采用数据辅助的大规模MIMO信道半盲迭代估计

由于大规模多输入多输出(Multiple-Input Multiple-Output,MIMO)信道衰落参数的维度较高,导致最优估计算法计算量大且需要的导频数较多而影响到频谱效率。为降低计算复杂度并减少导频开销,提出了两种基于期望最大化(Expectation Maximization,EM)估计的半盲迭代改进算法。利用少量正交导频序列估计出信道初值,通过用户与基站间信道的大尺度衰落系数把用户分簇,根据这些系数按比例地分配接收噪声,再利用数据的统计特性推导出信道衰落参数的均值和方差。仿真结果表明,当导频数远少于待估计参数的个数时,半盲估计算法的均方误差(Mean Square Error,MSE)优于导频估计的极大似然(Maximum likelihood,ML)算法。     

Do Investors Care about the Auditor's Economic Dependence on the Client?*

In this study, we investigate whether investor perceptions of the financial reporting credibility of Big 5 audits are related to the auditor's economic dependence on the client as measured by nonaudit as well as total (audit and nonaudit) fees paid to the incumbent auditor. We use the client‐specific ex ante cost of equity capital as a proxy for investor perceptions of financial reporting credibility and examine auditor fees both as a proportion of the revenues of the audit firm and as a proportion of the revenues of the audit firm's practice office through which the audit was conducted. Our findings suggest that both nonaudit and total fees are perceived negatively by investors' that is, the higher the fees paid to the auditor, the greater the implied threat to auditor independence, and the lower the financial reporting credibility of a Big 5 audit. Furthermore, our findings appear to be largely unrelated to corporate governance: investors do not perceive the auditor as compensating for weak governance. Separately, recent anecdotal evidence suggests that declining revenues from nonaudit services' as a result of recent regulatory restrictions” are being offset by substantial increases in audit fees. Other things being equal, rising audit fees imply higher profit margins for audit services, indicating that the audit function may no longer be a loss leader. Thus, to the extent that investors perceive total fees negatively, recent regulatory initiatives to limit nonaudit fees may not have adequately addressed the perceived, if not the actual, threat to auditor independence posed by fees.     

示波极谱法测定中草药中痕量钴的研究

钴(Ⅱ)与3-噻唑偶氮-5-氨基苯酚在pH值为8.0的硼砂-盐酸缓冲溶液中的反应有一灵敏的极谱络合吸附波,其峰电位在-0.74V左右,钴质量浓度在 0.001～1.4μg·mL-1范围内与二次导数峰电流呈线性关系,检出限为0.0005μg·mL-1。对电极反应机理进行了探讨,所拟方法适用于中草药中钴含量的测定。     

面向双智城市基础设施建设的标准化设计探讨

随着智慧城市基础设施与智能网联汽车协同发展的加速推进,智慧交通、城市治理、5G通讯、无人驾驶等领域的迅猛发展,使交通路口处出现杆体林立错综复杂、箱体分散杂乱无章的现象。通过创新首个多杆合一、多感合一、多箱合一的“双智标准路口”设计方法,实现智慧城市基础设施和智能网联设备的系统化布局。该设计理念已在北京市高级别无人驾驶示范区落地实施完成,于60 km2内城市道路实现车路云一体化功能覆盖。     

基于百度指数的三亚市5A级景区网络关注度时空特征分析

网络关注度对游客的出行前兆具有预测性,能够帮助指导旅游管理部门提前预警并做出科学合理的决策与规划,助推旅游业可持续发展。以海南省龙头旅游城市三亚为研究对象,基于百度指数,通过提取三亚市3家5A级滨海型旅游景区2012—2021年百度指数日样本,并运用季节集中度指数、地域集中度指数、赫芬达尔指数、首位度指数等指标从时间分布特征、空间分布特征两个角度对三亚市5A景区网络关注特征进行研究,并对其影响因素进行剖析。研究发现：三亚5A景区近5年来的网络关注度整体呈逐年下降的趋势;三亚市5A级景区的网络关注度受季节变化较为明显,冬季、初春、暑假、国庆小长假、春节小长假是旅游的高峰期,其中2月是一年中网络关注度的峰值;节假日期间反映出网络关注度对游客出游动态具有“前置”效应,并可能存在游客“错峰”出行的现象;空间分布具有集聚性,其中以海南省内、海南省周围地区以及经济较为发达的地区对三亚市5A景区关注度较高;空间直线距离、相对湿度差、平均温度差、气候舒适度对三亚市风景区网络关注度的影响较大。     

Interest rate corridors and reserves

This paper evaluates reserves regimes versus interest rate corridors, which have become competing frameworks for monetary policy implementation. Rate corridors, relying on lending and deposit facilities to create ceilings and floors for overnight interest rates, evince mixed results on controlling volatility. Reserve requirements allow period-average smoothing of interest rates but, even if remunerated, are subject to reserve avoidance activities. A system of voluntary, period-average reserve commitments could offer equivalent rate-smoothing advantages. If central banks created symmetric opportunity costs of meeting or falling short of period-average reserve requirements (or commitments), they could achieve flat reserve demand on settlement day.     

On the robustness of simple and optimal monetary policy rules

This is a discussion of the paper “Simple versus Optimal Rules as Guides to Policy” by Brock, Durlauf, Nason and Rondina (BDNR) presented in November 2006 at Carnegie-Mellon University under the auspices of the Carnegie-Rochester Conference Series on Public Policy. I review the authors’ arguments, present a few suggestions for extension and outline where I think at least one strand of the literature should be heading.     

Foreign Aid, the Real Exchange Rate, and Economic Growth in the Aftermath of Civil Wars

Foreign aid, the real exchange rate (RER), and economic growthare three key variables that shape the aftermath of civil warsin many developing countries. Panel estimations drawn from asample of 39 conflict and 44 nonconflict countries between 1970and 2004 indicate that although postconflict countries receivelarger aid flows and exhibit moderate RER overvaluation afterpeace is attained, overvaluation cannot be traced to aid. Yetforeign aid is among the significant determinants of the equilibriumRER. Aid is also an important determinant of economic growth,particularly after peace is reached. Aid exhibits decreasingreturns, however, and interacts negatively with RER overvaluation.RER overvaluation reduces growth, but this effect is amelioratedby financial development. Postconflict policies should thereforeaim to use aid prudently, avoid RER misalignment, and supportfinancial and capital market development to achieve high andstable growth in the aftermath of war and beyond.