排序方式: 共有49条查询结果,搜索用时 15 毫秒
41.
C. R. Davidson D. G. Foursa A. Lucero O. Sinkin W. Patterson A. Pilipetskii G. Mohs Neal S. Bergano 《中国光学快报(英文版)》2010,(9):831-836
We provide a review of our recent 100-Gb/s, high spectral efficiency (SE) experiment targeting transoceanic and regional undersea transmission distances. We demonstrated that simple pre-filtering at the transmitter together with a maximum a posteriori probability (MAP) detection algorithm can significantly improve SE. We transmitted 96×100-Gb/s pre-filtered polarization division multiplexed return-to-zero quadrature phase shift keyed (PDM-RZ-QPSK) channels with 300% SE over 10608 km using 52-km spans of 150-μm 2 fiber and simple single-stage erbium-doped fiber amplifiers (EDFAs). We also achieved 400% SE over 4368 km using similar techniques. 相似文献
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We have performed a series of neutron diffraction experiments from the magnetic order and the vortex lattice in single crystal
ErNi2B2C. The incommensurate magnetic structure develops additional even harmonics below the ‘ferromagnetic’ ordering temperature,
T
F of 2.3 K. This feature and the existence of rods of diffuse scattering suggest the development of ferromagnetic microdomain
walls. The magnetic structure is very sensitive to the application of a magnetic field with changes in modulation vector and
harmonic content. Studies of the vortex lattice show the presence of a 45° reorientation transition and a distorted hexagonal
to square transition as a function of applied field. Further distortions of the vortex lattice occur at T
N, but no changes are seen at T
F. 相似文献
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46.
Robert A. Mosey 《Tetrahedron letters》2009,50(3):295-3213
We report herein a racemic key intermediate in the synthesis of salinosporamide A via a tert-alkyl amino hydroxy carboxylic ester produced in an ene-type reaction of an oxazolone with an enol ether. 相似文献
47.
van Der Lee AM van Druten NJ van Exter MP Woerdman JP Poizat JP Grangier P 《Physical review letters》2000,85(22):4711-4714
We investigate the impact of the Petermann-excess-noise factor K>/=1 on the possibility of intensity noise squeezing of laser light below the standard quantum limit. Using an N-mode model, we show that squeezing is limited to a floor level of 2(K-1) times the shot noise limit. Thus, even a modest Petermann factor significantly impedes squeezing, which becomes impossible when K>/=1.5. This appears as a serious limitation for obtaining sub-shot-noise light from practical semiconductor lasers. We present experimental evidence for our theory. 相似文献
48.
Conventional density functional theory (DFT) fails for strongly correlated electron systems due to large intra-atomic self-interaction errors. The DFT+U method provides a means of overcoming these errors through the use of a parametrized potential that employs an exact treatment of quantum mechanical exchange interactions. The parameters that enter into this potential correspond to the spherically averaged intra-atomic Coulomb (U) and exchange (J) interactions. Recently, we developed an ab initio approach for evaluating these parameters on the basis of unrestricted Hartree-Fock (UHF) theory, which has the advantage of being free of self-interaction errors and does not require experimental input [Mosey and Carter, Phys. Rev. B 76, 155123 (2007)]. In this work, we build on that method to develop a more robust and convenient ab initio approach for evaluating U and J. The new technique employs a relationship between U and J and the Coulomb and exchange integrals evaluated using the entire set of UHF molecular orbitals (MOs) for the system. Employing the entire set of UHF MOs renders the method rotationally invariant and eliminates the difficulty in selecting unambiguously the MOs that correspond to localized states. These aspects overcome two significant deficiencies of our earlier method. The new technique is used to evaluate U and J for Cr(2)O(3), FeO, and Fe(2)O(3). The resulting values of U-J are close to empirical estimates of this quantity for each of these materials and are also similar to results of constrained DFT calculations. DFT+U calculations using the ab initio parameters yield results that are in good agreement with experiment. As such, this method offers a means of performing accurate and fully predictive DFT+U calculations of strongly correlated electron materials. 相似文献
49.
Christopher I. Maxwell C. Tony Liu Alexei A. Neverov Nicholas J. Mosey Robert Stan Brown 《Journal of Physical Organic Chemistry》2012,25(5):437-449
The base‐promoted solvolysis of a series of O,O‐dimethyl O‐aryl and O,O‐dimethyl O‐alkyl phosphorothioates (1) as well as O,O‐dimethyl O‐aryl and O,O‐dimethyl O‐alkyl phosphates (2) was studied computationally by density functional theory methods in methanol and water continuum media to determine the transition between concerted and stepwise processes. In addition, an experimental study was undertaken on the solvolysis of these series in basic methanol and water. The computations indicate that the solvolytic mechanism for series 1 involves lyoxide attack anti to the leaving group in a concerted manner with good leaving groups having pKaLg values < 12.3 in methanol and in a stepwise fashion with the formation of a 5‐coordinate thiophosphorane intermediate when the pKaLg > 12.3. A similar transition from concerted to stepwise mechanism occurs with series 2 in methanol as well as with series 1 and 2 in water, although for the aqueous solvolyses with hydroxide nucleophile, the transitions between concerted and stepwise mechanisms occur with better leaving groups than in the case in methanol. The computational data allow the construction of Brønsted plots of log k2?OS versus pKaLg in methanol and water, which are compared with the experimental Brønsted plots determined with these series previously and with new data determined in this work. Both the computational and experimental Brønsted data reveal discontinuities in the plots between substrates bearing O‐aryl and O‐alkyl leaving groups, with the gradients of the plots being far steeper than, and non‐collinear with, the O‐aryl leaving groups for solvolysis of the O‐alkyl‐containing substrates. These discontinuities signify that care should be exercised in interpreting breaks in Brønsted plots in terms of changes in rate‐limiting steps that signify the formation of an intermediate during a solvolytic process. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献