Electrical Conductance of Molecular Wires

Molecular wires (MW) are the fundamental building blocks for molecular electronic devices. They consist of a molecular unit connected to two continuum reservoirs of electrons (usually metallic leads). We rely on Landauer theory as the basis for studying the conductance properties of MW systems. This relates the lead to lead current to the transmission probability for an electron to scatter through the molecule. Two different methods have been developed for the study of this scattering. One is based on a solution of the Lippmann-Schwinger equation and the other solves for the {\bf t} matrix using Schroedinger's equation. We use our methodology to study two problems of current interest. The first MW system consists of 1,4 benzene-dithiolate (BDT) bonded to two gold nanocontacts. Our calculations show that the conductance is sensitive to the chemical bonding between the molecule and the leads. The second system we study highlights the interesting phenomenon of antiresonances in MW. We derive an analytic formula predicting at what energies antiresonances should occur in the transmission spectra of MW. A numerical calculation for a MW consisting of filter molecules attached to an active molecule shows the existence of an antiresonance at the energy predicted by our formula.Comment: 14 pages, 5 figure

Brief clinical report: prune belly syndrome in an anencephalic male

We describe a postmature anencephalic infant with atrophy of the abdominal musculature (prune belly syndrome). Other associations of these conditions are noted

Effects of Friedreich's ataxia (GAA)(n)·(TTC)(n) repeats on RNA synthesis and stability

Expansions of (GAA)(n) repeats within the first intron of the frataxin gene reduce its expression, resulting in a hereditary neurodegenerative disorder, Friedreich's ataxia. While it is generally believed that expanded (GAA)(n) repeats block transcription elongation, fine mechanisms responsible for gene repression are not fully understood. To follow the effects of (GAA)(n)·(TTC)(n) repeats on gene expression, we have chosen E. coli as a convenient model system. (GAA)(n)·(TTC)(n) repeats were cloned into bacterial plasmids in both orientations relative to a promoter, and their effects on transcription and RNA stability were evaluated both in vitro and in vivo. Expanded (GAA)(n) repeats in the sense strand for transcription caused a significant decrease in the mRNA levels in vitro and in vivo. This decrease was likely due to the tardiness of the RNA polymerase within expanded (GAA)(n) runs but was not accompanied by the enzyme's dissociation and premature transcription termination. Unexpectedly, positioning of normal- and carrier-size (TTC)(n) repeats into the sense strand for transcription led to the appearance of RNA transcripts that were truncated within those repetitive runs in vivo. We have determined that these RNA truncations are consistent with cleavage of the full-sized mRNAs at (UUC)(n) runs by the E. coli degradosome

Synthesis and Isolation of {110}-Faceted Gold Bipyramids and Rhombic Dodecahedra

Two {110}-faceted gold nanostructures—rhombic dodecahedra and obtuse triangular bipyramids—have been synthesized via a Ag-assisted, seed-mediated growth method. The combination of a Cl−-containing surfactant with a low concentration of Ag+ plays a role in the stabilization of the {110} facets. To the best of our knowledge, this is the first reported synthesis of a {110}-faceted bipyramid structure

Synthesis and Isolation of {110}-Faceted Gold Bipyramids and Rhombic Dodecahedra

Two {110}-faceted gold nanostructures—rhombic dodecahedra and obtuse triangular bipyramids—have been synthesized via a Ag-assisted, seed-mediated growth method. The combination of a Cl−-containing surfactant with a low concentration of Ag+ plays a role in the stabilization of the {110} facets. To the best of our knowledge, this is the first reported synthesis of a {110}-faceted bipyramid structure

Analysis of Collectivism and Egoism Phenomena within the Context of Social Welfare

Comparative benefits provided by the basic social strategies including collectivism and egoism are investigated within the framework of democratic decision-making. In particular, we study the mechanism of growing "snowball" of cooperation.Comment: 12 pages, 5 figures. Translated from Russian. Original Russian Text published in Problemy Upravleniya, 2008, No. 4, pp. 30-3

A Directional Entropic Force Approach to Assemble Anisotropic Nanoparticles into Superlattices

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/102143/1/14230_ftp.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/102143/2/ange_201306009_sm_miscellaneous_information.pd

Towards a Tetravalent Chemistry of Colloids

We propose coating spherical particles or droplets with anisotropic nano-sized objects to allow micron-scale colloids to link or functionalize with a four-fold valence, similar to the sp3 hybridized chemical bonds associated with, e.g., carbon, silicon and germanium. Candidates for such coatings include triblock copolymers, gemini lipids, metallic or semiconducting nanorods and conventional liquid crystal compounds. We estimate the size of the relevant nematic Frank constants, discuss how to obtain other valences and analyze the thermal distortions of ground state configurations of defects on the sphere.Comment: Replaced to improve figures. 4 figures Nano Letter