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951.
《Electroanalysis》2005,17(20):1878-1885
The advantages and limitations of impedimetric sensors based on Ti/TiO2 architectures are described. Titanium dioxide (titania) was potentiostatically formed onto titanium electrodes of 2 mm diameter, at 10 and 30 V in 1 M H2SO4. The thickness of the titania layers was ellipsometrically determined to be 30 and 86 nm respectively and they are highly insulating with charge‐transfer resistances in the MΩ range, as they were measured with electrochemical impedance spectroscopy under specific experimental conditions. Low voltage anodization (<10 V) results to amorphous TiO2, whereas at higher applied voltages (>25 V), anatase is the predominant form. SEM images are indicative of quite smooth, compact coatings without any severe cracks. 相似文献
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954.
The traditional Micro-perforated plate (MPP) is a kind of clean and non-polluting absorption structure in the middle and high frequency and has been widely used in the field of noise control. However, the sound absorption performance is dissatisfied at low frequencies when the air-cavity depth is restricted. In this paper, a mechanical impedance plate (MIP) is introduced into the traditional MPP structure and a Helmholtz resonator is attached to the MIP. Mechanical impedance plate (MIP) provides a good absorption at low frequency by using mechanism of mechanical resonance and the acoustic energy is dissipated in the form of heat with viscoelastic material. Helmholtz resonator can fill in the defect of the poor absorption effect between the Micro-perforated plate (MPP) and the mechanical impedance plate (MIP). The acoustic impedance of the proposed sound absorber is investigated by using acoustic electric analogy method and impedance transfer method. The influence of the tube’s length of Helmholtz resonator and the number of Helmholtz resonator on the sound absorption is studied. The corresponding results are in agreement with the theoretical calculation and prove that the composite structure has the characteristics of improving the low frequency sound absorption property. 相似文献
955.
The present study deals with an exact analysis of free transverse vibrations of annular plates having small core and sliding inner edge and the outer edge being elastically restrained based on classical plate theory. This study focuses mainly on the influence of variations in the elastic restraint parameters on the fundamental frequencies of plate vibration. The natural frequencies for the first six modes of annular plate vibrations are computed for different materials and varying values of the radius parameter and these natural frequencies may correspond to either axisymmetric and/or non-axisymmetric modes of plate vibration. The extensive data of values of fundamental frequency parameter presented in this paper is believed to be of use in the design of acoustic underwater transducers, ocean and naval structures, compressor and pump elements, offshore platforms. These results may serve as bench mark values for researchers to validate their results obtained using approximate numerical methods. 相似文献
956.
Simultaneously with the fact that vehicle industry has been able to lower the noise emission from driving vehicles, tire/pavement noise has become the most significant source of traffic noise. In order to reduce it, low noise surfaces are seen as a practical solution. One of these types of surfaces may be elaborated with bituminous mixtures with crumb tire rubber added to the binder in high content by a wet process. However, the generation mechanisms involved in the tire/pavement sound and the reasons of the noise attenuation achieved with these mixtures are not so clear. This study analyses the different generation mechanisms that take place in the tire/pavement sound generation in these crumb tire rubber pavements. The surface properties of the in-service pavement, which are most important in controlling the acoustic performance (texture, acoustic absorption and dynamic stiffness or mechanical impedance), have been measured for the characterization of a test track constructed with and without crumb tire rubber. After results correlation of these surface characteristics in a pavement with crumb tire rubber added by a wet process, it seems that the parameters of roughness and texture could have a relevant role in the global tire/pavement sound emission, whereas dynamic stiffness influence is relatively minor. 相似文献
957.
Taissir Hentati Leila Bouazizi Mohamed Taktak Hassen Trabelsi Mohamed Haddar 《Applied Acoustics》2016
The identification of the physical parameters of porous materials presents an important field of research, in which many identification methods are developed. One of those methods is presented in this paper. In fact, a multi-levels inverse identification method is developed in order to estimate these physical parameters. The proposed method is based on the minimization of the difference between a reference acoustic absorption coefficient of a porous material and the computed values. The minimization is done according three levels, in each level an acoustic model of porous material is used to evaluate one or two parameters. Finally, the five physical parameters of the porous materials are deduced. The proposed method is applied to Polyurethane foam material. The obtained results are satisfying with small values of errors and with estimated acoustic absorption coefficient reaching the reference one. 相似文献
958.
The NASA Langley Research Center Curved Duct Test Rig (CDTR) is designed to test aircraft engine nacelle liner samples in an environment approximating that of the engine on a scale that approaches the full scale dimensions of the aft bypass duct. The modal content of the sound in the duct can be determined and the modal content of the sound incident on the liner test section can be controlled. The effect of flow speed, up to Mach 0.5 in the test section, can be investigated. The results reported in this paper come from a study to evaluate the effect of duct configuration on the acoustic performance of single degree of freedom (SDOF) perforate-over-honeycomb liners. Variations of duct configuration include: asymmetric (liner on one side and hard wall opposite) and symmetric (liner on both sides) wall treatment; inlet and exhaust orientation, in which the sound propagates either against or with the flow; and straight and curved (outlet is offset from the inlet by one duct width) flow path. The effect that duct configuration has on the overall acoustic performance is quantified. The redistribution of incident mode content is shown, in particular the mode scatter effect that liner symmetry has on symmetric and asymmetric incident mode shapes. The Curved Duct Test Rig is shown to be a valuable tool for the evaluation of acoustic liner concepts. 相似文献
959.
操作条件对DMFC阴极电化学阻抗谱参数的影响 总被引:1,自引:0,他引:1
通过降低阴极催化剂载量强化了阴极氧还原反应的电化学极化, 测量了不同操作条件下直接甲醇燃料电池(DMFC)的极化曲线和交流阻抗谱,并提出了改进的等效电路模型LR(CR)(QR(LR))用以分析温度、空气流量和甲醇流量对DMFC阴极电化学反应和传质极化过程的影响. 研究结果表明, 提高工作温度会导致更多的甲醇渗透到阴极, 加大阴极氧气还原反应的电荷转移电阻; 只有采用大的空气流量,才会有效地防止水淹, 加大氧气向催化剂层的传质, 促进阴极反应的进行; 适当提高甲醇的流量可以促进阳极和阴极电化学反应的进行, 但是过高的甲醇流速可能会降低电极表面的温度, 加剧甲醇的渗透. 相似文献
960.
Adsorption of concanavalin A and lentil lectin on platinum electrode was investigated through electrochemical impedance spectroscopy and cyclic voltammetry. By using ferro/ferricyanide system to probe the electrochemical interface it was possible to model the EIS data with a simple equivalent circuit. The blocking effect for electron transfer reactions observed with these proteins, indicated that they readily adsorb on platinum surface and that the degree of adsorption is related to the state of the proteins. When the proteins are in the presence of divalent cations (Ca2+ and Mn2+) they adsorb less strongly than in their absence. There is also evidence that at least convanavalin A retains its biological activity in the adsorbed state. 相似文献