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Sample records for valence bond vb

  1. Valence-Bond Theory and Chemical Structure.

    ERIC Educational Resources Information Center

    Klein, Douglas J.; Trinajstic, Nenad

    1990-01-01

    Discussed is the importance of valence bond theory on the quantum-mechanical theory of chemical structure and the nature of the chemical bond. Described briefly are early VB theory, development of VB theory, modern versions, solid-state applications, models, treatment in textbooks, and flaws in criticisms of valence bond theory. (KR)

  2. The Valence Bond Interpretation of Molecular Geometry.

    ERIC Educational Resources Information Center

    Smith, Derek W.

    1980-01-01

    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)

  3. Chemical Bonding: The Orthogonal Valence-Bond View

    PubMed Central

    Sax, Alexander F.

    2015-01-01

    Chemical bonding is the stabilization of a molecular system by charge- and spin-reorganization processes in chemical reactions. These processes are said to be local, because the number of atoms involved is very small. With multi-configurational self-consistent field (MCSCF) wave functions, these processes can be calculated, but the local information is hidden by the delocalized molecular orbitals (MO) used to construct the wave functions. The transformation of such wave functions into valence bond (VB) wave functions, which are based on localized orbitals, reveals the hidden information; this transformation is called a VB reading of MCSCF wave functions. The two-electron VB wave functions describing the Lewis electron pair that connects two atoms are frequently called covalent or neutral, suggesting that these wave functions describe an electronic situation where two electrons are never located at the same atom; such electronic situations and the wave functions describing them are called ionic. When the distance between two atoms decreases, however, every covalent VB wave function composed of non-orthogonal atomic orbitals changes its character from neutral to ionic. However, this change in the character of conventional VB wave functions is hidden by its mathematical form. Orthogonal VB wave functions composed of orthonormalized orbitals never change their character. When localized fragment orbitals are used instead of atomic orbitals, one can decide which local information is revealed and which remains hidden. In this paper, we analyze four chemical reactions by transforming the MCSCF wave functions into orthogonal VB wave functions; we show how the reactions are influenced by changing the atoms involved or by changing their local symmetry. Using orthogonal instead of non-orthogonal orbitals is not just a technical issue; it also changes the interpretation, revealing the properties of wave functions that remain otherwise undetected. PMID:25906476

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

    ERIC Educational Resources Information Center

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

    2008-01-01

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

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

    ERIC Educational Resources Information Center

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

    2008-01-01

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

  6. Recasting wave functions into valence bond structures: A simple projection method to describe excited states.

    PubMed

    Racine, Julien; Hagebaum-Reignier, Denis; Carissan, Yannick; Humbel, Stphane

    2016-03-30

    A method is proposed to obtain coefficients and weights of valence bond (VB) determinants from multi configurational wave functions. This reading of the wave functions can apply to ground states as well as excited states. The method is based on projection operators. Both energetic and overlap-based criteria are used to assess the quality of the resulting VB wave function. The approach gives a simple access to a VB rewriting for low-lying states, and it is applied to the allyl cation, to the allyl radical and to the ethene (notably to the V-state). For these states, large overlap between VB and multi reference wave functions are easily obtained. The approach proves to be useful to propose an interpretation of the nature of the V-state of ethene. 2015 Wiley Periodicals, Inc. PMID:26786547

  7. Generalized resonating valence bond description of cyclobutadiene

    SciTech Connect

    Voter, A.F.; Goddard, W.A. III

    1986-05-28

    The low-lying electronic states of square and rectangular cyclobutadiene (CBD) are calculated by using the generalized resonating valence bond (GRVB) method and compared with the results from Hartree-Fock and configuration interaction wavefunctions. We find that simple valence bond concepts correctly predict the sequence of excited states (including ground-state singlet) and the distortion to a rectangular geometry for the ground state. Contrary to common expectation, we find that the singlet ground state of square CBD has 22 kcal of resonance energy (relative to a single valence bond structure). Thus, CBD is not antiresonant, though it is much less stable than normal conjugated systems.

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

    PubMed

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

    2014-07-21

    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

  9. When valence bond wave functions are analyzed through QTAIM: Conceptual incompatibilities in H2

    NASA Astrophysics Data System (ADS)

    Ferro-Costas, David; Mosquera, Ricardo A.

    2015-01-01

    Hydrogen molecule was chosen, for simplicity, to analyze its valence bond (VB) wave function with the Quantum Theory of Atoms in Molecules (QTAIM). We find that the usual association of its covalent and ionic contributions to individual Lewis structures does not agree with the localization and delocalization indices between both hydrogens defined within the QTAIM framework. Concretely, we analyzed the dependence of both indices with the internuclear distance and with different ionic/covalent relative weightings. The results indicate that QTAIM localization and delocalization indices should not be estimated from interpretations of the VB wave function in terms of the Lewis model.

  10. 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

    Halpern, Arthur M.; Glendening, Eric D.

    2013-01-01

    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

  11. 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

    Halpern, Arthur M.; Glendening, Eric D.

    2013-01-01

    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…

  12. 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)

    Chen, Zhenhua; Chen, Xun; Wu, Wei

    2013-04-01

    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.

  13. 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

    Chen, Zhenhua; Chen, Xun; Wu, Wei

    2013-04-28

    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

  14. Physics of Resonating Valence Bond Spin Liquids

    NASA Astrophysics Data System (ADS)

    Wildeboer, Julia Saskia

    This thesis will investigate various aspects of the physics of resonating valence bond spin liquids. After giving an introduction to the world that lies beyond Landau's priciple of symmetry breaking, e.g. giving an overview of exotic magnetic phases and how they can be described and (possibly) found, we will study a spin-rotationally invariant model system with a known parent Hamiltonian, and argue its ground state to lie within a highly sought after exotic phase, namely the Z2 quantum spin liquid phase. A newly developed numerical procedure --Pfaffian Monte Carlo-- will be introduced to amass evidence that our model Hamiltonian indeed exhibits a Z2 quantum spin liquid phase. Subsequently, we will prove a useful mathematical property of the resonating valence bond states: these states are shown to be linearly independent. Various lattices are investigated concerning this property, and its applications and usefullness are discussed. Eventually, we present a simplified model system describing the interplay of the well known Heisenberg interaction and the Dzyaloshinskii-Moriya (DM) interaction term acting on a sawtooth chain. The effect of the interplay between the two interaction couplings on the phase diagram is investigated. To do so, we employ modern techniques such as the density matrix renormalization group (DMRG) scheme. We find that for weak DM interaction the system exhibits valence bond order. However, a strong enough DM coupling destroys this order.

  15. The variational subspace valence bond method

    SciTech Connect

    Fletcher, Graham D.

    2015-04-07

    The variational subspace valence bond (VSVB) method based on overlapping orbitals is introduced. VSVB provides variational support against collapse for the optimization of overlapping linear combinations of atomic orbitals (OLCAOs) using modified orbital expansions, without recourse to orthogonalization. OLCAO have the advantage of being naturally localized, chemically intuitive (to individually model bonds and lone pairs, for example), and transferrable between different molecular systems. Such features are exploited to avoid key computational bottlenecks. Since the OLCAO can be doubly occupied, VSVB can access very large problems, and calculations on systems with several hundred atoms are presented.

  16. The variational subspace valence bond method

    NASA Astrophysics Data System (ADS)

    Fletcher, Graham D.

    2015-04-01

    The variational subspace valence bond (VSVB) method based on overlapping orbitals is introduced. VSVB provides variational support against collapse for the optimization of overlapping linear combinations of atomic orbitals (OLCAOs) using modified orbital expansions, without recourse to orthogonalization. OLCAO have the advantage of being naturally localized, chemically intuitive (to individually model bonds and lone pairs, for example), and transferrable between different molecular systems. Such features are exploited to avoid key computational bottlenecks. Since the OLCAO can be doubly occupied, VSVB can access very large problems, and calculations on systems with several hundred atoms are presented.

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

    ERIC Educational Resources Information Center

    Magnasco, Valerio

    2008-01-01

    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…

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

    ERIC Educational Resources Information Center

    Magnasco, Valerio

    2008-01-01

    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

  19. Charge-Shift Bonding Emerges as a Distinct Electron-Pair Bonding Family from Both Valence Bond and Molecular Orbital Theories.

    PubMed

    Zhang, Huaiyu; Danovich, David; Wu, Wei; Brada, Benot; Hiberty, Philippe C; Shaik, Sason

    2014-06-10

    The charge-shift bonding (CSB) concept was originally discovered through valence bond (VB) calculations. Later, CSB was found to have signatures in atoms-in-molecules and electron-localization-function and in experimental electron density measurements. However, the CSB concept has never been derived from a molecular orbital (MO)-based theory. We now provide a proof of principle that an MO-based approach enables one to derive the CSB family alongside the distinctly different classical family of covalent bonds. In this bridging energy decomposition analysis, the covalent-ionic resonance energy, RECS, of a bond is extracted by cloning an MO-based purely covalent reference state, which is a constrained two-configuration wave function. The energy gap between this reference state and the variational TCSCF ground state yields numerical values for RECS, which correlate with the values obtained at the VBSCF level. This simple MO-based method, which only takes care of static electron correlation, is already sufficient for distinguishing the classical covalent or polar-covalent bonds from charge-shift bonds. The equivalence of the VB and MO-based methods is further demonstrated when both methods are augmented by dynamic correlation. Thus, it is shown from both MO and VB perspectives that the bonding in the CSB family does not arise from electron correlation. Considering that the existence of the CSB family is associated also with quite a few experimental observations that we already reviewed ( Shaik , S. , Danovich , D. , Wu , W. , and Hiberty , P. C. Nat. Chem. , 2009 , 1 , 443 - 449 ), the new bonding concept has passed by now two stringent tests. This derivation, on the one hand, supports the new concept and on the other, it creates bridges between the two main theories of electronic structure. PMID:26580761

  20. Three-Electron Bond Valence-Bond Structures for the Ditetracyanoethylene Dianion.

    PubMed

    Harcourt, Richard D

    2015-05-12

    Using valence-bond structures of the types ? ? and A?B or A-?B to represent diatomic three-electron bonds, two types of valence-bond structures are constructed for the cyclic 6-electron 4-center bonding unit that is present in the ditetracyanoethylene dianion. These latter valence-bond structures, which are obtained by singlet spin-pairing the antibonding electrons of two three-electron bonds, are examples of increased-valence structures. It is shown that increased-valence structures that use the ? ? three-electron bond structure, which relate easily to their component Lewis structures, should be preferred to those that involve the A?B or A-?B three-electron bond structures. STO-6G weights are reported for the two 6-electron 4-center increased-valence structures for the [C2]2(2-) component of the ditetracyanoethylene dianion. PMID:26574402

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

    ERIC Educational Resources Information Center

    Pauling, Linus; Herman, Zelek S.

    1984-01-01

    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)

  2. Valence-bond theory of compounds of transition metals

    PubMed Central

    Pauling, Linus

    1975-01-01

    An equation relating the strength (bondforming power) of an spd hybrid bond orbital to the angles it makes with other bond orbitals is formulated and applied in the discussion of the structures of transition-metal carbonyls and other substances by the valence-bond method. The rather simple theory gives results that agree well with those obtained by the complicated and laborious calculation of sets of orthogonal hybrid bond orbitals with maximum strength. PMID:16592279

  3. A valence bond study of the Bergman cyclization: geometric features, resonance energy, and nucleus-independent chemical shift (NICS) values

    PubMed

    Galbraith; Schreiner; Harris; Wei; Wittkopp; Shaik

    2000-04-14

    The Bergman cyclization of (Z)-hex-3-ene-1,5-diynes (1, enediynes), which produces pharmacologically important DNA-cleaving biradicals (1,4-benzyne, 2), was studied by using Hartree-Fock (HF) and density-functional theory (DFT) based valence bond (VB) methods (VB-HF and VB-DFT, respectively). We found that only three VB configurations are needed to arrive at results not too far from complete active space [CASSCF(6 x 6)] computations, while the quality of VB-DTF utilizing the same three configurations improves upon CASSCF(6 x 6) analogous to CASPT2. The dominant VB configuration in 1 contributes little to 2, while the most important biradical configuration in 2 plays a negligible role in 1. The avoided crossing of the energy curves of these two configurations along the reaction coordinate leads to the transition state (TS). As a consequence of the shape and position of the crossing section, the changes in geometry and in the electronic wavefunction along the reaction coordinate are non-synchronous; the TS is geometrically approximately 80% product-like and electronically approximately 70% reactant-like. While the pi resonance in the TS is very small, it is large (64.4 kcal mol(-1)) for 2 (cf. benzene=61.5 kcal mol(-1)). As a consequence, substituents operating on the sigma electrons should be much more effective in changing the Bergman reaction cyclization barrier. Furthermore, additional sigma resonance in 2 results in unusually high values for the nucleus-independent chemical shift (NICS, a direct measure for aromaticity). Similarly, the high NICS value of the TS is due mostly to sigma resonance to which the NICS procedure is relatively sensitive. PMID:10840967

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

    SciTech Connect

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

    2006-08-15

    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.

  5. Extended quantum dimer model and novel valence-bond phases

    NASA Astrophysics Data System (ADS)

    Nakata, Kouki; Totsuka, Keisuke

    2011-01-01

    We extend the quantum dimer model (QDM) introduced by Rokhsar and Kivelson so as to construct a concrete example of the model which exhibits the first-order phase transition between different valence-bond solids suggested recently by Batista and Trugman and look for the possibility of other exotic dimer states. We show that our model contains three exotic valence-bond phases (herringbone, checkerboard and dimer smectic) in the ground-state phase diagram and that it realizes the phase transition from the staggered valence-bond solid to the herringbone. The checkerboard phase has four-fold rotational symmetry, while the dimer smectic, in the absence of quantum fluctuations, has massive degeneracy originating from partial ordering only in one of the two spatial directions. A resonance process involving three dimers resolves this massive degeneracy and the dimer smectic becomes ordered (order from disorder).

  6. Two states are not enough: quantitative evaluation of the valence-bond intramolecular charge-transfer model and its use in predicting bond length alternation effects.

    PubMed

    Jarowski, Peter D; Mo, Yirong

    2014-12-15

    The structural weights of the canonical resonance contributors used in the Two-state valence-bond charge-transfer model, neutral (N, R1) and ionic (VB-CT, R2), to the ground states and excited states of a series of linear dipolar intramolecular charge-transfer chromophores containing a buta-1,3-dien-1,4-diyl bridge have been computed by using the block-localized wavefunction (BLW) method at the B3LYP/6-311+G(d) level to provide the first quantitative assessment of this simple model. Ground- and excited-state analysis reveals surprisingly low ground-state structural weights for the VB-CT resonance form using either this Two-state model or an expanded Ten-state model. The VB-CT state is found to be more prominent in the excited state. Individual resonance forms were structurally optimized to understand the origins of the bond length alternation (BLA) of the bridging unit. Using a Wheland energy-based weighting scheme, the weighted average of the optimized bond lengths with the Two-state model was unable to reproduce the BLA features with values 0.04 to 0.02? too large compared to the fully delocalized (FD) structure (BLW: ca. -0.13 to -0.07?, FD: ca. -0.09 to -0.05?). Instead, an expanded Ten-state model fit the BLA values of the FD structure to within only 0.001? of FD. PMID:25338915

  7. 1D valence bond solids in a magnetic field

    NASA Astrophysics Data System (ADS)

    Iaizzi, Adam; Sandvik, Anders W.

    2015-09-01

    A Valence bond solid (VBS) is a nonmagnetic, long-range ordered state of a quantum spin system where local spin singlets are formed in some regular pattern. We here study the competition between VBS order and a fully polarized ferromagnetic state as function of an external magnetic field in a one-dimensional extended Heisenberg model—the J-Q2 model— using stochastic series expansion (SSE) quantum Monte Carlo simulations with directed loop updates. We discuss the ground state phase diagram.

  8. Valence-bond quantum Monte Carlo algorithms defined on trees.

    PubMed

    Deschner, Andreas; Srensen, Erik S

    2014-09-01

    We present a class of algorithms for performing valence-bond quantum Monte Carlo of quantum spin models. Valence-bond quantum Monte Carlo is a projective T=0 Monte Carlo method based on sampling of a set of operator strings that can be viewed as forming a treelike structure. The algorithms presented here utilize the notion of a worm that moves up and down this tree and changes the associated operator string. In quite general terms, we derive a set of equations whose solutions correspond to a whole class of algorithms. As specific examples of this class of algorithms, we focus on two cases. The bouncing worm algorithm, for which updates are always accepted by allowing the worm to bounce up and down the tree, and the driven worm algorithm, where a single parameter controls how far up the tree the worm reaches before turning around. The latter algorithm involves only a single bounce where the worm turns from going up the tree to going down. The presence of the control parameter necessitates the introduction of an acceptance probability for the update. PMID:25314561

  9. Nonorthogonal orbital based N-body reduced density matrices and their applications to valence bond theory. IV. The automatic implementation of the Hessian based VBSCF method

    NASA Astrophysics Data System (ADS)

    Chen, Xun; Chen, Zhenhua; Wu, Wei

    2014-11-01

    In this paper, the Hessian matrix of valence bond (VB) self-consistent field (VBSCF) energy with respect to orbitals are evaluated by applying the nonorthogonal orbital based N-body reduced density matrices, which was presented in Paper I. To this end, an automatic formula/code generator (AFCG) is developed; with which the matrix elements between internally contracted excited configurations of VB wave function and the corresponding codes are generated automatically. Compared to the tedious manual formula deducing and implementing, AFCG is much more convenient and efficient, and enables us to avoid troublesome debugging. With the help of AFCG, the Hessian-based Newton-Raphson algorithm is implemented for the VBSCF orbital optimization. Test calculations indicate that the Newton-Raphson algorithm converges quadratically and has much better convergence behavior than the gradient-based LBFGS algorithms. Furthermore, a combined approach with LBFGS and Newton-Raphson algorithms is applied to reduce the total CPU time of the calculation.

  10. Mesoscopic resonating valence bond system on a triple dot.

    PubMed

    Le Hur, Karyn; Recher, Patrik; Dupont, Emilie; Loss, Daniel

    2006-03-17

    We theoretically introduce a mesoscopic pendulum from a triple dot. The pendulum is fastened through a singly occupied dot (spin qubit). Two other strongly capacitively coupled islands form a double-dot charge qubit with one electron in excess oscillating between the two low-energy charge states (1,0) and (0,1). The triple dot is placed between two superconducting leads. Under realistic conditions, the main proximity effect stems from the injection of resonating singlet (valence) bonds on the triple dot. This gives rise to a Josephson current that is charge- and spin-dependent and, as a consequence, exhibits a distinct resonance as a function of the superconducting phase difference. PMID:16605773

  11. Resonating Valence Bond states for low dimensional S=1 antiferromagnets

    NASA Astrophysics Data System (ADS)

    Liu, Zheng-Xin; Zhou, Yi; Ng, Tai-Kai

    2014-03-01

    We study S = 1 spin liquid states in low dimensions. We show that the resonating-valence-bond (RVB) picture of S = 1 / 2 spin liquid state can be generalized to S = 1 case. For S = 1 system, a many-body singlet (with even site number) can be decomposed into superposition of products of two-body singlets. In other words, the product states of two-body singlets, called the singlet pair states (SPSs), are over complete to span the Hilbert space of many-body singlets. Furthermore, we generalized fermionic representation and the corresponding mean field theory and Gutzwiller projected stats to S = 1 models. We applied our theory to study 1D anti-ferromagnetic bilinear-biquadratic model and show that both the ground states (including the phase transition point) and the excited states can be understood excellently well within the framework. Our method can be applied to 2D S = 1 antiferromagnets.

  12. Molecular orbital study of the bond-valence sum rule using Lewis-electron pair theory.

    PubMed

    Mohri, Fumihito

    2003-04-01

    The bond-valence sum rule has been examined by molecular-orbital methods related to spin-coupling matrix theory [Okada & Fueno (1976). Bull. Chem. Soc. Jpn, 49, 1524-1530], to give a new formulation of the Lewis-electron pair concept. It is shown that the 'pair-coupling population' between atoms M and X exhibits the same behaviour as the bond valence between them. A quantum chemical definition for bond valence is proposed and successfully applied to Al(2)Cl(6), Te(4)Cl(16) and Al(2)Be(3)(SiO(3))(6) (beryl). Using an alternative bond-valence definition it is shown that for oxides the bond valence can possibly be taken as the double pair-coupling population. PMID:12657813

  13. Valence bond phases in S = 1/2 Kane-Mele-Heisenberg model

    NASA Astrophysics Data System (ADS)

    Zare, Mohammad H.; Mosadeq, Hamid; Shahbazi, Farhad; Jafari, S. A.

    2014-11-01

    The phase diagram of the Kane-Mele-Heisenberg model in a classical limit [47] contains disordered regions in the coupling space, as the result of competition between different terms in the Hamiltonian, leading to frustration in finding a unique ground state. In this work we explore the nature of these phases in the quantum limit, for a S = 1/2. Employing exact diagonalization in Sz and nearest neighbour valence bond bases, and bond and plaquette valence bond mean field theories, we show that the disordered regions are divided into ordered quantum states in the form of plaquette valence bond crystals and staggered dimerized phases.

  14. Order Parameter to Characterize Valence-Bond-Solid States in Quantum Spin Chains

    NASA Astrophysics Data System (ADS)

    Nakamura, Masaaki; Todo, Synge

    2003-03-01

    We propose an order parameter to characterize valence-bond-solid (VBS) states in quantum spin chains, given by the ground-state expectation value of a unitary operator appearing in the Lieb-Schultz-Mattis argument. We show that the order parameter changes the sign according to the number of valence bonds (broken valence bonds) at the boundary for periodic (open) systems. This allows us to determine the phase transition point in between different VBS states. We demonstrate this theory in the successive dimerization transitions of the bond-alternating Heisenberg chains and spin ladders using the quantum Monte Carlo method.

  15. Valence bond solid (AKLT) state from t2 g electrons

    NASA Astrophysics Data System (ADS)

    Koch-Janusz, Maciej; Khomskii, Daniel; Sela, Eran

    2015-03-01

    The models constructed by Affleck, Kennedy, Lieb, and Tasaki (AKLT) describe gapped quantum spin liquids with fractionalized boundary spin excitations. The AKLT spin-spin interactions consist of projection operators onto the maximal possible spin formed between nearest neighbours, which involves a linear combination of powers of the Heisenberg coupling (S-->i .S-->j) n, making these states difficult to realize. Indeed, except for the one dimensional spin-1 case, simple antiferromagnetic Heisenberg interactions which are typically found in magnetic insulators, do not stabilize these spin liquid states, but rather generate conventional antiferromagnetically ordered states. We show that this type of interactions can be generated by orbital physics in multiorbital Mott insulators. Motivated by microscopic modeling of spin-orbit entangled Mott insulators such as the layered hexagonal Iridates, we focus on t2 g electrons on the honeycomb lattice and propose a physical realization of the spin- 3 / 2 AKLT state. Interestingly enough, the valence bond solid (AKLT) state found for the noninteracting electrons survives the increase of the on-site (Hubbard) repulsion, but it changes to the antiferromagnetic Neel state with increase of the Hund's rule coupling.

  16. Resonating-Valence-Bond Liquid in Low Dimensions

    NASA Astrophysics Data System (ADS)

    Ohkawa, Fusayoshi J.

    2014-12-01

    The Hubbard model in D dimensions, with the on-site repulsion U and the transfer integral between nearest neighbors - t/sqrt{D} , is studied on the basis of the Kondo-lattice theory. If U/|t| ? 1, |n - 1| ? |t|/(DU), where n is the number of electrons per unit cell, and D is so small that |J|/D ? kBTc, where J = -4t2/U and Tc is 0 K for D = 1 and is the highest critical temperature among possible ones for D ? 2, a low-T phase where Tc < T ? |J|/(kBD) is a frustrated electron liquid. Since the liquid is stabilized by the Kondo effect in conjunction with the resonating-valence-bond (RVB) mechanism, it is simply the RVB electron liquid; in one dimension, it is also the Tomonaga-Luttinger liquid. The Kondo energy of the RVB liquid is kBTK = O(|J|/D); its effective Fermi energy is O(kBTK). A midband appears on the chemical potential between the upper and lower Hubbard bands; the Hubbard gap is a pseudogap. As regards the density of states per unit cell of the midband, its bandwidth is O(kBTK) or O(|J|/D), its peak height is O(1/U), and its spectral weight is O[t2/(DU2)]. Since the midband almost disappears in the Heisenberg limit, the RVB electron liquid in the Heisenberg limit is simply the RVB spin liquid. The RVB electron and spin liquids adiabatically continue to each other. Since local moments form in a high-T phase where T ? TK, the high-T phase is simply the Mott insulator.

  17. Comprehensive derivation of bond-valence parameters for ion pairs involving oxygen.

    PubMed

    Gagn, Olivier Charles; Hawthorne, Frank Christopher

    2015-10-01

    Published two-body bond-valence parameters for cation-oxygen bonds have been evaluated via the root mean-square deviation (RMSD) from the valence-sum rule for 128 cations, using 180,194 filtered bond lengths from 31,489 coordination polyhedra. Values of the RMSD range from 0.033-2.451?v.u. (1.1-40.9% per unit of charge) with a weighted mean of 0.174?v.u. (7.34% per unit of charge). The set of best published parameters has been determined for 128 ions and used as a benchmark for the determination of new bond-valence parameters in this paper. Two common methods for the derivation of bond-valence parameters have been evaluated: (1) fixing B and solving for R(o); (2) the graphical method. On a subset of 90 ions observed in more than one coordination, fixing B at 0.37? leads to a mean weighted-RMSD of 0.139?v.u. (6.7% per unit of charge), while graphical derivation gives 0.161?v.u. (8.0% per unit of charge). The advantages and disadvantages of these (and other) methods of derivation have been considered, leading to the conclusion that current methods of derivation of bond-valence parameters are not satisfactory. A new method of derivation is introduced, the GRG (generalized reduced gradient) method, which leads to a mean weighted-RMSD of 0.128?v.u. (6.1% per unit of charge) over the same sample of 90 multiple-coordination ions. The evaluation of 19 two-parameter equations and 7 three-parameter equations to model the bond-valence-bond-length relation indicates that: (1) many equations can adequately describe the relation; (2) a plateau has been reached in the fit for two-parameter equations; (3) the equation of Brown & Altermatt (1985) is sufficiently good that use of any of the other equations tested is not warranted. Improved bond-valence parameters have been derived for 135 ions for the equation of Brown & Altermatt (1985) in terms of both the cation and anion bond-valence sums using the GRG method and our complete data set. PMID:26428406

  18. Comprehensive derivation of bond-valence parameters for ion pairs involving oxygen

    PubMed Central

    Gagné, Olivier Charles; Hawthorne, Frank Christopher

    2015-01-01

    Published two-body bond-valence parameters for cation–oxygen bonds have been evaluated via the root mean-square deviation (RMSD) from the valence-sum rule for 128 cations, using 180 194 filtered bond lengths from 31 489 coordination polyhedra. Values of the RMSD range from 0.033–2.451 v.u. (1.1–40.9% per unit of charge) with a weighted mean of 0.174 v.u. (7.34% per unit of charge). The set of best published parameters has been determined for 128 ions and used as a benchmark for the determination of new bond-valence parameters in this paper. Two common methods for the derivation of bond-valence parameters have been evaluated: (1) fixing B and solving for R o; (2) the graphical method. On a subset of 90 ions observed in more than one coordination, fixing B at 0.37 Å leads to a mean weighted-RMSD of 0.139 v.u. (6.7% per unit of charge), while graphical derivation gives 0.161 v.u. (8.0% per unit of charge). The advantages and disadvantages of these (and other) methods of derivation have been considered, leading to the conclusion that current methods of derivation of bond-valence parameters are not satisfactory. A new method of derivation is introduced, the GRG (generalized reduced gradient) method, which leads to a mean weighted-RMSD of 0.128 v.u. (6.1% per unit of charge) over the same sample of 90 multiple-coordination ions. The evaluation of 19 two-parameter equations and 7 three-parameter equations to model the bond-valence–bond-length relation indicates that: (1) many equations can adequately describe the relation; (2) a plateau has been reached in the fit for two-parameter equations; (3) the equation of Brown & Altermatt (1985 ▸) is sufficiently good that use of any of the other equations tested is not warranted. Improved bond-valence parameters have been derived for 135 ions for the equation of Brown & Altermatt (1985 ▸) in terms of both the cation and anion bond-valence sums using the GRG method and our complete data set. PMID:26428406

  19. Valence-Bond Crystal and Anisotropic Excitation Spectrum on 3-Dimensionally Frustrated Pyrochlore

    NASA Astrophysics Data System (ADS)

    Isoda, Makoto; Mori, Shigeyoshi

    1998-12-01

    The valence-bond crystal is proposed as a ground state of spin-1/2Heisenberg antiferromagnet on 3-dimensional fully frustrated pyrochlore bythe bond-operator theory. This crystal, formed as a set of RVB-liketetrahedral singlet states, has lower energy than the state consisting oftwo dimers in a tetrahedron. The spectra of triplet excitation have afinite gap and a symmetry lower than that of the lattice. The comparisonwith Y(Sc)Mn2 is discussed.

  20. Nature of the chemical bond and origin of the inverted dipole moment in boron fluoride: a generalized valence bond approach.

    PubMed

    Fantuzzi, Felipe; Cardozo, Thiago Messias; Nascimento, Marco Antonio Chaer

    2015-05-28

    The generalized product function energy partitioning (GPF-EP) method has been applied to investigate the nature of the chemical bond and the origin of the inverted dipole moment of the BF molecule. The calculations were carried out with GPF wave functions treating all of the core electrons as a single Hartree-Fock group and the valence electrons at the generalized valence bond perfect-pairing (GVB-PP) or full GVB levels, with the cc-pVTZ basis set. The results show that the chemical structure of both X (1)?(+) and a (3)? states is composed of a single bond. The lower dissociation energy of the excited state is attributed to a stabilizing intraatomic singlet coupling involving the B 2sp-like lobe orbitals after bond dissociation. An increase of electron density on the B atom caused by the reorientation of the boron 2sp-like lobe orbitals is identified as the main responsible effect for the electric dipole inversion in the ground state of BF. Finally, it is shown that ? back-bonding from fluorine to boron plays a minor role in the electron density displacement to the bonding region in both states. Moreover, this effect is associated with changes in the quasi-classical component of the electron density only and does not contribute to covalency in either of the states. Therefore, at least for the case of the BF molecule, the term back-bonding is misleading, since it does not contribute to the bond formation. PMID:25531385

  1. Oxidative bond formation and reductive bond cleavage at main group metal centers: reactivity of five-valence-electron MX? radicals.

    PubMed

    Protchenko, Andrey V; Dange, Deepak; Blake, Matthew P; Schwarz, Andrew D; Jones, Cameron; Mountford, Philip; Aldridge, Simon

    2014-08-01

    Monomeric five-valence-electron bis(boryl) complexes of gallium, indium, and thallium undergo oxidative M-C bond formation with 2,3-dimethylbutadiene, in a manner consistent with both the redox properties expected for M(II) species and with metal-centered radical character. The weaker nature of the M-C bond for the heavier two elements leads to the observation of reversibility in M-C bond formation (for indium) and to the isolation of products resulting from subsequent B-C reductive elimination (for both indium and thallium). PMID:25036798

  2. Insights into the Electronic Structure of Molecules from Generalized Valence Bond Theory.

    PubMed

    Dunning, Thom H; Xu, Lu T; Takeshita, Tyler Y; Lindquist, Beth A

    2016-03-24

    In this article we describe the unique insights into the electronic structure of molecules provided by generalized valence bond (GVB) theory. We consider selected prototypical hydrocarbons as well as a number of hypervalent molecules and a set of first- and second-row valence isoelectronic species. The GVB wave function is obtained by variationally optimizing the orbitals and spin coupling in the valence bond wave function. The GVB wave function is a generalization of the Hartree-Fock (HF) wave function, lifting the double occupancy restriction on a subset of the HF orbitals as well as the associated orthogonality and spin coupling constraints. The GVB wave function includes a major fraction (if not all) of the nondynamical correlation energy of a molecule. Because of this, GVB theory properly describes bond formation and can answer one of the most compelling questions in chemistry: How are atoms changed by molecular formation? We show that GVB theory provides a unified description of the nature of the bonding in all of the above molecular species as well as contributing new insights into the well-known, but poorly understood, first-row anomaly. PMID:26909685

  3. Resonating-Valence-Bond Physics Is Not Always Governed by the Shortest Tunneling Loops

    NASA Astrophysics Data System (ADS)

    Ralko, Arnaud; Rousochatzakis, Ioannis

    2015-10-01

    It is well known that the low-energy sector of quantum spin liquids and other magnetically disordered systems is governed by short-ranged resonating-valence bonds. Here we show that the standard minimal truncation to the nearest-neighbor valence-bond basis fails completely even for systems where it should work the most, according to received wisdom. This paradigm shift is demonstrated for the quantum spin-1 /2 square kagome, where strong geometric frustration, similar to the kagome, prevents magnetic ordering down to zero temperature. The shortest tunneling events bear the strongest longer-range singlet fluctuations, leading to amplitudes that do not drop exponentially with the length of the loop L , and to an unexpected loop-six valence-bond crystal, which is otherwise very high in energy at the minimal truncation level. The low-energy effective description gives in addition a clear example of correlated loop processes that depend not only on the type of the loop but also on its lattice embedding, a direct manifestation of the long-range nature of the virtual singlets.

  4. Resonating-Valence-Bond Physics Is Not Always Governed by the Shortest Tunneling Loops.

    PubMed

    Ralko, Arnaud; Rousochatzakis, Ioannis

    2015-10-16

    It is well known that the low-energy sector of quantum spin liquids and other magnetically disordered systems is governed by short-ranged resonating-valence bonds. Here we show that the standard minimal truncation to the nearest-neighbor valence-bond basis fails completely even for systems where it should work the most, according to received wisdom. This paradigm shift is demonstrated for the quantum spin-1/2 square kagome, where strong geometric frustration, similar to the kagome, prevents magnetic ordering down to zero temperature. The shortest tunneling events bear the strongest longer-range singlet fluctuations, leading to amplitudes that donot drop exponentially with the length of the loop L, and to an unexpected loop-six valence-bond crystal, which is otherwise very high in energy at the minimal truncation level. The low-energy effective description gives in addition a clear example of correlated loop processes that depend not only on the type of the loop but also on its lattice embedding, a direct manifestation of the long-range nature of the virtual singlets. PMID:26550898

  5. Quantum computational capability of a 2D valence bond solid phase

    SciTech Connect

    Miyake, Akimasa

    2011-07-15

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

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

    PubMed Central

    Petersson, G. A.

    1974-01-01

    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. PMID:16592172

  7. Strongly correlated valence electrons and core-level chemical bonding of Lithium at terapascal pressures

    NASA Astrophysics Data System (ADS)

    Hu, Anguang; Zhang, Fan

    2015-03-01

    As the simplest pure metal, lithium exhibits some novel properties on electrical conductivity and crystal structures under high pressure. All-electron density functional theory simulations, recently developed by using the linear combination of localized Slater atomic orbitals, revealed that the bandwidth of its valence bands remains almost unchanged within about 3.5 eV even up to a terapascal pressure range. This indicates that the development from delocalized to strongly correlated electronic systems takes place under compression, resulting in metal-semiconductor and superconductivity transitions together with a sequence of new high-pressure crystal phases, discovered experimentally. In contrast to the valence bands, the core-level bands become broadening up to about 10 eV at terapascal pressures. It means the transformation from chemical non-bonding to bonding for core electrons. Thus, dense lithium under compression can be characterized as core-level chemical bonding and a completely new class of strongly correlated materials with narrow bands filled in s-electron shells only.

  8. Consistent theory of underdoped cuprates: Evolution of the resonating valence bond state from half filling

    NASA Astrophysics Data System (ADS)

    Sarker, Sanjoy K.; Lovorn, Timothy

    2010-07-01

    Using continuity, we derive a renormalized Hamiltonian from the parent t-J model to describe the properties of underdoped cuprates. The theory is constrained to agree with the behavior at half filling, which is well described by the Arovas-Auerbach valence bond state in which bosonic spinons are paired into singlets. Spinon states evolve continuously into the doped region preserving their symmetry. We assume that moving holes rapidly destroy magnetic order, which leads to a gap in the spinon spectrum and strongly renormalizes the theory. The spin gap leads to two different types hopping terms for renormalized holes. In one, a fermionic holon hops within the same sublattice accompanied by a singlet backflow, giving rise to a non-Fermi-liquid normal state with novel properties. Spinon singlets condense below a pseudogap temperature T? ( < spin gap temperature T0 ), which allows holons to propagate coherently, forming a spinless Fermi liquid, but without an observable holon Fermi surface. Above T? , holons are localized. This is the so-called strange metal phase, which is actually a new type of insulator since its resistivity would be infinite at T=0 . In the second term a pair of holons belonging to opposite sublattices hop, accompanied by a singlet backflow. In the presence of the singlet condensate holon pairs condense, leading to d -wave superconductivity; the symmetry is primarily determined by the symmetry of the valence bond state at half filling. The metal and the superconductor preserve the two-sublattice character of the valence bond state. A careful examination of the nuclear magnetic resonance, tunneling, and transport data shows that the predictions of the theory is consistent with experimental results. Remarkably, the existence of the spin gap provides a natural explanation for the phenomenon of two dimensionality of the normal state in the presence of interplane hopping. The marked asymmetry between hole-doped and electron-doped cuprates is also easily explained.

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

    SciTech Connect

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

    2008-05-30

    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).

  10. Competing valence bond and symmetry-breaking Mott states of spin-3/2 fermions on a honeycomb lattice

    NASA Astrophysics Data System (ADS)

    Jakab, D.; Szirmai, E.; Lewenstein, M.; Szirmai, G.

    2016-02-01

    We investigate magnetic properties of strongly interacting four component spin-3/2 ultracold fermionic atoms in the Mott insulator limit with one particle per site in an optical lattice with honeycomb symmetry. In this limit, atomic tunneling is virtual, and only the atomic spins can exchange. We find a competition between symmetry-breaking and liquidlike disordered phases. Particularly interesting are valence bond states with bond centered magnetizations, situated between the ferromagnetic and conventional valence bond phases. In the framework of a mean-field theory, we calculate the phase diagram and identify an experimentally relevant parameter region where a homogeneous SU(4) symmetric Affleck-Kennedy-Lieb-Tasaki-like valence bond state is present.

  11. Complementary method to locate atomic coordinates by combined searching method of structure-sensitive indexes based on bond valence method

    NASA Astrophysics Data System (ADS)

    Song, Zhen; Liu, Xiao-Lang; He, Li-Zhu; Xia, Zhi-Guo; Liu, Quan-Lin

    2015-10-01

    Bond valence method illustrates the relation between valence and length of a particular bond type. This theory has been used to predict structure information, but the effect is very limited. In this paper, two indexes, i.e., global instability index (GII) and bond strain index (BSI), are adopted as a judgment of a search-match program for prediction. The results show that with GII and BSI combined as judgment, the predicted atom positions are very close to real ones. The mechanism and validity of this searching program are also discussed. The GII & BSI distribution contour map reveals that the predicted function is a reflection of exponential feature of bond valence formula. This combined searching method may be integrated with other structure-determination method, and may be helpful in refining and testifying light atom positions. Project supported by the National Natural Science Foundation of China (Grant No. 51272027).

  12. Emergent SO(5) Symmetry at the Néel to Valence-Bond-Solid Transition

    NASA Astrophysics Data System (ADS)

    Nahum, Adam; Serna, P.; Chalker, J. T.; Ortuño, M.; Somoza, A. M.

    2015-12-01

    We show numerically that the "deconfined" quantum critical point between the Néel antiferromagnet and the columnar valence-bond solid, for a square lattice of spin 1 /2 , has an emergent SO(5) symmetry. This symmetry allows the Néel vector and the valence-bond solid order parameter to be rotated into each other. It is a remarkable (2 +1 )-dimensional analogue of the SO (4 )=[SU (2 )×SU (2 )]/Z2 symmetry that appears in the scaling limit for the spin-1 /2 Heisenberg chain. The emergent SO(5) symmetry is strong evidence that the phase transition in the (2 +1 )-dimensional system is truly continuous, despite the violations of finite-size scaling observed previously in this problem. It also implies surprising relations between correlation functions at the transition. The symmetry enhancement is expected to apply generally to the critical two-component Abelian Higgs model (noncompact CP 1 model). The result indicates that in three dimensions there is an SO(5)-symmetric conformal field theory that has no relevant singlet operators, so is radically different from conventional Wilson-Fisher-type conformal field theories.

  13. Empirical valence bond models for reactive potential energy surfaces: A parallel multilevel genetic program approach

    NASA Astrophysics Data System (ADS)

    Bellucci, Michael A.; Coker, David F.

    2011-07-01

    We describe a new method for constructing empirical valence bond potential energy surfaces using a parallel multilevel genetic program (PMLGP). Genetic programs can be used to perform an efficient search through function space and parameter space to find the best functions and sets of parameters that fit energies obtained by ab initio electronic structure calculations. Building on the traditional genetic program approach, the PMLGP utilizes a hierarchy of genetic programming on two different levels. The lower level genetic programs are used to optimize coevolving populations in parallel while the higher level genetic program (HLGP) is used to optimize the genetic operator probabilities of the lower level genetic programs. The HLGP allows the algorithm to dynamically learn the mutation or combination of mutations that most effectively increase the fitness of the populations, causing a significant increase in the algorithm's accuracy and efficiency. The algorithm's accuracy and efficiency is tested against a standard parallel genetic program with a variety of one-dimensional test cases. Subsequently, the PMLGP is utilized to obtain an accurate empirical valence bond model for proton transfer in 3-hydroxy-gamma-pyrone in gas phase and protic solvent.

  14. Emergent SO(5) Symmetry at the Nel to Valence-Bond-Solid Transition.

    PubMed

    Nahum, Adam; Serna, P; Chalker, J T; Ortuo, M; Somoza, A M

    2015-12-31

    We show numerically that the "deconfined" quantum critical point between the Nel antiferromagnet and the columnar valence-bond solid, for a square lattice of spin 1/2, has an emergent SO(5) symmetry. This symmetry allows the Nel vector and the valence-bond solid order parameter to be rotated into each other. It is a remarkable (2+1)-dimensional analogue of the SO(4)=[SU(2)SU(2)]/Z_{2} symmetry that appears in the scaling limit for the spin-1/2 Heisenberg chain. The emergent SO(5) symmetry is strong evidence that the phase transition in the (2+1)-dimensional system is truly continuous, despite the violations of finite-size scaling observed previously in this problem. It also implies surprising relations between correlation functions at the transition. The symmetry enhancement is expected to apply generally to the critical two-component Abelian Higgs model (noncompact CP^{1} model). The result indicates that in three dimensions there is an SO(5)-symmetric conformal field theory that has no relevant singlet operators, so is radically different from conventional Wilson-Fisher-type conformal field theories. PMID:26765019

  15. Z2 gauge theory for valence bond solids on the kagome lattice

    NASA Astrophysics Data System (ADS)

    Hwang, Kyusung; Huh, Yejin; Kim, Yong Baek

    2015-11-01

    We present an effective Z2 gauge theory that captures various competing phases in spin-1/2 kagome lattice antiferromagnets: the topological Z2 spin liquid (SL) phase, and the 12-site and 36-site valence bond solid (VBS) phases. Our effective theory is a generalization of the recent Z2 gauge theory proposed for SL phases by Wan and Tchernyshyov. In particular, we investigate possible VBS phases that arise from vison condensations in the SL. In addition to the 12-site and 36-site VBS phases, there exists 6-site VBS that is closely related to the symmetry-breaking valence bond modulation patterns observed in the recent density matrix renormalization group simulations. We find that our results have remarkable consistency with a previous study using a different Z2 gauge theory. Motivated by the lattice geometry in the recently reported vanadium oxyfluoride kagome antiferromagnet, our gauge theory is extended to incorporate lowered symmetry by inequivalent up and down triangles. We investigate effects of this anisotropy on the 12-site, 36-site, and 6-site VBS phases. The 12-site VBS is stable to anisotropy while the 36-site VBS undergoes severe dimer melting. Interestingly, any analog of the 6-site VBS is not found in this approach. We discuss the implications of these findings and also compare the results with a different type of Z2 gauge theory used in previous studies.

  16. Transport pathways for mobile ions in disordered solids from the analysis of energy-scaled bond-valence mismatch landscapes.

    PubMed

    Adams, Stefan; Rao, R Prasada

    2009-05-01

    Structure-property relationships provide valuable guidelines for a systematic development of functional materials. Here an augmented bond-valence approach is worked out that is linked directly to the energy scale. This energy-scaled bond-valence approach is then used to identify ion-conduction pathways and to establish structure-property relationships in complex disordered solids using lithium silicate glasses as model systems. Representative local structure models of glassy solid electrolytes as a basis for the pathway analysis are derived from molecular dynamics simulations. Predictions of the bond-valence model from a static structure model are compared to a complete trajectory analysis, showing a high degree of agreement. The method yields consistent results when changing the simulation force field and is applicable to a wide range of glasses. PMID:19370216

  17. 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)

    Chen, Zhenhua; Chen, Xun; Wu, Wei

    2013-04-01

    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 d^2 n_β ^2 for VB matrix elements and 3-RDM evaluation, while the computational costs of other procedures are negligible, where n, m, d, and nβ are the numbers of variable occupied active orbitals, basis functions, determinants, and active β 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.

  18. 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

    Chen, Zhenhua; Chen, Xun; Wu, Wei

    2013-04-28

    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(β)(2) for VB matrix elements and 3-RDM evaluation, while the computational costs of other procedures are negligible, where n, m, d, and n(β )are the numbers of variable occupied active orbitals, basis functions, determinants, and active β 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

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

    PubMed

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

    2007-12-21

    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

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

    PubMed

    Xu, Enhua; Li, Shuhua

    2013-11-01

    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

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

    SciTech Connect

    Xu, Enhua; Li, Shuhua

    2013-11-07

    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.

  2. Resonating Valence Bonds and Mean-Field d-Wave Superconductivity in Graphite

    SciTech Connect

    Black-Schaffer, Annica M.

    2010-04-27

    We investigate the possibility of inducing superconductivity in a graphite layer by electronic correlation effects. We use a phenomenological microscopic Hamiltonian which includes nearest neighbor hopping and an interaction term which explicitly favors nearest neighbor spin-singlets through the well-known resonance valence bond (RVB) character of planar organic molecules. Treating this Hamiltonian in mean-field theory, allowing for bond-dependent variation of the RVB order parameter, we show that both s- and d-wave superconducting states are possible. The d-wave solution belongs to a two-dimensional representation and breaks time reversal symmetry. At zero doping there exists a quantum critical point at the dimensionless coupling J/t = 1.91 and the s- and d-wave solutions are degenerate for low temperatures. At finite doping the d-wave solution has a significantly higher T{sub c} than the s-wave solution. By using density functional theory we show that the doping induced from sulfur absorption on a graphite layer is enough to cause an electronically driven d-wave superconductivity at graphite-sulfur interfaces. We also discuss applying our results to the case of the intercalated graphites as well as the validity of a mean-field approach.

  3. Mixed valency in quadruple hydrogen-bonded dimers of bis(biimidazolate)dirhodium complexes.

    PubMed

    Jin-Long; Matsuda, Yuki; Uemura, Kazuhiro; Ebihara, Masahiro

    2015-03-01

    Dirhodium complexes with biimidazole (H2bim) ligands [Rh2(O2CR)2(H2bim)2Cl2] (R = Bu ([1Cl2]), Pr ([2Cl2])), [Rh2(O2CBu)2(H2bim)2](PF6)2 ([1](PF6)2), [Rh2(O2CBu)2(H2bim)2(PPh3)2](PF6)2 ([1(PPh3)2](PF6)2), and [Rh2(O2CPr)2(H2bim)2(PPh3)2]Cl2 ([2(PPh3)2]Cl2) have been synthesized. Deprotonation of the biimidazole complexes afforded the quadruply hydrogen-bonded dimers of the biimidazolate complexes [Rh2(O2CR)2(Hbim)2(PPh3)2]2 (R = Bu ([1'(PPh3)2]2) and Pr ([2'(PPh3)2]2)). Complementary hydrogen bonds between the Hbim(-) ligands are not coplanar because the Hbim(-) ions in one dirhodium complex are not parallel (the dihedral angle between them is ca. 15). A cyclic voltammogram of [1'(PPh3)2]2 shows two sets of two consecutive oxidation waves in CH2Cl2. The one-electron-oxidized species of [1'(PPh3)2]2 showed no intervalence charge-transfer band in the electronic spectrum and an axially symmetrical ESR spectrum with hyperfine structure because of two phosphorus atoms. These observations show that the odd electron is localized in a ?(Rh-Rh) orbital on one dirhodium unit. Theoretical calculations indicate that an oxidized complex [Rh2(O2CMe)2(bim)2(PMe3)2](-) hydrogen bonded with a biimidazole complex [Rh2(O2CMe)2(H2bim)2(PMe3)2](2+) was a stable mixed-valence complex. PMID:25692759

  4. Property of the Valence-Bond Ordering in Molecular Superconductor with a Quasi-Triangular Lattice

    NASA Astrophysics Data System (ADS)

    Yamamoto, Takashi; Nakazawa, Yasuhiro; Tamura, Masafumi; Nakao, Akiko; Fukaya, Atsuko; Kato, Reizo; Yakushi, Kyuya

    2014-05-01

    We have investigated the property of the non-magnetic insulating state of a pressure-induced molecular superconductor with a quasi-triangular lattice consisting of tight dimer units applying vibrational and reflectance spectroscopy to monoclinic-phase of C2H5(CH3)3P[Pd(dimt)2]2 (dmit = 1,3-dithiole-2-thione-4,5-dithiolate). From the analyses of the spectra, it is founded that two asymmetric dimers form a weakly bounded tetramer and the 2D layer is a slightly anisotropic. Theses results indicate that the cooperation between nearest Coulomb repulsions and valence bond order, which is operative for the anisotropic system of triclinic-phase of C2H5(CH3)3P[Pd(dimt)2]2, inhibits spin frustration in the monoclinic-phase. Our result also suggests that a half-filled picture does not always hold for the molecular superconductors consisting of tight dimer units.

  5. Structural and magnetic properties of Ba2LuMoO6: a valence bond glass.

    PubMed

    Coomer, Fiona C; Cussen, Edmund J

    2013-02-27

    We report here the synthesis of the site ordered double perovskite Ba(2)LuMoO(6). Rietveld refinement of room temperature powder x-ray diffraction measurements indicates that it crystallizes in the cubic space group Fm3m, with a = 8.3265(1) ?. Powder neutron diffraction data indicate that, unusually, this cubic symmetry is maintained down to 2 K, with [Formula: see text], Mo(5+) 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 Ba(2)YMoO(6), which is a valence bond glass. PMID:23343826

  6. Resonating valence bond and {sigma}-charge density wave phases in a benzannulated phenalenyl radical.

    SciTech Connect

    Bag, P.; Itkis, M. E.; .Pal, S. K; Donnadieu, B.; Tham, F. S.; Park, H.; Schlueter, J. A.; Siegrist, T.; Haddon, R. C.; Materials Science Division; Univ. of California of Riverside; Florida State Univ.

    2010-01-01

    We report the preparation of the first benzannulated phenalenyl neutral radical conductor (18), and we show that the compound displays unprecedented solid state behavior: the structure is dominated by two sets of intermolecular interactions: (1) a {pi}-chain structure with superimposed {pi}-overlap of the benzannulated phenalenyls along [0 0 1], and (2) an interchain overlap involving a pair of carbon atoms (C4) along [0 1 0]. The {pi}-chain-type stacking motif is reminiscent of previously reported phenalenyl radicals and the room temperature structure (space group P2/c) together with the conductivity of {sigma}{sub RT} = 0.03 S/cm and the Pauli-like magnetic susceptibility are best described by the resonating valence bond (RVB) model. The interchain interaction is unstable with respect to the formation of a {sigma}-charge density wave ({sigma}-CDW) involving pairs of C4 carbon atoms between adjacent radicals and this phase is characterized by the P2{sub 1}/c space group which involves a doubling of the unit cell along the [0 1 0] direction. The RVB and CDW phases compete for structural occupancy throughout the whole temperature range (15-293 K) with the RVB phase predominating at 15 and 293 K and the {sigma}-CDW phase achieving a maximum structural occupancy of about 60% at 150 K where it produces clearly discernible effects on the magnetism and conductivity.

  7. Emergent quantum criticality from fractionalizing one-dimensional SO(5) symmetric valence-bond solid states

    NASA Astrophysics Data System (ADS)

    Rao, Wen-Jia; Cai, Kang; Wan, Xin; Zhang, Guang-Ming

    2015-12-01

    A common feature of topological phases of matter is the fractionalization of the quantum number in their low-energy excitations. Such information is encoded in their ground state wave functions, but emerges in the bipartite entanglement spectra. The symmetric extensive bipartition is an effective novel method to create deconfined fractionalized edge particles in the reduced subsystem, which lead to quantum critical behavior associated with the transition from the topological phase to its adjacent trivial phase. Here we report the interesting results revealed by applying this method to the one-dimensional SO(5) symmetric valence-bond solid state being a spin-2 symmetry protected topological phase. From the finite-size entanglement spectrum, we find the lowest level to be an SO(5) singlet with a logarithmic entanglement entropy. Surprisingly, the first excited level is also an SO(5) singlet and the spectral gap scales with the subsystem size as LA-? with ? ?1.978 . In the thermodynamic limit, a novel quantum criticality emerges with SO(5) spinons and their four-body singlet bound states as elementary excitations, hence ruling out the possibility of being described by a conformal field theory. Moreover, the entanglement Hamiltonian can be determined as an SO(5) symmetric nearest neighbor spin-3/2 quadruple-quadruple interaction with a negative coupling. Our work thus demonstrates the power of this new method in the study of quantum criticality encoded in the topological ground states.

  8. Valence bond and enzyme catalysis: a time to break down and a time to build up.

    PubMed

    Sharir-Ivry, Avital; Varatharaj, Rajapandian; Shurki, Avital

    2015-05-01

    Understanding enzyme catalysis and developing ability to control of it are two great challenges in biochemistry. A few successful examples of computational-based enzyme design have proved the fantastic potential of computational approaches in this field, however, relatively modest rate enhancements have been reported and the further development of complementary methods is still required. Herein we propose a conceptually simple scheme to identify the specific role that each residue plays in catalysis. The scheme is based on a breakdown of the total catalytic effect into contributions of individual protein residues, which are further decomposed into chemically interpretable components by using valence bond theory. The scheme is shown to shed light on the origin of catalysis in wild-type haloalkane dehalogenase (wt-DhlA) and its mutants. Furthermore, the understanding gained through our scheme is shown to have great potential in facilitating the selection of non-optimal sites for catalysis and suggesting effective mutations to enhance the enzymatic rate. PMID:25808731

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

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

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

  10. Néel and valence-bond crystal phases of frustrated two-dimensional Heisenberg models

    NASA Astrophysics Data System (ADS)

    Moukouri, S.

    2008-02-01

    I use an improved version of the two-step density-matrix renormalization group method to study ground-state properties of the two-dimensional (2D) Heisenberg model on the checkerboard lattice. In this version, the Hamiltonian is projected on a tensor product of two-leg ladders instead of chains. This allows investigations of 2D isotropic models. I show that this method can describe both the magnetically disordered and ordered phases. The ground-state phases of the checkerboard model as J2 increases are (i) Néel with Q=(π,π) , (ii) a valence-bond crystal (VBC) of plaquettes, (iii) Néel with Q=(π/2,π) , and (iv) a VBC of crossed dimers. In agreement with previous results, I find that at the isotropic point J2=J1 , the ground state is made of weakly interacting plaquettes with a large gap Δ≈0.67J1 to triplet excitations. The same approach is also applied to the J1-J2 model. There is no evidence of a columnar dimer phase in the highly frustrated regime.

  11. Nonorthogonal orbital based n-body reduced density matrices and their applications to valence bond theory. III. Second-order perturbation theory using valence bond self-consistent field function as reference

    NASA Astrophysics Data System (ADS)

    Chen, Zhenhua; Chen, Xun; Ying, Fuming; Gu, Junjing; Zhang, Huaiyu; Wu, Wei

    2014-10-01

    Using the formulas and techniques developed in Papers I and II of this series, the recently developed second-order perturbation theory based on a valence bond self-consistent field reference function (VBPT2) has been extended by using the internally contracted correction wave function. This ansatz strongly reduces the size of the interaction space compared to the uncontracted wave function and thus improves the capability of the VBPT2 method dramatically. Test calculations show that internally contracted VBPT2 using only a small number of reference valence bond functions, can give results as accuracy as the VBPT2 method and other more sophisticated methods such as full configuration interaction and multireference configuration interaction.

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

    NASA Astrophysics Data System (ADS)

    Fritsch, A.; Ducasse, L.

    1991-06-01

    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 utilis la mthode Diagrammatic Valence Bond (DVB) pour analyser les proprits lectroniques de clusters monodimensionnels (1 D), dont les solutions exactes ont t obtenues au moyen d'un hamiltonien du type Hubbard (tendu). Un essai de calcul par des mthodes SCF semi-empiriques des paramtres de corrlation intrasite U, intersites V (premier voisin) et V2 (second voisin) a t men et les valeurs obtenues ont t compares aux donnes tires de l'exprience. Une classification possible des sels M{2}X (M : molcule organique, X^- anion), dcoule des structures cristallographiques et des mesures de conductivit : les composs d'un premier groupe ont une structure dimrise et un comportement semi-conducteur 300 K tandis que ceux d'un deuxime groupe s'empilent de manire rgulire ou quasi-rgulire, sont mtalliques 300 K et leur localisation lectronique est modifie entre 100-200 K. Dans le premier cas, les calculs DVB conduisent une description de l'tat fondamental localis en termes d'une forte onde de densit de liaison. L'effet du terme entre second voisins V2 demeure faible bien qu'il puisse modifier les corrlations de charge longue distance ainsi que le comportement magntique. Les susceptibilits magntiques ? calcules sur un cycle de 8 sites sont en bon accord avec l'exprience 300 K et c'est pour V2 voisin de V/2 que la dpendance de ? avec la temprature est reproduite de faon la plus satisfaisante. Dans le second cas, des calculs ab initio modles tendent montrer que la dimrisation lectronique pourrait tre modifie par le potentiel des anions. Une modification des intgrales de transfert intra- et inter-dimres rend compte qualitativement de la variation de la rsistivit en fonction de la temprature. Les rsultats DVB sur des anneaux de 12 sites montrent que cette diffrence entrane une nette augmentation de la localisation lorsque les corrlations sont prises en compte, en comparaison du cas rgulier observ haute temprature.

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

    PubMed

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

    2014-06-16

    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

  14. Two-hole localization mechanism for electronic bond rupture of surface atoms by laser-induced valence excitation of semiconductors

    SciTech Connect

    Tanimura, K.; Inami, E.; Kanasaki, J.; Hess, Wayne P.

    2006-07-15

    We examine the mechanism of electronic bond rupture on semiconductor surfaces induced by laser-generated nonequilibrium three-dimensional valence excitation associated with strong carrier diffusion. For such excited systems, the density of subsurface valence holes that contribute to two-hole localization on the surface is characterized by quasi-Fermi-levels and effective temperature. The rate of two-hole localization, formulated for equilibrated two-dimensional electronic systems by Sumi [Surf. Sci. 248, 382 (1991)], is reformulated, and a simple analytical expression is yielded for moderate excitation densities. The resulting theoretical model has been successfully applied in the analysis of recent laser-induced atomic desorption experiments on InP and Si surfaces.

  15. Two-Hole Localization Mechanism for Electron Bond Rupture of Surface Atoms by Laser-Induced Valence Excitation of Semiconductors

    SciTech Connect

    Tanimura, Katsumi; Inami, E.; Kanasaki, J.; Hess, Wayne P.

    2006-07-16

    We examine the mechanism of electronic bond rupture on semiconductor surfaces induced by laser-generated three-dimensional non-equilibrium valence excitation associated with strong carrier diffusion. For such excited systems, the density of sub-surface valence holes that contribute to two-hole localization on the surface is characterized by quasi Fermi level and effective temperature. The rate of two-hole localization, formulated for equilibrated two-dimensional electronic systems by Sumi [Surf. Sci, 248, 382 (1991)], is re-formulated, and a simple analytical expression is yielded for moderate excitation densities. The resulting theoretical model has been successfully applied in the analysis of recent laser-induced atomic desorption experiments on InP and Si surfaces

  16. Insights into the Electronic Structure of Ozone and Sulfur Dioxide from Generalized Valence Bond Theory: Bonding in O3 and SO2.

    PubMed

    Takeshita, Tyler Y; Lindquist, Beth A; Dunning, Thom H

    2015-07-16

    There are many well-known differences in the physical and chemical properties of ozone (O3) and sulfur dioxide (SO2). O3 has longer and weaker bonds than O2, whereas SO2 has shorter and stronger bonds than SO. The O-O2 bond is dramatically weaker than the O-SO bond, and the singlet-triplet gap in SO2 is more than double that in O3. In addition, O3 is a very reactive species, while SO2 is far less so. These disparities have been attributed to variations in the amount of diradical character in the two molecules. In this work, we use generalized valence bond (GVB) theory to characterize the electronic structure of ozone and sulfur dioxide, showing O3 does indeed possess significant diradical character, whereas SO2 is effectively a closed shell molecule. The GVB results provide critical insights into the genesis of the observed difference in these two isoelectronic species. SO2 possesses a recoupled pair bond dyad in the a"(π) system, resulting in SO double bonds. The π system of O3, on the other hand, has a lone pair on the central oxygen atom plus a pair of electrons in orbitals on the terminal oxygen atoms that give rise to a relatively weak π interaction. PMID:26068052

  17. Correlation of molecular valence- and K-shell photoionization resonances with bond lengths

    NASA Technical Reports Server (NTRS)

    Sheehy, J. A.; Gil, T. J.; Winstead, C. L.; Farren, R. E.; Langhoff, P. W.

    1989-01-01

    The relationship between the interatomic distance and the positions of valence-shell and K-shell sigma(asterisk) photoionization resonances is investigated theoretically for the molecules C2, F2, N2, O2, CO, NO, C2H2, C2H4, C2H6, HCN, H2CO, N20, CO2, and C2N2. The results of molecular-orbital computations are presented in three-dimensional diagrams, which are shown to be similar to the wave functions of a particle in a cylindrical well, confirming the validity of free-electron molecular-orbital (FEMO) approximations for modeling the potential along the symmetry axis. FEMO orbital energies and resonance positions are found to be in good agreement with previous theoretical and experimental results. Also included is a Feshbach-Fano analysis of the relevance of virtual-valence orbitals to the appearance of single-channel resonances in molecular photoionization cross sections.

  18. The Quadruple Bonding in C2 Reproduces the Properties of the Molecule.

    PubMed

    Shaik, Sason; Danovich, David; Braida, Benoit; Hiberty, Philippe C

    2016-03-14

    Ever since Lewis depicted the triple bond for acetylene, triple bonding has been considered as the highest limit of multiple bonding for main elements. Here we show that C2 is bonded by a quadruple bond that can be distinctly characterized by valence-bond (VB) calculations. We demonstrate that the quadruply-bonded structure determines the key observables of the molecule, and accounts by itself for about 90 % of the molecule's bond dissociation energy, and for its bond lengths and its force constant. The quadruply-bonded structure is made of two strong π bonds, one strong σ bond and a weaker fourth σ-type bond, the bond strength of which is estimated as 17-21 kcal mol(-1) . Alternative VB structures with double bonds; either two π bonds or one π bond and one σ bond lie at 129.5 and 106.1 kcal mol(-1) , respectively, above the quadruply-bonded structure, and they collapse to the latter structure given freedom to improve their double bonding by dative σ bonding. The usefulness of the quadruply-bonded model is underscored by "predicting" the properties of the (3) Σ+u state. C2 's very high reactivity is rooted in its fourth weak bond. Thus, carbon and first-row main elements are open to quadruple bonding! PMID:26880488

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

    NASA Astrophysics Data System (ADS)

    Becca, Federico; Iqbal, Yasir; Poilblanc, Didier

    2011-03-01

    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 | > 0.09J1 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 non-trivial flux pattern and large dimerization.

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

    NASA Astrophysics Data System (ADS)

    Iqbal, Yasir; Becca, Federico; Poilblanc, Didier

    2011-03-01

    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.

  1. Efficient automatic screening for Li ion conductive inorganic oxides with bond valence pathway models and percolation algorithm

    NASA Astrophysics Data System (ADS)

    Nakayama, Masanobu; Kimura, Mayumi; Jalem, Randy; Kasuga, Toshihiro

    2016-01-01

    Fast ion conductive solid oxide electrolytes are urgently needed because of the development of batteries, fuel cells, and sensors. Ab initio density functional theory can predict ionic conductivities with high accuracy, although it often requires large computational resources and time. In this paper, we use empirical bond valence relations [Adams et al., Phys. Status Solidi A 208, 1746 (2011)] and a percolation algorithm for fast, efficient, fully automated evaluation of migration energies for Li ion conduction in 14 olivine-type LiMXO4 compounds. The results showed a high correlation coefficient with the ab initio density functional theory (DFT) approach, indicating that our method could be attractive for identifying fast ion conductors in databases of numerous candidates.

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

    NASA Astrophysics Data System (ADS)

    Huh, Yejin; Punk, Matthias; Sachdev, Subir

    2013-06-01

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

  3. The graphite core valence valence Auger spectrum

    NASA Astrophysics Data System (ADS)

    Calliari, L.; Speranza, G.; Lascovich, J. C.; Santoni, A.

    2002-04-01

    The graphite core-valence-valence (CVV) Auger spectrum is analysed, within a one-particle approximation, by comparison to the X-ray excited valence band (VB) photoemission spectrum, whose structure is well understood in terms of the graphite density of states (DOS). The aim is to identify the electron states originating the components into which the CVV spectrum is resolved by double differentiation. Contributions assigned to self-folds of VB photoemission features and hence due to transitions coupling electrons from the same DOS feature, dominate the spectrum away from the middle region, while folds between different features are important in the middle region. A single particle approximation proves to be adequate to account for the low binding energy, mostly p-like, part of the spectrum. It brakes down however in the high binding energy, mainly s-like, region where spectral distortion is ascribed to a nonnegligible (?2 eV) Coulomb repulsion between final state holes of s-symmetry.

  4. On the transferability of electron density in binary vanadium borides VB, V3B4 and VB2.

    PubMed

    Terlan, Brgehan; Akselrud, Lev; Baranov, Alexey I; Borrmann, Horst; Grin, Yuri

    2015-12-01

    Binary vanadium borides are suitable model systems for a systematic analysis of the transferability concept in intermetallic compounds due to chemical intergrowth in their crystal structures. In order to underline this structural relationship, topological properties of the electron density in VB, V3B4 and VB2 reconstructed from high-resolution single-crystal X-ray diffraction data as well as derived from quantum chemical calculations, are analysed in terms of Bader's Quantum Theory of Atoms in Molecules [Bader (1990). Atoms in Molecules: A Quantum Theory, 1st ed. Oxford: Clarendon Press]. The compounds VB, V3B4 and VB2 are characterized by a charge transfer from the metal to boron together with two predominant atomic interactions, the shared covalent B-B interactions and the polar covalent B-M interactions. The resembling features of the crystal structures are well reflected by the respective B-B interatomic distances as well as by ?(r) values at the B-B bond critical points. The latter decrease with an increase in the corresponding interatomic distances. The B-B bonds show transferable electron density properties at bond critical points depending on the respective bond distances. PMID:26634735

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

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

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

  6. On The Nature of the Halogen Bond.

    PubMed

    Wang, Changwei; Danovich, David; Mo, Yirong; Shaik, Sason

    2014-09-01

    The wide-ranging applications of the halogen bond (X-bond), notably in self-assembling materials and medicinal chemistry, have placed this weak intermolecular interaction in a center of great deal of attention. There is a need to elucidate the physical nature of the halogen bond for better understanding of its similarity and differences vis--vis other weak intermolecular interactions, for example, hydrogen bond, as well as for developing improved force-fields to simulate nano- and biomaterials involving X-bonds. This understanding is the focus of the present study that combines the insights of a bottom-up approach based on ab initio valence bond (VB) theory and the block-localized wave function (BLW) theory that uses monomers to reconstruct the wave function of a complex. To this end and with an aim of unification, we studied the nature of X-bonds in 55 complexes using the combination of VB and BLW theories. Our conclusion is clear-cut; most of the X-bonds are held by charge transfer interactions (i.e., intermolecular hyperconjugation) as envisioned more than 60 years ago by Mulliken. This is consistent with the experimental and computational findings that X-bonds are more directional than H-bonds. Furthermore, the good linear correlation between charge transfer energies and total interaction energies partially accounts for the success of simple force fields in the simulation of large systems involving X-bonds. PMID:26588518

  7. Analysis of Bonding Patterns in the Valence Isoelectronic series O-3, S-3, SO2 and OS2 in Terms of Oriented Quasi-Atomic Molecular Orbitals

    SciTech Connect

    Glezakou, Vassiliki Alexandra; Elbert, Stephen T.; Xantheas, Sotiris S.; Ruedenberg, Klaus

    2010-08-26

    A novel analysis of the chemical bonding pattern in the valence isoelectronic series of triatomic molecules O3, S3, SO2 and OS2 is reported. The analysis is based on examining the bond order matrix elements between the Oriented Localized Molecular Orbitals (OLMOs) that are localized on the three individual left (L), center (C) and right (R) atoms. The analysis indicates that there is a (L-C) and (C-R) π-bonding interaction and a (L-R) π−antibonding interaction. This finding supports the previously proposed "partial biradical" interpretation of these triatomic systems, which had recently been challenged.

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

    NASA Astrophysics Data System (ADS)

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

    2006-06-01

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

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

    NASA Astrophysics Data System (ADS)

    Sandvik, Anders

    2005-03-01

    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).

  10. Valence-bond-solid phases and quantum phase transitions in two-dimensional spin models with four-site interactions

    NASA Astrophysics Data System (ADS)

    Sandvik, A. W.; Melko, R. G.; Scalapino, D. J.

    2006-02-01

    We discuss zero-temperature phase transititions from an antiferromagnetic ground state into a valence-bond-solid (VBS) in two different square-lattice quantum spin models. In one limit these models reduce to the standard S = 1/2 XY and Heisenberg models, respectively, which have long-range antiferromagnetic order at T = 0. Introducing particular types of four-spin interactions, amenable to quantum Monte Carlo (QMC) simulation without negative-sign problems, drives phase transitions into VBS states with broken Z4 symmetry. It has recently been argued that continuous quantum phase transitions of this nature represent a new class of deconfined quantum-critical points [Senthil et al., Science 303, 1490 (2004)], which are not captured within the standard Ginzburg-Landau framework of phase transitions. Here we discuss a QMC study aimed at accurately characterizing the transition in the XY model. We find some evidence that the transition is actually weakly first-order, but other scenarios, such as a continuous transition violating hyperscaling, also cannot be completely ruled out. For the Heisenberg model with four-spin interactions we have confirmed that a VBS state exists. Preliminary finite-size scaling results show consistency with a continuous transition into the Nel state, with dynamic exponent z = 1. This model is thus a candidate for deconfined quantum criticality.

  11. Charge Order Instability in Doped Resonating Valence Bond State and Magnetic Orbits from Reconstructed Fermi Surface in Underdoped Cuprates

    NASA Astrophysics Data System (ADS)

    Zhang, Long; Mei, Jia-Wei

    2015-03-01

    Recent experiments reveal incommensurate charge density wave (CDW) and quantum oscillations (QO) in the pseudogap phase of underdoped cuprates. In this work, we take a phenomenological synthesis of the resonating valence bond (RVB) state and the CDW order. Starting from the Yang-Rice-Zhang (YRZ) ansatz for the Green's function of the RVB state, we show that the CDW instability at wavevectors connecting the tips of the Fermi arcs can induce Fermi surface reconstruction. We find three primary magnetic orbits in the QO spectrum, the CDW-induced electron-like ? and hole-like ? orbits and the ? orbit enclosing the initial nodal YRZ hole pockets due to magnetic breakdown. Their combinations naturally explain the multi-component QO pattern observed in experiments. The ? orbit encloses an area satisfying the generalized Luttinger theorem. The cyclotron mass of the ? orbit increases monotonically with doping in agreement with the optical Hall angle measurements , while that of the ? orbit is enhanced as the CDW order vanishes on approaching two critical dopings. However, we find that the enhancement of mHα is overestimated in QO experiments due to the ignorance of the impact of the CDW order suppression with increasing temperature. Work supported by the NBRPC Grant No. 2010CB923003, by the Government of Canada through Industry Canada and by the Province of Ontario through the Ministry of Research.

  12. 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)

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

    1982-01-01

    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.

  13. Lattice effects in the quasi-two-dimensional valence-bond-solid Mott insulator EtMe3P[Pd(dmit)2]2

    NASA Astrophysics Data System (ADS)

    Manna, Rudra Sekhar; de Souza, Mariano; Kato, Reizo; Lang, Michael

    2014-01-01

    The organic charge-transfer salt EtMe3P[Pd(dmit)2]2 is a quasi-two-dimensional Mott insulator with localized spins S =1/2 residing on a distorted triangular lattice. Here we report measurements of the uniaxial thermal expansion coefficients ?i along the in-plane i =a and c axis as well as along the out-of-plane b axis for temperatures 1.4 K?T?200 K. Particular attention is paid to the lattice effects around the phase transition at TVBS=25 K into a low-temperature valence-bond-solid phase and the paramagnetic regime above where effects of short-range antiferromagnetic correlations can be expected. The salient results of our study include (i) the observation of strongly anisotropic lattice distortions accompanying the formation of the valence-bond-solid phase, and (ii) a distinct anomaly in the thermal expansion coefficients in the paramagnetic regime around 40 K. Our results demonstrate that upon cooling through TVBS the in-plane c axis, along which the valence bonds form, contracts while the second in-plane a axis elongates by the same relative amount. Surprisingly, the dominant effect is observed for the out-of-plane b axis which shrinks significantly upon cooling through TVBS. The pronounced anomaly in ?i around 40 K is attributed to short-range magnetic correlations. It is argued that the position of this maximum, relative to that in the magnetic susceptibility around 70 K, speaks in favor of a more anisotropic triangular-lattice scenario for this compound than previously thought.

  14. Metal-Metal Bonding in Trinuclear, Mixed-Valence [Ti3X12](4-) (X = F, Cl, Br, I) Face-Shared Complexes.

    PubMed

    Hewage, Jinasena W; Cavigliasso, Germn; Stranger, Robert

    2015-11-16

    Metal-metal bonding in structurally characterized In4Ti3Br12, comprising linear, mixed-valence d(1)d(2)d(1) face-shared [Ti3Br12](4-) units with a Ti-Ti separation of 3.087 and strong antiferromagnetic coupling (? = -1216 K), has been investigated using density functional theory. The antiferromagnetic configuration, in which the single d electron on each terminal Ti(III) (d(1)) metal center is aligned antiparallel to the two electrons occupying the central Ti(II) (d(2)) metal site, is shown to best agree with the reported structural and magnetic data and is consistent with an S = 0 ground state in which two of the four metal-based electrons are involved in a two-electron, three-center ? bond between the Ti atoms (formal Ti-Ti bond order of ?0.5). However, the unpaired spin densities on the Ti sites indicate that while the metal-metal ? interaction is strong, the electrons are not fully paired off and consequently dominate the ground state antiferromagnetic coupling. The same overall partially delocalized bonding regime is predicted for the other three halide [Ti3X12](4-) (X = F, Cl, I) systems with the metal-metal bonding becoming weaker as the halide group is descended. The possibility of bond-stretch isomerism was also examined where one isomer has a symmetric structure with identical Ti-Ti bonds while the other is unsymmetric with one short and one long Ti-Ti bond. Although calculations indicate that the latter form is more stable, the barrier to interconversion between equivalent unsymmetric forms, where the short Ti-Ti bond is on one side of the trinuclear unit or the other, is relatively small such that at room temperature only the averaged (symmetric) structure is likely to be observed. PMID:26523831

  15. Generalized valence bond description of the ground states (X(1)Σg(+)) of homonuclear pnictogen diatomic molecules: N2, P2, and As2.

    PubMed

    Xu, Lu T; Dunning, Thom H

    2015-06-01

    The ground state, X1Σg+, of N2 is a textbook example of a molecule with a triple bond consisting of one σ and two π bonds. This assignment, which is usually rationalized using molecular orbital (MO) theory, implicitly assumes that the spins of the three pairs of electrons involved in the bonds are singlet-coupled (perfect pairing). However, for a six-electron singlet state, there are five distinct ways to couple the electron spins. The generalized valence bond (GVB) wave function lifts this restriction, including all of the five spin functions for the six electrons involved in the bond. For N2, we find that the perfect pairing spin function is indeed dominant at Re but that it becomes progressively less so from N2 to P2 and As2. Although the perfect pairing spin function is still the most important spin function in P2, the importance of a quasi-atomic spin function, which singlet couples the spins of the electrons in the σ orbitals while high spin coupling those of the electrons in the π orbitals on each center, has significantly increased relative to N2 and, in As2, the perfect pairing and quasi-atomic spin couplings are on essentially the same footing. This change in the spin coupling of the electrons in the bonding orbitals down the periodic table may contribute to the rather dramatic decrease in the strengths of the Pn2 bonds from N2 to As2 as well as in the increase in their chemical reactivity and should be taken into account in more detailed analyses of the bond energies in these species. We also compare the spin coupling in N2 with that in C2, where the quasi-atomic spin coupling dominants around Re. PMID:26575549

  16. Electronic structure and chemical bonding of {alpha}- and {beta}-CeIr{sub 2}Si{sub 2} intermediate valence compounds

    SciTech Connect

    Matar, Samir F.; Poettgen, Rainer; Chevalier, Bernard

    2012-02-15

    The dimorphism of the intermediate valence ternary cerium silicide CeIr{sub 2}Si{sub 2} in the ThCr{sub 2}Si{sub 2} ({alpha}) and CaBe{sub 2}Ge{sub 2} ({beta}) modifications is addressed in the framework of the density functional theory. The geometry optimization is in good agreement with the experiment and the subsequent establishment of the energy-volume equation of state (EOS) indicates a stabilization of the {beta}-type relative to the {alpha}-type concomitant with the trend of the cerium valence, changing to tetravalent in {beta}-CeIr{sub 2}Si{sub 2}. This is equally shown from the site projected DOS and from the large increase of the electronic contribution to the specific heat. The chemical bonding indicates the strongest bonding interactions within the Ir-Si substructure in both varieties. Stabilization of {beta}-CeIr{sub 2}Si{sub 2} with almost tetravalent cerium is in good agreement with Th{sup IV}Ir{sub 2}Si{sub 2} which exclusively crystallizes in the CaBe{sub 2}Ge{sub 2} type. The EOS behavior of different RIr{sub 2}Si{sub 2} (R=Th, Ce, La) is comparatively discussed. - Graphical abstract: The crystal structures of {alpha}- and {beta}-CeIr{sub 2}Si{sub 2}. Relevant interatomic distances (A), the three-dimensional [Ir{sub 2}Si{sub 2}] networks and the crystallographically independent iridium and silicon sites are indicated. Highlights: Black-Right-Pointing-Pointer Energy stabilization of (HT) {beta}-CeIr{sub 2}Si{sub 2} versus (LT) {alpha}-CeIr{sub 2}Si{sub 2} from DFT methods. Black-Right-Pointing-Pointer Concomitant with the change of Ce valence to tetravalent (HT)-enhanced specific heat. Black-Right-Pointing-Pointer Equations of states for La, Ce and Th members with CeIr{sub 2}Si{sub 2} resembling tetravalent-Th. Black-Right-Pointing-Pointer Chemical bonding shows changes on the {l_brace}Ir{sub 2}Si{sub 2}{r_brace} intralayer and Ce{sup IV}-Ir bonds.

  17. Chemical-shift tensors of heavy nuclei in network solids: a DFT/ZORA investigation of (207)Pb chemical-shift tensors using the bond-valence method.

    PubMed

    Alkan, Fahri; Dybowski, C

    2015-10-14

    Cluster models are used in calculation of (207)Pb NMR magnetic-shielding parameters of ?-PbO, ?-PbO, Pb3O4, Pb2SnO4, PbF2, PbCl2, PbBr2, PbClOH, PbBrOH, PbIOH, PbSiO3, and Pb3(PO4)2. We examine the effects of cluster size, method of termination of the cluster, charge on the cluster, introduction of exact exchange, and relativistic effects on calculation of magnetic-shielding tensors with density functional theory. Proper termination of the cluster for a network solid, including approximations such as compensation of charge by the bond-valence (BV) method, is essential to provide results that agree with experiment. The inclusion of relativistic effects at the spin-orbit level for such heavy nuclei is an essential factor in achieving agreement with experiment. PMID:26345261

  18. Qgui: A high-throughput interface for automated setup and analysis of free energy calculations and empirical valence bond simulations in biological systems.

    PubMed

    Isaksen, Geir Villy; Andberg, Tor Arne Heim; Åqvist, Johan; Brandsdal, Bjørn Olav

    2015-07-01

    Structural information and activity data has increased rapidly for many protein targets during the last decades. In this paper, we present a high-throughput interface (Qgui) for automated free energy and empirical valence bond (EVB) calculations that use molecular dynamics (MD) simulations for conformational sampling. Applications to ligand binding using both the linear interaction energy (LIE) method and the free energy perturbation (FEP) technique are given using the estrogen receptor (ERα) as a model system. Examples of free energy profiles obtained using the EVB method for the rate-limiting step of the enzymatic reaction catalyzed by trypsin are also shown. In addition, we present calculation of high-precision Arrhenius plots to obtain the thermodynamic activation enthalpy and entropy with Qgui from running a large number of EVB simulations. PMID:26080356

  19. 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

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

    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)

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

    SciTech Connect

    Ponou, Simeon; Lidin, Sven; Zhang, Yuemei; Miller, Gordon J.

    2014-04-18

    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 c12 with a = 23.1481(4) Å, b = 4.4736(1) Å, c = 11.0128(2) Å, V = 1140.43(4) Å3, 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 f5c2. 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.

  1. Relation between the structure of black phosphorus and the structure of its photoelectron spectrum, due to the electrons of the inner valence bands, and their role in the chemical bond

    SciTech Connect

    Gagarin, S.G.; Teterin, Yu.A.

    1986-01-01

    On the basis of calculations by the extended Hueckel method it was shown that there is a relation between the structure of the photoelectron spectrum of black phosphorus, arising from the electrons of the valence bands, and its structure in the solid phase. The bonding (or antibonding) character of these bands and the preferred contribution from the electrons of the inner valence bands to the chemical bonding of the phosphorus atoms were established. It was noted the main conclusions about the nature of the bond in the atomic crystal can be reached on the basis of the cluster approximation, whereas the band structure has to be taken into account for the interpretation of the individual details of the spectrum.

  2. The Haldane State in CsNiCl 3 Detected by Magnetization Measurements —Observation of Quantum-Classical Crossover and the Valence Bond Solid State—

    NASA Astrophysics Data System (ADS)

    Asano, Takayuki; Ajiro, Yoshitami; Mekata, Mamoru; Kamishima, Kenji; Koui, Katsuhiko; Goto, Tsuneaki; Furusawa, Masahiro; Hori, Hidenobu

    1997-02-01

    We have confirmed from susceptibility and magnetization measurements that the Haldane state really exists in 1D phase of CsNiCl3 which undergoes 3D ordering at T N=4.8 K. The observed susceptibility at low fields follows the predicted curve for the S=1 quantum chain with energy gap (Δ/k B˜10 K) down to near T N. A more definite evidence for the Haldane state is given by studying the effect of the nonmagnetic impurities. We have revealed a real existence of S=1/2 edge states characteristic of the Haldane state and further revealed a crossover from the quantum to classical regimes as a function of both temperature and field. The result is consistent with the model that at low temperatures (TValence-Bond-Solid while at high temperatures (T>|J|/k B) and high fields (H>H G) the system is not in the Haldane state any more.

  3. High-throughput design and optimization of fast lithium ion conductors by the combination of bond-valence method and density functional theory.

    PubMed

    Xiao, Ruijuan; Li, Hong; Chen, Liquan

    2015-01-01

    Looking for solid state electrolytes with fast lithium ion conduction is an important prerequisite for developing all-solid-state lithium secondary batteries. By combining the simulation techniques in different levels of accuracy, e.g. the bond-valence (BV) method and the density functional theory (DFT), a high-throughput design and optimization scheme is proposed for searching fast lithium ion conductors as candidate solid state electrolytes for lithium rechargeable batteries. The screening from more than 1000 compounds is performed through BV-based method, and the ability to predict reliable tendency of the Li(+) migration energy barriers is confirmed by comparing with the results from DFT calculations. ?-Li3PS4 is taken as a model system to demonstrate the application of this combination method in optimizing properties of solid electrolytes. By employing the high-throughput DFT simulations to more than 200 structures of the doping derivatives of ?-Li3PS4, the effects of doping on the ionic conductivities in this material are predicted by the BV calculations. The O-doping scheme is proposed as a promising way to improve the kinetic properties of this materials, and the validity of the optimization is proved by the first-principles molecular dynamics (FPMD) simulations. PMID:26387639

  4. High-throughput design and optimization of fast lithium ion conductors by the combination of bond-valence method and density functional theory

    NASA Astrophysics Data System (ADS)

    Xiao, Ruijuan; Li, Hong; Chen, Liquan

    2015-09-01

    Looking for solid state electrolytes with fast lithium ion conduction is an important prerequisite for developing all-solid-state lithium secondary batteries. By combining the simulation techniques in different levels of accuracy, e.g. the bond-valence (BV) method and the density functional theory (DFT), a high-throughput design and optimization scheme is proposed for searching fast lithium ion conductors as candidate solid state electrolytes for lithium rechargeable batteries. The screening from more than 1000 compounds is performed through BV-based method, and the ability to predict reliable tendency of the Li+ migration energy barriers is confirmed by comparing with the results from DFT calculations. ?-Li3PS4 is taken as a model system to demonstrate the application of this combination method in optimizing properties of solid electrolytes. By employing the high-throughput DFT simulations to more than 200 structures of the doping derivatives of ?-Li3PS4, the effects of doping on the ionic conductivities in this material are predicted by the BV calculations. The O-doping scheme is proposed as a promising way to improve the kinetic properties of this materials, and the validity of the optimization is proved by the first-principles molecular dynamics (FPMD) simulations.

  5. High-throughput design and optimization of fast lithium ion conductors by the combination of bond-valence method and density functional theory

    PubMed Central

    Xiao, Ruijuan; Li, Hong; Chen, Liquan

    2015-01-01

    Looking for solid state electrolytes with fast lithium ion conduction is an important prerequisite for developing all-solid-state lithium secondary batteries. By combining the simulation techniques in different levels of accuracy, e.g. the bond-valence (BV) method and the density functional theory (DFT), a high-throughput design and optimization scheme is proposed for searching fast lithium ion conductors as candidate solid state electrolytes for lithium rechargeable batteries. The screening from more than 1000 compounds is performed through BV-based method, and the ability to predict reliable tendency of the Li+ migration energy barriers is confirmed by comparing with the results from DFT calculations. β-Li3PS4 is taken as a model system to demonstrate the application of this combination method in optimizing properties of solid electrolytes. By employing the high-throughput DFT simulations to more than 200 structures of the doping derivatives of β-Li3PS4, the effects of doping on the ionic conductivities in this material are predicted by the BV calculations. The O-doping scheme is proposed as a promising way to improve the kinetic properties of this materials, and the validity of the optimization is proved by the first-principles molecular dynamics (FPMD) simulations. PMID:26387639

  6. First-order superfluid to valence-bond solid phase transitions in easy-plane SU (N ) magnets for small N

    NASA Astrophysics Data System (ADS)

    D'Emidio, Jonathan; Kaul, Ribhu K.

    2016-02-01

    We consider the easy-plane limit of bipartite SU (N ) Heisenberg Hamiltonians, which have a fundamental representation on one sublattice and the conjugate to fundamental on the other sublattice. For N =2 the easy plane limit of the SU(2) Heisenberg model is the well-known quantum X Y model of a lattice superfluid. We introduce a logical method to generalize the quantum X Y model to arbitrary N , which keeps the Hamiltonian sign-free. We show that these quantum Hamiltonians have a world-line representation as the statistical mechanics of certain tightly packed loop models of N colors in which neighboring loops are disallowed from having the same color. In this loop representation we design an efficient Monte Carlo cluster algorithm for our model. We present extensive numerical results for these models on the two dimensional square lattice, where we find the nearest neighbor model has superfluid order for N ≤5 and valence-bond order for N >5 . By introducing SU (N ) easy-plane symmetric four-spin couplings we are able to tune across the superfluid-VBS phase boundary for all N ≤5 . We present clear evidence that this quantum phase transition is first order for N =2 and N =5 , suggesting that easy-plane deconfined criticality runs away generically to a first-order transition for small N .

  7. Valence band spectra of 4d and 5d silicides

    NASA Astrophysics Data System (ADS)

    Yarmoshenko, Yu M.; Shamin, S. N.; Elokhina, L. V.; Dolgih, V. E.; Kurmaev, E. Z.; Bartkowski, S.; Neumann, M.; Ederer, D. L.; Gransson, K.; Nolng, B.; Engstrm, I.

    1997-10-01

    A full study of the electronic structure of 4d and 5d silicides (RuSi, RhSi, PdSi, OsSi, IrSi, 0953-8984/9/43/023/img14, PtSi) is undertaken including XPS VB and XES (0953-8984/9/43/023/img15 and 0953-8984/9/43/023/img16) measurements and LMTO band structure calculations. It is found that d bands which dominate the density of states are more localized with increasing atomic number Z of the transition metal. A strong hybridization between silicon 3p and transition metal d states occurs over the entire valence band. Si 3s states are found to be not mixed with Si 3p and nd states but Si 3d states participate in bonding and hybridize with transition metal d states. The non-bonding character of the majority of nd states is not confirmed for 4d and 5d silicides.

  8. Unprecedented structural variations in trinuclear mixed valence Co(II/III) complexes: theoretical studies, pnicogen bonding interactions and catecholase-like activities.

    PubMed

    Hazari, Alokesh; Kanta Das, Lakshmi; Kadam, Ramakant M; Bauz, Antonio; Frontera, Antonio; Ghosh, Ashutosh

    2015-02-28

    Three new mixed valence trinuclear Co(II/III) compounds cis-[Co3L2(MeOH)2(N3)2(?1,1-N3)2] (1), trans-[Co3L2(H2O)2(N3)2(?1,1-N3)2](H2O)2 (2) and [Co3L(R)2(N3)3(?1,3-N3)] (3) have been synthesized by reacting a di-Schiff base ligand (H2L) or its reduced form [H2LR] (where H2L= N,N'-bis(salicylidene)-1,3-propanediamine and H2LR= N,N'-bis(2-hydroxybenzyl)-1,3-propanediamine) with cobalt perchlorate hexahydrate and sodium azide. All three products have been characterized by IR, UV-Vis and EPR spectroscopies, ESI-MS, elemental, powder and single crystal X-ray diffraction analyses. Complex 2 is an angular trinuclear species in which two terminal octahedral Co(III)N2O4 centers coordinate to the central octahedral cobalt(II) ion through ?2-phenoxido oxygen and ?1,1-azido nitrogen atoms along with two mutually cis-oxygen atoms of methanol molecules. On the other hand, in linear trinuclear complex , in addition to the ?2-phenoxido and ?1,1-azido bridges with terminal octahedral Co(III) centres, the central Co(II) is bonded with two mutually trans-oxygen atoms of water molecules. Thus the cis-trans configuration of the central Co(II) is solvent dependent. In complex 3, the two terminal octahedral Co(III)N2O4 centers coordinate to the central penta-coordinated Co(II) ion through double phenoxido bridges along with the nitrogen atom of a terminal azido ligand. In addition, the two terminal Co(III) are connected through a ?1,3-azido bridge that participates in pnicogen bonding interactions (intermolecular N-N interaction) as an acceptor. Both the cis and trans isomeric forms of 1 and 2 have been optimized using density functional theory (DFT) calculations and it is found that the cis configuration is energetically more favorable than the trans one. However, the trans configuration of 2 is stabilized by the hydrogen bonding network involving a water dimer. The pnicogen bonding interactions have been demonstrated using MEP surfaces and CSD search which support the counter intuitive electron acceptor ability of the ?1,3-azido ligand. Complexes 1-3 exhibit catecholase-like activities in the aerial oxidation of 3,5-di-tert-butylcatechol to the corresponding o-quinone. Kinetic data analyses of this oxidation reaction in acetonitrile reveal that the catecholase-like activity follows the order: 1 (kcat = 142 h(-1)) > 3 (kcat = 99 h(-1)) > 2 (kcat = 85 h(-1)). Mechanistic investigations of the catalytic behaviors by X-band EPR spectroscopy and estimation of hydrogen peroxide formation indicate that the oxidation reaction proceeds through the reduction of Co(III) to Co(II). PMID:25611163

  9. 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

    Schneider, Jochen M.; Music, Denis; Sun Zhimei

    2005-03-15

    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.

  10. Fabrication of VB2/Air Cells for Electrochemical Testing

    PubMed Central

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

    2013-01-01

    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

  11. DERIVATION AND SIGNIFICANCE OF VALENCE MOLECULAR CONNECTIVITY

    EPA Science Inventory

    The physical basis for valence molecular connectivity was studied. The sigma sup upsilon and sigma values are cardinal numbers describing the electronic structure of atoms in their valence states. The value (sigma sup upsilon) + (sigma) describes the volume of a bonding atom whil...

  12. An electron diffraction and bond valence sum study of the space group symmetries and structures of the photocatalytic 1:1 ordered A2InNbO 6 double perovskites ( A=Ca 2+, Sr 2+, Ba 2+)

    NASA Astrophysics Data System (ADS)

    Ting, V.; Liu, Y.; Withers, R. L.; Krausz, E.

    2004-03-01

    A careful investigation has been carried out into the space group symmetries, structures and crystal chemistries of the 1:1 B-site ordered double perovskites A2InNbO 6 ( A=Ca 2+, Sr 2+, Ba 2+) using a combination of bond valence sum calculations, powder XRD and electron diffraction. A recent investigation of these compounds by Yin et al. reported a random distribution of In 3+ and Nb 5+ ions onto the perovskite B-site positions of these compounds and hence Pm 3m ( a= ap, subscript p for parent perovskite sub-structure) space group symmetry for the A=Ba and Sr compounds and Pnma( a= ap+ bp, b=- ap+ bp, c=2 cp) space group symmetry for the A=Ca compound. A careful electron diffraction study, however, shows that both the A=Ca and Sr compounds occur at room temperature in P12 1/ n1 ( a= ap+ bp, b=- ap+ bp, c=2 cp) perovskite-related superstructure phases while the A=Ba compound occurs in the Fm 3m , a=2 ap, elpasolite structure type. Bond valence sum calculations are used to explain why this should be so as well as to provide a useful first-order approximation to the structures of each of the compounds.

  13. Combined valence bond-molecular mechanics potential-energy surface and direct dynamics study of rate constants and kinetic isotope effects for the H +C2H6 reaction

    NASA Astrophysics Data System (ADS)

    Chakraborty, Arindam; Zhao, Yan; Lin, Hai; Truhlar, Donald G.

    2006-01-01

    This article presents a multifaceted study of the reaction H +C2H6?H2+C2H5 and three of its deuterium-substituted isotopologs. First we present high-level electronic structure calculations by the W1, G3SX, MCG3-MPWB, CBS-APNO, and MC-QCISD/3 methods that lead to a best estimate of the barrier height of 11.80.5kcal/mol. Then we obtain a specific reaction parameter for the MPW density functional in order that it reproduces the best estimate of the barrier height; this yields the MPW54 functional. The MPW54 functional, as well as the MPW60 functional that was previously parametrized for the H +CH4 reaction, is used with canonical variational theory with small-curvature tunneling to calculate the rate constants for all four ethane reactions from 200 to 2000 K. The final MPW54 calculations are based on curvilinear-coordinate generalized-normal-mode analysis along the reaction path, and they include scaled frequencies and an anharmonic C-C bond torsion. They agree with experiment within 31% for 467-826 K except for a 38% deviation at 748 K; the results for the isotopologs are predictions since these rate constants have never been measured. The kinetic isotope effects (KIEs) are analyzed to reveal the contributions from subsets of vibrational partition functions and from tunneling, which conspire to yield a nonmonotonic temperature dependence for one of the KIEs. The stationary points and reaction-path potential of the MPW54 potential-energy surface are then used to parametrize a new kind of analytical potential-energy surface that combines a semiempirical valence bond formalism for the reactive part of the molecule with a standard molecular mechanics force field for the rest; this may be considered to be either an extension of molecular mechanics to treat a reactive potential-energy surface or a new kind of combined quantum-mechanical/molecular mechanical (QM/MM) method in which the QM part is semiempirical valence bond theory; that is, the new potential-energy surface is a combined valence bond molecular mechanics (CVBMM) surface. Rate constants calculated with the CVBMM surface agree with the MPW54 rate constants within 12% for 534-2000 K and within 23% for 200-491 K. The full CVBMM potential-energy surface is now available for use in variety of dynamics calculations, and it provides a prototype for developing CVBMM potential-energy surfaces for other reactions.

  14. Utrecht Echelle spectroscopy of a flare in VB 8

    NASA Astrophysics Data System (ADS)

    Martn, E. L.

    1999-01-01

    Very high-resolution (R ~ 110 000) spectroscopic observations of the very low-mass star VB 8, obtained with the Utrecht Echelle spectrograph (UES), are presented. A flare occurred during the third of a series of four consecutive spectra. This event produced significant enhancement in the strength of the emission lines of He i D3 and H? in VB 8, as well as a filling up of some but not all atomic absorption lines, and a weakening of the ? TiO bandheads at 705.4 and 712.5 nm. Core emission in the Na i D1, D2 and K i 769.9-nm resonance lines also became stronger during the flare. Other very low-mass stars observed with the same instrumental configuration include GJ 406 and VB 10. The UES spectrum of VB 8 is compared with these. In particular, VB 10 appears to have a lower gravity than VB 8, indicating a lower age and a smaller mass which could be very close to the substellar mass limit for solar metallicity.

  15. Nature of the Xe(VI) -N Bonds in F6 XeNCCH3 and F6 Xe(NCCH3 )2 and the Stereochemical Activity of Their Xenon Valence Electron Lone Pairs.

    PubMed

    Haner, Jamie; Matsumoto, Kazuhiko; Mercier, Hélène P A; Schrobilgen, Gary J

    2016-03-24

    The recently reported syntheses and X-ray crystal structures of the highly endothermic compounds F6 XeNCCH3 and F6 Xe(NCCH3 )2 ⋅CH3 CN provide the first, albeit weakly covalent, Xe(VI) -N bonds. The XeF6 unit of F6 XeNCCH3 possesses distorted octahedral (C3v ) symmetry similar to gas-phase XeF6 , whereas the XeF6 unit of F6 Xe(NCCH3 )2 ⋅CH3 CN possesses C2v symmetry. Herein, the natural bond orbital (NBO), atoms in molecules (AIM), electron localization function (ELF), and molecular electrostatic potential surface (MEPS) analyses show that the Xe valence electron lone pairs (VELPs) of both compounds are stereochemically active. The Xe VELPS are diffuse and ineffectively screen their Xe cores so that the Xe VELP positions correspond to the most electrophilic regions of the MEPS, which enables the opposing N VELP of CH3 CN to coordinate to this region. These bonds are predominantly electrostatic in nature and are interpreted as σ-hole interactions. PMID:26918266

  16. A valence-bond diatomics-in-molecules model for the formation of Na + and Na 2+ ions from the interaction of excited sodium atoms with a tungsten surface

    NASA Astrophysics Data System (ADS)

    Kuntz, Philip J.

    1985-04-01

    Potential energy surfaces for Na( 2S, 2P) interacting with a partially covered tungsten surface are computed within the framework of the method of diatomics-in-molecules (DIM). Only two sodium atoms are considered explicitly but the effect of all of the adsorbed sodium is taken into account through its influence on the fragment matrix elements in the DIM formulation. Na 2+ wavefunctions are approximated by valence-bond calculations for the 2? g+ and 2? u+ manifolds. The three lowest potential energy surfaces of the polyatomic system suggest plausible pathways for the production of Na + and Na 2+ ions from the interaction of Na( 2P) atoms with the metal surface as observed by Auschwitz and Lacmann.

  17. Levels of valence.

    PubMed

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

    2013-01-01

    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

  18. Levels of Valence

    PubMed Central

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

    2013-01-01

    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

  19. The valence band structure of Ag{sub x}Rh{sub 1–x} alloy nanoparticles

    SciTech Connect

    Yang, Anli; Sakata, Osami; Kusada, Kohei; Kobayashi, Hirokazu; Yayama, Tomoe; Ishimoto, Takayoshi; Yoshikawa, Hideki; Koyama, Michihisa; and others

    2014-10-13

    The valence band (VB) structures of face-centered-cubic Ag-Rh alloy nanoparticles (NPs), which are known to have excellent hydrogen-storage properties, were investigated using bulk-sensitive hard x-ray photoelectron spectroscopy. The observed VB spectra profiles of the Ag-Rh alloy NPs do not resemble simple linear combinations of the VB spectra of Ag and Rh NPs. The observed VB hybridization was qualitatively reproduced via a first-principles calculation. The electronic structure of the Ag{sub 0.5}Rh{sub 0.5} alloy NPs near the Fermi edge was strikingly similar to that of Pd NPs, whose superior hydrogen-storage properties are well known.

  20. Dynamics of dipole- and valence bound anions in iodide-adenine binary complexes: A time-resolved photoelectron imaging and quantum mechanical investigation

    NASA Astrophysics Data System (ADS)

    Stephansen, Anne B.; King, Sarah B.; Yokoi, Yuki; Minoshima, Yusuke; Li, Wei-Li; Kunin, Alice; Takayanagi, Toshiyuki; Neumark, Daniel M.

    2015-09-01

    Dipole bound (DB) and valence bound (VB) anions of binary iodide-adenine complexes have been studied using one-color and time-resolved photoelectron imaging at excitation energies near the vertical detachment energy. The experiments are complemented by quantum chemical calculations. One-color spectra show evidence for two adenine tautomers, the canonical, biologically relevant A9 tautomer and the A3 tautomer. In the UV-pump/IR-probe time-resolved experiments, transient adenine anions can be formed by electron transfer from the iodide. These experiments show signals from both DB and VB states of adenine anions formed on femto- and picosecond time scales, respectively. Analysis of the spectra and comparison with calculations suggest that while both the A9 and A3 tautomers contribute to the DB signal, only the DB state of the A3 tautomer undergoes a transition to the VB anion. The VB anion of A9 is higher in energy than both the DB anion and the neutral, and the VB anion is therefore not accessible through the DB state. Experimental evidence of the metastable A9 VB anion is instead observed as a shape resonance in the one-color photoelectron spectra, as a result of UV absorption by A9 and subsequent electron transfer from iodide into the empty ?-orbital. In contrast, the iodide-A3 complex constitutes an excellent example of how DB states can act as doorway state for VB anion formation when the VB state is energetically available.

  1. Draft Genome Sequence of Tolypothrix boutellei Strain VB521301

    PubMed Central

    Chandrababunaidu, Mathu Malar; Singh, Deeksha; Sen, Diya; Bhan, Sushma; Das, Subhadeep; Gupta, Akash

    2015-01-01

    We report here the draft genome sequence of the filamentous nitrogen-fixing cyanobacterium Tolypothrix boutellei strain VB521301. The organism is lipid rich and hydrophobic and produces polyunsaturated fatty acids which can be harnessed for industrial purpose. The draft genome sequence assembled into 11,572,263bp with 70 scaffolds and 7,777 protein coding genes. PMID:25700407

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

    PubMed

    Beck, John Frederick; Mo, Yirong

    2007-01-15

    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

  3. Coulombic Models in Chemical Bonding.

    ERIC Educational Resources Information Center

    Sacks, Lawrence J.

    1986-01-01

    Compares the coulumbic point charge model for hydrogen chloride with the valence bond model. It is not possible to assign either a nonpolar or ionic canonical form of the valence bond model, while the covalent-ionic bond distribution does conform to the point charge model. (JM)

  4. Electronic structure and bonding in four-coordinate organometallic complexes of aluminum. Valence photoelectron spectra of BHT-H, Me sub 3 Al(PMe sub 3 ), and Me sub 2 (BHT)Al(PMe sub 3 )

    SciTech Connect

    Lichtenberger, D.L.; Hogan, R.H. ); Healy, M.D.; Barron, A.R. )

    1990-04-25

    The He I valence photoelectron spectra of the Lewis acid-base adducts Me{sub 3}Al(PMe{sub 3}) and Me{sub 2}(BHT)Al(PMe{sub 3}) (BHT{minus}H = 2,6-di-tert-butyl-4-methylphenol) have been obtained to characterize the electronic structure and bonding in four-coordinate organometallic complexes of aluminum. To aid in the assignment of the spectrum of Me{sub 2}(BHT)Al(PMe{sub 3}), the spectrum of the free alcohol, BHT-H, was also obtained. The first and second ionizations of the free BHT-H alcohol show vibrational progressions associated with the symmetric C-C phenyl ring stretching modes, consistent with the b{sub 1} and a{sub 2} {pi} ionizations, respectively, of monosubstituted phenyl rings. In the photoelectron spectrum of BHT coordinated to aluminum in Me{sub 2}(BHT)Al(PMe{sub 3}), the corresponding phenoxide a{sub 2} ionization retains the vibrational structure, but the individual vibrational components are lost in the ionization that corresponds most closely with the b{sub 1}. The loss of vibrational fine structure associated with ionization from the phenyl {pi} b{sub 1} orbital in the coordinated phenoxide shows that the phenoxide is involved in a {pi} interaction with the Me{sub 2}Al(PMe{sub 3}) portion of the molecule.

  5. An ab initio study of core-valence correlation. [in atoms

    NASA Technical Reports Server (NTRS)

    Partridge, H.; Bauschlicher, C. W., Jr.; Walch, S. P.; Liu, B.

    1983-01-01

    Especially in the cases of the first two columns of the periodic table, the inclusion of core-valence correlation in ab initio CI calculations yields a contraction of the atomic valence shell and improves both calculated atomic ionization potentials and atomic energy separations. For the alkali dimers Na2, K2, and Rb2, the presently calculated bond lengths are in excellent agreement with experiments when core-valence is included. In addition, the valence dissociation energies are accurate.

  6. Climatology of Vb cyclones, physical mechanisms and their impact on extreme precipitation over Central Europe

    NASA Astrophysics Data System (ADS)

    Messmer, M.; Gómez-Navarro, J. J.; Raible, C. C.

    2015-09-01

    Cyclones, which develop over the western Mediterranean and move northeastward are a major source of extreme weather and known to be responsible for heavy precipitation over the northern side of the Alpine range and Central Europe. As the relevant processes triggering these so-called Vb events and their impact on extreme precipitation are not yet fully understood, this study focuses on gaining insight into the dynamics of past events. For this, a cyclone detection and tracking tool is applied to the ERA-Interim reanalysis (1979-2013) to identify prominent Vb situations. Precipitation in the ERA-Interim and the E-OBS data sets is used to evaluate case-to-case precipitation amounts and to assess consistency between the two data sets. Both data sets exhibit high variability in precipitation amounts among different Vb events. While only 23 % of all Vb events are associated with extreme precipitation, around 15 % of all extreme precipitation days (99 percentile) over the northern Alpine region and Central Europe are induced by Vb events, although Vb cyclones are rare events (2.3 per year). To obtain a better understanding of the variability within Vb events, the analysis of the 10 heaviest and lowest precipitation Vb events reveals noticeable differences in the state of the atmosphere. These differences are most pronounced in the geopotential height and potential vorticity field, indicating a much stronger cyclone for heavy precipitation events. The related differences in wind direction are responsible for the moisture transport around the Alps and the orographical lifting along the northern slopes of the Alps. These effects are the main reasons for a disastrous outcome of Vb events, and consequently are absent in the Vb events associated with low precipitation. Hence, our results point out that heavy precipitation related to Vb events is mainly related to large-scale dynamics rather than to thermodynamic processes.

  7. Deciphering the Genome Sequences of the Hydrophobic Cyanobacterium Scytonema tolypothrichoides VB-61278

    PubMed Central

    Das, Abhishek; Panda, Arijit; Singh, Deeksha; Chandrababunaidu, Mathu Malar; Mishra, Gyan Prakash; Bhan, Sushma

    2015-01-01

    Scytonema tolypothrichoides VB-61278, a terrestrial cyanobacterium, can be exploited to produce commercially important products. Here, we report for the first time a 10-Mb draft genome assembly of S. tolypothrichoides VB-61278, with 214 scaffolds and 7,148 putative protein-coding genes. PMID:25838486

  8. VB12-coated Gel-Core-SLN containing insulin: Another way to improve oral absorption.

    PubMed

    He, Haibing; Wang, Puxiu; Cai, Cuifang; Yang, Rui; Tang, Xing

    2015-09-30

    To improve the oral absorption of insulin, a novel carrier of Vitamin B12 (VB12) gel core solid lipid nanopaticles (Gel-Core-SLN, GCSLN) was designed with a gel core, lipid matrix and VB12-coated surface. VB12-stearate was synthesized and characterized by infrared spectroscopy (IR), nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry (MS). Sol-gel conversion following ultrasonic heating and double emulsion technology were combined to implant the insulin-containing gel into solid lipid nanoparticles (SLN). The influence of the mode of administration, food, the amount of VB12-stearate and the particle size on the oral absorption of insulin incorporated in the VB12-GCSLN was investigated. The determined partition coefficient (LogP) of VB12-stearate in a dichloromethane (DCM)-water system was 3.4. This new structure of VB12-GCSLN had higher insulin encapsulation efficiency (EE) of 55.9%, a lower burst release of less than 10% in the first 2h. In vivo studies demonstrated that stronger absorption of insulin with a relative pharmacological availability (PA) of 9.31% compared with the normal insulin-loaded SLN and GCSLN and fairly stable blood glucose levels up to 12h were maintained without any sharp fluctuations. This study suggests that VB12-GCSLN containing insulin appears to be a promising nano carrier for oral delivery of biomacromolecules with relatively high pharmacological availability. PMID:26253378

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

    ERIC Educational Resources Information Center

    Smith, Derek W.

    2005-01-01

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

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

    ERIC Educational Resources Information Center

    Smith, Derek W.

    2005-01-01

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

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

    SciTech Connect

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

    2014-05-28

    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 ?E{sub V} 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 ?E{sub V}?=?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, ?E{sub B,CL} ???E{sub B,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 ?E{sub V}{sup CNL}?=?2.65??0.3?eV agrees well with the experimental ?E{sub V}.

  12. Vb-type cyclones and their role in extreme precipitation events in Central Europe

    NASA Astrophysics Data System (ADS)

    Messmer, Martina; José Gómez-Navarro, Juan; Raible, Christoph C.

    2015-04-01

    Extreme weather situations are of major relevance for society, since they lead to great economical and personal damage. In Central Europe, one important source of extreme precipitation accompanied by large flooding events is the so-called Vb-event, classified by W. J. Van Bebber in 1891. Vb-events are defined as cyclones developing over the western Mediterranean that move north eastward. They can uptake large amounts of moisture, which is then transported towards the Alps and Central Europe, inducing heavy precipitation and flooding events. Despite their importance the relevant processes triggering Vb-events and their impact in extreme precipitation are not yet fully understood. The overall goal of this study research is to understand the dynamics of the past events and to provide a reliable climatology, which would provide a first guess for future behaviour of these potentially disastrous situations. A cyclone detection and tracking tool is applied to ERA Interim reanalysis (1979-2013) in order to identify the most prominent Vb-situations. Vb-events are detected and tracked in the geopotential height at 850 hPa. Subsequently, the cyclones are automatically filtered with criteria based on the origin and end of the track, which allows us discarding those paths that should not be considered as Vb-events. Precipitation in the ERA Interim and E-OBS database is used to evaluate the precipitation amounts corresponding to each case and to assess the consistency between datasets. ERA Interim and E-OBS data consistently indicate that there is great variability in precipitation amounts within different Vb-events. While it is expected that Vb-events are associated with extreme precipitation, this is only true for about one quarter of all cases. Nevertheless around 15% of extreme precipitation days (99 percentile) over the Alpine region are triggered by Vb-events. In order to obtain a better understanding of the large variability in Vb-events, the ten heaviest and lowest precipitation Vb-events are studied in more detail. Results reveal noticeable differences in the state of the atmosphere that lead to heavy precipitation. These differences are most pronounced in the geopotential height and potential vorticity field. The associated differences in wind direction in different elevations are responsible for the moisture transport around the Alps and the orographical lifting along the Alps. These effects are the main reasons for the disastrous outcome of Vb-events and consequently are missing in the driest Vb-events. The results indicate that heavy precipitation is mainly related to large-scale dynamics rather than to thermodynamic processes, as could be expected.

  13. Isolation and characterization of the pea cytochrome c oxidase Vb gene.

    PubMed

    Kubo, Nakao; Arimura, Shin-Ichi; Tsutsumi, Nobuhiro; Kadowaki, Koh-Ichi; Hirai, Masashi

    2006-11-01

    Three copies of the gene that encodes cytochrome c oxidase subunit Vb were isolated from the pea (PscoxVb-1, PscoxVb-2, and PscoxVb-3). Northern Blot and reverse transcriptase-PCR analyses suggest that all 3 genes are transcribed in the pea. Each pea coxVb gene has an N-terminal extended sequence that can encode a mitochondrial targeting signal, called a presequence. The localization of green fluorescent proteins fused with the presequence strongly suggests the targeting of pea COXVb proteins to mitochondria. Each pea coxVb gene has 5 intron sites within the coding region. These are similar to Arabidopsis and rice, although the intron lengths vary greatly. A phylogenetic analysis of coxVb suggests the occurrence of gene duplication events during angiosperm evolution. In particular, 2 duplication events might have occurred in legumes, grasses, and Solanaceae. A comparison of amino acid sequences in COXVb or its counterpart shows the conservation of several amino acids within a zinc finger motif. Interestingly, a homology search analysis showed that bacterial protein COG4391 and a mitochondrial complex I 13 kDa subunit also have similar amino acid compositions around this motif. Such similarity might reflect evolutionary relationships among the 3 proteins. PMID:17426763

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

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

    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.

  15. Myosin Vb Mobilizes Recycling Endosomes and AMPA Receptors for Postsynaptic Plasticity

    PubMed Central

    Wang, Zhiping; Edwards, Jeffrey G.; Riley, Nathan; Provance, D. William; Karcher, Ryan; Li, Xiang-dong; Davison, Ian G.; Ikebe, Mitsuo; Mercer, John A.; Kauer, Julie A.; Ehlers, Michael D.

    2008-01-01

    Summary Learning-related plasticity at excitatory synapses in the mammalian brain requires the trafficking of AMPA receptors and the growth of dendritic spines. However, the mechanisms that couple plasticity stimuli to the trafficking of postsynaptic cargo are poorly understood. Here we demonstrate that myosin Vb (MyoVb), a Ca2+-sensitive motor, conducts spine trafficking during long-term potentiation (LTP) of synaptic strength. Upon activation of NMDA receptors and corresponding Ca2+ influx, MyoVb associates with recycling endosomes (REs), triggering rapid spine recruitment of endosomes and local exocytosis in spines. Disruption of MyoVb or its interaction with the RE adaptor Rab11-FIP2 abolishes LTP-induced exocytosis from REs and prevents both AMPA receptor insertion and spine growth. Furthermore, induction of tight binding of MyoVb to actin using an acute chemical genetic strategy eradicates LTP in hippocampal slices. Thus, Ca2+-activated MyoVb captures and mobilizes of REs for AMPA receptor insertion and spine growth, providing a mechanistic link between the induction and expression of postsynaptic plasticity. PMID:18984164

  16. Micro-Valences: Perceiving Affective Valence in Everyday Objects

    PubMed Central

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

    2012-01-01

    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 scenes 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. PMID:22529828

  17. An electron diffraction and bond valence sum study of the space group symmetries and structures of the photocatalytic 1:2 B site ordered A3CoNb 2O 9 perovskites ( A=Ca 2+, Sr 2+, Ba 2+)

    NASA Astrophysics Data System (ADS)

    Ting, V.; Liu, Y.; Withers, R. L.; Norn, L.

    2004-07-01

    A careful investigation has been carried out into the space group symmetries, structures and crystal chemistries of the 1:2 B-site ordered triple perovskites A3Co 2+Nb 5+2O 9 ( A=Ca 2+, Sr 2+, Ba 2+) using a combination of bond valence sum calculations, powder XRD and electron diffraction. A recent investigation of these compounds by Yin et al. reported a random distribution of Co 2+ and Nb 5+ ions onto the perovskite B-site positions and hence Pm 3m ( a= ap, subscript p for parent perovskite sub-structure) space group symmetry for the A=Ba and Sr compounds and a monoclinically distorted variant thereof (although no space group was given) in the case of the A=Ca compound. An electron diffraction study, however, shows that the A=Ba compound occurs in a 1:2 B site ordered trigonal P 3m1 , ah= bp- cp, bh= cp- ap, ch= ap+ bp+ cp structure type while both the A=Ca and Sr compounds occur at room temperature in monoclinic P12 1/ c1, am=[ 112] p, bm=[1 10] p, cm=3[110] p, perovskite-related structure types. The latter monclinic structure type can be described as a modulated variant of the 1:2 B site ordered trigonal P 3m1 structure type with the additional modulations associated with a b-b-c+ octahedral tilt sequence. Bond valence sum calculations are used to explain why this should be so as well as to provide a useful zeroth-order approximation to the structures of each of the compounds.

  18. Valence photoelectron spectroscopy of Gd silicides

    SciTech Connect

    Braicovich, L. ); Puppin, E.; Lindau, I. ); Iandelli, A.; Olcese, G.L.; Palenzona, A. )

    1990-02-15

    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.

  19. Stoichiometry, Coordination, and Interatomic Distances in Simple Valence Crystals

    NASA Astrophysics Data System (ADS)

    Hansen, Staffan

    1993-07-01

    A simple valence or haplotype crystal is defined as a valence crystal of binary composition A xB y, with one coordination number, CN( A), for all cations and one, CN( B), for all anions. Valence crystals have electroneutral formulas with respect to formal atomic valences ( V A, V B) and each cation is surrounded entirely by anions and vice versa. Known haplotype structures include a majority of textbook examples of binary inorganic structures. Two simple rules apply to haplotypes: x V A = y V B and x CN( A) = y CN( B). These two rules strongly limit the number of possible combinations of atomic valence, composition, and coordination. A clear connection is shown to exist in known haplotypes between the coordination number of the majority atom and the dimensionality of strong bonding, which in turn has a great influence on crystal properties. In haplotypes with three-dimensional bonding, an observed relationship between composition and interatomic distances is shown to be a consequence of the rather regular coordination figures present in this group of structures.

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

    SciTech Connect

    Wernet, Ph.; Godehusen, K.; Gaudin, J.; Schwarzkopf, O.; Eberhardt, W.; Odelius, M.

    2009-07-03

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

  1. VB-111: a novel anti-vascular therapeutic for glioblastoma multiforme.

    PubMed

    Gruslova, Aleksandra; Cavazos, David A; Miller, Jessica R; Breitbart, Eyal; Cohen, Yael C; Bangio, Livnat; Yakov, Niva; Soundararajan, Anu; Floyd, John R; Brenner, Andrew J

    2015-09-01

    Glioblastoma multiforme (GBM) is among the most highly vascularized of solid tumors, contributing to the infiltrative nature of the disease, and conferring poor outcome. Due to the critical dependency of GBM on growth of new endothelial vasculature, we evaluated the preclinical activity of a novel adenoviral gene therapy that targets the endothelium within newly formed blood vessels for apoptosis. VB-111, currently in phase II clinical trials, consists of a non-replicating Adenovirus 5 (El deleted) carrying a proapoptotic human Fas-chimera (transgene) under the control of a modified murine promoter (PPE-1-3) which specifically targets endothelial cells within the tumor vasculature. Here we report that a single intravenous dose of 2.5נ10(11) or 1נ10(11) VPs was sufficient to extend survival in nude rats bearing U87MG-luc2 or nude mice bearing U251-luc, respectively. Bioluminescence imaging of nude rats showed that VB-111 effectively inhibited tumor growth within four weeks of treatment. This was confirmed in a select group of animals by MRI. In our mouse model we observed that 3 of 10 nude mice treated with VB-111 completely lost U251 luciferase signal and were considered long term survivors. To assess the antiangiogenic effects of VB-111, we evaluated the tumor-associated microvaculature by CD31, a common marker of neovascularization, and found a significant decrease in the microvessel density by IHC. We further assessed the neovasculature by confocal microscopy and found that VB-111 inhibits vascular density in two separate mouse models bearing U251-RFP xenografts. Collectively, this study supports the clinical development of VB-111 as a treatment for GBM. PMID:26108658

  2. Implementation of RS-485 Communication between PLC and PC of Distributed Control System Based on VB

    NASA Astrophysics Data System (ADS)

    Lian Zhang, Chuan; Da Huang, Zhi; Qing Zhou, Gui; Chong, Kil To

    2015-05-01

    This paper focuses on achieving RS-485 communication between programmable logical controller (PLC) and PC based on visual basic 6.0 (VB6.0) on an experimental automatic production line. Mitsubishi FX2N PLCs and a PC are chosen as slave stations and main station, respectively. Monitoring software is developed using VB6.0 for data input/output, flow control and online parameters setting. As a result, all functions are fulfilled with robust performance. It is concluded from results that one PC can monitor several PLCs using RS-485 communication.

  3. Reversible conversion of valence-tautomeric copper metal-organic frameworks dependent single-crystal-to-single-crystal oxidation/reduction: a redox-switchable catalyst for C-H bonds activation reaction.

    PubMed

    Huang, Chao; Wu, Jie; Song, Chuanjun; Ding, Ran; Qiao, Yan; Hou, Hongwei; Chang, Junbiao; Fan, Yaoting

    2015-06-28

    Upon single-crystal-to-single-crystal (SCSC) oxidation/reduction, reversible structural transformations take place between the anionic porous zeolite-like Cu(I) framework and a topologically equivalent neutral Cu(I)Cu(II) mixed-valent framework. The unique conversion behavior of the Cu(I) framework endowed it as a redox-switchable catalyst for the direct arylation of heterocycle C-H bonds. PMID:25994106

  4. Order in the resonating singlet valence plaquette model in three dimensions.

    NASA Astrophysics Data System (ADS)

    Pankov, Sergey; Moessner, Roderich; Sondhi, Shivaji

    2005-03-01

    We study a generalization of resonating valence bond (RVB) physics to three dimensions. In two dimensions short-range RVB models can exhibit fundamentally interesting phenomena like quantum liquid states with topological order and fractionalization. Whereas in the RVB case, the basic degree of freedom can be thought of as an SU(2) singlet (valence) bond between two spins, in resonating singlet valence plaquette (RSVP) physics, it corresponds to an SU(4) singlet comprising four sites; this might arise for example in a spin-orbital model. Here, we discuss the detailed phase diagram for the simplest case -- the Rokhsar-Kivelson RSVP model on the cubic lattice.

  5. Reactive Force Fields via Explicit Valency

    NASA Astrophysics Data System (ADS)

    Kale, Seyit

    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.

  6. Bonding with parallel spins: high-spin clusters of monovalent metal atoms.

    PubMed

    Danovich, David; Shaik, Sason

    2014-02-18

    Bonding is a glue of chemical matter and is also a useful concept for designing new molecules. Despite the fact that electron pairing remains the bonding mechanism in the great majority of molecules, in the past few decades scientists have had a growing interest in discovering novel bonding motifs. As this Account shows, monovalent metallic atoms having exclusively parallel spins, such as (11)Li10, (11)Au10, and (11)Cu10, can nevertheless form strongly bound clusters, without having even one traditional bond due to electron pairing. These clusters, which also can be made chiral, have high magnetic moments. We refer to this type as no-pair ferromagnetic (NPFM) bonding, which characterizes the (n+1)Mn clusters, which were all predicted by theoretical computations. The small NPFM alkali clusters that have been "synthesized" to date, using cold-atom techniques, support the computational predictions. In this Account, we describe the origins of NPFM bonding using a valence bond (VB) analysis, which shows that this bonding motif arises from bound triplet electron pairs that spread over all the close neighbors of a given atom in the cluster. The bound triplet pair owes its stabilization to the resonance energy provided by the mixing of the local ionic configurations, [(3)M(??)(-)]M(+) and M(+)[(3)M(??)(-)], and the various excited covalent configurations (involving pz and dz(2) atomic orbitals) into the repulsive covalent structure (3)(M??M) with the s(1)s(1) electronic configuration. The NPFM bond of the bound triplet is described by a resonating wave function with "in-out" and "out-in" pointing hybrids. The VB model accounts for the tendency of NPFM clusters to assume polyhedral shapes with rather high symmetry. In addition, this model explains the very steep rise of the bonding energy per atom (De/n), which starts out small in the (3)M2 dimer (<1 kcal/mol) and reaches 12-19 kcal/mol for clusters with 10 atoms. The model further predicts that usage of heteroatomic clusters should increase the bonding energy of an NPFM cluster. These NPFM clusters are excited state species. We suggest here stabilizing these states and making them accessible, for example, by using magnetic fields, or a combination of magnetic and electric fields. The advent of NPFM clusters offers new horizons in chemistry and enriches the scope of chemical bonding. These prospects form a strong incentive to investigate the origins of the bound triplet pairs and further chart the territory of NPFM clusters, for example, in clusters of Be, Mg, or Zn, possibly in clusters of their monosubstituted species, and the group III metalloids, such as B, Al, as well as in transition metals such as Sc. PMID:23941238

  7. Analysis of the linear response function relating AL to VB{sub s} for individual substorms

    SciTech Connect

    Blanchard, G.T.; McPherron, R.L.

    1995-10-01

    Time series of the AL index and rectified solar wind electric field are used to study solar wind coupling to auroral ionospheric currents during individual substorms. Calculation of the individual filters is accompanied by representing them as the product of two simple filters: a low-pass filter that accounts for the response of the ionospheric electric field to the reconnection electric field, and a filter composed of delta function. The delta functions each have the effect of delaying and scaling the response of AL relative to VB{sub s} without distorting the waveform of VB{sub s}. Nearly all significant correlation between AL and VB{sub s} can be accounted for when the second filter contains only two components. This result suggests that the westward electrojet indexed by AL is controlled by two distinct processes, both proportional to VB{sub s}. For an ensemble of 117 isolated substorms the average prediction efficiency of a filter with two delays is 71%. If one were able to determine the exact values of the two delays and the two gain factors prior to an event, then one would be able to estimate the instantaneous magnetospheric response function. The authors examined season, universal time, and prior activity as possible factors controlling the magnitude of the parameters but found no apparent relationships. Until such relations are found the average parameters provide the best estimate but account for only 47% of the variance in the AL index. 20 refs., 10 figs.

  8. Mixed Valence Niobium

    NASA Astrophysics Data System (ADS)

    Keating, Steven James

    1992-01-01

    The structural, crystal-chemical, and electrical properties of perovskites are reviewed, with respect to metallic phases similar to tungsten bronze. Phase diagrams are presented for the SrO-NbO-NbO_{2.5 } and SrNbO_3-KNbO _3-rm Sr_{0.5}NbO _3 ternaries, and for the SrNbO_3 -rm Sr_{0.5}NbO_3 binary. The influence of oxygen partial pressure, temperature, melting, and solid solutions affecting the perovskite phase rm Sr_{x}NbO _3 (0.75 <= x < 1.0) are detailed. The phase rm Sr_5Nb_4O_{15-y} (0.0 <= y <= 1.04) is discussed and XRD data are presented. The effects of A-cation substitutions in the rm A_{x}NbO_3 (A = K^+, Ba^{2+ }, Sr^{2+}, La^{3+}, Gd^ {3+}, Y^{3+} ) perovskite have been investigated. Large ions such as K^+ and Ba^ {2+} cause x to approach unity, whereas smaller ions such as Sr^{2+} and La^{3+} increase the ability of the A-site to accommodate vacancies (i.e. x < 1). Ba^{2+} results in an increase in the lattice parameter of the perovskite, whereas K^+ (which requires oxidation of Nb^{4+} to Nb^{5+}) results in a lattice parameter decrease, even though it has an ionic radius similar to Ba^{2+} . A unique relationship between unit cell volume and valence is established, suggesting that the oxidation state of the NbO_6 network dictates the lattice parameters and stability of the perovskite. The resistivity variation for rm Sr_{x}NbO_3, (Ba,Sr)NbO _3, (K,Sr)NbO_3, and (rm K_{0.5}Sr_ {0.5})NbO_3 indicates metallic behavior between 298K and 77K. Resistivity increased as the Nb was oxidized from Nb^{4+} to Nb^{5+}, but metallic properties persisted to at least Nb^ {5+}/(Nb^{5+} + Nb^{4+}) = 0.5. The influence of the exchanges Sr^{2+} = Ba^{2+} and V_{rm A} + Sr ^{2+} = 2K^+ on the electrical resistivity of the perovskite suggests ordering or band structure effects which are orders of magnitude stronger than those observed in metal alloys. Magnetic susceptibility measurements indicate Pauli-paramagnetism. At low temperature (<15K), the paramagnetic susceptibility is obscured by superconductivity of NbN and Nb impurities. No evidence of an oxide superconductor was found in the Sr-Nb-O system.

  9. A Multidimensional Measure of Work Valences

    ERIC Educational Resources Information Center

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

    2012-01-01

    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

  10. Valence-band orbital character of CdO: A synchrotron-radiation photoelectron spectroscopy and density functional theory study

    NASA Astrophysics Data System (ADS)

    Mudd, J. J.; Lee, Tien-Lin; Muoz-Sanjos, V.; Ziga-Prez, J.; Payne, D. J.; Egdell, R. G.; McConville, C. F.

    2014-04-01

    N-type CdO is a transparent conducting oxide (TCO) which has promise in a number of areas including solar cell applications. In order to realize this potential a detailed knowledge of the electronic structure of the material is essential. In particular, standard density functional theory (DFT) methods struggle to accurately predict fundamental material properties such as the band gap. This is largely due to the underestimation of the Cd 4d binding energy, which results in a strong hybridization with the valence-band (VB) states. In order to test theoretical approaches, comparisons to experiment need to be made. Here, synchrotron-radiation photoelectron spectroscopy (SR-PES) measurements are presented, and comparison with three theoretical approaches are made. In particular the position of the Cd 4d state is measured with hard x-ray PES, and the orbital character of the VB is probed by photon energy dependent measurements. It is found that LDA + U using a theoretical U value of 2.34 eV is very successful in predicting the position of the Cd 4d state. The VB photon energy dependence reveals the O 2p photoionization cross section is underestimated at higher photon energies, and that an orbital contribution from Cd 5p is underestimated by all the DFT approaches.

  11. Synthesis, structure, and bonding of orthorhombic R5Au2Te2 (R = Lu, Ho, Dy, Y). Electronic structure of the binary parent valence compound Eu5As4.

    PubMed

    Chai, Ping; Corbett, John D

    2011-11-01

    Four examples of R(5)Au(2)Te(2) (vec = 29 e(-); R = Lu, Ho, Dy, Y) have been synthesized by high-temperature solid-state techniques, isotypic examples of Tm(5)Sb(2)Si(2) (vec = 33 e(-)) and binary Eu(5)As(4) (vec = 30 e(-)). The crystal structure was established for Lu(5)Au(2)Te(2), (orthorhombic Cmce (No. 64), a = 15.056(2), b = 7.749(1), c = 7.754(1) , and Z = 4), in which pairs of tellurium layers alternate with two-dimensional (2D) Lu(5)Au(2) slabs that are aggregated in such a way that each Au(2)-centered bi-trigonal prism (BTP) of Lu interconnects four other identical units, with the remaining cavities filled by nominal body-centered Lu cubes. The metal-metal aggregation in this structure provides a novel building unit in ternary rare-earth-metal-rich tellurides. Linear-muffin-tin-orbital (LMTO) electronic structure calculations and COHP analyses reveal that Lu(5)Au(2)Te(2) is a poor metal with Au(2) dimers and strong polar Lu-Au and Lu-Te interactions. The first theoretical analysis of the binary parent structure Eu(5)As(4) (vec = 30 e(-)) provides a simpler description of the equivalent orbital interactions and a closed shell gap in terms of the idealized (Eu(2+))(5)(As(2)(4-))(As(3-))(2) representation, particularly for the explicit filled As(2) levels ?(s), ?(s)*, ?(p), ?, ?*, plus empty ?(p)*. Crystal Orbital Hamilton Population (-COHP) data illuminate the prominent roles that polar bonding of Eu-As or Lu-Te and Lu-Au and relativistic effects with gold play in these, the former corresponding to 83% and 86% of the total Hamilton population for Eu(5)As(4) and Lu(5)Au(2)Te(2), respectively. PMID:21991925

  12. Forming Beliefs: Why Valence Matters.

    PubMed

    Sharot, Tali; Garrett, Neil

    2016-01-01

    One of the most salient attributes of information is valence: whether a piece of news is good or bad. Contrary to classic learning theories, which implicitly assume beliefs are adjusted similarly regardless of valence, we review evidence suggesting that different rules and mechanisms underlie learning from desirable and undesirable information. For self-relevant beliefs this asymmetry generates a positive bias, with significant implications for individuals and society. We discuss the boundaries of this asymmetry, characterize the neural system supporting it, and describe how changes in this circuit are related to individual differences in behavior. PMID:26704856

  13. Hydrogen multicentre bonds

    NASA Astrophysics Data System (ADS)

    Janotti, Anderson; van de Walle, Chris G.

    2007-01-01

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

  14. Draft Genome Sequence of the Terrestrial Cyanobacterium Scytonema millei VB511283, Isolated from Eastern India

    PubMed Central

    Sen, Diya; Chandrababunaidu, Mathu Malar; Singh, Deeksha; Sanghi, Neha; Ghorai, Arpita; Mishra, Gyan Prakash; Madduluri, Madhavi

    2015-01-01

    We report here the draft genome sequence of Scytonema millei VB511283, a cyanobacterium isolated from biofilms on the exterior of stone monuments in Santiniketan, eastern India. The draft genome is 11,627,246 bp long (11.63 Mb), with 118 scaffolds. About 9,011 protein-coding genes, 117 tRNAs, and 12 rRNAs are predicted from this assembly. PMID:25744984

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

    PubMed Central

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

    2009-01-01

    Members of the COG2244 protein family are integral membrane proteins involved in synthesis of a variety of extracellular polymers. In several cases, these proteins have been suggested to move lipid-linked oligomers across the membrane or, in the case of Escherichia coli MviN, to flip the lipid II peptidoglycan precursor. Bacillus subtilis SpoVB was the first member of this family implicated in peptidoglycan synthesis and is required for spore cortex polymerization. Three other COG2244 members with high similarity to SpoVB are encoded within the B. subtilis genome. Mutant strains lacking any or all of these genes (yabM, ykvU, and ytgP) in addition to spoVB are viable and produce apparently normal peptidoglycan, indicating that their function is not essential in B. subtilis. Phenotypic changes associated with loss of two of these genes suggest that they function in peptidoglycan synthesis. Mutants lacking YtgP produce long cells and chains of cells, suggesting a role in cell division. Mutants lacking YabM exhibit sensitivity to moenomycin, an antibiotic that blocks peptidoglycan polymerization by class A penicillin-binding proteins. This result suggests that YabM may function in a previously observed alternate pathway for peptidoglycan strand synthesis. PMID:19648239

  16. Evolution of substellar 'brown' dwarfs and the evolutionary status of VB8B

    NASA Technical Reports Server (NTRS)

    Stringfellow, Guy S.

    1986-01-01

    Detailed evolutionary calculations for stars near and below the minimum main sequence (MS) mass are presented, and the results are compared to VB8B. The standard set of stellar equations are solved, and the influence of both high and low grain opacities is assessed. All masses less than 0.08 solar are found to evolve to 0.0001 solar luminosities in a billion years or less. Both 0.08 solar mass and 0.075 solar mass stars become MS stars after five billion years, but with luminosities substantially below 0.0001 solar. The best fit to VB8B is 0.06 + or - 0.02 solar mass, but less than 0.8 solar mass. Depending upon its very precise mass, VB8B can be either a substellar brown dwarf with an age of 0.3-3 billion years, or an MS star with an age anywhere from two billion years to a Hubble time.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    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.

  19. Aesthetic valence of visual illusions

    PubMed Central

    Stevanov, Jasmina; Marković, Slobodan; Kitaoka, Akiyoshi

    2012-01-01

    Visual illusions constitute an interesting perceptual phenomenon, but they also have an aesthetic and affective dimension. We hypothesized that the illusive nature itself causes the increased aesthetic and affective valence of illusions compared with their non-illusory counterparts. We created pairs of stimuli. One qualified as a standard visual illusion whereas the other one did not, although they were matched in as many perceptual dimensions as possible. The phenomenal quality of being an illusion had significant effects on “Aesthetic Experience” (fascinating, irresistible, exceptional, etc), “Evaluation” (pleasant, cheerful, clear, bright, etc), “Arousal” (interesting, imaginative, complex, diverse, etc), and “Regularity” (balanced, coherent, clear, realistic, etc). A subsequent multiple regression analysis suggested that Arousal was a better predictor of Aesthetic Experience than Evaluation. The findings of this study demonstrate that illusion is a phenomenal quality of the percept which has measurable aesthetic and affective valence. PMID:23145272

  20. Fundamental aspects of recoupled pair bonds. I. Recoupled pair bonds in carbon and sulfur monofluoride

    NASA Astrophysics Data System (ADS)

    Dunning, Thom H.; Xu, Lu T.; Takeshita, Tyler Y.

    2015-01-01

    The number of singly occupied orbitals in the ground-state atomic configuration of an element defines its nominal valence. For carbon and sulfur, with two singly occupied orbitals in their 3P ground states, the nominal valence is two. However, in both cases, it is possible to form more bonds than indicated by the nominal valenceup to four bonds for carbon and six bonds for sulfur. In carbon, the electrons in the 2s lone pair can participate in bonding, and in sulfur the electrons in both the 3p and 3s lone pairs can participate. Carbon 2s and sulfur 3p recoupled pair bonds are the basis for the tetravalence of carbon and sulfur, and 3s recoupled pair bonds enable sulfur to be hexavalent. In this paper, we report generalized valence bond as well as more accurate calculations on the a4?- states of CF and SF, which are archetypal examples of molecules that possess recoupled pair bonds. These calculations provide insights into the fundamental nature of recoupled pair bonds and illustrate the key differences between recoupled pair bonds formed with the 2s lone pair of carbon, as a representative of the early p-block elements, and recoupled pair bonds formed with the 3p lone pair of sulfur, as a representative of the late p-block elements.

  1. Equilibrium CO bond lengths

    NASA Astrophysics Data System (ADS)

    Demaison, Jean; Csszr, Attila G.

    2012-09-01

    Based on a sample of 38 molecules, 47 accurate equilibrium CO bond lengths have been collected and analyzed. These ultimate experimental (reEX), semiexperimental (reSE), and Born-Oppenheimer (reBO) equilibrium structures are compared to reBO estimates from two lower-level techniques of electronic structure theory, MP2(FC)/cc-pVQZ and B3LYP/6-311+G(3df,2pd). A linear relationship is found between the best equilibrium bond lengths and their MP2 or B3LYP estimates. These (and similar) linear relationships permit to estimate the CO bond length with an accuracy of 0.002 within the full range of 1.10-1.43 , corresponding to single, double, and triple CO bonds, for a large number of molecules. The variation of the CO bond length is qualitatively explained using the Atoms in Molecules method. In particular, a nice correlation is found between the CO bond length and the bond critical point density and it appears that the CO bond is at the same time covalent and ionic. Conditions which permit the computation of an accurate ab initio Born-Oppenheimer equilibrium structure are discussed. In particular, the core-core and core-valence correlation is investigated and it is shown to roughly increase with the bond length.

  2. Electronegativity and the Bond Triangle

    ERIC Educational Resources Information Center

    Meek, Terry L.; Garner, Leah D.

    2005-01-01

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

  3. Electronegativity and the Bond Triangle

    ERIC Educational Resources Information Center

    Meek, Terry L.; Garner, Leah D.

    2005-01-01

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

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

    SciTech Connect

    Aleman, S.E.

    2001-07-17

    The task was to compute the maximum aluminum-oxide and oxide-coolant temperatures of assemblies cladded in 99 plus 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. The information in this report will be used to evaluate the potential for cladding corrosion of the Mark 25 assembly.

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

    SciTech Connect

    1985-04-01

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

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

    SciTech Connect

    Aleman, S.E.

    2001-07-17

    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.

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

    SciTech Connect

    Kozyukhin, S.; Golovchak, R.; Kovalskiy, A.; Shpotyuk, O.; Jain, H.

    2011-04-15

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

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

    SciTech Connect

    Landa, A; Soderlind, P

    2011-04-11

    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.

  9. Myosin Vb and Rab11a regulate phosphorylation of ezrin in enterocytes.

    PubMed

    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

    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

  10. ?-Amyloid peptide is internalized into chick retinal neurons and alters the distribution of myosin Vb.

    PubMed

    Oliveira, Leandro T; Matos, Priscila A; Provance, David William; de Mello, Fernando G; Andrade, Leonardo R; Sorenson, Martha M; Salerno, Vernica P

    2012-03-01

    The most common neurodegenerative disorder afflicting the aging human population is Alzheimer's disease (AD). A major hallmark of AD is dementia from a loss of neuronal function, attributed to the presence and accumulation of ?-amyloid (A?) peptide into senile plaques. Preceding senile plaque formation, abnormalities in axons can be observed as changes in morphologies and intracellular trafficking. Recently, it has been recognized that A? also accumulates within neurons and this intraneuronal A? accumulation has been reported to be critical in the disruption of synapses and cognitive function. Here, we report on the internalization of a fluorescently labeled A? peptide into cultured chick retinal neurons. The pattern of A? distribution during the time course of incubation is reminiscent of the endocytic pathway. Furthermore, the distribution of the internalized A? peptide converges with that of myosin Vb and both relocalize from the axon to cell body. These observations are consistent with the hypothesis that AD proceeds as a result of an imbalance between A? production and A? clearance, suggesting a role for myosin Vb in this process. PMID:22241730

  11. Planar tetracoordinate carbon species CLi3E with 12-valence-electrons.

    PubMed

    Guo, Jiayi; Chai, Haoyu; Duan, Qian; Qin, Jieming; Shen, Xiande; Jiang, Dayong; Hou, Jianhua; Yan, Bing; Li, Zhiru; Gu, Fenglong; Li, Qianshu

    2016-02-01

    We exhibit theoretically a series of 12-valence-electron pentaatomic species CLi3E (E = N, P, As, Sb, Bi) and CLi3E(+) (E = O, S, Se, Te, Po). The analyses of potential energy surfaces indicate that the C2v structures with a planar tetracoordinate carbon are the global minimum in these species except for E = N, P. A localized C[double bond, length as m-dash]E double bond is found in the planar tetracoordinate carbon species. The molecular orbitals and the valence populations reveal that the C[double bond, length as m-dash]E double bonds in CLi3E are different from those in CLi3E(+). The thermodynamic and kinetic calculations show that some of the planar tetracoordinate carbon species are stable and are likely to exist in the gas phase. PMID:26796982

  12. The Pauling 3-Electron Bond: A Recommendation for the Use of the Linnett Structure.

    ERIC Educational Resources Information Center

    Harcourt, Richard D.

    1985-01-01

    Recommends the Linnett structure IV (as in VIII for molecular oxygen) for future use when a valence-bond structure for a Pauling 3-electron bond is required. Examples are provided to illustrate why this recommendation is made. (JN)

  13. Cluster molecular orbital description of the electronic structures of mixed-valence iron oxides and silicates

    USGS Publications Warehouse

    Sherman, David M.

    1986-01-01

    A molecular orbital description, based on spin-unrestricted X??-scattered wave calculations, is given for the electronic structures of mixed valence iron oxides and silicates. The cluster calculations show that electron hopping and optical intervalence charge-transger result from weak FeFe bonding across shared edges of FeO6 coordination polyhedra. In agreement with Zener's double exchange model, FeFe bonding is found to stabilize ferromagnetic coupling between Fe2+ and Fe3+ cations. ?? 1986.

  14. A method for systematic site-to-bond conversion of directed graphs

    NASA Astrophysics Data System (ADS)

    Duarte, J. A. M. S.

    1990-01-01

    A graph-theoretic method for the complete derivability of bond graphs from their site counterparts is described. Bond perimeter, valence, and cyclomatic number distributions as well as spatial extent measures can be systematically generated when coupled with a site valence partition in the original graph. Relevant consequences for bond configurations include the facts that (i) percolation perimeter and cyclomatic number distributions are equivalent, (ii) geometrical susceptibilities are not independent, and (iii) a critical site/bond ratio exists.

  15. Fundamental aspects of recoupled pair bonds. I. Recoupled pair bonds in carbon and sulfur monofluoride

    SciTech Connect

    Dunning, Thom H. Xu, Lu T.; Takeshita, Tyler Y.

    2015-01-21

    The number of singly occupied orbitals in the ground-state atomic configuration of an element defines its nominal valence. For carbon and sulfur, with two singly occupied orbitals in their {sup 3}P ground states, the nominal valence is two. However, in both cases, it is possible to form more bonds than indicated by the nominal valence—up to four bonds for carbon and six bonds for sulfur. In carbon, the electrons in the 2s lone pair can participate in bonding, and in sulfur the electrons in both the 3p and 3s lone pairs can participate. Carbon 2s and sulfur 3p recoupled pair bonds are the basis for the tetravalence of carbon and sulfur, and 3s recoupled pair bonds enable sulfur to be hexavalent. In this paper, we report generalized valence bond as well as more accurate calculations on the a{sup 4}Σ{sup −} states of CF and SF, which are archetypal examples of molecules that possess recoupled pair bonds. These calculations provide insights into the fundamental nature of recoupled pair bonds and illustrate the key differences between recoupled pair bonds formed with the 2s lone pair of carbon, as a representative of the early p-block elements, and recoupled pair bonds formed with the 3p lone pair of sulfur, as a representative of the late p-block elements.

  16. 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)

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

    2014-04-01

    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.

  17. Adsorption mechanism and valency of catechol-functionalized hyperbranched polyglycerols

    PubMed Central

    Krysiak, Stefanie; Wei, Qiang; Rischka, Klaus; Hartwig, Andreas; Haag, Rainer

    2015-01-01

    Summary Nature often serves as a model system for developing new adhesives. In aqueous environments, mussel-inspired adhesives are promising candidates. Understanding the mechanism of the extraordinarily strong adhesive bonds of the catechol group will likely aid in the development of adhesives. With this aim, we study the adhesion of catechol-based adhesives to metal oxides on the molecular level using atomic force microscopy (AFM). The comparison of single catechols (dopamine) with multiple catechols on hyperbranched polyglycerols (hPG) at various pH and dwell times allowed us to further increase our understanding. In particular, we were able to elucidate how to achieve strong bonds of different valency. It was concluded that hyperbranched polyglycerols with added catechol end groups are promising candidates for durable surface coatings. PMID:26150898

  18. Phylogenetic footprinting of the human cytochrome c oxidase subunit VB promoter.

    PubMed

    Bachman, N J; Yang, T L; Dasen, J S; Ernst, R E; Lomax, M I

    1996-09-01

    The human COX5B gene encodes subunit Vb of cytochrome c oxidase (COX). COX Vb is 1 of the 10 subunits of the mitochondrial COX complex encoded by a nuclear gene. We have defined a region in the human COX5B promoter essential for gene expression and shown by phylogenetic footprinting of 11 primate COX5B promoters that many cis-regulatory elements in this region are evolutionarily conserved. The transcription start site of human COX5B was mapped 58 bp upstream of the initiation Met codon by primer extension using a thermostable reverse transcriptase. A 475-bp region (-456 to +20) of the human COX5B gene was shown to function as a promoter for the chloramphenicol acetyl transferase (CAT) gene in expression vectors when transfected into HeLa cells. The human COX5B gene is located in a CpG island and contains several potential binding sites for the transcription factor Sp1, but no consensus TATA box element. Several sequence elements associated with the transcriptional regulation of respiratory genes were also found in the promoter and 5' flanking region, including a single NRF-1 site and two 9-bp direct repeats containing binding sites for ets-domain proteins, such as NRF-2/GABP. Many features of the human COX5B promoter are conserved in the COX5B promoters of primates, in particular, the presence of a single binding site for NRF-1 and multiple sites for Sp1 and NRF-2/GABP. Electrophoretic mobility shift assays demonstrate that the conserved NRF-1 site in primate COX5B promoters is specifically recognized by a factor present in HeLa nuclear extracts. Phylogenetic footprinting has identified additional conserved elements that may also function as binding sites for regulatory factors. PMID:8806766

  19. 30 CFR 57.22314 - Flow-control devices (V-A and V-B mines).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Flow-control devices (V-A and V-B mines). 57.22314 Section 57.22314 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND...

  20. 30 CFR 57.22314 - Flow-control devices (V-A and V-B mines).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Flow-control devices (V-A and V-B mines). 57.22314 Section 57.22314 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR... MINES Safety Standards for Methane in Metal and Nonmetal Mines Equipment § 57.22314 Flow-control...

  1. The Chemical Bond in C2.

    PubMed

    Hermann, Markus; Frenking, Gernot

    2016-03-14

    Quantum chemical calculations using the complete active space of the valence orbitals have been carried out for Hn CCHn (n=0-3) and N2 . The quadratic force constants and the stretching potentials of Hn CCHn have been calculated at the CASSCF/cc-pVTZ level. The bond dissociation energies of the C-C bonds of C2 and HC≡CH were computed using explicitly correlated CASPT2-F12/cc-pVTZ-F12 wave functions. The bond dissociation energies and the force constants suggest that C2 has a weaker C-C bond than acetylene. The analysis of the CASSCF wavefunctions in conjunction with the effective bond orders of the multiple bonds shows that there are four bonding components in C2 , while there are only three in acetylene and in N2 . The bonding components in C2 consist of two weakly bonding σ bonds and two electron-sharing π bonds. The bonding situation in C2 can be described with the σ bonds in Be2 that are enforced by two π bonds. There is no single Lewis structure that adequately depicts the bonding situation in C2 . The assignment of quadruple bonding in C2 is misleading, because the bond is weaker than the triple bond in HC≡CH. PMID:26756311

  2. Electronic structure factors of Si-H bond activation by transition metals. Valence photoelectron spectra of (. eta. sup 5 -C sub 5 H sub 4 CH sub 3 )Mn(CO)(PMe sub 3 )HSiCl sub 3 and (. eta. sup 5 -C sub 5 H sub 4 CH sub 3 )Mn(CO)(PMe sub 3 )HSiHPh sub 2 (Me = CH sub 3 , Ph = C sub 6 H sub 5 )

    SciTech Connect

    Lichtenberger, D.L.; Rai-Chaudhuri, A. )

    1990-03-07

    The valence photoelectron spectra of ({eta}{sup 5}-C{sub 5}H{sub 4}CH{sub 3})Mn(CO)(L)HSiCl{sub 3} and ({eta}{sup 5}-C{sub 5}H{sub 4}CH{sub 3})Mn(CO)(L)HSiHPh{sub 2}, where L is CO or P(CH{sub 3}){sub 3}, are compared to determine the effect of ligand substitution at the metal center on Si-H bond activation. Metal centers that are more electron rich may promote more complete oxidative addition of the Si-H bond to the metal. The shifts in the metal and ligand ionization energies and the relative intensities of ionizations in the He I and He II photoelectron experiments show that the metal in ({eta}{sup 5}-C{sub 5}H{sub 4}CH{sub 3})Mn(CO)(PMe{sub 3})HSiCl{sub 3} is best represented by a formal oxidation state of III (d{sub 4} electron count). This indicates nearly complete oxidative addition of the Si-H bond to the metal center and results in independent Mn-H and Mn-Si bonds. In contrast, the splitting and intensity pattern of the metal-based ionizations of ({eta}{sup 5}-C{sub 5}H{sub 4}CH{sub 3})Mn(CO)(PMe{sub 3})HSiHPh{sub 2} reflect the formal d{sup 6} electron count of a metal corresponding to oxidation state I. The extent of electron charge density shift from the metal to the ligand is also small, as evidenced by the negligible shifts of these ionizations from those of the related ({eta}{sup 5}-C{sub 5}H{sub 4}CH{sub 3})Mn(CO){sub 2}(PMe{sub 3}) complex. These observations indicate that the electronic structure of the Si-H interaction with the metal in this complex is in the initial stages of Si-H bond addition to the metal, before oxidative addition has become prevalent. 25 refs., 6 figs., 1 tab.

  3. Bent Bonds and Multiple Bonds.

    ERIC Educational Resources Information Center

    Robinson, Edward A.; Gillespie, Ronald J.

    1980-01-01

    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)

  4. Avoided valence transition in a plutonium superconductor

    PubMed Central

    Ramshaw, B. J.; Shekhter, Arkady; McDonald, Ross D.; Betts, Jon B.; Mitchell, J. N.; Tobash, P. H.; Mielke, C. H.; Bauer, E. D.; Migliori, Albert

    2015-01-01

    The d and f electrons in correlated metals are often neither fully localized around their host nuclei nor fully itinerant. This localized/itinerant duality underlies the correlated electronic states of the high-Tc cuprate superconductors and the heavy-fermion intermetallics and is nowhere more apparent than in the 5f valence electrons of plutonium. Here, we report the full set of symmetry-resolved elastic moduli of PuCoGa5the highest Tc superconductor of the heavy fermions (Tc = 18.5 K)and find that the bulk modulus softens anomalously over a wide range in temperature above Tc. The elastic symmetry channel in which this softening occurs is characteristic of a valence instabilitytherefore, we identify the elastic softening with fluctuations of the plutonium 5f mixed-valence state. These valence fluctuations disappear when the superconducting gap opens at Tc, suggesting that electrons near the Fermi surface play an essential role in the mixed-valence physics of this system and that PuCoGa5 avoids a valence transition by entering the superconducting state. The lack of magnetism in PuCoGa5 has made it difficult to reconcile with most other heavy-fermion superconductors, where superconductivity is generally believed to be mediated by magnetic fluctuations. Our observations suggest that valence fluctuations play a critical role in the unusually high Tc of PuCoGa5. PMID:25737548

  5. Avoided valence transition in a plutonium superconductor.

    PubMed

    Ramshaw, B J; Shekhter, Arkady; McDonald, Ross D; Betts, Jon B; Mitchell, J N; Tobash, P H; Mielke, C H; Bauer, E D; Migliori, Albert

    2015-03-17

    The d and f electrons in correlated metals are often neither fully localized around their host nuclei nor fully itinerant. This localized/itinerant duality underlies the correlated electronic states of the high-Tc cuprate superconductors and the heavy-fermion intermetallics and is nowhere more apparent than in the 5f valence electrons of plutonium. Here, we report the full set of symmetry-resolved elastic moduli of PuCoGa5--the highest Tc superconductor of the heavy fermions (Tc = 18.5 K)--and find that the bulk modulus softens anomalously over a wide range in temperature above Tc. The elastic symmetry channel in which this softening occurs is characteristic of a valence instability--therefore, we identify the elastic softening with fluctuations of the plutonium 5f mixed-valence state. These valence fluctuations disappear when the superconducting gap opens at Tc, suggesting that electrons near the Fermi surface play an essential role in the mixed-valence physics of this system and that PuCoGa5 avoids a valence transition by entering the superconducting state. The lack of magnetism in PuCoGa5 has made it difficult to reconcile with most other heavy-fermion superconductors, where superconductivity is generally believed to be mediated by magnetic fluctuations. Our observations suggest that valence fluctuations play a critical role in the unusually high Tc of PuCoGa5. PMID:25737548

  6. Action versus valence in decision making

    PubMed Central

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

    2014-01-01

    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

  7. Valence resonance states of N2/-/

    NASA Technical Reports Server (NTRS)

    Krauss, M.; Neumann, D.

    1973-01-01

    Resonant scattering observed in the transmission of electrons between 9 and 11 eV in collision with N2 has been attributed to the attachment of the scattered electron to an excited valence state. Resonance valence excited states of N2(-) are calculated that could support this hypothesis. Although calculated and observed resonance energies are in close agreement, the calculations do not reflect the observed complex angular behavior of the scattered electron.

  8. 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

    Beck, Johannes . E-mail: j.beck@uni-bonn.de; Kusterer, Christian; Hoffmann, Rolf-Dieter; Poettgen, Rainer

    2006-08-15

    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}.

  9. 30 CFR 57.22314 - Flow-control devices (V-A and V-B mines).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Flow-control devices (V-A and V-B mines). 57.22314 Section 57.22314 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Safety Standards for Methane in Metal...

  10. 30 CFR 57.22314 - Flow-control devices (V-A and V-B mines).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Flow-control devices (V-A and V-B mines). 57.22314 Section 57.22314 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Safety Standards for Methane in Metal...

  11. Removal of Vanadium from Molten AluminumPart II. Kinetic Analysis and Mechanism of VB2 Formation

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

    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.

  12. 30 CFR 57.22231 - Actions at 0.25 percent methane (I-B, II-B, V-B, and VI mines).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Actions at 0.25 percent methane (I-B, II-B, V-B... AND 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 mines). If methane reaches 0.25 percent in...

  13. 30 CFR 57.22238 - Actions at 2.0 percent methane (I-B, II-B, V-B, and VI mines).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Actions at 2.0 percent methane (I-B, II-B, V-B... AND 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 mines). If methane reaches 2.0 percent in the...

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

    PubMed Central

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

    2012-01-01

    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. PMID:24961258

  15. The valence-fluctuating ground state of plutonium

    PubMed Central

    Janoschek, Marc; Das, Pinaki; Chakrabarti, Bismayan; Abernathy, Douglas L.; Lumsden, Mark D.; Lawrence, John M.; Thompson, Joe D.; Lander, Gerard H.; Mitchell, Jeremy N.; Richmond, Scott; Ramos, Mike; Trouw, Frans; Zhu, Jian-Xin; Haule, Kristjan; Kotliar, Gabriel; Bauer, Eric D.

    2015-01-01

    A central issue in material science is to obtain understanding of the electronic correlations that control complex materials. Such electronic correlations frequently arise because of the competition of localized and itinerant electronic degrees of freedom. Although the respective limits of well-localized or entirely itinerant ground states are well understood, the intermediate regime that controls the functional properties of complex materials continues to challenge theoretical understanding. We have used neutron spectroscopy to investigate plutonium, which is a prototypical material at the brink between bonding and nonbonding configurations. Our study reveals that the ground state of plutonium is governed by valence fluctuations, that is, a quantum mechanical superposition of localized and itinerant electronic configurations as recently predicted by dynamical mean field theory. Our results not only resolve the long-standing controversy between experiment and theory on plutonium’s magnetism but also suggest an improved understanding of the effects of such electronic dichotomy in complex materials. PMID:26601219

  16. The valence-fluctuating ground state of plutonium.

    PubMed

    Janoschek, Marc; Das, Pinaki; Chakrabarti, Bismayan; Abernathy, Douglas L; Lumsden, Mark D; Lawrence, John M; Thompson, Joe D; Lander, Gerard H; Mitchell, Jeremy N; Richmond, Scott; Ramos, Mike; Trouw, Frans; Zhu, Jian-Xin; Haule, Kristjan; Kotliar, Gabriel; Bauer, Eric D

    2015-07-01

    A central issue in material science is to obtain understanding of the electronic correlations that control complex materials. Such electronic correlations frequently arise because of the competition of localized and itinerant electronic degrees of freedom. Although the respective limits of well-localized or entirely itinerant ground states are well understood, the intermediate regime that controls the functional properties of complex materials continues to challenge theoretical understanding. We have used neutron spectroscopy to investigate plutonium, which is a prototypical material at the brink between bonding and nonbonding configurations. Our study reveals that the ground state of plutonium is governed by valence fluctuations, that is, a quantum mechanical superposition of localized and itinerant electronic configurations as recently predicted by dynamical mean field theory. Our results not only resolve the long-standing controversy between experiment and theory on plutonium's magnetism but also suggest an improved understanding of the effects of such electronic dichotomy in complex materials. PMID:26601219

  17. The valence-fluctuating ground state of plutonium

    SciTech Connect

    Janoschek, Marc; Das, Pinaki; Chakrabarti, Bismayan; Abernathy, Douglas L.; Lumsden, Mark D.; Lawrence, John M.; Thompson, Joe D.; Lander, Gerard H.; Mitchell, Jeremy N.; Richmond, Scott; Ramos, Mike; Trouw, Frans; Zhu, Jian -Xin; Haule, Kristjan; Kotliar, Gabriel; Bauer, Eric D.

    2015-07-10

    A central issue in material science is to obtain understanding of the electronic correlations that control complex materials. Such electronic correlations frequently arise because of the competition of localized and itinerant electronic degrees of freedom. Although the respective limits of well-localized or entirely itinerant ground states are well understood, the intermediate regime that controls the functional properties of complex materials continues to challenge theoretical understanding. We have used neutron spectroscopy to investigate plutonium, which is a prototypical material at the brink between bonding and nonbonding configurations. In addition, our study reveals that the ground state of plutonium is governed by valence fluctuations, that is, a quantum mechanical superposition of localized and itinerant electronic configurations as recently predicted by dynamical mean field theory. Our results not only resolve the long-standing controversy between experiment and theory on plutonium’s magnetism but also suggest an improved understanding of the effects of such electronic dichotomy in complex materials.

  18. Neuroanatomical correlates of categorizing emotional valence.

    PubMed

    Beatty, Erin L; Vartanian, Oshin; Muller-Gass, Alexandra; Robertson, John A; Mandel, David R; Stergiopoulos, Stergios

    2014-06-11

    Categorization is fundamental to cognition, and evidence suggests that categorizing emotional stimuli holds a privileged position in human information processing. According to theories on embodied emotion, the subjective emotional feeling elicited by a stimulus plays a causal role in its categorization. Using functional MRI, we tested the hypothesis that categorizing emotional stimuli in terms of valence would activate structures involved in valence-specific experience of emotion. On each trial, two pictures from the International Affective Picture System were presented successively. Upon viewing the second picture, participants categorized it as belonging to the same valence category as or a different valence category from the first picture. Categorization activated an exclusively left-lateralized set of regions implicated in taxonomic categorization (i.e. judging whether two items are of the same kind) including the middle temporal gyrus and precuneus, as well as the posterior cingulate cortex. Critically, for negative pictures categorization activated structures that underlie the experience of negative emotions (anterior insula, left orbitofrontal cortex), whereas for positive pictures categorization activated structures that underlie the experience of positive emotions (dorsomedial and ventromedial prefrontal cortex). Consistent with predictions derived from theories on embodied emotion, these results suggest that experience of emotion contributes to categorizing emotional valence. PMID:24922349

  19. The role of valence-band excitation in laser ablation of KCl

    NASA Technical Reports Server (NTRS)

    Haglund, Richard F., Jr.; Tang, Kai; Bunton, Patrick H.; Wang, Ling-Jun

    1991-01-01

    We present recent measurements of excited-atom and ion emission from KCl surfaces illuminated by vacuum-ultraviolet synchrotron radiation (h-nu = 8-28 eV) and ultraviolet laser light (h-nu = 4 eV). At low intensities characteristic of the synchrotron experiments, excited atoms are desorbed by simple valence-band excitation process involving the metallization of the KCl surface. At the higher intensities typical of laser desorption and ablation, we observe a strong decrease in K emission as a function of the number of laser shots, but an essentially constant yield of Cl. K(+) and Cl(-) emission at high intensities show similar behavior. The energetics of these desorption phenomena can be treated in a bond-orbital model which shows that creation of a single valence hole is sufficient to excite an ion to an anti-bonding state.

  20. Molybdenum Valence in Basaltic Silicate Melts

    NASA Technical Reports Server (NTRS)

    Danielson, L. R.; Righter, K.; Newville, M.; Sutton, S.; Pando, K.

    2010-01-01

    The moderately siderophile element molybdenum has been used as an indicator in planetary differentiation processes, and is particularly relevant to core formation [for example, 1-6]. However, models that apply experimental data to an equilibrium differentiation scenario infer the oxidation state of molybdenum from solubility data or from multivariable coefficients from metal-silicate partitioning data [1,3,7]. Partitioning behavior of molybdenum, a multivalent element with a transition near the J02 of interest for core formation (IW-2) will be sensitive to changes in JO2 of the system and silicate melt structure. In a silicate melt, Mo can occur in either 4+ or 6+ valence state, and Mo6+ can be either octahedrally or tetrahedrally coordinated. Here we present first XANES measurements of Mo valence in basaltic run products at a range of P, T, and JO2 and further quantify the valence transition of Mo.

  1. Myosin Vb uncoupling from RAB8A and RAB11A elicits microvillus inclusion disease.

    PubMed

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

    2014-07-01

    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. PMID:24892806

  2. The bondons: the quantum particles of the chemical bond.

    PubMed

    Putz, Mihai V

    2010-01-01

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

  3. Measurement of valence-band offset at native oxide/BaSi2 interfaces by hard x-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Takabe, Ryota; Du, Weijie; Ito, Keita; Takeuchi, Hiroki; Toko, Kaoru; Ueda, Shigenori; Kimura, Akio; Suemasu, Takashi

    2016-01-01

    Undoped n-type BaSi2 films were grown on Si(111) by molecular beam epitaxy, and the valence band (VB) offset at the interface between the BaSi2 and its native oxide was measured by hard x-ray photoelectron spectroscopy (HAXPES) at room temperature. HAXPES enabled us to investigate the electronic states of the buried BaSi2 layer non-destructively thanks to its large analysis depth. We performed the depth-analysis by varying the take-off angle (TOA) of photoelectrons as 15°, 30°, and 90° with respect to the sample surface and succeeded to obtain the VB spectra of the BaSi2 and the native oxide separately. The VB maximum was located at -1.0 eV from the Fermi energy for the BaSi2 and -4.9 eV for the native oxide. We found that the band bending did not occur near the native oxide/BaSi2 interface. This result was clarified by the fact that the core-level emission peaks did not shift regardless of TOA (i.e., analysis depth). Thus, the barrier height of the native oxide for the minority-carriers in the undoped n-BaSi2 (holes) was determined to be 3.9 eV. No band bending in the BaSi2 close to the interface also suggests that the large minority-carrier lifetime in undoped n-BaSi2 films capped with native oxide is attributed not to the band bending in the BaSi2, which pushes away photogenerated minority carriers from the defective surface region, but to the decrease of defective states by the native oxide.

  4. Affective Priming with Associatively Acquired Valence

    ERIC Educational Resources Information Center

    Aguado, Luis; Pierna, Manuel; Saugar, Cristina

    2005-01-01

    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

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

    PubMed

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

    2007-03-29

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

  6. Sticker Bonding.

    ERIC Educational Resources Information Center

    Frazier, Laura Corbin

    2000-01-01

    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)

  7. Bond Issues.

    ERIC Educational Resources Information Center

    Pollack, Rachel H.

    2000-01-01

    Notes trends toward increased borrowing by colleges and universities and offers guidelines for institutions that are considering issuing bonds to raise money for capital projects. Discussion covers advantages of using bond financing, how use of bonds impacts on traditional fund raising, other cautions and concerns, and some troubling aspects of

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

    NASA Astrophysics Data System (ADS)

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

    2010-03-01

    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.

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

    SciTech Connect

    Lepine, Sebastien; DiStefano, Rosanne E-mail: rd@cfa.harvard.edu

    2012-04-10

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

    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.

  11. Pauling bond strength, bond length and electron density distribution

    SciTech Connect

    Gibbs, Gerald V.; Ross, Nancy L.; Cox, David F.; Rosso, Kevin M.; Iversen, Bo B.; Spackman, M. A.

    2014-01-18

    A power law regression equation, = 1.46(<ρ(rc)>/r)-0.19, connecting the average experimental bond lengths, , with the average accumulation of the electron density at the bond critical point, <ρ(rc)>, between bonded metal M and oxygen atoms, determined at ambient conditions for oxide crystals, where r is the row number of the M atom, is similar to the regression equation R(M-O) = 1.39(ρ(rc)/r)-0.21 determined for three perovskite crystals for pressures as high as 80 GPa. The two equations are also comparable with those, = 1.43(/r)-0.21, determined for a large number of oxide crystals at ambient conditions and = 1.39(/r)-0.22, determined for geometry optimized hydroxyacid molecules, that connect the bond lengths to the average Pauling electrostatic bond strength, , for the M-O bonded interactions. On the basis of the correspondence between the two sets of equations connecting ρ(rc) and the Pauling bond strength s with bond length, it appears that Pauling’s simple definition of bond strength closely mimics the accumulation of the electron density between bonded pairs of atoms. The similarity of the expressions for the crystals and molecules is compelling evidence that the M-O bonded interactions for the crystals and molecules 2 containing the same bonded interactions are comparable. Similar expressions, connecting bond lengths and bond strength, have also been found to hold for fluoride, nitride and sulfide molecules and crystals. The Brown-Shannon bond valence, σ, power law expression σ = [R1/(R(M-O)]N that has found wide use in crystal chemistry, is shown to be connected to a more universal expression determined for oxides and the perovskites, <ρ(rc)> = r[(1.41)/]4.76, demonstrating that the bond valence for a bonded interaction is likewise closely connected to the accumulation of the electron density between the bonded atoms. Unlike the Brown-Shannon expression, it is universal in that it holds for the M-O bonded interactions for a relatively wide range of M atoms of the periodic table. The power law equation determined for the oxide crystals at ambient conditions is similar to the power law expression <ρ(rc)> = r[1.46/]5.26 determined for the perovskites at pressures as high as 80 GPa, indicating that the intrinsic connection between R(M-O) and ρ(rc) that holds at ambient conditions also holds, to a first approximation, at high pressures.

  12. Valence atom with bohmian quantum potential: the golden ratio approach

    PubMed Central

    2012-01-01

    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). PMID:23146157

  13. Evolution of the Mlct Band Following Changes in Oxidation State for Highly Coupled Mixed Valence Complexes

    NASA Astrophysics Data System (ADS)

    Lear, Benjamin J.; Chisholm, Malcolm H.

    2009-06-01

    The MLCT band for a series of dimers composed of pairs of quadruply bonded metal-metal units ([MM(CH_3CO_2)_3]_2-?_2-oxalate; where M=Mo or W) is examined in both the neutral and +1 (mixed valence) states. The MLCT band for the neutral state of these complexes exhibits clear vibronic features that are greatly reduced in intensity upon generation of the mixed valence state. Utilizing the time dependent theory of spectroscopy as developed by Eric Heller, these results (together with Raman spectra and TD-DFT calculations) are used in order to draw conclusions concerning the potential energy surfaces involved in the MLCT transition for these complexes. In particular, we are concerned with changes to the offset of the ground and excited state potential energy surfaces that occur along the coordinates involved in the vibronic coupling and which accompany changes in oxidation state. The insight thus gained is used in order to understand the degree of electronic coupling present in mixed valence species and to comment on the classification of mixed valence complexes.

  14. Pion valence-quark parton distribution function

    NASA Astrophysics Data System (ADS)

    Chang, Lei; Thomas, Anthony W.

    2015-10-01

    Within the Dyson-Schwinger equation formulation of QCD, a rainbow ladder truncation is used to calculate the pion valence-quark distribution function (PDF). The gap equation is renormalized at a typical hadronic scale, of order 0.5 GeV, which is also set as the default initial scale for the pion PDF. We implement a corrected leading-order expression for the PDF which ensures that the valence-quarks carry all of the pion's light-front momentum at the initial scale. The scaling behavior of the pion PDF at a typical partonic scale of order 5.2 GeV is found to be (1 - x) ?, with ? ? 1.6, as x approaches one.

  15. Strong electron correlations in cobalt valence tautomers

    NASA Astrophysics Data System (ADS)

    LaBute, M. X.; Kulkarni, R. V.; Endres, R. G.; Cox, D. L.

    2002-03-01

    We have examined cobalt based valence tautomer molecules such as Co(SQ)2(phen) using density functional theory (DFT) and variational configuration interaction (VCI) approaches based upon a model Hamiltonian. Our DFT results extend earlier work by finding a reduced total energy gap (order 0.6 eV) between high-temperature and low-temperature states when we fully relax the coordinates (relative to experimental ones). Furthermore, we demonstrate that a charge transfer picture based upon formal valence arguments succeeds qualitatively while failing quantitatively due to strong covalency between the Co 3d orbitals and ligand p orbitals. With the VCI approach, we argue that the high-temperature, high spin phase is strongly mixed valent, with about 30% admixture of Co (III) into the predominantly Co(II) ground state. We confirm this mixed valence through a fit to the XANES spectra. Moreover, the strong electron correlations of the mixed valent phase provide an energy lowering of about 0.2-0.3 eV of the high-temperature phase relative to the low-temperature one. Finally, we use the domain model to account for the extraordinarily large entropy and enthalpy values associated with the transition.

  16. Stark spectroscopy of mixed-valence systems.

    PubMed

    Silverman, Lisa N; Kanchanawong, Pakorn; Treynor, Thomas P; Boxer, Steven G

    2008-01-13

    Many mixed-valence systems involve two or more states with different electric dipole moments whose magnitudes depend upon the charge transfer distance and the degree of delocalization; these systems can be interconverted by excitation of an intervalence charge transfer transition. Stark spectroscopy involves the interaction between the change in dipole moment of a transition and an electric field, so the Stark spectra of mixed-valence systems are expected to provide quantitative information on the degree of delocalization. In limiting cases, a classical Stark analysis can be used, but in intermediate cases the analysis is much more complex because the field affects not only the band position but also the intrinsic bandshape. Such non-classical Stark effects lead to widely different bandshapes. Several examples of both classes are discussed. Because electric fields are applied to immobilized samples, complications arise from inhomogeneous broadening, along with other effects that limit our ability to extract unique parameters in some cases. In the case of the radical cation of the special pair in photosynthetic reaction centres, where the mixed-valence system is in a very complex but structurally well-defined environment, a detailed analysis can be performed. PMID:17827128

  17. The nature of the fourth bond in the ground state of C2: the quadruple bond conundrum.

    PubMed

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

    2014-05-19

    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

  18. A comparative study of dissociation of thymidine molecules following valence or core photoionization

    NASA Astrophysics Data System (ADS)

    Itl, E.; Huels, M. A.; Rachlew, E.; Kooser, K.; Hgerth, T.; Kukk, E.

    2013-11-01

    We have studied the fragmentation of gas phase thymidine following valence and core ionization using synchrotron radiation, combined with electron energy and ion mass resolved detection in coincidence. To identify certain fragment masses 13C labelled thymidine was also used. We find that in large part, the photofragmentation of thymidine can be described as separated thymine and 2-deoxy-d-ribose cations. However, also the intact thymidine radical cation, formation of intact base and sugar cations from glycosidic bond cleavage and several new thymidine-specific fragments are observed after valence ionization. Conversely, at the photoionization of C 1s electrons neither parent thymidine cations nor any fragments above 55 amu were detected, and only ion pairs with small masses survive core ionization, Auger decay and the subsequent Coulomb separation of the DNA sub-unit. This demonstrates the genotoxic nature of soft x-rays which in cells induce complex clustered damage similar to those yielded by heavy particles.

  19. Institutional Bonding.

    ERIC Educational Resources Information Center

    Allard, M. June

    Institutional bonding was examined at a public, urban commuter college with exceptionally high attrition and visibly low morale. Changes in bonding and attrition were measured 6 years after a 2-year effort to develop school identity and student feelings of membership. It was found that a simple index of campus morale is provided by level of

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

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

    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 km 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.

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

    SciTech Connect

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

    2011-09-09

    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.

  2. Evidence for valence quark-hadron duality

    SciTech Connect

    Niculescu, I.; Armstrong, C.S.; Arrington, J.

    1999-04-01

    A newly obtained data sample of inclusive electron-nucleon scattering from both hydrogen and deuterium targets is analyzed. These JLab data are in the nucleon resonance region in the four-momentum transfer range between 0.3 and 5 (GeV/c){sup 2}. The data are in agreement with SLAC data at similar kinematics, and are found to follow an average scaling curve. The inclusion of low-momentum transfer data yields a scaling curve resembling deep inelastic neutrino-nucleus scattering data, suggesting a sensitivity to the valence quarks only.

  3. Functional Consequences of Amino Acid Substitutions to GerVB, a Component of the Bacillus megaterium Spore Germinant Receptor▿

    PubMed Central

    Christie, Graham; Lazarevska, Milena; Lowe, Christopher R.

    2008-01-01

    The extreme metabolic dormancy and resistance properties of spores formed by members of the Bacillus and Clostridium genera are lost upon exposure to a variety of small-molecule germinants. Germinants are known to interact in an as yet undefined manner with cognate receptor complexes that reside in the inner membrane that surrounds the spore protoplast. The receptor itself is a complex of at least three proteins, and in this study we identify amino acid residues, predicted to lie in loop regions of GerVB on the exterior aspect of the membrane, that influence the Bacillus megaterium spore germination response. Three consecutive residues adjacent to putative transmembrane domain 10 (TM10) were demonstrated to mediate to various degrees the proline germinative response while also influencing germination in response to leucine, glucose, and inorganic salts, suggesting that this region may be part of a ligand binding pocket. Alternatively, substitutions in this region may affect the conformation of associated functionally important TM regions. Leucine- and KBr-mediated germination was also influenced by substitutions in other outer loop regions. These observations, when considered with accompanying kinetic analyses that demonstrate cooperativity between germinants, suggest that binding sites for the respective germinants are in close spatial proximity in the receptor but do not overlap. Additionally, proline recognition was conferred to a chimeric receptor when TM regions associated with the putative binding loop were present, indicating that residues in TM9 and/or TM10 of GerVB are also of functional importance in the proline-induced germinative response. PMID:18203825

  4. The DIET from semiconductor surfaces by excitation of valence electrons

    NASA Astrophysics Data System (ADS)

    Kanasaki, Jun'ichi; Okano, Akiko; Ishikawa, Ken'ichi; Nakai, Yasuo; Itoh, Noriaki

    1995-06-01

    We discuss the desorption induced by electronic transitions (DIET) of constituent atoms from several types of non-metallic solids, particularly the DIET from semiconductors by valence electron excitations. We first classify the non-metallic solids into type A, in which no self-trapping of excitons occurs, and type B, in which self-trapping occurs. We argue that in type B solids the localization of electron-hole pairs or excitons through the self-trapping on the surfaces induces the Menzel-Gomer-Redhead-type anti-bonding state resulting in DIET. For the DIET from type A non-metals, typically semiconductors, in which the self-trapping is not induced, we derive two important characteristics: (1) the emission is related to defects on the surfaces and (2) single electronic excitation cannot induce the emissions. The recent experimental observations of laser-induced emissions satisfying these characteristics for the DIET from semiconductors are surveyed. Furthermore we present experimental evidence demonstrating that the observed emissions are of the electronic origin: the emission occurs dominantly when the excitation is localized on the surface. Finally, surface phenomena, such as laser ablation and dry etching, related to the DIET from semiconductors, and the applications of the DIET from semiconductors are discussed.

  5. The valence-fluctuating ground state of plutonium

    DOE PAGESBeta

    Janoschek, Marc; Das, Pinaki; Chakrabarti, Bismayan; Abernathy, Douglas L.; Lumsden, Mark D.; Lawrence, John M.; Thompson, Joe D.; Lander, Gerard H.; Mitchell, Jeremy N.; Richmond, Scott; et al

    2015-07-10

    A central issue in material science is to obtain understanding of the electronic correlations that control complex materials. Such electronic correlations frequently arise because of the competition of localized and itinerant electronic degrees of freedom. Although the respective limits of well-localized or entirely itinerant ground states are well understood, the intermediate regime that controls the functional properties of complex materials continues to challenge theoretical understanding. We have used neutron spectroscopy to investigate plutonium, which is a prototypical material at the brink between bonding and nonbonding configurations. In addition, our study reveals that the ground state of plutonium is governed bymore » valence fluctuations, that is, a quantum mechanical superposition of localized and itinerant electronic configurations as recently predicted by dynamical mean field theory. Our results not only resolve the long-standing controversy between experiment and theory on plutonium’s magnetism but also suggest an improved understanding of the effects of such electronic dichotomy in complex materials.« less

  6. The role of electron correlation in the cobalt valence tautomers

    NASA Astrophysics Data System (ADS)

    Labute, Montiago; Kulkarni, R.; Cox, D. L.

    2001-03-01

    Molecules consisting of a single transition metal atom ligated to o-quinone derived complexes have been observed by several groups to undergo a valence crossover, which may be induced themally, by photoexcitation, or by applying pressure[1]. The tautomer crossover is from high-spin to low-spin via metal atom to o-quinone ligand electron-transfer accompanied by a bond length change which is 0.15Åin the Co(3,5-DTBSQ)_2(N-N) molecule. Current semi-classical thermodynamic descriptions yield unphysically large entropy changes through the crossover. To investigate a possible role for quantum mechanical electron correlation effects, we model the molecule as a finite size Anderson "impurity" system using a variational ansatz for the many body wave-function. Model parameters are derived through atomic physics and a mean-field fit to Kohn-Sham eigenvalues. We will relate our model to magnetic susceptibility data, and optical and x-ray absorption spectra. [1] Adams, D.M.; Hendrickson, D.N. J. Am. Chem. Soc. 1996, 118, 11515-11528

  7. VB-201, an oxidized phospholipid small molecule, inhibits CD14- and Toll-like receptor-2-dependent innate cell activation and constrains atherosclerosis

    PubMed Central

    Mendel, I; Feige, E; Yacov, N; Salem, Y; Levi, I; Propheta-Meiran, O; Shoham, A; Ishai, E; George, J; Harats, D; Breitbart, E

    2014-01-01

    Atherosclerosis is an inflammatory disease of the vascular wall. Activated monocytes and dendritic cells (DC) in the intima layer of the vasculature promote atherogenesis. Toll-like receptor (TLR)-2 and TLR-4, which are predominantly expressed on these cells and mediate their activation, are essential for atherosclerosis development. In this study we demonstrate that VB-201, an oxidized phospholipid (Ox-PL) small molecule, inhibits TLR signalling restricted to TLR-2 and TLR-4 in human and mouse monocytes and DC. Mechanistically, we show that VB-201 binds directly to TLR-2 and CD14, the TLR-4 co-receptor, to impair downstream cues and cytokine production. In a rabbit model, oral administration of VB-201 constrained atherosclerosis progression. This effect was not due to reduced cholesterol abundance, as hyperlipidaemia was sustained. We suggest that VB-201 may counter inflammation where TLR-2 and/or CD14 complicity is essential, and is therefore beneficial for the treatment of atherosclerosis. PMID:24116867

  8. 30 CFR 57.22222 - Ventilation materials (I-A, I-B, I-C, II-A, III, V-A, and V-B mines).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ....22222 Ventilation materials (I-A, I-B, I-C, II-A, III, V-A, and V-B mines). Brattice cloth and ventilation tubing shall be approved by MSHA in accordance with 30 CFR part 7, or shall bear a BC or...

  9. 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

    1994-09-01

    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.

  10. Hydrogen atom abstraction from C-H, P-H, Si-H, and Sn-H bonds by the triplet excited state of the tetrakis(. mu. -pyrophosphito)diplatinum(II) tetraanion. Spectroscopic observation of the mixed-valence hydride complexes Pt/sub 2/(. mu. -P/sub 2/O/sub 5/H/sub 2/)/sub 4/H/sup 4 -/

    SciTech Connect

    Roundhill, D.M.; Atherton, S.J.; Shen, Z.

    1987-09-30

    Pulse radiolysis of aqueous solutions of Pt/sub 2/(..mu..-P/sub 2/O/sub 5/H/sub 2/)/sub 4//sup 4 -/ at pH 4 with added t-BuOH gives Pt/sub 2/(..mu..-P/sub 2/O/sub 5/H/sub 2/)/sub 4/H/sup 4 -/ via reaction with an electron and a proton. Pulsed-laser photolysis (Nd-YAG at 355 nm) of aqueous solutions of Pt/sub 2/(..mu..-P/sub 2/O/sub 5/H/sub 2/)/sub 4//sup 4 -/ with added isopropyl alcohol, phosphorus acid, or hypophosphorous acid also gives Pt/sub 2/(..mu..-P/sub 2/O/sub 5/H/sub 2/)/sub 4//sup 4 -/ by hydrogen atom abstraction. The mixed-valence hydride is similarly formed in methanolic solutions of (PPN)/sub 4/(Pt/sub 2/(..mu..-P/sub 2/O/sub 5/H/sub 2/)/sub 4/) from added triethylsilane or tributyltin hydride. The intermediacy of the Me/sub 2/COH radical is evidenced by the formation of both pinacol and acetone in the photochemically catalyzed dehydrogenation of isopropyl alcohol with Pt/sub 2/(..mu..-P/sub 2/O/sub 5/H/sub 2/)/sub 4//sup 4 -/ in aqueous solution. The other radical, Pt/sub 2/(..mu..-P/sub 2/O/sub 5/H/sub 2/)/sub 4/H/sup 4 -/, disproportionates to Pt/sub 2/(..mu..-P/sub 2/O/sub 5/H/sub 2/)/sub 4/H/sub 2//sup 4 -/ and Pt/sub 2/(..mu..-P/sub 2/O/sub 5/H/sub 2/)/sub 4//sup 4 -/. The Bu/sub 3/Sn radical has been detected by transient difference laser spectroscopy in solutions containing Pt/sub 2/(..mu..-P/sub 2/O/sub 5/H/sub 2/)/sub 4/H/sub 2//sup 4 -/ and Bu/sub 3/SnH. The quenching rates for hydrogen atoms donors with the /sup 3/A/sub 2u/ state of Pt/sub 2/(..mu..-P/sub 2/O/sub 5/H/sub 2/)/sub 4//sup 4 -/*, as measured by the Stern-Volmer equation, are given and compared.

  11. Valence modulations in CeRuSn

    NASA Astrophysics Data System (ADS)

    Feyerherm, R.; Dudzik, E.; Proke, K.; Mydosh, J. A.; Huang, Y.-K.; Pttgen, R.

    2014-07-01

    CeRuSn exhibits an extraordinary room temperature structure at 300 K with the coexistence of two types of Ce ions, namely trivalent Ce 3+ and intermediate-valent Ce(4-? )+, in a metallic environment. The ordered arrangement of these two Ce types on specific crystallographic sites results in a doubling of the unit cell along the c axis with respect to the basic monoclinic CeCoAl-type structure. Below room temperature, structural modulation transitions with very broad hysteresis have been reported from measurements of various bulk properties. X-ray diffraction revealed that at low temperatures the doubling of the CeCoAl-type structure is replaced by a different modulated ground state, approximating a near tripling of the basic CeCoAl cell. The transition is accompanied by a significant contraction of the c axis. We present new x-ray absorption near-edge spectroscopy data at the Ce L3 absorption edge, measured on a freshly cleaved surface of a CeRuSn single crystal. In contrast to our previous report, the new data exhibit small but significant variations as a function of temperature that are consistent with a transition of a fraction of Ce3+ ions to the intermediate valence state, analogous to the ? ?? transition in elemental cerium, when cooling through the structural transitions of CeRuSn. Such results in a valence-modulated state.

  12. Does fluorine participate in halogen bonding?

    PubMed

    Eskandari, Kiamars; Lesani, Mina

    2015-03-16

    When R is sufficiently electron withdrawing, the fluorine in the R-F molecules could interact with electron donors (e.g., ammonia) and form a noncovalent bond (F???N). Although these interactions are usually categorized as halogen bonding, our studies show that there are fundamental differences between these interactions and halogen bonds. Although the anisotropic distribution of electronic charge around a halogen is responsible for halogen bond formations, the electronic charge around the fluorine in these molecules is spherical. According to source function analysis, F is the sink of electron density at the F???N BCP, whereas other halogens are the source. In contrast to halogen bonds, the F???N interactions cannot be regarded as lump-hole interactions; there is no hole in the valence shell charge concentration (VSCC) of fluorine. Although the quadruple moment of Cl and Br is mainly responsible for the existence of ?-holes, it is negligibly small in the fluorine. Here, the atomic dipole moment of F plays a stabilizing role in the formation of F???N bonds. Interacting quantum atoms (IQA) analysis indicates that the interaction between halogen and nitrogen in the halogen bonds is attractive, whereas it is repulsive in the F???N interactions. Virial-based atomic energies show that the fluorine, in contrast to Cl and Br, stabilize upon complex formation. According to these differences, it seems that the F???N interactions should be referred to as "fluorine bond" instead of halogen bond. PMID:25652256

  13. Experimental study of the valence band of Bi2Se3

    DOE PAGESBeta

    Heremans, Joseph; Gao, Yibin; He, Bin; Androulakis, Yiannis; Parker, David S

    2014-01-01

    The valence band of Bi2Se3 is investigated with Shubnikov - de Haas measurements, galvanomagnetic and thermoelectric transport. At low hole concentration, the hole Fermi surface is closed and box-like, but at higher concentrations it develops tube-like extensions that are open. The experimentally determined density-of-states effective mass is lighter than density-functional theory calculations predict; while we cannot give a definitive explanation for this, we suspect that the theory may lack sufficient precision to compute room-temperature transport properties, such as the Seebeck coefficient, in solids in which there are Van der Waals interlayer bonds.

  14. Effect of position of methyl substituent in piperidinedithiocarbamate on the ZnS4N chromophore: Synthesis, spectral, valence-bond parameters and single crystal X-ray structural studies on bis(2-methylpiperidinecarbodithioato-S,S‧)-(pyridine)zinc(II) and bis(4-methylpiperidinecarbodithioato-S,S‧)(pyridine)zinc(II)

    NASA Astrophysics Data System (ADS)

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

    2009-11-01

    Two Zn(II)monomethyl substituted piperidinedithiocarbamates with ZnS 4N chromophores have been synthesized ([Zn(2-mpipdtc) 2(py)] ( 1) and [Zn(4-mpipdtc) 2(py)] ( 2) (where 2-mpipdtc = 2-methylpiperidinedithiocarbamate, 4-mpipdtc = 4-methylpiperidinedithiocarbamate and py = pyridine)) from [Zn(2-mpipdtc) 2] and [Zn(4-mpipdtc) 2], respectively. Their structures and properties have been characterized by IR, 1H and 13C NMR spectroscopy. The structures of both the complexes were determined by single crystal X-ray crystallography. IR spectra of the complexes 1 and 2 show the thioureide νC-N band at 1431 and 1445 cm -1, respectively. In the case of complex 1, the thioureide νC-N values are shifted to lower wave number compared to 2. This may be due to the steric effect of the ortho-methyl group in the 2-mpipdtc resulting in a decrease in the double bond character of the C-N bond. The methyl protons are more deshielded in 1 (1.28 ppm) than that found in 2 (0.98 ppm), due to deshielding decrease with increase in distance from the metal centre. The 13C NMR peaks of the group N 13CS 2 are found in both cases, at around 202 ppm, which indicates the bidentate character of the ligands. Single crystal X-ray structural analysis of 1 and 2 showed that the zinc atom is pentacoordinated with four sulfur atoms from the dithiocarbamate and one nitrogen atom from the pyridine. Both the complexes adopt a geometry which is intermediate between the tetragonal pyramid (C 4v) and trigonal bipyramid (D 3h). From the τ values, the coordination geometry of 1 and 2 is described as being 38.9% and 36.1% along the pathway of distortion from tetragonal pyramid toward trigonal bipyramid.

  15. Distinguishing Bonds.

    PubMed

    Rahm, Martin; Hoffmann, Roald

    2016-03-23

    The energy change per electron in a chemical or physical transformation, ΔE/n, may be expressed as Δχ̅ + Δ(VNN + ω)/n, where Δχ̅ is the average electron binding energy, a generalized electronegativity, ΔVNN is the change in nuclear repulsions, and Δω is the change in multielectron interactions in the process considered. The last term can be obtained by the difference from experimental or theoretical estimates of the first terms. Previously obtained consequences of this energy partitioning are extended here to a different analysis of bonding in a great variety of diatomics, including more or less polar ones. Arguments are presented for associating the average change in electron binding energy with covalence, and the change in multielectron interactions with electron transfer, either to, out, or within a molecule. A new descriptor Q, essentially the scaled difference between the Δχ̅ and Δ(VNN + ω)/n terms, when plotted versus the bond energy, separates nicely a wide variety of bonding types, covalent, covalent but more correlated, polar and increasingly ionic, metallogenic, electrostatic, charge-shift bonds, and dispersion interactions. Also, Q itself shows a set of interesting relations with the correlation energy of a bond. PMID:26910496

  16. Valence Effects in Reasoning About Evaluative Traits

    PubMed Central

    Heyman, Gail D.; Giles, Jessica W.

    2010-01-01

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

  17. Ti 3p electrons: core or valence?

    SciTech Connect

    Deskins, N. Aaron

    2009-03-16

    The debate over where Ti 3p electrons should be placed (in the core or valence) has been addressed using pseudopotential-based density functional theory. This work has focused on the TiO2 rutile phase using two different Ti pseudopotentials with 4 or 10 valence electrons, depending on how the Ti 3p electrons are treated. The electronic structure of bulk TiO2 are very similar for the two potentials, and both potentials show similar bulk properties (lattice parameters, bulk modulus). Adsorption of several different types of molecules on a (110) surface gives similar results for organic and inorganic molecules, while adsorption of metal atoms leads to noticeable differences in adsorption energies (26% difference between the two pseudopotentials). This discrepancy is attributed to a larger change in the electronic state of Ti upon metal adsorption, compared to organic or inorganic molecule adsorption. The results also show that the two pseudopotential methods describe oxygen vacancies slightly differently, with a difference in vacancy formation energy being 0.32 eV. Ti in other oxidation states was modeled and both pseudopotentials work reasonably well. This study shows that the 3p electrons can often be treated as core states, but care must be taken to verify that this does not affect the simulation accuracy. Funding was provided by the Department of Energy, Office of Basic Energy Sciences. Computational resources were provided by the Molecular Science Computing Facility located at the Environmental Molecular Science Laboratory in Richland, WA and the National Energy Research Scientific Computing Center at Lawrence Berkeley National Laboratory. All work was performed at Pacific Northwest National Laboratory (PNNL). Battelle operates PNNL for the U.S. Department of Energy.

  18. Relationship Between Infrared Intensity Theories: Electro-Optical Parameters And Bond Polar Parameters

    NASA Astrophysics Data System (ADS)

    Galabov, Boris; Dudev, T.

    1989-12-01

    Mathematical and physical aspects are analysed of the relationship between two theoretical formulations of infrared intensities employing parameters associated with chemical bonds: the valence optical theory and bond polar parameters method. Parallel applications of the two theories in analysing experimental IR intensity data for methylchloride are presented.

  19. High Resolution Core Valence Valence Auger Electron Specroscopy on Free Molecules

    NASA Astrophysics Data System (ADS)

    Svensson, S.; Karlsson, L.

    1992-01-01

    Recent experimental results from Core Valence Valence (CVV) Auger electron spectroscopy on free molecules are discussed. The practical use of calculated potential curves for the dicationic final states is illustrated using the NO molecule as an example. The assignment of the CVV spectra to get experimental potential curves for the dicationic states of diatomic molecules is reviewed. The spin-orbit splitting of the initial core hole state in the Auger process is discussed and is related to the molecular field splitting of the Core levels. The importance of making monochromatized photon-impact experiments in order to study the high energy satellites is underlined. The Auger shake-up satellite spectrum of the N2 molecule is discussed as an example and it is found that the participator transitions dominate this spectrum.

  20. Teaching Valence Shell Electron Pair Repulsion (VSEPR) Theory

    ERIC Educational Resources Information Center

    Talbot, Christopher; Neo, Choo Tong

    2013-01-01

    This "Science Note" looks at the way that the shapes of simple molecules can be explained in terms of the number of electron pairs in the valence shell of the central atom. This theory is formally known as valence shell electron pair repulsion (VSEPR) theory. The article explains the preferred shape of chlorine trifluoride (ClF3),…

  1. Teaching Valence Shell Electron Pair Repulsion (VSEPR) Theory

    ERIC Educational Resources Information Center

    Talbot, Christopher; Neo, Choo Tong

    2013-01-01

    This "Science Note" looks at the way that the shapes of simple molecules can be explained in terms of the number of electron pairs in the valence shell of the central atom. This theory is formally known as valence shell electron pair repulsion (VSEPR) theory. The article explains the preferred shape of chlorine trifluoride (ClF3),

  2. Experimental and theoretical electron momentum spectroscopic study of the valence electronic structure of tetrahydrofuran under pseudorotation.

    PubMed

    Ning, C G; Huang, Y R; Zhang, S F; Deng, J K; Liu, K; Luo, Z H; Wang, F

    2008-11-01

    The most populated structure of tetrahydrofuran (THF) has been investigated in our previous study using electron momentum spectroscopy (EMS). Because of the relatively low impact energy (600 eV) and low energy resolution (DeltaE = 1.20 eV) in the previous experiment, only the highest occupied molecular orbital (HOMO) of THF was investigated. The present study reports the most recent high-resolution EMS of THF in the valence space for the first time. The binding energy spectra of THF are measured at 1200 and 2400 eV plus the binding energies, respectively, for a series of azimuthal angles. The experimentally obtained binding energy spectra and orbital momentum distributions (MDs) are employed to study the orbital responses of the pseudorotation motion of THF. The outer valence Greens function (OVGF), the OVGF/6-311++G** model, and density function theory (DFT)-based SAOP/et-pVQZ model are employed to simulate the binding energy spectra. The orbital momentum distributions (MDs) are produced using the DFT-based B3LYP/aug-cc-pVTZ model, incorporating thermodynamic population analysis. Good agreement between theory and experiment is achieved. Orbital MDs of valence orbitals exhibit only slight differences with respect to the impact energies at 1200 and 2400 eV, indicating validation of the plane wave impulse approximation (PWIA). The present study has further discovered that the orbital MDs of the HOMO in the low-momentum region (p < 0.70 a.u) change significantly with the pseudorotation angle, phi, giving a v-shaped cross section, whereas the innermost valence orbital of THF does not vary with pseudorotation, revealing a very different bonding mechanism from the HOMO. The present study explores an innovative approach to study pseudorotation of sugar puckering, which sheds a light to study other biological systems with low energy barriers among ring-puckering conformations. PMID:18842033

  3. Generalized valence-force-field model of (Ga,In)(N,P) ternary alloys

    NASA Astrophysics Data System (ADS)

    Biswas, Koushik; Franceschetti, Alberto; Lany, Stephan

    2008-08-01

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

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

    SciTech Connect

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

    2008-01-01

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

  5. 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)

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

    2009-03-01

    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.

  6. Charge Fluctuations and the Valence Transition in Yb under Pressure

    SciTech Connect

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

    2009-04-21

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

  7. Yankee bonds

    SciTech Connect

    Delaney, P. )

    1993-10-01

    Yankee and Euromarket bonds may soon find their way into the financing of power projects in Latin America. For developers seeking long-term commitments under build, own, operate, and transfer (BOOT) power projects in Latin America, the benefits are substantial.

  8. CORRELATION BETWEEN METAL-CERAMIC BOND STRENGTH AND COEFFICIENT OF LINEAR THERMAL EXPANSION DIFFERENCE

    PubMed Central

    Lopes, Stella Crosara; Pagnano, Valéria Oliveira; Rollo, João Manuel Domingos de Almeida; Leal, Mônica Barbosa; Bezzon, Osvaldo Luiz

    2009-01-01

    The purpose of this study was to evaluate the metal-ceramic bond strength (MCBS) of 6 metal-ceramic pairs (2 Ni-Cr alloys and 1 Pd-Ag alloy with 2 dental ceramics) and correlate the MCBS values with the differences between the coefficients of linear thermal expansion (CTEs) of the metals and ceramics. Verabond (VB) Ni-Cr-Be alloy, Verabond II (VB2), Ni-Cr alloy, Pors-on 4 (P), Pd-Ag alloy, and IPS (I) and Duceram (D) ceramics were used for the MCBS test and dilatometric test. Forty-eight ceramic rings were built around metallic rods (3.0 mm in diameter and 70.0 mm in length) made from the evaluated alloys. The rods were subsequently embedded in gypsum cast in order to perform a tensile load test, which enabled calculating the CMBS. Five specimens (2.0 mm in diameter and 12.0 mm in length) of each material were made for the dilatometric test. The chromel-alumel thermocouple required for the test was welded into the metal test specimens and inserted into the ceramics. ANOVA and Tukey's test revealed significant differences (p=0.01) for the MCBS test results (MPa), with PI showing higher MCBS (67.72) than the other pairs, which did not present any significant differences. The CTE (10-6 °C-1) differences were: VBI (0.54), VBD (1.33), VB2I (-0.14), VB2D (0.63), PI (1.84) and PD (2.62). Pearson's correlation test (r=0.17) was performed to evaluate of correlation between MCBS and CTE differences. Within the limitations of this study and based on the obtained results, there was no correlation between MCBS and CTE differences for the evaluated metal-ceramic pairs. PMID:19274398

  9. Site Specific Phosphorylation of Cytochrome c Oxidase Subunits I, IVi1 and Vb in Rabbit Hearts Subjected to Ischemia/Reperfusion

    PubMed Central

    Fang, Ji-Kang; Prabu, Subbuswamy K.; Sepuri, Naresh B.; Raza, Haider; Anandatheerthavarada, Hindupur K.; Galati, Domenico; Spear, Joseph; Avadhani, Narayan G.

    2007-01-01

    We have mapped the sites of ischemia/reperfusion induced phosphorylation of cytochrome c oxidase (CcO) subunits in rabbit hearts by using a combination of Blue Native gel/Tricine gel electrophoresis and nano-LC-MS/MS approaches. We used precursor ion scanning combined with neutral loss scanning and found that mature CcO subunit I was phosphorylated at tandem Ser115/Ser116 positions, subunit IVi1 at Thr52 and subunit Vb at Ser40. These sites are highly conserved in mammalian species. Molecular modeling suggests that phosphorylation sites of subunit I face the inter membrane space while those of subunits IVi1 and Vb face the matrix side. PMID:17349628

  10. Radiation thermal processes in Cr13Mo2NbVB steel - the material of the fuel assembly shell in reactor BN-350 under mechanical tests

    NASA Astrophysics Data System (ADS)

    Larionov, A. S.; Dikov, A. S.; Poltavtseva, V. P.; Kislitsin, S. B.; Kuimova, M. V.; Chernyavskii, A. V.

    2015-04-01

    Regularities of changes of structural-phase state and mechanical properties of steel 13Mo2NbVB - the material of the fuel assembly shell in reactor BN-350 after various mechanical tests at 350C are experimentally studied. The formation of microprecipitations FeMo, enriched or depleted with molybdenum was found in the short-time mechanical tests, which is the cause of thermal hardening of irradiated Cr13Mo2NbVB steel and its destruction by the ductile-brittle mechanism. On the basis of long-time creep tests it was shown that the material of the spent fuel assembly shell has sufficient resource for long-time storage in the temperature and force conditions simulating long-time storage of spent nuclear fuel.

  11. Inelastic neutron scattering in valence fluctuation compounds

    SciTech Connect

    Jon M Lawrence

    2011-02-15

    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.

  12. 30 CFR 57.22232 - Actions at 0.5 percent methane (I-B, II-A, II-B, IV, V-B, and VI mines).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Actions at 0.5 percent methane (I-B, II-A, II-B, IV, V-B, and VI mines). 57.22232 Section 57.22232 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES...

  13. 30 CFR 57.22234 - Actions at 1.0 percent methane (I-A, I-B, III, V-A, and V-B mines).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Actions at 1.0 percent methane (I-A, I-B, III, V-A, and V-B mines). 57.22234 Section 57.22234 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Safety...

  14. 30 CFR 57.22231 - Actions at 0.25 percent methane (I-B, II-B, V-B, and VI mines).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Actions at 0.25 percent methane (I-B, II-B, V-B, and VI mines). 57.22231 Section 57.22231 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Safety Standards...

  15. 30 CFR 57.22222 - Ventilation materials (I-A, I-B, I-C, II-A, III, V-A, and V-B mines).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Ventilation materials (I-A, I-B, I-C, II-A, III, V-A, and V-B mines). 57.22222 Section 57.22222 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Safety...

  16. 30 CFR 57.22238 - Actions at 2.0 percent methane (I-B, II-B, V-B, and VI mines).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Actions at 2.0 percent methane (I-B, II-B, V-B, and VI mines). 57.22238 Section 57.22238 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Safety Standards...

  17. 30 CFR 57.22238 - Actions at 2.0 percent methane (I-B, II-B, V-B, and VI mines).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Actions at 2.0 percent methane (I-B, II-B, V-B, and VI mines). 57.22238 Section 57.22238 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Safety Standards...

  18. 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

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Actions at 2.0 percent methane (I-B, II-B, V-B, and VI mines). 57.22238 Section 57.22238 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Safety Standards...

  19. 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

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Actions at 0.25 percent methane (I-B, II-B, V-B, and VI mines). 57.22231 Section 57.22231 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Safety Standards...

  20. 30 CFR 57.22231 - Actions at 0.25 percent methane (I-B, II-B, V-B, and VI mines).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Actions at 0.25 percent methane (I-B, II-B, V-B, and VI mines). 57.22231 Section 57.22231 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Safety Standards...

  1. 30 CFR 57.22222 - Ventilation materials (I-A, I-B, I-C, II-A, III, V-A, and V-B mines).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Ventilation materials (I-A, I-B, I-C, II-A, III, V-A, and V-B mines). 57.22222 Section 57.22222 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Safety...

  2. 30 CFR 57.22222 - Ventilation materials (I-A, I-B, I-C, II-A, III, V-A, and V-B mines).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ....22222 Ventilation materials (I-A, I-B, I-C, II-A, III, V-A, and V-B mines). Brattice cloth and ventilation tubing shall be approved by MSHA in accordance with 30 CFR part 7, or shall bear a BC or VT... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Ventilation materials (I-A, I-B, I-C, II-A,...

  3. Selective extraction based on poly(MAA-VB-EGMDA) monolith followed by HPLC for determination of hordenine in plasma and urine samples.

    PubMed

    Chen, Yonggang; Meng, Junhua; Zou, Jili; An, Jing

    2015-06-01

    Hordenine is an active compound found in several foods, herbs and beer. In this work, a novel sorbent was fabricated for selective solid-phase extraction (SPE) of hordenine in biological samples. The organic polymer sorbent was synthesized in one step in the plastic barrel of a syringe by a pre-polymerization solution consisting of methacrylic acid (MAA), 4-vinylphenylboronic acid (VB) and ethylene glycol dimethacrylate (EGDMA). The conditions for preparation were optimized to generate a poly(MAA-VB-EGMDA) monolith with good permeability. The monolith exhibited good enrichment efficiency towards hordenine. By using tyramine as the internal standard, a poly(MAA-VB-EGMDA)-based SPE-HPLC method was established for analysis of hordenine. Conditions for SPE, including volume of eluting solvent, pH of sample solution, sampling rate and sample volume, were optimized. The proposed SPE-HPLC method presented good linearity (R(2) ?=?0.9992) within 10-2000?ng/mL and the detection limits was 3?ng/mL, which is significantly more sensitive than reported methods. The method was also applied in plasma and urine samples; good capability of removing matrices was observed, while hordenine in low content was well extracted and enriched. The recoveries were from 90.6 to 94.7% and from 89.3 to 91.5% for the spiked plasma and urine samples, respectively, with the relative standard deviations <4.7%. PMID:25355709

  4. Emotion and language: valence and arousal affect word recognition.

    PubMed

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

    2014-06-01

    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. PMID:24490848

  5. Emotion and language: Valence and arousal affect word recognition

    PubMed Central

    Brysbaert, Marc; Warriner, Amy Beth

    2014-01-01

    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. The present study 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. PMID:24490848

  6. Evaluative Conditioning Induces Changes in Sound Valence

    PubMed Central

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

    2012-01-01

    Through evaluative conditioning (EC) a stimulus can acquire an affective value by pairing it with another affective stimulus. While many sounds we encounter daily have acquired an affective value over life, EC has hardly been tested in the auditory domain. To get a more complete understanding of affective processing in auditory domain we examined EC of sound. In Experiment 1 we investigated whether the affective evaluation of short environmental sounds can be changed using affective words as unconditioned stimuli (US). Congruency effects on an affective priming task for conditioned sounds demonstrated successful EC. Subjective ratings for sounds paired with negative words changed accordingly. In Experiment 2 we investigated whether extinction occurs, i.e., whether the acquired valence remains stable after repeated presentation of the conditioned sound without the US. The acquired affective value remained present, albeit weaker, even after 40 extinction trials. These results provide clear evidence for EC effects in the auditory domain. We will argue that both associative as well as propositional processes are likely to underlie these effects. PMID:22514545

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

    NASA Astrophysics Data System (ADS)

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

    1997-04-01

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

  8. 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

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Mechanical ventilation (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines). 57.22201 Section 57.22201 Mineral Resources MINE SAFETY AND HEALTH....22201 Mechanical ventilation (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines). All mines...

  9. 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, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 false Mechanical ventilation (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines). 57.22201 Section 57.22201 Mineral Resources MINE SAFETY AND HEALTH....22201 Mechanical ventilation (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines). All mines...

  10. 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, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Mechanical ventilation (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines). 57.22201 Section 57.22201 Mineral Resources MINE SAFETY AND HEALTH....22201 Mechanical ventilation (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines). All mines...

  11. 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, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Mechanical ventilation (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines). 57.22201 Section 57.22201 Mineral Resources MINE SAFETY AND HEALTH....22201 Mechanical ventilation (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines). All mines...

  12. 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

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Mechanical ventilation (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines). 57.22201 Section 57.22201 Mineral Resources MINE SAFETY AND HEALTH....22201 Mechanical ventilation (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines). All mines...

  13. Valence band anticrossing in GaBixAs1-x

    SciTech Connect

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

    2007-07-11

    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.

  14. Photon energy dependent valence band response of metallic nanoparticles.

    PubMed

    Jänkälä, K; Tchaplyguine, M; Mikkelä, M-H; Björneholm, O; Huttula, M

    2011-10-28

    We show that the valence band response to photon impact in metallic nanoparticles is highly energy dependent. This is seen as drastic variations of cross sections in valence photoionization of free and initially charge-neutral nanosized metal clusters. The effect is demonstrated in a combined experimental and theoretical study of Rb clusters. The experimental findings are interpreted theoretically using a jellium model and superatom description. The variations are attributed to the changing overlap with the photon energy between the wave functions of diffuse delocalized valence electrons and continuum electrons producing a series of minima in the cross section. PMID:22107629

  15. 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

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

    2008-01-01

    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. PMID:19920898

  16. Pi Bond Orders and Bond Lengths

    ERIC Educational Resources Information Center

    Herndon, William C.; Parkanyi, Cyril

    1976-01-01

    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)

  17. Pressure versus temperature effects on intramolecular electron transfer in mixed-valence complexes.

    PubMed

    Scheins, Stephan; Overgaard, Jacob; Timco, Grigore A; Stash, Adam; Chen, Yu-Sheng; Larsen, Finn K; Christensen, Mogens; Jrgensen, Mads R V; Madsen, Solveig R; Schmkel, Mette S; Iversen, Bo B

    2013-01-01

    Mixed-valence trinuclear carboxylates, [M(3)O(O(2)CR)(6)L(3)] (M = metal, L = terminal ligand), have small differences in potential energy between the configurations M(II)M(III)M(III)?M(III)M(II)M(III)?M(III)M(III)M(II), which means that small external changes can have large structural effects, owing to the differences in coordination geometry between M(2+) and M(3+) sites (e.g., about 0.2? for Fe-O bond lengths). It is well-established that the electron transfer (ET) between the metal sites in these mixed-valence molecules is strongly dependent on temperature and on the specific crystal environment; however, herein, for the first time, we examine the effect of pressure on the electron transfer. Based on single-crystal X-ray diffraction data that were measured at 15, 90, 100, 110, 130, 160, and 298?K on three different crystals, we first unexpectedly found that our batch of Fe(3)O (O(2)CC(CH(3))(3))(6)(C(5)H(5)N)(3) (1) exhibited a different temperature dependence of the ET process than previous studies of compound 1 have shown. We observed a phase transition at around 130?K that was related to complete valence trapping and Hirshfeld surface analysis revealed that this phase transition was governed by a subtle competition between C-H???? and ????? intermolecular interactions. Subsequent high-pressure single-crystal X-ray diffraction at pressures of 0.15, 0.35, 0.45, 0.74, and 0.96?GPa revealed that it was not possible to trigger the phase transition (i.e., valence trapping) by a reduction of the unit-cell volume, owing to this external pressure. We conclude that modulation of the ET process requires anisotropic changes in the intermolecular interactions, which occur when various directional chemical bonds are affected differently by changes in temperature, but not by the application of pressure. PMID:23169277

  18. A Valence Isomer Trapping Procedure for Introductory Organic Laboratory.

    ERIC Educational Resources Information Center

    Kurtz, David W.; Johnson, Richard P.

    1989-01-01

    Described is an experiment which illustrates valence isomerization, the trapping of a reactive intermediate and retrosynthetic analysis applied to the Diels-Alder reaction. Included is a background discussion, experimental procedures, and a discussion of the analysis. (CW)

  19. Differential impact of beliefs on valence and arousal

    PubMed Central

    Nicolle, Antoinette; Goel, Vinod

    2012-01-01

    Many cognitive accounts of emotional processing assume that emotions have representational content that can be influenced by beliefs and desires. It is generally thought that emotions also have non-cognitive, affective components, including valence and arousal. To clarify the impact of cognition on these affective components we asked participants to rate sentences along cognitive and affective dimensions. For the former case, participants rated the believability of the material. For the latter case, they provided valence and arousal ratings. Across two experiments, we show that valence and arousal are differently influenced by beliefs, suggesting that these two largely independent affective components of emotion differ in their cognitive penetrability. While both components depended upon overall comprehension of sentence meaning, only valence was influenced by the consistency of the sentences with participants’ beliefs (i.e., whether it was believable or unbelievable). We discuss the implications of these findings for understanding cognition-emotion relationships. PMID:22783982

  20. An inducible mouse model for microvillus inclusion disease reveals a role for myosin Vb in apical and basolateral trafficking.

    PubMed

    Schneeberger, Kerstin; Vogel, Georg F; Teunissen, Hans; van Ommen, Domenique D; Begthel, Harry; El Bouazzaoui, Layla; van Vugt, Anke H M; Beekman, Jeffrey M; Klumperman, Judith; Müller, Thomas; Janecke, Andreas; Gerner, Patrick; Huber, Lukas A; Hess, Michael W; Clevers, Hans; van Es, Johan H; Nieuwenhuis, Edward E S; Middendorp, Sabine

    2015-10-01

    Microvillus inclusion disease (MVID) is a rare intestinal enteropathy with an onset within a few days to months after birth, resulting in persistent watery diarrhea. Mutations in the myosin Vb gene (MYO5B) have been identified in the majority of MVID patients. However, the exact pathophysiology of MVID still remains unclear. To address the specific role of MYO5B in the intestine, we generated an intestine-specific conditional Myo5b-deficient (Myo5bfl/fl;Vil-CreERT2) mouse model. We analyzed intestinal tissues and cultured organoids of Myo5bfl/fl;Vil-CreERT2 mice by electron microscopy, immunofluorescence, and immunohistochemistry. Our data showed that Myo5bfl/fl;Vil-CreERT2 mice developed severe diarrhea within 4 d after tamoxifen induction. Periodic Acid Schiff and alkaline phosphatase staining revealed subapical accumulation of intracellular vesicles in villus enterocytes. Analysis by electron microscopy confirmed an almost complete absence of apical microvilli, the appearance of microvillus inclusions, and enlarged intercellular spaces in induced Myo5bfl/fl;Vil-CreERT2 intestines. In addition, we determined that MYO5B is involved not only in apical but also basolateral trafficking of proteins. The analysis of the intestine during the early onset of the disease revealed that subapical accumulation of secretory granules precedes occurrence of microvillus inclusions, indicating involvement of MYO5B in early differentiation of epithelial cells. By comparing our data with a novel MVID patient, we conclude that our mouse model completely recapitulates the intestinal phenotype of human MVID. This includes severe diarrhea, loss of microvilli, occurrence of microvillus inclusions, and subapical secretory granules. Thus, loss of MYO5B disturbs both apical and basolateral trafficking of proteins and causes MVID in mice. PMID:26392529

  1. Mn 3s exchange splitting in mixed-valence manganites.

    SciTech Connect

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

    2002-03-15

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

  2. Inelastic collisions of positrons with one-valence-electron targets

    NASA Technical Reports Server (NTRS)

    Abdel-Raouf, Mohamed Assad

    1990-01-01

    The total elastic and positronium formation cross sections of the inelastic collisions between positrons and various one-valence-electron atoms, (namely hydrogen, lithium, sodium, potassium and rubidium), and one-valence-electron ions, (namely hydrogen-like, lithium-like and alkaline-earth positive ions) are determined using an elaborate modified coupled-static approximation. Special attention is devoted to the behavior of the Ps cross sections at the energy regions lying above the Ps formation thresholds.

  3. Bonded Lubricants

    NASA Technical Reports Server (NTRS)

    1977-01-01

    Another spinoff to the food processing industry involves a dry lubricant developed by General Magnaplate Corp. of Linden, N.J. Used in such spacecraft as Apollo, Skylab and Viking, the lubricant is a coating bonded to metal surfaces providing permanent lubrication and corrosion resistance. The coating lengthens equipment life and permits machinery to be operated at greater speed, thus increasing productivity and reducing costs. Bonded lubricants are used in scores of commercia1 applications. They have proved particularly valuable to food processing firms because, while increasing production efficiency, they also help meet the stringent USDA sanitation codes for food-handling equipment. For example, a cookie manufacturer plagued production interruptions because sticky batter was clogging the cookie molds had the brass molds coated to solve the problem. Similarly, a pasta producer faced USDA action on a sanitation violation because dough was clinging to an automatic ravioli-forming machine; use of the anti-stick coating on the steel forming plates solved the dual problem of sanitation deficiency and production line downtime.

  4. Basics of Fidelity Bonding.

    ERIC Educational Resources Information Center

    Kahn, Steven P.

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

  5. Studies of fullerenes and carbon nanotubes by an extended bond order potential

    NASA Astrophysics Data System (ADS)

    Che, Jianwei; Cagin, Tahir; Goddard, William A., III

    1999-09-01

    We present a novel approach to combine bond order potentials with long-range nonbond interactions. This extended bond order potential consistently takes into account bond terms and nonbond terms. It not only captures the advantages of the bond order potentials (i.e. simulating bond forming and breaking), but also systematically includes the nonbond contributions to energy and forces in studying the structure and dynamics of covalently bonded systems such as graphite, diamond, nanotubes, fullerenes and hydrocarbons, in their crystal and melt forms. Using this modified bond order potential, we studied the structure and thermal properties (including thermal conductivity) of C60 crystal, and the elastic properties and plastic deformation processes of the single-walled and double-walled nanotubes. This extended bond order potential enables us to simulate large deformations of a nanotube under tensile and compressive loads. The basic formulation in this paper is transferable to other bond order potentials and traditional valence force fields.

  6. Multiplet-Splitting of the Quasi-Atomic-Like Core-Valence-Valence Auger Spectra of Zinc Metal

    NASA Astrophysics Data System (ADS)

    Yuan, Jian-Min

    2001-10-01

    Multiplet-splitting of the quasi-atomic-like core-valence-valence (CVV) Auger spectra of zinc metal is calculated by explicitly considering the so-called hole-hole interaction in the final valence states of the Auger transition. We assume that before the Auger transition occurs, the occupied valence states relax to screen the core-hole which results in a redistribution of the valence electrons, in particular within the atom that contains a hole in the core. The supercell method is used to calculate the electronic states concerned by the Auger transition, which is accomplished by the self-consistent full-potential linearized augmented plane wave method. In each supercell, one atom is considered to have a core-hole and many others without it. Due to relaxation and screening, the valence states at the site of the Auger transition are more localized compared with those in the ground-state metal. The multiplet peaks of the quasi-atomic-like CVV Auger spectra of zinc metal are obtained by calculating the Auger transition matrix elements between the referred states.

  7. Sequential and Prosodic Design of English and Greek Non-Valenced News Receipts

    ERIC Educational Resources Information Center

    Kaimaki, Marianna

    2012-01-01

    Results arising from a prosodic and interactional study of the organization of everyday talk in English suggest that news receipts can be grouped into two categories: valenced (e.g., "oh good") and non-valenced (e.g., "oh really"). In-depth investigation of both valenced and non-valenced news receipts shows that differences in their prosodic

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

    ERIC Educational Resources Information Center

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

    2009-01-01

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

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

    ERIC Educational Resources Information Center

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

    2009-01-01

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

  10. Atomic bonding in the AlLiB14

    NASA Astrophysics Data System (ADS)

    Wan, L. F.; Beckman, S. P.

    2015-09-01

    The underlying nature of atomic bonds in the orthorhombic AlLiB14 crystal is studied using first-principles methods. Significant charge transfer is observed upon bonding, which is responsible to maintain good mechanical strength of the crystal. Individual bonding or anti-bonding states are identified which explains the correlation between the optimal mechanical strength and the electronic occupation of individual atomic orbitals. When the Fermi level is 0.35 eV inside the valence band the crystal has its maximum strength, which is the nominal position of the Fermi level in the experimentally-observed, off-stoichometric orthorhombic borides. These results indicate that the soft-phonon modes previously identified in the literature allow the crystal to reach the optimal stability. Due to the unique crystallographic symmetry, the impact of uniaxial compressive strain on the individual bonds is also examined in the end.

  11. 2D multipartite valence bond states in quantum anti-ferromagnets

    SciTech Connect

    Rico, E. Briegel, H.J.

    2008-09-15

    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.

  12. Crystal structure, physical properties and bond valence analysis of NaLuP2O7

    NASA Astrophysics Data System (ADS)

    Bjaoui, Anis; Horchani-Naifer, Karima; Hajji, Mounir; Frid, Mokhtar

    2014-05-01

    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) , b = 5.3473(5) , c = 12.756(1) , ? = 103.174 (1), V = 597.67 (9) 3, 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.

  13. A New Conformation With an Extraordinarily Long, 3.04 Å Two-Electron, Six-Center Bond Observed for the π-[TCNE]2 (2-) Dimer in [NMe4 ]2 [TCNE]2 (TCNE=Tetracyanoethylene).

    PubMed

    Graham, Adora G; Mota, Fernando; Shurdha, Endrit; Rheingold, Arnold L; Novoa, Juan J; Miller, Joel S

    2015-09-14

    [NMe4 ]2 [TCNE]2 (TCNE=tetracyanoethenide) formed from the reaction of TCNE and (NMe4 )CN in MeCN has νCN IR absorptions at 2195, 2191, 2172, and 2156 cm(-1) and a νCC absorption at 1383 cm(-1) that are characteristic of reduced TCNE. The TCNEs have an average central CC distance of 1.423 Å that is also characteristic of reduced TCNE. The reduced TCNE forms a previously unknown non-eclipsed, centrosymmetric π-[TCNE]2 (2-) dimer with nominal C2 symmetry, 12 sub van der Waals interatomic contacts <3.3 Å, a central intradimer separation of 3.039(3) Å, and comparable intradimer C⋅⋅⋅N distances of 3.050(3) and 2.984(3) Å. The two pairs of central C⋅⋅⋅C atoms form a ∢C-C⋅⋅⋅C-C of 112.6° that is substantially greater than the 0° observed for the eclipsed D2h π-[TCNE]2 (2-) dimer possessing a two-electron, four-center (2e(-) /4c) bond with two C⋅⋅⋅C components from a molecular orbital (MO) analysis. A MO study combining CAS(2,2)/MRMP2/cc-pVTZ and atoms-in-molecules (AIM) calculations indicates that the non-eclipsed, C2 π-[TCNE]2 (2-) dimer exhibits a new type of a long, intradimer bond involving one strong C⋅⋅⋅C and two weak C⋅⋅⋅N components, that is, a 2e(-) /6c bond. The C2 π-[TCNE]2 (2-) conformer has a singlet, diamagnetic ground state with a thermally populated triplet excited state with J/kB =1000 K (700 cm(-1) ; 86.8 meV; 2.00 kcal mol(-1) ; H=-2 JSa ⋅Sb ); at the CAS(2,2)/MBMP2 level the triplet is computed to be 9.0 kcal mol(-1) higher in energy than the closed-shell singlet ground state. The results from CAS(2,2)/NEVPT2/cc-pVTZ calculations indicate that the C2 and D2h conformers have two different local metastable minima with the C2 conformer being 1.3 kcal mol(-1) less stable. The different natures of the C2 and D2h conformers are also noted from the results of valence bond (VB) qualitative diagram that shows a 10e(-) /6c bond with one C⋅⋅⋅C and two C⋅⋅⋅N bonding components for the C2 conformer as compared to the 6e(-) /4c bond for the D2h conformer with two C⋅⋅⋅C bonding components. PMID:26223479

  14. Nitrogen valence electronic structure in the strong chemisorption limit: Molecular adsorption on Cr(110) and O/Cr(110)

    NASA Astrophysics Data System (ADS)

    Shinn, Neal D.

    1990-05-01

    Nitrogen adsorption and dissociation on clean and oxygen-dosed Cr(110) surfaces have been studied with angle-integrated synchrotron-radiation ultraviolet photoelectron spectroscopy (UPS) and work-function measurements. At 90 K, nitrogen adsorbs molecularly via a mobile precursor state and exhibits UPS valence-orbital peaks at binding energies of 12.7 (weak), 8.4, and 7.1 eV with respect to the Fermi level; these positions and separations suggest an unusual N2(ads) valence electronic structure similar to that of ``?-bonded'' N2 on Fe(111). Thermal dissociation of N2(ads) commences at 100 K but remains incomplete until ~265 K. Chemisorbed N2 increases the work function ? by 0.1+/-0.1 eV, whereas annealing the adlayer to 300 K subsequently reduces ? by 0.7 eV due to dissociation. At 300 K, only dissociative chemisorption is observed but with a reduced sticking probability and a lower saturation coverage compared with thermally dissociating a molecular adlayer. A surface-sensitive Cr valence-band feature is identified which (i) shifts to increasing binding energy with N2 adsorption, but (ii) exhibits different coverage-dependent behavior for isoelectronic N2(ads) and CO(ads). Low coverages of chemisorbed oxygen do not inhibit N2 adsorption but co-adsorption effects are observed when a N2(ads) saturated surface is exposed to large oxygen doses. Consideration of these results in comparison with other nitrogen chemisorption studies shows that the bonding of nitrogen to Cr(110) is not well described by the usual ?-donation and ?-backbonding concepts. A bonding geometry with both nitrogen atoms coordinated to chromium atoms is proposed in spite of the absence of surface hollow sites usually invoked to account for such a species.

  15. The relation between valence and arousal in subjective experience.

    PubMed

    Kuppens, Peter; Tuerlinckx, Francis; Russell, James A; Barrett, Lisa Feldman

    2013-07-01

    Affect is basic to many if not all psychological phenomena. This article examines 2 of the most fundamental properties of affective experience--valence and arousal--asking how they are related to each other on a moment to moment basis. Over the past century, 6 distinct types of relations have been suggested or implicitly presupposed in the literature. We critically review the available evidence for each proposal and argue that the evidence does not provide a conclusive answer. Next, we use statistical modeling to verify the different proposals in 8 data sets (with Ns ranging from 80 to 1,417) where participants reported their affective experiences in response to experimental stimuli in laboratory settings or as momentary or remembered in natural settings. We formulate 3 key conclusions about the relation between valence and arousal: (a) on average, there is a weak but consistent V-shaped relation of arousal as a function of valence, but (b) there is large variation at the individual level, so that (c) valence and arousal can in principle show a variety of relations depending on person or circumstances. This casts doubt on the existence of a static, lawful relation between valence and arousal. The meaningfulness of the observed individual differences is supported by their personality and cultural correlates. The malleability and individual differences found in the structure of affect must be taken into account when studying affect and its role in other psychological phenomena. PMID:23231533

  16. Effects of valence and divided attention on cognitive reappraisal processes

    PubMed Central

    Leclerc, Christina M.; Kensinger, Elizabeth A.

    2014-01-01

    Numerous studies have investigated the neural substrates supporting cognitive reappraisal, identifying the importance of cognitive control processes implemented by prefrontal cortex (PFC). This study examined how valence and attention affect the processes used for cognitive reappraisal by asking participants to passively view or to cognitively reappraise positive and negative images with full or divided attention. When participants simply viewed these images, results revealed few effects of valence or attention. However, when participants engaged in reappraisal, there was a robust effect of valence, with the reappraisal of negative relative to positive images associated with more widespread activation, including within regions of medial and lateral PFC. There also was an effect of attention, with more lateral PFC recruitment when regulating with full attention and more medial PFC recruitment when regulating with divided attention. Within two regions of medial PFC and one region of ventrolateral PFC, there was an interaction between valence and attention: in these regions, divided attention reduced activity during reappraisal of positive but not negative images. Critically, participants continued to report reappraisal success even during the Divided Attention condition. These results suggest multiple routes to successful cognitive reappraisal, depending upon image valence and the availability of attentional resources. PMID:24493837

  17. Contextual valence modulates the neural dynamics of risk processing.

    PubMed

    Zheng, Ya; Li, Qi; Wang, Kai; Wu, Haiyan; Liu, Xun

    2015-07-01

    A well-known bias in risky decision making is that most people tend to be risk averse when gains are salient but risk seeking when losses are salient. The present study addressed the neural dynamics of this process by recording ERPs during a gambling task in a gain and a loss context. Behaviorally, participants were found to be risk averse in the gain context but risk neutral in the loss context. During the anticipation stage, an increased stimulus-preceding negativity was elicited by high- versus low-risk choices in the gain but not the loss context. During the outcome-appraisal stage, the feedback-related negativity was larger after high- versus low-risk choices in the gain instead of the loss context. For the P300, an outcome valence effect (a larger P300 for gain vs. loss outcomes) emerged following the high- versus low-risk decisions in the gain but not the loss context. Our findings suggest that risk processing can be modulated by the context of valence during the anticipation stage and by both the contextual valence and the outcome valence during the outcome-appraisal stage, which may be driven by the motivational salience imposed by the context of valence. PMID:25664392

  18. Theory of Valence Transition in BiNiO_{3}.

    PubMed

    Naka, Makoto; Seo, Hitoshi; Motome, Yukitoshi

    2016-02-01

    Motivated by the colossal negative thermal expansion recently found in BiNiO_{3}, the valence transition accompanied by the charge transfer between the Bi and Ni sites is theoretically studied. We introduce an effective model for Bi-6s and Ni-3d orbitals taking into account the valence skipping of Bi cations, and investigate the ground-state and finite-temperature phase diagrams within the mean-field approximation. We find that the valence transition is caused by commensurate locking of the electron filling in each orbital associated with charge and magnetic orderings, and the critical temperature and the nature of the transitions are strongly affected by the relative energy between the Bi and Ni levels and the effective electron-electron interaction in the Bi sites. The obtained phase diagram well explains the temperature- and pressure-driven valence transitions in BiNiO_{3} and the systematic variation of valence states for a series of Bi and Pb perovskite oxides. PMID:26894723

  19. Space-Valence Priming with Subliminal and Supraliminal Words

    PubMed Central

    Ansorge, Ulrich; Khalid, Shah; Knig, Peter

    2013-01-01

    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. PMID:23439863

  20. Theory of Valence Transition in BiNiO3

    NASA Astrophysics Data System (ADS)

    Naka, Makoto; Seo, Hitoshi; Motome, Yukitoshi

    2016-02-01

    Motivated by the colossal negative thermal expansion recently found in BiNiO3 , the valence transition accompanied by the charge transfer between the Bi and Ni sites is theoretically studied. We introduce an effective model for Bi -6 s and Ni -3 d orbitals taking into account the valence skipping of Bi cations, and investigate the ground-state and finite-temperature phase diagrams within the mean-field approximation. We find that the valence transition is caused by commensurate locking of the electron filling in each orbital associated with charge and magnetic orderings, and the critical temperature and the nature of the transitions are strongly affected by the relative energy between the Bi and Ni levels and the effective electron-electron interaction in the Bi sites. The obtained phase diagram well explains the temperature- and pressure-driven valence transitions in BiNiO3 and the systematic variation of valence states for a series of Bi and Pb perovskite oxides.

  1. On the bond distance in methane

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

    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.

  2. Direct double photoionization of the valence shell of Be

    SciTech Connect

    Citrini, F.; Malegat, L.; Selles, P.; Kazansky, A.K.

    2003-04-01

    The hyperspherical R-matrix method with semiclassical outgoing waves is used to study the direct double photoionization (DPI) of the valence shell of the lightest alkaline earth-metal Be. The absolute fully integrated, singly, doubly, and triply differential cross sections obtained are compared with the single set of measurements available and with recent calculations based on the convergent close coupling and time-dependent close coupling methods. The level of agreement between all these data is very encouraging. A comparison is also made between the DPI of He and the direct DPI of the valence shell of Be. It confirms that the electron-electron correlations are stronger in the valence 2s shell of Be than in the 1s shell of He, thus contributing to a desirable clarification.

  3. Highly Selective Dissociation of a Peptide Bond Following Excitation of Core Electrons.

    PubMed

    Lin, Yi-Shiue; Tsai, Cheng-Cheng; Lin, Huei-Ru; Hsieh, Tsung-Lin; Chen, Jien-Lian; Hu, Wei-Ping; Ni, Chi-Kung; Liu, Chen-Lin

    2015-06-18

    The controlled breaking of a specific chemical bond with photons in complex molecules remains a major challenge in chemistry. In principle, using the K-edge absorption of a particular atomic element, one might excite selectively a specific atomic entity in a molecule. We report here highly selective dissociation of the peptide bonds in N-methylformamide and N-methylacetamide on tuning the X-ray wavelength to the K-edge absorption of the atoms connected to (or near) the peptide bond. The high selectivity (56-71%) of this cleavage arises from the large energy shift of X-ray absorption, a large overlap of the 1s orbital and the valence π* orbital that is highly localized on a peptide bond with antibonding character, and the relatively low bond energy of the peptide bonds. These characteristics indicate that the high selectivity on bond dissociation following core excitation could be a general feature for molecules containing peptide bonds. PMID:25988354

  4. From mixed valence to the Kondo lattice regime

    NASA Astrophysics Data System (ADS)

    Kumar, Pramod; Vidhyadhiraja, N. S.

    2011-12-01

    Many heavy fermion materials are known to cross over from the Kondo lattice regime to the mixed valence regime or vice versa as a function of pressure or doping. We study this crossover theoretically by employing the periodic Anderson model within the framework of the dynamical mean field theory. Changes occurring in the dynamics and transport across this crossover are highlighted. As the valence is decreased (increased) relative to the Kondo lattice regime, the Kondo resonance broadens significantly, while the lower (upper) Hubbard band moves closer to the Fermi level. The resistivity develops a two peak structure in the mixed valence regime: a low temperature coherence peak and a high temperature ‘Hubbard band’ peak. These two peaks merge, yielding a broad shallow maximum upon decreasing the valence further. The optical conductivity likewise exhibits an unusual absorption feature (shoulder) in the deep mid-infrared region, which grows in intensity with decreasing valence. The involvement of the Hubbard bands in dc transport and of the effective f-level in the optical conductivity are shown to be responsible for the anomalous transport properties. A two-band hybridization-gap model, which neglects incoherent effects due to many-body scattering, commonly employed to understand the optical response in these materials is shown to be inadequate, especially in the mixed valence regime. Comparison of theory with experiment carried out for (a) dc resistivities of CeRhIn5, Ce2Ni3Si5, CeFeGe3 and YbIr2Si2, (b) pressure dependent resistivity of YbInAu2 and CeCu6, and (c) optical conductivity measurements in YbIr2Si2 yields excellent agreement.

  5. Valence structure effects in the stopping of swift ions

    NASA Astrophysics Data System (ADS)

    Sigmund, P.; Sharma, A.; Schinner, A.; Fettouhi, A.

    2005-04-01

    The valence structure of a material may affect the stopping of swift charged particles primarily via Z2 structure, atom-molecule differences, gas-solid differences and metal-insulator differences. These material effects have a common physical origin and can therefore be considered from a unified point of view. Theoretical arguments focus on the effect of binding and orbital motion of the target electrons as well as projectile screening and Barkas-Andersen effect. Generally, valence effects depend on the atomic number, charge state and velocity of the projectile. Reference is made to recent calculations on the basis of binary stopping theory as well as experimental findings.

  6. Valence-differential spectroscopy of Co-Fe cyanide films

    NASA Astrophysics Data System (ADS)

    Moritomo, Y.; Nakada, F.; Kurihara, Y.

    2009-03-01

    Electrochromism is extensively investigated for practical application of display and memory devices. To develop the material, reliable information on the optical and electronic properties of the solid film is indispensable. Here, we propose valence-differential spectroscopy that can selectively extract the spectral components related to the oxidized/reduced metal site. We applied the spectroscopy to Co2+-Fe2+? and Co2+?-Fe2+ cyanide films with finely control of averaged valence (?) of the transition metal by external electric pulses. The spectroscopy revealed transition energy E, width ?, and oscillator strength f of the spectral components related to the transition metal.

  7. A diabatic representation including both valence nonadiabatic interactions and spin-orbit effects for reaction dynamics.

    PubMed

    Valero, Rosendo; Truhlar, Donald G

    2007-09-01

    A diabatic representation is convenient in the study of electronically nonadiabatic chemical reactions because the diabatic energies and couplings are smooth functions of the nuclear coordinates and the couplings are scalar quantities. A method called the fourfold way was devised in our group to generate diabatic representations for spin-free electronic states. One drawback of diabatic states computed from the spin-free Hamiltonian, called a valence diabatic representation, for systems in which spin-orbit coupling cannot be ignored is that the couplings between the states are not zero in asymptotic regions, leading to difficulties in the calculation of reaction probabilities and other properties by semiclassical dynamics methods. Here we report an extension of the fourfold way to construct diabatic representations suitable for spin-coupled systems. In this article we formulate the method for the case of even-electron systems that yield pairs of fragments with doublet spin multiplicity. For this type of system, we introduce the further simplification of calculating the triplet diabatic energies in terms of the singlet diabatic energies via Slater's rules and assuming constant ratios of Coulomb to exchange integrals. Furthermore, the valence diabatic couplings in the triplet manifold are taken equal to the singlet ones. An important feature of the method is the introduction of scaling functions, as they allow one to deal with multibond reactions without having to include high-energy diabatic states. The global transformation matrix to the new diabatic representation, called the spin-valence diabatic representation, is constructed as the product of channel-specific transformation matrices, each one taken as the product of an asymptotic transformation matrix and a scaling function that depends on ratios of the spin-orbit splitting and the valence splittings. Thus the underlying basis functions are recoupled into suitable diabatic basis functions in a manner that provides a multibond generalization of the switch between Hund's cases in diatomic spectroscopy. The spin-orbit matrix elements in this representation are taken equal to their atomic values times a scaling function that depends on the internuclear distances. The spin-valence diabatic potential energy matrix is suitable for semiclassical dynamics simulations. Diagonalization of this matrix produces the spin-coupled adiabatic energies. For the sake of illustration, diabatic potential energy matrices are constructed along bond-fission coordinates for the HBr and the BrCH(2)Cl molecules. Comparison of the spin-coupled adiabatic energies obtained from the spin-valence diabatics with those obtained by ab initio calculations with geometry-dependent spin-orbit matrix elements shows that the new method is sufficiently accurate for practical purposes. The method formulated here should be most useful for systems with a large number of atoms, especially heavy atoms, and/or a large number of spin-coupled electronic states. PMID:17691756

  8. What Determines Bond Costs. Municipal Bonds Series.

    ERIC Educational Resources Information Center

    Young, Douglas; And Others

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

  9. Chemical Bonds II

    ERIC Educational Resources Information Center

    Sanderson, R. T.

    1972-01-01

    The continuation of a paper discussing chemical bonding from a bond energy viewpoint, with a number of examples of single and multiple bonds. (Part I appeared in volume 1 number 3, pages 16-23, February 1972.) (AL)

  10. Entrapping a Group-VB Transition Metal, Vanadium, within an Endohedral Metallofullerene: VxSc3-xN@Ih-C80 (x = 1, 2).

    PubMed

    Wei, Tao; Wang, Song; Lu, Xing; Tan, Yuanzhi; Huang, Jing; Liu, Fupin; Li, Qunxiang; Xie, Suyuan; Yang, Shangfeng

    2016-01-13

    So far the entrapped metals for the isolated endohedral metallofullerenes (EMFs) are primarily limited to rare earth metals, whereas except group-IVB metals, whether it is possible to entrap other d-block transition metals remains unclear. Herein we report the successful entrapment of the group-VB transition metal vanadium(V) into fullerene cage, affording the heretofore unknown V-containing EMFs. Two novel V-containing EMFs-VxSc3-xN@C80 (x = 1, 2)-were isolated, and their molecular structures were unambiguously determined by X-ray crystallography to be Ih(7)-C80 cage entrapping the planar VSc2N/V2ScN clusters. VxSc3-xN@Ih(7)-C80 (x = 1, 2) were further characterized by UV-vis-NIR and ESR spectroscopies and electrochemistry, revealing that the electronic and magnetic properties of VxSc3-xN@Ih(7)-C80 (x = 1, 2) are tunable upon varying the number of entrapped V atoms (i.e., x value). The molecular structures and electronic properties of VxSc3-xN@Ih(7)-C80 (x = 1, 2) were further compared with those of the reported analogous EMFs based on lanthanide metals and the adjacent group-IVB transition metal Ti, revealing the peculiarity of the group-VB transition metal V-based EMFs. PMID:26645852

  11. NMR studies of ordered structures and valence states in the successive valence-transition system EuPtP

    NASA Astrophysics Data System (ADS)

    Mito, T.; Nishitani, K.; Koyama, T.; Muta, H.; Maruyama, T.; Prist, G.; Ueda, K.; Kohara, T.; Mitsuda, A.; Sugishima, M.; Wada, H.

    2014-11-01

    We have studied EuPtP, which undergoes two successive valence transitions at TA240 K and TB200 K by 31P-nuclear magnetic resonance (NMR) measurements. From the analysis of NMR spectra, we obtained plausible ordered structures and Eu valence states in three phases divided by TA and TB. These ordered structures well explain observed inequivalent P sites and the intensity ratio of the NMR spectra arising from these P sites. The results are also in good accordance with mean Eu valence measured by the x-ray absorption spectroscopy. We also discuss Eu 4 f states and the origin of the transitions from the measurements of nuclear spin lattice relaxation rate and hyperfine coupling constant.

  12. Social Learning Modulates the Lateralization of Emotional Valence

    ERIC Educational Resources Information Center

    Shamay-Tsoory, Simone G.; Lavidor, Michal; Aharon-Peretz, Judith

    2008-01-01

    Although neuropsychological studies of lateralization of emotion have emphasized valence (positive vs. negative) or type (basic vs. complex) dimensions, the interaction between the two dimensions has yet to be elucidated. The purpose of the current study was to test the hypothesis that recognition of basic emotions is processed preferentially by

  13. Recognizing the Emotional Valence of Names: An ERP Study

    ERIC Educational Resources Information Center

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

    2013-01-01

    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…

  14. Vection Modulates Emotional Valence of Autobiographical Episodic Memories

    ERIC Educational Resources Information Center

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

    2013-01-01

    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…

  15. Racah materials: role of atomic multiplets in intermediate valence systems

    PubMed Central

    Shick, A. B.; Havela, L.; Lichtenstein, A. I.; Katsnelson, M. I.

    2015-01-01

    We address the long-standing mystery of the nonmagnetic insulating state of the intermediate valence compound SmB6. Within a combination of the local density approximation (LDA) and an exact diagonalization (ED) of an effective discrete Anderson impurity model, the intermediate valence ground state with the f-shell occupation ?n4f??=?5.6 is found for the Sm atom in SmB6. This ground state is a singlet, and the first excited triplet state ~3?meV higher in the energy. SmB6 is a narrow band insulator already in LDA, with the direct band gap of ~10?meV. The electron correlations increase the band gap which now becomes indirect. Thus, the many-body effects are relevant to form the indirect band gap, crucial for the idea of topological Kondo insulator" in SmB6. Also, an actinide analog PuB6 is considered, and the intermediate valence singlet ground state is found for the Pu atom. We propose that [Sm, Pu]B6 belong to a new class of the intermediate valence materials with the multi-orbital Kondo-like" singlet ground-state. Crucial role of complex spin-orbital f??nf??n+1 multiplet structure differently hybridized with ligand states in such Racah materials is discussed. PMID:26490021

  16. Border Crossing in "Multicultural Australia": A Study of Cultural Valence.

    ERIC Educational Resources Information Center

    Smolicz, J. J.; Hudson, D. M.; Secombe, M. J.

    1998-01-01

    Discusses "border crossing" by individuals who augment their cultural valence through acquiring competence in and positive attitudes toward other cultures. Reports on two studies carried out according to the principles of humanistic sociology and based on memoirs written by university graduates. (Author/VWL)

  17. Recognizing the Emotional Valence of Names: An ERP Study

    ERIC Educational Resources Information Center

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

    2013-01-01

    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

  18. Real-time observation of valence electron motion.

    SciTech Connect

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

    2010-08-05

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

  19. Vection Modulates Emotional Valence of Autobiographical Episodic Memories

    ERIC Educational Resources Information Center

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

    2013-01-01

    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

  20. Emotional Valence and Arousal Effects on Memory and Hemispheric Asymmetries

    ERIC Educational Resources Information Center

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

    2010-01-01

    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

  1. Racah materials: role of atomic multiplets in intermediate valence systems

    NASA Astrophysics Data System (ADS)

    Shick, A. B.; Havela, L.; Lichtenstein, A. I.; Katsnelson, M. I.

    2015-10-01

    We address the long-standing mystery of the nonmagnetic insulating state of the intermediate valence compound SmB6. Within a combination of the local density approximation (LDA) and an exact diagonalization (ED) of an effective discrete Anderson impurity model, the intermediate valence ground state with the f-shell occupation ?=?5.6 is found for the Sm atom in SmB6. This ground state is a singlet, and the first excited triplet state ~3?meV higher in the energy. SmB6 is a narrow band insulator already in LDA, with the direct band gap of ~10?meV. The electron correlations increase the band gap which now becomes indirect. Thus, the many-body effects are relevant to form the indirect band gap, crucial for the idea of topological Kondo insulator" in SmB6. Also, an actinide analog PuB6 is considered, and the intermediate valence singlet ground state is found for the Pu atom. We propose that [Sm, Pu]B6 belong to a new class of the intermediate valence materials with the multi-orbital Kondo-like" singlet ground-state. Crucial role of complex spin-orbital f??nf??n+1 multiplet structure differently hybridized with ligand states in such Racah materials is discussed.

  2. Paradigms and Plastic Facts in the History of Valence.

    ERIC Educational Resources Information Center

    Zavaleta, David

    1988-01-01

    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)

  3. a New Approach to the Mixed Valence Problem

    NASA Astrophysics Data System (ADS)

    Coleman, Piers

    The mixed valence compounds are a class of rare earth compounds & alloys containing Ce, Sm, Eu, Tm or Yb ions in which the 4f electrons are able to tunnel from well inside their rare earth hosts into the surrounding electron sea, giving rise to valence fluctuations between two atomic configurations of the rare earth ions f ('n) (DBLARR) f ('n-1) + e('-). In these compounds of f electrons play an important role in conduction, leading to many novel features in the equilibrium and transport properties. The electrons in the mixed valence compounds are highly correlated and the modelling of their behaviour constitutes a strong coupling problem. This dissertation studies the mixed valence problem using the infinite U Anderson model to describe the hybridisation of the f electrons with band electrons. Section 1 reviews the physical aspects of the mixed valence problem. Section 2 presents a new exact reformulation of the Anderson model in which the singlet state of the rare earth ion is presented by a "slave boson" field and the spinning state by a spin j fermion. In this more convenient representation all operators obey standard commutation algebras and standard quantum field theory tools can be applied to the impurity and lattice problems. Section 3 examines the limit of large spin degeneracy N in the slave boson theory and shows this limit to be classical. 1/N plays the role of Planck's constant. The "classical" phase diagram is derived and the effects of quantum fluctuations at finite N studied. Section 4 applies scaling arguments to the Kondo lattice model and shows that large degeneracy enhances local spin fluctuations, leading to the stabilisation of a non magnetic ground state with narrow band excitations.

  4. Bond paths are not chemical bonds.

    PubMed

    Bader, Richard F W

    2009-09-24

    This account takes to task papers that criticize the definition of a bond path as a criterion for the bonding between the atoms it links by mistakenly identifying it with a chemical bond. It is argued that the notion of a chemical bond is too restrictive to account for the physics underlying the broad spectrum of interactions between atoms and molecules that determine the properties of matter. A bond path on the other hand, as well as being accessible to experimental verification and subject to the theorems of quantum mechanics, is applicable to any and all of the interactions that account for the properties of matter. It is shown that one may define a bond path operator as a Dirac observable, making the bond path the measurable expectation value of a quantum mechanical operator. Particular attention is given to van der Waals interactions that traditionally are assumed to represent attractive interactions that are distinct from chemical bonding. They are assumed by some to act in concert with Pauli repulsions to account for the existence of condensed states of molecules. It is such dichotomies of interpretation that are resolved by the experimental detection of bond paths and the delineation of their properties in molecular crystals. Specific criticisms of the stabilization afforded by the presence of bond paths derived from spectroscopic measurements performed on dideuteriophenanthrene are shown to be physically unsound. The concept of a bond path as a "bridge of density" linking bonded atoms was introduced by London in 1928 following the definition of the electron density by Schrdinger in 1926. These papers marked the beginning of the theory of atoms in molecules linked by bond paths. PMID:19722600

  5. Ultrafast Charge Transfer of a Valence Double Hole in Glycine Driven Exclusively by Nuclear Motion.

    PubMed

    Li, Zheng; Vendrell, Oriol; Santra, Robin

    2015-10-01

    We explore theoretically the ultrafast transfer of a double electron hole between the functional groups of glycine after K-shell ionization and subsequent Auger decay. Although a large energy gap of about 15 eV initially exists between the two electronic states involved and coherent electronic dynamics play no role in the hole transfer, we find that the double hole is transferred within 3 to 4 fs between both functional ends of the glycine molecule driven solely by specific nuclear displacements and non-Born-Oppenheimer effects. The nuclear displacements along specific vibrational modes are of the order of 15% of a typical chemical bond between carbon, oxygen, and nitrogen atoms and about 30% for bonds involving hydrogen atoms. The time required for the hole transfer corresponds to less than half a vibrational period of the involved nuclear modes. This finding challenges the common wisdom that nuclear dynamics of the molecular skeleton are unimportant for charge transfer processes at the few-femtosecond time scale and shows that they can even play a prominent role. It also indicates that in x-ray imaging experiments, in which ionization is unavoidable, valence electron redistribution caused by nuclear dynamics might be much faster than previously anticipated. Thus, non-Born-Oppenheimer effects may affect the apparent electron densities extracted from such measurements. PMID:26551809

  6. Charge-displacement analysis via natural orbitals for chemical valence: Charge transfer effects in coordination chemistry

    NASA Astrophysics Data System (ADS)

    Bistoni, Giovanni; Rampino, Sergio; Tarantelli, Francesco; Belpassi, Leonardo

    2015-02-01

    We recently devised a simple scheme for analyzing on quantitative grounds the Dewar-Chatt-Duncanson donation and back-donation in symmetric coordination complexes. Our approach is based on a symmetry decomposition of the so called Charge-Displacement (CD) function quantifying the charge flow, upon formation of a metal (M)-substrate (S) bond, along the M-S interaction axis and provides clear-cut measures of donation and back-donation charges in correlation with experimental observables [G. Bistoni et al., Angew. Chem., Int. Ed. 52, 11599 (2013)]. The symmetry constraints exclude of course from the analysis most systems of interest in coordination chemistry. In this paper, we show how to entirely overcome this limitation by taking advantage of the properties of the natural orbitals for chemical valence [M. Mitoraj and A. Michalak, J. Mol. Model. 13, 347 (2007)]. A general scheme for disentangling donation and back-donation in the CD function of both symmetric and non-symmetric systems is presented and illustrated through applications to M-ethyne (M = Au, Ni and W) coordination bonds, including an explicative study on substrate activation in a model reaction mechanism.

  7. Vibrational effects on valence electron momentum distributions of CH{sub 2}F{sub 2}

    SciTech Connect

    Watanabe, Noboru; Yamazaki, Masakazu; Takahashi, Masahiko

    2014-12-28

    We report an electron momentum spectroscopy study of vibrational effects on the electron momentum distributions for the outer valence orbitals of difluoromethane (CH{sub 2}F{sub 2}). The symmetric noncoplanar (e,2e) experiment has been performed at an incident electron energy of 1.2 keV. Furthermore, a theoretical calculation of the electron momentum distributions of the CH{sub 2}F{sub 2} molecule has been carried out with vibrational effects being involved. It is shown from comparisons between experiment and theory that it is essential to take into account influences of the CH{sub 2} asymmetric stretching and CH{sub 2} rocking vibrational modes for a proper understanding of the electron momentum distribution of the 2b{sub 1} orbital having the CH-bonding character. The results of CH{sub 2}F{sub 2}and additional theoretical calculations for (CH{sub 3}){sub 2}O and H{sub 2}CO molecules strongly suggest that vibrational effects on electron momentum distributions tend to be appreciable for non-total symmetry molecular orbitals delocalized over some equivalent CH-bond sites.

  8. Ultrafast Charge Transfer of a Valence Double Hole in Glycine Driven Exclusively by Nuclear Motion

    NASA Astrophysics Data System (ADS)

    Li, Zheng; Vendrell, Oriol; Santra, Robin

    2015-10-01

    We explore theoretically the ultrafast transfer of a double electron hole between the functional groups of glycine after K -shell ionization and subsequent Auger decay. Although a large energy gap of about 15 eV initially exists between the two electronic states involved and coherent electronic dynamics play no role in the hole transfer, we find that the double hole is transferred within 3 to 4 fs between both functional ends of the glycine molecule driven solely by specific nuclear displacements and non-Born-Oppenheimer effects. The nuclear displacements along specific vibrational modes are of the order of 15% of a typical chemical bond between carbon, oxygen, and nitrogen atoms and about 30% for bonds involving hydrogen atoms. The time required for the hole transfer corresponds to less than half a vibrational period of the involved nuclear modes. This finding challenges the common wisdom that nuclear dynamics of the molecular skeleton are unimportant for charge transfer processes at the few-femtosecond time scale and shows that they can even play a prominent role. It also indicates that in x-ray imaging experiments, in which ionization is unavoidable, valence electron redistribution caused by nuclear dynamics might be much faster than previously anticipated. Thus, non-Born-Oppenheimer effects may affect the apparent electron densities extracted from such measurements.

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

    ERIC Educational Resources Information Center

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

    2010-01-01

    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

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

    ERIC Educational Resources Information Center

    Porfeli, Erik; Ferrari, Lea; Nota, Laura

    2013-01-01

    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

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

    ERIC Educational Resources Information Center

    Porfeli, Erik; Ferrari, Lea; Nota, Laura

    2013-01-01

    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…

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

    ERIC Educational Resources Information Center

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

    2009-01-01

    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

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

    SciTech Connect

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

    2009-03-02

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

  14. Cloning and sequencing of cDNA encoding for the testis-specific fox (Vulpes vulpes) sperm polypeptide Vb of the cytochrome C oxidase.

    PubMed

    Verdier, Yann; Farr, Guillaume; Rouet, Nelly; Kele, Zoltan; Janky, Tams; Bou, Franck

    2005-01-01

    Identification of fox (Vulpes vulpes) sperm antigens was carried out to assess their interest as a potential target for a contraceptive vaccine. We report here the cloning and sequencing of fSP8, a fox sperm protein of 14.7 kd. fSP8 was isoantigenic in foxes, as it was recognized by sera of both male and female foxes immunized with fox sperm proteins. No glycosylation was detected, on fSP8, as shown both by deglycosylation assay and lectin labeling. To determine the fSP8 sequence, the NH2-terminal sequence was first obtained, and a piece of cDNA was amplified from testicular RNA by Rapid Amplification of cDNA extremities polymerase chain reaction. This piece was used to screen a cDNA library from fox testis by Southern blot. A sequence of 879 base pairs was obtained, which includes a major open reading frame coding for 128 amino acids. Mass spectrometric analyses have confirmed the position of the open reading frame. Analysis of the predicted amino acids sequence revealed no apparent transmembrane regions. Comparison of the protein sequence with the Prosite database demonstrated a homology with the Zinc binding site of the subunit Vb of the cytochrome c oxidase. On the C-terminal extremity, fSP8 presents a high homology to the Vb polypeptide of the cytochrome c oxidase from bovine, mouse, and human; however the 34 amino acids on the NH2-extremity were specific to fSP8. Moreover, it was demonstrated that this sequence was testis-specific. This could contribute to the antigenicity of this protein. fSP8 is one of the first fox sperm antigens to be cloned and sequenced. PMID:15866998

  15. Hydroxide-catalyzed bonding

    NASA Technical Reports Server (NTRS)

    Gwo, Dz-Hung (Inventor)

    2003-01-01

    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.

  16. Conduction and Valence Band Offsets in WSe2 -Graphene Heterostructures

    NASA Astrophysics Data System (ADS)

    Kim, Kyounghwan; Larentis, Stefano; Fallahazad, Babak; Lee, Kayoung; Xue, Jiamin; Dillen, David; Corbet, Chris; Tutuc, Emanuel

    2015-03-01

    We investigate the electron transport in graphene-WSe2 heterostructures realized using a layer-by-layer transfer. Lateral electron transport shows ambipolar behavior characteristic of graphene, with a marked saturation at high positive (negative) gate bias, associated with the population of the conduction (valence) band in WSe2. The graphene carrier density dependence on gate bias was extracted from magneto-transport measurements. Using WSe2 as a top dielectric in dual-gate graphene field-effect transistors, we determine the WSe2 dielectric constant along the c-axis. By combining the graphene density dependence on gate bias in back-gated graphene-WSe2 heterostructures with the WSe2 dielectric constant, we determine the offset between the graphene charge neutrality point and the WSe2 conduction and valence bands. This work was supported by NRI, NSF and Intel.

  17. Improved extraction of valence transversity distributions from inclusive dihadron production

    NASA Astrophysics Data System (ADS)

    Radici, Marco; Courtoy, A.; Bacchetta, Alessandro; Guagnelli, Marco

    2015-05-01

    We present an updated extraction of the transversity parton distribution based on the analysis of pion-pair production in deep-inelastic scattering off transversely polarized targets in collinear factorization. Data for proton and deuteron targets make it possible to perform a flavor separation of the valence components of the transversity distribution, using di-hadron fragmentation functions taken from the semi-inclusive production of two pion pairs in back-to-back jets in e + e - annihilation. The e + e - data from Belle have been reanalyzed using the replica method and a more realistic estimate of the uncertainties on the chiral-odd interference fragmentation function has been obtained. Then, the transversity distribution has been extracted by using the most recent and more precise COMPASS data for deep-inelastic scattering off proton targets. Our results represent the most accurate estimate of the uncertainties on the valence components of the transversity distribution currently available.

  18. Valence-band states of ion-bombarded polystyrene

    SciTech Connect

    Terrasi, A. ); Foti, G. ); Hwu, Y. ); Margaritondo, G. )

    1991-08-01

    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.

  19. Feedback Valence Affects Auditory Perceptual Learning Independently of Feedback Probability

    PubMed Central

    Amitay, Sygal; Moore, David R.; Molloy, Katharine; Halliday, Lorna F.

    2015-01-01

    Previous studies have suggested that negative feedback is more effective in driving learning than positive feedback. We investigated the effect on learning of providing varying amounts of negative and positive feedback while listeners attempted to discriminate between three identical tones; an impossible task that nevertheless produces robust learning. Four feedback conditions were compared during training: 90% positive feedback or 10% negative feedback informed the participants that they were doing equally well, while 10% positive or 90% negative feedback informed them they were doing equally badly. In all conditions the feedback was random in relation to the listeners responses (because the task was to discriminate three identical tones), yet both the valence (negative vs. positive) and the probability of feedback (10% vs. 90%) affected learning. Feedback that informed listeners they were doing badly resulted in better post-training performance than feedback that informed them they were doing well, independent of valence. In addition, positive feedback during training resulted in better post-training performance than negative feedback, but only positive feedback indicating listeners were doing badly on the task resulted in learning. As we have previously speculated, feedback that better reflected the difficulty of the task was more effective in driving learning than feedback that suggested performance was better than it should have been given perceived task difficulty. But contrary to expectations, positive feedback was more effective than negative feedback in driving learning. Feedback thus had two separable effects on learning: feedback valence affected motivation on a subjectively difficult task, and learning occurred only when feedback probability reflected the subjective difficulty. To optimize learning, training programs need to take into consideration both feedback valence and probability. PMID:25946173

  20. Effects of valence-valence, core-valence, and core-core correlations on the fine-structure energy levels in Al-like ions

    SciTech Connect

    Hao Lianghuan; Jiang Gang; Hou Haijun

    2010-02-15

    This paper reports on multiconfiguration Dirac-Hartree-Fock calculations for both allowed and intercombination transitions and fine structure referring to the levels of a term in highly charged aluminum like ions. Results for fine-structure energy levels, the term splitting, the wavelengths, transition rates, and thereby the branching ratios and lifetimes for the Al-like 3s{sup 2}3p-3s3p{sup 2} transitions in the ions Fe XIV-Au LXVII are reported and compared with other theories and experiments, using the codes GRASP2K. Our calculated fine-structure energy levels are in excellent agreement with the experimental results and the experimentally compiled energy values of the National Institute for Standards and Technology wherever available. The calculated values including core-valence correlation are found to be similar and to compare very well with other theoretical and experimental values for medium-Z ions. For higher Z the inclusion of the valence correlation gives results in excellent agreement with those from many-body perturbation theory. We believe that our extensive calculated values can guide experimentalists in identifying the fine-structure levels in their future work. From our radiative decay rates we have also calculated radiative lifetimes of some fine-structure levels. In this calculation we also predict new data for several fine-structure levels where no other theoretical and/or experimental results are available.

  1. Predicting the Valence of a Scene from Observers’ Eye Movements

    PubMed Central

    R.-Tavakoli, Hamed; Atyabi, Adham; Rantanen, Antti; Laukka, Seppo J.; Nefti-Meziani, Samia; Heikkilä, Janne

    2015-01-01

    Multimedia analysis benefits from understanding the emotional content of a scene in a variety of tasks such as video genre classification and content-based image retrieval. Recently, there has been an increasing interest in applying human bio-signals, particularly eye movements, to recognize the emotional gist of a scene such as its valence. In order to determine the emotional category of images using eye movements, the existing methods often learn a classifier using several features that are extracted from eye movements. Although it has been shown that eye movement is potentially useful for recognition of scene valence, the contribution of each feature is not well-studied. To address the issue, we study the contribution of features extracted from eye movements in the classification of images into pleasant, neutral, and unpleasant categories. We assess ten features and their fusion. The features are histogram of saccade orientation, histogram of saccade slope, histogram of saccade length, histogram of saccade duration, histogram of saccade velocity, histogram of fixation duration, fixation histogram, top-ten salient coordinates, and saliency map. We utilize machine learning approach to analyze the performance of features by learning a support vector machine and exploiting various feature fusion schemes. The experiments reveal that ‘saliency map’, ‘fixation histogram’, ‘histogram of fixation duration’, and ‘histogram of saccade slope’ are the most contributing features. The selected features signify the influence of fixation information and angular behavior of eye movements in the recognition of the valence of images. PMID:26407322

  2. Predicting the Valence of a Scene from Observers' Eye Movements.

    PubMed

    R-Tavakoli, Hamed; Atyabi, Adham; Rantanen, Antti; Laukka, Seppo J; Nefti-Meziani, Samia; Heikkilä, Janne

    2015-01-01

    Multimedia analysis benefits from understanding the emotional content of a scene in a variety of tasks such as video genre classification and content-based image retrieval. Recently, there has been an increasing interest in applying human bio-signals, particularly eye movements, to recognize the emotional gist of a scene such as its valence. In order to determine the emotional category of images using eye movements, the existing methods often learn a classifier using several features that are extracted from eye movements. Although it has been shown that eye movement is potentially useful for recognition of scene valence, the contribution of each feature is not well-studied. To address the issue, we study the contribution of features extracted from eye movements in the classification of images into pleasant, neutral, and unpleasant categories. We assess ten features and their fusion. The features are histogram of saccade orientation, histogram of saccade slope, histogram of saccade length, histogram of saccade duration, histogram of saccade velocity, histogram of fixation duration, fixation histogram, top-ten salient coordinates, and saliency map. We utilize machine learning approach to analyze the performance of features by learning a support vector machine and exploiting various feature fusion schemes. The experiments reveal that 'saliency map', 'fixation histogram', 'histogram of fixation duration', and 'histogram of saccade slope' are the most contributing features. The selected features signify the influence of fixation information and angular behavior of eye movements in the recognition of the valence of images. PMID:26407322

  3. Valency configuration of transition metal impurities in ZnO

    SciTech Connect

    Petit, Leon; Schulthess, Thomas C; Svane, Axel; Temmerman, Walter M; Szotek, Zdzislawa; Janotti, Anderson

    2006-01-01

    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.

  4. Shell structure, emerging collectivity, and valence p-n interactions

    NASA Astrophysics Data System (ADS)

    Cakirli, R. B.

    2014-03-01

    The structure of atomic nuclei depends on the interactions of its constituents, protons and neutrons. These interactions play a key role in the development of configuration mixing and in the onset of collectivity and deformation, in changes to the single particle energies and magic numbers, and in the microscopic origins of phase transitional behavior. Particularly important are the valence proton-neutron interactions which can be studied experimentally using double differences of binding energies extracted from high-precision mass measurements. The resulting quantities, called ?Vpn, are average interaction strengths between the last two protons and the last two neutrons. Focusing on the Z=50-82, N=82-126 shells, we have considered a number of aspects of these interactions, ranging from their relation to the underlying orbits, their behaviour near close shells and throughout major shells, their relation to the onset of collectivity and deformation, and the appearance of unexpected spikes in ?Vpn values for a special set of heavy nuclei with nearly equal numbers of valence protons and neutrons. We have calculated spatial overlaps between proton and neutron Nilsson orbits and compared these with the experimental results. Finally we also address the relation between masses (separation energies), changes in structure and valence nucleon number.

  5. Core-core and core-valence correlation

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

    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.

  6. Chromium valences in ureilite olivine and implications for ureilite petrogenesis

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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). Chromium in olivine in all eleven samples was found to be dominated by the divalent species, with valences ranging from 2.10 0.02 (1?) to 2.46 0.04. The non-chromite-bearing ureilites have the most reduced Cr, with a weighted mean valence of 2.12 0.01, i.e., Cr2+/Cr3+ = 7.33. All low-Fo chromite-bearing ureilites have more oxidized Cr, with valences ranging from 2.22 0.03 to 2.46 0.04. EET 96328, whose chromite grain we interpret as a late-crystallizing phase, yielded a reduced Cr valence of 2.15 0.07, similar to the non-chromite-bearing samples. Based on the measured Cr valences, magmatic (1200-1300 C) oxygen fugacities (fO2) of the non-chromite-bearing samples were estimated to be in the range IW-1.9 to IW-2.8 (assuming basaltic melt composition), consistent with fO2 values obtained by assuming olivine-silica-iron metal (OSI) equilibrium. For the primary chromite-bearing-ureilites, the corresponding fO2 were estimated (again, assuming basaltic melt composition) to be ?IW to IW+1.0, i.e., several orders of magnitude more oxidizing than the conditions estimated for the chromite-free ureilites. In terms of Fo and Cr valence properties, ureilites appear to form two groups rather than a single Cr-valence (or fO2) vs. Fo trend. The chromite-bearing ureilites show little variation in Fo (?74-76) but significant variation in Cr valence, while the non-chromite-bearing ureilites show significant variation in Fo (?77-95) and little variation in Cr valence. These groups are unrelated to petrologic type (i.e., olivine-pigeonite, olivine-orthopyroxene, or augite-bearing). The chromite-bearing ureilites also have lower contents of Cr in olivine than most non-chromite-bearing ureilites, consistent with predictions based on Cr olivine/melt partitioning in spinel saturated vs. non-spinel-saturated systems. Under the assumption that at magmatic temperatures graphite-gas equilibria controlled fO2 at all depths on the ureilite parent body, we conclude: (1) that ureilite precursor materials having the Fo and Cr valence properties now observed in ureilites are unlikely to have been preserved during planetary processing; and (2) that the Fo and Cr valence properties now observed in ureilites are consistent with having been established by high-temperature carbon redox control over a range of depths on a plausible-sized ureilite parent body. The apparent limit on ureilite Fo values around 74-76 suggests that the precursor material(s) had bulk mg# ? that of LL chondrites.

  7. Measurement of valence band structure in arbitrary dielectric films

    SciTech Connect

    Uhm, Han S.; Choi, Eun H.

    2012-10-15

    A new way of measuring the band structure of various dielectric materials using the secondary electron emission from Auger neutralization of ions is introduced. The first example of this measurement scheme is the magnesium oxide (MgO) films with respect to the application of the films in the display industries. The density of state in the valence bands of MgO film and MgO film with a functional layer (FL) deposited over a dielectric surface reveals that the density peak of film with a FL is considerably less than that of film, thereby indicating a better performance of MgO film with functional layer in display devices. The second example of the measurement is the boron-zinc oxide (BZO) films with respect to the application of the films to the development of solar cells. The measurement of density of state in BZO film suggests that a high concentration of boron impurity in BZO films may enhance the transition of electrons and holes through the band gap from the valence to the conduction band in zinc oxide crystals; thereby improving the conductivity of the film. Secondary electron emission by the Auger neutralization of ions is highly instrumental for the determination of the density of states in the valence band of dielectric materials.

  8. Kondo universality, energy scales, and intermediate valence in plutonium

    SciTech Connect

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

    2009-07-15

    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.

  9. Character disposition and behavior type: influences of valence on preschool children's social judgments.

    PubMed

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

    2009-12-01

    The authors studied the influences of valence information on preschool children's (n = 47) moral (good or bad), liking (liked or disliked by a friend), and consequence-of-behavior (reward or punishment) judgments. The authors presented 8 scenarios describing the behavior valence, positive valence (help, share), negative valence (verbal insult, physical aggression), and disposition valence (nice or mean) of characters in social interaction with a friend. Overall, character disposition and behavior valence significantly influenced children's judgments. Moral, liking, and consequence-of-behavior judgments varied significantly by character disposition for both positive behavior scenarios. In contrast, there were fewer significant findings as a function of character disposition for negative behavior scenarios, suggesting that the negative behavior cue somewhat diminished the effect of character disposition on children's judgments. The authors discuss preschool students' coordination of information about valence of behavior and character disposition and the students' reluctance to judge that misbehavior warrants punitive consequence. PMID:20034187

  10. Diffusion bonding aeroengine components

    NASA Astrophysics Data System (ADS)

    Fitzpatrick, G. A.; Broughton, T.

    1988-10-01

    The use of diffusion bonding processes at Rolls-Royce for the manufacture of titanium-alloy aircraft engine components and structures is described. A liquid-phase diffusion bonding process called activated diffusion bonding has been developed for the manufacture of the hollow titanium wide chord fan blade. In addition, solid-state diffusion bonding is being used in the manufacture of hollow vane/blade airfoil constructions mainly in conjunction with superplastic forming and hot forming techniques.

  11. Bonding silicones with epoxies

    SciTech Connect

    Tira, J.S.

    1980-01-01

    It is shown that silicones, both room temperature vulcanizing (RTV) and millable rubber (press cured) can be successfully bonded to other materials using plasma treatment and epoxy adhesives. The plasma treatment using dry air atmosphere increases the surface energy of the silicone and thus provides a lower water contact angle. This phenomenon allows the epoxy adhesive to wet the silicone surface and ultimately bond. Bond strengths are sufficiently high to result in failures in the silicone materials rather than the adhesive bond.

  12. Chemical Bonding Forces and Metallization of Hydrogen

    NASA Astrophysics Data System (ADS)

    Naumov, Ivan; Hemley, Russell; Carnegie Inst of Washington Collaboration

    2015-03-01

    Recent theoretical and experimental studies reveal that compressed molecular hydrogen at 200-350 GPa transforms to layered structures consisting of distorted graphene sheets. The new phases of dense solid hydrogen contrast with the long-held view that symmetric close-packed, ambient alkali-metal-like structures form at these high pressures -this raises the question about the nature and fate of molecular bonding in hydrogen on compression. The realization of such unexpected structures can be explained by consideration of simple low-dimensional model systems- H6 rings and graphene-like monolayers. Both molecular quantum chemistry and well-tested solid state approaches show that these model systems like aromatic hydrocarbons exhibit a special stability, associated with the completely filled set of bonding orbitals or valence bands. This close-shell effect persists in progressing to the real layered structures where it prevents the dielectric energy gap from closing, thus delaying the pressure-induced metallization. The latter nevertheless can occur upon further compression via destroying the closed shell electronic structure which is mainly determined by the 1s electrons. The most likely scenario is the lowering of the bonding bands (their bottoms) stemming from the unoccupied atomic 2s and 2p orbitals. This research was supported by EFree, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award DESC0001057.

  13. RELATIVISTIC MODIFICATIONS OF COVALENT BONDING IN HEAVY ELEMENTS: CALCULATIONS FOR TlH

    SciTech Connect

    Pitzer, Kenneth S.; Christiansen, Phillip A.

    1980-11-20

    A test is presented of the proposal of Pyper that an "orthogonal triplet bond" is an important factor in the bonding of hydrogen to a very heavy element with a single p{sub 1/2} valence electron. The potential curve for TlH was calculated by relativistic quantum methods on two bases: (a) excluding promotion of the p{sub 1/2} spinor and allowing the orthogonal triplet interaction and (b) allowing partial promotion of the p{sub 1/2} spinor by p{sub 3/2} participation and thereby approaching a normal sigma bond. The potential curve for the normal sigma bond was also calculated by suppressing the spin-orbit term. From these results and literature information it is concluded that the orthogonal triplet interaction makes no significant contribution to bonding. Certain other aspects of the effect of relativity on bonding are also discussed.

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

    PubMed

    Hnninen, Mikko M; Vlivaara, Juha; Mota, Antonio J; Colacio, Enrique; Lloret, Francesc; Sillanp, Reijo

    2013-02-18

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

  15. Two-electron bond-orbital model, 2

    NASA Technical Reports Server (NTRS)

    Huang, C.; Moriarty, J. A.; Sher, A.

    1976-01-01

    The two-electron bond-orbital model of tetrahedrally-coordinated solids is generalized and its application extended. All intrabond matrix elements entering the formalism are explicitly retained, including the direct overlap S between the anion and cation sp3 hybrid wavefunctions. Complete analytic results are obtained for the six two-electron eigenvalues and eigenstates of the anion-cation bond in terms of S, one-electron parameters V2 and V3, and two-electron correlation parameters V4, V5 and V6. Refined formulas for the dielectric constant and the nuclear exchange and pseudodipolar coefficients, as well as new expressions for the valence electron density, polarity of the bond and the cohesive energy, are then derived. The theory gives a good account of the experimentally observed trends in all properties considered and approximate quantitative agreement is achieved for the pseudodipolar coefficient.

  16. Rapid adhesive bonding concepts

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

    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.

  17. Bonding Effects on the Slip Differences in the B 1 Monocarbides

    NASA Astrophysics Data System (ADS)

    De Leon, Nicholas; Yu, Xiao-xiang; Yu, Hang; Weinberger, Christopher R.; Thompson, Gregory B.

    2015-04-01

    Differences in plasticity are usually attributed to significant changes in crystalline symmetry or the strength of the interatomic bonds. In the B 1 monocarbides, differences in slip planes exist at low temperatures despite having the same structure and very similar bonding characteristics. Our experimental results demonstrate concretely that HfC slips on {110 } planes while TaC slips on {111 } planes. Density functional theory calculations rationalize this difference through the formation of an intrinsic stacking fault on the {111 } planes, formation of Shockley partials, and enhanced metallic bonding because of the valence filling of electrons between these transitional metal carbides.

  18. Bonding effects on the slip differences in the B1 monocarbides.

    PubMed

    De Leon, Nicholas; Yu, Xiao-Xiang; Yu, Hang; Weinberger, Christopher R; Thompson, Gregory B

    2015-04-24

    Differences in plasticity are usually attributed to significant changes in crystalline symmetry or the strength of the interatomic bonds. In the B1 monocarbides, differences in slip planes exist at low temperatures despite having the same structure and very similar bonding characteristics. Our experimental results demonstrate concretely that HfC slips on {110} planes while TaC slips on {111} planes. Density functional theory calculations rationalize this difference through the formation of an intrinsic stacking fault on the {111} planes, formation of Shockley partials, and enhanced metallic bonding because of the valence filling of electrons between these transitional metal carbides. PMID:25955056

  19. Pancake ?-? Bonding Goes Double: Unexpected 4e/All-Sites Bonding in Boron- and Nitrogen-Doped Phenalenyls.

    PubMed

    Tian, Yong-Hui; Sumpter, Bobby G; Du, Shiyu; Huang, Jingsong

    2015-06-18

    Chemical bonding interactions are the main driving force for the formation of molecules and materials from atoms. The two-electron/multicenter pancake ?-? bonding found in phenalenyl (PLY, 1) radical ?-dimers is intriguing due to its unconventional nature of covalent bonding for molecular aggregations and its propensity to induce unique optical, electronic, and magnetic properties. By using high-level quantum chemistry calculations, we show that the B- or N-doped PLYs (2 and 4), usually considered closed-shell and therefore trifling, can be rendered open-shell singlet by proper edge substitutions (3 and 5). The resulting two unpaired valence electrons on each molecular unit contribute to the formation of a genuine pancake-shaped 4e/all-sites double ?-? bonding upon intermolecular ?-dimerization, in contrast to the 2e/half-sites single ?-? bonding in the parent PLY ?-dimers. The unusual double ?-? bonding motif discovered in these PLY analogues may broaden the landscape of, and find new applications for, intermolecular covalent bonding interactions. PMID:26266612

  20. Bonding thermoplastic polymers

    DOEpatents

    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

    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.

  1. Prospective bonding applications

    NASA Astrophysics Data System (ADS)

    Ancenay, H.; Benazet, D.

    1981-07-01

    Adhesive bonding in industry and in the laboratory is surveyed and prospects for its wider utilization are assessed. The economic impact of bonding technology on industry is discussed. Research is reviewed, centering on the development of nondestructive testing and inspection techniques. Traditional (wood) as well as new materials susceptible to bonding are considered. Applications in construction and civil engineering, in aeronautics, and in the automobile industry are covered. The use of glues in mechanical constructions, in assembling cylindrical parts, and in metal-metal bonding are examined. Hybrid assembling and bonding of composite materials are included.

  2. Generally Contracted Valence-Core/Valence Basis Sets for Use with Relativistic Effective Core Potentials and Spin-Orbit Coupling Operators

    SciTech Connect

    Ermler, Walter V.; Tilson, Jeffrey L.

    2012-12-15

    A procedure for structuring generally contracted valence-core/valence basis sets of Gaussian-type functions for use with relativistic effective core potentials (gcv-c/v-RECP basis sets) is presented. Large valence basis sets are enhanced using a compact basis set derived for outer core electrons in the presence of small-core RECPs. When core electrons are represented by relativistic effective core potentials (RECPs), and appropriate levels of theory, these basis sets are shown to provide accurate representations of atomic and molecular valence and outer-core electrons. Core/valence polarization and correlation effects can be calculated using these basis sets through standard methods for treating electron correlation. Calculations of energies and spectra for Ru, Os, Ir, In and Cs are reported. Spectroscopic constants for RuO2+, OsO2+, Cs2 and InH are calculated and compared with experiment.

  3. Creating σ-holes through the formation of beryllium bonds.

    PubMed

    Brea, Oriana; Mó, Otilia; Yáñez, Manuel; Alkorta, Ibon; Elguero, José

    2015-09-01

    Through the use of ab initio theoretical models based on MP2/aug-cc-pVDZ-optimized geometries and CCSD(T)/aug-cc-pVTZ and CCSD(T)/aug-c-pVDZ total energies, it has been shown that the significant electron density rearrangements that follow the formation of a beryllium bond may lead to the appearance of a σ-hole in systems that previously do not exhibit this feature, such as CH3 OF, NO2 F, NO3 F, and other fluorine-containing systems. The creation of the σ-hole is another manifestation of the bond activation-reinforcement (BAR) rule. The appearance of a σ-hole on the F atoms of CH3 OF is due to the enhancement of the electronegativity of the O atom that participates in the beryllium bond. This atom recovers part of the charge transferred to Be by polarizing the valence density of the F into the bonding region. An analysis of the electron density shows that indeed this bond becomes reinforced, but the F atom becomes more electron deficient with the appearance of the σ-hole. Importantly, similar effects are also observed even when the atom participating in the beryllium bond is not directly attached to the F atom, as in NO2 F, NO3 F, or NCF. Hence, whereas the isolated CH3 OF, NO2 F, and NO3 F are unable to yield F⋅⋅⋅Base halogen bonds, their complexes with BeX2 derivatives are able to yield such bonds. Significant cooperative effects between the new halogen bond and the beryllium bond reinforce the strength of both noncovalent interactions. PMID:26212472

  4. The site occupation and valence of Mn ions in the crystal lattice of Sr{sub 4}Al{sub 14}O{sub 25} and its deep red emission for high color-rendering white light-emitting diodes

    SciTech Connect

    Chen, Lei; Xue, Shaochan; Chen, Xiuling; Bahader, Ali; Deng, Xiaorong; Zhao, Erlong; Jiang, Yang; Chen, Shifu; Chan, Ting-Shan; Zhao, Zhi; Zhang, Wenhua

    2014-12-15

    Highlights: Different valences of Mn ions in Sr{sub 4}Al{sub 14}O{sub 25} were identified using XANES and EPR. Red luminescence was attributed to Mn{sup 4+} occupying the center of AlO{sub 6} octahedron. The Mn{sup 3+} incorporated in the center of AlO{sub 4} tetrahedron was non-luminescent. The bond-valence theory was used to analyze the effective valences of cations. A white LED device with CRI up to Ra 93.23 was packaged by using the red phosphor. - Abstract: The synthesis and component of red phosphor, Sr{sub 4}Al{sub 14}O{sub 25}: Mn, were optimized for application in white light-emitting diodes. The microstructure and morphology were investigated by the X-ray diffraction and scanning electron microscopy. Different valences of Mn ions in Sr{sub 4}Al{sub 14}O{sub 25} were discriminated using the electron paramagnetic resonance and X-ray absorption near-edge structure spectroscopy techniques. The bond-valence theory was used to analyze the effective valences of Sr{sup 2+} and Al{sup 3+} in Sr{sub 4}Al{sub 14}O{sub 25}. As a result, the strong covalence of Al{sup 3+} in the AlO{sub 4} tetrahedron other than in the AlO{sub 6} octahedron is disclosed. The deep red emission is attributed to Mn{sup 4+} occupying the center of AlO{sub 6} octahedron. The mechanism of energy transfer is mainly through dipoledipole interaction, revealed by the analyses of critical distance and concentration quench. A high color rendering white LED prototype with color-rendering index up to Ra 93.23 packaged by using the red phosphor demonstrates its applicability.

  5. Simple Bond Cleavage

    SciTech Connect

    Gary S. Groenewold

    2005-08-01

    Simple bond cleavage is a class of fragmentation reactions in which a single bond is broken, without formation of new bonds between previously unconnected atoms. Because no bond making is involved, simple bond cleavages are endothermic, and activation energies are generally higher than for rearrangement eliminations. The rate of simple bond cleavage reactions is a strong function of the internal energy of the molecular ion, which reflects a loose transition state that resembles reaction products, and has a high density of accessible states. For this reason, simple bond cleavages tend to dominate fragmentation reactions for highly energized molecular ions. Simple bond cleavages have negligible reverse activation energy, and hence they are used as valuable probes of ion thermochemistry, since the energy dependence of the reactions can be related to the bond energy. In organic mass spectrometry, simple bond cleavages of odd electron ions can be either homolytic or heterolytic, depending on whether the fragmentation is driven by the radical site or the charge site. Simple bond cleavages of even electron ions tend to be heterolytic, producing even electron product ions and neutrals.

  6. Neural correlates of valence generalization in an affective conditioning paradigm.

    PubMed

    Schick, Anita; Adam, Ruth; Vollmayr, Barbara; Kuehner, Christine; Kanske, Philipp; Wessa, Michle

    2015-10-01

    In case of uncertainty, predictions that are based on prior, similar experiences guide our decision by processes of generalization. Over-generalization of negative information has been identified as an important feature of several psychopathologies, including anxiety disorders and depression, and might underlie biased interpretation of ambiguous information. Here, we investigated the neural correlates of valence generalization to ambiguous stimuli using a translational affective conditioning task during fMRI. Twenty-five healthy individuals participated in a conditioning procedure with (1) an initial acquisition phase, where participants learned the positive and negative valence of two different tones (reference tones) through their responses and subsequent feedback and (2) a test phase, where participants were presented with the previously learned reference tones and three additional tones with intermediate frequency to the learned reference tones. By recording the responses to these intermediate stimuli we were able to assess the participants interpretation of ambiguous tones as either positive or negative. Behavioral results revealed a graded response pattern to the three intermediate tones, which was mirrored on the neural level. More specifically, parametric analyses OF BOLD responses to all five tones revealed a linear effect in bilateral anterior insula and SMA with lowest activation to the negative reference tone and highest activation to the positive negative tone. In addition, a cluster in the SMA showed a reverse-quadratic response, i.e., the strongest response for the most ambiguous tone. These findings suggest overlapping regions in the salience network that mediate valence generalization and decision-making under ambiguity, potentially underlying biased ambiguous cue interpretation. PMID:26057359

  7. Nucleon and pion distribution functions in the valence region

    NASA Astrophysics Data System (ADS)

    Holt, Roy J.; Roberts, Craig D.

    2010-10-01

    An experimental and theoretical perspective is provided on the behavior of unpolarized distribution functions for the nucleon and pion on the valence-quark domain, namely, Bjorken x?0.4 . This domain is a key to much of hadron physics; e.g., a hadron is defined by its flavor content and that is a valence-quark property. Furthermore, its accurate parametrization is crucial to the provision of reliable input for large collider experiments. The focus is on experimental extractions of distribution functions via electron and muon inelastic scattering, and from Drell-Yan interactions; and on theoretical treatments that emphasize an explanation of the distribution functions, providing an overview of major contemporary approaches and issues. Valence-quark physics is a compelling subject, which probes at the heart of our understanding of the standard model. There are numerous outstanding and unresolved challenges, which experiment and theory must confront. In connection with experiment, an explanation that an upgraded Jefferson Laboratory facility is well suited to provide new data on the nucleon is provided, while a future electron-ion collider could provide essential new data for the mesons. There is also great potential in using Drell-Yan interactions, at FNAL, CERN, J-PARC, and GSI, to push into the large- x domain for both mesons and nucleons. Furthermore, it is argued that explanation, in contrast to modeling and parametrization, requires a widespread acceptance of the need to adapt theory: to the lessons learnt already from the methods of nonperturbative quantum-field theory and a fuller exploitation of those methods.

  8. Pion and kaon valence-quark parton distribution functions

    SciTech Connect

    Nguyen, Trang; Bashir, Adnan; Roberts, Craig D.; Tandy, Peter C.

    2011-06-15

    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.

  9. 3p valence photoelectron spectrum of Ar clusters

    SciTech Connect

    Hergenhahn, Uwe; Barth, Silko; Ulrich, Volker; Mucke, Melanie; Joshi, Sanjeev; Lischke, Toralf; Lindblad, Andreas; Rander, Torbjoern; Oehrwall, Gunnar; Bjoerneholm, Olle

    2009-04-15

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

  10. Kondo and mixed-valence regimes in multilevel quantum dots

    SciTech Connect

    Chudnovskiy, A. L.; Ulloa, S. E.

    2001-04-15

    We investigate the dependence of the ground state of a multilevel quantum dot on the coupling to an external fermionic system and on the interactions in the dot. As the coupling to the external system increases, the rearrangement of the effective energy levels in the dot signals the transition from the Kondo regime to a mixed-valence (MV) regime. The MV regime in a two-level dot is characterized by an intrinsic mixing of the levels in the dot, resulting in nonperturbative subtunneling and supertunneling phenomena that strongly influence the Kondo effect.

  11. Pion and kaon valence-quark parton distribution functions.

    SciTech Connect

    Nguyen, T.; Bashir, A.; Roberts, C. D.; Tandy, P. C.

    2011-06-16

    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.

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

    SciTech Connect

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

    2005-12-15

    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.

  13. Homometallic Cubane Clusters: Participation of Three-Coordinated Hydrogen in 60-Valence Electron Cubane Core.

    PubMed

    Yuvaraj, K; Roy, Dipak Kumar; Mondal, Bijan; Varghese, Babu; Ghosh, Sundargopal

    2015-09-01

    This work describes the synthesis, structural characterizations, and electronic structures of a series of novel homometallic cubane clusters [(Cp*Ru)2{Ru(CO)2}2BH(?3-E)(?-H)B(?-H)3M], (2, M = Cp*Ru, E = CO; 3, M = Ru(Cp*Ru)2(?-CO)3(?-H)BH), E = BH), [(Cp*Ru)3(?3-CO)(BH)3(?3-H)3], 4, and [(Cp*Ru)2(?3-CO){Ru(CO)3}2(BH)2(?-H)B], 5 (Cp* = ?(5)-C5Me5). These cubane clusters have been isolated from a thermally driven reaction of diruthenium analogue of pentaborane(9) [(Cp*RuH)2B3H7], 1, and [Ru3(CO)12]. Structural and spectroscopic studies revealed the existence of triply bridged hydrogen (?3-H) atoms that participate as a vertex in the cubane core formation for compounds 2, 3, and 4. In addition, the crystal structure of these clusters clearly confirms the presence of an electron precise borane ligand (borylene fragment) which is triply bridged to the trimetallic units. Bonding of these novel complexes has been studied computationally by DFT methods, and the studies demonstrate that the cubane clusters 2 and 3 possess 60 cluster valence electrons (cves) with six metal-metal bonds. All the new compounds have been characterized in solution by mass spectrometry; IR; and (1)H, (11)B, and (13)C NMR studies, and the structural types were unequivocally established by crystallographic analysis of compounds 2-5. PMID:26347293

  14. Charge Transfer Pathways in Three Isomers of Naphthalene-Bridged Organic Mixed Valence Compounds.

    PubMed

    Schmidt, Hauke C; Spulber, Mariana; Neuburger, Markus; Palivan, Cornelia G; Meuwly, Markus; Wenger, Oliver S

    2016-01-15

    Naphthalene was substituted at different positions with two identical triarylamine moieties to result in species which are mixed-valence compounds in their one-electron oxidized forms. They were investigated by cyclic voltammetry, optical absorption, EPR spectroscopy, X-ray crystallography, and DFT calculations. When the two redox-active triarylamine moieties are connected to the 2- and 6-positions of the naphthalene bridge, their electronic communication is significantly stronger than when they are linked to the 1- and 5-positions, and this can be understood on the basis of a simple through-bond charge transfer pathway model. However, this model fails to explain why electronic communication between triarylamine moieties in the 1,5- and 1,8-isomers is similarly strong, indicating that through-space charge transfer pathways play an important role in the latter. In particular, charge transfer in the 1,8-isomer is likely to occur between the triarylamino C atoms in ?-position to the naphthalene linker because the respective atoms are only about 3 apart from each other, and because they carry significant spin density in the one-electron oxidized forms of triarylamines. This particular through-space charge transfer pathway might be generally important in molecular structures based on the 1,8-disubstituted naphthalene pillaring motif. PMID:26711318

  15. Prediction of the bond lengths, vibrational frequencies, and bond dissociation energy of octahedral seaborgium hexacarbonyl, Sg(CO){sub 6}

    SciTech Connect

    Nash, C.S.; Bursten, B.E.

    1999-11-24

    The recent syntheses of several new elements (including the recent reports of elements 116 and 118), coupled with the controversy surrounding the naming of elements 104--109, have stimulated a great interest in the chemistry of the transactinide elements. This contribution addresses hypothetical hexacarbonyl complex of seaborgium (Sg, element 106), which is predicted to be a 6d-block transition element with six valence electrons, analogous to Cr, Mo, and W. The authors have previously predicted that, if it were to exist, Sg(CO){sub 6} would exhibit metal-carbonyl bonding that is very similar to that in Cr(CO){sub 6}, Mo(CO){sub 6}, and W(CO){sub 6}, and quite unlike that of the unknown valence isoelectronic actinide complex U(CO){sub 6}. This finding is in accord with the scant experimental data available for Sg. The relativistic DV-X{alpha} method used in the earlier paper facilitated the analysis of the molecular orbitals of Sg(CO){sub 6}, but did not allow for the calculation of total-energy properties, such as bond lengths and vibrational frequencies. Here the authors will use the superior methodology they have applied to other transactinide molecules to compare the bond lengths, vibrational frequencies, and CO dissociation energy of hypothetical Sg(CO){sub 6} to those of Mo(CO){sub 6} and W(CO){sub 6}.

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

    PubMed Central

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

    2013-01-01

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

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

    PubMed

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

    2012-10-01

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

  18. Coupled-cluster based basis sets for valence correlation calculations.

    PubMed

    Claudino, Daniel; Gargano, Ricardo; Bartlett, Rodney J

    2016-03-14

    Novel basis sets are generated that target the description of valence correlation in atoms H through Ar. The new contraction coefficients are obtained according to the Atomic Natural Orbital (ANO) procedure from CCSD(T) (coupled-cluster singles and doubles with perturbative triples correction) density matrices starting from the primitive functions of Dunning et al. [J. Chem. Phys. 90, 1007 (1989); ibid. 98, 1358 (1993); ibid. 100, 2975 (1993)] (correlation consistent polarized valence X-tuple zeta, cc-pVXZ). The exponents of the primitive Gaussian functions are subject to uniform scaling in order to ensure satisfaction of the virial theorem for the corresponding atoms. These new sets, named ANO-VT-XZ (Atomic Natural Orbital Virial Theorem X-tuple Zeta), have the same number of contracted functions as their cc-pVXZ counterparts in each subshell. The performance of these basis sets is assessed by the evaluation of the contraction errors in four distinct computations: correlation energies in atoms, probing the density in different regions of space via 〈r(n)〉 (-3 ≤ n ≤ 3) in atoms, correlation energies in diatomic molecules, and the quality of fitting potential energy curves as measured by spectroscopic constants. All energy calculations with ANO-VT-QZ have contraction errors within "chemical accuracy" of 1 kcal/mol, which is not true for cc-pVQZ, suggesting some improvement compared to the correlation consistent series of Dunning and co-workers. PMID:26979680

  19. Tunable topological valence in nematic shells on spherocylindrical colloidal particles.

    PubMed

    de Oliveira, E J L; de Oliveira, I N; Lyra, M L; Mirantsev, L V

    2016-01-01

    We perform molecular dynamics simulations of the orientational ordering on nematic shells delimited by spherocylindrical nanoscopic colloidal particles. We show that under conditions of degenerate planar anchoring, the equilibrium director field structure in these shells exhibits pairs of +1/2 topological defects at the poles of spherical cups in the absence of an external electric field. In addition, a certain number of pairs of 1/2 defects occurs on the spherical cups far from the poles, thus resulting in a total of eight valence spots. A strong field applied along the main spherocylindrical axis removes the 1/2 defect pairs while it coalesces the polar ones into a single +1 topological defect. A strong transverse field destroys all defects on the spherical cups but generates four +1/2 defects in the cylindrical part. Therefore, an external field can be used to control the number of valence centers in spherocylindrical nematic shells, thus unveiling their capability of acting as multivalent building blocks for nanophotonic devices. PMID:26871131

  20. An ecological valence theory of human color preference

    PubMed Central

    Palmer, Stephen E.; Schloss, Karen B.

    2010-01-01

    Color preference is an important aspect of visual experience, but little is known about why people in general like some colors more than others. Previous research suggested explanations based on biological adaptations [Hurlbert AC, Ling YL (2007) Curr Biol 17:623625] and color-emotions [Ou L-C, Luo MR, Woodcock A, Wright A (2004) Color Res Appl 29:381389]. In this article we articulate an ecological valence theory in which color preferences arise from peoples average affective responses to color-associated objects. An empirical test provides strong support for this theory: People like colors strongly associated with objects they like (e.g., blues with clear skies and clean water) and dislike colors strongly associated with objects they dislike (e.g., browns with feces and rotten food). Relative to alternative theories, the ecological valence theory both fits the data better (even with fewer free parameters) and provides a more plausible, comprehensive causal explanation of color preferences. PMID:20421475

  1. +2 Valence Metal Concentrations in Lion Creek, Oakland, California

    NASA Astrophysics Data System (ADS)

    Vazquez, P.; Zedd, T.; Chagolla, R.; Dutton-Starbuck, M.; Negrete, A.; Jinham, M.; Lapota, M.

    2012-12-01

    Seven major creeks exist within the City of Oakland, California. These creeks all flow in the southwest direction from forested hills down through densely populated streets where they become susceptible to urban runoff. Lion Creek has been diverted to engineered channels and underground culverts and runs directly under our school (Roots International) before flowing into the San Leandro Bay. One branch of the creek begins near an abandoned sulfur mine. Previous studies have shown that extremely high levels of lead, arsenic and iron exist in this portion of the creek due to acid mine drainage. In this study +2 valence heavy metals concentration data was obtained from samples collected from a segment of the creek located approximately 2.8 miles downstream from the mine. Concentrations in samples collected at three different sites along this segment ranged between 50 ppb and 100 ppb. We hypothesize that these levels are related to the high concentration of +2 valence heavy metals at the mining site. To test this hypothesis, we have obtained samples from various locations along the roughly 3.75 miles of Lion Creek that are used to assess changes in heavy metals concentration levels from the mining site to the San Leandro Bay.

  2. Tunable topological valence in nematic shells on spherocylindrical colloidal particles

    NASA Astrophysics Data System (ADS)

    de Oliveira, E. J. L.; de Oliveira, I. N.; Lyra, M. L.; Mirantsev, L. V.

    2016-01-01

    We perform molecular dynamics simulations of the orientational ordering on nematic shells delimited by spherocylindrical nanoscopic colloidal particles. We show that under conditions of degenerate planar anchoring, the equilibrium director field structure in these shells exhibits pairs of +1 /2 topological defects at the poles of spherical cups in the absence of an external electric field. In addition, a certain number of pairs of 1 /2 defects occurs on the spherical cups far from the poles, thus resulting in a total of eight valence spots. A strong field applied along the main spherocylindrical axis removes the 1 /2 defect pairs while it coalesces the polar ones into a single +1 topological defect. A strong transverse field destroys all defects on the spherical cups but generates four +1 /2 defects in the cylindrical part. Therefore, an external field can be used to control the number of valence centers in spherocylindrical nematic shells, thus unveiling their capability of acting as multivalent building blocks for nanophotonic devices.

  3. Coupled-cluster based basis sets for valence correlation calculations

    NASA Astrophysics Data System (ADS)

    Claudino, Daniel; Gargano, Ricardo; Bartlett, Rodney J.

    2016-03-01

    Novel basis sets are generated that target the description of valence correlation in atoms H through Ar. The new contraction coefficients are obtained according to the Atomic Natural Orbital (ANO) procedure from CCSD(T) (coupled-cluster singles and doubles with perturbative triples correction) density matrices starting from the primitive functions of Dunning et al. [J. Chem. Phys. 90, 1007 (1989); ibid. 98, 1358 (1993); ibid. 100, 2975 (1993)] (correlation consistent polarized valence X-tuple zeta, cc-pVXZ). The exponents of the primitive Gaussian functions are subject to uniform scaling in order to ensure satisfaction of the virial theorem for the corresponding atoms. These new sets, named ANO-VT-XZ (Atomic Natural Orbital Virial Theorem X-tuple Zeta), have the same number of contracted functions as their cc-pVXZ counterparts in each subshell. The performance of these basis sets is assessed by the evaluation of the contraction errors in four distinct computations: correlation energies in atoms, probing the density in different regions of space via (-3 ≤ n ≤ 3) in atoms, correlation energies in diatomic molecules, and the quality of fitting potential energy curves as measured by spectroscopic constants. All energy calculations with ANO-VT-QZ have contraction errors within "chemical accuracy" of 1 kcal/mol, which is not true for cc-pVQZ, suggesting some improvement compared to the correlation consistent series of Dunning and co-workers.

  4. Mixed valence of iron in minerals with cation clusters

    NASA Astrophysics Data System (ADS)

    Amthauer, Georg; Rossman, George R.

    1984-06-01

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

  5. Ligand-hole localization in oxides with unusual valence Fe

    PubMed Central

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

    2012-01-01

    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. PMID:22690318

  6. Intracranial markers of emotional valence processing and judgments in music.

    PubMed

    Omigie, Diana; Dellacherie, Delphine; Hasboun, Dominique; Clément, Sylvain; Baulac, Michel; Adam, Claude; Samson, Séverine

    2015-01-01

    The involvement of the amygdala and orbitofrontal cortex in the processing of valenced stimuli is well established. However, less is known about the extent to which activity in these regions reflects a stimulus' physical properties, the individual subjective experience it evokes, or both. We recorded cortical electrical activity from five epileptic patients implanted with depth electrodes for presurgical evaluation while they rated "consonant" and "dissonant" musical chords using a "pleasantness" scale. We compared the pattern of responses in the amygdala and orbitofrontal cortex when trials were sorted by pleasantness judgments relative to when they were sorted by the acoustic properties known to influence emotional reactions to musical chords. This revealed earlier differential activity in the amygdala in the physical properties-based, relative to in the judgment-based, analyses. Thus, our results demonstrate that the amygdala has, first and foremost, a high initial sensitivity to the physical properties of valenced stimuli. The finding that differentiations in the amygdala based on pleasantness ratings had a longer latency suggests that in this structure, mediation of emotional judgment follows accumulation of sensory information. This is in contrast to the orbitofrontal cortex where sensitivity to sensory information did not precede differentiation based on affective judgments. PMID:25496511

  7. Aggression proneness: Transdiagnostic processes involving negative valence and cognitive systems.

    PubMed

    Verona, Edelyn; Bresin, Konrad

    2015-11-01

    Aggressive behavior is observed in persons with various mental health problems and has been studied from the perspectives of neuroscience and psychophysiology. The present research reviews some of the extant experimental literature to help clarify the interplay between domains of functioning implicated in aggression proneness. We then convey a process-oriented model that elucidates how the interplay of the Negative Valence and Cognitive System domains of NIMH's Research Domain Criteria (RDoC) helps explain aggression proneness, particularly reactive aggression. Finally, we report on a study involving event-related potential (ERP) indices of emotional and inhibitory control processing during an emotional-linguistic go/no-go task among 67 individuals with histories of violence and criminal offending (30% female, 44% African-American) who reported on their aggressive tendencies using the Buss-Perry Aggression Questionnaire. Results provide evidence that tendencies toward angry and aggressive behavior relate to reduced inhibitory control processing (no-go P3) specifically during relevant threat-word blocks, suggesting deterioration of cognitive control by acute or sustained threat sensitivity. These findings highlight the value of ERP methodologies for clarifying the interplay of Negative Valence and Cognitive System processes in aggression proneness. PMID:25816797

  8. Valence holes observed in nanodiamonds dispersed in water

    NASA Astrophysics Data System (ADS)

    Petit, Tristan; Pflger, Mika; Tolksdorf, Daniel; Xiao, Jie; Aziz, Emad F.

    2015-02-01

    Colloidal dispersion is essential for most nanodiamond applications, but its influence on nanodiamond electronic properties remains unknown. Here we have probed the electronic structure of oxidized detonation nanodiamonds dispersed in water by using soft X-ray absorption and emission spectroscopies at the carbon and oxygen K edges. Upon dispersion in water, the ?* transitions from sp2-hybridized carbon disappear, and holes in the valence band are observed.Colloidal dispersion is essential for most nanodiamond applications, but its influence on nanodiamond electronic properties remains unknown. Here we have probed the electronic structure of oxidized detonation nanodiamonds dispersed in water by using soft X-ray absorption and emission spectroscopies at the carbon and oxygen K edges. Upon dispersion in water, the ?* transitions from sp2-hybridized carbon disappear, and holes in the valence band are observed. Electronic supplementary information (ESI) available: Experimental methods, details on XAS/XES normalization and background correction procedures. See DOI: 10.1039/c4nr06639a

  9. Bonded semiconductor substrate

    DOEpatents

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

    2010-07-13

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

    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.

  11. A local view of bonding and diffusion at metal surfaces

    SciTech Connect

    Feibelman, P.J.

    1996-09-01

    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.

  12. Prediction of initial emission rates of 2-butoxyethanol from consumer products using equilibrium headspace concentrations: an application of the vapor pressure and boundary layer (VB) model.

    PubMed

    Zhu, Jiping; Li, Henrik; Korchinski, Mark; Fellin, Phil

    2005-11-01

    The initial emission rate of volatile organic compounds (VOCs) from consumer products is important for assessing potential human exposure to VOCs in products. The vapor pressure and boundary layer (VB) model developed in the past was used to predict the emission rates of VOCs in the fast decaying phase from petroleum-based wet materials. This study has extended the model to largely water-based products. Study results have shown a good agreement (ratio = 1.01, r2 = 0.89) between model-predicted initial emission rates (ER0) of 2-butoxyethanol (2-BE) based on its equilibrium headspace concentration and experimentally measured ER0 in a small dynamic environmental chamber for 20 consumer products. These water-based products included wood surface treating stains, general cleaning agents, and degreasers with 2-BE concentrations over a wide range. The results also demonstrated a dependency between the headspace concentrations of the target analytes and the water content in the liquid. But dependency on water content had no effect on the use of headspace concentration to predict the ER0. The ER0 of 2-BE in the products ranged from 100 to 3000 mg m(-2) h(-1). In the majority of cases, the 2-BE concentration range in individual products indicated in the Material Safety Data Sheet agreed with the measured data. PMID:16294857

  13. Chemical bonding technology

    NASA Technical Reports Server (NTRS)

    Plueddemann, E.

    1986-01-01

    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.

  14. Energy pulse bonding

    NASA Technical Reports Server (NTRS)

    Smith, G. C.

    1972-01-01

    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.

  15. 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, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Approved testing devices (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines). 57.22227 Section 57.22227 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL...

  16. 30 CFR 57.22501 - Personal electric lamps (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Personal electric lamps (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines). 57.22501 Section 57.22501 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL...

  17. 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

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Approved testing devices (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines). 57.22227 Section 57.22227 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL...

  18. 30 CFR 57.22501 - Personal electric lamps (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Personal electric lamps (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines). 57.22501 Section 57.22501 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL...

  19. 30 CFR 57.22501 - Personal electric lamps (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Personal electric lamps (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines). 57.22501 Section 57.22501 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL...

  20. Comparison of brain capillary endothelial cell-based and epithelial (MDCK-MDR1, Caco-2, and VB-Caco-2) cell-based surrogate blood-brain barrier penetration models.

    PubMed

    Hellinger, Eva; Veszelka, Szilvia; Tth, Andrea E; Walter, Fruzsina; Kittel, Agnes; Bakk, Mnika Laura; Tihanyi, Kroly; Hda, Viktor; Nakagawa, Shinsuke; Duy, Thuy Dinh Ha; Niwa, Masami; Deli, Mria A; Vastag, Monika

    2012-10-01

    An accurate means of predicting blood-brain barrier (BBB) penetration and blood-brain partitioning of NCEs (new chemical entities) would fulfill a major need in pharmaceutical research. Currently, an industry-standard BBB drug penetration model is not available. Primary brain capillary endothelial cells, optionally co-cultured with astrocytes and/or pericytes, are the most valued models of BBB. For routine use, establishing and maintaining a co-culture system is too costly and labor intensive. Alternatively, non-cerebral cell lines such as MDCK-MDR1 are used, and most recently, the suitability of native and modified Caco-2 for predicting brain penetration has also come under investigation. This study provides comparative data on the morphology and functionality of the high integrity brain capillary endothelial BBB model (EPA: triple culture of brain capillary endothelial cells with pericytes and astrocytes) and the epithelial cell-based (native Caco-2, high P-glycoprotein expressing vinblastine-treated VB-Caco-2 and MDCK-MDR1) surrogate BBB models. Using a panel of 10 compounds VB-Caco-2 and MDCK-MDR1 cell lines show restrictive paracellular pathway and BBB-like selective passive permeability that makes them comparable to the rat brain BBB model, which gave correlation with the highest r(2) value with in vivo permeability data. In bidirectional assay, the VB-Caco-2 and the MDCK-MDR1 models identified more P-glycoprotein drug substrates than the rat brain BBB model. While the complexity and predictive value of the BBB model is the highest, for the screening of NCEs to determine whether they are efflux substrates or not, the VB-Caco-2 and the MDCK-MDR1 models may provide a simple and inexpensive tool. PMID:22906709

  1. 30 CFR 57.22501 - Personal electric lamps (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Personal electric lamps (I-A, I-B, I-C, II-A... Illumination 57.22501 Personal electric lamps (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines). Electric lamps used for personal illumination shall be approved by MSHA under the requirements of 30...

  2. 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, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Approved testing devices (I-A, I-B, I-C, II-A... Ventilation 57.22227 Approved testing devices (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines). (a... requirements of 30 CFR parts 18, 21, 22, 23, 27, and 29. Such devices shall be maintained in......

  3. Integrated neural representations of odor intensity and affective valence in human amygdala.

    PubMed

    Winston, Joel S; Gottfried, Jay A; Kilner, James M; Dolan, Raymond J

    2005-09-28

    Arousal and valence are proposed to represent fundamental dimensions of emotion. The neural substrates for processing these aspects of stimuli are studied widely, with recent studies of chemosensory processing suggesting the amygdala processes intensity (a surrogate for arousal) rather than valence. However, these investigations have assumed that a valence effect in the amygdala is linear such that testing valence extremes is sufficient to infer responses across valence space. In this study, we tested an alternative hypothesis, namely that valence responses in the amygdala are nonlinear. Using event-related functional magnetic resonance imaging, we measured amygdala responses to high- and low-concentration variants of pleasant, neutral, and unpleasant odors. Our results demonstrate that the amygdala exhibits an intensity-by-valence interaction in olfactory processing. In other words, the effect of intensity on amygdala activity is not the same at all levels of valence. Specifically, the amygdala responds differentially to high (vs low)-intensity odor for pleasant and unpleasant smells but not for neutral smells. This implies that the amygdala codes neither intensity nor valence per se, but a combination that we suggest reflects the overall emotional value of a stimulus. PMID:16192380

  4. DMFT Study for Valence Fluctuations in the Extended Periodic Anderson Model

    NASA Astrophysics Data System (ADS)

    Shinzaki, Ryu; Nasu, Joji; Koga, Akihisa

    2016-02-01

    We study valence fluctuations at finite temperatures in the extended periodic Anderson model, where the Coulomb interaction between conduction and localized f-electrons is taken into account, using dynamical mean-field theory combined with the continuous-time quantum Monte Carlo (CT-QMC) method. The valence transition with the hysteresis is clearly found, indicating the first-order phase transition between the Kondo and mixed-valence states. We demonstrate that spin correlation rapidly develops when the system approaches the valence transition point. The comparison of the impurity solvers, the CT-QMC, non-crossing approximation, and one-crossing approximation, is also addressed.

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

    NASA Astrophysics Data System (ADS)

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

    2000-06-01

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

  6. A vibrational study of the nature of hydroxyl groups chemical bonding in two aluminium hydroxides.

    PubMed

    Jodin-Caumon, Marie-Camille; Humbert, Bernard; Phambu, Nsoki; Gaboriaud, Fabien

    2009-06-01

    Lengths, strengths and valences of OH bonds in the two aluminium hydroxides gibbsite and bayerite were determined on the basis of vibrational spectral data. The uncoupled OD stretching modes in the range 2400-2800cm(-1) were recorded by means of infrared diffuse reflectance, thereby avoiding effects of surface, vibrational coupling or particle shape. The assignment of the corresponding Raman spectra resulted in the determination of harmonic wavenumbers, force constants and anharmonicity coefficients of bulk OH groups in the two minerals. OH bond lengths deduced from these data varied from 0.964A to 0.975A in gibbsite and 0.962A to 0.973A in bayerite. These lengths appear to correspond to weak H-bonds contrary to previously recognized data from X-ray diffraction and neutron diffraction studies. Finally, bond valences were calculated on the basis of these new bond lengths and discussed as a function of crystallographic structures and the nature of hydrogen bonding in these two structures. PMID:19167269

  7. Mother-Child Bonding.

    ERIC Educational Resources Information Center

    Pearce, Joseph Chilton

    1994-01-01

    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)

  8. Chemical Bonds I

    ERIC Educational Resources Information Center

    Sanderson, R. T.

    1972-01-01

    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)

  9. The Sibling Bond.

    ERIC Educational Resources Information Center

    Bank, Stephen P.; Kahn, Michael D.

    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

  10. The dissociative bond.

    PubMed

    Gordon, Nirit

    2013-01-01

    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

  11. Planning Successful Bond Campaigns.

    ERIC Educational Resources Information Center

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

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

  12. Shape Bonding method

    NASA Technical Reports Server (NTRS)

    Pontius, James T. (Inventor)

    2010-01-01

    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.

  13. Wood Bond Testing

    NASA Technical Reports Server (NTRS)

    1989-01-01

    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.

  14. Tetrel Bonding Interactions.

    PubMed

    Bauzá, Antonio; Mooibroek, Tiddo J; Frontera, Antonio

    2016-02-01

    Tetrel (Tr) bonding is first placed into perspective as a σ-hole bonding interaction with atoms of the Tr family. An sp(3) R4 Tr unit has four σ-holes with which a Lewis base can form a complex. We then highlight some inspiring crystal structures where Tr bonding is obvious, followed by an account of our own work. We have shown that Tr bonding is ubiquitous in the solid state and we have highlighted that Tr bonding with carbon is possible when C is placed in the appropriate chemical context. We hope that this account serves as an initial guide and source of inspiration for others wishing to exploit this vastly underexplored interaction. PMID:26814022

  15. Ultrasonically bonded value assembly

    NASA Technical Reports Server (NTRS)

    Salvinski, R. J. (inventor)

    1975-01-01

    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.

  16. Fullerene valence photoemission time delay near ionization cavity minima

    NASA Astrophysics Data System (ADS)

    Magrakvelidze, Maia; Anstine, Dylan; Dixit, Gopal; Madjet, Mohamed; Chakraborty, Himadri

    2015-05-01

    We investigate photoemission quantum phases and associated Wigner-Smith time delays for HOMO and HOMO-1 electrons of a C60 molecule using time-dependent local density approximation (TDLDA). The interference oscillations in C60 valence emissions produce series of minima whose energy separation depends on the molecular size. We show that the quantum phase associated with these minima exhibits rapid variations due to electron correlations, causing rich structures in the photoemission time delay. Besides fullerenes, the detection of photoemission minima in metal clusters suggests a possible universality of the phenomenon in cluster systems, or even quantum dots, that confine finite-sized electron gas. The work predicts a new research direction to apply attosecond metrology, such as RABITT, in the world of nanosystems. This work was supported by the U.S. National Science Foundation.

  17. Incautiously Optimistic: Positively-Valenced Cognitive Avoidance in Adult ADHD

    PubMed Central

    Knouse, Laura E.; Mitchell, John T.

    2015-01-01

    Clinicians who conduct cognitive-behavioral therapy (CBT) targeting attention-deficit/hyperactivity disorder (ADHD) in adulthood have noted that their patients sometimes verbalize overly positive automatic thoughts and set overly optimistic goals. These cognitions are frequently related to failure to engage in compensatory behavioral strategies emphasized in CBT. In this paper, we offer a functional analysis of this problematic pattern, positively-valenced cognitive avoidance, and suggest methods for addressing it within CBT for adult ADHD. We propose that maladaptive positive cognitions function to relieve aversive emotions in the short-term and are therefore negatively reinforced but that, in the long-term, they are associated with decreased likelihood of active coping and increased patterns of behavioral avoidance. Drawing on techniques from Behavioral Activation (BA), we offer a case example to illustrate these concepts and describe step-by-step methods for clinicians to help patients recognize avoidant patterns and engage in more active coping. PMID:25908901

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

    NASA Technical Reports Server (NTRS)

    Ting, David; Gunapala, Sarath; Bandara, Sumith

    2004-01-01

    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.

  19. Time flies with music whatever its emotional valence.

    PubMed

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

    2010-10-01

    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 shifted the bisection function toward the right, thus increasing the bisection point value (point of subjective equality). This indicates that the duration of a melody is judged shorter than that of a non-melodic control stimulus, thus confirming that "time flies" when we listen to music. Nevertheless, sensitivity to time was similar for all the auditory stimuli. Furthermore, the temporal bisection functions did not differ as a function of musical mode. PMID:20674884

  20. Expectation modulates neural representations of valence throughout the human brain.

    PubMed

    Ramayya, Ashwin G; Pedisich, Isaac; Kahana, Michael J

    2015-07-15

    The brain's sensitivity to unexpected gains or losses plays an important role in our ability to learn new behaviors (Rescorla and Wagner, 1972; Sutton and Barto, 1990). Recent work suggests that gains and losses are ubiquitously encoded throughout the human brain (Vickery et al., 2011), however, the extent to which reward expectation modulates these valence representations is not known. To address this question, we analyzed recordings from 4306 intracranially implanted electrodes in 39 neurosurgical patients as they performed a two-alternative probability learning task. Using high-frequency activity (HFA, 70-200 Hz) as an indicator of local firing rates, we found that expectation modulated reward-related neural activity in widespread brain regions, including regions that receive sparse inputs from midbrain dopaminergic neurons. The strength of unexpected gain signals predicted subjects' abilities to encode stimulus-reward associations. Thus, neural signals that are functionally related to learning are widely distributed throughout the human brain. PMID:25937489

  1. Kondo destruction and valence fluctuations in an Anderson model.

    PubMed

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

    2012-08-24

    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, ?-YbAlB(4), 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. PMID:23002763

  2. Kondo Destruction and Valence Fluctuations in an Anderson Model

    NASA Astrophysics Data System (ADS)

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

    2012-08-01

    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.

  3. Nanostructured high valence silver oxide produced by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Dellasega, D.; Facibeni, A.; Di Fonzo, F.; Russo, V.; Conti, C.; Ducati, C.; Casari, C. S.; Li Bassi, A.; Bottani, C. E.

    2009-03-01

    Among silver oxides, Ag 4O 4, i.e. high valence Ag(I)Ag(III) oxide, is interesting for applications in high energy batteries and for the development of antimicrobial coatings. We here show that ns UV pulsed laser deposition (PLD) in an oxygen containing atmosphere allows the synthesis of pure Ag 4O 4 nanocrystalline thin films, permitting at the same time to control the morphology of the material at the sub-micrometer scale. Ag 4O 4 films with a crystalline domain size of the order of tens of nm can be deposited provided the deposition pressure is above a threshold (roughly 4 Pa pure O 2 or 20 Pa synthetic air). The formation of this particular high valence silver oxide is explained in terms of the reactions occurring during the expansion of the ablated species in the reactive atmosphere. In particular, expansion of the PLD plasma plume is accompanied by formation of low stability Ag-O dimers and atomic oxygen, providing reactive species at the substrate where the film grows. Evidence of reactive collisions in the expanding ablation plume is obtained by analysis of the plume visible shape in inert and reactive atmospheres. In addition, we show how the dimensionless deposition parameter L, relating the target-to-substrate distance to the ablation plume maximum expansion length, can be used to classify different growth regimes. It is thus possible to vary the stoichiometry and the morphology of the films, from compact and columnar to foam-like, by controlling both the gas pressure and the target-to-substrate distance.

  4. Materials with intermediate valence ; a comparison with transition metals

    NASA Astrophysics Data System (ADS)

    Mott, N. F.

    A discussion of metallic intermediate valence materials is given, particularly of hybridisation between the 4f and the conduction band δ. If n, 1 - n are the numbers of ions in each of two charge states, the variation of n with temperature is described. Resistivity is ascribed to scattering of the conduction electrons into the 4f band. The mechanism is compared with that in transition metals and their alloys, particularly Pd1-xAg x. The resistivity can be very large, of order of the Ioffe-Regel value 1/3 e2/ħa. It is argued that both here and in metallic alloys, this can only occur with a two-band model. At high temperatures there is some evidence that s-f scattering does not occur. On discute des matériaux métalliques à valence intermédiaire, en particulier de l'hybridation entre la bande 4f et la bande de conduction. Notant n et 1 - n les nombres d'ions dans chacun des deux états de charge, on décrit la variation de n avec la température. Le mécanisme est comparé avec celui des métaux de transition et de leurs alliages, particulièrement Pd1-xAg x. La résistivité peut être très grande, de l'ordre de la valeur de Ioffe-Regel 1/3 e2/ħa. On donne des arguments tendant à prouver que ceci ne peut se produire que dans le cadre d'un modèle à 2 bandes. Il y a des évidences qu'à haute température la diffusion s-f n'a pas lieu.

  5. A density functional for core-valence correlation energy.

    PubMed

    Ranasinghe, Duminda S; Frisch, Michael J; Petersson, George A

    2015-12-01

    A density functional, εCV-DFT(ρc, ρv), describing the core-valence correlation energy has been constructed as a linear combination of εLY P (corr)(ρc), εV WN5 (corr)(ρc, ρv), εPBE (corr)(ρc, ρv), εSlater (ex)(ρc, ρv), εHCTH (ex)(ρc, ρv), εHF (ex)(ρc, ρv), and FCV-DFTNi,Zi, a function of the nuclear charges. This functional, with 6 adjustable parameters, reproduces (±0.27 kcal/mol rms error) a benchmark set of 194 chemical energy changes including 9 electron affinities, 18 ionization potentials, and 167 total atomization energies covering the first- and second-rows of the periodic table. This is almost twice the rms error (±0.16 kcal/mol) obtained with CCSD(T)/MTsmall calculations, but less than half the rms error (±0.65 kcal/mol) obtained with MP2/GTlargeXP calculations, and somewhat smaller than the rms error (±0.39 kcal/mol) obtained with CCSD/MTsmall calculations. The largest positive and negative errors from εCV-DFT(ρc, ρv) were 0.88 and -0.75 kcal/mol with the set of 194 core-valence energy changes ranging from +3.76 kcal/mol for the total atomization energy of propyne to -9.05 kcal/mol for the double ionization of Mg. Evaluation of the εCV-DFT(ρc, ρv) functional requires less time than a single SCF iteration, and the accuracy is adequate for any model chemistry based on the CCSD(T) level of theory. PMID:26646873

  6. A density functional for core-valence correlation energy

    NASA Astrophysics Data System (ADS)

    Ranasinghe, Duminda S.; Frisch, Michael J.; Petersson, George A.

    2015-12-01

    A density functional, ɛCV-DFT(ρc, ρv), describing the core-valence correlation energy has been constructed as a linear combination of ɛLY Pcorr(ρc), ɛV WN5corr(ρc, ρv), ɛPBEcorr(ρc, ρv), ɛSlaterex(ρc, ρv), ɛHCTHex(ρc, ρv), ɛHFex(ρc, ρv), and F CV -DFT (" separators=" N i , Z i ) , a function of the nuclear charges. This functional, with 6 adjustable parameters, reproduces (±0.27 kcal/mol rms error) a benchmark set of 194 chemical energy changes including 9 electron affinities, 18 ionization potentials, and 167 total atomization energies covering the first- and second-rows of the periodic table. This is almost twice the rms error (±0.16 kcal/mol) obtained with CCSD(T)/MTsmall calculations, but less than half the rms error (±0.65 kcal/mol) obtained with MP2/GTlargeXP calculations, and somewhat smaller than the rms error (±0.39 kcal/mol) obtained with CCSD/MTsmall calculations. The largest positive and negative errors from ɛCV-DFT(ρc, ρv) were 0.88 and -0.75 kcal/mol with the set of 194 core-valence energy changes ranging from +3.76 kcal/mol for the total atomization energy of propyne to -9.05 kcal/mol for the double ionization of Mg. Evaluation of the ɛCV-DFT(ρc, ρv) functional requires less time than a single SCF iteration, and the accuracy is adequate for any model chemistry based on the CCSD(T) level of theory.

  7. Metal–Metal Bonding in Uranium–Group 10 Complexes

    PubMed Central

    2016-01-01

    Heterobimetallic complexes containing short uranium–group 10 metal bonds have been prepared from monometallic IUIV(OArP-κ2O,P)3 (2) {[ArPO]− = 2-tert-butyl-4-methyl-6-(diphenylphosphino)phenolate}. The U–M bond in IUIV(μ-OArP-1κ1O,2κ1P)3M0, M = Ni (3–Ni), Pd (3–Pd), and Pt (3–Pt), has been investigated by experimental and DFT computational methods. Comparisons of 3–Ni with two further U–Ni complexes XUIV(μ-OArP-1κ1O,2κ1P)3Ni0, X = Me3SiO (4) and F (5), was also possible via iodide substitution. All complexes were characterized by variable-temperature NMR spectroscopy, electrochemistry, and single crystal X-ray diffraction. The U–M bonds are significantly shorter than any other crystallographically characterized d–f-block bimetallic, even though the ligand flexes to allow a variable U–M separation. Excellent agreement is found between the experimental and computed structures for 3–Ni and 3–Pd. Natural population analysis and natural localized molecular orbital (NLMO) compositions indicate that U employs both 5f and 6d orbitals in covalent bonding to a significant extent. Quantum theory of atoms-in-molecules analysis reveals U–M bond critical point properties typical of metallic bonding and a larger delocalization index (bond order) for the less polar U–Ni bond than U–Pd. Electrochemical studies agree with the computational analyses and the X-ray structural data for the U–X adducts 3–Ni, 4, and 5. The data show a trend in uranium–metal bond strength that decreases from 3–Ni down to 3–Pt and suggest that exchanging the iodide for a fluoride strengthens the metal–metal bond. Despite short U–TM (transition metal) distances, four other computational approaches also suggest low U–TM bond orders, reflecting highly transition metal localized valence NLMOs. These are more so for 3–Pd than 3–Ni, consistent with slightly larger U–TM bond orders in the latter. Computational studies of the model systems (PH3)3MU(OH)3I (M = Ni, Pd) reveal longer and weaker unsupported U–TM bonds vs 3. PMID:26942560

  8. Metal-Metal Bonding in Uranium-Group 10 Complexes.

    PubMed

    Hlina, Johann A; Pankhurst, James R; Kaltsoyannis, Nikolas; Arnold, Polly L

    2016-03-16

    Heterobimetallic complexes containing short uranium-group 10 metal bonds have been prepared from monometallic IU(IV)(OAr(P)-κ(2)O,P)3 (2) {[Ar(P)O](-) = 2-tert-butyl-4-methyl-6-(diphenylphosphino)phenolate}. The U-M bond in IU(IV)(μ-OAr(P)-1κ(1)O,2κ(1)P)3M(0), M = Ni (3-Ni), Pd (3-Pd), and Pt (3-Pt), has been investigated by experimental and DFT computational methods. Comparisons of 3-Ni with two further U-Ni complexes XU(IV)(μ-OAr(P)-1κ(1)O,2κ(1)P)3Ni(0), X = Me3SiO (4) and F (5), was also possible via iodide substitution. All complexes were characterized by variable-temperature NMR spectroscopy, electrochemistry, and single crystal X-ray diffraction. The U-M bonds are significantly shorter than any other crystallographically characterized d-f-block bimetallic, even though the ligand flexes to allow a variable U-M separation. Excellent agreement is found between the experimental and computed structures for 3-Ni and 3-Pd. Natural population analysis and natural localized molecular orbital (NLMO) compositions indicate that U employs both 5f and 6d orbitals in covalent bonding to a significant extent. Quantum theory of atoms-in-molecules analysis reveals U-M bond critical point properties typical of metallic bonding and a larger delocalization index (bond order) for the less polar U-Ni bond than U-Pd. Electrochemical studies agree with the computational analyses and the X-ray structural data for the U-X adducts 3-Ni, 4, and 5. The data show a trend in uranium-metal bond strength that decreases from 3-Ni down to 3-Pt and suggest that exchanging the iodide for a fluoride strengthens the metal-metal bond. Despite short U-TM (transition metal) distances, four other computational approaches also suggest low U-TM bond orders, reflecting highly transition metal localized valence NLMOs. These are more so for 3-Pd than 3-Ni, consistent with slightly larger U-TM bond orders in the latter. Computational studies of the model systems (PH3)3MU(OH)3I (M = Ni, Pd) reveal longer and weaker unsupported U-TM bonds vs 3. PMID:26942560

  9. The law of constant rejection. [chemical bonding in crystals

    NASA Technical Reports Server (NTRS)

    Philpotts, J. A.

    1978-01-01

    Improvements in analytical technique, study of multielement partitioning in natural systems, and improvements in ionic radius values have permitted construction of Onuma diagrams, in which the logarithm of partition coefficient is plotted versus ionic radius. The optimum radii, corresponding to crystallographic sites, do change in response to changes in major element composition for any particular mineral-type. In natural systems elements compete for sites rather than substituting for another element. It is proposed on empirical grounds, for equilibrium ionic bonding, that Onuma diagram curves for a particular lattice site are parabolic near optimum radius, linear elsewhere, parallel for different valences, and mirror images on opposite sides of optimum. Deviations may be due to overlapping peaks, liquid structure, polyvalence, bonding differences, contamination, kinetics, alteration, etc. However, dominant crystal-chemical control is indicated.

  10. Metal to metal multiple bonds in ordered assemblies

    PubMed Central

    Chisholm, Malcolm H.

    2007-01-01

    The synthesis and properties of metalmetal (MM) quadruply bonded compounds of molybdenum and tungsten in liquid crystalline phases are described. Covalently linked MM quadruply bonded complexes, dimers of dimers, are shown to give rise to mixed valence complexes upon oxidation and the degree of electron delocalization is shown to be correlated with the M2? bridge ? interactions. Class III behavior or complete delocalization is observed to M2 to M2 distances of up to 14 ?. When the M2 unit is attached to oligothiophenes via a carboxylate tether, the photophysical properties of the thienyl units are greatly modified due to M2?thienyl ? conjugation and spinorbit coupling. This leads to long-lived emissive states and electroluminescence in solid-state devices. PMID:17299047

  11. Beryllium dimer: a bond based on non-dynamical correlation.

    PubMed

    El Khatib, Muammar; Bendazzoli, Gian Luigi; Evangelisti, Stefano; Helal, Wissam; Leininger, Thierry; Tenti, Lorenzo; Angeli, Celestino

    2014-08-21

    The bond nature in beryllium dimer has been theoretically investigated using high-level ab initio methods. A series of ANO basis sets of increasing quality, going from sp to spdf ghi contractions, has been employed, combined with HF, CAS-SCF, CISD, and MRCI calculations with several different active spaces. The quality of these calculations has been checked by comparing the results with valence Full-CI calculations, performed with the same basis sets. It is shown that two quasi-degenerated partly occupied orbitals play a crucial role to give a qualitatively correct description of the bond. Their nature is similar to that of the edge orbitals that give rise to the quasi-degenerated singlet-triplet states in longer beryllium chains. PMID:24866399

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

    PubMed Central

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

    2011-01-01

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

  13. Effects of Emotional Valence and Arousal on Recollective and Nonrecollective Recall

    ERIC Educational Resources Information Center

    Gomes, Carlos F. A.; Brainerd, Charles J.; Stein, Lilian M.

    2013-01-01

    The authors investigated the effects of valence and arousal on memory using a dual-process model that quantifies recollective and nonrecollective components of recall without relying on metacognitive judgments to separate them. The results showed that valenced words increased reconstruction (a component of nonrecollective retrieval) relative to

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

    ERIC Educational Resources Information Center

    Nakanishi, Masayuki

    1988-01-01

    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

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

    ERIC Educational Resources Information Center

    Sypniewski, Bernard Paul

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

  16. PREPARATION OF STANDARDS FOR VALENCE STATE MEASUREMENT BY X-RAY FLUORESCENCE

    EPA Science Inventory

    The preparation and characterization of standard samples representing several valence states for sulfur, vanadium, and chromium are described. The standards will be used by the U.S. Environmental Protection Agency to investigate the potential for determining valence state by high...

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

    ERIC Educational Resources Information Center

    Jansari, Ashok; Rodway, Paul; Goncalves, Salvador

    2011-01-01

    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

  18. 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...

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

    ERIC Educational Resources Information Center

    Jansari, Ashok; Rodway, Paul; Goncalves, Salvador

    2011-01-01

    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…

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

    PubMed

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

    2011-01-01

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

  1. Valence Change Driven by Constituent Element Substitution in the Mixed-Valence Quasicrystal and Approximant Au-Al-Yb

    NASA Astrophysics Data System (ADS)

    Matsukawa, Shuya; Tanaka, Katsumasa; Nakayama, Mika; Deguchi, Kazuhiko; Imura, Keiichiro; Takakura, Hiroyuki; Kashimoto, Shiro; Ishimasa, Tsutomu; Sato, Noriaki K.

    2014-03-01

    Quantum criticality has been considered to be specific to crystalline materials such as heavy fermions. Very recently, however, the Tsai-type quasicrystal Au51Al34Yb15 has been reported to show unusual quantum critical behavior. To obtain a deeper understanding of this new material, we have searched for other Tsai-type cluster materials. Here, we report that the metal alloys Au44Ga41Yb15 and Ag47Ga38Yb15 are members of the 1/1 approximant to the Tsai-type quasicrystal and that both possess no localized magnetic moment. We suggest that the Au-Al-Yb system is located near the border of the divalent and trivalent states of the Yb ion; we also discuss a possible origin of the disappearance of magnetism, associated with the valence change, by the substitution of the constituent elements.

  2. Valence fluctuations of europium in the boride Eu4Pd29+x B8.

    PubMed

    Gumeniuk, Roman; Schnelle, Walter; Ahmida, Mahmoud A; Abd-Elmeguid, Mohsen M; Kvashnina, Kristina O; Tsirlin, Alexander A; Leithe-Jasper, Andreas; Geibel, Christoph

    2016-03-23

    We synthesized a high-quality sample of the boride Eu4Pd29+x B8 (x  =  0.76) and studied its structural and physical properties. Its tetragonal structure was solved by direct methods and confirmed to belong to the Eu4Pd29B8 type. All studied physical properties indicate a valence fluctuating Eu state, with a valence decreasing continuously from about 2.9 at 5 K to 2.7 at 300 K. Maxima in the T dependence of the susceptibility and thermopower at around 135 K and 120 K, respectively, indicate a valence fluctuation energy scale on the order of 300 K. Analysis of the magnetic susceptibility evidences some inconsistencies when using the ionic interconfigurational fluctuation (ICF) model, thus suggesting a stronger relevance of hybridization between 4f and valence electrons compared to standard valence-fluctuating Eu systems. PMID:26895077

  3. Dissociated representations of irritation and valence in human primary olfactory cortex.

    PubMed

    Zelano, C; Montag, J; Johnson, B; Khan, R; Sobel, N

    2007-03-01

    Irritation and negative valence are closely associated in perception. However, these perceptual aspects can be dissociated in olfaction where irritation can accompany both pleasant and unpleasant odorants. Whereas the sensation of odor reflects transduction at olfactory receptors, irritation reflects concurrent transduction of the odorant at trigeminal receptors. Thus a stimulus can be either a pure olfactant activating the olfactory receptors only or a bimodal odorant activating both types of receptors. Using event-related functional magnetic resonance imaging and a 2 x 2 experimental design contrasting odorant valence (pleasant/unpleasant) and odorant type (pure olfactant/bimodal) we found activity in piriform cortex to be associated with valence, and not type, of odors. In contrast, activity in the olfactory tubercle was associated with type, and not valence, of odors. Importantly, this was found when perceived intensity was held equal across odorants. These findings suggest that dissociable neural substrates subserve the encoding of irritation and valence in olfaction. PMID:17215504

  4. Identifying words that emerge into consciousness: Effects of word valence and unconscious previewing.

    PubMed

    Prioli, Simone C; Kahan, Todd A

    2015-09-01

    Words with negative valence capture attention and this increase in attentional resources typically enhances perceptual processing. Recently, data using continuous flash suppression (CFS) appear to contradict this. In prior research when Chinese words were unconsciously presented in CFS and contrast was raised until the word was identified, RTs to identify words with negative valence were slower than RTs to words with neutral valence. This result might be limited to situations where a logographic writing system is used and could reflect a type of cognitive aftereffect where previewing the word causes habituation. Data (N=60) indicate that results generalize from a logographic (Chinese) to an orthographic writing system (English). In addition, when words were previewed in CFS RTs were slowed for words with negative valence relative to words with neutral valence and this was reversed when words were shown binocularly. Implications for theories of unconscious word processing and cognitive aftereffects are discussed. PMID:25982055

  5. Valence fluctuations of europium in the boride Eu4Pd29+x B8

    NASA Astrophysics Data System (ADS)

    Gumeniuk, Roman; Schnelle, Walter; Ahmida, Mahmoud A.; Abd-Elmeguid, Mohsen M.; Kvashnina, Kristina O.; Tsirlin, Alexander A.; Leithe-Jasper, Andreas; Geibel, Christoph

    2016-03-01

    We synthesized a high-quality sample of the boride Eu4Pd29+x B8 (x  =  0.76) and studied its structural and physical properties. Its tetragonal structure was solved by direct methods and confirmed to belong to the Eu4Pd29B8 type. All studied physical properties indicate a valence fluctuating Eu state, with a valence decreasing continuously from about 2.9 at 5 K to 2.7 at 300 K. Maxima in the T dependence of the susceptibility and thermopower at around 135 K and 120 K, respectively, indicate a valence fluctuation energy scale on the order of 300 K. Analysis of the magnetic susceptibility evidences some inconsistencies when using the ionic interconfigurational fluctuation (ICF) model, thus suggesting a stronger relevance of hybridization between 4f and valence electrons compared to standard valence-fluctuating Eu systems.

  6. The Halogen Bond

    PubMed Central

    2016-01-01

    The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design. PMID:26812185

  7. The Halogen Bond.

    PubMed

    Cavallo, Gabriella; Metrangolo, Pierangelo; Milani, Roberto; Pilati, Tullio; Priimagi, Arri; Resnati, Giuseppe; Terraneo, Giancarlo

    2016-02-24

    The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design. PMID:26812185

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

    PubMed

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

    2010-01-01

    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

  9. Skin-depth lattice strain, core-level trap depression and valence charge polarization of Al surfaces

    NASA Astrophysics Data System (ADS)

    Wang, Yan; Bo, Maolin; Liu, Yonghui; Guo, Yongling; Wang, Haibin; Yue, Jian; Huang, Yongli

    2016-01-01

    Clarifying the origin for surface core-level shift (SCLS) and gaining quantitative information regarding the coordination-resolved local strain, binding energy (BE) shift and cohesive energy change have been a challenge. Here, we show that a combination of the bond order-length-strength (BOLS) premise, X-ray photoelectron spectroscopy (XPS) and the ab initio density functional theory (DFT) calculations of aluminum (Al) 2p3/2 energy shift of Al surfaces has enabled us to derive such information, namely, (i) the 2p3/2 energy of an isolated Al atom (72.146 ± 0.003eV) and its bulk shift (0.499 eV); (ii) the skin lattice contracts by up to 12.5% and the BE density increases by 70%; and (iii) the cohesive energy drops up to 38%. It is affirmed that the shorter and stronger bonds between under-coordinated atoms provide a perturbation to the Hamiltonian and hence lead to the local strain, quantum entrapment and valence charge polarization. Findings should help in understanding the phenomena of surface pre-melting and skin-high elasticity, in general.

  10. Valence-to-Core X-Ray Emission Spectroscopy as a Tool for Investigation of Organometallic Systems

    NASA Astrophysics Data System (ADS)

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

    2007-02-01

    The fine structure of X-ray emission satellite lines just below the Fermi level (K? satellite lines), which arise from transitions from valence bands to the core 1s level in 3d transition metals, is a developing technique and the full potential is not well known or understood. On the basis of DFT calculations for some theoretical model complexes that are relevant in bioinorganic chemistry we show that the method can be used to distinguish bonds of the metal atom with different light atoms O/N/C even if the coordination geometries are exactly the same, which is not possible using EXAFS or XANES spectroscopy. Moreover the method is sensitive to the bonding of H to the ligands, which allows to discriminate, for example, between OH- and water near the metal. Both these aspects clearly demonstrate that the K? satellite lines yield information that is complementary to traditional X-ray absorption spectroscopy. Good agreement between theoretical and experimental spectra for a complex Mn system was also achieved.

  11. Structure and bonding of [(SIPr)AgX] (X = Cl, Br, I and OTf).

    PubMed

    Wong, Valerie H L; White, Andrew J P; Hor, T S Andy; Hii, King Kuok Mimi

    2015-12-01

    A series of iso-structural complexes [(SIPr)AgX] (X = Cl, Br, I, OTf; SIPr = 1,3-bis(2,6-diisopropylphenyl)imidazolidene) were synthesised, including the first example of a N-heterocyclic carbene silver(i) complex containing an O-bound triflate. Bond Energy Dissociation and Natural Orbitals for Chemical Valence bond analyses (BEDA & ETS-NOCV) revealing a significant NHC ? M ?-back-donation, which influences the stability and sigma-donicity of these complexes. PMID:26489888

  12. Bonding aerogels with polyurethanes

    SciTech Connect

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

    1989-11-01

    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.

  13. Crystal structure of a mixed-valence μ-oxide Sn12 cluster

    PubMed Central

    Kireenko, Marina M.; Zaitsev, Kirill V.; Karlov, Sergey S.; Egorov, Mikhail P.; Churakov, Andrei V.

    2014-01-01

    The mixed-valence μ-oxide Sn12 cluster, deca­carbonyl­tetra-μ4-oxido-hexa-μ3-oxido-tetra­kis­[μ-2,2′-(pyridine-2,6-di­yl)bis(1,1-di­phenyl­ethano­lato)]deca­tin(II)ditin(IV)dimolyb­denum(O)(2 Mo—Sn) toluene hepta­solvate, [Mo2Sn12(C33H27NO2)4O10(CO)10]·7C7H8, has a crystallographically imposed inversion centre. The asymmetric unit also contains three and a half toluene solvent mol­ecules, one of which is disordered about a centre of symmetry. The complex mol­ecule comprises six distinct Sn atom species with four different coordination numbers, namely 3, 4, 5, and 6. The SnII atoms forming the central Sn10O10 core adopt distorted trigonal–pyramidal, square-pyramidal and octa­hedral coordination geometries provided by the μ-oxide atoms and by the O- and N-donor atoms of two pyridinedi­ethano­late ligands. The terminal SnIV atoms have distorted trigonal–bipyramidal coordination geometries, with a μ4-oxide atom and the N atom of a pyridinedi­ethano­late ligand occupying the axial positions, and the Mo atom of a Mo(CO)5 group and the alk­oxy O atoms of a ligand forming the equatorial plane. In the crystal, weak intra- and inter­molecular C—H⋯O hydrogen bonds are observed. PMID:25484784

  14. Core-Valence Auger Spectra of the Simple Metals.

    NASA Astrophysics Data System (ADS)

    Davis, Linda Rae

    A comprehensive study of the core-valence-valence (CVV) Auger line shapes for the simple metals, Li, Be, Na, Mg, and Al, is presented. Calculations of these line shapes are performed with a static many-body model which treats the (static) screening of a core hole by conduction electrons with a phenomenological potential. Our model is applicable only to the simple metals, because free-electron theory is used to describe the conduction electrons. The model is implemented with a finite-particle, determinantal approach, and many-body Auger matrix elements are calculated explicitly using a local approximation. The many-body effects which arise from the core-conduction interaction are treated exactly within the model. The dependence of the model line shapes (i) on parameters specifying the metal and core level, (ii) on approximation of the model, and (iii) on the many-body effects produced by the core -conduction interaction are examined in detail. Also, model calculations of the simple-metal CVV spectra for which data exist are presented. Empirical fits of the model calculations to reported data are achieved for the Li(KVV), Be(KVV), Mg(L(,2,3)VV), and Al(L(,2,3)VV) spectra. In all of these cases, the screening of the core hole by conduction electrons is found to have both s-like and p-like character. One -electron and static many-body calculations have also been performed by other authors for some of the simple-metal spectra. Our model and results are compared to those from the other calculations. Although one-electron theory has reproduced several of the reported simple-metal line shapes, our calculations are the only many-body calculations to produce line shapes in agreement with data. Model calculations for the final reported spectrum, the Mg(KVV), are not presented, because the Mg K core hole is not sufficiently long-lived for our model to be valid. Our expectations concerning the unreported Na(L(,2,3)VV) spectrum are discussed. From our empirical fits and model study, we conclude that the many-body effects which are introduced by the core-conduction interaction, although weak, significantly influence the CVV line shapes of the simple metals. This conclusion is suggestive of the inadequacy of the one-electron theory of CVV line shapes, even in cases of simple-metal spectra.

  15. Orthodontic bonded retainers.

    PubMed

    Butler, Jonathan; Dowling, Paul

    2005-01-01

    Retention is usually necessary following orthodontic treatment to overcome the elastic recoil of the periodontal supporting fibres and to allow remodelling of the alveolar bone. The degree of change is variable and largely unpredictable. Bonded lingual retainers have been shown to be an effective means of retaining aligned anterior teeth in the post-treatment position in the long term. Two basic designs of lingual bonded retainers are currently in use. Rigid mandibular canine-to-canine retainers are attached to the canines only. They are effective in maintaining intercanine width but less so in preventing individual tooth rotations. Flexible spiral wire retainers are bonded to each tooth in the segment, their flexibility allowing for physiological movement of the teeth. This design is more effective at preventing rotation of the bonded teeth. Failure of bonded retainers may occur at the wire-composite interface, at the adhesive-enamel interface or as a stress fracture of the wire. Failure of a retainer may lead to unwanted tooth movement. In many cases it will be possible to repair the appliance in the mouth. However, in some instances it will be necessary to replace the retainer. A disadvantage of fixed retainers is that they complicate oral hygiene procedures, and favour the accumulation of plaque and calculus. Despite this, the presence of a bonded retainer appears to cause no increase in incidence of caries or periodontal disease. Use of interdental cleaning aids is required to ensure adequate oral hygiene. PMID:15789987

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

    NASA Astrophysics Data System (ADS)

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

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

  17. The unique bonding characteristics of beryllium and the Group IIA metals

    NASA Astrophysics Data System (ADS)

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

    2011-04-01

    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.

  18. Heavy-Fermion Valence-Bond Liquids in Ultracold Atoms: Cooperation of the Kondo Effect and Geometric Frustration.

    PubMed

    Isaev, L; Rey, A M

    2015-10-16

    We analyze a microscopic mechanism behind the coexistence of a heavy Fermi liquid and geometric frustration in Kondo lattices. We consider a geometrically frustrated periodic Anderson model and demonstrate how orbital fluctuations lead to a Kondo-screened phase in the limit of extreme strong frustration when only local singlet states participate in the low-energy physics. We also propose a setup to realize and study this exotic state with SU(3)-symmetric alkaline-earth cold atoms. PMID:26550882

  19. Heavy-Fermion Valence-Bond Liquids in Ultracold Atoms: Cooperation of the Kondo Effect and Geometric Frustration

    NASA Astrophysics Data System (ADS)

    Isaev, L.; Rey, A. M.

    2015-10-01

    We analyze a microscopic mechanism behind the coexistence of a heavy Fermi liquid and geometric frustration in Kondo lattices. We consider a geometrically frustrated periodic Anderson model and demonstrate how orbital fluctuations lead to a Kondo-screened phase in the limit of extreme strong frustration when only local singlet states participate in the low-energy physics. We also propose a setup to realize and study this exotic state with S U (3 ) -symmetric alkaline-earth cold atoms.

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

    PubMed Central

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

    2010-01-01

    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. PMID:20547393

  1. Manipulating the contribution of approach-avoidance to the perturbation of economic choice by valence

    PubMed Central

    Wright, Nicholas D.; Morris, Laurel S.; Guitart-Masip, Marc; Dolan, Raymond J.

    2013-01-01

    Economic choices are strongly influenced by whether potential outcomes entail gains or losses. We examined this influence of outcome valence in an economic risk task. We employed three experiments based on our task, each of which provided novel findings, and which together better characterize and explain how outcome valence influences risky choice. First, we found that valence perturbed an individual's choices around that individual's base-level of risk-taking, a base-level consistent across time, and context. Second, this perturbation by valence was highly context dependent, emerging when valence was introduced as a dimension within a decision-making setting, and being reversed by a change in task format (causing more gambling for gains than losses and the reverse). Third, we show this perturbation by valence is explicable by low-level approach-avoidance processes, an hypothesis not previously tested by a causal manipulation. We revealed such an effect, where individuals were less disposed to choose a riskier option with losses when they had to approach (go) as opposed to avoid (nogo) that option. Our data show valence perturbs an individual's choices independently of the impact of risk, and causally implicate approach-avoidance processes as important in shaping economic choice. PMID:24363641

  2. From semantics to feelings: how do individuals with schizophrenia rate the emotional valence of words?

    PubMed

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

    2012-01-01

    Schizophrenia is characterized by both emotional and language abnormalities. However, in spite of reports of preserved evaluation of valence of affective stimuli, such as pictures, it is less clear how individuals with schizophrenia assess verbal material with emotional valence, for example, the overall unpleasantness/displeasure relative to pleasantness/attraction of a word. This study aimed to investigate how schizophrenic individuals rate the emotional valence of adjectives, when compared with a group of healthy controls. One hundred and eighty-four adjectives differing in valence were presented. These adjectives were previously categorized as "neutral," "positive" (pleasant), or "negative" (unpleasant) by five judges not participating in the current experiment. Adjectives from the three categories were matched on word length, frequency, and familiarity. Sixteen individuals with schizophrenia diagnosis and seventeen healthy controls were asked to rate the valence of each word, by using a computerized version of the Self-Assessment Manikin (Bradley and Lang, 1994). Results demonstrated similar ratings of emotional valence of words, suggesting a similar representation of affective knowledge in schizophrenia, at least in terms of the valence dimension. PMID:22966437

  3. The electronic properties of mixed valence hydrated europium chloride thin film.

    PubMed

    Silly, M G; Charra, F; Lux, F; Lemercier, G; Sirotti, F

    2015-07-28

    We investigate the electronic properties of a model mixed-valence hydrated chloride europium salt by means of high resolution photoemission spectroscopy (HRPES) and resonant photoemission spectroscopy (RESPES) at the Eu 3d ? 4f and 4d ? 4f transitions. From the HRPES spectra, we have determined that the two europium oxidation states are homogeneously distributed in the bulk and that the hydrated salt film is exempt from surface mixed valence transition. From the RESPES spectra, the well separated resonant contributions characteristic of divalent and trivalent europium species (4f(6) and 4f(7) final states, respectively) are accurately extracted and quantitatively determined from the resonant features measured at the two edges. The partial absorption yield spectra, obtained by integrating the photoemission intensity in the valence-band region, can be well reproduced by atomic multiplet calculation at the M(4,5) (3d-4f) absorption edge and by an asymmetric Fano-like shape profile at the N(4,5) (4d-4f) absorption edge. The ratio of Eu(2+) and Eu(3+) species measured at the two absorption edges matches with the composition of the mixed valence europium salt as determined chemically. We have demonstrated that the observed spectroscopic features of the mixed valence salt are attributed to the mixed-valence ground state rather than surface valence transition. HRPES and RESPES spectra provide reference spectra for the study of europium salts and their derivatives. PMID:26105214

  4. Valence Auger decay following 3 s photoionization in potassium

    NASA Astrophysics Data System (ADS)

    Palaudoux, J.; Sheinerman, S.; Soronen, J.; Huttula, S.-M.; Huttula, M.; Jnkl, K.; Andric, L.; Ito, K.; Lablanquie, P.; Penent, F.; Bizau, J.-M.; Guilbaud, S.; Cubaynes, D.

    2015-07-01

    We have studied photoionization in the inner valence 3 s subshell of K and the spectroscopic properties of the two 3 s-1(1S) and (3S) resulting states. Similar to the Rb and Cs cases, the lifetime widths of the (1S) and (3S) states are found to be markedly different, due to the electron correlation effects. The main part of the study deals with the subsequent Auger decay of the 3 s-1 states, which have the particularity to involve low energy (5 eV ) Auger electrons. A magnetic bottle spectrometer with a multicoincidence technique has been used to observe and filter the Auger spectra with respect to the K2 + final state. The evolution of these Auger spectra has been investigated near the ionization threshold. They show strong post-collision interaction (PCI) effects, which are well reproduced by semiclassical and eikonal models. They reveal the importance of the photoelectron-Auger-electron interaction associated with these low energy Auger electrons.

  5. Electrochemical modification of Surface valence - Cr precipitates on LSCF surfaces

    NASA Astrophysics Data System (ADS)

    Finsterbusch, Martin; Schaefer, J. A.; Eigenbrodt, B. C.; Walker, R. A.; Lussier, A.; Idzerda, Y. U.

    2010-10-01

    Interactions of gaseous Cr contaminants with the perovskite material LSCF (La0.6Sr0.4Co0.2Fe0.8O3) commonly used as cathode for Solid Oxide Fuel Cells (SOFC) were investigated by means of X-ray absorption Spectroscopy (XAS) and Raman Spectroscopy. The setup consisted of a model cell with a GDC (Gd0.1Ce0.9O2) electrolyte pellet with a LSCF cathode on both sides in a Cr containing sample holder. The chemical structure and valency of the precipitate were found to depend on the electrochemical conditions of the surface, particularly on the bias voltage and not the total current density present in the cell. Cr^6+ spinels were found to form under high bias voltage, while under low bias voltage mostly Cr2O3 was formed. The influence of the contact material (Au vs. Ag) and the effect of quenching were investigated by Raman Spectroscopy under operating conditions (800 C in air). XAS unlike EDS, XRD or XPS is a precise and valuable tool for the direct measurement of the oxidation state of transition metals in compounds if the concentration is low (contamination) and the substrate is porous.

  6. Toxoplasma gondii infection enhances the kairomonal valence of rat urine

    PubMed Central

    Vasudevan, Anand; Vyas, Ajai

    2014-01-01

    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. PMID:25075300

  7. The Effect of Action Valence and Race on 3- to 8-Year-Old Children's Social Cognitive Judgments

    ERIC Educational Resources Information Center

    Arterberry, Martha E.; Hughes, Brittany C.; Mejia, Barbara

    2015-01-01

    The present study investigated children's judgments of actions as a function of the valence of the action and the race of the actor. Three- to 8-year-old children were read an illustrated storybook in which 1 character did not share (a negatively valenced action) and the other character was helpful (a positively valenced action). The race of the…

  8. The Effect of Action Valence and Race on 3- to 8-Year-Old Children's Social Cognitive Judgments

    ERIC Educational Resources Information Center

    Arterberry, Martha E.; Hughes, Brittany C.; Mejia, Barbara

    2015-01-01

    The present study investigated children's judgments of actions as a function of the valence of the action and the race of the actor. Three- to 8-year-old children were read an illustrated storybook in which 1 character did not share (a negatively valenced action) and the other character was helpful (a positively valenced action). The race of the

  9. Positively Valenced Stimuli Facilitate Creative Novel Metaphoric Processes by Enhancing Medial Prefrontal Cortical Activation

    PubMed Central

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

    2013-01-01

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

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

    SciTech Connect

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

    2014-05-28

    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.

  11. Formation of unprecedented actinidecarbon triple bonds in uranium methylidyne molecules

    PubMed Central

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

    2007-01-01

    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. PMID:18024591

  12. Asymmetric bifurcated halogen bonds.

    PubMed

    Novk, Martin; Foroutan-Nejad, Cina; Marek, Radek

    2015-03-01

    Halogen bonding (XB) is being extensively explored for its potential use in advanced materials and drug design. Despite significant progress in describing this interaction by theoretical and experimental methods, the chemical nature remains somewhat elusive, and it seems to vary with the selected system. In this work we present a detailed DFT analysis of three-center asymmetric halogen bond (XB) formed between dihalogen molecules and variously 4-substituted 1,2-dimethoxybenzene. The energy decomposition, orbital, and electron density analyses suggest that the contribution of electrostatic stabilization is comparable with that of non-electrostatic factors. Both terms increase parallel with increasing negative charge of the electron donor molecule in our model systems. Depending on the orientation of the dihalogen molecules, this bifurcated interaction may be classified as '?-hole - lone pair' or '?-hole - ?' halogen bonds. Arrangement of the XB investigated here deviates significantly from a recent IUPAC definition of XB and, in analogy to the hydrogen bonding, the term bifurcated halogen bond (BXB) seems to be appropriate for this type of interaction. PMID:25656525

  13. Strength of Chemical Bonds

    NASA Technical Reports Server (NTRS)

    Christian, Jerry D.

    1973-01-01

    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.

  14. Surface analysis in composite bonding

    NASA Technical Reports Server (NTRS)

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

    1982-01-01

    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.

  15. ?-Hole aerogen bonding interactions.

    PubMed

    Bauz, Antonio; Frontera, Antonio

    2015-10-14

    In this manuscript we combine high level ab initio calculations (RI-MP2/aug-cc-pVTZ) and the analysis of several crystal structures to demonstrate the existence of ?-hole aerogen bonding interactions in Xe(iv) compounds. The ability of XeF4 and Xe(OMe)4 to interact with electron rich molecules is rationalized using several computational tools, including molecular electrostatic potential surfaces, energetic and geometric features of the complexes and "atoms in molecules" (AIM) and Natural Bond Orbital (NBO) analyses. We have found support for the ?-hole interaction involving the xenon atom from the solid state architecture of several X-ray structures retrieved from the crystal structural depot. Particularly, ?-hole aerogen bonding interactions are quite common in the solid state of Xe(IV) compounds. PMID:26252726

  16. Insulation bonding test system

    NASA Technical Reports Server (NTRS)

    Beggs, J. M.; Johnston, G. D.; Coleman, A. D.; Portwood, J. N.; Saunders, J. M.; Redmon, J. W.; Porter, A. C. (Inventor)

    1984-01-01

    A method and a system for testing the bonding of foam insulation attached to metal is described. The system involves the use of an impacter which has a calibrated load cell mounted on a plunger and a hammer head mounted on the end of the plunger. When the impacter strikes the insulation at a point to be tested, the load cell measures the force of the impact and the precise time interval during which the hammer head is in contact with the insulation. This information is transmitted as an electrical signal to a load cell amplifier where the signal is conditioned and then transmitted to a fast Fourier transform (FFT) analyzer. The FFT analyzer produces energy spectral density curves which are displayed on a video screen. The termination frequency of the energy spectral density curve may be compared with a predetermined empirical scale to determine whether a igh quality bond, good bond, or debond is present at the point of impact.

  17. Theory of Auger electron and appearance-potential spectroscopy from solids with partially filled valence bands: Effects of valence-band-core interaction

    NASA Astrophysics Data System (ADS)

    Potthoff, M.; Braun, J.; Borstel, G.; Nolting, W.

    1993-05-01

    CVV Auger electron and appearance-potential spectra of solids are well known to exhibit strong satellite features depending on the ratio of on-site Coulomb interaction among the valence-band electrons U and the width of the free Bloch band W. We present a theory that additionally includes the effects of the Coulomb interaction between the valence-band electrons and the core electrons Uc. The spectra are influenced by the screening of the core hole in the initial state for Auger electron spectroscopy (AES), the sudden response of the valence-band electrons after the destruction of the core hole and, for appearance-potential spectroscopy (APS), by the scattering at the core hole in the final state. These effects become important especially for systems with partially filled energy bands. For APS, however, the Uc interaction already yields nontrivial effects for the limiting case of a completely empty valence band. The localized core hole implies a breakdown of translational symmetry in the distribution of the valence-band electrons, which renders the calculation more difficult. But, extending the theory to finite temperatures, we will show that the translational symmetry may be reestablished in a formal way. Both the AES and APS intensities are directly related to a proper three-particle spectral density that exactly reflects the crystal periodicity. Within the framework of the single-band Hubbard model, which is extended to include the Uc interaction, we calculate the three-particle spectral density in a generalized ladder approximation. The Uc interaction is treated by means of perturbation theory. We develop the theory for the zeroth- and first-order contributions and look at the interesting limiting cases of a completely filled and empty valence band.

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

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

    The bond dissociation energies (De) of C2H2, C2H4, C2H6, N2, N2H2, and N2H4 are studied at various levels of correlation treatment. The convergence of De 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) De 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. 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.

  19. Non-linear valence electron dynamics in metallic clusters

    NASA Astrophysics Data System (ADS)

    Calvayrac, F.

    This work deals with the response of the valence electrons of simple metal clusters to various excitations, in a purely dynamical context. It is related to various recent experiments where the methods based on linear response fail. The electronic motion is solved in direct time, the wavefunctions being discretized on an evenly spaced grid. The theoretical framework is the time dependent density functional theory, restricted to a version local in time and space (LSDA). The other parts of the clusters are either a jellium or an explicit ionic background exerting local or non-local pseudopotentials. The ionic dynamics is discussed, as well as the relevance of various observables. The corresponding numerical techniques are given: either a selfconsistent Crank-Nicholson method is used, approximated by an alternate propagation in every space direction, or a method alternating between direct and Fourier space. The equations suggest a parallel treatment. Several examples of application are given. The case of Na9+ is thoroughly discussed, then the less simple case of Na11+. Spectra obtained for sodium clusters deposited on sodium chlorine surfaces are shown. An example of a simulation with a moving ionic background is handled: the transfer to the ionic degrees of freedom of the energy deposited in a twelve sodium atoms cluster by a femtosecond laser pulse is discussed. The electronic resonance spectrum for a linear carbon cluster C5 is then given. In the conclusion, the work is discussed as well as possible improvements and developments from the theoretical or numerical point of view. Ce travail aborde la rponse des lectrons de valence d'agrgats de mtaux simples diverses excitations, dans un contexte purement dynamique, en relation avec diverses expriences rcentes que les mthodes fondes sur la rponse linaire sont incapables d'aborder. Le mouvement de ces lectrons est rsolu directement en temps, leurs fonctions d'onde tant discrtises sur une grille rgulire en espace. Le cadre thorique repose sur la thorie de la fonctionnelle de la densit dpendant du temps, restreinte une version locale en temps et en espace (LSDA). Les autres constituants des agrgats sont soit un jellium, soit un fond ionique explicite agissant par des pseudopotentiels locaux ou non-locaux. La dynamique de ce fond ionique est discute, ainsi que la pertinence de diffrentes observables. Les techniques numriques correspondantes sont prsentes. Il s'agit soit d'un traitement Crank-Nicholson autocohrent, approch par une propagation successive dans chacune des directions d'espace, soit d'un traitement alternant entre l'espace direct et celui de Fourier. Les quations utilises suggrent un traitement parallle. Plusieurs exemples d'application sont alors donns. Nous discutons en dtail le cas de Na9^+, puis le cas moins simple de Na{11}^+. Nous donnons des spectres obtenus pour des agrgats de sodium dposs sur une surface de chlorure de sodium. Puis, nous abordons un exemple de simulation avec fond ionique mouvant par dynamique molculaire. Nous discutons ainsi le transfert aux ions de l'nergie dpose par un laser femtoseconde dans un agrgat Na12. Nous prsentons enfin le spectre obtenu pour la rsonance lectronique dans un agrgat de carbone linaire C5. Nous concluons alors sur le travail effectu et les dveloppements ou amliorations possibles sur le plan thorique comme numrique.

  20. Insurance and bonding

    SciTech Connect

    Katzman, M.T.

    1989-01-01

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

  1. Metallic Adhesion and Bonding

    NASA Technical Reports Server (NTRS)

    Ferrante, J.; Smith, J. R.; Rose, J. H.

    1984-01-01

    Although metallic adhesion has played a central part in much tribological speculation, few quantitative theoretical calculations are available. This is in part because of the difficulties involved in such calculations and in part because the theoretical physics community is not particularly involved with tribology. The calculations currently involved in metallic adhesion are summarized and shown that these can be generalized into a scaled universal relationship. Relationships exist to other types of covalent bonding, such as cohesive, chemisorptive, and molecular bonding. A simple relationship between surface energy and cohesive energy is offered.

  2. Thermal Variation of Ce Valence in Mixed ValenceKondo Lattice Systems CeT2(Si1-xGex)2 with T= Mn and Ni

    SciTech Connect

    Liang,G.; Croft, M.

    2008-01-01

    The results on the thermal variation of Ce L3-valence in CeT2(Si1-xGex)2 series with 0{le}x{le}1 and T=Mn and Ni are reported. It is observed that for both series, the Ce valence increases with decreasing temperature and has little thermal variation for samples in the nearly trivalent regime. The magnitude of this thermal variation in the T=Mn series is much greater than in the T=Ni series. The results are explained by the degenerate Anderson model and correlated with the specific heat data.

  3. Dynamic and electro-optical non-equivalency of NH bonds in amino groups of aniline, aminotoluenes and monohalogen-substituted anilines in their H-bonded 1 : 1 and 1 : 2 complexes

    NASA Astrophysics Data System (ADS)

    Borisenko, V. E.; Morev, A. V.

    1994-06-01

    The spectra of 1 : 2 H-bonded complexes of aniline, aminotoluene and mono- (F, Cl, Br)-substituted anilines with acetonitrile, tetrahydrofuran, dimethyl formamide, dimethyl sulphoxide and hexamethylphosphoramide were studied in the region of the stretching and deformation vibrations of the amino group. The spectral moments M(0) and M(1) and the effective half-width 2( M(2)) {1}/{2} of the absorption bands of the amino group valence vibrations and the frequencies of the deformational vibrations of the 1 : 2 complexes were determined taking into account Fermi resonance phenomena. Force constants, valence angles γ(HNH) and electro-optical parameters ∂μ/∂ q and ∂μ/∂ q' of the NH-bonds of the amino group were calculated. A comparative investigation of the parameters of the amino group of free molecules and 1 : 1 and 1 : 2 complexes was carried out. The force constants and electro-optical parameters of bonded NH groups in 1 : 1 and 1 : 2 complexes were shown to be non-equivalent. Dynamic and electro-optical non-equivalence of the bonds increase with the growth of H-bond stability. The transition from free molecules to bonded ones in 1 : 2 complexes is accompanied by a significant increase in the valence angles γ(HNH). The parameters of linear regression equations combining geometric, dynamic and spectral characteristics of the aniline amino group in H-bonded complexes are defined. The amino group electro-optical parameters of substituted anilines, ∂μ/∂ q and ∂μ/∂ q', depend significantly on the character and position of the substituents in the aniline aromatic ring and on the properties of the proton-accepting molecules.

  4. Effect of Pr Valence State on Interfacial Structure and Electrical Properties of Pr Oxide/PrON/Ge Gate Stack Structure

    NASA Astrophysics Data System (ADS)

    Kato, Kimihiko; Sakashita, Mitsuo; Takeuchi, Wakana; Kondo, Hiroki; Nakatsuka, Osamu; Zaima, Shigeaki

    2011-04-01

    In this study, we investigated the valence state and chemical bonding state of Pr in a Pr oxide/PrON/Ge structure. We clarified the relationship between the valence state of Pr and the Pr oxide/Ge interfacial reaction using Pr oxide/Ge and Pr oxide/PrON/Ge samples. We found the formation of three Pr oxide phases in Pr oxide films; hexagonal Pr2O3 (h-Pr2O3) (Pr3+), cubic Pr2O3 (c-Pr2O3) (Pr3+), and c-PrO2 (Pr4+). We also investigated the effect of a nitride interlayer on the interfacial reaction in Pr oxide/Ge gate stacks. In a sample with a nitride interlayer (Pr oxide/PrON/Ge), metallic Pr-Pr bonds are also formed in the c-Pr2O3 film. After annealing in H2 ambient, the diffusion of Ge into Pr oxide is not observed in this sample. Pr-Pr bonds probably prevent the interfacial reaction and Ge oxide formation, considering that the oxygen chemical potential of this film is lower than that of a GeO2/Ge system. On the other hand, the rapid thermal oxidation (RTO) treatment terminates the O vacancies and defects in c-Pr2O3. As a result, c-PrO2 with tetravalent Pr is formed in the Pr oxide/PrON/Ge sample with RTO. In this sample, the leakage current density is effectively decreased in comparison with the sample without RTO. Hydrogen termination works effectively in Pr oxide/PrON/Ge samples with and without RTO, and we can achieve an interface state density of as low as 4 1011 eV-1cm-2.

  5. Oxygen barometry of basaltic glasses based on vanadium valence determinations using synchrotron microXANES

    SciTech Connect

    Sutton, S.R.; Karner, J.M.; Papike, J.J.; Delaney, J.S.; Shearer, C.K.; Newville, M.; Eng, P.; Rivers, M.; Dyar, M.D.

    2004-10-27

    We describe here a new, non-destructive method for valence determinations of vanadium and oxygen fugacity estimates for basaltic glasses with spatial resolution of a few micrometers using synchrotron x-ray absorption near edge structure (XANES) spectroscopy. A promising proxy for oxygen fugacity is the valence of vanadium because it a large number of valence states in nature (2+, 3+, 4+ and 5+) and is ubiquitous in earth and planetary materials . We describe here a new, non-destructive method for valence determinations of vanadium and oxygen fugacity estimates for basaltic glasses with spatial resolution of a few micrometers using synchrotron x-ray absorption near edge structure (XANES) spectroscopy. Details of this method and applications to martian, lunar and terrestrial glasses are described and also in accompanying abstracts.

  6. Subjective Reality: The Influence of Perceived and Objective Conversational Valence on Binge Drinking Determinants.

    PubMed

    Hendriks, Hanneke; Putte, Bas van den; de Bruijn, Gert-Jan

    2015-01-01

    Previous studies have shown that interpersonal communication, and particularly perceived conversational valence (i.e., the perceived negativity or positivity of conversations) about health topics, influences health determinants. On the basis of 43 dyads (N = 86) discussing the topic of alcohol consumption, this study is the first to show that whereas perceived and objective conversational valence are positively related, only perceived conversational valence is a significant predictor of binge drinking attitudes and intentions. Thus, subjective reality matters more than objective reality. Furthermore, only the perceived valence of the participants' own contributions-and not of their conversation partners--influences binge drinking intentions, indicating that self-persuasion is more influential than persuasion by others. Thus, conversations in which discussants themselves express negative opinions about unhealthy behaviors can enhance public health. PMID:25848964

  7. Of Caucasians, Asians, and Giraffes: The Influence of Categorization and Target Valence on Social Projection.

    PubMed

    Machunsky, Maya; Walther, Eva

    2015-09-01

    Past research has indicated that social projection is moderated by categorization, with more projection onto ingroups than onto outgroups. However, a few studies have reported elevated levels of projection even onto outgroups. In line with recent evidence, we hypothesized that positive target valence is the key feature of conditions that elicit projection onto outgroups. The present research extends previous findings by testing whether the effect of valence occurs independent of categorization, with increased levels of projection onto positive ingroup and non-ingroup targets alike. We designed two experiments in which target valence was manipulated by means of evaluative conditioning. Category membership was varied by using faces of Caucasians, Asians, and giraffes. The results supported our valence hypothesis. Counter-intuitively, we also found higher levels of projection onto giraffes than onto humans. These findings suggest that current cognition-based models of projection are not sufficient to account for the whole range of projection phenomena. PMID:26160332

  8. The valence of Ce in CeRu 2 and CeIr 3 thru superconductivity

    NASA Astrophysics Data System (ADS)

    Hakimi, M.; Huber, J. G.

    1985-12-01

    A scheme is presented whereby valences for Ceof 3.9 inCeRu2 and 3.6 inCeIr3 are assigned thru superconductivity. Isostructural superconductors XRu2 and XIr3 ( X = La, CeandTh) are required. The superconducting transition temperatures ( Tc) of pseudo-binary compounds have been measured. The compositional variation of Tc going directly from the La (trivalent) to the Th (tetravalent) compound is matched by that going from the La to the Ce to the Th compound when an intermediate valence is assigned to Ce. It is argued that Ru 4d-bands and Ir 5d-bands are responsible for the superconductivity, and that valence electrons supplied by the X ions toward filling those bands determine Tc. Constant Ce valences are assumed, and account is taken for Ce 4f resonant state depression of Tcin ( X, Ce) Ir3 pseudo-binary compounds.

  9. An Intracranial EEG Study of the Neural Dynamics of Musical Valence Processing.

    PubMed

    Omigie, Diana; Dellacherie, Delphine; Hasboun, Dominique; George, Nathalie; Clement, Sylvain; Baulac, Michel; Adam, Claude; Samson, Severine

    2015-11-01

    The processing of valence is known to recruit the amygdala, orbitofrontal cortex, and relevant sensory areas. However, how these regions interact remains unclear. We recorded cortical electrical activity from 7 epileptic patients implanted with depth electrodes for presurgical evaluation while they listened to positively and negatively valenced musical chords. Time-frequency analysis suggested a specific role of the orbitofrontal cortex in the processing of positively valenced stimuli while, most importantly, Granger causality analysis revealed that the amygdala tends to drive both the orbitofrontal cortex and the auditory cortex in theta and alpha frequency bands, during the processing of valenced stimuli. Results from the current study show the amygdala to be a critical hub in the emotion processing network: specifically one that influences not only the higher order areas involved in the evaluation of a stimulus's emotional value but also the sensory cortical areas involved in the processing of its low-level acoustic features. PMID:24904066

  10. Overlap valence quarks on a twisted mass sea: A case study for mixed action lattice QCD

    NASA Astrophysics Data System (ADS)

    Cichy, Krzysztof; Drach, Vincent; García-Ramos, Elena; Herdoíza, Gregorio; Jansen, Karl

    2013-04-01

    We discuss a lattice QCD mixed action investigation employing Wilson maximally twisted mass sea and overlap valence fermions. Using four values of the lattice spacing, we demonstrate that the overlap Dirac operator assumes a point-like locality in the continuum limit. We also show that by adopting suitable matching conditions for the sea and valence theories a consistent continuum limit for the pion decay constant and light baryon masses can be obtained. Finally, we confront results for sea-valence mixed meson masses and the valence scalar correlator with corresponding expressions of chiral perturbation theory. This allows us to extract low energy constants of mixed action chiral perturbation which characterize the strength of unitarity violations in our mixed action setup.

  11. Match between cue and memory valence during autobiographical memory recall in depression.

    PubMed

    Young, Kymberly D; Erickson, Kristine; Drevets, Wayne C

    2012-08-01

    Major depressive disorder (MDD) is associated with deficits in recalling specific autobiographical memories. The current study goal was to assess whether emotionally valenced cue words led to memories of similar emotional valence and whether this pattern differed between 12 unmedicated MDD and 14 healthy control participants. Both groups recalled autobiographical memories in response to positive, negative, and neutral cue words. Positive and neutral cues prompted recall of positive memories less often in the MDD group than in the controls. MDD participants recalled fewer specific and more categorical memories than controls; however, the proportion of specific memories didn't differ across memory valences. The MDD group had fewer specific memories in response to positive and neutral cues than the controls. These results suggest that the MDD participants may process positive stimuli differently than healthy controls and that their recall of specific autobiographical memories is impaired, regardless of the affective valence of those memories. PMID:23045855

  12. Of two minds: forming and changing valence-inconsistent implicit and explicit attitudes.

    PubMed

    Rydell, Robert J; McConnell, Allen R; Mackie, Diane M; Strain, Laura M

    2006-11-01

    Because different processes underlie implicit and explicit attitudes, we hypothesized that they are differentially sensitive to different kinds of information. We measured implicit and explicit attitudes over time, as different types of attitude-relevant information about a single attitude object were presented. As expected, explicit attitudes formed and changed in response to the valence of consciously accessible, verbally presented behavioral information about the target. In contrast, implicit attitudes formed and changed in response to the valence of subliminally presented primes, reflecting the progressive accretion of attitude object-evaluation pairings. As a consequence, when subliminal primes and behavioral information were of opposite valence, people formed implicit and explicit attitudes of conflicting valence. PMID:17176426

  13. THE VALENCE AND METHYLATION STATE OF ARSENIC DETERMINES ITS POTENCY IN INTERACTION WITH THE MITOTIC APPARATUS

    EPA Science Inventory

    We have previously shown that the cytotoxic and genotoxic potency of arsenicals is dependent upon their valence and methylation state. Trivalent methylated arsenicals are much more potent DNA damaging agents than are their inorganic and pentavalent counterparts. Furthermore, thei...

  14. Theoretical study of valence orbital response to guanine tautomerization in coordinate and momentum spaces

    NASA Astrophysics Data System (ADS)

    Yang, Zejin; Duffy, Patrick; Zhu, Quan; Takahashi, Masahiko; Wang, Feng

    2015-10-01

    The binding energy spectra and electron momentum spectra of eight stable guanine tautomers are calculated in the complete valence space. The present results show that the canonical keto (C=O) guanine N(9)H tautomer (GU1) possesses the largest dipole moment, molecular electronic spatial extent, molecular hardness value, and the minimum first vertical ionization potential (VIP). Valence orbital profile investigations find that several orbitals remain almost unchanged during tautomerization, such as frontier highest occupied molecular orbital 39a and 18a. Several orbitals with interchanged order and inverse direction in charge spatial orientations are also detected. Outer valence orbitals (with smaller VIPs) show more complex orbital shapes in the momentum space than those of inner ones (larger VIPs) due mainly to the relatively strong inter-orbital interaction and delocalized electronic distributions. Proton rotation along C-O(H) and C-N(H) axes within hexagonal ring causes smaller influence to orbital profiles than those of proton migration within pentagonal and/or hexagonal rings. Orbital variation trends between enol (GU3-GU5) and keto (GU1, GU2, GU6-GU8) tautomers are observed, including the signature orbitals of enol form, the variation tendency of total orbital intensity, and the variation order of the maximum orbital intensity. In the outer valence momentum space (outside 26a), orbital composed by pz electrons show single peak with a gradual increasing peak site from 0.5 a.u. of inner valence orbital to 1.0 a.u. of outer valence orbital, whereas orbitals composed by px,y electrons form double peaks with respective sites at about 0.5 and 1.5 a.u., only three px,y-orbitals present single peaks (33a,34a,36a). The general variation trends in the complete valence space for all the valence orbitals on their intensities, peak sites, and orbital components are concluded.

  15. Dangling bonds and vacancies in germanium

    NASA Astrophysics Data System (ADS)

    Weber, J. R.; Janotti, A.; Van de Walle, C. G.

    2013-01-01

    The quest for metal-oxide-semiconductor field-effect transistors (MOSFETs) with higher carrier mobility has triggered great interest in germanium-based MOSFETs. Still, the performance of germanium-based devices lags significantly behind that of their silicon counterparts, possibly due to the presence of defects such as dangling bonds (DBs) and vacancies. Using screened hybrid functional calculations we investigate the role of DBs and vacancies in germanium. We find that the DB defect in germanium has no levels in the band gap; it acts as a negatively charged acceptor with the (0/-1) transition level below the valence-band maximum (VBM). This explains the absence of electron-spin-resonance observations of DBs in germanium. The vacancy in germanium has a much lower formation energy than the vacancy in silicon and is stable in a number of charge states, depending on the position of the Fermi level. We find the (0/-1) and (-1/-2) transition levels at 0.16 and 0.38 eV above the VBM; the spacing of these levels is explained based on the strength of intraorbital repulsion. We compare these results with calculations for silicon, as well as with available experimental data.

  16. Coexistence of solvated electron and benzene-centered valence anion in the negatively charged benzene-water clusters

    NASA Astrophysics Data System (ADS)

    Zhang, Meng; Zhao, Jing; Liu, Jinxiang; Zhou, Lianwen; Bu, Yuxiang

    2013-01-01

    We present a combined M06 functional calculation and ab initio molecular dynamics simulation study of an excess electron (EE) in a microhydrated aromatic complex (modeled by benzene (Bz)-water binary clusters, Bz(H2O)n). Calculated results illustrate that Bz ring and water clusters are indeed linked through the ?⋯HO interactions in the neutral Bz(H2O)n (n = 1-8) clusters, and the size of the water cluster does not influence the nature of its interaction with the ? system for the oligo-hydrated complexes. The states and the dynamics of an EE trapped in such Bz-water clusters were also determined. All of possible localized states for the EE can be roughly classified into two types: (i) single, ring-localized states (the Bz-centered valence anions) in which an EE occupies the LUMO of the complexes originating from the LUMO (?*) of the Bz ring, and the ?⋯HO interactions are enhanced for increase of electron density of the Bz ring. In this mode, the carbon skeleton of the Bz part is significantly deformed due to increase of electron density and nonsymmetric distribution of electron density induced by the interacting H-O bonds; (ii) solvated states, in which an EE is trapped directly as a surface state by the dangling hydrogen atoms of water molecules or as a solvated state in a mixed cavity formed by Bz and water cluster. In the latter case, Bz may also participate in capturing an EE using its C-H bonds in the side edge of the aromatic ring as a part of the cavity. In general, a small water cluster is favorable to the Bz-centered valence anion state, while a large one prefers a solvated electron state. Fluctuations and rearrangement of water molecules can sufficiently modify the relative energies of the EE states to permit facile conversion from the Bz-centered to the water cluster-centered state. This indicates that aromatic Bz can be identified as a stepping stone in electron transfer and the weak ?⋯HO interaction plays an important role as the driving force in conversion of the two states.

  17. Bond dissociation energies and bond orders for some astrophysical molecules

    NASA Astrophysics Data System (ADS)

    Reddy, R. R.; Viswanath, R.

    1989-06-01

    The bond dissociation energies for various astrophysically important diatomic molecules have been determined using a formula in which bond dissociation energies are the sum of the geometric average of the component bond energies and 32.058 times the Pauling electronegativity difference. Bond orders are estimated according to the formula of Reddy et al. (1985, 1987). The results confirm the definition of bond order given by Politzer (1969). The estimated bond energies are found to agree well with previous values and to give an error of 8 percent, as compared to the error of 26.8 percent found using Pauling's (1960) equation.

  18. Flax Fiber - Interfacial Bonding

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Measured flax fiber physical and chemical properties potentially impact bonding and thus stress transfer between the matrix and fiber within composites. These first attempts at correlating flax fiber quality and biofiber composites contain the initial steps towards identifying key flax fiber charac...

  19. Dialogic Bonds and Boundaries.

    ERIC Educational Resources Information Center

    Khawaja, Mabel

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

  20. Bonding without Tears.

    ERIC Educational Resources Information Center

    Akeroyd, F. Michael

    1982-01-01

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