Context-free grammars to detect straight segments and a novel polygonal approximation method

A new method for the polygonal approximation is presented. The method is based on the search for break points through a context-free grammar, that accepts digital straight segments with loss of information, as well as the decrease in the error committed employing the comparison of a tolerable error. We present an application of our method to different sets of objects widely used, as well as a comparison of our results with the best results reported in the literature, proving that our method achieves better values of error criteria. Besides, a new way to find polygonal approximations, with context-free grammars to recognize digital straight segments without loss of pixels, it is also addressed.     

Data requirements for neutron activation: Part I: Cross sections

Existing neutron cross section libraries such as EAF-2003 contain a large number of reactions. Of these only a small proportion are significant in the production of the nuclides that dominate activation quantities such as activity or γ-dose rate at various decay times. These reactions were identified in a recent extensive set of calculations on all the elements and reported in the ‘Activation Handbook’. These 1340 reactions are considered here and the set of reactions with no differential or integral data are listed and prioritised. A set of 339 reactions with very limited possibility of measurement are given; these require further study by theoretical calculations. A set of 100 reactions with either discrepant or no data, that might be measurable are listed and are recommended to be the subject of future experimental work.     

长期不同施肥对玉米田间杂草生物多样性的影响

通过田间小区试验,研究了长期不同施肥对田间杂草总密度、优势杂草组成及生物多样性的影响。结果表明:综合施用N、P、K肥,不仅降低了田间杂草的总密度,降低了优势杂草在群落中的比重,而且有利于维持田间杂草的生物多样性;不施用N或P肥,田间杂草的总密度增大,优势杂草的比重也明显增强,但不利于维持田间杂草的生物多样性。所以,平衡施用N、P、K肥,有利于维持农田生态系统中的生物多样性,并能更好地进行杂草控制。     

企业档案利用研究的现状及主要观点

通过对企业档案利用文献的量化分析与梳理,得出研究者更多关注利用时的安全与保密,而较少关心开放、公开和公示的结论。期望通过转变观念、确立共享理念、主动参与、运用信息技术和利用模式的多样化、个性化来改变企业档案利用的现状。     

基于MPEG-7主色描述符的图像检索

主色描述符作为MPEG-7的一种颜色描述子被广泛的应用于图像检索。通过一种有效的,结构紧凑的,直观的模式,主色描述符描述了一幅图像中的具有代表性的颜色特征。一种新的基于固定数目的MPEG-7主色描述符的图像检索算法被提出。特征提取的过程不再需要阙值的干预以及主色数目固定为8个。直方图相交算法用来衡量特征,从而简化了相似度的计算。实验结果表明,此方法的查准率和查全率高于非固定数目的主色检索方法。     

综合颜色和Contourlet直方图的图像检索方法

为提高图像检索性能,使用Harris彩色点提取器提取颜色特征点,设计一种基于颜色特征点的环形颜色直方图,在对图像进行Contourlet变换的基础上,提出Contourlet直方图的概念,改进其旋转不变性,并提取图像的纹理信息。仿真实验结果表明,该方法能够快速准确地检索彩色图像。     

Convertibility of Function Points into COSMIC Function Points: A study using Piecewise Linear Regression

Background

COSMIC Function Points and traditional Function Points (i.e., IFPUG Function Points and more recent variation of Function Points, such as NESMA and FISMA) are probably the best known and most widely used Functional Size Measurement methods. The relationship between the two kinds of Function Points still needs to be investigated. If traditional Function Points could be accurately converted into COSMIC Function Points and vice versa, then, by measuring one kind of Function Points, one would be able to obtain the other kind of Function Points, and one might measure one or the other kind interchangeably. Several studies have been performed to evaluate whether a correlation or a conversion function between the two measures exists. Specifically, it has been suggested that the relationship between traditional Function Points and COSMIC Function Points may not be linear, i.e., the value of COSMIC Function Points seems to increase more than proportionally to an increase of traditional Function Points.

Objective

This paper aims at verifying this hypothesis using available datasets that collect both FP and CFP size measures.

Method

Rigorous statistical analysis techniques are used, specifically Piecewise Linear Regression, whose applicability conditions are systematically checked. The Piecewise Linear Regression curve is a series of interconnected segments. In this paper, we focused on Piecewise Linear Regression curves composed of two segments. We also used Linear and Parabolic Regressions, to check if and to what extent Piecewise Linear Regression may provide an advantage over other regression techniques. We used two categories of regression techniques: Ordinary Least Squares regression is based on the usual minimization of the sum of squares of the residuals, or, equivalently, on the minimization of the average squared residual; Least Median of Squares regression is a robust regression technique that is based on the minimization of the median squared residual. Using a robust regression technique helps filter out the excessive influence of outliers.

Results

It appears that the analysis of the relationship between traditional Function Points and COSMIC Function Points based on the aforementioned data analysis techniques yields valid significant models. However, different results for the various available datasets are achieved. In practice, we obtained statistically valid linear, piecewise linear, and non-linear conversion formulas for several datasets. In general, none of these is better than the others in a statistically significant manner.

Conclusions

Practitioners interested in the conversion of FP measures into CFP (or vice versa) cannot just pick a conversion model and be sure that it will yield the best results. All the regression models we tested provide good results with some datasets. In practice, all the models described in the paper - in particular, both linear and non-linear ones - should be evaluated in order to identify the ones that are best suited for the specific dataset at hand.     

TTC估计系统误差分析及修正

在运动图像序列中利用目标稳定的特征点进行跟踪,从而计算目标尺度变化率以进一步进行TTC（Time-To-Contact) 估计,是目前应用较多的被动测距方法,但由于图像的离散化采样,在图像中进行尺度测量不可避免地带来了很大的误差,本文在对TTC估计系统进行了一系列误差分析后,根据TTC系统的特点对TTC估计结果进行一元线性回归修正,以提高估计精度和抗干扰能力,实验结果证明了该方法的有效性。     

臭氧对生物增强活性炭系统中菌群稳定性影响研究

为提高生物增强活性炭(BEAC)工艺的生物稳定性,进行臭氧工艺对固定的优势菌群稳定性的影响研究。结果表明,臭氧投加量1.5～2.5mg/L,接触时间大于10min时,可有效杀灭进水中的杂菌,且产生的余臭氧量(小于0.25mg/L)不会影响后续工艺中优势菌群的生物活性。通过对比臭氧—BEAC和单独BEAC工艺滤料表面菌群组成随运行时间的变化规律,臭氧—BEAC工艺优势菌在活性炭表面始终占主导地位,菌种组成及生态结构未发生改变,有较好的生物稳定性。单独BEAC工艺运行至6个月时,菌群组成发生较大变化,优势菌数量减少。通过扫描电镜观察,运行6个月的臭氧—BEAC炭上形成菌体重叠的菌团结构,并有较多未被生物覆盖的滤料表面和空缺的地方。单独BEAC工艺活性炭表面粗糙结构较少,被大量污染物与菌团相互包裹的颗粒所覆盖。