Pentagonal Network Research Articles

Electronic and Structural Properties of Si46: A Novel Solid of Silicon Fullerenes

ABSTRACTWe report the electronic structure of the S46 lattice having a just lnm-size unit cell and has been optimized within the density-functional theory. The Si46 lattice studied is the real geometry of Si atoms crystallized with metal atoms, and consists essentially of dodecahedral-cage Si20 fullerenes proposed by us previously. Although all the Si atoms are tetrahedrally coordinated, its electronic structure is found to be considerably different from that of the diamond Si lattice due to the pentagonal Si-Si network. Si46 is an important new Si semiconductor to be synthesized in the future. We also report the electronic structure of Na2Ba6Si46. The material is found to be metallic and the Fermi-level density of states is very high due to the hybridization between Si and Ba states, which should be of essential importance for the superconductivity observed in Na and Ba codoped Si46.

Sublimed C60 films for tribology

Fullerenes take the form of hollow, geodesic domes, which are formed from a network of pentagons and hexagons. The C60 molecule has the highest possible symmetry (icosahedral) and assumes the shape of a soccer ball. At room temperature, fullerene molecules pack in a face-centered-cubic lattice bonded with weak van der Waals attractions. Fullerenes can be dissolved in solvents such as toluene and benzene and easily sublimed. The resilience, high load bearing capacity, low surface energy, high chemical stability, and spherical shape of C60 molecules and weak intermolecular bonding offer great potential for various mechanical and tribological applications. Sublimed films of C60 have been produced and friction and wear performance of these films in various operating environments are the subject of this letter.

Immunoelectron microscopic evidence for the extended conformation of light chains in clathrin trimers

Clathrin is a major component of the basket-like network of hexagons and pentagons that forms the "coat" on the cytoplasmic face of the plasma membrane and the trans Golgi network during the invagination of coated pits. Soluble clathrin is a three-legged structure (triskelion) comprising three identical heavy chains and three different light chains located toward the center of the triskelion on the proximal segment of the leg. All mammalian light chains contain a central domain of 10 heptad repeats, which is necessary for the interaction with heavy chain. Because the repeats are characteristic of alpha helical coiled coils, we proposed that the central domain had an extended conformation (Kirchhausen, T., Scarmato, P., and Harrison, S. C. et al. (1987) Science 236, 320-324). However, an alternative model has recently been proposed (Nathke, I. S., Heuser, J., Lupas, A., Stock, J., Turck, C. W., and Brodsky, F. M. (1992) Cell 68, 899-910). Here, we use single-molecule electron microscopy of clathrin decorated with monoclonal antibodies directed against different epitopes on light chains to show that the light chain central domain has an extended conformation and reaches along most of the proximal segment of the heavy chain leg.

Fullerene (C60) Films for Solid Lubrication

The advent of techniques for producing gram quantities of a new form of stable, pure, solid carbon, designated as fullerene, opens a profusion of possibilities to be explored in many disciplines including tribology. Fullerenes take the form of hollow, geodesic domes, which are formed from a network of pentagons and hexagons with covalently bonded carbon atoms. The C60 molecule has the highest possible symmetry (icosaliedral) and assumes the shape of a soccer ball. At room temperature, fullerene molecules pack in a face centered cubic (fee) lattice bonded with weak van der Waals attractions. Fullerenes can be dissolved in solvents such as toluene and benzene and are easily sublimed. The low surface energy, high chemical stability, spherical shape, weak intermolecular bonding, and high load bearing capacity of C60 molecules offer potential for various mechanical and tribological applications. This paper describes the crystal structure and properties of fullerenes and proposes a mechanism for self-lubricatin...

Observations of the Egg-shell Structures Controlled by Gene Action in Bombyx mori

The surface patterns and the structures of transverse sections of the egg-shells of mutant Grey egg alleles in the silkworm, Bombyx mori, have been examined with the scanning electron microscope. The principal surface pattern of the egg-shell is a network of hexagons or pentagons. The shapes and the sizes of the polygons are different among the strains of Grey egg alleles. The micropyle on the anterior end is surrounded with a pattern like a single-petaled flower. These patterns do not so much differ among strains of Grey egg alleles. Small pores, aeropyles, open at each corner of the polygons, on the knobs which rest in every polygon, or at the furrow between the knobs. The location of the aeropyles differs among different strains. The structures of transverse sections of the egg-shell are composed of the outer, middle, and inner layers. Grey egg alleles affect mainly the formation of the middle layer in the egg-shells and cause an abnormal lamellar structure in the layer. The gene interactions between Grey egg alleles are also noted in the formation of the middle layer.