凹槽叶顶冷气射流对涡轮叶尖泄漏流动的影响

涡轮叶尖泄漏流动对涡轮通道内流动损失有着显著影响,叶顶冷气射流对控制叶尖泄漏流动和改善涡轮叶尖气热性能有重要意义.本文利用数值模拟方法,研究了叶顶冷气喷射位置和喷射流量对高压涡轮凹槽叶顶间隙泄漏流动控制的影响.文中重点分析了泄漏流动结构及涡轮气动效率的变化,探讨了冷气对刮削涡这一间隙内主控流动结构演化的影响.研究表明,...     

超临界CO2布雷登循环热电联供系统多目标优化

本文研究了以超临界CO₂布雷登循环为原动机的热电联供系统,对系统主要运行参数进行了分析,得到运行参数对于系统热力学性能和经济性能的影响规律。同时,以一次能源利用率和单位输出成本作为目标函数,采用多目标遗传算法对系统进行了优化;在优化结果的基础上,通过TOPSIS法决策出最优解,并与单目标最优解进行对比。结果表明,透平进口温度、透平进口压力和压缩机进口温度的增大有利于系统效率的提高;作为代价,成本也相应增加。在热电比0~4范围内,尽可能增大热电比能够最大程度上降低系统的单位输出成本,提高能源的利用率。     

卟啉钯敏化剂构效性质与三线态-三线态湮灭上转换性能研究

上转换发光是一种将长波长的激发光转化为短波长发射的反斯托克斯发光现象,三线态-三线态湮灭上转换（TTA-UC）能够在较低密度能量下被激发,且上转换量子产率高,因此获得研究者们广泛关注。关于敏化剂分子结构与上转换发光性能相关性的研究一直是TTA-UC研究领域的重要热点,选择两种代表性的卟啉钯光敏剂[PdOEP-八乙基卟啉钯(Ⅱ)和PdBrTPP-四溴苯基卟啉钯(Ⅱ)]与蒽衍生物9,10-(4-羟甲基)苯基蒽p-DHMPA发光剂组合上转换体系作为研究模型,通过一系列合成工作获得材料分子后,进一步比较两种敏化剂的光谱性质与体系最终上转换性能之间关系。通过细致研究敏化剂和发光剂的荧光发射和寿命等光谱性质对敏化剂系间窜越,三线态-三线态能量转移及三线态-三线态湮灭等能量传递过程的影响后,发现在532 nm处的摩尔吸光系数PdBrTPP (10.8 cm-1·mmol-1)大于PdOEP (3.0 cm-1·mmol-1);三线态寿命PdBrTPP (173.13 μs)大于PdOEP (109.21 μs)。但与p-DHMPA配对时光敏剂与发光剂的三线态能级差ΔE_TT,PdOEP (0.140 eV)却高于PdBrTPP (0.062 eV),通过Stern-Volmer方程得到Stern-Volmer猝灭常数K_SV和双分子猝灭常数k_q值也是PdOEP略高,最终表现出上转换阈值PdOEP/p-DHMPA (22.40 mW·cm-2)小于PdBrTPP/p-DHMPA (29.78 mW·cm-2),上转换发光效率Φ_UC,PdOEP/p-DHMPA (28.3％)大于PdBrTPP/p-DHMPA (26.8％)。因此,卟啉钯敏化剂的构效对三重态湮灭上转换发光效率影响最为重要的决定因素是敏化剂三线态高低。对于不同的敏化剂,在分子主体结构、摩尔吸光系数与三线态寿命等光谱参数差别不大的情况下,敏化剂的三线态能级越高,就将会具有更大的上转换发光效率。然而如果以总上转换能力指标来评价,PdBrTPP的共轭结构能够提升其在激发波长处吸收更多光子的能力,具有比PdOEP更高的摩尔吸光系数,造成其总上转换能力η比PdOEP高3.4倍。因此从上转换总效能指标来评价,通过敏化剂分子设计调控其在激发光波长处的摩尔吸光系数也不失为一种简单易行的方法。     

大型综合医院室外声景观评价影响因素分析——以长沙市中心医院为例

大型综合医院室外本是医患康复疗养、舒缓身心的场所,但并未引起足够的重视,噪声影响严重,声景观较差.该文以长沙市中心医院为例,通过定点实测结合问卷调查的方式,探究影响大型综合医院室外声景观评价结果的因素.结果表明:长沙市中心医院室外声景观整体满意度一般,语义词调查结果整体偏向贬义负值,受访者身份、调查时间和声源构成对声景...     

Conditioning convex and nonconvex problems

Two ways of defining a well-conditioned minimization problem are introduced and related, with emphasis on the quantitative aspects. These concepts are used to study the behavior of the solution sets of minimization problems for functions with connected sublevel sets, generalizing results of Attouch-Wets in the convex case. Applications to continuity properties of subdifferentials and to projection mappings are pointed out.We are grateful to M. Valadier for pointing out, during a lecture by the author in Montpellier in October 1990 presenting the main results of the present paper, that existence results in Section 2 of the present paper can be dissociated from estimates.     

经典局域共振型水声超材料的吸隔声性能研究*

基于水声超材料吸声机理和多层平行介质平面波理论,建立局域共振型水声超材料结构,通过COMSOL进行建模计算,研究该结构的吸声性能机理,此外为了验证钢背衬的隔声性能,在该水声超材料结构基础上添加一层0.005m厚的钢背衬进行仿真对比。研究结果表明,在频段为200Hz-4000Hz时,水声超材料声学性能较好,吸声性能整体较优,且添加钢背衬的水声超材料隔声性能较优,甚至在某频率点达到15dB的隔声差值;此外通过位移场图进一步揭示水声超材料的吸声机理,发现水声超材料结构的位移场和钢背衬都对吸声性能会产生影响,钢背衬通过影响共振吸收来影响吸声性能,而位移场则通过位移幅度大小影响吸声性能。     

The AME 2020 atomic mass evaluation (I). Evaluation of input data,and adjustment procedures

This is the first of two articles(Part I and Part II)that presents the results of the new atomic mass evaluation,Ame2020.It includes complete information on the experimental input data that were used to derive the tables of recommended values which are given in Part II.This article describes the evaluation philosophy and procedures that were implemented in the selection of specific nuclear reaction,decay and mass-spectrometric data which were used in a least-squares fit adjustment in order to determine the recommended mass values and their uncertainties.All input data,including both the accepted and rejected ones,are tabulated and compared with the adjusted values obtained from the least-squares fit analysis.Differences with the previous Ame2016 evaluation are discussed and specific examples are presented for several nuclides that may be of interest to Ame users.     

Statistical and Visual Analysis of Audio,Text, and Image Features for Multi-Modal Music Genre Recognition

We present a multi-modal genre recognition framework that considers the modalities audio, text, and image by features extracted from audio signals, album cover images, and lyrics of music tracks. In contrast to pure learning of features by a neural network as done in the related work, handcrafted features designed for a respective modality are also integrated, allowing for higher interpretability of created models and further theoretical analysis of the impact of individual features on genre prediction. Genre recognition is performed by binary classification of a music track with respect to each genre based on combinations of elementary features. For feature combination a two-level technique is used, which combines aggregation into fixed-length feature vectors with confidence-based fusion of classification results. Extensive experiments have been conducted for three classifier models (Naïve Bayes, Support Vector Machine, and Random Forest) and numerous feature combinations. The results are presented visually, with data reduction for improved perceptibility achieved by multi-objective analysis and restriction to non-dominated data. Feature- and classifier-related hypotheses are formulated based on the data, and their statistical significance is formally analyzed. The statistical analysis shows that the combination of two modalities almost always leads to a significant increase of performance and the combination of three modalities in several cases.     

Evaluation of Transparent Optical Network Performance in Presence of Incoherent Homodyne Crosstalk

A simple method to evaluate the performance of transparent optical networks (TON) that takes into account the incoherent homodyne crosstalk, signal distortion, inter-symbol interference (ISI), amplified spontaneous emission (ASE) noise, and arbitrary optical and electrical filters is proposed. This method combines the effect of the incoherent homodyne crosstalk with an exhaustive Gaussian approximation for the influence of ASE noise, signal distortion, and ISI. It is shown that the incoherent homodyne crosstalk penalty depends on the ASE noise accumulated in the TON, ISI, and extinction ratio. The proposed method estimates are compared with experimental results published by other authors. Good agreement is observed for one, two, and four incoherent homodyne crosstalk signals, revealing that the proposed method provides accurate estimates even when the methods based on a Gaussian approximation for the incoherent homodyne crosstalk fail. The proposed method is used to assess the performance of a TON composed by optical add-drop multiplexers based on arrayed waveguide gratings. Results reveal that incoherent homodyne crosstalk, ASE noise, and ISI impair the TON performance and, therefore, none can be neglected in the TON design.     

The Effect of Speaking Sample Duration on Determination of Habitual Pitch

The purpose of this study was to investigate if there was an effect of duration of speaking on determination of habitual pitch. Five speaking periods commonly used to elicit habitual pitch in clinical voice evaluations were compared (1, 5, 15, 30, and 60 seconds). Thirty female speakers with normal voices participated. Results of a within-subject univariate F-test revealed a statistically significant (p < 0.001) difference in habitual pitch among the speaking periods. Habitual pitch for the 1-second and 60-second speaking periods were found to be statistically significantly (p < 0.05) different than all remaining speaking periods, and the habitual pitch for the 30-second speaking period was found to be statistically significantly (p < 0.05) different than 60-second speaking period. Implications for the use of various speaking durations when determining habitual pitch are discussed, as is the possibility of a speaking duration effect on determination of other pitch-related voice parameters.