含双裂纹圆截面悬臂梁的损伤识别研究

裂纹的萌生和扩展直接影响构件的振动响应,对构件的安全可靠性具有重要影响．本文以圆截面悬臂梁为对象,结合转角模态振型和模态频率等高线,研究了一种双裂纹识别技术．首先,基于应力强度因子和卡氏定理推导了无裂纹梁单元和含裂纹梁单元的刚度矩阵;在此基础上,建立了含裂纹圆截面悬臂梁的有限元动力学方程;然后,结合裂纹对梁转角模态振型和模态频率的影响,提出了双裂纹识别策略．最后,通过算例讨论了双裂纹识别策略的可行性．结果表明,圆截面悬臂梁的模态转角在裂纹位置出现突变,裂纹深度越大转角突变值越大;将识别出的裂纹位置作为已知参数,通过模态频率等高线法,可以准确地识别出双裂纹的深度．     

On the Distribution of r-Full and l-Free Integersin Short Intervals

 We study the distribution of r-full and l-free numbers in short intervals () and sharpen Kr?tzel’s and Wu’s results. (Received 22 June 1999; in revised form 4 October 1999)     

Sr~(2+(置换对Eu~(2+)掺杂钙长石晶体结构和光谱特性的影响

采用高温固相法在弱还原气氛下制备了Ca0.955-xSrxAl2Si2O8:Eu2+(x=0~0.9)系列荧光粉,研究了Sr2+置换Ca2+对晶体结构和光谱特性的影响。Sr2+进入CaAl2Si2O8晶格与Ca2+发生类质同相替代形成连续固溶体,物相从CaAl2Si2O8相(Triclinic,P1)逐渐转换为SrAl2Si2O8相(Monoclinic,I2/c),晶胞参数a,b,c和晶胞体积都随Sr2+置换量呈线性增加,α,β和γ在置换量为0.1~0.7区间缓慢减小,超过0.7后呈线性急剧减小。位于250~410 nm区间的宽带激发光谱由4个激发峰构成,表观峰值位于356 nm。Eu2+占据两种格位形成两个发光中心,分别产生430和468 nm发射,宽带发射光谱位于390~550 nm区间,呈现近白色发光。控制Sr2+含量可使表观发射峰位置在408~434 nm之间移动,强度随Sr2+含量增加而增强。     

微波检测实验——微波相位与含湿物质含水量变化关系的研究

指出了在物理实验课程中开设微波实验的必要性,介绍已经开展的微波实验项目,着重介绍在测定含湿物质含水量的微波检测实验中进行的有关微波相位与含水量变化关系的研究,并说明该实验的特点和意义.     

环形HYLTE喷管耦合段及光腔区流场的数值模拟

参考传热学相关理论,估算燃烧室的传热损耗分数及相应的平衡温度,确定了主喷管的入口参数设置。在此基础上,对环形HYLTE喷管的耦合段及光腔区流场进行3维的数值模拟,给出了F原子质量分数、静温、静压的空间分布,得到了光腔区各支谱线的小信号增益系数变化曲线。将计算结果与实验结果进行比对,光谱测量结果及移动光轴实验证实了计算模型的合理性。     

Mass Cultivation of Microalgae on Animal Wastewater: a Sequential Two-Stage Cultivation Process for Energy Crop and Omega-3-Rich Animal Feed Production

In this study, 97 microalgal strains purchased from algae bank and 50 microalgal strains isolated from local waters in Minnesota were screened for their adaptability growing on a 20-fold diluted digested swine manure wastewater (DSMW). A pool of candidate strains well adapted to the DSMW was established through a high-throughput screening process. Two top-performing facultative heterotrophic strains with high growth rate (0.536?day^?1 for UMN 271 and 0.433?day^?1 for UMN 231) and one strain with high omega-3 unsaturated fatty acid (EPA, 3.75?% of total fatty acids for UMN 231) were selected. Subsequently, a sequential two-stage mixo-photoautotrophic culture strategy was developed for biofuel and animal feed production as well as simultaneous swine wastewater treatment using above two strains. The maximal biomass concentration and lipid content at the first and second stages reached 2.03?g/L and 23.0?%, and 0.83?g/L and 19.0?% for UMN 271 and UMN 231, respectively. The maximal nutrient removals for total phosphorus and ammonia after second-stage cultivation were 100 and 89.46?%, respectively. The experiments showed that this sequential two-stage cultivation process has great potential for economically viable and environmentally friendly production of both renewable biofuel and high-value animal feed and at the same time for animal wastewater treatment.     

High pressure γ-to-β phase transition in bulk and nanocrystalline In2Se3

Pressure-dependent phase transitions of In₂Se₃ bulk powders and nanowire samples were studied at room temperature using synchrotron X-ray diffraction and a diamond anvil cell. γ-In₂Se₃, metastable under ambient conditions, transforms into to the stable high pressure β phase between 2.8 and 3.2?GPa in bulk powder samples and at slightly higher pressures, between 3.2 and 3.7?GPa, in nanowire samples. While the γ phase bulk modulus is similar to that of the β phase, the decrease due to pressure in the unit cell parameter ratio, c/a, is less than half the decrease seen in the β phase. First-principles calculations show that γ-In₂Se₃ has a higher energy and unit-cell volume than β-In₂Se₃, consistent with the experimental observations.     

乳状液膜分离肌酐的研究

以液体石蜡为膜相、以氧化环糊精为内相捕捉剂制备一种新的乳状液膜，尝试运用其清除分离肌酐。实验发现当外相肌酐溶液浓度为1．3g/L，载体月桂醛含量为5％，内相氧化环糊精浓度为10％时，乳状液膜吸附容量为22．5mg／g。内相氧化环糊精的浓度对单位吸附量起决定作用。此种吸附剂对氨基酸吸附量仅为肌酐的1／10，这为其在含大量氨基酸的人体环境中有效的清除肌酐提供了优良的选择性。     

On a Diophantine Inequality Over Primes (II)

In this short note we prove that if 1 < c < 81/40, c ≠ 2, N is a large real number, then the Diophantine inequality is solvable, where p ₁,···,p ₅ are primes.