检索结果-南通市图书馆

Modulators for Terahertz Communication: The Current State of the Art

在线全文

学校读者我要写书评

暂无评论

Research 2019年第1期2019卷 895-916页

作者： z.T.Ma z.x.Geng z.Y.Fan J.Liu H.D.Chen College of Science Minzu University of ChinaBeijing 100081China School of Information Engineering Minzu University of ChinaBeijing 100081China State Key Laboratory for Integrated Optoelectronics Institute of SemiconductorsChinese Academy of SciencesBeijing 100083China State Key Laboratory of Superlattices and Microstructures Institute of SemiconductorsChinese Academy of SciencesBeijing 100083China

With the increase of communication frequency,terahertz(THz)communication technology has been an important research feld;particularly the terahertz modulator is becoming one of the core devices in THz communication *** modulation performance of a THz communication system depends on the characterization of THz *** modulators based on diferent principles and materials have been studied and ***,they are still on the way to practical application due to low modulation speed,narrow bandwidth,and insufcient modulation ***,we review the research progress of THz modulator in recent years and evaluate devices critically and *** focus on the working principles such as electric,optical,optoelectrical,thermal,magnetic,programmable metamaterials and nonlinear modulation methods for THz wave with semiconductors,metamaterials,and 2D materials(such as graphene,molybdenum disulfde,and tungsten disulfde).Furthermore,we propose a guiding rule to select appropriate materials and modulation methods for specifc applications in THz communication.

关键词： modulator communication narrow

Room-temperature ferroelectricity in A-site ordered Ruddlesden-Popper Li_(2)CaTa_(2)O_(7) ceramics

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Materiomics 2020年第3期6卷 593-599页

作者： B.H.zhang z.z.Hu B.H.Chen x.Q.Liu x.M.Chen Laboratory of Dielectric Materials School of Materials Science and EngineeringZhejiang UniversityNo.38 Zheda RoadHangzhou310027China

In the present work,the crystal structure,ferroelectric and dielectric properties of the dense single-phase Li_(2)CaTa_(2)O_(7) ceramics with A-site ordered double-layer Ruddlesden-Popper structures have been investigated by the experiments and first-principles calculations.A polar Pna21 phase was determined by the Rietveld refinement against the x-ray diffraction pattern at room temperature,and it was confirmed by its lowest calculated energy and rigid phonon *** ferroelectricity was found by observing the ferroelectric hysteresis loop at room temperature,and its remanent polarization was similar to the value calculated from the Berry phase and Born effective charge *** ferroelectricity is a nonconventional proper one since its polarization is induced from the displacement of oxygen anions instead of tantalum cations based on the individual atomic polarization.A first-order transition from an antiferroelectric to paraelectric phase around 900 K was found by the DSC and variable-temperature dielectric *** the present work,the room-temperature ferroelectricity is experimental confirmed in the present ceramics,inspiring the search for new ferroelectricity in the ceramics with A-site ordered Ruddlesden-Popper structures.

关键词： Ferroelectricity A-site ordered ruddlesden-popper Dielectric response First-principles calculation

BRIGHT LONG AFTERGLOW PHOSPHORESCENCE GLASS MADE OF SrAl_(2)O_(4): Eu^(2+), Dy^(3+) AND GLASS FRITS

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Acta Metallurgica Sinica(English Letters) 2005年第6期18卷 736-740页

作者： x. Y. zhang z. F. Cao L.P. Lu z.H. Bai W.z. Wang x. C. Wang Department of Materials Science and Engineering Changchun University of Science and Technology Changchun 130022 China

Bright long afterglow phosphorescence glasses were prepared by using SrAl2O4： Eu^2＋, Dy^3＋ phosphors and suitable glass frits together. The SrAl2O4： Eu^2＋, Dy^3＋ phosphors were initially prepared by the solid reaction method. Three kinds of glass frits were prepared to match the SrAl2O4： Eu^2＋, Dy^3＋ phosphors. Effects of the compositions of the glass frits, the ratios of the phosphors to the frits us well us the firing temperature and firing times on the properties of the samples were discussed. xRD analysis indicated the samples exhibited the typical diffraction peaks of SrAlwO4： Eu^2＋, Dy^3＋. The emission spectra of the samples showed broad bands peaking at *** excitation spectra of the samples showed broad bands ranging from 300 to 480hm. These are believed due to the 5d4f-4f transitions of Eu^2＋ in the SrAl2O4： Eu^2＋, Dy^3＋ phosphors. The afterglow luminescence of the samples excited by a 40W fluorescence lamp for 30min can be observed in the dark for more lOh with the naked eyes. It can find wide applications in many fields.

关键词： long afterglow phosphorescence glass StAl2O4 :Eu^2+ Dy^3+,glass frit

Calculation of transient dynamic stress intensity factors at bimaterial interface cracks using a SBFEM-based frequency-domain approach

在线全文

学校读者我要写书评

暂无评论

Science China(Physics,Mechanics & Astronomy) 2008年第5期51卷 519-531页

作者： z.J.yang A.J.DEEKS College of Civil Engineering and Architecture Zhejiang University School of Civil and Resource Engineering University of Western Australia

A frequency-domain approach based on the semi-analytical scaled boundary finite element method(SBFEM) was developed to calculate dynamic stress intensity factors(DSIFs) at bimaterial interface cracks subjected to transient ***-cause the stress solutions of the SBFEM in the frequency domain are analytical in the radial direction,and the complex stress singularity at the bimaterial interface crack tip is explicitly represented in the stress solutions,the mixed-mode DSIFs were calculated directly by *** complex frequency-response functions of DSIFs were then used by the fast Fourier transform(FFT) and the inverse FFT to calculate time histories of DSIFs.A benchmark example was *** re-sults were obtained by modelling the example with a small number of degrees of freedom due to the semi-analytical nature of the SBFEM.

关键词： scaled boundary finite element method bimaterial interface crack frequency domain dynamic stress intensity factors fast Fourier transform

Finite element simulations on the mechanical properties of MHS materials

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 2007年第1期23卷 65-75页

作者： z. Y. Gao T. x. Yu D. Karagiozova Department of Mechanical Engineering Hong Kong University of Science &Technology Clear Water Bay Kowloon Hong Kong China Institute of Mechanics Bulgarian Academy of Sciences Acad. G. Bonchev Street Block 4 Sofia 1113 Bulgaria

Finite element simulations are carried out to examine the mechanical behavior of the metallic hollow sphere （MHS） material during their large plastic deformation and to estimate the energy absorbing capacity of these materials under uniaxial compression. A simplified model is proposed from experimental observations to describe the connection between the neighboring spheres, which greatly improves the computation efficiency. The effects of the governing physical and geometrical parameters are evaluated; whilst a special attention is paid to the plateau stress, which is directly related to the energy absorbing capacity. Finally, the empirical functions of the relative material density are proposed for the elastic modulus, yield strength and plateau stress for FCC packing arrangement of hollow spheres, showing a good agreement with the experimental results obtained in our previous study.

关键词： Cellular material Hollow sphere Large plastic deformation Numerical simulation FEM

NEW VIEW ABOUT BAINITIC TRANSFORMATION IN STEEL

在线全文

学校读者我要写书评

暂无评论

Acta Metallurgica Sinica(English Letters) 1999年第3期12卷 229-234页

作者： Liu, C.C. Liu, z. Chen, G.x. Tsinghua Univ Beijing China

The bainitic transformation was analyzed according to the factors such as morphology, crystallography, mechanical property of bainite and transformation kinetics. It was found that the bainitic transformation is controlled by displacive mechanism and self-tempering of displacive microstructure, i.e. bainite is the product of such procedure during which undercooled austenite first transforms into one certain displacive microstructure by displacive mechanism and then this microstructure experiences self-tempering. With this idea, several questions that can not be illustrated only by displacive transformation mechanism can be explained successfully.

关键词： Bainite Morphology Steel

Stability analysis of the simplest Takagi-Sugeno fuzzy control system using circle criterion

在线全文

学校读者我要写书评

暂无评论

Journal of Systems Engineering and Electronics 2007年第2期18卷 311-319页

作者： Lu Hongqian Huang xianlin Gao x. z. Ban xiaojun Yin Hang Dept. of Control Theory and Engineering Harbin Inst. of Technology Harbin 150001 P. R. China Inst. of Intelligent Power Electronics Helsinki Univ. of Technology Espoo Finland

A frequency-domain-based sufficient condition is derived to guarantee the globally asymptotic stability of the simplest Takagi-Sugeno （T-S） fuzzy control system by using the circle criterion. The analysis is performed in the frequency domain, and hence the condition is of great significance when the frequency-response method, which is widely used in the linear control theory and practice, is employed to synthesize the simplest T-S fuzzy controller. Besides, this sufficient condition is featured by a graphical interpretation, which makes the condition straightforward to be used. Comparisons are drawn between the performance of the simplest T-S fuzzy controller and that of the linear compensator. Two numerical examples are presented to demonstrate how this sufficient condition can be applied to both stable and unstable plants.

关键词： T-S fuzzy controller, Stability analysis Circle criterion Frequency response method.

Dynamic Behavior of Bubble Interface During Boiling

在线全文

学校读者我要写书评

暂无评论

Journal of Thermal Science 2002年第4期11卷 308-319页

作者： x.F.Peng z.Wang D.J.Lee Department of Thermal Engineering Tsinghua UniversityDepartment of Thermal Engineering Tsinghua UniversityDepartment of Chemical Engineering Taiwan University Beijing 100084 China Beijing 100084 China Taipei 106 China

A brief review with discussions is conducted for some pertinent works, done and ongoing in the Laboratory of Phase-Change and Interfacial Phenomena at Tsinghua University, on interfacial behavior of vapor bubbles and interfacial transport phenomena during liquid nucleation boiling. From a sequence of experimental investigations, some new phenomena, particularly, the visually observed interfacial transport phenomena or processes including jet-like flows, bubble interaction and spatial scale effect, were described in this article. The interfacial effects and transport phenomena associated with surface tension gradients caused by temperature and concentration variations were theoretically analyzed to reveal the marked influence on bubble interfacial shape and dynamic behavior, the bubble dynamics including nucleation, bubble motion and coalescence. Several theoretical models and methods were proposed to describe the dynamic characteristics and explain the physics of interfacial phenomena/processes. The

关键词： boiling interfacial phenomena transport process phase change bubble.

Modified spherical cavity-expansion model for projectile penetration into concrete targets

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 2019年第3期35卷 518-534页

作者： Y.Peng H.Wu Q.Fang x.z.Kong College of Liberal Arts and Sciences National University of Defense TechnologyChangsha 410073China Key Laboratory of Performance Evolution and Control for Engineering Structures Tongji UniversityShanghai 200092China Research Institute of Structural Engineering and Disaster Reduction College of Civil EngineeringTongji UniversityShanghai 200092China State Key Laboratory for Disaster Prevention and Mitigation of Explosion and Impact PLA Amy Engineering UniversityNanjing 210007China

A modified spherical cavity-expansion model is developed in this paper.(1) We introduce a piecewise hyperbolic yield criterion suitable for pressure less than fc/3 to describe the mechanical behavior in the elastic region for the elastic-plastic response and modify the crack occurrence condition for the elastic-cracked-plastic response.(2) The hyperbolic yield criterion and a piecewise equation of state (EOS) are adopted for a better description of the plastic behavior of concrete material. Then, the modified model is validated by several projectile penetration tests in both the normal strength concrete (NSC) and ultra-high performance cement-based composite (UHPCC) targets. Finally, the hydrostatic pressure of the targets under rigid ogive-nosed projectile penetrations is found to be nearly within (0, 1.6 GPa), which usually exceeds the range that the shear strength-pressure test data covered. The influence of yield criterion on depth of penetration is discussed and it is recommended that the pressure should arrive at least 400 MPa in the related triaxial compression tests.

关键词： Dynamic cavity-expansion model Projectile Penetration Concrete Depth of penetration