Tunable spectral continuous shift of high-order harmonic generation in atoms by a plasmon-assisted shaping pulse

We delve into the phenomenon of high-order harmonic generation within a helium atom under the influence of a plasmon-assisted shaping pulse.Our findings reveal an intriguing manipulation of the frequency peak position in the harmonic emission by adjusting the absolute phase parameter within the frequency domain of the shaping pulse.This phenomenon holds potential significance for experimental setups necessitating precisely tuned single harmonics.Notably,we observe a modulated shift in the created harmonic photon energy,spanning an impressive range of 1.2 eV.This frequency peak shift is rooted in the asymmetry exhibited by the rising and falling edges of the laser pulse,directly influencing the position of the peak frequency emission.Our study quantifies the dependence of this tuning range and the asymmetry of the laser pulse,offering valuable insights into the underlying mechanisms driving this phenomenon.Furthermore,our investigation uncovers the emergence of semi-integer order harmonics as the phase parameter is altered.We attribute this discovery to the intricate interference between harmonics generated by the primary and secondary return cores.This observation introduces an innovative approach for generating semi-integer order harmonics,thus expanding our understanding of high-order harmonic generation.Ultimately,our work contributes to the broader comprehension of complex phenomena in laser-matter interactions and provides a foundation for harnessing these effects in various applications,particularly those involving precise spectral control and the generation of unique harmonic patterns.

Recent advances of computational aeroacoustics

Computational aeroacoustics （CAA） is an interdiscipline of aeroacoustics and computational fluid dynamics （CFD） for the investigation of sound generation and propagation from various aeroacoustics problems. In this review, the foundation and research scope of CAA are introduced firstly. A review of the early advances and applications of CAA is then briefly surveyed, focusing on two key issues, namely, high order finite difference scheme and non-reflecting boundary condition. Furthermore, the advances of CAA during the past five years are highlighted. Finally, the future prospective of CAA is briefly discussed.

Variable Stiffness Identification and Configuration Optimization of Industrial Robots for Machining Tasks

Industrial robots are increasingly being used in machining tasks because of their high flexibility and intelligence.However,the low structural stiffness of a robot significantly affects its positional accuracy and the machining quality of its operation equipment.Studying robot stiffness characteristics and optimization methods is an effective method of improving the stiffness performance of a robot.Accordingly,aiming at the poor accuracy of stiffness modeling caused by approximating the stiffness of each joint as a constant,a variable stiffness identification method is proposed based on space gridding.Subsequently,a task-oriented axial stiffness evaluation index is proposed to quantitatively assess the stiffness performance in the machining direction.In addition,by analyzing the redundant kinematic characteristics of the robot machining system,a configuration optimization method is further developed to maximize the index.For numerous points or trajectory-processing tasks,a configuration smoothing strategy is proposed to rapidly acquire optimized configurations.Finally,experiments on a KR500 robot were conducted to verify the feasibility and validity of the proposed stiffness identification and configuration optimization methods.

Optimization and Evaluation of a Vehicular Exhaust Heat Recovery System

Exhaust waste heat recovery system based on organic Rankine cycle(ORC)has been considered as an effective method to achieve energy conservation and emissions reduction of engine.The performance of adiesel engine with an on-board ORC exhaust heat recovery system was evaluated through simulations in this study.The combined system was optimized through controlling the exhaust gas mass flow rate entering the ORC system.The models of the engine with ORC system were developed in GT-suite and Simulink environment.The validation results showed high accuracy of the models.The performance of the system recovering heat from different exhaust gas mass flow rates was evaluated.The comparative analysis of the performance between the optimized and un-optimized system was also presented.The results indicated that the exhaust gas mass flow rate had significant effects on the system performance.Integration with the onboard ORC system could effectively improve the engine power performance.The power output of the engineORC combined system with optimization had further improvement,and the maximum improvement could reach up to 1.16 kW.

Dynamic Mechanical Behavior and Failure Mechanism of Polymer Composites Embedded with Tetraneedle-Shaped ZnO Whiskers

Quasi-static and dynamic mechanical properties of glass-fiber reinforced polymer composites embedded with and without tetraneedle-shaped ZnO whiskers(T-ZnOw)in two loading directions are investigated by a split Hopkinson pressure bar.The stress-strain curves,ultimate strength,failure strain and elastic modulus are obtained and the failure mechanism of the composites is investigated by a high-speed camera and a scanning electron microscope.Strain rate effects on the mechanical behavior are discussed and the corresponding models are derived by fitting the experimental data.The experimental results show that the composites with T-ZnOw under dynamic loading have multiple failure modes and better mechanical properties.Finally,the strengthening and toughening mechanisms of T-ZnOw are analyzed.It is shown that T-ZnOw can improve mechanical properties of the composites,and can make the composites have some new features.The present results provide a reliable basis for advanced composite design and manufacture,and have broad applications in the field of aerospace.

A Reconfigurable Mobile Launch Pad for Multiple Launchers

A launch pad is an important part of the launch vehicle system.It bears the weight of launch vehicles and payloads,and is burnt due to the high-temperature and high-pressure gas flow during launch.This study analyzes the development of launch pads in the world,reviews a reconfigurable mobile launch pad for multiple launchers,then proposes common points and development trends of future launch pads in the world.

Printability disparities in heterogeneous material combinations via laser directed energy deposition:a comparative study

Additive manufacturing provides achievability for the fabrication of bimetallic and multi-material structures;however,the material compatibility and bondability directly affect the parts’formability and final quality.It is essential to understand the underlying printability of different material combinations based on an adapted process.Here,the printability disparities of two common and attractive material combinations(nickel-and iron-based alloys)are evaluated at the macro and micro levels via laser directed energy deposition(DED).The deposition processes were captured using in situ high-speed imaging,and the dissimilarities in melt pool features and track morphology were quantitatively investigated within specific process windows.Moreover,the microstructure diversity of the tracks and blocks processed with varied material pairs was comparatively elaborated and,complemented with the informative multi-physics modeling,the presented non-uniformity in mechanical properties(microhardness)among the heterogeneous material pairs was rationalized.The differences in melt flow induced by the unlike thermophysical properties of the material pairs and the resulting element intermixing and localized re-alloying during solidification dominate the presented dissimilarity in printability among the material combinations.This work provides an in-depth understanding of the phenomenological differences in the deposition of dissimilar materials and aims to guide more reliable DED forming of bimetallic parts.

Experimental and numerical study on improvement performance by wave parallel flow field in a proton exchange membrane fuel cell

The performance and operation stability of proton exchange membrane fuel cells(PEMFCs)are closely related to the transportation of reactants and water management in the membrane electrode assembly(MEA)and flow field.In this paper,a new three-dimensional wave parallel flow field(WPFF)in cathode was designed and analyzed throughout simulation studies and an experimental method.The experimental results show that the performance of PEMFC with WPFF outperforms that of PEMFC with straight parallel flow field(SPFF).Specifically,the peak power density increased by 13.45%for the PEMFC with WPFF as opposed to PEMFC with SPFF.In addition,the flow field with area of 11.56 cm^(2) was formed by the assembly of transparent end plate used for cathode and the traditional graphite plate used for anode.To understand the mechanism of the novel flow field improving the performance of PEMFC,a model of PEMFC was proposed based on the geometry,operating conditions and MEA parameters.The thickness of gas diffusion layers(GDL),catalytic layers(CL)and proton exchange membrane were measured by scanning electron microscope.The simulation result shows that compared with SPFF,the WPFF based PEMFC promote the oxygen transfer from flow channel to the surface of CL through GDL,and it was beneficial to remove the liquid water in the flow channel and the MEA.

Sulfide@hydroxide core–shell nanostructure via a facile heating-electrodeposition method for enhanced electrochemical and photoelectrochemical water oxidation

Designing low-cost,easy-fabricated,highly stable and active electrocatalysts for oxygen evolution reaction(OER) is crucial for electrochemical(EC) and solar-driven photoelectrochemical(PEC) water splitting.By using a facile heating-electrodeposition method,here we fabricated a porous but crystalline Fe-doped Ni3 S2.A thin porous surface NiFe hydroxide layer(~10 nm) is then formed through OER-running.By virtue of the core Fe-doped Ni3 S2 with good conductivity and the shell NiFe hydroxide surface with good electrocatalytic activity,the core-shell nanostructure on Ni foam exhibits excellent OER activity in 1 M NaOH,needing only 195 and 230 mV to deliver 10 and 100 mA/cm^(2),respectively,much more superior to those of 216 and 259 mV for the sample deposited under normal temperature.The enhanced photo-response of the sulfide@hydroxide core-shell structure was also demonstrated,due to the efficient transfer of photo-generated carriers on the core/shell interface.More interestingly,it shows a good compatibility with Si based photoanode,which exhibits an excellent PEC performance with an onset potential of 0.86 V vs.reversible hydrogen electrode,an applied bias photon-to-current efficiency of 5.5% and a durability for over 120 h under AM 1.5 G 1 sun illumination,outperforming the state-of-the-art Si based photoanodes.

Short-time Fourier Transform Using Odd Symmetric Window Function

In this paper,a novel time–frequency(TF)analysis method,called the short-time Fourier transform using odd symmetric window function(OSTFT),is proposed using odd symmetric window function to replace the conventional even window function of STFT.Different from conventional STFT acquiring the amplitude maximum at time and frequency centers,OSTFT acquires the minimum amplitude of 0.Hence,OSTFT can obtain a TF representation(TFR)with high TF resolution by utilizing the leaked energy rather than restraining it.It is worth to mention that the proposed OSTFT can vitiate the effect of window size we choose on the TFR obtained.Furthermore,it also has a good performance on signals with complex instantaneous frequencies(IFs),even crossing IFs.Because we just replace the conventional window function of STFT,the time-consuming of the proposed OSTFT is at the same level as the conventional STFT.The effectiveness of proposed OSTFT has been validated on two complex multi-component simulated numerical signals and a signal collected from the brown bat.

Novel AC Servo Rotating and Linear Composite Driving Device for Plastic Forming Equipment

The existing plastic forming equipment are mostly driven by traditional AC motors with long trans- mission chains, low efficiency, large size, low precision and poor dynamic response are the common disadvantages. In order to realize high performance forming processes, the driving device should be improved, especially for com- plicated processing motions. Based on electric servo direct drive technology, a novel AC servo rotating and linear composite driving device is proposed, which features implementing both spindle rotation and feed motion with- out transmission, so that compact structure and precise control can be achieved. Flux switching topology is employed in the rotating drive component for strong robustness, and fractional slot is employed in the linear direct drive component for large force capability. Then the mechanical structure for compositing rotation and linear motion is designed. A device prototype is manufactured, machining of each component and the whole assembly are presented respectively. Commercial servo amplifiers are utilized to construct the control system of the proposed device. To validate the effectiveness of the proposed composite driving device, experimental study on thedynamic test benches are conducted. The results indicate that the output torque can attain to 420 N-m and the dynamic tracking errors are less than about 0.3 rad in the rotating drive, the dynamic tracking errors are less than about 1.6 mm in the linear feed. The proposed research provides a method to construct high efficiency and accu- racy direct driving device in plastic forming equipment.

一类活动发射平台驱动控制系统网络设计

In order to ensure that a mobile launch platform is able to transport a launch vehicle which is assembled vertically on a complex orbit,a communication network for the drive control system was designed.Based on the char-acteristics of equipment of the drive control system and its position,Industrial Ethernet and Profibus were selected.To meet the requirements for reliability and maintainability of aerospace products,the communication network featured a hot redundant to avoid single point failure risk,so that if any point in the system fails,the control strategy of standby switches using heartbeat detection and parity check would ensure the normal communication and failure diagnostics,which could enable the transport mission of the launch vehicle to be completed smoothly.

新一代运载火箭发射燃气动力学数值模拟

By using the mesh resolution control method based on the nozzle scale,a paralleled super numerical simulation and high-quality mesh model of the launch jet dynamics for new-generation launch vehicles was developed.Based upon this,a transient numerical simulation method,combining the pressure and velocity,tightly coupled algorithm and SST turbulence model,was used to complete the unsteady numerical simulation of the launch jet dynamics of the new-generation launch vehicles.The numerical simulation results of the launch jet dynamics,for the new-generation launch vehicles,demonstrated that despite the complex structure of the launch platform,the jet flows of the core stage and booster engines were generally smoothly channeled into the double deflecting trench through the launch platform’s diversion hole at the initial stage of ignition.After the lift off,the jet flows of the core stage and the booster engines began to affect and ablate the grillage-shaped beam and the adjoined surface of the launch platform adjacent to the booster engines.At a higher altitude after lift off,it could be seen for the new-generation launch vehicles the ablation range of high temperature and high-speed jet flows on the launch platform further expanded,which would have a severe ablation effect on the fuel filling tower near the booster engines and even all the support arms.The numerical simulation of launch jet dynamics also established that the jet flows embers at the bottom of the core stage rocket body continued to be affected for an extended period of time due to the large number of nozzles in the new-generation launch vehicles engine and the weak suction effect of the jet flows in the core-stage engines.

12点调平系统及其应急预案措施

With high stability,strong bearing capacity and other characteristics,multi-point leveling systems have been widely used in various industries.The mobile platform here uses a 12-point leveling system,which is mainly composed of the mechanical transmission system of the supporting arm,a hydraulic drive system and an electrical control system.The leveling is realized through the proportional lifting of the arms in four quadrants.In order to ensure the smooth conduct of launch missions,emergency plans were made for the leveling system incase of failure of a single arm.

Effect of Heat Treatments on Tribology Property of Ti6Al4V Alloy Under Dry Friction

Ti6Al4V alloy manufactured by electron powder bed fusion(EPBF)was separately heat-treated by stress-relief annealing at 600℃,annealing at 800℃,and solid solution at 920℃ for 1 h.Then,the friction and wear tests were conducted on the samples before and after heat treatment to analyze the properties and mechanism of friction and wear behavior.Results show that the sample annealed at 600℃ for 1 h has the optimal wear resistance,and the wear mass loss reduces by 44%.The sample annealed at 800℃ for 1 h possesses the optimal anti-friction performance,and the coefficient of friction reduces by 14%.This research provides a simple heat treatment method to improve the friction and wear resistance of Ti6Al4V alloy manufactured by EPBF.

Research on vibration suppression of a mistuned blisk by a piezoelectric network

The work aims to provide a further investigation of the dynamic characteristics of an integral bladed disk（also called ‘blisk＇） with a Parallel Piezoelectric Network（PPN）. The PPN is constructed by parallelly interconnecting the piezoelectric patches distributed in the blisk. Two kinds of PPN are considered, namely mono-periodic PPN and bi-periodic PPN. The former has a piezoelectric patch in each sector, and the later has one patch every few sectors. The vibration suppression performance of both kinds of PPN has been studied through modal analysis, forced response analysis, and statistical analysis. The research results turn out that the PPN will only affect mechanical frequencies near the electrical frequency clusters slightly, and the bi-periodic PPN will make the nodal diameter spectrum of the modes more complex, but the amplitude corresponding to the new nodal diameter component is much smaller than that of the nodal diameter component corresponding to the mono-periodic system. The mechanical coupling between the blades and the disk plays an important role in the damping effect of the PPN, and it should be paid attention to in applications. The mono-periodic PPN can effectively suppress the amplitude magnification of the forced response induced by the mistuning of the blisk; meanwhile, it can mitigate the vibration localization of the mistuned electromechanical system. If piezoelectric patches are set only in part of the sectors, the bi-periodic PPN still has a vibration suppression ability, but the effect is related to the number and spatial distribution of the piezoelectric patches.

Biomimetic Material Simulating Solar Spectrum Reflection Characteristics of Yellow Leaf

To counter the threat of hyperspectral detection, it is necessary to develop biomimetic materials to simulate the solar spectral re- flection characteristics of plant leaf accurately. Two kinds ofmembranaceous yellow biomimetic materials were prepared by dispersing the particles of chrome titanium yellow and iron oxide yellow as fillers in polyvinyl alcohol films respectively. Reflectance and transmittance of the biomimetic materials were measured, and absorption and scattering coefficients of the biomimetic materials were inverted with a four-flux model. Results indicate that the biomimetic material adopting chrome titanium yellow particles can simulate the solar spectrum reflection characteristics of yellow leaf because of the similar absorption and scattering characteristics. The biomimetic material adopting iron oxide yellow particles cannot simulate the spectrum reflection characteristics of yellow leaf near the wavelength of 900 nm due to the characteristic absorption of the iron oxide. When the volume fraction of the chrome titanium yellow particles is lower than 2.12%, the absorption and scattering coefficients both increase approximately linearly with the volume fraction, indicating that the particles can scatter radiation independently. Therefore, the reflectance of the biomimetic material can be regulated through linearly changing of the volume fraction of the chrome titanium yellow particles.

Effects of Probe Support on the Stall Characteristics of a Low-Speed Axial Compressor

In order to investigate the effects of probe support on the stall characteristics of micro compressors, an experiment was carried out on a large-scale low-speed research compressor according to the principle of geometric similarity. A cylindrical probe support intruding to 50% blade span was mounted at 50% chord upstream from the rotor blade leading edge. The static pressure rise characteristic of the compressor is measured, with and without the probe support respectively. The dynamic compressor behavior from pre-stall to full stall was also measured. The results indicate that the stability margin of the compressor is lowered after installing the probe support. The stall inception is aroused by modal wave disturbances. The disturbances developed into two stall cells smoothly before installing the probe support, while the disturbances first developed into a single stall cell then splitting into two stall cells after installing the probe support. The presence of probe support lowers the initial intensity of the rotating stall of the compressor, while it doesn't alter the intensity of the rotation stall after the compressor enters into full stall.