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Numerical and experimental study on keyhole and melt flow dynamics during laser welding of aluminium alloys under subatmospheric pressures
摘要： Porosity defects was highly related to the keyhole and melt flow dynamic during laser welding process. In this paper, a novel 3D numerical model was developed to describe the keyhole dynamic and melt flow behaviors during laser welding of 5A06 aluminium alloy under subatmospheric pressures. The effect of ambient pressure on laser welding process was taken into consideration by optimizing the boiling point of aluminium alloy and recoil pressure of evaporated metallic vapor jets based on vapor–liquid equilibria calculation and Wilson equation. A moving hybrid heat source model was employed to describe the laser energy distribution under subatmospheric pressures. Numerical results indicated that a wider and deeper keyhole with less humps was produced under subatmospheric pressure comparing with that of atmospheric pressure. The vortices in the rear keyhole wall became unapparent or even disappeared with the decrease of ambient pressures. The melt flow velocity on the keyhole wall was larger under a lower pressure. A smaller difference between boiling point and melting point was produced and this led to the formation of a thinner keyhole wall and improved the stability of molten pool. Larger recoil pressure produced under subatmospheric pressure was responsible for the weakened vortices and enhanced melt flow velocity. Bigger keyhole opening size, larger melt flow velocity, thinner keyhole and the weakened vortices all resulted into the reduction of porosity defects during laser welding of aluminium alloys. Based on the simulation results, the plasma distribution, weld formation and porosity defects had been demonstrated. The compared results showed that the simulation results exhibited good agreements with the experimental ones.
关键词： Porosity defects,Keyhole stability,Numerical simulation,Subatmospheric pressure,Melt flow dynamic,Laser welding
更新于2025-11-28 14:24:20
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Practical methodology for <i>in situ</i> measurement of micro flow rates using laser diode absorption sensors
摘要： A laser diode-based flowmeter based on the infrared absorption method that can measure in situ micro flow rates from 0.2 to 20 ml h?1 was developed. A 1450 nm laser absorbed in water was irradiated to form a heated spot at 0 mm, and the temperature was measured upstream and downstream of the heated spot. The flow rate was measured by the temperature difference obtained by two diode lasers and photodetectors upstream and downstream of the heated spot. We measured the temperature profile of the flow rate by changing the temperature measurement position and the heating laser energy upstream and downstream of the heated spot, and compared the measurements with the simulation results. As the flow rate increased, the temperature profile shifted downstream, and the measured temperature upstream and downstream were analyzed according to the flow rate. The flow measurement range was adjusted according to the temperature measurement position. Increasing the energy of the heating laser also improved the measurement accuracy in the lower flow range. The developed flowmeter was calibrated by the gravimetric method, and the deviation and measurement uncertainty according to the flow rate were obtained. The maximum measurement uncertainty was 6.8% at a 1 ml h?1 flow rate, and the minimum measurement uncertainty was 1.78% at 8 ml h?1. Thus, it was confirmed that the flow rate can be measured through the temperature difference gauged using a simple diode laser set. Using the laser diode-based flowmeter developed in this study, one can measure the flow rate in situ without injecting contaminants, such as particles, for measurements without cutting the piping. In addition, it can be manufactured in a miniaturized form at a low cost, and thus, it can be used for multi-drug infusion analysis, semiconductor process monitoring, etc.
关键词： near infrared absorption,diode laser,micro flow rate,thermal mass flowmeter
更新于2025-11-25 10:30:42
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Silanized quantum dots as labels in lateral flow test strips for C-reactive protein
摘要： The paper describes the first use of silanized semiconductor core-shell quantum dots as fluorescent labels for macromolecule, C-reactive protein determination in blood plasma. The controlled synthesis of CdSe cores, with successive shells of CdS, CdZnS, ZnS and coating with transparent, stable, and inert silica shell, provides quantum dots with a narrow emission band, high quantum yield, and prolonged signal stability. Finally, the quantum dots were conjugated with specific antibodies via carboxylic groups on the silica surface. The method was further used for the immunochromatographic assay of C-reactive protein, a diagnostically important inflammatory biomarker. Assays with both the fluorescent QDs and a widely used colloidal gold label were developed in parallel and compared. The silanized quantum dots provide a more sensitive assay with a detection limit of 1 ng/mL for C-reactive protein in standard solutions, whereas the common assay has a detection limit of 10 ng/mL. The possibility of quantitative evaluation of analyte content by a portable device was demonstrated; the accuracy of the measurements was in the range of 5%–10%. The tests were used to determine C-reactive proteins in human plasma samples. The selected optimized protocol for these samples is based on a 4-fold dilution. The final working range of the assay, 4–1,200 ng/mL, covers practically all important interval of C-reactive protein values for the characterization of acute, chronic, and local inflammatory processes. Due to their high physical stability and inertness as well as intense, stable, and reproducible fluorescence, silanized quantum dots may be applied for high-sensitive assays for different analytes.
关键词： C-reactive protein,Quantum dots,silanization,lateral flow immunoassay
更新于2025-11-19 16:46:39
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Particle transport mode during flash sintering of sodium bismuth titanate ceramic
摘要： In this work, the NBT ceramics are successfully flash sintered at a direct current 30 mA/mm2 for 30 s under different initial electric field. Subsequently, the actual temperature of samples is estimated by blackbody radiation theory under different conditions. The calculation results show that the sample temperature is close to the densification temperature of NBT ceramics used in conventional method. The rapid densification mechanism is discussed by wetting of local contact particles due to the asymmetrical Joule heating. In particular, we analyzed the particle transport mode during flash sintering in terms of particle diffusion. It is believed that the transform in the particles transport mode from solid diffusion to flow mass transfer accelerated the particles diffusion rate, which ensure the particle rearrangement and achieve the local shrinkage of particles in a short period of time.
关键词： Flow mass transfer,Flash sintering,Joule heating,Particles transport
更新于2025-11-14 14:48:53
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Void fraction measurement using imaging and phase isolation method in horizontal annular flow
摘要： A new imaging method was proposed to measure the void fraction of annular flow based on phase isolation technology in horizontal circular tube. As gas liquid mixture passes through the phase isolation device, which is arranged upstream, a strong swirl flow is created, due to centrifugal effect. Liquid phase is pushed to the tube wall and forms a uniform liquid film, while the gas phase is concentrated to the tube center and forms a gas core. This rectified core-annular flow has more smooth and clear phase interface than that of natural annular flow, which makes the accurate measurement of some inherent flow parameters of gas-liquid two phase flow become available and much easier. The backlight collimated illumination and high resolution CCD camera were employed to capture the gas core and liquid film. A calibration experiment was conducted to acquire accurate edge detection criterion for recognition of phase interface. The image morphological characteristics of core-annular flow and the beam path diagram of imaging procedure were analyzed in detail and the corresponding image processing algorithm was developed. The working fluid were air and water and the range of void fraction covered in experiment were 0.736-0.978(Usg=4.35m/s-39.12m/s, Usl=0.016m/s-0.504m/s). For each experiment condition, about 800 raw images were processed to obtain average result. Comparisons to a representative mode of void fraction of natural annular flow showed that the void fraction of the core-annular flow rectified by the phase isolation device keeps consistent well with that of natural annular flow in the range of low gas volume fraction, but becomes a little lower than the later as gas volume fraction become very high.
关键词： void fraction,annular flow,imaging,core-annular flow,phase isolation
更新于2025-09-23 15:23:52
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Quantitative Image Analysis of Cellular Morphology Using Amnis???? ImageStreamX Mark II Imaging Flow Cytometer: A Comparison against Conventional Methods
摘要： Chemotaxis, the directional cell migration guided by chemoattractant gradients, plays essential roles in many physiological processes, such as recruitment of neutrophils to sites of inflammation. Neutrophils detect chemoattractants by G protein-coupled receptors (GPCRs). Chemoattractant stimuli activate multiple signaling pathways to regulate directional migration of neutrophils. Recently, we identified a novel GPCR-mediated PLCβγ/ PKCβ/PKD1 signaling axis that regulates cofilin activity through cofilin phosphatase slingshot 2 (SSH2) and remodels actin cytoskeleton during neutrophil chemotaxis. In the future, it will be important to understand how multiple signaling pathways are spatiotemporally regulated to precisely control the rapid remodeling of actin cytoskeleton in the leading front of chemotaxing neutrophils.
关键词： Flow,Brightfield,Imaging,Fluorescence,Cytometry
更新于2025-09-23 15:23:52
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Head-to-head comparison of the diagnostic performances of Rubidium-PET and SPECT with CZT camera for the detection of myocardial ischemia in a population of women and overweight individuals
摘要： Background. The aim of this study was to compare the diagnostic performances for the detection of myocardial ischemia of 82-Rb-PET-MPS and 99m-Tc-SPECT-MPS in overweight individuals and women. Methods and Results. Men with BMI ≥ 25 and women referred for MPS were considered for inclusion. All individuals underwent 99m-Tc-SPECT-MPS with CZT cameras and 82-Rb-PET-MPS in 3D-mode. Individuals with at least one positive MPS were referred for coronary angiography (CA) with FFR measurements. A criterion for positivity was a composite endpoint including significant stenosis on CA or, in the absence of CA, the occurrence of acute coronary event during the following year. 313 patients (46% women) with mean BMI of 31.8 ± 6.5 were included. Sensitivity for the detection of myocardial ischemia was higher with 82-Rb-PET-MPS compared with 99m-Tc-SPECT-MPS (85% vs. 57%, P < .05); specificity was equally high with both imaging techniques (93% vs. 94%, P > .05). 82-Rb-PET allowed for a more accurate detection of patients with a high-risk coronary artery disease (HR-CAD) than 99m-Tc-SPECT-MPS (AUC = 0.86 vs. 0.75, respectively; P = .04). Conclusions. In women and overweight individuals, 82-Rb-PET-MPS provides higher sensitivity for the detection of myocardial ischemia than 99m-Tc-SPECT-MPS thanks to a better image quality and an improved detection of HR-CAD.
关键词： CZT camera,MPI,Diagnostic and prognostic application,PET,Myocardial blood flow,SPECT,82-Rubidium,CAD
更新于2025-09-23 15:23:52
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Human activity recognition via optical flow: decomposing activities into basic actions
摘要： Recognizing human activities using automated methods has emerged recently as a pivotal research theme for security-related applications. In this research paper, an optical flow descriptor is proposed for the recognition of human actions by considering only features derived from the motion. The signature for the human action is composed as a histogram containing kinematic features which include the local and global traits. Experimental results performed on the Weizmann and UCF101 databases confirmed the potentials of the proposed approach with attained classification rates of 98.76% and 70%, respectively, to distinguish between different human actions. For comparative and performance analysis, different types of classifiers including Knn, decision tree, SVM and deep learning are applied to the proposed descriptors. Further analysis is performed to assess the proposed descriptors under different resolutions and frame rates. The obtained results are in alignment with the early psychological studies reporting that human motion is adequate for the perception of human activities.
关键词： Optical flow,Motion descriptor,Action recognition,Decomposing activities
更新于2025-09-23 15:23:52
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Dense Descriptors for Optical Flow Estimation: A Comparative Study
摘要： Estimating the displacements of intensity patterns between sequential frames is a very well-studied problem, which is usually referred to as optical flow estimation. The first assumption among many of the methods in the field is the brightness constancy during movements of pixels between frames. This assumption is proven to be not true in general, and therefore, the use of photometric invariant constraints has been studied in the past. One other solution can be sought by use of structural descriptors rather than pixels for estimating the optical flow. Unlike sparse feature detection/description techniques and since the problem of optical flow estimation tries to find a dense flow field, a dense structural representation of individual pixels and their neighbors is computed and then used for matching and optical flow estimation. Here, a comparative study is carried out by extending the framework of SIFT-flow to include more dense descriptors, and comprehensive comparisons are given. Overall, the work can be considered as a baseline for stimulating more interest in the use of dense descriptors for optical flow estimation.
关键词： feature descriptors,optical flow estimation,dense descriptors
更新于2025-09-23 15:23:52
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The influence of the thermal wake due to pulsating optical discharge on the aerodynamic-drag force
摘要： The influence of a thermal wake due to gas injection and due to a pulsating optical discharge (POD) on the aerodynamic-drag force of a body in a supersonic air flow with Mach number M = 1.45 are experimentally examined. With the help of a single-component aerodynamic balance, the influence of the injected subsonic jet and the thermal wake produced by POD on the aerodynamic drag of a hemisphere-on-cylinder model was studied. It is shown that the observed aerodynamic-force reduction phenomenon can be made more pronounced by increasing the laser power and pulse repetition frequency, or by decreasing the distance between the model and the pulsating optical discharge. The maximum aerodynamic-force reduction (up to 15%) due to the thermal-wake action was observed at a maximum laser-radiation power of W = 2.3 kW and at a pulse rate of f = 90 kHz. The joint effect due to the argon jet and due to the POD caused an aerodynamic-drag force reduction reaching 30%.
关键词： thermal wake,gas injection,CO2-laser,supersonic flow,pulsating optical discharge,aerodynamic-drag force
更新于2025-09-23 15:23:52