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.     

Two-octave spectral broadening of subnanojoule Cr:forsterite femtosecond laser pulses in tapered fibers

Spectral broadening of femtosecond Cr:forsterite laser pulses is enhanced due to the use of tapered fibers. Supercontinuum generation with unamplified subnanojoule femtosecond Cr:forsterite laser pulses is observed for the first time. With 40-fs 0.6-nJ pulses of 1.25-μm Cr:forsterite laser radiation coupled into a tapered fiber having a taper waist diameter of about 2 μm and a taper waist length of 90 mm, we observed the spectra spanning more than two octaves at the output of the fiber in the regime of anomalous group-velocity dispersion. This result opens the way for the creation of compact femtosecond Cr:forsterite laser plus tapered fiber systems for optical metrology and biomedical applications. Received: 23 October 2001 / Accepted: 16 January 2002 / Published online: 14 March 2002     

Fluorine-induced chemiluminescence detection of phosphine,alkyl phosphines and monophosphinate esters

Summary Phosphine, alkylated phosphines and monophosphinate esters are detected with high sensitivity in capillary gas chromatography (GC) by their chemiluminescent reactions with molecular fluorine. Detection limits are estimated to be 1.3 pg, 0.5 pg, 8 pg, and 17 pg for phosphine, trimethyl phosphine, trimethyl phosphinate ester, and triethyl phosphine, respectively. As found earlier with alkylated sulfur, selenium and tellurium compounds, the detector exhibits a linear response. For triethyl phosphine, a linear range of greater than three orders of magnitude was demonstrated. Emission spectra were obtained for the trimethyl phosphine and triethyl phosphine systems. Chemiluminescence emitters include electronically excited HCF, vibrationally excited HF, and an unknown species in the trimethyl phosphine system. Banded emission from vibrationally excited HF and a broad continuum were observed for both trimethyl phosphine and triethyl phosphine; however, HCF emission was observed only for TMP. Under the conditions employed, the principal emitter is HCF for trimethyl phosphine and HF and the unknown emitter for triethyl phosphine. This detector may have important applications in investigations of the biogeochemical cycling of phosphorus.     

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.     

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.     

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.     

Fluorescence parameters and their interpretation

The observed fluorescence parameters (spectrum, quantum yield and lifetime) of an aromatic compound in solution usually differ from its molecular fluorescence parameters, due to self-absorption, secondary fluorescence and/or self-quenching. Neglect of these factors has caused errors in the interpretation of fluorescence data.