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1

Valence-Bond Theory and Chemical Structure.  

ERIC Educational Resources Information Center

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

Klein, Douglas J.; Trinajstic, Nenad

1990-01-01

2

Valence-bond description of chemical reactions on Born-Oppenheimer molecular dynamics trajectories  

Microsoft Academic Search

The nature of chemical bonds on dynamic paths was investigated using the complete active space valence-bond (CASVB) method and the Born-Oppenheimer dynamics. To extract the chemical bond picture during reactions, a scheme to collect contributions from several VB (resonance) structures into a small numbers of indices was introduced. In this scheme, a tree diagram for the VB structures is constructed

Nao Noguchi; Haruyuki Nakano

2009-01-01

3

A valence bond study of TiF3  

Microsoft Academic Search

The tractability of Valence Bonds calculations on molecules containing heavy atoms is investigated. Limited-structure VB wavefunctions for several states of TiF3+ are presented. It is concluded that, with a suitable pseudo-potential approximation for the core electrons and a short GTO expansion of the minimal STO basis, reasonably accurate VB studies of the spectroscopic properties of diatomic molecules containing heavy atoms

P. J. Carrington; P. G. Walton

1973-01-01

4

A valence bond study of TiF  

Microsoft Academic Search

The tractability of Valence Bonds calculations on molecules containing heavy atoms is investigated. Limited-structure VB wavefunctions for several states of TiF are presented. It is concluded that, with a suitable pseudo-potential approximation for the core electrons and a short GTO expansion of the minimal STO basis, reasonably accurate VB studies of the spectroscopic properties of diatomic molecules containing heavy atoms

P. J. Carrington; P. G. Walton

1973-01-01

5

Classical Fluctuating Charge Theories: The Maximum Entropy Valence Bond Formalism and Relationships to Previous Models  

E-print Network

Classical Fluctuating Charge Theories: The Maximum Entropy Valence Bond Formalism and Relationships approach to classical charge transfer theories based on valence bond (VB) theory and the maximum entropy as electronegativity equalization, theories for describing charge flow in molecules. We introduce a new unifying

Morales, Jorge Alberto

6

Correlated valence-bond states  

NASA Astrophysics Data System (ADS)

We study generalizations of the singlet-sector amplitude-product (AP) states in the valence-bond basis of S=1/2 quantum spin systems. In the standard AP states, the weight of a tiling of the system into valence bonds (singlets of two spins) is a product of amplitudes depending on the length of the bonds. We here introduce correlated AP (CAP) states, in which the AP is further multiplied by factors depending on two bonds connected to a pair of sites (here nearest neighbors). While the standard AP states can describe a phase transition between an antiferromagnetic (Néel) state and a valence-bond solid (VBS) in one dimension (which we also study here), in two dimensions it cannot describe VBS order. With the CAP states, Néel-VBS transitions are realized as a function of some parameter describing the bond correlations. We here study such phase transitions of CAP wave functions on the square lattice. We find examples of direct first-order Néel-VBS transitions, as well as cases where there is an extended U(1) spin liquid phase intervening between the Néel and VBS states. In the latter case the transitions are continuous and we extract critical exponents and address the issue of a possible emergent U(1) symmetry in the near-critical VBS. We also consider variationally optimized CAP states for the standard Heisenberg model in one and two dimensions and the J-Q model in two dimensions, with the latter including four-spin interactions (Q) in addition to the Heisenberg exchange (J) and harboring VBS order for large Q/J. The optimized CAP states lead to significantly lower variational energies than the simple AP states for these models.

Lin, Yu-Cheng; Tang, Ying; Lou, Jie; Sandvik, Anders W.

2012-10-01

7

Valence-bond description of chemical reactions on Born-Oppenheimer molecular dynamics trajectories  

NASA Astrophysics Data System (ADS)

The nature of chemical bonds on dynamic paths was investigated using the complete active space valence-bond (CASVB) method and the Born-Oppenheimer dynamics. To extract the chemical bond picture during reactions, a scheme to collect contributions from several VB (resonance) structures into a small numbers of indices was introduced. In this scheme, a tree diagram for the VB structures is constructed with the numbers of the ionic bonds treated as generation. A pair of VB structures is related to each other if one VB structure is transferred into the other by changing a covalent bond to an ionic bond. The former and latter VB structures are named parent and child structures, respectively. The weights of the bond pictures are computed as the sum of the CASVB occupation numbers running from the top generation to the bottom along the descent of the VB structures. Thus, a number of CASVB occupation numbers are collected into a small number of indices, and a clear bond picture may be obtained from the CASVB wave function. The scheme was applied to the hydrogen exchange reaction H2+F-->H+HF and the Diels-Alder reaction C5H6(cyclopentadiene)+CH2=CH2(ethylene)-->C7H10(norbornene). In both the reactions, the scheme gave a clear picture for the Born-Oppenheimer dynamics trajectories. The reconstruction of the bonds during reactions was well described by following the temporal changes in weight.

Noguchi, Nao; Nakano, Haruyuki

2009-04-01

8

Valence-bond isomers of aromatic compounds  

Microsoft Academic Search

After a brief survey of the history of valence-bond isomers of aromatic compounds, new syntheses and the reactions of these isomers reported in the last decade are reviewed. In the second chapter, the valence-bond isomers of homoaromatic compounds, especially benzene derivatives, are described and in the third chapter those of heterocyclic compounds. Photoreactions of perfluoroalkylated aromatic compounds afford valence-bond isomers

Yoshiro Kobayashi; Itsumaro Kumadaki

9

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

10

Generalized resonating valence bond description of cyclobutadiene  

SciTech Connect

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

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

1986-05-28

11

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

12

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

PubMed

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

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

2014-07-21

13

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

14

Semionic resonating valence-bond states  

NASA Astrophysics Data System (ADS)

The nature of the kagome Heisenberg antiferromagnet (HAFM) is under ongoing debate. While recent evidence points towards a Z2 topological spin liquid, the exact nature of the topological phase is still unclear. In this paper, we introduce semionic resonating valence-bond (RVB) states, this is, resonating valence-bond states which are in the Z2-ordered double-semion phase, and study them using projected entangled pair states. We investigate their physics and study their suitability as an ansatz for the HAFM, as compared to a conventional RVB state which is in the toric-code Z2 topological phase. In particular, we find that a suitably optimized "semionic simplex RVB" outperforms the equally optimized conventional "simplex RVB" state, and that the entanglement spectrum (ES) of the semionic RVB behaves very differently from the ES of the conventional RVB, which suggests using the ES to discriminate the two phases. Finally, we also discuss the possible relevance of space-group symmetry breaking in valence-bond wave functions with double-semion topological order.

Iqbal, Mohsin; Poilblanc, Didier; Schuch, Norbert

2014-09-01

15

Reentrant valence transition in EuO at high pressures: beyond the bond-valence model.  

PubMed

The pressure-dependent relation between Eu valence and lattice structure in model compound EuO is studied with synchrotron-based x-ray spectroscopic and diffraction techniques. Contrary to expectation, a 7% volume collapse at ?45??GPa is accompanied by a reentrant Eu valence transition into a lower valence state. In addition to highlighting the need for probing both structure and electronic states directly when valence information is sought in mixed-valent systems, the results also show that widely used bond-valence methods fail to quantitatively describe the complex electronic valence behavior of EuO under pressure. PMID:23030187

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

2012-07-13

16

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

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

17

Charge-shift bonding--a class of electron-pair bonds that emerges from valence bond theory and is supported by the electron localization function approach.  

PubMed

This paper deals with a central paradigm of chemistry, the electron-pair bond. Valence bond (VB) theory and electron-localization function (ELF) calculations of 21 single bonds demonstrate that along the two classical bond families of covalent and ionic bonds, there exists a class of charge-shift bonds (CS bonds) in which the fluctuation of the electron pair density plays a dominant role. In VB theory, CS bonding manifests by way of a large covalent-ionic resonance energy, RE(CS), and in ELF by a depleted basin population with large variances (fluctuations). CS bonding is shown to be a fundamental mechanism that is necessary to satisfy the equilibrium condition, namely the virial ratio of the kinetic and potential energy contributions to the bond energy. The paper defines the atomic propensity and territory for CS bonding: Atoms (fragments) that are prone to CS bonding are compact electronegative and/or lone-pair-rich species. As such, the territory of CS bonding transcends considerations of static charge distribution, and involves: a) homopolar bonds of heteroatoms with zero static ionicity, b) heteropolar sigma and pi bonds of the electronegative and/or electron-pair-rich elements among themselves and to other atoms (e.g., the higher metalloids, Si, Ge, Sn, etc), c) all hypercoordinate molecules. Several experimental manifestations of charge-shift bonding are discussed, such as depleted bonding density, the rarity of ionic chemistry of silicon in condensed phases, and the high barriers of halogen-transfer reactions as compared to hydrogen-transfers. PMID:16086335

Shaik, Sason; Danovich, David; Silvi, Bernard; Lauvergnat, David L; Hiberty, Philippe C

2005-10-21

18

Density embedded VB/MM: a hybrid ab initio VB/MM with electrostatic embedding.  

PubMed

A hybrid QM/MM method that combines ab initio valence-bond (VB) with molecular mechanics (MM) is presented. The method utilizes the ab initio VB approach to describe the reactive fragments and MM to describe the environment thus allows VB calculations of reactions in large biological systems. The method, termed density embedded VB/MM (DE-VB/MM), is an extension of the recently developed VB/MM method. It involves calculation of the electrostatic interaction between the reactive fragments and their environment using the electrostatic embedding scheme. Namely, the electrostatic interactions are represented as one-electron integrals in the ab initio VB Hamiltonian, hence taking into account the wave function polarization of the reactive fragments due to the environment. Moreover, the assumptions that were utilized in an earlier version of the method, VB/MM, to formulate the electrostatic interactions effect on the off-diagonal matrix elements are no longer required in the DE-VB/MM methodology. Using DE-VB/MM, one can calculate, in addition to the adiabatic ground state reaction profile, the energy of the diabatic VB configurations as well as the VB state correlation diagram for the reaction. The abilities of the method are exemplified on the identity SN2 reaction of a chloride anion with methyl chloride in aqueous solution. Both the VB configurations diagram and the state correlation diagram are presented. The results are shown to be in very good agreement with both experimental and other computational data, suggesting that DE-VB/MM is a proper method for application to different reactivity problems in biological systems. PMID:18293950

Sharir-Ivry, Avital; Crown, Hadar A; Wu, Wei; Shurki, Avital

2008-03-20

19

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

20

Optical implementation and entanglement distribution in Gaussian valence bond states  

NASA Astrophysics Data System (ADS)

We study Gaussian valence bond states of continuous variable systems obtained as the outputs of projection operations from an ancillary space of M infinitely entangled bonds connecting neighboring sites applied at each ofN sites of a harmonic chain. The entanglement distribution in Gaussian valence bond states can be controlled by varying the input amount of entanglement engineered in a (2M+ 1)-mode Gaussian state known as the building block, which is isomorphic to the projector applied at a given site. We show how this mechanism can be interpreted in terms of multiple entanglement swapping from the chain of ancillary bonds, through the building blocks. We provide optical schemes to produce bisymmetric three-mode Gaussian building blocks (which correspond to a single bond, M = 1), and study the entanglement structure in the output Gaussian valence bond states. Finally, the usefulness of such states for quantum communication protocols with continuous variables, like telecloning and teleportation networks, is discussed.

Adesso, G.; Ericsson, M.

2007-08-01

21

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

22

1262 J. Phys. Chem. 1984, 88, 1262-1268 Alkali Oxides. Analysis of Bonding and Explanation of the Reversal in Ordering of the  

E-print Network

), generalized valence bond (GVB), and configuration in- teraction (CI), in order to elucidate the bonding the core orbitals are solved for self-consistentlywith the valence electrons. In Figure 1 we compare is the antisymmetrizer or determinant operator): (i) the simple valence bond (VB) wave function *VB = AZ[(Na+core)(Cl+ c

Goddard III, William A.

23

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

24

Exploring covalently bonded diamondoid particles with valence photoelectron spectroscopy  

E-print Network

We investigated the electronic structures of diamondoid particles in the gas phase, utilizing valence photoelectron spectroscopy. The samples were singly or doubly covalently bonded dimers or trimers of the lower diamondoids. Both bond type and the combination of the bonding partners affect the overall electronic structures. For singly bonded particles we observe a small impact of the bond type on the electronic structure, whereas for doubly bonded particles the connecting bond is the deciding factor, determining the electronic structure of the uppermost occupied orbitals. In the singly bonded particles a superposition of the bonding partner orbitals determines the overall electronic structure. The strength of quantum confinement effects, i.e., the localization of electrons, depends on the bonding partner orbital energy difference. The experimental findings correspond well to density functional theory computations.

Zimmermann, Tobias; Knecht, Andre; Fokin, Andrey A; Koso, Tetyana V; Chernish, Lesya V; Gunchenko, Pavel A; Schreiner, Peter R; Möller, Thomas; Rander, Torbjörn

2013-01-01

25

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

26

Specificity, flexibility and valence of DNA bonds guide emulsion architecture  

E-print Network

The specificity and thermal reversibility of DNA interactions have enabled the self-assembly of crystal structures, self-replicating materials and colloidal molecules. Grafting DNA onto liquid interfaces of emulsions leads to exciting new architectural possibilities due to the mobility of the DNA ligands and the patches they form between bound droplets. Here we show that the size and number of these adhesion patches (valency) can be controlled. Valence 2 leads to flexible polymers of emulsion droplets, while valence above 4 leads to rigid droplet networks. A simple thermodynamic model quantitatively describes the increase in the patch size with droplet radii, DNA concentration and the stiffness of the tether to the sticky-end. The patches are formed between droplets with complementary DNA strands or alternatively with complementary colloidal nanoparticles to mediate DNA binding between droplets. This emulsion system opens the route to directed self-assembly of more complex structures through distinct DNA bonds with varying strengths and controlled valence and flexibility.

Lang Feng; Lea-Laetitia Pontani; Remi Dreyfus; Paul Chaikin; Jasna Brujic

2013-02-28

27

Valence bond liquids and solids in geometrically frustrated magnets  

NASA Astrophysics Data System (ADS)

Frustrated magnets are models of strongly interacting systems. Frustration reveals itself through a vast degeneracy of the classical ground state and is responsible for a large number of soft modes that destroy spin order. Possible alternative phases that could emerge in place of the Néel state are: (a) The valence-bond solid (VBS), in which bond averages < Si ot Sj >, rather than spins themselves, form a periodic structure. (b) The valence-bond liquid (VBL), in which any bond order is absent, but there is hidden topological order, similar to that in the fractional quantum Hall effect. In recent years particular attention has been paid to the Heisenberg antiferromagnet on the pyrochlore lattice---a 3D network of corner-sharing tetrahedra---and its 2D analogs. It has been established that a spin-lattice coupling stabilizes the VBS in the pyrochlores (Yamashita and Ueda, Tchernyshyov et al.); the related spin-Peierls phase transition has been observed in ZnCr_2O4 (S.-H. Lee et al.). Fouet et al. have found numerically that quantum spins (S=1/2) on the checkerboard lattice form a VBS. Until recently, systematic approaches---such as the 1/S and 1/N expansions---to the problem of the ground state in the pyrochlore have met with little success: the remaining degeneracy in the first nontrivial order is still very large. New technical developments (Henley) have allowed us to construct explicitly all ground states at order 1/S and characterize the resulting phases for two pyrochlore-like lattices. We find a VBS---resembling that of Fouet et al.---on the checkerboard lattice and a VBL in a 2D pyrochlore slab. A study of the 3D pyrochlore is in progress.

Tchernyshyov, Oleg

2003-03-01

28

Valence-Bond Quantum Monte Carlo Algorithms Defined on Trees  

E-print Network

We present a new class of algorithms for performing valence-bond quantum Monte Carlo of quantum spin models. Valence-bond quantum Monte Carlo is a T=0 Monte Carlo method based on sampling of a set of operator-strings that can be viewed as forming a tree-like 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 new 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 acceptanc...

Deschner, Andreas

2014-01-01

29

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

30

Bond valence sums and structural studies of antimony complexes containing Sb bonded only to O ligands  

Microsoft Academic Search

New R0 values for Sb(III)–O of 1.955(13) Å and for Sb(V)–O of 1.912(12) Å were derived from a bond valence sum, or BVS, analysis of of 123 SbOn fragments with n=3–7. These R0 values can be used to calculate the oxidation state, or OS, of Sb in complexes where Sb is bonded only to O ligands. If the OS of

Ruth C. Palenik; Khalil A. Abboud; Gus J. Palenik

2005-01-01

31

Hybrid valence-bond states for universal quantum computation  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

32

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

33

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

SciTech Connect

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

Tu Honghao; Zhang Guangming; Xiang Tao; Liu Zhengxin; Ng Taikai [Department of Physics, Tsinghua University, Beijing 100084 (China); Institute of Physics, Chinese Academy of Sciences, P.O. Box 603, Beijing 100190 (China) and Institute of Theoretical Physics, Chinese Academy of Sciences, P.O. Box 2735, Beijing 100190 (China); Department of Physics, Hong Kong University of Science and Technology, Kowloon, Hong Kong (China)

2009-07-01

34

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

35

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

36

A valence bond model for electron-rich hypervalent species: application to SFn (n=1, 2, 4), PF5 , and ClF3.  

PubMed

Some typical hypervalent molecules, SF4 , PF5 , and ClF3 , as well as precursors SF ((4) ?(-) state) and SF2 ((3) B1 state), are studied by means of the breathing-orbital valence bond (BOVB) method, chosen for its capability of combining compactness with accuracy of energetics. A unique feature of this study is that for the first time, the method used to gain insight into the bonding modes is the same as that used to calculate the bonding energies, so as to guarantee that the qualitative picture obtained captures the essential physics of the bonding system. The (4) ?(-) state of SF is shown to be bonded by a three-electron ? bond assisted by strong ? back-donation of dynamic nature. The linear (3) B1 state of SF2 , as well as the ground states of SF4 , PF5 and ClF3 , are described in terms of four VB structures that all have significant weights in the range 0.17-0.31, with exceptionally large resonance energies arising from their mixing. It is concluded that the bonding mode of these hypervalent species and isoelectronic ones complies with Coulson's version of the Rundle-Pimentel model, but assisted by charge-shift bonding. The conditions for hypervalence to occur are stated. PMID:24976382

Braida, Benoit; Ribeyre, Tristan; Hiberty, Philippe C

2014-07-28

37

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

38

Valence bond studies of the barrier to rotation around the N?N bond of N 2O 4  

NASA Astrophysics Data System (ADS)

The recent redetermination of the barrier to rotation around the N?N bond of N 2O 4 by Koput, Seibert and Winnewisser is used to focus attention on the primary valence bond explanation of the "cis-O?O overlap" contribution to this barrier. The explanation involves cis-O?O overlap-dependent resonance between covalent (NO 2NO 2) structures with "long" or formal N?O bonds, and resonance of these structures with the ionic (NO -2NO +2, NO +2NO -2) structures that are obtained from them via cis-O - ? O electron transfer in the planar conformer. The results of some ab initio valence bond calculations for both N 2O 2 and N 2O 4 are used to illustrate the phenomenon.

Harcourt, Richard D.

1994-02-01

39

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

E-print Network

that the VDC-MOVB method has been described previously. Employing the symmetric SN2 reaction between NH3 and CH bond (MOVB) approach to construct the CDC diabatic and adiabatic states for a chemical reaction. Note method is a reasonable model for VB simulations of condensed phase reactions. The results indicate

Minnesota, University of

40

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

ERIC Educational Resources Information Center

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

Fox, Marye Anne; Matsen, F. A.

1985-01-01

41

ForReview.Confidential-ACS An Effective Hamiltonian Molecular OrbitalValence Bond (MOVB)  

E-print Network

for Chemical Reactions Applied to the Nucleophilic Substitution Reaction of Hydrosulfide Ion and Chloromethane Molecular OrbitalValence Bond (MOVB) Approach for Chemical Reactions Applied to the Nucleophilic evaluated. The EH-MOVB method has been applied to the nucleophilic substitution reaction between

Minnesota, University of

42

Spinon excitation spectra of the resonating valence bond states in the high temperature superconducting cuprates  

NASA Astrophysics Data System (ADS)

Magnetic excitations of the resonating valence bond (RVB) states were searched in high temperature superconducting cuprates by Raman scattering. Ho et al. [C.-M. Ho et al., Phys. Rev. Lett. 86 (2001) 1626] disclosed that the spin excitation in the two-dimensional resonating valence bond state has a magnon-like dispersion and a spinon continuum above it. The density of states of the spin excitation has a peak at 1.5 J which is lower than the 2.36 J of the spin wave. We found that the A spectra have a broad peak at 1.5 J in common at the underdoped region of p?0.15 in LSCO, Bi2201, and Bi2212 and p?0.1 in YBCO. The B peak and the B peak in the two-magnon region have a fine structure of the spin wave. The carrier density dependence is discussed.

Sugai, S.; Takayanagi, Y.; Hosokawa, T.; Suzuki, H.; Hayamizu, N.; Muroi, T.; Sone, Y.; Mabuchi, H.

2010-12-01

43

Large scale valence-bond calculations on diatomic molecules: Aspects of spectral compression  

Microsoft Academic Search

Progress is reported in performing large scale valence-bond calculations of the ground and electronically excited Born-Oppenheimer eigenstates of diatomic molecules. A code suite for this purpose has been devised which combines spin-free methods in enumerating electronic configurations in terms of the standard tableau functions devised by one of us (GG - Crunch Code) with an efficient Slater-orbital-based integrals package (Smiles

Peter W. Langhoff; Michal Ben-Nun; Jeffrey Mills; Kyle Rollin; Michael Bromley; Jerry Boatz; Gordon Gallup

2010-01-01

44

Quantum computational capability of a 2D valence bond solid phase  

SciTech Connect

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

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

2011-07-15

45

A Valence-Bond Nonequilibrium Solvation Model for a Twisting Cyanine Dye  

E-print Network

We study a two-state valence-bond electronic Hamiltonian model of non-equilibrium solvation during the excited-state twisting reaction of monomethine cyanines. These dyes are of interest because of the strong environment-dependent enhancement of their fluorescence quantum yield that results from suppression of competing non-radiative decay via twisted internal charge-transfer (TICT) states. For monomethine cyanines, where the ground state is a superposition of structures with different bond and charge localization, there are two twisting pathways with different charge localization in the excited state. The Hamiltonian designed to be as simple as possible consistent with a few well-enumerated assumptions. It is defined by three parameters and is a function of two $\\pi$-bond twisting angle coordinates and a single solvation coordinate. For parameters corresponding to symmetric monomethines, there are two low-energy twisting channels on the excited-state surface that lead to a manifold of twisted intramolecular ...

McConnell, Sean; Olsen, Seth

2014-01-01

46

Comparison of ion sites and diffusion paths in glasses obtained by molecular dynamics simulations and bond valence analysis  

NASA Astrophysics Data System (ADS)

Based on molecular dynamics simulations of a lithium metasilicate glass we study the potential of bond valence sum calculations to identify sites and diffusion pathways of mobile Li ions in a glassy silicate network. We find that the bond valence method is not well suitable to locate the sites, but allows one to estimate the number of sites. Spatial regions of the glass determined as accessible for the Li ions by the bond valence method can capture up to 90% of the diffusion path. These regions however entail a significant fraction that does not belong to the diffusion path. Because of this low specificity, care must be taken to determine the diffusive motion of particles in amorphous systems based on the bond valence method. The best identification of the diffusion path is achieved by using a modified valence mismatch in the BV analysis that takes into account that a Li ion favors equal partial valences to the neighboring oxygen ions. Using this modified valence mismatch it is possible to replace hard geometric constraints formerly applied in the BV method. Further investigations are necessary to better understand the relation between the complex structure of the host network and the ionic diffusion paths.

Müller, Christian; Zienicke, Egbert; Adams, Stefan; Habasaki, Junko; Maass, Philipp

2007-01-01

47

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

NASA Astrophysics Data System (ADS)

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

Sarker, Sanjoy K.; Lovorn, Timothy

2010-07-01

48

Interlayer charge dynamics of the uniform resonating-valence-bond state  

SciTech Connect

The physical properties along the {ital c} axis of the uniform resonating-valence-bond state are studied. The physical electron, i.e., the composite particle of a spinon and a holon, hops between the layers incoherently. Conductivity, thermopower, thermal conductivity, and Hall constant are calculated and compared with the experiments in high-{ital T}{sub {ital c}} cuprates. The renormalization group equation is obtained for the interlayer hopping {ital t}{sub {ital c}} which is found to be marginally relevant. The effects of the spin gap are also discussed.

Nagaosa, N. [Department of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113 (Japan)] [Department of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113 (Japan)

1995-10-01

49

Empirical valence bond model of an SN2 reaction in polar and nonpolar solvents  

NASA Astrophysics Data System (ADS)

A new model for the substitution nucleophilic reaction (SN2) in solution is described using the empirical valence bond (EVB) method. The model includes a generalization to three dimensions of a collinear gas phase EVB model developed by Mathis et al. [J. Mol. Liq. 61, 81 (1994)] and a parametrization of solute-solvent interactions of four different solvents (water, ethanol, chloroform, and carbon tetrachloride). The model is used to compute (in these four solvents) reaction free energy profiles, reaction and solvent dynamics, a two-dimensional reaction/solvent free energy map, as well as a number of other properties that in the past have mostly been estimated.

Benjamin, Ilan

2008-08-01

50

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

51

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

E-print Network

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

Jesper Lykke Jacobsen; Hubert Saleur

2007-11-21

52

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

E-print Network

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

Jacobsen, Jesper Lykke

2011-01-01

53

Exact Valence Bond Entanglement Entropy and Probability Distribution in the XXX Spin Chain and the Potts Model  

NASA Astrophysics Data System (ADS)

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

Jacobsen, J. L.; Saleur, H.

2008-02-01

54

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

NASA Astrophysics Data System (ADS)

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

Chen, Zhenhua; Chen, Xun; Wu, Wei

2013-04-01

55

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

56

Optical one-way quantum computing with a simulated valence-bond solid  

E-print Network

One-way quantum computation proceeds by sequentially measuring individual spins (qubits) in an entangled many-spin resource state. It remains a challenge, however, to efficiently produce such resource states. Is it possible to reduce the task of generating these states to simply cooling a quantum many-body system to its ground state? Cluster states, the canonical resource for one-way quantum computing, do not naturally occur as ground states of physical systems. This led to a significant effort to identify alternative resource states that appear as ground states in spin lattices. An appealing candidate is a valence-bond-solid state described by Affleck, Kennedy, Lieb, and Tasaki (AKLT). It is the unique, gapped ground state for a two-body Hamiltonian on a spin-1 chain, and can be used as a resource for one-way quantum computing. Here, we experimentally generate a photonic AKLT state and use it to implement single-qubit quantum logic gates.

Lavoie, Jonathan; Zeng, Bei; Bartlett, Stephen D; Resch, Kevin J

2010-01-01

57

A multistate empirical valence bond model for solvation and transport simulations of OH- in aqueous solutions.  

PubMed

We describe a new multistate empirical valence bond (MS-EVB) model of OH(-) in aqueous solutions. This model is based on the recently proposed "charged ring" parameterization for the intermolecular interaction of hydroxyl ion with water [Ufimtsev, et al., Chem. Phys. Lett., 2007, 442, 128] and is suitable for classical molecular simulations of OH(-) solvation and transport. The model reproduces the hydration structure of OH(-)(aq) in good agreement with experimental data and the results of ab initio molecular dynamics simulations. It also accurately captures the major structural, energetic, and dynamic aspects of the proton transfer processes involving OH(-) (aq). The model predicts an approximately two-fold increase of the OH(-) mobility due to proton exchange reactions. PMID:19830325

Ufimtsev, Ivan S; Kalinichev, Andrey G; Martinez, Todd J; Kirkpatrick, R James

2009-11-01

58

Hidden Order and Dynamics in Supersymmetric Valence Bond Solid States -- Super-Matrix Product State Formalism  

E-print Network

Supersymmetric valence bond solid models are extensions of the VBS model, a paradigmatic model of `solvable' gapped quantum antiferromagnets, to the case with doped fermionic holes. In this paper, we present a detailed analysis of physical properties of the models. For systematic studies, a supersymmetric version of the matrix product formalism is developed. On 1D chains, we exactly evaluate the hole-doping behavior of various physical quantities, such as the spin/charge excitation spectrum, superconducting order parameter. A generalized hidden order is proposed, and the corresponding string non-local order parameter is also calculated. The behavior of the string order parameter is discussed in the light of the entanglement spectrum.

Kazuki Hasebe; Keisuke Totsuka

2011-05-18

59

Molecular mechanics-valence bond method for planar conjugated hydrocarbon cations  

NASA Astrophysics Data System (ADS)

We present an extension of the molecular mechanics-valence bond (MMVB) hybrid method to study ground and excited states of planar conjugated hydrocarbon cations. Currently, accurate excited state calculations on these systems are limited to expensive ab initio studies of smaller systems: up to 15 active electrons in 16 ? orbitals with complete active space self-consistent field (CASSCF) theory using high symmetry. The new MMVB extension provides a faster, cheaper treatment to investigate larger cation systems with more than 24 active orbitals. Extension requires both new matrix elements and new parameters: In this paper we present both, for the limited planar case. The scheme is tested for the planar radical cations of benzene, naphthalene, anthracene, and phenanthrene. Calculated MMVB relative energies are in good agreement with CASSCF results for equilibrium geometries on the ground and first excited states, and conical intersections.

Hall, Katherine F.; Tokmachev, Andrei M.; Bearpark, Michael J.; Boggio-Pasqua, Martial; Robb, Michael A.

2007-10-01

60

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

PubMed Central

Metallo-dithiolene non-innocence is explored in an oxomolybdenum-bis(dithione) complex, [Mo4+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.

2013-01-01

61

Can aromaticity coexist with diradical character? An ab initio valence bond study of S2N2 and related 6?-electron four-membered rings E2N2 and E4(2+) (E=S, Se, Te).  

PubMed

A series of 6?-electron 4-center species, E(2)N(2) and E(4)(2+) (E=S, Se, Te) is studied by means of ab initio valence bond methods with the aims of settling some controversies on 1) the diradical character of these molecules and 2) the radical sites, E or N, of the preferred diradical structure. It was found that for all molecules, the cumulated weights of the two possible diradical structures are always important and close to 50 %, making these molecules comparable to ozone in terms of diradical character. While the two diradical structures are degenerate in the E(4)(2+) dications, they have on the contrary strongly unequal weights in the E(2)N(2) neutral molecules. In these three molecules, the electronic structure is dominated by one diradical structure, in which the radical sites are the two nitrogen atoms, while the other diradical structure is much less important. The ordering of the various VB structures in terms of their calculated weights is confirmed by the relative energies of individual VB structures. In all cases, the major diradical structure (or both diradical structures when they are degenerate) is (are) the lowest one(s), while the covalent VB structures lie higher in energy. The vertical resonance energies are considerable in S(2)N(2) and S(4)(2+), about 80 % of the estimated value for benzene, and diminish as one goes down the periodic table (S?Se?Te). This confirms the aromatic character of these species, as already demonstrated for S(2)N(2) on the basis of magnetic criteria. This and the high weights and stabilities of one or both diradical structures in all systems indicates that aromaticity and diradical character do not exclude each other, contrary to what is usually claimed. Furthermore, it is shown that the diradical structures find their place in a collective electron flow responsible for the ring currents in the ? system of these species. PMID:22275164

Braïda, Benoît; Lo, Aurélien; Hiberty, Philippe C

2012-02-01

62

The valence charge polarization induced by the shorter and stronger bonds between under-coordinated gold atoms  

Microsoft Academic Search

Relativistic density functional theory calculations have been conducted to examine the effect of atomic under-coordination. The calculated results agree exceedingly well with experimental observations: skin-depth bond contraction, chain end stats polarization, potential well depression, core level shift, and the valence charge polarization of gold nanostructures. Consistency between calculations and experimental observations affirms the prediction of the bond-order-length-strength (BOLS) correlation theory

Xi Zhang; Jer-lai Kuo; Mingxia Gu; Xiaofeng Fan; Ping Bai; Qing Gong Song; Chang Q Sun

2010-01-01

63

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

PubMed

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

Xu, Enhua; Li, Shuhua

2013-11-01

64

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

NASA Astrophysics Data System (ADS)

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

2013-11-01

65

A practical valence bond method: a configuration interaction method approach with perturbation theoretic facility.  

PubMed

The previously developed valence bond configuration interaction (VBCI) method (Wu, W.; Song, L.; Cao, Z.; Zhang, Q.; Shaik, S., J. Phys. Chem. A, 2002, 105, 2721) that borrows the general CI philosophy of the MO theory, is further extended in this article, and its methodological features are improved, resulting in three accurate and cost-effective procedures: (a) the effect of quadruplet excitation is incorporated using the Davidson correction, such that the new procedure reduces size consistency problems, with due improvement in the quality of the computational results. (b) A cost-effective procedure, named VBCI(D, S), is introduced. It includes doubly excited structures for active electrons and singly excited structures for inactive pairs. The computational results of VBCI(D, S) match those of VBCISD with much less computational effort than VBCISD. (c) Finally, a second-order perturbation theory is utilized as a means of configuration selection, and lead to considerable reduction of the computational cost, with little or no loss in accuracy. Applications of the new procedures to bond energies and barriers of chemical reactions are presented and discussed. PMID:14735567

Song, Lingchun; Wu, Wei; Zhang, Qianer; Shaik, Sason

2004-03-01

66

Finite-temperature valence-bond-solid transition of quantum spins in two dimensions  

NASA Astrophysics Data System (ADS)

The S=1/2 Heisenberg model on the 2D square lattice with four- or six-neighbor spin interactions (JQ model) hosts a quantum phase transition between Néel and valence-bond-solid (VBS) ground states. The deconfined quantum critical (DQC) point, predicted by the theory of Senthil et al.[1], may be realized in this model [2]. Here we study the finite-temperature phase transition between the VBS (Z4 symmetry breaking) to the paramagnetic state. We find continuously changing exponents with the correlation-length exponent ? close to the Ising value far from the T=0 critical point, and diverging when the critical temperature Tc->0^+. This is in accord with the DQC theory, according to which the transition for Tc->0^+ should approach a Kosterlitz-Thouless fixed point.[4pt] [1] T. Senthil, L. Balents, S. Sachdev, A. Vishwanath, and M. P. A. Fisher, Phys. Rev. B 70, 144407 (2004).[0pt] [2] R. K. Kaul, R. G. Melko, A. W. Sandvik, arXiv:1204.5405.

Jin, Songbo; Sandvik, Anders

2013-03-01

67

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

68

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

PubMed

Using the formulas and techniques developed in Papers I and II of this series, the recently developed second-order perturbation theory based on a valence bond self-consistent field reference function (VBPT2) has been extended by using the internally contracted correction wave function. This ansatz strongly reduces the size of the interaction space compared to the uncontracted wave function and thus improves the capability of the VBPT2 method dramatically. Test calculations show that internally contracted VBPT2 using only a small number of reference valence bond functions, can give results as accuracy as the VBPT2 method and other more sophisticated methods such as full configuration interaction and multireference configuration interaction. PMID:25296795

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

2014-10-01

69

The inseparability of resonating valence bond and on-site pairing long-range orders in doped Hubbard models  

Microsoft Academic Search

The concept of the resonating valence bond (RVB) state was originally proposed by Anderson (1987) for the ground state of the positive-U Hubbard model. However, the on-site pairing long-range order is expected to exist in the ground state of the negative-U Hubbard model and to be incompatible with the RVB order. In this article, we shall rigorously prove that, in

Guang-Shan Tian

1994-01-01

70

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

71

Physics of the resonating valence bond (pseudogap) state of the doped mott insulator: spin-charge locking.  

PubMed

The properties of the pseudogap phase above T(C) of the high-T(C) cuprate superconductors are described by showing that the Anderson-Nambu SU(2) spinors of a resonating valence bond spin gap "lock" to those of the electron charge system because of the resulting improvement of kinetic energy. This enormously extends the range of the vortex liquid state in these materials. A heuristic description of the nonlocal electrodynamics of this pseudogap-vortex liquid state is proposed. PMID:16486498

Anderson, P W

2006-01-13

72

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

73

Development of a bond-valence molecular-dynamics model for complex oxides Young-Han Shin, Valentino R. Cooper, Ilya Grinberg, and Andrew M. Rappe*  

E-print Network

, and the energy of 180° domain walls. The success of this simple and physically motivated model makes and covalent bonding. The development of a specific variant of this model for ferroelectric PbTiO3 PT and with experimental data. Bond-valence molecular dynamics BVMD simulations for PT show a ferroelectric transition

Rappe, Andrew M.

74

On the possibility of the observation of valence electron density for individual bonds in proteins in conventional difference maps.  

PubMed

In the last decade, high-resolution data have become available for macromolecular objects. Furthermore, ultrahigh-resolution diffraction data (resolution close to 0.6 A) have been collected for several protein crystals. This allows the study of fine details of the electron-density distribution such as the deformation density, i.e. the deviation of the experimentally determined electron density from the density composed of 'free' non-bonded atoms. This paper discusses the resolution and atomic temperature factors necessary to make the valence electron density visible at individual bonds in conventional difference maps for macromolecules. The study of theoretical maps calculated by quantum-chemistry methods allows estimation of these conditions; these results are confirmed by analysis of experimental maps for Leu-enkephalin and antifreeze protein RD1. A resolution limit close to 0.6 A was found to be highly important for refinement even when the maps were calculated at lower resolution. The refinement of the same models at near to 0.9 A resolution results in artificially increased values of the atomic displacement parameters and does not permit bond electron density to be visible in difference maps. To some extent, overestimation of the atomic displacement parameters may be restricted if dummy bond electrons are used in the refinement. PMID:14747702

Afonine, Pavel V; Lunin, Vladimir Y; Muzet, Nicolas; Urzhumtsev, Alexandre

2004-02-01

75

Liquids more stable than crystals in particles with limited valence and flexible bonds  

NASA Astrophysics Data System (ADS)

All liquids (except helium owing to quantum effects) crystallize at low temperatures, forming ordered structures. The competition between disorder, which stabilizes the liquid phase, and energy, which leads to a preference for the crystalline structure, inevitably favours the crystal when the temperature is lowered and entropy becomes progressively less relevant. The liquid state survives at low temperatures only as a glass, an out-of-equilibrium arrested state of matter. This textbook description holds inevitably for atomic and molecular systems, where particle interactions are set by quantum-mechanical laws. The question remains whether it holds for colloidal particles, where interparticle interactions are usually short-ranged and tunable. Here we show that for patchy colloids with limited valence, conditions can be found for which the liquid phase is stable even in the zero-temperature limit. Our results offer fresh cues for understanding the stability of gels and the glass-forming ability of molecular network glasses.

Smallenburg, Frank; Sciortino, Francesco

2013-09-01

76

Low-temperature spin dynamics of a valence bond glass in Ba2YMoO6  

NASA Astrophysics Data System (ADS)

We carried out ac magnetic susceptibility measurements and muon spin relaxation spectroscopy on the cubic double perovskite Ba2YMoO6, down to 50 mK. Below ?1 K the muon relaxation is typical of a magnetic insulator with a spin-liquid type ground state, i.e. without broken symmetries or frozen moments. However, the ac susceptibility revealed a dilute-spin-glass-like transition below ?1 K. Antiferromagnetically coupled Mo5+ 4d1 electrons in triply degenerate t2g orbitals are in this material arranged in a geometrically frustrated fcc lattice. Bulk magnetic susceptibility data has previously been interpreted in terms of a freezing to a heterogeneous state with non-magnetic sites where 4d1 electrons have paired in spin-singlets dimers, and residual unpaired Mo5+ 4d1 electron spins. Based on the magnetic heat capacity data it has been suggested that this heterogeneity is the result of kinetic constraints intrinsic to the physics of the pure system (possibly due to topological overprotection) leading to a self-induced glass of valence bonds between neighbouring 4d1 electrons. The muon spin relaxation (?SR) unambiguously points to a heterogeneous state with a static arrangement of unpaired electrons in a background of (valence bond) dimers between the majority of Mo5+ 4d electrons. The ac susceptibility data indicate that the residual magnetic moments freeze into a dilute-spin-glass-like state. This is in apparent contradiction with the muon-spin decoupling at 50 mK in fields up to 200 mT, which indicates that, remarkably, the time scale of the field fluctuations from the residual moments is ?5 ns. Comparable behaviour has been observed in other geometrically frustrated magnets with spin-liquid-like behaviour and the implications of our observations on Ba2YMoO6 are discussed in this context.

de Vries, M. A.; Piatek, J. O.; Misek, M.; Lord, J. S.; Rønnow, H. M.; Bos, J.-W. G.

2013-04-01

77

Valence bond diatomics-in-molecules (DIM) treatment of collinear interactions of Group IIa and IIb metal atoms with hydrogen halides: Application to the CaHCl system  

Microsoft Academic Search

A recently developed formulation of the semiempirical valence bond diatomics-in-molecules (DIM) method is applied to the study of collinear MHX systems, where M is a Group IIa or IIb metal atom and X is a halogen atom. In particular, ground and excited state potential energy surfaces for reactions involving the three collinear arrangements of Ca, H, and Cl are considered.

Alan D. Isaacson; James T. Muckerman

1980-01-01

78

Sodium hydrogen dipicolinate dipicolinic acid trihydrate: Synthesis, structure, and valence bond sums  

Microsoft Academic Search

The synthesis and crystal structure of sodium hydrogen dipicolinate dipicolinic acid trihydrate, NaHdipic · H2dipic · 3H2O,I, is reported. There is a hydrogen bonded H3(dipic)2- unit in which an Hdipic- ion functions as a tridentate chelate to the Na+ ion while the second H2dipic functions as a monodentate ligand and bridging unit. The Na+ ion is in the center of

Kim Browning; Khalil A. Abboud; Gus J. Palenik

1995-01-01

79

Bond valence sums in coordination chemistry. The calculation of the oxidation state of samarium in complexes containing samarium bonded only to oxygen.  

PubMed

A simple method is presented for calculating the oxidation state of Sm in complexes where Sm is bonded only to O ligands. A total of 88 SmO(n)() fragments with n = 4-12 were retrieved from the Cambridge Structural Database and were analyzed using the bond valence sum (BVS) method. New R(0) values for Sm(II)-O of 2.116(21) A and for Sm(III)-O of 2.055(13) A were derived. The average R(0) value of 2.086 A gives a good approximation of the oxidation state of the Sm ion, either +2 or +3, from the observed distances without any assumptions. The Sm-O distances for +2 and +3 complexes with coordination numbers of 4-11 are tabulated and reflect the requirement that the BVS must equal the oxidation state. The distances for CN = 12 were not included because of problems with the reported crystal structures. Several X-ray structure determinations where the BVS and the oxidation state did not agree are discussed. PMID:12691581

Palenik, Gus J

2003-04-21

80

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

PubMed

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

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

2014-04-21

81

Practical application of extended valence bond diatomic calculations to the method of diatomics-in-molecules for NeHe+2  

Microsoft Academic Search

Potential energy curves for the lowest two 2Sigma states and the lowest 2Pi state of NeHe+ were calculated using the valence bond method with minimal and extended basis sets. It is shown how this ab initio information, together with information on the He2, He+2, and NeHe molecules obtained from other sources, can be incorporated into a minimal basis diatomics-in-molecules (DIM)

J. Kendrick; P. J. Kuntz

1979-01-01

82

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.

83

Valence band and core-level photoemission of Au/Ge(001): Band mapping and bonding sites  

NASA Astrophysics Data System (ADS)

We have used photoemission spectroscopy in order to investigate the electronic states and chemical bonding related to Au induced atomic chains on the Ge(001) surface. Angle-resolved photoemission reveals two types of dispersions around the Fermi level whose intensities strongly depend on the incident photon energy. Around h? =100eV, the band structure is dominated by an electronlike band of mainly one-dimensional (1D) character, which shows Tomonaga-Luttinger-like power-law behavior in the k-integrated spectral function. In contrast, lower photon energies reveal a metallic holelike dispersion which resembles the Ge bulk structure with its heavy-hole, light-hole, and split-off branches. The Au 4f core-level spectra show two doublets indicating two different Au bonding sites, whereas the Ge 3d core-level shows two surface components and one bulk component.

Meyer, S.; Dudy, L.; Schäfer, J.; Blumenstein, C.; Höpfner, P.; Umbach, T. E.; Dollinger, A.; Cui, X. Y.; Patthey, L.; Claessen, R.

2014-09-01

84

Discrete iridium pyridonate chains with variable metal valence: nature and energetics of the Ir-Ir bonding from DFT calculations.  

PubMed

The structure of the Ir(I) complex [Ir2(mu-OPy)2(CO)4] (Opy = 2-pyridonate) has been fully characterized in its head-to-head (A) configuration as a "dimer of dimers" AA in which two binuclear complexes are connected by means of a weak, but unsupported, iridium-iridium interaction (Ir(2)...Ir(2A) 2.9808(6) A). The head-to-tail isomer, referred to as B, was found in equilibrium with A in solution. It has been shown that this complex can be oxidized by diiodine to give iridium chains with highly selective configurations and general formula I-[Ir2(mu-OPy)2(CO)4]n-I (n = 1-3). The synthesis of IAI (1), of the isomers IAAI (2AA) and IABI (2AB), and of IABAI (3) is reported. DFT calculations have been carried out on A and B and on the known isomers of 1-3, as well as on two isomers of the hypothetic chain of eight Ir(1.25) atoms corresponding to n = 4. The stability of the metal chain is assigned to a 2-electron/2n-center sigma bond delocalized along the metal backbone and supplemented with a weak attractive interaction of the metallophilic type. Calculations confirm that further oxidation of the Ir chains corresponding to n > 1 by iodine, yielding the cleavage of one or two unsupported bond(s), is a highly exothermic process. The formation of the I-[Ir2(mu-OPy)2(CO)4]n-I chains is also computed to be exothermic, either highly for n = 1 or still significantly for n = 2 and 3. At variance with these results, the formation of an octanuclear chain is predicted to be no more than marginally exothermic (DeltaG = 1.7 kcal.mol(-1)), mainly because of interligand strain induced by the steric bulk of the amidate rings. PMID:16156611

Villarroya, B Eva; Tejel, Cristina; Rohmer, Marie-Madeleine; Oro, Luis A; Ciriano, Miguel A; Bénard, Marc

2005-09-19

85

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

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 [Formula: see text] 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

86

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

87

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

SciTech Connect

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

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

1986-01-01

88

Mercury Nozzle Status V.B. Graves  

E-print Network

Mercury Nozzle Status V.B. Graves Hg Jet Design Meeting Princeton University Nov 15, 2004 #12;OAK RIDGE NATIONAL LABORATORY U. S. DEPARTMENT OF ENERGY Hg Jet Design Meeting ­ 15 Nov 2004 Nozzle ­ 15 Nov 2004 Design Issues · Desire mechanically attached nozzle for changeout during cold testing

McDonald, Kirk

89

Spectroscopic constants of diatomic molecules computed correcting Hartree-Fock or general-valence-bond potential-energy curves with correlation-energy functionals  

NASA Astrophysics Data System (ADS)

The Kohn-Sham energy with exact exchange [using the exact Hartree-Fock (HF) exchange but an approximate correlation-energy functional] may be computed very accurately by adding the correlation obtained from the HF density to the total HF energy. Three density functionals are used: local spin density (LSD), LSD with self-interaction correction, and LSD with generalized gradient correction. This scheme has been extended (Lie-Clementi, Colle-Salvetti, and Moscardo-San-Fabian) to be used with general-valence-bond (GVB) energies and wave functions, so that the extra correlation included in the GVB energy is not counted again. The effect of all these approximate correlations on HF or GVB spectroscopic constants (Re,?e, and De) is studied. Approximate relations showing how correlation affects them are derived, and may be summarized as follows: (1) the effect on Re and ?e depends only on the correlation derivative at Re, and (2) the effect on De depends mainly on the correlation difference between quasidissociated and equilibrium geometries. A consequence is that all the correlation corrections tested here give larger ?e and De and shorter Re than the uncorrected HF or GVB values. This trend is correct for De for both HF and GVB. For Re and ?e, it is correct in most cases for GVB, but it often fails for the HF cases. A comparison is made with Kohn-Sham calculations with both exchange and correlation approximated. As a final conclusion, it is found that, within the present scheme, a qualitatively correct HF or GVB potential-energy curve, together with a correlation-energy approximation with correct dissociation behavior, is crucial for obtaining good estimates of spectroscopic constants.

Pérez-Jordá, José M.; San-Fabián, Emilio; Moscardó, Federico

1992-04-01

90

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

NASA Astrophysics Data System (ADS)

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

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

2008-11-01

91

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

92

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...

93

The valence band structure of AgxRh1-x alloy nanoparticles  

NASA Astrophysics Data System (ADS)

The valence band (VB) structures of face-centered-cubic Ag-Rh alloy nanoparticles (NPs), which are known to have excellent hydrogen-storage properties, were investigated using bulk-sensitive hard x-ray photoelectron spectroscopy. The observed VB spectra profiles of the Ag-Rh alloy NPs do not resemble simple linear combinations of the VB spectra of Ag and Rh NPs. The observed VB hybridization was qualitatively reproduced via a first-principles calculation. The electronic structure of the Ag0.5Rh0.5 alloy NPs near the Fermi edge was strikingly similar to that of Pd NPs, whose superior hydrogen-storage properties are well known.

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

2014-10-01

94

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

PubMed

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

Mitoraj, Mariusz P; Michalak, Artur

2013-11-01

95

Bi-Zn bond formation in liquid ammonia solution: [Bi-Zn-Bi]4-, a linear polyanion that is iso(valence)-electronic to CO2.  

PubMed

Reactions of the zinc(I) complex [Zn2(Mesnacnac)2] (Mesnacnac = [(2,4,6-Me3C6H2)NC(Me)]2CH) with solid K3Bi2 dissolved in liquid ammonia yield crystals of the compound K4[ZnBi2]?(NH3)12 (1), which contains the molecular, linear heteroatomic [Bi-Zn-Bi](4-) polyanion (1?a). This anion represents the first example of a three-atomic molecular ion of metal atoms being iso(valence)-electronic to CO2 and being synthesized in solution. The analogy of the discrete [Bi-Zn-Bi](4-) anion and the polymeric ?(1)[(ZnBi4/2)(4-)] unit to monomeric CO2 and polymeric SiS2 is rationalized. PMID:24989142

Benda, Christian B; Köchner, Tobias; Schäper, Raphaela; Schulz, Stephan; Fässler, Thomas F

2014-08-18

96

Levels of Valence  

PubMed Central

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

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

2013-01-01

97

X-ray photoelectron investigation of the valence-band electronic structure of superconducting Y-Ba-Cu oxide  

Microsoft Academic Search

The valence-band electronic structure of single-phase YBaâCuâOââ\\/sub delta\\/ orthorhombic (superconducting) and tetragonal (nonsuperconducting) materials was studied at room temperature using x-ray photoelectron spectroscopy. The valence-band (VB) data have very clearly resolved spectral features and appear to yield more information than the core-level spectra which are hybrid states of combined Cu 2p, Cu 3d, and O 2p states. The difference in

M. Frommer

1988-01-01

98

X-ray photoelectron investigation of the valence-band electronic structure of superconducting Y-Ba-Cu oxide  

Microsoft Academic Search

The valence-band electronic structure of single-phase YBa2Cu3O7-delta orthorhombic (superconducting) and tetragonal (nonsuperconducting) materials was studied at room temperature using x-ray photoelectron spectroscopy. The valence-band (VB) data have very clearly resolved spectral features and appear to yield more information than the core-level spectra which are hybrid states of combined Cu 2p, Cu 3d, and O 2p states. The difference in the

M. H. Frommer

1988-01-01

99

Nodeless valence (pseudo)spinors.  

PubMed

Atomic calculations using small-core relativistic effective core potentials (RECPs) explicitly treating outer core electrons are used to define two-component nodeless valence spinors (NVSs) and nodeless valence pseudospinors (NVPSs). Errors attributable to nonlocal electron repulsion interactions that arise from large-core RECPs are shown to result from the inherent arbitrariness in the choice of match points and number of derivatives that define shape-consistent pseudospinors, as well as the positions of radial nodes that reside in the outer core regions of atoms. Self-consistent field calculations in omegaomega-coupling for InH and InCl using RECPs derived from NVSs and NVPSs are reported. Increased bond distances relative to those calculated using very-large-core RECPs for In agree with those due to frozen 4d(3/2) and 4d(5/2) spinors and a small-core RECP. Results for AmCl+2 also reveal that the shortening in the bond length is recovered when the very-large-core RECP is derived using nodeless valence (pseudo)spinors. PMID:11206384

Ermler, W C; Marino, M M

2001-01-01

100

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

NASA Astrophysics Data System (ADS)

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

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

2008-05-01

101

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

102

VB2004 DELEGAVB2004 DELEGAVB2004 DELEGAVB2004 DELEGAVB2004 DELEGATE PACKTE PACKTE PACKTE PACKTE PACK Dear VB2004 delegate,  

E-print Network

, followed by dinner and entertainment. Dress code: VB invites delegates to attend this event in black tie and Friday 1 October. Partners' meal requirements will be billed separately by Virus Bulletin. Please's business and financial district and the world renowned shopping area along the Magnificent Mile

Solworth, Jon A.

103

582 J. Am. Chem. SOC.1986, 108, 582-584 Theoretical Studies of Transition-Metal Hydrides. 1. Bond  

E-print Network

: We present here consistent ab initio calculations (generalized valence bond plus configuration calculations involve all-electron ab initio wave functions with a basis consistingof an optimized valence calculation was a generalized valence bond (GVB) wave function with the valence bond spin eigenfunction [GVB

Goddard III, William A.

104

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

105

Mixed-valence manganites  

Microsoft Academic Search

Mixed-valence manganese oxides (R1-x Ax)MnO3 (R=rare-earth cation, A=alkali or alkaline earth cation), with a structure similar to that of perovskite CaTiO3, exhibit a rich variety of crystallographic, electronic and magnetic phases. Historically they led to the formulation of new physical concepts such as double exchange and the Jahn-Teller polaron. More recent work on thin films has revealed new phenomena, including

J. M. D. Coey

1999-01-01

106

Theoretical Chemistry of The 7p Series of Superheavy Elements II. The Relativistic Molecular Orbital and Kappa Valence Methods  

Microsoft Academic Search

The relativistic generalizations of both molecular orbital and spin-valence (the Kappa valence method) theories are used to investigate the covalent bonds that can be formed by the ground relativistic configuration of a heavy element containing a non-closed subshell of {p} or p valence electrons. Both theories predict that {p}-H and p-H bonds are not greatly weakened compared with normal covalent

N. C. Pyper

1982-01-01

107

Electronic configuration and bond energy  

Microsoft Academic Search

Conclusions  The original interpretation of the method of molecular orbitals as a theory of valency, in which the single electron possesses\\u000a bonding power was based on the assumption that non-premoted electrons are bonding and premoted ones are anti-bonding or non-bonding.\\u000a This assumption is not the outcome of any requirements of theory but is an empirical postulate, which seeks justification\\u000a in experimental

R. K. Asundi; R. Samuel

1936-01-01

108

Mixed-valence manganites  

NASA Astrophysics Data System (ADS)

Mixed-valence manganese oxides (R1-x Ax)MnO3 (R=rare-earth cation, A=alkali or alkaline earth cation), with a structure similar to that of perovskite CaTiO3, exhibit a rich variety of crystallographic, electronic and magnetic phases. Historically they led to the formulation of new physical concepts such as double exchange and the Jahn-Teller polaron. More recent work on thin films has revealed new phenomena, including colossal magnetoresistance near the Curie temperature, dense granular magnetoresistance and optically-induced magnetic phase transitions. This review gives an account of the literature on mixed-valence manganites, placing new results in the context of established knowledge of these materials, and other magnetic semiconductors. Issues addressed include the nature of the electronic ground states, the metal-insulator transition as a function of temperature, pressure and applied magnetic field, the electronic transport mechanisms, dielectric and magnetic polaron formation, magnetic localization, the role of cation disorder and the Jahn-Teller effect. Sample preparation, and the properties of related ferromagnetic oxides are also discussed.

Coey, J. M. D.

1999-03-01

109

Lattice Dynamics of Black Phosphorus. I. Valence Force Field Model  

Microsoft Academic Search

Calculation of the lattice dynamical properties of black phosphorus, which is a narrow-gap covalent semiconductor with a layered structure, based on the valence force field model is presented. The results obtained are in good agreement with the experiments, except for infrared active optical modes. The results are discussed in connection with the crystal structure and the chemical-bonding nature of black

Chioko Kaneta; Hiroshi Katayama-Yoshida; Akira Morita

1986-01-01

110

Micro-Valences: Perceiving Affective Valence in Everyday Objects  

PubMed Central

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

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

2012-01-01

111

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

112

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

PubMed

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

Danovich, David; Shaik, Sason

2014-02-18

113

A Role of myosin Vb and Rab11-FIP2 in the aquaporin-2 shuttle.  

PubMed

Arginine-vasopressin (AVP) regulates water reabsorption in renal collecting duct principal cells. Its binding to Gs-coupled vasopressin V2 receptors increases cyclic AMP (cAMP) and subsequently elicits the redistribution of the water channel aquaporin-2 (AQP2) from intracellular vesicles into the plasma membrane (AQP2 shuttle), thereby facilitating water reabsorption from primary urine. The AQP2 shuttle is a paradigm for cAMP-dependent exocytic processes. Using sections of rat kidney, the AQP2-expressing cell line CD8, and primary principal cells, we studied the role of the motor protein myosin Vb, its vesicular receptor Rab11, and the myosin Vb- and Rab11-binding protein Rab11-FIP2 in the AQP2 shuttle. Myosin Vb colocalized with AQP2 intracellularly in resting and at the plasma membrane in AVP-treated cells. Rab11 was found on AQP2-bearing vesicles. A dominant-negative myosin Vb tail construct and Rab11-FIP2 lacking the C2 domain (Rab11-FIP2-DeltaC2), which disrupt recycling, caused condensation of AQP2 in a Rab11-positive compartment and abolished the AQP2 shuttle. This effect was dependent on binding of myosin Vb tail and Rab11-FIP2-DeltaC2 to Rab11. In summary, we identified myosin Vb as a motor protein involved in AQP2 recycling and show that myosin Vb- and Rab11-FIP2-dependent recycling of AQP2 is an integral part of the AQP2 shuttle. PMID:17156409

Nedvetsky, Pavel I; Stefan, Eduard; Frische, Sebastian; Santamaria, Katja; Wiesner, Burkhard; Valenti, Giovanna; Hammer, John A; Nielsen, Søren; Goldenring, James R; Rosenthal, Walter; Klussmann, Enno

2007-02-01

114

Mixed Valence Niobium  

NASA Astrophysics Data System (ADS)

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

Keating, Steven James

1992-01-01

115

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

E-print Network

methods (generalized valence bond/configuration interaction). The electronic-state spectrum reveals five is nucleophilic and the other electrophilic. A series of generalized valence bond (GVB) studies on high- oxidation have the form 6 with a covalent metal-carbon double bond 6 involving a s bond composed of one electron

Goddard III, William A.

116

Photoelectron Spectra and Valence Shell Orbital Structures of Groups V and VI Hydrides  

Microsoft Academic Search

Photoelectron spectra are reported for the hydrides of group V and VI elements. Vibrational structure has been observed in bands associated with all but the inner-most valence orbitals. It has been used to obtain changes in bond angles or bond distances which result from the ionization of successive molecular orbitals. Ionization from the inner (1a1) orbitals of the hydrides has

A. W. Potts; W. C. Price

1972-01-01

117

Covalent Bonding in Ammonia from Several Perspectives Frank Rioux  

E-print Network

Covalent Bonding in Ammonia from Several Perspectives Frank Rioux College of St. Benedict and St-quantum approach to chemical bonding was stimulated in part by the observation that half the elements types of valence electrons - three equivalent bonding pairs and one non-bonding pair. Unfortunately

Rioux, Frank

118

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

NASA Astrophysics Data System (ADS)

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

Mudd, J. J.; Lee, Tien-Lin; Muñoz-Sanjosé, V.; Zúñiga-Pérez, J.; Payne, D. J.; Egdell, R. G.; McConville, C. F.

2014-04-01

119

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

120

CNDO\\/2 and INDO all-valence-electron calculations on the dipole moment of iodine compounds  

Microsoft Academic Search

An application of the semi-empirical CNDO\\/2 and INDO methods to calculate the molecular dipole moment of iodine compounds\\u000a has been made with all-valence electron scheme. Equilibrium geometries are obtained using experimental bond lengths and the\\u000a various semi-empirical parameters required inscf-mo scheme are obtained from atomic Hartree-Fock calculations and by comparison withab initio calculations. Bothsp andspd valence basis sets are used.

V. Santhanam; J. Sobhanadri

1985-01-01

121

Electronegativity and the Bond Triangle  

ERIC Educational Resources Information Center

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

Meek, Terry L.; Garner, Leah D.

2005-01-01

122

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

NASA Astrophysics Data System (ADS)

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

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

2010-04-01

123

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

PubMed Central

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

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

2012-01-01

124

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

Code of Federal Regulations, 2013 CFR

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

2013-07-01

125

30 CFR 57.22218 - Seals and stoppings (III, V-A, and V-B mines).  

...NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Safety Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22218 Seals and stoppings (III, V-A, and V-B mines)....

2014-07-01

126

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

127

Crossover and valence band K? X-rays of chromium oxides  

NASA Astrophysics Data System (ADS)

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

Fazini?, Stjepko; Mandi?, Luka; Kav?i?, Matjaž; Boži?evi?, Iva

2011-06-01

128

Electronic States of Aminonitrene (1,l-Diazine). A Study of the Endwise Bonding of Dinitrogenla  

E-print Network

using generalized valence bond (GVB) and configuration interaction (GVB-CI) wave functions. We find-Fock (HF), generalized valence bondlo (GVB), and configuration interaction (GVB-CI) calculations on both7111 Electronic States of Aminonitrene (1,l-Diazine). A Study of the Endwise Bonding

Goddard III, William A.

129

Valence quarks and $k_T$ factorisation  

E-print Network

We study in the $k_T$ factorisation framework jet production at LHC energies. In particular we are interested in valence quark and gluon initiated jets. The calculation of the relevant hard matrix element is presented. A CCFM like evolutionequation for valence quark distribution is solved and the cross section for valence quark and gluon initiated process is calculated using Monte Carlo event generator CASCADE.

Michal Deák; Hannes Jung; Krzysztof Kutak

2008-07-15

130

Asymptotic analysis of steady solutions of the KdVB equation with application to resonant sloshing  

NASA Astrophysics Data System (ADS)

The forced Korteweg-de Vries equation with Burgers’ damping (fKdVB) on a periodic domain, which arises as a model for water waves in a shallow tank with forcing near resonance, is considered. A method for construction of asymptotic solutions is presented, valid in cases where dispersion and damping are small. Through variation of a detuning parameter, families of resonant solutions are obtained providing detailed insight into the resonant response character of the system and allowing for direct comparison with the experimental results of Chester and Bones (1968).

Amundsen, D. E.; Cox, E. A.; Mortell, M. P.

2007-11-01

131

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

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

132

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

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

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

135

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

136

UV photoelectron spectroscopy at near ambient pressures: mapping valence band electronic structure changes from Cu to CuO.  

PubMed

Valence band (VB) changes and hence electronic structure evolution was directly observed with low kinetic energy (KE) electrons at near ambient pressure (NAP) conditions with He I photon source in a custom built laboratory ambient pressure photoelectron spectrometer (Lab-APPES). Polycrystalline Cu surfaces were gradually oxidized in O2 to Cu2O, to a mixture of Cu2O + CuO, and finally to CuO between 300 and 625 K and at NAP. Typical VB features for Cu, Cu2O, and CuO were observed, and the results corroborate well with core level and Auger spectral changes. High mean free path associated with low KE electrons, very low or no inelastic scattering, and effective pumping and the design of electrostatic lens regime help to minimize the electron attenuation at NAP conditions. The present results extend the capabilities of the APPES tool to explore the in situ evolution of electronic structure of materials at NAP and high temperatures. PMID:24601627

Roy, Kanak; Gopinath, Chinnakonda S

2014-04-15

137

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

...2014-07-01 false Actions at 0.25 percent methane (I-B, II-B, V-B, and VI mines...NONMETAL MINES Safety Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22231 Actions at 0.25 percent methane (I-B, II-B, V-B, and VI...

2014-07-01

138

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

...2014-07-01 false Actions at 2.0 percent methane (I-B, II-B, V-B, and VI mines...NONMETAL MINES Safety Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22238 Actions at 2.0 percent methane (I-B, II-B, V-B, and VI...

2014-07-01

139

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

140

From Vicious Walkers to TASEP. T.C. Dorlas, A.M. Povolotsky, V.B. Priezzhev  

E-print Network

From Vicious Walkers to TASEP. T.C. Dorlas, A.M. Povolotsky, V.B. Priezzhev August 7, 2008 Abstract and the vicious walkers model. We calculate the survival probability for this model and obtain the scaling we mention two of them. The first one is the vicious walkers (VW) model that has been introduced

Dorlas, Teunis C.

141

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

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

2014-07-01

142

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

143

Three-body and one-body channels of the Auger core-valence-valence decay: A simplified approach  

E-print Network

approximation, one can assume that the valence electrons remain frozen during the core ioniza- tion, and in the initial state of the Auger decay the valence configuration is the same as in the ground state. The intraThree-body and one-body channels of the Auger core-valence-valence decay: A simplified approach

Marini, Andrea

144

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

145

The bondons: the quantum particles of the chemical bond.  

PubMed

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

Putz, Mihai V

2010-01-01

146

Size-consistent wave functions for nondynamical correlation energy: The valence active space optimized orbital coupled-cluster  

E-print Network

as the difference between full configuration interaction within the space of all valence orbitals and a single of the other elec- trons. The mean-field model describes chemical bonding by a single electronic configuration there are two electronic configurations, ( )2 and ( *)2 , that equally contribute to the wave function of two

Krylov, Anna I.

147

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

148

Mixed Valence and Spin Fluctuations in Cerium  

NASA Astrophysics Data System (ADS)

The pseudobinary alloys Ce(Ni(,x)Co(,1-x))(,2), (Ce(,x)La(,1-x))Ni(,2) and (Ce(,x)Y(,1-x))Ni(,2), where 0 < x < 1, have been studied. The room temperature lattice constant, the magnetic susceptibility in the 6 to 300 K temperature range, the low temperature specific heat in the 0.4 to 25 K range and the electrical resistivity in the 0.4 to 300 K range were measured. Additionally, X -ray absorption around L(,3) edge has been studied using the synchroton radiation. Both, thermodynamic and L(,3) probes yield similar results for the changes of valence of Ce across these systems. We have established that Ce is in the saturated valence state in the Ce(Ni(,x)Co(,1 -x))(,2) for x < 0.25. The valence decreases with x in the 0.25 to 1 concentration range. Similarly, the valence of Ce decreases in the (Ce, Y)Ni(,2) systems upon substitution of Y for Ce. The results obtained for the (Ce(,x)La(,1 -x))Ni(,2) system are interpreted in terms of changes of the Ce('3+) impurity levels. Spin fluctuations due to the 3d electrons play an important role in these systems.

Andraka, Bohdan

149

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

150

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

PubMed

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

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

2014-05-19

151

Precision calculations of atoms with few valence electrons  

Microsoft Academic Search

We discuss the possibility of using pair-equations for the construction of the effective Hamiltonian $H_{\\\\rm eff}$ for valence electrons of an atom. The low-energy part of atomic spectrum is found by solving the eigenvalue problem for $H_{\\\\rm eff}$. In this way it is possible to account efficiently for the valence-valence and core-valence correlations. We tested this method on a toy

M G Kozlov

2003-01-01

152

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

153

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

PubMed

Microvillus inclusion disease (MVID) is a severe form of congenital diarrhea that arises from inactivating mutations in the gene encoding myosin Vb (MYO5B). We have examined the association of mutations in MYO5B and disruption of microvillar assembly and polarity in enterocytes. Stable MYO5B knockdown (MYO5B-KD) in CaCo2-BBE cells elicited loss of microvilli, alterations in junctional claudins, and disruption of apical and basolateral trafficking; however, no microvillus inclusions were observed in MYO5B-KD cells. Expression of WT MYO5B in MYO5B-KD cells restored microvilli; however, expression of MYO5B-P660L, a MVID-associated mutation found within Navajo populations, did not rescue the MYO5B-KD phenotype but induced formation of microvillus inclusions. Microvilli establishment required interaction between RAB8A and MYO5B, while loss of the interaction between RAB11A and MYO5B induced microvillus inclusions. Using surface biotinylation and dual immunofluorescence staining in MYO5B-KD cells expressing mutant forms of MYO5B, we observed that early microvillus inclusions were positive for the sorting marker SNX18 and derived from apical membrane internalization. In patients with MVID, MYO5B-P660L results in global changes in polarity at the villus tips that could account for deficits in apical absorption, loss of microvilli, aberrant junctions, and losses in transcellular ion transport pathways, likely leading to the MVID clinical phenotype of neonatal secretory diarrhea. PMID:24892806

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

2014-07-01

154

Entropically patchy particles: engineering valence through shape entropy.  

PubMed

Patchy particles are a popular paradigm for the design and synthesis of nanoparticles and colloids for self-assembly. In "traditional" patchy particles, anisotropic interactions arising from patterned coatings, functionalized molecules, DNA, and other enthalpic means create the possibility for directional binding of particles into higher-ordered structures. Although the anisotropic geometry of nonspherical particles contributes to the interaction patchiness through van der Waals, electrostatic, and other interactions, how particle shape contributes entropically to self-assembly is only now beginning to be understood. The directional nature of entropic forces has recently been elucidated. A recently proposed theoretical framework that defines and quantifies directional entropic forces demonstrates the anisotropic-that is, patchy-nature of these emergent, attractive forces. Here we introduce the notion of entropically patchy particles as the entropic counterpart to enthalpically patchy particles. Using three example "families" of shapes, we show how to modify entropic patchiness by introducing geometric features to the particles via shape operations so as to target specific crystal structures assembled here with Monte Carlo simulations. We quantify the emergent entropic valence via a potential of mean force and torque. We show that these forces are on the order of a few kBT at intermediate densities below the onset of crystallization. We generalize these shape operations to shape anisotropy dimensions, in analogy with the anisotropy dimensions introduced for enthalpically patchy particles. Our findings demonstrate that entropic patchiness and emergent valence provide a way of engineering directional bonding into nanoparticle systems, whether in the presence or absence of additional, non-entropic forces. PMID:24359081

van Anders, Greg; Ahmed, N Khalid; Smith, Ross; Engel, Michael; Glotzer, Sharon C

2014-01-28

155

Valence anion of thymine in the DNA pi-stack.  

PubMed

Most of theoretical data on the stability of radical anions supported by nucleic acid bases have been obtained for anions of isolated nucleobases, their nucleosides, or nucleotides. This approach ignores the hallmark forces of DNA, namely, hydrogen bonding and pi-stacking interactions. Since these interactions might be crucial for the electron affinities of nucleobases bound in DNA, we report for the first time on the stability of the thymine valence anion in trimers of complementary bases possessing the regular B-DNA geometry but differing in base sequence. In order to estimate the energetics of electron attachment to a trimer, we developed a thermodynamic cycle employing all possible two-body interaction energies in the neutral and anionic duplex as well as the adiabatic electron affinity of isolated thymine. All calculations were carried out at the MP2 level of theory with the aug-cc-pVDZ basis set. The two-body interaction energies were corrected for the basis set superposition error, and in benchmark systems, they were extrapolated to the basis set limit and supplemented with correction for higher order correlation terms calculated at the CCSD(T) level. We have demonstrated that the sequence of nucleic bases has a profound effect on the stability of the thymine valence anion: the anionic 5'-CTC-3' (6.0 kcal/mol) sequence is the most stable configuration, and the 5'-GTG-3' (-8.0 kcal/mol) trimer anion is the most unstable species. On the basis of obtained results, one can propose DNA sequences that are different in their vulnerability to damage by low energy electron. PMID:18954049

Koby?ecka, Monika; Leszczynski, Jerzy; Rak, Janusz

2008-11-19

156

Triple-pomeron dynamics: valence vs. glue  

E-print Network

Three pomerons are known to couple via the gluon loop and interactions of this kind which are responsible for high-mass diffraction are described in terms of the gluonic structure function of the QCD pomeron. We show that the triple-pomeron coupling via the light quark loop associated with the ``valence'' in the pomeron is of the same strength as the purely gluonic coupling. The large $Q^2$ behavior of this new contribution is described by the DLLA evolution from the non-perturbative $f\\bar f$ valence state of the pomeron. Numerical estimates of the high-mass diffraction structure functions based on the consistent account of both couplings are in good agreement with experimental data.

V. R. Zoller

2004-12-28

157

Pion Valence-quark Parton Distribution Function  

E-print Network

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

Lei Chang; Anthony W. Thomas

2014-10-30

158

Correlated topological insulators with mixed valence.  

PubMed

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

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

2013-03-01

159

Pattern classification of valence in depression?  

PubMed Central

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

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

2013-01-01

160

Mixed valence/dipole-bound dianions  

SciTech Connect

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

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

1999-12-01

161

Valence skipping driven superconductivity and charge Kondo effect  

NASA Astrophysics Data System (ADS)

Valence skipping in metallic compounds can give rise to an unconventional superconductivity. Several elements in the periodic table show valence skipping (or valence missing), for example, Bi forms the compounds in valence states +3 and +5. The doping of valence skipping elements will induce superconductivity and this will lead to a possibility of high temperature superconductivity. We consider the Wolf model with negative-U impurities, and show a phase diagram including superconducting phase. The superconducting state is changed into a metallic state with a local singlet as the attractive interaction |U| increases. There is a high temperature region near the boundary.

Yanagisawa, Takashi; Hase, Izumi

2013-11-01

162

Formation of an unconventional Ag valence state in Ag2NiO2  

NASA Astrophysics Data System (ADS)

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

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

2007-05-01

163

Hydrogen bond connectivity in jennite from ab initio simulations  

SciTech Connect

The protonation scheme and the hydrogen bond connectivity in the structure of jennite were investigated by ab initio molecular dynamics simulations. The calculated statistics of hydrogen bonds at ambient conditions is consistent with the protonation scheme proposed by Bonaccorsi et al. (2004) based on the bond valence theory. The protons in the system are associated with the {identical_to}2Ca-OH linkage and H{sub 2}O molecules. The dangling Si-O bond on the bridging tetrahedra is de-protonated. The proton dynamics revealed in the molecular dynamic simulations explains the apparent discrepancies in the NMR and X-ray diffraction studies of jennite.

Churakov, Sergey V. [Paul Scherrer Institut, Laboratory for Waste Management, CH-5232 Villigen PSI (Switzerland)], E-mail: sergey.churakov@psi.ch

2008-12-15

164

Barrier-free proton transfer in the valence anion of 2'-deoxyadenosine-5'-monophosphate. II. A computational study.  

PubMed

The propensity of four representative conformations of 2(')-deoxyadenosine-5(')-monophosphate (5(')-dAMPH) to bind an excess electron has been studied at the B3LYP6-31++G(d,p) level. While isolated canonical adenine does not support stable valence anions in the gas phase, all considered neutral conformations of 5(')-dAMPH form adiabatically stable anions. The type of an anionic 5(')-dAMPH state, i.e., the valence, dipole bound, or mixed (valence/dipole bound), depends on the internal hydrogen bond(s) pattern exhibited by a particular tautomer. The most stable anion results from an electron attachment to the neutral syn-south conformer. The formation of this anion is associated with a barrier-free proton transfer triggered by electron attachment and the internal rotation around the C4(')-C5(') bond. The adiabatic electron affinity of the a_south-syn anion is 1.19 eV, while its vertical detachment energy is 1.89 eV. Our results are compared with the photoelectron spectrum (PES) of 5(')-dAMPH(-) measured recently by Stokes et al., [J. Chem. Phys. 128, 044314 (2008)]. The computational VDE obtained for the most stable anionic structure matches well with the experimental electron binding energy region of maximum intensity. A further understanding of DNA damage might require experimental and computational studies on the systems in which purine nucleotides are engaged in hydrogen bonding. PMID:18247957

Koby?ecka, Monika; Gu, Jiande; Rak, Janusz; Leszczynski, Jerzy

2008-01-28

165

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

166

Unusual valency and magnetic order in silver nickelates  

NASA Astrophysics Data System (ADS)

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

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

2007-03-01

167

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

168

Valence electron momentum distributions in zinc  

Microsoft Academic Search

The valence 4s electron momentum distribution in zinc has been measured using EMS at a total energy of 1000 eV. It is in good agreement with the momentum distributions given by the Hartree-Fock 4s wavefunction. The (3d)-1 cross section has also been measured and excitation of the 3d10 4p(2P1\\/22P3\\/2) ion states is observed, showing the importance of the 3d10 4p2

A.-M. Grisogono; J. Mitroy; R. Pascual; G. Stefani; E. Weigold

1988-01-01

169

Involvement of cytochrome c oxidase subunits Va and Vb in the regulation of cancer cell metabolism by Bcl-2.  

PubMed

Bcl-2 has been shown to promote survival of cancer cells by maintaining a slight pro-oxidant state through elevated mitochondrial respiration during basal conditions. On oxidative stress, Bcl-2 moderates mitochondrial respiration through cytochrome c oxidase (COX) activity to prevent an excessive buildup of reactive oxygen species (ROS) by-production from electron transport activities. However, the underlying molecular mechanism(s) of Bcl-2-mediated ROS regulation and its impact on carcinogenesis remain unclear. In this study, we show that Bcl-2 expression positively influences the targeting of nuclear-encoded COX Va and Vb to the mitochondria of cancer cells. In addition, evidence is presented in support of a protein-protein interaction between COX Va and Bcl-2, involving the BH2 domain of Bcl-2. Interestingly, episodes of serum withdrawal, glucose deprivation or hypoxia aimed at inducing early oxidative stress triggered Bcl-2-overexpressing cells to preserve mitochondrial levels of COX Va while depressing COX Vb, whereas the reverse was observed in mock-transfected cells. The unique manner in which Bcl-2 adjusted COX subunits during these physiological stress triggers had a profound impact on the resultant decrease in COX activity and maintenance of mitochondrial ROS levels, thus delineating a novel mechanism for the homeostatic role of Bcl-2 in the redox biology and metabolism of cancer cells. PMID:19834492

Chen, Z X; Pervaiz, S

2010-03-01

170

Electron correlations and chemical bonds in aggregates of monovalent elements. A poor man's description  

E-print Network

and its approximations. 1.1 DIMERS. - For a dimer of hydrogen atoms with valence electrons in Is orbitals93 Electron correlations and chemical bonds in aggregates of monovalent elements. A poor man limit, we analyse the role of electron interactions and correlations on the nature of bonding

Boyer, Edmond

171

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

172

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

173

Valence modulations in CeRuSn  

NASA Astrophysics Data System (ADS)

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

Feyerherm, R.; Dudzik, E.; Prokeš, K.; Mydosh, J. A.; Huang, Y.-K.; Pöttgen, R.

2014-07-01

174

Calculations of energy levels for atoms with several valence electrons  

Microsoft Academic Search

A new ab initio method for doing high-accuracy calculations for atoms with more than one valence electron is described. An effective Hamiltonian\\u000a for the valence electrons is formed using many body perturbation theory for the residual core-valence interaction. The configuration\\u000a interaction method is used then to find the energy levels of the atom. Application to thallium shows that this method

V. A. Dzuba; V. V. Flambaum; M. G. Kozlov

1996-01-01

175

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

Microsoft Academic Search

Several structural features, including electron transfer between atoms of different electronegativity, oxygen deficiency, and unsynchronized resonance of valence bonds, as well as tight binding of atoms and the presence of both hypoelectronic and hyperelectronic elements, cooperatre to confer metallic properties and high-temperature superconductivity on compounds such as (Sr,Ba,Y,La)2CuO4-y. .AE

Linus Pauling

1987-01-01

176

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

177

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

PubMed

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

Lu, Yuhui; Lent, Craig

2011-09-01

178

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

179

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

NASA Astrophysics Data System (ADS)

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

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

2009-03-01

180

Ab initio calculation of the KRb dipole moments S. Kotochigova, P. S. Julienne, and E. Tiesinga  

E-print Network

, USA Received 2 April 2003; published 11 August 2003 The relativistic configuration interaction valence dipole moments of the 1,3 electronic states of the KRb ground configuration, which dissociate to the K(4s of in- ternuclear separation R, using an ab initio configuration in- teraction valence-bond VB method 10

Kotochigova, Svetlana

181

The bonding electron density in aluminum.  

PubMed

Aluminum is considered to approach an "ideal" metal or free electron gas. The valence electrons move freely, as if unaffected by the presence of the metal ions. Therefore, the electron redistribution due to chemical bonding is subtle and has proven extremely difficult to determine. Experimental measurements and ab initio calculations have yielded substantially different results. We applied quantitative convergent-beam electron diffraction to aluminum to provide an experimental determination of the bonding electron distribution. Calculation of the electron distribution based on density functional theory is shown to be in close agreement. Our results yield an accurate quantitative correlation between the anisotropic elastic properties of aluminum and the bonding electron and electrostatic potential distributions. PMID:21436448

Nakashima, Philip N H; Smith, Andrew E; Etheridge, Joanne; Muddle, Barrington C

2011-03-25

182

Robustness of Quantum Criticality of Valence Fluctuations  

NASA Astrophysics Data System (ADS)

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

Watanabe, Shinji; Miyake, Kazumasa

2013-08-01

183

Excited states of the water molecule: Analysis of the valence and Rydberg character  

NASA Astrophysics Data System (ADS)

The excited states of the water molecule have been analyzed by using the extended quantum-chemical multistate CASPT2 method, namely, MS-CASPT2, in conjunction with large one-electron basis sets of atomic natural orbital type. The study includes 13 singlet and triplet excited states, both valence and 3s-, 3p-, and 3d-members of the Rydberg series converging to the lowest ionization potential and the 3s- and 3p-Rydberg members converging to the second low-lying state of the cation, 1A12. The research has been focused on the analysis of the valence or Rydberg character of the low-lying states. The computation of the 1B11 state of water at different geometries indicates that it has a predominant 3s-Rydberg character at the equilibrium geometry of the molecule but it becomes progressively a valence state described mainly by the one-electron 1b1?4a1 promotion, as expected from a textbook of general chemistry, upon elongation of the O-H bonds. The described valence-Rydberg mixing is established to be originated by a molecular orbital (MO) Rydbergization process, as suggested earlier by R. S. Mulliken [Acc. Chem. Res. 9, 7 (1976)]. The same phenomenon occurs also for the 1A21 state whereas a more complex behavior has been determined for the 2A11 state, where both MO Rydbergization and configurational mixing take place. Similar conclusions have been obtained for the triplet states of the molecule.

Rubio, Mercedes; Serrano-Andrés, Luis; Merchán, Manuela

2008-03-01

184

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

Code of Federal Regulations, 2013 CFR

...percent methane (I-B, II-B, V-B, and VI mines). 57.22238 Section 57.22238 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH...

2013-07-01

185

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

Code of Federal Regulations, 2011 CFR

...I-B, II-A, II-B, IV, V-B, and VI mines). 57.22232 Section 57.22232 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH...

2011-07-01

186

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

Code of Federal Regulations, 2011 CFR

...I-B, I-C, II-A, III, V-A, and V-B mines). 57.22202 Section 57.22202 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH...

2011-07-01

187

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

Code of Federal Regulations, 2010 CFR

...I-B, I-C, II-A, III, V-A, and V-B mines). 57.22202 Section 57.22202 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH...

2010-07-01

188

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

Code of Federal Regulations, 2012 CFR

...I-B, II-A, II-B, IV, V-B, and VI mines). 57.22232 Section 57.22232 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH...

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

Code of Federal Regulations, 2013 CFR

...percent methane (I-B, II-B, V-B, and VI mines). 57.22231 Section 57.22231 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH...

2013-07-01

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

Code of Federal Regulations, 2012 CFR

...methane (I-A, I-B, III, V-A, and V-B mines). 57.22234 Section 57.22234 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH...

2012-07-01

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

Code of Federal Regulations, 2010 CFR

...percent methane (I-B, II-B, V-B, and VI mines). 57.22231 Section 57.22231 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH...

2010-07-01

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

Code of Federal Regulations, 2011 CFR

...methane (I-A, I-B, III, V-A, and V-B mines). 57.22234 Section 57.22234 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH...

2011-07-01

193

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

Code of Federal Regulations, 2010 CFR

...I-B, II-A, II-B, IV, V-B, and VI mines). 57.22232 Section 57.22232 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH...

2010-07-01

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

Code of Federal Regulations, 2011 CFR

...percent methane (I-B, II-B, V-B, and VI mines). 57.22231 Section 57.22231 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH...

2011-07-01

195

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

Code of Federal Regulations, 2010 CFR

...methane (I-A, I-B, III, V-A, and V-B mines). 57.22234 Section 57.22234 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH...

2010-07-01

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

Code of Federal Regulations, 2012 CFR

...percent methane (I-B, II-B, V-B, and VI mines). 57.22238 Section 57.22238 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH...

2012-07-01

197

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

Code of Federal Regulations, 2013 CFR

...methane (I-A, I-B, III, V-A, and V-B mines). 57.22234 Section 57.22234 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH...

2013-07-01

198

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

Code of Federal Regulations, 2013 CFR

...I-B, I-C, II-A, III, V-A, and V-B mines). 57.22202 Section 57.22202 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH...

2013-07-01

199

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

Code of Federal Regulations, 2011 CFR

...percent methane (I-B, II-B, V-B, and VI mines). 57.22238 Section 57.22238 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH...

2011-07-01

200

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

Code of Federal Regulations, 2010 CFR

...percent methane (I-B, II-B, V-B, and VI mines). 57.22238 Section 57.22238 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH...

2010-07-01

201

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

Code of Federal Regulations, 2012 CFR

...percent methane (I-B, II-B, V-B, and VI mines). 57.22231 Section 57.22231 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH...

2012-07-01

202

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

Code of Federal Regulations, 2013 CFR

...I-B, II-A, II-B, IV, V-B, and VI mines). 57.22232 Section 57.22232 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH...

2013-07-01

203

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

Code of Federal Regulations, 2012 CFR

...I-B, I-C, II-A, III, V-A, and V-B mines). 57.22202 Section 57.22202 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH...

2012-07-01

204

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

205

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

206

High resolution conversion electron spectroscopy of valence electron configurations  

Microsoft Academic Search

Measurements of conversion electrons from the outermost valence shells of ion implanted, dilute impurity probe atoms in solids are reported. The measured spectra are directly related to the local density and angular momentum character of the occupied electron states at the probe atom. Thus the valence electron configuration of implanted probe atoms in solids has been investigated. First results for

Jon Wulff Petersen; Gerd Weyer; Eugen Holzschuh; Walter Kundig

1990-01-01

207

EMOTIONAL VALENCE CATEGORIZATION USING HOLISTIC IMAGE FEATURES V. Yanulevskaya,  

E-print Network

, trained by ground truth from psychology studies. The train- ing data contains emotional valences scoredEMOTIONAL VALENCE CATEGORIZATION USING HOLISTIC IMAGE FEATURES V. Yanulevskaya, J.C. van Gemert, K, The Netherlands # University Clinic of Bonn Department of Medical Psychology Bonn, Germany ABSTRACT Can a machine

Geusebroek, Jan-Mark

208

EMOTIONAL VALENCE CATEGORIZATION USING HOLISTIC IMAGE FEATURES V. Yanulevskaya,  

E-print Network

, trained by ground truth from psychology studies. The train- ing data contains emotional valences scoredEMOTIONAL VALENCE CATEGORIZATION USING HOLISTIC IMAGE FEATURES V. Yanulevskaya, J.C. van Gemert, A, The Netherlands # University Clinic of Bonn Department of Medical Psychology Bonn, Germany ABSTRACT Can a machine

Sebe, Nicu

209

Gaussian basis sets of quadruple zeta valence quality for atoms H-Kr  

NASA Astrophysics Data System (ADS)

We present Gaussian basis sets of quadruple zeta valence quality with a segmented contraction scheme for atoms H to Kr. This extends earlier work on segmented contracted split valence (SV) and triple zeta valence (TZV) basis sets. Contraction coefficients and orbital exponents are fully optimized in atomic Hartree-Fock (HF) calculations. As opposed to other quadruple zeta basis sets, the basis set errors in atomic ground-state HF energies are less than 1 mEh and increase smoothly across the Periodic Table, while the number of primitives is comparably small. Polarization functions are taken partly from previous work, partly optimized in atomic MP2 calculations, and for a few cases determined at the HF level for excited atomic states nearly degenerate with the ground state. This leads to basis sets denoted QZVP for HF and density functional theory (DFT) calculations, and for some atoms to a larger basis recommended for correlated treatments, QZVPP. We assess the performance of the basis sets in molecular HF, DFT, and MP2 calculations for a sample of diatomic and small polyatomic molecules by a comparison of energies, bond lengths, and dipole moments with results obtained numerically or using very large basis sets. It is shown that basis sets of quadruple zeta quality are necessary to achieve an accuracy of 1 kcal/mol per bond in HF and DFT atomization energies. For compounds containing third row as well as alkaline and earth alkaline metals it is demonstrated that the inclusion of high-lying core orbitals in the active space can be necessary for accurate correlated treatments. The QZVPP basis sets provide sufficient flexibility to polarize the core in those cases. All test calculations indicate that the new basis sets lead to consistent accuracies in HF, DFT, or correlated treatments even in critical cases where other basis sets may show deficiencies.

Weigend, Florian; Furche, Filipp; Ahlrichs, Reinhart

2003-12-01

210

Charge Fluctuations and the Valence Transition in Yb under Pressure  

SciTech Connect

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

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

2009-04-21

211

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

212

Basics of Fidelity Bonding.  

ERIC Educational Resources Information Center

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

Kahn, Steven P.

213

Evaluative Conditioning Induces Changes in Sound Valence  

PubMed Central

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

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

2012-01-01

214

Chemistry of Materials 1989, 1,83-101 How C-C Bonds Are Formed and How They Influence  

E-print Network

properties. In the UC2structure, both uranium-carbon bonding and carbon-carbon bonding are enhanced upon,has a substantialgap between the valence and conduction bands. The pairingof carbon atoms in Dy, with late transition-metal elements. Early transition-metal carbides of the same composition do not exist

Li, Jing

215

Precision calculations of atoms with few valence electrons  

Microsoft Academic Search

We discuss the possibility of using pair-equations for the construction of\\u000athe effective Hamiltonian $H_{\\\\rm eff}$ for valence electrons of an atom. The\\u000alow-energy part of atomic spectrum is found by solving the eigenvalue problem\\u000afor $H_{\\\\rm eff}$. In this way it is possible to account efficiently for the\\u000avalence-valence and core-valence correlations. We tested this method on a toy

M. G. Kozlov

2004-01-01

216

Valence band anticrossing in GaBixAs1-x  

SciTech Connect

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

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

2007-07-11

217

PHYSICAL REVIEW B 88, 104102 (2013) Reinterpretation of the bond-valence model with bond-order formalism: An improved  

E-print Network

phase transitions19 and domain wall motion in PbTiO3,20 as well as the structure and dynamics. INTRODUCTION The use of ferroelectric perovskite oxides in a variety of technological applications has prompted

Rappe, Andrew M.

218

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

219

A Valence Isomer Trapping Procedure for Introductory Organic Laboratory.  

ERIC Educational Resources Information Center

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

Kurtz, David W.; Johnson, Richard P.

1989-01-01

220

Differential impact of beliefs on valence and arousal  

PubMed Central

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

Nicolle, Antoinette; Goel, Vinod

2012-01-01

221

Mn 3s exchange splitting in mixed-valence manganites.  

SciTech Connect

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

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

2002-03-15

222

Crystal Chemistry and Properties of Mixed Valence Copper Oxides  

Microsoft Academic Search

The role played by the mixed valence of oxides of transition elements in the metal-like properties is well known since the discovery of the sodium tungsten bronzes NaâWOâ by Hagg and Magneli. The synthesis of mixed valence copper oxides with metal-like properties has opened the route to the discovery of superconductivity at high temperature in the LaâCuOâ-type family. The chemistry

B. Raveau; C. Michel

1989-01-01

223

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

224

Emotional Valence and the Free-Energy Principle  

PubMed Central

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

Joffily, Mateus; Coricelli, Giorgio

2013-01-01

225

Core-valence correlations for atoms with open shells  

E-print Network

We present an efficient method of inclusion of the core-valence correlations into the configuration interaction (CI) calculations. These correlations take place in the core area where the potential of external electrons is approximately constant. A constant potential does not change the core electron wave functions and Green's functions. Therefore, all operators describing interaction of $M$ valence electrons and $N-M$ core electrons (the core part of the Hartree-Fock Hamiltonian $V^{N-M}$, the correlation potential $\\hat\\Sigma_1({\\bf r},{\\bf r'},E)$ and the screening of interaction between valence electrons by the core electrons $\\hat\\Sigma_2$) may be calculated with all $M$ valence electrons removed. This allows one to avoid subtraction diagrams which make accurate inclusion of the core-valence correlations for $M>2$ prohibitively complicated. Then the CI Hamiltonian for $M$ valence electrons is calculated using orbitals in complete $V^{N}$ potential (the mean field produced by all electrons); $\\hat\\Sigma_1...

Dzuba, V A

2007-01-01

226

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

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

2014-07-01

227

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

E-print Network

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

Carrasco, Marisa

228

Syntheses, crystal structures, and bond valence sum analyses of lanthanide complexes with a planar pentadentate ligand  

Microsoft Academic Search

The syntheses and X-ray crystal structures of the Eu, Gd, Dy, Ho, and Er nitrate complexes of the pentadentate ligand 2,6-diacetylpyridine bis acetic acid hydrazone, or H2dapaah, are reported. The complexes can be divided into 3 groups depending on the number of water molecules per metal ion. The Ln·4H2O complexes with Eu, Gd and Dy are isomorphous, with the Ln

Ruth C. Palenik; Khalil A. Abboud; Stephen P. Summers; Laurel L. Reitfort; Gus J. Palenik

2006-01-01

229

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

230

Extending first principles modeling with crystal chemistry: a bond-valence based classical  

E-print Network

such as domain wall shifting, ion transport, and doping and vacancy effects. In addition, DFT is a zero functional theory (DFT) calculations can be constructed to study complex ferroelectric oxides. This model variety of complex oxides are used as ferroelectric materials in modern technol- ogy. These materials

Rappe, Andrew M.

231

Diffusion Bonding of Metals.  

National Technical Information Service (NTIS)

The need to reduce the cost and weight of aerospace metallic structures has led to increased interest in solid state and liquid phase diffusion bonding processes, especially in combination with superplastic forming. The bonding mechanisms and bonding tech...

P. G. Partridge

1989-01-01

232

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

233

Combined configuration-superposition and many-particle perturbation calculations for atoms with two valence electrons  

E-print Network

valence electrons M. G. Kozlov and S. G. Porsev*) B. P. Konstantinov St. Petersburg Institute of Nuclear with two valence electrons. An effective Hamiltonian for the valence electrons is formulated by many- particle perturbation theory with respect to the residual interaction of the valence electrons

Kozlov, Mikhail G

234

Design-atom approach for the QM/MM covalent boundary: A design-carbon atom with five valence electrons  

PubMed Central

A critical issue underlying the accuracy and applicability of the combined quantum mechanical/molecular mechanical (QM/MM) methods is how to describe the QM/MM boundary across covalent bonds. Inspired by the ab initio pseudo-potential theory, here we introduce a novel design-atom approach for a more fundamental and transparent treatment of this QM/MM covalent boundary problem. The main idea is to replace the boundary atom of the active part with a design-atom, which has a different number of valence electrons but very similar atomic properties. By modifying the Troullier-Martins scheme, which has been widely employed to construct norm-conserving pseudo-potentials for density functional calculations, we have successfully developed a design-carbon atom with five valence electrons. Tests on a series of molecules yield very good structural and energetic results, and indicate its transferability in describing a variety of chemical bonds, including double and triple bonds. PMID:17902888

Xiao, Chuanyun; Zhang, Yingkai

2009-01-01

235

Surface mixed valence in Sm and SmB/sub 6/  

SciTech Connect

Surface-sensitive photoelectron measurements reveal bulk-to-surface shifts of the Sm 4f/sup 6/ level which imply inhomogeneous valence mixing on the surface of Sm and SmB/sub 6/. The surface valence fraction is estimated to be the same for both materials. The measurements take advantage of a large resonant enhancement of 4f electron emission due to 4d ..-->.. 4f photon absorption, and detailed spectra showing this phenomena are presented. It is shown that the 4d hole in the 4d ..-->.. 4f absorption process stabilizes the 4f state by approx. 4 --7 eV. Exposure of Sm films to oxygen is found to eliminate, rather than increase, the emission from the surface 4f/sup 6/ state, showing that the 4f/sup 6/ state does not arise from oxygen contamination. Observed variations in Sm film spectra are described, including the finding in some films of an unexplained photoemission peak 2.4 eV below the Fermi level. SmB/sub 6/ also displays a broad band of Auger emission when a boron 1s core hole is created, and this is ascribed to electrons in the boron 2p bonding band. Various trends in 4d and 4f binding energies for Sm and SmB/sub 6/ are pointed out and discussed.

Allen, J.W.; Johansson, L.I.; Lindau, I.; Hagstroem, S.B.

1980-02-15

236

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

PubMed Central

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

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

2013-01-01

237

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

238

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

239

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

240

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

241

Core-valence correlations for atoms with open shells  

SciTech Connect

We present an efficient method of inclusion of the core-valence correlations into the configuration interaction (CI) calculations. These correlations take place in the core area where the potential of external electrons is approximately constant. A constant potential does not change the core electron wave functions and Green's functions. Therefore, all operators describing interaction of M valence electrons and N-M core electrons [the core part of the Hartree-Fock Hamiltonian V{sup N-M}, the correlation potential {sigma}{sub 1}(r,r{sup '},E), and the screening of interaction between valence electrons by the core electrons {sigma}{sub 2}] may be calculated with all M valence electrons removed. This allows one to avoid subtraction diagrams which make accurate inclusion of the core-valence correlations for M>2 prohibitively complicated. Then the CI Hamiltonian for M valence electrons is calculated using orbitals in complete V{sup N} potential (the mean field produced by all electrons); {sigma}{sub 1}+{sigma}{sub 2} are added to the CI Hamiltonian to account for the core-valence correlations. We calculate {sigma}{sub 1} and {sigma}{sub 2} using many-body perturbation theory in which dominating classes of diagrams are included in all orders. We use neutral Xe I and all positive ions up to Xe VIII as a testing ground. We found that the core electron density for all these systems is practically the same. Therefore, we use the same {sigma}{sub 1} and {sigma}{sub 2} to build the CI Hamiltonian in all these systems (M=1,2,3,4,5,6,7,8). Good agreement with experiment for energy levels and Lande factors is demonstrated for all cases from Xe I to Xe VIII.

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

2007-05-15

242

Reaction of Li/Cl phosphinidenoid complexes with a phosphite substituted ketone: access to complexes with a novel mixed-valence polycyclic P,C-ligand system.  

PubMed

Reaction of Li/Cl phosphinidenoid pentacarbonyltungsten(0) complexes 2a,b (R = CH(SiMe3)2, Cp*) with bifunctional phosphite-substituted ketone 3 yielded tungsten complexes 4a,b having a novel mixed-valence polycyclic P,C-cage ligand with a P–P bond. DFT calculations provide insight into an unusual product formation pathway. PMID:23760069

Abdrakhmanova, Liliya; Espinosa, Arturo; Streubel, Rainer

2013-08-01

243

Kbeta\\/Kalpha X-Ray Intensity Ratio Studies on the Valence Electronic States of 3d-Transition Metals in Some of Their Compounds  

Microsoft Academic Search

Our studies on Kbeta\\/Kalpha X-ray intensity ratios of some of the technologically important 3d-transition metal compounds have been reviewed. Comparison of the experimental results with single-configuration Dirac-Fock calculations provided important information on the valence states of the transition metals in various compounds, which can be helpful in understanding the nature of bonding in the compounds.

F. Pawlowski; M. Polasik; S. Raj; H. C. Padhi

2000-01-01

244

Cobalt lawsone complexes: searching for new valence tautomers.  

PubMed

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

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

2013-04-21

245

Space-Valence Priming with Subliminal and Supraliminal Words  

PubMed Central

To date it is unclear whether (1) awareness-independent non-evaluative semantic processes influence affective semantics and whether (2) awareness-independent affective semantics influence non-evaluative semantic processing. In the current study, we investigated these questions with the help of subliminal (masked) primes and visible targets in a space-valence across-category congruence effect. In line with (1), we found that subliminal space prime words influenced valence classification of supraliminal target words (Experiment 1): classifications were faster with a congruent prime (e.g., the prime “up” before the target “happy”) than with an incongruent prime (e.g., the prime “up” before the target “sad”). In contrast to (2), no influence of subliminal valence primes on the classification of supraliminal space targets into up- and down-words was found (Experiment 2). Control conditions showed that standard masked response priming effects were found with both subliminal prime types, and that an across-category congruence effect was also found with supraliminal valence primes and spatial target words. The final Experiment 3 confirmed that the across-category congruence effect indeed reflected priming of target categorization of a relevant meaning category. Together, the data jointly confirmed prediction (1) that awareness-independent non-evaluative semantic priming influences valence judgments. PMID:23439863

Ansorge, Ulrich; Khalid, Shah; Konig, Peter

2013-01-01

246

Could 2003 VB12 (Sedna) Have Formed In Situ Within A Massive, Disk-Like Extension of the Kuiper Belt?  

NASA Astrophysics Data System (ADS)

The discovery of the large (H=1.7) distant object, 2003 VB12, aka Sedna (Brown, Trujillo, and Rabinowitz 2004), is exciting on several grounds, not the least of which are the implications of its large size (D 2000 km) and distant, excited orbit (q 76 AU, a 532 AU, i 12 deg, e 0.86). Sedna's highly eccentric orbit clearly suggests it has been severely dynamically disturbed since its accretion, which must have occurred with e 0 and i 0. Early commentary on Sedna's origin (e.g., Brown et al., 2004; Morbidelli & Levison 2004) has centered on a formation location at <50 AU, with transport to the present orbit having resulted from a strong scattering event by a massive planet or a nearby star. Here I examine the viability of an alternate, in situ accretion (e.g., near 76 or 500 AU, Sedna's q and a) scenario, which would have been followed by dynamical evolution to the present orbit. Consider first a ``primordial formation" scenario taking 100-300 Myr, consistent with current accretion model results in the Kuiper Belt (e.g., Stern & Colwell 1997; Kenyon 2002). Doing so, we estimate that as little as 10 Earth masses of solids could have been required in a disk stretching from 70 to 100 AU region to produce Sedna-scale objects. If however Sedna formed in a very wide disk extending from 70 to 500 AU, then a significantly less plausible outer disk mass of 80-240 Earth masses in solids is implied. The implications of these results, which would require a more extended and massive Kuiper Disk, reminiscent of some broad extrasolar disks 100s of AU in extent, will be discussed.

Stern, S. A.

2004-05-01

247

2-Electron 3-Atom Bond in Side-on (n2) Uranyl (V) Superoxo Complexes  

SciTech Connect

Theoretical calculations suggest a novel two-electron three-atom bonding scheme for complexation of O2 with U(V) compounds, leading to the stabilization of superoxo complexes in the side-on (?2) configuration. This binding motif is likely to play an important role in the oxidative processes involving trans-uranium compounds having valence 5ff electrons.

V. S. Bryantsev; W. A. de Jong; K. C. Cossel; M. S. Diallo; W. A. Goddard III; G. S. Groenewold; W. Chien; M. J. Stipdonk

2008-07-01

248

Chemical Bonding: The Classical Description sharing or transferring electrons between atoms  

E-print Network

Chemical Bonding: The Classical Description sharing or transferring electrons between atoms LEWIS electron dot diagram -> formula (SF6) VSEPR (valence-shell electron-pair repulsion) theory Molecular Structure (w/o quantum mechanics) Chapter. 3 Two or more atoms approach -> their electrons interact and form

Ihee, Hyotcherl

249

Weak morphology dependent valence band structure of boron nitride  

NASA Astrophysics Data System (ADS)

We report a hard X-ray photoelectron spectroscopy (HX-PES) investigation on valence band structure of Boron Nitrides (BN) having different morphologies, including nanosheets, nanotubes, and micro-sized particles. Very weak morphology/valence band structure dependence was observed. For each case, the B-N ?-band overlapping with ?-band between 0 to -12.5 eV and the s-band below -15 eV were identified. No obvious morphology-induced band shifts and intensity variations were observed. First-principles calculations based on density functional theory were performed and the results were compared with the experimental data. This theoretical analysis well explains the weak morphology dependent valence band spectra of BN nanomaterials obtained during HX-PES measurements.

Zhi, Chunyi; Ueda, Shigenori; Zeng, Haibo; Wang, Xuebin; Tian, Wei; Wang, Xi; Bando, Yoshio; Golberg, Dmitri

2013-08-01

250

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.

251

Valence-differential spectroscopy of Co-Fe cyanide films  

NASA Astrophysics Data System (ADS)

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

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

2009-03-01

252

LET'S BOND! A Chemical Bonding Webquest  

NSDL National Science Digital Library

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

Hicken, Mrs.

2009-04-08

253

Investing in Bonds.com  

NSDL National Science Digital Library

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

254

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

255

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

256

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

PubMed

Theoretical studies about reaction mechanisms are usually limited to the determination of the energetic paths that connect reactants, transition states, and products. Recently, our group proposed the structural evolution, which has provided insights about the molecular structure changes occurring along a reaction path. Structural evolution may be defined as the development of a chemical reaction system across the partitioning of the nuclear configuration space into a finite number of structural regions defined on account of the topology of a scalar field, e.g., the electron density. In this paper, we present a tool to investigate within the framework of the Quantum Theory of Atoms in Molecules the evolvement of the Valence Shell Charge Concentration, the VSCC evolution, which is the description of the changes of electron density concentrations and depletions around the bonding area of an atom. The VSCC evolution provides supplementary information to the structural evolution because it allows the analysis of valence shells within a structural region, i.e., a subset of R(Q) with the same connectivity among the atoms forming a molecule. This new approach constitutes also a complement to the Valence-Shell Electron Pair Repulsion (VSEPR) model because it gives an account of the adjustments of electron pairs in the valence shell of an atom across a chemical reaction. The insertion reaction in the hydroformylation reaction of ethylene, the reduction of cyclohexanone with lithium aluminum hydride, the oxidation of methanol with chlorochromate, and the bimolecular nucleophilic substitution of CH(3)F with F(-) are used as representatives examples of the application of the VSCC evolution. Overall, this paper shows how the VSCC evolution through an analysis of the modifications of local charge concentrations and depletions in individual steps of a chemical reaction gives new insights about these processes. PMID:21923082

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

2011-11-17

257

Paradigms and Plastic Facts in the History of Valence.  

ERIC Educational Resources Information Center

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

Zavaleta, David

1988-01-01

258

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

259

Affective valence of words impacts recall from auditory working memory  

Microsoft Academic Search

There is limited evidence on the influence of affective stimuli on auditory working memory. The reported study investigated whether emotional auditory words interfere with ongoing auditory processing of words in auditory working memory. On each trial, words with negative, neutral, and positive affective valence were simultaneously presented on three different speakers. Participants recalled the word presented from the centre speaker

Fumiko Gotoh

2012-01-01

260

Affective valence of words impacts recall from auditory working memory  

Microsoft Academic Search

There is limited evidence on the influence of affective stimuli on auditory working memory. The reported study investigated whether emotional auditory words interfere with ongoing auditory processing of words in auditory working memory. On each trial, words with negative, neutral, and positive affective valence were simultaneously presented on three different speakers. Participants recalled the word presented from the centre speaker

Fumiko Gotoh

2011-01-01

261

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

2014-06-11

262

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

263

Effective valence proton numbers for nuclei with Z˜64  

NASA Astrophysics Data System (ADS)

The subshell effect for nuclei with proton number Z˜ 64 has been known for many years. The most economic way to consider this effect is to use the effective valence proton number. In this Brief Report we extract effective valence proton numbers for nuclei in this region by using the systematics of the first 2+ energies (E21+) of even-even nuclei, the ratios of the first 4+ and 6+ state energies with respect to E21+ (R4 and R6), the B(E2) values, the quadrupole deformation parameters e2, and anomalous g factors of the 21+ state for even-even nuclei. It is noticed that these physical quantities saturate when NpNn, the product of the valence proton number and the valence neutron number, is large enough; on the other hand, they go to saturation at different “speeds.” We show that the subshell effect is more evident for E21+ and yrast state energy ratios (R4 and R6), and relatively less for other quantities.

Fu, G. J.; Jiang, H.; Zhao, Y. M.; Arima, A.

2011-09-01

264

The Magnetic Interaction of a Valence Electron with Inner Shells  

Microsoft Academic Search

The magnetic interaction terms between two electrons are well known. By using antisymmetric wave functions the diagonal terms of the energy matrix for this interaction are calculated for an electronic configuration consisting of a valence electron and a closed shell. From the diagonal elements the doublet separation is easily obtained by applying the energy sum rule. The direct integrals, that

M. H. Johnson; G. Breit

1933-01-01

265

Intermediate valence in Yb Intermetallic compounds Jon Lawrence  

E-print Network

ion model: Two nearly-degenerate localized configurations form hybridized w.f.: a [4f13(5d6s)3> + b [4 configurations: conduction electrons hop on and off the 4f impurity orbital. Hybridization strength = V2 where1 Intermediate valence in Yb Intermetallic compounds Jon Lawrence University of California, Irvine

Lawrence, Jon

266

Reduction in switching current using a low-saturation magnetization Co-Fe-(Cr, V)B free layer in MgO-based magnetic tunnel junctions  

Microsoft Academic Search

Magnetic properties, magnetoresistance (MR), and spin-transfer switching of magnetic tunnel junctions having a structure of Co60Fe20B20 3 nm\\/MgO 1 nm\\/(Co75Fe25)80-XCr(V)XB20 2 nm (X=0-25) were investigated. Magnetization of the (Co-Fe)-(Cr, V)-B free layer decreased from 1.2 T before substitution to 0.6 T at Cr of 10% (0.8 T at V of 10%). The MR ratio and a resistance-area product (RA) before

Hitoshi Kubota; Akio Fukushima; Kay Yakushiji; Satoshi Yakata; Shinji Yuasa; Koji Ando; Mikihiko Ogane; Yasuo Ando; Terunobu Miyazaki

2009-01-01

267

A Common Eurozone Bond  

Microsoft Academic Search

Introduction\\u000aThe sovereign bond yields of the Eurozone, or more correctly the euro area, have since the introduction of the Euro undergone a bond yield compression. However, as can be seen in table 1, these bond yields started to diverge considerably around mid 2008 following the recent financial crisis and increased sovereign risk. Yields on Greek, Irish, and Portuguese bond

Erik Welin

2010-01-01

268

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

269

Making and Breaking Bonds  

NSDL National Science Digital Library

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

Consortium, The C.

2011-12-11

270

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

271

Chemical bonding between uranium and oxygen in U 6+-containing compounds  

NASA Astrophysics Data System (ADS)

Electronic parameters of a suite of hexavalent uranium compounds measured with X-ray photoelectron spectroscopy (XPS) have been collected. The binding energy difference, ?BE = BE (O 1s) - BE (U 4f 7/2), was used to characterize the valence electron transfer on the formation of the U-O bonds. The chemical bonding effects were considered on the basis of published structural and XPS data for U 6+-bearing compounds. An empirical relationship is obtained between ?BE and the mean U-O bond distance, L(U-O).

Atuchin, Victor V.; Zhang, Zhaoming

2012-01-01

272

Porous cobalt, nitrogen-codoped carbon nanostructures from carbon quantum dots and VB12 and their catalytic properties for oxygen reduction.  

PubMed

The porous cobalt, nitrogen-codoped carbon materials (Co/N/C) were synthesized by a facile one-step pyrolysis of vitamin B12 (VB12) and carbon quantum dots (CQDs). Varying the initial mass ratio of CQDs and VB12 leads to controllable concentrations of Co (0% to 3.68%) and N (0% to 5.88%) after pyrolysis. The obtained Co/N/C was evaluated by oxygen reduction reaction (ORR) in both alkaline and acid media. Particularly, the Co/N/C with 1.12% Co and 2.92% N prepared at 700 °C (Co1.12/N2.92/C-700) exhibited the best catalytic ability for ORR with a cathodic peak at -0.165 and 0.185 V (vs. SCE) in 0.1 M KOH and 0.1 M HClO4 solution, respectively, which are comparable to that of Pt/C (20%). The Co1.12/N2.92/C-700 also showed long-term stability and high methanol tolerance, which outperformed commercial Pt/C (20%). PMID:25338313

Yang, Yanmei; Liu, Juan; Han, Yuzhi; Huang, Hui; Liu, Naiyun; Liu, Yang; Kang, Zhenhui

2014-12-14

273

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

274

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

PubMed Central

We discuss a spectroscopic method to determine the character of chemical bonding and for the identification of metal ligands in coordination and bioinorganic chemistry. It is based on the analysis of satellite lines in x-ray emission spectra that arise from transitions between valence orbitals and the metal ion 1s level (valence-to-core XES). The spectra, in connection with calculations based on density functional theory (DFT), provide information that is complementary to other spectroscopic techniques, in particular x-ray absorption (XANES and EXAFS). The spectral shape is sensitive to protonation of ligands and allows ligands, which differ only slightly in atomic number (e.g. C, N, O...), to be distinguished . A theoretical discussion of the main spectral features is presented in terms of molecular orbitals for a series of Mn model systems: [Mn(H2O)6]2+, [Mn(H2O)5OH]+, [Mn(H2O)5NH2]+ and [Mn(H2O)5NH3]2+. An application of the method, with comparison between theory and experiment, is presented for solvated Mn2+ ion in water and three Mn coordination complexes, namely [LMn(acac)N3]BPh4, [LMn(B2O3Ph2)(ClO4)] and [LMn(acac)N]BPh4 where L represents 1,4,7-trimethyl-1,4,7-triazacyclononane, acac stands for the 2,4-pentanedionate anion and B2O3Ph2 represents the 1,3-diphenyl-1,3-dibora-2-oxapropane-1,3-diolato dianion. PMID:19663435

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

2009-01-01

275

Configuration interaction calculation of the specific mass shift for atoms with few valence electrons.  

E-print Network

Configuration interaction calculation of the specific mass shift for atoms with few valence use valence configuration interaction method to calculate specific mass shift for several atoms and ions with few valence electrons. Note: This is a work sheet and by no means a draft of the paper. I

Kozlov, Mikhail G

276

On the binding of electrons to nitromethane: Dipole and valence bound anions  

E-print Network

On the binding of electrons to nitromethane: Dipole and valence bound anions R. N. Comptona) and H when the molecule possesses a lower energy valence anion configuration as well as a dipole-bound state valence and dipole-bound anions of the nitromethane molecule are studied using negative ion photoelectron

Simons, Jack

277

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

278

Superatom-atom super-bonding in metallic clusters: a new look to the mystery of an Au20 pyramid.  

PubMed

Using the super valence bond model, a generalized chemical picture for the electronic shells of an Au20 pyramid is given. It is found that Au20 can be viewed to be a superatomic molecule, of which its superatomic 16c-16e core (T) is in D(3)S hybridization bonded with four vertical Au atoms for the molecule-like (TAu4) electronic shell-closure. Based on such a superatom-atom bonding model, TX4 (X = F, Cl, or Br) are predicted to be very stable. Such a superatom-atom T-Au/T-X bonding enriches the scope of chemistry. PMID:25259476

Cheng, Longjiu; Zhang, Xiuzhen; Jin, Baokang; Yang, Jinlong

2014-10-01

279

Theoretical calculations of valence states in Fe-Mo compounds  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

280

Configuration of the valence neutrons of 17B  

Microsoft Academic Search

The reaction cross section of 17B on 12C target at (43.7±2.4) MeV\\/u has been measured at the Radioactive Ion Beam Line in Lanzhou (RIBLL). The root-mean-square matter radius (Rrms) was deduced to be (2.92±0.10) fm, while the Rrms of the core and the valence neutron distribution are 2.28 fm and 5.98 fm respectively. Assuming a ``core plus 2n'' structure in

Meng Wang; Zheng-Guo Hu; Hu-Shan Xu; Zhi-Yu Sun; Jian-Song Wang; Guo-Qing Xiao; Wen-Long Zhan; Xue-Ying Zhang; Chen Li; Rui-Shi Mao; Hong-Bin Zhang; Tie-Cheng Zhao; Zhi-Guo Xu; Yue Wang; Ruo-Fu Chen; Tian-Heng Huang; Hui Gao; Fei Jia; Fen Fu; Qi Gao; Jian-Long Han; Xue-Heng Zhang; Chuan Zheng; Yu-Hong Yu; Rui-Rui Fan; Bo Li; Zhong-Yan Guo

2008-01-01

281

All-Valence Electron CNDO Calculations on Transition Metal Complexes  

Microsoft Academic Search

The CNDO-II approximate SCF molecular orbital method is extended to include molecules containing atoms of the first transition series. Valence orbitals explicitly considered in the transition atoms are 3d, 4s, and 4p. Calculations are reported for the monoxides of Sc, Ti, V, and Cu, using three sets of orbital exponents. The results are compared, where possible, with those obtained by

D. W. Clack; N. S. Hush; J. R. Yandle

1972-01-01

282

Determination of manganese valence in complex La?Mn perovskites  

Microsoft Academic Search

We describe a chemical method for determining the manganese concentration and average oxidation state in mixed-valence compounds, and in particular in complex La?Mn perovskites. The method is based on two independent iodometric titrations, with amperometric dead-stop end-point detection. The oxygen stoichiometry and the molecular weight of the compounds can also be evaluated if secondary phases or multi-valent elements different from

F. Licci; G. Turilli; P. Ferro

1996-01-01

283

An efficient polarization propagator approach to valence electron excitation spectra  

Microsoft Academic Search

A practical polarization propagator method devised for the treatment of valence electron excitations in atoms and molecules is presented. This method, referred to as (second-order) algebraic-diagrammatic construction (ADC(2)), allows for a theoretical description of single and double excitations consistently through second and first order, respectively, of perturbation theory. The computational scheme is essentially an eigenvalue problem of a Hermitian secular

A. B. Trofimov; J. Schirmer

1995-01-01

284

Dipole Transitions in Atoms and Ions With One Valence Electron  

Microsoft Academic Search

Oscillator strengths, atomic transition probabilities and photoionisation cross-sections have been calculated for alkali-like atoms and ions, i.e., for atomic systems with one valence electron outside the spherical core. Calculations have been performed in one-electron approximation with allowance for polarisation of the core by an external electric monochromatic field. The including of this effect leads to a change of the matrix

B N Chichkov; V P Shevelko

1981-01-01

285

Developments in the n-electron valence state perturbation theory  

Microsoft Academic Search

A short summary of the n-electron valence state perturbation theory (NEVPT) is provided, and the defects inherent in cases of quasi-degeneration are underscored. A new version of the theory, called QD-NEVPT, based on quasi-degenerate perturbation theory, is presented. The new theory introduces an effective interaction among the zero-order wave functions and overcomes the difficulties of state-specific NEVPT. An application concerning

Celestino Angeli; Stefano Borini; Alex Cavallini; Mirko Cestari; Renzo Cimiraglia; Lara Ferrighi; Manuel Sparta

2006-01-01

286

Higher valency ion substitution into the manganese oxide framework.  

PubMed

A new route for higher valency ion substitution into the manganese oxide (OMS-2) framework is reported. Isomorphously substituted vanadium and niobium OMS-2 were hydrothermally synthesized at 200 degrees C for a period of 2 days. Characterization by XRD, elemental analysis, Raman spectroscopy, and resistivity studies proved that vanadium was incorporated into the manganese oxide structure. The presence of vanadium in the framework changes the electrical properties, making the material very attractive for water sensing applications. PMID:15212514

Polverejan, Mihai; Villegas, Josanlet C; Suib, Steven L

2004-06-30

287

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

288

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

289

Kondo universality, energy scales, and intermediate valence in plutonium  

SciTech Connect

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

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

2009-07-15

290

Singular Valence Fluctuations at a Kondo Destroyed Quantum Critical Point  

NASA Astrophysics Data System (ADS)

Recent experiments on the heavy fermion superconductor beta-YbAlB4 have indicated that this compound satisfies quantum critical scaling [1]. Motivated by the observation of mixed valency in this material [2], we study the Kondo destruction physics in the mixed-valence regime [3] of a particle-hole asymmetric Anderson impurity model with a pseudogapped density of states. In the vicinity of the quantum critical point we determine the finite temperature spin and charge susceptibilities by utilizing a continuous time quantum Monte Carlo method [4] and the numerical renormalization group. We show that this mixed-valence quantum critical point displays a Kondo breakdown effect. Furthermore, we find that both dynamic spin and charge susceptibilities obey frequency over temperature scaling, and that the static charge susceptibility diverges with a universal exponent. Possible implications of our results for beta-YbAlB4 are discussed. [1] Matsumoto et al, Science 331, 316 (2011). [2] Okawaet al, Physical Review Letters 104, 247201 (2010). [3] J. H. Pixley, S. Kirchner, Kevin Ingersent and Q. Si, arXiv:1108.5227v1 (2011). [4] M. Glossop, S. Kirchner, J. H. Pixley and Q. Si, Phys. Rev. Lett. 107, 076404 (2011).

Pixley, Jedediah; Kirchner, Stefan; Ingersent, Kevin; Si, Qimiao

2012-02-01

291

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

292

Observation of Valence State Change in Layered Li1-yNi1/3Mn1/3Co1/3O2  

SciTech Connect

Valence state changes in Li1-yNi1/3Mn1/3Co1/3O2 were investigated using hard and soft X-ray absorption fine structure (XAFS) measurements. Reversible changes in the M-O bond lengths and in the position of the M L-edge peak (M Ni, Co) were observed during the first charge and discharge cycle. These results demonstrate that Li de-intercalation/intercalation proceeds mainly by changes in the valence states of the Ni and Co cations. In addition, it has been shown that the host material LiNi1/3Mn1/3Co1/3O2 had a surface structure free of Li2CO3.

Kobayashi, Hironori; Tatsumi, Kuniaki [Research Institute for Ubiquitous Energy Devices, National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, Osaka, 563-8577 (Japan); Arachi, Yoshinori [Unit of Chemistry, Faculty of Engineering, Kansai University, Suita, Osaka, 564-8680 (Japan); Emura, Shuichi [Institute of Scientific and Industrial Research (ISIR), Osaka University, Ibaraki, Osaka, 567-0047 (Japan); Handa, Katsumi [SR Center, Ritsumeikan University, Kusatsu, Shiga, 525-8577 (Japan)

2007-02-02

293

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

294

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

PubMed

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

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

2014-07-01

295

Energy pulse bonding  

NASA Technical Reports Server (NTRS)

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

Smith, G. C.

1972-01-01

296

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

297

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

298

Hydrogen bonding and anaesthesia  

NASA Astrophysics Data System (ADS)

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

Sándorfy, C.

2004-12-01

299

Bond-order potential for silicon B. A. Gillespie,1 X. W. Zhou,2 D. A. Murdick,1 H. N. G. Wadley,1 R. Drautz,3 and D. G. Pettifor3  

E-print Network

- ture simulation. Density-functional theory DFT calculates the full electronic configuration of a systemBond-order potential for silicon B. A. Gillespie,1 X. W. Zhou,2 D. A. Murdick,1 H. N. G. Wadley,1 R. The potential addresses both the and bonding and the valence of this sp-valent element. The interatomic

Wadley, Haydn

300

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

Code of Federal Regulations, 2010 CFR

...II-A, II-B, III, IV, V-A, and V-B mines). 57.22227 Section 57.22227 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH...

2010-07-01

301

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

Code of Federal Regulations, 2013 CFR

...II-A, II-B, III, IV, V-A, and V-B mines). 57.22227 Section 57.22227 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH...

2013-07-01

302

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

303

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

Code of Federal Regulations, 2011 CFR

...II-A, II-B, III, IV, V-A, and V-B mines). 57.22227 Section 57.22227 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH...

2011-07-01

304

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

Code of Federal Regulations, 2012 CFR

...II-A, II-B, III, IV, V-A, and V-B mines). 57.22227 Section 57.22227 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH...

2012-07-01

305

Comparative study of the Pros and Cons of Programming languages Java, Scala, C++, Haskell, VB .NET, AspectJ, Perl, Ruby, PHP & Scheme - a Team 11 COMP6411-S10 Term Report  

E-print Network

With the advent of numerous languages it is difficult to realize the edge of one language in a particular scope over another one. We are making an effort, realizing these few issues and comparing some main stream languages like Java, Scala, C++, Haskell, VB .NET, AspectJ, Perl, Ruby, PHP and Scheme keeping in mind some core issues in program development.

Dwarampudi, Venkatreddy; Shah, Jivitesh; Sebastian, Nikhil Joseph; Kanigicharla, Nitin

2010-01-01

306

30 CFR 57.22501 - Personal electric lamps (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines).  

Code of Federal Regulations, 2010 CFR

30 ? Mineral Resources ? 1 ? 2010-07-01 ? 2010-07-01 ? false ? Personal electric lamps (I-A, I-B, I-C, II-A, II-B, III, IV, V-A, and V-B mines). ? 57.22501 ? Section 57.22501 ? Mineral Resources ? MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR ? METAL AND NONMETAL MINE SAFETY AND...

2010-07-01

307

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

SciTech Connect

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

Ermler, Walter V.; Tilson, Jeffrey L.

2012-12-15

308

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

309

Anodic bonded graphene  

Microsoft Academic Search

We show how to prepare graphene samples on a glass substrate with the anodic bonding method. In this method, a graphite precursor in flake form is bonded to a glass substrate with the help of an electrostatic field and then cleaved off to leave few layer graphene on the substrate. Now that several methods are available for producing graphene, the

Adrian Balan; Rakesh Kumar; Mohamed Boukhicha; Olivier Beyssac; Jean-Claude Bouillard; Dario Taverna; William Sacks; Massimiliano Marangolo; Emanuelle Lacaze; Roger Gohler; Walter Escoffier; Jean-Marie Poumirol; Abhay Shukla

2010-01-01

310

The Sibling Bond.  

ERIC Educational Resources Information Center

The relationships among brothers and sisters are infinitely varied, but whatever their characteristics, these bonds last throughout life. This book examines the sibling relationship as a distinctive emotional, passionate, painful, and solacing power. Chapter 1, "Unraveling the Sibling Bond," addresses research on siblings and development of the…

Bank, Stephen P.; Kahn, Michael D.

311

Measuring Abnormal Bond Performance  

Microsoft Academic Search

We analyze the empirical power and specification of test statistics designed to detect abnormal bond returns in corporate event studies, using monthly and daily data. We find that test statistics based on frequently used methods of calculating abnormal monthly bond returns are biased. Most methods implemented in monthly data also lack power to detect abnormal returns. We also consider unique

Hendrik Bessembinder; Kathleen M. Kahle; William F. Maxwell; Danielle Xu

2009-01-01

312

Water's Hydrogen Bond Strength  

Microsoft Academic Search

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

Martin Chaplin

2007-01-01

313

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.

314

Wood Bond Testing  

NASA Astrophysics Data System (ADS)

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

315

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

316

Crystal chemistry and properties of mixed valence copper oxides  

SciTech Connect

The role played by the mixed valence of oxides of transition elements in the metal-like properties is well known since the discovery of the sodium tungsten bronzes Na{sub x}WO{sub 3} by Hagg and Magneli. The synthesis of mixed valence copper oxides with metal-like properties has opened the route to the discovery of superconductivity at high temperature in the La{sub 2}CuO{sub 4}-type family. The chemistry of copper oxides offers great possibilities for nonstoichiometry on the oxygen sublattice because of the Jahn-Teller effect of cooper than can induce several coordinations in the same framework: octahedral (CuO{sub 6}), pyramidal (CuO{sub 5}), and square planar (CuO{sub 4}). Thus, one can easily imagine that starting from a perfect octahedral framework it could be possible to create tunnels or cage structures, or lamellar oxides by removing oxygen atoms. Similarly, it can be expected that such oxygen- deficient copper oxides will be able to intercalate oxygen and return to the stoichiometric phase. The perovskite structure, with its great flexibility, is a potential candidate for such a realization. However, the Cu(II)-Cu(III) mixed valence in oxides is not so easily obtained. Before 1980 trivalent copper could only be stabilized in some oxides under oxygen pressures of several kbars. More recently basic cations like the alkaline earths were introduced as guest elements in the copper oxygen host lattice in order to stabilize the upper oxidation state Cu(III) under normal oxygen pressure. Several series of oxides were produced that can be classified mainly as having either a tunnel structure or a layered structure.

Raveau, B.; Michel, C. (Lab. de Cristallographie Sciences des Materiaux, CRISMAT, 14032 Caen Cedex (FR))

1989-01-01

317

A vibrational study of the nature of hydroxyl groups chemical bonding in two aluminium hydroxides  

NASA Astrophysics Data System (ADS)

Lengths, strengths and valences of OH bonds in the two aluminium hydroxides gibbsite and bayerite were determined on the basis of vibrational spectral data. The uncoupled OD stretching modes in the range 2400-2800 cm -1 were recorded by means of infrared diffuse reflectance, thereby avoiding effects of surface, vibrational coupling or particle shape. The assignment of the corresponding Raman spectra resulted in the determination of harmonic wavenumbers, force constants and anharmonicity coefficients of bulk OH groups in the two minerals. OH bond lengths deduced from these data varied from 0.964 Å to 0.975 Å in gibbsite and 0.962 Å to 0.973 Å in bayerite. These lengths appear to correspond to weak H-bonds contrary to previously recognized data from X-ray diffraction and neutron diffraction studies. Finally, bond valences were calculated on the basis of these new bond lengths and discussed as a function of crystallographic structures and the nature of hydrogen bonding in these two structures.

Jodin-Caumon, Marie-Camille; Humbert, Bernard; Phambu, Nsoki; Gaboriaud, Fabien

2009-06-01

318

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

PubMed

We numerically study a simple model for thermoreversible 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 nonergodic state. We find that there are two distinct arrest lines for the system: a glass line at high packing fraction, and a 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 nonergodicity 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. PMID:16599726

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

2006-03-28

319

Electronic and transport properties of Cobalt-based valence tautomeric molecules and polymers  

NASA Astrophysics Data System (ADS)

The advancement of molecular spintronics requires further understandings of the fundamental electronic structures and transport properties of prototypical spintronics molecules and polymers. Here we present a density functional based theoretical study of the electronic structures of Cobalt-based valence tautomeric molecules Co^III(SQ)(Cat)L Co^II(SQ)2L and their polymers, where SQ refers to the semiquinone ligand, and Cat the catecholate ligand, while L is a redox innocent backbone ligand. The conversion from low-spin Co^III ground state to high-spin Co^II excited state is realized by imposing an on-site potential U on the Co atom and elongating the Co-N bond. Transport properties are subsequently calculated by extracting electronic Wannier functions from these systems and computing the charge transport in the ballistic regime using a Non-Equilibrium Green's Function (NEGF) approach. Our transport results show distinct charge transport properties between low-spin ground state and high-spin excited state, hence suggesting potential spintronics devices from these molecules and polymers such as spin valves.

Chen, Yifeng; Calzolari, Arrigo; Buongiorno Nardelli, Marco

2011-03-01

320

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

321

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

322

X-ray Crystal Structure Analysis and Ru Valence of Ba4Ru3O10 Single Crystals  

NASA Astrophysics Data System (ADS)

We present a single-crystalline x-ray diffraction study on Ba4Ru3O10 consisting of corner-shared Ru3O12 trimers. The crystal structure is redetermined from 78 to 300 K across an antiferromagnetic transition at 105 K. The orthorhombic symmetry (Cmca, space group No. 64) is preserved at all temperatures measured. This structure presents exceptionally long Ru--O distances characterized by a significant distribution within the Ru3O12 trimer. A bond valence sum calculation suggests that the charge disproportionation within the Ru3O12 trimer emerges even at room temperature, which we ascribe to molecular orbital formation in the Ru3O12 trimer, as supported by the results of recent theoretical calculations. On the basis of the analyzed crystal structure, the electronic states and the nature of the phase transition at 105 K are discussed.

Igarashi, Taichi; Nogami, Yoshio; Klein, Yannick; Rousse, Gwenaelle; Okazaki, Ryuji; Taniguchi, Hiroki; Yasui, Yukio; Terasaki, Ichiro

2013-10-01

323

Experimental and theoretical investigation of simple terminal group 6 arsenide As[triple bond]MF3 molecules.  

PubMed

Laser-ablated group 6 metal atoms react with NF3 and PF3 to form the simple lowest energy N[triple bond]MF3 and P[triple bond]MX3 products, and this investigation has been extended to AsF3. Mo and W atoms react with AsF3 upon excitation by laser ablation or UV irradiation to form stable trigonal As[triple bond]MF3 terminal arsenides. These molecules are identified by comparison of the closely related infrared spectra of the analogous phosphide species and with frequencies calculated by density functional theory and multiconfigurational second order perturbation theory (CASSCF/CASPT2). Computed CASSCF/CASPT2 triple bond lengths for the As[triple bond]MoF3 and As[triple bond]WF3 molecules are 2.240 A and 2.250 A, respectively. The natural bond orders calculated by CASSCF/CASPT2 decrease from 2.67 to 2.60 for P[triple bond]MoF3 to As[triple bond]MoF3 and from 2.74 to 2.70 for P[triple bond]WF3 to As[triple bond]WF3 as the arsenic valence orbitals are less effective than those of phosphorus in bonding to each metal atom and the larger metal orbital size becomes more compatible with the arsenic valence orbitals. The Cr atom reaction gives the arsinidene AsF=CrF2 product instead of the higher energy As[triple bond]CrF3 molecule as the Cr (VI) state is not supported by the softer pnictides. PMID:19413289

Wang, Xuefeng; Andrews, Lester; Knitter, Marta; Malmqvist, Per-Ake; Roos, Björn O

2009-05-28

324

Electronic structure and bonding properties of Si-doped hydrogenated amorphous carbon films  

NASA Astrophysics Data System (ADS)

This work investigates the C K-edge x-ray absorption near-edge structure (XANES), valence-band photoelectron spectroscopy (PES), and Fourier transform infrared (FTIR) spectra of Si-doped hydrogenated amorphous carbon films. The C K-edge XANES and valence-band PES spectra indicate that the sp2/sp3 population ratio decreases as the amount of tetramethylsilane vapor precursor increases during deposition, which suggest that Si doping% enhances sp3 and reduces sp2-bonding configurations. FTIR spectra show the formation of a polymeric sp3 C -Hn structure and Si -Hn bonds, which causes the Young's modulus and hardness of the films to decrease with the increase of the Si content.

Ray, S. C.; Bao, C. W.; Tsai, H. M.; Chiou, J. W.; Jan, J. C.; Kumar, K. P. Krishna; Pong, W. F.; Tsai, M.-H.; Wang, W.-J.; Hsu, C.-J.; Okpalugo, T. I. T.; Papakonstantinou, P.; McLaughlin, J. A.

2004-11-01

325

Anatomy of bond formation. Domain-averaged fermi holes as a tool for the study of the nature of the chemical bonding in Li(2), Li(4), and F(2).  

PubMed

Domain-averaged Fermi hole (DAFH) analysis represents a relatively new strategy for extracting useful new insights into electronic structure and bonding from correlated wave functions. We analyze a full-valence CASSCF description of the Li4 rhombus, in order to discern the role played by the domains of the non-nuclear attractors in the sharing of the valence electrons. Similarly we examine the electron reorganization that accompanies the bond dissociation process in the Li2 molecule, which also features such a non-nuclear attractor for a significant range of nuclear separations. Full-CI wave functions for H2, for a wide range of bond lengths, are used to determine how robust are the DAFH descriptions from full-valence CASSCF wave functions to the incorporation of dynamical electron correlation. Comparisons are made, for H2 and Li4, with a much cheaper strategy in which restricted Kohn-Sham orbitals from B3LYP calculations are inserted into a simplified DAFH expression which applies at the restricted Hartree-Fock level. We also investigate the breaking of the relatively weak F-F bond in F2, in order to determine the extent to which the DAFH analysis of such a system differs from that of a more conventional homopolar bond, such as the one in H2. PMID:17636965

Ponec, Robert; Cooper, David L

2007-11-01

326

Perfluoro effects in the occupied and virtual valence orbitals of hexafluorobenzene  

NASA Astrophysics Data System (ADS)

The complete valence shell photoelectron spectrum of hexafluorobenzene has been recorded with synchrotron radiation and the observed structure has been interpreted using ab initio ionization energies and relative spectral intensities. The theoretical predictions for the single-hole ionic states due to outer valence shell ionization agree satisfactorily with the experimental results. Ionization from the inner valence, essential F 2s, orbitals is strongly influenced by many-body effects and the intensity is spread amongst numerous satellites. Photoelectron angular distributions and branching ratios have been determined both experimentally and theoretically, and demonstrate that shape resonances affect the valence shell photoionization dynamics. Some of the shape resonances have been associated with virtual valence orbitals. An assessment of the perfluoro effect on the occupied and virtual valence orbitals of hexafluorobenzene has been carried out by comparing the present results for C6F6 with similar data for C6H6.

Decleva, P.; Stener, M.; Holland, D. M. P.; Potts, A. W.; Karlsson, L.

2007-07-01

327

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

E-print Network

Chemical Bonding, again · ionic bonding (in salts): transfer of e- · covalent bonding (organicJ/mol Li+ (g) + F¯ (g) #12;The Covalent Bond H H HH+ HHH · + · H ! H : H Lewis electron-dot structures single bond, a shared pair of electrons The Covalent Bond H H HH+ HH #12;E N E R G Y kJ/mol distance 74

Zakarian, Armen

328

The law of constant rejection. [chemical bonding in crystals  

NASA Technical Reports Server (NTRS)

Improvements in analytical technique, study of multielement partitioning in natural systems, and improvements in ionic radius values have permitted construction of Onuma diagrams, in which the logarithm of partition coefficient is plotted versus ionic radius. The optimum radii, corresponding to crystallographic sites, do change in response to changes in major element composition for any particular mineral-type. In natural systems elements compete for sites rather than substituting for another element. It is proposed on empirical grounds, for equilibrium ionic bonding, that Onuma diagram curves for a particular lattice site are parabolic near optimum radius, linear elsewhere, parallel for different valences, and mirror images on opposite sides of optimum. Deviations may be due to overlapping peaks, liquid structure, polyvalence, bonding differences, contamination, kinetics, alteration, etc. However, dominant crystal-chemical control is indicated.

Philpotts, J. A.

1978-01-01

329

The role of valence quarks in proton fragmentation  

NASA Astrophysics Data System (ADS)

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

van Hove, L.

1981-06-01

330

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

331

+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

332

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

333

Thermomechanical properties of graphene: valence force field model approach.  

PubMed

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

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

2012-05-01

334

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

335

Effect of interfacial bond type on the electronic and structural properties of GaSb/InAs superlattices  

SciTech Connect

We have investigated the effects of interfacial bond configuration on the electronic and structural properties of thin (001)GaSb/InAs superlattices by using state-of-the-art ab initio molecular dynamics techniques to calculate the electronic and structural properties of two twelve-atom model GaSb/InAs superlattices which have been constructed to contain only In-Sb (model 1) or Ga-As (model 2) interface bonds, respectively. We find the strain at the interface to be different in the two cases. In model 1, the In and Sb atoms at the interface move away from each other toward the InAs and GaSb layers, respectively, increasing the interfacial separation (4.3% greater than in bulk InSb) and compressing the back bonds to the atoms in the layer below the interface. In model 2 the Ga and As atoms move toward each other, decreasing the interplanar separation at the interface (3.2% smaller than in bulk GaAs) and stretching the back bonds to the neighboring Sb and In atoms, respectively. We calculate the valence band offset for the Ga-As bonded structure to be 0.15 eV smaller than that for the model containing only In-Sb bonds. This smaller band offset leads to more mixing of As p character into the highest lying valence band of the superlattice and results in a 0.015 eV smaller spin-orbit splitting at the valence band edge of the Ga-As bonded structure. This result is consistent with the 0.05 eV larger band gap observed for Ga-As bonded structures in recent photoconductivity measurements made on both Ga-As and In-Sb bonded samples grown by molecular-beam epitaxy. 16 refs., 1 fig.

Hemstreet, L.A. [Naval Research Lab., Washington, DC (United States)] [Naval Research Lab., Washington, DC (United States); Fong, C.Y. [Univ. of California, Davis, CA (United States)] [Univ. of California, Davis, CA (United States); Nelson, J.S. [Sandia National Labs., Albuquerque, NM (United States)] [Sandia National Labs., Albuquerque, NM (United States)

1993-07-01

336

Combined configuration-superposition and many-particle perturbation calculations for atoms with two valence electrons  

Microsoft Academic Search

A new high-precision method is used to calculate the characteristics of atoms with two valence electrons. An effective Hamiltonian\\u000a for the valence electrons is formulated by many-particle perturbation theory with respect to the residual interaction of the\\u000a valence electrons with the core. The configuration-superposition method is then used to find the energy levels of the atom.\\u000a The application of the

M. G. Kozlov; S. G. Porsev

1997-01-01

337

Bonding character of SiO 2 stishovite under high pressures up to 30 Gpa  

Microsoft Academic Search

The charge density and bond character of the rutile-type structure of SiO2 (stishovite) under compression to 30 GPa were investigated by X-ray diffraction study using synchrotron radiation and AgK? rotating anode X-ray generator through a newly devised diamond-anvil cell. The valence electron density was determined by\\u000a least-squares refinement including the ? parameter and the electron population in the X-ray atomic

T. Yamanaka; T. Fukuda; J. Mimaki

2002-01-01

338

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

E-print Network

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

Sóbester, András

339

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

PubMed

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

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

2013-12-01

340

Study of the valence state and electronic structure in Sr(2)FeMO(6) (M = W, Mo, Re and Sb) double perovskites.  

PubMed

The knowledge of the oxidation state of the transition metal cations in Sr(2)FeMO(6) (M = W, Mo, Re and Sb) double perovskites is of paramount importance to understand their appealing magnetoresistive or magnetic properties. We present a systematic investigation of the valences of Fe, W, Mo, Re and Sb cations in these perovskites using three different and complementary techniques of analysis. We have used a diffraction method, neutron powder diffraction (NPD), coupled with the bond-valence model; and two spectroscopy methods, X-ray photoemission spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). These two techniques are also complementary since XPS analyses the surface of the samples whereas XAS probes the bulk material. The analysis of the Fe K-edge spectra of the four samples shows a clear shift of the Fe K-edge as the valence of iron increases in the sequence M = W, Mo, Re and Sb. In addition, XANES pre-edge structures unveil a progressive reduction in the occupancy level of the Fe-3d band as the oxidation state of iron increases along the sequence M = W, Mo, Re and Sb. Finally, XANES computations have determined the electronic structures of Sr(2)FeWO(6), Sr(2)FeMoO(6), Sr(2)FeReO(6) and Sr(2)FeSbO(6). PMID:20877841

Retuerto, M; Jiménez-Villacorta, F; Martínez-Lope, M J; Huttel, Y; Roman, E; Fernández-Díaz, M T; Alonso, J A

2010-11-01

341

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

NASA Astrophysics Data System (ADS)

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

Harcourt, Richard D.

1990-03-01

342

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

343

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

344

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

345

Mixed-valence biferrocenes: Pronounced anion dependence of valence detrapping and effects of an asymmetric crystal lattice  

SciTech Connect

The effect of changing the anion from I{sub 3}{sup {minus}} to either PF{sub 6}{sup {minus}} or SbF{sub 6}{sup {minus}} upon the rate of intramolecular electron transfer in salts of the mixed-valence 1{prime},1{prime}{double prime}-dibenzylbiferrocenium cation is investigated. Single-crystal X-ray structures are presented for 1{prime},1{prime}{double prime}-dibenzylbiferrocene (1), 1{prime},1{prime}{double prime}-dibenzylbiferrocenium hexafluorophosphate (2), and 1{prime},1{prime}{double prime}-dibenzylbiferrocenium hexafluoroantimonate (3). A center of symmetry (planar fulvalenide ligand) and a trans conformation characterize the Fe{sub 2}{sup II} molecule in 1. The PF{sub 6}{sup {minus}} anion was found to be disordered in two positions, one with an occupancy of 64% and the other 36%. The packing in complex 2 is that of layers of mixed-valence cations with the small PF{sub 6}{sup {minus}} anions sandwiched between the layers. The SbF{sub 6}{sup {minus}} anion in complex 3 was not found to be disordered at either temperature; however, at 298 K the thermal parameters for this anion are large.

Webb, R.J. (Univ. of California at San Diego, La Jolla (USA) Univ. of Illinois, Urbana (USA)); Geib, S.J.; Staley, D.L.; Rheingold, A.L. (Univ. of Delaware, Newark (USA)); Hendrickson, D.N. (Univ. of California at San Diego, La Jolla (USA))

1990-06-20

346

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

347

Orthodontic bonded retainers.  

PubMed

Retention is usually necessary following orthodontic treatment to overcome the elastic recoil of the periodontal supporting fibres and to allow remodelling of the alveolar bone. The degree of change is variable and largely unpredictable. Bonded lingual retainers have been shown to be an effective means of retaining aligned anterior teeth in the post-treatment position in the long term. Two basic designs of lingual bonded retainers are currently in use. Rigid mandibular canine-to-canine retainers are attached to the canines only. They are effective in maintaining intercanine width but less so in preventing individual tooth rotations. Flexible spiral wire retainers are bonded to each tooth in the segment, their flexibility allowing for physiological movement of the teeth. This design is more effective at preventing rotation of the bonded teeth. Failure of bonded retainers may occur at the wire-composite interface, at the adhesive-enamel interface or as a stress fracture of the wire. Failure of a retainer may lead to unwanted tooth movement. In many cases it will be possible to repair the appliance in the mouth. However, in some instances it will be necessary to replace the retainer. A disadvantage of fixed retainers is that they complicate oral hygiene procedures, and favour the accumulation of plaque and calculus. Despite this, the presence of a bonded retainer appears to cause no increase in incidence of caries or periodontal disease. Use of interdental cleaning aids is required to ensure adequate oral hygiene. PMID:15789987

Butler, Jonathan; Dowling, Paul

2005-01-01

348

LETTER TO THE EDITOR: The bond ionicity of MB2 (M = Mg, Ti, V, Cr, Mn, Zr, Hf, Ta, Al and Y)  

NASA Astrophysics Data System (ADS)

The bond ionicity in biborides MB2 (M = Mg, Ti, V, Cr, Mn, Zr, Hf, Ta, Al and Y) has been studied by using the complex chemical bond theory based on a generalization of the Phillips-Van Vechten-Levine scheme. The ionicity of M-B bonds decreases in the following order: Mg, Al, Mn, Y, Cr, Zr, Hf, Nb, Ta, V and Ti. The Mg-B bond in MgB2 has the largest value of ionicity of 96.8% among these examined diborides. Our calculations support the recent results of band structure calculations that Mg atoms are fully ionized so that they can donate valence electrons to the system. The observed superconductivity loss in the solid solution Mg1-xAlxB2 with x>0.1 can be understood in terms of the ionicity and the number of valence electrons.

Chen, X. L.; Tu, Q. Y.; He, M.; Dai, L.; Wu, L.

2001-07-01

349

Valence-shell photoionization of chlorinelike Ar{sup +} ions  

SciTech Connect

Absolute cross-section measurements for valence-shell photoionization of Ar{sup +} ions are reported for photon energies ranging from 27.4 to 60.0 eV. The data, taken by merging beams of ions and synchrotron radiation at a photon energy resolution of 10 meV, indicate that the primary ion beam was a statistically weighted mixture of the {sup 2}P{sub 3/2}{sup o} ground state and the {sup 2}P{sub 1/2}{sup o} metastable state of Ar{sup +}. Photoionization of this Cl-like ion is characterized by multiple Rydberg series of autoionizing resonances superimposed on a direct photoionization continuum. Observed resonance line shapes indicate interference between indirect and direct photoionization channels. Resonance features are spectroscopically assigned and their energies and quantum defects are tabulated. The measurements are satisfactorily reproduced by theoretical calculations based on an intermediate coupling semirelativistic Breit-Pauli approximation.

Covington, A. M.; Aguilar, A.; Covington, I. R.; Hinojosa, G.; Shirley, C. A.; Phaneuf, R. A.; Alvarez, I.; Cisneros, C.; Dominguez-Lopez, I.; Sant'Anna, M. M.; Schlachter, A. S.; Ballance, C. P.; McLaughlin, B. M. [Department of Physics, MS 220, University of Nevada, Reno, Nevada 89557-0058 (United States); Instituto de Ciencias Fisicas, Universidad Nacional Autonoma de Mexico, Apartado Postal 6-96, Cuernavaca 62131, Morelos (Mexico); Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720 (United States); Department of Physics, Auburn University, Auburn, Alabama 36840 (United States); Institute for Theoretical Atomic and Molecular Physics, Harvard Smithsonian Center for Astrophysics, 60 Garden Street, MS-14, Cambridge, Massachusetts 02138 (United States)

2011-07-15

350

Conduction and valence band discontinuities in some new semiconductor heterojunctions.  

PubMed

Conduction and valence band discontinuities (band offsets) in the heterojunctions consisting of ZnO/4H-SiC, ZnO/GaAs, MgO/4H-SiC, MgO/AIN, InN/ZnO, InN/GaAs, MgO/InN, and InN/4H-SiC, were precisely determined by X-ray photoelectron spectroscopy (XPS) measurement. As an example, the XPS measurement on the ZnO/4H-SiC heterojunction is described in detail in the beginning of the section of the experiments. We also analyzed several factors which may have impact on the band offset in a practical heterojunction. The deviation in band offset induced by both polar and non-polar heterojunction band bending from the true value was also characterized by taking into account the intrinsic polarization field in the heterojunction consisting of the two polar materials. PMID:22413217

Zhu, Qinsheng; Wu, Ju; Li, Chengming; Wang, Zhanguo

2011-11-01

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 compounds. The results clearly indicate that as much as 33 % rare earth isovalent volume contraction can

Paris-Sud XI, Université de

352

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

353

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

E-print Network

A mixed-valence copper coordination polymer generated by hydrothermal metal/ligand redox reactions A novel coordination polymer of mixed-valence copper(I,II) with 4,4A-bipyridine and in situ oxidized frameworks of coordination polymers, based on complexes of transition metals and multifunctional bridging

Li, Jing

354

Emotional control of nociceptive reactions (ECON): Do affective valence and arousal play a role?  

Microsoft Academic Search

Prior research suggests emotional picture-viewing modulates motoric (nociceptive flexion reflex), autonomic (skin conductance response, heart rate acceleration), and subjective (pain rating) reactions to noxious electrodermal stimulation. The present study sought to determine whether emotional valence and arousal contribute to nociception modulation. To do so, pictures varying in emotional content (erotica, food, neutral, loss, attack) were chosen to manipulate emotional valence

Jamie L. Rhudy; Amy E. Williams; Klanci M. McCabe; Jennifer L. Russell; Lauren J. Maynard

2007-01-01

355

Emotional control of nociceptive reactions (ECON): Do affective valence and arousal play a role?  

Microsoft Academic Search

Prior research suggests emotional picture-viewing modulates motoric (nociceptive flexion reflex), autonomic (skin conductance response, heart rate acceleration), and subjective (pain rating) reactions to noxious electrodermal stimulation. The present study sought to determine whether emotional valence and arousal contribute to nociception modulation. To do so, pictures varying in emotional content (erotica, food, neutral, loss, attack) were chosen to manipulate emotional valence

Jamie L. Rhudy; Amy E. Williams; Klanci M. McCabe; Jennifer L. Russell; Lauren J. Maynard

2008-01-01

356

Interpersonal Valence Dimensions as Discriminators of Communication Contexts: An Empirical Assessment of Dyadic Linkages.  

ERIC Educational Resources Information Center

The capability of 14 interpersonal dimensions to predict dyadic communication contexts was investigated in this study. Friend, acquaintance, co-worker, and family contexts were examined. The interpersonal valence construct, based on a coactive or mutual-causal paradigm, encompasses traditional source-valence components (credibility, power,…

Garrison, John P.; And Others

357

Valence calculations of actinide anion binding energies: all bound 7p and 7s attachments  

E-print Network

for neutral configurations with two additional valence electrons, i.e. 5fn 7s2 ground state configurationsValence calculations of actinide anion binding energies: all bound 7p and 7s attachments Steven M 49931 (Dated: June 9, 2009) DRAFT SUBMITTED TO PRA 6/5/09 Relativistic configuration

Beck, Donald R.

358

Valence electron excitations and plasmon oscillations in thin films, surfaces, interfaces and small particles  

Microsoft Academic Search

Plasmon oscillation is a collective excitation of electrons in a valence band of a solid material. The motion and polarization of valence electrons under the impact of a fast moving charged particle directly reflect the solid state properties of the material. Oscillations of surface charges depend sensitively on dielectric properties of the material and, more importantly, on the geometrical configuration

Z. L. Wang

1996-01-01

359

Valence Electron Ionization Dynamics of Chromium by a Photoelectron Imaging Technique: J+  

E-print Network

Valence Electron Ionization Dynamics of Chromium by a Photoelectron Imaging Technique: J+ Dependent an electronic configurational change from 3d4 (5 D)4s4p(1 P°) to 3d4 4s(6 DJ+) occurs. The photo- electron ionization process, in which the synchrotron radiation source is mainly used.16-19 The valence-electron

Kim, Sang Kyu

360

A study of the valence shell electronic structure and photoionization dynamics of selenophene  

Microsoft Academic Search

The photoelectron spectrum of selenophene has been recorded using synchrotron radiation in the photon energy range 20-80 eV and the inner valence region has been studied in detail for the first time. Green's function methods have been employed to evaluate the energies and spectral intensities of all valence shell ionization transitions and the results have facilitated an interpretation of the

I. Powis; I. L. Zaytseva; A. B. Trofimov; J. Schirmer; D. M. P. Holland; A. W. Potts; L. Karlsson

2007-01-01

361

Vibrational effects on the electron momentum distributions of valence orbitals of formamide  

E-print Network

Vibrational effects on the electron momentum distributions of valence orbitals of formamide Y. R energy spectra and electron momentum distributions were interpreted using symmetry adapted cluster-configuration interaction theory, outer valence Green function, and DFT-B3LYP methods. The ordering of 10a and 2a orbitals

Wang, Yayu

362

Combining Semantic and Acoustic Features for Valence and Arousal Recognition in Speech  

E-print Network

Combining Semantic and Acoustic Features for Valence and Arousal Recognition in Speech Seliz G for dimensional speech recognition improves the results. Moreover, we show that valence is better estimated using interaction (HCI) as well. There has been great advances in neutral speech recognition since fifties which

363

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.

364

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

365

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-XA 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 XA 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 XA bonds, for not only X = H/Cl/Li investigated here but also any atom involved in intermolecular bonding. PMID:25127185

Shahi, Abhishek; Arunan, Elangannan

2014-10-01

366

Influence of emotional valence and arousal on the spread of activation in memory.  

PubMed

Controversy still persists on whether emotional valence and arousal influence cognitive activities. Our study sought to compare how these two factors foster the spread of activation within the semantic network. In a lexical decision task, prime words were varied depending on the valence (pleasant or unpleasant) or on the level of emotional arousal (high or low). Target words were carefully selected to avoid semantic priming effects, as well as to avoid arousing specific emotions (neutral). Three SOA durations (220, 420 and 720 ms) were applied across three independent groups. Results indicate that at 220 ms, the effect of arousal is significantly higher than the effect of valence in facilitating spreading activation while at 420 ms, the effect of valence is significantly higher than the effect of arousal in facilitating spreading activation. These findings suggest that affect is a sequential process involving the successive intervention of arousal and valence. PMID:24715543

Jhean-Larose, Sandra; Leveau, Nicolas; Denhière, Guy

2014-11-01

367

Insulation bonding test system  

NASA Technical Reports Server (NTRS)

A method and a system for testing the bonding of foam insulation attached to metal is described. The system involves the use of an impacter which has a calibrated load cell mounted on a plunger and a hammer head mounted on the end of the plunger. When the impacter strikes the insulation at a point to be tested, the load cell measures the force of the impact and the precise time interval during which the hammer head is in contact with the insulation. This information is transmitted as an electrical signal to a load cell amplifier where the signal is conditioned and then transmitted to a fast Fourier transform (FFT) analyzer. The FFT analyzer produces energy spectral density curves which are displayed on a video screen. The termination frequency of the energy spectral density curve may be compared with a predetermined empirical scale to determine whether a igh quality bond, good bond, or debond is present at the point of impact.

Beggs, J. M.; Johnston, G. D.; Coleman, A. D.; Portwood, J. N.; Saunders, J. M.; Redmon, J. W.; Porter, A. C. (inventors)

1984-01-01

368

Reduction in switching current using a low-saturation magnetization Co-Fe-(Cr, V)-B free layer in MgO-based magnetic tunnel junctions  

NASA Astrophysics Data System (ADS)

Magnetic properties, magnetoresistance (MR), and spin-transfer switching of magnetic tunnel junctions having a structure of Co60Fe20B20 3 nm/MgO 1 nm/(Co75Fe25)80-XCr(V)XB20 2 nm (X=0-25) were investigated. Magnetization of the (Co-Fe)-(Cr, V)-B free layer decreased from 1.2 T before substitution to 0.6 T at Cr of 10% (0.8 T at V of 10%). The MR ratio and a resistance-area product (RA) before substitution were, respectively, about 130% and about 2 ? ?m2. The MR ratio decreased to 80% at Cr of 10% and 40% at V of 10%. The RA values were almost independent of the composition. The intrinsic switching current density (Jc0) decreased from 15 to 8 MA/cm2 at Cr of 10% and 12 MA/cm2 for V of 10%. Upon the further increase in Cr and V, stable switching was difficult to observe. In summary, Jc0 decreased to half in the case of Cr, but the effect was small for V.

Kubota, Hitoshi; Fukushima, Akio; Yakushiji, Kay; Yakata, Satoshi; Yuasa, Shinji; Ando, Koji; Ogane, Mikihiko; Ando, Yasuo; Miyazaki, Terunobu

2009-04-01

369

Teachers' Domain: Ionic Bonding  

NSDL National Science Digital Library

This Flash interactive tutorial explores ionic bondingâa type of chemical bond formed between two ions with opposite charges. Learners investigate how the transfer of electrons between atoms creates ions and how the mutual attraction of these charged particles forms ionic bonds. It also discusses trends in the periodic table to help learners comprehend how the structure of an ionic compound relates to its formula. Teachers' Domain is a growing collection of more than 1,000 free educational resources compiled by researchers and experienced teachers to promote the use of digital resources in the classroom.

2011-08-16

370

Investing in Bonds  

E-print Network

, also known as strips, are fixed-income securi- ties that do not pay any periodic interest, or ?coupon,? like regular bonds. Instead, the bond is sold at a deep discount from its face value and at maturity the bondholder collects all of the compounded... or the par amount, whichever is greater. Like other Treasury securi- ties, they?re safe and are guaran- teed by the full faith and credit of the U.S. government. Inflation- Indexed securities are exempt from state and local taxes, although fed- eral income...

Johnson, Jason; Polk, Wade

2002-08-12

371

Cooperativity in beryllium bonds.  

PubMed

A theoretical study of the beryllium bonded clusters of the (iminomethyl)beryllium hydride and (iminomethyl)beryllium fluoride [HC(BeX)=NH, X = H, F] molecules has been carried out at the B3LYP/6-311++G(3df,2p) level of theory. Linear and cyclic clusters have been characterized up to the decamer. The geometric, energetic, electronic and NMR properties of the clusters clearly indicate positive cooperativity. The evolution of the molecular properties, as the size of the cluster increases, is similar to those reported in polymers held together by hydrogen bonds. PMID:24452820

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

2014-03-01

372

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 (De) of C2H2, C2H4, C2H6, N2, N2H2, and N2H4 are studied at various levels of correlation treatment. The convergence of De with respect to the one-particle basis is studied at the single-reference modified coupled-pair-functional (MCPF)level. At all levels of correlation treatment, the errors in the bond dissociation energies increase with the degree of multiple bond character. The multireference configuration-interaction (MRCI) De values, corrected for an estimate of higher excitations, are in excellent agreement with those determined using the size-extensive averaged-coupled-pair-functional (ACPF) method. The full-valence complete-active-space self-consistent-field (CASSCF)/MRCI calculations are reproduced very well by MRCI calculations based on a CASSCF calculation that includes in the active space only those electrons involved in the C-C or N-N bonds.

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

1991-01-01

373

Dependence of intramolecular valence delocalization on crystal form in mixed-valence trinuclear iron phenylacetate [Fe 2 III Fe II O(PhCH 2 CO 2 ) 6 (py) 3  

Microsoft Academic Search

A dependence of intramolecular valence delocalization on crystal form in mixed-valence trinuclear iron phenylacetate [Fe2IIIFeIIO(PhCH2CO2)6(py)3] was found. This complex was obtained in two different crystal forms: a columnar and a needle crystal form. Mössbauer spectra of the columnar crystals show a temperature-dependent valence delocalization, while the needle crystals show a trapped mixed-valence state from a lower temperature up to room

M. Yoshida; T. Nakamoto; S. Kawata; M. Katada; H. Sano

1994-01-01

374

Dependence of intramolecular valence delocalization on crystal form in mixed-valence trinuclear iron phenylacetate [Fe{2\\/III}FeIIO(PhCH2CO2)6(py)3  

Microsoft Academic Search

A dependence of intramolecular valence delocalization on crystal form in mixed-valence trinuclear iron phenylacetate [Fe{2\\/III}FeIIO(PhCH2CO2)6(py)3] was found. This complex was obtained in two different crystal forms: a columnar and a needle crystal form. Mössbauer spectra of the columnar crystals show a temperature-dependent valence delocalization, while the needle crystals show a trapped mixed-valence state from a lower temperature up to room

M. Yoshida; T. Nakamoto; S. Kawata; M. Katada; H. Sano

1994-01-01

375

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

PubMed

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

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

2013-10-21

376

19 CFR 113.12 - Bond application.  

Code of Federal Regulations, 2010 CFR

...Duties 1 2010-04-01 2010-04-01 false Bond application. 113.12 Section 113.12 Customs...HOMELAND SECURITY; DEPARTMENT OF THE TREASURY CUSTOMS BONDS Bond Application and Approval of Bond § 113.12 Bond...

2010-04-01

377

EPR test of the resonating-valence-bond theory of superconductivity in C sub 60 K sub n  

SciTech Connect

EPR experiments on powder samples of C{sub 60}K{sub {ital n}} are presented. The results contradict the basic assumption of a negative Hubbard {ital U}, which has been used to explain the superconductivity in fullerenes. The apparent orbital nondegeneracy of the observed state is explained in terms of a generalized dynamic Jahn-Teller effect.

Mehran, F.; Schell-Sorokin, A.J. (IBM Research Division, Thomas J. Watson Research Center, Yorktown Heights, New York 10598 (United States)); Brown, C.A. (IBM Research Division, Almaden Research Center, San Jose, California 95120-6099 (United States))

1992-10-01

378

Nel and valence-bond crystal order on a distorted kagome lattice: Implications for Zn-paratacamite  

E-print Network

doping, this material undergoes a structural distortion which relieves the frustration and introduces Recently, a number of spin-1/2 frustrated magnetic insu- lators have been discovered without any sign of distortion allowing the amount of geometric frustration to be tuned directly by an experimentalist. As such

Sørensen, Erik S.

379

Empirical valence bond simulations of the hydride transfer step in the monoamine oxidase B catalyzed metabolism of dopamine.  

PubMed

Monoamine oxidases (MAOs) A and B are flavoenzymes responsible for the metabolism of biogenic amines such as dopamine, serotonin and noradrenaline. In this work, we present a comprehensive study of the rate-limiting step of dopamine degradation by MAO B, which consists in the hydride transfer from the methylene group of the substrate to the flavin moiety of the FAD prosthetic group. This article builds on our previous quantum chemical study of the same reaction using a cluster model (Vianello et al., Eur J Org Chem 2012; 7057), but now considering the full dimensionality of the hydrated enzyme with extensive configurational sampling. We show that MAO B is specifically tuned to catalyze the hydride transfer step from the substrate to the flavin moiety of the FAD prosthetic group and that it lowers the activation barrier by 12.3 kcal mol(-1) compared to the same reaction in aqueous solution, a rate enhancement of more than nine orders of magnitude. Taking into account the deprotonation of the substrate prior to the hydride transfer reaction, the activation barrier in the enzyme is calculated to be 16.1 kcal mol(-1) , in excellent agreement with the experimental value of 16.5 kcal mol(-1) . Additionally, we demonstrate that the protonation state of the active site residue Lys296 does not have an influence on the hydride transfer reaction. Proteins 2014; 82:3347-3355. © 2014 Wiley Periodicals, Inc. PMID:25220264

Repi?, Matej; Vianello, Robert; Purg, Miha; Duarte, Fernanda; Bauer, Paul; Kamerlin, Shina C L; Mavri, Janez

2014-12-01

380

High Solubility of Hetero-Valence Ion (Cu2+) for Reducing Phase Transition and Thermal Expansion of ZrV1.6P0.4O7  

NASA Astrophysics Data System (ADS)

Large thermal expansion at room temperature and high phase transition temperature of ZrV2O7 limit its practical applications and are reduced by the high solubility of hetero-valence ion (Cu2+) on the basis of an equal-valence substitution of P5+ for V5+. The temperature-dependent Raman spectra show that Zr0.9 Cu0.1 V1.6 P0.4 O6.9 maintains a normal parent cubic structure till 173K and transforms to a 3 × 3 × 3 cubic superstructure below 173K. Temperature dependent x-ray diffraction patterns of Zr0.9 Cu0.1 V1.6 P0.4 O6.9 show near zero and negative thermal expansion. High solubility of lower valence Cu2+ relates to an equal-valence substitution of smaller P5+ for V5+, which extends the bond angle of V(P)—O—V in ZrV1.6 P0.4 O7 close to 180°. The change of microstructure is considered to be responsible for reduced phase transition temperature and thermal expansion.

Yuan, Bao-He; Yuan, Huan-Li; Song, Wen-Bo; Liu, Xian-Sheng; Cheng, Yong-Guang; Chao, Ming-Ju; Liang, Er-Jun

2014-07-01

381

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

382

Bonding without Tears.  

ERIC Educational Resources Information Center

Discusses merits of using sigma-pi model of ethylene as a teaching aid in introductory organic chemistry. The nonmathematical treatment of sigma-pi bonding is then extended to such phenomena as conjugation, hyperconjugation, Markovnikoff addition, aromaticity, and aromatic substitution. (SK)

Akeroyd, F. Michael

1982-01-01

383

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

384

Lying about the valence of affective pictures: an fMRI study.  

PubMed

The neural correlates of lying about affective information were studied using a functional magnetic resonance imaging (fMRI) methodology. Specifically, 13 healthy right-handed Chinese men were instructed to lie about the valence, positive or negative, of pictures selected from the International Affective Picture System (IAPS) while their brain activity was scanned by a 3T Philip Achieva scanner. The key finding is that the neural activity associated with deception is valence-related. Comparing to telling the truth, deception about the valence of the affectively positive pictures was associated with activity in the inferior frontal, cingulate, inferior parietal, precuneus, and middle temporal regions. Lying about the valence of the affectively negative pictures, on the other hand, was associated with activity in the orbital and medial frontal regions. While a clear valence-related effect on deception was observed, common neural regions were also recruited for the process of deception about the valence of the affective pictures. These regions included the lateral prefrontal and inferior parietal regions. Activity in these regions has been widely reported in fMRI studies on deception using affectively-neutral stimuli. The findings of this study reveal the effect of valence on the neural activity associated with deception. Furthermore, the data also help to illustrate the complexity of the neural mechanisms underlying deception. PMID:20811624

Lee, Tatia M C; Lee, Tiffany M Y; Raine, Adrian; Chan, Chetwyn C H

2010-01-01

385

High and low roads to odor valence? A choice response-time study  

PubMed Central

Valence and edibility are two important features of olfactory perception, but it remains unclear how they are read out from an olfactory input. For a given odor object (e.g., the smell of rose or garlic), does perceptual identification of that object necessarily precede retrieval of information about its valence and edibility, or alternatively, are these processes independent? In the present study, we studied rapid, binary perceptual decisions regarding odor detection, object identity, valence, and edibility for a set of common odors. We found that decisions regarding odor-object identity were faster than decisions regarding odor valence or edibility, but slower than detection. Mediation analysis revealed that odor valence and edibility decision response times were predicted by a model in which odor-object identity served as a mediator along the perceptual pathway from detection to both valence and edibility. According to this model, odor valence is determined through both a “low road” that bypasses odor objects and a “high road” that utilizes odor-object information. Edibility evaluations are constrained to processing via the high road. The results outline a novel causal framework that explains how major perceptual features might be rapidly extracted from odors through engagement of odor objects early in the processing stream. PMID:23875569

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

2014-01-01

386

First-principles study of valence and structural transitions in EuO under pressure  

NASA Astrophysics Data System (ADS)

The electronic structure of EuO under pressure is studied using the self-interaction corrected local spin density approximation. EuO, which at ambient conditions crystallizes in the NaCl (B1) structure, is predicted to undergo an isostructural insulator to metal transition at 48 GPa. This transition is associated with a change of valence from a divalent to an intermediate valent state, with the resulting effective valency of 2.35. The pressure range between 48 and 70 GPa is characterized by the competition between an intermediate valent B1 structured phase and a CsCl (B2) structured phase where both the divalent and intermediate valence configurations are in play. Eventually, at pressures above 70 GPa, the intermediate valent B2 phase prevails. The effective Eu valence in the B2 intermediate valence phase is around 2.28, i.e., a decrease in effective valence occurs. This scenario is in line with the reentrant valence behavior observed in recent pressure experiments.

Petit, L.; Szotek, Z.; Lüders, M.; Temmerman, W. M.; Svane, A.

2014-07-01

387

Superatom-atom super-bonding in metallic clusters: a new look to the mystery of an Au20 pyramid  

NASA Astrophysics Data System (ADS)

Using the super valence bond model, a generalized chemical picture for the electronic shells of an Au20 pyramid is given. It is found that Au20 can be viewed to be a superatomic molecule, of which its superatomic 16c-16e core (T) is in D3S hybridization bonded with four vertical Au atoms for the molecule-like (TAu4) electronic shell-closure. Based on such a superatom-atom bonding model, TX4 (X = F, Cl, or Br) are predicted to be very stable. Such a superatom-atom T-Au/T-X bonding enriches the scope of chemistry.Using the super valence bond model, a generalized chemical picture for the electronic shells of an Au20 pyramid is given. It is found that Au20 can be viewed to be a superatomic molecule, of which its superatomic 16c-16e core (T) is in D3S hybridization bonded with four vertical Au atoms for the molecule-like (TAu4) electronic shell-closure. Based on such a superatom-atom bonding model, TX4 (X = F, Cl, or Br) are predicted to be very stable. Such a superatom-atom T-Au/T-X bonding enriches the scope of chemistry. Electronic supplementary information (ESI) available: Computational details, AdNDP chemical bonding of ten 10c-2e bonds of Au20, and optimized structures of TM4 and TX4, low-lying isomers of TAu4, and geometries of T4+, T4-, T2-, [Cu@T]- and [Cu@T]3-. See DOI: 10.1039/c4nr03550j

Cheng, Longjiu; Zhang, Xiuzhen; Jin, Baokang; Yang, Jinlong

2014-10-01

388

Advanced Bonding\\/Joining Techniques  

Microsoft Academic Search

\\u000a In this chapter, three advanced bonding\\/joining techniques, adhesive bonding, direct bonding, and lead-free soldering, are\\u000a presented. For each technique, we first review the bonding principles and applications in electronic industries, followed\\u000a by novel bonding materials and processes.\\u000a \\u000a \\u000a For adhesive bonding, four popular adhesives, epoxy resins, silicon resins, polymides, and acrylics, are reviewed. Two new\\u000a adhesives, liquid crystal polymer (LCP) and

Chin C. Lee; Pin J. Wang; Jong S. Kim

389

Bent Chemical Bonds: Present theories and experimental results concerning electrons in some specific molecules are discussed.  

PubMed

The obvious and not original conclusion is that the results obtained from considerations of sp(3) hybridization in the substituted methanes breaks down as soon as all of the bonding atoms are not equivalent. Indeed, the concept of sp(3) localized carbon hybrids may be invalid even for tetrahedral molecules like CCl(4) where the result of tetrahedral angles may be inferred from a naive hard sphere model. In other words the electrons in CCl(4) have a more delocalized molecular quality than the apparently more localized atomic quality in CH(4). This result implies that perhaps a Hartree-Fock treatment of the outer valence electrons in the substituted methanes (frozen inner atomic shells) might give a fairly good description of the electron distribution. On the other hand, the valence bond method would have to be carried well past the convenient approximation of perfect pairing. McWeeny and Ohno (23) were quite optimistic about the frozen inner atomic shell approximation in their treatment of H(2)O. As far as the strained small-ring compounds it appears the bending of a bond is a function of where one decides to draw the line between localized and delocalized character. Finally, no more appropriate ending could be contrived than a classic quote by Professor R. S. Mulliken (37), "I believe the chemical bond is not so simple as some people seem to think." PMID:17837492

Flygare, W H

1963-06-14

390

Influence of 5f electrons on structure and bonding in the actinide-hydrogen intermetallics  

SciTech Connect

Complexa phases form for the Th + H and U + H systems that are found with no other metals. In the Pa + H system, simple bcc C15 Laves and A15 phases can form, dependent on temperature and composition. The phase transformations appear to b magnetically driven, as a resutl of the decoupling of the metallic 5f electron bonding that occurs during hydriding; the C15 phases contain two kinds of Pa atoms-the one sublattice being still fully f-bonded and the other magnetic. This is a unique situation in solid state physics which defies a valence description. A similar situation obtains for A15 ..beta.. - UH/sub 3/ structure. The parent metals themselves exhibit electronegativities not unlike those of the mid-3d transition metals (e.g., Fe) because the valence electrons re tied up in metallic bonding. However, under the driving force for hydriding, the lattices can open up, decoupling the f-bonding and inducing magnetism. The systems then aggressively form very stable hydrides typical of highly-electropositive metals. Beyond uranium the trivalent metallic state is favored and rare-earth-like hydrides are found for Np + H and Pu + H. Nevertheless, the solid-state and transport properties are markedly different than for the rare-earth hydrides, showing that the latent influence of the 5f electrons is still strong.

Ward, J.W.

1984-01-01

391

Positively Valenced Stimuli Facilitate Creative Novel Metaphoric Processes by Enhancing Medial Prefrontal Cortical Activation  

PubMed Central

A metaphor is a figure of speech in which a subject is symbolic of another unrelated object. In the present study, we examined neural patterns associated with both novel unfamiliar and conventional familiar metaphoric processing, and how these patterns are modulated by affective valence. Prior to fMRI scanning, participants received a list of word pairs (novel unfamiliar metaphors as well as conventional familiar metaphors) and were asked to denote the valence (positive, negative, or neutral) of each word pair. During scanning, participants had to decide whether the word pairs formed meaningful or meaningless expressions. Results indicate that participants were faster and more accurate at deciding that positively valenced metaphors were meaningful compared to neutral metaphors. These behavioral findings were accompanied by increased activation in the medial prefrontal cortex (mPFC), posterior cingulate cortex (PCC), and the right inferior parietal lobe (RIPL). Specifically, positively valenced novel unfamiliar metaphors elicited activation in these brain regions in addition to the left superior temporal gyrus when compared to neutral novel metaphors. We also found that the mPFC and PCC mediated the processing of positively valenced metaphors when compared to negatively valenced metaphors. Positively valenced conventional metaphors, however, elicited different neural signatures when contrasted with either neutral or negatively valenced conventional metaphors. Together, our results indicate that positively valenced stimuli facilitate creative metaphoric processes (specifically novel metaphoric processes) by mediating attention and cognitive control processes required for the access, integration, and selection of semantic associations via modulation of the mPFC. The present study is important for the development of neural accounts of emotion-cognition interactions required for creativity, language, and successful social functioning in general. PMID:23637686

Subramaniam, Karuna; Beeman, Mark; Faust, Miriam; Mashal, Nira

2013-01-01

392

Amalgam shear bond strength to dentin using different bonding agents.  

PubMed

This study evaluated the shear bond strength of amalgam to dentin using five different bonding agents: Amalgambond Plus, Optibond, Imperva Dual, All-Bond 2, and Clearfil Liner Bond. Flat dentin surfaces obtained by grinding the occlusal portion of 50 human third molars were used for this study. To contain the amalgam on the tooth surface, cylindrical plastic molds were placed on the dentin and secured with sticky wax. The bonding agents were then applied according to the manufacturers' instructions or light activated and Tytin amalgam was condensed into the plastic molds. The samples were thermocycled and shear bond strengths were determined using an Instron Universal Testing Machine. Analysis by one-way ANOVA indicated significant difference between the five groups (P < 0.05). The bond strength of amalgam to dentin was significantly higher with Amalgambond Plus using the High-Performance Additive than with the other four bonding agents. PMID:9028242

Vargas, M A; Denehy, G E; Ratananakin, T

1994-01-01

393

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

394

Electrochemical modification of Surface valence - Cr precipitates on LSCF surfaces  

NASA Astrophysics Data System (ADS)

Interactions of gaseous Cr contaminants with the perovskite material LSCF (La0.6Sr0.4Co0.2Fe0.8O3) commonly used as cathode for Solid Oxide Fuel Cells (SOFC) were investigated by means of X-ray absorption Spectroscopy (XAS) and Raman Spectroscopy. The setup consisted of a model cell with a GDC (Gd0.1Ce0.9O2) electrolyte pellet with a LSCF cathode on both sides in a Cr containing sample holder. The chemical structure and valency of the precipitate were found to depend on the electrochemical conditions of the surface, particularly on the bias voltage and not the total current density present in the cell. Cr^6+ spinels were found to form under high bias voltage, while under low bias voltage mostly Cr2O3 was formed. The influence of the contact material (Au vs. Ag) and the effect of quenching were investigated by Raman Spectroscopy under operating conditions (800 C in air). XAS unlike EDS, XRD or XPS is a precise and valuable tool for the direct measurement of the oxidation state of transition metals in compounds if the concentration is low (contamination) and the substrate is porous.

Finsterbusch, Martin; Schaefer, J. A.; Eigenbrodt, B. C.; Walker, R. A.; Lussier, A.; Idzerda, Y. U.

2010-10-01

395

Finite Element Analysis of Valence Band Structure of Square Quantum Well Under the Electric Field  

NASA Astrophysics Data System (ADS)

Valence band structure with spin-orbit (SO) coupling of GaAs/Ga1-xAlxAs square quantum well (SQW) under the electric field by a calculation procedure based on a finite element method (FEM) is investigated using the multiband effective mass theory (?c {k}?ot ?c {p} method). The validity of the method is confirmed with the results of D. Ahn, S. L. Chuang and Y. C. Chang (J. Appl. Phys. 64 (1998) 4056), who calculated valence band structure, using axial approximation for Luttinger-Kohn Hamiltonian and finite difference method. Our results demonstrated that SO coupling and electric field have significant effects on the valence band structure.

Gunes, M.; Kasapoglu, E.; Sari, H.; Akgungor, K.; Sökmen, I.

396

Core and valence electrons in atoms and ions: configuration interaction calculations  

Microsoft Academic Search

Summary. The partitioning of ground-state atoms or ions into inner spherical cores with radius $r_{\\\\rm b}^{\\\\phantom\\\\ast}$ and outer valence regions extending from $r_{\\\\rm b}^{\\\\phantom\\\\ast}$ to infinity is explored with the help of the expression $E^{\\\\rm v}=\\\\frac{1}{3}(T^{\\\\rm v}+2V^{\\\\rm v})$ for the valence-region energy (where $T^{\\\\rm v}\\\\!$ and $V^{\\\\rm v}$ are, respectively, the kinetic and potential energies of the ‘valence electrons’ $N^{\\\\rm

Normand Desmarais; Sándor Fliszár

1996-01-01

397

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

398

New Effective Core Method (Effective Core Potential and Valence Basis Set) for Al Clusters and Nanoparticles and Heteronuclear Al-Containing Molecules  

SciTech Connect

In previous work we have shown that the PBE0 hybrid density functional method with the MG3 all-electron basis set is an accurate method for calculating the atomization energies of small aluminum clusters (Al2-Al7). However, the MG3 basis set is very expensive for molecules much larger than Al13; therefore, we have developed a new effective core potential (ECP) method for aluminum to reduce the cost of obtaining accurate results for nanoparticles. Our method involves a hybrid of the Stuttgart semiempirical effective core potential and the compact effective potential (CEP) potential, and it uses a newly optimized polarized valence triple-? basis set. The combination of the new ECP and the new polarized valence triple-? basis set for Al is called the Minnesota effective core (MEC) method for Al. The method was optimized with a training set of atomization energies and geometries for AlH, AlC, AlO, AlCCH, Al2H, Al2C, Al2O, and Al3 and atomization energies of three Al13 structures, and we tested it on six test sets composed of 20 atomization energies for systems as large as Al13. We also present an improved all-electron polarized triple split basis set for oxygen, called 6-311+G(d*,p). For the test sets, the mean unsigned error (MUE) of the new method with respect to PBE0/MG3 is 0.06 eV for atomization energies and 0.007 Å for bond lengths, which constitutes a very significant improvement over the quality of the results that can be obtained with effective core potentials and valence basis sets in the literature (of the eight methods in the literature, the best previous method had average errors of 0.63 eV and 0.036 Å). We have also tested the MEC method with a variety of hybrid density functional theory, hybrid meta density functional theory, and pure GGA and meta GGA functionals and found that the average MUE, relative to each functional with all-electron basis sets, is 0.04 eV for atomization energies and 0.009 Å for bond lengths for the new effective core method and 0.16-0.20 eV and 0.013-0.033 Å for effective core potential and valence basis sets in the literature.

Schultz, Nathan E.; Truhlar, Donald G.

2005-01-31

399

Identification of Ectonucleotide Pyrophosphatase/Phosphodiesterase 3 (ENPP3) as a Regulator of N-Acetylglucosaminyltransferase GnT-IX (GnT-Vb)*  

PubMed Central

Our previous studies on a ?1,6-N-acetylglucosaminyltransferase, GnT-IX (GnT-Vb), a homolog of GnT-V, indicated that the enzyme has a broad GlcNAc transfer activity toward N-linked and O-mannosyl glycan core structures and that its brain-specific gene expression is regulated by epigenetic histone modifications. In this study, we demonstrate the existence of an endogenous inhibitory factor for GnT-IX that functions as a key regulator for GnT-IX enzymatic activity in Neuro2a (N2a) cells. We purified this factor from N2a cells and found that it is identical to ectonucleotide pyrophosphatase/phosphodiesterase 3 (ENPP3), as evidenced by mass spectrometry and by the knockdown and overexpression of ENPP3 in cultured cells. Kinetic analyses revealed that the mechanism responsible for the inhibition of GnT-IX caused by ENPP3 is the ENPP3-mediated hydrolysis of the nucleotide sugar donor substrate, UDP-GlcNAc, with the resulting generation of UMP, a potent and competitive inhibitor of GnT-IX. Indeed, ENPP3 knockdown cells had significantly increased levels of intracellular nucleotide sugars and displayed changes in the total cellular glycosylation profile. In addition to chaperones or other known regulators of glycosyltransferases, the ENPP3-mediated hydrolysis of nucleotide sugars would have widespread and significant impacts on glycosyltransferase activities and would be responsible for altering the total cellular glycosylation profile and modulating cellular functions. PMID:23960081

Korekane, Hiroaki; Park, Jong Yi; Matsumoto, Akio; Nakajima, Kazuki; Takamatsu, Shinji; Ohtsubo, Kazuaki; Miyamoto, Yasuhide; Hanashima, Shinya; Kanekiyo, Kenji; Kitazume, Shinobu; Yamaguchi, Yoshiki; Matsuo, Ichiro; Taniguchi, Naoyuki

2013-01-01

400

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

401

Low temperature reactive bonding  

DOEpatents

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

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

1995-01-01

402

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

403

Chemisorptive bonding of carbon monoxide on nickel (001): Formulation and application of a new pseudofunctional electron muffin tin approach  

Microsoft Academic Search

The nature of chemisorptive bonding of carbon monoxide on single-crystal transition metal surfaces, particularly Ni(001) and Fe(110) is reviewed in terms of valence-level shifts in photoemission, characteristic stretching frequencies, two-dimensional electron-band structure and adsorbate-site location. The experimentally determined data for many of these parameters are critically compared to a first-principle, total-energy slab-calculation approach developed by the writers called the pseudo-functional

R. V. Kasowski; T. Rhodin; M.-H. Tsai

1986-01-01

404

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

405

Rapid Adhesive Bonding of Composites  

NASA Technical Reports Server (NTRS)

Strong bonds created in less time and with less power than use of conventional bonding methods. Rapid adhesive bonding (RAB) technique for composites uses high-frequency induction heating toroids to quickly heat metallic susceptor impregnated with thermoplastic adhesive or sandwiched between thermoset or thermoplastic adhesive cloths or films. Susceptor steel screen or perforated steel foil.

Stein, B. A.; Tyeryar, J. R.; Fox, R. L.; Sterling, S. Elmo, Jr.; Buckley, J. D.; Inge, Spencer V., Jr.; Burcher, L. G.; Wright, Robert E., Jr.

1986-01-01

406

Bond financing in volatile times.  

PubMed

A competitive landscape for providers and changing market conditions require an understanding of key capital sources: tax-exempt bonds remain an attractive capital source. Credit enhancement for bonds is more expensive and more difficult to find than it was in years past. Direct bond purchases by commercial banks mitigate the traditional risks. PMID:24701850

Gould, Kenneth A; Blanda, Christopher M

2014-03-01

407

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

408

Coexistence of solvated electron and benzene-centered valence anion in the negatively charged benzene-water clusters  

NASA Astrophysics Data System (ADS)

We present a combined M06 functional calculation and ab initio molecular dynamics simulation study of an excess electron (EE) in a microhydrated aromatic complex (modeled by benzene (Bz)-water binary clusters, Bz(H2O)n). Calculated results illustrate that Bz ring and water clusters are indeed linked through the ?⋯HO interactions in the neutral Bz(H2O)n (n = 1-8) clusters, and the size of the water cluster does not influence the nature of its interaction with the ? system for the oligo-hydrated complexes. The states and the dynamics of an EE trapped in such Bz-water clusters were also determined. All of possible localized states for the EE can be roughly classified into two types: (i) single, ring-localized states (the Bz-centered valence anions) in which an EE occupies the LUMO of the complexes originating from the LUMO (?*) of the Bz ring, and the ?⋯HO interactions are enhanced for increase of electron density of the Bz ring. In this mode, the carbon skeleton of the Bz part is significantly deformed due to increase of electron density and nonsymmetric distribution of electron density induced by the interacting H-O bonds; (ii) solvated states, in which an EE is trapped directly as a surface state by the dangling hydrogen atoms of water molecules or as a solvated state in a mixed cavity formed by Bz and water cluster. In the latter case, Bz may also participate in capturing an EE using its C-H bonds in the side edge of the aromatic ring as a part of the cavity. In general, a small water cluster is favorable to the Bz-centered valence anion state, while a large one prefers a solvated electron state. Fluctuations and rearrangement of water molecules can sufficiently modify the relative energies of the EE states to permit facile conversion from the Bz-centered to the water cluster-centered state. This indicates that aromatic Bz can be identified as a stepping stone in electron transfer and the weak ?⋯HO interaction plays an important role as the driving force in conversion of the two states.

Zhang, Meng; Zhao, Jing; Liu, Jinxiang; Zhou, Lianwen; Bu, Yuxiang

2013-01-01

409

Donor level of bond-center hydrogen in germanium  

NASA Astrophysics Data System (ADS)

We apply Laplace deep-level transient spectroscopy (LDLTS) in situ after low-temperature proton implantation into crystalline n -type germanium and identify a deep metastable donor center. The activation energy of the donor emission is ˜110 meV when extrapolated to zero electric field. We obtain the split patterns of the emission signal for uniaxial stress applied along three major crystal directions < 100 > , < 110 > , and < 111 > , and conclude that the symmetry of the center is trigonal. We compare the annealing characteristics with those of bond-center hydrogen in silicon and with those of a trigonal center in germanium previously identified as bond-center hydrogen by in situ local-mode infrared absorption spectroscopy. From this comparison it is concluded that the observed donor emission originates from bond-center hydrogen. Infrared absorption also revealed another trigonal center tentatively ascribed to hydrogen occupying an antibonding configuration. A search for a corresponding deep level (as a hole or electron trap) failed, indicating that such level must be near midgap or resonant with (close to) the valence band.

Dobaczewski, L.; Nielsen, K. Bonde; Zangenberg, N.; Nielsen, B. Bech; Peaker, A. R.; Markevich, V. P.

2004-06-01

410

Determination of the bulk cobalt valence state of co-perovskites containing surface-adsorbed impurities.  

PubMed

We used thermogravimetric hydrogen reduction and iodometric titration to determine the bulk valence state of cobalt in Co-perovskites containing surface carbonate hydroxide or hydroxyl groups. It could be shown that thermogravimetric hydrogen reduction experiments are very sensitive to volatile surface groups, but due to their volatility, they can be specified and the bulk valence state of cobalt can still be deduced from these experiments. The iodometric titration is less sensitive to small volatile surface impurities, but precaution has to be taken that oxygen or iodine does not escape from the solution during dissolution of the sample. Best results were obtained if the sample was titrated during dissolution in a closed argon floated titration apparatus. We tested the two methods using LaCoO3 perovskite as a sample with a known valence state. Both methods delivered satisfactory results, and the valence state could be determined with an accuracy of better than 1%. PMID:17037932

Haas, O; Ludwig, Chr; Wokaun, A

2006-10-15

411

Effective Charge Transfer Distances in Cyanide-Bridged Mixed-Valence Transition Metal Complexes  

E-print Network

Effective Charge Transfer Distances in Cyanide-Bridged Mixed-Valence Transition Metal Complexes theory (Oh; Boxer J. Am. Chem. Soc. 1990, 112, 8161). Stark spectra are reported for a series of cyanide

Boxer, Steven G.

412

Core and valence electrons in atoms and ions: configuration interaction calculations  

Microsoft Academic Search

Summary The partitioning of ground-state atoms or ions into inner spherical cores with radius ?b and outer valence regions extending from ?b to infinity is explored with the help of the expression \\u000a

Normand Desmarais; Sándor Fliszár

1996-01-01

413

Evidence for equilibrium gels of valence-limited particles.  

PubMed

We explore the formation and structure of gels produced from solutions of the aromatic dipeptide derivative molecule fluorenylmethoxycarbonyl-diphenylalanine (Fmoc-FF) in dimethyl sulfoxide (DMSO). Mixing these solutions with water results in the self-assembly of Fmoc-FF molecules into space-filling fibrous networks, exhibiting mechanical properties characteristic of gels. Using confocal fluorescence microscopy, we observe the gel transition in situ and find that, upon the addition of water, the solution undergoes a rapid transition to a non-equilibrium state forming ?2 ?m spheres, followed by the formation of fibers 5-10 nm in diameter, nucleating at a sphere surface and expanding into the solution as the remaining spheres dissolve, extending the network. The gel aging process is associated with the network becoming increasingly uniform through apparent redissolution/reaggregation of the Fmoc-FF molecules, corresponding to the observed increase in the elastic modulus to a plateau value. We demonstrate that this increase in uniformity and elastic modulus can be expedited by controlling the temperature of the system, as well as that these gels are thermally reversible, further indicating that the system is in equilibrium in its fibrous network state. X-ray scattering information suggests that the packing of the molecules within a fiber is based on ?-? stacking of ?-sheets, consistent with models proposed in the literature for similar systems, implying that each particle (molecule) possesses a limited number of interaction sites. These observations provide experimental evidence that these low molecular weight gelator molecules can be considered valence-limited "patchy" particles, which associate at low enough temperature to form equilibrium gels. PMID:25155031

Dudukovic, Nikola A; Zukoski, Charles F

2014-10-21

414

Valence, arousal, and task effects in emotional prosody processing  

PubMed Central

Previous research suggests that emotional prosody processing is a highly rapid and complex process. In particular, it has been shown that different basic emotions can be differentiated in an early event-related brain potential (ERP) component, the P200. Often, the P200 is followed by later long lasting ERPs such as the late positive complex. The current experiment set out to explore in how far emotionality and arousal can modulate these previously reported ERP components. In addition, we also investigated the influence of task demands (implicit vs. explicit evaluation of stimuli). Participants listened to pseudo-sentences (sentences with no lexical content) spoken in six different emotions or in a neutral tone of voice while they either rated the arousal level of the speaker or their own arousal level. Results confirm that different emotional intonations can first be differentiated in the P200 component, reflecting a first emotional encoding of the stimulus possibly including a valence tagging process. A marginal significant arousal effect was also found in this time-window with high arousing stimuli eliciting a stronger P200 than low arousing stimuli. The P200 component was followed by a long lasting positive ERP between 400 and 750 ms. In this late time-window, both emotion and arousal effects were found. No effects of task were observed in either time-window. Taken together, results suggest that emotion relevant details are robustly decoded during early processing and late processing stages while arousal information is only reliably taken into consideration at a later stage of processing. PMID:23801973

Paulmann, Silke; Bleichner, Martin; Kotz, Sonja A.

2013-01-01

415

Key ingredients of the alkali atom - metal surface interaction: Chemical bonding versus spectral properties  

NASA Astrophysics Data System (ADS)

The interaction of alkali atoms with metal surfaces is reviewed. The peculiar electronic configuration of such atoms, with only one valence electron participating in the bond formation, suggested simple pictures to describe their interaction with a metal surface. But it was early evident that the adsorption properties depend on many aspects, related to the electronic structure of constituents, leading, for example, to different degrees of ionicity/covalency of the alkali atom-metal bond. Sophisticated theoretical modeling tried to shed light on this aspect. The spectral properties are the ultimate features in determining how the systems interact with each other. In this review the electronic and spectral properties are discussed focusing on different theoretical representations of the physical system and on their consequences. Surface projected energy gaps of the substrate as well as the substrate continuous spectrum are key aspects in determining the nature of the interaction and bonding with alkali adsorbates.

Trioni, M. I.; Achilli, S.; Chulkov, E. V.

2013-05-01

416

Americium Valence Control Experiments in the Dissolved Solution of Irradiated Nuclear Fuel  

Microsoft Academic Search

A method based on valence control and solvent extraction is presented for separating minor actinides (Am, Np) from nuclear fuel reprocessing solution. With this method, Am is adjusted from trivalence to hexavalence by adding 1.6M (NH4)2S2O8 and 0.01 M AgNO3 to the solution of irradiated nuclear fuel. In the present study, the resulting valence of Am was determined by spectrophotometry.

Mamoru KAMOSHIDA; Tetsuo FUKASAWA; Pumio KAWAMURA

1999-01-01

417

Photochemically-Induced Valency Adjustment of Plutonium and Neptunium in Nitric Acid Solution Using Mercury Lamp  

Microsoft Academic Search

A photochemically-induced valency adjustment method has been studied to remove Np from the mixed nitric acid solutions of Pu and Np in connection with the Purex reprocessing. The valencies of Pu and Np ions were adjusted to be Pu(HI) and Np(V) under the initial conditions and their concentrations were 1x10 and 1x10 mol·dm, respectively. The experiments were carried out under

Yukio WADA; Kouji WADA; Takayuki GOIBUCHI; Hiroshi TOMIYASU

1994-01-01

418

Resonant Photoemission Spectroscopy and Theoretical Calculation of the Valence Band Structure in Chromium Aluminum Oxynitride  

Microsoft Academic Search

The electronic structure of chromium aluminum oxynitride has been investigated using resonant photoemission spectroscopy (RPES) and the discrete variational (DV)-Xalpha method. The RPES measurement of the electronic structure around the Cr 2p3\\/2 absorption edges exhibited significant resonant interference behavior for Cr 3d valence electrons, whereas it exhibited small resonant interference behavior for N 2p valence electrons. Therefore this RPES method

Youngmin Choi; Hyunju Chang; Beyong-Hwan Ryu; Kijeong Kong; Jae Do Lee; Kwangsoo No

2003-01-01

419

First-Principles Theory of Intermediate-Valence f-electron Systems  

Microsoft Academic Search

We propose a first-principles based method for calculating the electronic structure and total energy of solids in an intermediate-valence configuration. The method takes into account correlation effects (d-f Coulomb interaction) and many-body renormalization of the effective hybridization parameter of the f system. As an example, the formation of a pressure-induced intermediate-valence state in Yb is considered and its electronic structure

M. Colarieti-Tosti; M. I. Katsnelson; M. Mattesini; S. I. Simak; R. Ahuja; B. Johansson; C. Dallera; O. Eriksson

2004-01-01

420

Valence Electronic Structure of YBCO Probed by X-ray Standing Waves  

Microsoft Academic Search

The photoelectron emission spectrum of the valence band of the high-temperature superconductor YBa2Cu3O7-delta (YBCO) in the X-ray regime is dominated by contributions from the copper sites (d states) because of the comparably large cross section. With the help of the x-ray standing wave (XSW) technique in combination with photoelectron spectroscopy, it is possible to separate the contributions to the valence

Jorg Zegenhagen; Sebastian Thiess; Tien-Lin Lee; Carmela Aruta; Chengtian Lin; Federica Venturini; Nicholas Brookes; Bruce C. C. Cowie

2008-01-01

421

Core polarisation corrections to multipole operators for valence-electron wavefunctions  

Microsoft Academic Search

Corrections to valence-electron transition operators are needed when matrix elements are calculated with wavefunctions obtained from a valence-electron model Schrodinger equation. Electric multipole operators are analysed and correction terms of O(r-6) are derived for the dipole operator. It is shown that the new O(r-6) terms involve dipole-quadrupole interactions of the form (1\\/r).(1\\/r).

C. Laughlin

1989-01-01

422

Light hadron spectroscopy using domain wall valence quarks on an asqtad sea  

Microsoft Academic Search

We calculate the light hadron spectrum in full QCD using two plus one flavor asqtad sea quarks and domain wall valence quarks. Meson and baryon masses are calculated on a lattice of spatial size L≈2.5fm, and a lattice spacing of a≈0.124fm, for pion masses as light as mpi≈300MeV, and compared with the results by the MILC Collaboration with asqtad valence

Andre Walker-Loud; Huey-Wen Lin; David Richards; Robert Edwards; M. Engelhardt; G. T. Fleming; Ph. Hägler; B. Musch; M. F. Lin; H. Meyer; J. W. Negele; A. V. Pochinsky; M. Procura; S. Syritsyn; C. J. Morningstar; K. Orginos; D. B. Renner; W. Schroers

2009-01-01

423

Venues, valences, and public policy: a study of committee bias and the development of pesticides  

E-print Network

VENUES, VALENCES, AND PUBLIC POLICY: A STUDY OF COMMITTEE BIAS AND THE DEVELOPMENT OF PESTICIDES A Thesis by Jeffery Charles Talbert Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment... of the requirements for the degree of MASTER OF ARTS May 1991 Major Subject: Political Science VENUES, VALENCES, AND PUBLIC POLICY: A STUDY OF COMMITTEE BIAS AND THE DEVELOPMENT OF PESTICIDES A Thesis by Jeffery Charles Talbert Approved as to style...

Talbert, Jeffery Charles

2012-06-07

424

Mobile linkers on DNA-coated colloids: valency without patches  

E-print Network

. In this case, the correct procedure is to replace e???Gij(ri,rj) by its average over all possible grafting points. Hence, the effective, single-bond strength between types ? and ? residing on colloids A and B, respectively, will be given by ??? (RA,RB) =grafting makes it possible to control the specificity of inter-particle interactions3–5: two grafted ssDNA sequences bearing complementary Watson-Crick sequences can hybridise to form a double-stranded DNA (dsDNA) bridge between two particles...

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

2014-01-01

425

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

SciTech Connect

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

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

2011-05-07

426

A combined theoretical and experimental study of simple terminal group 6 nitride and phosphide N[triple bond]MX3 and P[triple bond]MX3 molecules.  

PubMed

Organometallic complexes containing terminal metal nitrides and phosphides are important synthetic reagents. Laser-ablated group 6 metal atoms react with NF 3, PF 3, and PCl 3 to form the simple lowest energy N[triple bond]MF 3, and P[triple bond]MX 3 products following insertion and halogen transfer, with the exception of P[triple bond]CrF3, which is a higher energy species and is not observed. The E[triple bond]MX3 pnictide metal trihalide molecules are identified from both argon and neon matrix infrared spectra and frequencies calculated by density functional theory and multiconfigurational second-order perturbation theory (CASSCF/CASPT2). These simple terminal nitrides involve strong triple bonds, which range from 2.80 to 2.77 to 2.59 natural bond order for M = W, Mo, and Cr, respectively, as computed by CASSCF/CASPT2, and the M[triple bond]N stretching frequencies also follow this order. The terminal phosphides are weaker with bond orders 2.74, 2.67, and 2.18, respectively, as the more diffuse 3p orbitals are less effective for bonding to the more compact metal valence d orbitals. PMID:18693715

Wang, Xuefeng; Andrews, Lester; Lindh, Roland; Veryazov, Valera; Roos, Björn O

2008-09-01

427

Thermodynamics of the first-order valence transition in YbInCu{sub 4}  

SciTech Connect

We present measurements of the specific heat and complete elastic moduli of YbInCu{sub 4} as a function of temperature in order to complement existing thermal expansion data. Together these data allow a complete analysis of the thermodynamics of the first-order isostructural valence transition in YbInCu{sub 4}. The Clausius-Clapeyron equation predicts well the measured pressure dependence of the valence transition temperature. Estimates of the Gruneisen parameter from thermodynamic measurements and from pressure-dependent magnetic susceptibility in both the high-temperature and low-temperature phases of YbInCu{sub 4} are in good agreement. On the other hand, a Gruneisen analysis of the change in Kondo temperature at the valence transition fails, emphasizing the importance of carrier-density changes associated with the valence transition, unlike in the case of the {gamma}-{alpha} transition in elemental Ce. Finally, we address the issue of precursive rounding in the elastic moduli for temperatures greater than the valence transition temperature and argue that thermodynamically YbInCu{sub 4}{close_quote}s valence transition is indeed first order. {copyright} {ital 1998} {ital The American Physical Society}

Sarrao, J.L. [MST Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [MST Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Ramirez, A.P. [Bell Laboratories, Lucent Technology, Murray Hill, New Jersey 07974 (United States)] [Bell Laboratories, Lucent Technology, Murray Hill, New Jersey 07974 (United States); Darling, T.W.; Freibert, F.; Migliori, A. [MST Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [MST Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Immer, C.D.; Fisk, Z. [National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306 (United States)] [National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306 (United States); Uwatoko, Y. [Department of Physics, Saitama University, Urawa, Saitama 338 (Japan)] [Department of Physics, Saitama University, Urawa, Saitama 338 (Japan)

1998-07-01

428

1. , VATA VB -BA VV 24. VBVC=2VB.-  

E-print Network

Watt*hour), what is the minimal monthly bill? Assume now that no heat pump is used, but instead we heat the house: 2.69kJ) 8. A house is heated during the winter using a heat pump such that it is maintained at 25º is lost from the house is estimated to be 25 kW. Assuming the cost of work is 15 cents / (k

Barkai, Eli

429

The Surface Pattern Vb a Vb in Spanish  

ERIC Educational Resources Information Center

Describes a study using transformational generative grammar to demonstrate that the frequently used structure "verb a verb" in Spanish is to be interpreted in three ways. Conclusions are drawn for the teaching of Spanish as a foreign language. (AMH)

Foster, David William

1977-01-01

430

Qualifying Energy Conservation Bonds  

E-print Network

1Qualified Energy Construction Bonds (QECB’s) CATEE Conference December 18, 2013 ESL-KT-13-12-39 CATEE 2013: Clean Air Through Energy Efficiency Conference, San Antonio, Texas Dec. 16-18 • Originally authorized by the Energy Improvement & Extension... are QECB’s ESL-KT-13-12-39 CATEE 2013: Clean Air Through Energy Efficiency Conference, San Antonio, Texas Dec. 16-18 • 70% of allocation must be for public use, 30% of allocation MAY be used for a private activity • Representative projects include school...

Briggs, J.

2013-01-01

431

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

432

Electronic structure and bonding of the 3d transition metal borides, MB, M =Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu through all electron ab initio calculations  

NASA Astrophysics Data System (ADS)

The electronic structure and bonding of the ground and some low-lying states of all first row transition metal borides (MB), ScB, TiB, VB, CrB, MnB, FeB, CoB, NiB, and CuB have been studied by multireference configuration interaction (MRCI) methods employing a correlation consistent basis set of quintuple cardinality (5Z). It should be stressed that for all the above nine molecules, experimental results are essentially absent, whereas with the exception of ScB and CuB the remaining seven species are studied theoretically for the first time. We have constructed full potential energy curves at the MRCI/5Z level for a total of 27 low-lying states, subsequently used to extract binding energies, spectroscopic parameters, and bonding schemes. In addition, some 20 or more states for every MB species have been examined at the MRCI/4Z level of theory. The ground state symmetries and corresponding binding energies (in kcal/mol) are ?-5(ScB), 76; ?6(TiB), 65; ?+7(VB), 55; ?+6(CrB), 31; ?5(MnB), 20; ?-4(FeB), 54; ?3(CoB), 66; ?+2(NiB), 79; and ?+1(CuB), 49.

Tzeli, Demeter; Mavridis, Aristides

2008-01-01

433

The effects of smoking and abstinence on experience of happiness and sadness in response to positively valenced, negatively valenced, and neutral film clips  

Microsoft Academic Search

Incentive motivation theories of addiction suggest that behavioural concomitants of compromised mesocorticolimbic reward activity during abstinence might include decreased affective reactions to natural reinforcers. This study tested implications for hedonic reactions in abstinent smokers. It was hypothesised that positively valenced (pleasurable) film clips would elicit lower ratings of happiness in abstinent than satiated smokers. Twenty-nine smokers, randomly assigned to either

Lynne Dawkins; Sarah Acaster; Jane H. Powell

2007-01-01

434

27 CFR 17.107 - Strengthening bonds.  

Code of Federal Regulations, 2010 CFR

... 2010-04-01 false Strengthening bonds. 17.107 Section 17.107 Alcohol...USED IN MANUFACTURING NONBEVERAGE PRODUCTS Bonds and Consents of Sureties § 17.107 Strengthening bonds. Whenever the amount of a bond on...

2010-04-01

435

27 CFR 25.96 - Superseding bond.  

Code of Federal Regulations, 2010 CFR

... Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX AND TRADE BUREAU, DEPARTMENT OF THE TREASURY LIQUORS BEER Bonds and Consents of Surety § 25.96 Superseding bond. When the principal submits a new bond to supersede a bond...

2010-04-01

436

27 CFR 19.241 - Operations bond-distilled spirits plant and adjacent bonded wine cellar.  

Code of Federal Regulations, 2010 CFR

...false Operations bond-distilled spirits plant and adjacent bonded wine cellar. 19...TREASURY LIQUORS DISTILLED SPIRITS PLANTS Bonds and Consents of Surety § 19.241 Operations bond—distilled spirits plant and adjacent bonded wine cellar....

2010-04-01

437

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

Federal Register 2010, 2011, 2012, 2013

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

2012-05-31

438

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

439

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

... 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

440

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

441

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

Code of Federal Regulations, 2011 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....

2011-04-01

442

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

443

Solder extrusion pressure bonding process and bonded products produced thereby  

DOEpatents

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

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

1992-06-16

444

Solder extrusion pressure bonding process and bonded products produced thereby  

DOEpatents

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

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

1992-01-01

445

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

446

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

447

O the Use of Core Polarization Potentials to Account for Core-Valence Correlation Effects in Quantum Chemical Valence-Only Electronic Structure Calculations: Evaluation of Molecular Integrals Over Gaussian Basis Functions  

Microsoft Academic Search

Quantum chemical valence-only electronic structure calculations have been performed for 22 states of NaK using full-valence configuration interaction, effective core potentials to provide the core-valence orthogonality constraints, and independent-particle core polarization functions (W. J. Stevens, D. D. Konowalow, and L. B. Ratcliff, J. Chem. Phys. 80, 1215-1224 (1984); L. B. Ratcliff, D. D. Konowalow, and W. J. Stevens, J. Mol.

Lyn Braxton Ratcliff

1989-01-01

448

Dangling-bond defects and hydrogen passivation in germanium  

NASA Astrophysics Data System (ADS)

The application of germanium in complementary metal-oxide semiconductor (CMOS) technology is hampered by high interface-state densities, the microscopic origin of which has remained elusive. Using first-principles calculations, we have investigated the atomic and electronic structure of prototype germanium dangling-bond defects [1]. The computational approach is based on density functional theory, and in order to overcome band-gap problems we have also performed quasiparticle calculations based on the GW approach. Surprisingly, the germanium dangling bonds give rise to electronic levels below the valence-band maximum. They therefore occur exclusively in the negative charge state, explaining why they have eluded observation with electron spin resonance. The associated fixed charge is likely responsible for threshold-voltage shifts and poor performance of n-channel transistors. At silicon/silicon dioxide interfaces, hydrogen is successfully used to passivate dangling-bond defects. We have therefore also investigated the interaction of hydrogen with germanium. In contrast to silicon and other semiconductors in which hydrogen behaves as an amphoteric impurity, interstitial hydrogen in germanium is stable only in the negative charge state, i.e., it behaves exclusively as an acceptor. Passivation of dangling bonds by hydrogen will therefore be ineffective, again explaining experimental observations. Other cases where unusual interfacial defects and problems with hydrogen passivation may occur will be discussed. Work performed in collaboration with A. Janotti, P. Rinke, and C. G. Van de Walle, and supported by the Semiconductor Research Corporation. 1. J. R. Weber, A. Janotti, P. Rinke, and C. G. Van de Walle, Appl. Phys. Lett. 91, 142101 (2007).

Weber, Justin R.

2008-03-01

449

First singlet (n,pi*) excited state of hydrogen-bonded complexes between water and pyrimidine.  

PubMed

Hydrogen bonds from water to excited-state formaldehyde and from water to excited-state pyridine have been shown to display novel motifs to traditional hydrogen bonds involving ground states, with, in particular for H2O:pyridine, strong interactions involving the electron-rich pi cloud dominating the (n,pi) excited state. We investigate H2O:pyrimidine and various dihydrated species and reveal another motif, one in which the hydrogen bonding can dramatically alter the electronic structure of the excited state. Such effects are rare for ground-state interactions for which hydrogen bonding usually acts to merely perturb the electronic structure of the participating molecules. It arises as the (n,pi*) excitation of isolated pyrimidine is delocalized over both nitrogens but asymmetric hydrogen bonding causes it to localize on just the noninteracting atom. As a result, the excited-state hydrogen bond in H2O:pyrimidine is suprisingly very similar to the ground-state structure. These results lead to an improved understanding of the spectroscopy of pyrimidine in liquid water, and to the prediction that stable excited-state hydrogen bonds in H2O:pyrimidine should be observable, despite failure of experiments to actually do so. They also provide a simple model for the intricate control over primary charge separation in photosynthesis exerted by hydrogen bonding, and for solvent-induced electron localization in symmetric mixed-valence complexes. All conclusions are based on strong parallels found between the results of calculations performed using density-functional theory (DFT) and time-dependent DFT (TDDFT), complete-active-space self-consistent-field (CASSCF) with second-order perturbation-theory correction (CASPT2) theory, and equation-of-motion coupled cluster (EOM-CCSD) theory, calculations that are verified through detailed comparison of computed properties with experimental data for both the isolated molecules and the ground-state hydrogen bond. PMID:16833480

Cai, Zheng-Li; Reimers, Jeffrey R

2005-03-01

450

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

451

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, Jose L. O.; Bigand, Emmanuel

2013-01-01

452

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

453

Amygdala responses to Valence and its interaction by arousal revealed by MEG.  

PubMed

It is widely accepted that the amygdala plays a crucial role in the processing of emotions. The precise nature of its involvement is however unclear. We hypothesized that ambivalent findings from neuroimaging studies that report amygdala's activity in emotions, are due to distinct functional specificity of amygdala's sub-divisions and specifically to differential reactivity to arousal and valence. The goal of the present study is to characterize the amygdala response to affective stimuli by disentangling the contributions of arousal and valence. Our hypothesis was prompted by recent reports claiming anatomical sub-divisions of amygdala based on cytoarchitecture and the functional maps obtained from diverse behavioral, emotional, and physiological stimulation. We measured magnetoencephalography (MEG) recordings from 12 healthy individuals passively exposed to affective stimuli from the International Affective Picture System (IAPS) collection using a 2 (Valence levels)× 2 (Arousal levels) design. Source power was estimated using a beamformer technique with the activations referring to the amygdala sub-divisions defined through probabilistic cytoarchitectonic maps. Right laterobasal amygdala activity was found to mediate negative valence (elicited by unpleasant stimuli) while left centromedial activity was characterized by an interaction of valence by arousal (arousing pleasant stimuli). We did not find a main effect for amygdala activations in any of its sub-divisions for arousal modulation. To the best of our knowledge, our findings from non-invasive MEG data indicate for the first time, a distinct functional specificity of amygdala anatomical sub-divisions in the emotional processing. PMID:23688672

Styliadis, Charalampos; Ioannides, Andreas A; Bamidis, Panagiotis D; Papadelis, Christos

2014-07-01

454

On the (un)conditionality of automatic attitude activation: the valence proportion effect.  

PubMed

Affective priming studies have shown that participants are faster to pronounce affectively polarized target words that are preceded by affectively congruent prime words than affectively polarized target words that are preceded by affectively incongruent prime words. We examined whether affective priming of naming responses depends on the valence proportion (i.e., the proportion of stimuli that are affectively polarized). In one group of participants, experimental trials were embedded in a context of filler trials that consisted of affectively polarized stimulus materials (i.e., high valence proportion condition). In a second group, the same set of experimental trials was embedded in a context of filler trials consisting of neutral stimuli (i.e., low valence proportion condition). Results showed that affective priming of naming responses was significantly stronger in the high valence proportion condition than in the low valence proportion condition. We conclude that (a) subtle aspects of the procedure can influence affective priming of naming responses, (b) finding affective priming of naming responses does not allow for the conclusion that affective stimulus processing is unconditional, and (c) affective stimulus processing depends on selective attention for affective stimulus information. PMID:21668095

Everaert, Tom; Spruyt, Adriaan; De Houwer, Jan

2011-06-01

455

Dependence of the rate of intramolecular electron transfer on crystal form in mixed-valence trinuclear iron phenylacetate complex  

Microsoft Academic Search

A dependence of the rate of intramolecular electron transfer on crystal form in mixed-valence trinuclear iron phenylacetate, [Fe2IIIFeIIO(O2CCH2Ph)6(py)3](py=pyridine), was found. This complex was obtained in two different crystal forms: a columnar and a needle crystal form. Mo¨ssbauer spectra of the columnar crystals showed a temperature-dependent valence detrapping, whereas the needle crystals showed a trapped mixed-valence state from a lower temperature

Tadahiro Nakamoto; Mizuho Yoshida; Susumu Kitagawa; Motomi Katada; Kazutoyo Endo; Hirotoshi Sano

1996-01-01

456

Bond strengths of ceramic brackets using different bonding techniques.  

PubMed

A series of laboratory investigations was carried out to compare the shear-type bond strengths and site of bond failure of ceramic orthodontic brackets bonded to etched enamel. When light-cured composite resin was used as the luting agent, there was no reduction in bond strength when using 2.5 per cent nitric acid to etch the enamel, compared to 37 per cent phosphoric acid. The use of the two resin modified glass ionomer cements were found to give rise to significantly lower bond strengths than composite resin when used for placing ceramic brackets. Significantly less composite resin remained on the enamel surface following bracket removal in those samples etched with nitric acid. PMID:7786864

Blight, S J; Lynch, E

1995-02-01

457

EFFECTS OF USG CURRENT AND BONDING LOAD ON BONDING FORMATION IN QFN STACKED DIE PACKAGE  

Microsoft Academic Search

Gold is commonly used as bonding wire that connects the die bond pad and substrate. Bond power and bond force are the main factors during wire bonding process in order to get the robust ball bonding. The objective of this investigation is to determine the effect of power and force on bonding process for 99.99% gold wire for wire type

A. Jalar; S. A. Radzi; M. A. A. Hamid

2008-01-01

458

Experiencing activation: energetic arousal and tense arousal are not mixtures of valence and activation.  

PubMed

R. E. Thayer (1989) proposed 2 types of activation: energetic arousal (awake-tired) and tense arousal (tense-calm). This view has been challenged by claims that energetic arousal and tense arousal are mixtures of valence and a single activation dimension. The authors present a direct test of this hypothesis by computing the correlation between the residuals of energetic arousal and tense arousal after removing the shared variance with valence. Whereas the valence activation hypothesis predicts a strong positive correlation between the 2 residuals, the authors found that it was not significantly different from 0. This finding reaffirms the view of energetic arousal and tense arousal as 2 distinct types of activation. PMID:12899373

Schimmack, Ulrich; Reisenzein, Rainer

2002-12-01

459

Unified understanding of the valence transition in the rare-earth monochalcogenides under pressure  

NASA Astrophysics Data System (ADS)

Valence instability is a key ingredient of the unusual properties of f electron materials, yet a clear understanding is lacking as it involves a complex interplay between f electrons and conduction states. Here we propose a unified picture of pressure-induced valence transition in Sm and Yb monochalcogenides, considered as a model system for mixed valent 4f-electron materials. Using high-resolution x-ray-absorption spectroscopy, we show that the valence transition is driven by the promotion of a 4f electron specifically into the lowest unoccupied (LU) 5d t2g band. We demonstrate with a promotional model that the nature of the transition at low pressures is intimately related to the density of states of the LU band, while at high pressures it is governed by the hybridization strength.

Jarrige, I.; Yamaoka, H.; Rueff, J.-P.; Lin, J.-F.; Taguchi, M.; Hiraoka, N.; Ishii, H.; Tsuei, K. D.; Imura, K.; Matsumura, T.; Ochiai, A.; Suzuki, H. S.; Kotani, A.

2013-03-01

460

A rift between implicit and explicit conditioned valence in human pain relief learning  

PubMed Central

Pain is aversive, but does the cessation of pain (‘relief’) have a reward-like effect? Indeed, fruitflies avoid an odour previously presented before a painful event, but approach an odour previously presented after a painful event. Thus, event-timing may turn punishment to reward. However, is event-timing also crucial in humans who can have explicit cognitions about associations? Here, we show that stimuli associated with pain-relief acquire positive implicit valence but are explicitly rated as aversive. Specifically, the startle response, an evolutionarily conserved defence reflex, is attenuated by stimuli that had previously followed a painful event, indicating implicit positive valence of the conditioned stimulus; nevertheless, participants explicitly evaluate these stimuli as ‘emotionally negative’. These results demonstrate a rift between the implicit and explicit conditioned valence induced by pain relief. They might explain why humans in some cases are attracted by conditioned stimuli despite explicitly judging them as negative. PMID:20356893

Andreatta, Marta; Muhlberger, Andreas; Yarali, Ayse; Gerber, Bertram; Pauli, Paul

2010-01-01