时频方法分析长骨中的超声导波及皮质骨厚度

超声导波在长骨中传播时,接收信号中含有相互叠加的多个导波模式。本文提出将希尔伯特-黄变换(HHT)用于分析叠加的多模式导波信号,将其分解成许多单个独立的模式,然后对分解出的模式求得其对应频率下的群速度,并与短时傅里叶变换所得的结果进行比较。通过与理论计算结果比较,可得到长骨皮质骨的厚度。研究结果表明,实验得到的厚度与实际厚度一致。说明通过测量导波模式的速度可以评价皮质骨的厚度,也说明HHT方法是一种识别叠加多模式导波信号的有效方法。      

Detection of long bones based on Barker code excited ultrasonic guided waves

Single pulse excited ultrasonic guided wave surfers high attenuation during the propagation in long bones.This results in small amplitude and low signal-to-noise ratio(SNR)of measured signals.Thus,the Barker code excitation is introduced into long bone detection to improve the quality of received signals,due to its efficiency in increasing amplitude and SNR.Both simulation and in vitro experiment were performed,and the results were decoded by the weighted match filter(WMF) and the finite impulse response- least squares inverse filter(FIRLSIF),respectively.The comparison between the results of Barker code excitation and sine pulse excitation was presented.For 13-bit Barker code excitation,WMF produced 13 times larger amplitude than sine pulse excitation,while FIR-LSIF achieved higher peak-sidelobe-level(PSL) of —63.59 dB and better performance in noise suppression.The results show that the Barker code excited guided waves have the potential to be applied to the long bone detection.     

Study on the mean trabecular bone spacing based on fundamental frequency estimation method

Ultrasonic backscatter signals from the cancellous bone can be used to diagnose osteoporosis effectively due to its ability to provide the information of bone microstructure. Mean trabecular bone spacing(MTBS)is one of the important parameters for characterization of bone microstructure.This paper proposed a MTBS estimating method based on the fundamental frequency estimation,which was applied to backscatter signals from simulations, and in vitro bovine trabeculae.The estimated MTBS were compared with those of simplified inverse filter tracking(SIFT)algorithm and autoregressive(AR)cepstrum method.The results demonstrated that the proposed method is very robust for the MTBS estimation with more precise estimates and smaller estimated variance in the presence of a small signal-to-noise ratio (SNR),and a large scattering strength ratio of diffuse scatterers to regular ones.     

Alternative methods of identifying the oxidation of metallic nanoparticles embedded in a matrix

We compare methods for valence-state analysis based on energy-loss near-edge structure (ELNES), including the white-line ratio (WLR), pre-edge peak (prepeak) and post-edge peak (postpeak) techniques. Starting from multiple-scattering calculations, we correlate the appearance of a prepeak in the O-K edge and postpeak in the L-edge with oxidation of a transition metal (TM). The ability to use more than one technique is especially advantageous for a nanocomposite of metallic nanoparticles embedded in a matrix, as we show for the case of iron nanoparticles in a silica matrix.     

基频估计算法研究平均骨小梁间距

超声背散射信号能提供松质骨微结构信息从而能有效的诊断骨质疏松,而平均骨小梁间距(MTBS)是表征松质骨微结构的重要参数之一.本文提出了一种基频估计的MTBS估计算法,对仿真信号和离体牛胫骨松质骨中的超声背散射信号分别进行分析处理,并和现有的两种算法(简易反向滤波跟踪(SIFT)算法和AR倒谱法)进行比较.实验结果表明基频估计算法对噪卢和随机散射回波有更好的鲁棒性,在信噪比较低和随机散射回波幅度较大时估计值更加精确,且有很好的方差性能.充分说明了本文算法是一种有效的MTBS估计算法.     

吡咯亚胺配体与过渡金属的反应性及其催化烯烃聚合

在经典的Brookhart吡啶双亚胺后过渡金属烯烃聚合催化剂基础上,用吡咯五元环代替吡啶六元环骨架可得到具有不同电子效应的新型吡咯亚胺配体.通过吡咯环特殊的电子效应和位阻效应可设计出种类繁多的有别于吡啶亚胺配体的配合物.综述了吡咯亚胺配体与前过渡金属(Ti,Zr等)、后过渡金属(Fe,Co,Ni,Pd等)、稀土金属(Y...     

骨折长骨中超声导波传播特性的仿真研究

采用超声导波评价长骨骨折已成为近两年来的一个研究热点.本文采用混合边界元方法(HBEM)对超声导波在骨裂长骨中的传播情况以及各导波模式的反射系数和透射系数进行了数值分析.研究结果表明,入射导波模式经由裂纹处模式转换后依然保持为主要接收模式不变.对某一裂纹,各模式透射系数常在相近的频率点上达到局部峰值.对于不同深宽比(d/w)裂纹,某些模式透射系数曲线局部峰值所对应的频率存在着相互错开的现象,这些结果可用于选择最优入射导波模式和频率,以便更好地定量评价骨质以及骨裂状况.     

Hydrothermal Synthesis and Crystal Structure of a Novel Polyoxometalate K(C_4N_2H_(12))_4(C_4N_2H_(11))_(2-)[Mo_8~ⅤMo_4~ⅥCdP_8O_(54)(OH)_8]F·6H_2O

The title compound 1 has been synthesized by the reaction of H_2MoO_4, CdCl_2, H_3PO_4, KF, piperazine hexahydrate and water in aqueous solution under mild hydrothermal conditions. Single-crystal X-ray analysis reveals that the title compound crystallizes in the triclinic system, space group P(-1) with a = 14.049(3), b = 15.972(3), c = 20.043(4) (A), α = 85.82(3), β = 81.28(3),γ = 67.15(3)°, V= 4095.9(14) (A)~3, M_r = 3204.62, Z=2,D_c = 2.598 g/cm~3,μ = 2.360 mm~(-1), F(000) = 3124, the final R = 0.0314, wR = 0.0826 and S = 0.989 for 18592 observed reflections with I > 2σ(I). The crystal packing is stabilized by N-H…O and O-H…O intra- and intermolecular hydrogen bonds to form an infinite 3D network.     

Photogeneration of carbon dioxide from polypropylene film stabilized by hindered amines

Infrared spectrometric measurements have been used to measure the amount of carbon dioxide generated by UVA irradiation of polypropylene film stabilized with 0.5% of three different hindered amine light stabilizers (HALS). The measurements were made in situ, using a specially constructed glass cell fitted with CaF₂ windows. In each case the amount of photogenerated carbon dioxide was less than that from a HALS-free polypropylene film of similar thickness. The amount of photogenerated CO₂ was greatest in oxygen that had been pre-saturated with water and the amount of CO₂ evolved depended on the grade of HALS. In dry oxygen, although the differences between the films containing different HALS were much reduced the amount of CO₂ continued to be smaller than that from the HALS-free polymer. The sensitivity of CO₂ photogeneration to the presence of HALS provides new evidence of the relevance of the CO₂ photogeneration method to the diagnosis of photosensitivity of polymers and the influence of stabilizing additives.     

A Simple and Rapid Label-free Fluorimetric “Turn Off-on” Sensor for Cadmium Detection Using Glutathione-capped CdS Quantum Dots

A convenient label-free fluorescence(FL) nanoprobe for rapid detection of cadmium(Cd) was established using glutathione-capped CdS quantum dots(QDs) and 1,10-phenanthroline(phen). The prepared CdS QDs exhibited a strong FL emission at 536 nm, which could be quenched by phen due to the photoinduced hole transfer(PHT) mechanism. The existence of Cd effectively recovered the FL intensity of CdS QDs, which was due to the easy detachment of phen from the surface of QDs to form[Cd(phen)₂(H₂O)₂]²⁺ in solution. Cd concentrations were linearly correlated with the FL intensity in the range of 0.0625-1.25 μmol/L under the optimized conditions and the detection limit was 0.01 μmol/L. Finally, the Cd concentration was accurately quantified in real water sample using the proposed sensor.