A New Composite Material on the Base of Carbon Nanotubes and Boron Clusters B12 as the Base for High-Performance Supercapacitor Electrodes

We explore the quantum capacitance, stability, and electronic properties of single-walled carbon nanotubes decorated with B12 icosahedral boron clusters by first-principle calculation methods implemented in the SIESTA code. After the optimization of the built supercells, the B12 clusters formed bonds with the walls of the carbon nanotubes and demonstrated metallic properties in all cases. The network of carbon nanotubes with its large area and branched surface is able to increase the capacity of the electric double-layer capacity, but the low quantum capacity of each nanotube in this network limits its application in supercapacitors. We found that the addition of boron clusters to both the outer and inner walls increased the quantum capacitance of carbon nanotubes. The calculation of the transmission function near the Fermi energy showed an increase in the conductivity of supercells. It was also found that an increase in the concentration of boron clusters in the structure led to a decrease in the heat of formation that positively affects the stability of supercells. The calculation of the specific charge density showed that with an increase in the boron concentration, the considered material demonstrated the properties of an asymmetric electrode.

Свойства оптических керамик КО1 и КО2 при модификации их поверхности углеродными нанотрубками

The research results of the modification of the properties of the optical inorganic materials, such as: optical ceramic КО1(MgF2) and КО2(ZnS) have been presented. Essential change of the basic parameters of these inorganic matrixes, which surface has been modified with the carbon nanotubes under the application of the laser oriented deposition technique, has been established. The main features of the carbon nanotubes have been taken into account, which have been connected with their branched surface, large hardness of the C-C bonds and small value of the refractive index. Analytical and quantum-chemical calculations as well as the experimental results have been presented, which have been connected with the change of the spectral, mechanical and wetting characteristics of the chosen inorganic matrixes.

Genetic and Biochemical Characterizations of Enzymes Involved in Streptococcus pneumoniae Serotype 2 Capsule Synthesis Demonstrate that Cps2T (WchF) Catalyzes the Committed Step by Addition of β1-4 Rhamnose, the Second Sugar Residue in the Repeat Unit

ABSTRACTFive genes (cps2E,cps2T,cps2F,cps2G, andcps2I) are predicted to encode the glycosyltransferases responsible for synthesis of theStreptococcus pneumoniaeserotype 2 capsule repeat unit, which is polymerized to yield a branched surface structure containing glucose-glucuronic acid linked to a glucose-rhamnose-rhamnose-rhamnose backbone. Cps2E is the initiating glycosyltransferase, but experimental evidence supporting the functions of the remaining glycosyltransferases is lacking. To biochemically characterize the glycosyltransferases, the donor substrate dTDP-rhamnose was first synthesized using recombinantS. pneumoniaeenzymes Cps2L, Cps2M, Cps2N, and Cps2O. Inin vitroassays with each of the glycosyltransferases, only reaction mixtures containing recombinant Cps2T, dTDP-rhamnose, and the Cps2E product (undecaprenyl pyrophosphate glucose) generated a new product, which was consistent with lipid-linked glucose-rhamnose.cps2T,cps2F, andcps2Ideletion mutants produced no detectable capsule, but trace amounts of capsule were detectable in Δcps2Gmutants, suggesting that Cps2G adds a nonbackbone sugar. All Δcps2F, Δcps2G, and Δcps2Imutants contained different secondary suppressor mutations incps2E, indicating that the initial mutations were lethal in the absence of reduced repeat unit synthesis. Δcps2Tmutants did not contain secondary mutations affecting capsule synthesis. The requirement for secondary mutations in mutants lacking Cps2F, Cps2G, and Cps2I indicates that these activities occur downstream of the committed step in capsule synthesis and reveal that Cps2T catalyzes this step. Therefore, Cps2T is the β1-4 rhamnosyltransferase that adds the second sugar to the repeat unit and, as the committed step in type 2 repeat unit synthesis, is predicted to be an important point of capsule regulation.

CONTACT STRUCTURES, σ-CONFOLIATIONS AND CONTAMINATIONS IN 3-MANIFOLDS

We propose in this paper a method for studying contact structures in 3-manifolds by means of branched surfaces. We explain what it means for a contact structure to be carried by a branched surface embedded in a 3-manifold. To make the transition from contact structures to branched surfaces, we first define auxiliary objects called σ-confoliations and pure contaminations, both generalizing contact structures. We study various deformations of these objects and show that the σ-confoliations and pure contaminations obtained by suitably modifying a contact structure remember the contact structure up to isotopy. After defining tightness for all pure contaminations in a natural way, generalizing the definition of tightness for contact structures, we obtain some conditions on (the embedding of) a branched surface in a 3-manifold sufficient to guarantee that any pure contamination carried by the branched surface is tight. We also find conditions sufficient to prove that a branched surface carries only overtwisted (non-tight) contact structures. Our long-term goal in developing these methods is twofold: Not only do we want to study tight contact structures and pure contaminations, but we also wish to use them as tools for studying 3-manifold topology.