排序方式: 共有23条查询结果,搜索用时 21 毫秒
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p palan BS 《Physical review letters》1987,58(16):1597-1599
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Molar extinction coefficients of some carbohydrates viz. l-arabinose (C5H10O5), d-glucose (C6H12O6), d-mannose (C6H12O6), d-galactose (C6H12O6), d(-) fructose (C6H12O6) and maltose (C12H24O12) in aqueous solutions have been determined at 81, 356, 511, 662, 1173 and 1332 keV by gamma ray transmission method in a
narrow beam good geometry set-up. These coefficients have been found to depend upon the photon energy following a 4-parameter
polynomial. These extinction coefficients for different sugars having the same molecular formula have same values varying
within experimental uncertainty. Within concentration ranges studied, Beer-Lambert law is obeyed very well. 相似文献
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A moving zone of quiet for narrowband noise in a one-dimensional duct using virtual sensing 总被引:1,自引:0,他引:1
Petersen CD Zander AC Cazzolato BS Hansen CH 《The Journal of the Acoustical Society of America》2007,121(3):1459-1470
A frequent problem in active noise control is that the zone of quiet created at the error sensor tends to be very small. This means that the error sensor generally needs to be located close to an observer's ear, which might not always be a convenient or feasible solution. Virtual sensing is a method that can move the zone of quiet away from the error sensor to a desired location that is spatially fixed. This method has been investigated previously, and has shown potential to improve the performance of an active noise control system. However, it is very likely that the desired location of the zone of quiet is not spatially fixed. An active noise control system incorporating a virtual sensing method thus has to be able to create a moving zone of quiet that tracks the observer's ears. This paper presents a method for creating a moving zone of quiet based on the LMS virtual microphone technique. To illustrate the proposed method, it is implemented in an acoustic duct and narrowband control results are presented. These results show that a moving zone of quiet was effectively created inside the duct for narrowband noise. 相似文献
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van Eis MJ van Der Linde BS de Kanter FJ de Wolf WH Bickelhaupt F 《The Journal of organic chemistry》2000,65(14):4348-4354
In contrast to the terminal phosphinidene complex PhPW(CO)(5) (2), which adds to [5]metacyclophane (1) in a 1,4-fashion, dichlorocarbene preferentially adds in a 1,2-fashion to the formal "anti-Bredt" type double bond of the aromatic ring of 1 to afford the norcaradiene 11b, which immediately rearranges to the bridged cycloheptatriene 12b and further by a [1,5] sigmatropic chlorine migration to the isomeric 13b as the first observable product. More slowly, the latter isomerizes via a dissociative mechanism to give 15b. A computational study supports the notion that the [1,5] chlorine migration in the rearrangement 12b --> 13b, for which an activation barrier of 70.2 kJ mol(-)(1) was calculated, is essentially concerted with minor charge separation. In contrast, the analogous [1,5] chlorine migration in the flat model compound 7,7-dichlorocycloheptatriene (12a) displays features of a dissociative pathway. 相似文献
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This paper builds on earlier work by the same authors to derive expressions for the time-averaged acoustic energy density in the frequency domain using the auto- and cross-spectral densities of multiple microphone elements. Expressions for the most common three-dimensional geometric arrangements are derived. Simplified expressions for use with two channel spectrum analysers are also presented. 相似文献
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Farzin Ghanadi Maziar Arjomandi Benjamin Cazzolato Anthony Zander 《International Journal of Computational Fluid Dynamics》2014,28(5):219-231
In this study, a large eddy simulation of the three-dimensional shear flow over a flow-excited Helmholtz resonator has been implemented. The simulations have been performed over a wide range of flow speeds to analyse the effect of the inlet flow properties on the excitation condition. For validation proposes, the results obtained from the numerical simulations have been compared with published experimental data and show that numerical modelling provides an accurate representation of the pressure fluctuations inside the cavity. The main objective of this paper is to gain an understanding of the flow features over a flow-excited Helmholtz resonator. To this end, using the numerical model, the interaction of a turbulent boundary layer with a Helmholtz resonator has been considered, and the characteristics of the flow inside the resonator and over the orifice for various flow conditions are also analysed. 相似文献
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Dumuid PM Cazzolato BS Zander AC 《The Journal of the Acoustical Society of America》2006,119(1):372-381
Filters are commonly used in sound reproduction and communication systems as a means of compensating for the response of the electro-acoustic plant. Two commonly used filter designs in the field of acoustics are the time reversal filter and the Tikhonov inverse filter. In this paper the influence of transducer sensitivities on the performance of these filters is examined. It is shown that the sensitivity of the transducers can negatively affect the performance of the resulting filter. To compensate for the decrease in performance, diagonal preconditioning can be implemented in the system. It is shown that by using diagonal matrices, which minimize the condition number of the system, the loss in performance arising from unbalanced sensitivities is minimized. This paper proposes an algorithm to find such a set of diagonal matrices and results are presented showing the improvements in performance arising from the modified filter design. 相似文献