《硅光电池特性》实验教学探索和实践

为了更好地培养全校本科生的创新思维和动手实践能力,探索了适合九零后学生的教学方法。针对实验中存在的一些问题,引导学生积极思考,找到一些快速完成实验并且大大降低仪器损耗率的实验技巧,实现学生、教师、学校三方共赢的目标。     

Phase Transitions in a Highly Anisotropic Antiferromagnetic Heisenberg Toda Chain

The behavior of the antiferromagnetic spin 112 Heisenberg Toda chain is investigated in a space of interactions which include exchange anisotropy, bond alternation and Toda-like spinlattice coupling by means of coherent-state for spin. We analyse magnetically driven lattice instabilities and find that multiphase structure only occurs under the condition, of bond alternation. Three phase diagrams and tricritical points are obtained and some relevant physical properties are discussed.     

超声诊断骨质疏松症中松质骨的模型

骨质疏松症(OP)是老龄化社会中影响健康的一个重要问题，超声技术已成为诊断骨质疏松症的一种常用方法。文中综述了近年来用超声诊断骨质疏松症中松质骨模型研究的进展，对棒状模型、流体多孔介质模型(Biot理论)和层状模型(schoenberg理论)进行了分析和讨论，指出了各理论模型存在的缺陷，对下一步的研究工作提出了建议。     

Reflection and transmission characteristics of ultrasonic guided waves in fractured long bone

Assessment of fractured long bone using ultrasonic guided wave（GW） has gained considerable attention.This paper focuses on using the hybrid boundary element method （HBEM） to analyze the propagation characteristics of ultrasonic GW in fractured long bones. The reflection coefficients（RC） and transmission coefficients（TC） for different depth-to-width ratio（d/w） cracks were numerically calculated and analyzed.It has been shown that the primary output modes,which include the transmission and reflection modes,are the same as the incidence modes.For some cracks,different TC curves always got the local maxima in adjacent frequencies.For different d/w cracks,most of the TC curves had local maxima which are not overlapped.These simulation results are helpful to optimize the modes and frequencies of the incidence GWs for quantitatively evaluating the bone quality and providing the numeral results of the cracks in long cortical bones.     

超声轴向传播技术评价长骨的研究

用超声轴向传播技术评价长骨状况已成为近年来的一个研究热点。本文首先介绍了第一到达波(FAS)法、超声Lamb波及柱面导波法在评价长骨皮质骨状况方面的研究进展,最后分析和讨论了当前研究中存在的问题及应该研究的方向。     

骨小梁中超声背散射信号的频率分析及其微结构的估计

骨质疏松症是一种骨强度下降的全身性骨骼疾病,骨强度的下降是骨量减少和骨微结构退化的共同结果。相比于传统的超声透射方法,超声背散射法可提供更多的骨微结构信息,而对于松质骨结构的建模能有助于结构信息的获取。本文将骨小梁简化为单圆柱模型(圆柱状的单根骨小梁浸于骨髓中),并基于此模型对超声背散射与频率的关系进行分析。用铝线代替骨小梁做仿体实验,通过实验与理论结果的比较来验证单圆柱模型的可行性。     

松质骨超声背散射信号的谱信息熵判断方法

在松质骨超声背散射评价的实际应用中,如何快速准确地判断接收到的信号中是否包含有效背散射信号是一个重要问题。提出一种基于谱信息熵的背散射信号判断方法。对在体采集的984例成人跟骨处临床数据,采用该方法判断背散射信号的有效性,将判断结果与经验判断结果进行对照分析,并分析该方法中的信号区间长度和谱信息熵分段数对判断结果的影响。结果表明,当信号区间长度为13μs,谱信息熵分段数为15~20时,该方法可以获得最佳的判断结果(准确度〉95%,灵敏度〉99%,特异度〉87%),并且计算时间极短(1.5 ms)。因此采用谱信息熵方法判断背散射信号的有效性,可以满足超声骨质评价中对准确性和实时性的要求。     

采用超声导波特征参量的骨质疏松识别方法

骨质的定期检测对骨质疏松的防治至关重要。本文研究了骨质疏松对超声导波在人体长骨中传播的影响。提出采用多尺度小波变换方法对接收到的导波信号进行处理,通过分析在不同传播距离下高阶小波细节分量所占信号总能量的变化,来判断是否患有骨质疏松症。在13位志愿者的小腿胫骨上进行超声测量,得到导波信号。经多尺度小波变换方法的分析处理结果显示在13位志愿者中,有7位志愿者的超声导波信号随着传播距离的改变,其主要频率成分发生了明显的变化,显示这7位志愿者患有骨质疏松症。这一诊断结果与X射线技术诊断结果相比,准确率可以达到92.3%,表明本文所提出的利用小波多尺度变换方法对长骨进行超声诊断具有较好的潜力。     

Joint spectrogram segmentation and ridge-extraction method for separating multimodal guided waves in long bones

Ultrasonic guided waves (GWs) can be used to evaluate long bones effectively because of the ability to provide the information of the whole bone. In this study, a joint spectrogram segmentation and ridge-extraction (JSSRE) method was proposed to separate multiple modes in long bones. First, the Gabor time-frequency transform was applied to obtain the spectrogram of multimodal signals. Then, a multi-class image segmentation algorithm was used to find the corresponding region of each mode in the spectrogram, including an improved watershed transform and a region growing procedure. Finally, the ridges were extracted and the time domain signals representing individual modes were reconstructed from these ridges in each region. The validations of this method were discussed by simulated multimodal signals with different signal-to-noise ratios (SNR). The correlation coefficients between the original signals without noise and the reconstructed signals were calculated to analyze the results quantitatively. The results showed that the extracted ridges were in good agreement with generated theoretical dispersion curves, and the reconstructed signals were highly related to the original signals, even under the SNR=3 dB situation.     

充粘液管材中超声纵向轴对称导波的频散特性分析

模拟分析充粘液管内径-壁厚比和超声纵向轴对称导波波包宽度的关系。考虑了衰减的情况下,在各传播距离、频厚积和激发脉冲周数上,采用脉冲回波法,分析了导波的频散特性。结果表明:对于特定的材料,当频厚积一定时,充粘液管材中传播的导波特性只与内径-壁厚比有关;各高阶模式的截止频厚积随内径-壁厚比的增大而减小。用L(0,1)模式检测内径-壁厚比在4附近的充粘液管时灵敏度较低;而用L(0,2)模式检测内径-壁厚比在9.2附近的管时灵敏度较低。对于不同内径-壁厚比的充粘液管,检测中应当用不同的纵向轴对称导波模式,所用的激发脉冲周数和频厚积也应当不同。