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1

A valence bond study of the dioxygen molecule.  

PubMed

The dioxygen molecule has been the subject of valence bond (VB) studies since 1930s, as it was considered as the first "failure" of VB theory. The object of this article is to provide an unambiguous VB interpretation for the nature of chemical bonding of the molecule by means of modern VB computational methods, VBSCF, BOVB, and VBCI. It is shown that though the VBSCF method can not provide quantitative accuracy for the strongly electronegative and electron-delocalized molecule because of the lack of dynamic correlation, it still gives a correct qualitative analysis for wave function of the molecule and provides intuitive insights into chemical bonding. An accurate quantitative description for the molecule requires higher levels of VB methods that incorporate dynamic correlation. The potential energy curves of the molecule are computed at the various VB levels. It is shown that there exists a small hump in the PECs of VBSCF for the ground state, as found in previous studies. However, higher levels of VB methods dissolve the hump. The BOVB and VBCI methods reproduce the dissociation energies and other physical properties of the ground state and the two lowest excited states in very good agreement with experiment and with sophisticated MO based methods, such as the MRCI method. PMID:17061244

Su, Peifeng; Song, Lingchun; Wu, Wei; Hiberty, Philippe C; Shaik, Sason

2007-01-15

2

On the Relative Merits of Non-Orthogonal and Orthogonal Valence Bond Methods Illustrated on the Hydrogen Molecule  

ERIC Educational Resources Information Center

|Valence bond (VB) is one of the cornerstone theories of quantum chemistry. Even if in practical applications the molecular orbital (MO) approach has obtained more attention, some basic chemical concepts (such as the nature of the chemical bond and the failure of the single determinant-based MO methods in describing the bond cleavage) are normally…

Angeli, Celestino; Cimiraglia, Renzo; Malrieu, Jean-Paul

2008-01-01

3

Resonance and aromaticity: an ab initio valence bond approach.  

PubMed

Resonance energy is one of the criteria to measure aromaticity. The effect of the use of different orbital models is investigated in the calculated resonance energies of cyclic conjugated hydrocarbons within the framework of the ab initio Valence Bond Self-Consistent Field (VBSCF) method. The VB wave function for each system was constructed using a linear combination of the VB structures (spin functions), which closely resemble the Kekulé valence structures, and two types of orbitals, that is, strictly atomic (local) and delocalized atomic (delocal) p-orbitals, were used to describe the ?-system. It is found that the Pauling-Wheland's resonance energy with nonorthogonal structures decreases, while the same with orthogonalized structures and the total mean resonance energy (the sum of the weighted off-diagonal contributions in the Hamiltonian matrix of orthogonalized structures) increase when delocal orbitals are used as compared to local p-orbitals. Analysis of the interactions between the different structures of a system shows that the resonance in the 6? electrons conjugated circuits have the largest contributions to the resonance energy. The VBSCF calculations also show that the extra stability of phenanthrene, a kinked benzenoid, as compared to its linear counterpart, anthracene, is a consequence of the resonance in the ?-system rather than the H-H interaction in the bay region as suggested previously. Finally, the empirical parameters for the resonance interactions between different 4n+2 or 4n ? electrons conjugated circuits, used in Randi?'s conjugated circuits theory or Herdon's semi-emprical VB approach, are quantified. These parameters have to be scaled by the structure coefficients (weights) of the contributing structures. PMID:22559175

Rashid, Zahid; van Lenthe, Joop H; Havenith, Remco W A

2012-05-04

4

The Valence-Bond Theory of Molecular Structure. III. Cyclobutadiene and Benzene  

Microsoft Academic Search

The revised valence-bond (VB) theory of previous papers is applied in non-empirical calculation of the lower pi -electron levels of cyclobutadiene and benzene. For the first of these molecules, complete sets of all non-polar and polar, singlet and triplet structures are employed; for the second, 89 singlet and 69 triplet structures were selected from the complete sets of 175 singlet

R. McWeeny

1955-01-01

5

Valence-bond analysis of extended Hubbard models: Charge-transfer excitations of molecular conductors  

Microsoft Academic Search

The low-energy charge transfer (CT) excitation characteristic of both pi-molecular conductors and complex-ion-radical salts is interpreted as a nearest-neighbor Coulomb interaction V that is comparable to the bandwidth, 4|t|. Partly filled segregated regular stacks in organic conductors are represented by extended Hubbard models, whose exact CT energies and intensities are obtained by diagrammatic valence-bond (VB) methods for four electrons on

S. Mazumdar; Z. G. Soos

1981-01-01

6

Valence-bond states for quantum computation  

SciTech Connect

We propose a way of universal quantum computation by doing joint measurements on distributed singlets. We show how these joint measurements become local measurements when the singlets are interpreted as the virtual components of a large valence-bond state. This proves the equivalence of the cluster-state-based quantum computational model and the teleportation-based model, and we discuss several features and possible extensions. We show that all stabilizer states have a very simple interpretation in terms of valence-bond solids, which allows to understand their entanglement properties in a transparent way.

Verstraete, F.; Cirac, J.I. [Max-Planck-Institut fuer Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching (Germany)

2004-12-01

7

Nonorthogonal orbital based N-body reduced density matrices and their applications to valence bond theory. I. Hamiltonian matrix elements between internally contracted excited valence bond wave functions.  

PubMed

In this series, the n-body reduced density matrix (n-RDM) approach for nonorthogonal orbitals and their applications to ab initio valence bond (VB) methods are presented. As the first paper of this series, Hamiltonian matrix elements between internally contracted VB wave functions are explicitly provided by means of nonorthogonal orbital based RDM approach. To this end, a more generalized Wick's theorem, called enhanced Wick's theorem, is presented both in arithmetical and in graphical forms, by which the deduction of expressions for the matrix elements between internally contracted VB wave functions is dramatically simplified, and the matrix elements are finally expressed in terms of tensor contractions of electronic integrals and n-RDMs of the reference VB self-consistent field wave function. A string-based algorithm is developed for the purpose of evaluating n-RDMs in an efficient way. Using the techniques presented in this paper, one is able to develop new methods and efficient algorithms for nonorthogonal orbital based many-electron theory much easier than by use of the first quantized formulism. PMID:23635123

Chen, Zhenhua; Chen, Xun; Wu, Wei

2013-04-28

8

Nonorthogonal orbital based N-body reduced density matrices and their applications to valence bond theory. I. Hamiltonian matrix elements between internally contracted excited valence bond wave functions  

NASA Astrophysics Data System (ADS)

In this series, the n-body reduced density matrix (n-RDM) approach for nonorthogonal orbitals and their applications to ab initio valence bond (VB) methods are presented. As the first paper of this series, Hamiltonian matrix elements between internally contracted VB wave functions are explicitly provided by means of nonorthogonal orbital based RDM approach. To this end, a more generalized Wick's theorem, called enhanced Wick's theorem, is presented both in arithmetical and in graphical forms, by which the deduction of expressions for the matrix elements between internally contracted VB wave functions is dramatically simplified, and the matrix elements are finally expressed in terms of tensor contractions of electronic integrals and n-RDMs of the reference VB self-consistent field wave function. A string-based algorithm is developed for the purpose of evaluating n-RDMs in an efficient way. Using the techniques presented in this paper, one is able to develop new methods and efficient algorithms for nonorthogonal orbital based many-electron theory much easier than by use of the first quantized formulism.

Chen, Zhenhua; Chen, Xun; Wu, Wei

2013-04-01

9

Colloids with valence and specific directional bonding.  

PubMed

The ability to design and assemble three-dimensional structures from colloidal particles is limited by the absence of specific directional bonds. As a result, complex or low-coordination structures, common in atomic and molecular systems, are rare in the colloidal domain. Here we demonstrate a general method for creating the colloidal analogues of atoms with valence: colloidal particles with chemically distinct surface patches that imitate hybridized atomic orbitals, including sp, sp(2), sp(3), sp(3)d, sp(3)d(2) and sp(3)d(3). Functionalized with DNA with single-stranded sticky ends, patches on different particles can form highly directional bonds through programmable, specific and reversible DNA hybridization. These features allow the particles to self-assemble into 'colloidal molecules' with triangular, tetrahedral and other bonding symmetries, and should also give access to a rich variety of new microstructured colloidal materials. PMID:23128225

Wang, Yufeng; Wang, Yu; Breed, Dana R; Manoharan, Vinothan N; Feng, Lang; Hollingsworth, Andrew D; Weck, Marcus; Pine, David J

2012-11-01

10

On Short Ranged Resonating Valence Bond Liquids  

NASA Astrophysics Data System (ADS)

Over 40 years ago, P W Anderson proposed the short ranged resonating valence bond state as an alternative to Neel order in antiferromagnets with strong fluctuations---in hindsight, the first proposal for a topologically ordered Z2 spin liquid. In the last year, convincing numerical evidence has accumulated for the existence of such Z2 spin liquids in short ranged Hamiltonians on simple lattices in two dimensions. I will sketch the intellectually productive historical route between these two developments and survey what we now know about the physics of the short ranged RVB and allied states of matter.

Sondhi, Shivaji

2013-03-01

11

Reentrant valence transition in EuO at high pressures : beyond the bond-valence model  

SciTech Connect

The pressure-dependent relation between Eu valence and lattice structure in model compound EuO is studied with synchrotron-based x-ray spectroscopic and diffraction techniques. Contrary to expectation, a 7% volume collapse at {approx}45 GPa is accompanied by a reentrant Eu valence transition into a lower valence state. In addition to highlighting the need for probing both structure and electronic states directly when valence information is sought in mixed-valent systems, the results also show that widely used bond-valence methods fail to quantitatively describe the complex electronic valence behavior of EuO under pressure.

Souza-Neto, N.M.; Zhao, J.; Alp, E.; Shen, G.; Sinogeikin, S. V.; Lapertot, G.; Haskel, D. (X-Ray Science Division); (Laboratorio Nacional de Luz Suncrotron-LNLS); (Carnegie Institution of Washington); (Commissariat a l'Energie Atomique)

2012-07-12

12

Reentrant Valence Transition in EuO at High Pressures: Beyond the Bond-Valence Model  

NASA Astrophysics Data System (ADS)

The pressure-dependent relation between Eu valence and lattice structure in model compound EuO is studied with synchrotron-based x-ray spectroscopic and diffraction techniques. Contrary to expectation, a 7% volume collapse at ?45GPa is accompanied by a reentrant Eu valence transition into a lower valence state. In addition to highlighting the need for probing both structure and electronic states directly when valence information is sought in mixed-valent systems, the results also show that widely used bond-valence methods fail to quantitatively describe the complex electronic valence behavior of EuO under pressure.

Souza-Neto, N. M.; Zhao, J.; Alp, E. E.; Shen, G.; Sinogeikin, S. V.; Lapertot, G.; Haskel, D.

2012-07-01

13

Valence-bond states: Link models  

SciTech Connect

An isotropic anti-ferromagnetic quantum state on a square lattice is characterized by symmetry arguments only. By construction, this quantum state is the result of an underlying valence bond structure without breaking any symmetry in the lattice or spin spaces. A detailed analysis of the correlations of the quantum state is given (using a mapping to a 2D classical statistical model and methods in field theory like mapping to the non-linear sigma model or bosonization techniques) as well as the results of numerical treatments (regarding exact diagonalization and variational methods). Finally, the physical relevance of the model is motivated. A comparison of the model to known anti-ferromagnetic Mott-Hubbard insulators is given by means of the two-point equal-time correlation function obtained (i) numerically from the suggested state and (ii) experimentally from neutron scattering on cuprates in the anti-ferromagnetic insulator phase.

Rico, E. [Fakultat fuer Physik, Universitaet Wien, Boltzmanngasse 5, A-1090 Vienna (Austria)], E-mail: enrique.ortega@univie.ac.at; Huebener, R. [Institut fuer Theoretische Physik, Universitaet Innsbruck, Technikerstrasse 25, A-6020 Innsbruck (Austria); Institut fuer Quantenoptik und Quanteninformation der Osterreichischen Akademie der Wissenschaften, Innsbruck (Austria); Montangero, S. [Institut fuer Quanteninformationsverarbeitung, Universitaet Ulm, D-89069 Ulm (Germany); NEST-CNR-INFM and Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa (Italy); Moran, N. [Department of Mathematical Physics, National University of Ireland, Maynooth (Ireland); Pirvu, B. [Fakultat fuer Physik, Universitaet Wien, Boltzmanngasse 5, A-1090 Vienna (Austria); Vala, J. [Department of Mathematical Physics, National University of Ireland, Maynooth (Ireland); Dublin Institute for Advanced Studies, School of Theoretical Physics, 10 Burlington Road, Dublin (Ireland); Briegel, H.J. [Institut fuer Theoretische Physik, Universitaet Innsbruck, Technikerstrasse 25, A-6020 Innsbruck (Austria); Institut fuer Quantenoptik und Quanteninformation der Osterreichischen Akademie der Wissenschaften, Innsbruck (Austria)

2009-09-15

14

Hydrogen-abstraction reactivity patterns from A to Y: the valence bond way.  

PubMed

"Give us insight, not numbers" was Coulson's admonition to theoretical chemists. This Review shows that the valence bond (VB)-model provides insights and some good numbers for one of the fundamental reactions in nature, the hydrogen-atom transfer (HAT). The VB model is applied to over 50 reactions from the simplest H + H(2) process, to P450 hydroxylations and H-transfers among closed-shell molecules; for each system the barriers are estimated from raw data. The model creates a bridge to the Marcus equation and shows that H-atom abstraction by a closed-shell molecule requires a higher barrier owing to the additional promotion energy needed to prepare the abstractor for H-abstraction. Under certain conditions, a closed-shell abstractor can bypass this penalty through a proton-coupled electron transfer (PCET) mechanism. The VB model links the HAT and PCET mechanisms conceptually and shows the consequences that this linking has for H-abstraction reactivity. PMID:22566272

Lai, Wenzhen; Li, Chunsen; Chen, Hui; Shaik, Sason

2012-05-04

15

Spin-coupled valence bond theory  

NASA Astrophysics Data System (ADS)

In the spin-coupled description of molecular electronic structure, an N-electron system is described by N distinct-but non-orthogonal-orbitals, whose spins are coupled to the required resultant S in all possible ways. The coefficients of the basis functions comprising the orbitals and the coefficients of the different spin functions are fully optimized. The orbitals are frequently highly localized, and hence the model incorporates considerable electron correlation while retaining a high degree of visuality. The spin-coupled wave function is refined by non-orthogonal configuration interaction, and the final wave functions are of high quality but very compact. The various aspects of this theory are illustrated by a series of examples of increasing complexity: the H2 molecule, the BeH molecule, the 3B1 and lA1 states of CH2 and the cycloaddition of CH2 to ethenes, the 7t-electron system of benzene, and diazomethane (CH2N2). The results provide clear descriptions of the electronic structure and the associated processes. In benzene, the six ? orbitals are highly localized, with far-reaching implications for the description of aromatic systems. The case of diazomethane shows that the central N atom takes part in fiv. electron-pair bonds, and the same is true for a series of molecules such as N2O, Hcno, NO2, and CH2NHO (nitrone), whose structures have long caused problems in valency theory.

Cooper, D. L.; Gerratt, J.; Raimondi, M.

16

Exploring covalently bonded diamondoid particles with valence photoelectron spectroscopy.  

PubMed

We investigated the valence electronic structure of diamondoid particles in the gas phase, utilizing valence photoelectron spectroscopy. The samples were singly or doubly covalently bonded dimers or trimers of the lower diamondoids. Both the bond type and the combination of bonding partners are shown to affect the overall electronic structure. For singly bonded particles, we observe a small impact of the bond on the electronic structure, whereas for doubly bonded particles, the connecting bond determines the electronic structure of the highest occupied orbitals. In the singly bonded particles a superposition of the bonding partner orbitals determines the overall electronic structure. The experimental findings are supported by density functional theory computations at the M06-2X/cc-pVDZ level of theory. PMID:24007000

Zimmermann, Tobias; Richter, Robert; Knecht, Andre; Fokin, Andrey A; Koso, Tetyana V; Chernish, Lesya V; Gunchenko, Pavel A; Schreiner, Peter R; Möller, Thomas; Rander, Torbjörn

2013-08-28

17

Bond-valence methods for pKa prediction. II. Bond-valence, electrostatic, molecular geometry, and solvation effects  

Microsoft Academic Search

In a previous contribution, we outlined a method for predicting (hydr)oxy-acid and oxide surface acidity constants based on three main factors: bond valence, Me O bond ionicity, and molecular shape. Here, electrostatics calculations and ab initio molecular dynamics simulations are used to qualitatively show that Me O bond ionicity controls the extent to which the electrostatic work of proton removal

Barry R. Bickmore; Kevin M. Rosso; Christopher J. Tadanier; Eric J. Bylaska; Darrin Doud

2006-01-01

18

Valence-bond theory of compounds of transition metals  

PubMed Central

An equation relating the strength (bondforming power) of an spd hybrid bond orbital to the angles it makes with other bond orbitals is formulated and applied in the discussion of the structures of transition-metal carbonyls and other substances by the valence-bond method. The rather simple theory gives results that agree well with those obtained by the complicated and laborious calculation of sets of orthogonal hybrid bond orbitals with maximum strength.

Pauling, Linus

1975-01-01

19

A valence bond model for aqueous Cu(II) and Zn(II) ions in the AMOEBA polarizable force field.  

PubMed

A general molecular mechanics (MM) model for treating aqueous Cu(2+) and Zn(2+) ions was developed based on valence bond (VB) theory and incorporated into the atomic multipole optimized energetics for biomolecular applications (AMOEBA) polarizable force field. Parameters were obtained by fitting MM energies to that computed by ab initio methods for gas-phase tetra- and hexa-aqua metal complexes. Molecular dynamics (MD) simulations using the proposed AMOEBA-VB model were performed for each transition metal ion in aqueous solution, and solvent coordination was evaluated. Results show that the AMOEBA-VB model generates the correct square-planar geometry for gas-phase tetra-aqua Cu(2+) complex and improves the accuracy of MM model energetics for a number of ligation geometries when compared to quantum mechanical (QM) computations. On the other hand, both AMOEBA and AMOEBA-VB generate results for Zn(2+)-water complexes in good agreement with QM calculations. Analyses of the MD trajectories revealed a six-coordination first solvation shell for both Cu(2+) and Zn(2+) ions in aqueous solution, with ligation geometries falling in the range reported by previous studies. PMID:23212979

Xiang, Jin Yu; Ponder, Jay W

2012-12-05

20

Bond-valence methods for p K a prediction. II. Bond-valence, electrostatic, molecular geometry, and solvation effects  

Microsoft Academic Search

In a previous contribution, we outlined a method for predicting (hydr)oxy-acid and oxide surface acidity constants based on three main factors: bond valence, Me–O bond ionicity, and molecular shape. Here, electrostatics calculations and ab initio molecular dynamics simulations are used to qualitatively show that Me–O bond ionicity controls the extent to which the electrostatic work of proton removal departs from

Barry R. Bickmore; Kevin M. Rosso; Christopher J. Tadanier; Eric J. Bylaska; Darrin Doud

2006-01-01

21

Fate of the Resonating Valence Bond in Graphene  

NASA Astrophysics Data System (ADS)

We apply a variational wave function capable of describing qualitatively and quantitatively the so-called ”resonating valence bond” (RVB) in realistic materials, by improving standard ab initio calculations by means of quantum Monte Carlo methods. In this framework we clearly identify the Kekulé and Dewar contributions to the chemical bond of the benzene molecule and establish the corresponding RVB energy of these structures (?0.01eV/atom). We apply this method to unveil the nature of the chemical bond in undoped graphene, providing an estimate of the RVB energy gain, and show that this picture remains only within a small ”resonance length” of a few atomic units.

Marchi, Mariapia; Azadi, Sam; Sorella, Sandro

2011-08-01

22

Fate of the resonating valence bond in graphene.  

PubMed

We apply a variational wave function capable of describing qualitatively and quantitatively the so-called "resonating valence bond" (RVB) in realistic materials, by improving standard ab initio calculations by means of quantum Monte Carlo methods. In this framework we clearly identify the Kekulé and Dewar contributions to the chemical bond of the benzene molecule and establish the corresponding RVB energy of these structures (?0.01 eV/atom). We apply this method to unveil the nature of the chemical bond in undoped graphene, providing an estimate of the RVB energy gain, and show that this picture remains only within a small "resonance length" of a few atomic units. PMID:21929194

Marchi, Mariapia; Azadi, Sam; Sorella, Sandro

2011-08-19

23

Implementation of generalized valence bond-inspired coupled cluster theories  

NASA Astrophysics Data System (ADS)

We present an implementation of the recently proposed imperfect pairing (IP) and generalized valence bond restricted coupled cluster (GVB-RCC) methods. Our algorithm centers on repeated construction of Coulomb and exchange matrices. These operations are the computational bottleneck, scaling with the third power of system size for large systems. Robust optimization of the valence orbitals is attained using a geometrically consistent form of direct minimization. Analytic gradients of the IP and GVB-RCC energies are also obtained by a simple modification of the energy optimization scheme. As an illustration of the potential of these new methods, we use IP to compute the equilibrium geometry and energetics of a Si9H12 cluster that is a crude model for silicon dimerization on the Si(001) surface. We thus demonstrate a valuable role for IP and GVB-RCC as a diagnostic for the accuracy of reduced active space calculations as compared to their full valence analogs.

van Voorhis, Troy; Head-Gordon, Martin

2002-11-01

24

On the Construction of Diabatic and Adiabatic Potential Energy Surfaces Based on Ab Initio Valence Bond Theory‡  

PubMed Central

A theoretical model is presented for deriving effective diabatic states based on ab initio self-consistent field valence bond (VBSCF) theory by reducing the multi-configurational VB Hamiltonian into an effective two-state model. We describe two computational approaches for the optimization of the effective diabatic configurations, resulting in two ways of interpreting such effective diabatic states. In the variational diabatic configuration (VDC) method, the energies of the individual diabatic states are variationally minimized. In the consistent diabatic configuration (CDC) method, both the configuration coefficients and orbital coefficients are simultaneously optimized to minimize the adiabatic ground-state energy in VBSCF calculations. In addition, we describe a mixed molecular orbital and valence bond (MOVB) approach to construct the CDC diabatic and adiabatic states for a chemical reaction, whereas the VDC-MOVB method has been described previously. Employing the symmetric SN2 reaction between NH3 and CH3NH3+ as a test system, we found that the results from ab initio VBSCF and from MOVB calculations are in good agreement, suggesting that the computationally efficient MOVB method is a reasonable model for VB simulations of condensed phase reactions. The results indicate that CDC and VDC diabatic states converge, respectively, to covalent and ionic states as the molecular geometries are distorted from the minimum of the respective diabatic state along the reaction coordinate. Furthermore, the resonance energy that stabilizes the energy of crossing between the two diabatic states, resulting in the transition state of the adiabatic ground-state reaction, has a strong dependence on the overlap integral between the two diabatic states and is a function of both the exchange integral and the total diabatic ground-state energy.

Song, Lingchun; Gao, Jiali

2009-01-01

25

Topologically distinct classes of valence-bond solid states with their parent Hamiltonians  

Microsoft Academic Search

We present a general method to construct one-dimensional translationally invariant valence-bond solid states with a built-in Lie group G and derive their matrix product representations. The general strategies to find their parent Hamiltonians are provided so that the valence-bond solid states are their unique ground states. For quantum integer-spin-S chains, we discuss two topologically distinct classes of valence-bond solid states:

Tu Honghao; Zhang Guangming; Xiang Tao; Liu Zhengxin; Ng Taikai

2009-01-01

26

Resonating valence bond wave functions and classical interacting dimer models.  

PubMed

We relate properties of nearest-neighbor resonating valence-bond (NNRVB) wave functions for SU(g) spin systems on two-dimensional bipartite lattices to those of fully packed interacting classical dimer models on the same lattice. The interaction energy can be expressed as a sum of n-body potentials V(n), which are recursively determined from the NNRVB wave function on finite subgraphs of the original lattice. The magnitude of the n-body interaction V(n) (n>1) is of order O(g(-(n-1))) for small g(-1). The leading term is a two-body nearest-neighbor interaction V2(g) favoring two parallel dimers on elementary plaquettes. For SU(2) spins, using our calculated value of V2(g=2), we find that the long-distance behavior of the bond-energy correlation function is dominated by an oscillatory term that decays as 1/|r|? with ??1.22. This result is in remarkable quantitative agreement with earlier direct numerical studies of the corresponding wave function, which give ??1.20. PMID:23004328

Damle, Kedar; Dhar, Deepak; Ramola, Kabir

2012-06-15

27

Topologically distinct classes of valence-bond solid states with their parent Hamiltonians  

SciTech Connect

We present a general method to construct one-dimensional translationally invariant valence-bond solid states with a built-in Lie group G and derive their matrix product representations. The general strategies to find their parent Hamiltonians are provided so that the valence-bond solid states are their unique ground states. For quantum integer-spin-S chains, we discuss two topologically distinct classes of valence-bond solid states: one consists of two virtual SU(2) spin-J variables in each site and another is formed by using two SO(2S+1) spinors. Among them, a spin-1 fermionic valence-bond solid state, its parent Hamiltonian, and its properties are discussed in detail. Moreover, two types of valence-bond solid states with SO(5) symmetries are further generalized and their respective properties are analyzed as well.

Tu Honghao; Zhang Guangming; Xiang Tao; Liu Zhengxin; Ng Taikai [Department of Physics, Tsinghua University, Beijing 100084 (China); Institute of Physics, Chinese Academy of Sciences, P.O. Box 603, Beijing 100190 (China) and Institute of Theoretical Physics, Chinese Academy of Sciences, P.O. Box 2735, Beijing 100190 (China); Department of Physics, Hong Kong University of Science and Technology, Kowloon, Hong Kong (China)

2009-07-01

28

Entanglement in gapless resonating-valence-bond states  

NASA Astrophysics Data System (ADS)

We study resonating-valence-bond (RVB) states on the square lattice of spins and of dimers, as well as SU(N)-invariant states that interpolate between the two. These states are ground states of gapless models, although the SU(2)-invariant spin RVB state is also believed to be a gapped liquid in its spinful sector. We show that the gapless behavior in spin and dimer RVB states is qualitatively similar by studying the Rényi entropy for splitting a torus into two cylinders. We compute this exactly for dimers, showing it behaves similarly to the familiar one-dimensional log term, although not identically. We extend the exact computation to an effective theory believed to interpolate among these states. By numerical calculations for the SU(2) RVB state and its SU(N)-invariant generalizations, we provide further support for this belief. We also show how the entanglement entropy behaves qualitatively differently for different values of the Rényi index n, with large values of n proving a more sensitive probe here, by virtue of exhibiting a striking even/odd effect.

Stéphan, Jean-Marie; Ju, Hyejin; Fendley, Paul; Melko, Roger G.

2013-01-01

29

Chemical Bonds and Valence States of Atoms in Monocarbides and Mononitrides of D-Transition Metals.  

National Technical Information Service (NTIS)

On the basis of the metallic bond model described earlier, the chemical bond and atomic valency in these phases are considered. It is shown that the character of the interatomic bond in nitrides and carbides is identical. Electron transfer between the com...

P. P. Kuz'menko

1975-01-01

30

Distortion of V{sup z+}O{sub n} coordination polyhedra and parameters of the bond valence model for V-O bonds in inorganic crystals  

SciTech Connect

The dependences of average V-O distances in inorganic compounds of vanadium of different valence on the degree of distortion of coordination polyhedra have been obtained by careful statistical treatment of modern structural data banks. Values of bond lengths in undistorted (regular) polyhedra are recommended. Theoretical analysis of the statistical data made it possible to calculate the most likely values of the parameters of the bond valence model: the interatomic distance for the single (two-electron) bond, corresponding to the single valence, and the bond softness parameter. Calculations of the sums of bond valences for some complicated cases (different coordination numbers, mixed vanadium valence) confirmed reliability of the recommended parameters.

Urusov, V. S., E-mail: urusov@geol.msu.ru [Moscow State University (Russian Federation); Serezhkin, V. N. [Samara State University (Russian Federation)

2009-03-15

31

Bond-valence-sum study on possible candidates for high-Tc oxide superconductors  

NASA Astrophysics Data System (ADS)

Relationships between crystal structures and electronic states of layered transition-metal oxides have been analyzed in the light of bond valence sums. Parameters are introduced representing excess charge and internal strain in the central MO2 planes (M = 3d transition metal) and characterizing the electronic states of those oxides. Correlations between the superconducting transition temperature and those bond-valence-sum parameters are investigated for the high-Tc cuprate compounds and the possibility of making nonsuperconducting oxides superconducting is discussed.

Tanaka, Shigenori; Fukushima, Noburu; Niu, Hiromi; Ando, Ken

1990-11-01

32

Paired-permanent approach for VB theory (II)  

Microsoft Academic Search

Paired-permanent approach for VB theory is extensively developed. Canonical expansion of a paired-permanent is deduced. Furthermore,\\u000a it is shown that a paired-permanent may be expressed in terms of the products of sub-paired-permanents of any given order\\u000a and their corresponding minors. Anab initio spin-free valence bond program, called Xiamen, is implemented by using paired-permanent approach. Test calculation shows\\u000a that Xiamen package

Lingchun Song; Yan Luo; Kunming Dong; Wei Wu; Yirong Mo; Qianer Zhang

2001-01-01

33

Bond-valence model for metal cluster compounds. II. Matrix effect.  

PubMed

The bond-valence model was commonly considered as inappropriate to metal cluster compounds, but recently it was shown that the model provides unique information on the lattice strains and stabilization mechanisms in (TM)6-chalcohalides, Mx(TM)6Ly (TM = transition metal, L = the chalcogen and/or halogen ligands; M = counter-cation). The previous study was mainly devoted to the non-uniform distribution of the anion valences (bond-valence sums) around clusters. This and the previous paper are focused on two additional phenomena: (i) a steric conflict between counter-cations and the cluster-ligand framework resulting in `common' lattice strains [previous paper: Levi et al. (2013). Acta Cryst. B69, 419-425], and (ii) steric conflict between the small (TM)6-cluster and the large coordination polyhedron around the cluster or so-called matrix effect (this paper). It was shown that both phenomena can be well described by changes in the bond-valence parameters. This paper demonstrates that the matrix effect results in high strains in the TM-L bonds in most of the (TM)6-chalcohalides (TM = Nb, Mo, W and Re). In spite of this, the violations for the total TM valence are minimal, because the cluster stretching is fully or partially compensated by compression of the TM-L bonds. As a result, the influence of the matrix effect on the material stability is rather positive: it decreases the volume of the structural units and in many cases ensures a more favorable distribution of the bond valences around TM atoms, stabilizing the cluster compound. PMID:24056351

Levi, Elena; Aurbach, Doron; Isnard, Olivier

2013-09-19

34

Maximized string order parameters in the valence bond solid states of quantum integer spin chains  

NASA Astrophysics Data System (ADS)

We propose a set of maximized string order parameters to describe the hidden topological order in the valence bond solid states of quantum integer spin-S chains. These optimized string order parameters involve spin-twist angles corresponding to ZS+1 rotations around z or x-axes, suggesting a hidden ZS+1 × ZS+1 symmetry. Our results also suggest that a local triplet excitation in the valence bond solid states carries a ZS+1 topological charge measured by these maximized string order parameters.

Tu, Hong-Hao; Zhang, Guang-Ming; Xiang, Tao

2009-07-01

35

Correlation functions in SU(2)-invariant resonating-valence-bond spin liquids on nonbipartite lattices.  

PubMed

We introduce a Monte Carlo scheme based on sampling of Pfaffians to investigate Anderson's resonating-valence-bond (RVB) spin liquid wave function on the kagome and the triangular lattice. This eliminates a sign problem that prevents utilization of the valence bond basis in Monte Carlo studies for nonbipartite lattices. Studying lattice sizes of up to 600 sites, we calculate singlet-singlet and spin-spin correlations and demonstrate how the lattice symmetry is restored within each topological sector as the system size is increased. Our findings are consistent with the expectation that the nearest-neighbor RVB states describe a topological spin liquid on these nonbipartite lattices. PMID:23083280

Wildeboer, Julia; Seidel, Alexander

2012-10-05

36

Ab initio calculations of the pi-electronic structures of pyridine by valence-bond method  

Microsoft Academic Search

Ab initio valence-bond calculations of the pi-electronic energy levels, pi-electron densities and bond orders for pyridine have been carried out on the basis of the complete set of non-polar and polar structures. The atomic orbitals have been assumed to be Slater orbitals. The multiple exchange integrals have been taken into account completely by the orthogonalization of the pi-atomic orbitals. The

Shozaburo Takekiyo

1978-01-01

37

Empirical valence bonds: A reactive classical potential for sulphuric acid and water  

NASA Astrophysics Data System (ADS)

A two state multi-proton empirical valence bond (EVB) model is developed for molecular clusters of sulphuric acid, bisulphate, hydronium and water. A particle swarm optimisation (PSO) scheme is used to fit the parameters of the EVB model to DFT level data. The key feature of the model is that it allows proton transfer to be modelled within classical molecular dynamics.

Stinson, Jake L.; Kathmann, Shawn M.; Ford, Ian J.

2013-05-01

38

Nitrobenzene valence bond structures: evidence in support of ''through-resonance'' from /sup 17/O shieldings  

SciTech Connect

/sup 17/O shieldings in nitrobenzenes have been found to be sensitive to the electronic character of para substituents precisely in the manner anticipated from consideration of valence bond structure. Furthermore, the large sensitivity to electron density changes indicates /sup 17/O to be an attractive probe of electron distributions.

Fraser, R.R. (Univ. of Ottawa, Ontario, Canada); Ragauskas, A.J.; Stothers, J.B.

1982-11-17

39

Bond-valence model for metal cluster compounds. I. Common lattice strains.  

PubMed

The bond-valence model was commonly considered as inappropriate to metal cluster compounds, but recently it was shown that the model provides unique information on the lattice strains and stabilization mechanisms in (TM)6-chalcohalides (TM = transition metal in the cluster). The previous study was mainly devoted to the non-uniform distribution of the anion valences (bond-valence sums) around clusters. This and the following paper focuses on two additional phenomena: (i) a steric conflict between counter-cations and the cluster-ligand framework resulting in `common' lattice strains (this paper), and (ii) steric conflict between the small (TM)6-cluster and the large coordination polyhedron around the cluster or so-called matrix effect [the next paper; Levi et al. (2013), Acta Cryst. B69, 426-438]. It was shown that both phenomena can be well described by changes in the bond-valence parameters. The calculations were based on the structural data known to date for a variety of (TM)6-cluster compounds, Mx(TM)6Ly (TM = Nb, Mo, W and Re; M = various additional cations, L = the chalcogen and/or halogen ligands). The results were used to explain the structural peculiarities of these compounds with remarkable physical properties and the mechanisms of their stabilization. PMID:24056350

Levi, Elena; Aurbach, Doron; Isnard, Olivier

2013-09-19

40

Resonating valence bond state in LaâCuOâ and superconductivity  

Microsoft Academic Search

The oxide superconductors, particularly those recently discovered that are based on LaâCuOâ, have a set of peculiarities that suggest a common, unique mechanism: they tend in every case to occur near a metal-insulator transition into an odd-electron insulator with peculiar magnetic properties. This insulating phase is proposed to be the long-sought resonating-valence-bond state or quantum spin liquid hypothesized in 1973.

P. W. ANDERSON

1987-01-01

41

Resonating Valence Bond States in 2 and 3D: Brief History and Recent Examples  

Microsoft Academic Search

Resonating Valence Bond states are quantum spin liquids, having low energy spin-half (spinon) or spin-1 excitations. Although spins are `disordered', they posses subtle topological orders and some times chiral orders. RVB states are easily appreciated and seem natural in the quantum fluctuation dominated 1D world. In 2 and 3D, competing orders such as antiferromagnetism, charge order or even superconductivity often

G. Baskaran

2006-01-01

42

Doping an optimized resonance-valence-bond state: A picture of spin-charge separation  

Microsoft Academic Search

A systematic ``loop-gas'' formalism is developed for a general study of the resonance-valence-bond (RVB) states of a quantum antiferromagnet. At half-filling, we obtain analytic, parameter-free RVB amplitudes which reproduce virtually exact ground-state energy and spin excitation spectrum. A doped hole is then modeled by a holon-spinon pair moving on this optimized RVB background. Its energy is in excellent agreement with

Yong-Cong Chen; Zheng-Yu Weng

1996-01-01

43

Quantum computational capability of a 2D valence bond solid phase  

SciTech Connect

Highlights: > Our model is the 2D valence bond solid phase of a quantum antiferromagnet. > Universal quantum computation is processed by measurements of quantum correlations. > An intrinsic complexity of strongly-correlated quantum systems could be a resource. - Abstract: Quantum phases of naturally-occurring systems exhibit distinctive collective phenomena as manifestation of their many-body correlations, in contrast to our persistent technological challenge to engineer at will such strong correlations artificially. Here we show theoretically that quantum correlations exhibited in the 2D valence bond solid phase of a quantum antiferromagnet, modeled by Affleck, Kennedy, Lieb, and Tasaki (AKLT) as a precursor of spin liquids and topological orders, are sufficiently complex yet structured enough to simulate universal quantum computation when every single spin can be measured individually. This unveils that an intrinsic complexity of naturally-occurring 2D quantum systems-which has been a long-standing challenge for traditional computers-could be tamed as a computationally valuable resource, even if we are limited not to create newly entanglement during computation. Our constructive protocol leverages a novel way to herald the correlations suitable for deterministic quantum computation through a random sampling, and may be extensible to other ground states of various 2D valence bond phases beyond the AKLT state.

Miyake, Akimasa, E-mail: amiyake@perimeterinstitute.ca [Perimeter Institute for Theoretical Physics, 31 Caroline Street North, Waterloo Ontario, N2L 2Y5 (Canada)

2011-07-15

44

Classical trajectory models for electronically nonadiabatic collision processes: A classical valence bond model for electronic degrees of freedom  

Microsoft Academic Search

A classical interpretation of the Dirac–Van Vleck spin version of valence bond theory is used to obtain a classical model for electronic degrees of freedom within the valence bond framework. The approach is illustrated by deriving the explicit forms of the classical Hamiltonians, involving electronic and heavy particle degrees of freedom, for the H–H2, F–H2, and O–H2 systems. It is

William H. Miller; Ann E. Orel

1981-01-01

45

Classical trajectory models for electronically nonadiabatic collision processes: A classical valence bond model for electronic degrees of freedom  

Microsoft Academic Search

A classical interpretation of the Dirac--Van Vleck spin version of valence bond theory is used to obtain a classical model for electronic degrees of freedom within the valence bond framework. The approach is illustrated by deriving the explicit forms of the classical Hamiltonians, involving electronic and heavy particle degrees of freedom, for the H--Hâ, F--Hâ, and O--Hâ systems. It is

William H. Miller; Ann E. Orel

1981-01-01

46

Orbital imaging and assessment of different orbital models for the valence shell of methanol  

Microsoft Academic Search

The momentum distributions of the valence orbitals of methanol have been studied by electron momentum spectroscopy (EMS) and Hartree–Fock (HF), multi-reference singles and doubles configuration interaction (MRSD-CI), localized valence bond (VB) and density functional theory (DFT) calculations. The experiment was performed using a multichannel EMS spectrometer at a total energy of 1200 eV plus the binding energy. Binding-energy spectra measured

J. Rolke; Y. Zheng; C. E. Brion; Z. Shi; Saul Wolfe; E. R. Davidson

1999-01-01

47

The Breathing Orbital Valence Bond Method in Diffusion Monte Carlo: C-H Bond Dissociation ofAcetylene  

SciTech Connect

This study explores the use of breathing orbital valence bond (BOVB) trial wave functions for diffusion Monte Carlo (DMC). The approach is applied to the computation of the carbon-hydrogen (C-H) bond dissociation energy (BDE) of acetylene. DMC with BOVB trial wave functions yields a C-H BDE of 132.4 {+-} 0.9 kcal/mol, which is in excellent accord with the recommended experimental value of 132.8 {+-} 0.7 kcal/mol. These values are to be compared with DMC results obtained with single determinant trial wave functions, using Hartree-Fock orbitals (137.5 {+-} 0.5 kcal/mol) and local spin density (LDA) Kohn-Sham orbitals (135.6 {+-} 0.5 kcal/mol).

Domin, D.; Braida, Benoit; Lester Jr., William A.

2008-05-30

48

d-Wave Resonating Valence Bond States of Fermionic Atoms in Optical Lattices  

SciTech Connect

We study controlled generation and measurement of superfluid d-wave resonating valence bond (RVB) states of fermionic atoms in 2D optical lattices. Starting from loading spatial and spin patterns of atoms in optical superlattices as pure quantum states from a Fermi gas, we adiabatically transform this state to an RVB state by a change of the lattice parameters. Results of exact time-dependent numerical studies for ladders systems are presented, suggesting generation of RVB states on a time scale smaller than typical experimental decoherence times.

Trebst, Simon [Theoretische Physik, Eidgenoessische Technische Hochschule Zuerich, CH-8093 Zurich (Switzerland); Computational Laboratory, Eidgenoessische Technische Hochschule Zuerich, CH-8092 Zurich (Switzerland); Microsoft Research and Kavli Institute for Theoretical Physics, University of California, Santa Barbara, California 93106 (United States); Schollwoeck, Ulrich [Institut fuer Theoretische Physik C, RWTH Aachen, D-52056 Aachen (Germany); Troyer, Matthias [Theoretische Physik, Eidgenoessische Technische Hochschule Zuerich, CH-8093 Zurich (Switzerland); Zoller, Peter [Institute for Theoretical Physics, University of Innsbruck, and Institute for Quantum Optics and Quantum Information of the Austrian Academy of Science, 6020 Innsbruck (Austria)

2006-06-30

49

The empirical valence bond as an effective strategy for computer-aided enzyme design.  

PubMed

The ability of the empirical valence bond (EVB) to be used in screening active site residues in enzyme design is explored in a preliminary way. This validation is done by comparing the ability of this approach to evaluate the catalytic contributions of various residues in chorismate mutase. It is demonstrated that the EVB model can serve as an accurate tool in the final stages of computer-aided enzyme design (CAED). The ability of the model to predict quantitatively the catalytic power of enzymes should augment the capacity of current approaches for enzyme design. PMID:19229886

Vardi-Kilshtain, Alexandra; Roca, Maite; Warshel, Arieh

2009-04-01

50

Bond-valence sums for Tc–O systems from EXAFS data  

Microsoft Academic Search

Literature data for structures containing exclusively Tc–O bonds were used to calculate unit-valence parameters R0 for Tc(VII), Tc(VI), Tc(V) (five-coordinate), Tc(V) (six-coordinate), Tc(IV) and Tc(III) as 1.909, 1.955, 1.870, 1.859, 1.841 and 1.768 Å, respectively. A second method of estimating R0 was developed to validate the calculated values for these oxidation states because crystallographic data are limited. The method was

Dennis W. Wester; Nancy J. Hess

2005-01-01

51

Dual Mappings and Phase Transitions in a Short - Random Valence Bond Theory.  

NASA Astrophysics Data System (ADS)

This thesis describes calculations done in 3-D Short-Range Random Valence Bond theory. After reviewing the background of SRRVB and how it can be derived, I cover the technique of dual mappings, with a particular emphasis on the Compact U(1) model, the monopole loop gas picture, and the confinement/deconfinement phase transition. The argument is then made that an equivalent phase transition may exist in the 3-D SRRVB, based on its mapping onto a similar monopole loop gas picture, albeit complicated by the presence of Berry phases. Building on results from the 2-D model, I also argue for the existence of a second phase transition; this being the melting from a Valence -Bond Crystal to a Quantum Spin Liquid. To demonstrate the existence of one or both of these phase transitions, I have proformed numerical simulations using Monte Carlo. The confinement/deconfinement phase transition is tracked using both hysteresis and Wilson loop measurements, starting from the Compact U(1) model and slowly modifying the background and the anisotropy. The VBC/QSL phase transition is investigated by direct modeling of the J-V version of the SRRVB and measuring various correlation functions.

Sienko, Tanya Christine

52

Emergence of superconductivity, valence bond order, and Mott insulators in Pd[(dmit)2] based organic salts.  

PubMed

The EtMe(3)P and EtMe(3)Sb triangular organic salts are distinguished from other Pd[(dmit)(2)] based salts, as they display valence bond and no long-range order, respectively. Under pressure, a superconducting phase is revealed in EtMe(3)P near the boundary of valence bond order. We use slave-rotor theory with an enlarged unit cell to study competition between uniform and broken translational symmetry states, offering a theoretical framework capturing the superconducting, valence bond order, spin liquid, and metallic phases on an isotropic triangular lattice. Our finite temperature phase diagram manifests a remarkable resemblance to the phase diagram of the EtMe(3)P salt, where the reentrant transition of insulator-metal-insulator type can be explained by an entropy difference between the metal and U(1) spin liquid. We predict different temperature dependence of the specific heat between the spin liquid and metal. PMID:21405417

Rau, Jeffrey G; Kee, Hae-Young

2011-02-04

53

Can aromaticity coexist with diradical character? An ab initio valence bond study of S2N2 and related 6?-electron four-membered rings E2N2 and E4(2+) (E=S, Se, Te).  

PubMed

A series of 6?-electron 4-center species, E(2)N(2) and E(4)(2+) (E=S, Se, Te) is studied by means of ab initio valence bond methods with the aims of settling some controversies on 1) the diradical character of these molecules and 2) the radical sites, E or N, of the preferred diradical structure. It was found that for all molecules, the cumulated weights of the two possible diradical structures are always important and close to 50 %, making these molecules comparable to ozone in terms of diradical character. While the two diradical structures are degenerate in the E(4)(2+) dications, they have on the contrary strongly unequal weights in the E(2)N(2) neutral molecules. In these three molecules, the electronic structure is dominated by one diradical structure, in which the radical sites are the two nitrogen atoms, while the other diradical structure is much less important. The ordering of the various VB structures in terms of their calculated weights is confirmed by the relative energies of individual VB structures. In all cases, the major diradical structure (or both diradical structures when they are degenerate) is (are) the lowest one(s), while the covalent VB structures lie higher in energy. The vertical resonance energies are considerable in S(2)N(2) and S(4)(2+), about 80 % of the estimated value for benzene, and diminish as one goes down the periodic table (S?Se?Te). This confirms the aromatic character of these species, as already demonstrated for S(2)N(2) on the basis of magnetic criteria. This and the high weights and stabilities of one or both diradical structures in all systems indicates that aromaticity and diradical character do not exclude each other, contrary to what is usually claimed. Furthermore, it is shown that the diradical structures find their place in a collective electron flow responsible for the ring currents in the ? system of these species. PMID:22275164

Braïda, Benoît; Lo, Aurélien; Hiberty, Philippe C

2012-01-24

54

Exact Valence Bond Entanglement Entropy and Probability Distribution in the XXX Spin Chain and the Potts Model  

NASA Astrophysics Data System (ADS)

We determine exactly the probability distribution of the number Nc of valence bonds connecting a subsystem of length L?1 to the rest of the system in the ground state of the XXX antiferromagnetic spin chain. This provides, in particular, the asymptotic behavior of the valence-bond entanglement entropy SVB=?Nc?ln?2=(4ln?2)/(?2)ln?L disproving a recent conjecture that this should be related with the von Neumann entropy, and thus equal to (1)/(3)ln?L. Our results generalize to the Q-state Potts model.

Jacobsen, J. L.; Saleur, H.

2008-02-01

55

Spin triplet excitations for a valence bond solid on the kagome lattice  

NASA Astrophysics Data System (ADS)

One of the most promising candidate ground states for the quantum antiferromagnetic Heisenberg model on the kagome lattice is the valence bond solid (VBS) with a 36-site unit cell. We present a theory of triplet excitation spectra about this ground state using bond operator formalism. In particular we obtain dispersions of all 18 triplet modes in the reduced Brillouin zone. In the bond operator mean-field theory, it is found that a large number of triplet modes are nondispersive. In particular, the lowest triplet excitation is nondispersive and degenerate with a dispersive mode at the zone center. Away from the zone center, the lowest triplet is separated from two other flat modes by a small energy gap. Quantum fluctuations are considered by taking into account scattering processes of two triplets and their bound-state formation, which leads to a downward renormalization of the lowest spin triplet gap. The dispersion of the lowest triplet excitation in the VBS state is compared with the dispersive lower bound of the triplet continuum expected in competing spin liquid phases. Implications to future neutron-scattering experiments are discussed.

Yang, Bohm-Jung; Kim, Yong Baek; Yu, Jaejun; Park, Kwon

2008-06-01

56

Mott transition in a valence-bond solid insulator with a triangular lattice.  

PubMed

We have investigated the Mott transition in a quasi-two-dimensional Mott insulator EtMe{3}P[Pd(dmit){2}]{2} with a spin-frustrated triangular-lattice in hydrostatic pressure and magnetic-field [Et and Me denote C2H5 and CH3, respectively, and Pd(dmit){2} (dmit=1,3-dithiole-2-thione-4,5-dithiolate,dithiolate) is an electron-acceptor molecule]. In the pressure-temperature (P-T) phase diagram, a valence-bond solid phase is found to neighbor the superconductor and metal phases at low temperatures. The profile of the phase diagram is common to those of Mott insulators with antiferromagnetic order. In contrast to the antiferromagnetic Mott insulators, the resistivity in the metallic phase exhibits anomalous temperature dependence, rho=rho{0}+AT(2.5). PMID:18233536

Shimizu, Y; Akimoto, H; Tsujii, H; Tajima, A; Kato, R

2007-12-19

57

Inner valence shell bonding mechanism of n-butane studied using orbital momentum distributions of its conformational isomers  

NASA Astrophysics Data System (ADS)

The inner valence shell bonding mechanism has been studied using orbital topologies and their momentum distributions for the four most significant n-butane conformational isomers. The conformational isomers are due to rotation about the central C-C bond from the global energy minimum structure, the anti-butane isomer (A) with the dihedral angle, dgr = 0°, giving two transition states (B and D) and a local minimum (C). The wavefunctions of the conformers calculated using RHF/TZVP and B3LYP/TZVP methods are directly mapped onto their orbital momentum distributions using the one-electron and plane wave impulse approximations. The inner valence orbital topologies and momentum distributions are analysed in detail to reveal their anisotropy and symmetry correlation as the angle dgr deviates from the reference structure. Such important orbital information is largely indistinguishable in coordinate space. The present work demonstrates that only the innermost valence molecular orbital of n-butane is dominated by the carbon 2s-atomic orbitals (AOs); the remaining inner valence orbitals are dominated by the central carbon 2s-AOs and 2p-AOs. This evidence breaks down the classification of the 'valence molecular orbitals of a CnH2n+2 alkane into n inner valence levels in the C2s region, well separated from the n + 2 outer molecular orbitals of dominant C2p + H1s character'.

Wang, Feng; Downton, Matthew

2004-02-01

58

Ab initio calculations of the pi-electron structures of aniline by the valence-bond method  

Microsoft Academic Search

Ab initio valence bond calculations of the pi-electron energy levels, pi-electron densities and bond orders for aniline have been carried out on the basis of the complete set of non-polar and polar structures. The atomic orbitals have been assumed to be Slater orbitals. The multiple exchange integrals have been taken into account completely by the orthogonalization of the pi-atomic orbitals.

Shozaburo Takekiyo

1988-01-01

59

Nitrobenzene valence bond structures: evidence in support of ''through-resonance'' from ¹⁷O shieldings  

Microsoft Academic Search

¹⁷O shieldings in nitrobenzenes have been found to be sensitive to the electronic character of para substituents precisely in the manner anticipated from consideration of valence bond structure. Furthermore, the large sensitivity to electron density changes indicates ¹⁷O to be an attractive probe of electron distributions.

Robert R. Fraser; Arthur J. Ragauskas; J. B. Stothers

1982-01-01

60

Valence-bond crystal and lattice distortions in a pyrochlore antiferromagnet with orbital degeneracy  

NASA Astrophysics Data System (ADS)

We discuss the ground state properties of a spin- 1/2 magnetic ion with threefold t2g orbital degeneracy on a highly frustrated pyrochlore lattice, like Ti3+ ion in B-spinel MgTi2O4 . We formulate an effective spin-orbital Hamiltonian and study its low energy sector by constructing several exact eigenstates in the limit of vanishing Hund’s coupling. We find that orbital degrees of freedom modulate the spin-exchange energies, release the infinite spin degeneracy of pyrochlore structure, and drive the system to a nonmagnetic spin-singlet manifold. The latter is a collection of spin-singlet dimers and is, however, highly degenerate with respect to dimer orientations. This “orientational” degeneracy is then lifted by a magneto-elastic interaction that optimizes the previous energy gain by distorting the bonds in suitable directions and leading to a tetragonal phase. In this way a valence bond crystal state is formed, through the condensation of dimers along helical chains running around the tetragonal c axis, as actually observed in MgTi2O4 . The orbitally ordered pattern in the dimerized phase is predicted to be of ferro type along the helices and of antiferro type between them. Finally, through analytical considerations as well as numerical ab initio simulations, we predict a possible experimental tool for the observation of such an orbital ordering, through resonant x-ray scattering.

di Matteo, S.; Jackeli, G.; Perkins, N. B.

2005-07-01

61

Valence-Bond Crystal, and Lattice Distortions in a Pyrochlore Antiferroma  

NASA Astrophysics Data System (ADS)

We discuss the ground state properties of a spin 1/2 magnetic ion with threefold t2g orbital degeneracy on a highly frustrated pyrochlore lattice, like Ti^3+ ion in B-spinel MgTi2O4. We formulate an effective spin-orbital Hamiltonian and study its low energy sector by constructing several exact-eigenstates in the limit of vanishing Hund's coupling. We find that orbital degrees of freedom modulate the spin-exchange energies, release the infinite spin-degeneracy of pyrochlore structure, and drive the system to a non-magnetic spin-singlet manifold. The latter is a collection of spin-singlet dimers and is, however, highly degenerate with respect of dimer orientations. This ``orientational'' degeneracy is then lifted by a magneto-elastic interaction that optimizes the previous energy gain by distorting the bonds in suitable directions and leading to a tetragonal phase. In this way a valence bond crystal state is formed, through the condensation of dimers along helical chains running around the tetragonal c-axis, as actually observed in MgTi2O4.

Perkins, N.; di Matteo, S.; Jackeli, G.

2007-03-01

62

Finite-temperature valence-bond-solid transition of quantum spins in two dimensions  

NASA Astrophysics Data System (ADS)

The S=1/2 Heisenberg model on the 2D square lattice with four- or six-neighbor spin interactions (JQ model) hosts a quantum phase transition between Néel and valence-bond-solid (VBS) ground states. The deconfined quantum critical (DQC) point, predicted by the theory of Senthil et al.[1], may be realized in this model [2]. Here we study the finite-temperature phase transition between the VBS (Z4 symmetry breaking) to the paramagnetic state. We find continuously changing exponents with the correlation-length exponent ? close to the Ising value far from the T=0 critical point, and diverging when the critical temperature Tc->0^+. This is in accord with the DQC theory, according to which the transition for Tc->0^+ should approach a Kosterlitz-Thouless fixed point.[4pt] [1] T. Senthil, L. Balents, S. Sachdev, A. Vishwanath, and M. P. A. Fisher, Phys. Rev. B 70, 144407 (2004).[0pt] [2] R. K. Kaul, R. G. Melko, A. W. Sandvik, arXiv:1204.5405.

Jin, Songbo; Sandvik, Anders

2013-03-01

63

Structural and magnetic properties of Ba2LuMoO6: a valence bond glass  

NASA Astrophysics Data System (ADS)

We report here the synthesis of the site ordered double perovskite Ba2LuMoO6. Rietveld refinement of room temperature powder x-ray diffraction measurements indicates that it crystallizes in the cubic space group F m\\bar {3}m, with a = 8.3265(1) Å. Powder neutron diffraction data indicate that, unusually, this cubic symmetry is maintained down to 2 K, with S=\\frac{1}{2}, Mo5+ ions situated on the frustrated face-centred cubic lattice. Despite dc-susceptibility measurements showing Curie-Weiss behaviour with strong antiferromagnetic interactions at T ? 200 K, there is no evidence of long range magnetic ordering at 2 K. At T ? 50 K, susceptibility measurements indicate a loss in moment to ˜18% of the expected value, and there is a corresponding loss in the magnitude of the magnetic exchange. The structural and magnetic properties of this compound are compared with the related compound Ba2YMoO6, which is a valence bond glass.

Coomer, Fiona C.; Cussen, Edmund J.

2013-02-01

64

Resonating valence bond trial wave functions with both static and dynamically determined Marshall sign structure  

NASA Astrophysics Data System (ADS)

We construct energy-optimized resonating valence bond wave functions as a means to sketch out the zero-temperature phase diagram of the square-lattice quantum Heisenberg model with competing nearest- (J1) and next-nearest-neighbor (J2) interactions. Our emphasis is not on achieving an accurate representation of the magnetically disordered intermediate phase (centered on a relative coupling g=J2/J1˜(1)/(2) and whose exact nature is still controversial) but on exploring whether and how the Marshall sign structure breaks down in the vicinity of the phase boundaries. Numerical evaluation of two- and four-spin correlation functions is carried out stochastically using a worm algorithm that has been modified to operate in either of two modes: one in which the sublattice labeling is fixed beforehand and another in which the worm manipulates the current labeling so as to sample various sign conventions. Our results suggest that the disordered phase evolves continuously out of the (?,?) Néel phase and largely inherits its Marshall sign structure; on the other hand, the transition from the magnetically ordered (?,0) phase is strongly first order and involves an abrupt change in the sign structure and spatial symmetry as the result of a level crossing.

Zhang, Xiaoming; Beach, K. S. D.

2013-03-01

65

From an Antiferromagnet to a Valence Bond Solid: Evidence for a First Order Phase Transition  

NASA Astrophysics Data System (ADS)

Using a loop-cluster algorithm we investigate the spin 12 Heisenberg antiferromagnet on a square lattice with exchange coupling J and a four-spin interaction of strength Q. We confirm the existence of a phase transition separating antiferromagnetism at J/Q>Jc/Q from a valence bond solid (VBS) state at J/QJc/Q the staggered magnetization, the spin stiffness, and the spinwave velocity of the antiferromagnet are determined by fitting Monte Carlo data to analytic results from the systematic low-energy effective field theory for magnons. Finally, we also investigate the physics of the VBS state at J/Q

Nyfeler, M.; Jiang, F.-J.; Wiese, U.-J.; Chandrasekharan, S.

2009-08-01

66

Development of a bond-valence based interatomic potential for BiFeO3 for accurate molecular dynamics simulations.  

PubMed

We present an atomistic potential for BiFeO(3) based on the principles of bond-valence (BV) and bond-valence vector (BVV) conservation. The validity of this model potential is tested for both canonical ensemble (NVT) and isobaric-isothermal ensemble (NPT) molecular dynamics (MD) simulations. The model reproduces the ferroelectric-to-paraelectric phase transition in both NVT and NPT MD simulations and the temperature dependence of the local structure in BiFeO(3). The calculated domain wall energies for 71°, 109°and 180° walls agree well with density functional theory results. The success of our simple model potential for BiFeO(3) indicates that BV and BVV conservation provides a firm basis for the development of accurate atomistic potentials for complex oxides. PMID:23399759

Liu, Shi; Grinberg, Ilya; Rappe, Andrew M

2013-02-12

67

Characterizing boson density wave and valence bond orders in a lattice by its dual vortex degree of freedoms  

NASA Astrophysics Data System (ADS)

A duality transformation in quantum field theory is usually established first through partition functions. It is always important to explore the dual relations between various correlation functions in the transformation. Here, we explore such a dual relation to study quantum phases and phase transitions in an extended boson Hubbard model at 1/3 (2/3) filling on a triangular lattice. We develop systematically a simple and effective way to use the vortex degree of freedoms on dual lattices to characterize both the density wave and valence bond symmetry breaking patterns of the boson insulating states in the direct lattices. In addition to a checkerboard charge density wave (X-CDW) and a stripe CDW, we find a novel CDW-VBS phase which has both local CDW and local valence bond solid (VBS) orders. Implications on QMC simulations are addressed. The possible experimental realizations of cold atoms loaded on optical lattices are discussed.

Chen, Yan; Ye, Jinwu

2013-03-01

68

Continuous quantum phase transition between two topologically distinct valence bond solid states associated with the same spin value  

SciTech Connect

We propose a one-dimensional quantum Heienberg spin-2 chain, which exhibits two topologically distinct valence bond solid states in two different solvable limits. We then construct the phase diagram and study the quantum phase transition between these two states using infinite time evolving block decimation algorithms. From the scaling relation between the entanglement entropy and the correlation length, we determine that the central charge for the underlying critical conformal field theory is around two.

Zheng Dong; Zhang Guangming [Department of Physics, Tsinghua University, Beijing 100084 (China); Xiang Tao [Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190 (China); Lee, Dung-Hai [Department of Physics, University of California at Berkeley, Berkeley, California 94720 (United States); Material Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

2011-01-15

69

Concerning the Structure of the Valence Zone of Chalcopyrite-Type Bonds.  

National Technical Information Service (NTIS)

Compatibility relationships are found for the representations of groups (T sub d, sup 2) and (D sub 2d, sup 12). With the aid of these relationships, changes in the structure of the valence zone are analyzed for the transition from valence crystals with t...

V. A. Chaldyshev G. F. Karavaev

1974-01-01

70

Valence bond solids for SU(n) spin chains: Exact models, spinon confinement, and the Haldane gap  

NASA Astrophysics Data System (ADS)

To begin with, we introduce several exact models for SU(3) spin chains: First is a translationally invariant parent Hamiltonian involving four-site interactions for the trimer chain, with a threefold degenerate ground state. We provide numerical evidence that the elementary excitations of this model transform under representation 3¯ of SU(3) if the original spins of the model transform under representation 3. Second is a family of parent Hamiltonians for valence bond solids of SU(3) chains with spin representations 6, 10, and 8 on each lattice site. We argue that of these three models, only the latter two exhibit spinon confinement and, hence, a Haldane gap in the excitation spectrum. We generalize some of our models to SU(n) . Finally, we use the emerging rules for the construction of valence bond solid states to argue that models of antiferromagnetic chains of SU(n) spins, in general, possess a Haldane gap if the spins transform under a representation corresponding to a Young tableau consisting of a number of boxes ? which is divisible by n . If ? and n have no common divisor, the spin chain will support deconfined spinons and not exhibit a Haldane gap. If ? and n have a common divisor different from n , it will depend on the specifics of the model including the range of the interaction.

Greiter, Martin; Rachel, Stephan

2007-05-01

71

Empirical valence bond simulations of the chemical mechanism of ATP to cAMP conversion by anthrax edema factor.  

PubMed

The two-metal catalysis by the adenylyl cyclase domain of the anthrax edema factor toxin was simulated using the empirical valence bond (EVB) quantum mechanical/molecular mechanical approach. These calculations considered the energetics of the nucleophile deprotonation and the formation of a new P-O bond in aqueous solution and in the enzyme-substrate complex present in the crystal structure models of the reactant and product states of the reaction. Our calculations support a reaction pathway that involves metal-assisted transfer of a proton from the nucleophile to the bulk aqueous solution followed by subsequent formation of an unstable pentavalent intermediate that decomposes into cAMP and pyrophosphate (PPi). This pathway involves ligand exchange in the first solvation sphere of the catalytic metal. At 12.9 kcal/mol, the barrier for the last step of the reaction, the cleavage of the P-O bond to PPi, corresponds to the highest point on the free energy profile for this reaction pathway. However, this energy is too close to the value of 11.4 kcal/mol calculated for the barrier of the nucleophilic attack step to reach a definitive conclusion about the rate-limiting step. The calculated reaction mechanism is supported by reasonable agreement between the experimental and calculated catalytic rate constant decrease caused by the mutation of the active site lysine 346 to arginine. PMID:23480863

Mones, Letif; Tang, Wei-Jen; Florián, Jan

2013-04-02

72

Valence bond glass on an fcc lattice in the double Perovskite Ba2YMoO6.  

PubMed

We report on the unconventional magnetism in the cubic B-site ordered double perovskite Ba2YMoO6, using ac and dc magnetic susceptibility, heat capacity and muon spin rotation. No magnetic order is observed down to 2 K while the Weiss temperature is approximately -160 K. This is ascribed to the geometric frustration in the lattice of edge-sharing tetrahedra with orbitally degenerate Mo5+ s=1/2 spins. Our experimental results point to a gradual freezing of the spins into a disordered pattern of spin singlets, quenching the orbital degeneracy while leaving the global cubic symmetry unaffected, and providing a rare example of a valence bond glass. PMID:20482134

de Vries, M A; McLaughlin, A C; Bos, J-W G

2010-04-27

73

Optical conductivity of visons in Z2 spin liquids close to a valence bond solid transition on the kagome lattice  

NASA Astrophysics Data System (ADS)

We consider Z2 spin liquids on the kagome lattice on the verge of a valence bond solid (VBS) transition, where vortex excitations carrying Z2 magnetic flux—so-called visons—condense. We show that these vison excitations can couple directly to the external electromagnetic field, even though they carry neither spin nor charge. This is possible via a magnetoelastic coupling mechanism recently identified. [Potter, Senthil, and Lee, arXiv:1301.3495; Hao, Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.85.174432 85, 174432 (2012)] For the case of transitions to a 36-site unit cell VBS state, the corresponding finite ac conductivity has a specific power-law frequency dependence, which is related to the crossover exponent of the quantum critical point. The visons’ contribution to the optical conductivity at transitions to VBS states with a 12-site unit cell vanishes, however.

Huh, Yejin; Punk, Matthias; Sachdev, Subir

2013-06-01

74

Low-temperature spin dynamics of a valence bond glass in Ba2YMoO6  

NASA Astrophysics Data System (ADS)

We carried out ac magnetic susceptibility measurements and muon spin relaxation spectroscopy on the cubic double perovskite Ba2YMoO6, down to 50 mK. Below ?1 K the muon relaxation is typical of a magnetic insulator with a spin-liquid type ground state, i.e. without broken symmetries or frozen moments. However, the ac susceptibility revealed a dilute-spin-glass-like transition below ?1 K. Antiferromagnetically coupled Mo5+ 4d1 electrons in triply degenerate t2g orbitals are in this material arranged in a geometrically frustrated fcc lattice. Bulk magnetic susceptibility data has previously been interpreted in terms of a freezing to a heterogeneous state with non-magnetic sites where 4d1 electrons have paired in spin-singlets dimers, and residual unpaired Mo5+ 4d1 electron spins. Based on the magnetic heat capacity data it has been suggested that this heterogeneity is the result of kinetic constraints intrinsic to the physics of the pure system (possibly due to topological overprotection) leading to a self-induced glass of valence bonds between neighbouring 4d1 electrons. The muon spin relaxation (?SR) unambiguously points to a heterogeneous state with a static arrangement of unpaired electrons in a background of (valence bond) dimers between the majority of Mo5+ 4d electrons. The ac susceptibility data indicate that the residual magnetic moments freeze into a dilute-spin-glass-like state. This is in apparent contradiction with the muon-spin decoupling at 50 mK in fields up to 200 mT, which indicates that, remarkably, the time scale of the field fluctuations from the residual moments is ?5 ns. Comparable behaviour has been observed in other geometrically frustrated magnets with spin-liquid-like behaviour and the implications of our observations on Ba2YMoO6 are discussed in this context.

de Vries, M. A.; Piatek, J. O.; Misek, M.; Lord, J. S.; Rønnow, H. M.; Bos, J.-W. G.

2013-04-01

75

Bond-valence methods for p K a prediction: critical reanalysis and a new approach 1 1 Associate editor: C. M. Eggleston  

Microsoft Academic Search

Bond-valence methods for the prediction of (hydr)oxide solution monomer and surface functional group acidity constants are examined in light of molecular structures calculated using ab initio methods. A new method is presented that is based on these calculated structures, and it is shown that previously published methods have neglected one or more of four essential features of a generalized model.

Barry R. Bickmore; Christopher J. Tadanier; Kevin M. Rosso; Will D. Monn; Dennis L. Eggett

2004-01-01

76

High-Order Coupled Cluster Method (CCM) Calculations for Quantum Magnets with Valence-Bond Ground States  

NASA Astrophysics Data System (ADS)

In this article, we prove that exact representations of dimer and plaquette valence-bond ket ground states for quantum Heisenberg antiferromagnets may be formed via the usual coupled cluster method (CCM) from independent-spin product (e.g. Néel) model states. We show that we are able to provide good results for both the ground-state energy and the sublattice magnetization for dimer and plaquette valence-bond phases within the CCM. As a first example, we investigate the spin-half J 1- J 2 model for the linear chain, and we show that we are able to reproduce exactly the dimerized ground (ket) state at J 2/ J 1=0.5. The dimerized phase is stable over a range of values for J 2/ J 1 around 0.5, and results for the ground-state energies are in good agreement with the results of exact diagonalizations of finite-length chains in this regime. We present evidence of symmetry breaking by considering the ket- and bra-state correlation coefficients as a function of J 2/ J 1. A radical change is also observed in the behavior of the CCM sublattice magnetization as we enter the dimerized phase. We then consider the Shastry-Sutherland model and demonstrate that the CCM can span the correct ground states in both the Néel and the dimerized phases. Once again, very good results for the ground-state energies are obtained. We find CCM critical points of the bra-state equations that are in agreement with the known phase transition point for this model. The results for the sublattice magnetization remain near to the "true" value of zero over much of the dimerized regime, although they diverge exactly at the critical point. Finally, we consider a spin-half system with nearest-neighbor bonds for an underlying lattice corresponding to the magnetic material CaV4O9 (CAVO). We show that we are able to provide excellent results for the ground-state energy in each of the plaquette-ordered, Néel-ordered, and dimerized regimes of this model. The exact plaquette and dimer ground states are reproduced by the CCM ket state in their relevant limits. Furthermore, we estimate the range over which the Néel order is stable, and we find the CCM result is in reasonable agreement with the results obtained by other methods. Our new approach has the dual advantages that it is simple to implement and that existing CCM codes for independent-spin product model states may be used from the outset. Furthermore, it also greatly extends the range of applicability to which the CCM may be applied. We believe that the CCM now provides an excellent choice of method for the study of systems with valence-bond quantum ground states.

Farnell, D. J. J.; Richter, J.; Zinke, R.; Bishop, R. F.

2009-04-01

77

Low-energy physical properties of high- Tc superconducting Cu oxides: A comparison between the resonating valence bond and experiments  

NASA Astrophysics Data System (ADS)

In a recent review by Anderson and co-workers, it was pointed out that an early resonating valence bond (RVB) theory is able to explain a number of unusual properties of high-temperature superconducting (SC) Cu oxides. Here we extend previous calculations to study more systematically the low-energy physical properties of the plain vanilla d -wave RVB state, and to compare the results with the available experiments. We use a renormalized mean-field theory combined with variational Monte Carlo and power Lanczos methods to study the RVB state of an extended t-J model in a square lattice with parameters suitable for the hole-doped Cu oxides. The physical observable quantities we study include the specific heat, the linear residual thermal conductivity, the in-plane magnetic penetration depth, the quasiparticle energy at the antinode (?,0) , the superconducting energy gap, the quasiparticle spectra, and the Drude weights. The traits of nodes (including kF , the Fermi velocity vF , and the velocity along Fermi surface v2 ), and the SC order parameter are studied. Comparisons of the theory and the experiments in cuprates show an overall qualitative agreement, especially on their doping dependences.

Yang, Kai-Yu; Shih, C. T.; Chou, C. P.; Huang, S. M.; Lee, T. K.; Xiang, T.; Zhang, F. C.

2006-06-01

78

The nature of chemical bonds from PNOF5 calculations.  

PubMed

Natural orbital functional theory (NOFT) is used for the first time in the analysis of different types of chemical bonds. Concretely, the Piris natural orbital functional PNOF5 is used. It provides a localization scheme that yields an orbital picture which agrees very well with the empirical valence shell electron pair repulsion theory (VSEPR) and Bent's rule, as well as with other theoretical pictures provided by valence bond (VB) or linear combination of atomic orbitals-molecular orbital (LCAO-MO) methods. In this context, PNOF5 provides a novel tool for chemical bond analysis. In this work, PNOF5 is applied to selected molecules that have ionic, polar covalent, covalent, multiple (? and ?), 3c-2e, and 3c-4e bonds. PMID:22615195

Matxain, Jon M; Piris, Mario; Uranga, Jon; Lopez, Xabier; Merino, Gabriel; Ugalde, Jesus M

2012-05-21

79

Chemical Bond Characterization of a Mixed-Valence Tri-Cobalt Complex, Co3(?-admtrz)4(?-OH)2(CN)6·2H2O.  

PubMed

Charge density study of a mixed-valence tri-cobalt compound, Co3(?-admtrz)4(?-OH)2(CN)6·2H2O (1) (admtrz = 3,5-dimethyl-4-amino-1,2,4-triazole), is investigated based on high resolution X-ray diffraction data and density functional theory (DFT) calculations. The molecular structure of this compound contains three cobalt atoms in a linear fashion, where two terminal ones are Co(III) at a low-spin (LS) state and a central one is Co(II) at a high-spin (HS) state with a total spin quantum number, Stotal, of 3/2. It is centrosymmetric with the center of inversion located at the central Co atom (Co2). The Co2 ion is linked with each terminal cobalt (Co1) ion through two ?-admtrz ligands and a ?-OH ligand in a CoN4O2 coordination, where the Co1 is bonded additionally to three CN ligands with CoN2OC3 coordination. The combined experimental and theoretical charge density study identifies the different characters of two types of cobalt ions; more pronounced charge concentration and depletion features in the valence shell charge concentration (VSCC) are found in the Co(III) ion than in the Co(II) ion, and d-orbital populations also show the difference. According to topological properties associated with the bond critical point (BCP), the Co1-C(N) bond is the strongest among all the Co-ligand bonds in this compound; the Co-O is stronger than Co-N bond. Again Co1-O is stronger than Co2-O, so as the Co1-N being stronger than Co2-N bond. The electronic configuration of each type of Co atom is further characterized through magnetic measurement, Co-specific X-ray absorption near edge spectroscopy (XANES), and X-ray emission spectra (XES). PMID:24044777

Wu, Lai-Chin; Weng, Tsu-Chien; Hsu, I-Jui; Liu, Yi-Hung; Lee, Gene-Hsiang; Lee, Jyh-Fu; Wang, Yu

2013-09-17

80

Can QTAIM topological parameters be a measure of hydrogen bonding strength?  

PubMed

The block-localized wave function (BLW) method, which is the simplest variant of ab initio valence bond (VB) theory, together with the quantum theory of atoms in molecules (QTAIM) approach, have been used to probe the intramolecular hydrogen bonding interactions in a series of representative systems of resonance-assisted hydrogen bonds (RAHBs). RAHB is characteristic of the cooperativity between the ?-electron delocalization and hydrogen bonding interactions and is identified in many biological systems. While the deactivation of the ? resonance in these RAHB systems by the use of the BLW method is expected to considerably weaken the hydrogen bonding strength, little change on the topological properties of electron densities at hydrogen bond critical points (HBCPs) is observed. This raises a question of whether the QTAIM topological parameters can be an effective measure of hydrogen bond strength. PMID:22574938

Mo, Yirong

2012-05-17

81

Semiempirical valence bond potential energy surfaces for simple chemical reactions: 1A' states of H2O and H2F  

NASA Astrophysics Data System (ADS)

A semiemprical valence bond method is employed to study the potential energy surfaces (PESs) of the lowest 1A' states of H2O and isoelectronic H2F+. The calculation is based on the search for the electronic configurations which play the most important rôle in the formation of the stable electronic states of the molecules and the relevant diatomic fragments. Several approximations are used to reduce the number of permutations in the calculation of the energy matrix. The Moffit atoms-in-molecule approximation is used to correct for the atomic errors arising from the poor basis set. The computed data for the lowest electronic states of OH, HF, HF+, H2O and H2F+, as well as the general behaviour of the PESs for different molecular geometries, are in good agreement with the available ab initio and experimental data.

Zembekov, A. A.

82

Atomic Structure and Valence: Level II, Unit 10, Lesson 1; Chemical Bonding: Lesson 2; The Table of Elements: Lesson 3; Electrolysis: Lesson 4. Advanced General Education Program. A High School Self-Study Program.  

ERIC Educational Resources Information Center

|This self-study program for high-school level contains lessons on: Atomic Structure and Valence, Chemical Bonding, The Table of Elements, and Electrolysis. Each of the lessons concludes with a Mastery Test to be completed by the student. (DB)|

Manpower Administration (DOL), Washington, DC. Job Corps.

83

Ionicity, atomic radii, and structure in the layered dichalcogenides of group IVb, Vb, and VIb transition metals  

Microsoft Academic Search

Pauling's electronegativities are introduced in considerations of bond lengths, lattice constants, atomic radii, charge densities, structures, and heats of formation of the layered dichalcogenides of Groups IVb, Vb, and VIb transition metals. Strong correlations are found between these and the fractional ionic character of the metal-chalcogen bonds as defined by Pauling. A critical effective radius ratio is defined that separates

F. R. Gamble

1974-01-01

84

New Ternary Sulfide Compounds of Low Valence Molybdenum Showing Molybdenum-Molybdenum Bonds in the Form of Chains or Octahedral Clusters.  

National Technical Information Service (NTIS)

Ternary sulfide compounds of low valence molybdenum were synthesized at temperatures from 1000 to 1200 C forming two distinct phases. The trivalent molybdenum sulfides are magnetic semiconductors. The bivalent molybdenum compounds show promise as a new cl...

R. Chevrel

1977-01-01

85

Fabrication of VB2/Air Cells for Electrochemical Testing.  

PubMed

A technique to investigate the properties and performance of new multi-electron metal/air battery systems is proposed and presented. A method for synthesizing nanoscopic VB2 is presented as well as step-by-step procedure for applying a zirconium oxide coating to the VB2 particles for stabilization upon discharge. The process for disassembling existing zinc/air cells is shown, in addition construction of the new working electrode to replace the conventional zinc/air cell anode with a the nanoscopic VB2 anode. Finally, discharge of the completed VB2/air battery is reported. We show that using the zinc/air cell as a test bed is useful to provide a consistent configuration to study the performance of the high-energy high capacity nanoscopic VB2 anode. PMID:23962835

Stuart, Jessica; Lopez, Ruben; Lau, Jason; Li, Xuguang; Waje, Mahesh; Mullings, Matthew; Rhodes, Christopher; Licht, Stuart

2013-08-05

86

The physical origin of large covalent-ionic resonance energies in some two-electron bonds.  

PubMed

This study uses valence bond (VB) theory to analyze in detail the previously established finding that alongside the two classical bond families of covalent and ionic bonds, which describe the electron-pair bond, there exists a distinct class of charge-shift bonds (CS-bonds) in which the fluctuation of the electron pair density plays a dominant role. Such bonds are characterized by weak binding, or even a repulsive, covalent component, and by a large covalent-ionic resonance energy RE(cs) that is responsible for the major part, or even for the totality, of the bonding energy. In the present work, the nature of CS-bonding and its fundamental mechanisms are analyzed in detail by means of a VB study of some typical homonuclear bonds (H-H, H3C-CH3, H2N-NH2, HO-OH, F-F, and Cl-Cl), ranging from classical-covalent to fully charge-shift bonds. It is shown that CS-bonding is characterized by a covalent dissociation curve with a shallow minimum situated at long interatomic distances, or even a fully repulsive covalent curve. As the atoms that are involved in the bond are taken from left to right or from bottom to top of the periodic table, the weakening effect of the adjacent bonds or lone pairs increases, while at the same time the reduced resonance integral, that couples the covalent and ionic forms, increases. As a consequence, the weakening of the covalent interaction is gradually compensated by a strengthening of CS-bonding. The large RE(cs) quantity of CS-bonds is shown to be an outcome of the mechanism necessary to establish equilibrium and optimum bonding during bond formation. It is shown that the shrinkage of the orbitals in the covalent structure lowers the potential energy, V, but excessively raises the kinetic energy, T, thereby tipping the virial ratio off-balance. Subsequent addition of the ionic structures lowers T while having a lesser effect on V, thus restoring the requisite virial ratio (T/-V = 1/2). Generalizing to typically classical covalent bonds, like H-H or C-C bonds, the mechanism by which the virial ratio is obeyed during bond formation is primarily orbital shrinkage, and therefore the charge-shift resonance energy has only a small corrective effect. On the other hand, for bonds bearing adjacent lone pairs and/or involving electronegative atoms, like F-F or Cl-Cl, the formation of the bond corresponds to a large increase of kinetic energy, which must be compensated for by a large participation or covalent-ionic mixing. PMID:17328432

Hiberty, Philippe C; Ramozzi, Romain; Song, Lingchun; Wu, Wei; Shaik, Sason

2007-01-01

87

Myosin Vb Is Associated with Plasma Membrane Recycling Systems  

Microsoft Academic Search

Myosin Va is associated with discrete vesicle populations in a number of cell types, but little is known of the function of myosin Vb. Yeast two-hybrid screening of a rabbit parietal cell cDNA library with dominant active Rab11a (Rab11aS20V) identified myosin Vb as an interacting protein for Rab11a, a marker for plasma membrane recycling systems. The isolated clone, corresponding to

Lynne A. Lapierre; Ravindra Kumar; Chadwick M. Hales; Jennifer Navarre; Sheela G. Bhartur; Jason O. Burnette; D. William; John A. Mercer; Martin Bahler; James R. Goldenring

2001-01-01

88

Maximum-valence radii of transition metals  

PubMed Central

In many of their compounds the transition metals have covalence 9, forming nine bonds with use of nine hybrid spd bond orbitals. A set of maximum-valence single-bond radii is formulated for use in these compounds. These radii are in reasonably good agreement with observed bond lengths. Quadruple bonds between two transition metal atoms are about 50 pm (iron-group atoms) or 55 pm (palladium and platinum-group atoms) shorter than single bonds. This amount of shortening corresponds to four bent single bonds with the best set of bond angles, 79.24° and 128.8°.

Pauling, Linus

1975-01-01

89

Theoretical description of halogen bonding - an insight based on the natural orbitals for chemical valence combined with the extended-transition-state method (ETS-NOCV).  

PubMed

In the present study we have characterized the halogen bonding in selected molecules H3N-ICF3 (1-NH 3 ), (PH3)2C-ICF3 (1-CPH 3 ), C3H7Br-(IN2H2C3)2C6H4 (2-Br), H2-(IN2H2C3)2C6H4 (2-H 2 ) and Cl-(IC6F5)2C7H10N2O5 (3-Cl), containing from one halogen bond (1-NH 3 , 1-CPH 3 ) up to four connections in 3-Cl (the two Cl-HN and two Cl-I), based on recently proposed ETS-NOCV analysis. It was found based on the NOCV-deformation density components that the halogen bonding C-X (…) B (X-halogen atom, B-Lewis base), contains a large degree of covalent contribution (the charge transfer to X (…) B inter-atomic region) supported further by the electron donation from base atom B to the empty ?*(C-X) orbital. Such charge transfers can be of similar importance compared to the electrostatic stabilization. Further, the covalent part of halogen bonding is due to the presence of ?-hole at outer part of halogen atom (X). ETS-NOCV approach allowed to visualize formation of the ?-hole at iodine atom of CF3I molecule. It has also been demonstrated that strongly electrophilic halogen bond donor, [C6H4(C3H2N2I)2][OTf]2, can activate chemically inert isopropyl bromide (2-Br) moiety via formation of Br-I bonding and bind the hydrogen molecule (2-H 2 ). Finally, ETS-NOCV analysis performed for 3-Cl leads to the conclusion that, in terms of the orbital-interaction component, the strength of halogen (Cl-I) bond is roughly three times more important than the hydrogen bonding (Cl-HN). PMID:22669533

Mitoraj, Mariusz P; Michalak, Artur

2012-06-06

90

Geometrical frustration in the spin liquid ?'-Me3EtSb[Pd(dmit)2]2 and the valence-bond solid Me3EtP[Pd(dmit)2]2.  

PubMed

We show that the electronic structures of the title compounds predicted by density functional theory are well described by tight binding models. We determine the frustration ratio, J'/J, of the Heisenberg model on the anisotropic triangular lattice, which describes the spin degrees of freedom in the Mott insulating phase for a range of Pd(dmit)2 salts. All of the antiferromagnetic materials studied have J'/J is < or approximately equal to 0.5 or J'/J > or approximately equal to 0.9, and all salts with 0.5 < or approximately equal to J'/J < or approximately equal to 0.9 are known, experimentally, to be charge ordered valence-bond solids or spin liquids. PMID:23002879

Scriven, E P; Powell, B J

2012-08-29

91

Enhancement of sp3-bonding in high-bias-voltage grown diamond-like carbon thin films studied by x-ray absorption and photoemission spectroscopy  

Microsoft Academic Search

X-ray absorption near-edge structure (XANES) and valence-band photoemission spectroscopy (VB-PES) were used to elucidate the electronic and mechanical properties of diamond-like carbon (DLC) thin films deposited by the plasma-enhanced chemical vapour deposition method at various bias voltages (Vb) using a C2H2 vapour precursor in an Ar+ atmosphere. The increase of Vb is found to increase and decrease the contents of

S. C. Ray; C. W. Pao; H. M. Tsai; J. W. Chiou; W. F. Pong; M.-H. Tsai; T. I. T. Okpalugo; P. Papakonstantinou; T. W. Pi

2007-01-01

92

Levels of Valence  

PubMed Central

The distinction between the positive and the negative is fundamental in our emotional life. In appraisal theories, in particular in the component process model of emotion (Scherer, 1984, 2010), qualitatively different types of valence are proposed based on appraisals of (un)pleasantness, goal obstructiveness/conduciveness, low or high power, self-(in)congruence, and moral badness/goodness. This multifaceted conceptualization of valence is highly compatible with the frequent observation of mixed feelings in real life. However, it seems to contradict the one-dimensional conceptualization of valence often encountered in psychological theories, and the notion of valence as a common currency used to explain choice behavior. Here, we propose a framework to integrate the seemingly disparate conceptualizations of multifaceted valence and one-dimensional valence by suggesting that valence should be conceived at different levels, micro and macro. Micro-valences correspond to qualitatively different types of evaluations, potentially resulting in mixed feelings, whereas one-dimensional macro-valence corresponds to an integrative “common currency” to compare alternatives for choices. We propose that conceptualizing levels of valence may focus research attention on the mechanisms that relate valence at one level (micro) to valence at another level (macro), leading to new hypotheses, and addressing various concerns that have been raised about the valence concept, such as the valence-emotion relation.

Shuman, Vera; Sander, David; Scherer, Klaus R.

2013-01-01

93

Renewable highest capacity VB2/air energy storage.  

PubMed

The first renewable electrochemical energy system which stores more energy than gasoline is presented, and with an order of magnitude higher capacity than lithium-ion batteries, VB(2) opens a pathway towards electric vehicles with a viable driving range. PMID:18622436

Licht, Stuart; Wu, Huiming; Yu, Xingwen; Wang, Yufei

2008-06-17

94

Metal-metal bonding in mixed valence Ni2(5+) complexes and spectroscopic evidence for a Ni2(6+) species.  

PubMed

Dinickel(II) complexes of the ligands N,N'-di-p-anisylformamidinate (DAniF) and N,N',N''-triphenylguanidinate (TPG) have been synthesized and crystallographically characterized, along with their one-electron-oxidized analogues. In both systems, the Ni-Ni distances become shorter by approximately 0.1 A upon oxidation, in accord with the proposal that the resulting Ni2(5+) complexes are appropriately described as having one electron removed from a metal-based sigma orbital and an overall Ni-Ni bond order of 1/2. Although conventional DFT calculations on the model compounds Ni2(HNCHNH)4 and [Ni2(HNCHNH)4]+ appear to predict that the lowest energy state of the latter species would have one unpaired electron in an essentially ligand-based orbital. A single-point calculation of Ni2(DAniF)4 employing the geometry of its crystal structure with the full ligand included reveals a reversal of the previously predicted order of the HOMO and HOMO-1, and suggests that the unpaired electron in [Ni2(DAniF)4]+ is in a metal-based orbital of sigma symmetry. This is verified by the axial EPR spectrum of the compound in solution. The compound Ni2(DAniF)4 shows an unexpectedly rich cyclic voltammogram with four stepwise reversible oxidation waves. Coulometric experiments show that the doubly oxidized species has a significant lifetime at -25 degrees C, and by spectroelectrochemistry, its UV-vis spectrum was recorded. We propose that this species contains a Ni2(6+) core with a single Ni-Ni sigma bond. PMID:16711689

Berry, John F; Bothe, Eberhard; Cotton, F Albert; Ibragimov, Sergey A; Murillo, Carlos A; Villagran, Dino; Wang, Xiaoping

2006-05-29

95

Visualizing Valence Electron Structure  

NASA Astrophysics Data System (ADS)

The purpose of this research is to effectively model and understand Density Functional Theory (DFT). DFT uses the electron density to model the ground state electronic structure of atoms, molecules, and solids. We calculate and visualize the gradient of the electron density, its Laplacian, and the kinetic energy density, also derived from the electron density, for the AE6 test set of molecules. This set of six molecules accurately represents the DFT prediction of atomization energies of a plethora of molecules. Calculations were done using the ABINIT DFT code. Pseudopotentials were used to represent the individual atom cores, keeping an accurate representation of valence interactions. By using these density- derived functions we can better visualize and interpret intermolecular phenomenon caused by electron interactions, like the effects of a triple bond on the entire structure of the molecule, or the effect of electron affinity of an individual atom within a molecule. These physical variables are used in DFT to help predict the electron-electron interaction energy of a molecule, and knowing how they relate to each other may help better model this. Ultimately, we hope to effectively use our results to understand and improve the Density Functional method for modeling electronic structure.

Kuna, Aeryk; Cancio, Antonio

2011-10-01

96

Calculation of Valence State Energies from Thermochemical Data  

Microsoft Academic Search

THE predictive power inherent in the concept of intrinsic bond energies has led to many attempts to calculate the energy of the hypothetical valence state of an atom in a molecule1-7. The intrinsic bond energy I can be defined1 by the equation: where DeltaHf is the atomic heat of formation of a molecule, V is the energy of the valence

Bernard Siegel; Seymour Siegel

1963-01-01

97

THE PROPOSED GIANT PLANET ORBITING VB 10 DOES NOT EXIST  

SciTech Connect

We present high-precision relative radial velocities of the very low mass star VB 10 that were obtained over a time span of 0.61 years as part of an ongoing search for planets around stars at the end of the main sequence. The radial velocities were measured from high-resolution near-infrared spectra obtained using the CRIRES instrument on the Very Large Telescope with an ammonia gas cell. The typical internal precision of the measurements is 10 m s{sup -1}. These data do not exhibit significant variability and are essentially constant at a level consistent with the measurement uncertainties. Therefore, we do not detect the radial velocity variations of VB 10 expected due to the presence of an orbiting giant planet similar to that recently proposed by Pravdo and Shaklan based on apparent astrometric perturbations. In addition, we do not confirm the {approx}1 km s{sup -1} radial velocity variability of the star tentatively detected by Zapatero Osorio and colleagues with lower precision measurements. Our measurements rule out planets with M {sub p} > 3 M {sub Jup} and the orbital period and inclination suggested by Pravdo and Shaklan at better than 5{sigma} confidence. We conclude that the planet detection claimed by Pravdo and Shaklan is spurious on the basis of this result. Although the outcome of this work is a non-detection, it illustrates the potential of using ammonia cell radial velocities to detect planets around very low mass stars.

Bean, Jacob L.; Seifahrt, Andreas; Reiners, Ansgar; Dreizler, Stefan [Institut fuer Astrophysik, Georg-August-Universitaet, Friedrich-Hund-Platz 1, 37077 Goettingen (Germany); Hartman, Henrik; Nilsson, Hampus [Lund Observatory, Lund University, P.O. Box 43, 22100 Lund (Sweden); Henry, Todd J. [Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30302 (United States); Wiedemann, Guenter [Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg (Germany)], E-mail: bean@astro.physik.uni-goettingen.de

2010-03-01

98

The Proposed Giant Planet Orbiting VB 10 Does Not Exist  

NASA Astrophysics Data System (ADS)

We present high-precision relative radial velocities of the very low mass star VB 10 that were obtained over a time span of 0.61 years as part of an ongoing search for planets around stars at the end of the main sequence. The radial velocities were measured from high-resolution near-infrared spectra obtained using the CRIRES instrument on the Very Large Telescope with an ammonia gas cell. The typical internal precision of the measurements is 10 m s-1. These data do not exhibit significant variability and are essentially constant at a level consistent with the measurement uncertainties. Therefore, we do not detect the radial velocity variations of VB 10 expected due to the presence of an orbiting giant planet similar to that recently proposed by Pravdo & Shaklan based on apparent astrometric perturbations. In addition, we do not confirm the ~1 km s-1 radial velocity variability of the star tentatively detected by Zapatero Osorio and colleagues with lower precision measurements. Our measurements rule out planets with M p > 3 M Jup and the orbital period and inclination suggested by Pravdo & Shaklan at better than 5? confidence. We conclude that the planet detection claimed by Pravdo & Shaklan is spurious on the basis of this result. Although the outcome of this work is a non-detection, it illustrates the potential of using ammonia cell radial velocities to detect planets around very low mass stars. Based on observations made with ESO Telescopes at the Paranal Observatories under program ID 182.C-0748.

Bean, Jacob L.; Seifahrt, Andreas; Hartman, Henrik; Nilsson, Hampus; Reiners, Ansgar; Dreizler, Stefan; Henry, Todd J.; Wiedemann, Günter

2010-03-01

99

Valence, Covalence, Hypervalence, Oxidation State, and Coordination Number  

ERIC Educational Resources Information Center

|Valence as a numerical measure of an atom's combining power, expressed by the number of bonds it forms in a molecular formulation of the compound in question, was unable to cope with coordination compounds. The covalence of an atom is the nearest model equivalent, but is subject to ambiguity since it often depends on which bonding model is being…

Smith, Derek W.

2005-01-01

100

Effect of phase formation on valence band photoemission and photoresonance study of Ti\\/Ni multilayers using synchrotron radiation  

Microsoft Academic Search

This paper presents investigation of Ti–Ni alloy phase formation and its effect on valence band (VB) photoemission and photoresonance study of as-deposited as well as annealed Ti\\/Ni multilayers (MLs) up to 600°C using synchrotron radiation. For this purpose [Ti (50Å)\\/Ni (50Å)]X10 ML structures were deposited by using electron-beam evaporation technique under ultra-high vacuum (UHV) conditions. Formation of different phases of

Pramod Bhatt; S. M. Chaudhari

2006-01-01

101

Micro-Valences: Perceiving Affective Valence in Everyday Objects  

PubMed Central

Perceiving the affective valence of objects influences how we think about and react to the world around us. Conversely, the speed and quality with which we visually recognize objects in a visual scene can vary dramatically depending on that scene’s affective content. Although typical visual scenes contain mostly “everyday” objects, the affect perception in visual objects has been studied using somewhat atypical stimuli with strong affective valences (e.g., guns or roses). Here we explore whether affective valence must be strong or overt to exert an effect on our visual perception. We conclude that everyday objects carry subtle affective valences – “micro-valences” – which are intrinsic to their perceptual representation.

Lebrecht, Sophie; Bar, Moshe; Barrett, Lisa Feldman; Tarr, Michael J.

2012-01-01

102

Functional characterization of mutations in the myosin Vb gene associated with microvillus inclusion disease  

PubMed Central

Objectives Microvillus inclusion disease (MVID) is a rare autosomal recessive enteropathy characterized by intractable diarrhea and malabsorption. Recently, various MYO5B gene mutations have been identified in MVID patients. Interestingly, several MVID patients showed only a MYO5B mutation in one allele (heterozygous) or no mutations in the MYO5B gene, illustrating the need to further functionally characterize the cell biological effects of the MYO5B mutations. Methods The genomic DNA of nine patients diagnosed with microvillus inclusion disease was screened for MYO5B mutations, and qPCR and immunohistochemistry on the material of two patients was performed to investigate resultant cellular consequences. Results We demonstrate for the first time that MYO5B mutations can be correlated with altered myosin Vb mRNA expression and with an aberrant subcellular distribution of the myosin Vb protein. Moreover, we demonstrate that the typical and myosin Vb–controlled accumulation of rab11a-and FIP5-positive recycling endosomes in the apical cytoplasm of the cells is abolished in MVID enterocytes, which is indicative for altered myosin Vb function. Also, we report 8 novel MYO5B mutations in 9 MVID patients of various etnic backgrounds, including compound heterozygous mutations. Conclusions Our functional analysis indicate that MYO5B mutations can be correlated with an aberrant subcellular distribution of the myosin Vb protein and apical recycling endosomes which, together with the additional compound heterozygous mutations, significantly strengthen the link between MYO5B and MVID.

Szperl, Agata M.; Golachowska, Magdalena R.; Bruinenberg, Marcel; Prekeris, Rytis; Thunnissen, Andy-Mark W. H.; Karrenbeld, Arend; Dijkstra, Gerard; Hoekstra, Dick; Mercer, David; Ksiazyk, Janusz; Wijmenga, Cisca; Wapenaar, Martin C.; Rings, Edmond H. H. M.; van IJzendoorn, Sven C. D.

2010-01-01

103

Antibodies specific for VB8 receptor peptide suppress experimental autoimmune encephalomyelitis.  

PubMed

Recent studies from our laboratory have shown, for the first time, that a synthetic peptide from that TCR VB chain used preferentially by encephalitogenic T cells induced the formation of protective, MHC class I-restricted T cells and prevented the development of EAE in Lewis rats. In this report we 1) demonstrate that immunization with the TCR-VB8-39-59 peptide generated peptide-specific antibodies that protect against experimental autoimmune encephalomyelitis induced by either of the two distinct encephalitogenic epitopes of basic protein, and 2) characterize the production and biologic functions of rat and rabbit antibody responses to the TCR peptide. The antibodies in both species increased in titer over time, were highly specific for the immunogen by direct reaction and inhibition assays, stained only VB8+ T cells, and suppressed clinical signs and to lesser extent the number of histologic lesions of experimental autoimmune encephalomyelitis mediated by VB8+ T cells. Coupled with our previous work, these results indicate that both humoral and cellular responses to the TCR-VB8-39-59 peptide can contribute independent immunoregulatory effects on encephalitogenic T lymphocytes that use common V region genes in response to epitopes of myelin basic protein. PMID:1693637

Hashim, G A; Vandenbark, A A; Galang, A B; Diamanduros, T; Carvalho, E; Srinivasan, J; Jones, R; Vainiene, M; Morrison, W J; Offner, H

1990-06-15

104

Neutron-diffraction studies and bond valence sums of charge neutrally doped Nd{sub 1{minus}2x}Ca{sub x}Th{sub x}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}  

SciTech Connect

Equal amounts of Ca and Th have been doped into the Nd{sub 1{minus}2x}Ca{sub x}Th{sub x}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} superconductor with x=0, 0.015, 0.03, 0.05, and 0.10. This causes a fast and linear decrease of the superconducting transition temperature, T{sub c}. A single orthorhombic phase was observed with x-ray diffraction except for weak additional lines for the x=0.10 sample, suggesting a solubility limit below x=0.10. Neutron-diffraction measurements were performed and bond valence sums (BVS{close_quote}s) were calculated. The results showed a small increase in the Cu2-O4 distance and a nearly constant Cu2 valence. The total hole density in the plane, V{sub {minus}} as defined by Tallon, remains almost constant with doping in contrast to the decrease observed for Ca-Pr doping. Other results from the BVS calculations also indicate differences between Ca-Th and Ca-Pr doping in the NdBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} compound. {copyright} {ital 1997} {ital The American Physical Society}

Lundqvist, P.; Rapp, O. [Solid State Physics, The Royal Institute of Technology, S-100 44 Stockholm (Sweden); Tellgren, R. [Inorganic Chemistry, ngstroem Laboratory, Uppsala University, Box 538, S-751 21 Uppsala (Sweden); Bryntse, I. [Inorganic Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm (Sweden)

1997-08-01

105

Valence band and band gap photoemission study of (1 1 1) In 2O 3 epitaxial films under interactions with oxygen, water and carbon monoxide  

Microsoft Academic Search

Synchrotron radiation ultraviolet photoemission experiments at photon energies of 150 and 49eV were performed on an epitaxial layer of (111) In2O3 with good crystallinity as established by a standard scanning probe and diffraction methods. Valence band (VB) and band gap photoemission spectra were monitored under separate oxygen, water and carbon monoxide exposures (100L) at different activation temperatures within the range

V. Brinzari; G. Korotcenkov; M. Ivanov; V. Nehasil; V. Matolin; K. Masek; M. Kamei

2007-01-01

106

Real-Time Evolution of the Valence Electronic Structure in a Dissociating Molecule  

SciTech Connect

Time-resolved valence band photoelectron spectroscopy with a temporal resolution of 135 fs is used to map the entire occupied valence electronic structure of photoexcited gas-phase Br{sub 2} molecules during dissociation. The observed shifting and mixing of valence energy levels defines a transition period where the system appears to be intermediate between atoms and molecules. The surprisingly short bond breaking or dissociation time is determined by monitoring in real time how the photoelectron multiplet structure of the free atom arises from the valence states of the photoexcited molecule.

Wernet, Ph.; Godehusen, K.; Gaudin, J.; Schwarzkopf, O.; Eberhardt, W. [Helmholtz-Zentrum Berlin, Albert-Einstein-Strasse 15, D-12489 Berlin (Germany); Odelius, M. [FYSIKUM, Stockholm University, AlbaNova, S-106 91 Stockholm (Sweden)

2009-07-03

107

Valence photoelectron spectroscopy of Gd silicides  

SciTech Connect

Gd{sub 3}Si{sub 5}, GdSi, and Gd{sub 5}Si{sub 3} were investigated with photoemission spectroscopy in the photon-energy range 40.8--149 eV by exploiting the energy dependence of the photoemission cross sections and the valence resonance at the crossing of the Gd 4{ital d}-4{ital f} threshold. The modification of the spectra versus photon energy, along with their stoichiometry dependence, show the relevance of covalent mixed Gd 5{ital d}--Si 3{ital sp} states in the formation of the chemical bond. In the region close to the Fermi level an increase of the {ital d} contribution is observed. These points are discussed in connection with the existing models of the silicide bond.

Braicovich, L. (Istituto di Fisica, Politecnico di Milano, P.za Leonardo da Vinci 32, 20133 Milano, Italy (IT)); Puppin, E.; Lindau, I. (Stanford Electronics Laboratories, Stanford University, Stanford, California 94305 (USA)); Iandelli, A.; Olcese, G.L.; Palenzona, A. (Istituto di Chimica Fisica, Universita di Genova, Corso Europa, Palazzo delle Scienze, 16132 Genova, (Italy))

1990-02-15

108

Valence, arousal and word associations  

Microsoft Academic Search

This study aimed at testing the relative effects of valence and arousal on the generation of unusual first associates in response to non-emotional inducers. To examine this question, four specific moods varying along both the valence and the arousal dimensions were induced: happiness (positive mood, high arousal), serenity (positive mood, low arousal), anger (negative mood, high arousal) and sadness (negative

Anne-Laure Gilet; Christophe Jallais

2011-01-01

109

Chemical vapor deposition of group IVb, Vb, and VIb elements with nonmetals. A literature review. Information circular  

Microsoft Academic Search

The Bureau of Mines reviewed the chemical vapor deposition (CVD) literature on the nonmetal binary and ternary compounds of the group IVB, VB, and VIB elements, with emphasis directed to the following nonmetals: B, C, N, O, and Si. This review examines each of these binary and selected ternary compounds of the group IVB, VB, and VIB elements as coatings

H. O. McDonald; J. B. Stephenson

1983-01-01

110

Chemical Vapor Deposition of Group IVB, VB, and VIB Elements; a Literature Review.  

National Technical Information Service (NTIS)

The Bureau of Mines reviewed the chemical vapor deposition (CVD) literature of the group IVB, VB, and VIB elements. This review was used in the Bureau's research to provide erosion-, abrasion-, and corrosion-resistant coatings for valve components used in...

H. O. McDonald J. B. Stephenson

1979-01-01

111

Chemical vapor deposition of group IVB, VB, and VIB elements; a literature review. Information circular  

Microsoft Academic Search

The Bureau of Mines reviewed the chemical vapor deposition (CVD) literature of the group IVB, VB, and VIB elements. This review was used in the Bureau's research to provide erosion-, abrasion-, and corrosion-resistant coatings for valve components used in coal gasification units. This report attempts to bring together the many CVD references that have been published since 1966. Each of

H. O. McDonald; J. B. Stephenson

1979-01-01

112

Quantum-chemical calculations of triphenyl compounds of the VB group elements  

Microsoft Academic Search

Various approximations of the MO-LCAO method were used to study the effect of the electronic structure upon the spectra of triphenyl derivatives of the VB group elements. Both the chemical and optical properties of aromatic derivatives of these elements in their trivalent states have to be interpreted on the basis of the overall influence of electronic effects operating in opposite

N. P. Borisova; L. N. Petrov

1972-01-01

113

Geometrical requirements for transition-metal-centered aromatic boron wheels: the case of VB10(-).  

PubMed

A class of transition-metal-centered aromatic boron wheels (D(nh)-M©B(n)(q-)) have been recently produced and characterized according to an electronic design principle. Here we investigate the interplay between electronic and geometric requirements for the molecular wheels using the case of VB(10)(-), which is isoelectronic to the decacoordinated molecular wheels, Ta©B(10)(-) and Nb©B(10)(-). Photoelectron spectra of VB(10)(-) are observed to be broad and complicated with relatively low electron binding energies, in contrast to the simple and high electron binding energies observed for the molecular wheels of its heavier congeners. An unbiased global minimum search found the most stable isomer of VB(10)(-) to be a singlet "boat"-like structure (C(2)), in which the V atom is coordinated to a quasi-planar B(10) unit. A similar triplet C(2v) boat-like isomer is found to be almost degenerate to the C(2) structure, whereas the beautiful molecular wheel structure, D(10h)-V©B(10)(-), is significantly higher in energy on the potential energy surface. Therefore, even though the VB(10)(-) system fulfills the electronic requirement to form a D(10h)-M©B(10)(-) aromatic molecular wheel, the V atom is too small to stabilize the ten-membered boron ring. PMID:22968622

Li, Wei-Li; Romanescu, Constantin; Piazza, Zachary A; Wang, Lai-Sheng

2012-10-21

114

The research and implementation of job submission system based on VB and BPFTP Server  

Microsoft Academic Search

Job Management is the important step that the teacher instructs students. In order to realize job submission in the computer room of low configuration, this paper brings forward the job submission system based on VB and BPFTP Server, analyzes the setting methods of user management, and illustrates the implementation process of job submission.

Hong Yan; Ying Li

2011-01-01

115

Carbonic anhydrase inhibitors. The mitochondrial isozyme VB as a new target for sulfonamide and sulfamate inhibitors.  

PubMed

A lately discovered carbonic anhydrase (hCA, EC 4.2.1.1), the mitochondrial hCA VB, was cloned, expressed, and purified. Kinetic parameters proved it to be 3.37 times more effective than hCA VA as a catalyst for the physiological reaction, with kcat = 9.5 x 10(5) s(-1) and kcat/K(M) = 9.8 x 10(7) M(-1) s(-1), being second only to hCA II among the 16 isoforms presently known in humans. We investigated the inhibition of hCA VB with a library of sulfonamides/sulfamates, some of which are clinically used compounds. Benzenesulfonamides were ineffective inhibitors, whereas derivatives bearing 4-amino, 4-hydrazino, 4-methyl, 4-carboxy moieties or halogenated sulfanilamides were more effective (Ki's of 1.56-4.3 microM). Among the 10 clinically used compounds, acetazolamide, benzolamide, topiramate, and indisulam showed effective inhibitory activity (Ki's of 18-62 nM). Three compounds showed better activity against hCA VB over hCA II, among which were sulpiride and ethoxzolamide, which were 2 times more effective inhibitors of the mitochondrial over the cytosolic isozyme. hCA VB is a druggable target and some of its inhibitors may lead to the development of novel antiobesity therapies. PMID:16302824

Nishimori, Isao; Vullo, Daniela; Innocenti, Alessio; Scozzafava, Andrea; Mastrolorenzo, Antonio; Supuran, Claudiu T

2005-12-01

116

SKIN BLISTERS AND HAIR LOSS IN A RAT MUTANT CALLED VIBRISSAELESS (vb)  

Microsoft Academic Search

A radiation-induced autosomal recessive mutant in the rat called vibrissaeless (vb), has been described and studied. Mutants have abnormal hair growth, the hairs being reduced in number and length. Mutant animals form blisters which then erode, crust, and heal without scars. The blisters can be artificially produced by friction and result from intraepidermal separation which is suprabasilar in position. To

Marvin A. Lutzner; Carl T. Hansen

1975-01-01

117

A Multidimensional Measure of Work Valences  

ERIC Educational Resources Information Center

|Work valence is derived from expectancy-valence theory and the literature on children's vocational development and is presumed to be a general appraisal of work that emerges during the childhood period. Work valence serves to promote and inhibit the motivation and tasks associated with vocational development. A measure of work valence, composed…

Porfeli, Erik J.; Lee, Bora; Weigold, Ingrid K.

2012-01-01

118

A Multidimensional Measure of Work Valences  

ERIC Educational Resources Information Center

Work valence is derived from expectancy-valence theory and the literature on children's vocational development and is presumed to be a general appraisal of work that emerges during the childhood period. Work valence serves to promote and inhibit the motivation and tasks associated with vocational development. A measure of work valence, composed of…

Porfeli, Erik J.; Lee, Bora; Weigold, Ingrid K.

2012-01-01

119

Hydrogen multicentre bonds  

NASA Astrophysics Data System (ADS)

The concept of a chemical bond stands out as a major development in the process of understanding how atoms are held together in molecules and solids. Lewis' classical picture of chemical bonds as shared-electron pairs evolved to the quantum-mechanical valence-bond and molecular-orbital theories, and the classification of molecules and solids in terms of their bonding type: covalent, ionic, van der Waals and metallic. Along with the more complex hydrogen bonds and three-centre bonds, they form a paradigm within which the structure of almost all molecules and solids can be understood. Here, we present evidence for hydrogen multicentre bonds-a generalization of three-centre bonds-in which a hydrogen atom equally bonds to four or more other atoms. When substituting for oxygen in metal oxides, hydrogen bonds equally to all the surrounding metal atoms, becoming fourfold coordinated in ZnO, and sixfold coordinated in MgO. These multicentre bonds are remarkably strong despite their large hydrogen-metal distances. The calculated local vibration mode frequency in MgO agrees with infrared spectroscopy measurements. Multicoordinated hydrogen also explains the dependence of electrical conductivity on oxygen partial pressure, resolving a long-standing controversy on the role of point defects in unintentional n-type conductivity of ZnO (refs 8-10).

Janotti, Anderson; van de Walle, Chris G.

2007-01-01

120

Cloning and expression of VB12-independent methionine synthase gene responsive to alkaline stress in rice.  

PubMed

VB12-independent methionine synthase is present in higher plants, and catalyzes the methylation of C-homocysteine to form methionine, which is very important for methylation reactions and syntheses of polyamines and ethylene. Under the alkaline condition, using cDNA-RAPD method, a new VB12-independent methionine synthase gene has been cloned and characterized for the first time in rice in this study. The results exhibited that, the cDNA gene entailed 2740 bp, had single copy in the rice genome and encoded peptide of 765 amino acids, the peptide showed 92% and 83% identity with that from Mesembryanthemum cystallinum (U84889) and Cathararanthus roseus (X83499), respectively. It enhanced the transcription more greatly after sodium carbonate treatment for 12 h and 24 h than that of sodium chloride treatment, and then obviously reduced in 48 h later, suggesting that it is related to this stress tolerance in rice. PMID:12693099

Xie, Guo-Sheng; Liu, Shen-Kui; Takano, Tetsuo; You, Zong-Bin; Zhang, Duan-Pin

2002-12-01

121

Homologues of the Bacillus subtilis SpoVB Protein Are Involved in Cell Wall Metabolism ?  

PubMed Central

Members of the COG2244 protein family are integral membrane proteins involved in synthesis of a variety of extracellular polymers. In several cases, these proteins have been suggested to move lipid-linked oligomers across the membrane or, in the case of Escherichia coli MviN, to flip the lipid II peptidoglycan precursor. Bacillus subtilis SpoVB was the first member of this family implicated in peptidoglycan synthesis and is required for spore cortex polymerization. Three other COG2244 members with high similarity to SpoVB are encoded within the B. subtilis genome. Mutant strains lacking any or all of these genes (yabM, ykvU, and ytgP) in addition to spoVB are viable and produce apparently normal peptidoglycan, indicating that their function is not essential in B. subtilis. Phenotypic changes associated with loss of two of these genes suggest that they function in peptidoglycan synthesis. Mutants lacking YtgP produce long cells and chains of cells, suggesting a role in cell division. Mutants lacking YabM exhibit sensitivity to moenomycin, an antibiotic that blocks peptidoglycan polymerization by class A penicillin-binding proteins. This result suggests that YabM may function in a previously observed alternate pathway for peptidoglycan strand synthesis.

Vasudevan, Pradeep; McElligott, Jessica; Attkisson, Christa; Betteken, Michael; Popham, David L.

2009-01-01

122

Bond Lengths and Bond Strengths in Compounds of the 5F Elements.  

National Technical Information Service (NTIS)

The variation of bond length (D) with bond strength (S) in normal valence compounds of 3d, 4d, 5d-4f, and 6d-5f elements can be represented approximately as D(S) = D(0.5) F(S), where D(0.5) is a characteristic constant for a given bond and F(S) an empiric...

W. H. Zachariasen

1975-01-01

123

Kekule valence structures revisited. Innate degrees of freedom of PI-electron couplings  

SciTech Connect

For individual Kekule valence structures we consider the smallest possible number of placements of CC double bonds such that a Kekule structure is fully determined. The number may be viewed as special weighting scheme for individual Kekule valence structures. Alternatively its reciprocal indicates the degree of a long-range order in a Kekule structure. Contributions from individual Kekule valence structure add to a novel structural invariant F, the innate degree of freedom associated to a conjugated system. We find that F correlates well with the molecular resonance energy. 8 refs., 3 figs.

Randic, M.; Klein, D.J.

1985-01-01

124

Symmetry and broken-symmetry in molecular orbital descriptions of unstable molecules. 3. The nature of chemical bonds of spin frustrated systems.  

PubMed

Symmetry and broken symmetry in the molecular orbital description of spin frustration systems have been investigated in relation to the resonating valence bond (RVB) theory of the spin liquid state and non-BCS superconductivity. Broken symmetry (BS) and resonating BS (RBS) molecular orbital (MO) methods have been employed to obtain resonating valence bond (RVB)-type explanations of spin frustrated systems. RBS MO solutions are expanded using the localized molecular orbitals (LMO) to elucidate a universal MO-VB description. The BS and RBS MO descriptions of triangular spin frustrated systems corresponding to transition structures for exchange-forbidden radical insertions were investigated in comparison with the RVB-type explanations of such systems. The BS and RBS calculations by the use of three different axial (SDW) solutions or three noncollinear GSO (helical SDW) solutions of a triangular hydrogen cluster were performed to obtain potential curves with and without resonance (quantum) effects. The resonating GSO (noncollinear) state responsible for short-range correlation was found to be the most stable for the system. The reliability of the approximate spin projection (AP) procedure to eliminate the high-spin component was also elucidated, comparing with the AP BS and RBS potential curves. The BS GSO (GHF) computations of several triangular systems, N(CH(2))(3), (CH(2))(3), and Mn(II)(3)O(4), were performed to obtain total energies and total spin angular momentums and effective exchange integrals (J) between local spins, which are crucial for construction of effective spin Hamiltonian models. The exact diagonalization of the Heisenberg models was also performed to depict the energy levels and magnetic susceptibility curves for triangular and kagome lattices to elucidate spin frustration effects and related quantum spin behaviors. Implications of the computational results have been discussed in relation to magnetic properties of several triangular and kagome systems synthesized recently and the superconductivity of triangular systems discovered recently. PMID:19908878

Kawakami, T; Takeda, R; Nishihara, S; Saito, T; Shoji, M; Yamada, S; Yamanaka, S; Kitagawa, Y; Okumura, M; Yamaguchi, K

2009-12-31

125

Molecular Invariants: Atomic Group Valence.  

National Technical Information Service (NTIS)

Molecular invariants may be deduced in a very compact way through Grassman algebra. In this work, a generalized valence is defined for an atomic group; it reduces to the Known expressions for the case of an atom in a molecule. It is the same for the corre...

K. C. Mundim M. Giambiagi M. S. Giambiagi

1988-01-01

126

Beyond valence in customer dissatisfaction  

Microsoft Academic Search

Dissatisfied customers may express their dissatisfaction behaviorally. These behavioral responses may impact the firms' profitability. How do we model the impact of emotions on satisfaction and subsequent customer behaviors? There are essentially two approaches: the valence-based approach and the specific emotions approach. The authors indicate theoretically and show empirically that it matters to distinguish these approaches in services research. Dissatisfaction

Marcel Zeelenberg; Rik Pieters

2004-01-01

127

Electronegativity and the Bond Triangle  

ERIC Educational Resources Information Center

The usefulness of the bond triangle for categorizing compounds of the main-group elements may be extended by the use of weighted average electronegativities to allow distinction between compounds of the same elements with different stoichiometries. In such cases a higher valency for the central atom leads to greater covalent character and the…

Meek, Terry L.; Garner, Leah D.

2005-01-01

128

Electronegativity and the Bond Triangle  

ERIC Educational Resources Information Center

|The usefulness of the bond triangle for categorizing compounds of the main-group elements may be extended by the use of weighted average electronegativities to allow distinction between compounds of the same elements with different stoichiometries. In such cases a higher valency for the central atom leads to greater covalent character and the…

Meek, Terry L.; Garner, Leah D.

2005-01-01

129

Mechanism and Regulation of the Two-component FMN-dependent Monooxygenase ActVA-ActVB from Streptomyces coelicolor*  

PubMed Central

The ActVA-ActVB system from Streptomyces coelicolor is a two-component flavin-dependent monooxygenase involved in the antibiotic actinorhodin biosynthesis. ActVB is a NADH:flavin oxidoreductase that provides a reduced FMN to ActVA, the monooxygenase that catalyzes the hydroxylation of dihydrokalafungin, the precursor of actinorhodin. In this work, using stopped-flow spectrophotometry, we investigated the mechanism of hydroxylation of dihydrokalafungin catalyzed by ActVA and that of the reduced FMN transfer from ActVB to ActVA. Our results show that the hydroxylation mechanism proceeds with the participation of two different reaction intermediates in ActVA active site. First, a C(4a)-FMN-hydroperoxide species is formed after binding of reduced FMN to the monooxygenase and reaction with O2. This intermediate hydroxylates the substrate and is transformed to a second reaction intermediate, a C(4a)-FMN-hydroxy species. In addition, we demonstrate that reduced FMN can be transferred efficiently from the reductase to the monooxygenase without involving any protein·protein complexes. The rate of transfer of reduced FMN from ActVB to ActVA was found to be controlled by the release of NAD+ from ActVB and was strongly affected by NAD+ concentration, with an IC50 of 40 ?m. This control of reduced FMN transfer by NAD+ was associated with the formation of a strong charge·transfer complex between NAD+ and reduced FMN in the active site of ActVB. These results suggest that, in Streptomyces coelicolor, the reductase component ActVB can act as a regulatory component of the monooxygenase activity by controlling the transfer of reduced FMN to the monooxygenase.

Valton, Julien; Mathevon, Carole; Fontecave, Marc; Niviere, Vincent; Ballou, David P.

2008-01-01

130

Reply to Isgur's comments on valence QCD  

SciTech Connect

We reply to Isgur's critique that is directed at some of the conclusions drawn from the lattice simulation of valence QCD, regarding the valence quark model and effective chiral theories. (c) 2000 The American Physical Society.

Liu, K. F. [SLAC, P.O. Box 4349, Stanford, California 94309 (United States); Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506 (United States); Dong, S. J. [Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506 (United States); Draper, T. [Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506 (United States); Sloan, J. [Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506 (United States); Spatial Technology, Boulder, Colorado 80301 (United States); Wilcox, W. [Department of Physics, Baylor University, Waco, Texas 76798 (United States); Woloshyn, R. M. [TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia, Canada V6T 2A3 (Canada)

2000-06-01

131

Bonding study of TiC and TiN. I. High-precision x-ray-diffraction determination of the valence-electron density distribution, Debye-Waller temperature factors, and atomic static displacements in TiC0.94 and TiN0.99  

NASA Astrophysics Data System (ADS)

Single-crystal, high-precision, high-resolution x-ray-diffraction measurements of the substoichiometric refractory compounds TiC and TiN have been performed with AgK? radiation. Severe anisotropic general extinction affects the intense low-order reflections. Inhomogeneity in the mosaic spread and domain size produces small but significant differences between reflection and antireflection for the same plane of diffraction. These effects have been modeled and refined together with a scale factor, isotropic thermal parameters, a population parameter of the nonmetal site, the amplitude of metal-atom static displacements around nonmetal vacancies, and an atomic model which includes occupancy factors of the separate orbital contributions of the valence electrons combined with ? expansion-contraction parameters. At convergence, the ``agreement indices'' (or ``reliability factors'') were R=0.0025 for TiC0.94 and R=0.0023 for TiN0.99. The refined population parameters indicate a chemical composition of TiC0.939(9) and TiN0.99(2). The mean-square amplitudes of thermal vibrations, Ti=0.002 38(2) AṦ, C=0.003 35(8) AṦ, Ti=0.002 94(1) AṦ, and N=0.003 08(12) AṦ are consistent with the respective atomic masses. 36% of the metal atoms in TiC0.94 are involved in a relaxation around the nonmetal vacancies, being displaced from their sublattice sites by 0.097(2) Å along [100]. No evidence for static displacements was found in TiN0.99. The valence-electron density distribution can be described satisfactorily in terms of deformed atoms. No buildup of charge density occurs between atomic sites. Our analysis, similar to a Mulliken partitioning, shows first that ionicity is important, with a charge transfer from the metal to the nonmetal of [2.1(4)]e in the carbide and [1.9(4)]e in the nitride, and secondly that the charge asphericity around the metal atoms is larger in the former than in the latter, while no departure from spherical symmetry is observed around the nonmetal atoms. The titanium 3d electrons can be split into a spherical shell that contains [1.27(6)]e plus an excess of [0.24(5)]e shared by two orbitals of eg symmetry in the carbide and conversely into a spherical shell that contains [0.88(11)]e plus an excess of [0.12(9)]e shared by three orbitals of t2g symmetry in the nitride. This suggests that the metal-to-metal bonding is similar in TiC and in TiN while the metal-to-nonmetal bonding is greater in TiC than in TiN.

Dunand, A.; Flack, H. D.; Yvon, K.

1985-02-01

132

LXIV. The Chemical Bond in Semiconductors  

Microsoft Academic Search

A survey of all known semiconductors suggests that it is useful to discuss the existence and properties of a specific ‘ semiconducting bond ’. A valence bond treatment of semiconductors, because it takes account of the properties of the specific atoms present, furnishes certain results which are not provided by the usual band model treatment. Most important of these are

E. MOOSER; W. B. PEARSON

1956-01-01

133

Asymptotic analysis of steady solutions of the KdVB equation with application to resonant sloshing  

NASA Astrophysics Data System (ADS)

The forced Korteweg-de Vries equation with Burgers’ damping (fKdVB) on a periodic domain, which arises as a model for water waves in a shallow tank with forcing near resonance, is considered. A method for construction of asymptotic solutions is presented, valid in cases where dispersion and damping are small. Through variation of a detuning parameter, families of resonant solutions are obtained providing detailed insight into the resonant response character of the system and allowing for direct comparison with the experimental results of Chester and Bones (1968).

Amundsen, D. E.; Cox, E. A.; Mortell, M. P.

2007-11-01

134

Sodium-sulfur battery development. Phase VB final report, October 1, 1981--February 28, 1985  

SciTech Connect

This report describes the technical progress made under Contract No. DE-AM04-79CH10012 between the U.S. Department of Energy, Ford Aerospace & Communications Corporations and Ford Motor Company, for the period 1 October 1981 through 28 February 1985, which is designated as Phase VB of the Sodium-Sulfur Battery Development Program. During this period, Ford Aerospace held prime technical responsibility and Ford Motor Company carried out supporting research. Ceramatec, Inc., was a major subcontractor to Ford Aerospace for electrolyte development and production.

NONE

1985-04-01

135

Vibrator (vb): a spinocerebellar system degeneration with autosomal recessive inheritance in mice.  

PubMed

Vibrator (gene symbol vb), an autosomal recessive mutation, occurred spontaneously in the DBA/2J strain of mice, was rescued by a single cross to C57BL/6J and subsequent brother X sister mating, and has been mapped near shaker-2 (sh-2) and vestigial tail (vt) on chromosome 11. The name emphasizes the unusually rapid (18-20 Hz) postural action tremor expressed in juvenile homozygotes. Selected neurons in spinal cord, and later in brainstem and cerebellum, show progressive degenerative changes featuring dilated cisternae of endoplasmic reticulum in cell bodies, dendrites and axons, with eventual severe intracellular vacuolation and some cell death. PMID:7139332

Weimar, W R; Lane, P W; Sidman, R L

1982-11-18

136

Carbonic anhydrase inhibitors: the inhibition profiles of the human mitochondrial isoforms VA and VB with anions are very different.  

PubMed

The first anion inhibition study of the mitochondrial human carbonic anhydrase (hCA, EC 4.2.1.1) isoform hCA VB is reported. Fluoride, chloride, bromide, iodide, cyanate, thiocyanate, cyanide, azide, bicarbonate, carbonate, nitrate, nitrite, hydrogen sulfide, bisulfite, sulfate, sulfamide, sulfamic acid, phenylboronic acid and phenylarsonic acid were compared as inhibitors of the two mitochondrial isozymes hCA VA and hCA VB. These enzymes are involved in biosynthetic reactions leading to fatty acid and Krebs cycle intermediates biosynthesis in addition to acting as catalysts for the interconversion of carbon dioxide and bicarbonate. The anion inhibition profiles of the two isoforms are dramatically different. The best hCA VB inhibitors were cyanate, thiocyanate, cyanide and hydrogensulfide (K(I)s of 80-76 microM) whereas the least effective ones were the halides (K(I)s of 11-72 mM), with the best inhibitor being fluoride and the least effective ones bromide and iodide. Whereas hCA VA is not sensitive to bicarbonate inhibition (K(I) of 82 mM) similarly to the cytosolic isoform hCA II, hCA VB is well inhibited by this anion, with a K(I) of 0.71 mM. Overall, hCA VB is more sensitive to anion inhibitors as compared to hCA VA. Such data support prior suggestions that the two mitochondrial isozymes play different physiological functions. PMID:17761422

Nishimori, Isao; Innocenti, Alessio; Vullo, Daniela; Scozzafava, Andrea; Supuran, Claudiu T

2007-08-15

137

Bond-Valence Constraints on Liquid Water Structure  

Microsoft Academic Search

The recent controversy about the structure of liquid water pits a new model involving water molecules in relatively stable rings-and-chains structures against the standard model that posits water molecules in distorted tetrahedral coordination. Molecular dynamics (MD) simulationsboth classical and ab initioalmost uniformly support the standard model, but since none of them can yet reproduce all the anomalous properties of water,

Barry R. Bickmore; Kevin M. Rosso; I. David Brown; Sebastien N. Kerisit

2009-01-01

138

Short range resonating valence bond theories and superconductivity  

SciTech Connect

The authors consider the nature of superconductivity near a spin-liquid state with a large spin-excitation-gap. They argue that the quantum-dimer-model with holes is a good approximation in this limit. The insulator is shown to be exactly equivalent to compact quantum electrodynamics, and has a massive spectrum. The doped system is a superconductor with a low density phase characterized by tightly bound pairs and a high density phase with two weakly coupled condensates.

Fradkin, E. (Illinois Univ., Urbana, IL (USA). Dept. of Physics); Kivelson, S. (California Univ., Los Angeles, CA (USA). Dept. of Physics)

1990-02-01

139

p6 chiral resonating valence bonds in the kagome antiferromagnet  

NASA Astrophysics Data System (ADS)

The kagome Heisenberg antiferromagnet is mapped onto an effective Hamiltonian on the star superlattice by contractor renormalization. A comparison of ground-state energies on large lattices to density matrix renormalization group justifies truncation of effective interactions at range 3 (36 sites). Within our accuracy, magnetic and translational symmetries are not broken (i.e., a spin liquid ground state). However, we discover doublet spectral degeneracies which signal the onset of p6 chirality symmetry breaking. This is understood by a simple mean field analysis. Experimentally, the p6 chiral order parameter should split the optical phonon degeneracy near the zone center. The addition of weak next to nearest neighbor coupling is discussed.

Capponi, Sylvain; Chandra, V. Ravi; Auerbach, Assa; Weinstein, Marvin

2013-04-01

140

p6 - Chiral Resonating Valence Bonds in the Kagome Antiferromagnet  

NASA Astrophysics Data System (ADS)

The Kagome Heisenberg antiferromagnet is mapped onto an effective Hamiltonian on the star superlattice by Contractor Renormalization. Comparison of ground state energies on large lattices to Density Matrix Renormalization Group justifies truncation of effective interactions at range 3. Within our accuracy, magnetic and translational symmetries are not broken (i.e. a spin liquid ground state). However, we discover doublet spectral degeneracies which signal the onset of p6 - chirality symmetry breaking. This is understood by simple mean field analysis. Experimentally, the p6 chiral order parameter should split the optical phonons degeneracy near the zone center. Addition of weak next to nearest neighbor coupling is discussed.

Auerbach, Assa; Capponi, Sylvain; Chandra, V. Ravi; Weinstein, Marvin

2013-03-01

141

Emotional valence and the functions  

Microsoft Academic Search

Differences between positive and negative autobiographical memories are often explained with reference to hypothesized evolutionary\\u000a functions. Generally, it has been proposed that autobiographical memory serves directive, self-, and social functions. However,\\u000a the relationship between emotional valence and the three functions has never been studied. In Study 1, participants generated\\u000a memories that mapped onto each of the three functions. Directive memories

Anne S. Rasmussen; Dorthe Berntsen

2009-01-01

142

ALLOYING-DRIVEN PHASE STABILITY IN GROUP-VB TRANSITION METALS UNDER COMPRESSION  

SciTech Connect

The change in phase stability of Group-VB (V, Nb, and Ta) transition metals due to pressure and alloying is explored by means of first-principles electronic-structure calculations. It is shown that under compression stabilization or destabilization of the ground-state body-centered cubic (bcc) phase of the metal is mainly dictated by the band-structure energy that correlates well with the position of the Kohn anomaly in the transverse acoustic phonon mode. The predicted position of the Kohn anomaly in V, Nb, and Ta is found to be in a good agreement with data from the inelastic x-ray or neutron scattering measurements. In the case of alloying the change in phase stability is defined by the interplay between the band-structure and Madelung energies. We show that band-structure effects determine phase stability when a particular Group-VB metal is alloyed with its nearest neighbors within the same d-transition series: the neighbor with less and more d electrons destabilize and stabilize the bcc phase, respectively. When V is alloyed with neighbors of a higher (4d- or 5d-) transition series, both electrostatic Madelung and band-structure energies stabilize the body-centered-cubic phase. The opposite effect (destabilization) happens when Nb or Ta is alloyed with neighbors of the 3d-transition series.

Landa, A; Soderlind, P

2011-04-11

143

Valence electronic structure of tantalum carbide and nitride  

NASA Astrophysics Data System (ADS)

The valence electronic structures of tantalum carbide (TaC) and tantalum nitride (TaN) are studied by using the empirical electronic theory (EET). The results reveal that the bonds of these compounds have covalent, metallic and ionic characters. For a quantitative analysis of the relative strength of these components, their ionicities have been calculated by implanting the results of EET to the PVL model. It has been found that the ionicity of tantalum carbide is smaller than that of tantalum nitride. The EET results also reveal that the covalent electronic number of the strongest bond in the former is larger than that of the latter. All these suggest that the covalent bond of TaC is stronger than that of TaN, which coincides to that deduced from the first-principles method.

Fan, Changzeng; Sun, Liling; Wei, Zunjie; Ma, Mingzhen; Liu, Riping; Zeng, Songyan; Wang, Wenkui

2007-12-01

144

Bonding and phase transitions in transition metal dichalcogenide layer compounds  

Microsoft Academic Search

The electronic structure of the transition metal dichalcogenide layer compounds is studied using hybridised orbitals appropriate to the transition metal atom coordination. Non-bonding orbitals on the transition metal atoms give the conduction electron bands which are responsible for the charge-density-wave phase transitions in the VB compounds, and the band structure of 1T- and 2H-TaS2 is found using tight binding. The

J. E. Inglesfield

1980-01-01

145

Valence band structure of binary chalcogenide vitreous semiconductors by high-resolution XPS  

SciTech Connect

High-resolution X-ray photoelectron spectroscopy (XPS) is used to study regularities in the formation of valence band electronic structure in binary As{sub x}Se{sub 100-x}, As{sub x}S{sub 100-x}, Ge{sub x}Se{sub 100-x} and Ge{sub x}S{sub 100-x} chalcogenide vitreous semiconductors. It is shown that the highest occupied energetic states in the valence band of these materials are formed by lone pair electrons of chalcogen atoms, which play dominant role in the formation of valence band electronic structure of chalcogen-rich glasses. A well-expressed contribution from chalcogen bonding p electrons and more deep s orbitals are also recorded in the experimental valence band XPS spectra. Compositional dependences of the observed bands are qualitatively analyzed from structural and compositional points of view.

Kozyukhin, S., E-mail: sergkoz@igic.ras.ru [Russian Academy of Science, Institute of General and Inorganic Chemistry (Russian Federation); Golovchak, R. [Lviv Scientific Research Institute of Materials of SRC 'Carat' (Ukraine); Kovalskiy, A. [Lehigh University, Department of Materials Science and Engineering (United States); Shpotyuk, O. [Lviv Scientific Research Institute of Materials of SRC 'Carat' (Ukraine); Jain, H. [Lehigh University, Department of Materials Science and Engineering (United States)

2011-04-15

146

AVE Bond Index in the H-Bond of the Watson-Crick Pairs.  

National Technical Information Service (NTIS)

The normal Watson-Crick base pairs are treated as super-molecules. The properties of the electronic distribution along the N-H...Y bonds are studied in an all-valence-electrons calculation, through a bond index formula devised for non-orthogonal basis. El...

M. de Giambiagi M. S. Giambiagi W. Barroso Filho

1981-01-01

147

Single Amino Acid Replacements in an Antigenic Peptide Are Sufficient to Alter the TCR Vb Repertoire of the Responding CD81 Cytotoxic Lymphocyte Population1  

Microsoft Academic Search

with peptides 8 -11 amino acids long. T cell responses triggered by certain antigenic peptides are restricted to a limited number of TCR Vb elements. The precise role of the peptide in causing this restricted TCR Vb expansion in vivo remains unclear. To address this issue, we immunized C57BL\\/6 mice with the immunodominant peptide of the vesicular stomatitis virus (VSV)

Alexis M. Kalergis; Toshiro Ono; Fuming Wang; Teresa P. DiLorenzo; Shinichiro Honda; Stanley G. Nathenson

148

Exoplanet Detection Combining Astrometric and Radial Velocity Measurements. Application to VB10b  

NASA Astrophysics Data System (ADS)

Ground based astrometry hasn't been very successful in detecting extrasolar planets. The reasons for that is the relatively long time baselines required, instrumental stability requirements and calibration related issues. In addition to that, the number of free parameters is large compared to other methods (such as radial velocities) and additional information is often required to constrain the true nature of the candidate signals. An example is the recently announced astrometric detection of a planet around the low mass star VB10, where a careful reanalysis of the data with existing Doppler measurements casts some doubts on the true nature of the announced low mass companion. Follow-up observations on this object (both astrometric and spectroscopic) have been obtained. We present the results of this campaign and a detailed analysis of the allowed orbital solutions which confirm/rule out the presence of this candidate.

Anglada-Escudé, Guillem; Shkolnik, E.; Weinberger, A.; Thompson, I.; Osip, D.

2010-01-01

149

On the valence of surprise.  

PubMed

While surprise is a common emotion in everyday life, some of its fundamental characteristics are still unclear. For example, what does surprise feel like, positive or negative? The emotion literature has been somewhat unclear about the experiential valence of surprise. Surprise has been depicted as a pre-affective state, or as an emotion that can be both positive and negative, depending on the goal conduciveness of the surprising event. Based on recent work on cognitive consistency and neuroscientific/psychophysiological studies on surprise, we explored the possibility that surprise may be a (mildly) negative emotion in a study of autobiographical recall of unexpected and surprising events (Experiment 1) and in two studies of facial expressions of surprise (Experiments 2 and 3a/b). The studies show that experience of surprise and the perception of surprise in others may indeed be initially negative. We furthermore show how linguistic features of surprise and the temporal dynamics may have contributed to previous confusion regarding its valence. PMID:23560688

Noordewier, Marret K; Breugelmans, Seger M

2013-04-08

150

M1-x[W2O2X6] with M=K+, Tl+, Ag+, Hg2+, Pb2+; X=Cl, Br—A class of mixed valence tungsten (IV,V) compounds with layered structures, W W bonds and high conductivity  

NASA Astrophysics Data System (ADS)

The crystal structure of WOCl3, determined on the basis of powder diffraction data (tetragonal, P42/mnm, a=10.6856(6), c=3.8537(2)), is isotypic to WOI3 and contains one-dimensional strands of edge-sharing double-octahedral W2O4/2Cl6 groups connected via common corners in trans position. A W W bond of 2.99 Å is present within the planar W2Cl6 groups. A series of non-stochiometric, mixed valence W(IV,V) compounds M1-x[W2O2Cl6] can be obtained from WOCl3 by reaction with metal halides (TlCl, KCl, PbCl2) or by reaction of elemental Hg with WOCl4. All were characterized by single crystal structure determinations and EDX measurements (Tl0.981(2)[W2O2Cl6]: monoclinic, C2/m, a=12.7050(4), b=3.7797(1), c=10.5651(3)Å, ?=107.656(1)°; K0.84(2)[W2O2Cl6]: monoclinic, C2/m, a=12.812(3), b=3.7779(6), c=10.196(3)Å, ?=107.422(8)°; Pb0.549(3)[W2O2Cl6]: orthorhombic, Immm,a=3.7659(1), b=9.8975(4), c=12.1332(6)Å; Hg0.554(6)[W2O2Cl6]: monoclinic, C2/m, a=12.8361(8), b=3.7622(3), c=10.2581(9)Å, ?=113.645(3)°). Two representatives of this family of compounds have already been reported: Na[W2O2Br6] [Y.-Q. Zhang, K. Peters, H.G. von Schnering, Z. Anorg. Allg. Chem. 624 (1998) 1415 1418] and Ag0.74[W2O2Br6] [S. Imhaïne, C. Perrin, M. Sergent, Mat. Res. Bull. 33 (1998) 927 933]. The Ag containing compound can be obtained from elemental Ag and WOBr3. The crystal structure, originally reported in the triclinic system, was redetermined and shown to be monoclinic with space group C2/m (a=13.7338(10), b=3.7769(3), c=10.7954(9)Å, ?=112.401(3)°). The crystal structures of these compounds are in close relationship to the structure of WOCl3 and all contain W2O4/2X6 (X=Cl, Br) double strands with the mono and divalent cations coordinated by the terminal halogen atoms of the W2X6 groups and a short W W bond (2.85 Å for X=Cl). A cube-shaped coordination environment is present for M=Tl, K and a trigonal-prismatic coordination for M=Ag, Hg. Hg0.55[W2O2Cl6] is a semiconductor with a non-Arrhenius behaviour, high specific conductivity of 0.05 ? 1 cm-1 and a very small activation energy of 0.03 eV. Hg0.55[W2O2Cl6] and Ag0.8[W2O2Br6] show a temperature independent paramagnetism with a magnetic moment around 300×10 6 cm3 mol 1.

Beck, Johannes; Kusterer, Christian; Hoffmann, Rolf-Dieter; Pöttgen, Rainer

2006-08-01

151

Orbital overlap and chemical bonding.  

PubMed

The chemical bonds in the diatomic molecules Li(2)-F(2) and Na(2)-Cl(2) at different bond lengths have been analyzed by the energy decomposition analysis (EDA) method using DFT calculations at the BP86/TZ2P level. The interatomic interactions are discussed in terms of quasiclassical electrostatic interactions DeltaE(elstat), Pauli repulsion DeltaE(Pauli) and attractive orbital interactions DeltaE(orb). The energy terms are compared with the orbital overlaps at different interatomic distances. The quasiclassical electrostatic interactions between two electrons occupying 1s, 2s, 2p(sigma), and 2p(pi) orbitals have been calculated and the results are analyzed and discussed. It is shown that the equilibrium distances of the covalent bonds are not determined by the maximum overlap of the sigma valence orbitals, which nearly always has its largest value at clearly shorter distances than the equilibrium bond length. The crucial interaction that prevents shorter bonds is not the loss of attractive interactions, but a sharp increase in the Pauli repulsion between electrons in valence orbitals. The attractive interactions of DeltaE(orb) and the repulsive interactions of DeltaE(Pauli) are both determined by the orbital overlap. The net effect of the two terms depends on the occupation of the valence orbitals, but the onset of attractive orbital interactions occurs at longer distances than Pauli repulsion, because overlap of occupied orbitals with vacant orbitals starts earlier than overlap between occupied orbitals. The contribution of DeltaE(elstat) in most nonpolar covalent bonds is strongly attractive. This comes from the deviation of quasiclassical electron-electron repulsion and nuclear-electron attraction from Coulomb's law for point charges. The actual strength of DeltaE(elstat) depends on the size and shape of the occupied valence orbitals. The attractive electrostatic contributions in the diatomic molecules Li(2)-F(2) come from the s and p(sigma) electrons, while the p(pi) electrons do not compensate for nuclear-nuclear repulsion. It is the interplay of the three terms DeltaE(orb), DeltaE(Pauli), and DeltaE(elstat) that determines the bond energies and equilibrium distances of covalently bonded molecules. Molecules like N(2) and O(2), which are usually considered as covalently bonded, would not be bonded without the quasiclassical attraction DeltaE(elstat). PMID:17024702

Krapp, Andreas; Bickelhaupt, F Matthias; Frenking, Gernot

2006-12-13

152

Recent advances in the practical and accurate calculation of core and valence XPS spectra of polymers: from interpretation to simulation?  

Microsoft Academic Search

Core and valence X-ray Photoelectron Spectroscopies (XPS) are routinely used to obtain information on the chemical composition, bonding and homogeneity of polymer surfaces. In spite of their apparent conceptual simplicity, Core and Valence Electron Binding Energies (CEBEs and VEBEs) a few electron-volts (eV) or fractions of an eV apart are difficult to interpret. We present some results obtained with various

Christophe Bureau; Delano P. Chong; Kazunaka Endo; Joseph Delhalle; Gérard Lecayon; Alain Le Moël

1997-01-01

153

Depression and information valence influence depressive cognition  

Microsoft Academic Search

The current study examined two possible antecedents of depressive cognition: diagnostic status and information varying in positive, neutral, or negative valence. The participants were 62 elders: 26 outpatients with a major depressive disorder and 36 community controls. These subjects were randomly assigned to one of three conditions of valenced information given by means of three versions of short stories followed

Susan E. Krantz; Dolores Gallagher-Thompson

1990-01-01

154

Valence-band structure of the ferromagnetic semiconductor GaMnAs investigated by resonant tunneling spectroscopy  

NASA Astrophysics Data System (ADS)

The origin of ferromagnetism in the prototype ferromagnetic semiconductor GaMnAs is still controversial due to the insufficient understanding of its band structure and Fermi level position. Here, we investigate the valence-band (VB) structure of GaMnAs by analyzing the resonant tunneling levels of the GaMnAs quantum well (QW) in double-barrier heterostructures. The resonant levels including the heavy-hole first state (HH1) are clearly observed in the metallic GaMnAs QW with the Curie temperature (T/C) of 60 K, which indicates that no holes reside in the VB of GaMnAs in the equilibrium condition. Clear enhancement of tunnel magnetoresistance induced by resonant tunneling is demonstrated. We find that the resonant levels formed in the GaMnAs QW are well explained by using the transfer matrix method with the 6x6 {kp} Hamiltonian and small p-d exchange Hamiltonian. The VB structure of GaMnAs is well reproduced by that of GaAs with a small exchange splitting energy of 3-5 meV and with the Fermi level lying at ˜ 30 meV higher than HH1 in the bandgap. Furthermore, we show our more recent results of resonant tunneling spectroscopy on various surface GaMnAs films (Mn concentration: 6-15/, T/C: 71-154 K) grown on an AlAs layer, where the resonant levels are formed by confinement of the VB holes by the surface Schottky barrier and the AlAs barrier. We systematically investigate the thickness dependence of the resonant levels in GaMnAs by precisely etching the surface of GaMnAs. We find that the p-d exchange interaction is negligibly small (3-5 meV) and that the Fermi level exists in the bandgap. This work was performed in collaboration with I. Muneta, P. N. Hai, K. Takata, and M. Tanaka, and partly supported by Grant-in-Aids for Scientific Research, the Special Coordination Programs for Promoting Science and Technology, and FIRST Program by JSPS.[4pt] [1] S. Ohya et al., Phys. Rev. Lett. 104, 167204 (2010).[0pt] [2] S. Ohya et al., arXiv:1009.2235.

Ohya, Shinobu

2011-03-01

155

Influence of VB group doped TiO2 on photovoltaic performance of dye-sensitized solar cells  

NASA Astrophysics Data System (ADS)

Dye-sensitized solar cell with VB group (vanadium (V), niobium (Nb) and tantalum (Ta)) doped TiO2 prepared by hydrothermal method shows a higher photovoltaic efficiency compared with the undoped TiO2. All the VB doping shift the flat band potential positively and increase the doping density which is investigated by Mott–Schottky plot. The positive shift of flat band potential improves the driving force of injecting electron from the LUMO of dye to the conduction band of TiO2 and the photocurrent. On the other hand, the increase of doping density accelerates transfer rate of electrons in TiO2 than the un-doped, which is confirmed by intensity-modulated photocurrent. V-, Nb-, Ta-doped TiO2 exhibited photovoltaic performance with 7.80%, 8.33%, 8.18%, respectively, compared with that of the cells based on pure TiO2 (7.42%).

Liu, Jia; Duan, Yandong; Zhou, Xiaowen; Lin, Yuan

2013-07-01

156

A new noncentrosymmetric vanadoborate: synthesis, crystal structure and characterization of K2SrVB5O12.  

PubMed

A new noncentrosymmetric vanadoborate compound, K(2)SrVB(5)O(12), is synthesized by the high temperature solution method. It crystallizes in the monoclinic space group P2(1) (no. 4) with lattice constants a = 6.618(3) Å, b = 8.378(4) Å, c = 9.974(5) Å, ? = 99.789(6)°, Z = 2. The structure consists of vanadoborate anionic layers with K(+) and Sr(2+) cations filling the void spaces via electrostatic interactions to form the three-dimensional network. The TG-DSC curves and the UV-Vis-NIR diffuse reflectance spectrum were measured. Band structures and density of states were calculated. The powder second harmonic generation (SHG) effect of K(2)SrVB(5)O(12) is similar to that of KH(2)PO(4) (KDP). PMID:22728567

Chen, Songjie; Pan, Shilie; Zhao, Wenwu; Yu, Hongwei; Wu, Hongping; Yang, Zhihua; Yang, Yun

2012-06-22

157

Edge versus interior in the chemical bonding of graphene materials  

Microsoft Academic Search

A notable phenomenon is described involving the polarization of valence electrons that operates in the edge regions of graphene materials, including compact polyaromatic hydrocarbon (PAH) molecules, because of the mismatch between interior and perimeter chemical bonds. The topology of hexagonal-shaped zigzag-edged systems, with alternating perimeter CC bond lengths, enhances the effect, making recognition easier, compared to graphene ribbons where it

Michael R. Philpott; Yoshiyuki Kawazoe

2009-01-01

158

An Atom-Specific Look at the Surface Chemical Bond  

Microsoft Academic Search

High resolution x-ray emission spectroscopy is shown to reveal unprecedented details of the chemical bond formed between a molecule and a transition metal surface. An atom and symmetry projected view of the bonding orbitals is obtained. We find that all outer and inner valence orbitals of the molecule change due to the surface interaction. New types of molecular states are

Anders Nilsson; Martin G. Weinelt; Tomas Wiell; Peter Bennich; O. Karis; Nial Wassdahl; J. Stöhr; Mahesh G. Samant

1997-01-01

159

[The VB system: a new modular osteosynthesis material involving both screws and wires].  

PubMed

VB is an osteosynthesis system for the stabilisation of small fragments, which combines the benefits of both wires and screws. It is a modular system comprising a threaded pin and a ring. The threaded pin is first positioned. Then a ring is grasped and opened by the progressive angulation of a screwdriver. Still anchored on the screwdriver, the ring slides easily on the pin. It is clamped on the pin by simply removing the screwdriver and the pin is then cut. This modular system includes 1.8 and 1.1 mm pins and different types of rings (threaded or non threaded, with or without collars). The system is easy to handle and can be introduced using an open or percutaneous technique, allowing compression or distraction. Our preliminary series, performed in accordance with National clinical trial protocol (Huriet) consisted of 50 cases in 24 patients (five women and 19 men) with an average age of 48 years, and a follow-up of more than six months. Fourteen cases of fractures (28 implants) were treated as emergencies (two radial heads, one capitellum, one trochlea of the humerus, seven distal radius fractures, one trapezium, two metacarpals) and 12 cases (22 implants) were elective cases: arthrodesis (one trapezo-metacarpal, one intermetacarpal, two interphalangeal, two carpal), non-union (six scaphoids, one phalangeal) and one phalangeal malunion. Hardware removal was performed in 16 cases. No implant failure has been detected. One case, a DIP arthrodesis, had a suspicion of sepsis which led to the removal of the implants at six weeks. The results of this study have convinced us of the merits of the system, which combines the advantages of both wires and screws. The system allows the user to perform either distraction or compression, and to adjust the force by hand. Compared to the fixed amount of compression produced by lag screws, this feature seems to be a real step forward. PMID:11885383

Dubert, T; Valenti, P; Dinh, A; Osman, N

2002-01-01

160

STRONG CONSTRAINTS TO THE PUTATIVE PLANET CANDIDATE AROUND VB 10 USING DOPPLER SPECTROSCOPY  

SciTech Connect

We present new radial velocity (RV) measurements of the ultra-cool dwarf VB 10, which was recently announced to host a giant planet detected with astrometry. The new observations were obtained using optical spectrographs (MIKE/Magellan and ESPaDOnS/CFHT) and cover 65% of the reported period of 270 days. The nominal precision of the new Doppler measurements is about 150 m s{sup -1} while their standard deviation is 250 m s{sup -1}. However, there are indications that such a larger variation is due to uncontrolled systematic errors. We apply least-squares periodograms to identify the most significant signals and evaluate their false alarm probabilities (FAPs). We show that this method is the proper generalization to astrometric data because (1) it mitigates the coupling of the orbital parameters with the parallax and proper motion, and (2) it permits a direct generalization to include nonlinear Keplerian parameters in a combined fit to astrometry and RV data. Our analysis of the astrometry alone uncovers the reported 270 day period and an even stronger signal at {approx}50 days. We estimate the uncertainties in the parameters using a Markov chain Monte Carlo approach. Although the new data alone cannot rule out the presence of a candidate, when combined with published RV measurements, the FAPs of the best solutions grow to unacceptable levels strongly suggesting that the observed astrometric wobble is not due to an unseen companion. The new measurements put an upper limit of m sin i {approx} 2.5 m {sub jup} for a companion with a period shorter than one year and moderate eccentricities.

Anglada-Escude, Guillem; Shkolnik, Evgenya L.; Weinberger, Alycia J. [Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015 (United States); Thompson, Ian B. [Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Osip, David J. [Las Campanas Observatory, Carnegie Institution of Washington, Colina El Pino Casilla 601, La Serena (Chile); Debes, John H. [Goddard Space Flight Center, NASA Postdoctoral Program, 8463 Greenbelt Rd, Greenbelt, MD 20770 (United States)], E-mail: anglada@dtm.ciw.edu, E-mail: shkolnik@dtm.ciw.edu, E-mail: weinberger@dtm.ciw.edu, E-mail: ian@obs.carnegiescience.edu, E-mail: dosip@lco.cl, E-mail: john.H.debes@nasa.gov

2010-03-01

161

The bondons: the quantum particles of the chemical bond.  

PubMed

By employing the combined Bohmian quantum formalism with the U(1) and SU(2) gauge transformations of the non-relativistic wave-function and the relativistic spinor, within the Schrödinger and Dirac quantum pictures of electron motions, the existence of the chemical field is revealed along the associate bondon particle B? characterized by its mass (m(B?)), velocity (v(B?)), charge (e(B?)), and life-time (t(B?)). This is quantized either in ground or excited states of the chemical bond in terms of reduced Planck constant ?, the bond energy E(bond) and length X(bond), respectively. The mass-velocity-charge-time quaternion properties of bondons' particles were used in discussing various paradigmatic types of chemical bond towards assessing their covalent, multiple bonding, metallic and ionic features. The bondonic picture was completed by discussing the relativistic charge and life-time (the actual zitterbewegung) problem, i.e., showing that the bondon equals the benchmark electronic charge through moving with almost light velocity. It carries negligible, although non-zero, mass in special bonding conditions and towards observable femtosecond life-time as the bonding length increases in the nanosystems and bonding energy decreases according with the bonding length-energy relationship Ebond[kcal/mol]×Xbond[A0]=182019, providing this way the predictive framework in which the B? particle may be observed. Finally, its role in establishing the virtual states in Raman scattering was also established. PMID:21151435

Putz, Mihai V

2010-10-28

162

Chemical Bonds  

NSDL National Science Digital Library

Electrons are key to forming the two broad categories of chemical bonds: covalent and ionic. Atoms, which have a nucleus surrounded by electrons, are represented in several different ways. In the Chemical Bonds activity, students explore the different kinds of chemical bonds that can form, ranging from non-polar covalent to ionic. In the model depicted above students adjust the electronegativity of two atoms and see the effect it has on electron distribution and bond type.

Consortium, The C.

2011-12-11

163

The distribution of the valence electron density in predominantly ionic crystals with different Bravais sublattices  

Microsoft Academic Search

Based on the theory of the local-density functional, self-consistent valence electron densities are calculated for CaO with\\u000a a rock-salt lattice, CaF2 with a fluorite lattice, K2O with an antifluorite lattice, and for their constituent sublattices. It is shown that in the crystals with different Bravais\\u000a sublattices, the anionic sublattice is a framework with covalent bonds containing a metal sublattice inside

Yu. N. Zhuravlev; A. S. Poplavnoi

2003-01-01

164

Sticker Bonding.  

ERIC Educational Resources Information Center

|Introduces a science activity on the bonding of chemical compounds. Assigns students the role of either a cation or anion and asks them to write the ions they may bond with. Assesses students' understanding of charge, bonding, and other concepts. (YDS)|

Frazier, Laura Corbin

2000-01-01

165

Sticker Bonding.  

ERIC Educational Resources Information Center

Introduces a science activity on the bonding of chemical compounds. Assigns students the role of either a cation or anion and asks them to write the ions they may bond with. Assesses students' understanding of charge, bonding, and other concepts. (YDS)

Frazier, Laura Corbin

2000-01-01

166

Chemical bond analysis of the crystal growth of KDP and ADP  

Microsoft Academic Search

The bond valence model is employed to calculate the bond strength of constituent chemical bonds formed between growth units in both potassium dihydrogen phosphate (KDP) and ammonium dihydrogen phosphate (ADP) crystals, with the aim to predict and control the crystal shape. After calculating and comparing the relative growth rates of all selected planes, which are related to the crystallographic structure

Dongli Xu; Dongfeng Xue

2006-01-01

167

On the Detectability of a Predicted Mesolensing Event Associated with the High Proper Motion Star VB 10  

NASA Astrophysics Data System (ADS)

Extrapolation of the astrometric motion of the nearby low-mass star VB 10 indicates that sometime in late 2011 December or during the first 2-3 months of 2012, the star will make a close approach to a background point source. Based on astrometric uncertainties, we estimate a 1 in 2 chance that the distance of closest approach ?min will be less than 100 mas, a 1 in 5 chance that ?min < 50 mas, and a 1 in 10 chance that ?min < 20 mas. The last would result in a microlensing event with a 6% magnification in the light from the background source and an astrometric shift of 3.3 mas. The lensing signal will however be significantly diluted by the light from VB 10, which is 1.5 mag brighter than the background source in B band, 5 mag brighter in I band, and 10 mag brighter in K band, making the event undetectable in all but the bluer optical bands. However, we show that if VB 10 happens to harbor a ~1 MJ planet on a moderately wide (?0.18 AU-0.84 AU) orbit, there is a chance (1% to more than 10%, depending on the distance of closest approach and orbital period and inclination) that a passage of the planet closer to the background source will result in a secondary event of higher magnification. The detection of secondary events could be made possible with a several-times-per-night multi-site monitoring campaign. Based on observations made with the NASA/ESA Hubble Space Telescope, and obtained from the Hubble Legacy Archive, which is a collaboration between the Space Telescope Science Institute (STScI/NASA), the Space Telescope European Coordinating Facility (ST-ECF/ESA), and the Canadian Astronomy Data Centre (CADC/NRC/CSA).

Lépine, Sébastien; DiStefano, Rosanne

2012-04-01

168

Valence-quark distributions in the pion  

SciTech Connect

We calculate the pion's valence-quark momentum-fraction probability distribution using a Dyson-Schwinger equation model. Valence quarks with an active mass of 0.30 GeV carry 71% of the pion's momentum at a resolving scale q{sub 0}=0.54 GeV=1/(0.37 fm). The shape of the calculated distribution is characteristic of a strongly bound system and, evolved from q{sub 0} to q=2 GeV, it yields first, second, and third moments in agreement with lattice and phenomenological estimates, and valence-quarks carrying 49% of the pion's momentum. However, pointwise there is a discrepancy between our calculated distribution and that hitherto inferred from parametrizations of extant pion-nucleon Drell-Yan data.

Hecht, M. B.; Roberts, C. D.; Schmidt, S. M.

2001-02-01

169

Fluctuating valence in a correlated solid and the anomalous properties of delta-plutonium.  

PubMed

Although the nuclear properties of the late actinides (plutonium, americium and curium) are fully understood and widely applied to energy generation, their solid-state properties do not fit within standard models and are the subject of active research. Plutonium displays phases with enormous volume differences, and both its Pauli-like magnetic susceptibility and resistivity are an order of magnitude larger than those of simple metals. Curium is also highly resistive, but its susceptibility is Curie-like at high temperatures and orders antiferromagnetically at low temperatures. The anomalous properties of the late actinides stem from the competition between itinerancy and localization of their f-shell electrons, which makes these elements strongly correlated materials. A central problem in this field is to understand the mechanism by which these conflicting tendencies are resolved in such materials. Here we identify the electronic mechanisms responsible for the anomalous behaviour of late actinides, revisiting the concept of valence using a theoretical approach that treats magnetism, Kondo screening, atomic multiplet effects and crystal field splitting on the same footing. We find that the ground state in plutonium is a quantum superposition of two distinct atomic valences, whereas curium settles into a magnetically ordered single valence state at low temperatures. The f(7) configuration of curium is contrasted with the multiple valences of the plutonium ground state, which we characterize by a valence histogram. The balance between the Kondo screening and magnetism is controlled by the competition between spin-orbit coupling, the strength of atomic multiplets and the degree of itinerancy. Our approach highlights the electronic origin of the bonding anomalies in plutonium, and can be applied to predict generalized valences and the presence or absence of magnetism in other compounds starting from first principles. PMID:17392780

Shim, J H; Haule, K; Kotliar, G

2007-03-29

170

Chemical bonding in hypervalent molecules. The dominance of ionic bonding and negative hyperconjugation over d-orbital participation  

Microsoft Academic Search

Does sulfur form six covalent bonds in CHâSOâCl, FâS{triple bond}N or carbon or phosphorus five bonds in FâC=O⁻, FâP=O After a brief history of the viewpoints on hypervalent bonding and a comparison of analysis methods (with CHâSOâCl as example), natural population and natural bond orbital analysis is applied to a series of 32-valence-electron species of XâXY type (CFâ, FâNO, OâClF,

Alan E. Reed; P. von Rague Schleyer

1990-01-01

171

Attitude Formation Through Exploration: Valence Asymmetries  

Microsoft Academic Search

The formation of attitudes toward novel objects was examined as a function of exploratory behavior. An initial experiment, in which participants played a computer game that required them to learn which stimuli, when sampled, produced favorable or unfavorable outcomes, demonstrated learning, attitude formation, and generalization to novel objects. The findings also revealed 2 interesting valence asymmetries: a learning asymmetry involving

Russell H. Fazio; J. Richard Eiser; Natalie J. Shook

2004-01-01

172

Masked emotional priming beyond global valence activations  

Microsoft Academic Search

An immense body of research demonstrates that emotional facial expressions can be processed unconsciously. However, it has been assumed that such processing takes place solely on a global valence-based level, allowing individuals to disentangle positive from negative emotions but not the specific emotion. In three studies, we investigated the specificity of emotion processing under conditions of limited awareness using a

Michaela Rohr; Juliane Degner; Dirk Wentura

2011-01-01

173

Masked emotional priming beyond global valence activations  

Microsoft Academic Search

An immense body of research demonstrates that emotional facial expressions can be processed unconsciously. However, it has been assumed that such processing takes place solely on a global valence-based level, allowing individuals to disentangle positive from negative emotions but not the specific emotion. In three studies, we investigated the specificity of emotion processing under conditions of limited awareness using a

Michaela Rohr; Juliane Degner; Dirk Wentura

2012-01-01

174

Prospective memory, emotional valence, and multiple sclerosis  

Microsoft Academic Search

Cognitive impairments in multiple sclerosis (MS) extend to tasks demanding prospective memory (PM): remembering to perform an intended act during ongoing activity. This study investigated whether emotional content influenced the effects of MS on PM, following evidence that emotional valence can influence other aspects of memory. Thirty participants with MS were compared to 30 controls on a PM task, Virtual

Peter G. Rendell; Julie D. Henry; Louise H. Phillips; Xochitl de la Piedad Garcia; Patricia Booth; Patricia Phillips; Matthias Kliegel

2012-01-01

175

Affective Priming with Associatively Acquired Valence  

ERIC Educational Resources Information Center

Three experiments explored the effect of affectively congruent or incongruent primes on evaluation responses to positive or negative valenced targets (the "affective priming" effect). Experiment 1 replicated the basic affective priming effect with Spanish nouns: reaction time for evaluative responses (pleasant/unpleasant) were slower on…

Aguado, Luis; Pierna, Manuel; Saugar, Cristina

2005-01-01

176

Core-Level And Valence-Band Study Using Angle-Integrated Photoemission on LaFeAsO(0.9)F(0.1)  

SciTech Connect

Using angle-integrated photoemission spectroscopy we have probed the novel LaFeAsO{sub 0.9}F{sub 0.1} superconductor over a wide range of photon energies and temperatures. We have provided a full characterization of the orbital character of the valence-band (VB) density of states (DOS) and of the magnitude of the d-p hybridization energy. Finally, we have identified two characteristic temperatures: 90 K where a pseudogap-like feature appears to close and 120 K where a sudden change in the DOS near E{sub F} occurs. We associate these phenomena with the spin density wave magnetic ordering and the structural transition seen in the parent compound, respectively. These results suggest the important role of electron correlation, spin physics, and structural distortion in the physics of Fe-based superconductors.

Garcia, D.R.; Jozwiak, C.; Hwang, C.G.; Fedorov, A.; Hanrahan, S.M.; Wilson, S.D.; Rotundu, C.R.; Freelon, B.K.; Birgeneau, R.J.; Bourret-Courchesne, E.; Lanzara, A.

2009-05-18

177

Valence skipping driven superconductivity and charge Kondo effect  

NASA Astrophysics Data System (ADS)

Valence skipping in metallic compounds can give rise to an unconventional superconductivity. Several elements in the periodic table show valence skipping (or valence missing), for example, Bi forms the compounds in valence states +3 and +5. The doping of valence skipping elements will induce superconductivity and this will lead to a possibility of high temperature superconductivity. We consider the Wolf model with negative-U impurities, and show a phase diagram including superconducting phase. The superconducting state is changed into a metallic state with a local singlet as the attractive interaction |U| increases. There is a high temperature region near the boundary.

Yanagisawa, Takashi; Hase, Izumi

2013-11-01

178

Pattern classification of valence in depression?  

PubMed Central

Neuroimaging biomarkers of depression have potential to aid diagnosis, identify individuals at risk and predict treatment response or course of illness. Nevertheless none have been identified so far, potentially because no single brain parameter captures the complexity of the pathophysiology of depression. Multi-voxel pattern analysis (MVPA) may overcome this issue as it can identify patterns of voxels that are spatially distributed across the brain. Here we present the results of an MVPA to investigate the neuronal patterns underlying passive viewing of positive, negative and neutral pictures in depressed patients. A linear support vector machine (SVM) was trained to discriminate different valence conditions based on the functional magnetic resonance imaging (fMRI) data of nine unipolar depressed patients. A similar dataset obtained in nine healthy individuals was included to conduct a group classification analysis via linear discriminant analysis (LDA). Accuracy scores of 86% or higher were obtained for each valence contrast via patterns that included limbic areas such as the amygdala and frontal areas such as the ventrolateral prefrontal cortex. The LDA identified two areas (the dorsomedial prefrontal cortex and caudate nucleus) that allowed group classification with 72.2% accuracy. Our preliminary findings suggest that MVPA can identify stable valence patterns, with more sensitivity than univariate analysis, in depressed participants and that it may be possible to discriminate between healthy and depressed individuals based on differences in the brain's response to emotional cues.

Habes, I.; Krall, S.C.; Johnston, S.J.; Yuen, K.S.L.; Healy, D.; Goebel, R.; Sorger, B.; Linden, D.E.J.

2013-01-01

179

Edge versus interior in the chemical bonding of graphene materials  

NASA Astrophysics Data System (ADS)

A notable phenomenon is described involving the polarization of valence electrons that operates in the edge regions of graphene materials, including compact polyaromatic hydrocarbon (PAH) molecules, because of the mismatch between interior and perimeter chemical bonds. The topology of hexagonal-shaped zigzag-edged systems, with alternating perimeter CC bond lengths, enhances the effect, making recognition easier, compared to graphene ribbons where it is weak. The phenomenon is delineated in ab initio density-functional theory calculations of the electronic structure of a 4 nm diameter hexagonal zigzag-edged molecule C486H54 , chosen because it is a representative of larger ones. Using CC bond length as a surrogate measure, we map the polarization of valence electrons from the perimeter to the center. In a pattern that mimics the bonding, the polarization of the two outermost sets of edge bonds (transverse along rows and radial connecting nested rows of carbon atoms) is impressed on the graphene interior bonds with amplitude that decreases rapidly from the perimeter to the center. All bonds display a decaying oscillation with radial bonds longer than transverse bonds at the same location. This difference leads to a characteristic quinoidal pattern of CC bonds linking the zigzag hexagonal edges joined at each apex. The phenomenon and its analysis are applicable to geometries periodic or not, substituent modified edges and interior.

Philpott, Michael R.; Kawazoe, Yoshiyuki

2009-06-01

180

Barrier-free proton transfer in the valence anion of 2'-deoxyadenosine-5'-monophosphate. II. A computational study  

NASA Astrophysics Data System (ADS)

The propensity of four representative conformations of 2'-deoxyadenosine-5'-monophosphate (5'-dAMPH) to bind an excess electron has been studied at the B3LYP/6-31++G(d,p) level. While isolated canonical adenine does not support stable valence anions in the gas phase, all considered neutral conformations of 5'-dAMPH form adiabatically stable anions. The type of an anionic 5'-dAMPH state, i.e., the valence, dipole bound, or mixed (valence/dipole bound), depends on the internal hydrogen bond(s) pattern exhibited by a particular tautomer. The most stable anion results from an electron attachment to the neutral syn-south conformer. The formation of this anion is associated with a barrier-free proton transfer triggered by electron attachment and the internal rotation around the C4'-C5' bond. The adiabatic electron affinity of the a_south-syn anion is 1.19 eV, while its vertical detachment energy is 1.89 eV. Our results are compared with the photoelectron spectrum (PES) of 5'-dAMPH- measured recently by Stokes et al., [J. Chem. Phys. 128, 044314 (2008)]. The computational VDE obtained for the most stable anionic structure matches well with the experimental electron binding energy region of maximum intensity. A further understanding of DNA damage might require experimental and computational studies on the systems in which purine nucleotides are engaged in hydrogen bonding.

Koby?ecka, Monika; Gu, Jiande; Rak, Janusz; Leszczynski, Jerzy

2008-01-01

181

Barrier-free proton transfer in the valence anion of 2'-deoxyadenosine-5'-monophosphate. II. A computational study.  

PubMed

The propensity of four representative conformations of 2(')-deoxyadenosine-5(')-monophosphate (5(')-dAMPH) to bind an excess electron has been studied at the B3LYP6-31++G(d,p) level. While isolated canonical adenine does not support stable valence anions in the gas phase, all considered neutral conformations of 5(')-dAMPH form adiabatically stable anions. The type of an anionic 5(')-dAMPH state, i.e., the valence, dipole bound, or mixed (valence/dipole bound), depends on the internal hydrogen bond(s) pattern exhibited by a particular tautomer. The most stable anion results from an electron attachment to the neutral syn-south conformer. The formation of this anion is associated with a barrier-free proton transfer triggered by electron attachment and the internal rotation around the C4(')-C5(') bond. The adiabatic electron affinity of the a_south-syn anion is 1.19 eV, while its vertical detachment energy is 1.89 eV. Our results are compared with the photoelectron spectrum (PES) of 5(')-dAMPH(-) measured recently by Stokes et al., [J. Chem. Phys. 128, 044314 (2008)]. The computational VDE obtained for the most stable anionic structure matches well with the experimental electron binding energy region of maximum intensity. A further understanding of DNA damage might require experimental and computational studies on the systems in which purine nucleotides are engaged in hydrogen bonding. PMID:18247957

Koby?ecka, Monika; Gu, Jiande; Rak, Janusz; Leszczynski, Jerzy

2008-01-28

182

Evaluating the Nature of Chemical Bonds Based on Probabilistic Models  

NASA Astrophysics Data System (ADS)

A theoretical measure of the ionicity based on different mathematical concepts is presented in this research. Considering the distribution of valence electrons on each atom in a bond, we assume that the chemical properties of the atom can be expressed by means of probability. Using the introduced probability, different probabilistic models such as classical, fuzzy and information theoretical models have been employed to introduce new descriptors of bond ionicity. The ionicities were calculated for 12 heterodiatomic molecules and the bonds were classified in terms of covalency vs. ionicity. It was found that our proposed ionicity descriptors correlate well with the partial ionic character of the bonds.

Mohajeri, A.; Dasmeh, P.

183

Electron valence band of zirconium tetrafluoride  

NASA Astrophysics Data System (ADS)

The partial p- and d-electron densities of states (DOS's) in the valence band of ?-ZrF4 were experimentally profiled through recording its Zr MIV,V and Zr LII emission bands (spectra) by the x-ray spectrometer of an electron probe apparatus. Ab initio calculations were performed to determine the concentrations of individual F- and Zr-atom symmetry groups to the DOS and the number of states. The DOS maxima positions were found to correlate well with the measured peaks of the two bands.

Kemister, G.; Warmi?ski, T.

1996-02-01

184

Charge distribution and chemical bond in layered indium iodide single crystals (in Ukrainian)  

Microsoft Academic Search

Using the valence zone electron charge density data calculated with the wave functions of pseudopotential Hamiltonian, the chemical bond features are studied for the layered indium iodide single crystal. A mixed ionic--covalent type of the chemical bond is revealed and justified by the analysis performed on the basis of the concept of differential deformation density and the density Laplacian. The

M. I. Kolinko

1998-01-01

185

Synthesis and characterization of homo- and heterodinuclear M(II)-M'(III) (M(II) = Mn or Fe, M'(III) = Fe or Co) mixed-valence supramolecular pseudo-dimers. The effect of hydrogen bonding on spin state selection of M(II).  

PubMed

Reaction of H(3)L(1), the Schiff base condensate of tris(2-aminoethyl)amine with three equivalents of 5-methyl-1H-pyrazole-3-carboxaldehyde, with manganese(II)perchlorate or iron(II)tetrafluoroborate results in the isolation of [MH(3)L(1)]X(2) (M = Mn and X = ClO(4) and M = Fe and X = BF(4)). These complexes are high spin d(5) and d(6), respectively, as inferred from the long M-N bond distances obtained by single crystal X-ray diffraction for both and variable temperature magnetic susceptibility and Mössbauer spectroscopy for the iron complex. Aerobic treatment of a solution of [CoH(3)L(1)](2+) with three equivalents of potassium hydroxide produced [CoL(1)]. Homonuclear pseudo-dimers were prepared by the aerobic reaction of [FeH(3)L(1)](BF(4))(2) with 1.5 equivalents of potassium hydroxide to give {[FeH(1.5)L(1)](BF(4))}(2) or by the metathesis reaction of [FeH(2)L(1)][FeHL(1)](ClO(4))(2) with sodium hexafluorophosphate to give [FeH(3)L(1)][FeL(1)](PF(6))(2). The complexes were characterized by EA, IR, ESI-MS, variable temperature single crystal x-ray diffraction and Mössbauer spectroscopy. The iron(III) atom is low spin while the iron(II) atom is spin crossover. Heteronuclear pseudo-dimers were prepared by the 1:1 reaction of [FeH(3)L(1)](BF(4))(2) or [MnH(3)L(1)](ClO(4))(2) with [CoL(1)]. [MH(3)L(1)][CoL(1)](X)(2) (M = Fe and X = BF(4) or M = Mn and X = ClO(4)), were characterized by IR, EA, variable temperature single crystal X-ray diffraction and Mössbauer spectroscopy in the iron case. The data support a spin crossover and high spin assignment for the iron(II) and manganese(II), respectively. DFT calculations demonstrate that the spin state of the iron(II) atom in {[FeH(3)L(1)][FeL(1)]}(2+) changes from high spin to low spin as the iron(II)-iron(III) distance decreases. This is supported by experimental results and is a result of hydrogen bonding interactions which cause a significant compression of the M(II)-N(pyrazole) bond distances. PMID:21103467

Brewer, Cynthia T; Brewer, Greg; Butcher, Ray J; Carpenter, Everett E; Schmiedekamp, Ann M; Schmiedekamp, Carl; Straka, Alison; Viragh, Carol; Yuzefpolskiy, Yevgeniy; Zavalij, Peter

2010-11-19

186

Topology maps of bond descriptors based on the kinetic energy density and the essence of chemical bonding.  

PubMed

Analysis of the kinetic energy density within a molecule identifies patterns in its electronic structure that are intuitively linked to familiar concepts of chemical bonding. The function ?(r), termed localized-orbital locator and based on the positive-definite kinetic energy density ?+, is employed to characterize classes of covalent bonds in terms of its full topology of all critical points of rank three. Not only does ?(r) reveal patterns in chemical bonding, it also discloses features and the influence of extended electronic cores. Gradient paths define the extension of the valence space around an atomic centre; they separate various core level regions from bonding domains, and partition molecules in sensible bonded subunits. Location and ?(r)-values of critical points add a quantitative aspect to the bond characterization; profiles of unconventional chemical linkages such as charge-shift bonds emerge in a natural way. PMID:23450168

Jacobsen, Heiko

2013-04-14

187

Molecular tectonics: crystal engineering of mixed valence Fe(II)/Fe(III) solid solutions.  

PubMed

Based on isostructurality between crystals formed upon combining the dicationic tecton 2 with either M(3)Fe(III)(CN)(6) or M(4)Fe(II)(CN)(6) (M = Cs), a rare example of an H-bonded mixed valence Fe(ii)-Fe(iii) solid solution ((Cs(2)2(3)-[Fe(II)(CN)(6)](2))(0.83)(2(3)-[Fe(III)(CN)(6)](2))(0.17))) and curious necklace-like composite crystals were generated. PMID:20107633

Dechambenoit, Pierre; Ferlay, Sylvie; Kyritsakas, Nathalie; Hosseini, Mir Wais

2009-11-30

188

Valence ionization of L-proline amino acid: Experimental and theoretical study  

NASA Astrophysics Data System (ADS)

High resolution valence photoelectron spectrum of L-proline, up to 20 eV, was recorded using He-I radiation (21.218 eV) as ionization source in the gas phase. The thermal stability of the sample was checked by recording its mass spectrum at different temperatures to select the proper temperature for evaporating the sample without degradation. Symmetry adapted cluster/configuration interaction (SAC-CI) method based on the single and double excitation (SD-R) operators and natural bonding orbital (NBO) calculations were employed to calculate and assign the photoelectron bands of the four most stable conformers of gaseous L-proline, respectively.

Fathi, F.; Farrokhpour, H.

2013-04-01

189

Valence Isomerization of a 1,3-Diphosphacyclobutane-2,4-diyl: Photochemical Ring Closure to 2,4-diphosphabicyclo  

PubMed

The bond stretch isomer 1,3-diphosphacyclobutane-2,4-diyl 1 was transformed photochemically to give the previously unknown 2,4-diphosphabicyclo[1.1.0]butane 2, which itself can be converted thermally into gauche-1,4-diphosphabutadiene 3. The crystal structures of these three energy-rich valence isomers of 1,2-diphosphete have been determined. R=SiMe(3); Mes*=2,4,6-tBu(3)C(6)H(2). PMID:10540410

Niecke; Fuchs; Nieger

1999-10-18

190

Exploring Scaling Laws of Valence Neutron Distributions for Medium Nuclei  

Microsoft Academic Search

The root-mean-square radii of the valence neutron distributions for many nuclei in He-Mo mass range are calculated in the framework of the single-particle potential model. The scaling laws of valence neutron distributions are obtained by analyzing the relations between the radii and the binding energies of the valence neutrons. Based on these scaling laws, the necessary conditions for the occurrence

Yan-Qing Guo; Zhong-Zhou Ren

2010-01-01

191

Mulliken-Hush analysis of a bis(triarylamine) mixed-valence system with a N...N distance of 28.7 A.  

PubMed

An organic mixed valence compound with a spacer length of 25 unsaturated bonds separating two amine redox centres was synthesised and the electron transfer behaviour was investigated in the context of a Mulliken-Hush analysis in order to estimate the longest redox centre separation for which an intervalence charge transfer band can be observed. PMID:16832503

Heckmann, Alexander; Amthor, Stephan; Lambert, Christoph

2006-06-13

192

Influence of valence, electronegativity, atomic radii, and crest-trough interaction with phonons on the high-temperature copper oxide superconductors  

Microsoft Academic Search

Several structural features, including electron transfer between atoms of different electronegativity, oxygen deficiency, and unsynchronized resonance of valence bonds, as well as tight binding of atoms and the presence of both hypoelectronic and hyperelectronic elements, cooperatre to confer metallic properties and high-temperature superconductivity on compounds such as (Sr,Ba,Y,La)2CuO4-y. .AE

Linus Pauling

1987-01-01

193

Diffusion bonding  

DOEpatents

1. A method for joining beryllium to beryllium by diffusion bonding, comprising the steps of coating at least one surface portion of at least two beryllium pieces with nickel, positioning a coated surface portion in a contiguous relationship with an other surface portion, subjecting the contiguously disposed surface portions to an environment having an atmosphere at a pressure lower than ambient pressure, applying a force upon the beryllium pieces for causing the contiguous surface portions to abut against each other, heating the contiguous surface portions to a maximum temperature less than the melting temperature of the beryllium, substantially uniformly decreasing the applied force while increasing the temperature after attaining a temperature substantially above room temperature, and maintaining a portion of the applied force at a temperature corresponding to about maximum temperature for a duration sufficient to effect the diffusion bond between the contiguous surface portions.

Anderson, Robert C. (Oak Ridge, TN)

1976-06-22

194

First principles and valence force field study of III-V quaternary alloys  

NASA Astrophysics Data System (ADS)

We report on the elastic properties and formation energies of GaxIn1-xPyN1-y quaternary alloys using first principles and valence force field (VFF) calculations. The elastic constants of the binary compounds (GaP, InP, GaN, and InN) were calculated using the local density approximation (LDA). The resulting VFF parameters, ? (bond stretching) and ? (bond angle bending) were used within the Keating model to calculate the formation energies of GaInP, GaInN, InPN, and GaPN ordered structures. We found that the VFF formation energies of phosphide-nitride alloys (e.g. GaPN) were not in very good agreement with the LDA formation energies. Conventionally, the bond bending parameter ? for a ternary alloy is chosen as the arithmetic mean of the binary constituents. To improve the accuracy of the VFF model, we lifted such restriction on the ?-parameter and we also introduced the parameter ? (bond length-bond angle interaction). The VFF parameters ?, ?, and ? were fitted to the LDA-calculated formation energies of a large number of ternary ordered structures and were used to calculate the formation energy of the GaxIn1-xPyN1-y quaternary alloy.

Biswas, Koushik; Franceschetti, Alberto; Lany, Stephan

2008-03-01

195

Character Disposition and Behavior Type: Influences of Valence on Preschool Children's Social Judgments  

Microsoft Academic Search

The authors studied the influences of valence information on preschool children's (n = 47) moral (good or bad), liking (liked or disliked by a friend), and consequence-of-behavior (reward or punishment) judgments. The authors presented 8 scenarios describing the behavior valence, positive valence (help, share), negative valence (verbal insult, physical aggression), and disposition valence (nice or mean) of characters in social

Elaine F. Jones; Marvin Tobias; Danielle Pauley; Nicole Renick Thomson; Shawana Lewis Johnson

2009-01-01

196

Generalized Valence-Force-Field Model of (Ga,In)(N,P) Ternary Alloys  

SciTech Connect

We present a generalized valence-force-field (VFF) model for the ternary III-V alloys (III=Ga, In and V=N, P) to predict the formation energies and atomic structures of ordered and disordered alloy configurations. For each alloy (GaInN, GaInP, GaNP, and InNP) the VFF parameters, which include bond-angle/bond-length interactions, are fitted to the first-principles calculated formation energies of 30 ternary structures. Compared to standard approaches where the VFF parameters are transferred from the individual binary III-V compounds, our generalized VFF approach predicts alloy formation energies and atomic structures with considerably improved accuracy. Using this generalized approach and random realizations in large supercells (4096 atoms), we determine the temperature-composition phase diagram, i.e., the binodal and spinodal decomposition curves, of the (Ga, In) (N, P) ternary alloys.

Biswas, K.; Franceschetti, A.; Lany, S.

2008-01-01

197

Valence Effects in Reasoning About Evaluative Traits.  

PubMed

Reasoning about evaluative traits was investigated among a group of 7- and 8-year-olds (N = 34), a group of 11- to 13-year olds (N = 25), and a group of adults (N = 23) to determine whether their inferences would be sensitive to the valence of social and academic traits. Four aspects of trait-relevant beliefs were examined: (1) malleability, (2) stability over time, (3) origin in terms of nature versus nurture, and (4) an inference criterion that concerns how readily traits are inferred. Although there was evidence of an age-related decrease in the tendency to emphasize positive information, participants of all ages responded that positive traits are less malleable and more stable over time than negative traits, that the positive influences of biological and environmental factors are likely to override the negative influences, and that competence can be more readily inferred from positive outcomes than from negative outcomes. PMID:20953297

Heyman, Gail D; Giles, Jessica W

2004-01-01

198

Positive and Negative Valence within the Five-Factor Model  

Microsoft Academic Search

Tellegen and Walker (in press) have argued that highly evaluative adjectives provide significant information about personality and should not be excluded from trait taxonomic studies. Their analyses have identified two evaluative dimensions labeled Positive Valence (PV) and Negative Valence (NV). This study examines the meaning of these evaluative dimensions from the perspective of the five-factor model. Participants in the Baltimore

Robert R. McCrae

1995-01-01

199

Emotional valence and physical space: limits of interaction.  

PubMed

According to the body-specificity hypothesis, people associate positive things with the side of space that corresponds to their dominant hand and negative things with the side corresponding to their nondominant hand. Our aim was to find out whether this association holds also true for a response time study using linguistic stimuli, and whether such an association is activated automatically. Four experiments explored this association using positive and negative words. In Exp. 1, right-handers made a lexical judgment by pressing a left or right key. Attention was not explicitly drawn to the valence of the stimuli. No valence-by-side interaction emerged. In Exp. 2 and 3, right-handers and left-handers made a valence judgment by pressing a left or a right key. A valence-by-side interaction emerged: For positive words, responses were faster when participants responded with their dominant hand, whereas for negative words, responses were faster for the nondominant hand. Exp. 4 required a valence judgment without stating an explicit mapping of valence and side. No valence-by-side interaction emerged. The experiments provide evidence for an association between response side and valence, which, however, does not seem to be activated automatically but rather requires a task with an explicit response mapping to occur. PMID:21928929

de la Vega, Irmgard; de Filippis, Mónica; Lachmair, Martin; Dudschig, Carolin; Kaup, Barbara

2011-09-19

200

Relationship of Goal Level to Valence and Instrumentality  

Microsoft Academic Search

Eight experiments were conducted to explore the relationships between goal level, valence, and instrumentality. Valence, measured in terms of anticipated satisfaction across a range of performance levels, was strongly but negatively related to goal level. This finding was explained by showing that low goals entail using less stringent standards for self-evaluation than do high goals. Instrumentality was positively associated with

Anthony J. Mento; Edwin A. Locke; Howard J. Klein

1992-01-01

201

Ozone Model for Bonding of an O2 to Heme in Oxyhemoglobin  

Microsoft Academic Search

Several rather different models of the Fe-O2 bond in oxyhemoglobin have previously been proposed, none of which provide a satisfactory explanation of several properties. We propose a new model for the bonding of an O2 to the Fe of myoglobin and hemoglobin and report ab initio generalized valence bond and configuration interaction calculations on FeO2 that corroborate this model. Our

William A. Goddard; Barry D. Olafson

1975-01-01

202

Electronic Structures and Chemical Bonding of TiX2 (X=S, Se, and Te)  

Microsoft Academic Search

A systematic study of the electronic structures and chemical bonding of the titanium dichalcogenide TiX2 (X=S, Se, and Te) layered structures is performed by a first-principles molecular orbital calculation using the discrete-variational (DV)-Xalpha cluster method. The intra- and interlayer chemical bonding properties are also investigated using the bond overlap population. Valence band structures obtained by the calculation are in good

Yang-Soo Kim; Masataka Mizuno; Isao Tanaka; Hirohiko Adachi

1998-01-01

203

On role of the 3d atomic orbital in the chemical bonding of sulfur fluorides  

NASA Astrophysics Data System (ADS)

The electronic structure of SF2, SF4, SF6 and S2F2 was studied, using the DV-X[alpha] molecular orbital method. The chemical bonding of these sulfur fluorides was characterized using the Mulliken population analysis. We determined the 1s~3d as an appropriate basis set for sulfur atom. Near-linear correlations were found between the valence of sulfur and the 3d orbital population and between the valence of the sulfur atom and the effective charge. We confirm that the 3d orbital of sulfur should be taken as a valence orbital.

Tanaka, Kumiko; Sekine, Rika; Onoe, Jun; Nakamatsu, Hirohide

204

Charge Fluctuations and the Valence Transition in Yb under Pressure  

SciTech Connect

We present a dynamical mean field theory study of the valence transition (f{sup 14} {yields} f{sup 13}) in elemental, metallic Yb under pressure. Our calculations reproduce the observed valence transition as reflected in the volume dependence of the 4f occupation. The transition is accelerated by heating, and suggests quasiparticle or Kondo-like structure in the spectra of the trivalent end state, consistent with the early lanthanides. Results for the local charge fluctuations and susceptibility, however, show novel signatures uniquely associated with the valence transition itself, indicating that Yb is a fluctuating valence material in contrast to the intermediate valence behavior seen in the early trivalent lanthanides Ce, Pr, and Nd.

Ylvisaker, E R; Kunes, J; McMahan, A K; Pickett, W E

2009-04-21

205

Vection modulates emotional valence of autobiographical episodic memories.  

PubMed

We examined whether illusory self-motion perception ('vection') induced by viewing upward and downward grating motion stimuli can alter the emotional valence of recollected autobiographical episodic memories. We found that participants recollected positive episodes more often while perceiving upward vection. However, when we tested a small moving grating or a static grating that produced little or no vection, no modulation of emotional valence was observed. We propose that modulation of emotional valence by vection is caused by the mood congruency effect. To test this hypothesis, we examined whether vection direction affected participants' mood. Consequently, upward vection had a strongly positive effect on mood. The results indicate a close relationship between perceived self-motion direction and the emotional valence of recollected autobiographical episodic memories, and that the change in participant's mood with vection direction may underlie the modulation of the valence of recollected memories. PMID:23063264

Seno, Takeharu; Kawabe, Takahiro; Ito, Hiroyuki; Sunaga, Shoji

2012-10-11

206

Valence Band X-Ray Emission Spectra of Compressed Germanium  

SciTech Connect

We report measurements of the valence band width in compressed Ge determined from x-ray emission spectra below the Ge K edge. The width of the valence band does not show any pressure dependence in the semiconducting diamond-type structure of Ge below 10 GPa. On the other hand, in the metallic {beta}-Sn phase above 10 GPa the valence band width increases under compression. Density-functional calculations show an increasing valence band width under compression both in the semiconducting phase (contrary to experiment) and in the metallic {beta}-Sn phase of Ge (in agreement with observed pressure-induced broadening). The pressure-independent valence band width in the semiconducting phase of Ge appears to require theoretical advances beyond the density-functional theory or the GW approximation.

Struzhkin, Viktor V.; Mao Hokwang; Lin Jungfu; Hemley, Russell J. [Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington, DC 20015 (United States); Tse, John S.; Ma Yanming [Steacie Institute for Molecular Science, National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario, K1A 0R6 (Canada); Hu, Michael Y.; Chow, Paul [HPCAT, Carnegie Institution of Washington, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Kao Chichang [NSLS, Brookhaven National Laboratory, Upton, New York 11973 (United States)

2006-04-07

207

A phase I clinical study of VB4-845: weekly intratumoral administration of an anti-EpCAM recombinant fusion protein in patients with squamous cell carcinoma of the head and neck.  

PubMed

VB4-845 is a scFv-Pseudomonas exotoxin A fusion construct that targets epithelial cell adhesion molecule (EpCAM). A phase I trial was conducted to determine the maximum tolerated dose (MTD) of VB4-845 when administered as weekly intratumoral (IT) injections to patients with squamous cell carcinoma of the head and neck (SCCHN). Secondary objectives included the evaluation of the safety, tolerability, pharmacokinetic profile, and immunogenicity, and a preliminary assessment of tumor response. Twenty patients with advanced, recurrent SCCHN were treated weekly for four weeks in ascending dose cohorts of 100, 200, 330, 500, 700, and 930 microg. The MTD was established as 930 microg with a dose limiting toxicity of elevated liver enzymes in two of five patients. VB4-845 therapy was well tolerated with common treatment-related adverse events of injection site reactions, fever, gastrointestinal disorders, and elevated liver enzyme levels. All patients developed antibodies to VB4-845 by the end of the study, but only seven patients had neutralizing antibodies. Preliminary efficacy data found 87.5% of EpCAM-positive patients had a positive response to VB4-845 therapy. Noninjected dermal metastases were also resolved in one patient. VB4-845 IT therapy is safe and feasible and warrants further clinical evaluation for the treatment of SCCHN. PMID:19920898

MacDonald, Glen C; Rasamoelisolo, Michèle; Entwistle, Joycelyn; Cizeau, Jeannick; Bosc, Denis; Cuthbert, Wendy; Kowalski, Mark; Spearman, Maureen; Glover, Nick

2009-02-06

208

Valence-electron spectral change and charge transfer mechanism of CaSi 2 during CaSi 2?H 2O reaction  

NASA Astrophysics Data System (ADS)

The changes in the valence electron states of CaSi 2 during the chemical reaction with H 2O have been investigated by Auger valence electron spectroscopy (AVES). The drastic changes in the valence electron spectra of 3s and 3p states, which are caused by the oxidization of the Si atoms in CaSi 2, were observed in Si[2s, 2p, V] spectra for CaSi 2 after the reaction. In particular, the Si[2s, 2p, V] spectra of CaSi 2 samples reacted with H 2O at 60 or 80°C for 3 h were almost similar to that of SiO 2. The peak shift of Ca[2p, 3p, 3p] Auger transition toward the lower energy side has been observed, suggesting the formation of bonds between Ca 3p and O orbitals. New peaks due to Ca?O or Ca?OH bonds also appeared in the valence electron region of Ca[2p, 3p, V] Auger transition. The charge transfer and the chemical-bond formation can be well demonstrated by AVES during the CaSi 2?H 2O reaction.

Abe, S.; Nakayama, H.; Nishino, T.; Iida, S.

1997-04-01

209

Capturing and quantifying the dynamics of valenced emotions and valenced events of the organism-environment system.  

PubMed

The events we encounter and the emotions we experience are valenced-they are positively or negatively charged. Although these occurrences seem to be distributed irregularly throughout the day, the two experiments presented here reveal systematicity in the temporal dynamics of affective experience using a variety of time-series analyses. In Experiment 1, participants used a portable button to respond to event valence (the positive or negative charge of an event in the environment) or affective valence (one's positive or negative feeling at the time of responding). This methodology yields signed response durations, indexing the valence and intensity of an occurrence, and inter-response intervals, indexing their distribution. These measures revealed that valenced occurrences are correlated with both temporally proximal and remote occurrences. Experiment 2 validated the methodology employed in Experiment 1 using artificial, laboratory-created event structures. Implications of dynamical approaches to understanding emotion are discussed. PMID:22980452

Isenhower, Robert W; Frank, T D; Kay, Bruce A; Carello, Claudia

2012-10-01

210

The Valence of Titanium in Refractory Forsterite  

SciTech Connect

Models of melts in equilibrium with refractory forsterite (RF) suggest that RF contains trivalent Ti (Pack et al., 2005), with major implications for the origin of RF. We tested this prediction, measuring Ti valence by XANES in RF from Tagish Lake. One of the more intriguing components of unequilibrated chondrites is the population of relatively Ca-, Al-rich, Fe-poor isolated olivine grains known as 'refractory forsterite'. Some workers have concluded that these grains formed in and were released from chondrules. Other workers, noting that these grains occur in all major types of unequilibrated chondrites yet have many features in common, favor a single, pre-chondrule source from which the grains were distributed into their present hosts. Thought by some to be condensates, refractory forsterite (RF) grains have been found in chondrules, but their high CaO contents and trends of decreasing CaO contents from core to rim are inconsistent with closed-system fractional crystallization, so those grains must be relict. Previous workers calculated the compositions of melts parental to RF from the minor and trace element contents of RF grains and known olivine/liquid partition coefficients. Results indicated that melts in equilibrium with RF would have been uniformly enriched in refractory lithophile elements by {approx}20 x CI, as is observed in many refractory inclusions. Two exceptions are V, for which enrichments <20 x CI were derived, and Ti, for which enrichments of 50-65 x CI were obtained. For V, the depletion was attributed to its enhanced volatility under reducing conditions. The inferred Ti content is higher than observed in refractory inclusions. This rather unreasonable result was obtained using the olivine/liquid partition coefficient for Ti{sup 4+} (D{sub Ti{sup 4+}}). A higher D for Ti would allow lower Ti contents in parental melts, and noted that the larger ionic radius of Ti{sup 3+} relative to that of Ti{sup 4+} could yield a D{sub Ti{sup 3+}} that is a factor of {approx}50 greater than D{sub Ti{sup 4+}}. The presence of significant proportions of Ti{sup 3+} in RF would provide important evidence of reducing conditions where the grains formed, support the model of [8] and rule out formation in typical, FeO-bearing chondrules. To test the prediction of [8], we have used X-ray absorption near-edge structure (XANES) analysis to determine the valence of Ti in two RF grains from the Tagish Lake carbonaceous chondrite.

Simon, S.B.; Sutton, S.; Newville, M.; Grossman, L. (UofC)

2007-03-06

211

Basics of Fidelity Bonding.  

ERIC Educational Resources Information Center

|Fidelity bonds are important for an agency to hold to protect itself against any financial loss that can result from dishonest acts by its employees. Three types of fidelity bonds are available to an agency: (1) public official bonds; (2) dishonesty bonds; and (3) faithful performance bonds. Public official bonds are required by state law to be…

Kahn, Steven P.

212

Evaluative Conditioning Induces Changes in Sound Valence  

PubMed Central

Through evaluative conditioning (EC) a stimulus can acquire an affective value by pairing it with another affective stimulus. While many sounds we encounter daily have acquired an affective value over life, EC has hardly been tested in the auditory domain. To get a more complete understanding of affective processing in auditory domain we examined EC of sound. In Experiment 1 we investigated whether the affective evaluation of short environmental sounds can be changed using affective words as unconditioned stimuli (US). Congruency effects on an affective priming task for conditioned sounds demonstrated successful EC. Subjective ratings for sounds paired with negative words changed accordingly. In Experiment 2 we investigated whether extinction occurs, i.e., whether the acquired valence remains stable after repeated presentation of the conditioned sound without the US. The acquired affective value remained present, albeit weaker, even after 40 extinction trials. These results provide clear evidence for EC effects in the auditory domain. We will argue that both associative as well as propositional processes are likely to underlie these effects.

Bolders, Anna C.; Band, Guido P. H.; Stallen, Pieter Jan

2012-01-01

213

Valence band anticrossing in GaBixAs1-x  

SciTech Connect

The optical properties of GaBixAs1-x (0.04< x< 0.08) grown by molecular beam epitaxy have been studied by photomodulated reflectance spectroscopy. The alloys exhibit a strong reduction in the bandgap as well as an increase in the spin-orbit splitting energy with increasing Bi concentration. These observations are explained by a valence band anticrossing model, which shows that a restructuring of the valence band occurs as the result of an anticrossing interaction between the extended states of the GaAs valence band and the resonant T2 states of the Bi atoms.

Alberi, K.; Dubon, O. D.; Walukiewicz, W.; Yu, K. M.; Bertulis, K.; Krotkus, A.

2007-07-11

214

Pressure-Induced Valence Change and Hydrogen Disorder in Fe(OH)2  

NASA Astrophysics Data System (ADS)

Vibrational and Mössbauer spectroscopy reveal that pressure causes the hydrogen lattice of brucite-structured Fe(OH)2 to become disordered above 10 GPa, leading to self-oxidation of Fe2+----P---->Fe3++e^{-}. This result documents one mechanism by which water (hydrogen) dissolved in the Earth's mantle can induce changes in valence and chemical bonding at depth, regardless of buffering by other mineral phases. Infrared absorption (IR) and Raman (R) spectroscopy at 7-21 GPa and 293 K show that the A_{2u} (IR) and A_{1g} (R) OH-stretching modes decrease with pressure (-1.3 \\pm 0.1 cm^{-1}/GPa and -4.9 \\pm 0.2 cm^{-1}/GPa, respectively) in a manner expected for hydrogen-bonded systems. Both modes show non-linear broadening, with a \\sim 4-fold increase in width over the experimental pressure range. This is interpreted as a signature of the hydrogen-ion positions becoming disordered, as previously proposed for the isostructural Mg(OH)_{2}, Ca(OH)_{2} and Co(OH)_{2}, and attributed to the effects of H - H Coulombic repulsion caused by compression along the c- crystallographic axis. In the case of Fe(OH)_{2}$, Mössbauer spectroscopy reveals the internal (self-) oxidation of the Fe site at starting at similar pressures as the hydrogen disordering. Displacement (and disordering) of H alters the Coulomb potential at the iron site, thus furnishing the driving force for delocalization of the weakly bonded 3d electron of Fe. Once the electron is lost from Fe, the site remains oxidized on decompression apparently because of the affinity of iron for the 3+ oxidation state. Thus, the hydrogen disordering is observed to be reversible upon decompression, whereas the self-oxidation is not. Such changes in valence can strongly affect the phase stability, minor- and trace-element partitioning, and transport properties of ''water''-bearing minerals in the Earth's mantle.

Speziale, S.; Milner, A.; Pasternak, M. P.; Zaug, J. M.; Jeanloz, R.

2004-12-01

215

Use of valence band Auger electron spectroscopy to study thin film growth: oxide and diamond-like carbon films  

NASA Astrophysics Data System (ADS)

It is demonstrated how Auger line shape analysis with factor analysis (FA), least-squares fitting and even simple peak height measurements may provide detailed information about the composition, different chemical states and also defect concentration or crystal order. Advantage is taken of the capability of Auger electron spectroscopy to give valence band structure information with high surface sensitivity and the special aspect of FA to identify and discriminate quantitatively unknown chemical species. Valence band spectra obtained from Ni, Fe, Cr and NiFe40Cr20 during oxygen exposure at room temperature reveal the oxidation process in the initial stage of the thin layer formation. Furthermore, the carbon chemical states that were formed during low energy C(+) and Ne(+) ion irradiation of graphite are delineated and the evolution of an amorphous network with sp3 bonds is disclosed. The analysis represents a unique method to quantify the fraction of sp3-hybridized carbon in diamond-like materials.

Steffen, H. J.

1994-12-01

216

Differential impact of beliefs on valence and arousal  

PubMed Central

Many cognitive accounts of emotional processing assume that emotions have representational content that can be influenced by beliefs and desires. It is generally thought that emotions also have non-cognitive, affective components, including valence and arousal. To clarify the impact of cognition on these affective components we asked participants to rate sentences along cognitive and affective dimensions. For the former case, participants rated the believability of the material. For the latter case, they provided valence and arousal ratings. Across two experiments, we show that valence and arousal are differently influenced by beliefs, suggesting that these two largely independent affective components of emotion differ in their cognitive penetrability. While both components depended upon overall comprehension of sentence meaning, only valence was influenced by the consistency of the sentences with participants’ beliefs (i.e., whether it was believable or unbelievable). We discuss the implications of these findings for understanding cognition-emotion relationships.

Nicolle, Antoinette; Goel, Vinod

2012-01-01

217

Relaxation and Cross Section Effects in Valence Band Photoemission Spectroscopy.  

National Technical Information Service (NTIS)

Various problems relating to the interpretation of valence band x-ray photoemission (XPS) spectra of solids are discussed. The experiments and calculations reported herein deal with the following questions: (1) To what extent do many-body effects manifest...

F. R. McFeely

1976-01-01

218

Are bonds bent. To what extent do bond orbitals follow nuclear motions  

SciTech Connect

In order to make definitive statements about bent bonds and orbital following accurate ab initio self-consistent valence bond orbitals have been obtained for CH/sub 4/, NH/sub 3/, H/sub 2/O, and H/sub 2/S as a function of nuclear geometry. The directions of the orbitals are uniquely determined by the energy minimization criterion. It is found that the bonding orbitals on the central atoms are normally bent a small amount at equilibrium unless constrained to be otherwise by symmetry. More striking is the fact that in almost all cases these orbitals remain nearly stationary as the nuclei undergo bending motions about equilibrium. At the same time there are changes in hybridization which occur in a direction in accord with chemical intuition. Localized molecular orbital calculations were also carried out for comparison purposes. They lead to the same qualitative conclusion that, in general, orbital stasis is a much better approximation than complete orbital following.

Chipman, D.M. (Univ. of Notre Dame, IN); Palke, W.E.; Kirtman, B.

1980-05-07

219

Mixed-valence compound-based biosensor.  

PubMed

A cobalt(II)hexacyanoferrate-based biosensor has been prepared simply by codeposition of an enzyme, together with the electrochemical formation of a cobalt (II)hexacyanoferrate compound electrochemically. The compound can be generated at a constant potential of -0.05 V (vs. Ag/AgCl). This compound possesses the catalytic property of reducing hydrogen peroxide to water at the operating potential of 0.0 V vs. Ag/AgCl. The mixed-valence compound-based biosensor possesses an unique interference-independent feature, which is important for biomedical application; this feature is attributed to the low overvoltage characteristic of cobalt (II)hexacyanoferrate. The electrochemical glucose biosensor responds to a series of glucose injections with linearity up to 5 mM (with correlation coefficient R = 0.9999) and the sensitivity of the linear portion is 733 nA/(cm2 x mM). The detection limit is 2 x 10(-6)M (S/N = 3). Both the potential-dependent electron transfer rate constant and the apparent Michaelis-Menten constant were studied in rotating disk experiments. The apparent Michaelis-Menten constant, Km' calculated from the slope of the "Lineweaver-Burke" type reciprocal plot is 28 mM. A fast-response characteristic is observed in the rotating disk experiment and the 95% response time is 14.5 sec. No response was observed from the addition of either 2 x 10(-4)M galactose, acetaminophen, ascorbic acid, uric acid, cysteine, tyrosine, dopamine, or 1,4-dihydroxyquinone in the absence and/or in the presence of 5 x 10(-4)M glucose. PMID:10099513

Lin, M S; Wu, Y C; Jan, B I

1999-01-01

220

Mn 3s exchange splitting in mixed-valence manganites.  

SciTech Connect

We present Mn 3s x-ray photoelectron spectra of manganese oxides with the Mn formal valency from 2+ to 4+. We found that the Sr{sup 2+} doping or cation deficiency in manganites do not change the Mn 3s splitting in manganites with the Mn formal valency from 3.0+ to 3.3+. We suggest that doping holes are localized in O 2p states.

Galakhov, V. R.; Demeter, M.; Bartkowski, S.; Neumann, M.; Ovechkina, N. A.; Kurmaev, E. Z.; Lobachevskaya, N. I.; Mukovskii, Ya. M.; Mitchell, J.; Ederer, D. L.; Russian Academy of Sciences; Univ. of Osnabruck; Moscow State Steel and Alloys Inst.; Tulane Univ.

2002-03-15

221

Valence orbital momentum distributions in s-triazine  

Microsoft Academic Search

Valence orbital momentum distributions, rho(q), are obtained for s-triazine, CâHâNâ, from (e,2e) spectroscopy and split valence SCFMO calculations. The separation energy spectrum simulated using the calculated rho(q) and ionization energies from Green's function calculations is in good agreement with experiment from 9--20 eV, but at higher energy the simulated spectrum has higher intensity than experiment, indicating that the Green's function

S. Hiser; D. J. Chornay; M. A. Coplan; J. H. Moore; J. A. Tossell

1985-01-01

222

Valence orbital momentum distributions in s-triazine  

Microsoft Academic Search

Valence orbital momentum distributions, &rgr;(q), are obtained for s-triazine, C3H3N3, from (e,2e) spectroscopy and split valence SCFMO calculations. The separation energy spectrum simulated using the calculated &rgr;(q) and ionization energies from Green’s function calculations is in good agreement with experiment from 9–20 eV, but at higher energy the simulated spectrum has higher intensity than experiment, indicating that the Green’s function

S. Hiser; D. J. Chornay; M. A. Coplan; J. H. Moore; J. A. Tossell

1985-01-01

223

Spectroscopic valence of cerium in cerium-lanthanum-iron compounds  

Microsoft Academic Search

In Ce2Fe14B and Ce2Fe17, cerium is mixed valent and nonmagnetic. Any structural or compositional modification of these intermetallics which induces cerium to become trivalent and develop a local 4f moment should result in compounds with enhanced magnetostrictions, magnetocrystalline anisotropies, and net magnetic moments. Due to the dependence of cerium valence on steric volume, one approach for manipulating the valence is

T. W. Capehart; R. K. Mishra; C. D. Fuerst; G. P. Meisner; F. E. Pinkerton; J. F. Herbst

1997-01-01

224

Spectroscopic valence of cerium in cerium-lanthanum-iron compounds  

Microsoft Academic Search

In CeâFeââB and CeâFeââ, cerium is mixed valent and nonmagnetic. Any structural or compositional modification of these intermetallics which induces cerium to become trivalent and develop a local 4f moment should result in compounds with enhanced magnetostrictions, magnetocrystalline anisotropies, and net magnetic moments. Due to the dependence of cerium valence on steric volume, one approach for manipulating the valence is

T. W. Capehart; R. K. Mishra; C. D. Fuerst; G. P. Meisner; F. E. Pinkerton; J. F. Herbst

1997-01-01

225

Bonded Interactions and the Crystal Chemistry of Minerals: A Review  

SciTech Connect

Connections established during the 20th century between bond length, radii, bond strength, bond valence and crystal and molecular chemistry are briefly reviewed followed with a survey of the physical properties of the electron density distributions for a variety of minerals and representative molecules, recently generated with first-principles local density based quantum mechanical methods. The structures for several minerals, geometry-optimized at ambient conditions and at a variety of pressures, match those determined experimentally within several percent. The structures and the physical properties of model experimental electron density distributions determined with high resolution and high energy synchrotron single crystal X-ray diffraction data also closely match those calculated with first principles methods. As the electron density is progressively accumulated and locally concentrated between pairs of bonded atoms, the nuclei are progressively shielded and the bond lengths and the bonded radii of the atoms decrease. Concomitant with the decrease in bond length, the local kinetic density energy increases while the potential energy and the electronic energy densities both decrease for intermediate and shared interactions with the potential energy dominating the local energy for the shorter bonded interactions. The shorter the bonds, the more negative the local electronic energy density, the greater the stabilization and the greater the shared character of the bonded interactions.

Gibbs, Gerald V.; Downs, R. T.; Cox, David F.; Ross, Nancy L.; Prewitt, C. T.; Rosso, Kevin M.; Lippmann, Thomas; Kirfel, Armin

2008-02-26

226

Emotional Valence and the Free-Energy Principle  

PubMed Central

The free-energy principle has recently been proposed as a unified Bayesian account of perception, learning and action. Despite the inextricable link between emotion and cognition, emotion has not yet been formulated under this framework. A core concept that permeates many perspectives on emotion is valence, which broadly refers to the positive and negative character of emotion or some of its aspects. In the present paper, we propose a definition of emotional valence in terms of the negative rate of change of free-energy over time. If the second time-derivative of free-energy is taken into account, the dynamics of basic forms of emotion such as happiness, unhappiness, hope, fear, disappointment and relief can be explained. In this formulation, an important function of emotional valence turns out to regulate the learning rate of the causes of sensory inputs. When sensations increasingly violate the agent's expectations, valence is negative and increases the learning rate. Conversely, when sensations increasingly fulfil the agent's expectations, valence is positive and decreases the learning rate. This dynamic interaction between emotional valence and learning rate highlights the crucial role played by emotions in biological agents' adaptation to unexpected changes in their world.

Joffily, Mateus; Coricelli, Giorgio

2013-01-01

227

Emotional valence and the free-energy principle.  

PubMed

The free-energy principle has recently been proposed as a unified Bayesian account of perception, learning and action. Despite the inextricable link between emotion and cognition, emotion has not yet been formulated under this framework. A core concept that permeates many perspectives on emotion is valence, which broadly refers to the positive and negative character of emotion or some of its aspects. In the present paper, we propose a definition of emotional valence in terms of the negative rate of change of free-energy over time. If the second time-derivative of free-energy is taken into account, the dynamics of basic forms of emotion such as happiness, unhappiness, hope, fear, disappointment and relief can be explained. In this formulation, an important function of emotional valence turns out to regulate the learning rate of the causes of sensory inputs. When sensations increasingly violate the agent's expectations, valence is negative and increases the learning rate. Conversely, when sensations increasingly fulfil the agent's expectations, valence is positive and decreases the learning rate. This dynamic interaction between emotional valence and learning rate highlights the crucial role played by emotions in biological agents' adaptation to unexpected changes in their world. PMID:23785269

Joffily, Mateus; Coricelli, Giorgio

2013-06-13

228

Semiconductor wafer bonding  

Microsoft Academic Search

When mirror-polished, flat, and clean wafers are brought into contact, they are locally attracted to each other and adhere or bond. This phenomenon is known as semiconductor wafer bonding. Different adhesion forces (van der Waals forces, hydrogen bonding) are the reason for the bonding effect at room temperature. The different bonding mechanisms acting in dependence on the surface conditions (hydrophilic,

M. Reiche

2006-01-01

229

Unbinding force of chemical bonds and tensile strength in strong crystals  

NASA Astrophysics Data System (ADS)

A model of covalent and ionic bond strength is proposed in terms of the tensile unbinding force by introducing the concept of the effectively bonded valence electron (EBVE) number of a chemical bond. Bond strength proves to be exclusively dependent on two microscopic parameters: bond length and EBVE number. This model allows us to determine bond strength for a variety of crystals and accounts for the observation that a low-coordination number of binding atoms has a tendency to higher bond strength. For crystals of simple structures, we propose linking bond strength to the theoretical tensile strength of a crystal; the latter reproduces the results of first-principles calculations. The model also allows for the assessment of the theoretical tensile strength of graphene and single-walled nanotubes constructed with typical material systems.

Guo, Xiaoju; Wang, Li-Min; Xu, Bo; Liu, Zhongyuan; Yu, Dongli; He, Julong; Wang, Hui-Tian; Tian, Yongjun

2009-12-01

230

Valence-Bond Crystal in a Pyrochlore Antiferromagnet with Orbital Degeneracy  

NASA Astrophysics Data System (ADS)

We discuss the ground state of a pyrochlore lattice of threefold orbitally degenerate S=1/2 magnetic ions. We derive an effective spin-orbital Hamiltonian and show that the orbital degrees of freedom can modulate the spin exchange, removing the infinite spin-degeneracy characteristic of pyrochlore structures. The resulting state is a collection of spin-singlet dimers, with a residual degeneracy due to their relative orientation. This latter is lifted by a magnetoelastic interaction, induced in the spin-singlet phase space, that forces a tetragonal distortion. Such a theory provides an explanation for the helical spin-singlet pattern observed in the B spinel MgTi2O4.

di Matteo, S.; Jackeli, G.; Lacroix, C.; Perkins, N. B.

2004-08-01

231

Valence-bond crystal in a pyrochlore antiferromagnet with orbital degeneracy.  

PubMed

We discuss the ground state of a pyrochlore lattice of threefold orbitally degenerate S=1/2 magnetic ions. We derive an effective spin-orbital Hamiltonian and show that the orbital degrees of freedom can modulate the spin exchange, removing the infinite spin-degeneracy characteristic of pyrochlore structures. The resulting state is a collection of spin-singlet dimers, with a residual degeneracy due to their relative orientation. This latter is lifted by a magnetoelastic interaction, induced in the spin-singlet phase space, that forces a tetragonal distortion. Such a theory provides an explanation for the helical spin-singlet pattern observed in the B spinel MgTi2O4. PMID:15324275

Di Matteo, S; Jackeli, G; Lacroix, C; Perkins, N B

2004-08-13

232

LETTER TO THE EDITOR: Bond-valence analysis on the structural effects in magnetoresistive manganese perovskites  

Microsoft Academic Search

For the 0953-8984\\/10\\/48\\/001\\/img6 perovskites that show colossal-magnetoresistance (CMR) behaviour, we use the global instability index, R1, as a measure of the influence of the static lattice effects on the magnetic and electrical properties. These effects arise from the size mismatch between the ions at A and Mn sites as well as the size distribution of ions at A sites. A

G. H. Rao; K. Bärner; I. D. Brown

1998-01-01

233

2D multipartite valence bond states in quantum anti-ferromagnets  

SciTech Connect

A quantum anti-ferromagnetic spin-1 model is characterised on a 2D lattice with the following requirements: (i) The Hamiltonian is made out of nearest neighbour interactions. (ii) It is homogeneous, translational and rotational invariant. (iii) The ground state is a real singlet state of SU(2) (non-chiral). (iv) It has a local spin-1 representation. Along the way to characterise the system, connections with classical statistical mechanics and integrable models are explored. Finally, the relevance of the model in the physics of low dimensional anti-ferromagnetic Mott-Hubbard insulators is discussed.

Rico, E. [Institut fuer Theoretische Physik, Universitat Innsbruck, Technikerstrasse 25, A-6020 Innsbruck (Austria); Institute of Quantum Optics and Quantum Information of the Austrian Academy of Science, A-6020 Innsbruck (Austria); Fakultat fuer Physik, Universitat Wien, Boltzmanngasse 5, A-1090 Wien (Austria)], E-mail: enrique.ortega@univie.ac.at; Briegel, H.J. [Institut fuer Theoretische Physik, Universitat Innsbruck, Technikerstrasse 25, A-6020 Innsbruck (Austria); Institute of Quantum Optics and Quantum Information of the Austrian Academy of Science, A-6020 Innsbruck (Austria)

2008-09-15

234

Phase behavior and critical activated dynamics of limited-valence DNA nanostars.  

PubMed

Colloidal particles with directional interactions are key in the realization of new colloidal materials with possibly unconventional phase behaviors. Here we exploit DNA self-assembly to produce bulk quantities of "DNA stars" with three or four sticky terminals, mimicking molecules with controlled limited valence. Solutions of such molecules exhibit a consolution curve with an upper critical point, whose temperature and concentration decrease with the valence. Upon approaching the critical point from high temperature, the intensity of the scattered light diverges with a power law, whereas the intensity time autocorrelation functions show a surprising two-step relaxation, somehow reminiscent of glassy materials. The slow relaxation time exhibits an Arrhenius behavior with no signs of criticality, demonstrating a unique scenario where the critical slowing down of the concentration fluctuations is subordinate to the large lifetime of the DNA bonds, with relevant analogies to critical dynamics in polymer solutions. The combination of equilibrium and dynamic behavior of DNA nanostars demonstrates the potential of DNA molecules in diversifying the pathways toward collective properties and self-assembled materials, beyond the range of phenomena accessible with ordinary molecular fluids. PMID:24019470

Biffi, Silvia; Cerbino, Roberto; Bomboi, Francesca; Paraboschi, Elvezia Maria; Asselta, Rosanna; Sciortino, Francesco; Bellini, Tommaso

2013-09-09

235

What Determines Bond Costs. Municipal Bonds Series.  

ERIC Educational Resources Information Center

|Public officials in small towns who participate infrequently in the bond market need information about bond financing. This publication, one in a series of booklets published by the Western Rural Development Center using research gathered between 1967-77, discusses factors influencing the marketability and cost of bond financing for towns and…

Young, Douglas; And Others

236

Chemical Bonding Technology.  

National Technical Information Service (NTIS)

Primers employed in bonding together the various material interfaces in a photovoltaic module are being developed. The approach develops interfacial adhesion by generating actual chemical bonds between the various materials bonded together. The current st...

E. Plueddemann

1986-01-01

237

Evidence for valence hole localization in the Auger decay and fragmentation of carbon and silicon tetrafluorides  

SciTech Connect

Monochromatic synchrotron radiation was used to excite selectively core electrons of the carbon and fluorine atoms in carbon tetrafluoride and silicon and fluorine in silicon tetrafluoride. The fragmentation processes were examined using time-of-flight mass spectroscopy. The mass spectra show the distribution of ions collected in coincidence with low and high energy electrons. Distinct changes in the mass spectra with atomic site of excitation and photon energy are observed. The observation of F/sup 2 +/ ions following fluorine 1s excitation in SiF/sub 4/ provides significant evidence for a ''valence bond depopulation'' mechanism involving the formation of a localized, two-hole final state that persists on the time scale of fragmentation. In contrast, no F/sup 2 +/ was observed for CF/sub 4/, which indicates that fragmentation for this molecule is more characteristic of a delocalized two-hole state.

Lapiano-Smith, D.A.; Ma, C.I.; Wu, K.T.; Hanson, D.M.

1989-02-15

238

?-Si3N4(0001)/Si(111) interface: Phosphorus defects, valence band offsets, and their role of passivating the interface states  

NASA Astrophysics Data System (ADS)

This work investigates the ?-Si3N4(0001)/Si(111) interface based on a model with fully saturated interface bonds. The charge transfer at the interface and band alignment are calculated. The band alignment is corrected by GW0 calculations. Furthermore, we investigate how substitutional phosphorus defects affect the electronic structure of the interface, in particular how they saturate the interface states and modify the valence band offsets.

Flage–Larsen, E.; Løvvik, O. M.; Fang, C. M.; Kresse, G.

2013-10-01

239

A comparative study of Hamilton and overlap population methods for the analysis of chemical bonding  

Microsoft Academic Search

The utility of Hamilton population analysis-a partitioning of the electronic energy of a molecule-is investigated within a one-electron molecular orbital framework of the extended Hückel type. The classical Mulliken overlap population description of the valence electron density in terms of one- and two-center ``atom'' and ``bond'' contributions, respectively, provides the starting point for the development of an atom-bond energy partitioning

Wingfield V. Glassey; Roald Hoffmann

2000-01-01

240

The unique bonding characteristics of beryllium and the Group IIA metals  

Microsoft Academic Search

Having closed valence sub-shells, the alkaline earth atoms participate in covalent bonding via orbital hybridization and exchange interactions, with additional contributions from dispersion interactions. Starting from a closed ns2 configuration imparts different characteristics to the chemistry of this group, as compared to metals that have open-shell atomic ground states. Theoretical studies of the bonding of the Group IIA metals have

Michael C. Heaven; Vladimir E. Bondybey; Jeremy M. Merritt; Alexey L. Kaledin

2011-01-01

241

Relativistic effects on the electronic structure and chemical bonding of UF6  

Microsoft Academic Search

We have studied the relativistic effects in the electronic structure and chemical bonding for the ground state of UF6, using the relativistic and nonrelativistic discrete-variational X? molecular orbital calculations. It is found that two relativistic effects appear in the valence levels; the energy level splitting and upward shift of energies of the molecular orbitals. From the Mulliken population analysis of

Jun Onoe; Kazuo Takeuchi; Hirohide Nakamatsu; Takeshi Mukoyama; Rika Sekine; Bong-Il Kim; Hirohiko Adachi

1993-01-01

242

Recognizing the emotional valence of names: an ERP study.  

PubMed

Unlike common nouns, person names refer to unique entities and generally have a referring function. We used event-related potentials to investigate the time course of identifying the emotional meaning of nouns and names. The emotional valence of names and nouns were manipulated separately. The results show early N1 effects in response to emotional valence only for nouns. This might reflect automatic attention directed towards emotional stimuli. The absence of such an effect for names supports the notion that the emotional meaning carried by names is accessed after word recognition and person identification. In addition, both names with negative valence and emotional nouns elicited late positive effects, which have been associated with evaluation of emotional significance. This positive effect started earlier for nouns than for names, but with similar durations. Our results suggest that distinct neural systems are involved in the retrieval of names' and nouns' emotional meaning. PMID:23467262

Wang, Lin; Zhu, Zude; Bastiaansen, Marcel; Hagoort, Peter; Yang, Yufang

2013-03-05

243

Nondipole effects in molecular nitrogen valence shell photoionization.  

SciTech Connect

Nondipole photoelectron parameters {zeta} have been obtained experimentally for the outer-valence 3{sigma}{sub g}, 1{pi}{sub {mu}} and 2{sigma}{sub {mu}} shells in molecular nitrogen from threshold to {approx} 200 eV photon energy. Significant nondipole effects are observed even in the immediate threshold regions of these valence-shell distributions. The results of preliminary calculations for the 3{sigma}{sub g} and 2{sigma}{sub {mu}} clarify the origins of the observed features in terms of contributing molecular symmetry channels. Theory and experiment are in excellent accord, suggesting that the large nondipole effects previously observed in atoms and the K-shells of molecules can also appear at low photon energies in the outer-valence shells of molecules.

Hemmers, O.; Guillemin, R.; Rolles, D.; Wolska, A.; Lindle, D. W.; Kanter, E. P.; Kraessig, B.; Southworth, S. H.; Wehlitz, R.; Zimmermann, B.; McKoy, V.; Langhoff, P. W.; Chemistry; Univ. of Nevada; LBNL; Univ. of Wisconsin; Max Planck Inst. for the Physics of Complex Systems; California Inst. of Tech.; Univ. of California

2005-01-01

244

Valence states of Sm in SmRuSn3  

NASA Astrophysics Data System (ADS)

To obtain a better insight into the nature of valence states of Sm ionsinSmRuSn3 and to verify the differing conclusions reached by T. Fukuhara, I. Sakamoto, and H. Sato [J. Phys. Condens. Matter 3, 8917 (1991)] and C. Godart et al. [Phys. Rev. B 48, 16 402 (1993)], we have systematically analyzed the magnetic-susceptibility data by considering the effects of crystalline electric field, exchange interaction, and valence fluctuation. In this compound, Sm ions occupy two different sites, 6d and 2a, in the ratio of 3:1. Our analysis shows that Sm ions at the 6d site are in a trivalent state and those at the 2a sites are in a valence fluctuating state. This supports the claim made by C. Godart et al. [Phys. Rev. B 48, 16 402 (1993)].

Chinchure, Aravind D.; Mazumdar, Chandan; Marathe, V. R.; Nagarajan, R.; Gupta, L. C.; Shah, S. S.

1994-07-01

245

Weak morphology dependent valence band structure of boron nitride  

NASA Astrophysics Data System (ADS)

We report a hard X-ray photoelectron spectroscopy (HX-PES) investigation on valence band structure of Boron Nitrides (BN) having different morphologies, including nanosheets, nanotubes, and micro-sized particles. Very weak morphology/valence band structure dependence was observed. For each case, the B-N ?-band overlapping with ?-band between 0 to -12.5 eV and the s-band below -15 eV were identified. No obvious morphology-induced band shifts and intensity variations were observed. First-principles calculations based on density functional theory were performed and the results were compared with the experimental data. This theoretical analysis well explains the weak morphology dependent valence band spectra of BN nanomaterials obtained during HX-PES measurements.

Zhi, Chunyi; Ueda, Shigenori; Zeng, Haibo; Wang, Xuebin; Tian, Wei; Wang, Xi; Bando, Yoshio; Golberg, Dmitri

2013-08-01

246

Emotional valence and arousal effects on memory and hemispheric asymmetries.  

PubMed

This study examined predictions based upon the right hemisphere (RH) model, the valence-arousal model, and a recently proposed integrated model (Killgore & Yurgelun-Todd, 2007) of emotion processing by testing immediate recall and recognition memory for positive, negative, and neutral verbal stimuli among 35 right-handed women. Building upon methodologies of previous studies, we found that words presented to the right visual field/left hemisphere (RVF/LH) were recalled and recognized more accurately than words presented to the left visual field/right hemisphere (LVF/RH), and we found significant valence by visual field interactions. Some findings were consistent with one of the models evaluated whereas others were consistent with none of the models evaluated. Our findings suggest that an integration of the RH and valence-arousal models may best account for the findings with regard to hemispheric lateralization of memory for emotional stimuli. PMID:20579798

Mneimne, Malek; Powers, Alice S; Walton, Kate E; Kosson, David S; Fonda, Samantha; Simonetti, Jessica

2010-07-01

247

Bond Paths Are Not Chemical Bonds  

NASA Astrophysics Data System (ADS)

This account takes to task papers that criticize the definition of a bond path as a criterion for the bonding between the atoms it links by mistakenly identifying it with a chemical bond. It is argued that the notion of a chemical bond is too restrictive to account for the physics underlying the broad spectrum of interactions between atoms and molecules that determine the properties of matter. A bond path on the other hand, as well as being accessible to experimental verification and subject to the theorems of quantum mechanics, is applicable to any and all of the interactions that account for the properties of matter. It is shown that one may define a bond path operator as a Dirac observable, making the bond path the measurable expectation value of a quantum mechanical operator. Particular attention is given to van der Waals interactions that traditionally are assumed to represent attractive interactions that are distinct from chemical bonding. They are assumed by some to act in concert with Pauli repulsions to account for the existence of condensed states of molecules. It is such dichotomies of interpretation that are resolved by the experimental detection of bond paths and the delineation of their properties in molecular crystals. Specific criticisms of the stabilization afforded by the presence of bond paths derived from spectroscopic measurements performed on dideuteriophenanthrene are shown to be physically unsound. The concept of a bond path as a "bridge of density" linking bonded atoms was introduced by London in 1928 following the definition of the electron density by Schrödinger in 1926. These papers marked the beginning of the theory of atoms in molecules linked by bond paths.

Bader, Richard F. W.

2009-09-01

248

Valence fluctuations and quasiparticle multiplets in plutonium chalcogenides and pnictides  

NASA Astrophysics Data System (ADS)

The spectra of Pu chalcogenides and pnictides are computed with dynamical mean field theory within the local density approximation (LDA+DMFT) and interpreted with the aid of valence histograms and slave-boson calculations. We find the chalcogenides are mixed-valent (nf=5.2) materials with a strongly T -dependent low-energy density of states and a triplet of quasiparticle peaks below the Fermi level. Furthermore, we predict a doublet of reflected peaks above the Fermi level. In the pnictides, the raising of f6 states relative to f5 suppresses valence fluctuations, resulting in integral-valent (nf=5.0) local-moment metals.

Yee, Chuck-Hou; Kotliar, Gabriel; Haule, Kristjan

2010-01-01

249

Valence state of Sm in SmRuSn3  

NASA Astrophysics Data System (ADS)

T. Fukuhara, I. Sakamoto, and H. Sato [J. Phys.: Condens. Matter 3, 8917 (1991)] reported valence fluctuations of Sm ions in SmRuSn3, which orders antiferromagnetically at 6 K. We have carried out x-ray, microprobe, heat-capacity, susceptibility, and resistivity measurements on a sample of nearly the same stoichiometry. There are two inequivalent Sm sites in SmRuSn3 and from the analysis of our data we conclude that Sm ions at one site are in the trivalent state and those at the second site are either divalent or weakly valence fluctuating.

Godart, C.; Mazumdar, Chandan; Dhar, S. K.; Nagarajan, R.; Gupta, L. C.; Padalia, B. D.; Vijayaraghavan, R.

1993-12-01

250

Savings Bonds Value Calculator  

NSDL National Science Digital Library

From the Federal Reserve Bank of New York, this site computes the redemption value of users's US savings bonds. Easy-to-use pull-down menus allow visitors to enter information such as the date of issue and face value of their Series E bonds, Series EE bonds, and Series S bonds. After entering the information, the Calculator will then show a chart of issue dates and denominations and actual worth of the bonds, if cashed within a set period of time.

251

Electro-magneto-thermosensitive complex fluids based on polyvinyl alcohol with variable-valence metals and orthophosphoric acid  

NASA Astrophysics Data System (ADS)

the conditions of formation and fields of application of the hybrid inorganic-organic complexes based on polyvinyl alcohol (PVA), variable-valence metals, polyacids, heteropolyacids and orthophosphoric acid are evaluated by rheological methods with regard for electrophysical, optical and sorption properties. The modification of hydrogen-bonded complexes with the applied electric, magnetic, thermal fields and sorption of water vapor changing the system of inter- and intramolecular hydrogen bonds are discussed. Evaluation is made of an influence of the type and concentration of components on the properties and structure of the complexes. The presence of sensitivity of the compositions to applied fields is related to formation acid of the structure- sensitive complexes between PVA molecules and metal ions Cu2+, Ni2+, Co2+, Fe3+ as well as the orthophosphoric acid or polyacids.

Lazareva, Tatiana G.; Kabisheva, Inessa V.; Il'Yushchenko, Irina A.

1998-07-01

252

Investing in Bonds.com  

NSDL National Science Digital Library

Investing in Bonds was created by the Bond Market Association to educate investors about the benefits of bonds investing. The Investor's Guide to Bond Basics educates investors about the types of bonds available, criteria for evaluating a bond, a guide to buying bonds, bond investment strategies and a glossary of bond market terms. The Bond Market section provides an overview of the U.S. bond market while the Investor's Checklist section takes the investor step-by-step through the bond investment decision process. Investors will also find sections with information on municipal bonds, corporate bonds, mortgage securities and U.S. Inflation-Indexed Securities.

253

A bond-topological approach to theoretical mineralogy: crystal structure, chemical composition and chemical reactions  

NASA Astrophysics Data System (ADS)

Here, I describe a theoretical approach to the structure and chemical composition of minerals based on their bond topology. This approach allows consideration of many aspects of minerals and mineral behaviour that cannot be addressed by current theoretical methods. It consists of combining the bond topology of the structure with aspects of graph theory and bond-valence theory (both long range and short range), and using the moments approach to the electronic energy density-of-states to interpret topological aspects of crystal structures. The structure hierarchy hypothesis states that higher bond-valence polyhedra polymerize to form the (usually anionic) structural unit, the excess charge of which is balanced by the interstitial complex (usually consisting of large low-valence cations and (H2O) groups). This hypothesis may be justified within the framework of bond topology and bond-valence theory, and may be used to hierarchically classify oxysalt minerals. It is the weak interaction between the structural unit and the interstitial complex that controls the stability of the structural arrangement. The principle of correspondence of Lewis acidity-basicity states that stable structures will form when the Lewis-acid strength of the interstitial complex closely matches the Lewis-base strength of the structural unit, and allows us to examine the factors that control the chemical composition and aspects of the structural arrangements of minerals. It also provides a connection between a structure, the speciation of its constituents in aqueous solution and its mechanism of crystallization. The moments approach to the electronic energy density-of-states provides a link between the bond topology of a structure and its thermodynamic properties, as indicated by correlations between average anion coordination number and reduced enthalpy of formation from the oxides for [6]Mg{/m [4]}Si n O( m+2 n) and MgSO4(H2O) n .

Hawthorne, Frank C.

2012-11-01

254

Opposing influences of affective state valence on visual cortical encoding.  

PubMed

Positive and negative emotional states are thought to have originated from fundamentally opposing approach and avoidance behaviors. Furthermore, affective valence has been hypothesized to exert opposing biases in cognitive control. Here we examined with functional magnetic resonance imaging whether the opposing influences of positive and negative states extend to perceptual encoding in the visual cortices. Based on prior behavioral research, we hypothesized that positive states would broaden and negative states would narrow visual field of view (FOV). Positive, neutral, and negative states were induced on alternating blocks. To index FOV, observers then viewed brief presentations (300 ms) of face/place concentric center/surround stimuli on interleaved blocks. Central faces were attended, rendering the place surrounds unattended. As face and place information was presented at different visual eccentricities, our physiological metric of FOV was a valence-dependent modulation of place processing in the parahippocampal place area (PPA). Consistent with our hypotheses, positive affective states increased and negative states decreased PPA response to novel places as well as adaptation to repeated places. Individual differences in self-reported positive and negative affect correlated inversely with PPA encoding of peripheral places, as well as with activation in the mesocortical prefrontal cortex and amygdala. Psychophysiological interaction analyses further demonstrated that valence-dependent responses in the PPA arose from opponent coupling with extrafoveal regions of the primary visual cortex during positive and negative states. These findings collectively suggest that affective valence differentially biases gating of early visual inputs, fundamentally altering the scope of perceptual encoding. PMID:19494142

Schmitz, Taylor W; De Rosa, Eve; Anderson, Adam K

2009-06-01

255

Vection Modulates Emotional Valence of Autobiographical Episodic Memories  

ERIC Educational Resources Information Center

|We examined whether illusory self-motion perception ("vection") induced by viewing upward and downward grating motion stimuli can alter the emotional valence of recollected autobiographical episodic memories. We found that participants recollected positive episodes more often while perceiving upward vection. However, when we tested a small moving…

Seno, Takeharu; Kawabe, Takahiro; Ito, Hiroyuki; Sunaga, Shoji

2013-01-01

256

Real-time observation of valence electron motion.  

SciTech Connect

The superposition of quantum states drives motion on the atomic and subatomic scales, with the energy spacing of the states dictating the speed of the motion. In the case of electrons residing in the outer (valence) shells of atoms and molecules which are separated by electronvolt energies, this means that valence electron motion occurs on a subfemtosecond to few-femtosecond timescale (1 fs = 10{sup -15} s). In the absence of complete measurements, the motion can be characterized in terms of a complex quantity, the density matrix. Here we report an attosecond pump-probe measurement of the density matrix of valence electrons in atomic krypton ions. We generate the ions with a controlled few-cycle laser field and then probe them through the spectrally resolved absorption of an attosecond extreme-ultraviolet pulse, which allows us to observe in real time the subfemtosecond motion of valence electrons over a multifemtosecond time span. We are able to completely characterize the quantum mechanical electron motion and determine its degree of coherence in the specimen of the ensemble. Although the present study uses a simple, prototypical open system, attosecond transient absorption spectroscopy should be applicable to molecules and solid-state materials to reveal the elementary electron motions that control physical, chemical and biological properties and processes.

Goulielmakis, E.; Loh, Z.-H.; Wirth, A.; Santra, R.; Rohringer, N.; Yakovlev, V. S.; Zherebtsov, S.; Pfeifer, T.; Azzeer, A. M.; Kling, M. F.; Leone, S. R.; Krausz, F.; Chemical Sciences and Engineering Division; Max-Planck-Insti. fur Quantenoptik; Univ. of California at Berkeley; LBNL; Univ. of Chicago; LLNL; Ludwig-Maximilians-Univ.; King Saud Univ.

2010-08-05

257

Mixed valence of Sm on metal single-crystal surfaces  

SciTech Connect

Results of a photoemission study of Sm on a Cu(100) single crystal surface are reported. From the binding energy of the Sm 4f levels it is concluded that the mixed valence of Sm on Cu(100) is of a heterogeneous nature. It is suggested that this conclusion also applies to Al(111) and Al(100).

Andersen, J.N.; Chorkendorff, I.; Onsgaard, J.; Ghijsen, J.; Johnson, R.L.; Grey, F.

1988-03-15

258

Tagging Multiple Emotional Stimuli: Negative Valence Has Little Benefit  

ERIC Educational Resources Information Center

|Six experiments examined the influence of emotional valence on the tagging and enumeration of multiple targets. Experiments 1, 5 and 6 found that there was no difference in the efficiency of tagging/enumerating multiple negative or positive stimuli. Experiment 2 showed that, when neutral-expression face distractors were present, enumerating…

Watson, Derrick G.; Blagrove, Elisabeth

2012-01-01

259

Time flies with music whatever its emotional valence  

Microsoft Academic Search

The present study used a temporal bisection task to investigate whether music affects time estimation differently from a matched auditory neutral stimulus, and whether the emotional valence of the musical stimuli (i.e., sad vs. happy music) modulates this effect. The results showed that, compared to sine wave control music, music presented in a major (happy) or a minor (sad) key

Sylvie Droit-Volet; Emmanuel Bigand; Danilo Ramos; José Lino Oliveira Bueno

2010-01-01

260

Recognizing the Emotional Valence of Names: An ERP Study  

ERIC Educational Resources Information Center

|Unlike common nouns, person names refer to unique entities and generally have a referring function. We used event-related potentials to investigate the time course of identifying the emotional meaning of nouns and names. The emotional valence of names and nouns were manipulated separately. The results show early N1 effects in response to…

Wang, Lin; Zhu, Zude; Bastiaansen, Marcel; Hagoort, Peter; Yang, Yufang

2013-01-01

261

Valence topological charge-transfer indices for dipole moments  

Microsoft Academic Search

New topological valence charge-transfer (CT) indices are applied to the calculation of dipole moments. The dipole moments calculated by algebraic and vector semisums of the CT indices are defined. The combination of the CT indices allows the estimation of the dipole moments. The model is generalized for molecules with heteroatoms. The ability of the indices for the description of the

Francisco Torrens

2003-01-01

262

Valence state at the surface of rare-earth metals  

Microsoft Academic Search

The valence state of a rare-earth metal surface is investigated by using general properties of the surface tension of metals. Thereby it is concluded that samarium is likely to have a divalent or partly divalent surface on top of its trivalent bulk phase, which agrees with recent spectroscopic observations. Also californium metal is discussed from this point of view. Finally,

Börje Johansson

1979-01-01

263

Modulation of hypothalamus and amygdalar activation levels with stimulus valence  

PubMed Central

In spite of long-standing evidence showing that the hypothalamus is instrumental in generating behaviors associated with positive and negative emotions, little is known about the role of the hypothalamus in normal human emotional processing. Recent findings have suggested that the hypothalamus plays a role beyond mere control of HPA-axis function; this is also supported by the existence of rich anatomical connections between the hypothalamus and the amygdala, a region known for its important role in emotional processing. However, evidence of emotion-induced hypothalamic activity from neuroimaging studies has been inconsistent, possibly due to methodological limitations (e.g., low spatial resolution). Taking advantage of recent improvements in fMRI technology we set out to explore a possible valence-dependent modulation of hypothalamic activity. Using second order parametric analysis of high-resolution BOLD fMRI, we assessed hypothalamic activation patterns during passive viewing of visual stimuli of varying valence, and compared the results with the activity pattern in the amygdalae, i.e. nuclei with known valence-dependent activity profiles. We show that both hypothalamic and amygdalar activation is modulated by the second-order stimulus valence term, i.e., there is increased neural activity following the processing of both positive and negative stimuli. Our results suggest that the hypothalamus may serve a role in generating emotions broader than generally assumed.

Karlsson, K.AE.; Windischberger, C.; Gerstl, F.; Mayr, W.; Siegel, J.M.; Moser, E.

2012-01-01

264

A model of candidate location with endogenous valence  

Microsoft Academic Search

This work gives a theoretical explanation of the increase in campaign spending and polarization in the US politics. I assume that the effectiveness of persuasive advertisement, and of costly valence campaigning in general, positively depends on the share of nonpartisan voters. Hence a decline in the number of partisan voters in a constituency results in greater campaign spending by the

Alexei V. Zakharov

2008-01-01

265

Can emotional valence in stories be determined from words?  

Microsoft Academic Search

In spite of the growing interest witnessed in the study of the relationship between emotion and language, the determination of the emotional valence of sentences, paragraphs or texts has so far attracted little attention. To bridge this gap, a technique based on the emotional aspect of words is presented. In this preliminary study, we have compared the affective tones of

Yves Bestgen

1994-01-01

266

Emotional Valence and Arousal Effects on Memory and Hemispheric Asymmetries  

ERIC Educational Resources Information Center

|This study examined predictions based upon the right hemisphere (RH) model, the valence-arousal model, and a recently proposed integrated model (Killgore & Yurgelun-Todd, 2007) of emotion processing by testing immediate recall and recognition memory for positive, negative, and neutral verbal stimuli among 35 right-handed women. Building upon…

Mneimne, Malek; Powers, Alice S.; Walton, Kate E.; Kosson, David S.; Fonda, Samantha; Simonetti, Jessica

2010-01-01

267

Superatomic orbitals in sixteen-coordinate M@Li16 bonded by metallic bonds.  

PubMed

Based on density-functional calculation and genetic algorithm structure search, we propose a series of 16-coordinate core-shell clusters: M@Li(16)(M = Ca, Sr, Ba, Ti, Zr, Hf). A tetrahedral (T(d)) structure with an outer shell of 16 lithium atoms and one enclosed heavy atom is found to be the global minimum in the structural exploration of BaLi(16) based on genetic algorithm. This structure also has lower energy compared to the other isomers we employed in all the MLi(16) clusters. In this structure, the atoms are bonded together by metallic bonds with alkali (IA) and alkaline-earth (IIA) metal atoms. Their corresponding first electronic shells are closed with significant energy gaps because their total numbers of valence electrons fulfil the 18-electron rule. Such a combination could be extended to 20-electron systems by enclosing IVB elements. With simple valence electrons and highly symmetric structures, superatomic molecular orbitals are identified in all of the T(d) clusters. PMID:22437545

Gu, Xiao; Chen, Guo-hong; Ji, Min; Yao, Yong-xin; Gong, Xin-gao

2012-03-21

268

The Bond Market Association  

NSDL National Science Digital Library

The Bond Market Association "represents securities firms and banks that underwrite, trade and sell debt securities." Their web site is divided into several sections. The Research Desk presents the results of research conducted by the association, including forecasts of economic growth and analysis of bond market trends. The Legislative Issues and Regulatory sections provide a summary of legislative and regulatory developments of interest to the bond market community. Market Practices contains guidelines and procedures to be followed in the bond market. The site also provides information to investors on how to invest in corporate bonds, tax-exempt municipal bonds, and mortgage securities.

1998-01-01

269

Valence transition and magnetic ordering in Sn doped EuPd 2 Si 2  

Microsoft Academic Search

The sharp, temperature induced, continuous valence transition in EuPd2Si2 is drastically changed by doping with Sn at the Si site upto 5 at. %. Only a first order valence transition occurs for a 3% Sn doped sample and the 2+ component which survives the valence transition orders magnetically at 4.2 K. No valence transition at all occurs for a 5%

S. N. Mishra; H. G. Devare

1983-01-01

270

Valence transition and magnetic ordering in Sn doped EuPd2Si2  

Microsoft Academic Search

The sharp, temperature induced, continuous valence transition in EuPd2Si2 is drastically changed by doping with Sn at the Si site upto 5 at. %. Only a first order valence transition occurs for a 3% Sn doped sample and the 2+ component which survives the valence transition orders magnetically at 4.2 K. No valence transition at all occurs for a 5%

S. N. Mishra; H. G. Devare

1983-01-01

271

Structure and bonding in [M(6)O(19)](n-) isopolyanions.  

PubMed

The structure and bonding in [M(6)O(19)](n-) isopolyanions of Nb, Ta, Mo, and W have been investigated using density-functional methods. The computational-experimental agreement is good for the geometrical parameters of Mo and W species but less satisfactory for Nb and Ta clusters. The electronic structure of the anions has been probed with molecular-orbital, Mulliken-Mayer, and bonding-energy approaches. The results have indicated that M-O interactions are largely M d-O p in character and that sigma and pi bonds link the metal centers to terminal and bridging (O(b)) oxygen atoms. Some M-O(b) bonds exhibit a [M(4)O(4)] closed-loop structure, but this orbital-interaction mode has not been found to make a particularly outstanding contribution to the bonding stability of the molecules. Mayer indexes correspond to (fractional) multiple, approximately single, and low-order character for terminal, bridging, and internal bonds, respectively, and the valency analysis has yielded similar bonding capacities for the different oxygen atoms. A distribution of the negative charge over all types of oxygen sites and metal charges considerably smaller than the formal oxidation states have been obtained from the Mulliken analysis. Minimal structural changes have been detected on reduction of molybdates and tungstates, in accord with the general properties of the orbitals occupied by the added electrons. PMID:11925167

Bridgeman, Adam J; Cavigliasso, Germán

2002-04-01

272

The pursuit of happiness in music: retrieving valence with high-level musical descriptors  

Microsoft Academic Search

In the study of music emotions, valence is normally referred as one of the emotional dimensions that describes music appraisal of happiness, whose scale goes from sad to happy. Nevertheless, related literature shows that valence is known to be particularly difficult to be predicted by a computational model. As valence is a contextual music feature, it is assumed here that

Jose Fornari; Tuomas Eerola

273

Valence-Specific Laterality Effects in Vocal Emotion: Interactions with Stimulus Type, Blocking and Sex  

ERIC Educational Resources Information Center

|Valence-specific laterality effects have been frequently obtained in facial emotion perception but not in vocal emotion perception. We report a dichotic listening study further examining whether valence-specific laterality effects generalise to vocal emotions. Based on previous literature, we tested whether valence-specific laterality effects…

Schepman, Astrid; Rodway, Paul; Geddes, Pauline

2012-01-01

274

X-ray Emission Spectroscopy to Study Ligand Valence Orbitals in Mn Coordination Complexes  

SciTech Connect

We discuss a spectroscopic method to determine the character of chemical bonding and for the identification of metal ligands in coordination and bioinorganic chemistry. It is based on the analysis of satellite lines in X-ray emission spectra that arise from transitions between valence orbitals and the metal ion 1s level (valence-to-core XES). The spectra, in connection with calculations based on density functional theory (DFT), provide information that is complementary to other spectroscopic techniques, in particular X-ray absorption (XANES and EXAFS). The spectral shape is sensitive to protonation of ligands and allows ligands, which differ only slightly in atomic number (e.g., C, N, O...), to be distinguished. A theoretical discussion of the main spectral features is presented in terms of molecular orbitals for a series of Mn model systems: [Mn(H2O)6]2+, [Mn(H2O)5OH]+, [Mn(H2O)5NH2]+, and [Mn(H2O)5NH3]2+. An application of the method, with comparison between theory and experiment, is presented for the solvated Mn2+ ion in water and three Mn coordination complexes, namely [LMn(acac)N3]BPh4, [LMn(B2O3Ph2)(ClO4)], and [LMn(acac)N]BPh4, where L represents 1,4,7-trimethyl-1,4,7-triazacyclononane, acac stands for the 2,4-pentanedionate anion, and B2O3Ph2 represents the 1,3-diphenyl-1,3-dibora-2-oxapropane-1,3-diolato dianion.

Smolentsev, Grigory; Soldatov, Alexander V; Messinger, Johannes; Merz, Kathrin; Weyhermuller, Thomas; Bergmann, Uwe; Pushkar, Yulia; Yano, Junko; Yachandra, Vittal K.; Glatzel, Pieter

2009-03-02

275

Societal Bonding and Delinquency  

Microsoft Academic Search

Travis Hirschi's (1969) theory of control has amassed considerable empirical support since its development and has become one of the dominant explanations of delinquent behavior. Control theory's basic premise is that people with strong bonds to society are less likely to deviate from conventional behavior than those with weak bonds. In this article bonding theory is applied to a severely

Karen Witchcoff Knight; Tony Tripodi

1996-01-01

276

Bonded flexible pipe  

Microsoft Academic Search

This paper presents an overview of bonded flexible pipe improvements primarily driven by environmental safety as applied to offshore development using mobile production systems. Bonded pipe is a flexible pipe where the steel reinforcement is integrated and bonded to a vulcanized elastomeric material. Textile material is included in the structure to obtain additional structural reinforcement or to separate elastomeric layers.

Val M. Northcutt

2000-01-01

277

Thin die bonding techniques  

Microsoft Academic Search

Picking and bonding 50-micron thick chips presents new challenges to the die bonder industry. Extensive development efforts have identified a number of process challenges and solutions. This paper summarizes Esec's most recent learning's pertaining to the thin die bonding process. Problems with standard die bonding chip pick up and epoxy-dispensing techniques are discussed and solutions identified. Two novel pick solutions

J. Medding; R. Stalder; M. Niederhauser; P. Stoessel

2004-01-01

278

Hydrophobic silicon wafer bonding  

Microsoft Academic Search

Silicon wafers with hydrophilic surfaces can be bonded at room temperature (RT). This has been attributed to the presence of OH groups on the mating surfaces that form hydrogen bonds between the two wafers.19 Hydrophobic Si wafers prepared by a dip in diluted HF without subsequent water rinse have shown a similar RT bonding performance.3 Dispersion van der Waals forces

Q.-Y. Tong; E. Schmidt; U. Gösele; M. Reiche

1994-01-01

279

The valence electronic structure of multiferroic BiFeO3 from high energy X-ray photo-electron spectroscopy and first principles theory  

NASA Astrophysics Data System (ADS)

BiFeO3 (BFO) is a multi-functional material with high ferroelectric and magnetic ordering temperature. Here we have investigated the electronic structure of (001) oriented 100nm rhombohedral BFO thin films using high energy X-ray photoelectron spectroscopy (XPS). By making use of the energy dependence of the relative cross sections for different states, we were able to selectively probe the elemental contributions to the valence band . At high energies, states with high main quantum number will have a higher relative probability for photo-ionization, i.e., the Bi 6s and 6p contributions in the valence region are enhanced relative to the Fe 3d and O 2p. We find that the Bi 6p states hybridize strongly with the valence band dominated by the Fe 3d and O 2p states, resulting in a splitting of the 3d states due to bonding and anti-bonding combinations with the Bi 6p. Our results thus suggest that a previously relatively ignored electronic interaction needs to be considered for BFO and related Bi-TMOs. Ab initio calculations indicate the importance of screened Coulomb correlations to describe Bi and Fe electronic states.

Knut, R.; Faleev, S.; Mazumdar, Dipanjan; Mryasov, O.; Gupta, Arunava; Karis, O.

2012-02-01

280

Zener Double Exchange from Local Valence Fluctuations in Magnetite  

SciTech Connect

Magnetite (Fe3O4) is a mixed valent system where electronic conductivity occurs on the B site (octahedral) iron sublattice of the spinel structure. Below Tv = 123 K, a metal-insulator transition occurs which is argued to arise from the charge ordering of 2+ and 3+ iron valences on the B sites (Verwey transition). Inelastic neutron scattering measurements show that optical spin waves propagating on the B site sublattice (~80 meV) are shifted upwards in energy above TV due to the occurrence of B-B ferromagnetic double exchange in the mixed valent phase. The double exchange interaction affects only spin waves of 5 symmetry, not all modes, indicating that valence fluctuations are slow and the double exchange is constrained by short-range electron correlations above Tv.

McQueeney, Robert John [Iowa State University; Yethiraj, M. [Bragg Institute, ANSTO; Chang, S. [National Institute of Standards and Technology (NIST); Montfrooij, W. [University of Missouri, Columbia; Perring, T. G. [ISIS Facility, Rutherford Appleton Laboratory; Honig, J. M. [University of Purdue; Metcalf, P. [Purdue University

2007-01-01

281

Nucleon separation energies in the valence correlation scheme  

NASA Astrophysics Data System (ADS)

In this paper we study the one- and two-nucleon separation energies (Sn, Sp, S2n, and S2p) by using the Atomic-Mass-Evaluation-2011 Preview. We show the linear dependence of separation energies, previously investigated for Sn and Sp of even-even nuclei, in terms of ?Np+?Nn (Np and Nn is the valence proton number and valence neutron number, respectively, with respect to the nearest magic closure), hold in a broader sense. It is applicable equally well to odd-mass and odd-odd nuclei. New odd-even staggerings are found for Sn and Sp, and are discussed by using the pairing interaction and the symmetry energy. Predictive power of these simple relations is discussed.

Jiang, H.; Fu, G. J.; Bao, M.; He, Z.; Zhao, Y. M.; Arima, A.

2012-07-01

282

Origins of Phase Transitions in Valence Fluctuating YbPd  

NASA Astrophysics Data System (ADS)

The cubic YbPd compound undergoes two first-order phase transitions at T1=125 K and T2=105 K. We report the experimental results of the X-ray diffraction (XRD) and electron diffraction of single crystals of YbPd at low temperatures. Below T1, the (h00) Bragg peaks (h: an integer) are split into two subpeaks. Below T2, the superlattice reflections of (n/2,0,0) (n: an odd number) in the XRD patterns and the superlattice spots of (1/2,0,0), (0,1/2,0), and (1/2,1/2,0) in the electron diffraction profile appear, which suggests the valence order of YbPd. We discuss two possible structures, assuming a tetragonal symmetry below T1. The origins of the transitions at T1 and T2 are probably the band Jahn--Teller effect and the valence order, respectively.

Mitsuda, Akihiro; Sugishima, Masaki; Hasegawa, Takumi; Tsutsui, Satoshi; Isobe, Masahiko; Ueda, Yutaka; Udagawa, Masayuki; Wada, Hirofumi

2013-08-01

283

Tagging multiple emotional stimuli: negative valence has little benefit.  

PubMed

Six experiments examined the influence of emotional valence on the tagging and enumeration of multiple targets. Experiments 1, 5 and 6 found that there was no difference in the efficiency of tagging/enumerating multiple negative or positive stimuli. Experiment 2 showed that, when neutral-expression face distractors were present, enumerating negative targets was faster overall, but was only more efficient for small numbers of targets. Experiments 3 and 4 determined that this negative target advantage was most likely caused by increased attentional guidance to negatively-valenced stimuli and was not based on simple visual feature differences. The findings suggest that a multiple-target negative stimulus advantage will only occur under conditions of attentional competition, and for relatively small numbers of targets. The results are discussed in relation to theories of multiple- and single-item processing, threat-priority mechanisms, and the types of representations that support different attentional tasks. PMID:22201468

Watson, Derrick G; Blagrove, Elisabeth

2011-12-26

284

Valence structure of alkaline and post-transition metal oxides  

Microsoft Academic Search

As a stepping point to predicting band gaps and electronic structure of more complicated materials based on alkaline and post-transition metal oxides, we examine the valence structure of these simple binary oxides using both high resolution X-ray emission spectroscopy and a variety of density functional theory calculations. We confirm that the new modified Becke-Johnson (mBJ) extension of the Perdew-Burke-Ernzerhoff (PBE96)

John A. McLeod; Robert J. Green; Nikolay A. Skorikov; L. D. Finkelstein; Mahmoud Abu-Samak; Ernst Z. Kurmaev; Alexander Moewes

2011-01-01

285

Effective Shell-Model Interactions from the Valence Cluster Expansion  

Microsoft Academic Search

The ab initio No-Core Shell Model (NCSM) has had considerable success in describing the binding energies, excitation spectra and other physical properties of light nuclei, A12. Following the idea of Ref. [2], we develop a valence cluster expansion to construct effective 2- and 3-body Hamiltonians for the 0p-shell by performing 12phi NCSM calculations for A=6 and 7 nuclei and explicitly

A. F. Lisetskiy; M. K. G. Kruse; B. R. Barrett; P. Navratil; I. Stetcu; J. P. Vary

2008-01-01

286

Dynamical reconstruction of the valence exciton in LiF  

Microsoft Academic Search

We have used inelastic x-ray scattering, coupled with recently developed inversion techniques, to reconstruct the structure and dynamics of the valence exciton in the prototype alkali halide LiF. Our inversions, which yield resolutions deltax = 0.533 å and deltat = 20.67 as (2.067 x10-17 s), reveal that the exciton forms in less than 50 as, oscillates with a period of

Peter Abbamonte; Wei Ku; Tim Graber; James Reed; Serban Smadici; Abhay Shukla; Jean-Pascal Rueff

2008-01-01

287

Heavy drinking relates to positive valence ratings of alcohol cues.  

PubMed

A positive family history of alcohol use disorders (FH) is a robust predictor of personal alcohol abuse and dependence. Exposure to problem-drinking models is one mechanism through which family history influences alcohol-related cognitions and drinking patterns. Similarly, exposure to alcohol advertisements is associated with alcohol involvement and the relationship between affective response to alcohol cues and drinking behavior has not been well established. In addition, the collective contribution that FH, exposure to different types of problem-drinking models (e.g. parents, peers) and personal alcohol use have on appraisal of alcohol-related stimuli has not been evaluated with a large sample. We investigated the independent effects of FH, exposure to problem-drinking models and personal alcohol use on valence ratings of alcohol pictures in a college sample. College students (n = 227) completed measures of personal drinking and substance use, exposure to problem-drinking models, FH and ratings on affective valence of 60 alcohol pictures. Greater exposure to non-familial problem-drinkers predicted greater drinking among college students (beta = 0.17, P < 0.01). However, personal drinking was the only predictor of valence ratings of alcohol pictures (beta = -0.53, P < 0.001). Personal drinking level predicted valence ratings of alcohol cues over and above FH, exposure to problem-drinking models and demographic characteristics. This suggests that positive affective responses to alcohol pictures are more a function of personal experience (i.e. repeated heavy alcohol use) than vicarious learning. PMID:18855802

Pulido, Carmen; Mok, Alex; Brown, Sandra A; Tapert, Susan F

2008-10-09

288

A model of candidate location with endogenous valence  

Microsoft Academic Search

This work gives a theoretical explanation for the increase in campaign spending and party polarization in U.S. politics. I\\u000a assume that the effectiveness of persuasive advertising, and of costly valence campaigning in general, positively depends\\u000a on the share of nonpartisan voters. A decline in the number of partisan voters in a constituency results in greater campaign\\u000a spending by the candidates.

Alexei V. Zakharov

2009-01-01

289

Valence-band photoemission and optical absorption in nickel compounds  

Microsoft Academic Search

Photoemission, optical-absorption, and isochromat spectra of NiO and NiCl2 are studied theoretically by the consideration of configuration interactions within the metal-ligand cluster. It is shown that the satellites in the valence-band photoemission spectra contain significant d7 final-state components produced by photoemission of a d electron from the largely d8-like ground state and that final states giving the main lines are

Atsushi Fujimori; Fujio Minami

1984-01-01

290

Spectroscopic valence of cerium in cerium-lanthanum-iron compounds  

NASA Astrophysics Data System (ADS)

In Ce2Fe14B and Ce2Fe17, cerium is mixed valent and nonmagnetic. Any structural or compositional modification of these intermetallics which induces cerium to become trivalent and develop a local 4f moment should result in compounds with enhanced magnetostrictions, magnetocrystalline anisotropies, and net magnetic moments. Due to the dependence of cerium valence on steric volume, one approach for manipulating the valence is to increase the cell volume of these phases by forming pseudoternaries or pseudobinaries of these compounds with lanthanum. In this work, we report the spectroscopic valence of cerium obtained from the cerium L3 edge of La2-xCexFe14B, La2-xCexFe17, and selected hydrides and nitrides of these intermetallics. In La2-xCexFe14B the average cerium valence is found to decrease only slightly with increasing lanthanum content. Analysis of the extended x-ray absorption fine structure of the cerium and lanthanum L3 edges from the La2-xCexFe14B series is only consistent with cerium preferentially occupying the small 4f rare-earth site in the tetragonal Nd2Fe14B structure. In La2-xCexFe17 the shift of cerium towards the trivalent state with decreasing x is more pronounced, but the shift is incomplete over the range of compositions investigated (x>=1). Although these results do not exclude the possibility of trivalent cerium in some of these compounds, none of the compounds provided unambiguous evidence of trivalent cerium.

Capehart, T. W.; Mishra, R. K.; Fuerst, C. D.; Meisner, G. P.; Pinkerton, F. E.; Herbst, J. F.

1997-05-01

291

Kondo universality, energy scales, and intermediate valence in plutonium  

NASA Astrophysics Data System (ADS)

On the basis of the concepts of an intermediate-valence (IV) regime, an analysis is carried out of macroscopic properties of the ? and ? phases of plutonium, as well as of several model systems based on rare earth elements. Within a single-site approximation (SSA), the characteristic Kondo interaction energy, the f-electron shell occupation number, the effective degeneracy of the ground-state f multiplet, and the crystal field splitting energy are estimated. The ground state in plutonium is considered as a quantum-mechanical superposition of states with different valences. The temperature dependence of the static magnetic susceptibility of ? plutonium is calculated. It is shown that ? plutonium satisfies the Wilson and Kadowaki-Woods universal relations, whereby it can be classified as a Kondo system. At the same time, the problem of the position of plutonium in the general classification of solids, as well as the problem of the temperature dependence of magnetic susceptibility of ? plutonium, remains open. The concept of multiple intermediate valence (MIV) is put forward as a possible means for solving the above problems. The MIV regime is characterized by fluctuations from the basic configuration 3+ to the states 4+ and 2+, which make a fundamental difference between plutonium and 4 f electron systems based, say, on samarium.

Clementyev, E. S.; Mirmelstein, A. V.

2009-07-01

292

Core-valence double photoionization of the CS(2) molecule.  

PubMed

Double photoionization spectra of the CS(2) molecule have been recorded using the TOF-PEPECO technique in combination with synchrotron radiation at the photon energies h?=220, 230, 240, 243, and 362.7 eV. The spectra were recorded in the S 2p and C 1s inner-shell ionization regions and reflect dicationic states formed out of one inner-shell vacancy and one vacancy in the valence region. MCSCF calculations were performed to model the energies of the dicationic states. The spectra associated with a S 2p vacancy are well structured and have been interpreted in some detail by comparison to conventional S 2p and valence photoelectron spectra. The lowest inner-shell-valence dicationic state is observed at the vertical double ionization energy 188.45 eV and is associated with a (2p(3/2))(-1)(2?(g))(-1) double vacancy. The spectrum connected to the C 1s vacancy shows a distinct line at 310.8 eV, accompanied by additional broad features at higher double ionization energies. This line is associated with a (C?1s)(-1)(2?(g))(-1) double vacancy. PMID:20831316

Andersson, E; Niskanen, J; Hedin, L; Eland, J H D; Linusson, P; Karlsson, L; Rubensson, J-E; Carravetta, V; Agren, H; Feifel, R

2010-09-01

293

Singular Valence Fluctuations at a Kondo Destroyed Quantum Critical Point  

NASA Astrophysics Data System (ADS)

Recent experiments on the heavy fermion superconductor beta-YbAlB4 have indicated that this compound satisfies quantum critical scaling [1]. Motivated by the observation of mixed valency in this material [2], we study the Kondo destruction physics in the mixed-valence regime [3] of a particle-hole asymmetric Anderson impurity model with a pseudogapped density of states. In the vicinity of the quantum critical point we determine the finite temperature spin and charge susceptibilities by utilizing a continuous time quantum Monte Carlo method [4] and the numerical renormalization group. We show that this mixed-valence quantum critical point displays a Kondo breakdown effect. Furthermore, we find that both dynamic spin and charge susceptibilities obey frequency over temperature scaling, and that the static charge susceptibility diverges with a universal exponent. Possible implications of our results for beta-YbAlB4 are discussed. [1] Matsumoto et al, Science 331, 316 (2011). [2] Okawaet al, Physical Review Letters 104, 247201 (2010). [3] J. H. Pixley, S. Kirchner, Kevin Ingersent and Q. Si, arXiv:1108.5227v1 (2011). [4] M. Glossop, S. Kirchner, J. H. Pixley and Q. Si, Phys. Rev. Lett. 107, 076404 (2011).

Pixley, Jedediah; Kirchner, Stefan; Ingersent, Kevin; Si, Qimiao

2012-02-01

294

Kondo universality, energy scales, and intermediate valence in plutonium  

SciTech Connect

On the basis of the concepts of an intermediate-valence (IV) regime, an analysis is carried out of macroscopic properties of the {alpha} and {delta} phases of plutonium, as well as of several model systems based on rare earth elements. Within a single-site approximation (SSA), the characteristic Kondo interaction energy, the f-electron shell occupation number, the effective degeneracy of the ground-state f multiplet, and the crystal field splitting energy are estimated. The ground state in plutonium is considered as a quantum-mechanical superposition of states with different valences. The temperature dependence of the static magnetic susceptibility of {delta} plutonium is calculated. It is shown that {delta} plutonium satisfies the Wilson and Kadowaki-Woods universal relations, whereby it can be classified as a Kondo system. At the same time, the problem of the position of plutonium in the general classification of solids, as well as the problem of the temperature dependence of magnetic susceptibility of {delta} plutonium, remains open. The concept of multiple intermediate valence (MIV) is put forward as a possible means for solving the above problems. The MIV regime is characterized by fluctuations from the basic configuration 3+ to the states 4+ and 2+, which make a fundamental difference between plutonium and 4f electron systems based, say, on samarium.

Clementyev, E. S.; Mirmelstein, A. V., E-mail: mirmelstein@mail.r [Russian Federal Nuclear Center-Zababakhin Russian Research Institute of Technical Physics, Division of Experimental Physics (Russian Federation)

2009-07-15

295

Ferromagnetic dinuclear mixed-valence Mn(II)/Mn(III) complexes: building blocks for the higher nuclearity complexes. structure, magnetic properties, and density functional theory calculations.  

PubMed

A series of six mixed-valence Mn(II)/Mn(III) dinuclear complexes were synthesized and characterized by X-ray diffraction. The reactivity of the complexes was surveyed, and structures of three additional trinuclear mixed-valence Mn(III)/Mn(II)/Mn(III) species were resolved. The magnetic properties of the complexes were studied in detail both experimentally and theoretically. All dinuclear complexes show ferromagnetic intramolecular interactions, which were justified on the basis of the electronic structures of the Mn(II) and Mn(III) ions. The large Mn(II)-O-Mn(III) bond angle and small distortion of the Mn(II) cation from the ideal square pyramidal geometry were shown to enhance the ferromagnetic interactions since these geometrical conditions seem to favor the orthogonal arrangement of the magnetic orbitals. PMID:23363337

Hänninen, Mikko M; Välivaara, Juha; Mota, Antonio J; Colacio, Enrique; Lloret, Francesc; Sillanpää, Reijo

2013-01-30

296

Electron-Rich Three-Center Bonding:  Role of s,p Interactions across the p-Block  

Microsoft Academic Search

This paper analyzes the importance of s,p mixingsa necessary addition to the simplest Rundle- Pimentel picturesand periodic and group trends in electron-rich three-center bonding. Our analysis proceeds through a detailed quantum chemical study of the stability of electron-rich three-center bonding in triatomic 22-valence electron anions. To provide interpretations, a perturbational molecular orbital (MO) analysis of s,p mixing is carried out.

Markéta L. Munzarová; Roald Hoffmann

2002-01-01

297

How are hydrogen bonds modified by metal binding?  

PubMed

We have used density functional theory calculations to investigate how the hydrogen-bond strength is modified when a ligand is bound to a metal using over 60 model systems involving six metals and eight ligands frequently encountered in metalloproteins. We study how the hydrogen-bond geometry and energy vary with the nature of metal, the oxidation state, the coordination number, the ligand involved in the hydrogen bond, other first-sphere ligands, and different hydrogen-bond probe molecules. The results show that, in general, the hydrogen-bond strength is increased for neutral ligands and decreased for negatively charged ligands. The size of the effect is mainly determined by the net charge of the metal complex, and all effects are typically decreased when the model is solvated. In water solution, the hydrogen-bond strength can increase by up to 37 kJ/mol for neutral ligands, and that of negatively charged ligands can increase (for complexes with a negative net charge) or decrease (for positively charged complexes). If the net charge of the complex does not change, there is normally little difference between different metals or different types of complexes. The only exception is observed for sulphur-containing ligands (Met and Cys) and if the ligand is redox-active (e.g. high-valence Fe-O complexes). PMID:23543233

Husberg, Charlotte; Ryde, Ulf

2013-03-31

298

Study of Local Valence Electronic States of SiO2 Ultrathin Films Grown on Si(111) by Using Auger Photoelectron Coincidence Spectroscopy: Upward Shift of Valence-Band Maximum Depending on the Interface Structure  

NASA Astrophysics Data System (ADS)

To clarify the factors governing the local valence electronic states of SiO2 ultrathin films, we have measured the Si-L23VV--Sin+-2p Auger-electron photoelectron coincidence spectra (n = 0, 1, 2, 3, 4, where n represents the number of oxygen atoms bonded to Si) of SiO2 thermally grown on a Si(111)-7×7 surface [SiO2/Si(111)]. The results indicate that the valence electronic states in the vicinity of the Sin+ sites shift to deeper binding energies as n increases. Furthermore, Si4+-L23VV Auger electron spectra, measured as a function of SiO2 thickness, taken in coincidence with Si4+-2p photoelectron emission show that the valence-band maximum (VBM) of the SiO2 layer shifts by 2.7 ± 1.0 eV toward the Fermi level when SiO2 thickness is decreased to ?1 monolayer (ML). This upward shift is much larger than that for a SiO2 layer with a thickness of ?1 ML thermally grown on Si(100)-2×1 (about 1.6 eV). We attribute the large shift in the VBM of SiO2/Si(111) with a 1-ML-thick SiO2 layer to the formation of SiO2 islands on the 7×7 structure and to the presence of Si1+ atoms adjacent to the SiO2 sites.

Kakiuchi, Takuhiro; Fujita, Narihiko; Mase, Kazuhiko; Tanaka, Masatoshi

2012-07-01

299

Influence of alloy microstructure on the microshear bond strength of basic alloys to a resin luting cement.  

PubMed

The aim of this study was to evaluate the influence of microstructure and composition of basic alloys on their microshear bond strength (µSBS) to resin luting cement. The alloys used were: Supreme Cast-V (SC), Tilite Star (TS), Wiron 99 (W9), VeraBond II (VBII), VeraBond (VB), Remanium (RM) and IPS d.SIGN 30 (IPS). Five wax patterns (13 mm in diameter and 4mm height) were invested, and cast in a centrifugal casting machine for each basic alloy. The specimens were embedded in resin, polished with a SiC paper and sandblasted. After cleaning the metal surfaces, six tygon tubes (0.5 mm height and 0.75 mm in diameter) were placed on each alloy surface, the resin cement (Panavia F) was inserted, and the excess was removed before light-curing. After storage (24 h/37°C), the specimens were subjected to µSBS testing (0.5 mm/min). The data were subjected to a one-way repeated measures analysis of variance and Turkey's test (?=0.05). After polishing, their microstructures were revealed with specific conditioners. The highest µSBS (mean/standard deviation in MPa) were observed in the alloys with dendritic structure, eutectic formation or precipitation: VB (30.6/1.7), TS (29.8/0.9), SC (30.6/1.7), with the exception of IPS (31.1/0.9) which showed high µSBS but no eutectic formation. The W9 (28.1/1.5), VBII (25.9/2.0) and RM (25.9/0.9) showed the lowest µSBS and no eutectic formation. It seems that alloys with eutectic formation provide the highest µSBS values when bonded to a light-cured resin luting cement. PMID:23306223

Bauer, José; Costa, José Ferreira; Carvalho, Ceci Nunes; Souza, Douglas Nesadal de; Loguercio, Alessandro Dourado; Grande, Rosa Helena Miranda

300

A local view of bonding and diffusion at metal surfaces  

SciTech Connect

First-principles density functional calculations and corresponding experimental results underline the importance of basic chemical concepts, such as coordination, valence saturation and promotion-hybridization energetics, in understanding bonding and diffusion of atoms at and on metal surfaces. Several examples are reviewed, including outer-layer relaxations of clean hcp(0001) surfaces, liquid-metal-embrittlement energetics, separation energies of metal-adatom dimers, concerted substitutional self-diffusion on fcc(001) surfaces, and adsorption and diffusion barrier sites for adatoms near steps.

Feibelman, P.J.

1996-09-01

301

The hydrogen bond  

Microsoft Academic Search

The concept of the hydrogen bond is a century old but remains youthful because of its vital role in so many branches of science and because of continued advances in experiment, theory and simulation. We discuss the structural and energetic characteristics of normal hydrogen bonds X–H···Y as well as some exceptions to the normal, including proton-shared and ion-pair bonds. We

A. D. Buckingham; J. E. Del Bene; S. A. C. McDowell

2008-01-01

302

BONDING ALUMINUM METALS  

DOEpatents

A process is given for bonding aluminum to aluminum. Silicon powder is applied to at least one of the two surfaces of the two elements to be bonded, the two elements are assembled and rubbed against each other at room temperature whereby any oxide film is ruptured by the silicon crystals in the interface; thereafter heat and pressure are applied whereby an aluminum-silicon alloy is formed, squeezed out from the interface together with any oxide film, and the elements are bonded.

Noland, R.A.; Walker, D.E.

1961-06-13

303

Semiconductor Wafer Bonding  

Microsoft Academic Search

When mirror-polished, flat, and clean wafers of almost any material are brought into contact at room temperature, they are locally attracted to each other by van der Waals forces and adhere or bond. This phenomenon is referred to as wafer bonding. The most prominent applications of wafer bonding are silicon-on-insulator (SOI) devices, silicon-based sensors and actuators, as well as optical

U. Gosele; Q.-Y. Tong

1998-01-01

304

One Bond Strategy  

NSDL National Science Digital Library

Provided by SmartMoney.com (see the May 20, 1999 Scout Report for Business & Economics), this quick and easy yet thorough guide takes readers through the process of developing a bond portfolio. At the site, users will find help on deciding how much to invest in bonds, how to divide their portfolio, and tips on investing for both income and profit. First, however, visitors might want to wet their feet in the bond primer section, which covers all the basics, explains the yield curve, offers a calculator and glossary, and throws in "ten things your broker won't tell you about bonds" for good measure.

2001-01-01

305

Recent advances in the practical and accurate calculation of core and valence XPS spectra of polymers: From interpretation to simulation?  

NASA Astrophysics Data System (ADS)

Core and valence X-ray Photoelectron Spectroscopies (XPS) are routinely used to obtain information on the chemical composition, bonding and homogeneity of polymer surfaces. In spite of their apparent conceptual simplicity, Core and Valence Electron Binding Energies (CEBEs and VEBEs) a few electron-volts (eV) or fractions of an eV apart are difficult to interpret. We present some results obtained with various recent theoretical approaches. An emphasis is made on a procedure based on the Density Functional Theory (DFT) that enables the calculation of CEBEs and VEBEs which are in remarkable agreement with experiment. The method has been tested on numerous small (3-6 atoms) to fairly large (15-25 atoms) molecules, and shows an average absolute deviation with experiment of only 0.20 eV for CEBEs and 0.30 eV for VEBEs, i.e. compatible with the resolution of the best XPS experiments carried out at the moment. Besides the quality of its predictions, the procedure takes advantage of the speed and CPU time scaling of DFT as a function of system size: it is computationally tractable, even for surprisingly large systems such as polymers, and may be an interesting accurate alternative to interpret and simulate XPS-probing on real systems. We illustrate the usefullness and pitfalls of this approach in fundamental as well as applied fields such as in the study of Polyacrylonitrile (PAN), Polytetrafluoroethylene (PTFE), Polyvinyldifluoride (PVdF) and ?-Aminopropyltriethoxysilane (?-APS, an adhesion promoter).

Bureau, C.; Lecayon, G.; Le Moël, A.; Chong, D. P.; Endo, K.; Delhalle, J.

1997-08-01

306

Strong electron correlations in cobalt valence tautomers: Evidence from X-ray Absorption  

NASA Astrophysics Data System (ADS)

At least a third of all proteins and enzymes contain an "active site" which possesses one or more transition metal atoms. The charge/spin state of the metal atom displays sensitivity to coordination geometry and species. We have studied a unique model system of this behavior in the cobalt valence tautomer molecules. With changing temperature, they exhibit a reversible transition that consists of changes in the Co-O and Co-N bond lengths and a concomitant crossover from high-spin to low-spin with some charge redistribution on the molecule. Using a simple model has been proposed (M.X. LaBute, R.V. Kulkarni, R.G. Endres, D.L. Cox, paper accepted by J. Chem. Phys.) that treats the correlations beyond Hartree-Fock among the 3d electrons of the cobalt site, we have calculated the Co K-edge XANES. We are able to identify, for the first time, spectral weight in the high-T state that results from a correlations-driven resonance state. In addition, we calculate a prediction for the Co L-edge XAS which, to our knowledge, has not been previously done. We compare our theoretical calculation to new experimental data. Finally, we discuss the distinction between absorption structures that are the result of covalency and true signatures of strong correlations effects.

Labute, Montiago; Kulkarni, Rahul; Endres, Robert; Cox, Daniel

2002-03-01

307

A molecular mechanics valence force field for sulfonamides derived by ab initio methods  

SciTech Connect

Molecular mechanics valence force field parameters for the sulfonamide group, SO[sub 2]NH, have been derived from ab initio calculations at the RHF/6-31G* level of theory. The force field parameters were designed to be used in conjunction with existing parameters from the MM2/MMP2 force field. The new parameters are demonstrated to accurately reproduce the ab initio optimized geometries of four molecules that contain the sulfonamide group. The strategy used in force field parametrization is discussed. The conformational flexibility of the sulfonamide group has been investigated. Calculations at the RHF/6-31G* level reveal the existence of two stable conformers and that interconversion is achieved by nitrogen inversion rather than rotation about the S-N bond. The energetic effects of expanding the basis set to 6-31G** and of including MP2 and MP3 corrections for electron correlation are discussed. The geometries and Mulliken charges for the ab initio optimized structures are also reported.

Nicholas, J.B.; Burke, B.J.; Hopfinger, A.J. (Univ. of Illinois, Chicago (United States)); Vance, R.; Martin, E. (DowElanco, Walnut Creek, CA (United States))

1991-11-28

308

3p valence photoelectron spectrum of Ar clusters  

SciTech Connect

The shape of the outer valence (3p) photoelectron spectrum of Ar clusters is investigated by vacuum ultraviolet photoionization with synchrotron radiation. We show the dependence of the spectrum on cluster size and the change in its shape with photon energy. Inelastic losses due to intracluster photoelectron scattering are most important for changes in the photoelectron main line and explain the appearance of additional peaks. A comparison of our results to earlier work on bulk condensed Ar and Ar thin films is given. Evidence for a deviation of the photoionization cross sections for clusters from the atomic ones has not been found.

Hergenhahn, Uwe; Barth, Silko; Ulrich, Volker; Mucke, Melanie; Joshi, Sanjeev; Lischke, Toralf; Lindblad, Andreas; Rander, Torbjoern; Oehrwall, Gunnar; Bjoerneholm, Olle [Max-Planck-Institut fuer Plasmaphysik, EURATOM Association, Boltzmannstr. 2, 85748 Garching (Germany); Department of Physics and Materials Science, Uppsala University, P.O. Box 530, SE-751 21 Uppsala (Sweden)

2009-04-15

309

Optical properties of semiconductor nanocrystals with degenerate valence band  

NASA Astrophysics Data System (ADS)

The energy spectrum and wave functions of holes in CdSe and CdS nanocrystals have been calculated. It is shown that in CdS nanocrystals the lowest quantum size level (QSL) of holes has p-type symmetry and optical transitions between this state and the lowest QSL of electrons are forbidden. The radiative lifetimes in CdSe nanocrystals are estimated to be of the order of 23 ns. The real structure of the valence bands have been shown to increase the electron-hole pair - polar phonons coupling with decreasing nanocrystal size.

Efros, Al. L.

310

Visionlearning: Chemical Bonding  

NSDL National Science Digital Library

This digital learning module provides an easily-understood overview of chemical bonding for users with little formal background in chemistry or physics. It explores ionic bonding through the example of sodium (an alkali metal) reacting with chlorine gas to produce common table salt. A concept simulation further illustrates the process.

Carpi, Anthony

2011-07-12

311

Halogen bonding: Recent advances  

Microsoft Academic Search

Halogen bonding (XB), as a directional interaction between covalently bound halogen atoms (XB donor) and Lewis bases (A, XB acceptor), has been recently intensively investigated as a powerful tool in crystal engineering. After a short review on the origin and general features of halogen bonding, current developments towards (i) the elaboration of three-dimensional networks, (ii) the interaction with anionic XB

Marc Fourmigué

2009-01-01

312

The Sibling Bond.  

ERIC Educational Resources Information Center

|The relationships among brothers and sisters are infinitely varied, but whatever their characteristics, these bonds last throughout life. This book examines the sibling relationship as a distinctive emotional, passionate, painful, and solacing power. Chapter 1, "Unraveling the Sibling Bond," addresses research on siblings and development of the…

Bank, Stephen P.; Kahn, Michael D.

313

The dissociative bond.  

PubMed

Dissociation leaves a psychic void and a lingering sense of psychic absence. How do 2 people bond while they are both suffering from dissociation? The author explores the notion of a dissociative bond that occurs in the aftermath of trauma--a bond that holds at its core an understanding and shared detachment from the self. Such a bond is confined to unspoken terms that are established in the relational unconscious. The author proposes understanding the dissociative bond as a transitional space that may not lead to full integration of dissociated knowledge yet offers some healing. This is exemplified by R. Prince's (2009) clinical case study. A relational perspective is adopted, focusing on the intersubjective aspects of a dyadic relationship. In the dissociative bond, recognition of the need to experience mutual dissociation can accommodate a psychic state that yearns for relationship when the psyche cannot fully confront past wounds. Such a bond speaks to the need to reestablish a sense of human relatedness and connection when both parties in the relationship suffer from disconnection. This bond is bound to a silence that becomes both a means of protection against the horror of traumatic memory and a way to convey unspoken gestures toward the other. PMID:23282044

Gordon, Nirit

2013-01-01

314

Planning Successful Bond Campaigns.  

ERIC Educational Resources Information Center

|This document contains specific recommendations for conducting bond campaigns. It outlines the three major considerations of any bond campaign: (1) committee organization and appointment; (2) time lines; and (3) getting out the vote. The publication focuses on the need for total community involvement and outlines some of the components for…

North Carolina State Dept. of Public Instruction, Raleigh. Div. of School Support.

315

Theory and experiment on laser-enabled inner-valence Auger decay of rare-gas atoms  

SciTech Connect

In rare-gas atoms, an inner-valence shell ns hole cannot be filled by Auger decay because of an energy deficiency. We show theoretically and experimentally that by adding a moderately intense infrared laser, Auger decay is possible with decay rates increasing dramatically for laser intensities {>=}10{sup 13} W/cm{sup 2}. For Xe atoms, the simulated laser-enabled Auger decay yields are comparable with the experimental one, while for Ar atoms, the simulated ones are much smaller. We attribute the discrepancies to screening effects of the photoelectron. Laser-enabled Auger decay is of fundamental importance for understanding attosecond science, and is also important for experimental applications in ultrafast atomic, molecular, and materials dynamics using x rays. More importantly it may provide a way to control the Auger decay time and selectively break chemical bonds of molecules using a control infrared laser field.

Tong, X. M. [Institute of Materials Science, Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573 (Japan); Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577 (Japan); Ranitovic, P.; Hogle, C. W.; Murnane, M. M.; Kapteyn, H. C. [JILA and Department of Physics, University of Colorado and NIST, Boulder, Colorado 80309-0440 (United States); Toshima, N. [Institute of Materials Science, Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573 (Japan)

2011-07-15

316

Bond-quality characterization of silicon-glass anodic bonding  

Microsoft Academic Search

A simple testing method is presented that allows the comparison of the bond quality for anodically bonded wafers. An array of parallel metal lines of predetermined thickness is formed on a glass wafer. The estimation of the bond quality can be performed by visual inspection after the bonding. This method enables comparison of the anodic-bonding process performance for different glasses,

Svetlana Tatic-Lucic; John Ames; Bill Boardman; David McIntyre; Paul Jaramillo; Larry Starr; Myoungho Lim

1997-01-01

317

Wood Bond Testing  

NASA Astrophysics Data System (ADS)

A joint development program between Hartford Steam Boiler Inspection Technologies and The Weyerhaeuser Company resulted in an internal bond analyzer (IBA), a device which combines ultrasonics with acoustic emission testing techniques. It is actually a spinoff from a spinoff, stemming from a NASA Lewis invented acousto-ultrasonic technique that became a system for testing bond strength of composite materials. Hartford's parent company, Acoustic Emission Technology Corporation (AET) refined and commercialized the technology. The IBA builds on the original system and incorporates on-line process control systems. The IBA determines bond strength by measuring changes in pulsar ultrasonic waves injected into a board. Analysis of the wave determines the average internal bond strength for the panel. Results are displayed immediately. Using the system, a mill operator can adjust resin/wood proportion, reduce setup time and waste, produce internal bonds of a consistent quality and automatically mark deficient products.

1989-01-01

318

Pressure-Induced Valence Transition in Antiferromagnet EuRh2Si2  

NASA Astrophysics Data System (ADS)

Considering the unique properties of EuRh2Si2 from the viewpoint of the Eu valence, we have examined its physical properties under external pressure. At ambient pressure, EuRh2Si2 is an antiferromagnet with a Néel temperature TN of 25 K, and the Eu ion is in the divalent state. The application of pressure up to 0.84 GPa slightly shifts TN toward higher values. Under pressures higher than 1.00 GPa, an abrupt first-order valence transition emerges simultaneously with the disappearance of antiferromagnetism. For P=1.17 GPa, the valence change associated with valence transition is roughly estimated to be ˜0.19 from the thermal expansion anomaly. The valence transition temperature Tv increases rapidly with increasing pressure. The temperature--pressure phase diagram of EuRh2Si2 is very similar to those of the other systems showing pressure-induced valence transition.

Mitsuda, Akihiro; Hamano, Suguru; Araoka, Nobutaka; Yayama, Hideki; Wada, Hirofumi

2012-02-01

319

Developmental changes in effects of risk and valence on adolescent decision-making?  

PubMed Central

Recent research on risky decision-making in adults has shown that both the risk in potential outcomes and their valence (i.e., whether those outcomes involve gains or losses) exert dissociable influences on decisions. We hypothesised that the influences of these two crucial decision variables (risk and valence) on decision-making would vary developmentally during adolescence. We adapted a risk-taking paradigm that provides precise metrics for the impacts of risk and valence. Decision-making in 11–16 year old female adolescents was influenced by both risk and valence. However, their influences assumed different developmental patterns: the impact of valence diminished with age, while there was no developmental change in the impact of risk. These different developmental patterns provide further evidence that risk and valence are fundamentally dissociable constructs and have different influences on decisions across adolescence.

Wolf, Laura K.; Wright, Nicholas D.; Kilford, Emma J.; Dolan, Raymond J.; Blakemore, Sarah-Jayne

2013-01-01

320

A time-based account of the perception of odor objects and valences.  

PubMed

Is human odor perception guided by memory or emotion? Object-centered accounts predict that recognition of unique odor qualities precedes valence decoding. Valence-centered accounts predict the opposite: that stimulus-driven valence responses precede and guide identification. In a speeded response time study, participants smelled paired odors, presented sequentially, and indicated whether the second odor in each pair belonged to the same category as the first (object evaluation task) or whether the second odor was more pleasant than the first (valence evaluation task). Object evaluation was faster and more accurate than valence evaluation. In a complementary experiment, participants performed an identification task, in which they indicated whether an odor matched the previously presented word label. Responses were quicker for odors preceded by semantically matching, rather than nonmatching, word labels, but results showed no evidence of interference from valence on nonmatching trials. These results are in accordance with object-centered accounts of odor perception. PMID:22961773

Olofsson, Jonas K; Bowman, Nicholas E; Khatibi, Katherine; Gottfried, Jay A

2012-09-06

321

A Time-Based Account of the Perception of Odor Objects and Valences  

PubMed Central

Is human odor perception guided by memory or emotion? Object-centered accounts predict that recognition of unique odor qualities precedes valence decoding. Valence-centered accounts predict the opposite: that stimulus-driven valence responses precede and guide identification. In a speeded response time study, participants smelled paired odors, presented sequentially, and indicated whether the second odor in each pair belonged to the same category as the first (object evaluation task) or whether the second odor was more pleasant than the first (valence evaluation task). Object evaluation was faster and more accurate than valence evaluation. In a complementary experiment, participants performed an identification task, in which they indicated whether an odor matched the previously presented word label. Responses were quicker for odors preceded by semantically matching, rather than nonmatching, word labels, but results showed no evidence of interference from valence on nonmatching trials. These results are in accordance with object-centered accounts of odor perception.

Olofsson, Jonas K.; Bowman, Nicholas E.; Khatibi, Katherine; Gottfried, Jay A.

2013-01-01

322

Perfluoro effects in the occupied and virtual valence orbitals of hexafluorobenzene  

NASA Astrophysics Data System (ADS)

The complete valence shell photoelectron spectrum of hexafluorobenzene has been recorded with synchrotron radiation and the observed structure has been interpreted using ab initio ionization energies and relative spectral intensities. The theoretical predictions for the single-hole ionic states due to outer valence shell ionization agree satisfactorily with the experimental results. Ionization from the inner valence, essential F 2s, orbitals is strongly influenced by many-body effects and the intensity is spread amongst numerous satellites. Photoelectron angular distributions and branching ratios have been determined both experimentally and theoretically, and demonstrate that shape resonances affect the valence shell photoionization dynamics. Some of the shape resonances have been associated with virtual valence orbitals. An assessment of the perfluoro effect on the occupied and virtual valence orbitals of hexafluorobenzene has been carried out by comparing the present results for C6F6 with similar data for C6H6.

Decleva, P.; Stener, M.; Holland, D. M. P.; Potts, A. W.; Karlsson, L.

2007-07-01

323

The Pursuit of Happiness in Music: Retrieving Valence with Contextual Music Descriptors  

Microsoft Academic Search

In the study of music emotions, Valence is usually referred to as one of the dimensions of the circumplex model of emotions\\u000a that describes music appraisal of happiness, whose scale goes from sad to happy. Nevertheless, related literature shows that\\u000a Valence is known as being particularly difficult to be predicted by a computational model. As Valence is a contextual music

José Fornari; Tuomas Eerola

2008-01-01

324

Ligand-hole localization in oxides with unusual valence Fe  

PubMed Central

Unusual high-valence states of iron are stabilized in a few oxides. A-site-ordered perovskite-structure oxides contain such iron cations and exhibit distinct electronic behaviors at low temperatures, e.g. charge disproportionation (4Fe4+ ? 2Fe3+ + 2Fe5+) in CaCu3Fe4O12 and intersite charge transfer (3Cu2+ + 4Fe3.75+ ? 3Cu3+ + 4Fe3+) in LaCu3Fe4O12. Here we report the synthesis of solid solutions of CaCu3Fe4O12 and LaCu3Fe4O12 and explain how the instabilities of their unusual valence states of iron are relieved. Although these behaviors look completely different from each other in simple ionic models, they can both be explained by the localization of ligand holes, which are produced by the strong hybridization of iron d and oxygen p orbitals in oxides. The localization behavior in the charge disproportionation of CaCu3Fe4O12 is regarded as charge ordering of the ligand holes, and that in the intersite charge transfer of LaCu3Fe4O12 is regarded as a Mott transition of the ligand holes.

Chen, Wei-Tin; Saito, Takashi; Hayashi, Naoaki; Takano, Mikio; Shimakawa, Yuichi

2012-01-01

325

X-ray absorption spectra theory in variable valency compounds  

NASA Astrophysics Data System (ADS)

The theory of X-ray absorption and emission at electron transitions from the inner 2p, 4d shells is developed for the systems with intermediate valency when the coupling energy of the f level turns out to be comparable with Fermi energy and the wavefunction of the ground state is a quantum superposition of states of different configurations of f electrons, ?nf...4fn> + ?1 - nf...4fn-1s> with 4f level average occupation number nf. It is shown that due to different screening of a localized hole by electron in various electron configurations 4fn and 4fn-1s, the absorption spectrum contains two well resolved sharp peaks with relative intensities 1 - nf and nf. The effect of the hole finite lifetime results in partial smearing of the spectrum and gives rise to two Lorentz maxima observed experimentally in the absorption LIII, MIV, MV spectra near the absorption edge (XANES) in a whole series of compounds with intermediate valency on the basis of Ce, Sm, Tm, Eu. The theory also explains qualitatively correctly the character of variation of SmSe absorption spectrum under pressure.

Kocharyan, A. N.

1987-01-01

326

Mixed valence of iron in minerals with cation clusters  

NASA Astrophysics Data System (ADS)

The valence and distribution of iron in vivianite, lazulite, babingtonite, rockbridgeite, acmite, aegirine-augite, hedenbergite, and ilvaite were studied with optical and Mössbauer spectroscopy. Optically activated intervalence charge transfer between Fe2+ and Fe3+ in neighboring sites through common edges or faces is observed in all these minerals irrespective of the polymerization of the iron-oxygen polyhedra ranging from finite clusters to infinite structural units. However, a distinct decrease occurs in the energy of the corresponding optical absorption band with increasing number of Fe2+ and Fe3+ ions involved in the charge transfer process. Thermally activated electron delocalization between Fe2+ and Fe3+ occurs only if Fe2+ and Fe3+ occupy crystallographically equivalent or geometrically very similar neighboring sites which share common edges to form extended structural units such as the ribbon in ilvaite. If the Fe-O polyhedra form finite clusters of two, three, or four polyhedra (e.g., in vivianite, lazulite, and babingtonite, respectively) no thermally-activated mixed-valence states of iron are observed. In aegirine, extended regions of the M1 chain are statistically occupied by Fe2+ and Fe3+ giving rise to thermally-activated electron delocalization in addition to the intervalence band in the optical absorption spectrum. The intensity of the optical intervalence absorption has been measured in a number of systems: ? values range from 60 to 210.

Amthauer, Georg; Rossman, George R.

1984-06-01

327

An ecological valence theory of human color preference  

PubMed Central

Color preference is an important aspect of visual experience, but little is known about why people in general like some colors more than others. Previous research suggested explanations based on biological adaptations [Hurlbert AC, Ling YL (2007) Curr Biol 17:623–625] and color-emotions [Ou L-C, Luo MR, Woodcock A, Wright A (2004) Color Res Appl 29:381–389]. In this article we articulate an ecological valence theory in which color preferences arise from people’s average affective responses to color-associated objects. An empirical test provides strong support for this theory: People like colors strongly associated with objects they like (e.g., blues with clear skies and clean water) and dislike colors strongly associated with objects they dislike (e.g., browns with feces and rotten food). Relative to alternative theories, the ecological valence theory both fits the data better (even with fewer free parameters) and provides a more plausible, comprehensive causal explanation of color preferences.

Palmer, Stephen E.; Schloss, Karen B.

2010-01-01

328

Recoil effects in valence band photoemission of organic solids.  

PubMed

Recoil effects in valence band X-ray photoelectron spectroscopy (XPS) are studied for both abb-trifluorostyrene and styrene molecular crystal systems. The gradual changes of XPS spectra excited by several photon energies are theoretically investigated within the tight-binding approximation and harmonic approximation of lattice vibrations and have been explained in terms of not only atomic mass but also atomic orbital (AO) population. The recoil effect of valence band photoemission strongly depends on the population and partial photoionization cross section (PICS) of AOs as well as the masses of composite atoms. In abb-trifluorostyrene F 2p dominant bands show the recoil shift close to free F atom recoil shift, and C 2s dominant bands show that to free C atom recoil shift, whereas the mixed bands of C and F give rise to the peak asymmetries due to their different recoil shifts. For these systems, hydrogen contribution is negligibly small which is in contrast to our previous results for the crystals composed of small organic molecules. We also discuss some potential uses of the recoil shifts for these systems. PMID:23441983

Shang, Ming-Hui; Fujikawa, Takashi; Ueno, Nobuo

2013-03-18

329

27 CFR 24.147 - Operations bond or unit bond.  

Code of Federal Regulations, 2013 CFR

...TREASURY ALCOHOL WINE Establishment and Operations Bonds and Consents of Surety § 24.147 Operations bond or unit bond. Notwithstanding the provisions of § 24.146, each person intending to commence or to continue business...

2013-04-01

330

Structural evolution and valence electron-state change during ultra thin silicon-oxide growth  

NASA Astrophysics Data System (ADS)

We have studied valence electron-state changes of Si during initial oxidation of Si(111) clean surface, HF-treated Si(001) and Si(111) surfaces by Auger valence electron spectroscopy (AVES). The results showed that the valence electron-state changes during initial oxidation were sensitively reflected in Si[2s,2p,V] (V=3s,3p) AVES spectra and that they depended on both initial surface treatment and surface orientation. The local valence electron-states, local density of states in other words, showed the characteristic-structure evolution depending on the initial surface treatment and surface orientation.

Shimizu, A.; Abe, S.; Nakayama, H.; Nishino, T.; Iida, S.

2000-06-01

331

Chapter 19 Characteristics of Chemical Bond in Perovskite-Type Hydrides  

Microsoft Academic Search

The electronic structure of typical perovskite-type hydrides, MMgH3 (M=Na, K, Rb), CaNiH3 and SrPdH3, are simulated to understand the nature of the chemical bond between constituent ions in them using the DV-X? molecular orbital method. For MMgH3, it is found that the valence band consists mainly of the H 1s and Mg 3s, 3p components, and the M s, p

Yoshifumi Shinzato; Kenji Komiya; Yoshitaka Takahashi; Hiroshi Yukawa; Masahiko Morinaga; Shinichi Orimo

2008-01-01

332

Real-time study of the modification of the peptide bond by atomic calcium.  

PubMed

Strong chemical interaction between bacterial surface protein layers and calcium atoms deposited in situ on top was revealed by means of photoemission spectroscopy. The interaction appears to mainly happen at the oxygen site of the peptide bonds and involves a large charge transfer from Ca 4s states into the peptide backbone. Chemical kinetics of this reaction was characterized using time-dependent valence band photoemission, and the reaction rate constant was determined. PMID:21338139

Kummer, Kurt; Vyalikh, Denis V; Blüher, Anja; Sivkov, Victor; Maslyuk, Volodymyr V; Bredow, Thomas; Mertig, Ingrid; Mertig, Michael; Molodtsov, Serguei L

2011-02-22

333

Theoretical analysis of the charge-storage states in diphenylpolyenes with one to seven double bonds  

Microsoft Academic Search

The semiempirical Austin Model 1 (AM1) and the nonempirical pseudopotential valence effective Hamiltonian (VEH) methods have been applied for the investigation of the doping-induced electronic and geometrical changes in a series of conjugated molecules. The series consists of diphenylpolyenes with an even number of carbons and extends from stilbene to diphenyltetradecaheptaene, i.e., one to seven double bonds in the polyene

J. L. Bre´das

1994-01-01

334

Dielectric Methods of Studying the Chemical Bond and the Concept of Electronegativity  

NASA Astrophysics Data System (ADS)

The history and contemporary theories of the polarisation of molecules and crystals are considered and a systematic survey is given of dipole moments and bond ionicities in molecular chemical compounds and also of the effective charges of atoms in crystals. An interpretation of these results is given from the standpoint of the electronegativity concept. Views concerning the effective valencies and coordination numbers of atoms in crystals are considered. Bibliography of 207 references.

Batsanov, Stepan S.

1982-07-01

335

Identification of Ectonucleotide Pyrophosphatase/Phosphodiesterase 3 (ENPP3) as a Regulator of N-Acetylglucosaminyltransferase GnT-IX (GnT-Vb).  

PubMed

Our previous studies on a ?1,6-N-acetylglucosaminyltransferase, GnT-IX (GnT-Vb), a homolog of GnT-V, indicated that the enzyme has a broad GlcNAc transfer activity toward N-linked and O-mannosyl glycan core structures and that its brain-specific gene expression is regulated by epigenetic histone modifications. In this study, we demonstrate the existence of an endogenous inhibitory factor for GnT-IX that functions as a key regulator for GnT-IX enzymatic activity in Neuro2a (N2a) cells. We purified this factor from N2a cells and found that it is identical to ectonucleotide pyrophosphatase/phosphodiesterase 3 (ENPP3), as evidenced by mass spectrometry and by the knockdown and overexpression of ENPP3 in cultured cells. Kinetic analyses revealed that the mechanism responsible for the inhibition of GnT-IX caused by ENPP3 is the ENPP3-mediated hydrolysis of the nucleotide sugar donor substrate, UDP-GlcNAc, with the resulting generation of UMP, a potent and competitive inhibitor of GnT-IX. Indeed, ENPP3 knockdown cells had significantly increased levels of intracellular nucleotide sugars and displayed changes in the total cellular glycosylation profile. In addition to chaperones or other known regulators of glycosyltransferases, the ENPP3-mediated hydrolysis of nucleotide sugars would have widespread and significant impacts on glycosyltransferase activities and would be responsible for altering the total cellular glycosylation profile and modulating cellular functions. PMID:23960081

Korekane, Hiroaki; Park, Jong Yi; Matsumoto, Akio; Nakajima, Kazuki; Takamatsu, Shinji; Ohtsubo, Kazuaki; Miyamoto, Yasuhide; Hanashima, Shinya; Kanekiyo, Kenji; Kitazume, Shinobu; Yamaguchi, Yoshiki; Matsuo, Ichiro; Taniguchi, Naoyuki

2013-08-19

336

Isolation of a mixed valence diiron hydride: evidence for a spectator hydride in hydrogen evolution catalysis.  

PubMed

The mixed-valence diiron hydrido complex (?-H)Fe2(pdt)(CO)2(dppv)2 ([H1](0), where pdt =1,3-propanedithiolate and dppv = cis-1,2-C2H2(PPh2)2), was generated by reduction of the differous hydride [H1](+) using decamethylcobaltocene. Crystallographic analysis shows that [H1](0) retains the stereochemistry of its precursor, where one dppv ligand spans two basal sites and the other spans apical and basal positions. The Fe---Fe bond elongates to 2.80 from 2.66 Å, but the Fe-P bonds only change subtly. Although the Fe-H distances are indistinguishable in the precursor, they differ by 0.2 Å in [H1](0). The X-band electron paramagnetic resonance (EPR) spectrum reveals the presence of two stereoisomers, the one characterized crystallographically and a contribution of about 10% from a second symmetrical (sym) isomer wherein both dppv ligands occupy apical-basal sites. The unsymmetrical (unsym) arrangement of the dppv ligands is reflected in the values of A((31)P), which range from 31 MHz for the basal phosphines to 284 MHz for the apical phosphine. Density functional theory calculations were employed to rationalize the electronic structure of [H1](0) and to facilitate spectral simulation and assignment of EPR parameters including (1)H and (31)P hyperfine couplings. The EPR spectra of [H1](0) and [D1](0) demonstrate that the singly occupied molecular orbital is primarily localized on the Fe center with the longer bond to H, that is, Fe(II)-H···Fe(I). The coupling to the hydride is A((1)H) = 55 and 74 MHz for unsym- amd sym-[H1](0), respectively. Treatment of [H1](0) with H(+) gives 0.5 equiv of H2 and [H1](+). Reduction of D(+) affords D2, leaving the hydride ligand intact. These experiments demonstrate that the bridging hydride ligand in this complex is a spectator in the hydrogen evolution reaction. PMID:23383865

Wang, Wenguang; Nilges, Mark J; Rauchfuss, Thomas B; Stein, Matthias

2013-02-21

337

29 CFR 2580.412-20 - Use of existing bonds, separate bonds and additional bonding.  

Code of Federal Regulations, 2013 CFR

...long as a particular bond meets the requirements...this part as to the persons required to be bonded...c) Use of separate bonds. The choice of whether persons required to be bonded...separately or under the same bond, whether given...

2013-07-01

338

Mixed-valence biferrocenes: Pronounced anion dependence of valence detrapping and effects of an asymmetric crystal lattice  

SciTech Connect

The effect of changing the anion from I{sub 3}{sup {minus}} to either PF{sub 6}{sup {minus}} or SbF{sub 6}{sup {minus}} upon the rate of intramolecular electron transfer in salts of the mixed-valence 1{prime},1{prime}{double prime}-dibenzylbiferrocenium cation is investigated. Single-crystal X-ray structures are presented for 1{prime},1{prime}{double prime}-dibenzylbiferrocene (1), 1{prime},1{prime}{double prime}-dibenzylbiferrocenium hexafluorophosphate (2), and 1{prime},1{prime}{double prime}-dibenzylbiferrocenium hexafluoroantimonate (3). A center of symmetry (planar fulvalenide ligand) and a trans conformation characterize the Fe{sub 2}{sup II} molecule in 1. The PF{sub 6}{sup {minus}} anion was found to be disordered in two positions, one with an occupancy of 64% and the other 36%. The packing in complex 2 is that of layers of mixed-valence cations with the small PF{sub 6}{sup {minus}} anions sandwiched between the layers. The SbF{sub 6}{sup {minus}} anion in complex 3 was not found to be disordered at either temperature; however, at 298 K the thermal parameters for this anion are large.

Webb, R.J. (Univ. of California at San Diego, La Jolla (USA) Univ. of Illinois, Urbana (USA)); Geib, S.J.; Staley, D.L.; Rheingold, A.L. (Univ. of Delaware, Newark (USA)); Hendrickson, D.N. (Univ. of California at San Diego, La Jolla (USA))

1990-06-20

339

Correlation among electronegativity, cation polarizability, optical basicity and single bond strength of simple oxides  

NASA Astrophysics Data System (ADS)

A suitable relationship between free-cation polarizability and electronegativity of elements in different valence states and with the most common coordination numbers has been searched on the basis of the similarity in physical nature of both quantities. In general, the cation polarizability increases with decreasing element electronegativity. A systematic periodic change in the polarizability against the electronegativity has been observed in the isoelectronic series. It has been found that generally the optical basicity increases and the single bond strength of simple oxides decreases with decreasing the electronegativity. The observed trends have been discussed on the basis of electron donation ability of the oxide ions and type of chemical bonding in simple oxides.

Dimitrov, Vesselin; Komatsu, Takayuki

2012-12-01

340

Bonding aerogels with polyurethanes  

SciTech Connect

Aerogels, porous silica glasses with ultra-fine cell size (30nm), are made by a solution gelation (sol-gel) process. The resulting gel is critical point dried to densities from 0.15--0.60 g/cc. This material is machinable, homogeneous, transparent, coatable and bondable. To bond aerogel an adhesive should have long cure time, no attack on the aerogel structure, and high strength. Several epoxies and urethanes were examined to determine if they satisfied these conditions. Bond strengths above 13 psi were found with double bubble and DP-110 epoxies and XI-208/ODA-1000 and Castall U-2630 urethanes. Hardman Kalex Tough Stuff'' A-85 hardness urethane gave 18 psi bond strength. Hardman A-85, Tuff-Stuff'' was selected for further evaluation because it produced bond strengths comparable to the adherend cohesive strength. 5 refs., 2 figs.

Matthews, F.M.; Hoffman, D.M.

1989-11-01

341

Adhesive for composite bonding.  

National Technical Information Service (NTIS)

Adhesive bonding is a viable option for structural joining of carbon fiber reinforced epoxy composites. Recent examples from laboratory programs include a composite tube joined to a flared composite collar (skirt) to provide a means for mechanical attachm...

R. E. Lyon C. M. Walkup J. T. Matthews.

1989-01-01

342

Bonding Silicones with Epoxies.  

National Technical Information Service (NTIS)

It is shown that silicones, both room temperature vulcanizing (RTV) and millable rubber (press cured) can be successfully bonded to other materials using plasma treatment and epoxy adhesives. The plasma treatment using dry air atmosphere increases the sur...

J. S. Tira

1980-01-01

343

Halogen bonding: the ?-hole  

Microsoft Academic Search

Halogen bonding refers to the non-covalent interactions of halogen atoms X in some molecules, RX, with negative sites on others.\\u000a It can be explained by the presence of a region of positive electrostatic potential, the ?-hole, on the outermost portion\\u000a of the halogen’s surface, centered on the R–X axis. We have carried out a natural bond order B3LYP analysis of

Timothy Clark; Matthias Hennemann; Jane S. Murray; Peter Politzer

2007-01-01

344

The essential role of charge-shift bonding in hypervalent prototype XeF2  

NASA Astrophysics Data System (ADS)

Hypervalency in XeF2 and isoelectronic complexes is generally understood in terms of the Rundle-Pimentel model (which invokes a three-centre/four-electron molecular system) or its valence bond version as proposed by Coulson, which replaced the old expanded octet model of Pauling. However, the Rundle-Pimentel model is not always successful in describing such complexes and has been shown to be oversimplified. Here using ab initio valence bond theory coupled to quantum Monte Carlo methods, we show that the Rundle-Pimentel model is insufficient by itself in accounting for the great stability of XeF2, and that charge-shift bonding, wherein the large covalent-ionic interaction energy has the dominant role, is a major stabilizing factor. The energetic contribution of the old expanded octet model is also quantified and shown to be marginal. Generalizing to isoelectronic systems such as ClF3, SF4, PCl5 and others, it is suggested that charge-shift bonding is necessary, in association with the Rundle-Pimentel model, for hypervalent analogues of XeF2 to be strongly bonded.

Braïda, Benoît; Hiberty, Philippe C.

2013-05-01

345

The essential role of charge-shift bonding in hypervalent prototype XeF?.  

PubMed

Hypervalency in XeF? and isoelectronic complexes is generally understood in terms of the Rundle-Pimentel model (which invokes a three-centre/four-electron molecular system) or its valence bond version as proposed by Coulson, which replaced the old expanded octet model of Pauling. However, the Rundle-Pimentel model is not always successful in describing such complexes and has been shown to be oversimplified. Here using ab initio valence bond theory coupled to quantum Monte Carlo methods, we show that the Rundle-Pimentel model is insufficient by itself in accounting for the great stability of XeF?, and that charge-shift bonding, wherein the large covalent-ionic interaction energy has the dominant role, is a major stabilizing factor. The energetic contribution of the old expanded octet model is also quantified and shown to be marginal. Generalizing to isoelectronic systems such as ClF?, SF?, PCl? and others, it is suggested that charge-shift bonding is necessary, in association with the Rundle-Pimentel model, for hypervalent analogues of XeF? to be strongly bonded. PMID:23609093

Braïda, Benoît; Hiberty, Philippe C

2013-04-07

346

Valence-shell photoionization of chlorinelike Ar{sup +} ions  

SciTech Connect

Absolute cross-section measurements for valence-shell photoionization of Ar{sup +} ions are reported for photon energies ranging from 27.4 to 60.0 eV. The data, taken by merging beams of ions and synchrotron radiation at a photon energy resolution of 10 meV, indicate that the primary ion beam was a statistically weighted mixture of the {sup 2}P{sub 3/2}{sup o} ground state and the {sup 2}P{sub 1/2}{sup o} metastable state of Ar{sup +}. Photoionization of this Cl-like ion is characterized by multiple Rydberg series of autoionizing resonances superimposed on a direct photoionization continuum. Observed resonance line shapes indicate interference between indirect and direct photoionization channels. Resonance features are spectroscopically assigned and their energies and quantum defects are tabulated. The measurements are satisfactorily reproduced by theoretical calculations based on an intermediate coupling semirelativistic Breit-Pauli approximation.

Covington, A. M.; Aguilar, A.; Covington, I. R.; Hinojosa, G.; Shirley, C. A.; Phaneuf, R. A.; Alvarez, I.; Cisneros, C.; Dominguez-Lopez, I.; Sant'Anna, M. M.; Schlachter, A. S.; Ballance, C. P.; McLaughlin, B. M. [Department of Physics, MS 220, University of Nevada, Reno, Nevada 89557-0058 (United States); Instituto de Ciencias Fisicas, Universidad Nacional Autonoma de Mexico, Apartado Postal 6-96, Cuernavaca 62131, Morelos (Mexico); Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720 (United States); Department of Physics, Auburn University, Auburn, Alabama 36840 (United States); Institute for Theoretical Atomic and Molecular Physics, Harvard Smithsonian Center for Astrophysics, 60 Garden Street, MS-14, Cambridge, Massachusetts 02138 (United States)

2011-07-15

347

Interacting Rydberg and valence states in radicals and molecules  

NASA Astrophysics Data System (ADS)

This review discusses low-lying (n = 3) Rydberg electronic states of molecules and radicals, in particular those that result in mixed configurations and participate in non-adiabatic interactions. Rydberg-valence interactions are ubiquitous in molecules and radicals and have important effects on potential energy surface shapes, spectroscopy, and dissociation dynamics. The review emphasises selected properties that are affected by these interactions and illustrates them with several examples, mostly involving free radicals, in which collaboration between experimental and theoretical investigations has been crucial for understanding. Specifically, the cases of substituted methyl, vinyl, and hydroxyalkyl radicals are described, as well as Rydberg states of diazomethane and the ethyl radical. The issue of triple conical intersections is also briefly discussed.

Reisler, Hanna; Krylov, Anna I.

348

Isotope-shift calculations for atoms with one valence electron  

SciTech Connect

This work presents a method for the ab initio calculation of isotope shift in atoms and ions with one valence electron above closed shells. As a zero approximation, we use relativistic Hartree-Fock and then calculate correlation corrections. The main motivation for developing the method comes from the need to analyze whether different isotope abundances in early universe can contribute to the observed anomalies in quasar absorption spectra. The current best explanation for these anomalies is the assumption that the fine-structure constant {alpha} was smaller at early epoch. We test the isotope-shift method by comparing the calculated and experimental isotope shift for the alkali-metal and alkali-metal-like atoms Na, Mg II, K, Ca II and Ba II. The agreement is found to be good. We then calculate the isotope shift for some astronomically relevant transitions in Si II and Si IV, Mg II, Zn II, and Ge II.

Berengut, J. C.; Dzuba, V. A.; Flambaum, V. V. [School of Physics, University of New South Wales, Sydney 2052, (Australia)

2003-08-01

349

Theory of chemical bonds in metalloenzymes IV: Hybrid-DFT study of Rieske-type [2Fe bond 2S] clusters  

NASA Astrophysics Data System (ADS)

The Rieske-type [2Fe bond 2S] cores of electron-transfer (ET) proteins in the mitochondrial respiratory chain have unusual properties, such as redox potentials and spectroscopy. In this study, part IV of a series, the inherent molecular structures and characteristic electronic structures of the Rieske-type [2Fe bond 2S] clusters are investigated using broken-symmetry hybrid density functional theory (BS-HDFT). Geometry optimizations for the oxidized and reduced states were performed and their characteristic vibrational modes are assigned. Magnetic properties are investigated using model Hamiltonians to describe the electron delocalization and the unsymmetric property. The parameters of the model Hamiltonian, such as exchange coupling J, valence delocalization B, and potential energy difference ?, are evaluated from the BS-HDFT calculations. The valence localization and excitation energy (?E) of the Rieske-type [2Fe bond 2S] cluster are discussed. The chemical bond nature is characterized by chemical indices from natural orbital analysis. Our theoretical results are reasonably consistent with experimental results.

Shoji, Mitsuo; Koizumi, Kenichi; Kitagawa, Yasutaka; Yamanaka, Shusuke; Okumura, Mitsutaka; Yamaguchi, Kizashi

350

The unique bonding characteristics of beryllium and the Group IIA metals  

NASA Astrophysics Data System (ADS)

Having closed valence sub-shells, the alkaline earth atoms participate in covalent bonding via orbital hybridization and exchange interactions, with additional contributions from dispersion interactions. Starting from a closed ns2 configuration imparts different characteristics to the chemistry of this group, as compared to metals that have open-shell atomic ground states. Theoretical studies of the bonding of the Group IIA metals have been pursued for many years, and they are known to be challenging for ab initio electronic structure methods. The bonding motifs have been examined, and the differences between beryllium and the remainder of the group explored. Experimental studies that probe the bonding, particularly for beryllium, have lagged behind the theoretical work. In the present Letter we describe our recent spectroscopic and theoretical investigations of simple beryllium compounds, and discuss these results in terms of their relationship to the properties of the heavier Group IIA elements.

Heaven, Michael C.; Bondybey, Vladimir E.; Merritt, Jeremy M.; Kaledin, Alexey L.

2011-04-01

351

Linguistic Types and the Valence of Operators in Applicative Universal Grammar.  

ERIC Educational Resources Information Center

The relationship between linguistic types and the valence of operators on the genotype level of Applicative Universal Grammar (AUG) is examined. Assuming that the "t" and "s" types may be treated as zero-place operators, a relationship is found between the valence of an operator and its genotype, which explains the difference between types…

Sypniewski, Bernard Paul

352

The right-hemisphere and valence hypotheses: could they both be right (and sometimes left)?  

Microsoft Academic Search

The two halves of the brain are believed to play different roles in emotional processing, but the specific contribution of each hemisphere continues to be debated. The right-hemisphere hypothesis suggests that the right cerebrum is dominant for processing all emotions regardless of affective valence, whereas the valence specific hypothesis posits that the left hemisphere is specialized for processing positive affect

William D. S. Killgore; Deborah A. Yurgelun-Todd

2007-01-01

353

Corporate Social Responsibility Priming and Valence of CSR Framing on CSR Judgments  

Microsoft Academic Search

This study tested the effects of corporate social responsibility (CSR) priming (without CSR priming vs. CSR priming) and valence of CSR framing (positive framing vs. negative framing) on how participants judged a target corporation's CSR practices and formed attitude toward the target corporation. Results suggested that the main effects of CSR priming and valence of CSR framing affected participants' judgments

Alex Wang; Ronald B. Anderson

2008-01-01

354

Valence isomerization of cyclohepta-1,3,5-triene and its heteroelement analogues  

PubMed Central

Summary The valence isomerization of the all-carbon and heteroelement analogues of cyclohepta-1,3,5-triene into the corresponding bicyclo[4.1.0]hepta-2,4-dienes is reviewed to show the impact of the heteroatom on the stability of both valence isomers. The focus is on the parent systems and their synthetic applications.

Jansen, Helen; Slootweg, J Chris

2011-01-01

355

A Model for Valence Using a Color Component in Affective Video Content Analysis  

Microsoft Academic Search

This paper proposes a model which is able to detect differences in the valence level of the content of video data. The valence level is the degree of pleasantness in the scene. This detecting is done by means of analyzing the colors of the frames and linking these colors to emotional states. This model is obtained through a literature study

Iwan de Kok

2006-01-01

356

Dissociable modulation of overt visual attention in valence and arousal revealed by topology of scan path.  

PubMed

Emotional stimuli have evolutionary significance for the survival of organisms; therefore, they are attention-grabbing and are processed preferentially. The neural underpinnings of two principle emotional dimensions in affective space, valence (degree of pleasantness) and arousal (intensity of evoked emotion), have been shown to be dissociable in the olfactory, gustatory and memory systems. However, the separable roles of valence and arousal in scene perception are poorly understood. In this study, we asked how these two emotional dimensions modulate overt visual attention. Twenty-two healthy volunteers freely viewed images from the International Affective Picture System (IAPS) that were graded for affective levels of valence and arousal (high, medium, and low). Subjects' heads were immobilized and eye movements were recorded by camera to track overt shifts of visual attention. Algebraic graph-based approaches were introduced to model scan paths as weighted undirected path graphs, generating global topology metrics that characterize the algebraic connectivity of scan paths. Our data suggest that human subjects show different scanning patterns to stimuli with different affective ratings. Valence salient stimuli (with neutral arousal) elicited faster and larger shifts of attention, while arousal salient stimuli (with neutral valence) elicited local scanning, dense attention allocation and deep processing. Furthermore, our model revealed that the modulatory effect of valence was linearly related to the valence level, whereas the relation between the modulatory effect and the level of arousal was nonlinear. Hence, visual attention seems to be modulated by mechanisms that are separate for valence and arousal. PMID:21494331

Ni, Jianguang; Jiang, Huihui; Jin, Yixiang; Chen, Nanhui; Wang, Jianhong; Wang, Zhengbo; Luo, Yuejia; Ma, Yuanye; Hu, Xintian

2011-04-06

357

Dissociable Modulation of Overt Visual Attention in Valence and Arousal Revealed by Topology of Scan Path  

PubMed Central

Emotional stimuli have evolutionary significance for the survival of organisms; therefore, they are attention-grabbing and are processed preferentially. The neural underpinnings of two principle emotional dimensions in affective space, valence (degree of pleasantness) and arousal (intensity of evoked emotion), have been shown to be dissociable in the olfactory, gustatory and memory systems. However, the separable roles of valence and arousal in scene perception are poorly understood. In this study, we asked how these two emotional dimensions modulate overt visual attention. Twenty-two healthy volunteers freely viewed images from the International Affective Picture System (IAPS) that were graded for affective levels of valence and arousal (high, medium, and low). Subjects' heads were immobilized and eye movements were recorded by camera to track overt shifts of visual attention. Algebraic graph-based approaches were introduced to model scan paths as weighted undirected path graphs, generating global topology metrics that characterize the algebraic connectivity of scan paths. Our data suggest that human subjects show different scanning patterns to stimuli with different affective ratings. Valence salient stimuli (with neutral arousal) elicited faster and larger shifts of attention, while arousal salient stimuli (with neutral valence) elicited local scanning, dense attention allocation and deep processing. Furthermore, our model revealed that the modulatory effect of valence was linearly related to the valence level, whereas the relation between the modulatory effect and the level of arousal was nonlinear. Hence, visual attention seems to be modulated by mechanisms that are separate for valence and arousal.

Ni, Jianguang; Jiang, Huihui; Jin, Yixiang; Chen, Nanhui; Wang, Jianhong; Wang, Zhengbo; Luo, Yuejia; Ma, Yuanye; Hu, Xintian

2011-01-01

358

High temperature susceptibility, valence and volume anomaly of some Ce-compounds  

Microsoft Academic Search

The magnetic susceptibility of some Ce intermetallic compounds was measured up to 1200 K. Using the susceptibility and the valence from LIII-X-ray absorption we calculate the fluctuation temperatures. For alpha-type Ce compounds we separate the volume anomaly into one part due to fractional valence and a rest which we find to scale with the fluctuation temperature.

P. Weidner; K. Keulerz; R. Löhe; B. Roden; J. Röhler; B. Wittershagen; D. Wohlleben

1985-01-01

359

Interpersonal Valence Dimensions as Discriminators of Communication Contexts: An Empirical Assessment of Dyadic Linkages.  

ERIC Educational Resources Information Center

|The capability of 14 interpersonal dimensions to predict dyadic communication contexts was investigated in this study. Friend, acquaintance, co-worker, and family contexts were examined. The interpersonal valence construct, based on a coactive or mutual-causal paradigm, encompasses traditional source-valence components (credibility, power,…

Garrison, John P.; And Others

360

Analysis on experimental valence charge density in germanium at RT and 200 K  

Microsoft Academic Search

The electronic structure and hence the valence charge distribution of germanium at 296 and 200K has been elucidated from structure factors measured by X-ray diffraction experiment using maximum entropy method (MEM) and multipole model. The methods adopted here are used to extract the fine details of the charge density distribution in the valence region. The charge density evaluated using both

S. Israel; K. S. Syed Ali; R. A. J. R. Sheeba; R. Saravanan

2009-01-01

361

Relational Bonds and Loyalty: The Bonds that Tie  

Microsoft Academic Search

This paper explores the effect of financial, social and structural bonds on the loyalty of Arabic five star hotel guests. Three different measures of loyalty are used; attitudinal, behavioural and combined to identify how the three relational bonds affect loyalty. The results show that social and structural bonds increase all types of loyalty whereas financial bonds only increase attitudinal and

Ahmad Shammout; Michael Polonsky; Michael Edwardson

362

Effects of Emotion on Associative Recognition: Valence and Retention Interval Matter  

PubMed Central

In two experiments, we examined the effects of emotional valence and arousal on associative binding. Participants studied negative, positive, and neutral word pairs, followed by an associative recognition test. In Experiment 1, with a short-delayed test, accuracy for intact pairs was equivalent across valences, whereas accuracy for rearranged pairs was lower for negative than for positive and neutral pairs. In Experiment 2, we tested participants after a one-week delay and found that accuracy was greater for intact negative than for intact neutral pairs, whereas rearranged pair accuracy was equivalent across valences. These results suggest that, although negative emotional valence impairs associative binding after a short delay, it may improve binding after a longer delay. The results also suggest that valence, as well as arousal, needs to be considered when examining the effects of emotion on associative memory.

Pierce, Benton H.; Kensinger, Elizabeth A.

2011-01-01

363

Effects of valence and arousal on written word recognition: time course and ERP correlates.  

PubMed

Models of affect assume a two-dimensional framework, composed of emotional valence and arousal. Although neuroimaging evidence supports a neuro-functional distinction of their effects during single word processing, electrophysiological studies have not yet compared the effects of arousal within the same category of valence (positive and negative). Here we investigate effects of arousal and valence on written lexical decision. Amplitude differences between emotion and neutral words were seen in the early posterior negativity (EPN), the late positive complex and in a sustained slow positivity. In addition, trends towards interactive effects of valence and arousal were observed in the EPN, showing larger amplitude for positive, high-arousal and negative, low-arousal words. The results provide initial evidence for interactions between arousal and valence during processing of positive words and highlight the importance of both variables in studies of emotional stimulus processing. PMID:23142715

Citron, Francesca M M; Weekes, Brendan S; Ferstl, Evelyn C

2012-11-06

364

Halogen bonds as orthogonal molecular interactions to hydrogen bonds  

Microsoft Academic Search

Halogen bonds (X-bonds) are shown to be geometrically perpendicular to and energetically independent of hydrogen bonds (H-bonds) that share a common carbonyl oxygen acceptor. This orthogonal relationship is accommodated by the in-plane and out-of-plane electronegative potentials of the oxygen, which are differentially populated by H- and X-bonds. Furthermore, the local conformation of a peptide helps to define the geometry of

Andrea Regier Voth; Patricia Khuu; Keita Oishi; P. Shing Ho

2009-01-01

365

Properties of chemically bonded phases  

Microsoft Academic Search

Retention on non-polar chemically-bonded stationary phases depends on the silica carrier, the kind of bonded silane, the surface concentration of bonded alkyl groups and the number of surface silanol groups before and after chemical modification. The influence of carbon content of bonded phases, column temperature and how the eluent mixture has been prepared on solute retention is demonstrated. For comparison

H. Engelhardt; G. Ahr

1981-01-01

366

26 CFR 1.144-1 - Qualified small issue bonds, qualified student loan bonds, and qualified redevelopment bonds.  

Code of Federal Regulations, 2013 CFR

...small issue bonds, qualified student loan bonds, and qualified redevelopment...small issue bonds, qualified student loan bonds, and qualified redevelopment...bonds per taxpayer). (c) Effective dates. For effective dates of §§ 1.144-0...

2013-04-01

367

Insurance and bonding  

SciTech Connect

Societal risk management in industrial democracies relies upon mechanisms of prior restraint rather than on responsibility for the consequence of accidents. The evolution of risk management from one based upon private, voluntary standard of risk management from one based upon private, voluntary standard setting to one based upon restraint is reviewed. While insurance and bonding historically have played a major role in private management of catastrophic risks, their role has been underutilized in the current, restraint-based mode. The conditions under the insurance and bonding that can serve as a tool for risk regulation are illustrated in the arena of toxic pollution risks. 45 refs., 1 fig.

Katzman, M.T.

1989-01-01

368

Doping of the Bi-Sr-Ca-Cu-O system with V(B) elements and the effect on Bi2Sr2Ca2Cu3O(y) phase formation  

NASA Astrophysics Data System (ADS)

In the present work the authors have systematically studied the effect of the high-valency cations V(5+), Nb(5+) and Ta(5+) on the formation of high T(sub 0) 2223 phase and found that doping any one of them can significantly enhance the formation of 2223 phase. Their role is quite similar to that of Pb for stabilizing the 2223 phase. Results show that doping with V(5+), Nb(5+) or Ta(5+) high-valency cations greatly enhances the formation of 2223 phase; the optimum nominal composition is Bi( 1.6)M(0.4)Sr2Ca2Cu3O(y) (M = V, Nb or Ta). The authors suggests that the beneficial effect of promoting the formation of 2223 phase might be a general property of doping with high-valency cations. The beneficial origin of doping with high-valency cations in Bi-based material was also discussed.

Li, Yanrong; Yang, Bangchao

1994-04-01

369

Ionic conduction, bond valence analysis of structure-property relationships of NaHoP2O7  

NASA Astrophysics Data System (ADS)

Single crystals of NaHoP2O7 diphosphate have been prepared by the flux method and its structural and physical properties have been investigated. It crystallizes in the monoclinic system with the space group P21/n and its parameters are: a=8.6796(4) Å, b=5.3677(2) Å, c=13.6904(6) Å, ?=106.120° (2), V=612.75 (5) Å3, Z=4. The structure of NaHoP2O7 consists of a three-dimensional framework of HoO6 octahedra, linked by P2O7 diphosphate units, forming tunnels running parallel to [0 1 0], which are occupied by Na atoms. The infrared and Raman vibrational spectra have been investigated. Activation energy was obtained from Arrhenius plots (Ln ?T versus 1000/T) and found to be 1.27 eV. The coupling of the structural analysis with the BVS model for NaHoP2O7 has better interpret the measurements of the ionic conductivity and the most probably transport pathway model was determined.

Béjaoui, Anis; Horchani-Naifer, Karima; Férid, Mokhtar

2013-08-01

370

Valence Scaling of Dynamic Facial Expressions Is Altered in High-Functioning Subjects with Autism Spectrum Disorders: An FMRI Study  

ERIC Educational Resources Information Center

|FMRI was performed with the dynamic facial expressions fear and happiness. This was done to detect differences in valence processing between 25 subjects with autism spectrum disorders (ASDs) and 27 typically developing controls. Valence scaling was abnormal in ASDs. Positive valence induces lower deactivation and abnormally strong activity in ASD…

Rahko, Jukka S.; Paakki, Jyri-Johan; Starck, Tuomo H.; Nikkinen, Juha; Pauls, David L.; Katsyri, Jari V.; Jansson-Verkasalo, Eira M.; Carter, Alice S.; Hurtig, Tuula M.; Mattila, Marja-Leena; Jussila, Katja K.; Remes, Jukka J.; Kuusikko-Gauffin, Sanna A.; Sams, Mikko E.; Bolte, Sven; Ebeling, Hanna E.; Moilanen, Irma K.; Tervonen, Osmo; Kiviniemi, Vesa

2012-01-01

371

Developmental Reversals in False Memory: Effects of Emotional Valence and Arousal  

PubMed Central

Do the emotional valence and arousal of events distort children’s memories? Do valence and arousal modulate counterintuitive age increases in false memory? We investigated those questions in children, adolescents, and adults using the Cornell/Cortland Emotion Lists, a word list pool that induces false memories and in which valence and arousal can be manipulated factorially. False memories increased with age for unpresented semantic associates of word lists, and net accuracy (the ratio of true memory to total memory) decreased with age. These surprising developmental trends were more pronounced for negatively-valenced materials than for positively-valenced materials, they were more pronounced for high-arousal materials than for low-arousal materials, and developmental increases in the effects of arousal were small in comparison to developmental increases in the effects of valence. These findings have ramifications for legal applications of false-memory research: Materials that share the emotional hallmark of crimes (events that are negatively valenced and arousing) produced the largest age increases in false memory and the largest age declines in net accuracy.

Brainerd, C. J.; Holliday, R. E.; Reyna, V. F.; Yang, Y.; Toglia, M. P.

2010-01-01

372

High and low roads to odor valence? A choice response-time study.  

PubMed

Valence and edibility are two important features of olfactory perception, but it remains unclear how they are read out from an olfactory input. For a given odor object (e.g., the smell of rose or garlic), does perceptual identification of that object necessarily precede retrieval of information about its valence and edibility, or alternatively, are these processes independent? In the present study, we studied rapid, binary perceptual decisions regarding odor detection, object identity, valence, and edibility for a set of common odors. We found that decisions regarding odor-object identity were faster than decisions regarding odor valence or edibility, but slower than detection. Mediation analysis revealed that odor valence and edibility decision response times were predicted by a model in which odor-object identity served as a mediator along the perceptual pathway from detection to both valence and edibility. According to this model, odor valence is determined through both a "low road" that bypasses odor objects and a "high road" that utilizes odor-object information. Edibility evaluations are constrained to processing via the high road. The results outline a novel causal framework that explains how major perceptual features might be rapidly extracted from odors through engagement of odor objects early in the processing stream. (PsycINFO Database Record (c) 2013 APA, all rights reserved). PMID:23875569

Olofsson, Jonas K; Bowman, Nicholas E; Gottfried, Jay A

2013-07-22

373

From Semantics to Feelings: How Do Individuals with Schizophrenia Rate the Emotional Valence of Words?  

PubMed Central

Schizophrenia is characterized by both emotional and language abnormalities. However, in spite of reports of preserved evaluation of valence of affective stimuli, such as pictures, it is less clear how individuals with schizophrenia assess verbal material with emotional valence, for example, the overall unpleasantness/displeasure relative to pleasantness/attraction of a word. This study aimed to investigate how schizophrenic individuals rate the emotional valence of adjectives, when compared with a group of healthy controls. One hundred and eighty-four adjectives differing in valence were presented. These adjectives were previously categorized as “neutral,” “positive” (pleasant), or “negative” (unpleasant) by five judges not participating in the current experiment. Adjectives from the three categories were matched on word length, frequency, and familiarity. Sixteen individuals with schizophrenia diagnosis and seventeen healthy controls were asked to rate the valence of each word, by using a computerized version of the Self-Assessment Manikin (Bradley and Lang, 1994). Results demonstrated similar ratings of emotional valence of words, suggesting a similar representation of affective knowledge in schizophrenia, at least in terms of the valence dimension.

Pinheiro, Ana P.; McCarley, Robert W.; Thompson, Elizabeth; Goncalves, Oscar F.; Niznikiewicz, Margaret

2012-01-01

374

Critical cluster size for mixed valence in small matrix-isolated Sm clusters  

SciTech Connect

From L/sub 3/ absorption measurement, information on the valence and size of small matrix-isolated Sm clusters is obtained by analyzing the x-ray-absorption near-edge structure and the extended x-ray-absorption fine structure (EXAFS). Depending on the mean cluster size, which is a function of the atomic concentration (Sm to rare-gas atom ratio), every valence between 2.0 and 3.0 is reproducibly achievable. At very low Sm concentrations the samples have the atomic valence; at a critical concentration capprox. =1:100 a steep rise of the valence up to v = 2.6 is found. Then, with increasing metal concentration, the Sm-cluster valence approaches the valence of the solid. From EXAFS analysis, a mean cluster size of 13 atoms for clusters with v = 2.6 follows. The mixed valence of the Sm atoms is explained by the pressure exerted on the Sm cluster by the distorted rare-gas lattice (the rare gas is Ne, Ar, or Kr).

Niemann, W.; Malzfeldt, W.; Rabe, P.; Haensel, R.; Luebcke, M.

1987-01-15

375

Valence resolution of ambiguous facial expressions using an emotional oddball task.  

PubMed

Previous research suggests that neural and behavioral responses to surprised faces are modulated by explicit contexts (e.g., "He just found $500"). Here, we examined the effect of implicit contexts (i.e., valence of other frequently presented faces) on both valence ratings and ability to detect surprised faces (i.e., the infrequent target). In Experiment 1, we demonstrate that participants interpret surprised faces more positively when they are presented within a context of happy faces, as compared to a context of angry faces. In Experiments 2 and 3, we used the oddball paradigm to evaluate the effects of clearly valenced facial expressions (i.e., happy and angry) on default valence interpretations of surprised faces. We offer evidence that the default interpretation of surprise is negative, as participants were faster to detect surprised faces when presented within a happy context (Exp. 2). Finally, we kept the valence of the contexts constant (i.e., surprised faces) and showed that participants were faster to detect happy than angry faces (Exp. 3). Together, these experiments demonstrate the utility of the oddball paradigm to explore the default valence interpretation of presented facial expressions, particularly the ambiguously valenced facial expression of surprise. PMID:21707167

Neta, Maital; Davis, F Caroline; Whalen, Paul J

2011-06-27

376

Valence anions in complexes of adenine and 9-methyladenine with formic acid: stabilization by intermolecular proton transfer.  

PubMed

Photoelectron spectra of adenine-formic acid (AFA(-)) and 9-methyladenine-formic acid (MAFA(-)) anionic complexes have been recorded with 2.540 eV photons. These spectra reveal broad features with maxima at 1.5-1.4 eV that indicate formation of stable valence anions in the gas phase. The neutral and anionic complexes of adenine/9-methyladenine and formic acid were also studied computationally at the B3LYP, second-order Møller-Plesset, and coupled-cluster levels of theory with the 6-31++G** and aug-cc-pVDZ basis sets. The neutral complexes form cyclic hydrogen bonds, and the most stable dimers are bound by 17.7 and 16.0 kcal/mol for AFA and MAFA, respectively. The theoretical results indicate that the excess electron in both AFA(-) and MAFA(-) occupies a pi* orbital localized on adenine/9-methyladenine, and the adiabatic stability of the most stable anions amounts to 0.67 and 0.54 eV for AFA(-) and MAFA(-), respectively. The attachment of the excess electron to the complexes induces a barrier-free proton transfer (BFPT) from the carboxylic group of formic acid to a N atom of adenine or 9-methyladenine. As a result, the most stable structures of the anionic complexes can be characterized as neutral radicals of hydrogenated adenine (9-methyladenine) solvated by a deprotonated formic acid. The BFPT to the N atoms of adenine may be biologically relevant because some of these sites are not involved in the Watson-Crick pairing scheme and are easily accessible in the cellular environment. We suggest that valence anions of purines might be as important as those of pyrimidines in the process of DNA damage by low-energy electrons. PMID:17263404

Mazurkiewicz, Kamil; Hara?czyk, Maciej; Gutowski, Maciej; Rak, Janusz; Radisic, Dunja; Eustis, Soren N; Wang, Di; Bowen, Kit H

2007-02-01

377

19 CFR 113.11 - Bond approval.  

Code of Federal Regulations, 2013 CFR

...CUSTOMS BONDS Bond Application and Approval of Bond § 113.11 Bond approval. Each person who is required by law, regulation, or specific instruction to post a bond to secure a Customs transaction or multiple...

2013-04-01

378

Dialogic Bonds and Boundaries.  

ERIC Educational Resources Information Center

|A study of literature cannot be divorced from cultural contexts, nor can it ignore the humanist vision in interpreting literary texts. To discover dialogic bonds and boundaries between the reader and the text, or the writer and the audience, English classes should have two objectives: (1) to explore the diversity of perspectives, and (2) to…

Khawaja, Mabel

379

Bonding with the Past.  

ERIC Educational Resources Information Center

|An interview with Linda Mayro, archaeologist and cultural resources manager for Pima County, Arizona, discusses efforts of local groups to preserve local Native-American and Mexican cultural-heritage sites in oppositon to commercial land developers. A public information campaign led to passage of a $6.4 million historic preservation bond. (SAS)|

Common Ground: Archeology and Ethnography in the Public Interest, 1998

1998-01-01

380

Bonded Retainers - Clinical Reliability  

Microsoft Academic Search

Bonded retainers have become a very important retention appliance in orthodontic treatment. They are popular because they are considered reliable, independent of patient cooperation, highly efficient, easy to fabricate, and almost invisible. Of these traits, reliability is the subject of this clinical study. A total of 549 patients with retainers were analyzed with regard to wearing time, extension of the

Dietmar Segner; Bettina Heinrici

2000-01-01

381

Bonding without Tears.  

ERIC Educational Resources Information Center

|Discusses merits of using sigma-pi model of ethylene as a teaching aid in introductory organic chemistry. The nonmathematical treatment of sigma-pi bonding is then extended to such phenomena as conjugation, hyperconjugation, Markovnikoff addition, aromaticity, and aromatic substitution. (SK)|

Akeroyd, F. Michael

1982-01-01

382

Photochemical tissue bonding  

DOEpatents

Photochemical tissue bonding methods include the application of a photosensitizer to a tissue and/or tissue graft, followed by irradiation with electromagnetic energy to produce a tissue seal. The methods are useful for tissue adhesion, such as in wound closure, tissue grafting, skin grafting, musculoskeletal tissue repair, ligament or tendon repair and corneal repair.

Redmond, Robert W. (Brookline, MA); Kochevar, Irene E. (Charlestown, MA)

2012-01-10

383

Positively valenced stimuli facilitate creative novel metaphoric processes by enhancing medial prefrontal cortical activation.  

PubMed

A metaphor is a figure of speech in which a subject is symbolic of another unrelated object. In the present study, we examined neural patterns associated with both novel unfamiliar and conventional familiar metaphoric processing, and how these patterns are modulated by affective valence. Prior to fMRI scanning, participants received a list of word pairs (novel unfamiliar metaphors as well as conventional familiar metaphors) and were asked to denote the valence (positive, negative, or neutral) of each word pair. During scanning, participants had to decide whether the word pairs formed meaningful or meaningless expressions. Results indicate that participants were faster and more accurate at deciding that positively valenced metaphors were meaningful compared to neutral metaphors. These behavioral findings were accompanied by increased activation in the medial prefrontal cortex (mPFC), posterior cingulate cortex (PCC), and the right inferior parietal lobe (RIPL). Specifically, positively valenced novel unfamiliar metaphors elicited activation in these brain regions in addition to the left superior temporal gyrus when compared to neutral novel metaphors. We also found that the mPFC and PCC mediated the processing of positively valenced metaphors when compared to negatively valenced metaphors. Positively valenced conventional metaphors, however, elicited different neural signatures when contrasted with either neutral or negatively valenced conventional metaphors. Together, our results indicate that positively valenced stimuli facilitate creative metaphoric processes (specifically novel metaphoric processes) by mediating attention and cognitive control processes required for the access, integration, and selection of semantic associations via modulation of the mPFC. The present study is important for the development of neural accounts of emotion-cognition interactions required for creativity, language, and successful social functioning in general. PMID:23637686

Subramaniam, Karuna; Beeman, Mark; Faust, Miriam; Mashal, Nira

2013-04-26

384

Influence of 5f electrons on structure and bonding in the actinide-hydrogen intermetallics  

SciTech Connect

Complexa phases form for the Th + H and U + H systems that are found with no other metals. In the Pa + H system, simple bcc C15 Laves and A15 phases can form, dependent on temperature and composition. The phase transformations appear to b magnetically driven, as a resutl of the decoupling of the metallic 5f electron bonding that occurs during hydriding; the C15 phases contain two kinds of Pa atoms-the one sublattice being still fully f-bonded and the other magnetic. This is a unique situation in solid state physics which defies a valence description. A similar situation obtains for A15 ..beta.. - UH/sub 3/ structure. The parent metals themselves exhibit electronegativities not unlike those of the mid-3d transition metals (e.g., Fe) because the valence electrons re tied up in metallic bonding. However, under the driving force for hydriding, the lattices can open up, decoupling the f-bonding and inducing magnetism. The systems then aggressively form very stable hydrides typical of highly-electropositive metals. Beyond uranium the trivalent metallic state is favored and rare-earth-like hydrides are found for Np + H and Pu + H. Nevertheless, the solid-state and transport properties are markedly different than for the rare-earth hydrides, showing that the latent influence of the 5f electrons is still strong.

Ward, J.W.

1984-01-01

385

Valence calculations of lanthanide anion binding energies: a comprehensive study  

NASA Astrophysics Data System (ADS)

We have applied a methodology of universal jls restrictions on the 4f^n subgroup of relativistic configuration-interaction calculations of progressively more complex lanthanide anionsootnotetextS. M. O'Malley and D. R. Beck, Phys. Rev. A 77, 012505 (2008).^,ootnotetextS. M. O'Malley and D. R. Beck, Phys. Rev. A 78, 012510 (2008).^,ootnotetextS. M. O'Malley and D. R. Beck, Phys. Rev. A, in press.. Our completed study of the row predicts bound 6p attachments to all lanthanide ground state configurations except Yb, additional 6p attachments to excited opposite parity configurations in Tb and Lu, and 6s attachments to excited open-6s thresholds in La, Ce, Pr, and Gd. In total we predict more than 100 bound states for the lanthanide anions, and we hope this comprehensive study encourages further experimentalootnotetexte.g. V. T. Davis et al., Nucl. Instrum. Methods Phys. Res. B 241, 118 (2005).^,ootnotetexte.g. C. W. Walter et al., Phys. Rev. A 76, 052702 (2007). interest in these anions. Such measurements will be useful in ``fine tuning'' these ab initio binding energies to account for missing core-valence correlation and the approximations that were necessary in these complex calculations.

O'Malley, Steven M.; Beck, Donald R.

2009-05-01

386

Valence and Conduction Band Evolution of InGaN  

NASA Astrophysics Data System (ADS)

Nitride alloy based laser diodes (LD) and light emitting diodes (LED) have been very successful and have recently become commercially available. The optically active layers are often made of single or multiple quantum layers of In_xGa_1-xN, with x = .7. The success of these devices has been primarily due to engineering developments of growth and manufacturing. But a shortfall in the physical understanding of the optically active processes may hinder the further and presently unknown potential applications of these and next generation devices. The source of light emission from InGaN active layers is still disputed. It has been suggested that InN nanocrystals phase seperate from the bulk of the InGaN and form the sole source of emission(K.P.O'Donnell et al, Phys Rev Lett 82 237 1999). We present partial density of states (PDOS) of the valence and conduction bands of a series of MBE grown InGaN samples measured by the technique of soft X-ray emission and absorption spectroscopies.

Ryan, Philip; Downes, J. E.; McGuinness, C.; Moustakas, T. D.; Smith, K. E.

2001-03-01

387

Effective Shell-Model Interactions from the Valence Cluster Expansion  

NASA Astrophysics Data System (ADS)

The ab initio No-Core Shell Model (NCSM) has had considerable success in describing the binding energies, excitation spectra and other physical properties of light nuclei, A<=12 e.g. [1]. However, it becomes rather challenging to produce converged results for nuclei with A>12. Following the idea of Ref. [2], we develop a valence cluster expansion to construct effective 2- and 3-body Hamiltonians for the 0p-shell by performing 12? NCSM calculations for A=6 and 7 nuclei and explicitly projecting the many-body Hamiltonians onto the 0? space. We separate these effective Hamiltonians into 0-, 1- and 2-body contributions (also 3-body for A=7) and analyze the systematic behavior of these different parts as a function of the mass number A and size of the NCSM basis space. The role of effective 3- and higher-body interactions for A>6 will be discussed. [1] P. Navratil, J.P.Vary, B.R.Barrett, Phys. Rev. C. 62, 054311 (2000). [2] P. Navratil, M. Thoresen, and B. R. Barrett, Phys. Rev. C. 55, R573 (1997).

Lisetskiy, A. F.; Kruse, M. K. G.; Barrett, B. R.; Navratil, P.; Stetcu, I.; Vary, J. P.

2008-10-01

388

Quasicrystalline valence bands in decagonal AlNiCo  

NASA Astrophysics Data System (ADS)

Quasicrystals are metallic alloys that possess perfect long-range structural order, in spite of the fact that their rotational symmetries are incompatible with long-range periodicity. The exotic structural properties of this class of materials are accompanied by physical properties that are unexpected for metallic alloys. Considerable progress in resolving the geometric structures of quasicrystals has been made using X-ray and neutron diffraction, and concepts such as the quasi-unit-cell model have provided theoretical insights. But the basic properties of the valence electronic states-whether they are extended as in periodic crystals or localized as in amorphous materials-are still largely unresolved. Here we investigate the electronic bandstructure of quasicrystals through angle-resolved photoemission experiments on decagonal Al71.8Ni14.8Co13.4. We find that the s-p and d states exhibit band-like behaviour with the symmetry of the quasiperiodic lattice, and that the Fermi level is crossed by dispersing d-bands. The observation of free-electron-like bands, distributed in momentum space according to the surface diffraction pattern, suggests that the electronic states are not dominated by localization.

Rotenberg, Eli; Theis, W.; Horn, K.; Gille, P.

2000-08-01

389

Electrochemical uranium valence control in centrifugal solvent extraction contactors  

SciTech Connect

In the Purex process for the reprocessing of spent nuclear fuel, the partitioning of uranium and plutonium generally requires a reducing agent for the valence change of Pu(IV) to Pu(III). Modified mixer-settlers and pulsed columns with internal electrodes have been developed for the simultaneous electroreduction and solvent extraction, and the utility of this partitioning method has been demonstrated for the reprocessing of light water reactor and fast breeder reactor (FBR) fuels. Short-residence solvent extraction contractors are needed for the reprocessing of high-burnup fuels to reduce the radiation damage to the organic solvent. Centrifugal contactors, the currently preferred machines, have inherent spatial limitations for the incorporation of electrodes. External electrolytic reduction cells could be used, provided the chemical stability of the reduced species (U(IV) and Pu(III)) can be assured. The feasibility of in-tandem operation of a multistage centrifugal contactor and an electrolytic reduction cell was investigated, and the applicability of this method to the reprocessing of FBR fuel was tested by means of computer models developed from experimental results.

Schneider, A.; Pschirer, D.M.

1988-01-01

390

Quasicrystalline valence bands in decagonal AlNiCo  

PubMed

Quasicrystals are metallic alloys that possess perfect long-range structural order, in spite of the fact that their rotational symmetries are incompatible with long-range periodicity. The exotic structural properties of this class of materials are accompanied by physical properties that are unexpected for metallic alloys. Considerable progress in resolving the geometric structures of quasicrystals has been made using X-ray and neutron diffraction, and concepts such as the quasi-unit-cell model have provided theoretical insights. But the basic properties of the valence electronic states--whether they are extended as in periodic crystals or localized as in amorphous materials--are still largely unresolved. Here we investigate the electronic bandstructure of quasicrystals through angle-resolved photoemission experiments on decagonal Al71.8Ni14.8Co13.4. We find that the s-p and d states exhibit band-like behaviour with the symmetry of the quasiperiodic lattice, and that the Fermi level is crossed by dispersing d-bands. The observation of free-electron-like bands, distributed in momentum space according to the surface diffraction pattern, suggests that the electronic states are not dominated by localization. PMID:10949295

Rotenberg; Theis; Horn; Gille

2000-08-10

391

Pressure and photo-induced phase transition in mixed-valence gold complexes  

Microsoft Academic Search

The pressure- and photo-induced phase transition in mixed-valence gold complexes of Cs2Au2X6(X = Cl, Br, and I) has been investigated by means of the Raman scattering. The Raman-active Au-X stretching modes were deactivated by the pressure, which indicates a pressure-induced phase transition from the mixed-valence (MV) state to the single-valence (SV) state. The electronic phase diagrams of Cs2Au2X6(X = Cl

X. J. Liu; Y. Moritomo; A. Nakamura; N. Kojima

2001-01-01

392

Photoion mass spectroscopy and valence photoionization of hypoxanthine, xanthine and caffeine  

NASA Astrophysics Data System (ADS)

Photoionization mass spectra of hypoxanthine, xanthine and caffeine were measured using the photoelectron-photoion coincidence technique and noble gas resonance radiation at energies from 8.4 to 21.2 eV for ionization. The fragmentation patterns for these compounds show that hydrogen cyanide is the main neutral loss species at higher photon energies, while photoionization below 16.67 eV led predominantly to the parent ion. The valence photoelectron spectra of this family of molecules were measured over an extended energy range, including the inner C, N and O 2s valence orbitals. The observed ion fragments were related to ionization of the valence orbitals.

Feyer, Vitaliy; Plekan, Oksana; Richter, Robert; Coreno, Marcello; Prince, Kevin C.

2009-03-01

393

Complex Materials for Molecular Spintronics Applications: Cobalt Bis(dioxolene) Valence Tautomers, from Molecules to Polymers  

NASA Astrophysics Data System (ADS)

Using first principles calculations we predict a complex multifunctional behavior in cobalt bis(dioxolene) valence tautomeric compounds. Molecular spin-state switching is shown to dramatically alter electronic properties and corresponding transport properties. This spin state dependence has been demonstrated for technologically-relevant coordination polymers of valence tautomers as well as for novel conjugated polymers with valence tautomeric functionalization. As a result these materials are proposed as promising candidates for spintronic devices that can couple magnetic bistability with novel electrical and spin conduction properties. Our findings pave the way to the fundamental understanding and future design of active multifunctional organic materials for spintronics applications.

Buongiorno Nardelli, Marco; Calzolari, Arrigo; Chen, Yifeng; Dougherty, Daniel; Shultz, David

2013-03-01

394

Regulation of murine cytochrome c oxidase Vb gene expression during myogenesis: YY-1 and heterogeneous nuclear ribonucleoprotein D-like protein (JKTBP1) reciprocally regulate transcription activity by physical interaction with the BERF-1/ZBP-89 factor.  

PubMed

A transcription suppressor element (sequence -481 to -320) containing a G-rich motif (designated GTG) and a newly identified CAT-rich motif (designated CATR) was previously shown to modulate expression of the mouse cytochrome c oxidase Vb gene during myogenesis. Here, we show that the GTG element is critical for transcription activation in both undifferentiated and differentiated myocytes. Mutations of the CATR motif abolished transcription repression in myoblasts while limiting transcription activation in differentiated myotubes, suggesting contrasting functional attributes of this DNA motif at different stages of myogenesis. Results show that the activity of the transcription suppressor motif is modulated by an orchestrated interplay between ubiquitous transcription factors: ZBP-89, YY-1, and a member of the heterogeneous nuclear ribonucleoprotein D-like protein (also known as JKTBP1) family. In undifferentiated muscle cells, GTG motif-bound ZBP-89 physically and functionally interacted with CATR motif-bound YY-1 to mediate transcription repression. In differentiated myotubes, heterogeneous nuclear ribonucleoprotein D-like protein/JKTBP1 bound to the CATR motif exclusive of YY-1 and interacted with ZBP-89 in attenuating repressor activity, leading to transcription activation. Our results show a novel mechanism of protein factor switching in transcription regulation of the cytochrome c oxidase Vb gene during myogenesis. PMID:15190078

Boopathi, Ettickan; Lenka, Nibedita; Prabu, Subbuswamy K; Fang, Ji-Kang; Wilkinson, Frank; Atchison, Michael; Giallongo, Agata; Avadhani, Narayan G

2004-06-09

395

New Effective Core Method (Effective Core Potential and Valence Basis Set) for Al Clusters and Nanoparticles and Heteronuclear Al-Containing Molecules  

SciTech Connect

In previous work we have shown that the PBE0 hybrid density functional method with the MG3 all-electron basis set is an accurate method for calculating the atomization energies of small aluminum clusters (Al2-Al7). However, the MG3 basis set is very expensive for molecules much larger than Al13; therefore, we have developed a new effective core potential (ECP) method for aluminum to reduce the cost of obtaining accurate results for nanoparticles. Our method involves a hybrid of the Stuttgart semiempirical effective core potential and the compact effective potential (CEP) potential, and it uses a newly optimized polarized valence triple-? basis set. The combination of the new ECP and the new polarized valence triple-? basis set for Al is called the Minnesota effective core (MEC) method for Al. The method was optimized with a training set of atomization energies and geometries for AlH, AlC, AlO, AlCCH, Al2H, Al2C, Al2O, and Al3 and atomization energies of three Al13 structures, and we tested it on six test sets composed of 20 atomization energies for systems as large as Al13. We also present an improved all-electron polarized triple split basis set for oxygen, called 6-311+G(d*,p). For the test sets, the mean unsigned error (MUE) of the new method with respect to PBE0/MG3 is 0.06 eV for atomization energies and 0.007 Å for bond lengths, which constitutes a very significant improvement over the quality of the results that can be obtained with effective core potentials and valence basis sets in the literature (of the eight methods in the literature, the best previous method had average errors of 0.63 eV and 0.036 Å). We have also tested the MEC method with a variety of hybrid density functional theory, hybrid meta density functional theory, and pure GGA and meta GGA functionals and found that the average MUE, relative to each functional with all-electron basis sets, is 0.04 eV for atomization energies and 0.009 Å for bond lengths for the new effective core method and 0.16-0.20 eV and 0.013-0.033 Å for effective core potential and valence basis sets in the literature.

Schultz, Nathan E.; Truhlar, Donald G.

2005-01-31

396

The electronic structure of gas phase croconic acid compared to the condensed phase: More insight into the hydrogen bond interaction  

NASA Astrophysics Data System (ADS)

The electronic structure of croconic acid in the gas phase has been investigated by means of core level and valence band photoemission spectroscopy and compared with hybrid Heyd-Scuseria-Ernzerhof density functional theory calculations. The results have been compared with the corresponding ones of the condensed phase. In the gas phase, due to the absence of hydrogen bond intermolecular interactions, the O 1 s core level spectrum shows a shift of binding energy between the hydroxyl (O-H) and the carbonyl group (C=O) of 2.1 eV, which is larger than the condensed phase value of 1.6 eV. Interestingly, such a shift decreases exponentially with the increase of the O-H distance calculated from theory. The significant differences between the gas and condensed phase valence band spectra highlight the important role played by the hydrogen bonding in shaping the electronic structure of the condensed phase.

Bisti, F.; Stroppa, A.; Perrozzi, F.; Donarelli, M.; Picozzi, S.; Coreno, M.; de Simone, M.; Prince, K. C.; Ottaviano, L.

2013-01-01

397

A novel bonding technique to bond CTE mismatched devices  

Microsoft Academic Search

Thermal expansion mismatch between electronic devices and their substrates induces stresses in the assembly during bonding and operation. These stresses in extreme cases cause cracking of the electronic device during bonding. For GaAs devices back-side bonded to a high conductivity artificial diamond substrate using Au-Sn solder, analytical and numerical analyses were conducted to determine the bonding stresses in the GaAs

B. Chandran; W. F. Schmidt; M. H. Gordon

1996-01-01

398

The Evolution of Bond Theory  

NSDL National Science Digital Library

In chemistry lectures we have little time to discuss the history of chemistry. This simulation begins with the development of valence concepts in the 19th century. We will step back into the 19th century to see how theories of chemical combination changed during that time.

399

Improving humidity bond reliability of copper bonding wires  

Microsoft Academic Search

There is growing interest in Cu wire bonding for LSI interconnection due to cost savings and better electrical and mechanical properties. Conventional bare Cu bonding wires, in general, are severely limited in their use compared to Au wires. A coated Cu bonding wire (EX1) has been developed for LSI application. EX1 is a Pd-coated Cu wire to enhance the bondability.

Tomohiro Uno; Takashi Yamada

2010-01-01

400

CRIMINAL PROCEDURE Bonds and Recognizes: Regulate Bail Bond Recovery Agents  

Microsoft Academic Search

The Act establishes that the surety limit on criminal bonds can be no higher than twelve percent on bonds in the amount of $ 10,000 or less and no higher than fifteen percent on bonds in amounts greater than $ 10,000. Additionally, the Act defines bail recovery agent, establishes prerequisites for those people serving as bail recovery agents, and provides

Kevin Thomas McMurry

1999-01-01

401

Full inclusion of symmetry in constructing Wannier functions: Chemical bonding in MgO and TiO 2 crystals  

Microsoft Academic Search

Chemical bonding in MgO and TiO2 crystals is analyzed using a minimal basis consisting of atomic-type Wannier functions (AWFs) centered at atomic sites in\\u000a the crystal and constructed from Bloch states of the energy bands originating from the valence states of the atoms. A method\\u000a proposed earlier for constructing Wannier functions is improved. Symmetrization of the initial Bloch function basis

R. A. Évarestov; D. E. Usvyat; V. P. Smirnov

2003-01-01

402

Bonding in Beryllium Clusters  

NASA Astrophysics Data System (ADS)

Beryllium clusters provide an ideal series for exploring the evolution from discrete molecules to the metallic state. The beryllium dimer has a formal bond order of zero, but the molecule is weakly bound. In contrast, bulk-phase beryllium is a hard metal with a high melting point. Theoretical calculations indicate that the bond energies increase dramatically for Ben clusters in the range n=2-6. A triplet ground state is found for n=6, indicating an early emergence of metallic properties. There is an extensive body of theoretical work on smaller Ben clusters, in part because this light element can be treated using high-level methods. However, the apparent simplicity of beryllium is deceptive, and the calculations have proved to be challenging owing to strong electron correlation and configuration interaction effects. Consequently, these clusters have become benchmark systems for the evaluation of a wide spectrum of quantum chemistry methods.

Heaven, Michael C.; Merritt, Jeremy M.; Bondybey, Vladimir E.

2011-05-01

403

THE VALENCE AND METHYLATION STATE OF ARSENIC DETERMINES ITS POTENCY IN INTERACTION WITH THE MITOTIC APPARATUS  

EPA Science Inventory

We have previously shown that the cytotoxic and genotoxic potency of arsenicals is dependent upon their valence and methylation state. Trivalent methylated arsenicals are much more potent DNA damaging agents than are their inorganic and pentavalent counterparts. Furthermore, thei...

404

Halo and devil effects demonstrate valenced-based influences on source-monitoring decisions.  

PubMed

Source attributions based on positive versus negative valence were examined in four experiments. The two sources were individuals who were depicted positively or negatively, and the content of their statements was similarly valenced. When valenced information about the sources was provided after learning the statements, test biases to attribute positive statements to the positive source and negative statements to the negative source were strongly present. Providing the same information prior to learning improved memory, but did not entirely eliminate test biases based on valence. Signal detection analysis suggests that these "halo effect" biases are criterion-based and not memory-based. Therefore, the results are more consistent with descriptions of source-monitoring processes that can benefit from familiarity-based partial information as opposed to descriptions in which source monitoring is primarily recollection-based. PMID:12763008

Cook, Gabriel I; Marsh, Richard L; Hicks, Jason L

2003-06-01

405

Simulations with different lattice Dirac operators for valence and sea quarks  

NASA Astrophysics Data System (ADS)

We discuss simulations with different lattice Dirac operators for sea and valence quarks. A goal of such a “mixed” action approach is to probe deeper the chiral regime of QCD by enabling simulations with light valence quarks. This is achieved by using chiral fermions as valence quarks while computationally inexpensive fermions are used in the sea sector. Specifically, we consider Wilson sea quarks and Ginsparg-Wilson valence quarks. The local Symanzik action for this mixed theory is derived to O(a), and the appropriate low energy chiral effective Lagrangian is constructed, including the leading O(a) contributions. Using this Lagrangian one can calculate expressions for physical observables and determine the Gasser-Leutwyler coefficients by fitting them to the lattice data.

Bär, Oliver; Rupak, Gautam; Shoresh, Noam

2003-06-01

406

Valence values of the cations in selenospinel Cu(Cr,Ti)2Se4  

NASA Astrophysics Data System (ADS)

A long-standing issue about the Cu valency in selenospinel CuCr2Se4 was investigated by soft x-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD). Using the sensitivity of XAS and XMCD to the valence value of transition metal ion and its local symmetry, we checked the valence value of each cation in selenospinel CuCrxTi2-xSe4 (x = 1.0, 1.1, 1.5, and 2.0) and obtained spectroscopic evidence that a small amount of the Cu cation changes the valency from Cu(I) to Cu(II) as the Cr concentration increases from 1.0 to 2.0. Dependence of the Cu(II) concentration and the mean field magnetic exchange energy on the Cr concentration suggests the Cu d-hole plays a crucial role in the intriguing magnetic/electrical properties of CuCr2Se4.

Noh, Han-Jin; Han, S.-W.; Oh, S.-J.; Kang, J.-S.; Lee, S. S.; Kim, G.; Kim, J.-Y.; Lee, H.-G.; Yeo, S.; Cheong, S.-W.

2006-03-01

407

Valence values of the cations in selenospinel Cu(Cr,Ti)2Se4  

NASA Astrophysics Data System (ADS)

A long-standing issue about the Cu valency in selenospinel CuCr2Se4 was investigated by soft X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD). Using the sensitivity of XAS and XMCD to the valence value of transition metal ion and its local symmetry, we checked the valence value of each cation in selenospinel CuCrxTi 2-xSe4 (x = 1.0, 1.1, 1.5, and 2.0) and obtained spectroscopic evidence that a small amount of the Cu cation changes the valency from Cu(I) to Cu(II) as the Cr concentration increases from 1.0 to 2.0. Dependence of the Cu(II) concentration and the mean field magnetic exchange energy on the Cr concentration suggests the Cu d-hole could play a crucial role in the intriguing magnetic/electrical properties of CuCr2Se4.

Noh, H.-J.; Kang, J.-S.; Lee, S. S.; Kim, G.; Han, S.-W.; Oh, S.-J.; Kim, J.-Y.; Lee, H.-G.; Yeo, S.; Guha, S.; Cheong, S.-W.

2007-04-01

408

Size-dependent valence change in small Pr, Nd, and Sm clusters isolated in solid Ar  

SciTech Connect

The L/sub III/ absorption thresholds of Pr, Nd, and Sm clusters isolated in solid Ar are marked by prominent white lines. The lines ascribed to divalent and trivalent rare-earth metals are well separated in energy. From the relative intensities of these lines an average valence of the rare-earth atoms in the cluster has been determined. For dimers and trimers the average valence is close to 2, the value for free atoms. For clusters consisting of more than 20 atoms the average valence approaches 3, the value for bulk metals. In between the valence changes abruptly, indicating the existence of a critical cluster size of approximately 5 atoms for Pr and Nd and of 13 atoms for Sm.

Luebcke, M.; Sonntag, B.; Niemann, W.; Rabe, P.

1986-10-15

409

Electron Redistribution in Mixed Valence Cytochrome Oxidase Following Photolysis of Carboxy-Oxidase,  

National Technical Information Service (NTIS)

The transport of electrons in the oxidase is frequently viewed as unidirectional except when energy-dependent reverse electron transport occurs. In this communication, electron redistribution between redox centers in nonliganded mixed valence oxidase will...

H. J. Harmon

1988-01-01

410

Chromium Valency Response and Environmental Fate in Three-Phase Aquatic Microcosms.  

National Technical Information Service (NTIS)

Factors affecting the valency, solubility, transport, and biogeochemical fate of chromium in an aquatic environment were investigated and assessed utilizing a physical model. Three-phase, atmosphere-water-sediment, microcosms were utilized in a semi-conti...

M. F. Conway

1984-01-01

411

Oxygen barometry of basaltic glasses based on vanadium valence determinations using synchrotron microXANES  

SciTech Connect

We describe here a new, non-destructive method for valence determinations of vanadium and oxygen fugacity estimates for basaltic glasses with spatial resolution of a few micrometers using synchrotron x-ray absorption near edge structure (XANES) spectroscopy. A promising proxy for oxygen fugacity is the valence of vanadium because it a large number of valence states in nature (2+, 3+, 4+ and 5+) and is ubiquitous in earth and planetary materials . We describe here a new, non-destructive method for valence determinations of vanadium and oxygen fugacity estimates for basaltic glasses with spatial resolution of a few micrometers using synchrotron x-ray absorption near edge structure (XANES) spectroscopy. Details of this method and applications to martian, lunar and terrestrial glasses are described and also in accompanying abstracts.

Sutton, S.R.; Karner, J.M.; Papike, J.J.; Delaney, J.S.; Shearer, C.K.; Newville, M.; Eng, P.; Rivers, M.; Dyar, M.D. (UNM); (Rutgers); (Mount Holyoke); (UC)

2004-10-27

412

Coexistence of solvated electron and benzene-centered valence anion in the negatively charged benzene-water clusters  

NASA Astrophysics Data System (ADS)

We present a combined M06 functional calculation and ab initio molecular dynamics simulation study of an excess electron (EE) in a microhydrated aromatic complex (modeled by benzene (Bz)-water binary clusters, Bz(H2O)n). Calculated results illustrate that Bz ring and water clusters are indeed linked through the ?...HO interactions in the neutral Bz(H2O)n (n = 1-8) clusters, and the size of the water cluster does not influence the nature of its interaction with the ? system for the oligo-hydrated complexes. The states and the dynamics of an EE trapped in such Bz-water clusters were also determined. All of possible localized states for the EE can be roughly classified into two types: (i) single, ring-localized states (the Bz-centered valence anions) in which an EE occupies the LUMO of the complexes originating from the LUMO (?*) of the Bz ring, and the ?...HO interactions are enhanced for increase of electron density of the Bz ring. In this mode, the carbon skeleton of the Bz part is significantly deformed due to increase of electron density and nonsymmetric distribution of electron density induced by the interacting H-O bonds; (ii) solvated states, in which an EE is trapped directly as a surface state by the dangling hydrogen atoms of water molecules or as a solvated state in a mixed cavity formed by Bz and water cluster. In the latter case, Bz may also participate in capturing an EE using its C-H bonds in the side edge of the aromatic ring as a part of the cavity. In general, a small water cluster is favorable to the Bz-centered valence anion state, while a large one prefers a solvated electron state. Fluctuations and rearrangement of water molecules can sufficiently modify the relative energies of the EE states to permit facile conversion from the Bz-centered to the water cluster-centered state. This indicates that aromatic Bz can be identified as a stepping stone in electron transfer and the weak ?...HO interaction plays an important role as the driving force in conversion of the two states.

Zhang, Meng; Zhao, Jing; Liu, Jinxiang; Zhou, Lianwen; Bu, Yuxiang

2013-01-01

413

Bond Properties of Liquid Adhesive.  

National Technical Information Service (NTIS)

Studies were conducted on a liquid adhesive used to bond circuit laminates to rigid plastic components. Areas investigated include: adhesive formulation, factors influencing bond strength, laminate cleaning, and automated adhesive application. (ERA citati...

G. W. Bohnert

1982-01-01

414

IMPROVED BONDING METHOD  

DOEpatents

An improved process of bonding aluminum to aluminum without fusion by ultrasonic vibrations plus pressure is described. The surfaces to be bonded are coated with an aqueous solution of alkali metal stearate prior to assembling for bonding. (AEC) O H19504 Present information is reviewed on steady state proliferation, differentiation, and maturation of blood cells in mammals. Data are cited from metabolic tracer studies, autoradiographic studies, cytologic studies, studies of hematopoietic response to radiation injuries, and computer analyses of blood cell production. A 3-step model for erythropoiesis and a model for granulocyte kinetics are presented. New approaches to the study of lymphocytopoiesis described include extracorporeal blood irradiation to deplete lymphocytic tissue without direct injury to the formative tissues as a means to study the stressed system, function control, and rates of proliferation. It is pointed out that present knowledge indicates that lymphocytes comprise a mixed family, with diverse life spans, functions, and migration patterns with apparent aimless recycling from modes to lymph to blood to nodes that has not yet been quantitated. Areas of future research are postulated. (70 references.) (C.H.)

Padgett, E.V. Jr.; Warf, D.H.

1964-04-28

415

Hydrocarbon bond dissociation energies  

SciTech Connect

The best available values for homolytic bond dissociation energies (BDEs) of various classes of neutral compounds are considered in this review. (BDEs in ionic species is a legitimate subject that is touched on briefly and could easily be included in a longer review. The same can be said for heterolytic BDEs, which are not reviewed as such, although some of the ionic thermochemical data discussed yield values for these processes.) The major emphasis is on hydrocarbons and their nitrogen, oxygen, sulfur, halogen, and silicon-containing derivations, but limited data for inorganic molecules are included. The focus is particularly on prototypical radicals whose heats of formation, formerly thought to be well in hand, have recently been called into serious question. The intent is to include all the major types of sigma bonds, if not all specific cases where known or estimatable heats of formation allow bond dissociation energies to be generated. This review attempts to acknowledge all the standard techniques for measuring BDEs in polyatomic molecules and to offer critical analysis of selected portions of the literature. This leaves values that the authors recommend as the most likely to be correct at the time of this writing. 246 references, 9 tables.

McMillen, D.F.; Golden, D.M.

1982-01-01

416

Bistable mixed-valence molecular architectures for bit storage  

NASA Astrophysics Data System (ADS)

The work examines the possible realization of bit storage at the molecular scale using mixed valence compounds i.e. the existence of two stable and degenerate forms associated with the 0 and 1 positions of the bit. The proposed systems are constituted of two donors (D) and acceptor (A), or one donor and two acceptors, juxtaposed in DAD or ADA architectures. Our proposals take advantage of the possibility of donor—acceptor complexes to exhibit either complete or partial charge transfer. The first system we propose has an essentially neutral ground state. However, the potential energy surface (PES) presents two degenerated minima associated with a partial charge transfer between the donor and one of the two acceptor molecules (A ?-D ?+1 A and AD ?+ A ?-). Systems presenting a complete charge transfer give rise to two stable, weakly coupled, and degenerate ionic electronic states, A - A + A and AD + A - for an ADA architecture and D + A -D and DA -D + for a DAD In these cases, the two forms differ by both their intramolecular geometries and the relative positions of their constituents. It seems rather difficult to conceive such bistable molecular systems using closed-shell molecules, while a donor radical and a closed-shell acceptor or an acceptor radical and closed-shell donor can generate very stable ionic states. It is assumed that the relative positions of the donor and acceptor molecules can be fixed using chemical bridges constituted of rigid or flexible ligands. The writing and reading processes are discussed for each system as well as the information stability when a large number of bits are juxtaposed on a surface.

Guihery, Nathalie; Durand, Gérard; Lepetit, Marie-Bernadette

1994-05-01

417

Valence, arousal, and task effects in emotional prosody processing  

PubMed Central

Previous research suggests that emotional prosody processing is a highly rapid and complex process. In particular, it has been shown that different basic emotions can be differentiated in an early event-related brain potential (ERP) component, the P200. Often, the P200 is followed by later long lasting ERPs such as the late positive complex. The current experiment set out to explore in how far emotionality and arousal can modulate these previously reported ERP components. In addition, we also investigated the influence of task demands (implicit vs. explicit evaluation of stimuli). Participants listened to pseudo-sentences (sentences with no lexical content) spoken in six different emotions or in a neutral tone of voice while they either rated the arousal level of the speaker or their own arousal level. Results confirm that different emotional intonations can first be differentiated in the P200 component, reflecting a first emotional encoding of the stimulus possibly including a valence tagging process. A marginal significant arousal effect was also found in this time-window with high arousing stimuli eliciting a stronger P200 than low arousing stimuli. The P200 component was followed by a long lasting positive ERP between 400 and 750 ms. In this late time-window, both emotion and arousal effects were found. No effects of task were observed in either time-window. Taken together, results suggest that emotion relevant details are robustly decoded during early processing and late processing stages while arousal information is only reliably taken into consideration at a later stage of processing.

Paulmann, Silke; Bleichner, Martin; Kotz, Sonja A.

2013-01-01

418

Chiral perturbation theory for staggered sea quarks and Ginsparg-Wilson valence quarks  

SciTech Connect

We study lattice QCD with staggered sea and Ginsparg-Wilson valence quarks. The Symanzik effective action for this mixed lattice theory, including the lattice spacing contributions of O(a{sup 2}), is derived. Using this effective theory we construct the leading-order chiral Lagrangian. The masses and decay constants of pseudoscalars containing two Ginsparg-Wilson valence quarks are computed at one-loop order.

Baer, Oliver [Institute of Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8571 (Japan); Bernard, Claude [Department of Physics, Washington University, St. Louis, Missouri 63130 (United States); Rupak, Gautam [Los Alamos National Laboratory, Theoretical Division T-16, Los Alamos, New Mexico 87545 (United States); Shoresh, Noam [Department of Physics, Boston University, Boston, Massachusetts 02215 (United States)

2005-09-01

419

Many-body calculation of the valence photoemission spectrum of Fe(CO)5  

Microsoft Academic Search

The valence photoemission spectrum of Fe(CO)5 is calculated by the ADC(3) Green’s function method. The overall agreement with the experiment is good. It is shown that the quasiparticle picture (QPP) for the outer and inner valence levels (except the 8a‘2 level) derived primarily from CO ligand orbitals breaks down completely due to the one-hole\\/two-hole–one-particle (1h\\/2h1p) charge transfer (CT) coupling in

M. Ohno; W. von Niessen

1991-01-01

420

Role of the topology on the magnetic properties of mixed-valence trinuclear manganese clusters  

Microsoft Academic Search

The magnetic behavior of mixed-valence trinuclear clusters d5-d4-d4 is discussed on the basis of a model that takes into acount the competing effect between valence delocalization and both Heisenberg exchange and distortion of the trimer. For the first time, the different transfer pathways are taken into account. As far as the magnetic properties are concerned, the model anticipates drastic differences

C. J. Gómez-García; E. Coronado; R. Georges; G. Pourroy

1992-01-01

421

Valence Control and Solvent Extraction of Americium in the Presence of Ammonium Phosphotungstate  

Microsoft Academic Search

Fundamental investigations on valence control and solvent extraction of americium were carried out to develop a method for americium separation from reprocessing solution. In order to adjust americium valency from III to IV and VI, (NH4)10P2W 17O61 synthesized was used as complexant stabilizing Am(IV). Oxidation behavior of americium was investigated as a function of (NH4)10P2W 17O61 americium ratio. Using 0.1M

Mamoru KAMOSHIDA; Tetsuo FUKASAWA; Fumio KAWAMURA

1998-01-01

422

Evidence for ``held-back'' valence quarks from particle ratios in pp and pp collisions  

NASA Astrophysics Data System (ADS)

We show that recently measured particle ratios in the central region of pp and pp collisions give valuable information on the fate of valence quarks in a soft hadronic collision, indicating that a valence quark from each initial hadron is ``held back'' with a small momentum fraction. This mechanism is a key feature of the dual parton fragmentation approach to low-pT multiparticle production.

Capella, A.; Tran Thanh van, J.; Sukhatme, U. P.

1983-06-01

423

Photochemically-Induced Valency Adjustment of Plutonium and Neptunium in Nitric Acid Solution Using Mercury Lamp  

Microsoft Academic Search

A photochemically-induced valency adjustment method has been studied to remove Np from the mixed nitric acid solutions of Pu and Np in connection with the Purex reprocessing. The valencies of Pu and Np ions were adjusted to be Pu(HI) and Np(V) under the initial conditions and their concentrations were 1x10 and 1x10 mol·dm, respectively. The experiments were carried out under

Yukio WADA; Kouji WADA; Takayuki GOIBUCHI; Hiroshi TOMIYASU

1994-01-01

424

Resonance-assisted hydrogen bonds revisited. Resonance stabilization vs. charge delocalization.  

PubMed

The origins of stabilization in the short strong hydrogen bonds commonly referred to as "resonance-assisted" (RAHB) have been revisited using the modern valence-bond theory, the hybrid variational-perturbational interaction energy decomposition scheme and atoms in molecules (AIM) analysis. Dimers of carboxylic acids and amides have been chosen as the model structures for intermolecular RAHBs, while for the intramolecular case malondialdehyde and its substituted derivatives have been selected. The estimated (negligible) resonance stabilization energies and relative magnitudes of interaction energy components indicate that the origin of stabilization in the studied complexes is charge-delocalization. Although in the case of intramolecular RAHBs the resonance effects are much more pronounced, still they are a relatively minor contribution to the total stabilization energy. In fact, the estimated resonance stabilization energies diminish with an increasing strength of the hydrogen bond (as indicated by AIM and structural descriptors). PMID:23322083

Góra, Robert W; Maj, Micha?; Grabowski, S?awomir J

2013-01-15

425

Optimal loading of molecular bonds.  

PubMed

A corollary of the Bell equation of bond rupture is that the bond transfers a maximal impulse during its lifetime when the applied force equals k(B)T/x*. It is proposed that the designs of biological systems converge toward loading bonds with this optimal force to minimize the need for self-healing and to optimize energy transfer. PMID:23025846

Hess, Henry

2012-10-03

426

46 CFR Sec. 10 - Bonds.  

Code of Federal Regulations, 2012 CFR

...AUTHORITY MASTER LUMP SUM REPAIR CONTRACT-NSA-LUMPSUMREP Sec. 10 Bonds...payment bonds required by Article 14 of the NSA-LUMPSUMREP Contract. The stand- ard...payment bond requirements of Article 14 of the NSA-LUMPSUMREP Contract, the...

2012-10-01

427

Thermodynamics of the first-order valence transition in YbInCu{sub 4}  

SciTech Connect

We present measurements of the specific heat and complete elastic moduli of YbInCu{sub 4} as a function of temperature in order to complement existing thermal expansion data. Together these data allow a complete analysis of the thermodynamics of the first-order isostructural valence transition in YbInCu{sub 4}. The Clausius-Clapeyron equation predicts well the measured pressure dependence of the valence transition temperature. Estimates of the Gruneisen parameter from thermodynamic measurements and from pressure-dependent magnetic susceptibility in both the high-temperature and low-temperature phases of YbInCu{sub 4} are in good agreement. On the other hand, a Gruneisen analysis of the change in Kondo temperature at the valence transition fails, emphasizing the importance of carrier-density changes associated with the valence transition, unlike in the case of the {gamma}-{alpha} transition in elemental Ce. Finally, we address the issue of precursive rounding in the elastic moduli for temperatures greater than the valence transition temperature and argue that thermodynamically YbInCu{sub 4}{close_quote}s valence transition is indeed first order. {copyright} {ital 1998} {ital The American Physical Society}

Sarrao, J.L. [MST Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Ramirez, A.P. [Bell Laboratories, Lucent Technology, Murray Hill, New Jersey 07974 (United States); Darling, T.W.; Freibert, F.; Migliori, A. [MST Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Immer, C.D.; Fisk, Z. [National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306 (United States); Uwatoko, Y. [Department of Physics, Saitama University, Urawa, Saitama 338 (Japan)

1998-07-01

428

Experimental and theoretical study of core-valence double photoionization of OCS  

SciTech Connect

O 1s, C 1s, and S 2p core-valence double ionization electron spectra of the OCS molecule have been obtained experimentally by a time-of-flight photoelectron-photoelectron coincidence spectroscopy technique. In order to analyze and assign the spectral features observed, we present a protocol for computing core-valence ionization energies of such systems. The protocol is based on a restricted active space multiconfigurational self-consistent field (MCSCF) methodology with a freeze-relax procedure to guarantee a correct core-valence state root index without variational collapse. Corrections for extended dynamical correlation and core-core correlation, respectively, are made by multiconfigurational perturbation theory and by uncontracted basis set Moeller-Plesset theory. Envisioning applications to larger molecules, a spin-restricted open-shell density functional method is also applied for the lowest core-valence energies. Furthermore, cross sections through a scheme for computing multiatom Auger transitions generating core-valence holes are presented. We find that the procedure outlined is capable of deriving the energy onset of core-valence ionization within a fraction of an eV and that assignments can be made of the most salient spectral features.

Niskanen, J. [Department of Physics, University of Oulu, Box 3000, FIN-90014 Oulu (Finland); Department of Theoretical Chemistry, School of Biotechnology, Royal Institute of Technology, SE-10691 Stockholm (Sweden); Carravetta, V. [Institute of Chemical Physical Processes, CNR, via Moruzzi 1, I-56124, Pisa (Italy); Vahtras, O.; Aagren, H. [Department of Theoretical Chemistry, School of Biotechnology, Royal Institute of Technology, SE-10691 Stockholm (Sweden); Aksela, H. [Department of Physics, University of Oulu, Box 3000, FIN-90014 Oulu (Finland); Andersson, E.; Hedin, L.; Karlsson, L.; Rubensson, J.-E.; Feifel, R. [Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120 Uppsala (Sweden); Linusson, P. [Department of Physics, Stockholm University, AlbaNova University Centre, SE-10691 Stockholm (Sweden); Eland, J. H. D. [Department of Chemistry, Physical and Theoretical Chemistry Laboratory, Oxford University, South Parks Road, Oxford OX1 3QZ (United Kingdom); Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120 Uppsala (Sweden)

2010-10-15

429

The power of emotional valence-from cognitive to affective processes in reading.  

PubMed

The comprehension of stories requires the reader to imagine the cognitive and affective states of the characters. The content of many stories is unpleasant, as they often deal with conflict, disturbance or crisis. Nevertheless, unpleasant stories can be liked and enjoyed. In this fMRI study, we used a parametric approach to examine (1) the capacity of increasing negative valence of story contents to activate the mentalizing network (cognitive and affective theory of mind, ToM), and (2) the neural substrate of liking negatively valenced narratives. A set of 80 short narratives was compiled, ranging from neutral to negative emotional valence. For each story mean rating values on valence and liking were obtained from a group of 32 participants in a prestudy, and later included as parametric regressors in the fMRI analysis. Another group of 24 participants passively read the narratives in a three Tesla MRI scanner. Results revealed a stronger engagement of affective ToM-related brain areas with increasingly negative story valence. Stories that were unpleasant, but simultaneously liked, engaged the medial prefrontal cortex (mPFC), which might reflect the moral exploration of the story content. Further analysis showed that the more the mPFC becomes engaged during the reading of negatively valenced stories, the more coactivation can be observed in other brain areas related to the neural processing of affective ToM and empathy. PMID:22754519

Altmann, Ulrike; Bohrn, Isabel C; Lubrich, Oliver; Menninghaus, Winfried; Jacobs, Arthur M

2012-06-28

430

Valence, Arousal, and Cognitive Control: A Voluntary Task-Switching Study  

PubMed Central

The present study focused on the interplay between arousal, valence, and cognitive control. To this end, we investigated how arousal and valence associated with affective stimuli influenced cognitive flexibility when switching between tasks voluntarily. Three hypotheses were tested. First, a valence hypothesis that states that the positive valence of affective stimuli will facilitate both global and task-switching performance because of increased cognitive flexibility. Second, an arousal hypothesis that states that arousal, and not valence, will specifically impair task-switching performance by strengthening the previously executed task-set. Third, an attention hypothesis that states that both cognitive and emotional control ask for limited attentional resources, and predicts that arousal will impair both global and task-switching performance. The results showed that arousal affected task-switching but not global performance, possibly by phasic modulations of the noradrenergic system that reinforces the previously executed task. In addition, positive valence only affected global performance but not task-switching performance, possibly by phasic modulations of dopamine that stimulates the general ability to perform in a multitasking environment.

Demanet, Jelle; Liefooghe, Baptist; Verbruggen, Frederick

2011-01-01

431

Silver(I) complexes of the weakly coordinating solvents SO(2) and CH(2)Cl(2): crystal structures, bonding, and energetics of [Ag(OSO)][Al{OC(CF(3))(3)}(4)], [Ag(OSO)(2/2)][SbF(6)], and [Ag(CH(2)Cl(2))(2)][SbF(6)].  

PubMed

Pushing the limits of coordination chemistry: The most weakly coordinated silver complexes of the very weakly coordinating solvents dichloromethane and liquid sulfur dioxide were prepared. Special techniques at low temperatures and the use of weakly coordinating anions allowed structural characterization of [Ag(OSO)][Al{OC(CF(3))(3)}(4)], [Ag(OSO)(2/2)][SbF(6)], and [Ag(Cl(2)CH(2))(2)][SbF(6)] (see figure). An investigation of the bonding shows that these complexes are mainly stabilized by electrostatic monopole-dipole interactions.The synthetically useful solvent-free silver(I) salt Ag[Al(pftb)(4)] (pftb=--OC(CF(3))(3)) was prepared by metathesis reaction of Li[Al(pftb)(4)] with Ag[SbF(6)] in liquid SO(2). The solvated complexes [Ag(OSO)][Al(pftb)(4)], [Ag(OSO)(2/2)][SbF(6)], and [Ag(CH(2)Cl(2))(2)][SbF(6)] were prepared and isolated by special techniques at low temperatures and structurally characterized by single-crystal X-ray diffraction. The SO(2) complexes provide the first examples of coordination of the very weak Lewis base SO(2) to silver(I). The SO(2) molecule in [Ag(OSO)][Al(pftb)(4)] is eta(1)-O coordinated to Ag(+), while the SO(2) ligands in [Ag(OSO)(2/2)][SbF(6)] bridge two Ag(+) ions in an eta(2)-O,O' (trans,trans) manner. [Ag(CH(2)Cl(2))(2)][SbF(6)] contains [Ag(CH(2)Cl(2))(2)](+) ions linked through [SbF(6)](-) ions to give a polymeric structure. The solid-state silver(I) ion affinities (SIA) of SO(2) and CH(2)Cl(2), based on bond lengths and corresponding valence units in the corresponding complexes and tensimetric titrations of Ag[Al(pftb)(4)] and Ag[SbF(6)] with SO(2) vapor, show that SO(2) is a weaker ligand to Ag(+) than the commonly used weakly coordinating solvent CH(2)Cl(2) and indicated that binding strength of SO(2) to silver(I) in the silver(I) salts increases with increasing size of the corresponding counteranion ([Al(pftb)(4)](-)>[SbF(6)](-)). The experimental findings are in good agreement with theoretical gas-phase ligand-binding energies of [Ag(L)(n)](+) (L=SO(2), CH(2)Cl(2); n=1, 2) and solid-state enthalpies obtained from Born-Fajans-Haber cycles by using the volume-based thermodynamics (VBT) approach. Bonding analysis (VB, NBO, MO) of [Ag(L)(n)](+) suggests that these complexes are almost completely stabilized by electrostatic interaction, that is, monopole-dipole interaction, with almost no covalent contribution by electron donation from the ligand orbitals into the vacant 5s orbital of Ag(+). All experimental findings and theoretical considerations demonstrate that SO(2) is less covalently bound to Ag(+) than CH(2)Cl(2) and support the thesis that SO(2) is a polar but non-coordinating solvent towards Ag(+). PMID:19449357

Decken, Andreas; Knapp, Carsten; Nikiforov, Grigori B; Passmore, Jack; Rautiainen, J Mikko; Wang, Xinping; Zeng, Xiaoqing

2009-06-22

432

Electronic Structure and Bonding in Clusters: Theoretical Studies  

NASA Astrophysics Data System (ADS)

The electronic structures of small Al n , n=5, 9, 13, clusters with bulk geometry are studied using the ab initio Hartree-Fock-LCAO method. The cluster ground states have always multiplicity higher than the lowest possible value. However, the energy difference between ground and lowest low spin state decreases with increasing cluster size. The energy range of the Al n cluster valence levels is comparable with the width of the occupied part of the 3 sp band in bulk Al. The different binding mechanisms that arise when a CO molecule interacts with Al n clusters in different coordination sites are analyzed in detail with the constrained space orbital variation (CSOV) method. Electrostatic and polarization contributions to the interaction are found to be important. Among charge transfer (donation) contributions ? electron transfer from Al n to CO corresponding to ? backbonding is energetically more important than ? electron transfer from CO to Al n characterizing the ? bond.

Hermann, K.; Hass, H. J.; Bagus, P. S.

1986-06-01

433

Connecting [NiFe]- and [FeFe]-hydrogenases: mixed-valence nickel-iron dithiolates with rotated structures.  

PubMed

New mixed-valence iron-nickel dithiolates are described that exhibit structures similar to those of mixed-valence diiron dithiolates. The interaction of tricarbonyl salt [(dppe)Ni(pdt)Fe(CO)(3)]BF(4) ([1]BF(4), where dppe = Ph(2)PCH(2)CH(2)PPh(2) and pdt(2-) = -SCH(2)CH(2)CH(2)S-) with P-donor ligands (L) afforded the substituted derivatives [(dppe)Ni(pdt)Fe(CO)(2)L]BF(4) incorporating L = PHCy(2) ([1a]BF(4)), PPh(NEt(2))(2) ([1b]BF(4)), P(NMe(2))(3) ([1c]BF(4)), P(i-Pr)(3) ([1d]BF(4)), and PCy(3) ([1e]BF(4)). The related precursor [(dcpe)Ni(pdt)Fe(CO)(3)]BF(4) ([2]BF(4), where dcpe = Cy(2)PCH(2)CH(2)PCy(2)) gave the more electron-rich family of compounds [(dcpe)Ni(pdt)Fe(CO)(2)L]BF(4) for L = PPh(2)(2-pyridyl) ([2a]BF(4)), PPh(3) ([2b]BF(4)), and PCy(3) ([2c]BF(4)). For bulky and strongly basic monophosphorus ligands, the salts feature distorted coordination geometries at iron: crystallographic analyses of [1e]BF(4) and [2c]BF(4) showed that they adopt "rotated" Fe(I) centers, in which PCy(3) occupies a basal site and one CO ligand partially bridges the Ni and Fe centers. Like the undistorted mixed-valence derivatives, members of the new class of complexes are described as Ni(II)Fe(I) (S = ½) systems according to electron paramagnetic resonance spectroscopy, although with attenuated (31)P hyperfine interactions. Density functional theory calculations using the BP86, B3LYP, and PBE0 exchange-correlation functionals agree with the structural and spectroscopic data, suggesting that the spin for [1e](+) is mostly localized in a Fe(I)-centered d(z(2)) orbital, orthogonal to the Fe-P bond. The PCy(3) complexes, rare examples of species featuring "rotated" Fe centers, both structurally and spectroscopically incorporate features from homobimetallic mixed-valence diiron dithiolates. Also, when the NiS(2)Fe core of the [NiFe]-hydrogenase active site is reproduced, the "hybrid models" incorporate key features of the two major classes of hydrogenase. Furthermore, cyclic voltammetry experiments suggest that the highly basic phosphine ligands enable a second oxidation corresponding to the couple [(dxpe)Ni(pdt)Fe(CO)(2)L](+/2+). The resulting unsaturated 32e(-) dications represent the closest approach to modeling the highly electrophilic Ni-SI(a) state. In the case of L = PPh(2) (2-pyridyl), chelation of this ligand accompanies the second oxidation. PMID:22838645

Schilter, David; Rauchfuss, Thomas B; Stein, Matthias

2012-07-27

434

Bonding characteristics, thermal expansibility, and compressibility of RXO(4) (R = rare earths, X = P, As) within monazite and zircon structures.  

PubMed

Systematically theoretical research was performed on the monazite- and zircon-structure RXO(4) (R = Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; X = P, As) series by using the chemical bond theory of dielectric description. The chemical bond properties of R-O and X-O bonds were presented. In the zircon phase, the covalency fractions of X-O bonds increased in the order of V-O < As-O < P-O, which was in accordance with the ionic radii and electronegative trends, and the covalency fractions of R-O bonds varied slightly due to the lanthanide contraction. While in the monazite phase, both R-O and X-O bonds were divided into two groups by their covalency fractions. The contributions from the bond to the lattice energy, linear thermal expansion coefficient (LTEC), and bulk modulus were explored. The X-O bonds with short bond lengths and high chemical valence made greater contributions to the lattice energy and performed nearly rigidly during the deformation. A regular variation of lattice energy, LTEC, and bulk modulus with the ionic radii of the lanthanides was observed in both monazite and zircon phases. PMID:19323526

Li, Huaiyong; Zhang, Siyuan; Zhou, Shihong; Cao, Xueqiang

2009-05-18

435

Hydrogen bonding and proton transfer in small hydroxylammonium nitrate clusters: A theoretical study  

NASA Astrophysics Data System (ADS)

Structures and energies of gas-phase hydroxylammonium nitrate (HAN), HONH3NO3, are determined using density functional theory and the 6-311++G(d,p) basis set. Three stable configurations are found for HAN which involve strong hydrogen bonding between hydroxylamine and nitric acid molecules. In the most stable configuration, both the oxygen and the nitrogen of hydroxylamine are hydrogen bonded to sites on the nitric acid molecule. In the less stable HAN structures only the oxygen or the nitrogen of hydroxylamine are hydrogen bonded. Two stable structures for the (HAN)2 complex are investigated. The more stable structure is ionic, with the nitric acid proton having transferred to the nitrogen of hydroxylamine. Strong electrostatic and hydrogen-bonding interactions stabilize this structure. The other stable form of (HAN)2 has fewer hydrogen bonds and is composed of interacting neutral nitric acid and hydroxylamine molecules. Binding energies are determined for all structures along with corrections for basis set superposition errors in the HAN molecules. Proton exchange reaction paths are studied for the HAN configurations. The saddle points for the proton exchange process are ionic forms of HAN with interacting HONH3+ and NO3- moieties. These ionic structures are 13.5 and 13.6 kcal/mol higher in energy than the neutral hydrogen-bonded complexs of HONH2 and HNO3 from which they are formed. The electrostatic attractions between the ions are sufficient to stabilize the ionic form of (HAN)2, whereas in the HAN ``monomer'' the interaction energy for single HONH3+ and NO3- ions is not sufficient to compensate for the energy required for proton transfer from nitric acid to the hydroxylamine group. A correlation based on the bond-valence theory which describes the bond lengths of the hydrogen bonds is examined for the complexes. All the hydrogen bonds follow the correlation well.

Alavi, Saman; Thompson, Donald L.

2003-08-01

436

Low temperature reactive bonding  

SciTech Connect

Disclosed is a joining technique that requires no external heat source and generates very little heat. It involves the reaction of thin multilayered films deposited on faying (closely fit or joining) surfaces to create a stable compound that functions as an intermediate or braze material in order to create a high strength bond. While high temperatures are reached in the reaction of the multilayer film, very little heat is generated because the films are very thin. It is essentially a room temperature joining process. It can be used for joining silicon wafers and integrated circuits.

Makowiecki, D.M.; Bionta, R.M.

1995-06-23

437

Low temperature reactive bonding  

DOEpatents

The joining technique is disclosed that requires no external heat source and generates very little heat during joining. It involves the reaction of thin multilayered films deposited on faying surfaces to create a stable compound that functions as an intermediate or braze material in order to create a high strength bond. While high temperatures are reached in the reaction of the multilayer film, very little heat is generated because the films are very thin. It is essentially a room temperature joining process. 5 figures.

Makowiecki, D.M.; Bionta, R.M.

1995-01-17

438

Mixed-valence heptanuclear iron complexes with ferromagnetic interaction.  

PubMed

Three new Prussian blue analogues, heptanuclear mixed-valence iron complexes of the type [Fe(II)(CN)(6){Fe(III)(1(-2H))}(6)]Cl(2)·nH(2)O, were synthesized and structurally and spectrally characterized, and their magnetic properties were investigated (1(-2H) corresponds to doubly deprotoned Schiff-base pentadentate ligands 1a, N,N'-bis(2-hydroxybenzylidene)-1,5-diamino-3-azapentane, 1b, N,N'-bis(3-ethoxy-2-hydroxybenzylidene)-1,7-diamino-4-azaheptane, or 1c, N,N'-bis(3-methoxy-2-hydroxybenzylidene)-1,6-diamino-3-azahexane). These compounds were formed by assembling the [Fe(CN)(6)](4-) building block with mononuclear complexes of the [Fe(1(-2H))Cl] type. X-ray structure analysis revealed that the complexes adopt a star-like architecture: the Fe(II) ion lies at the very center, and on its octahedral nodes the Fe(III) sites are coordinated in the Fe(II)-C?N-Fe(III) manner. The Schiff-base pentadentate ligand moiety 1(-2H) coordinates a single Fe(III) center in two complexes 3b and 3c. Ligands 1a(-2H) in the complex cation of 3a adopt an unusual coordination mode: three donor atoms of the same ligand (one O and two N) coordinate one Fe(III), whereas the remaining N' and O' donor atoms coordinate the neighboring Fe(III) center creating the {Fe(ON(2))(N'O')N?} chromophore involving two 1a(-2H) ligand moieties. Moreover, three Fe(III) centers are interconnected with three 1a(-2H) ligands in such a manner that two {Fe(III)(3)(1a(-2H))(3)} units form two intramolecular rings. Magnetic investigation of the heptanuclear complexes revealed the high-spin state of all six Fe(III) coordination sites (s = 5/2), while the very central Fe(II) site is in the low-spin state (s = 0). At low temperature, the ferromagnetic exchange interactions stay evident for all three complexes. Mössbauer spectra of compounds 3a and 3b revealed a presence of two different doublets for both compounds: the major doublet is related to six Fe(III) high-spin coordination sites and the minor doublet refers to the low-spin very central Fe(II). PMID:23145981

Šalitroš, Ivan; Bo?a, Roman; Herchel, Radovan; Moncol, Ján; Nemec, Ivan; Ruben, Mario; Renz, Franz

2012-11-12

439

Mixed valence in YBaFe(2)O(5).  

PubMed

YBaFe(2)O(5) has been synthesized by heating a nanoscale citrate precursor in a carefully controlled reducing environment. Successful synthesis of a single-phase sample can only be achieved in a narrow window of oxygen partial pressures and temperatures. YBaFe(2)O(5) adopts an oxygen-deficient perovskite-type structure, which contains double layers of corner sharing FeO(5) square pyramids separated by Y(3+) ions. At T(N) congruent with 430 K, tetragonal (P4/mmm) and paramagnetic YBaFe(2)O(5) orders antiferromagnetically (AFM) experiencing a slight orthorhombic distortion (Pmmm). Around this temperature, it can be characterized as a class-III mixed valence (MV) compound, where all iron atoms exist as equivalent MV Fe(2.5+) ions. The magnetic structure is characterized by AFM Fe-O-Fe superexchange coupling within the double layers and a ferromagnetic Fe-Fe direct-exchange coupling between neighboring double layers. Upon cooling below approximately 335 K, a premonitory charge ordering (2Fe(2.5+) --> Fe(2.5+delta) + Fe(2.5)(-delta)) into a class-II MV phase takes place. This transition is detected by differential scanning calorimetry, but powder diffraction techniques fail to detect any volume change or a long-range structural order. At approximately 308 K, a complete charge ordering (2Fe(2.5+) --> Fe(2+) + Fe(3+)) into a class-I MV compound takes place. This charge localization triggers a number of changes in the crystal, magnetic, and electronic structure of YBaFe(2)O(5). The magnetic structure rearranges to a G-type AFM structure, where both the Fe-O-Fe superexchange and the Fe-Fe direct-exchange couplings are antiferromagnetic. The crystal structure rearranges (Pmma) to accommodate alternating chains of Fe(2+) and Fe(3+) running along b and an unexpectedly large cooperative Jahn-Teller distortion about the high-spin Fe(2+) ions. This order of charges does not fulfill the Anderson condition, and it rather corresponds to an ordering of doubly occupied Fe(2+) d(xz) orbitals. Comparisons with YBaMn(2)O(5) and YBaCo(2)O(5) are made to highlight the impact of changing the d-electron count. PMID:12588147

Woodward, Patrick M; Karen, Pavel

2003-02-24

440

Laplacian of charge density for binuclear complexes: The metal-metal bond in the Rh 24+ unit  

NASA Astrophysics Data System (ADS)

The Laplacian of the charge density has been computed for models of the binuclear complexes Rh 2(tcl) 4 ( 1) and Rh 2(tcl) 4CO ( 2), with tcl=thiocaprolactamate. The inner-valence shell charge concentration (i-VSCC) of the rhodium atom exhibits eight maxima in agreement with the pattern predicted by the crystal field theory assumptions. The rhodium-rhodium bond in complexes 1 and 2 is not characterized by large accumulations of charge between both metals. As previously suggested by electron deformation density analysis, the metal-metal bond does not behave like usual covalent bonds. The analysis of Laplacian charge-density maps suggests a weakening of the rhodium-rhodium bond induced by axial CO coordination.

Bo, Carles; Poblet, Josep M.; Bénard, Marc

1990-05-01

441

Ab initio study of valence and Rydberg states of CH3Br.  

PubMed

We performed configuration interaction ab initio calculations on the valence and 5s, 5p(a(1)), and 5p(e) Rydberg bands of the CH(3)Br molecule as a function of the methyl-bromide distance for frozen C(3v) geometries. The valence state potential energy curves are repulsive, the Rydberg state ones are similar to the one of the CH(3)Br(+) ion with a minimum at short distance. One state emerging from the 5p(e) band has valence and ion-pair characters as distance increases and the corresponding potential curve has a second minimum at large distance. This state has a very strong parallel electric dipole transition moment with the ground state and plays a central role in UV photon absorption spectra. It is also responsible for the parallel character of the anisotropy parameters measured in ion-pair production experiments. In each band, there is a single state, which has a non-negligible transition moment with the ground state, corresponding to a transition perpendicular to the molecular axis of symmetry, except for the 5p(e) band where it is parallel. The perpendicular transition moments between ground and valence states increase sharply as methyl-bromide distance decreases due to a mixing between valence and 5s Rydberg band at short distance. In each band, spin orbit interaction produces a pair of states, which have significant transition moments with the ground one. In the valence band, the mixing between singlet and triplet states is weak and the perpendicular transition to the (1)Q(1) state is dominant. In each Rydberg band, however, spin-orbit interaction is larger than the exchange interaction and the two significant transition moments with the ground state have comparable strengths. The valence band has an additional state ((1)Q(0)) with significant parallel transition moment induced by spin-orbit interaction with the ground state at large distance. PMID:19566152

Escure, Christelle; Leininger, Thierry; Lepetit, Bruno

2009-06-28

442

27 CFR 19.165 - Unit bonds.  

Code of Federal Regulations, 2013 CFR

...Unit bonds. (a) Unit bond covering operations and withdrawals. If a person is otherwise required to file bonds for both operations at...distilled spirits plants, the person may instead submit a single unit bond that provides all of...

2013-04-01

443

27 CFR 19.161 - Operations bond.  

Code of Federal Regulations, 2013 CFR

...Requirements for Operations and Withdrawal Bonds § 19.161 Operations bond. (a) General. Any person who intends to establish a distilled spirits plant must furnish an operations bond (or a unit bond, see § 19.165)...

2013-04-01

444

Analysis of valence-electron structures of Y/sub 3/Al/sub 5/O/sub 12/(YAG) and Al/sub 2/O/sub 3/, Cr/sub 2/O/sub 2/ (Ruby), a study of certain properties of these laser materials related to their valence-electron structures  

SciTech Connect

A direct method of determination of the valence-electron structure from its crystal structure has been presented by the writer at XIIth International Congress of Crystallography, at Ottawa, 1981. Here the method is applied to determine the valence-electron structures of Y/sub 3/Al/sub 5/O/sub 12/ (YAG) and Al/sub 2/O/sub 3/, Cr/sub 2/O/sub 3/ (ruby) to see how certain properties of these laser materials are related to their valence-electron structures. The first point observed is the very strong, continuous, but zig-zag three-dimensional fractional covalent M-O bond nets (M = Al or Cr) being connected with the high melting points, the great resistance against the puncture by the strong laser beam. In the case of Nd-YAG, the distortion caused by the replacement of the Y atoms by almost the same size Nd atoms is small. On the other hand, because of the similarity of the valence-electron structures of ..cap alpha..-Al/sub 2/O/sub 3/ and Cr/sub 2/O/sub 3/, the replacement of Al atoms by the little larger size Cr atoms in small amount is easily understood. The large atomic spins of magnetic moment m/sub B/ = 2.76 ..mu../sub B/ (= experiment value, the theoretical m/sub B/ = 2.70/sub 2/ ..mu../sub B/) of Cr atoms pointing parallel to the c axis of the hexagonal lattice, is found to be due to the direction of the spin situated in the space of lowest density space of the valence-electron cloud distribution. This agrees with the result of ..cap alpha..-Fe disclosed in the paper Electron theory of the magnetic moment structures of ..cap alpha..-Fe, epsilon-Co, Ni from neutron diffraction experiments presented at the Symposium on Neutron Scattering, Argonne National Laboratory, 1981. This will be found also true in many other oxides like ..cap alpha..-Fe/sub 2/O/sub 3/, FeTiO/sub 3/, MnTiO/sub 3/ and so on.

Yu, S.H.; Yu, L.H.

1982-01-01

445

27 CFR 40.138 - Approval of bond and extension of coverage of bond.  

Code of Federal Regulations, 2013 CFR

...TOBACCO Bonds and Extensions of Coverage of Bonds § 40.138 Approval of bond and extension of coverage of bond. No person shall commence operations under any bond, nor extend his operations, until he receives from the appropriate TTB...

2013-04-01

446

27 CFR 44.127 - Approval of bond and extension of coverage of bond.  

Code of Federal Regulations, 2013 CFR

...TAX Bonds and Extensions of Coverage of Bonds § 44.127 Approval of bond and extension of coverage of bond. No person shall commence operations under any bond, nor extend his operations, until he receives from the appropriate TTB...

2013-04-01

447

Effect of pressure-induced freezing on the energy of the intervalence electronic absorption band of a binuclear mixed-valence complex  

SciTech Connect

The results of a study of the effect of pressure-induced freezing on the energy of the intravalence-transfer (IT) band of the I/sub 3//sup /minus// salt of the mixed-valence diferrocenylacetylene cation are reported. Spectra taken at pressures below and above the freezing point exhibit peak shifts significantly to lower energy but by less than 40% of the predicted value. It is proposed that for intramolecular electron transfer within a large metal complex with pi electrons, the field supplied by the ligands in addition to that of the electrons in the metal-ligand bond plus that of a relatively rigid solvation shell dilutes the effect of the dielectric continuum. 15 references, 1 figure.

Hammack, W.S.; Drickamer, H.G.; Lowery, M.D.; Hendrickson, D.N.

1988-04-06

448

Independent structural and valence state transitions in the cation-ordered double perovskites Ba{sub 2-x}Sr{sub x}TbIrO{sub 6}  

SciTech Connect

Synchrotron X-ray and neutron powder diffraction were used to investigate the formation, structure and bonding in the double perovskite Ba{sub 2-x}Sr{sub x}TbIrO{sub 6} solid solutions. The results showed that these oxides all exhibit ordering of the Tb and Ir cations in a double perovskite-type structure. Three distinct structural types differing in symmetry and/or valence states were formed depending on the precise Ba:Sr ratio on the perovskite A site; x=<0.3 cubic (Fm3-bar m) with Tb{sup 4+} and Ir{sup 4+}; 0.4==1.2 monoclinic (P2{sub 1}/n) with Tb{sup 3+} and Ir{sup 5+}. The transitions between these appear to be first order in nature.

Zhou Qingdi [Centre for Structural Biology and Chemistry, School of Chemistry, University of Sydney, Sydney, NSW 2006 (Australia); Kennedy, Brendan J. [Centre for Structural Biology and Chemistry, School of Chemistry, University of Sydney, Sydney, NSW 2006 (Australia)]. E-mail: kennedyb@chem.usyd.edu.au

2005-11-15

449

[SIBSytem: innovation for bracket bonding?].  

PubMed

The orthodontic bracket placement has known two major improvements these last fifty years: first with the ability of bonding brackets directly on the enamel (Newmann 1965); second with the indirect bonding procedure introduced by Silvermann and Cohen in 1972. If we put aside the technological evolutions of bonding materials (brackets and adhesives), few refinements have occurred regarding the protocols in this period of time. Furthermore, direct bonding procedure seems to be used by a majority of orthodontists despite the rapidity, accuracy and ergonomics promised by indirect bonding protocol. The main originality of the system detailed in this article is to bond orthodontic brackets in a virtually predetermined position with indirect bonding advantages but with the efficiency of direct bonding because the adhesive is applied directly on the bracket base without pre-bonding necessity. This innovation has been allowed by the use of up-to-date CFAO technology. The article first describes the two components of the SIBSystem (SIBClip and SIBTray) and details the manufacturing stages. The clinical use is then evoked as well as the cautions and limits of this innovative bonding system. PMID:23719248

Moreau, Alexis

2013-05-30

450

Bond dissociation energies in second-row compounds.  

PubMed

Heats of formation at 0 and 298 K are predicted for PF3, PF5, PF3O, SF2, SF4, SF6, SF2O, SF2O2, and SF4O as well as a number of radicals derived from these stable compounds on the basis of coupled cluster theory [CCSD(T)] calculations extrapolated to the complete basis set limit. In order to achieve near chemical accuracy (+/-1 kcal/mol), additional corrections were added to the complete basis set binding energies based on frozen core coupled cluster theory energies: a correction for core-valence effects, a correction for scalar relativistic effects, a correction for first-order atomic spin-orbit effects, and vibrational zero-point energies. The calculated values substantially reduce the error limits for these species. A detailed comparison of adiabatic and diabatic bond dissociation energies (BDEs) is made and used to explain trends in the BDEs. Because the adiabatic BDEs of polyatomic molecules represent not only the energy required for breaking a specific bond but also contain any reorganization energies of the bonds in the resulting products, these BDEs can be quite different for each step in the stepwise loss of ligands in binary compounds. For example, the adiabatic BDE for the removal of one fluorine ligand from the very stable closed-shell SF6 molecule to give the unstable SF5 radical is 2.8 times the BDE needed for the removal of one fluorine ligand from the unstable SF5 radical to give the stable closed-shell SF4 molecule. Similarly, the BDE for the removal of one fluorine ligand from the stable closed-shell PF3O molecule to give the unstable PF2O radical is higher than the BDE needed to remove the oxygen atom to give the stable closed-shell PF3 molecule. The same principles govern the BDEs of the phosphorus fluorides and the sulfur oxofluorides. In polyatomic molecules, care must be exercised not to equate BDEs with the bond strengths of given bonds. The measurement of the bond strength or stiffness of a given bond represented by its force constant involves only a small displacement of the atoms near equilibrium and, therefo