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1

The Valence Bond Interpretation of Molecular Geometry.  

ERIC Educational Resources Information Center

Presents ways in which the valence bond (VB) theory describes the bonding and geometry of molecules, following directly from earlier principles laid down by Pauling and others. Two other theories (molecular orbital approach and valence shell electron pair repulsion) are discussed and compared to VB. (CS)

Smith, Derek W.

1980-01-01

2

Valence Bond Theory and Superconductivity.  

National Technical Information Service (NTIS)

Two necessary criteria for a theory of superconductivity are a phase coherence of the wave function and an attractive electron-electron interaction. We review how the BCS theory achieves these criteria and then show how a valence bond wave function can al...

R. P. Messmer R. B. Murphy

1987-01-01

3

Thinking and computing valence bond in organic chemistry 1 Dedicated to the memory of Professor Joseph Gerratt, in appreciation of his outstanding contributions to modern ab initio valence bond methodology. 1  

Microsoft Academic Search

This paper presents a short survey of some recent ab initio valence bond methods and their applications, and is aimed at justifying and encouraging a valence bond view of organic chemistry, as complementary to the molecular orbital approach.In the first section, the qualitative VB description of the elementary interactions is recalled and compared to the MO model. It is shown

Philippe C. Hiberty

1998-01-01

4

Valence bond all the way: from the degenerate H-exchange to cytochrome P450.  

PubMed

This is a personalized Perspective on the development of a valence bond (VB) view of chemical reactivity (J. Am. Chem. Soc., 1981, 103, 3692) as a LEGO process whereby one constructs "reactivity objects", such as barriers, transition states, and reaction intermediates from VB building blocks, and thereby understands and predicts chemical reactivity in a unified manner. In so doing, I have tried to give the reader a panoramic set of applications, from the simple H-exchange reaction all the way to alkane hydroxylation by cytochrome P450 (Prog. Phys. Org. Chem. 1985, 15, 197; Angew. Chem., Int. Ed., 1999, 38, 586). PMID:20574583

Shaik, Sason

2010-08-21

5

A tutorial for understanding chemical reactivity through the valence bond approach.  

PubMed

This is a tutorial on the usage of valence bond (VB) diagrams for understanding chemical reactivity in general, and hydrogen atom transfer (HAT) reactivity in particular. The tutorial instructs the reader how to construct the VB diagrams and how to estimate HAT barriers from raw data, starting with the simplest reaction H + H2 and going all the way to HAT in the enzyme cytochrome P450. Other reactions are treated as well, and some unifying principles are outlined. The tutorial projects the unity of reactivity treatments, following Coulson's dictum "give me insight, not numbers", albeit with its modern twist: giving numbers and insight. PMID:24710199

Usharani, Dandamudi; Lai, Wenzhen; Li, Chunsen; Chen, Hui; Danovich, David; Shaik, Sason

2014-07-21

6

Valence-Bond Monte Carlo Study of Random-Singlet Phase Formation  

NASA Astrophysics Data System (ADS)

In valence-bond Monte Carlo (VBMC)ootnotetextA. Sandvik, PRL 95, 207203 (2005). the ground state of a quantum spin system is sampled directly from the valence-bond (VB) basis --- a useful basis for visualizing the properties of singlet ground states. For example, the ground state of the uniform AFM spin-12 Heisenberg chain is characterized by strongly fluctuating bonds with power-law length distribution, while in the random-singlet phase (RSP) of a random Heisenberg chain these bonds, while still having a power-law length distribution, lock into a particular VB state on long length scales.ootnotetextD. S. Fisher, PRB 50, 3799 (1994). We use VBMC to directly probe the formation of a RSP by calculating both the average number of bonds nL leaving a block of L spins (the VB entanglement entropyootnotetextF. Alet, et al., PRL 99, 117204 (2007).), and its fluctuations, ?nL^2 = <- . For the uniform chain they have been calculated exactlyootnotetextJ. L. Jacobsen and H. Saleur, PRL 100, 087205 (2008). and shown to grow logarithmically with L --- signaling the strong bond fluctuations. For random chains while nL grows logarithmically with L, we find ?nL^2 saturate for large L, signaling the ``freezing" of the bonds into a particular random singlet state.

Tran, Huan; Bonesteel, Nicholas

2009-03-01

7

Exploring the Nature of the H[subscript 2] Bond. 1. Using Spreadsheet Calculations to Examine the Valence Bond and Molecular Orbital Methods  

ERIC Educational Resources Information Center

A three-part project for students in physical chemistry, computational chemistry, or independent study is described in which they explore applications of valence bond (VB) and molecular orbital-configuration interaction (MO-CI) treatments of H[subscript 2]. Using a scientific spreadsheet, students construct potential-energy (PE) curves for several…

Halpern, Arthur M.; Glendening, Eric D.

2013-01-01

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

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

10

Orbital Exponent Optimization in Elementary VB Calculations of the Chemical Bond in the Ground State of Simple Molecular Systems  

ERIC Educational Resources Information Center

Orbital exponent optimization in the elementary ab-initio VB calculation of the ground states of H[subscript 2][superscript +], H[subscript 2], He[subscript 2][superscript +], He[subscript 2] gives a fair description of the exchange-overlap component of the interatomic interaction that is important in the bond region. Correct bond lengths and…

Magnasco, Valerio

2008-01-01

11

The valence bond way: reactivity patterns of cytochrome P450 enzymes and synthetic analogs.  

PubMed

The preceding decade has witnessed an immense surge of activity in the bioinorganic chemistry of transition metal enzymes and synthetic analogs that model their operation. The wide range of research covers both experimental and theoretical investigations of structure and reactivity patterns. Theory, and especially density functional theory (DFT), has become a very useful tool, an important partner of experiment in resolving structural and mechanistic issues. This flare of activity has generated a great deal of knowledge on intermediates, transition states, barriers, rate constants, rate-equilibrium relationships, stereoselectivity, and so forth. This abundance of acquired knowledge has created the need for establishing order, namely, the outlining of broad generalizations, as well as the creation of a more-intuitive interface between experimental and theoretical data. The valence bond (VB) diagram model, originally developed for organic reactions, is such a theoretical framework that has the potential to guide the requisite generalizations in the field of bioinorganic chemical reactivity. In this Account, we briefly describe the principles of construction of VB diagrams for bioinorganic reactions, detailing applications in the booming research area of heme enzyme (specifically cytochrome P450) reactivity, and particularly two archetypal reactions of these enzymes, alkane hydroxylation and thioether sulfoxidation. For congruence with the lingua franca of bioinorganic chemistry, the VB model is formulated to create bridges to (i) the molecular orbital (MO) description, (ii) the oxidation state formulation of transition metal complexes, and (iii) widely used concepts such as the Bell-Evans-Polanyi (BEP) principle. The VB diagram model reveals the origins of the barrier, describes the formation of transition states and reaction intermediates, and allows the prediction of barrier heights and structure-reactivity relationships. Thus, from the VB diagram model, we can rationalize the mechanistic selection during alkane hydroxylation compared with thioether sulfoxidation, as well as the different behaviors of the spin states during the reactions with the active species of P450, the high-valent iron oxo species called compound I (Cpd I). Furthermore, the VB model leads to expressions that enable us to estimate barrier heights from easily accessible reactant properties, such as bond energies, ionization potential, and electron affinities. We further show that the model is not limited to these archetypal processes: its applicability is wider and more general. Accordingly, we outline the potential applications of these principles to other reactions of P450 (such as olefin epoxidation and arene hydroxylation) and to similar reactions of nonheme enzymes and synthetic models. The VB diagram model leads to a unified understanding of complex bioinorganic transformations, creates order in the data, and provides an important framework for making useful predictions. PMID:20527755

Shaik, Sason; Lai, Wenzhen; Chen, Hui; Wang, Yong

2010-08-17

12

The Menshutkin reaction in the gas phase and in aqueous solution: a valence bond study.  

PubMed

The recently developed (L. Song, W. Wu, Q. Zhang, S. Shaik, J. Phys. Chem. A 2004, 108, 6017-6024) valence bond method coupled to a polarized continuum model (VBPCM) is applied to the Menshutkin reaction, NH3+CH3Cl-->CH3NH3(+)+Cl-, in the gas phase and in aqueous solution. The computed barriers and reaction energies at the level of the breathing orbital VB method (P. C. Hiberty, J. P. Flament, E. Noizet, Chem. Phys. Lett. 1992, 189, 259), BOVB and VBPCM//BOVB, are comparable to CCSD(T) and CCSD(T)//PCM results and to experimental values in solution. The gas-phase reaction is endothermic and leads to an ion-pair complex via a late transition state. By contrast, the reaction in the aqueous phase is exothermic and leads to separate solvated ions as reaction products, via an early transition state. The VB calculations provide also the reactivity parameters needed to apply the valence bond state correlation diagram method, VBSCD (S. Shaik, A. Shurki, Angew. Chem. Int. Ed. 1999, 38, 586). It is shown that the reactivity parameters along with their semiempirical derivations provide together a satisfactory qualitative and quantitative account of the barriers. PMID:18061916

Su, Peifeng; Ying, Fuming; Wu, Wei; Hiberty, Philippe C; Shaik, Sason

2007-12-21

13

Superconductivity as a Synchronous Spatial Alternation of Valence Bonds.  

National Technical Information Service (NTIS)

A new theoretical model for superconductivity is proposed which depends on a pairing in real space (valence bonds). Pair-pair correlations establish an ordered array of such pairs and a synchronous alternation among equivalent coherent spatial arrays of v...

R. P. Messmer

1987-01-01

14

Reinterpretation of the bond-valence model with bond-order formalism: An improved bond-valence-based interatomic potential for PbTiO3  

NASA Astrophysics Data System (ADS)

We present a modified bond-valence model of PbTiO3 based on the principles of bond-valence and bond-valence vector conservation. The relationship between the bond-valence model and the bond-order potential is derived analytically in the framework of a tight-binding model. An energy term, bond-valence vector energy, is introduced into the atomistic model and the potential parameters are reoptimized. This model potential can be applied both to canonical-ensemble (NVT) and isobaric-isothermal ensemble (NPT) molecular dynamics (MD) simulations. This model reproduces the experimental phase transition in NVT MD simulations and also exhibits the experimental sequence of temperature-driven and pressure-driven phase transitions in NPT simulations. We expect that this improved bond-valence model can be applied to a broad range of inorganic materials.

Liu, Shi; Grinberg, Ilya; Takenaka, Hiroyuki; Rappe, Andrew M.

2013-09-01

15

Valence-Bond Concepts in Coordination Chemistry and the Nature of Metal-Metal Bonds.  

ERIC Educational Resources Information Center

Discusses the valence-bond method, applying it to some coordination compounds of metals, especially those involving metal-metal bonds. Suggests that transition metals can form as many as nine covalent bonds, permitting valence-theory to be extended to transition metal compounds in a more effective way than has been possible before. (JN)

Pauling, Linus; Herman, Zelek S.

1984-01-01

16

Electron-nucleon resonance model of valence bond  

SciTech Connect

The formation of valence bonds is traditionally considered as the displacement of electronic orbitals in space between interacting atoms. At the same time, a number of experimental facts, in particular, the existence of four-dimensional structural symmetry between the filling of electron shells and periodic properties of elements, require a change in the standard valence concept. A model in which valence bonds are caused by the resonant interaction between the shell electrons of one atom and the protons of another atom seems to be more adequate.

Magarshak, Yu., E-mail: Ym4@nyu.ed [MathTech Incorporation (United States)

2008-05-15

17

Bond length-bond valence relationships with particular reference to polyoxometalate chemistry  

Microsoft Academic Search

Bond length-bond valence relationships have been investigated fundamentally with emplasis on the M-O bonds in polyoxo compounds\\u000a (M=MoVI, WVI, VV, NbV, TaV). A large number of errors of different types has been made in the derivation of practically all of the published functions\\u000a and\\/or of the relevant parameters. Considering all sources of errors, bond length-bond valence functions and the relevant

K. Tytko; J. Mehmke; D. Kurad

18

Golden ratio and bond-valence parameters of hydrogen bonds of hydrated borates  

Microsoft Academic Search

A quantitative understanding of microscopic characteristics of hydrogen bonds in various compounds is quite important for the deep study of structure-property relationships of functional crystals. The present work skillfully applies the well-known Golden ratio in the quantitative analysis of bond lengths of O–H?O hydrogen bonds. On the basis of the bond valence sum model, the bond-valence parameters d0 of the

Daqiu Yu; Dongfeng Xue; Henryk Ratajczak

2006-01-01

19

Solvent-induced red-shifts for the proton stretch vibrational frequency in a hydrogen-bonded complex. 1. A valence bond-based theoretical approach.  

PubMed

A theory is presented for the proton stretch vibrational frequency ?AH for hydrogen (H-) bonded complexes of the acid dissociation type, that is, AH···B ? A(-)···HB(+)(but without complete proton transfer), in both polar and nonpolar solvents, with special attention given to the variation of ?AH with the solvent's dielectric constant ?. The theory involves a valence bond (VB) model for the complex's electronic structure, quantization of the complex's proton and H-bond motions, and a solvent coordinate accounting for nonequilibrium solvation. A general prediction is that ?AH decreases with increasing ? largely due to increased solvent stabilization of the ionic VB structure A(-)···HB(+) relative to the neutral VB structure AH···B. Theoretical ?AH versus 1/? slope expressions are derived; these differ for polar and nonpolar solvents and allow analysis of the solvent dependence of ?AH. The theory predicts that both polar and nonpolar slopes are determined by (i) a structure factor reflecting the complex's size/geometry, (ii) the complex's dipole moment in the ground vibrational state, and (iii) the dipole moment change in the transition, which especially reflects charge transfer and the solution phase proton potential shapes. The experimental proton frequency solvent dependence for several OH···O H-bonded complexes is successfully accounted for and analyzed with the theory. PMID:24807301

Kiefer, Philip M; Pines, Ehud; Pines, Dina; Hynes, James T

2014-07-17

20

Self-optimized resonating-valence-bond trial wavefunctions  

NASA Astrophysics Data System (ADS)

The spin singlet ground state of a quantum antiferromagnet can be expanded in the overcomplete basis of valence bond states. [1] To first approximation, the weight associated with each configuration is factorizable into a product of individual bond amplitudes. For nonfrustrated antiferromagnets with local interactions, mean field calculations indicate that the amplitudes are generically powerlaw in the bond length with exponent d+1, where d is the dimension of the lattice. Such states can be employed as the initial trial state for a valence bond projector calculation of the exact ground state. [2] Moreover, the amplitudes can be determined self- consistently by measuring the statistics of the bonds appear in the projected state and feeding this information back into the trial state. It is also possible to build some of the neglected bond-bond correlations into the trial state itself. The next level of approximation is to factorize the weights in terms of amplitudes that depend on the lengths and orientations of two valence bonds. Again, these amplitudes can be self-optimized in a simulation by matching them to the bond-- bond correlations of the projected state. [1] K. S. D. Beach and A. W. Sandvik, Nucl. Phys. B 750, 142 (2006).[2] A. W. Sandvik, Phys. Rev. Lett. 95, 207203 (2005).

Beach, Kevin; Sandvik, Anders

2007-03-01

21

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

SciTech Connect

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 ideality, bond valence controls the extent of solvation of individual functional groups, and bond valence and molecular shape controls local dielectric response. These results are consistent with our model of acidity, but completely at odds with other methods of predicting acidity constants for use in multisite complexation models. In particular, our ab initio molecular dynamics simulations of solvated monomers clearly indicate that hydrogen bonding between (hydr)oxo-groups and water molecules adjusts to obey the valence sum rule, rather than maintaining a fixed valence based on the coordination of the oxygen atom as predicted by the standard MUSIC model.

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

2006-08-15

22

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

NASA Astrophysics Data System (ADS)

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 ideality, bond valence controls the extent of solvation of individual functional groups, and bond valence and molecular shape control local dielectric response. These results are consistent with our model of acidity, but completely at odds with other methods of predicting acidity constants for use in multisite complexation models. In particular, our ab initio molecular dynamics simulations of solvated monomers clearly indicate that hydrogen bonding between (hydr)oxo-groups and water molecules adjusts to obey the valence sum rule, rather than maintaining a fixed valence based on the coordination of the oxygen atom as predicted by the standard MUSIC model. However, we also show how our method for p Ka prediction could be improved using ab initio molecular dynamics simulations of solvated surfaces.

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

2006-08-01

23

Quantitative harmonization of the three molecular orbital, valence bond, and broken symmetry approaches to the exchange coupling constant: Corrections and discussion  

NASA Astrophysics Data System (ADS)

Three current methods, used to evaluate exchange coupling constants in molecular magnetism, i.e., the molecular orbital (MO) model [Hay et al., J. Am. Chem. Soc. 94, 4884 (1975)], the valence bond (VB) model [Kahn and Briat, J. Chem. Soc. Trans. II 72, 268 (1976)], and the broken symmetry (BS) model [Noodleman, J. Chem. Phys. 74, 5737 (1981)], have been revisited. In effect, the three published antiferromagnetic contributions seem mutually inconsistent, as far as their magnitudes are concerned. As it turns out, the VB term -2?S, where ? is the singly occupied MO gap in the triplet state and S the (natural) magnetic orbital overlap, is shown to be overestimated by a factor of 2 (the VB ferromagnetic term, supposedly small, is actually of the order of ?S>0). Moreover, Noodleman's explicit condition derived from the variational optimization of the BS state energy results in fact from the implicit neglect of the VB ionic contribution right from the start of his methodology. Alternative (both rigorous and approximate) expressions are proposed in both VB and BS cases. The MO approach, although not being the best physically appropriate for the study of weakly interacting monomers (i.e., defined by S2<<1), is left untouched at this level of the theory.

Mouesca, Jean-Marie

2000-12-01

24

Valence-bond entanglement entropy of frustrated spin chains  

NASA Astrophysics Data System (ADS)

We extend the definition of the recently introduced valence-bond entanglement entropy to arbitrary SU(2) wave functions of S=1/2 spin systems. Thanks to a reformulation of this entanglement measure in terms of a projection, we are able to compute it with various numerical techniques for frustrated spin models. We provide extensive numerical data for the one-dimensional J1-J2 spin chain where we are able to locate the quantum phase transition by using the scaling of this entropy with the block size. We also systematically compare with the scaling of the von Neumann entanglement entropy. We finally underline that the valence-bond entropy definition does depend on the choice of bipartition so that, for frustrated models, a “good” bipartition should be chosen, for instance, according to the Marshall sign.

Alet, Fabien; McCulloch, Ian P.; Capponi, Sylvain; Mambrini, Matthieu

2010-09-01

25

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

26

Measurement-Based Quantum Computing with Valence-Bond  

NASA Astrophysics Data System (ADS)

Measurement-based quantum computing (MBQC) is a model of quantum computing that proceeds by sequential measurements of individual spins in an entangled resource state. However, it remains a challenge to produce efficiently such resource states. Would it be possible to generate these states by simply cooling a quantum many-body system to its ground state? Cluster states, the canonical resource states for MBQC, do not occur naturally as unique ground states of physical systems. This inherent hurdle has led to a significant effort to identify alternative resource states that appear as ground states in spin lattices. Recently, some interesting candidates have been identified with various valence-bond-solid (VBS) states. In this review, we provide a pedagogical introduction to recent progress regarding MBQC with VBS states as possible resource states. This study has led to an interesting interdisciplinary research area at the interface of quantum information science and condensed matter physics.

Kwek, Leong Chuan; Wei, Zhaohui; Zeng, Bei

27

Resonating valence bond states in the PEPS formalism  

NASA Astrophysics Data System (ADS)

We study resonating valence bond (RVB) states in the projected entangled pair states (PEPS) formalism. Based on symmetries in the PEPS description, we establish relations between the toric code state, the orthogonal dimer state, and the SU(2) singlet RVB state on the kagome lattice: We prove the equivalence of toric code and dimer state, and devise an interpolation between the dimer state and the RVB state. This interpolation corresponds to a continuous path in Hamiltonian space, proving that the RVB state is the fourfold degenerate ground state of a local Hamiltonian on the (finite) kagome lattice. We investigate this interpolation using numerical PEPS methods, studying the decay of correlation functions, the change of overlap, and the entanglement spectrum, none of which exhibits signs of a phase transition.

Schuch, Norbert; Poilblanc, Didier; Cirac, J. Ignacio; Pérez-García, David

2012-09-01

28

Quantum phase transitions around the staggered valence-bond solid  

NASA Astrophysics Data System (ADS)

Motivated by recent numerical results, we study the quantum phase transitions between Z2 spin-liquid, Néel-ordered, and various valence-bond solid (VBS) states on the honeycomb and square lattices, with emphasis on the staggered VBS. In contrast to the well-understood columnar VBS order, the staggered VBS is not described by an XY-order parameter with ZN anisotropy close to these quantum phase transitions. Instead, we demonstrate that on the honeycomb lattice, the staggered VBS is more appropriately described as an O(3)- or CP(2)-order parameter with cubic anisotropy, while on the square lattice it is described by an O(4)- or CP(3)-order parameter.

Xu, Cenke; Balents, Leon

2011-07-01

29

Valence Bond Interpretation of Elastic Anisotropy in B.C.C. Transition Metals.  

National Technical Information Service (NTIS)

Valence bond theory provides a practical microscopic phenomeno-logical context for interpretation of many properties of transition metals. In body centered cubic (b.c.c.) transition metals, the partition of the total bonding hybrids into nearest-neighbour...

D. R. Hay P. D. Parikh

1969-01-01

30

Entanglement in valence-bond-solid states and quantum search  

NASA Astrophysics Data System (ADS)

The present dissertation covers two independent subjects: (i) The quantum entanglement in Valence-Bond-Solid states, and (ii) quantum database search algorithms. Both subjects are presented in a self-contained and pedagogical way. (i) The first chapter is a through introduction to the subject of quantum entanglement in Valence-Bond-Solid (VBS) states defined on a lattice or graph. The VBS state was first introduced as the ground state of the celebrated Affleck-Kennedy-Lieb-Tasaki (AKLT) spin chain model in statistical mechanics. Then it became essential in condensed matter physics, quantum information and measurement-based quantum computation. Recent studies elucidated important entanglement properties of the VBS state. We start with the definition of a general AKLT model and the construction of VBS ground states. A subsystem is introduced and described by the density matrix. Exact spectrum properties of the density matrix are proved and discussed. Density matrices of 1-dimensional models are diagonalized and the entanglement entropies (the von Neumann entropy and Renyi entropy) are calculated. The entropies take saturated value and the density matrix is proportional to a projector in the large subsystem limit. (ii) The second chapter is a detailed introduction to the subject of quantum database search algorithms. The problem of searching a large database (a Hilbert space) for a target item is performed by the famous Grover algorithm which locates the target item with probability 1 and a quadratic speed up compared with the corresponding classical algorithm. If the database is partitioned into blocks and one is searching for the block containing the target item instead of the target item itself, then the problem is referred to as partial search. Partial search trades accuracy for speed and the most efficient version is the Grover-Radhakrishnan-Korepin (GRK) algorithm. The target block can be further partitioned into subblocks so that GRK can be performed in a sequence called a hierarchy. We formulate the Grover search and GRK partial search and prove that a GRK hierarchy is less efficient than a direct GRK partial search.

Xu, Ying

31

Topological and entanglement properties of resonating valence bond wave functions  

NASA Astrophysics Data System (ADS)

We examine in details the connections between topological and entanglement properties of short-range resonating valence bond (RVB) wave functions using projected entangled pair states (PEPS) on kagome and square lattices on (quasi)infinite cylinders with generalized boundary conditions (and perimeters with up to 20 lattice spacings). By making use of disconnected topological sectors in the space of dimer lattice coverings, we explicitly derive (orthogonal) “minimally entangled” PEPS RVB states. For the kagome lattice, using the quantum Heisenberg antiferromagnet as a reference model, we obtain the finite-size scaling with increasing cylinder perimeter of the vanishing energy separations between these states. In particular, we extract two separate (vanishing) energy scales corresponding (i) to insert a vison line between the two ends of the cylinder and (ii) to pull out and freeze a spin at either end. We also investigate the relations between bulk and boundary properties and show that, for a bipartition of the cylinder, the boundary Hamiltonian defined on the edge can be written as a product of a highly nonlocal projector, which fundamentally depends upon boundary conditions, with an emergent (local) SU(2)-invariant one-dimensional (superfluid) t-J Hamiltonian, which arises due to the symmetry properties of the auxiliary spins at the edge. This multiplicative structure, a consequence of the disconnected topological sectors in the space of dimer lattice coverings, is characteristic of the topological nature of the states. For minimally entangled RVB states, it is shown that the entanglement spectrum, which reflects the properties of the (gapless or gapped) edge modes, is a subset of the spectrum of the local Hamiltonian, e.g., half of it for the kagome RVB state, providing a simple argument on the origin of the topological entanglement entropy S0=-ln2 of the Z2 spin liquid. We propose to use these features to probe topological phases in microscopic Hamiltonians, and some results are compared to existing density matrix renormalization group data.

Poilblanc, Didier; Schuch, Norbert; Pérez-García, David; Cirac, J. Ignacio

2012-07-01

32

The Resonating-Valence-Bond Theory of Superconductivity: Crest Superconductors and Trough Superconductors.  

National Technical Information Service (NTIS)

The generally accepted theory of electric superconductivity of metals is based upon an assumed interaction between the conduction electrons and phonons in the crystal. The resonating-valence-bond theory, which is a theory of the electronic structure of me...

L. Pauling

1968-01-01

33

Definitions of entanglement entropy of spin systems in the valence-bond basis  

NASA Astrophysics Data System (ADS)

The valence-bond structure of spin-1/2 Heisenberg antiferromagnets is closely related to quantum entanglement. We investigate definitions of entanglement entropy based on individual valence bonds connecting two subsystems, as well as shared loops of the transposition graph (overlap) of two valence-bond states [1]. We reformulate a previously used definition based on valance bonds in the wave function as a true ground state expectation value, and find that its scaling for the Heisenberg chain agrees with an exact result. The loop-based entanglement entropy of the two-dimensional Heisenberg model is shown to satisfy the area law (with an additive logarithmic correction), unlike single-bond definitions (which exhibit multiplicative logarithmic corrections). [4pt] [1] Y.-C. Lin and A.W. Sandvik, arXiv:1005.0821.

Lin, Yu-Cheng; Sandvik, Anders

2011-03-01

34

Experimental realization of plaquette resonating valence-bond states with ultracold atoms in optical superlattices.  

PubMed

The concept of valence-bond resonance plays a fundamental role in the theory of the chemical bond and is believed to lie at the heart of many-body quantum physical phenomena. Here we show direct experimental evidence of a time-resolved valence-bond quantum resonance with ultracold bosonic atoms in an optical lattice. By means of a superlattice structure we create a three-dimensional array of independent four-site plaquettes, which we can fully control and manipulate in parallel. Moreover, we show how small-scale plaquette resonating valence-bond (RVB) states with s- and d-wave symmetry can be created and characterized. We anticipate our findings to open the path towards the creation and analysis of many-body RVB states in ultracold atomic gases. PMID:23003151

Nascimbène, S; Chen, Y-A; Atala, M; Aidelsburger, M; Trotzky, S; Paredes, B; Bloch, I

2012-05-18

35

Block-Localized Density Functional Theory (BLDFT), Diabatic Coupling, and Their Use in Valence Bond Theory for Representing Reactive Potential Energy Surfaces  

PubMed Central

A multistate density functional theory in the framework of the valence bond model is described. The method is based on a block-localized density functional theory (BLDFT) for the construction of valence-bond-like diabatic electronic states and is suitable for the study of electron transfer reactions and for the representation of reactive potential energy surfaces. The method is equivalent to a valence bond theory with the treatment of the localized configurations by using density functional theory (VBDFT). In VBDFT, the electron densities and energies of the valence bond states are determined by BLDFT. A functional estimate of the off-diagonal matrix elements of the VB Hamiltonian is proposed, making use of the overlap integral between Kohn–Sham determinants and the exchange-correlation functional for the ground state substituted with the transition (exchange) density. In addition, we describe an approximate approach, in which the off-diagonal matrix element is computed by wave function theory using block-localized Kohn–Sham orbitals. The key feature is that the electron density of the adiabatic ground state is not directly computed nor used to obtain the ground-state energy; the energy is determined by diagonalization of the multistate valence bond Hamiltonian. This represents a departure from the standard single-determinant Kohn–Sham density functional theory. The multistate VBDFT method is illustrated by the bond dissociation of H2+ and a set of three nucleophilic substitution reactions in the DBH24 database. In the dissociation of H2+, the VBDFT method yields the correct asymptotic behavior as the two protons stretch to infinity, whereas approximate functionals fail badly. For the SN2 nucleophilic substitution reactions, the hybrid functional B3LYP severely underestimates the barrier heights, while the approximate two-state VBDFT method overcomes the self-interaction error, and overestimates the barrier heights. Inclusion of the ionic state in a three-state model, VBDFT(3), significantly improves the computed barrier heights, which are found to be in accord with accurate results. The BLDFT method is a versatile theory that can be used to analyze conventional DFT results to gain insight into chemical bonding properties, and it is illustrated by examining the intricate energy contributions to the ion–dipole complex stabilization.

Cembran, Alessandro; Song, Lingchun; Mo, Yirong; Gao, Jiali

2010-01-01

36

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

2013-10-01

37

A multistate empirical valence bond model for solvation and transport simulations of OHin aqueous solutions  

Microsoft Academic Search

We describe a new multistate empirical valence bond (MS-EVB) model of OHin aqueous solutions. This model is based on the recently proposed ''charged ring'' parameterization for the intermolecular interaction of hydroxyl ion with water (Ufimtsev, et al., Chem. Phys. Lett., 2007, 442 ,1 28) and is suitable for classical molecular simulations of OHsolvation and transport. The model reproduces the hydration

Ivan S. Ufimtsev; Andrey G. Kalinichev; Todd J. Martinezw; R. James Kirkpatrickc

2009-01-01

38

Transport Pathways for Ions in Disordered Solids from Bond Valence Mismatch Landscapes  

Microsoft Academic Search

Starting from the simple bond valence (BV) concept commonly used to judge the plausibility of atomic positions in inorganic crystal structures, a method to analyze energy landscapes and to identify transport pathways for mobile ions in solid electrolytes has been developed. The approach is particularly valuable for analysing transport mechanisms and structure conductivity relationships in disordered solids, where the averaged

S. Adams

2006-01-01

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

2013-10-01

40

Valence force field-based Monte Carlo bond-rotation method for the determination of sp2-bonded carbon structures  

NASA Astrophysics Data System (ADS)

We present a valence force field (VFF)-based Monte Carlo (MC) bond-rotation method capable of identifying stable sp2-bonded carbon configurations. The VFF contains four parameters that are adjusted to fit density functional theory (DFT) calculations for both planar and non-planar model structures; the simple VFF model is shown to reliably reproduce the DFT energetics of disordered sp2-bonded carbon with various topologies and sizes. The MC bond-rotation method combined with the VFF is demonstrated to be effective in determining minimum-energy sp2-bonded carbon structures, such as topological defects and fullerenes with different sizes. The computational approach is also applied to investigate possible configurations of multi-vacancy defects (V2n, 2 <= n <= 8) and their relative stability.

Lee, Sangheon; Hwang, Gyeong S.

2011-11-01

41

Frustrated magnetism and resonating valence bond physics in two-dimensional kagome-like magnets  

NASA Astrophysics Data System (ADS)

We explore the phase diagram and the low-energy physics of three Heisenberg antiferromagnets which, like the kagome lattice, are networks of corner-sharing triangles but contain two sets of inequivalent short-distance resonance loops. We use a combination of exact diagonalization, analytical strong-coupling theories, and resonating valence bond approaches, and scan through the ratio of the two inequivalent exchange couplings. In one limit, the lattices effectively become bipartite, while at the opposite limit heavily frustrated nets emerge. In between, competing tunneling processes result in short-ranged spin correlations, a manifold of low-lying singlets (which can be understood as localized bound states of magnetic excitations), and the stabilization of valence bond crystals with resonating building blocks.

Rousochatzakis, Ioannis; Moessner, Roderich; van den Brink, Jeroen

2013-11-01

42

Pinwheel valence-bond solid and triplet excitations in the two-dimensional deformed kagome lattice  

NASA Astrophysics Data System (ADS)

Determining ground states of correlated electron systems is fundamental to understanding unusual phenomena in condensed-matter physics. A difficulty, however, arises in a geometrically frustrated system in which the incompatibility between the global topology of an underlying lattice and local spin interactions gives rise to macroscopically degenerate ground states, potentially prompting the emergence of quantum spin states, such as resonating valence bond and valence-bond solid (VBS). Although theoretically proposed to exist in a kagome lattice-one of the most highly frustrated lattices in two dimensions being comprised of corner-sharing triangles-such quantum-fluctuation-induced states have not been observed experimentally. Here we report the first realization of the `pinwheel' VBS ground state in the S=1/2 deformed kagome lattice antiferromagnet Rb2Cu3SnF12 (refs 12, 13). In this system, a lattice distortion breaks the translational symmetry of the ideal kagome lattice and stabilizes the VBS state.

Matan, K.; Ono, T.; Fukumoto, Y.; Sato, T. J.; Yamaura, J.; Yano, M.; Morita, K.; Tanaka, H.

2010-11-01

43

A Valence Bond Model to Evaluate Electronic Parameters for Charge Transport in Organic Aggregates  

NASA Astrophysics Data System (ADS)

A semi-empirical quantum-chemical model based on a fragment orbital formalism is presented to assess molecular parameters relevant to charge transport in organic crystals. The mixed Valence-Bond/Hartree-Fock approach provides a single and efficient framework to evaluate the electronic polarization effects induced by localized charge carriers and the associated impact on the matrix elements mediating electron migration in the hopping regime. This formalism is applied here to anthracene clusters of increasing sizes.

Aurel, Philippe; Fritsch, Alain; Ducasse, Laurent; Linares, Mathieu; Cornil, Jérôme; Beljonne, David; Castet, Frédéric

2007-12-01

44

Quantum Melting of Valence-Bond Crystal Insulators and Novel Supersolid Phase at Commensurate Density  

Microsoft Academic Search

Bosonic and fermionic Hubbard models on the checkerboard lattice are studied numerically for infinite on-site repulsion. At particle density n=1\\/4 and strong nearest-neighbor repulsion, insulating Valence-Bond crystals (VBC) of resonating particle pairs are stabilized. Their melting into superfluid or metallic phases under increasing hopping is investigated at T=0K. We identify a novel and unconventional commensurate VBC supersolid region, precursor to

Arnaud Ralko; Fabien Trousselet; Didier Poilblanc

2010-01-01

45

The Pairwise Correlated Generalized Valence Bond Model of Electronic Structure I; The Estimation of Pair Energies from Orbital Overlaps  

PubMed Central

A new method for the accurate a priori calculation of atomic and molecular energies is proposed. The new method agrees with experiment to within less than 1 kcal/mole in all cases examined thus far, and is applicable to excited states and to transition states for chemical reactions. Since the new method corrects the results of generalized valence bond calculations for the effects of electron pair correlations, we call the new method the pairwise correlated generalized valence bond method.

Petersson, G. A.

1974-01-01

46

Properties of Resonating-Valence-Bond Spin Liquids and Critical Dimer Models  

NASA Astrophysics Data System (ADS)

We use Monte Carlo simulations to study properties of resonating-valence-bond (RVB) spin liquid states for s=1/2 spins on 2D square lattices. It is well known that the spin-spin correlations decay exponentially in these states, but we find that the four-spin (valence-bond-solid, VBS, type) correlations are critical [1]. We compare various properties of the RVB with those of the classical dimer model (CDM), i.e., the exact ground state wavefunction of the critical Rokhsar-Kivelson quantum dimer model. It is well known that the CDM maps to a height model with a gradient-squared elasticity governed by a stiffness constant K. We show that also the RVB has such an effective classical field theory description, namely its (i) four-spin (dimer) correlations (ii) probabilities of different winding number sectors, and (iii) separation of monomer defect pairs, are all consistent with the same value of K (which is higher than in the CDM, i.e., the RVB is closer to an ordered VBS state). In addition to the short-bond RVB we also consider systems with longer bonds, and again find consistency with the height-model description. We discuss implications of the critical fluctuations of the RVB states. [4pt] [1] Y. Tang, A. W. Sandvik, and C. L. Henley, arXiv:1010.6146.

Tang, Ying; Sandvik, Anders W.; Henley, Christopher L.

2011-03-01

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

Electronic polarization effects on charge carriers in anthracene: A valence bond study  

NASA Astrophysics Data System (ADS)

A semiempirical quantum-chemical model based on a fragment orbital formalism is presented to assess molecular parameters relevant to charge transport in organic crystals. The mixed valence bond/Hartree-Fock approach provides an efficient integrated framework to evaluate the electronic polarization effects induced by localized charge carriers and the associated impact on the matrix elements mediating electron migration in the hopping regime. This formalism, applied here to anthracene clusters of increasing sizes and dimensionalities, yields the electrostatic and polarization contributions to the total interaction energy of the neutral and charged aggregates and leads to a reduction in the effective bandwidth by ˜10%-20% as a result of the polarization cloud.

Castet, Frédéric; Aurel, Philippe; Fritsch, Alain; Ducasse, Laurent; Liotard, Daniel; Linares, Mathieu; Cornil, Jérôme; Beljonne, David

2008-03-01

49

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

50

Gossamer superconductor, Mott insulator, and resonating valence bond state in correlated electron systems.  

PubMed

Gutzwiller variational method is applied to an effective two-dimensional Hubbard model to examine the recently proposed gossamer superconductor by Laughlin (LANL cond-mat/0209269). The ground state at half filled electron density is a gossamer superconductor for smaller intrasite Coulomb repulsion U and a Mott insulator for larger U. The gossamer superconducting state is similar to the resonating valence bond superconducting state, except that the chemical potential is approximately pinned at the mid of the two Hubbard bands away from the half filled. PMID:12785916

Zhang, F C

2003-05-23

51

On the valence bond solid in the presence of Dzyaloshinskii-Moriya interaction  

NASA Astrophysics Data System (ADS)

We examine the stability of the valence bond solid (VBS) phase against the Dzyaloshinskii-Moriya (DM) interaction in the bipartite lattice. We consider the VBS states in the AKLT model as well as the one in the Sandvik model in the 4× L lattice. We found that the VBS is very stable against the DM interaction qin the AKLT model. There is no quantum phase transition in the AKLT+DM case. However, the VBS spin gap closes in the Sandvik model due to the DM interaction.

Liao, Chen-Nan; Chern, Chyh-Hong

2011-01-01

52

Quantum Melting of Valence-Bond Crystal Insulators and Novel Supersolid Phase at Commensurate Density  

NASA Astrophysics Data System (ADS)

Bosonic and fermionic Hubbard models on the checkerboard lattice are studied numerically for infinite on-site repulsion. At particle density n=1/4 and strong nearest-neighbor repulsion, insulating Valence-Bond crystals (VBC) of resonating particle pairs are stabilized. Their melting into superfluid or metallic phases under increasing hopping is investigated at T=0K. We identify a novel and unconventional commensurate VBC supersolid region, precursor to the melting of the bosonic crystal. Hardcore bosons (spins) are compared to fermions (electrons), as well as positive to negative (frustrating) hoppings.

Ralko, Arnaud; Trousselet, Fabien; Poilblanc, Didier

2010-03-01

53

Quantum melting of valence-bond crystal insulators and novel supersolid phase at commensurate density.  

PubMed

Bosonic and fermionic Hubbard models on the checkerboard lattice are studied numerically for infinite on-site repulsion. At particle density n=1/4 and strong nearest-neighbor repulsion, insulating Valence-Bond crystals (VBC) of resonating particle pairs are stabilized. Their melting into superfluid or metallic phases under increasing hopping is investigated at T=0 K. We identify a novel and unconventional commensurate VBC supersolid region, precursor to the melting of the bosonic crystal. Hardcore bosons (spins) are compared to fermions (electrons), as well as positive to negative (frustrating) hoppings. PMID:20366561

Ralko, Arnaud; Trousselet, Fabien; Poilblanc, Didier

2010-03-26

54

Experimentally quantifying small-molecule bond activation using valence-to-core X-ray emission spectroscopy.  

PubMed

This work establishes the ability of valence-to-core X-ray emission spectroscopy (XES) to serve as a direct probe of N2 bond activation. A systematic series of iron-N2 complexes has been experimentally investigated and the energy of a valence-to-core XES peak was correlated with N-N bond length and stretching frequency. Computations demonstrate that, in a simple one-electron picture, this peak arises from the N2 2s2s ?* orbital, which becomes less antibonding as the N-N bond is weakened and broken. Changes as small as 0.02 Å in the N-N bond length may be distinguished using this approach. The results thus establish valence-to-core XES as an effective probe of small molecule activation, which should have broad applicability in transition-metal mediated catalysis. PMID:23862983

Pollock, Christopher J; Grubel, Katarzyna; Holland, Patrick L; DeBeer, Serena

2013-08-14

55

Linear independence of nearest neighbor valence bond states on several 2D lattices  

NASA Astrophysics Data System (ADS)

We show for several two-dimensional lattices that the spin-1/2 nearest neighbor valence bond states are linearly independent. To do so, we utilize and further develop a method recently introduced [1] for the kagome lattice. This method relies on the identification of an appropriate cell for the respective lattice, for which a certain local linear independence property can be demonstrated. Whenever this can be achieved, linear independence follows for arbitrarily large lattices that can be covered by such cells, for open or periodic boundary conditions. We report that this method is applicable to a number of 2D lattices including the kagome, honeycomb, square, pentagonal I and II, and the star lattice. Applications of general linear independence properties, such as the derivation of effective quantum dimer models, are discussed. Furthermore, motivated by a spin-1/2 Hamiltonian on the kagome lattice that has Anderson's resonating-valence-bond (RVB) spin liquid wave function(s) as ground state(s) [1], we mention possibilities to study the properties of this RVB wave function for the kagome and other frustrated lattices using Monte Carlo techniques. [1] A. Seidel, Phys. Rev. B 80, 165131 (2009).

Wildeboer, Julia; Seidel, Alexander

2011-03-01

56

Valence-Bond Monte Carlo for Chains of Non-Abelian Quasiparticles  

NASA Astrophysics Data System (ADS)

In non-Abelian FQH states, quasiparticles carry quantum numbers (topological charge) which characterize a degenerate Hilbert space. When these quasiparticles are close enough together, the degeneracy of this Hilbert space is lifted and the quasiparticles are said to interact. Here we show that the valence-bond Monte Carlo method introduced by Sandvik for spin-1/2 systems can be generalized to simulate 1D chains of such interacting non-Abelian quasiparticles. For uniform chains, our Monte Carlo results for the ground state energy agree with known exact values.^1 For random chains we confirm numerically that, as expected, the ground state freezes into a random singlet phase. By suitably generalizing the notion of valence-bond entanglement entropy to the non-Abelian case we also confirm the predicted result^3 that in this phase the entropy of a block of length L scales as S^VBL˜d3 2L, where d is the quantum dimension of the quasiparticles. Work supported by US DOE.

Tran, Huan; Bonesteel, Nick

2008-03-01

57

Nonorthogonal orbital based N-body reduced density matrices and their applications to valence bond theory. II. An efficient algorithm for matrix elements and analytical energy gradients in VBSCF method  

NASA Astrophysics Data System (ADS)

In this paper, by applying the reduced density matrix (RDM) approach for nonorthogonal orbitals developed in the first paper of this series, efficient algorithms for matrix elements between VB structures and energy gradients in valence bond self-consistent field (VBSCF) method were presented. Both algorithms scale only as nm4 for integral transformation and d2n?2 for VB matrix elements and 3-RDM evaluation, while the computational costs of other procedures are negligible, where n, m, d, and n? are the numbers of variable occupied active orbitals, basis functions, determinants, and active ? electrons, respectively. Using tensor properties of the energy gradients with respect to the orbital coefficients presented in the first paper of this series, a partial orthogonal auxiliary orbital set was introduced to reduce the computational cost of VBSCF calculation in which orbitals are flexibly defined. Test calculations on the Diels-Alder reaction of butadiene and ethylene have shown that the novel algorithm is very efficient for VBSCF calculations.

Chen, Zhenhua; Chen, Xun; Wu, Wei

2013-04-01

58

Nonorthogonal orbital based N-body reduced density matrices and their applications to valence bond theory. II. An efficient algorithm for matrix elements and analytical energy gradients in VBSCF method.  

PubMed

In this paper, by applying the reduced density matrix (RDM) approach for nonorthogonal orbitals developed in the first paper of this series, efficient algorithms for matrix elements between VB structures and energy gradients in valence bond self-consistent field (VBSCF) method were presented. Both algorithms scale only as nm(4) for integral transformation and d(2)n(?)(2) for VB matrix elements and 3-RDM evaluation, while the computational costs of other procedures are negligible, where n, m, d, and n(? )are the numbers of variable occupied active orbitals, basis functions, determinants, and active ? electrons, respectively. Using tensor properties of the energy gradients with respect to the orbital coefficients presented in the first paper of this series, a partial orthogonal auxiliary orbital set was introduced to reduce the computational cost of VBSCF calculation in which orbitals are flexibly defined. Test calculations on the Diels-Alder reaction of butadiene and ethylene have shown that the novel algorithm is very efficient for VBSCF calculations. PMID:23635124

Chen, Zhenhua; Chen, Xun; Wu, Wei

2013-04-28

59

Emergence of Superconductivity, Valence Bond Order, and Mott Insulators in Pd[(dmit)2] Based Organic Salts  

NASA Astrophysics Data System (ADS)

The EtMe3P and EtMe3Sb 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 EtMe3P 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 EtMe3P 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.

Rau, Jeffrey G.; Kee, Hae-Young

2011-02-01

60

Screening possible solid electrolytes by calculating the conduction pathways using Bond Valence method  

NASA Astrophysics Data System (ADS)

Inorganic solid electrolytes have distinguished advantages in terms of safety and stability, and are promising to substitute for conventional organic liquid electrolytes. However, low ionic conductivity of typical candidates is the key problem. As connective diffusion path is the prerequisite for high performance, we screen for possible solid electrolytes from the 2004 International Centre for Diffraction Data (ICDD) database by calculating conduction pathways using Bond Valence (BV) method. There are 109846 inorganic crystals in the 2004 ICDD database, and 5295 of them contain lithium. Except for those with toxic, radioactive, rare, or variable valence elements, 1380 materials are candidates for solid electrolytes. The rationality of the BV method is approved by comparing the existing solid electrolytes' conduction pathways we had calculated with those from experiments or first principle calculations. The implication for doping and substitution, two important ways to improve the conductivity, is also discussed. Among them Li2CO3 is selected for a detailed comparison, and the pathway is reproduced well with that based on the density functional studies. To reveal the correlation between connectivity of pathways and conductivity, ?/?-LiAlO2 and Li2CO3 are investigated by the impedance spectrum as an example, and many experimental and theoretical studies are in process to indicate the relationship between property and structure. The BV method can calculate one material within a few minutes, providing an efficient way to lock onto targets from abundant data, and to investigate the structure-property relationship systematically.

Gao, Jian; Chu, Geng; He, Meng; Zhang, Shu; Xiao, RuiJuan; Li, Hong; Chen, LiQuan

2014-05-01

61

Continuous ferromagnetic to valence-bond-solid transition in a quantum XY model with ring exchange  

NASA Astrophysics Data System (ADS)

On the basis of quantum Monte Carlo simulations, it has been argued that a ring exchange interaction K added to the standard S=1/2 XY model with pair exchange J leads to a T=0 valence-bond-solid (VBS) phase at a critical K/J ? 8 [1]. Contrary to conventional expectations, this appears to be a continuous quantum phase transition, and it may hence be a realization of a recently proposed [2] class of ``deconfined'' quantum-critical points. In this talk, improved simulation results will be discussed that enable a better quantitative characterization of the quantum-critical behavior at the ferromagnetic--VBS transition. [1] A. W. Sandvik, S. Daul, R. R. P. Singh, and D. J. Scalapino, Phys. Rev. Lett. 89, 247201 (2002). [2] T. Senthil, A. Vishwanath, L. Balents, S. Sachdev, and M. P. A. Fisher, cond-mat/0311326.

Sandvik, A. W.; Scalapino, D. J.

2004-03-01

62

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

2007-12-21

63

Skin-resolved local bond contraction, core electron entrapment, and valence charge polarization of Ag and Cu nanoclusters.  

PubMed

Consistency between density functional theory (DFT) calculations and experimental observations confirmed our predictions on the behaviour of local bonds, and the electron binding energy of cuboctahedral and Marks decahedral structures of Ag and Cu nanoclusters. The shorter and stronger bonds between under-coordinated atoms cause local densification and quantum entrapment of the core electrons, which polarize the otherwise conducting electrons (valence electrons). Such strong localization may result in extraordinary catalytic and plasmonic properties in Ag and Cu nanoclusters. PMID:24691894

Ahmadi, Shideh; Zhang, Xi; Gong, Yinyan; Chia, Chin Hua; Sun, Chang Q

2014-05-21

64

Block correlated second order perturbation theory with a generalized valence bond reference function  

SciTech Connect

The block correlated second-order perturbation theory with a generalized valence bond (GVB) reference (GVB-BCPT2) is proposed. In this approach, each geminal in the GVB reference is considered as a “multi-orbital” block (a subset of spin orbitals), and each occupied or virtual spin orbital is also taken as a single block. The zeroth-order Hamiltonian is set to be the summation of the individual Hamiltonians of all blocks (with explicit two-electron operators within each geminal) so that the GVB reference function and all excited configuration functions are its eigenfunctions. The GVB-BCPT2 energy can be directly obtained without iteration, just like the second order Møller–Plesset perturbation method (MP2), both of which are size consistent. We have applied this GVB-BCPT2 method to investigate the equilibrium distances and spectroscopic constants of 7 diatomic molecules, conformational energy differences of 8 small molecules, and bond-breaking potential energy profiles in 3 systems. GVB-BCPT2 is demonstrated to have noticeably better performance than MP2 for systems with significant multi-reference character, and provide reasonably accurate results for some systems with large active spaces, which are beyond the capability of all CASSCF-based methods.

Xu, Enhua; Li, Shuhua, E-mail: shuhua@nju.edu.cn [School of Chemistry and Chemical Engineering, Key Laboratory of Mesoscopic Chemistry of Ministry of Education, Institute of Theoretical and Computational Chemistry, Nanjing University, Nanjing 210093 (China)] [School of Chemistry and Chemical Engineering, Key Laboratory of Mesoscopic Chemistry of Ministry of Education, Institute of Theoretical and Computational Chemistry, Nanjing University, Nanjing 210093 (China)

2013-11-07

65

Block correlated second order perturbation theory with a generalized valence bond reference function.  

PubMed

The block correlated second-order perturbation theory with a generalized valence bond (GVB) reference (GVB-BCPT2) is proposed. In this approach, each geminal in the GVB reference is considered as a "multi-orbital" block (a subset of spin orbitals), and each occupied or virtual spin orbital is also taken as a single block. The zeroth-order Hamiltonian is set to be the summation of the individual Hamiltonians of all blocks (with explicit two-electron operators within each geminal) so that the GVB reference function and all excited configuration functions are its eigenfunctions. The GVB-BCPT2 energy can be directly obtained without iteration, just like the second order Mo?ller-Plesset perturbation method (MP2), both of which are size consistent. We have applied this GVB-BCPT2 method to investigate the equilibrium distances and spectroscopic constants of 7 diatomic molecules, conformational energy differences of 8 small molecules, and bond-breaking potential energy profiles in 3 systems. GVB-BCPT2 is demonstrated to have noticeably better performance than MP2 for systems with significant multi-reference character, and provide reasonably accurate results for some systems with large active spaces, which are beyond the capability of all CASSCF-based methods. PMID:24206291

Xu, Enhua; Li, Shuhua

2013-11-01

66

Rule-based trial wave functions for generalized valence bond theory  

SciTech Connect

We present a general method suitable for automatic generation of trial wave functions for generalized valence bond (GVB) descriptions of large molecules. This method uses pseudo-Hartree-Fock (P-HF) molecular orbitals formed from HF atomic orbitals but without Fock matrix diagonalization. The occupied P-HF orbitals are projected onto atomic basis functions to obtain GVB first natural orbitals, and the unoccupied HF orbitals are projected to obtain GVB second natural orbitals. This method (denoted GVB-INIT) is fast because no HF wave functions need be calculated and because the localization is piecewise atomic. In conjunction with the recently developed GVB-DIIS method for converging GVB wave functions and the new pseudospectral programs (PS-GVB) for the Fock matrix elements, GVB-INIT makes calculation of highly correlated GVB wave functions quite practical. The efficacy of GVB-INIT is illustrated by application to several cases including GVB wave functions with up to 26 correlated pairs. 17 refs., 7 tabs.

Langlois, J.M.; Yamasaki, Terumasa; Muller, R.P.; Goddard, W.A. III (California Institute of Technology, Pasadena, CA (United States))

1994-12-22

67

Quantum criticality and deconfinement in phase transitions between valence bond solids  

NASA Astrophysics Data System (ADS)

We consider spin-half quantum antiferromagnets in two spatial dimensions in the quantum limit, where the spins are in a valence bond solid (VBS) phase. The transition between two such VBS phases is studied. In some cases, an interesting second-order transition controlled by a fixed line with varying critical exponents is found. A specific example is provided by an antiferromagnetically coupled bilayer system on the honeycomb lattice where a continuous quantum phase transition can generically exist between two VBS phases. Furthermore, these critical points are deconfined, in the sense that gapped spin- 1/2 spinon excitations emerge right at the transition. The low-energy physics of this critical point (up to marginally irrelevant interactions) contains just a free quadratically dispersing “photon.” The phase structure on one side of this continuous transition is very intricate, consisting of a series of infinitely closely spaced further transitions in a “devil’s staircase” form. Analogies with previous examples of deconfined quantum criticality are emphasized. Closely related transitions in single layer systems are explored. These are second order only at some multicritical points. The solvable Rokshar-Kivelson point of quantum dimer models of single layer systems is found to correspond to a nongeneric multicritical point.

Vishwanath, Ashvin; Balents, L.; Senthil, T.

2004-06-01

68

Simulating finite-momentum states of quantum spin systems in the valence bond basis  

NASA Astrophysics Data System (ADS)

Quantum spin systems such as the Heisenberg model can be simulated numerically in the valence bond basis, as an alternative to the standard basis of eigenstates of the S^zi operators [1]. One advantage of this approach is that also the triplet sector can be studied based on the configurations generated in the singlet sector [1,2]. This way an improved estimator for the singlet-triplet gap can be constructed. Here we show that also finite-momentum triplet states can be studied [in practice for q close to 0 or ? due to a phase problem], thus allowing us to calculate the triplet dispersion E(q). Matrix elements are also accessible. These matrix elements give directly the magnon weight in the dynamic structure factor S(q,?). We also discuss how deconfined spinon excitations can be detected in this approach. 10.5cm [1] A. W. Sandvik, Phys. Rev. Lett. 95, 207203 (2005).[2] K. S. D. Beach and A. W. Sandvik, Nucl. Phys. B 750, 142 (2006).

Sandvik, Anders; Beach, Kevin

2007-03-01

69

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

70

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

71

A valence-bond approach to the electronic localization in 3/4 filled systems  

NASA Astrophysics Data System (ADS)

The Diagrammatic Valence Bond (DVB) method has been used to investigate the electronic properties of one-dimensionnal (1 D) clusters, for which exact solutions were obtained within the framework of an (extended) Hubbard hamiltonian. The correlation parameters, U, V and V2 are tentatively calculated by means of SCF semi-empirical methods and compared to the data issued from experiment. From the crystal structures and the conductivity data, the M{2}X salts (M : organic molecule, X^- anion) may be classified in two groups : on one hand, the compounds with a dimerized structure which are semi-conductor at 300 K and, on another hand, the systems with a regular or quasi-regular 1 D stacking which are metallic at 300 K and which exhibit a change in the electronic localization around 100-200 K. For the first class, the DVB calculations lead to a strong bond order wave picture for the localized ground state. The effect of the next nearest neighbor V2 is small although it may affect long distance charge correlations and the magnetic behavior. The magnetic susceptibility ? calculations on a 8 sites ring lead to a good agreement with 300 K experimental data and the temperature dependence of ? is best reproduced with V2 close to V/2. For the second class, it is shown that, the electronic dimerization might be modified by the anion potential, as indicated by model ab initio calculations. The behavior of the resistivity as a function of temperature is qualitatively described by a change in the intra and interdimer transfer integrals. The DVB results on 12 sites rings indicate that this difference leads to an enhanced localization when the correlations are turned on compared to the high temperature regular system. Nous avons utilisé la méthode Diagrammatic Valence Bond (DVB) pour analyser les propriétés électroniques de clusters monodimensionnels (1 D), dont les solutions exactes ont été obtenues au moyen d'un hamiltonien du type Hubbard (étendu). Un essai de calcul par des méthodes SCF semi-empiriques des paramètres de corrélation intrasite U, intersites V (premier voisin) et V2 (second voisin) a été mené et les valeurs obtenues ont été comparées aux données tirées de l'expérience. Une classification possible des sels M{2}X (M : molécule organique, X^- anion), découle des structures cristallographiques et des mesures de conductivité : les composés d'un premier groupe ont une structure dimérisée et un comportement semi-conducteur à 300 K tandis que ceux d'un deuxième groupe s'empilent de manière régulière ou quasi-régulière, sont métalliques à 300 K et leur localisation électronique est modifiée entre 100-200 K. Dans le premier cas, les calculs DVB conduisent à une description de l'état fondamental localisé en termes d'une forte onde de densité de liaison. L'effet du terme entre second voisins V2 demeure faible bien qu'il puisse modifier les corrélations de charge à longue distance ainsi que le comportement magnétique. Les susceptibilités magnétiques ? calculées sur un cycle de 8 sites sont en bon accord avec l'expérience à 300 K et c'est pour V2 voisin de V/2 que la dépendance de ? avec la température est reproduite de façon la plus satisfaisante. Dans le second cas, des calculs ab initio modèles tendent à montrer que la dimérisation électronique pourrait être modifiée par le potentiel des anions. Une modification des intégrales de transfert intra- et inter-dimères rend compte qualitativement de la variation de la résistivité en fonction de la température. Les résultats DVB sur des anneaux de 12 sites montrent que cette différence entraîne une nette augmentation de la localisation lorsque les corrélations sont prises en compte, en comparaison du cas régulier observé à haute température.

Fritsch, A.; Ducasse, L.

1991-06-01

72

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

2013-03-13

73

Evidence of valence bond condensation in the frustrated cluster magnet LiZn2Mo3O8  

NASA Astrophysics Data System (ADS)

The reduced molybdenum oxide LiZn2Mo3O8 is a Mott insulating material built of two dimensional layers of magnetic Mo3O13 triangular clusters, arranged on a triangular lattice. Between these magnetic layers are disordered non-magnetic LiZn2 layers. The formal oxidation state and calculations show each molybdenum cluster collectively produces a S=1/2 moment. The ``triangle of triangles'' arrangement of magnetic clusters gives rise to exciting frustrated magnetic physics while also preventing Jahn-teller instabilities and site disorder seen in single ion frustrated systems. In addition, the structure allows for facile electronic doping of the magnetic layers. Structural and measured physical properties and ongoing research will be discussed. The evidence discussed indicates the formation of an exotic condensed valence bond state, reminiscent of the long-sought resonating valence bond state.

Sheckelton, John; Neilson, James; Soltan, Daniel; McQueen, Tyrel

2013-03-01

74

Possible valence-bond condensation in the frustrated cluster magnet LiZn2Mo3O8.  

PubMed

The emergence of complex electronic behaviour from simple ingredients has resulted in the discovery of numerous states of matter. Many examples are found in systems exhibiting geometric magnetic frustration, which prevents simultaneous satisfaction of all magnetic interactions. This frustration gives rise to complex magnetic properties such as chiral spin structures, orbitally driven magnetism, spin-ice behaviour exhibiting Dirac strings with magnetic monopoles, valence-bond solids and spin liquids. Here we report the synthesis and characterization of LiZn(2)Mo(3)O(8), a geometrically frustrated antiferromagnet in which the magnetic moments are localized on small transition-metal clusters rather than individual ions. By doing so, first-order Jahn-Teller instabilities and orbital ordering are prevented, allowing the strongly interacting magnetic clusters in LiZn(2)Mo(3)O(8) to probably give rise to an exotic condensed valence-bond ground state reminiscent of the proposed resonating valence-bond state. Our results also link magnetism on clusters to geometric magnetic frustration in extended solids, demonstrating a new approach for unparalleled chemical control and tunability in the search for collective, emergent electronic states of matter. PMID:22561902

Sheckelton, J P; Neilson, J R; Soltan, D G; McQueen, T M

2012-06-01

75

Chemical composition, crystal structure, and their relationships with the intrinsic properties of spinel-type crystals based on bond valences.  

PubMed

Spinel-type crystals may possess complex and versatile chemical composition and crystal structure, which leads to difficulty in constructing relationships among the chemical composition, crystal structure, and intrinsic properties. In this work, we develop new empirical methods based on bond valences to estimate the intrinsic properties, namely, compressibility and thermal expansion of complex spinel-type crystals. The composition-weighted average of bond force constants in tetrahedral and octahedral coordination polyhedra is derived as a function of the composition-weighted average of bond valences, which can be calculated according to the experimental chemical composition and crystal structural parameters. We discuss the coupled effects of tetrahedral and octahedral frameworks on the aforementioned intrinsic properties. The bulk modulus could be quantitatively calculated from the composition-weighted average of bond force constants in tetrahedral and octahedral coordination polyhedra. In contrast, a quantitative estimation of the thermal expansion coefficient could be obtained from the composition-weighted average of bond force constants in octahedral coordination polyhedra. These empirical methods have been validated by the results obtained for a new complex quaternary spinel-type oxynitride Mg0.268Al2.577O3.733N0.267 as well as MgAl2O4 and Al2.85O3.45N0.55 from the literature. Further, these empirical methods have the potential to be extensively applied in other types of complex crystals. PMID:24871452

Liu, Xiao; Wang, Hao; Lavina, Barbara; Tu, Bingtian; Wang, Weimin; Fu, Zhengyi

2014-06-16

76

Multi-state empirical valence bond MD modeling of hydroxyl ion transfer in aqueous environments  

NASA Astrophysics Data System (ADS)

Physical and chemical properties of mineral-water interfaces control many important geochemical and environmental processes, such as mineral weathering and soil development, surface ion adsorption and ion exchange, the mobility of contaminants in surface and groundwater systems, and removal and sequestration of atmospheric CO2. The interaction of water with minerals can substantially affect the properties of both phases, including the structure and dynamics of the interfacial water films and the reactivity and functionality of the substrate surface. These mineral-water interactions are principally controlled by the substrate structure, composition and surface charge distribution, which widely vary among minerals. However, the surfaces of most oxides are well-known to be hydroxylated in contact with liquid water or with atmospheric water vapor at normal relative humidities. Thus, the mineral surface chemistry of common oxides, hydroxides and silicates of the Earth's near-surface environment is strongly affected by the pH dependent reactions of protonation/deprotonation. Local electron density variations due to structural substitutions or defects can also provide negatively or positively charged surface sites that can significantly influence the structure and dynamics of the interfacial hydrogen bonding network and catalyze the protonation/deprotonation reactions at the surface. With the ultimate goal of developing quantitatively accurate molecular models of reactive mineral surfaces, we present here first results for the simplest system that exhibits water-hydroxide proton transfer: a single OH^- ion in liquid water. We have modeled proton transfer in this system with molecular dynamics (MD) simulation using the multi-state empirical valence bond approach (MS-EVB), in which the classical Newtonian equations of motion are integrated using a specifically developed MS-EVB force field. The empirical parameters of the EVB Hamiltonian matrix elements are fitted to reproduce the potential energy surface of the H3O2^- molecule as well as the geometries and energies of small (H2O)_nOH^- clusters calculated by ab- initio methods at the RHF 6-31G**/MP2 level with a conductor-like screening model (COSMO). The COSMO model mimics the presence of surrounding solvent and thereby correctly represents the electronic structure of the hydrated species, which is qualitatively different from that of the gas phase anion. This technique was used to study the structure and dynamics of the solvated OH^- ion, the structure and dynamics of the solvent water, and H-exchange among these species. Analysis of OH^- diffusion shows that the Grotthuss shuttling mechanism plays a crucial role and approximately doubles the diffusion rate in comparison with the system where this shuttling was artificially quenched.

Ufimtsev, I. S.; Kalinichev, A. G.; Martinez, T. J.; Kirkpatrick, R.

2006-12-01

77

Strong valence-band offset bowing of ZnO1-xSx enhances p-type nitrogen doping of ZnO-like alloys.  

PubMed

Photoelectron spectroscopy, optical characterization, and density functional calculations of ZnO1-xSx reveal that the valence-band (VB) offset E(v)(x) increases strongly for small S content, whereas the conduction-band edge E(c)(x) increases only weakly. This is explained as the formation of local ZnS-like bonds in the ZnO host, which mainly affects the VB edge and thereby narrows the energy gap: E(g)(x=0.28) approximately E(g)(ZnO)-0.6 eV. The low-energy absorption tail is a direct Gamma(v)-->Gamma(c) transition from ZnS-like VB. The VB bowing can be utilized to enhance p-type N(O) doping with lower formation energy DeltaH(f) and shallower acceptor state in the ZnO-like alloys. PMID:17155274

Persson, Clas; Platzer-Björkman, Charlotte; Malmström, Jonas; Törndahl, Tobias; Edoff, Marika

2006-10-01

78

Plaquette valence-bond solid in the square-lattice J1-J2 antiferromagnet Heisenberg model: A bond operator approach  

NASA Astrophysics Data System (ADS)

We study the plaquette valence-bond solid phase of the spin-1/2J1-J2 antiferromagnet Heisenberg model on the square lattice within the bond-operator theory. We start by considering four S =1/2 spins on a single plaquette and determine the bond operator representation for the spin operators in terms of singlet, triplet, and quintet boson operators. The formalism is then applied to the J1-J2 model and an effective interacting boson model in terms of singlets and triplets is derived. The effective model is analyzed within the harmonic approximation and the previous results of Zhitomirsky and Ueda [Phys. Rev. B 54, 9007 (1996), 10.1103/PhysRevB.54.9007] are recovered. By perturbatively including cubic (triplet-triplet-triplet and singlet-triplet-triplet) and quartic interactions, we find that the plaquette valence-bond solid phase is stable within the parameter region 0.340.48J1, it is related to a singlet-singlet excitation at the X =(?/2,0) point of the tetramerized Brillouin zone.

Doretto, R. L.

2014-03-01

79

Néel-State to Valence-Bond-Solid Transition on the Honeycomb Lattice: Evidence for Deconfined Criticality  

NASA Astrophysics Data System (ADS)

We study a spin-1/2 SU(2) model on the honeycomb lattice with nearest-neighbor antiferromagnetic exchange J that favors Néel order and competing six-spin interactions Q that favor a valence-bond-solid (VBS) state in which the bond energies order at the “columnar” wave vector K=(2?/3,-2?/3). We present quantum Monte Carlo evidence for a direct continuous quantum phase transition between Néel and VBS states, with exponents and logarithmic violations of scaling consistent with those at analogous deconfined critical points on the square lattice. Although this strongly suggests a description in terms of deconfined criticality, the measured threefold anisotropy of the phase of the VBS order parameter shows unusual near-marginal behavior at the critical point.

Pujari, Sumiran; Damle, Kedar; Alet, Fabien

2013-08-01

80

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

2013-04-16

81

Valence-bond crystal in the extended kagome spin-(1)/(2) quantum Heisenberg antiferromagnet: A variational Monte Carlo approach  

NASA Astrophysics Data System (ADS)

The highly frustrated spin-(1)/(2) quantum Heisenberg model with both nearest (J1) and next-nearest (J2) neighbor exchange interactions is revisited by using an extended variational space of projected wave functions that are optimized with state-of-the-art methods. Competition between modulated valence-bond crystals (VBCs) proposed in the literature and the Dirac spin liquid (DSL) is investigated. We find that the addition of a small ferromagnetic next-nearest-neighbor exchange coupling |J2|>0.09J1 leads to stabilization of a 36-site unit cell VBC, although the DSL remains a local minimum of the variational parameter landscape. This implies that the VBC is not trivially connected to the DSL; instead it possesses a nontrivial flux pattern and large dimerization.

Iqbal, Yasir; Becca, Federico; Poilblanc, Didier

2011-03-01

82

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

2010-04-30

83

Application of the valence bond mixing configuration diagrams to hypervalency in trihalide anions: a challenge to the Rundle-Pimentel model.  

PubMed

The X(3)(-) hypercoordinated anions (H, F, Cl, Br, I) are studied by means of the breathing-orbital valence bond ab initio method. The valence bond wave functions describe the different X(3)(-) complexes in terms of only six valence bond structures and yield energies relative to the two exit channels, X(2) + X(-) and X(2)(-) + X(*), in very good agreement with reference CCSD(T) calculations. Although H(3)(-) is unstable and dissociates to H(2) + H(-), all the trihalogen anions are stable intermediates, Br(3)(-) and I(3)(-) being more stable than F(3)(-) and Cl(3)(-). As a challenge to the traditional Rundle-Pimentel model, the different energies of the hypercoordinated species relative to the normal-valent dissociation products X(2) + X(-) are interpreted in terms of valence bond configuration mixing diagrams and found to correlate with a single parameter of the X(2) molecule, its singlet-triplet energy gap. Examination of the six-structure wave functions show that H(3)(-), Cl(3)(-), Br(3)(-), and I(3)(-) share the same bonding picture and can be mainly described in terms of the interplay of two Lewis structures. On the other hand, F(3)(-) is bonded in a different way and possesses a significant three-electron bonding character that is responsible for the dissociation of this complex to F(2)(-) + F(*), instead of the more stable products F(2) + F(-). This counterintuitive preference for the thermodynamically disfavored exit channel is found to be an experimental manifestation of the large charge-shift resonance energy that generally characterizes fluorine-containing bonds. PMID:18808099

Braïda, Benoît; Hiberty, Philippe C

2008-12-18

84

Ab initio valence bond calculation of intermolecular forces using a non-orthogonal basis set: HeHe and HeLi systems  

Microsoft Academic Search

A variational valence bond method of calculating intermolecular forces is presented. Its main feature is the use of a non-orthogonal basis set in order to avoid overextension basis errors. Test calculations of the dispersion energy in HeHe and HeLi systems are shown.

P. Cremaschi; G. Morosi; M. Raimondi; M. Simonetta

1979-01-01

85

Tuning of valence States, bonding types, hierarchical structures, and physical properties in copper/halide/isonicotinate system.  

PubMed

Seven cupric halide coordination polymers, namely [Cu5(OH)3Br3(ina)4] (1), [Cu5(OH)3Cl3(ina)4] (2), [Cu2(OH)Cl(ina)2] (3), [Cu3(OH)2Cl2(ina)2]·2H2O (4), [Cu3(OH)2Br2(ina)2]·2H2O (5), [Cu2Cl2(ina)2(H2O)2] (6), [Cu2Cl(ina)2(gca)(H2O)] (7), cupric complex templated cuprous halide [Cu(II)(Me-ina)2(H2O)][Cu(I)5Br7] (8), and organic templated cuprous halide Me2-ina[Cu2Br3] (9) (Hina = isonicotinic acid), were prepared from the starting materials of cupric halide and Hina via fine-tuning solvothermal reactions. According to valence states of copper, 1-7 are copper(II) complexes, 8 is a mixed-valent Cu(I,II) complex, while 9 is a Cu(I) compound. According to bonding types of halides, nine complexes can be classified as three types: complexes 1-3 include only normal X-Cu bond (X = halide); complexes 4-7 include normal X-Cu bond and X···Cu weak bond; complexes 8 and 9 include normal X-Cu bond and X···H-C halogen hydrogen bonds. Complexes 1 and 2 are isomorphic three-dimensional (3D) pcu topological metal organic frameworks (MOFs) with butterfly-like Cu4(?3-OH)2X2 and steplike Cu6(?3-OH)4 cores as nodes, showing strong ferromagnetic couplings. Complex 3 also is a pcu topological MOF with only butterfly-like Cu4(?3-OH)2Cl2 clusters as nodes, presenting spin canting antiferromagnetic behavior. Isostructural 4 and 5 are Cu3(OH)2 clusters based two-dimensional (2D) (4,4) layers, which are extended into 3D eight-connected networks via weak Cu···X bonds, showing ferromagnetic coupling. Antiferromagnetic 6 is a simple one-dimensional coordination polymer, which is extended via weak Cu···Cl bonds into 3D (3,4)-connected networks. Paramagnetic 7 is a ladderlike polymer, which is extended into 2D (3,4)-connected layer via weak Cu···Cl bonds. The syntheses of polymeric cupric complexes 1-7 mainly result from differences in reactant ratio and pH value. Utilization of reducing methanol generated novel cubane-containing [Cu5Br7](2-) chain templated by paddlewheel-like [Cu(II)(Me-ina)2](2+) 8 and face-shared dimer-containing [Cu2Br3](-) chain templated by N-methylated and O-esterificated Me2-ina 9. Complex 9 exhibits a strong red emission and a weaker green emission upon excitation. PMID:24712729

Liu, Min-Min; Hou, Juan-Juan; Qi, Zhi-Kai; Duan, Li Na; Ji, Wen-Juan; Han, Cai-Yun; Zhang, Xian-Ming

2014-04-21

86

Valence bond crystals in the kagome spin-1/2 Heisenberg antiferromagnet: Symmetry classification and projected wave function study  

NASA Astrophysics Data System (ADS)

We present a hierarchical group theoretical classification and representation of Valence bond crystal (VBC) phases on the kagome lattice. Starting from the most symmetric parent VBC, we enumerate and give the ansatz for all 6, 12, and 36-site unit cell VBC's in order of increasing number of broken point group symmetry elements. We treat the VBC's within the class of Gutzwiller projected fermonic variational wave functions, which are optimized using a sophisticated implementation of the stochastic reconfiguration method. In particular, for the spin-1/2 quantum Heisenberg antiferromagnetic model, we show that the U(1) Dirac spin liquid is remarkably stable (locally and globally) with respect to all possible VBC patterns enumerated. However, upon addition of a small ferromagnetic next-nearest-neighbor coupling we find that the lowest energy state is a non-trivial generalized 36-site VBC, which can be regarded as being continuously connected to a uniform RVB spin liquid. We also communicate the ground state energy on the kagome 48 site cluster for the nearest-neighbor spin-1/2 quantum Heisenberg antiferromagnetic model, using the technique of application of a few Lanczos steps (within a variational Monte carlo scheme) on the U(1) Dirac spin liquid and the uniform RVB wave function.

Iqbal, Yasir; Becca, Federico; Poilblanc, Didier

2012-02-01

87

Finite-temperature properties of quantum Lifshitz transitions between valence-bond solid phases: An example of local quantum criticality  

NASA Astrophysics Data System (ADS)

We study the finite-temperature properties of quantum magnets close to a continuous quantum phase transition between two distinct valence-bond solid phases in two spatial dimension. Previous work has shown that such a second order quantum “Lifshitz” transition is described by a free field theory and is hence tractable, but is nevertheless nontrivial. At T>0 , we show that while correlation functions of certain operators exhibit ?/T scaling, they do not show analogous scaling in space. In particular, in the scaling limit, all such correlators are purely local in space, although the same correlators at T=0 decay as a power law. This provides a valuable microscopic example of a certain kind of local quantum criticality. The local form of the correlations arises from the large density of soft modes present near the transition that are excited by temperature. We calculate exactly the autocorrelation function for such operators in the scaling limit. Going beyond the scaling limit by including irrelevant operators leads to finite spatial correlations that are also obtained.

Ghaemi, Pouyan; Vishwanath, Ashvin; Senthil, T.

2005-07-01

88

Magnetic to valence-bond-solid transition in an S=1/2 XY model with ring-exchange  

NASA Astrophysics Data System (ADS)

Within the Landau-Ginzburg-Wilson framework, phase transitions between two ordered phases with different symmetries are generically of first order, or there is a region of coexistence of the two phases. However, It has recently been argued [1] that there is a generic class of continuous order-order quantum phase transitions, where the critical point is characterized by deconfined spinon degrees of freedom. Evidence of such a transition, between a magnetic (or superfluid in a bosonic representation) and a valence-bond-solid (VBS) phase had previously been observed in large-scale quantum Monte Carlo simulations [2] of a 2D XY model which in addition to the standard nearest-neighbor exchange J contains a four-particle exchange of strength K. The VBS phase in this model is not favored by the J and K interactions individually (the K-only model has an Ising-like antigerromagnetic ground state), but emerges out of competition between the two terms. Here I will discuss recent efforts [3] to characterize the magnetic-VBS transition in more detail (extracting the critical exponents) and comparing the behavior with predictions of the deconfined quantum-criticality scenario. 2mm [1] T. Senthil, A. Vishwanath, L. Balents, S. Sachdev, and M. P. A. Fisher, Science 303, 1490 (2004).[2] A. W. Sandvik, S. Daul, R. R. P. Singh, and D. J. Scalapino, Phys. Rev. Lett. 89, 247201 (2002).[3] A. W. Sandvik, R. G. Melko, and D. J. Scalapino (work in progress).

Sandvik, Anders

2005-03-01

89

Quantum phase transition between the Z2 spin liquid and valence bond crystals on a triangular lattice  

NASA Astrophysics Data System (ADS)

We study the quantum phase transition between the Z2 spin liquid and valence bond solid (VBS) orders on a triangular lattice. With a fully isotropic triangular lattice, the transition from a columnar or resonating-plaquette VBS order can either be first order or there could be two transitions with an intermediate phase. If the transition splits into two, then the Z2 spin liquid will first experience a first-order q =3 Potts transition to a new nematic Z2 spin liquid that breaks the 2?/3 lattice rotation symmetry (but retain translation symmetry, unlike the VBS states). The second transition will then take this new nematic Z2 spin liquid to a columnar or resonating-plaquette VBS state through a second-orderthree-dimensional (3D) XY* transition. On a distorted triangular lattice, the degeneracy between some of the different columnar VBS orders is lifted, and the phase transition can reduce to a single 3D XY * transition.

Slagle, Kevin; Xu, Cenke

2014-03-01

90

Chemical bonding and charge redistribution - Valence band and core level correlations for the Ni/Si, Pd/Si, and Pt/Si systems  

NASA Technical Reports Server (NTRS)

Via a systematic study of the correlation between the core and valence level X-ray photoemission spectra, the nature of the chemical bonding and charge redistribution for bulk transition metal silicides has been examined. Particular emphasis is placed on Pt2Si and PtSi. It is observed that the strength of the metal (d)-silicon (p) interaction increases in the order Ni2Si, Pd2Si, Pt2Si. It is also observed that both the metal and silicon core lines shift to higher binding energy as the silicides are formed. The notion of charge redistribution for metallic bonds is invoked to explain these data.

Grunthaner, P. J.; Grunthaner, F. J.; Madhukar, A.

1982-01-01

91

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, S(total), 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

2013-10-01

92

Generalization of the singlet sector valence-bond loop algorithm to antiferromagnetic ground states with total spin Stot = 1/2  

NASA Astrophysics Data System (ADS)

We develop a generalization of the singlet sector valence-bond basis projection algorithm of Sandvik, Beach, and Evertz (Sandvik 2005 Phys. Rev. Lett. 95 207203 Beach and Sandvik 2006 Nucl. Phys. B 750 142 Sandvik and Evertz 2010 Phys. Rev. B 82 024407) to cases in which the ground state of an antiferromagnetic Hamiltonian has total spin Stot = 1/2 in a finite-size system. We explain how various ground state expectation values may be calculated by using generalizations of the estimators developed in the singlet case, and illustrate the power of the method by calculating the ground state spin texture and bond energies in an L × L Heisenberg antiferromagnet with L odd and free boundaries.

Banerjee, Argha; Damle, Kedar

2010-08-01

93

Study of the mechanism of formation of CH 2 (2A1, 2B1) from C (2P) H2 using spin-coupled valence bond theory  

NASA Astrophysics Data System (ADS)

The spin-coupled valence bond method is used to study the formation of CH+2 in its lowest 2A1 and 2B1 states for perpendicular approaches by C+(2P) to H2. The potential surfaces for these two states have been extensively mapped out at the spin-coupled level. These wave functions show that in both states there is a sudden switch-over from C+(2P) + H2 character to a CH+2 complex with two C-H bonds. This accords with recent experimental studies (K. M. Ervin and P. B. Armentrout, 1986, J. chem. Phys., 84, 6738). The positions and heights of potential barriers, and the positions and depths of long-range wells, are in good agreement with extensive M.O.-CI studies (D. H. Liskow et al., 1974, J. chem. Phys., 61, 2507; S. Saki et al., 1981, 15, 5398). The calculations include important technical innovations for the introduction of core-valence orthogonality, and the maintenance of the characteristic symmetry of the spin-coupled orbitals. Additional correlation has been included at sensitive regions of the surfaces, but this simply gives a uniform energy lowering with no significant change in the shapes of the surfaces or in the character of the wave functions.

Walters, S. G.; Penotti, F.; Gerratt, J.; Raimondi, M.

94

Crystal chemical aspects of vanadium: Polyhedral geometries, characteristic bond valences, and polymerization of (VO{sub n}) polyhedra  

Microsoft Academic Search

The distribution of bond lengths in (V{sup 3+}Oâ) polyhedra shows a maximum between 1.98 and 2.04 â«, and limits of 1.88 and 2.16 â«, respectively. The bond lengths in (V{sup 4+}O{sub n}) and (V{sup 5+}O{sub n}) (n = 5,6) polyhedra show distinct populations which allow us to define the following types of bonds: (1a) vanadyl bonds in (V{sup 4+}O{sub n})

M. Schindler; F. C. Hawthorne; W. H. Baur

2000-01-01

95

Modified generalized valence-bond method: A simple correction for the electron correlation missing in generalized valence-bond wave functions; Prediction of double-well states for Cr2 and Mo2  

Microsoft Academic Search

A new method for wave functions especially suited to studies of transition-metal systems is proposed and applied to H2, N2, Cr2, and Mo2, where it provides accurate bond energies and bond distances. The resulting potential curve for ground-state Cr2 has a double well, and experiments to detect this unusual feature are suggested. The Mo2 studies lead to an assignment for

Marvin M. Goodgame; William A. Goddard III

1985-01-01

96

On the efficiency of VBSCF algorithms, a comment on "An efficient algorithm for energy gradients and orbital optimization in valence bond theory".  

PubMed

We comment on the paper [Song et al., J. Comput. Chem. 2009, 30, 399]. and discuss the efficiency of the orbital optimization and gradient evaluation in the Valence Bond Self Consistent Field (VBSCF) method. We note that Song et al. neglect to properly reference Broer et al., who published an algorithm [Broer and Nieuwpoort, Theor. Chim. Acta 1988, 73, 405] to use a Fock matrix to compute a matrix element between two different determinants, which can be used for an orbital optimization. Further, Song et al. publish a misleading comparison with our VBSCF algorithm [Dijkstra and van Lenthe, J. Chem. Phys. 2000, 113, 2100; van Lenthe et al., Mol. Phys. 1991, 73, 1159] to enable them to favorably compare their algorithm with ours. We give detail timings in terms of different orbital types in the calculation and actual timings for the example cases. PMID:22278948

van Lenthe, J H; Broer-Braam, H B; Rashid, Z

2012-03-30

97

Valence-bond crystal in the extended Kagom'e spin-1/2 quantum Heisenberg antiferromagnet: A variational Monte Carlo approach  

NASA Astrophysics Data System (ADS)

The highly-frustrated spin-1/2 quantum Heisenberg model with both nearest (J1) and next-nearest (J2) neighbor exchange interactions is revisited by using an extended variational space of projected wave functions that are optimized with state-of-the-art methods. Competition between modulated valence-bond crystals (VBC) proposed in the literature and the Dirac spin liquid (DSL) is investigated. We find that the addition of a small ferromagnetic next-nearest-neighbor exchange coupling |J2|>0.09 J1 leads to stabilization of a 36-site unit cell VBC, although the DSL remains a local minimum of the variational parameter landscape. This implies that the VBC is not trivially connected to the DSL: instead it possesses a non-trivial flux pattern and large dimerization.

Becca, Federico; Iqbal, Yasir; Poilblanc, Didier

2011-03-01

98

Continuous Quantum Phase Transition between an Antiferromagnet and a Valence-Bond Solid in Two Dimensions: Evidence for Logarithmic Corrections to Scaling  

NASA Astrophysics Data System (ADS)

The antiferromagnetic to valence-bond-solid phase transition in the two-dimensional J-Q model (an S=1/2 Heisenberg model with four-spin interactions) is studied using large-scale quantum Monte Carlo simulations. The results support a continuous transition of the ground state, in agreement with the theory of “deconfined” quantum criticality. There are, however, large corrections to scaling, of logarithmic or very slowly decaying power-law form, which had not been anticipated. This suggests that either the SU(N) symmetric noncompact CPN-1 field theory for deconfined quantum criticality has to be revised or that the theory for N=2 (as in the system studied here) differs significantly from N?? (where the field theory is analytically tractable).

Sandvik, Anders W.

2010-04-01

99

Impurity spin texture at the critical point between Néel-ordered and valence-bond-solid states in two-dimensional SU(3) quantum antiferromagnets  

NASA Astrophysics Data System (ADS)

We study the impurity physics at a continuous quantum phase transition from an SU(3) symmetric Néel-ordered state to a valence-bond-solid state that breaks lattice symmetries, using quantum Monte Carlo techniques. This continuous transition is expected to be an example of “deconfined criticality” in an SU(3) symmetric system. We find that the spin-texture induced by a missing-spin defect at the transition takes on a finite-size scaling form consistent with expectations from standard scaling arguments at a scale-invariant quantum critical point, albeit with significant subleading power-law finite size corrections that we analyze in detail. Together with recently found logarithmic violations of scaling at similar continuous transitions in the SU(2) case, our results provide indirect evidence of the existence of operators that become marginal as N is reduced to 2 in the field theoretical description of these deconfined critical points.

Banerjee, Argha; Damle, Kedar; Alet, Fabien

2011-06-01

100

Hydrogen-bonded assemblies of two-electron reduced mixed-valence [XMo12O40] (X = P and Si) with p-phenylenediamines.  

PubMed

Hydrogen-bonded assemblies of the two-electron reduced mixed-valence Keggin clusters [PMo(12)O(40)](5-) and [SiMo(12)O(40)](6-) were obtained by the one-pot electron-transfer reactions between p-phenylenediamine (PPD) or 2,3,5,6-tetramethyl-PPD (TMPPD) (donors) and H(+)(3)[PMo(12)O(40)](3-) or H(+)(4)[SiMo(12)O(40)](4-) (acceptors) in CH(3)CN. The redox states of the [PMo(12)O(40)](5-) and [SiMo(12)O(40)](6-) clusters were confirmed by the redox titrations and electronic absorption measurements. In (HPPD(+))(3)(H(+))(2)[PMo(12)O(40)](5-)(CH(3)CN)(3-6) (1), the N-H ~ O hydrogen-bonded interactions between the monoprotonated HPPD(+) (or diprotonated H2PPD(2+)) and the [PMo(12)O(40)](5-) resulted in a windmill-like assembly and hydrophilic one-dimensional channels are formed with a cross-sectional area of 0.065 nm(2), and these are filled by the CH(3)CN molecules. Also, the CH(3)CN molecules in salt 1 were removed by immersing the single crystals of 1 into H(2)O, CH(3)OH, and C(2)H(5)OH solvents. In the compound, (HTMPPD(+))(6)[SiMo(12)O(40)](6-)(CH(3)CN)(6) (2), the N-H ~ O hydrogen-bonded interactions between the monoprotonated HTMPPD(+) molecules and the [SiMo(12)O(40)](6-) formed a "Saturn-ring"-like assembly. Each Saturn-ring was arranged into an hexagonally packed array via hydrogen-bonded and ?-stacking interactions of HTMPPD(+), while the CH(3)CN solvent present in salt 2 are only found in the zero-dimensional isolated cavities. PMID:21671561

Akutagawa, Tomoyuki; Kudo, Fumito; Tsunashima, Ryo; Noro, Shin-ichiro; Cronin, Leroy; Nakamura, Takayoshi

2011-07-18

101

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

102

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.

103

Combining quantum wavepacket ab initio molecular dynamics with QM/MM and QM/QM techniques: Implementation blending ONIOM and empirical valence bond theory.  

PubMed

We discuss hybrid quantum-mechanics/molecular-mechanics (QM/MM) and quantum mechanics/quantum mechanics (QM/QM) generalizations to our recently developed quantum wavepacket ab initio molecular dynamics methodology for simultaneous dynamics of electrons and nuclei. The approach is a synergy between a quantum wavepacket dynamics, ab initio molecular dynamics, and the ONIOM scheme. We utilize this method to include nuclear quantum effects arising from a portion of the system along with a simultaneous description of the electronic structure. The generalizations provided here make the approach a potentially viable alternative for large systems. The quantum wavepacket dynamics is performed on a grid using a banded, sparse, and Toeplitz representation of the discrete free propagator, known as the "distributed approximating functional." Grid-based potential surfaces for wavepacket dynamics are constructed using an empirical valence bond generalization of ONIOM and further computational gains are achieved through the use of our recently introduced time-dependent deterministic sampling technique. The ab initio molecular dynamics is achieved using Born-Oppenheimer dynamics. All components of the methodology, namely, quantum dynamics and ONIOM molecular dynamics, are harnessed together using a time-dependent Hartree-like procedure. We benchmark the approach through the study of structural and vibrational properties of molecular, hydrogen bonded clusters inclusive of electronic, dynamical, temperature, and critical quantum nuclear effects. The vibrational properties are constructed through a velocity/flux correlation function formalism introduced by us in an earlier publication. PMID:18698890

Sumner, Isaiah; Iyengar, Srinivasan S

2008-08-01

104

Valence State Driven Site Preference in the Quaternary Compound Ca5MgAgGe5: An Electron-Deficient Phase with Optimized Bonding.  

PubMed

The quaternary phase Ca5Mg0.95Ag1.05(1)Ge5 (3) was synthesized by high-temperature solid-state techniques, and its crystal structure was determined by single-crystal diffraction methods in the orthorhombic space group Pnma - Wyckoff sequence c(12) with a = 23.1481(4) Å, b = 4.4736(1) Å, c = 11.0128(2) Å, V = 1140.43(4) Å(3), Z = 4. The crystal structure can be described as linear intergrowths of slabs cut from the CaGe (CrB-type) and the CaMGe (TiNiSi-type; M = Mg, Ag) structures. Hence, 3 is a hettotype of the hitherto missing n = 3 member of the structure series with the general formula R2+nT2X2+n, previously described with n = 1, 2, and 4. The member with n = 3 was predicted in the space group Cmcm - Wyckoff sequence f(5)c(2). The experimental space group Pnma (in the nonstandard setting Pmcn) corresponds to a klassengleiche symmetry reduction of index two of the predicted space group Cmcm. This transition originates from the switching of one Ge and one Ag position in the TiNiSi-related slab, a process that triggers an uncoupling of each of the five 8f sites in Cmcm into two 4c sites in Pnma. The Mg/Ag site preference was investigated using VASP calculations and revealed a remarkable example of an intermetallic compound for which the electrostatic valency principle is a critical structure-directing force. The compound is deficient by one valence electron according to the Zintl concept, but LMTO electronic structure calculations indicate electronic stabilization and overall bonding optimization in the polyanionic network. Other stability factors beyond the Zintl concept that may account for the electronic stabilization are discussed. PMID:24745932

Ponou, Siméon; Lidin, Sven; Zhang, Yuemei; Miller, Gordon J

2014-05-01

105

Importance of the antigen-binding valency and the nature of the cross-linking bond in ricin A-chain conjugates with antibody.  

PubMed

As a continuation of our work on toxin A-chain conjugates with antitumor antibodies for selective delivery of the toxin to the target cells, four ricin A-chain conjugates were prepared by linking A-chain to Fab' or F(ab')2 of rabbit IgG against L1210 with or without employing a cross-linking agent, N,N'-o-phenylenedimaleimide (PDM), N-succinimidyl 3-(2-pyridyldithio)propionate (SPDP) or N-succinimidyl m-(N-maleimido)benzoate (SMB), and the effects of antigen-binding valency and of the nature of the cross-linking bond on their in vitro cytotoxicity were studied. The relative potencies of the conjugates in terms of IC94's were as follows: F(ab')2-SPDP-A-chain, 100; Fab'-S-S-A-chain, 21; F(ab')2-SMB-A-chain, 1.3; Fab'-PDM-A-chain 0.38. Among the four conjugates, F(ab')2-SPDP-A-chain and Fab'-S-S-A-chain can be cleaved into the homing and the cytotoxic components with 2 mM 2-mercaptoethanol. These results suggest that divalency in antigen-binding and susceptibility of the cross-linking bond to cleavage by mercapto reagent are desirable for high potency. Protein synthesis in a cell-free system of rabbit reticulocyte lysate was inhibited by Fab'-S-S-A-chain and by Fab'-PDM-A-chain as effectively as by free A-chain, indicating that the liberation of A-chain is not important, at least on ribosomes, but it is important for the A-chain to reach a ribosome after binding of the conjugates to the cell-surface. PMID:7096308

Masuho, Y; Kishida, K; Saito, M; Umemoto, N; Hara, T

1982-05-01

106

Valence-bond crystals in the kagomé spin-1/2 Heisenberg antiferromagnet: a symmetry classification and projected wave function study  

NASA Astrophysics Data System (ADS)

In this paper, we do a complete classification of valence-bond crystals (VBCs) on the kagomé lattice based on general arguments of symmetry only and thus identify many new VBCs for different unit cell sizes. For the spin-1/2 Heisenberg antiferromagnet, we study the relative energetics of competing gapless spin liquids (SLs) and VBC phases within the class of Gutzwiller-projected fermionic wave functions using variational Monte Carlo techniques, hence implementing exactly the constraint of one fermion per site. By using a state-of-the-art optimization method, we conclusively show that the U(1) Dirac SL is remarkably stable towards dimerizing into all 6-, 12- and 36-site unit cell VBCs. This stability is also preserved on addition of a next-nearest-neighbor super-exchange coupling of both antiferromagnetic and ferromagnetic (FM) type. However, we find that a 36-site unit cell VBC is stabilized on addition of a very small next-nearest-neighbor FM super-exchange coupling, i.e. |J2| ? 0.045, and this VBC is the same in terms of space-group symmetry as that obtained in an effective quantum dimer model study. It breaks reflection symmetry, has a nontrivial flux pattern and is a strong dimerization of the uniform RVB SL.

Iqbal, Yasir; Becca, Federico; Poilblanc, Didier

2012-11-01

107

FAST TRACK COMMUNICATION: On the crystal and magnetic ordering structures of clinoatacamite, ?-Cu2(OD)3Cl, a proposed valence bond solid  

NASA Astrophysics Data System (ADS)

Frustrated magnetic systems provide routes to exploring degeneracies and creating new electronic states. While there has been extensive theoretical study concerning the effects in the S = 1/2 quantum limit, little is known experimentally because of the scarcity of model materials, in particular systems with the pyrochlore and kagomé lattices of corner-sharing tetrahedra and triangles, respectively. Much interest has developed from the discovery of herbertsmithite, ZnCu3(OH)6Cl2, a material for which magnetic order has not yet been found, and its proposal as a model S = 1/2 kagomé antiferromagnet. This work reopened the debate over the nature of the ground state for this archetypal quantum magnet and had led to recent theoretical suggestions that resonance effects, similar to those used to explain aromaticity in benzene, crystallize an exotic localized spin structure called a valence bond solid (VBS) from the quantum spin liquid phase. Inspired by the work on herbertsmithite, studies of the parent material clinoatacamite, ?-Cu2(OH)3Cl, in which the kagomé layers, that are separated by Zn2+ in herbertsmithite, are coupled by Cu2+ ions have led to suggestions that the exchange interactions connecting these spins to those in the kagomé layers are only weak, which allows a transition to occur at T~18 K to a VBS, made up of singlets formed from the dimerized spins of the kagomé planes. We present neutron diffraction studies of the crystallographic and magnetic structures that cast doubt on this interpretation and instead indicate significant coupling of all the Cu spins. Further, we find that the low temperature transition is associated with a canted ferromagnetic structure which is incompatible with the VBS.

Wills, A. S.; Henry, J.-Y.

2008-11-01

108

Myosin Vb Is Associated with Plasma Membrane Recycling Systems  

PubMed Central

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 the carboxyl terminal 60 kDa of the myosin Vb tail, interacted with all members of the Rab11 family (Rab11a, Rab11b, and Rab25). GFP-myosin Vb and endogenous myosin Vb immunoreactivity codistributed with Rab11a in HeLa and Madin-Darby canine kidney (MDCK) cells. As with Rab11a in MDCK cells, the myosin Vb immunoreactivity was dispersed with nocodazole treatment and relocated to the apical corners of cells with taxol treatment. A green fluorescent protein (GFP)-myosin Vb tail chimera overexpressed in HeLa cells retarded transferrin recycling and caused accumulation of transferrin and the transferrin receptor in pericentrosomal vesicles. Expression of the myosin Vb tail chimera in polarized MDCK cells stably expressing the polymeric IgA receptor caused accumulation of basolaterally endocytosed polymeric IgA and the polymeric IgA receptor in the pericentrosomal region. The myosin Vb tail had no effects on transferrin trafficking in polarized MDCK cells. The GFP-myosin Va tail did not colocalize with Rab11a and had no effects on recycling system vesicle distribution in either HeLa or MDCK cells. The results indicate myosin Vb is associated with the plasma membrane recycling system in nonpolarized cells and the apical recycling system in polarized cells. The dominant negative effects of the myosin Vb tail chimera indicate that this unconventional myosin is required for transit out of plasma membrane recycling systems.

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

2001-01-01

109

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

2013-01-01

110

Bonding  

NSDL National Science Digital Library

Bonding Purpose: To review the 3 Types of Bonds and the 4 Intermolecular Forces. Assignment: Answer the following questions on a separate piece of paper: 1) List the 3 types of bonding, give descriptions and one example of each 2) List the 4 intermolecular forces and draw examples of each. Be ...

Cutting, Mrs.

2008-03-08

111

Effect of the valence electron concentration on the bulk modulus and chemical bonding in Ta{sub 2}AC and Zr{sub 2}AC (A=Al, Si, and P)  

SciTech Connect

We have studied the effect of the valence electron concentration, on the bulk modulus and the chemical bonding in Ta{sub 2}AC and Zr{sub 2}AC (A=Al, Si, and P) by means of ab initio calculations. Our equilibrium volume and the hexagonal ratio (c/a) agree well (within 2.7% and 1.2%, respectively) with previously published experimental data for Ta{sub 2}AlC. The bulk moduli of both Ta{sub 2}AC and Zr{sub 2}AC increase as Al is substituted with Si and P by 13.1% and 20.1%, respectively. This can be understood since the substitution is associated with an increased valence electron concentration, resulting in band filling and an extensive increase in cohesion.

Schneider, Jochen M.; Music, Denis; Sun Zhimei [Materials Chemistry, RWTH Aachen, Kopernikusstr.16, D-52074 Aachen (Germany)

2005-03-15

112

Galvanomagnetic effects in A2VB3VI  

NASA Astrophysics Data System (ADS)

Magnetoresistivity of A2VB3VI-based compounds has been investigated (H~0÷89 kE, T=0,5÷4,2 K). Oscillation of magnetoresistivity, Shubnikov de Gaas oscillation has been observed at high magnetic fields (H>30 kE). The charge carrier concentration and area of extreme cross section of Fermi surface by plane, perpendicular to magnetic field have been evaluated from oscillation period. A52B63-based compounds are used as high effective thermoelectric transformers [1]. Recently, the interest to these compounds increases due to the perspectivities of widening of working temperature range and increase of thermoelectric efficiency of A52B63 compounds, doped by different impurities [2-6]. Therefore the investigation of fundamental characteristics of these compounds is not only extended our representation on band structure, also has a practical meaning. In the present work the results of investigations of galvanomagnetic effects in layered A52B63 compounds which have rhombohedral structure and crystallize in sp.gr. D3d (R÷m) [1], are given. The layers in A52B63 compounds consist of five monoatomic hexagonal grids alternating in sequence in B(1)-A-B(2)-A-B(1). Atom B(2) has 6 nearest atoms B(1). The bond between B(1)-A-B(2)-A-B(1) layers-quintets is of weak Van-der-Vaals type, but in layers of B(1)-A and A-B(2) bonds have covalent character with small fraction of ionic bond. Single crystals under investigation have been were grown by Bridgman method from components with stoichiometric relationship. It is known, that by synthesis of A52B63 compounds from the melt of stoichiometric structure are characterized by presence of a significant amount of own points defects conditioned by transition of A atoms into the position of B atoms. These antistructural defects are the acceptors. Concentration of holes is p~1019cm-3. Investigations have been carried out in temperature range 0,5÷300K and magnetic field up to 8 Tl. At galvanomagnetic investigations the sample is placed in the centre of superconductive solenoid. Measurements are carried out by selective method under the alternating current by 20 Hz frequency. The current magnitude does not exceed 1MA. The current is directed along the layer plane, magnetic field is perpendicular to layer plane.

Kerimova, T. G.; Abdullayev, N. A.; Mustafayeva, K. M.

2009-03-01

113

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

2013-11-01

114

Chaetoglobosin Vb from endophytic Chaetomium globosum: absolute configuration of chaetoglobosins.  

PubMed

One new cytochalasan alkaloid, chaetoglobosin V(b) (1), together with two structurally related known compounds, chaetoglobosin V (2) and chaetoglobosin G (3), was isolated from the ethyl acetate extract of a culture of the endophytic fungus Chaetomium globosum, associated with the leaves of Ginkgo biloba tree. The structures of the isolated compounds were elucidated by spectroscopic methods including 1D and 2D NMR and mass spectrometry. The absolute configuration of chaetoglobosin V(b) (1) was established by means of electronic circular dichroism (CD) spectroscopy, on the basis of the comparison between the CD spectrum of (+)-1 with that calculated with time-dependent density functional theory method for a simplified model. The correlation between compounds 1-3 was demonstrated by a biomimetic transformation of chaetoglobosin G (3) under mild conditions in chaetoglobosins V and V(b) (1 and 2). The isolated metabolites were tested against some phytopathogens. PMID:22593034

Xue, Min; Zhang, Qiang; Gao, Jin-Ming; Li, He; Tian, Jun-Mian; Pescitelli, Gennaro

2012-08-01

115

Valence band dependence on thermal treatment of gold doped glasses and glass ceramics  

NASA Astrophysics Data System (ADS)

This paper reports x-ray photoemission spectroscopy results regarding the nucleation and growing process of gold nanoparticles (AuNPs) in CaO-SiO2-P2O5 bioactive glasses heat treated at different temperatures. The analysis of the valence band (VB) spectra is discussed in terms of the AuNPs' shape, size, and distribution at the sample surface at different temperatures. Moreover, the theoretical VB photoemission spectra of the investigated samples are presented, and their agreement with experimentally obtained spectra is discussed in detail.

Radu, T.; Benea, D.; Ciceo-Lucacel, R.; Ponta, O.; Simon, S.

2012-02-01

116

Teaching software development of digital image processing based on VB  

Microsoft Academic Search

In order to make the student easily understand the image processing theory and combine theory teaching with practical teaching of this technology, it is very important to develop a set of software suitable for teaching. This paper discusses image processing technique based on Visual Basic (VB) and a set of teaching software of digital image processing is developed by this

Dou Zhenhai; Wang Yajing; Chen Wengang

2010-01-01

117

Levels of valence.  

PubMed

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. PMID:23717292

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

2013-01-01

118

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

119

Myosin-Vb functions as a dynamic tether for peripheral endocytic compartments during transferrin trafficking  

PubMed Central

Background Myosin-Vb has been shown to be involved in the recycling of diverse proteins in multiple cell types. Studies on transferrin trafficking in HeLa cells using a dominant-negative myosin-Vb tail fragment suggested that myosin-Vb was required for recycling from perinuclear compartments to the plasma membrane. However, chemical-genetic, dominant-negative experiments, in which myosin-Vb was specifically induced to bind to actin, suggested that the initial hypothesis was incorrect both in its site and mode of myosin-Vb action. Instead, the chemical-genetic data suggested that myosin-Vb functions in the actin-rich periphery as a dynamic tether on peripheral endosomes, retarding transferrin transport to perinuclear compartments. Results In this study, we employed both approaches, with the addition of overexpression of full-length wild-type myosin-Vb and switching the order of myosin-Vb inhibition and transferrin loading, to distinguish between these hypotheses. Overexpression of full-length myosin-Vb produced large peripheral endosomes. Chemical-genetic inhibition of myosin-Vb after loading with transferrin did not prevent movement of transferrin from perinuclear compartments; however, virtually all myosin-Vb-decorated particles, including those moving on microtubules, were halted by the inhibition. Overexpression of the myosin-Vb tail caused a less-peripheral distribution of early endosome antigen-1 (EEA1). Conclusion All results favored the peripheral dynamic tethering hypothesis.

Provance, D William; Addison, Erin J; Wood, Patrick R; Chen, David Z; Silan, Colleen M; Mercer, John A

2008-01-01

120

How resonance assists hydrogen bonding interactions: an energy decomposition analysis.  

PubMed

Block-localized wave function (BLW) method, which is a variant of the ab initio valence bond (VB) theory, was employed to explore the nature of resonance-assisted hydrogen bonds (RAHBs) and to investigate the mechanism of synergistic interplay between pi delocalization and hydrogen-bonding interactions. We examined the dimers of formic acid, formamide, 4-pyrimidinone, 2-pyridinone, 2-hydroxpyridine, and 2-hydroxycyclopenta-2,4-dien-1-one. In addition, we studied the interactions in beta-diketone enols with a simplified model, namely the hydrogen bonds of 3-hydroxypropenal with both ethenol and formaldehyde. The intermolecular interaction energies, either with or without the involvement of pi resonance, were decomposed into the Hitler-London energy (DeltaEHL), polarization energy (DeltaEpol), charge transfer energy (DeltaECT), and electron correlation energy (DeltaEcor) terms. This allows for the examination of the character of hydrogen bonds and the impact of pi conjugation on hydrogen bonding interactions. Although it has been proposed that resonance-assisted hydrogen bonds are accompanied with an increasing of covalency character, our analyses showed that the enhanced interactions mostly originate from the classical dipole-dipole (i.e., electrostatic) attraction, as resonance redistributes the electron density and increases the dipole moments in monomers. The covalency of hydrogen bonds, however, changes very little. This disputes the belief that RAHB is primarily covalent in nature. Accordingly, we recommend the term "resonance-assisted binding (RAB)" instead of "resonance-assisted hydrogen bonding (RHAB)" to highlight the electrostatic, which is a long-range effect, rather than the electron transfer nature of the enhanced stabilization in RAHBs. PMID:17143867

Beck, John Frederick; Mo, Yirong

2007-01-15

121

Revisiting the Valence-Band and Core-Level Photoemission Spectra of NiO  

NASA Astrophysics Data System (ADS)

We have reexamined the valence-band (VB) and core-level electronic structure of NiO by means of hard and soft x-ray photoemission spectroscopies. The spectral weight of the lowest energy state was found to be enhanced in the bulk sensitive Ni 2p core-level spectrum. A configuration-interaction model including a bound state screening has shown agreement with the core-level spectrum and off- and on-resonance VB spectra. These results identify the lowest energy states in the core-level and VB spectra as the Zhang-Rice (ZR) doublet bound states, consistent with the spin-fermion model and recent ab initio calculations within dynamical mean-field theory. The results indicate that the ZR character first ionization (the lowest hole-addition) states are responsible for transport properties in NiO and doped NiO.

Taguchi, M.; Matsunami, M.; Ishida, Y.; Eguchi, R.; Chainani, A.; Takata, Y.; Yabashi, M.; Tamasaku, K.; Nishino, Y.; Ishikawa, T.; Senba, Y.; Ohashi, H.; Shin, S.

2008-05-01

122

Revisiting the valence-band and core-level photoemission spectra of NiO.  

PubMed

We have reexamined the valence-band (VB) and core-level electronic structure of NiO by means of hard and soft x-ray photoemission spectroscopies. The spectral weight of the lowest energy state was found to be enhanced in the bulk sensitive Ni 2p core-level spectrum. A configuration-interaction model including a bound state screening has shown agreement with the core-level spectrum and off- and on-resonance VB spectra. These results identify the lowest energy states in the core-level and VB spectra as the Zhang-Rice (ZR) doublet bound states, consistent with the spin-fermion model and recent ab initio calculations within dynamical mean-field theory. The results indicate that the ZR character first ionization (the lowest hole-addition) states are responsible for transport properties in NiO and doped NiO. PMID:18518558

Taguchi, M; Matsunami, M; Ishida, Y; Eguchi, R; Chainani, A; Takata, Y; Yabashi, M; Tamasaku, K; Nishino, Y; Ishikawa, T; Senba, Y; Ohashi, H; Shin, S

2008-05-23

123

VB2 : an architecture for interaction in synthetic worlds  

Microsoft Academic Search

This paper describes the VB2 architecture for the construction of three-dimensional interactive applications. The system's state and behavior are uniformly represented as a network of interrelated objects. Dynamic components are modeled by active variables, while multi-way relations are modeled by hierarchical constraints. Daemons are used to sequence between system states in reaction to changes in variable values The constraint network

Enrico Gobbetti; Jean-Francis Balaguer; Daniel Thalmann

1993-01-01

124

Valence charge density in indium arsenide  

NASA Astrophysics Data System (ADS)

Valence charge densities of zinc-blende structure InAs calculated using an ab initio pseudopotential method are reported. It is found that as zinc-blende structure InAs is compressed, the changes in the charge density are gradual even as the volume at which it is unstable in favour of a rock salt structure is passed, and that under pressure the bond charges tend to move away from the anion sites towards the bond center sites.

Singh, David; Varshni, Y. P.

1985-08-01

125

Direct determination of the band offset in atomic layer deposited ZnO/hydrogenated amorphous silicon heterojunctions from X-ray photoelectron spectroscopy valence band spectra  

NASA Astrophysics Data System (ADS)

The chemical composition and band alignment at the heterointerface between atomic layer deposition-grown zinc oxide (ZnO) and hydrogenated amorphous silicon (a-Si:H) is investigated using monochromatized X-ray photoelectron spectroscopy. A new approach for obtaining the valence band offset ?EV is developed, which consists in fitting the valence band (VB) spectrum obtained for a-Si:H with a thin ZnO overlayer as the sum of experimentally obtained VB spectra of a bulk a-Si:H film and a thick ZnO film. This approach allows obtaining ?EV = 2.71 ± 0.15 eV with a minimum of assumptions, and also yields information on the change in band bending of both substrate and ZnO film. The band offset results are compared to values obtained using the usual approach of comparing valence band edge-to-core level energy differences, ?EB,CL - ?EB,VB. Furthermore, a theoretical value for the VB offset is calculated from the concept of charge neutrality level line-up, using literature data for the charge neutrality levels and the experimentally determined ZnO/a-Si:H interface dipole. The thus obtained value of ?EVCNL = 2.65 ± 0.3 eV agrees well with the experimental ?EV.

Korte, L.; Rößler, R.; Pettenkofer, C.

2014-05-01

126

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

127

Mapping of the antigenic and allergenic epitopes of Lol p VB using gene fragmentation  

Microsoft Academic Search

The recombinant proteins of Lol p VA and Lol p VB expressed in E. coli reacted with IgE antibodies from sera of allergic patients and mAbs FMC A7 and PpV1. Cross-absorption analyses using these recombinant proteins showed that Lol p VA and Lol p VB possess both similar and unique IgE binding determinants. Gene fragmentation was utilized to localize the

E. K. Ong; R. B. Knox; M. B. Singh

1995-01-01

128

Removal of Vanadium from Molten Aluminum-Part I. Analysis of VB2 Formation  

NASA Astrophysics Data System (ADS)

Aluminum has been used as an alternative to copper for electrical conductor applications. However, the presence of certain impurities in aluminum, such as V, Ti, Zr, Cr, and Fe, has detrimental effect on its electrical conductivity. These impurities can be removed by the addition of an Al-B master alloy containing AlB2 or AlB12 phase, known as boron treatment. The detailed mechanism of borides formation, however, is not well understood. In the current study, a systematic investigation of vanadium diborides (VB2) formation in the Al-V-B alloys was carried out. The study comprised thermodynamic assessment and experimental investigation on the Al-V-B system under typical industrial processing conditions. It was predicted from thermodynamic analysis that VB2 are stable borides of V and do not dissolve readily in the temperatures ranging from 948 K to 1173 K (675 °C to 900 °C). The experimental investigation showed that the mechanism of VB2 formation and V removal in an Al-V-B system is complex as it involves a number of steps such as chemical reaction, mass transfers in bulk liquid and inside the VB2 ring, and diffusions of B and V through the VB2 layer. Comparative analysis of thermodynamic and experimental results showed that the aluminum alloys were far from equilibrium and that the overall process was limited by the kinetics of B diffusion through the VB2 ring.

Khaliq, Abdul; Rhamdhani, Muhammad Akbar; Brooks, Geoffrey A.; Grandfield, John F.

2014-04-01

129

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

130

Theoretical calculation of the mixing enthalpies of 21 IIIB-IVB, IIIB-VB and IVB-VB binary alloy systems  

NASA Astrophysics Data System (ADS)

The calculation of the formation/mixing enthalpies of binary alloys is an important problem. There have been no systematic theoretical calculations of the mixing enthalpies for group B alloy systems using the famous Miedema theory or from the theoretical methods of first principle. Therefore such calculations for the 21 binary group IIIB-IVB, IIIB-VB and IVB-VB metal alloy systems are performed systematically for the first time using a subregular model. The results show that the agreement between the calculations and experimental data is pretty good and could be accepted from the theoretical or experimental points of view. From the present results and those in other two papers by the authors, it also can be concluded that the subregular model can be used for calculating the mixing enthalpies for all the 36 alloy systems combined with the 9 group B metals of Zn, Cd, Ga, In, Tl, Sn, Pb, Sb and Bi.

Zhang, Bangwei; Liao, Shuzhi; Shu, Xiaolin; Xie, Haowen; Yuan, Xiaojian

2013-06-01

131

Valence and diffuse-bound anions of noble-gas complexes with uracil  

NASA Astrophysics Data System (ADS)

Valence-bound (VB) and diffuse-bound (DB) anions of noble-gas (Ar, Kr, and Xe) complexes with uracil have been studied with ab initio methods. MP2 optimizations revealed minima corresponding to anions of both kinds in each case. Coupled-cluster singles and doubles with perturbative triples, CCSD(T), and electron propagator single-point calculations were performed in order to assess vertical and adiabatic electron detachment energies of these complexes. Ab initio electron propagator calculations employed the outer valence Green's function and partial third-order approximations, and the algebraic diagrammatic construction in third order. Basis set effects have been systematically examined. DB anions of all three complexes were adiabatically bound, with calculated adiabatic electron attachment energies below 0.06 eV. Corresponding vertical electron detachment energies were below 0.1 eV. As to VB anions, only the Xe complex had a positive adiabatic electron detachment energy, of 0.01 eV, with a corresponding vertical electron detachment energy of 0.6 eV. These computational findings are consistent with the interpretation of results previously obtained experimentally by Hendricks et al.

Streit, Lívia; Dolgounitcheva, O.; Zakrzewski, V. G.; Ortiz, J. V.

2012-11-01

132

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

133

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

134

ChsVb, a Class VII Chitin Synthase Involved in Septation, Is Critical for Pathogenicity in Fusarium oxysporum? †  

PubMed Central

A new myosin motor-like chitin synthase gene, chsVb, has been identified in the vascular wilt fungus Fusarium oxysporum f. sp. lycopersici. Phylogenetic analysis of the deduced amino acid sequence of the chsVb chitin synthase 2 domain (CS2) revealed that ChsVb belongs to class VII chitin synthases. The ChsVb myosin motor-like domain (MMD) is shorter than the MMD of class V chitin synthases and does not contain typical ATP-binding motifs. Targeted disrupted single (?chsVb) and double (?chsV ?chsVb) mutants were unable to infect and colonize tomato plants or grow invasively on tomato fruit tissue. These strains were hypersensitive to compounds that interfere with fungal cell wall assembly, produced lemon-like shaped conidia, and showed swollen balloon-like structures in hyphal subapical regions, thickened walls, aberrant septa, and intrahyphal hyphae. Our results suggest that the chsVb gene is likely to function in polarized growth and confirm the critical importance of cell wall integrity in the complex infection process of this fungus.

Martin-Urdiroz, Magdalena; Roncero, M. Isabel G.; Gonzalez-Reyes, Jose Antonio; Ruiz-Roldan, Carmen

2008-01-01

135

Reactive Force Fields via Explicit Valency  

NASA Astrophysics Data System (ADS)

Computational simulations are invaluable in elucidating the dynamics of biological macromolecules. Unfortunately, reactions present a fundamental challenge. Calculations based on quantum mechanics can predict bond formation and rupture; however they suffer from severe length- and time-limitations. At the other extreme, classical approaches provide orders of magnitude faster simulations; however they regard chemical bonds as immutable entities. A few exceptions exist, but these are not always trivial to adopt for routine use. We bridge this gap by providing a novel, pseudo-classical approach, based on explicit valency. We unpack molecules into valence electron pairs and atomic cores. Particles bear ionic charges and interact via pairwise-only potentials. The potentials are informed of quantum effects in the short-range and obey dissociation limits in the long-range. They are trained against a small set of isolated species, including geometries and thermodynamics of small hydrides and of dimers formed by them. The resulting force field captures the essentials of reactivity, polarizability and flexibility in a simple, seamless setting. We call this model LEWIS, after the chemical theory that inspired the use of valence pairs. Following the introduction in Chapter 1, we initially focus on the properties of water. Chapter 2 considers gas phase clusters. To transition to the liquid phase, Chapter 3 describes a novel pairwise long-range compensation that performs comparably to infinite lattice summations. The approach is suited to ionic solutions in general. In Chapters 4 and 5, LEWIS is shown to correctly predict the dipolar and quadrupolar response in bulk liquid, and can accommodate proton transfers in both acid and base. Efficiency permits the study of proton defects at dilutions not accessible to experiment or quantum mechanics. Chapter 6 discusses explicit valency approaches in other hydrides, forming the basis of a reactive organic force field. Examples of simple proton transfer and more complex reactions are discussed. Chapter 7 provides a framework for variable electron spread. This addition resolves some of the inherent limitations of the former model which implicitly assumed that electron spread was not affected by the environment. A brief summary is provided in Chapter 8.

Kale, Seyit

136

Chemical bonding in the boron buckyball  

Microsoft Academic Search

A symmetry analysis of the valence shell in the boron buckyball B80, shows a perfect match with the symmetry of the valence shell in C60 .The cap atoms participate in the bonding by 30 orbitals which transform as the sigma bonds along the 6-6 edges. Far reaching consequences for chemical and physical properties of B80, which until now only exists

Arnout Ceulemans; Jules Tshishimbi Muya; G. Gopakumar; Minh Tho Nguyen

2008-01-01

137

Chemical bonding in the boron buckyball  

Microsoft Academic Search

A symmetry analysis of the valence shell in the boron buckyball B80 shows a perfect match with the symmetry of the valence shell in C60. The cap atoms participate in the bonding by 30 orbitals which transform as the ?-bonds along the 6–6 edges. Far reaching consequences for chemical and physical properties of B80, which until now only exists in

Arnout Ceulemans; Jules Tshishimbi Muya; G. Gopakumar; Minh Tho Nguyen

2008-01-01

138

Developmental Expression of the Neuron-specific N-Acetylglucosaminyltransferase Vb (GnT-Vb/IX) and Identification of Its in Vivo Glycan Products in Comparison with Those of Its Paralog, GnT-V*  

PubMed Central

The severe phenotypic effects of altered glycosylation in the congenital muscular dystrophies, including Walker-Warburg syndrome, muscle-eye-brain disease, Fukuyama congenital muscular dystrophy, and congenital muscular dystrophy 1D, are caused by mutations resulting in altered glycans linked to proteins through O-linked mannose. A glycosyltransferase that branches O-Man, N-acetylglucosaminyltransferase Vb (GnT-Vb), is highly expressed in neural tissues. To understand the expression and function of GnT-Vb, we studied its expression during neuromorphogenesis and generated GnT-Vb null mice. A paralog of GnT-Vb, N-acetylglucosaminyltransferase (GnT-V), is expressed in many tissues and brain, synthesizing N-linked, ?1,6-branched glycans, but its ability to synthesize O-mannosyl-branched glycans is unknown; conversely, although GnT-Vb can synthesize N-linked glycans in vitro, its contribution to their synthesis in vivo is unknown. Our results showed that deleting both GnT-V and GnT-Vb results in the total loss of both N-linked and O-Man-linked ?1,6-branched glycans. GnT-V null brains lacked N-linked, ?1,6-glycans but had normal levels of O-Man ?1,6-branched structures, showing that GnT-Vb could not compensate for the loss of GnT-V. By contrast, GnT-Vb null brains contained normal levels of N-linked ?1,6-glycans but low levels of some O-Man ?1,6-branched glycans. Therefore, GnT-V could partially compensate for GnT-Vb activity in vivo. We found no apparent change in ?-dystroglycan binding of glycan-specific antibody IIH6C4 or binding to laminin in GnT-Vb null mice. These results demonstrate that GnT-V is involved in synthesizing branched O-mannosyl glycans in brain, but the function of these branched O-mannosyl structures is unresolved using mice that lack these glycosyltransferases.

Lee, Jin Kyu; Matthews, Russell T.; Lim, Jae-Min; Swanier, Kiara; Wells, Lance; Pierce, J. Michael

2012-01-01

139

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

140

Effect of the atomic composition of the surface on the electron surface states in topological insulators A{2/V}B{3/VI}  

NASA Astrophysics Data System (ADS)

The results of the theoretical investigation of the surface electronic structure of A{2/V}B{3/VI} compounds containing topologically protected surface states are reported. The ideal Bi2Te3, Bi2Se3, and Sb2Te3 surfaces and surfaces with an absent external layer of chalcogen atoms, which were observed experimentally as monolayer terraces, have been considered. It has been shown that the discrepancy between the calculated Fermi level and the value measured in the photoemission experiments can be attributed to the presence of the “dangling bond” states on the surface of the terraces formed by semimetal atoms. The fraction of such terraces on the surface has been estimated.

Eremeev, S. V.; Koroteev, Yu. M.; Chulkov, E. V.

2010-04-01

141

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

142

The influence of spectral nudging in simulating individual Vb-events with COSMO-CLM  

NASA Astrophysics Data System (ADS)

In previous studies certain European cyclones have been investigated in terms of related extreme precipitation events in Austria. Those systems passing the Mediterranean are of special interest as the atmospheric moisture content is increased. It has been shown in recent investigations that state-of-the-art RCMs can approximately reproduce observed heavy precipitation characteristics. This provides a basic confidence in the models ability to capture future changes of such events under increased greenhouse gas conditions as well. In this contribution we focus on high spatial and temporal scales and assess the currently achievable accuracy in the simulation of Vb-events. The state-of-the-art regional climate model CCLM is applied in a hindcast-mode to the case of individual Vb-events in August 2002 and Mai/June 2013. Besides the conventional forcing of the regional climate model at its lateral boundaries a spectral nudging technique is applied. This means that inside the model area the regional model is forced to accept the analysis for large scales whereas it has no effect on the small scales. The simulations for the Vb-events mentioned above covering the European domain have been varied systematically by changing nudging factor, number of nudged waves, nudged variables, and other parameters. The resulting precipitation amounts have been compared to E-OBS gridded European precipitation data set and a recent high spatially resolved precipitation data set for Austria (GPARD-6). Varying the spectral nudging setup in the short-term Vb-cases helps us on one hand learn something about 3D-processes during Vb-events e.g. vorticity and formation but on the other hand identify the model deficiencies. The results show, that increasing the number of nudged waves from 1 to 7 as well as the choice of the variables used in the nudging process have a large influence on the development of the low pressure system and the related precipitation patterns. On the contrary, the nudging factor or the definition of the uppermost pressure level for the nudging are of low impact on the results.

Paumann, Manuela; Anders, Ivonne; Hofstätter, Michael; Chimani, Barbara

2014-05-01

143

Unbinding force of chemical bonds and tensile strength in strong crystals  

Microsoft Academic Search

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

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

2009-01-01

144

Calculation of valence electron momentum densities using the projector augmented-wave method  

Microsoft Academic Search

We present valence electron Compton profiles calculated within the density-functional theory using the all-electron full-potential projector augmented-wave method (PAW). Our results for covalent (Si), metallic (Li, Al) and hydrogen-bonded ((H2O)2) systems agree well with experiments and computational results obtained with other band-structure and basis-set schemes. The PAW basis set describes the high-momentum Fourier components of the valence wave functions accurately

I. Makkonen; M. Hakala; M. J. Puska

2005-01-01

145

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

146

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

147

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

148

Aluminum-Oxide Temperatures on the Mark VB, VE, VR, 15, and Mark 25 Assemblies  

SciTech Connect

The task was to compute the maximum aluminum-oxide and oxide-coolant temperatures of assemblies cladded in 99+ percent aluminum. The assemblies considered were the Mark VB, VE, V5, 15 and 25. These assemblies consist of nested slug columns with individual uranium slugs cladded in aluminum cans. The CREDIT code was modified to calculate the oxide film thickness and the aluminum-oxide temperature at each axial increment. This information in this report will be used to evaluate the potential for cladding corrosion of the Mark 25 assembly.

Aleman, S.E.

2001-07-17

149

Operation and performance of the CNSE Vistec VB300 electron beam lithography system  

NASA Astrophysics Data System (ADS)

At the end of 2008, the College of Nanoscale Science and Engineering (CNSE) formally accepted a Vistec VB300 Gaussian electron beam lithography system. The system is a key component of the overall lithography strategy of the College and complements existing state of the art tooling for 193nm immersion, Extreme Ultra Violet and nanoimprint. The demonstrated resolving power of the system easily exceeds that of the facility's optical scanners. Together with 300mm wafer compatibility, and a class 1 mini environment, the system is well poised to execute its primary mission of supporting a variety of programs in post CMOS device integration. For a 300mm tool to be able to exchange wafers with other tooling in a full flow line it is necessary to pass stringent backside metal contamination testing. TXRF (total reflection x-ray fluorescence) testing performed with 300mm wafers on the VB300 satisfied the permitted metal contamination levels and cleared the way for introduction of ebeam patterned wafers into the process flow. Most of the tooling in the 300mm line handles wafers in front opening universal pods (FOUPS). With the relatively low throughput of the system (hours per wafer, not wafers per hour), this type of interface is not required. In order to maintain a low level of defects, 300mm wafers are removed from the FOUPS in the class 1 mini environment and loaded into the system. In addition to the 300mm capability, the system supports a wide range of wafer sizes, photomasks and piece parts. This enables the platform to support the 200mm activities at the College as well as the small samples frequently encountered with novel materials that have no support tooling available for 200mm and 300mm wafer sizes. The VB300 platform readily met the Vistec standard acceptance test specifications. The paper presents details of the acceptance test together with examples of additional work in progress that includes implementation of rigorous tool monitor standards, imprint template fabrication and mix and match overlay between the VB300 and optical patterning tools.

Hartley, J. G.; Groves, T. R.; Bonam, R.; Raghunathan, A.; Ruan, J.; McClelland, A.; Crosland, N.; Cunanan, J.; Han, K.

2010-03-01

150

Many-body core-valence partitioning  

Microsoft Academic Search

We discuss the physics related to partitioning core and valence electrons, a common approach taken so that one need deal only with valence electrons in subsequent work. We present an approach to core-valence partitioning which explicitly includes many-body correlations, unlike traditional single-body approaches (such as Hartree Fock or the local-density approximation). Effects of intracore and core-valence correlations are incorporated in

Eric Shirley; Richard Martin

1993-01-01

151

Myosin Vb and Rab11a regulate phosphorylation of ezrin in enterocytes.  

PubMed

Microvilli at the apical surface of enterocytes allow the efficient absorption of nutrients in the intestine. Ezrin activation by its phosphorylation at T567 is important for microvilli development, but how such ezrin phosphorylation is controlled is not well understood. We demonstrate that a subset of kinases that phosphorylate ezrin closely co-distributes with apical recycling endosome marker Rab11a in the subapical domain. Expression of dominant-negative Rab11a mutant or depletion of the Rab11a-binding motor protein myosin Vb prevents the subapical enrichment of Rab11a and these kinases and inhibits ezrin phosphorylation and microvilli development, without affecting the polarized distribution of ezrin itself. We observe a similar loss of the subapical enrichment of Rab11a and the kinases and reduced phosphorylation of ezrin in microvillus inclusion disease, which is associated with MYO5B mutations, intestinal microvilli atrophy and malabsorption. Thus, part of the machinery for ezrin activation depends on recycling endosomes controlled by myosin Vb and Rab11a which, we propose, might act as subapical signaling platforms that enterocytes use to regulate development of microvilli and maintain human intestinal function. PMID:24413175

Dhekne, Herschel S; Hsiao, Nai-Hua; Roelofs, Pieter; Kumari, Meena; Slim, Christiaan L; Rings, Edmond H H M; van Ijzendoorn, Sven C D

2014-03-01

152

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

153

Spin-coupled VB description of the potential energy surfaces for the reaction Be + +H2 --> BeH + +H  

Microsoft Academic Search

The spin-coupled VB method is used to study potential energy surfaces of the reaction Be++H2 ? BeH++H, BeH+H+. Four collinear paths on the potential were chosen corresponding to (i) Be+H2, R(Be–H2) varied with R(H–H) fixed, (ii) BeH+H, R(BeH–H) varied with R(Be–H) fixed, (iii) R(H–H) varied with Re(Be–H2) fixed, and (iv) R(Be–H) varied with R(BeH–H) fixed. The spin-coupled VB theory provides

M. Raimondi; J. Gerratt

1983-01-01

154

Molecular characterization and endophytic nature of the root-associated fungus Meliniomyces variabilis (LtVB3)  

Microsoft Academic Search

The root-associated fungus LtVB3 was formerly reported as a potential, new biocontrol agent of Verticillium yellows of Chinese\\u000a cabbage and Fusarium wilt of tomato. According to molecular phylogenetic analysis of the ITS 1-5.8S rDNA-ITS 2 gene regions\\u000a and morphological characteristics, LtVB3 is here identified as Meliniomyces\\u000a variabilis, a recently described species [formerly called “Variable White Taxon” (VWT)] in a new

Nobuaki Ohtaka; Kazuhiko Narisawa

2008-01-01

155

30 CFR 57.22231 - Actions at 0.25 percent methane (I-B, II-B, V-B, and VI mines).  

Code of Federal Regulations, 2013 CFR

...2013-07-01 false Actions at 0.25 percent methane (I-B, II-B, V-B, and VI mines...NONMETAL MINES Safety Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22231 Actions at 0.25 percent methane (I-B, II-B, V-B, and VI...

2013-07-01

156

30 CFR 57.22238 - Actions at 2.0 percent methane (I-B, II-B, V-B, and VI mines).  

Code of Federal Regulations, 2013 CFR

...2013-07-01 false Actions at 2.0 percent methane (I-B, II-B, V-B, and VI mines...NONMETAL MINES Safety Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22238 Actions at 2.0 percent methane (I-B, II-B, V-B, and VI...

2013-07-01

157

Spectroscopic studies, fluorescence quenching by molecular oxygen and amplified spontaneous emission of 1,4-bis [2-(2-pyridyl) vinyl] benzene (P2VB) diolefinic laser dye  

NASA Astrophysics Data System (ADS)

The UV-visible electronic absorption spectra, molar absorptivity, fluorescence spectra, fluorescence quantum yield and excited state lifetime of 1,4-bis [2-(2-pyridyl) vinyl] benzene P2VB were measured in different solvents. The fluorescence quenching of P2VB by molecular oxygen was also studied using lifetime measurements. A 2 × 10-4 mol dm-3 solution of P2VB in dimethyl formamide (DMF) gave amplified spontaneous emission (ASE) in blue spectral region with emission maximum at 420 nm upon pumping by 337.1 nitrogen laser pulse. The photochemical quantum yields (?c) of trans-cis photoisomerization of P2VB were calculated in different organic solvents. The photoreactivity of P2VB are also studied PMMA matrix.

El-Daly, Samy A.; Ebeid, E. M.

2014-04-01

158

Electronic structure, structural stability, mechanical and superconducting properties of group VB nitrides: A first principles study  

NASA Astrophysics Data System (ADS)

The electronic, structural, mechanical and superconducting properties of group VB mononitrides are investigated by means of first principles calculation based on density functional theory with generalized gradient approximation. The calculated ground state properties are in good agreement with previous experimental and theoretical results. Among the three crystallographic structures that have been investigated, the hexagonal WC phase is found to more stable than the cubic ones. Under high pressure, a series of structural phase transition from WC ? NaCl ? CsCl phase is also predicted in VN, NbN and TaN. The calculated elastic constants indicate that all the three nitrides are mechanically stable at ambient pressure. The estimated Zener ratio and linear compressibility coefficients Kc/Ka reveals that these materials exhibit elastic anisotropy. The estimated superconducting transition temperature (Tc) values as a function of pressure for VN, NbN and TaN are 35.5, 37.5 and 30.5 K respectively.

Asvini Meenaatci, A. T.; Rajeswarapalanichamy, R.; Iyakutti, K.

2013-05-01

159

30 CFR 57.22314 - Flow-control devices (V-A and V-B mines).  

Code of Federal Regulations, 2013 CFR

...NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Safety Standards for Methane in Metal and Nonmetal Mines Equipment § 57.22314 Flow-control devices (V-A and V-B mines). Oil...

2013-07-01

160

Mitochondrial carbonic anhydrase CA VB: Differences in tissue distribution and pattern of evolution from those of CA VA suggest distinct physiological roles  

PubMed Central

A cDNA for a second mouse mitochondrial carbonic anhydrase (CA) called CA VB was identified by homology to the previously characterized murine CA V, now called CA VA. The full-length cDNA encodes a 317-aa precursor that contains a 33-aa classical mitochondrial leader sequence. Comparison of products expressed from cDNAs for murine CA VB and CA VA in COS cells revealed that both expressed active CAs that localized in mitochondria, and showed comparable activities in crude extracts and in mitochondria isolated from transfected COS cells. Northern blot analyses of total RNAs from mouse tissues and Western blot analyses of mouse tissue homogenates showed differences in tissue-specific expression between CA VB and CA VA. CA VB was readily detected in most tissues, while CA VA expression was limited to liver, skeletal muscle, and kidney. The human orthologue of murine CA VB was recently reported also. Comparison of the CA domain sequence of human CA VB with that reported here shows that the CA domains of CA VB are much more highly conserved between mouse and human (95% identity) than the CA domains of mouse and human CA VAs (78% identity). Analysis of phylogenetic relationships between these and other available human and mouse CA isozyme sequences revealed that mammalian CA VB evolved much more slowly than CA VA, accepting amino acid substitutions at least 4.5 times more slowly since each evolved from its respective human–mouse ancestral gene around 90 million years ago. Both the differences in tissue distribution and the much greater evolutionary constraints on CA VB sequences suggest that CA VB and CA VA have evolved to assume different physiological roles.

Shah, Gul N.; Hewett-Emmett, David; Grubb, Jeffrey H.; Migas, Mary C.; Fleming, Robert E.; Waheed, Abdul; Sly, William S.

2000-01-01

161

Bent Bonds and Multiple Bonds.  

ERIC Educational Resources Information Center

Considers carbon-carbon multiple bonds in terms of Pauling's bent bond model, which allows direct calculation of double and triple bonds from the length of a CC single bond. Lengths of these multiple bonds are estimated from direct measurements on "bent-bond" models constructed of plastic tubing and standard kits. (CS)

Robinson, Edward A.; Gillespie, Ronald J.

1980-01-01

162

Action versus valence in decision making  

PubMed Central

The selection of actions, and the vigor with which they are executed, are influenced by the affective valence of predicted outcomes. This interaction between action and valence significantly influences appropriate and inappropriate choices and is implicated in the expression of psychiatric and neurological abnormalities, including impulsivity and addiction. We review a series of recent human behavioral, neuroimaging, and pharmacological studies whose key design feature is an orthogonal manipulation of action and valence. These studies find that the interaction between the two is subject to the critical influence of dopamine. They also challenge existing views that neural representations in the striatum focus on valence, showing instead a dominance of the anticipation of action.

Guitart-Masip, Marc; Duzel, Emrah; Dolan, Ray; Dayan, Peter

2014-01-01

163

Valence atom with bohmian quantum potential: the golden ratio approach  

PubMed Central

Background The alternative quantum mechanical description of total energy given by Bohmian theory was merged with the concept of the golden ratio and its appearance as the Heisenberg imbalance to provide a new density-based description of the valence atomic state and reactivity charge with the aim of clarifying their features with respect to the so-called DFT ground state and critical charge, respectively. Results The results, based on the so-called double variational algorithm for chemical spaces of reactivity, are fundamental and, among other issues regarding chemical bonding, solve the existing paradox of using a cubic parabola to describe a quadratic charge dependency. Conclusions Overall, the paper provides a qualitative-quantitative explanation of chemical reactivity based on more than half of an electronic pair in bonding, and provide new, more realistic values for the so-called “universal” electronegativity and chemical hardness of atomic systems engaged in reactivity (analogous to the atoms-in-molecules framework).

2012-01-01

164

The valence electronic structure of isotactic polystyrene revisited  

NASA Astrophysics Data System (ADS)

We present a comparison between the experimental UPS spectrum of polystyrene and a theoretically simulated spectrum derived from valence effective Hamiltonian (VEH) calculations. The calculations are carried out on a stereoregular helical isotactic polystyrene chain where the bonds joining the backbone to the phenyl groups are trans relative to the backbone (defining an isotactic polystyrene conformation denoted i-PS). This conformation is different from that considered in a previous work (Brédas and Street (1985)) where the backbone-phenyl bonds were gauche with respect to the backbone (i''-PS conformation). The theoretical UPS spectra produced by the i-PS and i''-PS conformations present subtle yet significant differences which, when comparison is made to experiment, all point in favor of the i-PS conformation considered in this work. This resolves some of the discrepancies between theory and experiment from previous work.

Ortí, E.; Stafström, S.; Brédas, J. L.

1989-12-01

165

Crossover from impurity to valence band in diluted magnetic semiconductors: Role of Coulomb attraction by acceptors  

NASA Astrophysics Data System (ADS)

The crossover between an impurity band (IB) and a valence band (VB) regime as a function of the magnetic impurity concentration in a model for diluted magnetic semiconductors (DMSs) is studied systematically by taking into consideration the Coulomb attraction between the carriers and the magnetic impurities. The density of states and the ferromagnetic transition temperature of a spin-fermion model applied to DMSs are evaluated using dynamical mean-field theory and Monte Carlo (MC) calculations. It is shown that the addition of a square-well-like attractive potential can generate an IB at small enough Mn doping x for values of the p - d exchange J that are not strong enough to generate one by themselves. We observe that the IB merges with the VB when x?xc where xc is a function of J and the Coulomb strength V . Using MC simulations, we demonstrate that the range of the Coulomb attraction plays an important role. While the on-site attraction, which has been used in previous numerical simulations, effectively renormalizes J for all values of x , an unphysical result, a nearest-neighbor range attraction renormalizes J only at very low dopings, i.e., until the bound holes wave functions start to overlap. Thus, our results indicate that the Coulomb attraction can be neglected to study Mn-doped GaSb , GaAs , and GaP in the relevant doping regimes, but it should be included in the case of Mn-doped GaN , which is expected to be in the IB regime.

Popescu, F.; ?en, C.; Dagotto, E.; Moreo, A.

2007-08-01

166

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

167

Oxygen defects in langasite (La 3Ga 5SiO 14) single crystal grown by vertical Bridgman (VB) method  

Microsoft Academic Search

Defects related to oxygen and other impurities in piezoelectric langasite (La3Ga5SiO14; LGS) single crystals grown by the vertical Bridgman (VB) method was investigated. The resistivity of an LGS crystal grown in an Ar atmosphere was about one-order higher than that grown in air. However, after annealing in air it decreased to the same level as that of LGS crystal grown

T. Taishi; T. Hayashi; N. Bamba; Y. Ohno; I. Yonenaga; K. Hoshikawa

2007-01-01

168

Simultaneous conditioning of valence and arousal.  

PubMed

Evaluative conditioning (EC) refers to the change in the valence of a conditioned stimulus (CS) due to its pairing with a positive or negative unconditioned stimulus (US). To the extent that core affect can be characterised by the two dimensions of valence and arousal, EC has important implications for the origin of affective responses. However, the distinction between valence and arousal is rarely considered in research on EC or conditioned responses more generally. Measuring the subjective feelings elicited by a CS, the results from two experiments showed that (1) repeated pairings of a CS with a positive or negative US of either high or low arousal led to corresponding changes in both CS valence and CS arousal, (2) changes in CS arousal, but not changes in CS valence, were significantly related to recollective memory for CS-US pairings, (3) subsequent presentations of the CS without the US reduced the conditioned valence of the CS, with conditioned arousal being less susceptible to extinction and (4) EC effects were stronger for high arousal than low arousal USs. The results indicate that the conditioning of affective responses can occur simultaneously along two independent dimensions, supporting evidence in related areas that calls for a consideration of both valence and arousal. Implications for research on EC and the acquisition of emotional dispositions are discussed. PMID:24116885

Gawronski, Bertram; Mitchell, Derek G V

2014-06-01

169

Removal of Vanadium from Molten Aluminum—Part II. Kinetic Analysis and Mechanism of VB2 Formation  

NASA Astrophysics Data System (ADS)

Transition metal impurities such as vanadium (V), titanium (Ti), zirconium (Zr), and chromium (Cr) reduce the electrical conductivity of smelter grade aluminum. These impurities are removed by the addition of boron-bearing substances (AlB12/AlB2) and the process is called boron treatment. The quality of the alloy and the economy of boron treatment can be improved by understanding the kinetics and mechanism of VB2 formation in molten aluminum. Currently, there is limited published information on the heterogeneous kinetics of the boron treatment. In this study, an investigation of the kinetics of V removal from molten Al-1 wt pct V alloys during boron treatment at 1023 K (750 °C) was carried out. The effects of stirring (natural, mechanical, and gas), reaction temperature, and the levels of boron addition were analyzed. The kinetics of the process could be described in two stages. The rate was faster in the early stage of reaction and was halted after 10 minutes. It was concluded that the early stage of reaction was controlled by the mass transfer of V in molten aluminum. In the second stage of reaction, it was concluded that the kinetics was controlled by the diffusion of B through a VB2 layer formed in the early stage of reaction. It was observed from microscopy analysis that the ring of VB2 disintegrated during gas stirring of bulk melt and consequently the kinetics of reaction was enhanced.

Khaliq, Abdul; Rhamdhani, Muhammad Akbar; Brooks, Geoffrey A.; Grandfield, John F.

2014-04-01

170

M{sub 1-x}[W{sub 2}O{sub 2}X{sub 6}] with M=K{sup +}, Tl{sup +}, Ag{sup +}, Hg{sup 2+}, Pb{sup 2+}; X=Cl, Br-A class of mixed valence tungsten (IV,V) compounds with layered structures, W-W bonds and high conductivity  

SciTech Connect

The crystal structure of WOCl{sub 3}, determined on the basis of powder diffraction data (tetragonal, P4{sub 2}/mnm, a=10.6856(6), c=3.8537(2)), is isotypic to WOI{sub 3} and contains one-dimensional strands of edge-sharing double-octahedral W{sub 2}O{sub 4/2}Cl{sub 6} groups connected via common corners in trans position. A W-W bond of 2.99A is present within the planar W{sub 2}Cl{sub 6} groups. A series of non-stochiometric, mixed valence W(IV,V) compounds M{sub 1-x}[W{sub 2}O{sub 2}Cl{sub 6}] can be obtained from WOCl{sub 3} by reaction with metal halides (TlCl, KCl, PbCl{sub 2}) or by reaction of elemental Hg with WOCl{sub 4}. All were characterized by single crystal structure determinations and EDX measurements (Tl{sub 0.981(2)}[W{sub 2}O{sub 2}Cl{sub 6}]: monoclinic, C2/m, a=12.7050(4), b=3.7797(1), c=10.5651(3)A, {beta}=107.656(1){sup o}; K{sub 0.84(2)}[W{sub 2}O{sub 2}Cl{sub 6}]: monoclinic, C2/m, a=12.812(3), b=3.7779(6), c=10.196(3)A, {beta}=107.422(8){sup o}; Pb{sub 0.549(3)}[W{sub 2}O{sub 2}Cl{sub 6}]: orthorhombic, Immm,a=3.7659(1), b=9.8975(4), c=12.1332(6)A; Hg{sub 0.554(6)}[W{sub 2}O{sub 2}Cl{sub 6}]: monoclinic, C2/m, a=12.8361(8), b=3.7622(3), c=10.2581(9)A, {beta}=113.645(3){sup o}). Two representatives of this family of compounds have already been reported: Na[W{sub 2}O{sub 2}Br{sub 6}] [Y.-Q. Zhang, K. Peters, H.G. von Schnering, Z. Anorg. Allg. Chem. 624 (1998) 1415-1418] and Ag{sub 0.74}[W{sub 2}O{sub 2}Br{sub 6}] [S. Imhaine, C. Perrin, M. Sergent, Mat. Res. Bull. 33 (1998) 927-933]. The Ag containing compound can be obtained from elemental Ag and WOBr{sub 3}. 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)A, {beta}=112.401(3){sup o}). The crystal structures of these compounds are in close relationship to the structure of WOCl{sub 3} and all contain W{sub 2}O{sub 4/2}X{sub 6} (X=Cl, Br) double strands with the mono and divalent cations coordinated by the terminal halogen atoms of the W{sub 2}X{sub 6} groups and a short W-W bond (2.85A for X=Cl). A cube-shaped coordination environment is present for M=Tl, K and a trigonal-prismatic coordination for M=Ag, Hg. Hg{sub 0.55}[W{sub 2}O{sub 2}Cl{sub 6}] is a semiconductor with a non-Arrhenius behaviour, high specific conductivity of 0.05{omega}{sup -1}cm{sup -1} and a very small activation energy of 0.03eV. Hg{sub 0.55}[W{sub 2}O{sub 2}Cl{sub 6}] and Ag{sub 0.8}[W{sub 2}O{sub 2}Br{sub 6}] show a temperature independent paramagnetism with a magnetic moment around 300x10{sup -6}cm{sup 3}mol{sup -1}.

Beck, Johannes [Institut fuer Anorganische Chemie, Rheinische Friedrich-Wilhelms-Universitaet, Gerhard-Domagk-Strasse 1, D-53121 Bonn (Germany)]. E-mail: j.beck@uni-bonn.de; Kusterer, Christian [Institut fuer Anorganische Chemie, Rheinische Friedrich-Wilhelms-Universitaet, Gerhard-Domagk-Strasse 1, D-53121 Bonn (Germany); Hoffmann, Rolf-Dieter [Institut fuer Anorganische und Analytische Chemie, Westfaelische Wilhelms-Universitaet, D-48149 Muenster (Germany); Poettgen, Rainer [Institut fuer Anorganische und Analytische Chemie, Westfaelische Wilhelms-Universitaet, D-48149 Muenster (Germany)

2006-08-15

171

Modelling ab initio non-bonded interactions for sigma bond, pi bond, and lone pair orbitals  

NASA Astrophysics Data System (ADS)

Ab initio eigenvalue splittings between symmetric and anti-symmetric combinations of energetically degenerate and environmentally equivalent molecular orbitals (MOs) are presented for pairs of ethane molecules and pairs of formaldehyde molecules in various geometrical configurations and as a function of separation. These weak non-bonded orbital interactions are computed for the MO of C?C sigma bond character in ethane, and for MOs of C?O pi bond character and those of axial and perpendicular oxygen lone pair character in formaldehyde. The relationship between simple orbital overlaps and the Hartree—Fock splittings in this beyond-van-der-Waals distance range is examined using overlaps based on valence bond wavefunctions constructed from single zeta Slater type orbitals. The role of the hydrogen atoms interposed in the region between the interacting MOs is examined. The suitability of the computed interactions as calibrations of effective transfer integrals needed in macromolecular electronic analyses is discussed.

Gruschus, James M.; Kuki, Atsuo

1992-05-01

172

Chemical bonding effects in X-ray spectral analysis  

Microsoft Academic Search

In this review we examine the use of chemical bonding effects apparent in x-ray spectra (chemical shift, change in shape and intensity of the lines) for qualitative and quantitative analysis of the chemical state of elements (charge state, valency, coordination number, chemical bond type, etc.), and also for direct identification of chemical compounds. In this connection, we examine methods of

L. N. Mazalov; B. A. Treiger

1983-01-01

173

Action versus valence in decision making.  

PubMed

The selection of actions, and the vigor with which they are executed, are influenced by the affective valence of predicted outcomes. This interaction between action and valence significantly influences appropriate and inappropriate choices and is implicated in the expression of psychiatric and neurological abnormalities, including impulsivity and addiction. We review a series of recent human behavioral, neuroimaging, and pharmacological studies whose key design feature is an orthogonal manipulation of action and valence. These studies find that the interaction between the two is subject to the critical influence of dopamine. They also challenge existing views that neural representations in the striatum focus on valence, showing instead a dominance of the anticipation of action. PMID:24581556

Guitart-Masip, Marc; Duzel, Emrah; Dolan, Ray; Dayan, Peter

2014-04-01

174

Myosin Vb uncoupling from RAB8A and RAB11A elicits microvillus inclusion disease  

PubMed Central

Microvillus inclusion disease (MVID) is a severe form of congenital diarrhea that arises from inactivating mutations in the gene encoding myosin Vb (MYO5B). We have examined the association of mutations in MYO5B and disruption of microvillar assembly and polarity in enterocytes. Stable MYO5B knockdown (MYO5B-KD) in CaCo2-BBE cells elicited loss of microvilli, alterations in junctional claudins, and disruption of apical and basolateral trafficking; however, no microvillus inclusions were observed in MYO5B-KD cells. Expression of WT MYO5B in MYO5B-KD cells restored microvilli; however, expression of MYO5B-P660L, a MVID-associated mutation found within Navajo populations, did not rescue the MYO5B-KD phenotype but induced formation of microvillus inclusions. Microvilli establishment required interaction between RAB8A and MYO5B, while loss of the interaction between RAB11A and MYO5B induced microvillus inclusions. Using surface biotinylation and dual immunofluorescence staining in MYO5B-KD cells expressing mutant forms of MYO5B, we observed that early microvillus inclusions were positive for the sorting marker SNX18 and derived from apical membrane internalization. In patients with MVID, MYO5B-P660L results in global changes in polarity at the villus tips that could account for deficits in apical absorption, loss of microvilli, aberrant junctions, and losses in transcellular ion transport pathways, likely leading to the MVID clinical phenotype of neonatal secretory diarrhea.

Knowles, Byron C.; Roland, Joseph T.; Krishnan, Moorthy; Tyska, Matthew J.; Lapierre, Lynne A.; Dickman, Paul S.; Goldenring, James R.; Shub, Mitchell D.

2014-01-01

175

Access to B=S and B=Se double bonds via sulfur and selenium insertion into a B-H bond and hydrogen migration.  

PubMed

Stable compounds with a boron-chalcogen (S or Se) valence double bond have been prepared via sequences involving insertion of the chalcogen into a B-H bond and subsequent hydrogen migration. X-ray diffraction studies and density functional theory calculations on the resulting compounds provide convincing evidence for the boron-chalcogen multiple bonding. PMID:20698655

Wang, Hao; Zhang, Jianying; Hu, Hongfan; Cui, Chunming

2010-08-18

176

Middle School Chemistry: Energy Levels, Electrons, and Covalent Bonding  

NSDL National Science Digital Library

This multimedia lesson for Grades 7-8 features eight animations and a hands-on lab to explore the role of valence electrons in covalent bonding. The multimedia approach provides an opportunity to visualize the attractions between atoms that result in covalent bonds. The lab investigation uses a 9-volt battery, alligator clips, and pencils to show how electrical energy can break the covalent bonds in water molecules. Editor's Note: Covalent bonding occurs when electrons are shared between atoms; ionic bonding occurs when electrons are transferred between atoms. The processes are quite different. This module very effectively explores both formation and breaking of covalent bonds. Allow two class periods.

Galvan, Patti; Kessler, Jim

2011-08-17

177

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

178

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

179

Subliminal Affect Valence Words Change Conscious Mood Potency but Not Valence: Is This Evidence for Unconscious Valence Affect?  

PubMed Central

Whether or not affect can be unconscious remains controversial. Research claiming to demonstrate unconscious affect fails to establish clearly unconscious stimulus conditions. The few investigations that have established unconscious conditions fail to rule out conscious affect changes. We report two studies in which unconscious stimulus conditions were met and conscious mood changes measured. The subliminal stimuli were positive and negative affect words presented at the objective detection threshold; conscious mood changes were measured with standard manikin valence, potency, and arousal scales. We found and replicated that unconscious emotional stimuli produced conscious mood changes on the potency scale but not on the valence scale. Were positive and negative affects aroused unconsciously, but reflected consciously in potency changes? Or were the valence words unconscious cognitive causes of conscious mood changes being activated without unconscious affect? A thought experiment is offered as a way to resolve this dilemma.

Shevrin, Howard; Panksepp, Jaak; Brakel, Linda A. W.; Snodgrass, Michael

2012-01-01

180

Strong Constraints to the Putative Planet Candidate around VB 10 Using Doppler Spectroscopy  

NASA Astrophysics Data System (ADS)

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-1 while their standard deviation is 250 m s-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 ~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 ~ 2.5 m jup for a companion with a period shorter than one year and moderate eccentricities. Based on observations collected with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile, at the W. M. Keck Observatory, and the Canada-France-Hawaii Telescope (CFHT). The Keck Observatory is operated as a scientific partnership between the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W. M. Keck Foundation. CFHT is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientique of France, and the University of Hawaii.

Anglada-Escudé, Guillem; Shkolnik, Evgenya L.; Weinberger, Alycia J.; Thompson, Ian B.; Osip, David J.; Debes, John H.

2010-03-01

181

Stellar Activity at the End of the Main Sequence: GHRS Observations of the M8 Ve Star VB 10  

NASA Technical Reports Server (NTRS)

We present Goddard High Resolution Spectrograph observations of the M8 Ve star VB 10 (equal to G1 752B), located very near the end of the stellar main sequence, and its dM3.5 binary companion G1 752A. These coeval stars provide a test bed for studying whether the outer atmospheres of stars respond to changes in internal structure as stars become fully convective near mass 0.3 solar mass (about spectral type M5), where the nature of the stellar magnetic dynamo presumably changes, and near the transition from red to brown dwarfs near mass 0.08 solar mass (about spectral type M9), when hydrogen burning ceases at the end of the main sequence. We obtain upper limits for the quiescent emission of VB 10 but observe a transition region spectrum during a large flare, which indicates that some type of magnetic dynamo must be present. Two indirect lines of evidence-scaling from the observed X-ray emission and scaling from a time-resolved flare on AD Leo suggest that the fraction of the stellar bolometric luminosity that heats the transition region of VB 10 outside of obvious flares is comparable to, or larger than, that for G1 752A. This suggests an increase in the magnetic heating rates, as measured by L(sub line)/L(sub bol) ratios, across the radiative/convective core boundary and as stars approach the red/brown dwarf boundary. These results provide new constraints for dynamo models and models of coronal and transition-region heating in late-type stars.

Linsky, Jeffrey L.; Wood, Brian E.; Brown, Alexander; Giampapa, Mark S.; Ambruster, Carol

1995-01-01

182

ON THE DETECTABILITY OF A PREDICTED MESOLENSING EVENT ASSOCIATED WITH THE HIGH PROPER MOTION STAR VB 10  

SciTech Connect

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 {rho}{sub min} will be less than 100 mas, a 1 in 5 chance that {rho}{sub min} < 50 mas, and a 1 in 10 chance that {rho}{sub 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 {approx}1 M{sub J} planet on a moderately wide ( Almost-Equal-To 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.

Lepine, Sebastien [Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024 (United States); DiStefano, Rosanne, E-mail: lepine@amnh.org, E-mail: rd@cfa.harvard.edu [Harvard Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2012-04-10

183

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

NASA Astrophysics Data System (ADS)

Synchrotron radiation ultraviolet photoemission experiments at photon energies of 150 and 49 eV were performed on an epitaxial layer of (1 1 1) In 2O 3 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 (100 L) at different activation temperatures within the range utilized for chemiresistive gas sensors (160-450 °C). Large changes in photoemission response within the whole VB were observed for all gases. Regular shifts of the valence band edge relative to the Fermi energy were found under gas exposures on two kinds of surface (partially reduced or partially oxidized), and are interpreted as changes of surface potential. Treatments in oxygen resulted in upward band bending (˜0.5 eV at T = 320 °C). Regardless of activation temperature, treatments in water resulted in downward band bending, but with small changes (<0.1 eV). Reduction properties of carbon monoxide were observed only at high temperatures of T ? 370 °C. At temperatures of 160 and 250 °C unusual "oxidizing" behavior of CO was observed with upward band bending of ˜0.7 eV (160 °C). Oxidizing and reducing effects of the gas interactions with the (1 1 1) In 2O 3 surface in all cases were accompanied by a corresponding behavior, i.e., a decrease or increase in photoemission response from so-called defect states in the band gap near the top of the valence band. The increases of photoemission within a band gap with maxima at binding energies (BE) of 0.4 (O 2-induced peak) and 1.0 eV (CO-induced peak) were, respectively, found for interactions with O 2 and CO for low temperatures ( T = 160 and 250 °C). These responses were ascribed to acceptor-like electronic levels of O 2 and CO chemisorption states, respectively. A definite split of the top VB peak (BE ˜ 4.0 eV) was found under CO dosing at 160 °C. Established knowledge of the CO interaction with the (1 1 1) In 2O 3 surface explains earlier revealed acceptor-like behavior of In 2O 3 film conductivity during CO detection at operational temperatures lower than 250 °C through the formation of acceptor-like electronic levels of adsorbed CO molecules.

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

2007-12-01

184

Valence shell direct double photodetachment in polyanions  

NASA Astrophysics Data System (ADS)

A valence shell study of electrosprayed insulin protein polyanion photodetachment was carried out on a vacuum ultra-violet synchrotron radiation beamline coupled to a radiofrequency ion trap, for both close- and open-shell species. A two-electron photodetachment is observed, which arises from two different mechanisms that are disentangled: a sequential multi-photon absorption and a direct one-photon two-electron process. The threshold for the direct double-electron ejection is measured at 11.4 eV and corresponds to electronic excitation in the valence shell, which makes it the first observation of direct double photodetachment in the valence shell. The results are discussed in the light of previous knowledge from multiple photoionization and ab initio calculations on model polyanions. Double photodetachment appears to be a relaxation mechanism that leads to oxidized anions of striking stability, a feature of high relevance in radiobiology.

Brunet, Claire; Antoine, Rodolphe; Dugourd, Philippe; Duflot, Denis; Canon, Francis; Giuliani, Alexandre; Nahon, Laurent

2013-06-01

185

Evidence for Valence Alternation in Amorphous Selenium  

NASA Astrophysics Data System (ADS)

A molecular-dynamics simulation has been carried out for amorphous selenium. The simulation used 64 atoms as well as 216 atoms in a constant volume simple cubic cell. The pair correlation function g(r) and structure factors S(Q) were computed and compared with experimental and previous theoretical data. The coordination number is exactly 2 in both 64 atoms and 216 atoms model. In 64 atoms model, only 1 intimate valence alternation pair (IVAP) type defect was produced. The majority defect types are IVAP and valence alternation pair (VAP) in 216 atoms model. The electronic density function of state and the localization of the electronic state also manisfest some characternistic of VAP defect type. The results give a theoretical evidence for valence alternation in a-Se.

Xiaodong, Zhang; Drabold, D. A.

1998-05-01

186

Dynamics of Valence Fluctuating Rare Earth Compounds  

NASA Astrophysics Data System (ADS)

This thesis reports on calculations of dynamical properties for valence fluctuating rare earth compounds based upon the degenerate Anderson Hamiltonian for magnetic impurities in metals. The main theme in this document is of the viability of the narrow many body "Kondo resonance" for providing a unifying account of the experimental results for valence fluctuators. Exploiting a recently developed self-consistent perturbation theory, numerical calculations have been made of (i) transport properties for Ce impurities in metals, (ii) finite temperature photoemission spectra for Ce and Yb valence fluctuating compounds, and (iii) magnetic relaxation rates for valence fluctuating Ce compounds. In reference to (i), a quantitative one parameter fit agrees over four temperature decades with the resistivity of Ce(,x)La(,1 -x)B(,6), (ii) photoemission spectra calculated with only a change of hybridization strength qualitatively reproduce (alpha)-Ce and (gamma)-Ce data, and (iii) calculated magnetic relaxation rates reproduce the qualitative features of many valence fluctuators as well as an observed high temperature T(' 1/2) law. A rigorous calibration of the calculation method is provided by successful comparison of calculated thermodynamic quantities with exact Bethe Ansatz and Fermi Liquid theory results. The pathology known to exist for this self-consistent approach for low frequencies and temperatures is examined, and it is shown that many reliable results can be extracted despite the pathology. The possibility of phonon assisted conduction electron scattering into the 4f "Kondo resonance" is examined, and is shown to be capable of reproducing the scale of measured resistivity, thermopower, and infrared absorptivity of concentrated valence fluctuating systems, although the detailed agreement is less successful than for (i) through (iii) above. Finally, (a) some exact results for the transport properties of the related resonant level model are presented and compared with approximate memory function calculations and (b) a systematic numerical study of deviations from threshold behaviour in core-level x-ray photoemission spectra in metals is presented.

Cox, Daniel Lee

187

Towards wireless emotional valence detection from EEG.  

PubMed

Intelligent affective computers can have many medical and non-medical applications. However today's affective computers are limited in scope by their transferability to other application environments or that they monitor only one aspect of physiological emotion expression. Here, the use of a wireless EEG system, which can be implemented in a body area network, is used to investigate the potential of monitoring emotional valence in EEG, for application in real-life situations. The results show 82% accuracy for automatic classification of positive, negative and neutral valence based on film clip viewing, using features containing information on both the frequency content of the EEG and how this changes over time. PMID:22254773

Brown, Lindsay; Grundlehner, Bernard; Penders, Julien

2011-01-01

188

Nature of valence transition and spin moment in Ag(n)V(+) clusters.  

PubMed

Evolution in the atomic structure, bonding characteristics, stability, and the spin magnetic moment of neutral and cationic AgnV clusters has been investigated using first-principles density functional approach with gradient corrected functional. It is shown that at small sizes, the V 4s states hybridize with Ag states to form 1S and 1P like superatomic orbitals, whereas the 3d states are localized on V giving the V atom an effective valence of 1 or 2. Starting from Ag8V(+), the V 3d states begin to participate in the bonding by hybridizing with the nearly free electron gas to form 1D superatomic orbitals increasing the V atom effective valence toward 5. For the cationic clusters, this changing valence results in three shell closures that lead to stable species. These occur for cationic clusters containing 5, 7, and 14 Ag atoms. The first two stable species correspond to filled 1S and 1P shells in two and three dimensions with a valence of 2 for V, whereas the closure at 14 Ag atoms correspond to filled 1S, 1P, and 1D shells with V site exhibiting a valence of 5. The transition from filled 1S and 1P shells to filled 1S, 1P, and 1D shells is confirmed by a quenching of the spin magnetic moment. The theoretical findings are consistent with the observed drops in intensity in the mass spectrum of AgnV(+) clusters after 5, 7, and 14 Ag atoms. PMID:24824084

Medel, Victor M; Reber, Arthur C; Chauhan, Vikas; Sen, Prasenjit; Köster, Andreas M; Calaminici, Patrizia; Khanna, Shiv N

2014-06-11

189

Inhomogeneous effect of particle size on core-level and valence-band electrons: Size-dependent electronic structure of Cu3N nanoparticles  

NASA Astrophysics Data System (ADS)

The present study reports a clear evidence and physical significance of an inhomogeneous effect of particle size on electrons originating from various electronic levels of copper nitride nanoparticles. X-ray photoelectron and optical absorption spectroscopy studies reveal that a direct modification of the valence band due to size effects explained by the more appropriate surface bond contraction model results in a strong increase in the binding energy of valence-band electrons as compared to core-level electrons.

Balamurugan, B.; Maruyama, Toshiro

2006-07-01

190

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

191

The nature of the fourth bond in the ground state of c2 : the quadruple bond conundrum.  

PubMed

Does, or doesn't C2 break the glass ceiling of triple bonding? This work provides an overview on the bonding conundrum in C2 and on the recent discussions regarding our proposal that it possesses a quadruple bond. As such, we focus herein on the main point of contention, the 4th?bond of C2 , and discuss the main views. We present new data and an overview of the nature of the 4th?bond-its proposed antiferromagnetically coupled nature, its strength, and a derivation of its bond energy from experimentally based thermochemical data. We address the bond-order conundrum of C2 arising from generalized VB (GVB) calculations by comparing it to HC?CH, and showing that the two molecules behave very similarly, and C2 is in no way an exception. We analyse the root cause of the deviation of C2 from the Badger Rule, and demonstrate that the reason for the smaller force constant (FC) of C2 relative to HC?CH has nothing to do with the bond energies, or with the number of bonds in the two molecules. The FC is determined primarily by the bond length, which is set by the balance between the bond length preferences of the ?- versus ?-bonds in the two molecules. This interplay in the case of C2 clearly shows the fingerprints of the 4th?bond. Our discussion resolves the points of contention and shows that the arguments used to dismiss the quadruple bond nature of C2 are not well founded. PMID:24782210

Danovich, David; Hiberty, Philippe C; Wu, Wei; Rzepa, Henry S; Shaik, Sason

2014-05-19

192

Reservoir impact assessment in sub-Saharan Africa: The Volta Basin Water Allocation System (VB-WAS)  

NASA Astrophysics Data System (ADS)

In the Volta River Basin, infrastructure watershed development with respect to the impact of climate conditions is hotly debated due to the lack of adequate tools to model the consequences of such development. The Volta basin drains an area of approx. 400 000 km² of the subhumid to semiarid West-African savannah zone and is shared by six riparian countries. The region is characterized by erratic rainfall patterns, and domestic and agricultural water users in the upper regions of the Basin complete with hydropower generation in the south for increasingly scarce water resources. There is an ongoing debate on the impact of further development of small, medium and large reservoirs on the water level of Lake Volta. The GLOWA Volta Project (GVP) has developed a Volta Basin Water Allocation System (VB-WAS), a decision support tool that allows assessing the impact of infrastructure development in the basin on the availability of current and future water resources, given the current or future climate conditions. The simulated historic and future discharge time series of the coupled climate-hydrological model (MM5/WaSiM) serve as input data for a river basin management model (MIKE BASIN). MIKE BASIN uses a network approach, and allows fast simulations of water allocation and of the consequences of different development scenarios on the available water resources. Furthermore it is possible to up set up climate scenario time series scenarios for an assessment of the consequences of extreme climate conditions. Within a case study analysis the impact of small and medium scale reservoir development on the water resources of the Volta basin has been evaluated under different climatic conditions. For the evaluation of the impact of large reservoir development in particular the impact of Bui dam, which is under construction on the Black Volta River in Ghana, on the water level of Lake Volta has been simulated with the VB-WAS model. The VB-WAS model allows a quantified impact assessment of small, medium and large scale reservoir development within the Volta basin and can be used as an objective communication basis for water management issues.

Leemhuis, C.; Jung, G.; Kasei, R.; Liebe, J.

2009-04-01

193

Valence band and core level X-ray photoelectron spectroscopy of lead sulfide nanoparticle polymer composites  

NASA Astrophysics Data System (ADS)

Valence band and core level X-ray photoelectron spectroscopy (XPS) were used to probe lead sulfide (PbS) nanoparticle -polymer nanocomposites. Composite materials were prepared by trapping commercially available monodisperse 3 and 10 nm PbS nanoparticles in two polymers, the non-conducting polymer, polystyrene, and the conjugated polymer, poly(2-methoxy-5-(2'-ethyl-hexyloxy)- p-phenylene vinylene (referred to below as MEH-PPV). The nanocomposites prepared from commercial nanoparticles underwent oxidation, mainly to form lead sulfate. However, the narrow size distributions of the commercial nanoparticles allowed observation of distinct changes in the valence band from the 3 to 10 nm nanoparticles. Nanocomposites of 2-5 and 4-7 nm PbS nanoparticles were synthesized by growing the particles in poly(vinyl alcohol) (referred to below as PVA) and MEH-PPV, respectively. These composites both indicated the formation of lead sulfide nanoparticles. Furthermore, the XP spectra for the PVA/PbS composite displayed bonding between the PbS nanoparticles and the polymer while MEH-PPV showed no PbS -polymer bonding. The nanoparticles synthesized in MEH-PPV did not undergo oxidation. The particle size distributions of the synthesized nanoparticles were too broad to display size-dependent changes in the valence band.

Asunskis, Daniel J.; Hanley, Luke

2007-10-01

194

Forming Bonds.  

ERIC Educational Resources Information Center

Explains how one North Carolina school district was able to pass high-dollar bond issues for school construction. Discusses the planning and bidding processes, and the district's philosophy towards incorporating innovative changes in design and equipment. (GR)

Spoor, Dana L.

1998-01-01

195

30 CFR 57.22202 - Main fans (I-A, I-B, I-C, II-A, III, V-A, and V-B mines).  

Code of Federal Regulations, 2010 CFR

...2009-07-01 2009-07-01 false Main fans (I-A, I-B, I-C, II-A, III...Mines Ventilation § 57.22202 Main fans (I-A, I-B, I-C, II-A, III, V-A, and V-B mines). (a) Main fans shall beâ (1) Installed on the...

2009-07-01

196

Final report from VFL Technologies for the pilot-scale thermal treatment of Lower East Fork Poplar Creek floodplain soils. LEFPC Appendices, Volume 3, Appendix V-B  

SciTech Connect

This report consists of appendix V-B which contains the final verification run data package. Validation of analytical data is presented for Ecotek LSI. Analytical results are included of both soil and creek bed samples for the following contaminants: metals; metals (TCLP); uranium; gross alpha/beta; and polychlorinated biphenyls.

NONE

1994-09-01

197

Correlated topological insulators with mixed valence.  

PubMed

We propose the local density approximation+Gutzwiller method incorporating a Green's function scheme to study the topological physics of correlated materials from the first principles. Applying this method to typical mixed valence materials SmB(6), we find its nontrivial Z(2) topology, indicating that SmB(6) is a strongly correlated topological insulator. The unique feature of this compound is that its surface states contain three Dirac cones in contrast to most known topological insulators. PMID:23496729

Lu, Feng; Zhao, JianZhou; Weng, Hongming; Fang, Zhong; Dai, Xi

2013-03-01

198

Correlated Topological Insulators with Mixed Valence  

NASA Astrophysics Data System (ADS)

We propose the local density approximation+Gutzwiller method incorporating a Green’s function scheme to study the topological physics of correlated materials from the first principles. Applying this method to typical mixed valence materials SmB6, we find its nontrivial Z2 topology, indicating that SmB6 is a strongly correlated topological insulator. The unique feature of this compound is that its surface states contain three Dirac cones in contrast to most known topological insulators.

Lu, Feng; Zhao, JianZhou; Weng, Hongming; Fang, Zhong; Dai, Xi

2013-03-01

199

Mixed valence/dipole-bound dianions  

SciTech Connect

The possibility of binding two electrons to a molecule utilizing two distinct electron binding sites (i.e., one valence- and one dipole-binding center) is studied using {ital ab initio} electronic structure methods. It is found that if the electron binding energy of the dipole-binding site is large enough to overcome the Coulomb repulsion produced by the valence-bound electron, the dianion can be electronically stable with respect to the corresponding monoanion. It is also found that, for reasonable dipole- and valence-binding strengths, the separation between the two sites can be small enough to render the species within the current realm of synthetic possibility. Numerical results are presented for the dianions of LiCN{hor_ellipsis}LiCC-PF{sub 5} and LiCN{hor_ellipsis}LiCN{hor_ellipsis}LiCC-PF{sub 5}, whose vertical electronic stabilities are 0.120 and 0.808 eV, and whose stabilities with respect to fragmentation (i.e., loss of LiCN{sup {minus}}) are 3.9 and 36.5 kcal/mol [including zero point energy (ZPE)], respectively. {copyright} {ital 1999 American Institute of Physics.}

Skurski, P. [Henry Eyring Center for Theoretical Chemistry, Department of Chemistry, University of Utah, Salt Lake City, Utah 84112 (United States)] [Henry Eyring Center for Theoretical Chemistry, Department of Chemistry, University of Utah, Salt Lake City, Utah 84112 (United States); [Department of Chemistry, University of Gdansk, 80-952 Gdansk (Poland); Gutowski, M. [Materials Resources, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States)] [Materials Resources, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States); Simons, J. [Henry Eyring Center for Theoretical Chemistry, Department of Chemistry, University of Utah, Salt Lake City, Utah 84112 (United States)] [Henry Eyring Center for Theoretical Chemistry, Department of Chemistry, University of Utah, Salt Lake City, Utah 84112 (United States)

1999-12-01

200

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

201

Solitonic Generation of Valence Alternation Pairs in As2S3  

NASA Astrophysics Data System (ADS)

The crystal structure of As2S3 has degeneracies of two kinds as shown in a previous paper. By inserting locally other possible degenerate structures to a ground state, valence alternation pairs (VAP) can be generated as soliton like defects. The degeneracies concerning the arrangement of lone pairs and the directions of interhelix covalent bonds lead, respectively, to the generations of the VAPs of C1-C3 and P2-P4 types. We calculate the structures and formation energies of the VAP’s by using a valence force field model. The formation energy of a VAP is large in multilayered crystal but much reduced in a single layer suggesting its easy production in amorphous regions. Production of VAP’s induces changes of the layer structure in a surrounding region.

Shimoi, Yukihiro; Fukutome, Hideo

1990-08-01

202

Formation of an unconventional Ag valence state in Ag2NiO2  

NASA Astrophysics Data System (ADS)

The Ag ion in the recently synthesized novel material Ag2NiO2 adopts an extremely unusual valency of (1)/(2) , leaving the Ni ion as 3+ , rather than the expected 2+ . Using first-principles calculations, we show that this mysterious subvalent state emerges due to a strong bonding-antibonding interaction between the two Ag layers that drives the lower band beneath the O p complex, eliminating the possibility of a conventional Ag 1+ valence state. The strong renormalization of the specific heat coefficient ? is likely due to strong spin fluctuations that stem from nearly complete compensation of the ferromagnetic (metallic double exchange and 90° superexchange) and antiferromagnetic (conventional superexchange via Ni-O-Ag-O-Ni path) interactions.

Johannes, M. D.; Streltsov, S.; Mazin, I. I.; Khomskii, D. I.

2007-05-01

203

Ab initio calculation of core-valence-valence Auger spectra in closed shell systems  

NASA Astrophysics Data System (ADS)

We propose an ab initio method to evaluate the core-valence-valence Auger spectrum of systems with filled valence bands. The method is based on the Cini-Sawatzky theory and aims at estimating the parameters by first-principles calculations in the framework of density-functional theory (DFT). Photoemission energies and the interaction energy for the two holes in the final state are evaluated by performing DFT simulations for the system with varied population of electronic levels. Transition matrix elements are taken from atomic results. The approach takes into account the nonsphericity of the density of states of the emitting atom, spin-orbit interaction in core and valence, and nonquadratic terms in the total-energy expansion with respect to fractional occupation numbers. It is tested on two benchmark systems, Zn and Cu metals, leading in both cases to L23M45M45 Auger peaks within 2 eV from the experimental ones. Detailed analysis is presented on the relative weight of the various contributions considered in our method, providing the basis for future development. Especially problematic is the evaluation of the hole-hole interaction for systems with broad valence bands: our method underestimates its value in Cu, while we obtain excellent results for this quantity in Zn.

Fratesi, G.; Trioni, M. I.; Brivio, G. P.; Ugenti, S.; Perfetto, E.; Cini, M.

2008-11-01

204

Electronic structure and chemical bonding of zirconium disulfide  

Microsoft Academic Search

This paper involves the carrying out of the first-principle molecular-orbital calculations for ZrS2 with a model cluster composed of 129 atoms. The nature and intensity of intra- and interlayer chemical bondings are also\\u000a investigated by use of the bond overlap population. The valence band structure produced by this calculation agrees well with\\u000a experimental results reported from X-ray photoelectron spectroscopy. Each

Yang-Soo Kim; Hyun-Chul Ko; Hwa-Soo Park

2000-01-01

205

X-ray Photoemission Studies and Bonding in Amorphous Chalcogens.  

National Technical Information Service (NTIS)

Trends in x-ray photoelectron (XPS) spectra of chalcogens which relate to their bonding are discussed. Valence band spectra of disordered S are reported along with measurements in the same apparatus of amorphous Se and Te. Each chalcogen's spectrum has a ...

G. B. Fisher R. B. Shalvoy

1976-01-01

206

Energy Correlation among Three Photoelectrons Emitted in Core-Valence-Valence Triple Photoionization of Ne  

SciTech Connect

The direct observation of triple photoionization involving one inner shell and two valence electrons is reported. The energy distribution of the three photoelectrons emitted from Ne is obtained using a very efficient multielectron coincidence method using the magnetic bottle electron spectroscopic technique. A predominance of the direct path to triple photoionization for the formation of Ne{sup 3+} in the 1s2s{sup 2}2p{sup 4} configuration is observed. It is demonstrated that the energy distribution evolves with photon energy and indicates a significant difference with triple photoionization involving only valence electrons.

Hikosaka, Y.; Soejima, K. [Department of Environmental Science, Niigata University, Niigata 950-2181 (Japan); Lablanquie, P.; Penent, F.; Palaudoux, J.; Andric, L. [UPMC, Universite Paris 06, LCPMR, 11 rue Pierre et Marie Curie, 75231 Paris Cedex 05 (France); CNRS, LCPMR (UMR 7614), 11 rue Pierre et Marie Curie, 75231 Paris Cedex 05 (France); Shigemasa, E. [UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585 (Japan); Suzuki, I. H.; Nakano, M.; Ito, K. [Photon Factory, Institute of Materials Structure Science, Oho, Tsukuba 305-0801 (Japan)

2011-09-09

207

Energy correlation among three photoelectrons emitted in core-valence-valence triple photoionization of Ne.  

PubMed

The direct observation of triple photoionization involving one inner shell and two valence electrons is reported. The energy distribution of the three photoelectrons emitted from Ne is obtained using a very efficient multielectron coincidence method using the magnetic bottle electron spectroscopic technique. A predominance of the direct path to triple photoionization for the formation of Ne3+ in the 1s 2s2 2p4 configuration is observed. It is demonstrated that the energy distribution evolves with photon energy and indicates a significant difference with triple photoionization involving only valence electrons. PMID:22026663

Hikosaka, Y; Lablanquie, P; Penent, F; Palaudoux, J; Andric, L; Soejima, K; Shigemasa, E; Suzuki, I H; Nakano, M; Ito, K

2011-09-01

208

A paramagnetic bonding mechanism for diatomics in strong magnetic fields.  

PubMed

Elementary chemistry distinguishes two kinds of strong bonds between atoms in molecules: the covalent bond, where bonding arises from valence electron pairs shared between neighboring atoms, and the ionic bond, where transfer of electrons from one atom to another leads to Coulombic attraction between the resulting ions. We present a third, distinct bonding mechanism: perpendicular paramagnetic bonding, generated by the stabilization of antibonding orbitals in their perpendicular orientation relative to an external magnetic field. In strong fields such as those present in the atmospheres of white dwarfs (on the order of 10(5) teslas) and other stellar objects, our calculations suggest that this mechanism underlies the strong bonding of H(2) in the (3)?(u)(+)(1?(g)1?(u)*) triplet state and of He(2) in the (1)?(g)(+)(1?(g)(2)1?(u)(*2)) singlet state, as well as their preferred perpendicular orientation in the external field. PMID:22822146

Lange, Kai K; Tellgren, E I; Hoffmann, M R; Helgaker, T

2012-07-20

209

Separability Between Valence and Conduction Bands in Transition Metal Clusters  

SciTech Connect

Simplified theories of transition metal electronic structure have been postulated for many decades. Here we test one such approximation, namely separate treatments of d (valence) and s/p (conduction) electrons in transition metal clusters, within a density functional formalism. Two different basic approaches are considered: (a) an independent-band approximation, in which the d- and s/p-bands interact only via the ?-dependent components of the Kohn-Sham operator; and (b) a more realistic approximation, in which the lowest-energy d- and s/p-orbitals (separately derived) are allowed to interact through explicit off-diagonal coupling matrix elements. Results are presented for the energy differences among three structural forms (icosahedral, cuboctahedral and truncated decahedral) of 13-atom Ni and Pt clusters. We demonstrate that an explicit decoupling of the d- and s/p-bands does not produce accurate results for the clusters considered here, not even for nickel, i.e., the transition metal for which d-s/p mixing should be at its minimum. By contrast, allowing the lowest energy orbitals of the two separate bands to interact improves the results considerably, and assures a fair description of metal-metal bonding. This suggests simplified models that exclude explicit d-s/p coupling should be employed with caution.

Apra, Edoardo; Carter, Emily A.; Fortunelli, Alessandro

2004-07-30

210

Unusual valency and magnetic order in silver nickelates  

NASA Astrophysics Data System (ADS)

Ag2NiO2 forms as a triangular based layered nickelate, with a structure identical to the well-studied alkali nickelates LiNiO2 or NaNiO2, but with a double layer of Ag between the oxide planes. The metallic intercalant ions give rise to highly unusual valence state for silver: Ag^1/2+. We show that the reason for the underoxidation is that the two silver ions form extremely strong bonding-antibonding bands, pushing the lowest Ag-s derived band beneath the (filled) O p complex. This additionally preserves metallicity down to the lowest measured temperatures and gives rise to complex, competing magnetic interactions. The resulting spin fluctuations may explain the large discrepancy (too large for phonon renormalization) between calculated and measured linear specific heat coefficients. Our calculations do not support a controversial cooperative Jahn-Teller distortion, but a comparison with calculations and experiments for single-layer AgNiO2 suggests that magnetically driven charge disproportionation may instead explain the observed structural transition.

Streltsov, Sergey; Johannes, M. D.; Mazin, I. I.; Khomskii, D. I.

2007-03-01

211

The Valence Band Structure of Tellurium. III. The Landau Levels  

Microsoft Academic Search

The Landau levels are calculated for two upper valence bands of tellurium. The peak positions and intensities of the cyclotron resonance and of the inter-valence band magneto-absorption are calculated. Effects of the \\\\mbi{k}-linear terms on them are elucidated. For the magnetic field perpendicular to the c-axis, the Landau levels of the uppermost valence band are doubly degenerate at low magnetic

Kenji Nakao; Takao Doi; Hiroshi Kamimura

1971-01-01

212

Electron hopping in the Mössbauer spectrum of mixed valence freudenbergite  

NASA Astrophysics Data System (ADS)

Samples of pure ferric, ferrous and mixed valence freudenbergite were prepared by different techniques. The 57Fe Mössbauer spectra of the single valence samples showed poorly resolved quadrupole splittings for the ferric sample, two well-resolved quadrupole splittings for the ferrous sample and electron hopping at, and above, room temperature for the mixed valence sample, which disappeared on lowering the temperature to 50 K.

Cashion, J. D.; Lashtabeg, A.; Vance, E. R.; Ryan, D. H.

2014-04-01

213

Structural anomalies in Nd2-xCexCuO4-y: Evidence for mixed valence and charge transfer  

Microsoft Academic Search

The electron oxide superconductors Nd2-xCexCuO4-y have been investigated by X-ray diffraction, XPS, magnetization and resistivity measurements. We found that Ce-ions lie between the 3+ and 4+ valence states, and that sharp changes in various bond-lengths occur near x=0.15 coinciding with the onset of superconductivity. The later has been taken as evidence for electron-transfer to the CuO2-layers. The results and their

P. H. Hor; Y. Y. Xue; Y. Y. Sun; Y. C. Tao; Z. J. Huang; W. Rabalais; C. W. Chu

1989-01-01

214

Valence and salience contribute to nucleus accumbens activation  

PubMed Central

Different accounts of nucleus accumbens (NAcc) function have emphasized its role in representing either valence or salience during incentive anticipation. In an event-related FMRI experiment, we independently manipulated valence and salience by cuing participants to anticipate certain and uncertain monetary gains and losses. NAcc activation correlated with both valence and salience. On trials with certain outcomes, NAcc activation increased for anticipated gains and decreased for anticipated losses. On trials with uncertain outcomes, NAcc activation increased for both anticipated gains and losses but did not differ between them. These findings suggest that NAcc activation separately represents both valence and salience, consistent with its hypothesized role in appetitive motivation.

Cooper, Jeffrey C.; Knutson, Brian

2007-01-01

215

Experimental investigation of core-valence double photoionization.  

PubMed

Core-valence double photoionization has been observed in Ne atoms and N2 molecules using a magnetic-bottle time of flight spectrometer. The multielectron coincidence data sets give complete information on the energy correlations between all emitted electrons, which supports a detailed description of the core-valence double photoionization processes including direct spectroscopy of the core-valence doubly ionized states, the final states populated by their Auger decay and details of the dynamics of core-valence double photoionization for selected states. PMID:17026099

Hikosaka, Y; Aoto, T; Lablanquie, P; Penent, F; Shigemasa, E; Ito, K

2006-08-01

216

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

SciTech Connect

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)/sub 2/CuO/sub 4-//sub y/. .AE

Pauling, L.

1987-07-13

217

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

NASA Astrophysics Data System (ADS)

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

Pauling, Linus

1987-07-01

218

Self-doping of molecular quantum-dot cellular automata: mixed valence zwitterions.  

PubMed

Molecular quantum-dot cellular automata (QCA) is a promising paradigm for realizing molecular electronics. In molecular QCA, binary information is encoded in the distribution of intramolecular charge, and Coulomb interactions between neighboring molecules combine to create long-range correlations in charge distribution that can be exploited for signal transfer and computation. Appropriate mixed-valence species are promising candidates for single-molecule device operation. A complication arises because many mixed-valence compounds are ions and the associated counterions can potentially disrupt the correct flow of information through the circuit. We suggest a self-doping mechanism which incorporates the counterion covalently into the structure of a neutral molecular cell, thus producing a zwitterionic mixed-valence complex. The counterion is located at the geometrical center of the QCA molecule and bound to the working dots via covalent bonds, thus avoiding counterion effects that bias the system toward one binary information state or the other. We investigate the feasibility of using multiply charged anion (MCA) boron clusters, specifically closo-borate dianion, as building blocks. A first principle calculation shows that neutral, bistable, and switchable QCA molecules are possible. The self-doping mechanism is confirmed by molecular orbital analysis, which shows that MCA counterions can be stabilized by the electrostatic interaction between negatively charged counterions and positively charged working dots. PMID:21755091

Lu, Yuhui; Lent, Craig

2011-09-01

219

Scenarios for the Origin of the Orbits of the Trans-Neptunian Objects 2000 CR105 and 2003 VB12 (Sedna)  

NASA Astrophysics Data System (ADS)

Explaining the origin of the orbits of 2000 CR105 (a=230 AU, q=44 AU) and 2003 VB12 (a=531 AU, q=74 AU, unofficially known as Sedna) is a major test for our understanding of the primordial evolution of the outer solar system. Gladman et al. have shown that 2000 CR105 could not have been a normal member of the scattered disk that had its perihelion distance increased by chaotic diffusion. The same conclusion also clearly applies to 2003 VB12. In this paper, we explore five seemingly promising mechanisms to explain the origin of the orbits of these peculiar objects: (1) the passage of Neptune through a high-eccentricity phase, (2) the past existence of massive planetary embryos in the Kuiper belt or the scattered disk, (3) the presence of a massive trans-Neptunian disk at early epochs that perturbed highly inclined scattered-disk objects, (4) encounters with other stars that perturbed the orbits of some of the solar system's trans-Neptunian planetesimals, and (5) the capture of extrasolar planetesimals from low-mass stars or brown dwarfs encountering the Sun. Of all these mechanisms, the ones giving the most satisfactory results are those related to the passage of stars (4 and 5). An important advantage of both stellar-passage scenarios is that all the resulting objects with large perihelion distances also have large semimajor axes. This is in good agreement with the fact that 2000 CR105 and 2003 VB12 have semimajor axes larger than 200 AU and no other bodies with similar perihelion distances but smaller semimajor axes have yet been discovered. We favor mechanism 4, since it produces an orbital element distribution that is more consistent with the observations, unless 2000 CR105 and 2003 VB12 represent a population more massive than a few tenths of an Earth mass, in which case this mechanism is not viable.

Morbidelli, Alessandro; Levison, Harold F.

2004-11-01

220

Single-crystal growth of langasite (La 3Ga 5SiO 14) by the vertical Bridgman (VB) method in air and in an Ar atmosphere  

Microsoft Academic Search

Piezoelectric langasite (La3Ga5SiO14, LGS) single crystals were grown by the vertical Bridgman (VB) method in air and in an Ar atmosphere. In the Ar atmosphere, a colorless-transparent crack-free LGS single crystal, 1in. in diameter, was grown using raw material with a slightly Ga-rich composition, while in air an orange-colored transparent LGS crystal was grown. Any other phases could not be

Toshinori Taishi; Takayuki Hayashi; Tatsuo Fukami; Keigo Hoshikawa; Ichiro Yonenaga

2007-01-01

221

A virus-based miRNA suppression (VbMS) system for miRNA loss-of-function analysis in plants.  

PubMed

MicroRNAs (miRNAs) play key roles in plant development and defense against pathogens. To establish the function of individual miRNAs, gain-of-function analysis is usually done by overexpressing a specific miRNA in transgenic plants and has proved very effective. Loss-of-function analysis by the target mimic method is now also increasingly being used. The mimics expressed in the transgenic plants sequester a specific miRNA and lead to changed phenotypes that elucidate miRNA function. However, it takes time to obtain the transgenic plants. To avoid using transgenic plants, we have developed a virus-based miRNA suppression system (VbMS) based on a Tobacco rattle virus vector. The target mimic sequences of miR156, miR319, or miR164 were introduced into the viral genomic RNA, which was then inoculated to Arabidopsis thaliana plants. The resulting phenotypes were consistent with previous reports from transgenic plants, and the expression of targets of the miRNAs was also increased showing that the activity of the miRNAs had been inhibited. VbMS developed here is validated for loss-of-function analysis of miRNA in plants. Moreover, since only simple agroinfiltration rather than transformation is needed, VbMS is suitable for large-scale approaches to miRNA function analysis in plants. PMID:24664983

Yan, Fei; Guo, Weixia; Wu, Gentu; Lu, Yuwen; Peng, Jiejun; Zheng, Hongying; Lin, Lin; Chen, Jianping

2014-05-01

222

30 CFR 57.22227 - Approved testing devices (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines).  

Code of Federal Regulations, 2013 CFR

...NONMETAL MINES Safety Standards for Methane in Metal and Nonmetal Mines Ventilation...V-A, and V-B mines). (a) Methane monitoring devices and portable, battery-powered...self-contained devices used for measuring methane, other gases, and contaminants...

2013-07-01

223

Effect of phenyl and benzyl group in heterocyclic dithiocarbamates on the ZnS 4N chromophore: Synthesis, spectral, valence-bond parameters and single crystal X-ray structural studies on (pyridine)bis(1,2,3,4-tetrahydroquinolinedithiocarbamato)zinc(II) and (pyridine)bis(1,2,3,4-tetrahydroisoquinolinedithiocarbamato)zinc(II)  

NASA Astrophysics Data System (ADS)

Two Zn(II)dithiocarbamates with ZnS 4N chromophores have been synthesized ([Zn(thqdtc) 2(py)] ( 1) and [Zn(thiqdtc) 2(py)] ( 2) (where thqdtc = 1,2,3,4-tetrahydroquinolinedithiocarbamate, thiqtc = 1,2,3,4-tetrahydroisoquinolinedithiocarbamate and py = pyridine)) from [Zn(thqdtc) 2] ( 3) and [Zn(thiqdtc) 2] ( 4), respectively. Their structures and properties have been characterized by IR and NMR spectra. The structures of both the complexes were determined by single crystal X-ray crystallography. The observed deshielding of the H-2 protons for 1 and 3 and H-1 and H-3 protons for 2 and 4 in the 1H NMR spectra is attributed to the drift of electrons from the nitrogen of the NR 2 group, forcing a high electron density towards sulfur via the thioureide ?-system. In the 13C NMR spectra, the most important thioureide (N 13CS 2) carbon signals are observed in the region 204-207 ppm. The upfield shift of NCS 2 carbon signal for 1 (204.2 ppm) from the chemical shift value of 2 (206.9 ppm) is due to electron withdrawing resonance effect of phenyl ring thereby decreasing the double bond character in tetrahydroquinolinedithiocarbamate, whereas benzyl group in tetrahydroisoquinolinedithiocarbamate cannot participate in resonance delocalization in the same way. Single crystal X-ray structural analysis of 1 and 2 showed that the zinc atom is pentacoordinated with four sulfur atoms from the dithiocarbamate ligands and one nitrogen atom from the pyridine. VBS values support the correctness of the determined structure. The lower VBS value of 2 is due to the steric effect exerted by the thiqdtc. The phenyl and benzyl group in the heterocyclic dithiocarbamates influences the electronic properties of 1 and 2. The shift of ? C- N(thioureide) and thioureide N 13CS 2 carbon signals are correlated with the electronic effects of the dithiocarbamate ligands.

Srinivasan, N.; Thirumaran, S.; Ciattini, Samuele

2009-03-01

224

Self-Consistent Valence Charge Density of the 1T Layer Compounds TiS2, TiSe2, ZrS2 and ZrSe2  

Microsoft Academic Search

A systematic presentation of the valence charge densities for TiS2, TiSe2, ZrS2 and ZrSe2 is given in the form of contour maps. The effects of the variation of the Xalpha constant alpha and the layer height parameter are studied. The bonding mechanism is also discussed. The more metallic nature of the valence charge density of TiSe2 in the hexagonal metal

J. von Boehm; H. Isomäki; P. Krusius

1980-01-01

225

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

226

The k3? Valence State of CO  

NASA Astrophysics Data System (ADS)

The high-resolution VUV k3?( v = 2, 3, 5) ? X1? +( v = 0) "forbidden" absorption bands of CO have been observed and rotationally analyzed in the wavenumber range 90 000-98 000 cm -1, confirming the recent 3? assignment for the upper valence state given by Baker et al. ( Chem. Phys.178, 569-579 (1993)). It is also shown that the k3? 2( v = 3) spin-orbit component is responsible for the indirect predissociation at J = 31 in the E1?( v = 0) state, while the k3? 0( v = 5) spin-orbit component is responsible for the indirect predissociation at J = 7 in the E1?( v = 1) state.

Baker, J.; Launay, F.

1994-05-01

227

Modulation of DNA condensation by cation valence  

NASA Astrophysics Data System (ADS)

Aggrecan is a negatively charged bottlebrush-shaped proteoglycan in the extracellular matrix, with unique polyelectrolyte properties. Aggrecan-hyaluronic acid aggregates are responsible for the compressive resilience of articular cartilage. Unlike linear polyelectrolytes such as DNA, aggrecan is insensitive to the presence of multivalent counterions (e.g., calcium ions) and self-assembles into micro-gels in near-physiological salt solutions. These features are preserved by aggrecan adsorbed on mica surfaces. To probe both the nature of aggrecan assemblies in solution and their surface interactions, we image the aggrecan assemblies adsorbed on mica surface using Atomic Force Microscopy The effect of counterion valence on the hydration-dehydration properties of the aggrecan assemblies will be discussed.

Chandran, Preethi; Dimitriadis, Emilios; Silva, Candida; Basser, Peter; Horkay, Ferenc

2011-03-01

228

Robustness of Quantum Criticality of Valence Fluctuations  

NASA Astrophysics Data System (ADS)

The mechanism of emergence of robust quantum criticality in Yb- and Ce-based heavy electron systems under pressure is analyzed theoretically. By constructing a minimal model for quasicrystal Yb15Al34Au51 and its approximant, we show that quantum critical points of the first-order valence transition of Yb appear in the ground-state phase diagram with their critical regimes being overlapped to be unified, giving rise to a wide quantum critical regime. This well explains the robust unconventional criticality observed in Yb15Al34Au51 under pressure. We also discuss broader applicability of this mechanism to other Yb- and Ce-based systems such as ?-YbAlB4 showing unconventional quantum criticality.

Watanabe, Shinji; Miyake, Kazumasa

2013-08-01

229

Valence Effects in Reasoning About Evaluative Traits  

PubMed Central

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.

Heyman, Gail D.; Giles, Jessica W.

2010-01-01

230

Chalcogen bond: a sister noncovalent bond to halogen bond.  

PubMed

A sister noncovalent bond to halogen bond, termed chalcogen bond, is defined in this article. By selecting the complexes H(2)CS...Cl(-), F(2)CS...Cl(-), OCS...Cl(-), and SCS...Cl(-) as models, the bond-length change, interaction energy, topological property of the electron charge density and its Laplacian, and the charge transfer of the chalcogen bond have been investigated in detail theoretically. It was found that the similar misshaped electron clouds of the chalcogen atom and the halogen atom result in the similar properties of the chalcogen bond and the halogen bond. Experimental results are in good agreement with the theoretical predictions. PMID:19537765

Wang, Weizhou; Ji, Baoming; Zhang, Yu

2009-07-16

231

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

232

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

233

Pi Bond Orders and Bond Lengths  

ERIC Educational Resources Information Center

Discusses three methods of correlating bond orders and bond lengths in unsaturated hydrocarbons: the Pauling theory, the Huckel molecular orbital technique, and self-consistent-field techniques. (MLH)

Herndon, William C.; Parkanyi, Cyril

1976-01-01

234

Real-time observation of valence electron motion  

Microsoft Academic Search

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

Eleftherios Goulielmakis; Zhi-Heng Loh; Adrian Wirth; Robin Santra; Nina Rohringer; Vladislav S. Yakovlev; Sergey Zherebtsov; Thomas Pfeifer; Abdallah M. Azzeer; Matthias F. Kling; Stephen R. Leone; Ferenc Krausz; Max-Planck-Insti. fur Quantenoptik

2010-01-01

235

Confounding valence and arousal: What really underlies political orientation?  

PubMed

The negative valence model of political orientation proposed by Hibbing et al. is comprehensive and thought-provoking. We agree that there is compelling research linking threat to conservative political beliefs. However, we propose that further research is needed before it can be concluded that negative valence, rather than arousal more generally, underlies the psychological motivations to endorse conservative political belief. PMID:24970452

Tritt, Shona M; Inzlicht, Michael; Peterson, Jordan B

2014-06-01

236

On the Relationship between Value Orientation, Valences, and Academic Achievement  

ERIC Educational Resources Information Center

Value orientations are believed to influence learning in school. We assume that this influence is mediated by the valences attached to specific school subjects. In a questionnaire study (704 students from 36 classes) achievement and well-being value orientations were measured. Students also rated valence scales for the school subjects German and…

Fries, Stefan; Schmid, Sebastian; Hofer, Manfred

2007-01-01

237

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

2009-01-01

238

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 Central

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 ?g. The MTD was established as 930 ?g 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.

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

2008-01-01

239

Hybrid exchange-correlation functional for core, valence, and Rydberg excitations: Core-valence-Rydberg B3LYP  

NASA Astrophysics Data System (ADS)

The core-valence-Rydberg Becke's three-parameter exchange (B3)+Lee-Yang-Parr (LYP) correlation functional (CVR-B3LYP) is proposed as a means to improve descriptions of Rydberg excitations of core-valence B3LYP (CV-B3LYP). CV-B3LYP describes excitations from both core and occupied valence orbitals to unoccupied valence orbitals with high accuracy but fails to describe those to Rydberg orbitals. CVR-B3LYP, which adopts the appropriate portions of Hartree-Fock exchange for unoccupied valence and Rydberg regions separately, overcomes the disadvantage of CV-B3LYP. Numerical assessment confirms that time-dependent density functional theory calculations with CVR-B3LYP succeed in describing not only core excitations but also Rydberg excitations with reasonable accuracy.

Nakata, Ayako; Imamura, Yutaka; Nakai, Hiromi

2006-08-01

240

Inelastic neutron scattering in valence fluctuation compounds  

SciTech Connect

The valence fluctuation compounds are rare earth intermetallics where hybridization of the nearly-localized 4f electrons with the conduction electrons leads to incorporation of the 4f's into the itinerant states. This hybridization slows down the conduction electrons and hence gives them a heavy effective mass, justifying application of the term 'heavy Fermion' (HF) to these materials. During the project period, we grew large single crystals of several such compounds and measured their properties using both standard thermodynamic probes and state-of-the-art inelastic neutron scattering. We obtained three main results. For the intermediate valence compounds CePd{sub 3} and YbAl{sub 3}, we showed that the scattering of neutrons by the fluctuations of the 4f magnetic moment does not have the momentum dependence expected for the itinerant heavy mass state; rather, the scattering is more typical of a localized spin fluctuation. We believe that incoherent scattering localizes the excitation. For the heavy Fermion compound Ce(Ni{sub 0.935}Pd{sub 0.065}){sub 2}Ge{sub 2}, which sits at a T = 0 critical point for transformation into an antiferromagnetic (AF) phase, we showed that the scattering from the AF fluctuations does not exhibit any of the divergences that are expected at a phase transition. We speculate that alloy disorder profoundly suppresses the growth of the fluctuating AF regions, leading to short range clusters rather than regions of infinite size. Finally, we explored the applicability of key concepts used to describe the behavior of rare earth heavy Fermions to uranium based HF compounds where the 5f electrons are itinerant as opposed to localized. We found that scaling laws relating the spin fluctuation energy measured in neutron scattering to the low temperature specific heat and susceptibility are valid for the uranium compounds, once corrections are made for AF fluctuations; however, the degeneracy of the high temperature moment is smaller than expected for rare-earth-like Hund's rule behavior, essentially because the orbital moment is suppressed for itinerant 5f electrons. We also found that the standard local-moment-based theory of the temperature dependence of the specific heat, susceptibility and neutron scattering fails badly for URu{sub 2}Zn{sub 20} and UCo{sub 2}Zn{sub 20}, even though the theory is phenomenally successful for the closely related rare earth compound YbFe{sub 2}Zn{sub 20}. Both these results highlight the distinction between the itineracy of the 5f's and the localization of the 4f's. It is our hope that these results are sufficiently significant as to stimulate deeper investigation of these compounds.

Jon M Lawrence

2011-02-15

241

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

242

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

243

Sedna (2003 VB12)  

NSDL National Science Digital Library

This page presents the available telescopic images and artist conceptions of this Kuyper Belt Object. The page was produced by Michael Brown at the California Institute of Technology and Chad Trujillo at the Gemini Observatory who discovered it

Brown, Michael; Technology, California I.

244

On the Valence of Silver in Argentic Oxide.  

National Technical Information Service (NTIS)

The results of a literature survey on the valence of silver in argentic oxide (AgO) are presented. Physical and chemical evidence indicates the presence of both trivalent and monovalent silver in argentic oxide, but no divalent silver. (Author)

E. H. Ostrander G. L. Cohen

1964-01-01

245

Mixed-Valence Porphyrin ?-Cation Radical Derivatives: Electrochemical Investigations  

PubMed Central

The electrochemistry of [Cu(OEP)] and [Ni(OEP)] are compared with the mixed-valence ?-cations [Cu(OEP•/2)]2+and[Ni(OEP•/2)]2+. These electrochemical studies, carried out with cyclic voltametry and hydrodynamic voltametry, show that the mixed valence ?-cations have distinct electrochemical properties, although the differences between the [M(OEP)]+/0 and [M(OEP•/2)]2+/0 processes are subtle.

Scheidt, W. Robert; Buentello, Kristin E.; Ehlinger, Noelle; Cinquantini, Arnaldo; Fontani, Marco; Laschi, Franco

2008-01-01

246

Valence bands and Davydov splittings in solid ortho-hydrogen  

Microsoft Academic Search

Starting from the Coulson model for the ground state of H2, the valence electronic states of ortho-hydrogen crystals are calculated. The maximum value of the Davydov splittings is 1.1 eV at k=0. It is shown that at any point of the Brillouin zone cube edges the Davydov splittings vanish because of time reversal symmetry and all valence bands become degenerate.

L. A. Gomez; G. Pastori Parravicini; L. Resca; R. Resta

1973-01-01

247

Valence photoionization of the LiCl monomer and dimer  

NASA Astrophysics Data System (ADS)

This paper reports a study of valence photoionization of the LiCl monomer and dimer. The behavior of the photoionization partial cross section for molecular valence orbitals was measured as a function of photon energy between 15 and 35 eV. A square-integrable-function method was used to model the ionization partial cross section in both the LiCl monomer and dimer.

Niskanen, J.; Urpelainen, S.; Aksela, S.; Aksela, H.; Vahtras, O.; Carravetta, V.; Ågren, H.

2010-04-01

248

Mixed-Valence Porphyrin ?-Cation Radical Derivatives: Electrochemical Investigations.  

PubMed

The electrochemistry of [Cu(OEP)] and [Ni(OEP)] are compared with the mixed-valence ?-cations [Cu(OEP•/2)]2+and[Ni(OEP•/2)]2+. These electrochemical studies, carried out with cyclic voltametry and hydrodynamic voltametry, show that the mixed valence ?-cations have distinct electrochemical properties, although the differences between the [M(OEP)](+/0) and [M(OEP•/2)]2+/0 processes are subtle. PMID:19421310

Scheidt, W Robert; Buentello, Kristin E; Ehlinger, Noelle; Cinquantini, Arnaldo; Fontani, Marco; Laschi, Franco

2008-05-01

249

On the relationship between value orientation, valences, and academic achievement  

Microsoft Academic Search

Value orientations are believed to influence learning in school. We assume that this influence is mediated by the valences\\u000a attached to specific school subjects. In a questionnaire study (704 students from 36 classes) achievement and well-being value\\u000a orientations were measured. Students also rated valence scales for the school subjects German and Mathematics and reported\\u000a their respective grades. In order to

Stefan Fries; Sebastian Schmid; Manfred Hofer

2007-01-01

250

Valence Band Density of States of Cu3Si Studied by Soft X-Ray Emission Spectroscopy and a First-Principle Molecular Orbital Calculation  

NASA Astrophysics Data System (ADS)

A systematic study of the valence band structure of Cu3Si has been performed by soft X-ray emission spectroscopy and a first-principle molecular orbital calculation using the discrete-variational (DV)-X? cluster model. The existence of Cu 4s, 4p states in the valence band and their important contributions to the valence band as that of Cu 3d are indicated together with previously reported ones. The high-binding energy peak in the Si L2,3 emission spectrum is considered to originate mainly from the Si-Si 3s bonding state but also have a certain contribution of Si 3s bonding state with Cu 4s, 4p. On the other hand, the low-binding energy peaks in the Si L2,3 emission band are attributed to both the antibonding states of Si 3s and the bonding states of Si 3d with Cu 4s, 4p and Cu 3d. The bonding states of Si 3s with Cu 4s, 4p and Cu 3d are expected to exist in the lower part of the valence band for ?\\prime-Cu3Si on the basis of the theoretical calculations. As for Si p states, the high-binding energy peak and the low-binding energy peak in the Si K? emission spectrum should be attributed to the Si 3p bonding state and antibonding state with Cu 3d and Cu 4s, 4p, respectively, according to the theoretical calculations. A comparison is made between experimental spectra and theoretical density of states.

An, Zhenlian; Kamezawa, Chihiro; Hirai, Masaaki; Kusaka, Masahiko; Iwami, Motohiro

2002-12-01

251

Valence resolution of facial expressions using an emotional oddball task  

PubMed Central

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 serve as an implicit context to resolve the valence ambiguity of surprised facial expressions, but that this implicit context does not completely override the default negativity.

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

2012-01-01

252

On the bond distance in methane  

NASA Technical Reports Server (NTRS)

The equilibrium bond distance in methane was optimized using coupled-pair functional and contracted CI wave functions, and a Gaussian basis that includes g-type functions on carbon and d-type functions on hydrogen. The resulting bond distance, when corrected for core-valence correlation effects, agrees with the experimental value of 2.052 a(0) to within the experimental uncertainty of 0.002 a(0). The main source of error in the best previous studies, which showed discrepancies with experiment of 0.007 a(0) is shown to be basis set incompleteness. In particular, it is important that the basis set be close to saturation, at least for the lower angular quantum numbers.

Bowen-Jenkins, Philippa; Pettersson, Lars G. M.; Siegbahn, Per; Almloef, Jan; Taylor, Peter R.

1987-01-01

253

X-ray photoemission studies and bonding in amorphous chalcogens  

Microsoft Academic Search

Trends in X-ray photoelectron (XPS) spectra of chalcogens which relate to their bonding are discussed. Valence band spectra of disordered S are reported along with measurements in the same apparatus of amorphous Se and Te. Each chalcogen's spectrum has a minimum about 7 eV below E(F), between the largely p-derived states nearer E(F) and the s-derived states. The p states

G. B. Fisher; R. B. Shaluoy

1976-01-01

254

X-ray photoemission studies and bonding in amorphous chalcogens  

Microsoft Academic Search

Trends in x-ray photoelectron (XPS) spectra of chalcogens which relate to their bonding are discussed. Valence band spectra of disordered S are reported along with measurements in the same apparatus of amorphous Se and Te. Each chalcogen’s spectrum has a minimum about 7 eV below EF, between the largely p-derived states nearer EF and the s-derived states. The p states

Galen B. Fisher; Richard B. Shalvoy

1976-01-01

255

X-ray photoemission studies and bonding in amorphous chalcogens  

Microsoft Academic Search

Trends in x-ray photoelectron (XPS) spectra of chalcogens which relate to their bonding are discussed. Valence band spectra of disordered S are reported along with measurements in the same apparatus of amorphous Se and Te. Each chalcogen's spectrum has a minimum about 7 eV below EF, between the largely p-derived states nearer EF and the s-derived states. The p states

Galen B. Fisher; Richard B. Shalvoy

1976-01-01

256

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

Microsoft Academic Search

We discuss the ground state properties of a spin 1\\/2 magnetic ion with\\u000athreefold $t_{2g}$ orbital degeneracy on a highly frustrated pyrochlore\\u000alattice, like Ti$^{3+}$ ion in B-spinel MgTi$_2$O$_4$. We formulate an\\u000aeffective spin-orbital Hamiltonian and study its low energy sector by\\u000aconstructing several exact-eigenstates in the limit of vanishing Hund's\\u000acoupling. We find that orbital degrees of freedom modulate

S. Di Matteo; G. Jackeli; N. B. Perkins

2005-01-01

257

Valence-Bond Crystal in a Pyrochlore Antiferromagnet with Orbital Degeneracy  

Microsoft Academic Search

We discuss the ground state of a pyrochlore lattice of\\u000athreefold-orbitally-degenerate $S=1\\/2$ magnetic ions. We derive an effective\\u000aspin-orbital Hamiltonian and show that the orbital degrees of freedom can\\u000amodulate the spin exchange, removing the infinite spin-degeneracy\\u000acharacteristic of pyrochlore structures. The resulting state is a collection of\\u000aspin-singlet dimers, with a residual degeneracy due to their relative\\u000aorientation. This

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

2004-01-01

258

Valence-Bond Crystal in a Pyrochlore Antiferromagnet with Orbital Degeneracy  

Microsoft Academic Search

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

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

2004-01-01

259

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

Microsoft Academic Search

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

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

2005-01-01

260

Crystal structure, physical properties and bond valence analysis of NaLuP2O7  

NASA Astrophysics Data System (ADS)

Single crystals of a diphosphate NaLuP2O7 have been synthesized by the flux method and characterized by single-crystal X-Ray diffraction. NaLuP2O7 crystallizes in the monoclinic system with P21/n space group with cell parameters: a = 8.9985(8) Å, b = 5.3473(5) Å, c = 12.756(1) Å, ? = 103.174° (1), V = 597.67 (9) Å3, Z = 4. Its structure consists of a three-dimensional framework of P2O7 units that are corner-shared by LuO6 octahedra, forming tunnels running parallel to [010] which are occupied by Na atoms. NaLuP2O7 powder was characterized by XRD, SEM, FTIR and Raman spectroscopy. The activation energy of (1.49 eV) obtained by electrical measurements suggests the charge carriers to be the sodium cations. The activation energies obtained from impedance and loss spectra were analyzed in order to explain the mechanism of conduction. The correlation between ionic conductivity of NaLuP2O7 and its crystallographic structure was investigated and the most probable transport pathway model was determined.

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

2014-05-01

261

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

262

First-principle study on bonding mechanism of ZnO by LDA + U method  

NASA Astrophysics Data System (ADS)

The electronic structure and the bonding mechanism of ZnO have been studied by using the Full-Potential Linear Augmented Plane Wave (FP-LAPW) method within the density-functional theory (DFT) based on LDA + U exchange correlation potential. The valence and the bonding charge density are calculated and compared with those derived from LDA and GGA to describe the bonding mechanism. The charge transfer along with the bonding process is analyzed by using the theory of Atoms in Molecules (AIM). The bonding, the topological characteristics and the p d coupling effects on the bonding mechanism of ZnO are shown quantitatively with the critical points (CPs) along the bonding trajectory and the charge in the atomic basins. Meanwhile, the bonding characteristics for wurtzite, zinc blende and rocksalt phase of ZnO are discussed systematically in the present paper.

Zhou, G. C.; Sun, L. Z.; Zhong, X. L.; Chen, Xiaoshuang; Wei, Lu; Wang, J. B.

2007-08-01

263

Nature of PO bonds in phosphates.  

PubMed

Making use of a combination of ab initio calculated geometries, orbital energies, and orbital spatial distributions as well as experimental information about bond lengths, bond energies, vibrational frequencies, and dipole moments, the nature of the terminal PO bond in phosphates such as (MeO)(3)PO was probed and compared to the case in MeO-P=O where P is trivalent and a PO pi bond is thus assumed to exist. We find that the MeO-P and terminal PO bond lengths in (MeO)(3)PO are essentially the same as in MeO-P=O and the terminal PO lengths are substantially shorter than single P-OMe bond lengths. We also find that the HOMO orbital energies in the two compounds are within 0.1 eV of one another and that these orbitals have spatial characteristics much like one would expect of a bonding pi orbital connecting two atoms from different rows of the periodic table. Using this data, making a comparison to the more familiar bonding arising in N(2), CO, and BF, and taking note of the dipole moments in compounds known to possess dative bonds, we conclude that it is best to represent the terminal PO bond in phosphates in terms of valence-bond structures such as (MeO)(3)P=O in which the formal charges are P(0)O(0) and where a single PO pi bond exists. However, when it comes to characterizing the PO antibonding pi* orbitals, significant differences arise. Electronic structure methods were able to identify the pi* orbital of MeO-P=O and to determine its energy (the MeO-P=O(-) anion is even bound). Similar attempts to identify the PO pi* orbital in the unbound (MeO)(3)P=O(-) anion lead us to conclude that this anion state is probably so strongly coupled to the continuum (i.e., to states corresponding to (MeO)(3)P=O plus a free electron) that it is so short lived as to be undetectable in experiments. PMID:19378976

Gamoke, Benjamin; Neff, Diane; Simons, Jack

2009-05-14

264

Emotion and language: Valence and arousal affect word recognition.  

PubMed

Emotion influences most aspects of cognition and behavior, but emotional factors are conspicuously absent from current models of word recognition. The influence of emotion on word recognition has mostly been reported in prior studies on the automatic vigilance for negative stimuli, but the precise nature of this relationship is unclear. Various models of automatic vigilance have claimed that the effect of valence on response times is categorical, an inverted U, or interactive with arousal. In the present study, we used a sample of 12,658 words and included many lexical and semantic control factors to determine the precise nature of the effects of arousal and valence on word recognition. Converging empirical patterns observed in word-level and trial-level data from lexical decision and naming indicate that valence and arousal exert independent monotonic effects: Negative words are recognized more slowly than positive words, and arousing words are recognized more slowly than calming words. Valence explained about 2% of the variance in word recognition latencies, whereas the effect of arousal was smaller. Valence and arousal do not interact, but both interact with word frequency, such that valence and arousal exert larger effects among low-frequency words than among high-frequency words. These results necessitate a new model of affective word processing whereby the degree of negativity monotonically and independently predicts the speed of responding. This research also demonstrates that incorporating emotional factors, especially valence, improves the performance of models of word recognition. (PsycINFO Database Record (c) 2014 APA, all rights reserved). PMID:24490848

Kuperman, Victor; Estes, Zachary; Brysbaert, Marc; Warriner, Amy Beth

2014-06-01

265

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

Code of Federal Regulations, 2010 CFR

...bonds, separate bonds and additional bonding. 2580.412-20 Section 2580...DEPARTMENT OF LABOR TEMPORARY BONDING RULES UNDER THE EMPLOYEE RETIREMENT INCOME SECURITY ACT OF 1974 TEMPORARY BONDING RULES General Bond Rules §...

2009-07-01

266

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

Code of Federal Regulations, 2010 CFR

...bonds, separate bonds and additional bonding. 2580.412-20 Section 2580...DEPARTMENT OF LABOR TEMPORARY BONDING RULES UNDER THE EMPLOYEE RETIREMENT INCOME SECURITY ACT OF 1974 TEMPORARY BONDING RULES General Bond Rules §...

2010-07-01

267

Unusual structure, bonding and properties in a californium borate  

NASA Astrophysics Data System (ADS)

The participation of the valence orbitals of actinides in bonding has been debated for decades. Recent experimental and computational investigations demonstrated the involvement of 6p, 6d and/or 5f orbitals in bonding. However, structural and spectroscopic data, as well as theory, indicate a decrease in covalency across the actinide series, and the evidence points to highly ionic, lanthanide-like bonding for late actinides. Here we show that chemical differentiation between californium and lanthanides can be achieved by using ligands that are both highly polarizable and substantially rearrange on complexation. A ligand that suits both of these desired properties is polyborate. We demonstrate that the 5f, 6d and 7p orbitals are all involved in bonding in a Cf(III) borate, and that large crystal-field effects are present. Synthetic, structural and spectroscopic data are complemented by quantum mechanical calculations to support these observations.

Polinski, Matthew J.; Garner, Edward B.; Maurice, Rémi; Planas, Nora; Stritzinger, Jared T.; Parker, T. Gannon; Cross, Justin N.; Green, Thomas D.; Alekseev, Evgeny V.; van Cleve, Shelley M.; Depmeier, Wulf; Gagliardi, Laura; Shatruk, Michael; Knappenberger, Kenneth L.; Liu, Guokui; Skanthakumar, S.; Soderholm, Lynda; Dixon, David A.; Albrecht-Schmitt, Thomas E.

2014-05-01

268

Unusual structure, bonding and properties in a californium borate.  

PubMed

The participation of the valence orbitals of actinides in bonding has been debated for decades. Recent experimental and computational investigations demonstrated the involvement of 6p, 6d and/or 5f orbitals in bonding. However, structural and spectroscopic data, as well as theory, indicate a decrease in covalency across the actinide series, and the evidence points to highly ionic, lanthanide-like bonding for late actinides. Here we show that chemical differentiation between californium and lanthanides can be achieved by using ligands that are both highly polarizable and substantially rearrange on complexation. A ligand that suits both of these desired properties is polyborate. We demonstrate that the 5f, 6d and 7p orbitals are all involved in bonding in a Cf(III) borate, and that large crystal-field effects are present. Synthetic, structural and spectroscopic data are complemented by quantum mechanical calculations to support these observations. PMID:24755589

Polinski, Matthew J; Garner, Edward B; Maurice, Rémi; Planas, Nora; Stritzinger, Jared T; Parker, T Gannon; Cross, Justin N; Green, Thomas D; Alekseev, Evgeny V; Van Cleve, Shelley M; Depmeier, Wulf; Gagliardi, Laura; Shatruk, Michael; Knappenberger, Kenneth L; Liu, Guokui; Skanthakumar, S; Soderholm, Lynda; Dixon, David A; Albrecht-Schmitt, Thomas E

2014-05-01

269

Semantic memory: distinct neural representations for abstractness and valence.  

PubMed

The hypothesis that abstract words are grounded in emotion has been supported by behavioral research and corpus studies of English words. A recent neuroimaging study reported that a single brain region, the rostral anterior cingulate cortex (rACC), is responsive to abstract words, and is furthermore modulated by the emotional valence. This finding is surprising because the rACC is not commonly associated with semantic processing. It is possible that the effects observed were driven not by abstractness, but rather by valence, since the abstract words used in that study were significantly more emotional than the concrete words. We tested this hypothesis by presenting participants with words that were abstract/concrete, as well as emotionally valenced/neutral in a 2×2 factorial design. Activations to emotional words overlapped with both abstract and concrete activations throughout the brain. An ROI analysis revealed that the rACC was responsive to valence, not abstractness, when concreteness and valence unconfounded. PMID:24561187

Skipper, Laura M; Olson, Ingrid R

2014-03-01

270

The acoustic correlates of valence depend on emotion family.  

PubMed

The voice expresses a wide range of emotions through modulations of acoustic parameters such as frequency and amplitude. Although the acoustics of individual emotions are well understood, attempts to describe the acoustic correlates of broad emotional categories such as valence have yielded mixed results. In the present study, we analyzed the acoustics of emotional valence for different families of emotion. We divided emotional vocalizations into "motivational," "moral," and "aesthetic" families as defined by the OCC (Ortony, Clore, and Collins) model of emotion. Subjects viewed emotional scenarios and were cued to vocalize congruent exclamations in response to them, for example, "Yay!" and "Damn!". Positive valence was weakly associated with high-pitched and loud vocalizations. However, valence interacted with emotion family for both pitch and amplitude. A general acoustic code for valence does not hold across families of emotion, whereas family-specific codes provide a more accurate description of vocal emotions. These findings are consolidated into a set of "rules of expression" relating vocal dimensions to emotion dimensions. PMID:24495430

Belyk, Michel; Brown, Steven

2014-07-01

271

Space-Valence Priming with Subliminal and Supraliminal Words  

PubMed Central

To date it is unclear whether (1) awareness-independent non-evaluative semantic processes influence affective semantics and whether (2) awareness-independent affective semantics influence non-evaluative semantic processing. In the current study, we investigated these questions with the help of subliminal (masked) primes and visible targets in a space-valence across-category congruence effect. In line with (1), we found that subliminal space prime words influenced valence classification of supraliminal target words (Experiment 1): classifications were faster with a congruent prime (e.g., the prime “up” before the target “happy”) than with an incongruent prime (e.g., the prime “up” before the target “sad”). In contrast to (2), no influence of subliminal valence primes on the classification of supraliminal space targets into up- and down-words was found (Experiment 2). Control conditions showed that standard masked response priming effects were found with both subliminal prime types, and that an across-category congruence effect was also found with supraliminal valence primes and spatial target words. The final Experiment 3 confirmed that the across-category congruence effect indeed reflected priming of target categorization of a relevant meaning category. Together, the data jointly confirmed prediction (1) that awareness-independent non-evaluative semantic priming influences valence judgments.

Ansorge, Ulrich; Khalid, Shah; Konig, Peter

2013-01-01

272

Valence dependent asymmetric release of norepinephrine in the basolateral amygdala.  

PubMed

Emerging evidence from literature on humans suggests the valence of emotionally laden environmental stimuli may dictate whether amygdala activation is greater in one hemisphere relative to the contralateral side. However, only a paucity of animal studies attempt to unravel the mechanisms underlying the selective, valence-dependent initiation of activity in the amygdala of opposing hemispheres. The present studies assessed whether exposure to positive or negative appetitive conditions in an operant learning task differentially impacts norepinephrine activation of the left versus right amygdala, respectively. Dialysate samples of norepinephrine were collected from the basolateral nucleus of male Sprague-Dawley rats. Fluctuations in norepinephrine activity were sampled during training conditions involving an abrupt shift (i.e., increase or decrease) in the magnitude of food rewards normally provided for bar press responses. In a subsequent study, dialysate samples of norepinephrine were collected before, during, and after presentation of a negatively valenced stimulus involving footshock delivery during Pavlovian fear conditioning. Norepinephrine concentrations in the left but not right basolateral amygdala were elevated in groups presented with a positive experience of an unexpected increase in food reward after bar pressing (p < .01), relative to respective controls. In contrast, exposure to negatively valenced events involving a reduction in expected food rewards after bar pressing or presentation of a footshock during fear conditioning produced significant increases in norepinephrine output sampled from only the right but not left basolateral amygdala. These findings demonstrate that the valence of a learning event is selective in initiating asymmetric activation of the basolateral amygdala. PMID:20939663

Young, Erica J; Williams, Cedric L

2010-10-01

273

Bond strengths of two dental bonding systems.  

PubMed

A new bonding system named Kevloc has been introduced. It is based on acrylization of the metal surface with the goal of preventing the occurrence of a marginal gap between the metal and the resin. The purpose of this investigation was to determine the values of the shear bond strength achieved using the Kevloc technique on Ag-Pd (Auropal SE) and Co-Cr (Basil S) alloys and to compare them with those obtained with the OVS technique. The shear bond strengths were measured with the Smitz-Schulmayer shear test in a universal testing machine for polymer materials. A microscope image analyzer was used to measure the thickness of bonding layers and to reveal the possible occurrence of the marginal gap with both techniques. No marginal gap was detected with either technique. Kevloc provided better results than OVS only in a group of specimens tested after polymerization. Immersion in water and thermocycling reduced the initially high bond strength values of Kevloc specimens, whereas the bond strength values of OVS specimens remained unchanged regardless of which aging treatment was used. Microscopic examination did not reveal the existence of the marginal gap for either bonding system. According to the results obtained, it can be concluded that the Kevloc bonding system does not provide better shearing bond strength than the OVS bonding system. PMID:10920659

Vojvodic, D; Jerolimov, V; Zabarovic, D; Loncar, A

2000-07-01

274

?-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

275

The covered bond market  

Microsoft Academic Search

The covered bond market offers investors an alternative to developed country government securities. The valuation of covered bonds is complex. While there is some evidence of differences in the pricing of these bonds by nationality of issuer, these appear to be only weakly related to differences in the respective legislative frameworks. Recent cases show the pricing of covered bonds to

Frank Packer; Ryan Stever; Christian Upper

2007-01-01

276

Wire Bond Temperature Sensor  

Microsoft Academic Search

This work reports the first demonstration of a bond pad test structure with embedded thermopile sensors for the measurement of the transient temperature response during the wire bonding operation. This paper will present the design and operation of the bond pad test structure and show and discuss temperature measurements during the wire bonding operation. The test structure can be used

Shivesh Suman; Michael Gaitan; Yogendra Joshi; George Harman

277

Magnetism and bonding in graphene nanodots with H modified interior, edge, and apex  

Microsoft Academic Search

Ab initio density functional theory calculations of hexagonal shaped zigzag edged graphene nanodot molecules, modified by the addition of atomic H to interior and perimeter sites, predict significant changes to the hexagonally sectored spin distribution and chemical bonding of the originals. The redistribution of Kohn-Sham levels at the top of the valence manifold from parent to derivative hint at large

Michael R. Philpott; Prabhat; Yoshiyuki Kawazoe

2011-01-01

278

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

279

Valence-band warping in tight-binding models  

NASA Astrophysics Data System (ADS)

The spin-orbit nearest-neighbor sp3s* model is widely believed able to reproduce accurately the valence bands of most III-V and group-IV semiconductors, essential for modeling the in-plane dispersion of valence- and inter-band quantum heterostructures. To check this belief, we study valence-band warping in the spin-orbit sp3s* model including interactions up to second-nearest-neighbor, providing exact, analytic formulas for the [110] and [111] light- and heavy-hole masses. Surprisingly, we find that the second-nearest-neighbor model offers significantly more flexibility in fitting these masses independently of those along [001] than does the nearest-neighbor model.

Boykin, Timothy B.; Gamble, Lisa J.; Klimeck, Gerhard; Bowen, R. Chris

1999-03-01

280

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.

281

Direct bonding and beyond  

Microsoft Academic Search

We present a number of recent evaluations of direct bonding, a glueless bonding technology, performed under ambient conditions. If combined with bond-strengthening, this geometry-conserving technology is well suited for an application in far ultraviolet immersion lithography. Our term beyond direct bonding refers to taking at least one additional technological step beyond direct bonding, involving chemical interface engineering, advanced silicon-on-insulator (SOI)

Jan Haisma; Nico Hattu; Esther Steding; Jan C. G. Vervest

2007-01-01

282

LET'S BOND! A Chemical Bonding Webquest  

NSDL National Science Digital Library

Today we are going to use the internet to explore chemical bonding! Even though there are just a few questions for each website, you need to read the entire content. Don't worry about understanding all of it, but make sure that you are familiar with it! Stay on task and have fun! Let's start with some basics. Click on the link below and answer the questions on your worksheet under "Bonding Basics". Bonding Basics Good job! Lets move on and talk about ions. Ions are a big part of bonding, so make sure you get this section down pat! Click on the ...

Hicken, Mrs.

2009-04-08

283

Valence-delocalization in F4TCNQ Salts of Biferrocenes  

Microsoft Academic Search

Variable-temperature Mössbauer spectra were measured for biferrocenium F4TCNQ (2) and 1?,1???-diethylbiferroceniumF4TCNQ (3) in order to elucidate their mixed-valence states, where F4TCNQ = 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane. A valence-delocalization between Fe(II) and Fe(III) sites on elevating the temperature was observed for 2; The Mössbauer spectra of 2 below 298 K consisted of two quadrupole doubets corresponding to the Fe(II) and Fe(III) atoms in 2,

Seiichiro Iijima; Fumio Mizutani

1998-01-01

284

Kernel density estimation applied to bond length, bond angle, and torsion angle distributions.  

PubMed

We describe the method of kernel density estimation (KDE) and apply it to molecular structure data. KDE is a quite general nonparametric statistical method suitable even for multimodal data. The method generates smooth probability density function (PDF) representations and finds application in diverse fields such as signal processing and econometrics. KDE appears to have been under-utilized as a method in molecular geometry analysis, chemo-informatics, and molecular structure optimization. The resulting probability densities have advantages over histograms and, importantly, are also suitable for gradient-based optimization. To illustrate KDE, we describe its application to chemical bond length, bond valence angle, and torsion angle distributions and show the ability of the method to model arbitrary torsion angle distributions. PMID:24746022

McCabe, Patrick; Korb, Oliver; Cole, Jason

2014-05-27

285

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.

286

Hydroxide-catalyzed bonding  

NASA Technical Reports Server (NTRS)

A method of bonding substrates by hydroxide-catalyzed hydration/dehydration involves applying a bonding material to at least one surface to be bonded, and placing the at least one surface sufficiently close to another surface such that a bonding interface is formed between them. A bonding material of the invention comprises a source of hydroxide ions, and may optionally include a silicate component, a particulate filling material, and a property-modifying component. Bonding methods of the invention reliably and reproducibly provide bonds which are strong and precise, and which may be tailored according to a wide range of possible applications. Possible applications for bonding materials of the invention include: forming composite materials, coating substrates, forming laminate structures, assembly of precision optical components, and preparing objects of defined geometry and composition. Bonding materials and methods of preparing the same are also disclosed.

Gwo, Dz-Hung (Inventor)

2003-01-01

287

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

288

30 CFR 57.22201 - Mechanical ventilation (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines).  

Code of Federal Regulations, 2013 CFR

...II-A, II-B, III, IV, V-A, and V-B mines). 57.22201 Section 57.22201 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH...

2013-07-01

289

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

290

Valence Band of Cubic Semiconductors from Viewpoint of Clifford Algebra  

Microsoft Academic Search

Full Text PDF In this paper the properties of semiconductors having cubic symmetry are considered in a real multidimensional Euclidean space within the formalism of multivector Clifford algebra rather than, usually used for this purpose, complex Hilbert space. In particular, it is demonstrated how the valence band energy spectrum and spin properties may be calculated within Cl5 Clifford algebra and

A. Dargys

2009-01-01

291

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 emotional…

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

2013-01-01

292

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

293

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

294

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

295

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

296

Photofragmentation of a DNA nucleoside thymidine; valence- vs. core ionization  

NASA Astrophysics Data System (ADS)

The photofragmentation of free thymidine molecule has been studied using combined electron- and ion spectroscopy. The results show that valence- and core ionization processes produce very different fragmentation patterns and that regardless of the photon energy, the photoionization leads almost always to dissociation of the thymidine molecule.

Itälä, E.; Kooser, K.; Hägerth, T.; Rachlew, E.; Huels, M. A.; Kukk, E.

2012-11-01

297

Bonding in Boron Hydrides.  

National Technical Information Service (NTIS)

Unique preferred localized valence structures for B2H6, B4H10, B5H11, and B6H10 have been found from accurate self-consistent field wavefunctions by maximizing Coulomb repulsions of electron pairs within orbitals. Objective evidence has thus been obtained...

W. N. Lipscomb

1972-01-01

298

Paradigms and Plastic Facts in the History of Valence.  

ERIC Educational Resources Information Center

Traces the development of bonding theory and notes the influence of preconceived theory upon this development. Considers ideas of alchemy, Newton, Dalton, Lewis, and quantum mechanics. Suggests a move away from conservative descriptive approaches of bonding theory. (ML)

Zavaleta, David

1988-01-01

299

[Indirect bonding technics].  

PubMed

The indirect bonding technique is pivotal for success in lingual orthodontics. There are different laboratory techniques available for indirect positioning and bonding of lingual brackets. Different approaches are presented and described to perform a clinical application. PMID:19552882

Sorel, Olivier; Mehdi, Sarah; Mano, Marie-Charlotte

2009-06-01

300

Direct bonding and beyond  

NASA Astrophysics Data System (ADS)

We present a number of recent evaluations of direct bonding, a glueless bonding technology, performed under ambient conditions. If combined with bond-strengthening, this geometry-conserving technology is well suited for an application in far ultraviolet immersion lithography. Our term beyond direct bonding refers to taking at least one additional technological step beyond direct bonding, involving chemical interface engineering, advanced silicon-on-insulator (SOI) technology, whereby the unwanted influence of dilatation mismatch is obviated. The combination of successive direct bonding, nanopillar lattice structures and silicon-technological engineering makes it possible for us to arrange quantum dots, wires, and planes in a transversal cascade. We also address the interrelationship between direct bonding and elasticity, as well as plasticity; the latter is in relation to direct bonded glass wafers that are thermally treated to create the geometric shape, e.g., required for specific lab-on-a-chip components with a three-dimensional overall configuration.

Haisma, Jan; Hattu, Nico; (Dook) Pulles, J. T. C. M.; Steding, Esther; Vervest, Jan C. G.

2007-09-01

301

Covalent and Ionic Bonds  

NSDL National Science Digital Library

Atoms can attain a more stable arrangement of electrons in their outermost shell by interacting with one another. An ionic bond is formed when electrons are transferred from one atom to the other. A covalent bond is formed when electrons are shared between atoms. The two cases shown represent extremes; often, covalent bonds form with a partial transfer (unequal sharing of electrons), resulting in a polar covalent bond

BEGIN:VCARD VERSION:2.1 FN:Bruce Alberts N:Alberts;Bruce REV:2005-04-16 END:VCARD; BEGIN:VCARD VERSION:2.1 FN:Dennis Bray N:Bray;Dennis REV:2005-04-16 END:VCARD; BEGIN:VCARD VERSION:2.1 FN:Alexander Johnson N:Johnson;Alexander REV:2005-04-16 END:VCARD; BEGIN:VCARD VERSION:2.1 FN:Julian Lewis N:Lewis;Julian REV:2005-04-16 END:VCARD; BEGIN:VCARD VERSION:2.1 FN:Martin Raff N:Raff;Martin REV:2005-04-16 END:VCARD; BEGIN:VCARD VERSION:2.1 FN:Keith Roberts N:Roberts;Keith REV:2005-04-16 END:VCARD

1998-07-01

302

Allosteric Disulfide Bonds  

Microsoft Academic Search

\\u000a Protein disulfide bonds link cysteine residues in the polypeptide chain. The bonds contribute, sometimes crucially, to protein\\u000a stability and function and are strongly conserved through the evolution of species. By analyzing the conservation of all structurally\\u000a validated disulfide bonds across 29 completely sequenced eukaryotic genomes, we found that disulfide-bonded cysteines are\\u000a even more conserved than tryptophan – the most conserved

Jason W. H. Wong; Philip J. Hogg

303

Orbital momentum profiles and binding energy spectra for the complete valence shell of molecular fluorine.  

National Technical Information Service (NTIS)

The first electronic structural study of the complete valence shell binding energy spectrum of molecular fluorine, encompassing both the outer and inner valence regions, is reported. These binding energy spectra as well as the individual orbital momentum ...

Y. Zheng C. E. Brion M. J. Brunger K. Zhao A. M. Grisogono

1996-01-01

304

Rapid adhesive bonding concepts  

NASA Technical Reports Server (NTRS)

Adhesive bonding in the aerospace industry typically utilizes autoclaves or presses which have considerable thermal mass. As a consequence, the rates of heatup and cooldown of the bonded parts are limited and the total time and cost of the bonding process is often relatively high. Many of the adhesives themselves do not inherently require long processing times. Bonding could be performed rapidly if the heat was concentrated in the bond lines or at least in the adherends. Rapid adhesive bonding concepts were developed to utilize induction heating techniques to provide heat directly to the bond line and/or adherends without heating the entire structure, supports, and fixtures of a bonding assembly. Bonding times for specimens are cut by a factor of 10 to 100 compared to standard press bonding. The development of rapid adhesive bonding for lap shear specimens (per ASTM D1003 and D3163), for aerospace panel bonding, and for field repair needs of metallic and advanced fiber reinforced polymeric matrix composite structures are reviewed.

Stein, B. A.; Tyeryar, J. R.; Hodges, W. T.

1984-01-01

305

Acrylic mechanical bond tests  

SciTech Connect

The tensile strength of bonded acrylic is tested as a function of bond joint thickness. 0.125 in. thick bond joints were found to posses the maximum strength while the acceptable range of joints varied from 0.063 in. to almost 0.25 in. Such joints are used in the Sudbury Neutrino Observatory.

Wouters, J.M.; Doe, P.J.

1991-02-01

306

Solvation dependence of valence electronic states of water diluted in organic solvents probed by soft X-ray spectroscopy.  

PubMed

Knowledge of hydrogen bonds is important in a wide range of scientific fields. However, information on the electronic state of hydrogen bonded molecules in liquids and solutions is still limited. We applied X-ray emission and absorption spectroscopy to observe the electronic state around oxygen of water and investigate the solvent dependence of occupied and unoccupied valence electronic states of water in acetonitrile, 3-methylpyridine, and ethylenediamine at room temperature under atmospheric pressure. Based on the direct comparison of the spectra, the pronounced variation of the unoccupied 2b2 state of water in acetonitrile and 3-methylpyridine was assigned to the difference of the dipole-dipole interaction and the donor hydrogen bond. For ethylenediamine solution, an enhancement of the peak structure in the post-edge region of X-ray absorption spectra and an evident shoulder structure on the higher energy side of the occupied 1b1 state in X-ray emission spectra were observed. Although ethylenediamine has two amino groups that can form the hydrogen bonds as a proton donor, the obtained results indicate that the amino groups of ethylenediamine also act as a proton acceptor in the hydrogen bond between water molecules. A systematic peak intensity variation of the pre-edge peak corresponding to the lowest unoccupied molecular orbital, 4a1, was also found through the comparison of three organic solvents. Since the peak intensity tends to decrease with increasing number of hydrogen bonds, the results can be interpreted by the covalency of hydrogen bonds. PMID:24756213

Tokushima, Takashi; Horikawa, Yuka; Takahashi, Osamu; Arai, Hidemi; Sadakane, Koichiro; Harada, Yoshihisa; Takata, Yasutaka; Shin, Shik

2014-05-14

307

The kinetic energy change on covalent bond formation  

PubMed Central

Stimulated by an analysis of the classical molecular orbital and valence bond descriptions of the two-electron normal covalent bond (both faulty), the argument is made that there exist good representations of the kinetic energy change ?T, on nonpolar covalent bond formation in a diatomic molecule, of the form ?T(R) = ?F(R - r?)S(r?)dr?. Here F is a nonlinear response function which itself involves the overlap S. The kinetic change is known to satisfy the sum rule ?0??T(R)dR = Z?Z? exactly; it is shown how this can be built into the treatment by the use of Fourier transform methods. Also considered is ?0??T(R)R2dR, which is an important additional property of the kinetic energy change. Representation of ?T(R) as a Morse function, already known to be highly accurate, is shown to exactly conform to the proposed form.

March, Norman H.; Parr, Robert G.; Mucci, Joe F.

1981-01-01

308

Distinct Brain Systems Underlie the Processing of Valence and Arousal of Affective Pictures  

ERIC Educational Resources Information Center

Valence and arousal are thought to be the primary dimensions of human emotion. However, the degree to which valence and arousal interact in determining brain responses to emotional pictures is still elusive. This functional MRI study aimed to delineate neural systems responding to valence and arousal, and their interaction. We measured neural…

Nielen, M. M. A.; Heslenfeld, D. J.; Heinen, K.; Van Strien, J. W.; Witter, M. P.; Jonker, C.; Veltman, D. J.

2009-01-01

309

Work Valence as a Predictor of Academic Achievement in the Family Context  

ERIC Educational Resources Information Center

This study asserts a theoretical model of academic and work socialization within the family setting. The presumed associations between parents' work valences, children's work valences and valence perceptions, and children's academic interest and achievement are tested. The results suggest that children's perceptions of parents…

Porfeli, Erik; Ferrari, Lea; Nota, Laura

2013-01-01

310

Neural Systems Subserving Valence and Arousal During the Experience of Induced Emotions  

Microsoft Academic Search

The circumplex model of affect construes all emotions as linear combinations of 2 independent neurophysiological dimensions, valence and arousal. We used functional magnetic resonance imaging to identify the neural networks subserving valence and arousal, and we assessed, in 10 participants, the associations of the BOLD (blood oxygen level-dependent) response, an indirect index of neural activity, with ratings of valence and

Tiziano Colibazzi; Jonathan Posner; Zhishun Wang; Daniel Gorman; Andrew Gerber; Shan Yu; Hongtu Zhu; Alayar Kangarlu; Yunsuo Duan; James A. Russell; Bradley S. Peterson

2010-01-01

311

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

ERIC Educational Resources Information Center

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…

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

2010-01-01

312

Analytic bond-order potential for predicting structural trends across the sp -valent elements  

NASA Astrophysics Data System (ADS)

An analytic interatomic bond-order potential (BOP) is derived that depends explicitly on the group number of the sp -valent element. This is achieved by generalizing the previously published BOP for group-IV elements by extrapolating from half-full occupancy using a simple envelope function for the upper bound of the bond order. This interatomic potential predicts the structural trends across the sp -valent elements that are found by our tight-binding reference calculations and observed by experiment. Unlike empirical interatomic potentials this theoretically derived BOP includes the valence-dependent character of the bonding naturally within its remit.

Drautz, Ralf; Murdick, Dewey A.; Nguyen-Manh, Duc; Zhou, Xiaowang; Wadley, Haydn N. G.; Pettifor, David G.

2005-10-01

313

Bonding thermoplastic polymers  

DOEpatents

We demonstrate a new method for joining patterned thermoplastic parts into layered structures. The method takes advantage of case-II permeant diffusion to generate dimensionally controlled, activated bonding layers at the surfaces being joined. It is capable of producing bonds characterized by cohesive failure while preserving the fidelity of patterned features in the bonding surfaces. This approach is uniquely suited to production of microfluidic multilayer structures, as it allows the bond-forming interface between plastic parts to be precisely manipulated at micrometer length scales. The bond enhancing procedure is easily integrated in standard process flows and requires no specialized equipment.

Wallow, Thomas I. (Fremont, CA); Hunter, Marion C. (Livermore, CA); Krafcik, Karen Lee (Livermore, CA); Morales, Alfredo M. (Livermore, CA); Simmons, Blake A. (San Francisco, CA); Domeier, Linda A. (Danville, CA)

2008-06-24

314

ELECTRONIC AND CHEMICAL PROPERTIES OF PD IN BIMETALLIC SYSTEMS: HOW MUCH DO WE KNOW ABOUT HETERONUCLEAR METAL-METAL BONDING?  

SciTech Connect

The experimental and theoretical studies described above illustrate the complex nature of the heteronuclear metal-metal bond. In many cases, bimetallic bonding induces a significant redistribution of charge around the bonded metals. This redistribution of charge is usually linked to the strength of the bimetallic bond, affects the position of the core and valence levels of the metals, and can determine the chemical reactivity of the system under study. New concepts are emerging [22,23,34,36] and eventually the coupling of experiment and theory can be useful for designing more efficient bimetallic catalysts [98,106,107].

RODRIGUEZ,J.A.

2001-09-27

315

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

316

Intermediate-valence icosahedral Au-Al-Yb quasicrystal  

NASA Astrophysics Data System (ADS)

A quasiperiodic intermediate-valence (IV) system is realized in an icosahedral Au-Al-Yb quasicrystal. X-ray absorption spectroscopy near the Yb L3 edge indicates that quasiperiodically arranged Yb ions assume a mean valence of 2.61, between a divalent state (4f14, J=0) and a trivalent one (4f13, J=7/2). Magnetization measurements demonstrate that the 4f holes in this quasicrystal have a localized character. The magnetic susceptibility shows a Curie-Weiss behavior above ˜100 K with an effective magnetic moment of 3.81?B per Yb. Moreover, a crystalline approximant to this quasicrystal is an IV compound. We propose a heterogeneous IV model for the quasicrystal, whereas the crystalline approximant is most likely a homogeneous IV system. At temperatures below ˜10 K, specific heat and magnetization measurements reveal non-Fermi-liquid behavior in both the quasicrystal and its crystalline approximant without either doping, pressure, or field tuning.

Watanuki, Tetsu; Kashimoto, Shiro; Kawana, Daichi; Yamazaki, Teruo; Machida, Akihiko; Tanaka, Yukinori; Sato, Taku J.

2012-09-01

317

Theoretical calculations of valence states in Fe-Mo compounds  

NASA Astrophysics Data System (ADS)

The half-metallic ferromagnetic double perovskite compound Sr2FeMoO6 is considered as an important material for spintronic applications. It appears to be fundamental to understand the role of electronic parameters controlling the half-metallic ground state. Fe-Mo double perovskites usually present some degree of Fe/Mo disorder which generally increases with doping. In this work, we study the valence states of Fe-Mo cations in the off-stoichiometric system Sr2Fe1+xMo1?xO6 (?1 <= x <= 1/3) with disorder. Our results for Fe and Mo valence states are obtained using the Green functions and the renormalization perturbation expansion method. The model is based on a correlated electron picture with localized Fe-spins and conduction Mo-electrons interacting with the local spins via a double-exchange-type mechanism.

Estrada, F.; Noverola, H.; Suárez, J. R.; Navarro, O.; Avignon, M.

2014-04-01

318

Valence-band states of ion-bombarded polystyrene  

SciTech Connect

Ion-bombarded polystyrene with a 0.5-keV Ar{sup +} beam has been investigated by means of photoelectron spectroscopy performed with synchrotron radiation. After a dose of 10{sup 15} ions/cm{sup 2} the evolution of the valence band of the bombarded sample towards an amorphous carbonlike configuration is reported. From the analysis of valence-band spectra we estimated the out-diffusion of hydrogen and showed that its electronic states remain well identified and stable until the hydrogen presence is about 35% with respect to the pristine sample. Finally, comparison with mass spectroscopy measurements on deuterated polystyrene has been performed to determine hydrogen evolution during the ion irradiation.

Terrasi, A. (Istituto di Metodologie e Tecnologie per la Microelettronica, CNR, Corso Italia 57, 95129 Catania, Italy (IT)); Foti, G. (Dipartimento di Fisica, Universita di Catania, Corso Italia 57, 95129 Catania, (Italy)); Hwu, Y. (Synchrotron Radiation Center, University of Wisconsin-Madison, 3731 Schneider Drive, Stoughton, Wisconsin 53589-3097 (USA)); Margaritondo, G. (Ecole Polytechnique Federale de Lausanne, Department de Physique, PHB-Ecublens, CH 1015 Lausanne, (Switzerland))

1991-08-01

319

Valence Band of Cubic Semiconductors from Viewpoint of Clifford Algebra  

NASA Astrophysics Data System (ADS)

Full Text PDF In this paper the properties of semiconductors having cubic symmetry are considered in a real multidimensional Euclidean space within the formalism of multivector Clifford algebra rather than, usually used for this purpose, complex Hilbert space. In particular, it is demonstrated how the valence band energy spectrum and spin properties may be calculated within Cl5 Clifford algebra and SO(5) symmetry group related with it.

Dargys, A.

2009-08-01

320

Spectroscopic valence of cerium in cerium-lanthanum-iron compounds  

SciTech Connect

In Ce{sub 2}Fe{sub 14}B and Ce{sub 2}Fe{sub 17}, 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 L{sub 3} edge of La{sub 2{minus}x}Ce{sub x}Fe{sub 14}B, La{sub 2{minus}x}Ce{sub x}Fe{sub 17}, and selected hydrides and nitrides of these intermetallics. In La{sub 2{minus}x}Ce{sub x}Fe{sub 14}B 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 L{sub 3} edges from the La{sub 2{minus}x}Ce{sub x}Fe{sub 14}B series is only consistent with cerium preferentially occupying the small 4f rare-earth site in the tetragonal Nd{sub 2}Fe{sub 14}B structure. In La{sub 2{minus}x}Ce{sub x}Fe{sub 17} 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{ge}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. {copyright} {ital 1997} {ital The American Physical Society}

Capehart, T.W.; Mishra, R.K.; Fuerst, C.D.; Meisner, G.P.; Pinkerton, F.E.; Herbst, J.F. [Physics Department, General Motors Research Development Center, 30500 Mound Road, Warren, Michigan 48090-9055 (United States)] [Physics Department, General Motors Research Development Center, 30500 Mound Road, Warren, Michigan 48090-9055 (United States)

1997-05-01

321

Neptunium and plutonium valence adjustment in enriched uranium processing  

Microsoft Academic Search

In initial operation of a new flowsheet for recovery of highly irradiated enriched uranium by solvent extraction with 7.5 vol percent tri-n-butyl phosphate, valence adjustment of plutonium and neptunium with ferrous sulfamate was ineffective; plutonium was not rejected as desired, and neptunium was partially lost to waste. Laboratory studies demonstrated that ferrous sulfamate, added to both the aqueous feed solution

M. C. Thompson; G. A. Burney; M. L. Hyder

1976-01-01

322

An empirical analysis of valence in electoral competition  

Microsoft Academic Search

Spatial models of voting have dominated mathematical political theory since the seminal work of Downs. The Downsian model\\u000a assumes that each elector votes on the basis of his utility function which depends only on the distance between his preferred\\u000a policy platform and the ones proposed by candidates. A succession of papers introduces valence issues into the model, i.e.,\\u000a candidates’ characteristics

Fabian Gouret; Guillaume Hollard; Stéphane Rossignol

2011-01-01

323

On the interpretation of molecular valence Auger spectra  

Microsoft Academic Search

The interpretation of molecular valence Auger spectra by means of abinitio computational methods is discussed. As alternatives to self-consistent-field optimizations of the full Auger spectrum, the feasibility of a procedure based on single ionization potentials and of CI calculations using frozen orbitals is tested. Numerical calculations are performed for the CO, N2, NO, and CO2 molecules, which show especially structure-rich

1981-01-01

324

Weak bond screening system  

NASA Astrophysics Data System (ADS)

Consideration is given to the development of a weak bond screening system which is based on the utilization of a high power ultrasonic (HPU) technique. The instrumentation of the prototype bond strength screening system is described, and the adhesively bonded specimens used in the system developmental effort are detailed. Test results obtained from these specimens are presented in terms of bond strength and level of high power ultrasound irradiation. The following observations were made: (1) for Al/Al specimens, 2.6 sec of HPU irradiation will screen weak bond conditions due to improper preparation of bonding surfaces; (2) for composite/composite specimens, 2.0 sec of HPU irradiation will disrupt weak bonds due to under-cured conditions; (3) for Al honeycomb core with composite skin structure, 3.5 sec of HPU irradiation will disrupt weak bonds due to bad adhesive or oils contamination of bonding surfaces; and (4) for Nomex honeycomb with Al skin structure, 1.3 sec of HPU irradiation will disrupt weak bonds due to bad adhesive.

Chuang, S. Y.; Chang, F. H.; Bell, J. R.

325

Study of Hydrogen Bonding in Small Water Clusters with Density Functional Theory Calculations  

SciTech Connect

The unique characteristics of hydrogen bonding have left our understanding of liquid water far from complete in terms of its structure and properties. In order to better describe the hydrogen bond in water, we seek to understand the electronic states which show sensitivity to hydrogen bonding. We investigate the structure of unoccupied valence states by performing X-ray Absorption calculations on water clusters using Density Functional Theory. For each water cluster, studying how valence electronic structure is perturbed by changes in the local hydrogen bonding environment facilitates our description of the hydrogen bond. Also in this framework, we move toward a depiction of local structures in liquid water by comparison to experimental X-ray absorption spectra. We find consistent localization along internal bonds in the electronic structures of pre- and post-edge states for single-donor species. In addition, we propose a molecular orbital bonding-antibonding picture to explain this directional localization from dimer calculations, and show that the pre- and post-edge spectral regions have a resulting relationship.

Wendlandt, Johanna; /Wisconsin U., Madison /SLAC, SSRL

2005-12-15

326

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

327

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

328

Valency configuration of transition metal impurities in ZnO  

SciTech Connect

We use the self-interaction corrected local spin-density approximation to investigate the ground state valency configuration of transition metal (TM=Mn, Co) impurities in n- and p-type ZnO. We find that in pure Zn{sub 1-x}TM{sub x}O, the localized TM{sup 2+} configuration is energetically favored over the itinerant d-electron configuration of the local spin density (LSD) picture. Our calculations indicate furthermore that the (+/0) donor level is situated in the ZnO gap. Consequently, for n-type conditions, with the Fermi energy {epsilon}F close to the conduction band minimum, TM remains in the 2+ charge state, while for p-type conditions, with {epsilon}F close to the valence band maximum, the 3+ charge state is energetically preferred. In the latter scenario, modeled here by co-doping with N, the additional delocalized d-electron charge transfers into the entire states at the top of the valence band, and hole carriers will only exist, if the N concentration exceeds the TM impurity concentration.

Petit, Leon [ORNL; Schulthess, Thomas C [ORNL; Svane, Axel [University of Aarhus, Denmark; Temmerman, Walter M [Daresbury Laboratory, UK; Szotek, Zdzislawa [Daresbury Laboratory, UK; Janotti, Anderson [University of California, Santa Barbara

2006-01-01

329

Core-core and core-valence correlation  

NASA Technical Reports Server (NTRS)

The effect of (1s) core correlation on properties and energy separations was analyzed using full configuration-interaction (FCI) calculations. The Be 1 S - 1 P, the C 3 P - 5 S and CH+ 1 Sigma + or - 1 Pi separations, and CH+ spectroscopic constants, dipole moment and 1 Sigma + - 1 Pi transition dipole moment were studied. The results of the FCI calculations are compared to those obtained using approximate methods. In addition, the generation of atomic natural orbital (ANO) basis sets, as a method for contracting a primitive basis set for both valence and core correlation, is discussed. When both core-core and core-valence correlation are included in the calculation, no suitable truncated CI approach consistently reproduces the FCI, and contraction of the basis set is very difficult. If the (nearly constant) core-core correlation is eliminated, and only the core-valence correlation is included, CASSCF/MRCI approached reproduce the FCI results and basis set contraction is significantly easier.

Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Taylor, Peter R.

1988-01-01

330

On pleasure and thrill: The interplay between arousal and valence during visual word recognition.  

PubMed

We investigated the interplay between arousal and valence in the early processing of affective words. Event-related potentials (ERPs) were recorded while participants read words organized in an orthogonal design with the factors valence (positive, negative, neutral) and arousal (low, medium, high) in a lexical decision task. We observed faster reaction times for words of positive valence and for those of high arousal. Data from ERPs showed increased early posterior negativity (EPN) suggesting improved visual processing of these conditions. Valence effects appeared for medium and low arousal and were absent for high arousal. Arousal effects were obtained for neutral and negative words but were absent for positive words. These results suggest independent contributions of arousal and valence at early attentional stages of processing. Arousal effects preceded valence effects in the ERP data suggesting that arousal serves as an early alert system preparing a subsequent evaluation in terms of valence. PMID:24815948

Recio, Guillermo; Conrad, Markus; Hansen, Laura B; Jacobs, Arthur M

2014-07-01

331

Bimetallic Thermochemistry: Perturbations in M-H and M-C Bonds Due to the Presence of M'.  

National Technical Information Service (NTIS)

The effect of perturbing the environment of a transition metal-ligand (M-L) complex by the addition of another metal atom, M', was investigated by ab initio generalized valence bond/correlation-consistent configuration interaction methods. We have examine...

G. G. Reynolds E. A. Carter

1994-01-01

332

Bonded semiconductor substrate  

DOEpatents

Ge/Si and other nonsilicon film heterostructures are formed by hydrogen-induced exfoliation of the Ge film which is wafer bonded to a cheaper substrate, such as Si. A thin, single-crystal layer of Ge is transferred to Si substrate. The bond at the interface of the Ge/Si heterostructures is covalent to ensure good thermal contact, mechanical strength, and to enable the formation of an ohmic contact between the Si substrate and Ge layers. To accomplish this type of bond, hydrophobic wafer bonding is used, because as the invention demonstrates the hydrogen-surface-terminating species that facilitate van der Waals bonding evolves at temperatures above 600.degree. C. into covalent bonding in hydrophobically bound Ge/Si layer transferred systems.

Atwater, Jr.; Harry A. (South Pasadena, CA), Zahler; James M. (Pasadena, CA)

2010-07-13

333

Energy pulse bonding  

NASA Technical Reports Server (NTRS)

To eliminate many of the present termination problems a technique called energy pulse bonding (EPB) was developed. The process demonstrated the capability of: (1) joining conductors without prior removal of insulations, (2) joining conductors without danger of brittle intermetallics, (3) increased joint temperature capability, (4) simultaneous formation of several bonds, (5) capability of higher joint density, and (6) a production oriented process. The following metals were successfully bonded in the solid state: copper, beryllium copper, phosphor bronze, aluminum, brass, and Kovar.

Smith, G. C.

1972-01-01

334

Chemical bonding technology  

NASA Technical Reports Server (NTRS)

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 status of the program is described along with the progress toward developing two general purpose primers for ethylene vinyl acetate (EVA), one for glass and metals, and another for plastic films.

Plueddemann, E.

1986-01-01

335

Indirect bonding technique.  

PubMed

Accurate bracket placement is the key for the successful treatment of an orthodontic case. With indirect bonding, not only is the bracket placement more accurate but this technique also significantly reduces chairtime. In this article, the author explains use of thermal glue in an indirect bonding technique. In cases of constricted arches, a modified rapid maxillary expander can be used along with indirect bonding to reduce overall treatment time. PMID:17190232

Kothari, Ashok

2006-01-01

336

Teachers' Domain: Covalent Bonding  

NSDL National Science Digital Library

This Flash interactive tutorial explores covalent bonding, a type of chemical bond that involves sharing of electrons. Learners investigate the attractive and repulsive forces that act on atomic particles and how the sharing of electrons can keep atoms together. See how two hydrogen atoms interact with each other to create a covalent bond. Learn about patterns in the periodic table and how electrostatic potential energy determines the bond length. Teachers' Domain is a growing collection of more than 1,000 free educational resources compiled by researchers and experienced teachers to promote the use of digital resources in the classroom.

2011-08-16

337

The computation of C-C and N-N bond dissociation energies for singly, doubly, and triply bonded systems  

NASA Technical Reports Server (NTRS)

The bond dissociation energies (D sub e) of C2H2, C2H4, C2H6, N2, N2H2, and N2H4 are studied at various levels of correlation treatment. The convergence of D sub e with respect to the one particle basis is studied at the single reference modified coupled-pair functional (MCPF) level. At all levels of correlation treatment, the errors in the bond dissociation energies increase with the degree of multiple bond character. The multireference configuration interaction (MRCI) D sub e values, corrected for an estimate of higher excitations, are in excellent agreement with those determined using the size extensive averaged coupled pair functional (ACPF) method. It was found that the full valence complete active space self consistent field (CASSCF)/MRCI calculations are reproduced very well by MRCI calculations based on a CASSCF calculation that includes in the active space only those electrons involved in the C-C or N-N bonds. To achieve chemical accuracy (1 kcal/mole) for the D sub e values of the doubly bonded species C2H4 and N2H2 requires one particle basis sets including up through h angular momentum functions (l = 5) and a multireference treatment of electron correlation: still higher levels of calculation are required to achieve chemical accuracy for the triply bonded species C2H2 and N2.

Langhoff, Stephen R.; Bauschlicher, Charles W., Jr.; Taylor, Peter R.

1989-01-01

338

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

339

30 CFR 57.22201 - Mechanical ventilation (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines).  

Code of Federal Regulations, 2010 CFR

30 Ç Mineral Resources Ç 1 Ç 2009-07-01 Ç 2009-07-01 Ç false Ç Mechanical ventilation (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines). Ç 57.22201 Ç Section 57.22201 Ç Mineral Resources Ç MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR Ç METAL AND NONMETAL MINE SAFETY AND...

2009-07-01

340

Engineering and biological characterization of VB6-845, an anti-EpCAM immunotoxin containing a T-cell epitope-depleted variant of the plant toxin bouganin.  

PubMed

The clinical development of immunotoxins in the treatment of solid tumors has been impeded in part, by the induction of an immune response directed primarily against the toxin moiety. Bouganin, a type I ribosome inactivating protein isolated from the leaf of Bougainvillea spectabilis Willd, was mutated to remove the T-cell epitopes while preserving the biological activity of the wild-type molecule. The T-cell epitope-depleted variant of bouganin (de-bouganin) was genetically linked to an anti-epithelial cell adhesion molecule (EpCAM) Fab moiety via a peptidic linker containing a furin proteolytic site to create the fusion construct VB6-845. To determine the optimal construct design for VB6-845, several dicistronic units where de-bouganin was genetically linked to either the N-terminal or C-terminal of either the heavy or light chain were engineered. Only the C-terminal variants expressed the full-length molecule. An in vitro assessment of the biological activity of VB6-845 showed that it bound and selectively killed EpCAM-positive cell lines with a greater potency than many commonly used chemotherapeutic agents. In vivo efficacy was demonstrated using an EpCAM-positive human tumor xenograft model in SCID mice with the majority of the mice treated being tumor free at the end of the study. PMID:19483652

Cizeau, Jeannick; Grenkow, Danielle M; Brown, Jennifer G; Entwistle, Joycelyn; MacDonald, Glen C

2009-01-01

341

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

342

Interactive Pi Bonding Effects  

NSDL National Science Digital Library

This application demonstrates the effect of pi bonding on the one-electron ligand field splitting in an octahedral. By clicking on the appropriate buttons students can see how D changes when you move from ligands with no pi bonding capability to pi donor and pi acceptor ligands.

343

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

344

Chemical Bonds I  

ERIC Educational Resources Information Center

Chemical bonding is discussed from a bond energy, rather than a wave mechanics, viewpoint. This approach is considered to be more suitable for the average student. (The second part of the article will appear in a later issue of the journal.) (AL)

Sanderson, R. T.

1972-01-01

345

Mother-Child Bonding.  

ERIC Educational Resources Information Center

Examines the nature of mother-child bonding from the prenatal stage through early infancy, discussing how the mother's actions, even before birth, stimulate her child's senses. Explains the crucial role that physical contact, breastfeeding, and visual stimuli have on mother-child bonding in human and animal newborns. (MDM)

Pearce, Joseph Chilton

1994-01-01

346

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.

347

Shape Bonding method  

NASA Technical Reports Server (NTRS)

The present invention is directed to a method of bonding at least two surfaces together. The methods step of the present invention include applying a strip of adhesive to a first surface along a predefined outer boundary of a bond area and thereby defining a remaining open area there within. A second surface, or gusset plate, is affixed onto the adhesive before the adhesive cures. The strip of adhesive is allowed to cure and then a second amount of adhesive is applied to cover the remaining open area and substantially fill a void between said first and second surfaces about said bond area. A stencil may be used to precisely apply the strip of adhesive. When the strip cures, it acts as a dam to prevent overflow of the subsequent application of adhesive to undesired areas. The method results in a precise bond area free of undesired shapes and of a preferred profile which eliminate the drawbacks of the prior art bonds.

Pontius, James T. (Inventor)

2010-01-01

348

Technology of bonding elastomers  

NASA Astrophysics Data System (ADS)

The paper reviews current bonding theories and examines the application of these concepts to the production of reliable commercial bonding elastomers. Fundamental aspects of elastomer bonding (such as the elastomer surface thermodynamics, the mechanics of the adhesive failure, and the elastomer self-adhesion) are discussed along with the types of elastomers and the technology used in producing these compounds, with particular consideration given to the factors affecting the strength and durability of elastomer bonds. Tables are presented listing elastomers' designations according to ASTM D1418; the elastomers' surface properties; the elastomer surface energy dispersive and polar components; the commonly used elastomer types selected to meet specific ASTM test requirements; the ASTM adhesion test methods; and selected metal primers, cover coats, and bonding agents.

Symes, Ted; Oldfield, David

349

Wood Bond Testing  

NASA Technical Reports Server (NTRS)

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

350

Ultrasonically bonded value assembly  

NASA Technical Reports Server (NTRS)

A valve apparatus capable of maintaining a fluid-tight seal over a relatively long period of time by releasably bonding a valve member to its seat is described. The valve member is bonded or welded to the seat and then released by the application of the same energy to the bond joint. The valve member is held in place during the bonding by a clamping device. An appropriate force device can activate the opening and closing of the valve member. Various combinations of material for the valve member and valve seat can be utilized to provide an adequate sealing bond. Aluminum oxide, stainless steel, inconel, tungsten carbide as hard materials and copper, aluminum, titanium, silver, and gold as soft materials are suggested.

Salvinski, R. J. (inventor)

1975-01-01

351

Theoretical study of wandering free valence in some free radicals  

SciTech Connect

In this work the authors studied the ground state and transition state in tautomer interconversions of 2-R-hydroxyethylenes, model systems for describing wandering valence in free radicals. Quantitative chemical calculations of the free radicals of 2-R-hydroxyethylenes have been carried out with R = H, Li, BeH, and BH/sub 2/ using the Hartree-Fock-Roothaan method with STO-3GF basis sets, and with R = H, BH/sub 2/, and CH/sub 3/ using the semiempirical method MOLCAO SSP in approximation to MINDO/3 method with optimized geometries for the ground state and transition state.

Raevskii, N.I.; Borisov, Yu.A.

1986-11-01

352

Pion and kaon valence-quark parton distribution functions  

SciTech Connect

A rainbow-ladder truncation of QCD's Dyson-Schwinger equations, constrained by existing applications to hadron physics, is employed to compute the valence-quark parton distribution functions of the pion and kaon. Comparison is made to {pi}-N Drell-Yan data for the pion's u-quark distribution and to Drell-Yan data for the ratio u{sub K}(x)/u{sub {pi}}(x): the environmental influence of this quantity is a parameter-free prediction, which agrees well with existing data. Our analysis unifies the computation of distribution functions with that of numerous other properties of pseudoscalar mesons.

Nguyen, Trang [Center for Nuclear Research, Department of Physics, Kent State University, Kent, Ohio 44242 (United States); Bashir, Adnan [Instituto de Fisica y Matematicas, Universidad Michoacana de San Nicolas de Hidalgo, Morelia, Michoacan 58040 (Mexico); Kavli Institute for Theoretical Physics China, CAS, Beijing 100190 (China); Roberts, Craig D. [Kavli Institute for Theoretical Physics China, CAS, Beijing 100190 (China); Physics Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Department of Physics, Center for High Energy Physics and the State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871 (China); Tandy, Peter C. [Kavli Institute for Theoretical Physics China, CAS, Beijing 100190 (China)

2011-06-15

353

Pion and kaon valence-quark parton distribution functions.  

SciTech Connect

A rainbow-ladder truncation of QCD's Dyson-Schwinger equations, constrained by existing applications to hadron physics, is employed to compute the valence-quark parton distribution functions of the pion and kaon. Comparison is made to {pi}-N Drell-Yan data for the pion's u-quark distribution and to Drell-Yan data for the ratio u{sub K}(x)/u{sub {pi}}(x): the environmental influence of this quantity is a parameter-free prediction, which agrees well with existing data. Our analysis unifies the computation of distribution functions with that of numerous other properties of pseudoscalar mesons.

Nguyen, T.; Bashir, A.; Roberts, C. D.; Tandy, P. C. (Physics); (Kent State Univ.); (Univ. Michoacana de San Nicolas de Hidalgo); (Kavli Inst. for Theoretical Physics China); (Peking Univ.)

2011-06-16

354

Core-valence double photoionization of atomic mercury  

NASA Astrophysics Data System (ADS)

Multielectron coincidence spectroscopy has been used to study core 4f valence 5d, 6s double photoionization of atomic mercury. Multiconfiguration Dirac-Fock calculations were performed to calculate the energies and to estimate the single-photon intensities of the 4f13(5d96s2+5d106s1) double-ionized states of atomic mercury. Reasonable agreement between the measured and simulated spectra is found if the relaxation effects of the bound-state density is taken into account in the computation of the photoionization amplitudes.

Huttula, M.; Huttula, S.-M.; Fritzsche, S.; Lablanquie, P.; Penent, F.; Palaudoux, J.; Andric, L.

2014-01-01

355

Trinuclear, Oxo-Bridged, Mixed-Valence Iron Mercaptocarboxylates  

Microsoft Academic Search

Mixed carboxylates and mercaptocarboxylates of mixed-valence FeIIFeIII with general formula [FeII-FeIII2O(OOCR)3(OOCR'SH)3L3](where R = C13H27, C15H31 or C17H35; R'= CH2 or C6H4 and L = pyridine) were successfully prepared by substitution of [FeIIFeIII2O(OAc)6(H2O)3] with straight chain carboxylic acids and mercaptocarboxylic acids. The title products have been characterized by elemental analyses, molar conductances and magnetic susceptibility measurements, i.r., electronic and Mössbauer spectral

Ashutosh K. Pandey; Tarkeshwar Gupta; Balram P. Baranwal

2004-01-01

356

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

357

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

NASA Astrophysics Data System (ADS)

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 ?1013 W/cm2. 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.; Ranitovic, P.; Hogle, C. W.; Murnane, M. M.; Kapteyn, H. C.; Toshima, N.

2011-07-01

358

Analytic bond-order potential for the gallium arsenide system  

NASA Astrophysics Data System (ADS)

An analytic, bond-order potential (BOP) is proposed and parametrized for the gallium arsenide system. The potential addresses primary (?) and secondary (?) bonding and the valence-dependent character of heteroatomic bonding, and it can be combined with an electron counting potential to address the distribution of electrons on the GaAs surface. The potential was derived from a tight-binding description of covalent bonding by retaining the first two levels of an expanded Green’s function for the ? and ? bond-order terms. Predictions using the potential were compared with independent estimates for the structures and binding energy of small clusters (dimers, trimers, and tetramers) and for various bulk lattices with coordinations varying from 4 to 12. The structure and energies of simple point defects and melting transitions were also investigated. The relative stabilities of the (001) surface reconstructions of GaAs were well predicted, especially under high-arsenic-overpressure conditions. The structural and binding energy trends of this GaAs BOP generally match experimental observations and ab initio calculations.

Murdick, D. A.; Zhou, X. W.; Wadley, H. N. G.; Nguyen-Manh, D.; Drautz, R.; Pettifor, D. G.

2006-01-01

359

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

360

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

361

Structural, bonding, dynamical, and electronic properties of liquid silicon: An ab initio molecular-dynamics study  

Microsoft Academic Search

We report an extensive first-principles molecular-dynamics study of metallic liquid silicon. Our description of the local order is in excellent agreement with x-ray- and neutron-diffraction experiments. The difference in internal energy between the simulated liquid phase and the crystal agrees well with the experimental enthalpy of melting. Analysis of the valence-electronic-charge density shows persistence of some covalent bonds in the

I. Stich; R. Car; M. Parrinello

1991-01-01

362

Electronic structures and chemical bonds of cobaltite and Ni-doped  

Microsoft Academic Search

The relation among electronic structure, chemical bond and thermoelectric property of Ca3 Co2 O6 and Ni-doped was studied by density function theory and discrete variation method (DFT-DVM). The results indicate that the\\u000a highest valence band (HVB) and the lowest conduction, band(LCB) are mainly attributed to Co3d, Ni3d and O2p atomic orbitals.\\u000a The property of a semiconductor is shown from the

Min Xinmin; Xing Xueling; Zhu Lei

2005-01-01

363

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

2013-04-01

364

Thermomechanical properties of graphene: valence force field model approach.  

PubMed

Using the valence force field model of Perebeinos and Tersoff (2009 Phys. Rev. B 79 241409(R)), different energy modes of suspended graphene subjected to tensile or compressive strain are studied. By carrying out Monte Carlo simulations it is found that: (i) only for small strains (|?| valence force field model results in a temperature independent bending modulus for graphene, and (viii) the Grüneisen parameter is estimated to be 0.64. PMID:22475745

Lajevardipour, A; Neek-Amal, M; Peeters, F M

2012-05-01

365

Ab initio valence force field calculations for quartz  

NASA Astrophysics Data System (ADS)

We have derived valence force constants for the tetrahedral SiO4 unit and the inter-tetrahedral SiOSi linkage from previous ab initio molecular orbital calculations on H4SiO4 and H6Si2O7 using a split-valence polarized Gaussian basis set (6-31G*), and used these to calculate the infrared and Raman active vibrational modes of ?-quartz. The calculation gives frequencies approximately 15% greater than experiment, as expected from harmonic force constants obtained at this level of Hartree-Fock theory, but the calculation gives the correct distribution of modes within each frequency range. Calculated 28 30 Si and 16 18 O isotope shifts and pressure shifts to 6 GPa are also in reasonable agreement with experiment. We have also used our ab initio force field to calculate the vibrational spectrum for ?-quartz. The results suggest either that inclusion of a torsional force constant is important for determining the stability of this high temperature polymorph, or that the ?-quartz has a disordered structure with lower symmetry (P62) domains, as suggested by earlier diffraction studies.

McMillan, Paul F.; Hess, Anthony C.

1990-03-01

366

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

367

Control of bond-strain-induced electronic phase transitions in iron perovskites.  

PubMed

Unusual electronic phase transitions in the A-site ordered perovskites LnCu3Fe4O12 (Ln: trivalent lanthanide ion) are investigated. All LnCu3Fe4O12 compounds are in identical valence states of Ln(3+)Cu(2+)3Fe(3.75+)4O12 at high temperature. LnCu3Fe4O12 with larger Ln ions (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb) show an intersite charge transfer transition (3Cu(2+) + 4Fe(3.75+) ? 3Cu(3+) + 4Fe(3+)) in which the transition temperature decreases from 360 to 240 K with decreasing Ln ion size. In contrast, LnCu3Fe4O12 with smaller Ln ions (Ln = Dy, Ho, Er, Tm Yb, Lu) transform into a charge-disproportionated (8Fe(3.75+) ? 5Fe(3+) + 3Fe(5+)) and charge-ordered phase below ?250-260 K. The former series exhibits metal-to-insulator, antiferromagnetic, and isostructural volume expansion transitions simultaneously with intersite charge transfer. The latter shows metal-to-semiconductor, ferrimagnetic, and structural phase transitions simultaneously with charge disproportionation. Bond valence calculation reveals that the metal-oxygen bond strains in these compounds are classified into two types: overbonding or compression stress (underbonding or tensile stress) in the Ln-O (Fe-O) bond is dominant in the former series, while the opposite stresses or bond strains are found in the latter. Intersite charge transfer transition temperatures are strongly dependent upon the global instability indices that represent the structural instability calculated from the bond valence sum, whereas the charge disproportionation occurs at almost identical temperatures, regardless of the magnitude of structural instability. These findings provide a new aspect of the structure-property relationship in transition metal oxides and enable precise control of electronic states by bond strains. PMID:24224928

Yamada, Ikuya; Etani, Hidenobu; Tsuchida, Kazuki; Marukawa, Shohei; Hayashi, Naoaki; Kawakami, Takateru; Mizumaki, Masaichiro; Ohgushi, Kenya; Kusano, Yoshihiro; Kim, Jungeun; Tsuji, Naruki; Takahashi, Ryoji; Nishiyama, Norimasa; Inoue, Toru; Irifune, Tetsuo; Takano, Mikio

2013-12-01

368

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

369

Strained-Bond Semiconductors.  

National Technical Information Service (NTIS)

Theories of strained-bond semiconductors and superconductors have been developed that promise to have significant impact on future electronic devices of interest to the Air Force. These include: (a) development of a theory of high-temperature superconduct...

J. D. Dow

1994-01-01

370

All about Chemical Bonding  

NSDL National Science Digital Library

Stephen Lower, a retired professor at Simon Fraser University, created this expansive and instructive website as a supplement to formal chemistry education for undergraduate students. Visitors will find in-depth descriptions along with several diagrams dealing with chemical bonding issues including their properties, shared-electron covalent bonds, hybrid orbitals, coordination complexes, and metals and semiconductors. General chemistry students looking for assistance should visit this well-developed educational site.

Lower, Stephen

371

Comment on a CASSCF study of the Fe?O 2 bond in a dioxygen heme complex  

NASA Astrophysics Data System (ADS)

It is indicated that several early papers on the Fe(II)( S=1)?O 2( S=1) theory of bonding for the Fe?O 2 linkage of oxyhaemoglobin and oxymyoglobin have been overlooked in most subsequent publications. Valence bond considerations are used to help show that the results of a recent CASSCF study by Yamamoto and Kashiwagi do not preclude the possibility that the primary mode of Fe?O 2 bonding could involve the Fe(II)( S=1)?O 2( S=1) formulation.

Harcourt, Richard D.

1990-03-01

372

Correlation Between Bond Reliability and Solid Phase Bonding Techniques for Contaminated Bonding Surfaces.  

National Technical Information Service (NTIS)

The relationship between bond reliability and the solid phase bonding technique used to interconnect on contaminated substrates has been investigated. Hybrid microcircuit substrates were contaminated with Shipley 1350H photoresist. Solid phase bonds on th...

D. W. Bushmire P. H. Holloway

1975-01-01

373

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

NASA Astrophysics Data System (ADS)

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)-X? 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 agreement with experimental results obtained by X-ray photoemission spectroscopy. Each peak in the density of states (DOS) is identified from the viewpoint of chemical bonding. There is a considerably strong covalent bonding between Ti and chalcogen atoms in TiX2. The covalency of chemical bonding is shown to increase and the ionicity to decrease in the series of TiS2 TiSe2 TiTe2. Both in intra- and interlayer chalcogen-chalcogen bonding and intralayer Ti Ti bonding are much weaker than Ti-chalcogen intralayer bonding. However, interlayer interaction is found to be not purely of the van der Waals type.

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

1998-09-01

374

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

375

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

376

Kondo Destruction and Valence Fluctuations in an Anderson Model  

NASA Astrophysics Data System (ADS)

Unconventional quantum criticality in heavy-fermion systems has been extensively analyzed in terms of a critical destruction of the Kondo effect. Motivated by a recent demonstration of quantum criticality in a mixed-valent heavy-fermion system, ?-YbAlB4, we study a particle-hole-asymmetric Anderson impurity model with a pseudogapped density of states. We demonstrate Kondo destruction at a mixed-valent quantum critical point, where a collapsing Kondo energy scale is accompanied by a singular charge-fluctuation spectrum. Both spin and charge responses scale with energy over temperature (?/T) and magnetic field over temperature (H/T). Implications for unconventional quantum criticality in mixed-valence heavy fermions are discussed.

Pixley, J. H.; Kirchner, Stefan; Ingersent, Kevin; Si, Qimiao

2012-08-01

377

Inter-Valence-Subband/Conduction-Band-Transport IR Detectors  

NASA Technical Reports Server (NTRS)

Infrared (IR) detectors characterized by a combination of (1) high-quantum-efficiency photoexcitation of inter-valence-subband transitions of charge carriers and (2) high-mobility conduction- band transport of the thus-excited charge carriers have been proposed in an effort to develop focal-plane arrays of such devices for infrared imaging. Like many prior quantum-well infrared photodetectors (QWIPs), the proposed devices would be made from semiconductor heterostructures. In order to obtain the combination of characteristics mentioned above, the proposed devices would be designed and fabricated in novel InAs/GaSb superlattice configurations that would exploit a phenomenon known in the semiconductor art as type-II broken-gap band offset.

Ting, David; Gunapala, Sarath; Bandara, Sumith

2004-01-01

378

Topological crystalline Kondo insulator in mixed valence ytterbium borides.  

PubMed

The electronic structures of two mixed valence insulators YbB6 and YbB12 are studied by using the local density approximation supplemented with the Gutzwiller method and dynamic mean field theory. YbB6 is found to be a moderately correlated Z2 topological insulator, similar to SmB6 but having much larger bulk band gap. Notably, YbB12 is revealed to be in a new novel quantum state, strongly correlated topological crystalline Kondo insulator, which is characterized by its nonzero mirror Chern number. The surface calculations find an odd (three) and an even (four) number of Dirac cones for YbB6 and YbB12, respectively. PMID:24483913

Weng, Hongming; Zhao, Jianzhou; Wang, Zhijun; Fang, Zhong; Dai, Xi

2014-01-10

379

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

380

Optimized conditions for imaging the effects of bonding charge density in electron microscopy.  

PubMed

We report on the observability of valence bonding effects in aberration-corrected high resolution electron microscopy (HREM) images along the [010] projection of the mineral Forsterite (Mg?SiO?). We have also performed exit wave restorations using simulated noisy images and have determined that both the intensities of individual images and the modulus of the restored complex exit wave are most sensitive to bonding effects at a level of 25% for moderately thick samples of 20-25 nm. This relatively large thickness is due to dynamical amplification of bonding contrast arising from partial de-channeling of 1s states. Simulations also suggest that bonding contrast is similarly high for an un-corrected conventional electron microscope, implying an experimental limitation of signal to noise ratio rather than spatial resolution. PMID:21193268

Ciston, J; Kim, J S; Haigh, S J; Kirkland, A I; Marks, L D

2011-06-01

381

Molecular correlated insulating state in low-valence layered nickelates  

NASA Astrophysics Data System (ADS)

In recent years, there has been an effort on artificially creating Fermi surfaces that resemble those of the superconducting cuprates. A Ni^3+:d^7 (one eg electron) configuration can be made into the electron-like analog of the d^9 (one eg hole) cuprate electronic structure.[1] Another cleaner alternative would be to grow low-valence Ni^+:d^9 compounds, which have recently become available through synthesis[2] of members of the series Lan+1NinO2n+2. We present LDA+U calculations on the layered compounds La4Ni3O8 [3] and La3Ni2O6, with three and two NiO2 layers, respectively. Electron count implies very low Ni formal valencies: 1.33+ and 1.5+, respectively. If charge order is present, Ni^+:d^9 could occur in a geometry similar to that of the cuprates. However, this is not the case. Both compounds are insulators, which we can attribute to quantum confinement in the NiO2 tri/bi-layers. The only states close to the Fermi level are Ni d3z^2-r^2, which couple along the c-axis (Ni trimers or dimers). The insulating behavior must be viewed from a molecular orbital viewpoint, after AFM order within layers has narrowed the bands. Insulating behavior is that of a "molecular" Mott insulator rather than a charge-ordered insulator. [1] J. Chaloupka and G. Khaliullin, PRL 100, 016404 (2008). [2] V. V. Poltavets et al., Phys. Rev. Lett. 102, 046405 (2009). [3] V. Pardo and W.E. Pickett, arXiv:1008.2707.

Pardo, Victor; Pickett, Warren E.

2011-03-01

382

Adhesive for composite bonding  

SciTech Connect

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 attachment. Another application involves adhesive bonding of a close-tolerance composite ring to the inside of a tapered, cylindrical composite penetrator case in order to provide a load bearing surface for prestressing the internal package. The adhesive bond in both of these applications is the critical load bearing component and must sustain large shearing stresses in order to maintain the structural integrity and viability of the part. The ideal adhesive would be a low viscosity (<10 poise) liquid with a long pot life, good wetting characteristics and high ultimate shear strength when cured at moderate (<50{degree}C) temperature. An adhesive with these characteristics would allow for the production of defect-free bonds by capillary wetting or squeezing flow of the adhesive into the narrow (.005{double prime}) annular space between the concentric composite parts. Since adhesives possessing these characteristics were not known to be available commercially, candidate materials were evaluated for this application. In this paper we present bond shear strength data and selected physical properties for some epoxy adhesive formulations. 7 refs., 5 figs., 2 tabs.

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

1989-11-27

383

Strength of Chemical Bonds  

NASA Technical Reports Server (NTRS)

Students are not generally made aware of the extraordinary magnitude of the strengths of chemical bonds in terms of the forces required to pull them apart. Molecular bonds are usually considered in terms of the energies required to break them, and we are not astonished at the values encountered. For example, the Cl2 bond energy, 57.00 kcal/mole, amounts to only 9.46 x 10(sup -20) cal/molecule, a very small amount of energy, indeed, and impossible to measure directly. However, the forces involved in realizing the energy when breaking the bond operate over a very small distance, only 2.94 A, and, thus, f(sub ave) approx. equals De/(r - r(sub e)) must be very large. The forces involved in dissociating the molecule are discussed in the following. In consideration of average forces, the molecule shall be assumed arbitrarily to be dissociated when the atoms are far enough separated so that the potential, relative to that of the infinitely separated atoms, is reduced by 99.5% from the potential of the molecule at the equilibrium bond length (r(sub e)) for Cl2 of 1.988 A this occurs at 4.928 A.

Christian, Jerry D.

1973-01-01

384

Fundamentals of fiber bonding in thermally point-bonded nonwovens  

NASA Astrophysics Data System (ADS)

Thermal point bonding (TPB) uses heat and pressure to bond a web of fibers at discrete points imparting strength to the manufactured fabric. This process significantly reduces the strength and elongation of the bridging fibers between bond points while strengthening the web. Single fiber experiments were performed with four structurally different polypropylene fibers to analyze the inter-relationships between fiber structure, fiber properties and bonding process. Two fiber types had a low birefringence sheath or surface layer while the remaining had uniform birefringence profiles through their thickness. Bonds were formed between isolated pairs of fibers by subjecting the fibers to a calendering process and simulating TPB process conditions. The dependence of bond strength on bonding temperature and on the type of fiber used was evaluated. Fiber strengths before and after bonding were measured and compared to understand the effect of bonding on fiber strength. Additionally, bonded fiber strength was compared to the strength of single fibers which had experienced the same process conditions as the bonded pairs. This comparison estimated the effect of mechanical damage from pressing fibers together with steel rolls while creating bonds in TPB. Interfiber bond strength increased with bonding temperature for all fiber types. Fiber strength decreased with increasing bonding temperature for all fiber types except for one type of low birefringent sheath fibers. Fiber strength degradation was unavoidable at temperatures required for successful bonding. Mechanical damage from compression of fibers between rolls was an insignificant factor in this strength loss. Thermal damage during bonding was the sole significant contributor to fiber strength degradation. Fibers with low birefringence skins formed strong bonds with minimal fiber strength loss and were superior to fibers without such surface layers in TPB performance. A simple model to predict the behavior of a two-bond fabric strip was developed and it demonstrated the negative effect of inhomogeneous straining of fibers arising from the commonly used diamond bond shape and pervasive fiber-to-fiber elongation variability on fabric strength.

Chidambaram, Aparna

385

A Policy-Capturing Investigation of Expectancy Theory Models of Valence and Force.  

National Technical Information Service (NTIS)

The purpose of this thesis was to examine the valence and force models of Vroom's expectancy theory of motivation. In particular, this study was designed to (1) use policy capturing to test the valence model and determine if knowledge of second-level vale...

N. C. Wagner

1979-01-01

386

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

387

Group Motivation and Group Task Performance: The Expectancy-Valence Theory Approach.  

ERIC Educational Resources Information Center

Investigated effects of group motivation on group task performance. Created two levels of valence, expectancy and instrumentality. Valence variable reflected on group productivity on unstructured and task persistence measures. Expectancy variable's effect was on task persistence measure. Instrumentality affected group productivity on structured…

Nakanishi, Masayuki

1988-01-01

388

A CASSCF-CCI study of the valence and lower excited states of the benzene molecule  

Microsoft Academic Search

Abinitio complete active space (CAS) SCF and contracted CI calculations have been carried out for all valence and the lower Rydberg states of the benzene molecule. The CASSCF active space comprised 12 ?-type molecular orbitals and the basis set included both polarization functions and diffuse functions in order to describe properly both valence and Rydberg type orbitals. Resulting excitation energies

J. Mauricio O. Matos

1987-01-01

389

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

390

VALENCE STATES OF SULFUR IN POLLUTION SAMPLES BY X-RAY ANALYSIS  

EPA Science Inventory

A flat single crystal spectrometer was configured to measure the valence band x-ray spectra of various forms of sulfur in air pollutants. While most different valence states showed differences in the structure of the K sub beta band, particular emphasis was placed on distinguishi...

391

Effects of Valence and Extremity of eWOM on Attitude toward the Brand and Website  

Microsoft Academic Search

Two studies were conducted to examine the influence of valence and extremity of consumer product reviews on attitude toward the brand and attitude toward the website. Each experiment was a one factor (valence\\/extremity: extremely negative, moderately negative, extremely positive) between-subjects design with a control group. Results in both studies showed that although extremely positive reviews increased attitude toward the brand,

Mira Lee; Shelly Rodgers; Mikyoung Kim

2009-01-01

392

Identifying Facial Emotions: Valence Specific Effects and an Exploration of the Effects of Viewer Gender  

ERIC Educational Resources Information Center

The valence hypothesis suggests that the right hemisphere is specialised for negative emotions and the left hemisphere is specialised for positive emotions (Silberman & Weingartner, 1986). It is unclear to what extent valence-specific effects in facial emotion perception depend upon the gender of the perceiver. To explore this question 46…

Jansari, Ashok; Rodway, Paul; Goncalves, Salvador

2011-01-01

393

Formation of unprecedented actinidecarbon triple bonds in uranium methylidyne molecules  

PubMed Central

Chemistry of the actinide elements represents a challenging yet vital scientific frontier. Development of actinide chemistry requires fundamental understanding of the relative roles of actinide valence-region orbitals and the nature of their chemical bonding. We report here an experimental and theoretical investigation of the uranium methylidyne molecules X3UCH (X = F, Cl, Br), F2ClUCH, and F3UCF formed through reactions of laser-ablated uranium atoms and trihalomethanes or carbon tetrafluoride in excess argon. By using matrix infrared spectroscopy and relativistic quantum chemistry calculations, we have shown that these actinide complexes possess relatively strong UC triple bonds between the U 6d-5f hybrid orbitals and carbon 2s-2p orbitals. Electron-withdrawing ligands are critical in stabilizing the U(VI) oxidation state and sustaining the formation of uranium multiple bonds. These unique UC-bearing molecules are examples of the long-sought actinide-alkylidynes. This discovery opens the door to the rational synthesis of triple-bonded actinidecarbon compounds.

Lyon, Jonathan T.; Hu, Han-Shi; Andrews, Lester; Li, Jun

2007-01-01

394

The enthalpies of the solutions of liquid metals in the liquid chalcogens--the structure and the chemical bond around solute metals  

Microsoft Academic Search

The enthalpies of the solutions of several B metals in the liquid chalcogen can be calculated by using a cluster model around the solute metal. For a given coordination number and numbers of the valence electrons of the solute metal, the ionicity of the metal?chalcogen bond was also estimated. The calculated enthalpies coincide fairly well with those of the experimental

Takashi Maekawa; Toshio Yokokawa

1975-01-01

395

Surface analysis in composite bonding  

NASA Technical Reports Server (NTRS)

The role of the interfacial region in determining the bond strength and durability of composite bonds is discussed. The characterization of a variety of carbon fibers including Celion 6000 using both scanning electron microscopy and X-ray photoelectron spectroscopy is discussed. The emphasis is on composite bonding, that is, the adhesive bonding between composites in contrast to fiber-matrix interaction. The primary objective of the research is the characterization of composite surfaces before adhesive bonding and after fracture of bonded specimens. Work done on the analysis of composite samples pretreated in a number of ways prior to bonding is detailed.

Messick, D. L.; Wightman, J. P.

1982-01-01

396

The effects of emotional valence on hemispheric processing of metaphoric word pairs.  

PubMed

Recent theories of metaphor comprehension discuss the cognitive substrates involved in processing metaphors. However, the role of valence perception during metaphor comprehension has received little attention. The present study aims to examine the effect of emotional valence on metaphor processing, as well as the interaction between this effect and hemispheric differences. Metaphoric, literal, and meaningless word pairs were presented to 43 participants who performed a semantic judgment task. Results showed that processing of metaphors with negative valence was faster when done in the right hemisphere as compared with the left hemisphere. These findings indicate that emotional valence interacts with cognitive processes of metaphor comprehension. We discuss valence with respect to the class inclusion model and the fine versus coarse semantic coding model of metaphor processing. PMID:24328525

Mashal, Nira; Itkes, Oksana

2014-09-01

397

The dominant contributions of the inner valence electrons to the positron annihilation process in methanol  

NASA Astrophysics Data System (ADS)

The positron–electron annihilation gamma-ray spectra of methanol have been studied in the present work. The contributions of the bound electrons to the Doppler-shift of gamma-ray spectra have been analysed as well. These bound electrons are divided into three groups: core, inner valence and outer valence rather than the conventional two groups: core and valence in the positron annihilation process in the present work. The results obtained show a dominance of the inner valence electrons of methanol rather than the electrons occupied in the highest occupied molecular orbital (HOMO) in the positron–electron annihilation process. These inner valence electrons occupied in 3a? and 4a? orbitals consist of over 80% outermost atomic 2s electrons in oxygen and carbon atoms. That the positron prefers to annihilate with these outermost s electrons in atoms is suggested.

Ma, Xiaoguang; Wang, Lizhi; Yang, Chuanlu

2014-03-01

398

Fractional valency and kink conduction mechanism in quasi-one-dimensional molecular systems  

SciTech Connect

The authors consider the connection between fractional valence and electrical conductivity of donor-acceptor molecular crystals for which one-dimensional anisotropy is characteristic and seek to answer the observation that donor-acceptor crystals with fractional valence display higher conductivity than those with integral valence by proving, using a Hamiltonian and a Wigner lattice for the crystal, that donor-acceptor molecular crystals with fractional valence have some additional degeneracy in the ground state and that this circumstance is responsible for the existence in such systems of electronic excitations of the kink type which, in the general case, carry a fractional charge and may provide high electrical conductivity. Their qualitative analysis of Wigner lattices for the real molecular crystals TTF-TCNQ and NMP-TCNQ, compared against organic semiconductors, shows that energy-degenerate structures exist for ionic valences of one half, one third, and two thirds.

Ovchinnikov, A.A.; Ukrainskii, T.I.

1987-09-01

399

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

400

Adhesive bond degradation sensor  

NASA Astrophysics Data System (ADS)

Early detection of adhesive bond degradation using sensing elements embedded within the 100um bond-line of aluminium epoxy adhesive joints has been demonstrated. Sensing elements of varying heights were fabricated at the ends of narrow conductors on a flexi-circuit carrier. This construction simulates the active sensing region on a patented silicon adhesive bond degradation sensor and has been used to characterize the sensing elements without the expense and time associated with fabricating the complete integrated silicon sensor. The highest elements on the flexi-circuit serve both as electrical pickup studs, providing a circuit from the flexi-circuit to the top aluminium plate, and as spacers to ensure that the shorter sensing elements do not contact the aluminium plate. The non-contacting sensing elements are thus arranged to be close to the metal/adhesive interface and are sensitive to any change in conductivity in this region due to release of ions as the interface is degraded by the environment. Accelerated aging tests were performed on flexi-circuit sensors embedded in the bond-line of double cantilever beam specimens. The specimens were immersed in 50° C water and pre-loaded to just initiate a crack. Load on the specimen was then maintained by applying a constant load point displacement with a very low velocity to ensure that the environment would degrade the bond-line in advance of the crack front. The change of load and the conductivity measured by the sensing elements were then logged with time. The onset of bond degradation was detected approximately 10-20 mm ahead of the crack tip.

Wilson, Alan R.; Olsson-Jacques, Christina; Muscat, Richard F.

2002-12-01

401

Development of wavelength-dispersive soft X-ray emission spectrometers for transmission electron microscopes--an introduction of valence electron spectroscopy for transmission electron microscopy.  

PubMed

Two types of wavelength-dispersive soft X-ray spectrometers, a high-dispersion type and a conventional one, for transmission electron microscopes were constructed. Those spectrometers were used to study the electronic states of valence electrons (bonding electrons). Both spectrometers extended the acceptable energy regions to higher than 2000 eV. The best energy resolution of 0.08 eV was obtained for an Al L-emission spectrum by using the high-dispersion type spectrometer. By using the spectrometer, C K-emission of carbon allotropes, Cu L-emission of Cu(1-x)Zn(x) alloys and Pt M-emission spectra were presented. The FWHM value of 12 eV was obtained for the Pt Malpha-emission peak. The performance of the conventional one was also presented for ZnS and a section specimen of a multilayer device. W-M and Si-K emissions were clearly resolved. Soft X-ray emission spectroscopy based on transmission electron microscopy (TEM) has an advantage for obtaining spectra from a single crystalline specimen with a defined crystal setting. As an example of anisotropic soft X-ray emission, C K-emission spectra of single crystalline graphite with different crystal settings were presented. From the spectra, density of states of pi- and sigma-bondings were separately derived. These results demonstrated a method to analyse the electronic states of valence electrons of materials in the nanometre scale based on TEM. PMID:20371492

Terauchi, Masami; Koike, Masato; Fukushima, Kurio; Kimura, Atsushi

2010-01-01

402

Formations of mixed-valence oxovanadiumV,IV citrates and homocitrate with N-heterocycle chelated ligand.  

PubMed

Dimeric mixed-valence oxovanadium citrate [V 2O 3(phen) 3(Hcit)].5H 2O ( 1) (H 4cit = citric acid, phen = 1,10-phenanthroline) was isolated from a weak acidic medium. It could be converted quantitatively into a tetrameric oxovanadium citrate adduct of 1,10-phenanthroline [V 2O 3(phen) 3(Hcit) 2(phen) 3O 3V 2].12H 2O ( 2). This was supported by the trace of infrared spectra and X-ray diffraction patterns. The two compounds feature a bidentate citrate group that chelates only to one vanadium center through their negatively charged alpha-alkoxy and alpha-carboxy oxygen atoms, while the other beta-carboxy and beta-carboxylic acid groups are free to participate in strong intramolecular and intermolecular hydrogen bonding [2.45(1) in 1 and 2.487(2) A in 2], respectively. This is also the case of homocitrato vanadate(V/IV) [V 2O 3(phen) 3( R, S-H 2homocit)]Cl.6H 2O ( 3) (H 4homocit = homocitric acid), which features a binding mode similar to that found in the R-homocitrato iron molybdenum cofactor of Mo-nitrogenase. Moreover, the homocitrato vanadate(V) [VO 2(phen) 2] 2[V 2O 4( R,S-H 2homocit) 2].4H 2O.2C 2H 5OH ( 4) is isolated as a molecular precursor for the formation of mixed-valence complex 3. The V-O alpha-alkoxy and V-O alpha-carboxy bond distances of homocitrate complexes 3 and 4 are 1.858(4) and 1.968(6) av and 2.085(4) and 1.937(5) A, respectively. They are shorter than those of homocitrate to FeVco (2.15 A). The gamma-carboxy groups of coordinated homocitrato complexes 3 and 4, and the free homocitrate salt Na 3(Hhomocit).H 2O ( 5), form strong hydrogen bonds with the chloride ion and the water molecule [2.982(5) in 3, 2.562(9) in 4, and 2.763(1) A in 5], respectively. PMID:18722422

Chen, Can-Yu; Zhou, Zhao-Hui; Chen, Hong-Bin; Huang, Pei-Qiang; Tsai, Khi-Rui; Chow, Yuan L

2008-10-01

403

Enhancing effects of electron-withdrawing groups and metallic ions on halogen bonding in the YC6F4X···C2H8N2 (X = Cl, Br, I; Y = F, CN, NO2, LiNC+, NaNC+) complex.  

PubMed

Halogen-bonding interactions are highly directional intermolecular interactions that are often important in crystal engineering. In this work, the second-order Møller-Plesset perturbation theory (MP2) calculations and the quantum theory of "atoms in molecules" (QTAIM) and noncovalent interaction (NCI) studies were carried out on a series of X···N halogen bonds between substituted haloperfluoroarenes C6F4XY (X = Cl, Br, I; Y = F, CN, NO2) as bond donors and 1,2-diaminoethane as bond acceptor. Our research supports earlier work that electron-withdrawing substituents produce an enhancement effect on the size of the ?-hole and the maximum positive electrostatic potentials (VS,max), which further strengthens the halogen bonding. The metallic ion M(+) (M(+) = Li(+), Na(+)) has the ability to enhance the size of both the ?-hole and VS,max value with the formation of [MNCC6F4X](+), resulting in more electronic charge transfer away from the halogen atom X and an increase in the strength of the halogen bond. It is found that the values of V(S,max) at the ?-holes are linear in relation to the halogen-bonded interaction energies and the halogen-bonding interaction distance, indicating that the electrostatic interaction plays a key role in the halogen-bonding interactions. The values of V(S,max) at the ?-holes are also linear in relation to the electron density ?(b), its Laplacian nabla(2)?b, and -Gb/Vb of XB, indicating that the topological properties (?b, nabla(2)?b) and energy properties (Gb, Vb) at the BCPs are correlated with the electrostatic potentials. PMID:24237250

Han, Na; Zeng, Yanli; Li, Xiaoyan; Zheng, Shijun; Meng, Lingpeng

2013-12-01

404

Theoretical Studies of Electronic Spectra and Bonding of AlCl/AlF(X^1{?}^+, a^3{?}, A^1{?}) with Excited States Exhibiting Recoupled Pair Bonding  

NASA Astrophysics Data System (ADS)

Ground electronic state rotational lines of AlCl and AlF have been observed in the circumstellar envelope of IRC +10216, and electronic transitions of AlF have been observed in sunspot umbra. We have performed high-level ab initio MRCI+Q and RCCSD(T) calculations with large correlation consistent basis sets up to augmented sextuple zeta quality including core-valence correlation effects on the ground state (X^1{?}^+) and two lowest excited states (a^3{?}, A^1{?}) of AlF and AlCl. Theoretical spectroscopic constants as well as vibrational and rotational spectra will be presented and compared with experiment. We will also discuss the nature of the bonding in these states. The excited states are formed via recoupled pair bonds, in which the Al 3s^2 pair of electrons is decoupled to allow one of its electrons to recouple with a halogen to form a bond.

Leiding, Jeff; Woon, David E.; Dunning, Thom H.; , Jr.

2011-06-01

405

Hydrogen bond and halogen bond inside the carbon nanotube  

NASA Astrophysics Data System (ADS)

The hydrogen bond and halogen bond inside the open-ended single-walled carbon nanotubes have been investigated theoretically employing the newly developed density functional M06 with the suitable basis set and the natural bond orbital analysis. Comparing with the hydrogen or halogen bond in the gas phase, we find that the strength of the hydrogen or halogen bond inside the carbon nanotube will become weaker if there is a larger intramolecular electron-density transfer from the electron-rich region of the hydrogen or halogen atom donor to the antibonding orbital of the X-H or X-Hal bond involved in the formation of the hydrogen or halogen bond and will become stronger if there is a larger intermolecular electron-density transfer from the electron-rich region of the hydrogen or halogen atom acceptor to the antibonding orbital of the X-H or X-Hal bond. According to the analysis of the molecular electrostatic potential of the carbon nanotube, the driving force for the electron-density transfer is found to be the negative electric field formed in the carbon nanotube inner phase. Our results also show that the X-H bond involved in the formation of the hydrogen bond and the X-Hal bond involved in the formation of the halogen bond are all elongated when encapsulating the hydrogen bond and halogen bond within the carbon nanotube, so the carbon nanotube confinement may change the blue-shifting hydrogen bond and the blue-shifting halogen bond into the red-shifting hydrogen bond and the red-shifting halogen bond. The possibility to replace the all electron nanotube-confined calculation by the simple polarizable continuum model is also evaluated.

Wang, Weizhou; Wang, Donglai; Zhang, Yu; Ji, Baoming; Tian, Anmin

2011-02-01

406

Synthesis and characterization of MnCrO4, a new mixed-valence antiferromagnet.  

PubMed

A new orthorhombic phase, MnCrO4, isostructural with MCrO4 (M = Mg, Co, Ni, Cu, Cd) was prepared by evaporation of an aqueous solution, (NH4)2Cr2O7 + 2 Mn(NO3)2, followed by calcination at 400 °C. It is characterized by redox titration, Rietveld analysis of the X-ray diffraction pattern, Cr K edge and Mn K edge XANES, ESR, magnetic susceptibility, specific heat and resistivity measurements. In contrast to the high-pressure MnCrO4 phase where both cations are octahedral, the new phase contains Cr in a tetrahedral environment suggesting the charge balance Mn(2+)Cr(6+)O4. However, the positions of both X-ray absorption K edges, the bond lengths and the ESR data suggest the occurrence of some mixed-valence character in which the mean oxidation state of Mn is higher than 2 and that of Cr is lower than 6. Both the magnetic susceptibility and the specific heat data indicate an onset of a three-dimensional antiferromagnetic order at TN ? 42 K, which was confirmed also by calculating the spin exchange interactions on the basis of first principles density functional calculations. Dynamic magnetic studies (ESR) corroborate this scenario and indicate appreciable short-range correlations at temperatures far above TN. MnCrO4 is a semiconductor with activation energy of 0.27 eV; it loses oxygen on heating above 400 °C to form first Cr2O3 plus Mn3O4 and then Mn1.5Cr1.5O4 spinel. PMID:24090277

Nalbandyan, Vladimir B; Zvereva, Elena A; Yalovega, Galina E; Shukaev, Igor L; Ryzhakova, Anastasiya P; Guda, Alexander A; Stroppa, Alessandro; Picozzi, Silvia; Vasiliev, Alexander N; Whangbo, Myung-Hwan

2013-10-21

407

Parental Bonding Instrument  

Microsoft Academic Search

The view that those with obsessive compulsive disorder or obsessional personality have been exposed to overcontrolling and overcritical parenting is examined. Two measures of obsessionality (the Maudsley Obsessional-Compulsive Inventory and the Leyton Obsessionality Inventory) were completed by 344 nonclinical subjects. They also scored their parents on the Parental Bonding Instrument (PBI), a measure assessing perceived levels of parental care and

L. C. Cavedo; G. Parker

1994-01-01

408

Bonding with Your Baby  

MedlinePLUS

... your area. Breastfeeding and bottle-feeding are both natural times for bonding. Infants respond to the smell and touch of their mothers, as well as the responsiveness of the parents to their needs. In an uncomplicated birth, caregivers try to take advantage of the infant's ...

409

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

410

Bonding in cementitious composites  

Microsoft Academic Search

These proceedings discuss the papers presented at the symposium on the subject of high performance cement composites. Some of the topics discussed were; calcium hydroxides treated ceramics microspheres and mechanical properties of high temperature light weight cements; microstructure and chemical variations of class F fly ash; microstructure and bond strength of cement and crack propagation as detected by laser holography

Mindess

1988-01-01

411

Bond strength comparison of color change adhesives for orthodontic bonding.  

PubMed

This study investigated whether three different color change light-cured orthodontic bonding adhesives have comparable shear bond strengths to a conventional light-cured orthodontic bonding adhesive. The sample of 240 bovine incisors was divided into four groups of 60 each. Each group tested one of four orthodontic bonding adhesives: 3M Unitek Transbond PLUS, Ormco Gréngloo, Ormco Blúgloo, and 3M Unitek Transbond XT (control). The four groups were further divided into two subgroups of 30 with shear bond strength tested at two different times (15 minutes and 24 hours) post-bond. The shear bond strength was measured on a universal testing machine. The data were analyzed by two-way analysis of variance and post-hoc comparisons (Fisher's PLSD) at the 0.05 level of significance. The average shear bond strength was greater at 24 hours than at 15 minutes for Transbond PLUS, Blúgloo, and Transbond XT. For Gréngloo, the average shear bond strength was greater at 15 minutes than at 24 hours. Gréngloo tested at 15 minutes had the highest average shear bond strength. Gréngloo tested at 24 hours had the lowest average shear bond strength. All four orthodontic bonding adhesives demonstrated bond strengths considered to be clinically acceptable for orthodontic purposes. PMID:21667823

Duers, Michael W; English, Jeryl D; Ontiveros, Joe C; Powers, John M; Bussa, Harry I; Frey, Gary N; Gallerano, Ronald L; Paige, Sebastian Z

2011-03-01

412

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

413

Environmental variables and releasing-valence transfer in stimulus-directed pecking of chicks.  

PubMed

Releasing valence transfer occurs when the power or valence to release responses is transferred from a primary releasing stimulus to a second, initially neutral, stimulus. In the exemplar, pecking responses by neonatal chicks are released and directed by a pointed object operated to make pecking movements. Stimuli attached to or pecked by the arrow thereby acquire enhanced releasing valence. Chicks peck at matching stimuli in preference to comparable but unenhanced stimuli. Research reported here shows that primary and transferred releasing valences are differentially affected by environmental variables. Specific findings were Pecking by chicks occurs only within a narrow range of ambient temperature. Outside of this range, pecking is low in frequency and insensitive to valence-enhanced release. Pecking by chicks appears to be finely tuned to arrow peck rates between 120 and 180 pecks per minute. Within this range, frequency of pecks by chicks is low whereas the percentage of pecks to the valence-enhanced stimulus is maximal. The maternal food call was a weak releaser of pecking by chicks with no valence-enhancing properties. PMID:3606528

Suboski, M D

1987-05-01

414

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

2011-12-01

415

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

416

40 CFR Requirements - Surfacer, Topcoat, Final Repair, Glass Bonding Primer, and Glass Bonding Adhesive Emission...  

Code of Federal Regulations, 2010 CFR

...Glass Bonding Primer, and Glass Bonding Adhesive Emission Limitations and the...Glass Bonding Primer, and Glass Bonding Adhesive Emission Limitations § 63...Glass Bonding Primer, and Glass Bonding Adhesive Emission Limitations and...

2010-07-01

417

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

418

Chromium valences in ureilite olivine and implications for ureilite petrogenesis  

NASA Astrophysics Data System (ADS)

Ureilites are a group of ultramafic achondrites commonly thought to be residues of partial melting on a carbon-rich asteroid. They show a large variation in FeO content (olivine Fo values ranging from ˜74 to 95) that cannot be due to igneous fractionation and suggests instead variation in oxidation state. The presence of chromite in only a few of the most ferroan (Fo 75-76) samples appears to support such a model. MicroXANES analyses were used in this study to determine the valence states of Cr (previously unknown) in olivine cores of 11 main group ureilites. The goal of this work was to use a method that is independent of Fo to determine the oxidation conditions under which ureilites formed, in order to evaluate whether the ureilite FeO-variation is correlated with oxidation state, and whether it is nebular or planetary in origin. Two of the analyzed samples, LEW 88774 (Fo 74.2) and NWA 766 (Fo 76.7) contain primary chromite; two others, LAP 03587 (Fo 74.4) and CMS 04048 (Fo 76.2) contain sub-micrometer-sized exsolutions of chromite + Ca-rich pyroxene in olivine; and one, EET 96328 (Fo 85.2) contains an unusual chromite grain of uncertain origin. No chromite has been observed in the remaining six samples (Fo 77.4-92.3).

Goodrich, C. A.; Sutton, S. R.; Wirick, S.; Jercinovic, M. J.

2013-12-01

419

Thermoelectric transport in the coupled valence-band model  

NASA Astrophysics Data System (ADS)

The Boltzmann transport equation (BTE) is applied to the problem of thermoelectric transport in p-type semiconductors whose valence band-structure is describable in terms of two bands degenerate at the ? point. The Seebeck coefficient and mobility are calculated from the solution to two coupled BTEs, one for each band, with interband scattering and scattering by inelastic mechanisms treated exactly by the application of an algorithm developed by the authors in an earlier work. Most treatments of this problem decouple the two bands by neglecting certain terms in the BTE, greatly simplifying the mathematics: the error in the Seebeck coefficient and mobility introduced by this approximation is quantified by comparing with the exact solution. Degenerate statistics has been assumed throughout, and the resulting formalism is therefore valid at high hole concentrations. Material parameters are used that have been deduced from optical, strain and other experiments often not directly related to hole transport. The formulations in this work thus do not use adjustable or fitting parameters. The transport coefficients of heavily doped gallium antimonide, a typical high-efficiency p-type thermoelectric material, are calculated and agreement to experimentally determined values is found to be satisfactory.

Ramu, Ashok T.; Cassels, Laura E.; Hackman, Nathan H.; Lu, Hong; Zide, Joshua M. O.; Bowers, John E.

2011-02-01

420

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

421

Toxoplasma gondii infection enhances the kairomonal valence of rat urine  

PubMed Central

Many animals use chemicals as pheromones to communicate between individuals of the same species, for example to influence mate choice or to assert dominance. Pheromonal communication is an open broadcast system that can be intercepted by unintended receivers such as predators and prey. We have recently reported that male rats infected by the protozoan parasite Toxoplasma gondii become more attractive to female rats. This suggests a facilitatory effect of infection on rat pheromone production. In view of the open nature of pheromonal communication, we postulate that Toxoplasma gondii infection collateraly enhances kairomonal valence of infected rats to their prey. We compared the strength of kairomonal interception by mice when using scent marks from rats infected with Toxoplasma gondii vs. marks from uninfected control rats. Mice exhibited greater avoidance to both fresh urine and aged rat urine marks obtained from infected animals. These results indicate that, at least in some cases, parasitism can result in opportunity costs for hosts by making prey species more averse to them.

Vasudevan, Anand; Vyas, Ajai

2014-01-01

422

Finite element analysis of valence band structures in quantum wires  

NASA Astrophysics Data System (ADS)

Valence band structures with spin-orbit (SO) coupling of quantum wires (QWRs), are investigated using the multiband effective-mass theory by a calculation procedure based on a finite-element method (FEM). The results are also compared to those obtained by finite difference method (FDM) and obtained by FEM without SO coupling. We expect FEM and FDM methods to give similar results, but the FDM has a limitation in dealing with various quantum wire shapes. In the case of QWR with small strains, the SO coupling effect does not greatly change subband energies and the trends of the subband dispersions. On the other hand, in the case of QWR with large strains, the subband energies of all states including the first state are considerably affected by the SO coupling. The amplitudes of the heavy-hole and light-hole wave functions have nonzero mixings even at the zone center (ky=0) in contrast to the case of quantum wells. It is found that the matrix elements for the TE polarization greatly increase due to the SO coupling effect.

Park, Seoung-Hwan; Ahn, Doyeol; Lee, Yong-Tak

2004-08-01

423

Breakdown of ionic character of molecular alkali bromides in inner-valence photoionization  

NASA Astrophysics Data System (ADS)

The inner-valence region of alkali bromide XBr (X=Li, Na, K, Rb) vapours has been studied experimentally by means of synchrotron radiation excited photoelectron spectroscopy. Experimental spectra were analyzed by comparing them with available theoretical results and previous experiments. Ionic character of alkali bromides is seen to change in the inner-valence region with increasing atomic number of the alkali atom. A mechanism involving mixing between Br 4s and Rb 4p orbitals has been suggested to account for the fine structure observed in inner-valence ionization region of RbBr.

Karpenko, A.; Iablonskyi, D.; Urpelainen, S.; Kettunen, J. A.; Cao, W.; Huttula, M.; Aksela, H.

2014-05-01

424

Breakdown of ionic character of molecular alkali bromides in inner-valence photoionization.  

PubMed

The inner-valence region of alkali bromide XBr (X=Li, Na, K, Rb) vapours has been studied experimentally by means of synchrotron radiation excited photoelectron spectroscopy. Experimental spectra were analyzed by comparing them with available theoretical results and previous experiments. Ionic character of alkali bromides is seen to change in the inner-valence region with increasing atomic number of the alkali atom. A mechanism involving mixing between Br 4s and Rb 4p orbitals has been suggested to account for the fine structure observed in inner-valence ionization region of RbBr. PMID:24880294

Karpenko, A; Iablonskyi, D; Urpelainen, S; Kettunen, J A; Cao, W; Huttula, M; Aksela, H

2014-05-28

425

Chemical environment and Ce valence: Global trends in transition-metal compounds  

SciTech Connect

Results of L/sub III/ absorption spectroscopy measurements on a wide range of Ce--transition-metal (T) compounds are presented and Ce valence-state estimates are made. We are able to identify extremely regular trends in the response of the Ce valence and Ce-T hybridization strength to systematic variations in the solid-state chemical environment. Our work facilitates identification of the specific elements in the T-metal electronic structure which drive the Ce valence-state change.

Neifeld, R.A.; Croft, M.; Mihalisin, T.; Segre, C.U.; Madigan, M.; Torikachvili, M.S.; Maple, M.B.; DeLong, L.E.

1985-11-15

426

Bond Graphs III: Bond Graphs and Electrical Networks  

Microsoft Academic Search

Electrical networks are defined and a definition of when a bond graph and an electrical network are equivalent is given. Bond graphs and electrical networks are defined to be primitive if they contain no transformers or gyrators. A bond graph is defined to be realisable if it is equivalent to an electrical network and primitively realisable if it is equivalent

John D. Lamb; Gregory M. Asher; Douglas R. Woodall

1997-01-01

427

Nickel-palladium bond pads for copper wire bonding  

Microsoft Academic Search

The semiconductor packaging industry is undergoing a step-change transition from gold to copper wire bonding brought on by a quadrupling of gold cost over the last 8years. The transition has been exceptionally rapid over the last 3years and virtually all companies in the industry now have significant copper wire bonding production. Among the challenges to copper wire bonding is the

Horst Clauberg; Petra Backus; Bob Chylak

2011-01-01

428

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

429

Study of the U(1)-Z4 cross-over in 2D valance-bond-solids  

NASA Astrophysics Data System (ADS)

We consider the 2D Heisenberg model in the overcomplete basis of valence bonds. By tuning matrix elements corresponding closely to the diagonal and off-diagonal terms in Rokhsar-Kivelson quantum dimer model, we show, using a projector quantum Monte Carlo technique, that there is a quantum phase transition into a valence-bond-solid (VBS) state. This system allows us to study the cross-over length-scale [1] associated with emergent U(1) symmetry of the VBS order parameter [2], which has up until now not been possible in other systems [3], where the VBS order is weaker and prohibitively large system sizes are needed to observe the stabilization of a manifestly Z4-symmetric VBS. [1] J. Lou, A. W. Sandvik, and L. Balents, Arxiv:0704.1472. [2] T. Senthil, A. Vishwanath, L. Balents, S. Sachdev, and M. P. A. Fisher, Science 303, 1490 (2004). [3] A. W. Sandvik, Phys. Rev. Lett 98, 227202 (2007).

Lou, Jie; Sandvik, Anders

2008-03-01

430

Low temperature reactive bonding  

DOEpatents

The joining technique 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.

Makowiecki, Daniel M. (Livermore, CA); Bionta, Richard M. (Livermore, CA)

1995-01-01

431

Strained-bond semiconductors  

Microsoft Academic Search

Theories of strained-bond semiconductors and superconductors have been developed that promise to have significant impact on future electronic devices of interest to the Air Force. These include: (1) development of a theory of high-temperature superconductivity based on the idea of strained-layer superlattices, (2) elucidation of the physics of doping in Type-2 semiconductor superlattices, which is now central to the development

John D. Dow

1994-01-01

432

40 CFR Requirements - Surfacer, Topcoat, Final Repair, Glass Bonding Primer, and Glass Bonding Adhesive Emission...  

Code of Federal Regulations, 2010 CFR

... Surfacer, Topcoat, Final Repair, Glass Bonding Primer, and Glass Bonding Adhesive Emission Limitations Requirements Compliance...Repair, Glass Bonding Primer, and Glass Bonding Adhesive Emission...

2010-07-01

433

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

434

Disulfide bonds of acetylcholinesterase  

SciTech Connect

The positions of the inter- and intrasubunit disulfide bridges were established for the 11S form of acetylcholinesterase (AChE) isolated from Torpedo californica. A major form of AChE localized within the basal lamina of the synapse is a dimensionally asymmetric molecule which contains either two (13S) or three (17S) sets of catalytic subunits linked to collagenous and non-collagenous structural subunits. Limited proteolysis yields a tetramer of catalytic subunits which sediments at 11S. Each catalytic subunit contains 8 cysteine residues. Initially, these Cys residues were identified following trypsin digestion of the reduced protein alkylated with (/sup 14/C)-iodoacetate. Peptides were resolved by gel filtration followed by reverse phase HPLC. To determine the disulfide bonding profile, native non-reduced 11S AChE was treated with a fluorescent, sulfhydryl-specific reagent, monobromobimane, prior to proteolytic digestion. One fluorescent Cys peptide was identified indicating that a single sulfhydryl residue was present in its reduced form. Three pairs of disulfide bonded peptides were identified, sequenced, and localized in the polypeptide chain. The Cys residue that is located in the C-terminal tryptic peptide was disulfide bonded to an identical peptide and thus forms the intersubunit crosslink. Finally, the cysteine positions have been compared with the sequence of the homologous protein, thyroglobulin. Both likely share a common pattern of folding.

MacPhee-Quigley, K.; Vedvick, T.; Taylor, P.; Taylor, S.

1986-05-01

435

ChemTeacher: Metallic Bonds  

NSDL National Science Digital Library

ChemTeacher compiles background information, videos, articles, demonstrations, worksheets and activities for high school teachers to use in their classrooms. The Metallic Bonds page includes resources for teaching students about metallic bonding.

2011-01-01

436

ChemTeacher: Ionic Bonds  

NSDL National Science Digital Library

ChemTeacher compiles background information, videos, articles, demonstrations, worksheets and activities for high school teachers to use in their classrooms. The Ionic Bonds page includes resources for teaching students about ionic bonding.

2011-01-01

437

ChemTeacher: Covalent Bonds  

NSDL National Science Digital Library

ChemTeacher compiles background information, videos, articles, demonstrations, worksheets and activities for high school teachers to use in their classrooms. The Covalent Bonds page includes resources for teaching students about covalent bonding.

2011-01-01

438

C-H...Cl relevant discrepancy on structure, magnetic and electronic conductivity of two mixed-valence Cu{sup I}Cu{sup II} coordination polymers  

SciTech Connect

Two mixed-valence Cu{sup I}Cu{sup II} coordination polymers [Cu{sup I}Cu{sup II}(qdiol)ClL]{sub n} (qdiol{sup 2-}=2,3-dioxyquinoxalinate, L=2,2'-bipyridine, 1; L=1,10-phenanthroline, 2) were obtained in basic ethanolic solution of CuCl{sub 2}, 1,4-dihydro-2,3-quinoxalinedione and L under the solvothermal condition. 1 and 2 are similar in composition, but differ remarkably in structure. The coordination modes of Cu{sup II}, qdiol{sup 2-} and L are identical in both complexes. But the Cu{sup I} ions are two- and three-coordinated, and the Cl{sup -} ions are terminal and bridging, in 1 and 2, respectively, which are relevant to the significantly different C-H...Cl hydrogen bonding pattern of bpy and phen. The temperature variable magnetic susceptibilities show that 1 is paramagnetic and 2 is weakly antiferromagnetic. The complex impedance spectroscopic studies indicate that both 1 and 2 are semiconductors and 2 is more conducting. - Graphical Abstract: Subtly different C-H...Cl bonding nature leads to diverse coordination modes and supramolecular networks, as well as physical properties of two Cu{sup I}Cu{sup II} coordination polymers with similar compositions. Highlights: > Two new Cu(I)-Cu(II) mixed-valence coordination polymers are obtained. > Environments of Cu(I) and Cl are different caused by C-H...Cl H-bonding. > Supramolecular networks are hence diverse. > Magnetic and semiconducting properties are influenced by the structures.

Shi Ling [School of Chemistry and Environment, South China Normal University, Guangzhou 510006 (China); Yang Ping [School of Chemistry and Environment, South China Normal University, Guangzhou 510006 (China); School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou 510631 (China); Huang Guang; Li Qian [School of Chemistry and Environment, South China Normal University, Guangzhou 510006 (China); Wang Ning [Research Institute of Tsinghua University in Shenzhen, Shenzhen 518055 (China); Wu Jianzhong, E-mail: wujzh@scnu.edu.cn [School of Chemistry and Environment, South China Normal University, Guangzhou 510006 (China); Yu Ying [School of Chemistry and Environment, South China Normal University, Guangzhou 510006 (China)

2011-07-15

439

Characterization of CF bonds with multiple-bond character: bond lengths, stretching force constants, and bond dissociation energies.  

PubMed

Isoelectronic C=F(+) and C=O bonds contained in fluoro-substituted carbenium ions, aldehydes, and ketones are investigated with regard to their bond properties by utilizing the vibrational spectra of these molecules. It is demonstrated that bond dissociation energies (BDEs), bond lengths, vibrational stretching frequencies, and bond densities are not reliable descriptors of the bond strength. The latter is related to the intrinsic BDE, which corresponds to nonrelaxed dissociation products retaining the electronic structure and geometry they have in the molecule. It is shown that the harmonic stretching force constants k(a) of the localized internal coordinate vibrations (adiabatic vibrational modes) reflect trends in the intrinsic BDEs. The k(a) values of both CO and CF bonds are related to the bond lengths through a single exponential function. This observation is used to derive a common bond order n for 46 CO- and CF-containing molecules that reliably describes differences in bonding. CF bonds in fluorinated carbenium ions possess bond orders between 1.3 and 1.7 as a result of significant pi back-bonding from F to C, which is sensitive to electronic effects caused by substituents at the carbenium center. Therefore, the strength of the C=F(+) bond can be used as a sensor for (hyper)conjugation and other electronic effects influencing the stability of the carbenium ion. The diatomic C=F(+) ion has a true double bond due to pi donation from the F atom. The characterization of CF bonds with the help of adiabatic stretching modes is also applied to fluoronium ions (n = 0.3-0.6) and transition states involving CF cleavage and HF elimination (n = 0.7-0.8). PMID:19152353

Kraka, Elfi; Cremer, Dieter

2009-03-01

440

Bounded Analytic Bond-Order Potentials for ? and ? Bonds  

NASA Astrophysics Data System (ADS)

Novel analytic bond-order potentials (BOP's) are derived for the ? and ? bonds of sp-valent systems that are correctly bounded from above by unity. We show that these BOP's allow the concept of single, double, triple, and conjugate bonds in carbon systems to be quantified, the average error compared to accurate tight-binding predictions being only 1% for the ? bonds and 15% for the ? bonds. Although molecular dynamics simulations are an order of magnitude slower than with standard Tersoff potentials, these new BOP's provide the first ``classical'' interatomic potentials that handle both structural differentiation and radical formation naturally within its framework.

Pettifor, D. G.; Oleinik, I. I.