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991.
We present a method for the measurements of complex transmission coefficient through high transmission loss samples using three-sensors, two impedance tubes, monotonic wave excitation, and phase sensitive detection. Having demonstrated the effectiveness of the method on perforated plates measurements have been made on locally resonant sonic materials (LRSMs). The transmission losses of perforated plates are found to decrease with decreasing frequency down to 120 Hz, following the mass law. For the LRSM’s panels with the same area mass density but different compositions, the local resonance frequency (at which the transmission loss is maximum) is found to vary according to the predesigned value. Transmission losses as high as 96.5 dB at 630 Hz and 87 dB at 250 Hz can be measured with good accuracy, with corresponding phase spectra that match the theoretical prediction of LRSMs, confirming the reliability of the transmission data. 相似文献
992.
A condition for reducing transmission loss of a dielectric-coated metallic hollow waveguide is shown theoretically when the inner metallic surface is not perfect. It is also shown that the transmission loss for CO2 laser light is 10.6 μm wavelength is able to be estimated from an attenuation spectrum of a short waveguide. By fabricating a ZnSe coated Ag hollow waveguide of short length, we have shown that it has a lower loss than a Ge coated waveguide for CO2 laser light. 相似文献
993.
994.
The depth profiling of O 1s energy loss in silicon oxide near the SiO2/Si interface was performed using extremely small probing depth. As a result, the energy loss of O 1s photoelectrons with threshold energy of 3.5 eV was found. This value of 3.5 eV is much smaller than the SiO2 bandgap of 9.0 eV, but quite close to direct interband transition at Γ point in energy band structure of silicon. This can be explained by considering the penetration of electronic states from silicon substrate into silicon oxide up to 0.6 nm from the interface. In addition, the penetrating depth is larger than the thickness of the compositional transition layer. 相似文献
995.
Two methods for the absolute calibration of flow calorimeters (used for measuring the differences in heat capacities of two fluids) have been investigated. In the recommended method of calibration, a change in the flow rate of the fluids is used to minic a change in the heat capacity of the fluid. In the other method of calibration, heat loss is measured using a fluid of known heat capacity, and it is assumed this heat loss is constant. This calibration method is not recommended because the heat loss is, in general, not constant. For some calorimeters the difference between the two methods of calibration is negligible, while for others erros as high as 40% are caused by choosing the wrong method. A detailed analysis of the heat losses in this kind of calorimetry shows why the two calibration methods give different results and leads to various methods of improving calorimeter construction and operation. Because chemical standardization is far more convenient for routine use, the recommended absolute calibration method has been used to establish 3.00 mol-kg–1 aqueous NaCl as a chemical standard for temperatures between 325 and 600K at 17.7 MPa. 相似文献
996.
可变产量的理性产出范围研究 总被引:1,自引:0,他引:1
本从机会成本损失最小化的角度出发,对可变立量的三个阶段的两种划分方法所确定的两种不同的理性产出范围进行了分析,分析结果表明。可变产量的理性产出范围应在最小边际成本所对应的产出量到边际成本与产品的预期价格相等所对应的产出量之间。 相似文献
997.
998.
Reactivity of ambient volatile organic compounds (VOCs) in summer of 2004 in Beijing 总被引:2,自引:0,他引:2
Shan Huang Min Shao Sihua Lu Ying Liu 《中国化学快报》2008,19(5):573-576
Ambient volatile organic compounds (VOCs) were sampled at six sites in Beijing in the summer of 2004 and analyzed by GCMS. The chemical reactivities of 73 quantified VOCs species were evaluated by OH loss rates (LOH) and ozone formation potentials (OFPs). Top 15 reactive species, mainly alkenes and aromatics, were identified by these two methods, and accounted for more than 70% of total reactivity of VOCs. In urban areas, isoprene was the most reactive species in term of OH loss rate, contributing 11.4% to the LOH of VOCs. While toluene, accounting for 9.4% of OFPs, appeared to have a long-time role in the photochemical processes. Tongzhou site is obviously influenced by local chemical industry, but the other five sites showed typical urban features influenced mainly by vehicular emissions. 相似文献
999.
Linex损失及PA样本下单边截断型分布族参数函数的EB估计 总被引:1,自引:0,他引:1
在Linex损失函数下,运用同分布PA样本密度函数的核估计方法,构造了一类单边截断型分布族参数函数的EB估计,并建立了它的收敛速度.在一定条件下,证明了这个收敛速度可充分接近1. 相似文献
1000.