Gamma-Gamma信道下紫外光近直视分集接收

针对直升机降落过程中产生的中等强度湍流劣化紫外光通信质量的问题,提出了Gamma Gamma信道下的紫外光近直视通信模型,推导出考虑闪烁衰减的误码率公式,并引入分集接收技术抑制湍流效应,采用仿真进行性能对比。结果表明,在中等强度湍流条件下,闪烁衰减导致信噪比降低173～21 dB,误码率增加92～267×104倍;湍流强度越强,通信系统的误码率越高;在相同条件下,最大比合并(MRC)性能最佳,等增益合并(EGC)次之,选择性合并(SC)最差,且天线数量增加,能提升紫外光通信系统效能。在中等强度湍流信道中,采用分集接收技术能够有效抑制衰落影响,提升通信质量。     

基于IEEE1394总线的无线光通信系统

利用光总线进行通信可以极大的提高无线光通信系统的整体性能。文章将IEEE1394总线和无线光通信系统的优势结合起来,使用IEEE1394总线连接无线光通信设备,提出了一种新的无线通信方案,实现了高速无线传输,重点给出了IEEE1394设备与光通信设备间的接口电路的实现方法。     

一种基于可见光通信的无线局域网系统设计与仿真

可见光通信是一种采用白光LED作为光源的光无线通信技术,具有发射功率高、无处不在、无电磁干扰、节约能源等优点。提出一种基于可见光通信的无线局域网系统,给出了可见光无线局域网的关键组成部分的设计方案。仿真结果表明,基于该方案的可见光通信系统可以满足无线局域网内用户通信的需求,具有较好的通信性能。     

振动和大气湍流对星地光通信链路性能的影响

在星地光通信下行链路中,光束不仅受到卫星振动的影响,还有大气湍流的影响。分析了卫星振动和大气湍流对星地光通信下行链路的联合影响,结果表明,即使很小的瞄准振动和大气湍流也会急剧降低通信性能。     

日本通信塑料研究的新进展

当前塑料已在电气通信领城被广泛使用。譬如电缆绝缘被覆层,通信管道,各种仪器设备的印刷线路板、机器罩壳,连接器和度盘部件等。日本电气通信研究所最近主要就光纤被覆材料、轻化卫星重量、降低卫星制造成本的各种塑料复合材料以及LSI蔽光和密封材料等方面进行了积极地研究,取得了一些新的进展。一、作光通信普及用材为了使光通信能大量地普及,如何把光导纤维电缆的成本降低和性能提高则是至关     

纳米技术在光通信中的应用

光通信的发展在于元器件的发展,而元器件的发展要从材料上进行革命。纳米技术的应用研究表明可以突破传统极限,使微电子和光电子的结合更加紧密,光电器件的性能大大提高,纳米技术在通信领域的作用且受到世界各国的广泛重视。本文在介绍纳米技术的基本概念、纳米材料的性能、特点基础上重点阐述了纳米技术在光通信中的应用。     

自由空间光通信中的数字喷泉码方法

为了克服大气衰减和光强起伏对自由空间光通信性能的影响,信道编码是解决大气湍流信道影响的关键技术.数字喷泉码是一种无固定码率的信道编码方法,其中度分布是数字喷泉码设计的基础,本文采用开关度分布的方法,并给出其开关点最佳值.实验仿真结果表明,分别在自由空间光通信系统的弱湍流和强湍流环境条件下,数字喷泉码相比于RS码有较好的编码增益,数字喷泉码中的开关度分布相较于二进制指数度分布、鲁棒孤子度分布,在相同的信噪比条件下,开关度分布的误码率更低,信息速率的下降趋势也最少,同时双开关度分布与单开关度分布相比,对于自由空间光通信系统的性能提升更大.因此,双开关度分布数字喷泉码能有效抑制大气湍流的影响,大幅度地提高自由空间光通信系统性能.     

160 Gbps光通信系统中光纤准直器的基准插入损耗与功率代价研究

在几何光学和高斯光束传输理论的基础上,运用矩阵光学原理与高斯光束耦合理论,分析了基于自聚焦透镜光纤准直器引入高速光通信系统的基本插入损耗、回波损耗等特性,并采用光纤衰减基准测试方法对理论计算进行了实验验证.在160 Gbps光通信系统中分析了该器件对系统传输性能的影响,对误码率曲线进行了测试对比,讨论了光纤准直器增大系统功率代价的原因.     

浅谈光纤通信发展的三个方向

光纤通信经历了五个阶段的发展已经成为现代通信主要的传输方式，本文探讨了未来光纤通信发展的三个方向分别是相干光通信、光孤子通信和全光通信网。     

基于地形信息的平流层通信系统传播衰减预测

给出了一种基于地形信息的预测平流层通信系统大尺度衰落的算法，包括地形重建和传播衰减计算，及编程实现的方法，计算出了平流层空中平台到某一区域的大尺度传播衰减，并根据该算法针对地形变化对传播衰减的影响进行了仿真，结果表明，平流层通信系统的传播衰减受地形变化的影响比地面通信系统小得多，在没有平流层通信实测数据的情况下，上述预测算法对仿真通信系统性能具有重要意义。     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Characterization of Ordovician carbonate reservoirs, southeastern Saskatchewan, Canada

The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3～4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰～ -7.8‰, PDB) and matrix dolomites (-6.6‰～ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084～0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078～0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

A computer generator for randomly layered structures

AcomputergeneratorforrandomlylayeredstructuresYUJia shun1,2,HEZhen hua2(1.TheInstituteofGeologicalandNuclearSciences,NewZealand;2.StateKeyLaboratoryofOilandGasReservoirGeologyandExploitation,ChengduUniversityofTechnology,China)Abstract:Analgorithmisintrod…     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the