Application of granular mechanics to the analysis of solid propellants

In this paper a theoretical method is developed for analyzing the mechanical behavior of granular solid propellant materials. The granular nature of the material is specifically taken into account and, the analysis allows for a media composed of non-uniformly sized particles with random stacking configuration. The voids between the particles are assumed to be filled with an elastic, homogeneous binder material. Three types of internal forces are assumed to be acting; the normal and tangential contact forces between the granular particles and, the elastic stresses in the binder. The paper consists of three main parts. First a model is developed to represent a general granular medium. Subsequently, in the second part this model is used to analyze the response of a granular medium to hydrostatic pressure loading. Finally the stress-strain relations are derived for a general loading condition. Because of the presence of the non-conservative frictional forces between the granular particles, the deformation of such a medium depends on the loading history. Consequently the stress-strain relations are in a differential, or incremental form

The decay of hot KK space

The non-perturbative instabilities of hot Kaluza-Klein spacetime are investigated. In addition to the known instability of hot space (the nucleation of 4D black holes) and the known instability of KK space (the nucleation of bubbles of nothing by quantum tunneling), we find two new instabilities: the nucleation of 5D black holes, and the nucleation of bubbles of nothing by thermal fluctuation. These four instabilities are controlled by two Euclidean instantons, with each instanton doing double duty via two inequivalent analytic continuations; thermodynamic instabilities of one are shown to be related to mechanical instabilities of the other. I also construct bubbles of nothing that are formed by a hybrid process involving both thermal fluctuation and quantum tunneling. There is an exact high-temperature/low-temperature duality that relates the nucleation of black holes to the nucleation of bubbles of nothing.Comment: v2: minor improvements; new appendix on merger poin

A Southern Hemispheric influence on the North Atlantic through a shallow atmospheric circulation response

Previous research has discussed the importance of meridional migrations of the North Atlantic Subtropical High (NASH) on U.S. precipitation patterns, but the mechanisms that control these meridionial migrations are virtually unknown. We have observed that, under certain conditions, a southward migration of the NASH is associated with deep tropical incursions of cold surges from the winter hemisphere over South America. When upper tropospheric winds are westerly over Amazonia, cold surges originating from extratropical South America can penetrate deep into the tropics and increase geopotential height over a broad region span from equatorial South America, across the intra-American seas, and into the subtropics of the Northern Atlantic, with anomalies exceeding +1 standard deviation to at least 18°N. The anomalous geopotential and temperature gradients associated with the South American cold surge induces a shallow tropical meridional circulation. The latter in turn increases the lower tropospheric geopotential height over the tropical to subtropical North Atlantic, leading to the equatorward expansion of the NASH. This study uncovers the importance of shallow circulations in the cross-equatorial teleconnection.Geological Science