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. 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

  3. Measurement of the low energy spectral contribution in coincidence with valence band (VB) energy levels of Ag(100) using VB-VB coincidence spectroscopy

    NASA Astrophysics Data System (ADS)

    Joglekar, P. V.; Gladen, R.; Lim, Z. H.; Shastry, K.; Hulbert, S. L.; Weiss, A. H.

    2015-03-01

    A set of coincidence measurements were obtained for the study and measurement of the electron contribution arising from the inter-valence band (VB) transitions along with the inelastically scattered VB electron contribution. These Auger-unrelated contributions arise in the Auger spectrum (Ag 4p NVV) obtained using Auger Photoelectron Coincidence Spectroscopy (APECS). The measured Auger-unrelated contribution can be eliminated from Auger spectrum to obtain the spectrum related to Auger. In our VB-VB coincidence measurement, a photon beam of energy 180eV was used to probe the Ag(100) sample. The coincidence spectrum was obtained using two Cylindrical Mirror Analyzers (CMA's). The scan CMA measured the low energy electron contribution in the energy range 0-70eV in coincidence with VB electrons measured by the fixed CMA. In this talk, we present the data obtained for VB-VB coincidence at the valence band energy of 171eV along with the coincidence measurements in the energy range of 4p core and valence band. NSF DMR 0907679, NSF Award Number: 1213727. Use of the National Synchrotron Light Source, Brookhaven National Laboratory, was supported by the U.S. DOE, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886.

  4. 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

  5. Semionic resonating valence bond states

    E-print Network

    Mohsin Iqbal; Didier Poilblanc; Norbert Schuch

    2014-08-06

    The nature of the kagome Heisenberg antiferromagnet (HAFM) is under ongoing debate. While recent evidence points towards a Z_2 topological spin liquid, the exact nature of the topological phase is still unclear. In this paper, we introduce semionic Resonating Valence Bond (RVB) states, this is, Resonating Valence Bond states which are in the Z_2 ordered double-semion phase, and study them using Projected Entangled Pair States (PEPS). We investigate their physics and study their suitability as an ansatz for the HAFM, as compared to a conventional RVB state which is in the Toric Code Z_2 topological phase. In particular, we find that a suitably optimized "semionic simplex RVB" outperforms the equally optimized conventional "simplex RVB" state, and that the entanglement spectrum (ES) of the semionic RVB behaves very differently from the ES of the conventional RVB, which suggests to use the ES to discriminate the two phases. Finally, we also discuss the possible relevance of space group symmetry breaking in valence bond wavefunctions with double-semion topological order.

  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. How valence bond theory can help you understand your (bio)chemical reaction.

    PubMed

    Shurki, Avital; Derat, Etienne; Barrozo, Alexandre; Kamerlin, Shina Caroline Lynn

    2015-03-01

    Almost a century has passed since valence bond (VB) theory was originally introduced to explain covalent bonding in the H2 molecule within a quantum mechanical framework. The past century has seen constant improvements in this theory, with no less than two distinct Nobel prizes based on work that is essentially developments in VB theory. Additionally, ongoing advances in both methodology and computational power have greatly expanded the scope of problems that VB theory can address. In this Tutorial Review, we aim to give the reader a solid understanding of the foundations of modern VB theory, using a didactic example of a model SN2 reaction to illustrate its immediate applications. This will be complemented by examples of challenging problems that at present can only be efficiently addressed by VB-based approaches. Finally, the ongoing importance of VB theory is demonstrated. It is concluded that VB will continue to be a major driving force for chemistry in the century to come. PMID:25352378

  8. Bond valence at mixed occupancy sites. I. Regular polyhedra.

    PubMed

    Bosi, Ferdinando

    2014-10-01

    Bond valence sum calculations at mixed occupancy sites show the occurrence of systematic errors leading to apparent violations of the Valence Sum Rule (bond valence theory) in regular and unstrained bonding environments. The systematic deviation of the bond valence from the expected value is observed in the long-range structure, and is discussed from geometric and algebraic viewpoints. In the valence-length diagram, such a deviation arises from discrepancies between the intersection points of the long-range bond valences and the theoretical bond valences with the valence-length curves of involved cations. Three factors cause systematic errors in the bond valences: difference in atomic valences, bond valence parameters Ri (the length of a bond of unit valence) and bond valence parameters bi (the bond softness) between the involved cations over the same crystallographic site. One important consequence strictly related to the systematic errors is that they lead to erroneous bond strain values for mixed occupancy sites indicating underbonding or overbonding that actually does not exist. PMID:25274520

  9. Valence bond solid states with symplectic symmetry

    NASA Astrophysics Data System (ADS)

    Schuricht, Dirk; Rachel, Stephan

    2008-07-01

    We introduce a one-dimensional valence bond solid (VBS) state with symplectic symmetry SP(n) and construct the corresponding parent Hamiltonian. We argue that there is a gap in the spectrum. We calculate exactly the static correlation functions, which fall off exponentially. Hence the model introduced here shares all properties of the Haldane scenario for integer-spin quantum antiferromagnets. We further show that the VBS state possesses string order and discuss its generalization to higher dimensions.

  10. Valence Bond Crystal on the Hyperkagome Antiferromagnet

    Microsoft Academic Search

    Emil Bergholtz; Andreas Lauchli; Roderich Moessner

    2011-01-01

    We describe our recent work that indicates that the ground state of the antiferromagnetic spin-1\\/2 Heisenberg model on the highly frustrated, three-dimensional, hyper-kagome lattice is a valence bond crystal (VBC). Performing a series expansion around an arbitrary dimer covering on the hyper-kagome we find that a ground state with a huge (72 site) unit cell is selected by the quantum

  11. The variational subspace valence bond method.

    PubMed

    Fletcher, Graham D

    2015-04-01

    The variational subspace valence bond (VSVB) method based on overlapping orbitals is introduced. VSVB provides variational support against collapse for the optimization of overlapping linear combinations of atomic orbitals (OLCAOs) using modified orbital expansions, without recourse to orthogonalization. OLCAO have the advantage of being naturally localized, chemically intuitive (to individually model bonds and lone pairs, for example), and transferrable between different molecular systems. Such features are exploited to avoid key computational bottlenecks. Since the OLCAO can be doubly occupied, VSVB can access very large problems, and calculations on systems with several hundred atoms are presented. PMID:25854233

  12. Stoichiometric Valence and Structural Valence--Two Different Sides of the Same Coin: "Bonding Power"

    E-print Network

    Wang, Xiqu

    concept is one of the cornerstones of chemistry. Valence,[1] that is, the bonding power of atoms,[2 that in subject indexes of most modern chemistry textbooks one finds terms such as "valence electrons", "valence and SbH3, one pnictide atom is equivalent to three hydrogen atoms and one mole of a pnic- tide

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

    NASA Astrophysics Data System (ADS)

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

    2012-07-01

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

  14. Valence Bond Crystal on the Hyperkagome Antiferromagnet

    NASA Astrophysics Data System (ADS)

    Bergholtz, Emil; Lauchli, Andreas; Moessner, Roderich

    2011-03-01

    We describe our recent work that indicates that the ground state of the antiferromagnetic spin-1/2 Heisenberg model on the highly frustrated, three-dimensional, hyper-kagome lattice is a valence bond crystal (VBC). Performing a series expansion around an arbitrary dimer covering on the hyper-kagome we find that a ground state with a huge (72 site) unit cell is selected by the quantum fluctuations. The regularity and favorable energetics of our series expansion establishes the VBC as a serious contender to the earlier spin liquid proposals. We find that the ground state supports many, very low lying, excitations in the singlet sector and that the low energy spinful excitations (spinons and triplons) are effectively confined to various emergent lower-dimensional structures. If applicable to the recently studied sodium iridate compound, Na 4 Ir 3 O8 , this scenario has interesting observable implications, such as spatially anisotropic neutron scattering spectra and possibly multiple finite temperature signatures in the magnetic specific heat due to a multi-step breaking of discrete symmetries. Most saliently, here---as for several proposed states for analogous kagome and pyrochlore magnets---one might expect a clearly resolved Ising transition at relatively high temperature. Ref: E.J. Bergholtz, A.M. Lauchli and R. Moessner, Phys. Rev. Lett., in press (2010) [arXiv:1010.1345

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

    PubMed

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

    2012-06-01

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

  16. 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…

  17. 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)

  18. Valence-bond theory of compounds of transition metals

    PubMed Central

    Pauling, Linus

    1975-01-01

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

  19. A Valence Bond Model for Aqueous Cu(II) and Zn(II) Ions in the AMOEBA Polarizable Force Field

    PubMed Central

    Xiang, Jin Yu; Ponder, Jay W.

    2013-01-01

    A general molecular mechanics (MM) model for treating aqueous Cu2+ and Zn2+ ions was developed based on valence bond (VB) theory and incorporated into the AMOEBA polarizable force field. Parameters were obtained by fitting molecular mechanics energies to that computed by ab initio methods for gas phase tetra- and hexa-aqua metal complexes. Molecular dynamics (MD) simulations using the proposed AMOEBA-VB model were performed for each transition metal ion in aqueous solution and solvent coordination was evaluated. Results show the AMOEBA-VB model generates the correct square-planar geometry for gas phase tetra-aqua Cu2+ complex and improves the accuracy of MM model energetics for a number of ligation geometries when compared to quantum mechanical (QM) computations. On the other hand, both AMOEBA and AMOEBA-VB generate results for Zn2+-water complexes in good agreement with QM calculations. Analyses of the MD trajectories revealed a 6-coordination first solvation shell for both Cu2+ and Zn2+ ions in aqueous solution, with ligation geometries falling in the range reported by previous studies. PMID:23212979

  20. Dzyloshinskii-Moriya interactions in valence bond systems II

    NASA Astrophysics Data System (ADS)

    Tovar, Mayra; Raman, Kumar; Shtengel, Kirill

    2009-03-01

    We investigate the effect of Dzyaloshinskii-Moriya interactions on the low temperature magnetic susceptibility for a system whose low energy physics is dominated by short-range valence bonds (singlets). Our general perturbative approach is applied to specific models expected to be in this class, including the Shastry-Sutherland model of the spin-dimer compound SrCu2(BO3)2 and the antiferromagnetic Heisenberg model of the recently discovered S=1/2 kagome compound ZnCu3(OH)6Cl2. The central result is that a short-ranged valence bond phase, when perturbed with Dzyaloshinskii-Moriya interactions, will remain time-reversal symmetric in the absence of a magnetic field but the susceptibility will be nonzero in the zero temperature limit. Applied to ZnCu3(OH)6Cl2, this model provides an avenue for reconciling experimental results, such as the lack of magnetic order and lack of any sign of a spin gap, with known theoretical facts about the kagome Heisenberg antiferromagnet.

  1. Dzyaloshinskii-Moriya interactions in valence bond systems I

    NASA Astrophysics Data System (ADS)

    Shtengel, Kirill; Raman, Kumar; Tovar, Mayra

    2009-03-01

    We investigate the effect of Dzyaloshinskii-Moriya interactions on the low temperature magnetic susceptibility for a system whose low energy physics is dominated by short-range valence bonds (singlets). Our general perturbative approach is applied to specific models expected to be in this class, including the Shastry-Sutherland model of the spin-dimer compound SrCu2(BO3)2 and the antiferromagnetic Heisenberg model of the recently discovered S=1/2 kagome compound ZnCu3(OH)6Cl2. The central result is that a short-ranged valence bond phase, when perturbed with Dzyaloshinskii-Moriya interactions, will remain time-reversal symmetric in the absence of a magnetic field but the susceptibility will be nonzero in the zero temperature limit. Applied to ZnCu3(OH)6Cl2, this model provides an avenue for reconciling experimental results, such as the lack of magnetic order and lack of any sign of a spin gap, with known theoretical facts about the kagome Heisenberg antiferromagnet.

  2. Dzyaloshinskii-Moriya interactions in valence-bond systems

    NASA Astrophysics Data System (ADS)

    Tovar, Mayra; Raman, Kumar S.; Shtengel, Kirill

    2009-01-01

    We investigate the effect of Dzyaloshinskii-Moriya interactions on the low-temperature magnetic susceptibility for a system whose low energy physics is dominated by short-range valence bonds (singlets). Our general perturbative approach is applied to specific models expected to be in this class, including the Shastry-Sutherland model of the spin-dimer compound SrCu2(BO3)2 and the antiferromagnetic Heisenberg model of the recently discovered S=1/2 kagomé compound ZnCu3(OH)6Cl2 . The central result is that a short-ranged valence-bond phase, when perturbed with Dzyaloshinskii-Moriya interactions, will remain time-reversal symmetric in the absence of a magnetic field but the susceptibility will be nonzero in the T?0 limit. Applied to ZnCu3(OH)6Cl2 , this model provides an avenue for reconciling experimental results, such as the lack of magnetic order and lack of any sign of a spin gap, with known theoretical facts about the kagomé Heisenberg antiferromagnet.

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

    NASA Astrophysics Data System (ADS)

    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.

  4. Competing valence bond crystals in the kagome quantum dimer model

    NASA Astrophysics Data System (ADS)

    Poilblanc, Didier; Misguich, Grégoire

    2011-12-01

    The singlet dynamics, which plays a major role in the physics of the spin-1/2 quantum Heisenberg antiferromagnet (QHAF) on the kagome lattice, can be approximately described by projecting onto the nearest-neighbor valence bond (NNVB) singlet subspace. We revisit here the effective quantum dimer model, which originates from the latter NNVB-projected Heisenberg model via a nonperturbative Rokhsar-Kivelson-like scheme. By using Lanczos exact diagonalization on a 108-site cluster supplemented by a careful symmetry analysis, it is shown that a previously found 36-site valence bond crystal (VBC) in fact competes with a new type of 12-site “resonating-columnar” VBC. Interestingly, these two VBCs “emerge” in different topological sectors. The exceptionally large degeneracy of the ground-state multiplets (144 on our 108-site cluster) and the proximity of a Z2 dimer liquid have implications for the interpretation of numerical results on the QHAF, which are outlined. The possibility of a chiral VBC (i.e., spontaneously breaking time-reversal symmetry) is also discussed.

  5. Hybrid valence-bond states for universal quantum computation

    NASA Astrophysics Data System (ADS)

    Wei, Tzu-Chieh; Haghnegahdar, Poya; Raussendorf, Robert

    2014-10-01

    The spin-3/2 Affleck-Kennedy-Lieb-Tasaki (AKLT) valence-bond state on a hexagonal lattice was shown to be a universal resource state for measurement-based quantum computation (MBQC). Can AKLT states of higher spin magnitude support universal MBQC? We demonstrate that several hybrid two-dimensional AKLT states involving a mixture of spin-2 and other lower-spin entities, such as spin-3/2 and spin-1, are also universal for MBQC. This significantly expands universal resource states in the AKLT family. Even though frustration may be a hindrance to quantum computational universality, lattices can be modified to yield AKLT states that are universal. The family of AKLT states thus provides a versatile playground for quantum computation.

  6. Hybrid valence-bond states for universal quantum computation

    E-print Network

    Tzu-Chieh Wei; Poya Haghnegahdar; Robert Raussendorf

    2015-01-29

    The spin-3/2 Affleck-Kennedy-Lieb-Tasaki (AKLT) valence-bond state on the hexagonal lattice was shown to be a universal resource state for measurement-based quantum computation (MBQC). Can AKLT states of higher spin magnitude support universal MBQC? We demonstrate that several hybrid 2D AKLT states involving mixture of spin-2 and other lower-spin entities, such as spin-3/2 and spin-1, are also universal for MBQC. This significantly expands universal resource states in the AKLT family. Even though frustration may be a hinderance to quantum computational universality, lattices can be modified to yield AKLT states that are universal. The family of AKLT states thus provides a versatile playground for quantum computation.

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

    E-print Network

    Hong-Hao Tu; Guang-Ming Zhang; Tao Xiang; Zheng-Xin Liu; Tai-Kai Ng

    2009-07-02

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

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

    PubMed

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

    2014-11-12

    The phase diagram of the Kane-Mele-Heisenberg model in a classical limit [47] contains disordered regions in the coupling space, as the result of competition between different terms in the Hamiltonian, leading to frustration in finding a unique ground state. In this work we explore the nature of these phases in the quantum limit, for a S = 1/2. Employing exact diagonalization in Sz and nearest neighbour valence bond bases, and bond and plaquette valence bond mean field theories, we show that the disordered regions are divided into ordered quantum states in the form of plaquette valence bond crystals and staggered dimerized phases. PMID:25336537

  9. Valence bond phases in S = 1/2 Kane–Mele–Heisenberg model

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

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

    SciTech Connect

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

    2009-03-15

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

  11. Ab initio valence-bond cluster model for ionic solids: Alkaline-earth oxides

    NASA Astrophysics Data System (ADS)

    Lorda, A.; Illas, F.; Rubio, J.; Torrance, J. B.

    1993-03-01

    A linear M-O-M (M=metal, O=oxygen) cluster embedded in a Madelung field, and also including the quantum effects of the neighboring ions, is used to represent the alkaline-earth oxides. For this model an ab initio wave function is constructed as a linear combination of Slater determinants written in an atomic orbital basis set, i.e., a valence-bond wave function. Each valence-bond determinant (or group of determinants) corresponds to a resonating valence-bond structure. We have obtained ab initio valence-bond cluster-model wave functions for the electronic ground state and the excited states involved in the optical-gap transitions. Numerical results are reasonably close to the experimental values. Moreover, the model contains the ionic model as a limiting case and can be readily extended and improved.

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

    PubMed Central

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

    2010-01-01

    A multistate density functional theory in the framework of the valence bond model is described. The method is based on a block-localized density functional theory (BLDFT) for the construction of valence-bond-like diabatic electronic states and is suitable for the study of electron transfer reactions and for the representation of reactive potential energy surfaces. The method is equivalent to a valence bond theory with the treatment of the localized configurations by using density functional theory (VBDFT). In VBDFT, the electron densities and energies of the valence bond states are determined by BLDFT. A functional estimate of the off-diagonal matrix elements of the VB Hamiltonian is proposed, making use of the overlap integral between Kohn–Sham determinants and the exchange-correlation functional for the ground state substituted with the transition (exchange) density. In addition, we describe an approximate approach, in which the off-diagonal matrix element is computed by wave function theory using block-localized Kohn–Sham orbitals. The key feature is that the electron density of the adiabatic ground state is not directly computed nor used to obtain the ground-state energy; the energy is determined by diagonalization of the multistate valence bond Hamiltonian. This represents a departure from the standard single-determinant Kohn–Sham density functional theory. The multistate VBDFT method is illustrated by the bond dissociation of H2+ and a set of three nucleophilic substitution reactions in the DBH24 database. In the dissociation of H2+, the VBDFT method yields the correct asymptotic behavior as the two protons stretch to infinity, whereas approximate functionals fail badly. For the SN2 nucleophilic substitution reactions, the hybrid functional B3LYP severely underestimates the barrier heights, while the approximate two-state VBDFT method overcomes the self-interaction error, and overestimates the barrier heights. Inclusion of the ionic state in a three-state model, VBDFT(3), significantly improves the computed barrier heights, which are found to be in accord with accurate results. The BLDFT method is a versatile theory that can be used to analyze conventional DFT results to gain insight into chemical bonding properties, and it is illustrated by examining the intricate energy contributions to the ion–dipole complex stabilization. PMID:20228960

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

    PubMed

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

    2009-10-13

    A multistate density functional theory in the framework of the valence bond model is described. The method is based on a block-localized density functional theory (BLDFT) for the construction of valence-bond-like diabatic electronic states and is suitable for the study of electron transfer reactions and for the representation of reactive potential energy surfaces. The method is equivalent to a valence bond theory with the treatment of the localized configurations by using density functional theory (VBDFT). In VBDFT, the electron densities and energies of the valence bond states are determined by BLDFT. A functional estimate of the off-diagonal matrix elements of the VB Hamiltonian is proposed, making use of the overlap integral between Kohn-Sham determinants and the exchange-correlation functional for the ground state substituted with the transition (exchange) density. In addition, we describe an approximate approach, in which the off-diagonal matrix element is computed by wave function theory using block-localized Kohn-Sham orbitals. The key feature is that the electron density of the adiabatic ground state is not directly computed nor used to obtain the ground-state energy; the energy is determined by diagonalization of the multistate valence bond Hamiltonian. This represents a departure from the standard single-determinant Kohn-Sham density functional theory. The multistate VBDFT method is illustrated by the bond dissociation of H2+ and a set of three nucleophilic substitution reactions in the DBH24 database. In the dissociation of H2+, the VBDFT method yields the correct asymptotic behavior as the two protons stretch to infinity, whereas approximate functionals fail badly. For the S(N)2 nucleophilic substitution reactions, the hybrid functional B3LYP severely underestimates the barrier heights, while the approximate two-state VBDFT method overcomes the self-interaction error, and overestimates the barrier heights. Inclusion of the ionic state in a three-state model, VBDFT(3), significantly improves the computed barrier heights, which are found to be in accord with accurate results. The BLDFT method is a versatile theory that can be used to analyze conventional DFT results to gain insight into chemical bonding properties, and it is illustrated by examining the intricate energy contributions to the ion-dipole complex stabilization. PMID:20228960

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

    PubMed

    Levi, Elena; Aurbach, Doron; Isnard, Olivier

    2013-10-01

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

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

    PubMed

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

    2015-05-28

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

  16. 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)

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

    PubMed

    Levi, Elena; Aurbach, Doron; Isnard, Olivier

    2013-10-01

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

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

    Microsoft Academic Search

    Arnaud Ralko; Fabien Trousselet; Didier Poilblanc

    2010-01-01

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

  19. Valence-Bond-Solid state entanglement in a 2-D Cayley tree

    E-print Network

    Heng Fan; Vladimir Korepin; Vwani Roychowdhury

    2005-11-17

    The Valence-Bond-Solid (VBS) states are in general ground states for certain gapped models. We consider the entanglement of VBS states on a two-dimensional Cayley tree. We show that the entropy of the reduced density operator does not depend on the whole size of the Cayley tree. We also show that asymptotically, the entropy is liearly proportional to the number of singlet states cut by the reduced density operator of the VBS state.

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

    SciTech Connect

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

    2011-07-15

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

  1. Exact results for SU(3) spin chains: Trimer states, valence bond solids, and their parent Hamiltonians

    NASA Astrophysics Data System (ADS)

    Greiter, Martin; Rachel, Stephan; Schuricht, Dirk

    2007-02-01

    We introduce several exact models for SU(3) spin chains: (1) a translationally invariant parent Hamiltonian involving four-site interactions for the trimer chain, with a threefold degenerate ground state. We provide numerical evidence that the elementary excitations of this model transform under representation 3¯ of SU(3) if the original spins of the model transform under representation 3. (2) a family of parent Hamiltonians for valence bond solids of SU(3) chains with spin representations 6, 10, and 8 on each lattice site. We argue that of these three models, only the latter two exhibit spinon confinement, and a Haldane gap in the excitation spectrum.

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

    PubMed

    Ralko, Arnaud; Trousselet, Fabien; Poilblanc, Didier

    2010-03-26

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

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

    NASA Astrophysics Data System (ADS)

    Ralko, Arnaud; Trousselet, Fabien; Poilblanc, Didier

    2010-03-01

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

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

    PubMed

    Bellucci, Michael A; Coker, David F

    2011-07-28

    We describe a new method for constructing empirical valence bond potential energy surfaces using a parallel multilevel genetic program (PMLGP). Genetic programs can be used to perform an efficient search through function space and parameter space to find the best functions and sets of parameters that fit energies obtained by ab initio electronic structure calculations. Building on the traditional genetic program approach, the PMLGP utilizes a hierarchy of genetic programming on two different levels. The lower level genetic programs are used to optimize coevolving populations in parallel while the higher level genetic program (HLGP) is used to optimize the genetic operator probabilities of the lower level genetic programs. The HLGP allows the algorithm to dynamically learn the mutation or combination of mutations that most effectively increase the fitness of the populations, causing a significant increase in the algorithm's accuracy and efficiency. The algorithm's accuracy and efficiency is tested against a standard parallel genetic program with a variety of one-dimensional test cases. Subsequently, the PMLGP is utilized to obtain an accurate empirical valence bond model for proton transfer in 3-hydroxy-gamma-pyrone in gas phase and protic solvent. PMID:21806098

  5. Implementation of umbrella integration within the framework of the empirical valence bond approach

    PubMed Central

    Chakravorty, Dhruva K.; Kumarasiri, Malika; Soudackov, Alexander V.; Hammes-Schiffer, Sharon

    2009-01-01

    The umbrella integration method for calculating the potential of mean force (PMF) for a chemical reaction is implemented within the empirical valence bond (EVB) framework. In this implementation, the PMF is generated along the energy gap reaction coordinate, and the biasing potential is the difference between the mapping potential, which is defined to be a linear combination of the valence bond state energies, and the EVB ground state energy. The umbrella integration method is based on the derivative of the PMF with respect to the reaction coordinate. An analytical expression for this derivative applicable to certain types of EVB potentials is presented. The advantages of the umbrella integration method are illustrated by the application of both umbrella integration and the weighted histogram analysis method to the hydride transfer reaction catalyzed by the enzyme dihydrofolate reductase. This application demonstrates that the umbrella integration method reduces the statistical errors, converges efficiently, and does not require significantly overlapping windows. A modified version of the weighted histogram analysis method that shares these advantages is also proposed and implemented. PMID:19319209

  6. Emergent Separation of Valence Bond Regimes in LiZn2Mo3O8

    NASA Astrophysics Data System (ADS)

    McQueen, Tyrel

    2015-03-01

    LiZn2Mo3O8 is a S = 1/2 triangular lattice antiferromagnet in which the basic magnetic building block is an Mo3O13 cluster rather than an individual ion. Rather than forming the 120° ordered magnetic state expected for a Heisenberg nearest neighbor triangular antiferromagnet, LiZn2Mo3O8 instead favors a complex valence bond order across different energy and lengthscales: approximately two thirds of the spins form singlets at T ~ 100 K, while the remainder form valence bonds at lower temperature, as indicated by inelastic neutron scattering. No static magnetic order is detected by uSR down to T = 0.05 K. What is the origin of this spontaneous separation into different regimes of magnetic fluctuations? Recent experimental data, including the impact of hole doping, will be compared to different theoretical models that have been proposed for this behavior, including an emergent honeycomb lattice by octahedral rotations and partial charge ordering driven by extra intracluster degrees of freedom. Supported by U.S. DoE Basic Energy Sciences, Materials Sciences & Engineering DE-FG02-08ER46544.

  7. Exact valence bond entanglement entropy and probability distribution in the XXX spin chain and the Potts model

    E-print Network

    Jesper Lykke Jacobsen; Hubert Saleur

    2007-11-21

    By relating the ground state of Temperley-Lieb hamiltonians to partition functions of 2D statistical mechanics systems on a half plane, and using a boundary Coulomb gas formalism, we obtain in closed form the valence bond entanglement entropy as well as the valence bond probability distribution in these ground states. We find in particular that for the XXX spin chain, the number N_c of valence bonds connecting a subsystem of size L to the outside goes, in the thermodynamic limit, as = (4/pi^2) ln L, disproving a recent conjecture that this should be related with the von Neumann entropy, and thus equal to 1/(3 ln 2) ln L. Our results generalize to the Q-state Potts model.

  8. Exact valence bond entanglement entropy and probability distribution in the XXX spin chain and the Potts model

    E-print Network

    Jacobsen, Jesper Lykke

    2011-01-01

    By relating the ground state of Temperley-Lieb hamiltonians to partition functions of 2D statistical mechanics systems on a half plane, and using a boundary Coulomb gas formalism, we obtain in closed form the valence bond entanglement entropy as well as the valence bond probability distribution in these ground states. We find in particular that for the XXX spin chain, the number N_c of valence bonds connecting a subsystem of size L to the outside goes, in the thermodynamic limit, as = (4/pi^2) ln L, disproving a recent conjecture that this should be related with the von Neumann entropy, and thus equal to 1/(3 ln 2) ln L. Our results generalize to the Q-state Potts model.

  9. 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

  10. X-ray powder diffraction studies and bond-valence analysis of Hg 2Sb 2O 7

    Microsoft Academic Search

    V. I. Sidey; P. M. Milyan; O. O. Semrad; A. M. Solomon

    2008-01-01

    The crystal structure of Hg2Sb2O7 has been refined using X-ray powder diffraction technique. Hg2Sb2O7 crystallizes in the cubic pyrochlore structure type, space group Fd3¯m, with the lattice parameter a=10.3525(5)Å, Z=8, Dc=9.060(1)g\\/cm3. The Rietveld refinement procedure was stopped when the intensity residual RB=3.25% had been reached.In the bond-valence analysis of the crystal structure of Hg2Sb2O7, the values of the bond-valence parameters

  11. Valence-bond non-equilibrium solvation model for a twisting monomethine cyanine

    NASA Astrophysics Data System (ADS)

    McConnell, Sean; McKenzie, Ross H.; Olsen, Seth

    2015-02-01

    We propose and analyze a two-state valence-bond model of non-equilibrium solvation effects on the excited-state twisting reaction of monomethine cyanines. Suppression of this reaction is thought responsible for environment-dependent fluorescence yield enhancement in these dyes. Fluorescence is quenched because twisting is accompanied via the formation of dark twisted intramolecular charge-transfer (TICT) states. For monomethine cyanines, where the ground state is a superposition of structures with different bond and charge localizations, there are two possible twisting pathways with different charge localizations in the excited state. For parameters corresponding to symmetric monomethines, the model predicts two low-energy twisting channels on the excited-state surface, which leads to a manifold of TICT states. For typical monomethines, twisting on the excited state surface will occur with a small barrier or no barrier. Changes in the solvation configuration can differentially stabilize TICT states in channels corresponding to different bonds, and that the position of a conical intersection between adiabatic states moves in response to solvation to stabilize either one channel or the other. There is a conical intersection seam that grows along the bottom of the excited-state potential with increasing solvent polarity. For monomethine cyanines with modest-sized terminal groups in moderately polar solution, the bottom of the excited-state potential surface is completely spanned by a conical intersection seam.

  12. Valence bond structures for the D2h isomer of N2O4 and some isomers of S3O2 and S3O.

    PubMed

    Harcourt, Richard D

    2007-07-01

    The construction of valence bond structures of the increased-valence type is re-described for the D2h isomer of N2O4 and applied to obtain the corresponding valence bond structures for isomers of S3O2 and S3O, each of which has at least one six-electron four-center bonding unit. It is discussed how the S-O and S-S bond properties that are associated with the S3O2 and S3O increased-valence structures are in qualitative accord with the calculated bond lengths. The qualitative six-electron four-center molecular orbital theory for the symmetrical O-S-S-O component of each S3O2 isomer is related to the increased-valence structure for the six electrons. An increased-valence structure for the lowest-energy S3O2 isomer is equivalent to a restricted form of resonance between 16 Lewis-type valence bond structures. The two types of S-S bond length are used to provide empirical estimates of the weights for these Lewis structures and are compared with those obtained from the results of STO-6G valence bond calculations for the 3Sigma- ground state of SO. PMID:17569526

  13. Two crucial experimental tests of the resonating valence bond--Luttinger liquid interlayer tunneling theory of high- Tc superconductivity

    SciTech Connect

    Anderson, P.W. (Joseph Henry Laboratories of Physics, Jadwin Hall, Princeton University, Princeton, NJ (USA))

    1990-08-01

    The resonating valence bond--Luttinger liquid theory for the high-{Tc} normal state permits some predictions about the effect of superconductivity on two measures of the one-particle Green's function: angle-resolved photoemission and tunneling for a high-{Tc}--insulator--high-{Tc} junction. These are compared to preliminary experimental data.

  14. Ab initio molecular dynamics with correlated molecular wave functions: Generalized valence bond molecular dynamics and simulated annealing

    Microsoft Academic Search

    Bernd Hartke; Emily A. Carter

    1992-01-01

    We present an abinitio molecular dynamics algorithm at the generalized valence bond level. It does not need a precalculated potential energy surface or model Hamiltonian; instead the nuclei move according to first principles forces derived from the electronic wave function which in turn follows the movement of the nuclei. This technique includes the dominant static electron correlations, it can treat

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

    SciTech Connect

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

    2013-11-07

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

  16. Resonating valence bonds and mean-field d -wave superconductivity in graphite

    NASA Astrophysics Data System (ADS)

    Black-Schaffer, Annica M.; Doniach, Sebastian

    2007-04-01

    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 Tc 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.

  17. Simulating a two-dimensional frustrated spin system with fermionic resonating-valence-bond states

    NASA Astrophysics Data System (ADS)

    Chou, Chung-Pin; Chen, Hong-Yi

    2014-07-01

    The frustrated Heisenberg J1-J2 model on a square lattice is numerically investigated by variational Monte Carlo simulations. We propose an antiferromagnetic fermion resonating-valence-bond (AF-fRVB) state that has the ability to examine the entire phase diagram in the J1-J2 model. Two phase transition points, the second order around J2/J1=0.45 and the first order around J2/J1=0.6, can be extracted more clearly than the conventional bosonic RVB state. At the maximally frustrated point (J2/J1=0.5), the AF-fRVB state shows the variational ground-state energy in the thermodynamic limit very close to the one estimated by the projected entangled pair state at the largest bond dimension available. On the other hand, in the frustrated regime 0.4?J2/J1?0.5, AF-fRVB states with exts2 (using the terminology in the field of iron-based superconductors) and dxy pairing symmetries are degenerate in the thermodynamic limit, implying the existence of gapless Dirac excitations in the spinon spectrum.

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

    SciTech Connect

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

    2000-05-01

    The distribution of bond lengths in (V{sup 3+}O{sub 6}) polyhedra shows a maximum between 1.98 and 2.04 {angstrom}, and limits of 1.88 and 2.16 {angstrom}, respectively. The bond lengths in (V{sup 4+}O{sub n}) and (V{sup 5+}O{sub n}) (n = 5,6) polyhedra show distinct populations which allow us to define the following types of bonds: (1a) vanadyl bonds in (V{sup 4+}O{sub n}) polyhedra, shorter than 1.74 {angstrom}; (1b) vanadyl bonds in (V{sup 5+}O{sub 5}) polyhedra, shorter than 1.76 {angstrom}; (1c) vanadyl bonds in (V{sup 5+}O{sub 6}) polyhedra, shorter than 1.74 {angstrom}; (2a) equatorial bonds in (V{sup 4+}O{sub n}) polyhedra, in the range 1.90 to 2.12 {angstrom}; (2b) equatorial bonds in (V{sup 5+}O{sub 5}) polyhedra, longer than 1.76 {angstrom}; (2c) equatorial bonds in (V{sup 5+}O{sub 6}) polyhedra with one vanadyl bond, in the range 1.74 to 2.10 {angstrom}; (2d) equatorial bonds in (V{sup 5+}O{sub 6}) polyhedra with two vanadyl bonds, in the range 1.80 to 2.00 {angstrom}; (3a) trans bonds in (V{sup 4+}O{sub 6}) polyhedra, longer than 2.10 {angstrom}; (3b) trans bonds in (V{sup 5+}O{sub 6}) polyhedra with two vanadyl bonds, longer than 2.025 {angstrom}. The average equatorial bond length in (V{sup 4+}O{sub n}) and (V{sup 5+}O{sub n}) polyhedra can be used to calculate the mean valence state of V in mixed-valent structures. The authors define characteristic bond valences for vanadyl, equatorial, and trans bonds in different coordinations and examine which binary linkages are possible and which linkages occur in minerals and synthetic compounds. Here, V{sup 5+}-O-V{sup 5+}, V{sup 5+}-O-V{sup 4+}, and V{sup 4+}-O-V{sup 4+} linkages between vanadyl-trans and equatorial-equatorial bonds occur often in synthetic compounds, whereas the corresponding V{sup 4+}-O-V{sup 4+} linkages are rare in minerals.

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

    NASA Astrophysics Data System (ADS)

    Adams, S.

    2006-06-01

    Starting from the simple bond valence (BV) concept commonly used to judge the plausibility of atomic positions in inorganic crystal structures, a method to analyze energy landscapes and to identify transport pathways for mobile ions in solid electrolytes has been developed. The approach is particularly valuable for analysing transport mechanisms and structure conductivity relationships in disordered solids, where the averaged information directly available from crystallographic methods cannot provide a sufficiently detailed picture. For systems where ion transport occurs in a nearly rigid matrix, e.g. ion conducting glasses, the BV analysis may be based on static structure models from reverse Monte Carlo fits to experimental diffraction data. The assumption that conduction pathways correspond to structure regions where the BV mismatch for the mobile ion remains below a threshold value then enables us to predict activation energy and ionic conductivity of ion conducting glasses from the relative volume of the percolating pathways in the structure model. Moreover BV mismatch landscapes provide further insight into transport mechanisms as they allow enumerating the number of accessible sites for mobile ions (irrespective of their occupancy), as well as quantifying the reduced local dimensionality or the medium-range ordering of transport pathways. The BV analysis of molecular dynamics simulation trajectories extends the application range to systems involving complex reorientation processes (provided that suitable empirical force-fields are available for a system) and permits to extract information on time and temperature dependencies.

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

    PubMed

    Mabuchi, Takuya; Fukushima, Akinori; Tokumasu, Takashi

    2015-07-01

    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. PMID:26156482

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

    NASA Astrophysics Data System (ADS)

    Sandvik, Anders; Beach, Kevin

    2007-03-01

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

  2. 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

  3. A perturbative approach to the valence charge density in tetrahedrally bonded semiconductors

    Microsoft Academic Search

    C. M. Bertoni; V. Bortolani; C. Calandra; F. Nizzoli

    1973-01-01

    An equation for the charge density in terms of the dielectric matrix of the crystal is used to study the valence electron distribution in covalent and partially ionic semiconductors. Through a perturbation expansion of the dielectric matrix in terms of the ion pseudopotential, the authors write the valence charge density as a series of powers of the pseudopotential. The calculated

  4. arXiv:0710.0626v2[cond-mat.str-el]7Jan2008 Valence bond solid order near impurities in two-dimensional

    E-print Network

    arXiv:0710.0626v2[cond-mat.str-el]7Jan2008 Valence bond solid order near impurities in two perturbation is represented by an uncompensated Berry phase. The "boundary" critical theory for these classes

  5. Transitions to valence-bond solid order in a honeycomb lattice antiferromagnet

    NASA Astrophysics Data System (ADS)

    Pujari, Sumiran; Alet, Fabien; Damle, Kedar

    2015-03-01

    We use quantum Monte Carlo methods to study the ground-state phase diagram of a S =1 /2 honeycomb lattice magnet in which a nearest-neighbor antiferromagnetic exchange J (favoring Néel order) competes with two different multispin interaction terms: a six-spin interaction Q3 that favors columnar valence-bond solid (VBS) order, and a four-spin interaction Q2 that favors staggered VBS order. For Q3˜Q2?J , we establish that the competition between the two different VBS orders stabilizes Néel order in a large swath of the phase diagram even when J is the smallest energy scale in the Hamiltonian. When Q3?(Q2,J ) [ Q2?(Q3,J ) ], this model exhibits at zero temperature phase transition from the Néel state to a columnar (staggered) VBS state. We establish that the Néel-columnar VBS transition is continuous for all values of Q2, and that critical properties along the entire phase boundary are well characterized by critical exponents and amplitudes of the noncompact CP1 (NCCP1) theory of deconfined criticality, similar to what is observed on a square lattice. However, a surprising threefold anisotropy of the phase of the VBS order parameter at criticality, whose presence was recently noted at the Q2=0 deconfined critical point, is seen to persist all along this phase boundary. We use a classical analogy to explore this by studying the critical point of a three-dimensional X Y model with a fourfold anisotropy field which is known to be weakly irrelevant at the three-dimensional X Y critical point. In this case, we again find that the critical anisotropy appears to saturate to a nonzero value over the range of sizes accessible to our simulations.

  6. Generalized valence bond description of chalcogen-nitrogen compounds. I. NS, F(NS), and H(NS).

    PubMed

    Takeshita, Tyler Y; Dunning, Thom H

    2015-03-01

    The electronic structures of the ground states (X(2)?) of NS and those (X(1)A') of F(NS) and H(NS), where X(NS) collectively refers to the XNS and NSX isomers, were analyzed within the framework of generalized valence bond theory. The ground state of NS has a recoupled pair ? bond, which has a profound effect on its reactivity. For example, the lowest-energy isomer of F(NS) is NSF, which has a recoupled pair bond dyad with N-SF and NS-F bonds lengths and strengths similar to their covalent counterparts in NS and SF. The ground state of NSH, on the other hand, is only weakly bound with a NS-H bond energy 40.20 kcal/mol smaller than that in SH and a N-SH bond energy 40.20 kcal/mol less than that in NS. At its equilibrium geometry, the NSH molecule is best viewed as derived from the N((2)D) + SH(X(2)?) separated fragments, with the weak NS-H bond resulting from unfavorable interactions between the SH bond pair and the nitrogen lone pair. Addition of F/H atoms to the nitrogen atom in NS disrupts the NS recoupled pair bond, which weakens both the FN-S/HN-S and F-NS/H-NS bonds. In contrast to the formation of recoupled pair ? bonds, formation of the recoupled pair ? bond in NS is expressed as a change in the spin-coupling coefficients, rather than an interchange of the orbitals. PMID:25628034

  7. 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?(?) system, resulting in SO double bonds. The ? 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 ? interaction. PMID:26068052

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

    SciTech Connect

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

    2006-07-16

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

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

    SciTech Connect

    Tanimura, K.; Inami, E.; Kanasaki, J. [Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); Hess, Wayne P. [Pacific Northwest National Laboratory, Richland, Washington 99352 (United States)

    2006-07-15

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

  10. The cations [ICNI] + and [H 3N?NH 3] 2+—natural bond orbital analysis and some valence bond considerations

    Microsoft Academic Search

    Richard D. Harcourt; Thomas M. Klapötke; Peter S. White

    1998-01-01

    The structure and bonding of the linear (Cxv) [ICNI]+ cation are compared and contrasted with the situation found for the also linear [HCNH]+ cation. The linearity of [ICNI]+, its unusually short N-1 and C-1 bonds, and relatively long C?N bond, are ascribed to delocalizations of the iodine px and py electrons into the unfilled antibonding ??, (C?N) and ??y(C?N) MOs.

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

    NASA Astrophysics Data System (ADS)

    Greiter, Martin; Rachel, Stephan

    2007-05-01

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

  12. 13498 J. Phys. Chem. 1994,98, 13498-13505 Rule-Based Trial Wave Functions for Generalized Valence Bond Theory

    E-print Network

    Goddard III, William A.

    13498 J. Phys. Chem. 1994,98, 13498-13505 Rule-Based Trial Wave Functions for Generalized Valence Bond Theory Jean-MarcLanglois,?Terumasa Yamasaki,' Richard P. Muller? and William A. Goddard 111; In Final Form: October 4, 1994@ We present a general method suitable for automatic generation of trial wave

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

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

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

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

    SciTech Connect

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

    2010-08-26

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

  15. The graphite core valence valence Auger spectrum

    NASA Astrophysics Data System (ADS)

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

    2002-04-01

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

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

    NASA Astrophysics Data System (ADS)

    Zhang, Long; Mei, Jia-Wei

    2015-03-01

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

  17. Finding transition structures in extended systems: A strategy based on a combined quantum mechanics-empirical valence bond approach

    NASA Astrophysics Data System (ADS)

    Sierka, Marek; Sauer, Joachim

    2000-04-01

    A method for efficient localization and description of stationary points on the potential energy surface of extended systems is presented. It is based on Warshel's empirical valence bond approach, for which we propose a modification, and combines the potential function description of the total system with a quantum mechanical description of the reaction site (QM-Pot). We describe the implementation of the method in the QMPOT program, which is basically an optimizer for minima and saddle points and has interfaces to existing quantum mechanical (e.g., TURBOMOLE, GAUSSIAN94) and interatomic potential function codes (e.g., GULP, DISCOVER). The power of the method is demonstrated for proton transfer reactions in zeolite catalysts, which may have as many as 289 atoms in the unit cell. As a test case the zeolite chabazite is considered in this study. Its limited unit cell size (37 atoms) makes comparison with the full periodic ab initio limit possible. The inclusion of long-range effects due to the periodic crystal structure by the QM-Pot method proves crucial in obtaining reliable results. The combined quantum mechanics-interatomic potential function calculations yield reaction barriers within 6 kJ/mol and reaction energies within 3.5 kJ/mol of the periodic ab initio limit. The zero-point vibrational energy corrected reaction barriers are between 58 and 97 kJ/mol for the six different proton jump paths. These are density functional results employing the B3LYP functional.

  18. JOURNAL DE PHYSIQUE Colloque C4, supplment au n" 4, Tome 40, avril 1979, page C4-228 BOA valence bonding with f-character in highly coordinated actinides

    E-print Network

    Paris-Sud XI, Université de

    JOURNAL DE PHYSIQUE Colloque C4, supplément au n" 4, Tome 40, avril 1979, page C4-228 BOA valence Orbital Approximation (BOA) valence bonding hybridized orbitals are characte- rized by two lobes of high and the CrUS3 structures, respectively [3, 4]. The BOA method involves using the Cf and Gf orbitals

  19. 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)).

  20. An Effective Hamiltonian Molecular Orbital-Valence Bond (MOVB) Approach for Chemical Reactions Applied to the Nucleophilic Substitution Reaction of Hydrosulfide Ion and Chloromethane

    PubMed Central

    Song, Lingchun; Mo, Yirong; Gao, Jiali

    2009-01-01

    An effective Hamiltonian mixed molecular orbital and valence bond (EH-MOVB) method is described to obtain an accurate potential energy surface for chemical reactions. Building upon previous results on the construction of diabatic and adiabatic potential surfaces using ab initio MOVB theory, we introduce a diabatic-coupling scaling factor to uniformly scale the ab initio off-diagonal matrix element H12 such that the computed energy of reaction from the EH-MOVB method is in agreement with the target value. The scaling factor is very close to unity, resulting in minimal alteration of the potential energy surface of the original MOVB model. Furthermore, the relative energy between the reactant and product diabatic states in the EH-MOVB method can be improved to match the experimental energy of reaction. A key ingredient in the EH-MOVB theory is that the off-diagonal matrix elements are functions of all degrees of freedom of the system and the overlap matrix is explicitly evaluated. The EH-MOVB method has been applied to the nucleophilic substitution reaction between hydrosulfide and chloromethane to illustrate the methodology and the results were matched to reproduce the results from ab initio valence bond self-consistent valence bond (VBSCF) calculations. The diabatic coupling (the off-diagonal matrix element in the generalized secular equation) has small variations along the minimum energy reaction path in the EH-MOVB model, whereas it shows a maximum value at the transition state and has nearly zero values in the regions of the ion-dipole complexes from VBSCF calculations. The difference in the diabatic coupling stabilization is attributed to the large overlap integral in the computationally efficient MOVB method. PMID:20047006

  1. Many-Body Spin Berry Phases Emerging from the ?-Flux State: Competition between Antiferromagnetism and the Valence-Bond-Solid State

    NASA Astrophysics Data System (ADS)

    Tanaka, Akihiro; Hu, Xiao

    2005-07-01

    We uncover new topology-related features of the ?-flux saddle-point solution of the D=2+1 Heisenberg antiferromagnet. We note that symmetries of the spinons sustain a built-in competition between antiferromagnetic (AFM) and valence-bond-solid (VBS) orders, the two tendencies central to recent developments on quantum criticality. An effective theory containing an analogue of the Wess-Zumino-Witten term is derived, which generates quantum phases related to AFM monopoles with VBS cores, and reproduces Haldane’s hedgehog Berry phases. The theory readily generalizes to ?-flux states for all D.

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

    SciTech Connect

    Matar, Samir F., E-mail: matar@icmcb-bordeaux.cnrs.fr [CNRS, Universite de Bordeaux, ICMCB, 87 Avenue du Docteur Albert Schweitzer, 33600 Pessac (France); Poettgen, Rainer, E-mail: pottgen@uni-muenster.de [Institut fuer Anorganische Universitaet Muenster, Corrensstrasse 30, D-48149 Muenster (Germany); Chevalier, Bernard, E-mail: chevalie@icmcb-bordeaux.cnrs.fr [CNRS, Universite de Bordeaux, ICMCB, 87 Avenue du Docteur Albert Schweitzer, 33600 Pessac (France)

    2012-02-15

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

  3. Charge distribution in arylhydrazine-centered mixed valence compounds with smaller bridges (five to nine bonds between closest nitrogens).

    PubMed

    Nelsen, Stephen F; Schultz, Kevin P

    2009-05-01

    Charge distribution in six aromatic-bridged, aryldialkylhydrazine-centered mixed valence radical cations is discussed through consideration of their optical spectra. The compounds considered have two 2-phenyl-2,3-diazabicyclo-[2.2.2]octane-3-yl (HyPh) charge-bearing units linked by a 1,4-phenylene bridge and its p-methoxyphenyl (HyAn) analogue, as well as the (HyPh)(2)-substituted 1,4-naphthalene, 2,6-naphthalene, 9,10-anthracene, and 4,4'-biphenyl compounds in methylene chloride and acetonitrile. Consideration of band shape and position leads us to assign the 1,4-phenylene- and 2,6-naphthalene-bridged compounds as charge-delocalized (class III) in both solvents, but the 1,4-naphthalene-bridged one lies closer to the borderline, and appears to be charge-localized (class II) in acetonitrile. The 4,4'-biphenyl-bridged compound is clearly class II in acetonitrile, and possibly also in methylene chloride. The lowest energy absorption band for the 9,10-anthracene-bridged compound is assigned as a bridge-to-HyPh band, and its charge distribution is not clear. Problems with the often-used relationship that the electronic coupling is half the transition energy for the lowest energy band of class III mixed valence compounds are discussed, as is interpretation of the vertical reorganization energy near the class II, class III borderline. PMID:19354243

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

    NASA Astrophysics Data System (ADS)

    Sumner, Isaiah; Iyengar, Srinivasan S.

    2008-08-01

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

  5. Unified studies of chemical bonding structures and resonant scattering in light neutron-excess systems, 10,12Be

    NASA Astrophysics Data System (ADS)

    Ito, Makoto; Ikeda, Kiyomi

    2014-09-01

    The generalized two-center cluster model (GTCM), which can treat covalent, ionic and atomic configurations in general systems with two inert cores plus valence nucleons, is formulated in the basis of the microscopic cluster model. In this model, the covalent configurations constructed by the molecular orbital (MO) method and the atomic (or ionic) configuration obtained by the valence bonding (VB) method can be handled in a consistent manner. The GTCM is applied to the light neutron-rich system 10,12Be = ? + ? + Xn (X = 2, 4). The continuous and smooth changes of the neutron orbits from the covalent MO states to the ionic VB states are clearly observed in the adiabatic energy surfaces (AESs), which are the energy curves obtained with a variation of the ?-? distance. The energy levels obtained from the AESs nicely reproduce the recent observations over a wide energy region. The individual spectra are characterized in terms of chemical-bonding-like structures, such as the covalent MO or ionic VB structures, according to analysis of their intrinsic wave functions. From the analysis of AESs, the formation of the mysterious 0_2+ states in 10,12Be, which have anomalously small excitation energies in comparison to a naive shell-model prediction, is investigated. A large enhancement in a monopole transition from a ground MO state to an ionic ? + 6,8He VB state is found, which seems to be consistent with a recent observation. In the unbound region, the structure problem, which handles the total system of ? + ? + Xn (X = 2, 4) as a bound or quasi-bound state, and the reaction problem, induced by the collision of an asymptotic VB state of ? + 6,8He, are combined by the GTCM. The properties of unbound resonant states are discussed in close connection to the reaction mechanism, and some enhancement factors originating from the properties of the intrinsic states are predicted in the reaction observables.

  6. Mechanoenzymatic Characterization of Human Myosin Vb

    Microsoft Academic Search

    Shinya Watanabe; Katsuhide Mabuchi; Reiko Ikebe; Mitsuo Ikebe

    2006-01-01

    There are three isoforms of class V myosin in mammals. While myosin Va has been studied well, little is known about the function of other myosin V isoforms (Vb and Vc) at a molecular level. Here we report the mechanoenzymatic function of human myosin Vb (HuM5B) for the first time. Electron microscopic observation showed that HuM5B has a double-headed structure

  7. 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(?1,1-N3)2] (1), trans-[Co3L2(H2O)2(N3)2(?1,1-N3)2]·(H2O)2 (2) and [Co3L(R)2(N3)3(?1,3-N3)] (3) have been synthesized by reacting a di-Schiff base ligand (H2L) or its reduced form [H2LR] (where H2L= N,N'-bis(salicylidene)-1,3-propanediamine and H2LR= N,N'-bis(2-hydroxybenzyl)-1,3-propanediamine) with cobalt perchlorate hexahydrate and sodium azide. All three products have been characterized by IR, UV-Vis and EPR spectroscopies, ESI-MS, elemental, powder and single crystal X-ray diffraction analyses. Complex 2 is an angular trinuclear species in which two terminal octahedral Co(III)N2O4 centers coordinate to the central octahedral cobalt(II) ion through ?2-phenoxido oxygen and ?1,1-azido nitrogen atoms along with two mutually cis-oxygen atoms of methanol molecules. On the other hand, in linear trinuclear complex , in addition to the ?2-phenoxido and ?1,1-azido bridges with terminal octahedral Co(III) centres, the central Co(II) is bonded with two mutually trans-oxygen atoms of water molecules. Thus the cis-trans configuration of the central Co(II) is solvent dependent. In complex 3, the two terminal octahedral Co(III)N2O4 centers coordinate to the central penta-coordinated Co(II) ion through double phenoxido bridges along with the nitrogen atom of a terminal azido ligand. In addition, the two terminal Co(III) are connected through a ?1,3-azido bridge that participates in pnicogen bonding interactions (intermolecular N-N interaction) as an acceptor. Both the cis and trans isomeric forms of 1 and 2 have been optimized using density functional theory (DFT) calculations and it is found that the cis configuration is energetically more favorable than the trans one. However, the trans configuration of 2 is stabilized by the hydrogen bonding network involving a water dimer. The pnicogen bonding interactions have been demonstrated using MEP surfaces and CSD search which support the counter intuitive electron acceptor ability of the ?1,3-azido ligand. Complexes 1-3 exhibit catecholase-like activities in the aerial oxidation of 3,5-di-tert-butylcatechol to the corresponding o-quinone. Kinetic data analyses of this oxidation reaction in acetonitrile reveal that the catecholase-like activity follows the order: 1 (kcat = 142 h(-1)) > 3 (kcat = 99 h(-1)) > 2 (kcat = 85 h(-1)). Mechanistic investigations of the catalytic behaviors by X-band EPR spectroscopy and estimation of hydrogen peroxide formation indicate that the oxidation reaction proceeds through the reduction of Co(III) to Co(II). PMID:25611163

  8. Bonding

    MedlinePLUS

    ... is a procedure that uses a tooth-colored composite resin (plastic) to repair a tooth. Bonding can ... cleaned regularly by a dental hygienist. Risks The composite resin used in bonding isn't nearly as ...

  9. Baseplate Testing V.B. Graves

    E-print Network

    McDonald, Kirk

    Baseplate Testing V.B. Graves P.T. Spampinato MERIT VRVS Meeting Oct 4, 2006 #12;2VRVS Meeting 4 Sept 2006 OAK RIDGE NATIONAL LABORATORY U. S. DEPARTMENT OF ENERGY Load Testing of Common Baseplate design · Load test performed on structures to verify strength and test adjusting mechanisms · Estimated

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

    SciTech Connect

    Yang, Anli [Synchrotron X-ray Station at SPring-8, National Institute for Materials Science (NIMS), 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148 (Japan); Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), 7 Goban-cho, Chiyoda-ku, Tokyo 102-0076 (Japan); Sakata, Osami, E-mail: SAKATA.Osami@nims.go.jp [Synchrotron X-ray Station at SPring-8, National Institute for Materials Science (NIMS), 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148 (Japan); Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), 7 Goban-cho, Chiyoda-ku, Tokyo 102-0076 (Japan); Synchrotron X-ray Group, Quantum Beam Unit, NIMS, 1-1-1 Kouto, Sayo-cho, Hyogo 679-5148 (Japan); Kusada, Kohei; Kobayashi, Hirokazu [Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), 7 Goban-cho, Chiyoda-ku, Tokyo 102-0076 (Japan); Division of Chemistry, Graduate School of Science, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto 606-8502 (Japan); Yayama, Tomoe; Ishimoto, Takayoshi [Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), 7 Goban-cho, Chiyoda-ku, Tokyo 102-0076 (Japan); INAMORI Frontier Research Center, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); Yoshikawa, Hideki [Surface Chemical Analysis Group, Nano Characterization Unit, NIMS, 1-2-1 Sengen, Tsukuba 305-0047 (Japan); Koyama, Michihisa [Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), 7 Goban-cho, Chiyoda-ku, Tokyo 102-0076 (Japan); INAMORI Frontier Research Center, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); International Institute for Carbon-Neutral Energy Research, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); 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.

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

    PubMed

    Mitoraj, Mariusz P; Michalak, Artur

    2013-11-01

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

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

    NASA Astrophysics Data System (ADS)

    Kuntz, Philip J.

    1985-04-01

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

  13. Shift of x-ray-photoelectron core levels in Bi sub 2 Sr sub 2 Ca sub 1 minus x Y sub x Cu sub 2 O sub y : An explanation by bond-valence-sum calculation

    SciTech Connect

    Itti, R.; Munakata, F.; Ikeda, K.; Yamauchi, H.; Koshizuka, N.; Tanaka, S. (Superconductivity Research Laboratory, International Superconductivity Technology Center, 1-10-13 Shinonome, Koto-ku, Tokyo 135, Japan (JP))

    1991-03-01

    Shifts of the binding energies of x-ray-photoelectron core levels are observed in the Bi{sub 2}Sr{sub 2}Ca{sub 1{minus}{ital x}}Y{sub {ital x}}Cu{sub 2}O{sub {ital y}} system when {ital x} is varied. It is pointed out that this is due to the change in the chemical environment associated with the changes of the interatomic distances. We show that the so-called bond-valence-sum calculation is useful for the explanation of the shift; and propose that this method is generally applicable in explaining or predicting the shift of core levels in any system with a variable composition.

  14. SLAMM Source Code Attribute VB_Name = "CalcMainModule".................................................................................................................................2

    E-print Network

    Pitt, Robert E.

    E-1 Appendix E SLAMM Source Code Attribute VB_Name = "CalcMainModule".................................................................................................................................2 Attribute VB_Name = "CalcPollutants" ....................................................................................................................................38 Attribute VB_Name = "Procedures

  15. 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)

  16. 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

  17. Levels of valence.

    PubMed

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

    2013-01-01

    The distinction between the positive and the negative is fundamental in our emotional life. In appraisal theories, in particular in the component process model of emotion (Scherer, 1984, 2010), qualitatively different types of valence are proposed based on appraisals of (un)pleasantness, goal obstructiveness/conduciveness, low or high power, self-(in)congruence, and moral badness/goodness. This multifaceted conceptualization of valence is highly compatible with the frequent observation of mixed feelings in real life. However, it seems to contradict the one-dimensional conceptualization of valence often encountered in psychological theories, and the notion of valence as a common currency used to explain choice behavior. Here, we propose a framework to integrate the seemingly disparate conceptualizations of multifaceted valence and one-dimensional valence by suggesting that valence should be conceived at different levels, micro and macro. Micro-valences correspond to qualitatively different types of evaluations, potentially resulting in mixed feelings, whereas one-dimensional macro-valence corresponds to an integrative "common currency" to compare alternatives for choices. We propose that conceptualizing levels of valence may focus research attention on the mechanisms that relate valence at one level (micro) to valence at another level (macro), leading to new hypotheses, and addressing various concerns that have been raised about the valence concept, such as the valence-emotion relation. PMID:23717292

  18. Different symmetry of the magnetization-direction dependence between the impurity band and valence band in GaMnAs

    NASA Astrophysics Data System (ADS)

    Muneta, Iriya; Kanaki, Toshiki; Ohya, Shinobu; Tanaka, Masaaki

    2015-03-01

    In semiconductors with heavily doped with nonmagnetic shallow acceptors, an impurity band (IB) is formed around the valence band (VB) top and merged with VB. As a result, the parabolic VB top is strongly deformed in a non-parabolic dispersion. In GaMnAs, however, the VB top keeps the parabolic dispersion though there is energy overlap between VB and IB, which is completely different from the conventional nonmagnetic semiconductors. Here, we measure tunneling anisotropic magnetoresistance on GaMnAs tunnel devices in a spectroscopic way, analyze the magnetization-direction and energy dependence of the density of states (DOS), and investigate the different symmetry between VB and IB to clarify the mysterious overlap between the two bands. We find that the magnetization-direction dependence of VB DOS is mainly four-fold symmetry along [100] which is the same as the crystal symmetry, while that of IB DOS is mainly two-fold symmetry along [110] unlike the crystal symmetry. These results reveal the unique band structures of Mn-doped III-V ferromagnetic semiconductors. This work was partly supported by Grant-in-Aids for Scientific Research including Specially Promoted Research, I.M. thanks the JSPS research Fellowship Program for Young Scientists.

  19. Mapping of the apple scab-resistance gene Vb.

    PubMed

    Erdin, N; Tartarini, S; Broggini, G A L; Gennari, F; Sansavini, S; Gessler, C; Patocchi, A

    2006-10-01

    Apple scab, caused by the fungus Venturia inaequalis, is the major production constraint in temperate zones with humid springs. Normally, its control relies on frequent and regular fungicide applications. Because this control strategy has come under increasing criticism, major efforts are being directed toward the breeding of scab-resistant apple cultivars. Modern apple breeding programs include the use of molecular markers, making it possible to combine several different scab-resistance genes in 1 apple cultivar (pyramiding) and to speed up the breeding process. The apple scab-resistance gene Vb is derived from the Siberian crab apple 'Hansen's baccata #2', and is 1 of the 6 "historical" major apple scab-resistance genes (Vf, Va, Vr, Vbj, Vm, and Vb). Molecular markers have been published for all these genes, except Vr. In testcross experiments conducted in the 1960s, it was reported that Vb segregated independently from 3 other major resistance genes, including Vf. Recently, however, Vb and Vf have both been mapped on linkage group 1, a result that contrasts with the findings from former testcross experiments. In this study, simple sequence repeat (SSR) markers were used to identify the precise position of Vb in a cross of 'Golden Delicious' (vbvb) and 'Hansen's baccata #2' (Vbvb). A genome scanning approach, a fast method already used to map apple scab-resistance genes Vr2 and Vm, was used, and the Vb locus was identified on linkage group 12, between the SSR markers Hi02d05 and Hi07f01. This finding confirms the independent segregation of Vb from Vf. With the identification of SSR markers linked to Vb, another major apple scab-resistance gene has become available; breeders can use it to develop durable resistant cultivars with several different resistance genes. PMID:17213905

  20. {sup 2}J{sub COC} spin-spin coupling constants across glycosidic linkages exhibit a valence bond-angle dependence

    SciTech Connect

    Cloran, F.; Carmichael, I.; Serianni, A.S.

    2000-01-19

    The recent intense interest in the biological functions and biomedical applications of oligosaccharides has stimulated renewed efforts to improve experimental tools for the determination of their conformational properties. NMR spectroscopy provides the most detailed structural information in solution derived mainly from {sup 1}H-{sup 1}H NOEs and more recently from {sup 3}J{sub COCH}values across their constituent O-glycosidic linkages. However, in many cases, these linkages are not conformationally rigid, and identifying those that exhibit flexibility requires the use of multiple NMR parameters which provide the needed redundancy to make such determinations with confidence. In ongoing efforts to develop trans-O-glycosidic {sup 2}J{sub COC} and {sup 3}J{sub COCC} values as conformational constraints, it was shown recently that {sup 2}J{sub COC} across an O-glycosidic linkage depends mainly on the {phi} torsion angle and considerably less so on {psi}, using an experimentally derived projection resultant rule. This rule predicts that more negative projection resultants translate into more negative {sup 2}J{sub CCC} and, by analogy, into more negative {sup 2}J{sub COC}. The authors show that the COC bond angle also influences {sup 2}J{sub COC} magnitude, with increasing angle producing more negative coupling.

  1. Chem 350 Jasperse Ch. 1 Normal Bonding; Drawing Lewis Structures 1 Normal Bonds (Sections 1.2-1.5)

    E-print Network

    Jasperse, Craig P.

    Chem 350 Jasperse Ch. 1 Normal Bonding; Drawing Lewis Structures 1 Normal Bonds (Sections 1.2-1.5) Summary of Normal, Ideal Bonding (No Formal Charge) Valence Electrons Valence Bonds Lone Pairs C 4 4 0 N 5: (Sections 1.4-5) 1. Try to provide normal bonding for C, N, O atoms if possible. (Works > 95% of time) 2

  2. The valence bond solid in quasicrystals

    E-print Network

    Anatol N. Kirillov; Vladimir E. Korepin

    2009-09-11

    A generalized model of Heisenberg quantum antiferromagnet on an arbitrary graph is constructed so that the VBS is the unique ground state. The norm of the base state and equal time multi point correlation functions are computed in terms of generalized hyper geometric functions. For the one-dimensional periodic Heisenberg model we present a method of computing multi point correlation functions based on the study of a commuting family of transfer matrices. The connection of multi point correlators with Young tableaux and Gegenbauer polynomials is found.

  3. MERIT Hg System Testing V.B. Graves

    E-print Network

    McDonald, Kirk

    Hg Delivery System · Syringe pump · Hydraulic power unit w/control system · Optical diagnostic systemMERIT Hg System Testing Status V.B. Graves P.T. Spampinato Neutrino Factory Muon Collider. DEPARTMENT OF ENERGY Outline · Requirements review · System description · Testing to date · Preparations

  4. Draft Genome Sequence of Tolypothrix boutellei Strain VB521301

    PubMed Central

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

    2015-01-01

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

  5. 17/09/200417/09/2004 Bibliothque de mathmatiques et informatique-vbBibliothque de mathmatiques et informatique-vb 11 Le catalogue commun desLe catalogue commun des

    E-print Network

    Gutkin, Boris

    17/09/200417/09/2004 Bibliothèque de mathématiques et informatique-vbBibliothèque de mathématiques et informatique-vb 11 Le catalogue commun desLe catalogue commun des bibliothèques de l informatique-vbBibliothèque de mathématiques et informatique-vb 22 ChoisirChoisir un catalogue ou une

  6. Research on communication between computer and PLC based on VB

    Microsoft Academic Search

    Hui Fang; Wei Tang

    2012-01-01

    This paper mainly introduces the communication between computer and S7–200PLC of Siemens, in which host computer (PC) adopts MSComm control in VB6.0, a visual programming language, to implement the data communication between console computer (S7–200 PLC) and computer, based on free port communication protocol. Communication protocol format is user-defined in this paper, so huge data communication in real time can

  7. Cloning, characterization, and expression of the spoVB gene of Bacillus subtilis.

    PubMed Central

    Popham, D L; Stragier, P

    1991-01-01

    Mutation of the spoVB gene in Bacillus subtilis causes the production of spores containing a defective cortex and unable to acquire heat resistance. The spoVB locus is highly linked to another spo locus, spoIIIF, characterized by a single mutation (I. L. Lamont and J. Mandelstam, J. Gen. Microbiol. 130:1253-1261, 1984). A 18-kb DNA region overlapping the spoIIIF-spoVB region was cloned in successive steps starting from a Tn917 insertion in the nic locus. The exact location of the spoIIIF and spoVB loci was defined with various integrative plasmids carrying subfragments of that region. DNA sequencing established that spoIIIF and spoVB are a single monocistronic locus encoding a 518-amino-acid polypeptide with features of an integral membrane protein. The precise location of the spoIIIF590 and spoVB91 mutations in that unique open reading frame was determined, and both mutations were sequenced. A null mutation was engineered in the spoIIIF-spoVB locus and led to a typical spoVB phenotype, identical to the phenotype created by either spoIIIF590 or spoVB91, suggesting that the original spoIIIF mutant contained a secondary mutation arresting sporulation at an earlier stage. A transcriptional spoVB-lacZ fusion was constructed, and its expression was found to be directly dependent on RNA polymerase containing sigma E. A null mutation of spoVB had no effect on expression of sspB and cotA, members of the sigma G- and sigma K-controlled regulons respectively, while expression of cotC, a member of the latest known mother cell regulon, was delayed and strongly reduced. These results are consistent with SpoVB being involved in cortex biosynthesis and affecting only indirectly expression of late sporulation genes. PMID:1744050

  8. THE PROPOSED GIANT PLANET ORBITING VB 10 DOES NOT EXIST

    SciTech Connect

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

    2010-03-01

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

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

    PubMed Central

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

    2015-01-01

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

  10. Analysis of valence electron structures (VES) of intermetallic Fe 3Al compounds

    Microsoft Academic Search

    Yin Yansheng; Wang Wen Xiang; Shi Zhongliang

    1995-01-01

    Based on the empirical electron theory of solids and molecules, analysis of valence electron structures is made on Fe3Al intermetallic compounds. The bonding complex model of the DO3 cell is set up. Some preliminary attempts to discover the relationship between alloy composition, structure and properties and the Fe3Al alloy phase valence electron structure are presented.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  12. REVIEW ARTICLE: Valence fluctuation phenomena

    Microsoft Academic Search

    J. M. Lawrence; P. S. Riseborough; R. D. Parks

    1981-01-01

    Valence fluctuation phenomena occur in rare-earth compounds in which the proximity of the 4f level to the Fermi energy leads to instabilities of the charge configuration (valence) and\\/or of the magnetic moment. The authors review the experimental results observed in the subset of such systems for which the 4f ions form a lattice with identical valence on each site. The

  13. 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

    2015-06-11

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

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

    Microsoft Academic Search

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

    1995-01-01

    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

  15. Origin of the correlation of the rate constant of substrate hydroxylation by nonheme iron(IV)-oxo complexes with the bond-dissociation energy of the C-H bond of the substrate.

    PubMed

    Latifi, Reza; Bagherzadeh, Mojtaba; de Visser, Sam P

    2009-07-01

    Mononuclear nonheme iron containing systems are versatile and vital oxidants of substrate hydroxylation reactions in many biosystems, whereby the rate constant of hydroxylation correlates with the strength of the C-H bond that is broken in the process. The thermodynamic reason behind these correlations, however, has never been established. In this work results of a series of density functional theory calculations of substrate hydroxylation by a mononuclear nonheme iron(IV)-oxo oxidant with a 2 His/1 Asp structural motif analogous to alpha-ketoglutarate dependent dioxygenases are presented. The calculations show that these oxidants are very efficient and able to hydroxylate strong C-H bonds, whereby the hydrogen abstraction barriers correlate linearly with the strength of the C-H bond of the substrate that is broken. These trends have been rationalized using a valence bond (VB) curve-crossing diagram, which explains the correlation using electron transfer mechanisms in the hydrogen abstraction processes. We also rationalized the subsequent reaction step for radical rebound and show that the barrier is proportional to the electron affinity of the iron(III)-hydroxo intermediate complex. It is shown that nonheme iron(IV)-hydroxo complexes have a larger electron affinity than heme iron(IV)-hydroxo complexes and therefore also experience larger radical rebound barriers, which may have implications for product distributions and rearrangement reactions. Thus, detailed comparisons between heme and nonheme iron(IV)-oxo oxidants reveal the fundamental differences in monoxygenation capabilities of these important classes of oxidants in biosystems and synthetic analogues for the first time and enable us to make predictions of experimental processes. PMID:19472231

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

    PubMed

    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 (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(4)?(-) 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. PMID:25612695

  17. NMR Parameters and Geometries of OHN and ODN Hydrogen Bonds of Pyridine–Acid Complexes

    Microsoft Academic Search

    Hans-Heinrich Limbach; Mariusz Pietrzak; Shasad Sharif; Peter M. Tolstoy; Ilya G. Shenderovich; Sergei N. Smirnov; Nikolai S. Golubev; Gleb S. Denisov

    2004-01-01

    In this paper, equations are proposed which relate various NMR parameters of OHN hydrogen-bonded pyridine-acid complexes to their bond valences which are in turn correlated with their hydrogen-bond geometries. As the valence bond model is strictly valid only for weak hydrogen bonds appropriate empirical correction fac- tors are proposed which take into ac- count anharmonic zero-point energy vi- brations. The

  18. 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…

  19. Inexpensive determinations of valence virtual MOs for CI calculations

    NASA Astrophysics Data System (ADS)

    Illas, Francesc; Merchan, Manuela; Pelissier, Michel; Marlieuu&,cedil; Jean-Paul

    1986-09-01

    The full treatment of the non-dynamical correlation energy (i.e. the correlation within a shell of valence occupied and virtual MOs) is hihgly desirable since it is strongly shape and distance dependent, and ensures a proper dissociation into the HF ground state of the free atoms. The ideal way to achieve this goal is the valence CAS SCF procedure, which is rapidly very expensive. The present paper tries to define valence virtual MOs to perform full CAS CI or to use them in other approximate CI expansions. Very limited MC SCF procedures involving a few pair-wise excitations are sufficient to generate well-defined valence MOs. One may sometimes use virtual valence MOs from the upper valence multiplet but in many cases this procedure fails, the high-spin arrangement tending to avoid the ? bond region where it becomes too repulsive. The projection of the SCF atomic orbitals of the free atom in the virtual molecular space (Levy's PAO) is very efficient; this procedure may be improved by a proper definition of the hybridized AOs, i.e. the linear combination of the AOs which are most occupied in the molecular Fock space. The MOs defined from these four procedures prove to give CAS CI energies which are very close to the CAS SCF result, at a very low price. On the contrary, the usual improved virtual MOs defined from SCF calculations of the cation, or with an increased nuclear charge to compensate the excess repulsion of the Fock operator, fail to define valence virtual MOs even if they concentrate the spatial extension of the lowest virtual MOs. The quality of our MO sets is compared at the valence CAS CI level and through the convergence of the iterative multireference second-order Møller-Plesset CIPSI algorithm. Three comparisons concern a triply bonded molecule (N 2), an non-Lewis structure (Na 4), and an intermolecular complex Cu…CO, which is proved to be weakly bound. To obtain reliable potential curves in selected CI algorithms, it is recommended to give an (almost) constant physical meaning to all MOs.

  20. Mixed Valence Niobium

    NASA Astrophysics Data System (ADS)

    Keating, Steven James

    1992-01-01

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

  1. Valence band states and polarized optical emission from nonpolar and semipolar III–nitride quantum well optoelectronic devices

    NASA Astrophysics Data System (ADS)

    Zhao, Yuji; Farrell, Robert M.; Wu, Yuh-Renn; Speck, James S.

    2014-10-01

    Nonpolar and semipolar III–nitride quantum wells (QWs) and devices have been extensively studied due to their unique valence band (VB) structure and polarized optical emission. Unlike conventional c-plane oriented III–nitride QWs, the low crystal symmetry and unbalanced biaxial stress in nonpolar and semipolar QWs separates the topmost VBs and gives rise to polarized optical emission. Since the first experimental reports on nonpolar devices, research on this topic has progressed very rapidly and has covered nonpolar m-plane and a-plane QWs and devices as well as semipolar (11\\bar{2}2), (20\\bar{2}1), and (20\\bar{2}\\bar{1}) QWs and devices. Issues such as strain, plane inclination angle (with respect to the c-plane), indium composition, temperature, and their impact on QW VB structure and device performance have been extensively studied. In this paper we review the physical background and theoretical analysis of the VB states and polarized optical emission of nonpolar and semipolar structures and discuss their potential impacts on optoelectronic devices. Experimental results for nonpolar and semipolar light-emitting diodes and laser diodes will be covered along with additional discussions on the potential applications and challenges related to their unique physical properties.

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

  3. Valence Quarks Polarization from COMPASS

    E-print Network

    A. Korzenev

    2007-04-26

    A first evaluation of the polarized valence quark distribution $\\Delta u_v(x)+\\Delta d_v(x)$ from the COMPASS experiment (CERN/SPS) is presented. The data were collected by COMPASS in the years 2002--2004 using a 160 GeV polarized muon beam scattered off a large polarized $^6$LiD target and cover the range $1< Q^2 < 100$ GeV$^2$ and $0.006valence quarks.

  4. Presented at the 17th EC PVSEC Munich October 2001 Paper VB1.40

    E-print Network

    Romeo, Alessandro

    - tional solar cell materials such as c-Si and GaAs. 2. EXPERIMENTAL DETAILS AND RESULTS The CdTe solar for thin film solar cells. For CdTe these light soaking effects are generally beneficial since meta stablePresented at the 17th EC PVSEC Munich October 2001 Paper VB1.40 1 1. INTRODUCTION Solar cells

  5. Entanglement and Bond Fluctuations in Random Singlet Phases

    Microsoft Academic Search

    Huan Doan Tran

    2010-01-01

    The set of valence-bond states --- states in which localized spin-1\\/2 particles are correlated in singlet pairs said to be connected by valence bonds --- provides a useful basis for visualizing singlet ground states of quantum spin systems. For example, the ground state of the uniform one-dimensional nearest-neighbor spin-1\\/2 antiferromagnetic (AFM) Heisenberg model (the prototypical spin-liquid state) can be viewed

  6. Three-dimensional valency mapping in ceria nanocrystals.

    PubMed

    Goris, Bart; Turner, Stuart; Bals, Sara; Van Tendeloo, Gustaaf

    2014-10-28

    Using electron tomography combined with electron energy loss spectroscopy (EELS), we are able to map the valency of the Ce ions in CeO2-x nanocrystals in three dimensions. Our results show a clear facet-dependent reduction shell at the surface of ceria nanoparticles; {111} surface facets show a low surface reduction, whereas at {001} surface facets, the cerium ions are more likely to be reduced over a larger surface shell. Our generic tomographic technique allows a full 3D data cube to be reconstructed, containing an EELS spectrum in each voxel. This possibility enables a three-dimensional investigation of a plethora of material-specific physical properties such as valency, chemical composition, oxygen coordination, or bond lengths, triggering the synthesis of nanomaterials with improved properties. PMID:25286190

  7. Measurement of the background in Auger-Photoemission Spectra (APECS) associated with multi-electron and inelastic valence band photoemission processes

    NASA Astrophysics Data System (ADS)

    Joglekar, Prasad; Shastry, Karthik; Hulbert, Steven; Weiss, Alex

    2014-03-01

    Auger Photoelectron Coincidence Spectroscopy (APECS), in which the Auger spectra is measured in coincidence with the core level photoelectron, is capable of pulling difficult to observe low energy Auger peaks out of a large background due mostly to inelastically scattered valence band photoelectrons. However the APECS method alone cannot eliminate the background due to valence band VB photoemission processes in which the initial photon energy is shared by 2 or more electrons and one of the electrons is in the energy range of the core level photoemission peak. Here we describe an experimental method for estimating the contributions from these background processes in the case of an Ag N23VV Auger spectra obtained in coincidence with the 4p photoemission peak. A beam of 180eV photons was incident on a Ag sample and a series of coincidence measurements were made with one cylindrical mirror analyzer (CMA) set at a fixed energies between the core and the valence band and the other CMA scanned over a range corresponding to electrons leaving the surface between 0eV and the 70eV. The spectra obtained were then used to obtain an estimate of the background in the APECS spectra due to multi-electron and inelastic VB photoemission processes. NSF, Welch Foundation.

  8. Aesthetic valence of visual illusions

    PubMed Central

    Stevanov, Jasmina; Markovi?, 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

  9. Valency Primitives as Dictionary Realisations

    E-print Network

    Žele, Andreja

    2007-01-01

    are valency verbal semantemes re- alised by appropriate basic verbs such as bivati (‘to be/live/exist/dwell’), ?utiti (‘to feel’); govoriti/re?i (‘to speak/say’), misliti (‘to think’), gledati (‘to watch’), hoteti (‘to want’), želeti (‘to wish’); delovati... (‘to act’), deti (‘to put’), vzeti (‘to take’), igrati (se) (‘to play’); spreminjati (se) (‘to change’); iti (‘to go’), hoditi (‘to walk’)); 2) subcategorical semantemes as actant semantemes or possible actant roles – including with regard to (in...

  10. Multiple intermediate valence in plutonium

    Microsoft Academic Search

    A. V. Mirmelstein; E. S. Clementyev; O. V. Kerbel

    2009-01-01

    On the basis of the concepts of an intermediate-valence (IV) regime, an empirical model is proposed that quantitatively describes\\u000a the magnetic susceptibility, specific heat, and effective atomic volume of the low-temperature ? phase and the gallium or\\u000a aluminum-stabilized face-centered cubic (fcc) ? phase of plutonium metal. The results of the paper allow one to estimate the\\u000a entropy change associated with

  11. 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.

  12. The flavin reductase ActVB from Streptomyces coelicolor: characterization of the electron transferase activity of the flavoprotein form

    E-print Network

    Laurent Filisetti; Julien Valton; Marc Fontecave; Vincent Nivière

    2015-01-07

    The flavin reductase ActVB is involved in the last step of actinorhodin biosynthesis in Streptomyces coelicolor. Although ActVB can be isolated with some FMN bound, this form was not involved in the flavin reductase activity. By studying the ferric reductase activity of ActVB, we show that its FMN-bound form exhibits a proper enzymatic activity of reduction of iron complexes by NADH. This shows that ActVB active site exhibits a dual property with regard to the FMN. It can use it as a substrate that goes in and off the active site or as a cofactor to provide an electron transferase activity to the polypeptide.

  13. 30 CFR 57.22314 - Flow-control devices (V-A and V-B mines).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ...and Nonmetal Mines Equipment § 57.22314 Flow-control devices (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...

  14. 30 CFR 57.22314 - Flow-control devices (V-A and V-B mines).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ...and Nonmetal Mines Equipment § 57.22314 Flow-control devices (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...

  15. 30 CFR 57.22314 - Flow-control devices (V-A and V-B mines).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ...and Nonmetal Mines Equipment § 57.22314 Flow-control devices (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...

  16. 30 CFR 57.22314 - Flow-control devices (V-A and V-B mines).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ...and Nonmetal Mines Equipment § 57.22314 Flow-control devices (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...

  17. 30 CFR 57.22314 - Flow-control devices (V-A and V-B mines).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ...and Nonmetal Mines Equipment § 57.22314 Flow-control devices (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...

  18. Mine Hydrogeology Information Management System Based on VB and MapObjects

    Microsoft Academic Search

    Fan Shu-kai; Wu Qiang; Pan Guo-ying; Liu Shou-qiang

    2010-01-01

    Abstract-According to the problem existed in the work of mine hydrogeology information management, based on the analysis of functional requirement and system structure of mine hydrogeology information management system, mine hydrogeology information management system was developed on the basis of MapObjects , with VB 6.0 as development language, and with Access 2000 as back-end database. The system realized the inputting,

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

    PubMed

    Sen, Diya; Chandrababunaidu, Mathu Malar; Singh, Deeksha; Sanghi, Neha; Ghorai, Arpita; Mishra, Gyan Prakash; Madduluri, Madhavi; Adhikary, Siba Prasad; Tripathy, Sucheta

    2015-01-01

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

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

    PubMed Central

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

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  2. Valence fluctuations in ferromagnetic 4f systems

    Microsoft Academic Search

    W. Nolting; A. Ramakanth

    1986-01-01

    We investigate the coexistence of ferromagnetism and intermediate valence in 4f systems which have ferromagnetic ground states in the normal-valence phase and fluctuate between a magnetic (J!=0) and a nonmagnetic (J=0) state in the intermediate-valence phase. We use a model which is generated from the well-known s-f model by inclusion of a hybridization term. The alloy analogy of the model

  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. Adsorption mechanism and valency of catechol-functionalized hyperbranched polyglycerols

    PubMed Central

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

    2015-01-01

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

  5. Water durability of resin bond to precious metal alloys using adhesive resins containing adhesion promoting monomers.

    PubMed

    Kadoma, Yoshinori; Kojima, Katsunori

    2005-12-01

    Adhesive resins for precious metals were prepared by adding an adhesion promoting monomer to MMA-PMMA/TBBO resin. Precious metal alloys bonded by the adhesive resin were thermocycled 0, 1,000, 2,000, or 4,000 times in water between 4 and 60 degrees C, and tensile bond strengths were measured. Debonded metal surfaces after the tensile test were analyzed based on an area of cohesive failure. Three-way ANOVA revealed that all the three parameters--adherend, adhesive monomer, and number of thermal cycles--exhibited a significant influence on bond strength. Bond strength significantly decreased with increasing number of thermal cycles except for resin with 9,10-epithiodecyl 4-vinylbenzoate (EP8VB) to Au alloy. Mean bond strength of adhesive resin with 9,10-epithiodecyl methacrylate (EP8MA), EP8VB, or 3,4-epithiobutyl 2,2-bis(methacryloyloxymethyl)propionate (EP2BMA) exceeded 22 MPa after 4,000 thermal cycles. Analysis of debonded surfaces revealed the applicability of EP8MA, EP8VB, and EP2BMA as an adhesive monomer component of adhesive resin formulations. PMID:16445009

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

    SciTech Connect

    NONE

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-03-01

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

  8. Chemical Bonds

    NSDL National Science Digital Library

    The Concord Consortium

    2011-12-11

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

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

    PubMed

    Putz, Mihai V

    2010-01-01

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

  10. 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.

  11. Rapid Recycling of ?2-Adrenergic Receptors is Dependent on the Actin Cytoskeleton and Myosin Vb

    PubMed Central

    Millman, Ellen E.; Zhang, Haibin; Zhang, Haixia; Godines, Veronica; Bean, Andrew J.; Knoll, Brian J.; Moore, Robert H.

    2009-01-01

    For the ?2-adrenergic receptor (?2AR), published evidence suggests that an intact actin cytoskeleton is required for the endocytosis of receptors and their proper sorting to the rapid recycling pathway. We have characterized the role of the actin cytoskeleton in the regulation of ?2AR trafficking in HEK293 cells using two distinct actin filament disrupting compounds, cytochalasin D and latrunculin B. In cells pretreated with either drug, ?2AR internalization into transferrin-positive vesicles was not altered, but both agents significantly decreased the rate at which ?2ARs recycled to the cell surface. In latrunculin B-treated cells, nonrecycled ?2ARs were localized to EEA1-positive endosomes and also accumulated in the recycling endosome, but only a small fraction of receptors localized to LAMP-positive late endosomes and lysosomes. Treatment with latrunculin B also markedly enhanced the inhibitory effect of rab11 overexpression on receptor recycling. Dissociating receptors from actin by expression of the myosin Vb tail fragment resulted in missorting of ?2ARs to the recycling endosome, while the expression of various CART fragments or the depletion of actinin-4 had no detectable effect on ?2AR sorting. These results indicate that the actin cytoskeleton is required for the efficient recycling of ?2ARs, a process that likely is dependent on myosin Vb. PMID:18785920

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

    Microsoft Academic Search

    Nobuaki Ohtaka; Kazuhiko Narisawa

    2008-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Ohya, Shinobu

    2011-03-01

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

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

    Microsoft Academic Search

    Gian Paolo Brivio; Guido Fratesi; Mario Italo Trioni; Simona Ugenti; Enrico Perfetto; Michele Cini

    2009-01-01

    We propose an ab initio method to evaluate the core-valence-valence Auger spectrum of systems with filled valence bands. The method is based on the Cini-Sawatzky theory, and aims at estimating the parameters by first-principles calculations in the framework of DFT. Photoemission energies and the interaction energy for the two holes in the final state are evaluated by performing DFT simulations

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

    Microsoft Academic Search

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

    2008-01-01

    We propose an ab initio method to evaluate the core-valence-valence Auger spectrum of systems with filled valence bands. The method is based on the Cini-Sawatzky theory and aims at estimating the parameters by first-principles calculations in the framework of density-functional theory (DFT). Photoemission energies and the interaction energy for the two holes in the final state are evaluated by performing

  16. Oxygenation mediating the valence density-of-states and work function of Ti(0001) skin.

    PubMed

    Li, Lei; Meng, Fanling; Tian, Hongwei; Hu, Xiaoying; Zheng, Weitao; Sun, Chang Q

    2015-04-21

    Consistency between density function theory calculations and photoelectron spectroscopy observations confirmed predictions based on the framework of bond-band-barrier (3B) correlation notation [Sun, Prog. Mater. Sci., 2003, 48, 521-685] that an oxygen adsorbate interacts with Ti(0001) skin atoms to form a tetrahedron with creation of four valence density-of-state features: O-Ti bonding electron pairs, O nonbonding lone pairs, Ti electronic holes, and Ti antibonding dipoles. Formation of the dipoles lowers the work function of the Ti(0001) skin and electron-hole generation turns the metallic Ti(0001) into the semiconductive O-Ti(0001). Findings confirm the universality of the 3B correlation in understanding the dynamics of oxygen chemisorption and the associated valence electrons involved in the process of oxidation. PMID:25777318

  17. Valence photoionization and the following fragmentation pathways in Sb{sub 4} clusters

    SciTech Connect

    Urpelainen, S.; Calo, A.; Partanen, L.; Huttula, M.; Aksela, S.; Aksela, H. [Department of Physics, University of Oulu, P.O. Box 3000, Oulu 90014 (Finland); Niskanen, J. [Department of Physics, University of Oulu, P.O. Box 3000, Oulu 90014 (Finland); Theoretical Chemistry, Royal Institute of Technology, Roslagstullsbacken 15, S-106 91 Stockholm (Sweden); Kukk, E. [Department of Physics and Astronomy, University of Turku, FIN-20014 Turku (Finland)

    2009-10-15

    The valence photoelectron spectrum of Sb{sub 4} clusters and the following fragmentation patterns have been studied using synchrotron radiation and electron-ion coincidence technique. An experimental photoelectron spectrum of the 5t{sub 2} ionization of Sb{sub 4} is presented. Theoretical molecular calculations, together with the existing data on the noble gas xenon, were used to describe the experimental results. The bonding properties of the molecular orbitals involved are used to qualitatively describe the dissociation process.

  18. Nature of the Frequency Shift of Hydrogen Valence Vibrations

    E-print Network

    Zhyganiuk, I V

    2015-01-01

    The physical nature of a frequency shift of hydrogen valence vibrations in a water molecule due to its interaction with neighbor molecules has been studied. Electrostatic forces connected with the multipole moments of molecules are supposed to give a dominating contribution to the intermolecular interaction. The frequency shift was calculated in the case where two neighbor molecules form a dimer. The obtained result is in qualitative agreement with the frequency shifts observed for water vapor, hexagonal ice, and liquid water, as well as for aqueous solutions of alcohols. This fact testifies to the electrostatic nature of H-bonds used to describe both the specific features of the intermolecular interaction in water and the macroscopic properties of the latter.

  19. HELP FOR DEBUGGING VB CODES Debugging is an essential part of programming. Even for an experienced programmer most

    E-print Network

    Clement, Prabhakar

    1 1 HELP FOR DEBUGGING VB CODES Debugging is an essential part of programming. Even. The goal of this tutorial is to introduce you to tools that can help fix your buggy code. There are 3 kinds. They are easy to fix and are caught by the compilers and pointed out to you. Adding OPTION EXPLICIT will help

  20. Draft Genome Sequence of Vibrio sp. Strain Vb278, an Antagonistic Bacterium Isolated from the Marine Sponge Sarcotragus spinosulus

    PubMed Central

    Gonçalves, Ana C. S.; Franco, Telma; Califano, Gianmaria; Dowd, Scot E.; Pohnert, Georg

    2015-01-01

    We report here the draft genome sequence of Vibrio sp. Vb278, a biofilm-producing strain isolated from the marine sponge Sarcotragus spinosulus, showing in vitro antibacterial activity. The annotated genome displays a range of symbiotic factors and the potential for the biosynthesis of several biologically active natural products. PMID:26021918

  1. Production of brevicin 286 by Lactobacillus brevis VB286 and partial characterization.

    PubMed

    Coventry, M J; Wan, J; Gordon, J B; Mawson, R F; Hickey, M W

    1996-01-01

    Brevicin 286 was produced by Lactobacillus brevis VB286 isolated from vacuum-packaged meat and was partially purified by ammonium sulphate precipitation, gel filtration and dialysis. The bacteriocin was susceptible to proteolytic enzymes, stable to heating at 100 degrees C particularly under acidic against Listeria sp. Production of brevicin 286 was optimal during exponential growth at 20 degrees C. Higher rates of cell growth occurred between 30 and 37 degrees C but with little or no expression of brevicin 286. A food-grade formulation consisting of 4% yeast extract and 1% glucose was found to be adequate for optimal brevicin 286 production and the bacteriocin-containing culture supernate was successfully spray dried with full recovery of antibacterial activity in the resultant powder. PMID:8698657

  2. Induction of apoptosis by VB1 in breast cancer cells: the role of reactive oxygen species and Bcl-2 family proteins.

    PubMed

    Liu, Li-Hua; Zhou, Ying-Jun; Ding, Lan; Zhang, Shun-Zhi; Sun, Ji; Cao, Jian-Guo

    2014-02-01

    We have previously reported that the EVn-50 mixture of vitexins (lignan compounds) containing the purified vitexin (neolignan) compound, 6-hydroxy-4(4-hydroxy-3-methoxyphenyl)-3-hydroxymethyl?7-methoxy-3,4-dihydro-2-naphthaldehyde, termed VB1, exhibits potent anticancer activity through the induction of apoptosis in several types of cancer cells, including MDA-MB?231 cells. However, the exact molecular mechanisms by which VB1 induces apoptosis in MDA-MB?231 cells have not yet been fully elucidated. In this study, to our knowledge, we provide for the first time mechanistic evidence that VB1-induced apoptosis in the human breast cancer line, MDA-MB-231, is associated with the generation of reactive oxygen species (ROS), the activation of caspases and the modulation of the expression of myeloid leukemia cell differentiation protein 1 (Mcl?1), B cell lymphoma?2 (Bcl-2) and Bcl-2-associated X (Bax) proteins. The silencing of Mcl-1 by RNA interference enhanced VB1-induced apoptosis. In addition, VB1 did not induce ROS generation or apoptosis in the immortalized non?cancerous breast cell line, MCF-10A. Our findings reveal a novel mechanism underlying VB1-induced apoptosis, and highlight VB1 as a promising candidate for the therapy of human breast cancer. PMID:24276280

  3. 2180 J. Am. Chem. SOC.1986, 108, 2180-2191 Bonding in Transition-Metal-Methylene Complexes. 2.

    E-print Network

    Goddard III, William A.

    2180 J. Am. Chem. SOC.1986, 108, 2180-2191 Bonding in Transition-Metal-Methylene Complexes. 2. (Ru methods (generalized valence bond/configuration interaction). The electronic-state spectrum reveals five separation and mode of metal-carbon bonding. The ground state has *A2symmetry and contains covalent M-C u

  4. On the density matrix definition of valency

    Microsoft Academic Search

    Omar G. Stradella; Hugo O. Villar; Eduardo A. Castro

    1986-01-01

    In a recent article Gopinathan and Jug have proposed a definition of atomic valency which had previously been given by Armstrong, Perkins and Stewart for closed shell molecules. The validity and interpretation of this definition for open shell systems is discussed. A new parameter for structural analysis, the free electron index, is presented.

  5. Double-valence-fluctuating molecules and superconductivity

    Microsoft Academic Search

    J. E. Hirsch; D. J. Scalapino

    1985-01-01

    We discuss the possibility of ``double-valence-fluctuating'' molecules, having two ground-state configurations differing by two electrons. We propose a possible realization of such a molecule, and experimental ways to look for it. We argue that a weakly coupled array of such molecules should give rise to a strong-coupling Shafroth-Blatt-Butler superconductor, with a high transition temperature.

  6. Double-valence-fluctuating molecules and superconductivity

    Microsoft Academic Search

    J. E. Hirsch; D. J. Scalapino

    1985-01-01

    We discuss the possibility of ''double-valence-fluctuating'' molecules, having two ground-state configurations differing by two electrons. We propose a possible realization of such a molecule, and experimental ways to look for it. We argue that a weakly coupled array of such molecules should give rise to a strong-coupling Shafroth-Blatt-Butler superconductor, with a high transition temperature.

  7. 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…

  8. Valence band anticrossing in highly mismatched alloys

    NASA Astrophysics Data System (ADS)

    Alberi, Kirstin Mclean

    Semiconductor alloys offer the ability to tune certain material parameters such as the band gap or carrier effective mass through precise control of the alloy composition, allowing them to be optimized for specific device requirements. While many alloys demonstrate near linear composition dependencies in these properties, those containing isoelectronic anion species that are significantly mismatched in electronegativity or ionization energy, known as highly mismatched alloys (HMA), exhibit substantial deviation from this trend. Here, the optical and electrical properties of HMAs containing dilute concentrations of large metallic anions are investigated in the context of a valence band anticrossing (VBAC) theory. Minority species with low ionization energies often introduce localized p-states near the valence band edge of the host semiconductor. Hybridization of these localized states with the extended p-states of the host may be described by a 12 x 12 Hamiltonian and produces a splitting of the alloy valence band into E+ and E - states. Photomodulated reflectance studies coupled with the VBAC theory confirm that the band gap bowing observed in GaSbxAs1-x and GaBixAs1-x is caused by an upward movement of the valence band edge as a result of the anticrossing interaction between the E+ and E- states. The valence band restructuring also adversely affects hole transport in these alloys through an increase in the heavy hole effective mass and the addition of an alloy disorder scattering mechanism. Finally, the VBAC theory has been extended to group IV HMAs as well as to the dilute magnetic semiconductor Ga1-x MnxAs, both of which exhibit strong hole localization at the minority species sites.

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

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

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

  10. On the sufficiency of compound target specification of isolated vowels and vowels in /bVb/ syllables.

    PubMed

    Andruski, J E; Nearey, T M

    1992-01-01

    It has been suggested [e.g., Strange et al., J. Acoust. Soc. Am. 74, 695-705 (1983); Verbrugge and Rakerd, Language Speech 29, 39-57 (1986)] that the temporal margins of vowels in consonantal contexts, consisting mainly of the rapid CV and VC transitions of CVC's, contain dynamic cues to vowel identity that are not available in isolated vowels and that may be perceptually superior in some circumstances to cues which are inherent to the vowels proper. However, this study shows that vowel-inherent formant targets and cues to vowel-inherent spectral change (measured from nucleus to offglide sections of the vowel itself) persist in the margins of /bVb/ syllables, confirming a hypothesis of Nearey and Assmann [J. Acoust. Soc. Am. 80, 1297-1308 (1986)]. Experiments were conducted to test whether listeners might be using such vowel-inherent, rather than coarticulatory information to identify the vowels. In the first experiment, perceptual tests using "hybrid silent center" syllables (i.e., syllables which contain only brief initial and final portions of the original syllable, and in which speaker identity changes from the initial to the final portion) show that listeners' error rates and confusion matrices for vowels in /bVb/ syllables are very similar to those for isolated vowels. These results suggest that listeners are using essentially the same type of information in essentially the same way to identify both kinds of stimuli. Statistical pattern recognition models confirm the relative robustness of nucleus and vocalic offglide cues and can predict reasonably well listeners' error patterns in all experimental conditions, though performance for /bVb/ syllables is somewhat worse than for isolated vowels. The second experiment involves the use of simplified synthetic stimuli, lacking consonantal transitions, which are shown to provide information that is nearly equivalent phonetically to that of the natural silent center /bVb/ syllables (from which the target measurements were extracted). Although no conclusions are drawn about other contexts, for speakers of Western Canadian English coarticulatory cues appear to play at best a minor role in the perception of vowels in /bVb/ context, while vowel-inherent factors dominate listeners' perception. PMID:1737887

  11. Effect of phonons in mixed valence systems

    Microsoft Academic Search

    M. Avignon; F. Brouers; K. H. Bennemann

    1979-01-01

    The effect of electron-phon on coupling on valence fluctuations in rare-earth systems is studied. It is shown that the electron-phonon coupling affects both the important electronic parameters and the phonon- frequencies, in particular the short-wavelength longitudinal optical phonons. Electronic phase transitions in d- and f- electron systems like transition metals and rare-earth metals are particularly interesting due to strong electron-

  12. Fluctuating valence in SmS

    Microsoft Academic Search

    K. W. H. Stevens

    1976-01-01

    In the ground state of normal SmS, each rare-earth ion is in a (4f)67F0 state, with all the other electrons filling valence bands. The symmetry of the ground state is therefore known. From an examination of the observed properties it is reasoned that when the lattice collapses under hydrostatic pressure (preserving the cubic symmetry) the new ground state has the

  13. Mixed valence/dipole-bound dianions

    SciTech Connect

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

    1999-12-01

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

  14. Pattern classification of valence in depression?

    PubMed Central

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

    2013-01-01

    Neuroimaging biomarkers of depression have potential to aid diagnosis, identify individuals at risk and predict treatment response or course of illness. Nevertheless none have been identified so far, potentially because no single brain parameter captures the complexity of the pathophysiology of depression. Multi-voxel pattern analysis (MVPA) may overcome this issue as it can identify patterns of voxels that are spatially distributed across the brain. Here we present the results of an MVPA to investigate the neuronal patterns underlying passive viewing of positive, negative and neutral pictures in depressed patients. A linear support vector machine (SVM) was trained to discriminate different valence conditions based on the functional magnetic resonance imaging (fMRI) data of nine unipolar depressed patients. A similar dataset obtained in nine healthy individuals was included to conduct a group classification analysis via linear discriminant analysis (LDA). Accuracy scores of 86% or higher were obtained for each valence contrast via patterns that included limbic areas such as the amygdala and frontal areas such as the ventrolateral prefrontal cortex. The LDA identified two areas (the dorsomedial prefrontal cortex and caudate nucleus) that allowed group classification with 72.2% accuracy. Our preliminary findings suggest that MVPA can identify stable valence patterns, with more sensitivity than univariate analysis, in depressed participants and that it may be possible to discriminate between healthy and depressed individuals based on differences in the brain's response to emotional cues. PMID:24179819

  15. Pattern classification of valence in depression.

    PubMed

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

    2013-01-01

    Neuroimaging biomarkers of depression have potential to aid diagnosis, identify individuals at risk and predict treatment response or course of illness. Nevertheless none have been identified so far, potentially because no single brain parameter captures the complexity of the pathophysiology of depression. Multi-voxel pattern analysis (MVPA) may overcome this issue as it can identify patterns of voxels that are spatially distributed across the brain. Here we present the results of an MVPA to investigate the neuronal patterns underlying passive viewing of positive, negative and neutral pictures in depressed patients. A linear support vector machine (SVM) was trained to discriminate different valence conditions based on the functional magnetic resonance imaging (fMRI) data of nine unipolar depressed patients. A similar dataset obtained in nine healthy individuals was included to conduct a group classification analysis via linear discriminant analysis (LDA). Accuracy scores of 86% or higher were obtained for each valence contrast via patterns that included limbic areas such as the amygdala and frontal areas such as the ventrolateral prefrontal cortex. The LDA identified two areas (the dorsomedial prefrontal cortex and caudate nucleus) that allowed group classification with 72.2% accuracy. Our preliminary findings suggest that MVPA can identify stable valence patterns, with more sensitivity than univariate analysis, in depressed participants and that it may be possible to discriminate between healthy and depressed individuals based on differences in the brain's response to emotional cues. PMID:24179819

  16. Excited potential energy surfaces of CH[sub 3]SH from the [ital ab] [ital initio] effective valence shell Hamiltonian method

    SciTech Connect

    Stevens, J.E.; Freed, K.F.; Arendt, M.F. (The James Franck Institute and the Department of Chemistry, The University of Chicago, Chicago, Illinois 60637 (United States)); Graham, R.L. (Cray Research, Inc., Egan, Minnesota 55123 (United States))

    1994-09-15

    The ground and first and second [sup 1][ital A][double prime] potential surfaces of methyl mercaptan (CH[sub 3]SH) are calculated as a function of the C--S and S--H bond coordinates using the [ital ab] [ital initio] effective valence shell Hamiltonian ([ital H][sup [nu

  17. 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

  18. Valence change by in situ XAS in surface modified LiMn 2O 4 for Li-ion battery

    Microsoft Academic Search

    Hong-Wei Chan; Jenq-Gong Duh; Jyh-Fu Lee

    2006-01-01

    The surface-modified cathode material in Li-ion battery was synthesized to decrease the side reactions at the interface between the cathode electrode and electrolyte. It is aimed to reduce the fading rate and to enhance the electrochemical performance, particularly at high C rate. In this study, microstructure, valence change and variation of bonding state in the surface-modified LiMn2O4 were examined and

  19. Experimental study of the valence band of Bi2Se3

    SciTech Connect

    Heremans, Joseph [Ohio State University, Columbus; Gao, Yibin [Ohio State University, Columbus; He, Bin [Ohio State University, Columbus; Androulakis, Yiannis [GENTHERM; Parker, David S [ORNL

    2014-01-01

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

  20. Water durability of resin bond to pure gold treated with various adhesion promoting thiirane monomers.

    PubMed

    Kadoma, Yoshinori; Kojima, Katsunori; Tamaki, Yoh; Nomura, Yoshiaki

    2007-01-01

    Adhesion promoting monomers for precious metals, 2,3-epithiopropyl methacrylate (EP1MA), 4,5-epithiopentyl methacrylate (EP3MA), 9,10-epithiodecyl methacrylate (EP8MA), 10,11-epithioundecyl methacrylate (EP9MA), 9,10-epithiodecyl 4-vinylbenzoate (EP8VB), 2,3-epithiocyclohexyl methacrylate (EPCHMA), and 3,4-epithiobutyl 2,2-bis(methacryloyloxymethyl)-propionate (EP2BMA), were used as surface treatment agents for pure gold to improve the durability of resin bonds against water. Treated specimens were butt-jointed together with MMA-PMMA resins, and tensile bond strength was measured after 2,000 thermal cycles in water. Bond strength to precious metal alloys was also determined under the same condition to clarify the influence of metal composition. The adhesion performance of thiirane monomers to pure gold highly depended on their chemical structure. EP3MA, EP8MA, EP9MA, EP8VB, and EP2BMA showed excellent performance, while EP1MA exhibited a moderate one and EPCHMA a poor one. The comparison of pure gold with precious metal alloys revealed the usefulness of pure gold as a standard, common adherend for bond strength evaluations. PMID:17410890

  1. 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.

  2. 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)

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

    NASA Astrophysics Data System (ADS)

    Lépine, Sébastien; DiStefano, Rosanne

    2012-04-01

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

  4. 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.

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

    SciTech Connect

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

    2012-04-10

    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.

  6. 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. PMID:21826759

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

    SciTech Connect

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

    2008-01-01

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

  8. 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.

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

    PubMed Central

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

    2009-01-01

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

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

    SciTech Connect

    Reed, A.E.; von Rague Schleyer, P. (Universitaet Erlangen-Nuernberg (Germany, F.R.))

    1990-02-14

    Does sulfur form six covalent bonds in CH{sub 3}SO{sub 2}Cl, F{sub 3}S{triple bond}N or carbon or phosphorus five bonds in F{sub 3}C=O{sup {minus}}, F{sub 3}P=O After a brief history of the viewpoints on hypervalent bonding and a comparison of analysis methods (with CH{sub 3}SO{sub 2}Cl as example), natural population and natural bond orbital analysis is applied to a series of 32-valence-electron species of X{sub 3}XY type (CF{sub 4}, F{sub 3}NO, O{sub 3}ClF, O{sub 3}PS{sup 3{minus}}, F{sub 3}SN, etc.). The {sigma}-bonding in these systems is found to be significantly ionic, and the strongly polar {sigma}*{sub AX} orbitals are found to be more effective electron acceptors than the extra-valence d{sub {pi}} (A) orbitals. By generalizing our discussion to n-coordinate 8n-valence-electron species (HF{sub 2}{sup {minus}}, BF{sub 3}, ClO{sub 4}{sup {minus}}, F{sub 4}SO, F{sub 5}TeO{sup {minus}}, IF{sub 6}{sup +}, OXeF{sub 6}, etc.) and their reduced analogues that have one or more lone pairs on the central atom (SF{sub 4}, IF{sub 6}{sup {minus}}, ClF{sub 3}, etc.), we provide a classification of hypervalent (and many nonhypervalent) molecules. The simple, qualitative bonding concepts for hypervalent molecules developed here supercede the inaccurate and misleading dsp{sup 3} and d{sup 2}sp{sup 3} models that are still in widespread use.

  11. 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 ?* orbital that is highly localized on a peptide bond with antibonding character, and the relatively low bond energy of the peptide bonds. These characteristics indicate that the high selectivity on bond dissociation following core excitation could be a general feature for molecules containing peptide bonds. PMID:25988354

  12. Dissociated neural representations of intensity and valence in human olfaction

    Microsoft Academic Search

    A. K. Anderson; K. Christoff; I. Stappen; D. Panitz; D. G. Ghahremani; G. Glover; J. D. E. Gabrieli; N. Sobel

    2003-01-01

    Affective experience has been described in terms of two primary dimensions: intensity and valence. In the human brain, it is intrinsically difficult to dissociate the neural coding of these affective dimensions for visual and auditory stimuli, but such dissociation is more readily achieved in olfaction, where intensity and valence can be manipulated independently. Using event-related func- tional magnetic resonance imaging

  13. Dissociated neural representations of intensity and valence in human olfaction

    Microsoft Academic Search

    K. Christoff; I. Stappen; D. Panitz; D. G. Ghahremani; G. Glover; J. D. E. Gabrieli; A. K. Anderson; N. Sobel

    2003-01-01

    Affective experience has been described in terms of two primary dimensions: intensity and valence. In the human brain, it is intrinsically difficult to dissociate the neural coding of these affective dimensions for visual and auditory stimuli, but such dissociation is more readily achieved in olfaction, where intensity and valence can be manipulated independently. Using event-related functional magnetic resonance imaging (fMRI),

  14. 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

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

    NASA Astrophysics Data System (ADS)

    Svensson, S.; Karlsson, L.

    1992-01-01

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

  16. Nature of PO bonds in phosphates.

    PubMed

    Gamoke, Benjamin; Neff, Diane; Simons, Jack

    2009-05-14

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

  17. 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)

  18. Bonding with Grandparents

    MedlinePLUS

    ... Sports: Keeping Kids Safe Concussions: What to Know Bonding With Grandparents KidsHealth > Parents > School & Family Life > Family ... encouraging a close relationship can benefit everyone involved. Bonding Benefits Establishing a bond with grandparents can benefit ...

  19. Bonding with Your Baby

    MedlinePLUS

    ... the child's social and cognitive development. Why Is Bonding Important? Bonding is essential for a baby. Studies ... as biological parents and their children. Back Continue Bonding With Daddy Men these days spend more time ...

  20. 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

    ...2010-07-01 false Actions at 2.0 percent methane (I-B, II-B, V-B, and VI mines). 57.22238 Section 57.22238 Mineral Resources ...Nonmetal Mines Ventilation § 57.22238 Actions at 2.0 percent methane...

  1. 29 CFR 2580.412-20 - Use of existing bonds, separate bonds and additional bonding.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

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

  2. 29 CFR 2580.412-20 - Use of existing bonds, separate bonds and additional bonding.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

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

  3. 29 CFR 2580.412-20 - Use of existing bonds, separate bonds and additional bonding.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

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

  4. 29 CFR 2580.412-20 - Use of existing bonds, separate bonds and additional bonding.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

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

  5. 29 CFR 2580.412-20 - Use of existing bonds, separate bonds and additional bonding.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

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

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

    PubMed Central

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

    2008-01-01

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

  7. 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

  8. Inelastic neutron scattering in valence fluctuation compounds

    SciTech Connect

    Jon M Lawrence

    2011-02-15

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

  9. The Valence of Titanium in Refractory Forsterite

    SciTech Connect

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

    2007-03-06

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

  10. Nature of Atomic Bonding and Atomic Structure in the Phase-Change Ge2Sb2Te5 Glass

    NASA Astrophysics Data System (ADS)

    Xu, M.; Cheng, Y. Q.; Sheng, H. W.; Ma, E.

    2009-11-01

    Using electronic structure calculations, we demonstrate a global valence alternation in the amorphous Ge2Sb2Te5, a prototype phase-change alloy for data storage. The resulting p bonding profoundly influences the local atomic structure, leading to right-angle components similar to those in the crystalline counterpart of this chalcogenide glass. The dominance of p bonding is revealed by (i) distributions of the coordination number (CN) and the bond angle, for truly bonded atoms determined based on the electron localization function, and (ii) a direct evaluation of the p (and s) orbital occupation probability for the CN=3 Ge atoms that form 90° bonds with neighbors.

  11. Nature of atomic bonding and atomic structure in the phase-change Ge2Sb2Te5 glass.

    PubMed

    Xu, M; Cheng, Y Q; Sheng, H W; Ma, E

    2009-11-01

    Using electronic structure calculations, we demonstrate a global valence alternation in the amorphous Ge2Sb2Te5, a prototype phase-change alloy for data storage. The resulting p bonding profoundly influences the local atomic structure, leading to right-angle components similar to those in the crystalline counterpart of this chalcogenide glass. The dominance of p bonding is revealed by (i) distributions of the coordination number (CN) and the bond angle, for truly bonded atoms determined based on the electron localization function, and (ii) a direct evaluation of the p (and s) orbital occupation probability for the CN=3 Ge atoms that form 90 degree bonds with neighbors. PMID:20365937

  12. 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.

  13. Valence band anticrossing in GaBixAs1-x

    SciTech Connect

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

    2007-07-11

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

  14. Valence contrast by synchrotron resonance scattering: Application to a mixed-valence manganese compound

    SciTech Connect

    Gao, Y.; Frost-Jensen, A.; Pressprich, M.R. [State Univ. of New York, Buffalo, NY (United States)] [and others

    1992-11-04

    The tunability of synchrotron radiation makes it possible to vary the scattering power of atoms of specific elements in the vicinity of the atomic absorption edges. The effect is due to the contribution of low-lying electronically excited states to the X-ray scattering process, which is accounted for in the second Born approximation of X-ray scattering theory. The variation of the anomalous components of the atomic scattering, f{prime} and f{double_prime}, may be used to create a contrast between multiwavelength results that can be applied in the determination of atomic site occupancy. In addition, the variation shows a chemical shift which is about 2.5 eV for each increase in unit of formal valency of vanadium, and about 5 eV for Fe in Fe{sup II}(NH{sub 4}){sub 2}(SO{sub 4}){sub 2}{center_dot}6H{sub 2}O relative to Fe{sup III}(NO{sub 3}){sub 3}. This difference can be used to obtain direct information on the electronic environment of specific atoms, as shown in powder diffraction studies of mixed-valence solids by Attfield (Eu{sub 3}O{sub 4}), by Wilkinson, Cheetham, and Cox (GaCl{sub 2}), and in our work on NbSe{sub 3}. We report here on a first application to a mixed-valence molecular crystal, in which f{prime} is determined from the refinement of a set of selected reflection data collected at eight wavelengths on both sides of the absorption edge. 9 refs., 3 figs., 2 tabs.

  15. Charge Transfer and Bonding in Endohedral Fullerenes from High-Energy Spectroscopy

    Microsoft Academic Search

    Mark S. Golden; Thomas Pichler; Petra Rudolf

    2004-01-01

    This contribution deals with the investigation of charge transfer and bonding in endohedral fullerenes in the solid state using high-energy spectroscopies such as photoemission and x-ray absorption. An overview is given of the detailed and direct information that can be won as regards the valence state of the encapsulated species, the degree of hybridisation between the electronic states of the

  16. 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)

  17. Valence state of Ti in conductive nanowires in sapphire

    NASA Astrophysics Data System (ADS)

    Mizoguchi, Teruyasu; Sakurai, Masaki; Nakamura, Atsutomo; Matsunaga, Katsuyuki; Tanaka, Isao; Yamamoto, Takahisa; Ikuhara, Yuichi

    2004-10-01

    In order to reveal the valence state of Ti in conductive nanowires in sapphire, near-edge x-ray-absorption fine structures (NEXAFS) were observed. From experimental and theoretical studies on NEXAFS of reference compounds including rutile, anatase, and Ti2O3 , it was found that the valence state of Ti can be identified by regarding the positions of the spectral onset and the shoulder in the main peak of Ti-K NEXAFS. The valence states of Ti doped Al2O3 polycrystalline specimens which were annealed at oxidized and reduced atmospheres were determined to be +4 and +3 , respectively. The solubility limit of Ti in Al2O3 polycrystal was found to be between 1000ppm to 1.0% at the both atmospheres. The spectrum from Ti nanowires in sapphire has a lot of similarities to the reduced specimen, the valence state was therefore concluded to be +3 .

  18. Investing in Bonds.com

    NSDL National Science Digital Library

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

  19. Photoemission study of valence fluctuation in YbCu2

    Microsoft Academic Search

    A. Fujimori; T. Shimizu; H. Yasuoka

    1987-01-01

    Mixed-valence YbCu2 has been studied by x-ray and ultraviolet photoemission spectroscopy (XPS and UPS). UPS results reveal a bulk divalent (4f14-->4f13) peak ~0.3 eV below the Fermi level, and a valence of 2.2 is deduced from XPS. These values are compared with the ground-state magnetic susceptibility, the specific heat, and the magnetic relaxation rate of 4f electrons by using the

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

    NASA Technical Reports Server (NTRS)

    Abdel-Raouf, Mohamed Assad

    1990-01-01

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

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

    PubMed Central

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

    2008-01-01

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

  2. Semiempirical modeling free energy surfaces for proton transfer in polar aprotic solvents

    Microsoft Academic Search

    M. V. Vener; I. V. Rostov; A. V. Soudackov; M. V. Basilevsky

    2000-01-01

    A method of calculation of a free-energy surface (FES) of the proton transfer (PT) reaction in a polar aprotic solvent is developed. This is based on the two-state (valence bond) VB description of the solute combined with recent continuum medium models. Its essential new feature is an explicit quantum-chemical treatment of VB wave functions, including internal electronic structure of a

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

    PubMed Central

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

    2012-01-01

    Previous research suggests that neural and behavioral responses to surprised faces are modulated by explicit contexts (e.g., “He just found $500”). Here, we examined the effect of implicit contexts (i.e., valence of other frequently presented faces) on both valence ratings and ability to detect surprised faces (i.e., the infrequent target). In Experiment 1, we demonstrate that participants interpret surprised faces more positively when they are presented within a context of happy faces, as compared to a context of angry faces. In Experiments 2 and 3, we used the oddball paradigm to evaluate the effects of clearly valenced facial expressions (i.e., happy and angry) on default valence interpretations of surprised faces. We offer evidence that the default interpretation of surprise is negative, as participants were faster to detect surprised faces when presented within a happy context (Exp. 2). Finally, we kept the valence of the contexts constant (i.e., surprised faces) and showed that participants were faster to detect happy than angry faces (Exp. 3). Together, these experiments demonstrate the utility of the oddball paradigm to serve as an implicit context to resolve the valence ambiguity of surprised facial expressions, but that this implicit context does not completely override the default negativity. PMID:21707167

  4. Pressure-Induced Intermetallic Valence Transition in BiNiO3

    NASA Astrophysics Data System (ADS)

    Azuma, Masaki; Tsujimoto, Masahiko; Ishiwata, Shintaro; Isoda, Seiji; Shimakawa, Yuichi; Takano, Mikio; Carlsson, Sandra; Rodgers, Jennifer; Attfield, J. Paul; Tucker, Matthew G.

    2008-03-01

    The valence state change of BiNiO3 perovskite under pressure has been investigated by a powder neutron diffraction study and electronic state calculations. At ambient pressure, BiNiO3 has the unusual charge distribution Bi^3+0.5Bi^5+0.5Ni^2+O3 with ordering of Bi^3+ and Bi^5+ charges on the A sites of a highly distorted perovskite structure. High pressure neutron diffraction measurements and Bond valence sum calculations show that the pressure-induced melting of the charge disproportionated state leads to a simultaneous charge transfer from Ni to Bi, so that the high pressure phase is metallic Bi^3+Ni^3+O3. This unprecedented charge transfer between A and B site cations coupled to electronic instabilities at both sites leads to a variety of ground states, and it is predicted that a Ni-charge disproportionated state should also be observable. [1] M. Azuma et al., J. Am. Chem. Soc., 129, (2007) 14433.

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

    PubMed Central

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

    2013-01-01

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

  6. Valence-bond states in dynamical Jahn-Teller molecular systems

    Microsoft Academic Search

    Giuseppe Santoro; Leonardo Guidoni; Alberto Parola; Erio Tosatti

    1997-01-01

    We discuss a hopping model of electrons between idealized molecular sites with a local orbital degeneracy and a dynamical Jahn-Teller effect, for crystal field environments of sufficiently high symmetry. For the Mott-insulating case (one electron per site and large Coulomb repulsions), in the simplest twofold degenerate situation, we are led to consider a particular exchange Hamiltonian, describing two isotropic spin-1\\/2

  7. Valence-bond study of the /H2, D2/ exchange reaction mechanism.

    NASA Technical Reports Server (NTRS)

    Freihaut, B.; Raff, L. M.

    1973-01-01

    The exchange reaction of H2 with D2 to form 2 HD is important in that it is fundamentally the simplest four-body exchange reaction and should therefore represent a model system on which various theories of reactions dynamics might be tested. A number of theoretical and experimental investigations carried out on this system are reviewed. It is concluded that a Y yields T yields Y mechanism for the (H2, D2) exchange is not a low energy pathway that would make theory compatible with the shock-tube experiments of Bauer and Ossa (1966) and of Burcat and Lifshits (1967).

  8. Running head: Enhanced sensitivity to negative word valence Murder, she wrote: Enhanced sensitivity to negative word valence

    E-print Network

    Carrasco, Marisa

    1 Running head: Enhanced sensitivity to negative word valence Murder, she wrote: Enhanced the hypothesis that negative stimuli enjoy preferential access to perceptual processing. #12;3 Murder, she wrote

  9. LET'S BOND! A Chemical Bonding Webquest

    NSDL National Science Digital Library

    Mrs. Hicken

    2009-04-08

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

  10. X-ray, ultraviolet, and synchrotron radiation excited inner-valence photoelectron spectra of CH4

    NASA Astrophysics Data System (ADS)

    Göthe, M. Carlsson; Wannberg, B.; Karlsson, L.; Svensson, S.; Baltzer, P.; Chau, F. T.; Adam, M.-Y.

    1991-02-01

    The inner-valence electron states of the methane molecule have been studied by means of x-ray, synchrotron radiation, and UV-photoelectron spectroscopy. Five correlation satellites have been identified and a detailed study has been carried out of the 2a-11 single hole state. For this state a Franck-Condon analysis has been performed, suggesting an equilibrium bond distance of 1.279 Å. The vibrational lines have a Lorentzian shape and the linewidth increases gradually with the vibrational quantum number. This probably indicates a reduction of the lifetime of the vibrational states due to predissociation. A discussion of the potential curves related to the correlation satellites is included.

  11. Probing valence and spin situations in selective ruthenium–iminoquinonoid frameworks. An experimental and DFT analysis

    Microsoft Academic Search

    Hemlata Agarwala; Dipanwita Das; Shaikh M. Mobin; Tapan Kumar Mondal; Goutam Kumar Lahiri

    2011-01-01

    The ruthenium–iminoquinone complexes, [Ru(tpm)(Cl)(Q)]+ [tpm=tris(1-pyrazolyl)methane, Q=3,5-di-tert-butyl-N-aryl-1,2-benzoquinonemonoimine, where aryl=C6H5, [1]+; m-(OCH3)2C6H3, [2]+; m-(Cl)2C6H3, [3]+] have been synthesized. The sensitive bond distances of “Q” in [1](ClO4) and [2](ClO4), C–O: 1.294(8), 1.281(2)Å; C–N: 1.352(8), 1.335(2)Å; and C–C(meta): 1.366(10)\\/1.367(9)Å, 1.364(2)\\/1.353(2)Å, respectively, and other analytical as well as theoretical (DFT) events suggest the valence configuration of [RuIII(tpm)(Cl)(QSq?)]+ for [1]+–[3]+. The paramagnetic [1]+–[3]+ show sharp 1H

  12. Quantum-chemical investigation of structure and valence isomerizations of perdehydrotetrasilacyclobutadiene

    SciTech Connect

    Glukhovtsev, M.N.; Simkin, B.Ya.; Minkin, V.I.; Kirienkova, T.V.

    1988-01-01

    The structure and valence isomerizations of perdehydrotetrasilacyclobutadiene (Si/sub 4/) are discussed on the basis of concepts of cyclic ..pi..- and sigma-conjugation. Calculations by the MINDO/3 and MNDO methods established two types of geometric configurations with D/sub 4h/ symmetry for both the singlet and triplet states of perdehydrotetrasilacyclobutadiene, differing in inversion of the HOMO and LUMO. Neither D/sub 4h/ configuration of the singlet state corresponds to minima on the potential energy surface, and these configurations are distorted, one toward a rectangular structure with D/sub 2h/ symmetry with alternation of bond lengths in the ring, and the other toward a rhombic bicyclic structure with D/sub 2h/ symmetry. The latter structure corresponds to the global minimum on the potential energy surface of the Si/sub 4/.

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

    PubMed

    McCabe, Patrick; Korb, Oliver; Cole, Jason

    2014-05-27

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

  14. Model of electron-proton correlation in quasi-one-dimensional halogen-bridged mixed-valence complexes: Role of proton motion

    NASA Astrophysics Data System (ADS)

    Matsushita, Eiko

    1995-06-01

    The role of interchain hydrogen (H) bonds in one-dimensional electron systems is studied in halogen-bridged mixed-valence transition-metal complexes. A cluster theory is developed to predict the proton-induced ordering among charge-density-wave (CDW) chains in terms of pseudospin formalism for proton motion on H bonds. It is pointed out that the electron-proton coupling can control the CDW state which is produced from the competition between electron-electron and electron-phonon coupling.

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

    NASA Astrophysics Data System (ADS)

    Yuan, Jian-Min

    2001-10-01

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

  16. Channel Bonding Notes 03/25/2004 Channel Bonding Notes

    E-print Network

    Jain, Amit

    Channel Bonding Notes 03/25/2004 Channel Bonding Notes Luke Hindman Department of Computer Science by attempting to use the Linux kernel bonding driver (bonding.o) to implement channel bonding on the master node. However, each time I would bring up the bonded interface (bond0) I would loose communication

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  18. Supplement To: OHO Hydrogen Bond Geometries and NMR Chemical Shifts: From Equilibrium Structures to Geometric H\\/D Isotope Effects, with Applications for Water, Protonated Water, and Compressed Ice

    Microsoft Academic Search

    Hans-Heinrich Limbach; Peter M. Tolstoy; Natalia Pérez-Hernández; Jing Guo; Ilya G. Shenderovich; Gleb S. Denisov

    2009-01-01

    Hydrogen bond geometries and 1 H NMR chemical shifts of OHO hy- drogen-bonded systems have been analyzed using an improved valence bond order model. This model predicts that the heavy atom hydrogen bond coordinateq2?=?r1 + r2 is a function of the proton coordinate q1 = ½(r1 - r2), where r1 and r2 represent the OH and the HO distances. In

  19. THM growth of (Cd, Mn)Te single crystal with the source ingot synthesized by VB method

    NASA Astrophysics Data System (ADS)

    Liang, Wei; Qin, Kaifeng; Zhang, Jijun; Meng, Hua; Wu, Wenqi; Liang, Xiaoyan; Min, Jiahua; Wang, Linjun

    2015-06-01

    The (Cd0.9, Mn0.1)Te crystal was grown by the Traveling Heater method (THM) from the indium-doped source ingot (Cd0.9, Mn0.1)Te which had been synthesized by the Vertical Bridgman (VB) method. The indium-doped (Cd0.9, Mn0.1)Te single crystal with the diameter of 31 mm and length of 130 mm was obtained. The variation of the Mn content was about ±1% along the length of (Cd, Mn)Te: In ingot, and the concentration of Te inclusions in the crystal was ~104 cm-3 with the average diameter of 8-12 ?m. Te solvent showed purifying effects during the THM crystal growth, and the indium dopant distributed along the crystal with the concentration of 6.8-10 ppm. IR transmittance and PL spectrum measurements revealed that the as-grown (Cd, Mn)Te crystal possessed high crystalline quality, and its resistivity was up to 6.2×109 ? cm. Under the 59.5 keV 241Am irradiation, the planar (Cd, Mn)Te detector showed an energy resolution of 12.7%.

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

    SciTech Connect

    Pitzer, Kenneth S.; Christiansen, Phillip A.

    1980-11-20

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

  1. 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%. Copyright © 2014 John Wiley & Sons, Ltd. PMID:25355709

  2. Essays on corporate bonds

    E-print Network

    Bao, Jack (Jack C.)

    2009-01-01

    This thesis consists of three empirical essays on corporate bonds, examining the role of both credit risk and liquidity. In the first chapter, I test the ability of structural models of default to price corporate bonds in ...

  3. 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. PMID:23368375

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

    PubMed

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

    2015-07-01

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

  5. Cobalt lawsone complexes: searching for new valence tautomers.

    PubMed

    Ribeiro, Marcos A; Lanznaster, Maurício; Silva, Marcos M P; Resende, Jackson A L C; Pinheiro, Maurício V B; Krambrock, Klaus; Stumpf, Humberto O; Pinheiro, Carlos B

    2013-04-21

    Bi-stable molecular systems presenting valence tautomerism are associated with the development of new functional materials, which can be used for applications in organic electric conductors, optoelectronic and molecular magnetic devices. The properties of these materials can be adjusted with slight chemical changes and can be induced by external stimuli. Typical examples of valence tautomer compounds are coordination complexes of Co and o-dioxolene ligands, notably quinone like ones. In the search for a new class of cobalt complexes presenting valence tautomerism we report herein the synthesis and characterization of five new coordination compounds of cobalt and 2-hydroxy-1,4-naphthoquinone (lawsone or shortly Law). Complexes [Co(Law)2(im)2]·C6H5CH3 (1), [Co(Law)2(py)2]·CH3OH (2), [Co(Law)2(phen)]·(C4H8O)2 (3), [Co(Law)2(2,2-bpy)]·C6H5CH3 (4) and [Co(Law)2(2,2-bpy)] (5) were synthesized and fully characterized by X-ray diffraction and EPR techniques in a wide range of temperatures and under illumination. Despite presenting similar molecular and geometry packing of the valence tautomer complexes of cobalt and o-dioxolenes, neither structural nor electronic evidence of valence tautomerism could be found in the Co and lawsone complexes. PMID:23423385

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  7. Bonding effects on the slip differences in the b1 monocarbides.

    PubMed

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

    2015-04-24

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

  8. 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.

  9. Bonding silicones with epoxies

    SciTech Connect

    Tira, J.S.

    1980-01-01

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

  10. Allosteric Disulfide Bonds

    Microsoft Academic Search

    Jason W. H. Wong; Philip J. Hogg

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

  11. 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.

  12. The kinetic energy change on covalent bond formation

    PubMed Central

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

    1981-01-01

    Stimulated by an analysis of the classical molecular orbital and valence bond descriptions of the two-electron normal covalent bond (both faulty), the argument is made that there exist good representations of the kinetic energy change ?T, on nonpolar covalent bond formation in a diatomic molecule, of the form ?T(R) = ?F(R - r?)S(r?)dr?. Here F is a nonlinear response function which itself involves the overlap S. The kinetic change is known to satisfy the sum rule ?0??T(R)dR = Z?Z? exactly; it is shown how this can be built into the treatment by the use of Fourier transform methods. Also considered is ?0??T(R)R2dR, which is an important additional property of the kinetic energy change. Representation of ?T(R) as a Morse function, already known to be highly accurate, is shown to exactly conform to the proposed form. PMID:16593098

  13. Making and Breaking Bonds

    NSDL National Science Digital Library

    The Concord Consortium

    2011-12-11

    Atoms collide and, under certain circumstances, react to form bonds with one another. The process of association is the bonding of atoms into a molecule while dissociation is the process by which a molecule breaks apart into simpler groups of atoms, individual atoms, or ions. Students interact with a molecular dynamics model to explore the making and breaking of bonds.

  14. 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.

  15. 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].

  16. Bonding thermoplastic polymers

    DOEpatents

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

    2008-06-24

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

  17. Prospective bonding applications

    NASA Astrophysics Data System (ADS)

    Ancenay, H.; Benazet, D.

    1981-07-01

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

  18. 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

  19. The pion parton distribution function in the valence region

    E-print Network

    K. Wijesooriya; P. E. Reimer; R. J. Holt

    2005-09-08

    The parton distribution function of the pion in the valence region is extracted in a next-to-leading order analysis from Fermilab E-615 pionic Drell-Yan data. The effects of the parameterization of the pion's valence distributions are examined. Modern nucleon parton distributions and nuclear corrections were used and possible effects from higher twist contributions were considered in the analysis. In the next-to-leading order analysis, the high-$x$ dependence of the pion structure function differs from that of the leading order analysis, but not enough to agree with the expectations of pQCD and Dyson-Schwinger calculations.

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

    SciTech Connect

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

    2005-12-15

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

    We have studied EuPtP, which undergoes two successive valence transitions at TA˜240 K and TB˜200 K by 31P-nuclear magnetic resonance (NMR) measurements. From the analysis of NMR spectra, we obtained plausible ordered structures and Eu valence states in three phases divided by TA and TB. These ordered structures well explain observed inequivalent P sites and the intensity ratio of the NMR spectra arising from these P sites. The results are also in good accordance with mean Eu valence measured by the x-ray absorption spectroscopy. We also discuss Eu 4 f states and the origin of the transitions from the measurements of nuclear spin lattice relaxation rate and hyperfine coupling constant.

  2. 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.

  3. Valence topological charge-transfer indices for dipole moments

    Microsoft Academic Search

    Francisco Torrens

    2003-01-01

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

  4. Cortisol and Memory Retrieval in Humans: Influence of Emotional Valence

    Microsoft Academic Search

    O. T. WOLF; S. KUHLMANN; C. BUSS; D. H. HELLHAMMER; C. KIRSCHBAUMc

    2004-01-01

    Glucocorticoids secreted in response to stress modulate memory in animals and humans. Studies in rodents suggest that glucocorticoids enhance memory consolidation but impair delayed retrieval. Similar negative effects on memory retrieval have been reported in humans. The human studies so far have not addressed the issue of emotional valence, which conceivably could modulate the effects of cortisol on retrieval. The

  5. Semantic Category Effect and Emotional Valence in Female University Students

    ERIC Educational Resources Information Center

    Brousseau, Geri; Buchanan, Lori

    2004-01-01

    The semantic category effect represents a category dissociation between biological and nonbiological objects in picture naming. The aim of this preliminary study was to further examine this phenomenon, and to explore the possible association between the effect and subjective emotional valence for the named objects. Using a speeded picture naming…

  6. Valence orbital momentum distributions in s-triazine

    SciTech Connect

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

    1985-06-15

    Valence orbital momentum distributions, rho(q), are obtained for s-triazine, C/sub 3/H/sub 3/N/sub 3/, from (e,2e) spectroscopy and split valence SCFMO calculations. The separation energy spectrum simulated using the calculated rho(q) and ionization energies from Green's function calculations is in good agreement with experiment from 9--20 eV, but at higher energy the simulated spectrum has higher intensity than experiment, indicating that the Green's function calculation underestimates the complexity of the inner valence region. The calculated momentum distributions have their maxima at higher values than observed experimentally for the outermost valence orbitals, but the difference in momentum distributions between the antisymmetric 4e' N2p lone pair orbital of s-triazine and the N2p lone pair orbital of ammonia is reproduced well by the calculations. Similarly, calculated and experimental differences of Fourier transformed rho(q) for the 4e' and 3a/sup prime//sub 1/ N2p lone pair orbitals of triazine are in agreement and can be interpreted using plots of 4e' and 3a/sup //sub 1/ orbital averages and differences from the SCFMO calculations. The Fourier transformed momentum distribution of the 4e' orbital clearly shows the presence of both nearest-neighbor C and second-nearest-neighbor N interactions.

  7. Valence state at the surface of rare-earth metals

    Microsoft Academic Search

    Börje Johansson

    1979-01-01

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

  8. 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. PMID:25279648

  9. 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…

  10. Non-linear valence electron dynamics in metallic clusters

    Microsoft Academic Search

    F. Calvayrac

    1998-01-01

    This work deals with the response of the valence electrons of simple metal clusters to various excitations, in a purely dynamical context. It is related to various recent experiments where the methods based on linear response fail. The electronic motion is solved in direct time, the wavefunctions being discretized on an evenly spaced grid. The theoretical framework is the time

  11. Valence Fluctuations and Coherence in Cerium Based Compounds

    Microsoft Academic Search

    Yang-Yuan Chen

    1987-01-01

    At the beginning of this thesis the phenomena of valence fluctuations and coherence are described. Fair agreement between experimental observation and theories exists for the Kondo ion case, but a lack of theory about coherence hampers comparison to existing experiments. In this thesis experimental results are first checked by Kondo theory in the Kondo ion regime (high T). Anomalies observed

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

    E-print Network

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

    2014-08-27

    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 non-specific 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.

  13. Opposing influences of affective state valence on visual cortical encoding.

    PubMed

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

    2009-06-01

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

  14. 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…

  15. Real-time observation of valence electron motion.

    SciTech Connect

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

    2010-08-05

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

  16. 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…

  17. 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…

  18. 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}.

  19. Bonded semiconductor substrate

    DOEpatents

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

    2010-07-13

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

  20. Semiconductor Wafer Bonding

    Microsoft Academic Search

    U. Gosele; Q.-Y. Tong

    1998-01-01

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

  1. Energy pulse bonding

    NASA Technical Reports Server (NTRS)

    Smith, G. C.

    1972-01-01

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

  2. 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.

  3. 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.

  4. X-ray emission spectroscopy to study ligand valence orbitals in Mn coordination complexes

    PubMed Central

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

    2009-01-01

    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 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. PMID:19663435

  5. One Bond Strategy

    NSDL National Science Digital Library

    2001-01-01

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

  6. Hydrogen bonding and anaesthesia

    NASA Astrophysics Data System (ADS)

    Sándorfy, C.

    2004-12-01

    General anaesthetics act by perturbing intermolecular associations without breaking or forming covalent bonds. These associations might be due to a variety of van der Waals interactions or hydrogen bonding. Neurotransmitters all contain OH or NH groups, which are prone to form hydrogen bonds with those of the neurotransmitter receptors. These could be perturbed by anaesthetics. Aromatic rings in amino acids can act as weak hydrogen bond acceptors. On the other hand the acidic hydrogen in halothane type anaesthetics are weak proton donors. These two facts together lead to a probable mechanism of action for all general anaesthetics.

  7. Mapping the Valence States of Transition-Metal Elements Using Energy-Filtered Transmission Electron Microscopy

    E-print Network

    Wang, Zhong L.

    The properties of transition-metal oxides are related to the presence of elements with mixed valences, such as MnMapping the Valence States of Transition-Metal Elements Using Energy-Filtered Transmission Electron and Co. Spatial mapping of the valence-state distribution of transition-metal elements is a challenge

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

    ERIC Educational Resources Information Center

    Schepman, Astrid; Rodway, Paul; Geddes, Pauline

    2012-01-01

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

  9. Chemical Bonding, again ionic bonding (in salts): transfer of e-

    E-print Network

    Zakarian, Armen

    Chemical Bonding, again · ionic bonding (in salts): transfer of e- · covalent bonding (organic molecules, non-metals): sharing e- · metallic bonding: electron pooling (delocalization) Lewis electron 3A 4A 5A 6A 7A 8A 2 3 (exceptions) #12;Ionic Bonding Model See sample problem 9.1 4Na + O2 ! 2Na2O

  10. 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)

  11. 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…

  12. Convertible Bonds as \\

    Microsoft Academic Search

    Jeremy C. Stein

    1992-01-01

    This paper argues that corporations may use convertible bonds as an indirect (albeit possibly risky) method for getting equity into their capital structures in situations where adverse selection problems make a conventional stock issue unattractive. Unlike other theories of convertible bond issuance, the model of this paper highlights: 1) the importance of call provisions on convertibles; and 2) the significance

  13. PBGA wire bonding development

    Microsoft Academic Search

    W. K. Shu

    1996-01-01

    In a PBGA package, the existence of a glass transition temperature of 170~215°C for PCB substrate puts an upper ceiling to the usable wire bond temperature. The low thermal conductivity of PCB substrate and the need for a thicker material make fine pad pitch wire bonding even more difficult to do. To compensate for the limitation in thermal energy, high

  14. Ultrasonically bonded value assembly

    NASA Technical Reports Server (NTRS)

    Salvinski, R. J. (inventor)

    1975-01-01

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

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

    PubMed

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

    2012-01-01

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

  16. Emotional valence differentially affects encoding and retrieval of prospective memory in older adults.

    PubMed

    Ballhausen, Nicola; Rendell, Peter G; Henry, Julie D; Joeffry, Sebastian; Kliegel, Matthias

    2015-09-01

    Studies manipulating emotional valence in prospective memory (PM) have so far revealed inconsistent results. In the present study, two experiments were conducted to systematically disentangle the effects of varying emotional valence in the encoding versus retrieval phase of PM in older adults. Results showed that, while cue valence at retrieval had no influence on PM performance, at encoding both positive and negative valence resulted in reduced PM performance. Findings suggest that emotional valence may have an influence on mnemonic processes at encoding rather than modifying cue detection in aging. PMID:25633458

  17. Results from overlap valence quarks on a twisted mass sea

    E-print Network

    Nicolas Garron; Luigi Scorzato

    2007-10-16

    We present results of lattice computations using overlap fermions on a twisted mass background. $N_f=2$ full QCD gauge configurations have been produced by the ETM Collaboration with very light pions (down to less than 300 MeV), with small lattice spacing ($a \\approx 0.09$ fm) and large volumes ($V/a^4=24^3\\times 48$). By profiting of the good chiral properties of the overlap operator for the valence quarks, it is also possible to have a precise (and unquenched) determination of those physical quantities where the chiral properties are crucial. In order to have unquenched results, we match the valence quark mass with the sea quark mass. We also perform computations with different quark masses in order to simulate (partially quenched) Strange and Charm quarks. A typical application is the computation of $B_K$, for which we present first results.

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  19. Excited-State Mixed Valence in Transition Metal Complexes

    Microsoft Academic Search

    Edward A. Plummer; Jeffrey I. Zink

    2006-01-01

    Mixed valence in the lowest-energy metal-to-ligand charge-transfer excited state of di-(4-acetylpyridine)tetraammineruthenium(II) com- plexes is defined and analyzed. The excited state has two interchangeably equivalent ligands with different oxidation states. The electronic absorption band energies, selection rules, and bandwidths are analyzed quantitatively in terms of the signs and orientations of the transition dipole moments, sign and magnitude of the coupling, and

  20. Valence-band photoemission and optical absorption in nickel compounds

    Microsoft Academic Search

    Atsushi Fujimori; Fujio Minami

    1984-01-01

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

  1. Self-consistent perturbation theory for dynamics of valence fluctuations

    Microsoft Academic Search

    Y. Kuramoto

    1983-01-01

    A perturbation-theoretic scheme is developed for dynamics of valence fluctuations in rare-earth systems with unstable 4f shells. The theory is formulated in close analogy to the standard Green-function method for many-body systems but without use of the linked-cluster theorem. This formulation regards hybridization between 4f and conduction-band states as perturbation and naturally incorporates the strong on-site 4f-electron correlation. Some favorable

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

    Microsoft Academic Search

    E. S. Clementyev; A. V. Mirmelstein

    2009-01-01

    On the basis of the concepts of an intermediate-valence (IV) regime, an analysis is carried out of macroscopic properties\\u000a of the ? and ? phases of plutonium, as well as of several model systems based on rare earth elements. Within a single-site\\u000a approximation (SSA), the characteristic Kondo interaction energy, the f-electron shell occupation number, the effective degeneracy of the ground-state

  3. Theory of Valence-Fluctuating Tm Impurities. I

    Microsoft Academic Search

    Tetsuro Saso

    1989-01-01

    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

  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. PMID:18855802

  5. Magnetic-field Manipulation of Chemical Bonding in Artificial Molecules

    E-print Network

    Constantine Yannouleas; Uzi Landman

    2001-09-10

    The effect of orbital magnetism on the chemical bonding of lateral, two-dimensional artificial molecules is studied in the case of a 2e double quantum dot (artificial molecular hydrogen). It is found that a perpendicular magnetic field reduces the coupling (tunneling) between the individual dots and, for sufficiently high values, it leads to complete dissociation of the artificial molecule. The method used is building on Lowdin's work on Projection Operators in Quantum Chemistry; it is a spin-and-space unrestricted Hartree-Fock method in conjunction with the companion step of the restoration of spin and space symmetries via Projection Techniques (when such symmetries are broken). This method is able to describe the full range of couplings in two-dimensional double quantum dots, from the strong-coupling regime exhibiting delocalized molecular orbitals to the weak-coupling and dissociation regimes associated with a Generalized Valence Bond combination of atomic-type orbitals localized on the individual dots.

  6. Metal to metal multiple bonds in ordered assemblies

    PubMed Central

    Chisholm, Malcolm H.

    2007-01-01

    The synthesis and properties of metal–metal (MM) quadruply bonded compounds of molybdenum and tungsten in liquid crystalline phases are described. Covalently linked MM quadruply bonded complexes, dimers of dimers, are shown to give rise to mixed valence complexes upon oxidation and the degree of electron delocalization is shown to be correlated with the M2? bridge ? interactions. Class III behavior or complete delocalization is observed to M2 to M2 distances of up to 14 ?. When the M2 unit is attached to oligothiophenes via a carboxylate tether, the photophysical properties of the thienyl units are greatly modified due to M2?–thienyl ? conjugation and spin–orbit coupling. This leads to long-lived emissive states and electroluminescence in solid-state devices. PMID:17299047

  7. SiO and GeO bonded interactions as inferred from the bond critical point properties of electron density distributions

    NASA Astrophysics Data System (ADS)

    Gibbs, G. V.; Boisen, M. B.; Hill, F. C.; Tamada, O.; Downs, R. T.

    The topological properties of the electron density distributions for more than 20 hydroxyacid, geometry optimized molecules with SiO and GeO bonds with 3-, 4-, 6- and 8-coordinate Si and Ge cations were calculated. Electronegativities calculated with the bond critical point (bcp) properties of the distributions indicate, for a given coordination number, that the electronegativity of Ge ( 1.85) is slightly larger than that of Si ( 1.80) with the electronegativities of both atoms increasing with decreasing bond length. With an increase in the electron density, the curvatures and the Laplacian of the electron density at the critical point of each bond increase with decreasing bond length. The covalent character of the bonds are assessed, using bond critical point properties and electronegativity values calculated from the electron density distributions. A mapping of the (3, -3) critical points of the valence shell concentrations of the oxide anions for bridging SiOSi and GeOGe dimers reveals a location and disposition of localized nonbonding electron pairs that is consistent with the bridging angles observed for silicates and germanates. The bcp properties of electron density distributions of the SiO bonds calculated for representative molecular models of the coesite structure agree with average values obtained in X-ray diffraction studies of coesite and danburite to within 5%.

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

    SciTech Connect

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

    2009-07-15

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

  9. Coupled-cluster calculations for valence systems around O-16

    E-print Network

    J. R. Gour; P. Piecuch; M. Hjorth-Jensen; M. Wloch; D. J. Dean

    2005-07-21

    We study the ground and low-lying excited states of O-15, O-17, N-15, and F-17 using modern two-body nucleon-nucleon interactions and the suitably designed variants of the ab initio equation-of-motion coupled-cluster theory aimed at an accurate description of systems with valence particles and holes. A number of properties of O-15, O-17, N-15, and F-17, including ways the energies of ground and excited states of valence systems around O-16 change as functions of the number of nucleons, are correctly reproduced by the equation-of-motion coupled-cluster calculations. Within a harmonic oscillator basis and large effective model spaces, our results are converged for the chosen two-body Hamiltonians. Thus, all disagreements with experiment are, most likely, due to the degrees of freedom such as three-body interactions not accounted for in our effective two-body Hamiltonians. In particular, the calculated binding energies of O-15/N-15 and O-17/F-17 enable us to rationalize the discrepancy between the experimental and recently published [Phys. Rev. Lett. 94, 212501 (2005)] equation-of-motion coupled-cluster excitation energies for the Jpi=3- state of O-16. The results demonstrate the feasibility of the equation-of-motion coupled-cluster methods to deal with valence systems around closed-shell nuclei and to provide precise results for systems beyond A=16.

  10. Sketching the pion's valence-quark generalised parton distribution

    DOE PAGESBeta

    Mezrag, C.; Chang, L.; Moutarde, H.; Roberts, C.D.; Rodríguez-Quintero, J.; Sabatié, F.; Schmidt, S.M.

    2015-02-01

    In order to learn effectively from measurements of generalised parton distributions (GPDs), it is desirable to compute them using a framework that can potentially connect empirical information with basic features of the Standard Model. We sketch an approach to such computations, based upon a rainbow-ladder (RL) truncation of QCD’s Dyson–Schwinger equations and exemplified via the pion’s valence dressed-quark GPD, Hv?(x, ?, t). Our analysis focuses primarily on ?=0, although we also capitalise on the symmetry-preserving nature of the RL truncation by connecting Hv?(x, ?=±1, t)with the pion’s valence-quark parton distribution amplitude. We explain that the impulse-approximation used hitherto to definemore »the pion’s valence dressed-quark GPD is generally invalid owing to omission of contributions from the gluons which bind dressed-quarks into the pion. A simple correction enables us to identify a practicable improvement to the approximation for Hv?(x, 0, t), expressed as the Radon transform of a single amplitude. Therewith we obtain results for Hv?(x, 0, t)and the associated impact-parameter dependent distribution, qv?(x, |#2;b?|), which provide a qualitatively sound picture of the pion’s dressed-quark structure at ahadronic scale. We evolve the distributions to a scale ?=2GeV, so as to facilitate comparisons in future with results from experiment or other nonperturbative methods.« less

  11. Coupled-cluster calculations for valence systems around O16

    NASA Astrophysics Data System (ADS)

    Gour, J. R.; Piecuch, P.; Hjorth-Jensen, M.; W?och, M.; Dean, D. J.

    2006-08-01

    We study the ground and low-lying excited states of O15, O17, N15, and F17 using modern two-body nucleon-nucleon interactions and the suitably designed variants of the ab initio equation-of-motion coupled-cluster theory aimed at an accurate description of systems with valence particles and holes. A number of properties of O15, O17, N15, and F17, including ways the energies of ground and excited states of valence systems around O16 change as functions of the number of nucleons, are correctly reproduced by the equation-of-motion coupled-cluster calculations performed in up to eight major-oscillator shells. Certain disagreements with experiment are in part because of the degrees of freedom such as three-body interactions not accounted for in our effective two-body Hamiltonians. In particular, the calculated binding energies of O15/N15 and O17/F17 enable us to rationalize the discrepancy between the experimental and recently published [Phys. Rev. Lett. 94, 212501 (2005)] equation-of-motion coupled-cluster excitation energies for the J?=3- state of O16. Our calculations demonstrate the feasibility of the equation-of-motion coupled-cluster methods to deal with valence systems around closed-shell nuclei and to provide results for systems beyond A=16.

  12. Basic features of the pion valence-quark distribution function

    NASA Astrophysics Data System (ADS)

    Chang, Lei; Mezrag, Cédric; Moutarde, Hervé; Roberts, Craig D.; Rodríguez-Quintero, Jose; Tandy, Peter C.

    2014-10-01

    The impulse-approximation expression used hitherto to define the pion's valence-quark distribution function is flawed because it omits contributions from the gluons which bind quarks into the pion. A corrected leading-order expression produces the model-independent result that quarks dressed via the rainbow-ladder truncation, or any practical analogue, carry all the pion's light-front momentum at a characteristic hadronic scale. Corrections to the leading contribution may be divided into two classes, responsible for shifting dressed-quark momentum into glue and sea-quarks. Working with available empirical information, we use an algebraic model to express the principal impact of both classes of corrections. This enables a realistic comparison with experiment that allows us to highlight the basic features of the pion's measurable valence-quark distribution, q?(x); namely, at a characteristic hadronic scale, q?(x)?(1 for x?0.85; and the valence-quarks carry approximately two-thirds of the pion's light-front momentum.

  13. Valency configuration of transition metal impurities in ZnO

    SciTech Connect

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

    2006-01-01

    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. Kissing bonds A kissing bond is adhesively bonded but holds little of the strength usually

    E-print Network

    Sóbester, András

    Kissing bonds · A kissing bond is adhesively bonded but holds little of the strength usually weight saving and excellent stress transfer. · The ability to reliably assess defects in adhesive bonds · To develop a non destructive method to assess the integrity of adhesive bonds using pulsed phase thermography

  15. Bonding Effect on F Kalpha Satellite Structure Produced by 84MeV N4+

    Microsoft Academic Search

    M. Uda; H. Endo; K. Maeda; Y. Awaya; M. Kobayashi; Y. Sasa; H. Kumagai; T. Tonuma

    1979-01-01

    The intensity distributions of F Kalpha satellites produced by 84-MeV N4+ bombardment displayed a significant chemical effect. The dependence of the intensity distributions of several fluorides on the chemical environment is discussed in relation to the Pauling bond ionicity or covalency. A refilling of vacancies by ligand valence electrons prior to the x-ray emission accounted for the observed satellite distributions

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

    NASA Astrophysics Data System (ADS)

    Hao, Liang-Huan; Jiang, Gang; Hou, Hai-Jun

    2010-02-01

    This paper reports on multiconfiguration Dirac-Hartree-Fock calculations for both allowed and intercombination transitions and fine structure referring to the levels of a term in highly charged aluminum like ions. Results for fine-structure energy levels, the term splitting, the wavelengths, transition rates, and thereby the branching ratios and lifetimes for the Al-like 3s23p-3s3p2 transitions in the ions Fe XIV-Au LXVII are reported and compared with other theories and experiments, using the codes GRASP2K. Our calculated fine-structure energy levels are in excellent agreement with the experimental results and the experimentally compiled energy values of the National Institute for Standards and Technology wherever available. The calculated values including core-valence correlation are found to be similar and to compare very well with other theoretical and experimental values for medium-Z ions. For higher Z the inclusion of the valence correlation gives results in excellent agreement with those from many-body perturbation theory. We believe that our extensive calculated values can guide experimentalists in identifying the fine-structure levels in their future work. From our radiative decay rates we have also calculated radiative lifetimes of some fine-structure levels. In this calculation we also predict new data for several fine-structure levels where no other theoretical and/or experimental results are available.

  17. Wafer-Level Thermocompression Bonds

    E-print Network

    Tsau, Christine H.

    Thermocompression bonding of gold is a promising technique for achieving low temperature, wafer-level bonding without the application of an electric field or complicated pre-bond cleaning procedure. The presence of a ductile ...

  18. Spin-polarized Auger electrons in core-valence-valence decays of 3d impurities in metals

    SciTech Connect

    Trioni, M. I. [ETSF and CNISM, UdR Milano Bicocca, via Cozzi 53, I-20125 Milano (Italy); Zanetti, A. [Dipartimento di Scienza dei Materiali, Universita di Milano-Bicocca, via Cozzi 53, I-20125 Milano (Italy); Fratesi, G.; Brivio, G. P. [ETSF and CNISM, UdR Milano Bicocca, via Cozzi 53, I-20125 Milano (Italy); Dipartimento di Scienza dei Materiali, Universita di Milano-Bicocca, via Cozzi 53, I-20125 Milano (Italy)

    2009-04-15

    The spin polarization of the emitted electrons from 3d impurities in simple metal hosts in a core-valence-valence Auger process is analyzed in terms of a first-principles density-functional theory approach, by using the golden rule. The relationship between the spin-dependent local density of states, the magnetic moments of the 3d atoms and the energy-dependent and total spin polarization of the Auger electrons is discussed. It is shown how to estimate the magnetic moment of the impurities from a measure of the total spin polarization of the Auger electrons. This can be achieved considering (i) that the Auger signal is simply due to the impurities only, (ii) the very locality of the Auger phenomenon, and (iii) a simple and general relationship between the spin polarization and the magnetic moment of the impurity which we show to be independent of the metal host.

  19. Icosahedron oligomerization and condensation in intermetallic compounds. Bonding and electronic requirements.

    PubMed

    Tillard-Charbonnel, M; Manteghetti, A; Belin, C

    2000-04-17

    Icosahedron-based clustering has been found to be very common in intermetallics, particularly for group 13 and early p-block icosogen elements. Linking of the icosahedral building blocks depends on the valence electron concentrations. Vertex-, edge-, or face-sharing icosahedra occur as the structure compensates for electron deficiency. Some examples of icosahedron-based clusters have been selected for an analysis of the relationships between the structural features (icosahedron oligomerization, atomic defects, etc.) and the bonding and electronic requirements. The extended Hückel method has been used with either a molecular approach or an electronic band structure calculation to rationalize bonding in the intermetallic framework. PMID:12526555

  20. Valence ionized states of iron pentacarbonyl and ?5-cyclopentadienyl cobalt dicarbonyl studied by symmetry-adapted cluster-configuration interaction calculation and collision-energy resolved Penning ionization electron spectroscopy

    Microsoft Academic Search

    Ryoichi Fukuda; Masahiro Ehara; Hiroshi Nakatsuji; Naoki Kishimoto; Koichi Ohno

    2010-01-01

    Valence ionized states of iron pentacarbonyl Fe(CO)5 and ?5-cyclopentadienyl cobalt dicarbonyl Co(?5-C5H5)(CO)2 have been studied by ultraviolet photoelectron spectroscopy, two-dimensional Penning ionization electron spectroscopy (2D-PIES), and symmetry-adapted cluster-configuration interaction calculations. Theory provided reliable assignments for the complex ionization spectra of these molecules, which have metal-carbonyl bonds. Theoretical ionization energies agreed well with experimental observations and the calculated wave functions could

  1. Gold Thermocompression Wafer Bonding

    E-print Network

    Spearing, S. Mark

    Thermocompression bonding of gold is a promising technique for the fabrication and packaging microelectronic and MEMS devices. The use of a gold interlayer and moderate temperatures and pressures results in a hermetic, ...

  2. Characterization of anodic bonding

    E-print Network

    Tudryn, Carissa Debra, 1978-

    2004-01-01

    Anodic bonding is a common process used in MicroElectroMechanical Systems (MEMS) device fabrication and packaging. Polycrystalline chemical vapor deposited (CVD) silicon carbide (SiC) is emerging as a new MEMS device and ...

  3. Hydrogen bonds animation

    NSDL National Science Digital Library

    Northland Community and Technical College Biology Department

    2007-12-12

    This color animation of water molecules interacting and forming hydrogen bonds is a hybrid between a PowerPoint slide show an an animation. Students can replay portions or click next if they do not need to replay a segment.

  4. 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)

  5. 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.

  6. Roof bolt bond tester

    SciTech Connect

    Not Available

    1982-01-01

    An intrinsically safe, electronic instrument has been developed that determines the holding quality of a fully grouted roof bolt by testing the integrity of the resin bond to both the bolt and to the surrounding rock.

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

    SciTech Connect

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

    2011-07-15

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

  8. All about Chemical Bonding

    NSDL National Science Digital Library

    Lower, Stephen

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

  9. 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.

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

    PubMed

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

    2011-06-01

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

  11. Water's Hydrogen Bond Strength

    E-print Network

    Martin Chaplin

    2007-06-10

    Water is necessary both for the evolution of life and its continuance. It possesses particular properties that cannot be found in other materials and that are required for life-giving processes. These properties are brought about by the hydrogen bonded environment particularly evident in liquid water. Each liquid water molecule is involved in about four hydrogen bonds with strengths considerably less than covalent bonds but considerably greater than the natural thermal energy. These hydrogen bonds are roughly tetrahedrally arranged such that when strongly formed the local clustering expands, decreasing the density. Such low density structuring naturally occurs at low and supercooled temperatures and gives rise to many physical and chemical properties that evidence the particular uniqueness of liquid water. If aqueous hydrogen bonds were actually somewhat stronger then water would behave similar to a glass, whereas if they were weaker then water would be a gas and only exist as a liquid at sub-zero temperatures. The overall conclusion of this investigation is that water's hydrogen bond strength is poised centrally within a narrow window of its suitability for life.

  12. 30 CFR 581.33 - Bonds and bonding requirements.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ...Resources 2 2013-07-01 2013-07-01 false Bonds and bonding requirements. 581.33 Section 581.33 Mineral Resources...CONTINENTAL SHELF Financial Considerations § 581.33 Bonds and bonding requirements. (a) When the leasing notice...

  13. Fair Scheduling on Parallel Bonded Channels with Intersecting Bonding Groups

    E-print Network

    Martin, Jim

    Fair Scheduling on Parallel Bonded Channels with Intersecting Bonding Groups Gongbing Hong, James for providing weighted sharing of aggregate capacity in networks having parallel bonded channels in which a single channel may simultaneously be a member of multiple bonding groups. Our work is motivated

  14. 30 CFR 281.33 - Bonds and bonding requirements.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ...Resources 2 2011-07-01 2011-07-01 false Bonds and bonding requirements. 281.33 Section 281.33 Mineral Resources...CONTINENTAL SHELF Financial Considerations § 281.33 Bonds and bonding requirements. (a) When the leasing notice...

  15. 30 CFR 581.33 - Bonds and bonding requirements.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ...Resources 2 2014-07-01 2014-07-01 false Bonds and bonding requirements. 581.33 Section 581.33 Mineral Resources...CONTINENTAL SHELF Financial Considerations § 581.33 Bonds and bonding requirements. (a) When the leasing notice...

  16. 30 CFR 581.33 - Bonds and bonding requirements.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ...Resources 2 2012-07-01 2012-07-01 false Bonds and bonding requirements. 581.33 Section 581.33 Mineral Resources...CONTINENTAL SHELF Financial Considerations § 581.33 Bonds and bonding requirements. (a) When the leasing notice...

  17. Silicon Wafer Bonding by Modified Surface Activated Bonding Methods

    Microsoft Academic Search

    Chenxi Wang; E. Higurashi; T. Suga

    2007-01-01

    8-inch Si-Si wafer bonding at room temperature is performed by means of two modified surface activated bonding (SAB) methods respectively, namely the SAB with nano-adhesion layer and sequential plasma activated bonding (SPAB). And post-annealing processes in atmospheric air utilized do not aim to improve the bonding strength, but to investigate void formation if the bonded wafers heated in subsequent heated

  18. Advanced copper wire bonding technology

    Microsoft Academic Search

    Hong Meng Ho

    2010-01-01

    Wire bonding is the most dominant form of first-level chip interconnects in microelectronics with gold wire bonding taking the lead for the past few decades. Today, it is evident that the shift from gold to copper wire bonding is genuinely picking up, due to both a surge in gold prices and recent developments in copper wire bonding technology. The course

  19. Wire bonds over active circuits

    Microsoft Academic Search

    Gail Heinen; Roger J. Stierman; Darvin Edwards; L. Nye

    1994-01-01

    A reliable process-for wire bonding over active integrated circuits, which are subsequently assembled in plastic packages, has been developed. This technology accommodates reducing the silicon die area required for bond pads and for on-chip bussing. Further, it supports area array wire bonding by allowing larger bond pads with relaxed pitch without sacrificing silicon area. This is accomplished by processing an

  20. Chemical Bonding and Thermodynamics in Superconductivity and Superfluidity

    NASA Astrophysics Data System (ADS)

    Love, Peter

    2012-05-01

    Superconductivity and superfluidity are physical states that occur in a variety of chemical and physical systems. These physical states share a common type of real, or virtual, chemical bonding. Each of the systems discussed herein contain at least one real, or effective, coordinate covalent bond. This is formed from an electron pair donor species and an electron pair acceptor species. When the electronegativity difference between the electron pair donor and acceptor species is sufficiently small, the resultant coordinate covalent bond density can be substantial. If delocalized, this bond density can result in a significant increase in the electron pair orbital volume relative to that of the parent species, and an increase in the valence shell orbital entropy. In terms of the normalized Gibbs-Helmholtz equation, this results in a concomitant decrease in free energy of the delocalized electronic system. A decrease in free energy to negative values can support a boson state, and superconductivity. A clear example of these principles is the occurrence of superconductivity in the ceramic material, MgB2. These generalizations apply to superconducting elements, high temperature superconductors, superconducting alloys, and equivalently to superfluid 4He.

  1. Sketching the pion's valence-quark generalised parton distribution

    E-print Network

    C. Mezrag; L. Chang; H. Moutarde; C. D. Roberts; J. Rodriguez-Quintero; F. Sabatie; S. M. Schmidt

    2014-11-24

    In order to learn effectively from measurements of generalised parton distributions (GPDs), it is desirable to compute them using a framework that can potentially connect empirical information with basic features of the Standard Model. We sketch an approach to such computations, based upon a rainbow-ladder (RL) truncation of QCD's Dyson-Schwinger equations and exemplified via the pion's valence dressed-quark GPD, $H_\\pi^{\\rm v}(x,\\xi,t)$. Our analysis focuses primarily on $\\xi=0$, although we also capitalise on the symmetry-preserving nature of the RL truncation by connecting $H_\\pi^{\\rm v}(x,\\xi=\\pm 1,t)$ with the pion's valence-quark parton distribution amplitude. We explain that the impulse-approximation used hitherto to define the pion's valence dressed-quark GPD is generally invalid owing to omission of contributions from the gluons which bind dressed-quarks into the pion. A simple correction enables us to identify a practicable improvement to the approximation for $H_\\pi^{\\rm v}(x,0,t)$, expressed as the Radon transform of a single amplitude. Therewith we obtain results for $H_\\pi^{\\rm v}(x,0,t)$ and the associated impact-parameter dependent distribution, $q_\\pi^{\\rm v}(x,|\\vec{b}_\\perp|)$, which provide a qualitatively sound picture of the pion's dressed-quark structure at an hadronic scale. We evolve the distributions to a scale $\\zeta=2\\,$GeV, so as to facilitate comparisons in future with results from experiment or other nonperturbative methods.

  2. A mixed-valence polyoxovanadate(III,IV) cluster with a calixarene cap exhibiting ferromagnetic V(III)-V(IV) interactions.

    PubMed

    Aronica, Christophe; Chastanet, Guillaume; Zueva, Ekaterina; Borshch, Serguei A; Clemente-Juan, Juan M; Luneau, Dominique

    2008-02-20

    A series of compounds (cat)[V6O6(OCH3)8(calix)(CH3OH)] was obtained under anaerobic conditions and solvothermal reaction of VOSO4 with p-tert-butylcalix[4]arene (calix) in methanol using different types of bases (Et4NOH, NH4OH, pyridine, Et3N). All compounds contain the same polyoxo(alkoxo)hexavanadate anion [V6O6(OCH3)8(calix)(CH3OH)]- (1) exhibiting a mixed valence {VIIIVIV5O19} core with the so-called Lindqvist structure coordinated to a calix[4]arene macrocycle and cocrystallizing with the conjugated acid of the base (cat = Et4N+, NH4(+), pyridinium, Et3NH+) involved in the synthesis process. The structures have been fully established from X-ray diffraction on single crystals and the mixed valence state has been confirmed by bond valence sum calculations. The magnetic behavior of all compounds are the same because of the polyalkoxohexavanadate anion [V6O6(OCH3)8(calix)(CH3OH)]- (1) and have been interpreted by DFT calculations. Thus the V(III)...V(IV) interactions are found to be weakly ferromagnetic (<5.5 cm(-1)) while the V(IV)...V(IV) are antiferromagnetic (-17.6; -67.6 cm(-1)). The set of the coupling exchange parameters allows a good agreement with the magnetic experimental data. PMID:18215045

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

    SciTech Connect

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

    2001-04-15

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

  4. Pion and kaon valence-quark parton distribution functions

    SciTech Connect

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

    2011-06-15

    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.

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

    SciTech Connect

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

    2011-06-16

    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.

  6. Quantitative analysis of valence electron energy-loss spectra of aluminium nitride

    Microsoft Academic Search

    Dorneich; Mullejans; Loughin; M. RUHLE

    1998-01-01

    Summary The optical properties and electronic structure of alumin- ium nitride are determined using valence electron energy- loss spectroscopy in a dedicated scanning transmission electron microscope. Quantitative analysis of the experi- mental valence electron energy-loss spectra to determine the electronic structure encompasses single scattering deconvolution of the valence electron energy-loss spectra to calculate the energy-loss function, Kramers-Kronig analysis of the

  7. 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. (inventors)

    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.

  8. Adhesive bond degradation sensor

    NASA Astrophysics Data System (ADS)

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

    2002-11-01

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

  9. Plasmon excitation in valence shell photoelectron spectroscopy for PAHs

    NASA Astrophysics Data System (ADS)

    Mishra, P. M.; Avaldi, L.; Bolognesi, P.; Prince, K. C.; Richter, R.; Kadhane, U.

    2015-01-01

    The photon energy dependence of photoelectron spectra (PES) for two members of the polycyclic aromatic hydrocarbon (PAH) family namely pyrene and fluorene is studied in FUV regime (15 - 40 eV) using high-resolution synchrotron photoelectron spectrometer. The difference in outer (? dominated) and inner (? dominated) valence relative photoelectron emission cross sections as a function of photon energy identifies the region of plasmon excitation (~ 15-27 eV). This excitation mode is present in the same region for both the molecule irrespective of the difference in their structure and symmetry. The feature is observed to be independent of the details of the molecular orbital associated with the outgoing electron. The results are in contradiction to the observed in benzene for inner valence bands. With the help of OVGF/cc-pVDZ calculations, the experimental bands are assigned as per their binding energy and symmetry. The first ionization potentials are estimated to be 7.436 ± 0.015 and 7.944 ± 0.055 eV for pyrene and fluorene, respectively.

  10. Thermomechanical properties of graphene: valence force field model approach.

    PubMed

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

    2012-05-01

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

  11. An ecological valence theory of human color preference

    PubMed Central

    Palmer, Stephen E.; Schloss, Karen B.

    2010-01-01

    Color preference is an important aspect of visual experience, but little is known about why people in general like some colors more than others. Previous research suggested explanations based on biological adaptations [Hurlbert AC, Ling YL (2007) Curr Biol 17:623–625] and color-emotions [Ou L-C, Luo MR, Woodcock A, Wright A (2004) Color Res Appl 29:381–389]. In this article we articulate an ecological valence theory in which color preferences arise from people’s average affective responses to color-associated objects. An empirical test provides strong support for this theory: People like colors strongly associated with objects they like (e.g., blues with clear skies and clean water) and dislike colors strongly associated with objects they dislike (e.g., browns with feces and rotten food). Relative to alternative theories, the ecological valence theory both fits the data better (even with fewer free parameters) and provides a more plausible, comprehensive causal explanation of color preferences. PMID:20421475

  12. +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.

  13. Millikelvin studies of mixed-valence HgSe:Fe

    NASA Astrophysics Data System (ADS)

    Lenard, A.; Dietl, T.; Sawicki, M.; Dobrowolski, W.; Dybko, K.; Sko?kiewicz, T.; Plesiewicz, W.; Miotkowska, S.; Witek, A.; Mycielski, A.

    1990-07-01

    Resistivity and magnetic susceptibility measurements of HgSe:Fe have been performed down to 30 mK and in the magnetic field range 50 mOe-3 kOe. Previously observed high conductivities of HgSe:Fe in the mixed valence region of Fe donors have been found to remain unchanged down to the lowest measured temperatures, indicating a minor influence of the resonant scattering and Kondo effect. This points to a weak k- d hybridization and substantiates classification of HgSe:Fe as an inhomogeneous mixed-valence system in which intersite Coulomb interactions impose spatial correlations in positions of charged centers. A resistive and inductive indication of superconductivity has been detected in some samples. The phenomenon is assigned to the presence of Hg-related superconducting inclusions and the associated proximity effect. This interpretation explains the field and temperature dependence of the resistivity and magnetic susceptibility, as well as being consistent with a sensitivity of the effect on deviations from stoichiometry and on annealing in Se vapor.

  14. Bond Functions and Core Correlation Energy Contributions To HeBe Potential

    NASA Astrophysics Data System (ADS)

    Shalabi, A. S.; Nour, E. M.; Abdel Halim, W. S.

    An empirical scheme for implementation of bond functions in heteronuclear diatomics is suggested and applied to HeBe using universal even-tempered functions. The effects of bond functions and core-correlation energy on the interaction potential of HeBe calculated at the uncorrelated (SCF) and correlated (MBPT and CC) levels are examined. The results confirm that an accuracy of sub ? Hartree level can be obtained using even-tempered functions with s-, p-, and d- symmetry and that bond functions of size {4s2p} for He and {6s3p} for Be recovers 100% of energy lowering obtained from the addition of 10d atom-centered functions to He and 13d atom centred functions to Be. The various treatments of the electron correlation, conclude that the system is interacting weakly with a well depth from 14.5-24.7 ?Eh at a separation near 9.1a0 compared with 20.7-25.5 ?Eh previously reported with a rather limited basis set. The most reliable well depth corrected for BSSE (19.0 ?Eh) was obtained at the CC-SD(T)level at separation of 8.71a0 taking into account the effects of bond functions and core correlation energy. Potential energy curves at the CC-SD(T) valence and CC-SD(T) valence + core correlation levels are analyzed in analytical forms in terms of exchange repulsion, induction and dispersion components.

  15. Bond University Queensland, Australia

    E-print Network

    Duchowski, Andrew T.

    Private fiber optic Internet network upon subscription o Within walking distance to campus o Large lagoon pool with water features overlooking Lake Orr o An RA from Bond University lives on site The Retreat o Adjacent to The Retreat o 2 and 3 bedrooms o Gourmet kitchen - stone kitchen tops & glass splash backs

  16. Investing in Bonds 

    E-print Network

    Johnson, Jason; Polk, Wade

    2002-08-12

    maturi- ty tend to have higher interest E-163 8-02 INVESTING IN BONDS Jason Johnson and Wade Polk* *Assistant Professor and Extension Economist?Management, and Extension Program Specialist?Risk Management, The Texas A&M University System rates (coupons...

  17. Thread bonds in molecules

    E-print Network

    Ivlev, B

    2015-01-01

    Unusual chemical bonds are proposed. Each bond is almost covalent but is characterized by the thread of a small radius $\\sim 0.6\\times 10^{-11}$cm, between two nuclei in a molecule. The main electron density is concentrated outside the thread as in a covalent bond. The thread is formed by the electron wave function which has a tendency to be singular on it. The singularity along the thread is cut off by electron "vibrations" due to the interaction with zero point electromagnetic oscillations. The electron energy has its typical value of (1-10)eV. Due to the small tread radius the uncertainty of the electron momentum inside the thread is large resulting in a large electron kinetic energy $\\sim 1 MeV$. This energy is compensated by formation of a potential well due to the reduction of the energy of electromagnetic zero point oscillations. This is similar to formation of a negative van der Waals potential. Thread bonds are stable and cannot be created or destructed in chemical or optical processes.

  18. Bonding silicones with epoxies

    Microsoft Academic Search

    Tira

    1980-01-01

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

  19. Bonding with the Past.

    ERIC Educational Resources Information Center

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

    1998-01-01

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

  20. Durability of bonded assemblies

    Microsoft Academic Search

    Karim Benzarti; Pierre Argoul; Francesco Freddi; Michel Frémond; Thi Hoa Tam Nguyen

    2009-01-01

    An advanced model coupling bulk and interfacial damages is proposed in order to predict the durability of adhesively bonded joints. The underlying theory, based on the principle of virtual power, is briefly presented in the first part of the paper. The second part is devoted to the validation the cited theory. The model is first implemented to describe the damage

  1. Photochemical tissue bonding

    DOEpatents

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

    2012-01-10

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

  2. Valence-to-Core X-Ray Emission Spectroscopy as a Tool for Investigation of Organometallic Systems

    SciTech Connect

    Smolentsev, Grigory; Soldatov, Alexander V. [Faculty of Physics, Rostov State University, 344090 Rostov-on-Don (Russian Federation); Messinger, Johannes; Merz, Katrin; Weyhermuller, Thomas [Max-Planck-Institute, Muehlheim (Germany); Pushkar, Yulia; Yano, Junko; Yachandra, Vittal K. [Lawrence Berkeley National Laboratory, Berkeley, CA (United States); Glatzel, Pieter [European Synchrotron Radiation Facility, Grenoble (France)

    2007-02-02

    The fine structure of X-ray emission satellite lines just below the Fermi level (K{beta} satellite lines), which arise from transitions from valence bands to the core 1s level in 3d transition metals, is a developing technique and the full potential is not well known or understood. On the basis of DFT calculations for some theoretical model complexes that are relevant in bioinorganic chemistry we show that the method can be used to distinguish bonds of the metal atom with different light atoms O/N/C even if the coordination geometries are exactly the same, which is not possible using EXAFS or XANES spectroscopy. Moreover the method is sensitive to the bonding of H to the ligands, which allows to discriminate, for example, between OH- and water near the metal. Both these aspects clearly demonstrate that the K{beta} satellite lines yield information that is complementary to traditional X-ray absorption spectroscopy. Good agreement between theoretical and experimental spectra for a complex Mn system was also achieved.

  3. Theory of first-order isostructural valence phase transitions in the mixed valence compounds YbIn1-xAgxCu4

    Microsoft Academic Search

    A. V. Goltsev; G. Bruls

    2001-01-01

    For describing the first-order isostructural valence phase transition in mixed-valence compounds we develop an approach based on the lattice Anderson model. We take into account the Coulomb interaction between localized f and conduction band electrons and two mechanisms of electron-lattice coupling. One is related to the volume dependence of the hybridization. The other is related to local deformations produced by

  4. Interfacial chemical bonding state and band alignment of CaF{sub 2}/hydrogen-terminated diamond heterojunction

    SciTech Connect

    Liu, J. W.; Liao, M. Y.; Cheng, S. H.; Imura, M. [Optical and Electronic Materials Unit, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan); Koide, Y. [Optical and Electronic Materials Unit, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan); Nanofabrication Platform, NIMS, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Center of Materials Research for Low Carbon Emission (CMRLC), NIMS, 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan)

    2013-03-28

    CaF{sub 2} films are deposited on hydrogen-terminated diamond (H-diamond) by a radio-frequency sputter-deposition technique at room temperature. Interfacial chemical bonding state and band alignment of CaF{sub 2}/H-diamond heterojunction are investigated by X-ray photoelectron spectroscopy. It is confirmed that there are only C-Ca bonds at the CaF{sub 2}/H-diamond heterointerface. Valence and conductance band offsets of the CaF{sub 2}/H-diamond heterojunciton are determined to be 3.7 {+-} 0.2 and 0.3 {+-} 0.2 eV, respectively. It shows a type I straddling band configuration. The large valence band offset suggests advantage of the CaF{sub 2}/H-diamond heterojunciton for the development of high power and high frequency field effect transistors.

  5. Nickel-palladium bond pads for copper wire bonding

    Microsoft Academic Search

    Horst Clauberg; Petra Backus; Bob Chylak

    2011-01-01

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

  6. Valence of titanium and vanadium in pyroxene in refractory inclusion interiors and rims

    E-print Network

    Grossman, Lawrence

    Valence of titanium and vanadium in pyroxene in refractory inclusion interiors and rims S.B. Simon 2007; available online 6 April 2007 Abstract The clinopyroxene in coarse-grained refractory inclusions valence in meteoritic clinopyroxene in refractory inclu- sions. Use of MicroXANES, a microbeam technique

  7. Strain dependence of valence band structure and intersubband transitions in coupled quantum wells

    Microsoft Academic Search

    Bozena Olejn??ková

    1996-01-01

    We have calculated the structure of the valence bands and its dependence on strain in a lattice mismatched quantum well, and in double quantum wells with equal and unequal well thicknesses. We have used the 4×4 Luttinger-Kohn Hamiltonian and the envelope function approximation. Further the character of the strain dependence of optical transitions in valence band was analysed in all

  8. Valence state and spin transitions of iron in Earth's mantle silicates Feiwu Zhang , Artem R. Oganov

    E-print Network

    Oganov, Artem R.

    of iron; spin transitions of iron; Earth's mantle; D" layer; perovskite; post-perovskite; substitutionValence state and spin transitions of iron in Earth's mantle silicates Feiwu Zhang , Artem R investigated the valence and spin states of iron impurities in the perovskite (Pv) and post- perovskite (PPv

  9. Association of limited valence patchy particles in two dimensions John Russo,a

    E-print Network

    Sciortino, Francesco

    and Francesco Sciortino*b Received 11th March 2010, Accepted 13th May 2010 DOI: 10.1039/c0sm00091d We reportAssociation of limited valence patchy particles in two dimensions John Russo,a Piero Tartagliab simulations of a simple model of particles with limited valence in two dimensions and compare the numerical

  10. Behavioral/Systems/Cognitive Independent Coding of Reward Magnitude and Valence in

    E-print Network

    Yeung, Nick

    Behavioral/Systems/Cognitive Independent Coding of Reward Magnitude and Valence in the Human Brain with monetary gains and losses of variable magnitude. The aim was to determine the sensitivity of each component to two critical features of reward stimuli: magnitude (small or large) and valence (win or loss

  11. Rapid Electrophysiological Brain Responses are Influenced by Both Valence and Magnitude

    E-print Network

    Rapid Electrophysiological Brain Responses are Influenced by Both Valence and Magnitude of Monetary options that could vary in both outcome valence (gain or loss) and outcome magnitude (larger or smaller and magnitude for both chosen and unchosen op- tions. Beginning even earlier, at around 150 msec, responses

  12. Valence, coordination number, and PAV cells in metallic rare earth compounds F. L. Carter

    E-print Network

    Paris-Sud XI, Université de

    Valence, coordination number, and PAV cells in metallic rare earth compounds F. L. Carter Naval, generalized coordination numbers, and Pauling's metallic valences are given for 24 intermetallic rare earth self-consistently it was necessary to increase the rare earth metal (/-character and hence decrease

  13. EELS analysis of cation valence states and oxygen vacancies in magnetic oxides

    E-print Network

    Wang, Zhong L.

    EELS analysis of cation valence states and oxygen vacancies in magnetic oxides Z.L. Wang*, J.S. Yin with mixed valences of transition elements. Electron energy- loss spectroscopy (EELS) in the transmission of practical importance. This paper reports our current progress in applying EELS for quantitative

  14. Experimental confirmation of two predictions of a vibronic coupling model for mixed-valence systems

    NASA Astrophysics Data System (ADS)

    Wong, K. Y.; Schatz, P. N.

    1984-07-01

    Both low-energy vibronic ("tunneling") transitions and "electronic" Raman scattering have been observed in mixed-valence systems, the former by Rice et al. in (TCNQ) 2- and latter by Tanino and Kobayashi in Wolffram's red salt. These observations are consistent with the predictions of a vibronic coupling medel (PKS) for mixed-valence dimer systems.

  15. PREPARATION OF STANDARDS FOR VALENCE STATE MEASUREMENT BY X-RAY FLUORESCENCE

    EPA Science Inventory

    The preparation and characterization of standard samples representing several valence states for sulfur, vanadium, and chromium are described. The standards will be used by the U.S. Environmental Protection Agency to investigate the potential for determining valence state by high...

  16. A mixed-valence copper coordination polymer generated by hydrothermal metal/ligand redox reactions

    E-print Network

    Li, Jing

    A mixed-valence copper coordination polymer generated by hydrothermal metal/ligand redox reactions A novel coordination polymer of mixed-valence copper(I,II) with 4,4A-bipyridine and in situ oxidized and crystallographically char- acterized to be a laminated structure via weak copper(II)­ oxygen interactions. Extended

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

    PubMed Central

    Jansen, Helen; Slootweg, J Chris

    2011-01-01

    Summary The valence isomerization of the all-carbon and heteroelement analogues of cyclohepta-1,3,5-triene into the corresponding bicyclo[4.1.0]hepta-2,4-dienes is reviewed to show the impact of the heteroatom on the stability of both valence isomers. The focus is on the parent systems and their synthetic applications. PMID:22238550

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

    PubMed

    Jansen, Helen; Slootweg, J Chris; Lammertsma, Koop

    2011-01-01

    The valence isomerization of the all-carbon and heteroelement analogues of cyclohepta-1,3,5-triene into the corresponding bicyclo[4.1.0]hepta-2,4-dienes is reviewed to show the impact of the heteroatom on the stability of both valence isomers. The focus is on the parent systems and their synthetic applications. PMID:22238550

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

    ERIC Educational Resources Information Center

    Jansari, Ashok; Rodway, Paul; Goncalves, Salvador

    2011-01-01

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

  20. Valence fluctuation of Yb in the superconducting ytterbium-rhodium stannides

    Microsoft Academic Search

    P. Bordet; J. L. Hodeau; P. Wolfers; G. Krill; F. Weiss; M. Marezio

    1987-01-01

    Yb LIII X-ray absorption edge measurements yielded 2.20+ and 2.50+ for the Yb valence in the Yb-Rh-Sn compounds with phase I and II', respectively. The former is superconducting (Tc ~ 8 K), and contains only one crystallographic site for Yb, which suggests that this atom is in a valence fluctuation state.

  1. Properties of Valence Nucleon Distributions for Halo Nuclei

    E-print Network

    C. J. Lin; H. Q. Zhang; Z. H. Liu; Y. W. Wu; F. Yang; M. Ruan

    2002-01-14

    With the binding energies and configurations determined experimentally, the root-mean-square radii are calculated for a number of single-particle states by numerically solving the Sch{\\"o}rdinger equations. By studying the relations between the radii and separation energies, the new scaling laws and necessary conditions for neutron halos and proton halos are established, respectively. Especially the existence region of true proton halos is pointed out. It is found that the effects of short-distance behaviours of valence nucleons at the edges of interaction potentials can not be disregarded. Moreover, by means of the radii of interaction potentials, the contributions of outer parts are estimated as the criterions of halos.

  2. Topological crystalline Kondo insulator in mixed valence ytterbium borides.

    PubMed

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

    2014-01-10

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

  3. Ab initio effective interactions for s d -shell valence nucleons

    NASA Astrophysics Data System (ADS)

    Dikmen, E.; Lisetskiy, A. F.; Barrett, B. R.; Maris, P.; Shirokov, A. M.; Vary, J. P.

    2015-06-01

    We perform ab initio no-core shell-model calculations for A =18 and 19 nuclei in a 4 ? ? , or Nmax=4 , model space by using the effective JISP16 and chiral N3LO nucleon-nucleon potentials and transform the many-body effective Hamiltonians into the 0 ? ? model space to construct the A -body effective Hamiltonians in the s d shell. We separate the A -body effective Hamiltonians with A =18 and A =19 into inert core, one-, and two-body components. Then we use these core, one-, and two-body components to perform standard shell-model calculations for the A =18 and A =19 systems with valence nucleons restricted to the s d shell. Finally, we compare the standard shell-model results in the 0 ? ? model space with the exact no-core shell-model results in the 4 ? ? model space for the A =18 and A =19 systems and find good agreement.

  4. 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.

  5. Neutron Spectroscopy of Valence Fluctuation Compounds of Cerium and Ytterbium

    Microsoft Academic Search

    A. P. Murani

    \\u000a At low temperatures, the magnetic response of Ce and Yb-based valence fluctuation systems consists of a broad inelastic lorentzian\\u000a distribution centered on a characteristic energy T\\u000a K\\u000a which varies from ~ 10 meV e.g. YbAgCu4 (1), Celn1.5Sni.5 (2) to ~ 35–55 meV, e.g. CeSn3 (3), YbAl3 (4), YbInAu2 (5), CePd3 (6, 7), going up to ~ 120–140 meV, e.g. CeRh2

  6. Expectation modulates neural representations of valence throughout the human brain.

    PubMed

    Ramayya, Ashwin G; Pedisich, Isaac; Kahana, Michael J

    2015-07-15

    The brain's sensitivity to unexpected gains or losses plays an important role in our ability to learn new behaviors (Rescorla and Wagner, 1972; Sutton and Barto, 1990). Recent work suggests that gains and losses are ubiquitously encoded throughout the human brain (Vickery et al., 2011), however, the extent to which reward expectation modulates these valence representations is not known. To address this question, we analyzed recordings from 4306 intracranially implanted electrodes in 39 neurosurgical patients as they performed a two-alternative probability learning task. Using high-frequency activity (HFA, 70-200Hz) as an indicator of local firing rates, we found that expectation modulated reward-related neural activity in widespread brain regions, including regions that receive sparse inputs from midbrain dopaminergic neurons. The strength of unexpected gain signals predicted subjects' abilities to encode stimulus-reward associations. Thus, neural signals that are functionally related to learning are widely distributed throughout the human brain. PMID:25937489

  7. Overlap Valence Quarks on a Twisted Mass Sea

    E-print Network

    Krzysztof Cichy; Vincent Drach; Elena Garcia-Ramos; Gregorio Herdoiza; Karl Jansen

    2010-11-02

    We present the results of an investigation of a mixed action approach of overlap valence and maximally twisted mass sea quarks. Employing a particular matching condition on the pion mass, we analyze the continuum limit scaling of the pion decay constant and the role of chiral zero modes of the overlap operator in this process. We employ gauge field configurations generated by the European Twisted Mass Collaboration with linear lattice size $L$ ranging from 1.3 to 1.9 fm. The continuum limit is taken at a fixed value of $L=1.3$ fm, employing three values of the lattice spacing and two values of the pion mass constructed from sea quarks only.

  8. ChemTeacher: Metallic Bonds

    NSDL National Science Digital Library

    2012-07-20

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

  9. ChemTeacher: Ionic Bonds

    NSDL National Science Digital Library

    2012-07-20

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

  10. ChemTeacher: Covalent Bonds

    NSDL National Science Digital Library

    2012-07-20

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

  11. The Illiquidity of Corporate Bonds

    E-print Network

    Bao, Jack

    This paper examines the illiquidity of corporate bonds and its asset-pricing implications. Using transactions data from 2003 to 2009, we show that the illiquidity in corporate bonds is substantial, significantly greater ...

  12. Valence band structure of Bi2Se3

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

    Bi2Se3 is an interesting candidate for thermoelectric application because Se is a more abundant element than Te, which is commercially used in Bi2Te3-based Peltier coolers. However, intrinsic Se vacancies dominate in Bi2Se3 and dope the material n-type. Due to unfavourable conduction band structure, n-type Bi2Se3 does not have a high power factor. Recently, it has been calculated that Bi2Se3 has a favourable valence band structure for thermoelectric application. In this presentation, high-quality p-type Bi2Se3 single crystals are prepared and Shubnikov de Haas measurement are carried out on them to characterize the band structure. Cross-sectional areas of Fermi surface are mapped out and compared with the theoretical calculation. Bi2Se3 is an interesting candidate for thermoelectric application because Se is a more abundant element than Te, which is commercially used in Bi2Te3-based Peltier coolers. However, intrinsic Se vacancies dominate in Bi2Se3 and dope the material n-type. Due to unfavourable conduction band structure, n-type Bi2Se3 does not have a high power factor. Recently, it has been calculated that Bi2Se3 has a favourable valence band structure for thermoelectric application. In this presentation, high-quality p-type Bi2Se3 single crystals are prepared and Shubnikov de Haas measurement are carried out on them to characterize the band structure. Cross-sectional areas of Fermi surface are mapped out and compared with the theoretical calculation. Funded by zt::plus

  13. Identifying words that emerge into consciousness: Effects of word valence and unconscious previewing.

    PubMed

    Prioli, Simone C; Kahan, Todd A

    2015-09-01

    Words with negative valence capture attention and this increase in attentional resources typically enhances perceptual processing. Recently, data using continuous flash suppression (CFS) appear to contradict this. In prior research when Chinese words were unconsciously presented in CFS and contrast was raised until the word was identified, RTs to identify words with negative valence were slower than RTs to words with neutral valence. This result might be limited to situations where a logographic writing system is used and could reflect a type of cognitive aftereffect where previewing the word causes habituation. Data (N=60) indicate that results generalize from a logographic (Chinese) to an orthographic writing system (English). In addition, when words were previewed in CFS RTs were slowed for words with negative valence relative to words with neutral valence and this was reversed when words were shown binocularly. Implications for theories of unconscious word processing and cognitive aftereffects are discussed. PMID:25982055

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

    PubMed

    Mashal, Nira; Itkes, Oksana

    2014-01-01

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

  15. Full inclusion of symmetry in constructing Wannier functions: Chemical bonding in MgO and TiO 2 crystals

    Microsoft Academic Search

    R. A. Évarestov; D. E. Usvyat; V. P. Smirnov

    2003-01-01

    Chemical bonding in MgO and TiO2 crystals is analyzed using a minimal basis consisting of atomic-type Wannier functions (AWFs) centered at atomic sites in\\u000a the crystal and constructed from Bloch states of the energy bands originating from the valence states of the atoms. A method\\u000a proposed earlier for constructing Wannier functions is improved. Symmetrization of the initial Bloch function basis

  16. Alternating anion-cation bond strengths in CdGeAs2: Application to the family of ternary pnictides

    Microsoft Academic Search

    J. Pascual; J. Pujol; L. Artus; J. Camassel

    1991-01-01

    We have investigated in great detail the low-temperature infrared (ir) transmission and polarized-Raman-scattering spectra of CdGeAs2. We identified all vibrational modes predicted from group-theory arguments and compared them with predictions of three- and four-parameter valence-force-field models. Assuming only nearest-neighbor interactions for the two different series of anion-cation bonds that define the ternary pnictide structure, we have found the resulting series

  17. Electronic structure and chemical bonding in PuO2

    NASA Astrophysics Data System (ADS)

    Teterin, Yu. A.; Maslakov, K. I.; Teterin, A. Yu.; Ivanov, K. E.; Ryzhkov, M. V.; Petrov, V. G.; Enina, D. A.; Kalmykov, St. N.

    2013-06-01

    Quantitative analysis of the x-ray photoelectron spectra structure in the binding energy (BE) range of 0 eV-˜35 eV for plutonium dioxide (PuO2) valence electrons was done. The BEs and structure of the core electronic shells (35 eV-1250 eV BE), as well as the relativistic discrete variation calculation results for the finite fragments of the PuO2 lattice and the data of other authors, were taken into account. The experimental data show that the many-body effects and the multiplet splitting contribute to the spectral structure much less than the outer (0 eV-˜15 eV) and the inner (˜15 eV-˜35 eV) valence molecular orbitals (OVMO and IVMO, respectively). The filled Pu 5f electronic states were shown to form in the PuO2 valence band. The Pu 6p electrons participate in the formation of both the IVMO and the OVMO (bands). The filled Pu 6p3/2 and the O 2s electronic shells were found to take maximum part in the IVMO formation. The MO composition and the sequence order in the BE range of 0 eV-˜35 eV in PuO2 were established. The experimental and theoretical data allowed a quantitative MO scheme for PuO2, which is fundamental for understanding both the chemical bond nature in plutonium dioxide and the interpretation of other x-ray spectra of PuO2.

  18. Continuing Conversation about Continuing Bonds

    ERIC Educational Resources Information Center

    Klass, Dennis

    2006-01-01

    The article is a response to the contributions the special issue of Death Studies on continuing bonds. The contributions indicate that the conversation among scholars has clarified our thinking on how bonds function in individual grief. The author discussed two issues to help keep the conversation moving: (a) the relationship of continuing bonds

  19. Cyclic Bonds in Branched Polymers

    E-print Network

    Kazumi Suematsu

    2015-02-19

    In the gelation theory it has been implicitly assumed that (I) a cyclic bond is a finite bond that returns to itself; (II) cyclic bonds distribute at random in network structures. In this paper these two assumptions are reexamined from a new point of view. The physical soundness of the assumptions are assessed through comparison with experimental observations.

  20. Low temperature gold wire bonding

    Microsoft Academic Search

    Y. M. Cheung; S. W; S. Ching

    1999-01-01

    We demonstrated that the bonding of gold wires for COB application was feasible at temperatures ~100°C or below by using a wedge bonder with a high frequency ultrasonic transducer (~138 kHz). An automatic rotary bondhead wedge bonder equipped with the transducer was employed to perform wire bonding. Bonding of gold wires was conducted on the aluminum pads of a test

  1. 46 CFR Sec. 10 - Bonds.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ...AUTHORITY MASTER LUMP SUM REPAIR CONTRACT-NSA-LUMPSUMREP Sec. 10 Bonds...payment bonds required by Article 14 of the NSA-LUMPSUMREP Contract. The stand- ard...payment bond requirements of Article 14 of the NSA-LUMPSUMREP Contract, the...

  2. 46 CFR Sec. 10 - Bonds.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ...AUTHORITY MASTER LUMP SUM REPAIR CONTRACT-NSA-LUMPSUMREP Sec. 10 Bonds...payment bonds required by Article 14 of the NSA-LUMPSUMREP Contract. The stand- ard...payment bond requirements of Article 14 of the NSA-LUMPSUMREP Contract, the...

  3. 46 CFR Sec. 10 - Bonds.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ...AUTHORITY MASTER LUMP SUM REPAIR CONTRACT-NSA-LUMPSUMREP Sec. 10 Bonds...payment bonds required by Article 14 of the NSA-LUMPSUMREP Contract. The stand- ard...payment bond requirements of Article 14 of the NSA-LUMPSUMREP Contract, the...

  4. BONDING PROCEDURES MUNICIPAL STREETS SEMINAR

    E-print Network

    BONDING PROCEDURES MUNICIPAL STREETS SEMINAR Ahlers & Cooney, P.C. Mark Cory & Minniette Bucklin Association, Polk County and Iowa Bar Associations and the National Association of Bond Lawyers. Mr. Cory has of governmental bonds, but she also advises clients with respect to issues involving economic development

  5. Low temperature reactive bonding

    DOEpatents

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

    1995-01-01

    The joining technique requires no external heat source and generates very little heat during joining. It involves the reaction of thin multilayered films deposited on faying surfaces to create a stable compound that functions as an intermediate or braze material in order to create a high strength bond. While high temperatures are reached in the reaction of the multilayer film, very little heat is generated because the films are very thin. It is essentially a room temperature joining process.

  6. NORTHWESTERN UNIVERSITY Crystallographic Perturbations to Valence Charge Density

    E-print Network

    Shull, Kenneth R.

    x-ray diffraction data. Precession electron diffraction (PED) is a technique which is gaining energy electron diffraction. By perturbing about the bond-centered pseudoatom model, we found of the electrons themselves, which is of greater importance than atomic positions in determining material

  7. The nature of NO-bonding in N-oxide group.

    PubMed

    ?ukomska, Marlena; Rybarczyk-Pirek, Agnieszka J; Jab?o?ski, Miros?aw; Palusiak, Marcin

    2015-07-01

    The nature of the NO-bond in the N-oxide group was investigated by means of combined theoretical calculations (including QTAIM and NBO approaches) and statistical analyses of the contents of crystal structure databases. The N-O bond in the N-oxide group should be classified as the NO donating bond with an important contribution of ON back-donation (of the ?-electron type, when available). The visualization of the Laplacian of electron density in the region of an oxygen valence sphere suggests the presence of two lone pairs for the imine-N-oxide group (characterized by effective ON back-donation). A detailed bonding analysis performed by means of natural resonance theory indicates that the N?O bond is of an order of magnitude clearly greater than 1. In addition, the stability of the N?O bond in various N-oxides was estimated. The analyses of the hydrogen- and halogen-bonded complexes of the N-oxides reveal strong Lewis basicity of the N-oxide group. The formation of H- and X-bonding leads to N?O bond elongation due to its structural, topological and spectroscopic characteristics. Moreover, in pyridine-N-oxide, the electron-withdrawing -NO2 group additionally stabilizes the N?O bond, whereas the opposite effect can be observed for the electron-donating-NH2 substituent. This is due to a substituent effect on the ?-type ON back-donation. As a result, the oxygen atom in pyridine-N-oxide may change its availability during intermolecular interaction formation, as revealed in the interaction energy, which changes by about half of the estimated total interaction energy. PMID:26051488

  8. Disulfide bonds of acetylcholinesterase

    SciTech Connect

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

    1986-05-01

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

  9. Valence Change Driven by Constituent Element Substitution in the Mixed-Valence Quasicrystal and Approximant Au–Al–Yb

    NASA Astrophysics Data System (ADS)

    Matsukawa, Shuya; Tanaka, Katsumasa; Nakayama, Mika; Deguchi, Kazuhiko; Imura, Keiichiro; Takakura, Hiroyuki; Kashimoto, Shiro; Ishimasa, Tsutomu; Sato, Noriaki K.

    2014-03-01

    Quantum criticality has been considered to be specific to crystalline materials such as heavy fermions. Very recently, however, the Tsai-type quasicrystal Au51Al34Yb15 has been reported to show unusual quantum critical behavior. To obtain a deeper understanding of this new material, we have searched for other Tsai-type cluster materials. Here, we report that the metal alloys Au44Ga41Yb15 and Ag47Ga38Yb15 are members of the 1/1 approximant to the Tsai-type quasicrystal and that both possess no localized magnetic moment. We suggest that the Au–Al–Yb system is located near the border of the divalent and trivalent states of the Yb ion; we also discuss a possible origin of the disappearance of magnetism, associated with the valence change, by the substitution of the constituent elements.

  10. Fingerprints of the hydrogen bond in the photoemission spectra of croconic acid condensed phase: An x-ray photoelectron spectroscopy and ab-initio study

    SciTech Connect

    Bisti, F. [Dipartimento di Fisica, Universita dell'Aquila, Via Vetoio 10, 67100, L'Aquila (Italy); Stroppa, A.; Picozzi, S. [CNR-SPIN L'Aquila, Via Vetoio 10, 67100 L'Aquila (Italy); Ottaviano, L. [Dipartimento di Fisica, Universita dell'Aquila, Via Vetoio 10, 67100, L'Aquila (Italy); CNR-SPIN L'Aquila, Via Vetoio 10, 67100 L'Aquila (Italy)

    2011-05-07

    The electronic structure of Croconic Acid in the condensed phase has been studied by comparing core level and valence band x-ray photoelectron spectroscopy experiments and first principles density functional theory calculations using the Heyd-Scuseria-Ernzerhof screened hybrid functional and the GW approximation. By exploring the photoemission spectra for different deposition thicknesses, we show how the formation of the hydrogen bond network modifies the O 1s core level lineshape. Moreover, the valence band can be explained only if the intermolecular interactions are taken into account in the theoretical approach.

  11. Evaluation of wire bonding performance, process conditions, and metallurgical integrity of chip on board wire bonds

    Microsoft Academic Search

    Daniel T. Rooney; Deepak Nager; David Geiger; Dongkai Shanguan

    2005-01-01

    Chip on board wire bonding presents challenges to modern wire bonding technology which include smaller, closely spaced wire bond pads; bonding to soft substrates without special processing and pad construction; and diverse first bond and second bond metallurgies. These challenges are addressed by extensive bonding accuracy tests, a design of experiments approach for optimizing wire bond process parameters, reliability testing,

  12. The Evolution of Bond Theory

    NSDL National Science Digital Library

    In chemistry lectures we have little time to discuss the history of chemistry. This simulation begins with the development of valence concepts in the 19th century. We will step back into the 19th century to see how theories of chemical combination changed during that time.

  13. Thermal phase transitions to valence-bond-solid phase in the two-dimensional generalized SU(N) Heisenberg models

    NASA Astrophysics Data System (ADS)

    Suzuki, Takafumi; Harada, Kenji; Matsuo, Haruhiko; Todo, Synge; Kawashima, Naoki

    2015-03-01

    We study thermal transitions of the generalized SU(N) Heisenberg models with four-body interactions on a square lattice and with six-body interactions on a honeycomb lattice. In both models for the N=3 and 4 cases, a singlet-dimer state is stabilized at a very low temperature, where a rotational symmetry of lattice is broken spontaneously. We discuss the universality class of thermal transition to the singlet dimer phases, performing quantum Monte Carlo calculations. From the finite-size scaling analysis, we find that the criticality for the square lattice case is well explained by the 2D weak Ising universality, while the 2D three-state Potts universality is observed in the honeycomb lattice case.

  14. d-Wave Resonating Valence Bond States of Fermionic Atoms in Optical Lattices Simon Trebst,1,2,3

    E-print Network

    Trebst, Simon

    states from a Fermi gas, we adiabatically transform this state to an RVB state by a change of the lattice a reservoir of a quantum degenerate Fermi gas [19] and adiabatically transforming this state to an RVB state, were originally introduced [1] as wave functions for insulating spin liquid ground states of Mott

  15. Performance of Small and Medium Split Valence Basis Sets in the Calculation of Hydrogen Bonding Properties with DFT Methods

    Microsoft Academic Search

    Kevin Riley

    2005-01-01

    As the speed of modern computers increases while their cost decreases it becomes possible to consider the use of ab initio methods to calculate properties of very large molecules. These types of calculations promise to greatly enhance our understanding of the structure and function of large molecular systems. It seems that the first step to take in making calculations on

  16. Quantum kagomé antiferromagnet in a magnetic field: Low-lying nonmagnetic excitations versus valence-bond crystal order

    Microsoft Academic Search

    D. C. Cabra; M. D. Grynberg; P. C. W. Holdsworth; A. Honecker; P. Pujol; J. Richter; D. Schmalfuß; J. Schulenburg

    2005-01-01

    We study the ground state properties of a quantum antiferromagnet on the kagomé lattice in the presence of a magnetic field, paying particular attention to the stability of the plateau at magnetization 1\\/3 of saturation and the nature of its ground state. We discuss fluctuations around classical ground states and argue that quantum and classical calculations at the harmonic level

  17. Spin-orbital resonating valence bond liquid on a triangular lattice: Evidence from finite-cluster diagonalization

    Microsoft Academic Search

    Jirí Chaloupka; Andrzej M. Oles

    2011-01-01

    We investigate the ground state of the d1 spin-orbital model for triply degenerate t2g orbitals on a triangular lattice that unifies intrinsic frustration of spin and orbital interactions with geometrical frustration. Using full or Lanczos exact diagonalization of finite clusters, we establish that the ground state of the spin-orbital model that interpolates between superexchange and direct exchange interactions on the

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

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

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

  19. Valence fluctuation in Sm1-xEuxS system: An X-ray absorption spectroscopic study

    Microsoft Academic Search

    R. K. Singhal; K. B. Garg

    1992-01-01

    Sm1-xEuxS (x = 0.10 to 0.85) alloys have been investigated using XANES (X-ray absorption near-edge structure) technique to examine the question of intermediate valence of Sm and Eu. SmLIII absorption edge data point to the intermediate valence of Sm, and the Sm valence data clearly exhibits a continoous valence transition of Sm with increasing Eu content. On the other hand,

  20. 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.

  1. 77 FR 32128 - Cancellation of Bond Subject to Enhanced Bonding Requirements Upon CBP's Acceptance of Qualified...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-05-31

    ...Cancellation of Bond Subject to Enhanced Bonding Requirements Upon CBP's Acceptance of...amount was calculated pursuant to enhanced bonding requirements (EBR bond) upon the agency's...INFORMATION: Background I. Enhanced Bonding Requirements In 2004, U.S....

  2. Features of chemical bonds based on the overlap polarizabilities: diatomic and solid-state systems with the frozen-density embedding approach.

    PubMed

    Moura, Renaldo T; Duarte, Gian C S; da Silva, Thiago E; Malta, Oscar L; Longo, Ricardo L

    2015-03-28

    The chemical bond overlap properties were obtained for alkali halides NaY (Y = F, Cl, Br), alkaline-earth chalcogenides MX (M = Ca, Mg and X = O, S, Se) and alkali and alkali-earth metals (Li, Na, and Mg) in diatomic and solid-state systems using an embedding approach based on the frozen density functional theory to simulate the crystalline effects. The computational protocol established provides errors for bond distances smaller than 1%. The results indicate that larger chemical bond covalency leads to larger absorption or scattering by the overlap region. The ionic specific valence and overlap polarizability are closely related to the valence orbital compactness measured by the sum of Mulliken electronegativities. The embedding approach used in this work makes it possible to quantify the effects of the crystalline environment on the chemical bond overlap properties. In the solid-state, the bond overlap charges are less polarizable, in cases of well-known ionic systems (provided by electronegativity differences), leading to smaller chemical bond covalency in solids than in diatomics. The spectroscopic properties of the polarizability of the electron density in the overlap region of a chemical bond could be measured in the 1-20 eV spectral region and could be used to characterize some bands in several spectra whose assignments are ambiguous or not available. PMID:25712634

  3. Bond Inspection by Impact Test

    NASA Astrophysics Data System (ADS)

    Yang, Y.; Xiang, D.; Qin, Y.; Li, F.; Coulter, R. V.

    2010-02-01

    Kissing bond detection has been a challenging issue for NDE of bonded structures in aeronautical industry. A novel impact test technique for bond inspection has been developed, which shows great potential for kissing bond detection. The impact test employs a solenoid to produce impact forces in a bonded structure, and the induced elastic wave in the structure was picked up by an EMAT sensor, which located side by side with the solenoid. Both solenoid and EMAT sensor are integrated into a tap header that is mounted onto an automatic 2-D scanner to realize an automatic 2-D scanning. Multiple samples with artificial defects including kissing bonds and disbonds were used to test the impact test technique. The results show that those bond defects in the samples can be detected by the developed impact test technique. For comparison purpose, those samples were also tested with traditional ultrasonic C-scan.

  4. Momentum Profile and Final Correlation Effects of Iso-butane Inner Valence by Binary (e, 2e) Spectroscopy

    E-print Network

    Wang, Yayu

    Momentum Profile and Final Correlation Effects of Iso-butane Inner Valence by Binary (e, 2e Momentum Profile and Final Correlation Effects of Iso-butane Inner Valence by Binary (e, 2e) Spectroscopy) The binding energy spectra and the momentum distributions of the valence orbitals of iso-butane, also known

  5. A class Vb chitin synthase in Colletotrichum graminicola is localized in the growing tips of multiple cell types, in nascent septa, and during septum conversion to an end wall after hyphal breakage

    Microsoft Academic Search

    A. Amnuaykanjanasin; L. Epstein

    2006-01-01

    Summary.  Previous complementation of a chitin synthase class Vb null mutant (Colletotrichum graminicola chsA) indicated that the encoded protein is responsible for approximately 30% of the conidial chitin, is essential for conidial\\u000a wall strength in media with high water potential, and contributes to strength of hyphal tips. We complemented a chsA null mutant with chsA fused to the green-fluorescent protein (sgfp)

  6. Pentaatomic planar tetracoordinate silicon with 14 valence electrons: a large-scale global search of SiX(n)Y(m)(q) (n?+?m?=?4; q?=?0, ±1, -2; X, Y?=?main group elements from H to Br).

    PubMed

    Xu, Jing; Ding, Yi-hong

    2015-03-01

    Designing and characterizing the compounds with exotic structures and bonding that seemingly contrast the traditional chemical rules are a never-ending goal. Although the silicon chemistry is dominated by the tetrahedral picture, many examples with the planar tetracoordinate-Si skeletons have been discovered, among which simple species usually contain the 17/18 valence electrons. In this work, we report hitherto the most extensive structural search for the pentaatomic ptSi with 14 valence electrons, that is, SiXnYm(q) (n?+?m?=?4; q?=?0, ±1, -2; X, Y?=?main group elements from H to Br). For 129 studied systems, 50 systems have the ptSi structure as the local minimum. Promisingly, nine systems, that is, Li3SiAs(2-), HSiY3 (Y?=?Al/Ga), Ca3SiAl(-), Mg4Si(2-), C2LiSi, Si3Y2 (Y?=?Li/Na/K), each have the global minimum ptSi. The former six systems represent the first prediction. Interestingly, in HSiY3 (Y?=?Al/Ga), the H-atom is only bonded to the ptSi-center via a localized 2c-2e ? bond. This sharply contradicts the known pentaatomic planar-centered systems, in which the ligands are actively involved in the ligand-ligand bonding besides being bonded to the planar center. Therefore, we proposed here that to generalize the 14e-ptSi, two strategies can be applied as (1) introducing the alkaline/alkaline-earth elements and (2) breaking the peripheral bonding. In light of the very limited global ptSi examples, the presently designed six systems with 14e are expected to enrich the exotic ptSi chemistry and welcome future laboratory confirmation. PMID:25430676

  7. Core-Valence Auger Spectra of the Simple Metals.

    NASA Astrophysics Data System (ADS)

    Davis, Linda Rae

    A comprehensive study of the core-valence-valence (CVV) Auger line shapes for the simple metals, Li, Be, Na, Mg, and Al, is presented. Calculations of these line shapes are performed with a static many-body model which treats the (static) screening of a core hole by conduction electrons with a phenomenological potential. Our model is applicable only to the simple metals, because free-electron theory is used to describe the conduction electrons. The model is implemented with a finite-particle, determinantal approach, and many-body Auger matrix elements are calculated explicitly using a local approximation. The many-body effects which arise from the core-conduction interaction are treated exactly within the model. The dependence of the model line shapes (i) on parameters specifying the metal and core level, (ii) on approximation of the model, and (iii) on the many-body effects produced by the core -conduction interaction are examined in detail. Also, model calculations of the simple-metal CVV spectra for which data exist are presented. Empirical fits of the model calculations to reported data are achieved for the Li(KVV), Be(KVV), Mg(L(,2,3)VV), and Al(L(,2,3)VV) spectra. In all of these cases, the screening of the core hole by conduction electrons is found to have both s-like and p-like character. One -electron and static many-body calculations have also been performed by other authors for some of the simple-metal spectra. Our model and results are compared to those from the other calculations. Although one-electron theory has reproduced several of the reported simple-metal line shapes, our calculations are the only many-body calculations to produce line shapes in agreement with data. Model calculations for the final reported spectrum, the Mg(KVV), are not presented, because the Mg K core hole is not sufficiently long-lived for our model to be valid. Our expectations concerning the unreported Na(L(,2,3)VV) spectrum are discussed. From our empirical fits and model study, we conclude that the many-body effects which are introduced by the core-conduction interaction, although weak, significantly influence the CVV line shapes of the simple metals. This conclusion is suggestive of the inadequacy of the one-electron theory of CVV line shapes, even in cases of simple-metal spectra.

  8. Theoretical Aspects of the Biological Catch Bond

    Microsoft Academic Search

    Oleg V. Prezhdo; Yuriy V. Pereverzev

    2009-01-01

    he biological catch bond is fascinating and counterintuitive. When an external force is applied to a catch bond, either in vivo or in vitro, the bond resists breaking and becomes stronger instead. In contrast, ordinary slip bonds, which represent the vast majority of biological and chemical bonds, dissociate faster when subjected to a force. Catch-bond behavior was first predicted theoretically

  9. Low temperature reactive bonding

    DOEpatents

    Makowiecki, D.M.; Bionta, R.M.

    1995-01-17

    The joining technique is disclosed that requires no external heat source and generates very little heat during joining. It involves the reaction of thin multilayered films deposited on faying surfaces to create a stable compound that functions as an intermediate or braze material in order to create a high strength bond. While high temperatures are reached in the reaction of the multilayer film, very little heat is generated because the films are very thin. It is essentially a room temperature joining process. 5 figures.

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

    SciTech Connect

    Karpenko, A., E-mail: oleksandr.karpenko@oulu.fi; Iablonskyi, D.; Kettunen, J. A.; Cao, W.; Huttula, M.; Aksela, H. [Department of Physical Sciences, University of Oulu, Box 3000, FI-90014 Oulu (Finland); Urpelainen, S. [Department of Physical Sciences, University of Oulu, Box 3000, FI-90014 Oulu (Finland); MAX IV Laboratory, Lund University, Box 118, SE-22100 Lund (Sweden)

    2014-05-28

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

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

    SciTech Connect

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

    1985-11-15

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

  12. 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.

  13. Plasma cleaning on bond pad surfaces for gold wire bonding

    Microsoft Academic Search

    Wu-Hu Li; Klaus Reingruber; Norbert Mais; Albert Acuesta; Christian Alde Yape

    2009-01-01

    Ar plasma was employed to remove\\/reduce the oxidation of two typical types of bond pad surfaces, namely aluminum (Al) surface and gold (Au)-coated palladium (Pd) surface, prior to Au wire-bonding process. Field emission scanning electron microscopy (FESEM) and Auger electron spectroscopy (AES) were employed to characterize the bond pad surfaces without and with the plasma cleaning. Processability and reliability results

  14. Solder extrusion pressure bonding process and bonded products produced thereby

    DOEpatents

    Beavis, Leonard C. (Albuquerque, NM); Karnowsky, Maurice M. (Albuquerque, NM); Yost, Frederick G. (Ceder Crest, NM)

    1992-01-01

    Production of soldered joints which are highly reliable and capable of surviving 10,000 thermal cycles between about -40.degree. C. and 110.degree. C. Process involves interposing a thin layer of a metal solder composition between the metal surfaces of members to be bonded and applying heat and up to about 1000 psi compression pressure to the superposed members, in the presence of a reducing atmosphere, to extrude the major amount of the solder composition, contaminants including fluxing gases and air, from between the members being bonded, to form a very thin, strong intermetallic bonding layer having a thermal expansion tolerant with that of the bonded members.

  15. Solder extrusion pressure bonding process and bonded products produced thereby

    DOEpatents

    Beavis, L.C.; Karnowsky, M.M.; Yost, F.G.

    1992-06-16

    Disclosed is a process for production of soldered joints which are highly reliable and capable of surviving 10,000 thermal cycles between about [minus]40 C and 110 C. Process involves interposing a thin layer of a metal solder composition between the metal surfaces of members to be bonded and applying heat and up to about 1000 psi compression pressure to the superposed members, in the presence of a reducing atmosphere, to extrude the major amount of the solder composition, contaminants including fluxing gases and air, from between the members being bonded, to form a very thin, strong intermetallic bonding layer having a thermal expansion tolerant with that of the bonded members.

  16. Toxoplasma gondii infection enhances the kairomonal valence of rat urine

    PubMed Central

    Vasudevan, Anand; Vyas, Ajai

    2014-01-01

    Many animals use chemicals as pheromones to communicate between individuals of the same species, for example to influence mate choice or to assert dominance. Pheromonal communication is an open broadcast system that can be intercepted by unintended receivers such as predators and prey. We have recently reported that male rats infected by the protozoan parasite Toxoplasma gondii become more attractive to female rats. This suggests a facilitatory effect of infection on rat pheromone production. In view of the open nature of pheromonal communication, we postulate that Toxoplasma gondii infection collateraly enhances kairomonal valence of infected rats to their prey. We compared the strength of kairomonal interception by mice when using scent marks from rats infected with Toxoplasma gondii vs. marks from uninfected control rats. Mice exhibited greater avoidance to both fresh urine and aged rat urine marks obtained from infected animals. These results indicate that, at least in some cases, parasitism can result in opportunity costs for hosts by making prey species more averse to them. PMID:25075300

  17. Quasicrystalline valence bands in decagonal AlNiCo

    PubMed

    Rotenberg; Theis; Horn; Gille

    2000-08-10

    Quasicrystals are metallic alloys that possess perfect long-range structural order, in spite of the fact that their rotational symmetries are incompatible with long-range periodicity. The exotic structural properties of this class of materials are accompanied by physical properties that are unexpected for metallic alloys. Considerable progress in resolving the geometric structures of quasicrystals has been made using X-ray and neutron diffraction, and concepts such as the quasi-unit-cell model have provided theoretical insights. But the basic properties of the valence electronic states--whether they are extended as in periodic crystals or localized as in amorphous materials--are still largely unresolved. Here we investigate the electronic bandstructure of quasicrystals through angle-resolved photoemission experiments on decagonal Al71.8Ni14.8Co13.4. We find that the s-p and d states exhibit band-like behaviour with the symmetry of the quasiperiodic lattice, and that the Fermi level is crossed by dispersing d-bands. The observation of free-electron-like bands, distributed in momentum space according to the surface diffraction pattern, suggests that the electronic states are not dominated by localization. PMID:10949295

  18. The polarised valence quark distribution from semi-inclusive DIS

    NASA Astrophysics Data System (ADS)

    Alekseev, M.; Alexakhin, V. Yu.; Alexandrov, Yu.; Alexeev, G. D.; Amoroso, A.; Arbuzov, A.; Bade?ek, B.; Balestra, F.; Ball, J.; Barth, J.; Baum, G.; Bedfer, Y.; Bernet, C.; Bertini, R.; Bettinelli, M.; Birsa, R.; Bisplinghoff, J.; Bordalo, P.; Bradamante, F.; Bravar, A.; Bressan, A.; Brona, G.; Burtin, E.; Bussa, M. P.; Chapiro, A.; Chiosso, M.; Cicuttin, A.; Colantoni, M.; Costa, S.; Crespo, M. L.; Dalla Torre, S.; Dafni, T.; Das, S.; Dasgupta, S. S.; de Masi, R.; Dedek, N.; Denisov, O. Yu.; Dhara, L.; Diaz, V.; Dinkelbach, A. M.; Donskov, S. V.; Dorofeev, V. A.; Doshita, N.; Duic, V.; Dünnweber, W.; Eversheim, P. D.; Eyrich, W.; Faessler, M.; Falaleev, V.; Ferrero, A.; Ferrero, L.; Finger, M.; Finger, M.; Fischer, H.; Franco, C.; Franz, J.; Friedrich, J. M.; Frolov, V.; Garfagnini, R.; Gautheron, F.; Gavrichtchouk, O. P.; Gazda, R.; Gerassimov, S.; Geyer, R.; Giorgi, M.; Gobbo, B.; Goertz, S.; Gorin, A. M.; Grabmüller, S.; Grajek, O. A.; Grasso, A.; Grube, B.; Gushterski, R.; Guskov, A.; Haas, F.; Hannappel, J.; von Harrach, D.; Hasegawa, T.; Heckmann, J.; Hedicke, S.; Heinsius, F. H.; Hermann, R.; Heß, C.; Hinterberger, F.; von Hodenberg, M.; Horikawa, N.; Horikawa, S.; D'Hose, N.; Ilgner, C.; Ioukaev, A. I.; Ishimoto, S.; Ivanov, O.; Ivanshin, Yu.; Iwata, T.; Jahn, R.; Janata, A.; Jasinski, P.; Joosten, R.; Jouravlev, N. I.; Kabuß, E.; Kang, D.; Ketzer, B.; Khaustov, G. V.; Khokhlov, Yu. A.; Kisselev, Yu.; Klein, F.; Klimaszewski, K.; Koblitz, S.; Koivuniemi, J. H.; Kolosov, V. N.; Komissarov, E. V.; Kondo, K.; Königsmann, K.; Konorov, I.; Konstantinov, V. F.; Korentchenko, A. S.; Korzenev, A.; Kotzinian, A. M.; Koutchinski, N. A.; Kouznetsov, O.; Kral, A.; Kravchuk, N. P.; Kroumchtein, Z. V.; Kuhn, R.; Kunne, F.; Kurek, K.; Ladygin, M. E.; Lamanna, M.; Le Goff, J. M.; Lednev, A. A.; Lehmann, A.; Levorato, S.; Lichtenstadt, J.; Liska, T.; Ludwig, I.; Maggiora, A.; Maggiora, M.; Magnon, A.; Mallot, G. K.; Mann, A.; Marchand, C.; Marroncle, J.; Martin, A.; Marzec, J.; Massmann, F.; Matsuda, T.; Maximov, A. N.; Meyer, W.; Mielech, A.; Mikhailov, Yu. V.; Moinester, M. A.; Mutter, A.; Nagaytsev, A.; Nagel, T.; Nähle, O.; Nassalski, J.; Neliba, S.; Nerling, F.; Neubert, S.; Neyret, D. P.; Nikolaenko, V. I.; Nikolaev, K.; Olshevsky, A. G.; Ostrick, M.; Padee, A.; Pagano, P.; Panebianco, S.; Panknin, R.; Panzieri, D.; Paul, S.; Pawlukiewicz-Kaminska, B.; Peshekhonov, D. V.; Peshekhonov, V. D.; Piragino, G.; Platchkov, S.; Pochodzalla, J.; Polak, J.; Polyakov, V. A.; Pretz, J.; Procureur, S.; Quintans, C.; Rajotte, J.-F.; Ramos, S.; Rapatsky, V.; Reicherz, G.; Reggiani, D.; Richter, A.; Robinet, F.; Rocco, E.; Rondio, E.; Rozhdestvensky, A. M.; Ryabchikov, D. I.; Samoylenko, V. D.; Sandacz, A.; Santos, H.; Sapozhnikov, M. G.; Sarkar, S.; Savin, I. A.; Schiavon, P.; Schill, C.; Schmitt, L.; Schönmeier, P.; Schröder, W.; Shevchenko, O. Yu.; Siebert, H.-W.; Silva, L.; Sinha, L.; Sissakian, A. N.; Slunecka, M.; Smirnov, G. I.; Sosio, S.; Sozzi, F.; Srnka, A.; Stinzing, F.; Stolarski, M.; Sugonyaev, V. P.; Sulc, M.; Sulej, R.; Tchalishev, V. V.; Tessaro, S.; Tessarotto, F.; Teufel, A.; Tkatchev, L. G.; Venugopal, G.; Virius, M.; Vlassov, N. V.; Vossen, A.; Webb, R.; Weise, E.; Weitzel, Q.; Windmolders, R.; Wirth, S.; Wi?licki, W.; Wollny, H.; Zaremba, K.; Zavertyaev, M.; Zemlyanichkina, E.; Zhao, J.; Ziegler, R.; Zvyagin, A.; Compass Collaboration

    2008-03-01

    The semi-inclusive difference asymmetry Ah+-h- for hadrons of opposite charge has been measured by the COMPASS experiment at CERN. The data were collected in the years 2002-2004 using a 160 GeV polarised muon beam scattered off a large polarised 6LiD target in the kinematic range 0.006 < x < 0.7 and 1 valence quark polarisation and provides an evaluation of the first moment of ?uv + ?dv which is found to be equal to 0.40 ± 0.07 (stat.) ± 0.06 (syst.) over the measured range of x at Q2 = 10 (GeV / c) 2. When combined with the first moment of g1d previously measured on the same data, this result favours a non-symmetric polarisation of light quarks ?ubar = - ?dbar at a confidence level of two standard deviations, in contrast to the often assumed symmetric scenario ?ubar = ?dbar = ?sbar = ?s.

  19. The polarised valence quark distribution from semi-inclusive DIS

    NASA Astrophysics Data System (ADS)

    Compass Collaboration; Alekseev, M.; Alexakhin, V. Yu.; Alexandrov, Yu.; Alexeev, G. D.; Amoroso, A.; Arbuzov, A.; Bade?ek, B.; Balestra, F.; Ball, J.; Barth, J.; Baum, G.; Bedfer, Y.; Bernet, C.; Bertini, R.; Bettinelli, M.; Birsa, R.; Bisplinghoff, J.; Bordalo, P.; Bradamante, F.; Bravar, A.; Bressan, A.; Brona, G.; Burtin, E.; Bussa, M. P.; Chapiro, A.; Chiosso, M.; Cicuttin, A.; Colantoni, M.; Costa, S.; Crespo, M. L.; Dalla Torre, S.; Dafni, T.; Das, S.; Dasgupta, S. S.; de Masi, R.; Dedek, N.; Denisov, O. Yu.; Dhara, L.; Diaz, V.; Dinkelbach, A. M.; Donskov, S. V.; Dorofeev, V. A.; Doshita, N.; Duic, V.; Dünnweber, W.; Eversheim, P. D.; Eyrich, W.; Faessler, M.; Falaleev, V.; Ferrero, A.; Ferrero, L.; Finger, M.; Finger, M.; Fischer, H.; Franco, C.; Franz, J.; Friedrich, J. M.; Frolov, V.; Garfagnini, R.; Gautheron, F.; Gavrichtchouk, O. P.; Gazda, R.; Gerassimov, S.; Geyer, R.; Giorgi, M.; Gobbo, B.; Goertz, S.; Gorin, A. M.; Grabmüller, S.; Grajek, O. A.; Grasso, A.; Grube, B.; Gushterski, R.; Guskov, A.; Haas, F.; Hannappel, J.; von Harrach, D.; Hasegawa, T.; Heckmann, J.; Hedicke, S.; Heinsius, F. H.; Hermann, R.; Heß, C.; Hinterberger, F.; von Hodenberg, M.; Horikawa, N.; Horikawa, S.; D'Hose, N.; Ilgner, C.; Ioukaev, A. I.; Ishimoto, S.; Ivanov, O.; Ivanshin, Yu.; Iwata, T.; Jahn, R.; Janata, A.; Jasinski, P.; Joosten, R.; Jouravlev, N. I.; Kabuß, E.; Kang, D.; Ketzer, B.; Khaustov, G. V.; Khokhlov, Yu. A.; Kisselev, Yu.; Klein, F.; Klimaszewski, K.; Koblitz, S.; Koivuniemi, J. H.; Kolosov, V. N.; Komissarov, E. V.; Kondo, K.; Königsmann, K.; Konorov, I.; Konstantinov, V. F.; Korentchenko, A. S.; Korzenev, A.; Kotzinian, A. M.; Koutchinski, N. A.; Kouznetsov, O.; Kral, A.; Kravchuk, N. P.; Kroumchtein, Z. V.; Kuhn, R.; Kunne, F.; Kurek, K.; Ladygin, M. E.; Lamanna, M.; Le Goff, J. M.; Lednev, A. A.; Lehmann, A.; Levorato, S.; Lichtenstadt, J.; Liska, T.; Ludwig, I.; Maggiora, A.; Maggiora, M.; Magnon, A.; Mallot, G. K.; Mann, A.; Marchand, C.; Marroncle, J.; Martin, A.; Marzec, J.; Massmann, F.; Matsuda, T.; Maximov, A. N.; Meyer, W.; Mielech, A.; Mikhailov, Yu. V.; Moinester, M. A.; Mutter, A.; Nagaytsev, A.; Nagel, T.; Nähle, O.; Nassalski, J.; Neliba, S.; Nerling, F.; Neubert, S.; Neyret, D. P.; Nikolaenko, V. I.; Nikolaev, K.; Olshevsky, A. G.; Ostrick, M.; Padee, A.; Pagano, P.; Panebianco, S.; Panknin, R.; Panzieri, D.; Paul, S.; Pawlukiewicz-Kaminska, B.; Peshekhonov, D. V.; Peshekhonov, V. D.; Piragino, G.; Platchkov, S.; Pochodzalla, J.; Polak, J.; Polyakov, V. A.; Pretz, J.; Procureur, S.; Quintans, C.; Rajotte, J.-F.; Ramos, S.; Rapatsky, V.; Reicherz, G.; Reggiani, D.; Richter, A.; Robinet, F.; Rocco, E.; Rondio, E.; Rozhdestvensky, A. M.; Ryabchikov, D. I.; Samoylenko, V. D.; Sandacz, A.; Santos, H.; Sapozhnikov, M. G.; Sarkar, S.; Savin, I. A.; Schiavon, P.; Schill, C.; Schmitt, L.; Schönmeier, P.; Schröder, W.; Shevchenko, O. Yu.; Siebert, H.-W.; Silva, L.; Sinha, L.; Sissakian, A. N.; Slunecka, M.; Smirnov, G. I.; Sosio, S.; Sozzi, F.; Srnka, A.; Stinzing, F.; Stolarski, M.; Sugonyaev, V. P.; Sulc, M.; Sulej, R.; Tchalishev, V. V.; Tessaro, S.; Tessarotto, F.; Teufel, A.; Tkatchev, L. G.; Venugopal, G.; Virius, M.; Vlassov, N. V.; Vossen, A.; Webb, R.; Weise, E.; Weitzel, Q.; Windmolders, R.; Wirth, S.; Wi?licki, W.; Wollny, H.; Zaremba, K.; Zavertyaev, M.; Zemlyanichkina, E.; Zhao, J.; Ziegler, R.; Zvyagin, A.

    2008-03-01

    The semi-inclusive difference asymmetry A-h for hadrons of opposite charge has been measured by the COMPASS experiment at CERN. The data were collected in the years 2002 2004 using a 160 GeV polarised muon beam scattered off a large polarised 6LiD target in the kinematic range 0.006valence quark polarisation and provides an evaluation of the first moment of ?u+?d which is found to be equal to 0.40±0.07(stat.)±0.06(syst.) over the measured range of x at Q=10 GeV. When combined with the first moment of g1d previously measured on the same data, this result favours a non-symmetric polarisation of light quarks ?u¯=-?d¯ at a confidence level of two standard deviations, in contrast to the often assumed symmetric scenario ?u¯=?d¯=?s¯=?s.

  20. Valence calculations of lanthanide anion binding energies: a comprehensive study

    NASA Astrophysics Data System (ADS)

    O'Malley, Steven M.; Beck, Donald R.

    2009-05-01

    We have applied a methodology of universal jls restrictions on the 4f^n subgroup of relativistic configuration-interaction calculations of progressively more complex lanthanide anionsootnotetextS. M. O'Malley and D. R. Beck, Phys. Rev. A 77, 012505 (2008).^,ootnotetextS. M. O'Malley and D. R. Beck, Phys. Rev. A 78, 012510 (2008).^,ootnotetextS. M. O'Malley and D. R. Beck, Phys. Rev. A, in press.. Our completed study of the row predicts bound 6p attachments to all lanthanide ground state configurations except Yb, additional 6p attachments to excited opposite parity configurations in Tb and Lu, and 6s attachments to excited open-6s thresholds in La, Ce, Pr, and Gd. In total we predict more than 100 bound states for the lanthanide anions, and we hope this comprehensive study encourages further experimentalootnotetexte.g. V. T. Davis et al., Nucl. Instrum. Methods Phys. Res. B 241, 118 (2005).^,ootnotetexte.g. C. W. Walter et al., Phys. Rev. A 76, 052702 (2007). interest in these anions. Such measurements will be useful in ``fine tuning'' these ab initio binding energies to account for missing core-valence correlation and the approximations that were necessary in these complex calculations.

  1. Electronic structure and bonding of the 3d transition metal borides, MB, M =Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu through all electron ab initio calculations

    NASA Astrophysics Data System (ADS)

    Tzeli, Demeter; Mavridis, Aristides

    2008-01-01

    The electronic structure and bonding of the ground and some low-lying states of all first row transition metal borides (MB), ScB, TiB, VB, CrB, MnB, FeB, CoB, NiB, and CuB have been studied by multireference configuration interaction (MRCI) methods employing a correlation consistent basis set of quintuple cardinality (5Z). It should be stressed that for all the above nine molecules, experimental results are essentially absent, whereas with the exception of ScB and CuB the remaining seven species are studied theoretically for the first time. We have constructed full potential energy curves at the MRCI/5Z level for a total of 27 low-lying states, subsequently used to extract binding energies, spectroscopic parameters, and bonding schemes. In addition, some 20 or more states for every MB species have been examined at the MRCI/4Z level of theory. The ground state symmetries and corresponding binding energies (in kcal/mol) are ?-5(ScB), 76; ?6(TiB), 65; ?+7(VB), 55; ?+6(CrB), 31; ?5(MnB), 20; ?-4(FeB), 54; ?3(CoB), 66; ?+2(NiB), 79; and ?+1(CuB), 49.

  2. The source of chemical bonding.

    PubMed

    Needham, Paul

    2014-03-01

    Developments in the application of quantum mechanics to the understanding of the chemical bond are traced with a view to examining the evolving conception of the covalent bond. Beginning with the first quantum mechanical resolution of the apparent paradox in Lewis's conception of a shared electron pair bond by Heitler and London, the ensuing account takes up the challenge molecular orbital theory seemed to pose to the classical conception of the bond. We will see that the threat of delocalisation can be overstated, although it is questionable whether this should be seen as reinstating the issue of the existence of the chemical bond. More salient are some recent developments in a longstanding discussion of how to understand the causal aspects of the bonding interaction--the nature of the force involved in the covalent link--which are taken up in the latter part of the paper. PMID:24984444

  3. Auger lineshape analysis

    NASA Astrophysics Data System (ADS)

    Madden, H. H.

    1983-03-01

    Auger transitions occurring at solid surfaces give spectra containing information on the energy distribution of valence electrons involved in the transition. Thus Auger Electron Spectroscopy (AES) can be used as a valence band (VB) Spectroscopy that is surface sensitive. Analyses of a number of core-valence-valence (CVV) Auger spectra are reviewed to illustrate the VB information contained in their lineshapes and to indicate current understanding of the physics of the Auger process as it applies to solids. The KVV spectrum from elemental beryllium is an example of a CW line that can be analyzed simply in terms of the sum of convolution products of independent-particle VB density-of-states (DOS) components. Other elemental solids for which such simple arguments suffice include Al, Si, Li, Ti, Co and B. The CW spectra from copper are discussed as examples of CW lineshapes that are distorted from those expected from simple VB DOS arguments because localization in the two-hole Auger final state for Cu makes hole-hole interactions important in determining the Auger lineshapes. Initial state screening is shown to influence the CVV lineshapes from Be as well as Cu. CVV spectra from the compound surfaces BeO and SiO 2 are analyzed using concepts of interatomic transitions as well as independent-parsite. ticle VB arguments. These spectra show that AES is a probe of the local DOS about the core-hole This ability of AES to give local bonding information is illustrated by analyses of CW spectra from multi-component surfaces which may be made in terms of the simple superposition of local-bonding signals. Thus the Si-L 23VV signal from silicon oxynitride is shown to be the superposition of signals representing elemental Si, Si-H, Si-N and Si-O bonding.

  4. Theory of Auger electron and appearance-potential spectroscopy from solids with partially filled valence bands: Effects of valence-band-core interaction

    NASA Astrophysics Data System (ADS)

    Potthoff, M.; Braun, J.; Borstel, G.; Nolting, W.

    1993-05-01

    CVV Auger electron and appearance-potential spectra of solids are well known to exhibit strong satellite features depending on the ratio of on-site Coulomb interaction among the valence-band electrons U and the width of the free Bloch band W. We present a theory that additionally includes the effects of the Coulomb interaction between the valence-band electrons and the core electrons Uc. The spectra are influenced by the screening of the core hole in the initial state for Auger electron spectroscopy (AES), the sudden response of the valence-band electrons after the destruction of the core hole and, for appearance-potential spectroscopy (APS), by the scattering at the core hole in the final state. These effects become important especially for systems with partially filled energy bands. For APS, however, the Uc interaction already yields nontrivial effects for the limiting case of a completely empty valence band. The localized core hole implies a breakdown of translational symmetry in the distribution of the valence-band electrons, which renders the calculation more difficult. But, extending the theory to finite temperatures, we will show that the translational symmetry may be reestablished in a formal way. Both the AES and APS intensities are directly related to a proper three-particle spectral density that exactly reflects the crystal periodicity. Within the framework of the single-band Hubbard model, which is extended to include the Uc interaction, we calculate the three-particle spectral density in a generalized ladder approximation. The Uc interaction is treated by means of perturbation theory. We develop the theory for the zeroth- and first-order contributions and look at the interesting limiting cases of a completely filled and empty valence band.

  5. 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. PMID:15530718

  6. VersaBond bone cement

    Microsoft Academic Search

    Tore Dalén; Kjell G. Nilsson

    2005-01-01

    VersaBond is a newly developed bone cement. To investigate its clinical performance, VersaBond was compared to Palacos R in a prospective randomized study in total knee replacement. Fifty-nine patients (61 knees) undergoing total knee replacement were randomized to either VersaBond or Palacos R bone cement and followed for 24 months using radiostereometric analysis (RSA).Up to 2 years there were no

  7. Beryllium and Strong Hydrogen Bonds

    Microsoft Academic Search

    T. Mark McCleskey; Brian L. Scott

    2009-01-01

    We compare beryllium to H and show that beryllium can displace H in many “strong hydrogen bonds” where Be as a “tetrahedral proton” (O-Be-O angle is tetrahedral as opposed to the nearly linear O-H—O angle) is thermodynamically preferred. The strong hydrogen bond provides two advantages. First, the O–X distance in a strong hydrogen bond is in the range 2.4–2.8 Å,

  8. 27 CFR 70.282 - Single bond in lieu of multiple bonds.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ...2011-04-01 2011-04-01 false Single bond in lieu of multiple bonds. 70...Occupational) Tax Bonds § 70.282 Single bond in lieu of multiple bonds. In the case of bonds required under this part, a single bond will not be accepted in lieu of...

  9. 27 CFR 70.282 - Single bond in lieu of multiple bonds.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ...2010-04-01 2010-04-01 false Single bond in lieu of multiple bonds. 70...Occupational) Tax Bonds § 70.282 Single bond in lieu of multiple bonds. In the case of bonds required under this part, a single bond will not be accepted in lieu of...

  10. 27 CFR 70.282 - Single bond in lieu of multiple bonds.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ...2012-04-01 2011-04-01 true Single bond in lieu of multiple bonds. 70...Occupational) Tax Bonds § 70.282 Single bond in lieu of multiple bonds. In the case of bonds required under this part, a single bond will not be accepted in lieu of...

  11. 27 CFR 70.282 - Single bond in lieu of multiple bonds.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ...2013-04-01 2013-04-01 false Single bond in lieu of multiple bonds. 70...Occupational) Tax Bonds § 70.282 Single bond in lieu of multiple bonds. In the case of bonds required under this part, a single bond will not be accepted in lieu of...

  12. Thermal Variation of Ce Valence in Mixed Valence–Kondo Lattice Systems CeT2(Si1-xGex)2 with T= Mn and Ni

    SciTech Connect

    Liang,G.; Croft, M.

    2008-01-01

    The results on the thermal variation of Ce L3-valence in CeT2(Si1-xGex)2 series with 0{le}x{le}1 and T=Mn and Ni are reported. It is observed that for both series, the Ce valence increases with decreasing temperature and has little thermal variation for samples in the nearly trivalent regime. The magnitude of this thermal variation in the T=Mn series is much greater than in the T=Ni series. The results are explained by the degenerate Anderson model and correlated with the specific heat data.

  13. Valence determination of manganese in battery cathode materials by high-resolution Mn Kalpha1 spectra.

    PubMed

    Konishi, Tokuzo; Tsubata, Toshio; Oku, Masaoki; Todorov, Yanko M; Yoshio, Masaki

    2005-07-01

    High-resolution the Mn Kalpha1 X-ray fluorescence spectra (HRXRF) were measured for a variety of manganese compounds, the oxidation number (valence) of which was from II to VII. Plots of the valence against the full width at half maximum (FWHM) and the chemical shift of the Kalpha1 X-ray fluorescence spectra give a curve and a liniar relation, respectively. The coefficient of correlation (R2) for the latter plot was 0.989 between valency II and VII. More excellent linearlity from III to IV was obtained with R2 = 0.995, which enabled us to determine the oxidation number of manganese atom in a nickel ion doped spinel structure, LiMn2O4 (LiNixMn(2-x)O4, with 0.2 < x < 0.42). From the valence of manganese ion obtained from HRXRF, the oxidation number of nickel ion is concluded to be divalent. PMID:16038510

  14. An Intracranial EEG Study of the Neural Dynamics of Musical Valence Processing.

    PubMed

    Omigie, Diana; Dellacherie, Delphine; Hasboun, Dominique; George, Nathalie; Clement, Sylvain; Baulac, Michel; Adam, Claude; Samson, Severine

    2014-06-01

    The processing of valence is known to recruit the amygdala, orbitofrontal cortex, and relevant sensory areas. However, how these regions interact remains unclear. We recorded cortical electrical activity from 7 epileptic patients implanted with depth electrodes for presurgical evaluation while they listened to positively and negatively valenced musical chords. Time-frequency analysis suggested a specific role of the orbitofrontal cortex in the processing of positively valenced stimuli while, most importantly, Granger causality analysis revealed that the amygdala tends to drive both the orbitofrontal cortex and the auditory cortex in theta and alpha frequency bands, during the processing of valenced stimuli. Results from the current study show the amygdala to be a critical hub in the emotion processing network: specifically one that influences not only the higher order areas involved in the evaluation of a stimulus's emotional value but also the sensory cortical areas involved in the processing of its low-level acoustic features. PMID:24904066

  15. 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...

  16. Bidirectional switch of the valence associated with a hippocampal contextual memory engram

    E-print Network

    Redondo, Roger L.

    The valence of memories is malleable because of their intrinsic reconstructive property. This property of memory has been used clinically to treat maladaptive behaviours. However, the neuronal mechanisms and brain circuits ...

  17. Optogenetic dissection of neural circuits underlying emotional valence and motivated behaviors

    E-print Network

    Nieh, Horng-An Edward

    The neural circuits underlying emotional valence and motivated behaviors are several synapses away from both defined sensory inputs and quantifiable motor outputs. Electrophysiology has provided us with a suitable means ...

  18. 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

  19. Too close for comfort: Stimulus valence moderates the influence of motivational orientation on distance perception

    E-print Network

    Krpan, Dario; Schnall, Simone

    2014-12-04

    and respond to valenced stimuli (e.g., Cacioppo et al., 1993; Centerbar & Clore, 2006; Duclos et al., 1989; Förster & Strack, 1996; Friedman & Förster, 2002, 2005a; Stepper & Strack, 1993; Strack, Martin, & Stepper, 1988; Wells & Petty, 1980). Indeed...

  20. Too close for comfort: Stimulus valence moderates the influence of motivational orientation on distance perception

    E-print Network

    Krpan, Dario; Krpan, Simone

    2014-10-22

    ; Duclos et al., 1989; Cacioppo et al., 1993; Stepper & Strack, 1993; Förster & Strack, 1996, Friedman, & Förster, 2002, 2005a; Centerbar & 2    Clore, 2006). Indeed, the compatibility hypothesis further suggests that evoking valence...

  1. Overlap valence quarks on a twisted mass sea: a case study for mixed action Lattice QCD

    E-print Network

    Krzysztof Cichy; Vincent Drach; Elena Garcia-Ramos; Gregorio Herdoiza; Karl Jansen

    2012-11-07

    We discuss a Lattice QCD mixed action investigation employing Wilson maximally twisted mass sea and overlap valence fermions. Using four values of the lattice spacing, we demonstrate that the overlap Dirac operator assumes a point-like locality in the continuum limit. We also show that by adopting suitable matching conditions for the sea and valence theories a consistent continuum limit for the pion decay constant and light baryon masses can be obtained. Finally, we confront results for sea-valence mixed meson masses and the valence scalar correlator with corresponding expressions of chiral perturbation theory. This allows us to extract low energy constants of mixed action chiral perturbation which characterize the strength of unitarity violations in our mixed action setup.

  2. 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

    2015-07-01

    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

  3. Resonant Photoemission Spectroscopy and Theoretical Calculation of the Valence Band Structure in Chromium Aluminum Oxynitride

    Microsoft Academic Search

    Youngmin Choi; Hyunju Chang; Beyong-Hwan Ryu; Kijeong Kong; Jae Do Lee; Kwangsoo No

    2003-01-01

    The electronic structure of chromium aluminum oxynitride has been investigated using resonant photoemission spectroscopy (RPES) and the discrete variational (DV)-Xalpha method. The RPES measurement of the electronic structure around the Cr 2p3\\/2 absorption edges exhibited significant resonant interference behavior for Cr 3d valence electrons, whereas it exhibited small resonant interference behavior for N 2p valence electrons. Therefore this RPES method

  4. Valence ab initio calculation of the potential energy curves for the Sr 2 dimer

    Microsoft Academic Search

    E. Czuchaj; M. Kro?nicki; H. Stoll

    2003-01-01

    The ground and excited states of the Sr2 molecule has been investigated by use of a two-valence-electron semi-empirical pseudopotential (PP(2)) and applying the internally contracted multireference CI method (ICMRCI) and complete active space SCF (CAS SCF) reference wavefunctions. In the calculations, core polarization and core-valence correlation have been accounted for by adding a core-polarization potential (CPP) to the hamiltonian. Moreover,

  5. Valence ab initio calculation of the potential-energy curves for the Ca 2 dimer

    Microsoft Academic Search

    E. Czuchaj; M. Krosnicki; H. Stoll

    2003-01-01

    The electronic structure of the Ca 2 molecule has been investigated by use of a two-valence-electron semiempirical pseudopotential and applying the internally contracted multireference configuration interaction method with complete-active-space self-consistent-field reference wave functions. Core–valence correlation effects have been accounted for by adding a core-polarization potential to the Hamiltonian. The ground-state properties of the Ca 2 and Ca 2 + dimers

  6. Venues, valences, and public policy: a study of committee bias and the development of pesticides 

    E-print Network

    Talbert, Jeffery Charles

    1991-01-01

    VENUES, VALENCES, AND PUBLIC POLICY: A STUDY OF COMMITTEE BIAS AND THE DEVELOPMENT OF PESTICIDES A Thesis by Jeffery Charles Talbert Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment... of the requirements for the degree of MASTER OF ARTS May 1991 Major Subject: Political Science VENUES, VALENCES, AND PUBLIC POLICY: A STUDY OF COMMITTEE BIAS AND THE DEVELOPMENT OF PESTICIDES A Thesis by Jeffery Charles Talbert Approved as to style...

  7. Electronic Structure and Valence Band Spectra of Bi4Ti3O12

    Microsoft Academic Search

    A. V. Postnikov; St. Bartkowski; F. Mersch; M. Neumann; E. Z. Kurmaev; V. M. Cherkashenko; S. N. Nemnonov; V. R. Galakhov

    1995-01-01

    The x-ray photoelectron valence band spectrum and x-ray emission valence-band spectra (Ti K _beta_5, Ti L_alpha, O K_alpha) of Bi4Ti3O12 are presented (analyzed in the common energy scale) and interpreted on the basis of a band-structure calculation for an idealized I4\\/mmm structure of this material.

  8. NMR and muSR studies of valence fluctuation and magnetism in Sm3Se4

    Microsoft Academic Search

    S. Takagi; H. Suzuki; A. Ochiai; T. Suzuki; A. Amato; R. Feyerherm; F. N. Gygax; A. Schenck

    1993-01-01

    Temperature-activated valence fluctuation has been concluded in a semiconducting compound Sm3Se4 from detailed temperature- and frequency-dependencies of the nuclear relaxation rates of 77Se NMR above about 130 K. Exploiting the different time-window of the mu+SR technique, the valence fluctuation in the lower-temperature range and the ground-state magnetic properties have also been investigated.

  9. Ground-state properties and magnetic excitations of the mixed valence state: Cerium-based alloys

    Microsoft Academic Search

    B. H. Grier; R. D. Parks; S. M. Shapiro; C. F. Majkrzak

    1981-01-01

    Both the static and dynamic magnetic behavior of the mixed valence system, Ce\\/sub 0.9-x\\/La\\/sub x\\/Th\\/sub 0.1\\/, have been studied through magnetic susceptibility and inelastic neutron scattering experiments. For small La concentrations (x< or approx. =0.09), the system exhibits a first-order valence transition to a strongly mixed valent ground state, whereas nearly integral valent, local moment behavior results for x> or

  10. Venues, valences, and public policy: a study of committee bias and the development of pesticides

    E-print Network

    Talbert, Jeffery Charles

    1991-01-01

    VENUES, VALENCES, AND PUBLIC POLICY: A STUDY OF COMMITTEE BIAS AND THE DEVELOPMENT OF PESTICIDES A Thesis by Jeffery Charles Talbert Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment... of the requirements for the degree of MASTER OF ARTS May 1991 Major Subject: Political Science VENUES, VALENCES, AND PUBLIC POLICY: A STUDY OF COMMITTEE BIAS AND THE DEVELOPMENT OF PESTICIDES A Thesis by Jeffery Charles Talbert Approved as to style...

  11. Spin-orbit configuration-interaction study of valence and Rydberg states of LiBe

    Microsoft Academic Search

    M. M. Marino; W. C. Ermler; C. W. Kern; V. E. Bondybey

    1992-01-01

    ital initio} spin--orbit full configuration-interaction calculations in the context of relativistic effective core potentials are reported for the weakly bound metal dimer LiBe, a three-valence-electron system. The effects of basis set on the energies of valence and Rydberg states of the cluster are discussed, as are the effects of configuration space selection on the energy of the latter states. Results

  12. Spin–orbit configuration-interaction study of valence and Rydberg states of LiBe

    Microsoft Academic Search

    M. M. Marino; W. C. Ermler; C. W. Kern; V. E. Bondybey

    1992-01-01

    Abinitio spin–orbit full configuration-interaction calculations in the context of relativistic effective core potentials are reported for the weakly bound metal dimer LiBe, a three-valence-electron system. The effects of basis set on the energies of valence and Rydberg states of the cluster are discussed, as are the effects of configuration space selection on the energy of the latter states. Results at

  13. Bonding and Structure of Intermetallics: A New Bond Order Potential

    Microsoft Academic Search

    D. G. Pettifor; M. Aoki; J. N. Murrell; A. Cottrell; A. M. Stoneham

    1991-01-01

    Intermetallics such as the transition metal aluminides present theorists with a challenge since bonding is not well described by currently available pair or embedded atom potentials. We show that a new angularly dependent, many-body potential for the bond order has all the necessary ingredients for an adequate description. In particular, by linearizing the moment-recursion coefficient relations, a cluster expansion is

  14. Bond pad surface quality for reliable wire bonding

    Microsoft Academic Search

    D. Martin Knotter; Ingrid A. Rink; Wim A. P. Claassen; Jos H. M. Philipsen

    The impact of fluoride and AlOx contaminants on the quality of wire bonding (Au to Al welding) has been measured. No or minor impact of these contaminants has been found with a standard ball shear test. Despite an accelerated lifetime test, the shear strength remains above the required specification limits. Intermetallic coverage, the percentage of the interface between the bond

  15. Connecting [NiFe]- and [FeFe]-Hydrogenases: Mixed-Valence Nickel-Iron Dithiolates With Rotated Structures

    PubMed Central

    Schilter, David; Rauchfuss, Thomas B.; Stein, Matthias

    2012-01-01

    A series of mixed-valence iron-nickel dithiolates is described that exhibits structures similar to those of mixed-valence diiron dithiolates. Interaction of tricarbonyl salt [(dppe)Ni(pdt)Fe(CO)3]BF4 ([1]BF4, dppe = Ph2PCH2CH2PPh2, pdtH2 = HSCH2CH2CH2SH) with P-donor ligands (L) afforded the substituted derivatives [(dppe)Ni(pdt)Fe(CO)2L]BF4 incorporating L = PHCy2 ([1a]BF4), PPh(NEt2)2 ([1b]BF4), P(NMe2)3 ([1c]BF4), P(i-Pr)3 ([1d]BF4) and PCy3 ([1e]BF4). The related precursor [(dcpe)Ni(pdt)Fe(CO)3]BF4 ([2]BF4, dcpe = Cy2PCH2CH2PCy2) gave the more electron-rich family of compounds [(dcpe)Ni(pdt)Fe(CO)2L]BF4 for L = PPh2(2-pyridyl) ([2a]BF4), PPh3 ([2b]BF4) and PCy3 ([2c]BF4). For bulky and strongly basic monophosphorus ligands, the salts feature distorted Fe coordination geometries: crystallographic analyses of [1e]BF4 and [2c]BF4 showed they adopt ‘rotated’ Fe(I) centers, in which PCy3 occupies a basal site and one CO ligand partially bridges the Ni and Fe centers. Like the undistorted mixed-valence derivatives, the new class of complexes are described as Ni(II)Fe(I) (S = ½) systems according to EPR spectroscopy, although with attenuated 31P hyperfine interactions. DFT calculations using the BP86, B3LYP, and PBE0 exchange-correlation functionals agree with the structural and spectroscopic data, suggesting that the spin for [1e]+ is localized in a Fe(I)-centered d(z2) orbital, orthogonal to the Fe-P bond. The PCy3 complexes, rare examples of species featuring ‘rotated’ Fe centers, both structurally and spectroscopically resemble mixed-valence diiron dithiolates. Also reproducing the NiS2Fe core of the [NiFe]-H2ase active site, the hybrid models incorporate key features of the two major classes of H2ase. Furthermore, cyclic voltammetry experiments suggest that the highly basic phosphine ligands enable a second oxidation corresponding to the couple [(dxpe)Ni(pdt)Fe(CO)2L]+/2+. The resulting unsaturated 32e? dications represent the closest approach to modeling the highly electrophilic Ni-SIa state. In the case of L = PPh2(2-pyridyl) chelation of this ligand accompanies the second oxidation. PMID:22838645

  16. Making and breaking of chemisorption bonds

    NASA Astrophysics Data System (ADS)

    Lundqvist, Bengt I.

    1982-07-01

    A brief review of recent contributions from surface physics to the understanding of chemisorption and desorption is given. The first question that is addressed is: What happens to a molecule when itcomes close to a metal surface? On the basis of self-consistent calculations for atoms [1,2] and molecules [3] on simple metal surfaces general trends and concepts are described and a scenario for H 2 on Mg(0001) is presented [4]. Except for the physisorption occuring at distances ˜ 3 Å or larger outside the surface the molecule-surface interaction is characterized by substantial redistributions of the electrons. Molecular electron energy levels are shifted and broadened. In particular, the antibonding affinity level of H 2 is shifted to lower energies. The spatial redistribution of the electrons is beneficial for an increased electron-proton interaction, and thereby for the chemisorption energy of H, i.e. for the constituents of H 2. The intramolecular bond between the constituents, on the other hand, is weakened on the surface by at least one order of magnitude and at some instances even becomes repulsive. The reason for this breaking of the molecular bond is the downward shift at the antibonding molecular-orbital resonance allowing its partial filling with conduction electrons from the metal [5]. Also for the dynamic aspects of the chemisorption, the variation of electron structure upon the molecular approach to the surface is of key importance. For instance, there can be electronic mechanisms for the dissipation of the molecular translational energy, required for the trapping of the molecule [6]. For the emission of ions, occuring in, e.g., sputtering, the variation of the electron structure of the emitted particle is also very important [7]. The second question concerns the desorption of adsorbed species upon electron or photon impact. A brief review is given of proposed mechanisms for electron- and photon-stimulated desorption, ESD and PSD, respectively [8]. The Redhead-Gomer-Menzel mechanism for ESD [9] assumes the incoming electron to excite a valence electron contributing to the adsorbate-substrate bond into an antibonding orbital. This changes the attractive potential energy curve of the adsorbate into a repulsive one, and the adparticle finds it energetically favourable to leave the surface, i.e., to desorb. The mechanism of Knotek and Feibelman [10] originated from studies of O + desorption from TiO 2, where the O + ion yield was found to increase considerably at incident electron energies that coincide with ionization potentials of core electrons of the metal ion. Their mechanism is an Auger decay model, where after the creation of a core hole there is a deexcitation by an interatomic Auger process, where due to the suddenness of the process and the Coulomb repulsion between electrons the Auger electron is likely to be followed by a second emitted electron. The resulting O + ion ends up on a repulsive potential-energy curve and desorbs. The mechanism has later been extended to intraatomic Auger processes and PSD and successfully applied to selective breaking of bonds [8].

  17. The power of emotional valence—from cognitive to affective processes in reading

    PubMed Central

    Altmann, Ulrike; Bohrn, Isabel C.; Lubrich, Oliver; Menninghaus, Winfried; Jacobs, Arthur M.

    2012-01-01

    The comprehension of stories requires the reader to imagine the cognitive and affective states of the characters. The content of many stories is unpleasant, as they often deal with conflict, disturbance or crisis. Nevertheless, unpleasant stories can be liked and enjoyed. In this fMRI study, we used a parametric approach to examine (1) the capacity of increasing negative valence of story contents to activate the mentalizing network (cognitive and affective theory of mind, ToM), and (2) the neural substrate of liking negatively valenced narratives. A set of 80 short narratives was compiled, ranging from neutral to negative emotional valence. For each story mean rating values on valence and liking were obtained from a group of 32 participants in a prestudy, and later included as parametric regressors in the fMRI analysis. Another group of 24 participants passively read the narratives in a three Tesla MRI scanner. Results revealed a stronger engagement of affective ToM-related brain areas with increasingly negative story valence. Stories that were unpleasant, but simultaneously liked, engaged the medial prefrontal cortex (mPFC), which might reflect the moral exploration of the story content. Further analysis showed that the more the mPFC becomes engaged during the reading of negatively valenced stories, the more coactivation can be observed in other brain areas related to the neural processing of affective ToM and empathy. PMID:22754519

  18. Deformation and bonding processes in aluminum ultrasonic wire wedge bonding

    NASA Astrophysics Data System (ADS)

    Krzanowski, James E.; Murdeshwar, Nikhil

    1990-09-01

    The ultrasonic wire bonding (UWB) process has been examined using transmission electron microscopy (TEM) and standard wire pull testing techniques. Al-0.5 wt.% Mg wires 75 ?m in diameter were bonded to pure and alloyed Al substrates. The bonding parameters, surface roughness, and surface contamination levels were variables in the experiments. Cross-section TEM specimens were made from these samples. TEM analysis was conducted on the wire, wire/substrate interface and substrate. Pull tests showed that for the Al substrates the surface roughness or the presence of contamination did not effect the bond strength, whereas for contaminated stainless steel substrates, a three ?m surface finish resulted in the highest bond pull strength. The TEM observations revealed features such as low-angle grain boundaries, dislocation loops and the absence of a high dislocation density, indicating that the wire and substrate were dynamically annealed during bonding. Based on the width of a zone near a grain boundary in the wire which was depleted of dislocation loops, it was estimated that local heating equivalent to a temperature of 250° C for 90 msec was achieved in the wire during bonding. No evidence was found for melting along the bond interface, indicating that UWB is a solid-state process. Based on the TEM observations of the bond interface and the pull tests, it is concluded that the ultrasonic vibrations clean the surfaces to be joined to the extent that a good bond can be obtained by intimate metal-metal contact in the clean areas.

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

    PubMed Central

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

    2013-01-01

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

  20. C-H⋯Cl relevant discrepancy on structure, magnetic and electronic conductivity of two mixed-valence Cu ICu II coordination polymers

    NASA Astrophysics Data System (ADS)

    Shi, Ling; Yang, Ping; Huang, Guang; Li, Qian; Wang, Ning; Wu, Jian-Zhong; Yu, Ying

    2011-07-01

    Two mixed-valence Cu ICu II coordination polymers [Cu ICu II(qdiol)ClL] n (qdiol 2-=2,3-dioxyquinoxalinate, L=2,2'-bipyridine, 1; L=1,10-phenanthroline, 2) were obtained in basic ethanolic solution of CuCl 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 II, qdiol 2- and L are identical in both complexes. But the Cu I ions are two- and three-coordinated, and the Cl - 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.

  1. Two-dimensional angle-resolved photoelectron spectroscopy using display analyzer—Atomic orbital analysis and characterization of valence band

    NASA Astrophysics Data System (ADS)

    Daimon, Hiroshi; Matsui, Fumihiko

    The information obtained by two-dimensional angle-resolved photoelectron spectroscopy in UPS (ultraviolet photoelectron spectroscopy) region is described. A display-type spherical mirror analyzer can measure wide-angle angular distribution of photoelectrons of one particular kinetic energy (binding energy) without changing the angles of incident light and the sample. The shape of the cross section of valence band, especially of the Fermi surface can be observed directly on the screen. Three-dimensional energy band and Fermi surface are obtained by scanning the binding energy of two-dimensional band mapping. In the case of linearly polarized light excitation the symmetry relation in the photoelectron excitation process can also be displayed as “angular distribution from atomic orbital ADAO”, which is used to distinguish the atomic orbitals constituting the energy band. An example is shown for the atomic orbital analysis of Cu Fermi surface at each k point. It was successfully revealed that the Cu 4p orbitals are aligned with their axes pointing outwards. Another important angular distribution is the “photoemission structure factor PSF”, which originates from the interference among photoelectron waves from individual atoms. PSF determines the intensity inequivalency between Brillouin zones and reveals the bonding character of the energy band.

  2. A wire bond reliability model

    Microsoft Academic Search

    T. L. Heleine; R. M. Murcko; S.-C. Wang

    1991-01-01

    A defect modeling approach is developed which allows the determination of the true failure rate with a minimal sample size. A model was developed using the proposed approach to estimate the failure rate of an aluminium\\/1% silicon wire ultrasonically bonded to aluminum and to gold pads. For this reliability model the variable was wire-bond width. Dependent upon the width of

  3. Failure Analysis of Wire Bonds

    Microsoft Academic Search

    Harry A. Schafft

    1973-01-01

    Failure analysis of wire bonds has an important part to play in determining the causes of microelectronic device failure and ways for making and using devices to achieve greater reliability. Several tests and procedures used in the failure analysis of wire bonds are reviewed. Some of the inferences. about possible causes of permanent or intermittent failure that can be drawn

  4. Social bonding: regulation by neuropeptides

    PubMed Central

    Lieberwirth, Claudia; Wang, Zuoxin

    2014-01-01

    Affiliative social relationships (e.g., among spouses, family members, and friends) play an essential role in human society. These relationships affect psychological, physiological, and behavioral functions. As positive and enduring bonds are critical for the overall well-being of humans, it is not surprising that considerable effort has been made to study the neurobiological mechanisms that underlie social bonding behaviors. The present review details the involvement of the nonapeptides, oxytocin (OT), and arginine vasopressin (AVP), in the regulation of social bonding in mammals including humans. In particular, we will discuss the role of OT and AVP in the formation of social bonds between partners of a mating pair as well as between parents and their offspring. Furthermore, the role of OT and AVP in the formation of interpersonal bonding involving trust is also discussed. PMID:25009457

  5. Equilibrium Pricing of Special Bearer Bonds

    Microsoft Academic Search

    Jayanth Rama Varma

    In 1981, the Government issued Special Bearer Bonds under a scheme which allowed people to invest their black money in these bonds and enjoy freedom from investigations and prosecutions for tax evasion in respect of their holdings of these bonds. Through these bonds are no longer available in tap, there is an active secondary market for these bonds; the complete

  6. hp calculators HP 50g Bond Price

    E-print Network

    Vetter, Frederick J.

    hp calculators HP 50g Bond Price The FINANCE menu Bond Price Practice solving for the price of a bond #12;hp calculators HP 50g Bond Price hp calculators - 2 - HP 50g Bond Price The FINANCE menu. To exit from this data entry screen, press the $ key. Figure 2 The HP 50g Financial solver follows

  7. hp calculators HP 50g Bond Yield

    E-print Network

    Vetter, Frederick J.

    hp calculators HP 50g Bond Yield The FINANCE menu Bond Yield Practice solving for the yield of a bond #12;hp calculators HP 50g Bond Yield hp calculators - 2 - HP 50g Bond Yield The FINANCE menu as Beg if chosen. To exit from this data entry screen, press the $ key. Figure 2 The HP 50g Financial

  8. Thermocompression bonding of alumina ceramics to metal

    Microsoft Academic Search

    S. Das; A. N. Tiwari; A. R. Kulkarni

    2004-01-01

    Alumina ceramics and Kovar with aluminum interlayer are pressed together under vacuum at temperatures around 600°C for joining. This process produces mechanically strong ceramic to metal bonds in one step in an economic manner. In order to arrive at the optimum conditions for solid-state bonding, effects of bonding temperature, pressure and time on the bond strength have been studied. Bonding

  9. Ab initio calculations of the electronic structure and bonding characteristics of LaB6

    NASA Astrophysics Data System (ADS)

    Hossain, Faruque M.; Riley, Daniel P.; Murch, Graeme E.

    2005-12-01

    Lanthanum hexaboride ( LaB6 , NIST SRM-660a) is widely used as a standard reference material for calibrating the line position and line shape parameters of powder diffraction instruments. The accuracy of this calibration technique is highly dependent on how completely the reference material is characterized. Critical to x-ray diffraction, this understanding must include the valence of the La atomic position, which in turn will influence the x-ray form factor (f) and hence the diffracted intensities. The electronic structure and bonding properties of LaB6 have been investigated using ab initio plane-wave pseudopotential total energy calculations. The electronic properties and atomic bonding characteristics were analyzed by estimating the energy band structure and the density of states around the Fermi energy level. The calculated energy band structure is consistent with previously reported experimental findings; de Haas-van Alphen and two-dimensional angular correlation of electron-positron annihilation radiation. In addition, the bond strengths and types of atomic bonds in the LaB6 compound were estimated by analyzing the Mulliken charge density population. The calculated result revealed the coexistence of covalent, ionic, and metallic bonding in the LaB6 system and partially explains its high efficiency as a thermionic emitter.

  10. Halogen bonding (X-bonding): A biological perspective

    PubMed Central

    Scholfield, Matthew R; Zanden, Crystal M Vander; Carter, Megan; Ho, P Shing

    2013-01-01

    The concept of the halogen bond (or X-bond) has become recognized as contributing significantly to the specificity in recognition of a large class of halogenated compounds. The interaction is most easily understood as primarily an electrostatically driven molecular interaction, where an electropositive crown, or ?-hole, serves as a Lewis acid to attract a variety of electron-rich Lewis bases, in analogous fashion to a classic hydrogen bonding (H-bond) interaction. We present here a broad overview of X-bonds from the perspective of a biologist who may not be familiar with this recently rediscovered class of interactions and, consequently, may be interested in how they can be applied as a highly directional and specific component of the molecular toolbox. This overview includes a discussion for where X-bonds are found in biomolecular structures, and how their structure–energy relationships are studied experimentally and modeled computationally. In total, our understanding of these basic concepts will allow X-bonds to be incorporated into strategies for the rational design of new halogenated inhibitors against biomolecular targets or toward molecular engineering of new biological-based materials. PMID:23225628

  11. Coordination-Resolved Spectrometrics of Local Bonding and Electronic Dynamics of Au Atomic Clusters, Solid Skins, and Oxidized Foils.

    PubMed

    Yu, Wang; Bo, Maolin; Huang, Yongli; Wang, Yan; Li, Can; Sun, Chang Q

    2015-07-20

    By using combination of bond-order-length-strength (BOLS) correlation, the tight-binding (TB) approach, and zone-selective photoelectron spectroscopy (ZPS), we were able to resolve local bond relaxation and the associated 4f7/2 core-level shift of Au atomic clusters, Au(100, 110, 111) skins, and Au foils exposed to ozone for different lengths of time. In addition to quantitative information, such as local bond length, bond energy, binding-energy density, and atomic cohesive energy, the results confirm our predictions that bond-order deficiency shortens and stiffens the bond between undercoordinated atoms, which results in local densification and quantum entrapment of bonding electrons. The entrapment perturbs the Hamiltonian, and hence, shifts the core-level energy accordingly. ZPS also confirms that oxidation enhances the effect of atomic undercoordination on the positive 4f7/2 energy shift, with the associated valence electron polarization contributing to the catalytic ability of undercoordinated Au atoms. PMID:25916877

  12. 27 CFR 19.152 - Types of bonds.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ...DEPARTMENT OF THE TREASURY ALCOHOL DISTILLED SPIRITS PLANTS Bonds and Consents of Surety Bonding Requirements for A Dsp § 19.152 Types of bonds. (a) Basic Bonds. There are two basic types of bonds: the operations bond, and the...

  13. 27 CFR 19.152 - Types of bonds.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ...DEPARTMENT OF THE TREASURY LIQUORS DISTILLED SPIRITS PLANTS Bonds and Consents of Surety Bonding Requirements for A Dsp § 19.152 Types of bonds. (a) Basic Bonds. There are two basic types of bonds: the operations bond, and the...

  14. 27 CFR 19.152 - Types of bonds.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ...DEPARTMENT OF THE TREASURY LIQUORS DISTILLED SPIRITS PLANTS Bonds and Consents of Surety Bonding Requirements for A Dsp § 19.152 Types of bonds. (a) Basic Bonds. There are two basic types of bonds: the operations bond, and the...

  15. 27 CFR 19.152 - Types of bonds.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ...DEPARTMENT OF THE TREASURY ALCOHOL DISTILLED SPIRITS PLANTS Bonds and Consents of Surety Bonding Requirements for A Dsp § 19.152 Types of bonds. (a) Basic Bonds. There are two basic types of bonds: the operations bond, and the...

  16. 29 CFR 2580.412-19 - Term of the bond, discovery period, other bond clauses.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ...DEPARTMENT OF LABOR TEMPORARY BONDING RULES UNDER THE EMPLOYEE RETIREMENT INCOME SECURITY ACT OF 1974 TEMPORARY BONDING RULES General Bond Rules § 2580...section 13, if, with respect to bonding coverage required under section...

  17. 29 CFR 2580.412-19 - Term of the bond, discovery period, other bond clauses.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ...DEPARTMENT OF LABOR TEMPORARY BONDING RULES UNDER THE EMPLOYEE RETIREMENT INCOME SECURITY ACT OF 1974 TEMPORARY BONDING RULES General Bond Rules § 2580...section 13, if, with respect to bonding coverage required under section...

  18. Valence Fluctuations and Coherence in Cerium Based Compounds.

    NASA Astrophysics Data System (ADS)

    Chen, Yang-Yuan

    At the beginning of this thesis the phenomena of valence fluctuations and coherence are described. Fair agreement between experimental observation and theories exists for the Kondo ion case, but a lack of theory about coherence hampers comparison to existing experiments. In this thesis experimental results are first checked by Kondo theory in the Kondo ion regime (high T). Anomalies observed at low temperature are then reported; these are believed to be the results of coherence. In CePd_3 the vanishing resistivity at low T can be destroyed by a very small amount of non-magnetic impurity substitution on the Ce sublattice. In the resistivity of CePd _3 the T^2 law at low T and the different pressure dependence from that at high T prove there is a third scale T_{ rm coh}, which is not the Kondo temperature T_{rm K} nor the temperature of the resistivity maximum T_ {rm max}, but which is thought to be associated with the coherence phenomena. Results for the susceptibility shed further light on the low temperature behavior. We also report results for a new set of heavy fermion compounds Ce_3X (X = In, Sn and Al). They have very small characteristic temperature scales and huge coefficients of specific heat gamma(0) (T_{rm K}^{~}5K, gamma(0) = 700 mJ/mole K^2 for Ce_3In and T _{rm K}^{~} 15K, gamma(0) = 300 mJ/mole K^2 for Ce_3Sn). An interesting phase transition is also observed in Ce _3In and Ce_3Al. A nice consistency for values of T_{ rm K} extracted by various methods and fair agreement between experiment and theories is found if proper account of the involvement of crystal fields. We also found anomalies in their thermodynamic properties, such as a peak in gamma(T) at T to0 and a very large ground state susceptibility, which are believed to relate to coherence. For a complete understanding of their properties more powerful experiments such as neutron scattering will be tried in the future.

  19. The first example of a mixed valence ternary compound of silver with random distribution of Ag(i) and Ag(ii) cations.

    PubMed

    Mazej, Zoran; Micha?owski, Tomasz; Goreshnik, Evgeny A; Jagli?i?, Zvonko; Ar?on, Iztok; Szyd?owska, Jadwiga; Grochala, Wojciech

    2015-06-28

    The reaction between colourless AgSbF6 and sky-blue Ag(SbF6)2 (molar ratio 2?:?1) in gaseous HF at 323 K yields green Ag3(SbF6)4, a new mixed-valence ternary fluoride of silver. Unlike in all other Ag(i)/Ag(ii) systems known to date, the Ag(+) and Ag(2+) cations are randomly distributed on a single 12b Wyckoff position at the 4[combining macron] axis of the I4[combining macron]3d cell. Each silver forms four short (4 × 2.316(7) Å) and four long (4 × 2.764(6) Å) contacts with the neighbouring fluorine atoms. The valence bond sum analysis suggests that such coordination would correspond to a severely overbonded Ag(i) and strongly underbonded Ag(ii). Thorough inspection of thermal ellipsoids of the fluorine atoms closest to Ag centres reveals their unusual shape, indicating that silver atoms must in fact have different local coordination spheres; this is not immediately apparent from the crystal structure due to static disorder of fluorine atoms. The Ag K-edge XANES analysis confirmed that the average oxidation state of silver is indeed close to +1?. The optical absorption spectra lack features typical of a metal thus pointing out to the semiconducting nature of Ag3(SbF6)4. Ag3(SbF6)4 is magnetically diluted and paramagnetic (?eff = 1.9 ?B) down to 20 K with a very weak temperature independent paramagnetism. Below 20 K weak antiferromagnetism is observed (? = -4.1 K). Replacement of Ag(i) with potassium gives K(i)2Ag(ii)(SbF6)4 which is isostructural to Ag(i)2Ag(ii)(SbF6)4. Ag3(SbF6)4 is a genuine mixed-valence Ag(i)/Ag(ii) compound, i.e. Robin and Day Class I system (localized valences), despite Ag(i) and Ag(ii) adopting the same crystallographic position. PMID:25815902

  20. Organic molecule adsorption on solid surfaces: chemical bonding, mutual polarisation and dispersion interaction

    NASA Astrophysics Data System (ADS)

    Schmidt, W. G.; Seino, K.; Preuss, M.; Hermann, A.; Ortmann, F.; Bechstedt, F.

    2006-12-01

    We discuss some of the most relevant bonding scenarios for the adsorption of organic molecules on solid surfaces from the perspective of first-principles calculations. The adsorption of uracil and phenanthrenequinone on Si(001) and the adsorption of adenine on Cu(110) and graphite(0001) surfaces serve as prototypical examples to highlight relevant molecule substrate interactions and their consequences for the properties of the adsystem. Covalent bonds formed during organic reactions with semiconductor surfaces significantly modify the structural and electronic properties of both the adsorbed molecules and the substrate. Organic molecule adsorption on metals may be driven by mutual polarisation that leads to substantial charge transfer and rehybridisation, despite small adsorption energies. Subtle effects related to the lowering of the kinetic energy of the valence electrons as well as dispersion forces, finally, govern the interaction between the organic molecules and chemically inert substrates such as graphite.