A polarization-independent optical directional coupler based on slot waveguides is proposed and analyzed by using rigorous full-vectorial analysis methods based on a finite-element scheme. Properly choosing materials and structural parameters makes the coupling length for quasi-TE modes become equal to that for quasi-TM modes. Tolerances to operating wavelength and structural parameters are also discussed. The proposed coupler can be used for highly integrated optical circuits without polarization diversity schemes. 相似文献
The near-field structure of strongly buoyant jet issuing from a square nozzle at low Froude and Reynolds numbers is studied
by using LIF flow visualization and time-resolved scanning PIV. These experimental techniques allow the visualization of unsteady
three-dimensional flow phenomenon occurring in the near-field of strongly buoyant jet. It is found that the buoyant jet is
unstable to the positive buoyancy forces, which promote the inflow motion near the nozzle exit. The surrounding low temperature
fluid moves into the nozzle inside along the nozzle corner and mixes with the high temperature fluid deep into the nozzle.
Then, the flow pattern inside the nozzle becomes highly complex to promote the laminar to turbulent transition of the jet.
The statistical flow characteristics of the strongly buoyant jet are evaluated from the scanning PIV measurement, and the
result indicates the presence of axisymmetric distributions of mean flow and velocity fluctuations in the circle of diameter
equal to the square side of the nozzle. 相似文献
In this paper, a new experimental technique for generating anaglyph stereo images for three-dimensional visualization of sculpture
arts is proposed. The images are taken at fixed distance using the imaging system consisting of single CCD camera and turntable.
This system allows generation of stereo images at variable distances from the target object. The feasibility study of this
technique is demonstrated by showing some anaglyph stereo images of a sculpture art. 相似文献
Recent reports [Jara‐Toro et al., Angew. Chem. Int. Ed. 2017 , 56, 2166 and PCCP 2018 , 20, 27885] suggest that the rate coefficient of OH reactions with alcohols would increase by up to two times in going from dry to high humidity. This finding would have an impact on the budget of alcohols in the atmosphere and it may explain differences in measured and modeled methanol concentrations. The results were based on a relative technique carried out in a small Teflon bag, which might suffer from wall reactions. The effect was reinvestigated using a direct fluorescence probe of OH radicals, and no catalytic effect of H2O could be found. Experiments in a Teflon bag were also carried out, but the results of Jara‐Toro et al. were not reproducible. Further theoretical calculations show that the water‐mediated reactions have negligible rates compared to the bare reaction and that even though water molecules can lower the barriers of reactions, they cannot make up for the entropy cost. 相似文献
Summary: Isothermal crystallization of an oriented blend of isotactic polystyrene (iPS) with poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) was studied by in situ polarized FT‐IR spectroscopy and wide‐angle X‐ray diffraction. The structural organization during the oriented crystallization consists of three stages. The first stage is the orientation relaxation of molecular chains of iPS and PPO, the degree of orientation of iPS increases in the second stage, and the oriented chains of iPS crystallize in the third stage.
The aerodynamic noise and the wake flow field in a cooling fan under actual operating conditions are studied with and without
winglets on the fan blades. In order to understand the influence of the winglet, the aerodynamic noise and the wake velocity
distribution are measured. The results indicated that overall noise level decreased and the noise spectrum was changed in
a low frequency range when the winglet was installed. It was found from the flow visualization and PIV measurement that the
influence of the winglet appeared in the traces of the tip vortices and the magnitude of vorticity was reduced in the near
wake region, which suggest the observed reduction in aerodynamic noise 相似文献
A notion of morphism of semi-stable type is a higher dimensional analogue of semi-stable degeneration over the unit disc.
For a proper surjective morphism of semi-stable type, the author constructed a cohomological mixed Hodge complex which gives
a candidate of the limit of Hodge structures. In this article we define finite increasing filtrations on the cohomological
mixed Hodge complex above and prove the E2-degeneracy of the spectral sequences obtained from these filtrations.
Received: 5 December 2000 / Revised version: 29 January 2002 相似文献
Iron-nickel ultrafine particles with a composition in the Invar region (38–50% Ni) were prepared by the gas-evaporation-coalescence technique. The chemical composition was checked by electronprobe microanalysis, while X-ray diffraction Rietveld refinement was used to characterize the structure as well as to estimate the particle size. The temperature and field dependence of the magnetizationM(B, T) was measured for 0B25 kOe in the temperature range 4.2 KT400 K. Transmission Mössbauer spectra were taken at room temperature and at liquid helium temperature. The results obtained show that the predominant phase is a disordered Ni-rich alloy.On leave from Physics Department, University of Khartoum, P.O. Box 321, Khartoum, Sudan. 相似文献
To gain insight on the absorption intensities, as well as the direction of the transition moment for the OH stretching vibration in alcohols and acids, we performed detailed analyses for nitric acid, acetic acid, methanol, tert-butyl alcohol, water, and OH radical. We obtained both the potential energy surface and the dipole moment function (DMF) by the B3LYP method and performed quantum mechanical vibrational calculation using the grid variational method based on the local mode model. In this work, we employed the sum rule of the absorption intensities for the one-dimensional (1-D) vibrational Hamiltonian to construct an effective 1-D DMF, which is responsible for the total sum of the overtone intensities. The direction of this effective DMF was found to be tilted away from the OH bond by about 30 degrees for the polyatomic molecules. The nonlinearity of the DMFs in the directions parallel and perpendicular to the OH bond is discussed to rationalize the tilting. Furthermore, we analyzed the effective 1-D DMFs with the vibrational wave function expansion method and derived the effective portion of the 1-D DMF that is responsible for the overtone transition moment. 相似文献