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Superhydrophobic surfaces have been shown to produce significant drag reduction in both laminar and turbulent flows by introducing an apparent slip velocity along an air-water interface trapped within the surface roughness. In the experiments presented within this study, we demonstrate the existence of a surface tension gradient associated with the resultant Marangoni flow along an air-water interface that causes the slip velocity and slip length to be significantly reduced. In this study, the slip velocity along a millimeter-sized air-water interface was investigated experimentally. This large-scale air-water interface facilitated a detailed investigation of the interfacial velocity profiles as the flow rate, interfacial curvature and interface geometry were varied. For the air-water interfaces supported above continuous grooves (concentric rings within a torsional shear flow) where no surface tension gradient exists, a slip velocity as high as 30% of the bulk velocity was observed. However, for the air-water interfaces supported above discontinuous grooves (rectangular channels in a Poiseuille flow), the presence of a surface tension gradient reduced the slip velocity and in some cases resulted in an interfacial velocity that was opposite to the main flow direction. The curvature of the air-water interface in the spanwise direction was found to dictate the details of the interfacial flow profile with reverse flow in the center of the interface for concave surfaces and along the outside of the interface for convex surfaces. The deflection of the air-water interface was also found to greatly affect the magnitude of the slip. Numerical simulations imposed with a relatively small surface tension gradient along the air-water interface were able to predict both the reduced slip velocity and back flow along the air-water interface.

Condition assessment of civil infrastructures is difficult due to technical and economic constraints associated with the scaling of sensing solutions. When scaled appropriately, a large sensor network will collect a vast amount of rich data that is difficult to directly link to the existing condition of the structure along with its remaining useful life. This paper presents a methodology to construct a surrogate model enabling diagnostic of structural components equipped with a dense sensor network collecting strain data. The surrogate model, developed as a matrix of discrete stiffness elements, is used to fuse spatial strain data into useful model parameters. Here, strain data is collected from a sensor network that consists of a novel sensing skin fabricated from large area electronics. The surrogate model is constructed by updating the stiffness matrix to minimize the difference between the model’s response and measured data, yielding a 2D map of stiffness reduction parameters. The proposed method is numerically validated on a plate equipped with 40 large area strain sensors. Results demonstrate the suitability of the proposed surrogate model for the condition assessment of structures using a dense sensor network.

Hydrogen-bond acidic (HBA) polymers are well-established adsorbents for organophosphorus compounds and nitroaromatic explosives detection. In this paper, we report two HBA polymers for detection of styrene vapors based on 434-MHz surface acoustic wave (SAW) chemical sensors. These polymers, dubbed PLF and LSFA, are pendent hexafluoroisopropanol (HFIP)-group modified polysiloxanes, which were synthesized by one-step hydrosilylation reaction. Real-time response studies of these two sensors showed that they are highly sensitive to styrene vapors with excellent selectivity. After exposure to 5 mg/m3 styrene vapor, the frequency shifts of the PLF and LSFA sensors have increased by 6.3 kHz and 3.2 kHz, respectively. The polymers are 20-fold less sensitive to toluene than to styrene while they have comparable sensitivity to 1-butene. In situ infrared spectroscopy studies demonstrated that the polymer–styrene interaction is attributed to the OH/π hydrogen bond between HFIP groups of the polymers and the ethylene group of styrene molecules.

In this work, utility theory is introduced to optimum aerodynamic shape design under uncertainty (also called robust aerodynamic design). Specifically, utility theory is used to formulate the objective function of the optimization problem. The advantage of the proposed approach over the commonly used weighted sum method is that it does not require the use of weighting factors or the addition of constraints on the statistical moments. The polynomial chaos expansion metamodel with the least-angle regression and the hyperbolic truncation scheme are used to accelerate the uncertainty propagation and the optimization process. The proposed approach is demonstrated on the optimum airfoil shape design under uncertainty at steady transonic conditions. Two design cases are considered. In both cases the drag coefficient is to be minimized subject to constraints on the lift coefficient and the airfoil thickness at two chordwise locations. The first case treats the Mach number as uncertainty parameter and the second case treats the Mach number and the lift coefficient at target as uncertain. The proposed method is compared with deterministic single-point optimization and multi-point optimization, and the standard robust design formulations. Results show that the proposed approach is capable of obtaining airfoil design of the lowest mean drag coefficient with the smallest standard deviation as compared to the other approaches. In the first case, the proposed approach yields a design with a mean drag coefficient comparable to the standard robust design (around 97.6 drag counts, cts), but with a significantly lower variance (0.6 cts versus 2.5 cts). In the second case, the proposed approach yielded a design with a higher mean drag coefficient than the standard approach (98.4 cts versus 97.6 cts), but with a lower standard deviation (4.1 cts versus 4.8 cts). In both cases, the deterministic approaches yield designs with comparable or lower drag coefficients but with significantly larger standard deviations.

This work introduces multifidelity metamodeling for reliability analysis of nondestructive testing (NDT) systems. Specifically, the Cokriging metamodel is utilized to accelerate the uncertainty propagation within model-assisted probability of detection (MAPOD) analysis of ultrasonic testing (UT) systems. The Cokriging multifidelity metamodel fuses a limited amount of data obtained from high-fidelity (HF) physics-based UT models, which are accurate but time-consuming to evaluate, with a conservative to large amount of data from low-fidelity (LF) physics-based UT models, which are less accurate but faster to evaluate. The resulting Cokriging metamodel is fast to evaluate and yields an accurate estimate of the output of the HF model. The proposed approach is demonstrated on three benchmark UT MAPOD cases involving spherically-void and pill-box shaped defects in flat aluminum plates using planar and focused transducers. The results show that a two-level Cokriging metamodel is capable of yielding estimations of the HF model that are globally accurate within 1% of the standard deviation of the testing points. Furthermore, the result show that the Cokriging metamodeling approach needs around one order of magnitude fewer training data points when compared to the current state-of-the-art approaches that rely on metamodels constructed with Kriging.

Human respiration is rich in physiological and pathological information for health assessment and illness prediction. In this work, an integrated triboelectric self-powered respiration sensor (TSRS) was developed for simultaneously monitoring human respiratory behaviors and NH3 concentration in exhaled gases. The TSRS based on Ce-doping ratio of 0.004 M exhibits a better selectivity and larger sensitivity of 20.13 ppm−1 compared with those synthesized in other doping ratios. Under the same moisture as the breathing gas (97.5%RH), the sensor holds greater sensitivity toward NH3 at low concentration (0.1–1 ppm) than that at high concentration (1–10 ppm), implying the capability in detecting trace level NH3 biomarker in human breathing gases. Furthermore, triggered by the expansion and contraction of chest during breathing, TSRS can spontaneously monitor human respiratory patterns and physiological process after physical exercise. Meanwhile, a theoretical modeling was established in terms of permittivity change under gas molecules adsorption and verified via finite element simulation to interpret the self-powered sensing behaviors. This research not only proposes a promising approach to develop an all-in-one wearable respiration monitoring system for personal health diagnosis but also sheds some light on the theoretical modeling of triboelectric self-powered gas-sensing in terms of permittivity change.

Nitrogen dioxide sensors with high sensitivity and low energy consumption are demanded for atmosphere sensing networks. Here, a self-powered room temperature NO2 sensor has been developed based on the conjugation between the triboelectric and photoelectric effect. By converting the mechanical motions into electricity, a triboelectric nanogenerator (TENG) serves as a power source to simultaneously drive chemoresistive gas sensing and UV illumination. Under a 5 Hz external impact, the output voltage drop across interdigital electrodes has a proportional relationship with the NO2 concentration. A self-powered optomechatronic gas sensor (OGS) with hydrothermal ZnO nanowires synthesized at a concentration of 0.035 mol/l exhibits a superior response (∼14.8) and sensitivity (0.302 ppm−1) than those synthesized at other concentrations. Furthermore, the influence of the external force frequency and rectification on the gas sensing properties was systematically investigated. It is found that the TENG induced built-in electric field can effectively modulate the internal quantum efficiency and thus the sensing performance of OGSs. This work not only paves the way for constructing self-powered optomechatronic devices and systems but also pushes forward the active multifunctional network node for environmental monitoring.

We reported on the development of pentacene nano-particles film modified microstructure silicon (MSS) for ammonia (NH3) gas sensors. The MSS was fabricated by alkaline etching process, then pentacene film and interdigital electrodes were deposited on the MSS surface by vacuum evaporation. The surface morphologies of the MSS and pentacene film were characterized by scanning electron microscope (SEM). And the properties of the sensor were measured at room temperature. The SEM images showed the MSS exhibited a uniform hemisphere array, and pentacene nano-particles film was formed evenly on the MSS surface. The fabricated sensor showed reversible and favorable response to NH3.

A strong hydrogen-bond acidic (HBA) polymer linear fluoroalcoholic polysiloxane (PLF), synthesized by one-step hydrosilylation, was introduced for 2,4-dinitrotoluene (2,4-DNT) detection using surface acoustic wave (SAW) devices. FT-IR spectra and 1H NMR spectra characterizations confirmed its molecular structure. Then, PLF was dissolved in chloroform, and spray coated onto a 434 MHz SAW device. And subsequently, the sensitivity and selectivity of the fabricated sensor were studied based on a SAW test platform. To 2,4-DNT of 1 ppm and 100 ppb (for DNT, 1 ppm = 8.1 mg/m3; 1 ppb = 8.1 μg/m3), the responses of the sensor rose 7.7 and 1.5 kHz, respectively. Furthermore, compared with some common interference vapors at 10 mg/m3, the response of the sensor to 2,4-DNT at 1 ppm was 5 times stronger. The sensitive property was attributed to the hydrogen bond interaction between the hexafluoroisopropanol (HFIP) group in PLF and the basic lone electron pairs of nitro-groups in 2,4-DNT. Comparison between the PLF sensor and hydroxyl group functionalized polymer (carbowax and MOBCD)-coated sensors was investigated, and the results showed that the PLF sensor exhibited better sensitivity. In a word, the PLF sensor exhibited fast response, negligible baseline drifts and excellent reversibility, indicating good candidates of HFIP group functionalized HBA polymers for practical nitroaromatic explosives detection.

Two kinds of toluene vapor sensors with different sensitive film structures, i.e., multi-walled carbon nanotubes (MWCNTs)-polyethylene oxide (PEO) composite film and MWCNTs-PEO bilayer film were fabricated. Both sensors were obtained by airbrushing the sensitive films on interdigitated electrodes (IDE). Response performances of both sensors to toluene vapor at room temperature were investigated. Scanning electron microscope (SEM) was used for morphology analysis of the sensitive films. The experimental results showed that sensors with bilayer films revealed a larger sensitivity than that with the composite films. The response and recovery times of both sensors were within 8 s. Moreover, sensors with bilayer films exhibited a modest selectivity to toluene vapor. The sensing mechanisms of both sensors were studied as well.

A hydrogen-bond acidic (HBA) polymer, poly{methyl[3-(2-hydroxyl, 4,6-bistrifluoromethyl)phenyl]propylsiloxane}(DKAP), was coated on a 434 MHz surface acoustic wave (SAW) device, and subsequently tested against sarin (GB) and soman (GD) vapour along with dimethyl methyl phosphonate (DMMP) at concentrations below 10 mg m−3. The direct detection of GB and GD in the sub mg m−3 range, indicated the high sensitivity of the sensor, and was demonstrated by the corresponding sensor which showed high reproducibility as well. However, the response of the sensor to the real agents was relatively smaller and slower than to the simulant DMMP. Towards the real agents, the time to reach an adsorption equilibrium was considerable (∼16 min) and a time-dependent linear response was observed in the initial >3 min for both the adsorption and the desorption processes. The sensor was also compared with other HBA polymers coated SAW sensors in terms of response characteristics, with emphasis on the kinetic response behaviour. The slow adsorption and desorption property of the DKAP sensor towards the real chemical agents was attributed to the effect of the size of the analytes and to the strength of hydrogen-bonding, respectively.

In this paper, micro gas chromatography columns were fabricated through the micro-electro-mechanical system (MEMS) technique. Two types of columns were designed, namely, open-tube and semi-packed columns. By comparing different structures, column efficiency was improved by embedding square posts in the channel to form a semi-packed column. The result showed that column efficiency of the semi-packed column reached 55 366 plates per m. This study was the first to report based on experimentation that MEMS-based columns can reach a plate number this high. The plate number was five times higher than the value previously reported. In addition, a 30 m-long Agilent HP-5 commercial capillary column was used to compare the results with findings obtained using a MEMS-based semi-packed column. The analytes were perfectly separated in both columns. The column efficiency of the HP-5 capillary column was 5490 plates per m, which was 10 times lower than that of the micro-fabricated, semi-packed column.

Two strong hydrogen-bond acidic (HBA) polymers DKAP and PLF, were coated onto 434 MHz surface acoustic wave (SAW) devices for rapid detection of an explosive compound, 2,4-dinitrotoluene (2,4-DNT). Sensitivity and selectivity of the polymer-coated sensors were studied by exposure to 2,4-DNT in the concentration range of 200 ppb to 1 ppm, as well as some common interferences at higher concentrations. The results showed that the DKAP sensor has a 4.6 times higher sensitivity to 2,4-DNT than PLF at the concentration of 1 ppm, while a further comparison indicated that their sensitivities to dimethyl methylphosphonate (DMMP) are essentially identical. The superior sensitive performance of DKAP to nitroaromatics as compared to PLF can be attributed to the dipolarity induced by the aromatic ring segments, which promotes π–π interactions between the explosive vapor and the polymer coating. In addition, the DKAP sensor exhibits a high response of 4.6 kHz to 200 ppb 2,4-DNT, with an extrapolated limit of detection (LOD) of 0.1 ppb, which is comparable to most sensitive polymer-coated sensors previously reported. Furthermore, both adsorption and recovery time of the DKAP sensor is much shorter than other related sensors. Sensor responses to possible common interferences are found to be 11–35 fold lower than to 2,4-DNT. In situ infrared spectroscopy studies were performed to demonstrate the hydrogen bonding between nitroaromatic compounds and the chemoselective polymers.

Ultrasonic testing (UT) is used to detect internal flaws in materials and to characterize material properties. In many applications, computational simulations are an important part of the inspection-design and analysis processes. Having fast surrogate models for UT simulations is key for enabling efficient inverse analysis and model-assisted probability of detection (MAPOD). In many cases, it is impractical to perform the aforementioned tasks in a timely manner using current simulation models directly. Fast surrogate models can make these processes computationally tractable. This paper presents investigations of using surrogate modeling techniques to create fast approximate models of UT simulator responses. In particular, we propose to integrate data-driven methods (here, kriging interpolation with variable-fidelity models to construct an accurate and fast surrogate model. These techniques are investigated using test cases involving UT simulations of solid components immersed in a water bath during the in...

This paper reports the fabrication and performance of a semi-packed column with wavy channel configuration. The 2-m long, 80-μ m wide, and 300-μ m deep column is made by deep reactive-ion etching (DRIE) technology, and contains embedded circular posts of 30 μ m in diameter. The posts and curved groove increase the overall surface area of the column, which leading to higher separation efficiency. In order to achieve an even flow velocity in the channel, the arrangement position, shape, size of embedded posts are explored by the finite element method (FEM) in the semi-packed wavy gas chromatography column. The simulation results show that the gas samples experience less variation in the velocity profile of the semi-packed wavy column than the semi-packed rectangular MEMS column, and possess shorter mass transfer distance than the open one. The micro-fabricated column is used to separate normal alkanes from C5 to C12 to test its performance. The experimental separation results indicate that the theoretical plate number obtained by the proposed semi-packed wavy gas chromatography device is about 4 times higher than that obtained from the open rectangular column under the same injection conditions.

Poly(diallyldimethylammonium chloride)/single-walled carbon nanotube (PDDA/SWNT) multilayered thin films were prepared on quartz crystal microbalance by layer-by-layer self-assembly technique, and their sensing properties to humidity were studied. The SWNTs were characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The composite films were observed by field-emission scanning electron microscope. Two types of SWNT humidity sensors were fabricated using SWNTs and carboxyl (COOH) modified SWNTs as sensitive material, respectively. The results showed that the sensitivity of the PDDA/SWNT–COOH humidity sensor was 20.23 % higher than that of the PDDA/SWNT sensor. In contrast, the latter had a much superior hysteresis property, and the reason to cause this phenomenon was discussed.

Single-walled carbon nanotube (SWNT) films were prepared on interdigitated electrodes by airbrush technique, and their sensing properties to dimethyl methylphosphonate (DMMP) were studied. The SWNT films were characterized by field-emission scanning electron microscope. The response to different concentrations of DMMP vapors were investigated at room temperature. The results showed that the capacitance of airbrush SWNT sensor decreased rapidly in varying concentrations ranging from 12 to 60 mg/m3 (2.4–12 ppm). The capacitance sensitivity was about 12.5 % when exposed to 12 mg/m3 DMMP vapor. The capacitance sensitivity was higher when the initial capacitance and loss tangent were higher and the SWNT film was denser. It was found that the capacitance sensitivity was nearly 10 times to the resistance sensitivity. The airbrush SWNT sensor exhibited highly and fast capacitance response, good repeatability and selectivity for DMMP vapor.

Single-walled carbon nanotube (SWNT) films were prepared on silicon/silica substrates by screen-printed technique at a wafer scale, and their sensing properties to dimethyl methylphosphonate (DMMP) were studied. The SWNT networks were characterized by field-emission scanning electron microscope. The resistance responses to different concentrations of DMMP vapors were investigated at room temperature. The results showed that the resistance changes of the screen-printed SWNT films increased rapidly in varying concentrations ranging from 20 to 200 ppm. The sensor exhibited high resistance responses, good reproducibility and excellent long-term stability for DMMP vapor detection. The screen-printed SWNT networks would be potentially extended to large-scale, low cost and simple manufacturing sensor applications.

Model cellulose surfaces have attracted increasing attention for studying interactions with cell wall matrix polymers and as substrates for enzymatic degradation studies. Quartz crystal microbalance with dissipation monitoring (QCM-D) solvent exchange studies showed that the water content of regenerated cellulose (RC) films was proportional to the film thickness (d) and was consistent with about five water molecules per anhydroglucose unit. Sulfated nanocrystalline cellulose (SNC) and desulfated nanocrystalline cellulose (DNC) films had comparable water contents and contained about five times more water than RC films. A cellulase mixture served as a probe for studies of substrate accessibility and degradation. Cellulase adsorption onto RC films was independent of d, whereas degradation times increased with d. However, adsorption onto SNC and DNC films increased with d, whereas cellulase degradation times for DNC films were independent of studied d. Enhanced access to guest molecules for SNC and DNC films revealed they are more porous than RC films.

Supercapacitor have attracted much attention due to its fast power supply, long cycle life, simple principle, etc. Supercapacitors are widely used in consumer electronics. Activated carbon is a typical material for electric double layer capacitor. Here, we study the electrochemical performance of an activated carbon (TF-B520) bulky paper electrode made by vacuum filtration method. Cyclic Voltammetry and Constant Current Charge/Discharge were used to test the electrode capacitance and the rate performance. The results showing that TF-B520 activated carbon balky paper electrodes have the highest capacitance of 120F/g at scan rate 1mV/s and good capacitor behaviour at scan rate below 20mV/s and current density below 250mA/g.

A new hexafluoroisopropanol groups functionalized hydrogen-bond acidic siloxane polymer for quartz crystal microbalance sensor (QCMs) application was synthesized via O-alkylation, Claisen rearrange, hydrosilylation and hexafluoroacetone groups (HFA) electrophilic addition reactions. This hexafluoroisopropanol-functionalized siloxane polymer was confirmed by FT-IR and 1H NMR, and coated onto an AT-cut 8 MHz QCM sensor to investigate its gas sensitive responses to eight different typical organic volatile chemical vapors. The results indicated that this new siloxane polymer exhibited an excellent performance on the detection of the organophosphorus nerve agent stimulant dimethyl methylphosphonate (DMMP) vapor, and the frequency changes of this functionalized siloxane polymer based QCM sensors to the DMMP vapor were completely linear and with a regression coefficient of 0.9993 in the concentration range of 10–60 ppm. In addition, the sensitivity of the fabricated QCM sensor to DMMP was up to 23.07 Hz/ppm, and it is much higher than that of the other chemical vapors under the same circumstances, the detection limits (LODs) of this fabricated QCM sensor was obtained as low as 0.13 ppm.

Poly-(bistriethylphosphine)-platinum-diethynylbenzene (Pt-DEB) was synthesized by dehydrohalogenation reaction. X-ray photoelectron spectroscopy (XPS), FTIR, and 1H-NMR spectra were used to identify the formation of Pt-DEB target material. Sensitive properties of Pt-DEB-based quartz crystal microbalance (QCM) sensor to various organic vapors such as trichloromethane, tetrahydrofuran, acetone, isopropyl alcohol, ethanol, and methanol have been studied. The results show that Pt-DEB has good reversibility, reproducibility, and linear sensitivity to organic vapors at room temperature. The sensitivity of Pt-DEB (dissolved in CHCl3) toward CHCl3 is clearly higher than that toward other analytes, and a larger molecular weight of alcohol has a higher sensitivity response. The Pt-DEB-based QCM gas sensor shows low detection limits ranging from 1.0 to 3.56 ppm for the organic vapors and stable performance during a period of 30 days. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

PurposeThe purpose of this paper is to show how a quartz crystal microbalance modified with poly (epichlorohydrin) (PECH) is fabricated and used for detection of acetone vapor using a spin‐coating method.Design/methodology/approachMeasurements are based on the frequency shifts due to the adsorption of acetone vapor on the surface of the modified electrodes. A first‐order linear time‐invariant (LTI) system model is used to simulate the sensor response.FindingsIt is found that frequency shifts are linear to the concentrations of analyte, and cycle test examination shows good repeatability. The sensitivity to acetone vapor is better than other volatile compounds. A good match result is obtained with the LTI system model.Originality/valueThe device performance opens a potential way for analyzing acetone vapor.

The polyaniline/PdO composite was synthesized by chemical oxidative polymerization of aniline with PdO nanoparticles. A methane gas sensor was made by deposition polyaniline/PdO thin films on a mass-type quartz crystal microbalance (QCM) device through layer-by-layer (LbL) self-assembly method. Scanning electron microscopy inspection shows that the polyaniline/PdO multilayers are formed with a dense network of nanofibers. The frequency responses of the polyaniline/PdO based QCM sensor to methane gas were measured at room temperature and 50 °C. It exhibited that the polyaniline/PdO based QCM gas sensor has a better response at room temperature than that at 50 °C. Meanwhile, the humidity effect is also discussed.

A new material-poly{methyl [3-(2-hydroxyl, 4,6-bistrifluoromethyl)phenyl]propylsiloxane} (PMTFMPS), which was sensitive to toxic organophosphate vapor, was synthesized via O-alkylation, claisen rearrange reaction and hydrosilylation reaction. The polymer was coated on quartz crystal microbalance (QCM) to investigate its gas sensitive properties to nerve agents’ simulant dimethyl methylphosphonate (DMMP) vapor, as well as other interfering vapors. It was found that QCM sensor responded linearly to DMMP vapor with a slope of 27 Hz/ppm in the 10–50 ppm range. The material was much more sensitive to DMMP than to other interfering vapors, thus high selectivity to DMMP was demonstrated. The influence of humidity on the sensor response was also examined. The results showed that the frequency shifts were about 60% when tested in 77% RH wet air than in dry N2. When compared with our previously studied unfluorinated phenol-modified siloxane PMPS, PMTFMPS exhibited sensitivity enhancement of 2.3 times and an increased resistance to humidity variations.

Surface plasmon resonance studies showed pullulan cinnamates (PCs) with varying degrees of substitution (DS) adsorbed onto regenerated cellulose surfaces from aqueous solutions below their critical aggregation concentrations. Results on cellulose were compared to PC adsorption onto hydrophilic and hydrophobic self-assembled thiol monolayers (SAMs) on gold to probe how different interactions affected PC adsorption. PC adsorbed onto methyl-terminated SAMs (SAM-CH(3))cellulosehydroxyl-terminated SAMs (SAM-OH) for high DS and increased with DS for each surface. Data for PC adsorption onto cellulose and SAM-OH surfaces were effectively fit by Langmuir isotherms; however, Freundlich isotherms were required to fit PC adsorption isotherms for SAM-CH(3) surfaces. Atomic force microscopy images from the solid/liquid interfaces revealed PC coatings were uniform with surface roughnesses2 nm for all surfaces. This study revealed hydrogen bonding alone could not explain PC adsorption onto cellulose and hydrophobic modification of water-soluble polysaccharides was a facile strategy for their conversion into surface modifying agents.

Quartz crystal microbalance (QCM) gas sensors based on polymeric material were fabricated and their gas response characteristics were examined for four simulant gases of chemical agents, which were dimethyl methyl phosphonate (DMMP), N,N-dimethylacetamide (DMA), 1,5-dichloropentane (DCP) and dichloroethane (DCE). For the selection of appropriate coating materials, both principal component analysis (PCA) and hierarchical cluster methods were applied to a data set collected from 15 QCM sensors for 12 analytes. Four appropriate coating materials were selected after optimizing the correlation between the 15 coating materials and the first four principal component (PC) factors. The four chosen polymers were used as sensitive component for a sensor array, and then PCA is adapted to classify four simulant gases. The results show that the QCM sensor array has high sensitivity and selectivity to four chemical agents.

ZnO nanoparticles and graphene oxide (GO) thin film were deposited on gold interdigital electrodes (IDEs) in sequence via simple spraying process, which was further restored to ZnO/reduced graphene oxide (rGO) bilayer thin film by the thermal reduction treatment and employed for ammonia (NH3) detection at room temperature. rGO was identified by UV-vis absorption spectra and X-ray photoelectron spectroscope (XPS) analyses, and the adhesion between ZnO nanoparticles and rGO nanosheets might also be formed. The NH3-sensing performances of pure rGO film and ZnO/rGO bilayer films with different sprayed GO amounts were compared. The results showed that ZnO/rGO film sensors exhibited enhanced response properties, and the optimal GO amount of 1.5 ml was achieved. Furthermore, the optimal ZnO/rGO film sensor showed an excellent reversibility and fast response/recovery rate within the detection range of 10-50 ppm. Meanwhile, the sensor also displayed good repeatability and selectivity to NH3. However, the interference of water molecules on the prepared sensor is non-ignorable; some techniques should be researched to eliminate the effect of moisture in the further work. The remarkably enhanced NH3-sensing characteristics were speculated to be attributed to both the supporting role of ZnO nanoparticles film and accumulation heterojunction at the interface between ZnO and rGO. Thus, the proposed ZnO/rGO bilayer thin film sensor might give a promise for high-performance NH3-sensing applications.

Two-dimensional benchmark cases involving lift-constrained drag minimization in inviscid and viscous transonic flows are solved using derivative-free multi-fidelity optimization algorithms (space mapping and manifold mapping) and are compared with direct gradient-based optimization algorithms using adjoint sensitivities and trust regions. With 8 B-spline design variables, the multi-fidelity algorithms yield optimized shapes comparable to the shapes obtained by the direct algorithms but at a fraction of the cost. In particular for the inviscid case, the multi-fidelity algorithms needed less than 150 equivalent high-fidelity model evaluations (only flow solutions) taking approximately 460 minutes on a HPC with 32 processors, whereas the direct algorithm needed 391 high-fidelity model evaluations (flow and adjoint) taking approximately 4,494 minutes on the same HPC. For the viscous case, the multi-fidelity algorithms yield an optimized shape using less than 125 equivalent high-fidelity evaluations taking approximately 17.4 hours on the HPC. The direct algorithm was unsuccessful in optimizing the baseline shape in this case. A simple variation of surrogate-based optimization, the sequential approximate optimization (SAO), is utilized to optimize the twist distribution of a rectangular unswept wing in inviscid flow. Using 3 Bspline design variables, the SAO algorithm is able to obtain an optimized design with a nearelliptic section lift distribution. The total optimization cost is 22 high-fidelity model evaluations or approximately 42.5 hours on a HPC with 32 processors.

We report a first-principles molecular dynamics study on Li-doped beta-phase manganese phthalocyanine (MnPc). Four electronegative sites next to pyrrole-bridging nitrogen atoms in single MnPc were characterized by analyzing electrostatic potentials. In one-dimensional stacked MnPc, six binding sites were unambiguously located, among which two were newly identified by both static and dynamic simulations. Molecular dynamics simulations were conducted to explore the underlying mechanism governing the diffusive motion of Li dopants. The continuous diffusion of Li atoms among these six binding sites of adjacent MnPc molecules has a distinct cooperative pair-hopping character. The activation energy is significantly lower for pair-hopping than for a single jump. Accepted version

A quartz crystal microbalance (QCM) modified with poly(vinylidene fluoride) (PVDF) was fabricated and used for detection of dimethyl methylphosphonate (DMMP) vapor, a simulant of nerve agents using a drop-coating method. Measurements were based on the frequency shifts due to the adsorption of DMMP vapor on the surface of the modified electrodes. It was found that frequency shifts were linear to the concentrations of analyte in the range of 5–60 ppm with a correlation coefficient of above 0.997. The influences of temperature and humidity on the sensors were also examined. Results showed that the sensitivity to DMMP vapor was almost identical in various humidity circumstances, and the sensitivity was higher in a lower temperature range.

Poly(vinylidene fluoride) (PVDF) was deposited onto a quartz crystal microbalance (QCM), using a standard Langmuir–Blodgett (LB) thin film deposition procedure. QCM technique was used to monitor the reproducibility of the LB film monolayer, and the fabricated QCM sensor was employed to detect the dimethyl methyl phosphonate (DMMP) vapor, a simulant of nerve agents. The results show that PVDF was successfully deposited from the water surface onto the quartz crystal substrate. The PVDF LB film is found to be highly sensitive to DMMP vapor, and frequency shifts are linear to the concentrations. The response of the sensor against DMMP is fast, large, and reversible. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

This study details the use of printing and other additive processes to fabricate a novel amperometric glucose sensor. The sensor was fabricated using a Au coated 12.7 μm thick polyimide substrate as a starting material, where micro-contact printing, electrochemical plating, chloridization, electrohydrodynamic jet (e-jet) printing, and spin coating were used to pattern, deposit, chloridize, print, and coat functional materials, respectively. We have found that e-jet printing was effective for the deposition and patterning of glucose oxidase inks with lateral feature sizes between ~5 to 1000 μm in width, and that the glucose oxidase was still active after printing. The thickness of the permselective layer was optimized to obtain a linear response for glucose concentrations up to 32 mM and no response to acetaminophen, a common interfering compound, was observed. The use of such thin polyimide substrates allow wrapping of the sensors around catheters with high radius of curvature ~250 μm, where additive and microfabrication methods may allow significant cost reductions.

In this paper, PLF, LSFA and DKAP, three linear hydrogen-bond acidic (HBA) polymers synthesized in our laboratory and one commercial available hyperbranched HBA polymer HC were coated on 434 MHz surface acoustic wave (SAW) devices for rapid detection of volatile organic sulfur compounds (VOSCs). Sensitivity and selectivity of the polymer-coated sensors were studied by exposing to VOSCs in the concentration range of 1 mg/m3 to 49 mg/m3, as well as some common interference vapors at 10 mg/m3. High sensitivity and selectivity of these sensors to VOSCs are demonstrated. The sensitivities are attributed to the lone pair electrons in the sulfur atoms, which act as electron donors and facilitate the hydrogenbond formation between the analytes and the hydroxy groups of HBA polymers. The sensitive mechanism is further confirmed by the calculated results based on density functional theory.

Here a promising approach is proposed to enhance the responsivity of a ZnO nanowires array based photodetector with metal-semiconductor-metal structure through piezo-phototronic effect. The ZnO nanowires arrays were synthesized on the surface of ZnO seedlayer via hydrothermal method. Using polarization charges created at metal-ZnO interface under strain to modulate the local Schottky barrier height (SBH), the responsivity of the prepared photon sensor was increased by as much as 107% when the device was subjected to a −0.67% compressive strain. This work not only strengthens the fundamental understanding of piezo-phototronic effect on photodetectors but also provides an efficient means for optimization/improvement of piezoelectric semiconductor nanowires based optoelectronic devices.

A two-channel gas chromatography column and a single-channel column were made by deep reactive-ion etching technology. The two short columns were coated with different stationary phases, and then linked without a modulator. This is to aim at increasing the sample capacity and achieving a higher separation efficiency in complex environments. The results show that the capacity of the connected column is approximately 4 and 1.5 times larger than that of the single- and two-channel columns, respectively. The linked column was utilized to separate a six-component mixture, composed of three simulants of nerve and blister agents and three interfering vapors. The results demonstrate that the combined column has a remarkably higher separation efficiency than the individual columns, and an acceptable resolution is achieved although the total length of the linked column is only 1.5 m.

Surface-bound water in protein solutions has been identified with a reduction in its freezing point. We studied the presence of such nonfreezing water (NFW) in various protein-polyelectrolyte, micelle-polyelectrolyte, and protein-protein (heteroprotein) coacervates, along with appropriate concentrated solutions of macromolecules alone, finding up to 15% w/w NFW for the heteroprotein coacervate of lactoferrin (LF) and β-lactoglobulin (BLG). The level of NFW is always higher in coacervates than in the control (single macromolecule) systems, particularly for protein-containing coacervates: a coacervate of bovine serum albumin (BSA) and poly(dimethyldiallylammonium chloride) (PDADMAC) showed a ratio of NFW/protein twice that of BSA alone (0.6 vs 0.3), with a similarly high ratio for LF-BLG coacervate. These results are attributed to the maximization of water-protein contacts, structural features that reflect the mode of sample assembly, as they are not seen in a noncoacervated LF-BLG solution with identical concentrations of all species.

Superhydrophobic patterns were fabricated on hydrophilic surfaces by selective painting. The impinging process of water droplets on these hybrid surfaces was investigated. The droplet can be split by impinging on the hydrophilic surface with a single stripe at a high velocity. The time to split the droplet is independent of the impact velocity and it is smaller than the contact time of a droplet impinging on the fully superhydrophobic surface. The volume ratios of the split mini-droplets could be precisely controlled by adjusting the landing position of the original droplet. The droplet could be split uniformly into more mini-marbles by increasing the stripe numbers.

Chemical warfare agents (CWAs) are recognized as serious threats of terrorist acts against the civilian population. Minimizing the impact of these threats requires early detection of the presence of CWAs. Cavity ring-down spectroscopy (CRDS) is an exquisitely sensitive technique for the detection of trace gaseous species. In this letter, the CRDS technique is employed using a pulsed quantum cascade laser for the detection of dimethyl methylphosphonate (DMMP). A limit of DMMP detection of approximately 77 ppb is achieved. The best achievable sensitivity that corresponds to noise-equivalent absorption is approximately 2 x 10(-7) cm(-1).

SummaryObjective To compare the image quality of spectral CT monochromatic imaging and conventional CT polychromatic imaging for analysing CTAs in patients with cervical cancer. Methods In this IRB approved prospective study, 60 patients who had been diagnosed with cervical cancer underwent pelvic arterial CTA between May 2013 and July 2013. They were randomly divided into two groups; one group (30 patients) received 120 kVp polychromatic imaging (conventional CT group) and the other group (30 patients) received spectral CT imaging (spectral CT group), while all patients in both the groups received injections of 1 ml/kg of contrast agent. A total of 101 sets of monochromatic images (40–140 keV) were obtained via data reconstruction in the spectral CT group, and the monochromatic images with the best contrast-to-noise ratio (CNR) between the common iliac artery and pelvic fat (i.e. the best monochromatic energy) were selected. The best monochromatic images for the spectral CT group and the polychromatic images for the conventional CT group were postprocessed and visualised in MIP, VR and CPR mode. The CT attenuation value, noise and CNR of bilateral common iliac arteries were measured with the best monochromatic energy, as well as with 70 keV, in the spectral CT group and in the conventional CT group. The quality of the CT images was evaluated with a 5-point scale. The CTDIvol and the dose-length product (DLP) of the two groups were measured, and the results were statistically analysed. Results When images were at 50±1 keV, the common iliac artery and pelvic fat had the highest CNR, which was 72.00% higher than the images at 70 keV (P=.001) in the spectral group, and thus, the images at 50±1 keV were considered to have the best monochromatic energy. The average CT value of the internal iliac artery, which had the best monochromatic energy from the spectral CT group, was higher than that of the images from the conventional CT group (603.96±62.68 vs 251.24±28.77; P