Numerical simulation of high-gradient magnetic filtration

We have reported on the results of a numerical simulation of high-gradient magnetic filtration of ultradisperse corrosion products from water coolants. These results have made it possible to establish optimal technical characteristics of high-gradient magnetic filters. The results have been used to develop test samples of high-gradient magnetic filters (HGMFs) with different magnetic systems to purify technological water media of atomic power plants from activated corrosion products.     

Study of the influence of native oxide layers on atomic force microscopy imaging of semiconductor surfaces

We have investigated the influence of the native oxide layer on semiconductor surfaces on the imaging properties of the atomic force microscope operated under ambient conditions by using epitaxial In_1–x Ga _x As layers grown by Metal-Organic Chemical Vapour Deposition (MOCVD) on (001) oriented InP substrates which have been kept under ambient conditions for two years. The thickness and composition of the native oxide layers were studied with ellipsometry and X-ray photoelectron spectroscopy, respectively. Subsequently, the sample surfaces were imaged by means of atomic force microscopy operated in air which revealed terrace structures separated by monoatomic steps. The obtained data were compared with the surface morphology which can be expected from the MOCVD growth process. The results suggest that an accurate study of semiconductor layer growth by atomic force microscopy in air is possible.     

1.55μm MOEMS可调谐光滤波器调谐性能模拟

建立了等效单层梁模型和一维集总模型,用经典力学理论和传输矩阵方法模拟了多层材料构成且具有四臂固支梁结构的1.55 μm Si基MOEMS (Micro-Opto-Electro-Mechanical-Systems)可调谐滤波器的调谐特性.模拟调谐系数与实验结果吻合较好.     

法拉第反常色散滤光器透射谱的普遍计算方法

报道了一种计算法拉第反常色散滤光器（ＦＡＤＯＦ）透射谱的普遍方法,该方法可计算不同碱金属元素工作在任意电偶极跃迁和任意磁场强度下的法拉第反常色散滤光器透射谱,对主动式和被动式法拉第反常色散滤光器同样适用,该方法还可进一步推广到其它类型的原子滤光器（如斯塔克型原子滤光器）的计算,给出了采用这种方法对铷主动式７７５．９ｎｍ法拉第反常色散滤光器透射谱的计算结果,与实验曲线符合较好。     

Construction and calibration of a multipurpose instrument to simultaneously measure dose,voltage and half-value layer in X-ray emission equipment

This work reports on the development of a multipurpose instrument that simultaneously measures delivered dose (air kerma), peak voltage (kVp) and half value layer (HVL) in X-ray machines. The device will help control quality of X-ray equipment routinely used in diagnostic and interventional radiological procedures. The measuring device is equipped with several attenuating filters of different materials and thicknesses, and Gafchromic^® XR-QA2 radiochromic films are used as sensitive elements. The films are scanned after being irradiated and the resulting color intensities indicate a relationship between the degree of film darkening under each individual filter and the quantities of interest, i.e. air kerma, kVp and HVL. Comparing HVL values measured using the proposed multipurpose instrument with those of a reference standard ionization chamber, discrepancy reached 8.4%. As for the kVp evaluation, anomalous results were observed for low atomic number materials and small thicknesses, especially for peak voltages higher than 70 kVp. However, for materials with higher Z and reasonable thickness, the calibration curve R × kVp was quite satisfactory, being R the ratio between the color intensities obtained with two distinct filters. We have also observed a decrease in the influence of Tungsten characteristic radiation on the calibration curve. These results suggest that the proposed instrument may be satisfactorily used to routinely control quality of X-ray equipment, estimating the radiation dose resulting from the direct beam, the applied voltage across the electrodes and the half value layer.     

A risk assessment study of heavy metals in ambient air by WD‐XRF spectrometry using aerosol‐generated filter standards

A risk assessment study of the air quality in the surrounding of roads covered with slags coming from the non‐ferrous metal industry was performed. A monitoring campaign was carried out at three locations in Flanders by collecting the PM10 fraction and the total suspended particulates (TSP) of the airborne dust particles, entrapping heavy metals, on membrane filters. The heavy metal concentration on the dust filters was determined by wavelength‐dispersive x‐ray fluorescence (WD‐XRF) spectrometry. The XRF calibration curves were set up with filter standards prepared in the laboratory using an aerosol‐generated loading system. The acquired WD‐XRF results were confirmed by inductively coupled plasma atomic emission spectrometric (ICP‐AES) measurements after acid digestion on a selected number of filters. Electron probe microanalysis (EPMA) confirmed that aerosol‐loaded filter standards and dust filters with a concentration level of the analyzed element below 3300 ng cm^?2 were homogeneously distributed. Dust filters with higher concentrations, and especially filters loaded with the TSP fraction, reflected an inhomogeneous distribution of the analyzed element on the filter. The WD‐XRF analytical results acquired in the monitoring campaign revealed that the concentration of Pb on the dust filters never exceeded the immission standard (yearly average) of 2000 ng m^?3. It can be stated that the impact on human health is limited and can still be reduced by covering the polluted roads with a layer of asphalt. Further evaluation of soil and water samples from the nearby surroundings reveals that the heavy metal content in the slags makes an important contribution to environmental pollution, especially the contamination of groundwater. Copyright © 2003 John Wiley & Sons, Ltd.     

Enhancement of the quantum efficiency of a fluorescence cesium filter

The dependence of the quantum efficiency of fluorescence cesium vapor filters, which allow one to select with a high contrast the desired narrow-band signal against the background of broadband (solar) radiation, is studied. The most important characteristic of such filters, apart from the spectral band, is the quantum efficiency; i.e., the ratio of the number of florescent photons to the number of absorbed photons of excitation. It is experimentally shown that addition of a buffer gas to working cesium atoms can substantially increase the quantum efficiency as compared with that of working atoms in vacuum. The dependence of the quantum efficiency on the characteristic of transitions that are involved in population of atomic levels from which fluorescence occurs, and the processes resulting in an increase in the quantum efficiency of atomic fluorescence filters are considered.     

降噪阵列参数对次声降噪系统性能的影响分析

次声降噪系统对提高次声监测能力具有重要作用,为分析次声降噪系统阵列结构参数变化对其降噪性能的影响规律,构建玫瑰型(rosette)管道滤波器降噪系统声电等效模型,进而利用风噪声模型和仿真数据对该模型的单进气口传递函数和系统降噪性能进行了定量分析,总结了不同阵列结构参数对该系统降噪性能的影响规律,最后对国际监测系统(International Monitoring System,IMS)玫瑰型管道滤波器的降噪性能进行了评估。仿真实验及分析结果表明:(1)进气口数量约取96,阵列尺寸约18 m,一、二级管内径取10~20 mm,一、二级合成腔体积不得超过1 L,系统能获得较好的降噪性能;(2)IMS玫瑰型管道滤波器符合最佳阵列参数设置要求;(3)满足最佳阵列参数设置的玫瑰型管道滤波器可大幅度地提高信噪比。该分析结果可为已有次声降噪系统提供性能评估,可对新的次声降噪系统设计提供参考。      

Imaging flow structure and species with atomic and molecular filters

Rayleigh and Raman scattering have not been widely used for flow field and combustion imaging because of their very low scattering cross-sections and because of interference from strong background light. With the use of sharp cut-off, atomic and molecular filters this background can be rejected while high throughput is maintained. The sharp cut-off edge of the filters provides for the possibility of using them for high-resolution spectral discrimination. Consequently, Rayleigh and Raman imaging are now becoming feasible and have the promise of providing quantitative images of temperature, velocity, pressure, density, species, and nonequilibrium phenomena. Because Rayleigh and Raman scattering arise from all molecules and are not affected by quenching, quantitative images can be taken of all dominant molecular species as well as thermodynamic and transport properties of complex flows, weakly ionized plasmas, and combusting fields.     

Temporal characteristics of narrow-band optical filters and their application in lidar systems

The temporal characteristics of two different narrow-band optical filters at 532 nm are reported. Both filters operate on the 4P(1/2) - 8S(1/2) atomic transition of potassium vapor, where the 4P(1/2) state is excited by a 770-nm, 10-ns laser pulse. The filters operate on the principle of circular birefringence induced by either the Faraday effect or two-photon transition, which is confirmed by experiments. The characteristic decay times of the filters are 5 and 0.015 mus, which is significant for the design of optical gating and signal processing with matched filters for ocean lidar.     

Methods and evaluation of frequency aging in distributed-feedback laser diodes for rubidium atomic clocks

Distributed-feedback laser diodes emitting at 780?nm have been evaluated, with respect to the aging of the injection current required for reaching the rubidium D2 resonance line. Results obtained for lasers operating in air and in vacuum for 9 months are reported. When operated at constant temperature, the laser current required for emission at the wavelength of the desired atomic resonance is found to decrease by 50 to 80?μA per month. The impact of this result on the lifetime and long-term performances of laser-pumped rubidium atomic clocks is discussed.     

Enhanced surface atomic step motion observed in real time after nanoindentation of NaCl(100)

The nanometer-scale indentation of a crystalline surface produces nanostructures that evolve on a timescale that is inaccessible to existing imaging methods for the vast majority of surfaces. We have been able to observe the dynamic evolution of the freshly cleaved surface of a NaCl(100) crystal after indentation with an atomic force microscope (AFM) in air. Here we present sequential AFM images featuring vertical atomic resolution which show that atomic terrace motion is greatly enhanced by the AFM indentation. Moreover, some of the nanometric features generated by the indentation become reassimilated into the crystalline surface structure of the surroundings of the indentation over a period of time of the order of several minutes.     

Study of a narrowband reflection filter with multi-channels

Reflection filters have various applications in optical communication and other systems.In this letter,we propose a narrowband high-reflection filter composed of dielectric and metallic layers,in which an optimized filter combined with an admittance-matching layer with broad stop band is achieved.The structure can be expressed as Sub ｜ （HL）13H2L（HL）313Cr0.84H ｜ air,with full-width at half-maximum （FWHM） bandwidth of 2.5 nm.Based on this structure,reflection filters with multi-peaks are presented,and the law of distribution of peak positions is drawn.     

EXAFS characterization of ferric oxyhydroxides

The EXAFS method has been used for investigating the local structures of ferric oxyhydroxides which are reaction products formed on an iron surface exposed to air or immersed in salt water. Fe K EXAFS spectra of two references of ferric oxyhydroxides, i.e. goethite and lepidocrocite, which are often detected as components of reaction products, have been also studied for comparison thereof. The two reference oxyhydroxides demonstrated different EXAFS spectra, which are interpreted based on the atomic local structures. Fe K EXAFS spectra and their radial distribution functions of the reaction products formed on an iron surface have been compared with those of the reference oxyhydroxides. This comparison shows that the first and second nearest neighboring structures around ferric ions in the reaction products are different from those of the two references. These results indicate that the local structures around ferric ions in the reaction products are disordered, although the atomic local structures of Fe–O may be described as being local structural units.     

Size Reduction of Tunable Micromachined Filters for High Speed Operations

The size reduction of tunable micromachined filters is carried out for high-speed wavelength tuning. We fabricated micromachined filters having a miniature structure with an air gap of 300 nm and a short cantilever of 45 μm, exhibiting fast response of below 3 μs.     

Analyses of transmission characteristics of Rb, Rb and Rb Faraday optical filters at 532 nm

In this paper, the transmission characteristics for Rb, ⁸⁵Rb and ⁸⁷Rb Faraday optical filters at 532 nm that can be used to detect the practical and important frequency-doubled Nd:YAG laser are analyzed and discussed. The theoretical model of an excited-state Faraday optical filter based on the hyperfine structures of atomic system in the intermediate field, what is to our knowledge, is firstly reported. This model predicts that the peak transmission is approximately 50% with an equivalent bandwidth of less than 3 GHz for filters operating on the 5P_1/2 → 10S_1/2 transition in Rb, ⁸⁵Rb and ⁸⁷Rb vapors, respectively. Moreover, the transmission property of ⁸⁷Rb atomic vapor is superior to that of Rb, ⁸⁵Rb atomic vapors, which makes it more suitable for the operation material of Faraday optical filters by comparison with natural Rb vapor.     

致冷多层干涉滤光片的光学特性

本文系统地研究了红外多层干涉滤光片的低温特性、并从薄膜的基本光学特性出发,推导了窄带滤光片、截止滤光片透射率与波长的温度效应.给出了截止滤光片截止波长的温度漂移公式.     

Evaluation of environmental filtration control of engineered nanoparticles using the Harvard Versatile Engineered Nanomaterial Generation System (VENGES)

Applying engineering controls to airborne engineered nanoparticles (ENPs) is critical to prevent environmental releases and worker exposure. This study evaluated the effectiveness of two air sampling and six air cleaning fabric filters at collecting ENPs using industrially relevant flame-made engineered nanoparticles generated using a versatile engineered nanomaterial generation system (VENGES), recently designed and constructed at Harvard University. VENGES has the ability to generate metal and metal oxide exposure atmospheres while controlling important particle properties such as primary particle size, aerosol size distribution, and agglomeration state. For this study, amorphous SiO₂ ENPs with a 15.4 nm primary particle size were generated and diluted with HEPA-filtered air. The aerosol was passed through the filter samples at two different filtration face velocities (2.3 and 3.5 m/min). Particle concentrations as a function of particle size were measured upstream and downstream of the filters using a specially designed filter test system to evaluate filtration efficiency. Real time instruments (FMPS and APS) were used to measure particle concentration for diameters from 5 to 20,000 nm. Membrane-coated fabric filters were found to have enhanced nanoparticle collection efficiency by 20–46 % points compared to non-coated fabric and could provide collection efficiency above 95 %.     

In-situ alpha spectrometry from air filters at ambient air pressure

The effect of collimation to the alpha-particle energy spectra was investigated for two different types of air filters, when the measurements were performed at ambient air pressure. Significant improvement of the energy resolution is possible if appropriate collimator is used. This is because only those alpha particles are detected entering the detector almost perpendicularly. We also show that although in-situ alpha spectrometry from air filters at ambient air pressure and with good energy resolution is possible, the accumulation of alpha-particle emitting aerosols in the surface of the collimator and the detector may deteriorate the registered spectrum. Therefore, the presence of possible spurious alpha peaks must be taken into account in continuous air monitoring.     

空气—氩气冷却ICP：有机溶液分析的工作条件及检出限研究

研究了冷却气含50%空气的ICP中,MIBK溶液里金属元素不同性质谱线的信背比与入射功率、观察高度、冷却气流量及冷却气中空气含量等工作条件的关系。测定了8种元素12条谱线的检出限并与氩有机ICP中相同谱线的检出限进行比较。另外还测定了在引入MIBK溶液的情况下,空气-氩气ICP中心通道的激发温度。结果表明,具有中等激发能的谱线在含50%空气的空气-氩气有机ICP中的检出限优于氩气有机ICP中的检出限。