X‐Ray Diffraction and Mössbauer Spectroscopy Studies of Pressure‐Induced Phase Transitions in a Mixed‐Valence Trinuclear Iron Complex

The mixed‐valence complex Fe₃O(cyanoacetate)₆(H₂O)₃ ( 1 ) has been studied by single‐crystal X‐ray diffraction analysis at pressures up to 5.3(1) GPa and by (synchrotron) Mössbauer spectroscopy at pressures up to 8(1) GPa. Crystal structure refinements were possible up to 4.0(1) GPa. In this pressure range, 1 undergoes two pressure‐induced phase transitions. The first phase transition at around 3 GPa is isosymmetric and involves a 60° rotation of 50 % of the cyanoacetate ligands. The second phase transition at around 4 GPa reduces the symmetry from rhombohedral to triclinic. Mössbauer spectra show that the complex becomes partially valence‐trapped after the second phase transition. This sluggish pressure‐induced valence‐trapping is in contrast to the very abrupt valence‐trapping observed when compound 1 is cooled from 130 to 120 K at ambient pressure.     

Crystal Structure Analysis of the Repair of Iron Centers Protein YtfE and Its Interaction with NO

Molecular mechanisms underlying the repair of nitrosylated [Fe–S] clusters by the microbial protein YtfE remain poorly understood. The X‐ray crystal structure of YtfE, in combination with EPR, magnetic circular dichroism (MCD), UV, and ¹⁷O‐labeling electron spin echo envelope modulation measurements, show that each iron of the oxo‐bridged Fe^II–Fe^III diiron core is coordinatively unsaturated with each iron bound to two bridging carboxylates and two terminal histidines in addition to an oxo‐bridge. Structural analysis reveals that there are two solvent‐accessible tunnels, both of which converge to the diiron center and are critical for capturing substrates. The reactivity of the reduced‐form Fe^II–Fe^II YtfE toward nitric oxide demonstrates that the prerequisite for N₂O production requires the two iron sites to be nitrosylated simultaneously. Specifically, the nitrosylation of the two iron sites prior to their reductive coupling to produce N₂O is cooperative. This result suggests that, in addition to any repair of iron centers (RIC) activity, YtfE acts as an NO‐trapping scavenger to promote the NO to N₂O transformation under low NO flux, which precedes nitrosative stress.     

Incarceration of Higher‐Order Fullerenes within Cyclotriveratrylene‐Based Hemicarcerands Allows Selective Isolation of C76, C78, and C84 from a Commercial Fullerene Mixture

Size‐complementary cyclotriveratrylene (CTV)‐based hosts can incarcerate C₇₆, C₇₈, and C₈₄, thus allowing the selective isolation of these higher‐order fullerenes from a commercially available mixture of fullerenes. The hemicarceplexes, formed after the encapsulation of the size‐complementary fullerenes within the hosts, are isolated by column chromatography and released at elevated temperature, thereby leading to the isolation of C₇₆/C₇₈ and C₈₄ in good purities (up to 95 and 88 %, respectively).     

Three new monoterpene glucosides from Sibiraea angustata

Three new monoterpene glycosides, named sibiraglycoside I(1), J(2) and K(3), were isolated from an aqueous extract of the aerial portion of Sibiraea angustata. Their structures were elucidated on the basis of extensive spectroscopic data analysis (including 1D and 2D NMR and MS experiments) and compared to literature data.     

基于分数阶可停振动系统的周期未知微弱信号检测方法

本文建立了分数阶可停振动系统, 其可停振动状态的改变对周期策动力敏感, 对零均值随机微小扰动不敏感, 这事实上为周期未知微弱信号检测提供了一种新的高效检测方法和判别标准. 与现有的利用混沌系统的大尺度周期状态变化检测周期未知弱信号的方法 需逐一尝试设置不同频率内置信号以便期望与待检周期信号发生共振不同, 利用分数阶可停振动系统的可停振动状态变化检测周期未知微弱信号的方法, 除了同样具有因为状态变化对周期信号的敏感性而能够实现极低检测门限的特点外, 还具有混沌系统信号检测所不具有的优点: 1)无需预先估计待检信号的周期; 2)无需计算系统状态的临界阈值; 3)可停振动状态可由本文设计的指数波动函数可靠地进行判断; 4)通过系统微分阶数的变化, 将检测系统层次化, 从而可得到比整数阶检测系统更低的检测门限, 特别是在色噪声环境下, 通过选取合适的微分阶数, 基于分数阶可停振动系统的微弱周期信号检测法能够大幅度的降低检测门限, 在本文的仿真试验中, 检测门限可达-182 dB. 关键词： 分数阶非线性系统 Duffing振子 弱信号检测     

超新星核中的夸克相变及夸克质量效应

分别基于组夸克质量模型和流夸克质量模型, 讨论了超新星核心区两味夸克物质到更稳定的三味夸克物质的相变过程. 结果表明, 两种质量模型下相变的特征时标都短于10^-8s, 且质量越小的流夸克质量模型的相变速率越快;组分夸克质量模型下所得到的超新星核区的s夸克丰度, 中微子丰度及中微子总能量(除温度)相比前人的结果有轻微的增加, 而流夸克质量模型下所得到的这些参量的增加更为明显, 采用流夸克质量模型更有利于超新星的中微子延迟爆发机理的成功. 关键词： 夸克相变 组分夸克质量 流夸克质量 超新星     

半导体量子阱中电子自旋弛豫和动量弛豫

根据电子自旋轨道耦合对自旋极化弛豫影响的DP机理进一步导出了半导体中电子自旋弛豫与动量弛豫及载流子浓度的关系，并采用飞秒抽运探测技术在室温下测量AlGaAs/GaAs 多量子阱中载流子浓度在 1×10¹⁷—1×10¹⁸cm^-3范围内，电子自旋弛豫时间由58ps增加至82 ps的变化情况，与理论计算值符合，说明了随着载流子浓度的增加，载流子间的频繁散射加速了电子动量驰豫，减弱了电子自旋轨道耦合作用，从而延长了电子自旋寿命. 关键词： 电子自旋轨道耦合 电子自旋弛豫和动量弛豫 飞秒光谱技术     

大学物理课程中“高等数学基础”教学——以应用为导向

本文给出了为大学物理课程学习做准备的数学基础的教学中的3个应用性原则,指出教学重点应放在让学生理解微分与导数、积分以及矢量运算几个方面的思想与方法,特别要让学生理解:微分表示变量的微小变化;导数在几何上表示函数曲线上切线的斜率,而且导数中分子和分母两个微分是既相关联又可以分开的量;积分的本质意义是求和,把物理问题转化为积分问题通常包括两个过程,一是积分区域无限细分,其目的在于化变为不变;二是无限求和.通过不定积分与定积分的关系可以帮助学生快速计算一些简单被积函数的积分.讲述积分的过程中,可以引入微分方程的概念及分离变量法求解的思想.矢量运算中的难点是标量积与矢量积的区别以及矢量求导.前者可通过力做功及力矩的概念帮助学生加深理解.而矢量求导可以结合曲线运动中的速度、加速度的计算让学生理解其思想与方法.     

态|ψ3(3)〉q中广义磁场分量的等幂次高次和压缩

根据量子力学中态的线性叠加原理,构造了由多模复共轭相干态|{Z_j^*〉_q(j=1,2,……q)、多模复共轭虚相干态|{iZ_j^*〉_q和多模真空态|{0_j}〉_q的线性叠加组成的第Ⅲ类三态叠加多模叠加态光场|ψ₃⁽³⁾〉_q.利用多模压缩态理论,研究了态|ψ₃⁽³⁾〉_q广义磁场分量(即第一正交相位分量)的广义非线性等幂次高次和压缩特性结果发现:当腔模总数q与压缩次数N之积qN取偶数时,态|ψ₃⁽³⁾〉_q广义磁场分量在一定条件下可分别呈现出周期性变化的、广义非线性等幂次奇数模—偶数次、偶数模—奇数次或偶数模—偶数次的高次和压缩效应.