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1

New bond-valence parameters for lanthanides.  

PubMed

The bond-valence method, especially the valence-sum rule, is very useful for checking if the structures formed by trivalent lanthanides are correct. In this work bond-valence parameters (Rij), which connect bond valences and bond lengths, have been computed for a large number of bonds taken from the Cambridge Structural Database, Version 5.24 (2002) [Allen (2002). Acta Cryst. B58, 380-388]. The calculated values of bond-valence parameters for metal-organic compounds decrease with an increase in lanthanide atomic number; the Rij values are also smaller than bond-valence parameters calculated for inorganic compounds. A summary of bond-valence sums calculated for Rij given in this work and reported in the literature, and a functional correlation between lanthanide-oxygen distances and coordination number are presented. PMID:15017089

Trzesowska, Agata; Kruszynski, Rafal; Bartczak, Tadeusz J

2004-04-01

2

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

ERIC Educational Resources Information Center

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

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

2008-01-01

3

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

PubMed

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

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

2015-02-23

4

Bond-valence parameters of lanthanides.  

PubMed

Ln-O and Ln-N bond-valence parameters have been computed in coordination complexes for lanthanides (Ln) at oxidation states other than +3 (Ce(IV), Sm(II), Eu(II) and Yb(II)). Moreover, Ln-Cl, Ln-S and Ln-C(pi-bonded) bond-valence parameters are presented, as calculated for coordination compounds. In general, the bond-valence parameters decrease in the order Ln-O > Ln-C > Ln-N > Ln-Cl > Ln-S. It has been found that the values of bond-valence parameters decrease with increasing lanthanide atomic number for coordination compounds. As expected, the values of lanthanide-oxygen and lanthanide-nitrogen bond-valence parameters diminish with increasing lanthanide oxidation state. Several examples are given where the total valence of the lanthanide ion is apparently incorrectly assigned, as well as cases where bond-valence method calculations confirm the doubtful oxidation state assignment. PMID:16983155

Trzesowska, Agata; Kruszynski, Rafal; Bartczak, Tadeusz J

2006-10-01

5

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

PubMed

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

Shaik, Sason

2010-08-21

6

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

NASA Astrophysics Data System (ADS)

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

Ferro-Costas, David; Mosquera, Ricardo A.

2015-01-01

7

New lanthanide-nitrogen bond-valence parameters.  

PubMed

The bond-valence parameters (R(ij)), which connect bond valences and bond lengths, have been computed for lanthanide-nitrogen bonds. It has been found that values of bond-valence parameters decrease with increasing lanthanide atomic number in coordination compounds, and that they are smaller than the R(ij) parameters of inorganic compounds. As expected, the lanthanide-nitrogen bond-valence parameters are larger than lanthanide-oxygen bond-valence parameters. There are no obvious dependencies between the number of N atoms in the coordination sphere and the bond-valence parameter value. PMID:16041092

Trzesowska, Agata; Kruszynski, Rafal; Bartczak, Tadeusz J

2005-08-01

8

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

PubMed

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

Bosi, Ferdinando

2014-10-01

9

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

PubMed

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

Chen, Zhenhua; Chen, Xun; Wu, Wei

2013-04-28

10

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

NASA Astrophysics Data System (ADS)

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

Chen, Zhenhua; Chen, Xun; Wu, Wei

2013-04-01

11

The variational subspace valence bond method.  

PubMed

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

Fletcher, Graham D

2015-04-01

12

Novel approach to the concept of bond-valence vectors.  

PubMed

A new approach to the old idea of deriving a bond-valence vector from the well-known bond-valence concept has been proposed. The foundation of the proposal is the previous electrostatic model in which bond valences are interpreted as electric fluxes. The outcome of this approach is actual vectorial quantities whose magnitudes are strictly but nonlinearly related to the scalar bond valences and are directed along the bond lines. It has been proved that the sum of all these bond-valence vectors drawn from a coordination center to its ligating atoms will be close to zero for the complete coordination sphere. Therefore, unlike the scalar bond valences, the obtained vectors provide information about the spatial arrangement of ligands. The geometrical consequences of the proposed bond-valence vector (BVV) model are analyzed for the geometries of the carbonates, phosphates, and five-coordinated organoaluminum compounds with CO3, PO4, and AlCO4 skeletons, respectively, retrieved from the Cambridge Structural Database. For acyclic carbonates this BVV model allows one to predict the O-C-O angles with a mean absolute error of 1.0 degrees using the empirical C-O distances only. Furthermore, this BVV model is able to quantitatively describe the strains in cyclic carbonates. The preliminary studies for NO2E, PO3E, and SO3E systems with a strongly stereoactive lone electron pair (E) show that the model may serve as a quantitative description of the lone electron pair effect on the coordination sphere. A great advantage of the presented BVV approach is that the derived relation between a bond-valence vector, bond valence, and bond length is given by an uncomplicated equation allowing quick and simple computations, thus providing a new analytical tool for describing the geometry of a coordination sphere that may be applied for structure validation. PMID:17948986

Zachara, Janusz

2007-11-12

13

Mixed valency in cerium oxide crystallographic phases: Valence of different cerium sites by the bond valence method  

Microsoft Academic Search

We have applied the bond valence method to cerium oxides to determine the oxidation states of the Ce ion at the various site symmetries of the crystals. The crystals studied include cerium dioxide and the two sesquioxides along with some selected intermediate phases which are crystallographically well characterized. Our results indicate that cerium dioxide has a mixed-valence ground state with

E. Shoko; M. F. Smith; Ross H. McKenzie

2009-01-01

14

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

ERIC Educational Resources Information Center

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

Pauling, Linus; Herman, Zelek S.

1984-01-01

15

Mixed valency in cerium oxide crystallographic phases: Determination of valence of the different cerium sites by the bond valence method  

Microsoft Academic Search

We have applied the bond valence method to cerium oxides to determine the\\u000aoxidation states of the Ce ion at the various site symmetries of the crystals.\\u000aThe crystals studied include cerium dioxide and the two sesquioxides along with\\u000asome selected intermediate phases which are crystallographically well\\u000acharacterized. Our results indicate that cerium dioxide has a mixed-valence\\u000aground state with

E. Shoko; M. F. Smith; Ross H. McKenzie

2008-01-01

16

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

PubMed Central

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

Xiang, Jin Yu; Ponder, Jay W.

2013-01-01

17

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

SciTech Connect

In a previous contribution, we outlined a method for predicting (hydr)oxy-acid and oxide surface acidity constants based on three main factors: bond valence, Me?O bond ionicity, and molecular shape. Here electrostatics calculations and ab initio molecular dynamics simulations are used to qualitatively show that Me?O bond ionicity controls the extent to which the electrostatic work of proton removal departs from ideality, bond valence controls the extent of solvation of individual functional groups, and bond valence and molecular shape controls local dielectric response. These results are consistent with our model of acidity, but completely at odds with other methods of predicting acidity constants for use in multisite complexation models. In particular, our ab initio molecular dynamics simulations of solvated monomers clearly indicate that hydrogen bonding between (hydr)oxo-groups and water molecules adjusts to obey the valence sum rule, rather than maintaining a fixed valence based on the coordination of the oxygen atom as predicted by the standard MUSIC model.

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

2006-08-15

18

Brown's bond valences, a measure of the strength of hydrogen bonds  

NASA Astrophysics Data System (ADS)

The intramolecular bond valences sOH of water molecules in condensed materials, which cannot be calculated with sufficient accuracy from experimental O?H bond lengths, have been determined indirectly from the intermolecular H⋯O distances using the equations s = 1 - ?sH⋯O and s' = {s O-H}/{(s O-H + ?s H⋯O) }. The bond valences s and s' thus obtained correlate almost linearly with the wavenumbers of the respective OD stretching modes of matrix isolated HDO molecules (slopes 2.79 × 10 -4 and 2.83 × 10 -4 v.u. cm, origins 1.79 × 10 -1 and 1.72 × 10 -1 v.u., respectively; v.u. = valence units). The bond valences and correlation curves established, which can be used for assigning hydrogen bonds even in the presence of multifurcated bonds, are discussed with respect to the physical reliability of s and s', the possible correction and improvement of inaccurate experimental O?H distances via the respective bond valences, and the significance of the direct proportionality of the bond valences to the wavenumbers of the stretches.

Lutz, H. D.; Jung, C.; Trömel, M.; Lösel, J.

1995-06-01

19

Generalized valence bond wave functions in quantum Monte Carlo  

NASA Astrophysics Data System (ADS)

We present a technique for using quantum Monte Carlo (QMC) to obtain high quality energy differences. We use generalized valence bond (GVB) wave functions, for an intuitive approach to capturing the important sources of static correlation, without needing to optimize the orbitals with QMC. Using our modifications to Walker branching and Jastrows, we can then reliably use diffusion quantum Monte Carlo to add in all the dynamic correlation. This simple approach is easily accurate to within a few tenths of a kcal/mol for a variety of problems, which we demonstrate for the adiabatic singlet-triplet splitting in methylene, the vertical and adiabatic singlet-triplet splitting in ethylene, 2+2 cycloaddition, and Be2 bond breaking.

Anderson, Amos G.; Goddard, William A.

2010-04-01

20

Valence-bond quantum Monte Carlo algorithms defined on trees  

NASA Astrophysics Data System (ADS)

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.

Deschner, Andreas; Sørensen, Erik S.

2014-09-01

21

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

PubMed Central

A theoretical model is presented for deriving effective diabatic states based on ab initio self-consistent field valence bond (VBSCF) theory by reducing the multi-configurational VB Hamiltonian into an effective two-state model. We describe two computational approaches for the optimization of the effective diabatic configurations, resulting in two ways of interpreting such effective diabatic states. In the variational diabatic configuration (VDC) method, the energies of the individual diabatic states are variationally minimized. In the consistent diabatic configuration (CDC) method, both the configuration coefficients and orbital coefficients are simultaneously optimized to minimize the adiabatic ground-state energy in VBSCF calculations. In addition, we describe a mixed molecular orbital and valence bond (MOVB) approach to construct the CDC diabatic and adiabatic states for a chemical reaction, whereas the VDC-MOVB method has been described previously. Employing the symmetric SN2 reaction between NH3 and CH3NH3+ as a test system, we found that the results from ab initio VBSCF and from MOVB calculations are in good agreement, suggesting that the computationally efficient MOVB method is a reasonable model for VB simulations of condensed phase reactions. The results indicate that CDC and VDC diabatic states converge, respectively, to covalent and ionic states as the molecular geometries are distorted from the minimum of the respective diabatic state along the reaction coordinate. Furthermore, the resonance energy that stabilizes the energy of crossing between the two diabatic states, resulting in the transition state of the adiabatic ground-state reaction, has a strong dependence on the overlap integral between the two diabatic states and is a function of both the exchange integral and the total diabatic ground-state energy. PMID:18828577

Song, Lingchun; Gao, Jiali

2009-01-01

22

A Resonating-Valence-Bond Theory of Metals and Intermetallic Compounds  

Microsoft Academic Search

The resonating-valence-bond theory of metals discussed in this paper differs from the older theory in making use of all nine stable outer orbitals of the transition metals, for occupancy by unshared electrons and for use in bond formation; the number of valency electrons is consequently considered to be much larger for these metals than has been hitherto accepted. The metallic

L. Pauling

1949-01-01

23

Valence bond supersolid in a bilayer extended Bose-Hubbard model  

NASA Astrophysics Data System (ADS)

The hardcore extended Bose Hubbard model on a bilayer square lattice with attractive (repulsive) interplane (intraplane) interactions has been investigated numerically. Focusing on the strong interplane hopping parameter regime, triplet valence bonds of dimers are stabilized to form valence bond checkerboard solid at quarter filling. Increasing the particle number we confirm the presence of the exotic valence bond supersolid phase, where the valence bond solid ordering and the boson superfluidity coexist. Rising further the particle number will lead to a checkerboard solid of dimer pair at half filling for strong intraplane repulsion, or a valence bond Mott insulator for weak repulsive interactions. We analyze the rich ground state phase diagrams of this model, which can be experimentally realized in optical lattices of cold atoms.

Ng, Kwai-Kong

2015-02-01

24

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

NASA Astrophysics Data System (ADS)

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.

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

2014-11-01

25

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

PubMed

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

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

2014-11-12

26

The itinerant resonating-valence-bond model for superconductivity  

SciTech Connect

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

Liu, S.H.

1987-08-01

27

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

PubMed

The bonding in the highly homoatomic np pi-np pi (n > or = 3)-bonded S2I42+ (three sigma + two pi bonds), the Se-I pi-bonded Se2I42+ (four sigma + one pi bonds), and their higher-energy isomers have been studied using modern DFT and ab initio calculations and theoretical analysis methods: atoms in molecules (AIM), molecular orbital (MO), natural bond orbital (NBO), and valence bond (VB) analyses, giving their relative energies, theoretical bond orders, and atomic charges. The aim of this work was to seek theory-based answers to four main questions: (1) Are the previously proposed simple pi*-pi* bonding models valid for S2I42+ and Se2I42+? (2) What accounts for the difference in the structures of S2I42+ and Se2I42+? (3) Why are the classically bonded isolobal P2I4 and As2I4 structures not adopted? (4) Is the high experimentally observed S-S bond order supported by theoretical bond orders, and how does it relate to high bond orders between other heavier main group elements? The AIM analysis confirmed the high bond orders and established that the weak bonds observed in S2I42+ and Se2I42+ are real and the bonding in these cations is covalent in nature. The full MO analysis confirmed that S2I42+ contains three sigma and two pi bonds, that the positive charge is essentially equally distributed over all atoms, that the bonding between S2 and two I2+ units in S2I42+ is best described by two mutually perpendicular 4c2e pi*-pi* bonds, and that in Se2I42+, two SeI2+ moieties are joined by a 6c2e pi*-pi* bond, both in agreement with previously suggested models. The VB treatment provided a complementary approach to MO analysis and provided insight how the formation of the weak bonds affects the other bonds. The NBO analysis and the calculated AIM charges showed that the minimization of the electrostatic repulsion between EI2+ units (E = S, Se) and the delocalization of the positive charge are the main factors that explain why the nonclassical structures are favored for S2I42+ and Se2I42+. The difference in the structures of S2I42+ and Se2I42+ is related to the high strength of the S-S pi bond compared to the weak S-I sigma bond and the additional stabilization from increased delocalization of positive charge in the structure of S2I42+ compared to the structure of Se2I42+. The investigation of the E2X42+ series (E = S, Se, Te; X = Cl, Br, I) revealed that only S2I42+ adopts the highly np pi-np pi (n > or = 3)-bonded structure, while all other dications favor the pi-bonded Se2I42+ structure. Theoretical bond order calculations for S2I42+ confirm the previously presented experimentally based bond orders for S-S (2.1-2.3) and I-I (1.3-1.5) bonds. The S-S bond is determined to have the highest reported S-S bond order in an isolated compound and has a bond order that is either similar to or slightly less than the Si-Si bond order in the proposed triply bonded [(Me3Si)2CH]2(iPr)SiSi triple bond SiSi(iPr)[CH(SiMe3)2]2 depending on the definition of bond orders used. PMID:17257010

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

2007-02-01

28

Resonating-Valence-Bond Liquid in Low Dimensions  

NASA Astrophysics Data System (ADS)

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

Ohkawa, Fusayoshi J.

2014-12-01

29

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

SciTech Connect

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

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

2009-03-15

30

An alternative strategy for count and storage of Kekulé and longer range resonance valence bond structures.  

PubMed

In this paper, we suggest a simple representation for notation of Kekulé valence bond (KVB) structures and longer range resonance valence bond (RVB) structures, which is called "the adjacency bonding array". In this representation, only an N component one-dimensional array is needed for inscribing each KVB or longer range RVB structure for an N-carbon system. Based on the adjacency bonding arrays, we develop very efficient algorithms for the systematic search of KVB and RVB structures as well as evaluation of the basis set overlap and Hamiltonian matrices. PMID:15807502

Cai, Fei; Shao, Heqing; Liu, Chungen; Jiang, Yuansheng

2005-01-01

31

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

PubMed Central

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

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

2010-01-01

32

The New Resonating Valence Bond Method for Ab-Initio Electronic Simulations  

E-print Network

The Resonating Valence Bond theory of the chemical bond was introduced soon after the discovery of quantum mechanics and has contributed to explain the role of electron correlation within a particularly simple and intuitive approach where the chemical bond between two nearby atoms is described by one or more singlet electron pairs. In this chapter Pauling's resonating valence bond theory of the chemical bond is revisited within a new formulation, introduced by P.W. Anderson after the discovery of High-Tc superconductivity. It is shown that this intuitive picture of electron correlation becomes now practical and efficient, since it allows us to faithfully exploit the locality of the electron correlation, and to describe several new phases of matter, such as Mott insulators, High-Tc superconductors, and spin liquid phases.

Sandro Sorella; Andrea Zen

2014-06-17

33

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

E-print Network

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.

Heng Fan; Vladimir Korepin; Vwani Roychowdhury

2005-11-17

34

Resonating valence bond state in LaâCuOâ and superconductivity  

Microsoft Academic Search

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

P. W. ANDERSON

1987-01-01

35

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

Microsoft Academic Search

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

G. Baskaran

2006-01-01

36

Orbital imaging and assessment of different orbital models for the valence shell of methanol. Comparison of electron momentum spectroscopy measurements with near-Hartree-Fock limit, MRSD-CI, localized valence bond and density functional theory  

NASA Astrophysics Data System (ADS)

The momentum distributions of the valence orbitals of methanol have been studied by electron momentum spectroscopy (EMS) and Hartree-Fock (HF), multi-reference singles and doubles configuration interaction (MRSD-CI), localized valence bond (VB) and density functional theory (DFT) calculations. The experiment was performed using a multichannel EMS spectrometer at a total energy of 1200 eV plus the binding energy. Binding-energy spectra measured in the energy range of 6-47 eV are presented for the azimuthal angles ?=0° and ?=8°. Synthetic binding-energy spectra from Green's function and HF calculations for the azimuthal angles ?=0° and ?=8° in the 6-47 eV energy region are also compared to experiment. In the inner valence region strong splitting of the 4a' and 3a' ionization is observed due to final-state electron correlation effects. The measured momentum profiles are compared with HF calculations at the level of the target HF approximation using basis sets ranging from simple (STO-3G) to large (110-GTO and Trun-pV5Z). DFT calculations at the level of the target Kohn-Sham approximation employing the local density approximation or hybrid functional methods and the large Trun-pV5Z basis set are also compared to experiment. The effects of electron correlation and relaxation are also investigated in the outer valence region by MRSD-CI calculations of the full ion-neutral overlap amplitude using the 110-G(CI) basis set. The shapes of all momentum profiles are well predicted by higher level theory. Some small discrepancy still exists between all theoretical treatments and experiment in the low-momentum region for the HOMO 2a? orbital. MRSD-CI or DFT (i.e. correlated) methods are needed to adequately describe the shape of the 7a' and (6a'+1a?) momentum profiles. The s-type character in the 5a' momentum profile is underestimated by HF theory and overemphasized by density functional theory (DFT). The 110-G(CI) calculation best predicts the shape for the 5a' momentum profile. The shapes of the experimental momentum profiles for the 4a' and 3a' are well-reproduced by large basis set HF and DFT calculations. In addition, nearly all the inner valence 4a' pole strength is found in the 20-28 eV region while the high-energy 28-47 eV region contains virtually all of the 3a' pole strength. Lastly, the HOMO and NHOMO momentum profiles are compared to the corresponding localized molecular orbitals (LMO) (i.e. the `lone-pair' orbitals of VSEPR or qualitative VB theory), the canonical molecular orbitals (CMO) of molecular orbital (MO) theory and the Kohn-Sham orbitals (KSO) of DFT used in the present work. The experimental results unequivocally support the delocalized CMO and KSO models and are very different from the LMO description. Although electron correlation effects are also important at low momenta in the 7a' NHOMO this orbital is also basically a CMO or KSO in character as shown by the CI and DFT calculations. It is noteworthy that the KSOs of DFT, often described as fictitious mathematical concepts, in fact very closely fit the experimental results and are very similar to the CMOs given by HF or CI calculations of the full ion-neutral overlap where necessary. These conclusions have profound implications for computer-aided molecular design, molecular modelling and molecular recognition.

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

1999-06-01

37

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

PubMed Central

A new method for the accurate a priori calculation of atomic and molecular energies is proposed. The new method agrees with experiment to within less than 1 kcal/mole in all cases examined thus far, and is applicable to excited states and to transition states for chemical reactions. Since the new method corrects the results of generalized valence bond calculations for the effects of electron pair correlations, we call the new method the pairwise correlated generalized valence bond method. PMID:16592172

Petersson, G. A.

1974-01-01

38

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

SciTech Connect

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

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

2008-05-30

39

Simplex valence-bond crystal in the spin-1 kagome Heisenberg antiferromagnet  

NASA Astrophysics Data System (ADS)

We investigate the ground-state properties of a spin-1 kagome antiferromagnetic Heisenberg model using tensor-network (TN) methods. We obtain the energy per site e0=-1.410 90 (2 ) , with D*=8 multiplets retained (i.e., a bond dimension of D =24 ), and e0=-1.4116 (4 ) from large-D extrapolation, by accurate TN calculations directly in the thermodynamic limit. The symmetry between the two kinds of triangles is spontaneously broken, with a relative energy difference of ? ?19 % , i.e, there is a trimerization (simplex) valence-bond order in the ground state. The spin-spin, dimer-dimer, and chirality-chirality correlation functions are found to decay exponentially with a rather short correlation length, showing that the ground state is gapped. We thus identify the ground state to be a simplex valence-bond crystal. We also discuss the spin-1 bilinear-biquadratic Heisenberg model on a kagome lattice, and determine its ground-state phase diagram. Moreover, we implement non-Abelian symmetries, here spin SU(2), in the TN algorithm, which improves the efficiency greatly and provides insight into the tensor structures.

Liu, Tao; Li, Wei; Weichselbaum, Andreas; von Delft, Jan; Su, Gang

2015-02-01

40

Interplane charge dynamics in a valence-bond dynamical mean-field theory of cuprate superconductors  

NASA Astrophysics Data System (ADS)

We present calculations of the interplane charge dynamics in the normal state of cuprate superconductors within the valence-bond dynamical mean-field theory. We show that by varying the hole doping, the c -axis optical conductivity and resistivity dramatically change character, going from metalliclike at large doping to insulatinglike at low doping. We establish a clear connection between the behavior of the c -axis optical and transport properties and the destruction of coherent quasiparticles as the pseudogap opens in the antinodal region of the Brillouin zone at low doping. We show that our results are in good agreement with spectroscopic and optical experiments.

Ferrero, M.; Parcollet, O.; Georges, A.; Kotliar, G.; Basov, D. N.

2010-08-01

41

Frustration-induced valence bond crystal and its melting in Mo3Sb7  

E-print Network

121/123Sb nuclear quadrupole resonance and muon spin relaxation experiments of Mo3Sb7 revealed symmetry breakdown to a nonmagnetic state below the transition recently found at TS=50 K. The transition is characterized by a distinct lattice dynamics suggested from narrowing of nuclear fields. We point out that the Mo sublatice is a unique three-dimensional frustrated lattice where nearest-neighbor and next-nearest-neighbor antiferromagnetic interactions compete, and propose that tetragonal distortion to release the frustration stabilizes long-range order of spin-singlet dimers, i.e., valence bond crystal, which is thermally excited to the dynamic state with cubic symmetry.

T. Koyama; H. Yamashita; Y. Takahashi; T. Kohara; I. Watanabe; Y. Tabata; H. Nakamura

2008-05-26

42

The Bond Valence Model as a Tool for Teaching Inorganic Chemistry: The Ionic Model Revisited  

NASA Astrophysics Data System (ADS)

The ionic model is shown to give a good description of most inorganic materials, such as salts, ceramics, and minerals, regardless of the covalent or ionic character of their bonds. The virtue of the model is its ability to treat chemical bonding using simple electrostatic theory, all the quantum mechanical effects being contained in a short-range potential that is treated empirically. By exploiting the properties of the electrostatic field, a rigorous but simple and intuitive bond model is developed (the bond valence model). This paper shows how the model can be used to explore the structural, chemical, and physical properties of inorganic compounds, including their stability and solubility. The online version of the paper explores further application, showing how the model can be used to understand hydrogen bonding, the factors that determine coordination number, and the unusual chemistry and physics of the new high-tech inorganic solids. The simplicity of the model, the insights it provides without the need for extensive computation, and its wide range of applicability make it particularly useful in teaching as well as research.

Brown, I. David

2000-08-01

43

Properties of resonating-valence-bond spin liquids and critical dimer models  

NASA Astrophysics Data System (ADS)

We use Monte Carlo simulations to study properties of Anderson's resonating-valence-bond (RVB) spin-liquid state on the square lattice (i.e., the equal superposition of all pairing of spins into nearest-neighbor singlet pairs) and compare with the classical dimer model (CDM). The latter system also corresponds to the ground state of the Rokhsar-Kivelson quantum dimer model at its critical point. We find that, although spin-spin correlations decay exponentially in the RVB, four-spin valence-bond-solid correlations are critical, qualitatively like the well-known dimer-dimer correlations of the CDM, but decaying more slowly (as 1/r? with ??1.20, compared with ?=2 for the CDM). We also compute the distribution of monomer (defect) pair separations, which decay by a larger exponent in the RVB than in the CDM. We further study both models in their different winding-number sectors and evaluate the relative weights of different sectors. Like the CDM, all the observed RVB behaviors can be understood in the framework of a mapping to a “height” model characterized by a gradient-squared stiffness constant K. Four independent measurements consistently show a value KRVB?1.6KCDM, with the same kinds of numerical evaluations of KCDM giving results in agreement with the rigorously known value KCDM=?/16. The background of a nonzero winding-number gradient W/L introduces spatial anisotropies and an increase in the effective K, both of which can be understood as a consequence of anharmonic terms in the height-model free energy, which are of relevance to the recently proposed scenario of “Cantor deconfinement” in extended quantum dimer models. In addition to the standard case of short bonds only, we also studied ensembles in which fourth-neighbor (bipartite) bonds are allowed at a density controlled by a tunable fugacity, resulting (as expected) in a smooth reduction of K.

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

2011-11-01

44

Resonating-valence-bond superconductors with fermionic projected entangled pair states  

NASA Astrophysics Data System (ADS)

We construct a family of simple fermionic projected entangled pair states (fPEPS) on the square lattice with bond dimension D =3 which are exactly hole-doped resonating valence bond (RVB) wave functions with short-range singlet bonds. Under doping the insulating RVB spin liquid evolves immediately into a superconductor with mixed d +is pairing symmetry whose pair amplitude grows as the square root of the doping. The relative weight between s-wave and d-wave components can be controlled by a single variational parameter c. We optimize our ansatz with respect to c for the frustrated t-J1-J2 model (including both nearest and next-nearest neighbor antiferromagnetic interactions J1 and J2, respectively) for J2?J1/2 and obtain an energy very close to the infinite-PEPS state (using full update optimization and same bond dimension). The orbital symmetry of the optimized RVB superconductor has predominant d-wave character, although we argue a residual (complex s-wave) time reversal symmetry breaking component should always be present. Connections of the results to the physics of superconducting cuprates and pnictides are outlined.

Poilblanc, Didier; Corboz, Philippe; Schuch, Norbert; Cirac, J. Ignacio

2014-06-01

45

Electron wave packet modeling of chemical bonding: Floating and breathing minimal packets with perfect-pairing valence-bond spin coupling  

NASA Astrophysics Data System (ADS)

A simple wave packet (WP) modeling of electrons in chemical bonding is examined. It is found that floating and breathing minimal Gaussian WPs with fully non-orthogonal perfect-pairing valence-bond spin coupling yield the ground state potential energy surfaces of LiH, BeH2, CH2, and H2O molecules of comparable quality to a high-level ab initio electron-correlated calculations. A simple form of core pseudo-potential with two parameters is shown to give proper modeling of core-valence interactions.

Ando, Koji

2012-01-01

46

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

NASA Astrophysics Data System (ADS)

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.

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

2015-02-01

47

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

48

Resonating Valence Bond Quantum Monte Carlo: Application to the ozone molecule  

E-print Network

We study the potential energy surface of the ozone molecule by means of Quantum Monte Carlo simulations based on the resonating valence bond concept. The trial wave function consists of an antisymmetrized geminal power arranged in a single-determinant that is multiplied by a Jastrow correlation factor. Whereas the determinantal part incorporates static correlation effects, the augmented real-space correlation factor accounts for the dynamics electron correlation. The accuracy of this approach is demonstrated by computing the potential energy surface for the ozone molecule in three vibrational states: symmetric, asymmetric and scissoring. We find that the employed wave function provides a detailed description of rather strongly-correlated multi-reference systems, which is in quantitative agreement with experiment.

Sam Azadi; Ranber Singh; Thomas D. Kühne

2015-02-24

49

A Valence Bond Description of Dizwitterionic Dithiolene Character in an Oxomolybdenum-bis(dithione).  

PubMed

Metallo-dithiolene non-innocence is explored in an oxomolybdenum-bis(dithione) complex, [Mo(4+)O(i-Pr2Pipdt)2Cl][PF6] (where i-Pr2Pipdt is N,N'-piperazine-2,3-dithione), that possesses a piperazine ring as an integral part of the dithiolene ligand. The title complex displays unusual spectroscopic features for a formally reduced Mo(IV) dithiolene complex, namely a low energy metal-to-ligand charge transfer band with appreciable intensity and C-C and C-S stretching frequencies that are markedly different from those of oxomolydenum complexes coordinated to dianionic dithiolene ligands. The electronic structure of the ligand has been described in valence bond terms as a resonance hybrid of dithione and dizwitterionic dithiolene contributing structures. PMID:23956683

Mtei, Regina P; Perera, Eranda; Mogesa, Benjamin; Stein, Benjamin; Basu, Partha; Kirk, Martin L

2011-12-01

50

Valence bond dynamical mean-field theory of doped Mott insulators with nodal/antinodal differentiation  

NASA Astrophysics Data System (ADS)

We introduce a valence bond dynamical mean-field theory of doped Mott insulators. It is based on a minimal cluster of two orbitals, each associated with a different region of momentum space and hybridized to a self-consistent bath. The low-doping regime is characterized by singlet formation and the suppression of quasiparticles in the antinodal regions, leading to the formation of Fermi arcs. This is described in terms of an orbital-selective transition in reciprocal space. The calculated tunneling and photoemission spectra are consistent with the phenomenology of the normal state of cuprates. We derive a low-energy description of these effects using a generalization of the slave-boson method.

Ferrero, M.; Cornaglia, P. S.; DeLeo, L.; Parcollet, O.; Kotliar, G.; Georges, A.

2009-03-01

51

Valence bond solid state induced by impurity frustration in Cr8Ni  

NASA Astrophysics Data System (ADS)

We provide a physically meaningful picture of the nature of the ground state of the Cr8Ni compound in the regime where it is a spin singlet. According to this picture, the anisotropy of the Ni atom in the Cr ring induces a dimerization in the molecule that makes the ground state to stabilize in a valence bond solid phase of virtual spins. We characterize rigorously this phase by means of a particular nonlocal order parameter that denoted the generalized string order parameter. In the completely antiferromagnetic regime, the system becomes frustrated. We have performed a numerical real-time evolution study of the correlations between the spin of the Ni impurity and the rest of the spins in order to show the reaction of the system under this frustration.

Almeida, J.; Martin-Delgado, M. A.; Sierra, G.

2009-03-01

52

Correlated geminal wave function for molecules: an efficient resonating valence bond approach.  

PubMed

We show that a simple correlated wave function, obtained by applying a Jastrow correlation term to an antisymmetrized geminal power, based upon singlet pairs between electrons, is particularly suited for describing the electronic structure of molecules, yielding a large amount of the correlation energy. The remarkable feature of this approach is that, in principle, several resonating valence bonds can be dealt simultaneously with a single determinant, at a computational cost growing with the number of electrons similar to more conventional methods, such as Hartree-Fock or density functional theory. Moreover we describe an extension of the stochastic reconfiguration method, which was recently introduced for the energy minimization of simple atomic wave functions. Within this extension the atomic positions can be considered as further variational parameters, which can be optimized together with the remaining ones. The method is applied to several molecules from Li(2) to benzene by obtaining total energies, bond lengths and binding energies comparable with much more demanding multiconfiguration schemes. PMID:15473777

Casula, Michele; Attaccalite, Claudio; Sorella, Sandro

2004-10-15

53

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

NASA Astrophysics Data System (ADS)

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.

Chou, Chung-Pin; Chen, Hong-Yi

2014-07-01

54

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

SciTech Connect

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

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

2013-11-07

55

Mixed Valency in Quadruple Hydrogen-Bonded Dimers of Bis(biimidazolate)dirhodium Complexes.  

PubMed

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

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

2015-03-01

56

Dioxygen activation and bond cleavage by mixed-valence cytochrome c oxidase  

PubMed Central

Elucidating the structures of intermediates in the reduction of O2 to water by cytochrome c oxidase is crucial to understanding both oxygen activation and proton pumping by the enzyme. In the work here, the reaction of O2 with the mixed-valence enzyme, in which only heme a3 and CuB in the binuclear center are reduced, has been followed by time-resolved resonance Raman spectroscopy. The results show that O=O bond cleavage occurs within the first 200 ?s after reaction initiation; the presence of a uniquely stable Fe—O—O(H) peroxy species is not detected. The product of this rapid reaction is a heme a3 oxoferryl (FeIV=O) species, which requires that an electron donor in addition to heme a3 and CuB must be involved. The available evidence suggests that the additional donor is an amino acid side chain. Recent crystallographic data [Yoshikawa, S., Shinzawa-Itoh, K., Nakashima, R., Yaono, R., Yamashita, E., Inoue, N., Yao, M., Fei, M. J., Libeu, C. P., Mizushima, T., et al. Science, in press; Ostermeier, C., Harrenga, A., Ermler, U. & Michel, H. (1997) Proc. Natl. Acad. Sci. USA 94, 10547–10553] show that one of the CuB ligands, His240, is cross-linked to Tyr244 and that this cross-linked tyrosyl is ideally positioned to participate in dioxygen activation. We propose a mechanism for O—O bond cleavage that proceeds by concerted hydrogen atom transfer from the cross-linked His—Tyr species to produce the product oxoferryl species, CuB2+—OH?, and the tyrosyl radical. This mechanism provides molecular structures for two key intermediates that drive the proton pump in oxidase; moreover, it has clear analogies to the proposed O—O bond forming chemistry that occurs during O2 evolution in photosynthesis. PMID:9653133

Proshlyakov, Denis A.; Pressler, Michelle A.; Babcock, Gerald T.

1998-01-01

57

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

SciTech Connect

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.

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

2000-05-01

58

Signatures of spin-triplet excitations in optical conductivity of valence bond solids  

NASA Astrophysics Data System (ADS)

We show that the optical responses below the Mott gap can be used to probe the spin-triplet excitations in valence bond solid (VBS) phases in Mott insulators. The optical conductivity in this regime arises due to the electronic polarization mechanism via virtual electron-hopping processes. We apply this mechanism to the Hubbard model with spin-orbit couplings and/or the corresponding spin model with significant Dzyaloshinskii-Moriya (DM) interactions, and compute the optical conductivity of VBS states on both ideal and deformed Kagome lattices. In the case of the deformed Kagome lattice, we study the antiferromagnet Rb2Cu3SnF12 with the pinwheel VBS state. In case of the ideal Kagome lattice, we explore the optical conductivity signatures of the spin-triplet excitations for three VBS states with (1) a 12-site unit cell, (2) a 36-site unit cell with six-fold rotation symmetry, and (3) a 36-site unit cell with three-fold rotation symmetry, respectively. We find that increasing the DM interactions generally leads to broad and smooth features in the optical conductivity with interesting experimental consequences. The optical conductivity reflects the features of the spin-triplet excitations that can be measured in future experiments.

Hwang, Kyusung; Bhattacharjee, Subhro; Kim, Yong Baek

2014-12-01

59

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

PubMed

We report here the synthesis of the site ordered double perovskite Ba(2)LuMoO(6). Rietveld refinement of room temperature powder x-ray diffraction measurements indicates that it crystallizes in the cubic space group Fm3m, with a = 8.3265(1) ?. Powder neutron diffraction data indicate that, unusually, this cubic symmetry is maintained down to 2 K, with [Formula: see text], Mo(5+) ions situated on the frustrated face-centred cubic lattice. Despite dc-susceptibility measurements showing Curie-Weiss behaviour with strong antiferromagnetic interactions at T ? 200 K, there is no evidence of long range magnetic ordering at 2 K. At T ? 50 K, susceptibility measurements indicate a loss in moment to ?18% of the expected value, and there is a corresponding loss in the magnitude of the magnetic exchange. The structural and magnetic properties of this compound are compared with the related compound Ba(2)YMoO(6), which is a valence bond glass. PMID:23343826

Coomer, Fiona C; Cussen, Edmund J

2013-02-27

60

Structural and magnetic properties of Ba2LuMoO6: a valence bond glass  

NASA Astrophysics Data System (ADS)

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

Coomer, Fiona C.; Cussen, Edmund J.

2013-02-01

61

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

PubMed

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

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

2014-06-16

62

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

NASA Astrophysics Data System (ADS)

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.

Pujari, Sumiran; Alet, Fabien; Damle, Kedar

2015-03-01

63

Generalized Valence Bond Description of Chalcogen-Nitrogen Compounds. I. NS, F(NS), and H(NS).  

PubMed

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

Takeshita, Tyler Y; Dunning, Thom H

2015-03-01

64

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

Microsoft Academic Search

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.

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

1998-01-01

65

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

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

66

Resonating valence-bond state in an orbitally degenerate quantum magnet with dynamical Jahn-Teller effect  

NASA Astrophysics Data System (ADS)

Short-range resonating valence-bond states in an orbitally degenerate magnet on a honeycomb lattice are studied. A quantum-dimer model is derived from the Hamiltonian which represents the superexchange interaction and the dynamical Jahn-Teller (JT) effect. We introduce two local units termed "spin-orbital singlet dimer," where two spins in a nearest-neighbor bond form a singlet state associated with an orbital polarization along the bond, and "local JT singlet," where an orbital polarization is quenched due to the dynamical JT effect. A derived quantum-dimer model consists of the hopping of the spin-orbital singlet dimers and the JT singlets, and the chemical potential of the JT singlets. We analyze the model by the mean-field approximation, and find that a characteristic phase, termed "JT liquid phase," where both the spin-orbital singlet dimers and the JT singlets move quantum mechanically, is realized. Possible scenarios for the recently observed non-magnetic-ordered state in Ba3CuSb2O9 are discussed.

Nasu, Joji; Ishihara, Sumio

2015-01-01

67

Influence of copper-sulfur covalency and copper-copper bonding on valence delocalization and electron transfer in the Cu{sub A} site of cytochrome c oxidase  

Microsoft Academic Search

In this communication, we explore the contributions of Cu-ligand and Cu-Cu bonding to valence delocalization and ET in the Cu{sub A} site of CcO. Sulfur K-edge X-ray absorption spectroscopy (XAS) provides the first direct experimental probe of copper-sulfur covalency in the half-occupied highest-energy molecular orbital (HOMO) of Cu{sub A} and two structurally-defined dithiolate-bridged models, delocalized mixed-valence 1 and dicupric 2.

K. R. Williams; D. R. Gamelin; L. B. LaCroix

1997-01-01

68

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

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

69

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

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

Song, Lingchun; Mo, Yirong; Gao, Jiali

2009-01-01

70

Influence of copper-sulfur covalency and copper-copper bonding on valence delocalization and electron transfer in the Cu{sub A} site of cytochrome c oxidase  

SciTech Connect

In this communication, we explore the contributions of Cu-ligand and Cu-Cu bonding to valence delocalization and ET in the Cu{sub A} site of CcO. Sulfur K-edge X-ray absorption spectroscopy (XAS) provides the first direct experimental probe of copper-sulfur covalency in the half-occupied highest-energy molecular orbital (HOMO) of Cu{sub A} and two structurally-defined dithiolate-bridged models, delocalized mixed-valence 1 and dicupric 2. The Cu coordination environment of each system in shown in chart 1. Electronic absorption (Abs) and magnetic circular dichroism (MCD) spectroscopies are used to measure the total inter-ion electronic coupling in Cu{sub A} and 1 through identification of the class III mixed-valence {Psi} {yields} {Psi}{sup *} transitions. The results from these techniques combine to define the pathways for delocalization in Cu{sub A} and 1 and to describe the individual Cu-S and Cu-Cu contributions to this process. The S K-edge data additionally reveal significant anisotropic Cu-ligand covalency, permitting comparison of competing N- and S-based ET pathways to and from the Cu{sub A} site. 20 refs., 2 figs.

Williams, K.R.; Gamelin, D.R.; LaCroix, L.B. [Stanford Univ., CA (United States); and others

1997-01-22

71

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

SciTech Connect

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.

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

72

Crystal structure of phospholipase PA2-Vb, a protease-activated receptor agonist from the Trimeresurus stejnegeri snake venom.  

PubMed

Phospholipase A2 (PLA2) is an important component in snake venoms. Here, an acidic PLA2, designated PA2-Vb was isolated from the Trimeresurus stejnegeri snake venom. PA2-Vb acts on a protease-activated receptor (PAR-1) to evoke Ca(2+) release through the inositol 1,4,5-trisphosphate receptor (IP3R) and induces mouse aorta contraction. PAR-1, phospholipase C and IP3R inhibitors suppressed PA2-Vb-induced aorta contraction. The crystal structure reveals that PA2-Vb has the typical fold of most snake venom PLA2. Several PEG molecules bond to a positively charged pocket. The finding offers a novel pharmacological basis of the structure for investigating the PAR-1 receptor and suggests potential applications for PA2-Vb in the vascular system. PMID:25447533

Zeng, Fuxing; Zhang, Wenjuan; Xue, Nairui; Teng, Maikun; Li, Xu; Shen, Bing

2014-12-20

73

Comparison between the performances of the spin-projected Hartree-Fock, generalized valence-bond, and spin-coupled approaches  

NASA Astrophysics Data System (ADS)

The total energies from spin-projected Hartree-Fock (spin-PHF), generalized valence-bond with perfect-pairing and strong orthogonality restrictions (GVB-PP-SO), and fully-variational spin-coupled (SC) calculations are compared for a series of unsaturated alternant hydrocarbons, ranging from trans buta-1,3-diene to naphthalene. The extent to which the spin-PHF and GVB-PP-SO wavefunctions for these molecules can approximate the more general SC wavefunction can be understood by analyzing the weights of the different modes of spin coupling in the full SC treatment. The spin-PHF wavefunction is found to display a surprising ability to capture more of the ?-space correlation effects in aromatic and antiaromatic systems than its GVB-PP-SO counterpart, even in the case of naphthalene, a molecule with 10 ? electrons.

Karadakov, Peter B.; Cooper, David L.

74

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

ERIC Educational Resources Information Center

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

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

75

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

PubMed

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 (10,12)Be = ? + ? + 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 (10,12)Be, 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 ? + (6,8)He 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 ? + (6,8)He, 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. PMID:25222183

Ito, Makoto; Ikeda, Kiyomi

2014-09-01

76

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

NASA Astrophysics Data System (ADS)

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.

Ito, Makoto; Ikeda, Kiyomi

2014-09-01

77

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

SciTech Connect

The quaternary phase Ca5Mg0.95Ag1.05(1)Ge5 (3) was synthesized by high-temperature solid-state techniques, and its crystal structure was determined by single-crystal diffraction methods in the orthorhombic space group Pnma – Wyckoff sequence c12 with a = 23.1481(4) Å, b = 4.4736(1) Å, c = 11.0128(2) Å, V = 1140.43(4) Å3, Z = 4. The crystal structure can be described as linear intergrowths of slabs cut from the CaGe (CrB-type) and the CaMGe (TiNiSi-type; M = Mg, Ag) structures. Hence, 3 is a hettotype of the hitherto missing n = 3 member of the structure series with the general formula R2+nT2X2+n, previously described with n = 1, 2, and 4. The member with n = 3 was predicted in the space group Cmcm – Wyckoff sequence f5c2. The experimental space group Pnma (in the nonstandard setting Pmcn) corresponds to a klassengleiche symmetry reduction of index two of the predicted space group Cmcm. This transition originates from the switching of one Ge and one Ag position in the TiNiSi-related slab, a process that triggers an uncoupling of each of the five 8f sites in Cmcm into two 4c sites in Pnma. The Mg/Ag site preference was investigated using VASP calculations and revealed a remarkable example of an intermetallic compound for which the electrostatic valency principle is a critical structure-directing force. The compound is deficient by one valence electron according to the Zintl concept, but LMTO electronic structure calculations indicate electronic stabilization and overall bonding optimization in the polyanionic network. Other stability factors beyond the Zintl concept that may account for the electronic stabilization are discussed.

Ponou, Simeon [Centre for Analysis and Synthesis, Lund University; Lidin, Sven [Centre for Analysis and Synthesis, Lund University; Zhang, Yuemei [Ames Laboratory; Miller, Gordon J. [Ames Laboratory

2014-04-18

78

Modern valence bond description of the electronic mechanism of a [1,3] sigmatropic rearrangement linking bicyclo[3.2.0]hept-2-ene and bicyclo[2.2.1]hept-2-ene (norbornene)  

NASA Astrophysics Data System (ADS)

Modern valence bond theory, in its spin-coupled (SC) form, is used to examine the bond-breaking and bond-making processes that take place along the lowest-energy path for a gas-phase [1,3] sigmatropic rearrangement linking bicyclo[3.2.0]hept-2-ene and bicyclo[2.2.1]hept-2-ene (norbornene). The changes within the SC wave functions depicting the direct "suprafacial with inversion" pathway reveal in a very clear cut way the singlet diradical character of structures along the plateau in the energy profile.

Karadakov, Peter B.; Cooper, David L.; Uhe, Andreas

79

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

PubMed

Three new mixed valence trinuclear Co(ii/iii) compounds cis-[Co3L2(MeOH)2(N3)2(?1,1-N3)2] (), trans-[Co3L2(H2O)2(N3)2(?1,1-N3)2]·(H2O)2 () and [Co3L(R)2(N3)3(?1,3-N3)] () have been synthesized by reacting a di-Schiff base ligand () or its reduced form [] (where = N,N'-bis(salicylidene)-1,3-propanediamine and = 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 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 , 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 and 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 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 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: (kcat = 142 h(-1)) > (kcat = 99 h(-1)) > (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

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

2015-02-10

80

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

SciTech Connect

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

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

2005-03-15

81

DERIVATION AND SIGNIFICANCE OF VALENCE MOLECULAR CONNECTIVITY  

EPA Science Inventory

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

82

Bonding  

MedlinePLUS

... between teeth Make teeth look longer Change the shape or color of teeth Sometimes, bonding also is used to ... a color that will most closely match the color of the tooth. He or she will shape the tooth with a drill (handpiece) if necessary, ...

83

On the generalized valence bond description of the anomeric and exo-anomeric effects: an ab initio conformational study of 2-methoxytetrahydropyran.  

PubMed

An ab initio conformational study of the alpha- and beta-glycosidic C1-O1 bonds has been carried out on the axial and equatorial forms of 2-methoxytetrahydropyran (2-MTHP) at the HF/6-31G(d,p) and GVB-PP/6-31G(d,p) levels of calculation. Six conformers of 2-MTHP were fully optimized at both levels. The calculations have shown that the conformer containing the (+sc) orientation around the axial C1-O1 bond is the most stable one and is favored over that bearing the (-sc) arrangement about the equatorial C1-O1 bond by 1.39 (HF) and 1.52 (GVB-PP)kcal/mol. The potential energy surfaces for rotating about the axial and equatorial C1-O1 bonds were constructed at the HF and GVB-PP levels. For each form of 2-MTHP the HF and GVB-PP potential curves exhibit similar profiles. This shows that both methods provide similar descriptions for the position of the conformational minima and for the values and location of the rotational barriers. In addition to the conformational study, a discussion concerning the nature of the chemical bond in acetal fragments and the origin of the anomeric and exo-anomeric effects is presented in terms of optimized non-orthogonal GVB orbitals of 2-MTHP. The intramolecular factors that respond for the order of stability and conformational changes in bond lengths of the conformers of 2-MTHP are examined in light of the GVB description. The problems associated with the use of the NBOs (natural bond orbitals) to analyze chemical bonding in the acetal fragments are discussed, and the choice for the GVB-PP description is justified. PMID:16054606

Bitzer, Rodrigo S; Barbosa, André G H; da Silva, Clarissa O; Nascimento, Marco A C

2005-09-26

84

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

PubMed

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

Beck, John Frederick; Mo, Yirong

2007-01-15

85

Investigation on the valence-band structure of ferromagnetic-semiconductor GaMnAs using spin-dependent resonant tunneling spectroscopy  

Microsoft Academic Search

We investigate the valence-band (VB) structure of ferromagnetic-semiconductor GaMnAs by analyzing the resonant tunneling levels of a GaMnAs quantum well (QW) in double-barrier heterostructures. The resonant level from the heavy-hole first state (HH1) is clearly observed in the metallic GaMnAs QW with the Curie temperature of 60 K, which indicates that no holes reside in the VB of GaMnAs in

Shinobu Ohya; Iriya Muneta; Pham Nam Hai; Masaaki Tanaka

2010-01-01

86

Structure, Bonding, and Europium Valence in Europium COBALT(2-X) Nickel(x) PHOSPHORUS(2) and Europium COPPER(1.75) PHOSPHORUS(2)  

Microsoft Academic Search

A range of ThCr_2Si_2 -type solid solutions, EuCo_ {2-x}Ni_{x}P_2, was synthesized and characterized by powder X-ray diffraction to explore the relationship between intermediate valent europium and P-P bonding. Tin flux synthesis produced substantial phase separation. Activated solid state synthesis yielded single phase samples for x = 1.0, 1.2, and 1.5 and two phase samples for x = 0.5 and 0.8.

Robert Michael Bornick

1993-01-01

87

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

SciTech Connect

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

Lichtenberger, D.L.; Hogan, R.H. (Univ. of Arizona, Tucson (USA)); Healy, M.D.; Barron, A.R. (Harvard univ., Cambridge, MA (USA))

1990-04-25

88

PREDICTING METAL BIOSORPTION PERFORMANCE , Diniz V.b  

E-print Network

PREDICTING METAL BIOSORPTION PERFORMANCE Naja G.a , Diniz V.b , Volesky B.b a Department seaweed biomass is well known for its outstanding metal biosorption performance. Biosorption of Cu2+ , Zn2 were confirmed quantitatively to be involved in the uptake process of heavy metals. Biosorption

Volesky, Bohumil

89

Draft Genome Sequence of Tolypothrix boutellei Strain VB521301  

PubMed Central

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

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

2015-01-01

90

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

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

91

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

ERIC Educational Resources Information Center

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

Smith, Derek W.

2005-01-01

92

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

93

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

Microsoft Academic Search

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

Shinobu Ohya

2011-01-01

94

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

PubMed Central

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

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

2015-01-01

95

Micro-valences: perceiving affective valence in everyday objects.  

PubMed

Perceiving the affective valence of objects influences how we think about and react to the world around us. Conversely, the speed and quality with which we visually recognize objects in a visual scene can vary dramatically depending on that scene's affective content. Although typical visual scenes contain mostly "everyday" objects, the affect perception in visual objects has been studied using somewhat atypical stimuli with strong affective valences (e.g., guns or roses). Here we explore whether affective valence must be strong or overt to exert an effect on our visual perception. We conclude that everyday objects carry subtle affective valences - "micro-valences" - which are intrinsic to their perceptual representation. PMID:22529828

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

2012-01-01

96

Structure and magnetic properties of R(FeVB) 12 compounds  

Microsoft Academic Search

Stable R(FeVB)12 compounds (R = Nd, Sm, Y) with the ThMn12-type tetragonal structure have been prepared. The Curie temperatures of these compounds are enhanced compared with the boron-free compounds. In some of these compounds the saturation magnetization at 4.2 K is also increased. A spin reorientation is observed at 130 K in Nd(FeVB)12. FOMP transitions occur at 4.2 K in

Y. C. Chuang; D. Zhang; T. Zhao; Z. D. Zhang; W. Liu; X. G. Zhao; X. K. Sun; F. R. de Boer

1995-01-01

97

Preliminary Notes/Comments V.B. Graves/P.T. Spampinato  

E-print Network

Preliminary Notes/Comments V.B. Graves/P.T. Spampinato 27Jun06 Summary Notes from the CERN Safety;Preliminary Notes/Comments V.B. Graves/P.T. Spampinato 27Jun06 5. Provide a means to contain the entire and Operations Review June 19-20, 2006 June 19th Notes 1. Fire propagation requirements at CERN prohibit the use

McDonald, Kirk

98

Cloning and DNA sequence analysis of an aac(3)-Vb gene from Serratia marcescens.  

PubMed Central

The AAC(3)-V resistance mechanism is characterized by high-level resistance to the aminoglycosides gentamicin, netilmicin, 2'-N-ethylnetilmicin, and 6'-N-ethylnetilmicin and moderate resistance levels to tobramycin. Serratia marcescens 82041944 contains an AA(3)-V resistance mechanism as determined from aminoglycoside resistance profiles. This strain, however, does not exhibit hybridization with a probe derived from the previously cloned aac(3)-Va gene, (R. Allmansberger, B. Bräu, and W. Piepersberg, Mol. Gen. Genet. 198:514-520, 1985). High-pressure liquid chromatography analysis of the acetylation products of sisomicin carried out by extracts of S. marcescens 82041944 have demonstrated the presence of an AAC(3) enzyme. We have cloned the gene encoding this acetyltransferase and have designated it aac(3)-Vb. Nucleotide sequence comparisons show that the aac(3)-Va and aac(3)-Vb genes are 72% identical. The predicted AAC(3)-Vb protein is 28,782 Da. Comparisons of the deduced amino acid sequences show 75% identity and 84% similarity between the AAC(3)-Va and AAC(3)-Vb proteins. The use of a DNA fragment internal to the aac(3)-Vb as a hybridization probe demonstrated that the aac(3)-Vb gene is very rare in clinical isolates possessing an AAC(3)-V mechanism. PMID:1444303

Rather, P N; Mierzwa, R; Hare, R S; Miller, G H; Shaw, K J

1992-01-01

99

Valence, arousal and word associations  

Microsoft Academic Search

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

Anne-Laure Gilet; Christophe Jallais

2011-01-01

100

Reactive Force Fields via Explicit Valency  

NASA Astrophysics Data System (ADS)

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

Kale, Seyit

101

Unbinding force of chemical bonds and tensile strength in strong crystals  

Microsoft Academic Search

A model of covalent and ionic bond strength is proposed in terms of the tensile unbinding force by introducing the concept of the effectively bonded valence electron (EBVE) number of a chemical bond. Bond strength proves to be exclusively dependent on two microscopic parameters: bond length and EBVE number. This model allows us to determine bond strength for a variety

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

2009-01-01

102

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

NASA Astrophysics Data System (ADS)

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

Hofstätter, M.; Chimani, B.

2012-04-01

103

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

PubMed

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

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

2015-01-21

104

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

NASA Astrophysics Data System (ADS)

The number of singly occupied orbitals in the ground-state atomic configuration of an element defines its nominal valence. For carbon and sulfur, with two singly occupied orbitals in their 3P ground states, the nominal valence is two. However, in both cases, it is possible to form more bonds than indicated by the nominal 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 a4?- states of CF and SF, which are archetypal examples of molecules that possess recoupled pair bonds. These calculations provide insights into the fundamental nature of recoupled pair bonds and illustrate the key differences between recoupled pair bonds formed with the 2s lone pair of carbon, as a representative of the early p-block elements, and recoupled pair bonds formed with the 3p lone pair of sulfur, as a representative of the late p-block elements.

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

2015-01-01

105

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

Microsoft Academic Search

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

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

106

JOB DESCRIPTION C#/VB Developer -ASP.NET -SQL 05,08 -HTML -AJAX  

E-print Network

JOB DESCRIPTION · C#/VB Developer - ASP.NET - SQL 05,08 - HTML - AJAX · Santa Rosa, CA Do you have phases of the software life cycle in the development of ASP.NET applications SUMMARY OF TECHNOLOGIES: C#, C++, ASP.NET, HTML, CSS, AJAX, XML, Visual Studio, SQL 2005, SQL 2008 ESSENTIAL SKILLS

Ravikumar, B.

107

Draft Genome Sequence of Cyanobacterium Hassallia byssoidea Strain VB512170, Isolated from Monuments in India  

PubMed Central

The draft genome assembly of Hassallia byssoidea strain VB512170 with a genome size of ~13 Mb and 10,183 protein-coding genes in 62 scaffolds is reported here for the first time. This is a terrestrial hydrophobic cyanobacterium isolated from monuments in India. We report several copies of luciferase and antibiotic genes in this organism. PMID:25745001

Singh, Deeksha; Chandrababunaidu, Mathu Malar; Panda, Arijit; Sen, Diya; Bhattacharyya, Sourav

2015-01-01

108

Microhardness of Czochralski-grown single crystals of VB{sub 2}  

SciTech Connect

Single crystals of congruent melting hexagonal VB{sub 2} were grown used a triarc furnace applying the Czochralski technique. Orientation dependent microhardness measurements on a single crystal reveal quasi similar hardness in the crystallographic directions <00.1> and <10.0>, whereas the <10.1> shows slightly lower values.

Bulfon, C.; Sassik, H. [Institut fuer Experimentalphysik, Wien (Austria)] [Institut fuer Experimentalphysik, Wien (Austria); Leithe-Jasper, A.; Rogl, P. [Universitaet Wien (Austria)] [Universitaet Wien (Austria)

1997-10-01

109

IFT1178, Programmation d'applications en VB IFT1178, session t 2012 1  

E-print Network

introduction à la programmation pour Excel et Access en VBA et VB.NET. Références: À discuter au premier cours VBA dans Excel et Access. Seuil : Pour réussir ce cours, la moyenne pondérée des examens doit être au. Préalable: Aucun. Cependant, une connaissance d'Excel et Access est souhaitable. Évaluation: Examens Examen

Montréal, Université de

110

APPENDIX V-b PROPOSED TIMELINE FOR MASTER'S DEGREE IN DENTAL SCIENCE: CLINICAL AND TRANSLATIONAL SCIENCE  

E-print Network

APPENDIX V-b PROPOSED TIMELINE FOR MASTER'S DEGREE IN DENTAL SCIENCE: CLINICAL AND TRANSLATIONAL Rotation ORB 580 ­ Fundamental of Dental Caries ORB 570 ­ Introduction to Dental Epidemiology ORB 503 ORB 495 ­ Research Project -Thesis Finalizing and Defense Emergency Medicine Rotation ORB 558

Goldman, Steven A.

111

Draft Genome Sequence of Cyanobacterium Hassallia byssoidea Strain VB512170, Isolated from Monuments in India.  

PubMed

The draft genome assembly of Hassallia byssoidea strain VB512170 with a genome size of ~13 Mb and 10,183 protein-coding genes in 62 scaffolds is reported here for the first time. This is a terrestrial hydrophobic cyanobacterium isolated from monuments in India. We report several copies of luciferase and antibiotic genes in this organism. PMID:25745001

Singh, Deeksha; Chandrababunaidu, Mathu Malar; Panda, Arijit; Sen, Diya; Bhattacharyya, Sourav; Adhikary, Siba Prasad; Tripathy, Sucheta

2015-01-01

112

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

PubMed

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

Chai, Ping; Corbett, John D

2011-11-01

113

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

PubMed Central

A new myosin motor-like chitin synthase gene, chsVb, has been identified in the vascular wilt fungus Fusarium oxysporum f. sp. lycopersici. Phylogenetic analysis of the deduced amino acid sequence of the chsVb chitin synthase 2 domain (CS2) revealed that ChsVb belongs to class VII chitin synthases. The ChsVb myosin motor-like domain (MMD) is shorter than the MMD of class V chitin synthases and does not contain typical ATP-binding motifs. Targeted disrupted single (?chsVb) and double (?chsV ?chsVb) mutants were unable to infect and colonize tomato plants or grow invasively on tomato fruit tissue. These strains were hypersensitive to compounds that interfere with fungal cell wall assembly, produced lemon-like shaped conidia, and showed swollen balloon-like structures in hyphal subapical regions, thickened walls, aberrant septa, and intrahyphal hyphae. Our results suggest that the chsVb gene is likely to function in polarized growth and confirm the critical importance of cell wall integrity in the complex infection process of this fungus. PMID:17993572

Martín-Urdíroz, Magdalena; Roncero, M. Isabel G.; González-Reyes, José Antonio; Ruiz-Roldán, Carmen

2008-01-01

114

Draft Genome Sequence of Bioactive-Compound-Producing Cyanobacterium Tolypothrix campylonemoides Strain VB511288  

PubMed Central

We report here the draft genome sequence of Tolypothrix campylonemoides VB511288, isolated from building facades in Santiniketan, India. The members of this genus produce several compounds of commercial importance. The draft assembly is 10,627,177 bases in 135 scaffolds, and it contains 7,886 protein-coding genes, 994 pseudogenes, 18 rRNA genes, and 76 tRNA genes. PMID:25838485

Das, Subhadeep; Singh, Deeksha; Madduluri, Madhavi; Chandrababunaidu, Mathu Malar; Gupta, Akash

2015-01-01

115

Groups VB and VIB oxides as nucleating agents in lithium disilicate glasses  

Microsoft Academic Search

Although the oxides of the Groups VB and VIB elements (Cr, Mo, Nb, Ta, V, W) have frequently been used as nucleating agents in glass-ceramics, there has been little rigorous study of their effects. A test of the effects of these oxides on the steady-state nucleation rate and induction period in homogeneously-nucleating lithium disilicate glass was made by substituting one

1988-01-01

116

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

PubMed Central

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

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

2015-01-01

117

An extrasynaptic GABAA receptor mediates tonic inhibition in thalamic VB neurons.  

PubMed

Whole cell patch-clamp recordings were obtained from thalamic ventrobasal (VB) and reticular (RTN) neurons in mouse brain slices. A bicuculline-sensitive tonic current was observed in VB, but not in RTN, neurons; this current was increased by the GABA(A) receptor agonist 4,5,6,7-tetrahydroisothiazolo-[5,4-c]pyridine-3-ol (THIP; 0.1 microM) and decreased by Zn(2+) (50 microM) but was unaffected by zolpidem (0.3 microM) or midazolam (0.2 microM). The pharmacological profile of the tonic current is consistent with its generation by activation of GABA(A) receptors that do not contain the alpha(1) or gamma(2) subunits. GABA(A) receptors expressed in HEK 293 cells that contained alpha(4)beta(2)delta subunits showed higher sensitivity to THIP (gaboxadol) and GABA than did receptors made up from alpha(1)beta(2)delta, alpha(4)beta(2)gamma(2s,) or alpha(1)beta(2)gamma(2s) subunits. Western blot analysis revealed that there is little, if any, alpha(3) or alpha(5) subunit protein in VB. In addition, co-immunoprecipitation studies showed that antibodies to the delta subunit could precipitate alpha(4), but not alpha(1) subunit protein. Confocal microscopy of thalamic neurons grown in culture confirmed that alpha(4) and delta subunits are extensively co-localized with one another and are found predominantly, but not exclusively, at extrasynaptic sites. We conclude that thalamic VB neurons express extrasynaptic GABA(A) receptors that are highly sensitive to GABA and THIP and that these receptors are most likely made up of alpha(4)beta(2)delta subunits. In view of the critical role of thalamic neurons in the generation of oscillatory activity associated with sleep, these receptors may represent a principal site of action for the novel hypnotic agent gaboxadol. PMID:16162835

Jia, Fan; Pignataro, Leonardo; Schofield, Claude M; Yue, Minerva; Harrison, Neil L; Goldstein, Peter A

2005-12-01

118

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

PubMed

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

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

2015-01-01

119

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

E-print Network

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.

Laurent Filisetti; Julien Valton; Marc Fontecave; Vincent Nivière

2015-01-07

120

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

NASA Technical Reports Server (NTRS)

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

Stringfellow, Guy S.

1986-01-01

121

Pauling bond strength, bond length and electron density distribution  

SciTech Connect

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

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

2014-01-18

122

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

123

Clustering of low-valence particles: Structure and kinetics  

NASA Astrophysics Data System (ADS)

We compute the structure and kinetics of two systems of low-valence particles with three or six freely oriented bonds in two dimensions. The structure of clusters formed by trivalent particles is complex with loops and holes, while hexavalent particles self-organize into regular and compact structures. We identify the elementary structures which compose the clusters of trivalent particles. At initial stages of clustering, the clusters of trivalent particles grow with a power-law time dependence. Yet at longer times fusion and fission of clusters equilibrates and clusters form a heterogeneous phase with polydispersed sizes. These results emphasize the role of valence in the kinetics and stability of finite-size clusters.

Markova, Olga; Alberts, Jonathan; Munro, Edwin; Lenne, Pierre-François

2014-08-01

124

Aesthetic valence of visual illusions  

PubMed Central

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

Stevanov, Jasmina; Markovi?, Slobodan; Kitaoka, Akiyoshi

2012-01-01

125

Biometric valence and arousal recognition  

Microsoft Academic Search

A real-time user-independent emotion detection system using physiological signals has been developed. The system has the ability to classify affective states into 2-dimensions using valence and arousal. Each dimension ranges from 1 to 5 giving a total of 25 possible affective regions. Physiological signals were measured using 3 biometric sensors for Blood Volume Pulse (BVP), Skin Conductance (SC) and Respiration

Christian Martyn Jones; Tommy Troen

2007-01-01

126

Valence Tautomeric Transition Metal Complexes  

Microsoft Academic Search

Valence d-orbital energies of the first row transition metals are close to the frontier ?-orbital energies of o-benzoquinones. Complexes prepared with quinone ligands most commonly have the quinone coordinated with the metal in the form of a semiquinonate (SQ) radical-anion or as a catecholate (Cat) dianion. In a few unique complexes it has been possible to observe intramolecular electron transfer

David N. Hendrickson; Cortlandt G. Pierpont

127

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

PubMed Central

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

Bredtmann, Timm; Ivanov, Misha; Dixit, Gopal

2014-01-01

128

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

USGS Publications Warehouse

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.

Sherman, D.M.

1986-01-01

129

Influence of yttrium on the interface valence electron density of thermal barrier coatings  

Microsoft Academic Search

Most of the bonding layers of thermal barrier coatings contain some yttrium to improve the physical consistency of the substrate and the ceramics layer. But the reason of the improvement and the proper yttrium content are not clear. In this paper, the valence electron densities ?hkl and ?u?v?w of the two sides and their difference ??min of the bonding layer\\/ceramic

Zhilin Li; Wei Liu; Yuanqi Wu

2007-01-01

130

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

SciTech Connect

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

NONE

1985-04-01

131

Myosin Vb Mediated Plasma Membrane Homeostasis Regulates Peridermal Cell Size and Maintains Tissue Homeostasis in the Zebrafish Epidermis  

PubMed Central

The epidermis is a stratified epithelium, which forms a barrier to maintain the internal milieu in metazoans. Being the outermost tissue, growth of the epidermis has to be strictly coordinated with the growth of the embryo. The key parameters that determine tissue growth are cell number and cell size. So far, it has remained unclear how the size of epidermal cells is maintained and whether it contributes towards epidermal homeostasis. We have used genetic analysis in combination with cellular imaging to show that zebrafish goosepimples/myosin Vb regulates plasma membrane homeostasis and is involved in maintenance of cell size in the periderm, the outermost epidermal layer. The decrease in peridermal cell size in Myosin Vb deficient embryos is compensated by an increase in cell number whereas decrease in cell number results in the expansion of peridermal cells, which requires myosin Vb (myoVb) function. Inhibition of cell proliferation as well as cell size expansion results in increased lethality in larval stages suggesting that this two-way compensatory mechanism is essential for growing larvae. Our analyses unravel the importance of Myosin Vb dependent cell size regulation in epidermal homeostasis and demonstrate that the epidermis has the ability to maintain a dynamic balance between cell size and cell number. PMID:25233349

Phatak, Mandar; Banerjee, Shamik; Mulay, Aditya; Deshpande, Ojas; Bhide, Sourabh; Jacob, Tressa; Gehring, Ines; Nuesslein-Volhard, Christiane; Sonawane, Mahendra

2014-01-01

132

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

SciTech Connect

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

Landa, A; Soderlind, P

2011-04-11

133

Valence atom with bohmian quantum potential: the golden ratio approach  

PubMed Central

Background The alternative quantum mechanical description of total energy given by Bohmian theory was merged with the concept of the golden ratio and its appearance as the Heisenberg imbalance to provide a new density-based description of the valence atomic state and reactivity charge with the aim of clarifying their features with respect to the so-called DFT ground state and critical charge, respectively. Results The results, based on the so-called double variational algorithm for chemical spaces of reactivity, are fundamental and, among other issues regarding chemical bonding, solve the existing paradox of using a cubic parabola to describe a quadratic charge dependency. Conclusions Overall, the paper provides a qualitative-quantitative explanation of chemical reactivity based on more than half of an electronic pair in bonding, and provide new, more realistic values for the so-called “universal” electronegativity and chemical hardness of atomic systems engaged in reactivity (analogous to the atoms-in-molecules framework). PMID:23146157

2012-01-01

134

Valences in Parallel Systems Henning Fernau  

E-print Network

(gsm). In this way, we can show new properties of ET0L languages, namely the non­closure under permutation, quasiinter­ section, valence gsm mappings and intersection with regular valence lan­ guages. Two other variants give some internal control on the application of single rules. Observe that most

135

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

136

Chemical bonding effects in X-ray spectral analysis  

Microsoft Academic Search

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

L. N. Mazalov; B. A. Treiger

1983-01-01

137

Bonding properties of Li2Ca and Mg2Ca  

NASA Astrophysics Data System (ADS)

We previously determined that the monovalent intermetallic compound Na2K has a negative formation enthalpy only because of relatively large energy band contributions which result in large multiatom covalent bonds. Here we calculate the bonding properties of the divalent Mg2Ca and mixed valence Li2Ca compounds crystallizing in the same MgZn2 structure as Na2K.

Zhu, Ming J.; Bylander, D. M.; Kleinman, Leonard

1996-12-01

138

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

139

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

NASA Astrophysics Data System (ADS)

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

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

2009-01-01

140

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

SciTech Connect

The crystal structure of WOCl{sub 3}, determined on the basis of powder diffraction data (tetragonal, P4{sub 2}/mnm, a=10.6856(6), c=3.8537(2)), is isotypic to WOI{sub 3} and contains one-dimensional strands of edge-sharing double-octahedral W{sub 2}O{sub 4/2}Cl{sub 6} groups connected via common corners in trans position. A W-W bond of 2.99A is present within the planar W{sub 2}Cl{sub 6} groups. A series of non-stochiometric, mixed valence W(IV,V) compounds M{sub 1-x}[W{sub 2}O{sub 2}Cl{sub 6}] can be obtained from WOCl{sub 3} by reaction with metal halides (TlCl, KCl, PbCl{sub 2}) or by reaction of elemental Hg with WOCl{sub 4}. All were characterized by single crystal structure determinations and EDX measurements (Tl{sub 0.981(2)}[W{sub 2}O{sub 2}Cl{sub 6}]: monoclinic, C2/m, a=12.7050(4), b=3.7797(1), c=10.5651(3)A, {beta}=107.656(1){sup o}; K{sub 0.84(2)}[W{sub 2}O{sub 2}Cl{sub 6}]: monoclinic, C2/m, a=12.812(3), b=3.7779(6), c=10.196(3)A, {beta}=107.422(8){sup o}; Pb{sub 0.549(3)}[W{sub 2}O{sub 2}Cl{sub 6}]: orthorhombic, Immm,a=3.7659(1), b=9.8975(4), c=12.1332(6)A; Hg{sub 0.554(6)}[W{sub 2}O{sub 2}Cl{sub 6}]: monoclinic, C2/m, a=12.8361(8), b=3.7622(3), c=10.2581(9)A, {beta}=113.645(3){sup o}). Two representatives of this family of compounds have already been reported: Na[W{sub 2}O{sub 2}Br{sub 6}] [Y.-Q. Zhang, K. Peters, H.G. von Schnering, Z. Anorg. Allg. Chem. 624 (1998) 1415-1418] and Ag{sub 0.74}[W{sub 2}O{sub 2}Br{sub 6}] [S. Imhaine, C. Perrin, M. Sergent, Mat. Res. Bull. 33 (1998) 927-933]. The Ag containing compound can be obtained from elemental Ag and WOBr{sub 3}. The crystal structure, originally reported in the triclinic system, was redetermined and shown to be monoclinic with space group C2/m (a=13.7338(10), b=3.7769(3), c=10.7954(9)A, {beta}=112.401(3){sup o}). The crystal structures of these compounds are in close relationship to the structure of WOCl{sub 3} and all contain W{sub 2}O{sub 4/2}X{sub 6} (X=Cl, Br) double strands with the mono and divalent cations coordinated by the terminal halogen atoms of the W{sub 2}X{sub 6} groups and a short W-W bond (2.85A for X=Cl). A cube-shaped coordination environment is present for M=Tl, K and a trigonal-prismatic coordination for M=Ag, Hg. Hg{sub 0.55}[W{sub 2}O{sub 2}Cl{sub 6}] is a semiconductor with a non-Arrhenius behaviour, high specific conductivity of 0.05{omega}{sup -1}cm{sup -1} and a very small activation energy of 0.03eV. Hg{sub 0.55}[W{sub 2}O{sub 2}Cl{sub 6}] and Ag{sub 0.8}[W{sub 2}O{sub 2}Br{sub 6}] show a temperature independent paramagnetism with a magnetic moment around 300x10{sup -6}cm{sup 3}mol{sup -1}.

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

2006-08-15

141

Avoided valence transition in a plutonium superconductor.  

PubMed

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

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

2015-03-17

142

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

NASA Astrophysics Data System (ADS)

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

Ohya, Shinobu

2011-03-01

143

Photophysics and photochemistry of naphthoylnaphthvalene, and photoinduced valence isomerization of highly strained aromatic compounds (Or Quinones) yielding the valene-type isomers as well as related photochromism and photo-electro dualchromism  

Microsoft Academic Search

The lowest excited singlet state of naphthoylnaphthvalene (NNV) undergoes valence isomerization yielding ground-state naphthoylnaphthalene\\u000a (NN) finally. Neither the lowest excited singlet nor triplet state of NN is formed upon excitation of NNV, and of particular\\u000a interest in photoinduced NNV?NNV valence isomerization is the existence of an intermediate which is probably either a bond-cloven\\u000a species or a valence isomer of NNV.

T. Nakayama; S. Miki; K. Hamanoue

2000-01-01

144

Chemical Bonds  

NSDL National Science Digital Library

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

The Concord Consortium

2011-12-11

145

Valence resonance states of N2/-/  

NASA Technical Reports Server (NTRS)

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

Krauss, M.; Neumann, D.

1973-01-01

146

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

147

Effect of the La addition content on valence electron structure and properties of ZrB 2 ceramics  

Microsoft Academic Search

ZrB2 is a combined bonding compound composed of strong covalent bonds which make it difficult to sinter and densify. Thus, rare\\u000a earth or other metal elements are usually used to be sintering additives to improve its sintering properties. To forecast\\u000a properties of ZrB2 solid solutions with addition of lanthanum, their valence electron structure (VES) was calculated by using the empirical

Jin-Ping Li; Yan Wang; Qing Liu; Xiao-Guang Luo

2010-01-01

148

Nature of the Frequency Shift of Hydrogen Valence Vibrations  

E-print Network

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.

Zhyganiuk, I V

2015-01-01

149

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

150

Neuroanatomical correlates of categorizing emotional valence.  

PubMed

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

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

2014-06-11

151

Development of a GMP Phase III purification process for VB4-845, an immunotoxin expressed in E. coli using high cell density fermentation.  

PubMed

VB4-845 is a recombinant immunotoxin comprised of an anti-epithelial cell adhesion molecule (EpCAM) scFv fused to a truncated form of the bacterial toxin, Pseudomonas exotoxin A. VB4-845, purified from TB fed-batch fermentation, showed clinical efficacy when administered locally to treat non-muscle invasive bladder cancer (NMIBC) and squamous cell carcinomas of the head and neck (SCCHN). Here, we describe the implementation of an Escherichia coli high cell density (HCD) cultivation and purification process for VB4-845. HCD cultivation was a prerequisite for achieving higher yields necessary for Phase III clinical trials and commercialization. Using this process, the VB4-845 titer in the supernatant was increased by 30-fold over the original TB fed-batch cultivation. To obtain clinical grade material, a process involving a five-step column purification procedure was implemented and led to an overall recovery of ? 40%. VB4-845 purity of >97% was achieved after the first three columns following the removal of low-molecular weight product-related impurities and aggregates. Endotoxins were effectively separated from VB4-845 on the Q-columns and by washing the Ni-column with a detergent buffer while host cell proteins were removed using ceramic hydroxyapatite. Comparability studies demonstrated that the purified product from the Phase III process was identical to the Phase II reference standard produced using TB fed-batch fermentation. PMID:21421055

Premsukh, Arjune; Lavoie, Joelle M; Cizeau, Jeannick; Entwistle, Joycelyn; MacDonald, Glen C

2011-07-01

152

Molybdenum Valence in Basaltic Silicate Melts  

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

153

The Bondons: The Quantum Particles of the Chemical Bond  

PubMed Central

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 (mB?), velocity (vB?), charge (eB?), and life-time (tB?). This is quantized either in ground or excited states of the chemical bond in terms of reduced Planck constant ?, the bond energy Ebond and length Xbond, respectively. The mass-velocity-charge-time quaternion properties of bondons’ particles were used in discussing various paradigmatic types of chemical bond towards assessing their covalent, multiple bonding, metallic and ionic features. The bondonic picture was completed by discussing the relativistic charge and life-time (the actual zitterbewegung) problem, i.e., showing that the bondon equals the benchmark electronic charge through moving with almost light velocity. It carries negligible, although non-zero, mass in special bonding conditions and towards observable femtosecond life-time as the bonding length increases in the nanosystems and bonding energy decreases according with the bonding length-energy relationship Ebond[kcal/mol]×Xbond[A0]=182019, providing this way the predictive framework in which the B? particle may be observed. Finally, its role in establishing the virtual states in Raman scattering was also established. PMID:21151435

Putz, Mihai V.

2010-01-01

154

Towards wireless emotional valence detection from EEG.  

PubMed

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

Brown, Lindsay; Grundlehner, Bernard; Penders, Julien

2011-01-01

155

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

NASA Astrophysics Data System (ADS)

Anthropogenically induced climate change has been hypothesized to add to the risk of extreme river floods because a warmer atmosphere can carry more water. In the case of the central European rivers Elbe and Oder, another possibility that has been considered is a more frequent occurrence of a weather situation of the type "Zugstrasse Vb," where a low-pressure system travels from the Adriatic region northeastward, carrying moist air and bringing orographic rainfall in the mountainous catchment areas (Erzgebirge, Sudeten, and Beskids). Analysis of long, homogeneous records of past floods allows us to test such ideas. M. Mudelsee and co-workers recently presented flood records for the middle parts of the Elbe and Oder, which go continuously back to A.D. 1021 and A.D. 1269, respectively. Here we review the reconstruction and assess the data quality of the records, which are based on combining documentary data from the interval up to 1850 and measurements thereafter, finding both the Elbe and Oder records to provide reliable information on heavy floods at least since A.D. 1500. We explain that the statistical method of kernel occurrence rate estimation can overcome deficiencies of techniques previously used to investigate trends in the occurrence of climatic extremes, because it (1) allows nonmonotonic trends, (2) imposes no parametric restrictions, and (3) provides confidence bands, which are essential for evaluating whether observed trends are real or came by chance into the data. We further give a hypothesis test that can be used to evaluate monotonic trends. On the basis of these data and methods, we find for both the Elbe and Oder rivers (1) significant downward trends in winter flood risk during the twentieth century, (2) no significant trends in summer flood risk in the twentieth century, and (3) significant variations in flood risk during past centuries, with notable differences between the Elbe and Oder. The observed trends are shown to be both robust against data uncertainties and only slightly sensitive to land use changes or river engineering, lending support for climatic influences on flood occurrence rate. In the case of winter floods, regional warming during the twentieth century has likely reduced winter flood risk via a reduced rate of strong river freezing (breaking ice at the end of winter may function as a water barrier and enhance a high water stage severely). In the case of summer floods, correlation analysis shows a significant, but weak, relation between flood occurrence and meridional airflow, compatible with a "Zugstrasse Vb" weather situation. The weakness of this relation, together with the uncertainty about whether this weather situation became more frequent, explains the absence of trends in summer flood risk for the Elbe and Oder in the twentieth century. We finally draw conclusions about flood disaster management and modeling of flood occurrence under a changed climate.

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

2004-12-01

156

Affective Priming with Associatively Acquired Valence  

ERIC Educational Resources Information Center

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

Aguado, Luis; Pierna, Manuel; Saugar, Cristina

2005-01-01

157

Edge versus interior in the chemical bonding of graphene materials  

NASA Astrophysics Data System (ADS)

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

Philpott, Michael R.; Kawazoe, Yoshiyuki

2009-06-01

158

Does fluorine participate in halogen bonding?  

PubMed

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

Eskandari, Kiamars; Lesani, Mina

2015-03-16

159

Silver- and gold-mediated nucleobase bonding.  

PubMed

We report the results of a density functional theory investigation of the bonding of nucleobases mediated by silver and gold atoms in the gas phase. Our calculations use the Becke exchange and Perdew-Wang correlation functional (BPW91) combined with the Stuttgart effective core potentials to represent the valence electrons of gold, silver, and platinum, and the all-electron DGTZVP basis set for C, H, N, and O. This combination was chosen based on tests on the metal atoms and tautomers of adenine, cytosine, and guanine. To establish a benchmark to understand the metal-mediated bonding, we calculated the binding energy of each of the base pairs in their canonical forms. Our calculations show rather strong bonds between the Watson-Crick base pairs when compared with typical values for N-H-N and N-H-O hydrogen bonds. The neutral metal atoms tend to bond near the nitrogen atoms. The effect of the metal atoms on the bonding of nucleobases differs depending on whether or not the metal atoms bond to one of the hydrogen-bonding sites. When the silver or gold atoms bond to a non-hydrogen-bonding site, the effect is a slight enhancement of the cytosine-guanine bonding, but there is almost no effect on the adenine-thymine pairing. The metal atoms can block one of the hydrogen-bonding sites, thus preventing the normal cytosine-guanine and adenine-thymine pairings. We also find that both silver and gold can bond to consecutive guanines in a similar fashion to platinum, albeit with a significantly lower binding energy. PMID:25107359

Acioli, Paulo H; Srinivas, Sudha

2014-08-01

160

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

NASA Astrophysics Data System (ADS)

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

Lépine, Sébastien; DiStefano, Rosanne

2012-04-01

161

Photoelectron spectroscopic study of the bonding in borane adducts  

Microsoft Academic Search

The bonding in the adducts BHâ.NHâ, BHâ.N(CHâ)â, BHâ.CO, BHâ.CNCHâ, BHâ.PFâ, and BHâ.P(CHâ)â are studied by using a combination of valence ionization potentials and core binding energies. The data indicate that ..pi.. back-bonding is significant only in BHâ.CO and BHâ.PFâ. The stabilization of the Lewis base lone pair upon coordination to BHâ is correlated with the proton affinity of the Lewis

David B. Beach; William L. Jolly

1985-01-01

162

Valence band parameters of wurtzite materials  

NASA Astrophysics Data System (ADS)

We deduced the valence band parameters of several würtzite materials (ZnS, CdS, CdSe, and GaN) by matching the results of existing full-band calculations of the energy spectrum with analytical expressions of the envelope-function formalism. The calculated A-, B-, and C-type hole dispersion relations show strongly anisotropic characteristics and anti-crossing features in spectrum due to band mixing effects. We demonstrated that for all materials considered except CdSe, the spherical cubic approximation for six Luttinger-like parameters holds with good accuracy, so that the anisotropy arises mainly owing to the crystal field splitting term. Thus, the top valence band may be described with (in addition to crystal field and spin-orbit splitting energies) only two Luttinger-like parameters, ?1 and ?2.

Jeon, J.-B.; Sirenko, Yu. M.; Kim, K. W.; Littlejohn, M. A.; Stroscio, M. A.

1996-08-01

163

Atomic structure and phase stability of InxGa1-xN random alloys calculated using a valence-force-field method  

Microsoft Academic Search

We have calculated the atomic structure and strain energy of the InxGa1-xN random alloy (0<=x<=1) based on 592~13 240-atom models. A valence-force-field method with the Keating potential is used for the strain energy calculation. We analyzed the bond-length and bond-angle distribution in the alloy due to the random fluctuation of the atom positions. The change in the average Ga-N and

Toshio Saito; Yasuhiko Arakawa

1999-01-01

164

Correlation weighting of valence shells in QSAR analysis of toxicity.  

PubMed

In the rainbow trout (Oncorhynchus mykiss), we studied the acute toxicity LC(50)-96 h of 274 organic pesticides with a wide variety of molecular structures. Optimization of correlation weights of local and global graph invariants (OCWLGI) gave quantitative structure-activity relationships (QSARs) for predicting toxicity. We used a labeled hydrogen-filled graph (LHFG) to elucidate the molecular structure. We also used the extended connectivity of zero ((0)EC(k)), first ((1)EC(k)), and second ((2)EC(k)) order, numbers of path lengths 2 (P2(k)) and 3 (P3(k)) starting from a given vertex in the LHFG, and valence shells of second order (S2(k)). S2(k) is the sum of the degree of vertices at distance 2 from a given vertex k. The presence of three-, five-, and six-member cycles and hydrogen bond indices suggested they might be used as global LHFG invariants. We applied this method to a broad set of pesticides, to predict toxicity for the trout. The best model used weighted S2(k) and global LHFG invariants. Statistical characteristics of this model are as follows: n=233, r(2)=0.7689, r(2)(pred)=0.7688, s=0.75, F=769 (training set); n=41, r(2)=0.6421, r(2)(pred)=0.4241, s=1.14, F=70 (test set). PMID:16460943

Toropov, Andrey A; Benfenati, Emilio

2006-06-01

165

The DIET from semiconductor surfaces by excitation of valence electrons  

NASA Astrophysics Data System (ADS)

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.

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

1995-06-01

166

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

SciTech Connect

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

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

2011-09-09

167

Experimental study of the valence band of Bi2Se3  

NASA Astrophysics Data System (ADS)

The valence band of Bi2Se3 is investigated by measuring the Shubnikov-de Haas effect as well as galvanomagnetic and thermoelectric transports. At low hole concentration, the hole Fermi surface is closed and boxlike, but at higher carrier concentrations it develops tubelike extensions that are open, in general agreement with our theoretical calculations. However, the experimentally determined density-of-states effective mass is smaller than density-functional-theory calculations predict; although 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 thermopower, in solids with interlayer van der Waals bonds.

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

2014-09-01

168

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

Microsoft Academic Search

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

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

2006-01-01

169

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

SciTech Connect

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

Pauling, L.

1987-07-13

170

Electronic structure and bonding of ozone  

NASA Astrophysics Data System (ADS)

The ground and low-lying states of ozone (O3) have been studied by multireference variational methods and large basis sets. We have constructed potential energy curves along the bending coordinate for (1,2) 1A', (1,2) 1A'', (1,2) 3A', and (1,2) 3A'' symmetries, optimizing at the same time the symmetric stretching coordinate. Thirteen minima have been located whose geometrical and energetic characteristics are in very good agreement with existing experimental data. Special emphasis has been given to the interpretation of the chemical bond through valence-bond-Lewis diagrams; their appropriate use captures admirably the bonding nature of the O3 molecule. The biradical character of its ground state, adopted long ago by the scientific community, does not follow from a careful analysis of its wave function.

Kalemos, Apostolos; Mavridis, Aristides

2008-08-01

171

Goldstone Boson's Valence-Quark Distribution  

E-print Network

Dynamical chiral symmetry breaking (DCSB) is one of the keystones of low-energy hadronic phenomena. Dyson-Schwinger equations provide a model-independent quark-level understanding and correlate that with the behaviour of the pion's Bethe-Salpeter amplitude. This amplitude is a core element in the calculation of pion observables and combined with the dressed-quark Schwinger function required by DCSB it yields a valence-quark distribution function for the pion that behaves as (1-x)^2 for x~1, in accordance with perturbative analyses. This behaviour can be verified at contemporary experimental facilities.

C. D. Roberts

2001-11-12

172

Thermal Recombination: Beyond the Valence Quark Approximation  

E-print Network

Quark counting rules derived from recombination models agree well with data on hadron production at intermediate transverse momenta in relativistic heavy-ion collisions. They convey a simple picture of hadrons consisting only of valence quarks. We discuss the inclusion of higher Fock states that add sea quarks and gluons to the hadron structure. We show that, when recombination occurs from a thermal medium, hadron spectra remain unaffected by the inclusion of higher Fock states. However, the quark number scaling for elliptic flow is somewhat affected. We discuss the implications for our understanding of data from the Relativistic Heavy Ion Collider.

B. Muller; R. J. Fries; S. A. Bass

2005-03-01

173

Anomalous Eu valence state and superconductivity in undoped Eu3Bi2S4F4.  

PubMed

We have synthesized a novel europium bismuth sulfofluoride, Eu3Bi2S4F4, by solid-state reactions in sealed evacuated quartz ampules. The compound crystallizes in a tetragonal lattice (space group I4/mmm, a = 4.0771(1) Å, c = 32.4330(6) Å, and Z = 2), in which CaF2-type Eu3F4 layers and NaCl-like BiS2 bilayers stack alternately along the crystallographic c axis. There are two crystallographically distinct Eu sites, Eu(1) and Eu(2) at the Wyckoff positions 4e and 2a, respectively. Our bond valence sum calculation, based on the refined structural data, indicates that Eu(1) is essentially divalent, while Eu(2) has an average valence of ??+2.64(5). This anomalous Eu valence state is further confirmed and supported, respectively, by Mössbauer and magnetization measurements. The Eu(3+) components donate electrons into the conduction bands that are mainly composed of Bi 6px and 6py states. Consequently, the material itself shows metallic conduction and superconducts at 1.5 K without extrinsic chemical doping. PMID:25314008

Zhai, Hui-Fei; Zhang, Pan; Wu, Si-Qi; He, Chao-Yang; Tang, Zhang-Tu; Jiang, Hao; Sun, Yun-Lei; Bao, Jin-Ke; Nowik, Israel; Felner, Israel; Zeng, Yue-Wu; Li, Yu-Ke; Xu, Xiao-Feng; Tao, Qian; Xu, Zhu-An; Cao, Guang-Han

2014-10-29

174

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

SciTech Connect

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

NONE

1994-09-01

175

VB Learning for DAG Structures 6.3. Estimating the marginal likelihood However this computational resource might be better spent simulating a single chain with a  

E-print Network

VB Learning for DAG Structures 6.3. Estimating the marginal likelihood However this computational resource might be better spent simulating a single chain with a more finely-grained annealing schedule concerns for estimating the marginal likelihoods in some very simple models, using functions of the vari

Daunizeau, Jean

176

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

PubMed Central

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

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

2014-01-01

177

Role of nuclear encoded subunit Vb in the assembly and stability of Cytochrome C oxidase complex: Implications in Mitochondrial dysfunction and ROS Production  

PubMed Central

Cytochrome c Oxidase (CcO) is a multisubunit bigenomic protein complex which catalyzes the last step of the mitochondrial electron transport chain. The nuclear encoded subunits are thought to have roles either in regulation or in the structural stability of the enzyme. Subunit Vb is a peripheral nuclear-encoded subunit of mammalian CcO that is dramatically reduced under hypoxia. Although it has been shown to contain different ligand binding sites and undergo modifications, its precise function is not known. In the present study we generated a cell line from RAW 264.7 murine macrophages, that has more than 80% reduced level of Vb. Functional analysis of these cells showed a loss of CcO activity, membrane potential and lower ability to generate ATP. Resolution of complexes on Blue native gel and two dimensional electrophoretic analysis showed an accumulation of subcomplexes of CcO and also reduced association with super complexes of the electron transfer chain. Furthermore, the mitochondria from CcO Vb knock down cells generated increased ROS and the cells were unable to grow on galactose containing medium. Pulse chase experiments suggest the role of CcO Vb subunit in the assembly of the complex. We show for the first time the role of a peripheral, non-transmembrane subunit in the formation as well as function of the terminal CcO complex. PMID:19338496

Galati, Domenico; Srinivasan, Satish; Raza, Haider; Prabu, Subbuswamy K.; Hardy, Michael; Karunakaran, Chandran; Lopez, Marcos; Kalyanaraman, Balaraman; Avadhani, Narayan G.

2009-01-01

178

Valence-shell autoionization of NO.  

SciTech Connect

Autoionization of valence and Rydberg states in NO over the 12.5-18 eV photon energy range was studied by vibrationally resolved photoelectron spectroscopy of the 2 {pi} orbital. Complex, oscillatory structure is observed in NO{sup +} (2 {pi}{sup 01}) {Chi}{sup 1} {Sigma}{sup +} partial cross sections, branching ratios, and photoelectron anisotropy parameters due to autoionizing valence states and Rydberg states associated with the 1 {pi}{sup -1} and 5 {sigma}{sup -1} channels. Autoionization of the 5 {sigma} {yields} np({pi}, {sigma}) ({upsilon}' = 0), n = 3-5 Rydberg states leading to the (5{sigma}{sup -1}) b{sup 3} {Pi} state of NO{sup +} produces very high vibrational levels of (2 {pi}{sup -1}) {Chi}{sup 1}{Sigma}{sup +}. Autoionization of the 5 {sigma} {yields} 3 p {pi} ({upsilon}' = 0) Rydberg state was characterized by resonance profiles of photoelectron cross sections and angular distributions

Southworth, S. H.; Ferrett, T. A.; Hardis, J. E.; Parr, A. C.; Dehmer, J. L.; Chemistry; Carleton College; National Inst. of Standards & Technology; National Science Foundation

2000-06-01

179

Valence quark distributions of the proton from maximum entropy approach  

NASA Astrophysics Data System (ADS)

We present an attempt using the maximum entropy principle to determine valence quark distributions in the proton at a very low resolution scale Q02. The initial three valence quark distributions are obtained with limited dynamical information from quark model and QCD theory. Valence quark distributions from this method are compared to the lepton deep inelastic scattering data, and the widely used CT10 and MSTW08 data sets. The obtained valence quark distributions are consistent with experimental observations and the latest global fits of parton distribution functions. The maximum entropy method is expected to be particularly useful in cases where relatively little information from QCD theory is given.

Wang, Rong; Chen, Xurong

2015-03-01

180

Investing in Bonds  

E-print Network

Bonds, which are issued by governments and corporations, can be an important part of one's investment portfolio. U.S. government bonds, municipal bonds, zero-coupon bonds and other types are described. Also learn strategies for coping with inflation...

Johnson, Jason; Polk, Wade

2002-08-12

181

Bonded Lubricants  

NASA Technical Reports Server (NTRS)

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.

1977-01-01

182

Modulation of DNA condensation by cation valence  

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

183

Modulus of unbounded valence subdivision rules  

E-print Network

Cannon, Floyd and Parry have studied the modulus of finite subdivision rules extensively. We investigate the properties of the modulus of subdivision rules with linear and exponential growth at every vertex, using barycentric subdivision and a subdivision rule for the Borromean rings as examples. We show that the subdivision rule arising from the Borromean rings is conformal, and conjecture that the subdivision rules for all alternating links are conformal. We show that the 1,2,3-tile criterion of Cannon, Floyd, and Parry is sufficient to prove conformality for linear growth, but not exponential growth. We show that the criterion gives a weaker form of conformality for subdivision rules of exponential growth at each vertex. We contrast this with the known, bounded-valence case, and illustrate our results with circle packings using Ken Stephenson's Circlepack.

Rushton, Brian

2011-01-01

184

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

ERIC Educational Resources Information Center

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

Fries, Stefan; Schmid, Sebastian; Hofer, Manfred

2007-01-01

185

Psychological Bulletin The Relation Between Valence and Arousal in Subjective  

E-print Network

and arousal can in principle show a variety of relations depending on person or circumstances. This casts a fundamental but neglected question about affect, asking how two of its basic dimensions--valence and arousalPsychological Bulletin The Relation Between Valence and Arousal in Subjective Experience Peter

Barrett, Lisa Feldman

186

Teaching Valence Shell Electron Pair Repulsion (VSEPR) Theory  

ERIC Educational Resources Information Center

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

Talbot, Christopher; Neo, Choo Tong

2013-01-01

187

Partial Ionic Bonding in Homogeneous Sodium Clusters  

E-print Network

In this work, we report an interesting observation of partial ionic bonding due to charge transfer in homogeneous sodium clusters. The charge transfer causes the electronic charge to accumulate on the surface, and the resulting charges on atoms range between +0.4 to -1.0 |e^-|. We also demonstrate that this disparity among effective charges on atoms is geometry dependent, such that atoms experiencing similar surrounding, have equal effective charge. It is speculated that this phenomenon will occur among other homogeneous clusters as well, and its extent will be defined by the valence electron delocalization.

Kaware, Vaibhav

2015-01-01

188

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

PubMed

Transition-metal K? X-ray emission spectroscopy (XES) is a developing technique that probes the occupied molecular orbitals of a metal complex. As an element-specific probe of metal centers, K? XES is finding increasing applications in catalytic and, in particular, bioinorganic systems. For the continued development of XES as a probe of these complex systems, however, the full range of factors which contribute to XES spectral modulations must be explored. In this report, an investigation of a series of oxo-bridged iron dimers reveals that the intensity of valence-to-core features is sensitive to the Fe-O-Fe bond angle. The intensity of these features has a well-known dependence on metal-ligand bond distance, but a dependence upon bond angle has not previously been documented. Herein, we explore the angular dependence of valence-to-core XES features both experimentally and computationally. Taken together, these results show that, as the Fe-O-Fe angle decreases, the intensity of the K?? feature increases and that this effect is modulated by increasing amounts of Fe np mixing into the O 2s orbital at smaller bond angles. The relevance of these findings to the identification of oxygenated intermediates in bioinorganic systems is highlighted, with special emphasis given to the case of soluble methane monooxygenase. PMID:25211540

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

2014-10-01

189

The valence problem of Pd4Br4Te3.  

PubMed

Pd(4)Br(4)Te(3) was prepared from Pd, Te, and PdBr(2) at 700 K. Its structure was determined by single-crystal X-ray diffraction to be triclinic, P$\\bar 1$, Pearson symbol aP22; a=842.5(2), b=845.0(3), c=864.8(3) pm; alpha=82.55(3), beta=73.36(2), gamma=88.80(2) degrees ; Z=2. The Br and Te atoms are arranged according to the motif of cubic closest-packed spheres in which every 15th position is vacant; the Pd atoms occupy 8/15 of the octahedral voids. The symmetry relations with the packing of spheres are derived. Prominent structural units are hollow cuboctahedral [(PdBrTe)(6)] units, the Pd atoms are positioned near the centers of the square faces of the Br(6)Te(6) cuboctahedra; the cuboctahedra and double-octahedral Pd(2)Br(4)Te(6) units are connected to strands by sharing triangular Te(3) faces. The strands are condensed by common Br atoms into layered assemblies. Conspicuously close Te--Te contacts in the Te(3) triangles indicate attractive Te--Te interactions. The valence puzzle is resolved by the formula Pd(+II)(4)Br(-I)(4)Te(-4/3)(3). Positive Te--Te Mulliken orbital populations and the Pd--K, Br--K, and Te--L(III) XANES spectra of Pd(4)Br(4)Te(3) referenced to the spectra of PdBr(2), K(2)PdBr(6), PdTe, and PdTe(2) are in accord with attractive Te--Te interactions. The measured semiconducting and diamagnetic properties are compatible with the derived picture of chemical bonding in Pd(4)Br(4)Te(3). PMID:17879245

Janetzky, Manuel; Rödel, Eva; Pietzonka, Clemens; Müller, Ulrich; Ressler, Thorsten; Harbrecht, Bernd

2007-01-01

190

Bonded Interactions and the Crystal Chemistry of Minerals: A Review  

SciTech Connect

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

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

2008-02-26

191

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

SciTech Connect

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.

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

1990-02-14

192

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

NASA Astrophysics Data System (ADS)

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

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

2009-06-01

193

Creation of "bonding structures" on nanoparticles  

NASA Astrophysics Data System (ADS)

Nanoparticles can be used as a new type of fundamental building blocks to construct macroscopic materials, and hierarchically organized nanoparticles often show enhanced properties originated from the collective interactions among these individual nanoscale building blocks. Taking one step further, colloidal molecules with well-defined architectures made by directed assembly of nanoparticles could serve as the basic structural units of more complex functional materials. This is highly desirable but challenging due to the lack of "bonding structures" on nanoparticles. In this thesis, we aim to create "bonding structures" on nanoparticles by modifying them with heterogeneously functionalized polymers bearing "click" moieties. We hypothesize that by controlling the location of "click" recognition pairs on nanoparticles, well-defined polymer linkers, nanoparticle geometry and reaction stoichiometry, the "directionality", "bonding length", and "valency" characteristics of real chemical bonds could be introduced on as-synthesized nanoparticles, which will help organize nanoparticles into colloidal molecules via highly specific and efficient "click" reactions. Using gold nanoparticles as models, we show here that well-defined, heterogeneously functionalized polymer chains bearing "click" recognition pairs can be prepared, and subsequently used to modify gold nanoparticles at controlled locations. Our future work is to study the broad utility of this strategy on creating "bonding structures" on nanoparticles to transform them into "artificial atoms", as well as the system design to assemble these nanoparticles into well-defined colloidal molecules.

Zheng, Wan

194

Inelastic neutron scattering in valence fluctuation compounds  

SciTech Connect

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

Jon M Lawrence

2011-02-15

195

Emotion and language: valence and arousal affect word recognition.  

PubMed

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

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

2014-06-01

196

96 $+& &%XS&~S*#* % (Fi) 28 W**+#*) .~R*%A**% #+a +4fi4ti % #+El&% 2603 % 3 R % 1 R *$v*&%%%B4+%  

E-print Network

96 $+& &%XS&~S*#* % (Fi) 28 W**+#*) .~R*%A**% #+a +4fi4ti % #+El&% 2603 % 3 R % 1 R *$v*&%%%B4+% 1?#@ % 0%) Z .&;6Fi&$X~+!fs 4 - a &4$4t* #+ fl &.s% 2603 % 3 R 2 *%%&mww¶fi% 4. (10%)Absorption of WNIS *#$.lt* $+El 4%@5 2603 % 3 R % 3 R *$&&2$%&rq4+2$ 7. (10%)The solubility-product constant for Ni2P207is 1

Huang, Haimei

197

Valence states and local environment of thallium and copper ions in some new high T sub c superconductors by XAS--  

SciTech Connect

This paper reports the valence states of cations inside for high T{sub c} thallium superconductors investigated by X-ray absorption spectroscopy at thallium L{sub III}, L{sub I} and copper K-edges. The thallium ions are observed on L{sub III} and L{sub I} edges in the Tl(III) valence state (empty 6s levels) in spite of large Tl-O distances in the (a,b) plane of the structure as deduced from X-ray diffraction. The presence of two types of Tl-O distances have been well established on XANES spectra and the F.T of EXAFS have shown the presence of two very short Tl-O bonds (2.03 A). The copper K-edges are characterized by the absence of Cu(I) state (3d{sup 10} line).

Studer, F.; Retoux, R.; Martin, C.; Michel, C.; Raveau, B. (Laboratoire de Cristallographie et Sciences des Materiaux, ISMRa, Bd du Marechal Juin, Universite de Caen, 14032 Caen Cedex, (FR)); Dartyge, E.; Fontaine, A.; Tourillon, G. (LURE, CNRS-MEN-CEA, 91405 Orsay Cedex (FR))

1989-07-01

198

Ce valence variation in intermetallic alloys: LIII absorption spectroscopy results  

NASA Astrophysics Data System (ADS)

LIII absorption spectroscopy measurements, using synchrotron radiation on the Ce1-xRxPd3, R=La3+, Y3+, Th4+, and U and the Ce1-xScxAl2 alloy systems are presented. The Ce valence variation from the LIII spectra analysis is correlated with the lattice-parameter variations in the alloys. The roles of the volume and valence of the substitutes in determining the Ce valence state are discussed. The results are discussed in terms of hybridization and current electronic theory.

Croft, M.; Neifeld, R.; Segre, C. U.; Raaen, S.; Parks, R. D.

1984-10-01

199

Positron annihilation with core and valence electrons  

E-print Network

$\\gamma$-ray spectra for positron annihilation with the core and valence electrons of the noble gas atoms Ar, Kr and Xe is calculated within the framework of diagrammatic many-body theory. The effect of positron-atom and short-range positron-electron correlations on the annihilation process is examined in detail. Short-range correlations, which are described through non-local corrections to the vertex of the annihilation amplitude, are found to significantly enhance the spectra for annihilation on the core orbitals. For Ar, Kr and Xe, the core contributions to the annihilation rate are found to be 0.55\\%, 1.5\\% and 2.2\\% respectively, their small values reflecting the difficulty for the positron to probe distances close to the nucleus. Importantly however, the core subshells have a broad momentum distribution and markedly contribute to the annihilation spectra at Doppler energy shifts $\\gtrsim3$\\,keV, and even dominate the spectra of Kr and Xe at shifts $\\gtrsim5$\\,keV. Their inclusion brings the theoretical ...

Green, D G

2015-01-01

200

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

Code of Federal Regulations, 2010 CFR

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

2010-07-01

201

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

Code of Federal Regulations, 2013 CFR

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

2013-07-01

202

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

Code of Federal Regulations, 2014 CFR

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

2014-07-01

203

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

Code of Federal Regulations, 2012 CFR

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

2012-07-01

204

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

Code of Federal Regulations, 2011 CFR

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

2011-07-01

205

Semiconductor wafer bonding  

NASA Astrophysics Data System (ADS)

When mirror-polished, flat, and clean wafers are brought into contact, they are locally attracted to each other and adhere or bond. This phenomenon is known as semiconductor wafer bonding. Different adhesion forces (van der Waals forces, hydrogen bonding) are the reason for the bonding effect at room temperature. The different bonding mechanisms acting in dependence on the surface conditions (hydrophilic, hydrophobic) are reviewed. Variations of the properties of bonded interfaces (structural, mechanical, electrical) during annealing are discussed. The focus is on low-temperature bonding techniques. Reasons for the formation of interface defects are presented. Applications of semiconductor wafer bonding for future developments are briefly summarized.

Reiche, M.

2006-03-01

206

Testing valence proton symmetry for Te and Cd  

NASA Astrophysics Data System (ADS)

To aid in the study of nuclei far from stability, various valence correlation schemes have been used to infer unknown properties of nuclei from known ones. One such valence correlation scheme is valence proton symmetry, which has been successfully tested for Xe and Pd pairs around the Z = 50 proton shell closure (Dewald 2008). To test the robustness of valence proton symmetry around mid-shell for the Te-Cd pairs, which is one proton pair closer to Z = 50, we measured the lifetimes of the 2^+1 level in ^116Te and ^118Te using the Recoil Distance Doppler Shift method. The results of this experiment will be presented. [4pt] A. Dewald et al. Phys. Rev. C 78, 051302 (2008)

Ahn, Tan; Bettermann, Linus; Casperson, Robert; Chevrier, Raphael; Heinz, Andreas; Ilie, Gabriela; McCarthy, David; Radeck, Desiree; Smith, Mallory; Werner, Volker; Williams, Elizabeth

2010-11-01

207

Unusual structure, bonding and properties in a californium borate  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

208

Inelastic collisions of positrons with one-valence-electron targets  

NASA Technical Reports Server (NTRS)

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.

Abdel-Raouf, Mohamed Assad

1990-01-01

209

Macroscopic and vibration spectroscopic evidence for specific bonding of arsenate on gibbsite  

Microsoft Academic Search

The As(V) adsorption onto gibbsite under different experimental conditions was examined. Macroscopic data suggests strong As(V) bonding on gibbsite possibly via a bidendate binuclear complexation mechanism. The As(V) adsorption was quantified with the charge distribution multi-site ions complexation (CD-MUSIC) model distributing the anion charge over 0- and 1-planes according to the modified Pauling's bond valence theory. In the dual-adsorbates system

R Weerasooriya; H. J Tobschall; H. K. D. K Wijesekara; A Bandara

2004-01-01

210

A New Approach to Reactive Potentials with Fluctuating Charges: Quadratic Valence-Bond Jorge Morales  

E-print Network

and a detailed review is available.2 Certainly these efforts have been influential, for example, the hard-soft acid- base theory of Pearson.3,4 However, they have also uncovered domains where the concept becomes to behave incorrectly in certain cases, presenting a stumbling block to widespread application

Morales, Jorge Alberto

211

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

NASA Technical Reports Server (NTRS)

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).

Freihaut, B.; Raff, L. M.

1973-01-01

212

2D multipartite valence bond states in quantum anti-ferromagnets  

SciTech Connect

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

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

2008-09-15

213

Integer Smith Form via the Valence: Experience with Large Sparse Matrices from Homology  

E-print Network

Integer Smith Form via the Valence: Experience with Large Sparse Matrices from Homology J-G. Dumas. VALENCE BASED SMITH FORM ALGORITHM #12;3. COMPUTING THE VALENCE #12;3.1 Chinese remaindering 3.1.1 Degree 3.3 An Alternative to the Valence 4. LOCAL SMITH FORM AT P #12;4.1 Elimination Method 4.2 Iterative

Villard, Gilles

214

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

ERIC Educational Resources Information Center

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

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

2009-01-01

215

Soft X-ray emission spectroscopy study of the valence electron states of ?-rhombohedral boron  

NASA Astrophysics Data System (ADS)

High energy-resolution boron K-emission spectra of single-crystalline ?-rhombohedral-boron (?-r-B) were measured with a newly developed soft X-ray emission spectroscopy (SXES) instrument attached to a conventional transmission electron microscope. The intensity profiles of the spectra, which correspond to the density of states of the valence bands with p-symmetry, were compared with those of amorphous boron (am-B), single-crystalline ?-rhombohedral-boron (?-r-B) and B4C. A characteristic shoulder structure appears in the spectrum of ?-r-B but not of am-B, ?-r-B or B4C. This structure should be due to the inter-cluster three-center bonding states among B12 clusters in ?-r-B.

Terauchi, Masami; Sato, Yohei; Hyodo, Hiroshi; Kimura, Kaoru

2009-06-01

216

Savings Bonds Value Calculator  

NSDL National Science Digital Library

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

217

LET'S BOND! A Chemical Bonding Webquest  

NSDL National Science Digital Library

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

Mrs. Hicken

2009-04-08

218

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

PubMed

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

McCabe, Patrick; Korb, Oliver; Cole, Jason

2014-05-27

219

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

NASA Astrophysics Data System (ADS)

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

Hawthorne, Frank C.

2012-11-01

220

Hydroxide-catalyzed bonding  

NASA Technical Reports Server (NTRS)

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

Gwo, Dz-Hung (Inventor)

2003-01-01

221

Sedna (2003 VB12)  

NSDL National Science Digital Library

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

Michael Brown

222

Valence band structure of AlN probed by photoluminescence  

NASA Astrophysics Data System (ADS)

Deep ultraviolet photoluminescence (PL) was employed to probe the valence band structure of AlN epilayers grown by metal organic chemical vapor deposition on c-plane sapphire substrates. At 10K, in addition to the dominant emission peak at 6.050eV polarized in the E ?c direction, we observed two additional emission peaks at 6.249 and 6.262eV polarized in the E ?c direction. These two emission lines are assigned to the recombination of free excitons related to the B and C valence bands. A more comprehensive picture of the valence band structure of AlN is thus directly obtained from the PL measurements.

Sedhain, A.; Lin, J. Y.; Jiang, H. X.

2008-01-01

223

Affective and restorative valences for three environmental categories.  

PubMed

The present study evaluated images of environments in three categories with different affective and restorative valences through two computerized assessments. A non-verbal computerized response scale and the Mexican Scale of Environmental Restoration Perception were employed. 104 students assessed the affective qualities of 117 images (47 natural, 37 urban with nature, and 33 built-up without nature) according to pleasure and activation dimensions. Then 96 students assessed 54 images with high and low valence for their restorative quality. Natural images were found to generate positive affective reactions of liking and activation and high restorative quality. Affective responses to urban with nature environments tended to be positive with moderate restorative quality. Built-up without nature environments were perceived as less pleasant and had low restorative quality. However, among built-up without nature environments, some settings with striking architectural qualities evoked positive affective valences. PMID:25402210

Martínez-Soto, Joel; Gonzales-Santos, Leopoldo; Barrios, Fernando A; Lena, Maria E Montero-López

2014-12-01

224

Essays on corporate bonds  

E-print Network

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 ...

Bao, Jack (Jack C.)

2009-01-01

225

Direct bonding and beyond  

NASA Astrophysics Data System (ADS)

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

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

2007-09-01

226

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

SciTech Connect

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.

Pitzer, Kenneth S.; Christiansen, Phillip A.

1980-11-20

227

Valence QCD: Connecting QCD to the quark model  

NASA Astrophysics Data System (ADS)

A valence QCD theory is developed to study the valence quark properties of hadrons. To keep only the valence degrees of freedom, the pair creation through the Z graphs is deleted in the connected insertions, whereas the sea quarks are eliminated in the disconnected insertions. This is achieved with a new ``valence QCD'' Lagrangian where the action in the time direction is modified so that the particle and antiparticle decouple. It is shown in this valence version of QCD that the ratios of isovector to isoscalar matrix elements (e.g., FA/DA and FS/DS ratios) in the nucleon reproduce the SU(6) quark model predictions in a lattice QCD calculation. We also consider how the hadron masses are affected on the lattice and discover new insights into the origin of dynamical mass generation. It is found that, within statistical errors, the nucleon and the ? become degenerate for the quark masses we have studied (ranging from 1 to 4 times the strange mass). The ? and ? become nearly degenerate in this range. It is shown that valence QCD has the C, P, T symmetries. The lattice version is reflection positive. It also has the vector and axial symmetries. The latter leads to a modified partially conserved axial Ward identity. As a result, the theory has a U(2NF) symmetry in the particle-antiparticle space. Through lattice simulation, it appears that this is dynamically broken down to Uq(NF)×Uq¯(NF). Furthermore, the lattice simulation reveals spin degeneracy in the hadron masses and various matrix elements. This leads to an approximate Uq(2NF)×Uq¯(2NF) symmetry which is the basis for the valence quark model. In addition, we find that the masses of N, ?,?,?,a1, and a0 all drop precipitously compared to their counterparts in the quenched QCD calculation. This is interpreted as due to the disappearance of the ``constituent'' quark mass which is dynamically generated through tadpole diagrams. The origin of the hyperfine splitting in the baryon is largely attributed to the Goldstone boson exchanges between the quarks. Both of these are the consequences of the lack of chiral symmetry in valence QCD. We discuss its implications concerning the models of hadrons.

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

1999-06-01

228

High valence 3p and transition metal based MOFs.  

PubMed

This article focuses on high valence 3p and transition metal based metal organic frameworks. In the first part we will discuss the complex solution chemistry of these metals which makes this sub-class of MOFs more of a challenge than the traditional low valence metal based MOFs. This is followed by a short review of the different classes of solids based on phosphonates, carboxylates and other linkers. Finally, we report some of the most relevant properties of these solids such as their chemical or thermal stability as well as their catalytic, redox- and photo-activities. PMID:24947910

Devic, Thomas; Serre, Christian

2014-08-21

229

Raman Sideband Cooling of Two-Valence-Electron Fermionic Atoms  

NASA Astrophysics Data System (ADS)

We propose a method for laser cooling two-valence-electron fermionic atoms. Our protocol employs resolved-sideband cooling on the stimulated Raman transition between the two magnetic sublevels (m = F and m = F - 1) of the ground state with total angular momentum F. The optical pumping from m = F - 1 to 1P1 are used to decouple atoms in the m = F - 1 state. We calculate the Raman coupling generated by an engineered optical lattice. The result shows that it is possible to laser cool the two-valence-electron fermionic atoms to the ground state. The atoms in the ground state provide a new system for quantum optics.

Li, Guo-Hui; Xu, Xin-Ye

2011-06-01

230

Bonding silicones with epoxies  

SciTech Connect

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.

Tira, J.S.

1980-01-01

231

Metal-Metal Bonds in Biology  

PubMed Central

Nickel-containing carbon monoxide dehydrogenases, acetyl-CoA synthases, nickel-iron hydrogenases, and diron hydrogenases are distinct metalloenzymes yet they share a number of important characteristics. All are O2-sensitive, with active-sites composed of iron and/or nickel ions coordinated primarily by sulfur ligands. In each case, two metals are juxtaposed at the “heart” of the active site, within range of forming metal-metal bonds. These active-site clusters exhibit multielectron redox abilities and must be reductively activated for catalysis. Reduction potentials are milder than expected based on formal oxidation state changes. When reductively activated, each cluster attacks an electrophilic substrate via an oxidative addition reaction. This affords a two-electron-reduced substrate bound to one or both metals of an oxidized cluster. M-M bonds have been established in hydrogenases where they serve to initiate the oxidative addition of protons and perhaps stabilize active sites in multiple redox states. The same may be true of the CODH and ACS active sites – Ni-Fe and Ni-Ni bonds in these sites may play critical roles in catalysis, stabilizing low-valence states and initiating oxidative addition of CO2 and methyl group cations, respectively. In this article, the structural and functional commonalities of these metalloenzyme active sites are described, and the case is made for the formation and use of metal-metal bonds in each enzyme mentioned. As a post-script, the importance of Fe-Fe bonds in the nitrogenase FeMoco active site is discussed. PMID:22119810

Lindahl, Paul A.

2011-01-01

232

Rapid adhesive bonding concepts  

NASA Technical Reports Server (NTRS)

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

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

1984-01-01

233

IMPROVED BONDING METHOD  

Microsoft Academic Search

An improved process of bonding aluminum to aluminum without fusion by ; ultrasonic vibrations plus pressure is described. The surfaces to be bonded are ; coated with an aqueous solution of alkali metal stearate prior to assembling for ; bonding. (AEC) O H19504 Present information is reviewed on steady state ; proliferation, differentiation, and maturation of blood cells in mammals.

E. V. Jr. Padgett; D. H. Warf

1964-01-01

234

Multiple bonding in the chromium dimer supported by two diazadiene ligands.  

PubMed

Analysis of the topology and delocalization of the electron density with the quantum theory of atoms in molecules (QTAIM) shows that the Cr(2) dimer when supported by two diazadiene ligands has a degree of bonding of 3.6--slightly less than that of a formal quadruple bond. The metal-ligand complex is held together by relatively weak dative bonds. Out-of-plane lone-pair-like charge concentrations on the nitrogen atoms are oriented so as to maximally avoid areas of charge concentration in the distorted inner-valence shell of the chromium atoms. PMID:19183038

DuPré, Donald B

2009-02-26

235

Two-electron bond-orbital model, 2  

NASA Technical Reports Server (NTRS)

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.

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

1976-01-01

236

The kinetic energy change on covalent bond formation  

PubMed Central

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

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

1981-01-01

237

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

NASA Astrophysics Data System (ADS)

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.

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

238

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

PubMed

We recently devised a simple scheme for analyzing on quantitative grounds the Dewar-Chatt-Duncanson donation and back-donation in symmetric coordination complexes. Our approach is based on a symmetry decomposition of the so called Charge-Displacement (CD) function quantifying the charge flow, upon formation of a metal (M)-substrate (S) bond, along the M-S interaction axis and provides clear-cut measures of donation and back-donation charges in correlation with experimental observables [G. Bistoni et al., Angew. Chem., Int. Ed. 52, 11599 (2013)]. The symmetry constraints exclude of course from the analysis most systems of interest in coordination chemistry. In this paper, we show how to entirely overcome this limitation by taking advantage of the properties of the natural orbitals for chemical valence [M. Mitoraj and A. Michalak, J. Mol. Model. 13, 347 (2007)]. A general scheme for disentangling donation and back-donation in the CD function of both symmetric and non-symmetric systems is presented and illustrated through applications to M-ethyne (M = Au, Ni and W) coordination bonds, including an explicative study on substrate activation in a model reaction mechanism. PMID:25725717

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

2015-02-28

239

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

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

240

Bonding thermoplastic polymers  

DOEpatents

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

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

2008-06-24

241

Prospective bonding applications  

NASA Astrophysics Data System (ADS)

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.

Ancenay, H.; Benazet, D.

1981-07-01

242

Hydrophobic silicon wafer bonding  

NASA Astrophysics Data System (ADS)

Wafers prepared by an HF dip without a subsequent water rinse were bonded at room temperature and annealed at temperatures up to 1100 °C. Based on substantial differences between bonded hydrophilic and hydrophobic Si wafer pairs in the changes of the interface energy with respect to temperature, secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM), we suggest that hydrogen bonding between Si-F and H-Si across two mating wafers is responsible for room temperature bonding of hydrophobic Si wafers. The interface energy of the bonded hydrophobic Si wafer pairs does not change appreciably with time up to 150 °C. This stability of the bonding interface makes reversible room-temperature hydrophobic wafer bonding attractive for the protection of silicon wafer surfaces.

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

1994-01-01

243

Valence neutron capture. gamma. -ray spectrum in /sup 54/Fe  

SciTech Connect

Neutron capture ..gamma..-ray spectra have been measured from the 7.76-keV s-wave and the 9.48-, 11.2-, and 14.4-keV p-wave resonances in /sup 54/Fe. The 7.76-keV resonance spectrum is in excellent agreement with valence model predictions.

Raman, S.; Slaughter, G.G.; Wells, J.C. Jr.; Allen, B.J.

1980-07-01

244

Isotope-shift calculations for atoms with one valence electron  

Microsoft Academic Search

This work presents a method for the ab initio calculation of isotope shift in atoms and ions with one valence electron above closed shells. As a zero approximation, we use relativistic Hartree-Fock and then calculate correlation corrections. The main motivation for developing the method comes from the need to analyze whether different isotope abundances in early universe can contribute to

J. C. Berengut; V. A. Dzuba; V. V. Flambaum

2003-01-01

245

Emotional Valence and Arousal Effects on Memory and Hemispheric Asymmetries  

ERIC Educational Resources Information Center

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

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

2010-01-01

246

Semantic Category Effect and Emotional Valence in Female University Students  

ERIC Educational Resources Information Center

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…

Brousseau, Geri; Buchanan, Lori

2004-01-01

247

Vection Modulates Emotional Valence of Autobiographical Episodic Memories  

ERIC Educational Resources Information Center

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

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

2013-01-01

248

Tagging Multiple Emotional Stimuli: Negative Valence Has Little Benefit  

ERIC Educational Resources Information Center

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

Watson, Derrick G.; Blagrove, Elisabeth

2012-01-01

249

Social Learning Modulates the Lateralization of Emotional Valence  

ERIC Educational Resources Information Center

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

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

2008-01-01

250

Recognizing the Emotional Valence of Names: An ERP Study  

ERIC Educational Resources Information Center

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

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

2013-01-01

251

Valence state at the surface of rare-earth metals  

Microsoft Academic Search

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

Börje Johansson

1979-01-01

252

Valence and Instrumentality Contributions to Understanding Occupational Preference.  

ERIC Educational Resources Information Center

An occupation is preferred on the basis of the match between valences and instrumentalities. Subjects rated their most preferred occupation as more instrumental for all types of outcomes in comparison to other occupations. The more valent the outcome, the more likely the preferred occupation is rated as more instrumental for that outcome. (Author)

Wheeler, Kenneth G.

1980-01-01

253

Real-time observation of valence electron motion.  

SciTech Connect

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

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

2010-08-05

254

Electronegativity and Valence Electron Spectrum of Room Temperature Ferromagnets  

Microsoft Academic Search

Materials that exhibit room temperature ferromagnetism (RTFM) are of interest in the fabrication of spintronic devices. RTFM has been observed in semiconductors, oxides and other non-magnetic materials and nanocrystals. There is yet no consensus on the origin of RTFM or how to predict the next RTFM. Here we study the electronegativity and valence electron count of known RTFMs as a

O. Paul Isikaku-Ironkwe

2009-01-01

255

Mobile linkers on DNA-coated colloids: valency without patches  

E-print Network

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.

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

2014-08-27

256

Mobile Linkers on DNA-Coated Colloids: Valency without Patches  

NASA Astrophysics Data System (ADS)

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.

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

2014-09-01

257

An experimental and theoretical study into the valence electronic structure of bicyclo[2.2.1]hepta-2,5-dione  

NASA Astrophysics Data System (ADS)

The results from an electron momentum spectroscopy (EMS) study of the outer valence electronic region of bicyclo[2.2.1]hepta-2,5-dione (C7H8O2) are reported for the first time. The measured binding energy spectra are presented for the azimuthal angles 0°, 10° and 0° + 10°, respectively, and are compared to new He(I) photoelectron spectroscopy results, which are measured as a part of this work. These experimental data are compared further with results from theoretical computations, using various methods including Hartree-Fock, density functional and an outer valence Green's function theory. Measured orbital momentum distributions are compared on an orbital by orbital basis against those obtained by calculations which employ the plane-wave impulse approximation. These calculations use orbital wavefunctions obtained from Hartree-Fock and density functional theory with a couple of generalized gradient approximation exchange correlation (XC) functionals and the DGauss triple zeta valence polarization basis set. Agreement between the measured and calculated momentum distributions was found to be only fair. Nonetheless, the orbital momentum distributions of the molecule still provide an orbital based assessment of the XC functionals of the density functional theory employed, and an understanding of the chemical bonding mechanisms within the species. Finally, the spectroscopic strengths calculated using outer valence Green's function theory are compared against those derived from our EMS measurements.

Jones, D. B.; Bolorizadeh, M. A.; Brunger, M. J.; Saha, S.; Wang, F.; Gleiter, R.; Bueber, J.; Winkler, D. A.

2006-06-01

258

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

SciTech Connect

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

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

2005-12-15

259

a New Approach to the Mixed Valence Problem  

NASA Astrophysics Data System (ADS)

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

Coleman, Piers

260

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

261

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

SciTech Connect

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

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

2009-03-02

262

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

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

263

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

ERIC Educational Resources Information Center

Do the emotional valence and arousal of events distort children's memories? Do valence and arousal modulate counterintuitive age increases in false memory? We investigated those questions in children, adolescents, and adults using the Cornell/Cortland Emotion Lists, a word list pool that induces false memories and in which valence and arousal can…

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

2010-01-01

264

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

ERIC Educational Resources Information Center

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

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

2009-01-01

265

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

ERIC Educational Resources Information Center

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

Schepman, Astrid; Rodway, Paul; Geddes, Pauline

2012-01-01

266

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

Microsoft Academic Search

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

Jose Fornari; Tuomas Eerola

267

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

Microsoft Academic Search

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

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

2010-01-01

268

Chemical bonding technology  

NASA Technical Reports Server (NTRS)

Primers employed in bonding together the various material interfaces in a photovoltaic module are being developed. The approach develops interfacial adhesion by generating actual chemical bonds between the various materials bonded together. The current status of the program is described along with the progress toward developing two general purpose primers for ethylene vinyl acetate (EVA), one for glass and metals, and another for plastic films.

Plueddemann, E.

1986-01-01

269

One Bond Strategy  

NSDL National Science Digital Library

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

2001-01-01

270

Reentrant Valence Transition in EuO at High Pressures: Beyond the Bond-Valence Model N. M. Souza-Neto,1,2,* J. Zhao,1  

E-print Network

, three-fold increase in magnetic ordering temperature is observed under applied pressures of up to % 14]. The relationship between crystal structure, electronic structure, and mag- netic ordering temperature has fueled Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA 2 Laborato´rio Nacional de Luz

Haskel, Daniel

271

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

PubMed

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

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

2012-01-01

272

The olfactory tubercle encodes odor valence in behaving mice.  

PubMed

Sensory information acquires meaning to adaptively guide behaviors. Despite odors mediating a number of vital behaviors, the components of the olfactory system responsible for assigning meaning to odors remain unclear. The olfactory tubercle (OT), a ventral striatum structure that receives monosynaptic input from the olfactory bulb, is uniquely positioned to transform odor information into behaviorally relevant neural codes. No information is available, however, on the coding of odors among OT neurons in behaving animals. In recordings from mice engaged in an odor discrimination task, we report that the firing rate of OT neurons robustly and flexibly encodes the valence of conditioned odors over identity, with rewarded odors evoking greater firing rates. This coding of rewarded odors occurs before behavioral decisions and represents subsequent behavioral responses. We predict that the OT is an essential region whereby odor valence is encoded in the mammalian brain to guide goal-directed behaviors. PMID:25788670

Gadziola, Marie A; Tylicki, Kate A; Christian, Diana L; Wesson, Daniel W

2015-03-18

273

Tagging multiple emotional stimuli: negative valence has little benefit.  

PubMed

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

Watson, Derrick G; Blagrove, Elisabeth

2012-06-01

274

Emotional valence and arousal interact in attentional control.  

PubMed

A recent study demonstrated that observers' ability to identify targets in a rapid visual sequence was enhanced when they simultaneously listened to happy music. In the study reported here, we examined how the emotion-attention relationship is influenced by changes in both mood valence (negative vs. positive) and arousal (low vs. high). We used a standard induction procedure to generate calm, happy, sad, and anxious moods in participants. Results for an attentional blink task showed no differences in first-target accuracy, but second-target accuracy was highest for participants with low arousal and negative affect (sad), lowest for those with strong arousal and negative affect (anxious), and intermediate for those with positive affect regardless of their arousal (calm, happy). We discuss implications of this valence-arousal interaction for the control of visual attention. PMID:18315803

Jefferies, Lisa N; Smilek, Daniel; Eich, Eric; Enns, James T

2008-03-01

275

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

Code of Federal Regulations, 2013 CFR

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

2013-07-01

276

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

Code of Federal Regulations, 2014 CFR

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

2014-07-01

277

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

Code of Federal Regulations, 2012 CFR

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

2012-07-01

278

The following changes to the EIA in the Yucca Mountain Rule Docket (A-95-12, V-B-2) were made in this document to correct typographical and other minor errors in the text.  

E-print Network

The following changes to the EIA in the Yucca Mountain Rule Docket (A-95-12, V-B-2) were made Radiation Protection Standards for Yucca Mountain, Nevada" Pg. ii Item 4.1 changed to read, "Performance Standards with Expected Values of TSPA-SR Calculations for a Repository at Yucca Mountain for Nominal

279

Self-consistent perturbation theory for dynamics of valence fluctuations  

Microsoft Academic Search

Dynamical properties of valence-fluctuating systems are studied at absolute zero of temperature. The self-consistent perturbation theory developed for rare-earth impurity systems is used with some refinement. The theory takes account of the orthogonality catastrophe caused by hybridization of 4f and conduction electrons. Extensive numerical results are reported for the 4f-electron density of states ?4f(?) and the dynamical magnetic susceptibility ?(?).

Y. Kuramoto; H. Kojima

1984-01-01

280

Basic features of the pion valence-quark distribution function  

NASA Astrophysics Data System (ADS)

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.

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

2014-10-01

281

Chromium valences in ureilite olivine and implications for ureilite petrogenesis  

NASA Astrophysics Data System (ADS)

Ureilites are a group of ultramafic achondrites commonly thought to be residues of partial melting on a carbon-rich asteroid. They show a large variation in FeO content (olivine Fo values ranging from ?74 to 95) that cannot be due to igneous fractionation and suggests instead variation in oxidation state. The presence of chromite in only a few of the most ferroan (Fo 75-76) samples appears to support such a model. MicroXANES analyses were used in this study to determine the valence states of Cr (previously unknown) in olivine cores of 11 main group ureilites. The goal of this work was to use a method that is independent of Fo to determine the oxidation conditions under which ureilites formed, in order to evaluate whether the ureilite FeO-variation is correlated with oxidation state, and whether it is nebular or planetary in origin. Two of the analyzed samples, LEW 88774 (Fo 74.2) and NWA 766 (Fo 76.7) contain primary chromite; two others, LAP 03587 (Fo 74.4) and CMS 04048 (Fo 76.2) contain sub-micrometer-sized exsolutions of chromite + Ca-rich pyroxene in olivine; and one, EET 96328 (Fo 85.2) contains an unusual chromite grain of uncertain origin. No chromite has been observed in the remaining six samples (Fo 77.4-92.3). Chromium in olivine in all eleven samples was found to be dominated by the divalent species, with valences ranging from 2.10 ± 0.02 (1?) to 2.46 ± 0.04. The non-chromite-bearing ureilites have the most reduced Cr, with a weighted mean valence of 2.12 ± 0.01, i.e., Cr2+/Cr3+ = 7.33. All low-Fo chromite-bearing ureilites have more oxidized Cr, with valences ranging from 2.22 ± 0.03 to 2.46 ± 0.04. EET 96328, whose chromite grain we interpret as a late-crystallizing phase, yielded a reduced Cr valence of 2.15 ± 0.07, similar to the non-chromite-bearing samples. Based on the measured Cr valences, magmatic (1200-1300 °C) oxygen fugacities (fO2) of the non-chromite-bearing samples were estimated to be in the range IW-1.9 to IW-2.8 (assuming basaltic melt composition), consistent with fO2 values obtained by assuming olivine-silica-iron metal (OSI) equilibrium. For the primary chromite-bearing-ureilites, the corresponding fO2 were estimated (again, assuming basaltic melt composition) to be ?IW to IW+1.0, i.e., several orders of magnitude more oxidizing than the conditions estimated for the chromite-free ureilites. In terms of Fo and Cr valence properties, ureilites appear to form two groups rather than a single “Cr-valence (or fO2) vs. Fo” trend. The chromite-bearing ureilites show little variation in Fo (?74-76) but significant variation in Cr valence, while the non-chromite-bearing ureilites show significant variation in Fo (?77-95) and little variation in Cr valence. These groups are unrelated to petrologic type (i.e., olivine-pigeonite, olivine-orthopyroxene, or augite-bearing). The chromite-bearing ureilites also have lower contents of Cr in olivine than most non-chromite-bearing ureilites, consistent with predictions based on Cr olivine/melt partitioning in spinel saturated vs. non-spinel-saturated systems. Under the assumption that at magmatic temperatures graphite-gas equilibria controlled fO2 at all depths on the ureilite parent body, we conclude: (1) that ureilite precursor materials having the Fo and Cr valence properties now observed in ureilites are unlikely to have been preserved during planetary processing; and (2) that the Fo and Cr valence properties now observed in ureilites are consistent with having been established by high-temperature carbon redox control over a range of depths on a plausible-sized ureilite parent body. The apparent limit on ureilite Fo values around 74-76 suggests that the precursor material(s) had bulk mg# ? that of LL chondrites.

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

2013-12-01

282

Valency configuration of transition metal impurities in ZnO  

SciTech Connect

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

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

2006-01-01

283

Core-core and core-valence correlation  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

284

Interactive Pi Bonding Effects  

NSDL National Science Digital Library

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

285

The dissociative bond.  

PubMed

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

Gordon, Nirit

2013-01-01

286

Planning Successful Bond Campaigns.  

ERIC Educational Resources Information Center

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

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

287

Chemical Bonds I  

ERIC Educational Resources Information Center

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

Sanderson, R. T.

1972-01-01

288

Interfacial bonding stability  

NASA Technical Reports Server (NTRS)

Interfacial bonding stability by in situ ellipsometry was investigated. It is found that: (1) gamma MPS is an effective primer for bonding ethylene vinyl acetate (EVA) to aluminum; (2) ellipsometry is an effective in situ technique for monitoring the stability of polymer/metal interfaces; (3) the aluminized back surface of silicon wafers contain significant amounts of silicon and may have glass like properties.

Boerio, J.

1984-01-01

289

Valenced Cues and Contexts Have Different Effects on Event-Based Prospective Memory  

PubMed Central

This study examined the separate influence and joint influences on event-based prospective memory task performance due to the valence of cues and the valence of contexts. We manipulated the valence of cues and contexts with pictures from the International Affective Picture System. The participants, undergraduate students, showed higher performance when neutral compared to valenced pictures were used for cueing prospective memory. In addition, neutral pictures were more effective as cues when they occurred in a valenced context than in the context of neutral pictures, but the effectiveness of valenced cues did not vary across contexts that differed in valence. The finding of an interaction between cue and context valence indicates that their respective influence on event-based prospective memory task performance cannot be understood in isolation from each other. Our findings are not consistent with by the prevailing view which holds that the scope of attention is broadened and narrowed, respectively, by positively and negatively valenced stimuli. Instead, our findings are more supportive of the recent proposal that the scope of attention is determined by the motivational intensity associated with valenced stimuli. Consistent with this proposal, we speculate that the motivational intensity associated with different retrieval cues determines the scope of attention, that contexts with different valence values determine participants’ task engagement, and that prospective memory task performance is determined jointly by attention scope and task engagement. PMID:25647484

Graf, Peter; Yu, Martin

2015-01-01

290

Role of Valence Fluctuations in the Superconductivity of Ce122 Compounds  

NASA Astrophysics Data System (ADS)

Pressure dependence of the Ce valence in CeCu2Ge2 has been measured up to 24 GPa at 300 K and to 17 GPa at 18-20 K using x-ray absorption spectroscopy in the partial fluorescence yield. A smooth increase of the Ce valence with pressure is observed across the two superconducting (SC) regions without any noticeable irregularity. The chemical pressure dependence of the Ce valence was also measured in Ce(Cu1-xNix)2Si2 at 20 K. A very weak, monotonic increase of the valence with x was observed, without any significant change in the two SC regions. Within experimental uncertainties, our results show no evidence for the valence transition with an abrupt change in the valence state near the SC II region, challenging the valence-fluctuation mediated superconductivity model in these compounds at high pressure and low temperature.

Yamaoka, H.; Ikeda, Y.; Jarrige, I.; Tsujii, N.; Zekko, Y.; Yamamoto, Y.; Mizuki, J.; Lin, J.-F.; Hiraoka, N.; Ishii, H.; Tsuei, K.-D.; Kobayashi, T. C.; Honda, F.; ?nuki, Y.

2014-08-01

291

Wood Bond Testing  

NASA Technical Reports Server (NTRS)

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

1989-01-01

292

Shape Bonding method  

NASA Technical Reports Server (NTRS)

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

Pontius, James T. (Inventor)

2010-01-01

293

Ultrasonically bonded value assembly  

NASA Technical Reports Server (NTRS)

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

Salvinski, R. J. (inventor)

1975-01-01

294

Nanomaterials. Programmable materials and the nature of the DNA bond.  

PubMed

For over half a century, the biological roles of nucleic acids as catalytic enzymes, intracellular regulatory molecules, and the carriers of genetic information have been studied extensively. More recently, the sequence-specific binding properties of DNA have been exploited to direct the assembly of materials at the nanoscale. Integral to any methodology focused on assembling matter from smaller pieces is the idea that final structures have well-defined spacings, orientations, and stereo-relationships. This requirement can be met by using DNA-based constructs that present oriented nanoscale bonding elements from rigid core units. Here, we draw analogy between such building blocks and the familiar chemical concepts of "bonds" and "valency" and review two distinct but related strategies that have used this design principle in constructing new configurations of matter. PMID:25700524

Jones, Matthew R; Seeman, Nadrian C; Mirkin, Chad A

2015-02-20

295

Beryllium dimer: a bond based on non-dynamical correlation.  

PubMed

The bond nature in beryllium dimer has been theoretically investigated using high-level ab initio methods. A series of ANO basis sets of increasing quality, going from sp to spdf ghi contractions, has been employed, combined with HF, CAS-SCF, CISD, and MRCI calculations with several different active spaces. The quality of these calculations has been checked by comparing the results with valence Full-CI calculations, performed with the same basis sets. It is shown that two quasi-degenerated partly occupied orbitals play a crucial role to give a qualitatively correct description of the bond. Their nature is similar to that of the edge orbitals that give rise to the quasi-degenerated singlet-triplet states in longer beryllium chains. PMID:24866399

El Khatib, Muammar; Bendazzoli, Gian Luigi; Evangelisti, Stefano; Helal, Wissam; Leininger, Thierry; Tenti, Lorenzo; Angeli, Celestino

2014-08-21

296

Torsionally controlled electronic coupling in mixed-valence oxodimolybdenum nitrosyl scorpionates--a DFT study.  

PubMed

The density functional theory (DFT) method has been used to study the electronic communication in strongly interacting oxo-bridged di-{Mo(II,I)(NO(+))}(3+,2+) complexes stabilized by tris(3-methylpyrazol-1-yl)borate, [Tp(Me)](-) (dihydroxy 1' and its modified analogs), having fully localized valences on the two Mo centers (Class I), despite a short (ca. 3.8 A) Mo...Mo distance. Structural and electrochemical (separation between the redox potentials Delta(red/ox)E(1/2)) properties and IR spectra (in particular the nu(NO) frequencies) obtained from the B3LYP calculations for 1' are successfully related to experimental values. Strongly twisted geometry with the (O)N-Mo1...Mo2-N(O) angle close to 90 degrees (confirmed by DFT modeling performed for 1'(-1,0,+1) and X-ray diffraction study of [{Mo(NO)(Tp(Me2))(OH)}(2)(mu-O)](-) (1) presented herein) is a common, though so far not fully understood, structural feature of this class of mu-oxo species, in contrast to the closely related {Mo(V)(=O)}(3+) analogs. This study shows that the orthogonality of the local equatorial planes for the two Mo centers may be rationalized by the electronic structure, namely from the balance between the destabilizing repulsion of the Mo-based (d, pi(x)*)(b) electron pairs versus a favorable but relatively weak electron delocalization. Strongly repelling electron pairs avoid each other, which enforces the twisted geometries and blocks the electron delocalization. Steric hindrance (a nonbonding repulsion of the adjacent Tp(x) ligands and the weak hydrogen-bonding interactions, i.e., OH...ON, OH...OH, and C-H...O((NO/OH))) is shown not to be decisive since neither the removal of the inner 3-Me groups of [Tp(Me)](-) in complex 1' nor the substitution of OH groups by OCH(3) ligands did substantially influence the dihedral twist angle in the minimum energy structure. Yet the relative orientation of the {Mo(NO)}(2+,3+) cores along with the position of the bridging oxygen (significantly bent upon reduction) controls the prospective intramolecular through-bond electron transfer in the mixed valence form. Our DFT modeling demonstrates that a maximum delocalization (via a hole-transfer mechanism) of the unpaired electron in 1'(-), measured as a spin population on the nonreduced Mo2 center, is achieved for the structure with a torsional deflection of 23 degrees, at a cost of 16.5 kcal/mol. These results show that the electron exchange along the Mo-O-Mo array in the originally fully valence-trapped {17e:16e}(-) complexes may be controlled and can be thermally activated (e.g., using a high-boiling solvent or by irradiation at ca. 50-200 cm(-1)). PMID:20799734

Roma?czyk, Piotr P; Noga, Klemens; W?odarczyk, Andrzej J; Nitek, Wojciech; Broclawik, Ewa

2010-09-01

297

Empirical corrections for anharmonic zero-point vibrations of hydrogen and deuterium in geometric hydrogen bond correlations  

Microsoft Academic Search

In this paper, empirical corrections for anharmonic ground-state vibrations of hydrogen and deuterium in the hydrogen bridges A–L?B, L=H, D are introduced into the geometric hydrogen bond correlation analysis based on the empirical Pauling valence bond orders. The method is verified using the examples of the hydrogen bonded anions in [(CO)5Cr–C?N?H?N?C–Cr(CO)5]? As(Ph)4+ (1h), in [(CO)5Cr–C?N?H?N?C–Cr(CO)5]? N(n-propyl)4+ (2h), in the model

Hans-Heinrich Limbach; Mariusz Pietrzak; Hans Benedict; Peter M. Tolstoy; Nikolai S. Golubev; Gleb S. Denisov

2004-01-01

298

Calculation of internal valence force constants for XY 4 ( Td) tetrahedral molecules  

NASA Astrophysics Data System (ADS)

Valence force constants have been calculated in terms of simple dependent rectilinear internal coordinates for a series of XY 4 tetrahedral molecules that have been studied from a vibrational point of view. These molecules include the tetrahydrides of carbon, silicon, germanium and tin, and the tetrafluorides of carbon, silicon and germanium. Using the most recent and reliable force constants in symmetry coordinates, the pure vibrational force field has been arrived at by applying Kuczera's treatment. The results show that the seven FR dependent constants are reduced to five F*R independent constants; the same occurs for the F0S independent force constants. The relationships f*r? = - f*'r? and f*'?? = - f*? - 4 f*?? are obtained from the sum rule in Kuczera's treatment. On the basis of Wilson's S vectors and from the interactions between the displacement coordinates, a method is proposed here to obtain the above relationships. This allows individual values to be assigned to the bending, bending—bending and bending—stretching force constants for the above-mentioned molecules, without the need for recourse to any model whatsoever. Likewise, in each case we have attempted to obtain an empirical function to fit the force constant values dependent on the bond lengths. This method allows us to some extent to predict the values of the force constants for some tetrahydride molecules of this group, which has not yet been studied experimentally.

Fernández Gómez, M.; López González, J. J.; Rajamanickam, N.; Martínez-Torres, E.

1992-08-01

299

Mode-coupling theory predictions for a limited valency attractive square-well model  

E-print Network

Recently we have studied, using numerical simulations, a limited valency model, i.e. an attractive square well model with a constraint on the maximum number of bonded neighbors. Studying a large region of temperatures $T$ and packing fractions $\\phi$, we have estimated the location of the liquid-gas phase separation spinodal and the loci of dynamic arrest, where the system is trapped in a disordered non-ergodic state. Two distinct arrest lines for the system are present in the system: a {\\it (repulsive) glass} line at high packing fraction, and a {\\it gel} line at low $\\phi$ and $T$. The former is essentially vertical ($\\phi$-controlled), while the latter is rather horizontal ($T$-controlled) in the $(\\phi-T)$ plane. We here complement the molecular dynamics results with mode coupling theory calculations, using the numerical structure factors as input. We find that the theory predicts a repulsive glass line -- in satisfactory agreement with the simulation results -- and an attractive glass line which appears to be unrelated to the gel line.

E. Zaccarelli; I. Saika-Voivod; A. J. Moreno; E. La Nave; S. V. Buldyrev; F. Sciortino; P. Tartaglia

2006-05-08

300

Intermolecular hydrogen bond energies in crystals evaluated using electron density properties: DFT computations with periodic boundary conditions.  

PubMed

The hydrogen bond (H-bond) energies are evaluated for 18 molecular crystals with 28 moderate and strong O-H···O bonds using the approaches based on the electron density properties, which are derived from the B3LYP/6-311G** calculations with periodic boundary conditions. The approaches considered explore linear relationships between the local electronic kinetic G(b) and potential V(b) densities at the H···O bond critical point and the H-bond energy E(HB). Comparison of the computed E(HB) values with the experimental data and enthalpies evaluated using the empirical correlation of spectral and thermodynamic parameters (Iogansen, Spectrochim. Acta Part A 1999, 55, 1585) enables to estimate the accuracy and applicability limits of the approaches used. The V(b)-E(HB) approach overestimates the energy of moderate H-bonds (E(HB) < 60 kJ/mol) by ~20% and gives unreliably high energies for crystals with strong H-bonds. On the other hand, the G(b)-E(HB) approach affords reliable results for the crystals under consideration. The linear relationship between G(b) and E(HB) is basis set superposition error (BSSE) free and allows to estimate the H-bond energy without computing it by means of the supramolecular approach. Therefore, for the evaluation of H-bond energies in molecular crystals, the G(b) value can be recommended to be obtained from both density functional theory (DFT) computations with periodic boundary conditions and precise X-ray diffraction experiments. PMID:22786749

Vener, M V; Egorova, A N; Churakov, A V; Tsirelson, V G

2012-11-01

301

Bonding with Your Baby  

MedlinePLUS

... baby feel the different textures of dad's face Building a Support System Of course, it's easier to ... can take nearly all of your attention and energy — especially for a breastfeeding mom. Bonding will be ...

302

Gold Thermocompression Wafer Bonding  

E-print Network

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, ...

Spearing, S. Mark

303

Characterization of anodic bonding  

E-print Network

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 ...

Tudryn, Carissa Debra, 1978-

2004-01-01

304

Hydrogen bonds animation  

NSDL National Science Digital Library

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.

Northland Community and Technical College Biology Department

2007-12-12

305

All about Chemical Bonding  

NSDL National Science Digital Library

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

Lower, Stephen

306

Sketching the pion's valence-quark generalised parton distribution  

E-print Network

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.

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

2014-11-24

307

Water's Hydrogen Bond Strength  

E-print Network

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.

Martin Chaplin

2007-06-10

308

Pion and kaon valence-quark parton distribution functions.  

SciTech Connect

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

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

2011-06-16

309

Pion and kaon valence-quark parton distribution functions  

SciTech Connect

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

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

2011-06-15

310

Aging and long-term memory for emotionally valenced events.  

PubMed

In 2008, 1103 ardent Boston Red Sox fans answered questions about their team's 2003 loss and 2004 win in baseball championship games with archrival New York Yankees. Contrary to predictions based on socioemotional selectivity theory, there were no significant interactions of age and event valence for accuracy in remembering event details, or for self-reported subjective vividness and rehearsal of the memories. Fans 65 years and older tended to remember feeling only sad about the 2003 loss, whereas fans 25 years and under tended to remember feeling both sad and angry. Individuals may remember emotional feelings based on remembered goals about an event. PMID:22888956

Breslin, Carolyn W; Safer, Martin A

2013-06-01

311

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

PubMed

The role of radial nodes, or of their absence, in valence orbitals for chemical bonding and periodic trends is discussed from a unified viewpoint. In particular, we emphasize the special role of the absence of a radial node whenever a shell with angular quantum number l is occupied for the first time (lack of "primogenic repulsion"), as with the 1s, 2p, 3d, and 4f shells. Although the consequences of the very compact 2p shell (e.g. good isovalent hybridization, multiple bonding, high electronegativity, lone-pair repulsion, octet rule) are relatively well known, it seems that some of the aspects of the very compact 3d shell in transition-metal chemistry are less well appreciated, e.g., the often weakened and stretched bonds at equilibrium structure, the frequently colored complexes, and the importance of nondynamical electron-correlation effects in bonding. PMID:17143872

Kaupp, Martin

2007-01-15

312

Relational Bonds and Loyalty: The Bonds that Tie  

Microsoft Academic Search

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

Ahmad Shammout; Michael Polonsky; Michael Edwardson

313

Influence of bonding atmosphere on low-temperature wafer bonding  

Microsoft Academic Search

The influence of bonding atmosphere was investigated for the wafer bonding at 25~200°C using a surface activated bonding method. The results of the analysis of activated Si surfaces under different vacuum background and the residual gases in vacuum before and after Ar fast atom beam irradiation is reported. Based on the analysis, bonding of Si wafers in nitrogen atmosphere is

Ying-Hui Wang; Tadatomo Suga

2010-01-01

314

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

PubMed Central

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

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

2013-01-01

315

Plasmon excitation in valence shell photoelectron spectroscopy for PAHs  

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

316

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

NASA Astrophysics Data System (ADS)

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.

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

2012-12-01

317

Intracranial markers of emotional valence processing and judgments in music.  

PubMed

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

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

2015-03-01

318

An ecological valence theory of human color preference.  

PubMed

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

Palmer, Stephen E; Schloss, Karen B

2010-05-11

319

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

PubMed

Facial stimuli have been shown to accrue a special status within visual processing, particularly when attention is prioritized to one face over another on the basis of affective content. This has been examined in relation to the ability of faces to guide or hold attention, or to resist attentional suppression. Previous work has shown that schematic faces can only be partially ignored and that the emotional valence of to-be-ignored faces has little effect. Given recent debates concerning the use of schematic faces, here we examined the ease with which photorealistic faces could be ignored. Although we found evidence of a partial preview benefit for these stimuli, the findings were complex, with stimulus salience, valence, and threat content interacting to affect both the strength of the benefit and target detection efficiency (Exps. 1-3). Experiment 4 then clarified the effects of physical salience and perceived stimulus similarity in the previous experiments, demonstrating that a combination of these factors is likely to account for the search patterns observed. PMID:24435898

Blagrove, Elisabeth; Watson, Derrick G

2014-04-01

320

Valence holes observed in nanodiamonds dispersed in water  

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

321

Ligand-hole localization in oxides with unusual valence Fe  

PubMed Central

Unusual high-valence states of iron are stabilized in a few oxides. A-site-ordered perovskite-structure oxides contain such iron cations and exhibit distinct electronic behaviors at low temperatures, e.g. charge disproportionation (4Fe4+ ? 2Fe3+ + 2Fe5+) in CaCu3Fe4O12 and intersite charge transfer (3Cu2+ + 4Fe3.75+ ? 3Cu3+ + 4Fe3+) in LaCu3Fe4O12. Here we report the synthesis of solid solutions of CaCu3Fe4O12 and LaCu3Fe4O12 and explain how the instabilities of their unusual valence states of iron are relieved. Although these behaviors look completely different from each other in simple ionic models, they can both be explained by the localization of ligand holes, which are produced by the strong hybridization of iron d and oxygen p orbitals in oxides. The localization behavior in the charge disproportionation of CaCu3Fe4O12 is regarded as charge ordering of the ligand holes, and that in the intersite charge transfer of LaCu3Fe4O12 is regarded as a Mott transition of the ligand holes. PMID:22690318

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

2012-01-01

322

An ecological valence theory of human color preference  

PubMed Central

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

Palmer, Stephen E.; Schloss, Karen B.

2010-01-01

323

Hydrogen bonding, halogen bonding and lithium bonding: an atoms in molecules and natural bond orbital perspective towards conservation of total bond order, inter- and intra-molecular bonding.  

PubMed

One hundred complexes have been investigated exhibiting D-X···A interactions, where X = H, Cl or Li and DX is the 'X bond' donor and A is the acceptor. The optimized structures of all these complexes have been used to propose a generalized 'Legon-Millen rule' for the angular geometry in all these interactions. A detailed Atoms in Molecules (AIM) theoretical analysis confirms an important conclusion, known in the literature: there is a strong correlation between the electron density at the XA bond critical point (BCP) and the interaction energy for all these interactions. In addition, we show that extrapolation of the fitted line leads to the ionic bond for Li-bonding (electrostatic) while for hydrogen and chlorine bonding, it leads to the covalent bond. Further, we observe a strong correlation between the change in electron density at the D-X BCP and that at the X···A BCP, suggesting conservation of the bond order. The correlation found between penetration and electron density at BCP can be very useful for crystal structure analysis, which relies on arbitrary van der Waals radii for estimating penetration. Various criteria proposed for shared- and closed-shell interactions based on electron density topology have been tested for H/Cl/Li bonded complexes. Finally, using the natural bond orbital (NBO) analysis it is shown that the D-X bond weakens upon X bond formation, whether it is ionic (DLi) or covalent (DH/DCl) and the respective indices such as ionicity or covalent bond order decrease. Clearly, one can think of conservation of bond order that includes ionic and covalent contributions to both D-X and X···A bonds, for not only X = H/Cl/Li investigated here but also any atom involved in intermolecular bonding. PMID:25127185

Shahi, Abhishek; Arunan, Elangannan

2014-11-14

324

Surface analysis in composite bonding  

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

325

Thio- and selenoglycosides as ligands for biomedically relevant lectins: valency-activity correlations for benzene-based dithiogalactoside clusters and first assessment for (di)selenodigalactosides.  

PubMed

Substitution of the oxygen atom in the glycosidic linkage by a disulfide bond or by selenium makes the resulting glycoside resistant to hydrolysis. To clarify the consequences for affinity to lectins we prepared benzene-based mono- to trivalent dithiogalactosides. Inhibitory capacity increased with valency for a plant toxin, the synthetic compounds potently blocking its binding to a lactose-presenting matrix and to cells. Human galectins were much less sensitive to the disulfides than the toxin. This differential response constitutes a beneficial effect to avoid cross-reactivity in vivo. Symmetrical selenodigalactoside and diselenodigalactoside were prepared and similarly tested. Both compounds proved rather equally bioactive for the toxin, graded activity was measured for human galectins. This result directs attention to further studies to relate Se-dependent alterations in bond angle and length as well as van der Waals radius to binding properties of selenoglycosides to biomedically relevant lectins. PMID:25599835

André, Sabine; Kövér, Katalin E; Gabius, Hans-Joachim; Szilágyi, László

2015-02-15

326

Strength of Chemical Bonds  

NASA Technical Reports Server (NTRS)

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

Christian, Jerry D.

1973-01-01

327

Asymmetric bifurcated halogen bonds.  

PubMed

Halogen bonding (XB) is being extensively explored for its potential use in advanced materials and drug design. Despite significant progress in describing this interaction by theoretical and experimental methods, the chemical nature remains somewhat elusive, and it seems to vary with the selected system. In this work we present a detailed DFT analysis of three-center asymmetric halogen bond (XB) formed between dihalogen molecules and variously 4-substituted 1,2-dimethoxybenzene. The energy decomposition, orbital, and electron density analyses suggest that the contribution of electrostatic stabilization is comparable with that of non-electrostatic factors. Both terms increase parallel with increasing negative charge of the electron donor molecule in our model systems. Depending on the orientation of the dihalogen molecules, this bifurcated interaction may be classified as '?-hole - lone pair' or '?-hole - ?' halogen bonds. Arrangement of the XB investigated here deviates significantly from a recent IUPAC definition of XB and, in analogy to the hydrogen bonding, the term bifurcated halogen bond (BXB) seems to be appropriate for this type of interaction. PMID:25656525

Novák, Martin; Foroutan-Nejad, Cina; Marek, Radek

2015-03-01

328

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

PubMed

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

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

2005-11-01

329

Microstructure, irradiation hardening and embrittlement of 13Cr2MoNbVB ferritic—martensitic steel after neutron irradiation at low temperatures  

NASA Astrophysics Data System (ADS)

Tensile mechanical tests and TEM-study of type 13Cr2MoNbVB ferritic-martensitic steel (Russian-made steel EP-450), neutron-irradiated at temperatures in the range 280-350°C up to doses of 85 dpa, have been carried out. At doses of 0.5-25 dpa, the increment of the yield stress in irradiated steel can be fitted by the equation ??, MPa = 300 × (dose) 0.2. As the dose increases, the yield stress increment reaches a maximum at 30-40 dpa and then begins to decrease. Damage dose and irradiation temperature dependencies of the ductility, upper shelf energy and ductile-to-brittle transition temperature have also been examined. A TEM-analysis revealed dislocation loops, void and ?'-precipitation in the microstructure of the irradiated steel. At damage doses higher than 40 dpa, a decrease of loop number density and increase of loop size seem to be the main reasons for irradiation softening and ductility improvement in the temperature interval 330-360°C.

Khabarov, V. S.; Dvoriashin, A. M.; Porollo, S. I.

1996-10-01

330

Biomolecular halogen bonds.  

PubMed

Halogens are atypical elements in biology, but are common as substituents in ligands, including thyroid hormones and inhibitors, which bind specifically to proteins and nucleic acids. The short-range, stabilizing interactions of halogens - now seen as relatively common in biology - conform generally to halogen bonds characterized in small molecule systems and as described by the ?-hole model. The unique properties of biomolecular halogen bonds (BXBs), particularly in their geometric and energetic relationship to classic hydrogen bonds, make them potentially powerful tools for inhibitor design and molecular engineering. This chapter reviews the current research on BXBs, focusing on experimental studies on their structure-energy relationships, how these studies inform the development of computational methods to model BXBs, and considers how BXBs can be applied to the rational design of more effective inhibitors against therapeutic targets and of new biological-based materials. PMID:25326832

Ho, P Shing

2015-01-01

331

Insurance and bonding  

SciTech Connect

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

Katzman, M.T.

1989-01-01

332

Molecular orbital (SCF-X??-SW) theory of metal-metal charge transfer processes in minerals - I. application to Fe2+???Fe3+ charge transfer and "electron delocalization" in mixed-valence iron oxides and silicates  

USGS Publications Warehouse

A number of mixed valence iron oxides and silicates (e.g., magnetite, ilvaite) exhibit thermally induced electron delocalization between adjacent Fe2+ and Fe3+ ions and optically induced electronic transitions which are assigned to Fe2+???Fe3+ intervalence charge transfer. In this paper, the mechanism of electron delocalization (i.e., polarons versus itinerant electrons) and the nature of optically induced intervalence charge-transfer in minerals are investigated using molecular orbital theory. SCF-X??-SW molecular orbital calculations were done for several mixed-valence (Fe2O10)15- clusters corresponding to edgesharing Fe2+ and Fe3+ coordination polyhedra. A spinunrestricted formalism was used so that the effect of ferromagnetic versus antiferromagnetic coupling of adjacent Fe2+ and Fe3+ cations could be determined. The molecular orbital results can be related to the polaron theory of solid state physics and the perturbation theory formalism used by Robin and Day (1967) and others to describe electron transfer in mixed valence compounds. Intervalence charge-transfer results from the overlap of Fe(3d) orbitals across the shared edges of adjacent FeO6 polyhedra to give weak Fe-Fe bonds. Electron delocalization, however, requires that adjacent Fe cations be ferromagnetically coupled. Antiferromagnetic coupling results in distinguishable Fe2+ and Fe3+ cations. Electronic transitions between the Fe-Fe bonding and Fe-Fe antibonding orbitals results in the optically-induced intervalence charge transfer bands observed in the electronic spectra of mixed valence minerals. Such transitions are predicted to be polarized along the metal-metal bond direction, in agreement with experimental observations. ?? 1987 Springer-Verlag.

Sherman, D.M.

1987-01-01

333

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

PubMed

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

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

2013-12-01

334

Valence Quark Polarization In the Nucleon And the Deuteron Data  

E-print Network

Within the framework of the so-called "valon" model, we argue that a substantial part of the nucleon spin, about 40%, is carried by the polarized valence quarks. The remaining is the result of cancellations between gluon polarization and the orbital angular momentum, where the gluon polarization is the dominant one. It is shown that the sea quark contribution to the spin of any hadron is simply marginal and consistent with zero. Our findings point to a substantially smaller value for a_8 thaninferred from hyperon- $\\beta$ decay, suggesting that fullSU(3) symmetric assumption needs to be reconsidered. New and emerging experimental data tend to support this finding. Finally, we show that within the model described here the experimental data on the polarized structure functions $g_{1}^{p,n,d}$ are reproduced.

Firooz Arash; Fatemeh Taghavi-Shahri

2008-08-21

335

Isotope-shift calculations for atoms with one valence electron  

SciTech Connect

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

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

2003-08-01

336

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

NASA Technical Reports Server (NTRS)

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

Ting, David; Gunapala, Sarath; Bandara, Sumith

2004-01-01

337

Bonding with the Past.  

ERIC Educational Resources Information Center

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

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

1998-01-01

338

Bonding silicones with epoxies  

Microsoft Academic Search

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

Tira

1980-01-01

339

Parental Bonding Instrument  

Microsoft Academic Search

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

L. C. Cavedo; G. Parker

1994-01-01

340

Fluoroepoxy Adhesives Bond Fluoroplastics  

NASA Technical Reports Server (NTRS)

Etching or other special preparation unnecessary. Experiments show fluoroepoxy compounds of high fluorine content adhere to fluoroplastics, without prior etching or other treatment of fluoroplastic surfaces. Compounds mixed with each other in approximately stoichiometric amounts and react to produce fluoroepoxy compounds adhering to fluoroplastics. Advantageous in bonding polymers having fluorine contents of 55 percent or more.

Lee, Sheng Yen

1989-01-01

341

Photochemical tissue bonding  

DOEpatents

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

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

2012-01-10

342

Periodic superstructures in tetrahedrally bonded homopolymers  

NASA Astrophysics Data System (ADS)

Using a lattice sum over single bipolaron potentials displaced by periodicity d, we have analytically obtained a solution for a bipolaron lattice for a tetrahedrally bonded homopolymer within the continuum model of Rice and Phillpot. This solution is used to derive the band structure, which consists of two bipolaron bands symmetrically located about the middle of the band gap in addition to the conduction and valence bands. The electronic density of states, chemical potential ?, and the energy of formation of a bipolaron lattice are also calculated as a function of the bipolaron density ?b. The bipolaron chemical potential lies between the conduction-band edge and the upper edge of the upper bipolaron band, indicating that the bipolaron lattice is energetically the most favorable charge configuration at low ?b. In the strict weak-coupling limit (infinite momentum cutoff ?) the bipolaron-bipolaron interaction is found to be repulsive and varies with bipolaron density as (1/?b)exp(-2/?b?p), ?p being the bipolaron characteristic length. Thus, the bipolaron lattice is stable only in the range 0

Saxena, Avadh; Cao, Wenwu

1988-10-01

343

Bonds, bands and elasticity of smithsonite rock  

NASA Astrophysics Data System (ADS)

The objective here is to spread out in detail the various fundamental state properties of smithsonite rock (ZnCO3) for which the most intrinsic quantities remain still unknown. First-principles electronic structure calculations based on the density functional theory with the pseudopotential method were performed using diverse functionals. A number of mechanical quantities were evaluated such as bulk modulus, elastic constants, Young's and shear moduli, and transversal and longitudinal sound velocities (VS and VP). Fitting the compression data of smithsonite to the third-order Birch-Murnaghan equation of state gives a bulk modulus of 124.17 GPa, which reflects an important rigidity compared to the other carbonates. The analysis of the band structure reveals a band-gap energy of 3.36 eV that is close enough to some semiconductors rather than insulators. Finally the chemical bonding was analyzed through the electronic charge density of the total contributions of the valence bands. A pronounced charge transfer was observed towards the carbonate ion, indicating thereby the ionic character of ZnCO3.

Bouibes, A.; Zaoui, A.; Tunega, D.

2013-07-01

344

Topological Crystalline Kondo Insulator in Mixed Valence Ytterbium Borides Hongming Weng,1,2  

E-print Network

Topological Crystalline Kondo Insulator in Mixed Valence Ytterbium Borides Hongming Weng,1 7 January 2014) The electronic structures of two mixed valence insulators YbB6 and YbB12 are studied theory. YbB6 is found to be a moderately correlated Z2 topological insulator, similar to SmB6 but having

Wang, Wei Hua

345

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

Microsoft Academic Search

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

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

2007-01-01

346

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

EPA Science Inventory

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

347

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

348

Valence Focus and Self-Esteem Lability: Reacting to Hedonic Cues in the Social Environment  

E-print Network

Valence Focus and Self-Esteem Lability: Reacting to Hedonic Cues in the Social Environment Paula R experience) demonstrated greater self-esteem lability (i.e., larger changes in self-esteem) to pleasant. Keywords: valence focus, emotion, self-esteem lability, experience sampling, social interactions Hedonic

Barrett, Lisa Feldman

349

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

ERIC Educational Resources Information Center

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

Jansari, Ashok; Rodway, Paul; Goncalves, Salvador

2011-01-01

350

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...

351

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

E-print Network

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

Paris-Sud XI, Université de

352

Reviews in the Neurosciences 241 Remembering emotional experiences: The contribution of valence and arousal  

E-print Network

(how negative or positive) and arousal (how calming or exciting). Although both dimensions appear and arousal (defined below) on declarative memory formation. Dimensions of Emotion: Arousal and Valence). The dimension of valence ranges from highly positive to highly negative, whereas the dimension of arousal ranges

Kensinger, Elizabeth A.

353

Intrasubject Predictions of Occupational Preference: The Effect of Manipulating Components of the Valence Model  

ERIC Educational Resources Information Center

The purposes of this study were (1) to test whether the occupational preferences of senior psychology majors could be predicted using a within-subjects analysis of Vroom's model; (2) to examine the predictive validity of valence and instrumentality measures, and (3) to compare the predictive validity of the weighted and unweighted valence models.…

Muchinsky, Paul M.; Taylor, M. Susan

1976-01-01

354

Effects of hedonic valence and physiological arousal on emotion: A comparison of two theoretical perspectives  

Microsoft Academic Search

Two theoretical perspectives concerned with how one emotional state may influence a subsequent one were examined. Zillmann's (1979) excitation transfer theory suggests that undetected residual arousal from a first state will transfer and intensify a subsequent state—regardless of the first state's hedonic valence. Baron's (1977) incompatible response model, on the other hand, suggests that the hedonic valence of an earlier

Nyla R. Branscombe

1985-01-01

355

I-Space: The Effects of Emotional Valence and Source of Music on Interpersonal Distance  

E-print Network

I-Space: The Effects of Emotional Valence and Source of Music on Interpersonal Distance Ana personal space, that is, the emotionally-tinged zone around the human body that people feel is ``their space''. We evaluated the effects of emotional valence (positive versus negative) and source (external

Sheldon, Nathan D.

356

Gel to glass transition in simulation of a valence-limited colloidal system  

E-print Network

We numerically study a simple model for thermo-reversible colloidal gelation in which particles can form reversible bonds with a predefined maximum number of neighbors. We focus on three and four maximally coordinated particles, since in these two cases the low valency makes it possible to probe, in equilibrium, slow dynamics down to very low temperatures $T$. By studying a large region of $T$ and packing fraction $\\phi$ we are able to estimate both the location of the liquid-gas phase separation spinodal and the locus of dynamic arrest, where the system is trapped in a disordered non-ergodic state. We find that there are two distinct arrest lines for the system: a {\\it glass} line at high packing fraction, and a {\\it gel} line at low $\\phi$ and $T$. The former is rather vertical ($\\phi$-controlled), while the latter is rather horizontal ($T$-controlled) in the $(\\phi-T)$ plane. Dynamics on approaching the glass line along isotherms exhibit a power-law dependence on $\\phi$, while dynamics along isochores follow an activated (Arrhenius) dependence. The gel has clearly distinct properties from those of both a repulsive and an attractive glass. A gel to glass crossover occurs in a fairly narrow range in $\\phi$ along low $T$ isotherms, seen most strikingly in the behavior of the non-ergodicity factor. Interestingly, we detect the presence of anomalous dynamics, such as subdiffusive behavior for the mean squared displacement and logarithmic decay for the density correlation functions in the region where the gel dynamics interferes with the glass dynamics.

Emanuela Zaccarelli; Ivan Saika-Voivod; Sergey V. Buldyrev; Angel J. Moreno; Piero Tartaglia; Francesco Sciortino

2006-05-04

357

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

NASA Astrophysics Data System (ADS)

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

Lou, Jie; Sandvik, Anders

2008-03-01

358

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

SciTech Connect

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.

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

359

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

SciTech Connect

A suitable relationship between free-cation polarizability and electronegativity of elements in different valence states and with the most common coordination numbers has been searched on the basis of the similarity in physical nature of both quantities. In general, the cation polarizability increases with decreasing element electronegativity. A systematic periodic change in the polarizability against the electronegativity has been observed in the isoelectronic series. It has been found that generally the optical basicity increases and the single bond strength of simple oxides decreases with decreasing the electronegativity. The observed trends have been discussed on the basis of electron donation ability of the oxide ions and type of chemical bonding in simple oxides. - Graphical abstract: This figure shows the single bond strength of simple oxides as a function of element electronegativity. A remarkable correlation exists between these independently obtained quantities. High values of electronegativity correspond to high values of single bond strength and vice versa. It is obvious that the observed trend in this figure is closely related to the type of chemical bonding in corresponding oxide. Highlights: Black-Right-Pointing-Pointer A suitable relationship between free-cation polarizability and electronegativity of elements was searched. Black-Right-Pointing-Pointer The cation polarizability increases with decreasing element electronegativity. Black-Right-Pointing-Pointer The single bond strength of simple oxides decreases with decreasing the electronegativity. Black-Right-Pointing-Pointer The observed trends were discussed on the basis of type of chemical bonding in simple oxides.

Dimitrov, Vesselin, E-mail: vesselin@uctm.edu [Department of Silicate Technology, University of Chemical Technology and Metallurgy, 8, Kl. Ohridski Blvd., Sofia 1756 (Bulgaria)] [Department of Silicate Technology, University of Chemical Technology and Metallurgy, 8, Kl. Ohridski Blvd., Sofia 1756 (Bulgaria); Komatsu, Takayuki, E-mail: komatsu@mst.nagaokaut.ac.jp [Department of Materials Science and Technology, Nagaoka University of Technology, 1603-1 Kamitomioka-cho, Nagaoka 940-2188 (Japan)] [Department of Materials Science and Technology, Nagaoka University of Technology, 1603-1 Kamitomioka-cho, Nagaoka 940-2188 (Japan)

2012-12-15

360

The Illiquidity of Corporate Bonds  

E-print Network

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 ...

Bao, Jack

361

ChemTeacher: Ionic Bonds  

NSDL National Science Digital Library

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

2012-07-20

362

ChemTeacher: Covalent Bonds  

NSDL National Science Digital Library

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

2012-07-20

363

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

NASA Astrophysics Data System (ADS)

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.

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

2015-03-01

364

Fermi surface of IrTe2 in the valence-bond state as determined by quantum oscillations  

NASA Astrophysics Data System (ADS)

We report the observation of the de Haas-van Alphen effect in IrTe2 measured using torque magnetometry at low temperatures down to 0.4 K and in high magnetic fields up to 33 T. IrTe2 undergoes a major structural transition around ˜283 (1 )K due to the formation of planes of Ir and Te dimers that cut diagonally through the lattice planes, with its electronic structure predicted to change significantly from a layered system with predominantly three-dimensional character to a tilted quasi-two-dimensional Fermi surface. Quantum oscillations provide direct confirmation of this unusual tilted Fermi surface and also reveal very light quasiparticle masses (less than 1 me ), with no significant enhancement due to electronic correlations. We find good agreement between the angular dependence of the observed and calculated de Haas-van Alphen frequencies, taking into account the contribution of different structural domains that form while cooling IrTe2.

Blake, S. F.; Watson, M. D.; McCollam, A.; Kasahara, S.; Johnson, R. D.; Narayanan, A.; Pascut, G. L.; Haule, K.; Kiryukhin, V.; Yamashita, T.; Watanabe, D.; Shibauchi, T.; Matsuda, Y.; Coldea, A. I.

2015-03-01

365

Valence-bond crystalline order in the s = 1/2 J1-J2 model on the honeycomb lattice.  

PubMed

Using the coupled cluster method we study the phase diagram of the spin-1/2 Heisenberg antiferromagnet on a honeycomb lattice with nearest-neighbour exchange coupling J1 > 0 and frustrating next-nearest-neighbour coupling J2 ? xJ1 > 0. In the range 0 < x < 1 we find four phases exhibiting respectively Néel, 6-spin plaquette, staggered dimer and Néel-II orderings, with quantum critical points at xc1 ? 0.207(3), xc2 ? 0.385(10) and xc3 ? 0.65(5). The transitions at xc1 and xc3 appear to be continuous (and hence deconfined) ones, while that at xc2 appears to be a direct first-order one. PMID:23824552

Bishop, R F; Li, P H Y; Campbell, C E

2013-07-31

366

The concept of bond order  

NASA Astrophysics Data System (ADS)

A method for obtaining precise charge densities in defined regions of space from ab initio molecular wavefunctions is employed to place the concept of bond order on a firm theoretical footing. The bond orders obtained for carbon—carbon bonds in a range of organic compounds are assessed: those for buta-1,3-diene confirm that it consists of essentially localised double and single bonds.

Elliott, Robert J.; Richards, W. Graham

367

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

NASA Astrophysics Data System (ADS)

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 ionic radius fluctuations of rare-earth ions accompanying valence fluctuations. The large f-state degeneracy allows us to use the 1/N expansion method. Within the model we develop a mean-field theory for the first-order valence phase transition in YbInCu4. It is shown that the Coulomb interaction enhances the exchange interaction between f and conduction-band electron spins and is the driving force of the phase transition. In the framework of our approach the first-order isostructural valence phase transition is a transition from a paramagnetic state with localized f electrons coupled weakly with conduction electrons to a ground state with strongly hybridized f and conduction-electron states. A comparison between the theoretical calculations and experimental measurements of the valence change, susceptibility, specific heat, entropy, elastic constants, and volume change in YbInCu4 and YbAgCu4 are presented, and a good quantitative agreement is found. On the basis of the model we describe the change of character of the transition into the ground state from a first-order valence phase transition to a continuous transition in the series of compounds YbIn1-xAgxCu4. We want to stress, however, that in all cases the ground state exhibits the properties that are typical of heavy fermions. The effect of pressure on physical properties of YbInCu4 is studied and the H-T phase diagram is found.

Goltsev, A. V.; Bruls, G.

2001-04-01

368

Core level spectroscopy of RbTiOPO4 and chemical bonding in KTiOPO4 crystal family  

Microsoft Academic Search

Valence band structure and electronic parameters of constituent element core levels of RbTiOPO4 have been analyzed with X-ray photoemission spectroscopy. Detailed photoemission spectra of the element core levels have been recorded under excitation by nonmonochromatic Al K? radiation (1486.6 eV). The Ti-O and P-O chemical bonding in RbTiOPO4 have been considered using binding energy difference parameters and compared with those

Vladimir K. Makukha; Viktor V. Atuchin; Valeriy G. Kesler

2010-01-01

369

Electronic States and Chemical Bondings of an Interstitial Cation in Ionic Compounds AgCl and NaCl  

Microsoft Academic Search

We have performed the electronic structure calculation of an interstitial cationic defect in AgCl and NaCl crystals, using the DV-Xalpha molecular orbital method. Ag-4d orbitals are well admixed with Cl-3p orbitals in the valence band, and the electronic structure of AgCl is quite different from that of NaCl. The cation-anion covalent bonding in AgCl is stronger than that in NaCl.

Katsuyuki Matsunaga; Isao Tanaka; Hirohiko Adachi

1996-01-01

370

Normally unoccupied states on C(111) (diamond) (2 x 1): Support for a relaxed. pi. -bonded chain model  

SciTech Connect

A normally unoccupied electronic state on the reconstructed (2 x 1) surface of C(111) (diamond) is characterized with angle-resolved two-photon photoelectron spectroscopy. The state is seen in the bulk band gap, lying 4.8 eV above the valence-band maximum. Comparison between the measured dispersion of this band and published theoretical band-structure calculations supports a relaxed Pandey ..pi..-bonded chain model of the surface reconstruction.

Kubiak, G.D.; Kolasinski, K.W.

1989-01-15

371

Bonding interactions through hydrogen  

Microsoft Academic Search

Hydride reductions are some of the most important reactions in synthetic organic chemistry. Typically, a hydride transfer reagent, such as LiAlH 4 or NaBH4, is dissolved in solution and undergoes reactions with carbon-heteroatom unsaturated bonds. The classic example of such reactivity is the synthesis of alcohols from ketones. We have found, using experimental methods, that the hydride affinity of AIH3

Daniel J Goebbert

2006-01-01

372

Continuing Conversation about Continuing Bonds  

ERIC Educational Resources Information Center

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…

Klass, Dennis

2006-01-01

373

Cyclic Bonds in Branched Polymers  

E-print Network

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.

Kazumi Suematsu

2015-02-19

374

46 CFR Sec. 10 - Bonds.  

Code of Federal Regulations, 2012 CFR

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

2012-10-01

375

46 CFR Sec. 10 - Bonds.  

Code of Federal Regulations, 2014 CFR

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

2014-10-01

376

46 CFR Sec. 10 - Bonds.  

Code of Federal Regulations, 2011 CFR

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

2011-10-01

377

46 CFR Sec. 10 - Bonds.  

Code of Federal Regulations, 2010 CFR

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

2010-10-01

378

46 CFR Sec. 10 - Bonds.  

Code of Federal Regulations, 2013 CFR

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

2013-10-01

379

Direct bonded space maintainers.  

PubMed

The aim of this study was to evaluate clinically a bonded space maintainer, which would reduce chair-side time and cost. Sixty appliances were fabricated from 0.7 mm stainless steel round wire and bonded using light-cured composite to the two teeth adjacent to the site of extraction of a posterior primary tooth. Twenty males and sixteen females (age range 5-9-years-old) were selected from the Pedodontic clinic of the State University of Rio de Janeiro. The sixty space maintainers were divided into two groups according to the site in which they were placed: a) absent first primary molar and b) absent second primary molar. Impressions and study models were obtained prior to and 6 months after bonding the appliances. During this period only 8.3% of failures were observed, most of them from occlusal or facial trauma. Student t-test did not show statistically significant alterations in the sizes of the maintained spaces during the trial period. PMID:8217886

Santos, V L; Almeida, M A; Mello, H S; Keith, O

1993-01-01

380

Disulfide bonds of acetylcholinesterase  

SciTech Connect

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

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

1986-05-01

381

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

ERIC Educational Resources Information Center

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

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

2012-01-01

382

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.

383

The nature of the metal-CO interaction and bonding  

NASA Technical Reports Server (NTRS)

The adsorption of CO on metal surfaces is represented by molecular orbital cluster models of CO at an on top site and adsorbed normal to the surface carbon end down. Ab initio SCF and MCSCF calculations are performed for several clusters. The new constrained space orbital variation CSOV approach is used to analyze the bonding and to compare CO adsorption on Al, representative of sp metals, with that on Cu, representative of transition metals. There is a large repulsion between the superposed free CO and metal charge distributions which is considerably smaller for Cu than for Al because there are fewer valence sigma electrons for Cu than for Al. The CSOV analysis shows that the metal to CO pi donation is much more important than the CO to metal sigma donation. It is also shown that for Cu, the d pi contribution to the metal pi donation is larger than the valence 4p pi contribution. The d pi donation is compared between Fe, Ni, and Cu and this donation and the metal-CO interaction are found to be different in the order Fe greater than Ni greater than Cu.

Bagus, P. S.; Nelin, C. J.; Bauschlicher, C. W., Jr.

1984-01-01

384

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

SciTech Connect

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

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

2011-07-15

385

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

Code of Federal Regulations, 2010 CFR

...issue bonds, qualified student loan bonds, and qualified...144-1 Internal Revenue INTERNAL REVENUE SERVICE, DEPARTMENT...issue bonds, qualified student loan bonds, and qualified...limitation on capital expenditures) or under...

2010-04-01

386

The effect of non-bonded attractive electronic (anomeric) interactions on conformation and geometry of organic phosphates and thiophosphates  

NASA Astrophysics Data System (ADS)

Substituted 1,3,2-dioxaphosphorinane-2-oxides and -2-sulfides are classified according to the conformation of the ring and the orientation (axial or equatorial) of the P=O/P=S bond. Geometrical parameters (torsion angles, valence angles and bond lengths) of 37 compounds are analyzed and several systematic class differences are observed. The anomeric effect, with emphasis on the n?(O)—? * (P-axial substituent) interaction, provides the basis for rationalizing conformational preferences as well as geometrical details. Mean experimental geometries are compared to ab initio calculated geometries for conformers of (HO) 2PH(O) and (HO) 2PH(S) mimicking the dioxaphosphorinanes.

van Nuffel, P.; Van Alsenoy, C.; Lenstra, A. T. H.; Geise, H. J.

1984-11-01

387

Hydrogen bonding in ionic liquids.  

PubMed

Ionic liquids (IL) and hydrogen bonding (H-bonding) are two diverse fields for which there is a developing recognition of significant overlap. Doubly ionic H-bonds occur when a H-bond forms between a cation and anion, and are a key feature of ILs. Doubly ionic H-bonds represent a wide area of H-bonding which has yet to be fully recognised, characterised or explored. H-bonds in ILs (both protic and aprotic) are bifurcated and chelating, and unlike many molecular liquids a significant variety of distinct H-bonds are formed between different types and numbers of donor and acceptor sites within a given IL. Traditional more neutral H-bonds can also be formed in functionalised ILs, adding a further level of complexity. Ab initio computed parameters; association energies, partial charges, density descriptors as encompassed by the QTAIM methodology (?BCP), qualitative molecular orbital theory and NBO analysis provide established and robust mechanisms for understanding and interpreting traditional neutral and ionic H-bonds. In this review the applicability and extension of these parameters to describe and quantify the doubly ionic H-bond has been explored. Estimating the H-bonding energy is difficult because at a fundamental level the H-bond and ionic interaction are coupled. The NBO and QTAIM methodologies, unlike the total energy, are local descriptors and therefore can be used to directly compare neutral, ionic and doubly ionic H-bonds. The charged nature of the ions influences the ionic characteristics of the H-bond and vice versa, in addition the close association of the ions leads to enhanced orbital overlap and covalent contributions. The charge on the ions raises the energy of the Ylp and lowers the energy of the X-H ?* NBOs resulting in greater charge transfer, strengthening the H-bond. Using this range of parameters and comparing doubly ionic H-bonds to more traditional neutral and ionic H-bonds it is clear that doubly ionic H-bonds cover the full range of weak through to very strong H-bonds. PMID:25582457

Hunt, Patricia A; Ashworth, Claire R; Matthews, Richard P

2015-02-23

388

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

NASA Astrophysics Data System (ADS)

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

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

2009-03-01

389

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

390

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

SciTech Connect

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

Karpenko, A., 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

391

[Power, status and valency in relationship to affective psychoses, schizoaffective and neurotic depression of patients].  

PubMed

The interrelationships of patients with affective psychoses and depressive neuroses were analysed by means of the Giessentest. They were categorised using Beckmanns approach to power, status and valency. The different frequency of these scores in the depressive subgroups underlined the interactional dimension of depression and the influence of gender variables as well. In particular neurotic depressive male patients tended to have asymmetric structures of relationships. The couple relationships of female patients suffering from depression or physical illness were characterised by a negative valency in the self-concept and a positive valency in the self as perceived by others. PMID:9471633

Böker, H; Nikisch, G; Budischewski, K; Himmighoffen, H

1997-12-01

392

Toxoplasma gondii infection enhances the kairomonal valence of rat urine  

PubMed Central

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

Vasudevan, Anand; Vyas, Ajai

2014-01-01

393

Magnetic properties of mixed-valence iron phosphate glasses  

NASA Astrophysics Data System (ADS)

Magnetic properties of mixed-valence iron phosphate glasses, where there coexist Fe2+ and Fe3+ ions, have been investigated. The molar fraction of Fe3+ with respect to the total iron ion, [Fe3+]/[Fetotal] , can be controlled by melting the glass at varied temperatures. Experiments of magnetic aging and memory effects as well as dynamic and static scaling analyses of relaxation time and nonlinear magnetic susceptibility have been performed to get insight into the nature of low-temperature magnetic phase of the glass system. The experimental results reveal that the iron phosphate glasses undergo paramagnet-spin-glass transitions at low temperatures. Temperature dependence of magnetic specific heat suggests that as the temperature is lowered, the magnetic moments start to be frozen at a temperature significantly higher than the spin-glass transition temperature accompanied by a deviation in magnetic susceptibility from Curie-Weiss law. The ratio of the absolute value of Weiss temperature to spin-glass transition temperature increases as the ratio [Fe3+]/[Fetotal] becomes larger. This behavior is explainable in terms of the difference in single-ion anisotropy between Fe3+ and Fe2+ ions.

Akamatsu, Hirofumi; Oku, Satoshi; Fujita, Koji; Murai, Shunsuke; Tanaka, Katsuhisa

2009-10-01

394

Quasicrystalline valence bands in decagonal AlNiCo  

PubMed

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

Rotenberg; Theis; Horn; Gille

2000-08-10

395

27 CFR 19.162 - Operations bond for distilled spirits plant and adjacent bonded wine cellar.  

Code of Federal Regulations, 2012 CFR

... Operations bond for distilled spirits plant and adjacent bonded wine cellar. 19...TREASURY LIQUORS DISTILLED SPIRITS PLANTS Bonds and Consents of Surety Requirements... Operations bond for distilled spirits plant and adjacent bonded wine cellar....

2012-04-01

396

27 CFR 19.162 - Operations bond for distilled spirits plant and adjacent bonded wine cellar.  

Code of Federal Regulations, 2014 CFR

... Operations bond for distilled spirits plant and adjacent bonded wine cellar. 19...TREASURY ALCOHOL DISTILLED SPIRITS PLANTS Bonds and Consents of Surety Requirements... Operations bond for distilled spirits plant and adjacent bonded wine cellar....

2014-04-01

397

27 CFR 19.162 - Operations bond for distilled spirits plant and adjacent bonded wine cellar.  

Code of Federal Regulations, 2013 CFR

... Operations bond for distilled spirits plant and adjacent bonded wine cellar. 19...TREASURY ALCOHOL DISTILLED SPIRITS PLANTS Bonds and Consents of Surety Requirements... Operations bond for distilled spirits plant and adjacent bonded wine cellar....

2013-04-01

398

Low temperature reactive bonding  

DOEpatents

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

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

1995-01-17

399

Bonding mechanism in ultrasonic gold ball bonds on copper substrate  

NASA Astrophysics Data System (ADS)

The effects of process parameters on bond formation in thermosonic gold ball bonding on a copper substrate at ambient temperatures have been investigated with scanning electron microscopy (SEM). A model was developed based on classical microslip theory to explain the general phenomena observed in the evolution of bond footprints left on the substrate. The specific effects of ultrasonic energy and complex stress distributions arising from tool geometry must be taken into consideration and were incorporated into the model. It was shown that relative motion existed at the bonding interface as microslip at lower powers, transitioning into gross sliding at higher powers. With increased normal bonding forces, the transition point into gross sliding occurred at higher ultrasonic bonding powers.

Lum, I.; Jung, J. P.; Zhou, Y.

2005-05-01

400

Silicon carbide wafer bonding by modified surface activated bonding method  

NASA Astrophysics Data System (ADS)

4H-SiC wafer bonding has been achieved by the modified surface activated bonding (SAB) method without any chemical-clean treatment and high temperature annealing. Strong bonding between the SiC wafers with tensile strength greater than 32 MPa was demonstrated at room temperature under 5 kN force for 300 s. Almost the entire wafer has been bonded very well except a small peripheral region and few voids. The interface structure was analyzed to verify the bonding mechanism. It was found an amorphous layer existed as an intermediate layer at the interface. After annealing at 1273 K in vacuum for 1 h, the bonding tensile strength was still higher than 32 MPa. The interface changes after annealing were also studied. The results show that the thickness of the amorphous layer was reduced to half after annealing.

Suga, Tadatomo; Mu, Fengwen; Fujino, Masahisa; Takahashi, Yoshikazu; Nakazawa, Haruo; Iguchi, Kenichi

2015-03-01

401

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...

402

Changing the conversation: the influence of emotions on conversational valence and alcohol consumption.  

PubMed

Health campaign effects may be improved by taking interpersonal communication processes into account. The current study, which employed an experimental, pretest-posttest, randomized exposure design (N?=?208), investigated whether the emotions induced by anti-alcohol messages influence conversational valence about alcohol and subsequent persuasion outcomes. The study produced three main findings. First, an increase in the emotion fear induced a negative conversational valence about alcohol. Second, fear was most strongly induced by a disgusting message, whereas a humorous appeal induced the least fear. Third, a negative conversational valence elicited healthier binge drinking attitudes, subjective norms, perceived behavioral control, intentions, and behaviors. Thus, health campaign planners and health researchers should pay special attention to the emotional characteristics of health messages and should focus on inducing a healthy conversational valence. PMID:23812888

Hendriks, Hanneke; van den Putte, Bas; de Bruijn, Gert-Jan

2014-10-01

403

Six-month-old Infants' Scanning of Meaningfully Distinct Infant-Directed Faces: Effects of Valence  

E-print Network

"smiling" eyes, smiling mouth (positive) Comforting ID faces: saddened eyes, frowning mouth (negative) Yet emotions: Valence specific effects and an exploration of the effects of viewer gender. Brain and Cognition

O'Toole, Alice J.

404

Optogenetic dissection of neural circuits underlying emotional valence and motivated behaviors  

E-print Network

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 ...

Nieh, Horng-An Edward

405

The effects of electronic delocalization in highly coupled mixed valence systems  

E-print Network

by Resonance Raman Spectroscopy. Journal of the Americanby Resonance Raman Spectroscopy. Journal of the AmericanRaman Spectroscopy of Strongly Coupled Mixed-Valence Cluster Dimers of Ruthenium. Journal

Lear, Benjamin James

2007-01-01

406

Fundamentals of glass-to-metal bonding. VA. Temperature and pressure dependence of the wettability of metals by glass. VB. Reactions of tantalum and sodium silicate glass. Fifth technical report  

Microsoft Academic Search

A suitable vacuum furnace has been constructed for studying the effects of temperature and pressure on the wettability of metals by glass. A system was completed that was capable of subjecting test combinations up to temperatures of 1400°C at a working pressure of 1 x 10⁻⁵ mm Hg. The mechanism of wetting with change in pressure and temperature is discussed

R. M. Fulrath; S. P. Mitoff; J. A. Pask

1955-01-01

407

Study of electronic structure and valence state of CeCo2 nanoparticles  

Microsoft Academic Search

We have performed the Ce L3-, M4,5-edge and Co L2,3-, K-edge x-ray absorption measurements to investigate the dependence of valence state and local electronic structures on different particles size of CeCo2. By monitoring the modifications in Ce L3- and M4,5-edges XAS spectra shape, the individual intensities of the two valence states reflect the mixed configuration in the ground state in

Chung-Li Dong; Ching-Lin Chang; Jinghua Guo

2005-01-01

408

Valence-band electronic structure of Co3O4 epitaxy on CoO(100)  

Microsoft Academic Search

Valence-band photoemission studies have been performed on a CoO(100) single crystal as it is slowly oxidized under 1×10-4 Torr O2 at 623 K, eventually forming a Co3O4 epitaxial film. The most significant changes occur in 3d-related features, with the peak located at the top of the valence band sharpening and shifting to lower binding energies as the spinel oxide forms.

Marjorie Langell; M. D. Anderson; G. A. Carson; L. Peng; S. Smith

1999-01-01

409

X-ray resonant scattering study of an intermediate-valence Ho-Ce alloy  

NASA Astrophysics Data System (ADS)

The magnetism of a DHCP Ho-Ce alloy has been investigated using X-ray magnetic resonant scattering. A self-consistent magnetic structure is proposed that agrees with diffraction data for three different cross sections (neutron, dipolar and quadrupolar). The spectroscopic valence of the Ce is found to be 3.27(5), and the Ce is in an intermediate-valence state in this alloy.

Goff, J. P.; Sarthour, R. S.; McMorrow, D. F.; Yakhou, F.; Vigliante, A.; Gibbs, D.; Ward, R. C. C.; Wells, M. R.

2001-05-01

410

Bond Dissociation Energies in Second-Row Compounds  

SciTech Connect

The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. Heats of formation at 0 and 298 K are predicted for PF?, PF?, PF?O, SF?, SF?, SF?, SF?O, SF?O?, and SF?O as well as a number of radicals derived from these stable compounds on the basis of coupled cluster theory [CCSD(T)] calculations extrapolated to the complete basis set limit. In order to achieve near chemical accuracy (±1 kcal/mol), additional corrections were added to the complete basis set binding energies based on frozen core coupled cluster theory energies: a correction for core-valence effects, a correction for scalar relativistic effects, a correction for first-order atomic spin-orbit effects, and vibrational zero-point energies. The calculated values substantially reduce the error limits for these species. A detailed comparison of adiabatic and diabatic bond dissociation energies (BDEs) is made and used to explain trends in the BDEs. Because the adiabatic BDEs of polyatomic molecules represent not only the energy required for breaking a specific bond but also contain any reorganization energies of the bonds in the resulting products, these BDEs can be quite different for each step in the stepwise loss of ligands in binary compounds. For example, the adiabatic BDE for the removal of one fluorine ligand from the very stable closed-shell SF? molecule to give the unstable SF? radical is 2.8 times the BDE needed for the removal of one fluorine ligand from the unstable SF? radical to give the stable closed-shell SF? molecule. Similarly, the BDE for the removal of one fluorine ligand from the stable closed-shell PF?O molecule to give the unstable PF?O radical is higher than the BDE needed to remove the oxygen atom to give the stable closed-shell PF? molecule. The same principles govern the BDEs of the phosphorus fluorides and the sulfur oxofluorides. In polyatomic molecules, care must be exercised not to equate BDEs with the bond strengths of given bonds. The measurement of the bond strength or stiffness of a given bond represented by its force constant involves only a small displacement of the atoms near equilibrium and, therefore, does not involve any reorganization energies, i.e., it may be more appropriate to correlate with the diabatic product states.

Grant, Daniel J.; Matus, Myrna H.; Switzer, Jackson R.; Dixon, David A.; Francisco, Joseph S.; Christe, Karl O.

2008-04-10

411

Fracture behavior of masonry bond  

NASA Astrophysics Data System (ADS)

In this study, three different mechanical tests and video microscopy experiments were preformed to characterize the fracture behavior of masonry bond. Mortars were fabricated under two different conditions: Mortars cast in plexiglass molds and; Mortars exposed to the interactions with dry masonry units. The mechanical properties of the mortar were significantly modified when the mortars experienced mortar/unit interactions. Also, different surface textures for the masonry units altered the strength of embedded mortar when identical mortars were used. It is strongly recommended that the in-situ mortar strength should be used rather than the cast mortar strength because dependence upon laboratory test results for determination of structural performance invites significant error. For masonry bond fracture, a test method was developed and used successfully to measure load-CMOD behavior until complete failure maintaining stable crack growth. It was found that the strength of in-situ mortar was an important indication of bond strength. Admixtures that had similar purposes for the bulk materials were dramatically different in bond strength. The bond strength was also significantly altered with different surface textures for the masonry. A new technique was performed to investigate the details of the fracture surface using video microscopy. Degree of bond was defined as an area fraction of the net bonded area. The bond strength was a strictly linear function of the degree of bond and when the bond strength was normalized with degree of bond. The applied fracture mechanics model, when both elastic and inelastic deformations were considered, always over-estimated the post-peak behavior. However, the post-peak behavior was successfully predicted when the model was modified to consider only elastic deformation. The analysis indicated that little toughening action took place during the fracture process and the fracture process zone at the crack tip was small relative to plain concrete and mortar. This was due to the highly brittle fracture nature associated with pre-determined weak crack path and relatively smooth crack surfaces. Using the relationship between degree of bond and bond strength, and the established fracture model, it was possible to describe the fracture behavior for an ideal perfect bond. As the degree of bond approaches 100%, bond strength increases but the work of fracture does not improve as a simple function of increase in the degree of bond.

Park, Cheolwoo

412

Bond Sensitivity to Silicone Contamination  

NASA Technical Reports Server (NTRS)

Currently during fabrication of the Space Shuttle booster rocket motors, the use of silicone and silicone-containing products is prohibited in most applications. Many shop aids and other materials containing silicone have the potential, if they make contact with a bond surface, to transfer some of the silicone to the substrates being bonded. Such transfer could result in a reduction of the bond strength or even failure of the subsequent bonds. This concern is driving the need to understand the effect of silicones and the concentration needed to affect a given bond-line strength. Additionally, as silicone detection methods used for materials acceptance improve what may have gone unnoticed earlier is now being detected. Thus, realistic silicone limits for process materials (below which bond performance is satisfactory) are needed rather than having an absolute no silicone permitted policy.

Caldwell, G. A.; Hudson, W. D.; Hudson, W. D.; Cash, Stephen F. (Technical Monitor)

2003-01-01

413

Better Bonded Ethernet Load Balancing  

SciTech Connect

When a High Performance Storage System's mover shuttles large amounts of data to storage over a single Ethernet device that single channel can rapidly become saturated. Using Linux Ethernet channel bonding to address this and similar situations was not, until now, a viable solution. The various modes in which channel bonding could be configured always offered some benefit but only under strict conditions or at a system resource cost that was greater than the benefit gained by using channel bonding. Newer bonding modes designed by various networking hardware companies, helpful in such networking scenarios, were already present in their own switches. However, Linux-based systems were unable to take advantage of those new modes as they had not yet been implemented in the Linux kernel bonding driver. So, except for basic fault tolerance, Linux channel bonding could not positively combine separate Ethernet devices to provide the necessary bandwidth.

Gabler, Jason

2006-09-29

414

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

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

415

The power of emotional valence—from cognitive to affective processes in reading  

PubMed Central

The comprehension of stories requires the reader to imagine the cognitive and affective states of the characters. The content of many stories is unpleasant, as they often deal with conflict, disturbance or crisis. Nevertheless, unpleasant stories can be liked and enjoyed. In this fMRI study, we used a parametric approach to examine (1) the capacity of increasing negative valence of story contents to activate the mentalizing network (cognitive and affective theory of mind, ToM), and (2) the neural substrate of liking negatively valenced narratives. A set of 80 short narratives was compiled, ranging from neutral to negative emotional valence. For each story mean rating values on valence and liking were obtained from a group of 32 participants in a prestudy, and later included as parametric regressors in the fMRI analysis. Another group of 24 participants passively read the narratives in a three Tesla MRI scanner. Results revealed a stronger engagement of affective ToM-related brain areas with increasingly negative story valence. Stories that were unpleasant, but simultaneously liked, engaged the medial prefrontal cortex (mPFC), which might reflect the moral exploration of the story content. Further analysis showed that the more the mPFC becomes engaged during the reading of negatively valenced stories, the more coactivation can be observed in other brain areas related to the neural processing of affective ToM and empathy. PMID:22754519

Altmann, Ulrike; Bohrn, Isabel C.; Lubrich, Oliver; Menninghaus, Winfried; Jacobs, Arthur M.

2012-01-01

416

Connecting [NiFe]- and [FeFe]-Hydrogenases: Mixed-Valence Nickel-Iron Dithiolates With Rotated Structures  

PubMed Central

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

Schilter, David; Rauchfuss, Thomas B.; Stein, Matthias

2012-01-01

417

Push-out bond strengths of two fiber post types bonded with different dentin bonding agents.  

PubMed

The aim of this study was to evaluate the regional push-out bond strengths for two fiber-reinforced post types using three different dentin bonding agents. Sixty single-rooted extracted human first premolar teeth were sectioned below the cemento-enamel junction, and the roots were endodontically treated. Following standardized post space preparations, the roots were divided into two fiber-post groups (Glassix and Carbopost), and further divided into three subgroups of 10 specimens each for the bonding systems self-etching dentin bonding agents (Clearfil SE Bond and Optibond all-in-one), and total-etching dentin bonding agent (XP Bond). A dual-cure resin luting cement (Maxcem) was then placed in the post spaces and posts were then seated into the root canals polymerized through the cervical portion. The roots were then cut into 3-mm thick sections. Push-out tests were performed at a crosshead speed of 0.5 mm/min. The data were analyzed with multivariate ANOVA (alpha = 0.05). The morphology of interface between different dentin bonding agents from the cervical sections were analyzed with SEM. Glass fiber-reinforced posts demonstrated significantly higher push-out bond strengths than carbon fiber-reinforced posts (p < 0.001). Bond strength values decreased significantly from the cervical to the apical root canal regions (p < 0.001). Self-etching dentin adhesive Clearfil SE Bond and total-etching dentin adhesive XP Bond demonstrated similar bond strengths values and this was significantly higher compared with the Optibond all-in-one in cervical root canal region. In conclusion, in all root segments, the glass fiber-reinforced posts provided significantly increased post retention than the carbon fiber-reinforced posts, regardless of the adhesive used. PMID:20091920

Topcu, Fulya Toksoy; Erdemir, Ugur; Sahinkesen, Gunes; Mumcu, Emre; Yildiz, Esra; Uslan, Ibrahim

2010-05-01

418

Bond failure patterns in vivo.  

PubMed

The aim of this study was to identify the presence and pattern of differences in bond failure between tooth types in vivo when bonding orthodontic brackets with the no-mix orthodontic composite adhesive Right-On. In vivo bond failure for a single operator was recorded for 108 consecutive patients undergoing fixed-appliance orthodontic treatment. The bond failure data were analyzed by survival analysis. Time to first failure or censorship was recorded for each bonded attachment. Overall failure in the sample matched previous clinical studies but conflicted with previous ex vivo bond strength data. Mandibular and posterior teeth had significantly higher rates of failure than did maxillary and anterior teeth. The type of attachment used had a significant effect on bond survival. The results of this study confirm that in vivo bond survival is not uniform for all teeth. Comparisons between the findings of this study and those of a previous ex vivo study by the same authors failed to validate ex vivo bond strength testing as clinically relevant. PMID:12750672

Linklater, Rognvald A; Gordon, Peter H

2003-05-01

419

Interfacial chemistry and valence band offset between GaN and Al{sub 2}O{sub 3} studied by X-ray photoelectron spectroscopy  

SciTech Connect

The interface region between Ga-face n-type GaN and Al{sub 2}O{sub 3} dielectric (achieved via atomic-layer deposition or ALD) is investigated by X-ray photoelectron spectroscopy (XPS). An increase in the Ga-O to Ga-N bond intensity ratio following Al{sub 2}O{sub 3} deposition implies that the growth of an interfacial gallium sub-oxide (GaO{sub x}) layer occurred during the ALD process. This finding may be ascribed to GaN oxidation, which may still happen following the reduction of a thin native GaO{sub x} by trimethylaluminum (TMA) in the initial TMA-only cycles. The valence band offset between GaN and Al{sub 2}O{sub 3}, obtained using both core-level and valence band spectra, is found to vary with the thickness of the deposited Al{sub 2}O{sub 3}. This observation may be explained by an upward energy band bending at the GaN surface (due to the spontaneous polarization induced negative bound charge on the Ga-face GaN) and the intrinsic limitation of the XPS method for band offset determination.

Duan, T. L.; Ang, D. S. [School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798 (Singapore)] [School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798 (Singapore); Pan, J. S. [Institute of Materials Research and Engineering, A-STAR (Agency for Science, Technology and Research), 3 Research Link, Singapore 117602 (Singapore)] [Institute of Materials Research and Engineering, A-STAR (Agency for Science, Technology and Research), 3 Research Link, Singapore 117602 (Singapore)

2013-05-20

420

Local Valence Electronic States and Valence-Band Maximum of Ultrathin Silicon Nitride Films on Si(111) Studied by Auger Photoelectron Coincidence Spectroscopy: Thickness and Interface Structure Dependence  

NASA Astrophysics Data System (ADS)

The local valence electronic states of Si3N4 films grown on Si(111)-7 × 7 [Si3N4/Si(111)] have been investigated by coincidence spectroscopy. The Si L23VV Auger electron spectra (AES) measured in coincidence with the Sin+ 2p photoelectrons of ?-Si3N4(0001)/Si(111)-8 × 8 indicate that the binding energy of the local valence electronic state at Sin+ increases as n increases. Si4+ L23VV AES measured as a function of the ?-Si3N4(0001) thickness show that the binding energy at the valence-band maximum (BEVBM) of ?-Si3N4(0001) decreases by 1.6 ± 0.5 eV as the Si3N4 thickness decreases from 3.6 to 0.7 Å. The large decrease is attributed to the hybridization of the valence electronic state of Si3N4 with those of neighboring subnitrides and to the formation of ?-Si3N4(0001) islands. The BEVBM value of the 3.6-Å-Si3N4/Si(111)-quadruplet decreases by 0.7 ± 0.6 eV from that of 3.6-Å-?-Si3N4(0001)/Si(111)-8 × 8. The decrease in BEVBM is attributed to the different interface structures.

Kakiuchi, Takuhiro; Tahara, Masashi; Mase, Kazuhiko; Nagaoka, Shin-ichi

2015-04-01

421

Making and breaking of chemisorption bonds  

NASA Astrophysics Data System (ADS)

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].

Lundqvist, Bengt I.

1982-07-01

422

Independent structural and valence state transitions in the cation-ordered double perovskites Ba{sub 2-x}Sr{sub x}TbIrO{sub 6}  

SciTech Connect

Synchrotron X-ray and neutron powder diffraction were used to investigate the formation, structure and bonding in the double perovskite Ba{sub 2-x}Sr{sub x}TbIrO{sub 6} solid solutions. The results showed that these oxides all exhibit ordering of the Tb and Ir cations in a double perovskite-type structure. Three distinct structural types differing in symmetry and/or valence states were formed depending on the precise Ba:Sr ratio on the perovskite A site; x=<0.3 cubic (Fm3-bar m) with Tb{sup 4+} and Ir{sup 4+}; 0.4==1.2 monoclinic (P2{sub 1}/n) with Tb{sup 3+} and Ir{sup 5+}. The transitions between these appear to be first order in nature.

Zhou Qingdi [Centre for Structural Biology and Chemistry, School of Chemistry, University of Sydney, Sydney, NSW 2006 (Australia); Kennedy, Brendan J. [Centre for Structural Biology and Chemistry, School of Chemistry, University of Sydney, Sydney, NSW 2006 (Australia)]. E-mail: kennedyb@chem.usyd.edu.au

2005-11-15

423

A new route to dual fluorescence: Spectroscopic properties of the valence tautomers of a 3-(2 H)-isoquinolinone derivative  

NASA Astrophysics Data System (ADS)

The isoquinolinone derivative 2-methyl-1,4-diphenylbenzo[g]isoquinolin-3(2 H)-one (MDP-BIQ) shows dual fluorescence emission with band positions and intensities that depend sensitively on the solvent. We show that this behavior arises from the fact that MDP-BIQ has two valence tautomers, one aromatic and one conjugated but non-aromatic, each of which are separately fluorescent. The aromatic tautomer, which has significant zwitterionic character, is stabilized by trace amounts of hydrogen-bond donors or Lewis acids. The relatively high fluorescence quantum yield of the aromatic tautomer (0.127 versus 2.4 × 10 -3 for the non-aromatic tautomer) makes this and similar molecules outstanding candidates for use in sensors and other optoelectronic applications.

Craig, Ian M.; Duong, Hieu M.; Wudl, Fred; Schwartz, Benjamin J.

2009-08-01

424

Wafer level glass frit bonding for MEMS hermetic packaging  

Microsoft Academic Search

Wafer level bonding is widely applied in the manufacture of sensors, actuators and CMOS MEMS. Bonding technology includes direct bonding, anodic bonding, eutectic bonding, adhesive bonding and glass frit bonding. Glass frit bonding has pattern-able, excellent sealing performances, high bonding strength, don't need apply any voltage during bonding process and less CTE mismatch compared to glass and silicon is more

Jin-Sheng Chang; Jing-Yuan Lin; Shu-Ching Ho; Yao-Jung Lee

2010-01-01

425

Bidirectional switch of the valence associated with a hippocampal contextual memory engram.  

PubMed

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 that enable the switching of the valence of memories remain largely unknown. Here we investigated these mechanisms by applying the recently developed memory engram cell- manipulation technique. We labelled with channelrhodopsin-2 (ChR2) a population of cells in either the dorsal dentate gyrus (DG) of the hippocampus or the basolateral complex of the amygdala (BLA) that were specifically activated during contextual fear or reward conditioning. Both groups of fear-conditioned mice displayed aversive light-dependent responses in an optogenetic place avoidance test, whereas both DG- and BLA-labelled mice that underwent reward conditioning exhibited an appetitive response in an optogenetic place preference test. Next, in an attempt to reverse the valence of memory within a subject, mice whose DG or BLA engram had initially been labelled by contextual fear or reward conditioning were subjected to a second conditioning of the opposite valence while their original DG or BLA engram was reactivated by blue light. Subsequent optogenetic place avoidance and preference tests revealed that although the DG-engram group displayed a response indicating a switch of the memory valence, the BLA-engram group did not. This switch was also evident at the cellular level by a change in functional connectivity between DG engram-bearing cells and BLA engram-bearing cells. Thus, we found that in the DG, the neurons carrying the memory engram of a given neutral context have plasticity such that the valence of a conditioned response evoked by their reactivation can be reversed by re-associating this contextual memory engram with a new unconditioned stimulus of an opposite valence. Our present work provides new insight into the functional neural circuits underlying the malleability of emotional memory. PMID:25162525

Redondo, Roger L; Kim, Joshua; Arons, Autumn L; Ramirez, Steve; Liu, Xu; Tonegawa, Susumu

2014-09-18

426

Ultrasonic phosphate bonding of nanoparticles.  

PubMed

Low intensity ultrasound-induced radicals interact with surface adsorbed orthophosphate to bond nanoparticles with high mechanical strength and surface area. Dissimilar materials could be bonded to form robust metallic, ceramic, and organic composite microparticles. 3D nanostructures of a hydrated and amorphous electrocatalyst with carbon nanotubes were also constructed which exceeded the resistance-limited efficiency of 2D electrodes. PMID:23893468

Bassett, David C; Merle, Geraldine; Lennox, Bruce; Rabiei, Reza; Barthelat, François; Grover, Liam M; Barralet, Jake E

2013-11-01

427

On integrable matrix product operators with bond dimension D = 4  

NASA Astrophysics Data System (ADS)

We construct and study a two-parameter family of matrix product operators of bond dimension D = 4. The operators M(x, y) act on ({\\Bbb{C}}_2)\\otimes N , i.e. the space of states of a spin-1/2 chain of length N. For the particular values of the parameters: x = 1/3 and y=1/\\sqrt{3} , the operator turns out to be proportional to the square root of the reduced density matrix of the valence-bond-solid state on a hexagonal ladder. We show that M(x, y) has several interesting properties when (x, y) lies on the unit circle centered at the origin: x2 + y2 = 1. In this case, we find that M(x, y) commutes with the Hamiltonian and all the conserved charges of the isotropic spin-1/2 Heisenberg chain. Moreover, M(x1, y1) and M(x2, y2) are mutually commuting if x^2i + y^2_i=1 for both i = 1 and 2. These remarkable properties of M(x, y) are proved as a consequence of the Yang–Baxter equation.

Katsura, Hosho

2015-01-01

428

Study of two-spin entanglement in singlet states  

NASA Astrophysics Data System (ADS)

We study the entanglement properties of two-spin subsystems in spin-singlet states. The average entanglement between two spins is maximized in a single valence-bond (VB) state. On the other hand, Ev2 (the average entanglement between a subsystem of two spins and the rest of the system) can be maximized through a homogenized superposition of the VB states. The maximal Ev2 rapidly increases with system size and saturates at its maximum allowed value. We adopt two ways of obtaining maximal Ev2 states: (1) imposing homogeneity on singlet states; and (2) generating isotropy in a general homogeneous state. By using these two approaches, we construct explicitly four-spin and six-spin highly entangled states that are both isotropic and homogeneous. Our maximal E2v states represent a new class of resonating-valence-bond states which we show to be the ground states of the infinite-range Heisenberg model.

Lone, M. Q.; Dey, A.; Yarlagadda, S.

2015-01-01

429

On the Chemical Bonding in the Intermetallic B32-Type Compounds LiMe (Me = Al, Zn, Ga, Cd, and In)  

NASA Astrophysics Data System (ADS)

The electronic charge distributions in the binary intermetallic B 32 phases LiMe with Me = Zn, Cd. AI, Ga and In have been calculated by the relativistic augmented plane wave method. It is found that the character of the contribution from the various electron bands to the chemical bond is different for the lower valence bands and for the higher valence-conduction bands. The lower valence bands are occupied by two electrons per formula unit LiMe and are predominantly of covalent s-p-type, formed by the diamond-like sublattice of the Me atoms. For all compounds the percentage p-like character is smaller than for the sp3 hybrid within the molecular orbital picture. The valence bands above the covalent bands are s-p-like bands with enhanced metallic character. Besides a large covalent contribution to the chemical bond in the intermetallic B32-type phases, a charge transfer from the lithium atoms to the lib and Ilia elements is found. The amount of charge transfer is distinctly smaller than one electron per formula unit LiMe. It is shown that the charge transfer is correlated to the differences in the electronegativities of the corresponding atoms.

Schmidt, P. C.

1985-04-01

430

Social bonding: regulation by neuropeptides  

PubMed Central

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

Lieberwirth, Claudia; Wang, Zuoxin

2014-01-01

431

Quantum Confinement in Hydrogen Bond  

E-print Network

In this work, the quantum confinement effect is proposed as the cause of the displacement of the vibrational spectrum of molecular groups that involve hydrogen bonds. In this approach the hydrogen bond imposes a space barrier to hydrogen and constrains its oscillatory motion. We studied the vibrational transitions through the Morse potential, for the NH and OH molecular groups inside macromolecules in situation of confinement (when hydrogen bonding is formed) and non-confinement (when there is no hydrogen bonding). The energies were obtained through the variational method with the trial wave functions obtained from Supersymmetric Quantum Mechanics (SQM) formalism. The results indicate that it is possible to distinguish the emission peaks related to the existence of the hydrogen bonds. These analytical results were satisfactorily compared with experimental results obtained from infrared spectroscopy.

Carlos da Silva dos Santos; Elso Drigo Filho; Regina Maria Ricotta

2015-02-09

432

Effects of methyl group substitution on metal-coordinated cyclopentadienyl rings. The core and valence ionizations of methylated tricarbonyl(eta/sup 5/-cyclopentadienyl)metal complexes  

SciTech Connect

Gas-phase He I, He II, and Mg K..cap alpha.. photoelectron spectra are reported for molecules of the type (eta/sup 5/-C/sub 5/H/sub 5-n/-(CH/sub 3/)/sub n/)M(CO)/sub 3/ where n = 0, 1, 5 and M = Mn, Re. The influence of methyl groups on the cyclopentadienyl ring is monitored by shifts in both core and valence ionization energies. This enables effective separation of electron density transfer (inductive) and ring-methyl orbital overlap (hyperconjugative) effects. While the shift in the ring e/sub 1/'' ionization is found to be primarily a hyperconjugative effect, the shift in the metal valence ionizations is caused essentially entirely by a shift of electron density toward the metal atom. A great proportion of this increased density is transferred to the carbonyls in the rhenium complexes than in the manganese complexes, indicating the greater back-bonding ability of the third-row atom. Further evidence of extensive Re-CO back-bonding is provided by the presence of vibrational fine structure on one of the predominantly metal ionizations of the rhenium complexes. This structure is the vibrational progression of the symmetric metal-carbon(CO) stretching mode. The long vibrational progression observed in this band and the frequency of the M-C stretch in the positive ion are direct evidence of considerable ..pi.. back-bonding from the metal to the carbonyls. The observed vibrational structure in the spin-orbit split rhenium d ionizations also leads to a definitive interpretation of the pattern of metal ionizations in such complexes. The origin of the characteristic splitting of the predominantly ring e/sub 1/'' ionization is also considered in detail. The data suggest that the carbon-carbon bond distances in the ring are distorted an average of 0.01 to 0.02 A from fivefold symmetry when coordinated to a d/sup 6/ ML/sub 3/ species. This is the first indication from gas-phase spectroscopy for such distortions.

Calabro, D.C.; Hubbard, J.L.; Blevins, C.H. II; Campbell, A.C.; Lichtenberger, D.L.

1981-11-18

433

Halogen bonding (X-bonding): A biological perspective  

PubMed Central

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

Scholfield, Matthew R; Zanden, Crystal M Vander; Carter, Megan; Ho, P Shing

2013-01-01

434

Determination of the valence band structure of an alkali phosphorus oxynitride glass: A synchrotron XPS study on LiPON  

NASA Astrophysics Data System (ADS)

Lithium phosphorus oxynitride (LiPON) is a solid state electrolyte commonly used in thin film batteries (TFBs). Advanced TFBs face the issue of detrimental electrode-electrolyte interlayer formation, related to the electronic structure of the interface. In this contribution, we study the valence band structure of LiPON using resonant photoemission and synchrotron photoemission with variable excitation energies. The identification of different valence band features is done according to the known valence band features of meta- and orthophosphates. Additionally we compare our results with partial density of states simulations from literature. We find that the valence band structure is similar to the known metaphosphates with an additional contribution of nitrogen states at the top of the valence band. From the results we conclude that synchrotron X-ray photoemission (XPS) is a useful tool to study the valence band structure of nitridated alkali phosphate glasses.

Schwöbel, André; Precht, Ruben; Motzko, Markus; Carrillo Solano, Mercedes A.; Calvet, Wolfram; Hausbrand, René; Jaegermann, Wolfram

2014-12-01

435

Hydrogen-bonded complexes of ?,?-unsaturated carboxylic esters with phenols: a molecular mechanics study  

NASA Astrophysics Data System (ADS)

The hydrogen-bonded complexes between phenol derivatives and methyl acrylate, methyl trans-crotonate and methyl trans-cinnamate were studied using the interactive molecular modelling program PCMODEL which uses the features of Allinger's MMX force field, including pi-valence electron self-consistent field (Pi-VESCF) calculations. The results successfully reproduce experimental ? H values associated with the formation of the hydrogen-bonded complexes and account for the experimentally observed dependences of ? H on the electron releasing/withdrawing abilities of the substituents in the phenol aromatic ring or in the ester. In addition, the conformational change in the ester moiety of the hydrogen-bonded complexes gives rise to energetically similar hydrogen bonds, in agreement with previous infrared spectroscopic results. In general, the results obtained confirm or expand the previous spectroscopic or quantum mechanical results of M. Dulce G. Faria (J. Mol. Struct., 263 (1991) 87; Vib. Spectrosc., 2 (1991) 43, 107), and lead to the possibility of successfully applying the MMX/Pi-VESCF method to the study of hydrogen-bonded complexes involving other biochemically important molecules.

da Silva, Jaão Bosco P.; Moura, Gustavo L. C.; Ramos, Mozart N.; Teixeira-Dias, José J. C.; Fausto, Rui

1994-01-01

436

Ab initio calculations of the electronic structure and bonding characteristics of LaB6  

NASA Astrophysics Data System (ADS)

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.

Hossain, Faruque M.; Riley, Daniel P.; Murch, Graeme E.

2005-12-01

437

Strained-bond semiconductors  

NASA Astrophysics Data System (ADS)

Theories of strained-bond semiconductors and superconductors have been developed that promise to have significant impact on future electronic devices of interest to the Air Force. These include: (1) development of a theory of high-temperature superconductivity based on the idea of strained-layer superlattices, (2) elucidation of the physics of doping in Type-2 semiconductor superlattices, which is now central to the development of high-speed field-effect transistors, (3) a theory of dimerization and reconstruction on (001) semiconductor surfaces, (4) theory of Mobius transforms as applied to physics and remote sensing, (5) new understanding of how defects affect the vibrational properties of semiconductors, (6) new methods of efficiently computing the trajectories of atoms in semiconductors by a priori molecular dynamics, (7) elucidation of the criteria affecting quantum-well luminescence from Si, (8) models of the effects of vacancies in large-gap Al(x)Ga(1-x)N alloys, (9) physics of rare-earth-doped silicon, (10) models of Co adsorption to silicon surfaces, (11) theories of how defects affect the properties of large band-gap superlattices, and (12) models of the effects of electronic structure on the properties of semiconductors.

Dow, John D.

1994-05-01

438

Experimental Constraints on the Partitioning and Valence of V and Cr in Garnet and Coexisting Glass  

NASA Technical Reports Server (NTRS)

A series of experiments with garnet and coexisting melt have been carried out across a range of oxygen fugacities (near hematite-magnetite (HM) to below the iron-wustite (IW) buffers) at 1.7 GPa to study the partitioning and valence of Cr and V in both phases. Experiments were carried out in a non end loaded piston cylinder apparatus, and the run products were analyzed with electron microprobe and xray absorption near edge structure (XANES) analysis at beamline 13-ID at the Advanced Photon Source of Argonne National Lab. The valence of vanadium and chromium were determined using the position and intensity of the Ka pre-edge peaks, calibrated on a series of Cr and Vbearing standard glasses. This technique has been applied to V and Cr in glasses and V in spinels previously, and in these isotropic phases there are no orientational effects on the XANES spectra (Righter et al., 2006, Amer. Mineral. 91, 1643-1656). We also now demonstrate this to be true for V and Cr in garnet. Also, previous work has shown that V has a higher valence in the glass (or melt) than in the coexisting spinel. This is also true for V in garnet-glass pairs in this study. Vanadium valence in garnets varies from 2.7 below the IW buffer to 3.7 near HM, and for coexisting glass it varies from 3.2 to 4.3. Vanadium valence measured in some natural garnets from mantle localities indicates V in the more reduced range at 2.5. Comparisons will be made between fO2 estimated from V valence and other methods for garnet-bearing mantle samples. In contrast, Cr valence measured in garnet and coexisting glass for all experimental and natural samples is 2.9- 3.0, suggesting that the valence of Cr does not vary within either phase across a large fO2 range. These results demonstrate that while V varies from 2+ to 3+ to 4+ in garnet-melt systems, Cr does not, and this will ultimately affect the partitioning behavior of these two elements in natural systems. Garnet/melt D(Cr) are between 12 and 17 across this range of fO2, whereas D(V) has the highest partition coefficient approx.3, near the IW buffer where the valence of V is almost entirely 3+.

Righter, K.; Sutton, S.; Berthet, S.; Newville, M.

2008-01-01

439

Music, emotion, and time perception: the influence of subjective emotional valence and arousal?  

PubMed Central

The present study used a temporal bisection task with short (<2 s) and long (>2 s) stimulus durations to investigate the effect on time estimation of several musical parameters associated with emotional changes in affective valence and arousal. In order to manipulate the positive and negative valence of music, Experiments 1 and 2 contrasted the effect of musical structure with pieces played normally and backwards, which were judged to be pleasant and unpleasant, respectively. This effect of valence was combined with a subjective arousal effect by changing the tempo of the musical pieces (fast vs. slow) (Experiment 1) or their instrumentation (orchestral vs. piano pieces). The musical pieces were indeed judged more arousing with a fast than with a slow tempo and with an orchestral than with a piano timbre. In Experiment 3, affective valence was also tested by contrasting the effect of tonal (pleasant) vs. atonal (unpleasant) versions of the same musical pieces. The results showed that the effect of tempo in music, associated with a subjective arousal effect, was the major factor that produced time distortions with time being judged longer for fast than for slow tempi. When the tempo was held constant, no significant effect of timbre on the time judgment was found although the orchestral music was judged to be more arousing than the piano music. Nevertheless, emotional valence did modulate the tempo effect on time perception, the pleasant music being judged shorter than the unpleasant music. PMID:23882233

Droit-Volet, Sylvie; Ramos, Danilo; Bueno, José L. O.; Bigand, Emmanuel

2013-01-01

440

Representational similarity of social and valence information in the medial pFC.  

PubMed

The human brain is remarkably adept at integrating complex information to form unified psychological representations of agents, objects, and events in the environment. Two domains in which this ability is particularly salient are the processing of social and valence information and are supported by common cortical areas in the medial pFC (MPFC). Because social information is often embedded within valenced emotional contexts, it is possible that activation patterns within the MPFC may represent both of these types of cognitive processes when presented simultaneously. The current study tested this possibility by employing a large-scale automated meta-analysis tool, together with multivoxel pattern analysis to investigate the representational similarity of social and valence information in the MPFC during fMRI. Using a representational similarity analysis, we found a high degree of representational similarity both within social dimensions and within valence dimensions, but not across them (e.g., positive social information was highly dissimilar to negative nonsocial information), in a ventral portion of the MPFC. These results were significantly correlated with a behaviorally measured similarity structure of the same stimuli, suggesting that a psychologically meaningful representation of social and valence information is reflected by multivoxel activation patterns in the ventral MPFC. PMID:25100218

Chavez, Robert S; Heatherton, Todd F

2015-01-01

441

Segregation of information about emotional arousal and valence in horse whinnies.  

PubMed

Studying vocal correlates of emotions is important to provide a better understanding of the evolution of emotion expression through cross-species comparisons. Emotions are composed of two main dimensions: emotional arousal (calm versus excited) and valence (negative versus positive). These two dimensions could be encoded in different vocal parameters (segregation of information) or in the same parameters, inducing a trade-off between cues indicating emotional arousal and valence. We investigated these two hypotheses in horses. We placed horses in five situations eliciting several arousal levels and positive as well as negative valence. Physiological and behavioral measures collected during the tests suggested the presence of different underlying emotions. First, using detailed vocal analyses, we discovered that all whinnies contained two fundamental frequencies ("F0" and "G0"), which were not harmonically related, suggesting biphonation. Second, we found that F0 and the energy spectrum encoded arousal, while G0 and whinny duration encoded valence. Our results show that cues to emotional arousal and valence are segregated in different, relatively independent parameters of horse whinnies. Most of the emotion-related changes to vocalizations that we observed are similar to those observed in humans and other species, suggesting that vocal expression of emotions has been conserved throughout evolution. PMID:25897781

Briefer, Elodie F; Maigrot, Anne-Laure; Mandel, Roi; Freymond, Sabrina Briefer; Bachmann, Iris; Hillmann, Edna

2015-01-01

442

Valence band offsets at zinc-blende heterointerfaces with misfit dislocations: A first-principles study  

NASA Astrophysics Data System (ADS)

The electronic states induced by misfit dislocations at zincblende CdTe/CdS, CdS/ZnS, and InP/GaP heterointerfaces and their impacts on the valence band offsets are investigated using first-principles calculations. The (100) and (110) heterointerfaces including perfect edge dislocations with a Burgers vector of (a)/(2)[11¯0] and a line vector of [001] are considered for each system. Two types of dislocation core structures are found: The “closed” core has four-membered rings only and contains threefold and fivefold coordinated cations, whereas the “open” core has ten-membered rings that involve threefold coordinated atoms. The closed core forms at the (110) interfaces and is energetically more favorable than the open core. The characteristics of dislocation-induced electronic states are heavily dependent on the system and core structure, but all have localized states in the valence and conduction bands. The localized states in the valence band mostly have anion-orbital characteristics, whereas those in the conduction band mainly have cation-orbital characteristics. Some, but not all, dislocation cores also induce electronic states in the gap between the higher of the valence band maxima and the lower of the conduction band minima in the two phases that constitute the interface. The explicit treatment of misfit dislocations changes the valence band offset between the regions at a distance of ˜1 nm or more from the heterointerface by typically ˜0.1 eV.

Hinuma, Yoyo; Oba, Fumiyasu; Tanaka, Isao

2013-08-01

443

Looking behaviour and preference for artworks: the role of emotional valence and location.  

PubMed

The position of an item influences its evaluation, with research consistently finding that items occupying central locations are preferred and have a higher subjective value. The current study investigated whether this centre-stage effect (CSE) is a result of bottom-up gaze allocation to the central item, and whether it is affected by item valence. Participants (n=50) were presented with three images of artistic paintings in a row and asked to choose the image they preferred. Eye movements were recorded for a subset of participants (n=22). On each trial the three artworks were either similar but different, or were identical and with positive valence, or were identical and with negative valence. The results showed a centre-stage effect, with artworks in the centre of the row preferred, but only when they were identical and of positive valence. Significantly greater gaze allocation to the central and left artwork was not mirrored by equivalent increases in preference choices. Regression analyses showed that when the artworks were positive and identical the participants' last fixation predicted preference for the central art-work, whereas the fixation duration predicted preference if the images were different. Overall the result showed that item valence, rather than level of gaze allocation, influences the CSE, which is incompatible with the bottom-up gaze explanation. We propose that the centre stage heuristic, which specifies that the best items are in the middle, is able to explain these findings and the centre-stage effect. PMID:25203454

Kreplin, Ute; Thoma, Volker; Rodway, Paul

2014-10-01

444

XPS investigation of Mn valence in lanthanum manganite thin films under variation of oxygen content  

NASA Astrophysics Data System (ADS)

The question whether LaMnO3 accepts doping with tetravalent cations such as cerium and thus allows the preparation of electron-doped mixed-valent lanthanum manganites has been discussed controversially so far. Against the background of this problem, we present a comparative x-ray photoemission (XPS) study of epitaxial La0.7Ce0.3MnO3 (LCeMO) and La0.7Ca0.3MnO3 (LCMO) thin films. We focus on the exchange splitting of the Mn 3s core level peak, which is a direct indicator of the Mn valence and allows us to quantify the Mn valence in the outermost 3nm of the films. We demonstrate that, depending on the oxygen content, the Mn valence can be tuned between a mixed Mn3+/4+ state and a mixed Mn2+/3+ state in both the LCeMO and the LCMO film. The oxygen content was varied by heating in ultrahigh vacuum for deoxygenation and in an oxygen atmosphere for reoxidation. In the LCeMO film, the deoxygenation not only changes the Mn valence, but also the Ce valence is driven from the 4+ towards the 3+ state.

Beyreuther, Elke; Grafström, Stefan; Eng, Lukas M.; Thiele, Christian; Dörr, Kathrin

2006-04-01

445

Macroscopic and vibration spectroscopic evidence for specific bonding of arsenate on gibbsite.  

PubMed

The As(V) adsorption onto gibbsite under different experimental conditions was examined. Macroscopic data suggests strong As(V) bonding on gibbsite possibly via a bidendate binuclear complexation mechanism. The As(V) adsorption was quantified with the charge distribution multi-site ions complexation (CD-MUSIC) model distributing the anion charge over 0- and 1-planes according to the modified Pauling's bond valence theory. In the dual-adsorbates system of As(III) and As(V), the As(III) adsorption was predicted up to pH 8 utilizing the binding constants derived for single-adsorbate data. However, with pH > 8, the modeled As(III) adsorption data is overestimating the experimental values. PMID:15081767

Weerasooriya, R; Tobschall, H J; Wijesekara, H K D K; Bandara, A

2004-06-01

446

Bonding in singlet and triplet butalene: insights from spin-coupled theory.  

PubMed

Spin-coupled (SC, equivalent to full generalized valence bond) calculations for the (1)Ag ground state of butalene at its optimal D2h planar geometry show that cross-ring Dewar-like modes of spin coupling are of comparable importance to the more usually considered Kekulé-like modes. There are marked similarities to the SC description of one of the isomers of benzo[1,2:4,5]dicyclobutadiene. A complication for both of these systems is the existence of SC solutions in which some of the orbitals resemble in- and out-of-phase combinations of semilocalized atom-centered orbitals. The lowest triplet state, for which a nonplanar C2v geometry is preferred, is somewhat more straightforward to analyze: the SC description of the (3)B2 state is dominated by a very simple pattern of two ? bonds and two well-localized triplet-coupled orbitals. PMID:25688829

Cooper, David L; Karadakov, Peter B; Duke, Brian J

2015-03-12

447

Mixed valency and site-preference chemistry for cerium and its compounds: A predictive density-functional theory study  

NASA Astrophysics Data System (ADS)

Cerium and its technologically relevant compounds are examples of anomalous mixed valency, originating from two competing oxidation states—itinerant Ce4+ and localized Ce3+. Under applied stress, anomalous transitions are observed but not well understood. Here we treat mixed valency as an "alloy" problem involving two valences with competing and numerous site-occupancy configurations. We use density-functional theory with Hubbard U (i.e., DFT+U) to evaluate the effective valence and predict properties, including controlling the valence by pseudoternary alloying. For Ce and its compounds, such as (Ce,La)2(Fe,Co)14B permanent magnets, we find a stable mixed-valent ? state near the spectroscopic value of ?s=3.53. Ce valency in compounds depends on its steric volume and local chemistry. For La doping, Ce valency shifts towards ?-like Ce3+, as expected from steric volume; for Co doping, valency depends on local Ce-site chemistry and steric volume. Our approach captures the key origins of anomalous valency and site-preference chemistry in complex compounds.

Alam, Aftab; Johnson, D. D.

2014-06-01

448

Mixed valency and site-preference chemistry for cerium and its compounds: A predictive density-functional theory study  

SciTech Connect

Cerium and its technologically relevant compounds are examples of anomalous mixed valency, originating from two competing oxidation states—itinerant Ce4+ and localized Ce3+. Under applied stress, anomalous transitions are observed but not well understood. Here we treat mixed valency as an “alloy” problem involving two valences with competing and numerous site-occupancy configurations. We use density-functional theory with Hubbard U (i.e., DFT+U) to evaluate the effective valence and predict properties, including controlling the valence by pseudoternary alloying. For Ce and its compounds, such as (Ce,La)2(Fe,Co)14B permanent magnets, we find a stable mixed-valent ? state near the spectroscopic value of ?s=3.53. Ce valency in compounds depends on its steric volume and local chemistry. For La doping, Ce valency shifts towards ?-like Ce3+, as expected from steric volume; for Co doping, valency depends on local Ce-site chemistry and steric volume. Our approach captures the key origins of anomalous valency and site-preference chemistry in complex compounds.

Alam, Aftab [Ames Laboratory; Johnson, Duane D. [Ames Laboratory

2014-06-01

449

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

SciTech Connect

The photoelectron spectra of the adenine-formic acid (AFA)- and 9-methyladenine-formic acid (MAFA)- anionic complexes have been recorded with 2.540 eV photons. These spectra reveal broad features with maxima at 1.5-1.4 eV that indicate formation of stable valence anions in the gas phase. The neutral and anionic complexes of adenine/9- methyladenine and formic acid were also studied computationally at the B3LYP, second order Møller-Plesset and coupled clusters levels of theory, with the 6-31++G** and aug-cc-pVDZ basis sets. The neutral complexes form cyclic hydrogen bonds and the most stable dimers are bound by 17.7 and 16.0 kcal/mol for AFA and MAFA, respectively. The theoretical results indicate that the excess electron in both (AFA)- and (MAFA)- occupies a p* orbital localized on adenine/9-methyladenine and the adiabatic stability of the most stable anions amounts to 0.67 and 0.54 eV for AFA- and MAFA-, respectively. The excess electron attachment to the complexes induces a barrierfree proton transfer (BFPT) from the carboxylic group of formic acid to a N atom of adenine or 9-mathyladenine. As a result, the most stable structures of the anionic complexes can be characterized as neutral radicals of hydrogenated adenine(9-methyladenine) solvated by a deprotonated formic acid. The BFPT to the N atoms of adenine may be biologically relevant because some of these sites are not involved in the Watson-Crick pairing scheme and are easily accessible in the cellular environment. We suggest that valence anions of purines might be as important as those of pyrimidines in the process of DNA damage by low energy electrons. The calculations were performed at the Academic Computer Center in Gda?sk (TASK) and at the Molecular Science Computing Facility (MSCF) in the William R. Wiley Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the U.S. Department of Energy's Office of Biological and Environmental Research and located at the Pacific Northwest National Laboratory, which is operated by Battelle for the US Department of Energy. The MSCF resources were available through a Computational Grand Challenge Application grant.

Mazurkiewicz, Kamil; Haranczyk, Maciej; Gutowski, Maciej S.; Rak, Janusz; Radisic, Dunja; Eustis, Soren; Wang, Di; Bowen, Kit H.

2007-02-07

450

Hydrogen Bonded Arrays: The Power of Multiple Hydrogen Bonds  

SciTech Connect

Hydrogen bond interactions in small covalent model compounds (i.e. deprotonated polyhydroxy alcohols) were measured by negative ion photoelectron spectroscopy. The experimentally determined vertical and adiabatic electron detachment energies for (HOCH2CH2)2CHO (2a), (HOCH2CH2) 3CO (3a) and (HOCH2CH2CH(OH)CH2)3CO (4a) reveal that hydrogen-bonded networks can provide enormous stabilizations, and that a single charge center not only can be stabilized by up to 3 hydrogen bonds but it can increase the interaction energy between non-charged OH groups by 5.8 kcal mol1 or more per hydrogen bond. This can lead to pKa values that are very different than in water, and provide some of the impetus for catalytic processes.

Shokri, Alireza; Schmidt, Jacob C.; Wang, Xue B.; Kass, Steven R.

2012-02-01

451

Method for vacuum fusion bonding  

DOEpatents

An improved vacuum fusion bonding structure and process for aligned bonding of large area glass plates, patterned with microchannels and access holes and slots, for elevated glass fusion temperatures. Vacuum pumpout of all components is through the bottom platform which yields an untouched, defect free top surface which greatly improves optical access through this smooth surface. Also, a completely non-adherent interlayer, such as graphite, with alignment and location features is located between the main steel platform and the glass plate pair, which makes large improvements in quality, yield, and ease of use, and enables aligned bonding of very large glass structures.

Ackler, Harold D. (Sunnyvale, CA); Swierkowski, Stefan P. (Livermore, CA); Tarte, Lisa A. (Livermore, CA); Hicks, Randall K. (Stockton, CA)

2001-01-01

452

Fusion bonding and alignment fixture  

DOEpatents

An improved vacuum fusion bonding structure and process for aligned bonding of large area glass plates, patterned with microchannels and access holes and slots, for elevated glass fusion temperatures. Vacuum pumpout of all the components is through the bottom platform which yields an untouched, defect free top surface which greatly improves optical access through this smooth surface. Also, a completely non-adherent interlayer, such as graphite, with alignment and location features is located between the main steel platform and the glass plate pair, which makes large improvements in quality, yield, and ease of use, and enables aligned bonding of very large glass structures.

Ackler, Harold D. (Sunnyvale, CA); Swierkowski, Stefan P. (Livermore, CA); Tarte, Lisa A. (Livermore, CA); Hicks, Randall K. (Stockton, CA)

2000-01-01

453

Coordination-resolved local bond contraction and electron binding-energy entrapment of Si atomic clusters and solid skins  

SciTech Connect

Consistency between x-ray photoelectron spectroscopy measurements and density-function theory calculations confirms our bond order-length-strength notation-incorporated tight-binding theory predictions on the quantum entrapment of Si solid skin and atomic clusters. It has been revealed that bond-order deficiency shortens and strengthens the Si-Si bond, which results in the local densification and quantum entrapment of the core and valence electrons. Unifying Si clusters and Si(001) and (111) skins, this mechanism has led to quantification of the 2p binding energy of 96.089?eV for an isolated Si atom, and their bulk shifts of 2.461?eV. Findings evidence the significance of atomic undercoordination that is of great importance to device performance.

Bo, Maolin; Huang, Yongli; Zhang, Ting [Key Laboratory of Low-Dimensional Materials and Application Technologies, Xiangtan University, Hunan 411105 (China); Wang, Yan, E-mail: ywang8@hnust.edu.cn, E-mail: ecqsun@ntu.edu.sg [Key Laboratory of Low-Dimensional Materials and Application Technologies, Xiangtan University, Hunan 411105 (China); School of Information and Electronic Engineering, Hunan University of Science and Technology, Hunan 411201 (China); Zhang, Xi [School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Li, Can [Center for Coordination Bond Engineering, School of Materials Science and Engineering, China Jiliang University, Hangzhou 330018 (China); Sun, Chang Q., E-mail: ywang8@hnust.edu.cn, E-mail: ecqsun@ntu.edu.sg [Key Laboratory of Low-Dimensional Materials and Application Technologies, Xiangtan University, Hunan 411105 (China); School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Center for Coordination Bond Engineering, School of Materials Science and Engineering, China Jiliang University, Hangzhou 330018 (China)

2014-04-14

454

Method of bonding  

DOEpatents

1. A method of making a fuel-containing structure for nuclear reactors, comprising providing an assembly comprising a plurality of fuel units; each fuel unit consisting of a core plate containing thermal-neutron-fissionable material, sheets of cladding metal on its bottom and top surfaces, said cladding sheets being of greater width and length than said core plates whereby recesses are formed at the ends and sides of said core plate, and end pieces and first side pieces of cladding metal of the same thickness as the core plate positioned in said recesses, the assembly further comprising a plurality of second side pieces of cladding metal engaging the cladding sheets so as to space the fuel units from one another, and a plurality of filler plates of an acid-dissolvable nonresilient material whose melting point is above 2000.degree. F., each filler plate being arranged between a pair of said second side pieces and the cladding plates of two adjacent fuel units, the filler plates having the same thickness as the second side pieces; the method further comprising enclosing the entire assembly in an envelope; evacuating the interior of the entire assembly through said envelope; applying inert gas under a pressure of about 10,000 psi to the outside of said envelope while at the same time heating the assembly to a temperature above the flow point of the cladding metal but below the melting point of any material of the assembly, whereby the envelope is pressed against the assembly and integral bonds are formed between plates, sheets, first side pieces, and end pieces and between the sheets and the second side pieces; slowly cooling the assembly to room temperature; removing the envelope; and dissolving the filler plates without attacking the cladding metal.

Saller, deceased, Henry A. (late of Columbus, OH); Hodge, Edwin S. (Columbus, OH); Paprocki, Stanley J. (Columbus, OH); Dayton, Russell W. (Columbus, OH)

1987-12-01