Geometric Obstacles Research Articles

Physically-based modeling: past, present, and future

Physically-based modeling: past, present, and future

The primitive idempotents of the clifford algebras and the amorphic spinor fibre bundles

We intend to clarify the “primitive idempotent” method of defining spinor bundles as fields of minimal ideas in some Clifford algebra bundles. The fundamental notion of “geometric Cliffordian spinoriality groups” is introduced, a notion similar to that of “groupes de spinorialité” defined previously [1d] by the author, but not equivalent. Existence conditions depend on the choice of the standard left ideal and provide a “chaotic character” for physics. Existence conditions of primitive idempotent fields imply drastic conditions. We give several examples. The primitive idempotent method brings algebraic tools, but raises a lot of geometric obstacles and cannot replace, improve or generalize the “ r -isotropic” approach [1].

The riddles of our galaxy

Abstract Paradoxically, it is more difficult to determine the structure of our own Galaxy than that of more remote ones. The difficulty comes from our position inside the system. In addition to this geometrical obstacle there is another: interstellar dust absorbs a large part of the visible light which comes to us from the stars and the atmosphere itself attenuates other wavelengths. Modern developments in spatial and radio astronomy have enabled our Galaxy to be explored extensively. But at the same time, new riddles are being set: our Galaxy is not as well known as might seem at first sight.

Amelioration of Roadside Obstacle Crashes

The paper describes a study of the geometric features and roadside obstacles at 300 fixed object crash sites and compares the findings with similar data for 300 comparison sites. The crash samples were for all levels of severity and were randomly selected from police files in three Georgia counties. The research validated the findings of a 1974 study of fatal object crash sites and confirmed that roadside modification projects should be focused first on locations with curvature greater than six degrees and negative (downhill) gradient of 2% or steeper. The study further indicated that ameliorative efforts should be concentrated on arterial and collector roads, along the outside of curves, in the vicinity of intersections, along the right side of one-way facilities, and on those objects nearest the pavement edge.

Effect of snow cover on obstacle performance of vehicles

Trafficability of terrain is a function of soft soil, hard or rough ground, geometric obstacles, vegetation, and the riverine environment. All of these terrain aspects are altered by cold temperatures and snow cover. This paper examines the effect of snow cover on obstacle crossing performance of vehicles. The mathematical expressions describing step negotiation, trench crossing, and slope climbing on snow-covered obstacles are given in terms of tracked vehicle, obstacle, and snow parameters. Tests of two tracked vehicles on snow-covered slopes, stream crossings, steps, and trenches were conducted, and some of the results were compared with computed values. Differences between computed and experimental values are attributed to neglecting slip-sinkage and track deflection in the computations.

On the Flow of Viscous Conducting Fluid past a Magnetized Sphere

This paper deals with the steady flow of viscous electrically conducting fluid past a spbere at whose center is loaded a magnetic dipole. The dipole axis is assumed to be parallel to the direction of the uniform flow. The dynamic and magnetic Reynolds numbers of the flow are supposed to be small. The flow field and the drag on the spbere are investigated for both small and large Hartmann numbers. The flow of viscous conducting fluid past a magnetic dipole with no geometrical obstacle is also considered as a limiting case of high Hartmann number flows.