天然紫草色素的超声波提取及稳定性研究

研究了超声波法和有机溶剂法提取天然紫草色素的工艺条件，超声波法可明显提高色素的提取速率。研究了不同温度、pH值、光及金属离子等条件对色素性能的影响。结果表明，pH值、热、光对紫草色素的性质影响不大，但强碱、强日光及某些金属离子对色素有一定的影响。     

测定葡萄糖氧化酶活力的一种简便方法

利用靛蓝胭脂红褪色分光光度法测定葡萄糖氧化酶催化葡萄糖溶液产生的过氧化氢浓度,经过标准曲线转换得到葡萄糖氧化酶的活力.研究了缓冲液pH值、水浴温度、靛蓝胭脂红用量等对葡萄糖氧化酶活力测定的影响.结果表明:利用靛蓝胭脂红褪色分光光度法测定葡萄糖氧化酶活力时,缓冲液最佳pH值为4、最佳水浴温度为100℃、靛蓝胭脂红最佳用量为1.3 mL.此方法的重现性较好,反应系统较稳定.     

试论卤化银彩色影像的光劣变

光是影响卤化银彩色影像耐久保存的重要因素.光的作用使卤化银彩色影像出现褪色、变色等病变,致使珍贵的信息无法获取.本文以显影生成染料的多层影像为对象,简述卤化银彩色影像的结构组成、成像原理,总结光对卤化银彩色影像的危害及其影响因素,提出预防卤化银彩色影像出现光劣变的策略.     

温度和pH值对雷克拉水解速率的影响

通过室内模拟研究的方法，试验探讨了温度、pH值对雷克拉在水溶液中水解速率的影响。结果表明：随着温度和pH值的升高，其降解速率也随之明显增大。     

光的波长对光化学反应速率的影响

光的波长(或频率)是影响光化学反应的一个重要因素。本文主要通过甲苯与溴发生取代反应的实验来验证可见光中处于不同波长的蓝光和红光对中学化学教材中的光卤化反应速率的影响;并对其进行了相关的理论解释。     

保加利亚乳杆菌富集硒的影响因素研究

本文研究了亚硒酸氢钠浓度、起始pH值、培养温度和培养时间对保加利亚乳杆菌富硒能力的影响。结果表明,培养温度为主要影响因素,培养基中亚硒酸氢钠浓度、培养时间和pH值为次要影响因素。在3个次要因素中,亚硒酸氢钠浓度的影响是主要的。最佳富集条件为培养温度37℃、亚硒酸氢钠浓度40μg/mL、培养时间48h和pH值6.2。     

油船货油舱内底板用钢腐蚀行为研究

研究了温度、NaCl浓度以及溶液的pH值等环境因素对WDH36NF油船货油舱内底板用钢腐蚀速率、腐蚀形貌的影响。结果表明:油船货油舱内底板用钢的腐蚀速率随温度升高而增加。NaCl浓度由5%增大到10%,内底板用钢的腐蚀速率随浓度增大而增加,NaCl浓度由10%增大到15%,内底板用钢的腐蚀速率减小。pH值由0.5增大到0.85,内底板用钢的腐蚀速率随pH值增大而增加,pH值由0.85增大到1.2,内底板用钢的腐蚀速率减小,并趋于平缓。     

基于Hessian矩阵的多结构光条纹中心快速提取方法

使用结构光方法对物体进行三维检测时,需要对图像中结构光条纹中心快速、准确提取。为提高检测速度,可向待测物体同时投射多结构光条。为实现多结构光条纹识别和亚像素中心快速提取,本文提出一种基于Hessian的多结构光条纹亚像素中心提取方法。该方法首先对多结构光条纹进行识别,根据识别的结构光条纹计算各条纹上的极值点,最后在极值点像素位置附近区域确定结构光条纹的亚像素中心。实验表明,该方法减小了Hessian矩阵算法的运算量,提高了结构光亚像素中心提取速度,能满足多结构光条纹识别和亚像素中心快速提取的需要。     

pH缓冲剂在酸性气田甲酸盐完井液中的应用

甲酸盐盐水完井液以其低腐蚀、保护储层等特性受到人们的青睐,其中一个重要原因是它具有固有的弱碱性。甲酸盐盐水完井液在酸性气田应用时,酸性气体（CO2和H2S）的侵入会降低体系pH值,从而增大腐蚀速率、加快甲酸盐的分解。本文提出用pH缓冲剂来保持完井液pH值的恒定,并推荐K2CO3-KHCO3组合。该组合能够维持pH值的稳定、抑制甲酸盐的分解并加速FeCO3腐蚀保护膜的形成。最后确定K2CO3加量为1．4％．KHCO3为1％．并提出需要维护的情况。     

对“探究影响酶促反应速率因素（pH）实验设计”的探讨

通过实验分析＂探究影响酶促反应速率因素（pH）实验＂过程中出现的现象,指出pH9条件下H2O2不稳定将影响实验结果。重新设计＂探究不同pH值影响酶促反应速率实验＂。     

The impact of reading material’s lexical accessibility on text fading effects in children’s reading performance

The acceleration phenomenon (AP) is defined by improvements in reading speed and reading comprehension, induced by an artificial text fading procedure corresponding to the previously determined fastest individual reading rate. Recent results, however, indicated that fading that is slower than the self-paced reading rate can produce comparable reading enhancements. As reading performance can be strongly influenced by the reading material, this study aimed at investigating to which extent reading enhancements induced by text fading depend on the reading material’s characteristics. We confronted 39 German third graders with a previously utilized text fading procedure, which was slower than their self-paced reading rate. Included text varied regarding to the lexical accessibility (LA), representing how well information can be accessed from the mental lexicon. Children’s reading rates increased statistically significant due to text fading for all LA levels. However, reading comprehension was sensitive to the text material’s characteristics: Reading comprehension enhancements were observable for easily accessible reading material, but not for material with intermediate or difficult levels of LA. Material that was difficult to retrieve from the mental lexicon even resulted in reduced reading comprehension in the fading condition. Possible influences on immediate lexical access, the impact of working memory capacity and implications for future AP research are discussed.     

FFH/MFSK系统抗干扰性能研究

针对FFH/MFSK通信系统的特点,推导了在赖斯衰落信道下,多音干扰产生的虚警检测概率和漏检概率数学表达式,并研究了不同参数对系统BER性能的影响. 仿真结果表明,在多音干扰功率大于一定值时,多音干扰数量是造成系统BER性能下降的主要因素.     

改进的强跟踪卡尔曼滤波器在MSINS/GPS组合导航中的应用研究

通过深入分析次优渐消因子的解算原理,提出了一种无须先验知识的多时变渐消因子估计方法,用于改进强跟踪卡尔曼滤波算法,并将其应用于MSINS/GPS浅组合中。采用多个次优渐消因子,分别对不同的数据通道进行渐消,可以有效提高滤波算法的跟踪能力。仿真结果表明,改进的强跟踪卡尔曼滤波算法解决了量测相关、初值选取敏感性等问题,可以提高系统的实时性、鲁棒性。     

非理想最大比合并的误码率下界

研究了信道估计的均方误差,利用无限长、非因果的维纳滤波器推导出了它的下界.通过对不同衰落信道多普勒谱的积分,求出了相应的信道估计均方误差下界的闭合表达式,并在此基础上得到了分集系统在独立同分布的衰落信道中采用最大比合并时的误码率下界.数值分析结果表明,非理想信道估计下最大比合并的误码率性能是以理想信道估计的结果为下界,并随着最大多普勒频移的增加或信道估计信噪比的减小而逐渐劣化.     

Concreteness fading in learning secondary school physics concepts

Concreteness fading has been proposed as a general instructional approach to support learning of abstract mathematics and science concepts. Accordingly, organizing external knowledge representations in a three-step concrete-to-idealized sequence should be more beneficial than the reverse, concreteness introduction, sequence. So far, evidence for the benefits of concreteness fading come mainly from studies investigating learning of basic mathematics concepts. Studies on learning natural science concepts are scarce and have not implemented the full three-step-sequence. In an experimental classroom study (N = 70), we compared concreteness fading and concreteness introduction in high school science education about electromagnetic induction using a detailed assessment. Furthermore, we explored whether these sequences differentially affect the use of the different representations during instruction. Both sequences were equally effective and there were no differences in using the representations. We discuss why our results question the proposed advantages of concreteness fading and highlight conceptual differences and learning goals across domains.     

一种新的扩展复数正交空时分组码

Recent research challenges in the wireless communication include the usage of diversity and efficient coding to improve data transmission quality and spectral efficiency. Space diversity uses multiple transmitting and/or receiving antennas to create independent fading channels without penalty in bandwidth efficiency. Space-time block coding is an encoding scheme for communication over Rayleigh fading channels using multiple transmitting antennas. Space-time block codes from complex orthogonal designs exist only for two transmitting antennas. This paper generalizes a new complex orthogonal space-time block code for four transmitting antennas, whose decoding complexity is very low. Simulations show that the generalized complex orthogonal space-time block code has low bit error rate, full rate and possibly large diversity.     

Secrecy Performance of Untrusted Relay’s Cooperation under Fading Channels

The secrecy performance of cooperation with an untrusted relay under a quasi-static fading channel is analyzed in this paper. An achievable secrecy rate is provided and the influence of selfish behavior of untrusted relay is analyzed. Furthermore, the secrecy performance of the scheme is discussed and compared with that of the case where the relay is just an eavesdropper. Simulation results show that the untrusted relay’s cooperation in the fading case reduces the outage probability from 1/2 to 1/3 and achieves a higher outage secrecy capacity.     

One Instructional Sequence Fits all? A Conceptual Analysis of the Applicability of Concreteness Fading in Mathematics,Physics, Chemistry,and Biology Education

To help students acquire mathematics and science knowledge and competencies, educators typically use multiple external representations (MERs). There has been considerable interest in examining ways to present, sequence, and combine MERs. One prominent approach is the concreteness fading sequence, which posits that instruction should start with concrete representations and progress stepwise to representations that are more idealized. Various researchers have suggested that concreteness fading is a broadly applicable instructional approach. In this theoretical paper, we conceptually analyze examples of concreteness fading in the domains of mathematics, physics, chemistry, and biology and discuss its generalizability. We frame the analysis by defining and describing MERs and their use in educational settings. Then, we draw from theories of analogical and relational reasoning to scrutinize the possible cognitive processes related to learning with MERs. Our analysis suggests that concreteness fading may not be as generalizable as has been suggested. Two main reasons for this are discussed: (1) the types of representations and the relations between them differ across different domains, and (2) the instructional goals between domains and subsequent roles of the representations vary.

     

多径衰落信道中的RAKE接收机性能研究

在移动通信中,分集接收是抵抗多径衰落的有效方法.文中对一种多径分集技术—RAKE接收机的原理进行了详细的描述,分析了其对多径衰落的补偿有效性.通过用MATLAB软件进行误码率仿真,可以看出,RAKE分集接收能收集多径信号能量,变矢量和为代数和,有效地减少多径衰落的影响,降低误比特率.检测中的分集重数L不超过路径总数时,分集重数L越大越好.     

MIMO无线光通信中编码方案的选择

在MIMO无线光通信中,最常用的两种编码是空时分组码(STBC)与分层空时编码(LSTC)。传输速率、误比特率、抗衰落性能是衡量通信系统的重要性能指标,采用Monte-Carlo方法进行仿真研究,根据系统在MIMO无线光通信中的性能指标来选择发送端是采用空时分组码还是采用分层空时编码,以满足在不同特性要求下达到误比特率、抗衰落性能与传输速率的最优化。结果表明,根据不同的性能指标选择不同的编码方式,更能有效地利用资源。