COMPACTLY SUPPORTED NON-TENSOR PRODUCT FORM TWO-DIMENSION WAVELET FINITE ELEMENT

Some theorems of compactly supported non-tensor product form two-dimension Daubechies wavelet were analysed carefully. Compactly supported non-tensor product form two-dimension wavelet was constructed, then non-tensor product form two dimension wavelet finite element was used to solve the deflection problem of elastic thin plate. The error order was researched. A numerical example was given at last.

Two-Dimensional Euler Adaptive Mesh Method on Detonation

The adaptive mesh refinement （AMR） method is applied in the 2-D Euler multi-component elasticplastic hydrodynamics code （MEPH2Y）. It is applied on detonation. Firstly, the AMR method is described, including a conservative spatial interpolation, the time integration methodology with the adapitve time increment and an adaptive computational region method. The advantage of AMR technique is exhibited by numerical examples, including the 1-D C-J detonation and the 2-D implosion ignited from a single point. Results show that AMR can promote the computational efficiency, keeping the accuracy in interesting regions.

EFFECT OF SUSPENDED SOLID PARTICLES ON UNSTABILITY OF TWO-DIMENSION MIXING LAYER

By considering the effect of suspended solid particles in the ordinary equations for two-dimension inviscid incompressible mixing layer, the Rayleigh equation and the modified Rayleigh equation are obtained. And then, by solving the corresponding eigen-value equations with numerical computational method, the relation curves between perturbation frequency and spacial growth rate of the mixing layer for the varying particle loading, ratio of particle velocity to fluid velocity and Stokes number are got. Sever al important conclusions on the effect of suspended solid particles on unstability of the mixing layer are presented in the end by analyzing all the relation curves.

Surface Topography of Fine-grained ZrO_2 Ceramic by Two-dimensional Ultrasonic Vibration Grinding

The surface quality of fine-grained ZrO2 engineering ceramic were researched using 270# diamond wheel both with and without work-piece two-dimension ultrasonic vibration grinding（WTDUVG）. By AFM images, the surface topography and the micro structure of the two-dimensional ultrasonic vibration grinding ceramics were especially analyzed. The experimental results indicate that the surface roughness is related to grinding vibration mode and the material removal mechanism. Surface quality of WTDUVG is superior to that of conventional grinding, and it is easy for two-dimensional ultrasonic vibration grinding that material removal mechanism is ductile mode grinding.

Advances and Challenges in Two‑Dimensional Organic–Inorganic Hybrid Perovskites Toward High‑Performance Light‑Emitting Diodes

Two-dimensional(2D)perovskites are known as one of the most promising luminescent materials due to their structural diversity and outstanding optoelectronic properties.Compared with 3D perovskites,2D perovskites have natural quantum well structures,large exciton binding energy(Eb)and outstanding thermal stability,which shows great potential in the next-generation displays and solidstate lighting.In this review,the fundamental structure,photophysical and electrical properties of 2D perovskite films were illustrated systematically.Based on the advantages of 2D perovskites,such as special energy funnel process,ultrafast energy transfer,dense film and low efficiency roll-off,the remarkable achievements of 2D perovskite light-emitting diodes(PeLEDs)are summarized,and exciting challenges of 2D perovskite are also discussed.An outlook on further improving the efficiency of pure-blue PeLEDs,enhancing the operational stability of PeLEDs and reducing the toxicity to push this field forward was also provided.This review provides an overview of the recent developments of 2D perovskite materials and LED applications,and outlining challenges for achieving the high-performance devices.

Frequency modulated weak signal detection based on stochastic resonance and genetic algorithm

Stochastic resonance system is subject to the restriction of small frequency parameter in weak signal detection,in order to solve this problem,a frequency modulated weak signal detection method based on stochastic resonance and genetic algorithm is presented in this paper. The frequency limit of stochastic resonance is eliminated by introducing carrier signal,which is multiplied with the measured signal to be injected in the stochastic resonance system,meanwhile,using genetic algorithm to optimize the carrier signal frequency,which determine the generated difference-frequency signal in the lowfrequency range,so as to achieve the stochastic resonance weak signal detection. Results showthat the proposed method is feasible and effective,which can significantly improve the output SNR of stochastic resonance,in addition,the system has the better self-adaptability,according to the operation result and output phenomenon,the unknown frequency of the signal to be measured can be obtained,so as to realize the weak signal detection of arbitrary frequency.

A 2D NiFe Bimetallic Metal–Organic Frameworks for Efficient Oxygen Evolution Electrocatalysis

The oxygen evolution reaction(OER) is the cornerstone for many important energy conversion devices, including metal–air battery and water splitting.Herein, an optimized NiFe-based metal–organic framework is developed as highly efficient active material for OER. It just needs a low overpotential of 0.31 V to deliver a current density of 10 mA cm-2 with a favorable Tafel slope of 43.7 mV dec-1 in 0.1 M KOH electrolyte for the as-prepared Ni0.75Fe0.25 BDC, which is superior to RuO2. This efficient catalytic performance is due to the introduction of Fe in Ni-based MOFs could benefit the kinetics and charge transfer efficiency, resulting in the optimal activity toward OER. Besides, the obtained active material demonstrates good stability, suggesting the great potential value in sustainable electrochemical energy storage and conversion devices.

In situ revealing the reconstruction behavior of monolayer rocksalt CoO nanosheet as water oxidation catalyst

The reconstruction during oxygen evolution reaction (OER) significantly affects the electronic and local geometry structure of metal sites in electrocatalyst.Compared with well-investigated cobalt-based materials,the reconstruction of rocksalt CoO with purely Co^(2+) in octahedral (Oh) coordination has not been revealed in detail.Herein,monolayer Co O supported on reduced graphene oxide (r GO) was synthesized via a one-pot hydrothermal strategy with calcinating in Ar atmosphere.The structure evolution of twodimension (2D) Co O/r GO during OER was revealed by in situ X-ray absorption spectroscopy (XAS).The transition from Co O toward Co3O_(4) already occurred at open circuit potential,further enhanced at 1.23 V (vs.RHE).The Co Ox(OH)ywas determined as the active phase at 1.53 V,displaying a tetrahedral Co coordination defective spinel Co_(3)O_(4) with the Co-O shell that featured the (oxy)hydroxide,not the standard Co OOH.After OER,the irreversible transition from CoO to Co_(3)O_(4) was observed.In contrast,in situ Raman spectra revealed a reversible amorphization process on Co_(3)O_(4)/r GO under operation conditions.Furthermore,this study indicated that the reconstruction behavior could be more effectively revealed by XAS using 2D materials.

A NEW APPROACH TO MANUFACTURING 3D WOVEN PREFORMS USED FOR STRUCTURAL COMPOSITES

The manufacturing of three-dimensional textile preforms used for composites started to re-ceive much attention in the last decade.The major barriers to accelerating the transition from thelamination of two-dimensional fabrics to manufacturing integral three-dimensional near-netshaped textile preforms are high cost and database deficiency.To reduce the cost of weaving three-dimensional preforms,and make full use of the potential of conventional looms,a rig was designedwhich can convert two-dimensional woven fabric to particular three-dimensional preforms wherethe yarn is orientated in the directions of maximum stress.

Shape/size controlling syntheses, properties and applications of two-dimensional noble metal nanocrystals

Two dimensional （2D） nanocrystals of noble metals （e.g., Au, Ag, Pt） often have unique structural and environmental properties which make them useful for applications in electronics, optics, sensors and biomedi- cines. In recent years, there has been a focus on discovering the fundamental mechanisms which govern the synthesis of the diverse geometries of these 2D metal nanocrystals （e.g., shapes, thickness, and lateral sizes）. This has resulted in being able to better control the properties of these 2D structures for specific applications. In this review, a brief historical survey of the intrinsic anisotropic properties and quantum size effects of 2D noble metal nanocrystals is given and then a summary of synthetic approaches to control their shapes and sizes is presented. The unique properties and fascinating applica- tions of these nanocrystals are also discussed.

Electrical contacts to two-dimensional transition-metal dichalcogenides

Two-dimensional(2D) transition-metal dichalcogenides(TMDCs) have attracted enormous interests as the novel channel materials for atomically thin transistors. Despite considerable progress in recent years, the transistor performance is largely limited by the excessive contact resistance at the source/drain interface. In this review, a summary of recent progress on improving electrical contact to TMDC transistors is presented. Several important strategies including topology of contacts, choice of metals and interface engineering are discussed.

Ab initio electronic transport study of two-dimensional silicon carbide-based p–n junctions

Two-dimensional silicon carbide（2d-SiC） is a viable material for next generation electronics due to its moderate,direct bandgap with huge potential.In particular,its potential for p–n junctions is yet to be explored.In this paper,three types of 2d-SiC-based p–n junctions with different doping configuration are modeled.The doping configurations refer to partially replacing carbon with boron or nitrogen atoms along the zigzag or armchair direction,respectively.By employing density functional theory,we calculate the transport properties of the SiC based p–n junctions and obtain negative differential resistance and high rectification ratio.We also find that the junction along the zigzag direction with lower doping density exhibits optimized rectification performance.Our study suggests that 2d-SiC is a promising candidate as a material platform for future nano-devices.

High-performance ultraviolet-visible photodetector with high sensitivity and fast response speed based on MoS_(2)-on-ZnO photogating heterojunction

Photogating is an effective strategy to modulate the channel conductance of the device with light-induced gate field or voltage,thereby improving the performance of optoelectronic devices.In this work,to overcome the long response time and low photoresponse of one-dimensional ZnO,a MoS_(2)-on-ZnO photogating vertical heterojunction photodetector is design and constructed.Herein,the ZnO nanowire with high carrier mobility can response ultraviolet light and supply a highspeed carrier transport channel,while the MoS_(2) flake as a photogating layer can response with visible light and transfer photogenerated electrons into the ZnO nanowire to adjust its conductivity.Thus,the irradiation of visible light is equivalent to applying a photo-induced gate voltage on the ZnO nanowire.In addition,the photogenerated electrons will not transmit through the MoS_(2) with low carrier mobility,so that not only the visible light response of the photodetector can be realized,but also its ultraviolet light response is able to be improved.Under ultraviolet light irradiation,the photoresponsivity of the photodetector can be reached to 273 A W-1and the response speed is less than 24 ms.More important,based on this unique heterojunction structure,MoS_(2)-on-ZnO photodetector also illustrates an excellent visible light response with a high photoresponsivity(74 A W-1) and fast response speed(<24 ms) due to the photogating effect.This work not only paves the way to design high-performance photodetectors with high photoresponsivity and fast response speed,but also provide a promising approach to improve the performance of optoelectronic devices using photogating effect.

Spatially-controlled porous nanoflake arrays derived from MOFs:An efficiently long-life oxygen electrode

The urge nt expectati on of the n ext-ge neratio n en ergy storage devices for electric vehicles has drive n researchers'atte ntion to the lithium-oxyge n(Li-O2)batteries due to the satisfied specific energy density.Herein,spatially-controlled CO3O4 nanoflake arrays with three-dimensional networked morphology are adopted as flexible and self-sta nding oxyge n cathodes in L1-O2 batteries.The spin el-phase CO3O4 nano flakes were con verted from two dimensi on metal-orga nic frameworks with abundant available cha nnels and large specific surface area.The open-structure nano flake arrays possess sufficie nt Li2O2/cathode contact interface,great bifunctional catalytic performa nee and adequate Li2O2 accommodation,leading to the enhanced electrochemical performance of the L1-O2 batteries.As expected,the binder-free porous CO3O4/CT cathode delivers a high capacity of 6,509 mAh·g^-1(200 mA·g^-1)and enhanced stability over 100 cycles(limited by 1,000 mAh·g^-1).In additi on,pouch-type Li-O2 batteries were successfully desig ned and cycled with CO3O4/CT cathode as oxyge n electrodes,dem on strating its potential application for flexible electronics and wearable energy storage devices.

超薄切片与剥离制备单层单晶二维量子点

二维(2D)原子级薄量子点(QDs)具有非凡的电学和光学性能.但是用于制备高质量2D量子点的通用、可靠技术仍然面临挑战.本文中,我们报道了一种简单的用超薄切片机垂直切割2D块体单晶,然后通过剥离来制备高质量单层单晶2D量子点的方法.所制备的2D量子点具有原始表面、高质量、高单层产率和高光致发光量子产率(WS2具有最高的光致发光量子产率18%).所制备的单层单晶二维量子点可作为一种有前途的低毒、生物相容性好、具有良好细胞通透性的荧光标记试剂.

Dimensionally confined nanosheets self-assembled through self-shielding multiple hydrogen bonding interactions in aqueous media

Herein,we adopt a simple supramolecular strategy to effectively control the tautomerism of ureidopyrimidinone(UPy)moiety and ultimately realize the complete arrangement of enol configuration.The obtained UPy derivatives containing self-complementary quadruple hydrogen bonding interactions can spontaneously self-assemble towards the formation of well-controlled,self-organized supramolecular nanostructure morphologies in both chloroform and water.The resulting aggregates had been fully characterized by various spectroscopy(absorption,emission)and microscopy(TEM,SEM and AFM)studies.It is anticipated that this study can provide an exact and excellent monomeric unit for controllable and precise supramolecular polymerization.The results achieved here also demonstrate the utility and feasibility of multiple hydrogen bonds to direct the self-assembly of small-molecule building blocks in aqueous media,which provides a strategy for the construction of well-defined and stable supramolecular architectures with chemical functionalities and physical properties as advanced materials for biological applications.

Analytical solutions for Earth discontinuous coverage of satellite constellation with repeating ground tracks

This paper presents an analytical model for calculating the Earth discontinuous coverage of satellite constellation with repeating ground tracks by integrating and extending the application of coverage region and route theory.Specifically,the visibility condition for a ground point is represented as a coverage region in the two-dimension map of visibility properties,and the trajectories of satellites with circular orbits and repeating ground tracks are converted to several inclined lines in the map.By analyzing the intersections of the lines and the edge of the coverage region,the coverage durations for the ground point can be calculated.Based on the point coverage,the variations of coverage characteristics along the parallel are analyzed,and the regional or global coverage characteristics of constellations can be obtained.Numerical examples show that the proposed method can accurately and rapidly calculate the coverage characteristics,e.g.revisit time and coverage time.The calculated results are extremely close to those of the Satellite Tool Kit(STK)and are also superior to the existing research results.The proposed analytical model can be a useful tool for constellation design and coverage performance analysis.

Picosecond electrical response in graphene/MoTe_(2) heterojunction with high responsivity in the near infrared region

Understanding the fundamental charge carrier dynamics is of great significance for photodetectors with both high speed and high responsivity.Devices based on two-dimensional(2D)transition metal dichalcogenides can exhibit picosecond photoresponse speed.However,2D materials naturally have low absorption,and when increasing thickness to gain higher responsivity,the response time usually slows to nanoseconds,limiting their photodetection performance.Here,by taking time-resolved photocurrent measurements,we demonstrated that graphene/MoTe_(2) van der Waals heterojunctions realize a fast 10 ps photoresponse time owing to the reduced average photocurrent drift time in the heterojunction,which is fundamentally distinct from traditional Dirac semimetal photodetectors such as graphene or Cd_(3)As_(2) and implies a photodetection bandwidth as wide as 100 GHz.Furthermore,we found that an additional charge carrier transport channel provided by graphene can ef-fectively decrease the photocurrent recombination loss to the entire device,preserving a high responsivity in the near-infrared region.Our study provides a deeper understanding of the ultrafast electrical response in van der Waals heterojunctions and offers a promising approach for the realization of photodetectors with both high responsivity and ultrafast electrical response.

Ultrasonographic evaluation of fetal facial anatomy (Ⅰ): ultrasonogr aphic features of normal fetal face in vitro study

Background Because of lacking skills in scanning the no rmal fetal facial structures and their corresponding ultrasonic features, misdia gnoses freguently occur. Therefore, we studied the appearance features and impro ved displaying skills of fetal facial anatomy in order to provide basis for prena tal diagnosis. Methods Twenty fetuses with normal facial anatomy from induced labor because of other malformations except facial anomalies were immersed in a water bath and then scanned ultrasonographically on coronal, sagittal and transverse planes to define the ultrasonic image features of normal anatomy. The coronal and sagittal planes obtained from the submandibular triangle were used for displaying the soft and hard palate in particular. Results Facial anatomic structures of the fetus can be clearly displayed through the three routine orthogonal planes. However, the soft and h ard palate can be displayed on the planes obtained from the submandibular triangle only. Conclusions The superficial soft tissues and deep bony structures of the fetal face can be recognized and evaluated by routine ultrasonographic images, which is a reliable prenatal diagnostic technique to evaluate the fetal facial anatomy. The soft and hard palate can be well demonstrated by the submandibular triangle approach.