英孚发布创意英语教材High Flyers

为进一步激发7至9岁儿童学习英语的主动性,英孚教育发布了由多国教育人士共同创作的创意教材。近日,《留学》应邀参加英孚教育在北京召开的媒体体验会,亲身感受了一套为7-9岁儿童量身定做的英语教材。这套名为"High Flyers"的教材研发历时三年,由多国教育界人士共同参与创作完成。英孚教育青少儿英语执行副总裁白皎宇告诉《留学》,High Flyers教材及课程引入了个性鲜明的动画人物,加入了多个实用的对话情景。

Plastic deformation behavior of a Cu-10Ta alloy under strong impact loading

In this work,a Cu-10Ta alloy with a copper to tantalum mass ratio of 9:1 is prepared using powder metallurgy technology.Physical properties of the alloy,including density,microstructure,melting point,and constant-volume specific heat,are tested.Via the split Hopkinson pressure bar(SHPB)and flyerplate impact experiments,the relationship between equivalent stress and equivalent plastic strain of the material is studied at temperatures of 298-823 K and under strain rates of 1×10^(-3)-5.2×10^(3)s^(-1),and the Hugoniot relationship at impact pressures of 1.46-17.25 GPa and impact velocities of 108-942 m/s is obtained.Evolution of the Cu-10Ta microstructure that occurs during high-strain-rate impact is analyzed.Results indicate that the Cu-10Ta alloy possesses good thermal stability,and at ambient temperatures of up to 50%its melting point,stress softening of less than 15%of the initial strength is observed.A modified J-C constitutive model is employed to accurately predict the variation of yield strength with strain rate.Under strong impact,the copper phase is identified as the primary source of plastic deformation in the Cu-10Ta alloy,while significant deformation of the high-strength tantalum particles is less pronounced.Furthermore,the longitudinal wave speed D is found to correlate linearly with the particle velocity u upon strong impact.Analysis reveals that the sound speed and spallation strength of the alloy increase with increasing impact pressure.

Research on the quasi-isentropic driving model of aluminized explosives in the detonation wave propagation direction

Taking CL-20(Hexanitrohexaazaisowurtzitane)-based aluminized explosives with high gurney energy as the research object, this research experimentally investigates the work capability of different aluminized explosive formulations when driving metal flyer plates in the denotation wave propagation direction.The research results showed that the formulations with 43 μm aluminum(Al) powder particles(The particle sizes of Al powder were in the range of 2~43 μm) exhibited the optimal performance in driving flyer plates along the denotation wave propagation direction. Compared to the formulations with Al powder 13 μm, the formulations with Al powder 2 μm delivered better performance in accelerating metal flyer plates in the early stage, which, however, turned to be poor in the later stage. The CL-20-based explosives containing 25% Al far under-performed those containing 15% Al. Based on the proposed quasi-isentropic hypothesis, relevant isentropy theories, and the functional relationship between detonation parameters and entropy as well as Al reaction degree, the characteristic lines of aluminized explosives in accelerating flyer plates were theoretically studied, a quasi-isentropic theoretical model for the aluminized explosive driving the flyer plate was built and the calculation methods for the variations of flyer plate velocity, Al reaction degree, and detonation product parameters with time and axial positions were developed. The theoretical model built is verified by the experimental results of the CL-20-based aluminized explosive driving flyer plate. It was found that the model built could accurately calculate the variations of flyer plate velocity and Al reaction degree over time. In addition, how physical parameters including detonation product pressure and temperature varied with time and axial positions was identified. The action time of the positive pressure after the detonation of aluminized explosives was found prolonged and the downtrend of the temperature was slowed down and even reversed to a slight rise due to the aftereffect reaction between the Al powder and the detonation products.

The interaction between a shaped charge jet and a single moving plate

Reactive armour is a very efficient add-on armour against shaped charge threats.Explosive reactive armour consists of one or several plates that are accelerated by an explosive.Similar but less violent acceleration of plates can also be achieved in a completely inert reactive armour.To be efficient against elongated jets,the motion of the plates needs to be inclined against the jet such that a sliding contact between the jet and the plates is established.This sliding contact causes a deflection and thinning of the jet.Under certain circumstances,the contact will become unstable,leading to severe disturbances on the jet.These disturbances will drastically reduce the jet penetration performance and it is therefore of interest to study the conditions that leads to an unstable contact.Previous studies on the interaction between shaped charge jets and flyer plates have shown that it is mainly the forward moving plate in an explosive reactive armour that is effective in disturbing the jet.This is usually attributed to the higher plate-to-jet mass flux ratio involved in the collision of the forward moving plate compared to the backward moving plate.For slow moving plates,as occurs in inert reactive armour,the difference in mass flux for the forward and backward moving plate is much lesser,and it is therefore of interest to study if other factors than the mass flux influences on the protection capability.In this work,experiments have been performed where a plate is accelerated along its length,interacting with a shaped charge jet that is fired at an oblique angle to the plate’s normal,either against or along the plate’s velocity.The arrangement corresponds to a jet interacting with a flyer plate from a reactive armour,with the exception that the collision velocity is the same for both types of obliquities in these experiments.The experiments show that disturbances on the jet are different in the two cases even though the collision velocities are the same.Numerical simulations of the interaction support the observation.The difference is attributed to the character of the contact pressure in the interaction region.For a backward moving plate,the maximum contact pressure is obtained at the beginning of the interaction zone and the contact pressure is therefore higher upstream than downstream of the jet while the opposite is true for a forward moving plate.A negative interface pressure gradient with respect to the jet motion results in a more stable flow than a positive,which means that the jet-plate contact is more stable for a backward moving plate than for a forward moving plate.A forward moving plate is thus more effective in disturbing the jet than a backward moving plate,not only because of the higher jet to plate mass flux ratio but also because of the character of the contact with the jet.

From concept to reality-A review to the primary test stand and its preliminary application in high energy density physics

Pulsed power technology,whereas the electrical energy stored in a relative long period is released in much shorter timescale,is an efficient method to create high energy density physics(HEDP)conditions in laboratory.Around the beginning of this century,China Academy of Engineering Physics(CAEP)began to build some experimental facilities for HEDP investigations,among which the Primary Test Stand(PTS),a multi-module pulsed power facility with a nominal current of 10 MA and a current rising time~90 ns,is an important achievement on the roadmap of the electro-magnetically driven inertial confinement fusion(ICF)researches.PTS is the first pulsed power facility beyond 10 TW in China.Therefore,all the technologies have to be demonstrated,and all the engineering issues have to be overcome.In this article,the research outline,key technologies and the preliminary HEDP experiments are reviewed.Prospects on HEDP research on PTS and pulsed power development for the next step are also discussed.

Theoretical Model for Calculating Electric-Power Curves Depicting Accelerated Flyer by Exploding Foil

A theoretical model for calculating electric-power curves of small-size foil during its electrical explosion is given.This technique is based on temperature dependence of foil conductivity.After taking into account the energy conversion of the foil explosion,the power-time curve is applied to the hydrodynamic code.One-dimensional numerical simulations of electric-explosion driving flyers are performed using this code.Calculated flyer velocities lie within ±8% of experimental data from Lawrence Livermore National Laboratory （LLNL）,and simulated history curves of flyer velocities coincide well with those measured using velocity interferometer system for any reflector （VISAR）,indicating a helpful work for design optimization of slapper detonators.

CALCULATION AND MEASUREMENT OF DYNAMIC EXPANSION OF ROVING FLYER

Roving flyer is an important part of roving frame. Its dynamic expansions affect the quality of rove greatly. The expansions are calculated by means of the general program SAP84 based on finite element method in this paper. Its measuring principle and usage are also described. The results of calculating and measuring are identical. The method presented in the paper is effective for studying the properties of roving flyer.

Method of Testing the Flyer Sensitivity of Explosives

By means of Mylar flyer shock explosives driven by electric gun, the method of testing the flyer initiation sensitivity of explosives is studied, and some experiments are done. The experimental results show that the test method established is correct, which is very important and instructive to study and evaluate the safety and reliability of explosives. For the moment, the test should be researched and discussed further..

Swiss Innovation Week 2019:Home of Drones,the New High Flyer of Swiss Industry

Following the successful Swiss Innovation Week(SIW)held in July 2018,the Embassy of Switzerland in China launches its 2nd edition from 12 to 14of June 2019.With Swiss drones as the brand-new theme,Switzerland’s drone ecosystem and innovation in the field of flying robots were present.According to various rankings,Switzerland is one of the most innovative countrie s in the world and also one of the most competitive co untries.

Rolling centrifuge repulsion Force Spacecraft

A Rolling Centrifugal Repulsion force UFO Introduction: Any object that rolls along a straight line will generate a centrifugal repulsive force that is away from the body being rolled, it is rolling centrifugal repulsive force. Utilizing this phenomenon, rolling the round ring along the edge of the UFO's disk will produce a constant lift, and then use the electric wheel technology to set the ballast rock at the bottom of the UFO to change the position of the ballast stone at the bottom of the chamber. In order to change the position of the center of gravity of the UFO, the purpose of driving the UFO can be achieved.

Applicability limits of the DAX test in plastic bonded explosives

The Disc Acceleration e Xperiment(DAX)is one of the most recent experimental methods of performance characterization of new energetic materials.A cylindrical explosive charge accelerates a thin metallic disc and its velocity is measured continuously using photonic Doppler velocimetry.The detonation velocity is measured simultaneously.The DAX test can be used to obtain the Chapman-Jouguet(CJ)detonation pressure and to describe detonation products expansion using reduced amount of explosive.A series of DAX tests was performed at various charge diameters and disc thicknesses with Semtex 1 A plastic bonded explosive and sensitized nitromethane.The DAX-like evaluation was also applied to previously measured data of Semtex 1A and A-IX-1 explosives.The optimum disc thickness is determined by the disc to explosive mass ratio of 0.01-0.08.The repeatability of the Semtex 1 A detonation pressure results is about four times lower compared to the pressed and liquid explosives.