Valency

About: Valency is a research topic. Over the lifetime, 1632 publications have been published within this topic receiving 26141 citations.

Multivalent Ion Transport through a Nanopore

Abstract: Ion transport through nanopores finds increasing applications in biophysical and chemical processes. Distinct ion transport behaviors have been identified in sub 10 nm diameter nanopores as a result of complex interactions between ions and the nanopore surface. So far, most studies have been for monovalent electrolytes with little attention paid to the effects of multivalent ions. Here we report on the pronounced effects of high ion valency on the ion mobility inside narrow pores of a few nanometer diameters. Results show that ion mobilities are significantly suppressed at high electrolyte concentrations (>0.5 M), which is attributed to the formation of ion pairs inside the nanopore. Analyses suggest that a nanopore can help partially dehydrate ions and confine the electric field lines from an ion inside the nanopore, which enhances the interactions between ions and promotes the formation of ion pairs. This physical picture is further supported by the free energy landscapes demonstrating the diminished energy barrier for ion pair formation inside a nanopore.

Modelling chemical reactions using constraint programming and molecular graphs

Abstract: Generating all constitutional isomers (chemical compounds that have the same molecular formula but different chemical structures) is a challenging problem. The structures are normally represented by molecular graphs, where vertices are atoms and edges are chemical bonds. The degree of a vertex in the graph represents the valency of the corresponding atom. The problem can be extended to generating all sets of molecules that can result from a reaction. I have formulated this chemistry problem as a constraint satisfaction problem (CSP). As an initial representation of the problem, I represent each bond as a pair of variables. The atoms are represented by integers and connected by the bonds. The domain of each variable is all of the atoms in the problem. Each atom must appear a fixed number of times (its valency). For example, consider a problem that consists of two oxygens, two carbons and four hydrogens, i.e. eight atoms in three types. The number of bonds is half the sum of the atoms' valencies. For the sample problem we need 8 bonds. It is easy to specify the valency constraint with help of the Ilog Solver constraint IloDistribute, which restricts the appearance of variables that take a given value in an array. We believe this is the first constraint encoding of the problem.

Mechanism of the electrical conductivity of quasibinary MoSe2-TaSe2 (Mo1−xTaxSe2) alloys

Abstract: 1. Ta in MoSe2 acts as an acceptor impurity, and alloying with it sharply increases the electrical conductivity of the compound. 2. At x=0.12 · 10−2, the compound Mo1−xTaxSe2 is a nondegenerate semiconductor; compounds with x≥ 0.56 · 10−2 must be classed as semimetals. 3. The effective masses of charge carriers in Mo1−xTaxSe2 alloys are close to m0. This indicates that holes generated as a result of alloying with tantalum are located in the valency zone (Fig. 1b).