准一维含铂混合价化合物中的激光诱导光吸收

本文研究准一维含铂卤素桥接混合价化合物(HMPC)中的激光诱导光吸收。在总结、分析实验事实的基础上,提出一个激光诱导光吸收机制,分别计算卤素(X)离子交替形变和描述极化子周围的X离子晶格形变这两种情况下的激光诱导光吸收谱,并与实验事实进行比较。 关键词：     

反射式非均匀掺杂负电子亲和光电阴极量子效率研究

内建电场对提高阴极量子效率有重要作用。为获得恒定的电场强度,需要用指数掺杂方式对光电阴极激活层进行掺杂。指数掺杂实际上是一种特殊的梯度掺杂,针对这种掺杂方式,建立了指数掺杂和均匀掺杂加权的量子效率公式。实验设计了4种掺杂浓度从1019~1018cm-3掺杂样品,测量样品的光谱响应曲线和量子效率曲线,并分别用均匀掺杂量子效率公式,指数掺杂量子效率公式和新建立的梯度掺杂量子效率公式这三种方式,对量子效率曲线进行了拟合,证明了该量子效率公式具有较高的拟合精度。     

V掺杂ZnO团簇的结构和磁性质

本文采用第一性原理密度泛函理论系统的研究了V原子单掺杂和双掺杂(ZnO)12团簇的结构和磁性质。我们考虑了三种掺杂方式：替代掺杂,外掺杂和内掺杂。单掺杂时,替代掺杂团簇是最稳定结构,而对于双掺杂,外掺杂团簇是最稳定结构。团簇磁矩主要来自V-3d态的贡献,4s和4p态也贡献了一小部分磁矩。由于轨道杂化,相邻的Zn和O原子上也产生少量自旋。V原子掺杂团簇的总磁矩与掺杂位置有关,说明V掺杂(ZnO)12团簇在可调磁矩的磁性材料领域有潜在应用价值。     

Co掺杂碲化锌团簇结构和磁性质

本文采用第一性原理密度泛函理论系统的研究了Co原子单掺杂和双掺杂(ZnTe)12团簇的结构和磁性质。考虑了两种掺杂方式：替代掺杂和间隙掺杂。不管是单掺杂还是双掺杂,间隙掺杂团簇都是最稳定结构。Co掺杂团簇的磁性依赖于Co原子周围环境。最重要的是,我们指出替代双掺杂团簇是铁磁耦合,在纳米量子器件领域有潜在的应用价值。     

Co掺杂碲化锌团簇结构和磁性质

本文采用第一性原理密度泛函理论系统的研究了Co原子单掺杂和双掺杂(ZnTe)12团簇的结构和磁性质。考虑了两种掺杂方式：替代掺杂和间隙掺杂。不管是单掺杂还是双掺杂,间隙掺杂团簇都是最稳定结构。Co掺杂团簇的磁性依赖于Co原子周围环境。最重要的是,我们指出替代双掺杂团簇是铁磁耦合,在纳米量子器件领域有潜在的应用价值。     

W-Cu共掺杂ZnO电子结构和光学性质

采用了基于密度泛函理论(DFT)的第一性原理平面波超软赝势方法,计算了本征ZnO, W单掺杂ZnO, Cu单掺杂ZnO,以及W-Cu共掺杂ZnO电子结构和光学性质.计算结果表明:W掺杂属于n型掺杂, Cu掺杂属于p型掺杂,单掺杂均可以提高ZnO的载流子浓度,从而改善ZnO的导电性. W-Cu共掺杂时ZnO进入简并状态,呈现金属性质.三种掺杂ZnO的吸收光谱均发生红移,其中W-Cu共掺杂时, ZnO对太阳光谱的吸收效果最好.     

Co掺杂ZnTe团簇结构和磁性质

本文采用第一性原理密度泛函理论系统的研究了Co原子单掺杂和双掺杂(ZnTe)_(12)团簇的结构和磁性质.考虑了两种掺杂方式:替代掺杂和间隙掺杂.不管是单掺杂还是双掺杂,间隙掺杂团簇都是最稳定结构.Co掺杂团簇的磁性依赖于Co原子周围环境.最重要的是,我们指出替代双掺杂团簇是铁磁耦合,在纳米量子器件领域有潜在的应用价值.     

V掺杂ZnO团簇的结构和磁性质

本文采用第一性原理密度泛函理论系统的研究了V原子单掺杂和双掺杂(ZnO)_(12)团簇的结构和磁性质.我们考虑了三种掺杂方式:替代掺杂,外掺杂和内掺杂.单掺杂时,替代掺杂团簇是最稳定结构,而对于双掺杂,外掺杂团簇是最稳定结构.团簇磁矩主要来自V-3d态的贡献,4s和4p态也贡献了一小部分磁矩.由于轨道杂化,相邻的Zn和O原子上也产生少量自旋.V原子掺杂团簇的总磁矩与掺杂位置有关,说明V掺杂(ZnO)_(12)团簇在可调磁矩的磁性材料领域有潜在应用价值.     

Fe掺杂ZnSe团簇结构和磁性质

采用密度泛函理论研究了Fe原子单掺杂和双掺杂(ZnSe)12团簇的结构、电子性质和磁性质.我们考虑了三种掺杂方式:替代掺杂,外掺杂和内掺杂.单掺杂时,外掺杂团簇是最稳定结构;而双掺杂时,内掺杂团簇是最稳定结构.团簇磁矩主要来自Fe-3d态的贡献,4s和4p态也贡献了一小部分磁矩.由于轨道杂化,相邻的Zn和Se原子上也产生少量自旋.不同掺杂团簇的总磁矩不同,在可调磁矩的磁性材料领域有潜在应用价值.     

红光量子点掺杂PVK体系的发光特性研究

无热处理制备了红光CdSe/ZnS量子点掺杂PVK的ITO/PVK:QDs/Alq3/Al结构电致发光器件.测试器件的发光光谱和电学特性等,研究了掺杂浓度(质量分数)对体系发光特性的影响,将非掺杂与掺杂体系做了比较,提出了优化掺杂体系的一些可行方案.量子点掺杂浓度较低时,主要为Alq3的发光;掺杂浓度为20%时,Alq3的发光得到抑制,红光发射最佳;继续增大掺杂浓度,QDs发光峰发生微弱红移,器件性能变差.与非掺杂体系相比,掺杂浓度合适的PVK:QDs体系大大提高了器件的稳定性.     

Design of an omnidirectional band gap independent of ambient media refractive indices by using a heterostructure magnetic photonic crystal

This paper aims to study the general conditions under which omnidirectional band gaps (OBGs) are achieved by using heterostructure magnetic photonic crystals (HMPCs). These structures contain periodic layers with alternative dielectric permittivity and magnetic permeability. The proposed design offers the stacking of two magnetic photonic crystals (MPCs), where one MPC has Brewster’s angle at TE polarization and another has the angle at TM polarization. The propagation of electromagnetic waves is investigated by means of the transfer matrix method. Also, the total reflection frequency range for any incident angle and polarization is discussed in this paper. As a conclusion, although each MPC has no OBG individually, the proposed HMPC may contain an OBG. The main advantage of the proposed design is that the obtained OBG is independent of the ambient media refractive index. Therefore, it can be used in engineering omnireflectors in integrated photonics.     

Reduction of turbulent boundary layer induced interior noise through active impedance control

The use of a single actuator tuned to an optimum impedance to control the sound power radiated from a turbulent boundary layer (TBL) excited aircraft panel into the aircraft interior is examined. An approach to calculating the optimum impedance is defined and the limitations on the reduction in radiated power by a single actuator tuned to that impedance are examined. It is shown that there are too many degrees of freedom in the TBL and in the radiation modes of the panel to allow a single actuator to control the radiated power. However, if the panel modes are lightly damped and well separated in frequency, significant reductions are possible. The implementation of a controller that presents a desired impedance to a structure is demonstrated in a laboratory experiment, in which the structure is a mass. The performance of such a controller on an aircraft panel is shown to be effective, if the actuator impedance is similar to but not the same as the desired impedance, provided the panel resonances are well separated in frequency and lightly damped.     

Recoil corrections to elastic electron scattering in the Breit approximation

Recoil corrections to the cross sections for elastic electron scattering from spin-0 nuclei are investigated in the Breit approximation. The form of the scattering amplitude in first- and second-Born approximation is investigated in detail using time-dependent perturbation theory, and it is found that the center-of-mass (CM) frame is particularly convenient to work in. Transformation equations relating the lab and CM frames are developed. Those parts of the second-Born amplitude which correspond to the Breit amplitude are isolated, and the Breit equation with the electromagnetic Breit interaction is investigated in detail. Corrections to the scattering cross sections which are inversely proportional to the nucleus mass (recoil corrections) are calculated. Numerical results are presented for the particular case of ¹⁶O.     

Analysis of the Hamiltonian formulations of linearized general relativity

The different forms of the Hamiltonian formulations of linearized General Relativity/spin-2 theories are discussed in order to show their similarities and differences. It is demonstrated that in the linear model, non-covariant modifications to the initial covariant Lagrangian (similar to those modifications used in full gravity) are in fact unnecessary. The Hamiltonians and the constraints are different in these two formulations but the structure of the constraint algebra and the gauge invariance derived from it are the same. It is shown that these equivalent Hamiltonian formulations are related to each other by a canonical transformation, which is explicitly given. The relevance of these results to the full theory of General Relativity is briefly discussed.     

Remarks on stratifying interactions in five dimensions

A geometric model is proposed in which the interaction types, namely the strong, weak, electromagnetic, and gravitational interactions, are stratified in a five-dimensional manifold. The strong and electromagnetic interactions are confined to disjoint four-spaces and the weak and gravitational interactions are proposed unified in a five-manifold bounded topologically by the strong and electromagnetic four-spaces. Further, some advantages of the five-dimensional approach to current-current interactions are discussed, and a five-dimensional approach to PCAC is presented. The model is presented in hopes of reconciling some contradictory lines of theoretical thought, and new fields for investigation are stressed.     

Large eddy simulation of multi-regime combustion with a two-progress variable approach for carbon monoxide

Simulations of two cases in a novel multi-regime burner configuration are undertaken using a presumed joint probability density function (PDF) approach with tabulated chemistry. The flame conditions are varied by changing the central jet equivalence ratio, which produces different multi-regime combustion modes in the non-premixed inner flame. An outer premixed flame and recirculation zone behind a bluff body are present to supply heat and combustion products to stabilise the inner flame. A two-progress variable approach is tested to improve predictions of carbon monoxide (CO) in the post-flame regions, where CO oxidation occurs. The large eddy simulation set-up and sub-grid combustion model are assessed through comparisons with time-averaged measurements for radial profiles at different streamwise locations. The jet break-up length, the shear layers and the mixture fraction distribution are well captured in both cases. The temperature distribution is well captured for the inner flame in each case but the temperature and mixture fraction are over predicted in the downstream regions of the outer premixed flame, which is due to increased dilatation that suppresses air entrainment. Improved predictions of the CO mass fraction are obtained for the outer premixed flames with the two-progress variable approach. Over predictions are seen in the upstream regions of the inner flame when the CO mass fraction is obtained from a look-up table, suggesting that the CO mass fraction should be transported to include the convection/diffusion balance in regions where there is no flame. Furthermore, transporting the CO mass fraction with a one-progress variable approach produces over predictions in the burnt regions, suggesting a two-progress variable model is needed to capture the consumption region of CO. The multi-regime combustion characteristics are observed to be stronger in flame MRB26b, where non-premixed and rich premixed combustion is present. For flame MRB18b, the non-premixed contribution is smaller and weak stratified combustion is observed.     

基于滤波法的光纤光栅传感解调方案

FBG传感器对应变和温度的敏感体现在其反射光中心波长的变化上，因此如何测量波长的变化就成为FBG传感器的关键。在光纤光栅的多种解调方法中，因滤波法的测量器件制作简单，测量系统简易、方便直观而被广泛应用。主要介绍了8种基于滤波法的解调方法，对它们各自的成本、检测精度、测量范围、器件制作以及适用的环境进行了详细的比较，分析了它们的优缺点，以便于在不同的检测条件下选用最佳的解调方案。重点介绍了光学小波滤波解调法，探讨了其测量系统的原理，并指出该方法可用于微弱信号的检测与处理。     

Gauge invariance and the dirac equation

The gauge invariance of the Dirac equation is reviewed and gauge-invariant operators are defined. The Hamiltonian is shown to be gauge dependent, and an energy operator is defined which is gauge invariant. Gauge-invariant operators corresponding to observables are shown to satisfy generalized Ehrenfest theorems. The time rate of change of the expectation value of the energy operator is equal to the expectation value of the power operator. The virial theorem is proved for a relativistic electron in a time-varying electromagnetic field. The conventional approach to probability amplitudes, using the eigenstates of the unperturbed Hamiltonian, is shown in general to be gauge dependent. A gaugeinvariant procedure for probability amplitudes is given, in which eigenstates of the energy operator are used. The two methods are compared by applying them to an electron in a zero electromagnetic field in an arbitrary gauge. Presented at the Dirac Symposium, Loyola University, New Orleans, May 1981.     

Remarks on (0,2) models and intermediate scale scenarios in string theory

Problems associated with large intermediate scales in string theory are discussed. It is shown that, in σ-model perturbation theory, the superpotential of theories with (2,2) supersymmetry is purely cubic. As a result, to exhibit flat directions with (0,2) supersymmetry, one needs to study only a small number of Yukawa couplings. Usually these flat directions are lifted by nonperturbative effects in the σ model. Examples where this is not the case, due to Cvetic and to Distler and Greene, are discussed. It is shown that in the former case, there are not, generically, extra massless particles to play the role of Higgs fields. The problems of proton decay, neutrino masses, and obtaining light Higgs fields in models with large intermediate scales are considered, and various difficulties with existing proposals are pointed out.     

Robustness to head misalignment of virtual sound imaging systems

When binaural sound signals are presented with two loudspeakers, the listener's ears are required to be in the relatively small region which is under control of the system. Misalignment of the head results in inaccurate synthesis of the binaural signals. Consequently, directional information associated with the acoustic signals is inaccurately reproduced. When the two loudspeakers are placed close together, the spatial rate of change of the generated sound field is much smaller than that generated by two loudspeakers spaced apart. Therefore, the performance of such a system is expected to be more robust to misalignment of the listener's head. Robustness of performance is investigated here with respect to head displacement in three translational and three rotational directions. A comparison is given between systems consisting of two loudspeakers either placed close together or spaced apart. The extent of effective control with head displacement and the resulting deterioration in directional information is investigated in the temporal and spectral domain by analyzing synthesized binaural signals. Subjective localization experiments are performed for cases in which notable differences in performance are expected from the previous analysis. It is shown that the system comprising two loudspeakers that are close together is very robust to misalignment of the listener's head.