非理想Buck Boost连续工作方式的平均法建模和仿真

开关变频器的高频化、软开关技术,以及新的控制技术和新的拓扑结构等给开关变换器的建模带来了许多亟待解决的问题,以往建模过程中的一些理想化假设将会引起很大偏差。本文借鉴三端开关器件模型法、时间平均等效电路法、能最守恒法的基本思想,研究了非理想Buck Boost在连续工作模式下的电路模型,揭示了考虑寄生参数建模的必要性,对实际应用有较大的指导意义。     

Non-destructive assessment of instrumental and sensory tenderness of lamb meat using NIR hyperspectral imaging

The purpose of this study was to develop and test a hyperspectral imaging system (900–1700 nm) to predict instrumental and sensory tenderness of lamb meat. Warner–Bratzler shear force (WBSF) values and sensory scores by trained panellists were collected as the indicator of instrumental and sensory tenderness, respectively. Partial least squares regression models were developed for predicting instrumental and sensory tenderness with reasonable accuracy (R_cv = 0.84 for WBSF and 0.69 for sensory tenderness). Overall, the results confirmed that the spectral data could become an interesting screening tool to quickly categorise lamb steaks in good (i.e. tender) and bad (i.e. tough) based on WBSF values and sensory scores with overall accuracy of about 94.51% and 91%, respectively. Successive projections algorithm (SPA) was used to select the most important wavelengths for WBSF prediction. Additionally, textural features from Gray Level Co-occurrence Matrix (GLCM) were extracted to determine the correlation between textural features and WBSF values.     

Application of near infrared spectroscopy for the rapid determination of antioxidant activity of bamboo leaf extract

This study was carried out to evaluate the feasibility of using near infrared (NIR) spectroscopy for determining three antioxidant activity indices of the extract of bamboo leaves (EBL), specifically 2,2-diphenyl-1-picrylhydrazyl (DPPH), ferric reducing/antioxidant power (FRAP), and 2,2′-azinobis-(3-ethylbenz-thiazoline-6-sulfonic acid) (ABTS). Four different linear and nonlinear regressions tools (i.e. partial least squares (PLS), multiple linear regression (MLR), back-propagation artificial neural network (BP-ANN), and least squares support vector machine (LS-SVM)) were systemically studied and compared in developing the model. Variable selection was first time considered in applying the NIR spectroscopic technique for the determination of antioxidant activity of food or agricultural products. On the basis of these selected optimum wavelengths, the established MLR calibration models provided the coefficients of correlation with a prediction (r_pre) of 0.863, 0.910, and 0.966 for DPPH, FARP, and ABTS determinations, respectively. The overall results of this study revealed the potential for use of NIR spectroscopy as an objective and non-destructive method to inspect the antioxidant activity of EBL.     

Application of successive projections algorithm for variable selection to determine organic acids of plum vinegar

Visible and near infrared (Vis/NIR) spectroscopy was investigated to determine the acetic, tartaric and lactic acids of plum vinegar based on a newly proposed combination of successive projections algorithm-least squares-support vector machine (SPA-LS-SVM). SPA, compared with regression coefficients (RC), was applied to select effective wavelengths (EWs) with least collinearity and redundancies. Five concentration levels (100%, 80%, 60%, 40% and 20%) of plum vinegar were studied. Multiple linear regression (MLR) and partial least squares (PLS) models were developed for comparison. The results indicated that SPA-LS-SVM achieved the optimal performance for three acids comparing with full-spectrum PLS, SPA-MLR, SPA-PLS, RC-PLS and RC-LS-SVM. The root mean square error of prediction (RMSEP) was 0.3581, 0.0714 and 0.0201 for acetic, tartaric and lactic acids, respectively. The overall results indicated that Vis/NIR spectroscopy incorporated to SPA-LS-SVM could be applied as an alternative fast and accurate method for the determination of organic acids of plum vinegars.     

三峡大坝泄洪建筑物水力学监测

本文主要介绍了三峡大坝泄洪建筑物在135m库水位时水力学观测成果.监测成果的完整性和系统性较好,为工程的验收、制定枢纽运行管理规程提供了科学依据。同时,对今后国内外高水头水利工程的设计和运行具有十分重要的参考价值。     

Projection data replenishment algorithm for limited angle tomography

A new iterative algorithm of tomographic reconstruction of objects on the basis of projection data available in a limited range of angles only is proposed. The algorithm is based on calculating artificial projections in those directions where projection data are unavailable. By means of numerical simulations, it is verified that the algorithm developed ensured high quality of reconstruction up to the angular interval of 45–60°.     

“水深平均二维数学模型”在跨河桥梁防洪评价壅水计算中的应用

近来,随着计算机技术的提高,出现利用计算机对跨河桥梁局部流场进行模拟并得出大桥设计壅水高度的方法。本文以扬州市文昌东路东延工程中的廖家沟大桥为例,介绍了采用"水深平均二维数学模型"进行壅水分析计算的基本方法和主要步骤,为防洪评价中的桥梁壅水计算提供新的计算模式。     

江苏如东地区风速数据分析及风能发电储量

通过分析江苏如东气象局公布的 2 0 0 2年 1～ 1 2月沿海地区的风速数据及所选用的风电机特性 ,研究了该地区的风能发电储量。在选用最优型的风电机时 ,考虑了计算得出的最优风速 ,并通过对该种风电机进行建模来描述其特性。通过分析计算 ,得出如东沿海地区 70 m高处的平均风速、风能平均功率密度和所选用风电机的年发电量。计算结果表明该地区风能发电储量十分丰富