bob手机在线登陆学报自然版

2020, 40(2): .

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2020, 40(2): .

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Influence of High-Temperature Strength of Substrate Steel on Barrel Life

GENG Xue-hao, ZHOU Ke-dong, HE Lei, QIAO Zi-ping

2020, 40(2): 121-128. doi:10.15918/j.tbit1001-0645.2019.088

Abstract(799) PDF(324)

Abstract:
According to the theories of coating shear failure mechanism and fatigue cumulative damage, a life prediction model of gun barrel was proposed based on the shear fatigue damage accumulation at the interface of coating and substrate in barrel. The interface shear stress of a small caliber gun barrel during a cooling cycle was calculated, then the fatigue life was predicted respectively for three barrels with different substrate materials, and the influence of high-temperature strength of substrate steel on barrel life was studied. The research results show that the high-temperature strength of substrate is a key factor which concerns barrel life, and the interface tensile strength decline caused by temperature rise is a significant inducement of coating failure and the end of barrel life. The increase of room-temperature strength of substrate is of little help to barrel life improvement, but the increase of high-temperature strength of substrate can observably enhance barrel life. The comparison of life test results and the prediction results verify the availability of life prediction model and the validity of prediction results.

Study on the Effect of Minimum Resistance Line on Blasting Effect of Bench Model

ZHANG Zhi-yu, DING Fei, LI Hong-chao, HUANG Yong-hui, XIE Shao-kai

2020, 40(2): 129-134. doi:10.15918/j.tbit1001-0645.2019.060

Abstract(808) PDF(213)

Abstract:
To study the effects of minimum resistance line on the step model exploding, a blasting experiment was conducted using pure concrete bench model with the similarity criterion. This experiment was monitored and analyzed by a high-speed camera, a transient signal measuring instrument, and a super dynamic strain tester. It was found that with the value increase ofW, the fragmented quality of blasted pile and the largest size of fragmentation increased, while the initial velocity of free surface, and the intersection angle of model charging center speed and horizontal direction decreased. Practically the decreasing speed of the intersection angle got slower with the value increase ofW. Also, with the value increase ofW, it was found that the largest vibration velocity increased at first and then decreased, and the main frequency of vibration decreased continually. Besides, the peak strain of free surface increased with the decrease of the distance from it to the exploding source.

Influence and Revision of Transverse Inertia Effect and Pressure Hardening Effect on Strain-Rate Hardening Effect of Compressive Strength of Concrete

GAO Guang-fa

2020, 40(2): 135-142,149. doi:10.15918/j.tbit1001-0645.2018.532

Abstract(870) PDF(332)

Abstract:
The compressive strength of concrete has a significant strain-rate hardening effect under a high strain-rate loading. However, some problems, such as transverse inertia effect, should be considered even if all conditions in the test process are perfect. And the strain-rate effect and pressure hardening effect are decoupling, so the part of dynamic increase factor which is on account of the increase of pressure must be excluded. Based on previous investigation results, the transverse inertia effect and pressure hardening effect were studied through theoretical analysis and numerical simulation and the true strain-rate effect of concrete was obtained. The study results show that with the increase of the radial size and strain-rate of the specimen, the decrease of sound velocity and the fracture strain of concrete material, the transverse inertia effect is more and more obvious. Compared with the concrete specimen, the strain-rate effect of concrete material is much smaller. Concrete material is a kind of structural material which contains a mass of micro-void and randomly distributed initial damage, so it should be a strain-rate hardening material.

Investigation of Specific Impulse Under Contact Explosion and Close-in Explosion Conditions Using Numerical Method

LI Zhen, LIU Yan, HUANG Feng-lei, YAN Jun-bo, YU Wen-li, LÜ Zhong-jie

2020, 40(2): 143-149. doi:10.15918/j.tbit1001-0645.2019.049

Abstract(980) PDF(364)

Abstract:
For contact explosion and close-in explosion, blast load distribution will be effected by the shape of explosive, the location of detonation point and product injection, which poses difficulties to theoretical analysis and engineering application. In order to study the specific impulse generated by contact explosion and close-in explosion, numerical simulations were made using the fluid-solid coupling method and PBM method according to a close-range explosive experiment done by Nansteel. The results showed that the simulation of the PBM model agreed well with the experimental results, while the fluid-solid coupling simulation results were only about 70% of the experimental values. The simulation results of contact explosion of isometric diameter ratio TNT column showed that the center point ’s specific impulse changed linearly with the diameter. The change of the core distance mainly affected the specific impulse within the 6 cm radius of the target center point when 640 g and 1 250 g TNT columns were used. Based on dimensional analysis, the empirical formula of specific impulse was obtained.

Research on High Accurate Measurement for Low Frequency and Weak Signal

LANG Ping, HAN Lei, LI Yan

2020, 40(2): 150-156. doi:10.15918/j.tbit1001-0645.2019.424

Abstract(1081) PDF(282)

Abstract:
The measurement of low frequency weak signal (MLFWS), especially in complex circumstances, has universal application in contemporary research. In this paper, a high accurate detection system (HADS), used in MLFWS with an amplitude of 0.01 nA or mV below 500 Hz, has been designed, based on the shortcomings of MLFWS including low accuracy, complex procedures, expensive equipment and so on at present. First of all, the noise sources and anti-interference actions of MLFWS in real environments were analyzed theoretically; secondly, HADS, used in MLFWS, was designed, based on the characteristics of MLFWS and anti-interference measures; finally, the performances of HADS were tested by debugging and human-based pulse signal detection experiments. The results demonstrate that HADS could achieve the detection error of less 0.5%, in the MLFWS with amplitude of 0.01 nA or mV below 500 Hz.The signal and noise ratio (SNR)was(60±2 )dB, and root mean square error(RMSE) was less than 5×10^-4, in the measurement of human-based pulse signal. In conclusion, HADS has excellent characteristics, including high accuracy, good anti-interference, stability, practicality, easy operation, low price and so on.

The Dynamic Properties and Control Method of a Flying Wing with High Aspect-Ratio and Strong Coupling Between Aeroelasticity and Flight Dynamics

ZHANG Shuo, WANG Zheng-jie, CHEN Hao

2020, 40(2): 157-162. doi:10.15918/j.tbit1001-0645.2019.076

Abstract(936) PDF(211)

Abstract:
This research investigated the dynamic properties of a flying wing aircraft with high aspect ratio and strong coupling between the flight dynamics and the aeroelasticity, and the corresponding control method. The inertial coupling between rigid-body DoF motion and elastic DoF motion were addressed by free-free modes of the whole aircraft. The double lattice vortex method and the rational function approximation (RFA) method were used for unsteady aerodynamic calculation. LQR method was used for the combined control law design to control the flight dynamics and elastic deformation simultaneously. Compared with the uncontrolled case, the designed close-loop control law could effectively reduce 60% of the pitching angle disturbance. It can be concluded that there is significant dynamic coupling between the short period and the first bending aeroelastic mode. The combine control law can generate dynamic elastic deformation which is always helpful to disturbance alleviation in the dynamic process.

Face Recognition of Small-Scale Dataset Based on Joint Loss Functions

ZHANG Xin-yu, YOU Ming-yu, ZHU Jiang, HAN Xuan

2020, 40(2): 163-168. doi:10.15918/j.tbit1001-0645.2018.470

Abstract(1343) PDF(249)

Abstract:
In order to solve the problems induced in face recognition with small-scale datasets that small data size along with large changes and over-fit trend during directly training with deep neural networks, a face recognition method was proposed based on small-scale datasets with joint loss functions. This method was arranged to finetune a pre-trained model trained with large-scale public facial datasets based on Softmax loss function to make full use of all parameters in the model and improve feature representation capability of the model. Compared with conventional feature postprocessing methods, the effectiveness of this method was verified and evaluated. Experiment results show that this method can largely improve the performance of face retrieval on school freshmen face dataset.

An Automated Detection and Verification Method for WebView Component Vulnerabilities

WANG Jia-jie, LIU Jian-xin, MA Yu-fei, SHAO Shuai, ZHANG Pu-han

2020, 40(2): 169-174. doi:10.15918/j.tbit1001-0645.2017.359

Abstract(855) PDF(234)

Abstract:
With Android WebView component widely used, its vulnerabilities will cause significant risks, but current detection methods which rely on static pattern matching have high rate of false positives. Therefore this paper proposes an automatic detection and verification method for WebView component vulnerabilities, based on static analysis and dynamic verification combination. The reachability analysis of vulnerable suspicious points was used to avoid the futile dynamic verification of invalid paths, for improving analysis efficiency. The data dependency analysis was combined with the dynamic verification that can simulate real attack behaviors to trigger and confirm vulnerabilities timely, for reducing false positives. The prototype tool XWebViewDigger has been developed and tested on 80 real Android applications, with 18 vulnerable applications detected and verified. Compared with current methods, the false positive rate was effectively reduced.

VTC-KSVD,a New Multi-Label Image Annotation Method Combining Visual Features with Tag Consistency

ZHANG Ju-li, HE Zhan-zhuang, DAI Tao, ZHANG Jun-yi

2020, 40(2): 175-181,188. doi:10.15918/j.tbit1001-0645.2019.153

Abstract(981) PDF(272)

Abstract:
A new method for multi-label image annotation was proposed based on the combination of visual features and tag consistency. Firstly, a tag consistency model TC-KSVD was established for the training images using the KSVD method. In order to further improve the annotation accuracy, multi-view visual features were incorporated into the model. This method was arranged not only to utilize the discriminant model of the training samples ’item labels and coding coefficients, but also to utilize the relationship between tags and the coding coefficients, so as to increase the discriminability of the dictionary and improve the annotation performance. The experimental results on the Corel5K datasets show that, the VTC-KSVD method with multi-view visual features and tag consistency can accurately find the neighbors with similar visual features and semantic features, which can significantly improve the annotation accuracy and can effectively alleviate the sparsity problem caused by limited training data.

A Novel of Pump Controlled Electric-Hydraulic Steering System for Wheel Loaders

YANG Jing, WANG Xiang-yu, QUAN Long, ZHANG Xiao-gang, CHENG Hang, ZHAO Bin

2020, 40(2): 182-188. doi:10.15918/j.tbit1001-0645.2018.465

Abstract(716) PDF(234)

Abstract:
The load sensing steering system, which is generally utilized in traditional wheel loaders, uses the fixed displacement pump to supply the hydraulic oil. However, there are a large overflow and throttling loss during the steering process. In order to improve the energy efficiency, a constant pump driven steering system was proposed. The constant pump was designed to be driven by servo motor, independently and directly used to supply the required flow for the proposed steering system. The steering speed of electric controlled steering wheel was adopted to control the speed of servo motor. Firstly, a co-simulation model of pump controlled electric-hydraulic steering system was established to analyze the feasibility of the steering system. Then, a test prototype of steering system was established to validate its dynamic characteristics. Finally, compared with the traditional load sensing steering system, the characteristics of pump controlled electric-hydraulic steering system were concluded. The results show that, based on the pump controlled electric-hydraulic steering system, the throttling losses can be reduced, the overflow losses can be eliminated during the steering process, and the energy consumption can be decreased by 56%. Apart from that, the shock and fluctuation of pressure can also be reclined, improving the system stability.

A Hardware-in-the-Loop Simulation System for Aircraft Braking

WU Shuai, PANG Bo, WEI Ren-lei, JIAO Zong-xia

2020, 40(2): 189-192,197. doi:10.15918/j.tbit1001-0645.2018.453

Abstract(744) PDF(263)

Abstract:
A mathematical model was proposed to describe the aircraft brake process. Firstly, analyzing the force of the aircraft and its wheels, a series of dynamic equations were established to solve the key variables in the entire braking process. And then, a Runge-Kutta method was used to obtain the solutions of differential dynamics equations. Finally, a hardware-in-the-loop simulation platform RTX was established to simulate and guarantee the real-time performance. Results show that, the simulation system can adapt for the experimental parameter changes to simulate the braking process under different actual conditions.

Velocity and Position Combined Control of Hydraulic Excavator Swing System Based on Handle Integral

HUANG Wei-nan, QUAN Long, CHENG Hang, GE Lei, DONG Zhi-xin, XIA Lian-peng

2020, 40(2): 193-197. doi:10.15918/j.tbit1001-0645.2018.457

Abstract(963) PDF(250)

Abstract:
The position of the hydraulic excavator swing system is usually controlled by operator. As a result, the production efficiency and positioning precision is low. To solve this problem, a velocity and position combined control strategy based on handle integral was proposed. To be compatible with the handle operation mode used in mobile machines, the input signal of the desired position was derived from the integral of the angular velocity determined by the swing angle of the electric handle. In this method, the pressure and velocity feedback control were also applied to improve the positioning precision and smoothness. Firstly, an electro-hydraulic simulation model and an experiment system were developed. The results show that higher positioning precision can be achieved with different desired angular displacement. The positioning error is only 0.5°. The position overshoot, velocity and pressure fluctuation are all avoided, and the dynamic characteristics are improved obviously.

Research on Risk Prediction of Unplanned Readmission

LI Jin-lin, ZHAO Xiu-lin, ZHANG Su-wei, ZHANG Zeng-bo, ZHU Jing-rong

2020, 40(2): 198-205,212. doi:10.15918/j.tbit1001-0645.2018.389

Abstract(1001) PDF(220)

Abstract:
To improve patients’ health, decrease unplanned hospital readmission rate, alleviate patients’ burden and prevent social resources waste, an unplanned hospital readmission risk prediction model was built, utilizing machine learning method and based on a dataset collected from a regional health care information platform of China. Different from existing works which only predict readmission risk, this research tried to model the problem from a multi-class classification view and predict readmission time and probability simultaneously. 10 classifiers were built by adjusting the parameters of neural network, random forest and support vector machine. Experiments on real dataset showed that the support vector machine classifier using polynomial kernel function performed best in terms of prediction accuracy, which was about 96.96%. The research result can assess readmission risk more precisely in time and probability based on patients’ historical health care data. With the help of the result, medical agencies can adopt proper interventions and reduce unplanned hospital readmission rate.

Tissue Distribution of Loureirin B in Rats Under Simulated Microgravity Effect

GUO Jing-jing, LI Yu-juan, CHEN Bo, KANG Li-ting, WANG Shi-bo, LI Yong-zhi, WANG Jia-ping, GAO Jian-yi

2020, 40(2): 206-212. doi:10.15918/j.tbit1001-0645.2018.438

Abstract(1024) PDF(259)

Abstract:
To study the tissue distribution of Loureirin B, an active ingredient of traditional Chinese medicine-dragons blood, and the potential effects of long-term simulated microgravity effect on drug distribution. SD rats were randomly divided into normal gravity group and simulated microgravity group. And rats were tail-suspended for 21 days to simulate microgravity effect. Single dose of 25 mg/kg Loureirin B was orally administered to all rats respectively. Heart, liver, spleen, lung, kidney, stomach, intestine, brain, testis and skeleton muscle samples were collected at 1 h postdosing. Concentration of Loureirin B in samples was determined by HPLC-MS/MS method to observe the effect of simulated microgravity effect on Loureirin B distributionin vivo. The results show that, Loureirin B is distributed significantly in the liver and stomach, followed by kidney, intestine, heart, spleen, skeletal muscle, lungand brain. The least distribution is found in brain. Compared with the normal gravity group, Loureirin B in the liver from the simulated microgravity rats is obviously increased by 47.7% (p<0.05), and the content of Loureirin B in rat brain is increased by 5.4-fold (p<0.05).Loureirin B is decreased significantly in the intestine and kidney with a decrease by 52.7% and 22.0% respectively (p<0.05).There is no dramatic difference in Loureirin B level of stomach, heart, lung, spleen, testis and skeletal muscle. Loureirin B distribution shows obvious tissue specificity. Loureirin B distribution in liver, intestine, brain and kidney of rats is evidently changed by long-term simulated microgravity effect.

Protective Effect of Bone Peptide in Osteoporosis Rats

LI Yu-juan, LIU Hua-yan, LUO Ke, CHEN Dong-sheng

2020, 40(2): 213-218. doi:10.15918/j.tbit1001-0645.2018.535

Abstract(751) PDF(271)

Abstract:
To study the protective effect of bone peptide on osteoporosis induced by retinoic acid in rats, an osteoporosis model was established by orally administration to SD rats with 70 mg/kg retinoic acid for two weeks. After 4-week oral administration of 40 mg/kg etedronate disodium or three doses of bone peptide (1.25, 2.50 and 5.00 g/kg) respectively, the rat femurs were collected for determination of HE, bone density, dry and ash weight, contents of Ca and P. Serum and urine were collected for assay of biochemical indicators. Results show that, compared with the control group, the bone density and bone trabeculae density are decreased in the model group, and the index is significantly increased after oral administration of medium and high doses of bone peptide. Three doses of bone peptide can significantly increase dry and ash weight of femur, contents of Ca and P.They also can increase the contents of BALP and BGP in rat serum, and decrease the level of TRACP-5b. The content of HOP in urine of rats in model group was increased dramatically and decreased significantly after oral administration of low dose of bone peptide. The positive drug showed obvious therapeutic effect in each index. Different doses of bone peptide could show a dose-dependent protective effect, while 2.50 g/kg bone peptide has the most obviously therapeutic effect on osteoporosis induced by retinoic acid in rats.

Ballistic Performance Simulation of Cylindrical Ceramic/ Titanium/Aramid Three-Layered Composite Targets and the Underlying Mechanism

FAN Qun-bo, LI Peng-ru, ZHOU Yu, LIU Xin

2020, 40(2): 219-226. doi:10.15918/j.tbit1001-0645.2019.135

Abstract(836) PDF(462)

Abstract:
Focusing on the process of the 53 type 7.62 mm armour-piercing projectile penetrating into the cylindrical ceramic/titanium/aramid three-layered composite targets, a study on ballistic performance numerical simulation was carried out. The simulation results show that the vertical incidence of projectile can cause cracks and fragmentations of ceramic layer, and eventually form pits on the titanium layer. The penetration depth of composite targets well agree with the experimental result, the relative error is only 9.4%. The percentages of energy dissipated by ceramic, titanium alloy and aramid layers are 83.77%, 13.77% and 2.46%, respectively. On this basis, setting the initial incident attitude angleθ₀from 0° to 70°, it is found that the ratio of energy dissipated by ceramic layer to the total energy is the largest in the process of projectile penetrating into targets. Further analysis of the ceramic layer shows that with the increase of initial incident attitude angleθ₀, the maximum force of ceramic layer decreases. Moreover, the action modes of projectile and target vary with the initial incident attitude angle. Energy analysis of ceramic layer shows that, the action mode is basically consistent with the mass loss. However, whenθ₀is 30°, the mass loss of ceramic layer is large, but the dissipated energy is relatively less.

An Extended Hamiltonian Algorithm for the Numerical Solution of the Nonlinear Matrix Equation

DUAN Xiao-min, ZHAO Xin-yu, SUN Hua-fei, JI Xue-ting

2020, 40(2): 227-230. doi:10.15918/j.tbit1001-0645.2018.495

Abstract(728) PDF(211)

Abstract:
In this paper, a second-order learning algorithm was used to solve a class of the nonlinear matrix equations. Specifically, the extended Hamiltonian algorithm was proposed based on manifold of positive definite symmetric matrices. Furthermore, this algorithm was compared with the multi-step iterative method to analyze its operation character. Finally, the simulation results show that, the convergence speed of the extended Hamiltonian algorithm is faster than the traditional algorithm.

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