低温烧结的PZT-BF-BCW系压电陶瓷

本文研究了锆钛酸铅(PZT)——铁酸铋(BF)——钨铜酸钡(BCW)系压电陶瓷的低温烧结特性,给出了组成对烧结温度及性能的影响结果。获得了烧结温度低(935℃/0.5h)且性能优良的配方:0.92PZT-0.05BF-0.03BCW+0.08wt%CuO,其主要电性能:K_p为47%,Q_m为950,ε_(33)~T/ε_0为850。并应用XRD、SEM和DTA等手段探讨了该系统瓷体的相组成和低温烧结机理。     

添加物对Ce—TZP力学性能的影响

本实验使用工业ZrO_2原料制备Ce—TZP,通过添加高弹性模量的Al_2O_3以提高Ce—TZP的断裂韧性,添加TiO_2以改善Ce—TZP的烧结性能,刘实验数据采用计算机技术处理分析,找出最佳的制备条件。实验结果表明,CeO_2的含量显著影响Ce—TZP的弯曲强度和断裂韧性,存在一个最佳值。添加少量Al_2O_3可以提高Ce—TZP的断裂韧性,添加少量的TiO_2,能加速扩散和烧结过程,但其断裂韧性却随了TiO_2添加量的增加而降低。     

PLZT多层陶瓷电容器瓷料的低温烧结

本文研究了反铁电体Pb(Cd_(1/2)W(1/2))O_3、Pb(Co_(1/2)W_(1/2))O_3及Pb(Mg_(1/2)W_(1/2))O_3和铁电体Ba(Cu_(1/2)W_(1/2))O_3及BiFeO_3对银改性的PLZT多层陶瓷电容器瓷料烧结的促进作用及其对瓷体介电性能的影响。并探讨了其低温烧结机理和介质损耗行为。     

火山灰水泥复合早强减水剂的研究

本文研究了一种新型的复合早强减水剂并试验了它在火山灰水泥中的使用效果。这种复合早强减水剂由一种非萘系减水剂AP与适量的无机盐组成,它的掺入,不仅可使水泥凝结时间正常,而且在水泥砂浆流动度相同的条件下,早期强度也有较大的提高。此外,本文还借助于XRD,DTA,TG,SEM等测试手段对复合早强减水剂的作用机理作了初步探讨。     

B替位Ca离子对BaTiO_3铁电相变的影响

用X和射线衍射、透射电镜、扫描电镜、介电性能与电导平衡等方法研究了B位Ca离子对BaTiO_3;陶瓷铁电相变的影响.X射线衍射数据表明,随着B位Ca离子含量的增加(直至5%)c/a比下降至接近1.从介电系数的温度关系可见:含5%B位与6%A位Ca离子的组份其居里峰展宽且下降至室温.发现了当含A位Ca离子(约5%)时,B位Ca离子含量的变化对降低居里点有较显著的作用.据此结果,本文发展了一套热力学模型以解释Ca掺杂BaTiO_3中B位Ca离子对居里峰移动与展宽的作用.     

热风条件下除湿送风的熔炼试验研究

在３００℃左右较高热风温度下对冲天炉熔炼的空气进行除湿送风，可进一步强化焦炭燃烧和传热过程，降低炉内的氧化性。试验表明，铁水温度提高１５～２５℃，熔化率提高１０％左右，炉渣氧化铁、合金元素烧损及焦耗进一步降低，为同时采用两种强化措施提供了依据。     

Forecasting Performance of Nonlinear Models for Intraday Stock Returns

We studied the predictability of intraday stock market returns using both linear and nonlinear time series models. For the S&P 500 index we compared simple autoregressive and random walk linear models with a range of nonlinear models, including smooth transition, Markov switching, artificial neural network, nonparametric kernel regression and support vector machine models for horizons of 5, 10, 20, 30 and 60 minutes. The empirical results indicate that nonlinear models outperformed linear models on the basis of both statistical and economic criteria. Specifically, although return serial correlation receded by around 10 minutes, return predictability still persisted for up to 60 minutes according to nonlinear models, even though profitability decreases as time elapses. More flexible nonlinear models such as support vector machines and artificial neural network did not clearly outperform other nonlinear models. Copyright © 2011 John Wiley & Sons, Ltd.     

A Rational Belief: The Method of Discovery in the Complex Variable

The importance of mathematics in the context of the scientific and technological development of humanity is determined by the possibility of creating mathematical models of the objects studied under the different branches of Science and Technology. The arithmetisation process that took place during the nineteenth century consisted of the quest to discover a new mathematical reality in which the validity of logic would stand as something essential and central. Nevertheless, in contrast to this process, the development of mathematical analysis within a framework that largely involves intuition and geometry is a fact that cannot go unnoticed amongst the mathematics community, as we shall show in this paper through the research made by Bernhard Riemann on complex variables.     

Polar actomyosin contractility destabilizes the position of the cytokinetic furrow

Cytokinesis, the physical separation of daughter cells at the end of mitosis, requires precise regulation of the mechanical properties of the cell periphery. Although studies of cytokinetic mechanics mostly focus on the equatorial constriction ring, a contractile actomyosin cortex is also present at the poles of dividing cells. Whether polar forces influence cytokinetic cell shape and furrow positioning remains an open question. Here we demonstrate that the polar cortex makes cytokinesis inherently unstable. We show that limited asymmetric polar contractions occur during cytokinesis, and that perturbing the polar cortex leads to cell shape oscillations, resulting in furrow displacement and aneuploidy. A theoretical model based on a competition between cortex turnover and contraction dynamics accurately accounts for the oscillations. We further propose that membrane blebs, which commonly form at the poles of dividing cells and whose role in cytokinesis has long been enigmatic, stabilize cell shape by acting as valves releasing cortical contractility. Our findings reveal an inherent instability in the shape of the dividing cell and unveil a novel, spindle-independent mechanism ensuring the stability of cleavage furrow positioning.     

掺钽和变温对铌酸锂晶体拉曼谱的影响

研究了LoTa_xNb_(1-x)O_3(x=0,0.0013,0.0052,1)晶体的拉曼光谱及拉曼散射随温度的变化.实验证明,随着晶体中含铅量的增加及温度的升高,拉曼谱峰红移,散射强度减小,峰宽增加.杂质钽的引入会改变晶体的内应力;温度的升高会增加模式振动的阻尼、晶格振动出现“失稳”,是造成上述现象的原因。