强脉冲CO_2激光破坏金膜反射镜的实验研究

<正>本文对在激光研制中常用的一些不同基底的金膜反射镜,用脉宽为1微秒的10.6微米脉冲CO_2激光器,在57焦耳/厘米~2、127焦耳/厘米~2、300焦耳/厘米~2三种能量密度下进行照射,将照射结果进行了显微观察和分析并对其破坏机制进行了初步的讨论.

关于“弹性圆柱薄壳的一般稳定性”问题

程世祜同志閱读了“弹性圆柱薄壳的一般稳定性”(刊登在本学报第5卷第1期)以后,曾就边界条件对失稳应力的临界值影响这一問題提出了与該文不同的意見,并写了“关于‘弹性圆柱薄壳的一般稳定性’問題”一文。 在程世祐同志的文章写就后,我們曾把它送給“弹性圆柱薄壳的一般稳定性”的原作者罗祖道、吳連元两位同志看过。“‘弹性圆柱薄壳的一般稳定性’的結束語”是这两位作者对程世祐同志提出的意見所作的解答,現在我們把这两篇有不同看法的短文一并在本期学报上发表。 組織学术討論是我們經常任务之一,希望广大的讀者能陆續对力学領域中的学术問題发表自己的意見,以使我国力学界的学术空气日益热烈。

Wave pattern characteristics of a two-phase nozzle flow by shock propagation

In this paper, the wave pattern characteristics of shock-induced two-phase nozzle Hows with the quiescent or moving dusty gas ahead of the incident-shock front has been investigated by using high-resolution numerical method. As compared with the corresponding results in single-phase nozzle flows of the pure gas, obvious differences between these two kinds of flows can be obtained.

Effect of phase-transformation on mechanical-behavior of dual-phase steel plate

The mechanical behavior of dual phase steel plates is affected by internal stresses created during martensite transformation. Analytical modelling of this effect is made by considering a unit cell made of martensite inclusion in a ferrite matrix. A large strain finite element analysis is then performed to obtain the plane stress deformation state. Displayed numerically are the development of the plastic zone and distribution of local state of stress and strain. Studied also are the shape configuration of the martensite (hard-phase) that influences the interfacial condition as related to stress transmission and damage. Internal stresses are found to enhance the global flow stress after yield initiation in the ferrite matrix. Good agreement is obtained between the analytical results and experimental observations.

Thermophoretic deposition of particles onto cold surfaces of bodies in two-dimensional and axisymmetric flows

The problem of thermophoretic deposition of small particles onto cold surfaces is studied in two-dimensional and axisymmetric flow fields. The particle concentration equation is solved numerically together with the momentum and energy equations in the laminar boundary layer with variable density effect included. It is shown explicitly to what extent the particle concentration and deposition rate at the wall are influenced by the density variation effect for external flow past bodies. The general numerical procedure is given for two-dimensional and axisymmetric cases and is illustrated with examples of thermophoretic deposition of particles in flows past a cold cylinder and a sphere.

Dependência de trajetória nos incentivos fiscais: fragmentação do empresariado na reforma tributária

Desde a promulgação da Constituição de 1988, todos os governos têm buscado realizar a reforma tributária. Há aparente consenso de que essa reforma precisa ser feita. No entanto, os insucessos nas propostas submetidas ao Congresso Nacional têm sido recorrentes. Essa dissertação busca explicar esse aparente insucesso a partir da análise evolutiva histórica de cinco tipos de incentivo fiscal: 1) regional (Sudam, Sudene e Zona Franca de Manaus); 2) guerra fiscal do ICMS; 3) exportação; 4) tributação simplificada (em especial o Simples); e 5) desenvolvimento econômico. O argumento central da pesquisa é o de que a política tributária desenvolvimentista e extrativa, adotada historicamente pelo Estado brasileiro e pautada pela concessão de incentivos fiscais, envolve interesses difíceis de serem revertidos - com características de dependência de trajetória -, que têm condicionado o comportamento do ator fundamental para o desenlace da reforma tributária - o empresariado -, o qual tem atuado de forma fragmentada e na busca por rendas, em vez de atuar de forma concertada buscando o objetivo coletivo pressuposto em uma reforma tributária. A pesquisa evidenciou ter havido uma dinâmica e relevante evolução do sistema tributário no período recente, vinculada em grande medida ao conjunto de incentivos fiscais que foram objeto de análise, o que afasta a hipótese de eventual paralisia decisória e relativizam as hipóteses de pontos de veto e de impasse entre interesses federativos como variáveis explicativas para o insucesso da reforma tributária.