Shadow Imaging Technique Research Articles

Flocculation of microalgae using extracellular polymeric substances (EPS) extracted from activated sludge

This study investigates the role of microbial extracellular polymeric substances (EPSs) as bioflocculants to harvest microalgae (water-microalgae separation). The EPS extracted from waste activated sludge (WAS) by heat extraction were fractionated into soluble EPS (S-EPS), loosely-bound EPS (LB-EPS) and tightly-bound EPS (TB-EPS) forms. All the EPSs facilitated the flocculation of microalgal cells from stable growth medium. Of those EPSs, the TB-EPS showed the highest flocculating activity (FA) resulting in the substantial decrease in the amount of EPS added in terms of total organic carbon (TOC) during flocculation. The FA of microalgae was improved with the increase in TB-EPS dose, however, excessive dose of TB-EPS adversely affected it due to destabilization. Both LB- and TB-EPS could be utilized for flocculating microalgae as a sustainable option to the existing chemical-based flocculants. In addition to the conventional assessments, the effectiveness of the two bioflocculants for floc forming was also confirmed using a novel assessment of lens-free shadow imaging technique (LSIT), which was firstly applied for the rapid and quantitative assessment of microalgal flocculation.

Hydrodynamics features of dispersed bubbles in the ventilated wake flow of a cylinder

Abstract An experimental study was conducted to investigate the 2D bubbly flow downstream of a cylinder. Sparsely distributed bubbles were produced using the ventilation method. The carrier flow was measured using the particle image velocimetry (PIV) technique. The shadow imaging technique was used to capture instantaneous bubbly flow images. An image-processing code was compiled to identify bubbles in acquired image, calculate the bubble equivalent diameter and the bubble velocity. The effects of Reynolds number and the flow rate of the injected air were considered. The result indicates that the carrier flow is featured by distinct flow structures and the wake region is suppressed as the upstream velocity increases. Regarding the bubbles trapped in the wake flow, the number of small bubbles increases with the upstream velocity. On the whole, the bubble velocity is slightly lower than that of the carrier flow. The consistency between small bubbles and the carrier flow is high in terms of velocity magnitude, which is justified near the wake edge. The difference between the bubble velocity and the carrier flow velocity is remarkable near the wake centerline. For certain Reynolds number, with the increase in the air flow rate, the bubble equivalent diameter increases and the bubble void fraction is elevated.

Spatial resolution study of soft X-ray laser backlight shadow imaging technique

The soft X-ray laser shadow imaging technique is a good tool for diagnosing shadow profiles near the critical surface of high-temperature dense plasma. The short-pulse plasma X-ray laser, driven by high-power laser, is used as the backlight, which spreads freely approximately 500 mm far, passes through the plasma to be diagnosed, and changes its optical path by using a multi-layer spherical lens and multi-layer plane mirror, is attenuated by filters, and is recorded by a soft X-ray charge-coupled device (CCD). The plasma to be diagnosed can be driven by one or multiple laser beams, according to the needs of the physical research being conducted, and is imaged onto the CCD surface through a multilayer spherical lens. The shadow profile image of the plasma to be diagnosed at a particular time is obtained by using the instantaneous photographic mode of short-pulse soft X-ray laser backlight imaging. Compared with the traditional keV hard X-ray backlight technique, the soft X-ray laser shadow imaging technique has two distinct advantages. One is the appropriate wavelength of the probe light, which makes it possible to diagnose plasma near the critical surfac, and the other is a better spatial resolution because of the use of mature multilayer optical elements for near-normal incidence imaging. However, there has been no systematic study on the extent to which the spatial resolution of the imaging technology can be achieved. In this study, a careful analysis is carried out considering three aspects:the optical path geometry, the diffraction limit, and the imaging aberration. The results show that a spatial resolution of approximately 2 m can be achieved. An experiment is carried out to measure the Rayleigh-Taylor instability of plasma from the lateral direction, by using the soft X-ray laser shadow imaging technique. Some microfluids with a width of several microns can be clearly distinguished in the experimental shadow image, indicating that the diagnostic technique has a good spatial resolution. Further analysis reveals that the main factor that limits the spatial resolution is the optical path geometry. It is possible to achieve a spatial resolution of up to 1 m by increasing the magnification, selecting CCDs with smaller receiving units, etc.

A Field-Portable Cell Analyzer without a Microscope and Reagents.

This paper demonstrates a commercial-level field-portable lens-free cell analyzer called the NaviCell (No-stain and Automated Versatile Innovative cell analyzer) capable of automatically analyzing cell count and viability without employing an optical microscope and reagents. Based on the lens-free shadow imaging technique, the NaviCell (162 × 135 × 138 mm3 and 1.02 kg) has the advantage of providing analysis results with improved standard deviation between measurement results, owing to its large field of view. Importantly, the cell counting and viability testing can be analyzed without the use of any reagent, thereby simplifying the measurement procedure and reducing potential errors during sample preparation. In this study, the performance of the NaviCell for cell counting and viability testing was demonstrated using 13 and six cell lines, respectively. Based on the results of the hemocytometer (de facto standard), the error rate (ER) and coefficient of variation (CV) of the NaviCell are approximately 3.27 and 2.16 times better than the commercial cell counter, respectively. The cell viability testing of the NaviCell also showed an ER and CV performance improvement of 5.09 and 1.8 times, respectively, demonstrating sufficient potential in the field of cell analysis.

When shock is shocked: Riemann problem dynamics at pulse ionization of a shock wave

We study the dynamics of the gas flow discontinuities after pulse ionization of a half space in front of a flat shock wave moving in a channel. Pulse volumetric electric discharge initiated in the vicinity of the shock concentrates in front of the shock and heats the gas there. The heating is shown to be very rapid. We use the shadow imaging technique and a high speed camera to study the flow pattern evolution after the discharge. The pattern consists of two shocks separated by a contact surface. This structure corresponds to the classical Riemann problem formulation. Based on the observed pattern, we estimate the amount of discharge energy converted to heat during the discharge time: the rate of temperature increase is in the order of several degrees K per nanosecond.

An on-chip instrument for white blood cells classification based on a lens-less shadow imaging technique

Routine blood tests provide important basic information for disease diagnoses. The proportions of three subtypes of white blood cells (WBCs), which are neutrophils, monocytes, lymphocytes, is key information for disease diagnosis. However, current instruments for routine blood tests, such as blood cell analyzers, flow cytometers, and optical microscopes, are cumbersome, time consuming and expensive. To make a smaller, automatic low-cost blood cell analyzer, much research has focused on a technique called lens-less shadow imaging, which can obtain microscopic images of cells in a lens-less system. Nevertheless, the efficiency of this imaging system is not satisfactory because of two problems: low resolution and imaging diffraction phenomena. In this paper, a novel method of classifying cells with the shadow imaging technique was proposed. It could be used for the classification of the three subtypes of WBCs, and the correlation of the results of classification between the proposed system and the reference system (BC-5180, Mindray) was 0.93. However, the instrument was only 10 × 10 × 10 cm, and the cost was less than $100. Depending on the lens-free shadow imaging technology, the main hardware could be integrated on a chip scale and could be called an on-chip instrument.

렌즈프리 그림자 이미징 기술을 이용한 실시간 미세조류 응집현상 분석법

렌즈프리 그림자 이미징 기술을 이용한 실시간 미세조류 응집현상 분석법

Nonlinear parametric sound enhancement through different fluid layer and its application to noninvasive measurement

Abstract This paper presents a theoretical and experimental study on the enhancement of secondary waves generated from a parametric array through different fluid layers in water. A theoretical analysis was carried out using the Burgers equation for nonlinear sound propagation through a fluid layer in water, and the enhancement ratio of secondary waves was studied. The result indicated that among the five types of fluid layers studied, the ethanol layer in water had the highest enhancement ratio for signal amplitudes because of nonlinear fluid properties of ethanol and the fluid/water interface. To confirm the theoretical result, experiments were carried out using an ethanol layer in water. The result indicated that the enhancement ratio of secondary waves increased by more than three times because of the ethanol layer and decreased gradually in the far field in water. The concept of different fluid layers combined with a shadow imaging technique was applied to the noninvasive measurement of a target square cylinder in water. It was found that the accuracy of the size measurement of the target structure in water using an ethanol layer was better than that of conventional nonlinear imaging.

Gas transfer in a bubbly wake flow

The present work reports simultaneous bubble size and gas transfer measurements in a bubbly wake flow of a hydrofoil, designed to be similar to a hydroturbine blade. Bubble size was measured by a shadow imaging technique and found to have a Sauter mean diameter of 0.9 mm for a reference case. A lower gas flow rate, greater liquid velocities, and a larger angle of attack all resulted in an increased number of small size bubbles and a reduced weighted mean bubble size. Bubble-water gas transfer is measured by the disturbed equilibrium technique. The gas transfer model of Azbel (1981) is utilized to characterize the liquid film coefficient for gas transfer, with one scaling coefficient to reflect the fact that characteristic turbulent velocity is replaced by cross-sectional mean velocity. The coefficient was found to stay constant at a particular hydrofoil configuration while it varied within a narrow range of 0.52-0.60 for different gas/water flow conditions.

Time-resolved shadowgraphs of transient plasma induced by spatiotemporally focused femtosecond laser pulses in fused silica glass.

We report on experimental observations of formation and evolution of transient plasma produced in fused silica glass with spatiotemporally focused (STF) femtosecond laser pulses using a pump-probe shadow imaging technique. Surprisingly, the observation shows that the track of the plasma is significantly curved, which is attributed to an asymmetric density distribution of the transient plasma produced in the focal volume caused by the pulse front tilt of the STF laser field.

Staining-free cell viability measurement technique using lens-free shadow imaging platform

Tests for cell viability, i.e., an assay quantifying the ratio of viable cells or tissues over the total cells or tissues within an index between 0 and 1 (or 0 and 100%), play an important role in cell or tissue culturing procedures. The viability test result, varying with several biological factors such as mechanical activity, motility, contraction, or mitotic activity of cells or tissues, is a crucial indicator in cell related research protocols including toxicity and anabolic activity assays. There are several well-established methods for evaluating cell viability, such as trypan blue assay, propidium iodide assay, 7-aminoactinomycin D assay and resazurin and formazan (MTT/XTT) assay. However, most of these methods determine viability using stained cell samples, which intern affect the cells morphology eventually making it unable to keep culturing the specimen. To address this issue, we have developed a novel shadow imaging technique to capture the diffraction patterns (shadow patterns) of micro objects without the use of any staining reagent. In this paper, we introduce a shadow imaging platform that can determine cell viability of more than 3000 human cancer cells immediately with a single digital image. Our custom-built lens-free shadow imaging platform consists of a compact, cost-effective light source, i.e., a light-emitting diode, and an optoelectronic image recording device, i.e., a complementary metal-oxide semiconductor image sensor. Three types of human cancer cell lines (Caco-2, HepG2, and MCF7) were incubated in 24-well plates, and H2O2 was added to track and compare the cell viability at each concentration tested. We obtained high correlation indices, with a minimum of 0.94, between the MTT assay and the shadow imaging platform. All these characterizations were done by custom developed automated detection algorithm. This algorithm analyzes the various elements of the diffraction pattern (shadow image), such as pixel intensity and connected pixel numbers, and counts the viable cells automatically, allowing the cell viability to be determined easily and immediately in a staining-free manner.

Bubble size characteristics in the wake of ventilated hydrofoils with two aeration configurations

Aerating hydroturbines have recently been proposed as an effective way to mitigate the problem of low dissolved oxygen in the discharge of hydroelectric power plants. The design of such a hydroturbine requires a precise understanding of the dependence of the generated bubble size distribution upon the operating conditions (viz. liquid velocity, air ventilation rate, hydrofoil configuration, etc.) and the consequent rise in dissolved oxygen in the downstream water. The purpose of the current research is to investigate the effect of location of air injection on the resulting bubble size distribution, thus leading to a quantitative analysis of aeration statistics and capabilities for two turbine blade hydrofoil designs. The two blade designs differed in their location of air injection. Extensive sets of experiments were conducted by varying the liquid velocity, aeration rate and the hydrofoil angle of attack, to characterize the resulting bubble size distribution. Using a shadow imaging technique to capture the bubble images in the wake and an in-house developed image analysis algorithm, it was found that the hydrofoil with leading edge ventilation produced smaller size bubbles as compared to the hydrofoil being ventilated at the trailing edge.

Mass transfer studies across ventilated hydrofoils: A step towards hydroturbine aeration

The water discharged by hydropower facilities is a matter of increasing concern due to poor downstream water quality. The use of auto-venting hydroturbines has been suggested as one of the best ways to mitigate low dissolved oxygen levels in the downstream water. Much of the design of auto-venting hydroturbines is currently performed with computational fluid dynamics (CFD) simulations. However, there is little information available to test and verify the performance of these simulations regarding gas transfer and bubble size distribution. This paper investigates the performance of a water tunnel test-bed for CFD simulations of an auto-venting hydroturbine through the use of a ventilated hydrofoil. Bubble size distributions are measured by a shadow imaging technique and found to have a Sauter mean diameter of 0.9mm for a reference case. Higher liquid velocities, a lower airflow rate and a higher angle of attack all resulted in a greater number of small bubbles and a lower weighted mean bubble size. Bubble-water oxygen transfer is measured by the disturbed equilibrium technique. The gas transfer model of Azbel (1981) is utilized to characterize the liquid film coefficient for oxygen transfer, with one scaling coefficient to reflect the fact that characteristic turbulent velocity is replaced by cross-sectional mean velocity. The value of the coefficient is found to stay constant at a particular hydrofoil configuration while it varied over a narrow range of 0.52–0.60 for different hydrofoil angles of attack. This suggests that it is an appropriate coefficient for flow over a ventilated hydrofoil and possibly other flow situations. These results can be used by investigators to test and verify their CFD model against known bubble size distributions and gas transfer in a water tunnel flow that has important similarities to an auto-venting hydroturbine.

Automation Highlights from the Literature

Automation Highlights from the Literature

A simple and low-cost device performing blood cell counting based on lens-free shadow imaging technique

Complete blood count (CBC) is a basic and important diagnostic procedure in pathological laboratories. However, current technologies such as hemocytometry, impedancemetry, or flow-cytometry, are either time-consuming or requiring bulky and high-cost of instrumentation. To address this issue we demonstrate a compact, cost-effective, and automated blood cell counting method based on the lens-free shadow imaging technique. For that a lens-free shadow imaging technique based blood cell counting device was fabricated using a blue light emitting diode (LED) and a complementary metal oxide semiconductor (CMOS) image sensor. The shadow images of the blood cells, i.e., diffraction patterns, were captured by the device and processed automatically using a custom developed algorithm to count and differentiate the cells. The comparative study from 21 outpatient whole blood samples was carried out with the fully automated hematology analyzer (LH 750, Beckman Coulter). The comparison between the lens-free shadow imaging device and the standard reference system showed correlation indices of 0.878 for red blood cell (RBC) and 0.927 for white blood cell (WBC). The linearity comparison gave a statistical trend of y=0.9432x with R2=0.99 for RBC and y=0.7395x with R2=0.92 for WBC. Also the correlation coefficient for WBC subpopulations, i.e., neutrophil, lymphocyte, and monocyte, for each individual sample was >0.90. This cost-effective and compact blood cell counting system can be utilized as a powerful point of care (POC) tool, which could play an important role in primary healthcare, especially in areas with limited resources. Since the system is capable to send the images wirelessly and process them on a moderate smart phone, therefore, the proposed system possesses great potential in telemedicine applications.

Thermal self-action of high-power continuous and pulse-periodic CO2 laser radiation in air: II. Laboratory experiments

Results of laboratory experiments on nonlinear propagation of high-power pulse-periodic and continuous CO2 laser radiation in a gas medium are presented. The experiments were carried out in a cell filled with a mixture of air and carbon dioxide in different partial concentrations (∼1–4%) under strong absorption and thermal blooming of laser radiation. The experimental conditions simulated the atmospheric propagation of high-power laser radiation along a kilometer-long path. Sharply focused laser beams were used; the regions of heat release along the beam channel were recorded by the shadow imaging technique. We found that, despite increased intensity, the focal waist of a laser beam is characterized by reduced heat release as compared to that in the pre- and postfocal beam regions. The saturation effect of the resonance absorption coefficient of CO2 at high pulse peak intensity (blooming effect) is considered as the most probable physical cause of the above feature. For continuous radiation, this effect is much weaker.

CMOS image sensor-based ELISA detector using lens-free shadow imaging platform

This paper presents a compact and cost-effective lens-free complementary metal-oxide-semiconductor (CMOS) image sensor based bacterial cell detection platform that can measure colorimetric light signals in the enzyme linked immunosorbent assay (ELISA) process. In this work, we first demonstrate the CMOS image sensor based shadow imaging platform as an ELISA detector and provide critical performance data that show this platform to be comparable or even better than that of a commercial ELISA reader. To evaluate the efficacy of the shadow imaging platform-based ELISA detector as a practical approach, the pathogenic bacteria Listeria monocytogenes (L. monocytogenes) and Salmonella typhimurium (S. typhimurium) were utilized within a conventional 96-well plate. To reduce the noise signal from unwanted particles and light scattering, a custom-made aperture cover and image processing procedures were developed. Because this platform employs a multi-million pixel CMOS image sensor enabling effective removal of noise signals that can not be achieved with a single pixel detector, i.e., conventional ELISA reader, it can perform more reproducible ELISA measurement. Combined with the shadow imaging technique, this approach holds great promise in many applications including blood analysis, pathogen detection, and environmental monitoring.

Visualization of secondary atomization in emulsified-fuel spray flow by shadow imaging

In this study, emulsified fuels having different dispersed water droplets and n-dodecane spray were injected separately into high-temperature inert gas, and their spray droplet behavior was studied. A measurement system consisting of high-speed video camera (125,000fps) coupled with a shadow imaging technique was used to visualize secondary atomization of spray droplets. In addition, the size distribution of the spray flow was measured using digital processing at different points. Although puffing (i.e. vapor eruption from droplet surface) and partial micro-explosion (i.e. a large part of the droplet bursts) were observed in this study, complete micro-explosion (i.e. the entire droplet bursts) was rarely observed. A certain amount of dispersed water was necessary to cause complete micro-explosion; however, the size of the dispersed water droplets (about 2–3μm) was insufficient to cause micro-explosion until coalescence is well progressed. In addition, the coalescence of dispersed water droplets had not progressed much because of the short waiting time of 20–30ms. Meanwhile, puffing occurred, regardless of coalescence, and it was sufficient to provide fine droplets, although less fine than those created by micro-explosion. As emulsified fuel moved downstream with heating, the droplet size significantly decreased; in contrast, heating had less effect on the droplet size of n-dodecane spray. Clearly, secondary atomization that included puffing improved spray characteristics, although the spray size of the emulsified fuel was larger than that of the original fuel near the injection point because of increased viscosity resulting from emulsification. Moreover, large dispersed water droplets improved the intensity of secondary atomization and provided a finer spray flow. The initial size of the dispersed water droplets played an important role in the spray characteristics of the emulsified fuel spray.

Lens-free shadow image based high-throughput continuous cell monitoring technique

A high-throughput continuous cell monitoring technique which does not require any labeling reagents or destruction of the specimen is demonstrated. More than 6000 human alveolar epithelial A549 cells are monitored for up to 72h simultaneously and continuously with a single digital image within a cost and space effective lens-free shadow imaging platform. In an experiment performed within a custom built incubator integrated with the lens-free shadow imaging platform, the cell nucleus division process could be successfully characterized by calculating the signal-to-noise ratios (SNRs) and the shadow diameters (SDs) of the cell shadow patterns. The versatile nature of this platform also enabled a single cell viability test followed by live cell counting. This study firstly shows that the lens-free shadow imaging technique can provide a continuous cell monitoring without any staining/labeling reagent and destruction of the specimen. This high-throughput continuous cell monitoring technique based on lens-free shadow imaging may be widely utilized as a compact, low-cost, and high-throughput cell monitoring tool in the fields of drug and food screening or cell proliferation and viability testing.

ULTRAFAST ELECTRON DIFFRACTIVE VOLTAMMETRY: GENERAL FORMALISM AND APPLICATIONS

We present a general formalism of ultrafast diffractive voltammetry approach as a contact-free tool to investigate the ultrafast surface charge dynamics in nanostructured interfaces. As case studies, the photoinduced surface charging processes in oxidized silicon surface and the hot electron dynamics in nanoparticle-decorated interface are examined based on the diffractive voltammetry framework. We identify that the charge redistribution processes appear on the surface, sub-surface, and vacuum levels when driven by intense femtosecond laser pulses. To elucidate the voltammetry contribution from different sources, we perform controlled experiments using shadow imaging techniques and N-particle simulations to aid the investigation of the photovoltage dynamics in the presence of photoemission. We show that voltammetry contribution associated with photoemission has a long decay tail and plays a more significant role in the nanosecond timescale, whereas the ultrafast voltammetry are dominated by local charge transfer, such as surface charging and molecular charge transport at nanostructured interfaces. We also discuss the general applicability of the diffractive voltammetry as an integral part of quantitative ultrafast electron diffraction methodology in researching different types of interfaces having distinctive surface diffraction and boundary conditions.