循环码的周期分布的新的计算公式

本文在［１］文的基础上进一步分析了循环码的周期分布的性质，给出了新的计算方法和公式，并且确定了一些熟知的循环码的周期分布。     

基于ARM9的视频点播系统的的设计

在计算机技术和流媒体技术的快速发展下,视频点播(VOD)系统得到了广泛的应用,伴随着嵌入式技术和网络技术的发展,出现了基于嵌入式的视频点播系统,本文介绍了基于ARM9的嵌入式视频点播系统的组成,重点阐述了该系统的工作原理、设计方案、软硬件模块的实现方法。     

航海计划的执行的海航日志的生成

深入地探讨了在电子海图的环境下航海计划的执行和航海日志的生成。     

高效的可追踪的基于ID的签名方案

密钥托管问题是基于ID的数字签名的主要缺陷,为了解决该问题,提出了可追踪的基于ID的签名(T-IBS,traceable ID-based signature)的定义及安全模型,并构造了一个不需要双线性对的T-IBS方案,在随机预言机模型与椭圆曲线离散对数假设下该方案是可证安全的.与已有的无密钥托管的签名方案相比,该方案的签名算法只需要一个加法群上的标量乘运算,而验证算法仅需3个标量乘运算,所以是目前效率最高的方案.     

基于LDP的VPLS的实施模型的比较

首先简要介绍了基于LDP的VPLS的工作原理,然后探讨了层次化体系结构下的两种VPLS的实施模型,比较了这几种不同实施模型的VPLS的特点和适用环境.     

基于VPN技术的安全的BLUEPAC的构建

Bluetooth Public Access在日益受到人们青睐的同时,其安全性也备受关注,在介绍BLUEPAC的基础上,对BLUEPAC存在的安全问题进行了分析,而虚拟专用网能防御这些非法的恶意攻击行为。具体分析了VPN通过附加安全隧道、用户认证和访问控制等技术来提供数据的安全性保障,最后给出了一种将VPN技术应用于无线局域网中的网络部署方案。     

改进遗传算法的配电网的无功优化的研究

电网的设备众多,网架结构复杂,常常会有大量有功损耗在电力系统的传输中,如何降低电网的有功损耗是电网安全稳定运行中需要考虑的一个重要问题。无功优化能够降低电网的有功损耗,保证电网的稳定运行,传统的无功优化遗传算法在求解最优解的过程中,会导致算法陷入局部最优解,无法得到全局的最优解。基于此,提出对传统遗传算法进行改进, 采用改进遗传算法来对配电网进行无功优化,改进主要通过引入交叉算子和变异算子,并通过设计的自适应函数,使得算法能够具有较好的全局搜索能力,从而得到更好的优化结果。通过实验仿真可以看出,方法能够有效降低电网的有功损耗,大大提高电网的达标率,具有十分重要的实践意义。     

Efficient near IR photoluminescence from gallium nitride layers doped with arsenic

Photoluminescence in the 1.2–1.4 eV spectral range from GaN:As layers grown on (0001) Al₂O₃ substrates was observed and studied. The photoluminescence is attributed to radiative recombination in GaAs nanocrystallites, self-organized in the GaN matrix during growth. The photoluminescence intensity attains a maximum at a growth temperature of ～780°C, which is explained by the competition between several temperature-dependent processes that affect the formation of GaAs nanocrystallites. Sharp emission lines were observed at the high-energy edge of the photoluminescence band. These lines are caused by an emission of bound excitons in the GaAs nanocrystallites and by phonon replicas of the bound-exciton emission. The energies of the corresponding optical phonons are typical of GaAs. The photoluminescence-excitation spectra exhibit features related to resonantly excited free and bound excitons as well as to excitons formed simultaneously with the emission of optical phonons.     

Luminescence of stepped quantum wells in GaAs/GaAlAs and InGaAs/GaAs/GaAlAs structures

Luminescence spectra of doped and undoped GaAs/GaAlAs and InGaAs/GaAs/GaAlAs structures containing several tens of stepped quantum wells (QW) are investigated. The emission bands related to free and bound excitons and impurity states are observed in QW spectra. The luminescence excitation spectra indicate that the relaxation of free excitons to the e1hh1 state proceeds via the exciton mechanism, whereas an independent relaxation of electrons and holes is specific to bound excitons and impurity states. The energy levels for electrons and holes in stepped QWs, calculated in terms of Kane’s model, are compared with the data obtained from the luminescence excitation spectra. The analysis of the relative intensities of emission bands related to e1hh1 excitons and exciton states of higher energy shows that, as the optical excitation intensity increases, the e1hh1 transition is more readily saturated at higher temperature, because the lifetime of excitons increases. Under stronger excitation, the emission band of electron-hole plasma arises and increases in intensity superlinearly. At an excitation level of ～10⁵ W/cm², excitons are screened and the plasma emission band dominates in the QW emission. Nonequilibrium luminescence spectra obtained in a picosecond excitation and recording mode show that the e1hh1 and e2hh2 radiative transitions are 100% polarized in the plane of QWs.     

Microchannel gate temperature analysis

Photoemission spectra of a GaAs gate material of a metal semiconductor field effect transistor (MESFET) were analyzed to nondestructively assess the submicron-size local gate temperature. Utilizing the micromanipulator, the laser beam was precisely adjusted to probe the exact position of the device gate. The emission spectral bands due to the interaction among photons, free excitons and impurity bound excitons in GaAs gate materials were measured and identified both at 299.1 K and 84.8 K. The shift of the band was found to be 16.30 meV for the free excitons when the device was not powered, while the band shift of the gate was 7.38 meV when the device was powered at 84.8 K. Simple first order calculations based on the theory of temperature shift of the bound excitons, predicts an inversely proportional relationship between the emission bandshift and temperature. Measurements using this technique found an increase of 97.0 K.     

The role of stacking faults and their associated 0.13 ev acceptor state in doped and undoped ZnO layers and nanostructures

An emission band at 3.31 eV is frequently observed in low-temperature photoluminescence (PL) measurements on ZnO p-doped with group-V elements, and also on nominally undoped ZnO layers and nanostructures. It has alternatively been ascribed to LO- or TO-phonon replicas of free excitons, to acceptor-bound excitons, to donor-acceptor pair transitions, to two-electron satellites of donor-bound excitons, or to free-to-bound transitions. This band frequently dominates the PL of ZnO nanostructures and layers at room temperature. Annealing leads to drastic changes in its intensity.We report on low-temperature cathodoluminescence measurements with very high spatial resolution and high-resolution transmission electron microscope investigations carried out on the same pieces of hetero-epitaxial ZnO samples with unusual layer orientation. These data allow us to correlate this emission unambiguously with c-plane stacking faults. The emission is found to be due to the recombination of a free electron with a hole bound to a relatively shallow acceptor state ≈130 meV above the valence band edge. Locally, these acceptor states occur in high concentrations of up to some 10¹⁸ cm⁻³, and thus lead to strong two-dimensional perturbations of the free carrier concentration. They have severe implications for the conductivity of layers and nanostructures in general, and on the interpretation of Hall and luminescence data in particular. Literature data are critically reviewed in the light of these findings.     

Specific features of luminescence spectra of ZnS:O and ZnS:Cu(O) crystals in the context of the band anticrossing theory

The anticrossing band theory, which specifies the change induced in the band structure by an isoelectronic impurity substantially distorting the lattice, is used to interpret the nature and specific features of the complex self-activated luminescence spectra of ZnS:O and ZnS:Cu(O). The light emission involving the self-activated luminescence centers SA and SAL, the spectral dependence of the emission components in relation to the content of dissolved oxygen, and the effects of the centers on the formation of bound excitons are considered. It is found that some absorption bands in the near-infrared spectral region are associated with the transitions between sublevels of the conduction band split in the presence of oxygen. On the basis of the experimental data, a heretofore unknown band model of ZnS:O is developed, and the Cu-induced modifications of the model are discussed. The effect of oxygen-containing agglomerates on the spectra is established. It is suggested that these agglomerates can be responsible for green emission from ZnS:Cu. The results complement the previously reported data of similar studies of ZnS:O and ZnS:Cu(O).     

Optical spectroscopy of excitonic states in CuInSe2

Optical properties of structurally perfect CuInSe₂ single crystals were studied in the temperature range of 4.2–300 K with the use of photoluminescence, optical absorption, optical reflection, and wavelength-modulated optical reflection (WMOR). The intense lines of free excitons A (～1.0414 eV) and B (～1.0449 eV) with a half-width of ～0.7 meV at 4.2 K are found to be related to two extrema of valence band split by a crystal field. The excitons emission line C (～1.2779 eV) in WMOR spectra are related to a lower valence band split-off by spin-orbit interaction. Within the context of the quasi-cubic Hopfield model, the parameters of valence band splitting Δ_CF=5.2 meV and Δ_SO=234.7 meV defined by the crystal and spin-orbit interaction, respectively, are calculated. In the region of the fundamental absorption edge, the lines of bound excitons are found with a half-width ～0.3 meV that is indicative of a high quality of grown CuInSe₂ crystals.     

Edge luminescence of ZnO nanorods on high-intensity optical excitation

The spectra of spontaneous and stimulated ultraviolet luminescence of ZnO nanorods annealed in air are studied at the temperature 4.2 K. The emission peaks corresponding to bound and free excitons and excitons interacting with excitons and exciton-impurity complexes are detected. It is found that high-temperature annealing induces an increase in the crystallite dimensions and a decrease in the number of point defects in the crystal structure of the nanorods. It is established that stimulated ultraviolet luminescence is initiated due to inelastic interaction of excitons in the case of increasing optical pumping intensity.     

GaNAs/GaAs量子阱的静压光致发光研究

在 1 5 K和 0～ 9GPa静压范围下测量了 Ga N0 .0 1 5As0 .985/ Ga As量子阱的光致发光谱。观察到了 Ga NAs阱和 Ga As垒的发光 ,发现 Ga NAs阱发光峰随压力的变化比 Ga As垒发光峰要小很多。当压力超过 2 .5 GPa后还观察到了与 Ga As中的 N等电子陷阱有关的一组新发光峰。用二能级模型及测得的 Ga As带边和 N等电子能级的压力行为计算了 Ga NAs发光峰随压力的变化 ,但计算结果与实验结果相差甚大 ,表明二能级模型并不完全适用。对观察到的 Ga NAs发光峰的强度和半宽随压力的变化也进行了简短讨论。     

Spectroscopic Studies of Photoexcitations in Regioregular and Regiorandom Polythiophene Films

Using a variety of optical probe techniques we studied the steady state and transient dynamics of charged and neutral photoexcitations in thin films of poly‐3‐alkyl thiophene with regioregular order, which forms self‐assembled lamellae structures with increased interchain interaction, as well as regiorandom order that keeps a chain‐like morphology. In regiorandom polythiophene films we found that intrachain excitons with correlated photoinduced absorption and stimulated emission bands are the primary photoexcitations; they give rise to a moderately strong photoluminescence band, and long‐lived triplet excitons and intrachain charged polarons. In regioregular polythiophene films, on the contrary we found that the primary photoexcitations are excitons with much larger interchain component; this results in lack of stimulated emission, vanishing intersystem crossing, and a very weak photoluminescence band. The long‐lived photoexcitations in regioregular polythiophene films are interchain excitons and delocalized polarons (DP) within the lamellae, with very small relaxation energy. The characteristic properties of the DP species are thoroughly investigated as a function of the alkyl side group of the polymer backbone, film deposition conditions and solvents used, as well as at high hydrostatic pressure. The quantum interference between the low energy absorption band of the DP species and a series of photoinduced infrared active vibrations, which give rise to antiresonances that are superimposed on the electronic absorption band is studied and explained by a Fano‐type interference mechanism, using the amplitude mode model.     

Exciton emission of crystalline Zn(S)Se thin films arranged in microcavities based on amorphous insulating coatings

A technology for the production of fully hybrid microcavities on the basis of Zn(S)Se films and amorphous insulating SiO₂/Ta₂O₅ coatings is proposed. The influence of all stages of the manufacturing cycle on the structure of exciton states in the Zn(S)Se films is demonstrated. This influence is reduced to four main effects: the appearance of a fine structure of emission lines related to free excitons; a decrease in the relative contribution of excitons bound at neutral acceptors to the exciton-emission spectrum; a shift of the emission lines related to exciton–impurity complexes and free excitons to lower frequencies; and a decrease in the splitting between emission lines related to heavy and light excitons. Samples of fully hybrid microcavities, in which the high structural and optical quality of Zn(S)Se films is retained, are fabricated.