Extended Quantum Dimer Model and novel valence-bond phases
Nakata, Kouki; Totsuka, Keisuke
2011-01-01
We extend the quantum dimer model (QDM) introduced by Rokhsar and Kivelson so as to construct a concrete example of the model which exhibits the first-order phase transition between different valence-bond solids suggested recently by Batista and Trugman and look for the possibility of other exotic dimer states. We show that our model contains three exotic valence-bond phases (herringbone, checkerboard and dimer smectic) in the ground-state phase diagram and that it realizes the phase transiti...
Liu, Shi; Grinberg, Ilya; Takenaka, Hiroyuki; Rappe, Andrew M.
2012-01-01
We present a modified bond-valence model of PbTiO$_3$ 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. A new energy term, bond-valence vector energy, is introduced into the atomistic model and the potential parameters are re-optimized. The new model potential can be applied both to canonical ensemble ($NVT$) and isobaric-i...
Extended quantum dimer model and novel valence-bond phases
International Nuclear Information System (INIS)
We extend the quantum dimer model (QDM) introduced by Rokhsar and Kivelson so as to construct a concrete example of the model which exhibits the first-order phase transition between different valence-bond solids suggested recently by Batista and Trugman and look for the possibility of other exotic dimer states. We show that our model contains three exotic valence-bond phases (herringbone, checkerboard and dimer smectic) in the ground-state phase diagram and that it realizes the phase transition from the staggered valence-bond solid to the herringbone. The checkerboard phase has four-fold rotational symmetry, while the dimer smectic, in the absence of quantum fluctuations, has massive degeneracy originating from partial ordering only in one of the two spatial directions. A resonance process involving three dimers resolves this massive degeneracy and the dimer smectic becomes ordered (order from disorder)
The itinerant resonating-valence-bond model for superconductivity
International Nuclear Information System (INIS)
It has been proposed by Anderson that the pairing interaction in high temperature superconductors La/sub 2-x/ Sr/sub x/ Cuo4 and Yba2Cu3O/sub 7-x/ is magnetic in origin, and the recent discovery of antiferromagnetic ordering in La2CuO4 has been regarded as strong evidence in support of this so-called resonating-valence-bond (RVB) model. Close examination of the ordered state of this material reveals that it is an itinerant antiferromagnet. Accordingly, the superconducting properties must also be studied using the itinerant model approach, rather than the local moment model discussed so far in literature. This paper reports an approximate solution of the itinerant RVB model of superconductivity. It is shown that superconductivity can take place in a narrow region of the parameter space, and that the fluctuating local exchange field causes the superconducting state to be gapless. 19 refs
Havenith, R.W.A.
2005-01-01
In this Letter, the formulation and implementation of a parallel response property code for non-orthogonal, valence bond wave-functions are described. Test calculations on benzene and cyclobutadiene show that the polarisability and magnetisability tensors obtained using valence bond theory are compa
International Nuclear Information System (INIS)
The dependences of average V-O distances in inorganic compounds of vanadium of different valence on the degree of distortion of coordination polyhedra have been obtained by careful statistical treatment of modern structural data banks. Values of bond lengths in undistorted (regular) polyhedra are recommended. Theoretical analysis of the statistical data made it possible to calculate the most likely values of the parameters of the bond valence model: the interatomic distance for the single (two-electron) bond, corresponding to the single valence, and the bond softness parameter. Calculations of the sums of bond valences for some complicated cases (different coordination numbers, mixed vanadium valence) confirmed reliability of the recommended parameters.
Supersymmetric Valence Bond Solid States
Arovas, Daniel P.; Hasebe, Kazuki; Qi, Xiao-Liang; Zhang, Shou-Cheng
2009-01-01
In this work we investigate the supersymmetric version of the valence bond solid (SVBS) state. In one dimension, the SVBS states continuously interpolate between the valence bond states for integer and half-integer spin chains, and they generally describe superconducting valence bond liquid states. Spin and superconducting correlation functions can be computed exactly for these states, and their correlation lengths are equal at the supersymmetric point. In higher dimensions, the wave function...
Modelling of Ion Transport in Solids with a General Bond Valence Based Force-Field
Directory of Open Access Journals (Sweden)
S. Adams
2010-12-01
Full Text Available Empirical bond length - bond valence relations provide insight into the link between structure of and ion transport in solid electrolytes. Building on our earlier systematic adjustment of bond valence (BV parameters to the bond softness, here we discuss how the squared BV mismatch can be linked to the absolute energy scale and used as a general Morse-type interaction potential for analyzing low-energy pathways in ion conducting solid or mixed conductors either by an energy landscape approach or by molecular dynamics (MD simulations. For a wide range of Lithium oxides we could thus model ion transport revealing significant differences to an earlier geometric approach. Our novel BV-based force-field has also been applied to investigate a range of mixed conductors, focusing on cathode materials for lithium ion battery (LIB applications to promote a systematic design of LIB cathodes that combine high energy density with high power density. To demonstrate the versatility of the new BV-based force-field it is applied in exploring various strategies to enhance the power performance of safe low cost LIB materials (LiFePO4, LiVPO4F, LiFeSO4F, etc..
A Valence-Bond Nonequilibrium Solvation Model for a Twisting Cyanine Dye
McConnell, Sean; Olsen, Seth
2014-01-01
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 ...
A modified two-state empirical valence bond model for proton transport in aqueous solutions
International Nuclear Information System (INIS)
A detailed analysis of the proton solvation structure and transport properties in aqueous solutions is performed using classical molecular dynamics simulations. A refined two-state empirical valence bond (aTS-EVB) method, which is based on the EVB model of Walbran and Kornyshev and the anharmonic water force field, is developed in order to describe efficiently excess proton transport via the Grotthuss mechanism. The new aTS-EVB model clearly satisfies the requirement for simpler and faster calculation, because of the simplicity of the two-state EVB algorithm, while providing a better description of diffusive dynamics of the excess proton and water in comparison with the previous two-state EVB models, which significantly improves agreement with the available experimental data. The results of activation energies for the excess proton and water calculated between 300 and 340 K (the temperature range used in this study) are also found to be in good agreement with the corresponding experimental data
A modified two-state empirical valence bond model for proton transport in aqueous solutions
Energy Technology Data Exchange (ETDEWEB)
Mabuchi, Takuya, E-mail: mabuchi@nanoint.ifs.tohoku.ac.jp [Graduate School of Engineering, Tohoku University, Sendai, Miyagi 980-8577 (Japan); Fukushima, Akinori; Tokumasu, Takashi [Institute of Fluid Science, Tohoku University, Sendai, Miyagi 980-8577 (Japan)
2015-07-07
A detailed analysis of the proton solvation structure and transport properties in aqueous solutions is performed using classical molecular dynamics simulations. A refined two-state empirical valence bond (aTS-EVB) method, which is based on the EVB model of Walbran and Kornyshev and the anharmonic water force field, is developed in order to describe efficiently excess proton transport via the Grotthuss mechanism. The new aTS-EVB model clearly satisfies the requirement for simpler and faster calculation, because of the simplicity of the two-state EVB algorithm, while providing a better description of diffusive dynamics of the excess proton and water in comparison with the previous two-state EVB models, which significantly improves agreement with the available experimental data. The results of activation energies for the excess proton and water calculated between 300 and 340 K (the temperature range used in this study) are also found to be in good agreement with the corresponding experimental data.
Laughlin, R B
2004-01-01
There is increasing circumstantial evidence that the cuprate superconductors, and correlated-electron materials generally, defy simple materials categorization because of their proximity to one or more continuous zero-temperature phase transitions. This implies that the fifteen-year confusion about the cuprates is not fundamental at all but simply overinterpreted quantum criticality--an effect that seems mysterious by virtue of its hypersensitivity to perturbations, i.e. to sample imperfections in experiment and small modifications of approximation schemes in theoretical modeling, but is really just an unremarkable phase transition of some kind masquerading as something important, a sheep in wolf's clothing. This conclusion is extremely difficult for most physicists even to think about because it requires admitting that an identifiable physical phenomenon might cause the scientific method to fail in some cases. For this reason I have decided to explain the problem in a way that is nonthreatening, easy to read...
Valence-dependent bond-order potentials for modeling Ni-based superalloys
International Nuclear Information System (INIS)
The creep properties of Ni-based superalloys degrade with time due to precipitation of topologically close-packed (tcp) phases. We have compiled a structure map of the occurrence of tcp phases for binary transition-metal (TM) compounds from experimental databases. The structure map highlights the well-known role of the average d-band filling for the stability of tcp phases. Atomistic modelling of tcp stability requires extending the second-moment approximation to the electronic density of states (DOS) by including up to at least the sixth moment. We have developed an analytic bond-order potential (BOP) that systematically takes into account higher moment contributions to the DOS and depends explicitly on the valence of the TM elements. By including up to sixth-moment terms the analytic BOP is able to reproduce the structural trend across the non-magnetic 4d and 5d TM series. For the parameterization of the new BOP, we performed extensive density functional theory (DFT) calculations of the elemental and binary compound phases of Ni, the technologically important alloying element Cr, and the refractory metals Mo, Re, and W. In particular, we investigated the tcp phases A15, C14, C15, C36, μ, σ, and χ for the Ni-Cr, Re-W, Mo-Re, and Mo-W binary systems. We discuss the structural trends of the DFT calculations and compare to the predictions of the analytic BOP within the canonical d-band model
A Valence Bond Model for Aqueous Cu(II) and Zn(II) Ions in the AMOEBA Polarizable Force Field
Xiang, Jin Yu; Ponder, Jay W.
2012-01-01
A general molecular mechanics (MM) model for treating aqueous Cu2+ and Zn2+ ions was developed based on valence bond (VB) theory and incorporated into the AMOEBA polarizable force field. Parameters were obtained by fitting molecular mechanics energies to that computed by ab initio methods for gas phase tetra- and hexa-aqua metal complexes. Molecular dynamics (MD) simulations using the proposed AMOEBA-VB model were performed for each transition metal ion in aqueous solution and solvent coordin...
The Valence Bond Interpretation of Molecular Geometry.
Smith, Derek W.
1980-01-01
Presents ways in which the valence bond (VB) theory describes the bonding and geometry of molecules, following directly from earlier principles laid down by Pauling and others. Two other theories (molecular orbital approach and valence shell electron pair repulsion) are discussed and compared to VB. (CS)
The variational subspace valence bond method
Energy Technology Data Exchange (ETDEWEB)
Fletcher, Graham D. [Argonne National Laboratory, 9700 South Cass Ave., Lemont, Illinois 60439 (United States)
2015-04-07
The variational subspace valence bond (VSVB) method based on overlapping orbitals is introduced. VSVB provides variational support against collapse for the optimization of overlapping linear combinations of atomic orbitals (OLCAOs) using modified orbital expansions, without recourse to orthogonalization. OLCAO have the advantage of being naturally localized, chemically intuitive (to individually model bonds and lone pairs, for example), and transferrable between different molecular systems. Such features are exploited to avoid key computational bottlenecks. Since the OLCAO can be doubly occupied, VSVB can access very large problems, and calculations on systems with several hundred atoms are presented.
Albrecht, Marc; Mila, Frederic
1995-01-01
We study the competition between magnetic order and valence bond order in a two dimensional (2D) frustrated Heisenberg model introduced some time ago by Shastry and Sutherland ({\\sc B. Sriram Shastry} and {\\sc Bill Sutherland}, {\\em Physica} 108{\\bf B},1069 (1981) ) for which a configuration of dimers is known to be the ground state in a certain range of parameters. Using exact diagonalisation of small clusters, linear spin wave theory and Schwinger boson mean field theory, we show that the t...
Multicenter bonds, bond valence and bond charge apportion
International Nuclear Information System (INIS)
In the same way that the valence of an atom issues from the definition of bond index, we shoe here that the three-center bond index lends itself to the definition of a bond valence. Within the charge of a bond, we show that its self-charge (i.e., the amount of electron kept by the atoms involved in the bond) is parted in a such a way that the more electronegative atom tends to allot more electronic charge than the other atom. We give examples of these quantities and discuss the results for different kinds of chemical systems. We also show some results for four-center indices and report six-center indices for hexagonal rings. (author). 54 refs., 4 figs., 8 tabs
Valence Bond Glass Phase in the Diluted Kagome Antiferromagnets
Singh, R. R. P.
2010-01-01
We present a theory for site dilution in the Valence Bond Crystal Phase of the Kagome Lattice Heisenberg Model. The presence of an empty site leads to strong singlet bond across the impurity. It also creates a free spin, which delocalizes inside the unit cell. Finite concentration of quenched impurities leads to a Valence Bond Glass phase. This phase has short-range Valence Bond order, no spin-gap, large spin susceptibilities, linear specific heat due to two-level systems, as well as singlet ...
Chemical bonding, elasticity, and valence force field models: a case study for alpha-Pt_2Si and PtSi
Klepeis, J. E.; Beckstein, O.; Pankratov, O.; Hart, G. L. W.
2001-01-01
We have carried out a detailed study of the chemical bonding for two room-temperature stable platinum silicide phases, tetragonal alpha-Pt_2Si and orthorhombic PtSi. An analysis of the valence electronic charge density reveals surprising evidence of covalent three-center bonds in both silicide phases, as well as two-dimensional metallic sheets in alpha-Pt_2Si. These elements of the bonding are further analyzed by constructing valence force field models using the results from recent first prin...
Czerwińska, Karolina; Madura, Izabela D; Zachara, Janusz
2016-04-01
The systematic analysis of the geometry of three-coordinate boron in boronic acid derivatives with a common [CBO2] skeleton is presented. The study is based on the bond-valence vector (BVV) model [Zachara (2007). Inorg. Chem. 46, 9760-9767], a simple tool for the identification and quantitative estimation of both steric and electronic factors causing deformations of the coordination sphere. The empirical bond-valence (BV) parameters in the exponential equation [Brown & Altermatt (1985). Acta Cryst. B41, 244-247] rij and b, for B-O and B-C bonds were determined using data deposited in the Cambridge Structural Database. The values obtained amount to rBO = 1.364 Å, bBO = 0.37 Å, rBC = 1.569 Å, bBC = 0.28 Å, and they were further used in the calculation of BVV lengths. The values of the resultant BVV were less than 0.10 v.u. for 95% of the set comprising 897 [CBO2] fragments. Analysis of the distribution of BVV components allowed for the description of subtle in- and out-of plane deviations from the `ideal' (sp(2)) geometry of boron coordination sphere. The distortions specific for distinct groups of compounds such as boronic acids, cyclic and acyclic esters, benzoxaboroles and hemiesters were revealed. In cyclic esters the direction of strains was found to be controlled by the ring size effect. It was shown that the syn or anti location of substituents on O atoms is decisive for the deformations direction for both acids and acyclic esters. The greatest strains were observed in the case of benzoxaboroles which showed the highest deviation from the zero value of the resultant BVV. The out-of-plane distortions, described by the vz component of the resultant BVV, were ascertained to be useful in the identification of weak secondary interactions on the fourth coordination site of the boron centre. PMID:27048726
A valence bond model for aqueous Cu(II) and Zn(II) ions in the AMOEBA polarizable force field.
Xiang, Jin Yu; Ponder, Jay W
2013-04-01
A general molecular mechanics (MM) model for treating aqueous Cu(2+) and Zn(2+) ions was developed based on valence bond (VB) theory and incorporated into the atomic multipole optimized energetics for biomolecular applications (AMOEBA) polarizable force field. Parameters were obtained by fitting MM 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 that the AMOEBA-VB model generates the correct square-planar geometry for gas-phase tetra-aqua Cu(2+) 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 Zn(2+)-water complexes in good agreement with QM calculations. Analyses of the MD trajectories revealed a six-coordination first solvation shell for both Cu(2+) and Zn(2+) ions in aqueous solution, with ligation geometries falling in the range reported by previous studies. PMID:23212979
The extended variant of the bond valence-bond length correlation curve for boron(III)-oxygen bonds
International Nuclear Information System (INIS)
The extended variant of the bond valence (s)-bond length (r) correlation curve for boron(III)-oxygen bonds has been closely approximated using the three-parameter function s = [k/(r - l)] - m, where s is measured in valence units (vu), r is measured in Aa, k = 0.53 Aa.vu, l = 0.975(1) Aa and m = 0.32 vu. The function s = exp[(r0 - r)/b] traditionally used in the modern bond valence model requires the separate set of the bond valence parameters (r0 = 1.362 Aa; b = 0.23 Aa) in order to approximate the above s-r curve for the bonds shorter than ∝1.3 Aa.
The extended variant of the bond valence-bond length correlation curve for boron(III)-oxygen bonds
Energy Technology Data Exchange (ETDEWEB)
Sidey, Vasyl [Uzhgorod National Univ. (Ukraine). Dept. of Chemistry and Research Institute for Physics and Chemistry of Solids
2015-07-01
The extended variant of the bond valence (s)-bond length (r) correlation curve for boron(III)-oxygen bonds has been closely approximated using the three-parameter function s = [k/(r - l)] - m, where s is measured in valence units (vu), r is measured in Aa, k = 0.53 Aa.vu, l = 0.975(1) Aa and m = 0.32 vu. The function s = exp[(r{sub 0} - r)/b] traditionally used in the modern bond valence model requires the separate set of the bond valence parameters (r{sub 0} = 1.362 Aa; b = 0.23 Aa) in order to approximate the above s-r curve for the bonds shorter than ∝1.3 Aa.
Entanglement in a Valence-Bond-Solid State
Fan, Heng; Korepin, Vladimir; Roychowdhury, Vwani
2004-01-01
We study entanglement in Valence-Bond-Solid state. It describes the ground state of Affleck, Kennedy, Lieb and Tasaki quantum spin chain. The AKLT model has a gap and open boundary conditions. We calculate an entropy of a subsystem (continuous block of spins). It quantifies the entanglement of this block with the rest of the ground state. We prove that the entanglement approaches a constant value exponentially fast as the size of the subsystem increases. Actually we proved that the density ma...
Valence-Bond Concepts in Coordination Chemistry and the Nature of Metal-Metal Bonds.
Pauling, Linus; Herman, Zelek S.
1984-01-01
Discusses the valence-bond method, applying it to some coordination compounds of metals, especially those involving metal-metal bonds. Suggests that transition metals can form as many as nine covalent bonds, permitting valence-theory to be extended to transition metal compounds in a more effective way than has been possible before. (JN)
Chemical Bonding: The Orthogonal Valence-Bond View
Directory of Open Access Journals (Sweden)
Alexander F. Sax
2015-04-01
Full Text Available Chemical bonding is the stabilization of a molecular system by charge- and spin-reorganization processes in chemical reactions. These processes are said to be local, because the number of atoms involved is very small. With multi-configurational self-consistent field (MCSCF wave functions, these processes can be calculated, but the local information is hidden by the delocalized molecular orbitals (MO used to construct the wave functions. The transformation of such wave functions into valence bond (VB wave functions, which are based on localized orbitals, reveals the hidden information; this transformation is called a VB reading of MCSCF wave functions. The two-electron VB wave functions describing the Lewis electron pair that connects two atoms are frequently called covalent or neutral, suggesting that these wave functions describe an electronic situation where two electrons are never located at the same atom; such electronic situations and the wave functions describing them are called ionic. When the distance between two atoms decreases, however, every covalent VB wave function composed of non-orthogonal atomic orbitals changes its character from neutral to ionic. However, this change in the character of conventional VB wave functions is hidden by its mathematical form. Orthogonal VB wave functions composed of orthonormalized orbitals never change their character. When localized fragment orbitals are used instead of atomic orbitals, one can decide which local information is revealed and which remains hidden. In this paper, we analyze four chemical reactions by transforming the MCSCF wave functions into orthogonal VB wave functions; we show how the reactions are influenced by changing the atoms involved or by changing their local symmetry. Using orthogonal instead of non-orthogonal orbitals is not just a technical issue; it also changes the interpretation, revealing the properties of wave functions that remain otherwise undetected.
Novel Order Parameter to Characterize Valence-Bond-Solid States
Nakamura, Masaaki; Todo, Synge
2002-01-01
We propose an order parameter to characterize valence-bond-solid (VBS) states in quantum spin chains, given by the ground-state expectation value of a unitary operator appearing in the Lieb-Schultz-Mattis argument. We show that the order parameter changes the sign according to the configuration of the valence bonds. This allows us to determine the phase transition point in between different VBS states accurately. We demonstrate this theory in the bond-alternating Heisenberg chain and in the f...
Exploring covalently bonded diamondoid particles with valence photoelectron spectroscopy
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
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.
Topological Structure of Phase Vortex in Resonating Valence Bond Superconductivity
Institute of Scientific and Technical Information of China (English)
SHI Xu-Guang; DUAN Yi-Shi
2006-01-01
In this paper, based on the Schrodinger equation and the ψ-mapping theory, the accurate expression for the gradient of resonating valence bond superconducting phase Θs is found. The expression of (△→)Θs is just the velocity flow (V) without considering the coefficient. The curl of (△→)Θs is where the vortex lies, and has important relation to δ2(ψ) and an important relation to the zero points of resonating valence bond superconducting order parameter ψ. The topological structure of the vortex is characterized by the ψ-mapping topological numbers Hopf-index and Brouwer degrees. The Ginzberg-Landau equation in resonating valence bond state also is discussed in this theory. The magnetic property is discussed also.
Resonating Valence Bond states for low dimensional S=1 antiferromagnets
Liu, Zheng-Xin; Zhou, Yi; Ng, Tai-Kai
2014-03-01
We study S = 1 spin liquid states in low dimensions. We show that the resonating-valence-bond (RVB) picture of S = 1 / 2 spin liquid state can be generalized to S = 1 case. For S = 1 system, a many-body singlet (with even site number) can be decomposed into superposition of products of two-body singlets. In other words, the product states of two-body singlets, called the singlet pair states (SPSs), are over complete to span the Hilbert space of many-body singlets. Furthermore, we generalized fermionic representation and the corresponding mean field theory and Gutzwiller projected stats to S = 1 models. We applied our theory to study 1D anti-ferromagnetic bilinear-biquadratic model and show that both the ground states (including the phase transition point) and the excited states can be understood excellently well within the framework. Our method can be applied to 2D S = 1 antiferromagnets.
Regional versus Global Entanglement in Resonating-Valence-Bond states
Chandran, A; Sen, A; Sen, U; Vedral, V; Chandran, Anushya; Kaszlikowski, Dagomir; Sen, Aditi; Sen, Ujjwal; Vedral, Vlatko
2007-01-01
We investigate the entanglement properties of resonating valence bond states on two and higher dimensional lattices, which play an important role in the theory of conductivity. We show that these states are genuinely multipartite entangled, while there is only a negligible amount of two-site entanglement. We comment on possible physical implications of our findings.
Hong, Gongyi; Rosta, Edina; Warshel, Arieh
2006-10-01
The empirical valence bond (EVB) model provides an extremely powerful way for modeling and analyzing chemical reactions in solutions and proteins. However, this model is based on the unverified assumption that the off diagonal elements of the EVB Hamiltonian do not change significantly upon transfer of the reacting system from one phase to another. This ad hoc assumption has been rationalized by its consistency with empirically observed linear free energy relationships, as well as by other qualitative considerations. Nevertheless, this assumption has not been rigorously established. The present work explores the validity of the above EVB key assumption by a rigorous numerical approach. This is done by exploiting the ability of the frozen density functional theory (FDFT) and the constrained density functional theory (CDFT) models to generate convenient diabatic states for QM/MM treatments, and thus to examine the relationship between the diabatic and adiabatic surfaces, as well as the corresponding effective off diagonal elements. It is found that, at least for the test case of S(N)()2 reactions, the off diagonal element does not change significantly upon moving from the gas phase to solutions and thus the EVB assumption is valid and extremely useful. PMID:17004821
Bond charge approximation for valence electron density in elemental semiconductors
International Nuclear Information System (INIS)
The spatial valence electron distribution in silicon and diamond is calculated in adiabatic bond charge approximation at zero temperature when bond charges have the Gaussian shape and their tensor character is taken into account. An agreement between theory and experiment has been achieved. For this purpose Xia's ionic pseudopotentials and Schulze-Unger's dielectric function are used. By two additional parameters Asub(B) and Zsub(B)sup(') we describe the spatial extent of the bond charge and local-field corrections, respectively. The parameter Zsub(B)sup(') accounts for the ratio between the Coulomb and exchange correlation interactions of the valence electrons and its silicon and diamond values have different signs. (author)
The application of cholesky decomposition in valence bond calculation.
Gong, Xiping; Chen, Zhenhua; Wu, Wei
2016-09-01
The Cholesky decomposition (CD) technique, used to approximate the two-electron repulsion integrals (ERIs), is applied to the valence bond self-consistent field (VBSCF) method. Test calculations on ethylene, C2 n H2 n +2 , and C2 n H4 n -2 molecules (n = 1-7) show that the performance of the VBSCF method is much improved using the CD technique, and thus, the integral transformation from basis functions to VB orbitals is no longer the bottleneck in VBSCF calculations. The errors of the CD-based ERIs and of the total energy are controlled by the CD threshold, for which a value of 10(-6) ensures to control the total energy error within 10(-6) Hartree. © 2016 Wiley Periodicals, Inc. PMID:27377531
Fievez, Tim; De Proft, Frank; Geerlings, Paul; Weckhuysen, Bert M.; Havenith, Remco W. A.
2011-01-01
The concept of bond ionicity, obtained via a valence bond analysis, is invoked in the interpretation of the catalytic activity of supported vanadium oxides, in analogy with previous work conducted within the framework of conceptual DFT. For a set of model clusters representing the vanadium oxide sup
Valence-bond stripes in cuprates: ARPES and inter-layer tunneling
Energy Technology Data Exchange (ETDEWEB)
Wollny, Alexander; Vojta, Matthias [Institut fuer Theoretische Physik, Universitaet zu Koeln (Germany)
2009-07-01
The effect of stripe formation in the underdoped cuprates has been a much discussed topic for more than ten years. Motivated by recent neutron scattering and STM experiments we develop a phenomenological mean-field model for valence-bond stripes dominated by local singlet formation. We explore the electronic spectrum for valence-bond stripes and its interplay with d-wave superconductivity. The results are compatible with ARPES data for La{sub 1.675}Eu{sub 0.2}Sr{sub 0.125}CuO{sub 4}. Further we derive the effect of long ranged stripe order (with and without magnetic ordering) on the interlayer tunneling between two CuO{sub 2}-layers, giving an alternative mechanism, besides the anti-phase SC scenario, for effective layer decoupling in La{sub 1.875}Ba{sub 0.125}CuO{sub 4}.
Valence-bond stripes in cuprates: ARPES and inter-layer tunneling
International Nuclear Information System (INIS)
The effect of stripe formation in the underdoped cuprates has been a much discussed topic for more than ten years. Motivated by recent neutron scattering and STM experiments we develop a phenomenological mean-field model for valence-bond stripes dominated by local singlet formation. We explore the electronic spectrum for valence-bond stripes and its interplay with d-wave superconductivity. The results are compatible with ARPES data for La1.675Eu0.2Sr0.125CuO4. Further we derive the effect of long ranged stripe order (with and without magnetic ordering) on the interlayer tunneling between two CuO2-layers, giving an alternative mechanism, besides the anti-phase SC scenario, for effective layer decoupling in La1.875Ba0.125CuO4.
Patil, Amol Baliram; Bhanage, Bhalchandra Mahadeo
2016-06-21
The nature of bonding interactions between the cation and the anion of an ionic liquid is at the heart of understanding ionic liquid properties. A particularly interesting case is a special class of ionic liquids known as protic ionic liquids. The extent of proton transfer in protic ionic liquids has been observed to vary according to the interacting species. Back proton transfer renders protic ionic liquids volatile and to be considered as inferior ionic liquids. We try to address this issue by employing modern ab initio valence bond theory calculations. The results indicate that the bonding in the cation and the anion of a prototypical ionic liquid, ethylammonium nitrate, is fundamentally different. It is neither characteristic of covalent/polar covalent bonding nor ionic bonding but rather charge shift bonding as a resonance hybrid of two competing ionic molecular electronic structure configurations. An investigation of other analogous protic ionic liquids reveals that this charge shift bonding seems to be a typical characteristic of protic ionic liquids while the ionic solid analogue compound ammonium nitrate has less charge shift bonding character as compared to protic ionic liquids. Further the extent of charge shift bonding character has been found to be congruent with the trends in many physicochemical properties such as melting point, conductivity, viscosity, and ionicity of the studied ionic liquids indicating that percentage charge shift character may serve as a key descriptor for large scale computational screening of ionic liquids with desired properties. PMID:27229870
Red-Shifting versus Blue-Shifting Hydrogen Bonds: Perspective from Ab Initio Valence Bond Theory.
Chang, Xin; Zhang, Yang; Weng, Xinzhen; Su, Peifeng; Wu, Wei; Mo, Yirong
2016-05-01
Both proper, red-shifting and improper, blue-shifting hydrogen bonds have been well-recognized with enormous experimental and computational studies. The current consensus is that there is no difference in nature between these two kinds of hydrogen bonds, where the electrostatic interaction dominates. Since most if not all the computational studies are based on molecular orbital theory, it would be interesting to gain insight into the hydrogen bonds with modern valence bond (VB) theory. In this work, we performed ab initio VBSCF computations on a series of hydrogen-bonding systems, where the sole hydrogen bond donor CF3H interacts with ten hydrogen bond acceptors Y (═NH2CH3, NH3, NH2Cl, OH(-), H2O, CH3OH, (CH3)2O, F(-), HF, or CH3F). This series includes four red-shifting and six blue-shifting hydrogen bonds. Consistent with existing findings in literature, VB-based energy decomposition analyses show that electrostatic interaction plays the dominating role and polarization plays the secondary role in all these hydrogen-bonding systems, and the charge transfer interaction, which denotes the hyperconjugation effect, contributes only slightly to the total interaction energy. As VB theory describes any real chemical bond in terms of pure covalent and ionic structures, our fragment interaction analysis reveals that with the approaching of a hydrogen bond acceptor Y, the covalent state of the F3C-H bond tends to blue-shift, due to the strong repulsion between the hydrogen atom and Y. In contrast, the ionic state F3C(-) H(+) leads to the red-shifting of the C-H vibrational frequency, owing to the attraction between the proton and Y. Thus, the relative weights of the covalent and ionic structures essentially determine the direction of frequency change. Indeed, we find the correlation between the structural weights and vibrational frequency changes. PMID:27074500
Resonant valence bond states in zinc vacancies induce the ferromagnetism of ZnO
Sun, Shih-Jye
2016-05-01
A theoretical model was proposed to investigate the mechanism of ferromagnetism in ZnO as well as to simulate the experimental result that the ferromagnetism can be enhanced by UV irradiation as UV photon energy is equivalent to the band gap. In the model, the spin moments arise from the trapped electrons in oxygen vacancy states and coexist with the itinerant electrons which reside in zinc vacancy states and fall into resonant valence bond states. Charge exchange between the conduction band of ZnO and both vacancy states makes electrons on both vacancy states delocalized and results in a decrease of the ferromagnetism as well.
Czech Academy of Sciences Publication Activity Database
Ponec, Robert
2005-01-01
Roč. 114, 1-3 (2005), s. 208-212. ISSN 1432-881X R&D Projects: GA AV ČR(CZ) IAA4072403 Institutional research plan: CEZ:AV0Z4072921 Keywords : bonding in solids * bond order * valence Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.179, year: 2005
Advances in Generalized Valence Bond-Coupled Cluster Methods for Electronic Structure Theory
Lawler, Keith Vanoy
2009-01-01
The electron-electron correlation term in the electronic energy of a molecule is the most difficult term to compute, yet it is of both qualitative and quantitative importance for a diverse range of chemical applications of computational quantum chemistry. Generalized Valence Bond-Coupled Cluster (GVB-CC) methods are computationally efficient, size-consistent wavefunction based methods to capture the most important static (valence) contributions to the correlation energy. Despite these advanta...
Valence Bond Solid Order Near Impurities in Two-Dimensional Quantum Antiferromagnets
Metlitski, Max A.; Sachdev, Subir
2008-01-01
Recent scanning tunneling microscopy (STM) experiments on underdoped cuprates have displayed modulations in the local electronic density of states, which are centered on a Cu-O-Cu bond [Kohsaka et al. Science 315 1380 (2007)]. As a paradigm of the pinning of such bond-centered ordering in strongly correlated systems, we present the theory of valence bond solid (VBS) correlations near a single impurity in a square lattice antiferromagnet. The antiferromagnet is assumed to be in the vicinity of...
The new Resonating Valence Bond Method for ab-initio Electronic Simulations
Sorella, Sandro
2013-01-01
The Resonating Valence Bond theory of the chemical bond was introduced soon after the discovery of quantum mechanics and has contributed to explain the role of electron correlation within a particularly simple and intuitive approach where the chemical bond between two nearby atoms is described by one or more singlet electron pairs. In this chapter Pauling's resonating valence bond theory of the chemical bond is revisited within a new formulation, introduced by P.W. Anderson after the discovery of High-Tc superconductivity. It is shown that this intuitive picture of electron correlation becomes now practical and efficient, since it allows us to faithfully exploit the locality of the electron correlation, and to describe several new phases of matter, such as Mott insulators, High-Tc superconductors, and spin liquid phases.
Maximized string order parameters in the valence bond solid states of quantum integer spin chains
Tu, Hong-Hao; Zhang, Guang-Ming; Xiang, Tao
2008-01-01
We propose a set of maximized string order parameters to describe the hidden topological order in the valence bond solid states of quantum integer spin-S chains. These optimized string order parameters involve spin-twist angles corresponding to $Z_{S+1}$ rotations around $z$ or $x$-axes, suggesting a hidden $Z_{S+1}\\times Z_{S+1}$ symmetry. Our results also suggest that a local triplet excitation in the valence bond solid states carries a $Z_{S+1}$ topological charge measured by these maximiz...
On the valence model for radiative capture
International Nuclear Information System (INIS)
We give several parametrizations for the elastic scattering and radiative capture cross sections for low neutron bombarding energy and discuss the relationship between the corresponding resonance parameters. We then peform an extensive investigation of the valence radiative capture model of Lane and Lynn. This model is formulated here in the frame of the shell-model approach. We exhibit the similarities and differences between our results and those derived from the R-matrix approach by Lane and Lynn on the one hand and from the optical-model approach by Lane and Mughabghab on the other hand. Particular attention is paid to the choice of the average potential well in the shell model approach, in relation to the proper way to identify theoretical quantities and phenomenological parameters. We show that practically equivalent results can be obtained from a complex average potential well and from a suitably chosen real potential well. The following topics are investigated formally and numerically: dependence of the various theoretical expressions on the choice of the (real or complex) average potential well; relative importance of external and internal capture; dependence of photon widths and background cross section on mass number (for thermal energy and for E=100 keV); dependence of the resonance parameters and background cross sections on energy, for A=60; comparison between experimental data and theoretical values for radiative capture on 56Fe and 60Ni. We discuss the conditions of validity of the valence capture model The contribution of the low-lying excited target states is investigated formally and numerically
Effects of Magnetic Field on the Valence Bond Property of the Double-Quantum-Dot Molecule
Institute of Scientific and Technical Information of China (English)
王立民; 罗莹; 马本堃
2002-01-01
The effects of the magnetic field on the valence bond property of the double-quantum-dot molecule are numerically studied by the finite element method and perturbation approach because of the absence of cylindrical symmetry in the horizontally coupled dots. The calculation results show that the energy value of the ground state changes differently from that of the first excited state with increasing magnetic field strength, and they cross under a certain magnetic field. The increasing magnetic field makes the covalent bond state change into an ionic bond state, which agrees qualitatively with experimental results and makes ionic bond states remain. The oscillator strength of transition between covalent bond states decreases distinctly with the increasing magnetic field strength, when the molecule is irradiated by polarized light. Such a phenomenon is possibly useful for actual applications.
Plaquette Valence Bond Theory of High-Temperature Superconductivity
Harland, M; Katsnelson, M I; Lichtenstein, A.I.
2016-01-01
We present a strong-coupling approach to the theory of high-temperature superconductivity based on the observation of a quantum critical point in the plaquette within the t,t' Hubbard model. The crossing of ground state energies in the N=2,3,4 sectors occurs for parameters close to the optimal doping. The theory predicts the maximum of the d(x2-y2)-wave order parameter at the border between localized and itinerant electron behavior and gives a natural explanation for the pseudo-gap formation ...
Ying, Fuming
2010-01-01
This thesis deals with two disjoint subdiciplines of quantum chemistry. One isthe most used electronic structure method today, density functional theory(DFT), and the other one of the least used electronic structure methods,valence bond theory (VB). The work on DFT is based on previous developments inthe department in density functional response theory and involves studies ofhyperfine coupling constants which are measured in electron paramagneticresonance experiments. The method employed i...
Resonating-Valence-Bond Physics Is Not Always Governed by the Shortest Tunneling Loops
Ralko, Arnaud; Rousochatzakis, Ioannis
2015-10-01
It is well known that the low-energy sector of quantum spin liquids and other magnetically disordered systems is governed by short-ranged resonating-valence bonds. Here we show that the standard minimal truncation to the nearest-neighbor valence-bond basis fails completely even for systems where it should work the most, according to received wisdom. This paradigm shift is demonstrated for the quantum spin-1 /2 square kagome, where strong geometric frustration, similar to the kagome, prevents magnetic ordering down to zero temperature. The shortest tunneling events bear the strongest longer-range singlet fluctuations, leading to amplitudes that do not drop exponentially with the length of the loop L , and to an unexpected loop-six valence-bond crystal, which is otherwise very high in energy at the minimal truncation level. The low-energy effective description gives in addition a clear example of correlated loop processes that depend not only on the type of the loop but also on its lattice embedding, a direct manifestation of the long-range nature of the virtual singlets.
Angeli, Celestino; Cimiraglia, Renzo; Malrieu, Jean-Paul
2008-01-01
Valence bond (VB) is one of the cornerstone theories of quantum chemistry. Even if in practical applications the molecular orbital (MO) approach has obtained more attention, some basic chemical concepts (such as the nature of the chemical bond and the failure of the single determinant-based MO methods in describing the bond cleavage) are normally…
Energy Technology Data Exchange (ETDEWEB)
Domin, D.; Braida, Benoit; Lester Jr., William A.
2008-05-30
This study explores the use of breathing orbital valence bond (BOVB) trial wave functions for diffusion Monte Carlo (DMC). The approach is applied to the computation of the carbon-hydrogen (C-H) bond dissociation energy (BDE) of acetylene. DMC with BOVB trial wave functions yields a C-H BDE of 132.4 {+-} 0.9 kcal/mol, which is in excellent accord with the recommended experimental value of 132.8 {+-} 0.7 kcal/mol. These values are to be compared with DMC results obtained with single determinant trial wave functions, using Hartree-Fock orbitals (137.5 {+-} 0.5 kcal/mol) and local spin density (LDA) Kohn-Sham orbitals (135.6 {+-} 0.5 kcal/mol).
Valence XPS structure and chemical bond in Cs2UO2Cl4
Directory of Open Access Journals (Sweden)
Teterin Yury A.
2016-01-01
Full Text Available Quantitative analysis was done of the valence electrons X-ray photoelectron spectra structure in the binding energy (BE range of 0 eV to ~35 eV for crystalline dicaesium tetrachloro-dioxouranium (VI (Cs2UO2Cl4. This compound contains the uranyl group UO2. The BE and structure of the core electronic shells (~35 eV-1250 eV, as well as the relativistic discrete variation calculation results for the UO2Cl4(D4h cluster reflecting U close environment in Cs2UO2Cl4 were taken into account. The experimental data show that many-body effects due to the presence of cesium and chlorine contribute to the outer valence (0-~15 eV BE spectral structure much less than to the inner valence (~15 eV-~35 eV BE one. The filled U5f electronic states were theoretically calculated and experimentally confirmed to be present in the valence band of Cs2UO2Cl4. It corroborates the suggestion on the direct participation of the U5f electrons in the chemical bond. Electrons of the U6p atomic orbitals participate in formation of both the inner (IVMO and the outer (OVMO valence molecular orbitals (bands. The filled U6p and the O2s, Cl3s electronic shells were found to make the largest contributions to the IVMO formation. The molecular orbitals composition and the sequence order in the binding energy range 0 eV-~35 eV in the UO2Cl4 cluster were established. The experimental and theoretical data allowed a quantitative molecular orbitals scheme for the UO2Cl4 cluster in the BE range 0-~35 eV, which is fundamental for both understanding the chemical bond nature in Cs2UO2Cl4 and the interpretation of other X-ray spectra of Cs2UO2Cl4. The contributions to the chemical binding for the UO2Cl4 cluster were evaluated to be: the OVMO contribution - 76%, and the IVMO contribution - 24 %.
Chen, Zhenhua; Chen, Xun; Wu, Wei
2013-04-01
In this series, the n-body reduced density matrix (n-RDM) approach for nonorthogonal orbitals and their applications to ab initio valence bond (VB) methods are presented. As the first paper of this series, Hamiltonian matrix elements between internally contracted VB wave functions are explicitly provided by means of nonorthogonal orbital based RDM approach. To this end, a more generalized Wick's theorem, called enhanced Wick's theorem, is presented both in arithmetical and in graphical forms, by which the deduction of expressions for the matrix elements between internally contracted VB wave functions is dramatically simplified, and the matrix elements are finally expressed in terms of tensor contractions of electronic integrals and n-RDMs of the reference VB self-consistent field wave function. A string-based algorithm is developed for the purpose of evaluating n-RDMs in an efficient way. Using the techniques presented in this paper, one is able to develop new methods and efficient algorithms for nonorthogonal orbital based many-electron theory much easier than by use of the first quantized formulism.
Application of bond valence method in the non-isovalent semiconductor alloy (GaN)$_{1-x}$(ZnO)$_x$
Liu, Jian
2015-01-01
This paper studies the bond valence method (BVM) and its application in the non-isovalent semiconductor alloy (GaN)$_{\\rm{1-x}}$(ZnO)$_{\\rm{x}}$. Particular attention is paid to the role of short-range order (SRO). A physical interpretation based on atomic orbital interaction is proposed and examined by density-functional theory (DFT) calculations. Combining BVM with Monte-Carlo simulations and a DFT-based cluster expansion model, bond-length distributions and bond-angle variations are predic...
Resonating Valence Bond Quantum Monte Carlo: Application to the ozone molecule
Azadi, Sam; Kühne, Thomas D
2015-01-01
We study the potential energy surface of the ozone molecule by means of Quantum Monte Carlo simulations based on the resonating valence bond concept. The trial wave function consists of an antisymmetrized geminal power arranged in a single-determinant that is multiplied by a Jastrow correlation factor. Whereas the determinantal part incorporates static correlation effects, the augmented real-space correlation factor accounts for the dynamics electron correlation. The accuracy of this approach is demonstrated by computing the potential energy surface for the ozone molecule in three vibrational states: symmetric, asymmetric and scissoring. We find that the employed wave function provides a detailed description of rather strongly-correlated multi-reference systems, which is in quantitative agreement with experiment.
International Nuclear Information System (INIS)
In order to guarantee the desired invariance properties of bond indices, the importance of expliciting the tensor character of the matrices concerned, so as to deal with a contraction in the tensor sense between a covariant index and a contravariant one is shown. An MO valence definition using Wiberg's indices is generalized to non-orthogonal bases and a straightforward definition of oxidation numbers is proposed. IEH calculations of their magnitudes for some appropriate examples are performed: they emphasize the role of 'secondary' bonds in N and C-containing compounds; the hydrogen behaviour in half-bonds and strong H-bonds is satisfactorily accounted for; valence and oxidation number values are assigned to Fe, Co and Ni in a few complexes. (Author)
Block correlated second order perturbation theory with a generalized valence bond reference function
International Nuclear Information System (INIS)
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
Resonating Valence Bonds and Mean-Field d-Wave Superconductivity in Graphite
Energy Technology Data Exchange (ETDEWEB)
Black-Schaffer, Annica M.
2010-04-27
We investigate the possibility of inducing superconductivity in a graphite layer by electronic correlation effects. We use a phenomenological microscopic Hamiltonian which includes nearest neighbor hopping and an interaction term which explicitly favors nearest neighbor spin-singlets through the well-known resonance valence bond (RVB) character of planar organic molecules. Treating this Hamiltonian in mean-field theory, allowing for bond-dependent variation of the RVB order parameter, we show that both s- and d-wave superconducting states are possible. The d-wave solution belongs to a two-dimensional representation and breaks time reversal symmetry. At zero doping there exists a quantum critical point at the dimensionless coupling J/t = 1.91 and the s- and d-wave solutions are degenerate for low temperatures. At finite doping the d-wave solution has a significantly higher T{sub c} than the s-wave solution. By using density functional theory we show that the doping induced from sulfur absorption on a graphite layer is enough to cause an electronically driven d-wave superconductivity at graphite-sulfur interfaces. We also discuss applying our results to the case of the intercalated graphites as well as the validity of a mean-field approach.
Halpern, Arthur M.; Glendening, Eric D.
2013-01-01
A three-part project for students in physical chemistry, computational chemistry, or independent study is described in which they explore applications of valence bond (VB) and molecular orbital-configuration interaction (MO-CI) treatments of H[subscript 2]. Using a scientific spreadsheet, students construct potential-energy (PE) curves for several…
Structural and magnetic properties of Ba2LuMoO6: a valence bond glass.
Coomer, Fiona C; Cussen, Edmund J
2013-02-27
We report here the synthesis of the site ordered double perovskite Ba(2)LuMoO(6). Rietveld refinement of room temperature powder x-ray diffraction measurements indicates that it crystallizes in the cubic space group Fm3m, with a = 8.3265(1) Å. Powder neutron diffraction data indicate that, unusually, this cubic symmetry is maintained down to 2 K, with [Formula: see text], Mo(5+) ions situated on the frustrated face-centred cubic lattice. Despite dc-susceptibility measurements showing Curie-Weiss behaviour with strong antiferromagnetic interactions at T ≥ 200 K, there is no evidence of long range magnetic ordering at 2 K. At T ≤ 50 K, susceptibility measurements indicate a loss in moment to ∼18% of the expected value, and there is a corresponding loss in the magnitude of the magnetic exchange. The structural and magnetic properties of this compound are compared with the related compound Ba(2)YMoO(6), which is a valence bond glass. PMID:23343826
Structural and magnetic properties of Ba2LuMoO6: a valence bond glass
International Nuclear Information System (INIS)
We report here the synthesis of the site ordered double perovskite Ba2LuMoO6. Rietveld refinement of room temperature powder x-ray diffraction measurements indicates that it crystallizes in the cubic space group F m 3-bar m, with a = 8.3265(1) Å. Powder neutron diffraction data indicate that, unusually, this cubic symmetry is maintained down to 2 K, with S= 1/2 , Mo5+ ions situated on the frustrated face-centred cubic lattice. Despite dc-susceptibility measurements showing Curie–Weiss behaviour with strong antiferromagnetic interactions at T ≥ 200 K, there is no evidence of long range magnetic ordering at 2 K. At T ≤ 50 K, susceptibility measurements indicate a loss in moment to ∼18% of the expected value, and there is a corresponding loss in the magnitude of the magnetic exchange. The structural and magnetic properties of this compound are compared with the related compound Ba2YMoO6, which is a valence bond glass. (fast track communication)
Comment on ''Valence QCD: Connecting QCD to the quark model''
International Nuclear Information System (INIS)
The author criticize certain conclusions about the physics of hadrons drawn from a ''valence QCD'' approximation to QCD. Lattice QCD is not just useful as a technique for calculating strong interaction observables like the proton mass: it can also be used to help understand QCD. This is the goal of the work described in reference 1. Its authors present a field theory which they call valence QCD (vQCD) which they hope can be identified with the valence quark model. The key feature built into vQCD is a form of suppression of Z-graphs, i.e., of quarks propagating backward in time. The authors make sound arguments for the importance of trying to capture the essence of the quark model in a field-theoretic framework, and present some interesting results (both theoretical and numerical) on vQCD. This comment is not directed at the goals of vQCD but rather at certain conclusions about the physics of hadrons which the authors have drawn from their work which the author considers unjustified. Foremost among these is the claim highlighted in their abstract that baryon hyperfine interactions are ''largely attributed to the Goldstone boson exchanges between the quarks'' and not to standard one-gluon-exchange (OGE) forces
Kee, Hae-Young
2014-03-01
The EtMe3P and EtMe3Sb nearly triangular organic salts are distinguished from most other Pd[(dmit)2] based salts, as they display valence bond and no long range order, respectively. Under pressure, a superconducting phase is revealed in EtMe3P near the boundary of valence bond order. We use slave-rotor theory with an enlarged unit cell to study competition between uniform and broken translational symmetry states, offering a theoretical framework capturing the superconducting, valence bond order, spin liquid, and metallic phases on an isotropic triangular lattice. Our finite temperature phase diagram manifests a remarkable resemblance to the phase diagram of the EtMe3P salt, where the re-entrant transitions of the type insulator-metal-insulator can be explained by an entropy difference between metal and the U(1) spin liquid. We find that the superconducting pairing symmetry is d +/- id , and predict different temperature dependences of the specific heat between the spin liquid and metal. Canadian Institute for Advanced Research, NSERC of Canada.
Indian Academy of Sciences (India)
Sarvesh Kumar Pandey; Prasanta Das; Puspendu K Das; Elangannan Arunan; Sadasivam Manogaran
2015-06-01
It has been shown earlier1 that the relaxed force constants (RFCs) could be used as a measure of bond strength only when the bonds form a part of the complete valence internal coordinates (VIC) basis. However, if the bond is not a part of the complete VIC basis, its RFC is not necessarily a measure of bond strength. Sometimes, it is possible to have a complete VIC basis that does not contain the intramolecular hydrogen bond (IMHB) as part of the basis. This means the RFC of IMHB is not necessarily a measure of bond strength. However, we know that IMHB is a weak bond and hence its RFC has to be a measure of bond strength. We resolve this problem of IMHB not being part of the complete basis by postulating `equivalent’ basis sets where IMHB is part of the basis at least in one of the equivalent sets of VIC. As long as a given IMHB appears in one of the equivalent complete VIC basis sets, its RFC could be used as a measure of bond strength parameter.
Tahat, Amani; Martí, Jordi
2016-07-01
Microscopic characteristics of an aqueous excess proton in a wide range of thermodynamic states, from low density amorphous ices (down to 100 K) to high temperature liquids under the critical point (up to 600 K), placed inside hydrophobic graphene slabs at the nanometric scale (with interplate distances between 3.1 and 0.7 nm wide) have been analyzed by means of molecular dynamics simulations. Water-proton and carbon-proton forces were modeled with a multistate empirical valence bond method. Densities between 0.07 and 0.02 Å(-3) have been considered. As a general trend, we observed a competition between effects of confinement and temperature on structure and dynamical properties of the lone proton. Confinement has strong influence on the local structure of the proton, whereas the main effect of temperature on proton properties is observed on its dynamics, with significant variation of proton transfer rates, proton diffusion coefficients, and characteristic frequencies of vibrational motions. Proton transfer is an activated process with energy barriers between 1 and 10 kJ/mol for both proton transfer and diffusion, depending of the temperature range considered and also on the interplate distance. Arrhenius-like behavior of the transfer rates and of proton diffusion are clearly observed for states above 100 K. Spectral densities of proton species indicated that in all states Zundel-like and Eigen-like complexes survive at some extent. © 2016 Wiley Periodicals, Inc. PMID:27189810
International Nuclear Information System (INIS)
The impact of actinides on the environment is mitigated by their interaction with particle surfaces and by incorporation into suitable waste forms. In both cases, a fundamental knowledge of the local co-ordination environment of actinide ions is essential for understanding their stability in various near-surface environments under a range of conditions. When actinide ions are sorbed on mineral surfaces, the extent to which the ions are immobilised depends on the type of surface complex or solid precipitate that forms. When incorporated into a glass or crystalline waste form, the stability of the actinide will depend in part on its redox state and local co-ordination environment. In both cases, XAFS spectroscopy can provide unique information on the number and types of first and, in certain cases, more distant neighbours, and their geometric arrangement (including inter-atomic distances and a measure of their disorder). When this structural information from XAFS spectroscopy is combined with Pauling bond valence theory and modem bond valences corrected for bond length variations, it is also possible to develop plausible models for their medium-range co-ordination environments (out to ≅ 4 Angstrom radial distance around the actinide) for both sorbed actinide ions and those present in a silicate glass or melt. We discuss results from several XAFS studies of the naturally occurring actinides uranium and thorium in sorption samples, silicate glasses and silicate melts at high temperature. (authors)
Valence tautomerism in synthetic models of cytochrome P450.
Das, Pradip Kumar; Samanta, Subhra; McQuarters, Ashley B; Lehnert, Nicolai; Dey, Abhishek
2016-06-14
CytP450s have a cysteine-bound heme cofactor that, in its as-isolated resting (oxidized) form, can be conclusively described as a ferric thiolate species. Unlike the native enzyme, most synthetic thiolate-bound ferric porphyrins are unstable in air unless the axial thiolate ligand is sterically protected. Spectroscopic investigations on a series of synthetic mimics of cytP450 indicate that a thiolate-bound ferric porphyrin coexists in organic solutions at room temperature (RT) with a thiyl-radical bound ferrous porphyrin, i.e., its valence tautomer. The ferric thiolate state is favored by greater enthalpy and is air stable. The ferrous thiyl state is favored by entropy, populates at RT, and degrades in air. These ground states can be reversibly interchanged at RT by the addition or removal of water to the apolar medium. It is concluded that hydrogen bonding and local electrostatics protect the resting oxidized cytP450 active site from degradation in air by stabilizing the ferric thiolate ground state in contrast to its synthetic analogs. PMID:27302948
Thermomechanical properties of graphene: valence force field model approach
International Nuclear Information System (INIS)
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 (|ε| ⪅ 0.02) is the total energy symmetrical in the strain, while it behaves completely differently beyond this threshold; (ii) the important energy contributions in stretching experiments are stretching, angle bending, an out-of-plane term, and a term that provides repulsion against π-π misalignment; (iii) in compressing experiments the two latter terms increase rapidly, and beyond the buckling transition stretching and bending energies are found to be constant; (iv) from stretching-compressing simulations we calculated the Young’s modulus at room temperature 350 ± 3.15 N m-1, which is in good agreement with experimental results (340 ± 50 N m-1) and with ab initio results (322-353) N m-1; (v) molar heat capacity is estimated to be 24.64 J mol-1 K-1 which is comparable with the Dulong-Petit value, i.e. 24.94 J mol-1 K-1, and is almost independent of the strain; (vi) nonlinear scaling properties are obtained from height-height correlations at finite temperature; (vii) the used valence force field model results in a temperature independent bending modulus for graphene, and (viii) the Grüneisen parameter is estimated to be 0.64. (paper)
In-Medium Pion Valence Distributions in a Light-Front Model
de Melo, J P B C; Ahmed, I
2016-01-01
Pion valence distributions in nuclear medium and vacuum are studied in a light-front constituent quark model. The in-medium input for studying the pion properties is calculated by the quark-meson coupling model. We find that the in-medium pion valence distribution, as well as the in-medium pion valence wave function, are substantially modified at normal nuclear matter density, due to the reduction in the pion decay constant.
Holmes, Sean T; Alkan, Fahri; Iuliucci, Robbie J; Mueller, Karl T; Dybowski, Cecil
2016-07-01
(29) Si and (31) P magnetic-shielding tensors in covalent network solids have been evaluated using periodic and cluster-based calculations. The cluster-based computational methodology employs pseudoatoms to reduce the net charge (resulting from missing co-ordination on the terminal atoms) through valence modification of terminal atoms using bond-valence theory (VMTA/BV). The magnetic-shielding tensors computed with the VMTA/BV method are compared to magnetic-shielding tensors determined with the periodic GIPAW approach. The cluster-based all-electron calculations agree with experiment better than the GIPAW calculations, particularly for predicting absolute magnetic shielding and for predicting chemical shifts. The performance of the DFT functionals CA-PZ, PW91, PBE, rPBE, PBEsol, WC, and PBE0 are assessed for the prediction of (29) Si and (31) P magnetic-shielding constants. Calculations using the hybrid functional PBE0, in combination with the VMTA/BV approach, result in excellent agreement with experiment. © 2016 Wiley Periodicals, Inc. PMID:27117609
Photoemission signatures of valence-bond stripes in cuprates: Long-range vs. short-range order
International Nuclear Information System (INIS)
Recent experiments indicate that the tendency toward the formation of unidirectional charge density waves ('stripes') is common to various underdoped cuprates. We discuss momentum-resolved spectral properties of valence-bond stripes, comparing the situations of ideal and short-range stripe order, the latter being relevant for weak and/or disorder-pinned stripes. We find clear signatures of ordered stripes, although matrix element effects suppress most shadow band features. With decreasing stripe correlation length, stripe signatures are quickly washed out, the only remaining effect being a broadening of antinodal quasiparticles. This insensitivity of photoemission to short-range stripe order may be employed to distinguish it from nematic order, e.g. in underdoped YBa2Cu3O6+δ.
Photoemission signatures of valence-bond stripes in cuprates: Long-range vs. short-range order
Energy Technology Data Exchange (ETDEWEB)
Wollny, Alexander [Institut fuer Theoretische Physik, Universitaet zu Koeln, Zuelpicher Strasse 77, 50937 Koeln (Germany); Vojta, Matthias, E-mail: vojta@thp.uni-koeln.d [Institut fuer Theoretische Physik, Universitaet zu Koeln, Zuelpicher Strasse 77, 50937 Koeln (Germany)
2009-10-15
Recent experiments indicate that the tendency toward the formation of unidirectional charge density waves ('stripes') is common to various underdoped cuprates. We discuss momentum-resolved spectral properties of valence-bond stripes, comparing the situations of ideal and short-range stripe order, the latter being relevant for weak and/or disorder-pinned stripes. We find clear signatures of ordered stripes, although matrix element effects suppress most shadow band features. With decreasing stripe correlation length, stripe signatures are quickly washed out, the only remaining effect being a broadening of antinodal quasiparticles. This insensitivity of photoemission to short-range stripe order may be employed to distinguish it from nematic order, e.g. in underdoped YBa{sub 2}Cu{sub 3}O{sub 6+d}elta.
d-wave stripes in cuprates: Valence bond order coexisting with nodal quasiparticles
Energy Technology Data Exchange (ETDEWEB)
Vojta, Matthias [Institut fuer Theoretische Physik, Universitaet Koeln, 50937 Koeln (Germany)
2008-07-01
We point out that unidirectional bond-centered charge-density-wave states in cuprates involve electronic order in both s- and d-wave channels, with non-local Coulomb repulsion suppressing the s-wave component. The resulting bond-charge-density wave, coexisting with superconductivity, is compatible with momentum-space features seen in recent photoemission and tunneling data and as well as in neutron-scattering measurements, once long-range order is destroyed by slow fluctuations or glassy disorder.
d-wave stripes in cuprates: Valence bond order coexisting with nodal quasiparticles
International Nuclear Information System (INIS)
We point out that unidirectional bond-centered charge-density-wave states in cuprates involve electronic order in both s- and d-wave channels, with non-local Coulomb repulsion suppressing the s-wave component. The resulting bond-charge-density wave, coexisting with superconductivity, is compatible with momentum-space features seen in recent photoemission and tunneling data and as well as in neutron-scattering measurements, once long-range order is destroyed by slow fluctuations or glassy disorder
Isaksen, Geir Villy; Andberg, Tor Arne Heim; Åqvist, Johan; Brandsdal, Bjørn Olav
2015-07-01
Structural information and activity data has increased rapidly for many protein targets during the last decades. In this paper, we present a high-throughput interface (Qgui) for automated free energy and empirical valence bond (EVB) calculations that use molecular dynamics (MD) simulations for conformational sampling. Applications to ligand binding using both the linear interaction energy (LIE) method and the free energy perturbation (FEP) technique are given using the estrogen receptor (ERα) as a model system. Examples of free energy profiles obtained using the EVB method for the rate-limiting step of the enzymatic reaction catalyzed by trypsin are also shown. In addition, we present calculation of high-precision Arrhenius plots to obtain the thermodynamic activation enthalpy and entropy with Qgui from running a large number of EVB simulations. PMID:26080356
Alkan, Fahri; Dybowski, C
2015-10-14
Cluster models are used in calculation of (207)Pb NMR magnetic-shielding parameters of α-PbO, β-PbO, Pb3O4, Pb2SnO4, PbF2, PbCl2, PbBr2, PbClOH, PbBrOH, PbIOH, PbSiO3, and Pb3(PO4)2. We examine the effects of cluster size, method of termination of the cluster, charge on the cluster, introduction of exact exchange, and relativistic effects on calculation of magnetic-shielding tensors with density functional theory. Proper termination of the cluster for a network solid, including approximations such as compensation of charge by the bond-valence (BV) method, is essential to provide results that agree with experiment. The inclusion of relativistic effects at the spin-orbit level for such heavy nuclei is an essential factor in achieving agreement with experiment. PMID:26345261
Lindquist, Beth A; Takeshita, Tyler Y; Dunning, Thom H
2016-05-01
Ozone (O3) and sulfur dioxide (SO2) are valence isoelectronic species, yet their properties and reactivities differ dramatically. In particular, O3 is highly reactive, whereas SO2 is chemically relatively stable. In this paper, we investigate serial addition of hydrogen atoms to both the terminal atoms of O3 and SO2 and to the central atom of these species. It is well-known that the terminal atoms of O3 are much more amenable to bond formation than those of SO2. We show that the differences in the electronic structure of the π systems in the parent triatomic species account for the differences in the addition of hydrogen atoms to the terminal atoms of O3 and SO2. Further, we find that the π system in SO2, which is a recoupled pair bond dyad, facilitates the addition of hydrogen atoms to the sulfur atom, resulting in stable HSO2 and H2SO2 species. PMID:27070292
Reduced form models of bond portfolios
Matti Koivu; Teemu Pennanen
2010-01-01
We derive simple return models for several classes of bond portfolios. With only one or two risk factors our models are able to explain most of the return variations in portfolios of fixed rate government bonds, inflation linked government bonds and investment grade corporate bonds. The underlying risk factors have natural interpretations which make the models well suited for risk management and portfolio design.
Energy Technology Data Exchange (ETDEWEB)
Esswein, A. J.; Veige, A. S.; Piccoli, P. M. B.; Schultz, A. J.; Nocera, D. G.; MIT
2008-03-24
Metal-metal cooperativity enables the reaction of carbon-based substrates at diiridium two-electron mixed valence centers. Arylation of Ir{sub 2}{sup 0,II}(tfepma){sub 3}Cl{sub 2} (1) (tfepma = bis[(bistrifluoroethoxy)phosphino]methylamine) with RMgBr (R = C{sub 6}H{sub 5} and C{sub 6}D{sub 5}) is followed by C-H bond activation to furnish the bridging benzyne complex Ir{sub 2}II,II(tfepma){sub 3}({mu}-C{sub 6}H4)(C{sub 6}H{sub 5})H (2), as the kinetic product. At ambient temperature, 2 isomerizes to Ir{sub 2}{sup I,III}(tfepma){sub 3}({mu}-C{sub 6}H4)(C{sub 6}H{sub 5})H (3) (k{sub obs} = 9.57 {+-} 0.10 x 10{sup -5} s{sup -1} at 31.8 C, {Delta}H{sup {+-}} = 21.7 {+-} 0.3 kcal/mol, {Delta}S{sup {+-}} = -7.4 {+-} 0.9 eu), in which the benzyne moiety is conserved and the Ir{sup III} center is ligated by terminal hydride and phenyl groups. The same reaction course is observed for arylation of 1 with C{sub 6}D{sub 5}MgBr to produce 2-d{sub 10} and 3-d{sub 10} accompanied by an inverse isotope effect, k{sub h}/k{sub d} = 0.44 (k{sub obs} = 2.17 {+-} 0.10 x 10{sup -4} s{sup -1} in C{sub 6}D{sub 6} solution at 31.8 C, {Delta}H{sup {+-}} = 24.9 {+-} 0.7 kcal/mol, {Delta}S{sup {+-}} = -6.4 {+-} 2.4 eu). 2 reacts swiftly with hydrogen to provide Ir{sub 2}{sup II,II}(tfepma){sub 3}H{sub 4} as both the syn and anti isomers (4-syn and 4-anti, respectively). The hydrides of 4-syn were directly located by neutron diffraction analysis. X-ray crystallographic examination of 2, 2-d{sub 10}, 3, and 4-syn indicates that cooperative reactivity at the bimetallic diiridium core is facilitated by the ability of the two-electron mixed valence framework to accommodate the oxidation state changes and ligand rearrangements attendant to the reaction of the substrate.
Bond graph modeling of centrifugal compression systems
Uddin, Nur; Gravdahl, Jan Tommy
2015-01-01
A novel approach to model unsteady fluid dynamics in a compressor network by using a bond graph is presented. The model is intended in particular for compressor control system development. First, we develop a bond graph model of a single compression system. Bond graph modeling offers a different perspective to previous work by modeling the compression system based on energy flow instead of fluid dynamics. Analyzing the bond graph model explains the energy flow during compressor surge. Two pri...
Chatterjee, Koushik; Pastorczak, Ewa; Jawulski, Konrad; Pernal, Katarzyna
2016-06-01
A perfect-pairing generalized valence bond (GVB) approximation is known to be one of the simplest approximations, which allows one to capture the essence of static correlation in molecular systems. In spite of its attractive feature of being relatively computationally efficient, this approximation misses a large portion of dynamic correlation and does not offer sufficient accuracy to be generally useful for studying electronic structure of molecules. We propose to correct the GVB model and alleviate some of its deficiencies by amending it with the correlation energy correction derived from the recently formulated extended random phase approximation (ERPA). On the examples of systems of diverse electronic structures, we show that the resulting ERPA-GVB method greatly improves upon the GVB model. ERPA-GVB recovers most of the electron correlation and it yields energy barrier heights of excellent accuracy. Thanks to a balanced treatment of static and dynamic correlation, ERPA-GVB stays reliable when one moves from systems dominated by dynamic electron correlation to those for which the static correlation comes into play.
Directory of Open Access Journals (Sweden)
VeraShuman
2013-05-01
Full Text Available 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 (unpleasantness, goal obstructiveness/conduciveness, low or high power, self- (incongruence, 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.
International Nuclear Information System (INIS)
In this paper, we do a complete classification of valence-bond crystals (VBCs) on the kagomé lattice based on general arguments of symmetry only and thus identify many new VBCs for different unit cell sizes. For the spin-1/2 Heisenberg antiferromagnet, we study the relative energetics of competing gapless spin liquids (SLs) and VBC phases within the class of Gutzwiller-projected fermionic wave functions using variational Monte Carlo techniques, hence implementing exactly the constraint of one fermion per site. By using a state-of-the-art optimization method, we conclusively show that the U(1) Dirac SL is remarkably stable towards dimerizing into all 6-, 12- and 36-site unit cell VBCs. This stability is also preserved on addition of a next-nearest-neighbor super-exchange coupling of both antiferromagnetic and ferromagnetic (FM) type. However, we find that a 36-site unit cell VBC is stabilized on addition of a very small next-nearest-neighbor FM super-exchange coupling, i.e. |J2| ≈ 0.045, and this VBC is the same in terms of space-group symmetry as that obtained in an effective quantum dimer model study. It breaks reflection symmetry, has a nontrivial flux pattern and is a strong dimerization of the uniform RVB SL. (paper)
Bond formation effects on the metal-insulator transition in the half-filled kagome Hubbard model
Higa, Ryota; Asano, Kenichi
2016-06-01
We study the metal-insulator transition in the half-filled Hubbard model on a Kagome lattice using the variational cluster approximation. The strong coupling limit of the model corresponds to the S =1 /2 Kagome Heisenberg antiferromagnet, which is known to have a singlet ground state, although its detail is still debated. As the results of the cluster methods generally depend much on the choice of the unit cluster, we have chosen the clusters that are compatible with these singlet ground states in the strong coupling case found so far, which basically consist of even number of sites. It is found that the correlated electrons on the Kagome lattice have a strong tendency to form valence-bond structures, which are the resonation of electrons on a single bond or several bonds forming loops. The zero-temperature metal-insulator transition at some interaction strength is possibly driven by the formation of such short range valence bonds and shows a second order character, which is distinctive from the Brinkman-Rice scenario. The electrons on these valence bonds further localizes onto each site as the interaction increases, and the valence bonds of electrons finally turn into magnetic singlet bonds between localized S =1 /2 spins, which are consistent with the ground states of the Kagome antiferromagnet.
Xu, Lu T; Dunning, Thom H
2015-06-01
The ground state, X1Σg+, of N2 is a textbook example of a molecule with a triple bond consisting of one σ and two π bonds. This assignment, which is usually rationalized using molecular orbital (MO) theory, implicitly assumes that the spins of the three pairs of electrons involved in the bonds are singlet-coupled (perfect pairing). However, for a six-electron singlet state, there are five distinct ways to couple the electron spins. The generalized valence bond (GVB) wave function lifts this restriction, including all of the five spin functions for the six electrons involved in the bond. For N2, we find that the perfect pairing spin function is indeed dominant at Re but that it becomes progressively less so from N2 to P2 and As2. Although the perfect pairing spin function is still the most important spin function in P2, the importance of a quasi-atomic spin function, which singlet couples the spins of the electrons in the σ orbitals while high spin coupling those of the electrons in the π orbitals on each center, has significantly increased relative to N2 and, in As2, the perfect pairing and quasi-atomic spin couplings are on essentially the same footing. This change in the spin coupling of the electrons in the bonding orbitals down the periodic table may contribute to the rather dramatic decrease in the strengths of the Pn2 bonds from N2 to As2 as well as in the increase in their chemical reactivity and should be taken into account in more detailed analyses of the bond energies in these species. We also compare the spin coupling in N2 with that in C2, where the quasi-atomic spin coupling dominants around Re. PMID:26575549
Bond diluted anisotropic quantum Heisenberg model
International Nuclear Information System (INIS)
Effects of the bond dilution on the critical temperatures, phase diagrams and the magnetization behaviors of the isotropic and anisotropic quantum Heisenberg model have been investigated in detail. For the isotropic case, bond percolation threshold values have been determined for several numbers of two (2D) and three (3D) dimensional lattices. In order to investigate the effect of the anisotropy in the exchange interaction on the results obtained for the isotropic model, a detailed investigation has been made on a honeycomb lattice. Some interesting results, such as second order reentrant phenomena in the phase diagrams have been found. - Highlights: • Anisotropic quantum Heisenberg model with bond dilution investigated. • Bond percolation threshold values given for 2D and 3D lattices in isotropic case. • Phase diagrams and ground state magnetizations investigated in detail. • Variation of the bond percolation threshold values with anisotropy determined
Valency and molecular structure
Cartmell, E
1977-01-01
Valency and Molecular Structure, Fourth Edition provides a comprehensive historical background and experimental foundations of theories and methods relating to valency and molecular structures. In this edition, the chapter on Bohr theory has been removed while some sections, such as structures of crystalline solids, have been expanded. Details of structures have also been revised and extended using the best available values for bond lengths and bond angles. Recent developments are mostly noted in the chapter on complex compounds, while a new chapter has been added to serve as an introduction t
Directory of Open Access Journals (Sweden)
Adrian Rodriguez Aguinaga
2015-06-01
Full Text Available This paper proposes a methodology to perform emotional states classification by the analysis of EEG signals, wavelet decomposition and an electrode discrimination process, that associates electrodes of a 10/20 model to Brodmann regions and reduce computational burden. The classification process were performed by a Support Vector Machines Classification process, achieving a 81.46 percent of classification rate for a multi-class problem and the emotions modeling are based in an adjusted space from the Russell Arousal Valence Space and the Geneva model.
van Lenthe, J H; Broer-Braam, H B; Rashid, Z
2012-03-30
We comment on the paper [Song et al., J. Comput. Chem. 2009, 30, 399]. and discuss the efficiency of the orbital optimization and gradient evaluation in the Valence Bond Self Consistent Field (VBSCF) method. We note that Song et al. neglect to properly reference Broer et al., who published an algorithm [Broer and Nieuwpoort, Theor. Chim. Acta 1988, 73, 405] to use a Fock matrix to compute a matrix element between two different determinants, which can be used for an orbital optimization. Further, Song et al. publish a misleading comparison with our VBSCF algorithm [Dijkstra and van Lenthe, J. Chem. Phys. 2000, 113, 2100; van Lenthe et al., Mol. Phys. 1991, 73, 1159] to enable them to favorably compare their algorithm with ours. We give detail timings in terms of different orbital types in the calculation and actual timings for the example cases. PMID:22278948
Bond diluted anisotropic quantum Heisenberg model
Akıncı, Ümit
2013-01-01
Effects of the bond dilution on the critical temperatures, phase diagrams and the magnetization behaviors of the isotropic and anisotropic quantum Heisenberg model have been investigated in detail. For the isotropic case, bond percolation threshold values have been determined for several numbers of two (2D) and three (3D) dimensional lattices. In order to investigate the effect of the anisotropy in the exchange interaction on the results obtained for the isotropic model, a detailed investigat...
Jewsbury, Philip; Lawley, Kenneth
1990-03-01
The separated atom or ( JAMAJBMB) coupling scheme is applied to the electronic structure of both ion pair and valence states of the heavier halogens and rare gas halides. Relative transition moments from low vibrational levels of selected ion pair states to all the valence states and the resulting radiative lifetimes are derived. σ↔σ electron transfer between atomic orbitals is assumed for parallel transitions. Russell-Saunders coupling is used for the atomic or ionic basis functions in the reference model. Departures from the model arising from partial jj coupling in the halogen positive ions and from intramolecular electrostatic effects each produce characteristic changes in the relative intensities of the various fluorescent systems from a given ion pair state. The effect of J and MJ state mixing between asymptotically degenerate valence states is discussed and ion pair → valence transition intensities are shown to be a sensitive function of this mixing.
Mechatronic modeling and simulation using bond graphs
Das, Shuvra
2009-01-01
Bond graphs are especially well-suited for mechatronic systems, as engineering system modeling is best handled using a multidisciplinary approach. Bond graphing permits one to see the separate components of an engineering system as a unified whole, and allows these components to be categorized under a few generalized elements, even when they come from different disciplines. In addition to those advantages, the bond graph offers a visual representation of a system from which derivation of the governing equations is algorithmic. This makes the design process accessible to beginning readers, prov
Directory of Open Access Journals (Sweden)
D. P. Samajdar
2014-01-01
Full Text Available The valence band anticrossing model has been used to calculate the heavy/light hole and spin-orbit split-off energies in InAs1-xBix and InSb1-xBix alloy systems. It is found that both the heavy/light hole, and spin-orbit split E+ levels move upwards in energy with an increase in Bi content in the alloy, whereas the split E− energy for the holes shows a reverse trend. The model is also used to calculate the reduction of band gap energy with an increase in Bi mole fraction. The calculated values of band gap variation agree well with the available experimental data.
Directory of Open Access Journals (Sweden)
Arumugam Manohar
2015-06-01
Full Text Available 2:1 adducts involving [Zn(dtc2]2 (dtc- = pipdtc-, H10C5NCS-2; dnpdtc-, (H3CCH2CH22NCS-2; dedtc-, (H5C22NCS-2; dmdtc-, (H3C2NCS-2; nmedtc-, HOCH2CH2(CH3NCS-2; deadtc-, (HOCH2CH22NCS-2 and 4,4' – bipyridine were prepared and characterized by elemental analyses, IR, UV-Visible, Cyclic voltammetric and thermal studies. IR spectra of the complexes show the reduction in the thioureide stretching frequency due to the increase in coordination around the zinc ion and the resultant increase in electron density. The charge transfer transitions are observed in the region 260 – 320 nm by electronic spectra. Thermal studies show a single stage weight loss. The cyclic voltammetric study on the complexes show an increase of electron density on zinc in the adducts compared to [Zn(dtc2]2. The bond valence sum(BVS analysis shows the values to be close to '2', which is equivalent to the formal oxidation state of zinc in the zinc complexes.
Modeling the Hydrogen Bond within Molecular Dynamics
Lykos, Peter
2004-01-01
The structure of a hydrogen bond is elucidated within the framework of molecular dynamics based on the model of Rahman and Stillinger (R-S) liquid water treatment. Thus, undergraduates are exposed to the powerful but simple use of classical mechanics to solid objects from a molecular viewpoint.
Valence-dependent influence of serotonin depletion on model-based choice strategy.
Worbe, Y; Palminteri, S; Savulich, G; Daw, N D; Fernandez-Egea, E; Robbins, T W; Voon, V
2016-05-01
Human decision-making arises from both reflective and reflexive mechanisms, which underpin goal-directed and habitual behavioural control. Computationally, these two systems of behavioural control have been described by different learning algorithms, model-based and model-free learning, respectively. Here, we investigated the effect of diminished serotonin (5-hydroxytryptamine) neurotransmission using dietary tryptophan depletion (TD) in healthy volunteers on the performance of a two-stage decision-making task, which allows discrimination between model-free and model-based behavioural strategies. A novel version of the task was used, which not only examined choice balance for monetary reward but also for punishment (monetary loss). TD impaired goal-directed (model-based) behaviour in the reward condition, but promoted it under punishment. This effect on appetitive and aversive goal-directed behaviour is likely mediated by alteration of the average reward representation produced by TD, which is consistent with previous studies. Overall, the major implication of this study is that serotonin differentially affects goal-directed learning as a function of affective valence. These findings are relevant for a further understanding of psychiatric disorders associated with breakdown of goal-directed behavioural control such as obsessive-compulsive disorders or addictions. PMID:25869808
ESTIMATING STRUCTURAL MODELS OF CORPORATE BOND PRICES
Max Bruche
2006-01-01
One of the strengths of structural models (or firm-value based models) of credit (e.g. Merton, 1974) as opposed to reduced-form models (e.g. Jarrow and Turnbull, 1995) is that they directly link the price of equity to default probabilities, and hence to the price of corporate bonds (and credit derivatives). Yet when these models are estimated on actual data, the existence of data other than equity prices is typically ignored. This paper describes how all available price data (equity prices, b...
LAMMPS Framework for Dynamic Bonding and an Application Modeling DNA
DEFF Research Database (Denmark)
Svaneborg, Carsten
2012-01-01
and bond types. When breaking bonds, all angular and dihedral interactions involving broken bonds are removed. The framework allows chemical reactions to be modeled, and use it to simulate a simplistic, coarse-grained DNA model. The resulting DNA dynamics illustrates the power of the present framework.......We have extended the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) to support directional bonds and dynamic bonding. The framework supports stochastic formation of new bonds, breakage of existing bonds, and conversion between bond types. Bond formation can be controlled to...... limit the maximal functionality of a bead with respect to various bond types. Concomitant with the bond dynamics, angular and dihedral interactions are dynamically introduced between newly connected triplets and quartets of beads, where the interaction type is determined from the local pattern of bead...
Bond-Ordering Model for the Glass Transition
Davatolhagh, Saeid; Patton, Bruce R.
2000-01-01
We consider the idea of bond ordering as a model for glass transition: a generic covalently bonded liquid may substantially reduce its energy through bond ordering, without undergoing significant structural order. This concept is developed for a model system using quantities such as a bond order parameter and susceptibility which provide new identification for calorimetric glass transition temperature. Monte Carlo simulation results exhibit bond ordering at intermediate temperatures uncorrela...
Effective interactions for valence-hole nuclei with modern meson-exchange potential models
International Nuclear Information System (INIS)
Within the framework of the folded-diagram theory, the authors have studied the effective interaction appropriate for hole-hole nuclei in the mass regions of 16O and 40Ca, using the Bonn and Paris potential models. To sum up the folded diagrams the renormalization procedure of Lee and Suzuki has been employed, using a so-called Q-box in which were included all one-body and two-body irreducible valence-linked diagrams through third order in perturbation theory. Discrepancies for the mass dependence of the effective interaction for several JT configurations with respect to empirically deduced mass dependencies is reported. The role of core polarization processes through third order were found to be one of the mechanisms behind these discrepancies. Compared to the results obtained with the Paris potential, more attraction is introduced by the Bonn potential for all matrix elements of concerns, a result which agrees well with previous findings for the particle-particle interaction in the same mass regions. A qualitative agreements with experimental data is obtained. 31 refs., 6 figs., 8 tabs
High Valence, Normal Valence and Unknown Valence
DEFF Research Database (Denmark)
Morsing, Thorbjørn Juul
Because of the diverse nature of this thesis, each of the six chapters are briey described individually. Chapter 1 details the synthesis and characterisation of a rare example of a ferromagnetically coupled chromium(III) dimer (Ph4P)4[(SCN)4Cr(OH)2Cr(NCS)4] 2 NCCH3. The compound has been characte......Because of the diverse nature of this thesis, each of the six chapters are briey described individually. Chapter 1 details the synthesis and characterisation of a rare example of a ferromagnetically coupled chromium(III) dimer (Ph4P)4[(SCN)4Cr(OH)2Cr(NCS)4] 2 NCCH3. The compound has been...... the serendipitous synthesis of the nitrido-bridged [Rh(en)3]2- [(CN)5MnNMn(CN)5]. The complex anion have previously been studied in the form of the mixed Rb4Na2-salt. In this earlier study, the nitrido-bridge was found to be asymmetrical with the axial ligands in an eclipsed formation. The complex was...... described as a mixed valence MnII/MnV system. This is not the case for the present system where the bridge is symmetrical, slightly bent and the axial ligands are in a staggered conformation. XANES measurements along with DFT calculations suggest that the Rb4Na2-salt is indeed best described as Mn...
Dynamic force spectroscopy on multiple bonds: experiments and model
Erdmann, T; Nassoy, P; Schwarz, U S
2007-01-01
We probe the dynamic strength of multiple biotin-streptavidin adhesion bonds under linear loading using the biomembrane force probe setup for dynamic force spectroscopy. Measured rupture force histograms are compared to results from a master equation model for the stochastic dynamics of bond rupture under load. This allows us to extract the distribution of the number of initially closed bonds. We also extract the molecular parameters of the adhesion bonds, in good agreement with earlier results from single bond experiments. Our analysis shows that the peaks in the measured histograms are not simple multiples of the single bond values, but follow from a superposition procedure which generates different peak positions.
Bond excitations in the pseudogap phase of the Hubbard Model
Macridin, Alexandru; Jarrell, Mark (Eds. )
2008-01-01
Using the dynamical cluster approximation, we calculate the correlation functions associated with the nearest neighbor bond operator which measure the z component of the spin exchange in the two-dimensional Hubbard model with $U$ equal to the bandwidth. We find that in the pseudogap region, the local bond susceptibility diverges at T=0. This shows the existence of degenerate bond spin excitation and implies quantum criticality and bond order formation when long range correlations are consider...
A dynamical model of the chemical bond
Hofmann, Holger F.
1996-01-01
A new approach to chemical bonding is introduced in order to provide an improved understanding of the connection between basic quantum mechanics and the covalent pair bond. It's focus is on the fact that the energy of the bond is largely given by the kinetic energy of the electrons, while the Coulomb forces are only comparable to the kinetic energy terms close to the atomic nuclei, where they define the shape and the size of the atomic orbitals. If atomic orbitals are used as a starting point...
DSE inspired model for the pion's valence dressed-quark GPD
Chang, L; Moutarde, H; Roberts, C D; Rodríguez-Quintero, J; Sabatié, F
2015-01-01
We sketch here an approach to the computation of generalised parton distributions (GPDs), based upon a rainbow-ladder (RL) truncation of QCD's Dyson-Schwinger equations and exemplified via the pion's valence dressed-quark GPD, $H_\\pi^{\\rm v}(x,\\xi,t)$. Our analysis focuses on the case of zero skewness, $\\xi=0$, and underlines that the impulse-approximation used hitherto to define the pion's valence dressed-quark GPD is generally invalid owing to omission of contributions from the gluons which bind dressed-quarks into the pion. A simple correction enables us to identify a practicable improvement to the approximation for $H_\\pi^{\\rm v}(x,0,t)$, expressed as the Radon transform of a single amplitude. Therewith we obtain results for $H_\\pi^{\\rm v}(x,0,t)$ and the associated impact-parameter dependent distribution, $q_\\pi^{\\rm v}(x,|\\vec{b}_\\perp|)$, which provide a qualitatively sound picture of the pion's dressed-quark structure at an hadronic scale.
Mangaud, E; de la Lande, A; Meier, C; Desouter-Lecomte, M
2015-12-14
The quantum dynamics of electron transfer in mixed-valence organic compounds is investigated using a reaction path model calibrated by constrained density functional theory (cDFT). Constrained DFT is used to define diabatic states relevant for describing the electron transfer, to obtain equilibrium structures for each of these states and to estimate the electronic coupling between them. The harmonic analysis at the diabatic minima yields normal modes forming the dissipative bath coupled to the electronic states. In order to decrease the system-bath coupling, an effective one dimensional vibronic Hamiltonian is constructed by partitioning the modes into a linear reaction path which connects both equilibrium positions and a set of secondary vibrational modes, coupled to this reaction coordinate. Using this vibronic model Hamiltonian, dissipative quantum dynamics is carried out using Redfield theory, based on a spectral density which is determined from the cDFT results. In a first benchmark case, the model is applied to a series of mixed-valence organic compounds formed by two 1,4-dimethoxy-3-methylphenylene fragments linked by an increasing number of phenylene bridges. This allows us to examine the coherent electron transfer in extreme situations leading to a ground adiabatic state with or without a barrier and therefore to the trapping of the charge or to an easy delocalization. PMID:26041466
A statistical model of hydrogen bond networks in liquid alcohols
Sillrén, Per; Bielecki, Johan; Mattsson, Johan; Börjesson, Lars; Matic, Aleksandar
2012-03-01
We here present a statistical model of hydrogen bond induced network structures in liquid alcohols. The model generalises the Andersson-Schulz-Flory chain model to allow also for branched structures. Two bonding probabilities are assigned to each hydroxyl group oxygen, where the first is the probability of a lone pair accepting an H-bond and the second is the probability that given this bond also the second lone pair is bonded. The average hydroxyl group cluster size, cluster size distribution, and the number of branches and leaves in the tree-like network clusters are directly determined from these probabilities. The applicability of the model is tested by comparison to cluster size distributions and bonding probabilities obtained from Monte Carlo simulations of the monoalcohols methanol, propanol, butanol, and propylene glycol monomethyl ether, the di-alcohol propylene glycol, and the tri-alcohol glycerol. We find that the tree model can reproduce the cluster size distributions and the bonding probabilities for both mono- and poly-alcohols, showing the branched nature of the OH-clusters in these liquids. Thus, this statistical model is a useful tool to better understand the structure of network forming hydrogen bonded liquids. The model can be applied to experimental data, allowing the topology of the clusters to be determined from such studies.
Pricing for Catastrophe Bonds Based on Expected-value Model
Directory of Open Access Journals (Sweden)
Junfei Chen
2013-02-01
Full Text Available As the catastrophes cannot be avoided and result in huge economic losses, therefore the compensation issue for catastrophe losses become an important research topic. Catastrophe bonds can effectively disperse the catastrophe risks which mainly undertaken by the government and the insurance companies currently and focus on capital more effectively in broad capital market, therefore to be an ideal catastrophe securities product. This study adopts Expectancy Theory to supplement and improve the pricing of catastrophe bonds based on Value Theory. A model of expected utility is established to determine the conditions of the expected revenue R of catastrophe bonds. The pricing model of the value function is used to get the psychological value of R,U (R-R‾, for catastrophe bonds. Finally, the psychological value is improved by the value according to expected utility and this can more accurately evaluate catastrophe bonds at a reasonable price. This research can provide decision-making for the pricing of catastrophe bonds.
Theoretical Model of Transformation Superlastic Diffusion Bonding for Eutectoid Steel
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
Based on current theories of diffusion and creep cavity closure at high temperature, a theoretical analysis of phase transformation diffusion bonding for T8/T8 eutectoid steel is carried out. The diffusion bonding is mainly described as two-stage process: Ⅰ The interfacial cavity with shape change from diamond to cylinder.Ⅱ The radius of the cylindrical cavity are reduced and eliminated gradually. A new theoretical model is established for the process of transformation superplastic diffusion bonding (TSDB) ...
Upper Secondary Teachers' Knowledge for Teaching Chemical Bonding Models
Bergqvist, Anna; Drechsler, Michal; Chang Rundgren, Shu-Nu
2016-01-01
Researchers have shown a growing interest in science teachers' professional knowledge in recent decades. The article focuses on how chemistry teachers impart chemical bonding, one of the most important topics covered in upper secondary school chemistry courses. Chemical bonding is primarily taught using models, which are key for understanding…
Haner, Jamie; Matsumoto, Kazuhiko; Mercier, Hélène P A; Schrobilgen, Gary J
2016-03-24
The recently reported syntheses and X-ray crystal structures of the highly endothermic compounds F6 XeNCCH3 and F6 Xe(NCCH3 )2 ⋅CH3 CN provide the first, albeit weakly covalent, Xe(VI) -N bonds. The XeF6 unit of F6 XeNCCH3 possesses distorted octahedral (C3v ) symmetry similar to gas-phase XeF6 , whereas the XeF6 unit of F6 Xe(NCCH3 )2 ⋅CH3 CN possesses C2v symmetry. Herein, the natural bond orbital (NBO), atoms in molecules (AIM), electron localization function (ELF), and molecular electrostatic potential surface (MEPS) analyses show that the Xe valence electron lone pairs (VELPs) of both compounds are stereochemically active. The Xe VELPS are diffuse and ineffectively screen their Xe cores so that the Xe VELP positions correspond to the most electrophilic regions of the MEPS, which enables the opposing N VELP of CH3 CN to coordinate to this region. These bonds are predominantly electrostatic in nature and are interpreted as σ-hole interactions. PMID:26918266
Modelling of the Through-air Bonding Process
Directory of Open Access Journals (Sweden)
M. Hossain
2009-06-01
Full Text Available A computational fluid dynamics (CFD modelling ofthe through-air bonding process of nonwoven fabricproduction is reported in this article. In the throughairprocess, hot air is passed through the fibrous webto heat and melt polymer fibers. Molten polymersubsequently flows to the point of contact betweenany two fibers to produce a bond. Two differentmodelling strategies are adapted to produce acomprehensive understanding of the through-airbonding process. In macroscale modelling, a CFDmodel is developed treating the whole web as aporous media in order to investigate the effect ofprocess parameters. Results reveal that the timerequired to heat and melt the fibers decreases with theincreasing porosity of the web and the velocity of hotair. The CFD modelling technique is then used toanalyze the bonding process at a more fundamentallevel by considering the bonding of individual fibersat microscale. The effects of the fiber diameter,bonding temperature and contact angle between twofibers on the bonding time are investigated. Resultsshow that the time required to bond fibers is weaklyrelated to bonding temperature and fiber diameter.Fiber orientation angle, on the other hand, hassignificant effect on the progression of bondformation.
Bond graph model-based fault diagnosis of hybrid systems
Borutzky, Wolfgang
2015-01-01
This book presents a bond graph model-based approach to fault diagnosis in mechatronic systems appropriately represented by a hybrid model. The book begins by giving a survey of the fundamentals of fault diagnosis and failure prognosis, then recalls state-of-art developments referring to latest publications, and goes on to discuss various bond graph representations of hybrid system models, equations formulation for switched systems, and simulation of their dynamic behavior. The structured text: • focuses on bond graph model-based fault detection and isolation in hybrid systems; • addresses isolation of multiple parametric faults in hybrid systems; • considers system mode identification; • provides a number of elaborated case studies that consider fault scenarios for switched power electronic systems commonly used in a variety of applications; and • indicates that bond graph modelling can also be used for failure prognosis. In order to facilitate the understanding of fault diagnosis and the presented...
Estimating Structural Models of Corporate Bond Prices in Indonesian Corporations
Directory of Open Access Journals (Sweden)
Lenny Suardi
2010-07-01
Full Text Available This paper applies the maximum likelihood (ML approaches to implementing the structural model of corporate bond, as suggested by Li and Wong (2008, in Indonesian corporations. Two structural models, extended Merton and Longstaff & Schwartz (LS models, are used in determining these prices, yields, yield spreads and probabilities of default. ML estimation is used to determine the volatility of firm value. Since firm value is unobserved variable, Duan (1994 suggested that the first step of ML estimation is to derive the likelihood function for equity as the option on the firm value. The second step is to ind parameters such as the drift and volatility of firm value, that maximizing this function. The firm value itself is extracted by equating the pricing formula to the observed equity prices. Equity, total liabilities, bond prices data and the firm's parameters (firm value, volatility of firm value, and default barrier are substituted to extended Merton and LS bond pricing formula in order to valuate the corporate bond.These models are implemented to a sample of 24 bond prices in Indonesian corporation during period of 2001-2005, based on criteria of Eom, Helwege and Huang (2004. The equity and bond prices data were obtained from Indonesia Stock Exchange for firms that issued equity and provided regular financial statement within this period. The result shows that both models, in average, underestimate the bond prices and overestimate the yields and yield spread.
Jiang, Jin-Wu
2015-08-01
We propose parametrizing the Stillinger-Weber potential for covalent materials starting from the valence force-field model. All geometrical parameters in the Stillinger-Weber potential are determined analytically according to the equilibrium condition for each individual potential term, while the energy parameters are derived from the valence force-field model. This parametrization approach transfers the accuracy of the valence force field model to the Stillinger-Weber potential. Furthermore, the resulting Stilliinger-Weber potential supports stable molecular dynamics simulations, as each potential term is at an energy-minimum state separately at the equilibrium configuration. We employ this procedure to parametrize Stillinger-Weber potentials for single-layer MoS2 and black phosphorous. The obtained Stillinger-Weber potentials predict an accurate phonon spectrum and mechanical behaviors. We also provide input scripts of these Stillinger-Weber potentials used by publicly available simulation packages including GULP and LAMMPS.
Application of Bond Graph Modeling for Photovoltaic Module Simulation
Directory of Open Access Journals (Sweden)
Madi S.
2016-01-01
Full Text Available In this paper, photovoltaic generator is represented using the bond-graph methodology. Starting from the equivalent circuit the bond graph and the block diagram of the photovoltaic generator have been derived. Upon applying bond graph elements and rules a mathematical model of the photovoltaic generator is obtained. Simulation results of this obtained model using real recorded data (irradiation and temperature at the Renewable Energies Development Centre in Bouzaréah – Algeria are obtained using MATLAB/SMULINK software. The results have compared with datasheet of the photovoltaic generator for validation purposes.
Minimal model for dynamic bonding in colloidal transient networks
Krinninger, Philip; Fortini, Andrea; Schmidt, Matthias
2016-04-01
We investigate a model for colloidal network formation using Brownian dynamics computer simulations. Hysteretic springs establish transient bonds between particles with repulsive cores. If a bonded pair of particles is separated by a cutoff distance, the spring vanishes and reappears only if the two particles contact each other. We present results for the bond lifetime distribution and investigate the properties of the van Hove dynamical two-body correlation function. The model displays crossover from fluidlike dynamics, via transient network formation, to arrested quasistatic network behavior.
Modelling of the Through-air Bonding Process
Hossain, M.; M. Acar, Ph.D.; Malalasekera, W.
2009-01-01
A computational fluid dynamics (CFD) modelling ofthe through-air bonding process of nonwoven fabricproduction is reported in this article. In the throughairprocess, hot air is passed through the fibrous webto heat and melt polymer fibers. Molten polymersubsequently flows to the point of contact betweenany two fibers to produce a bond. Two differentmodelling strategies are adapted to produce acomprehensive understanding of the through-airbonding process. In macroscale modelling, a CFDmodel is ...
Ab initio valence calculations in chemistry
Cook, D B
1974-01-01
Ab Initio Valence Calculations in Chemistry describes the theory and practice of ab initio valence calculations in chemistry and applies the ideas to a specific example, linear BeH2. Topics covered include the Schrödinger equation and the orbital approximation to atomic orbitals; molecular orbital and valence bond methods; practical molecular wave functions; and molecular integrals. Open shell systems, molecular symmetry, and localized descriptions of electronic structure are also discussed. This book is comprised of 13 chapters and begins by introducing the reader to the use of the Schrödinge
International Nuclear Information System (INIS)
Strain measurement using bonded resistance in HT-7U superconducting model coil goes along under low temperature (4.2 K), the authors choose WK-09-062TZ-120 strain gauge and M-Bond 600 adhesive made by Micro-Measurement INC. of America, then manage bonding technique properly and get satisfactory result
Bent, Henry A.; Weinhold, Frank
2007-01-01
The study presents and explains the various periodicity symbols, tables and models for the higher-order valency and donor-acceptor kinships used in chemistry. The described alternative tables are expected to improve the pedagogical consistency of the chemical periodicity patterns with better electronic behavior.
Midtvedt, Daniel; Croy, Alexander
2016-06-10
We compare the simplified valence-force model for single-layer black phosphorus with the original model and recent ab initio results. Using an analytic approach and numerical calculations we find that the simplified model yields Young's moduli that are smaller compared to the original model and are almost a factor of two smaller than ab initio results. Moreover, the Poisson ratios are an order of magnitude smaller than values found in the literature. PMID:27121075
Bond slip model for the simulation of reinforced concrete structures
International Nuclear Information System (INIS)
This paper presents a new finite element approach to model the steel-concrete bond effects. This model proposes to relate steel, represented by truss elements, with the surrounding concrete in the case where the two meshes are not necessary coincident. The theoretical formulation is described and the model is applied on a reinforced concrete tie. A characteristic stress distribution is observed, related to the transfer of bond forces from steel to concrete. The results of this simulation are compared with a computation in which a perfect relation between steel and concrete is supposed. It clearly shows how the introduction of the bond model can improve the description of the cracking process (finite number of cracks). (authors)
Political Culture and Covalent Bonding. A Conceptual Model of Political Culture Change
Directory of Open Access Journals (Sweden)
Camelia Florela Voinea
2015-01-01
Full Text Available Our class of models aims at explaining the dynamics of political attitude change by means of the dynamic changes in values, beliefs, norms and knowledge with which it is associated. The model constructs a political culture perspective over the relationship between macro and micro levels of a society and polity. The model defines the bonding mechanism as a basic mechanism of the political culture change by taking inspiration from the valence bonding theory in Chemistry, which has inspired the elaboration of the mechanisms and processes underlying the political culture emergence and the political culture control over the relationship between macro-level political entities and the micro-level individual agents. The model introduces operational definitions of the individual agent in political culture terms. The simulation model is used for the study of emergent political culture change phenomena based on individual interactions (emergent or upward causation as well as the ways in which the macro entities and emergent phenomena influence in turn the behaviors of individual agents (downward causation. The model is used in the ongoing research concerning the quality of democracy and political participation of the citizens in the Eastern European societies after the Fall of Berlin Wall. It is particularly aimed at explaining the long-term effect of the communist legacy and of the communist polity concept and organization onto the political mentalities and behaviors of the citizens with respect to democratic institutions and political power. The model has major implications in political socialization, political involvement, political behavior, corruption and polity modeling.
Modelling of spreading process: effect from hydrogen bonds
Institute of Scientific and Technical Information of China (English)
Li Xin; Hu Yuan-Zhong; Jiang Lan
2008-01-01
Lubricant spreading on solid substrates has drawn considerable attention not only for the microscopic wetting theory but also for the dramatic application in head-disk interface of magnetic storage drive systems. Molecular dynamic simulation based on a coarse-grained bead-spring model has been used to study such a spreading process.The spreading profiles indicate that the hydrogen bonds among lubricant molecules and the hydrogen bonds between lubricant molecules and polar atoms of solid substrates will complicate the spreading process in a tremendous degree.The hydrogen bonds among lubricant molecules will strengthen the lubricant combination intensity, which may hinder most molecules from flowing down to the substrates and diffusing along the substrates. And the hydrogen bonds between lubricant molecules and polar atoms of solid substrates will confine the lubricant molecules around polar atoms, which may hinder the molecules from diffusing along the substrates and cause precursor film to vanish.
Bond graph model for prediction of PWR natural circulation
International Nuclear Information System (INIS)
In operation of a Pressurized Water Reactor, natural circulation is an efficient, passive heat transfer mechanism for cooling. It is often employed for heat removal in operational transients, especially in long-term decay-heat removal operation. To simulate the dynamics of natural circulation, a bond graph representation of the PWR primary system and causal manipulation of the field equations has been modeled. The bond graph method calls for establishing the dynamic equations of multiport systems in state-variable form. Using the analogy of circuit elements in electrical networks, a bond graph consists of multiport capacitances, inertances, dissipations, sources of effort and flow, transformers, gyrators, and ideal junction elements. By treating each component in a PWR primary loop as a multiport element in the bond graph, a set of state-space equations representing the thermal/hydraulic responses of the loop is obtained. The state equations are then solved iteratively by using the program DYSIS developed by MIT
Modelling of spreading process: effect from hydrogen bonds
International Nuclear Information System (INIS)
Lubricant spreading on solid substrates has drawn considerable attention not only for the microscopic wetting theory but also for the dramatic application in head-disk interface of magnetic storage drive systems. Molecular dynamic simulation based on a coarse-grained bead-spring model has been used to study such a spreading process. The spreading profiles indicate that the hydrogen bonds among lubricant molecules and the hydrogen bonds between lubricant molecules and polar atoms of solid substrates will complicate the spreading process in a tremendous degree. The hydrogen bonds among lubricant molecules will strengthen the lubricant combination intensity, which may hinder most molecules from flowing down to the substrates and diffusing along the substrates. And the hydrogen bonds between lubricant molecules and polar atoms of solid substrates will confine the lubricant molecules around polar atoms, which may hinder the molecules from diffusing along the substrates and cause precursor film to vanish. (condensed matter: structure, mechanical and thermal properties)
Computational Tools To Model Halogen Bonds in Medicinal Chemistry.
Ford, Melissa Coates; Ho, P Shing
2016-03-10
The use of halogens in therapeutics dates back to the earliest days of medicine when seaweed was used as a source of iodine to treat goiters. The incorporation of halogens to improve the potency of drugs is now fairly standard in medicinal chemistry. In the past decade, halogens have been recognized as direct participants in defining the affinity of inhibitors through a noncovalent interaction called the halogen bond or X-bond. Incorporating X-bonding into structure-based drug design requires computational models for the anisotropic distribution of charge and the nonspherical shape of halogens, which lead to their highly directional geometries and stabilizing energies. We review here current successes and challenges in developing computational methods to introduce X-bonding into lead compound discovery and optimization during drug development. This fast-growing field will push further development of more accurate and efficient computational tools to accelerate the exploitation of halogens in medicinal chemistry. PMID:26465079
Directory of Open Access Journals (Sweden)
Fuqian Shi
2012-01-01
Full Text Available Emotional cellular (EC, proposed in our previous works, is a kind of semantic cell that contains kernel and shell and the kernel is formalized by a triple- L = , where P denotes a typical set of positive examples relative to word-L, d is a pseudodistance measure on emotional two-dimensional space: valence-arousal, and δ is a probability density function on positive real number field. The basic idea of EC model is to assume that the neighborhood radius of each semantic concept is uncertain, and this uncertainty will be measured by one-dimensional density function δ. In this paper, product form features were evaluated by using ECs and to establish the product style database, fuzzy case based reasoning (FCBR model under a defined similarity measurement based on fuzzy nearest neighbors (FNN incorporating EC was applied to extract product styles. A mathematical formalized inference system for product style was also proposed, and it also includes uncertainty measurement tool emotional cellular. A case study of style acquisition of mobile phones illustrated the effectiveness of the proposed methodology.
Upper Secondary Teachers' Knowledge for Teaching Chemical Bonding Models
Bergqvist, Anna; Drechsler, Michal; Rundgren, Shu-Nu Chang
2016-01-01
Researchers have shown a growing interest in science teachers' professional knowledge in recent decades. The article focuses on how chemistry teachers impart chemical bonding, one of the most important topics covered in upper secondary school chemistry courses. Chemical bonding is primarily taught using models, which are key for understanding science. However, many studies have determined that the use of models in science education can contribute to students' difficulties understanding the topic, and that students generally find chemical bonding a challenging topic. The aim of this study is to investigate teachers' knowledge of teaching chemical bonding. The study focuses on three essential components of pedagogical content knowledge (PCK): (1) the students' understanding, (2) representations, and (3) instructional strategies. We analyzed lesson plans about chemical bonding generated by 10 chemistry teachers with whom we also conducted semi-structured interviews about their teaching. Our results revealed that the teachers were generally unaware of how the representations of models they used affected student comprehension. The teachers had trouble specifying students' difficulties in understanding. Moreover, most of the instructional strategies described were generic and insufficient for promoting student understanding. Additionally, the teachers' rationale for choosing a specific representation or activity was seldom directed at addressing students' understanding. Our results indicate that both PCK components require improvement, and suggest that the two components should be connected. Implications for the professional development of pre-service and in-service teachers are discussed.
Energy Technology Data Exchange (ETDEWEB)
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
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.
Pairing preferences of the model mono-valence mono-atomic ions investigated by molecular simulation
International Nuclear Information System (INIS)
We carried out a series of potential of mean force calculations to study the pairing preferences of a series of model mono-atomic 1:1 ions with evenly varied sizes. The probabilities of forming the contact ion pair (CIP) and the single water separate ion pair (SIP) were presented in the two-dimensional plots with respect to the ion sizes. The pairing preferences reflected in these plots largely agree with the empirical rule of matching ion sizes in the small and big size regions. In the region that the ion sizes are close to the size of the water molecule; however, a significant deviation from this conventional rule is observed. Our further analysis indicated that this deviation originates from the competition between CIP and the water bridging SIP state. The competition is mainly an enthalpy modulated phenomenon in which the existing of the water bridging plays a significant role
Kim, Myung-Sun; Kang, Bit-Na; Lim, Jae Young
2016-01-01
Purpose Decision-making is the process of forming preferences for possible options, selecting and executing actions, and evaluating the outcome. This study used the Iowa Gambling Task (IGT) and the Prospect Valence Learning (PVL) model to investigate deficits in risk-reward related decision-making in patients with chronic schizophrenia, and to identify decision-making processes that contribute to poor IGT performance in these patients. Materials and methods Thirty-nine patients with schizophrenia and 31 healthy controls participated. Decision-making was measured by total net score, block net scores, and the total number of cards selected from each deck of the IGT. PVL parameters were estimated with the Markov chain Monte Carlo sampling scheme in OpenBugs and BRugs, its interface to R, and the estimated parameters were analyzed with the Mann–Whitney U-test. Results The schizophrenia group received significantly lower total net scores compared to the control group. In terms of block net scores, an interaction effect of group × block was observed. The block net scores of the schizophrenia group did not differ across the five blocks, whereas those of the control group increased as the blocks progressed. The schizophrenia group obtained significantly lower block net scores in the fourth and fifth blocks of the IGT and selected cards from deck D (advantageous) less frequently than the control group. Additionally, the schizophrenia group had significantly lower values on the utility-shape, loss-aversion, recency, and consistency parameters of the PVL model. Conclusion These results indicate that patients with schizophrenia experience deficits in decision-making, possibly due to failure in learning the expected value of each deck, and incorporating outcome experiences of previous trials into expectancies about options in the present trial. PMID:27175079
Bond Graph Modeling and Simulation of Mechatronic Systems
DEFF Research Database (Denmark)
Habib, Tufail; Nielsen, Kjeld; Jørgensen, Kaj Asbjørn
2012-01-01
One of the demanding steps in the design and development of Mechatronic systems is to develop the initial model to visualize the response of a system. The Bond Graph (BG) method is a graphical approach for the design of multidomain systems. That is ideal for visualizing the essential characterist......One of the demanding steps in the design and development of Mechatronic systems is to develop the initial model to visualize the response of a system. The Bond Graph (BG) method is a graphical approach for the design of multidomain systems. That is ideal for visualizing the essential...... characteristics of a system. This paper explores the BG method as a modeling approach to develop Mechatronic systems; a case study about the Radar Antenna pedestal drive system is comprehensively addressed. Flow of energy between different functional elements of the system and their causalities are analyzed...
Indifference of Defaultable Bonds with Stochastic Intensity models
Regis Houssou; Olivier Besson
2010-01-01
The utility-based pricing of defaultable bonds in the case of stochastic intensity models of default risk is discussed. The Hamilton-Jacobi- Bellman (HJB) equations for the value functions is derived. A finite difference method is used to solve this problem. The yield-spreads for both buyer and seller are extracted. The behaviour of the spread curve given the default intensity is analyzed. Finally the impacts of the risk aversion and the correlation coefficient are discussed.
Confining Bond Rearrangement in the Random Center Vortex Model
Altarawneh, Derar; Engelhardt, Michael
2015-01-01
We present static meson-meson and baryon--anti-baryon potentials in Z(2) and Z(3) random center vortex models for the infrared sector of Yang-Mills theory, i.e., hypercubic lattice models of random vortex world-surfaces. In particular, we calculate Polyakov loop correlators of two static mesons resp. (anti-)baryons in a center vortex background and observe that their expectation values follow the minimal area law and show bond rearrangement behavior. The static meson-meson and baryon--anti-baryon potentials are compared with theoretical predictions and lattice QCD simulations.
Confining bond rearrangement in the random center vortex model
Altarawneh, Derar; Höllwieser, Roman; Engelhardt, Michael
2016-03-01
We present static meson-meson and baryon-antibaryon potentials in Z (2 ) and Z (3 ) random center vortex models for the infrared sector of Yang-Mills theory, i.e., hypercubic lattice models of random vortex world surfaces. In particular, we calculate multiple Polyakov loop correlators corresponding to static meson-meson or baryon-antibaryon configurations in a center vortex background and observe that their expectation values follow the minimal area law, displaying bond rearrangement behavior, a characteristic expected for the confining dynamics of the strong interaction. The static meson-meson and baryon-antibaryon potentials are compared with theoretical predictions and lattice QCD simulations.
International Nuclear Information System (INIS)
We present in this paper a size-extensive formulation of a valence universal multi-reference coupled cluster (VU-MRCC) theory which uses a general incomplete model space (IMS). The earlier formulations by Mukherjee [D. Mukherjee, Chem. Phys. Lett. 125 (1986) 207] led to size-extensive Heff which was both connected and 'closed', thereby leading to size-extensive energies. However, this necessitated abandoning the intermediate normalization (IN) for the valence universal wave-operator Ω when represented as a normal ordered exponential cluster Ansatz Ω≡{exp(S)} with S as the cluster operator. The lack of IN stemmed from the excitation operator Sq-op which leads to excitations into the complementary model space by their action on at least one model function. The powers of Sq-op can in general bring a model function φi back to another model function φj, and this is the reason why Ω does not respect IN. Sq-op are all labelled by active orbitals only. To achieve connectivity of Heff, it must be a 'closed' operator. A closed operator is one which always produces a model function by its action on another model function. Since the decoupling conditions Lq-op=0, and Lop=0 for the transformed operator L=Ω-1HΩ would be in conflict with Ωq-op=1q-op, the model space projection of Ω, PΩP=P cannot be maintained for the normal ordered Ansatz. This leads to a somewhat awkward expression for Heff. Bera et al. [N. Bera, S. Ghosh, D. Mukherjee, S. Chattopadhyay, J. Phys. Chem. A 109 (2005) 11462] recently tried to simplify the expression for Heff, and accomplished this by introducing suitable counter-terms Xcl in Ω to enforce Ωcl=1cl. We show in this paper that Heff in this formulation leads to a disconnected Heff, though it is equivalent by a similarity transformation to a connected effective hamiltonian H∼eff. Guided by the insight gleaned from this demonstration, we have proposed in this paper a new form of the wave-operator which never generates any powers of Sq
Ising tricriticality in the extended Hubbard model with bond dimerization
Ejima, Satoshi; Essler, Fabian H. L.; Lange, Florian; Fehske, Holger
2016-06-01
We explore the quantum phase transition between Peierls and charge-density-wave insulating states in the one-dimensional, half-filled, extended Hubbard model with explicit bond dimerization. We show that the critical line of the continuous Ising transition terminates at a tricritical point, belonging to the universality class of the tricritical Ising model with central charge c =7 /10 . Above this point, the quantum phase transition becomes first order. Employing a numerical matrix-product-state based (infinite) density-matrix renormalization group method we determine the ground-state phase diagram, the spin and two-particle charge excitations gaps, and the entanglement properties of the model with high precision. Performing a bosonization analysis we can derive a field description of the transition region in terms of a triple sine-Gordon model. This allows us to derive field theory predictions for the power-law (exponential) decay of the density-density (spin-spin) and bond-order-wave correlation functions, which are found to be in excellent agreement with our numerical results.
Adsorption mechanism and valency of catechol-functionalized hyperbranched polyglycerols
Krysiak, Stefanie; Wei, Qiang; Rischka, Klaus; Hartwig, Andreas; Haag, Rainer
2015-01-01
Summary Nature often serves as a model system for developing new adhesives. In aqueous environments, mussel-inspired adhesives are promising candidates. Understanding the mechanism of the extraordinarily strong adhesive bonds of the catechol group will likely aid in the development of adhesives. With this aim, we study the adhesion of catechol-based adhesives to metal oxides on the molecular level using atomic force microscopy (AFM). The comparison of single catechols (dopamine) with multiple catechols on hyperbranched polyglycerols (hPG) at various pH and dwell times allowed us to further increase our understanding. In particular, we were able to elucidate how to achieve strong bonds of different valency. It was concluded that hyperbranched polyglycerols with added catechol end groups are promising candidates for durable surface coatings. PMID:26150898
Adsorption mechanism and valency of catechol-functionalized hyperbranched polyglycerols
Directory of Open Access Journals (Sweden)
Stefanie Krysiak
2015-05-01
Full Text Available Nature often serves as a model system for developing new adhesives. In aqueous environments, mussel-inspired adhesives are promising candidates. Understanding the mechanism of the extraordinarily strong adhesive bonds of the catechol group will likely aid in the development of adhesives. With this aim, we study the adhesion of catechol-based adhesives to metal oxides on the molecular level using atomic force microscopy (AFM. The comparison of single catechols (dopamine with multiple catechols on hyperbranched polyglycerols (hPG at various pH and dwell times allowed us to further increase our understanding. In particular, we were able to elucidate how to achieve strong bonds of different valency. It was concluded that hyperbranched polyglycerols with added catechol end groups are promising candidates for durable surface coatings.
THE VALENCE OF CORPUSCULAR PROTEINS.
Gorin, M H; Mover, L S
1942-07-20
BY THE USE OF TWO EXTREME MODELS: a hydrated sphere and an unhydrated rod the valence (net charge) of corpuscular proteins can be successfully calculated from electric mobility data by the Debye-Hückel theory (modified to include the effect of the ions in the ion atmosphere) in conjunction with the electrophoretic theory of Henry. As pointed out by Abramson, this permits a comparison with values for the valence from titration data. Electrometric titration measurements of serum albumin B (Kekwick) have been determined at several ionic strengths. These results, together with the available data in the literature for serum albumin B, egg albumin, and beta-lactoglobulin have been used to compare values for the valence calculated from measurements of titration, electrophoresis, and membrane potentials. The results indicate that the usual interpretation of titration curves is open to serious question. By extrapolation of the titration data to zero ionic strength and protein concentration, there results an "intrinsic" net charge curve describing the binding of H(+) (OH(-)) ion alone. This curve agrees closely, in each case, with values of the valence calculated from mobility data (which in turn are in close accord with those estimated from membrane potential measurements). The experimental titration curves in the presence of appreciable quantities of ions and protein deviate widely from the ideal curve. It is suggested that, under these conditions, binding of undissociated acid (base) leads to erroneous values for the net charge. This binding would not affect the electrophoretic mobility. Values of the net charge obtained by the two extreme models from electrophoretic data are in agreement within 15 to 20 per cent. The agreement between the cylindrical model and the titration data is somewhat better in each case than with the sphere; i.e., this comparison enables a choice to be made between asymmetry and hydration in the interpretation of results from sedimentation and
Energy Technology Data Exchange (ETDEWEB)
Freire, J J [Departamento de Ciencias y Tecnicas FisicoquImicas, Facultad de Ciencias, Universidad Nacional de Educacion a Distancia (UNED), Senda del Rey 9, 28040 Madrid (Spain)], E-mail: jfreire@invi.uned.es
2008-07-16
The bond fluctuation model with a bond potential has been applied to investigation of the glass transition of linear chains and chains with a regular disposition of small branches. Cooling and subsequent heating curves are obtained for the chain energies and also for the mean acceptance probability of a bead jump. In order to mimic different trends to vitrification, a factor B gauging the strength of the bond potential with respect to the long-range potential (i.e. the intramolecular or intermolecular potential between indirectly bonded beads) has been introduced. (A higher value of B leads to a preference for the highest bond lengths and a higher total energy, implying a greater tendency to vitrify.) Different cases have been considered for linear chains: no long-range potential, no bond potential and several choices for B. Furthermore, two distinct values of B have been considered for alternate bonds in linear chains. In the case of the branched chains, mixed models with different values of B for bonds in the main chain and in the branches have also been investigated. The possible presence of ordering or crystallization has been characterized by calculating the collective light scattering function of the different samples after annealing at a convenient temperature below the onset of the abrupt change in the curves associated with a thermodynamic transition. It is concluded that ordering is inherited more efficiently in the systems with branched chains and also for higher values of B. The branched molecules with the highest B values in the main chain bonds exhibit two distinct transitions in the heating curves, which may be associated with two glass transitions. This behavior has been detected experimentally for chains with relatively long flexible branches.
Vector-based model of elastic bonds for DEM simulation of solids
Kuzkin, Vitaly A
2012-01-01
A new model for computer simulation of solids, composed of bonded particles, is proposed. Vectors rigidly connected with particles are used for description of deformation of a single bond. The expression for potential energy of the bond and corresponding expressions for forces and moments are proposed. Formulas, connecting parameters of the model with longitudinal, shear, bending and torsional stiffnesses of the bond, are derived. It is shown that the model allows to describe any values of the bond stiffnesses exactly. Two different calibration procedures depending on bond length/thickness ratio are proposed. It is shown that parameters of model can be chosen so that under small deformations the bond is equivalent to either Bernoulli-Euler or Timoshenko rod or short cylinder connecting particles. Simple expressions, connecting parameters of V-model with geometrical and mechanical characteristics of the bond, are derived. Computer simulation of dynamical buckling of the straight discrete rod and discrete half-...
Representation of emotional valence in human brain
Viinikainen, Mikko
2012-01-01
All emotions can be evaluated with fair accuracy on the basis of their position on unpleasantness-pleasantness, or valence, dimension. Valence has been considered to be a linear continuum both on experiential and neural level, ranging from very unpleasant to very pleasant. However, using such a model it is difficult to explain complex emotional states, in which we can simultaneously experience unpleasantness and pleasantness, like during a rollercoaster ride or a horror film. Also experiments...
Mesoscale numerical modeling of plastic bonded explosives under shock loading
Directory of Open Access Journals (Sweden)
Shang Hailin
2015-01-01
Full Text Available Mesoscale responses of plastic bonded explosives under shock loading are investigated using material point method as implemented in the Uintah Computational Framework. The two-dimensional geometrical model which can approximately reflect the mesoscopic structure of plastic bonded explosives was created based on the Voronoi tessellation. Shock loading for the explosive was performed by a piston moving at a constant velocity. For the purpose of investigating the influence of shock strength on the responses of explosives, two different velocities for the piston were used, 200 m/s and 400 m/s, respectively. The simulation results indicate that under shock loading there forms some stress localizations on the grain boundary of explosive. These stress localizations lead to large plastic deformations, and the plastic strain energy transforms to thermal energy immediately, causing temperature to rise rapidly and form some hot spots on grain boundary areas. The comparison between two different piston velocities shows that with increasing shock strength, the distribution of plastic strain and temperature does not have significant change, but their values increase obviously. Namely, the higher the shock strength is, the higher the hot spot temperature will be.
Mesoscale numerical modeling of plastic bonded explosives under shock loading
Shang, Hailin; Zhao, Feng; Ji, Guangfu; Fu, Hua
2015-09-01
Mesoscale responses of plastic bonded explosives under shock loading are investigated using material point method as implemented in the Uintah Computational Framework. The two-dimensional geometrical model which can approximately reflect the mesoscopic structure of plastic bonded explosives was created based on the Voronoi tessellation. Shock loading for the explosive was performed by a piston moving at a constant velocity. For the purpose of investigating the influence of shock strength on the responses of explosives, two different velocities for the piston were used, 200 m/s and 400 m/s, respectively. The simulation results indicate that under shock loading there forms some stress localizations on the grain boundary of explosive. These stress localizations lead to large plastic deformations, and the plastic strain energy transforms to thermal energy immediately, causing temperature to rise rapidly and form some hot spots on grain boundary areas. The comparison between two different piston velocities shows that with increasing shock strength, the distribution of plastic strain and temperature does not have significant change, but their values increase obviously. Namely, the higher the shock strength is, the higher the hot spot temperature will be.
Advances in modeling and design of adhesively bonded systems
Kumar, S
2013-01-01
The book comprehensively charts a way for industry to employ adhesively bonded joints to make systems more efficient and cost-effective Adhesively bonded systems have found applications in a wide spectrum of industries (e.g., aerospace, electronics, construction, ship building, biomedical, etc.) for a variety of purposes. Emerging adhesive materials with improved mechanical properties have allowed adhesion strength approaching that of the bonded materials themselves. Due to advances in adhesive materials and the many potential merits that adhesive bonding offers, adhesive bonding has replac
Institute of Scientific and Technical Information of China (English)
高翔; 陈晓波; 黎军; 李家明
2013-01-01
本文论述价键优选法作为一种新颖的理论方法在材料结构预测与物性研究中的应用，特别是在低维数纳米结构如团簇与纳米线研究中所展示的优势。价键优选法以原子几何构型和电子云(主要是由费米能级附近的分子轨道组成，即广义前线轨道)空间分布来合理决定纳米结构的稳定构型的选取。本文以硅团簇为例说明价键优选法的特点，以及锂、钠、铍、镁等金属团簇为例说明价键优选法在结构预测与材料物性随尺寸演化规律研究中的应用，以锂离子在MoS纳米线中的吸附为例说明价键优选法在储能材料离子传导研究中的应用，最后总结价键优选法的进一步发展方向。%The optimum valence bond scheme is a new theoretical method in generating the initial geometric configurations in molecular dynamics simulations of cluster systems. We will present the application of such a new method to the prediction of nano-structures and the study of matter properties, especially for the low-dimensional nano-structures, such as clusters and nano wires. The optimum valence bond scheme uses the atomic geometry of structures and the space distribution of the valence electrons (mainly the molecular orbitals near the Fermi levels, i.e., the generalized frontier orbitals) to determine the possible stable geometric configurations of nano-structures. Silicon clusters are used to demonstrate the features of the optimum valence bond scheme. Metallic clusters such as those of lithium, sodium, beryllium and magnesium are used as examples to illustrate the application of the scheme to the prediction of structures and the studies of the evolution of the material properties with the sizes of clusters. We will use the adsorption process of lithium ion and MoS nano wire to illustrate the application of the optimum valence bond scheme in the studies of the ionic conduction mechanism of the energy storage materials. We
Modelling Static and Dynamic FRP-Concrete Bond Behaviour Using a Local Concrete Damage Model
Li, Xiaoqin; Chen, Jian-Fei; Lu, Yong; Yang, Zhenjun
2015-01-01
This paper presents a study on the bond behaviour of FRP-concrete bonded joints under static and dynamic loadings, by developing a meso-scale finite element model using the K&C concrete damage model in LS-DYNA. A significant number of single shear experiments under static pull-off loading were modelled with an extensive parametric study covering key factors in the K&C model, including the crack band width, the compressive fracture energy and the shear dilatation factor. It is demonstr...
Modelling Bonds & Credit Default Swaps using a Structural Model with Contagion
Helen Haworth; Christoph Reisinger; William Shaw
2007-01-01
This paper develops a two-dimensional structural framework for valuing credit default swaps and corporate bonds in the presence of default contagion. Modelling the values of related firms as correlated geometric Brownian motions with exponential default barriers, analytical formulae are obtained for both credit default swap spreads and corporate bond yields. The credit dependence structure is influenced by both a longer-term correlation structure as well as by the possibility of default conta...
Double site-bond percolation model for biomaterial implants
Mely, H
2011-01-01
We present a double site-bond percolation model to account, on the one hand, for the vascularization and/or resorption of biomaterial implant in bones and, on the other hand, for its mechanical continuity. The transformation of the implant into osseous material, and the dynamical formation/destruction of this osseous material is accounted for by creation and destruction of links and sites in two, entangled, networks. We identify the relevant parameters to describe the implant and its evolution, and separate their biological or chemical origin from their physical one. We classify the various phenomena in the two regimes, percolating or non-percolating, of the networks. We present first numerical results in two dimensions.
Vector-based model of elastic bonds for simulation of granular solids
Kuzkin, Vitaly A.; Asonov, Igor E.
2012-11-01
A model (further referred to as the V model) for the simulation of granular solids, such as rocks, ceramics, concrete, nanocomposites, and agglomerates, composed of bonded particles (rigid bodies), is proposed. It is assumed that the bonds, usually representing some additional gluelike material connecting particles, cause both forces and torques acting on the particles. Vectors rigidly connected with the particles are used to describe the deformation of a single bond. The expression for potential energy of the bond and corresponding expressions for forces and torques are derived. Formulas connecting parameters of the model with longitudinal, shear, bending, and torsional stiffnesses of the bond are obtained. It is shown that the model makes it possible to describe any values of the bond stiffnesses exactly; that is, the model is applicable for the bonds with arbitrary length/thickness ratio. Two different calibration procedures depending on bond length/thickness ratio are proposed. It is shown that parameters of the model can be chosen so that under small deformations the bond is equivalent to either a Bernoulli-Euler beam or a Timoshenko beam or short cylinder connecting particles. Simple analytical expressions, relating parameters of the V model with geometrical and mechanical characteristics of the bond, are derived. Two simple examples of computer simulation of thin granular structures using the V model are given.
Three-dimensional bonded-cell model for grain fragmentation
Cantor, D.; Azéma, E.; Sornay, P.; Radjai, F.
2016-07-01
We present a three-dimensional numerical method for the simulation of particle crushing in 3D. This model is capable of producing irregular angular fragments upon particle fragmentation while conserving the total volume. The particle is modeled as a cluster of rigid polyhedral cells generated by a Voronoi tessellation. The cells are bonded along their faces by a cohesive Tresca law with independent tensile and shear strengths and simulated by the contact dynamics method. Using this model, we analyze the mechanical response of a single particle subjected to diametral compression for varying number of cells, their degree of disorder, and intercell tensile and shear strength. In particular, we identify the functional dependence of particle strength on the intercell strengths. We find that two different regimes can be distinguished depending on whether intercell shear strength is below or above its tensile strength. In both regimes, we observe a power-law dependence of particle strength on both intercell strengths but with different exponents. The strong effect of intercell shear strength on the particle strength reflects an interlocking effect between cells. In fact, even at low tensile strength, the particle global strength can still considerably increase with intercell shear strength. We finally show that the Weibull statistics describes well the particle strength variability.
Physical Nature of Hydrogen Bond
Zhyganiuk, I V
2015-01-01
The physical nature and the correct definition of hydrogen bond (H-bond) are considered.\\,\\,The influence of H-bonds on the thermodynamic, kinetic, and spectroscopic properties of water is analyzed.\\,\\,The conventional model of H-bonds as sharply directed and saturated bridges between water molecules is incompatible with the behavior of the specific volume, evaporation heat, and self-diffusion and kinematic shear viscosity coefficients of water. On the other hand, it is shown that the variation of the dipole moment of a water molecule and the frequency shift of valence vibrations of a hydroxyl group can be totally explained in the framework of the electrostatic model of H-bond.\\,\\,At the same time, the temperature dependences of the heat capacity of water in the liquid and vapor states clearly testify to the existence of weak H-bonds.\\,\\,The analysis of a water dimer shows that the contribution of weak H-bonds to its ground state energy is approximately 4--5 times lower in comparison with the energy of electr...
Chikalov, Igor
2011-02-15
Background: Hydrogen bonds (H-bonds) play a key role in both the formation and stabilization of protein structures. They form and break while a protein deforms, for instance during the transition from a non-functional to a functional state. The intrinsic strength of an individual H-bond has been studied from an energetic viewpoint, but energy alone may not be a very good predictor.Methods: This paper describes inductive learning methods to train protein-independent probabilistic models of H-bond stability from molecular dynamics (MD) simulation trajectories of various proteins. The training data contains 32 input attributes (predictors) that describe an H-bond and its local environment in a conformation c and the output attribute is the probability that the H-bond will be present in an arbitrary conformation of this protein achievable from c within a time duration ?. We model dependence of the output variable on the predictors by a regression tree.Results: Several models are built using 6 MD simulation trajectories containing over 4000 distinct H-bonds (millions of occurrences). Experimental results demonstrate that such models can predict H-bond stability quite well. They perform roughly 20% better than models based on H-bond energy alone. In addition, they can accurately identify a large fraction of the least stable H-bonds in a conformation. In most tests, about 80% of the 10% H-bonds predicted as the least stable are actually among the 10% truly least stable. The important attributes identified during the tree construction are consistent with previous findings.Conclusions: We use inductive learning methods to build protein-independent probabilistic models to study H-bond stability, and demonstrate that the models perform better than H-bond energy alone. 2011 Chikalov et al; licensee BioMed Central Ltd.
Sittel, Wiebke; Basuki, Widodo W.; Aktaa, Jarir
2015-10-01
A modeling based optimization process of the solid state diffusion bonding is presented for joining ferritic oxide dispersion strengthened steels PM2000. An optimization study employing varying bonding temperatures and pressures results in almost the same strength and toughness of the bonded compared to the as received material. TEM investigations of diffusion bonded samples show a homogeneous distribution of oxide particles at the bonding seam similar to that in the bulk. Hence, no loss in strength or creep resistance due to oxide particle agglomeration is found, as verified by the mechanical properties observed for the joint.
Chikalov, Igor
2011-04-02
Hydrogen bonds (H-bonds) play a key role in both the formation and stabilization of protein structures. H-bonds involving atoms from residues that are close to each other in the main-chain sequence stabilize secondary structure elements. H-bonds between atoms from distant residues stabilize a protein’s tertiary structure. However, H-bonds greatly vary in stability. They form and break while a protein deforms. For instance, the transition of a protein from a nonfunctional to a functional state may require some H-bonds to break and others to form. The intrinsic strength of an individual H-bond has been studied from an energetic viewpoint, but energy alone may not be a very good predictor. Other local interactions may reinforce (or weaken) an H-bond. This paper describes inductive learning methods to train a protein-independent probabilistic model of H-bond stability from molecular dynamics (MD) simulation trajectories. The training data describes H-bond occurrences at successive times along these trajectories by the values of attributes called predictors. A trained model is constructed in the form of a regression tree in which each non-leaf node is a Boolean test (split) on a predictor. Each occurrence of an H-bond maps to a path in this tree from the root to a leaf node. Its predicted stability is associated with the leaf node. Experimental results demonstrate that such models can predict H-bond stability quite well. In particular, their performance is roughly 20% better than that of models based on H-bond energy alone. In addition, they can accurately identify a large fraction of the least stable H-bonds in a given conformation. The paper discusses several extensions that may yield further improvements.
Reliable four-point flexion test and model for die-to-wafer direct bonding
International Nuclear Information System (INIS)
For many years, wafer-to-wafer (W2W) direct bonding has been very developed particularly in terms of bonding energy measurement and bonding mechanism comprehension. Nowadays, die-to-wafer (D2W) direct bonding has gained significant attention, for instance, in photonics and microelectro-mechanics, which supposes controlled and reliable fabrication processes. So, whatever the stuck materials may be, it is not obvious whether bonded D2W structures have the same bonding strength as bonded W2W ones, because of possible edge effects of dies. For that reason, it has been strongly required to develop a bonding energy measurement technique which is suitable for D2W structures. In this paper, both D2W- and W2W-type standard SiO2-to-SiO2 direct bonding samples are fabricated from the same full-wafer bonding. Modifications of the four-point flexion test (4PT) technique and applications for measuring D2W direct bonding energies are reported. Thus, the comparison between the modified 4PT and the double-cantilever beam techniques is drawn, also considering possible impacts of the conditions of measures such as the water stress corrosion at the debonding interface and the friction error at the loading contact points. Finally, reliability of a modified technique and a new model established for measuring D2W direct bonding energies is demonstrated
Reliable four-point flexion test and model for die-to-wafer direct bonding
Energy Technology Data Exchange (ETDEWEB)
Tabata, T., E-mail: toshiyuki.tabata@cea.fr; Sanchez, L.; Fournel, F.; Moriceau, H. [Univ. Grenoble Alpes, F-38000 Grenoble, France and CEA, LETI, MINATEC Campus, F-38054 Grenoble (France)
2015-07-07
For many years, wafer-to-wafer (W2W) direct bonding has been very developed particularly in terms of bonding energy measurement and bonding mechanism comprehension. Nowadays, die-to-wafer (D2W) direct bonding has gained significant attention, for instance, in photonics and microelectro-mechanics, which supposes controlled and reliable fabrication processes. So, whatever the stuck materials may be, it is not obvious whether bonded D2W structures have the same bonding strength as bonded W2W ones, because of possible edge effects of dies. For that reason, it has been strongly required to develop a bonding energy measurement technique which is suitable for D2W structures. In this paper, both D2W- and W2W-type standard SiO{sub 2}-to-SiO{sub 2} direct bonding samples are fabricated from the same full-wafer bonding. Modifications of the four-point flexion test (4PT) technique and applications for measuring D2W direct bonding energies are reported. Thus, the comparison between the modified 4PT and the double-cantilever beam techniques is drawn, also considering possible impacts of the conditions of measures such as the water stress corrosion at the debonding interface and the friction error at the loading contact points. Finally, reliability of a modified technique and a new model established for measuring D2W direct bonding energies is demonstrated.
CoCo Bonds Valuation with Equity- and Credit-Calibrated First Passage Structural Models
Damiano Brigo; Jo\\~ao Garcia; Nicola Pede
2013-01-01
After the beginning of the credit and liquidity crisis, financial institutions have been considering creating a convertible-bond type contract focusing on Capital. Under the terms of this contract, a bond is converted into equity if the authorities deem the institution to be under-capitalized. This paper discusses this Contingent Capital (or Coco) bond instrument and presents a pricing methodology based on firm value models. The model is calibrated to readily available market data. A stress t...
Meso-scale three-dimensional modeling of bond in FRP-strengthened masonry
Ghiassi, Bahman; Oliveira, Daniel V.; Lourenço, Paulo B.; Marcari, Giancarlo
2012-01-01
Performance of masonry elements externally strengthened with fiber reinforced polymers (FRPs) is intrinsically dependent on the bond behavior between the composite material and masonry substrate. Therefore, a sound understanding of the interface behavior is crucial at the design stage. In this paper, a three-dimensional model based on the smeared crack modeling approach is presented for investigating the bond behavior in FRP-strengthened masonry elements. The threedimensional aspects of bond ...
Developing A Laser Shockwave Model For Characterizing Diffusion Bonded Interfaces
Energy Technology Data Exchange (ETDEWEB)
James A. Smith; Jeffrey M. Lacy; Barry H. Rabin
2014-07-01
12. Other advances in QNDE and related topics: Preferred Session Laser-ultrasonics Developing A Laser Shockwave Model For Characterizing Diffusion Bonded Interfaces 41st Annual Review of Progress in Quantitative Nondestructive Evaluation Conference QNDE Conference July 20-25, 2014 Boise Centre 850 West Front Street Boise, Idaho 83702 James A. Smith, Jeffrey M. Lacy, Barry H. Rabin, Idaho National Laboratory, Idaho Falls, ID ABSTRACT: The US National Nuclear Security Agency has a Global Threat Reduction Initiative (GTRI) which is assigned with reducing the worldwide use of high-enriched uranium (HEU). A salient component of that initiative is the conversion of research reactors from HEU to low enriched uranium (LEU) fuels. An innovative fuel is being developed to replace HEU. The new LEU fuel is based on a monolithic fuel made from a U-Mo alloy foil encapsulated in Al-6061 cladding. In order to complete the fuel qualification process, the laser shock technique is being developed to characterize the clad-clad and fuel-clad interface strengths in fresh and irradiated fuel plates. The Laser Shockwave Technique (LST) is being investigated to characterize interface strength in fuel plates. LST is a non-contact method that uses lasers for the generation and detection of large amplitude acoustic waves to characterize interfaces in nuclear fuel plates. However the deposition of laser energy into the containment layer on specimen’s surface is intractably complex. The shock wave energy is inferred from the velocity on the backside and the depth of the impression left on the surface from the high pressure plasma pulse created by the shock laser. To help quantify the stresses and strengths at the interface, a finite element model is being developed and validated by comparing numerical and experimental results for back face velocities and front face depressions with experimental results. This paper will report on initial efforts to develop a finite element model for laser
Organization of atomic bond tensions in model glasses
Kustanovich, T.; Rabin, Y.; Olami, Z.
2002-01-01
In order to understand whether internal stresses in glasses are correlated or randomly distributed, we study the organization of atomic bond tensions (normal forces between pairs of atoms). Measurements of the invariants of the atomic bond tension tensor in simulated 2D and 3D binary Lennard-Jones glasses, reveal new and unexpected correlations and provide support for Alexander's conjecture about the non-random character of internal stresses in amorphous solids.
Numerical Modelling of the Concrete/Rebar Bond
Phan, Thanh Song; Rossi, Pierre; Tailhan, Jean-Louis
2015-01-01
The simulation of the behaviour of the rebar-concrete bond is of primary importance for an accurate description of cracking processes in reinforced concrete structures and an improved prediction of their durability. In this paper, the methodology used to identify the mechanical behaviour of a rebar-concrete bond in the case of a particular steel reinforcement is first mentioned. The methodology consists in simulating the probabilistic mechanical behaviour of RC tie-beams (170 x 10 x 10 cm), s...
Gillespie, Ronald J.; And Others
1996-01-01
Presents an alternative approach to bonding and geometry--the electron domain model--which avoids some of the problems with the conventional approach. Discusses difficulties with the orbital model at the introductory level, electron spin and the Pauli exclusion principle, electron pair domains, nonequivalent domains, multiple bonds, and origins…
Modelling and simulation of power electronic systems using a bond graph formalism
Araújo, R.; Leite, V; Freitas, D
2002-01-01
This paper deals with the modelling of power electronic systems using the bond graph formalism. The switching components are modelled using an ideal representation so that a constant topology system is obtained. The purpose of the present contribution is to discuss a technique that combines bond graph energy-flow modelling and signal-flow modelling schemes for simulation and prototyping of signal processing algorithms in power electronics systems. In this paper, we will discuss models of the ...
Core and valence thermal vibrations in diamond, silicon, and germanium
Energy Technology Data Exchange (ETDEWEB)
Saravanan, R. (School of Physics, Madurai Kamaraj Univ. (India)); Balamurugan, P. (School of Physics, Madurai Kamaraj Univ. (India)); Mohanlal, S.K. (School of Physics, Madurai Kamaraj Univ. (India))
1994-08-01
An analysis is made using published X-ray data, for the thermal vibrations in diamond, silicon, and germanium. The overall thermal vibration is split into core and valence contributions, because valence electrons can oscillate with different phase and amplitude than core electrons due to bond polarizability. Using indigenously developed computer programs the published data are analyzed. In the first phase, the overall Debye-Waller factor of diamond, Si, and Ge together with scaling and extinction factors are refined using the method of least squares. In the second phase, the core and valence contributions of the harmonic temperature factor are evaluated. Finally, in the third phase, the core and valence contributions of the anharmonic temperature factor are evaluated. The error in the fitting procedure is less than 1% for Si and Ge and about 3% for diamond. (orig.)
Strong disorder fixed points in the two-dimensional random-bond Ising model
Picco, Marco; Honecker, Andreas; Pujol, Pierre
2006-01-01
The random-bond Ising model on the square lattice has several disordered critical points, depending on the probability distribution of the bonds. There are a finite-temperature multicritical point, called Nishimori point, and a zero-temperature fixed point, for both a binary distribution where the coupling constants take the values +/- J and a Gaussian disorder distribution. Inclusion of dilution in the +/- J distribution (J=0 for some bonds) gives rise to another zero-temperature fixed point...
Midtvedt, Daniel; Croy, Alexander
2016-06-01
We compare the simplified valence-force model for single-layer black phosphorus with the original model and recent ab initio results. Using an analytic approach and numerical calculations we find that the simplified model yields Young's moduli that are smaller compared to the original model and are almost a factor of two smaller than ab initio results. Moreover, the Poisson ratios are an order of magnitude smaller than values found in the literature.
The Mechanism of Covalent Bonding: Analysis within the Huckel Model of Electronic Structure
Nordholm, Sture; Back, Andreas; Backsay, George B.
2007-01-01
The commonly used Huckel model of electronic structure is employed to study the mechanisms of covalent bonding, a quantum effect related to electron dynamics. The model also explains the conjugation and aromaticity of planar hydrocarbon molecules completely.
Modelling the Loss of Steel-Concrete Bonds in Corroded Reinforced Concrete Beams
DEFF Research Database (Denmark)
Thoft-Christensen, Palle
The existing stochastic models for deterioration of reinforced concrete structures is extended by adding modelling of "loss of bond" due to corrosion between the reinforcement bars and the surrounding concrete....
International Nuclear Information System (INIS)
Highlights: → Based on the EET, the valence electron structures of MoSi2-based solid solution alloys have been analyzed using the average atom model. → Analysis of the valence electron structure and mechanical properties relationship. → The results of theoretic calculation have been verified by the experimental results. - Abstract: Based on the empirical electron theory (EET) of solids and molecules, the valence electron structures (VES) of MoSi2-based solid solution alloys have been analyzed using the average atom model. The results showed that with the increase of the W addition content, the hybridization steps of Mo and Si atom of the alloys occurred in C3 and 1, respectively. The hybridization step of W was always C5. The bond energy of the main bond branch, the covalence electron number on the strongest bond and the percentage of the total covalent electron numbers accounting for the total valence electron number of (Mo1-x, Wx)Si2 solid solutions increased with the increase of W addition content. These suggested that the addition of W would increase the melting point, hardness and strength and decrease the fracture toughness of (Mo1-x, Wx)Si2 solid solutions. Based on those results, MoSi2-based solid solution alloys were manufactured, and the results of the experiments were in accordance with those of the theory.
Softening of Phase Transition in 2D Potts Model Under Quenched Bond Randomness
Yaşar, Fatih; Gündüç, Yiğit; Çelik, Tarık
1997-01-01
We have simulated, by using cluster algorithm, the $q=8$ state Potts model in two-dimension with varying amount of quenched bond randomness. We have shown that there exist a finite size dependent threshold value of the introduced quenched bond randomness for rounding the first-order phase transition and this threshold value becomes smaller as the system size increased.
Analysis, Modeling and Simulation of Mechatronic Systems using the Bond Graph Method
Directory of Open Access Journals (Sweden)
A. Alabakhshizadeh
2011-01-01
Full Text Available The Bond Graph is the proper choice of physical system used for: (i Modeling which can be applied to systems combining multidisciplinary energy domains, (ii Analysis to provide a great value proposition for finding the algebraic loops within the system enabling the process of troubleshooting and eliminating the defects by using the proper component(s to fix the causality conflict even without being acquainted in the proper system, and (iii Simulation facilitated through derived state space equations from the Bond Graph model is solved using industrial simulation software, such as 20-Sim. The Bond Graph technique is a graphical language of modeling, in which component energy ports are connected by bonds that specify the transfer of energy between system components. Following a brief introduction of the Bond Graph methodology and techniques, two separate case studies are comprehensively addressed. The first case study is a systematic implementation of a fourth order electrical system and conversion to mechanical system while the second case study presents modeling of the Dielectric Electro Active Polymer (DEAP actuator. Building the systematic Bond Graph of multifaceted system and ease of switching between different domains are aims of the first case study while the second study shows how a complex mechatronic system could be analyzed and built by the Bond Graph. The respective Bond Graphs in each case is evaluated in the light of mathematical equations and simulations. Excellent correlation has been achieved between the simulation results and proper system equations.
Indirect consideration of un-bonded tendons in 1/4 PCCV model
International Nuclear Information System (INIS)
This paper concentrates on the development of a tendon model which can simulate slip behavior between un-bonded tendons and concrete for finite element modeling of 1/4 PCCV (1:4-scale prestressed concrete containment vessel) model. Differently from the bonded tendon depended on structural section, a stress increase beyond the effective value of initial prestress in the un-bonded tendon is mainly depended on the structural member. Therefore, the tendon stress in the un-bonded tendon can be represented as having uniform distribution along the length of the member if the friction loss is not included. To trace the structural response of prestressed concrete structures, accordingly, a modified stress-strain curve for the un-bonded tendon can be derived through performing the successive iterations. This indirect tendon model can take into account the slip effect between un-bonded tendon and concrete, and then it is incorporated into commercialized programs such as DIANA and ABAQUS which have the fundamental limitation in simulating the un-bonded tendon. Finally, the ultimate pressure capacity analyses of 1/4 PCCV model are carried out to evaluate the efficiency and applicability of this tendon model. The numerical results show that 1/4 PCCV represents the ultimate resisting capacity larger than 3 times of the design pressure. (authors)
International Nuclear Information System (INIS)
Highlights: • We simulate VXPS and UPS of (Li, C, N, O, F)-containing substances by DFT calculations. • To simulate AES of (Li, C, N, O, F)-atoms with our modified method of the kinetic energy. • We clarify electronic states of (Li, C, N, O, F)-containing substances from simulated results. - Abstract: Experimental valence X-ray photoelectron spectra (VXPS) and Auger electron spectra (AES) of (Li, C, N, O, F) elements of four solid substances [graphite, GaN, SiO2, LiF] are analyzed by density-functional theory calculations using the model molecules of the unit cell. For the calculations, we use deMon density functional theory (DFT) program to estimate VXPS, core-electron binding energies, and (Li, C, N, O, F)-KVV AES of the solid substances. In the AES simulations, we evaluate theoretical kinetic energies of the AES with our modified calculation method. The modified kinetic energies correspond to two final-state holes at the ground state and at the transition-state in DFT calculations, respectively. Experimental KVV AES of the (Li, C, N, O) atoms in the substances agree considerably well to simulation of AES obtained with the maximum kinetic energies of the atoms, while, the experimental F KVV AES of LiF is almost in accordance with the spectra from the transition-state kinetic energy calculations
Chemical bond fundamental aspects of chemical bonding
Frenking, Gernot
2014-01-01
This is the perfect complement to ""Chemical Bonding - Across the Periodic Table"" by the same editors, who are two of the top scientists working on this topic, each with extensive experience and important connections within the community. The resulting book is a unique overview of the different approaches used for describing a chemical bond, including molecular-orbital based, valence-bond based, ELF, AIM and density-functional based methods. It takes into account the many developments that have taken place in the field over the past few decades due to the rapid advances in quantum chemica
Automated Modeling and Simulation Using the Bond Graph Method for the Aerospace Industry
Granda, Jose J.; Montgomery, Raymond C.
2003-01-01
Bond graph modeling was originally developed in the late 1950s by the late Prof. Henry M. Paynter of M.I.T. Prof. Paynter acted well before his time as the main advantage of his creation, other than the modeling insight that it provides and the ability of effectively dealing with Mechatronics, came into fruition only with the recent advent of modern computer technology and the tools derived as a result of it, including symbolic manipulation, MATLAB, and SIMULINK and the Computer Aided Modeling Program (CAMPG). Thus, only recently have these tools been available allowing one to fully utilize the advantages that the bond graph method has to offer. The purpose of this paper is to help fill the knowledge void concerning its use of bond graphs in the aerospace industry. The paper first presents simple examples to serve as a tutorial on bond graphs for those not familiar with the technique. The reader is given the basic understanding needed to appreciate the applications that follow. After that, several aerospace applications are developed such as modeling of an arresting system for aircraft carrier landings, suspension models used for landing gears and multibody dynamics. The paper presents also an update on NASA's progress in modeling the International Space Station (ISS) using bond graph techniques, and an advanced actuation system utilizing shape memory alloys. The later covers the Mechatronics advantages of the bond graph method, applications that simultaneously involves mechanical, hydraulic, thermal, and electrical subsystem modeling.
Virtual multi-dimensional internal bonds model and its application in simulation of rock mass
Institute of Scientific and Technical Information of China (English)
ZHANG ZhenNan; GE XiuRun
2008-01-01
VMIB (virtual multi-dimensional internal bonds) is a multiscale mechanical model developed from the VIB (virtual internal bond) theory. In VIB theory, the solid material is considered to consist of random-distributed material particles in microscale. These particles are connected with normal bonds. The macro constitutive relation is derived from the cohesive law between particles. However, in VMIB, the micro particles are connected with both normal and shear bonds. The macro constitutive relation is derived in terms of bond stiffness coefficients. It has been theoretically certified that there exists a corresponding relationship between the two bond stiffness coefficients and the two macro material constants, i.e. the Young's modulus and Poisson ratio. This corresponding relationship suggests that it should be necessary and sufficient to simultaneously account for the normal and shear interactions between particles. Due to the fact that the fracture criterion is directly incorporated into the constitutive relation, both VIB and VMIB present many advantages in simulating fractures of materials. In the damage model of rock mass, a damage tensor is usually defined to describe the distribution of cracks. The damage value in one direction determines the relative stiffness of rock mass in this direction. In VMIB solid, the relative distribution density of micro bonds in one direction determines the relative macro stiffness of the material in this direction. The effects of the damage value and the relative distribution density of bonds are consistent. To simulate the failure behavior of rock mass with VMIB, the presented paper sets up a quantitative relationship between the damage tensor and the relative distribution density of bonds. Comparison of the theoretical and the experimental results shows that VMIB model can represent the effect of distributed cracks on rock mass with this relationship. The presented work provides a foundation for further simulating fracture
A new effective interaction for $0\\hbar\\omega$ shell model calculations in the sdpf valence space
Nowacki, F
2007-01-01
The neutron rich isotopes with Z<20, in particular those with neutron numbers around N=28,have been at the focus of a lot experimental and theoretical scrutiny during the last few years.Shell model calculations using the effective interaction SDPF-NR, were able to predictor to explain most of the properties featured by these nuclei. Prominent among them is the disappearance of the N=28 shell closure for Z<=16. We have incorporated to SDPF-NR some modifications, either on purely theoretical grounds or guided by new experimental information. The proposed interaction, SDPF-U, contains USD as its sd-shell part and KB3G as its pf-shell-part. Its range of applicability is enlarged and its reliability enhanced with respect to the earlier version.
Gradient Bundle Analysis: A Full Topological Approach to Chemical Bonding
Morgenstern, Amanda
2016-01-01
The "chemical bond" is a central concept in molecular sciences, but there is no consensus as to what a bond actually is. Therefore, a variety of bonding models have been developed, each defining the structure of molecules in a different manner with the goal of explaining and predicting chemical properties. This thesis describes the initial development of gradient bundle analysis (GBA), a chemical bonding model that creates a high resolution picture of chemical interactions within the charge density framework. GBA is based on concepts from the quantum theory of atoms in molecules (QTAIM), but uses a more complete picture of the topology and geometry of the electron charge density to understand and predict bonding interactions. Gradient bundles are defined as volumes bounded by zero-flux surfaces (ZFSs) in the gradient of the charge density with well-defined energies. The structure of gradient bundles provides an avenue for detecting the locations of valence electrons, which correspond to reactive regions in a ...
Numerical analysis of linear buckling of wind turbine blade with different trailing bonding models
Zhang, J. D.; Xu, Y.
2013-12-01
The work focus on the linear buckling analysis of wind turbine blade with different trailing bonding models. Based on finite element model, it has been demonstrated that there are some differences for buckling load factor between different models. Several different models are valid for buckling analysis.
Theoretical modeling of the catch-slip bond transition in biological adhesion
Gunnerson, Kim; Pereverzev, Yuriy; Prezhdo, Oleg
2006-05-01
The mechanism by which leukocytes leave the blood stream and enter inflamed tissue is called extravasation. This process is facilitated by the ability of selectin proteins, produced by the endothelial cells of blood vessels, to form transient bonds with the leukocytes. In the case of P-selectin, the protein bonds with P-selectin glycoprotein ligands (PSGL-1) produced by the leukocyte. Recent atomic force microscopy and flow chamber analyses of the binding of P-selectin to PSGL-1 provide evidence for an unusual biphasic catch-bond/slip-bond behavior in response to the strength of exerted force. This biphasic process is not well-understood. There are several theoretical models for describing this phenomenon. These models use different profiles for potential energy landscapes and how they change under forces. We are exploring these changes using molecular dynamics. We will present a simple theoretical model as well as share some of our early MD results for describing this phenomenon.
Teaching Molecular Geometry with the VSEPR Model
Gillespie, Ronald J.
2004-01-01
The first introduction to molecular geometry should be through the simple and easily understood VSEPR model, as the Valence Bond Theory and MO Theory suffer from limitations as far as understanding molecular geometry is concerned. The VSEPR model gives a perfectly satisfactory description of the bonding that follows directly from the Lewis model…
On the relation between hydrogen bonds, tetrahedral order and molecular mobility in model water
Pereyra, R G; Malaspina, D C; Carignano, M A
2013-01-01
We studied by molecular dynamics simulations the relation existing between the lifetime of hydrogen bonds, the tetrahedral order and the diffusion coefficient of model water. We tested four different models: SPC/E, TIP4P-Ew, TIP5P-Ew and Six-site, these last two having sites explicitly resembling the water lone pairs. While all the models perform reasonably well at ambient conditions, their behavior is significantly different for temperatures below 270 K. The models with explicit lone-pairs have a longer hydrogen bond lifetime, a better tetrahedral order and a smaller diffusion coefficient than the models without them.
Probing time-dependent mechanical behaviors of catch bonds based on two-state models
Xiaofeng Chen; Zhixiu Mao; Bin Chen
2015-01-01
With lifetime counter-intuitively being prolonged under forces, catch bonds can play critical roles in various sub-cellular processes. By adopting different “catching” strategies within the framework of two-state models, we construct two types of catch bonds that have a similar force-lifetime profile upon a constant force-clamp load. However, when a single catch bond of either type is subjected to varied forces, we find that they can behave very differently in both force history dependence an...
Determinants of the Government Bond Yield in Spain: A Loanable Funds Model
Directory of Open Access Journals (Sweden)
Yu Hsing
2015-07-01
Full Text Available This paper applies demand and supply analysis to examine the government bond yield in Spain. The sample ranges from 1999.Q1 to 2014.Q2. The EGARCH model is employed in empirical work. The Spanish government bond yield is positively associated with the government debt/GDP ratio, the short-term Treasury bill rate, the expected inflation rate, the U.S. 10 year government bond yield and a dummy variable representing the debt crisis and negatively affected by the GDP growth rate and the expected nominal effective exchange rate.
Modeling of Covalent Bonding in Solids by Inversion of Cohesive Energy Curves
Bazant, M Z; Bazant, Martin Z.; Kaxiras, Efthimios
1996-01-01
We provide a systematic test of empirical theories of covalent bonding in solids using an exact procedure to invert ab initio cohesive energy curves. By considering multiple structures of the same material, it is possible for the first time to test competing angular functions, expose inconsistencies in the basic assumption of a cluster expansion, and extract general features of covalent bonding. We test our methods on silicon, and provide the direct evidence that the Tersoff-type bond order formalism correctly describes coordination dependence. For bond-bending forces, we obtain skewed angular functions that favor small angles, unlike existing models. As a proof-of-principle demonstration, we derive a Si interatomic potential which exhibits comparable accuracy to existing models.
A diabatic state model for double proton transfer in hydrogen bonded complexes
McKenzie, Ross H
2014-01-01
Four diabatic states are used to construct a simple model for double proton transfer in hydrogen bonded complexes. Key parameters in the model are the proton donor-acceptor separation R and the ratio, D_1/D_2, between the proton affinity of a donor with one and two protons. Depending on the values of these two parameters the model describes four qualitatively different ground state potential energy surfaces, having zero, one, two, or four saddle points. In the limit D_2=D_1 the model reduces to two decoupled hydrogen bonds. As R decreases a transition can occur from a concerted to a sequential mechanism for double proton transfer.
A multiscale approach to model hydrogen bonding: The case of polyamide
Energy Technology Data Exchange (ETDEWEB)
Gowers, Richard J., E-mail: richard.gowers@manchester.ac.uk; Carbone, Paola, E-mail: paola.carbone@manchester.ac.uk [School of Chemical Engineering and Analytical Science, University of Manchester, Manchester M13 9PL (United Kingdom)
2015-06-14
We present a simple multiscale model for polymer chains in which it is possible to selectively remove degrees of freedom. The model integrates all-atom and coarse-grained potentials in a simple and systematic way and allows a fast sampling of the complex conformational energy surface typical of polymers whilst maintaining a realistic description of selected atomistic interactions. In particular, we show that it is possible to simultaneously reproduce the structure of highly directional non-bonded interactions such as hydrogen bonds and efficiently explore the large number of conformations accessible to the polymer chain. We apply the method to a melt of polyamide removing from the model only the degrees of freedom associated to the aliphatic segments and keeping at atomistic resolution the amide groups involved in the formation of the hydrogen bonds. The results show that the multiscale model produces structural properties that are comparable with the fully atomistic model despite being five times faster to simulate.
Valence neutron capture in 54Fe
International Nuclear Information System (INIS)
The neutron capture cross section of 54Fe has been measured with 0.2 per cent energy resolution from 2.5 to 500 keV. A large and significant correlation is observed between the s-wave reduced neutron widths and the corresponding total radiative widths. The valence model readily accounts for this correlation as well as a large fraction of the s-wave radiative widths. (author)
Bonding Energy and Growth Habit of Lithium Niobate Single Crystals
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
On the basis of crystallographic structure of lithium niobate (LN), the bonding energy was quantitatively calculated by the bond valence sum model, which was employed to investigate the crystal growth. A possible relationship between the crystal growth habit and chemical bonding energy of LN crystals are found. It is found that the higher the bond energy, the slower the growth rate, and the more important the plane. The analytical results indicate that (012) plane is the most influential face for the LN crystal growth, which consists well with the standard card (JCPDS Card: 20-0631) and our previous experimental observation. The current work shows that the chemical bond analysis of LN crystals allows us to predict its growth habit and thus to obtain the expected morphology during the spontaneous growth.
Valence fluctuations between two magnetic configurations
International Nuclear Information System (INIS)
The subject of this work is the study of a microscopic model which describes TmSe through its most important feature, i.e.: the valence fluctuations between two magnetic configurations. Chapter I is a general review of the most important physical properties of rare-earth systems with intermediate valence (I.V.) and a general description of experimental results and theoretical models on Tm compounds. In Chapter II the Hamiltonian model is discussed and the loss of rotational invariance is also analyzed. Chapter III is devoted to the study of non-stoichiometric Tsub(x)Se compounds. It is shown that these compounds can be considered as a mixture of TmSe (I.V. system) and Tm3+0.87Se. Chapter IV is devoted to the calculation of spin-and charge susceptibilities. The results obtained permit to explain the essential features of the neutron scattering spectrum in TmSe. In Chapter V, an exactly solvable periodic Hamiltonian is presented. From the experimental results, some fundamental features are deduced to describe TmSe as an intermediate valence system whose two accessible ionic configurations are magnetic (degenerated fundamental state). (M.E.L)
A Multidimensional Measure of Work Valences
Porfeli, Erik J.; Lee, Bora; Weigold, Ingrid K.
2012-01-01
Work valence is derived from expectancy-valence theory and the literature on children's vocational development and is presumed to be a general appraisal of work that emerges during the childhood period. Work valence serves to promote and inhibit the motivation and tasks associated with vocational development. A measure of work valence, composed of…
Bond graph modeling and validation of an energy regenerative system for emulsion pump tests.
Li, Yilei; Zhu, Zhencai; Chen, Guoan
2014-01-01
The test system for emulsion pump is facing serious challenges due to its huge energy consumption and waste nowadays. To settle this energy issue, a novel energy regenerative system (ERS) for emulsion pump tests is briefly introduced at first. Modeling such an ERS of multienergy domains needs a unified and systematic approach. Bond graph modeling is well suited for this task. The bond graph model of this ERS is developed by first considering the separate components before assembling them together and so is the state-space equation. Both numerical simulation and experiments are carried out to validate the bond graph model of this ERS. Moreover the simulation and experiments results show that this ERS not only satisfies the test requirements, but also could save at least 25% of energy consumption as compared to the original test system, demonstrating that it is a promising method of energy regeneration for emulsion pump tests. PMID:24967428
Bond Graph Modeling and Validation of an Energy Regenerative System for Emulsion Pump Tests
Directory of Open Access Journals (Sweden)
Yilei Li
2014-01-01
Full Text Available The test system for emulsion pump is facing serious challenges due to its huge energy consumption and waste nowadays. To settle this energy issue, a novel energy regenerative system (ERS for emulsion pump tests is briefly introduced at first. Modeling such an ERS of multienergy domains needs a unified and systematic approach. Bond graph modeling is well suited for this task. The bond graph model of this ERS is developed by first considering the separate components before assembling them together and so is the state-space equation. Both numerical simulation and experiments are carried out to validate the bond graph model of this ERS. Moreover the simulation and experiments results show that this ERS not only satisfies the test requirements, but also could save at least 25% of energy consumption as compared to the original test system, demonstrating that it is a promising method of energy regeneration for emulsion pump tests.
Universality aspects of the d=3 random-bond Blume-Capel model
Malakis, A.; Berker, A. Nihat; Fytas, N. G.; Papakonstantinou, T.
2012-01-01
The effects of bond randomness on the universality aspects of the simple cubic lattice ferromagnetic Blume-Capel model are discussed. The system is studied numerically in both its first- and second-order phase transition regimes by a comprehensive finite-size scaling analysis. We find that our data for the second-order phase transition, emerging under random bonds from the second-order regime of the pure model, are compatible with the universality class of the 3d random Ising model. Furthermo...
Lattice Dynamics of II-VI materials using adiabatic bond charge model
Rajput, B. D.; Browne, D. A.
1995-01-01
We extend the adiabatic bond charge model, originally developed for group IV semiconductors and III-V compounds, to study phonons in more ionic II-VI compounds with a zincblende structure. Phonon spectra, density of states and specific heats are calculated for six II-VI compounds and compared with both experimental data and the results of other models. We show that the 6-parameter bond charge model gives a good description of the lattice dynamics of these materials. We also discuss trends in ...
Cohesive zone modelling of wafer bonding and fracture: effect of patterning and toughness variations
International Nuclear Information System (INIS)
Direct wafer bonding has increasingly become popular in the manufacture of microelectromechanical systems and semiconductor microelectronics components. The success of the bonding process is controlled by variables such as wafer flatness and surface preparation. In order to understand the effects of these variables, spontaneous planar crack propagation simulations were performed using the spectral scheme in conjunction with a cohesive zone model. The fracture-toughness on the bond interface is varied to simulate the effect of surface roughness (nanotopography) and patterning. Our analysis indicated that the energetics of crack propagation is sensitive to the local surface property variations. The patterned wafers are tougher (well bonded) than the unpatterned ones of the same average fracture-toughness
Janus Nematic Colloids with Designable Valence
Directory of Open Access Journals (Sweden)
Simon Čopar
2014-05-01
Full Text Available Generalized Janus nematic colloids based on various morphologies of particle surface patches imposing homeotropic and planar surface anchoring are demonstrated. By using mesoscopic numerical modeling, multiple types of Janus particles are explored, demonstrating a variety of novel complex colloidal structures. We also show binding of Janus particles to a fixed Janus post in the nematic cell, which acts as a seed and a micro-anchor for the colloidal structure. Janus colloidal structures reveal diverse topological defect configurations, which are effectively combinations of surface boojum and bulk defects. Topological analysis is applied to defects, importantly showing that topological charge is not a well determined topological invariant in such patchy nematic Janus colloids. Finally, this work demonstrates colloidal structures with designable valence, which could allow for targeted and valence-conditioned self-assembly at micro- and nano-scale.
Gulkowska, Anna; Krauss, Martin; Rentsch, Daniel; Hollender, Juliane
2012-02-21
The mechanism of covalent bond formation of the model sulfonamide sulfathiazole (STZ) and the stronger nucleophile para-ethoxyaniline was studied in reactions with model humic acid constituents (quinones and other carbonyl compounds) in the absence and presence of laccase. As revealed by high resolution mass spectrometry, the initial bonding of STZ occurred by 1,2- and 1,4-nucleophilic additions of the aromatic amino group to quinones resulting in imine and anilinoquinone formation, respectively. Experiments using the radical scavenger tert-butyl-alcohol provided the same products and similar formation rates as those without scavenger indicating that probably not radical coupling reactions were responsible for the initial covalent bond formation. No addition with nonquinone carbonyl compounds occurred within 76 days except for a slow 1,4-addition to the β-unsaturated carbonyl 1-penten-3-one. The stability of covalent bonds against desorption and pressurized liquid extraction (PLE) was assessed. The recovery rates showed no systematic differences in STZ extractability between the two product types. This suggests that the strength of bonding is not controlled by the initial type of bond, but by the extent of subsequent incorporation of the reaction product into the formed polymer. This incorporation was monitored for (15)N aniline by (1)H-(15)N HMBC NMR spectroscopy. The initial 1,2- and 1,4-addition bonds were replaced by stronger heterocyclic forms with increasing incubation time. These processes could also hold true for soils, and a slow nonextractable residue formation with time could be related to a slow increase of the amount of covalently bound sulfonamide and the strength of bonding. PMID:22260423
Patton, Sarah C.; Beaujean, A. Alexander; Benedict, Helen E.
2014-01-01
The developmental trajectory of body image dissatisfaction is unclear. Researchers have investigated sociocultural and developmental risk factors; however, the literature needs an integrative etiological model. In 2009, Cheng and Mallinckrodt proposed a dual mediation model, positing that poor-quality parental bonds, via the mechanisms of…
Pseudo-Bond Graph model for the analysis of the thermal behavior of buildings
Directory of Open Access Journals (Sweden)
Merabtine Abdelatif
2013-01-01
Full Text Available In this work, a simplified graphical modeling tool, which in some extent can be considered in halfway between detailed physical and Data driven dynamic models, has been developed. This model is based on Bond Graphs approach. This approach has the potential to display explicitly the nature of power in a building system, such as a phenomenon of storage, processing and dissipating energy such as Heating, Ventilation and Air-Conditioning (HVAC systems. This paper represents the developed models of the two transient heat conduction problems corresponding to the most practical cases in building envelope, such as the heat transfer through vertical walls, roofs and slabs. The validation procedure consists of comparing the results obtained with this model with analytical solution. It has shown very good agreement between measured data and Bond Graphs model simulation. The Bond Graphs technique is then used to model the building dynamic thermal behavior over a single zone building structure and compared with a set of experimental data. An evaluation of indoor temperature was carried out in order to check our Bond Graphs model.
DNA Self-Assembly and Computation Studied with a Coarse-grained Dynamic Bonded Model
DEFF Research Database (Denmark)
Svaneborg, Carsten; Fellermann, Harold; Rasmussen, Steen
2012-01-01
We utilize a coarse-grained directional dynamic bonding DNA model [C. Svaneborg, Comp. Phys. Comm. (In Press DOI:10.1016/j.cpc.2012.03.005)] to study DNA self-assembly and DNA computation. In our DNA model, a single nucleotide is represented by a single interaction site, and complementary sites can...
Learners' Mental Models of Metallic Bonding: A Cross-Age Study
Coll, Richard K.; Treagust, David F.
2003-01-01
Mental models of metallic bonding held by learners from three academic levels, secondary school (year 12), undergraduate, and postgraduate, were probed using semistructured interviews including the use of Interviews-About-Events focus cards depicting metallic properties and cards containing depictions of models from curriculum material. The…
Luxford, Cynthia J.; Bretz, Stacey Lowery
2013-01-01
Chemistry students encounter a variety of terms, definitions, and classification schemes that many instructors expect students to memorize and be able to use. This research investigated students' descriptions of ionic and covalent bonding beyond definitions in order to explore students' knowledge about chemical bonding. Using Johnstone's Multiple…
Thermal-hydraulic modeling and analysis of hydraulic system by pseudo-bond graph
Institute of Scientific and Technical Information of China (English)
胡均平; 李科军
2015-01-01
To increase the efficiency and reliability of the thermodynamics analysis of the hydraulic system, the method based on pseudo-bond graph is introduced. According to the working mechanism of hydraulic components, they can be separated into two categories: capacitive components and resistive components. Then, the thermal-hydraulic pseudo-bond graphs of capacitive C element and resistance R element were developed, based on the conservation of mass and energy. Subsequently, the connection rule for the pseudo-bond graph elements and the method to construct the complete thermal-hydraulic system model were proposed. On the basis of heat transfer analysis of a typical hydraulic circuit containing a piston pump, the lumped parameter mathematical model of the system was given. The good agreement between the simulation results and experimental data demonstrates the validity of the modeling method.
Bond slip model in cylindrical reinforced concrete elements confined with stirrups
Coccia, Simona; Di Maggio, Erica; Rinaldi, Zila
2015-12-01
An analytical model able to evaluate the bond-slip law of confined reinforced concrete elements is developed and presented in this paper. The model is based on the studies developed by Tepfers and by den Uijl and Bigaj on the thick-walled cylinder model and extended to the case of the presence of transverse reinforcement. The bond strength and the considered failure modes (splitting or pull-out failure) are expressed as a function of the geometrical (concrete cover and transverse reinforcement) and mechanical (concrete strength) parameters of the element. The application of the proposed methodology allows to forecast the failure mode, and equations for the bond-slip law are finally proposed for a range of steel strain lower than the yielding one.
Modeling, Control and Analyze of Multi-Machine Drive Systems using Bond Graph Technique
Directory of Open Access Journals (Sweden)
J. Belhadj
2006-03-01
Full Text Available In this paper, a system viewpoint method has been investigated to study and analyze complex systems using Bond Graph technique. These systems are multimachine multi-inverter based on Induction Machine (IM, well used in industries like rolling mills, textile, and railway traction. These systems are multi-domains, multi-scales time and present very strong internal and external couplings, with non-linearity characterized by a high model order. The classical study with analytic model is difficult to manipulate and it is limited to some performances. In this study, a “systemic approach” is presented to design these kinds of systems, using an energetic representation based on Bond Graph formalism. Three types of multimachine are studied with their control strategies. The modeling is carried out by Bond Graph and results are discussed to show the performances of this methodology
International Nuclear Information System (INIS)
Several samples of the solid solutions CeRu1-xPdxSn and CeRh1-xPdxSn have been synthesized by arc-melting and characterized by X-ray powder diffraction. Guinier powder patterns prove that the ZrNiAl-type structure is the dominating one, besides the CeRuSn and TiNiSi type structures. The structures of CeRu0.28Pd0.72Sn (ZrNiAl type, P anti 62m, a = 751.95(3), c = 418.70(2) pm, wR2 = 0.0274, 332 F2 values, 14 variables) and CeRh0.66Pd0.34Sn (ZrNiAl type, P anti 62m, a = 750.26(3), c = 411.59(2) pm, wR2 = 0.0533, 358 F2 values, 14 variables) were refined from single crystal diffractometer data. Magnetic measurements in combination with XANES (X-Ray Absorption Near Edge Structure) clearly proved intermediate cerium valencies for most compounds and revealed the best fitting parameters for those with the ICF model (Interconfiguration fluctuation). The electrical resistivity is also influenced by the substitutions. At low and high valence electron counts (VECs) metallic character is present, while around the VEC of CeRhSn the typical resistivity behavior for valence fluctuating compounds is observed.
Arbitrage-free models of stocks and bonds
Durham, J. Benson
2013-01-01
A small but ambitious literature uses affine arbitrage-free models to estimate jointly U.S. Treasury term premiums and the term structure of equity risk premiums. Within this approach, this paper identifies the parameter restrictions that are consistent with a simple dividend discount model, extends the cross-section to Germany and France, averages across multiple observable-factor and market prices of risk specifications, and considers alternative samples for parameter estimation. The result...
A New Material Model for 2D FE Analysis of Adhesively Bonded Composite Joints
Zhao, Libin; Wang, Yana; TianLiang QIN; Zhang, Jianyu
2014-01-01
Effective and convenient stress analysis techniques play important roles in the analysis and design of adhesively bonded composite joints. A new material model is presented at the level of composite ply according to the orthotropic elastic mechanics theory and plane strain assumption. The model proposed has the potential to reserve nature properties of laminates with ply-to-ply modeling. The equivalent engineering constants in the model are obtained only by the material properties of unidirec...
Model building of disulfide bonds in proteins with known three-dimensional structure.
Hazes, B; Dijkstra, B W
1988-07-01
As an aid in the selection of sites in a protein where a disulfide bond might be engineered, a computer program has been developed. The algorithm starts with the generation of C beta positions from the N, C alpha and C atom coordinates available from a three-dimensional model. A first set of residue pairs that might form a disulfide bond is selected on the basis of C beta-C beta distances between residues. Then, for each residue in this set, S gamma positions are generated, which satisfy the requirement that, with ideal values for the C alpha-C beta and C beta-S gamma bond lengths and for the bond angle at C beta, the distance between S gamma of residue 1 and C beta of residue 2 in a pair (determined by the bond angle at S gamma 2) is at, or very close to its ideal value. Usually two acceptable S gamma positions are found for each half cystine, resulting in up to four different conformations for the disulfide bond. Finally, these conformations are subjected to an energy minimization procedure to remove large deviations from ideal geometry and their final energies are calculated. User input determines which final conformations are energetically acceptable. These conformations are written to a file to allow further analysis and e.g. inspection on a computer graphics device. PMID:3244694
Virtual multi-dimensional internal bonds model and its application in simulation of rock mass
Institute of Scientific and Technical Information of China (English)
2008-01-01
VMIB (virtual multi-dimensional internal bonds) is a multiscale mechanical model developed from the VIB (virtual internal bond) theory. In VIB theory,the solid mate-rial is considered to consist of random-distributed material particles in microscale. These particles are connected with normal bonds. The macro constitutive relation is derived from the cohesive law between particles. However,in VMIB,the micro particles are connected with both normal and shear bonds. The macro constitutive relation is derived in terms of bond stiffness coefficients. It has been theoretically certified that there exists a corresponding relationship between the two bond stiffness coefficients and the two macro material constants,i.e. the Young’s modulus and Poisson ratio. This corresponding relationship suggests that it should be necessary and sufficient to simultaneously account for the normal and shear interactions between particles. Due to the fact that the fracture criterion is directly incorporated into the constitutive relation,both VIB and VMIB present many advantages in simulating fractures of materials. In the damage model of rock mass,a damage tensor is usually defined to describe the distribution of cracks. The damage value in one direction determines the relative stiffness of rock mass in this direction. In VMIB solid,the relative distribution density of micro bonds in one direction determines the relative macro stiffness of the material in this direction. The effects of the damage value and the relative distribution density of bonds are consistent. To simulate the failure behavior of rock mass with VMIB,the presented paper sets up a quantitative relationship between the damage tensor and the rela-tive distribution density of bonds. Comparison of the theoretical and the experi-mental results shows that VMIB model can represent the effect of distributed cracks on rock mass with this relationship. The presented work provides a founda-tion for further simulating fracture
Poudel, Lokendra; Rulis, Paul; Liang, Lei; Ching, W. Y.
2014-08-01
We present a theoretical study of the electronic structure of four periodic B-DNA models labeled (AT)10,(GC)10, (AT)5(GC)5, and (AT-GC)5 where A denotes adenine, T denotes thymine, G denotes guanine, and C denotes cytosine. Each model has ten base pairs with Na counterions to neutralize the negative phosphate group in the backbone. The (AT)5(GC)5 and (AT-GC)5 models contain two and five AT-GC bilayers, respectively. When compared against the average of the two pure models, we estimate the AT-GC bilayer interaction energy to be 19.015 Kcal/mol, which is comparable to the hydrogen bonding energy between base pairs obtained from the literature. Our investigation shows that the stacking of base pairs plays a vital role in the electronic structure, relative stability, bonding, and distribution of partial charges in the DNA models. All four models show a highest occupied molecular orbital (HOMO) to lowest unoccupied molecular orbital (LUMO) gap ranging from 2.14 to 3.12 eV with HOMO states residing on the PO4 + Na functional group and LUMO states originating from the bases. Our calculation implies that the electrical conductance of a DNA molecule should increase with increased base-pair mixing. Interatomic bonding effects in these models are investigated in detail by analyzing the distributions of the calculated bond order values for every pair of atoms in the four models including hydrogen bonding. The counterions significantly affect the gap width, the conductivity, and the distribution of partial charge on the DNA backbone. We also evaluate quantitatively the surface partial charge density on each functional group of the DNA models.
Forming Beliefs: Why Valence Matters.
Sharot, Tali; Garrett, Neil
2016-01-01
One of the most salient attributes of information is valence: whether a piece of news is good or bad. Contrary to classic learning theories, which implicitly assume beliefs are adjusted similarly regardless of valence, we review evidence suggesting that different rules and mechanisms underlie learning from desirable and undesirable information. For self-relevant beliefs this asymmetry generates a positive bias, with significant implications for individuals and society. We discuss the boundaries of this asymmetry, characterize the neural system supporting it, and describe how changes in this circuit are related to individual differences in behavior. PMID:26704856
A Unified Bond Graph Modeling Approach for the Ejection Phase of the Cardiovascular System
Directory of Open Access Journals (Sweden)
LUBNA MOIN
2016-07-01
Full Text Available In this paper the unified Bond Graph model of the left ventricle ejection phase is presented, simulated and validated. The integro-differential and ordinary differential equations obtained from the bond graph models are simulated using ODE45 (Ordinary Differential Equation Solver on MATLAB and Simulink. The results, thus, obtained are compared with CVS (Cardiovascular System physiological data present in Simbiosys (a software for simulating biological systems and also with the CVS Wiggers diagram of heart cycle. As the cardiac activity is a multi domain process that includes mechanical, hydraulic, chemical and electrical events; therefore, for modeling such systems a unified modeling approach is needed. In this paper the unified Bond Graph model of the left ventricle ejection phase is proposed. The Bond Graph conventionalism approach is a graphical method principally powerful to portray multi-energy systems, as it is formulated on the portrayal of power exchanges. The model takes into account a simplified description of the left ventricle which is close to the medical investigation promoting the apperception and the dialogue between engineers and physiologists.
Shahid Ali; Vali Uddin; Lubna Moin
2009-01-01
This research paper basically explores and compares the different modeling and analysis techniques and than it also explores the model order reduction approach and significance. The traditional modeling and simulation techniques for dynamic systems are generally adequate for single-domain systems only, but the Bond Graph technique provides new strategies for reliable solutions of multi-domain system. They are also used for analyzing linear and non linear dynamic production system, artificial ...
A steel-concrete bond model for the simulation of industrial structures
International Nuclear Information System (INIS)
Reinforced concrete structures may have to fulfill functions that go beyond their simple mechanical resistance. During the cracking process, stresses are progressively transferred from steel to concrete through the steel-concrete interface. This stress transfer has a direct impact on the crack properties. Taking into account these effects seems thus essential to predict correctly the cracking of reinforced concrete structures. Different models exist to represent the steel-concrete bond behavior. However, these models are rarely compatible with large scale simulations (meshing difficulties, heavy computational cost..). To overcome these difficulties, a perfect relation between steel and concrete (same displacements) is generally considered for structural applications. In this contribution, a new finite element approach is proposed to represent the steel-concrete bond effects in a context adapted for large scale simulations. This thesis is divided in three parts: - the development of a finite element steel-concrete bond model adapted for large scale structural applications. This model takes into account mechanical interactions between concrete and steel reinforcement represented by truss elements. - the characterization of the steel-concrete bond behavior. A model for the bond stress-slip law based on experimental observations (experimental campaign on pull-out test carried out during the thesis and data of literature) is proposed. This model differentiates the case of a pull-out failure and of splitting failure and takes into account the material properties and the geometric characteristics of the structure. - an application of the proposed model on a structural element (beam). A four point bending beam is experimentally tested. This test aims to characterize the crack evolution (in particular the crack opening using the image correlation technique). Experimental results are then compared with numerical simulations taking into account the bond-slip effect between
Measurement and modelling of hydrogen bonding in 1-alkanol plus n-alkane binary mixtures
DEFF Research Database (Denmark)
von Solms, Nicolas; Jensen, Lars; Kofod, Jonas L.; Michelsen, Michael Locht; Kontogeorgis, Georgios
Two equations of state (simplified PC-SAFT and CPA) are used to predict the monomer fraction of 1-alkanols in binary mixtures with n-alkanes. It is found that the choice of parameters and association schemes significantly affects the ability of a model to predict hydrogen bonding in mixtures, eve...
Energy Technology Data Exchange (ETDEWEB)
Kuiken, Benjamin E. Van; Valiev, Marat; Daifuku, Stephanie L.; Bannan, Caitlin; Strader, Matthew L.; Cho, Hana; Huse, Nils; Schoenlein, Robert W.; Govind, Niranjan; Khalil, Munira
2013-04-26
Ruthenium L3-edge X-ray absorption (XA) spectroscopy probes unoccupied 4d orbitals of the metal atom and is increasingly being used to investigate the local electronic structure in ground and excited electronic states of Ru complexes. The simultaneous development of computational tools for simulating Ru L3-edge spectra is crucial for interpreting the spectral features at a molecular level. This study demonstrates that time-dependent density functional theory (TDDFT) is a viable and predictive tool for simulating ruthenium L3-edge XA spectroscopy. We systematically investigate the effects of exchange correlation functional and implicit and explicit solvent interactions on a series of RuII and RuIII complexes in their ground and electronic excited states. The TDDFT simulations reproduce all of the experimentally observed features in Ru L3-edge XA spectra within the experimental resolution (0.4 eV). Our simulations identify ligand-specific charge transfer features in complicated Ru L3-edge spectra of [Ru(CN)6]4- and RuII polypyridyl complexes illustrating the advantage of using TDDFT in complex systems. We conclude that the B3LYP functional most accurately predicts the transition energies of charge transfer features in these systems. We use our TDDFT approach to simulate experimental Ru L3-edge XA spectra of transition metal mixed-valence dimers of the form [(NC)5MII-CN-RuIII(NH3)5] (where M = Fe or Ru) dissolved in water. Our study determines the spectral signatures of electron delocalization in Ru L3-edge XA spectra. We find that the inclusion of explicit solvent molecules is necessary for reproducing the spectral features and the experimentally determined valencies in these mixed-valence complexes. This study validates the use of TDDFT for simulating Ru 2p excitations using popular quantum chemistry codes and providing a powerful interpretive tool for equilibrium and ultrafast Ru L3-edge XA spectroscopy.
Binomial Tree Model for Convertible Bond Pricing within Equity to Credit Risk Framework
K. Milanov; Kounchev, O.
2012-01-01
In the present paper we fill an essential gap in the Convertible Bonds pricing world by deriving a Binary Tree based model for valuation subject to credit risk. This model belongs to the framework known as Equity to Credit Risk. We show that this model converges in continuous time to the model developed by Ayache, Forsyth and Vetzal [2003]. To this end, both forms of credit risk modeling, the so-called reduced (constant intensity of default model for the underlying) and the so-called synthesi...
A broken-bond model for grain boundaries in face-centered cubic metals
Energy Technology Data Exchange (ETDEWEB)
Wolf, D. (Materials Science Division, Argonne National Laboratory, Argonne, IL (USA))
1990-10-01
The interrelation between the number of nearest-neighbor atomic bonds broken upon formation of a grain boundary in an fcc metal and the related zero-temperature boundary energy is investigated by atomistic simulation. Using both a Lennard--Jones and an embedded-atom-method potential, the structures and energies of symmetrical and asymmetrical tilt and twist boundaries are determined. As in free surfaces, a practically linear relationship between the nearest-neighbor miscoordination per unit area of the grain boundary and the related interface energy is obtained. The so-called random-boundary model, in which the interactions across the interface are assumed to be entirely randomized, is shown to provide a basis for understanding the role of broken bonds in both high-angle grain boundaries and free surfaces, thus naturally permitting the analysis of ideal cleavage-fracture energies. A detailed study of low-angle boundaries shows that only the dislocation cores---but not their strain fields---give rise to broken bonds. The complementarity between the dislocation model of Read and Shockley for low-angle boundaries and a broken-bond model for high-angle boundaries is thus elucidated.
Czech Academy of Sciences Publication Activity Database
Zalesny, R.; Bartkowiak, W.; Toman, Petr; Leszczynski, J.
2007-01-01
Roč. 337, 1-3 (2007), s. 77-80. ISSN 0301-0104 Grant ostatní: Polish Committee for Scientific Research and the Ministry of Education , Youth, and Sports of the Czech Republic(PL) CZ25 Institutional research plan: CEZ:AV0Z40500505 Keywords : polarizability * first hyperpolarizability * second hyperpolarizability * nonlinear optical properties Subject RIV: CD - Macromolecular Chemistry Impact factor: 1.805, year: 2007
International Nuclear Information System (INIS)
A new stress resultant constitutive model for reinforced concrete plates under cyclic solicitations is presented. This model is built by the periodic homogenisation approach using the averaging method and couples damage of concrete and periodic de-bonding between concrete and steel rebar. In one-dimensional situations, we derive a closed-form solution of the local problem useful to verify and set up the plate problem. The one dimensional macroscopic constitutive model involves a limited number of parameters, the sensibility of which is studied. Comparison to experimental results underlines the pertinence of the model by considering internal de-bonding in order to properly represent the mechanical dissipation occurring during cyclic loadings on reinforced concrete panels. (authors)
Herman, Agnieszka
2016-04-01
This paper presents theoretical foundations, numerical implementation and examples of application of the two-dimensional Discrete-Element bonded-particle Sea Ice model - DESIgn. In the model, sea ice is represented as an assemblage of objects of two types: disk-shaped "grains" and semi-elastic bonds connecting them. Grains move on the sea surface under the influence of forces from the atmosphere and the ocean, as well as interactions with surrounding grains through direct contact (Hertzian contact mechanics) and/or through bonds. The model has an experimental option of taking into account quasi-three-dimensional effects related to the space- and time-varying curvature of the sea surface, thus enabling simulation of ice breaking due to stresses resulting from bending moments associated with surface waves. Examples of the model's application to simple sea ice deformation and breaking problems are presented, with an analysis of the influence of the basic model parameters ("microscopic" properties of grains and bonds) on the large-scale response of the modeled material. The model is written as a toolbox suitable for usage with the open-source numerical library LIGGGHTS. The code, together with full technical documentation and example input files, is freely available with this paper and on the Internet.
Directory of Open Access Journals (Sweden)
A. Herman
2015-07-01
Full Text Available This paper presents theoretical foundations, numerical implementation and examples of application of a two-dimensional Discrete-Element bonded-particle Sea Ice model DESIgn. In the model, sea ice is represented as an assemblage of objects of two types: disk-shaped "grains", and semi-elastic bonds connecting them. Grains move on the sea surface under the influence of forces from the atmosphere and the ocean, as well as interactions with surrounding grains through a direct contact (Hertzian contact mechanics and/or through bonds. The model has an option of taking into account quasi-threedimensional effects related to space- and time-varying curvature of the sea surface, thus enabling simulation of ice breaking due to stresses resulting from bending moments associated with surface waves. Examples of the model's application to simple sea ice deformation and breaking problems are presented, with an analysis of the influence of the basic model parameters ("microscopic" properties of grains and bonds on the large-scale response of the modeled material. The model is written as a toolbox suitable for usage with the open-source numerical library LIGGGHTS. The code, together with a full technical documentation and example input files, is freely available with this paper and on the Internet.
International Nuclear Information System (INIS)
We present a general perturbative method for correcting a singles and doubles coupled-cluster energy. The coupled-cluster wave function is used to define a similarity-transformed Hamiltonian, which is partitioned into a zeroth-order part that the reference problem solves exactly plus a first-order perturbation. Standard perturbation theory through second-order provides the leading correction. Applied to the valence optimized doubles (VOD) approximation to the full-valence complete active space self-consistent field method, the second-order correction, which we call (2), captures dynamical correlation effects through external single, double, and semi-internal triple and quadruple substitutions. A factorization approximation reduces the cost of the quadruple substitutions to only sixth order in the size of the molecule. A series of numerical tests are presented showing that VOD(2) is stable and well-behaved provided that the VOD reference is also stable. The second-order correction is also general to standard unwindowed coupled-cluster energies such as the coupled-cluster singles and doubles (CCSD) method itself, and the equations presented here fully define the corresponding CCSD(2) energy. (c) 2000 American Institute of Physics
Kajikawa, Y.
2014-05-01
Experimental data on the thermoelectric properties of p-type CoSb3 reported by Caillat et al. [J. Appl. Phys. 80, 4442 (1996)] have been analyzed, assuming not only a pair of the first valence (v1) and the first conduction (c1) bands but also the second valence (v2) and the second conduction (c2) bands. By taking into account the excitation of carriers into the v2 and the c2 bands, the behavior of the Hall coefficient as well as that of the Seebeck coefficient at high temperatures is well explained. By taking into account the nonparabolicity of the v1 band, the temperature dependence of mobility is well explained with assuming scattering due to acoustic phonons, nonpolar and polar optical phonons, and ionized impurities. Furthermore, various material parameters of CoSb3, such as the band-gap energy, effective masses, and deformation potentials, have been deduced from fitting the calculation to the experimental data on the temperature dependences of the Hall coefficient, the mobility, and the Seebeck coefficient. Among them, the band-gap energy and the effective mass of the v1 band have been corrected from the original values estimated by Caillat et al. In addition, it is shown that the experimental data on the hole-concentration dependences of both the room-temperature Seebeck coefficient and the cyclotron mass are well reproduced by the theoretical calculation using the deduced values for the nonparabolic v1 band.
Guoan Huang; Guohe Deng; Lihong Huang
2009-01-01
The valuation for an American continuous-installment put option on zero-coupon bond is considered by Kim's equations under a single factor model of the short-term interest rate, which follows the famous Vasicek model. In term of the price of this option, integral representations of both the optimal stopping and exercise boundaries are derived. A numerical method is used to approximate the optimal stopping and exercise boundaries by quadrature formulas. Numerical results and discussions are pr...
Nishimori point in random-bond Ising and Potts models in 2D
A. Honecker; Jacobsen, J. L.; Picco, M.; Pujol, P.
2001-01-01
We study the universality class of the fixed points of the 2D random bond q-state Potts model by means of numerical transfer matrix methods. In particular, we determine the critical exponents associated with the fixed point on the Nishimori line. Precise measurements show that the universality class of this fixed point is inconsistent with percolation on Potts clusters for q=2, corresponding to the Ising model, and q=3
Canonical term-structure models with observable factors and the dynamics of bond risk premiums
Marcello Pericoli; Marco Taboga
2006-01-01
We study the dynamics of risk premiums on the German bond market, employing no-arbitrage term-structure models with both observable and unobservable state variables, recently popularized by Ang and Piazzesi (2003). We conduct a specification analisys based on a new canonical representation for this class of models. We find that risk premiums display a considerable variability over time, are strongly counter-cyclical and bear no significant relation to inflation.
A non-perturbative approach to the random-bond Ising model
International Nuclear Information System (INIS)
We study the N → 0 limit of the O(N) Gross-Neveu model in the framework of the massless form-factor approach. This model is related to the continuum limit of the Ising model with random bonds via the replica method. We discuss how this method may be useful in calculating correlation functions of physical operators. The identification of non-perturbative fixed points of the O(N) Gross-Neveu model is pursued by its mapping to a WZW model. (author). 30 refs, 1 fig
A Non-Perturbative Approach to the Random-Bond Ising Model
Cabra, D C; Mussardo, G; Pujol, P
1997-01-01
We study the N -> 0 limit of the O(N) Gross-Neveu model in the framework of the massless form-factor approach. This model is related to the continuum limit of the Ising model with random bonds via the replica method. We discuss how this method may be useful in calculating correlation functions of physical operators. The identification of non-perturbative fixed points of the O(N) Gross-Neveu model is pursued by its mapping to a WZW model.
Reply to Isgur's comments on valence QCD
International Nuclear Information System (INIS)
With the goal of understanding the complexity of QCD and the role of symmetry in dynamics, the authors studied a field theory called Valence QCD (VQCD) in which the Z graphs are forbidden so that the Fock space is limited to the valence quarks. The authors calculated nucleon form factors, matrix elements, and hadron masses both with this theory and with quenched QCD on a set of lattices with the same gauge background. Comparing the results of the lattice calculations in these two theories, the authors drew conclusions regarding the SU(6) valence quark model and chiral symmetry. While recognizing the goal of VQCD, Nathan Isgur disagrees on some of the conclusions the authors have drawn. The foremost objection raised in section 2 is to their suggestion that the major part of the hyperfine splittings in baryons is due to Goldstone boson exchange and not one-gluon-exchange (OGE) interactions. The logic of Isgur's objection is that VQCD yields a spectroscopy vastly different from quenched QCD and therefore the structure of the hadrons (to which hyperfine splittings in a quark model are intimately tied) is also suspect so no definite conclusions are possible. To put this into perspective it should be emphasized at the outset that spectroscopy is only one aspect of hadron physics examined in section 1. The authors have studied the axial and scalar couplings of nucleon in terms of FA/DA and FS/DS, the neutron to proton magnetic moment ratio μn/μp, and various form factors. None of these results reveal any pathologies of hadron structure and turn out to be close to the SU(6) relations, as expected. In fact this is what motivated the study of valence degrees of freedom via VQCD. In section 2 the authors address specific issues related to spectroscopy in VQCD. Isgur also presented more general arguments against the idea of boson exchange as a contributor to hyperfine effects. A cornerstone of his discussion is the unifying aspect of OGE in a quark model picture. The authors
Molecular invariants: atomic group valence
International Nuclear Information System (INIS)
Molecular invariants may be deduced in a very compact way through Grassman algebra. In this work, a generalized valence is defined for an atomic group; it reduces to the Known expressions for the case of an atom in a molecule. It is the same of the correlations between the fluctions of the atomic charges qc and qd (C belongs to the group and D does not) around their average values. Numerical results agree with chemical expectation. (author)
Screw-vector bond graphs for kinetic-static modelling and analysis of mechanisms
International Nuclear Information System (INIS)
This dissertation deals with the kinetic-static modelling and analysis of spatial mechanisms used in robotics systems. A framework is proposed, which embodies a geometrical and a network approach for kinetic-static modelling. For this purpose we use screw theory and bond graphs. A new form of bond graphs is introduced: the screw-vector bond graph, whose power variables are defined to be wrenches and twists expressed as intrinsic screw-vectors. The mechanism is then identified as a network, whose components are kinematic pairs and whose topology is described by a directed graph. A screw-vector Simple Junction Structure represents the topological constraints. Kinematic pairs are represented by one-port elements, defined by two reciprocal screw-vector spaces. Using dual bases of screw-vectors, a generic decomposition of kinematic pair elements is given. The reduction of kinetic-static models of series and parallel kinematic chains is used in order to derive kinetic-static functional models in geometric form. Thereupon, the computational causality assignment is adapted for the graphical analysis of the mobility and the functioning of spatial mechanisms, based on completely or incompletely specified models. (author)
Dotsenko, V S; Pujol, P; Dotsenko, Vladimir; Picco, Marco; Pujol, Pierre
1995-01-01
We find the cross-over behavior for the spin-spin correlation function for the 2D Ising and 3-states Potts model with random bonds at the critical point. The procedure employed is the renormalisation approach of the perturbation series around the conformal field theories representing the pure models. We obtain a crossover in the amplitude for the correlation function for the Ising model which doesn't change the critical exponent, and a shift in the critical exponent produced by randomness in the case of the Potts model. A comparison with numerical data is discussed briefly.
Theoretical modeling of infrared spectra of the hydrogen and deuterium bond in aspirin crystal
Ghalla, Houcine; Rekik, Najeh; Michta, Anna; Oujia, Brahim; Flakus, Henryk T.
2010-01-01
An extended quantum theoretical approach of the ν IR lineshape of cyclic dimers of weakly H-bonded species is proposed. We have extended a previous approach [M.E.-A. Benmalti, P. Blaise, H.T. Flakus, O. Henri-Rousseau, Chem. Phys. 320 (2006) 267] by accounting for the anharmonicity of the slow mode which is described by a "Morse" potential in order to reproduce the polarized infrared spectra of the hydrogen and deuterium bond in acetylsalicylic acid (aspirin) crystals. From comparison of polarized IR spectra of isotopically neat and isotopically diluted aspirin crystals it resulted that centrosymmetric aspirin dimer was the bearer of the crystal main spectral properties. In this approach, the adiabatic approximation is performed for each separate H-bond bridge of the dimer and a strong non-adiabatic correction is introduced into the model via the resonant exchange between the fast mode excited states of the two moieties. Within the strong anharmonic coupling theory, according to which the X-H→⋯Y high-frequency mode is anharmonically coupled to the H-bond bridge, this model incorporated the Davydov coupling between the excited states of the two moieties, the quantum direct and indirect dampings and the anharmonicity for the H-bond bridge. The spectral density is obtained within the linear response theory by Fourier transform of the damped autocorrelation functions. The evaluated spectra are in fairly good agreement with the experimental ones by using a minimum number of independent parameters. The effect of deuteration has been well reproduced by reducing simply the angular frequency of the fast mode and the anharmonic coupling parameter.
A bond graph approach to modeling the anuran vocal production system.
Kime, Nicole M; Ryan, Michael J; Wilson, Preston S
2013-06-01
Air-driven vocal production systems such as those found in mammals, birds, and anurans (frogs and toads) combine pneumatic and mechanical elements in species-specific ways to produce a diversity of communication signals. This study uses bond graphs to model a generalized anuran vocal production system. Bond graphs allow an incremental approach to modeling dynamic physical systems involving different domains. Anurans provide an example of how signal diversity results from variation in the structure and behavior of vocal system elements. This paper first proposes a bond graph model of the integrated anuran vocal system as a framework for future study. It then presents a simulated submodel of the anuran sound source that produces sustained oscillations in vocal fold displacement and air flow through the larynx. The modeling approach illustrated here should prove of general applicability to other biological sound production systems, and will allow researchers to study the biomechanics of vocal production as well as the functional congruence and evolution of groups of traits within integrated vocal systems. PMID:23742365
Cassino, Christopher
2005-01-01
Structural adhesives are materials that are capable of bearing significant loads in shear, and sometimes tension, over a range of strains and strain rates. Adhesively bonded structures can dissipate large amounts of mechanical energy and can be lighter and more efficient than many bolted or vibration welded parts. The largest barrier to using structural adhesives in more applications is the many challenges engineers are presented with when designing and analyzing adhesively bonded structures....
Optimized resonating valence bond state in square lattice: correlations & excitations
Directory of Open Access Journals (Sweden)
Z Nourbakhsh
2009-09-01
Full Text Available We consider RVB state as a variational estimate for the ground state of Heisenberg antiferromagnet in square lattice. We present numerical calculation of energy, spin-spin correlation function and spin excitation spectrum. We show, that the quantum flactuations reduce of magnetization respect to Neel order. Our results are in good agreement with other methods such as spin-wave calculation and series expansions.
Orientational bond and Néel order in the two-dimensional ionic Hubbard model
Hafez-Torbati, Mohsen; Uhrig, Götz S.
2016-05-01
Unconventional phases often occur where two competing mechanisms compensate. An excellent example is the ionic Hubbard model where the alternating local potential δ , favoring a band insulator (BI), competes with the local repulsion U , favoring a Mott insulator (MI). By continuous unitary transformations we derive effective models in which we study the softening of various excitons. The softening signals the instability towards new phases that we describe on the mean-field level. On increasing U from the BI in two dimensions, we find a bond-ordered phase breaking orientational symmetry due to a d -wave component. Then, antiferromagnetic order appears coexisting with the d -wave bond order. Finally, the d -wave order vanishes and a Néel-type MI persists.
Bayesian Network Based Fault Prognosis via Bond Graph Modeling of High-Speed Railway Traction Device
Directory of Open Access Journals (Sweden)
Yunkai Wu
2015-01-01
component-level faults accurately for a high-speed railway traction system, a fault prognosis approach via Bayesian network and bond graph modeling techniques is proposed. The inherent structure of a railway traction system is represented by bond graph model, based on which a multilayer Bayesian network is developed for fault propagation analysis and fault prediction. For complete and incomplete data sets, two different parameter learning algorithms such as Bayesian estimation and expectation maximization (EM algorithm are adopted to determine the conditional probability table of the Bayesian network. The proposed prognosis approach using Pearl’s polytree propagation algorithm for joint probability reasoning can predict the failure probabilities of leaf nodes based on the current status of root nodes. Verification results in a high-speed railway traction simulation system can demonstrate the effectiveness of the proposed approach.
Spin-splitting calculation for zincblende semiconductors using an atomic bond-orbital model
International Nuclear Information System (INIS)
We develop a 16-band atomic bond-orbital model (16ABOM) to compute the spin splitting induced by bulk inversion asymmetry in zincblende materials. This model is derived from the linear combination of atomic-orbital (LCAO) scheme such that the characteristics of the real atomic orbitals can be preserved to calculate the spin splitting. The Hamiltonian of 16ABOM is based on a similarity transformation performed on the nearest-neighbor LCAO Hamiltonian with a second-order Taylor expansion over k-vector at the Γ point. The spin-splitting energies in bulk zincblende semiconductors, GaAs and InSb, are calculated, and the results agree with the LCAO and first-principles calculations. However, we find that the spin-orbit coupling between bonding and antibonding p-like states, evaluated by the 16ABOM, dominates the spin splitting of the lowest conduction bands in the zincblende materials.
Spin-splitting calculation for zincblende semiconductors using an atomic bond-orbital model
Kao, Hsiu-Fen; Lo, Ikai; Chiang, Jih-Chen; Chen, Chun-Nan; Wang, Wan-Tsang; Hsu, Yu-Chi; Ren, Chung-Yuan; Lee, Meng-En; Wu, Chieh-Lung; Gau, Ming-Hong
2012-10-01
We develop a 16-band atomic bond-orbital model (16ABOM) to compute the spin splitting induced by bulk inversion asymmetry in zincblende materials. This model is derived from the linear combination of atomic-orbital (LCAO) scheme such that the characteristics of the real atomic orbitals can be preserved to calculate the spin splitting. The Hamiltonian of 16ABOM is based on a similarity transformation performed on the nearest-neighbor LCAO Hamiltonian with a second-order Taylor expansion over \\vec{k} at the Γ point. The spin-splitting energies in bulk zincblende semiconductors, GaAs and InSb, are calculated, and the results agree with the LCAO and first-principles calculations. However, we find that the spin-orbit coupling between bonding and antibonding p-like states, evaluated by the 16ABOM, dominates the spin splitting of the lowest conduction bands in the zincblende materials.
International Nuclear Information System (INIS)
Highlights: ► A 3D nonlinear FE model is developed of RC deep beams with web openings. ► We used cohesion elements to simulate bond. ► The developed FE model is suitable for analysis of such complex structures. -- Abstract: This paper aims to develop 3D nonlinear finite element (FE) models for reinforced concrete (RC) deep beams containing web openings and strengthened in shear with carbon fiber reinforced polymer (CFRP) composite sheets. The web openings interrupted the natural load path either fully or partially. The FE models adopted realistic materials constitutive laws that account for the nonlinear behavior of materials. In the FE models, solid elements for concrete, multi-layer shell elements for CFRP and link elements for steel reinforcement were used to simulate the physical models. Special interface elements were implemented in the FE models to simulate the interfacial bond behavior between the concrete and CFRP composites. A comparison between the FE results and experimental data published in the literature demonstrated the validity of the computational models in capturing the structural response for both unstrengthened and CFRP-strengthened deep beams with openings. The developed FE models can serve as a numerical platform for performance prediction of RC deep beams with openings strengthened in shear with CFRP composites.