Code obfuscation is a crucial technique for protecting software against reverse engineering and security attacks.Among various obfuscation methods,opaque predicates,which are recognized as flexible and promising,are w...Code obfuscation is a crucial technique for protecting software against reverse engineering and security attacks.Among various obfuscation methods,opaque predicates,which are recognized as flexible and promising,are widely used to increase control-flow complexity.However,traditional opaque predicates are increasingly vulnerable to Dynamic Symbolic Execution(DSE)attacks,which can efficiently identify and eliminate them.To address this issue,this paper proposes a novel approach for anti-DSE opaque predicates that effectively resists symbolic execution-based deobfuscation.Our method introduces two key techniques:single-way function opaque predicates,which leverage hash functions and logarithmic transformations to prevent constraint solvers from generating feasible inputs,and path-explosion opaque predicates,which generate an excessive number of execution paths,overwhelming symbolic execution engines.To evaluate the effectiveness of our approach,we implemented a prototype obfuscation tool and tested it against prominent symbolic execution engines.Experimental results demonstrate that our approach signifi-cantly increases resilience against symbolic execution attacks while maintaining acceptable performance overhead.This paper provides a robust and scalable obfuscation technique,contributing to the enhancement of software protection strategies in adversarial environments.展开更多
The aim of this paper is to simulate and study the early moments of the reactive ballistics of a large caliber projectile fired from a gun,combining 0D and 2D axisymmetric Computational Fluid Dynamics(CFD)approaches.F...The aim of this paper is to simulate and study the early moments of the reactive ballistics of a large caliber projectile fired from a gun,combining 0D and 2D axisymmetric Computational Fluid Dynamics(CFD)approaches.First,the methodology is introduced with the development of an interior ballistics(IB)lumped parameter code(LPC),integrating an original image processing method for calculating the specific regression of propellant grains that compose the gun propellant.The ONERA CFD code CEDRE,equipped with a Dynamic Mesh Technique(DMT),is then used in conjunction with the developed LPC to build a dedicated methodology to calculate IB.First results obtained on the AGARD gun and 40 mm gun test cases are in a good agreement with the existing literature.CEDRE is also used to calculate inter-mediate ballistics(first milliseconds of free flight of the projectile)with a multispecies and reactive approach either starting from the gun muzzle plane or directly following IB.In the latter case,an inverse problem involving a Latin hypercube sampling method is used to find a gun propellant configuration that allows the projectile to reach a given exit velocity and base pressure when IB ends.The methodology developed in this work makes it possible to study the flame front of the intermediate flash and depressurization that occurs in a base bleed(BB)channel at the gun muzzle.Average pressure variations in the BB channel during depressurization are in good agreement with literature.展开更多
Antifungal resistance is the leading cause of antifungal treatment failure in invasive candidiasis.Metabolic rewiring could become a new insight to account for antifungal resistance as to find innovative clinical ther...Antifungal resistance is the leading cause of antifungal treatment failure in invasive candidiasis.Metabolic rewiring could become a new insight to account for antifungal resistance as to find innovative clinical therapies.Here,we show that dynamic surface-enhanced Raman spectroscopy is a promising tool to identify the metabolic differences between fluconazole(Diflucan)-resistant and fluconazole(Diflucan)-sensitive Candida albicans through the signatures of biochemical components and complemented with machine learning algorithms and two-dimensional correlation spectroscopy,an underlying resistance mechanism,that is,the change of purine metabolites induced the resistance of Candida albicans has been clarified yet never reported anywhere.We hope the integrated methodology introduced in this work could be beneficial for the interpretation of cellular regulation,propelling the development of targeted antifungal therapies and diagnostic tools for more efficient management of severe antifungal resistance.展开更多
Based on the dynamical theory of multi-body systems with nonholonomic constraints and an algorithm for complementarity problems, a numerical method for the multi-body systems with two-dimensional Coulomb dry friction ...Based on the dynamical theory of multi-body systems with nonholonomic constraints and an algorithm for complementarity problems, a numerical method for the multi-body systems with two-dimensional Coulomb dry friction and nonholonomic constraints is presented. In particular, a wheeled multi-body system is considered. Here, the state transition of stick-slip between wheel and ground is transformed into a nonlinear complementarity problem （NCP）. An iterative algorithm for solving the NCP is then presented using an event-driven method. Dynamical equations of the multi-body system with holonomic and nonholonomic constraints are given using Routh equations and a con- straint stabilization method. Finally, an example is used to test the proposed numerical method. The results show some dynamical behaviors of the wheeled multi-body system and its constraint stabilization effects.展开更多
Although the research history of triboelectrification has been more than 2000 years, there are still many problems to be solved so far.The use of scanning probe microscopy provides an important way to quantitatively s...Although the research history of triboelectrification has been more than 2000 years, there are still many problems to be solved so far.The use of scanning probe microscopy provides an important way to quantitatively study the transfer, accumulation, and dissipation of triboelectric charges in the process of triboelectrification. Two-dimensional materials are considered to be key materials for new electronic devices in the post-Moore era due to their atomic-scale size advantages. If the electrostatic field generated by triboelectrification can be used to replace the traditional gate electrostatic field, it is expected to simplify the structure of two-dimensional electronic devices and reconfigure them at any time according to actual needs. Here, we investigate the triboelectrification process of various two-dimensional materials such as MoS_(2), WSe_(2),and ZnO. Different from traditional bulk materials, after two-dimensional materials are rubbed, the triboelectric charges generated may tunnel through the two-dimensional materials to the underlying substrate surface. Because the tunneling triboelectric charge is protected by the twodimensional material, its stable residence time on the substrate surface can reach more than 7 days, which is more than tens of minutes for the traditional triboelectric charge. In addition, the electrostatic field generated by the tunneling triboelectric charge can effectively regulate the carrier transport performance of two-dimensional materials, and the source–drain current of the field effect device regulated by the triboelectric floating gate is increased by nearly 60 times. The triboelectric charge tunneling phenomenon in two-dimensional materials is expected to be applied in the fields of new two-dimensional electronic devices and reconfigurable functional circuits.展开更多
The mass flow rate of a granular flow through an aperture under gravity is a long-standing challenge issue in physical science. We show that for steady flow field close to laminar flow, the dynamical equations togethe...The mass flow rate of a granular flow through an aperture under gravity is a long-standing challenge issue in physical science. We show that for steady flow field close to laminar flow, the dynamical equations together with the continue equation and Mohr-circle description of the stress are closed, and hence solvable. In a case of streamline guided by the two-dimensional hopper, we obtain a consistent condition and use it to determine the stress and the velocity distribution. Our result indicates that 3/2 power scaling behavior is recovered with a coefficient C(μ,α) being a function of frictional coefficient and the hopper angle. It is found that the predicted coefficient C(μ,α) is compatible with previous studies.展开更多
Increasing the recrystallization temperature to achieve better high-temperature performance is critical in the development of molybdenum alloys for ultrahightemperature applications,such as the newest generation of mu...Increasing the recrystallization temperature to achieve better high-temperature performance is critical in the development of molybdenum alloys for ultrahightemperature applications,such as the newest generation of multitype high-temperature nuclear reactors.In this study,an innovative strategy was proposed to improve the performance of molybdenum alloys at high temperature by using the two-dimensional MAX(where M is an early transition metal,A is an A-group element and X is C or N)ceramic material Ti_(3)AlC_(2).The relationships between flow stress,strain rate and temperature were studied.The microstructure,distribution of misorientation and evolution of dislocations in the Mo-Ti_(3)AlC_(2) alloy were analyzed.The microscopic mechanism of the Ti_(3)AlC_(2) phase in the molybdenum alloy at high temperatures was clarified.The experimental results showed that the peak flow stress of Mo-Ti_(3)AlC_(2) at 1600℃ reached 155 MPa,which was161.8% greater than that of pure Mo.The activation energy of thermal deformation of Mo-Ti_(3)AlC_(2) was as large as537 kJ·mol~(-1),which was 17.6% more than that of pure Mo.The recrystallization temperature reached 1600℃ or even higher.The topological reaction of the Ti_(3)AlC_(2) phase consumed a large amount of energy at high temperatures,resulting in increases in the deformation activation energy.Nanolayer structures of AlTi_3 and Ti-O Magneli-phase oxides(Ti_nO_(2n-1)) were formed in-situ,which relied on kink bands and interlayer slip,resulting in many dislocations during deformation.Therefore,the special two-dimensional of the structure Ti_(3)AlC_(2) ceramic inhibited the recrystallization behavior of the Mo alloy.The results of this study can provide theoretical guidance for the development of a new generation of molybdenum alloys for use in ultrahigh-temperature environments.展开更多
Two Relative-Residual-based Dynamic Schedules(RRDS) for Belief Propagation(BP) decoding of Low-Density Parity-Check(LDPC) codes are proposed,in which the Variable code-RRDS(VN-RRDS) is a greediness-reduced version of ...Two Relative-Residual-based Dynamic Schedules(RRDS) for Belief Propagation(BP) decoding of Low-Density Parity-Check(LDPC) codes are proposed,in which the Variable code-RRDS(VN-RRDS) is a greediness-reduced version of the Check code-RRDS(CN-RRDS).The RRDS only processes the variable(or check) node,which has the maximum relative residual among all the variable(or check) nodes in each decoding iteration,thus keeping less greediness and decreased complexity in comparison with the edge-based Variable-to-Check Residual Belief Propagation(VC-RBP) algorithm.Moreover,VN-RRDS propagates first the message which has the largest residual based on all check equations.For different types of LDPC codes,simulation results show that the convergence rate of RRDS is higher than that of VC-RBP while keeping very low computational complexity.Furthermore,VN-RRDS achieves faster convergence as well as better performance than CN-RRDS.展开更多
In this paper, we study stealthy cyber-attacks on actuators of cyber-physical systems(CPS), namely zero dynamics and controllable attacks. In particular, under certain assumptions, we investigate and propose condition...In this paper, we study stealthy cyber-attacks on actuators of cyber-physical systems(CPS), namely zero dynamics and controllable attacks. In particular, under certain assumptions, we investigate and propose conditions under which one can execute zero dynamics and controllable attacks in the CPS. The above conditions are derived based on the Markov parameters of the CPS and elements of the system observability matrix. Consequently, in addition to outlining the number of required actuators to be attacked, these conditions provide one with the minimum system knowledge needed to perform zero dynamics and controllable cyber-attacks. As a countermeasure against the above stealthy cyber-attacks, we develop a dynamic coding scheme that increases the minimum number of the CPS required actuators to carry out zero dynamics and controllable cyber-attacks to its maximum possible value. It is shown that if at least one secure input channel exists, the proposed dynamic coding scheme can prevent adversaries from executing the zero dynamics and controllable attacks even if they have complete knowledge of the coding system. Finally, two illustrative numerical case studies are provided to demonstrate the effectiveness and capabilities of our derived conditions and proposed methodologies.展开更多
Dynamic spectrum access(DSA) in cognitive radio(CR) networks became a challenging research area recently. In CR technology, the DSA between primary users(PUs) and secondary users(SUs) simultaneously can be achieved wi...Dynamic spectrum access(DSA) in cognitive radio(CR) networks became a challenging research area recently. In CR technology, the DSA between primary users(PUs) and secondary users(SUs) simultaneously can be achieved without degrading the performance of the PUs by SUs interference. This can be achieved by donating incentive power to the PUs in order to compensate the interference caused by the SUs. Consequently, PUs allow SUs to share the spectrum. In this paper, orthogonal codes-based dynamic spectrum access(OC-DSA) technique is proposed. OC-DSA technique employs orthogonality between PUs and SUs transmitted data symbols in addition to the incentive power donation. Compared to other techniques, the proposed technique uses a simple encoder at the SU network for the same PU network infrastructure. By applying orthogonal codes, the interference caused by SUs is canceled and hence the donated power to incentivize the PUs is reduced. Also, the SU packet rate is increased significantly. The simulation results show that the proposed technique provides effective improvements over other existing techniques in the signal strength and the bit error rate performance of both the PU network and the SU network at the receiver side. Moreover, the proposed technique requires less donated power to incentivize the PU and has higher packet rate.展开更多
The code benchmarking for hadron linac using the 3D Particle-In-Cell (PIC) code is an important task in the European framework “High Intensity Pulsed Proton Injector” (HIPPI). PARMILA and HALODYN are two of the code...The code benchmarking for hadron linac using the 3D Particle-In-Cell (PIC) code is an important task in the European framework “High Intensity Pulsed Proton Injector” (HIPPI). PARMILA and HALODYN are two of the codes involved in this work. Both of these codes have been developed and used for linac design and beam dynamics studies. In this paper, the simulation results of the beam dynamics were compared and analyzed. As predicted by two codes, the simulation results show some agreements. The physical design strategy which was adopted in two codes was also discussed.展开更多
In order to investigate the micro-process and inner mechanism of rock failure under impact loading, the laboratory tests were carried out on an improved split Hopkinson pressure bar （SHPB） system with synchronized m...In order to investigate the micro-process and inner mechanism of rock failure under impact loading, the laboratory tests were carried out on an improved split Hopkinson pressure bar （SHPB） system with synchronized measurement devices including a high-speed camera and a dynamic strain meter. The experimental results show that the specimens were in the state of good stress equilibrium during the post failure stage even when visible cracks were forming in the specimens. Rock specimens broke into strips but still could bear the external stress and keep force balance. Meanwhile, numerical tests with particle flow code （PFC） revealed that the failure process of rocks can be described by the evolution of micro-fractures. Shear cracks emerged firstly and stopped developing when the external stress was not high enough. Tensile cracks, however, emerged when the rock specimen reached its peak strength and played an important role in controlling the ultimate failure during the post failure stage.展开更多
Two-dimensional（2D） materials have been regarded as a promising nonlinear optical medium for fabricating versatile optical and optoelectronic devices. Among the various photonic applications, the employment of 2D ma...Two-dimensional（2D） materials have been regarded as a promising nonlinear optical medium for fabricating versatile optical and optoelectronic devices. Among the various photonic applications, the employment of 2D materials as nonlinear optical devices such as saturable absorbers for ultrashort pulse generation and shaping in ultrafast lasers is one of the most striking aspects in recent years. In this paper, we review the recent progress of 2D materials based pulse generation and soliton shaping in ultrafast fiber lasers, and particularly in the context of 2D materials-decorated microfiber photonic devices. The fabrication of 2D materials-decorated microfiber photonic devices, high performance mode-locked pulse generation, and the nonlinear soliton dynamics based on pulse shaping method are discussed. Finally, the challenges and the perspective of the 2D materials-based photonic devices as well as their applications are also discussed.展开更多
For the dynamic demand assessment of bridge structures under ship impact loading,it may be prudent to adopt analytical models which permit rapid analysis with reasonable accuracy.Herein,a nonlinear dynamic macro-eleme...For the dynamic demand assessment of bridge structures under ship impact loading,it may be prudent to adopt analytical models which permit rapid analysis with reasonable accuracy.Herein,a nonlinear dynamic macro-element is proposed and implemented to quantify the demand of bridge substructures subjected to ship collisions.In the proposed nonlinear macro-element,a combination of an elastic-plastic spring and a dashpot in parallel is employed to describe the mechanical behavior of ship-bows with strain rate effects.Based on the analytical model using the proposed macro-element,a typical substructure under 5000 deadweight tonnage(DWT) ship collision is discussed.Our analyses indicate that the responses of the structure using the nonlinear macro-element agree with the results from the high resolution model,but the efficiency and feasibility of the proposed method increase significantly in practical applications.Furthermore,comparisons between some current design codes(AASHTO,JTGD60-2004,and TB10002.1-2005) and the developed dynamic analysis method suggest that these design codes may be improved,at least to consider the effect of dynamic amplification on structural demand.展开更多
Incompressible viscous flows on curved surfaces are considered with respect to the interplay of surface geometry, curvature, and vorticity dynamics. Free flows and cylindrical wakes over a Gaussian bump are numericall...Incompressible viscous flows on curved surfaces are considered with respect to the interplay of surface geometry, curvature, and vorticity dynamics. Free flows and cylindrical wakes over a Gaussian bump are numerically solved using a surface vorticity- stream function formulation. Numerical simulations show that the Gaussian curvature can generate vorticity, and non-uniformity of the Gaussian curvature is the main cause. In the cylindrical wake, the bump dominated by the positive Gaussian curvature can significantly affect the vortex street by forming velocity depression and changing vorticity transport. The results may provide possibilities for manipulating surface flows through local change in the surface geometry.展开更多
Let Ф（u ×v, k, Aa, Ac） be the largest possible number of codewords among all two- dimensional （u ×v, k, λa, λc） optical orthogonal codes. A 2-D （u× v, k, λa, λ）-OOC with Ф（u× v, k, λ...Let Ф（u ×v, k, Aa, Ac） be the largest possible number of codewords among all two- dimensional （u ×v, k, λa, λc） optical orthogonal codes. A 2-D （u× v, k, λa, λ）-OOC with Ф（u× v, k, λa, λc） codewords is said to be maximum. In this paper, the number of codewords of a maximum 2-D （u × v, 4, 1, 3）-OOC has been determined.展开更多
This paper deals with dynamic airspace sectorization （DAS） problem by an improved genetic algorithm （iGA）. A graph model is first constructed that represents the airspace static structure. Then the DAS problem is ...This paper deals with dynamic airspace sectorization （DAS） problem by an improved genetic algorithm （iGA）. A graph model is first constructed that represents the airspace static structure. Then the DAS problem is formulated as a graph-partitioning problem to balance the sector workload under the premise of ensuring safety. In the iGA, multiple populations and hybrid coding are applied to determine the optimal sector number and airspace sectorization. The sector constraints are well satisfied by the improved genetic operators and protect zones. This method is validated by being applied to the airspace of North China in terms of three indexes, which are sector balancing index, coordination workload index and sector average flight time index. The improvement is obvious, as the sector balancing index is reduced by 16.5 %, the coordination workload index is reduced by 11.2 %, and the sector average flight time index is increased by 11.4 % during the peak-hour traffic.展开更多
To analyze the impact effect induced by vehicle-bridge coupling vibration during traffic congesting, hundreds and thousands of congestion scenarios consisting of various vehicle platoons were collected and used to dev...To analyze the impact effect induced by vehicle-bridge coupling vibration during traffic congesting, hundreds and thousands of congestion scenarios consisting of various vehicle platoons were collected and used to develop vehicle models as well as traffic congestion load models. Furthermore, the idling vehicle-bridge coupling model was established by the finite element method and the congestion models were applied to calculate dynamic impact factors. Compared with the value specified in Chinese codes, the calculated values were 1.15-2.67 times as large as the latter, which indicates the impact factors caused by idling vehicle-bridge coupling under congestion situations were much larger than those in normal traffic conditions. As a result, a calibration factor of 1.7 was recommended for bridge design or evaluation when considering vehicle-bridge coupling vibration under heavy traffic congestion. The proposed analytical model, analysis method, and results could also be beneficial references to further investigation in this field.展开更多
Quickly getting back the synchronism of a disturbed interconnected multi-area power system due to variations in loading condition is recognized as prominent issue related to automatic generation control(AGC).In this r...Quickly getting back the synchronism of a disturbed interconnected multi-area power system due to variations in loading condition is recognized as prominent issue related to automatic generation control(AGC).In this regard,AGC system based on fuzzy logic,i.e.,so-called FLAGC can introduce an effectual performance to suppress the dynamic oscillations of tie-line power exchanges and frequency in multi-area interconnected power system.Apart from that,simultaneous coordination scheme based on particle swarm optimization(PSO)along with real coded genetic algorithm(RCGA)is suggested to coordinate FLAGCs of the all areas.To clarify the high efficiency of aforementioned strategy,two different interconnected multi-area power systems,i.e.,three-area hydro-thermal power system and five-area thermal power system have been taken into account for relevant studies.The potency of this strategy has been thoroughly dealt with by considering the step load perturbation(SLP)in both the under study power systems.To sum up,the simulation results have plainly revealed dynamic performance of FLAGC as compared with conventional AGC(CAGC)in each power system in order to damp out the power system oscillations.展开更多
In this paper, we discuss a class of piecewise linear hyperbolic maps on the 2-torus. These maps arise in the second-order digital fdter with two＇ s complement arithmetic. By introducing codings underlying the map op...In this paper, we discuss a class of piecewise linear hyperbolic maps on the 2-torus. These maps arise in the second-order digital fdter with two＇ s complement arithmetic. By introducing codings underlying the map operations, we give some admissibility conditions for symbolic sequences and find some periodic properties of these symbolic sequences. Then we use these conditions to check the admissibility of periodic symbol sequences.展开更多
基金supported byOpen Foundation of Key Laboratory of Cyberspace Security,Ministry of Education of China(No.KLCS20240211)Henan Science and Technology Major Project No.241110210100.
文摘Code obfuscation is a crucial technique for protecting software against reverse engineering and security attacks.Among various obfuscation methods,opaque predicates,which are recognized as flexible and promising,are widely used to increase control-flow complexity.However,traditional opaque predicates are increasingly vulnerable to Dynamic Symbolic Execution(DSE)attacks,which can efficiently identify and eliminate them.To address this issue,this paper proposes a novel approach for anti-DSE opaque predicates that effectively resists symbolic execution-based deobfuscation.Our method introduces two key techniques:single-way function opaque predicates,which leverage hash functions and logarithmic transformations to prevent constraint solvers from generating feasible inputs,and path-explosion opaque predicates,which generate an excessive number of execution paths,overwhelming symbolic execution engines.To evaluate the effectiveness of our approach,we implemented a prototype obfuscation tool and tested it against prominent symbolic execution engines.Experimental results demonstrate that our approach signifi-cantly increases resilience against symbolic execution attacks while maintaining acceptable performance overhead.This paper provides a robust and scalable obfuscation technique,contributing to the enhancement of software protection strategies in adversarial environments.
基金the French Defense Innovation Agency (AID)the French Procurement Agency for Armament (DGA)ONERA's scientific direction for funding and supporting the present work
文摘The aim of this paper is to simulate and study the early moments of the reactive ballistics of a large caliber projectile fired from a gun,combining 0D and 2D axisymmetric Computational Fluid Dynamics(CFD)approaches.First,the methodology is introduced with the development of an interior ballistics(IB)lumped parameter code(LPC),integrating an original image processing method for calculating the specific regression of propellant grains that compose the gun propellant.The ONERA CFD code CEDRE,equipped with a Dynamic Mesh Technique(DMT),is then used in conjunction with the developed LPC to build a dedicated methodology to calculate IB.First results obtained on the AGARD gun and 40 mm gun test cases are in a good agreement with the existing literature.CEDRE is also used to calculate inter-mediate ballistics(first milliseconds of free flight of the projectile)with a multispecies and reactive approach either starting from the gun muzzle plane or directly following IB.In the latter case,an inverse problem involving a Latin hypercube sampling method is used to find a gun propellant configuration that allows the projectile to reach a given exit velocity and base pressure when IB ends.The methodology developed in this work makes it possible to study the flame front of the intermediate flash and depressurization that occurs in a base bleed(BB)channel at the gun muzzle.Average pressure variations in the BB channel during depressurization are in good agreement with literature.
基金supported by grants from the National Natural Science Foundation of China(Nos.22074015 and 82074428)Youth Talent Cultivation Initiation Fund of Zhongda Hospital,Southeast University(No.CZXM-GSP-RC110)to Hao Li+1 种基金Evidence-Based Capacity Building for TCM Specialty Therapies for Skin Diseases of National Administration of TCMInnovative Team Projects of Shanghai Municipal Commission of Health(No.2022CX011)to Fulun Li.
文摘Antifungal resistance is the leading cause of antifungal treatment failure in invasive candidiasis.Metabolic rewiring could become a new insight to account for antifungal resistance as to find innovative clinical therapies.Here,we show that dynamic surface-enhanced Raman spectroscopy is a promising tool to identify the metabolic differences between fluconazole(Diflucan)-resistant and fluconazole(Diflucan)-sensitive Candida albicans through the signatures of biochemical components and complemented with machine learning algorithms and two-dimensional correlation spectroscopy,an underlying resistance mechanism,that is,the change of purine metabolites induced the resistance of Candida albicans has been clarified yet never reported anywhere.We hope the integrated methodology introduced in this work could be beneficial for the interpretation of cellular regulation,propelling the development of targeted antifungal therapies and diagnostic tools for more efficient management of severe antifungal resistance.
基金Project supported by the National Natural Science Foundation of China(Nos.11372018 and 11572018)
文摘Based on the dynamical theory of multi-body systems with nonholonomic constraints and an algorithm for complementarity problems, a numerical method for the multi-body systems with two-dimensional Coulomb dry friction and nonholonomic constraints is presented. In particular, a wheeled multi-body system is considered. Here, the state transition of stick-slip between wheel and ground is transformed into a nonlinear complementarity problem （NCP）. An iterative algorithm for solving the NCP is then presented using an event-driven method. Dynamical equations of the multi-body system with holonomic and nonholonomic constraints are given using Routh equations and a con- straint stabilization method. Finally, an example is used to test the proposed numerical method. The results show some dynamical behaviors of the wheeled multi-body system and its constraint stabilization effects.
基金supported by the National Key Research and Development Program of China (No.2018YFA0703500)the National Natural Science Foundation of China(Nos.52232006,52188101,52102153,52072029,51991340,and 51991342)+2 种基金the Overseas Expertise Introduction Projects for Discipline Innovation (No.B14003)the China Postdoctoral Science Foundation (No.2021M700379)the Fundamental Research Funds for Central Universities(No.FRF-TP-18-001C1)。
文摘Although the research history of triboelectrification has been more than 2000 years, there are still many problems to be solved so far.The use of scanning probe microscopy provides an important way to quantitatively study the transfer, accumulation, and dissipation of triboelectric charges in the process of triboelectrification. Two-dimensional materials are considered to be key materials for new electronic devices in the post-Moore era due to their atomic-scale size advantages. If the electrostatic field generated by triboelectrification can be used to replace the traditional gate electrostatic field, it is expected to simplify the structure of two-dimensional electronic devices and reconfigure them at any time according to actual needs. Here, we investigate the triboelectrification process of various two-dimensional materials such as MoS_(2), WSe_(2),and ZnO. Different from traditional bulk materials, after two-dimensional materials are rubbed, the triboelectric charges generated may tunnel through the two-dimensional materials to the underlying substrate surface. Because the tunneling triboelectric charge is protected by the twodimensional material, its stable residence time on the substrate surface can reach more than 7 days, which is more than tens of minutes for the traditional triboelectric charge. In addition, the electrostatic field generated by the tunneling triboelectric charge can effectively regulate the carrier transport performance of two-dimensional materials, and the source–drain current of the field effect device regulated by the triboelectric floating gate is increased by nearly 60 times. The triboelectric charge tunneling phenomenon in two-dimensional materials is expected to be applied in the fields of new two-dimensional electronic devices and reconfigurable functional circuits.
基金Supported by the Key Research Program of Frontier Science of the Chinese Academy of Sciences under Grant No QYZDYSSW-SYS006
文摘The mass flow rate of a granular flow through an aperture under gravity is a long-standing challenge issue in physical science. We show that for steady flow field close to laminar flow, the dynamical equations together with the continue equation and Mohr-circle description of the stress are closed, and hence solvable. In a case of streamline guided by the two-dimensional hopper, we obtain a consistent condition and use it to determine the stress and the velocity distribution. Our result indicates that 3/2 power scaling behavior is recovered with a coefficient C(μ,α) being a function of frictional coefficient and the hopper angle. It is found that the predicted coefficient C(μ,α) is compatible with previous studies.
基金sponsored by National Key R&D Program of China (No.2020YFB2008400)Key Technology and Development Program of Henan Province (No.232102231024)。
文摘Increasing the recrystallization temperature to achieve better high-temperature performance is critical in the development of molybdenum alloys for ultrahightemperature applications,such as the newest generation of multitype high-temperature nuclear reactors.In this study,an innovative strategy was proposed to improve the performance of molybdenum alloys at high temperature by using the two-dimensional MAX(where M is an early transition metal,A is an A-group element and X is C or N)ceramic material Ti_(3)AlC_(2).The relationships between flow stress,strain rate and temperature were studied.The microstructure,distribution of misorientation and evolution of dislocations in the Mo-Ti_(3)AlC_(2) alloy were analyzed.The microscopic mechanism of the Ti_(3)AlC_(2) phase in the molybdenum alloy at high temperatures was clarified.The experimental results showed that the peak flow stress of Mo-Ti_(3)AlC_(2) at 1600℃ reached 155 MPa,which was161.8% greater than that of pure Mo.The activation energy of thermal deformation of Mo-Ti_(3)AlC_(2) was as large as537 kJ·mol~(-1),which was 17.6% more than that of pure Mo.The recrystallization temperature reached 1600℃ or even higher.The topological reaction of the Ti_(3)AlC_(2) phase consumed a large amount of energy at high temperatures,resulting in increases in the deformation activation energy.Nanolayer structures of AlTi_3 and Ti-O Magneli-phase oxides(Ti_nO_(2n-1)) were formed in-situ,which relied on kink bands and interlayer slip,resulting in many dislocations during deformation.Therefore,the special two-dimensional of the structure Ti_(3)AlC_(2) ceramic inhibited the recrystallization behavior of the Mo alloy.The results of this study can provide theoretical guidance for the development of a new generation of molybdenum alloys for use in ultrahigh-temperature environments.
基金supported by the Fundamental Research Funds for the Central Universities
文摘Two Relative-Residual-based Dynamic Schedules(RRDS) for Belief Propagation(BP) decoding of Low-Density Parity-Check(LDPC) codes are proposed,in which the Variable code-RRDS(VN-RRDS) is a greediness-reduced version of the Check code-RRDS(CN-RRDS).The RRDS only processes the variable(or check) node,which has the maximum relative residual among all the variable(or check) nodes in each decoding iteration,thus keeping less greediness and decreased complexity in comparison with the edge-based Variable-to-Check Residual Belief Propagation(VC-RBP) algorithm.Moreover,VN-RRDS propagates first the message which has the largest residual based on all check equations.For different types of LDPC codes,simulation results show that the convergence rate of RRDS is higher than that of VC-RBP while keeping very low computational complexity.Furthermore,VN-RRDS achieves faster convergence as well as better performance than CN-RRDS.
基金the financial support received from NATO under the Emerging Security Challenges Division programthe support received from NPRP (10-0105-17017) from the Qatar National Research Fund (a member of Qatar Foundation)+1 种基金the support received from the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Department of National Defence (DND) under the Discovery Grant and DND Supplemental Programssupported in part by funding from the Innovation for Defence Excellence and Security (IDEaS) program from the Department of National Defence (DND)。
文摘In this paper, we study stealthy cyber-attacks on actuators of cyber-physical systems(CPS), namely zero dynamics and controllable attacks. In particular, under certain assumptions, we investigate and propose conditions under which one can execute zero dynamics and controllable attacks in the CPS. The above conditions are derived based on the Markov parameters of the CPS and elements of the system observability matrix. Consequently, in addition to outlining the number of required actuators to be attacked, these conditions provide one with the minimum system knowledge needed to perform zero dynamics and controllable cyber-attacks. As a countermeasure against the above stealthy cyber-attacks, we develop a dynamic coding scheme that increases the minimum number of the CPS required actuators to carry out zero dynamics and controllable cyber-attacks to its maximum possible value. It is shown that if at least one secure input channel exists, the proposed dynamic coding scheme can prevent adversaries from executing the zero dynamics and controllable attacks even if they have complete knowledge of the coding system. Finally, two illustrative numerical case studies are provided to demonstrate the effectiveness and capabilities of our derived conditions and proposed methodologies.
文摘Dynamic spectrum access(DSA) in cognitive radio(CR) networks became a challenging research area recently. In CR technology, the DSA between primary users(PUs) and secondary users(SUs) simultaneously can be achieved without degrading the performance of the PUs by SUs interference. This can be achieved by donating incentive power to the PUs in order to compensate the interference caused by the SUs. Consequently, PUs allow SUs to share the spectrum. In this paper, orthogonal codes-based dynamic spectrum access(OC-DSA) technique is proposed. OC-DSA technique employs orthogonality between PUs and SUs transmitted data symbols in addition to the incentive power donation. Compared to other techniques, the proposed technique uses a simple encoder at the SU network for the same PU network infrastructure. By applying orthogonal codes, the interference caused by SUs is canceled and hence the donated power to incentivize the PUs is reduced. Also, the SU packet rate is increased significantly. The simulation results show that the proposed technique provides effective improvements over other existing techniques in the signal strength and the bit error rate performance of both the PU network and the SU network at the receiver side. Moreover, the proposed technique requires less donated power to incentivize the PU and has higher packet rate.
文摘The code benchmarking for hadron linac using the 3D Particle-In-Cell (PIC) code is an important task in the European framework “High Intensity Pulsed Proton Injector” (HIPPI). PARMILA and HALODYN are two of the codes involved in this work. Both of these codes have been developed and used for linac design and beam dynamics studies. In this paper, the simulation results of the beam dynamics were compared and analyzed. As predicted by two codes, the simulation results show some agreements. The physical design strategy which was adopted in two codes was also discussed.
基金Project(2015CB060200)supported by the National Basic Research and Development Program of ChinaProjects(51322403,51274254)supported by the National Natural Science Foundation of China
文摘In order to investigate the micro-process and inner mechanism of rock failure under impact loading, the laboratory tests were carried out on an improved split Hopkinson pressure bar （SHPB） system with synchronized measurement devices including a high-speed camera and a dynamic strain meter. The experimental results show that the specimens were in the state of good stress equilibrium during the post failure stage even when visible cracks were forming in the specimens. Rock specimens broke into strips but still could bear the external stress and keep force balance. Meanwhile, numerical tests with particle flow code （PFC） revealed that the failure process of rocks can be described by the evolution of micro-fractures. Shear cracks emerged firstly and stopped developing when the external stress was not high enough. Tensile cracks, however, emerged when the rock specimen reached its peak strength and played an important role in controlling the ultimate failure during the post failure stage.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61307058,61378036,11304101,and 11474108)Guangdong Natural Science Funds for Distinguished Young Scholar,China(Grant No.2014A030306019)+6 种基金Pearl River S&T Nova Program of Guangzhou,China(Grant No.2014J2200008)Program for Outstanding Innovative Young Talents of Guangdong Province,China(Grant No.2014TQ01X220)Program for Outstanding Young Teachers in Guangdong Higher Education Institutes,China(Grant No.YQ2015051)Science and Technology Project of Guangdong,China(Grant No.2016B090925004)Foundation for Young Talents in Higher Education of Guangdong,China(Grant No.2017KQNCX051)Science and Technology Program of Guangzhou,China(Grant No.201607010245)Scientific Research Foundation of Young Teacher of South China Normal University,China(Grant No.17KJ09)
文摘Two-dimensional（2D） materials have been regarded as a promising nonlinear optical medium for fabricating versatile optical and optoelectronic devices. Among the various photonic applications, the employment of 2D materials as nonlinear optical devices such as saturable absorbers for ultrashort pulse generation and shaping in ultrafast lasers is one of the most striking aspects in recent years. In this paper, we review the recent progress of 2D materials based pulse generation and soliton shaping in ultrafast fiber lasers, and particularly in the context of 2D materials-decorated microfiber photonic devices. The fabrication of 2D materials-decorated microfiber photonic devices, high performance mode-locked pulse generation, and the nonlinear soliton dynamics based on pulse shaping method are discussed. Finally, the challenges and the perspective of the 2D materials-based photonic devices as well as their applications are also discussed.
基金supported by the Ministry of Science and Technology of China (No. SLDRCE 09-B-08)the National Natural Science Foundation of China (Nos. 50978194 and 90915011)+1 种基金the Kwang-Hua Fund for College of Civil Engineering,Tongji Universitythe Fund of National Engineering and Research Center for Highways in Mountain Area (No. gsgzj-2010-01),China
文摘For the dynamic demand assessment of bridge structures under ship impact loading,it may be prudent to adopt analytical models which permit rapid analysis with reasonable accuracy.Herein,a nonlinear dynamic macro-element is proposed and implemented to quantify the demand of bridge substructures subjected to ship collisions.In the proposed nonlinear macro-element,a combination of an elastic-plastic spring and a dashpot in parallel is employed to describe the mechanical behavior of ship-bows with strain rate effects.Based on the analytical model using the proposed macro-element,a typical substructure under 5000 deadweight tonnage(DWT) ship collision is discussed.Our analyses indicate that the responses of the structure using the nonlinear macro-element agree with the results from the high resolution model,but the efficiency and feasibility of the proposed method increase significantly in practical applications.Furthermore,comparisons between some current design codes(AASHTO,JTGD60-2004,and TB10002.1-2005) and the developed dynamic analysis method suggest that these design codes may be improved,at least to consider the effect of dynamic amplification on structural demand.
基金supported by the National Natural Science Foundation of China(Nos.11472082 and11172069)
文摘Incompressible viscous flows on curved surfaces are considered with respect to the interplay of surface geometry, curvature, and vorticity dynamics. Free flows and cylindrical wakes over a Gaussian bump are numerically solved using a surface vorticity- stream function formulation. Numerical simulations show that the Gaussian curvature can generate vorticity, and non-uniformity of the Gaussian curvature is the main cause. In the cylindrical wake, the bump dominated by the positive Gaussian curvature can significantly affect the vortex street by forming velocity depression and changing vorticity transport. The results may provide possibilities for manipulating surface flows through local change in the surface geometry.
基金Supported by the National Natural Science Foundation of China(61071221,10831002)
文摘Let Ф（u ×v, k, Aa, Ac） be the largest possible number of codewords among all two- dimensional （u ×v, k, λa, λc） optical orthogonal codes. A 2-D （u× v, k, λa, λ）-OOC with Ф（u× v, k, λa, λc） codewords is said to be maximum. In this paper, the number of codewords of a maximum 2-D （u × v, 4, 1, 3）-OOC has been determined.
基金funded by the Joint Funds of the National Natural Science Foundation of China (61079001)
文摘This paper deals with dynamic airspace sectorization （DAS） problem by an improved genetic algorithm （iGA）. A graph model is first constructed that represents the airspace static structure. Then the DAS problem is formulated as a graph-partitioning problem to balance the sector workload under the premise of ensuring safety. In the iGA, multiple populations and hybrid coding are applied to determine the optimal sector number and airspace sectorization. The sector constraints are well satisfied by the improved genetic operators and protect zones. This method is validated by being applied to the airspace of North China in terms of three indexes, which are sector balancing index, coordination workload index and sector average flight time index. The improvement is obvious, as the sector balancing index is reduced by 16.5 %, the coordination workload index is reduced by 11.2 %, and the sector average flight time index is increased by 11.4 % during the peak-hour traffic.
基金Sponsored by the National Natural Science Foundation of China(Grant No.51708069)the Natural Science Foundation of Chongqing(Grant No.cstcstc2018jcyjA2535)。
文摘To analyze the impact effect induced by vehicle-bridge coupling vibration during traffic congesting, hundreds and thousands of congestion scenarios consisting of various vehicle platoons were collected and used to develop vehicle models as well as traffic congestion load models. Furthermore, the idling vehicle-bridge coupling model was established by the finite element method and the congestion models were applied to calculate dynamic impact factors. Compared with the value specified in Chinese codes, the calculated values were 1.15-2.67 times as large as the latter, which indicates the impact factors caused by idling vehicle-bridge coupling under congestion situations were much larger than those in normal traffic conditions. As a result, a calibration factor of 1.7 was recommended for bridge design or evaluation when considering vehicle-bridge coupling vibration under heavy traffic congestion. The proposed analytical model, analysis method, and results could also be beneficial references to further investigation in this field.
文摘Quickly getting back the synchronism of a disturbed interconnected multi-area power system due to variations in loading condition is recognized as prominent issue related to automatic generation control(AGC).In this regard,AGC system based on fuzzy logic,i.e.,so-called FLAGC can introduce an effectual performance to suppress the dynamic oscillations of tie-line power exchanges and frequency in multi-area interconnected power system.Apart from that,simultaneous coordination scheme based on particle swarm optimization(PSO)along with real coded genetic algorithm(RCGA)is suggested to coordinate FLAGCs of the all areas.To clarify the high efficiency of aforementioned strategy,two different interconnected multi-area power systems,i.e.,three-area hydro-thermal power system and five-area thermal power system have been taken into account for relevant studies.The potency of this strategy has been thoroughly dealt with by considering the step load perturbation(SLP)in both the under study power systems.To sum up,the simulation results have plainly revealed dynamic performance of FLAGC as compared with conventional AGC(CAGC)in each power system in order to damp out the power system oscillations.
基金Project supported by National Natural Science Foundation of Chi-na (Grant No .10471087) ,and Shanghai Municipal Commission ofEducation (Grant No .03AK33)
文摘In this paper, we discuss a class of piecewise linear hyperbolic maps on the 2-torus. These maps arise in the second-order digital fdter with two＇ s complement arithmetic. By introducing codings underlying the map operations, we give some admissibility conditions for symbolic sequences and find some periodic properties of these symbolic sequences. Then we use these conditions to check the admissibility of periodic symbol sequences.
