An improved lock detector for phase-locked communication receivers

A quadrature lock detector is incorporated in almost all coherent radio communication receivers. This commonly-used receiver subsystem is comprised of a quadrature phase detector that drives a low-pass filter, the output of which is subjected to a user-specified threshold to make a lock/unlock decision. Signal acquisition and phase lock are declared if an above threshold condition is observed. Unfortunately, this method of lock detection may yield a positive lock indication when the receiver is false locked; i.e., a classical quadrature lock detector may generate a false-positive lock indication. This tendency to produce an incorrect lock indication can be reduced significantly by using the new lock detector algorithm that is described here. Compared to the classical quadrature lock detector, the new lock detector is better able to differentiate between true phase lock and anomalous false lock. The classical quadrature lock detector is a simple, first-order approximation of the new lock detector algorithm. That is, the new lock detector algorithm consists of a classical quadrature detector that is augmented by a correction term.     

竞争情报计算机辅助系统的开发

Competitive Information System (CIS) is a computer-aided system for competitive intelligence, and is designed for the information requirements of the corporate strategic management. The development of CIS is an important part of corporate Strategic Information Planning (SIP), and CIS directly supports the strategic objects of the corporate. The life cycle of CIS includes traditional life cycle, prototyping life cycle, object-oriented life cycle and so on.     

超高挑空玻璃幕墙屋顶餐厅空调方案分析

本文对某高层建筑超高挑空的玻璃幕墙屋顶餐厅空调设计方案进行了分析。在确保餐厅使用要求的前提下,采用水环热泵空调和通风降温相结合的方式比单纯使用水环热泵,冬、夏季空调负荷均下降50％以上。屋顶餐厅通风降温设计时,需满足消防要求,防止过高的排风温度影响消防系统。     

浅析我国小孩学外语的最佳年龄

本文从二语习得的研究入手,讨论分析小孩外语学习的最合适的年龄。结合小孩学二语的优势以及关键期假说等相关理论研究以及二语学习与外语学习的特点,对我国目前的小学外语教学进行了探讨,最后提出个人的一点看法。     

“What is a good digital library?” – A quality model for digital libraries

In this article, we elaborate on the meaning of quality in digital libraries (DLs) by proposing a model that is deeply grounded in a formal framework for digital libraries: 5S (Streams, Structures, Spaces, Scenarios, and Societies). For each major DL concept in the framework we formally define a number of dimensions of quality and propose a set of numerical indicators for those quality dimensions. In particular, we consider key concepts of a minimal DL: catalog, collection, digital object, metadata specification, repository, and services. Regarding quality dimensions, we consider: accessibility, accuracy, completeness, composability, conformance, consistency, effectiveness, efficiency, extensibility, pertinence, preservability, relevance, reliability, reusability, significance, similarity, and timeliness. Regarding measurement, we consider characteristics like: response time (with regard to efficiency), cost of migration (with respect to preservability), and number of service failures (to assess reliability). For some key DL concepts, the (quality dimension, numerical indicator) pairs are illustrated through their application to a number of “real-world” digital libraries. We also discuss connections between the proposed dimensions of DL quality and an expanded version of a workshop’s consensus view of the life cycle of information in digital libraries. Such connections can be used to determine when and where quality issues can be measured, assessed, and improved – as well as how possible quality problems can be prevented, detected, and eliminated.     

Toward a systematic framework for research on dominant designs, technological innovations, and industrial change

The concept of a dominant design has taken on a quasi-paradigmatic status in analyses of the link between technological and industrial dynamics. A review of the empirical literature reveals a variety of interpretations about some aspects of the phenomenon such as its underlying causal mechanisms and its level of analysis. To stimulate further progress in empirical research on dominant designs, we advocate a standardization of terminology by conceptualizing products as complex artifacts that evolve in the form of a nested hierarchy of technology cycles. Such a nested complex system perspective provides both unambiguous definitions of dominant designs (stable core components that can be stable interfaces) and inclusion of multiple levels of analysis (system, subsystems, components). We introduce the concept of an operational principle and offer a systematic definition of core and peripheral subsystems based on the concept of pleiotropy. We also discuss how the proposed terminological standardization can stimulate cumulative research on dominant designs.