利用ACE值构造QC-LDPC码

为进一步提升中短码长下准循环低密度奇偶校验(Quasi-cyclic Low-density Parity-check,QC-LDPC) 码的纠错性能,提出了一种综合短环数目和环连通性的QC-LDPC码构造方法。首先,采用Golomb规则构造QC-LDPC码,对基矩阵中的部分元素进行替换预处理,初步降低短环数目;其次,采用所提的利用近似环外信息度（Approximate Cycle Extrinsic message degree,ACE）的消环掩模算法来优化QC-LDPC码,使得掩模后的校验矩阵具有较大的ACE平均值,最终完成QC-LDPC码的构造。该构造方法简单、通用性强,在短环数目和连通性间进行了平衡。与只考虑减少短环数目、增大围长等方法相比,该方法构造的QC-LDPC码有更加优异的纠错性能。     

公众预期、货币政策与宏观经济波动——基于Agent新凯恩斯模型的经验研究

本文将ACE建模思想纳入到新凯恩斯理论框架,构建基于Agent的新凯恩斯模型,并利用拓展后的模型研究货币政策对宏观经济波动的影响。研究结果显示,我国经济中存在25%的家户是完全理性,存在73%的厂商是有限理性;产出与通货膨胀对货币政策冲击的反应较传统新凯恩模型平缓,并且持续时间更长;货币政策冲击是通货膨胀波动的主要来源,真实货币余额的偏好冲击可以解释大部分的产出波动。因此,在考虑了有限理性以及适应性预期后,经济的内在传导机制发生了变化,理解公众预期形式对分析宏观政策的经济影响至关重要。     

向量分整序列非线性变换的研究

自Granger提出整数阶单整向量序列的协整概念以来,协整理论在国内外学者的共同努力下不断得到完善。关于向量时间序列的分数维单整的研究主要集中在分整的线性协整的存在性条件及性质研究。文中通过引入交换条件数学期望算法(ACE),研究分整时间序列的非线性变换的协整性,对最优非线性变换函数进行估计。     

Tourism Sustainability and Health Impacts in High Altitude Adventure,Cultural and Ecotourism Destinations: A Case Study of Nepal's Sagarmatha National Park

Sagarmatha National Park (SNP) is an ACE (adventure, cultural and ecotourism) high altitude destination. Many researchers argue that tourism development in the region is not sustainable and does not comply with ecotourism concepts. They report that SNP suffers considerable environmental, sociocultural and economic impacts. Health issues, despite the number of ailments commonly experienced by tourists, remain neglected in tourism literature. This study aims to investigate the health consequences of visiting SNP. Seven hundred and fifty questionnaires were given out during three separate seasons in 1999, of which 448 completed usable questionnaires were returned giving a 59.7% response rate. The results showthat despite good travel preparation, the majority of tourists (89.4%) suffer some form of health ailment. The most common ailments are mountain sickness, musculoskeletal pain, diarrhoea and respiratory infection. The study also shows several significant relationships between the incidence of health ailments and demographic profiles, motivation and satisfaction. It proposes that for high altitude ACE destinations like SNP, health issues should be a core component of destination management in order to ensure the sustainability of tourism development. High risk groups should be identified and tourism education should be targeted to both tourists and locals.     

A non-parametric analysis of ERM exchange rate fundamentals

In this paper we present evidence concerning the number of common stochastic trends in three major ERM exchange rates. The results indicate the presence of a single common trend driving these currencies and from this we suggest that the common trend can be considered as the non-parametric fundamentals for the three selected currencies. Using a non-parametric technique, the Alternating Conditional Expectations (ACE) algorithm, we obtain evidence for the existence of non-linearities for two out of three currencies with a functional form, related to the estimated non-parametric fundamentals, close to the S-shape given by the basic target zone model.      

Explaining rural land use change and reforestation: A causal-historical approach

Research on human-environment interactions is bedeviled by two key analytical challenges: integrating natural and social science information and demonstrating causal connections between proximate and distant influences. These challenges can be met by adopting an event-focused, causal-historical approach to research methodology, referred to here as Abductive Causal Eventism (ACE). With ACE, researchers construct causal histories of interrelated social and/or biophysical events backward in time and outward or inward in space through a process of eliminative inference and reasoning from effects to causes, called abduction. ACE is contrasted with three leading approaches to human-environment research: Land Change Science (LCS), Socio-ecological Systems (SES), and Political Ecology (PE). For illustration, ACE is applied to a study of post-War environmental change in two rural watersheds in Saint Lucia, West Indies. Findings reveal that the most consequential change has been the widespread reforestation of lands abandoned from farming. This change occurred irrespective of the type of land tenure, but was especially commonplace on lands with steeper slopes and further from roads. Reforestation during the 1960s and 1970s was caused by a combination of commodity market challenges, abandonment of subsistence cultivation in response to smaller family sizes, and sizable out-migrations of younger adults overseas. The expansion of banana cultivation in the 1960s and then again in the 1980s slowed and in places reversed this trend. But an especially large wave of farmland abandonment swept the island from the mid-1990s to early-2000s because the banana export market collapsed as a result of preferential market access being eroded by a series of WTO trade rulings. These effects have been reinforced by a surge in investment from return migrants and the tourism industry which has drawn labour out of farming while also creating economic incentive and political support for protecting more forests on both private estates and public lands. Yet, the post-War trend in reforestation may have ended as agriculture displays signs of rebounding and residential and tourism development expands unabated into the countryside. This study demonstrates the advantages of using ACE where explanations entail diverse types of causes operating across space and over time.     

一种新颖的低错误平层LDPC码构造方法

针对低密度奇偶校验(LDPC)码在高信噪比区域可能存在错误平层的缺点,提出了一种低错误平层LDPC码的新构造方法。该方法的基本矩阵由渐进边增长(PEG)算法与近似环额外信息度(ACE)算法相结合,目的是提升基本矩阵中环的连通性;然后将基于分割移位(PS)的循环移位系数矩阵对基本矩阵循环扩展,以此构造出校验矩阵。该方法除了能够改善高信噪比区域的错误平层,还具有码长、码率的任意可设性特点。仿真结果表明,PAP-LDPC(3 600,2 700)码在信噪比为4 dB以后并未出现明显的错误平层。