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991.
Verstraeten M Pursch M Eckerle P Luong J Desmet G 《Journal of chromatography. A》2011,1218(16):2252-2263
We report upon the experimental investigation of the heat transfer in low thermal mass LC (LTMLC) systems, used under temperature gradient conditions. The influence of the temperature ramp, the capillary dimensions, the material selection and the chromatographic conditions on the radial temperature gradients formed when applying a temperature ramp were investigated by a numerical model and verified with experimental temperature measurements. It was found that the radial temperature gradients scale linearly with the heating rate, quadratically with the radius of the capillary and inversely to the thermal diffusivity. Because of the thermal radial gradients in the liquid zone inside the capillary lead to radial viscosity and velocity gradients, they form an additional source of dispersion for the solutes. For a temperature ramp of 1 K/s and a strong temperature dependence of the retention of small molecules, the model predicts that narrow-bore columns (i.d. 2.1 mm) can be used. For a temperature ramp of 10 K/s, the maximal inner diameter is of the order of 1 mm before a substantial increase in dispersion occurs. 相似文献
992.
Shun Miyano 《Journal of Molecular Spectroscopy》2011,265(1):47-51
Mid-infrared absorption spectroscopy was applied to the detection of the hydroperoxyl radical (HO2) in pulsed laser photolysis combined with a laser absorption kinetics reactor. The transition of the ν3 vibrational band assigned to the O-O stretch mode around 1065 cm−1 was probed with a thermoelectrically cooled, continuous wave, mid-infrared, distributed feedback quantum cascade laser (QCL). The HO2 was generated through 355 nm photolysis of Cl2/1,4-c-C6H8/O2 mixtures. The mid-infrared absorption spectrum of the HO2 radical was recorded between 1064 and 1065.5 cm−1. The absorption line shapes were well represented by the Voigt profile. The nitrogen-broadening coefficients of the HO2 radical at 295 K were determined for four absorption lines around 1065 cm−1. Mid-infrared absorption detection using a QCL as a spectroscopic light source is a powerful method in spectroscopic and kinetics studies of the HO2 radical. 相似文献
993.
C.P. McRaven M.J. Cich Trevor J. Sears Daniel Hurtmans 《Journal of Molecular Spectroscopy》2011,266(1):43-51
We report measurements of self- and nitrogen-pressure broadening of the P(11) line in the ν1 + ν3 combination band of acetylene at 195 739.649 5135(80) GHz by absorption of radiation emitted by an extended cavity diode laser referenced to a femtosecond frequency comb. Broadening, shift and narrowing parameters were determined at 296 K. For the most appropriate, hard collision, model in units of cm−1/atm, we find 0.146317(27), 0.047271(104) and −0.0070819(22) for the acetylene self-broadening, narrowing and shift, and 0.081129(35), 0.022940(74) and −0.0088913(25) respectively, for the nitrogen-broadening parameters. The uncertainties are expressed as one standard deviation (in parenthesis) in units of the last digit reported. These parameters are 2-3 orders of magnitude more precise than those reported in previous measurements. Similar analyses of the experimental data using soft collision and simple Voigt lineshape models were made for comparison. 相似文献
994.
T.M. Petrova A.M. Solodov A.A. Solodov A.S. Dudaryonok N.N. Lavrentieva 《Journal of Quantitative Spectroscopy & Radiative Transfer》2011,112(18):2741-2749
Oxygen pressure induced broadening and shifting coefficients for water vapor absorption lines in the 8600–9010 cm−1 region have been measured and calculated. The spectra were recorded with a Bruker IFS 125HR spectrometer at a spectral resolution of 0.01 cm−1 for lines with angular moment of the upper states up to 10. Calculations of line broadening and shifting coefficients are performed using a semi-empirical approach. The method is based on the impact theory of broadening, and includes the correction factors whose parameters can be determined by fitting the broadening or shifting coefficients to the experimental data. The comparison of our calculations with the experimental values argues that the semi-empirical method is quite acceptable for the determination of the water vapor absorption line profile parameters. 相似文献
995.
996.
Zhenbo Xu 《Optics Communications》2011,284(13):3403-3407
The inverse return-zero (IRZ) modulation format and Manchester format were investigated as wavelength reusing schemes in the RoF downlink systems. Since both of the modulation formats featured power remaining in the bit slot regardless of the bit value, the downlink optical carrier can be reused as the uplink light source. The performances of two formats were analyzed in the symmetrical and asymmetrical duplex RoF system. It was found that IRZ is more suitable for symmetrical system, and the duty cycle of IRZ pulse is the critical factor on the asymmetrical RoF system performance. However the Manchester format demonstrated the large system tolerance on asymmetrical duplex RoF system with the receiver sensitivity degradation within 1 dB. 相似文献
997.
Carmina del Rio Campos Author Vitae Paloma R. Horche Author Vitae Alfredo Martin-Minguez Author Vitae 《Optics Communications》2011,284(5):1346-1353
Due to the fact that a metro network market is very cost sensitive, direct modulated schemes appear attractive. In this paper a CWDM (Coarse Wavelength Division Multiplexing) system is studied in detail by means of an Optical Communication System Design Software; a detailed study of the modulated current shape (exponential, sine and gaussian) for 2.5 Gb/s CWDM Metropolitan Area Networks is performed to evaluate its tolerance to linear impairments such as signal-to-noise-ratio degradation and dispersion. Point-to-point links are investigated and optimum design parameters are obtained. Through extensive sets of simulation results, it is shown that some of these shape pulses are more tolerant to dispersion when compared with conventional gaussian shape pulses. In order to achieve a low Bit Error Rate (BER), different types of optical transmitters are considered including strongly adiabatic and transient chirp dominated Directly Modulated Lasers (DMLs). We have used fibers with different dispersion characteristics, showing that the system performance depends, strongly, on the chosen DML-fiber couple. 相似文献
998.
Seo Ro Shin 《Optics Communications》2011,284(5):1243-1246
We present an experimental and theoretical study of the transmission of an arbitrarily polarized laser beam for a Doppler broadened rubidium vapor cell. As the polarization of the probe beam was varied from linear to circular, the transmission for the transitions Fg = 3 → Fe = 2, 3, 4 of the D2 line of 85Rb atoms was measured and compared with calculated results. In the calculation, the time-dependent absorption coefficient, calculated numerically from the density-matrix equation, was averaged over the velocity distribution and various transit time crossing the laser beam. The final transmission was obtained by considering the Gaussian profile of the laser beam. We found good agreement between experimental and calculated results. 相似文献
999.
Pingping Sun Dean Liu Yanli Zhang Yan Zhang Fang Liu Xuejie Zhang Jianqiang Zhu 《Optik》2011,122(24):2230-2233
By means of Collins diffraction integral, the propagation expression of an ultrashort laser pulse passing through a spatial filter is derived. The effects of the magnification of spatial filter on pulse broadening and distortion of pulse-front for the ultrashort optical pulse are analytically deduced and numerically simulated. It is found that pulse broadening and propagation time difference of a laser pulse getting through spatial filter is proportional to the magnification. As a conclusion, in an ultrashort pulse laser system with a large aperture, the effect of pulse broadening and distortion of pulse-front should be considered. 相似文献
1000.
Erbium doped fiber ring lasers (EDFRL) are being used to generate optical chaos for secure communication by modulating the cavity loss/pump power or exploiting nonlinearities. The security level in chaotic communication depends on degree of chaos quantified by the Lyapunov exponent and its variability which is determined by the number of tuneable system parameters which were limited to five main parameters, i.e. modulation index, modulation frequency, pump power, cavity gain and loss. In this study we have increased the number of tuneable parameters using square, triangular and sum of harmonics waveforms. We have analysed the effect on degree of chaos of phase and duty cycle of square modulating signal with gradual addition of harmonics. For the given cavity parameters, the Lyapunov exponents can be increased by more than fifteen times using square wave modulating signal and a duty cycle of 60%. The electrical parameters identified make generation of new chaotic sequences more flexible in a field deployed EDFRL chaotic system. 相似文献