1-取代-2-氨基苯并咪唑衍生物的理论计算及QSAR研究

在B3LYP/6-31＋g(d)计算水平下, 通过运用密度泛函理论(DFT)量子化学方法, 对7种1-取代-2-氨基苯并咪唑衍生物的电子结构特征进行了研究, 获得了它们的电离能、亲合能、化学硬度、化学软度、化学势、电负性、亲电性、分配系数、折射率、极化率、分子体积和分子表面积等参数. 结果表明, 在2-氨基苯并咪唑衍生物的1位引入取代基团, 对化合物的电荷布居和结构性质都有较大的影响|关联了定量结构-活性关系(QSAR), 7种化合物的半数致死量LD₅₀与极化率等有较好的相关性. 这些结果可为1-取代-2-氨基苯并咪唑衍生物的氧化代谢实验研究和毒性机理揭示等提供重要信息.     

材料二次电子产额对腔体双边二次电子倍增的影响

采用蒙特卡罗抽样与粒子模拟相结合的方法,数值研究了材料二次电子产额对腔体双边二次电子倍增瞬态演化及饱和特性的影响.研究发现:随着材料二次电子产额的增加,二次电子增长率以及稳态二次电子数目和振幅均呈现增加的趋势,放电电流起振时间逐步缩短,稳态电流幅值以及放电功率平均值和振幅值均呈现逐步增加并趋于饱和的规律,沉积功率波形延时以及脉宽呈现逐步增加并趋于饱和的趋势.粒子模拟给出了高/低二次电子产额情况下的电子相空间分布、电荷密度分布、平均碰撞能量、平均二次电子产额、二次电子数目和放电电流的细致物理图像.模拟结果表明:高二次电子产额材料,饱和时更倾向趋于单边二次电子倍增类型分布;低二次电子产额材料的二次电子倍增饱和特性由空间电荷场的"去群聚"效应和"反场"效应同时决定,而高二次电子产额材料的二次电子倍增饱和特性则主要是由发射面附近的强空间电荷场"反场"效应决定的.     

Microwave photonics reconfigurable mixer based on polarization modulator

A reconfigurable and stable mixer is proposed and demonstrated in this paper. It mainly consists of a dual-driven Mach–Zehnder modulator and a polarization modulator with several polarization controllers (PC) and polarizers (Pol). According to the theoretical analysis, different functions (such as single ended mixer, balanced mixer, I/Q mixer and image rejection mixer) can be realized by adjusting the PCs and Pols. The simulation results verify the possibility of multi-functions that realized by the reconfigurable mixer. In addition, another research on how the non-ideal parameters affect the image rejection ratio (ISR) and conversion efficiency of the mixer is also carried. The results show that both of them perform better as the extinction ratio gets higher. However, they are incurring a sharp decrease if the DC bias points deviate from the settled values. In the meantime, the results also indicate that the higher modulation indices lead to a better ISR. A 57.12 dB ISR can be achieved with conversion efficiency of ? 9.53 dB.     

Existence and stability of circular orbits in static and axisymmetric spacetimes

The existence and stability of timelike and null circular orbits (COs) in the equatorial plane of general static and axisymmetric (SAS) spacetime are investigated in this work. Using the fixed point approach, we first obtained a necessary and sufficient condition for the non-existence of timelike COs. It is then proven that there will always exist timelike COs at large \(\rho \) in an asymptotically flat SAS spacetime with a positive ADM mass and moreover, these timelike COs are stable. Some other sufficient conditions on the stability of timelike COs are also solved. We then found the necessary and sufficient condition on the existence of null COs. It is generally shown that the existence of timelike COs in SAS spacetime does not imply the existence of null COs, and vice-versa, regardless whether the spacetime is asymptotically flat or the ADM mass is positive or not. These results are then used to show the existence of timelike COs and their stability in an SAS Einstein-Yang-Mills-Dilaton spacetimes whose metric is not completely known. We also used the theorems to deduce the existence of timelike and null COs in some known SAS spacetimes.     

新型稀磁半导体Mn掺LiCaP的磁电性质

采用基于密度泛函理论的第一性原理平面波超软赝势方法,对纯LiCaP、Mn掺杂LiCaP、Li过量和不足时Mn掺杂LiCaP体系进行几何结构优化,计算并分析了体系的电子结构、能带结构、态密度等.结果表明:Li1±y(Ca1-xMnx) P(x=0. 125,y=0. 125)体系均表现为100%自旋注入,材料均具有半金属亚铁磁性,半金属性稳定,磁矩较大且主要来源于Mn掺入形成的深能级杂质带. Li过量时材料的导电性得到改善,Li不足时体系的居里温度(Tc)提高,说明LiCaP半导体的磁性和电性可以分别通过Mn的掺入和Li的含量进行调控.     

轨道序和巡游性对尖晶石结构钒氧化物AV2O4 (A = Mn,Fe, Co) 物性影响的研究

在尖晶石钒基氧化物AV_2O_4中,因为自旋阻挫、轨道序、巡游性等独特的内禀属性间存在着相互合作和竞争,所以该体系常常表现出复杂而有趣的物理现象。通过对A位磁性离子的调控,我们详细研究该体系中不同物性的起源,比如磁相变与结构相变的不同起因,局域和巡游电子的交叉行为等等。我们以Mn_(1-x)Co_x V_2O_4和Fe_(1-x)Co_x V_2O_4体系为研究对象,通过变温X射线衍射、磁化率、比热和中子散射等测试手段,结合第一性原理计算,对其物性起源进行了详细的研究。我们发现:(i)在低Co2+离子掺杂时,体系受到局域V~(3+)离子以及A位Fe~(2+)离子的轨道序作用,往往会在磁有序附近伴随着结构相变的出现,以至于弱化体系中钒离子独立形成的四面体造成的几何阻挫。这也说明Co~(2+)离子低掺杂下,该体系有着强的自旋–晶格耦合;(ii)在高Co~(2+)离子掺杂时,由于巡游性的增强,轨道序的弱化,JAB交换相互作用增强,体系也表现出明显的磁各向同性。因此磁相变温度向更高的温度移动,而结构相变温度向低温移动甚至消失。     

Sm~(3+),Sr~(2+)共掺杂对CeO_2基电解质性能影响的密度泛函理论+U计算

Sm~(3+),Sr~(2+)共掺杂CeO_2的离子电导率被证实可高达Sm~(3+)掺杂CeO_2离子电导率的近两倍,然而,共掺杂对CeO_2电导率的作用机理尚不明确.本文利用第一性原理计算的密度泛函理论+U方法,对Sm~(3+)和Sr~(2+)共掺杂的CeO_2进行了系统的研究,对比Sm~(3+)或Sr~(2+)单掺杂的CeO_2体系,计算并分析了共掺杂体系的电子态密度、能带结构、氧空位形成能以及氧空位迁移能等微观属性.计算结果表明,Sm~(3+),Sr~(2+)的共掺杂对CeO_2基电解质性能的提高具有协同效应,二者的共掺杂不仅能协同抑制CeO_2体系的电子电导率,还能在单掺杂CeO_2的基础上进一步降低氧空位形成能,Sm~(3+)的存在还有助于降低Sr~(2+)对氧空位的俘获作用,而Sr~(2+)的加入则能够在Sm~(3+)掺杂CeO_2的基础上进一步降低最低氧空位迁移能,爬坡式弹性能带方法计算表明共掺杂体系的氧空位迁移能最低可达0.314/0.295 eV,低于Sm~(3+)掺杂CeO_2的最低氧空位迁移能.研究揭示了Sm~(3+),Sr~(2+)共掺杂对CeO_2电导率的协同作用机理,对进一步研发其他高性能的共掺杂电解质材料具有重要的指导意义.     

铷原子气体自旋噪声谱的测量与改进

利用自主设计并制作的基于现场可编程门阵列的实时傅里叶变换采集卡(FFTsDAC),采用线偏振光检测碱金属铷原子气样品中的自旋随机涨落(即自旋噪声谱).详细讨论了背景噪声以及自旋噪声随探测光光强的变化关系,证实了自旋噪声来自于系统中自旋的随机涨落.对比了两种FFTsDAC(8 bit采样的FFTsDACl和12 bit采样的FFTsDAC2)的测量性能,分析了影响实验信噪比的因素.FFTsDAC2具有更高的测量效率和采样深度以及更长的单次采样时间,因而具有更高的信噪比和更好的频率分辨率,与数值模拟的结果一致.     

Localized states emission in type‐I GaAsSb/AlGaAs multiple quantum wells grown by molecular beam epitaxy

As an important candidate for novel infrared semiconductor lasers, the optical properties of GaAsSb‐based multiple quantum wells (MQWs) are crucial. The temperature‐ and excitation power‐dependent photoluminescence (PL) spectra of the GaAs_0.92Sb_0.08/Al_0.2Ga_0.8As MQWs, which were grown by molecular beam epitaxy, were investigated and are detailed in this work. Two competitive peaks were observed from 40 K to 90 K. The peak located at the low‐energy shoulder was confirmed to be localized states emission (LE) and the high‐energy side peak was confirmed to be free‐carrier emission by its temperature‐dependent emission peak position. It is observed that the LE peak exhibited a blueshift with the increase of laser excitation power, which can be ascribed to the band filling effect of localized states. Our studies have great significance for application of GaAsSb‐based MQWs in infrared semiconductor lasers.