无源光网络标准发展及关键技术研究

无源光网络(Passive Optical Network,PON)作为当今接入网的主要技术解决方案,具有带宽使用效率高、传输距离远、抗干扰能力强等特点.通过研究PON技术的发展动态,本文首先归纳了各种PON技术的产生背景和应用特点,整理出各技术间的连接关系及主要标准;其次介绍了PON技术的帧结构,并对带宽、波长、传输模式等PON技术的主要参数进行了汇总;然后将国内外研究热点进行划分,围绕媒体访问控制协议、帧结构、动态带宽分配算法、节能机制等关键技术,阐述了其研究现状及在PON中的重要作用;最后对PON技术的发展趋势进行了展望.     

Owner’s Risk Allocation and Contractor’s Role Behavior in a Project: A Parallel-mediation Model

Risk allocation decisions are of critical importance in project management. The present study proposes an explanation for how risk allocation in a contract motivates a contractor to cooperate with a project owner. Theories of risk allocation and trust were used to motivate the research. Using a survey methodology, we collected data concerning 124 construction projects in China. We found that risk allocation influenced the contractor’s role behavior through the contractor’s feeling of being trusted but not the contractor’s trust in the owner. Feeling of being trusted partially mediated the effect of risk allocation on the contractor’s in-role (i.e., contractual) behavior and fully mediated the effect on extra-role behavior. The study introduces a social and psychological view of the impacts of risk allocation to the project and engineering management literature. We contribute to theory by arguing and demonstrating the mediating effect of trust on the relationship between risk allocation and contractor behavior. From a practical standpoint, we conclude that contractual risk allocation has a significant impact on building a trusting relationship between owners and contractors and that contractors who feel trusted perform both contractually mandated actions and actions external to the contract more diligently, resulting in the likelihood of improved outcomes for both parties.     

Acquisition and pattern recognition of spectrum information of welding metal transfer

With the creation of a pattern recognition system for metal transfer mode, this article has collected five kinds of spectrum signals in gas metal arc welding (MIG, MAG and CO₂) and take them as training samples. These samples have been pretreated by computer, several key characteristic parameters of the spectrum signal have been creatively extracted, and a corresponding recognition function and a minimum-distance-classifier have been constructed. The results show that the pattern recognition of several kinds of metal transfer modes for the metal gas arc welding can be done successfully, and relative important parameters in welding process, such as the frequency of droplet transfer and the approximate diameter of each droplet, can also be obtained.     

轻便型γ能谱测井仪几个关键技术问题的探讨

为研制性能好，功能强，微机化学程度高的轻便型γ能谱测井仪，针对非油气测井工作的井口径小（〈φ６０ｍｍ）井身浅（〈１０００ｍ）等特点，探讨了γ能谱测井仪的轻便化，测量精度，信号传输技术，稳谱技术及微机化等关键技术问题。     

δ掺杂样品中空穴态的新行为

用有效质量理论研究了δ掺杂势中电子和空穴的行为。发现能量接近于δ势垒峰的空穴穿越势垒时能产生一系列谐振态。这些状态中的空穴波函数汇聚在势垒峰周围而同量子限制在势阱中的电子波函数交叠,产生光跃迁。用MBE生长的δ掺杂样品进行光调制光谱测量,发现明显的带间跃迁峰。测得的光谱峰同理论计算的能级相吻合,证实了δ势垒中空穴的新行为。     

一种连续波多站发射机及频谱分析

介绍了一种连续波多站发射机的新方案，从理论上对该机的发射频谱进行了分析，并与实际结果进行比较。理论和实际都证明该方案具有很好的交调抑制、谐波抑制和杂波抑制、相噪低等诸多优点。     

基于晶体双折射的光学FIR滤波器设计

提出建立在晶体双折射基础上，由晶体延迟片堆组成的光学FIR（Finite Impulse Response)滤波器设计方法，用以实现任意形状光谱输出。从FIR信号理论出发，建立了光学FIR滤波器数学模型，并分析了它与FIR滤波器的映射关系。在给出“输出反向传递法”来完成其光学实现同时，还以G／M滤波器设计实例证明其优良的光谱特性及角度特性。     

ST-102C式NaI(Tl)晶体中KX射线逃逸率的计算

本文对ST-102C式NaI(Tl)晶体中碘原子K层X射线的五种主要成分K_(α1)、K_(α2)、K_(β1)、K_(β2)和 K_(β3)的逃逸率分别进行了计算,然后根据五种 X 射线的相对强度进一步计算了加权平均逃逸率。计算中所选用的初始入射 X 射线能量在33.5—1000keV 之间。     

UO_2(HCOO)_2·H_2O在290K-10K的红外光谱及~(235)U-~(238)U同位素位移的研究

本文通过测定甲酸铀酰[UO_2(HCOO)_2·H_2O]在290K-10K的红外光谱,确定了该化合物铀酰基团(O-U-O)v_(as)振动峰位,研究了温度对峰宽、峰位的影响,并采用差减及峰内标法估算了甲酸铀酰在290K-10K的同位素位移值。测得290K,77K及10K时~(238)U的v_(as)值分别为931.90cm~(-1),930.82cm~(-1)和930.74cm~(-1),~(235)U-~(238)U同位素位移△v分别为0.63cm~(-1),0.67±0.18cm~(-1)和0.71±0.21cm~(-1),位移值与理论计算值接近。     

日本移动通信频率选择技术动向

本文介绍日本在移动通信中频率选择的技术动向以及开展移动通信频率资源的几项措施。