光通信中一种准循环非二进制LDPC码的新颖构造方法

在对目前普遍采用的非二进制低密度奇偶校验(NB -LDPC)码校验矩阵的准循环构造方法进行深入研究的基础上,提出了一种基于有限域的NB -LDPC码的立体构造方法,在构建基于有限域的基础矩阵后,运用立体扩展的方式构成循环 子矩阵,最终构造出具备准循环特性的非二进制校验矩阵。 通过对采用立体构造法构造的NB-LDPC码的性能仿真发现,与基于GF(2⁹)的 RS(511,5)相比,本文 构造的NB-LDPC码在误比特率(BER)为10－7时可 以增加3.3 dB的净编码增益(NCG);在BER为 10－6时,本文构造的LDPC码与采用传统准循环方式构造的二 进制LDPC码、随机构造 的二进制LDPC码、基于有限域构造的32进制准循环LDPC码和基于欧式 几何构造的64进制的循 环LDPC码比较,分别多获得了0.56、0.56、0.03dB的NCG。通过对本文 构造的NB-LDPC码性能仿真发现,这类具有高度结构化的NB-LDPC码不仅具备 准循环特性,有利于硬件实现,同时在中短码长情况时展现出较好的纠错性能。     

圭亚那乔治敦某五星级酒店暖通设计

详细介绍圭亚那乔治敦某五星级酒店空调系统在负荷计算、设备选型、空调系统自控、防排烟设计、LEED认证等设计情况。     

Use of fuzzy sets in developing code risk factors

Fuzzy set theory is used to produce risk factor values for a building code. Working through reliability indices, a transformation is developed to convert estimates of relative social importance of a building into code load factors. The importance estimates are found by surveying knowledgeable members of society or playing their roles, and by using fuzzy set theory to combine their views according to their significance. An extension, again using fuzzy set theory, brings in the use of multiple criteria on which to base judgements. An example gives risk factors close to those in an existing code.     

Performance of degree distribution based HARQ scheme for LDPC-coded OFDM system

This article studies the degree distribution property of low density parity check (LDPC) codes by Gaussian approximation (GA) and presents an efficient hybrid automatic repeat quest (HARQ) scheme for LDPC-coded orthogonal frequency division multiplexing (OFDM) system. In the scheme, the important bits with large degrees have high retransmission priorities and are mapped to the sub-carriers with better channel quality indicator (CQI) levels in the OFDM system. The new scheme provides more protection to the bits with large degrees and thus contributes more to the decoding process by offering more transmission power. In this way the system performance would be improved. The statistics and simulation results also prove the new scheme.     

Fast blind estimation algorithm for Hamming codes parameters

An algorithm is proposed for fast blindly estimating the length, the starting point and the parity-check matrix of the hamming code. First, an intercepted matrix is built by the data received, and by exploiting an assumed number of parity-check digits and the assumed starting point of the hamming code. Then, a parity-check matrix is obtained by the assumed primitive polynomial, and when all its row-vectors are dual codes of the intercepted matrix, the hamming code parameters could be estimated. Moreover, a theoretical analysis of the proposed algorithm is made. Simulation results verify the good performance of the proposed method.     

Durability of welded aluminium extrusion profiles and aluminium sheets in vehicle structures

Different approaches - the nominal stress, structural hot spot stress and notch stress approach - to analyse the fatigue strength of welded structures made from wrought aluminium alloys were studied. Experimental and numerical investigation was carried out for this purpose on detail specimens and components. The results shown here were generated during the research project “Extrusion profile and sheet metal structures of wrought aluminium alloys in vehicle construction” [1].The studies show that due to the existing guidelines, welds on structures made from aluminium alloys are sometimes designed very conservatively. It is possible to optimise and reliably design welded joints of thin sheet structures by applying the notch stress approach using the reference radius r_ref = 0.05 mm and the reference SN curves derived here.     

Life cycle cost and energy analysis of a Net Zero Energy House with solar combisystem

The Net Zero Energy House (NZEH) presented in this paper is an energy efficient house that uses available solar technologies to generate at least as much primary energy as the house uses over the course of the year. The computer simulation results show that it is technically feasible to reach the goal of NZEH in the cold climate of Montreal. In terms of the life cycle energy use, which considers the operating and embodied energy of the house, the energy payback time is 8.4–8.7 years, when the NZEH is compared with an average house that complies with the provincial code. The energy payback ratio of the combisystem is 3.5–3.8 compared with the heating system of conventional house. By converting solar energy, the combisystem supplies at least 3.5 times more energy than the energy invested for manufacturing and shipping the system. The life cycle cost analysis of the NZEH shows, however, that due to the high cost of the solar technologies and the low cost of electricity in Montreal, financial payback is never achieved.     

Online error correcting output codes

This article proposes a general extension of the error correcting output codes framework to the online learning scenario. As a result, the final classifier handles the addition of new classes independently of the base classifier used. In particular, this extension supports the use of both online example incremental and batch classifiers as base learners. The extension of the traditional problem independent codings one-versus-all and one-versus-one is introduced. Furthermore, two new codings are proposed, unbalanced online ECOC and a problem dependent online ECOC. This last online coding technique takes advantage of the problem data for minimizing the number of dichotomizers used in the ECOC framework while preserving a high accuracy. These techniques are validated on an online setting of 11 data sets from UCI database and applied to two real machine vision applications: traffic sign recognition and face recognition. As a result, the online ECOC techniques proposed provide a feasible and robust way for handling new classes using any base classifier.     

水平散射几何中子反射谱仪的三盘斩波器设计

为提高水平散射几何中子反射谱仪分辨,希望谱仪前端的中子斩波器能斩出脉冲强度大水平发散度较小的中子脉冲束流,采用新设计的三斩盘斩波器模型,运用Mcstas程序软件考察了不同物理参数下三盘斩波器的中子斩波特性.获得了特定物理条件下相关物理参数对束流强度和发散度的影响关系曲线.计算结果可为水平散射几何中子反射谱仪中三盘斩波器的设计及物理参数的选择提供理论依据.     

Risk-informed separation distances for hydrogen refueling stations

As part of the US Department of Energy Hydrogen, Fuel Cells & Infrastructure Technologies Program, Sandia National Laboratories is developing the technical basis for assessing the safety of hydrogen-based systems for use in the development/modification of relevant codes and standards. This work includes quantitative risk assessments (QRA) of hydrogen facilities. The QRAs are used to identify and quantify scenarios for the unintended release of hydrogen and thus help identify the code requirements that would reduce the risk at hydrogen facilities to acceptable levels.