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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. A VB/MM view of the identity S(N)2 valence-bond state correlation diagram in aqueous solution.

    PubMed

    Sharir-Ivry, Avital; Shurki, Avital

    2008-12-18

    The valence-bond state correlation diagram (VBSCD), which was developed by Shaik and co-workers is an excellent tool to understand reactivity patterns in chemical reactions. The strength of the model is in its ability to describe the whole spectrum of reaction types and unify them under a single general paradigm. Moreover, it allows one to understand, conceptualize, and predict chemical reactivity in a general as well as specific manner. As such, VBSCD is a valuable model. The model has been largely tested on various systems in the gas phase both qualitatively and quantitatively. However, its application to reactions in solution was given less attention because of the difficulties to represent solvent reorganization and estimate non-equilibrium solvation effects, which, on the basis of the model, are expected to be fundamental. The recently developed valence-bond molecular mechanics (VB/MM) method overcomes these difficulties because it involves explicit solvent molecules and thus allows quantitative examination of these solvent effects. This work presents a study of the identity S(N)2 reaction X(-) + H(3)CX --> XCH(3) + X(-); (X = F, Cl, Br, I) in aqueous solution. The various parameters that form the VBSCD model are calculated and compared with the corresponding model's estimated values. A relatively good agreement between the calculated and estimated values is found. It is shown that when facing quantitative considerations, the picture may not be as simplistic as in the qualitative study; yet, the fundamental nature of the description is unaffected. This indicates that combined together, the VB/MM approach and the VBSCD model offer a very powerful tool to study reactions in complex systems and understand their reactivity patterns. PMID:18620378

  4. Seniority Number in Valence Bond Theory.

    PubMed

    Chen, Zhenhua; Zhou, Chen; Wu, Wei

    2015-09-01

    In this work, a hierarchy of valence bond (VB) methods based on the concept of seniority number, defined as the number of singly occupied orbitals in a determinant or an orbital configuration, is proposed and applied to the studies of the potential energy curves (PECs) of H8, N2, and C2 molecules. It is found that the seniority-based VB expansion converges more rapidly toward the full configuration interaction (FCI) or complete active space self-consistent field (CASSCF) limit and produces more accurate PECs with smaller nonparallelity errors than its molecular orbital (MO) theory-based analogue. Test results reveal that the nonorthogonal orbital-based VB theory provides a reverse but more efficient way to truncate the complete active Hilbert space by seniority numbers.

  5. 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

  6. 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…

  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. Red-Shifting versus Blue-Shifting Hydrogen Bonds: Perspective from Ab Initio Valence Bond Theory.

    PubMed

    Chang, Xin; Zhang, Yang; Weng, Xinzhen; Su, Peifeng; Wu, Wei; Mo, Yirong

    2016-05-01

    Both proper, red-shifting and improper, blue-shifting hydrogen bonds have been well-recognized with enormous experimental and computational studies. The current consensus is that there is no difference in nature between these two kinds of hydrogen bonds, where the electrostatic interaction dominates. Since most if not all the computational studies are based on molecular orbital theory, it would be interesting to gain insight into the hydrogen bonds with modern valence bond (VB) theory. In this work, we performed ab initio VBSCF computations on a series of hydrogen-bonding systems, where the sole hydrogen bond donor CF3H interacts with ten hydrogen bond acceptors Y (═NH2CH3, NH3, NH2Cl, OH(-), H2O, CH3OH, (CH3)2O, F(-), HF, or CH3F). This series includes four red-shifting and six blue-shifting hydrogen bonds. Consistent with existing findings in literature, VB-based energy decomposition analyses show that electrostatic interaction plays the dominating role and polarization plays the secondary role in all these hydrogen-bonding systems, and the charge transfer interaction, which denotes the hyperconjugation effect, contributes only slightly to the total interaction energy. As VB theory describes any real chemical bond in terms of pure covalent and ionic structures, our fragment interaction analysis reveals that with the approaching of a hydrogen bond acceptor Y, the covalent state of the F3C-H bond tends to blue-shift, due to the strong repulsion between the hydrogen atom and Y. In contrast, the ionic state F3C(-) H(+) leads to the red-shifting of the C-H vibrational frequency, owing to the attraction between the proton and Y. Thus, the relative weights of the covalent and ionic structures essentially determine the direction of frequency change. Indeed, we find the correlation between the structural weights and vibrational frequency changes. PMID:27074500

  9. Red-Shifting versus Blue-Shifting Hydrogen Bonds: Perspective from Ab Initio Valence Bond Theory.

    PubMed

    Chang, Xin; Zhang, Yang; Weng, Xinzhen; Su, Peifeng; Wu, Wei; Mo, Yirong

    2016-05-01

    Both proper, red-shifting and improper, blue-shifting hydrogen bonds have been well-recognized with enormous experimental and computational studies. The current consensus is that there is no difference in nature between these two kinds of hydrogen bonds, where the electrostatic interaction dominates. Since most if not all the computational studies are based on molecular orbital theory, it would be interesting to gain insight into the hydrogen bonds with modern valence bond (VB) theory. In this work, we performed ab initio VBSCF computations on a series of hydrogen-bonding systems, where the sole hydrogen bond donor CF3H interacts with ten hydrogen bond acceptors Y (═NH2CH3, NH3, NH2Cl, OH(-), H2O, CH3OH, (CH3)2O, F(-), HF, or CH3F). This series includes four red-shifting and six blue-shifting hydrogen bonds. Consistent with existing findings in literature, VB-based energy decomposition analyses show that electrostatic interaction plays the dominating role and polarization plays the secondary role in all these hydrogen-bonding systems, and the charge transfer interaction, which denotes the hyperconjugation effect, contributes only slightly to the total interaction energy. As VB theory describes any real chemical bond in terms of pure covalent and ionic structures, our fragment interaction analysis reveals that with the approaching of a hydrogen bond acceptor Y, the covalent state of the F3C-H bond tends to blue-shift, due to the strong repulsion between the hydrogen atom and Y. In contrast, the ionic state F3C(-) H(+) leads to the red-shifting of the C-H vibrational frequency, owing to the attraction between the proton and Y. Thus, the relative weights of the covalent and ionic structures essentially determine the direction of frequency change. Indeed, we find the correlation between the structural weights and vibrational frequency changes.

  10. 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.

  11. The application of cholesky decomposition in valence bond calculation.

    PubMed

    Gong, Xiping; Chen, Zhenhua; Wu, Wei

    2016-09-01

    The Cholesky decomposition (CD) technique, used to approximate the two-electron repulsion integrals (ERIs), is applied to the valence bond self-consistent field (VBSCF) method. Test calculations on ethylene, C2 n H2 n +2 , and C2 n H4 n -2 molecules (n = 1-7) show that the performance of the VBSCF method is much improved using the CD technique, and thus, the integral transformation from basis functions to VB orbitals is no longer the bottleneck in VBSCF calculations. The errors of the CD-based ERIs and of the total energy are controlled by the CD threshold, for which a value of 10(-6) ensures to control the total energy error within 10(-6) Hartree. © 2016 Wiley Periodicals, Inc. PMID:27377531

  12. 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…

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. Valence bond cluster studies of alkali metal/semiconductor bonding

    NASA Astrophysics Data System (ADS)

    Tatar, Robert C.; Messmer, Richard P.

    1986-12-01

    We present results of cluster studies of alkali metal/semiconductor bonding. Using the Generalized Valence Bond (GVB) method, we find a remarkable consistency in the behavoir of bonding orbitals for a variety of systems, including: LiH, CLi4, LiH4 and several hypervalent systems, such as SiH3Li2, SiH4Li2. Our results show that the metal-semiconductor bonding in these systems can be understood in terms of a pairing between McAdon-Goddard type metallic bonding orbitals and a set of equivalent orbitals of the non-metallic species. We propose that the results are relevant to the initial stages of alkali overlayer growth on semiconductor surfaces and lead to a simple picture of the bonding including the transition from a non-conducting to a conducting layer. We have considered numerous proposed hypervalent structures in light of the above results and find that they can be understood.

  18. Exact valence bond entanglement entropy and probability distribution in the XXX spin chain and the potts model.

    PubMed

    Jacobsen, J L; Saleur, H

    2008-02-29

    We determine exactly the probability distribution of the number N_(c) of valence bonds connecting a subsystem of length L>1 to the rest of the system in the ground state of the XXX antiferromagnetic spin chain. This provides, in particular, the asymptotic behavior of the valence-bond entanglement entropy S_(VB)=N_(c)ln2=4ln2/pi(2)lnL disproving a recent conjecture that this should be related with the von Neumann entropy, and thus equal to 1/3lnL. Our results generalize to the Q-state Potts model.

  19. Valence bond distribution and correlation in bipartite Heisenberg antiferromagnets

    NASA Astrophysics Data System (ADS)

    Schwandt, David; Alet, Fabien; Oshikawa, Masaki

    2014-03-01

    Every singlet state of a quantum spin-1/2 system can be decomposed into a linear combination of valence bond basis states. The range of valence bonds within this linear combination as well as the correlations between them can reveal the nature of the singlet state and are key ingredients in variational calculations. In this work, we study the bipartite valence bond distributions and their correlations within the ground state of the Heisenberg antiferromagnet on bipartite lattices. In terms of field theory, this problem can be mapped to correlation functions near a boundary. In dimension d ≥2, a nonlinear σ model analysis reveals that at long distances the probability distribution P (r) of valence bond lengths decays as |r|-d-1 and that valence bonds are uncorrelated. By a bosonization analysis, we also obtain P(r )∝|r|-d-1 in d =1 despite the different mechanism. On the other hand, we find that correlations between valence bonds are important even at large distances in d =1, in stark contrast to d ≥2. The analytical results are confirmed by high-precision quantum Monte Carlo simulations in d =1, 2, and 3. We develop a single-projection loop variant of the valence bond projection algorithm, which is well designed to compute valence bond probabilities and for which we provide algorithmic details.

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

    PubMed

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

    2010-08-17

    The preceding decade has witnessed an immense surge of activity in the bioinorganic chemistry of transition metal enzymes and synthetic analogs that model their operation. The wide range of research covers both experimental and theoretical investigations of structure and reactivity patterns. Theory, and especially density functional theory (DFT), has become a very useful tool, an important partner of experiment in resolving structural and mechanistic issues. This flare of activity has generated a great deal of knowledge on intermediates, transition states, barriers, rate constants, rate-equilibrium relationships, stereoselectivity, and so forth. This abundance of acquired knowledge has created the need for establishing order, namely, the outlining of broad generalizations, as well as the creation of a more-intuitive interface between experimental and theoretical data. The valence bond (VB) diagram model, originally developed for organic reactions, is such a theoretical framework that has the potential to guide the requisite generalizations in the field of bioinorganic chemical reactivity. In this Account, we briefly describe the principles of construction of VB diagrams for bioinorganic reactions, detailing applications in the booming research area of heme enzyme (specifically cytochrome P450) reactivity, and particularly two archetypal reactions of these enzymes, alkane hydroxylation and thioether sulfoxidation. For congruence with the lingua franca of bioinorganic chemistry, the VB model is formulated to create bridges to (i) the molecular orbital (MO) description, (ii) the oxidation state formulation of transition metal complexes, and (iii) widely used concepts such as the Bell-Evans-Polanyi (BEP) principle. The VB diagram model reveals the origins of the barrier, describes the formation of transition states and reaction intermediates, and allows the prediction of barrier heights and structure-reactivity relationships. Thus, from the VB diagram model, we can

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

    PubMed

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

    2010-08-17

    The preceding decade has witnessed an immense surge of activity in the bioinorganic chemistry of transition metal enzymes and synthetic analogs that model their operation. The wide range of research covers both experimental and theoretical investigations of structure and reactivity patterns. Theory, and especially density functional theory (DFT), has become a very useful tool, an important partner of experiment in resolving structural and mechanistic issues. This flare of activity has generated a great deal of knowledge on intermediates, transition states, barriers, rate constants, rate-equilibrium relationships, stereoselectivity, and so forth. This abundance of acquired knowledge has created the need for establishing order, namely, the outlining of broad generalizations, as well as the creation of a more-intuitive interface between experimental and theoretical data. The valence bond (VB) diagram model, originally developed for organic reactions, is such a theoretical framework that has the potential to guide the requisite generalizations in the field of bioinorganic chemical reactivity. In this Account, we briefly describe the principles of construction of VB diagrams for bioinorganic reactions, detailing applications in the booming research area of heme enzyme (specifically cytochrome P450) reactivity, and particularly two archetypal reactions of these enzymes, alkane hydroxylation and thioether sulfoxidation. For congruence with the lingua franca of bioinorganic chemistry, the VB model is formulated to create bridges to (i) the molecular orbital (MO) description, (ii) the oxidation state formulation of transition metal complexes, and (iii) widely used concepts such as the Bell-Evans-Polanyi (BEP) principle. The VB diagram model reveals the origins of the barrier, describes the formation of transition states and reaction intermediates, and allows the prediction of barrier heights and structure-reactivity relationships. Thus, from the VB diagram model, we can

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

    PubMed

    Harcourt, Richard D

    2015-05-12

    Using valence-bond structures of the types Ȧ · Ḃ 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 Ȧ · Ḃ 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.

  3. 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)

  4. 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…

  5. 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.

  6. Application of valence-bond techniques to the study of weakly bound complexes. The potential energy surface of the Ne-CH(4) system.

    PubMed

    Cargnoni, F; Mella, M; Raimondi, M

    2007-05-28

    We present a comprehensive survey of the Molecular Orbital-Valence Bond (MO-VB) method, a theoretical scheme developed within the framework of the Valence Bond theory to deal with weakly bound intermolecular complexes. According to the MO-VB, the wavefunction of the system is expressed as a truncated non-orthogonal Configuration Interaction expansion, which is size extensive and a priori free of basis set superposition error. We report on the recent developments of the method, which extend the range of application of the MO-VB to intermolecular complexes with a quite large number of correlated electrons, showing that VB-based methods are nowadays a valid alternative to Molecular Orbital approaches also in this field. The MO-VB has been applied to study extensively the Ne-CH(4) complex, and compared with the more standard MP4 and CCSD(T) results. We determined two analytical Potential Energy Surfaces (PES) for this system, computed at MO-VB and MP4 level, which represent the first ones coming entirely from ab initio computations. The features of our potentials are discussed, and compared to the single analytical potential which includes the anisotropy available in the literature, determined about twenty years ago by Udo Buck and co-workers using a semiempirical approach [U. Buck, A. Kolhase, D. Secrest, T. Phillips, G. Scoles and F. Grein, Mol. Phys., 1985, 55, 1233]. The differences among the three PES are quite relevant, and are due to play a relevant role in the theoretical simulations of the dynamical properties of the Ne-CH(4) system. PMID:17508080

  7. Application of valence-bond techniques to the study of weakly bound complexes. The potential energy surface of the Ne-CH(4) system.

    PubMed

    Cargnoni, F; Mella, M; Raimondi, M

    2007-05-28

    We present a comprehensive survey of the Molecular Orbital-Valence Bond (MO-VB) method, a theoretical scheme developed within the framework of the Valence Bond theory to deal with weakly bound intermolecular complexes. According to the MO-VB, the wavefunction of the system is expressed as a truncated non-orthogonal Configuration Interaction expansion, which is size extensive and a priori free of basis set superposition error. We report on the recent developments of the method, which extend the range of application of the MO-VB to intermolecular complexes with a quite large number of correlated electrons, showing that VB-based methods are nowadays a valid alternative to Molecular Orbital approaches also in this field. The MO-VB has been applied to study extensively the Ne-CH(4) complex, and compared with the more standard MP4 and CCSD(T) results. We determined two analytical Potential Energy Surfaces (PES) for this system, computed at MO-VB and MP4 level, which represent the first ones coming entirely from ab initio computations. The features of our potentials are discussed, and compared to the single analytical potential which includes the anisotropy available in the literature, determined about twenty years ago by Udo Buck and co-workers using a semiempirical approach [U. Buck, A. Kolhase, D. Secrest, T. Phillips, G. Scoles and F. Grein, Mol. Phys., 1985, 55, 1233]. The differences among the three PES are quite relevant, and are due to play a relevant role in the theoretical simulations of the dynamical properties of the Ne-CH(4) system.

  8. On the activation of σ-bonds by electric fields: A Valence Bond perspective

    NASA Astrophysics Data System (ADS)

    Rincón, Luis; Mora, Jose R.; Torres, F. Javier; Almeida, Rafael

    2016-09-01

    The activation of non-polar σ -bonds induced by an electric field is studied from the perspective of the Valence Bond theory. As representative examples we study the dissociation of the H-H and C-H bonds of molecular hydrogen and methane, respectively, under the experience of an homogeneous as well as an heterogeneous field oriented along the bond axis. For all cases, the increase in the electric field have similar effects: (i) the stabilization of the potential energy, (ii) an increment of the equilibrium bond length and (iii) the transition from an homolytic dissociation mechanism to an heterolytic one when the bond is subjected under a strong enough field. These general observations are thoroughly explained using a simple Valence Bond model that involve the increment of the resonance energy between the covalent and the ionic structures, and the curve crossing between the two structures after some field strength.

  9. Mean bond-length variation in crystal structures: a bond-valence approach.

    PubMed

    Bosi, Ferdinando

    2014-08-01

    The distortion theorem of the bond-valence theory predicts that the mean bond length 〈D〉 increases with increasing deviation of the individual bond lengths from their mean value according to the equation 〈D〉 = (D' + ΔD), where D' is the length found in a polyhedron having equivalent bonds and ΔD is the bond distortion. For a given atom, D' is expected to be similar from one structure to another, whereas 〈D〉 should vary as a function of ΔD. However, in several crystal structures 〈D〉 significantly varies without any relevant contribution from ΔD. In accordance with bond-valence theory, 〈D〉 variation is described here by a new equation: 〈D〉 = (DRU + ΔDtop + ΔDiso + ΔDaniso + ΔDelec), where DRU is a constant related to the type of cation and coordination environment, ΔDtop is the topological distortion related to the way the atoms are linked, ΔDiso is an isotropic effect of compression (or stretching) in the bonds produced by steric strain and represents the same increase (or decrease) in all the bond lengths in the coordination sphere, ΔDaniso is the distortion produced by compression and stretching of bonds in the same coordination sphere, ΔDelec is the distortion produced by electronic effects. If present, ΔDelec can be combined with ΔDaniso because they lead to the same kind of distortions in line with the distortion theorem. Each D-index, in the new equation, corresponds to an algebraic expression containing experimental and theoretical bond valences. On the basis of this study, the ΔD index defined in bond valence theory is a result of both the bond topology and the distortion theorem (ΔD = ΔDtop + ΔDaniso + ΔDelec), and D' is a result of the compression, or stretching, of bonds (D' = DRU + ΔDiso). The deficiencies present in the bond-valence theory in explaining mean bond-length variations can therefore be overcome, and the observed variations of 〈D〉 in crystal structures can be

  10. The Nature of the Idealized Triple Bonds Between Principal Elements and the σ Origins of Trans-Bent Geometries-A Valence Bond Study.

    PubMed

    Ploshnik, Elina; Danovich, David; Hiberty, Philippe C; Shaik, Sason

    2011-04-12

    We describe herein a valence bond (VB) study of 27 triply bonded molecules of the general type X≡Y, where X and Y are main element atoms/fragments from groups 13-15 in the periodic table. The following conclusions were derived from the computational data: (a) Single π-bond and double π-bond energies for the entire set correlate with the "molecular electronegativity", which is the sum of the X and Y electronegativites for X≡Y. The correlation with the molecular electronegativity establishes a simple rule of periodicity: π-bonding strength generally increases from left to right in a period and decreases down a column in the periodic table. (b) The σ frame invariably prefers trans bending, while π-bonding gets destabilized and opposes the trans distortion. In HC≡CH, the π-bonding destabilization overrides the propensity of the σ frame to distort, while in the higher row molecules, the σ frame wins out and establishes trans-bent molecules with 2(1)/2 bonds, in accord with recent experimental evidence based on solid state (29)Si NMR of the Sekiguchi compound. Thus, in the trans-bent molecules "less bonds pay more". (c) All of the π bonds show significant bonding contributions from the resonance energy due to covalent-ionic mixing. This quantity is shown to correlate linearly with the corresponding "molecular electronegativity" and to reflect the mechanism required to satisfy the equilibrium condition for the bond. The π bonds for molecules possessing high molecular electronegativity are charge-shift bonds, wherein bonding is dominated by the resonance energy of the covalent and ionic forms, rather than by either form by itself.

  11. Topology of electron charge density for chemical bonds from valence bond theory: a probe of bonding types.

    PubMed

    Zhang, Lixian; Ying, Fuming; Wu, Wei; Hiberty, Philippe C; Shaik, Sason

    2009-01-01

    To characterize the nature of bonding we derive the topological properties of the electron charge density of a variety of bonds based on ab initio valence bond methods. The electron density and its associated Laplacian are partitioned into covalent, ionic, and resonance components in the valence bond spirit. The analysis provides a density-based signature of bonding types and reveals, along with the classical covalent and ionic bonds, the existence of two-electron bonds in which most of the bonding arises from the covalent-ionic resonance energy, so-called charge-shift bonds. As expected, the covalent component of the Laplacian at the bond critical point is found to be largely negative for classical covalent bonds. In contrast, for charge-shift bonds, the covalent part of the Laplacian is small or positive, in agreement with the weakly attractive or repulsive character of the covalent interaction in these bonds. On the other hand, the resonance component of the Laplacian is always negative or nearly zero, and it increases in absolute value with the charge-shift character of the bond, in agreement with the decrease of kinetic energy associated with covalent-ionic mixing. A new interpretation of the topology of the total density at the bond critical point is proposed to characterize covalent, ionic, and charge-shift bonding from the density point of view.

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

    PubMed

    Deschner, Andreas; Sørensen, 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

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

    PubMed

    Deschner, Andreas; Sørensen, 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.

  14. 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.

  15. Plaquette valence bond theory of high-temperature superconductivity

    NASA Astrophysics Data System (ADS)

    Harland, Malte; Katsnelson, Mikhail I.; Lichtenstein, Alexander I.

    2016-09-01

    We present a strong-coupling approach to the theory of high-temperature superconductivity based on the observation of a quantum critical point in the plaquette within the t ,t' Hubbard model. The crossing of ground-state energies in the N =2 -4 sectors occurs for parameters close to the optimal doping. The theory predicts the maximum of the dx2-y2-wave order parameter at the border between localized and itinerant electron behaviors and gives a natural explanation for the pseudogap formation via the soft-fermion mode related to local singlet states of the plaquette in the environment. Our approach follows the general line of resonating valence-bond theory stressing a crucial role of singlets in the physics of high-Tc superconductors but focuses on the formation of local singlets, similar to phenomena observed in frustrated one-dimensional quantum spin models.

  16. Overlap populations, bond orders and valences for 'fuzzy' atoms

    NASA Astrophysics Data System (ADS)

    Mayer, I.; Salvador, P.

    2004-01-01

    Proper definitions are proposed to calculate interatomic overlap populations, bond order (multiplicity) indices and actual atomic valences from the results of ab initio quantum chemical calculations, in terms of 'fuzzy' atoms, i.e., such divisions of the three-dimensional physical space into atomic regions in which the regions assigned to the individual atoms have no sharp boundaries but exhibit a continuous transition from one to another. The results of test calculations are in agreement with the classical chemical notions, exhibit unexpectedly small basis sensitivity and do not depend too much on the selection of the weight function defining the actual division of the space into 'fuzzy' atomic regions. The scheme is applicable on both SCF and correlated levels of theory. A free program is available.

  17. Negativity in the generalized Valence Bond Solid state

    NASA Astrophysics Data System (ADS)

    Santos, Raul A.; Korepin, V.

    2016-08-01

    Using a graphical presentation of the spin S one-dimensional Valence Bond Solid (VBS) state, based on the representation theory of the SU(2) Lie algebra of spins, we compute the spectrum of a mixed-state reduced density matrix. This mixed state of two blocks of spins A and B is obtained by tracing out the spins outside A and B, in the pure VBS state density matrix. We find in particular that the negativity of the mixed state is nonzero only for adjacent subsystems. The method introduced here can be generalized to the computation of entanglement properties in Levin-Wen models, that possess a similar algebraic structure to the VBS state in the ground state.

  18. 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

  19. Resonating valence bond wave functions and classical interacting dimer models.

    PubMed

    Damle, Kedar; Dhar, Deepak; Ramola, Kabir

    2012-06-15

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

  20. Modern ab initio valence bond theory calculations reveal charge shift bonding in protic ionic liquids.

    PubMed

    Patil, Amol Baliram; Bhanage, Bhalchandra Mahadeo

    2016-06-21

    The nature of bonding interactions between the cation and the anion of an ionic liquid is at the heart of understanding ionic liquid properties. A particularly interesting case is a special class of ionic liquids known as protic ionic liquids. The extent of proton transfer in protic ionic liquids has been observed to vary according to the interacting species. Back proton transfer renders protic ionic liquids volatile and to be considered as inferior ionic liquids. We try to address this issue by employing modern ab initio valence bond theory calculations. The results indicate that the bonding in the cation and the anion of a prototypical ionic liquid, ethylammonium nitrate, is fundamentally different. It is neither characteristic of covalent/polar covalent bonding nor ionic bonding but rather charge shift bonding as a resonance hybrid of two competing ionic molecular electronic structure configurations. An investigation of other analogous protic ionic liquids reveals that this charge shift bonding seems to be a typical characteristic of protic ionic liquids while the ionic solid analogue compound ammonium nitrate has less charge shift bonding character as compared to protic ionic liquids. Further the extent of charge shift bonding character has been found to be congruent with the trends in many physicochemical properties such as melting point, conductivity, viscosity, and ionicity of the studied ionic liquids indicating that percentage charge shift character may serve as a key descriptor for large scale computational screening of ionic liquids with desired properties.

  1. Modern ab initio valence bond theory calculations reveal charge shift bonding in protic ionic liquids.

    PubMed

    Patil, Amol Baliram; Bhanage, Bhalchandra Mahadeo

    2016-06-21

    The nature of bonding interactions between the cation and the anion of an ionic liquid is at the heart of understanding ionic liquid properties. A particularly interesting case is a special class of ionic liquids known as protic ionic liquids. The extent of proton transfer in protic ionic liquids has been observed to vary according to the interacting species. Back proton transfer renders protic ionic liquids volatile and to be considered as inferior ionic liquids. We try to address this issue by employing modern ab initio valence bond theory calculations. The results indicate that the bonding in the cation and the anion of a prototypical ionic liquid, ethylammonium nitrate, is fundamentally different. It is neither characteristic of covalent/polar covalent bonding nor ionic bonding but rather charge shift bonding as a resonance hybrid of two competing ionic molecular electronic structure configurations. An investigation of other analogous protic ionic liquids reveals that this charge shift bonding seems to be a typical characteristic of protic ionic liquids while the ionic solid analogue compound ammonium nitrate has less charge shift bonding character as compared to protic ionic liquids. Further the extent of charge shift bonding character has been found to be congruent with the trends in many physicochemical properties such as melting point, conductivity, viscosity, and ionicity of the studied ionic liquids indicating that percentage charge shift character may serve as a key descriptor for large scale computational screening of ionic liquids with desired properties. PMID:27229870

  2. 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.

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

    NASA Astrophysics Data System (ADS)

    Nakamura, Masaaki; Todo, Synge

    2002-07-01

    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, using the quantum Monte Carlo method.

  4. The itinerant resonating-valence-bond model for superconductivity

    SciTech Connect

    Liu, S.H.

    1987-08-01

    It has been proposed by Anderson that the pairing interaction in high temperature superconductors La/sub 2-x/ Sr/sub x/ Cuo/sub 4/ and Yba/sub 2/Cu/sub 3/O/sub 7-x/ is magnetic in origin, and the recent discovery of antiferromagnetic ordering in La/sub 2/CuO/sub 4/ has been regarded as strong evidence in support of this so-called resonating-valence-bond (RVB) model. Close examination of the ordered state of this material reveals that it is an itinerant antiferromagnet. Accordingly, the superconducting properties must also be studied using the itinerant model approach, rather than the local moment model discussed so far in literature. This paper reports an approximate solution of the itinerant RVB model of superconductivity. It is shown that superconductivity can take place in a narrow region of the parameter space, and that the fluctuating local exchange field causes the superconducting state to be gapless. 19 refs.

  5. Accounting for the differences in the structures and relative energies of the highly homoatomic np pi-np pi (n > or = 3)-bonded S2I4 2+, the Se-I pi-bonded Se2I4 2+, and their higher-energy isomers by AIM, MO, NBO, and VB methodologies.

    PubMed

    Brownridge, Scott; Crawford, Margaret-Jane; Du, Hongbin; Harcourt, Richard D; Knapp, Carsten; Laitinen, Risto S; Passmore, Jack; Rautiainen, J Mikko; Suontamo, Reijo J; Valkonen, Jussi

    2007-02-01

    The bonding in the highly homoatomic np pi-np pi (n > or = 3)-bonded S2I42+ (three sigma + two pi bonds), the Se-I pi-bonded Se2I42+ (four sigma + one pi bonds), and their higher-energy isomers have been studied using modern DFT and ab initio calculations and theoretical analysis methods: atoms in molecules (AIM), molecular orbital (MO), natural bond orbital (NBO), and valence bond (VB) analyses, giving their relative energies, theoretical bond orders, and atomic charges. The aim of this work was to seek theory-based answers to four main questions: (1) Are the previously proposed simple pi*-pi* bonding models valid for S2I42+ and Se2I42+? (2) What accounts for the difference in the structures of S2I42+ and Se2I42+? (3) Why are the classically bonded isolobal P2I4 and As2I4 structures not adopted? (4) Is the high experimentally observed S-S bond order supported by theoretical bond orders, and how does it relate to high bond orders between other heavier main group elements? The AIM analysis confirmed the high bond orders and established that the weak bonds observed in S2I42+ and Se2I42+ are real and the bonding in these cations is covalent in nature. The full MO analysis confirmed that S2I42+ contains three sigma and two pi bonds, that the positive charge is essentially equally distributed over all atoms, that the bonding between S2 and two I2+ units in S2I42+ is best described by two mutually perpendicular 4c2e pi*-pi* bonds, and that in Se2I42+, two SeI2+ moieties are joined by a 6c2e pi*-pi* bond, both in agreement with previously suggested models. The VB treatment provided a complementary approach to MO analysis and provided insight how the formation of the weak bonds affects the other bonds. The NBO analysis and the calculated AIM charges showed that the minimization of the electrostatic repulsion between EI2+ units (E = S, Se) and the delocalization of the positive charge are the main factors that explain why the nonclassical structures are favored for S2I42

  6. Accounting for the differences in the structures and relative energies of the highly homoatomic np pi-np pi (n > or = 3)-bonded S2I4 2+, the Se-I pi-bonded Se2I4 2+, and their higher-energy isomers by AIM, MO, NBO, and VB methodologies.

    PubMed

    Brownridge, Scott; Crawford, Margaret-Jane; Du, Hongbin; Harcourt, Richard D; Knapp, Carsten; Laitinen, Risto S; Passmore, Jack; Rautiainen, J Mikko; Suontamo, Reijo J; Valkonen, Jussi

    2007-02-01

    The bonding in the highly homoatomic np pi-np pi (n > or = 3)-bonded S2I42+ (three sigma + two pi bonds), the Se-I pi-bonded Se2I42+ (four sigma + one pi bonds), and their higher-energy isomers have been studied using modern DFT and ab initio calculations and theoretical analysis methods: atoms in molecules (AIM), molecular orbital (MO), natural bond orbital (NBO), and valence bond (VB) analyses, giving their relative energies, theoretical bond orders, and atomic charges. The aim of this work was to seek theory-based answers to four main questions: (1) Are the previously proposed simple pi*-pi* bonding models valid for S2I42+ and Se2I42+? (2) What accounts for the difference in the structures of S2I42+ and Se2I42+? (3) Why are the classically bonded isolobal P2I4 and As2I4 structures not adopted? (4) Is the high experimentally observed S-S bond order supported by theoretical bond orders, and how does it relate to high bond orders between other heavier main group elements? The AIM analysis confirmed the high bond orders and established that the weak bonds observed in S2I42+ and Se2I42+ are real and the bonding in these cations is covalent in nature. The full MO analysis confirmed that S2I42+ contains three sigma and two pi bonds, that the positive charge is essentially equally distributed over all atoms, that the bonding between S2 and two I2+ units in S2I42+ is best described by two mutually perpendicular 4c2e pi*-pi* bonds, and that in Se2I42+, two SeI2+ moieties are joined by a 6c2e pi*-pi* bond, both in agreement with previously suggested models. The VB treatment provided a complementary approach to MO analysis and provided insight how the formation of the weak bonds affects the other bonds. The NBO analysis and the calculated AIM charges showed that the minimization of the electrostatic repulsion between EI2+ units (E = S, Se) and the delocalization of the positive charge are the main factors that explain why the nonclassical structures are favored for S2I42

  7. 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

  8. 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.

    PubMed

    Chen, Xun; Chen, Zhenhua; Wu, Wei

    2014-11-21

    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. PMID:25416880

  9. Electronic Structure of pi Systems: Part II. The Unification of Huckel and Valence Bond Theories.

    ERIC Educational Resources Information Center

    Fox, Marye Anne; Matsen, F. A.

    1985-01-01

    Presents a new view of the electronic structure of pi systems that unifies molecular orbital and valence bond theories. Describes construction of electronic structure diagrams (central to this new view) which demonstrate how configuration interaction can improve qualitative predictions made from simple Huckel theory. (JN)

  10. An alternative empirical model for the relationship between the bond valence and the thermal expansion rate of chemical bonds.

    PubMed

    Sidey, Vasyl

    2015-08-01

    The relationship between the bond valence s and the thermal expansion rate of chemical bonds (dr/dT) has been closely approximated by using the alternative three-parameter empirical model (dr/dT) = (u + vs)(-1/w), where u, v and w are the refinable parameters. Unlike the s-(dr/dT) model developed by Brown et al. [(1997), Acta Cryst. B53, 750-761], this alternative model can be optimized for particular s-(dr/dT) datasets in the least-squares refinement procedure. For routine calculations of the thermal expansion rates of chemical bonds, the alternative model with the parameters u = -63.9, v = 2581.0 and w = 0.647 can be recommended.

  11. 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.

  12. Resonant valence bond states in zinc vacancies induce the ferromagnetism of ZnO

    NASA Astrophysics Data System (ADS)

    Sun, Shih-Jye

    2016-05-01

    A theoretical model was proposed to investigate the mechanism of ferromagnetism in ZnO as well as to simulate the experimental result that the ferromagnetism can be enhanced by UV irradiation as UV photon energy is equivalent to the band gap. In the model, the spin moments arise from the trapped electrons in oxygen vacancy states and coexist with the itinerant electrons which reside in zinc vacancy states and fall into resonant valence bond states. Charge exchange between the conduction band of ZnO and both vacancy states makes electrons on both vacancy states delocalized and results in a decrease of the ferromagnetism as well.

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

    PubMed

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

    2015-12-31

    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)]/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.

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

    PubMed

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

    2015-12-31

    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)]/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. Z2 gauge theory for valence bond solids on the kagome lattice

    NASA Astrophysics Data System (ADS)

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

    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. Particularly, interesting dimer melting effects are found in the 36-site VBS. We discuss the implications of our findings and also compare the results with a different type of Z2 gauge theory used in previous studies.

  17. Generalized Valence Bond Description of Chalcogen-Nitrogen Compounds. III. Why the NO-OH and NS-OH Bonds Are So Different.

    PubMed

    Takeshita, Tyler Y; Dunning, Thom H

    2016-09-01

    Crabtree et al. recently reported the microwave spectrum of nitrosyl-O-hydroxide (trans-NOOH), an isomer of nitrous acid, and found that this molecule has the longest O-O bond ever observed: 1.9149 Å ± 0.0005 Å. This is in marked contrast to the structure of the valence isoelectronic trans-NSOH molecule, which has a normal NS-OH bond length and strength. Generalized valence bond calculations show that the long bond in trans-NOOH is the result of a weak through-pair interaction that singlet couples the spins of the electrons in singly occupied orbitals on the hydroxyl radical and nitrogen atom, an interaction that is enhanced by the intervening lone pair of the oxygen atom in NO. The NS-OH bond is the result of the formation of a stable recoupled pair bond dyad, which accounts for both its length and strength.

  18. Generalized Valence Bond Description of Chalcogen-Nitrogen Compounds. III. Why the NO-OH and NS-OH Bonds Are So Different.

    PubMed

    Takeshita, Tyler Y; Dunning, Thom H

    2016-09-01

    Crabtree et al. recently reported the microwave spectrum of nitrosyl-O-hydroxide (trans-NOOH), an isomer of nitrous acid, and found that this molecule has the longest O-O bond ever observed: 1.9149 Å ± 0.0005 Å. This is in marked contrast to the structure of the valence isoelectronic trans-NSOH molecule, which has a normal NS-OH bond length and strength. Generalized valence bond calculations show that the long bond in trans-NOOH is the result of a weak through-pair interaction that singlet couples the spins of the electrons in singly occupied orbitals on the hydroxyl radical and nitrogen atom, an interaction that is enhanced by the intervening lone pair of the oxygen atom in NO. The NS-OH bond is the result of the formation of a stable recoupled pair bond dyad, which accounts for both its length and strength. PMID:27501366

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

    PubMed

    Rau, Jeffrey G; Kee, Hae-Young

    2011-02-01

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

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

    PubMed

    Rau, Jeffrey G; Kee, Hae-Young

    2011-02-01

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

  1. A modified two-state empirical valence bond model for proton transport in aqueous solutions

    SciTech Connect

    Mabuchi, Takuya; Fukushima, Akinori; Tokumasu, Takashi

    2015-07-07

    A detailed analysis of the proton solvation structure and transport properties in aqueous solutions is performed using classical molecular dynamics simulations. A refined two-state empirical valence bond (aTS-EVB) method, which is based on the EVB model of Walbran and Kornyshev and the anharmonic water force field, is developed in order to describe efficiently excess proton transport via the Grotthuss mechanism. The new aTS-EVB model clearly satisfies the requirement for simpler and faster calculation, because of the simplicity of the two-state EVB algorithm, while providing a better description of diffusive dynamics of the excess proton and water in comparison with the previous two-state EVB models, which significantly improves agreement with the available experimental data. The results of activation energies for the excess proton and water calculated between 300 and 340 K (the temperature range used in this study) are also found to be in good agreement with the corresponding experimental data.

  2. Entanglement Entropy and Topological Order in Resonating Valence-Bond Quantum Spin Liquids

    NASA Astrophysics Data System (ADS)

    Wildeboer, Julia; Seidel, Alexander; Melko, Roger

    On the triangular and kagome lattices, short-ranged resonating valence bond (RVB) wave functions can be sampled without the sign problem using a recently-developed Pfaffian Monte Carlo scheme. In this talk, we present a study of the Renyi entanglement entropy in these wave functions using a replica-trick method. Using various spatial bipartitions, including the Levin-Wen construction, our finite-size scaled Renyi entropy gives a topological contribution consistent with γ =ln (2) , as expected for a gapped ℤ2 quantum spin liquid. We prove that the mutual statistics are consistent with the toric code anyon model and rule out any other quasiparticle statistics such as the double semion model.

  3. 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.

  4. 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

  5. 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.

  6. Is it True That the Normal Valence-Length Correlation Is Irrelevant for Metal-Metal Bonds?

    PubMed

    Singh, Vijay; Dixit, Mudit; Kosa, Monica; Major, Dan Thomas; Levi, Elena; Aurbach, Doron

    2016-04-01

    The most intriguing feature of metal-metal bonds in inorganic compounds is an apparent lack of correlation between the bond order and the bond length. In this study, we combine a variety of literature data obtained by quantum chemistry and our results based on the empirical bond valence model (BVM), to confirm for the first time the existence of a normal exponential correlation between the effective bond order (EBO) and the length of the metal-metal bonds. The difference between the EBO and the formal bond order is attributed to steric conflict between the (TM)n cluster (TM=transition metal) and its environment. This conflict, affected mainly by structural type, should cause high lattice strains, but electron redistribution around TM atoms, evident from the BVM calculations, results in a full or partial strain relaxation. PMID:26929001

  7. Is it True That the Normal Valence-Length Correlation Is Irrelevant for Metal-Metal Bonds?

    PubMed

    Singh, Vijay; Dixit, Mudit; Kosa, Monica; Major, Dan Thomas; Levi, Elena; Aurbach, Doron

    2016-04-01

    The most intriguing feature of metal-metal bonds in inorganic compounds is an apparent lack of correlation between the bond order and the bond length. In this study, we combine a variety of literature data obtained by quantum chemistry and our results based on the empirical bond valence model (BVM), to confirm for the first time the existence of a normal exponential correlation between the effective bond order (EBO) and the length of the metal-metal bonds. The difference between the EBO and the formal bond order is attributed to steric conflict between the (TM)n cluster (TM=transition metal) and its environment. This conflict, affected mainly by structural type, should cause high lattice strains, but electron redistribution around TM atoms, evident from the BVM calculations, results in a full or partial strain relaxation.

  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. 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.

    PubMed

    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. PMID:25296795

  10. Electronic Structure and Bonding in Co-Based Single and Mixed Valence Oxides: A Quantum Chemical Perspective.

    PubMed

    Singh, Vijay; Major, Dan Thomas

    2016-04-01

    The mixed valence cobalt oxide, Co3O4, is a potential candidate as a photovoltaic (PV) material, which also exhibits intriguing chemical and catalytic properties. Here, we present a comparative study of the electronic, magnetic, and chemical bonding properties of mixed valence Co3O4 (i.e., Co(2+/3+)) with the related single valence CoO (i.e., Co(2+)) and Co2O3 (i.e., Co(3+)) oxides using density functional theory (DFT). We have employed a range of theoretical methods, including pure DFT, DFT+U, and a range-separated exchange-correlation functional (HSE06). We compare the electronic structure and band gap of the oxide materials, with available photoemission spectroscopy and optical band gaps. Our calculations suggest that the bonding between Co(3+) and O(2-) ions in Co2O3 and Co3O4 and Co(2+) and O(2-) ions in CoO and Co3O4 are rather different. We find that Co2O3 and Co3O4 are weakly correlated materials, whereas CoO is a strongly correlated material. Furthermore, our computed one-electron energy level diagrams reveal that strong Co-O antibonding states are present at the top of the valence band for all the cobalt oxides, hinting at a defect tolerant capacity in these materials. These results, which give a detailed picture of the chemical bonding in related single and mixed valence cobalt oxides, may serve as a guide to enhance the PV or photoelectrochemical activity of Co3O4, by reducing its internal defect states or changing its electronic structure by doping or alloying with suitable elements. PMID:27010797

  11. Electronic Structure and Bonding in Co-Based Single and Mixed Valence Oxides: A Quantum Chemical Perspective.

    PubMed

    Singh, Vijay; Major, Dan Thomas

    2016-04-01

    The mixed valence cobalt oxide, Co3O4, is a potential candidate as a photovoltaic (PV) material, which also exhibits intriguing chemical and catalytic properties. Here, we present a comparative study of the electronic, magnetic, and chemical bonding properties of mixed valence Co3O4 (i.e., Co(2+/3+)) with the related single valence CoO (i.e., Co(2+)) and Co2O3 (i.e., Co(3+)) oxides using density functional theory (DFT). We have employed a range of theoretical methods, including pure DFT, DFT+U, and a range-separated exchange-correlation functional (HSE06). We compare the electronic structure and band gap of the oxide materials, with available photoemission spectroscopy and optical band gaps. Our calculations suggest that the bonding between Co(3+) and O(2-) ions in Co2O3 and Co3O4 and Co(2+) and O(2-) ions in CoO and Co3O4 are rather different. We find that Co2O3 and Co3O4 are weakly correlated materials, whereas CoO is a strongly correlated material. Furthermore, our computed one-electron energy level diagrams reveal that strong Co-O antibonding states are present at the top of the valence band for all the cobalt oxides, hinting at a defect tolerant capacity in these materials. These results, which give a detailed picture of the chemical bonding in related single and mixed valence cobalt oxides, may serve as a guide to enhance the PV or photoelectrochemical activity of Co3O4, by reducing its internal defect states or changing its electronic structure by doping or alloying with suitable elements.

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

    SciTech Connect

    Miller, William H.; Orel, Ann E.

    1981-06-01

    A classical interpretation of the Dirac–Van Vleck spin version of valence bond theory is used in this research to obtain a classical model for electronic degrees of freedom within the valence bond framework. The approach is illustrated by deriving the explicit forms of the classical Hamiltonians, involving electronic and heavy particle degrees of freedom, for the H–H2, F–H2, and O–H2 systems. It is also shown how the initial conditions for both electronic and heavy particle degrees of freedom are chosen to carry out a classical trajectory simulation of collision processes. In addition, the attractive feature of this model is that it is as easily applicable to electronically nonadiabatic processes as it is to adiabatic ones.

  13. Ab initio determination of bond length dependence of the correlated valence shell Hamiltonian of CH: Comparison with semiempirical theories

    NASA Astrophysics Data System (ADS)

    Sun, Hosung; Freed, Karl F.

    1984-01-01

    The exact ab initio effective valence shell Hamiltonian, which is mimicked by semiempirical theories of valence, is calculated for CH at 11 bond lengths using quasidegenerate many-body perturbation theory to incorporate extensive correlation contributions. Least squares fits of the bond length dependence of the calculated CH matrix elements provide simple formulas which are compared with the intuitive forms introduced into semiempirical theories. Some of the semiempirical formulas, e.g., one-center, one-electron integrals and two-center, two-electron integrals, are in good agreement with our correlated ab initio calculations, while others display substantial departures. For example, the bond length dependence of one-center, two-electron integrals, which are assumed to be independent of bond length in semiempirical theories, is substantial but physically understandable. Corrections are found to the assumed proportionality of resonance and overlap integrals. The bond length dependence of nonclassical three-electron integrals is presented along with the hybrid and exchange integrals that are ignored in zero differential overlap methods.

  14. 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.

  15. Electronic structure and bond length dependence of the effective valence shell Hamiltonian of S2 as studied by quasidegenerate many-body perturbation theory

    NASA Astrophysics Data System (ADS)

    Wang, Xiao-Chuan; Freed, Karl F.

    1987-03-01

    The effective valence shell Hamiltonian (Hv) of S2 is calculated as a function of internuclear distance using quasidegenerate many-body perturbation theory with the full valence space spanned by eight valence orbitals. Calculated potential curves and excitation energies for several valence states are in good agreement with experiment and are compared with configuration interaction calculations using the same primitive basis. In order to test assumptions of semiempirical theories, we also perform a more approximate calculation of Hv in which the valence space is constructed as the union of the atomic valence spaces with the atomic orbitals taken from atomic SCF calculations. A new and important feature of this approximate, correlated Hv is the use of optimized valence and excited orbitals as determined from a constrained SCF procedure. The matrix elements of this approximate, correlated Hv are transformed to the original nonorthogonal atomic valence basis, and their bond length dependences are fit with simple analytical functions. Some calculated Hv matrix elements agree with the forms commonly postulated for semiempirical integrals, while others display quite different behavior. An example of the latter are the one-center, two-electron integrals which depend significantly on bond length in marked contrast to semiempirical theories which assume them to be bond length independent.

  16. Revised values of the bond-valence parameters for Te(IV)-O, Te(VI)-O and Te(IV)-Cl.

    PubMed

    Mills, Stuart J; Christy, Andrew G

    2013-04-01

    Bond-valence parameters r0 and b have been re-determined for Te(IV)-O: r0 = 1.9605 Å, b = 0.41; Te(VI)-O: r0 = 1.921 Å, b = 0.56; and Te(IV)-Cl: r0 = 2.3115 Å, b = 0.555. Bond distance data from 208 independent Te(IV)-O polyhedra, 118 Te(VI)-O polyhedra and 26 Te(IV)-Cl polyhedra were used, and all neighbours out to 3.5 Å were included. Root-mean square deviations of bond-valence sums on Te from ideal values were 0.1934, 0.1939 and 0.0865 v.u. The good fit for Te(IV)-O over a range of Te coordination numbers from 3 to 12 demonstrates that there is no essential difference in character between short `primary' Te-O bonds, oriented away from the Te lone pair, and longer `secondary' Te-O bonds on the same side of the Te atom as the lone pair. Comparison of bond-valence sums for Te-O polyhedra obtained using the new parameters with those calculated using earlier literature values shows that the new parameters give a narrower spread of calculated bond-valence sums, which means much closer to the formal valence for both oxidation states of tellurium.

  17. 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.

  18. Spin Nematics, Valence-Bond Solids, and Spin Liquids in SO(N) Quantum Spin Models on the Triangular Lattice.

    PubMed

    Kaul, Ribhu K

    2015-10-01

    We introduce a simple model of SO(N) spins with two-site interactions which is amenable to quantum Monte Carlo studies without a sign problem on nonbipartite lattices. We present numerical results for this model on the two-dimensional triangular lattice where we find evidence for a spin nematic at small N, a valence-bond solid at large N, and a quantum spin liquid at intermediate N. By the introduction of a sign-free four-site interaction, we uncover a rich phase diagram with evidence for both first-order and exotic continuous phase transitions. PMID:26550748

  19. Insights into the Electronic Structure of Ozone and Sulfur Dioxide from Generalized Valence Bond Theory: Addition of Hydrogen Atoms.

    PubMed

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

    2016-05-01

    Ozone (O3) and sulfur dioxide (SO2) are valence isoelectronic species, yet their properties and reactivities differ dramatically. In particular, O3 is highly reactive, whereas SO2 is chemically relatively stable. In this paper, we investigate serial addition of hydrogen atoms to both the terminal atoms of O3 and SO2 and to the central atom of these species. It is well-known that the terminal atoms of O3 are much more amenable to bond formation than those of SO2. We show that the differences in the electronic structure of the π systems in the parent triatomic species account for the differences in the addition of hydrogen atoms to the terminal atoms of O3 and SO2. Further, we find that the π system in SO2, which is a recoupled pair bond dyad, facilitates the addition of hydrogen atoms to the sulfur atom, resulting in stable HSO2 and H2SO2 species.

  20. Internal-strain effect on the valence band of strained silicon and its correlation with the bond angles

    SciTech Connect

    Inaoka, Takeshi Yanagisawa, Susumu; Kadekawa, Yukihiro

    2014-02-14

    By means of the first-principles density-functional theory, we investigate the effect of relative atom displacement in the crystal unit cell, namely, internal strain on the valence-band dispersion of strained silicon, and find close correlation of this effect with variation in the specific bond angles due to internal strain. We consider the [111] ([110]) band dispersion for (111) ((110)) biaxial tensility and [111] ([110]) uniaxial compression, because remarkably small values of hole effective mass m* can be obtained in this dispersion. Under the practical condition of no normal stress, biaxial tensility (uniaxial compression) involves additional normal compression (tensility) and internal strain. With an increase in the internal-strain parameter, the energy separation between the highest and second-highest valence bands becomes strikingly larger, and the highest band with conspicuously small m* extends remarkably down to a lower energy region, until it intersects or becomes admixed with the second band. This is closely correlated with the change in the specific bond angles, and this change can reasonably explain the above enlargement of the band separation.

  1. Thermochemical considerations and bond enthalpy ratios involving triatomic 16-valence electron neutrals and ions and some isoelectronically related pentaatomics

    NASA Astrophysics Data System (ADS)

    Deakyne, Carol A.; Norton, Lisa K.; Abele, Ashley M.; Ludden, Alicia K.; Liebman, Joel F.

    2007-11-01

    Following thermochemical studies and the accompanying analysis in the calorimetric literature, in earlier computational and conceptual studies we investigated the systematics of the mean bond enthalpy ratio /Dm°(XY) for 16-valence electron neutral and ionic triatomic species. For neutral species wherein X is a group 14 element and Y is from group 16, the ratio was ca. 0.8 rising to ca. 0.9 for the corresponding anions with X from group 13, and falling to ca. 0.7 for the cations with X from group 15. Good agreement between theory and experiment was found where admittedly the majority of the data for the latter is for the neutral species. In the current study at the G2 computational level (and G3 for selected systems), the related asymmetric valence isoelectronic triatomic species YXZ are discussed and this pattern calculationally preserved. The results are in concurrence with the one experimentally available datum for comparison, namely from the literature measured value for the enthalpy of formation of OCS. Other surprises and systematics are discussed as well for what otherwise might have been superficially considered to be simple species, for these and related pentaatomic species of the type HYXYH.

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

    PubMed

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

    2013-04-16

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

  3. On the Nature of Bonding in Parallel Spins in Monovalent Metal Clusters.

    PubMed

    Danovich, David; Shaik, Sason

    2016-05-27

    As we approach the Lewis model centennial, it may be timely to discuss novel bonding motifs. Accordingly, this review discusses no-pair ferromagnetic (NPFM) bonds that hold together monovalent metallic atoms using exclusively parallel spins. Thus, without any traditional electron-pair bonds, the bonding energy per atom in these clusters can reach 20 kcal mol(-1). This review describes the origins of NPFM bonding using a valence bond (VB) analysis, which shows that this bonding motif arises from bound triplet electron pairs that are delocalized over all the close neighbors of a given atom in the cluster. The VB model accounts for the tendency of NPFM clusters to assume polyhedral shapes with rather high symmetry and for the very steep rise of the bonding energy per atom. The advent of NPFM clusters offers new horizons in chemistry of highly magnetic species sensitive to magnetic and electric fields. PMID:27070320

  4. 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.

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

  6. 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.

  7. Electronic Model for CoO2 Layer Based Systems: Chiral Resonating Valence Bond Metal and Superconductivity

    NASA Astrophysics Data System (ADS)

    Baskaran, G.

    2003-08-01

    Takada et al. have reported superconductivity in layered NaxCoO2yH2O (Tc≈5 K). We model a reference neutral CoO2 layer as an orbitally nondegenerate spin-1/2 antiferromagnetic Mott insulator on a triangular lattice and NaxCoO2yH2O as electron doped Mott insulators described by a t-J model. It is suggested that at optimal doping chiral spin fluctuations enhanced by the dopant dynamics lead to a gapful d-wave superconducting state. A chiral resonating valence bond (RVB) metal, a parity and time (PT) reversal violating state with condensed RVB gauge fields, with a possible weak ferromagnetism, and low temperature p-wave superconductivity are also suggested at higher dopings.

  8. 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

  9. 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!

  10. Geometry of trigonal boron coordination sphere in boronic acids derivatives - a bond-valence vector model approach.

    PubMed

    Czerwińska, Karolina; Madura, Izabela D; Zachara, Janusz

    2016-04-01

    The systematic analysis of the geometry of three-coordinate boron in boronic acid derivatives with a common [CBO2] skeleton is presented. The study is based on the bond-valence vector (BVV) model [Zachara (2007). Inorg. Chem. 46, 9760-9767], a simple tool for the identification and quantitative estimation of both steric and electronic factors causing deformations of the coordination sphere. The empirical bond-valence (BV) parameters in the exponential equation [Brown & Altermatt (1985). Acta Cryst. B41, 244-247] rij and b, for B-O and B-C bonds were determined using data deposited in the Cambridge Structural Database. The values obtained amount to rBO = 1.364 Å, bBO = 0.37 Å, rBC = 1.569 Å, bBC = 0.28 Å, and they were further used in the calculation of BVV lengths. The values of the resultant BVV were less than 0.10 v.u. for 95% of the set comprising 897 [CBO2] fragments. Analysis of the distribution of BVV components allowed for the description of subtle in- and out-of plane deviations from the `ideal' (sp(2)) geometry of boron coordination sphere. The distortions specific for distinct groups of compounds such as boronic acids, cyclic and acyclic esters, benzoxaboroles and hemiesters were revealed. In cyclic esters the direction of strains was found to be controlled by the ring size effect. It was shown that the syn or anti location of substituents on O atoms is decisive for the deformations direction for both acids and acyclic esters. The greatest strains were observed in the case of benzoxaboroles which showed the highest deviation from the zero value of the resultant BVV. The out-of-plane distortions, described by the vz component of the resultant BVV, were ascertained to be useful in the identification of weak secondary interactions on the fourth coordination site of the boron centre. PMID:27048726

  11. 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 (π,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.

  12. Investigating hydroxide anion interfacial activity by classical and multi-state empirical valence bond molecular dynamics simulations

    SciTech Connect

    Dang, Liem X.; Wick, Collin D.

    2009-06-04

    Molecular dynamics simulations were carried out to understand the propensity of the hydroxide anion for the air-water interface. Two classes of molecular models were used, a classical polarizable model, and a polarizable multi-state empirical valence bond (MS-EVB) potential. The latter model was parameterized to reproduce the structures of small hydroxide-water clusters based on proton reaction coordinates. Furthermore, nuclear quantum effects were introduced into the MS-EVB model implicitly by refitting its potential energy function to account for them. The final MS-EVB model showed reasonable agreement with experiment and ab initio molecular dynamics simulations for dynamical and structural properties. The free energy profiles for both the classical and MS-EVB models were mapped out across the air-water interface, and the classical model gave a higher free energy at the interface with respect to bulk. The MS-EVB model gave a hydroxide anion that approached very close to the interface before it had a sharp increase in free energy at the Gibbs dividing surface. This showed a hydroxide anion that was present at the interface, but strongly repelled from its outer edge near the air. This work was supported by the US Department of Energy's Office of Basec Energy Sciences, Chemical Sciences program. Pacific northwest national Laboratory is operated by Battelle for DOE.

  13. 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-à-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

  14. Intramolecular C-H bond activation and redox isomerization across two-electron mixed valence diiridium cores.

    SciTech Connect

    Esswein, A. J.; Veige, A. S.; Piccoli, P. M. B.; Schultz, A. J.; Nocera, D. G.; MIT

    2008-03-24

    Metal-metal cooperativity enables the reaction of carbon-based substrates at diiridium two-electron mixed valence centers. Arylation of Ir{sub 2}{sup 0,II}(tfepma){sub 3}Cl{sub 2} (1) (tfepma = bis[(bistrifluoroethoxy)phosphino]methylamine) with RMgBr (R = C{sub 6}H{sub 5} and C{sub 6}D{sub 5}) is followed by C-H bond activation to furnish the bridging benzyne complex Ir{sub 2}II,II(tfepma){sub 3}({mu}-C{sub 6}H4)(C{sub 6}H{sub 5})H (2), as the kinetic product. At ambient temperature, 2 isomerizes to Ir{sub 2}{sup I,III}(tfepma){sub 3}({mu}-C{sub 6}H4)(C{sub 6}H{sub 5})H (3) (k{sub obs} = 9.57 {+-} 0.10 x 10{sup -5} s{sup -1} at 31.8 C, {Delta}H{sup {+-}} = 21.7 {+-} 0.3 kcal/mol, {Delta}S{sup {+-}} = -7.4 {+-} 0.9 eu), in which the benzyne moiety is conserved and the Ir{sup III} center is ligated by terminal hydride and phenyl groups. The same reaction course is observed for arylation of 1 with C{sub 6}D{sub 5}MgBr to produce 2-d{sub 10} and 3-d{sub 10} accompanied by an inverse isotope effect, k{sub h}/k{sub d} = 0.44 (k{sub obs} = 2.17 {+-} 0.10 x 10{sup -4} s{sup -1} in C{sub 6}D{sub 6} solution at 31.8 C, {Delta}H{sup {+-}} = 24.9 {+-} 0.7 kcal/mol, {Delta}S{sup {+-}} = -6.4 {+-} 2.4 eu). 2 reacts swiftly with hydrogen to provide Ir{sub 2}{sup II,II}(tfepma){sub 3}H{sub 4} as both the syn and anti isomers (4-syn and 4-anti, respectively). The hydrides of 4-syn were directly located by neutron diffraction analysis. X-ray crystallographic examination of 2, 2-d{sub 10}, 3, and 4-syn indicates that cooperative reactivity at the bimetallic diiridium core is facilitated by the ability of the two-electron mixed valence framework to accommodate the oxidation state changes and ligand rearrangements attendant to the reaction of the substrate.

  15. Change of the cerium valence with temperature - Structure and chemical bonding of HT-CeRhGe

    NASA Astrophysics Data System (ADS)

    Svitlyk, Volodymyr; Hermes, Wilfried; Chevalier, Bernard; Matar, Samir F.; Gaudin, Etienne; Voßwinkel, Daniel; Chernyshov, Dmitry; Hoffmann, Rolf-Dieter; Pöttgen, Rainer

    2013-07-01

    Polycrystalline CeRhGe was prepared via arc-melting of the elements. Its TiNiSi-related structures (space groups Pnma) were studied by powder diffraction using synchrotron radiation over the temperature range of 315-770 K. CeRhGe shows a first-order structural phase transition at 520 K upon heating. Ab initio elelectronic structure calculations give evidence for the depletion of the cerium 4f band in HT-CeRhGe and in consequence a redistribution of the electron density from the cerium to the rhodium atoms. Purely trivalent cerium atoms in the low-temperature modification (LT) change to intermediate-valent cerium in the high-temperature modification (HT). The integrated crystal orbital Hamilton populations show an enhancement of the Ce-Rh bonding in HT-CeRhGe. The three-dimensional [RhGe] polyanionic network shows drastic puckering of the [Rh3Ge3] hexagons in LT-CeRhGe and a flattening in HT-CeRhGe. The cerium valence change is accompanied by a drastic jump in the lattice parameters: a = 7.42249(8), b = 4.46699(5) and c = 7.1276(1) Å at 315 K vs. a = 7.24579(6), b = 4.47506(4) and c = 7.43579(6) Å at 570 K. Large shifts occur for the x parameter of the rhodium and the z parameter of the cerium atomic positions (Wyckoff sites 4c (x 1/4 z)).

  16. 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.

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

    PubMed

    Terlan, Bürgehan; 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 ρ(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

  18. The nature of chemical bonds from PNOF5 calculations.

    PubMed

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

    2012-06-18

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

  19. 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

  20. Use of bond-valence sums in modelling the diffuse scattering from PZN (PbZn1/3Nb2/3O3)

    PubMed Central

    Whitfield, R. E.; Welberry, T. R.; Paściak, M.; Goossens, D. J.

    2014-01-01

    This work extends previous efforts to model diffuse scattering from PZN (PbZn1/3Nb2/3O3). Earlier work [Welberry et al. (2005 ▶). J. Appl. Cryst. 38, 639–647; Welberry et al. (2006 ▶). Phys. Rev. B, 74, 224108] is highly prescriptive, using Monte Carlo simulation with very artificial potentials to induce short-range-order structures which were deduced as necessary from inspection of the data. While this gives valid results for the nature of the local structure, it does not strongly relate these structures to underlying crystal chemistry. In that work, the idea of the bond-valence sum was used as a guide to the expected behaviour of the atoms. This paper extends the use of the bond-valence sum from a qualitative guide to becoming a key aspect of the potential experienced by the atoms, through the idea of the global instability index, whose square has been shown to be proportional to the density functional theory energy of some systems when close to the minimum energy configuration.

  1. Neutron-diffraction studies and bond valence sums of charge neutrally doped Nd1-2xCaxThxBa2Cu3O7-δ

    NASA Astrophysics Data System (ADS)

    Lundqvist, P.; Rapp, Ö.; Tellgren, R.; Bryntse, I.

    1997-08-01

    Equal amounts of Ca and Th have been doped into the Nd1-2xCaxThxBa2Cu3O7-δ superconductor with x=0, 0.015, 0.03, 0.05, and 0.10. This causes a fast and linear decrease of the superconducting transition temperature, Tc. A single orthorhombic phase was observed with x-ray diffraction except for weak additional lines for the x=0.10 sample, suggesting a solubility limit below x=0.10. Neutron-diffraction measurements were performed and bond valence sums (BVS's) were calculated. The results showed a small increase in the Cu2-O4 distance and a nearly constant Cu2 valence. The total hole density in the plane, V- as defined by Tallon, remains almost constant with doping in contrast to the decrease observed for Ca-Pr doping. Other results from the BVS calculations also indicate differences between Ca-Th and Ca-Pr doping in the NdBa2Cu3O7-δ compound.

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

    PubMed

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

    2012-03-30

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

  3. 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.

  4. Valence-bond crystal in the extended Kagomé 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.

  5. 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.

  6. Multiple boron-boron bonds in neutral molecules: an insight from the extended transition state method and the natural orbitals for chemical valence scheme.

    PubMed

    Mitoraj, Mariusz P; Michalak, Artur

    2011-03-21

    We have analyzed the character of B═B and B≡B bonds in the neutral molecules of general form: LHB═BHL (2-L) and LB≡BL (3-L), for various ancillary ligands L attached to the boron center, based on a recently developed method that combines the extended transition state scheme with the theory of natural orbitals for chemical valence (ETS-NOCV). In the case of molecules with the B═B bond, 2-L, we have included L = PMe(3), PF(3), PCl(3), PH(3), C(3)H(4)N(2)═C(NHCH)(2), whereas for molecules containing the B≡B connection, 3-L, the following ligands were considered L = CO, PMe(3), PCl(3), (Me(2)NCH(2)CH(2)O)(2)Ge. The results led us to conclude that use of phosphorus ligands leads to strengthening of the B═B bond by 6.4 kcal/mol (for 2-PMe(3)), by 4.4 (for 2-PF(3)) and by 9.2 (for 2-PH(3)), when compared to a molecule developed on the experimental basis, 2-C(3)H(4)N(2) (ΔE(total) = -118.3 kcal/mol). The ETS scheme has shown that all contributions, that is, (i) orbital interaction ΔE(orb), (ii) Pauli repulsion ΔE(Pauli), and (iii) electrostatic stabilization ΔE(elstat), are important in determining the trend in the B═B bond energies, ΔE(total). ETS-NOCV results revealed that both σ(B═B) and π(B═B) contributions are responsible for the changes in ΔE(orb) values. All considered molecules of the type LB≡BL, 3-L, exhibit a stronger B≡B bond when compared to a double B═B connection in 2-L (|ΔE(total)| is lower by 11.8-42.5 kcal/mol, depending on the molecule). The main reason is a lower Pauli repulsion contribution noted for 3-CO, 3-PMe(3), and 3-PCl(3) molecules. In addition, in the case of 3-PMe(3) and 3-PCl(3), the orbital interaction term is more stabilizing; however, the effect is less pronounced compared to the drop in the Pauli repulsion term. In all of the systems with double and triple boron-boron bonds, the electronic factor (ΔE(orb)) dominates over the electrostatic contribution (ΔE(elstat)). Finally, the strongest B

  7. 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 .

  8. 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.

  9. 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

  10. A minimalistic approach to static and dynamic electron correlations: Amending generalized valence bond method with extended random phase approximation correlation correction.

    PubMed

    Chatterjee, Koushik; Pastorczak, Ewa; Jawulski, Konrad; Pernal, Katarzyna

    2016-06-28

    A perfect-pairing generalized valence bond (GVB) approximation is known to be one of the simplest approximations, which allows one to capture the essence of static correlation in molecular systems. In spite of its attractive feature of being relatively computationally efficient, this approximation misses a large portion of dynamic correlation and does not offer sufficient accuracy to be generally useful for studying electronic structure of molecules. We propose to correct the GVB model and alleviate some of its deficiencies by amending it with the correlation energy correction derived from the recently formulated extended random phase approximation (ERPA). On the examples of systems of diverse electronic structures, we show that the resulting ERPA-GVB method greatly improves upon the GVB model. ERPA-GVB recovers most of the electron correlation and it yields energy barrier heights of excellent accuracy. Thanks to a balanced treatment of static and dynamic correlation, ERPA-GVB stays reliable when one moves from systems dominated by dynamic electron correlation to those for which the static correlation comes into play. PMID:27369501

  11. Vibrational progressions in the valence ionizations of transition metal hydrides: evaluation of metal-hydride bonding and vibrations in (eta(5)-C(5)R(5))Re(NO)(CO)H [R = H, CH(3)].

    PubMed

    Lichtenberger, Dennis L; Gruhn, Nadine E; Rai-Chaudhuri, Anjana; Renshaw, Sharon K; Gladysz, John A; Jiao, Haijun; Seyler, Jeff; Igau, Alain

    2002-02-20

    The first examples of vibrational structure in metal-ligand sigma-bond ionizations are observed in the gas-phase photoelectron spectra of CpRe(NO)(CO)H and CpRe(NO)(CO)H [Cp = eta(5)-C(5)H(5), Cp = eta(5)-C(5)(CH(3))(5)]. The vibrational progressions are due to the Re-H stretch in the ion states formed by removal of an electron from the predominantly Re-H sigma-bonding orbitals. A vibrational progression is also observed in the corresponding ionization of the deuterium analogue, CpRe(NO)(CO)D, but with lower vibrational energy spacing as expected from the reduced mass effect. The vibrational progressions in these valence ionizations are directly informative about the nature of the metal-hydride bonding and electronic structure in these molecules. Franck-Condon analysis shows that for these molecules the Re-H or Re-D bond lengthens by 0.25(1) A when an electron is removed from the Re-H or Re-D sigma-bond orbital. This bond lengthening is comparable to that of H(2) upon ionization. Removal of an electron from the Re-H or Re-D bonds leads to a quantum-mechanical inner sphere reorganization energy (lambda(QM)) of 0.34(1) eV. These observations suggest that even in these low symmetry molecules the orbital corresponding to the Re-H sigma bond and the Re-H vibrational mode is very localized. Theoretical calculations of the electronic structure and normal vibrational modes of CpRe(NO)(CO)H support a localized two-electron valence bond description of the Re-H interaction.

  12. Polysulfide anions II: structure and vibrational spectra of the S4(2-) and S5(2-) anions. Influence of the cations on bond length, valence, and torsion angle.

    PubMed

    el Jaroudi, O; Picquenard, E; Demortier, A; Lelieur, J P; Corset, J

    2000-06-12

    The influence of the cations on bond length, valence, and torsion angle of S4(2-) and S5(2-) anions was examined in a series of solid alkali tetra- and pentasulfides by relating their Raman spectra to their known X-ray structures through a force-field analysis. The IR and Raman spectra of BaS4.H2O and the Raman spectra of (NH4)2S4.nNH3, gamma-Na2S4, and delta-Na2S5 are presented. The similarity of spectra of gamma-Na2S4 with those of BaS4.H2O suggests similar structures of the S4(2-) anions in these two compounds with a torsion angle smaller than 90 degrees. The variations of SS bond length, SSS valence angle, and dihedral angle of Sn2- anions are related to the polarization of the lone pair and electronic charge of the anion by the electric field of the cations. A correlation between the torsion angle and the SSS valence angle is shown as that previously reported between the length of the bond around which the torsion takes place and the dihedral angle value. These geometry changes are explained by the hyperconjugation concept and the electron long-pair repulsion.

  13. 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; Bauzá, Antonio; Frontera, Antonio; Ghosh, Ashutosh

    2015-02-28

    Three new mixed valence trinuclear Co(II/III) compounds cis-[Co3L2(MeOH)2(N3)2(μ1,1-N3)2] (1), trans-[Co3L2(H2O)2(N3)2(μ1,1-N3)2]·(H2O)2 (2) and [Co3L(R)2(N3)3(μ1,3-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 μ2-phenoxido oxygen and μ1,1-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 μ2-phenoxido and μ1,1-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 μ1,3-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

  14. Connecting a new non-adiabatic vibrational mass to the bonding mechanism of LiH: A quantum superposition of ionic and covalent states

    NASA Astrophysics Data System (ADS)

    Diniz, Leonardo G.; Alijah, Alexander; Adamowicz, Ludwik; Mohallem, José R.

    2015-07-01

    Non-adiabatic vibrational calculations performed with the accuracy of 0.2 cm-1 spanning the whole energy spectrum up to the dissociation limit for 7LiH are reported. A so far unknown v = 23 energy level is predicted. The key feature of the approach used in the calculations is a valence-bond (VB) based procedure for determining the effective masses of the two vibrating atoms, which depend on the internuclear distance, R. It is found that all LiH electrons participate in the vibrational motion. The R-dependent masses are obtained from the analysis of the simple VB two-configuration ionic-covalent representation of the electronic wave function. These findings are consistent with an interpretation of the chemical bond in LiH as a quantum mechanical superposition of one-electron ionic and covalent states.

  15. 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.

  16. Consequences of Optimal Bond Valence on Structural Rigidity and Improved Luminescence Properties in SrxBa2-xSiO4:Eu2+ Orthosilicate Phosphors

    SciTech Connect

    Denault, Kristin A.; Brgoch, Jakoah; Gaultois, Michael W.; Mikhailovsky, Alexander; Petry, Ralf; Winkler, Holger; DenBaars, Steven P.; Seshadri, Ram

    2014-08-19

    The orthosilicate phosphors SrxBa2–xSiO4:Eu2+ have now been known for over four decades and have found extensive recent use in solid-state white lighting. It is well-recognized in the literature and in practice that intermediate compositions in the solid-solutions between the orthosilicates Sr2SiO4 and Ba2SiO4 yield the best phosphor hosts when the thermal stability of luminescence is considered. We employ a combination of synchrotron X-ray diffraction, total scattering measurements, density functional theory calculations, and low-temperature heat capacity measurements, in conjunction with detailed temperature- and time-resolved studies of luminescence properties to understand the origins of the improved luminescence properties. We observe that in the intermediate compositions, the two cation sites in the crystal structure are optimally bonded as determined from bond valence sum calculations. Optimal bonding results in a more rigid lattice, as established by the intermediate compositions possessing the highest Debye temperature, which are determined experimentally from low-temperature heat capacity measurements. Greater rigidity in turn results in the highest luminescence efficiency for intermediate compositions at elevated temperatures.

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

    PubMed

    Scriven, E P; Powell, B J

    2012-08-31

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

  18. 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

  19. 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

  20. Fabrication of VB2/air cells for electrochemical testing.

    PubMed

    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

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

    NASA Astrophysics Data System (ADS)

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

    2012-02-01

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

  2. 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.

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

    PubMed

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

    2015-09-14

    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 π-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.

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

    SciTech Connect

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

    2015-09-14

    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 π-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.

  6. Highly efficient perturbative + variational strategy based on orthogonal valence bond theory for the evaluation of magnetic coupling constants. Application to the trinuclear Cu(ii) site of multicopper oxidases.

    PubMed

    Tenti, Lorenzo; Maynau, Daniel; Angeli, Celestino; Calzado, Carmen J

    2016-07-21

    A new strategy based on orthogonal valence-bond analysis of the wave function combined with intermediate Hamiltonian theory has been applied to the evaluation of the magnetic coupling constants in two AF systems. This approach provides both a quantitative estimate of the J value and a detailed analysis of the main physical mechanisms controlling the coupling, using a combined perturbative + variational scheme. The procedure requires a selection of the dominant excitations to be treated variationally. Two methods have been employed: a brute-force selection, using a logic similar to that of the CIPSI approach, or entanglement measures, which identify the most interacting orbitals in the system. Once a reduced set of excitations (about 300 determinants) is established, the interaction matrix is dressed at the second-order of perturbation by the remaining excitations of the CI space. The diagonalization of the dressed matrix provides J values in good agreement with experimental ones, at a very low-cost. This approach demonstrates the key role of d → d* excitations in the quantitative description of the magnetic coupling, as well as the importance of using an extended active space, including the bridging ligand orbitals, for the binuclear model of the intermediates of multicopper oxidases. The method is a promising tool for dealing with complex systems containing several active centers, as an alternative to both pure variational and DFT approaches.

  7. 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

  8. 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…

  9. An investigation report about the lack of VB1

    PubMed Central

    Zhu, Hangju

    2016-01-01

    From August 1 to September 26, 2012, 30 workers who had the symptom of edema in both lower limbs were reported in Yancheng, Four severe edemas in both lower limbs workers were sent to the hospital, and one person of the workers died. The epidemiology investigation and laboratory testing (in the urine loading tests, the concentration of VB1 of the workers living in the factory for more than half of the year decreased far below the normal values) were conducted to explore the cause. Furthermore, after one-week intramuscular injection of thiamine treatment, the clinical symptoms of the workers had been improved greatly. Finally, the lake of the thiamine (VB1) was considered to be the reason of this incident.

  10. An investigation report about the lack of VB1.

    PubMed

    Zhu, Hangju; Sun, Guiju; Zhu, Baoli

    2016-08-01

    From August 1 to September 26, 2012, 30 workers who had the symptom of edema in both lower limbs were reported in Yancheng, Four severe edemas in both lower limbs workers were sent to the hospital, and one person of the workers died. The epidemiology investigation and laboratory testing (in the urine loading tests, the concentration of VB1 of the workers living in the factory for more than half of the year decreased far below the normal values) were conducted to explore the cause. Furthermore, after one-week intramuscular injection of thiamine treatment, the clinical symptoms of the workers had been improved greatly. Finally, the lake of the thiamine (VB1) was considered to be the reason of this incident. PMID:27621883

  11. An investigation report about the lack of VB1

    PubMed Central

    Zhu, Hangju

    2016-01-01

    From August 1 to September 26, 2012, 30 workers who had the symptom of edema in both lower limbs were reported in Yancheng, Four severe edemas in both lower limbs workers were sent to the hospital, and one person of the workers died. The epidemiology investigation and laboratory testing (in the urine loading tests, the concentration of VB1 of the workers living in the factory for more than half of the year decreased far below the normal values) were conducted to explore the cause. Furthermore, after one-week intramuscular injection of thiamine treatment, the clinical symptoms of the workers had been improved greatly. Finally, the lake of the thiamine (VB1) was considered to be the reason of this incident. PMID:27621883

  12. 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.

  13. Multiple valence superatoms.

    PubMed

    Reveles, J U; Khanna, S N; Roach, P J; Castleman, A W

    2006-12-01

    We recently demonstrated that, in gas phase clusters containing aluminum and iodine atoms, an Al(13) cluster behaves like a halogen atom, whereas an Al(14) cluster exhibits properties analogous to an alkaline earth atom. These observations, together with our findings that Al(13)(-) is inert like a rare gas atom, have reinforced the idea that chosen clusters can exhibit chemical behaviors reminiscent of atoms in the periodic table, offering the exciting prospect of a new dimension of the periodic table formed by cluster elements, called superatoms. As the behavior of clusters can be controlled by size and composition, the superatoms offer the potential to create unique compounds with tailored properties. In this article, we provide evidence of an additional class of superatoms, namely Al(7)(-), that exhibit multiple valences, like some of the elements in the periodic table, and hence have the potential to form stable compounds when combined with other atoms. These findings support the contention that there should be no limitation in finding clusters, which mimic virtually all members of the periodic table.

  14. Multiple valence superatoms

    PubMed Central

    Reveles, J. U.; Khanna, S. N.; Roach, P. J.; Castleman, A. W.

    2006-01-01

    We recently demonstrated that, in gas phase clusters containing aluminum and iodine atoms, an Al13 cluster behaves like a halogen atom, whereas an Al14 cluster exhibits properties analogous to an alkaline earth atom. These observations, together with our findings that Al13− is inert like a rare gas atom, have reinforced the idea that chosen clusters can exhibit chemical behaviors reminiscent of atoms in the periodic table, offering the exciting prospect of a new dimension of the periodic table formed by cluster elements, called superatoms. As the behavior of clusters can be controlled by size and composition, the superatoms offer the potential to create unique compounds with tailored properties. In this article, we provide evidence of an additional class of superatoms, namely Al7−, that exhibit multiple valences, like some of the elements in the periodic table, and hence have the potential to form stable compounds when combined with other atoms. These findings support the contention that there should be no limitation in finding clusters, which mimic virtually all members of the periodic table. PMID:17121987

  15. 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.

  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 scene’s affective content. Although typical visual scenes contain mostly “everyday” objects, the affect perception in visual objects has been studied using somewhat atypical stimuli with strong affective valences (e.g., guns or roses). Here we explore whether affective valence must be strong or overt to exert an effect on our visual perception. We conclude that everyday objects carry subtle affective valences – “micro-valences” – which are intrinsic to their perceptual representation. PMID:22529828

  17. Theoretical description of hydrogen bonding in oxalic acid dimer and trimer based on the combined extended-transition-state energy decomposition analysis and natural orbitals for chemical valence (ETS-NOCV)

    PubMed Central

    Mitoraj, Mariusz P.; Kurczab, Rafał; Boczar, Marek

    2010-01-01

    In the present study we have analyzed hydrogen bonding in dimer and trimer of oxalic acid, based on a recently proposed charge and energy decomposition scheme (ETS-NOCV). In the case of a dimer, two conformations, α and β, were considered. The deformation density contributions originating from NOCV’s revealed that the formation of hydrogen bonding is associated with the electronic charge deformation in both the σ—(Δρσ) and π-networks (Δρπ). It was demonstrated that σ-donation is realized by electron transfer from the lone pair of oxygen on one monomer into the empty \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\rho_{H - O}^* $$\\end{document} orbital of the second oxalic acid fragment. In addition, a covalent contribution is observed by the density transfer from hydrogen of H-O group in one oxalic acid monomer to the oxygen atom of the second fragment. The resonance assisted component (Δρπ), is based on the transfer of electron density from the π—orbital localized on the oxygen of OH on one oxalic acid monomer to the oxygen atom of the other fragment. ETS-NOCV allowed to conclude that the σ(O---HO) component is roughly eight times as important as π (RAHB) contribution in terms of energetic estimation. The electrostatic factor (ΔEelstat) is equally as important as orbital interaction term (ΔEorb). Finally, comparing β-dimer of oxalic acid with trimer we found practically no difference concerning each of the O---HO bonds, neither qualitative nor quantitative. Figure The contours of deformation density σ- and π-contributions describing the hydrogen bonding between the monomers in the oxalic acid dimer, together with the corresponding ETS-NOCV-based orbital-interaction energies (in kcal/mol). PMID:20505966

  18. 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…

  19. 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. Rößler, 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 ΔE{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 ΔE{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, ΔE{sub B,CL} − ΔE{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 ΔE{sub V}{sup CNL} = 2.65 ± 0.3 eV agrees well with the experimental ΔE{sub V}.

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

    PubMed

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

    1995-03-01

    The recombinant proteins of Lol p VA and Lol p VB expressed in E. coli reacted with IgE antibodies from sera of allergic patients and mAbs FMC A7 and PpV1. Cross-absorption analyses using these recombinant proteins showed that Lol p VA and Lol p VB possess both similar and unique IgE binding determinants. Gene fragmentation was utilized to localize the antigenic and allergenic determinants of Lol p VB. When full-length cDNA of Lol p VB was digested into three fragments and expressed as the fusions from the glutathione transferase of pGEX vectors, fragments Met1-Val196 and Asp197-Val339 bound IgE while fragment Met1-Pro96 did not. The data suggest that there are at least two IgE binding determinants in Lol p VB. In addition, only fragment Met1-Val196 reacted with mAb PpV1. The localization of these determinants was further resolved using random fragment expression libraries. The mAb PpV1 determinant was near the N-terminal region of Lol p VB molecule. The IgE binding determinants were distributed in the central region: region I (amino acids 111-195) and II (199-254). These IgE binding determinants are conserved in Lol p VA.

  1. Evaluation of valence band top and electron affinity of SiO2 and Si-based semiconductors using X-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Fujimura, Nobuyuki; Ohta, Akio; Makihara, Katsunori; Miyazaki, Seiichi

    2016-08-01

    An evaluation method for the energy level of the valence band (VB) top from the vacuum level (VL) for metals, dielectrics, and semiconductors from the results of X-ray photoelectron spectroscopy (XPS) is presented for the accurate determination of the energy band diagram for materials of interest. In this method, the VB top can be determined by the energy difference between the onset of VB signals and the cut-off energy for secondary photoelectrons by considering the X-ray excitation energy (hν). The energy level of the VB top for three kinds of Si-based materials (H-terminated Si, wet-cleaned 4H-SiC, and thermally grown SiO2) has been investigated by XPS under monochromatized Al Kα radiation (hν = 1486.6 eV). We have also demonstrated the determination of the electron affinity for the samples by this measurement technique in combination with the measured and reported energy bandgaps (E g).

  2. Electron-pair density decomposition for core-valence separable systems.

    PubMed

    Wang, Jian; Wang, Yu; Ugalde, Jesus M

    2012-10-30

    The electron pair density of a core-valence separable system can be decomposed into three parts: core-core, core-valence, and valence-valence. The core-core part has a Hartree-Fock like structure. The core-valence part can be written as Γ(cv) (1,2) = γ(c) (1,1)γ(v) (2,2) - γ(c) (1,2)γ(v) (2,1) + γ(c) (2,2)γ(v) (1,1) - γ(c) (2,1)γ(v) (1,2), where only the 1-matrices from the core and valence orbitals contribute. The valence-valence part is left to be determined from the reduced frozen-core type wave function, which often contains the essential information on the electron correlation and the chemical bond. We demonstrate the analysis to the ground state of negative ion Li(-) and 2(1)Σ(u)(+) excited state of the Li(2) molecule.

  3. 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

  4. Valence-bound and diffuse-bound anions of 5-azauracil.

    PubMed

    Corzo, H H; Dolgounitcheva, O; Zakrzewski, V G; Ortiz, J V

    2014-08-28

    Structures, isomerization energies, and electron binding energies of 5-azauracil and its anions have been calculated ab initio with perturbative, coupled-cluster, and electron-propagator methods. Tautomeric structures, including those produced by proton transfer to a CH group, have been considered. Dyson orbitals and pole strengths from electron-propagator calculations validated a simple, molecular-orbital picture of anion formation. In one case, an electron may enter a delocalized π orbital, yielding a valence-bound (VB) anion with a puckered ring structure. The corresponding electron affinity is 0.27 eV; the vertical electron detachment energy (VEDE) of this anion 1.05 eV. An electron also may enter a molecular orbital that lies outside the nuclear framework, resulting in a diffuse-bound (DB) anion. In the latter case, the electron affinity is 0.06 eV and the VEDE of the DB anion is 0.09 eV. Another VB isomer that is only 0.02 eV more stable than the neutral molecule has a VEDE of 2.0 eV.

  5. Sensitivity Experiments on the Impact of Vb-Cyclones to Ocean Temperature and Soil Moisture Changes

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    Cyclones developing over the western Mediterranean and move northeastward are a major source of extreme weather and responsible for heavy precipitation over Central Europe. Gaining insight into these processes is crucial to improve the projection of changes in frequency and severity of these so-called Vb-cyclones under future climate change scenarios. This study explores the impact of climate change on Vb-events through a number of idealized sensitivity experiments that assess the role of the sea surface temperature (SST) and soil moisture and their contribution to the moisture content in the atmosphere in recent Vb-events. To achieve this task, we use the Weather Research and Forecasting model (WRF) to dynamically downscale the ERA Interim reanalysis, simulating five prominent Vb-events that led to extreme precipitation in Central Europe. WRF allows simulating a physical consistent response of Vb-cyclones to different SSTs and soil water volumes. The changes in SSTs are designed to follow the expected temperature changes in a future climate scenario. Additionally the corresponding uncertainty in such projections is considered. Results indicate that although an increase of the Mediterranean SSTs leads to increased precipitation over Central Europe, e.g. 136% greater precipitation in the +5 K experiment compared to the control simulation, a change in the high-impact region of Vb-events at the northern side of the Alps is not found. This counter-intuitive behavior seems to be related to the increase of atmospheric instability over the artificially heated SSTs. Thereby, precipitation notably increases over the east Adriatic coast in response to warmer SSTs, which corresponds to the first location where the air is lifted. However, Vb-events become less destructive in their high-impact region, due to high loss of atmospheric water. Further experiments demonstrate that changing the SSTs of the Atlantic invokes almost no reaction (around 1% change) with respect to

  6. Equilibrium CO bond lengths

    NASA Astrophysics Data System (ADS)

    Demaison, Jean; Császár, 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 Å within the full range of 1.10-1.43 Å, 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.

  7. 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.

  8. Characterization of Vc-Vb Particles Reinforced Fe-Based Composite Coatings Produced by Laser Cladding

    NASA Astrophysics Data System (ADS)

    Qu, K. L.; Wang, X. H.; Wang, Z. K.

    2016-03-01

    In situ synthesized VC-VB particles reinforced Fe-based composite coatings were produced by laser beam melting mixture of ferrovanadium (Fe-V) alloy, boron carbide (B4C), CaF2 and Fe-based self-melting powders. The results showed that VB particles with black regular and irregular blocky shape and VC with black flower-like shape were uniformly distributed in the coatings. The type, amount, and size of the reinforcements were influenced by the content of FeV40 and B4C powders. Compared to the substrate, the hardness and wear resistance of the composite coatings were greatly improved.

  9. Circulation Type Classifications and their nexus to Van Bebber's storm track Vb

    NASA Astrophysics Data System (ADS)

    Hofstätter, M.; Chimani, B.

    2012-04-01

    Circulation Type Classifications (CTCs) are tools to identify repetitive and predominantly stationary patterns of the atmospheric circulation over a certain area, with the purpose to enable the recognition of specific characteristics in surface climate variables. On the other hand storm tracks can be used to identify similar types of synoptic events from a non-stationary, kinematic perspective. Such a storm track classification for Europe has been done in the late 19th century by Van Bebber (1882, 1891), from which the famous type Vb and Vc/d remained up to the present day because of to their association with major flooding events like in August 2002 in Europe. In this work a systematic tracking procedure has been developed, to determine storm track types and their characteristics especially for the Eastern Alpine Region in the period 1961-2002, using ERA40 and ERAinterim reanalysis. The focus thereby is on cyclone tracks of type V as suggested by van Bebber and congeneric types. This new catalogue is used as a reference to verify the hypothesis of a certain coherence of storm track Vb with certain circulation types (e.g. Fricke and Kaminski, 2002). Selected objective and subjective classification schemes from the COST733 action (http://cost733.met.no/, Phillip et al. 2010) are used therefore, as well as the manual classification from ZAMG (Lauscher 1972 and 1985), in which storm track Vb has been classified explicitly on a daily base since 1948. The latter scheme should prove itself as a valuable and unique data source in that issue. Results show that not less than 146 storm tracks are identified as Vb between 1961 and 2002, whereas only three events could be found from literature, pointing to big subjectivity and preconception in the issue of Vb storm tracks. The annual number of Vb storm tracks do not show any significant trend over the last 42 years, but large variations from year to year. Circulation type classification CAP27 (Cluster Analysis of Principal

  10. 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…

  11. Crossover and valence band Kβ X-rays of chromium oxides

    NASA Astrophysics Data System (ADS)

    Fazinić, Stjepko; Mandić, Luka; Kavčič, Matjaž; Božičević, Iva

    2011-06-01

    Kβ X-ray spectra of chromium metal and selected chromium oxides were measured twice using medium resolution flat crystal spectrometer and high resolution spectrometer employing Johansson geometry after excitation with 2 MeV proton beams. The positions and intensities of crossover ( Kβ″) and valence ( Kβ2,5) band X-rays relative to the primary Kβ X-ray components were extracted in a consistent way. The results were compared with the existing data obtained by proton and photon induced ionization mechanisms and theoretical predictions. The obtained results in peak relative positions and intensities were analyzed in order to study dependence on the chromium oxidation states and chromium-oxygen bond lengths in selected chromium oxides. Our results obtained by both spectrometers confirm that the linear trend observed for the valence peak relative energy shift as a function of chromium oxidation number does not depend on the experimental resolution. Experimental results for normalized intensities (i.e. relative intensities divided with the number of chromium-oxygen pairs) of crossover and valence band X-rays obtained by both spectrometers are in very good agreement, and follow exponential relationship with the average Cr―O bond lengths in corresponding chromium oxides. The observed trends in crossover and valence X-rays normalized intensities could be used to measure the average chromium-oxygen bond length in various chromium oxides, with the sum of both crossover and valence X-ray normalized intensities being the most sensitive measure.

  12. 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.

  13. X-ray imaging of chemically active valence electrons during a pericyclic reaction.

    PubMed

    Bredtmann, Timm; Ivanov, Misha; Dixit, Gopal

    2014-11-26

    Time-resolved imaging of chemically active valence electron densities is a long-sought goal, as these electrons dictate the course of chemical reactions. However, X-ray scattering is always dominated by the core and inert valence electrons, making time-resolved X-ray imaging of chemically active valence electron densities extremely challenging. Here we demonstrate an effective and robust method, which emphasizes the information encoded in weakly scattered photons, to image chemically active valence electron densities. The degenerate Cope rearrangement of semibullvalene, a pericyclic reaction, is used as an example to visually illustrate our approach. Our work also provides experimental access to the long-standing problem of synchronous versus asynchronous bond formation and breaking during pericyclic reactions.

  14. X-ray imaging of chemically active valence electrons during a pericyclic reaction

    PubMed Central

    Bredtmann, Timm; Ivanov, Misha; Dixit, Gopal

    2014-01-01

    Time-resolved imaging of chemically active valence electron densities is a long-sought goal, as these electrons dictate the course of chemical reactions. However, X-ray scattering is always dominated by the core and inert valence electrons, making time-resolved X-ray imaging of chemically active valence electron densities extremely challenging. Here we demonstrate an effective and robust method, which emphasizes the information encoded in weakly scattered photons, to image chemically active valence electron densities. The degenerate Cope rearrangement of semibullvalene, a pericyclic reaction, is used as an example to visually illustrate our approach. Our work also provides experimental access to the long-standing problem of synchronous versus asynchronous bond formation and breaking during pericyclic reactions. PMID:25424639

  15. Proteolytic activity of Enterococcus faecalis VB63F for reduction of allergenicity of bovine milk proteins.

    PubMed

    Biscola, V; Tulini, F L; Choiset, Y; Rabesona, H; Ivanova, I; Chobert, J-M; Todorov, S D; Haertlé, T; Franco, B D G M

    2016-07-01

    With the aim of screening proteolytic strains of lactic acid bacteria to evaluate their potential for the reduction of allergenicity of the major bovine milk proteins, we isolated a new proteolytic strain of Enterococcus faecalis (Ent. faecalis VB63F) from raw bovine milk. The proteases produced by this strain had strong activity against caseins (αS1-, αS2-, and β-casein), in both skim milk and sodium caseinate. However, only partial hydrolysis of whey proteins was observed. Proteolysis of Na-caseinate and whey proteins, observed after sodium dodecyl sulfate-PAGE, was confirmed by analysis of peptide profiles by reversed-phase HPLC. Inhibition of proteolysis with EDTA indicated that the proteases produced by Ent. faecalis VB63F belonged to the group of metalloproteases. The optimal conditions for their activity were 42°C and pH 6.5. The majority of assessed virulence genes were absent in Ent. faecalis VB63F. The obtained results suggest that Ent. faecalis VB63F could be efficient in reducing the immunoreactivity of bovine milk proteins. PMID:27179865

  16. Bearer channel control protocol for the dynamic VB5.2 interface in ATM access networks

    NASA Astrophysics Data System (ADS)

    Fragoulopoulos, Stratos K.; Mavrommatis, K. I.; Venieris, Iakovos S.

    1996-12-01

    In the multi-vendor systems, a customer connected to an Access network (AN) must be capable of selecting a specific Service Node (SN) according to the services the SN provides. The multiplicity of technologically varying AN calls for the definition of a standard reference point between the AN and the SN widely known as the VB interface. Two versions are currently offered. The VB5.1 is simpler to implement but is not as flexible as the VB5.2, which supports switched connections. The VB5.2 functionality is closely coupled to the Broadband Bearer Channel Connection Protocol (B-BCCP). The B-BCCP is used for conveying the necessary information for dynamic resource allocation, traffic policing and routing in the AN as well as for information exchange concerning the status of the AN before a new call is established by the SN. By relying on such a protocol for the exchange of information instead of intercepting and interpreting signalling messages in the AN, the architecture of the AN is simplified because the functionality related to processing is not duplicated. In this paper a prominent B- BCCP candidate is defined, called the Service node Access network Interaction Protocol.

  17. 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

    2016-02-14

    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.

  18. 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

    2016-02-14

    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

  19. 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.

  20. 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.

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

    PubMed Central

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

    2012-01-01

    The severe phenotypic effects of altered glycosylation in the congenital muscular dystrophies, including Walker-Warburg syndrome, muscle-eye-brain disease, Fukuyama congenital muscular dystrophy, and congenital muscular dystrophy 1D, are caused by mutations resulting in altered glycans linked to proteins through O-linked mannose. A glycosyltransferase that branches O-Man, N-acetylglucosaminyltransferase Vb (GnT-Vb), is highly expressed in neural tissues. To understand the expression and function of GnT-Vb, we studied its expression during neuromorphogenesis and generated GnT-Vb null mice. A paralog of GnT-Vb, N-acetylglucosaminyltransferase (GnT-V), is expressed in many tissues and brain, synthesizing N-linked, β1,6-branched glycans, but its ability to synthesize O-mannosyl-branched glycans is unknown; conversely, although GnT-Vb can synthesize N-linked glycans in vitro, its contribution to their synthesis in vivo is unknown. Our results showed that deleting both GnT-V and GnT-Vb results in the total loss of both N-linked and O-Man-linked β1,6-branched glycans. GnT-V null brains lacked N-linked, β1,6-glycans but had normal levels of O-Man β1,6-branched structures, showing that GnT-Vb could not compensate for the loss of GnT-V. By contrast, GnT-Vb null brains contained normal levels of N-linked β1,6-glycans but low levels of some O-Man β1,6-branched glycans. Therefore, GnT-V could partially compensate for GnT-Vb activity in vivo. We found no apparent change in α-dystroglycan binding of glycan-specific antibody IIH6C4 or binding to laminin in GnT-Vb null mice. These results demonstrate that GnT-V is involved in synthesizing branched O-mannosyl glycans in brain, but the function of these branched O-mannosyl structures is unresolved using mice that lack these glycosyltransferases. PMID:22715095

  2. Rare beryllium icosahedra in the intermediate valence compound CeBe13.

    PubMed

    Wilson, Zakiya S; Macaluso, Robin T; Bauer, E D; Smith, J L; Thompson, J D; Fisk, Z; Stanley, George G; Chan, Julia Y

    2004-11-01

    Single-crystal X-ray diffraction experiments show that the Be atoms in CeBe13 form a Be12 icosahedra, which is a very unusual structural feature due, in part, to the remarkably low valence electron count of Be. Magnetization studies show that CeBe13 displays intermediate valence behavior, in which valence fluctuations between the Ce 4f0 and 4f1 states give rise to enhanced electronic specific heat and magnetic susceptibility. Calculations using ab initio theory were used to determine the electronic structure and bonding and to give insight into the relationship between the crystal structure, the bonding, and the intermediate valence behavior of CeBe13. The hybridization between the localized f electrons and the conduction electrons is responsible for the large values of the electronic specific heat coefficient (gamma approximately 100 mJ/mol K2) and magnetic susceptibility (chi approximately 1 x 10-3 emu/mol), which is in marked contrast to those of ordinary metals that have gamma approximately 1 mJ/mol K2 and chi approximately 1 x 10-5 emu/mol values. The magnetic susceptibility, chi = M/H versus T, of a single crystal of CeBe13 exhibits a broad maximum at Tmax approximately 130 K and is typical of intermediate valence systems with an unusually large energy scale (Kondo), TK approximately 500 K.

  3. Morphological Characteristics of Electrophysiologically Characterized Layer Vb Pyramidal Cells in Rat Barrel Cortex

    PubMed Central

    Loucif, Alexandre J. C.; Schubert, Dirk; Möck, Martin

    2016-01-01

    Layer Vb pyramidal cells are the major output neurons of the neocortex and transmit the outcome of cortical columnar signal processing to distant target areas. At the same time they contribute to local tactile information processing by emitting recurrent axonal collaterals into the columnar microcircuitry. It is, however, not known how exactly the two types of pyramidal cells, called slender-tufted and thick-tufted, contribute to the local circuitry. Here, we investigated in the rat barrel cortex the detailed quantitative morphology of biocytin-filled layer Vb pyramidal cells in vitro, which were characterized for their intrinsic electrophysiology with special emphasis on their action potential firing pattern. Since we stained the same slices for cytochrome oxidase, we could also perform layer- and column-related analyses. Our results suggest that in layer Vb the unambiguous action potential firing patterns "regular spiking (RS)" and "repetitive burst spiking (RB)" (previously called intrinsically burst spiking) correlate well with a distinct morphology. RS pyramidal cells are somatodendritically of the slender-tufted type and possess numerous local intralaminar and intracolumnar axonal collaterals, mostly reaching layer I. By contrast, their transcolumnar projections are less well developed. The RB pyramidal cells are somatodendritically of the thick-tufted type and show only relatively sparse local axonal collaterals, which are preferentially emitted as long horizontal or oblique infragranular collaterals. However, contrary to many previous slice studies, a substantial number of these neurons also showed axonal collaterals reaching layer I. Thus, electrophysiologically defined pyramidal cells of layer Vb show an input and output pattern which suggests RS cells to be more "locally segregating" signal processors whereas RB cells seem to act more on a "global integrative" scale. PMID:27706253

  4. Isolation and characterization of mucous exopolysaccharide (EPS) produced by Vibrio furnissii strain VB0S3.

    PubMed

    Bramhachari, P V; Kishor, P B Kavi; Ramadevi, R; Kumar, Ranadheer; Rao, B Rama; Dubey, Santosh Kumar

    2007-01-01

    Marine bacterial strains were isolated from coastal regions of Goa and screened for the strains that produce the highest amount of mucous exopolysaccharide (EPS). Our screening resulted in the identification of the strain Vibrio furnissii VB0S3 (hereafter called VB0S3), as it produced the highest EPS in batch cultures during the late logarithmic growth phase. The isolate was identified as VB0S3 based on morphological and biochemical properties. Growth and EPS production were studied in mineral salts medium supplemented with NaCl (1.5%) and glucose (0.2%). The exopolymer was recovered from the culture supernatant by using three volumes of cold ethanol precipitation and dialysis procedure. Chemical analyses of EPS revealed that it is primarily composed of neutral sugars, uronic acids, and proteins. Fourier-transform infrared (FT-IR) spectroscopy revealed the presence of carboxyl, hydroxyl, and amide groups, which correspond to a typical heteropolymeric polysaccharide, and the EPS also possessed good emulsification activity. The gas chromatographic analysis of an alditol-acetate derivatized sample of EPS revealed that it was mainly composed of galactose and glucose. Minor components found were mannose, rhamnose, fucose, ribose, arabinose, and xylose. EPS was readily isolated from culture supernatants, which suggests that the EPS was a slime-like exopolysaccharide. This is the first report of exopolysaccharide characterization that describes the isolation and characterization of an EPS expressed by Vibrio furnissii strain VB0S3. The results of the study contribute significantly and go a long way towards an understanding of the correlation between growth and EPS production, chemical composition, and industrial applications of the exopolysaccharide in environmental biotechnology and bioremediation.

  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.

  6. 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 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

  7. 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.

  8. 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)

  9. 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

  10. 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

  11. 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

  12. Probing valence orbital composition with iron Kbeta X-ray emission spectroscopy.

    PubMed

    Lee, Nicole; Petrenko, Taras; Bergmann, Uwe; Neese, Frank; DeBeer, Serena

    2010-07-21

    A systematic study of 12 ferric and ferrous Kbeta X-ray emission spectra (XES) is presented. The factors contributing to the Kbeta main line and the valence to core region of the spectra are experimentally assessed and quantitatively evaluated. While the Kbeta main line spectra are dominated by spin state contributions, the valence to core region is shown to have greater sensitivity to changes in the chemical environment. A density functional theory (DFT) based approach is used to calculate the experimental valence spectra and to evaluate the contributions to experimental intensities and energies. The spectra are found to be dominated by iron np to 1s electric dipole allowed transitions, with pronounced sensitivity to spin state, ligand identity, ligand ionization state, hybridization state, and metal-ligand bond lengths. These findings serve as an important calibration for future applications to iron active sites in biological and chemical catalysis. Potential applications to Compound II heme derivatives are highlighted.

  13. 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

  14. 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

  15. 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.

  16. 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.

  17. 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.

  18. Evidence for Valence Alternation in Amorphous Selenium

    NASA Astrophysics Data System (ADS)

    Xiaodong, Zhang; Drabold, D. A.

    1998-05-01

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

  19. Two-center two-electron covalent bonds with deficient bonding densities.

    PubMed

    Yang, Yang

    2012-10-18

    Electron-deficient covalent bonds are a type of covalent bonds without electron accumulation at their bonding regions. Compared with normal covalent bonds, they are quite sensitive to chemical environments. Electron-deficient and normal covalent bonds are not isolated from each other. An electron-deficient bond may change to a normal one upon the change of substituting groups. Neither bond elongation nor atom electronegativity is directly related to the electron deficiency in an electron-deficient bond. Atoms in molecules (AIM) analyses suggest that electron-deficient bonds are characterized by positive Laplacians and small ρ(BCP) values. The positive Laplacian is caused by insignificant electron accumulation perpendicular to the bond path. On the basis of electron localization function (ELF) descriptors, electron-deficient bonds have small basin populations, low η values and high relative fluctuations. There may be one or two bond basins for an electron-deficient bond. In addition, such a bond may correlate with two more valence basins close to the two participating atoms. Electron-deficient bonds are usually weak and long. This is consistent with the low s characters in their natural bond orbitals (NBOs).

  20. 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.

  1. 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…

  2. Valence of neptunium in intermetallic compounds

    SciTech Connect

    Spitsyn, V.I.; Ionova, G.V.

    1987-07-01

    The authors use Moessbauer spectroscopy and quantum chemical calculations to determine the valence and electronic structure of neptunium in its intermetallic forms with a variety of alloys. The isomeric shifts are measured on Np 237 nuclei. Quantum electronic properties and population density estimates are calculated within the framework of the Hartree-Fock-Slater method.

  3. 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

  4. 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…

  5. 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)

  6. 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

  7. 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... MINES Safety Standards for Methane in Metal and Nonmetal Mines Equipment § 57.22314 Flow-control devices... devices to control the release of liquid hydrocarbons and hazardous gases during the drilling...

  8. Painlevé analysis, nonlocal symmetry and explicit interaction solutions for supersymmetric mKdVB equation

    NASA Astrophysics Data System (ADS)

    Ren, Bo

    2016-08-01

    The N = 1 supersymmetric mKdVB system is transformed to a coupled bosonic system by using the bosonization approach. By a singularity structure analysis, the bosonized supersymmetric mKdVB (BSmKdVB) equation admits the Painlevé property. Starting from the standard truncated Painlevé method, the nonlocal symmetry for the BSmKdVB equation is obtained. To solve the first Lie's principle related with the nonlocal symmetry, the nonlocal symmetry is localized to the Lie point symmetry by introducing multiple new fields. Thanks to localization processes, similarity reductions for the prolonged systems are studied by the Lie point symmetry method. The interaction solutions among solitons and other complicated waves including Painlevé II waves and periodic cnoidal waves are given through the reduction theorems. The soliton-cnoidal wave interaction solutions are explicitly given by using the mapping and deformation method. The concrete soliton-cnoidal interaction solutions are displayed both in analytical and graphical ways.

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

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... (V-A and V-B mines). Oil recovery drill holes that penetrate oil bearing formations shall have devices to control the release of liquid hydrocarbons and hazardous gases during the drilling process. Such devices may be recovered for reuse after the formation has been depressurized or the well...

  10. 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...

  11. 30 CFR 57.22314 - Flow-control devices (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 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...

  12. Terrestrial chemical spill information system through remote sensing, GIS, and V.B. 6.0

    NASA Astrophysics Data System (ADS)

    Dwarakish, G. S.; Jeba S., Angel; Srinikethan, G.; Natesan, Usha

    2009-01-01

    India has made remarkable progress in creating a modern and diversified industrial base, since its independence. Most of the refineries, petrochemical and fertilizer industries are located in the coastal zone and catered by 12 major ports along the 7500 km length of Indian coastline. Since, transportation of crude oil and POL products from ports to refineries are mostly by pipelines, rail/ road, besides some quantity by barge/ ships along the coast, there will be chances of oil spill/leakage. Managing these events before and during their occurrence is imperative to the protection of people and natural resources. The present study was carried out with a view to develop Terrestrial Chemical Spill Information System [TCSIS], using Remote Sensing [RS], GIS and VB 6.0., for the Mangalore coastal zone industrial area of Dakshina Kannada district, Karnataka state, along West Coast of India. The study area lies between 74°45'00'' to 74°52'30''E longitude and 12°52'30'' to 13°00'00''N latitude. The database of TCSIS consists of both conventional data and RS data, and analysed using ERDAS Imagine 9.0 and ArcGIS 8.3 software. Different thematic maps prepared include LU/LC map, drainage map, road and pipeline network map, slope map, Digital Elevation Model, relative risk maps and pipeline route for the transportation of hazardous chemicals from port to refinery. The TCSIS module developed using RS, GIS and V.B.6.0, characterizes the ability of a spilled chemical to immediately impact human health, natural resources, and incorporates these into an overall measure of terrestrial chemical risk and aids in planning, preventing and responding to a terrestrial chemical spill.

  13. 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) ν, with ν ≃ 1.6, as x approaches one.

  14. Valence force field analysis of tetracyanoethylene

    NASA Astrophysics Data System (ADS)

    Michaelian, K. H.; Rieckhoff, K. E.; Voigt, E. M.

    1982-09-01

    A valence force field calculation for the out-of-plane modes of tetracyanoethylene is reported, which makes possible a straightforward assignment of the low-frequency vibrations, including several in-plane modes which previously could not be assigned with certainty. The present set of assignments is consistent with observed vibrational spectra, both for uncomplexed and for complexed tetracyanoethylene, and, for the planar vibrations, is supported by recently published force constant calculations.

  15. Human Amygdala Represents the Complete Spectrum of Subjective Valence

    PubMed Central

    Jin, Jingwen; Zelano, Christina; Gottfried, Jay A.

    2015-01-01

    Although the amygdala is a major locus for hedonic processing, how it encodes valence information is poorly understood. Given the hedonic potency of odor stimuli and the amygdala's anatomical proximity to the peripheral olfactory system, we combined high-resolution fMRI with pattern-based multivariate techniques to examine how valence information is encoded in the amygdala. Ten human subjects underwent fMRI scanning while smelling 9 odorants that systematically varied in perceived valence. Representational similarity analyses showed that amygdala codes the entire dimension of valence, ranging from pleasantness to unpleasantness. This unidimensional representation significantly correlated with self-reported valence ratings but not with intensity ratings. Furthermore, within-trial valence representations evolved over time, prioritizing earlier differentiation of unpleasant stimuli. Together, these findings underscore the idea that both spatial and temporal features uniquely encode pleasant and unpleasant odor valence in the amygdala. The availability of a unidimensional valence code in the amygdala, distributed in both space and time, would create greater flexibility in determining the pleasantness or unpleasantness of stimuli, providing a mechanism by which expectation, context, attention, and learning could influence affective boundaries for guiding behavior. SIGNIFICANCE STATEMENT Our findings elucidate the mechanisms of affective processing in the amygdala by demonstrating that this brain region represents the entire valence dimension from pleasant to unpleasant. An important implication of this unidimensional valence code is that pleasant and unpleasant valence cannot coexist in the amygdale because overlap of fMRI ensemble patterns for these two valence extremes obscures their unique content. This functional architecture, whereby subjective valence maps onto a pattern continuum between pleasant and unpleasant poles, offers a robust mechanism by which context

  16. 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.

  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 σ- versus π-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.

  18. The valence-fluctuating ground state of plutonium

    DOE PAGES

    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

  19. 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.

  20. 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...

  1. 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 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...

  2. 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 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...

  3. 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...

  4. 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 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...

  5. 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...

  6. 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 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...

  7. Draft Genome Sequence of Colistin-Resistant Acinetobacter baumannii Strain VB22595 Isolated from a Central Line-Associated Bloodstream Infection

    PubMed Central

    Veeraraghavan, Balaji; Anandan, Shalini; Ragupathi, Naveen Kumar Devanga; Vijayakumar, Saranya; Sethuvel, Dhiviya Prabaa Muthuirulandi

    2016-01-01

    Acinetobacter baumannii is an important emerging pathogen that causes health care-associated infections. In this study, we determined the genome of a multidrug-resistant clinical strain, VB22595, isolated from a hospital in Southern India. The draft genome indicates that strain VB22595 encodes a genome of ~3.92 Mb in size and does not contain plasmid derived MCR-1 for colistin resistance. PMID:27516521

  8. Representation of perceived sound valence in the human brain.

    PubMed

    Viinikainen, Mikko; Kätsyri, Jari; Sams, Mikko

    2012-10-01

    Perceived emotional valence of sensory stimuli influences their processing in various cortical and subcortical structures. Recent evidence suggests that negative and positive valences are processed separately, not along a single linear continuum. Here, we examined how brain is activated when subjects are listening to auditory stimuli varying parametrically in perceived valence (very unpleasant-neutral-very pleasant). Seventeen healthy volunteers were scanned in 3 Tesla while listening to International Affective Digital Sounds (IADS-2) in a block design paradigm. We found a strong quadratic U-shaped relationship between valence and blood oxygen level dependent (BOLD) signal strength in the medial prefrontal cortex, auditory cortex, and amygdala. Signals were the weakest for neutral stimuli and increased progressively for more unpleasant or pleasant stimuli. The results strengthen the view that valence is a crucial factor in neural processing of emotions. An alternative explanation is salience, which increases with both negative and positive valences.

  9. Anticipation selectively enhances interference exerted by pictures of negative valence.

    PubMed

    Kleinsorge, Thomas

    2009-01-01

    Recent evidence suggests that anticipation of negatively valenced pictures strongly increases interference exerted by the actual presentation of these pictures, while anticipation of positively valenced pictures leaves the impact of the actual presentation of positive pictures unaffected. However, there is some ambiguity as to whether anticipation of negative valence generally increases the impact of all emotional stimuli, or whether the effect of anticipation is specific for stimuli of negative valence. In the present experiments, different anticipation conditions were contrasted that differed with respect to the specificity of the information on which anticipations could be based. The data show that all anticipation conditions that entailed the possibility of the presentation of unpleasant stimuli selectively enhanced the impact of negatively valenced stimuli without affecting the impact of positively valenced stimuli.

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

    PubMed

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

    2011-01-01

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

  11. Experimental study of the valence band of Bi2Se3

    DOE PAGES

    Gao, Yi-Bin; He, Bin; Parker, David; Androulakis, Ioannis; Heremans, Joseph P.

    2014-09-26

    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.

  12. Silver- and gold-mediated nucleobase bonding.

    PubMed

    Acioli, Paulo H; Srinivas, Sudha

    2014-08-01

    We report the results of a density functional theory investigation of the bonding of nucleobases mediated by silver and gold atoms in the gas phase. Our calculations use the Becke exchange and Perdew-Wang correlation functional (BPW91) combined with the Stuttgart effective core potentials to represent the valence electrons of gold, silver, and platinum, and the all-electron DGTZVP basis set for C, H, N, and O. This combination was chosen based on tests on the metal atoms and tautomers of adenine, cytosine, and guanine. To establish a benchmark to understand the metal-mediated bonding, we calculated the binding energy of each of the base pairs in their canonical forms. Our calculations show rather strong bonds between the Watson-Crick base pairs when compared with typical values for N-H-N and N-H-O hydrogen bonds. The neutral metal atoms tend to bond near the nitrogen atoms. The effect of the metal atoms on the bonding of nucleobases differs depending on whether or not the metal atoms bond to one of the hydrogen-bonding sites. When the silver or gold atoms bond to a non-hydrogen-bonding site, the effect is a slight enhancement of the cytosine-guanine bonding, but there is almost no effect on the adenine-thymine pairing. The metal atoms can block one of the hydrogen-bonding sites, thus preventing the normal cytosine-guanine and adenine-thymine pairings. We also find that both silver and gold can bond to consecutive guanines in a similar fashion to platinum, albeit with a significantly lower binding energy.

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

    PubMed

    Heckmann, Alexander; Amthor, Stephan; Lambert, Christoph

    2006-07-28

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

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

    SciTech Connect

    Pauling, L.

    1987-07-13

    Several structural features, including electron transfer between atoms of different electronegativity, oxygen deficiency, and unsynchronized resonance of valence bonds, as well as tight binding of atoms and the presence of both hypoelectronic and hyperelectronic elements, cooperatre to confer metallic properties and high-temperature superconductivity on compounds such as (Sr,Ba,Y,La)/sub 2/CuO/sub 4-//sub y/. .AE

  15. Valence Effects in Reasoning About Evaluative Traits.

    PubMed

    Heyman, Gail D; Giles, Jessica W

    2004-01-01

    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

  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. 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.

  18. Extreme floods in central Europe over the past 500 years: Role of cyclone pathway ``Zugstrasse Vb''

    NASA Astrophysics Data System (ADS)

    Mudelsee, M.; BöRngen, M.; Tetzlaff, G.; Grünewald, U.

    2004-12-01

    Anthropogenically induced climate change has been hypothesized to add to the risk of extreme river floods because a warmer atmosphere can carry more water. In the case of the central European rivers Elbe and Oder, another possibility that has been considered is a more frequent occurrence of a weather situation of the type "Zugstrasse Vb," where a low-pressure system travels from the Adriatic region northeastward, carrying moist air and bringing orographic rainfall in the mountainous catchment areas (Erzgebirge, Sudeten, and Beskids). Analysis of long, homogeneous records of past floods allows us to test such ideas. M. Mudelsee and co-workers recently presented flood records for the middle parts of the Elbe and Oder, which go continuously back to A.D. 1021 and A.D. 1269, respectively. Here we review the reconstruction and assess the data quality of the records, which are based on combining documentary data from the interval up to 1850 and measurements thereafter, finding both the Elbe and Oder records to provide reliable information on heavy floods at least since A.D. 1500. We explain that the statistical method of kernel occurrence rate estimation can overcome deficiencies of techniques previously used to investigate trends in the occurrence of climatic extremes, because it (1) allows nonmonotonic trends, (2) imposes no parametric restrictions, and (3) provides confidence bands, which are essential for evaluating whether observed trends are real or came by chance into the data. We further give a hypothesis test that can be used to evaluate monotonic trends. On the basis of these data and methods, we find for both the Elbe and Oder rivers (1) significant downward trends in winter flood risk during the twentieth century, (2) no significant trends in summer flood risk in the twentieth century, and (3) significant variations in flood risk during past centuries, with notable differences between the Elbe and Oder. The observed trends are shown to be both robust against

  19. 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

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

    PubMed Central

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

    2014-01-01

    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

  1. 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.

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

    ERIC Educational Resources Information Center

    Fries, Stefan; Schmid, Sebastian; Hofer, Manfred

    2007-01-01

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

  3. 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),…

  4. 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 π-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 ν C- N(thioureide) and thioureide N 13CS 2 carbon signals are correlated with the electronic effects of the dithiocarbamate ligands.

  5. Architectural Representation of Valence in the Limbic System.

    PubMed

    Namburi, Praneeth; Al-Hasani, Ream; Calhoon, Gwendolyn G; Bruchas, Michael R; Tye, Kay M

    2016-06-01

    In order to thrive, animals must be able to recognize aversive and appetitive stimuli within the environment and subsequently initiate appropriate behavioral responses. This assignment of positive or negative valence to a stimulus is a key feature of emotional processing, the neural substrates of which have been a topic of study for several decades. Until recently, the result of this work has been the identification of specific brain regions, such as the basolateral amygdala (BLA) and nucleus accumbens (NAc), as important to valence encoding. The advent of modern tools in neuroscience has allowed further dissection of these regions to identify specific populations of neurons signaling the valence of environmental stimuli. In this review, we focus upon recent work examining the mechanisms of valence encoding, and provide a model for the systematic investigation of valence within anatomically-, genetically-, and functionally defined populations of neurons. PMID:26647973

  6. Chemical bonding in hypervalent molecules: is the octet rule relevant?

    PubMed

    Noury, Stéphane; Silvi, Bernard; Gillespie, Ronald J

    2002-04-22

    The bonding in a large number of hypervalent molecules of P, As, S, Se, Te, Cl, and Br with the ligands F, Cl, O, CH(3), and CH(2) has been studied using the topological analysis of the electron localization function ELF. This function partitions the electron density of a molecule into core and valence basins and further classifies valence basins according to the number of core basins with which they have a contact. The number and geometry of these basins is generally in accord with the VSEPR model. The population of each basin can be obtained by integration, and so, the total population of the valence shell of an atom can be obtained as the sum of the populations of all the valence basins which share a boundary with its core basin. It was found that the population of the V(A, X) disynaptic basin corresponding to the bond, where A is the central atom and X the ligand, varies with the electronegativity of the ligand from approximately 2.0 for a weakly electronegative ligand such as CH(3) to less than 1.0 for a ligand such as F. We find that the total population of the valence shell of a hypervalent atom may vary from close to 10 for a period 15 element and close to 12 for a group 16 element to considerably less than 8 for an electronegative ligand such as F. For example, the phosphorus atom in PF(5) has a population of 5.37 electrons in its valence shell, whereas the arsenic atom in AsMe5 has a population of 9.68 electrons in its valence shell. By definition, hypervalent atoms do not obey the Lewis octet rule. They may or may not obey a modified octet rule that has taken the place of the Lewis octet rule in many recent discussions and according to which an atom in a molecule always has fewer than 8 electrons in its valence shell. We show that the bonds in hypervalent molecules are very similar to those in corresponding nonhypervalent (Lewis octet) molecules. They are all polar bonds ranging from weakly to strongly polar depending on the electronegativity of the

  7. Bonds Boom.

    ERIC Educational Resources Information Center

    Reynolds, Cathryn

    1989-01-01

    The combined effect of the "Serrano" decision and Proposition 13 left California school districts with aging, overcrowded facilities. Chico schools won a $18.5 million general obligation bond election for facilities construction. With $11 billion needed for new school construction, California will need to tap local sources. A sidebar outlines…

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. Bond-length distributions for ions bonded to oxygen: alkali and alkaline-earth metals

    PubMed Central

    Gagné, Olivier Charles; Hawthorne, Frank Christopher

    2016-01-01

    ]-coordination. For alkali-metal and alkaline-earth-metal ions, there is a positive correlation between cation coordination number and the grand mean incident bond-valence sum at the central cation, the values varying from 0.84 v.u. for [5]K+ to 1.06 v.u. for [8]Li+, and from 1.76 v.u. for [7]Ba2+ to 2.10 v.u. for [12]Sr2+. Bond-valence arguments suggest coordination numbers higher than [12] for K+, Rb+, Cs+ and Ba2+. PMID:27484381

  13. Bond-length distributions for ions bonded to oxygen: alkali and alkaline-earth metals.

    PubMed

    Gagné, Olivier Charles; Hawthorne, Frank Christopher

    2016-08-01

    [4]- and [6]-coordination, Na(+) in [4]- and [6]-coordination. For alkali-metal and alkaline-earth-metal ions, there is a positive correlation between cation coordination number and the grand mean incident bond-valence sum at the central cation, the values varying from 0.84 v.u. for ([5])K(+) to 1.06 v.u. for ([8])Li(+), and from 1.76 v.u. for ([7])Ba(2+) to 2.10 v.u. for ([12])Sr(2+). Bond-valence arguments suggest coordination numbers higher than [12] for K(+), Rb(+), Cs(+) and Ba(2+). PMID:27484381

  14. Bond-length distributions for ions bonded to oxygen: alkali and alkaline-earth metals.

    PubMed

    Gagné, Olivier Charles; Hawthorne, Frank Christopher

    2016-08-01

    [4]- and [6]-coordination, Na(+) in [4]- and [6]-coordination. For alkali-metal and alkaline-earth-metal ions, there is a positive correlation between cation coordination number and the grand mean incident bond-valence sum at the central cation, the values varying from 0.84 v.u. for ([5])K(+) to 1.06 v.u. for ([8])Li(+), and from 1.76 v.u. for ([7])Ba(2+) to 2.10 v.u. for ([12])Sr(2+). Bond-valence arguments suggest coordination numbers higher than [12] for K(+), Rb(+), Cs(+) and Ba(2+).

  15. Fast and accurate predictions of covalent bonds in chemical space.

    PubMed

    Chang, K Y Samuel; Fias, Stijn; Ramakrishnan, Raghunathan; von Lilienfeld, O Anatole

    2016-05-01

    We assess the predictive accuracy of perturbation theory based estimates of changes in covalent bonding due to linear alchemical interpolations among molecules. We have investigated σ bonding to hydrogen, as well as σ and π bonding between main-group elements, occurring in small sets of iso-valence-electronic molecules with elements drawn from second to fourth rows in the p-block of the periodic table. Numerical evidence suggests that first order Taylor expansions of covalent bonding potentials can achieve high accuracy if (i) the alchemical interpolation is vertical (fixed geometry), (ii) it involves elements from the third and fourth rows of the periodic table, and (iii) an optimal reference geometry is used. This leads to near linear changes in the bonding potential, resulting in analytical predictions with chemical accuracy (∼1 kcal/mol). Second order estimates deteriorate the prediction. If initial and final molecules differ not only in composition but also in geometry, all estimates become substantially worse, with second order being slightly more accurate than first order. The independent particle approximation based second order perturbation theory performs poorly when compared to the coupled perturbed or finite difference approach. Taylor series expansions up to fourth order of the potential energy curve of highly symmetric systems indicate a finite radius of convergence, as illustrated for the alchemical stretching of H2 (+). Results are presented for (i) covalent bonds to hydrogen in 12 molecules with 8 valence electrons (CH4, NH3, H2O, HF, SiH4, PH3, H2S, HCl, GeH4, AsH3, H2Se, HBr); (ii) main-group single bonds in 9 molecules with 14 valence electrons (CH3F, CH3Cl, CH3Br, SiH3F, SiH3Cl, SiH3Br, GeH3F, GeH3Cl, GeH3Br); (iii) main-group double bonds in 9 molecules with 12 valence electrons (CH2O, CH2S, CH2Se, SiH2O, SiH2S, SiH2Se, GeH2O, GeH2S, GeH2Se); (iv) main-group triple bonds in 9 molecules with 10 valence electrons (HCN, HCP, HCAs, HSiN, HSi

  16. Fast and accurate predictions of covalent bonds in chemical space

    NASA Astrophysics Data System (ADS)

    Chang, K. Y. Samuel; Fias, Stijn; Ramakrishnan, Raghunathan; von Lilienfeld, O. Anatole

    2016-05-01

    We assess the predictive accuracy of perturbation theory based estimates of changes in covalent bonding due to linear alchemical interpolations among molecules. We have investigated σ bonding to hydrogen, as well as σ and π bonding between main-group elements, occurring in small sets of iso-valence-electronic molecules with elements drawn from second to fourth rows in the p-block of the periodic table. Numerical evidence suggests that first order Taylor expansions of covalent bonding potentials can achieve high accuracy if (i) the alchemical interpolation is vertical (fixed geometry), (ii) it involves elements from the third and fourth rows of the periodic table, and (iii) an optimal reference geometry is used. This leads to near linear changes in the bonding potential, resulting in analytical predictions with chemical accuracy (˜1 kcal/mol). Second order estimates deteriorate the prediction. If initial and final molecules differ not only in composition but also in geometry, all estimates become substantially worse, with second order being slightly more accurate than first order. The independent particle approximation based second order perturbation theory performs poorly when compared to the coupled perturbed or finite difference approach. Taylor series expansions up to fourth order of the potential energy curve of highly symmetric systems indicate a finite radius of convergence, as illustrated for the alchemical stretching of H 2+ . Results are presented for (i) covalent bonds to hydrogen in 12 molecules with 8 valence electrons (CH4, NH3, H2O, HF, SiH4, PH3, H2S, HCl, GeH4, AsH3, H2Se, HBr); (ii) main-group single bonds in 9 molecules with 14 valence electrons (CH3F, CH3Cl, CH3Br, SiH3F, SiH3Cl, SiH3Br, GeH3F, GeH3Cl, GeH3Br); (iii) main-group double bonds in 9 molecules with 12 valence electrons (CH2O, CH2S, CH2Se, SiH2O, SiH2S, SiH2Se, GeH2O, GeH2S, GeH2Se); (iv) main-group triple bonds in 9 molecules with 10 valence electrons (HCN, HCP, HCAs, HSiN, HSi

  17. Fast and accurate predictions of covalent bonds in chemical space.

    PubMed

    Chang, K Y Samuel; Fias, Stijn; Ramakrishnan, Raghunathan; von Lilienfeld, O Anatole

    2016-05-01

    We assess the predictive accuracy of perturbation theory based estimates of changes in covalent bonding due to linear alchemical interpolations among molecules. We have investigated σ bonding to hydrogen, as well as σ and π bonding between main-group elements, occurring in small sets of iso-valence-electronic molecules with elements drawn from second to fourth rows in the p-block of the periodic table. Numerical evidence suggests that first order Taylor expansions of covalent bonding potentials can achieve high accuracy if (i) the alchemical interpolation is vertical (fixed geometry), (ii) it involves elements from the third and fourth rows of the periodic table, and (iii) an optimal reference geometry is used. This leads to near linear changes in the bonding potential, resulting in analytical predictions with chemical accuracy (∼1 kcal/mol). Second order estimates deteriorate the prediction. If initial and final molecules differ not only in composition but also in geometry, all estimates become substantially worse, with second order being slightly more accurate than first order. The independent particle approximation based second order perturbation theory performs poorly when compared to the coupled perturbed or finite difference approach. Taylor series expansions up to fourth order of the potential energy curve of highly symmetric systems indicate a finite radius of convergence, as illustrated for the alchemical stretching of H2 (+). Results are presented for (i) covalent bonds to hydrogen in 12 molecules with 8 valence electrons (CH4, NH3, H2O, HF, SiH4, PH3, H2S, HCl, GeH4, AsH3, H2Se, HBr); (ii) main-group single bonds in 9 molecules with 14 valence electrons (CH3F, CH3Cl, CH3Br, SiH3F, SiH3Cl, SiH3Br, GeH3F, GeH3Cl, GeH3Br); (iii) main-group double bonds in 9 molecules with 12 valence electrons (CH2O, CH2S, CH2Se, SiH2O, SiH2S, SiH2Se, GeH2O, GeH2S, GeH2Se); (iv) main-group triple bonds in 9 molecules with 10 valence electrons (HCN, HCP, HCAs, HSiN, HSi

  18. In-silico bonding schemes to encode chemical bonds involving sharing of electrons in molecular structures.

    PubMed

    Punnaivanam, Sankar; Sathiadhas, Jerome Pastal Raj; Panneerselvam, Vinoth

    2016-05-01

    Encoding of covalent and coordinate covalent bonds in molecular structures using ground state valence electronic configuration is achieved. The bonding due to electron sharing in the molecular structures is described with five fundamental bonding categories viz. uPair-uPair, lPair-uPair, uPair-lPair, vPair-lPair, and lPair-lPair. The involvement of lone pair electrons and the vacant electron orbitals in chemical bonding are explained with bonding schemes namely "target vacant promotion", "source vacant promotion", "target pairing promotion", "source pairing promotion", "source cation promotion", "source pairing double bond", "target vacant occupation", and "double pairing promotion" schemes. The bonding schemes are verified with a chemical structure editor. The bonding in the structures like ylides, PCl5, SF6, IF7, N-Oxides, BF4(-), AlCl4(-) etc. are explained and encoded unambiguously. The encoding of bonding in the structures of various organic compounds, transition metals compounds, coordination complexes and metal carbonyls is accomplished.

  19. Valence modulates source memory for faces.

    PubMed

    Bell, Raoul; Buchner, Axel

    2010-01-01

    Previous studies in which the effects of emotional valence on old-new discrimination and source memory have been examined have yielded highly inconsistent results. Here, we present two experiments showing that old-new face discrimination was not affected by whether a face was associated with disgusting, pleasant, or neutral behavior. In contrast, source memory for faces associated with disgusting behavior (i.e., memory for the disgusting context in which the face was encountered) was consistently better than source memory for other types of faces. This data pattern replicates the findings of studies in which descriptions of cheating, neutral, and trustworthy behavior were used, which findings were previously ascribed to a highly specific cheater detection module. The present results suggest that the enhanced source memory for faces of cheaters is due to a more general source memory advantage for faces associated with negative or threatening contexts that may be instrumental in avoiding the negative consequences of encounters with persons associated with negative or threatening behaviors.

  20. 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

  1. Design-atom approach for the quantum mechanical/molecular mechanical covalent boundary: a design-carbon atom with five valence electrons.

    PubMed

    Xiao, Chuanyun; Zhang, Yingkai

    2007-09-28

    A critical issue underlying the accuracy and applicability of the combined quantum mechanical/molecular mechanical (QM/MM) methods is how to describe the QM/MM boundary across covalent bonds. Inspired by the ab initio pseudopotential theory, here we introduce a novel design atom approach for a more fundamental and transparent treatment of this QM/MM covalent boundary problem. The main idea is to replace the boundary atom of the active part with a design atom, which has a different number of valence electrons but very similar atomic properties. By modifying the Troullier-Martins scheme, which has been widely employed to construct norm-conserving pseudopotentials for density functional calculations, we have successfully developed a design-carbon atom with five valence electrons. Tests on a series of molecules yield very good structural and energetic results and indicate its transferability in describing a variety of chemical bonds, including double and triple bonds.

  2. Intramolecular interactions of L-phenylalanine: Valence ionization spectra and orbital momentum distributions of its fragment molecules.

    PubMed

    Ganesan, Aravindhan; Wang, Feng; Falzon, Chantal

    2011-02-01

    Intramolecular interactions between fragments of L-phenylalanine, i.e., phenyl and alaninyl, have been investigated using dual space analysis (DSA) quantum mechanically. Valence space photoelectron spectra (PES), orbital energy topology and correlation diagram, as well as orbital momentum distributions (MDs) of L-phenylalanine, benzene and L-alanine are studied using density functional theory methods. While fully resolved experimental PES of L-phenylalanine is not yet available, our simulated PES reproduces major features of the experimental measurement. For benzene, the simulated orbital MDs for 1e(1g) and 1a(2u) orbitals also agree well with those measured using electron momentum spectra. Our theoretical models are then applied to reveal intramolecular interactions of the species on an orbital base, using DSA. Valence orbitals of L-phenylalanine can be essentially deduced into contributions from its fragments such as phenyl and alaninyl as well as their interactions. The fragment orbitals inherit properties of their parent species in energy and shape (ie., MDs). Phenylalanine orbitals show strong bonding in the energy range of 14-20 eV, rather than outside of this region. This study presents a competent orbital based fragments-in-molecules picture in the valence space, which supports the fragment molecular orbital picture and building block principle in valence space. The optimized structures of the molecules are represented using the recently developed interactive 3D-PDF technique.

  3. 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 80°C for 3 h were almost similar to that of SiO 2. The peak shift of Ca[2p, 3p, 3p] Auger transition toward the lower energy side has been observed, suggesting the formation of bonds between Ca 3p and O orbitals. New peaks due to CaO or CaOH bonds also appeared in the valence electron region of Ca[2p, 3p, V] Auger transition. The charge transfer and the chemical-bond formation can be well demonstrated by AVES during the CaSi 2H 2O reaction.

  4. Diffusion bonding

    DOEpatents

    Anderson, Robert C.

    1976-06-22

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

  5. Semiempirical model of covalent bonding in silicon

    NASA Astrophysics Data System (ADS)

    Ackland, Graeme

    1989-11-01

    A simple, analytic model for energetics in silicon is presented. The model incorporates ionic core repulsions written as a pairwise repulsion between ions, and a cohesive energy written as a sum over valence-electron energies. The electrons form covalent bonds represented by pair potentials, and other interactions by a simple repulsive pair potential. The resulting model has a simpler interpretation and fewer parameters than previously published empirical potentials, yet yields structural results in better agreement with density-functional calculations and experimental observations. This shows that by representing cohesion in silicon explicitly in terms of electron bonds, and not by effective interactions between ions as has been done previously, a simple mathematical model can give a better insight into the physics of covalent bonding.

  6. Study of iron dimers reveals angular dependence of valence-to-core X-ray emission spectra.

    PubMed

    Pollock, Christopher J; Lancaster, Kyle M; Finkelstein, Kenneth D; DeBeer, Serena

    2014-10-01

    Transition-metal Kβ X-ray emission spectroscopy (XES) is a developing technique that probes the occupied molecular orbitals of a metal complex. As an element-specific probe of metal centers, Kβ XES is finding increasing applications in catalytic and, in particular, bioinorganic systems. For the continued development of XES as a probe of these complex systems, however, the full range of factors which contribute to XES spectral modulations must be explored. In this report, an investigation of a series of oxo-bridged iron dimers reveals that the intensity of valence-to-core features is sensitive to the Fe-O-Fe bond angle. The intensity of these features has a well-known dependence on metal-ligand bond distance, but a dependence upon bond angle has not previously been documented. Herein, we explore the angular dependence of valence-to-core XES features both experimentally and computationally. Taken together, these results show that, as the Fe-O-Fe angle decreases, the intensity of the Kβ″ feature increases and that this effect is modulated by increasing amounts of Fe np mixing into the O 2s orbital at smaller bond angles. The relevance of these findings to the identification of oxygenated intermediates in bioinorganic systems is highlighted, with special emphasis given to the case of soluble methane monooxygenase.

  7. Analysis of the valence electronic structures and calculation of the physical properties of Fe, Co, and Ni

    NASA Astrophysics Data System (ADS)

    Wu, Wenxia; Xue, Zhiyong; Hong, Xing; Li, Xiumei; Guo, Yongquan

    2009-06-01

    The valence electronic structures of Fe, Co and Ni have been investigated with Empirical Electron Theory of Solids and Molecules. The magnetic moments, Curie temperature, cohesive energy and melting point have been calculated according to the valence electronic structure. These calculations fit the experimental data very well. Based on the calculations, the magnetic moments are proportional to the number of 3d magnetic electrons. Curie temperatures are related to the magnetic electrons and the bond lengths between magnetic atoms. Cohesive energies increase with the increase of the number of covalent electrons, and the decrease of the number of magnetic and dumb pair electrons. The melting point is mainly related to the number of covalent electron pairs distributed in the strongest bond. The contribution from the lattice electrons is very small, the dumb pair electrons weaken the melting point; however, the contribution to melting point of the magnetic electrons can be neglected. It reveals that the magnetic and thermal properties are closely related to the valence electronic structures, and the changes or transitions between the electrons obviously affect the physical properties.

  8. Carbonic anhydrase activators: an activation study of the human mitochondrial isoforms VA and VB with amino acids and amines.

    PubMed

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

    2007-03-01

    The mitochondrial isozymes of human carbonic anhydrase (hCA, EC 4.2.1.1), hCA VA and hCA VB, were investigated for activation with a series of amino acids and amines. D-His, L-DOPA, histamine, dopamine, and 4-(2-aminoethyl)morpholine were excellent hCA VA activators, with KAs in the range of 10-130 nM. Good hCA VB activating effects were identified for L-His, D-Phe, D-DOPA, L-Trp, L-Tyr, serotonin, and 2-(2-aminoethyl)-pyridine, with KAs in the range of 44-110 nM. All these activators enhanced kcat, having no effect on KM, favoring thus the rate-determining step in the catalytic cycle, the proton transfer reactions between the active site and environment. The activation pattern of the two mitochondrial isoforms is very different from each other and as compared to those of the cytosolic isoforms hCA I and II. PMID:17174092

  9. Mixed-valence compound-based biosensor.

    PubMed

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

    1999-01-01

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

  10. Chalcogen bond: a sister noncovalent bond to halogen bond.

    PubMed

    Wang, Weizhou; Ji, Baoming; Zhang, Yu

    2009-07-16

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

  11. 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)

  12. Candidate Valence as a Predictor of Voter Preference.

    ERIC Educational Resources Information Center

    Andersen, Peter A.; Kibler, Robert J.

    1978-01-01

    Studies the effects of source valence, including source credibility, attraction, and homophyly, on voter preference in a Florida Democratic primary election campaign. Indicates that attitude homophyly is an excellent predictor of voter preference. (JMF)

  13. 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

  14. 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)

  15. Emotional Valence and the Free-Energy Principle

    PubMed Central

    Joffily, Mateus; Coricelli, Giorgio

    2013-01-01

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

  16. Input-specific contributions to valence processing in the amygdala.

    PubMed

    Correia, Susana S; Goosens, Ki A

    2016-10-01

    Reward and punishment are often thought of as opposing processes: rewards and the environmental cues that predict them elicit approach and consummatory behaviors, while punishments drive aversion and avoidance behaviors. This framework suggests that there may be segregated brain circuits for these valenced behaviors. The basolateral amygdala (BLA) is one brain region that contributes to both types of motivated behavior. Individual neurons in the BLA can favor positive over negative valence, or vice versa, but these neurons are intermingled, showing no anatomical segregation. The amygdala receives inputs from many brain areas and current theories posit that encoding of positive versus negative valence by BLA neurons is determined by the wiring of each neuron. Specifically, many projections from other brain areas that respond to positive and negative valence stimuli and predictive cues project strongly to the BLA and likely contribute to valence processing within the BLA. Here we review three of these areas, the basal forebrain, the dorsal raphe nucleus and the ventral tegmental area, and discuss how these may promote encoding of positive and negative valence within the BLA. PMID:27634144

  17. Emotional valence and the free-energy principle.

    PubMed

    Joffily, Mateus; Coricelli, Giorgio

    2013-01-01

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

  18. 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.

  19. High-pressure synchrotron Mössbauer and X-ray diffraction studies: Exploring the structure-related valence fluctuation in EuNi2P2

    NASA Astrophysics Data System (ADS)

    Li, Chunyu; Yu, Zhenhai; Bi, Wenli; Zhao, Jiyong; Hu, Michael Y.; Zhao, Jinggeng; Wu, Wei; Luo, Jianlin; Yan, Hao; Alp, Esen E.; Liu, Haozhe

    2016-11-01

    The high-pressure effect on valence fluctuation of the ThCr2Si2-type intermetallic compound EuNi2P2 has been investigated using in situ synchrotron Mössbauer spectroscopy (SMS). The isomer shift of 151Eu in EuNi2P2 increases monotonically with increasing pressure up to 50 GPa, suggesting a valence transition of the Eu from mixed toward trivalent. The synchrotron angle-dispersive X-ray diffraction (AD-XRD) experiment shows that EuNi2P2 remains in the tetragonal structure up to 32.5 GPa at room temperature. We propose that the evolutions of bonding distance with pressure have an obvious effect on the valence fluctuation.

  20. Inorganic electron transfer: sharpening a fuzzy border in mixed valency and extending mixed valency across supramolecular systems.

    PubMed

    Kubiak, Clifford P

    2013-05-20

    This article describes research from our laboratory on the chemistry and spectroscopic properties of inorganic mixed-valence complexes. After a brief review of the seminal work of Taube, Creutz, Day, Robin, Hush, and others in the 1960s and the confounding efforts to identify the borderline between class II and III mixed-valence systems in the 1990s and early 2000s, we describe our first experiments to observe and analyze the coalescence of ν(CO) band shapes in the 1D IR spectra of mixed-valence complexes of the type {[Ru3O(OAc)6(CO)(L)]2-BL}(-), where L = a pyridyl ligand and BL = pyrazine or 4,4'-bipyridine, to estimate rate constants of intramolecular electron transfer (ET). The strong involvement of the bridging ligands in mixed-valence complexes of this type was first identified in the appearance of totally symmetric vibrational modes of pyrazine bridging ligands in the IR because of strong vibronic coupling within a three-state metal cluster-bridge-metal cluster model. Application of the Brunschwig-Creutz-Sutin semiclassical three-state model of mixed valency accounts well for the appearance of two intervalence charge-transfer bands that are observed in the near-IR region of the electronic absorption spectra of these mixed-valence ions. The direct spectroscopic observation of "mixed-valence isomers", the two alternate charge distributions of a mixed-valence ion, are described. The equilibrium constants of mixed-valence isomers provide quantitative thermodynamic estimates of the electronic coupling, H(ab). The extent of delocalization in many of the mixed-valent bridged dimers of triruthenium clusters produces unusual behavior, especially rate constants for ET that are independent of normal solvent reorganization energies but do depend on solvent dynamical dipolar reorientation times. The strong dependence of rates on solvent dynamics is also found to produce a non-Arrhenius dependence of ET rate constants on temperature, faster rates in frozen solutions

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

  2. 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,…

  3. 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 σ-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.

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

    NASA Astrophysics Data System (ADS)

    Béjaoui, Anis; Horchani-Naifer, Karima; Hajji, Mounir; Férid, 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) Å, b = 5.3473(5) Å, c = 12.756(1) Å, β = 103.174° (1), V = 597.67 (9) Å3, Z = 4. Its structure consists of a three-dimensional framework of P2O7 units that are corner-shared by LuO6 octahedra, forming tunnels running parallel to [010] which are occupied by Na atoms. NaLuP2O7 powder was characterized by XRD, SEM, FTIR and Raman spectroscopy. The activation energy of (1.49 eV) obtained by electrical measurements suggests the charge carriers to be the sodium cations. The activation energies obtained from impedance and loss spectra were analyzed in order to explain the mechanism of conduction. The correlation between ionic conductivity of NaLuP2O7 and its crystallographic structure was investigated and the most probable transport pathway model was determined.

  5. Hard-core bosons on the kagome lattice: valence-bond solids and their quantum melting.

    PubMed

    Isakov, S V; Wessel, S; Melko, R G; Sengupta, K; Kim, Yong Baek

    2006-10-01

    Using large scale quantum Monte Carlo simulations and dual vortex theory, we analyze the ground state phase diagram of hard-core bosons on the kagome lattice with nearest-neighbor repulsion. In contrast with the case of a triangular lattice, no supersolid emerges for strong interactions. While a uniform superfluid prevails at half filling, two novel solid phases emerge at densities rho=1/3 and rho=2/3. These solids exhibit an only partial ordering of the bosonic density, allowing for local resonances on a subset of hexagons of the kagome lattice. We provide evidence for a weakly first-order phase transition at the quantum melting point between these solid phases and the superfluid.

  6. Hard-Core Bosons on the Kagome Lattice: Valence-Bond Solids and Their Quantum Melting

    NASA Astrophysics Data System (ADS)

    Isakov, S. V.; Wessel, S.; Melko, R. G.; Sengupta, K.; Kim, Yong Baek

    2006-10-01

    Using large scale quantum Monte Carlo simulations and dual vortex theory, we analyze the ground state phase diagram of hard-core bosons on the kagome lattice with nearest-neighbor repulsion. In contrast with the case of a triangular lattice, no supersolid emerges for strong interactions. While a uniform superfluid prevails at half filling, two novel solid phases emerge at densities ρ=1/3 and ρ=2/3. These solids exhibit an only partial ordering of the bosonic density, allowing for local resonances on a subset of hexagons of the kagome lattice. We provide evidence for a weakly first-order phase transition at the quantum melting point between these solid phases and the superfluid.

  7. 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.

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

    PubMed

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

    2013-09-24

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

  9. The electronic structure and optical properties of organic mixed valence anion radicals

    SciTech Connect

    Liberko, C.A.

    1992-01-01

    The electronic structure of planar and helical organic mixed valence anion radicals was studied. Cyanoimine derivatives of planar diquinones were synthesized and studied by electrochemical methods. Their anion radicals were generated electrochemically and found to be stable in air. These species had electronic absorptions in the near infrared region. The Visible and near infrared spectra as well as IR vibrational data are consistent with delocalized anion radicals. The molecular orbital energy level coefficients obtained from PPP semi-empirical molecular orbital calculations on neutral quinones, imides and cyanoimine derivatives of quinones, were used to correlate experimental data of their anion radicals. The calculation correlated the long wavelength absorptions of the anion radicals confirming that the absorptions arise from electronic transitions in delocalized species. The calculation was also valuable for assigning ESR hyperfine splittings. Including minor geometric perturbations in the calculation provides a method of predicting localization in mixed valence ion radicals. Helicene diquinones were studied by cyclic voltammetry. Their anion radicals, generated electrochemically, were studied by visible, near infrared, and ESR spectroscopies. The anion radicals were found to have electronic absorptions in the near infrared region tailing into the infrared. PPP calculations were consistent with the experimental data only if transannular interaction between the ends of the helix was included. The calculations and experimental observations are consistent with an electronic structure in which the anion radical is not only delocalized around the helix but also between the ends of the helix bonding them together in a Mobius fashion.

  10. 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 ``π-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 Φ by 0.1+/-0.1 eV, whereas annealing the adlayer to 300 K subsequently reduces Φ 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 σ-donation and π-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.

  11. Optical study of archetypical valence-fluctuating Eu systems.

    PubMed

    Guritanu, V; Seiro, S; Sichelschmidt, J; Caroca-Canales, N; Iizuka, T; Kimura, S; Geibel, C; Steglich, F

    2012-12-14

    We have investigated the optical conductivity of the prominent valence-fluctuating compounds EuIr(2)Si(2) and EuNi(2)P(2) in the infrared energy range to get new insights into the electronic properties of valence-fluctuating systems. For both compounds, we observe upon cooling the formation of a renormalized Drude response, a partial suppression of the optical conductivity below 100 meV, and the appearance of a midinfrared peak at 0.15 eV for EuIr(2)Si(2) and 0.13 eV for EuNi(2)P(2). Most remarkably, our results show a strong similarity with the optical spectra reported for many Ce- or Yb-based heavy-fermion metals and intermediate valence systems, although the phase diagrams and the temperature dependence of the valence differ strongly between Eu systems and Ce- or Yb-based systems. This suggests that the hybridization between 4f and conduction electrons, which is responsible for the properties of Ce and Yb systems, plays an important role in valence-fluctuating Eu systems.

  12. Social learning modulates the lateralization of emotional valence.

    PubMed

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

    2008-08-01

    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 the right prefrontal cortex (PFC), whereas recognition of complex social emotions is processed preferentially by the left PFC. Experiment 1 assessed the ability of healthy controls and patients with right and left PFC lesions to recognize basic and complex emotions. Experiment 2 modeled the patient's data of Experiment 1 on healthy participants under lateralized displays of the emotional stimuli. Both experiments support the Type as well as the Valence Hypotheses. However, our findings indicate that the Valence Hypothesis holds for basic but less so for complex emotions. It is suggested that, since social learning overrules the basic preference of valence in the hemispheres, the processing of complex emotions in the hemispheres is less affected by valence. PMID:18343548

  13. 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

  14. The acoustic correlates of valence depend on emotion family.

    PubMed

    Belyk, Michel; Brown, Steven

    2014-07-01

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

  15. Role of valence states of adsorbates in inelastic electron tunneling spectroscopy: A study of nitric oxide on Cu(110) and Cu(001)

    NASA Astrophysics Data System (ADS)

    Shiotari, Akitoshi; Okuyama, Hiroshi; Hatta, Shinichiro; Aruga, Tetsuya; Alducin, Maite; Frederiksen, Thomas

    2016-08-01

    We studied nitric oxide (NO) molecules on Cu(110) and Cu(001) surfaces with low-temperature scanning tunneling microscopy (STM) and density functional theory (DFT). NO monomers on the surfaces are characterized by STM images reflecting 2 π* resonance states located at the Fermi level. NO is bonded vertically to the twofold short-bridge site on Cu(110) and to the fourfold hollow site on Cu(001). When NO molecules form dimers on the surfaces, the valence orbitals are modified due to the covalent bonding. We measured inelastic electron tunneling spectroscopy (IETS) for both NO monomers and dimers on the two surfaces, and detected characteristic structures assigned to frustrated rotation and translation modes by density functional theory simulations. Considering symmetries of valence orbitals and vibrational modes, we explain the intensity of the observed IETS signals in a qualitative manner.

  16. Recognizing the emotional valence of names: an ERP study.

    PubMed

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

    2013-04-01

    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 valence only for nouns. This might reflect automatic attention directed towards emotional stimuli. The absence of such an effect for names supports the notion that the emotional meaning carried by names is accessed after word recognition and person identification. In addition, both names with negative valence and emotional nouns elicited late positive effects, which have been associated with evaluation of emotional significance. This positive effect started earlier for nouns than for names, but with similar durations. Our results suggest that distinct neural systems are involved in the retrieval of names' and nouns' emotional meaning.

  17. Processing emotional pictures and words: effects of valence and arousal.

    PubMed

    Kensinger, Elizabeth A; Schacter, Daniel L

    2006-06-01

    There is considerable debate regarding the extent to which limbic regions respond differentially to items with different valences (positive or negative) or to different stimulus types (pictures or words). In the present event-related fMRI study, 21 participants viewed words and pictures that were neutral, negative, or positive. Negative and positive items were equated on arousal. The participants rated each item for whether it depicted or described something animate or inanimate or something common or uncommon. For both pictures and words, the amygdala, dorsomedial prefrontal cortex (PFC), and ventromedial PFC responded equally to all high-arousal items, regardless of valence. Laterality effects in the amygdala were based on the stimulus type (word = left, picture = bilateral). Valence effects were most apparent when the individuals processed pictures, and the results revealed a lateral/medial distinction within the PFC: The lateral PFC responded differentially to negative items, whereas the medial PFC was more engaged during the processing of positive pictures.

  18. Valence Electronic Structure of Aqueous Solutions: Insights from Photoelectron Spectroscopy

    NASA Astrophysics Data System (ADS)

    Seidel, Robert; Winter, Bernd; Bradforth, Stephen E.

    2016-05-01

    The valence orbital electron binding energies of water and of embedded solutes are crucial quantities for understanding chemical reactions taking place in aqueous solution, including oxidation/reduction, transition-metal coordination, and radiation chemistry. Their experimental determination based on liquid-photoelectron spectroscopy using soft X-rays is described, and we provide an overview of valence photoelectron spectroscopy studies reported to date. We discuss principal experimental aspects and several theoretical approaches to compute the measured binding energies of the least tightly bound molecular orbitals. Solutes studied are presented chronologically, from simple electrolytes, via transition-metal ion solutions and several organic and inorganic molecules, to biologically relevant molecules, including aqueous nucleotides and their components. In addition to the lowest vertical ionization energies, the measured valence photoelectron spectra also provide information on adiabatic ionization energies and reorganization energies for the oxidation (ionization) half-reaction. For solutes with low solubility, resonantly enhanced ionization provides a promising alternative pathway.

  19. Valence Electronic Structure of Aqueous Solutions: Insights from Photoelectron Spectroscopy.

    PubMed

    Seidel, Robert; Winter, Bernd; Bradforth, Stephen E

    2016-05-27

    The valence orbital electron binding energies of water and of embedded solutes are crucial quantities for understanding chemical reactions taking place in aqueous solution, including oxidation/reduction, transition-metal coordination, and radiation chemistry. Their experimental determination based on liquid-photoelectron spectroscopy using soft X-rays is described, and we provide an overview of valence photoelectron spectroscopy studies reported to date. We discuss principal experimental aspects and several theoretical approaches to compute the measured binding energies of the least tightly bound molecular orbitals. Solutes studied are presented chronologically, from simple electrolytes, via transition-metal ion solutions and several organic and inorganic molecules, to biologically relevant molecules, including aqueous nucleotides and their components. In addition to the lowest vertical ionization energies, the measured valence photoelectron spectra also provide information on adiabatic ionization energies and reorganization energies for the oxidation (ionization) half-reaction. For solutes with low solubility, resonantly enhanced ionization provides a promising alternative pathway.

  20. Localized Multi-Reference Approach for Mixed-Valence Systems

    NASA Astrophysics Data System (ADS)

    Helal, W.; Evangelisti, S.; Leininger, T.; Maynau, D.

    2008-09-01

    The electronic structure and some important intra-molecular charge transfer parameters were investigated at CAS-SCF, MRCI, CAS+S and multi-reference localization levels of theory for purely organic mixed-valence molecules. In particular, a spiro cation has been taken as a model system. The potential energy surfaces of the ground and the lower three excited electronic states have been computed within a two-state model, at CAS-SCF using TZP basis for the spiro cation, and an adiabatic double-well potential has been obtained for the ground electronic state. Our analysis of the geometry through the reaction coordinate indicate that the spiro cation is a valence trapped bistable system. The effect of non-dynamical correlation, using a localized orbital approach, was found to be crucial for a quantitative description of the electronic structure and some important electron transfer parameters of these organic mixed-valence systems.

  1. Bond formation effects on the metal-insulator transition in the half-filled kagome Hubbard model

    NASA Astrophysics Data System (ADS)

    Higa, Ryota; Asano, Kenichi

    2016-06-01

    We study the metal-insulator transition in the half-filled Hubbard model on a Kagome lattice using the variational cluster approximation. The strong coupling limit of the model corresponds to the S =1 /2 Kagome Heisenberg antiferromagnet, which is known to have a singlet ground state, although its detail is still debated. As the results of the cluster methods generally depend much on the choice of the unit cluster, we have chosen the clusters that are compatible with these singlet ground states in the strong coupling case found so far, which basically consist of even number of sites. It is found that the correlated electrons on the Kagome lattice have a strong tendency to form valence-bond structures, which are the resonation of electrons on a single bond or several bonds forming loops. The zero-temperature metal-insulator transition at some interaction strength is possibly driven by the formation of such short range valence bonds and shows a second order character, which is distinctive from the Brinkman-Rice scenario. The electrons on these valence bonds further localizes onto each site as the interaction increases, and the valence bonds of electrons finally turn into magnetic singlet bonds between localized S =1 /2 spins, which are consistent with the ground states of the Kagome antiferromagnet.

  2. 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.

  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.

  4. The use and misuse of some positively valenced community concepts.

    PubMed

    Cowen, E L

    2001-02-01

    Considers the usage of four somewhat amorphous, but positively valenced, community mental health terms: primary prevention in mental health (and closely related notions such as wellness enhancement and positive psychology); resilience; charter schools; and empowerment. Use of these concepts often reflects a need to align with currently popular, "in"-terminology, rather than an intrinsic connection between what is being written about and a tight definition of the concept in question. Usages built primarily around a concept's positive valence and glitter tend to: (a) break down communication; (b) confuse rather than clarify; and (c) ultimately retard a field's growth and progress. PMID:11300664

  5. Valence QCD: Connecting QCD to the quark model

    SciTech Connect

    Liu, K.F.; Dong, S.J.; Draper, T.; Sloan, J.; Leinweber, D.; Wilcox, W.; Woloshyn, R.M.

    1999-06-01

    A valence QCD theory is developed to study the valence quark properties of hadrons. To keep only the valence degrees of freedom, the pair creation through the {ital Z} graphs is deleted in the connected insertions, whereas the sea quarks are eliminated in the disconnected insertions. This is achieved with a new {open_quotes}valence QCD{close_quotes} Lagrangian where the action in the time direction is modified so that the particle and antiparticle decouple. It is shown in this valence version of QCD that the ratios of isovector to isoscalar matrix elements (e.g., F{sub A}/D{sub A} and F{sub S}/D{sub S} ratios) in the nucleon reproduce the SU(6) quark model predictions in a lattice QCD calculation. We also consider how the hadron masses are affected on the lattice and discover new insights into the origin of dynamical mass generation. It is found that, within statistical errors, the nucleon and the {Delta} become degenerate for the quark masses we have studied (ranging from 1 to 4 times the strange mass). The {pi} and {rho} become nearly degenerate in this range. It is shown that valence QCD has the {ital C}, {ital P}, {ital T} symmetries. The lattice version is reflection positive. It also has the vector and axial symmetries. The latter leads to a modified partially conserved axial Ward identity. As a result, the theory has a U(2N{sub F}) symmetry in the particle-antiparticle space. Through lattice simulation, it appears that this is dynamically broken down to U{sub q}(N{sub F}){times}U{sub {bar q}}(N{sub F}). Furthermore, the lattice simulation reveals spin degeneracy in the hadron masses and various matrix elements. This leads to an approximate U{sub q}(2N{sub F}){times}U{sub {bar q}}(2N{sub F}) symmetry which is the basis for the valence quark model. In addition, we find that the masses of {ital N}, {Delta},{rho},{pi},a{sub 1}, and a{sub 0} all drop precipitously compared to their counterparts in the quenched QCD calculation. This is interpreted as due to the

  6. 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)

  7. 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…

  8. Puzzles in bonding and spectroscopy: the case of dicarbon.

    PubMed

    Macrae, Roderick M

    2016-01-01

    The unstable molecule C₂ has been of interest since its identification as the source of the "Swan band" features observable in the spectra offlames, carbon arcs, white dwarf stars, and comets, and it continues to serve as a focal point for experimental and theoretical discovery. Recent spectroscopic work has identified a quintet state of the molecule for the first time, while new insights into the bond order of C₂ in its ground state have been provided by sophisticated computational methods based on valence bond theory. This article gives a review of spectroscopic and computational work on C₂ including both historical background and the most recent discoveries. PMID:27120813

  9. Puzzles in bonding and spectroscopy: the case of dicarbon.

    PubMed

    Macrae, Roderick M

    2016-01-01

    The unstable molecule C₂ has been of interest since its identification as the source of the "Swan band" features observable in the spectra offlames, carbon arcs, white dwarf stars, and comets, and it continues to serve as a focal point for experimental and theoretical discovery. Recent spectroscopic work has identified a quintet state of the molecule for the first time, while new insights into the bond order of C₂ in its ground state have been provided by sophisticated computational methods based on valence bond theory. This article gives a review of spectroscopic and computational work on C₂ including both historical background and the most recent discoveries.

  10. 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…

  11. Inner valence-shell vacancy production and molecular fragmentation

    NASA Astrophysics Data System (ADS)

    Montenegro, E. C.; Tavares, A. C.; Luna, H.; Wolff, W.

    2015-09-01

    Fragmentation of complex molecules is studied linking the fragment-ions to the primary vacancies produced in their molecular orbitals. It is observed that a model based in such association describes well rather complex molecules. Deviations from this model are clear indications that inner valence-shells and double ionization plays a key role in the production of some fragments.

  12. Optical properties of mixed-valence platinum halides

    NASA Astrophysics Data System (ADS)

    Albin, Michael; Patterson, Howard H.

    1980-08-01

    Temperature dependent absorption spectra are reported for PtX 2-4 -PtX 2-6 doped in Cs 2ZrX 6 (X = Cl, Br). Intense, broad bands have been assigned as mixed-valence (MV) transitions. Vibronic structure has been observed for the MV bromide system. Our results are discussed in terms of a model proposed by Hush.

  13. 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…

  14. Tagging Multiple Emotional Stimuli: Negative Valence Has Little Benefit

    ERIC Educational Resources Information Center

    Watson, Derrick G.; Blagrove, Elisabeth

    2012-01-01

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

  15. Valence and spectral properties of rare-earth clusters

    NASA Astrophysics Data System (ADS)

    Peters, L.; Di Marco, I.; Litsarev, M. S.; Delin, A.; Katsnelson, M. I.; Kirilyuk, A.; Johansson, B.; Sanyal, B.; Eriksson, O.

    2015-07-01

    The rare earths are known to have intriguing changes of the valence, depending on the chemical surrounding or geometry. Here, we aim at predicting the transition of valence when passing from the atomic divalent limit to the bulk trivalent limit. This transition is analyzed by addressing clusters of various size for selected rare-earth elements, i.e., Sm, Tb, and Tm, via a theoretical treatment that combines density functional theory with atomic multiplet theory. Our results show that Tm clusters change from pure divalent to pure trivalent at a size of six atoms, while Tb clusters are already divalent for two atoms and stay so until eight atoms and the bulk limit. Instead, Sm clusters are respectively purely divalent up to eight atoms. For larger Sm clusters, a transition to a trivalent configuration is expected and likely accompanied by a regime of mixed valence. The valence of all rare-earth clusters, as a function of size, is predicted from the interpolation of our calculated results. These predictions are argued to be best investigated by spectroscopic measurements. To ease experimental analysis, we provide theoretical spectra, based on dynamical mean-field theory in the Hubbard I approximation.

  16. 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…

  17. 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  n–f  n+1 multiplet structure differently hybridized with ligand states in such Racah materials is discussed. PMID:26490021

  18. 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…

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

    PubMed

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

    2015-10-22

    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(  n)-f ( n+1) multiplet structure differently hybridized with ligand states in such Racah materials is discussed.

  20. Mobile linkers on DNA-coated colloids: valency without patches.

    PubMed

    Angioletti-Uberti, Stefano; Varilly, Patrick; Mognetti, Bortolo M; Frenkel, Daan

    2014-09-19

    Colloids coated with single-stranded DNA (ssDNA) can bind selectively to other colloids coated with complementary ssDNA. The fact that DNA-coated colloids (DNACCs) can bind to specific partners opens the prospect of making colloidal "molecules." However, in order to design DNACC-based molecules, we must be able to control the valency of the colloids, i.e., the number of partners to which a given DNACC can bind. One obvious, but not very simple approach is to decorate the colloidal surface with patches of single-stranded DNA that selectively bind those on other colloids. Here we propose a design principle that exploits many-body effects to control the valency of otherwise isotropic colloids. Using a combination of theory and simulation, we show that we can tune the valency of colloids coated with mobile ssDNA, simply by tuning the nonspecific repulsion between the particles. Our simulations show that the resulting effective interactions lead to low-valency colloids self-assembling in peculiar open structures, very different from those observed in DNACCs with immobile DNA linkers.

  1. Heavy Drinking Relates to Positive Valence Ratings of Alcohol Cues

    PubMed Central

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

    2009-01-01

    Background A positive family history of alcohol use disorders (FH) is a robust predictor of personal alcohol abuse and dependence. Exposure to problem-drinking models is one mechanism through which family history influences alcohol-related cognitions and drinking patterns. Similarly, exposure to alcohol advertisements is associated with alcohol involvement and the relationship between affective response to alcohol cues and drinking behavior has not been well established. In addition, the collective contribution that FH, exposure to different types of problem-drinking models (e.g., parents, peers), and personal alcohol use have on appraisal of alcohol-related stimuli has not been evaluated with a large sample. Objective We investigated the independent effects of FH, exposure to problem-drinking models, and personal alcohol use on valence ratings of alcohol pictures in a college sample. Method College students (N=227) completed measures of personal drinking and substance use, exposure to problem-drinking models, FH, and ratings on affective valence of 60 alcohol pictures. Results Greater exposure to non-familial problem-drinkers predicted greater drinking among college students (β = .17, p < .01). However, personal drinking was the only predictor of valence ratings of alcohol pictures (β= −.53, p < .001). Conclusions Personal drinking level predicted valence ratings of alcohol cues over and above FH, exposure to problem-drinking models, and demographic characteristics. This suggests that positive affective responses to alcohol pictures are more a function of personal experience (i.e., repeated heavy alcohol use) than vicarious learning. PMID:18855802

  2. "Plug-and-go" strategy to manipulate streptavidin valencies.

    PubMed

    Sun, Xun; Montiel, Daniel; Li, Hao; Yang, Haw

    2014-08-20

    The streptavidin-biotin set is one of the most widely utilized conjugation pairs in biotechnological applications. The tetravalent nature of streptavidin and its homologues, however, tends to result in such undesirable complications as cross-linking or ill-defined stoichiometry. Here, we describe a mutagenesis-free strategy to manipulate the valencies of wild-type streptavidin that only requires commercially available reagents. The basic idea is simple: one obtains the desired streptavidin valency by blocking off unwanted binding sites using ancillary biotin ("plug"); this way, the extraordinary fM-biotin-binding affinity is fully retained for the remaining sites in streptavidin. In the present implementation, the ancillary biotin is attached to an auxiliary separation handle, negatively charged DNA or His-tagged protein, via a photochemically or enzymatically cleavable linker. Mixing streptavidin with the ancillary biotin construct produces a distribution of streptavidin valencies. The subsequent chromatographic separation readily isolates the construct of desired streptavidin valency, and the auxiliary handles are easily removed afterward ("go"). We demonstrate how this "plug-and-go" strategy allows a precise control for the compositions of streptavidin-biotin conjugates at the single-molecule level. This low-entry-barrier protocol could further expand the application scope of the streptavidin technology.

  3. Voice and Valency in San Luis Potosi Huasteco

    ERIC Educational Resources Information Center

    Munoz Ledo Yanez, Veronica

    2014-01-01

    This thesis presents an analysis of the system of transitivity, voice and valency alternations in Huasteco of San Luis Potosi (Mayan) within a functional-typological framework. The study is based on spoken discourse and elicited data collected in the municipalities of Aquismon and Tancanhuitz de Santos in the state of San Luis Potosi, Mexico. The…

  4. Heavy drinking relates to positive valence ratings of alcohol cues.

    PubMed

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

    2009-01-01

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

  5. Valence shell charge concentration (VSCC) evolution: a tool to investigate the transformations within a VSCC throughout a chemical reaction.

    PubMed

    Cortés-Guzmán, Fernando; Gómez, Rosa María; Rocha-Rinza, Tomas; Sánchez-Obregón, María Azucena; Guevara-Vela, José Manuel

    2011-11-17

    Theoretical studies about reaction mechanisms are usually limited to the determination of the energetic paths that connect reactants, transition states, and products. Recently, our group proposed the structural evolution, which has provided insights about the molecular structure changes occurring along a reaction path. Structural evolution may be defined as the development of a chemical reaction system across the partitioning of the nuclear configuration space into a finite number of structural regions defined on account of the topology of a scalar field, e.g., the electron density. In this paper, we present a tool to investigate within the framework of the Quantum Theory of Atoms in Molecules the evolvement of the Valence Shell Charge Concentration, the VSCC evolution, which is the description of the changes of electron density concentrations and depletions around the bonding area of an atom. The VSCC evolution provides supplementary information to the structural evolution because it allows the analysis of valence shells within a structural region, i.e., a subset of R(Q) with the same connectivity among the atoms forming a molecule. This new approach constitutes also a complement to the Valence-Shell Electron Pair Repulsion (VSEPR) model because it gives an account of the adjustments of electron pairs in the valence shell of an atom across a chemical reaction. The insertion reaction in the hydroformylation reaction of ethylene, the reduction of cyclohexanone with lithium aluminum hydride, the oxidation of methanol with chlorochromate, and the bimolecular nucleophilic substitution of CH(3)F with F(-) are used as representatives examples of the application of the VSCC evolution. Overall, this paper shows how the VSCC evolution through an analysis of the modifications of local charge concentrations and depletions in individual steps of a chemical reaction gives new insights about these processes.

  6. 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)

  7. Unusual structure, bonding and properties in a californium borate

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  8. Unusual structure, bonding and properties in a californium borate.

    PubMed

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

    2014-05-01

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

  9. Normal coordinate analysis of bilirubin vibrational spectra: Effects of intramolecular hydrogen bonding

    NASA Astrophysics Data System (ADS)

    Yang, Bijun; Taylor, Robert C.; Morris, Michael D.; Wang, Xiu-Zhen; Wu, Jin-guang; Yu, Bao-Zhu; Xu, Guang-xian; Soloway, Roger D.

    1993-11-01

    Normal coordinate analyses are presented for half-bilirubin molecules. Calculations for the AB pyrromethenone include intramolecular hydrogen bonds, while those for the CD chromophore exclude intramolecular hydrogen bonds. Valence force-field parameters have been optimized to correlate closely with the IR and Raman spectra of the target molecules. The results of the calculations are compared with the spectra of bilirubin IXa and various model compounds in the solid state and solution.

  10. 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.

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

    PubMed

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

    2015-02-28

    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.

  12. 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.

  13. Vibrational effects on valence electron momentum distributions of CH2F2.

    PubMed

    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 (CH2F2). 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 CH2F2 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 CH2 asymmetric stretching and CH2 rocking vibrational modes for a proper understanding of the electron momentum distribution of the 2b1 orbital having the CH-bonding character. The results of CH2F2and additional theoretical calculations for (CH3)2O and H2CO 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.

  14. 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.

  15. 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

  16. Orthogonal natural atomic orbitals form an appropriate one-electron basis for expanding CASSCF wave functions into localized bonding schemes and their weights.

    PubMed

    Bachler, Vinzenz

    2007-09-01

    Localized bonding schemes and their weights have been obtained for the pi-electron system of nitrone by expanding complete active space self-consistent field wave functions into a set of Slater determinants composed of orthogonal natural atomic orbitals (NAOs) of Weinhold and Landis (Valency and Bonding: A Natural Bond Orbital Donor-Acceptor Perspective, 2005). Thus, the derived bonding schemes are close to orthogonal valence bond structures. The calculated sequence of bonding scheme weights accords with the sequence of genuine resonance structure weights derived previously by Ohanessian and Hiberty (Chem Phys Lett 1987, 137, 437), who employed nonorthogonal atomic orbitals. This accord supports the notion that NAOs form an appropriate orthogonal one-electron basis for expanding complete active space self-consistent field wave functions into meaningful bonding schemes and their weights.

  17. 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

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Ventilation materials (I-A, I-B, I-C, II-A, III....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...

  18. 30 CFR 57.22202 - Main fans (I-A, I-B, I-C, II-A, III, V-A, and V-B mines).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... reverse airstream shall be approved by MSHA under the appliable requirements of 30 CFR part 18; (2) Drive... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Main fans (I-A, I-B, I-C, II-A, III, V-A, and V... Main fans (I-A, I-B, I-C, II-A, III, V-A, and V-B mines). (a) Main fans shall be— (1) Installed on...

  19. 30 CFR 57.22202 - Main fans (I-A, I-B, I-C, II-A, III, V-A, and V-B mines).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... reverse airstream shall be approved by MSHA under the appliable requirements of 30 CFR part 18; (2) Drive... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Main fans (I-A, I-B, I-C, II-A, III, V-A, and V... Main fans (I-A, I-B, I-C, II-A, III, V-A, and V-B mines). (a) Main fans shall be— (1) Installed on...

  20. 30 CFR 57.22202 - Main fans (I-A, I-B, I-C, II-A, III, V-A, and V-B mines).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... reverse airstream shall be approved by MSHA under the appliable requirements of 30 CFR part 18; (2) Drive... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Main fans (I-A, I-B, I-C, II-A, III, V-A, and V... Main fans (I-A, I-B, I-C, II-A, III, V-A, and V-B mines). (a) Main fans shall be— (1) Installed on...

  1. 30 CFR 57.22202 - Main fans (I-A, I-B, I-C, II-A, III, V-A, and V-B mines).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... reverse airstream shall be approved by MSHA under the appliable requirements of 30 CFR part 18; (2) Drive... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Main fans (I-A, I-B, I-C, II-A, III, V-A, and V... Main fans (I-A, I-B, I-C, II-A, III, V-A, and V-B mines). (a) Main fans shall be— (1) Installed on...

  2. 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, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 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...

  3. 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, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 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...

  4. 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...

  5. 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...

  6. 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...

  7. 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...

  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, 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...

  9. Using Multiple Bonding Strategies.

    PubMed

    Larson, Thomas D

    2015-01-01

    There are many ways to bond to tooth structure, some micro-mechanical some chemical, some a combination. Different dentin bonding materials have different bonding strengths to differently prepared surfaces, and because of differences in their nature, different areas of tooth structure present peculiar bonding challenges. This paper will review a variety of material types, elucidating their particular bonding strengths and commenting on improved bonding strategies to increase durability, strength, and favorable pulpal response. In this discussion, resin dentin bonding systems, glass ionomers, Gluma, resin cements, and newer combined products will br reviewed. PMID:26485903

  10. Using Multiple Bonding Strategies.

    PubMed

    Larson, Thomas D

    2015-01-01

    There are many ways to bond to tooth structure, some micro-mechanical some chemical, some a combination. Different dentin bonding materials have different bonding strengths to differently prepared surfaces, and because of differences in their nature, different areas of tooth structure present peculiar bonding challenges. This paper will review a variety of material types, elucidating their particular bonding strengths and commenting on improved bonding strategies to increase durability, strength, and favorable pulpal response. In this discussion, resin dentin bonding systems, glass ionomers, Gluma, resin cements, and newer combined products will br reviewed.

  11. 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%.

  12. Blister formation on 13Cr2MoNbVB ferritic-martensitic steel exposed to hydrogen plasma

    NASA Astrophysics Data System (ADS)

    Nikitin, A. V.; Tolstolutskaya, G. D.; Ruzhytskyi, V. V.; Voyevodin, V. N.; Kopanets, I. E.; Karpov, S. A.; Vasilenko, R. L.; Garner, F. A.

    2016-09-01

    The influence of pre-irradiation specimen deformation level on surface blister formation and sub-surface cracking of dual-phase 13Cr2MoNbVB ferritic-martensitic steel was studied using glow discharge hydrogen plasma with ion energy of 1 keV to fluences of 2 × 1025 H/m2. Protium was used for most studies, but deuterium was used for measuring the depth dependence of hydrogen diffusion. Formation of blisters was observed in the temperature range 230-340 K. It was found that pre-irradiation deformation caused changes in the threshold fluences of blister formation and also in blister size distribution. Subsurface cracks located on grain boundaries far beyond the implantation zone were formed concurrently with blisters, arising from hydrogen diffusion and trapping at defects. It was observed that cracks as long as 1 mm in length were formed in 95% deformed steel at depths up to 500 μm from surface.

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

    NASA Astrophysics Data System (ADS)

    Hu, F.; Jiang, G.; Yang, J. M.; Wang, C. K.; Zhao, X. F.; Hao, L. H.

    2011-01-01

    We report on large ab initio calculation for the 4s^2- 4s4p transitions in the Zinc-like sequence, using the multi-configuration Dirac-Hartree-Fock method. Results for fine-structure energy levels, the wavelengths, transition rates and lifetimes between Z = 70 (Yb) and Z= 92 (U) are presented and compared with other theories and experiments. The calculated values including core-valence correlation are found to be similar and to compare very well with other theories and experiments values. We believe that our extensive calculated values can guide experimentalists in identifying the fine-structure levels in their future work.

  14. 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…

  15. 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…

  16. 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.

  17. Interchannel coupling effects in the valence photoionization of SF6

    NASA Astrophysics Data System (ADS)

    Jose, Jobin; Lucchese, Robert; Rescigno, Tom

    2014-05-01

    The complex Kohn and polyatomic Schwinger variational techniques have been employed to illustrate the interchannel coupling correlation effects in the valence photoionization dynamics of SF6. Partial photoionization cross sections and asymmetry parameters of six valence subshells (1t1 g, 5t1 u, 1t2 u, 3eg, 1t2 g, 4t1 u) are discussed in the framework of several theoretical and experimental studies. The complex Kohn results are in rather good agreement with experimental results, indicative of the fact that the interchannel coupling effects alter the photoionization dynamics significantly. We find that the dominant effect of interchannel coupling is to reduce the magnitude of shape resonant cross sections near threshold and to induce resonant features in other channels to which resonances are coupled.

  18. Covert face recognition relies on affective valence in congenital prosopagnosia.

    PubMed

    Bate, Sarah; Haslam, Catherine; Jansari, Ashok; Hodgson, Timothy L

    2009-06-01

    Dominant accounts of covert recognition in prosopagnosia assume subthreshold activation of face representations created prior to onset of the disorder. Yet, such accounts cannot explain covert recognition in congenital prosopagnosia, where the impairment is present from birth. Alternatively, covert recognition may rely on affective valence, yet no study has explored this possibility. The current study addressed this issue in 3 individuals with congenital prosopagnosia, using measures of the scanpath to indicate recognition. Participants were asked to memorize 30 faces paired with descriptions of aggressive, nice, or neutral behaviours. In a later recognition test, eye movements were monitored while participants discriminated studied from novel faces. Sampling was reduced for studied--nice compared to studied--aggressive faces, and performance for studied--neutral and novel faces fell between these two conditions. This pattern of findings suggests that (a) positive emotion can facilitate processing in prosopagnosia, and (b) covert recognition may rely on emotional valence rather than familiarity.

  19. Attosecond photoionization dynamics with stimulated core-valence transitions

    NASA Astrophysics Data System (ADS)

    You, Jhih-An; Rohringer, Nina; Dahlström, Jan Marcus

    2016-03-01

    We investigate ionization of neon atoms by an isolated attosecond pump pulse in the presence of two coherent extreme ultraviolet or x-ray probe fields. The probe fields are tuned to a core-valence transition in the residual ion and induce spectral shearing of the photoelectron distributions. We show that the photoelectron-ion coincidence signal contains an interference pattern that depends on the temporal structure of the attosecond pump pulse and the stimulated core-valence transition. Many-body perturbation theory is used to compute "atomic response times" for the processes and we find strikingly different behavior for stimulation to the outer-core hole (2 p ↔2 s ) and stimulation to the inner-core hole (2 p ↔1 s ). The response time of the inner-core transition is found to be comparable to that of state-of-the-art laser-based characterization techniques for attosecond pulses.

  20. Valence space techniques and QRPA vibrational mass parameters

    NASA Astrophysics Data System (ADS)

    Deloncle, I.; Lechaftois, F.; Péru, S.

    2016-06-01

    The vibrational mass parameters entering the quadrupolar 5DCH Hamiltonian are commonly obtained neglecting beyond mean-field correlations and the dynamical mean-field rearrangement. The Quasiparticle Random Phase Approximation (QRPA) framework would allow to avoid these disadvantages [1], if the computation time, when using density dependent force, was not prohibitive. Here, a significant time reduction is obtained by applying valence space (VS) techniques (energy cut-off and inert core) in QRPA calculations. The VS techniques allow to probe the physical content of the mass parameter. The QRPA mass parameter exhibit robustness toward VS limitations contrarily to the intrinsic QRPA outputs, that show deceptive appearance when an inert core is used. Excited states energy, and associated transition probabilities, should not be considered for optimizing the valence space limits.

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

    NASA Astrophysics Data System (ADS)

    Hawthorne, Frank C.

    2012-11-01

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

  2. Heavy drinking relates to positive valence ratings of alcohol cues.

    PubMed

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

    2009-01-01

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

  3. Valence holes observed in nanodiamonds dispersed in water.

    PubMed

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

    2015-02-21

    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 π* transitions from sp(2)-hybridized carbon disappear, and holes in the valence band are observed.

  4. 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.

  5. 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

  6. Valence Parity Renders z•-Type Ions Chemically Distinct

    PubMed Central

    Hubler, Shane L.; Jue, April; Keith, Jason; McAlister, Graeme C.; Craciun, Gheorghe; Coon, Joshua J.

    2009-01-01

    Here we report that the odd electron z•-type ions formed by the electron-based peptide dissociation methods (electron capture or transfer, ECD or ETD) have distinctive chemical compositions from other common product ion types. Specifically, b-, c-, and y-type ions have an odd number of atoms with an odd valence (e.g., N and H), while z•-type ions contain an even number of atoms with an odd valence. This tenet, referred to as the valence parity rule, mandates that no c-type ion shall have the same chemical composition, and by extension mass, as a z•-type ion. By experiment we demonstrate that nearly half of all observed c- and z•-type product ions resulting from 226 ETD product ion spectra can be assigned to a single, correct, chemical composition and ion type by simple inspection of the m/z peaks. The assignments provide (1) a platform to directly determine amino acid composition, (2) an input for database search algorithms, or (3) a basis for de novo sequence analysis. PMID:18444621

  7. Optoelectronic properties of valence-state-controlled amorphous niobium oxide

    NASA Astrophysics Data System (ADS)

    Onozato, Takaki; Katase, Takayoshi; Yamamoto, Akira; Katayama, Shota; Matsushima, Koichi; Itagaki, Naho; Yoshida, Hisao; Ohta, Hiromichi

    2016-06-01

    In order to understand the optoelectronic properties of amorphous niobium oxide (a-NbO x ), we have investigated the valence states, local structures, electrical resistivity, and optical absorption of a-NbO x thin films with various oxygen contents. It was found that the valence states of Nb ion in a-NbO x films can be controlled from 5+  to 4+  by reducing oxygen pressure during film deposition at room temperature, together with changing the oxide-ion arrangement around Nb ion from Nb2O5-like to NbO2-like local structure. As a result, a four orders of magnitude reduction in the electrical resistivity of a-NbO x films was observed with decreasing oxygen content, due to the carrier generation caused by the appearance and increase of an oxygen-vacancy-related subgap state working as an electron donor. The tunable optoelectronic properties of a-NbO x films by valence-state-control with oxygen-vacancy formation will be useful for potential flexible optoelectronic device applications.

  8. 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.

  9. 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 (1σ) 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

  10. 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

  11. 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.

  12. Interchannel coupling effects in the valence photoionization of SF6

    NASA Astrophysics Data System (ADS)

    Jose, J.; Lucchese, R. R.; Rescigno, T. N.

    2014-05-01

    The complex Kohn and polyatomic Schwinger variational techniques have been employed to illustrate the interchannel coupling correlation effects in the valence photoionization dynamics of SF6. Partial photoionization cross sections and asymmetry parameters of six valence subshells (1t1g, 5t1u, 1t2u, 3eg, 1t2g, 4t1u) are discussed in the framework of several theoretical and experimental studies. The complex Kohn results are in rather good agreement with experimental results, indicative of the fact that the interchannel coupling effects alter the photoionization dynamics significantly. We find that the dominant effect of interchannel coupling is to reduce the magnitude of shape resonant cross sections near the threshold and to induce resonant features in other channels to which resonances are coupled. The long-standing issue concerning ordering of the valence orbitals is addressed and confirmed 4t1u61t2g63eg4(5t1u6+1t2u6) 1t1g6 as the most likely ordering.

  13. 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.

  14. 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.

  15. Optoelectronic properties of valence-state-controlled amorphous niobium oxide.

    PubMed

    Onozato, Takaki; Katase, Takayoshi; Yamamoto, Akira; Katayama, Shota; Matsushima, Koichi; Itagaki, Naho; Yoshida, Hisao; Ohta, Hiromichi

    2016-06-29

    In order to understand the optoelectronic properties of amorphous niobium oxide (a-NbO x ), we have investigated the valence states, local structures, electrical resistivity, and optical absorption of a-NbO x thin films with various oxygen contents. It was found that the valence states of Nb ion in a-NbO x films can be controlled from 5+  to 4+  by reducing oxygen pressure during film deposition at room temperature, together with changing the oxide-ion arrangement around Nb ion from Nb2O5-like to NbO2-like local structure. As a result, a four orders of magnitude reduction in the electrical resistivity of a-NbO x films was observed with decreasing oxygen content, due to the carrier generation caused by the appearance and increase of an oxygen-vacancy-related subgap state working as an electron donor. The tunable optoelectronic properties of a-NbO x films by valence-state-control with oxygen-vacancy formation will be useful for potential flexible optoelectronic device applications. PMID:27168317

  16. On the valence fluctuation in the early actinide metals

    DOE PAGES

    Soderlind, P.; Landa, A.; Tobin, J. G.; Allen, P.; Medling, S.; Booth, C. H.; Bauer, E. D.; Cooley, J. C.; Sokaras, D.; Weng, T. -C.; et al

    2015-12-15

    In this study, recent X-ray measurements suggest a degree of valence fluctuation in plutonium and uranium intermetallics. We are applying a novel scheme, in conjunction with density functional theory, to predict 5f configuration fractions of states with valence fluctuations for the early actinide metals. For this purpose we perform constrained integer f-occupation calculations for the α phases of uranium, neptunium, and plutonium metals. For plutonium we also investigate the δ phase. The model predicts uranium and neptunium to be dominated by the f3 and f4 configurations, respectively, with only minor contributions from other configurations. For plutonium (both α and δmore » phase) the scenario is dramatically different. Here, the calculations predict a relatively even distribution between three valence configurations. The δ phase has a greater configuration fraction of f6 compared to that of the α phase. The theory is consistent with the interpretations of modern X-ray experiments and we present resonant X-ray emission spectroscopy results for α-uranium.« less

  17. On the valence fluctuation in the early actinide metals

    SciTech Connect

    Soderlind, P.; Landa, A.; Tobin, J. G.; Allen, P.; Medling, S.; Booth, C. H.; Bauer, E. D.; Cooley, J. C.; Sokaras, D.; Weng, T. -C.; Nordlund, D.

    2015-12-15

    In this study, recent X-ray measurements suggest a degree of valence fluctuation in plutonium and uranium intermetallics. We are applying a novel scheme, in conjunction with density functional theory, to predict 5f configuration fractions of states with valence fluctuations for the early actinide metals. For this purpose we perform constrained integer f-occupation calculations for the α phases of uranium, neptunium, and plutonium metals. For plutonium we also investigate the δ phase. The model predicts uranium and neptunium to be dominated by the f3 and f4 configurations, respectively, with only minor contributions from other configurations. For plutonium (both α and δ phase) the scenario is dramatically different. Here, the calculations predict a relatively even distribution between three valence configurations. The δ phase has a greater configuration fraction of f6 compared to that of the α phase. The theory is consistent with the interpretations of modern X-ray experiments and we present resonant X-ray emission spectroscopy results for α-uranium.

  18. Excitations of one-valence-proton, one-valence-neutron nucleus {sup 210}Bi from cold-neutron capture

    SciTech Connect

    Cieplicka-Oryńczak, N.; Fornal, B.; Szpak, B.; Leoni, S.; Bottoni, S.; Bazzacco, D.; Blanc, A.; Jentschel, M.; Köster, U.; Mutti, P.; Soldner, T.; Bocchi, G.; France, G. de; Simpson, G.; Urban, W.

    2015-10-15

    The low-spin structure of one-proton, one-neutron {sup 210}Bi nucleus was investigated in cold-neutron capture reaction on {sup 209}Bi. The γ-coincidence measurements were performed with use of EXILL array consisted of 16 HPGe detectors. The experimental results were compared to shell-model calculations involving valence particles excitations. The {sup 210}Bi nucleus offers the potential to test the effective proton-neutron interactions because most of the states should arise from the proton-neutron excitations. Additionally, it was discovered that a few states should come from the couplings of valence particles to the 3{sup −} octupole vibration in {sup 208}Pb which provides also the possibility of testing the calculations involving the core excitations.

  19. 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.

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

    PubMed Central

    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

    2015-01-01

    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

  2. Ferromagnetic bond of Li10 cluster: An alternative approach in terms of effective ferromagnetic sites.

    PubMed

    Donoso, Roberto; Rössler, Jaime; Llano-Gil, Sandra; Fuentealba, Patricio; Cárdenas, Carlos

    2016-09-01

    In this work, a model to explain the unusual stability of atomic lithium clusters in their highest spin multiplicity is presented and used to describe the ferromagnetic bonding of high-spin Li10 and Li8 clusters. The model associates the (lack of-)fitness of Heisenberg Hamiltonian with the degree of (de-)localization of the valence electrons in the cluster. It is shown that a regular Heisenberg Hamiltonian with four coupling constants cannot fully explain the energy of the different spin states. However, a more simple model in which electrons are located not at the position of the nuclei but at the position of the attractors of the electron localization function succeeds in explaining the energy spectrum and, at the same time, explains the ferromagnetic bond found by Shaik using arguments of valence bond theory. In this way, two different points of view, one more often used in physics, the Heisenberg model, and the other in chemistry, valence bond, come to the same answer to explain those atypical bonds. PMID:27608996

  3. Ferromagnetic bond of Li10 cluster: An alternative approach in terms of effective ferromagnetic sites

    NASA Astrophysics Data System (ADS)

    Donoso, Roberto; Rössler, Jaime; Llano-Gil, Sandra; Fuentealba, Patricio; Cárdenas, Carlos

    2016-09-01

    In this work, a model to explain the unusual stability of atomic lithium clusters in their highest spin multiplicity is presented and used to describe the ferromagnetic bonding of high-spin Li10 and Li8 clusters. The model associates the (lack of-)fitness of Heisenberg Hamiltonian with the degree of (de-)localization of the valence electrons in the cluster. It is shown that a regular Heisenberg Hamiltonian with four coupling constants cannot fully explain the energy of the different spin states. However, a more simple model in which electrons are located not at the position of the nuclei but at the position of the attractors of the electron localization function succeeds in explaining the energy spectrum and, at the same time, explains the ferromagnetic bond found by Shaik using arguments of valence bond theory. In this way, two different points of view, one more often used in physics, the Heisenberg model, and the other in chemistry, valence bond, come to the same answer to explain those atypical bonds.

  4. Si-Si bond as a deep trap for electrons and holes in silicon nitride

    NASA Astrophysics Data System (ADS)

    Karpushin, A. A.; Sorokin, A. N.; Gritsenko, V. A.

    2016-02-01

    A two-stage model of the capture of electrons and holes in traps in amorphous silicon nitride Si3N4 has been proposed. The electronic structure of a "Si-Si bond" intrinsic defect in Si3N4 has been calculated in the tight-binding approximation without fitting parameters. The properties of the Si-Si bond such as a giant cross section for capture of electrons and holes and a giant lifetime of trapped carriers have been explained. It has been shown that the Si-Si bond in the neutral state gives shallow levels near the bottom of the conduction band and the top of the valence band, which have a large cross section for capture. The capture of an electron or a hole on this bond is accompanied by the shift of shallow levels by 1.4-1.5 eV to the band gap owing to the polaron effect and a change in the localization region of valence electrons of atoms of the Si-Si bond. The calculations have been proposed with a new method for parameterizing the matrix elements of the tightbinding Hamiltonian taking into account a change in the localization region of valence electrons of an isolated atom incorporated into a solid.

  5. 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.

  6. 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.

  7. Bond percolation in films

    NASA Astrophysics Data System (ADS)

    Korneta, W.; Pytel, Z.

    1988-04-01

    Bond percolation in films with simple cubic structure is considered. It is assumed that the probability of a bond being present between nearest-neighbor sites depends on the distances to surfaces. Based on the relation between the Potts model and the bond percolation model, and using the mean-field approximation, the phase diagram and profiles of the percolation probability have been obtained.

  8. 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.

  9. Acrylic mechanical bond tests

    SciTech Connect

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

    1991-02-01

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

  10. 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.

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

    SciTech Connect

    RODRIGUEZ,J.A.

    2001-09-27

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

  12. 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 dipole–dipole 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.

  13. Valence state parameters of all transition metal atoms in metalloproteins--development of ABEEMσπ fluctuating charge force field.

    PubMed

    Yang, Zhong-Zhi; Wang, Jian-Jiang; Zhao, Dong-Xia

    2014-09-01

    To promote accuracy of the atom-bond electronegativity equalization method (ABEEMσπ) fluctuating charge polarizable force fields, and extend it to include all transition metal atoms, a new parameter, the reference charge is set up in the expression of the total energy potential function. We select over 700 model molecules most of which model metalloprotein molecules that come from Protein Data Bank. We set reference charges for different apparent valence states of transition metals and calibrate the parameters of reference charges, valence state electronegativities, and valence state hardnesses for ABEEMσπ through linear regression and least square method. These parameters can be used to calculate charge distributions of metalloproteins containing transition metal atoms (Sc-Zn, Y-Cd, and Lu-Hg). Compared the results of ABEEMσπ charge distributions with those obtained by ab initio method, the quite good linear correlations of the two kinds of charge distributions are shown. The reason why the STO-3G basis set in Mulliken population analysis for the parameter calibration is specially explained in detail. Furthermore, ABEEMσπ method can also quickly and quite accurately calculate dipole moments of molecules. Molecular dynamics optimizations of five metalloproteins as the examples show that their structures obtained by ABEEMσπ fluctuating charge polarizable force field are very close to the structures optimized by the ab initio MP2/6–311G method. This means that the ABEEMσπ/MM can now be applied to molecular dynamics simulations of systems that contain metalloproteins with good accuracy.

  14. The valence electronic structure and conformational flexibility of epichlorohydrin.

    PubMed

    Stranges, S; Alagia, M; Decleva, P; Stener, M; Fronzoni, G; Toffoli, D; Speranza, M; Catone, D; Turchini, S; Prosperi, T; Zema, N; Contini, G; Keheyan, Y

    2011-07-21

    The electronic structure of epichlorohydrin is investigated in the whole valence region by a combined experimental and theoretical study. The issue of controversial assignments of the molecular electronic structure is here addressed. Photoelectron spectra (PES) and Threshold Photoelectron spectra (TPES) of room temperature molecules in the gas phase are recorded. Geometries and energies of the stable conformers due to internal rotation of the C-C-C-Cl dihedral angle, gauche-II (g-II), gauche-I (g-I), and cis, are calculated, and the effect of the conformational flexibility on the photoionization energetics is studied by DFT and 2h-1p Configuration Interaction (CI) methods. Strong breakdown of the Koopmans Theorem (KT) is obtained for the four outermost ionizations, which are further investigated by higher level ab initio calculations. The full assignment of the spectrum is put on a firm basis by the combination of experimental and theoretical results. The orbital composition from correlated calculations is found closer to the DFT orbitals, which are then used to analyze the electronic structure of the molecule. The Highest Occupied Molecular Orbital (HOMO) and HOMO--2 are n(O)/n(Cl) mixed orbitals. The nature of each valence MO is generally preserved in all the conformers, although the magnitude of the n(O)/n(Cl) mixing in HOMO and HOMO--2 varies to some extent with the C-C-C-Cl dihedral angle. The low energy part of the HOMO PE band is predicted to be substantially affected by the conformational flexibility, as experimentally observed in the spectra. The rest of the spectrum is described in terms of the dominant conformer g-II, and a good agreement between experiment and theory is found. The inner-valence PE spectrum is characterized by satellite structures, due to electron correlation effects, which are interpreted by means of 2h-1p CI calculations.

  15. 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.

  16. Nucleon and pio distribution functions in the valence region.

    SciTech Connect

    Holt, R. J.; Roberts, C. D.

    2010-10-28

    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 {ge} 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.

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

    PubMed

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

    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 participantsí 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

  18. Bonding thermoplastic polymers

    DOEpatents

    Wallow, Thomas I.; Hunter, Marion C.; Krafcik, Karen Lee; Morales, Alfredo M.; Simmons, Blake A.; Domeier, Linda A.

    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.

  19. Periodic trends in bond dissociation energies. A theoretical study.

    PubMed

    Mó, Otilia; Yáñez, Manuel; Eckert-Maksić, Mirjana; Maksić, Zvonimir B; Alkorta, Ibón; Elguero, José

    2005-05-19

    Bond dissociation energies (BDEs) of all possible A-X single bonds involving the first- and second-row atoms, from Li to Cl, where the free valences are saturated by hydrogens, have been estimated through the use of the G3-theory and at the B3LYP/6-311+G(3df,2pd)//B3LYP/6-31G(2df,p) DFT level of theory. BDEs exhibit a periodical behavior. The A-X (A = Li, Be, B, Na, Mg, Al, and Si) BDEs show a steady increase along the first and the second row of the periodic table as a function of the atomic number Z(X). For A-X bonds involving electronegative atoms (A = C, N, O, F, P, S, and Cl) the bond energies achieve a maximum around Z(X) = 5. The same behavior is observed when BDEs are plotted against the electronegativity chi(X) of the atom X. Thus, for A-X bonds (A = Li, Be, B, Na, Mg, Al, Si), the BDEs for a fixed A increases, grosso modo, as the electronegativity differences between X and A increase, with some exceptions, which reflect the differences in the relaxation energies of the radicals produced upon the bond cleavage. A similar trend, albeit less pronounced, is found for single A-X bonds, where A = C, N, O, F, P, S, and Cl. However, there is an additional feature embodied in the enhancement of the strength of the A-boron bonds due to the ability of boron to act as a strong electron acceptor. The trends in bond lengths and charge densities at the bond critical points are in line with the aforementioned behavior.

  20. 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.

  1. 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.

  2. 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.

  3. Aging and long-term memory for emotionally valenced events.

    PubMed

    Breslin, Carolyn W; Safer, Martin A

    2013-06-01

    In 2008, 1103 ardent Boston Red Sox fans answered questions about their team's 2003 loss and 2004 win in baseball championship games with archrival New York Yankees. Contrary to predictions based on socioemotional selectivity theory, there were no significant interactions of age and event valence for accuracy in remembering event details, or for self-reported subjective vividness and rehearsal of the memories. Fans 65 years and older tended to remember feeling only sad about the 2003 loss, whereas fans 25 years and under tended to remember feeling both sad and angry. Individuals may remember emotional feelings based on remembered goals about an event.

  4. Pion and kaon valence-quark parton distribution functions

    NASA Astrophysics Data System (ADS)

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

    2011-06-01

    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 π-N Drell-Yan data for the pion’s u-quark distribution and to Drell-Yan data for the ratio uK(x)/uπ(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.

  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. Control of valence and conduction band energies in layered transition metal phosphates via surface functionalization.

    PubMed

    Lentz, Levi C; Kolb, Brian; Kolpak, Alexie M

    2016-05-18

    Layered transition metal phosphates and phosphites (TMPs) are a class of materials composed of layers of 2D sheets bound together via van der Waals interactions and/or hydrogen bonds. Explored primarily for use in proton transfer, their unique chemical tunability also makes TMPs of interest for forming large-scale hybrid materials. Further, unlike many layered materials, TMPs can readily be solution exfoliated to form single 2D sheets or bilayers, making them exciting candidates for a variety of applications. However, the electronic properties of TMPs have largely been unstudied to date. In this work, we use first-principles computations to investigate the atomic and electronic structure of TMPs with a variety of stoichiometries. We demonstrate that there exists a strong linear relationship between the band gap and the ionic radius of the transition metal cation in these materials, and show that this relationship, which opens opportunities for engineering new compositions with a wide range of band gaps, arises from constraints imposed by the phosphorus-oxygen bond geometry. In addition, we find that the energies of the valence and conduction band edges can be systematically tuned over a range of ∼3 eV via modification of the functional group extending from the phosphorus. Based on the Hammett constant of this functional group, we identify a simple, predictive relationship for the ionization potential and electron affinity of layered TMPs. Our results thus provide guidelines for systematic design of TMP-derived functional materials, which may enable new approaches for optimizing charge transfer in electronics, photovoltaics, electrocatalysts, and other applications. PMID:27157509

  7. Control of valence and conduction band energies in layered transition metal phosphates via surface functionalization.

    PubMed

    Lentz, Levi C; Kolb, Brian; Kolpak, Alexie M

    2016-05-18

    Layered transition metal phosphates and phosphites (TMPs) are a class of materials composed of layers of 2D sheets bound together via van der Waals interactions and/or hydrogen bonds. Explored primarily for use in proton transfer, their unique chemical tunability also makes TMPs of interest for forming large-scale hybrid materials. Further, unlike many layered materials, TMPs can readily be solution exfoliated to form single 2D sheets or bilayers, making them exciting candidates for a variety of applications. However, the electronic properties of TMPs have largely been unstudied to date. In this work, we use first-principles computations to investigate the atomic and electronic structure of TMPs with a variety of stoichiometries. We demonstrate that there exists a strong linear relationship between the band gap and the ionic radius of the transition metal cation in these materials, and show that this relationship, which opens opportunities for engineering new compositions with a wide range of band gaps, arises from constraints imposed by the phosphorus-oxygen bond geometry. In addition, we find that the energies of the valence and conduction band edges can be systematically tuned over a range of ∼3 eV via modification of the functional group extending from the phosphorus. Based on the Hammett constant of this functional group, we identify a simple, predictive relationship for the ionization potential and electron affinity of layered TMPs. Our results thus provide guidelines for systematic design of TMP-derived functional materials, which may enable new approaches for optimizing charge transfer in electronics, photovoltaics, electrocatalysts, and other applications.

  8. Korteweg-deVries-Burgers (KdVB) equation in a five component cometary plasma with kappa described electrons and ions

    NASA Astrophysics Data System (ADS)

    Michael, Manesh; Willington, Neethu T.; Jayakumar, Neethu; Sebastian, Sijo; Sreekala, G.; Venugopal, Chandu

    2016-07-01

    We investigate the existence of ion-acoustic shock waves in a five component cometary plasma consisting of positively and negatively charged oxygen ions, kappa described hydrogen ions, hot solar electrons, and slightly colder cometary electrons. The KdVB equation has been derived for the system, and its solution plotted for different kappa values, oxygen ion densities, as well as the temperature ratios for the ions. It is found that the amplitude of the shock wave decreases with increasing kappa values. The strength of the shock profile decreases with increasing temperatures of the positively charged oxygen ions and densities of negatively charged oxygen ions.

  9. Chiral signatures in angle-resolved valence photoelectron spectroscopy of pure glycidol enantiomers.

    PubMed

    Garcia, Gustavo A; Nahon, Laurent; Harding, Chris J; Powis, Ivan

    2008-03-28

    Photoionization of the chiral molecule glycidol has been investigated in the valence region. Photoelectron circular dichroism (PECD) curves have been obtained at various photon energies by using circularly polarized VUV synchrotron radiation and a velocity map imaging technique to record angle-resolved photoelectron spectra (PES). The measured chiral asymmetries vary dramatically with the photon energy as well as with the ionized orbital, improving the effective orbital resolution of the PECD spectrum with respect to the PES. Typical asymmetry factors of 5% are observed, but the peak values measured range up to 15%. The experimental results are interpreted by continuum multiple scattering (CMS-Xalpha) calculations for several thermally accessible glycidol conformers. We find that a nearly quantitative agreement between theory and experiments can be achieved for the ionization of several molecular orbitals. Owing to the sensitivity of PECD to molecular conformation this allows us to identify the dominant conformer. The influence of intramolecular hydrogen bond orbital polarization is found to play a small yet significant role in determining the chiral asymmetry in the electron angular distributions.

  10. Solvent-Triggered Cis/Trans Isomerism in Cobalt Dioxolene Chemistry: Distinguishing Effects of Packing on Valence Tautomerism.

    PubMed

    Panja, Anangamohan; Jana, Narayan Ch; Bauzá, Antonio; Frontera, Antonio; Mathonière, Corine

    2016-09-01

    In this article, the synthesis and X-ray crystal structures of two cis/trans isomers of valence tautomeric (VT) cobalt dioxolene compounds are reported. The cis isomer (1) was isolated from the polar protic methanol solvent as a kinetic product, whereas the less polar nonprotic solvent acetone yielded the trans isomer (2). It should be noted that, although some coordination polymers involving cobalt bis(dioxolene) with the cis disposition are known for bridging ancillary ligands, such an arrangement is unprecedented for mononuclear compounds. A careful study of intermocular interactions revealed that the methanol solvent does not have much influence on the crystal growth in 1, whereas acetone forms strong halogen-bonding interactions that are crucial in the solid-state architecture of 2. This behavior can likely be used in crystal engineering to design new organic-inorganic hybrid materials. The energy difference between the two isomers was examined using DFT calculations, confirming that the trans form is in the thermodynamic state whereas the cis isomer is a kinetic product that can be converted into the trans isomer with time. Finally, both isomers exhibit solvent loss at elevated temperatures that is accompanied by a change in magnetic properties, associated with an irreversible valence tautomerism. Our results highlight the crucial role of the solvents for the isolation of cis/trans isomers in cobalt dioxolene chemistry, as well as the distinguishing effects of intermolecular forces and the solid-state packing on VT behavior. PMID:27557848

  11. Solvent-Triggered Cis/Trans Isomerism in Cobalt Dioxolene Chemistry: Distinguishing Effects of Packing on Valence Tautomerism.

    PubMed

    Panja, Anangamohan; Jana, Narayan Ch; Bauzá, Antonio; Frontera, Antonio; Mathonière, Corine

    2016-09-01

    In this article, the synthesis and X-ray crystal structures of two cis/trans isomers of valence tautomeric (VT) cobalt dioxolene compounds are reported. The cis isomer (1) was isolated from the polar protic methanol solvent as a kinetic product, whereas the less polar nonprotic solvent acetone yielded the trans isomer (2). It should be noted that, although some coordination polymers involving cobalt bis(dioxolene) with the cis disposition are known for bridging ancillary ligands, such an arrangement is unprecedented for mononuclear compounds. A careful study of intermocular interactions revealed that the methanol solvent does not have much influence on the crystal growth in 1, whereas acetone forms strong halogen-bonding interactions that are crucial in the solid-state architecture of 2. This behavior can likely be used in crystal engineering to design new organic-inorganic hybrid materials. The energy difference between the two isomers was examined using DFT calculations, confirming that the trans form is in the thermodynamic state whereas the cis isomer is a kinetic product that can be converted into the trans isomer with time. Finally, both isomers exhibit solvent loss at elevated temperatures that is accompanied by a change in magnetic properties, associated with an irreversible valence tautomerism. Our results highlight the crucial role of the solvents for the isolation of cis/trans isomers in cobalt dioxolene chemistry, as well as the distinguishing effects of intermolecular forces and the solid-state packing on VT behavior.

  12. 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.

  13. 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.

  14. 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

  15. 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.

  16. 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

  17. +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.

  18. Valence-state reflectometry of complex oxide heterointerfaces

    DOE PAGES

    Hamann-Borrero, Jorge E.; Macke, Sebastian; Choi, Woo Seok; Sutarto, Ronny; He, Feizhou; Radi, Abdullah; Elfimov, Ilya; Green, Robert J.; Haverkort, Maurits W.; Zabolotnyy, Volodymyr B.; et al

    2016-09-16

    Emergent phenomena in transition-metal-oxide heterostructures such as interface superconductivity and magnetism have been attributed to electronic reconstruction, which, however, is difficult to detect and characterise. Here we overcome the associated difficulties to simultaneously address the electronic degrees of freedom and distinguish interface from bulk effects by implementing a novel approach to resonant X-ray reflectivity (RXR). Our RXR study of the chemical and valance profiles along the polar (001) direction of a LaCoO3 film on NdGaO3 reveals a pronounced valence-state reconstruction from Co3+ in the bulk to Co2+ at the surface, with an areal density close to 0.5 Co2+ ions permore » unit cell. An identical film capped with polar (001) LaAlO3 maintains the Co3+ valence over its entire thickness. As a result, we interpret this as evidence for electronic reconstruction in the uncapped film, involving the transfer of 0.5e– per unit cell to the subsurface CoO2 layer at its LaO-terminated polar surface.« less

  19. The role of valence quarks in proton fragmentation

    NASA Astrophysics Data System (ADS)

    van Hove, L.

    1981-06-01

    Following earlier theoretical and experimental work (Kalinowski et al. [6], Bourquin et al. [7]), baryon production by fragmentation of incident protons in high energy hadron collisions is re-investigated in terms of a fragmentation-recombination mechanism similar to a model proposed by Fukuda and Iso [4]. The multiplicities n f (B) for the various types of baryons B produced in proton fragmentation are expressed in terms of the probabilities a i for i=0, ..., 3 valence quarks of the incident proton to emerge in the baryon B and 3- i to emerge in mesons (following [7] we suppose that antibaryon production is mostly due to baryon-antibaryon pair production by a mechanism of non-fragmentation type, and this is taken into account in deducing n f (B) from baryon and antibaryon multiplicity data). The positivity of the a i is found to impose remarkably narrow constraints on the n f (B) for (meta)stable B, and we find the data to satisfy these constraints. We show furthermore that the data are compatible with uncorrelated behaviour of the valence quarks of the incident proton, each of them having a probability ≃ 0.6 to emerge in the fragmentation baryon B, and a probability ≃ 0.4 to emerge in a meson. We also briefly discuss the relation of our analysis to previous work on the recombination model of proton fragmentation and its possible extension to meson fragmentation.

  20. Ignoring real faces: effects of valence, threat, and salience.

    PubMed

    Blagrove, Elisabeth; Watson, Derrick G

    2014-04-01

    Facial stimuli have been shown to accrue a special status within visual processing, particularly when attention is prioritized to one face over another on the basis of affective content. This has been examined in relation to the ability of faces to guide or hold attention, or to resist attentional suppression. Previous work has shown that schematic faces can only be partially ignored and that the emotional valence of to-be-ignored faces has little effect. Given recent debates concerning the use of schematic faces, here we examined the ease with which photorealistic faces could be ignored. Although we found evidence of a partial preview benefit for these stimuli, the findings were complex, with stimulus salience, valence, and threat content interacting to affect both the strength of the benefit and target detection efficiency (Exps. 1-3). Experiment 4 then clarified the effects of physical salience and perceived stimulus similarity in the previous experiments, demonstrating that a combination of these factors is likely to account for the search patterns observed.

  1. Microscopic Examinations of Co Valences and Spin States in Electron-Doped LaCoO3

    NASA Astrophysics Data System (ADS)

    Tomiyasu, Keisuke; Koyama, Syun-Ichi; Watahiki, Masanori; Sato, Mika; Nishihara, Kazuki; Takahashi, Yuki; Onodera, Mitsugi; Iwasa, Kazuaki; Nojima, Tsutomu; Nojiri, Hiroyuki; Okamoto, Jun; Huang, Di-Jing; Yamasaki, Yuuichi; Nakao, Hironori; Murakami, Youichi

    2016-09-01

    We studied the Co valences and spin states in electron-doped LaCo1-yTeyO3 by measuring X-ray absorption spectra and electron spin resonance. The low-temperature insulating state involves the low-spin Co3+ state (S = 0) and the high-spin Co2+ state, where the latter is described by g = 3.8 and jeff = 1/2. The results, in concurrence with the electron-hole asymmetry confirmed in the electrical resistivity, coincide with the spin-blockade phenomenon in this system. Furthermore, we discuss the g factor in terms of the strong covalent-bonding nature and consider multiple origins of this phenomenon.

  2. Weak bond screening system

    NASA Astrophysics Data System (ADS)

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

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

  3. 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

  4. Expertise in video game playing is associated with reduced valence-concordant emotional expressivity.

    PubMed

    Weinreich, André; Strobach, Tilo; Schubert, Torsten

    2015-01-01

    In carefully selected groups of video game playing (VGP) experts and nonexperts, we examined valence-concordant emotional expressivity. We measured electromyographic (EMG) activity over the corrugator supercilii muscle while participants viewed pleasant, neutral, and unpleasant pictures. Potential group differences concerning valence-concordant expressivity may arise from differences concerning the participants' emotional reactivity. To control for such differences, we concomitantly measured skin conductance response (SCR) and, in a separate affect misattribution procedure (AMP), valence transfer from the same set of stimuli. Importantly, we found attenuated valence-concordant EMG activity over the corrugator supercilii muscle in VGP experts compared to nonexperts, but no differences were evident concerning SCR or valence transfer in the AMP. The findings suggest that expertise in VGP is particularly associated with reduced valence-concordant emotional expressivity.

  5. 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}.

  6. Comparison of the proton-transfer paths in hydrogen bonds from theoretical potential-energy surfaces and the concept of conservation of bond order III. O-H-O hydrogen bonds.

    PubMed

    Majerz, Irena; Olovsson, Ivar

    2010-01-01

    The quantum-mechanically derived reaction coordinates (QMRC) for the proton transfer in O-H-O hydrogen bonds have been derived from ab initio calculations of potential-energy surfaces. A comparison is made between the QMRC and the corresponding bond-order reaction coordinates (BORC) derived by applying the Pauling bond order concept together with the principle of conservation of bond order. In agreement with earlier results for N-H-N(+) hydrogen bonds there is virtually perfect agreement between the QMRC and BORC curves for intermolecular O-H-O hydrogen bonds. For intramolecular O-H-O hydrogen bonds, the donor and acceptor parts of the molecule impose strong constraints on the O···O distance and the QMRC does not follow the BORC relation in the whole range. The neutron-determined proton positions are located close to the theoretically calculated potential-energy minima, and where the QMRC and the BORC curves coincide with each other. The results confirm the universal character of intermolecular hydrogen bonds: BORC is identical with QMRC and the proton can be moved from donor to acceptor keeping its valency equal to 1. The shape of PES for intramolecular hydrogen bonds is more complex as it is sensitive to the geometry of the molecule as well as of the hydrogen bridge.

  7. 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.

  8. Bonded semiconductor substrate

    DOEpatents

    Atwater, Jr.; Harry A. , Zahler; James M.

    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.

  9. 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.

  10. 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.

  11. BONDING ALUMINUM METALS

    DOEpatents

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

    1961-06-13

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

  12. 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.

  13. Entrapping a Group-VB Transition Metal, Vanadium, within an Endohedral Metallofullerene: V(x)Sc(3-x)N@I(h)-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--V(x)Sc(3-x)N@C80 (x = 1, 2)--were isolated, and their molecular structures were unambiguously determined by X-ray crystallography to be I(h)(7)-C80 cage entrapping the planar VSc2N/V2ScN clusters. V(x)Sc(3-x)N@I(h)(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 V(x)Sc(3-x)N@I(h)(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 V(x)Sc(3-x)N@I(h)(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

  14. 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, II-B, III, IV, V-A, and V-B mines). 57.22501 Section 57.22501 Mineral Resources MINE SAFETY AND... Illumination § 57.22501 Personal electric lamps (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B...

  15. Vibrational effects on valence electron momentum distributions of ethylene.

    PubMed

    Watanabe, Noboru; Yamazaki, Masakazu; Takahashi, Masahiko

    2012-09-21

    We report an electron momentum spectroscopy study of vibrational effects on the electron momentum distributions for the outer valence orbitals of ethylene (C(2)H(4)). The symmetric noncoplanar (e,2e) experiment has been conducted at an impact energy of 1.2 keV. Furthermore, a theoretical method of calculating electron momentum distributions for polyatomic molecules has been developed with vibrational effects being involved. It is shown from comparisons between experiment and theory that taking into account effects of the CH(2) asymmetric stretching and CH(2) rocking vibrational modes of C(2)H(4) is essential for a proper understanding of the electron momentum distribution of the 1b(3g) molecular orbital.

  16. 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.

  17. Theory of Valence-Fluctuating Tm Impurities. I

    NASA Astrophysics Data System (ADS)

    Saso, Tetsuro

    1989-11-01

    A new formalism is presented for describing mixed valent Tm impurities fluctuating between two magnetic configurations. Based on the self-consistent perturbation scheme, the present formalism incorporates not only the valence fluctuation between 4f12 and 4f13, but also the multiscattering process of 4f13 and a conduction electron, yielding a singlet bound state. Thus the ground state is a Kondo singlet, which however is different from the ordinary Kondo state and conceptually new in that the length of the local moment of the impurity is fluctuating between the two values j{=}6 and J{=}7/2. Numerical calculations are presented for the spectral distribution function of these states. Systematic study of the Kondo temperature TK yields that TK is substantially low when the number of f electrons is close to 12. Contribution of the above scattering processes to the f-electron spectral function and the magnetic susceptibility is also disscussed.

  18. 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

  19. 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

  20. Ab initio valence-space theory for exotic nuclei

    NASA Astrophysics Data System (ADS)

    Holt, Jason

    2015-10-01

    Recent advances in ab initio nuclear structure theory have led to groundbreaking predictions in the exotic medium-mass region, from the location of the neutron dripline to the emergence of new magic numbers far from stability. Playing a key role in this progress has been the development of sophisticated many-body techniques and chiral effective field theory, which provides a systematic basis for consistent many-nucleon forces and electroweak currents. Within the context of valence-space Hamiltonians derived from the nonperturbative in-medium similarity renormalization group (IM-SRG) approach, I will discuss the importance of 3N forces in understanding and making new discoveries in the exotic sd -shell region. Beginning in oxygen, we find that the effects of 3N forces are decisive in explaining why 24O is the last bound oxygen isotope, validating first predictions of this phenomenon from several years ago. Furthermore, 3N forces play a key role in reproducing spectroscopy, including signatures of doubly magic 22,24O, and physics beyond the dripline. Similar improvements are obtained in new spectroscopic predictions for exotic fluorine and neon isotopes, where agreement with recent experimental data is competitive with state-of-the-art phenomenology. Finally, I will discuss first applications of the IM-SRG to effective valence-space operators, such as radii and E 0 transitions, as well as extensions to general operators crucial for our future understanding of electroweak processes, such as neutrinoless double-beta decay. This work was supported by NSERC and the NRC Canada.

  1. 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.

  2. 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…

  3. 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)

  4. Universal nanopatternable interfacial bonding.

    PubMed

    Ding, Yuzhe; Garland, Shaun; Howland, Michael; Revzin, Alexander; Pan, Tingrui

    2011-12-01

    A nanopatternable polydimethylsiloxane (PDMS) oligomer layer is demonstrated as an interfacial adhesive for its intrinsic transferability and universal adhesiveness. Utilizing the well-established surface modification and bonding techniques of PDMS surfaces, irreversible bonding is formed (up to 400 kPa) between a wide range of substrate pairs, representing ones within and across different materials categories, including metals, ceramics, thermoset, and thermoplastic polymers.

  5. 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.

  6. 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)

  7. 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

  8. 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.

  9. 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.

  10. 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

  11. 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

  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. Age influences the relation between subjective valence ratings and emotional word use during autobiographical memory retrieval.

    PubMed

    Ford, Jaclyn H; DiGirolamo, Marissa A; Kensinger, Elizabeth A

    2016-09-01

    Recent research reveals an age-related increase in positive autobiographical memory retrieval using a number of positivity measures, including valence ratings and positive word use. It is currently unclear whether the positivity shift in each of these measures co-occurs, or if age uniquely influences multiple components of autobiographical memory retrieval. The current study examined the correspondence between valence ratings and emotional word use in young and older adults' autobiographical memories. Positive word use in narratives was associated with valence ratings only in young adults' narratives. Older adults' narratives contained a consistent level of positive word use regardless of valence rating, suggesting that positive words and concepts may be chronically accessible to older adults during memory retrieval, regardless of subjective valence. Although a relation between negative word use in narratives and negative valence ratings was apparent in both young and older adults, it was stronger in older adults' narratives. These findings confirm that older adults do vary their word use in accordance with subjective valence, but they do so in a way that is different from young adults. The results also point to a potential dissociation between age-related changes in subjective valence and in positive word use. PMID:26274398

  14. 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…

  15. 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…

  16. 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…

  17. 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.

  18. 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.

  19. Valence fluctuations of europium in the boride Eu4Pd(29+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 Eu4Pd(29+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.

  20. Examining the role of emotional valence of mind wandering: All mind wandering is not equal.

    PubMed

    Banks, Jonathan B; Welhaf, Matthew S; Hood, Audrey V B; Boals, Adriel; Tartar, Jaime L

    2016-07-01

    To evaluate the role of emotional valence on the impact of mind wandering on working memory (WM) and sustained attention, we reanalyzed data from three independently conducted studies that examined the impact of stress on WM (Banks & Boals, 2016; Banks, Welhaf, & Srour, 2015) and sustained attention (Banks, Tartar, & Welhaf, 2014). Across all studies, participants reported the content of their thoughts at random intervals during the WM or sustained attention task. Thought probes in all studies included a core set of response options for task-unrelated thoughts (TUTs) that were negatively, positively, or neutrally emotionally valenced. In line with theories of emotional valenced stimuli on capture of attention, results suggest negatively valenced TUTs, but not positively valenced TUTs, were related to poorer WM and sustained attention in two studies. Neutral TUTs were related to poorer WM but not sustained attention performance. Implications for models of mind wandering are discussed.

  1. 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.

  2. 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.

  3. Emotions and language about motion: Differentiating affective dominance with syntax from valence with semantics.

    PubMed

    Freddi, Sébastien; Esteban, José; Dru, Vincent

    2015-12-15

    Motion as encoded in linguistic cues is used to differentiate affective valence and dominance. Participants were invited to rate their affective responses to different words along valence and dominance scales. The words were nouns describing static cues and verbs describing motion, connected to DOWN/UP and Avoidance/Approach cues. The results of three studies showed that valence and dominance could be differentiated through syntax and semantics of motion. On one hand, dominance feelings, compared to valence ones, are particularly influenced by motion encoded in syntactic classes (verbs vs. nouns). On the other hand, valence feelings, compared to dominance ones, are influenced by a semantics of motion through DOWN/UP and Avoidance/Approach cues, considered as polarities. A polarity correspondence effect is proposed to explain these results.

  4. Examining the role of emotional valence of mind wandering: All mind wandering is not equal.

    PubMed

    Banks, Jonathan B; Welhaf, Matthew S; Hood, Audrey V B; Boals, Adriel; Tartar, Jaime L

    2016-07-01

    To evaluate the role of emotional valence on the impact of mind wandering on working memory (WM) and sustained attention, we reanalyzed data from three independently conducted studies that examined the impact of stress on WM (Banks & Boals, 2016; Banks, Welhaf, & Srour, 2015) and sustained attention (Banks, Tartar, & Welhaf, 2014). Across all studies, participants reported the content of their thoughts at random intervals during the WM or sustained attention task. Thought probes in all studies included a core set of response options for task-unrelated thoughts (TUTs) that were negatively, positively, or neutrally emotionally valenced. In line with theories of emotional valenced stimuli on capture of attention, results suggest negatively valenced TUTs, but not positively valenced TUTs, were related to poorer WM and sustained attention in two studies. Neutral TUTs were related to poorer WM but not sustained attention performance. Implications for models of mind wandering are discussed. PMID:27310109

  5. Valence fluctuations of europium in the boride Eu4Pd(29+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 Eu4Pd(29+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

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

    PubMed

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

    2013-12-01

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

  7. Impurity signatures in two-dimensional materials in atomic-resolution valence-electron-energy-loss spectroscopic maps

    NASA Astrophysics Data System (ADS)

    Kapetanakis, Myron; Oxley, Mark; Zhou, Wu; Idrobo, Juan-Carlos; Pantelides, Sokrates

    The local atomic configurations and electronic states of impurities in 2D materials can be probed directly by several microscopy techniques. Probes of electronic excitations, however, lack spatial resolution. Here we demonstrate that valence-electron energy-loss spectroscopy in an aberration-corrected scanning transmission electron microscope yields atomic-resolution maps of electronic excitations that provide unique signatures of distinct bonding configuration impurities in 2D materials. We report simulations of the maps based on density functional theory and dynamical scattering theory, which agree with and provide direct interpretation of the observed features. The maps differentiate between different bonding configurations of impurities in graphene and hexagonal boron nitride. The theoretical analysis yields information on local electronic excitations, corresponding to impurity-induced bound, resonant and antiresonant states. The method stands to benefit from new monochromators and detectors that enhance spatial and energy resolution and constitutes a powerful alternative to optical spectroscopies for probing electronic and magnetic signatures related with impurities and defects. Supported by DOE Grant DE-FG02-0946554 and by DOE BES MSED.

  8. 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.

  9. 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

  10. 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

  11. 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

    ... methane, other gases, and contaminants in mine air shall be approved by MSHA under the applicable..., 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...

  12. 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, 2012 CFR

    2012-07-01

    ... methane, other gases, and contaminants in mine air shall be approved by MSHA under the applicable..., 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...

  13. 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

  14. Junk-Bond Colleges.

    ERIC Educational Resources Information Center

    Van Der Werf, Martin

    2003-01-01

    Describes how a long-predicted decline in the fortunes of small private colleges is beginning to show up in the bond market, as the number of colleges now rated in the junk category has nearly doubled. (EV)

  15. Bonding with your newborn

    MedlinePlus

    ... and your baby begin to feel a strong attachment with each other. You may feel great love ... L, Saison J, et al. Building a secure attachment bond with your baby. Helpguide.org. www.helpguide. ...

  16. Detecting Defective Solder Bonds

    NASA Technical Reports Server (NTRS)

    Paulson, R.; Barney, J.; Decker, H. J.

    1984-01-01

    Method is noncontact and nondestructive. Technique detects solder bonds in solar array of other large circuit board, using thermal-imaging camera. Board placed between heat lamp and camera. Poor joints indiated by "cold" spots on the infrared image.

  17. 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.

  18. Oxytocin specifically enhances valence-dependent parasympathetic responses.

    PubMed

    Gamer, Matthias; Büchel, Christian

    2012-01-01

    The evolutionarily highly conserved neuropeptide oxytocin seems to be involved in the regulation of complex forms of social behavior. It enhances the processing of positive social stimuli, reduces behavioral and neuroendocrine stress responses and modulates amygdala activity in humans. Moreover, it has been proposed that oxytocin dampens sympathetic nervous system activity. This hypothesis was tested in a double-blind, placebo-controlled study with 38 men either receiving 24 IU oxytocin intranasally or a placebo spray. While accomplishing an emotion classification task, electrodermal responses were measured as an index of sympathetic activity. Moreover, heart rate changes were recorded that are additionally mediated by the parasympathetic nervous system. Oxytocin enhanced differential heart rate responses to facial expressions as a function of the emotional valence, but had no effect on electrodermal activity or tonic measures of physiological arousal. These results indicate that oxytocin specifically modulates phasic activity of the parasympathetic nervous system which potentially reflects an increased motivational value of facial expressions following oxytocin treatment. Findings suggest that anxiolytic effects of oxytocin are not reflected in short-term sympathetic responses and may even be a consequence of rather than a prerequisite for improved social information processing. PMID:21641726

  19. 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.

  20. Thermoelectric transport in the coupled valence-band model

    NASA Astrophysics Data System (ADS)

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

    2011-02-01

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

  1. Valence Band Control of Metal Silicide Films via Stoichiometry.

    PubMed

    Streller, Frank; Qi, Yubo; Yang, Jing; Mangolini, Filippo; Rappe, Andrew M; Carpick, Robert W

    2016-07-01

    The unique electronic and mechanical properties of metal silicide films render them interesting for advanced materials in plasmonic devices, batteries, field-emitters, thermoelectric devices, transistors, and nanoelectromechanical switches. However, enabling their use requires precisely controlling their electronic structure. Using platinum silicide (PtxSi) as a model silicide, we demonstrate that the electronic structure of PtxSi thin films (1 ≤ x ≤ 3) can be tuned between metallic and semimetallic by changing the stoichiometry. Increasing the silicon content in PtxSi decreases the carrier density according to valence band X-ray photoelectron spectroscopy and theoretical density of states (DOS) calculations. Among all PtxSi phases, Pt3Si offers the highest DOS due to the modest shift of the Pt5d manifold away from the Fermi edge by only 0.5 eV compared to Pt, rendering it promising for applications. These results, demonstrating tunability of the electronic structure of thin metal silicide films, suggest that metal silicides can be designed to achieve application-specific electronic properties. PMID:27322019

  2. Valence Band Control of Metal Silicide Films via Stoichiometry.

    PubMed

    Streller, Frank; Qi, Yubo; Yang, Jing; Mangolini, Filippo; Rappe, Andrew M; Carpick, Robert W

    2016-07-01

    The unique electronic and mechanical properties of metal silicide films render them interesting for advanced materials in plasmonic devices, batteries, field-emitters, thermoelectric devices, transistors, and nanoelectromechanical switches. However, enabling their use requires precisely controlling their electronic structure. Using platinum silicide (PtxSi) as a model silicide, we demonstrate that the electronic structure of PtxSi thin films (1 ≤ x ≤ 3) can be tuned between metallic and semimetallic by changing the stoichiometry. Increasing the silicon content in PtxSi decreases the carrier density according to valence band X-ray photoelectron spectroscopy and theoretical density of states (DOS) calculations. Among all PtxSi phases, Pt3Si offers the highest DOS due to the modest shift of the Pt5d manifold away from the Fermi edge by only 0.5 eV compared to Pt, rendering it promising for applications. These results, demonstrating tunability of the electronic structure of thin metal silicide films, suggest that metal silicides can be designed to achieve application-specific electronic properties.

  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. 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.

  5. [XPS study on the influence of calcination conditions to cerium ion valence].

    PubMed

    Mei, Yan; Yan, Jian-ping; Nie, Zuo-ren

    2010-01-01

    For the system of Ce(NO3)2.6H2O and urea solution during homogeneous precipitation method, X-ray diffraction (XRD), infrared spectrum (IR) and especially X-ray photoelectron spectroscopy (XPS) were used to study and characterize the product structure, variety of cerium ion valence, compound surface character and kernel electronic configurations. The results of XRD and IR showed that calcination temperature had a great effect on the cerium ion valence. The products are orthorhombic Ce2 O(CO3)2.H2O with valence III by using homogeneous precipitation method directly. When heated from the temperature 200 degrees C to 250 degrees C, the product of CeO(CO3)2.H2O with valence VI was finally changed into stable CeO2 with valence IV. XPS was used to study the surface character and kernel electronic configurations of the three different compounds through fine scanning of O(1s), Ce(3d) and Ce(4d) apices, and the results approved that the compounds with different valences are caused by the different valence electronic configurations of the products.

  6. Valence force field analysis on nitrogen in silicon

    NASA Astrophysics Data System (ADS)

    Harada, H.; Ohkubo, I.; Mikayama, T.; Yamanaka, Y.; Inoue, N.

    2001-12-01

    Nitrogen doping attracts attention because it reduces void defects drastically. But the mechanism has not been clarified yet. Various configurations of nitrogen have been proposed by using the first principles calculation but there is no description how the stress plays a role in determining these nitrogen configurations. We reveal normal vibration modes corresponding to well-known infrared absorption peaks at 766 and 963 cm -1 of nitrogen split interstitial (N-N) and derive force constants for bond stretching and bond bending. Local strain energy near nitrogen is calculated for the optimized structures of N-N, nitrogen-vacancy complex, substitutional N and interstitial N. As a result, it is found that in structures of N-N and N 2-V 2 with filled electron orbitals, strain energy plays an important role in the determination of the stable structure.

  7. Structure and bonding in Yb4MgGe4: Yb2+/Yb3+ mixed-valency and charge separation.

    PubMed

    Tobash, Paul H; Bobev, Svilen

    2006-03-22

    Reported are the synthesis and the structural characterization of a new derivative of the RE5Tt4 family (RE = Rare-earth; Tt = Tetrel, = Si, Ge, i.e., group 14 element), Yb5-xMgxGe4 (x approximately 1). Crystal data for Yb4.04(1)Mg0.96(1)Ge4 at 23 degrees C: orthorhombic, space group Pnma (No. 62), Z = 4; a = 7.155(2) A, b = 14.769(5) A, c = 7.688(2) A; V = 812.5(4) A3. This phase is an example of a substitution of lanthanide metal (Yb) with a nonmagnetic element (Mg) within this structure type. Its structure can alternatively be described as an intergrowth of the hypothetical Yb2MgGe2, which features flat infinite [MgGe2]4- layers and the hypothetical YbGe with [Ge2]6- dimers. The flat [MgGe2]4- layers propagate in two dimensions (a and c), and they are offset by a distance of 1/4.a with respect to one another and are interspaced with layers of [Ge2]6- dimers and Yb cations filling the space between them. According to the structural and physical property data, Yb4MgGe4 is a heterogeneous mixed-valent compound, i.e. a system where one of the two symmetry-inequivalent Yb sites has atoms in closed-shell Yb2+ configuration, whereas the Yb3+ cations occupy a different crystallographic site.

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

    ERIC Educational Resources Information Center

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

    2012-01-01

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

  9. 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…

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

    PubMed

    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.

  11. 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.

  12. Isolation of dangling bond states on Si(100) surfaces for quantum information applications

    NASA Astrophysics Data System (ADS)

    Scherpelz, Peter; Galli, Giulia

    Hydrogen resist lithography allows dangling bonds to be created and manipulated on Si(100) surfaces, both for use as a controlled quantum system, and as a step in the deterministic placement of dopants at the single-atom level. However, previous experiments and computations have shown conflicting results on the location of dangling bond energy levels, which can impact their utility as qubits. Here we use large-scale density functional theory and many-body perturbation theory (GW) calculations to show that in clean, H-passivated Si(100)-(2x1) surfaces a singly-occupied dangling bond does not give rise to an electronic state isolated from the valence bands. However, very thin (1-3 nm) samples terminated by a (100) surface should provide isolated singly-occupied and doubly-occupied dangling bond states. We also explore the effect of strain, and consider novel uses of boron dopants

  13. The role of radial nodes of atomic orbitals for chemical bonding and the periodic table.

    PubMed

    Kaupp, Martin

    2007-01-15

    The role of radial nodes, or of their absence, in valence orbitals for chemical bonding and periodic trends is discussed from a unified viewpoint. In particular, we emphasize the special role of the absence of a radial node whenever a shell with angular quantum number l is occupied for the first time (lack of "primogenic repulsion"), as with the 1s, 2p, 3d, and 4f shells. Although the consequences of the very compact 2p shell (e.g. good isovalent hybridization, multiple bonding, high electronegativity, lone-pair repulsion, octet rule) are relatively well known, it seems that some of the aspects of the very compact 3d shell in transition-metal chemistry are less well appreciated, e.g., the often weakened and stretched bonds at equilibrium structure, the frequently colored complexes, and the importance of nondynamical electron-correlation effects in bonding.

  14. Spontaneous volume magnetostriction and non-Stoner behavior of the valence band in pure hcp Gd

    NASA Astrophysics Data System (ADS)

    Khmelevskyi, S.; Turek, I.; Mohn, P.

    2004-10-01

    Employing the disordered local moment formalism in combination with first-principles band-structure calculations, we study the behavior of the valence band in pure hcp Gd upon disorder of the local 4f GD moments. We show that the large value of the spontaneous volume magnetostriction in Gd is entirely due to changes in the magnetic state of the valence band at Tc and can be calculated in good agreement with experiment. The local exchange splitting of the valence band persists above Tc , which is in strong disagreement with the conventional Stoner picture. The analysis of our results provides a theoretical background for the discussion of recent photoemission experiments.

  15. 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.

  16. Photoion mass spectroscopy and valence photoionization of hypoxanthine, xanthine and caffeine

    NASA Astrophysics Data System (ADS)

    Feyer, Vitaliy; Plekan, Oksana; Richter, Robert; Coreno, Marcello; Prince, Kevin C.

    2009-03-01

    Photoionization mass spectra of hypoxanthine, xanthine and caffeine were measured using the photoelectron-photoion coincidence technique and noble gas resonance radiation at energies from 8.4 to 21.2 eV for ionization. The fragmentation patterns for these compounds show that hydrogen cyanide is the main neutral loss species at higher photon energies, while photoionization below 16.67 eV led predominantly to the parent ion. The valence photoelectron spectra of this family of molecules were measured over an extended energy range, including the inner C, N and O 2s valence orbitals. The observed ion fragments were related to ionization of the valence orbitals.

  17. Complex materials for molecular spintronics applications: cobalt bis(dioxolene) valence tautomers, from molecules to polymers.

    PubMed

    Calzolari, Arrigo; Chen, Yifeng; Lewis, Geoffrey F; Dougherty, Daniel B; Shultz, David; Nardelli, Marco Buongiorno

    2012-11-01

    Using first principles calculations, we predict a complex multifunctional behavior in cobalt bis(dioxolene) valence tautomeric compounds. Molecular spin-state switching is shown to dramatically alter electronic properties and corresponding transport properties. This spin state dependence has been demonstrated for technologically relevant coordination polymers of valence tautomers as well as for novel conjugated polymers with valence tautomeric functionalization. As a result, these materials are proposed as promising candidates for spintronic devices that can couple magnetic bistability with novel electrical and spin conduction properties. Our findings pave the way to the fundamental understanding and future design of active multifunctional organic materials for spintronics applications.

  18. A single-source precursor approach to solution processed indium arsenide thin films† †Electronic supplementary information (ESI) available: Table listing selected bond lengths and angles for InAs precursor complex. Cross-sectional SEM of InAs thin film. XPS depth profile spectra of InAs thin film. Valence band XPS of InAs thin film and standard. CCDC 1477895. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6tc02293f Click here for additional data file. Click here for additional data file.

    PubMed Central

    Marchand, Peter; Sathasivam, Sanjayan; Williamson, Benjamin A. D.; Pugh, David; Bawaked, Salem M.; Basahel, Sulaiman N.; Obaid, Abdullah Y.; Scanlon, David O.; Parkin, Ivan P.

    2016-01-01

    This paper reports the synthesis of the novel single-source precursor, [{(MeInAstBu)3}2(Me2InAs(tBu)H)2] and the subsequent first report of aerosol-assisted chemical vapour deposition of InAs thin films. Owing to the use of the single-source precursor, highly crystalline and stoichiometric films were grown at a relatively low deposition temperature of 450 °C. Core level XPS depth profiling studies showed some partial oxidation of the film surface, however this was self-limiting and disappeared on etch profiles. Valence band XPS analysis matched well with the simulated density of state spectrum. Hall effect measurements performed on the films showed that the films were n-type with promising resistivity (3.6 × 10–3 Ω cm) and carrier mobility (410 cm2 V–1 s–1) values despite growth on amorphous glass substrates. PMID:27774150

  19. 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.

  20. Pancake π-π 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 π-π bonding found in phenalenyl (PLY, 1) radical π-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 π-π bonding upon intermolecular π-dimerization, in contrast to the 2e/half-sites single π-π bonding in the parent PLY π-dimers. The unusual double π-π bonding motif discovered in these PLY analogues may broaden the landscape of, and find new applications for, intermolecular covalent bonding interactions.

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

    SciTech Connect

    Shi Ling; Yang Ping; Huang Guang; Li Qian; Wang Ning; Wu Jianzhong; Yu Ying

    2011-07-15

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

  2. 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-1·cm-2.

  3. 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.

  4. Biomolecular halogen bonds.

    PubMed

    Ho, P Shing

    2015-01-01

    Halogens are atypical elements in biology, but are common as substituents in ligands, including thyroid hormones and inhibitors, which bind specifically to proteins and nucleic acids. The short-range, stabilizing interactions of halogens - now seen as relatively common in biology - conform generally to halogen bonds characterized in small molecule systems and as described by the σ-hole model. The unique properties of biomolecular halogen bonds (BXBs), particularly in their geometric and energetic relationship to classic hydrogen bonds, make them potentially powerful tools for inhibitor design and molecular engineering. This chapter reviews the current research on BXBs, focusing on experimental studies on their structure-energy relationships, how these studies inform the development of computational methods to model BXBs, and considers how BXBs can be applied to the rational design of more effective inhibitors against therapeutic targets and of new biological-based materials.

  5. 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.

  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.

  8. Dissociating motivational direction and affective valence: specific emotions alter central motor processes.

    PubMed

    Coombes, Stephen A; Cauraugh, James H; Janelle, Christopher M

    2007-11-01

    We aimed to clarify the relation between affective valence and motivational direction by specifying how central and peripheral components of extension movements are altered according to specific unpleasant affective states. As predicted, premotor reaction time was quicker for extension movements initiated during exposure to attack than for extension movements initiated during exposure to all other valence categories (mutilation, erotic couples, opposite-sex nudes, neutral humans, household objects, blank). Exposure to erotic couples and mutilations yielded greater peak force than exposure to images of attack, neutral humans, and household objects. Finally, motor reaction time and peak electromyographic amplitude were not altered by valence. These findings indicate that unpleasant states do not unilaterally prime withdrawal movements, and that the quick execution of extension movements during exposure to threatening images is due to rapid premotor, rather than motor, reaction time. Collectively, our findings support the call for dissociating motivational direction and affective valence. PMID:17958705

  9. 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

  10. 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...

  11. Cooperativity in beryllium bonds.

    PubMed

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

    2014-03-01

    A theoretical study of the beryllium bonded clusters of the (iminomethyl)beryllium hydride and (iminomethyl)beryllium fluoride [HC(BeX)=NH, X = H, F] molecules has been carried out at the B3LYP/6-311++G(3df,2p) level of theory. Linear and cyclic clusters have been characterized up to the decamer. The geometric, energetic, electronic and NMR properties of the clusters clearly indicate positive cooperativity. The evolution of the molecular properties, as the size of the cluster increases, is similar to those reported in polymers held together by hydrogen bonds.

  12. Adolescents' responses to the gender valence of cigarette advertising imagery: the role of affect and the self-concept.

    PubMed

    Shadel, William G; Niaura, Raymond; Abrams, David B

    2004-12-01

    The studies presented in this manuscript evaluated the role that affect and the self-concept play in adolescent never smokers' reactions to the gender valence of cigarette advertising imagery. Study 1 (n=29; 59% female) revealed that adolescent females have more positive affective reactions to female-valenced cigarette advertising imagery compared to male-valenced cigarette advertising imagery. Study 2 (n=101; 56% female) revealed that adolescent females viewed female-valenced cigarette advertising imagery as more relevant to their self-concepts compared to male-valenced cigarette advertising imagery. Across both studies, male adolescents did not respond differently as a function of the gender valence of cigarette advertising imagery. Thus, female-valenced cigarette advertising imagery may have specific effects on never smoking female adolescents by enhancing positive affect and suggesting that women who smoke hold the same characteristics as do the young women themselves.

  13. 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.

  14. Hadronic physics with domain-wall valence and improved staggered sea quarks

    SciTech Connect

    D. B. Renner; W. Schroers; R. Edwards; G. T. Fleming; Ph. Hagler; J. W. Negele; K. Orginos; A. V. Pochinski; D. Richards

    2004-06-01

    With the advent of chiral fermion formulations, the simulation of light valence quarks has finally become realistic for numerical simulations of lattice QCD. The simulation of light dynamical quarks, however, remains one of the major challenges and is still an obstacle to realistic simulations. We attempt to meet this challenge using a hybrid combination of Asqtad sea quarks and domain-wall valence quarks. Initial results for the proton form factor and the nucleon axial coupling are presented.

  15. Chiral perturbation theory for staggered sea quarks and Ginsparg-Wilson valence quarks

    SciTech Connect

    Baer, Oliver; Bernard, Claude; Rupak, Gautam; Shoresh, Noam

    2005-09-01

    We study lattice QCD with staggered sea and Ginsparg-Wilson valence quarks. The Symanzik effective action for this mixed lattice theory, including the lattice spacing contributions of O(a{sup 2}), is derived. Using this effective theory we construct the leading-order chiral Lagrangian. The masses and decay constants of pseudoscalars containing two Ginsparg-Wilson valence quarks are computed at one-loop order.

  16. Strangeness in the Nucleon or the quark model beyond the valence approximation

    SciTech Connect

    Nathan Isgur

    1999-01-01

    Simple arguments based on unitarity indicate that meson loops diagrams, induced by an underlying qq pair creation process, should badly disturb the phenomenologically successful spectroscopy and dynamics of the valence quark model, including such simple but mysterious regularities as the OZI rule. The author discusses some recent progress in adding pair creation to the valence quark model in a way which provides rationale for the quark model's success.

  17. Hydrogen bond and halogen bond inside the carbon nanotube

    NASA Astrophysics Data System (ADS)

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

    2011-02-01

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

  18. Valence, arousal, and cognitive control: a voluntary task-switching study.

    PubMed

    Demanet, Jelle; Liefooghe, Baptist; Verbruggen, Frederick

    2011-01-01

    The present study focused on the interplay between arousal, valence, and cognitive control. To this end, we investigated how arousal and valence associated with affective stimuli influenced cognitive flexibility when switching between tasks voluntarily. Three hypotheses were tested. First, a valence hypothesis that states that the positive valence of affective stimuli will facilitate both global and task-switching performance because of increased cognitive flexibility. Second, an arousal hypothesis that states that arousal, and not valence, will specifically impair task-switching performance by strengthening the previously executed task-set. Third, an attention hypothesis that states that both cognitive and emotional control ask for limited attentional resources, and predicts that arousal will impair both global and task-switching performance. The results showed that arousal affected task-switching but not global performance, possibly by phasic modulations of the noradrenergic system that reinforces the previously executed task. In addition, positive valence only affected global performance but not task-switching performance, possibly by phasic modulations of dopamine that stimulates the general ability to perform in a multitasking environment.

  19. Distracted by pleasure: Effects of positive versus negative valence on emotional capture under load.

    PubMed

    Gupta, Rashmi; Hur, Young-Jin; Lavie, Nilli

    2016-04-01

    We report 3 experiments examining the effects of positive versus negative valence and perceptual load in determining attention capture by irrelevant emotional distractors. Participants performed a letter search task searching for 1 of 2 target letters (X or N) in conditions of either low perceptual load (circular nontarget letters) or high perceptual load (angular nontarget letters that are similar to the target letters). On 25% of the trials an irrelevant emotional distractor was presented at the display center and participants were instructed to ignore it. The distractor stimulus was either positive or negative and was selected from 3 different classes: IAPS pictures of erotica or mutilated bodies (Experiment 1), happy or angry faces (Experiment 2), and faces associated with gain or loss in a prior value-learning phase involving a betting game (Experiment 3). The results showed a consistent pattern of interaction of load and valence across the 3 experiments. Irrelevant emotional distractors produced interference effects on search reaction time (RT) in conditions of low load, with no difference between negative and positive valence. High perceptual load, however, consistently reduced interference from the negative-valence distractors, but had no effect on the positive-valence distractors. As these results were consistently found across 3 different categories of emotional distractors, they suggest the general conclusion that attentional capture by irrelevant emotional distractors depends on both their valence and the level of perceptual load in the task and highlight the special status of distractors associated with pleasure. PMID:26479771

  20. Determining the Oxygen Fugacity of Lunar Pyroclastic Glasses Using Vanadium Valence - An Update

    NASA Technical Reports Server (NTRS)

    Karner, J. M.; Sutton, S. R.; Papike, J. J.; Shearer, C. K.; Jones, J. H.; Newville, M.

    2004-01-01

    We have been developing an oxygen barometer based on the valence state of V (V(2+), V(3+), V(4+), and V(5+)) in solar system basaltic glasses. The V valence is determined by synchrotron micro x-ray absorption near edge structure (XANES), which uses x-ray absorption associated with core-electronic transitions (absorption edges) to reveal a pre-edge peak whose intensity is directly proportional to the valence state of an element. XANES has advantages over other techniques that determine elemental valence because measurements can be made non-destructively in air and in situ on conventional thin sections at a micrometer spatial resolution with elemental sensitivities of approx. 100 ppm. Recent results show that fO2 values derived from the V valence technique are consistent with fO2 estimates determined by other techniques for materials that crystallized above the IW buffer. The fO2's determined by V valence (IW-3.8 to IW-2) for the lunar pyroclastic glasses, however, are on the order of 1 to 2.8 log units below previous estimates. Furthermore, the calculated fO2's decrease with increasing TiO2 contents from the A17 VLT to the A17 Orange glasses. In order to investigate these results further, we have synthesized lunar green and orange glasses and examined them by XANES.