3D Fragments Research Articles

Bioisosterism as a molecular diversity descriptor: steric fields of single "topomeric" conformers.

The comparative molecular field analysis steric field of a single "topomeric" conformer is introduced as a molecular diversity descriptor particularly useful for combinatorial chemistry involving variations around a fixed "core". Using this new descriptor, 736 commercially available thiols are divided into 231 bioisosteric clusters, whose compositions agree at least as well with medicinal chemical experience and intuition as do clusters derived from Tanimoto differences between 2D fragment occurrences. However, in practice topomeric steric fields complement 2D fingerprints, being the two most frequently useful descriptors yet found for neighborhood-based design of combinatorial libraries.

Recognition of object classes from range data

We develop techniques for recognizing instances of 3D object classes (which may consist of multiple and/or repeated sub-parts with internal degrees of freedom, linked by parameterized transformations), from sets of 3D feature observations. Recognition of a class instance is structured as a search of an interpretation tree in which geometric constraints on pairs of sensed features not only prune the tree, but are used to determine upper and lower bounds on the model parameter values of the instance. A real-valued constraint propagation network unifies the representations of the model parameters, model constraints and feature constraints, and provides a simple and effective mechanism for accessing and updating parameter values. Recognition of objects with multiple internal degrees of freedom, including non-uniform scaling and stretching, articulations, and sub-part repetitions, is demonstrated and analysed for two different types of real range data: 3D edge fragments from a stereo vision system, and position/surface normal data derived from planar patches extracted from a range image.

Experimental orbital momentum distributions and bonding interactions

(e, 2e) spectroscopy has been used to obtain electron momentum distributions for the valence region of the gas-phase organometallic complex (η4-1,3-C4H6)-Fe(CO)3. The momentum distributions are compared with spherically averaged distributions calculated from ab initio SCF-MO wavefunctions for the complex at its energy optimized geometry. For binding energies of 8 to 11 eV, corresponding to ionization of electrons from molecular orbitals of the complex resulting from the interaction of C4H6 (butadiene) π and iron 3d fragment orbitals, the experimental momentum distributions are dominated by the contributions from the π HOMO of butadiene. The iron contributions to these orbitals are not readily apparent because of their small amplitude in the momentum region where the (e, 2e) experiment is sensitive. The momentum distributions at 12 to 13 eV have a distinctive double hump that is a reflection of butadiene σ orbital character. CO 5σ character appears in the momentum distributions at 14 to 15 eV.

Recent epic code developments for high velocity impact: 3D element arrangements and 2D fragment distributions

This paper presents recent developments in the three-dimensional EPIC-3 code and the two-dimensional EPIC-2 code. The EPIC-3 work provides a new symmetric arrangement of tetrahedral elements which is more accurate than the traditional non-symmetric arrangement. The EPIC-2 work provides an algorithm and examples of fragment distributions which occur after impact. Included are numbers of fragments for various sizes, masses, momenta, and kinetic energies.