HCl gas monitoring based on a QCM using morpholine-functional styrene-co-chloromethylstyrene copolymer coatings

Quartz resonators coated with various compositions of poly(styrene-co-chloromethyl styrene) reacted with morpholine as adsorption sites were fabricated for simply but accurately monitoring HCl gas in air. The exposure of all resonators to HCl gas irreversibly decreased the oscillation frequencies, indicating that these devices can be used for one-shot detection of HCl gas. The chemical structure and composition of the copolymer affected the sensitivity. The largest sensitivity was obtained for the copolymer having 40.0 mol% CMSt composition cross-linked with 5.0 mol% DVB. The sensitivity was 0.1 ppm/Hz for 10-min sensor operation, demonstrating a ppm level of HCl detection, although great interference was produced by changes in the humidity.     

Electrical response of electrospun PEDOT-PSSA nanofibers to organic and inorganic gases

Electrospun isolated nanofibers of poly(3,4-ethylenedioxythiophene) doped with (poly styrene sulfonic acid)-PEDOT-PSSA were used to sense vapors of several aliphatic alcohols. Due to the large surface to volume ratio and small quantity of active material used in their fabrication, these sensors have a similar or faster response time when compared to alcohol sensors based on PEDOT. Increasing the size of the alcohol molecule leads to longer response times, which is attributed to slower diffusion of the larger molecule into the polymer. The sensors were annealed in air at 70 °C and used to sense NH₃, HCl and NO₂ gas. The response time for NH₃ was faster than HCl, and the sensors showed a large initial response to NO₂ at room temperature which is very desirable, as some NO₂ gas sensors only operate at elevated temperatures. Electrospinning is a simple and inexpensive method of preparing PEDOT-PSSA nanofibers making it an attractive technique to fabricate polymer based low cost, rapid response and reusable gas sensors.     

Construction of a highly selective PVC-based membrane sensor for Ce(III) ions

A highly Ce(III) ion-selective poly vinyl chloride (PVC) membrane sensor based on N′-[(2-hydroxyphenyl)methylidene]-2-furohydrazide (NHMF) as an excellent sensing material is successfully developed. The electrode shows a good selectivity for Ce(III) ions with respect to most common cations including alkali, alkaline earth, transition and heavy metal ions. The proposed sensor exhibits a wide linear response with a slope of 19.4 ± 0.3 mV/decade over the concentration range of 1.0 × 10⁻⁵ to 1.0 × 10⁻¹ M, and a detection limit of 7.6 × 10⁻⁶ M of Ce(III) ions. The sensor response is independent of pH in the range of 3.5–10.0. The proposed electrode was applied as an indicator electrode in potentiometric titration of Ce(III) ions with EDTA and C₂O₄². It was also successfully applied in the determination of cerium ions in aqueous samples.     

Highly sensitive detection of HCl gas using a thin film of meso-tetra(4-pyridyl)porphyrin coated glass slide by optochemical method

The meso-tetra(4-pyridyl)porphyrin (MTPyP) deposited on glass slide by dip coating was used as a solid state sensor for HCl gas detection by optochemical method. Exposure of MTPyP coated glass slide to HCl gas results in the formation of protonated meso-tetra(4-pyridyl)porphyrin (PMTPyP). UV-vis and fluorescence spectral methods were used to study the protonation of MTPyP both in solution and on solid state. The absorption spectrum of MTPyP modified glass slide shows an intense Soret band at 427 nm, which is shifted to 470 nm upon exposure to HCl gas. The concentration of HCl gas was monitored from the absorbance changes of Soret band of PMTPyP at 470 nm. The detection limit of the solid state sensor was found to be 0.01 ppm. The recovery rate of the solid state was very fast and it was monitored by UV-vis and fluorescence techniques with successive exposure to HCl gas and ammonia vapor with nitrogen gas. The planarity and energy of the molecule have changed after exposed to HCl gas which was confirmed by ab-intio calculation using Gaussian software. The response of the solid state sensor towards HCl gas was highly stable for several months.     

Self-assembly of polyelectrolytic multilayer thin films of polyelectrolytes on quartz crystal microbalance for detecting low humidity

Low-humidity sensors were made by layer-by-layer (LBL) self-assembly of poly(4-styrenesulfonic acid-co-maleic acid) (PSSMA) or poly(styrenesulfonic acid) sodium salt (PSS) and poly(allylamine hydrochloride) (PAH) into multilayer thin films on a gold electrode of quartz crystal microbalance (QCM). The thin films were characterized by QCM and atomic force microscopy (AFM). The effects of maleic acid (MA) in PSSMA, the number of layers and the ionic strength on the low-humidity sensing properties (sensitivity) were compared with those of PSS. The sensitivity of the PSSMA/PAH multilayer thin film exceeded that of the PSS/PAH multilayer thin film when the multilayered thin films of polyelectrolytes were prepared from solutions without NaCl. The sensitivity of both PSSMA/PAH and PSS/PAH multilayered thin films was increased by increasing the number of layers and by adding salt to the deposition solution. The PSS/PAH multilayered thin film that was prepared from the solutions with NaCl had the highest sensitivity (1.923 −ΔHz/Δppm_v at 27.5 ppm_v) and a short response time. Spin-coating was also adopted to fabricate PSS-based low-humidity sensors for comparison.     

A fibre-optic oxygen sensor based on contact charge-transfer absorption

A fibre-optic oxygen (O₂) sensor monitoring at a wavelength of 400 nm has been successfully developed for the determination of gaseous O₂. Its working principle is based on the contact charge-transfer absorption of N,N-dimethyl-p-toluidine and O₂. The response to changes in O₂ concentrations is reversible and in good agreement with the Beer-Lambert law. The response and recovery times are 12 and 26 min, respectively. The sensor can detect a wide range of O₂ concentrations, ranging from 4.3 to 100% O₂. The precision is 1.45% (n=5) in a gas mixture of 95% O₂ in N₂ and the limit of detection is 4.3% O₂ (3σ_b). The sensor is stable with a 0.53% change in sensitivity per hour. There is a 0.25% °C⁻¹ decrease of the sensitivity of the sensor to O₂ in the range 20–34°C. Water vapour and nitrogen dioxide interfere slightly, whereas hydrogen sulphide and hydrogen chloride have moderate interference on the sensor. However, chlorine and sulphur dioxide seriously interfere with the sensor.     

Entropy maximisation and open queueing networks with priorities and blocking

A review is carried out on the characterisation and algorithmic implementation of an extended product-form approximation, based on the principle of maximum entropy (ME), for a wide class of arbitrary finite capacity open queueing network models (QNMs) with service and space priorities. A single server finite capacity GE/GE/1/N queue with R (R>1) distinct priority classes, compound Poisson arrival processes (CPPs) with geometrically distributed batches and generalised exponential (GE) service times is analysed via entropy maximisation, subject to suitable GE-type queueing theoretic constraints, under preemptive resume (PR) and head-of-line (HOL) scheduling rules combined with complete buffer sharing (CBS) and partial buffer sharing (PBS) management schemes stipulating a sequence of buffer thresholds {N=(N₁,…,N_R),0<N_i≤N_i−1,i=2,…,R}. The GE/GE/1/N queue is utilised, in conjunction with GE-type first two moment flow approximation formulae, as a cost-effective building block towards the establishment of a generic ME queue-by-queue decomposition algorithm for arbitrary open QNMs with space and service priorities under repetitive service blocking with random destination (RS-RD). Typical numerical results are included to illustrate the credibility of the ME algorithm against simulation for various network topologies and define experimentally pessimistic GE-type performance bounds. Remarks on the extensions of the ME algorithm to other types of blocking mechanisms, such as repetitive service blocking with fixed destination (RS-FD) and blocking-after-service (BAS), are included.     

Performance characteristic studies of glucose biosensors modified by (3-mercaptopropyl)trimethoxysilane sol–gel and non-conducting polyaniline

The materials (3-mercaptopropyl)trimethoxysilane (MPTMS) sol–gel and non-conducting polyaniline (PAn) were prepared for coating on two different amperometric biosensors fabricated by the immobilization of glucose oxidase (GOx) in conducting polyaniline (PA) as permselective membranes. A few performance characteristics of the MPTMS and the PAn-modified glucose sensors are comparable. In detecting 1 mM glucose, the biosensors’ response times were 11 and 12 s, respectively, and results from the repeating measurements (N = 10) showed that R.S.D. = 2.09 and 1.70%, respectively. The detection linearity of the two biosensors was up to 12.5 mM with R = 0.9989 and 0.9969. When they were used to detect 0.5 mM of ascorbic acid (AA), uric acid (UA), and acetaminophen at an anodic potential of 0.4 V, current signals were either insignificant or invisible. The PAn-coated glucose sensor exhibited superior sensitivity at 18.91 μA/(mM cm²), and a maximum current density of 3.70 mA/cm². GOx in the MPTMS-modified biosensor presented a stronger affinity to glucose with K_m = 48.87. More importantly, the stability of this biosensor is superior to that of the PAn-modified biosensor and has lasted for almost 5 months.     

Fabrication of a highly selective and sensitive Gd(III)-PVC membrane sensor based on N-(2-pyridyl)-N′-(4-nitrophenyl)thiourea

In this work we report the development of a highly selective and sensitive Gd(III) membrane based on N-(2-pyridyl)-N′-(4-nitrophenyl)thiourea (PyTu4NO₂) as an excellent neutral ion carrier. The Gd(III) sensor exhibits a Nernstian slope of 19.95 ± 0.3 mV per decade over the concentration range of 3.0 × 10⁻⁷ to 1.0 × 10⁻¹ M, and a detection limit of 3.0 × 10⁻⁷ M of Gd(III) ions. The potentiometric response of the sensor is independent of the solution pH in the range of 4.0–9.0. It manifests advantages of low detection limit, fast response time (10 s), and most significantly, very good selectivity with respect to a number of lanthanide ions (La, Ce, Sm, and Eu ions). It can be used at least for a period of 8 weeks without any significant divergences in its potential response. To assess its analytical applicability the proposed Gd(III) sensor was successfully applied as an indicator electrode in the titration of Gd(III) ion solutions with EDTA and for the determination of the fluoride ion in two mouth wash preparations. It was also used for the direct monitoring of Gd(III) ions in binary mixtures.     

基于图像块迭代和稀疏表示的超分辨率图像重建算法

针对待复原图像内容间差异和重建速度缓慢的问题,提出基于图像块迭代分类和稀疏表示的超分辨率图像重建算法。首先,根据阈值把图像迭代分块为三种不同形态。然后,对三种形态分别处理:在重建时,对4N×4N块利用双三次插值(BI)算法重建;对2N×2N块由K-奇异值分解(K-SVD)算法得到对应的高、低分辨率字典,通过正交匹配追踪(OMP)算法重建;对N×N块用形态成分分析(MCA)法分解为平滑层和纹理层,然后由各层相应的字典对通过OMP算法重建。将所提方法与基于稀疏基的方法、基于MCA的方法和基于两级与分频带字典的方法相比,所提算法在主观视觉效果、评测指标和重建速度上都有明显的改善。实验结果表明,该方法在图像的边缘块和不规则区域获得了更为精细的细节,重建效果更明显。     

A hybrid numerical/neurocomputing strategy for sensitivity analysis of nonlinear structures

A hybrid numerical/neurocomputing (HN/N) strategy is presented for the evaluation of selective sensitivity coefficients of nonlinear structures. In the hybrid strategy, multilayer feedforward neural networks are used to extend a range of the validity of predictions of sensitivity coefficients made by Padé approximants. To further increase the accuracy and the range of network predictions, a data expansion strategy is used in which additional training data are generated by using extrapolated values of the coefficients in a Taylor series. Within this strategy a number of techniques are examined for evaluating derivatives of response functions. The effectiveness of the HN/N strategy is assessed by performing numerical experiments for composite panels subjected to combined thermal and mechanical loads. It is shown that the HN/N strategy reduces the number of full-system analyses and allows obtaining selective information about the structural response and the sensitivity coefficients.     

Development of an optical hydrogen sulphide sensor

A hydrogen sulphide (H₂S)-sensitive optode film has been fabricated by immobilising tetraoctylammonium fluorescein mercury(II) acetate (TOFMA) and tri-n-butyl phosphate in a poly(vinyl chloride) (PVC) matrix. The optode film, coated on an overhead transparency film, was employed as a sensing device for fluorimetric detection of H₂S. The fluorescence intensity monitored at 553 nm (excitation at 503 nm) increased with increasing H₂S concentrations. The optode film showed a good, linear and reversible response to H₂S from 0 to 15 ppm (v/v). It was optically stable and the reproducible response of the film on exposure to 10 ppm (v/v) H₂S was extremely good. There was no sign of degradation after 8 h of continuous use. The response to H₂S levelled off at about 27.5 ppm The response and recovery times of the optical H₂S sensor were fast and less than 2 and 5 s, respectively. An optically-based sensor for H₂S determination was successfully developed. It was anticipated that the system could be used to monitor H₂S with a concentration range of 0–25 ppm (v/v) with satisfactory results. A proposed mechanism for the detection of H₂S by the optode films is described.     

Selective detection of HCHO gas using mixed oxides of ZnO/ZnSnO3

Mixed oxides of ZnO/ZnSnO₃ doped with Au element were prepared by a hydrothermal process. The crystal structure, composition and ceramic microstructure of the powders obtained were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results show that the product is the mixture of ZnO/ZnSnO₃; its particle size is about 500 nm with good dispersivity in shape. The sensitivity, selectivity, response and recovery properties of the ZnO/ZnSnO₃-based sensors were investigated by mixing a target gas in air. It is found that the sensors have remarkable sensitivity to HCHO vapor and satisfactory selectivity to other gases.     

低阻TiO_2基三甲胺气体传感器性能分析

按旁热式结构采用以TiO2为基质对InSb2O3Nb2O5氧化物不同的重量比去掺杂研制成的三甲胺(TMA)气体传感器,大幅度降低了加热功率和其在空气中的阻值,器件对响应TMA气体具有灵敏度高、响应时间快、恢复时间短、长期稳定等特点,对干扰气体NH3具有良好的选择性。     

掺杂三乙醇胺铜配合物的PVA复合薄膜/K+交换玻璃光波导器件检测SO2气体

三乙醇胺酮配合物气敏性研究发现,该配合物与二氧化硫气体作用时透光率发生变化。以此结果为依据在K 交换玻璃光波导表面固定三乙醇胺铜配合物掺杂的聚乙烯醇复合薄膜,研制出了二氧化硫气体传感元件,并在光波导传感检测系统中测定其传感特性。实验结果表明,本传感元件对低浓度(500×10-9～15×10-6)二氧化硫气体有良好的线性快速可逆响应,低浓度氯化氢、硫化氢、二氧化氮、氨气以及挥发性有机物蒸汽对二氧化硫气体的检测没有干扰,具有灵敏度和选择性高、可逆性好,结构简单和易制作等特点。     

EPR and DRS evidence for NO2 sensing in Al-doped ZnO

Zinc oxide (ZnO) is a well-known semiconducting multifunctional material wherein properties right from the morphology to gas sensitivity can be tailor-made by doping or surface modification. Aluminum (Al)-incorporated porous zinc oxide (Al:ZnO) exhibits good response towards NO₂ at low-operating temperature. The NO₂ gas concentration as low as 20 ppm exhibits S = 17% for 5 wt.% Al-incorporated ZnO. The NO₂ response increases with operating temperature and concentration and reaches to its maximum at 300 °C without any interference from other gases such as SO₃, HCl, LPG and alcohol. Physico-chemical characterization likes differential thermogravimetric analysis (TG-DTA) electron paramagnetic resonance (EPR) and diffused reflectance spectroscopy (DRS) have been used to understand the sensing behavior for pure and Al-incorporated ZnO. The TG-DTA depicts formation of ZnO phase at 287 °C. The EPR study reveals distinct variation for O⁻ (g = 2.003) and Zn interstitial (g = 1.98) defect sites in pure and Al:ZnO. The DRS studies elucidate signature of adsorbed NO_x species in aluminium-incorporated zinc oxide indicating its tendency to adsorb these species even at low temperatures. This paper is an attempt to correlate the gas sensing behavior with the physico-chemical studies such as EPR and DRS.     

TAA薄膜NO_2气敏元件的特性研究

用真空升华方法制作了ＴＡＡ薄膜ＮＯ２气敏元件，并研究了其室温条件下的响应特性．结果表明：该元件在室温下对ＮＯ２具有较高的灵敏度，可检测空气中含１×１０（－６）的ＮＯ２气体．该元件在１．７×１０（－６）～１７×１０（－６）浓度范围内对ＮＯ２呈线性响应，响应时间在３０ｓ内，恢复时间为几分钟的数量级。     

基于快速傅里叶变换的正弦信号频率高精度估计算法

为了进一步提高加性高斯白噪声背景中正弦信号的频率估计精度,提出了一种新的基于插值快速傅里叶变换(FFT)的正弦信号频率估计算法.首先,对N点正弦采样序列进行等长度时域补零延长,再进行 2N 点FFT; 然后, 搜索幅度最大离散谱线位置得到频率粗估计值; 最后, 采用幅度最大谱线以及原信号的离散时间傅里叶变换(DTFT)在幅度最大谱线左右两侧的两点抽样值进行精估计.仿真结果表明,当信号实际频率位于FFT两条离散谱线之间任意位置时,所提算法的频率估计均方根误差均接近克拉美罗下限,具有较好的一致性,估计精度高于Candan算法、Fang算法、三谱线合理结合(RCTSL)算法和Aboutanios算法, 且信噪比阈值较低,估计性能优于现有频率估计算法.     

Optical VOCs detection using poly(3-alkylthiophenes) with different side-chain lengths

The use of conjugated polymers in the gas and volatile organic compounds (VOCs) detections represents an advance in the development of the electronic noses. Polythiophenes show good thermal and environmental stability, are easily synthesized and they have been studied as gas and VOCs sensors using different principles or transduction techniques. Among these techniques, optical sensing has been attracted attention, mainly due to its versatility. However, conjugated polymer-based optical sensors are still less studied. This paper describes the use of two poly(3-alkylthiophenes) for VOCs optical detection. The sensing measurements were carried out using visible spectroscopy. Both polymers showed good sensitivity to the VOCs, showing fast and reversible responses with some hysteresis, and were unable to detect hydroxylated samples. Furthermore, it was demonstrated that the thickness of polymer films influences the intensity of the optical response. Although there is similarity in the superficial composition of the polymers films, demonstrated by their surface energies, they showed significant differences in their optical properties upon exposure to the VOCs.     

硅烷法固定ssDNA制作的压电式DNA传感器

利用硅烷法将ssDNA固化T方向切割、3.58MHz和10MHz石英晶体金电极上,构建了压电DNA传感器,建立了快速检测葡萄球菌肠毒素B(SEB)基因的方法。优化了固定SEB基因的条件,并用动态法、静态法和斑点杂交法进行了固化效果观察。结果表明:该传感器2h后,有较好响应;对不同长度DNA探针固化效果进行比较,169bp(即169个碱基)SEB探针固定和杂交效果较好;利用0.5mol/LNaOH进行电极洗脱,时间为45min,电极可以再生,且传感器可以重复使用3次;利用1.2mol/LNaOH和1.2mol/LHCl洗涤电极,该电极可多次再利用;固化好的电极于4℃条件下可以保存三周之久。