Enhanced H2S sensing characteristics of SnO2 nanowires functionalized with CuO

The CuO-functionalized SnO₂ nanowire (NW) sensors were fabricated by depositing a slurry containing SnO₂ NWs on a polydimethylsiloxane (PDMS)-guided substrate and subsequently dropping Cu nitrate aqueous solution. The CuO coating increased the gas responses to 20 ppm H₂S up to 74-fold. The R_a/R_g value of the CuO-doped SnO₂ NWs to 20 ppm H₂S was as high as 809 at 300 °C, while the cross-gas responses to 5 ppm NO₂, 100 ppm CO, 200 ppm C₂H₅OH, and 100 ppm C₃H₈ were negligibly low (1.5–4.0). Moreover, the 90% response times to H₂S were as short as 1–2 s at 300–400 °C. The selective detection of H₂S and enhancement of the gas response were attributed to the uniform distribution of the sensitizer (CuO) on the surface of the less agglomerated network of the SnO₂ NWs.     

Response time of nanostructured relative humidity sensors

Capacitive relative humidity (RH) sensors were fabricated by coating countersunk interdigitated electrode substrates with nanostructured TiO₂ films produced using glancing angle deposition. Areal capacitance increased from 1 nF cm⁻² to 800 nF cm⁻² as relative humidity was increased from 2% RH and 95% RH. For films deposited at 81° and with a thickness below 4 m, response time was (162±4) ms m⁻¹. Response times increased from 64 ms to 1440 ms as film thickness increased from 280 nm to 8.5 m. The linear dependence of response time with film thickness indicates that device response time is dominated by surface adsorption. Response time decreased with increasing deposition angle, with a slope of (−15.2±1.6) ms degree⁻¹ for the adsorption data, and (−17.3±2.5) ms degree⁻¹ for the desorption data. The optimum operating range of the sensors depends on deposition angle, and can be tuned to different ranges to match application needs.     

A technique for monitoring SO2 in combustion exhausts: Use of a non-Nernstian sensing element in combination with an upstream catalytic filter

Detection of sulfur dioxide (SO₂) at high temperature (600–750 °C) in the presence of some interferents found in combustion exhausts (NO₂, NO, CO₂, CO, and hydrocarbon (C₃H₆)) is described. The detection scheme involves use of a catalytic filter in front of a non-Nernstian (mixed-potential) sensing element. The catalytic filter was a Ni:Cr powder bed operating at 850 °C, and the sensing elements were pairs of platinum (Pt) and oxide (Ba-promoted copper chromite ((Ba,Cu)_xCr_yO_z) or Sr-modified lanthanum ferrite (LSF)) electrodes on yttria-stabilized zirconia. The Ni:Cr powder bed was capable of reducing the sensing element response to NO₂, NO, CO, and C₃H₆, but the presence of NO₂ or NO (“NO_x”, at 100 ppm by volume) still interfered with the SO₂ response of the Pt–(Ba,Cu)_xCr_yO_z sensing element at 600 °C, causing approximately a 7 mV (20%) reduction in the response to 120 ppm SO₂ and a response equivalent to about 20 ppm SO₂ in the absence of SO₂. The Pt–LSF sensing element, operated at 750 °C, did not suffer from this NO_x interference but at the cost of a reduced SO₂ response magnitude (120 ppm SO₂ yielded 10 mV, in contrast to 30 mV for the Pt-(Ba,Cu)_xCr_yO_z sensing element). The powder bed and Pt–LSF sensing element were operated continuously over approximately 350 h, and the response to SO₂ drifted downward by about 7%, with most of this change occurring during the initial 100 h of operation.     

Crossed zinc oxide nanorods for ultraviolet radiation detection

An ultraviolet photosensor has been successfully constructed by the in situ lift-out method in a focused ion beam system. The prototype consists of individual naturally self-assembled crossed ZnO nanorods grown by an aqueous solution process. The current–voltage (I–V) characteristics show linear behavior. The photosensor exhibits a response of 15 mA/W for UV light (361 nm) under 1 V bias. Response measurements showed that such a photosensor is suitable for low levels of ultraviolet detection. The method is simple, rapid and applicable to research prototypes for further studies of crossed ZnO nanorods for nano-device applications.     

Dynamic evolvement and formation of refractive microlenses self-assembled from evaporative polyurethane droplets

This paper proposed a method of microfabrication for the formation of hemispherical refractive microlenses by depositing a colloid evaporative droplet onto hydrophobic surfaces. The microdroplets made of polyurethane (PU) were self-driven by surface tension to evolve their three-dimensional (3D) shapes on the surface-treated substrate. The substrates were coated with low surface energy material (Teflon) to de-pin the fluids obeying classic Young–Laplace equation until drying. Array and size-variation experiments, corresponding to different placement and droplet volume, were performed for the shaping process in which the polymers of the drops were self-assembled to be hemispherical utilizing general principle of minimal surface energy. Using the hydrophobic surfaces, plano-convex shapes with spherical curvature were fabricated with micrometer dimensions (base radius between 70 and 1016 μm). The formed structures were observed to form themselves hemispherically by the de-wetting (de-pinning) process during most of evaporation. Moreover, the gravity flatting effect was further found for the larger drop (radius = 1016 μm) when compared to that of smaller one (radius = 118 μm). In the cases, both the modeling calculations and experimental results were performed and compared to illustrate the similar geometries with the contact angle (70°) using dimensionless analysis. In addition, one interesting and significant finding, based on close morphological inspection of the SEM picture, showed that the resulting elongational polymer chains (width 200 nm) stretched (extension 5 μm) on the surface nearby the corner of the contact area, indicating a shear stress occurrence. Compared to those previous methods operated on (soft-) photolithographic techniques, this present one could rapidly predict and microfabricate the hemispherical formation in terms of the radius, height, and contact angle. It is also potentially appropriate for smaller and complex placement by using drop-on-demand (DOD) nozzle arrays for mass-production process.     

Direct amperometric determination of l-ascorbic acid (Vitamin C) at octacyanomolybdate-doped-poly(4-vinylpyridine) modified electrode in fruit juice and pharmaceuticals

The glassy carbon electrode (GCE) modified with Mo(CN)₈⁴⁻-incorporated-poly(4-vinylpyridine) (PVP/Mo(CN)₈⁴⁻), which has been recently shown to possess several attractive attributes as an efficient electrocatalytic electrode for l-ascorbic acid oxidation and its estimation, is used for l-ascorbic acid estimation directly in orange fruit juice and Celin tablet in a 0.1 M H₂SO₄ acid solution without any special treatment. Constant potential amperometry at 570 mV (saturated calomel electrode, SCE) in stirred solutions is used for this purpose. A good correlation is attained with the official titrametric method. To understand the possible electrocatalytic reaction mechanism for the electro-oxidation of l-ascorbic acid, calibration graphs over the range 1 × 10⁻⁵ to 1 × 10⁻² mol dm⁻³ l-ascorbic acid are compared for the three electrodes, ca. PVP/Mo(CN)₈⁴⁻, undoped PVP, and GCE; the curvature at high ascorbic acid concentration for the PVP/Mo(CN)₈⁴⁻ electrode is explained in terms of Michaelis–Menten (MM) saturation kinetics. The apparent MM constant (K_M), the maximum catalytic current (i_M), the complex decomposition rate constant (k_c), and the heterogeneous modified electrode rate constant (k^′_ME) are calculated from three different approaches. A reasonably high value of ≈1 × 10⁻² cm s⁻¹ is obtained for k^′_ME, indicating efficient l-ascorbic acid mediation at the PVP/Mo(CN)₈⁴⁻ electrode, thus accounting for quite a high sensitivity of this modified film electrode compared to several other modified electrodes.     

Detection of Escherichia coli using CMOS array photo sensor-based enzyme biochip detection system

This work presents optical enzyme detection system based on the CMOS array photo sensor and 1 × 3 polymeric enzyme biochip for detecting Escherichia coli in a one-step procedure. This assay, using 4-methylumbelliferyl-β-d-glucuronide (MUG) as a fluorogenic substrate, had a detection limit of 0.1 U/ml for β-glucuronidase (GUD), which was approximately equal to a cell concentration of 10⁶ CFU/ml of E. coli. MUG was incorporated into lauryl tryptose broth at a final concentration of 100 μg/ml for immediate verification of the presence of E. coli in 1 × 3 polymeric enzyme biochip. The 40 strains of E. coli studied all produced GUD. Of another 36 strains of bacteria tested, one strain (Salmonella choleraesuis subsp. choleraesuis) yielded very small amounts of GUD after 24 h incubation. The optical enzyme detection system was sensitive and rapid.     

Ethanol gas sensor based on Al-doped ZnO nanomaterial with many gas diffusing channels

ZnO nanomaterial with multi-microstructures is synthesized by using normal pressure thermal evaporation and then doped with different Al₂O₃ contents by grinding in an agate mortar. The as-prepared Al-doped ZnO nanomaterials are characterized by X-ray diffraction and scanning electron microscopy. The characterization results show that all the compounds are wurtzite with hexagonal structure and are well crystallized. Channels/connecting holes arising from many kinds of ZnO microstructures are abundant. Both annealing and Al₂O₃-doping contributes to an increase in the quasi-one-dimensional and tri-dimensional microstructures. The as-prepared Al-doped ZnO nanomaterials show excellent gas responses to ethanol. The sensing mechanism of the ZnO-based nanomaterials with multi-microstructures is further analyzed by using the Effective Specific Surface Model. Excellent sensitivity (200) companied with short response time (8 s) and recovery time (10 s) to 3000 ppm ethanol is obtained with a ZnO-based sensor with 2 at.% Al₂O₃ at the operating temperature of 290 °C after the sensor is annealed at 500 °C.     

Dynamic behavior for a system of neutral functional differential equations

Consider the system of neutral functional differential equations

where r>0, F, . It is shown that if F is nondecreasing on , and some additional assumptions hold, then the ω limit set of every bounded solution of such a system with some initial conditions is composed of 2r-periodic solutions. Our results are new and complement some corresponding ones already known.     

Strongly Hamiltonian laceability of the even k-ary n-cube

The interconnection network considered in this paper is the k-ary n-cube that is an attractive variance of the well-known hypercube. Many interconnection networks can be viewed as the subclasses of the k-ary n-cubes include the cycle, the torus and the hypercube. A bipartite graph is Hamiltonian laceable if there exists a Hamiltonian path joining every two vertices which are in distinct partite sets. A bipartite graph G is strongly Hamiltonian laceable if it is Hamiltonian laceable and there exists a path of length N − 2 joining each pair of vertices in the same partite set, where N = |V(G)|. We prove that the k-ary n-cube is strongly Hamiltonian laceable for k is even and n  2.     

Electrochemical DNA biosensor for the detection of interaction between di[azino-di(5,6-azafluorene)-κ-NN′]dichlormanganous and DNA

A new Mn(II) complex of MnL₂Cl₂ (L = azino-di(5,6-azafluorene)-κ²-NN′) was synthesized and utilized as an electrochemical indicator for the determination of hepatitis B virus (HBV) based on its interaction with MnL₂Cl₂. The electrochemical behavior of interaction of MnL₂Cl₂ with salmon sperm DNA was investigated on glassy carbon electrode (GCE). In the presence of salmon sperm DNA, the peak current of [MnL₂]²⁺ was decreased and the peak potential was shifted positively without appearance of new peaks. The binding ratio between [MnL₂]²⁺ and salmon sperm DNA was calculated to be 2:1 and the binding constant was 3.72 × 10⁸ mol² L⁻². The extent of hybridization was evaluated on the basis of the difference between signals of [MnL₂]²⁺ with probe DNA before and after hybridization with complementary sequence. Control experiments performed with non-complementary and mismatch sequence demonstrated the good selectivity of the biosensor. With this approach, a sequence of the HBV could be quantified over the range from 1.76 × 10⁻⁸ to 1.07 × 10⁻⁶ mol L⁻¹, with a linear correlation of r = 0.9904 and a detection limit of 6.80 × 10⁻⁹ mol L⁻¹. Additionally, the binding mechanism was preliminarily discussed. The mode of interaction between MnL₂Cl₂ and DNA was found to be primary intercalation binding.     

Hydrogen sensors with double dipole layers using a Pd-mixture-Pd triple-layer sensing structure

This paper reports on new GaN sensors using a Pd-mixture-Pd triple-layer sensing structure to enhance their sensitivity to hydrogen at the tens of ppm level. The proposed hydrogen sensor biased with a constant voltage produced relatively high sensing responses of 4.84 × 10⁵% at 10,100 ppm and 8.7 × 10⁴% at 49.1 ppm H₂ in N₂. The corresponding barrier height variations are calculated to be 220 and 168 mV. When the sensor is biased by a constant current with maximum power consumption of 0.4 mW, a sensing voltage as an output signal showed a voltage shift of more than 17 V (the highest value ever reported) at 49.1 ppm H₂ in N₂. By comparison to Pd-deposited GaN sensors, the improvement in static-state performance is likely attributed to double dipole layers formed individually at the Pd–GaN interface and inside the mixture. Moreover, voltage transient response and current transient response to various hydrogen-containing gases were experimentally studied. The new finding is that the former response time is shorter than the latter one.     

Sample complexity of worst-case H-identification

We show that the sample complexity of qorst-case H^∞-identification is of order n², by proving that the minimal length of a fractional H^∞-cover for C_n, regarded as the linear space of complex-valued sequences of length n, is of order n². A unit vector u in ^∞ is a fractional H^∞-cover for C_n if for some

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for all rh ε C_n, where is the z-transform of h. We also give similar results for real-valued sequences.     

SnO2 thin films modified by the SnO2–Au nanocomposites: Response to reducing gases

The influence of the SnO₂ surface modification by the SnO₂–Au nanocomposites on conductivity response to such reducing gases as CO and H₂ has been analyzed in the present paper. Both initial SnO₂ films, subjected for surface modification, and SnO₂–Au nanocomposites were deposited by Successive Ionic Layer Deposition (SILD) method. The SnO₂–Au nanocomposites with Au/Sn ratio 1 were synthesized using HAuCl₄ and SnCl₂ precursors. The thickness of the Au-SnO₂ nanolayers varied from 0.7–1.0 nm to 10–15 nm. It was established that the increase in the thickness of the SnO₂–Au nanocomposite layer formed on the surface of the SnO₂ films was accompanied by both the improvement of sensor response and the decrease in response and recovery times. An explanation of the observed effects has been proposed.     

A generalization of ACP using Belnap’s logic

ACP is combined with Belnap’s four-valued logic via conditional composition (if–then–else). We show that the operators of ACP can be seen as instances of more general, conditional operators. For example, both the choice operator + and δ (deadlock) can be seen as instances of conditional composition, and the axiom x + δ = x follows from this perspective. Parallel composition is generalized to the binary conditional merge _ψ where covers the choice between interleaving and synchronization, and ψ determines the order of execution. The instance _BB is ACP’s parallel composition, where B (both) is the truth value that models both true and false in Belnap’s logic. Other instances of this conditional merge are sequential composition, pure interleaving and synchronous merge. We investigate the expression of scheduling strategies in the conditions of the conditional merge.     

Development of a wireless stress/strain measurement system integrated with pressure-sensitive nickel powder-filled cement-based sensors

A wireless stress/strain measurement system is developed by integrating with pressure-sensitive sensors for health monitoring of concrete structures. The pressure-sensitive stress/strain sensors are fabricated by using nickel powder-filled cement-based composite. The wireless stress/strain measurement system integrated with these sensors is tested with compressive stress/strain in the range from 0 MPa/0 μ to 2.5 MPa/311.5 μ for performance evaluation. Experimental results indicate that the electrical resistivity of pressure-sensitive nickel powder-filled cement-based stress/strain sensors changes linearly and reversibly with the compressive stress/strain, and its fractional change goes up to 42.719% under uniaxial compression. The relationship between input (compressive stress/strain) and output (the fractional change in electrical resistivity) of the wireless stress/strain measurement system integrated with pressure-sensitive sensors is Δρ = −0.16894σ/Δρ = −1336.5. The wireless stress/strain measurement system can be used to achieve a sensitivity to stress/strain of 16.894% MPa⁻¹/0.13365%μ⁻¹ (a gauge factor of 1336.5) and a stress/strain resolution of 150 Pa/0.02 μ. The newly developed wireless stress/strain measurement system integrated with pressure-sensitive nickel powder-filled cement-based sensors has such advantages as high sensitivity to stress/strain, high stress/strain resolution, simple circuit and low energy consumption.     

Interactions Between PVS and Maple in Symbolic Analysis of Control Systems

This paper presents a decision procedure for problems relating polynomial and transcendental functions. The procedure applies to functions that are continuously differentiable with a finite number of points of inflection in a closed convex set. It decides questions of the form ‘is f0?’, where {=,>,<}. An implementation of the procedure in Maple and PVS exploits the existing Maple, PVS and QEPCAD connections. It is at present limited to those twice differentiable functions whose derivatives are rational functions (rationally differentiable). This procedure is particularly applicable to the analysis of control systems in determining important properties such as stability.     

H2 sensing characteristics of highly textured Pd-doped SnO2 thin films

The effects of the crystallographic orientation on the H₂ gas sensing properties were investigated in highly oriented polycrystalline Pd-doped SnO₂ films, which were obtained using rf magnetron sputtering of a Pd (0.5 wt%)-SnO₂ target on various substrates (a-, m-, r-, and c-cut sapphire and quartz). All the films had a similar thickness (110 nm), root-mean-square (rms) roughness (1.3 nm), surface area, and chemical status (O, Sn, and Pd). However, the orientation of the films was strongly affected by the orientation of the substrates. The (1 0 1), (0 0 2), and (1 0 1) oriented films were grown on (a-cut), (m-cut), and (r-cut) Al₂O₃ substrates, respectively, and rather randomly oriented films were deposited on (0 0 0 1) (c-cut) Al₂O₃ and quartz substrates. In addition, the oriented Pd-doped SnO₂ films were highly textured and had in-plane orientation relationships with the substrates similar to the epitaxial films. The (1 0 1) Pd-doped SnO₂ films on and Al₂O₃ showed a considerably higher H₂ sensitivity, and their gas response decreased with increasing sensing temperature (400–550 °C). The films deposited on and (0 0 0 1) Al₂O₃ showed the maximum sensitivity at 500 °C. The comparison of the H₂ gas response between undoped and Pd-doped SnO₂ films revealed that the Pd-doping shifted the optimum sensing temperature to a lower value instead of improving the gas sensitivity.     

Analysis of interface states of metal–insulator–semiconductor photodiode with n-type silicon by conductance technique

A metal–insulator–semiconductor photodiode (MIS-PD) as active layer with n-type silicon as interdigitated Schottky electrodes has been fabricated. The current–voltage characteristics, density of interface states and photovoltaic properties of the MIS-PD diode have been investigated. The diode has a metal–insulator–semiconductor configuration with ideality factor higher than unity. The electronic parameters (ideality factor, series resistance and barrier height) of the diode were found to be 1.94, 2.23 × 10⁴ Ω and 0.74, respectively. At voltages between 0.13 and 0.50 V, the charge transport mechanism of the diode is controlled by space charge-limited current mechanism. The interface state density of the diode was found to vary from 5.54 × 10¹² to 5.67 × 10¹² eV⁻¹ cm⁻² with bias voltage. The Au/SiO₂/n-Si/Al device shows a photovoltaic behavior with a maximum open circuit voltage V_oc of 97.7 mV and short-circuit current I_sc of 17.4 μA under lower illumination intensities. The obtained electronic parameters confirm that the Au/SiO₂/n-Si/Al diode is a MIS type photodiode.