An Initial Assessment of Infiltration Material Selection for Selective Laser Sintered Preforms

High-temperature infiltration is an important process that is used to add strength to skeletal microstructures. In this study, particulate metal matrix composites (MMCs) are fabricated. MMCs are applied in a wide variety of industries, including military, aircraft, tooling and automotive. In this paper, various materials for infiltrating selective laser sintered (SLS) silicon carbide and titanium carbide preforms are considered based on fundamental knowledge of SLS and infiltration mechanics. Proposed infiltrant materials systems include an aluminum-silicon alloy infiltrant and a silicon carbide preform, ductile iron infiltrated into a titanium carbide preform, and commercially pure silicon infiltrated into a silicon carbide preform. The first two infiltrants are considered because they add ductility to the brittle silicon carbide or titanium carbide part, thus broadening the range of applications. They also will model a broader field of possible infiltrants, including magnesium and iron-based materials, (e.g., steel). Silicon is investigated because it adds strength to silicon carbide, is robust at high temperatures, and has a comparable coefficient of thermal expansion. Presented is a feasibility assessment of these systems based on infiltration theory.Mechanical Engineerin

Report for 1901

Cover title.Mode of access: Internet

Results of experiments at State Experiment Station, Baton Rouge, La., in corn, cotton, forage crops, tobacco, etc.

Cover title.Mode of access: Internet

On the Possibility of Anisotropic Curvature in Cosmology

In addition to shear and vorticity a homogeneous background may also exhibit anisotropic curvature. Here a class of spacetimes is shown to exist where the anisotropy is solely of the latter type, and the shear-free condition is supported by a canonical, massless 2-form field. Such spacetimes possess a preferred direction in the sky and at the same time a CMB which is isotropic at the background level. A distortion of the luminosity distances is derived and used to test the model against the CMB and supernovae (using the Union catalog), and it is concluded that the latter exhibit a higher-than-expected dependence on angular position. It is shown that future surveys could detect a possible preferred direction by observing ~ 20 / (\Omega_{k0}^2) supernovae over the whole sky.Comment: Extended SNe analysis and corrected some CMB results. Text also extended and references added. 8 pages, 5 figure

Bouncing Anisotropic Universes with Varying Constants

We examine the evolution of a closed, homogeneous and anisotropic cosmology subject to a variation of the fine structure 'constant', \alpha, within the context of the theory introduced by Bekenstein, Sandvik, Barrow and Magueijo, which generalises Maxwell's equations and general relativity. The variation of \alpha permits an effective ghost scalar field, whose negative energy density becomes dominant at small length scales, leading to a bouncing cosmology. A thermodynamically motivated coupling which describes energy exchange between the effective ghost field and the radiation field leads to an expanding, isotropizing sequence of bounces. In the absence of entropy production we also find solutions with stable anisotropic oscillations around a static universe.Comment: 9 pages, 5 figure

Inhomogeneous Gravity

We study the inhomogeneous cosmological evolution of the Newtonian gravitational 'constant' G in the framework of scalar-tensor theories. We investigate the differences that arise between the evolution of G in the background universes and in local inhomogeneities that have separated out from the global expansion. Exact inhomogeneous solutions are found which describe the effects of masses embedded in an expanding FRW Brans-Dicke universe. These are used to discuss possible spatial variations of G in different regions. We develop the technique of matching different scalar-tensor cosmologies of different spatial curvature at a boundary. This provides a model for the linear and non-linear evolution of spherical overdensities and inhomogeneities in G. This allows us to compare the evolution of G and \dot{G} that occurs inside a collapsing overdense cluster with that in the background universe. We develop a simple virialisation criterion and apply the method to a realistic lambda-CDM cosmology containing spherical overdensities. Typically, far slower evolution of \dot{G} will be found in the bound virialised cluster than in the cosmological background. We consider the behaviour that occurs in Brans-Dicke theory and in some other representative scalar-tensor theories.Comment: 15 pages, 15 figures. Submitted to MNRAS. References adde