Construção de quadrados mágicos pelo método do passo uniforme

Lehmer (1929) analisa matematicamente o método do passo uniforme para construção de quadrados mágicos de ordem impar. Ele divide sua análise em várias etapas. Na primeira delas, envolvendo a discussão de condições necessárias e suficientes para o preenchimento do quadrado pelo método, o autor afirma que se dois números guardarem entre si uma certa relação, eles serão designados a ocupar a mesma célula do quadrado causando seu não preenchimento. A análise do preenchimento pelo método do passo uniforme envolve a resolução de um sistema linear módulo n. Nesse trabalho, discutimos o comportamento das soluções desse sistema quando o método falha no preenchimento. Como consequência, concluímos que números que guardam a relação mencionada nunca ocupam a mesma célula. A análise das condições necessárias e suficientes para obter quadrados mágicos segundo a definição de Lehmer (1929) envolve a resolução de equações de congruências lineares a duas variáveis. Nesse trabalho, detalhamos os resultados de Lehmer (1929). A análise das condições necessárias e suficientes para obtenção de quadrados mágicos, como são reconhecidos usualmente, também envolve a resolução de equações de congruências lineares a duas variáveis. Discutimos o comportamento das soluções dessas equações para obter diagonais principais mágicas. Como consequência, mostramos que diagonais principais mágicas são obtidas se e somente se as coordenadas iniciais guardarem certas relações

Criptografia: Da origem aos dias atuais

Esta pesquisa foi realizada com a intenção de motivar o estudo da criptografia, mostrando que a matemática e a comunicação estão presentes em diversos momentos, tanto no passado quanto no presente. Este trabalho mostra a origem da criptoanálise e toda a sua evolução dando ênfase nos mecanismos de codificação e decodificação através de exemplos práticos. Além disso, alguns métodos criptográficos são destacados como a cifra de substituição monoalfabética, a cifra de Vigenère, a criptografia RSA que é o método mais conhecido de criptografia de chave pública, as cifras de Hill, o método das transformações lineares e o método de Rabin, devido a sua grande importância para a evolução de sistemas computacionais e assinaturas digitais entre outros. Por fim, mostra-se a importância e a necessidade dos recursos criptográficos nos dias de hoje, na tentativa de impedir que hackers e pessoas que fazem mau uso do conhecimento matemático possam causar danos a sociedade, seja por uma simples mensagem ou até mesmo através de situações mais imprudentes como as transações bancárias indevidas

Resources of the Wadge and Pedro Banks

Sri Lanka's interest in trawler fishing dates back to 1902 when a Colombo merchant attempted to operate a trawler off Sri Lanka's waters. The next attempt was made in 1907. These attempts did not proceed any further. Between 1920 and 1923 a very comprehensive survey of the littoral waters around the island was carried out. One of the principal aims of the survey was to investigate the possibility of trawler fishing in the seas around. Malpas (1926) and Pearson and Malpas (1926) reporting the results of the survey indicated that the Wadge and Pedro banks were the only areas available for commercial trawler operations and indicated that the fish resources in the two banks could be profitably exploited. Commercial exploitation of the Wadge bank commenced in 1928 and a fishery is now firmly established in the bank. The Marine Biologist and the Director of fisheries in their administration reports and Sivalingam and Medcof (1957) and the author (1965) have reported on the progress of the Wadge bank fishery. Some of the trends indicated by an analysis of the records of the commercial trawling operations are further discussed in this paper.

Wadge Bank trawl fishery studies. Pt. 5. Rational exploitation of the resident demersal stock

The general history of the trawl fishery of the Wadge Bank off Cape Comorin, South India (Fig. 1), the nature and composition of its demersal fish population, and the present state of its fishery has been given by various authors (Malpas 1926, Pearson and Malpas 1926, Sivalingam and Medcof 1957, Medcof 1963, Mendis 1965a, 1965b, Sivalingam 1966a, 1966b, 1969a and 1969b). It has been shown earlier (Sivalingam and Medcof 1957, Sivalingam 1969a) that the Wadge Bank stock is made up of two groups. The resident stock which is present on the fishing grounds throughout the year and the migrant stock that appears on the fishing grounds only during the southwest monsoon months. The object of this paper is to discuss the effect of fishing on the resident stock between 1945 and 1962 and based on the information available; assess the maximum sustained yield of the resident stock. The "Bigfish" of the resident stock is the mainstay of the Wadge Bank trawl fishery (Sivalingam 1969a) and it will be shown that this stock has been overexploited from 1953 to 1957. The first sign of recovery was evident in 1960 and continued till 1962. The data since 1962 are not available to the author for analysis. It has been reported by Mendis (1965b) that considerable expansion of the trawler fleet was anticipated in 1966, and if so, the history of the fishery from 1953 to 1957 may be repeated. The assessment presented in this paper should form a rational basis for management programs.

Seasonal variation in the distribution and availability of Carangids ("Paraw" and "Parati") in the Wadge Bank

The Wadge Bank has been exploited regularly by Ceylon based trawlers since 1955 (Sivalingam & Medcof 1957). The bank is about 4,000 sq. miles in extent (Malpas 1926) and is located south of Cape Comorin within the Continental Shelf of India (Fig. 1). Carangids are taken in large numbers during the months of the south west monsoon (Sivalingam 1966). The quantity, in which the Carangids are captured as shown by the fishing records, is large enough to influence the total catch from the bank during these months (Fig. 2). Carangids are held in high esteem as excellent quality food fishes and accordingly constitute a commercially important group. This paper records the results of a detailed examination of the past fishing records in respect of this group, based on the analysis of the catch and fishing effort for the years 1957 to 1962. The distribution pattern of this group of fish in the Wadge Bank is discussed.

Small mesh trawling

Experimental trawling operations for bottom fish were first begun in 1920 and consisted of surveys of the continental shelf around Ceylon and the west and east coasts of India. These preliminary surveys showed that the continental shelf of Ceylon was either very poor in bottom fish or that the ground was so rough that trawling has proved to be economically not sustainable (Malpas, 1926). Although a considerable amount of trawling has been carried out using small-meshed trawls, there is no record of the details of the gear used or any account of the relative efficiency of the different designs of trawls used in the operations. Experimental operations were, therefore, carried out off 80 h.p. boats such as m.f.v. Canadian and North Star, to select the most effective gear for these boats. In more recent times experiments were also conducted to select the most effective trawling gear for the 11-Ton boats of the Ceylon Fisheries Corporation. The results are reported in this publication.

中国树鼩的寄生虫调查研究

树鼩是一种新开发的小型实验动物. 研究树鼩的寄生虫对保护树鼩群体, 保证准确的实验结果, 以及寻找人类疾病的动物模型等方面都有着重要的实用意义和理论意义. 关于缅甸、越南、婆罗洲、马来西亚、马来亚、印度、和印度尼西亚树鼩的体内外寄生虫研究, 国外学者已作过许多研究(Dunn, 1963, 1964; Van Peenen等, 1967;Durette-Desset等, 1975, 1981; File, 1974; Quentin等, 1975, 1977; Chabaud等, 1975;Ohbayashi等, 1983; Betteron等, 1977; Betterton, 1979, 1980; Myers, 1960; Orihel, 1966; Nandi, 1982; Manning等, 1972; Mallin等, 1972; Schmidt等, 1977; Houdemer, 1938; Heyneman 等, 1965; Jordan,1926; Durden 等, 1984)。

养殖水体氨氮污染生物修复技术研究

在渔业资源和可养殖水面有限的情况下,必然要在水产养殖上寻求渔业的可持续发展,如增加养殖密度,提高单位水体产量。养殖密度的增加,对养殖系统及排放废水的附近水域都会产生负面影响。由于鱼类排泄物和残饵直接进入水体,导致氨氮浓度升高,已成为制约鱼类生产、造成水体富营养化的主要环境因素。对治理氨氮污染这一世界性的课题,笔者就去除养殖水体氨氮的微生物种群、固定化技术、生物强化技术以及人工湿地生态工程技术等做一综述,以期把握研究热点,推进水产养殖的可持续发展。

盐泽螺旋藻与其他螺旋藻的比较研究

研究了盐泽螺旋藻的形态、生理生化特性和在不同条件下的生长状况,并与其他螺旋藻进行了比较。盐泽螺旋藻、极大螺旋藻和钝顶螺旋藻在蛋白质的含量、氨基酸组分以及可见光吸收光谱等方面差别不大。盐泽螺旋藻的生长速度最快(世代时间为8.4h)。极大螺旋藻、钝顶螺旋藻1926和钝顶螺旋藻2340的世代时间分别为11、11.8和14.8h。盐泽螺旋藻的光合作用和呼吸作用强度亦大于极大螺旋藻和钝顶螺旋藻。此外,这种藻对盐分和温度还具有较宽的适应范围,在形态上也和其他3种螺旋藻有较大之差异。

基于弱信号检测理论的离散小波变换域数字水印盲检测算法

水印检测是数字水印技术的一个关键步骤,但是目前所提出的绝大多数水印检测算法既不具备赖以支撑的理论基础,其检测性能也不是优化的.利用数字水印的不可感知特性,应用弱信号检测理论进行水印检测的研究.首先从图像小波变换系数的统计特性出发,利用广义高斯分布(GGD)来建立小波细节子带系数的统计分布模型;然后针对水印嵌入强度未知的情况,将水印检测问题转化为非高斯噪声中具有未知参数的确定性信号的检测,在弱信号条件下提出一种离散小波变换(DWT)域图像水印的优化盲检测算法.检测性能分析表明,该检测算法能够实现恒虚警率水印检测.实验结果验证了检测性能理论分析的有效性和实际性能的优越性.

一个基于双线性映射的前向安全门限签名方案

将前向安全的概念引入到基于双线性映射的门限签名方案中,提出了一个基于双线性映射的前向安全的门限签名方案.该方案将签名密钥分散到签名成员集合中,采用各成员部分密钥前向更新的方式实现了签名密钥的前向更新,增强了签名密钥的安全性,使得签名方案具有前向安全性.另外,由于部分密钥具有前向更新的特性,从而方案有效防止了移动攻击.对该方案的安全性进行了分析,分析表明,该方案是安全、有效的.

国内外海洋热能转换概况

一、前言海洋热能转换(Ocean Thermal Energy Conversion OTEC)这一概念早在1881年法国物理学家 D~1 Arsonval 就提出来了。他设想在热带海洋表面温海水与深层冷海水之间，设置闭式朗肯循环，把海洋中所储存的太阳热能转换为电能。为实现这一设想，D~1Arsonval 的学生，法国工程师 G.Claude 于1926年在一个海水温差发电的模拟装置上使