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Mechanical degradation mechanism of rock under seismic disturbance stress
No full textDuring the action of periodic seismic disturbance stress, the rock mass surrounding buried structures will show fatigue damage owing to cyclic loading. To explore the fatigue characteristics and mechanical degradation mechanism of this process, fatigue loading and uniaxial compression tests were carried out on gypsum samples. The conclusions are as follows. With increasing seismic wave amplitude, the stress loading and unloading velocity gradually increases, and the opening of the stress–strain hysteresis loop gradually increases. With increasing seismic wave frequency, the dip angle of hysteresis loops gradually inclines to the σ-axis (where σ is stress), and the variation amplitude of hysteresis loops on the ε-axis (where ε is strain) decreases gradually. This shows that the greater the amplitude of the seismic wave and the lower the frequency, the greater the damage to rock. Under seismic wave disturbance, with increasing number of disturbances, the original cracks in the sample gradually spread and infiltrate the rock, and secondary cracks gradually develop, indicating that the physical and mechanical properties of the rock gradually deteriorate. There is a strong correlation between the acoustic emission of samples and the stages of the stress–time curve for uniaxial compression. According to the acoustic emission characteristics, the stress– time curve can be divided into four stages: the initial loading stage, the stable crack growth stage, the unstable crack growth to failure stage and the post-peak stage. Compared with the sample before fatigue, the peak strain decreases significantly and the impact energy index increases significantly after fatigue loading. This indicates that some original cracks in the sample are compressed under seismic disturbance, the brittleness of the sample is enhanced and the rockburst tendency is greatly enhanced
Are Chinese loess deposits essentially continuous?
Full text linkWe conducted a paleomagnetic examination of the last glacial loess of three representative profiles along an east-west transect in the central Loess Plateau in order to assess the continuity of Chinese loess. The results show that the Xifeng and Luochuan profiles record the Laschamp geomagnetic excursion but with different morphologies. Together with the published results from Weinan, southern plateau, our results suggest that sedimentation of the last glacial loess in the central-southern plateau was continuous at the time scale equivalent to the duration of the Laschamp excursion (~2 kyr), but probably episodic at finer time scales (<2 kyr). No geomagnetic excursion was found at the Yichuan profile near the Yellow River valley, where loess accumulation may be strongly affected by local environmental changes and thus may have been discontinuous. Both site location and time scale therefore need to be considered when considering continuity of Chinese loess.<br/
The Influences of Chromium Addition on the Corrosion Behaviors of Ni3Al-Intermetallic Compounds in Aqreous Solutions
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Projections and power reduction property for generalized identities of symmetric elements
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Rapid and specific detection of the thermostable direct haemolysin gene in Vibrio parahaemolyticus by the polymerase chain reaction
No full textPan-americanismo no Brasil: uma abordagem conceitual a partir do Estado Novo
Full text linkDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Filosofia e Ciências Humanas, Programa de Pós-Graduação em História, Florianópolis, 2013.Esta dissertação objetivou investigar o conceito de pan-americanismo no Brasil, suas repercussões, ressignificações e práticas políticas a ele associados durante o período que culminou com o envolvimento do país na Segunda Guerra Mundial, enfatizando as aparentes contradições entre uma ideia de pan-americanismo e o discurso de sustentação do Estado Novo. Como história de um conceito político, apoiada nas considerações de Reinhart Kosselleck e Quentin Skinner, a busca pelos antecedentes do pan-americanismo no Brasil se fez necessária, de modo a elucidar as maneiras com que o conceito repercutiu no país desde suas origens nos Estados Unidos, e os desdobramentos posteriores das Conferências Pan-Americanas e das atividades da União Pan-Americana. Tal busca serviu para elucidar os elementos de um "pan-americanismo brasileiro", ou seja, de um conceito externo que foi apropriado em um diferente contexto com diferentes fins políticos durante as três primeiras décadas do século XX. Isso faz a ligação entre a "ideia pan-americana" e a política externa brasileira do período Vargas e, mais especificamente, do Estado Novo, quando o Brasil foi para a guerra. Foi visto, assim, que o Estado Novo utilizou o pan-americanismo como instrumento de aproximação aos Estados Unidos, com objetivos de premência sobre a América do Sul durante um período de crise mundial, e ao mesmo tempo viu-se obrigado a reajustar o discurso da ?ideia pan-americana? aos princípios antiliberais que sustentavam o regime, sofrendo as consequências políticas desta tentativa de ajuste. Abstract : This dissertation aimed to investigate the concept of pan Americanism in Brazil, its repercussions, meanings and political uses associated to it during the period that culminated with the involvement in the Second World War, emphasizing the apparent contradictions related to a pan American idea and the ideas that sustained the Brazilian Estado Novo regime. As a history of a political concept, supported by the considerations of Reinhart Koselleck and Quentin Skinner, the search for the previous history of pan Americanism in Brazil was necessary. It elucidated the ways which the concept reverberated in Brazil since its origins in the United States, and its later results at the Pan American Conferences and the activities of the Pan American Union. This search helped in elucidating the elements of a "Brazilian pan Americanism", i. e., a foreign concept which was reframed to a different context with different political aims during the first three decades of the 20th century. From this on, it was possible to establish a connection between the "pan American idea" and the Vargas regime foreign policy, mainly, the Estado Novo, when Brazil went to war. It was found that the Estado Novo used pan Americanism as an instrument for approach towards United States, aiming a South American prevalence during the period of world crisis, and, at the same time, was obliged to adjust the pan American discourse to the anti-liberal principles that sustained the regime
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