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It is shown that by taking advantage of the maximum in the spectral dependence of the coupling coefficient, very broad-band symmetric and asymmetric single-mode planar couplers can be designed. The symmetric coupler allows at least 95.6% coupling between the two cores over the wavelength range 1.3–1.58 m, while the asymmetric coupler can act as a 3 dB splitter with only ±1.6% variation in the splitting ratio over the wavelength range 1.3–1.67 m. In both cases, the design includes the curved input-output arms, and the estimated bend loss is approximately 0.1 dB. 相似文献
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We review the important features of the right-angle X-junction diffraction model and discuss both its theoretical framework and its validity range. In addition, we present explicit new results from BPM calculations that show that the analytical model aptly describes the dominant physical processes involved and provides bounds on the numerical results. We also address some misinterpretations of the model that have recently appeared in the literature. 相似文献
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(±)-Dibromophakellin has been synthesized in two steps from a known alkene intermediate. The key step in the synthesis is the NBS olefin activation to facilitate the addition of a guanidine molecule across the double bond. 相似文献
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A new stereoselective version of the Schmidt reaction has been discovered by Aubé and co-workers (J. Am. Chem. Soc. 2003, 125, 7914-7922). Quantum chemical calculations reported in this paper were carried out to examine the observed diastereoselectivities. The azide attack step is found to be reversible, but a thermodynamic preference for the equatorial attack product is observed. The final stereoselectivity of the reaction is determined by the axial/equatorial ratio of the chiral substituent in the resulting intermediate. In the case of 2-R-hydroxypropyl azides, interesting axial/equatorial preferences are observed. In particular, the phenyl substituent shows a preference for the axial position resulting from a novel interaction with a N(2) cationic group. 相似文献
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Analysis of a TE011 mode composite sapphire-rutile dielectric resonator has been carried out to study the temperature variation of resonance
frequency, close to the Cs atomic clock hyperfine frequency of 9.192 GHz. The complementary behavior of dielectric permittivity
with temperature of the composite has been exploited to obtain the desired turning point in the resonant frequency. The frequency
of the composite structure is found to be independent of the shield diameter beyond four times the puck diameter. 相似文献
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Dr. Philipp Beck Theresa A. Lansdell Nicole M. Hewlett Prof. Dr. Jetze J. Tepe Prof. Dr. Michael Groll 《Angewandte Chemie (International ed. in English)》2015,54(9):2830-2833
The proteasome represents an invaluable target for the treatment of cancer and autoimmune disorders. The application of proteasome inhibitors, however, remains limited to blood cancers because their reactive headgroups and peptidic scaffolds convey unfavorable pharmacodynamic properties. Thus, the discovery of more drug‐like lead structures is indispensable. In this study, we present the first structure of the proteasome in complex with an indolo‐phakellin that exhibits a unique noncovalent binding mode unparalleled by all hitherto reported inhibitors. The natural product inspired pentacyclic alkaloid binds solely and specificially into the spacious S3 subpocket of the proteasomal β5 substrate binding channel, gaining major stabilization through halogen bonding with the protein backbone. The presented compound provides an ideal scaffold for the structure‐based design of subunit‐specific nonpeptidic proteasome‐blockers. 相似文献
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Nonlinear Dynamics - Gradient deficient beam elements (commonly known as cable elements in the literature) based on the absolute nodal coordinate formulation (ANCF) have great potential for... 相似文献
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We quantify the magnitude of the power loss incurred when a square-core buried channel waveguide (BCW) is spliced to a standard circular-core telecommunications fibre. With a view to minimizing the dissipated power, we show that a simple equal-core-area criterion provides an elegant means of determining the optimum core dimensions. This result is found to hold for more general BCW cross-sections that possess a reasonable degree of symmetry. The fundamental problems of waveguide misalignment and angular tilt are also investigated and their effect on splice loss is quantified. Our theoretical model is applied to both single- and twin-core waveguides. 相似文献