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241.
Nonlinear-Ion-Acoustic-Wave Instability, Threshold, Half Width of Trapped Region and Transition Region
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Nonlinear Landau damping of ion acoustic wave (IAW) is one of the most important phenomena in the ionosphere and in space and laboratory plasma as well. The instability growth rate of the IAW with electron drift, the amplitude threshold for exciting the nonlinear effects, the half widths of the trapped region with the trapped electrons are studied experimentally. Under the experimental conditions, it is shown that there is a frequency range of 140--160 kHz, within which the growth rate has the largest value of about 6×104--1.5×105 s-1. We obtain the transitional region width caused by collisions theoretically and experimentally, for the first time to our knowledge. The experimental results are in good agreement with the theoretical prediction. 相似文献
242.
本文报道一种新型Pt/碳化树脂催化剂的制各方法,用该法制备的催化剂具有高分散金属和高机械强度,用于库仑法微量测定有机氧元素取得满意结果。文中对催化剂特点,Pt颗粒在催化剂表面的分布及微观形貌作了初步研究。 相似文献
243.
Zhengping Fu Beifang Yang Zhen Wang Hongwei Yan Jian Zuo Xianming Liu 《Solid State Communications》2006,138(4):179-183
By glycine-nitrate combustion route and followed by 900 °C annealing in air, ZnO-MgO nanocomposite with heterojunction-like structures between ZnO and MgO phase was successfully produced. The ultraviolet photoluminescence band from ZnO is enhanced by the incorporation of MgO, as compared to the pure ZnO synthesized via the similar route. The charge transfer required by electronic equilibrium across the junction creates an electron depletion region in ZnO phase, which greatly changes the electron states of visible emission-related defects, as a result, the band-edge emission is enhanced while the visible emission in ZnO is suppressed. This mechanism may provide an effective way to modify the emission property of nanomaterials. 相似文献
244.
C S Zuo A Mahmood A D Sherry 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2001,151(1):101-106
The lanthanide complex, thulium 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (TmDOTA-), has been investigated as an agent for MR thermometry in vivo. The chemical shifts of the TmDOTA- protons were highly sensitive to temperature at a clinically relevant field strength, yet insensitive to pH and the presence of Ca2+. Given the excellent stability of lanthanide-DOTA complexes and high thermal sensitivity, TmDOTA- is expected to be a good candidate for MR thermometry in vivo. 相似文献
245.
Cuihong Li Chunjie Zhou Haiyan Zheng Xiaodong Yin Zicheng Zuo Huibiao Liu Yuliang Li 《Journal of polymer science. Part A, Polymer chemistry》2008,46(6):1998-2007
A new poly(p‐phenylene ethynylene) derivative with pendant 2,2′‐bipyridyl groups and glycol units (PPE‐bipy) has been prepared, and its metal ion sensing properties were investigated. The polymer of PPE‐bipy exhibited high selectivity for Hg2+ as compared with Li+, Na+, K+, Ba2+, Ca2+, Mg2+, Al3+, Mn2+, Ag+, Zn2+, Pb2+, Ni2+, Cd2+, Cu2+, Co,2+ and Fe3+ in THF/EtOH (1:1, v/v) solution. The fluorescence of PPE‐bipy was efficiently quenched by Hg2+ ions, and the detection limit was found to be 8.0 nM in a THF/EtOH (1:1, v/v) solvent system. PPE‐bipy also showed a selective chromogenic behavior toward Hg2+ ions by changing the color of the solution from slight yellow to colorless, which can be detected with the naked eye. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1998–2007, 2008 相似文献
246.
The phase transition in the alloys Pd0.8 Si0.2 and Pd0.75 Si0.20 Ag0.05 have been investigated through the quadrupole interaction of111Cd impurities. The quadrupole interactions were measured by means of the TDPAC technique from room temperature up to about
870 K. The variation of the quadrupole interaction with temperature in the alloy PdSiAg shows aT
3/2 dependence below and above 629 K, with coefficientsB=5.43(25)·10−5 K−3/2 andB=3.70(15)·10−5 K−3/2, respectively. This demonstrates that the alloy undergoes a phase transition around 629 K. The existence of two electric
field gradients observed in the alloy PdSi,V
zz
(1)=3.47(54)·1017 V/cm2 andV
zz
(2)=2.29(36)·1017 V/cm2, indicates that there are two different111Cd sites. The corresponding fractionsf
1 andf
2 strongly depend on temperature. Below 520 K, most111Cd nuclei are subject to the higher EFGV
zz
(1) (f
1≈70%), whereas above 520 Kf
1 falls rapidly to zero andV
zz
(2) becomes dominant. The temperature dependences of thef
1 andf
2 reveal a picture of the phase transition between the two crystal structures. 相似文献
247.
248.
对名义组份为Bi_2Sr_(2-x)□_xCuO_y(x=0.1,0.2,0.3,0.4,0.5,0.6,0.7,其中□为空位)的系列样品的微结构进行了研究。电子衍射的研究表明,缺Sr的Bi-2201相的调制波长随着x值的增加而明显减小。Raman散射结果则显示随着调制波长缩短,晶体的结构畸变加剧,晶格无序度增加。利用调制的晶格失配模型讨论了这种由缺Sr所造成的结构畸变行为,并由此指出在Bi系氧化物中非公度调制与晶格的有序度很可能是相关的,调制波长缩短,晶格无序度增加;反之则减小。
关键词: 相似文献
249.
250.
We report on synchrotron-based high-angle X-ray solution scattering measured to 2 A resolution for two synthetic DNA sequences for which there are conflicting X-ray crystal and solution NMR models. Our results demonstrate that high-angle X-ray scattering discriminates between differing X-ray crystal and NMR models for solution-state DNA and provides a direct, independent method for testing structural models and measuring solution-state configurational dispersions. 相似文献