Valency

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

Phase transitions in high-T c superconductive oxides

Abstract: Superconductivity is stabilized by the opening up of an energy gap at the Fermi Energy E F below the superconductor transition temperature T c ; any other mechanism that opens an energy gap at E F is competitive. In the high-T c bismuth oxides, a charge-density wave (CDW) is competitive; in the high-T c copper oxides the correlation splitting associated with localized electrons is competitive. In each class of oxide, stabilization of superconductivity requires the introduction of mixed valency. It is argued that suppression of a CDW or of localized magnetic moments and long-range magnetic order by the introduction of mixed valency is not a sufficient condition for high-T c superconductivity. A common feature of the superconductive phase in all the p-type high-T c oxides is a Fermi energy that cuts two bands, a [sgrave]∗ band of primarily cationic character (Bi-6s or Cu-3dx2-y2) and a π or π∗ band of primarily anionic character (O-2pπ). The transition from localized copper magnetic moments to Paul...

Deciphering Photochemical Reaction Pathways of Aqueous Tetrachloroauric Acid by X-ray Transient Absorption Spectroscopy.

Abstract: Photolysis reaction pathways of [Au(III)Cl4]- in aqueous solution have been investigated by time-resolved X-ray absorption spectroscopy. Ultraviolet excitation directly breaks the Au-Cl bond in [Au(III)Cl4]- to form [Au(II)Cl3]- that becomes highly reactive within 79 ps. Disproportionation of [Au(II)Cl3]- generates [Au(I)Cl2]-, which is stable for ≤10 μs. In contrast, intense near-infrared lasers photolyze water to generate hydrated electrons, which then reduce [Au(III)Cl4]- to [Au(II)Cl3]- at 5 ns. Hydrated electrons further induce a chain reaction from [Au(II)Cl3]- to [Au(0)Cl]- by successively removing one Cl-. The zero-valency Au anions quickly polymerize and condense to form Au nanoparticles, which become the dominating product after 400 s. Our results reveal that the condensation of zero-valency Au starts with dimerization of gold clusters coordinated with chloride ions rather than direct condensation of pristine Au atoms.

CP-recursion and the derivation of verb second in Germanic main and embedded clauses

Abstract: his paper will give an overview of the verb second (V2) phenomenon, as found in both main and embedded clauses in Germanic, and it will also explore a particular derivation of (embedded) V2, in terms of a cP/CP-distinction. All the Germanic languages except modern English (but including e. g. Old English) are V2, i. e. in all declarative main clauses and in all wh-questions, the inite verb is in the second position, regardless of whether the irst position is occupied by the subject or by some other constituent. his can be extended to yes/no-questions, provided it is assumed that the irst position in such questions is empty (and such an assumption is supported by the fact that it allows an account for Greenberg’s 1963: 83 “Universal 11”, cf. Vikner 2007). No particular type of embedded clause in Germanic ever requires V2, and although V2 is optionally possible in many embedded clauses, this is normally not the case for all types of embedded clauses, as e. g. embedded questions (almost) never allow V2 (Julien 2007, Vikner 2001, though see McCloskey 2006 and Biberauer 2015). As in Nyvad et al. (2016), I will explore a particular derivation of (embedded) V2, in terms of a cP/ CP-distinction, which may be seen as a version of the CP-recursion analysis (deHaan & Weerman 1986, Vikner 1995 and many others). he idea is that because embedded V2 clauses do not allow extraction, whereas other types of CP-recursion clauses do (Christensen et al. 2013a; Christensen et al. 2013b; Christensen & Nyvad 2014), CP-recursion in embedded V2 is assumed to be fundamentally diferent from other kinds of CP-recursion, in that main clause V2 and embedded V2 involve a CP (“big CP”), whereas other clausal projections above IP are instances of cP (“litle cP”).

K-Best Spanning Tree Dependency Parsing With Verb Valency Lexicon Reranking

Abstract: A novel method for hybrid graph-based dependency parsing of natural language text is proposed. It is based on k-best maximum spanning tree dependency parsing and evaluation of the spanning trees by using a verb valency lexicon for a given language as a reranking knowledge base. The approach is compared with existing state-of-the-art transition-based and graph-based approaches to dependency parsing. As the proposed generic method was developed specifically for improving the accuracy of Croatian dependency parsing, Croatian Dependency Treebank and CROVALLEX verb valency lexicon are used in the experiment. The suggested approach scored approximately 77.21% LAS, outperforming the tested state-of-the-art approaches by at least 2.68% LAS.