宏观分子自组装:一条架在分子和结构体之间的桥梁

文章介绍了一种新的分子自组装现象 :宏观分子自组装 .由一种新型的两亲性超支化多臂共聚物在丙酮中直接自组装形成厘米长度、毫米直径的宏观多壁螺旋管 .并对宏观管子的精细结构、性能进行了详细描述 ,同时阐述了宏观分子自组装机理 .宏观分子自组装现象的发现将分子自组装的研究领域推进到了宏观尺度范围 .     

Gax In1-xP缓冲层组分对InP自组装形貌影响的研究

应用缓冲层对自组装结构的作用能Er和自组装结构表面能E8 的协同作用分析了InP自组装结构在GaxIn1-xP缓冲层表面的形貌变化.计算发现缓冲层组分影响自组装结构的形貌.随着缓冲层与InP自组装结构之间应力的增加,InP岛倾向于拉长.理论计算还发现随着自组装结构体积的增大,自组装结构也随之拉长.而且缓冲层的参数决定了自组装结构最小能量状态时的体积大小.应用金属有机物化学气相沉积技术在GaAs衬底上生长了不同的InP/GaInP体系,并对实验得到的自组装体系形貌进行了分析.实验结果证实了以上的理论分析.     

超声自冲铆复合连接成形性及力学行为研究

该文选用6061和2A12航空铝合金薄板材料,进行自冲铆接和超声自冲铆复合连接试验,基于拉伸-剪切和电子显微镜测试,研究超声自冲铆接成形性及力学行为。结果表明：超声自冲铆接头较自冲铆接头的内锁量提升了44.8%;其钉头高度下降了34.4%;超声自冲铆接头的静载强度提升了18.1%,缓冲吸震性能提升了17.5%;超声焊接致使自冲铆接头的铆钉颈部与上板接触区域、铆钉腿部与上板接触区域形成固相焊;超声焊接可有效提高自冲铆接头的稳定性。     

纳米结构自组装和分子自组装体系

系统地总结并评述了纳主结构和自组装体系和分子自组装体系的最新进展,介绍了纳米结构自组装和分子自组装的基本概念,总结了几类自组和分子自组装体系的合成方法,例举了这类自组装体系的新特性及与下一代纳米结构器件之间的联系。     

氙灯泵浦的NYAB晶体调Q激光运转特性及实验研究

首次报道了氙灯泵浦的自激活自倍频NYAB复合功能晶体的BDN染料片调Q运转,获得了自倍频绿光单脉冲.测量了不同L和T_o情况下的绿光脉冲的能量、脉宽和峰值功率.文中还从理论上推导了自激活自倍频晶体调Q激光器的方程组.数值求解方程组,所得的理论数据与实验结果很好地相符.最后,讨论了进一步提高绿光脉冲峰值功率的途径.     

实时测量飞秒激光脉冲的二次谐波相关技术研究

本文介绍了一种具有飞秒分辨率实时监测激光脉宽的二次谐波自相关技术。该技术既可进行强度自相关测量,又可进行自标定的干涉自相关测量。干涉自相关测量精度达1fs,强度自相关测量相对误差为3.6%。     

光纤耦合自混合干涉测速系统的参数研究

针对光纤耦合自混合干涉测速系统的设计,采用F-P五镜腔模型分析了自混合干涉测速的基本原理,利用数值计算软件MATLAB研究了系统中各个参数对自混合信号波形的影响。对参数引起自混合信号波形“畸变”的情况,进行了参数的优化设计。为光纤耦合自混合测速系统设计,以及将其应用于爆轰波和冲击波研究中进行高速测量提供了参考。     

平行电磁场中里德堡氢原子的自相似结构研究

利用半经典方法研究了平行电磁场中里德堡氢原子的分形自相似现象. 通过研究平行电磁场中里德堡氢原子的逃逸时间和初始出射角间的关系, 发现了逃逸时间图的自相似结构, 并通过研究与图中冰柱对应的逃逸轨道, 得到了自相似结构和逃逸轨道之间的关系, 发现了该类自相似逃逸轨道满足的规律. 进一步研究了标度能量和标度磁场对体系动力学的影响, 表明标度能量和标度磁场均控制体系的分形自相似结构. 当标度能量或标度磁场比较小时, 没有自相似现象, 随着标度能量或标度磁场的增大, 自相似出现, 体系变复杂.     

自抗扰控制器在位置伺服系统中的参数整定及仿真应用

本文基于MATLAB/Simulink软件设计了自抗扰控制器,结合永磁同步电机控制系统各模块结构,实现了位置伺服系统的闭环仿真,利用仿真输出及时间、参数值绘制三维图象,通过对图象的分析验证了参数整定的新方法,实现了自抗扰控制器的参数整定。通过自抗扰和PI控制器的多组实验,对比了两种控制器在恒值、正弦、斜坡等给定输入下的跟踪效果,突出了自抗扰控制器的优势。最后,本文分析了自抗扰控制器的发展趋势,为自抗扰算法的进一步应用提供一定依据。     

飞秒孤子传输演化的数值研究

利用分步傅里叶法数值模拟了飞秒孤子在光纤中的传输演化过程。对光纤中单个孤子的传输及二阶孤子的自陡峭效应和自频移效应进行了分析,指出在一定的参数取值范围内,自频移效应对二阶fs孤子传输的影响要比自陡峭效应大,占主导地位,且对自陡峭效应有一定的抑制作用。     

Polarization Kinetics in Transparent Pb(Mg1/3Nb2/3)O3–23Pb(Zr0.53Ti0.47)O3 Ceramic

Physics of the Solid State - The polarization kinetics in a transparent Pb(Mg1/3Nb2/3)O3–23Pb(Zr0.53Ti0.47)O3 ferroceramic is investigated in the electric fields of 0 < E < 6...     

Crystallographic and magnetic structures of highT c related (Bi/Pb)2Sr2FeO6.25 determined by neutron powder diffraction

The structure of (Bi/Pb)₂Sr₂FeO_6.25 was refined from high resolution neutron powder diffraction data taken at 300 K and 5 K. The average structure is well described in the orthorhombic spacegroup Amaa witha=5.4254 Å,b=5.4909 Å andc=23.2245 Å. The FeO₆ octahedra are tilted by 2.7° towards (0 1 0). The oxygen positions in the (Bi/Pb)O-layers are consistent with the occurrence of (Bi/Pb)–O–(Bi/Pb) chains. Excess oxygen was located between these chains. Antiferromagnetic 3-dim ordering of the Fe-moments withM=(2, 1, 2) _B was observed at 5 K with the wavevector pointing along (1 0 0).     

Investigation the effects of the excess Pb content and annealing conditions on the microstructure and ferroelectric properties of PZT (52-48) films prepared by sol-gel method

The effects of the PbO volatilization, excess Pb content of PbZr_0.52Ti_0.48 (PZT) precursor, PbTiO₃ (PT) seeding layers and annealing condition on the microstructures, surface morphologies, preferred orientation and ferroelectric properties of PbZr_0.52Ti_0.48 films were systematically investigated. PZT films with a variety of excess Pb (0-20%) were spin-deposited on Si(1 0 0) and Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates by sol-gel technique. The films composition, Pb/Zr/Ti/O atom rate and Pb loss were semiquantitative analyzed by X-ray photoelectron spectrometer (XPS). When the excess Pb of PZT precursor was 10%, the Pb/Zr/Ti/O atomic rate of the fabricated films was very close to the designed rate of 1:0.52:0.48:3. The XRD and AFM investigations confirmed that PT seeding layer promoted the PZT films perovskite phase transformation and grains growth with (1 1 0) plane preferred orientation, accordingly lowered perovskite phase crystallization temperature and reduced Pb loss. The PZT films annealed in O₂ flow demonstrated better microstructure and ferroelectric properties comparing with films annealed in air by double remnant polarization increase and 8% coercive field increase. The underlying mechanism was also investigated.     

Phase evolution during the melting and recrystallization of ceramic core in the (Bi,Pb)-2223 tape

The phase evolution during melting and recrystallization of (Bi,Pb)₂Sr₂Ca₂Cu₃O₁₀ ((Bi,Pb)-2223) core in a Ag-sheathed monofilamentary tape has been investigated. The tape was fabricated by PIT process with powders containing nearly pure (Bi,Pb)-2223 phase. Short samples were melted at 805 °C, 808 °C, 812 °C, 816 °C, 831 °C, slowly cooled at 1.5 °C/h under flowing 1.6% O₂ balanced with argon and quenched in air at room temperature. X-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS) were applied for the phase identification. The results show that (Bi,Pb)-2223 core is partially melted into a liquid and alkaline earth cuprates (AECs), mainly 2:1-AEC, at 805 °C, 808 °C, 812 °C, and well reforms directly from the melt during the slow cooling. More (Bi,Pb)-2223 phase is decomposed at temperatures higher than 816 °C, but cannot recrystallize, indicating that a partial melting at some temperatures around a given temperature range is essential to (Bi,Pb)-2223 phase reformation. The melt composition moves from that between “2223” and “2212” stoichiometries towards 2212-like stoichiometry with increasing temperature. This seems to lead to the conclusion that (Bi,Pb)-2223 phase decomposes incongruently into a 2212-like liquid and (Ca,Sr)-cuprates. 2:1-AEC plays the most important role in (Bi,Pb)-2223 melt-recrystallization process. Our results also reveal that plate-like shape (Bi,Pb)-2223 grains can be obtained via melting and recrystallization if the optimum processing conditions are used.     

First-principles study for the atomic structures and electronic properties of PbTiO3 oxygen-vacancies (0 0 1) surface

The structural and electronic properties of fully-relaxed PbTiO₃ (0 0 1) oxygen-vacancy surface with PbO and TiO₂ terminations are investigated by first-principles calculations. In contrast to the perfect surface, the smaller surface rumples and interlayer distances have been found. The largest relaxation occurs on the second layer atoms not on the surface layer ones, and some in-gap Ti 3d states at about −1.1 eV below the Fermi-level are observed in the TiO₂-terminated surface caused by oxygen-vacancies. For the PbO-terminated surface, some in-gap Ti 3d states and Pb 6p states also move into the bulk midgap region to become partially occupied, and two different chemical states of the Pb 6s states were found. One is attributed to the bulk perovskite Pb atoms and another one is caused by the relaxation of surface Pb atoms. These theoretical results would give a good reference for the future experimental studies.     

Energy levels of perturbed 6p<Emphasis Type="Italic">n</Emphasis>d <Emphasis Type="Italic">J</Emphasis>=2 Rydberg states of Pb I by multichannel quantum defect theory

Energy levels of the odd-parity 6pnd J=2 Rydberg states of atomic lead are analyzed by the multichannel quantum defect theory (MQDT) with previous experimental energy levels. The obtained. Using these parameters, admixture coefficients for each level are calculated to designate the level denotations. The results show that strong channel mixings exist for the levels near the 6pnd (3/2)[5/2]₂ ⁰ and 6p6d (3/2)[3/2]₂ ⁰ pertubers. The five-channel model different from that in literature is used to predict 21 energy positions of 6pnd (1/2)[3/2]₂ ⁰ levels and to determine the denotations of all the 6pnd J=2 Rydberg states under 59788 cm⁻¹ for Pb I.     

Superconducting properties of ZnO-doped (Bi, Pb)-2223 thick film on Ni and NiO substrates prepared by spray deposition technique

The superconductivity of ZnO-doped (Bi, Pb)-2223 thick film on the Ni and NiO substrates, which was prepared by the spray deposition technique with cold forging, was investigated by characterizing the critical current density (J_c), the critical temperature (T_c), the orientation factor (f), and the microstructure of the film. The thickness of the thick film prepared by the spray deposition method was approximately 10 μm. The maximum J_c value of (Bi, Pb)-2223 film on NiO substrate was approximately 2200 A/cm² (I_c = 110 mA) when the film was sintered at 865 °C for 1 h with a cooling rate of 0.5 °C/min from 865 °C to 650 °C; in the case of Ni substrate, a maximum J_c value of approximately 2000 A/cm² (I_c = 100 mA) was obtained for the (Bi, Pb)-2223 thick film when a cooling rate was 3 °C/min. Such a difference in the J_c values of (Bi, Pb)-2223 thick film on Ni and NiO substrates is attributed to the presence of reaction layer at the (Bi, Pb)-2223 and substrate interface. In addition, the variations in the orientation factor of (Bi, Pb)-2223 thick film on NiO substrate related to those of J_c values. The J_c values of (Bi, Pb)-2223 film on NiO substrate with ZnO doping extremely depended on the amount of ZnO doping and the 0.5 wt% ZnO-doped (Bi, Pb)-2223 thick film deposited on NiO substrate, which was sintered at 835 °C for 1 h in air with a cooling rate of 1 °C/min, showed a J_c value of approximately 1200 A/cm² (I_c = 60 mA). Thus, it is considered that a small amount of ZnO doping was effective in lowering the sintering temperature of (Bi, Pb)-2223 thick film, resulting the improvement in the intragranular weak bonding or Josephson junction.     

Strange resonance production: probing chemical and thermal freeze-out in relativistic heavy ion collisions

The production and the observability of Λ(1520), K⁰(892) Φ and Δ(1232) hadron resonances in central Pb+Pb collisions at 160 A GeV is addressed. The rescattering probabilities of the resonance decay products in the evolution are studied. Strong changes in the reconstructable particle yields and spectra between chemical and thermal freeze-out are estimated. Abundances and spectra of reconstructable resonances are predicted.     

Effect of excess Pb on crystallinity and ferroelectric properties of PZT(40/60) films on LaNiO3 coated Si substrates by MOD technique

Pb(Zr_0.4Ti_0.6)O₃ [PZT(40/60)] films were deposited onto LaNiO₃ (LNO) coated Si substrates by metal-organic decomposition (MOD) technique. Excess Pb was incorporated in the film by using excess Pb (2%–15%) in the solution. The crystallinity and ferroelectric properties of PZT films were investigated by using X-ray diffraction (XRD), RT66A test system and HP4194 impedance analyzer, respectively. Rayleigh law was employed to analyze the defect concentration in the films. The results show that all the PZT films show the (1 0 0) preferential orientation with complete perovskite structure except for the 2% film displaying some pyrochlore phase. The (1 0 0) preferential orientation is mainly attributed to LNO bottom electrode, which has the highly (1 0 0) preferential orientation. The 10% film shows the best polarization and dielectric properties. The remnant polarization and coercive field are about 10.1 μC/cm² and 73 kV/cm under an electric field around 330 kV/cm, respectively. And the dielectric constant and dissipation factor are about 656 and 0.022 at a frequency of 1 kHz, respectively. The good ferroelectric properties of the 10% film are mainly attributed to the low defect concentration in the film.     

Pb~(2+)掺杂导致的CaF_2中Yb~(3+)离子三聚体合作发光猝灭

利用978 nm近红外光激发样品Ca F2∶Pb2+,Yb3+,在室温下观察到二价Pb2+离子在383 nm附近的紫外上转换发光。该发射峰对应于Pb2+离子的3P0"1A1g(1S0)跃迁。瞬态光谱测量结果表明:在这个材料体系中,Pb2+离子的激发来自于Yb3+离子三聚体的合作敏化。但是随着Pb2+离子掺杂浓度的提高,Yb3+离子三聚体遭到结构性破坏,导致其合作发光减弱。本文首次利用Pb2+离子掺杂造成Yb3+离子三聚体的结构性破坏,从而引起合作荧光猝灭,并对在Ca F2基质中因其他二价离子的掺入而造成的Yb3+三聚体合作发光猝灭给予了合理的解释。