Temporal aggregation and spurious instantaneous causality in multiple time series models

Large aggregation interval asymptotics are used to investigate the relation between Granger causality in disaggregated vector autoregressions (VARs) and associated contemporaneous correlation among innovations of the aggregated system. One of our main contributions is that we outline various conditions under which the informational content of error covariance matrices yields insight into the causal structure of the VAR. Monte Carlo results suggest that our asymptotic findings are applicable even when the aggregation interval is small, as long as the time series are not characterized by high levels of persistence.     

多种以太网交换机仿真教学系统的硬件设计与实现

在高等教育学校中,为了更好地培养IT专业学生的理论结合实际的能力,大多数学校都在寻找适合自身实验室条件和师资力量的实验设备,而以太网交换机实践教学作为计算机网络教学中的重要组成部分,也存在着这种需求.为了满足某高校计算机网络实验室对以太网交换机的市场需求,设计了一款多种以太网交换机仿真教学系统.综合考虑以太网交换机的发展现状和趋势,分析系统的功能需求和可行性后,采用了硬件层、驱动层和软件应用层三级体系结构,使用软硬件结合的方法进行实现.使用Realtek公司的以太网控制器RTL8309SC和德州仪器TI公司的MSP430F149单片机成功搭建了一个具有标准接口的硬件支持平台,实现了系统的硬件层和驱动层.该硬件支持平台可以为使用者搭建一个性价比较高的真实网络环境,由于是自主研发,所以可以更灵活地实现以太网交换机硬件相关实验,具有较强的实用价值.     

反拱法碳纤维加固RC梁的数值模拟分析

采用动力设备将钢筋混凝土梁向上反拱一定的弧度,然后在梁的下部外贴碳纤维布（CFRP）,待碳纤维布养护完全后,卸载,此时后加的碳纤维布与原钢筋混凝土梁同时进入工作状态。作者采用分析软件ANSYS模拟此过程,通过与直接用碳纤维布加固RC梁进行比较,得出反拱法加固RC梁能有效提高其承载能力,对类似工程具有一定的借鉴意义。     

基于单片机线性F/V转换系统的设计与实现

研究了一种线性F∕V转换系统。利用单片机来检测正弦波的频率,根据检测的频率确定D/A转换的数字量,控制TLC5615串行D/A芯片将频率信号转变为电压信号,使输出电压与频率大小呈线性关系,而且它们的线性关系是不经过原点的直线,而现有的F/V转换的器件都不能满足这种要求。     

基于GSM/GPRS的直流电机远程控制系统

给出了基于GSM/GPRS的直流电机远程控制系统的设计方案。在该方案中,C8051F330单片机产生PWM波形和开关量信号控制直流电机驱动模块L298N最终实现对直流电机的转速控制(由PWM的占空比决定)和正反转控制(由开关量信号决定),同时C8051F330单片机与GPRS模块MC55之间通过串口实现双向通信,因此,MC55在收到用户从远端发送来的"命令"(即短消息)后就可以通过C8051F330单片机最终实现对直流电机的控制。     

利用COSMIC电子密度数据分析全球NmF2

利用COSMIC掩星观测获得的电离层电子密度数据,对2009年不同季节的电离层F2层峰电子密度分布特征进行了研究.采用人工神经网络插值技术,以世界时、地理经度、纬度、F2层峰电子密度及地磁活动指数Kp作为人工神经网络输入层的5个神经元,以NmF2作为输出层神经元,获取全球分布的NmF2.结果显示,位于南半球的威德尔海异...     

单相交流参数测量仪设计

为了测量实验室中DC-AC逆变变频单相交流电参数,设计了基于MSP430F169单片机的单相交流参数测量仪.与采样、过零比较电路配合,利用单片机片内定时器测量频率和相位差;与采样、放大、精密整流和滤波电路配合,利用片内A/D转换器通过瞬时采样法测量电压、电流有效值并计算出视在功率、有功功率和无功功率.经原理样机验证可在LCM12864点阵显示器上显示出各参数测量值.     

Evaluation of the agronomic effectiveness of natural and partially acidulated phosphate rocks in several soils using32P isotopic dilution techniques

The agronomic effectiveness of two natural phosphate rocks (PRs) from North Carolina (USA) and Togo and their 50% partially acidulated products (PAPRs) was evaluated in two greenhouse experiments using³²P isotopic dilution techniques, namely L and A_L values.In the first experiment rye grass was grown in a soil from Ghana. While the proportion of P in the plant derived from the P fertilizer (Pdff) ranged on. the average from about 10% for the PRs up to 80% for the PAPRs, the P fertilizer recovery was less than 1% for a 60-day growth period. In the second experiment, average values of P in the maize plants derived from the PAPRs ranged from 35% to 75% in 3 different soils. Both PRs were ineffective with the exception of North Carolina PR in the Seibersdorf soil. The P fertilizer recovery was 0.25% for the North Carolina PR in this soil whereas the recovery values ranged from 1.2% to 1.6% for the PAPRs.Mean values of the relative fertilizer efficiency estimated from the L values of each soil were less than 1% for the PRs whereas the values for the PAPRs which were dependent on soil type ranged from 20% up to 45%. The coefficient of relative effect of partial acidulation, that was calculated from the ratio of A_L values for PR and PAPR in each soil indicated that partial acidulation increased the effectiveness of the natural PRs in all soils under study.This study showed that the use of³²P isotope dilution techniques allows an accurate measurement of the P availability from natural and modified PR products to crops. Another advantage is that quantitative comparison of the P sources under study, PRs and PAPRs in this case, can be made even in soils where there is no response to the applied P sources.     

一种户外多功能定位与测量装置的设计实现

本设计是针对在户外登山、旅行、勘测过程中常常既需要定位系统,又需要温度、高度、气压、湿度等参数测量系统的情况下,设计的一种多功能便携式测量工具。本系统采用STM32作为控制器,移植了μC/OS实时操作系统,驱动GPS模块和各种传感器模块,实现了数据的实时采集显示。本系统采用了0.96’OLED作为显示单元,STM32引入了低功耗模式,锂电池供电,提升了系统的便携性和低功耗。     

The kinetics of hydrogen transport through amorphous Pd82−yNiySi18 alloys (y=0-32) by analysis of anodic current transient

Hydrogen transport through amorphous Pd_82−yNi_ySi₁₈ alloys (y=0-32) was investigated in 0.1 M NaOH solution by analysis of the anodic current transient. It was found that the anodic current transient shows the non-Cottrell behaviour, but its shape and value remain nearly constant regardless of the hydrogen discharging potential. From the coincidence of the anodic current transient theoretically calculated with that experimentally measured, it is suggested that the change in surface concentration of hydrogen with time is uniquely given by the rate of hydrogen transfer from absorbed state at the electrode sub-surface to adsorbed state on the electrode surface. This means that neither the ‘constraint of constant concentration’ nor the ‘constraint by Butler-Volmer behaviour’ is effective at the electrode surface during hydrogen extraction. On the basis of the theoretical current-time relation under the ‘constraint by hydrogen transfer of absorbed state to adsorbed state’, the hydrogen diffusivity was determined to have an almost constant value of (1.3±0.4)×10⁻⁸ cm² s⁻¹, irrespective of the Ni content and in the absence of Ni. On the other hand, it is inferred that the rate constant of hydrogen transfer decreases markedly with increasing Ni content due to the Ni(OH)₂ layer formed on the electrode surface.