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Simultaneous monitoring of overlapped multi-wing structure by stereo-digital image correlation (stereo-DIC) may be used to quantify insect motion and deformation. We propose a dual stereo-DIC system based on multispectral imaging with a polarization RGB camera. Different fluorescent speckle patterns were fabricated on wings, which emit red and blue spectra under ultraviolet light that were imaged and separated using a polarization RGB camera and auxiliary optical splitting components. The resulting dual stereo-DIC system was validated through translation experiments with transparent sheets and reconstructed overlapped insect wings (cicadas). Dynamic measurements of the Ruban artificial flier indicate the efficacy of this approach to determining real insect flight behavior.

This paper proposes a method to merge stereo-digital image correlation (DIC) and electronic speckle pattern interferometry (ESPI) data by camera calibration. The proposed method is employed to verify the accuracy of full-field out-of-plate displacements measured by stereo-DIC in a cantilever beam test. The mean absolute error and the root mean square error (RMSE) of the full-field displacement measured by four-megapixel cameras are 0.849 µm and 1.08 µm at 60 mm field of view, respectively, and the RMSE of the central area is 0.615 µm. The errors are not uniformly distributed because of the imperfect calibration. When the lenses are changed and the field of view reaches 120 mm, the RMSE is 1.48 µm with uniform distribution. These accuracies could be traced back to the laser wavelength to confirm the stereo-DIC data. The proposed method can be used not only to verify the full-field measurement accuracy of DIC but also to determine the rigid-body displacement for ESPI with a high-precision stereo-DIC. Thus, the displacement vector can be obtained. Furthermore, it can unify the coordinate of multiple ESPI systems to achieve a large range of high-precision three-dimensional deformation measurements.

Camera calibration is crucial to the application of binocular measurement. However, many of the calibrations are carried out manually, so shaking of the calibration plate cannot be avoided. When the cameras are not synchronized or the exposure time is inconsistent, the image acquisition time of different cameras does not correspond strictly, which will introduce inevitable calibration errors. In this paper, two consecutive frames are collected instead of one frame, and the calibration data are corrected by the image acquisition time value returned by the camera. Experiments show that the proposed method can greatly reduce the re-projection error of calibration, and achieve higher calibration accuracy and less image quantity dependence.

Electronic speckle pattern interferometry (ESPI), a well-established technique for micro-deformation measurement, can be used to determine both in-plane and out-of-plane displacement components. Although many works in ESPI have been reported for three-dimensional (3D) displacement measurement, few works have focused on the simultaneous measurement of 3D deformation fields. Here we present an ESPI system that consists of three sub-interferometers for simultaneous measurement of all three displacement components and in-plane strain fields. A 3CCD color camera, a specially designed shifting stage, and three lasers with optimal wavelengths are used in this system. The lasers and 3CCD camera provide independent interferograms with different color signals, while the shifting stage allows the sub-interferometers to achieve simultaneous phase shifting. The results of color separation and experimental measurement demonstrate the utility of the system.

Accurate prediction of network traffic is very important in allocating network resources. With the rapid development of network technology, network traffic becomes more complex and diverse. The traditional network traffic prediction model cannot accurately predict the current network traffic within the effective time. This paper proposes a Network Traffic Prediction Model----NTAM-LSTM, which based on Attention Mechanism with Long and Short Time Memory. Firstly, the model preprocesses the historical dataset of network traffic with multiple characteristics. Then the LSTM network is used to make initial prediction for the processed dataset. Finally, attention mechanism is introduced to get more accurate prediction results. Compared with other network traffic prediction models, NTAM-LSTM prediction model can achieve higher prediction accuracy and take shorter running time.

A 3D-printed sub-terahertz lens for manipulating quasi-non-diffractive orbital angular momentum (OAM) waves is proposed in this paper. The proposed lens comprises all-dielectric elements that impose desired phase profiles on the incident waves by varying their height. Based on the concept of the Bessel beam launchers and the beam deflectors, quasi-non-diffractive OAM waves with a pre-defined deflection angle can be produced by the proposed lens. For verification, two lenses were 3D printed for producing OAM waves with a non-diffractive depth of 55.58λc (λc is the free-space wavelength at 140 GHz). Measured by a terahertz imaging camera, the desired quasi-non-diffractive OAM waves were observed behind the proposed lenses with expected non-diffractive performance and a large deflection angle of up to 47°.

Multi-camera stereo-digital image correlation (stereo-DIC) methods have gained popularity as non-contact methods for measuring high-spatial-resolution deformation of large engineering structures. Common multi-camera stereo-DIC methods can be classified into two types: target-based and calibration-based methods. Considering the wide application prospects of multi-camera stereo-DIC methods, it is important to study and compare the performances of these two types of multi-camera stereo-DIC methods. A four-point bending test of reinforced seawater sea-sand coral concrete (Coral-SWSSC) beams was conducted in this study to investigate the performance of multi-camera stereo-DIC in deformation measurement of slender components, and the measurement accuracy, robustness, and applicability of the two types of multi-camera stereo-DIC methods were compared and discussed. Furthermore, deformation analysis of reinforced Coral-SWSSC beams based on high-resolution multi-camera stereo-DIC methods was performed. The analysis showed that beams strengthened with basalt fiber-reinforced polymer wrapped steel tube and ultra high performance concrete (UHPC) can fully exploit the properties of Coral-SWSSC; the two strengthening materials demonstrated a higher compatibility, which compensates for the low strength defect of the Coral-SWSSC, making it a viable strengthening method. This study may promote the application of multi-camera stereo-DIC methods to measuring high-resolution deformation of large engineering structures.

The failure mode is crucial to the interfacial bond performance between carbon-fiber-reinforced polymer plates and steel substrates. Existing studies mainly focused on the cohesive failures in the adhesive; however, research on other types of failure modes is still limited. In this article, a series of single-shear bonded joints are prepared to investigate the bond behaviors of the carbon-fiber-reinforced polymer–steel interfaces based on carbon-fiber-reinforced polymer delamination failures and hybrid failures. Three kinds of adhesives—which have different tensile strengths and elastic moduli—and two kinds of carbon-fiber-reinforced polymer plates—which have different interlaminar shear strengths—are used to evaluate the influencing factors of carbon-fiber-reinforced polymer–steel interfaces. The three-dimensional digital image correlation technique is applied to measure the strain and the displacement on the surface of each specimen. The obtained test results include the strain distribution, the ultimate load, the failure mode, the load–slip curves, and the bond–slip relationships. For the carbon-fiber-reinforced polymer delamination mode, the results show that the load at the debonding stage is closely related to the interlaminar shear strength of the carbon-fiber-reinforced polymer plate, and the higher the interlaminar shear strength is, the greater the load. However, for the hybrid mode, the load of the whole test process is independent of the interlaminar shear strength of the carbon-fiber-reinforced polymer plate.

Mimic defense is an active defense theory, which aims to fundamentally change the “easy to attack and difficult to defend” situation of network security. In this paper, we propose an evaluation method based on the probability of being attack successfully, and improve the evaluation scheme of historical confidence. We combine the two evaluation schemes with the TOPSIS (technique for order performance by similarity to ideal solution) algorithm, and finally form a complete heterogeneous variant dynamic scheduling model. Different from traditional multi-mode voting algorithms, the effect of the heterogeneous degree in voting is considered, and we use Bayesian estimation to obtain the optimal result in the probabilistic sense. Finally, simulation results show that the proposed algorithm can effectively enhance the dynamic and security of the mimic defense model, and give full play to the characteristics of mimic defense.

A low-profile differentially fed dual-polarized antenna with high gain and isolation is proposed for fifth-generation (5G) microcell communications. By introducing two pairs of symmetrical meandering conductors to connect both ends of the radiating cross slots, a compact-size antenna with wide bandwidth can be achieved. By further adopting an artificial magnetic conductor-backed (AMC) reflector that is arranged below the radiating patches with a distance of 6 mm, the antenna profile can be reduced from $0.25\lambda _{c}$ to $0.13\lambda _{c}$ (where $\lambda _{c}$ is the free-space wavelength at the center frequency), while both the gain and frequency bandwidth are also enhanced. Furthermore, owing to the orthogonal differentially fed structure, the antenna element displays a high port isolation of 37 dB. Finally, by meticulously designing the feeding network, much narrower beamwidth can be yielded, and hence, the unidirectional gain is further improved. The measured results show that a lower-frequency bandwidth of 13.5% (3.26–3.73 GHz) with a gain of 15.7 ± 0.1 dBi and upper-frequency bandwidth of 7.6% (4.68–5.05 GHz) with 15.55 ± 0.05 dBi gain can be obtained by the proposed antenna array. In addition, port isolation better than 28 dB and stable radiation patterns can be achieved. With the aforementioned characteristics, the proposed antenna is a good candidate for future 5G microcell communications.

Previous study indicated that co-infusion of cord blood cells may potentially improve the outcome of haploidentical donor (HID) transplantation. In this study, we analyzed the outcomes of patients who underwent HID transplantation supported by cord blood when compared with HLA-matched unrelated donor (URD) transplantation. Starting in 2015, 40 patients with hematopoietic malignancies underwent HID transplantation and 26 patients underwent URD transplantation. Hematopoietic recovery, the incidences of grade II-IV acute graft-versus-host disease (GVHD) and chronic GVHD was comparable in the two groups. At two year, the relapse risk in HID group was significantly lower than in URD group (RR 4.630; 95%CI, 1.081-19.839

Calibrating stereo digital image correlation (stereo-DIC) is crucial for 3D deformation measurements. Existing stereo-DIC calibration methods mainly rely on a well-made planar target with additional specific coding to perform pre-calibration. In this paper, a new method is proposed to calibrate a stereo-DIC system automatically with feature correspondences in an unconstrained scene. In contrast to traditional methods, the proposed method is scale-independent and does not require assumptions such as planarity. More importantly, it is capable of correcting disturbed external parameters in real time. With inverse depth parameterization, a stereo-DIC system can be effectively calibrated by a carefully designed bundle adjustment framework. Subsequently, a fast correction strategy based on massive-point subset tracking is derived to recalibrate the disturbed stereo-DIC system. The proposed method overcomes the predicament of reduced measurement accuracy due to the unavoidable disturbance of external parameters in dynamic deformation measurements. Experiments were conducted to verify the effectiveness of the proposed method.

We propose an adaptive filter method based on a deformable window shape to remove the noise of wrapped phase fringe patterns in electronic speckle pattern interferometry (ESPI). The filter kernel automatically adjusts its size, shape, and direction according to the direction and curvature of the phase fringe pattern. The direction of a phase fringe pattern is determined using a gradient-based method. Fringe curvature is estimated based on the calculated direction and fitted phase contours. Simulations were performed to evaluate the proposed method, and the results were compared with those of the 2-D windowed Fourier transform filtering (WFTF) algorithm and the medial filter technique. Simulated and experimental results show that the new approach can provide more effective de-noising for phase fringe patterns compared to the other two methods, using few parameters.

Copious studies have focused on the bond behavior under monotonic loading. However, relative research under quasi-static cyclic loading is still limited. In order to improve the understanding of the bond behavior of CFRP-steel interfaces under quasi-static cyclic loading, an experimental study was conducted in this paper. A series of the CFRP-steel single-shear specimens were manufactured to investigate the effects of bond length, adhesive thickness, adhesive type and loading procedures on the bond behavior of CFRP-steel interfaces. Strains and displacements on the specimen surface were measured by three-dimensional digital image correlation (3D-DIC) technology. The interfacial damage and the threshold load were analysed. The experimental results showed that the loading procedures had no effect on the ultimate loads of specimens with Sikadur-30 (CN), while the ultimate loads of specimens with. Araldite-2015 (CN) under quasi-static cyclic loading were less than those under monotonic loading. The bond-slip relationships under monotonic loading showed bilinear and trilinear shapes for the specimens with adhesives Sikadur-30 (CN) and Araldite-2015 (CN), respectively. The envelope lines of the load-slip and the bond-slip relationship tested under quasi-static cyclic loading could be traced by those under monotonic loading. Relationships between the damage parameter D and the normalized energy dissipation wd/Gf and the normalized slip Si/Sf were established by fitting experimental data. Based on the test results, the threshold loads could be detected for each specimen under the monotonic loading procedure, which was approximately 52.5% and 39.5% of the ultimate load for the specimens with adhesive Sikadur-30 (CN) and Araldite-2015 (CN), respectively.

The compressive mechanical properties of perforated hollow-sphere structures (PHSSs) are studied through experiments and numerical simulations. In a PHSS, hollow spheres perforated with several holes, which are to open the inner volumes and surface areas of the hollow spheres, are connected in simple cubic (SC), body centered cubic (BCC) or face centered cubic (FCC) pattern. In experiments, the unit cell and multi cell structures in the BCC arrangement are fabricated through 3D printing technology, and the results indicate deformation behaviors similar to those of classic hollow-sphere structures. Then, the effects of geometric properties, such as wall thickness, hole diameter, linking neck radius, and the spatial arrangement of the spheres, on the structural Young's modulus and initial yield stress are calculated and analyzed using the finite element method (FEM). Finally, the relationships between the mechanical properties and relative densities of different sphere arrangements are also obtained by nonlinear fitting.

The bond–slip degradation relationship between carbon fiber-reinforced polymer and steel in a freeze–thaw environment is crucial to evaluate the long-term service performance of steel structures strengthened with carbon fiber-reinforced polymer plates. However, limited studies on the durability and long-term performance of the carbon fiber-reinforced polymer-steel-bonded interface are the major obstacle for the application of carbon fiber-reinforced polymer plates in strengthening steel structures. This paper reports an experimental study to investigate the effects of the carbon fiber-reinforced polymer bond length and the freeze–thaw cycles on the bond behavior of the carbon fiber-reinforced polymer-steel-bonded interface. The three-dimensional digital image correlation technique is applied to obtain displacements and strains on the surface of the single-shear specimen. The experimental results present herein include the failure mode, the ultimate load, the carbon fiber-reinforced polymer strain distribution, the displacement distribution, and the bond–slip relationship. The results show that the ultimate load increases with increasing bond length until a certain bond length value is reached, after which the ultimate load remained approximately constant, and the ultimate loads of carbon fiber-reinforced polymer-steel interface decrease gradually under freeze–thaw cycles. The bond–slip parameters degradation models are proposed, and the bond–slip degradation relationship under the freeze–thaw cycles is established. Finally, the bond–slip degradation relationship is confirmed through comparisons with the experimental results.

The cohesin complex regulates sister chromatid cohesion, chromosome organization, gene expression, and DNA repair. Cohesin is a ring complex composed of four core subunits and seven regulatory subunits. In an effort to comprehensively identify additional cohesin-interacting proteins, we used gene editing to introduce a dual epitope tag into the endogenous allele of each of 11 known components of cohesin in cultured human cells, and we performed MS analyses on dual-affinity purifications. In addition to reciprocally identifying all known components of cohesin, we found that cohesin interacts with a panoply of splicing factors and RNA-binding proteins (RBPs). These included diverse components of the U4/U6.U5 tri-small nuclear ribonucleoprotein complex and several splicing factors that are commonly mutated in cancer. The interaction between cohesin and splicing factors/RBPs was RNA- and DNA-independent, occurred in chromatin, was enhanced during mitosis, and required RAD21. Furthermore, cohesin-interacting splicing factors and RBPs followed the cohesin cycle and prophase pathway of cell cycle–regulated interactions with chromatin. Depletion of cohesin-interacting splicing factors and RBPs resulted in aberrant mitotic progression. These results provide a comprehensive view of the endogenous human cohesin interactome and identify splicing factors and RBPs as functionally significant cohesin-interacting proteins.

Elastic moduli, including Young’s modulus, shear modulus, bulk modulus, etc, are key parameters that are used to characterize the ability of a solid material to resist various types of deformation. The moduli can be extracted from the natural frequencies of a cantilever beam. In this paper, the relationships between moduli and natural frequencies, for the first time, are quantified by the finite element method. The optimized three-dimensional proportion of the cantilever beam is selected to be implemented simple error compensation. Experimentally, to precisely obtain the natural frequencies of the cantilever beam, an efficient time-averaged electronic speckle pattern interferometry(ESPI) system has been developed. The efficiency and precision are reflected in the following aspects: firstly, according to the slender character of the cantilever beam, a large shear optical path arrangement is designed to facilitate isolation from environmental interference; secondly, a resonance search method, based on the moiré effect is employed to recognize the natural frequencies accurately and efficiently; thirdly, a novel dynamic phase-shifting method is proposed based on the arrangement of the large shear optical path for clearer visualization of the mode shape of the cantilever beam. The proposed methods are verified by three kinds of common materials. The results suggest that Young’s modulus and shear modulus derived from natural frequencies are higher than the known value, and the error compensation can significantly reduce the calculation error. Furthermore, the experiments carried out on the woven carbon fiber reinforced plastic laminates illustrate the potential of the proposed methods in the evaluation of elastic moduli of composites. Given that the exciter attached to the specimen surfaces can be replaced with some special counterparts, the proposed ESPI system has considerable potential to test the objects loaded in some extreme environments, e.g. at high temperatures or underwater, where contact detection methods are difficult to be implemented.

In this paper, a general scheme is proposed for dual-band orbital angular momentum (OAM) multiplexing based on a single-layer reflective geometric metasurface. As an OAM multiplexer, the proposed metasurface can distinguish different incidences featuring different incident angles, transform them into OAM waves with different topological charges (TCs) and control their reflection angle by modifying the k-space of the incidences simultaneously. In this way, the incidences can be combined into a coaxial beam without mutual interference because of the inherent orthogonality of different OAM modes. To achieve dual-band OAM multiplexing, a single-layer metal-insulator-metal (MIM) meta-atom that can independently impose arbitrary phase profiles on incidences at two different frequencies is designed. Based on it, a geometric metasurface is proposed for multiplexing OAM waves at 7 GHz and 14 GHz simultaneously. The simulated results show that eight independent data channels are created in a broadside beam when eight off-axis incidences carrying different information impinge on the proposed metasurface. This phenomenon indicates that the proposed metasurface can effectively achieve multiplexing by combining frequency and OAM domains to boost the channel capacity in wireless communications.

In fringe projection profilometry (FPP), non-sinusoidal fringes due to the gamma effect of a projector will cause measurement errors. To solve this problem, a binary defocusing technique has been introduced in recent years, yet the appropriate defocusing is hard to evaluate quantitatively. An innovative approach to quantify binary defocusing in real-time is proposed. No matter how the projector and camera are arranged in FPP system, the fringe period in a captured defocusing fringe image is strictly varying; therefore, unlike previous methods, the proposed method uses a limited window for defocusing evaluation. This not only improves the accuracy of defocusing evaluation, but also greatly improves the evaluation speed, thus in turn enabling real-time evaluation. In addition, numerical differentiation is introduced on the window using a modified five-interval-point algorithm to effectively improve the sensitivity to improper (inadequate or excessive) defocusing. The difference between the numerical differentiation and its fundamental harmonic extracted by Levenberg–Marquardt iterative is taken as an evaluation value of binary defocusing. The smaller the difference, the more appropriate is the defocusing. By minimizing this difference, the most appropriate defocusing can be obtained quantitatively. Both numerical simulations and experiments validate the high sensitivity and high speed of the proposed method.

Measuring the three-dimensional (3D) deformation of submerged objects through different media with the stereo digital image correlation (stereo-DIC) method involves the refractive optical imaging problem where the non-linear transmission of light is induced by a change of medium density. The problem invalidates the underlying single viewpoint assumption of the perspective model in regular stereo-DIC, thereby resulting in erroneous measurements of 3D shape and deformation. In this work, we propose a refractive stereo-DIC method that overcomes the problem by considering light refraction in 3D reconstruction. We formulate a full refractive reconstruction geometry description based on Snell’s law of flat refraction and the regular triangulation. This allows the true shape to be effectively reconstructed by tracing and establishing the refracted ray-paths based on the regular 3D reconstruction, without reformulating the camera model and image formation. The refractive stereo-DIC is finally established by integrating the refractive 3D reconstruction into the regular DIC framework for measuring accurate 3D shape and deformation of submerged objects. We experiment the proposed approach with underwater 3D shape and deformation measurements. Both results prove its feasibility and correctness, further heralding our approach as a flexible solution that could readily extend the stereo-DIC to fluid-immersed 3D deformation characterization.

Fringe projection profilometry using the phase-shifting technique enables high-precision, high-speed and flexible measurements. Among them, the two-step phase-shifting method has become an important approach to coordinate the accuracy and measurement speed; methods especially based on the amount of phase-shift of π/2, π or 3π/2 can improve time efficiency by reducing steps in unique way. In this paper, a phase iterative technique is proposed and established for two-step phase-shifting with arbitrary phase shift. The general mathematical scheme and parameters linear and nonlinear optimization of the proposed method are described in detail. The simulational and experimental results show that the proposed technique is an effective and precise phase detection method for two-step phase-shifting profilometry.

When operating within the environments rich with sodium chloride, steel bars of reinforced concrete structures are often subject to corrosion caused by surrounding erosive materials, and the associated rust expansion force due to corrosion takes a critical role in determining the durability of relevant reinforced concrete structures. By investigating the corrosion course of steel reinforcement with theory of elasticity, a numerical rust expansion model is established for the moment of concrete surface rupture based on non-uniform sin function. Cuboid reinforced concrete specimen with squared cross sections is tested to analyze the rust expansion when concrete cracks due to corrosive forces. The utility of the established expansion model is validated by numerical simulation with Abaqus through the comparison between the associated outcomes. The impacts of steel bar diameter and concrete cover thickness on the magnitude of rust expansion force are discussed.

Concrete cracking caused by corrosion of reinforcement could significantly shorten the durability of reinforced concrete structure. It remains critical to investigate the process and mechanism of the corrosion occurring to concrete reinforcement and establish the theoretical prediction model of concrete expansion force for the whole process of corrosion cracking of reinforcement. Under the premise of uniform corrosion of reinforcing steel bars, the elastic mechanics analysis method is adopted to analyze the entire process starting from the corrosion of steel bars to the cracking of concrete due to corrosion. A relationship model between the expansion force of corrosion of steel bars and the surface strain of concrete is established. On the cuboid reinforced concrete specimens with square cross-sections, accelerated corrosion tests are carried out to calibrate and verify the established model. The model can be able to estimate the real-time expansion force of reinforced concrete at any time of the whole process from the initiation of steel corrosion to the end of concrete cracking by measuring the surface strain of concrete. It could be useful for quantitative real-time monitoring of steel corrosion in concrete structures.

A novel Microcystis bloom caused by Microcystis densa has occurred in a typical subtropical reservoir every spring and summer since 2012, and it has caused several ecological and economic losses. To determine the environmental factors that influence the growth and physiological characteristics of M. densa, we investigated the variations in physicochemical factors and M. densa cell density from 2007 to 2017. The results showed that the urea-N concentration increased significantly (from 0.02 ± 0.00–0.20 ± 0.01 mg N l−1), whereas other factors did not vary significantly. NO3−-N and urea-N concentrations were higher than the NH4+-N concentration during the M. densa bloom. The nitrogen composition changed, and urea-N and NO3−-N became a major nitrogen sources in the reservoir. Water temperature and increased urea-N concentrations were the primary factors that influenced variations in M. densa cell density (45.5%, p

Cohesin is a multiprotein ring complex that regulates 3D genome organization, sister chromatid cohesion, gene expression, and DNA repair. Cohesin is known to be ubiquitinated, although the mechanism, regulation, and effects of cohesin ubiquitination remain poorly defined. We previously used gene editing to introduce a dual epitope tag into the endogenous allele of each of 11 known components of cohesin in human HCT116 cells. Here we report that mass spectrometry analysis of dual-affinity purifications identified the USP13 deubiquitinase as a novel cohesin-interacting protein. Subsequent immunoprecipitation/Western blots confirmed the endogenous interaction in HCT116, 293T, HeLa, and RPE-hTERT cells; demonstrated that the interaction occurs specifically in the soluble nuclear fraction (not in the chromatin); requires the ubiquitin-binding domains (UBA1/2) of USP13; and occurs preferentially during DNA replication. Reciprocal dual-affinity purification of endogenous USP13 followed by mass spectrometry demonstrated that cohesin is its primary interactor in the nucleus. Ectopic expression and CRISPR knockout of USP13 showed that USP13 is paradoxically required for both deubiquitination and ubiquitination of cohesin subunits in human cells. USP13 was dispensable for sister chromatid cohesion in HCT116 and HeLa cells, whereas it was required for the dissociation of cohesin from chromatin as cells transit through mitosis. Together these results identify USP13 as a new cohesin-interacting protein that regulates the ubiquitination of cohesin and its cell cycle regulated interaction with chromatin.

For dealing with the problem of receiving multimode orbital-angular momentum (OAM) waves resulting from different beam divergence angles of OAM waves with different topological charges, it is essential to control the beam divergence angles of OAM waves. In this paper, a method is proposed to control the beam divergence angles of multi-mode OAM waves without modifying the inherent topological charges by a reflective metasurface. Based on this method, a reflective metasurface is properly designed to generate dual-mode OAM waves with equal beam divergence angle. As a dual-mode OAM waves generator, the reflective metasurface is composed of 31x31 metal-insulator-metal elements which is capable to manipulate dual-polarized electromagnetic waves (EMWs) independently. Furthermore, as a beam divergence controller, the reflective metasurface is properly divided into two regions that are responsible for +1 mode and +3 mode OAM waves generations. In this way, dual-mode OAM waves with equal beam divergence angle can be generated by the proposed reflective metasurface. The proposed design provides an efficient technology to control the beam divergence angles of multi-mode OAM waves flexibly, which is conductive to simplify the receiving device in OAM based communication systems.

With the increase in digital image correlation (DIC) applications, it is an important task to realize the fully automatic measurement and provide an automatic deformation measurement sensor. Keeping this in mind, we propose an automatic speckle region selection method for DIC. This method can be divided into three main steps: initial contour selection, active contour computation, and morphological operation. The sum of modulus of the local intensity gradient vector of the local image is used to determine the initial contour, the active contour computation is driven by improved automatic local Gaussian distribution fitting energy, and the morphological closing operation is finally conducted to achieve better robustness. Experimental results show that the root mean squared error of the localization is less than 0.8260 pixels. We further integrate the proposed method into an open-source DIC software, and the fully automatic deformation analysis is realized. The fully automatic deformation measurement will further widen the application scope of DIC, especially in the field of smart robotics and smart city.

For achieving more multiplexing degrees, a method to generate and multiplex dual-polarized electromagnetic waves carrying orbital angular momentum(OAM) by a single reflective metasurface is proposed in this paper. Base on this method, a dual- polarized reflective metasurface that can generate eight OAM beams combined into a coaxial beam in terahertz regime is properly designed and simulated to verify this method. According to the simulation results, the proposed method provides an efficient way for a metasurface to generate and multiplex dual- polarized electromagnetic waves carrying OAM.

Recovering the geometric shape of deformable objects from images is essential to optical three-dimensional (3D) deformation measurements and is also actively pursued by researchers. Most of the existing techniques retrieve the shape data with triangulation based on pre-estimated stereo correspondences. In this paper, we instead propose to recover depth information directly from images of a binocular vision system for 3D deformation estimation. Given a calibrated geometry of the system, the reprojection error is parameterized by the depth and then described with local intensity dissimilarity between a stereo pair in considering spatial deformation. Afterward, a correlation adjustment model is formulated to estimate the depth parameter by minimizing the error. As a solving strategy, we show the Gauss-Newton linearization of the proposed model and its initialization. 3D displacement estimation based on depth information is also presented. Experiments, including rigid translation and bending deformation measurements, are conducted to verify the performance of the proposed method. Results show that the proposed method is accurate yet precise in 3D deformation estimations. Other underlying developments are underway.

China is a major coal-producing country that consumes large amounts of coal every year. Due to the existence of many small coal kilns using backward mining methods, numerous worked-out areas have been formed. The coal mines were abandoned with no mitigation, so air penetrates into the roadways and contacts the coal seams; as a result, the residual coal seams spontaneously ignite to form coal fires. These coal fires have burned millions of tons of valuable coal resources and caused serious environmental problems. To implement fire suppression more effectively, coal fire detection is a key technology. In this paper, thermal infrared remote sensing from unmanned aerial vehicle combined with a surface survey is used to identify the range of coal fires in the Huojitu coal mine in Shenmu city. The scopes and locations of the fire zones are preliminarily delineated, which provides an accurate basis for the development of fire suppression projects.

A novel polarimetric imaging system is proposed, which is based on one complementary metal-oxide-semiconductor (CMOS) camera and double-layer prisms pair. Four polarizers, whose axes were set at different angles and affixed to the four prisms. The CMOS camera is used to simultaneously record the intensity of the light passing through the prisms with four specific polarization information. An algorithm is adopted to align and correct parallax to generate accurate Stokes parameters. Indoor and outdoor experimental performances verify the effectiveness and high measurement accuracy of the proposed system.

To reduce the difficulty of traditional data-mining methods in deep analysis of emerging capacity index mechanisms for a complex air defense system of systems (ADSOS), a novel backtracking analysis approach based on force-sparsed stacked-autoencoding (FS-SAE) neural networks is proposed. Using the method of big-data correlation analysis, community structure analysis in complex networks, and principle component analysis based on the mission task, the networked structure of an index system for ADSOS, which was a relatively complete architecture with a well-defined meaning, was obtained. An FS-SAE backtracking analysis model was build based on heuristic knowledge from the obtained networked index system structure. The emerging relations between the capacity indices of an ADSOS were formalized. Then, the formation mechanism and contribution rate of capacity indices were studied, and the validity of this approach was validated by the simulation data. The experimental results show that formalized presentation for the emergence process of capacity indices of ADSOS based on the proposed model not only reflects the complexity characteristics of nonlinearity and uncertainty in the emergence process, but also give a general defined meaning for the index structure of the ADSOS. It provides a feasible method for commanders to deeply understand, manage, and control the complex operation system of systems.

An interesting phase-shift lateral shearing interferometry system was proposed to evaluate the thermal residual stress distribution in transparent specimen. The phase-shift interferograms was generated by moving a parallel plane plate. Based on analyzing the fringes deflected by deformation and refractive index change, the stress distribution can be obtained. To verify the validity of the proposed method, a typical experiment was elaborately designed to determine thermal residual stresses of a transparent PMMA plate subjected to the flame of a lighter. The sum of in-plane stress distribution was demonstrated. The experimental data were compared with values measured by digital gradient sensing method. Comparison of the results reveals the effectiveness and feasibility of the proposed method.

Common optical methods are not suitable for accurate measurement of elastic modulus of specimens with initial bending because it is rather difficult to separate the axial strain caused by the axial load from the surface strain which consists of the axial strain and the bending strain caused by additional bending moment. Inspired by the strain-gauge technique, averaging the two strains on the opposite surfaces can eliminate the effect of bending strain of the specimen with initial bending, which is easily implemented by dual-reflector imaging and two-dimensional digital image correlation (2D-DIC). With dual-reflector imaging, the front and rear surfaces of the specimen are recorded by using a single digital camera. Consequently, the strains of two optical extensometers constructed on these two surfaces are obtained with common 2D-DIC, and averaging these strains can eliminate the effect of bending moment and out-of-plane motion of the specimen. Therefore, the elastic modulus can be determined with high measurement accuracy. The effectiveness of the proposed method was first verified using self-manufactured tensile equipment which leads to large out-of-plane motion during the test. Furthermore, uniaxial tensile tests of stainless-steel specimens, including static and continuous tensile tests, were conducted to evaluate the accuracy of the proposed method. The experimental results show good agreement between elastic modulus obtained using the proposed method and a strain gauge and the relative error between them is less than 0.5%, which shows excellent performance of the proposed method on accurate measurement of elastic modulus of specimens with initial bending.

Stereo-digital image correlation (stereo-DIC) is now a standard technique for determination of the mechanical properties of materials and structures. In stereo-DIC, cameras are assumed to be motionless after camera calibration, so the three-dimensional (3D) reconstruction can be implemented using pre-calibrated parameters. However, this assumption is not true in some situations, such as drop test, seismic shaking table test and non-laboratory environment. Due to the presence of ground shaking or wind blowing, it's almost impossible to avoid camera motion in these experiments even if mechanical fixing is adopted. Camera motion during the experiment can undoubtedly introduce significant errors on measured results. Generally, camera motion can be divided into pair motion and relative motion. The influence of these two kinds of motion on stereo-DIC measurement is different and worth of separate study. Keep this in mind, in this paper, the influence of camera motion on stereo-DIC is investigated and the effects of pair motion and relative motion are examined separately using precisely controllable simulated experiments. Specifically, by integrating into the stereo matching, the speckle-based compensation method for relative motion is proposed and the accuracy of the compensation methods is analyzed in detail. The reduction of camera motion-induced systematic errors will be helpful for the further applications of stereo-DIC in non-laboratory environments and engineering fields.

In the surface imaging of underwater structures, long working distance will reduce image quality due to the turbidity of water. To acquire high definition and large field of view (FOV) images for surface detection, a short-working-distance underwater imaging system is proposed based on camera array. A multi-view calibration and rectification method is developed. A look-up table (LUT) method and a multi-resolution spline (MRS) method are applied to stitch array images real-time and seamlessly. Experiments both in the air and in the water are conducted. Strength and weakness of the LUT and MRS methods are discussed. Based on the results, the effectiveness in surface detection of underwater structures is verified.

This paper firstly presents a brief review on the representations of speckle fringe pattern in vibration measurement using time-averaged electronic speckle pattern interference (ESPI) method. Based on laser phase noise, a new representation of speckle fringe intensity generated by real-time subtraction ESPI method for vibrating measurement is then proposed. In the experimental performance, the real-time subtraction ESPI method is employed to inspect the vibrating response of a closed-cell aluminum foam cantilever beam. In contract with the results of the finite elemental method simulation, the vibration mode shapes obtained by the ESPI method are well agreed with numerical prediction. The optical vibration analysis is also carried out to determine the effective Young’s modulus of aluminum foam, and the results verify the validation of the ESPI method for investigation on mechanical properties of metal foam materials.

The aim of this paper is to establish and validate a portable device for the local three dimensional deformation measurements using a single camera combined with a triangular prism mirror and two mirrors. The mirrors were utilized to convert a single camera into a stereo image system, which views a test object from two different directions and records the surface images of the test specimen on the two halves of the camera sensor in order to achieve a three-dimensional measurement. The proposed system consists of a single camera and the reflection system was integrated into a portable device to achieve a truly portable, low-cost, local three-dimensional deformation measurement, one-time calibration and easy implementation in situ. The optical design and measurement procedures to obtain the three-dimensional (3D) deformation measurements of the proposed system were described in detail. The efficiency and precision of the proposed system were verified by measuring the displacements of a translated flat plate. As a practical application, the proposed system is used to measure the out-of-plane displacement of an aluminum circular plate with a central load. Moreover, the normal strain measurement of a plastic beam under symmetric four-point bending via an outer loading frame was also presented. The measurement results are in good accordance with the data obtained by strain gauges. The experimental results revealed that the proposed system was practicable and effective for the local three-dimensional deformation measurement. This system well-suited to both laboratory and field condition and will have significant application in the fields of engineering.

In this paper, a high-precision and flexible intrinsic and extrinsic parameters calibration method for non-overlapping array cameras is proposed. In the camera array system, each camera employs an individual planar calibration board to achieve intrinsic parameters calibration. Without assistance of any other coded or un-coded target, the extrinsic parameters of array cameras can be flexibly calibrated based on close-range photogrammetry. To overcome the disadvantages of low precision under a large field of view in close-range photogrammetry, a refinement coordinates mapping (RCM) method to achieve high-precision reconstruction of targets is developed. The principles of single-camera calibration, close-range photogrammetry, and the extrinsic calibration method are introduced, respectively. Experiments are performed to analyze the stability of single-camera calibration and the world coordinates reconstruction of targets. The results of the re-projection error in extrinsic parameters calibration show that the developed RCM method has high precision.