基于德兴铜矿变频调速系统的节能分析

本文从矿山企业实际应用出发,充分分析了大型设备负载的共性问题,通过仿真得出相关机械设备的节能减耗的最佳方法。并将该方法应用于异步电动机的工作方案中,经过实际运行的检验,此类方法及方案能有效地降低企业的能耗,提高能源的利用率。     

Implications of market microstructure for realized variance measurement

Volatility measuring and estimation based on intra-day high-frequency data has grown in popularity during the last few years. A significant part of the research uses volatility and variance measures based on the sum of squared high-frequency returns. These volatility measures, introduced and mathematically justified in a series of papers by Andersen et al. [1999. (Understanding, optimizing, using and forecasting) realized volatility and correlation. Leonard N. Stern School Finance Department Working Paper Series, 99-061, New York University; 2000a. The distribution of realized exchange rate volatility. Journal of the American Statistical Association 96, no. 453: 42–55; 2000b. Exchange rate returns standardized by realized volatility are (nearly) Gaussian. Multinational Finance Journal 4, no. 3/4: 159–179; 2003. Modeling and forecasting realized volatility. NBER Working Paper Series 8160.] and Andersen et al. 2001a. Modeling and forecasting realized volatility. NBER Working Paper Series 8160., are referred to as ‘realized variance’. From the theory of quadratic variations of diffusions, it is possible to show that realized variance measures, based on sufficiently frequently sampled returns, are error-free volatility estimates. Our objective here is to examine realized variance measures, where well-documented market microstructure effects, such as return autocorrelation and volatility clustering, are included in the return generating process. Our findings are that the use of squared returns as a measure for realized variance will lead to estimation errors on sampling frequencies adopted in the literature. In the case of return autocorrelation, there will be systematic biases. Further, we establish increased standard deviation in the error between measured and real variance as sampling frequency decreases and when volatility is non-constant.     

Computing optimal rebalance frequency for log-optimal portfolios in linear time

The pure form of log-optimal investment strategies are often considered to be impractical due to the inherent need for continuous rebalancing. It is however possible to improve investor log utility by adopting a discrete-time periodic rebalancing strategy. Under the assumptions of geometric Brownian motion for assets and approximate log-normality for a sum of log-normal random variables, we find that the optimum rebalance frequency is a piecewise continuous function of investment horizon. One can construct this rebalance strategy function, called the optimal rebalance frequency function, up to a specified investment horizon given a limited trajectory of the expected log of portfolio growth when the initial portfolio is never rebalanced. We develop the analytical framework to compute the optimal rebalance strategy in linear time, a significant improvement from the previously proposed search-based quadratic time algorithm.     

Portfolio selection with higher moments

We propose a method for optimal portfolio selection using a Bayesian decision theoretic framework that addresses two major shortcomings of the traditional Markowitz approach: the ability to handle higher moments and parameter uncertainty. We employ the skew normal distribution which has many attractive features for modeling multivariate returns. Our results suggest that it is important to incorporate higher order moments in portfolio selection. Further, our comparison to other methods where parameter uncertainty is either ignored or accommodated in an ad hoc way, shows that our approach leads to higher expected utility than competing methods, such as the resampling methods that are common in the practice of finance.     

Optimal payoffs under state-dependent preferences

Most decision theories, including expected utility theory, rank-dependent utility theory and cumulative prospect theory, assume that investors are only interested in the distribution of returns and not in the states of the economy in which income is received. Optimal payoffs have their lowest outcomes when the economy is in a downturn, and this feature is often at odds with the needs of many investors. We introduce a framework for portfolio selection within which state-dependent preferences can be accommodated. Specifically, we assume that investors care about the distribution of final wealth and its interaction with some benchmark. In this context, we are able to characterize optimal payoffs in explicit form. Furthermore, we extend the classical expected utility optimization problem of Merton to the state-dependent situation. Some applications in security design are discussed in detail and we also solve some stochastic extensions of the target probability optimization problem.     

大动态下扩频码捕获的一种改进方法

针对现有扩频码捕获方法在大动态下捕获时间长、硬件资源消耗大、动态适应性差的 问题,提出了一种改进的扩频码捕获方法。新方法把码钟多普勒的补偿放在本地扩频码上进 行,先对接收信号进行降采样和存储再进行频率分槽和补偿,一次采样实现了所有频率槽的 搜索。计算结果表明,完成同样的捕获过程新方法所需时间和存储器容量不到原方法的1/5 ,且具备更强的动态适应能力。     

综合模块化浮空器中继系统设计

通过剖析浮空器自身优点,结合它在通信中继应用领域的优势及研究情况,对比传 统的通信中继系统,提出一种浮空器中继系统设计架构。其硬件采用综合模块化设计,软件 采用分层设计。对设计中所需解决的关键技术进行了可行性分析,同时,展望了其未来在提 升空中平台通信中继能力方面的应用。     

The Deaton paradox in a long memory context with structural breaks

This article contributes to the Permanent Income Hypothesis (PIH) and excess consumption smoothness debate in the context of fractional integration. We show that the excess consumption smoothness result is a consequence of the quarterly data frequency commonly employed in the empirical work. In fact, the I(1) hypothesis is rejected for the income process with monthly data in favour of a fractional integration order lower than 1. Moreover, if a structural break is taken into account, we observe a substantial reduction in the degree of consumption smoothness, especially after the break found in 1975.     

Incorporating daily market uncertainty data into a conventional short-run dynamic model: the case of the black-market exchange rate in Iran

The effect of market uncertainty on a country’s currency, while widely recognized, is either omitted from mainstream models or addressed using low-frequency series, which are typically subject to aggregation bias and substantial lags. In this article, we propose a new mixed-data sampling (MIDAS) modelling framework that enables us to incorporate the asymmetric daily effects of market uncertainty in a conventional monthly error correction model. We achieve this by proxying market uncertainty via the value of a ‘safe haven’ asset (gold) that investors reallocate towards in the face of heightened market risk. We apply the model to the Iranian black-market exchange rate, using a mix of the daily price of gold (28 June 2010–19 August 2018) and monthly data (July 2010-July 2018) on relative prices. Our results indicate that purchasing power parity (PPP) holds despite the recent unprecedented depreciations in the Iranian currency arising from several rounds of international sanctions. We also find that increased uncertainty can lead to instantaneous and substantial depreciations, whereas stabilization back towards the PPP path is much more sluggish.     

Do Sales of Foreign Exchange Reserves Lead to Currency Appreciation?

We employ novel time‐stamped reserve sales data, provided by the Czech National Bank (CNB), to carry out a time‐series analysis of the exchange rate implications of Czech reserve sales aimed at mitigating valuation losses on Euro‐denominated assets. The sales were explicitly not intended to influence the value of the koruna relative to the euro. The period under study includes a well‐defined regime change in the CNB's approach to reserves sales, allowing us to address whether the manner in which the sales are carried out matters for their influence on the relative value of the domestic currency. We find little evidence that reserve sales influence the exchange rate when sales are carried out on a discretionary and relatively infrequent basis. However, when the sales are carried out daily, we find a statistically and economically significant appreciation of the domestic currency follows.