In this work, several cycles of homogenization heat treatments were employed to improve continuous-annealing furnace roller fractures at Mobarakeh Steel Company. Previous studies revealed that roller fractures were caused by sigma phase embrittlement and an increase of precipitations in the microstructure. Therefore, impact samples were prepared from failed rollers and homogenization treatments were carried out at temperatures ranging from 950 to 1100 °C in increments of 50 °C for 2 h. After cooling the samples in different mediums (furnace, air, oil and water), the impact energy was experimentally determined. In order to investigate the microstructures, the sigma phase and precipitation contents, and fractured surfaces, optical microscopy metallography, X-ray and SEM examinations were performed respectively on fractured samples. The results of these investigations indicate that homogenization treatment at 1100 °C for 2 h, followed by cooling in air, resulted in a significant increase in impact energy, a decrease in sigma phase and other precipitation contents, and produced a ductile fracture surface. 相似文献
Bismuth vanadate (BiVO4) and lanthanum-doped bismuth vanadate (La-doped BiVO4) were prepared via the precipitation method. Their films were produced by simple drop-coating of the initial solutions over gold electrodes, which were coated over a glass substrate. The structural properties of BiVO4 and La-doped BiVO4 samples were studied using x-ray diffractometer, diffuse reflectance spectroscopy, scanning electron microscopy, atomic force microscopy, and compositional analysis. A chamber was designed to install the sensing device and also controllable tools for gas flow rate and temperature. Changes in the resistance of the prepared layers were recorded during exposure to various amounts of ethanol vapor at different temperatures. Both BiVO4 and La-doped BiVO4 layers showed measurable responses in the form of resistance drop (increased conductivity). The higher temperatures up to 450 °C led to stronger signals. The layer containing lanthanum showed signals with shorter recovery times. Introduction of lanthanum caused smaller crystallite sizes in addition to the formation of tetragonal phase of BiVO4. Presence of lanthanum increased the amounts of grain boundaries, magnitude of the response, and sensitivity. Sensitivity of La-doped BiVO4 was almost twice that of the BiVO4 at concentrations of 150–500 ppm of ethanol. Also, the correlation of the response as a function of concentration of ethanol in gas phase was exploited, and two different linear ranges were observed for the lower and higher concentrations. 相似文献
Implementation of different telecommunication systems based on wireless optical technologies requires careful awareness of the link conditions in order to predict the performance of each system and its expectations. Wireless optical communication channels, like telecommunication channels, have a fading phenomenon, which is called optical turbulence. A particular class of adaptive networks has the ability to move nodes and can move and converge to moving or static targets. The applications of these networks include dynamic and regional observation and pursuit of underwater military objects. The best type of communication technologies proposed for such networks is Visible Light Communication, or VLC, through which sensors, like the fish schools, with the optical communication between each other, move toward the targets. Investigating the impact of channel conditions and optical noise on these networks are other innovations of this research. In this paper, we model the behavior of a fish school in underwater VLC conditions using a mobile diffusion network. Our simulation results show the effects of water properties on the convergence of the mobile network nodes to a certain target. It is shown that as the water temperature, salinity level and the distance between the nodes increase, the convergence error rises and the nodes become departed from the target position.
Wireless sensor networks (WSNs) have been widely used in different applications. One of the most significant issues in WSNs is developing an efficient algorithm to monitor all the targets and, at the same time, extend the network lifetime. As sensors are often densely deployed, employing scheduling algorithms can be considered a promising approach that is able ultimately to result in extending total network lifetime. In this paper, we propose three learning automata-based scheduling algorithms for solving target coverage problem in WSNs. The proposed algorithms employ learning automata (LA) to determine the sensors that should be activated at each stage for monitoring all the targets. Additionally, we design a pruning rule and manage critical targets in order to maximize network lifetime. In order to evaluate the performance of the proposed algorithms, extensive simulation experiments were carried out, which demonstrated the effectiveness of the proposed algorithms in terms of extending the network lifetime. Simulation results also revealed that by a proper choice of the learning rate, a proper trade-off could be achieved between the network lifetime and running time. 相似文献
This paper deals with the idea of the orthogonal functions in the equivalent linearization of the nonlinear systems. Block Pulse (BP) function gives effective tools to approximate complex problems. The aim of this work is on using properties of the BP function as an orthogonal function in process of linearization. The BP functions have been used to propose an equivalent linearization method in the time domain to determine the unknown linearization coefficients. The accuracy of the proposed method compared with the other equivalent linearization approaches, including the regulation linearization and the dual criterion linearization methods. This study exploited the nonlinear Van der Pol oscillator system under stationary random excitation to demonstrate the feasibility of the proposed method. The validity of the analytical method is verified by applying different values of nonlinearity and intensity of excitation. Besides, by comparing the mean square responses and frequency response functions of the linearized systems for a wide range of nonlinearity depicted the present method is in agreement with other methods. 相似文献
Conventional clustering ensemble algorithms employ a set of primary results; each result includes a set of clusters which are emerged from data. Given a large number of available clusters, one is faced with the following questions: (a) can we obtain the same quality of results with a smaller number of clusters instead of full ensemble? (b) If so, which subset of clusters is more efficient to be used in the ensemble? In this paper, these two questions are going to be answered. We explore a clustering ensemble approach combined with a cluster stability criterion as well as a dataset simplicity criterion to discover the finest subset of base clusters for each kind of datasets. Also, a novel method is proposed in order to accumulate the selected clusters and to extract final partitioning. Although it is expected that by reducing the size of ensemble the performance decreases, our experimental results show that our selecting mechanism generally lead to superior results. 相似文献
In situ and homogeneous hydrolysis of urea was utilized to design a homogeneous precipitation method to synthesize the ZnCr2O4 functional material. The as‐prepared nanospinel was systematically studied in terms of crystal structure, morphology, texture, and light absorption. A well‐crystalline single phase of ZnCr2O4 nanospinel with a spongy network structure was obtained. Transmission electron microscopy and X‐ray diffraction observations confirmed the formation of monocrystalline nanoparticles of ZnCr2O4 with the nanosize of 13 nm. The synthesized nanospinel showed a low direct band gap value of 1.8 eV with appropriate absorption in the visible light region, which was a remarkable result for this route. 相似文献
Low water-wettability and oxidation resistance of graphite have limited its application in carbon containing refractory castables. The aims of this study are the improvement of water-wettability and the oxidation resistance of natural flaky graphite by applying an oxide coating on its surface. To develop the coating, magnesium aluminate spinel sol was formulated via a citrate–nitrate route and graphite powder was then added to the sol. The mixture was heat treated in appropriate temperature and atmosphere to get the polycrystalline MgAl2O4 coating on graphite particles surface. The microstructure of coating was studied by X-ray diffractometer, SEM and TEM. The water-wettability was evaluated by measuring the water drop contact angle and plotting the zeta potential vs. pH. The results showed the development of a stable nanocrystalline MgAl2O4 spinel coating which improved the water-wettability and oxidation resistance of graphite significantly. Also, characterization of the coating is explained with emphasis on its application importance. 相似文献