Synthesis of three novel anionic gemini surfactants and comparative studies of their assemble behavior in the presence of bovine serum albumin

Three novel anionic sulfonate gemini surfactants, sodium 4,4'-(10,19-dioxo-9,11,18,20-tetraazaoctacosane-9,20-diyl) dibenzenesulfonate (Surfactant I), sodium 4,4'-(12,21-dioxo-11,13,20,22-tetraazadotriacontane-11,22-diyl) dibenzenesulfonate (Surfactant II), and sodium 4,4'-(14,23-dioxo-13,15,22,24-tetraazahezatriacontane-13,24-diyl) dibenzenesulfonate (Surfactant III), with different lengths of hydrophobic tail have been synthesized, and their assembly behavior in the presence of bovine serum albumin (BSA) has been studied using spectral methods and molecular modeling methods at physiological pH and 298 K. Critical micelle concentrations (CMCs) of the three surfactants have been determined by surface tension measurements. Despite the obvious decrease of CMC with the increase of tail length, fluorescence spectra have shown much closer CAC in the presence of BSA. Surfactant II shows the highest CAC of 3.19 × 10(-5) mol L(-1) compared with the other two. The polarity of the microenvironment in BSA-surfactant systems has been investigated using pyrene as the probe. In addition, far-UV CD spectra studied the change of the secondary structure content of BSA caused by the three surfactants. The features of the assembly behavior were discussed by three concentration regions. Surfactant II could unfold the protein much more efficiently than the other two surfactants at low concentration, but at high concentration, the change of the secondary structure and the formation of hydrophobic microenvironment show a direct relationship to the length of the hydrophobic tail with the increase of the surfactant concentration.     

Effect of chain unsaturation on the self-association of tri- and tetraethylene glycol octyl ethers obtained by butadiene telomerization

2,7-Octadienyl ethers of tri- and tetraethylene glycol (C(8:2)E(3) and C(8:2)E(4)) have been synthesized by the atom-economical butadiene telomerization of the corresponding poly(ethylene glycols). On one hand, this synthetic path is attractive because it is expeditious and environmentally benign, and on the other hand, it provides unconventional amphiphiles for which the lipophilic chains possess two double bonds. These two unsaturations increase the global hydrophilicity of the compound, which is also highlighted by the modelization of the compounds using the conductor-like screening model for real solvents (COSMO-RS). The behavior of C(8:2)E(3) and C(8:2)E(4) in binary amphiphile/water and ternary amphiphile/oil/water systems is therefore greatly modified compared to that of the conventional fully saturated homologues (C(8)E(3) and C(8)E(4)) that are easily obtained after hydrogenation. This results in a lowered efficiency of the unsaturated compounds for oil solubilization. The usual Winsor-type microemulsion systems are formed, and for the same oil, the DLS investigation of the microstructure of the Winsor I microemulsion does not highlight any difference in the self-association between the unsaturated and saturated compounds.     

FeAl(B2) 合金La, Ac, Sc 和 Y 元素微合金化的第一性原理研究

采用基于密度泛函理论的第一性原理计算方法, 研究了稀土元素(La, Ac, Sc 和 Y) 微合金化对FeAl (B2) 有序金属间化合物合金晶体结构、 弹性和电子性能的影响. 计算结果表明: 稀土元素Y 易于取代Fe位, 而Sc, La和Ac易于取代Al位, 其中Ac元素的加入使晶格点阵发生最大的变形. 弹性性能的计算表明La, Ac, Sc 和 Y 元素的加入可以改善FeAl (B2) 的塑性, 其中Fe₇Al₈Sc具有最好的塑性和硬度. 稀土元素对合金性能的影响, 主要是由于稀土原子的加入改变了Fe和Al电子之间的杂化作用. 计算结果与已有的试验结果和理论结果相一致.     

采用Al/TaN叠层电极提高Si基Ge PIN光电探测器的性能

金属与Ge材料接触由于存在强烈的费米钉扎效应, 导致金属电极与n型Ge接触引入较大的接触电阻, 限制了Si基Ge探测器响应带宽. 本文报道了在SOI衬底上外延Ge单晶薄膜并制备了不同台面尺度的Ge PIN光电探测器. 对比了电极分别为金属Al和Al/TaN叠层的具有相同器件结构的SOI基Ge PIN光电探测器的暗电流、响应度以及响应带宽等参数. 发现在Al与Ge之间增加一薄层TaN可有效减小n型Ge的接触电阻, 将台面直径为24 μ的探测器在1.55 μ的波 长和-1 V偏压下的3 dB响应带宽提高了4倍. 同时, 器件暗电流减小一个数量级, 而响应度提高了2倍. 结果表明, 采用TaN薄层制作金属与Ge接触电极, 可有效钝化金属与Ge界面, 减轻费米钉扎效应, 降低金属与n-Ge接触的势垒高度, 因而减小接触电阻和界面复合电流, 提高探测器的光电性能.     

自由质点测地线仿射参量时空坐标系

以时序t为自变量,可给出自由质点空间测地线的参数方程组{Xⁱ(t)},借助于仿射参量R(t)变换实现测地线微分方程的齐次化, 推导出仿射参量R满足的一阶微分方程、获得以有理数C_u为标志的序列解析解R.基于R定义平直四维坐标系{t,r,θ,φ}的空间距离单位,建立自由质点测地线仿射参量时空坐标系{t,ξ,θ,φ}.研究{t,ξ,θ,φ}中狭义相对论时空间隔模型度规张量g的对角化过程, 发现与对角化度规对应的特征量t₁(t,ξ), τ₁(τ,ξ),t_t(t,τ,ξ),τ_τ1(t,τ,ξ); 从而推出时空坐标系{t,ξ,θ,φ}维数小于4.     

鞘场加速机理中质子束的特性与其初始尺寸的关系

为了研究激光鞘场中质子层的尺寸对质子束特性的影响,本文应用中国工程物理研究院 激光聚变研究中心的二维Particle-In-Cell (2D-PIC)数值模拟程序Flips2D进行了相关数值模拟研究. 研究了质子束总能量随时间的变化,得出了加速持续过程与激光脉冲持续时间的关系; 研究了质子层的宽度对加速后质子束发散角和能谱的影响;研究了质子层的厚与加速后质子束 发散角和能谱的关系;得出了质子层的初始尺寸对加速后质子特性的影响规律.     

用于诊断纳秒脉冲电流的微分环现场标定技术

分析了用于纳秒脉冲电流测量的微分环标定难点,提出微分环现场标定方法。通过脉冲形成线脉冲充电以解决微分环标定中信噪比较低、可信度较差等问题;分析了脉冲形成线充电时间、充电电压及脉冲形成开关击穿电压等回路参数对标定结果的影响。基于闪光二号加速器,对测量二极管电流的微分环进行了现场标定,前级隔离开关平均击穿电压为25 kV时,微分环标定回路电流达到1.3 kA,微分环灵敏度为9.311010,方差为0.151010。     

Actively Q-switched mode-locked Yb-doped fiber laser with high mode-locking contrast

Reliable Q-switched and mode-locked operation of Yb-doped fiber lasers is investigated by employing an acousto-optic modulator (AOM) in a linear cavity configuration. The widths and shapes of the Q-switched envelopes mainly depend on the external modulation frequency of the AOM and near symmetric Q-switched pulses can be generated. Within the Q-switched envelopes, harmonic mode-locked pulses with near 100% modulation depth at the 40 MHz repetition rate are experimentally observed.     

Beam focusing from double subwavelength metallic slits filled with nonlinear material surrounded by dielectric surface gratings

Based on the radiation properties of surface plasmon polaritons (SPPs) can be controlled by adjusting the refractive indexes of dielectric materials in the metallic slits, a novel plasmonic focusing structure formed by two subwavelength metal apertures filled with Kerr nonlinear material surrounded by surface dielectric gratings is proposed and demonstrated numerically. Directions of radiation fields are determined by the phase difference of the surface waves at the exit interface and resonance property of each surface grating. Numerical simulations using two-dimensional (2D) Finite-Difference Time-Domain (FDTD) method verify that the deflection angle and focal length can be controlled easily by changing the intensity of incident light, dynamically tunable on-axis and off-axis focusing effects can be achieved.     

Experimental investigation on a software synchronous optical sampling technique based on periodically poled lithium niobate

A software synchronous optical sampling system is constructed based on sum frequency generation (SFG) in periodically poled lithium niobate (PPLN). Five gigahertz of a non-return-to-zero (NRZ) data signal is sampled by sampling pulse with the repetition frequency of 29.31 MHz. The power of the SFG light is set at 23 dBm, and an eye diagram is successfully recovered. A band-pass filter is added before the sampling pulse is subjected to erbium-doped fiber amplifier to reduce gain competition and ensure a high power level of SFG.