Pattern selection in three dimensional dendritic growth

We study the selection of the shape and growth velocity of three dimensional dendritic crystals in cubically anisotropic materials. We demonstrate that aside from minor additional complexities due to the lack of axisymmetry, the recently discovered mechanism of "microscopic solvability" can be extended to these systems and used to find a unique needle crystal solution of the equations of thermal diffusion-controlled solidification. We compare the predictions of this approach with measured growth rates in succinonitrile. Finally, we extend our analysis to determine the ratio of the sidebranch wavelength to the tip radius.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27133/1/0000126.pd

The impact on retrieval effectiveness of skewed frequency distributions

We present an analysis of word senses that provides a fresh insight into the impact of word ambiguity on retrieval effectiveness with potential broader implications for other processes of information retrieval. Using a methodology of forming artificially ambiguous, words known as pseudo-words, and through reference to other researchers’ work, the analysis illustrates that the distribution of the frequency of occurrence of the senses of a word plays a strong role in ambiguity’s impact on effectiveness. Further investigation shows that this analysis may also be applicable to other processes of retrieval, such as Cross Language Information Retrieval, query expansion, retrieval of OCR’ed texts, and stemming. The analysis appears to provide a means of explaining, at least in part, reasons for the processes’ impact (or lack of it) on effectiveness

Alterações físicas introduzidas por diferentes níveis de compactação em latossolo vermelho-escuro textura média Physical alterations induced by compaction of a coarse silty dark red latosol

Visando avaliar o efeito de diferentes níveis de compactação nos atributos físicos: densidade do solo, porosidade total, conteúdos volumétricos de sólidos e de água e distribuição dos poros para retenção de água/ar, diferentes quantidades de massa de um Latossolo Vermelho-Escuro textura média foram introduzidas mediante uma prensa hidráulica em anéis de PVC de 0,88 dm³. Utilizando fórmulas desenvolvidas na mecânica dos solos e com os valores de densidades obtidos no feixe de raios-gama e densidade de partículas, observou-se que a aplicação de uma carga (pressão) sobre o solo reduziu linearmente tanto a porosidade total como o espaço de aeração, e aumentou na mesma magnitude os conteúdos volumétricos de sólidos e o de água.<br>This research was conducted with the objective of studying physical alterations due to different levels of compaction in a coarse silty Dark Red Latosol (Oxisol). Compaction was obtained through a hydraulic press and bulk densities were checked in a gamma ray apparatus. Using soil mechanical equations, it was observed that the application of a strength over the soil reduced the total porosity and the aeration space, while increased in the same proportion the solid and water volumetric content