Speech enhancement based on multitaper spectrum and psychoacoustical weighting rule

Multitaper spectrum has lower variance than the traditional periodogram. The noise spectrum and the noise to noisy signal spectrum ratio (NNSR) were estimated from the multitaper spectrum of the noisy signal; the pre-enhanced speech for calculating the noise masking threshold was obtained by the spectral amplitude subtraction method, whose gain is a function of NNSR; the final enhanced speech was obtained by suppressing the Fourier spectrum of the noisy speech with the psychoacoustical weighting rule incorporating the noise masking threshold. Because of the low variance feature of the multitaper spectrum, a modified offset formula was proposed to calculate the noise masking threshold, thus the reconstructed speech with this modification has an improvement in MBSD (Modified Bark Spectral Distortion). When a maximum limitation less than one to the psychoacoustical weighting rule is further proposed, the higher the input SNR (> 0 dB) is, the more improvement the segmental SNR and the overall SNR have. The informal listening tests show that there is little speech distortion for the enhanced speech processed by the proposed method, the background noise is reduced much and free of musical noise.     

NIR光谱的LLE-PLS非线性建模方法及应用

传统的偏最小二乘(PLS)建模方法不能有效反映近红外(NIR)光谱与分析样本的物理化学性质之间存在的非线性关系。局部线性嵌入(LLE)是一种新的非线性降维方法,属于流形学习方法,它能有效地发现高维数据中的本真低维结构。结合LLE和PLS,提出一种近红外光谱非线性建模的新方法,并用于建立丹参多酚酸盐柱层析过程中丹酚酸B含量的回归校正模型。该方法首先用LLE对NIR光谱数据降维,再用PLS建立校正模型。结果表明,与多元散射校正、一阶导等预处理方法结合PLS建模比较,参数优化后的LLE-PLS方法能更准确地预测丹酚酸B的含量,其交叉验证均方根误差为0.128 mg·mL-1、决定系数为0.998 8。基于NIR光谱及LLE-PLS建模,可实现丹参多酚酸盐柱层析过程的在线检测。     

基于二维重组和动态窗格的水质检测紫外-可见光谱去噪算法

立足于成功研制的紫外-可见光谱水质检测多参数测量系统,针对紫外-可见光谱水质多参数原位实时检测在精度、灵敏度、稳定性等方面的实际需要,开展了基于二维重组和动态窗格的水质检测紫外-可见光谱去噪算法的研究,以此提高紫外-可见光谱水质检测的测量精度。光谱法水质检测系统通常使用工业级低成本光谱仪,其输出光谱包含明显的非平稳噪声。传统去噪法难以在滤除噪声的同时保留谱线细节。而且,原位实时水质检测条件下,被测水样可能快速变化,传统去噪法中常用的多次采样求均值法将产生额外的测量误差。引入的去噪算法通过对水样光谱进行等间隙连续采样,将光谱数据张成由光谱轴和时间轴构成的二维矩阵,经过二维小波变换后,设置一个可变宽度的窗格在系数矩阵中水平滑动,使用窗格内的小波系数计算得到动态去噪阈值,并随窗格滑动构建去噪阈值向量,由此进行光谱去噪。其中,窗格宽度由相邻区域的噪声方差变化率决定,变化率较高的区域缩小窗格宽度,反之则扩大宽度。实验结果表明,这种去噪算法不仅能有效去除光谱中的非平稳噪声,而且能保留光谱的细节信息,有助于提高仪器的测量精度。与此同时,由于该算法并未使用时域平均,样本的快速变化对去噪性能的影响较小,适合在线或原位水质检测的水样本环境。     

药品近红外光谱通用性定量模型评价参数的选择

为寻找药品近红外通用性定量模型在建立过程中用于确立最优模型的关键评价参数组合,收集整理了目前各种商品化化学计量学软件及文献中的13个常用于评价近红外定量模型的统计学参数,结合人用药品注册技术要求国际协调会对于药品定量分析方法验证基本要求,对92个药品近红外通用性定量分析模型的这些参数进行了计算和分析。通过对各个参数之间相互关系的研究,确定了适合于药品近红外通用性定量分析模型评价的参数组合,并统计出了这些参数的数值范围：用于模型准确性评价的关键参数为交叉验证均方根误差/预测均方根误差、平均相对偏差和相对分析误差;大部分交叉验证均方根误差/预测均方根误差结果在3%以内,其中交叉验证均方根误差在数值上与平均绝对偏差相当,大部分相对分析误差值大于2,而平均相对偏差的数值与所建模型的类型(剂型、样品的包装形式)和待测成分含量的分布有关。模型线性评价关键参数为决定系数;大部分模型的决定系数在80%～100%之间。模型耐用性关键评价参数为预测均方根误差与交叉验证均方根误差的比值,大部分模型该参数在1.5以内。精密度评价关键参数为重复测定结果的标准差;该参数对于规范近红外的操作,以及考核模型能否在不同仪器间传递具有重要的意义,但目前药品近红外通用性定量模型对于分析精密度的关注较少,无法估计出具体数值范围。该研究不仅为药品近红外通用性模型的建立者和使用者提供了评价模型优劣的依据,也为完善药品近红外光谱通用性定量分析模型的参数评价体系提供了基础数据。     

可见/近红外光谱的油茶籽油三元体系掺假检测模型优化

采用可见/近红外光谱技术结合化学计量学方法对油茶籽油三元体系掺假进行定量检测研究。将菜籽油和花生油按不同比例掺入纯油茶籽油中,获得掺假样本。采集纯油茶籽油及掺假样本在350~1 800 nm范围内的可见/近红外光谱数据,随机分为校正集和预测集,并从不同建模波段、预处理方法及建模方法角度对掺假预测模型进行优化。研究结果表明,菜籽油、花生油和总掺伪量的最优建模波段及预处理方法分别为750~1 770,900~1 770 ,870~1 770 nm和多元散射校正(MSC)、标准归一化处理(SNV)和二阶微分,而最优的建模方法均为最小二乘支持向量机(LSSVM)。对于最优掺假模型,菜籽油、花生油和总掺伪量的预测集相关系数(R_p)和预测均方根误差(RMSEP)分别为0.963,0.982,0.993和2.1%,1.5%,1.8%。由此可见,可见/近红外光谱技术结合化学计量学方法可以用于油茶籽油的三元体系掺假定量检测。     

FTIR法研究氨基酸稀土配合物与磷脂的相互作用

利用傅里叶变换红外光谱（ＦＴＩＲ）法研究了不同类型氨基酸及其配合物与二棕榈酰磷脂酰胆碱脂质体浇铸膜的相互作用。结果表明，在有氨基酸存在下，二棕榈酰磷脂酰胆碱的红外谱图没有明显的变化；氨基酸稀土配合物与磷脂极性头基团有静电相互作用，作用的程度随稀土离子、氨基酸及稀土同氨基酸配比的不同而有所不同。     

Induced Diffraction in Phase-Mismatched Second-Harmonic Generation

We show analytically that in phase-mismatched second-harmonic generation, an effective diffraction is induced at the second-harmonic （SH） frequency. Numerical simulation results agree with the analytical predictions. Compared to the case of linear propagation, the effect of the overall diffraction at the SH frequency becomes doubled due to the induced diffraction, which causes an interesting result that the SH beam width will be larger than that of the fundamental field.     

Analysis of Frequency Spectrum of Laser-Induced Vibration of Microbeam Resonators

The vibration phenomenon during pulsed laser heating of micro-beams is investigated. The beam is made of silicon and is heated by a laser pulse with a non-Gaussian temporal profile and with an ultrashort pulse duration of 2ps, which incites vibration due to the thermoelastic damping effect. This coupled thermoelastic problem is solved using an analytical-numerical technique based on the Laplace transformation. The damping ratio and resonant frequency shift ratio of beams due to the air damping effect and the thermoelastic damping effect are also examined and discussed.     

A Method for Quantitative Analysis of Chemical Mixtures with THz Time Domain Spectroscopy

A method for analysing chemical mixtures quantitatively with terahertz time domain spectroscopy is proposed. The experimental results demonstrate the feasibility of this technique. Transmission coefficient of THz wave at the sample surface is taken into account to improve the analytic precision, lsomer mixtures are chosen as the experimental samples. Compared to similar techniques, the analytic precision could be improved evidently in this method.     

Time-resolved measurement of atomic emission enhancement by fs--ns dual-pulsed laser-induced breakdown spectroscopy

Time-resolved measurement of atomic emission enhancement is performed by using a 500-fs KrF laser pulse incident upon a high density supersonic O_{2} gas jet, synchronized with an orthogonal ns frequency-doubled Nd:YAG laser pulse. The ultra-short pulse serves as an igniter of the gas jet, and the subsequent ns-laser pulse significantly enhances the atomic emission. Analysis shows that the contributions to the enhancement effect are made mainly by the bremsstrahlung radiation and cascade ionization.