Hansen, Robert S.Burn, Katharine Z.Rigby, Cynthia M.Ashby, Emma K....
13页
查看更多>>摘要：Digital Image Correlation (DIC) is an optical measurement technique that can easily be adapted for high magnification applications. These high magnifications involve competing phenomena which must be balanced to produce the highest quality measurements. When out-of-plane displacements cause the specimen under investigation to move out of the depth of field, poor focus negatively affects the measurement. As a result, it is often recommended to reduce aperture size to improve the depth of field. However, smaller aperture sizes can also cause poor focus as the diffraction limit of light causes larger Airy disks, particularly at longer working distances. This work investigates the competing effects of both depth of field and Airy disk size in three test cases: higher magnification and shorter working distance, lower magnification and shorter working distance, and lower magnification and longer working distance. Different aperture sizes are found to change which effect dominates, and a recommendation for selecting the aperture setting to minimize measurement error from both phenomena is made.
查看更多>>摘要：The detection of O2 using optical techniques has now become very important and significant progress has been made in this area over the past few years. The measurement of O2 concentration is a key parameter for diverse applications such as in life sciences, environmental monitoring, industry and biological research, and luminescence-based sensors are a valuable tool for measurements of this type. Often commercial sensors are unable to respond within a short time frame and drift over time - this demonstrates the importance of developing and validating a new technological approach. Given that need, a new sensor has been developed, with a specially-formed tip design coated with a very thin Platinum(II) 5,10,15,20-Tetrakis(2,3,4,5,6-pentafluorophenyl)-porphyrin (PtTFPP)-containing a polystyrene layer. The performance and reproducibility of the sensor design has been studied by comparing three identically fabricated sensor probes, showing that the new probe design has extreme fast response times - of a maximum value, Delta t90max R--1 390 ms for increasing and Delta t90max R--1 250 ms for decreasing O2 concentrations. The sensors created had an accuracy of better than +/- 0.03 % O2 over the detection range investigated (between 0 % and 20 % O2) and showed a very stable performance over many hours of use. Examining this in detail through extended continuous use, over 12 h in a 0 % O2 solution, the probe stability was confirmed, showing a very low drift of luminescence decay time of R--10.025 %/h (0.01 mu s/h). Furthermore, the temperature 'cross-talk' has been studied in the important region between 25 degrees C and 40 degrees C (so that temperature corrections can be applied) and its mechanical stability, as well as allowing for compensation for any effects seen, has been confirmed. Given the success of the design developed, this work offers both an effective probe design and illustrates many important criteria for the selection of highly effective O2-sensitive coating materials and thus their use as a measurement tool for different quality control (QC) applications in industry.
Dutta, KishoreTalukdar, DhritimanBora, Siddhartha S.
9页
查看更多>>摘要：By using color vegetative indices and Otsu's thresholding, we develop a method for the segmentation of unhealthy leaves in cruciferous crops as a procedure of automatic early disease detection. We apply the method on aerial RGB images collected at two different sunlight conditions, both containing multiple plants of kohlrabi with bare soil and weeds in the background. By using the M-statistic, we show how the method comprising a redefine set of the vegetative index can better discriminate between healthy leaves, unhealthy leaves, and other backgrounds. Our study indicates that the vegetative indices need to be tuned according to the types of the crop for accurate identification of infectious parts of the plant through the image processing method. We discuss its implications in precision agriculture.
Telega, JanuszSzwaba, RyszardSmialek, Malgorzata A.
8页
查看更多>>摘要：This paper describes a method for nonintrusive compressible gas density measurement by means of automated analysis of interferograms using FFT (Fast Fourier Transform), and its implementation using DFT (Discrete Fourier Transform), that does make this measurement technique a fairly valuable and accessible experimental method. The presented approach makes it possible to use the finite fringe setting of the interferometer, thus reducing adjustment time. In the process of analysis, the errors originating from the imperfections of optical elements are reduced, and a digital image of a virtual infinite setting of the instrument is generated. As described here, the method is extremely beneficial, but not limited to, flows with shock wave - boundary layer interactions. A result of density measured for a flow with shock wave is presented.
查看更多>>摘要：Effective prestress change detection has a guiding effect on the safety of prestressed concrete structures. The measurement method of inductance-capacitance (LC) electromagnetic oscillation circuit can directly reflect the correlation between the stress of the steel strands and the electromagnetic resonance frequency. In this paper, the post-tensioned unbonded prestressed steel strands inside the structure are treated as a helical coil. Combined with the inductance characteristics of the helical coil in the resonance circuit and the characteristics of stress in the prestressed structure, the relationship between the load and the stress of the structure under vertical loading is analyzed. A function model of the stress and resonance frequency in the LC oscillation circuit is established. Then a 4.8 m long unbonded prestressed concrete beam is used for 0-55 kN vertical loading experiments and the electromagnetic resonance circuit is completed to detect the change of the resonance frequency increment of the steel strands with the measured stress increment. Theoretical analysis and experimental results show that the electromagnetic resonance circuit can effectively detect structural load stress changes that are positively related to the electromagnetic resonance frequency of the steel strands.
查看更多>>摘要：Coiled Tubing (CT) is disturbed by ocean loads when milling in deep water. The CT's axial force under different buckling states and ocean loads also varies. In this study, to analyze the influence of ocean load on the axial force of coiled tubing under different buckling states, we establish an experimental 'pipe-in-pipe' system under different ocean loads. By simulating the outer pipe's deformation under different ocean loads, the influence of buckling states and ocean loads on the CT's axial force transfer characteristics is studied. The results show that when the CT's buckling state is the same, the greater the ocean load, the greater is the axial force fluctuation. Additionally, when the ocean load is the same, the greater the CT's buckling degree, the greater is the axial force fluctuation, but the axial force transmission efficiency is improved. Besides, the ocean load has little effect on the axial force's transmission efficiency. The results provide theoretical guidance for deepwater milling using coiled tubing.
查看更多>>摘要：Sleep apnea refers to a sleep disorder consist of inconsistent breathing during sleep for extensive duration of time. During this, one faces difficulty in breathing leading to loss of oxygenated blood circulation in human body. It leads to damage in hippocampus region of the brain. Many medical problems like hypertension and inducing type two diabetes are also common in patients. The early-stage detection of apnea can save someone from these severe conditions. This work introduces the automatic apnea detection method using electrocardiogram (ECG) signals. The ECG signals are analyzed with the help of flexible analytic wavelet transform (FAWT) which allows the conversion of non-stationary ECG into predictable wavelets. Features for events of apnea and non-apnea are extracted by these wavelets. The extracted features are checked for their statistical significance and then fed into different kinds of machine learning algorithms for apnea events detection. In tested algorithms, the optimized ensemble is obtained the best classification results. The proposed approach for apnea detection has better performance as compared to other existing same dataset works.
查看更多>>摘要：This paper constitutes the first report on the uncertainty evaluation based on Guide to the expression of Uncertainty in Measurement (GUM) method for BPL long wave time service monitoring. First, the applicability of the GUM method was considered from two perspectives: the BPL long wave time service monitoring model and the monitoring data distribution. A complete monitoring measurement model was then established. Subsequently, the uncertainty sources were analyzed via Type A and Type B evaluation. The bootstrap method was used to compare and verify the standard uncertainty evaluation by the GUM method. Thus, the uncertainty results for BPL time service monitoring were obtained under the existing monitoring model and equipment conditions. Furthermore, this paper also provides certain suggestions for improving the quality of time service monitoring. This work is expected to facilitate methods and provide guidance for evaluating the uncertainty in corresponding monitoring systems of other land-based time service systems.
Valente, Nicholas A.do Cabo, Celso T.Mao, ZhuNiezrecki, Christopher...
14页
查看更多>>摘要：Phase-based motion magnification (PMM) has been widely implemented in the field of vibration and structural health monitoring for its non-invasive nature to reveal hidden system dynamics. The approach has shown success in magnifying subtle structural oscillatory motions for system identification and observation of operating shapes. Although this method has been implemented and is becoming increasingly popular, the amount of physical motion associated with the degree of magnification has yet to be quantified. Within this work, a synthetic simulation containing an oscillating geometry is presented to quantify its magnified pixel displacement. Computer vision techniques including centroid detection and edge-feature tracking via optical flow are adopted to quantify the relation between amplification and true motion. The quantification techniques are also tested and verified on an experimental structure with the use of a high-speed optical sensing system. Motion artifacts distort the integrity of the magnified motion, which can pose problems for accurate quantification. Image enhancement techniques such as the two-dimensional Wiener filter and Total Variation Denoising (TVD) are used to smooth the high-frequency content that is observed following magnification. Associative error concerning a discrete shift of the Gabor wavelet is analytically derived to show the justification of spatial aliasing. An adjusted bound on magnification is presented to display the limitations of the technique, while providing insight into associated error. The results of this work will help to enhance PMM from a qualitative evaluation tool to a quantitative measurement tool of magnified displacements.
查看更多>>摘要：In rolling bearings diagnostics, apart from the most commonly used vibration and noise measurements, temperature measurements are also taken. Further, the most common measurement method of bearings temperature is contact measurement of the temperature of the stationary outer ring of the bearing. However, simulation research proves that the most important thermal phenomena in the bearings occur in the contact area of the rolling elements and raceways. Temperature measurement of the moving rolling elements and the cages in bearings is possible only by non-contact methods. This paper describes the methodology of taking measurements during the diagnosis of rolling bearings using a thermal imaging camera. A procedure for parameterization of thermograms has been proposed, which enables the temperature of bearing elements to be determined. The key for this purpose was the emissivity coefficient epsilon and the temperature correction, related to the variable local values of epsilon of the tested bearing elements. The results of non-contact temperature measurements and the correction were verified by the contact method. The research included measurements of thermal processes taking place in new, undamaged tapered roller bearings. The tests were carried out on CBK 171 (SKF 63174) bearings. The selection of tapered roller bearings was dictated by the possibility of thermovision measurements of all the bearing elements.
NSTL
Elsevier