Local Clique Covering of Claw‐Free Graphs

A clique covering of a simple graph G is a collection of cliques of G covering all the edges of G such that each vertex is contained in at most k cliques. The smallest k for which G admits a clique covering is called the local clique cover number of G and is denoted by lcc(G). Local clique cover number can be viewed as the local counterpart of the clique cover number that is equal to the minimum total number of cliques covering all edges. In this article, several aspects of the local clique covering problem are studied and its relationships to other well‐known problems are discussed. In particular, it is proved that the local clique cover number of every claw‐free graph is at most , where Δ is the maximum degree of the graph and c is a constant. It is also shown that the bound is tight, up to a constant factor. Moreover, regarding a conjecture by Chen et al. (Clique covering the edges of a locally cobipartite graph, Discrete Math 219(1–3)(2000), 17–26), we prove that the clique cover number of every connected claw‐free graph on n vertices with the minimum degree δ, is at most , where c is a constant.     

Electron Transport in Quasi‐Two‐Dimensional Porous Network of Titania Nanoparticles,Incorporating Electrical and Optical Advantages in Dye‐Sensitized Solar Cells

The integration of fast electron transport and large effective surface area is critical to attaining higher gains in the nanostructured photovoltaic devices. Here, we report facilitated electron transport in the quasi‐two‐dimensional (Q2D) porous TiO₂. Liquid electrolyte dye‐sensitized solar cells were prepared by utilizing photoanodes based on the Q2D porous substructures. Due to electron confinement in a microscale porous medium, directional diffusion toward collecting electrode is induced into the electron transport. Our measurements based on the photocurrent and photovoltage time‐of‐flight transients show that at higher Fermi levels, the electron diffusion coefficient in the Q2D porous TiO₂ is about one order of magnitude higher when compared with the conventional layer of porous TiO₂. The results show that microstructuring of the porous TiO₂ leads to an approximately threefold improvement in the electron diffusion length. Such a modification may considerably affects the electrical functionality of moderate or low performance dye‐sensitized solar cells for which the internal gain or collection efficiency is typically low.     

Explorations on the asymmetric total synthesis of isoschizogamine

Two approaches to the synthesis of isoschizogamine were reported. Both routes utilized an efficient aza-Claisen rearrangement to establish the absolute stereochemistry of the all-carbon quaternary center in the natural product. In the first approach, a highly diastereoselective (10:1) hetero-Diels-Alder reaction was utilized to reach a densely functionalized tetrahydroquinoline derivative as an advanced intermediate to the targeted alkaloid. An acylamidine intermediate was prepared and studied in the intramolecular cyclization reaction under acidic conditions in our second approach.     

PVDF/PU blend membrane separator for lithium-ion batteries via non-solvent-induced phase separation (NIPS)

Membrane separator based on the polyvinylidene fluoride (PVDF) is prepared via the non-solvent-induced phase separation (NIPS) method with water and ethanol as non-solvent and a mixture of dimethylformamide (DMF) and acetone as solvent. The effect of various acetone/DMF ratios and non-solvent material on the physical and electrochemical properties of the separator is studied by FE-SEM, tensile strength, electrochemical AC-impedance spectroscopy (EIS), thermal stability, and linear sweep voltammetry (LSV). The charge-discharge studies are carried out by fabricating a lithium foil/polymer electrolyte membrane/LiFePO4 cell. The results show that with the change of solvent and non-solvent, the structure and morphology of the separator change and its physical and electrochemical properties. The results indicate that the membrane sample with non-solvent ethanol, acetone/DMF: 80/20 (wt/wt), and PVDF/PU: 95/5 (wt/wt) shows high porosity (66.3%) and high ionic conductivity (1.34 mS/cm) as well as excellent thermal stability.

     

On the role of substituent in noncovalent functionalization of graphene and organophosphor recognition: IQA and SAPT perspective

Despite importance of integrating organic molecules with graphene to fabricate graphene‐based electronic devices, the role of substituents and interface stabilizing forces are poorly understood. In this work, the interactions of 7,7,8,8‐tetracyanoquinodimethane (TCNQ), 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ), hydroquinone (Q), and tetrafluorohydroquinone (TFQ) with graphene have been investigated by means of interacting quantum atoms and SAPT(DFT). In addition, in context of potential design of a graphene‐based sensor for detection of the nerve agent sarin, we studied the interaction of graphene and the organic molecules with the dimethyl methylphosphonate (DMMP)—the molecule that mimics sarin. The results show that the organic molecules attach to graphene via C(sp²)?C(sp²), C(sp²)?C(sp) and H?π bonds. In addition, they trap DMMP via various linkages such as hydrogen, lonepair?π and H?π . The quantum effects play a significant role. The Pauli repulsion is responsible for p‐doping of graphene. The substituents are stabilized on graphene by the exchange‐correlation energy. The fluorination of the benzenoid ring raises the electron‐sharing . The through space and through bond effects of the fluorine atoms (‐F) increase the classical attraction of the cyano groups and benzenoid ring with graphene, respectively. When comparing performance of the ab initio and DFT methods, MP2 predicts too much attraction due to well‐known overestimation of the dispersion energy by the uncoupled dispersion component for benzene rings, while ω B97xD functional and SAPT(DFT) provide weaker interaction energies, in good agreement with each other.     

Anodic stripping voltammetric determination of silver ion at a carbon paste electrode modified with carbon nanotubes

A carbon paste electrode (CPE) was modified with multi-wall carbon nanotubes and successfully applied to the determination of silver ion by differential pulse anodic stripping voltammetry. Compared to a conventional CPE, a remarkably improved peak current response and sensitivity is observed. The analytical procedure consisted of an open circuit accumulation step for 2?min in ?0.4?V, this followed by an anodic potential scan between +0.2 and?+?0.6?V to obtain the voltammetric peak. The oxidation peak current is proportional to the concentration of silver ion in the range from 1.0?×?10^?8 to 1.0?×?10^?5?mol?L^?1, with a detection limit of 1.8?×?10^?9?mol?L^?1 after an accumulation time of 120?s. The relative standard deviation for 7 successive determinations of Ag(I) at 0.1???M concentration is 1.99%. The procedure was validated by determining Ag(I) in natural waters.

First-principle electronic, elastic, and optical study of cubic gallium nitride

The ab initio pseudopotential (PP) method within the generalized gradient approximation (GGA) has been used to investigate the electronic, elastic constants, and optical properties of zinc-blende GaN. An underestimated band gap along with higher DOS and squeezed energy bands around the fermi level is obtained. The d-band effect is briefly discussed for electronic band structure calculations. With the help of elastic constants, acoustic wave speeds are calculated in [100], [110], and [111] planes. The dielectric constant, refractive index, and its pressure coefficient are well illustrated. The effect of hydrostatic pressure is explicated for all these properties. The results of the present study are evaluated with the existing experimental and first-principle calculations.     

APPROXIMATION OF ADJOINT OF A MULTIPLIER ON BANACH ALGEBRAS

For a Banach algebra A,we denote by A* and A** the first and the second duals of A respectively.Let T be a mapping from A* to itself.In this article,we will investigate some stability results concernin...