排序方式: 共有19条查询结果,搜索用时 15 毫秒
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Mohammadi-Asl Saeed Nourinia Javad Ghobadi Changiz Majidzadeh Maryam Mostafapour Ehsan Haghshenas Alireza 《Wireless Personal Communications》2017,97(2):2131-2144
Wireless Personal Communications - A novel design of double-layer dual-band circularly polarized array antennas (DDCPAAs) is presented in this paper. First, a DDCP single antenna is introduced as... 相似文献
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Velayati Mahin Sabouri Zahra Masoudi Abdolhossein Mostafapour Asma Khatami Mehrdad Darroudi Majid 《SILICON》2022,14(13):7541-7554
Silicon - In this research, epoxy polyurethane-nano silica nanocomposites have been synthesized using an in-situ method, for which SiO2 nanocomposites had been initially ready in N,... 相似文献
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Saman Davoodi Amir Mostafapour 《The International Journal of Advanced Manufacturing Technology》2014,70(5-8):1125-1135
Pipelines leakage in power plant, petrochemical complexes, and refineries can lead to explosion, pollution, and severe physical damages, so precise and on time leak locating is very important. There are many techniques for detecting and locating the leakage. In this research, we represent the leak locating principle in pressurized gas pipelines by using acoustic emission theory. An algorithm for finding the location of continuous acoustic waves resulted from leakage is provided by MATLAB software. The used leak locating technique is a combination of wavelet transform, filtering, and cross-correlation methods. The resulted acoustic emission signals were analyzed into high and low frequencies by wavelet transform and available noises on them were omitted completely by filtering. Then de-noised acoustic emission signals were reconstructed. Time differences of de-noised waves were calculated precisely by using cross-correlation function. For studying the accuracy of used method, acoustic emission testing was done by continuous leakage source. The resulted signals of leakage were recorded by two acoustic sensors in two sides of leakage source, and time difference and leak location were calculated by using the algorithm. Several tests were done by changing sensor distance from leakage source and error percent of less than 3 % was resulted in leak locating that indicated high precision of used algorithm. 相似文献
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A. Mostafapour V. Gholizadeh 《The International Journal of Advanced Manufacturing Technology》2014,70(5-8):1113-1124
Some of the problems that occur during the welding process include the creation of coarse grains in the weld structure and the hardening of the weld region, which reduce the strength and impact resistance of the welded parts. One technique to improve the mechanical properties of weld is the application of mechanical vibration to the molten pool. In this article, the effect of vibrating the part during welding on the mechanical properties of steel plates has been investigated in the tungsten inert gas (TIG) welding process. The plate is made of stainless steel 304 with 2 mm in thickness. A filler material has also been used for welding so that the effect of vibration can be observed on the weld pool region. The experimental tests have been performed under different welding conditions with respect to voltage, current, welding speed, vibrations amplitude, and frequency. Then, the resultant mechanical properties of the tested parts were measured. Also, the microstructure obtained by applying the vibration has been examined. Based on these experimental results, the effect of mechanical vibration on mechanical properties of the weld was investigated. Moreover, considering the mechanical properties obtained from these experiments, the optimum values of amplitude, frequency, and welding speed were determined. 相似文献
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Leakage in high pressure pipes creates stress waves which transmitted through the pipe wall. These waves can be recorded by using acoustic sensor or accelerometer installed on the pipe wall. Knowing how these waves vibrate pipe is very important in continuous leak source locating process. In this paper the pipe radial displacement caused by acoustic emission due to leakage is modeled analytically. The standard form of Donnell’s nonlinear cylindrical shell theory is used to derive the motion equation of the pipe for simply supported boundary condition. Using Galerkin method, the motion equation has been solved and a system of nonlinear equations with 7 degrees of freedom is obtained. A MATLAB code according to Runge-Kutta numerical method is generated to solve these equations and derive the pipe radial displacement. To check the theoretical results, acoustic emission testing with continuous leak source and linear array of two sensors positioned on two sides of the leakage source were carried out. The major noise of recorded signals was removed through the wavelet transform and filtering technique. For better analysis, fast Fourier transform (FFT) was taken from theoretical and de-noised experimental results. Comparing the results showed that the frequency which carried the most amount of energy is the same that expresses excellent agreement between the theoretical and experimental results validating the analytical model. 相似文献
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CONCEPT: No consensus exists regarding the magnitude of the risk of noise-induced hearing loss (NIHL) associated with leisure noise, in particular, personal listening devices in young adults. OBJECTIVE: Examine the magnitude of hearing loss associated with personal listening devices and other sources of leisure noise in causing NIHL in young adults. STUDY DESIGN: Prospective auditory testing of college student volunteers with retrospective history exposure to home stereos, personal listening devices, firearms, and other sources of recreational noise. METHODS: Subjects underwent audiologic examination consisting of estimation of pure-tone thresholds, speech reception thresholds, and word recognition at 45 dB HL. RESULTS: Fifty subjects aged 18 to 30 years were tested. All hearing thresholds of all subjects (save one-a unilateral 30 dB HL threshold at 6 kHz) were normal, (i.e., 25 dB HL or better). A 10 dB threshold elevation (notch) in either ear at 3 to 6 kHz as compared with neighboring frequencies was noted in 11 (22%) subjects and an unequivocal notch (15 dB or greater) in either ear was noted in 14 (28%) of subjects. The presence or absence of any notch (small or large) did not correlate with any single or cumulative source of noise exposure. No difference in pure-tone threshold, speech reception threshold, or speech discrimination was found among subjects when segregated by noise exposure level. CONCLUSION: The majority of young users of personal listening devices are at low risk for substantive NIHL. Interpretation of the significance of these findings in relation to noise exposure must be made with caution. NIHL is an additive process and even subtle deficits may contribute to unequivocal hearing loss with continued exposure. The low prevalence of measurable deficits in this study group may not exclude more substantive deficits in other populations with greater exposures. Continued education of young people about the risk to hearing from recreational noise exposure is warranted. 相似文献
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Rajebi Saman Ghobadi Changiz Nourinia Javad Mostafapour Ehsan 《Wireless Personal Communications》2020,111(3):1761-1774
Wireless Personal Communications - A new, conformal and flexible slot microstrip antenna for treatment and ablation of cancerous tumors is proposed in this paper. The main purpose of the proposed... 相似文献