排序方式: 共有24条查询结果,搜索用时 31 毫秒
1.
2.
Fera A Dolbnya IP Grubel G Muller HG Ostrovskii BI Shalaginov AN de Jeu WH 《Physical review letters》2000,85(11):2316-2319
Coherent dynamic x-ray scattering has been used to study the thermally excited layer fluctuations in freely suspended smectic films of the compound 4O.8. Using 8-keV x rays and films with a thickness around 0.3 &mgr;m we resolve relaxation times down to a few &mgr;s. A combination of damped and oscillatory behavior is observed for the layer undulations, which can be attributed to inertial effects. These are due to the surface contribution to the free energy which cannot be disregarded for thin films. 相似文献
3.
Perrotta RR Winter AH Coldren WH Falvey DE 《Journal of the American Chemical Society》2011,133(39):15553-15558
Calculations at the DFT level predict that benzyl anions with strong π-electron-withdrawing groups in the meta position(s) have low energy diradical or triplet electronic states. Specifically, the 2-(3,5-dinitrophenyl)-1,3-dithiane carbanion is predicted to have nearly degenerate singlet and triplet states at the (U)B3LYP level as a free anion. Its lithium ion pair is predicted to be a ground-state triplet with a substantial (26 kcal/mol) singlet-triplet energy gap. Experiments on this anion using chemical trapping, NMR, and the Evans method strongly suggest that this anion is either a triplet or a ground-state singlet with a very low energy triplet state. 相似文献
4.
Yu-Chia Chang Larry A. Coldren 《Applied Physics A: Materials Science & Processing》2009,95(4):1033-1037
High-efficiency, high-speed, tapered-oxide-apertured vertical-cavity surface-emitting lasers (VCSELs) emitting at 980 nm have
been demonstrated. By carefully engineering the tapered oxide aperture, the mode volume can be greatly reduced without adding
much optical scattering loss for the device sizes of interest. Consequently, these devices can achieve higher bandwidth at
lower current and power dissipation. In addition, the parasitics are reduced by implementing deep oxidation layers and an
improved p-doping scheme in the top mirror. Our devices show modulation bandwidth exceeding 20 GHz, a record for 980 nm VCSELs. Moreover,
35 Gb/s operation has been achieved at only 10 mW power dissipation. This corresponds to a data-rate/power-dissipation ratio
of 3.5 Gbps/mW. Most importantly, our device structure is compatible with existing manufacturing processes and can be easily
manufactured in large volume making them attractive for optical interconnects. 相似文献
5.
6.
An electrorefractive index-controllable guide/antiguide optical intensity modulator has been created and characterized. The operating mechanism, beam propagation method simulation, device design and fabrication, and calculated and experimental results of this guide/antiguide modulator are given. The operational principle of the modulator is based on the field-induced waveguide (FIG) concept; that is, electric-field-induced refractive index changes cause the waveguide to be turned on and off electrically. The modulator is formed with a central narrow FIG electrode sandwiched between two antiguide electrodes. The electrooptic effects, along with carrier effects, have been exploited to adjust the refractive index under the guide and adjacent antiguide electrodes by changing reverse biases applied to them. The modulation is determined mainly by changing the lateral refractive index profiles. In the on state, a waveguide is formed under the central electrode, and the input light propagates along this waveguide. To realize the best off state, an antiguide situation is created that causes the light to diffract out of the central guide rapidly. An on/off ratio larger than 23 dB, a propagation loss 1 dB, and a record optical bandwidth from 1.0 to 1.55 m have been obtained for this modulator. 相似文献
7.
van Eis MJ van Der Linde BS de Kanter FJ de Wolf WH Bickelhaupt F 《The Journal of organic chemistry》2000,65(14):4348-4354
In contrast to the terminal phosphinidene complex PhPW(CO)(5) (2), which adds to [5]metacyclophane (1) in a 1,4-fashion, dichlorocarbene preferentially adds in a 1,2-fashion to the formal "anti-Bredt" type double bond of the aromatic ring of 1 to afford the norcaradiene 11b, which immediately rearranges to the bridged cycloheptatriene 12b and further by a [1,5] sigmatropic chlorine migration to the isomeric 13b as the first observable product. More slowly, the latter isomerizes via a dissociative mechanism to give 15b. A computational study supports the notion that the [1,5] chlorine migration in the rearrangement 12b --> 13b, for which an activation barrier of 70.2 kJ mol(-)(1) was calculated, is essentially concerted with minor charge separation. In contrast, the analogous [1,5] chlorine migration in the flat model compound 7,7-dichlorocycloheptatriene (12a) displays features of a dissociative pathway. 相似文献
8.
We have measured the propagation velocities of bulk acoustic waves in the simple cubic transition-metal oxide ReO3 by ultrasonic pulse propagation. The elastic stiffness constants at 300 K are: C11 = (47.9 ± 1.4) × 1011 dyne/cm2; C44 = (6.1 ± 0.2) × 1011 dyne/cm2; C12 = (?0.7 ± 2.8) × 1011 dyne/cm2. These elastic constants indicate a crystal with highly anisotropic shear propagation. The Debye temperature of the compound from these measurements is 528 K. This value is somewhat higher than previous results from specific heat and resistivity determinations. 相似文献
9.
10.