Aiming at the problem that infrared small target detection faces low contrast between the background and the target and insufficient noise suppression ability under the complex cloud background,an infrared small targe...Aiming at the problem that infrared small target detection faces low contrast between the background and the target and insufficient noise suppression ability under the complex cloud background,an infrared small target detection method based on the tensor nuclear norm and direction residual weighting was proposed.Based on converting the infrared image into an infrared patch tensor model,from the perspective of the low-rank nature of the background tensor,and taking advantage of the difference in contrast between the background and the target in different directions,we designed a double-neighborhood local contrast based on direction residual weighting method(DNLCDRW)combined with the partial sum of tensor nuclear norm(PSTNN)to achieve effective background suppression and recovery of infrared small targets.Experiments show that the algorithm is effective in suppressing the background and improving the detection ability of the target.展开更多
Nowadays, ultrafine explosives are widely used in military fields. Ultrafine 2,2',4,4',6,6'-hexanitrostilbene(HNS) has emerged as an optimal primer for explosion foil initiators due to its excellent therma...Nowadays, ultrafine explosives are widely used in military fields. Ultrafine 2,2',4,4',6,6'-hexanitrostilbene(HNS) has emerged as an optimal primer for explosion foil initiators due to its excellent thermal stability and high-voltage short-pulse initiation performance. However, the solid phase ripening of ultrafine HNS leads to a degradation in its impact detonation performance. Previous studies have indicated that residual dimethyl formamide(DMF), which is present in ultrafine HNS prepared using the recrystallization method, affects ultrafine HNS ripening. The mechanism of residual solvent effects on solid phase ripening of ultrafine HNS is unclear. In this work, the specific surface area(SSA) derived from small angle X-ray scattering(SAXS) was utilized for kinetic fitting analysis to explore the mechanism by which residual solvents enhance the solid phase ripening of ultrafine HNS. The results of the SSA measured by insitu SAXS under conditions of 150℃ for 40 h revealed that the sample with 0.2% residual DMF exhibited a 21.51% decrease in SSA, whereas the sample with only 0.04% residual DMF showed a decrease of 15.66%.Furthermore, the higher amounts of residual DMF accelerated the reduction in SSA with time. Kinetic fitting analysis demonstrated that reducing residual DMF would lower both the activation energy and the pre-exponential factor, consequently decreasing the rate constant of solid phase ripening. The mechanism was speculated that it primarily facilitated the Ostwald ripening(OR). Additionally, contrast variation small angle X-ray scattering(CV-SAXS) confirmed that coating of ultrafine HNS particles is an effective method for inhibiting ripening, significantly reducing both the rate and extent of ripening of ultrafine HNS. This study predicts how residual solvents impact the solid phase ripening process of ultrafine HNS and proposes strategies for enhancing the long-term stability of ultrafine explosives.展开更多
Rock residual strength,as an important input parameter,plays an indispensable role in proposing the reasonable and scientific scheme about stope design,underground tunnel excavation and stability evaluation of deep ch...Rock residual strength,as an important input parameter,plays an indispensable role in proposing the reasonable and scientific scheme about stope design,underground tunnel excavation and stability evaluation of deep chambers.Therefore,previous residual strength models of rocks established were reviewed.And corresponding related problems were stated.Subsequently,starting from the effects of bedding and whole life-cycle evolution process,series of triaxial mechanical tests of deep bedded sandstone with five bedding angles were conducted under different confining pressures.Then,six residual strength models considering the effects of bedding and whole life-cycle evolution process were established and evaluated.Finally,a cohesion loss model for determining residual strength of deep bedded sandstone was verified.The results showed that the effects of bedding and whole life-cycle evolution process had both significant influences on the evolution characteristic of residual strength of deep bedded sandstone.Additionally,residual strength parameters:residual cohesion and residual internal friction angle of deep bedded sandstone were not constant,which both significantly changed with increasing bedding angle.Besides,the cohesion loss model was the most suitable for determining and estimating the residual strength of bedded rocks,which could provide more accurate theoretical guidance for the stability control of deep chambers.展开更多
In this study,the cooling rate was manipulated by quenching with water of different temperatures(30,60 and 100℃).Surface and internal residual stresses in the quenched 6061 aluminum alloy samples were measured using ...In this study,the cooling rate was manipulated by quenching with water of different temperatures(30,60 and 100℃).Surface and internal residual stresses in the quenched 6061 aluminum alloy samples were measured using hole-drilling and crack compliance methods,respectively.Then,the processability of the quenched samples was evaluated at cryogenic temperatures.The mechanical properties of the as-aged samples were assessed,and microstructure evolution was analyzed.The surface residual stresses of samples W30℃,W60℃and W100℃is−178.7,−161.7 and−117.2 MPa,respectively along x-direction,respectively;and−191.2,−172.1 and−126.2 MPa,respectively along y-direction.The sample quenched in boiling water displaying the lowest residual stress(~34%and~60%reduction in the surface and core).The generation and distribution of quenching residual stress could be attributed to the lattice distortion gradient.Desirable plasticity was also exhibited in the samples with relatively low quenching cooling rates at cryogenic temperatures.The strengthes of the as-aged samples are 291.2 to 270.1 MPa as the quenching water temperature increase from 30℃to 100℃.Fine and homogeneous β"phases were observed in the as-aged sample quenched with boiling water due to the clusters and Guinier-Preston zones(GP zones)premature precipitated during quenching process.展开更多
Automatic modulation recognition(AMR)of radiation source signals is a research focus in the field of cognitive radio.However,the AMR of radiation source signals at low SNRs still faces a great challenge.Therefore,the ...Automatic modulation recognition(AMR)of radiation source signals is a research focus in the field of cognitive radio.However,the AMR of radiation source signals at low SNRs still faces a great challenge.Therefore,the AMR method of radiation source signals based on two-dimensional data matrix and improved residual neural network is proposed in this paper.First,the time series of the radiation source signals are reconstructed into two-dimensional data matrix,which greatly simplifies the signal preprocessing process.Second,the depthwise convolution and large-size convolutional kernels based residual neural network(DLRNet)is proposed to improve the feature extraction capability of the AMR model.Finally,the model performs feature extraction and classification on the two-dimensional data matrix to obtain the recognition vector that represents the signal modulation type.Theoretical analysis and simulation results show that the AMR method based on two-dimensional data matrix and improved residual network can significantly improve the accuracy of the AMR method.The recognition accuracy of the proposed method maintains a high level greater than 90% even at -14 dB SNR.展开更多
Large residual stresses would be generated in the laser additive manufactured(LAMed)structures after processing rapid and intense heating and cooling cycles with bad mechanical properties.Scholars have tried many meth...Large residual stresses would be generated in the laser additive manufactured(LAMed)structures after processing rapid and intense heating and cooling cycles with bad mechanical properties.Scholars have tried many methods to decrease the residual stress to prevent the structures from being broken and improve the mechanical properties.In this study,residual stress and mechanical properties of LAMed structures are analyzed,and the advanced measuring method,laser ultrasonic technique,is used to detect the residual stresses accumulated in the samples in time.The results show that when the solution temperature is less than T_(β)(992℃),the residual stress increases gradually with the increase of solution temperature,and when the temperature is more than T_(β)(992℃),Widmanstätten structure will significantly reduce the residual stress;the mechanical properties of the specimen decrease with the increase of the solution temperature,and the different cooling methods do not have much effect on the elastic properties of the specimen.Considering the residual stress and mechanical properties,the HT1 system used in this paper is the best.This study is of great significance for the reasonable suppression of residual stress and the regulation of mechanical properties of TC4 titanium alloy fabricated by laser additive manufacturing.展开更多
The residual elastic energy index is a scientific evaluation index for rockburst proneness.In laboratory test,it is sometimes difficult to obtain the post-peak curve or to test the rock sample several times,which make...The residual elastic energy index is a scientific evaluation index for rockburst proneness.In laboratory test,it is sometimes difficult to obtain the post-peak curve or to test the rock sample several times,which makes it impossible to calculate the residual elastic energy index accurately.Based on 241 sets of experimental data and four input indexes of density,elastic modulus,peak intensity and peak input strain energy,this study proposed a machine learning model combining k-means clustering algorithm and random forest regression model:cluster forest(CF)model.The research employed a stratified sampling method on the dataset to ensure the representativeness and balance of the samples.Subsequently,grid search and five-fold cross-validation were utilized to optimize the model’s hyperparameters,aiming to enhance its generalization capability and prediction accuracy.Finally,the performance of the optimal model was evaluated using a test set and compared with five other commonly used models.The results indicate that the CF model outperformed the other models on the testing set,with a mean absolute error of 6.6%,and an accuracy of 93.9%.The results of sensitivity analyses reveal the degree of influence of each variable on rockburst proneness and the applicability of the CF model when the input parameters are missing.The robustness and generalization ability of the model were verified by introducing experimental data from other studies,and the results confirmed the reliability and applicability of the model.Therefore,the model not only effectively simplifies the acquisition of the residual elastic energy index,but also shows excellent performance and wide applicability.展开更多
为解决光在水下传播过程中由吸收与散射效应导致的水下图像模糊、对比度低和颜色失真问题,提出一种基于Inception-Residual和生成对抗网络的水下图像增强算法。首先,将退化水下图像缩放至256×256×3大小,以获得用于训练模型的...为解决光在水下传播过程中由吸收与散射效应导致的水下图像模糊、对比度低和颜色失真问题,提出一种基于Inception-Residual和生成对抗网络的水下图像增强算法。首先,将退化水下图像缩放至256×256×3大小,以获得用于训练模型的数据集。接着,将Inception模块、残差思想、编码解码结构和生成对抗网络相结合,构建IRGAN(Generative Adversarial Network with Inception-Residual)模型来增强水下图像。然后,利用全局相似性、内容感知和色彩感知构造多项损失函数,约束生成网络和判别网络的对抗训练。最后,通过训练好的模型对退化水下图像进行处理以获得清晰的水下图像。实验结果表明与现有增强方法相比,所提算法增强的水下图像在PSNR、UIQM和IE指标上的平均值分别比第二名提升13.6%、4.1%和0.9%。在主观感知和客观评估中,增强后的水下图像在清晰度、对比度增强和颜色校正方面均得到改善。展开更多
For the product degradation process with random effect (RE), measurement error (ME) and nonlinearity in step-stress accelerated degradation test (SSADT), the nonlinear Wiener based degradation model with RE and ME is ...For the product degradation process with random effect (RE), measurement error (ME) and nonlinearity in step-stress accelerated degradation test (SSADT), the nonlinear Wiener based degradation model with RE and ME is built. An analytical approximation to the probability density function (PDF) of the product's lifetime is derived in a closed form. The process and data of SSADT are analyzed to obtain the relation model of the observed data under each accelerated stress. The likelihood function for the population-based observed data is constructed. The population-based model parameters and its random coefficient prior values are estimated. According to the newly observed data of the target product in SSADT, an analytical approximation to the PDF of its residual lifetime (RL) is derived in accordance with its individual degradation characteristics. The parameter updating method based on Bayesian inference is applied to obtain the posterior value of random coefficient of the RL model. A numerical example by simulation is analyzed to verify the accuracy and advantage of the proposed model.展开更多
The relationships among compression ratio and stress, compression ratio and residual oil of cake in pressing process of castor beans were studied using the test equipment under different states of oilseeds and ways of...The relationships among compression ratio and stress, compression ratio and residual oil of cake in pressing process of castor beans were studied using the test equipment under different states of oilseeds and ways of pressing manners. The results show that variation of stress increases nonlinearly and residual oil rate decreases with the increase of compression ratio. Lower residual oil of cake was obtained by pressing gently and frequently. Curve fitting on both relationships had been built and parameters for the model were obtained by least square procedure and deepening research on pressing process of the castor beans for castor oil. By assuming that the value of oil production is equivalent to the value of energy consumption, the critical compression ratio of intact seeds is 6.2 while that of crushed seeds is 3.6.展开更多
The accurate detection of cooperative targets plays a key and foundational role in unmanned aerial vehicle (UAV) landing autonomously. The standard method based on fixed threshold is too susceptible to both illuminati...The accurate detection of cooperative targets plays a key and foundational role in unmanned aerial vehicle (UAV) landing autonomously. The standard method based on fixed threshold is too susceptible to both illumination variations and interference. To overcome issues above, a robust detection algorithm with triple constraints for cooperative targets based on spectral residual (TCSR) is proposed. Firstly, by designing an asymmetric cooperative target, which comprises red background, green H and triangle target, the captured original image is converted into a Lab color space, whose saliency map is yielded by constructing the spectral residual. Then, the triple constraints are developed according to the prior knowledge of the cooperative target. Finally, the salient region in saliency map is considered as the cooperative target, and it meets the triple constraints. Experimental results in complex environments show that the proposed TCSR outperforms the standard methods in higher detection accuracy and lower false alarm rate.展开更多
The differential thermal expansion of the polycrystalline diamond layer and the tungsten carbide substrate results in large residual stresses as PDC cutters cooling after sintering.The residual stresses on the top sur...The differential thermal expansion of the polycrystalline diamond layer and the tungsten carbide substrate results in large residual stresses as PDC cutters cooling after sintering.The residual stresses on the top surface of the diamond layer of PDC were measured at five points along the radial direction of PDC using X-ray Diffraction Residual Stress Instrument,thus the stresses and their radial distribution were obtained.The results show that the stresses on the diamond surface are compressive,the biggest stress appears at the central point(about 1200 MPa),and that from the center to the edge of PDC,the magnitude of the stress decreases. A finite element analysis(FEA) was made to check the validity of the testing results.The FEA modeling results were found to correlate well with the measured values.Factors leading to the deviation between XRD experimental measurements and the calculations of residual stress by FEA were also analyzed.展开更多
Practical experiences gained in the past several years show that the thermal residual stress(TRS) is a main cause leading polycrystalline diamond compacts(PDC) to premature failure.It is the very important to measure ...Practical experiences gained in the past several years show that the thermal residual stress(TRS) is a main cause leading polycrystalline diamond compacts(PDC) to premature failure.It is the very important to measure the TRS accurately for optimizing the interface and improving the service performance of PDC.In this paper,the TRS in 1913 flat-interface PDC was measured using improved stress-release method(ISRM). The TRS on the surface of polycrystalline diamond(PCD) table was obtained,which can be used to calculate the radial thermal residual stress(RTRS) at the interface of PCD table via a refutation process.The obtained results show that there are compressive residual stress at the PCD table interface and in the most region of PCD table surface.The exception occurs near the outer diameter of the PCD table,where the PDC begins to bend and put the PCD table surface into a tension state,an undesirable state for a brittle material.The ISRM has covered the shortage existing in traditional stress-release method,in which only finite points on the surface of PCD table can be tested for one specimen and one time.Simple as the experimental procedures are,the test results are also very accurate and reliable.This method provides the theoretical and experimental basis for testing TRS of PDC accurately.展开更多
With the gradual depletion of mineral resources in the shallow part of the earth,resource exploitation continues to move deeper into the earth,it becomes a hot topic to simulate the whole process of rock strain soften...With the gradual depletion of mineral resources in the shallow part of the earth,resource exploitation continues to move deeper into the earth,it becomes a hot topic to simulate the whole process of rock strain softening,deformation and failure in deep environment,especially under high temperature and high pressure.On the basis of Lemaitre’s strain-equivalent principle,combined with statistics and damage theory,a statistical constitutive model of rock thermal damage under triaxial compression condition is established.At the same time,taking into account the existing damage model is difficult to reflect residual strength after rock failure,the residual strength is considered in this paper by introducing correction factor of damage variable,the model rationality is also verified by experiments.Analysis of results indicates that the damage evolution curve reflects the whole process of rock micro-cracks enclosure,initiation,expansion,penetration,and the formation of macro-cracks under coupled effect of temperature and confining pressure.Rock thermal damage shows logistic growth function with the increase of temperature.Under the same strain condition,rock total damage decreases with the rise of confining pressure.By studying the electron microscope images(SEM)of rock fracture,it is inferred that 35.40 MPa is the critical confining pressure of brittle to plastic transition for this granite.The model parameter F reflects the average strength of rock,and M reflects the morphological characteristics of rock stress–strain curves.The physical meanings of model parameters are clear and the model is suitable for complex stress states,which provides valuable references for the study of rock deformation and stability in deep engineering.展开更多
In this paper, a new one-dimensional phenomenological model is developed for the assessment of the ballistic performance of Adobe. Adobe is a masonry largely spread in areas of the world involved in military operation...In this paper, a new one-dimensional phenomenological model is developed for the assessment of the ballistic performance of Adobe. Adobe is a masonry largely spread in areas of the world involved in military operations. Addressing fundamental ballistic parameters such as residual velocity or penetration depth for this building technology is necessary. The model follows the hypotheses for the ballistic response of concrete targets to high velocity impacts, provided with a dominant contribution of shear friction typical of soils. The hypotheses at the basis of the model are consistent with all experimental evidence collected by authors on Adobe. Adobe brick and mortar belong to the material class of concrete,whereas the overall mechanical parameters are determined by the internal soil mixture, including the percentage of fibre reinforcement. Despite its relative simplicity, the model is capable of well predicting ballistic test results currently available in literature for Adobe, including the data of an experimental campaign recently performed by the authors on real Adobe walls in the field.展开更多
A small problem about soil particle regularization and contacts but essential to geotechnical engineering was studied.The soils sourced from Guangzhou and Xiamen were sieved into five different particle scale ranges(d...A small problem about soil particle regularization and contacts but essential to geotechnical engineering was studied.The soils sourced from Guangzhou and Xiamen were sieved into five different particle scale ranges(d<0.075 mm,0.075 mm≤d<0.1 mm,0.1 mm≤d<0.2 mm,0.2 mm≤d<0.5 mm and 0.5 mm≤d<1.0 mm)to study the structures and particle contacts of granite residual soil.The X-ray micro computed tomography method was used to reconstruct the microstructure of granite residual soil.The particle was identified and regularized using principal component analysis(PCA).The particle contacts and geometrical characteristics in 3D space were analyzed and summarized using statistical analyses.The results demonstrate that the main types of contact among the particles are face-face,face-angle,face-edge,edge-edge,edge-angle and angle-angle contacts for particle sizes less than 0.2 mm.When the particle sizes are greater than 0.2 mm,the contacts are effectively summarized as face-face,face-angle,face-edge,edge-edge,edge-angle,angle-angle,sphere-sphere,sphere-face,sphere-edge and sphere-angle contacts.The differences in porosity among the original sample,reconstructed sample and regularized sample are closely related to the water-swelling and water-disintegrable characteristics of granite residual soil.展开更多
In low signal-to-noise ratio(SNR)environments,the traditional radar emitter recognition(RER)method struggles to recognize multiple radar emitter signals in parallel.This paper proposes a multi-label classification and...In low signal-to-noise ratio(SNR)environments,the traditional radar emitter recognition(RER)method struggles to recognize multiple radar emitter signals in parallel.This paper proposes a multi-label classification and recognition method for multiple radar-emitter modulation types based on a residual network.This method can quickly perform parallel classification and recognition of multi-modulation radar time-domain aliasing signals under low SNRs.First,we perform time-frequency analysis on the received signal to extract the normalized time-frequency image through the short-time Fourier transform(STFT).The time-frequency distribution image is then denoised using a deep normalized convolutional neural network(DNCNN).Secondly,the multi-label classification and recognition model for multi-modulation radar emitter time-domain aliasing signals is established,and learning the characteristics of radar signal time-frequency distribution image dataset to achieve the purpose of training model.Finally,time-frequency image is recognized and classified through the model,thus completing the automatic classification and recognition of the time-domain aliasing signal.Simulation results show that the proposed method can classify and recognize radar emitter signals of different modulation types in parallel under low SNRs.展开更多
An adaptive method of residual life estimation for deteriorated products with two performance characteristics (PCs) was proposed, which was sharply different from existing work that only utilized one-dimensional degra...An adaptive method of residual life estimation for deteriorated products with two performance characteristics (PCs) was proposed, which was sharply different from existing work that only utilized one-dimensional degradation data. Once new degradation information was available, the residual life of the product being monitored could be estimated in an adaptive manner. Here, it was assumed that the degradation of each PC over time was governed by a Wiener degradation process and the dependency between them was characterized by the Frank copula function. A bivariate Wiener process model with measurement errors was used to model the degradation measurements. A two-stage method and the Markov chain Monte Carlo (MCMC) method were combined to estimate the unknown parameters in sequence. Results from a numerical example about fatigue cracks show that the proposed method is valid as the relative error is small.展开更多
基金Supported by the Key Laboratory Fund for Equipment Pre-Research(6142207210202)。
文摘Aiming at the problem that infrared small target detection faces low contrast between the background and the target and insufficient noise suppression ability under the complex cloud background,an infrared small target detection method based on the tensor nuclear norm and direction residual weighting was proposed.Based on converting the infrared image into an infrared patch tensor model,from the perspective of the low-rank nature of the background tensor,and taking advantage of the difference in contrast between the background and the target in different directions,we designed a double-neighborhood local contrast based on direction residual weighting method(DNLCDRW)combined with the partial sum of tensor nuclear norm(PSTNN)to achieve effective background suppression and recovery of infrared small targets.Experiments show that the algorithm is effective in suppressing the background and improving the detection ability of the target.
基金the Presidential Foundation of CAEP(Grant No.YZJJZQ2023005)the National Natural Science Foundation of China(Grant No.22375191).
文摘Nowadays, ultrafine explosives are widely used in military fields. Ultrafine 2,2',4,4',6,6'-hexanitrostilbene(HNS) has emerged as an optimal primer for explosion foil initiators due to its excellent thermal stability and high-voltage short-pulse initiation performance. However, the solid phase ripening of ultrafine HNS leads to a degradation in its impact detonation performance. Previous studies have indicated that residual dimethyl formamide(DMF), which is present in ultrafine HNS prepared using the recrystallization method, affects ultrafine HNS ripening. The mechanism of residual solvent effects on solid phase ripening of ultrafine HNS is unclear. In this work, the specific surface area(SSA) derived from small angle X-ray scattering(SAXS) was utilized for kinetic fitting analysis to explore the mechanism by which residual solvents enhance the solid phase ripening of ultrafine HNS. The results of the SSA measured by insitu SAXS under conditions of 150℃ for 40 h revealed that the sample with 0.2% residual DMF exhibited a 21.51% decrease in SSA, whereas the sample with only 0.04% residual DMF showed a decrease of 15.66%.Furthermore, the higher amounts of residual DMF accelerated the reduction in SSA with time. Kinetic fitting analysis demonstrated that reducing residual DMF would lower both the activation energy and the pre-exponential factor, consequently decreasing the rate constant of solid phase ripening. The mechanism was speculated that it primarily facilitated the Ostwald ripening(OR). Additionally, contrast variation small angle X-ray scattering(CV-SAXS) confirmed that coating of ultrafine HNS particles is an effective method for inhibiting ripening, significantly reducing both the rate and extent of ripening of ultrafine HNS. This study predicts how residual solvents impact the solid phase ripening process of ultrafine HNS and proposes strategies for enhancing the long-term stability of ultrafine explosives.
基金Projects(2024YFC3013801,2022YFC3004602)supported by the National Key R&D Program of ChinaProjects(U23B2093,52034009)supported by the National Natural Science Foundation of China。
文摘Rock residual strength,as an important input parameter,plays an indispensable role in proposing the reasonable and scientific scheme about stope design,underground tunnel excavation and stability evaluation of deep chambers.Therefore,previous residual strength models of rocks established were reviewed.And corresponding related problems were stated.Subsequently,starting from the effects of bedding and whole life-cycle evolution process,series of triaxial mechanical tests of deep bedded sandstone with five bedding angles were conducted under different confining pressures.Then,six residual strength models considering the effects of bedding and whole life-cycle evolution process were established and evaluated.Finally,a cohesion loss model for determining residual strength of deep bedded sandstone was verified.The results showed that the effects of bedding and whole life-cycle evolution process had both significant influences on the evolution characteristic of residual strength of deep bedded sandstone.Additionally,residual strength parameters:residual cohesion and residual internal friction angle of deep bedded sandstone were not constant,which both significantly changed with increasing bedding angle.Besides,the cohesion loss model was the most suitable for determining and estimating the residual strength of bedded rocks,which could provide more accurate theoretical guidance for the stability control of deep chambers.
基金Project(2021GK1040)supported by the Major Projects of Scientific and Technology Innovation of Hunan Province,ChinaProject(52375398)supported by the National Natural Science Foundation of China。
文摘In this study,the cooling rate was manipulated by quenching with water of different temperatures(30,60 and 100℃).Surface and internal residual stresses in the quenched 6061 aluminum alloy samples were measured using hole-drilling and crack compliance methods,respectively.Then,the processability of the quenched samples was evaluated at cryogenic temperatures.The mechanical properties of the as-aged samples were assessed,and microstructure evolution was analyzed.The surface residual stresses of samples W30℃,W60℃and W100℃is−178.7,−161.7 and−117.2 MPa,respectively along x-direction,respectively;and−191.2,−172.1 and−126.2 MPa,respectively along y-direction.The sample quenched in boiling water displaying the lowest residual stress(~34%and~60%reduction in the surface and core).The generation and distribution of quenching residual stress could be attributed to the lattice distortion gradient.Desirable plasticity was also exhibited in the samples with relatively low quenching cooling rates at cryogenic temperatures.The strengthes of the as-aged samples are 291.2 to 270.1 MPa as the quenching water temperature increase from 30℃to 100℃.Fine and homogeneous β"phases were observed in the as-aged sample quenched with boiling water due to the clusters and Guinier-Preston zones(GP zones)premature precipitated during quenching process.
基金National Natural Science Foundation of China under Grant No.61973037China Postdoctoral Science Foundation under Grant No.2022M720419。
文摘Automatic modulation recognition(AMR)of radiation source signals is a research focus in the field of cognitive radio.However,the AMR of radiation source signals at low SNRs still faces a great challenge.Therefore,the AMR method of radiation source signals based on two-dimensional data matrix and improved residual neural network is proposed in this paper.First,the time series of the radiation source signals are reconstructed into two-dimensional data matrix,which greatly simplifies the signal preprocessing process.Second,the depthwise convolution and large-size convolutional kernels based residual neural network(DLRNet)is proposed to improve the feature extraction capability of the AMR model.Finally,the model performs feature extraction and classification on the two-dimensional data matrix to obtain the recognition vector that represents the signal modulation type.Theoretical analysis and simulation results show that the AMR method based on two-dimensional data matrix and improved residual network can significantly improve the accuracy of the AMR method.The recognition accuracy of the proposed method maintains a high level greater than 90% even at -14 dB SNR.
基金Project(51771051)supported by the National Natural Science Foundation of ChinaProject(2021-MS-102)supported by the Natural Science Foundation of Liaoning Province,China+1 种基金Project(N2105021)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(230032)supported by the National Training Program of Innovation and Entrepreneurship for Undergraduates,China。
文摘Large residual stresses would be generated in the laser additive manufactured(LAMed)structures after processing rapid and intense heating and cooling cycles with bad mechanical properties.Scholars have tried many methods to decrease the residual stress to prevent the structures from being broken and improve the mechanical properties.In this study,residual stress and mechanical properties of LAMed structures are analyzed,and the advanced measuring method,laser ultrasonic technique,is used to detect the residual stresses accumulated in the samples in time.The results show that when the solution temperature is less than T_(β)(992℃),the residual stress increases gradually with the increase of solution temperature,and when the temperature is more than T_(β)(992℃),Widmanstätten structure will significantly reduce the residual stress;the mechanical properties of the specimen decrease with the increase of the solution temperature,and the different cooling methods do not have much effect on the elastic properties of the specimen.Considering the residual stress and mechanical properties,the HT1 system used in this paper is the best.This study is of great significance for the reasonable suppression of residual stress and the regulation of mechanical properties of TC4 titanium alloy fabricated by laser additive manufacturing.
基金Project(42077244)supported by the National Natural Science Foundation of ChinaProject(SDGZK2431)supported by the State Key Laboratory of Intelligent Construction and Healthy Operation and Maintenance of Deep Underground Engineering,Sichuan University,China。
文摘The residual elastic energy index is a scientific evaluation index for rockburst proneness.In laboratory test,it is sometimes difficult to obtain the post-peak curve or to test the rock sample several times,which makes it impossible to calculate the residual elastic energy index accurately.Based on 241 sets of experimental data and four input indexes of density,elastic modulus,peak intensity and peak input strain energy,this study proposed a machine learning model combining k-means clustering algorithm and random forest regression model:cluster forest(CF)model.The research employed a stratified sampling method on the dataset to ensure the representativeness and balance of the samples.Subsequently,grid search and five-fold cross-validation were utilized to optimize the model’s hyperparameters,aiming to enhance its generalization capability and prediction accuracy.Finally,the performance of the optimal model was evaluated using a test set and compared with five other commonly used models.The results indicate that the CF model outperformed the other models on the testing set,with a mean absolute error of 6.6%,and an accuracy of 93.9%.The results of sensitivity analyses reveal the degree of influence of each variable on rockburst proneness and the applicability of the CF model when the input parameters are missing.The robustness and generalization ability of the model were verified by introducing experimental data from other studies,and the results confirmed the reliability and applicability of the model.Therefore,the model not only effectively simplifies the acquisition of the residual elastic energy index,but also shows excellent performance and wide applicability.
文摘为解决光在水下传播过程中由吸收与散射效应导致的水下图像模糊、对比度低和颜色失真问题,提出一种基于Inception-Residual和生成对抗网络的水下图像增强算法。首先,将退化水下图像缩放至256×256×3大小,以获得用于训练模型的数据集。接着,将Inception模块、残差思想、编码解码结构和生成对抗网络相结合,构建IRGAN(Generative Adversarial Network with Inception-Residual)模型来增强水下图像。然后,利用全局相似性、内容感知和色彩感知构造多项损失函数,约束生成网络和判别网络的对抗训练。最后,通过训练好的模型对退化水下图像进行处理以获得清晰的水下图像。实验结果表明与现有增强方法相比,所提算法增强的水下图像在PSNR、UIQM和IE指标上的平均值分别比第二名提升13.6%、4.1%和0.9%。在主观感知和客观评估中,增强后的水下图像在清晰度、对比度增强和颜色校正方面均得到改善。
基金supported by the National Defense Foundation of China(71601183)
文摘For the product degradation process with random effect (RE), measurement error (ME) and nonlinearity in step-stress accelerated degradation test (SSADT), the nonlinear Wiener based degradation model with RE and ME is built. An analytical approximation to the probability density function (PDF) of the product's lifetime is derived in a closed form. The process and data of SSADT are analyzed to obtain the relation model of the observed data under each accelerated stress. The likelihood function for the population-based observed data is constructed. The population-based model parameters and its random coefficient prior values are estimated. According to the newly observed data of the target product in SSADT, an analytical approximation to the PDF of its residual lifetime (RL) is derived in accordance with its individual degradation characteristics. The parameter updating method based on Bayesian inference is applied to obtain the posterior value of random coefficient of the RL model. A numerical example by simulation is analyzed to verify the accuracy and advantage of the proposed model.
基金Project(201304608)supported by the State Forestry Administration of ChinaProject(31470594)supported by the National Natural Science Foundation of China
文摘The relationships among compression ratio and stress, compression ratio and residual oil of cake in pressing process of castor beans were studied using the test equipment under different states of oilseeds and ways of pressing manners. The results show that variation of stress increases nonlinearly and residual oil rate decreases with the increase of compression ratio. Lower residual oil of cake was obtained by pressing gently and frequently. Curve fitting on both relationships had been built and parameters for the model were obtained by least square procedure and deepening research on pressing process of the castor beans for castor oil. By assuming that the value of oil production is equivalent to the value of energy consumption, the critical compression ratio of intact seeds is 6.2 while that of crushed seeds is 3.6.
基金supported by the National Natural Science Foundation of China(61135001)the Scientific Research Program of Shaanxi Provincial Department of Education(16JK1499)+2 种基金the Doctoral Fund of Xi’an University of Science and Technology(2015QDJ007)the Cultivation of Xi’an University of Science and Technology(2014015)the Ministry of Education Key Laboratory of Information Fusion Technology(LIFT2015-G-1)
文摘The accurate detection of cooperative targets plays a key and foundational role in unmanned aerial vehicle (UAV) landing autonomously. The standard method based on fixed threshold is too susceptible to both illumination variations and interference. To overcome issues above, a robust detection algorithm with triple constraints for cooperative targets based on spectral residual (TCSR) is proposed. Firstly, by designing an asymmetric cooperative target, which comprises red background, green H and triangle target, the captured original image is converted into a Lab color space, whose saliency map is yielded by constructing the spectral residual. Then, the triple constraints are developed according to the prior knowledge of the cooperative target. Finally, the salient region in saliency map is considered as the cooperative target, and it meets the triple constraints. Experimental results in complex environments show that the proposed TCSR outperforms the standard methods in higher detection accuracy and lower false alarm rate.
文摘The differential thermal expansion of the polycrystalline diamond layer and the tungsten carbide substrate results in large residual stresses as PDC cutters cooling after sintering.The residual stresses on the top surface of the diamond layer of PDC were measured at five points along the radial direction of PDC using X-ray Diffraction Residual Stress Instrument,thus the stresses and their radial distribution were obtained.The results show that the stresses on the diamond surface are compressive,the biggest stress appears at the central point(about 1200 MPa),and that from the center to the edge of PDC,the magnitude of the stress decreases. A finite element analysis(FEA) was made to check the validity of the testing results.The FEA modeling results were found to correlate well with the measured values.Factors leading to the deviation between XRD experimental measurements and the calculations of residual stress by FEA were also analyzed.
基金supported by the Natural Science of Hunan(06JJ4062)
文摘Practical experiences gained in the past several years show that the thermal residual stress(TRS) is a main cause leading polycrystalline diamond compacts(PDC) to premature failure.It is the very important to measure the TRS accurately for optimizing the interface and improving the service performance of PDC.In this paper,the TRS in 1913 flat-interface PDC was measured using improved stress-release method(ISRM). The TRS on the surface of polycrystalline diamond(PCD) table was obtained,which can be used to calculate the radial thermal residual stress(RTRS) at the interface of PCD table via a refutation process.The obtained results show that there are compressive residual stress at the PCD table interface and in the most region of PCD table surface.The exception occurs near the outer diameter of the PCD table,where the PDC begins to bend and put the PCD table surface into a tension state,an undesirable state for a brittle material.The ISRM has covered the shortage existing in traditional stress-release method,in which only finite points on the surface of PCD table can be tested for one specimen and one time.Simple as the experimental procedures are,the test results are also very accurate and reliable.This method provides the theoretical and experimental basis for testing TRS of PDC accurately.
基金Projects(51604260,11802145)supported by the National Natural Science Foundation of ChinaProject(SKLGDUEK1204)supported by the State Key Laboratory for Geomechanics and Deep Underground Engineering,ChinaProject(BK20160416)supported by the Natural Science Foundation of Jiangsu Province of China
文摘With the gradual depletion of mineral resources in the shallow part of the earth,resource exploitation continues to move deeper into the earth,it becomes a hot topic to simulate the whole process of rock strain softening,deformation and failure in deep environment,especially under high temperature and high pressure.On the basis of Lemaitre’s strain-equivalent principle,combined with statistics and damage theory,a statistical constitutive model of rock thermal damage under triaxial compression condition is established.At the same time,taking into account the existing damage model is difficult to reflect residual strength after rock failure,the residual strength is considered in this paper by introducing correction factor of damage variable,the model rationality is also verified by experiments.Analysis of results indicates that the damage evolution curve reflects the whole process of rock micro-cracks enclosure,initiation,expansion,penetration,and the formation of macro-cracks under coupled effect of temperature and confining pressure.Rock thermal damage shows logistic growth function with the increase of temperature.Under the same strain condition,rock total damage decreases with the rise of confining pressure.By studying the electron microscope images(SEM)of rock fracture,it is inferred that 35.40 MPa is the critical confining pressure of brittle to plastic transition for this granite.The model parameter F reflects the average strength of rock,and M reflects the morphological characteristics of rock stress–strain curves.The physical meanings of model parameters are clear and the model is suitable for complex stress states,which provides valuable references for the study of rock deformation and stability in deep engineering.
文摘In this paper, a new one-dimensional phenomenological model is developed for the assessment of the ballistic performance of Adobe. Adobe is a masonry largely spread in areas of the world involved in military operations. Addressing fundamental ballistic parameters such as residual velocity or penetration depth for this building technology is necessary. The model follows the hypotheses for the ballistic response of concrete targets to high velocity impacts, provided with a dominant contribution of shear friction typical of soils. The hypotheses at the basis of the model are consistent with all experimental evidence collected by authors on Adobe. Adobe brick and mortar belong to the material class of concrete,whereas the overall mechanical parameters are determined by the internal soil mixture, including the percentage of fibre reinforcement. Despite its relative simplicity, the model is capable of well predicting ballistic test results currently available in literature for Adobe, including the data of an experimental campaign recently performed by the authors on real Adobe walls in the field.
基金Projects(41572277,41877229)supported by the National Natural Science Foundation of ChinaProject(2015A030313118)supported by the Natural Science Foundation of Guangdong Province,ChinaProject(201607010023)supported by the Science and Technology Program of Guangzhou,China
文摘A small problem about soil particle regularization and contacts but essential to geotechnical engineering was studied.The soils sourced from Guangzhou and Xiamen were sieved into five different particle scale ranges(d<0.075 mm,0.075 mm≤d<0.1 mm,0.1 mm≤d<0.2 mm,0.2 mm≤d<0.5 mm and 0.5 mm≤d<1.0 mm)to study the structures and particle contacts of granite residual soil.The X-ray micro computed tomography method was used to reconstruct the microstructure of granite residual soil.The particle was identified and regularized using principal component analysis(PCA).The particle contacts and geometrical characteristics in 3D space were analyzed and summarized using statistical analyses.The results demonstrate that the main types of contact among the particles are face-face,face-angle,face-edge,edge-edge,edge-angle and angle-angle contacts for particle sizes less than 0.2 mm.When the particle sizes are greater than 0.2 mm,the contacts are effectively summarized as face-face,face-angle,face-edge,edge-edge,edge-angle,angle-angle,sphere-sphere,sphere-face,sphere-edge and sphere-angle contacts.The differences in porosity among the original sample,reconstructed sample and regularized sample are closely related to the water-swelling and water-disintegrable characteristics of granite residual soil.
基金The authors would like to acknowledge National Natural Science Foundation of China under Grant 61973037 and Grant 61673066 to provide fund for conducting experiments.
文摘In low signal-to-noise ratio(SNR)environments,the traditional radar emitter recognition(RER)method struggles to recognize multiple radar emitter signals in parallel.This paper proposes a multi-label classification and recognition method for multiple radar-emitter modulation types based on a residual network.This method can quickly perform parallel classification and recognition of multi-modulation radar time-domain aliasing signals under low SNRs.First,we perform time-frequency analysis on the received signal to extract the normalized time-frequency image through the short-time Fourier transform(STFT).The time-frequency distribution image is then denoised using a deep normalized convolutional neural network(DNCNN).Secondly,the multi-label classification and recognition model for multi-modulation radar emitter time-domain aliasing signals is established,and learning the characteristics of radar signal time-frequency distribution image dataset to achieve the purpose of training model.Finally,time-frequency image is recognized and classified through the model,thus completing the automatic classification and recognition of the time-domain aliasing signal.Simulation results show that the proposed method can classify and recognize radar emitter signals of different modulation types in parallel under low SNRs.
基金Project(60904002)supported by the National Natural Science Foundation of China
文摘An adaptive method of residual life estimation for deteriorated products with two performance characteristics (PCs) was proposed, which was sharply different from existing work that only utilized one-dimensional degradation data. Once new degradation information was available, the residual life of the product being monitored could be estimated in an adaptive manner. Here, it was assumed that the degradation of each PC over time was governed by a Wiener degradation process and the dependency between them was characterized by the Frank copula function. A bivariate Wiener process model with measurement errors was used to model the degradation measurements. A two-stage method and the Markov chain Monte Carlo (MCMC) method were combined to estimate the unknown parameters in sequence. Results from a numerical example about fatigue cracks show that the proposed method is valid as the relative error is small.
