Optimization of free space optics parameters: An optimum solution for bad weather conditions

Free Space Optics Systems (FSO) is one of the most effective solutions, especially for atmospheric turbulence due to the weather and environment structure. Free space optics system suffers from various limitations. A well-known disadvantage of FSO is its sensitivity on local weather conditions-primarily to haze and rain, resulting in substantial loss of optical signal power over the communication path. The main objective of this article is to evaluate the quality of data transmission using Wavelength Division Multiplexing (WDM) with highlighting several factors that will affect the quality of data transmission. The results of these analyses are to develop a system of quality-free space optics for a high data rate transmission. From the result analysis, FSO wavelength with 1550 nm produces less effect in atmospheric attenuation. Short link range between the transmitter and receiver can optimize the FSO system transmission parameters or components. Based on the analysis, it is recommended to develop an FSO system of 2.5 Gbps with 1550 nm wavelength and link range up to 150 km at the clear weather condition of bit-error-rate (BER) 10⁻⁹.     

A modified Duckworth–Lewis method for adjusting targets in interrupted limited overs cricket

In this paper we present a modified Duckworth/Lewis method. The key modification is an improved functional form for the model describing the runs to be scored in an innings. In the course of our work we compare several alternative methods for resetting targets in limited overs cricket that have been proposed in the literature and conclude that the Duckworth/Lewis method is the most viable. Our analysis also suggests that it is reasonable to use a single method for both the 50-over and 20-over formats of the game.     

Developing mathematical competence: From the intended to the enacted curriculum

This study investigates the impact of a national reform in Sweden introducing mathematical competency goals. Data were gathered through interviews, classroom observations, and online surveys with nearly 200 teachers. Contrasting to most studies of this size, qualitative analyses were conducted. The results show that teachers are positive to the message, but the combination of using national curriculum documents and national tests to convey the reform message has not been sufficient for teachers to identify the meaning of the message. Thus, the teachers have not acquired the functional knowledge of the competence message required to modify their teaching in alignment with the reform. The results indicate that for complex reform messages, such as the competency message, to have intended impact on classroom practice, special attention needs to be put on the clarity of the message. To have high-stakes tests, for example, does not alone seem to be sufficient.     

以"N2分子的结构与性质"为例谈元素化学课堂教学的设计

以"N_2分子的结构与性质"为例说明元素化学课堂教学中的具体做法,教师引导学生复习化学键理论解释氮气分子结构与其化学性质之间的关系,组织学生以分组方式讨论光化学污染、工业合成氨等实际生产生活问题中的化学原理,由教师主讲化学模拟固氮的研究思路,而鼓励学生以报告形式展示热化学、电化学等氮活化科研课题的进展情况。     

Noise Temperature Increase Effect on Total Outage Analysis of an Interfered Satellite Link

The ever increasing demand for bandwidth and multimedia services has led to the employment of Ka and V band in modern satellite communication networks. In these frequency bands, rain attenuation is the most dominant fading mechanism deteriorating the performance of the Earth-space links. Moreover, interference due to propagation phenomena increases the outage time of the satellite links and should be taken into account for the reliable design of a satellite communication network. In this paper, a physical propagation model for the prediction of carrier-to-noise plus interference ratio statistics of a broadband satellite link incorporating the receiver noise temperature increase due to rain, is presented The obtained numerical results highlight the significance of the latter effect and investigate the impact of various operational, geometrical and climatic parameters in the total outage analysis. Some simple mathematical formulas for the prediction of the carrier-to-noise plus interference ratio, based on the above theoretical results, are also presented.     

Identification of rain cells from radar and stochastic modelling of space-time rainfall

We discuss two problems related to the utilization of weather radar: the automated identification of rain cells and the extension of cluster models to include the random variability of space-time rainfall within and between cells. The need for such extension emerges from visual inspection and formal analysis of radar reflectivity images. The algorithm proposed for the identification of cells is based on statistical techniques for the estimation of probability density mixtures. The algorithm does not assign pixels to cells deterministically; rather, it calculates the probability with which each pixel belongs to the different cells. Through an iterative procedure, the cell parameters and pixel probabilities are updated until the final identification of cells is reached. The second part of the paper deals with a generalization of cluster rainfall models in space and time. The models studied here combine an arbitrary birth point process with arbitrary random fields generated by the cells. Second-moment properties of these processes are derived.

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Sommario Vengono descritti i primi risulati di un lavoro in corso su due problemi legati all'uso del radar meteorologico: l'identificazione automatica delle celle di pioggia e l'estensione dei modelli a cluster per includere la variabilità casuale delle precipitazioni nello spazio e nel tempo all'interno e fra le celle. La necessità di tale estensione sorge sia dall'esame visivo, sia da un'analisi formale delle immagini della riflettività radar. L'algoritmo proposto per l'identificazione delle celle è basato sulle tecniche statistiche per la stima delle miscele di distribuzioni di densità di probabilità. L'algoritmo non assegna in maniera deterministica i singoli pixels alle celle, bensì calcola la probabilità con cui ogni pixel appartiene alle diverse celle. Attraverso una procedura iterativa si calcolano di volta in volta i parametri delle celle e le probabilità dei pixels, fino a che si raggiunge un assetto finale e le celle vengono identificate. Nella seconda parte del lavoro si tratta della generalizzazione dei modelli a cluster nello spazio e nel tempo. I modelli qui studiati combinano un processo arbitrario di occorrenza delle celle con un campo casuale arbitrario generato dalle celle. In particolare, sono derivate le proprietà generali dei secondi momenti di tali processi.

     

河北平原地裂缝产生的微观机理研究

分析了降雨和微结构失稳诱发的河北平原地裂缝机制。根据研究发现:(1) 根据近40a来华北平原的降雨量曲线图与地裂缝发生的时间图对比发现地裂缝多干旱年份的6-8月,地裂缝与农业灌溉用水密切相关。 (2)通过微结构突变失稳理论发现当应力状态满足孔隙微结构失稳判别式时,微结构元的变形状态将产生一个"跳跃",即会诱发微结构失稳崩塌。(3)地下水的抽取造成原饱和带土体颗粒之间有效接触力的增加,同时造成地下隐裂隙和空洞的形成。同时灌溉入渗引起的非饱和带土体含水量增加,不仅改变了颗粒的受力情况,更重要的是导致了颗粒间连接刚度的降低,导致微结构的失稳。     

以酸性铬蓝K作为氢供体的酶催化光度法测定过氧化氢

研究了以酸性铬蓝 K作为氢供体底物的过氧化氢酶 -过氧化氢催化反应体系 ,拟定了测定痕量过氧化氢的新的酶催化光度法。测得该体系的最大反应速率 Vmax值为 6.2 5× 1 0 -3 mol· L-1·S-1,米氏常数 Km值为 2 .78× 1 0 -5mol/L。测定过氧化氢的线性范围为 0 .0 3～ 0 .6mg/L。检出限为 4.6× 1 0 -4 mol/L。方法可应用于雨水中过氧化氢的测定     

基于雨课堂的任务导向式化学专业英语教学模式探索与实践

针对传统化学专业英语教学中存在的问题,提出将任务导向与雨课堂相结合的教学模式运用到专业英语课程的教学中。分析了任务导向与雨课堂相融合的特点,阐述了在专业英语教学中实施以雨课堂为基础的任务导向式教学环节与方法,利用问卷调查和定性对比方式考查了教学效果。结果发现,该教学模式能够显著地提高课堂气氛、师生互动度和学生参与度;融合雨课堂能显著提高任务教学的效果;雨课堂能一定程度地改善日常教学管理;该教学模式对学生兴趣和学业成绩的提高具有促进作用。     

大学物理研究性教学模式的实践研究

论述了研究性教学模式的特点和教师在教学中应具备的条件;通过研究性教学模式的设计对课堂教学、习题讨论、课程论文等环节进行了阐述．