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81.
A multiplexing method based on narrow diode-laser arrays (DLAs) in an axially symmetric configuration is described. The use of submillimeter narrow DLAs improves beam quality considerably in the slow-axis direction compared with typical 1-cm-wide DLAs. The axially symmetric geometry is advantageous for efficient spatial, wavelength, and polarization multiplexing. With narrow DLAs and an axially symmetric geometry, a small circular focus with more than 10-kW/mm2 average power density is possible. Theoretical calculations and preliminary experimental results are presented.  相似文献   
82.
电卡效应是极性材料中极化强度和温度的相互作用, 具有电卡效应的铁电陶瓷材料在高效固态制冷领域有很好的应用前景。本研究以Pb0.3CaxSr0.7-xTiO3 [PCST(x), x = 0.00, 0.05, 0.10, 0.15]陶瓷为对象, 系统研究了在电场作用下Ca含量对材料介电性能和铁电性能的影响, 并通过间接法计算了不同温度下材料的电卡温变。研究结果显示: Ca含量可显著调控PCST陶瓷的弥散相变特性, PCST(0.05)的相变弥散因子随外加电场的增大而增大, 可利用弥散相变在较宽温度区间内获得较大的电卡效应。经计算可得: PCST(0.05)在室温下可产生1.71 K的温变。当电场为8 kV/mm时, PCST(0.05)陶瓷在5~70 ℃的温度范围内, 绝热温变均大于1 K, 表现出优异的电卡效应。  相似文献   
83.
Tobacco leaves (Nicotiana tabacum L.), agricultural soil and pollute irrigated lake water samples were collected during 2005–2006 and analyzed for Cd and Ni by electrothermal atomic absorption spectrometry (ETAAS). A simple and efficient procedure was investigated for the complete decomposition of tobacco leaves using ultrasonic assisted acid pseudo-digestion method (UPDM). A Plackett–Burman experimental design was used as a multivariate strategy for the evaluation of seven factors/variables at once, while central composite were used to found optimum values of significant variables. The accuracy of the proposed methods was assessed by analyzing certified reference (CRM); Virginia tobacco leaves (CTA-VTL-2). The results being compared with those obtained by conventional wet acid digestion method. The result obtained by optimized method showed good agreement with the certified values and sufficiently high recovery 97.8 and 98.7% for Cd and Ni, respectively. Under optimal conditions, the detection limits (3σ) were evaluated to be 0.019 μg g−1 for Cd and 0.37 μg g−1 for Ni. The proposed method was successfully applied to the determination of Cd and Ni in raw, processed tobacco and different branded cigarettes samples.  相似文献   
84.
85.
A sensitive spectrophotometric method for the determination of freely dissolved copper concentrations in aqueous samples after preconcentration with hollow fiber membrane extraction has been developed. The method is based on the equilibrium sampling through a selective membrane into an acceptor solution containing 4-(pyridyl-2-azo)resorcinol (PAR), which serves as stripping agent and metal indicator. Negligible extraction of interferences and equilibrium enrichment of copper allowed for selective spectrophotometric determination of the Cu-PAR complex. Some important extraction parameters such as acceptor composition, shaking, equilibrium time, and sample volume were studied. The optimized methodology showed good linearity in the range of 5-100 microg/L, an enrichment factor of 93, good repeatability and reproducibility (RSDs < 6%, n = 6), and a detection limit of 4 microg/L. The cationic metals Ni2+, C(2+, Cd2+, Fe3+, Pb2+, Zn2+, and Mn2+ were shown not to interfere with the measurement of Cu2+. Measurements on samples containing mixtures of various ligands and cations were in good agreement with theoretically calculated concentrations, and the method was also applied to environmental samples. The developed technique requires less labor and less sophisticated equipment than conventional methods typically based on atomic absorption spectrometry or ICP.  相似文献   
86.
87.
He GS  Signorini R  Prasad PN 《Applied optics》1998,37(24):5720-5726
Two-photon-pumped (TPP) frequency-upconverted blue lasing of Coumarin 500 dye solution has been experimentally investigated. The shortest lasing wavelength was measured to be ~479 nm from a Coumarin 500 solution in chloroform pumped with ~800-nm laser pulses of ~5-ns duration. The spectral, temporal, and spatial structures as well as the output-input characteristics of TPP cavity lasing were measured with a 1-cm-long Coumarin 500 solution-filled quartz cuvette. The cavity lasing spectral structure and the numbers of longitudinal modes were easily controlled simply by attachment of an optical plate to the output window of the dye-solution cuvette. The net conversion efficiency from the absorbed 800-nm pump pulse energy to the blue-upconverted cavity lasing energy was ~4.8%.  相似文献   
88.
We describe a compact fiber-optic setup for three-dimensional topometry. The measuring principle is based on low-coherence interferometry in combination with a confocal microscope. Integrating an optical arrangement based on compact disk optics together with fiber optics into one sensor yields a compact unit. The sensor has a numerical aperture of 0.45 and is suitable for measuring large surface slopes with high spatial resolution. Further, a depth measuring range of more than 1 mm can be achieved. The capabilities of our setup for three-dimensional measurements are demonstrated.  相似文献   
89.
We have developed a methodology that can be used in reconstruction algorithms to quantify the optical coefficients and the geometrical cross section of a weakly abnormal optical target embedded in an otherwise homogeneous medium. This novel procedure uses differenttime-dependent point-spread functions to analyze the diffusive and absorptive contrasts obtained from time-of-flight measurements. Data obtained from time-resolved transillumination of a tissuelike phantom are used to test the accuracy of this new deconvolution methodology.  相似文献   
90.
1 IntrductionBroadbandwirelesscommunicationshavegainedincreasedinterestrecently .Owingtoitshightraffics,thereliabilityofitsairnetworkbecomesmoreimportant.Besidestherefinementofchannelcoding,thediversityisoneoftheimportanttech niquesemployedtomitigatethe…  相似文献   
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