Audible Threshold of Early Reflections with Different Orientations and Delays

Early reflection is an important component in an enclosed sound field. Due to the precedence effect, the early reflection may not be the dominant factor in sound source localization; however, it still has obvious influences on spatial position, loudness, timbre, and etc. Till now, there have sparse studies on evaluation of the audible threshold of early reflections with lacking of general and quantitative results. This work investigated the audible threshold of early reflection with a simplified sound field model under various experimental conditions including the combination of eight incidence angles and five time delays. Three-down-one-up adaptive strategy with three-interval three-alternative forced-choice (3I-3AFC) paradigm was used due to its efficiency and robustness. Results indicate that (1) the audible threshold of early reflections decreases monotonically with increasing time delay relative to the direct sound. Furthermore, a linear equation between early reflection threshold and time delay is established with correlation coefficient higher than 0.9; (2) When the direct sound and the reflection locate in the same half-plane, the audible threshold of early reflections decreases with increasing angle deviation between the direct sound and the reflection. Moreover, a front-back symmetry of early reflection threshold is observed for stimuli below 5 kHz; (3) Considerable variations in early reflection threshold are found among individuals, especially at large angle deviation and time delay of early reflections relative to the direct sound.     

The surface lubricative properties of PVA/PVP hydrogels treated with radiation used as artificial cartilage

In this work, poly(vinyl alcohol)/polyvinylpyrrolidone (PVA/PVP) hydrogels were prepared by cycled freezing and thawing process, and subsequently with irradiation crosslink processing. The exterior micro-structure and frictional coefficients of compound hydrogels with and without radiation treatment were compared. The changes of surface lubricative properties were observed in physiological condition in vitro. Without radiation treatment, the friction coefficient of PVA/PVP hydrogels increased rapidly in water because of the solubility and exudation of PVP, which could induce the decline of their lubricative action. While after radiation treatment, the surface lubricative properties of PVA/PVP hydrogels in water were improved and stable due to the crosslink between PVA and PVP.     

The effects of behavioral and structural assumptions in artificial stock market

Recent literature has developed the conjecture that important statistical features of stock price series, such as the fat tails phenomenon, may depend mainly on the market microstructure. This conjecture motivated us to investigate the roles of both the market microstructure and agent behavior with respect to high-frequency returns and daily returns. We developed two simple models to investigate this issue. The first one is a stochastic model with a clearing house microstructure and a population of zero-intelligence agents. The second one has more behavioral assumptions based on Minority Game and also has a clearing house microstructure. With the first model we found that a characteristic of the clearing house microstructure, namely the clearing frequency, can explain fat tail, excess volatility and autocorrelation phenomena of high-frequency returns. However, this feature does not cause the same phenomena in daily returns. So the Stylized Facts of daily returns depend mainly on the agents’ behavior. With the second model we investigated the effects of behavioral assumptions on daily returns. Our study implicates that the aspects which are responsible for generating the stylized facts of high-frequency returns and daily returns are different.     

超声波对木瓜蛋白酶催化活性影响的机理研究

木瓜蛋白酶经适当参数的超声波处理后酶活力提高。超声处理后酶的米氏常数Km变小,最大反应速率Vm也减小。超声处理后酶的紫外吸收光谱不变,荧光发射光谱也不改变,而差示光谱出现明显的正峰和负峰。研究结果表明,超声波处理后,木瓜蛋白酶的构型没有改变,而构象发生了变化。本文讨论了超声波影响木瓜蛋白酶活性的可能机理。     

Face centered cubic cobalt layer on Au(1 1 1): a magneto-optical study

It has been recently shown that Co can grow epitaxially on an Au(1 1 1) layer with a face centered cubic (FCC) structure, the Co[1 1 1] and Au[1 1 1] axes being oriented along each other. First magneto-optical studies of the FCC Co film structure are reported here. The differences in magnetic behavior for FCC and HCP-type Co films as a function of the layer thickness are underlined and interpreted in the framework of a phenomenological model.     

富锂三元层状正极材料的研究进展

富锂三元层状正极材料(xLi₂MnO₃·(1-x)LiMO₂(0<x<1,M=Mn,Ni,Co))因其远高于其它正极材料的放电比容量而被视为下一代锂离子电池正极材料的最佳选择之一,是未来锂离子电池研究和发展的重点。 但由于其循环性能差、库伦效率低等缺陷,富锂正极材料迟迟不能实现商业化生产。 本文将介绍近几年国内外富锂三元层状正极材料的最新研究进展,主要包括富锂三元层状正极材料的组成、制备技术、结构和性能研究以及包覆与掺杂等改性方面的研究进展,同时对富锂层状正极材料未来的发展趋势和前景作了展望。     

尖头碎片撞击小尺寸储罐的模拟实验

化工园区内,容器爆炸事故易引发多米诺效应,产生的碎片击中临近目标设备或装置可能造成事故后果升级。通过开展尖头碎片撞击小尺寸储罐模拟实验,得到了不同轴向撞击角的尖头碎片撞击不同壁厚小尺寸储罐的穿透形貌、穿透能量以及穿孔直径。结果表明:（1）尖头碎片以0°轴向撞击角穿透罐壁形成的穿孔正面近似圆形,以15°、30°及45°轴向撞击角撞击形成的穿孔正面近似椭圆形且有2个条形翻边,穿孔背面均呈现花瓣型开裂;（2）轴向撞击角越大,壁厚越大,所需的穿透能量越大;（3）轴向撞击角与壁厚对穿孔轴向直径影响显著,但穿孔环向直径变化幅度不大。最后,根据穿甲力学理论和动量守恒定理,推导出适用于0°~45°轴向撞击角的尖头碎片剩余速度理论计算公式。     

不同年龄群体的光生物效应评价方式

研究了照明光环境对不同年龄人群的光生物效应定量评价方式。从光照转换角度提出了一种考虑不同年龄人眼透射谱、瞳孔直径以及受光面积的节律因子模型,选取3种不同色温(3 000,4 000,6 000 K)的白光LED光源,在同种照度500 lx下实验测试其光谱分布,并对提出的节律因子进行计算,与之前标准中考虑年龄的修正因子方式进行了线性拟合对比分析。结果表明:在相同色温下,随着年龄的增大,节律因子值逐渐减少;而对于相同年龄,随着色温的增大,节律因子是变大的,此种规律与其他研究人员得出的实验结论一致。从线性拟合相关度上来看,三种色温下两种考虑年龄的节律因子的直线相关度分别为0.958 08,0.958 33,0.957 22,具有较高的相关性。较之于标准中的考虑透光谱方式,本文提出了另外一种考虑不同年龄人眼差异的光生物效应评价方式,尝试对人眼模型的透射谱进行绝对而不是相对效应的考虑方式。     

亚碘酰苯低聚物的结构与振动光谱18O-同位素效应的理论研究

应用LDA-PWC方法对亚碘酰苯低聚物HO-(PhIO)n-H (n＝1～10)(链末端以羟基结束)共10个模型分子进行了理论研究. 计算结果表明PhIO分子链大致呈“T”形, I—O链的两个I—O键键长非常接近, 同时发现I—O链产生扭转, 整个亚碘酰苯低聚物呈螺旋状结构. 应用B3LYP法得到HO-(PhIO)6-H更为精确的亚碘酰苯低聚物稳定构型, 平均I—O键长为0.2089 nm, 标准偏差为0.0007 nm. 理论计算表明在600～400 cm－1段, PhI18O的吸收峰向低波数方向移动, 与实验观测结果一致. 振动模式分析发现该段吸收峰均涉及氧原子, 18O同位素效应将降低各振动峰值的频率. 峰值移动最大的吸收峰为591/566 cm－1 (16O/18O), 与之对应的理论计算值为590.409/557.788 cm－1 (16O/18O), 属于对称伸缩振动ν(I—O—I). 吸收峰(443/436 cm－1)对应的理论计算值为460.627/439.158 cm－1 (16O/18O), 归属于不对称伸缩振动ν(I—O—I).     

Filtering noisy chaotic signal via sparse representation based on random frame dictionary

The denoising problem of impure chaotic signals is addressed in this paper. A method based on sparse representation is proposed, in which the random frame dictionary is generated by a chaotic random search algorithm. The numerical simulation shows the proposed algorithm outperforms those recently reported alternative denoising methods.