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Li CH Benedick AJ Fendel P Glenday AG Kärtner FX Phillips DF Sasselov D Szentgyorgyi A Walsworth RL 《Nature》2008,452(7187):610-612
Searches for extrasolar planets using the periodic Doppler shift of stellar spectral lines have recently achieved a precision of 60 cm s(-1) (ref. 1), which is sufficient to find a 5-Earth-mass planet in a Mercury-like orbit around a Sun-like star. To find a 1-Earth-mass planet in an Earth-like orbit, a precision of approximately 5 cm s(-1) is necessary. The combination of a laser frequency comb with a Fabry-Pérot filtering cavity has been suggested as a promising approach to achieve such Doppler shift resolution via improved spectrograph wavelength calibration, with recent encouraging results. Here we report the fabrication of such a filtered laser comb with up to 40-GHz (approximately 1-A) line spacing, generated from a 1-GHz repetition-rate source, without compromising long-term stability, reproducibility or spectral resolution. This wide-line-spacing comb, or 'astro-comb', is well matched to the resolving power of high-resolution astrophysical spectrographs. The astro-comb should allow a precision as high as 1 cm s(-1) in astronomical radial velocity measurements. 相似文献
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X. Wang C. A. Lessman D. B. Taylor T. K. Gartner 《Cellular and molecular life sciences : CMLS》1995,51(11):1097-1102
Gastrulation is characterized by dramatic cell migration which is thought to require the interaction of cell adhesion molecules with extracellular molecules. We have tested two novel peptides, a fibronectin peptide and a fibronectin receptor peptide, for their effects on gastrulation of the leopard frogRana pipiens. The fibronectin peptide DRVPHSRNSIT corresponds to residues 1373–1383 of the cell-binding domain of fibronectin; the receptor peptide DLYYLMDL corresponds to residues 124–131 of 1 subunit of a variety of integrins including 51. Either of these peptides significantly inhibited gastrulation after being microinjected into mid-blastulae. These results indicate that these sequences may correspond to the ligand/receptor interaction sites of fibronectin and its receptor(s). 相似文献
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合成了两个以含氮杂环芳基羧酸为配体的过渡金属配合物:[Mn(L)2(CH3OH)2(H2O)2](1)和[Co(L)2(H2O)4]·2H2O(2)(HL=4-(1-四氮唑基)苯甲酸),并采用.X-射线单晶衍射法测定了它们的晶体结构.分析结果表明,配合物1和2中的金属离子均采取八面体配位几何构型,但对相同配体的不同配位原子具有配位选择性:在1中,与Mn(Ⅰ)配位的是羧基上的氧原子,而在2中,与Co(Ⅱ)配位的是四氮唑基上的氮原子.另外,配合物1和2均通过分子间氢键作用将单核结构单元连接成三维超分子网络. 相似文献
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The dense interconnections that characterize neural networks are most readily implemented using optical signal processing. Optoelectronic 'neurons' fabricated from semiconducting materials can be connected by holographic images recorded in photorefractive crystals. Processes such as learning can be demonstrated using holographic optical neural networks. 相似文献
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无轴承同步电机旋转惯性振动抑制模型 总被引:1,自引:0,他引:1
给出无轴承电机的互感模型,据此导出了同步旋转惯性振动抑制力模型.该模型不仅适用于具有凸极型转子结构的无轴承同步电机,还适用于具有圆柱型转子结构的无轴承同步电机.给出同步旋转坐标系下的2极浮控4极无轴承电机的电感模型,据此导出适用于该种磁极配置无轴承电机的同步旋转惯性振动抑制力通用模型.仿真结果验证了所导出的旋转惯性振动抑制力模型的有效性. 相似文献
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贠超 《高技术通讯(英文版)》2009,15(4):388-393
We propose a novel vertical Bell Laboratories layered space-time (V-BLAST) based two-way relaying protocol that comprises two user terminals and one multi-antenna demodulate-and-forward (DMF) relay station. We consider the situation when these two user terminals employ different modulation types and investigate its detection techniques. The key feature of the detection techniques is that we quantify decision reliability at the relay station by introducing a so-called normalized correlation coefficient (CORR), rather than having full confidence in demodulation at the relay station. With the assistance of the normalized correlation coefficient, we develop detection methods at both the relay station and user terminals. In particular, we propose a CORR-based ordering algorithm at the relay station which can be applied to detection for general V-BLAST architectures. Simulation results demonstrate the superiority of the CORR-based ordering algorithm over the conventional signal-to-noise based ordering algorithm. Finally, we demonstrate overall error-performance of the V-BLAST-based DMF two-way relaying protocol via simulations. 相似文献