音调高跳速碰撞干扰对FH/MFSK系统的干扰性能分析

针对跳频/多路频移键控(FH/MFSK)通信系统的特点和较强的抗干扰能力,研究了一种动态阻塞干扰样式——高跳速碰撞干扰,分析了高跳速碰撞干扰的基本特性和优点,建立了一种音调高跳速碰撞干扰模型,分析了对FH/MFSK系统的干扰性能,并进行了FH/MFSK系统在高跳速碰撞干扰下的误码率性能仿真。仿真结果表明,高跳速碰撞干扰对跳频体制能构成较大的威胁。

沃尔沃XC90对决奥迪Q7 谁胜?—关注最新EURO NCAP测试成绩

"沃尔沃XC90—‘耗资110万美元研发新平台上的首款车型’、‘未来沃尔沃品牌的旗舰SUV车型’、‘世界上最安全的汽车之一’……关于XC90在沃尔沃品牌中的地位,不必多说,大家都知道。新一代奥迪Q7—新平台、新面貌、新内饰……Q7这个奥迪Q系列中的‘大佬’在换代之际实现了华丽转身。新一代Q7是基于第二代MLB平台打造的首款车型,这个根本的改变让其实现减重325kg。"

Micromixing in the Submerged Circulative Impinging Stream Reactor

Micromixing in the submerged circulative impinging stream reactor (SCISR) developed by the authors is investigated with the Bourne's reaction scheme. The values measured for the impinging velocity, u0, under the conditions of SCISR normal operation, only is of the order of 0.1m·s^-1, are much slower than that inferred,suggesting low power requirement for operation. The values of the characteristic time constant for micromixing,tM, determined in the impinging velocity range of 0.184m·s^-1 < u0 < 0.326m·s^-1 are ranged from 192ms to 87 ms, showing that impinging streams promotes micromixing very efficiently. The data follow approximately the relationship of tM∝ u0^-1.5. A comparative study shows that the micromixing performance of SCISR is much better than that of the traditional stirred tank reactor. The tM values predicted with the existing theoretical model are systematically longer than those measured by about 2--3 times, implying that the regularity of impinging streams promoting micromixing is unclear yet.

Grain refinement process of pure iron target under hypervelocity impact

The structure of ultrafine grain is formed at the crater bottom of pure iron target under hypervelocity impact. The microstructures of different layers at the crater bottom were characterized by optical microscopy （OM）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The cross-section observation was performed to reveal the grain refinement process driven by plastic deformation. Firstly, low energy dislocation structures （LEDS） such as dense dislocation walls （DDWs） and dislocation tangles （DTs） refine the original grains and form intersecting lamellar structures. With increasing strain, DDWs and DTs transform into subboundaries with small misorientations to separate lamellar structure to cells. Subboundaries are converted to high misorientation grain boundaries, so ultrafine grains are formed. The formation of ultrafine grains was discussed in the dynamic recrystallization process due to the large strain and strain rate induced by spherical shock wave.

The response of collision speed caused by the large bus to new flexible barrier

In order to study the response of collision speed caused by the large bus to new flexible barrier,in this paper,with the large bus as the carrier,the full-scale impact tests between flexible barrier and vehicle with the impact velocities of 40 km/h and 60 km/h were carried out separately,following the procedures of the test preparation,test processing,data acquisition, etc,which were based on the test platform of the Large Structure Crash Testing Laboratory of Changsha University of Science and Technology. The important test results which contain the damage of vehicles and barrier,the moving locus of vehicle,the occupant risk index,the maximum dynamic deformation, etc,were obtained through the analysis under the different collision speeds. These provide the necessary reference basis for the further research on the structure topology optimization and improve the comprehensive constraint performance to the flexible barrier.

Bcklund Transformation and Multisoliton Solutions in Terms of Wronskian Determinant for (2+1)-Dimensional Breaking Soliton Equations with Symbolic Computation

In this paper, two types of the （2＋1）-dimensional breaking soliton equations axe investigated, which describe the interactions of the Riemann waves with the long waves. With symbolic computation, the Hirota bilineax forms and Bgcklund transformations are derived for those two systems. Furthermore, multisoliton solutions in terms of the Wronskian determinant are constructed, which are verified through the direct substitution of the solutions into the bilineax equations. Via the Wronskian technique, it is proved that the Bgcklund transformations obtained are the ones between the （ N - 1）- and N-soliton solutions. Propagations and interactions of the kink-/bell-shaped solitons are presented. It is shown that the Riemann waves possess the solitonie properties, and maintain the amplitudes and velocities in the collisions only with some phase shifts.

Effect of Pd doping on CH_4 reactivity over Co_3O_4 catalysts from density-functional theory calculations

Palladium oxide(PdOx)and cobalt oxide(Co3O4)are efficient catalysts for methane(CH4)combustion,and Pd‐doped Co3O4catalysts have been found to exhibit better catalytic activities,which suggest synergism between the two components.We carried out first‐principles calculations at the PBE+U level to investigate the Pd‐doping effect on CH4reactivity over the Co3O4catalyst.Because of the structural complexity of the Pd‐doped Co3O4catalyst,we built Pd‐doped catalyst models using Co3O4(001)slabs with two different terminations and examined CH4reactivity over the possible Pd?O active sites.A low energy barrier of0.68eV was predicted for CH4dissociation over the more reactive Pd‐doped Co3O4(001)surface,which was much lower than the0.98and0.89eV that was predicted previously over the more reactive pure Co3O4(001)and(011)surfaces,respectively.Using a simple model,we predicted CH4reaction rates over the pure Co3O4(001)and(011)surfaces,and Co3O4(001)surfaces with different amounts of Pd dopant.Our theoretical results agree well with the available experimental data,which suggests a strong synergy between the Pd dopant and the Co3O4catalyst,and leads to a significant increase in CH4reaction rate.

Multidisciplinary Design Optimization of Crash Box with Negative Poisson’s Ratio Structure

To improve the crashworthiness and energy absorption performance,a novel crash box negative Poisson’s ratio(NPR)structure is proposed according to the characteristics of low speed collision of bumper system.Taking the peak collision force and the average collision force as two subsystems,a multidisciplinary collaborative optimization design is carried out,and its optimization results are compared with the ones optimized by NSGA-II algorithm.Simulation results show that the crashworthiness and energy absorption performance of the novel crash box is improved effectively based on the multidisciplinary optimization method.

Impact of Inert Metal Particles Flow on Aluminium Plate

Inert metal explosive,a new kind of explosive,is a mixture of high explosive and inert metal particle.When this kind of explosive is detonated,an inert metal particle flow will be formed by the ex-plosive product driving.To determine the characteristics of the movement of the metal particle flow,a series of aluminium plates were designed to be the targets on which the metal particle flow impacted.The test result was presented and a numerical model was set up to analyze the impact of the high speed inert metal particles on aluminium plate.Based on the numerical analysis,the relationship between the characteristic of the mark on the target plate and the initial condition of the inert metal particles was pro-posed.From the analysis of the impact on target plates,more information about the movement of the metal particles could be reconstructed.

Measurement of Collision Conditions in Magnetic Pulse Welding Processes

MPW （magnetic pulse welding） is a solid state joining technology that allows for the generation of strong metallic bonds, even between dissimilar metals. Due to the absence of external heat, critical intermetallic phases can largely be avoided. In this process, Lorentz forces are utilized for the rapid acceleration of at least one of the two metallic joining partners leading to the controlled high velocity impact between them. The measurement of the collision conditions and their targeted manipulation are the key factors of a successful process development. Optical measuring techniques are preferred, since they are not influenced by the prevalent strong magnetic field in the vicinity of the working coil. In this paper, the characteristic high velocity impact flash during MPW was monitored and evaluated using phototransistors in order to measure the time of the impact. The results are in good accordance with the established PDV （photon Doppler velocimetry） and show a good repeatability. Furthermore, the collision front velocity was investigated using adapted part geometries within a series of tests. This velocity component is one of the key parameters in MPW; its value decreases along the weld zone. With the help of this newly introduced measurement tool, the magnetic pressure distribution or the joining geometry can be adjusted more effectively.

A型不锈钢地铁车体耐撞性研究

轨道车辆车体基本性能的研究需要考虑多方面的因素,车体耐碰撞性是重要指标之一。以A型不锈钢地铁车体为研究对象,基于LS-DYNA碰撞仿真平台,分析了车辆在不同碰撞速度下车体的耐撞性能;然后,采用逼近法,获取了该型地铁车的最大碰撞安全速度,为车体的耐撞性设计提供了理论支撑。

Characterization of cooling rate and microstructure of Cu Sn melt droplet in drop on demand process

Different sized single droplets of Cu-6%Sn alloy were prepared by drop on demand(DOD)technique.The secondarydendrite arm spacing was measured and correlated with the droplet cooling rate by a semi-empirical formula.The microstructure ofdroplets was observed by optical microscopy(OM)and electro backscatter diffraction(EBSD).The dendrite feature of singledroplets depends on solidification rate,cooling medium and flight distance.When droplets collide with each other at temperaturesbetween solidus and liquidus,the dendrites and grains are refined obviously possibly because the collision enhances the heat transfer.The cooling rate of colliding droplets is estimated to be more than4×104K/s based on a Newton’s cooling model.The dendritesgrow along the colliding direction because of the temperature gradient induced by the internal flow inside the droplets.

Research on the 3-D Seismic Structures in Qinghai-Xizang Plateau

Based on the recording data from the analogue and broadband digital seismic stations in and around Qinghai-Xizang (Tibet) Plateau, the three dimensional (3-D) seismic velocity structures in Qinghai-Xizang Plateau were obtained by using the regional body wave tomography and surface wave tomography. The results from these two tomography methods have similar characteristics for P- and S-wave velocity structures in crust and upper mantle. They show that there are remarkable low velocity zones in the upper crust of Lhasa block in the southern Qinghai-Xizang Plateau and the lower crust and upper mantle of Qiangtang block in the northern Qinghai-Xizang Plateau. These phenomena may be related to the different steps of collision process in southern and northern Qinghai-Xizang Plateau.

Collision Simulation of Minibus at High Speed

Collision properties of minibus when traveling at high speed are studied. Based on the display dynamics and basic theoretical of contact collision analysis, the front crash finite element model of minibus is built by Hypermesh. The model is simulated under the 50 km/h by ANSYS/Ls-Dyna solver. Finally, the deformation of the front rail, B pillar acceleration curve and the steering column intrusion are got. It is important to improve safety design for minibus.

Performance improvement of car body structure in 100% frontal impact

During the 100%front impact,all the parts of front car will participate in the course;the crash stiffness of bodywork will also reach the peak.During the crash,rational structure of bodywork can resist the distortion,absorb more energy and get better mode of distortion and low deceleration rate,so as to meet the performance of crash safety.The paper mainly makes optimization analysis based on the problems of front side rails,subframe,firewall,and optimization cases are confirmed which can decrease the intrusion and deceleration rate of the whole car.The structure of bodywork after optimization can meet the performance of crash safety.

Ion-Pair Dissociations of Br CN by Electron Impacts

Ion-pair dissociation is an important molecular process and frequently happens when the target molecule is pumped to its electronically superexcited states. In contrast to the experimental studies of photoexcitation ion-pair dissociation, there are some experimental challenges in the electron-impact ion-pair dissociation study, in particular, on determination of the energetic threshold. Here we report an experimental development for the ion-pair dissociation study by using the monochromized electron impacts. As an example, the threshold of BrCN→Br^-+CN^+ is determined as 13.78 eV according to the appearance energy of CN^+ signals, meanwhile, the time-sliced ion velocity image of CN^+ is recorded at 16.09 eV and indicates an anisotropic distribution of the CN^+ momentum.

Simulation of bidirectional pedestrian flow in transfer station corridor based on multi forces

A good understanding of pedestrian movement in the transfer corridor is vital for the planning and design of the station,especially for efficiency and safety.A multi-force vector grid model was presented to simulate the movement of bidirectional pedestrian flow based on cellular automata and forces between pedestrians.The model improves rule-based characteristics of cellular automata,details forces between pedestrians and solves pedestrian collisions by a several-step updating method to simulate pedestrian movements.Two general scenarios in corridor were simulated.One is bidirectional pedestrian flow simulation with isolation facility,and the other is bidirectional pedestrian flow simulation without isolation facility,where there exists disturbance in the middle.Through simulation,some facts can be seen that pedestrians in the case with isolation facility have the largest speed and pedestrians in the case without isolation facility have the smallest speed; pedestrians in the case of unidirectional flow have the largest volume and pedestrians in the case of without isolation facility have the smallest volume.

Lower extremity injuries in vehicle-pedestrian collisions using a legform impactor model

Though the bumper of a vehicle plays a major role in protecting the vehicle body against damage in low speed impacts, many bumpers, particularly in large vehicles, are too stiff for pedestrian protection. In designing a bumper for an automobile, pedestrian protection is as important as bumper energy absorption in low speed collisions. To prevent lower extremity injuries in car-pedestrian collisions, it is important to determine the loadings that car front structures impart on the lower extremities and the mechanisms by which injury is caused by these loadings. The present work was focused on gaining more insight into the injury mechanisms leading to both ligament damage and bone fracture during bumper-pedestrian collisions. The European Enhanced Vehicle-safety Committee （EEVC） legform impactor model was introduced and validated against EEVCAVG17 criteria. The collision mechanism between a bumper and this legform impactor was investigated numerically using LS-DYNA software. To identify the effect of the bumper beam material on leg injuries, four analyses were performed on bumpers that had the same assembly but were made from different materials.

Calculation of laser induced collisional energy transfer in the Sr-Ca system

Based on the four-state model of laser-induced collisional energy transfer,the cross section of the collisional energy transfer in the Sr-Ca system is obtained.Various factors,including field intensity,relative speed,and temperature,which influence the collisional cross section,are discussed for illustrating the features of the Sr-Ca laser-induced collisional energy transfer(LICET) process.The calculated results show that the LICET spectral profiles obviously become narrower when the laser field intensity increases.The collision cross section rises with laser intensity and tends to saturate.In the vicinity of the spectral profile center,the cross section at fixed laser detuning becomes smaller as the relative speed and system temperature increase.The results indicate that the intermediate states strongly affect the spectral profile of LICET.

Continuum description for the characteristic resistance sensed by a cylinder colliding against granular medium

In this paper, we experimentally and theoretically study the resistance force that develops when a cylinder with a flat face colliding against dry quartzite sand. Observations from experimental data clearly show that the acceleration curves are characterized by a double-peak structure. The first agitated peak can be attributed to a shock process where sand responds elastically, and the valley bottom in the double-peak structure is related to a limited plastic load when a fully plastic region is formed in the sand, while the second agitated peak corresponds to a the occurrence of the maximum of viscous force in a homogeneous developed bulk flow. We use slip line theory (SL) developed in plastic mechanics to capture the value at the valley bottom, adopt the double shearing theory (DS), together with a Local Rheological Constitutive Law (LRCL) suggested in this paper, to capture the drag force generated in a homogeneous bulk flow. Good agreements in the comparisons between numerical and experimental results support the characteristic resistance by the cylinder to predict granular states.