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21.
Branko Drlja?aSvetislav Savovi? Alexandar Djordjevich 《Optics and Lasers in Engineering》2011,49(5):618-622
The time-dependent power flow equation, which is reduced to its time-independent counterpart is employed to calculate frequency response and bandwidth in addition to mode coupling and mode-dependent attenuation in a step-index plastic optical fiber. The frequency response is specified as a function of distance from the input fiber end. This is compared to reported measurements. Mode-dependent attenuation and mode dispersion and coupling are known to be strong in plastic optical fibers, leading to major implications for their frequency response in data transmission systems. 相似文献
22.
Visarath In Patrick LonghiniAndy Kho Norman LiuSuketu Naik Antonio PalaciosJoseph D. Neff 《Physica D: Nonlinear Phenomena》2011,240(8):701-708
A novel coupling scheme using M≥2 arrays of coupled nonlinear elements arranged in a specific configuration can produce multifrequency patterns or a frequency down-converting effect on an external (input) signal. In such a configuration, each array contains N≥3 nonlinear elements with similar dynamics and each element is coupled unidirectionally within the array. The subsequent arrays in the cascade are coupled in a similar fashion except that the coupling direction is arranged in the opposite direction with respect to that of the preceding array. Previous theoretical work and numerical results have already been reported in [P. Longhini, A. Palacios, V. In, J. Neff, A. Kho, A. Bulsara, Exploiting dynamical symmetry in coupled nonlinear elements for efficient frequency down-conversion, Phys. Rev. E 76 (2007) 026201]. This paper is focused on results of experiments implemented on two distinct systems: the first system is fabricated using discrete component circuits to approximate an overdamped bistable Duffing oscillator described by a quartic potential system, and the second system is built in a microcircuit, where the nonlinearity is described by a hyperbolic tangent function, with the option of applying an external signal to investigate resonant effects. In particular, the circuit implementations for each case use M=2 arrays, but their voltage oscillations already demonstrate that the frequency relations between each of the successive arrays decrease by a rational factor, conforming to earlier theoretical and numerical results for the general case containing M arrays. This behavior is important for efficient frequency down-converting applications which are essential in many communication systems where heterodyning is typically used and it involves multi-step processes with complicated circuitry. 相似文献
23.
24.
注入锁定激光器的边带锁频技术稳频系统优化分析 总被引:1,自引:0,他引:1
介绍了边带锁频技术稳频方法,推导出鉴频曲线,对稳频控制过程进行了分析.建立了注入锁定激光器的边带锁频技术稳频系统理论模型,讨论了相关参量对稳频效果的影响并且进行了优化.结果表明,增加入射光强,采用窄线宽的法布里-珀罗以及对法布里-珀罗进行高准确度温控都可以增强稳频效果.提出适用于注入锁定激光器的两种稳频方案并进行比较. 相似文献
25.
Froncisz W Camenisch TG Ratke JJ Anderson JR Subczynski WK Strangeway RA Sidabras JW Hyde JS 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2008,193(2):297-304
A reference arm W-band (94 GHz) microwave bridge with two sample-irradiation arms for saturation recovery (SR) EPR and ELDOR experiments is described. Frequencies in each arm are derived from 2 GHz synthesizers that have a common time-base and are translated to 94 GHz in steps of 33 and 59 GHz. Intended applications are to nitroxide radical spin labels and spin probes in the liquid phase. An enabling technology is the use of a W-band loop-gap resonator (LGR) [J.W. Sidabras, R.R. Mett, W. Froncisz, T.G. Camenisch, J.R. Anderson, J.S. Hyde, Multipurpose EPR loop-gap resonator and cylindrical TE011 cavity for aqueous samples at 94 GHz, Rev. Sci. Instrum. 78 (2007) 034701]. The high efficiency parameter (8.2 GW−1/2 with sample) permits the saturating pump pulse level to be just 5 mW or less. Applications of SR EPR and ELDOR to the hydrophilic spin labels 3-carbamoyl-2,2,5,5-tetra-methyl-3-pyrroline-1-yloxyl (CTPO) and 2,2,6,6,-tetramethyl-4-piperidone-1-oxyl (TEMPONE) are described in detail. In the SR ELDOR experiment, nitrogen nuclear relaxation as well as Heisenberg exchange transfer saturation from pumped to observed hyperfine transitions. SR ELDOR was found to be an essential method for measurements of saturation transfer rates for small molecules such as TEMPONE. Free induction decay (FID) signals for small nitroxides at W-band are also reported. Results are compared with multifrequency measurements of T1e previously reported for these molecules in the range of 2–35 GHz [J.S. Hyde, J.-J. Yin, W.K. Subczynski, T.G. Camenisch, J.J. Ratke, W. Froncisz, Spin label EPR T1 values using saturation recovery from 2 to 35 GHz. J. Phys. Chem. B 108 (2004) 9524–9529]. The values of T1e decrease at 94 GHz relative to values at 35 GHz. 相似文献
26.
Wei Han Wan-Guo Zheng Yi-Sheng Yang Ding-Xiang Cao Qi-Hua Zhu Lie-Jia Qian 《Optik》2008,119(3):122-126
In this paper, we studied efficient second-harmonic generation (SHG) of femtosecond pulses in both phase- and group-velocity-matched structures. Obtained results show that phase matching becomes more critical under conditions required for high levels of conversion efficiency. And the imperfect phase mismatch caused by mismatched group-velocity dispersion (GVD) will limit conversion efficiency as well as bandwidth of generated second-harmonic (SH) pulses. The spectral characteristics of the generated SH pulses and its conversion efficiency in the strong pump regime are investigated in detail. The acceptance bandwidth of nonlinear crystal in the high-efficiency SHG is redefined in the paper, and the definition is much closer to the practical application of design. 相似文献
27.
Velan SS 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,171(2):40-352
Longitudinal multispin orders provide an effective way for measurement of scalar couplings and also to probe molecular interactions and dynamics. Analysis of longitudinal orders has been made in strongly coupled AB and ABX spin systems to determine the dependence of strong coupling parameter on these orders. Experimental and simulated spectra of various longitudinal orders are illustrated for these spin systems. This general procedure can be extended to broad range of spin systems to understand the influence of strong coupling on longitudinal orders. 相似文献
28.
Frequency domain (FD) fluorescence lifetime data was collected for a series of 20 crude petroleum oils using a 405 nm excitation
source and over a spectral range of ~426 to ~650 nm. Average fluorescence lifetimes were calculated using three different
models: discrete multi-exponential, Gaussian distribution, and Lorentzian distribution. Fitting the data to extract accurate
average lifetimes using the various models proved easier and less time consuming for the FD data than with Time Correlated
Single Photon Counting (TCSPC) methods however the analysis of confidence intervals to the computed average lifetimes proved
cumbersome for both methods. The uncertainty in the average lifetime was generally larger for the discrete lifetime multi-exponential
model when compared to the distribution-based models. For the lifetime distributions, the data from the light crude oils with
long lifetimes generally fit to a single decay term. Heavier oils with shorter lifetimes required multiple decay terms. The
actual value for the average lifetime is more dependant on the specific fitting model employed than the data acquisition method
used. Correlations between average fluorescence lifetimes and physical and chemical parameters of the crude oils were made
with a view to developing a quantitative model for predicting the gross chemical composition of crude oils. It was found that
there was no significant benefit gained by using FD over TCSPC other than more rapid data analysis in the FD case. For the
FD data the Gaussian distribution model for fluorescence lifetime gave the best correlations with chemical composition allowing
a qualitative correlation to some bulk oil parameters.
相似文献
Alan G. RyderEmail: |
29.
The Aharonov-Bohm effect (ABE) for steady magnetic fields is a well known phenomenon. However, if the current in the infinite solenoid that creates the magnetic field is time-dependent, that is in the presence of both magnetic and electric fields, there is no agreement whether the effect would be present. In this note, we try to investigate time varying ABE by a direct calculation in a set-up with a weak time dependent magnetic field. We find that the electric field arising out of the time-varying magnetic field in the path of the electrons does not enter the action integral but only changes the path of the electron from the source to the slits and then on to the detector. We find a frequency dependent AB phase shift. At low frequencies the result smoothly approaches the one for a constant field as the frequency tends towards zero. On the other hand, for high frequencies such that the AB-phase induced in the path of the wave packet oscillates rapidly, the net effect will be very small which is borne out by our results. 相似文献
30.
This paper presents the theoretical analysis of adaptive multiuser RAKE receiver scheme in frequency selective fading channel for direct-sequence code division multiple access (DS-CDMA) system. Least mean square (LMS) algorithm is used to estimate the channel coefficients. Chaotic sequences are used as spreading sequence and corresponding bit error rate (BER) in closed form is derived for imperfect channel estimation conditions. Performances of chaotic sequences are compared with pseudorandom noise (PN) sequences. Under perfect synchronization assumption, various simulation results are shown to investigate the performance of the proposed system. 相似文献