature (200-440 oC) and duration (10-600 min) and CO2 concentration (~10 wt%) were examined. DF decomposition is characterized by the average absolute deviation (AAD) of GC peak area percentages of all individual components. A temperature-time window (400-420 2 oC, 0-60 min) where supercritical DF combustion in diesel engines may be possible was determined. CO2 as a diluent could prevent or reduce accumulation of solid deposits inside fuel pipes mainly due to an increased solubilization capacity of DF. Finally, different structures and morphologies of solid deposits observed under different batch thermal stressing conditions were discussed.
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Ronghong Lin et al.Perceived Depth in Non-Transitive Stereo Displays
http://surface.syr.edu/bce/41
http://surface.syr.edu/bce/41Fri, 14 Apr 2017 11:01:07 PDT
The separation between the eyes shapes the distribution of binocular disparities and gives a special role to horizontal disparities. However, for one-dimensional stimuli, disparity direction, like motion direction, is linked to stimulus orientation. This makes the perceived depth of one-dimensional stimuli orientation dependent and generally non-veridical. It also allows perceived depth to violate transitivity. Three stimuli, A, B, and C, can be arranged such that A > B (stimulus A is seen as farther than stimulus B when they are presented together) and B > C, yet A ≤ C. This study examines how the visual system handles the depth of A, B, and C when they are presented together, forming a pairwise inconsistent stereo display. Observers’ depth judgments of displays containing a grating and two plaids resolved transitivity violations among the component stimulus pairs. However, these judgments were inconsistent with judgments of the same stimuli within depth-consistent displays containing no transitivity violations. To understand the contribution of individual disparity signals, observers were instructed in subsequent experiments to judge the depth of a subset of display stimuli. This attentional instruction was ineffective; relevant and irrelevant stimuli contributed equally to depth judgments. Thus, the perceived depth separating a pair of stimuli depended on the disparities of the other stimuli presented concurrently. This context dependence of stereo depth can be approximated by an obligatory pooling and comparison of the disparities of oneand two-dimensional stimuli along an axis defined locally by the stimuli.
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Bart Farell et al.The Perception of Symmetry in Depth: Effect of Symmetry Plane Orientation.
http://surface.syr.edu/bce/40
http://surface.syr.edu/bce/40Fri, 14 Apr 2017 11:01:00 PDT
The visual system is sensitive to symmetries in the frontoparallel plane, and bilateral symmetry about a vertical axis has a particular salience. However, these symmetries represent only a subset of the symmetries realizable in three-dimensional space. The retinal image symmetries formed when viewing natural objects are typically the projections of three-dimensional objects—animals, for example—that have a symmetry in depth. To characterize human sensitivity to depth symmetry, experiments measured observers’ ability to discriminate stereo displays that were symmetrically distributed in depth and those that were asymmetrically distributed. Disparity values were distributed about one of four planes passing through the z-axis and differing in frontoparallel orientation. Asymmetrical patterns were generated by perturbing one of these disparities. Symmetrical-asymmetrical discrimination thresholds were lowest for symmetry about the vertical plane and highest for the horizontal plane. Thresholds for discriminating repetitions and non-repetitions of depth values did not differ across the four planes, whereas discriminations for depth gradients differed from both the symmetry and repetition cases. The heightened sensitivity to symmetry in depth about the vertical plane is a 3-D analog of 2-D mirror-image symmetry performance and could be its source.
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Bart FarellPerceived depth in non-transitive stereo displays.
http://surface.syr.edu/bce/39
http://surface.syr.edu/bce/39Fri, 14 Apr 2017 11:00:55 PDT
The separation between the eyes shapes the distribution of binocular disparities and gives a special role to horizontal disparities. However, for one-dimensional stimuli, disparity direction, like motion direction, is linked to stimulus orientation. This makes the perceived depth of one-dimensional stimuli orientation dependent and generally non-veridical. It also allows perceived depth to violate transitivity. Three stimuli, A, B, and C, can be arranged such that A > B (stimulus A is seen as farther than stimulus B when they are presented together) and B > C, yet A 6 C. This study examines how the visual system handles the depth of A, B, and C when they are presented together, forming a pairwise inconsistent stereo display. Observers’ depth judgments of displays containing a grating and two plaids resolved transitivity violations among the component stimulus pairs. However, these judgments were inconsistent with judgments of the same stimuli within depth-consistent displays containing no transitivity violations. To understand the contribution of individual disparity signals, observers were instructed in subsequent experiments to judge the depth of a subset of display stimuli. This attentional instruction was ineffective; relevant and irrelevant stimuli contributed equally to depth judgments. Thus, the perceived depth separating a pair of stimuli depended on the disparities of the other stimuli presented concurrently. This context dependence of stereo depth can be approximated by an obligatory pooling and comparison of the disparities of oneand two-dimensional stimuli along an axis defined locally by the stimuli.
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Bart Farell et al.Effective Permittivity of Dense Random Particulate Plasmonic Composites
http://surface.syr.edu/bce/38
http://surface.syr.edu/bce/38Fri, 06 Jul 2012 11:10:34 PDTSatvik N. Wani et al.Conductivity of N-Dimensional Composites Containing Hyperspherical Inclusion
http://surface.syr.edu/bce/37
http://surface.syr.edu/bce/37Tue, 27 Mar 2012 11:20:26 PDT
A problem of determining the macroscopic or effective thermal conductivity of an N-dimensional composite medium containing N-dimensional nonoverlapping hyperspherical inclusions is considered. Since the macroscopic conductivity is expected to become less sensitive to the detailed spatial distribution of the inclusions for N ≥ 4, only the special case of periodic arrangement of the inclusions is considered. An expression for the macroscopic conductivity correct to O(χ3N + 8), χ being the ratio of "diameter" of the inclusions to the spacing between them, is derived and the numerical results for the conductivity are presented as a function of χ and N for the two special cases of perfectly conducting and insulating inclusions. The effective conductivity of the composite is found to approach that of the continuous matrix in higher dimensions.
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Ashok S. SanganiTransport Processes in Random Arrays of Cylinders. II. Viscous Flow
http://surface.syr.edu/bce/36
http://surface.syr.edu/bce/36Tue, 27 Mar 2012 11:20:25 PDT
A numerical method is developed that takes into account the many-particle interactions in a rigorous manner to determine the effective thermal conductivity Km of a composite medium consisting of parallel circular cylinders of thermal conductivity ak suspended in a matrix of conductivity k. Numerical results for Km are presented for a wide range of a and o, the area fraction of the cylinders, after averaging over several computer-generated random arrays of cylinders. The results obtained via this exact method are compared with those of various approximate analytical methods to assess their utility in predicting Km.
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Ashok S. Sangani et al.Transport Processes in Random Arrays of Cylinders. I. Thermal Conduction
http://surface.syr.edu/bce/35
http://surface.syr.edu/bce/35Tue, 27 Mar 2012 11:20:23 PDT
A numerical method is developed that takes into account the many particle interactions in a rigorous manner to determine the effective thermal conductivity of Km of a composite medium consisting of parallel circular cylinders of thermal conductivity ak suspended in a matrix of conductivity k. Numerical results for Km are presented for a wide rane of a and o, the area fraction of the cylinders, after averaging over several computer-generated random arrays of cylinders. The results obtained via this exact method are compared with those of various approximate analystical methods to assess their utility in predicting Km.
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Ashok S. Sangani et al.Nusselt Number for Flow Perpendicular to Arrays of Cylinders in the Limit of Small Reynolds and Large Peclet Numbers
http://surface.syr.edu/bce/34
http://surface.syr.edu/bce/34Tue, 27 Mar 2012 11:20:22 PDT
The problem of determining the Nusselt number N, the nondimensional rate of heat or mass transfer, from an array of cylindrical particles to the surrounding fluid is examined in the limit of small Reynolds number Re and large Peclet number Pe. N in this limit can be determined from the details of flow in the immediate vicinity of the particles. These are determined accurately using a method of multipole expansions for both ordered and random arrays of cylinders. The results for N/Pe^1/3 are presented for the complete range of the area fraction of cylinders. The results of numerical simulations for random arrays are compared with those predicted using effective-medium approximations, and a good agreement between the two is found. A simple formula is given for relating the Nusselt number and the Darcy permeability of the arrays. Although the formula is obtained by fitting the results of numerical simulations for arrays of cylindrical particles, it is shown to yield a surprisingly accurate relationship between the two even for the arrays of spherical particles for which several known results exist in the literature suggesting thereby that this relationship may be relatively insensitive to the shape of the particles.
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Ashok S. Sangani et al.The Added Mass, Basset, and Viscous Drag Coefficients in Nondilute Bubbly Liquids Undergoing Small-Amplitude Oscillatory Motion
http://surface.syr.edu/bce/33
http://surface.syr.edu/bce/33Tue, 27 Mar 2012 11:20:20 PDT
The motion of bubbles dispersed in a liquid when a small-amplitude oscillatory motion is imposed on the mixture is examined in the limit of small frequency and viscosity. Under these conditions, for bubbles with a stress-free surface, the motion can be described in terms of added mass and viscous force coefficients. For bubbles contaminated with surface-active impurities, the introduction of a further coeflicient to parametrize the Basset force is necessary. These coefficients are calculated numerically for random configurations of bubbles by solving the appropriate multibubble interaction problem exactly using a method of multipole expansion. Results obtained by averaging over several configurations are presented. Comparison of the results with those for periodic arrays of bubbles shows that these coefficients are, in general, relatively insensitive to the detailed spatial arrangement of the bubbles. On the basis of this observation, it is possible to estimate them via simple formulas derived analytically for dilute periodic arrays. The effect of surface tension and density of bubbles (or rigid particles in the case where the no-slip boundary condition is applicable) is also examined and found to be rather small.
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Ashok S. Sangani et al.A Method for Determining Stokes Flow Around Particles Near a Wall or in a Thin Film Bounded by a Wall and a Gas-Liquid Interface
http://surface.syr.edu/bce/32
http://surface.syr.edu/bce/32Tue, 27 Mar 2012 11:20:19 PDT
A method for determining Stokes flow around particles near a wall or in a thin film bounded by a wall on one side and a nondeformable gas-liquid interface on the other side is developed. The no-slip boundary conditions at the wall are satisfied by constructing an image system based on Lamb’s multipoles. Earlier results for the image systems for the flow due to a point force or a force dipole are extended to image systems for force or source multipoles of arbitrary orders. For the case of a film, the image system consists of an infinite series of multipoles on both sides of the film. Accurate evaluation of the flow due to these images is discussed, including the use of Shanks transforms. The method is applied to several problems including chains of particles, radially expanding particles, drops, and porous particles.
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Ashok S. Sangani et al.Determination of Particle Size Distributions from Acoustic Wave Propagation Measurements
http://surface.syr.edu/bce/31
http://surface.syr.edu/bce/31Tue, 27 Mar 2012 11:20:18 PDT
The wave equations for the interior and exterior of the particles are ensemble averaged and combined with an analysis by Allegra and Hawley @J. Acoust. Soc. Am. 51, 1545 ~1972!# for the interaction of a single particle with the incident wave to determine the phase speed and attenuation of sound waves propagating through dilute slurries. The theory is shown to compare very well with the measured attenuation. The inverse problem, i.e., the problem of determining the particle size distribution given the attenuation as a function of frequency, is examined using regularization techniques that have been successful for bubbly liquids. It is shown that, unlike the bubbly liquids, the success of solving the inverse problem is limited since it depends strongly on the nature of particles and the frequency range used in inverse calculations.
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Ashok S. Sangani et al.Inclusion of Lubrication Forces in Dynamic Simulations
http://surface.syr.edu/bce/30
http://surface.syr.edu/bce/30Tue, 27 Mar 2012 11:20:16 PDT
A new method is described for incorporating close-field, lubrication forces between pairs of particles into the multiparticle Stokes flow calculations. The method is applied to the suspensions of both spherical as well as cyliridrical particles, and results computed by the method are shown to be in excellent agreement with the exact known results available in the literature.
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Ashok S. Sangani et al.An O(N) Algorithm for Stokes and Laplace Interactions of Particles
http://surface.syr.edu/bce/29
http://surface.syr.edu/bce/29Tue, 27 Mar 2012 11:20:15 PDT
A method for computing Laplace and Stokes interactions among N spherical particles arbitrarily placed in a unit cell of a periodic array is described. The method is based on an algorithm by Greengard and Rokhlin [J. Comput. Phys. 73, 325 (1987)] for rapidly summing the Laplace interactions among particles by organizing the particles into a number of different groups of varying sizes. The far-field induced by each group of particles is expressed by a multipole expansion technique into an equivalent field with its singularities at the center of the group. The resulting computational effort increases only linearly with N. The method is applied to a number of problems in suspension mechanics with the goal of assessing the efficiency and the potential usefulness of the method in studying dynamics of large systems. It is shown that reasonably accurate results for the interaction forces are obtained in most cases even with relatively low-order multipole expansions.
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Ashok S. Sangani et al.A Method for Computing Stokes Flow Interactions Among Spherical Objects and its Application to Suspensions of Drops and Porous Particles
http://surface.syr.edu/bce/28
http://surface.syr.edu/bce/28Tue, 27 Mar 2012 11:20:14 PDT
A method for computing Stokes flow interactions in suspensions of spherical objects is described in detail and applied to the suspensions of porous particles, drops, and bubbles to determine their hydrodynamic transport coefficients.
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Ashok S. Sangani et al.