排序方式: 共有113条查询结果,搜索用时 15 毫秒
11.
A novel apparatus for a sensitive test of the independence of the speed of optical waves from the propagation direction has been developed. It employs a monolithic ULE glass structure containing two orthogonal, crossing Fabry-Perot cavities which enable common mode rejection of certain disturbances. Highly accurate locking and cavity frequency read-out are achieved using laser frequency modulation at audio frequencies. Several systematic effects were characterized. Without rotation the root Allan variance (RAV) of the beat frequency reaches a minimum of 0.5 Hz (2 × 10−15) close to the thermal noise floor of the cavities. The performance of the apparatus under rotation is demonstrated by determining with improved accuracy one parameter of the standard model extension test theory, = (−1.0 ± 2.3) × 10−15, under simplifying assumptions. 相似文献
12.
Xiaodan Yu 《Applied Surface Science》2008,254(15):4444-4451
Periodic mesoporous composite catalysts, [(n-C4H9)4N]4[γ-SiW10O34(H2O)2]/SBA-15 (TBA-1*/SBA-15, where TBA-1* = [(n-C4H9)4N]4[γ-SiW10O34(H2O)2]), with TBA-1* loadings of 4.3-14.8% were prepared by simultaneous hydrolysis and co-condensation of the tetraethoxysilane (TEOS) in the presence of divacant Keggin-type polyoxometalate and triblock copolymer surfactant (P123) followed by hydrothermal treatment process. Structure integrity of the Keggin unit in as-prepared composites was studied by Fourier transform infrared spectroscopy (FT-IR), Raman scattering spectra, and 29Si magic-angle spinning (MAS) NMR. Periodic mesoporous structure of the composites was evaluated by low-angle X-ray powder diffraction (LXRD) patterns, nitrogen porosimetry, and transmission electron microscope (TEM) measurements. As-prepared TBA-1*/SBA-15 was used as an heterogeneous oxidation catalyst for the styrene epoxidation reaction to synthesize styrene oxide in the presence of dilute H2O2 (30%), and influences of solvent, molar ratio of styrene to H2O2, TBA-1* loading on the styrene conversion, styrene oxide yield and selectivity were considered. 相似文献
13.
Wavelet Cross-Spectrum Analysis of Multi-Scale Disturbance Instability and Transition on Sharp Cone Hypersonic Boundary Layer
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Experimental measurement of hypersonic boundary layer stability and transition on a sharp cone with a half angle of 5° is carried out at free-coming stream Mach number 6 in a hypersonic wind tunnel. Mean andfluctuation surface-thermal-flux characteristics of the hypersonic boundary layer flow are measured by Pt-thin-film thermocouple temperature sensors installed at 28 stations on the cone surface along longitudinal direction. At hypersonic speeds, the dominant flow instabilities demonstrate that the growth rate of the second mode tends to exceed that of the low-frequency mode. Wavelet-based cross-spectrum technique is introduced to obtain the multi-scale cross-spectral characteristics of the fluctuating signals in thefrequency range of the second mode. Nonlinear interactions both of the second mode disturbance and the first mode disturbance are demonstrated to be dominant instabilities in the initial stage of laminar-turbulence transition for hypersonic shear flow. 相似文献
14.
This work demonstrates a semi-automatic optical frequency counter based on two mode-locked fiber laser combs. The mode number
of the comb line involved in the optical frequency measurement is determined by operating the two laser combs at three different
repetition rates, with two of them similar enough to have the same mode number of the beating comb lines. The determination
of the mode number is independent of the frequency fluctuation of the laser under measurement. The whole measurement process
was automated, except for the frequency stabilization of the laser combs and the optimization of the beat signal–to–noise
ratio. 相似文献
15.
16.
P. Rosenbusch 《Applied physics. B, Lasers and optics》2009,95(2):227-235
We investigate the hyperfine transition of magnetically trapped non-condensed atoms. The two principal frequency shifts, the
second order Zeeman effect and the mean field interaction are considered. Analytic models of the mean frequency and its trap
induced spread are developed. Comparisons with existing experiments evaluate the role of the atoms’ oscillatory motion. The
analytic model proves to be equivalent to existing Monte Carlo simulations. The formulae provide a simple tool for optimising
the design of a new experiment. Applied to the two-photon transition |F=1,m
F
=−1〉→|F=2,m
F
=1〉 in 87Rb and the conditions of a typical atom chip experiment, a line spread as small as 11 mHz is predicted giving a quality factor
of 1012. The system is promising for application in precision instruments such as compact atomic clocks. 相似文献
17.
C. P. Yin T.-B. Wang J.-W. Dong Y. H. Chen H. Z. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(3):357-361
By means of transfer matrix method, we investigate the transmittance and
reflectance of Thue-Morse (T-M) structure composed of negative-permittivity
and negative-permeability materials. It is shown that the width and location
of an omnidirectional reflectance band remain invariant with the change of
generation order, and that the omnidirectional reflectance band is
determined by both TE and TM polarization, which different completely from
that in dielectric T-M structure. Moreover, a flat-top total transmission
band occurs around the same frequency in which the general zero average
permittivity and permeability are both satisfied in T-M structure. The basis
for these phenomena are presented and discussed. 相似文献
18.
A weakly nonlinear model is proposed for multimode Kelvin-Helmholtz instability. The second-order mode coupling formula for Kelvin-Helmholtz instability in two-dimensional incompressible fluid is presented by expanding the perturbation velocity potential to second order. It is found that there is an important resonance in the course of the sum frequency mode coupling but the difference frequency mode coupling does not have. This resonance makes the sum frequency mode coupling process relatively complex. The sum frequency mode coupling is strongly dependent on time especially when the density of the two fluids is adjacent and the difference frequency mode coupling is not. 相似文献
19.
Super-High Resolution Time Interval Measurement Method Based on Time-Space Relationships 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Based on the principle of quantized delay-time, a super-high resolution time interval measurement method is proposed based on time-space relationships. Using the delay-time stability that time and frequency signal travel in a specific medium, the measured time interval can be quantized. Combined with the phase coincidence detection technique, the measurement of time can be changed into the measurement of space length. The resolution and the stability of the measurement system are easily improved. Experimental results show that the measurement resolution of the measured time interval depends on the length difference of the double delay-time unit. When the length difference is set up on millimeter level or sub-millimeter level, super-high measurement resolution from hundreds of picosecond to tens of picosecond can be obtained. 相似文献
20.
S. N. Bagayev V. P. Chebotayev A. K. Dmitriyev A. E. Om Yu. V. Nekrasov B. N. Skvortsov 《Applied physics. B, Lasers and optics》1991,52(1):63-66
The observation of second-order Doppler-free optical resonances with a width of 50 Hz are reported for the first time. It was achieved due to the use of optical selection of cold particles from an absorbing gas. The experiments have been carried out by using a new laser spectrometer, supposed to obtain the saturated absorption resonances with a relative width 10–13–10–14. The results of experimental and theoretical studies of second-order Doppler-free effect influence on the shape of nonlinear optical resonances in transit-time conditions are considered. 相似文献