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Application of the Lattice-Boltzmann method to the modeling of population blob dynamics in 2D porous domains

COMPUTERS & MATHEMATICS WITH APPLICATIONS 2010年第7期59卷 2315-2325页

作者： Yiotis, A. G. Kainourgiakis, M. E. Kikkinides, E. S. Stubos, A. K. Natl Ctr Sci Res Demokritos Athens 15310 Greece Univ Western Macedonia Dept Mech Engn Kozani 50100 Greece

In the present paper, the Lattice-Boltzmann method is employed for the simulation of immiscible two-phase flow through a 20 porous domain when the volume fraction of the non-wetting phase is relatively low and thus it flows in the form of disconnected blobs. The flow problem is solved using an immiscible two-phase LB model where interfacial forces are expressed in terms of the chemical potential through the Gibbs-Duhem equation. We study the population dynamics of the non-wetting fluid blobs, namely the temporal evolution of the average blob size, with respect to the applied body force and the wetting phase volume fraction. Our results show that the system reaches a "steady state" where the average values of the studied parameters, such as the superficial velocities of both phases, and the number and size distribution of the blobs remain practically constant in time, although the temporal fluctuations around average values may be significant. We show that the average volume of the blobs decreases (and the population of the blobs increases) as the body force increases, namely as the viscous forces become dominant over capillary forces. The effect of the wetting volume fraction on the number of the blobs is more complex;as the wetting volume fraction decreases at constant body force, the blobs cover larger areas within the pore space producing larger pressure gradients and the dynamic breakup of blobs intensifies resulting in increasing blob numbers. However, below a critical value of the wetting volume fraction, the number of blobs begins to decrease and the non-wetting phase begins to span the entire pore network. (C) 2010 Elsevier Ltd. All rights reserved.

关键词： Lattice Boltzmann Two-phase flow blobs Porous media

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A model of plaid motion perception based on recursive Bayesian integration of the 1-D and 2-D motions of plaid features

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VISION RESEARCH 2010年第6期50卷 585-597页

作者： Dimova, Kameliya D. Denham, Michael J. Univ Plymouth Ctr Theoret & Computat Neurosci Plymouth PL4 8AA Devon England

We describe a theoretical and computational model of the perception of plaid pattern motion which fully accounts for the majority of cases in which misperception of the direction of motion of Type II plaids has been observed [Yo. C.. & Wilson, H. (1992) Perceived direction of moving two-dimensional patterns depends on duration, contrast. and eccentricity Vision Research 32, 135-147]. The model consists of two stages: ill the first stage local motion detectors signal both the one-dimensional (1-D) and two-dimensional (2-D) motion of the high luminance features (blobs) in the plaid pattern;in the second stage these local motion signals are combined using a recursive Bayesian least squares estimation process. We demonstrate both theoretically and using simulations of the computational model that the estimated direction of the plaid motion for Type II plaids is initially dominated by the 1-D motion of the longer edges of the elongated blobs, which is in a direction close to the vector sum direction of the component gratings The recursive estimation process which combines the local motion signals in the second stage of the model results in a dynamic shift in the estimated plaid direction towards the direction of the 2-D motion of the blobs. which corresponds to the veridical plaid direction. (C) 2010 Elsevier Ltd All rights reserved.

关键词： Plaid Motion Bayes Computational model blobs

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Loading in Grinding: Chemical Reactions in Steels and Stainless Steels

Loading in Grinding: Chemical Reactions in Steels and Stainl...

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13th International Symposium on Advances in Abrasive Technology/1st Cross-Strait Conference on Precision Machining

作者： Badger, Jeffrey Murphy, Stuart O'Donnell, Garret E. Grinding Doc Consulting 31415 Falling Shadows Dr Bulverde TX 78163 USA Trinity Coll Dublin Dept Mech Engn Dublin Ireland

ISBN: (纸本)9780878492428

Loading in grinding both chemical, in which the grit and the oxidized surface of the workpiece react, and mechanical, in which chips become embedded within the pores of the wheel causes significant problems such as increased wheel wear, higher grinding temperatures, and poor surface finish. This paper investigates the chemical reactions that occur between the aluminum-oxide abrasive and both steel and stainless steel and their effect on wheel wear and grinding forces. Tests were done on mild steel and stainless steel under dry conditions, with poor and moderate cooling and in the presence of steam. X-ray diffraction was used to measure aluminum deposits on the contact and rear faces of the chip and on the workpiece in regions where cutting was dominant and/or plowing and rubbing were dominant. Normal and tangential forces and wheel wear were measured and loading was quantified visually. Loading in stainless steels was found to occur almost immediately due to the mutual solubility of Cr2O3 and Al2O3 during the rubbing and plowing regimes, but during cutting there was not sufficient time to form an oxide layer. Coolant drastically reduces loading in stainless steel. Steam acts as a catalyst in oxide-layer formation, decreasing loading in regular steels and increasing loading in stainless steels. Wheel wear due to loading was found to be sporadic, with large groups of grits being ripped out of;he wheel. Assessing loading via the visual appearance, or "blackness", of the wheel can lead to incorrect conclusions.

关键词： Grinding loading oxidation blobs

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Investigation of Turbulent Transport and Shear Flows in the Edge of Toroidal Plasmas

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CONTRIBUTIONS TO PLASMA PHYSICS 2010年第8期50卷 718-723页

作者： Ramisch, M. Birkenmeier, G. Happel, T. Koehn, A. Mandizadeh, N. Manz, P. Nold, B. Wilcox, R. Anderson, D. T. Stroth, U. Univ Stuttgart Inst Plasmaforsch D-70569 Stuttgart Germany Asociac EURATOM CIEMAT Lab Nacl Fus Madrid 28040 Spain ABB Switzerland Ltd Corp Res CH-5405 Baden Switzerland Univ Wisconsin HSX Plasma Lab Madison WI 53706 USA

Intense Langmuir-probe measurements were carried out in the toroidal low-temperature plasma of the torsatron TJ-K in order to investigate the origin and dynamics of intermittent transport events, so-called blobs, at the transition from closed to open field lines. The statistical properties of the fluctuations at the plasma boundary agree with observations made in fusion edge plasmas. blobs were found to be generated locally through a change in turbulence drive across the separatrix. The non-linear spectral energy transfer from small-scale fluctuations into large-scale flows was measured with a 128-probe array. The results point to the transfer being a key loss channel for turbulence energy leading to a reduction in turbulent transport. Earlier observations [M.A. Pedrosa et al., Phys. Rev. Lett. 100, 215003 (2008)] of enhanced long-range correlations in the plasma potential through externally induced shear flows in TJ-II stellarator were verified. The newly measured correlation of zonal vorticity and Reynolds stress at induced flow shear indicates an enhancement of zonal-flow drive. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

关键词： blobs turbulent transport zonal flow Reynolds stress

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How many pixels make an image?

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VISUAL NEUROSCIENCE 2009年第1期26卷 123-131页

作者： Torralba, Antonio MIT Comp Sci & Artificial Intelligence Lab Cambridge MA 02139 USA

The human visual system is remarkably tolerant to degradation in image resolution: human performance in scene categorization remains high no matter whether low-resolution images or multimegapixel images are used. This observation raises the question of how many pixels are required to form a meaningful representation of an image and identify the objects it contains. In this article, we show that very small thumbnail images at the spatial resolution of 32 X 32 color pixels provide enough information to identify the semantic category of real-world scenes. Most strikingly, this low resolution permits observers to report, with 80% accuracy, four to five of the objects that the scene contains, despite the fact that some of these objects are unrecognizable in isolation. The robustness of the information available at very low resolution for describing semantic content of natural images could be an important asset to explain the speed and efficiently at which the human brain comprehends the gist of visual scenes.

关键词： Scene recognition Object segmentation Gist Thumbnails Natural images blobs

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Acceleration of Blob-Based Iterative Reconstruction Algorithm Using Tesla GPU

Acceleration of Blob-Based Iterative Reconstruction Algorith...

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IEEE Nuclear Science Symposium Conference 2009

作者： Andreyev, Andriy Sitek, Arkadiusz Celler, Anna Univ British Columbia Dept Radiol Vancouver BC Canada Harvard Med Sch Dept Radiol Boston MA USA Brigham & Womens Hosp Boston MA 02115 USA

ISBN: (纸本)9781424439614

Blob-based iterative image reconstruction techniques provide high-quality denoised images in the photon starving emission tomography. However, the attractiveness of blob-based iterative algorithms is devalued by their high demands on the computation time. In this study we investigate the use of graphic processing units (CPU) to parallelize the ray-driven blob-based OSEM reconstruction algorithm for SPECT. We obtained a speed-up factor of 14.7 as compared to the blob reconstruction performed using CPU. Therefore, the reconstruction time of blob-based image on CPU was comparable to the reconstruction time of voxel-based image on the CPU. The algorithm can be further accelerated by more effective utilization of the CPU register space and shared CPU memory, which we plan to implement in the future.

关键词： blobs GPU high-performance computing iterative reconstruction

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Pinhole SPECT reconstruction using blobs and resolution recovery

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IEEE TRANSACTIONS ON NUCLEAR SCIENCE 2006年第5期53卷 2719-2728页

作者： Andreyev, Andriy Defrise, Michel Vanhove, Christian Vrije Univ Brussel Dept Nucl Med B-1090 Brussels Belgium

We study the performance of an iterative reconstruction algorithm for single pinhole SPECT, in which the correction for pinhole blurring is realized by averaging multiple projection rays by means of a Gaussian quadrature method. In addition we compare the regularizing effect obtained by using blobs basis functions and voxels with and without postsmoothing. Contrast-noise and resolution-noise studies with a mathematical phantom show that blobs improve the tradeoff between bias and variance compared to voxels with the same grid spacing. The performance of the voxel reconstruction is improved significantly by using postsmoothing with a Gaussian kernel and by taking finer voxel sampling, but the results with blobs remain better provided the parameters of the blobs are carefully selected. We have also reconstructed measured pinhole data for a resolution phantom and for the bone scan of a rat. With these data the visual difference between the postsmoothed voxel reconstruction and the blob reconstruction is small.

关键词： blobs pinhole spect reconstruction regularization resolution recovery (RR)

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Real-time 3-D human body tracking using learnt models of behaviour

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COMPUTER VISION AND IMAGE UNDERSTANDING 2008年第2期109卷 112-125页

作者： Caillette, Fabrice Galata, Aphrodite Howard, Toby Univ Manchester Sch Comp Sci Adv Interfaces Grp Manchester M13 9PL Lancs England

In this paper, we introduce a 3-D human-body tracker capable of handling fast and complex motions in real-time. We build upon the Monte-Carlo Bayesian framework, and propose novel prediction and evaluation methods improving the robustness and efficiency of the tracker. The parameter space, augmented with first order derivatives, is automatically partitioned into Gaussian clusters each representing an elementary motion: hypothesis propagation inside each cluster is therefore accurate and efficient. The transitions between clusters use the predictions of a variable length Markov model which can explain high-level behaviours over a long history. Using Monte-Carlo methods, evaluation of model candidates is critical for both speed and robustness. We present a new evaluation scheme based on hierarchical 3-D reconstruction and blob-fitting, where appearance models and image evidences are represented by mixtures of Gaussian blobs. Our tracker is also capable of automatic-initialisation and self-recovery. We demonstrate the application of our tracker to long video sequences exhibiting rapid and diverse movements. (C) 2007 Elsevier Inc. All rights reserved.

关键词： real-time human-body tracking variable length Markov models Bayesian Monte-Carlo volumetric reconstruction visual-hull blobs cross-entropy Kullback-Leibler

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Functional organization of color domains in V1 and V2 of macaque monkey revealed by optical imaging

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CEREBRAL CORTEX 2008年第3期18卷 516-533页

作者： Lu, Haidong D. Roe, Anna W. Vanderbilt Univ Dept Psychol Nashville TN 37240 USA

Areas V1 and V2 of Macaque monkey visual cortex are characterized by unique cytochrome-oxidase (CO)-staining patterns. Initial electrophysiological studies associated CO blobs in V1 with processing of surface properties such as color and brightness and the interblobs with contour information processing. However, many subsequent studies showed controversial results, some supporting this proposal and others failing to find significant functional differences between blobs and interblobs. In this study, we have used optical imaging to map color-selective responses in V1 and V2. In V1, we find striking "blob-like" patterns of color response. Fine alignment of optical maps and CO-stained tissue revealed that color domains in V1 strongly associate with CO blobs. We also find color domains in V1 align along centers of ocular dominance columns. Furthermore, color blobs in V1 have low orientation selectivity and do not overlap with centers of orientation domains. In V2, color domains coincide with thin stripes;orientation-selective domains coincide with thick and pale stripes. We conclude that color and orientation-selective responses are preferentially located in distinct CO compartments in V1 and V2. We propose that the term "blob" encompasses both the concept of "CO blob" and "color domain" in V1.

关键词： blobs color cytochrome-oxidase optical imaging thin stripes

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Multi-feature vector flow for active contour tracking

Multi-feature vector flow for active contour tracking

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33rd IEEE International Conference on Acoustics, Speech and Signal Processing

作者： Olszewska, Joanna Isabelle De Vleeschower, Christophe Macq, Benoit Catholic Univ Louvain Commun Lab TELE B-1348 Louvain Belgium

ISBN: (纸本)9781424414833

In order to achieve both fast tracking and accurate object extraction, we present in this paper an original real-time active contour method, incorporating different feature maps into a common and homogeneous framework, defined by the multi-feature vector flow (MFVF). The MFVF active contour approach does not require any target prior model, and enables precise tracking of mobile deformable objects. The use of the MFVF, resulting from multiple selected features, brings robustness into the system towards complex situations, while our computationally efficient implementation of the MFVF scheme reaches the required speed range for tracking process. The proposed method has been successfully tested on real-world video sequences.

关键词： video real-time tracking active contours blobs gradient vector flow feature combination

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