查看更多>>摘要：Accurate positioning is one of the essential requirements for numerous applications of remote sensing data,especially in the event of a noisy or unreliable satellite signal.Toward this end,we present a novel framework for aircraft geo-localization in a large range that only requires a downward-facing monocular camera,an altimeter,a compass,and an open-source Vector Map(VMAP).The algorithm combines the matching and particle filter methods.Shape vector and correlation between two building contour vectors are defined,and a coarse-to-fine building vector matching(CFBVM)method is proposed in the matching stage,for which the original matching results are described by the Gaussian mixture model(GMM).Subsequently,an improved resampling strategy is designed to reduce computing expenses with a huge number of initial particles,and a credibility indicator is designed to avoid location mistakes in the particle filter stage.An experimental evaluation of the approach based on flight data is provided.On a flight at a height of 0.2 km over a flight distance of 2 km,the aircraft is geo-localized in a reference map of 11,025 km2 using 0.09 km2 aerial images without any prior information.The absolute localization error is less than 10 m.
查看更多>>摘要：The Marplex Convention was established to prevent the manufacture of unmarked plastic explosives and stipulates that a volatile detection agent must be added at the time of manufacture.However,to-date,laboratory testing remains the internationally accepted practice for identifying and quantifying the taggants stipulated in the Convention.In this project,portable FTIR and Raman instruments were tested for their ability to detect 2,3-dimethyl-2,3-dinitrobutane(DMDNB),the chemical marker incorporated in plastic explosives that are manufactured within Australia.While both FTIR and Raman instruments detected solid DMDNB(98％purity),field analysis of plastic explosives at an Australian Defence estab-lishment showed that both FTIR and Raman spectra were matched the relevant explosive(RDX or PETN),rather than the DMDNB taggant.For all three plastic explosives tested,the concentration of DMDNB was measured by SPME-GC-MS to be between 1.8 and 2％,greater than the minimum 1％concentration stipulated by the Marplex Convention.Additional testing with a plastic explosive analogue confirmed that the minor absorption peaks that would characterize low concentrations of DMDNB were masked by absorption bands from other compounds within the solid.Thus,while both FTIR and Raman spectros-copy are suitable for detection of plastic explosives,neither rely on the presence of DMDNB for detection.It is likely that similar results would be found for other taggants stipulated by the Marplex Convention,given they are also present in concentrations less than 1％.
查看更多>>摘要：This paper mainly focuses on the development of a learning-based controller for a class of uncertain mechanical systems modeled by the Euler-Lagrange formulation.The considered system can depict the behavior of a large class of engineering systems,such as vehicular systems,robot manipulators and satellites.All these systems are often characterized by highly nonlinear characteristics,heavy modeling uncertainties and unknown perturbations,therefore,accurate-model-based nonlinear control ap-proaches become unavailable.Motivated by the challenge,a reinforcement learning(RL)adaptive control methodology based on the actor-critic framework is investigated to compensate the uncertain me-chanical dynamics.The approximation inaccuracies caused by RL and the exogenous unknown distur-bances are circumvented via a continuous robust integral of the sign of the error(RISE)control approach.Different from a classical RISE control law,a tanh(·)function is utilized instead of a sign(·)function to acquire a more smooth control signal.The developed controller requires very little prior knowledge of the dynamic model,is robust to unknown dynamics and exogenous disturbances,and can achieve asymptotic output tracking.Eventually,co-simulations through ADAMS and MATLAB/Simulink on a three degrees-of-freedom(3-DOF)manipulator and experiments on a real-time electromechanical servo sys-tem are performed to verify the performance of the proposed approach.
查看更多>>摘要：Damage caused due to low-velocity impacts in composites leads to substantial deterioration in their residual strength and eventually provokes structural failure.This work presents an experimental investigation on the effects of different patch and parent laminate stacking sequences on the enhancement of impact strength of Carbon Fiber Reinforced Polymers(CFRP)composites by utilising the adhesively bonded external patch repair technique.Damage evolution study is also performed with the aid of Acoustic Emission(AE).Two different quasi-isotropic configurations were selected for the parent laminate,viz.,[45°/45°/0°/0°]s and[45°/0°/45°/0°]s.Quasi Static Indentation(QSI)test was performed on both the pristine laminates,and damage areas were detected by using the C-scan inspection technique.Damaged laminates were repaired by using a single-sided patch of two different configurations,viz.,[45°/45°/45°/45°]and[45°/0°/0°/45°],and employing a circular plug to fill the damaged hole.Four different combinations of repaired laminates with two configurations of each parent and patch laminate were produced,which were further subjected to the QSI test.The results reveal the effectiveness of the repair method,as all the repaired laminates show higher impact resistance compared to the respective pristine laminates.Patches of[45°/0°/0°/45°]configuration when repaired by taking[45°/45°/0°/0°]s and[45°/0°/45°/0°]s as parents exhibited 68％and 73％higher peak loads,respectively,than the respective pristine laminates.Furthermore,parent and patch of configuration[45°/0°/45°/0°]s and[45°/0°/0°/45°],respectively,attain the highest peak load,whereas[45°/45°/0°/0°]s and[45°/45°/45°/45°]combinations possess the most gradual decrease in the load.
查看更多>>摘要：The article introduces a finite element procedure using the bilinear quadrilateral element or four-node rectangular element(namely Q4 element)based on a refined first-order shear deformation theory(r-FSDT)and Monte Carlo simulation(MCS),so-called refined stochastic finite element method to inves-tigate the random vibration of functionally graded material(FGM)plates subjected to the moving load.The advantage of the proposed method is to use r-FSDT to improve the accuracy of classical FSDT,satisfy the stress-free condition at the plate boundaries,and combine with MCS to analyze the vibration of the FGM plate when the parameter inputs are random quantities following a normal distribution.The ob-tained results show that the distribution characteristics of the vibration response of the FGM plate depend on the standard deviation of the input parameters and the velocity of the moving load.Furthermore,the numerical results in this study are expected to contribute to improving the under-standing of FGM plates subjected to moving loads with uncertain input parameters.
查看更多>>摘要：Self-destructing chips have promising applications for securing data.This paper proposes a new concept of energetic diodes for the first time,which can be used for self-destructive chips.A simple two-step electrochemical deposition method is used to prepare ZnO/CuO/Al energetic diode,in which N-type ZnO and P-type CuO are constricted to a PN junction.This paper comprehensively discusses the material properties,morphology,semiconductor characteristics,and exploding performances of the energetic diode.Experimental results show that the energetic diode has typical rectification with a turn-on voltage of about 1.78 V and a reverse leakage current of about 3 × 10-4 A.When a constant voltage of 70 V loads to the energetic diode in the forward direction for about 0.14 s or 55 V loads in the reverse direction for about 0.17 s,the loaded power can excite the energetic diode exploding and the current rises to about 100 A.Due to the unique performance of the energetic diode,it has a double function of rectification and explosion.The energetic diode can be used as a logic element in the normal chip to complete the regular operation,and it can release energy to destroy the chip accurately.
查看更多>>摘要：Brain functional networks model the brain's ability to exchange information across different regions,aiding in the understanding of the cognitive process of human visual attention during target searching,thereby contributing to the advancement of camouflage evaluation.In this study,images with various camouflage effects were presented to observers to generate electroencephalography(EEG)signals,which were then used to construct a brain functional network.The topological parameters of the network were subsequently extracted and input into a machine learning model for training.The results indicate that most of the classifiers achieved accuracy rates exceeding 70％.Specifically,the Logistic algorithm ach-ieved an accuracy of 81.67％.Therefore,it is possible to predict target camouflage effectiveness with high accuracy without the need to calculate discovery probability.The proposed method fully considers the aspects of human visual and cognitive processes,overcomes the subjectivity of human interpretation,and achieves stable and reliable accuracy.
查看更多>>摘要：The high entropy alloys(HEAs)are the newly developed high-performance materials that have gained significant importance in defence,nuclear and aerospace sector due to their superior mechanical properties,heat resistance,high temperature strength and corrosion resistance.These alloys are man-ufactured by the equal mixing or larger proportions of five or more alloying elements.HEAs exhibit superior mechanical performance compared to traditional engineering alloys because of the extensive alloying composition and higher entropy of mixing.Solid state welding(SSW)techniques such as friction stir welding(FSW),rotary friction welding(RFW),diffusion bonding(DB)and explosive welding(EW)have been efficiently deployed for improving the microstructural integrity and mechanical properties of welded HEA joints.The HEA interlayers revealed greater potential in supressing the formation of dele-terious intermetallic phases and maximizing the mechanical properties of HEAs joints.The similar and dissimilar joining of HEAs has been manifested to be viable for HEA systems which further expands their industrial applications.Thus,the main objective of this review paper is to present a critical review of current state of research,challenges and opportunities and main directions in SSW of HEAs mainly CoCrFeNiMn and AlxCoCrFeNi alloys.The state of the art of problems,progress and future outlook in SSW of HEAs are critically reviewed by considering the formation of phases,microstructural evolution and mechanical properties of HEAs joints.
查看更多>>摘要：The poor thermal stability and high sensitivity severely hinder the practical application of hexani-trohexaazaisowurtzitane(CL-20).Herein,a kind of novel core@double-shell CL-20 based energetic composites were fabricated to address the above issues.The coordination complexes which consist of natural polyphenol tannic acid(TA)and FeⅢ were chosen to construct the inner shell,while the graphene sheets were used to build the outer shell.The resulting CL-20/TA-FeⅢ/graphene composites exhibited simultaneously improved thermal stability and safety performance with only 1 wt％double-shell content,which should be ascribed to the intense physical encapsulation effect from inner shell combined with the desensitization effect of carbon nano-materials from outer shell.The phase transition(e to y)temper-ature increased from 173.70 ℃ of pure CL-20 to 191.87 ℃ of CL-20/TA-FeⅢ/graphene composites.Meanwhile,the characteristic drop height(H50)dramatically increased from 14.7 cm of pure CL-20 to 112.8 cm of CL-20/TA-FeⅢ/graphene composites,indicating much superior safety performance after the construction of the double-shell structure.In general,this work has provided an effective and versatile strategy to conquer the thermal stability and safety issues of CL-20 and contributes to the future application of high energy density energetic materials.
查看更多>>摘要：It has been reported that the ply gap influences the ballistic resistance of spaced multi-ply fabric systems,but its working mechanism was not well-understood.This paper reports the experimental and numerical approaches and results of an investigation on the mechanisms that enable the improved ballistic per-formance of spaced multi-ply systems.Penetration tests were performed over a range of impact veloc-ities ranging from 200 m/s to 400 m/s.The results confirmed that the ply gap is beneficial to the energy absorption capability of the systems.This is because the front plies tend to absorb more energy when they are not immediately constrained by the rear plies.During a ballistic event,the gap relieves the reflection of the compressive pulse,prolonging the projectile engagement time with the front plies;on the other hand,the rear plies become increasingly less active in dissipating energy as the gap increases.When the gap is sufficiently widened to avoid any interference between the plies before the failure of the front ply,the responses of the whole system no longer vary.It was also found that the ballistic perfor-mance of the spaced systems is influenced by ply thickness,impact velocity,and the stacking order of the ply gap.
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