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11.
Compact CH4 sensor based on difference frequency mixing of diode lasers in quasi-phasematched LiNbO3. 总被引:1,自引:0,他引:1
A compact, portable and robust room temperature CH4 sensor is reported. By difference frequency mixing a 500 mW alpha-DFB diode laser at 1066 nm and an erbium-doped fiber amplified 1574 nm DFB diode laser in periodically poled lithium niobate up to 7 (mu)W of narrowband radiation at 3.3 microns is generated. Real-time monitoring of CH4 over a 7 day period using direct absorption in an open-path multipass cell (L = 36 m) demonstrates a detection precision of +/- 14 ppb. 相似文献
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Lancaster KM Sproules S Palmer JH Richards JH Gray HB 《Journal of the American Chemical Society》2010,132(41):14590-14595
Redox and spectroscopic (electronic absorption, multifrequency electron paramagnetic resonance (EPR), and X-ray absorption) properties together with X-ray crystal structures are reported for the type 2 Cu(II) C112D/M121E variant of Pseudomonas aeruginosa azurin. The results suggest that Cu(II) is constrained from interaction with the proximal glutamate; this structural frustration implies a "rack" mechanism for the 290 mV (vs NHE) reduction potential measured at neutral pH. At high pH (~9), hydrogen bonding in the outer coordination sphere is perturbed to allow axial glutamate ligation to Cu(II), with a decrease in potential to 119 mV. These results highlight the role played by outer-sphere interactions, and the structural constraints they impose, in determining the redox behavior of transition metal protein cofactors. 相似文献
14.
Tunable narrowband mid-infrared radiation from 3.25 to 4.4 μm is generated by a compact fiber-coupled, difference-frequency-based
spectrosopic source. A 20-mW external cavity diode laser (with a tuning range from 814 to 870 nm) and a 50-mW distributed-Bragg-reflector
diode-laser-seeded ytterbium-doped fiber amplifier operating at 1083 nm are difference-frequency mixed in a multi-grating,
temperature-controlled periodically poled LiNbO3 crystal. A conversion efficiency of 0.44 mW/(W2 cm) (corresponding to a power of ≈3 μW at 3.3 μm) represents the highest conversion efficiency reported for a portable device.
Performance characteristics of such a sensor and its application to spectroscopic detection of CO2, N2O, H2CO, HCl, NO2, and CH4 will be reported in this work.
Received: 14 May / Revised version: 24 June 1999 / Published online: 30 September 1999 相似文献
15.
Factorization theorems, and properties of sets of eigenvectors, are established for regular selfadjoint quatratic matrix polynomials L(λ) whose leading coefficeint is indefinite or possibly singular, and for which all eigenvalues are real of definite type. The two linear factors obtained have spectra which are just the eigenvalues of L(λ) of positive and negative types, respectively. 相似文献
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A high-power 83 W cladding-pumped Tm3+-Ho3+-doped silica fiber laser is reported. Using bidirectional 793 nm diode pumping, a maximum slope efficiency of 42% was produced after a threshold launched pump power of 12 W was exceeded. The laser operated at wavelengths near 2105 nm with moderate beam quality, i.e., M2 approximately 1.5. Further power scaling of the fiber laser was limited by thermal failure of the fiber ends. 相似文献
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Lancaster M Goodall DM Bergström ET McCrossen S Myers P 《Journal of chromatography. A》2005,1090(1-2):165-171
This paper presents the first study of imaging of spots on thin-layer chromatographic plates whilst still wet with solvent. Imaging and quantification of Sudan II after development with dichloromethane was carried out in both reflectance and transmission modes, using a charge coupled device (CCD) camera. The relationship between peak area and sample loading was established at low sample loading, and found to be linear over an order of magnitude for both wet and dry modes with r2-values > 0.99. All data processing was carried out using the Beer-Lambert equation. Curvature at high loadings in the plots of integrated absorbance as a function of sample loading was accounted for using an empirical expression designed for use with the Kubelka-Munk treatment and apparent absorbance of the stationary phase due to scattering. Results are consistent with an effective pathlength significantly longer than the thickness of the sorbent layer. The limit of detection on a dry plate (0.5 ng) was found to be lower than on a wetted plate (2 ng). Precision was found to be 1-4% RSD intra-plate and 8-14% RSD inter-plate. Results are compared with quantification of the same analyte on dried plates. 相似文献