Molecular dynamics simulations and experimental measurements of complex permittivity of aqueous solutions of NaCl at remote sensing frequencies

The dielectric properties of seawater are extremely important for ocean remote sensing at 5.1 and 13.6 GHz (frequencies that are commonly used by ocean remote sensing satellites). In this study, molecular dynamics simulations of aqueous sodium chloride solutions at mass concentrations between 1 and 10% and at the temperature ranges from 20 to 40°C were investigated. Cole-Cole equation was used to describe the frequency-dependent complex permittivity. The simulated results were compared with experimental results at 5.1 and 13.6 GHz, and proved to approximatively agree with experimental results.     

Quantitative millimetre wavelength spectrometry at pressures approaching atmospheric: Part I. Absolute determination of transition line strengths and sample concentrations with a confocal Fabry-Perot cavity spectrometer

The absolute determination of the millimetre wave power absorption coefficient of gas samples in a Fabry-Perot cavity whose resonant frequency is synchronised to a millimetre wavelength source is described. A theoretical treatment valid for pressures >200 Pa is developed. Absolute absorption coefficient measurements have been made on lines of SO₂ in the 50-60 GHz region that compared favourably with literature values. A calibration curve for SO₂ using the 59224.84 MHz line at 667 Pa over the concentration range 1-100% in N₂ has been produced. This technique could be especially useful for remote monitoring and process control applications because it is not necessary to scan the spectral line in order to determine the concentration of a species. The source runs at a single frequency coinciding with the peak of a millimetre wavelength (MMW) absorption line. This means that the technique could operate effectively at pressures up to and above atmospheric without the need for sophisticated MMW sources that can sweep across a wide frequency band.     

Wireless excitation of quartz crystals immersed in an aqueous fluid

A novel toroidal coil geometry able to induce remote acoustic waves in quartz crystals has been evaluated for the development of (bio)sensors. Remote acoustic generation in air was obtained for two alternative toroidal coils, with corresponding electrical impedance changes of 40 Omega for a PDMS- and 140 Omega for a ferrite-supported toroid respectively. It was found that the range of remote acoustic generation relative to the spiral coil standard was much improved, increasing the axial separation of their resonant sensing element from 0.1 mm to 20 mm, thereby allowing electromagnetic wave penetration across glass walls and fluid media to be utilised. Consideration of the transduction mechanism, along with measured cyclic changes in acoustic signal as a function of rotation, indicated that the large PDMS toroidal coil produced an asymmetric electric field. It was shown for the first time that a quartz crystal blank fully immersed in an aqueous fluid could support chemically sensitive shear acoustic standing waves that were excited and detected remotely. A signal to noise ratio of 30 ratio 1 at 20.13 MHz was achieved by placing a ferrite supported toroidal coil on the lower side of a glass beaker containing a 12 x 0.25 mm AT crystal blank and 1 mL of water. This discovery allows wireless shear acoustic wave measurements to be performed with total separation between the electronic detection system and assays undertaken in fluidic systems.     

High-altitude aircraft measurements of upwelling IR radiance: Prelude to FTIR from geosynchronous satellite

An aircraft version of the high-resolution interferometer sounder (HIS), a Fourier transform spectrometer designed for meteorological applications, has been used to measure the upwelling infrared emission of the earth with a resolving power on the order of 1000. HIS measurements from high-altitude NASA research aircraft have demonstrated that the high radiometric accuracies required for atmospheric temperature and humidity sounding (1°C absolute brightness temperature and 0.1° C RMS reproducibility) can be achieved. Calibration is accomplished using periodic views of two onboard high-emissivity blackbodies, servo controlled to 300 K and 240 K. For an interferometer, this approach relies on careful optical design and alignment to avoid unknown dependence of the responsivity on optical path difference. The aircraft model is a successful prototype for spacecraft versions for weather and climate monitoring.     

Tunable single-frequency diode laser at wavelength lambda = 1.645 microm for methane concentration measurements

This paper deals with the development of a novel single-frequency tunable diode laser with fiber-optic output for gas-analysis applications. The approach we propose is a convenient, simple and cheap solution for spectroscopy of single absorption lines of any gases having absorption bands in the optical fiber transparency window (0.7 microm/1.7 microm). The presence of fiber-optic output is an additional advantage for remote sensing applications. The laser operation is demonstrated as applied to R7 line of 2 nu(3) methane absorption band at lambda = 1.645 microm. The mode-hop-free tuning range of 35 GHz (1.2 cm(-1)) has been achieved.     

Tunable single-frequency diode laser at wavelength λ=1.65 μm for methane concentration measurements

This paper deals with the development of a novel single-frequency tunable diode laser with fiber-optic output for gas-analysis applications. The approach we propose is a convenient, simple and cheap solution for spectroscopy of single absorption lines of any gases having absorption bands in the optical fiber transparency window (0.7 microm/1.7 microm). The presence of fiber-optic output is an additional advantage for remote sensing applications. The laser operation is demonstrated as applied to R7 line of 2 nu(3) methane absorption band at lambda = 1.645 microm. The mode-hop-free tuning range of 35 GHz (1.2 cm(-1)) has been achieved.     

Near-infrared diode laser spectroscopy in chemical process and environmental air monitoring

This review covers the rapidly expanding field of near-infrared tunable diode laser spectroscopy where the availability of new lasers has led to the development of simple and inexpensive spectroscopic systems for the detection and monitoring of gas species. The latest diode lasers and the specific techniques associated with diode laser spectroscopy are described. Specific examples covering chemical vapour deposition reaction diagnostics, remote vehicle emission sensing, balloon-borne atmospheric monitoring and combustion diagnostics then illustrate the technique advantages of rapid, highly selective, in situ monitoring.     

Highly fluorescence Ta4C3 MXene quantum dots as fluorescent nanoprobe for heavy ion detection and stress monitoring of fluorescent hydrogels

Compared with other transition metal Mxene derived quantum dots（MQD_S）,Ta-based Mxene quantum dots have good functionality,but Ta-based Mxene quantum dots and their applications have not been studied so far.In this paper,we report for the first time the synthesis of high fluorescence quantum yield（QY） N-doped Ta₄ C₃ quantum dots（N-MQDs） using Ta₄ C₃ quantum dots in acid reflux damaged Ta₄ C₃ nanosheets as precursors and ...     

固相萃取-超高效液相色谱-串联质谱法同时测定大气降水中9种全氟化合物前体物质

采用固相萃取-超高效液相色谱-电喷雾串联三重四极杆质谱联用技术,建立了大气降水中9种全氟化合物前体物质的高通量检测方法。使用HLB固相萃取柱富集和净化降水样品中的目标化合物,以HSS T_3色谱柱(100mm×2.1 mm,1.7μm)为分析柱,甲醇和水作为流动相进行梯度洗脱。质谱以电喷雾负离子电离,采用多反应监测模式检测。9种目标化合物在0.05~5.00μg/L、0.5~50.0μg/L或5.00~500μg/L浓度范围内线性良好,相关系数为0.992 1~0.999 5,方法的检出限为0.05~7.9 ng/L;高、中、低3个添加水平的回收率为76.0%~106%,相对标准偏差为0.72%~13.7%。实验结果表明,该方法灵敏、准确,且具有检测范围广、分析速度快等特点,是一种适用于大气降水样品中全氟化合物前体物质检测分析的方法。     

PCA-LVQ法及其在RS-FTIR大气环境监测数据处理中的应用

将主成分分析(PCA)用于遥感傅里叶变换红外光谱(Remote Sensing Fourier Transform Infrared:RS-FTIR)的特征提取,结合学习矢量量化(LVQ)神经网络,实现了PCA-LVQ对大气中的8组分混合体系进行快速定性分析的建模方法。并与单纯的LVQ神经网络、反向传播人工神经网络(BP-ANN)得到的结果进行了比较。PCA-LVQ显示出较好的处理数据的能力,它不仅提高了运算速度,而且提高了模型的预测准确度,分类精度达到91.7%。PCA-LVQ的这一预测精度及运算速度,足以满足遥感傅里叶变换红外光谱对大气中有毒气体的实时、在线监测的需要。     

Remote determination of oxygen and water at millimetre wave frequencies using a fibre optic communications network

This paper describes the development of a remote millimetre wave (MMW) spectrometer capable of operation in the 57-66, 114-128 and 171-189 GHz bands. A 9.5-10.5 GHz signal from a yttrium iron garnet (YIG) source is carried via an infrared (IR) laser down a 1 km fibre-optic cable using a high-speed communications modulator. The 6th harmonic of the transmitted microwave signal is generated directly with an active sextrupler, which permits working in the 57-66 GHz band. For operation at 114-128 and 171-189 GHz, the 57-66 GHz output from the sextrupler is doubled or tripled by a further harmonic generator. Absorption line strength measurements and hence sample concentration determinations are undertaken using a Fabry-Perot cavity absorption cell. The spectroscopic data are recovered from the remote spectrometer by transmitting the rectified signal back over a further fibre-optic cable. Also described are the methods of cavity stabilisation and control across this fibre optic network. Oxygen determinations in the 57-66 and 114-128 GHz bands are performed to evaluate the performance of the spectrometer. A determination of water vapour in air at atmospheric pressure, at 183 GHz, is also presented, over a range of ∼5×10⁻⁵ to ∼0.025 volume fraction in air.     

H2O broadening of a CO2 line and its nearest neighbors near 6360 cm(-1)

Remote sensing of CO(2) requires high-fidelity reference data of spectral line parameters to be successful. The 6360 cm(-1) region is commonly used by satellites, field campaigns, and point-source gas sensors because it contains well-characterized and relatively isolated transitions of appropriate line strengths for atmospheric applications. However, the presence of gases other than CO(2), N(2), and O(2) can be a source of uncertainty for atmospheric measurements. Near 6360 cm(-1), there are numerous H(2)O and HDO transitions. Water makes up approximately 1-4% of Earth's lower atmosphere and can interfere with remote sensing measurements by (1) appearing as a direct spectral interference or (2) acting as a foreign broadener for CO(2) lines. The primary goal of this work was to quantify H(2)O broadening of CO(2) through precision spectroscopy measurements on the R16e transition at 6359.967 cm(-1) and its two nearest neighbors. A secondary goal was to assess the accuracy of H(2)O reference line parameters in the HITRAN 2008 database for spectrally removing typical levels of moisture from air samples containing approximately 400 ppm of CO(2).     

Spectroscopic characterization of a neon surface-wave sustained (2.45 GHz) discharge at atmospheric pressure

In this paper a spectroscopic study of a microwave (2.45 GHz) neon surface-wave sustained discharge (SWD) at atmospheric pressure in a quartz tube has been carried out in order to determine the plasma characteristic parameters (e.g. electron temperature and density, gas temperature, absorbed power per electron) and also to identify possible deviations from the thermodynamic equilibrium for this kind of microwave discharge. The results have been compared to experiments in the literature for other noble gas (helium and argon) SWDs generated under similar experimental conditions. Intermediate values between those of argon and helium plasmas were obtained for characteristic neon plasma parameters (temperatures and electron density). An important departure from the Saha equilibrium was exhibited by neon SWDs.     

Microwave and RF surface wave sustained discharges as plasma sources for plasma chemistry and plasma processing

The surface wave produced plasma belongs to a class of RF and microwave induced plasmas. It results from the propagation of an electromagnetic wave which uses the plasma column it sustains and the plasma tube as its sole propagating media. This type of plasma offers several advantages compared to the positive column plasma of dc discharges or to other RF and microwave produced plasmas. Surface wave plasmas require no internal electrodes, and they can be applied over an extremely broad range of wave frequencies (27 MHz to 10 GHz demonstrated) and gas pressures (about 10^–4 Torr to a few times the atmospheric pressures). Using the surface wave plasma technique, a large variety of plasma column diameters have been created (0.5–150 mm demonstrated) and no limitation on plasma column length (column up to 6 m long demonstrated) has been found. The surface wave produced plasma is used in elemental analysis and to sustain emission in lasing media. This article is intended as a guide for potential users of surface wave plasmas in the field of plasma processing and plasma chemistry.     

Performance of a 2,4-DNPH coated annular denuder/HPLC system for formaldehyde monitoring in air

Summary The performance of annular denuders coated with 2,4-dinitrophenylhydrazine for collection of atmospheric HCHO has been evaluated by HPLC/UV analysis of samples coming from laboratory tests and field experiments. A number of parameters, such as collection efficiency at varying air humidity, detection limit, operative capacity and temporal self-consistency have been investigated to optimize the denuder behaviour under different weather conditions and to obtain short-term concentration profiles of HCHO. Deviations between measurements made simultaneously by the DNPH denuder method and differential optical absorption spectrometry (DOAS) have been found to average approximately 30% in the 0–5 ppb HCHO concentration range.     

Opto-thermal Moisture Content and Moisture Depth Profile Measurements in Organic Materials

Opto-thermal transient emission radiometry(OTTER) is a infrared remote sensing technique, which has been successfully used in in vivo skin moisture content and skin moisture depth profiling measurements. In present paper, we extend this moisture content measurement capability to analyze the moisture content of fruit (tomato. grape, etc. ) skins, and to study the relationship between fruits ripening process and their sur-face moisture and moisture depth profiles.     

Infrared glass fibers for in-situ sensing, chemical and biochemical reactions

Infrared optical fibres based on chalcogenide glasses have been designed for evanescent wave spectroscopy. The sensitivity of the optical sensor is improved in tapering the sensing zone by chemical etching and the working optical domain of the system has been tested on a chloroform sample. This original remote sensor, based on the analysis of infrared signatures, has been applied to follow the fermentation process in cider fabrication as well as to detect and monitor a bacterial biofilm.     

A compact collinear AOTF Raman spectrometer

A compact, lightweight, completely packaged, uncooled, fully-automated collinear acousto-optic tunable-filter (AOTF) based spectrometer has been used to measure Raman spectra of three organic energetic materials (NQ, HMX, and TNT) using argon-ion laser excitation. Even though the resolution of the AOTF spectrometer is modest (7.4 cm(-1)) and it was not specifically designed for measuring Raman spectra, it has performed impressively. Such an instrument is specially useful for remote sensing and field measurements. In this paper, we will describe this instrument, present the measured Raman spectra and their comparison with the corresponding FT-IR spectra.     

Air flow assisted ionization for remote sampling of ambient mass spectrometry and its application

Ambient ionization methods are an important research area in mass spectrometry (MS) analysis. Under ambient conditions, the gas flow and atmospheric pressure significantly affect the transfer and focusing of ions. The design and implementation of air flow assisted ionization (AFAI) as a novel and effective, remote sampling method for ambient mass spectrometry are described herein. AFAI benefits from a high extracting air flow rate. A systematic investigation of the extracting air flow in the AFAI system has been carried out, and it has been demonstrated not only that it plays a role in the effective capture and remote transport of charged droplets, but also that it promotes desolvation and ion formation, and even prevents ion fragmentation during the ionization process. Moreover, the sensitivity of remote sampling ambient MS analysis was improved significantly by the AFAI method. Highly polar and nonpolar molecules, including dyes, pharmaceutical samples, explosives, drugs of abuse, protein and volatile compounds, have been successfully analyzed using AFAI-MS. The successful application of the technique to residue detection on fingers, large object analysis and remote monitoring in real time indicates its potential for the analysis of a variety of samples, especially large objects. The ability to couple this technique with most commercially available MS instruments with an API interface further enhances its broad applicability.     

Using silk-derived magnetic carbon nanocomposites as highly efficient Nanozymes and electromagnetic absorbing agents

Functional carbon nanomaterials have become the stars of many active research fields, such as electronics, energy, catalysis, imaging, sensing and biomedicine. Herein, a facile and one-pot strategy for generating ferromagnetic nanoparticles loaded on N-doped carbon nanosheets(Fe-N-CNS) is presented by salt-assisted high-temperature carbonization of natural silk proteins. Due to their graphitic structures,N-doping and ferromagnetic nanoparticles(FeN_x, FeO_y, FeC_z),...