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排序方式: 共有1294条查询结果,搜索用时 15 毫秒
1.
Golam Haider Krishna Sampathkumar Tim Verhagen Lukáš Nádvorník Farjana J. Sonia Václav Valeš Jan Sýkora Peter Kapusta Petr Němec Martin Hof Otakar Frank Yang-Fang Chen Jana Vejpravová Martin Kalbáč 《Advanced functional materials》2021,31(29):2102196
Recent advancements in isolation and stacking of layered van der Waals materials have created an unprecedented paradigm for demonstrating varieties of 2D quantum materials. Rationally designed van der Waals heterostructures composed of monolayer transition-metal dichalcogenides (TMDs) and few-layer hBN show several unique optoelectronic features driven by correlations. However, entangled superradiant excitonic species in such systems have not been observed before. In this report, it is demonstrated that strong suppression of phonon population at low temperature results in a formation of a coherent excitonic-dipoles ensemble in the heterostructure, and the collective oscillation of those dipoles stimulates a robust phase synchronized ultra-narrow band superradiant emission even at extremely low pumping intensity. Such emitters are in high demand for a multitude of applications, including fundamental research on many-body correlations and other state-of-the-art technologies. This timely demonstration paves the way for further exploration of ultralow-threshold quantum-emitting devices with unmatched design freedom and spectral tunability. 相似文献
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Adnan Köksal 《Journal of Infrared, Millimeter and Terahertz Waves》1997,18(8):1525-1537
A parametric study of linearly tapered slot antenna (LTSA) in air and a method for optimization of its pattern are presented. A method of moments code is utilized to investigate the behavior of LTSA’s as the length, height and the taper angle varies. It is shown that the antenna pattern can be improved using a top layer of dielectric material with varying permittivity. 相似文献
5.
Efficient driving-capability programmable frequency divider with a wide division ratio range 总被引:1,自引:0,他引:1
A programmable frequency divider with close-to-50% output duty-cycle, with a wide division ratio range, is presented. The proposed divider has also provisions for binary division ratio controls, and has demonstrated operation at frequencies as high as 3.5 GHz. With the above features, the proposed divider can be used in phase-locked loops, and is capable of driving various clocked circuits, which need different clock frequencies. The proposed divider has division ratios from 8 to 510, but it can easily be extended to higher ranges by simply adding more divider stages. The divider circuit has been realised in a 0.18-mum RF CMOS process. Test results show that the output duty-cycle is 50% when the division ratio is an even number. For odd division ratios the worst-case duty-cycle is 44.4% when the division ratio is 9. The output duty-cycle becomes closer to 50% when the division ratio is an increasing odd number. For each division ratio, the output duty-cycle remains constant for different chips, with different input frequencies from gigahertz down to kilohertz ranges, and with different power supply voltages. 相似文献
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本文研究了无线局域网中使信号频谱得到优化的一种简单OFDM子载波加载算法。此算法基于边缘自适应(Margin Adaptive)加载准则及其在室内无线信道上的性能。 相似文献
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In this work we present the discrete models for dynamic fracture of structures built of brittle materials. The models construction is based on Voronoi cell representation of the heterogeneous structure, with the beam lattice network used to model the cohesive and compressive forces between the neighboring cells. Each lattice component is a geometrically exact shear deformable beam which can describe large rigid body motion and the most salient fracture mechanisms. The latter can be represented through the corresponding form of the beam constitutive equations, which are derived either at microscale with random distribution of material properties or at a mesoscale with average deterministic values. The proposed models are also placed within the framework of dynamics, where special attention is paid to constructing the lattice network mass matrix as well as the corresponding time-stepping schemes. Numerical simulations of compression and bending tests is given to illustrate the models performance. 相似文献
9.
Adnan Morshed 《Journal of Architectural Education》2002,55(4):201-210
The early twentieth-century invention of the airplane brought on a cultural euphoria that influenced the works and writings of urbanists, architects, artists, and science-fiction writers during the 1920s and 1930s. Le Corbusier's urban design for Rio de Janeiro—which he sketched, so he claimed, from an airplane—offers a visual basis to study how the aesthetic experience of flight was translated spatially, visually, and politically into his design of the future city. The polemics informing Le Corbusier's aerial "discovery" of South American geography revealed that there was a new empowerment in the act of looking from above, and that the spatial characteristics of his subsequent design interventions evoked that empowerment. 相似文献
10.
Adnan Ibrahimbegovi Franois Frey 《International journal for numerical methods in engineering》1994,37(21):3659-3683
A consistent formulation of the geometrically linear shell theory with drilling rotations is obtained by the consistent linearization of the geometrically non-linear shell theory considered in Parts I and II of this work. It was also shown that the same formulation can be recovered by linearizing the governing variational principle for the three-dimensional geometrically non-linear continuum with independent rotation field. In the finite element implementation of the presented shell theory, relying on the modified method of incompatible modes, we were able to construct a four-node shell element which delivers a very high-level performance. In order to simplify finite element implementation, a shallow reference configuration is assumed over each shell finite element. This approach does not impair the element performance for the present four-node element. The results obtained herein match those obtained with the state-of-the-art implementations based on the classical shell theory, over the complete set of standard benchmark problems. 相似文献