Lucas-Kanade (LK) algorithm, usually used in optical flow filed, has recently received increasing attention from PIV community due to its advanced calculation efficiency by GPU acceleration. Although applications of this algorithm are continuously emerging, a systematic performance evaluation is still lacking. This forms the primary aim of the present work. Three warping schemes in the family of LK algorithm: forward/inverse/symmetric warping, are evaluated in a prototype flow of a hierarchy of multiple two-dimensional vortices. Second-order Newton descent is also considered here. The accuracy & efficiency of all these LK variants are investigated under a large domain of various influential parameters. It is found that the constant displacement constraint, which is a necessary building block for GPU acceleration, is the most critical issue in affecting LK algorithm’s accuracy, which can be somehow ameliorated by using second-order Newton descent. Moreover, symmetric warping outbids the other two warping schemes in accuracy level, robustness to noise, convergence speed and tolerance to displacement gradient, and might be the first choice when applying LK algorithm to PIV measurement.

Evaluating the accuracy performance of Lucas-Kanade algorithm in the circumstance of PIV application

This paper reports on a new technique of measurements of microbubble position in three dimensions with high time-resolution. The technique is based on micro digital holographic particle tracking velocimetry. In this technique, an intensity profile is constructed from a holographic image of a microbubble where the profile results in showing two peaks. The distance between the two peaks appears to relate to the size of the microbubble's diameter. The three-dimensional position of the bubble can be detected by the center of the two peaks and the center point of the bubble image focused by a digital hologram. We also theoretically obtained the intensity profile of a microbubble by considering a refraction of light on a bubble surface to a ring-shaped aperture model. The theoretically obtained distance between the two peaks is found to be in good agreement with the values obtained experimentally.

Detection of microbubble position by a digital hologram.

Laser speckle imaging (LSI) is a noninvasive and full-field optical imaging technique which produces two-dimensional blood flow maps of tissues from the raw laser speckle images captured by a CCD camera without scanning. We present a hardware-friendly algorithm for the real-time processing of laser speckle imaging. The algorithm is developed and optimized specifically for LSI processing in the field programmable gate array (FPGA). Based on this algorithm, we designed a dedicated hardware processor for real-time LSI in FPGA. The pipeline processing scheme and parallel computing architecture are introduced into the design of this LSI hardware processor. When the LSI hardware processor is implemented in the FPGA running at the maximum frequency of 130 MHz, up to 85 raw images with the resolution of 640×480 pixels can be processed per second. Meanwhile, we also present a system on chip (SOC) solution for LSI processing by integrating the CCD controller, memory controller, LSI hardware processor, and LCD display controller into a single FPGA chip. This SOC solution also can be used to produce an application specific integrated circuit for LSI processing.

https://www.spiedigitallibrary.org/journals/journal-of-biomedical-optics/volume-16/issue-11/116008/Dedicated-hardware-processor-and-corresponding-system-on-chip-design-for/10.1117/1.3651772.pdf

Dedicated hardware processor and corresponding system-on-chip design for real-time laser speckle imaging

The DEM (Discrete Element Method) is one option for studying the kinematic behaviour of cylindrical pellets. The DEM experiments attempted to optimize the numerical model parameters that affected time and velocity as a cylindrical vessel emptied. This vessel was filled with cylindrical pellets. Optimization was accomplished by changing the coefficient of friction between particles and selecting the length accuracy grade of the sample cylindrical pellets. The initial state was a series of ten vessel-discharge experiments evaluated using PIV (Particle Image Velocimetry). The cylindrical pellet test samples were described according to their length in three accuracy grades. These cylindrical pellet length accuracy grades were subsequently used in the DEM simulations. The article discusses a comparison of the influence of the length accuracy grade of cylindrical pellets on optimal calibration of time and velocity when the cylindrical vessel is emptied. The accuracy grade of cylindrical pellet length in the DEM sample plays a significant role in relation to the complexity of a created simulation.

https://www.mdpi.com/2227-9717/7/2/101/pdf

Discrete Element Method Model Optimization of Cylindrical Pellet Size

Copper nanoparticles were synthesized using lithium ions to increase the aqueous electrical conductivity of the solution and precisely control the size, shape, and size distribution of the particles. In this study, the conventional approach of increasing particle size by the concentration of copper ions and PGPPE in a copper chloride solution was compared to increasing the concentration of lithium chloride when the copper chloride concentration was held constant. Particle size and shape were characterized by TEM, and the size distribution of the particles at different concentrations was obtained by particle size analysis. Increasing the concentration of copper ion in the solution greatly increased the aqueous electric conductivity and the size of the particles but led to a wide size distribution ranging from 150 nm to 400 nm and rough particle morphology. The addition of lithium ions increased the size of the particles, but maintains them in a range of 250 nm. In addition the particles exhibited spherical shape as determined by TEM. The addition of lithium ions to the solution has the potential to synthesize nanoparticles with optimal characteristics for printing applications by maintaining a narrow size range and spherical shape.

https://downloads.hindawi.com/journals/jnt/2012/469834.pdf

Effect of Lithium Ions on Copper Nanoparticle Size, Shape, and Distribution

A high time-resolution measurement of flow field in a glass plate with glass cover with two holes was done by a micro-DHPTV system. The two holes mentioned here were also inside the photo-curable resin. Particle measurement was carried out during a 2 s time period that covered the time it took for the curing of resin. This curing time was theoretically calculated from the irradiation flux of the Ultraviolet (UV) source employed in the experiment. Moreover, temperature dependence of photo-curable resin was evaluated by measuring the resin at changing temperatures. Consequently, the tracking of seeding particles could instantaneously be recorded. The 3-D displacements, obtained from the particles being tracked, took place primarily along the direction of the depth. These values were found to be in good agreement with the theoretically calculated displacement values obtained from UV irradiation flux. Moreover, the displacement during photo-curing appeared to be proportional to the increase in temperature.

Three-Dimensional Measurements of Photo-curing Process With Photo-curable Resin for UV-Nanoimprint by Micro-digital-Holographic-PTV

Special-purpose computer for Particle Image Velocimetry

High time-resolution flow field measurement in the glass plate with covered glass with two holes is performed by micro-DHPTV system The glass plate with covered glass has two holes that are inside photo-curable resin The particle measurement is performed during two seconds; the measurement time is covered for curing time The theoretically curing time is estimated from the irradiation flux of UV source Moreover, photo-curable resin with changing of temperature is measured to evaluate dependence of temperature Consequently, the seeding particle tracking can be obtained instantaneously The three-dimensional displacement from the tracking is mainly caused at the depth direction The value is in good agreement with the theoretical displacement from UV irradiation flux Moreover, it is found that the photo curing of the displacement appears to be proportional to increasing the temperature

Gaku Sorimachi

Papers

Three-Dimensional Measurements of Photo-curing Process With Photo-curable Resin for UV-Nanoimprint by Micro-digital-Holographic-PTV

Special-purpose computer for Particle Image Velocimetry

Three-dimensional measurements of photo curing with process with photo-curable resin for UV-nanoimprint by micro-digital-holographic-PTV