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For the agricultural development of dumps, increase in land use efficiency and protection of food security, to verify the safety, efficacy and sustainability of field-applied arbuscular mycorrhizal fungi (AMF) inoculum, and to exclude the risk of potential biological invasion, in this study, we determined the effect of AMF inoculation and intercropping patterns (maize-soybean) on the temporal dynamics of soil parameters, native AMF communities and crop yields. AMF communities were analyzed using Illumina MiSeq. A total of 448 AMF operational taxonomic units (OTUs) belonging to six genera and nine families were identified. AMF inoculation treatment significantly improved the yield of intercropping maize and increased the content of available phosphorus. AMF diversity was significantly influenced by cropping pattern and growth stage, but not by the inoculation treatment. Inoculation altered the AMF community composition in the early growth stage and facilitated a more complex AMF network in the early and late growth stages. These results indicate that AMF inoculation affects native AMF only in the early stage, and its impact on yield may be the consequence of cumulative effects due to the advantages of plant growth and nutrient uptake in the early stage.

Traditional videometric method can not be used in the measurement of large flexible cable-net structure for its large overall size and small partial size. A videometrics technique was proposed in this work to measure the topography and deformation of a large cable net structure. Tiny spots with high brightness (and large gray gradient) are used to mark the cable net nodes. By arranging the imaging light path properly, the light spot markers can be enlarged and accurately identified in the captured images. The relationship between the imaging parameters and the gray distribution of the light spot markers were derived and verified. And a topographical measurement experiment of a cable net structure was carried out with the proposed videometrics technique. The topography/deformation of the cable net can be measured with tiny-light spot markers, and the effectiveness and robustness of the technique on topography and deformation measurement of large cable-net structures are demonstrated.

For the digital image correlation (DIC) method, the measurement of specimens with complex shapes may encounter difficulties due to the time-consuming recognition of region of interest (ROI), and the indeterminate parameter selection caused by the non-uniform deformation. This paper proposes an automatic DIC for the measurement of structures with complex shapes. An automatic ROI segmentation is developed by combining a convolutional neural network and image morphology, so the boundary of the specimen can be acquired accurately and efficiently. In dealing with the non-uniform deformation, a strain-related automatic selection of DIC parameters is developed, in which the sampling intervals and the subset sizes at different areas can be automatically determined. Both results of the simulated experiment and real experiment show that, by combing the two approaches with segmentation-aided DIC, the proposed automatic DIC can characterize the complex deformation including the boundary of the structures effectively.

The use of supervised neural networks is a new approach to solving digital image correlation (DIC) problems, but the existing methods solely adopt the black-box neural network, i.e., the mapping from speckle image pair (reference image and deformed image) to multiple deformation fields (displacement fields and strain fields) is directly established without considering the physical constraints between the fields, causing a low level of accuracy that is even inferior to that of Subset-DIC. In this work, we proposed a deep learning model by introducing strain-displacement relations into a neural network, in which the effect of errors both in displacement and strain are considered in the network training. The back-propagation process of the proposed model is derived, and the solution scheme is implemented by Python. The performance of the proposed model is evaluated by simulation and real DIC experiments, and the results show that adding physical constraints to the neural network can significantly improve prediction accuracy.

As a natural graded material, bamboo has gradually increasing elastic modulus along the radial direction from the inner to the outer skin. Accurate measurement of the modulus distribution plays an important role in bamboo-based structural design. However, it is difficult to characterise this modulus distribution by using conventional testing approaches on bamboo slices. A more effective method was developed in this study for the inverse identification of gradually varying material properties. The method is based on the digital image correlation and finite element model updating techniques. The radial distribution of the elastic modulus of bamboo was obtained through only one four-point bending test. The inversely identified modulus distribution was verified through uniaxial tensile tests on sliced bamboo strips and microscopic observation of the volume fraction distribution of its vascular bundle. The results showed that the elastic modulus of the bamboo material decreased from the outer skin (20 GPa) to the inner skin (2 GPa), which is in good consistence with the tensile test results on sliced specimens.

As a critical material in very/high-temperature gas-cooled reactors, graphite material directly affects the safety of the reactor core structures. Owing to the complex structures of graphite material in reactors, the material typically undergoes complex stress states. It is, therefore, necessary to study its mechanical properties, failure modes, and strength criteria under complex stress states so as to provide guidance for the core structure design. In this study, compressive failure tests were performed for graphite material under the condition of different confining pressures, and the effects of confining pressure on the triaxial compressive strength and Young's modulus of graphite material were studied. More specifically, graphite material based on the fracture surfaces and fracture angles, the graphite specimens were found to exhibit four types of failure modes, i.e., tension failure, shear-tension failure, tension-shear failure and shear failure, with increasing confining pressure. In addition, the Mohr strength envelope of the graphite material was obtained, and different strength criteria were compared. It showed that the parabolic Mohr-Coulomb criterion is more suitable for the strength evaluation for the graphite material.

Bayer chromatic cameras are increasingly being used in photogrammetry for high-accuracy deformation measurements. However, studies on the quantitative accuracy evaluation of different photogrammetric methods using Bayer chromatic images are lacking, as the influence mechanism of chromatic images on measurement accuracy is unclear. This work performed substantial tests to investigate the influence of chromatic images on the photogrammetric measurement accuracy. Firstly, the spatial resolution and signal-to-noise ratio (SNR) of chromatic images were quantitatively evaluated. The performance of Bayer chromatic images was found to be systematically worse than the monochromatic counterparts with the same imaging configurations. Different photogrammetric measurements were then carried out using monochromatic and chromatic images. The measurement accuracy from chromatic images was significantly lower than that from monochromatic images, except for the grid method with square-profile fringes. Therefore, it is recommended to use monochromatic cameras for carrying out deformation measurements, unless there is a requirement of colour identification.

Digital image correlation (DIC) is a popular photomechanics method for deformation measurement. The conventional subset-based DIC method obtains the displacement vectors at the subset centers, but cannot calculate the deformation on the specimen edges, which may contain very useful information because specimens usually have greater deformation on edges, especially on curved edges due to stress concentration. In this study, the capability of a mesh-based DIC method using 8-node quadrilateral elements (Q8-mesh-DIC) in boundary deformation measurement was investigated and highlighted for specimens with non-uniform deformation. The results were compared with those obtained by some conventional subset-based DIC methods, and the accuracy of the boundary deformation measurement was verified through simulated and real experiments. The Q8-mesh-DIC appears to be more suitable for the boundary deformation measurement of non-uniform deformation fields.

Background Effects on maize were assessed of dual inoculation with arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSE) isolated from other plant species. Methods Suspensions of DSE isolated from Stipa krylovii were prepared at different densities (2, 4, and 8 × 105 CFU mL− 1) and inoculated separately (AMF or DSE) or together (AMF + DSE), to explore their effects on maize growth. Results Inoculation with AMF or medium and high densities of DSE and combined inoculation (AMF + DSE) increased plant above-ground growth and altered root morphology. Differences in plant growth were attributable to differences in DSE density, with negative DSE inoculation responsiveness at low density. AMF promoted plant above-ground growth more than DSE and the high density of DSE promoted root development more than AMF. Combined inoculation might lead to synergistic growth effects on maize at low density of DSE and competitive effects at medium and high DSE densities. Conclusions AMF and DSE co-colonized maize roots and they had positive effects on the host plants depending on DSE density. These findings indicate the optimum maize growth-promoting combination of AMF and DSE density and provide a foundation for further exploration of potentially synergistic mechanisms between AMF and DSE in physiological and ecological effects on host plants.

We investigated image distortion induced by the coupling effect between the self-heating of a digital camera and environmental temperature, and then proposed a model to explain the relationship between environmental temperature and thermal-induced image distortion. First, we analyzed the heat transfer between the (self-heating) camera and the environment to elucidate the relationship between the environmental and camera-component temperatures. Next, we analyzed the thermal-induced change of imaging optical path to derive the relationship between the camera-component temperatures and image distortion. Finally, we established and verified a new model for thermal-induced image distortion. Our results indicate that camera-self-heating-induced image distortion forms a special case described by our model.

Nuclear graphite is a typical quasi-brittle material used in nuclear reactors. Damage can easily generate and accumulate under loads due to widespread defects (such as cracks or holes) inside the material and thereby cause the degradation of material properties. Studies have shown that nuclear graphite exhibits different damage evolution behaviours under tensile and compressive loading. In this paper, experiments were first carried out to measure the stress concentration factors of L-shaped graphite specimens with different corner radii subjected to tension. Subsequently, finite element models with and without damage evolution were established, and different damage evolution laws were considered for tension and compression in the damage model. The importance of damage on stress concentration prediction of graphite components was emphasized by comparing the experimental and numerical simulation results.

Contact between two or more structures is common in engineering applications. The maximum loading capacity (characterised by the ultimate strength) of such structures must be considered for their structural reliability design. However, a quantitative assessment of the ultimate strength of contact structures is currently lacking because their failure mechanism is unclear. In the present study, the failure mechanism of line contact structures was experimentally investigated, and an ultimate strength assessment was proposed based on the mechanism. Specifically, the correspondence between the global mechanical behaviour and local deformation of line contact structures was established using an experimental system. We found that the global failure of a line contact structure is attributed to the change in the topological structure of yield zones. That is, the merging of yield zones leads to the global failure of such structures. Based on this mechanism, a general expression for the ultimate strength of line contact structures was established. The validity and accuracy of the proposed assessment were validated experimentally.

Most photogrammetry-based object position and attitude measurement systems use area cameras for two-dimensional (2D) image acquisition. However, the large volume of 2D images provided by area cameras limits the image capture speed, thus preventing the application of such methods to some high-speed measurements. Linear camera-based systems cannot be used to obtain real-time position and attitude parameters of non-specially designed objects because of scanning imaging and optimisation requirements. In this work, a novel position and attitude measurement method based on linear cameras was proposed. The position and attitude of objects can be obtained by analysing simultaneously recorded images of a specially designed five-line plane target using two calibrated linear cameras. This method can be used to carry out high-speed measurement of position and attitude parameters because no scanning imaging is required. In the present paper, we introduce the principle of this method, present verifications based on virtual and actual experiments, and analyse the main factors that affect measurement error.

Nuclear graphite is a type of quasi-brittle material, in which the ratio of the tensile strength to the compressive strength is higher than that of ceramic and hard rock materials. In this case, it is difficult to achieve a perfect splitting mode when the Brazilian splitting test is used to measure the tensile strength of such materials, leading to significant measurement errors. In this study, a ring compression test for measuring the tensile strength of the nuclear graphite material was proposed, and related principles and experimental verification were presented. The results showed that a regular tensile failure mode can be achieved using ring compression tests, and the tensile strength of nuclear graphite can be accurately measured. Furthermore, it was found that the accuracy obtained from ring compression tests was much higher than that from Brazilian splitting tests.

Characterizing global mechanical behavior accurately is important for a detailed understanding of the deformation mechanism of rock material. In this paper, a new characterization model of the global mechanical behavior of rock is proposed, based on the structural characteristics of rock deformation. Uniaxial compression tests were carried out using the digital image correlation method and acoustic emission to obtain the interrelationship between mechanical behavior and deformation evolution. The test results show that the appearance of deformation localization leads to non-linear evolution of global mechanical behavior in a rock specimen. Further, due to the gradual evolution of deformation localization bands, the rock specimen evolves from a complete whole to a rock structure with a &ldquo, weak interlayer&rdquo, Thus, the global mechanical behavior of the rock specimen depends heavily on the structural evolution process, especially when close to failure. A simplified characterization model was established according to the deformation process. The finite element method was used to verify the rationality of the proposed structural model. The verification result showed that under uniaxial compression, the structural model can reproduce the global mechanical behavior evolution process of the rock specimen.

Digital cameras represented by industrial cameras are widely used as image acquisition sensors in the field of image-based mechanics measurement, and their thermal effect inevitably induces thermal-induced errors of the mechanics measurement. To deeply understand the errors, the research for digital camera&rsquo, s thermal effect is necessary. This study systematically investigated the heat transfer processes and temperature characteristics of a working digital camera. Concretely, based on the temperature distribution of a typical working digital camera, the heat transfer of the working digital camera was investigated, and a model describing the temperature variation and distribution was presented and verified experimentally. With this model, the thermal equilibrium time and thermal equilibrium temperature of the camera system were calculated. Then, the influences of thermal parameters of digital camera and environmental temperature on the temperature characteristics of working digital camera were simulated and experimentally investigated. The theory analysis and experimental results demonstrate that the presented model can accurately describe the temperature characteristics and further calculate the thermal equilibrium state of working digital camera, all of which contribute to guiding mechanics measurement and thermal design based on such camera sensors.

Because of the limitations of the direct tension method, indirect methods such as Brazil tests or ring compression tests are widely applied to measure the tensile strength of brittle materials. However, in most cases of indirect method application, empirical equations that have been derived based on the assumption of a linear elastic material are used, and the effects of damage on the tensile strength measurements are ignored. Thus, in this study, ring-shaped nuclear graphite IG-11 specimens were subjected to diametrical compression tests to study the effects of damage evolution on tensile strength measurements. By analysing the experimental results and the damage evolution law obtained via an inverse method and finite element analysis, the true uniaxial tensile strength of IG-11 was accurately obtained. The results indicate that damage plays an important role in the tensile strength measurement of the nuclear graphite material when an indirect method is used. This study is also useful as a reference for obtaining accurate tensile strength predictions for other types of brittle materials.

Polymeric line contact structures are increasingly being used in engineering applications, so that the determination of the yield strength of the structures is of great importance. However, experimental investigation has shown that the current prediction of the yield strength in engineering provides conservative results relative to the actual yield behaviour of the structures. In the present study, a more accurate assessment for the yield strength of a line contact structure is proposed and, more importantly, this assessment was verified by a series of specially designed line contact tests based on optical full-field measurements. Specifically, the validity of this proposed assessment was examined by loading and unloading a polymeric line contact structure at different loading levels, and its accuracy was validated by singly loading line contact structures made from different polymeric materials until the occurrence of significant global plastic deformation. The experimental results confirmed that this proposed yield strength assessment enables accurate determination of the yield behaviour of line contact structures.

Arbuscular mycorrhizal fungi (AMF) contribute to the restoration of soil ecological functions and may facilitate the revegetation of degraded ecosystems by decreasing abiotic and biotic stresses on plants. The diversity and composition of AMF communities on the revegetation were assessed during an open-cast mining dump reclamation chronosequence of the soil at

The diversity, composition and ecological guilds of soil fungal communities in relation to revegetation were assessed during an open-cast mining dump reclamation chronosequence of the soil

An improved digital image correlation (DIC) scheme termed spatial-temporal subset-based DIC (STS-DIC) that incorporates the temporal continuity of deformation is proposed. Provided that displacement at a certain physical point on a specimen in several successive frames is temporally continuous and can be expressed as a linear relationship over time, the STS-DIC scheme is constructed between the reference subset and spatial-temporal deformed subset consisting of several subsets from a period of successive frames. The proposed method is verified by simulated speckle images and experimental tests featuring different types of deformation. Compared to the traditional subset-based DIC, the STS-DIC proposed in this paper takes advantage of noise suppression so as to improve the accuracy, especially for speckle images with larger noise. More importantly, it is found that the computational demand of STS-DIC is much lower than that of mesh-based (global) DIC incorporating the temporal continuity, despite achieving comparable accuracy. Therefore, STS-DIC is expected to be useful as a practical and flexible tool in complex-environment measurements with low signal-to-noise-ratio speckle images.

A label free and easy-to-prepare optical sensor with high mechanical strength for the fast and visible response to tension and pH variables was reported. An elastic nanocomposite hydrogel was successfully fabricated by in situ free-radical co-polymerization of N , N -dimethylacrylamide (DMAA), acrylic acid (AA) and aluminum oxide nanoparticles (Al 2 O 3 NPs). DMAA and AA could form effective cross-linkage with Al 2 O 3 NPs via hydrogen binding, electrostatic interaction and bidentate bridging. By encapsulating polymethyl methacrylate (PMMA) colloidal arrays into the hydrogels, the optical nanocomposite hydrogels (ONHs) can be easily obtained. This three-dimensionally ordered array exhibits a stop band, and the optical hydrogels can tune the bright color from blue to cyan, green, yellow green, yellow, orange and then finally red by mechanical stimulation of uniaxial tension within 50% strain following Bragg’s law. The mechanical and optical properties can be adjusted via changing the fraction of AA and polymerization time. Meanwhile, the mechanical and optical responses were reversible for more than 10 times without deterioration. Besides, this material has rapid response to the changing of pH and the full-color change was observed. Owing to the high biocompatibility of nanocomposite hydrogel (NC gel) system and the excellent mechanical strength and water-stability of these ONHs, this optical sensor has high potential to be applied in biomedical field as tension or pH sensor for the intraocular pressure measurement and tonometry and blood gas analysis.

Cardiovascular disease is now increasingly threatening to humanity. The accurate prediction of patients’ condition is significant to early prevention. This paper describes our research about how to predict patients’ risk of cardiovascular disease by processing their physical examination reports. We use five items (systolic pressure, diastolic pressure, triglyceride, high-density lipoprotein cholesterol and low-density lipoprotein cholesterol) to quantizer this risk in our research. To extract useful information from the medical records, we use natural language processing (NLP) method. To conserve the sentence into digital data, we use term frequency-inverse document frequency (TF-IDF) algorithm to extract major information from medical reports. Principal component analysis (PCA) algorithm is used to reduce the high dimension of text information data. Additionally, we extracted easy-transform numerical features and category features. Combining all these features, we use the xgboost algorithm to make final predictions. The results turn out to be well that the mean square error and relative error can be restricted to an acceptable low level.

Marker coordinate recognition (MCR) is widely used in fields such as medical character positioning, artificial intelligence control, and motion and deformation monitoring. Registration algorithms are often applied to improve the accuracy of MCR. However, external conditions such as light and temperature induce a temporal variation in the grey level during image acquisition, thereby reducing measurement accuracy. To overcome this problem, a mechanical constraint is introduced into marker point image processing, and an algorithm that incorporates the temporal continuity of deformation is proposed. A detailed derivation of this algorithm is generated, and the algorithm's performance is systematically validated through numerical and experimental tests. The results show that the proposed method yields accurate measurements accuracy but with a slight increase in computational cost. The proposed method can be used to improve deformation measurement and position accuracy.

Nuclear graphite is widely used as a moderator, reflector, and core structure material in very/high temperature gas-cooled reactors. However, because graphite may experience impacts with medium-low velocities during its transport and installation or under extreme conditions such as severe earthquakes, it is necessary to evaluate the dynamic fracture toughness of graphite to assess the safety of the reactors. The ASTM standard recommends a formula to calculate the fracture toughness; however, this formula includes the crack length parameter, which cannot be measured accurately in a dynamic process. To enable the accurate measurement of the dynamic crack propagation length of graphite and subsequently obtain the fracture toughness, a virtual extensometer method based on digital image correlation was established in this study. Three-point bending experiments were conducted using pre-cracked specimens to obtain the dynamic fracture toughness of graphite IG11 under medium-low impact velocities. The results indicated that the dynamic fracture toughness of graphite IG11 increased with the increase in the impact velocities, and its value was substantially higher than the static fracture toughness in certain cases. The proposed approach involves a simple operation, yields a high accuracy, and can enable automatic calculation. Moreover, this approach can be used to evaluate the dynamic fracture performance of other brittle or quasi-brittle materials.

Because it lacks sufficient descriptive power regarding the appropriate scale effect, conventional continuum mechanics is not applicable to the rapidly developing field of micro-nanoscale structures and devices. To accurately describe the scale effect on multi-scale structures, a number of high-order medium theories have been developed, with micropolar theory being the most prominent. However, because micropolar theory lacks a clear definition of the boundary displacement distribution, researchers have reached disparate conclusions regarding the scale dependence of the mechanical behaviour of heterogeneous materials. The goal of this study was to experimentally verify which set of conclusions was most accurate and determine the rationality of applying micropolar theory to micro-nanoscale structures. To achieve this, a series of three-point bendings were carried out in accordance with micropolar theory, with the experimental results confirming the scale effect in several heterogeneous micropolar medium materials. In addition, the law governing the micro-element relative rotational angle was further analysed, and further analysis of the scale effect in the micropolar medium material validated the applicability of micropolar theory to the analysis of the mechanical properties of such materials.

A new photogrammetry based measurement technique for contact areas in line contact structures is developed. From the data collected by this technique, a method for measuring the contact strength of contact structures in high temperature applications is proposed. The contact strength of a line contact structure of polyimide at different temperatures is measured; the results show that the increase in temperature decreases the contact strength of the structure. The effect of temperature on the contact strength is studied by investigating the occurrence and evolution of yielding core within the structure at different temperatures. The decrease in the yield strength and elastic modulus of the polyimide material at high temperature induces core yielding at lower loads and eases the propagation of core yielding to the surface.

Subset-based digital image correlation (DIC) has limitations in subset size selection for heterogeneous deformation field measurement. To maintain good spatial resolution, selecting sufficiently small subsets is necessary, but the measurement resolution is reduced because of poor matching information, inducing large errors in the correlation matching procedure. Spatial-temporal subset digital image correlation (STS-DIC) incorporates the temporal continuity of displacement in the deformation analysis. This can increase the matching information of subset in the temporal dimension. Here, the advantages of STS-DIC for the measurement of heterogeneous deformation fields were investigated through simulations and experiments. The results demonstrated that the measurement resolution was improved while ensuring a good spatial resolution for heterogeneous deformation field measurement by using STS-DIC. Finally, STS-DIC was applied to calculate the displacement field near a precast crack, and the stress intensity factors were calculated accurately from high accuracy displacement fields.

In a high-speed stereovision system, high-speed cameras (HSCs) are used to record images and time information, and the measurement accuracy depends on the time precision of the cameras. When two HSCs are used in a binocular stereovision system, the image acquisitions of both cameras are unlikely to start simultaneously. The images that are supposed to be captured at the “same time” may record different states of the test object during an experiment, which will cause measurement errors. In this work, a theoretical model was established to correlate the start-up time difference (STD) and the STD-induced measurement errors of a binocular stereovision system. A simulation of the deflection of a cantilever beam verified the accuracy of the theoretical model. A suggestion of the experimental layout was discussed to reduce the STD-induced measurement errors in one direction, and a method was proposed to correct the STD-induced measurement errors. The effectiveness of the correction method was validated by two experiments, that is, the trajectory of a marker point and the out-of-plane deformation of a bubble. The results showed that the absolute errors of the marker point trajectory were almost negligible and the deformation contours of the bubble were more symmetric after the correction. This correction method should be useful for three-dimensional measurements of physical quantities using a binocular stereovision system.

Over the past few years, natural language processing is getting much attraction from more scholars and institutions. Knowledge graph has been regarded as a crucial role in pushing natural language understanding forward. The task of information extraction is the first step to build a large-scale knowledge graph, which means to identify information from the natural language text and extract it in the form of entity and relation triplets. Some joint learning method have been proposed in this domain recently. In this paper, we inherit the idea of joint learning, use a simple, lightweight but effective structure to solve this task and compare our method with some recent algorithms on the benchmark dataset NYT and WebNLG. Results show that our method can get an improvement in F1 score.