Controllability properties of nonlinear behaviors

This paper proposes a topological framework for the analysis of the time shift on behaviors. It is shown that controllability is not a property of the time shift, while chain controllability is. This also leads to a global decomposition of behaviors.

     

On the use of nickel foil strain gages at varying temperatures

When a strain gage made of nickel foil attached on the surface of a specimen is subjected to repeated loads, the elastic stress is measured by observing slip-bands in the foil resulting from repeated strain. Calibration studies with rotating-bending tests at various temperatures between room temperature and 350°C are performed on round steel bars with nickel foil. The relation between the threshold stress for the first appearance of slip-bands and the number of stress cycles is examined at varying temperatures, which provides the calibration values of the nickel foil tested at varying temperatures. Assuming that the first appearance of slip-bands is based on the linear cumulative damage law, the calibration values at varying temperatures are calculated from those established by the calibration tests at several constant temperatures. It is found that the calculated calibration values agree well with the results obtained by the calibration tests at varying temperatures and that the calculation applying the linear cumulative damage law is a useful method to presume the calibration values at varying temperatures without performing the experiment.     

森林地表火火行为预测预报系统

本文从地表火蔓延的本质入手，建立了一整套求解地表火行为特征量的数学模型，并运用现代软件编制技术，成功地编制出预测预报地表火行为的计算机软件。该系统能预测复杂地形、气象条件和可燃物分布情形下，火蔓延过程中不同阶段的火行为状况。算例结果表明，系统在预测结果的合理性和准确性等方面优于美国的BEHAVE程序。     

建构主义教学观对教师教学行为的影响

注重知识传输的传统教学弊端日益显现。建构主义教学主张学生在教师指导下 ,通过情境合作、交流、会话 ,积极主动地进行意义建构。这种教学观对教师提出了新的挑战 ,要求教师转变其教学行为。     

Preparation of polymethylsilsesquioxanes by the base‐catalyzed hydrolytic polycondensation of triisopropoxy(methyl)silane

Base‐catalyzed hydrolytic polycondensation of trialkoxymethylsilane was investigated to synthesize polymethylsilsesquioxanes (PMSs). The reaction of trimethoxy(methyl)silane and triethoxy(methyl)silane with tetramethylammonium hydroxide, tetrabutylammonium hydroxide, and also coline gave insoluble gels. Polymethylsilsesquioxane (PMS‐IP) was obtained by the reaction of triisopropoxy(methyl)silane (MTIPS) with tetrabutylammonium hydroxide as a catalyst. PMS‐IP was composed primarily of T² and T³ units. The percentage of T³ units and the molecular weight of PMS‐IP increased with increases in the molar ratios of catalyst and water to MTIPS and with the reaction time. PMS‐IP was soluble in organic solvents, except for methanol, and was separated by extraction with hexane and methanol into low‐ and high‐molecular‐weight fractions of M_w 2800–4000 and 7300–88,300, respectively. PMS‐IP coating films were prepared by dip coating on the organic, inorganic, and metal substrates, using the acetone–isopropyl alcohol solution of PMS‐IP. Since PMS‐IP solutions prepared with tetrabutylammonium hydroxide were hardly used because of the low content of hydroxy groups in the polymer, they showed low adhesion when compared with those solutions prepared with hydrochloric acid. The dielectric constant of the coating film prepared from the high‐molecular‐weight PMS‐IP was 2.6. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3623–3630, 2005     

东鞍山贫铁矿石磁选预富集行为

针对东鞍山贫铁矿石(Fe质量分数34.60%)中含有赤铁矿、磁铁矿和少量的菱铁矿,提出了一种弱磁粗选-高梯度扫选的预富集工艺,并借助XRD、铁的化学物相分析及扫描电镜(SEM)考察了磁场强度和原料磨矿细度对东鞍山铁矿石预富集行为的影响.结果表明,在磨矿细度-0.074mm占70%(质量分数)、弱磁粗选磁场强度120mT、高梯度扫选Ⅰ磁场强度300mT及高梯度扫选Ⅱ磁场强度800mT的条件下,可获得Fe质量分数42.67%、回收率95.45%的预富集精矿;磁铁矿富集于弱磁粗选作业中,赤铁矿和菱铁矿在高梯度扫选作业中得到有效富集,尾矿中丢失的铁矿物主要为微细粒赤铁矿(＜10μm),由于受到的磁性捕获力弱而无法得到回收.     

磁性花生壳负载钯催化剂的制备及催化氨硼烷释氢性能

以高锰酸钾改性后的花生壳为原料,通过共沉淀法制备了磁性花生壳(PSK-Fe_3O_4)复合材料,并以其为载体制备了磁性花生壳负载钯催化剂(Pd/PSK-Fe_3O_4).以XRD、FT-IR、TEM、XPS、TG等表征手段对该催化剂进行了表征,并将其应用于催化氨硼烷水解释氢.结果表明:Pd/PSK-Fe_3O_4催化剂在催化氨硼烷水解反应中表现出较好的催化活性,其转换频率(TOF)为6.7 mol_(H2)·mol_(Pd)~(-1)·min~(-1),表观活化能(E_(app))为28.0 kJ mol~(-1).Pd/PSK-Fe_3O_4催化氨硼烷水解释氢反应对于催化剂浓度和氨硼烷浓度的反应级数分别为一级和零级.此外,循环实验表明该催化剂具有较好的循环稳定性.     

A STUDY ON THE COUNTER-INTUITIVE BEHAVIORS OF PIN-ENDED BEAMS UNDER PROJECTILE IMPACT

The counter-intuitive behaviors of pin-ended beams under the projectile impact are investigated with ANSYS/LS-DYNA in this paper. It studies in detail their displacement-time history curves, final deformed shapes, energy relationships and projectile impact velocity ranges related to their counter-intuitive behaviors. The influences of the impact positions on their counterintuitive behaviors are also discussed. The results show that no matter where the impact position on the beam is, the counter-intuitive behaviors of pinned beams will occur as long as the impacting velocity lies within a proper range. Corresponding to the occurring of the counter-intuitive behaviors, the rebounding number in the displacement history curves of the beams decreases from a few times to zero with an increase of the impact velocity. The final deformation modes of the beam corresponding to the counter-intuitive behaviors will appear in symmetrical and unsym-metrical forms no matter where the impact position is; the impact velocity of the first-occurring of the counter-intuitive behaviors of the beam increases slowly with the deviation of the impact position away from the mid-span.     

钨合金的冲击动力学性质及细微观结构的影响

简单介绍了钨合金(主要为W-Ni-Fe)的制备工艺和常用热处理方法,其后着重从动 态力学性能、剪切带的实验观察和研究、细微观结构对材料力学性能的影响等几方 面总结和评述了近年来针对钨合金取得的主要结果.并在文章的最后初步提出了有 前景的几个研究方向.     

Applicability of normal and shear stress cells embedded in cohesionless materials

A normal stress cell and a shear stress cell have been designed and tested under very varied conditions including permanent strain. Results pooled from nine different tests with the cells embedded in cohesionless materials (sand and wheat) showed that the coefficient of variation of the normal stress-cell sensitivity was 0.04, while it was 0.10 for the shear cell. The agreement between predicted and measured sensitivity was considered to be good for the normal stress cell and reasonably good for the shear stress cell. The shear cell showed a systematic dependence, within acceptable limits, of the total stress state in the surrounding material. A qualitative explanation of this phenomenon is given. Paper was presented at the SEM VI International Congress on Experimental Mechanics held in Portland, OR in June 6–10, 1988.