Carbon-film-based humidity sensor containing sodium or potassium. Recovery effect

The paper describes the recovery effect of some modified carbon films applied as a humidity-sensitive resistor. The carbon films were prepared using mixtures of furfuryl alcohol and NaOH (or KOH) solution. The films have been tested as humidity-rensitive resistors. FT-IR investigations revealed that due to oxygen and carbon dioxide chemisorption the carbon surface was covered by polar surface functional groups. The electric resistance of such films with oxidised surface is extremely sensitive to contact with water vapour. On the contrary, the sensitivity of newly obtained Na (or K)-modified carbon films towards water vapour was found to be relatively minor before ageing. The process of humidity sensitivity development (caused by oxidation of carbon surface) is reversible, i.e., the sensitivity disappears upon HCl and/or heat treatment but recovers after a sufficiently long storage in air.     

Polyisoprene-nanostructured carbon composite – A soft alternative for pressure sensor application

Latest related research shows natural polyisoprene-nanostructured carbon composite (PNCC) as a promising piezoresistive material for soft pressure sensors. The main advantages of PNCC over conventional sensors are exceptional sensitivity in pressure range from 0.1 to 10 bar and possibility to be embedded into completely soft (hyper-elastic) structures.In this work we have elaborated a completely soft (hyper-elastic) PNCC pressure sensor prototype, made using functional multi-layer approach, when elementary layers of PNCC with different conductive filler concentration are cured together and form a uniform sensor body with integrated soft (hyper-elastic) electrodes. We proposed also a theoretical model to explain the observed positive piezoresistivity and used it for fitting of our experimental results.The prototype system elaborated could be used for counting interface events between sensor and external environmental factor. The achieved result could be a step towards the artificial skin, capable to sense non-destructive interaction with the external influence.     

Flexible vapour sensors using single walled carbon nanotubes

Thin, strongly adhering films of single-walled carbon nanotube bundles (SWNT) on flexible substrates such as poly(ethyleneterephthalate) (PET) were used for vapour sensing (hexane, toluene, acetone, chloroform, acetonitrile, methanol, water, etc.). These sensors are extremely easy to fabricate using the line patterning method. For example, ‘4-probe’ sensor patterns are drawn on a computer and then printed on overhead transparency (PET) sheets. These PET patterns were coated with films of electronically conductive SWNT bundles (1–2 μm thick) by dip-coating in aqueous surfactant-supported dispersions and mounted in glass chambers equipped for vapour sensing. Experiments conducted under saturated vapour conditions in air showed sensor responses that correlated well with solvent polarity [E_T(30) scale]. Similar results were obtained under controlled vapour conditions (no air) at 10,000 ppm. Control experiments using films of carbon black on PET (Aquadag-E^®), also prepared by the line patterning method, showed very little response to vapours under identical experimental conditions. The sensors are very flexible, e.g., they can be bent to diameters as small as 10 mm without significantly compromising sensor function.     

橡胶中炭黑分散度的自动判别

本文对目前橡胶行业普遍采用的显微照相法，作了很大改进，具体有：在计算机屏幕 上清晰地显示炭黑粒子在橡胶中分布的彩色图案，找出决定橡胶质量等级的特征，取得合理 刻划炭黑粒子分散性的数量指标，提出层次分析判别法, 由计算机自动判别出待测胶料炭黑 分散度的级别，国内目前尚无同类技术．     

Novel e-nose for the discrimination of volatile organic biomarkers with an array of carbon nanotubes (CNT) conductive polymer nanocomposites (CPC) sensors

We report the original design of a new type of electronic nose (e-nose) consisting of only five sensors made of hierarchically structured conductive polymer nanocomposites (CPC). Each sensor benefits from both the exceptional electrical properties of carbon nanotubes (CNT) used to build the conductive architecture and the spray layer by layer (sLbL) assembly technique, which provides the transducers with a highly specific 3D surface structure. Excellent sensitivity and selectivity were obtained by optimizing the amount of CNT with five different polymer matrices: poly(caprolactone) (PCL), poly(lactic acid) (PLA), poly(carbonate) (PC), poly(methyl methacrylate) (PMMA) and a biobased polyester (BPR). The ability of the resulting e-nose to detect nine organic solvent vapours (isopropanol, tetrahydrofuran, dichloromethane, n-heptane, cyclohexane, methanol, ethanol, water and toluene), as well as biomarkers for lung cancer detection in breath analysis, has been demonstrated. Principal component analysis (PCA) proved to be an excellent pattern recognition tool to separate vapour clusters.     

Vapor sensing properties of thermoplastic polyurethane multifilament covered with carbon nanotube networks

The volatile organic compound (VOC) vapor sensing properties of a novel kind of thermoplastic polyurethane multifilament - carbon nanotubes (TPU-CNTs) composites is studied. And the sensing is based on changes in the electrical resistance of the composites due to vapor contact. The composites were readily obtained by adhering CNTs on the surface layer of TPU by means of simply immersing pure TPU multifilament into CNT dispersion. The uniformly formed nanotube networks on the outer layer of composite multifilament are favorable for providing efficient conductive pathways. The resulting TPU-CNTs composites show good reproducibility and fast response (within seconds) of electrical resistance change in cyclic exposure to diluted VOC and pure dry air. The vapor sensing behaviors of the composites are related to CNT content, vapor concentration, and polar solubility parameters of the target vapors. A relatively low vapor concentration of 0.5% is detectable, and a maximum relative resistance change of 900% is obtained for the composite with 0.8 wt.% CNT loading when sensing 7.0% chloroform. It is proposed that both the disconnection of CNT networks caused by swelling effects of the TPU matrix and the adsorption of VOC molecules on the CNTs are responsible for the vapor sensing behavior of TPU-CNTs composite, while the former effect plays the major role.     

Room temperature hydrogen gas sensor nanocomposite based on Pd-decorated multi-walled carbon nanotubes thin films

Multi-walled carbon nanotubes (MWCNTs) are successfully processed in the form of thin films (buckypapers), and their morphology and electrical behaviour are characterized. The MWCNTs are synthesized by the floating catalyst chemical vapour deposition process. The effects of a sequence of treatments applied for MWCNTs purification on the buckypapers electrical behaviour are also examined. Nanocomposite thin films constituted of pristine and purified MWCNTs and Pd nanoparticles are prepared in order to evaluate their viability as H₂ sensors at room temperature. For this purpose, the electrical resistance of the nanocomposite films in atmospheres with different H₂ concentrations, is determined. Scanning electron microscopy (SEM) images show that the buckypapers and the nanocomposite films are 2D structures constituted by randomly oriented MWCNTs. The buckypapers present a semiconductor-like electrical behaviour as determined by the standard four point method. Room temperature resistivity values of around 10⁻³ Ω m are assessed. Nanocomposite films show different electrical behaviour depending on the purification treatment applied to the MWCNTs employed. Furthermore, the electrical resistance of the nanocomposite films is found to increase when the measurements are performed in H₂ atmosphere. Values of H₂ sensitivity at room temperature of the nanocomposite films up to 2.15% are determined for H₂ average concentration higher than 350 ppm with short recovery time.     

A hybrid chemiresistive sensor system for the detection of organic vapors

A five node sensor array, consisting of three films of gold nanoparticles functionalized with p-terphenylthiol, dodecanethiol and mercapto-(triethylene glycol) methyl ether, and films of poly(3-hexylthiophene) and polypyrrole, was integrated into a portable, microprocessor-based system. The system was evaluated for the detection of chloroform, diisopropyl methylphosphonate (DIMP), ethanol, hexane, methanol, and toluene vapors. Direct comparison of the five sensor films with respect to sensitivity, response time and recovery time was made by measurement of the resistance changes upon simultaneous exposure to each analyte. In general, the sensor films responded, with greatest sensitivity, to organic analyte molecules with similar chemical functionality (e.g., polarity). For example, the dodecanethiol-functionalized gold nanoparticle film sensor excelled at detecting hexane, while the mercapto-(triethylene glycol) methyl ether-functionalized nanoparticle film exhibited superb detection of ethanol and chloroform. Although the poly(3-hexylthiophene) film was very sensitive to polar analytes, including DIMP, in many cases it suffered from relatively long recovery times. Following training of the sensor system, successful differentiation and detection of the analytes were realized using a relatively simple algorithm based on “minimization of the squares of differences” method. The ability of the system to optimally differentiate these analytes is considered within the context of principal component analysis, and the effects of long-term sensor drift are discussed.     

An optimal shifting vector approach for efficient probabilistic design

The application of reliability-based design optimization (RBDO) is hindered by the unbearable computational cost in the structure reliability evaluating process. This study proposes an optimal shifting vector (OSV) approach to enhance the efficiency of RBDO. In OSV, the idea of using an optimal shifting vector in the decoupled method and the notation of conducting reliability analysis in the super-sphere design space are proposed. The shifted limit state function, instead of the specific performance function, is used to identify the inverse most probable point (IMPP) and derive the optimal shifting vector for accelerating the optimization process. The super-sphere design space is applied to reduce the number of constraints and design variables for the novel reliability analysis model. OSV is very efficient for highly nonlinear problems, especially when the contour lines of the performance functions vary widely. The computation capability of the proposed method is demonstrated and compared to existing RBDO methods using four mathematical and engineering examples. The comparison results show that the proposed OSV approach is very efficient.     

基于多壁纳米碳管的传感器对甲苯的气敏性研究

传感器的基底为Al2O3,上面真空溅射了叉指金电极,在电极之间涂布微量多壁纳米碳管悬浊液,干燥后作为气敏膜.室温下测试电极暴露于甲苯气体前后的电阻变化,发现吸附了甲苯后电极的导电能力下降,且下降的幅度与被测甲苯浓度有良好的线性关系.该实验结果预示着多壁纳米碳管是一种良好的室温下检测甲苯的敏感材料.对该气敏响应的产生机理本文进行了一些初步的探讨.     

Piezoresistive polypropylene–carbon nanofiber composites as mechanical transducers

This paper describes a strain sensor based on a polypropylene–carbon nanofiber (PP–CNF) composite film, fabricated by twin screw extrusion and compression molding, which is an inexpensive industrial polymer production technique. Its working principle is based on the piezoresistive effect showed by this kind of composites. Strain sensing by variation of the electrical resistance of the sensor was tested by a four-point bending method. Furthermore, the dependence of the gauge factor as a function of the deformation and velocity of deformation was calculated. The reproducibility of the electrical response of the material was also tested by applying up to forty loading–unloading cycles. The experimental results showed that PP–CNF films have an overall appropriate response for being used as piezoresistive deformation sensors, with a small non-linear response, typical of composites within the percolation threshold. Finally, electrical equivalent model of the sensor was developed and the experimental data was tested against it, showing good agreement.     

Design and verification of a lightweight reliable virtual machine monitor for a many-core architecture

Virtual machine monitors (VMMs) play a central role in cloud computing. Their reliability and availability are critical for cloud computing. Virtualization and device emulation make the VMM code base large and the interface between OS and VMM complex. This results in a code base that is very hard to verify the security of the VMM. For example, a misuse of a VMM hyper-call by a malicious guest OS can corrupt the whole VMM. The complexity of the VMM also makes it hard to formally verify the correctness of the system’s behavior. In this paper a new VMM, operating system virtualization (OSV), is proposed. The multiprocessor boot interface and memory configuration interface are virtualized in OSV at boot time in the Linux kernel. After booting, only inter-processor interrupt operations are intercepted by OSV, which makes the interface between OSV and OS simple. The interface is verified using formal model checking, which ensures a malicious OS cannot attack OSV through the interface. Currently, OSV is implemented based on the AMD Opteron multi-core server architecture. Evaluation results show that Linux running on OSV has a similar performance to native Linux. OSV has a performance improvement of 4%–13% over Xen.     

Development of wireless compressive/relaxation-stress measurement system integrated with pressure-sensitive carbon black-filled silicone rubber-based sensors

In order to detect the installation compressive stress and monitor the stress relaxation between two bending surfaces on a defensive furnishment, a wireless compressive-stress/relaxation-stress measurement system based on pressure-sensitive sensors is developed. The flexible pressure-sensitive stress sensor array is fabricated by using carbon black-filled silicone rubber-based composite. The wireless stress measurement system integrated with this sensor array is tested with compressive stress in the range from 0 MPa to 3 MPa for performance evaluation. Experimental results indicate that the fractional change in electrical resistance of the pressure-sensitive stress sensor changes linearly and reversibly with the compressive stress, and its fractional change goes up to 355% under uniaxial compression; the change rate of the electrical resistance can track the relaxation stress and give out a credible measurement in the process of stress relaxation. The relationship between input (compressive stress) and output (the fractional change in electrical resistance) of the pressure-sensitive sensor is ΔR/R₀ = σ × 1.2 MPa^?1. The wireless compressive stress measurement system can be used to achieve sensitivity of 1.33 V/MPa to the stress at stress resolution of 920.3 Pa. The newly developed wireless stress measurement system integrated with pressure-sensitive carbon black-filled silicone rubber-based sensors has advantages such as high sensitivity to stress, high stress resolution, simple circuit and low energy consumption.     

普通话发音评估性能改进

为减少噪声环境对评估性能的影响,该文将PNCC参数引入普通话发音评估。结果表明,其评分相关性在普通话测试实录音数据库上较传统MFCC参数提高了6.6%。在此基础上,对汉语声学模型拆分方法进行了研究,提出将声母介音+韵母模型拆分方法应用到发音评估中。使用这种拆分方式的评估系统总错误率降低5.6%,专家打分相关性则提高了0.056。该文还对模型最佳状态数的选取进行讨论,并提出模型状态数混合和不同配置综合评分两种混合评分方案,在相关性上较同等条件下3状态模型分别提高了0.021和0.017。     

Optical parameters of calix[4]arene films and their response to volatile organic vapors

The Langmuir-Blodgett (LB) technique was employed to produce thin LB films using an amphiphilic calix-4-resorcinarene onto different substrates such as quartz, gold coated glass and quartz crystals. The characteristics of the calix LB films are assessed by UV-visible, quartz crystal microbalance (QCM) and surface plasmon resonance (SPR) measurements. UV-vis and QCM measurements indicated that this material deposited very well onto the solid substrates with a transfer ratio of >0.95. Using SPR data, the thickness and refractive index of this LB film are determined to be 1.14 nm/deposited layer and 1.6 respectively. The sensing application of calixarene LB films towards volatile organic vapors such as chloroform, benzene, toluene and ethanol vapors is studied by the SPR technique. The response of this LB film to saturated chloroform vapor is much larger than for the other vapors. The response is fast and fully recoverable. It can be proposed that this sensing material deposited onto gold coated glass substrates has a good sensitivity and selectivity for chloroform vapor. This material may also find potential applications in the development of room temperature organic vapor sensing devices.     

Sinc interpolation based method for compensation of ionospheric dispersion effects on BOC signals with high subcarrier rate高速率子载波BOC信号基于sinc插值的电离层色散效应补偿方法

Binary Offset Carrier (BOC) signals with high subcarrier rate such as AltBOC(15,10) and cos-BOC(15,2.5) have been adopted for the next generation of Global Navigation Satellite System (GNSS) to make full use of the allocated spectrum. However, the two main lobes of the BOC signals are tremendously separated in the frequency spectrum and the group delay of the two lobes are greatly dispersed due to ionospheric dispersion. The signals will suffer extremely severe distortion caused by the group delay dispersion including waveform ripples, power losses and correlation function asymmetries. In this paper, a novel time domain sinc interpolation based ionospheric dispersion compensation method is proposed to eliminate the distortion to the BOC signals. Firstly, the time domain model of BOC signal under the dispersive ionosphere is developed. Afterwards, based on the model, the two signal main lobes are aligned by sinc interpolation so that the ionospheric dispersion effects are almost mitigated. Taking Galileo E5 AltBOC(15,10) signal as an example, the performance of the proposed method is evaluated by simulation and test. The results show that the proposed method is able to more effectively compensate the ionospheric dispersion with fewer computational loads versus existing methods.     

An insight into the dispersion of changes in cloned and non-cloned code: A genealogy based empirical study

In this paper, we present an in-depth empirical study of a new metric, change dispersion, that measures the extent changes are scattered throughout the code of a software system. Intuitively, highly dispersed changes, the changes that are scattered throughout many software entities (such as files, classes, methods, and variables), should require more maintenance effort than the changes that only affect a few entities. In our research we investigate change dispersion on the code-base of a number of subject systems as a whole, and separately on each system's cloned and non-cloned code. Our central objective is to determine whether cloned code negatively affects software evolution and maintenance. The granularity of our focus is at the method level.Our experimental results on 16 open source subject systems written in four different programming languages (Java, C, C#, and Python) involving two clone detection tools (CCFinderX and NiCad) and considering three major types of clones (Type 1: exact, Type 2: dissimilar naming, and Type 3: some dissimilar code) suggests that change dispersion has a positive and statistically significant correlation with the change-proneness (or instability) of source code. Cloned code, especially in Java and C systems, often exhibits a higher change dispersion than non-cloned code. Also, changes to Type 3 clones are more dispersed compared to changes to Type 1 and Type 2 clones. According to our analysis, a primary cause of high change dispersion in cloned code is that clones from the same clone class often require corresponding changes to ensure they remain consistent.     

晴空状态下飞机尾流的雷达反射模型

尾流对电磁波的散射主要是由于飞机在大气中飞行时对大气扰动使其折射率改变引起的.尾流的形状大小及强度等主要由飞机飞行重量、飞行速度及机翼结构等参数决定.利用尾流预测模型得到了在仿真区域内各离散网格点上的水蒸汽、位温等保守被动参量的值,并由此分析了尾流大气中折射系数的起伏特性,构建了晴空状态下飞机尾流的折射系数起伏的雷达反射模型.根据层流理论的Bragg散射原理得出飞机尾流RCS随频率、时间变化的关系,为飞机尾流的电磁散射特性计算提供了很好的电磁模型.     

Interaction of thin films of hydroxo-oxobis(8-quinolyloxo) vanadium (V) with ammonia vapour

Hydroxo-oxobis(8-quinolyloxo) vanadium (V) organometallic complex has been prepared as thin films from dichloromethane solution by spin coating and the kinetics of its interaction with ammonia vapour is investigated using surface plasmon resonance (SPR) technique. Thin film parameters are deduced from SPR measurements as well as spectroscopic ellipsometry and UV–vis spectral absorption measurements. Initial exposure to ammonia vapour has resulted in a permanent change to the baseline of the measured kinetic response, which is explained by the formation of the ammonium salt of the complex. Further exposures to ammonia vapour after 24 h and beyond, are shown to be highly reversible, which can be ascribed to formation of hydrogen bonding of second ammonia molecule with the highly negatively charged ammonium salt of the vanadium complex. Exposures to other organic vapours such as ethanol, chloroform and benzene are also studied in order to examine the selectivity of this material to ammonia vapour.     

电容耦合电阻层析成像并行电阻测量原理研究

传统的电阻层析成像(ERT)系统的电极与被测介质直接接触,容易产生电极极化、电化学腐蚀等问题,近年来出现的电容耦合非接触电导测量技术与ERT技术相结合的电容耦合电阻层析成像系统提出了一种新的非接触测量方法来解决此问题。但是目前该系统的电阻测量原理决定了其测量模式是串行的,成为限制系统数据采集速度的一个重要因素。针对该问题,本文引入了新的测量模型,提出了并行电阻测量原理,实现了数据采集系统,大大提高了系统速度。本文主要研究内容包括:分析了新型传感器的测量模型,提出了新的电阻求解方法;利用有限元法获得了新测量模型下管道内灵敏场分布;研制了相应的12电极样机系统。初步实验测试结果表明,该系统在具有较好测量精度的同时,其数据采集速度可达120帧/s,有效提高了电容耦合电阻层析成像系统的实时性。