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31.
Namieśnik J Zabiegała B Kot-Wasik A Partyka M Wasik A 《Analytical and bioanalytical chemistry》2005,381(2):279-301
The current state-of-the-art of passive sampling and/or extraction methods for long-term monitoring of pollutants in different environmental compartments is discussed in this review. Passive dosimeters that have been successfully used to monitor organic and inorganic contaminants in air, water, sediments, and soil are presented. The application of new approaches to the determination of pollutants at the sampling stage is discussed. The main milestones in the development of passive techniques for sampling and/or extraction of analytes, and in biomonitors used in environmental analysis, are summarized in this review. Passive samplers and biomonitors are compared. 相似文献
32.
Air monitoring is the quantitative-qualitative assessment of the extent of pollutants. It is performed to ensure compliance with legislation and to evaluate control measures and mitigation solutions. There are numerous approaches to measure airborne formaldehyde (FA), ranging from passive sampling techniques to remote sensing devices. Research of sampling procedures and analytical methods was performed in a scientific database and on the web to offer a scenario of the devices and techniques that can be used to assess FA exposure. Moreover, in the design of FA assessment, some crucial aspects were considered, such as standard atmosphere generation for devices calibration. This review summarizes the tools and basics used in FA air monitoring, useful to organize a functional monitoring strategy for assessment of FA concentration levels. An insight into the sampling and analysis of FA is provided. Recent advances in solid sorbent technology allow analysts to use these devices coupled to chromatographic instruments. A comparison of the strengths and weaknesses of analytical methods (gas-/liquid-chromatography coupled with mass spectrometry or UV detection, chromogenic, colorimetric, electrochemical determination) and sampling devices (impregnated papers, solid sorbents, liquid sorbents, bubblers, impingers, micro-impingers, denuder samplers, sealed bags, canisters) methods are illustrated. This survey found that a monitoring strategy should be planned considering the most appropriate methodology in terms of costs and practicability. Therefore, it is necessary to know the aspects that can make the chosen strategy suitable and valid for the exposure scenario under investigation. 相似文献
33.
Flapping-powered propulsion is used by many animals to locomote through air or water. Here we review recent experimental and numerical studies on self-propelled mechanical systems powered by a flapping motion. These studies improve our understanding of the mutual interaction between actively flapping bodies and surrounding fluids. The results obtained in these works provide not only new insights into biolocomotion but also useful information for the bio-mimetic design of artificial flyers and swimmers. 相似文献
34.
35.
Light pulses of 149 m wavelength and 700 ps duration are generated by non-collinear phase-matched difference frequency mixing of laser pulses at 1053.5 and 1061 nm in a (110) cut GaP crystal. The pump laser pulses are generated in a time-synchronized mode-locked double-frequency Nd:glass laser system consisting of a silicate glass branch and a phosphate glass branch. A photon conversion efficiency of 4 × 10–6 is achieved. The non-linear susceptibility constant of GaP is determined to be d
14 = (10 ± 1) pm V–1. 相似文献
36.
Grzegorz Stepniak Lukasz Maksymiuk Jerzy Siuzdak 《Optical and Quantum Electronics》2007,39(15):1281-1288
Frequency response of passive optical network (PON) based on multimode fibers is investigated. The network comprises fibers,
connectors and splitters/couplers. It is shown that due to mode filtering at splitters, the frequency response is different
for different network nodes in otherwise symmetrical network. 相似文献
37.
We present a systematic way to compute the scaling exponents of the structure functions of the Kraichnan model of turbulent
advection in a series of powers of ξ, adimensional coupling constant measuring the degree of roughness of the advecting velocity
field. We also investigate the relation between standard and renormalization group improved perturbation theory. The aim is
to shed light on the relation between renormalization group methods and the statistical conservation laws of the Kraichnan
model, also known as zero modes. 相似文献
38.
用坩埚下降法生长了Tm3+掺杂浓度分别为0.8%和1.3%的优质大尺寸LiYF4(LYF)单晶体。测定了单晶体的吸收光谱、发射光谱,并计算了3F4能级的的最大吸收截面与最大发射截面分别为0.25×10-20 cm2和0.33×10-20 cm2。以796 nm半导体激光器(LD)为泵浦源,采用短平板腔结构模型研究了Tm掺杂LYF单晶体在~2.0μm波段的激光输出性能。当LD泵浦功率为3.4 W时,Tm∶YLF晶体的最大激光输出功率为1.88 W,相应的光光转换效率和斜率效率分别为51%和57%。使用半导体可饱和吸收镜抽运Tm掺杂LYF单晶体,测试其在~2.0μm波段连续波锁模激光运转。当最大抽运功率为3.5 W时,获得锁模激光的最大平均输出功率为200 mW,此时锁模脉冲宽度~20 ps,对应的重复频率63.86 MHz,中心谱线为1.88μm。结果表明,Tm掺杂LYF单晶体是一种具有较好物理性能的~2μm波段超... 相似文献
39.
We have experimentally and analytically studied transport of a passive scalar in the wake of a thin flat plate located at
the centerline of a planar contraction with flat walls. The constant Launder parameter in the contraction, K = 6.25 ×10 − 6, was twice the value required for a turbulent boundary layer to relaminarize. In addition to the mixing analysis inside the
contraction, layer mixing is also investigated downstream, where the flow continues inside a constant cross-section channel.
In order to generate the passive scalar, the airflow above the plate was heated and the temperature stratification in the
wake was traced by measuring the temperature field using constant current anemometry. Using different plate lengths, we found
that the degree of mixing, obtained at a given position in the straight channel, is a function of the distance from the plate
trailing edge to the contraction outlet. For a plate which does not protrude into the straight channel, we demonstrate the
existence of an optimal trailing edge-contraction outlet distance that results in the lowest possible degree of mixing at
a given downstream position in the straight channel. This finding is also supported by a semi-empirical relationship based
on our developed self-similar solution for mixing layers in planar contractions. 相似文献
40.