Hyperfine interactions at 181Hf(→181Ta) impurities implanted in Er2O3 and Gd2O3: structural and electronic dependence of the EFG in bixbyite sesquioxides

The time-differential-perturbed γ-γ angular-correlation technique (TDPAC) with ion-implanted ¹⁸¹Hf tracers has been applied to study the hyperfine interactions of ¹⁸¹Ta impurities in the cubic bixbyite structure of Er ₂ O ₃ and Gd ₂ O ₃ . The TDPAC experiments were performed in air in the temperature range 300-1073 K (in the case of Er ₂ O ₃ ) and 300-1173 K (in the case of Gd ₂ O ₃ ). Three electrical-quadrupole interactions were found in each oxide in the whole studied temperature range. Two of them were attributed to the electric-field gradients (EFG) acting on ¹⁸¹Ta probes substitutionally located on the two nonequivalent free-of-defects cation sites of the bixbyite structure. The EFG results are compared with predictions of the point-charge model and discussed together with previous results obtained with the probes ¹¹¹Cd and ¹⁸¹Ta in other isomorphous sesquioxides. The temperature dependence of the hyperfine parameters for both oxides is also discussed in terms of dilatometric expansion data. Received 29 December 2000 and Received in final form 8 March 2001     

二阶常系数非齐次线性微分方程解法的简化

通过对二阶常系数非齐次线性微分方程的特解y*的推导过程,探讨出一种求y*的简化运算.     

风冷热泵空调器节能分析与优化

空调节能分析,传统的办法就是对空调系统各设备的热损失进行计算分析,设法提高热效率,来保证充分利用能量之目的。现有的理论和实践已证实这种传统的方法是不完善的,甚至会误入歧途。节能的分析及优化已不只是能的量的问题,而是能的质与量的综合估价的问题。通过对热泵系统的Yong分析、模拟出各部位的Yong损失情况,提出系统的节能部位和应采取的措施,使整个系统的Yong损失为最小,Yong效率最大,实现热泵节能优化。     

P＆amp;H 2800XP电铲提升缓慢无力故障诊断

分析了P&H2800XP电铲产生故障的原因,阐述了解决K-925提升电机由于磁极老化造成电机提升缓慢无力的对策。     

La2—xSrxCuO4和La2—xNdxCuO4＋y的键共价性计算

使用复杂晶体化学键理论计算了Ｌａ２－ｘＳｒｘＣｕＯ４和Ｌａ２－ｘＮｄｘＣｕＯ４＋ｙ中各键的健共价性,讨论了键性随着掺杂的变化规律,研究表明,对于２１４结构,没有发现明显的化学键性与超导温度的关系,因此２１４结构中有关超导现象产生的机理还有待于进一步研究。     

Open-path trace gas detection of ammonia based on cavity-enhanced absorption spectroscopy

A compact open-path optical ammonia detector is developed. A tunable external-cavity diode laser operating at 1.5 μm is used to probe absorptions of ammonia via the cavity-enhanced absorption (CEA) technique. The detector is tested in a climate chamber. The sensitivity and linearity of this system are studied for ammonia and water at atmospheric pressure. A cluster of closely spaced rovibrational overtone and combination band transitions, observed as one broad absorption feature, is used for the detection of ammonia. On these molecular transitions a detection limit of 100 ppb (1 s) is determined. The ammonia measurements are calibrated independently with a chemiluminescence monitor. Compared to other optical open-path detection methods in the 1–2 μm region, the present result shows an improved sensitivity for contactless ammonia detection by over one order of magnitude. Using the same set-up, a detection limit of 100 ppm (1 s) is determined for the detection of water at atmospheric pressure. Received: 19 January 2000 / Revised version: 6 March 2000 / Published online: 7 June 2000     

3.4% NaCl介质中铁点蚀行为的表面拉曼光谱成像研究

本文利用共焦拉曼光谱技术结合对铁电极的合适的粗糙化预处理,现场研究了３．４％ＮａＣｌ腐蚀介质听电极的点蚀行为,获得了点蚀坑内腐蚀产物的表面增强拉曼光谱,成功地将表面增强拉曼光谱技术拓宽至铁的腐蚀行为的研究中,利用共焦拉曼光谱仪的成像技术研究了位于６６０ｃｍ＾－１处点蚀产物的二维分布图。研究表明：在校正电位铁表面发生点蚀后,点蚀坑内腐蚀产物不是以单一物种存在,而是多种铁氧化合物共存,且这些铁的氧化腐蚀产物的点蚀坑内的分布也极不均匀。     

Crystal-chemistry aspects and electric-field-gradient (EFG) dispersion in Ca-gallogermanate-type structures studied by Mössbauer spectroscopy

The crystal field disorder in some trigonal germanates of the type X_3-yLn_yFe_2+yGe_4-yO₁₄ (X = Ba, Sr; Ln = La, Nd; y = 0, 1) is studied by ⁵⁷Fe M?ssbauer effect. The dispersion of the electric field gradient (EFG) at the octahedral sites of these compounds is investigated. A correlation of the experimental and calculated EFG data with some crystal-chemistry aspects is presented. Received 3 February 1999     

三阶微分方程的Liapunov型不等式

研究了三阶微分方程：ｙ’’’（ｔ）＋ｑ（ｔ）ｙ″（ｔ）＋Ｐ（ｔ）ｙ（ｔ）＝０（ｑ（ｔ）,ｐ（ｔ）∈（〔０,＋∞）,Ｒ））的振荡解ｙ（ｔ）在其棹邻两个或３个零点间的性质,从而得到其系数满足的一些不等式,并统一了已有的一些结果。     

Si_(1-x-y)Ge_xC_y合金薄膜电学性能的研究

采用射频共溅射复合靶(Si Ge 石墨C)技术制备Si1-x-yGexCy三元合金薄膜.Si,Ge和C的含量用其靶的相对面积来表示,对样品的后退火处理是在N2气保护下恒温30min后自然降温到室温.通过IR,Raman和XPS的测量结果表明,所制备的薄膜中含有Si,Ge,C3种元素,有较明显的Si-C,Si-Ge,Ge-C键合.通过电阻率—温度谱ρ-T的测量研究薄膜的电学性能,测量了不同C含量和不同温度退火后薄膜ρ-T关系的变化,发现随C含量的增加电阻率增大,激活能也增大;450℃退火后电阻率普遍变小,激活能也变小,对这一规律性的结果作了解释