Self-assembling of micro-patterned titanium oxide films for gas sensors

Metal oxide nanoparticles are interesting building blocks for realizing films for a number of applications that include bio- and -chemical sensing. In the present work TiO₂ nanoparticles have been used for a self-assembling procedure to realize lined-up micro-patterned titanium oxide films. The high surface-to-volume ratio makes these structures suitable to adsorb gases. Morphological, compositional and structural characterization have been performed in order to determine the features of the assembling. The analysis of electrical behaviour of the ordered films in controlled atmosphere allowed us to test the gas sensing properties.     

Size effect on mechanical properties of TiO2 capped nanotubes investigated using in situ transmission electron microscopy

In situ transmission electron microscopy nanoindentation tests are used to measure the compressive fracture and mechanical properties of individual titanium oxide (TiO₂) capped nanotubes. The average critical loads ranged from 3.6 to 9.6 μN. Individual TiO₂ capped nanotubes with lengths of 8–10 μm were found to have Young’s modulus values of ~2.2–9.4 GPa and work energy values of ~3.1–6.6 × 10^?13 J. The results indicate that the Young’s modulus and tensile strength depend on capped nanotube length.     

A selective room temperature formaldehyde gas sensor using TiO2 nanotube arrays

A new gas sensor using TiO₂ nanotube arrays was fabricated and explored for formaldehyde detection at room temperature. Highly ordered vertically grown TiO₂ nanotube arrays were synthesized by using the conventional electrochemical anodization process. The sensor using the fabricated nanotube arrays as the sensing elements demonstrated a good response to different concentrations of formaldehyde from 10 to 50 ppm and a very good selectivity over other reducing gas species such as ethanol and ammonia at room temperature. While the exact sensing mechanism is unclear, some possibilities are briefly discussed.     

Sensing properties of chemically sprayed TiO2 thin films using Ni, Ir, and Rh as catalysts

The purpose of this work is double, to analyze the influence of (i) the addition of different catalysts and (ii) the implementation of different procedures to introduce them in the titanium dioxide (TiO₂) thin films, in order to improve the film sensitivity for detecting oxygen. For reaching these objectives, TiO₂ thin films were deposited on alumina substrates by the ultrasonic spray pyrolysis (USP) technique employing titanium(IV) oxide acetylacetonate (TiO(acac)₂) as a titanium precursor, and pure methanol as a solvent. Iridium, nickel, and rhodium were the three catalysts used, which were incorporated by impregnation and USP onto the TiO₂ thin films surface. The electrical characterization, consisting in surface resistance measurements of the films, in a mixture of oxygen and zero-grade air, was performed using interdigitated gold electrodes contacted on the alumina substrates. From these, the film response or resistance change of the TiO₂ films was estimated. Single TiO₂ thin films measured at 400 °C displayed a response of the order of 0.02 and 0.18 to oxygen of 1000 and 10,000 ppm, respectively, whereas TiO₂ thin films using impregnated rhodium proved to have the highest response to O₂, with a value in the order of 2.5 to a concentration of 1000 ppm of O₂ diluted in zero-grade air at an optimal operating temperature of 250 °C.     

Using a TiO2/ZnO double-layer film for improving the sensing performance of ZnO based NO gas sensor

NO gas sensors, based on ZnO thin film (ZnO_film), TiO₂ nanoparticulate film (TiO₂NP), and TiO₂NP/ZnO_film double-layer film, were fabricated, and their sensing characteristics towards NO gas were investigated in this study. The maximal response of a ZnO_film deposited onto a rougher Al₂O₃ substrate, towards NO gas, was higher than that of a ZnO_film deposited on a smoother glass substrate. Although the sensing response of the TiO₂NPs itself towards NO gas was minute, the TiO₂NP/ZnO_film double-layer film showed enhanced response as compared with TiO₂NP or ZnO_film single-layer film. In addition, the sensor response of the TiO₂NP/ZnO_film double-layer film was strongly influenced by the annealing time for the film preparation; the maximum response to NO was enhanced about 6.2 times as the annealing time was increased from 30 min to 2 h. Based on the XPS results, the increase in the transition zone between TiO₂NP and ZnO_film along with the appearance of Ti³⁺ state was noticed when the annealing time was increased. With the high sensitive TiO₂NP/ZnO_film/Al₂O₃ electrode, the limit of detection (S/N = 3) can be achieved at 8.8 ppb. The double-layer TiO₂NP/ZnO_film also showed improved selectivities with respect to NO₂ and CO.     

Separate assessment of chemoresistivity and Schottky-type gas sensitivity in M–metal oxide–M′ structures

Maximum response levels reported for chemoresistive sensors span from less than 10 to over 10⁸. These differences are attributed to either the different micro- and nano-structured oxide pallets used or the properties of the metal–metal oxide junctions provided. Here, we report separate measurements and model-based estimations of the chemical responses arising from these different origins. The results quantitatively connect the observed responses to the parameters of the metal and metal oxide components of the device. It is shown that while the peak chemoresistive response is microstructure-dependent, the highest attainable Schottky-type gas sensitivity is almost microstructure-independent and is determined by the intrinsic properties of the materials involved. Measurements carried out on different Ag–TiO₂–Ti, Au–TiO₂–Ti and Ti–TiO₂–Ti structures verified the estimations: While chemoresistive responses in TiO₂ can hardly rise over 10², atmosphere-sensitive noble metal–TiO₂ junctions can cause responses as high as ∼10⁷.     

Effects of the self-contained breathing apparatus and fire protective clothing on maximal oxygen uptake

To examine the effects of firefighting personal protective ensemble (PPE) and self-contained breathing apparatus (SCBA) on exercise performance, 12 males completed two randomly ordered, graded exercise treadmill tests (GXT_PPE and GXT_PT). Maximal oxygen consumption (VO_2max) during GXT_PPE was 17.3% lower than the GXT_PT in regular exercise clothing (43.0 ± 5.7 vs. 52.4 ± 8.5 ml/kg per min, respectively). The lower VO_2max during the PPE condition was significantly related (r = 0.81, p < 0.05) to attenuated peak ventilation (142.8 ± 18.0 vs. 167.1 ± 15.6 l/min), which was attributed to a significant reduction in tidal volume (2.6 ± 10.4 vs. 3.2 ± 0.4 l). Breathing frequency at peak exercise was unchanged (55 ± 7 vs. 53 ± 7 breaths/min). The results of this investigation demonstrate that PPE and the SCBA have a negative impact on VO_2max. These factors must be considered when evaluating aerobic demands of fire suppression work and the fitness levels of firefighters.     

基于遗传算法优化小波神经网络的短期天然气负荷预测

天然气负荷预测对于燃气经营企业尤其重要,对保证天然气管网的用气量、优化管网的调度具有重要意义.传统的天然气预测模型预测精度低、模型泛化程度低.为了克服模型缺陷,提出了一种基于遗传算法优化小波神经网络的天然气负荷预测模型.通过遗传算法对小波神经网络的阈值以及网络连接权值等参数进行优化,从而建立预测效果最好的模型,通过企业提供的历史门站数据对预测模型进行验证.仿真结果表明,使用遗传算法优化网络参数的小波神经网络提高了模型的预测精度,具有一定的工程应用价值.     

Lead-free piezoceramic cymbal actuator

Lead-free piezoelectric ceramic 0.90(Bi_1/2Na_1/2)TiO₃-0.05(Bi_1/2K_1/2)TiO₃-0.05BaTiO₃ (abbreviated as BNT-BKT-BT5) is used as the driving element in a cymbal actuator with titanium endcaps. Both the electrical and mechanical properties of the lead-free piezoceramic cymbal are compared with that of the lead zirconate titanate (PZT) cymbal. It is found that the performance of the lead-free ceramic cymbal actuator is comparable to those fabricated using hard PZT ceramic driving element because BNT-BKT-BT5 has reasonable piezoelectric coefficients and low density.     

α-MoO3/TiO2 core/shell nanorods: Controlled-synthesis and low-temperature gas sensing properties

Crystalline α-MoO₃/TiO₂ core/shell nanorods are fabricated by a hydrothermal method and subsequent annealing processes under H₂/Ar flow and in the ambient atmosphere. The shell layer is composed of crystalline TiO₂ particles with a diameter of 2-6 nm, and its thickness can be easily controlled in the range of 15-45 nm. The core/shell nanorods show enhanced sensing properties to ethanol vapor compared to bare α-MoO₃ nanorods. The sensing mechanism is different from that of other one-dimensional metal oxide core/shell nanostructures due to very weak response of TiO₂ nanoparticles to ethanol. The enhanced sensing properties can be explained by the change of type II heterojunction barrier formed at the interface between α-MoO₃ and TiO₂ in the different gas atmosphere. The present results demonstrate a novel sensing mechanism available for gas sensors with high performance.     

Use of genetic programming to diagnose venous thromboembolism in the emergency department

Pulmonary thromboembolism as a cause of respiratory complaints is frequently undiagnosed and requires expensive imaging modalities to diagnose. The objective of this study was to determine if genetic programming could be used to classify patients as having or not having pulmonary thromboembolism using exhaled ventilatory and gas indices as genetic material. Using a custom-built exhaled oxygen and carbon dioxide analyzer; exhaled flows, volumes, and gas partial pressures were recorded from patients for a series of deep exhalation and 30 s tidal volume breathing. A diagnosis of pulmonary embolism was made by contrast-enhanced computerized tomography angiography of the chest and indirect venography supplemented by 90-day follow-up. Genetic programming developed a series of genomes comprising genes of exhaled CO₂, O₂, flow, volume, vital signs, and patient demographics from these data and their predictions were compared to the radiological results. We found that 24 of 178 patients had pulmonary embolism. The best genome consisted of four genes: the minimum flow rate during the third 30 s period of tidal breathing, the average peak exhaled CO₂ during the first 30 s period of tidal breathing, the average peak of the exhaled O₂ during the first 30 s period of tidal breathing, and the average peak exhaled CO₂ during the fourth period of tidal breathing, which immediately followed a deep exhalation. This had 100% sensitivity and 91% specificity on the construction population and 100% and 82%, respectively when tested on the separate validation population. Genetic programming using only data obtained from exhaled breaths was very accurate in classifying patients with suspected pulmonary thromboembolism.     

Turbulent mass transfer of Al2O3 and TiO2 electrolyte nanofluids in circular tube

Experimental study was performed to investigate turbulent mass transfer in straight circular tube. Electrochemical limiting diffusion current technique was used to measure the mass transfer coefficient in fully developed hydrodynamics and under developed mass transfer region. TiO₂ and γ-Al₂O₃ nanoparticles were added into the electrolyte solution (ES) to make electrolyte nanofluids (ENF). Measurements revealed that enhancement in mass transfer reaches 10 % in a 0.01 vol% γ-Al₂O₃/electrolyte nanofluid while 18 % in a 0.015 vol% TiO₂/electrolyte nanofluid relative to the base ES. Mass transfer coefficients increased with nanoparticles concentration up to an optimum concentration (0.01 % in γ-Al₂O₃/electrolyte nanofluid and 0.015 % in TiO₂/electrolyte nanofluid) while decreased by increasing nanoparticles concentration further. Enhancement ratio which is the ratio of the mass transfer coefficient of nanofluid to that of the base fluid was a function of nanoparticle concentration and was independent of Reynolds number. The mechanisms of nanoparticles Brownian motion and nanoparticles clustering were used to describe the behavior of the enhancement ratio in ENF.     

Detection of ammonia in the ppt range based on a composite optical waveguide pH sensor

An optical waveguide (OWG) pH sensor with two thin guiding layers (composite OWG) was fabricated, and its application to sensing extremely low concentrations of ammonia was demonstrated. The highly sensitive element based on a titanium dioxide (TiO₂) film was deposited onto the surface of a potassium ion (K⁺) exchanged glass OWG by RF sputtering. The surface of the TiO₂ film was coated with a thin film of a pH indicator dye (bromothymol blue, BTB) by spin coating. With optimum thickness of BTB film at about 46 nm and of TiO₂ films at 18–20 nm, this system proved to be an extremely sensitive ammonia sensor. The experimental results of the optimum conditions on BTB and TiO₂ film thicknesses were close to theoretically calculated values. The sensor easily detected 1 parts per trillion (ppt) ammonia reversibly, and had a short response time. The present sensor is also characterized by low cost, simple structure and facile fabrication.     

Thermal stability, electrical conductivity and ammonia sensing studies on p-toluenesulfonic acid doped polyaniline:titanium dioxide (pTSA/Pani:TiO2) nanocomposites

Electrically conductive p-toluenesulfonic acid (pTSA) doped polyaniline (Pani):titanium dioxide (TiO₂) nanocomposites (pTSA/Pani:TiO₂) were prepared by in situ polymerization of aniline with TiO₂ nanoparticles. Thus formed pTSA/Pani:TiO₂ nanocomposites were characterized by Fourier transform infra-red (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The sensitivity of the nanocomposites towards low concentrations of aqueous ammonia was examined and compared with that of the pure Pani. It was found that the resistivity of pTSA doped nanocomposites increases on exposure to ammonia at room temperature. The nanocomposites were found to possess superior ammonia sensing capacity as compared to pure Pani and it showed linear relationship between the responses and the ammonia concentration. The Fourier transform infrared (FTIR) spectroscopy was used to explain the sensing mechanism. A novel mechanism for the interaction process between the sensing material and ammonia has also been proposed.     

Stable electrical,morphological and optical properties of titanium dioxide nanoparticles affected by annealing temperature

Different TiO₂ synthesization processes give different properties. Most of researches in material studies only focus on the morphological and optical properties of TiO₂ while lacking in the effort of achieving stable electrical properties of the material. In engineering, stable electrical properties are vital in order to develop a device. Moreover, current technology needs more nanostructure application to enhance the performance of devices. In this paper, TiO₂ nanoparticle was synthesized by sol–gel method using 1:0.1:9 ratios of titanium isopropoxide:acetic acid:ethanol, respectively. This synthesized TiO₂ was able to respond in extremely small and consistent electrical reading (nanoampere). This metal oxide is good enough to be used as a material to develop ultra-high sensitive biosensor. Annealing process on the TiO₂ film was able to improve its’ electrical conductivity. The three layers TiO₂ coating were annealed at 400, 500, 600 and 700 °C and the surface morphologies, structural also electro-optical properties were studied using FESEM, XRD, UV–Vis and Keithley 6485 picoammeter. The XRD pattern shows the presence of stable anatase and rutile structures even at low temperature, whereas FESEM shows that annealing temperature affects the particle size. The optical band gap of TiO₂ thin films decreases from 3.74 to 3.34 eV as the annealing temperature increases. The current-to-voltage characteristics show that the conductivity decreases as the annealing temperature varies from 400to 700 °C. The output measurements indicated an improvement in electrical properties with annealing temperature.

     

Microstructure control of TiO2 nanotubular films for improved VOC sensing

Porous gas sensing films composed of TiO₂ nanotubes were fabricated for the detection of volatile organic compounds (VOCs), such as alcohol and toluene. In order to control the microstructure of TiO₂ nanotubular films, ball-milling treatments were used to shorten the length of TiO₂ nanotubes and to improve the particle packing density of the films without destroying their tubular morphology and crystal structure. The ball-milling treatment successfully modified the porosity of the gas sensing films by inducing more intimate contacts between nanotubes, as confirmed by scanning electron microscopy (SEM) and mercury porosimetry. The sensor using nanotubes after the ball-milling treatment for 3 h exhibited an improved sensor response and selectivity to toluene (50 ppm) at the operating temperature of 500 °C. However, an extensive ball-milling treatment did not enhance the original sensor response, probably owing to a decrease in the porosity of the film. The results obtained indicated the importance of the microstructure control of sensing layers in terms of particle packing density and porosity for detecting large sized organic gas molecules.     

Synthesis and characterisation of nanosized TiO2-ZrO2 binary system prepared by an aqueous sol-gel process: Physical and sensing properties

Nanostructured TiO₂-ZrO₂ thin films and powders were prepared by a straightforward aqueous particulate sol-gel route. Titanium (IV) isopropoxide and zirconium (IV) acetate hydrate were used as precursors, and hydroxypropyl cellulose was used as a polymeric fugitive agent in order to increase the specific surface area. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy revealed that the powder were crystallised at the low temperature of 500 °C, containing anatase-TiO₂ and tetragonal-ZrO₂ phases. Furthermore, it was found that ZrO₂ retarded the anatase-to-rutile transformation up to 900 °C. The activation energies for crystallite growth of TiO₂ and ZrO₂ components in the binary system were calculated 10.16 and 3.12 kJ/mol, respectively. Transmission electron microscope (TEM) image showed that one of the smallest crystallite sizes was obtained for TiO₂-ZrO₂ binary mixed oxide, being 5 nm at 500 °C. Field emission scanning electron microscope (FESEM) analysis revealed that the deposited thin films had nanostructured morphology with the average grain size of 20 nm at 500 °C and 36 nm at 900 °C. Thin films produced under optimised conditions showed excellent microstructural properties for gas sensing applications. They exhibited a remarkable response towards low concentrations of CO and NO₂ gases at low operating temperature of 150 °C, resulted in an increase of thermal stability of sensing films as well as a decrease in the power consumption. Furthermore, calibration curves revealed that TiO₂-ZrO₂ sensor follows the power law, S = A[gas]^B (where S is sensor response, coefficients A and B are constants and [gas] is gas concentration) for the two types of gases, and it has excellent capability for the detection of low gas concentrations.     

Modeling Reactive Multimedia: Events and Behaviors

This paper explores the idea of reactivity in multimedia, and proposes systems which can react to continuously-evolving behaviors as well as to more traditional discrete events. The idea is presented in a scenario as well as in a number of small programming examples.The illustrative examples are written in the Fran system. Fran provides a high-level programming model for animations, built in the Haskell functional programming language. Whilst we use Fran for illustration—and indeed we argue that the functional paradigm is a natural choice of host for such a system—we should stress that the notion of external behaviors within multimedia is independent of the programming environment chosen and could be incorporated into other systems such as SMIL.     

Experiences and expectations with CASE technology — An example from Slovenia

Adoption and current use, perceived benefits, problems, and expectations in the application of information system development methods and tools, specifically CASE technologies, are presented in the settings of Slovenia. Current practices and trends in the use of CASE technology were surveyed; major differences in the IS development approaches in organizations that currently use or do not use CASE were identified. The findings are believed to be indicative of some other new Central and Eastern European democracies that are at a comparable stage in developing their IS technology markets. Although most IS managers in Slovenia are aware of CASE technology or have considered its use, organizations with a comparatively high level of IS maturity - ones with some corporate IS development standards in place - actually use it. More than limited funding for investments in advanced information technology, the lack of related methodological and management knowledge and skills seems to be the major reason why system developers do not adopt it or, with limited use, slowly adopt CASE.