Do market-concentrated airports propagate more delays than less concentrated ones? A case study of selected U.S. airports

Airport congestion and widespread passenger discontent with airlines' poor on-time performance have recently led the Federal government to reduce peak-time operations at large airports such as Chicago O'Hare and New York John F. Kennedy. This paper proposes a methodology to compute delay propagation based on the discrete Fourier transform (DFT) at a sample of ten U.S. airports in summer 2000, 2007 and 2008. The sampled airports are different in terms of size, location and index of concentration.In this research, a flight is considered to be late if it arrives more than fifteen minutes past its schedule. Delay propagation is defined as the hourly ratio of two amplitudes: the one of late arrivals at a sampled airport to that of late arrivals at the final destinations served from that same sampled airport. The purpose of this study is to determine whether delay propagation differs at market-concentrated airports from less concentrated ones. Based on nonparametric tests and proximity analysis, there is no clear evidence that market-concentrated airports are different from less concentrated ones in terms of propagated delays.     

一种新的频率规划方法

本文针对目前频率规划中存在的问题，提出了利用专家系统和改进遗传算法及分层技术等来克服手工频率规划过于烦琐和电子地图要求极高及频带紧张的障碍，从而在缺少准确电子地图的情况下，借助专家的经验和知识同时利用改进的优化算法亦能给出较准确的频率规划方案。同时提出了改进的模糊似然推理方法。此外我们开发了智能多层频率规划ＣＡＤ软件包，并给出仿真结果。     

Some empirical evidence on the ‘discouraged worker’ effect

This note produces empirical evidence on the existence of a significant ‘discouraged worker’ effect in US data–namely, on the tendency for groups of secondary workers to move in and out of the labor force with the business cycle, looking for jobs when these are available, while giving up job search during recessions — by focusing on the behavior of the ‘not in the labor force’ series, as well as of two of its segments (‘going to school’, and ‘keeping house’), at the business-cycle frequencies. Both in the aggregate, and for a number of age–sex groups, the series display a clear counter-cyclical pattern, thus lending support to the discouraged worker notion.     

Bayesian Premium Rating with Latent Structure

We propose a fully Bayesian approach to non-life risk premium rating, based on hierarchical models with latent variables for both claim frequency and claim size. Inference is based on the joint posterior distribution and is performed by Markov Chain Monte Carlo. Rather than plug-in point estimates of all unknown parameters, we take into account all sources of uncertainty simultaneously when the model is used to predict claims and estimate risk premiums. Several models are fitted to both a simulated dataset and a small portfolio regarding theft from cars. We show that interaction among latent variables can improve predictions significantly. We also investigate when interaction is not necessary. We compare our results with those obtained under a standard generalized linear model and show through numerical simulation that geographically located and spatially interacting latent variables can successfully compensate for missing covariates. However, when applied to the real portfolio data, the proposed models are not better than standard models due to the lack of spatial structure in the data.     

FRID技术在物流仓储管理中的应用

物流业发展迅速,采用自动化技术来提高效率,但有很多工作仍需要人工完成,容易出错。而无线射频识别技术(RFID)在仓库中作为信息传递的载体,可以有效避免人工输入可能出现的失误,大大提高工作效率。利用RFID无限射频技术并结合ABC库存管理法对货物的入库、出库、盘点进行自动化管理,实现仓储的自动化管理。     

FDD LTE上行系统的频偏估计方案及实现

针对LTE系统对频偏十分敏感这一缺点,根据同一子载波在不同时刻由于频偏的存在导致相位偏转不同的特点,本文详细推导了一种基于导频的小数部分的频偏估计方案。通过仿真验证了此频偏估计方案在瑞利多径衰落信道下能实现较精确的频率跟踪。将此方案经优化移植到DSP平台上,通过测试,验证了在实际系统中同样能对子载波的频偏做出精确的估计,且能满足系统性能需求。     

利用MATLAB GUI实现空间滤波的实验仿真

利用阿贝成像原理和空间滤波系统,从改变频谱入手改造一副光学图像,进行光学信息处理。在此基础上,利用MATLAB图形用户界面建立了空间滤波实验的物理模型并进行了仿真模拟,从而实现了数字图像的处理。     

一种信号个数估计方法及其在测频中的应用

本文介绍一种高精度的数字测频算法———根MUSIC算法。通过分析发现,该算法在低信噪比(0 dB)的情况下,仍能得到高精度的频率估计值,其频率分辨率也比DFT高。然而,在电子侦察中要应用该方法进行测频,关键是首先要确定接收信号的个数。根据协方差矩阵特征值的大小分布特点,本文提出了差分中值法来确定信号个数,该方法的性能优于MDL准则。计算机仿真验证了该方法的可行性和稳健性。     

高斯噪声下差分跳频信号的高分辨率频率检测

差分跳频(DFH)是一种新的高速短波通信体制,它利用相邻跳变频率的变化而不是载频本身来携带信息。跳变频率检测是实现DFH的关键技术之一。本文利用四阶累积量研究了(色)高斯噪声下基于ARMA建模法的DFH信号频率检测,并针对由于模型阶数估计过高而产生的虚检频率,提出一种充分利用信号先验信息的改进算法。仿真结果证明了该方法的有效性,尤其是在低信噪比时仍然能够实现精确检测。     

Reconsidering the macroeconomics of the oil price in Germany: testing for causality in the frequency domain

This paper reconsiders the macroeconomics of the oil price for Germany. It investigates whether causality between the oil price and a selection of both macroeconomic and financial market variables differs between frequency bands. Both a bivariate frequency-wise causality measure and its higher-dimensional extension are applied. The main findings are that short-run causality exists between the oil price and variables such as short-term interest rates and the German share price index, while long-run causality is found between the oil price and long-term interest rates. Moreover, the oil price predicts the consumer price index at a high number of different frequencies, while no significant causality is found to run from the oil price to industrial production and the unemployment rate.