Phenological studies of selected savanna mosses of south-western Nigeria

It was established that there is little diversity of bryophytes in the derived savanna. Mosses were found in the sampling sites, whereas liverworts were rarely observed. The reproductive methods of four dominant sexually reproducing savanna mosses —Archidium ohioense, Bryum coronatum, Fissidens minutifolius andTrachycarpidium tisserantii were monitored over two consecutive rainy seasons. Protonemal and gametophyte production were noticed in the field in March/April, and capsule dehiscence and spore dispersal occurred in September/October. The sequential stages of development, starting with gametangial production and ending with the falling of the dehisced capsules, occurred within the rainy season. However,A. ohioense andT. tisserantii did not discharge their spores easily (cleistocarpous), unlike the stegocarpous speciesB. coronatum andF. minutifolius. Water availability and possibly high humidity may have contributed to growth. The short period between sex organ formation and dehiscence of capsule seen in these studies, compared with the longer period in some temperate mosses, may be an advantage for bryophytes in a savanna environment.     

架线式电机车安全制动距离的能量观

采用7t,10t架线式电机车和1t,3t矿车进行列车车组计算,讨论了安全制动距离对列车组成和运输能耗的影响。     

A ground‐level ozone forecasting model for Santiago,Chile

A physically based model for ground‐level ozone forecasting is evaluated for Santiago, Chile. The model predicts the daily peak ozone concentration, with the daily rise of air temperature as input variable; weekends and rainy days appear as interventions. This model was used to analyse historical data, using the Linear Transfer Function/Finite Impulse Response (LTF/FIR) formalism; the Simultaneous Transfer Function (STF) method was used to analyse several monitoring stations together. Model evaluation showed a good forecasting performance across stations—for low and high ozone impacts—with power of detection (POD) values between 70 and 100%, Heidke's Skill Scores between 40% and 70% and low false alarm rates (FAR). The model consistently outperforms a pure persistence forecast. Model performance was not sensitive to different implementation options. The model performance degrades for two‐ and three‐days ahead forecast, but is still acceptable for the purpose of developing an environmental warning system at Santiago. Copyright © 2002 John Wiley & Sons, Ltd.     

用边界元法分析试样宽度对非织造土工织物拉伸性能的影响

用边界元法从理论上分析非织造土工织物的拉伸性能。理论分析和试验表明：非织造土工织物的断裂强度随试样宽度的增加而增大。由于试样的不均匀性等原因，理论值一般高于试验值。通过回归分析得出非织遣土工织物试样宽度与断裂强度呈幂函数关系。     

Time‐simultaneous prediction band for a time series

I propose principles and methods for the construction of a time‐simultaneous prediction band for a univariate time series. The methods are entirely based on a learning sample of time trajectories, and make no parametric assumption about its distribution. Hence, the methods are general and widely applicable. The expected coverage probability of a band can be estimated by a bootstrap procedure. The estimate is likely to be less than the nominal level. Expected lack of coverage can be compensated for by increasing the coverage in the learning sample. Applications to simulated and empirical data illustrate the methods. Copyright © 2007 John Wiley & Sons, Ltd.     

Forecasting volatility by means of threshold models

The aim of this paper is to compare the forecasting performance of competing threshold models, in order to capture the asymmetric effect in the volatility. We focus on examining the relative out‐of‐sample forecasting ability of the SETAR‐Threshold GARCH (SETAR‐TGARCH) and the SETAR‐Threshold Stochastic Volatility (SETAR‐THSV) models compared to the GARCH model and Stochastic Volatility (SV) model. However, the main problem in evaluating the predictive ability of volatility models is that the ‘true’ underlying volatility process is not observable and thus a proxy must be defined for the unobservable volatility. For the class of nonlinear state space models (SETAR‐THSV and SV), a modified version of the SIR algorithm has been used to estimate the unknown parameters. The forecasting performance of competing models has been compared for two return time series: IBEX 35 and S&P 500. We explore whether the increase in the complexity of the model implies that its forecasting ability improves. Copyright © 2007 John Wiley & Sons, Ltd.     

Study on the Predicting System of Breaking Chip When PCD Tool Cutting Aluminum Alloy

In the field of automobile manufacture, during the aluminum alloy cutting, chip forming and breaking process are very complicated. It is affected by many facto rs. Automatic machining process can not be carried through if the chip enlaces t he workpiece or the tool. So the chip control and breaking are key technology. P CD tool has many traits, such as high cutting efficiency, machining precision an d wearability. It is desired that it be used for machining coloured metals.The p aper present the study of p...     

Unit roots versus other types of time heterogeneity,parameter time dependence and superexogeneity

This paper stresses the restrictive nature of the standard unit root/cointegration assumptions and examines a more general type of time heterogeneity, which might characterize a number of economic variables, and which results in parameter time dependence and misleading statistical inference. We show that in such cases ‘operational’ models cannot be obtained, and the estimation of time‐varying parameter models becomes necessary. For instance, economic processes subject to endemic change can only be adequately modelled in a state space form. This is a very important point, because unstable models will break down when used for forecasting purposes. We also discuss a new test for the null of cointegration developed by Quintos and Phillips (1993), which is based on parameter constancy in cointegrating regressions. Finally, we point out that, if it is possible to condition on a subset of superexogenous variables, parameter instability can be handled by estimating a restricted system. Copyright © 2002 John Wiley & Sons, Ltd.     

The performance of non‐linear exchange rate models: a forecasting comparison

In recent years there has been a considerable development in modelling non‐linearities and asymmetries in economic and financial variables. The aim of the current paper is to compare the forecasting performance of different models for the returns of three of the most traded exchange rates in terms of the US dollar, namely the French franc (FF/$), the German mark (DM/$) and the Japanese yen (Y/$). The relative performance of non‐linear models of the SETAR, STAR and GARCH types is contrasted with their linear counterparts. The results show that if attention is restricted to mean square forecast errors, the performance of the models, when distinguishable, tends to favour the linear models. The forecast performance of the models is evaluated also conditional on the regime at the forecast origin and on density forecasts. This analysis produces more evidence of forecasting gains from non‐linear models. Copyright © 2002 John Wiley & Sons, Ltd.     

不同药剂对破除播娘蒿种子休眠的效应

播娘蒿种子休眠的自动存作约需半年时间。研究了不同药剂对破除其休眠的效应。结果表明：药剂浸种可迅速打破其种子休眠,其中以３０％浸种３０ｍｉｎ,作用最显著,破眠率可达９３％,其次是３００×１０＾６ＧＡ浸种２４ｈ,ＮａＯＨ,ＰＥＧ,ＰＶＡ等作用较弱。