Abstract:In order to explore the lubrication performance of alcohols under high loads and high speeds conditions, especially the relationship between carbon-chain length and hydroxyl number and lubrication performance, the effects of carbon-chain length and hydroxyl number on the lubrication performance were well studied. The tribological properties of a series of alcohols were investigated by a four-ball tribological machine, and the effects of the carbon-chain length and the hydroxyl number on their lubricating properties were investigated by means of viscometer, transmission electron microscopy (TEM) and Raman. Experiments show that with the increasing of the carbon-chain length, the run-in period and the time for achieving stable friction coefficient were shorted, and the wear was reduced; with the increasing of the hydroxyl number, the wear decreased with no obvious run-in period and consistent fluctuation of friction coefficient for ethylene glycol and continuous decrease of friction coefficient for glycerol. It is found that friction-induced graphene is superior to amorphous carbon in effectively promoting the tribosystem to achieve the stable friction coefficient and shorten run-in period, which provides reference for the application of alcohols in the field of mechanical equipment.

Abstract:In order to improve the positioning ability of ultra wideband network in non-cooperative indoor environment, the theory of centreless positioning algorithm was used to solve and analyze the output distance information of ultra-wideband ranging, and the relative positioning results were obtained. The positioning results of the system were compared with the results of the photoelectric calibration system, and the accuracy was evaluated. The results show that, compared with the traditional ultra-wideband positioning model, the combination of ultra-wideband ranging and centreless positioning algorithm can realize the centreless positioning and the relative positions among nodes, and finally determine the relative positions among nodes. The combination of UWB ranging and centreless positioning algorithm has good stability and accuracy in relative positioning, and can be widely used in various indoor and outdoor scenes.

Abstract:In order to solve the problem that the impulse interference near the service frequency band of aviation radio navigation affects the receiver, and further improve the anti-jamming ability of GNSS system, a impulse interference suppression method based on STFRFT (short time fractional Fourier transform) was proposed. The optimal rotation order of the received signal was determined, and STFRFT was applied to the signal to obtain the two-dimensional distribution of time-frequency surface through coordinate rotation. Under the optimal order, the adaptive time-varying filter was used to separate the interference and the signal, so as to suppress the interference. The simulation results show that the adaptive filtering algorithm based on STFRFT has the best effect of eliminating interference compared with several traditional methods, and retains more useful signals while suppressing impulse interference. By combining STFRFT and adaptive time-varying filtering technology, the ability of suppressing impulse interference is improved, which provides some reference for the impulse anti-jamming technology of aviation radio navigation service.

Abstract:In order to solve the problems of low recognition accuracy and easily affected by illumination conditions in the gesture recognition, an improved YOLOv3 gesture recognition algorithm was proposed. Firstly, a smaller detection scale was added to the original three detection scales to improve the detection ability of small targets; secondly, DIoU was used instead of the original mean square error loss function as the coordinate error loss function, the improved focal loss function was used as the confidence loss function of the boundary frame, and the cross entropy was used as the loss function of the target classification loss function. The results show that when the improved YOLOv3 gesture recognition algorithm is applied to gesture detection, the map index reaches 90.38%, which is 6.62% higher than that before the improvement, and FPS is nearly twice as high as before. After the new model is trained by the improved YOLOv3 method, the gesture recognition accuracy is higher, the detection speed is faster, the overall recognition efficiency is greatly improved, the loss weights of simple samples and difficult samples are balanced, and the training quality and generalization ability of the model are effectively improved.

Abstract:Aiming at the problem of poor precision performance of traditional Bayesian model saliency detection algorithm, a Bayesian model saliency detection algorithm based on improved convex hull was proposed. Firstly, the foreground of the image was extracted by the manifold ranking algorithm, which was used as the prior probability in Bayesian model. Secondly, Harris corner detection algorithm based on color enhancement was used to detect the feature points of the image in three color spaces of RGB, HSV and CIELab; the convex hulls in RGB, HSV and CIELab spaces were constructed respectively; and the intersection of convex hulls were obtained. Thirdly, the saliency region map was calculated by Bayesian model according to the prior probability and the observed likelihood probability obtained by combining convex hulls and color histograms. Finally, the proposed algorithm was tested in two public data sets MSRA and ECSSD. The experimental results show that the proposed algorithm can suppress the background noise effectively and detect the salient areas completely. The test results of F-measure value in MSRA and ECSSD databases are 0.87 and 0.71 respectively, and the accuracy-recall rate curve is higher than that of traditional classical algorithms in complex image databases. The proposed algorithm improves the detection effect of the traditional classical algorithm and the accuracy of saliency map detection.

Abstract:In order to solve the problem that ant colony algorithm is easy to fall into local optimum in UAV route planning, an improved ant colony algorithm was proposed. The upper and lower limits of pheromone volatilization factor and pheromone were set to prevent ants from falling into local optimum because pheromone on short path was too high or pheromone on long path was too low. At the same time, under the influence of multiple heuristic factors, the overall length of the path was taken as an adaptive heuristic function factor to determine the state transition probability. When the path length was large, the adaptive heuristic function factor was small, which reduced the probability of choosing the path by the ant colony. The experimental results show that the improved algorithm reduces the path length by 6.4% and the variance of the optimal path length by 85.78%, which increases the consideration of environmental integrity, shortens the path length, reduces the number of iterations, and jumps out of the local optimum. In the case of increasing environmental complexity, the algorithm can effectively choose a better path and provide a theoretical basis for UAV route planning after introducing the adaptive heuristic function factor.

Abstract:Most of the real-life networks are heterogeneous networks that contain multiple types of nodes and edges, and heterogeneous networks integrate more information and contain richer semantic information than homogeneous networks. Heterogeneous network representation learning to have powerful modeling capabilities, enables to solve the heterogeneity of heterogeneous networks effectively, and to embed the rich structure information and semantic information of heterogeneous networks into low-dimensional node representations to facilitate downstream task applications. Through sorting out and classifying the current heterogeneous network representation learning methods at home and abroad, reviewed the current research status of heterogeneous network representation learning methods, compared the characteristics of each category model , introduced the related applications of heterogeneous network representation learning, and summarized and prospected the development trend of heterogeneous network representation learning methods. It is proposed that in-depth discussion can be carried out in the following aspects in future: First, avoid predefined meta-paths and fully release the automatic learning capabilities of the model; Second, design heterogeneous network representation learning method suitable for dynamic and large-scale networks.

Abstract:In order to avoid the irritation of metformin hydrochloride to the stomach and realize its release in the intestine, with metformin hydrochloride as the main drug and chitosan/sodium alginate as the composite support, the optimal formulation and preparation technology of metformin hydrochloride loaded pH-sensitive hydrogel microspheres were selected, and the pH-sensitivity and in vitro drug release characteristics were investigated. The formulation and process were optimized by single factor test and orthogonal test. The morphology was characterized by SEM. The entrapment efficiency and drug-loaded amount were determined by UV. The release degree was studied by rotating basket method. The results show that the optimized prescription is as following: chitosan and sodium alginate with a total concentration of 2%(mass-volume ratio), mass ratio of sodium alginate to chitosan =1∶1, mass ratio of drug to sodium alginate=2∶5, and 3.5% CaCl2(mass-volume ratio). The cumulative release rate is less than 4% in artificial gastric juice within 6 h, and up to 96.4% in artificial intestinal juice within 6 h. The formulation and process are stable and reliable, and the hydrogel microspheres have high mechanical strength, good biodegradability and stability. So it is a new metformin hydrochloride delivery system.

Abstract:As the side effects of antibiotics are becoming increasingly prominent and the number of approvals is declining year by year, it is urgent to develop other active substances that are similar in functions and not easy to develop drug resistance. Antimicrobial peptides (AMPs) have broad-spectrum antibacterial activities, thermal stability and unique mechanism of action. They can not only play the role of anti-bacterial infection in vivo and promote apoptosis of cancer cells, but also be used as chemotherapeutic agents against virus and antibacterial materials for hospital settings. In this paper, developments related to antimicrobial mechanisms and activities of antimicrobial peptides against drug-resistant bacteria, anticancer and antiviral infection in the field of medicine are systematically reviewed. The problems of stability, hemolytic and toxicity of antimicrobial peptides are elucidated and the development prospects of AMPs in medicine are provided. Further research on AMPs can be carried out in the following aspects in the future. 1) Antibacterial mechanism in vivo are studied to promote the development and application of antimicrobial peptides；2）Structures of AMPs are optimized by replacing and modifying amino acid residues and hybrid peptides are synthesized to improve their activities, reduce side effects and prevent drug resistance; 3）Application of delivery systems for AMPs or combination of AMPs with green natural extracts is investigated to improve their antibacterial activity and bioavailability.

Abstract:In order to improve the oxidation resistance of 304 stainless steel, SiO2 thin film was prepared on the surface of stainless steel by sol-gel method with tetraethyl orthosilicate (TEOS) as raw material. The effect of film layers on the high temperature oxidation resistance of stainless steel at 900 ℃ was studied by means of oxidation kinetics, XRD, SEM and EDS. The results show that the adhesion of SiO2 film to stainless steel matrix is good, which promotes the selective oxidation on the stainless steel surface and the formation of protective Cr2O3 and NiCr2O4 oxide layers. The high temperature oxidation resistance of stainless steel is improved remarkably. The oxidation resistance of the sample coated with three layers of SiO2 film proforms the best, and the oxidation weight gain and oxidation spalling of the sample are only 58.1% and 41.4% of the uncoated sample after 100 hours of cyclic oxidation at 900 ℃. The high temperature oxidation resistance of stainless steel is effectively improved through SiO2 film coating, which is another attempt of surface treatment method applied to high temperature environment, and provides reference for other thin films prepared by sol-gel method.

Abstract:In order to solve the problems of backward production technology, long processing cycle and low material utilization rate in traditional U-shaped steel tie rods, an integrated steel tie rod forming process was proposed. Taking the preform forming of 35 steel tie rod U-shaped head as the research object, a three-pass heating upsetting method was designed. The DEFORM-3D finite element software was used to analyze the simulation results of the temperature field and stress field after upsetting under different process conditions. The hot forming process parameters with better forming effect were discussed, and the feasibility of forming was verified through experiments. The results show that the optimum hot forming process parameters of each pass are as follows: the initial forging temperature of the first pass is 1 150 ℃, while the punch speed is 20 mm/s; the initial forging temperature of the second pass is 1 150 ℃, while the punch speed is 30 mm /s; the initial forging temperature of the third pass is 1 100 ℃, while the punch speed is 20 mm/s. Under the hot forming process parameters, the forming forces of each pass are 1 520, 2 090, 5 290 kN, and the expansion forces of each pass are 5 870, 6 710, 8 830 kN, respectively. After upsetting, the metal streamline distribution is reasonable, there is no crossover and folding phenomenon, and the forming effect is good. The equivalent stress distribution inside the part is relatively uniform while preparing the preform in the three-pass hot upsetting method, which can form a good quality part. It provides a certain reference for the upsetting aggregate process design and equipment selection of the U-shaped head perform of 35 steel tie rod.