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排序方式: 共有267条查询结果,搜索用时 15 毫秒
101.
Yuyi Feng Paul Kim Clayton A. Nemitz Kwang-Dae Kim Yoonseok Park Karl Leo James Dorman Jonas Weickert Yongtian Wang Lukas Schmidt-Mende 《自然科学进展(英文版)》2019,29(2):124-128
Hybrid nanostructures, comprising of a metal core and a semiconductor shell layer, show great potential for a new generation of low-cost solar cells due to their unique electronic and optical properties. However, experimental results have fallen far short of the ultra-high efficiency(i.e. beyond Shockley-Queisser limit) predicted by theoretical simulations. This limits the commercial application of these materials. Here, a non-transparent organic solar cell with an array of Ag/ZnO nanowires has been experimentally fabricated to increase the internal quantum efficiency(IQE) by a factor of 2.5 compared to a planar counterpart. This result indicates a significant enhancement of charge collection efficiency due to the ultrafast Ag nanowire channels. This hybrid nanostructure can also serve as a perfect back reflector for semi-transparent solar cells, which can result in enhanced light absorption by a factor of 1.8 compared to the reference samples. The enhanced charge collection and light absorption can make these Ag/ZnO nanostructures available for the application of modern optoelectronic devices. 相似文献
102.
Wei-li Cheng Zhong-ping Que Jin-shan Zhang Chun-xiang Xu Wei Liang Bong Sun You Sung Soo Park 《矿物冶金与材料学报》2013,20(1):49-56
The medium and warm deformation behaviors of an indirect-extruded Mg-8Sn-1Al-1Zn alloy were investigated by compression tests at temperatures between 298 and 523 K and strain rates of 0.001–10 s?1. It was found that the twinning-slip transition temperature was strain rate dependent, and all the true stress-true strain curves could be divided into two groups: concave and convex curves. Associated microstructural investigations indicated that the dynamic recrystallization (DRX) behavior of the alloy varied with deformation conditions. At high strain rate and low temperature, dynamically recrystallized grains preferentially nucleated and developed in the twinned regions, indicating that twinning-induced DRX was dominant. While, at low strain rate, DRX developed extensively at grain boundaries and twins, and the process of twinning contributed to both oriented nucleation and selective growth. For the studied alloy, cracks mainly initiated from the shear band and twinning lamellar over the ranges of temperature and strain rate currently applied. 相似文献
103.
P Wei WW Wong JS Park EE Corcoran SG Peisajovich JJ Onuffer A Weiss WA Lim 《Nature》2012,488(7411):384-388
Bacterial pathogens have evolved specific effector proteins that, by interfacing with host kinase signalling pathways, provide a mechanism to evade immune responses during infection. Although these effectors contribute to pathogen virulence, we realized that they might also serve as valuable synthetic biology reagents for engineering cellular behaviour. Here we exploit two effector proteins, the Shigella flexneri OspF protein and Yersinia pestis YopH protein, to rewire kinase-mediated responses systematically both in yeast and mammalian immune cells. Bacterial effector proteins can be directed to inhibit specific mitogen-activated protein kinase pathways selectively in yeast by artificially targeting them to pathway-specific complexes. Moreover, we show that unique properties of the effectors generate new pathway behaviours: OspF, which irreversibly inactivates mitogen-activated protein kinases, was used to construct a synthetic feedback circuit that shows novel frequency-dependent input filtering. Finally, we show that effectors can be used in T cells, either as feedback modulators to tune the T-cell response amplitude precisely, or as an inducible pause switch that can temporarily disable T-cell activation. These studies demonstrate how pathogens could provide a rich toolkit of parts to engineer cells for therapeutic or biotechnological applications. 相似文献
104.
Crack formation drives material failure and is often regarded as a process to be avoided. However, closer examination of cracking phenomena has revealed exquisitely intricate patterns such as spirals, oscillating and branched fracture paths and fractal geometries. Here we demonstrate the controlled initiation, propagation and termination of a variety of channelled crack patterns in a film/substrate system comprising a silicon nitride thin film deposited on a silicon substrate using low-pressure chemical vapour deposition. Micro-notches etched into the silicon substrate concentrated stress for crack initiation, which occurred spontaneously during deposition of the silicon nitride layer. We reproducibly created three distinct crack morphologies--straight, oscillatory and orderly bifurcated (stitchlike)--through careful selection of processing conditions and parameters. We induced direction changes by changing the system parameters, and we terminated propagation at pre-formed multi-step crack stops. We believe that our patterning technique presents new opportunities in nanofabrication and offers a starting point for atomic-scale pattern formation, which would be difficult even with current state-of-the-art nanofabrication methodologies. 相似文献
105.
科氏力对高速旋转汽轮机叶片动态特性的影响 总被引:4,自引:1,他引:4
采用解析的方法,建立了高速旋转汽轮机叶片中科氏力和科氏动应力的计算模型。该模型克服了以往在叶片动态特性分析时难以考虑科氏力影响的问题,导出了科氏动应力和非稳态气流动应力比值的计算公式以及科氏力和离心力比值的计算公式,并进行了实例分析.计算结果表明,科氏力对叶片轴向振动和扭转振动的固有频率没有影响,对切向振动的影响很小,可以忽略不计;科氏力所产生的动应力不到非稳态气流动应力的1%。 相似文献
106.
Coherent quantum state storage and transfer between two phase qubits via a resonant cavity 总被引:1,自引:0,他引:1
As with classical information processing, a quantum information processor requires bits (qubits) that can be independently addressed and read out, long-term memory elements to store arbitrary quantum states, and the ability to transfer quantum information through a coherent communication bus accessible to a large number of qubits. Superconducting qubits made with scalable microfabrication techniques are a promising candidate for the realization of a large-scale quantum information processor. Although these systems have successfully passed tests of coherent coupling for up to four qubits, communication of individual quantum states between superconducting qubits via a quantum bus has not yet been realized. Here, we perform an experiment demonstrating the ability to coherently transfer quantum states between two superconducting Josephson phase qubits through a quantum bus. This quantum bus is a resonant cavity formed by an open-ended superconducting transmission line of length 7 mm. After preparing an initial quantum state with the first qubit, this quantum information is transferred and stored as a nonclassical photon state of the resonant cavity, then retrieved later by the second qubit connected to the opposite end of the cavity. Beyond simple state transfer, these results suggest that a high-quality-factor superconducting cavity could also function as a useful short-term memory element. The basic architecture presented here can be expanded, offering the possibility for the coherent interaction of a large number of superconducting qubits. 相似文献
107.
108.
Choi Il-heung Oh Sang-heon Choi Dae-soo Park Chan-sik Hwang Dong-hwan Lee Sang-jeong 《武汉大学学报:自然科学英文版》2003,8(2):725-730
This paper proposed a design and implementation procedure of the Time Synchronization Module (TSM) for the Automatic Identification System (AIS). The proposed TSM module uses a Temperature Compensated Crystal Oscillator (TCXO) as a local reference clock, and consists of a Digitally Controlled Oscillator (DCO), a divider, a phase discriminator, and register blocks. The TSM measures time difference between the 1 PPS from the Global Navigation Satellite System (GNSS) receiver and the generated transmitter clock. The measured time difference is compensated by controlling the DCO and the transmit clock is synchronized to the Universal Time Coordinated (UTC). The designed TSM can also be synchronized to the reference time derived from the received message. The proposed module is tested using the experimental AIS transponder set. The experimental results show that the proposed module satisfies the functional and timing specification of the AIS technical standard, ITU-R M.1371. 相似文献
109.
R. G. MacDonald R. H. McCusker D. J. Blackwood J. A. Vanderhoof J. H. Y. Park 《Cellular and molecular life sciences : CMLS》1998,54(2):158-166
To determine if intestinal stromal cells secrete diffusible factors such as insulin-like growth factors (IGFs) capable of
regulating epithelial cell growth in vitro, stromal cells were isolated by enzymatic digestion of rat intestine. Incorporation
of [3H]thymidine into DNA and [14C]leucine into protein of IEC-6 cells, a model intestinal epithelial cell line, was significantly increased (two- to threefold)
when the IEC-6 cells were co-cultured with stromal cells, relative to IEC-6 cells grown alone. Medium conditioned by stromal
cells stimulated DNA synthesis of IEC-6 cells in a dose-dependent manner. Analysis of the conditioned medium revealed that
intestinal stromal cells secreted IGF-I, but little IGF-II, in addition to an M
r 32,000 IGF-binding protein (IGFBP-2) and an IGFBP having M
r∼ 24,000. We conclude that rat intestinal stromal cells secrete one or more diffusible factors, which may include IGF-I and
IGFBPs, capable of stimulating proliferation of IEC-6 cells in vitro.
Received 25 August 1997; received after revision 7 November 1997; accepted 20 November 1997 相似文献
110.
Lee S Pirogov A Kang M Jang KH Yonemura M Kamiyama T Cheong SW Gozzo F Shin N Kimura H Noda Y Park JG 《Nature》2008,451(7180):805-808
The motion of atoms in a solid always responds to cooling or heating in a way that is consistent with the symmetry of the given space group of the solid to which they belong. When the atoms move, the electronic structure of the solid changes, leading to different physical properties. Therefore, the determination of where atoms are and what atoms do is a cornerstone of modern solid-state physics. However, experimental observations of atomic displacements measured as a function of temperature are very rare, because those displacements are, in almost all cases, exceedingly small. Here we show, using a combination of diffraction techniques, that the hexagonal manganites RMnO3 (where R is a rare-earth element) undergo an isostructural transition with exceptionally large atomic displacements: two orders of magnitude larger than those seen in any other magnetic material, resulting in an unusually strong magneto-elastic coupling. We follow the exact atomic displacements of all the atoms in the unit cell as a function of temperature and find consistency with theoretical predictions based on group theories. We argue that this gigantic magneto-elastic coupling in RMnO3 holds the key to the recently observed magneto-electric phenomenon in this intriguing class of materials. 相似文献