To measure the concentration of CH4, we developed a thin film piezoelectric acoustic sensor (TFPAS), it accomplishes the detection of CH4 by the absorption of CH4 which can change the oscillation frequency of the piezoelectric crystal. The sensor is mainly composed by the piezoelectric film, sensitive film, silicon substrate and electrodes. The sensitive film is made up of nanometer-sized MgO scattered on pitch-based activated carbon fibers which has a strong adsorption of CH4. The piezoelectric film is a ZnO film which has very high piezoelectric characteristic parameters. The experimental results show that the sensitivity of the sensor to CH4 is very high. The response of the sensor to the presence of CH4 tested was found to be linear within a certain detection range and the detection error is less than 5%.
Abstract Highly sensitive detection of trace amounts of substances is crucial for broad applications in healthcare, environmental monitoring, antiterrorism, etc., where cost effectiveness and portability are often demanded. Here, an ultrasensitive sensor is reported that can detect an angstrom‐thick layer of adsorbed molecules through image acquisition and processing. The sensor features a centimeter‐scale plasmonic metasurface with spatially varying geometry, where the light scattering is dependent on both the adsorbed substances and spatial locations. When illuminated with narrowband light (such as from a light emitting diode), the intensity pattern recorded on the metasurface changes with the surface‐adsorbed molecules, enabling label‐free, sensitive, and spectrometer‐free molecular detection. The centimeter‐scale size of the sensing area interfaces well with consumer‐level imaging sensors on mobile devices without the need for microscopic optics and offers a high signal‐to‐noise ratio by leveraging the multimillion pixels for noise reduction. It is experimentally demonstrated that a single layer of Al 2 O 3 molecules deposited on the sensor, with a thickness of approximately one angstrom, can be detected by analyzing the images taken of the sensing chip. Furthermore, by integrating the sensor into a microfluidic setup, quantitative detection of BSA/anti‐BSA immune complex formation events is demonstrated, which agrees well with the Langmuir isotherm model.
The purpose of this paper is to study the change of sandstone properties during acid corrosion. With the help of velocity detection and chemical analysis, the mass loss, longitudinal wave velocity and the concentration of Ca2+ dissolved in the solution are analyzed. Experimental results show that: within 0∼30 days, the corrosion rate is the fastest, the mass loss rate, the wave growth rate and the growth rate of Ca2+ concentration are faster. Within 30∼60 days, the rate of change of the indexes are slower, indicating that corrosion rate became slow gradually. Within 60∼90 days, the indexes tend to be stable, indicating that corrosion rate tends to be stable, which shows that the acid corrosion of sandstone have certain stages. The corrosion rates of sandstone in solutions with different pH values are different. The stronger the acidity, the greater the corrosion rate, the rate of increase of Ca2+ and the increase rate of the wave velocity of the samples at the initial stage of the reaction.
Due to the special accumulation mode and reservoir characteristics of shale oil reservoirs, the reservoirs are very dense, with nano-scale pores and throats are developed, which results in high flow resistance of crude oil and low overall recovery of shale oil. Through the study of contact angle, interfacial tension and oil washing tests, the mechanism of interaction between different types of surfactants and shale oil rocks as well as crude oil is clarified, in order to judge whether the surfactant can be used to improve shale oil recovery. The results show that surfactant can change the surface wettability of shale oil rocks and reduce the interfacial tension, and finally realize the effect of improving the efficiency of oil washing.
In order to improve the reliability of gas monitoring in coal mine, we design a wireless sensor networks with the piezoelectric gas sensors, The wireless sensor networks is suitable for gas monitoring in the severe environment of coal mine. The networks' topology is sub-cluster type, and the cluster head node is selected in competitive method. Data fusion and routing of the cluster nodes are controlled by the cluster head node. In order to reduce information redundancy and energy consumption, we use coverage configuration protocol (CCP) to control nodes states to switch between three states of working, listening and sleeping, thus to maximize the number of sleeping nodes. We use a new type of thin film piezoelectric acoustic sensor (TFPAS) as the sensor node, this kind of sensor is of low power consumption, high sensitivity, which is suitable for wireless sensor networks.
Abstract Based on researches of a wastewater treatment plant for rural sewage treatment in Tongzhou District, Beijing city, efficiency of IFAS process was studied to support its broad-wide use in rural area. The results showed that, for the influents with COD, ammonia, TN and TP levels of 60-203mg/L, 9.5-40mg/L, 16-45mg/L and 1.2-4.7mg/L, highest removals of 91%, 98%, 78% and 93% can be obtained with levels of effluents below than 40mg/L, 1.5mg/L, 15mg/L and 1.0mg/L. Removals of the contaminants were low under low temperatures in winters.
In nanoimprint lithography, a release agent on the mold surface is usually necessary for easy demolding between the mold and the imprinted (thermal) resist. In this work, the thermal stability of 1H,1H,2H,2H-perfluorodecyltrichlorosilane (FDTS) monolayers is studied using x-ray photoelectron spectroscopy. The FDTS monolayers are deposited on Si (100) substrates via vapor phase reactions. Significant fluorine desorption of the monolayers is observed for samples annealed at 250 and 300 °C in air. The fluorine coverage decreases as a function of annealing time at a given annealing temperature. The desorption is proposed to be dependent on the monolayer packing details and may be influenced by the intermolecular heat transfer. Removal of the CF3 groups is found to be faster than that of the CF2 group as evidenced by the CF2/CF3 peak area ratios that increase with the annealing time. Sessile drop water contact angle and fluorine coverage evolution results show that the estimated useful coating lifetime is 180 min when the samples are annealed at 300 °C and ∼560 min when annealed at 250 °C. The peak position of the binding energy of the F 1s spectral line is related to the monolayer fluorine coverage and it may be a result of the interactions between the molecular chain and the negatively charged silicon substrate. Furthermore, nearly no chain desorption is detected for samples annealed in an inert environment, which may be attributed to the elimination of reactive oxygen and moisture molecules. The thermal degradation behaviors in ambient and inert atmosphere provide useful information for designing a nanoimprint process for the commercial manufacturing of polymeric microstructure and nanostructure.
In recent years, with the introduction of the concept of a local climate zone (LCZ), researchers have proved that adding an LCZ to the Weather Research and Forecasting (WRF) Model can improve the simulation effect. However, many existing studies cannot explain whether the improvement of accuracy in the model results is the effect of the refined zone or the effect of urban area correction, so they cannot explain the advantages of LCZ data. Therefore, this paper uses remote sensing images to generate two kinds of land use data sets and introduces them into the Weather Research and Forecasting Model coupled with the building energy model (WRF-BEM). In this paper, the two factors of urban area expansion and fine classification are considered, and three numerical examples are set up to simulate high-temperature weather in August 2019. The research shows that the simulated 2 m temperature of the scheme of correcting only urban area is the closest to the observed data. Although the RMSE in the 2 m temperature simulated by the LCZ scheme is 0.43 °C higher than that of the scheme of correcting only the urban area, it can well reproduce the spatial variation characteristics of 2 m temperature. In addition, different urban morphologies affect the spatial distribution of the surface urban heat islands in Beijing. High surface urban heat island effect zones mainly appear in the compact low-rise, compact mid-rise, and large low-rise types.
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