Coincidence isometries of a shifted square lattice

We consider the coincidence problem for the square lattice that is translated by an arbitrary vector. General results are obtained about the set of coincidence isometries and the coincidence site lattices of a shifted square lattice by identifying the square lattice with the ring of Gaussian integers. To illustrate them, we calculate the set of coincidence isometries, as well as generating functions for the number of coincidence site lattices and coincidence isometries, for specific examples.Comment: 10 pages, 1 figure; paper presented at Aperiodic 2009 (Liverpool

Genetic Selection for Enhanced Folding In Vivo Targets the Cys14-Cys38 Disulfide Bond in Bovine Pancreatic Trypsin Inhibitor

The periplasm provides a strongly oxidizing environment; however, periplasmic expression of proteins with disulfide bonds is often inefficient. Here, we used two different tripartite fusion systems to perform in vivo selections for mutants of the model protein bovine pancreatic trypsin inhibitor (BPTI) with the aim of enhancing its expression in Escherichia coli. This trypsin inhibitor contains three disulfides that contribute to its extreme stability and protease resistance. The mutants we isolated for increased expression appear to act by eliminating or destabilizing the Cys14-Cys38 disulfide in BPTI. In doing so, they are expected to reduce or eliminate kinetic traps that exist within the well characterized in vitro folding pathway of BPTI. These results suggest that elimination or destabilization of a disulfide bond whose formation is problematic in vitro can enhance in vivo protein folding. The use of these in vivo selections may prove a valuable way to identify and eliminate disulfides and other rate-limiting steps in the folding of proteins, including those proteins whose in vitro folding pathways are unknown. Antioxid. Redox Signal. 14, 973-984.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90494/1/ars-2E2010-2E3712.pd

Hybrid nanoparticles based on sulfides, oxides, and carbides

The methods for synthesis of hybrid nanoparticles based on sulfides, oxides, and carbides of heavy and transition metals were considered. The problem of the influence of the method of synthesis of the hybrid nanoparticles on their atomic structure, morphology of the nanomaterials, and functional properties was analyzed. The areas of practical use of the hybrid nanoparticles were proposed. © 2013 Springer Science+Business Media New York

Elastic Moduli of Nanoglasses and Melt-Spun Metallic Glasses by Ultrasonic Time-of-Flight Measurements

The elastic moduli of the metallic nanoglasses Fe$_{86}$Sc$_{14}$, Fe$_{90}$Sc$_{10}$, Cu$_{58}$Zr$_{42}$, and Cu$_{60}$Zr$_{40}$ were determined by measuring their longitudinal and shear wave velocities together with their densities. The data were compared to the elastic moduli of the conventional meltspun metallic glass counterparts of the same chemical composition. The elastic moduli for the nanoglasses were significantly smaller than those of the metallic glass counterparts. Finally, a comparison was made between the data for nanoglasses and metallic glasses from the literature

Elastic Moduli of Nanoglasses and Melt-Spun Metallic Glasses by Ultrasonic Time-of-Flight Measurements

The elastic moduli of the metallic nanoglasses Fe86Sc14, Fe90Sc10, Cu58Zr42, and Cu60Zr40 were determined by measuring their longitudinal and shear wave velocities together with their densities. The data were compared to the elastic moduli of the conventional melt-spun metallic glass counterparts of the same chemical composition. The elastic moduli for the nanoglasses were significantly smaller than those of the metallic glass counterparts. Finally, a comparison was made between the data for nanoglasses and metallic glasses from the literature

Synthesis of macrocyclic receptors with intrinsic fluorescence featuring quinizarin moieties

An unprecedented class of macrocycles with intrinsic fluorescence consisting of phenolic trimers and quinizarin is developed. Though they are lacking strong hydrogen bonds as observed in calixarenes, the two examples introduced here each adopt a vase-like conformation with all four aromatic units pointing in one direction (syn orientation). This “cone” conformation has been confirmed by NMR spectroscopy, molecular modeling, and X-ray crystallography. The laminar, electron-rich fluorophore as part of the macrocycle allows additional contacts to enclosed guest molecules

Processing and mechanical properties of magnesium-lithium composites containing steel fibers

Deformation-processed metal-metal composites (DMMC) of Mg-Li alloys containing steel reinforcing fibers were prepared by infiltrating a preform of steel wool with the molten matrix. The Li content was varied to control the crystal structure of the matrix; Mg-4 wt pct Li is hexagonal close packed (hcp), while Mg-12 wt pct Li is body-centered cubic (bcc). The low carbon steel used as the reinforcing fiber is essentially bcc. The hcp/bcc and bcc/bcc composites were subsequently deformed by rolling and by extrusion/swaging and mechanically tested to relate the tensile strength of the composites to true deformation strain. The hcp/bcc composites had limited formability at temperatures up to 400 °C, while the bcc/bcc composites had excellent formability during sheet rolling at room temperature but limited formability during swaging at room temperature. The tensile strengths of the hcp/bcc composite rod and the bcc/bcc composite sheet and rod increased moderately with deformation, though less than predicted from rule-of-mixtures (ROM) calculations. This article presents the experimental data for these DMMC materials and comments on the possible effect of texture development in the matrix and fiber phases on the deformation characteristics of the composite material

Comparison of the Structure of Grain Boundaries in Silicon and Diamond by Molecular-Dynamics Simulations

Molecular-dynamics simulations were used to synthesize nanocrystalline silicon with a grain size of up to 75 {angstrom} by crystallization of randomly misoriented crystalline seeds from the melt. The structures of the highly-constrained interfaces in the nanocrystal were found to be essentially indistinguishable from those of high-energy bicrystalline grain boundaries (GBs) and similar to the structure of amorphous silicon. Despite disorder, these GBs exhibit predominantly four-coordinated (sp{sup 3}-like) atoms and therefore have very few dangling bonds. By contrast, the majority of the atoms in high-energy bicrystalline GBs in diamond are three-coordinated (sp{sup 2}-like). Despite the large fraction of three-coordinated GB carbon atoms, they are rather poorly connected amongst themselves, thus likely preventing any type of graphite-like electrical conduction through the GBs

Comparison of the structure of grain boundaries in silicon and diamond by molecular-dynamics simulations

Molecular-dynamics simulations were used to synthesize nanocrystalline silicon with a grain size of up to 75 {angstrom} by crystallization of randomly misoriented crystalline seeds from the melt. The structures of the highly-constrained interfaces in the nanocrystal were found to be essentially indistinguishable from those of high-energy bicrystalline grain boundaries (GBs) and similar to the structure of amorphous silicon. Despite disorder, these GBs exhibit predominantly four-coordinated (sp{sup 3}-like) atoms and therefore have very few dangling bonds. By contrast, the majority of the atoms in high-energy bicrystalline GBs in diamond are three-coordinated (sp{sup 2}-like). Despite the large fraction of three-coordinated GB carbon atoms, they are rather poorly connected amongst themselves, thus likely preventing any type of graphite-like electrical conduction through the GBs