A Primitive-Based Reverse Modeling Method for Obtaining the Editable CAD model of Reversed Parts

By the traditional inversion methods, the model of the part reversed is obtained in mesh feature , which is hard to edit and redesign. In the paper, for the revised part, a modeling method to obtain the editable CAD mode was proposed. Firstly, an approach to construct the primitive structure tree used to describe the geometric structure of a part was proposed, by which the all the basic geometry primitives and their Boolean operations are logically arranged in tree format. Then, for each basic geometry primitive, a method to calculate the characteristics parameters and position and posture was proposed, which could be used to guide reversion measurement and modeling. For the basic primitives made of quadratic surface, a method for modeling the torus surface, whose model little research has been carried on, was proposed in which the torus surface equation is deduced by coordinate transformation method, has 8 independent parameters. Last, based on the guidance of primitive structure tree, a process for the characteristics parameters, minimum measuring points, forward modeling, positioning and assembly process was proposed, which could be used to direct measurements and to forward modeling. The example showed that the method proposed could be used to reverse the parts in the editable CAD model and provide for subsequent optimization design services.

Homology

This article examines how the concept of homology is used as an expression of generality in the life sciences. Throughout its long history, homology expressed a quest for generality in the understanding of animal anatomy by suggesting that a diversity of forms resulted from modifications of a single ‘primitive’ structure. However, the meaning of this quest as well as the practices associated with it changed considerably with the different theoretical context of the life sciences. Thus, homology was an element of continuity in the history of biology and played a central role in some developments, particularly the emergence of evolutionary theory. This article first considers the use of homology in pre-transformist comparative anatomy and how it paved the way for the conceptualization of evolutionary theory before discussing the rise of new meanings of homology in genetics.

Complete intersections primitive structures on space curves

A multiple structure [Formula: see text] on a smooth curve [Formula: see text] is said to be primitive if [Formula: see text] is locally contained in a smooth surface. We give some numerical conditions for a curve [Formula: see text] to be a primitive set theoretical complete intersection (i.e. to have a primitive structure which is a complete intersection).

An ornithurine bird from the Late Cretaceous of Alberta, Canada

The partial carpometacarpus of a basal ornithurine bird from the late Campanian of Dinosaur Provincial Park is described. Complete proximal fusion of the wrist and the presence of a pisiform process place this taxon in Ornithothoraces. Ornithurine synapomorphies include the large ventral ridge of the carpus and the concave proximal margin of the alular metacarpal, but the primitive structure of the pisiform process and extensor process preclude placement in Neornithes. The relatively thick walls of the bone and the distal placement of the extensor process are consistent with diving habits.