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排序方式: 共有267条查询结果,搜索用时 12 毫秒
261.
In this study, new ultrasound reflection and backscatter measurements in cancellous bone using a membrane-type hydrophone are proposed. A membrane hydrophone made of a piezoelectric polymer film mounted on an annular frame allows an incident ultrasound wave to pass through its aperture because it has no backing material. Therefore, in measurements using the membrane hydrophone, the receiving area could be located independently from the transmitting area. In addition, the size and shape of the receiving area, which corresponded to those of the electrode deposited on the piezoelectric film, could be arranged in various ways. To investigate the validity of the proposed measurements, before bench-top experiments, the reflected and backscattered waves from cancellous bone were numerically simulated using a finite-difference time-domain method. The reflection and backscatter parameters were measured on various receiving areas, and their correlation coefficients with the structural parameters in the cancellous bone were derived. The simulated results suggested that appropriate receiving areas for the reflection and backscatter measurements could exist and that the proposed measurements could be more effective for evaluating bone properties than conventional measurements. 相似文献
262.
An optimized strain demodulation method based on dynamic double matched fiber Bragg grating filtering 总被引:2,自引:0,他引:2
Biqiang Jiang Jianlin Zhao Chuan Qin Zhao Huang Fan Fan 《Optics and Lasers in Engineering》2011,49(3):415-418
An optimized strain demodulation method based on dynamic double matched fiber Bragg grating (FBG) filtering driven by a piezoelectric transducer (PZT) is proposed and experimentally demonstrated. Using an optimized triangular waveform to drive PZT, the nonlinear effect is eliminated, and extraction and processing of the peak signals are more convenient. Furthermore, taking advantage of double matched-FBGs and strain amplification structure to demodulate the Bragg wavelength, the wavelength scanning range can be extended to 6.3 nm, so that a large-scale and high-precision strain measurement can be achieved. The experimental results show that in the strain range of 0-3800με, the linearity of the relationship between strain and scanning time-difference is greater than 99.8%, and the stability of repeated measurements is up to 99.5%. This demodulation method can be widely applied in the FBG measurement system. 相似文献
263.
264.
Recently, nonlinear materials have attracted a great deal of attention because of their importance in designing new devices to meet a need range of optical systems. An intense investigation of the possibility of using these materials for all optical ultrafast applications is achieved by allowing their dielectric characteristics to be varied in such a way that a periodic perturbation of their refractive index along the length of the waveguide will be formed. The Finite-Difference Time-Domain (FDTD) method, on the other hand, has been proven to be one of the most powerful numerical techniques that are usefully applied to a wide range of optical devices. In this paper, a FDTD technique, developed for nonlinear structures, is used to analyze a nonlinear waveguide and periodic nonlinear structures that exhibit attractive properties that make them suitable for novel devices with wavelength tunable characteristics. More specifically, the Bodies of Revolution (BOR) FDTD numerical simulation method will be used to model the fiber Bragg Grating (FBG) and the direct integration method will be employed to include the effect of Self Phase Modulation (SPM) in this model. The combination of these techniques will result in a model that is used to analyze two different types of periodic nonlinear structure, FBG and Distributed Bragg Resonator (DBR). The nonlinear effect provides the designer an added degree of design flexibility for devices with wavelength tunable characteristics, for example, in the design of tunable filters, WDM systems and optical sensors. 相似文献
265.
The blood free fatty acids (FFAs), which provide energy to the cell and act as substrates in the synthesis of fats, lipoproteins, liposaccharides, and eicosanoids, involve in a number of important physiological processes. In the present study, matrix-assisted laser desorption/ionization-Fourier transform ion cyclotron resonance mass spectrometry (MALDI-FTICR MS) with ammonia-treated N-(1-naphthyl) ethylenediamine dihydrochloride (ATNEDC) as a novel MALDI matrix in a negative ion mode was employed to directly quantify serum FFAs. Multiple point internal standard calibration curves between the concentration ratios of individual fatty acids to internal standard (IS, C17:0) versus their corresponding intensity ratios were constructed for C14:0, C16:1, C16:0, C18:0, C18:1, C18:2, C18:3, C20:4, and C22:6, respectively, in their mixture, with correlation coefficients between 0.991 and 0.999 and limits of detection (LODs) between 0.2 and 5.4 μM, along with the linear dynamic range of more than two orders of magnitude. The results indicate that the multiple point internal standard calibration could reduce the impact of ion suppression and improve quantification accuracy in the MALDI mode. The quantitative results of nine FFAs from 339 serum samples, including 161 healthy controls, 118 patients with hyperglycemia and 60 patients without hyperglycemia show that FFAs levels in hyperglycemic patient sera are significantly higher than those in healthy controls and patients without hyperglycemia, and elevated FFA levels are also associated with increased levels of fasting blood glucose (FBG) in hyperglycemic patient sera. Serum FFAs were identified on the basis of the observed accurate molecular masses and reliable isotope distributions obtained by MALDI-FTICR MS. 相似文献
266.
波长扫描极值解调法实现光纤光栅应变和温度传感的测量 总被引:5,自引:0,他引:5
本文用可编程调谐光纤光栅环行腔激光器作扫描光源,采用波长扫描极值传感解调法对光纤光栅应变及温度进行了测量。应变测量范围为±2440με,灵敏度为0.016step/με;温度测量范围达608℃,灵敏度为0.13step/℃。 相似文献
267.