既要好用,也要好听 Jamo C 93 Ⅱ书架音箱/NAD C328数字功放

不知型道音本响刊系的统资应深该读是者目有前没市有场发卖现得,最小好型的音产响品系种统类在了",器主材要鉴原赏因"可栏以目总的结出成现以频下率几越点来:越第高一。,除价了格定实制惠安,装大以部外分,小小资群体都能够消费得起;第二,不会占据太多的空间,只需在家挪出一小片区域摆放即可;第三,操作/连接简单,相比资深发烧友玩的家庭影院/Hi-Fi系统,小型音响系统的功能设计更符合主流用户需要。这次要讲的是小型Hi-Fi系统是英国老牌音响NAD功放和Jamo(尊宝)书架音箱,中西结合的器材组合又能擦出什么样的火花?我们不妨往下慢慢细品。     

回馈中的若干激光物理效应

文中将两个激光物理概念"激光回馈效应"和"正交偏振激光"交叉结合,并向"纳米干涉技术"应用渗透产生新的结果."激光回馈效应"(又称激光自混合效应)是激光器的十分重要的物理现象,当激光器输出光束被前进路程上的反射面反射回激光内部时,这一现象总要发生."偏振"也是大多数类型的激光器输出光束的特性.腔内有量子阱、布儒斯特窗、双折射元件等偏振机制或元件时,激光器必是偏振输出.即使无此类元件,大多数类型激光器输出的每一个纵模(频率)也都是线偏振的,且相邻的两个纵模经常是正交偏振的.作者课题组发展了新类型的HeNe和Nd:YAG微片激光器:正交偏振激光器(双折射双频激光器)输出两个模(频率),模间隔可调且偏振态垂直.作者意识到,模(频率)间隔的改变(特别是很小的间隔)导致模竞争强度改变.还认识到,正交偏振特性正好可利用来研究这种改变:可用偏振分光镜将正交偏振激光束中的两正交模分开,以研究每个偏振态各自的特性和它们之间的相互作用.在研究之前,人们对外腔调谐的研究都是用一个反射镜将激光输出的光束的全部纵模(频率)反射回激光器.这就意味着不区分纵模多少及其间隔大小,不区别激光输出的偏振状态,不顾及激光频率之间的竞争.如果说以往是站在激光器外头研究回馈,研究是进入激光器内部研究回馈:由偏振器件将两正交偏振频率分开,研究每个偏振频率的回馈行为,研究它们之间的相互影响.作者课题组取得的主要发现点包括:(1)设计了(单模激光器腔调谐+PBS分开正交偏振两成分)的方法研究激光器模间作用、光强改变及偏振特性.(2)双折射双频激光器、M3弱反射并调谐:o、e光强度曲线均为类正弦;两频频差小于200 MHz时,o、e曲线的位相差随频差变大而减小;两频频差大于200 MHz时,o、e曲线位相差为相对腔长和相对频率分裂量的乘积.(3)双折射双频激光器、M3中等反射率并调谐:o、e光强度总是反向变化;一周期分为缓交换区和快交换区;两个等光强点:缓区的高于快区的.(4)单纵模激光器,M3高反射并欠准直,M3调谐:M3每位移λ/80,光强变化一个周期,即生成了纳米光条纹.(5)单纵模激光器,M3高反射并欠准直,M3调谐:M3每变向一次激光偏振态旋转90°一次.(6)外腔内有λ/4片、M3调谐:光强调制曲线倍频,即外腔长每变化λ/4,光强变化一个周期;曲线类似正弦全波整流;如波片快轴与光偏振方向平行或垂直,相邻周期偏振态正交;如波片快轴与激光器偏振方向夹45°角,偏振态不因M3调谐而变.(7)波片置外腔、M3调谐,强度曲线上一种偏振态占据宽度和一个周期宽度之比等于双折射元件位相延迟.(8)双折射一塞曼双频激光器,M3调谐:单偏振回馈,o、e光强调制曲线都为类正弦,变化趋势相反;双偏振回馈,o、e曲线的相位差因M3运动方向不同分别为π/2或3π/2.(9)Nd:YAG双频激光器、M3调谐,M3反射率越大,光强调制越深;频差是外腔自由光谱区1/2的偶数倍,调制深度最小;奇数倍时,调制深度最大.(10)用"任意位相差波片外腔、M3调谐:强度曲线上一种偏振态占据宽度和一个周期宽度之比等于双折射元件的位相延迟"的原理已制成新的波片测量仪,其具有高精度和可在位测量的特点.     

海森堡模型中概率及相应熵的计算分析

介绍海森堡模型的不同位型[N,n] （N为海森堡链总格点数, n为格点中自旋向下的电子数）中的体现本征值获取难易程度的本征值获取概率及其相应信息熵（香农所定义的）和体现模型体系关联程度的自旋向下电子发现概率、每一粒子的von Neumann及体系的平均von Neumann熵,可为量子计算与信息传递提供启示性信息。研究结果：(1)事件发生概率大于（小于）50%时,信息熵随概率增加而减小（增加）。(2)不同位型[N,n],当n（N）同, N（n）增加时：本征值获取概率减小,其相应的信息熵正确反映本征值获取的难易程度;模型参数一定时,格点中自旋向下电子发现概率与每一粒子的von Neumann及体系的平均von Neumann熵都分别减小（增加）。(3)位型[N,n]相同时, 每一粒子的von Neumann及体系的平均von Neumann熵随参数变化时出现拐点,显示体系发生量子相变的信息。(4)同位型[N,n]且同参数时处于海森堡链对称位置粒子的von Neumann熵相同。     

Modeling Electron and Hole Transport in Fluoroarene‐Oligothiopene Semiconductors: Investigation of Geometric and Electronic Structure Properties

A theoretical study using density functional theory is undertaken to gain insight into how the structural, electronic, and electron‐transfer characteristics of three Fluoroarene‐oligothiophene semiconductors influence the preferred transport of electrons versus holes in field‐effect transistor applications. The intermolecular electronic coupling interactions are analyzed through both a simplified energy‐splitting in dimer (ESID) model and as a function of the entire dimer Hamiltonian in order to understand the impact of site energy differences; our results indicate that these differences are generally negligible for the series and, hence, use of the ESID model is valid. In addition, we also investigate the reduction and oxidation processes to understand the magnitudes of the intramolecular reorganization energy for the charge‐hopping process and expected barrier heights for electron and hole injection into these materials. From the electronic coupling and intramolecular reorganization energies, estimates of the nearest‐neighbor electron‐transfer hopping rate constant for electrons are obtained. The ionization energetics suggest favored electron injection for the system with perfluoroarene groups at the end of the thiophene core, in agreement with experiments. The combined analyses of the electron‐transfer properties and ionization processes suggest possible ambipolar behavior for these materials under favorable device conditions.     

非均匀海森堡XY周期性链的纠缠

研究了各向同性海森堡XY链在非均匀磁场中纠缠的含时演化以及热纠缠的问题。纠缠在量子信息领域是个十分重要的资源,关于纠缠的度量和含时演化的研究就非常必要。我们主要对共生纠缠度进行了理论计算,通过数值模拟进行了分析。如果外磁场很小,最近邻耦合系数很大,共生纠缠度就在0和1之间振荡。如果外磁场很大,最近邻耦合系数很小,共生纠缠度的最大值会变小,甚至会消失。同时,随着海森堡自旋链中自旋数目的增加,纠缠会减小。随着温度的升高,热纠缠会快速的下降。随着外磁场的增加,热纠缠也会下降。只有在系统的非均匀度增加的时候,热纠缠才会增加。     

关于海森堡模型中一种并行算法实现的讨论

使用并行算法（简称Z分法）fortran编程计算获取海森堡模型位型[N,k] （N为海森堡链总格点数, k为格点中自旋向上的电子数）的最小本征值的最短时间。研究方法：使用置换群方法产生模型的能量矩阵,将能量矩阵对角化所得到的本征值构成数据群,采用Z（Z=1,2……）分法Fortran编程计算获得群中最小数据的最短(或最长)时间。研究结论：(1）同一位型[N,k],使用2分法获取模型位型[N,k]的最小本征值的时间最长,而不等分或满等分（此时Z=1或位型[N,k]的矩阵维数）时的时间最短且二者相等。(2）对于不同位型[N,k] ,Z相同而当N（k）同,k（N）增大时,获取模型最小本征值的最短时间增加。通过讨论海森堡模型获取最小本征值的时间计量可为研究者们在计算工作中作提高运算效率的借鉴。     

一维XY每森堡模型纠缠度的计算与相关分析

计算了一维XY 海森堡模型的基态纠缠度并作相关分析,为量子通信和量子计算提供启示性信息。将von Neumann 饷定义的纠缠度与模型的基态本征矢建立联系计算出该模型体系的基态纠缠度。计算结果表明(1) 总格点数N 相同,自旋向上电子数k 增加时,基态纠缠度η 增加k 相同N 增加时T) 减小,真实反映了此模型的关联性。(2) N 为偶数,位型[N, N/2] 时, η= 1 ,体现了自旋链格点中自旋向上和向下的电子数呈严格的对称性。(3) 模型参数不同, η 有别。但)η 在整个参数变化区间内的导率一致,体系为有纠缠的连续长程相,属于从有序到有序的相变。     

Spin-polarized currents in the tunnel contact of a normal conductor and a two-dimensional topological insulator

The spin filtering of electrons tunneling from the edge states of a two-dimensional topological insulator into a normal conductor under a magnetic field (external or induced due to proximity to a magnetic insulator) is studied. Calculations are performed for a tunnel contact of finite length between the topological insulator and an electronic multimode quantum strip. It is shown that the flow of tunneling electrons is split in the strip, so that spin-polarized currents arise in its left and right branches. These currents can be effectively controlled by the contact voltage and the chemical potential of the system. The presence of a magnetic field, which splits the spin subbands of the electron spectrum in the strip, gives rise to switching of the spin current between the strip branches.     

Effect of spin-orbit coupling on the spectrum of two-dimensional electrons in a magnetic field

The electron states in semiconductors with zinc-blende structure in an external magnetic field are studied taking into account the intrinsic spin splitting. The Hamiltonian of the spin-orbit coupling is written out using the method of invariants. Effects of modification of the energy spectrum of two-dimensional electrons in single and double quantum wells in a magnetic field oriented parallel to the interface planes are considered.     

Charge separation in organic photovoltaic cells

We consider a simple model for the geminate electron–hole separation process in organic photovoltaic cells, in order to illustrate the influence of dimensionality of conducting channels on the efficiency of the process. The Miller–Abrahams expression for the transition rates between nearest neighbor sites was used for simulating random walks of the electron in the Coulomb field of the hole. The non-equilibrium kinetic Monte Carlo simulation results qualitatively confirm the equilibrium estimations, although quantitatively the efficiency of the higher dimensional systems is less pronounced. The lifetime of the electron prior to recombination is approximately equal to the lifetime prior to dissociation. Their values indicate that electrons perform long stochastic walks before they are captured by the collector or recombined. The non-equilibrium free energy considerably differs from the equilibrium one. The efficiency of the separation process decreases with increasing the distance to the collector, and this decrease is considerably less pronounced for the three dimensional system. The simulation results are in good agreement with the extension of the continuum Onsager theory that accounts for the finite recombination rate at nonzero reaction radius and non-exponential kinetics of the charge separation process.     

The design of bipolar spin filtering junction in zigzag silicene nanoribbons

We performed first-principles simulation on the electronic structure of zigzag silicene nanoribbons (ZSiNRs), and found that semi-hydrogenation can break the extended π-bonding network of silicene, leaving the electrons in the unsaturated Si atoms localized and unpaired, and ferromagnetic semiconducting behavior can be obtained. While the fully hydrogenated ZSiNRs are found to be energetically degenerate and show wide band-gap semiconductor feature. Then, we designed and investigated the spin-dependent electron transport of a heterostructure, consisting of semi-hydrogenation ZSiNRs and ZSiNRs. The results show a perfect dual spin filtering effect at the parallel and antiparallel spin configuration with large bias range. The spin dependent electron transmission spectrum, band structure, transmission pathway, and the molecularly projected self-consistent Hamiltonian state are employed to investigate the physical origin of the spin-polarized effect.     

基于仿生模式识别思想的时间序列匹配

仿生模式识别是模式识别理论的一种新模型,它的出发点是要"认识"事物而非"区分"事物,理论的基点在于它确认了样本点在特征空间的连续性.本文根据仿生模式识别的基本思想,提出了一种时间序列匹配的新方法.该方法利用同类样本间的连续性规律,将时间序列排序,并在相邻的时间序列之间添加了若干新的时间序列,以增加样本点.对力感键盘按键压力序列进行分类实验的结果表明,新方法优于基于动态时间弯折的传统方法.