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Sample records for density matrix approach

  1. Density matrix renormalization group approach to the massive Schwinger model

    NASA Astrophysics Data System (ADS)

    Byrnes, T. M.; Sriganesh, P.; Bursill, R. J.; Hamer, C. J.

    2002-07-01

    The massive Schwinger model is studied using a density matrix renormalization group approach to the staggered lattice Hamiltonian version of the model. Lattice sizes up to 256 sites are calculated, and the estimates in the continuum limit are almost two orders of magnitude more accurate than previous calculations. Coleman's picture of ``half-asymptotic'' particles at a background field θ=π is confirmed. The predicted phase transition at finite fermion mass (m/g) is accurately located and demonstrated to belong in the 2D Ising universality class.

  2. A real-space stochastic density matrix approach for density functional electronic structure.

    PubMed

    Beck, Thomas L

    2015-12-21

    The recent development of real-space grid methods has led to more efficient, accurate, and adaptable approaches for large-scale electrostatics and density functional electronic structure modeling. With the incorporation of multiscale techniques, linear-scaling real-space solvers are possible for density functional problems if localized orbitals are used to represent the Kohn-Sham energy functional. These methods still suffer from high computational and storage overheads, however, due to extensive matrix operations related to the underlying wave function grid representation. In this paper, an alternative stochastic method is outlined that aims to solve directly for the one-electron density matrix in real space. In order to illustrate aspects of the method, model calculations are performed for simple one-dimensional problems that display some features of the more general problem, such as spatial nodes in the density matrix. This orbital-free approach may prove helpful considering a future involving increasingly parallel computing architectures. Its primary advantage is the near-locality of the random walks, allowing for simultaneous updates of the density matrix in different regions of space partitioned across the processors. In addition, it allows for testing and enforcement of the particle number and idempotency constraints through stabilization of a Feynman-Kac functional integral as opposed to the extensive matrix operations in traditional approaches. PMID:25969148

  3. Reduced density matrix hybrid approach: application to electronic energy transfer.

    PubMed

    Berkelbach, Timothy C; Markland, Thomas E; Reichman, David R

    2012-02-28

    Electronic energy transfer in the condensed phase, such as that occurring in photosynthetic complexes, frequently occurs in regimes where the energy scales of the system and environment are similar. This situation provides a challenge to theoretical investigation since most approaches are accurate only when a certain energetic parameter is small compared to others in the problem. Here we show that in these difficult regimes, the Ehrenfest approach provides a good starting point for a dynamical description of the energy transfer process due to its ability to accurately treat coupling to slow environmental modes. To further improve on the accuracy of the Ehrenfest approach, we use our reduced density matrix hybrid framework to treat the faster environmental modes quantum mechanically, at the level of a perturbative master equation. This combined approach is shown to provide an efficient and quantitative description of electronic energy transfer in a model dimer and the Fenna-Matthews-Olson complex and is used to investigate the effect of environmental preparation on the resulting dynamics.

  4. Reduced density matrix approach to calculation of electronic structure

    NASA Astrophysics Data System (ADS)

    Braams, Bastiaan J.; Jiang, Shidong; Nayakkankuppam, Madhu; Overton, Michael L.; Percus, Jerome K.

    1998-11-01

    The possibility of using the one-body and two-body reduced density matrices, rather than the many-body wavefunction, as the fundamental object of study for electronic structure calculations was actively explored in the 1960's and 1970's [1]-[3], but interest has waned since. In this approach the calculation of ground-state properties is reduced to a linear optimization problem subject to the representability conditions for the density matrices, which are a mixture of linear equalities and bounds on eigenvalues. We will review this approach, present a new family of representability conditions, and discuss our experience in using present-day methods for semi-definite programming for this application. [1] A. J. Coleman: Structure of fermion density matrices. Rev. Mod. Phys. 35 (1963) 668--689. [2] Claude Garrod and Jerome K. Percus: Reduction of the N-particle variational problem. J. Math. Phys. 5 (1964) 1756--1776. [3] M. Rosina and C. Garrod: The variational calculation of reduced density matrices. J. Comput. Phys. 18 (1975) 300--310.

  5. Eigenvalue density of linear stochastic dynamical systems: A random matrix approach

    NASA Astrophysics Data System (ADS)

    Adhikari, S.; Pastur, L.; Lytova, A.; Du Bois, J.

    2012-02-01

    Eigenvalue problems play an important role in the dynamic analysis of engineering systems modeled using the theory of linear structural mechanics. When uncertainties are considered, the eigenvalue problem becomes a random eigenvalue problem. In this paper the density of the eigenvalues of a discretized continuous system with uncertainty is discussed by considering the model where the system matrices are the Wishart random matrices. An analytical expression involving the Stieltjes transform is derived for the density of the eigenvalues when the dimension of the corresponding random matrix becomes asymptotically large. The mean matrices and the dispersion parameters associated with the mass and stiffness matrices are necessary to obtain the density of the eigenvalues in the frameworks of the proposed approach. The applicability of a simple eigenvalue density function, known as the Marenko-Pastur (MP) density, is investigated. The analytical results are demonstrated by numerical examples involving a plate and the tail boom of a helicopter with uncertain properties. The new results are validated using an experiment on a vibrating plate with randomly attached spring-mass oscillators where 100 nominally identical samples are physically created and individually tested within a laboratory framework.

  6. Electrically tunable spin polarization in silicene: A multi-terminal spin density matrix approach

    NASA Astrophysics Data System (ADS)

    Chen, Son-Hsien

    2016-05-01

    Recent realized silicene field-effect transistor yields promising electronic applications. Using a multi-terminal spin density matrix approach, this paper presents an analysis of the spin polarizations in a silicene structure of the spin field-effect transistor by considering the intertwined intrinsic and Rashba spin-orbit couplings, gate voltage, Zeeman splitting, as well as disorder. Coexistence of the stagger potential and intrinsic spin-orbit coupling results in spin precession, making any in-plane polarization directions reachable by the gate voltage; specifically, the intrinsic coupling allows one to electrically adjust the in-plane components of the polarizations, while the Rashba coupling to adjust the out-of-plan polarizations. Larger electrically tunable ranges of in-plan polarizations are found in oppositely gated silicene than in the uniformly gated silicene. Polarizations in different phases behave distinguishably in weak disorder regime, while independent of the phases, stronger disorder leads to a saturation value.

  7. Reconstructive approaches to one- and two-electron density matrix theory

    NASA Astrophysics Data System (ADS)

    Herbert, John Michael

    Novel computational methods for electronic structure theory are explored, in which the fundamental variable is either the one- or the two-electron reduced density matrix (1- or 2-RDM), rather than the electronic wavefunction. A unifying theme among these methods is density matrix reconstruction, that is, decoupling approximations that express higher-order density matrices as functionals of lower-order ones. On the 2-RDM side, a connected (extensive) version of the Contracted Schrodinger Equation (CSE) is developed, in which the basic unknowns are the RDM cumulants through order four. Reconstruction functionals that neglect the 3- and 4-RDM cumulants are examined and revealed to be significantly less accurate than suggested by previous minimal-basis results. Exact 3-RDM cumulants for some four-electron systems are calculated and found to be comparable in importance to unconnected products of lower-order cumulants. Decoupling approximations for the 3- and 4-RDM cumulants are developed based upon a renormalized, diagrammatic perturbation theory for the three- and four-particle Green's functions, in which the effective, pairwise interaction is extracted from the two-particle cumulant. Diagram rules suitable for both the time-dependent and time-independent versions of this perturbation theory are derived. Reconstructive approaches to natural orbital (1-RDM) functional theory are also examined, wherein the 2-RDM is parametrized in terms of the natural orbitals and their (generally fractional) occupancies. It is demonstrated, at the theorem level, that proposed "corrected Hartree" and "corrected Hartree-Fock" natural orbital functionals necessarily violate positivity of the 2-RDM, which is closely related to their failure to respect antisymmetry. Calculations demonstrate that negative eigenvalues of the 2-RDM are associated with a large, stabilizing (but ultimately spurious) contribution to the energy. Nevertheless, a partially self-interaction-corrected version of the

  8. A Comparative Study of Collagen Matrix Density Effect on Endothelial Sprout Formation Using Experimental and Computational Approaches.

    PubMed

    Shamloo, Amir; Mohammadaliha, Negar; Heilshorn, Sarah C; Bauer, Amy L

    2016-04-01

    A thorough understanding of determining factors in angiogenesis is a necessary step to control the development of new blood vessels. Extracellular matrix density is known to have a significant influence on cellular behaviors and consequently can regulate vessel formation. The utilization of experimental platforms in combination with numerical models can be a powerful method to explore the mechanisms of new capillary sprout formation. In this study, using an integrative method, the interplay between the matrix density and angiogenesis was investigated. Owing the fact that the extracellular matrix density is a global parameter that can affect other parameters such as pore size, stiffness, cell-matrix adhesion and cross-linking, deeper understanding of the most important biomechanical or biochemical properties of the ECM causing changes in sprout morphogenesis is crucial. Here, we implemented both computational and experimental methods to analyze the mechanisms responsible for the influence of ECM density on the sprout formation that is difficult to be investigated comprehensively using each of these single methods. For this purpose, we first utilized an innovative approach to quantify the correspondence of the simulated collagen fibril density to the collagen density in the experimental part. Comparing the results of the experimental study and computational model led to some considerable achievements. First, we verified the results of the computational model using the experimental results. Then, we reported parameters such as the ratio of proliferating cells to migrating cells that was difficult to obtain from experimental study. Finally, this integrative system led to gain an understanding of the possible mechanisms responsible for the effect of ECM density on angiogenesis. The results showed that stable and long sprouts were observed at an intermediate collagen matrix density of 1.2 and 1.9 mg/ml due to a balance between the number of migrating and proliferating

  9. Transfer Matrix Approach to 1d Random Band Matrices: Density of States

    NASA Astrophysics Data System (ADS)

    Shcherbina, Mariya; Shcherbina, Tatyana

    2016-08-01

    We study the special case of n× n 1D Gaussian Hermitian random band matrices, when the covariance of the elements is determined by the matrix J=(-W^2triangle +1)^{-1} . Assuming that n≥ CW log W≫ 1 , we prove that the averaged density of states coincides with the Wigner semicircle law up to the correction of order W^{-1}.

  10. Transfer Matrix Approach to 1d Random Band Matrices: Density of States

    NASA Astrophysics Data System (ADS)

    Shcherbina, Mariya; Shcherbina, Tatyana

    2016-09-01

    We study the special case of n× n 1D Gaussian Hermitian random band matrices, when the covariance of the elements is determined by the matrix J=(-W^2triangle +1)^{-1}. Assuming that n≥ CW log W≫ 1, we prove that the averaged density of states coincides with the Wigner semicircle law up to the correction of order W^{-1}.

  11. Nuclear motion effects on the density matrix of crystals: an ab initio Monte Carlo harmonic approach.

    PubMed

    Pisani, Cesare; Erba, Alessandro; Ferrabone, Matteo; Dovesi, Roberto

    2012-07-28

    In the frame of the Born-Oppenheimer approximation, nuclear motions in crystals can be simulated rather accurately using a harmonic model. In turn, the electronic first-order density matrix (DM) can be expressed as the statistically weighted average over all its determinations each resulting from an instantaneous nuclear configuration. This model has been implemented in a computational scheme which adopts an ab initio one-electron (Hartree-Fock or Kohn-Sham) Hamiltonian in the CRYSTAL program. After selecting a supercell of reasonable size and solving the corresponding vibrational problem in the harmonic approximation, a Metropolis algorithm is adopted for generating a sample of nuclear configurations which reflects their probability distribution at a given temperature. For each configuration in the sample the "instantaneous" DM is calculated, and its contribution to the observables of interest is extracted. Translational and point symmetry of the crystal as reflected in its average DM are fully exploited. The influence of zero-point and thermal motion of nuclei on such important first-order observables as x-ray structure factors and Compton profiles can thus be estimated.

  12. Implementing the density matrix embedding theory with the hierarchical mean-field approach

    NASA Astrophysics Data System (ADS)

    Qin, Jingbo; Jie, Quanlin; Fan, Zhuo

    2016-07-01

    We show an implementation of density matrix embedding theory (DMET) for the spin lattice of infinite size. It is indeed a special form of hierarchical mean-field (HMF) theory. In the method, we divide the lattice into a small part and a large part. View the small part as an impurity, embedding in the large part, which is viewed as the environment. We deal the impurity with a high accuracy method. But treat the environment with a low-level method: the states of the environment nearby the impurity are expressed by a set of multiple block product states, while the distant parts are treated by mean-field consideration. Our method allows for the computation of the ground state of the infinite two-dimensional quantum spin systems. In the text, we take the frustrated Heisenberg model as an example to test our method. The ground state energy we calculated can reach a high accuracy. We also calculate the magnetization, and the fidelity to study the quantum phase transitions.

  13. Canonical density matrix perturbation theory.

    PubMed

    Niklasson, Anders M N; Cawkwell, M J; Rubensson, Emanuel H; Rudberg, Elias

    2015-12-01

    Density matrix perturbation theory [Niklasson and Challacombe, Phys. Rev. Lett. 92, 193001 (2004)] is generalized to canonical (NVT) free-energy ensembles in tight-binding, Hartree-Fock, or Kohn-Sham density-functional theory. The canonical density matrix perturbation theory can be used to calculate temperature-dependent response properties from the coupled perturbed self-consistent field equations as in density-functional perturbation theory. The method is well suited to take advantage of sparse matrix algebra to achieve linear scaling complexity in the computational cost as a function of system size for sufficiently large nonmetallic materials and metals at high temperatures. PMID:26764847

  14. Canonical density matrix perturbation theory.

    PubMed

    Niklasson, Anders M N; Cawkwell, M J; Rubensson, Emanuel H; Rudberg, Elias

    2015-12-01

    Density matrix perturbation theory [Niklasson and Challacombe, Phys. Rev. Lett. 92, 193001 (2004)] is generalized to canonical (NVT) free-energy ensembles in tight-binding, Hartree-Fock, or Kohn-Sham density-functional theory. The canonical density matrix perturbation theory can be used to calculate temperature-dependent response properties from the coupled perturbed self-consistent field equations as in density-functional perturbation theory. The method is well suited to take advantage of sparse matrix algebra to achieve linear scaling complexity in the computational cost as a function of system size for sufficiently large nonmetallic materials and metals at high temperatures.

  15. Polarization observables in the longitudinal basis for pseudo-scalar meson photoproduction using a density matrix approach

    SciTech Connect

    Biplab Dey, Michael E. McCracken, David G. Ireland, Curtis A. Meyer

    2011-05-01

    The complete expression for the intensity in pseudo-scalar meson photoproduction with a polarized beam, target, and recoil baryon is derived using a density matrix approach that offers great economy of notation. A Cartesian basis with spins for all particles quantized along a single direction, the longitudinal beam direction, is used for consistency and clarity in interpretation. A single spin-quantization axis for all particles enables the amplitudes to be written in a manifestly covariant fashion with simple relations to those of the well-known CGLN formalism. Possible sign discrepancies between theoretical amplitude-level expressions and experimentally measurable intensity profiles are dealt with carefully. Our motivation is to provide a coherent framework for coupled-channel partial-wave analysis of several meson photoproduction reactions, incorporating recently published and forthcoming polarization data from Jefferson Lab.

  16. A time convolution less density matrix approach to the nonlinear optical response of a coupled system-bath complex

    SciTech Connect

    Richter, Marten Knorr, Andreas

    2010-04-15

    Time convolution less density matrix theory (TCL) is a powerful and well established tool to investigate strong system-bath coupling for linear optical spectra. We show that TCL equations can be generalised to the nonlinear optical response up to a chosen order in the optical field. This goal is achieved via an time convolution less perturbation scheme for the reduced density matrices of the electronic system. In our approach, the most important results are the inclusion of a electron-phonon coupling non-diagonal in the electronic states and memory effects of the bath: First, the considered model system is introduced. Second, the time evolution of the statistical operator is expanded with respect to the external optical field. This expansion is the starting point to explain how a TCL theory can treat the response up to in a certain order in the external field. Third, new TCL equations, including bath memory effects, are derived and the problem of information loss in the reduced density matrix is analysed. For this purpose, new dimensions are added to the reduced statistical operator to compensate lack of information in comparison with the full statistical operator. The theory is benchmarked with a two level system and applied to a three level system including non-diagonal phonon coupling. In our analysis of pump-probe experiments, the bath memory is influenced by the system state occupied between pump and probe pulse. In particular, the memory of the bath influences the dephasing process of electronic coherences developing during the time interval between pump and probe pulses.

  17. Obtaining Highly Excited Eigenstates of Many-Body Localized Hamiltonians by the Density Matrix Renormalization Group Approach.

    PubMed

    Khemani, Vedika; Pollmann, Frank; Sondhi, S L

    2016-06-17

    The eigenstates of many-body localized (MBL) Hamiltonians exhibit low entanglement. We adapt the highly successful density-matrix renormalization group method, which is usually used to find modestly entangled ground states of local Hamiltonians, to find individual highly excited eigenstates of MBL Hamiltonians. The adaptation builds on the distinctive spatial structure of such eigenstates. We benchmark our method against the well-studied random field Heisenberg model in one dimension. At moderate to large disorder, the method successfully obtains excited eigenstates with high accuracy, thereby enabling a study of MBL systems at much larger system sizes than those accessible to exact-diagonalization methods. PMID:27367405

  18. Quantum information aspects on bulk and nano interacting Fermi system: A spin-space density matrix approach

    NASA Astrophysics Data System (ADS)

    Afzali, R.; Ebrahimian, N.; Eghbalifar, B.

    2016-10-01

    By approximating the energy gap, entering nano-size effect via gap fluctuation and calculating the Green's functions and the space-spin density matrix, the dependence of quantum correlation (entanglement, discord and tripartite entanglement) on the relative distance of two electron spins forming Cooper pairs, the energy gap and the length of bulk and nano interacting Fermi system (a nodal d-wave superconductor) is determined. In contrast to a s-wave superconductor, quantum correlation of the system is sensitive to the change of the gap magnitude and strongly depends on the length of the grain. Also, quantum discord oscillates. Furthermore, the entanglement length and the correlation length are investigated. Discord becomes zero at a characteristic length of the d-wave superconductor.

  19. Theory of open quantum systems with bath of electrons and phonons and spins: Many-dissipaton density matrixes approach

    SciTech Connect

    Yan, YiJing

    2014-02-07

    This work establishes a strongly correlated system-and-bath dynamics theory, the many-dissipaton density operators formalism. It puts forward a quasi-particle picture for environmental influences. This picture unifies the physical descriptions and algebraic treatments on three distinct classes of quantum environments, electron bath, phonon bath, and two-level spin or exciton bath, as their participating in quantum dissipation processes. Dynamical variables for theoretical description are no longer just the reduced density matrix for system, but remarkably also those for quasi-particles of bath. The present theoretical formalism offers efficient and accurate means for the study of steady-state (nonequilibrium and equilibrium) and real-time dynamical properties of both systems and hybridizing environments. It further provides universal evaluations, exact in principle, on various correlation functions, including even those of environmental degrees of freedom in coupling with systems. Induced environmental dynamics could be reflected directly in experimentally measurable quantities, such as Fano resonances and quantum transport current shot noise statistics.

  20. Correlated Density Matrix Theory of Boson Superfluids

    NASA Astrophysics Data System (ADS)

    Ristig, M. L.; Senger, G.; Serhan, M.; Clark, J. W.

    1995-11-01

    A variational approach to unified microscopic description of normal and superfluid phases of a strongly interacting Bose system is proposed. We begin the formulation of an optimal theory within this approach through the diagrammatic analysis and synthesis of key distribution functions that characterize the spatial structure and the degree of coherence present in the two phases. The approach centers on functional minimization of the free energy corresponding to a suitable trial form for the many-body density matrix W(R, R‧) ∝ Φ(R) Q(R, R‧) Φ(R‧), with the wave function Φ and incoherence factor Q chosen to incorporate the essential dynamical and statistical correlations. In earlier work addressing the normal phase, Φ was taken as a Jastrow product of two-body dynamical correlation factors and Q was taken as a permanent of short-range two-body statistical bonds. A stratagem applied to the noninteracting Bose gas by Ziff, Uhlenbeck, and Kac is invoked to extend this ansatz to encompass both superfluid and normal phases, while introducing a variational parameter B that signals the presence of off-diagonal long-range order. The formal development proceeds from a generating functional Λ, defined by the logarithm of the normalization integral ∫ dR Φ2(R) Q(R, R). Construction of the Ursell-Mayer diagrammatic expansion of the generator Λ is followed by renormalization of the statistical bond and of the parameter B. For B ≡ 0, previous results for the normal phase are reproduced, whereas For B > 0, corresponding to the superfluid regime, a new class of anomalous contributions appears. Renormalized expansions for the pair distribution function g(r) and the cyclic distribution function Gcc(r) are extracted from Λ by functional differentiation. Standard diagrammatic techniques are adapted to obtain the appropriate hypernetted-chain equations for the evaluation of these spatial distribution functions. Corresponding results are presented for the internal energy

  1. Adiabatic approximation for the density matrix

    NASA Astrophysics Data System (ADS)

    Band, Yehuda B.

    1992-05-01

    An adiabatic approximation for the Liouville density-matrix equation which includes decay terms is developed. The adiabatic approximation employs the eigenvectors of the non-normal Liouville operator. The approximation is valid when there exists a complete set of eigenvectors of the non-normal Liouville operator (i.e., the eigenvectors span the density-matrix space), the time rate of change of the Liouville operator is small, and an auxiliary matrix is nonsingular. Numerical examples are presented involving efficient population transfer in a molecule by stimulated Raman scattering, with the intermediate level of the molecule decaying on a time scale that is fast compared with the pulse durations of the pump and Stokes fields. The adiabatic density-matrix approximation can be simply used to determine the density matrix for atomic or molecular systems interacting with cw electromagnetic fields when spontaneous emission or other decay mechanisms prevail.

  2. Rigorous investigation of the reduced density matrix for the ideal Bose gas in harmonic traps by a loop-gas-like approach

    SciTech Connect

    Beau, Mathieu; Savoie, Baptiste

    2014-05-15

    In this paper, we rigorously investigate the reduced density matrix (RDM) associated to the ideal Bose gas in harmonic traps. We present a method based on a sum-decomposition of the RDM allowing to treat not only the isotropic trap, but also general anisotropic traps. When focusing on the isotropic trap, the method is analogous to the loop-gas approach developed by Mullin [“The loop-gas approach to Bose-Einstein condensation for trapped particles,” Am. J. Phys. 68(2), 120 (2000)]. Turning to the case of anisotropic traps, we examine the RDM for some anisotropic trap models corresponding to some quasi-1D and quasi-2D regimes. For such models, we bring out an additional contribution in the local density of particles which arises from the mesoscopic loops. The close connection with the occurrence of generalized-Bose-Einstein condensation is discussed. Our loop-gas-like approach provides relevant information which can help guide numerical investigations on highly anisotropic systems based on the Path Integral Monte Carlo method.

  3. Polarizable Embedding Density Matrix Renormalization Group.

    PubMed

    Hedegård, Erik D; Reiher, Markus

    2016-09-13

    The polarizable embedding (PE) approach is a flexible embedding model where a preselected region out of a larger system is described quantum mechanically, while the interaction with the surrounding environment is modeled through an effective operator. This effective operator represents the environment by atom-centered multipoles and polarizabilities derived from quantum mechanical calculations on (fragments of) the environment. Thereby, the polarization of the environment is explicitly accounted for. Here, we present the coupling of the PE approach with the density matrix renormalization group (DMRG). This PE-DMRG method is particularly suitable for embedded subsystems that feature a dense manifold of frontier orbitals which requires large active spaces. Recovering such static electron-correlation effects in multiconfigurational electronic structure problems, while accounting for both electrostatics and polarization of a surrounding environment, allows us to describe strongly correlated electronic structures in complex molecular environments. We investigate various embedding potentials for the well-studied first excited state of water with active spaces that correspond to a full configuration-interaction treatment. Moreover, we study the environment effect on the first excited state of a retinylidene Schiff base within a channelrhodopsin protein. For this system, we also investigate the effect of dynamical correlation included through short-range density functional theory. PMID:27537835

  4. Vibrationally excited products after the photodesorption of NO from Pt(111): a two-mode open-system density matrix approach

    NASA Astrophysics Data System (ADS)

    Finger, Karin; Saalfrank, Peter

    1997-04-01

    The experimentally observed vibrational excitation of NO molecules photodesorbing from a Pt(111) surface is investigated numerically with the help of open-system density matrix theory. We extend Gadzuk's jumping wave packet model to treat DIET processes (desorption induced by electronic transitions, single-excitation limit) which is equivalent to a one-channel open system Liouville-von Neumann equation with coordinate-independent quenching, to cases when the electronic relaxation becomes coordinate-dependent. This allows for a more realistic but still economic and, hence, systematic study of DIET within a two-state, two-degrees of freedom model. Adopting "reasonable" Antoniewicz-type model potentials, we find that the experimental observations can semi-quantitatively be rationalized if an electronic quenching rate decreasing with increasing NO separation, is assumed. Preliminary two-mode DIMET simulations (desorption induced by multiple electronic transitions, multiple-excitation limit) within a stochastic wave packet approach are also presented.

  5. Interaction picture density matrix quantum Monte Carlo

    SciTech Connect

    Malone, Fionn D. Lee, D. K. K.; Foulkes, W. M. C.; Blunt, N. S.; Shepherd, James J.; Spencer, J. S.

    2015-07-28

    The recently developed density matrix quantum Monte Carlo (DMQMC) algorithm stochastically samples the N-body thermal density matrix and hence provides access to exact properties of many-particle quantum systems at arbitrary temperatures. We demonstrate that moving to the interaction picture provides substantial benefits when applying DMQMC to interacting fermions. In this first study, we focus on a system of much recent interest: the uniform electron gas in the warm dense regime. The basis set incompleteness error at finite temperature is investigated and extrapolated via a simple Monte Carlo sampling procedure. Finally, we provide benchmark calculations for a four-electron system, comparing our results to previous work where possible.

  6. Interaction picture density matrix quantum Monte Carlo.

    PubMed

    Malone, Fionn D; Blunt, N S; Shepherd, James J; Lee, D K K; Spencer, J S; Foulkes, W M C

    2015-07-28

    The recently developed density matrix quantum Monte Carlo (DMQMC) algorithm stochastically samples the N-body thermal density matrix and hence provides access to exact properties of many-particle quantum systems at arbitrary temperatures. We demonstrate that moving to the interaction picture provides substantial benefits when applying DMQMC to interacting fermions. In this first study, we focus on a system of much recent interest: the uniform electron gas in the warm dense regime. The basis set incompleteness error at finite temperature is investigated and extrapolated via a simple Monte Carlo sampling procedure. Finally, we provide benchmark calculations for a four-electron system, comparing our results to previous work where possible.

  7. Coupled-channels density-matrix approach to low-energy nuclear collision dynamics: A technique for quantifying quantum decoherence effects on reaction observables

    SciTech Connect

    Diaz-Torres, Alexis

    2010-11-15

    The coupled-channels density-matrix technique for nuclear reaction dynamics, which is based on the Liouville-von Neumann equation with Lindblad dissipative terms, is developed with the inclusion of full angular momentum couplings. It allows a quantitative study of the role and importance of quantum decoherence in nuclear scattering. Formulas of asymptotic observables that can reveal effects of quantum decoherence are given. A method for extracting energy-resolved scattering information from the time-dependent density matrix is introduced. As an example, model calculations are carried out for the low-energy collision of the {sup 16}O projectile on the {sup 154}Sm target.

  8. Symmetry groups, density-matrix equations and covariant Wigner functions

    NASA Astrophysics Data System (ADS)

    Santana, A. E.; Neto, A. Matos; Vianna, J. D. M.; Khanna, F. C.

    2000-06-01

    A representation theory for Lie groups is developed taking the Hilbert space, say Hw, of the w∗-algebra standard representation as the representation space. In this context the states describing physical systems are amplitude wave functions but closely connected with the notion of the density matrix. Then, based on symmetry properties, a general physical interpretation for the dual variables of thermal theories, in particular the thermofield dynamics (TFD) formalism, is introduced. The kinematic symmetries, Galilei and Poincaré, are studied and (density) amplitude matrix equations are derived for both of these cases. In the same context of group theory, the notion of phase space in quantum theory is analysed. Thus, in the non-relativistic situation, the concept of density amplitude is introduced, and as an example, a spin-half system is algebraically studied; Wigner function representations for the amplitude density matrices are derived and the connection of TFD and the usual Wigner-function methods are analysed. For the Poincaré symmetries the relativistic density matrix equations are studied for the scalar and spinorial fields. The relativistic phase space is built following the lines of the non-relativistic case. So, for the scalar field, the kinetic theory is introduced via the Klein-Gordon density-matrix equation, and a derivation of the Jüttiner distribution is presented as an example, thus making it possible to compare with the standard approaches. The analysis of the phase space for the Dirac field is carried out in connection with the dual spinor structure induced by the Dirac-field density-matrix equation, with the physical content relying on the symmetry groups. Gauge invariance is considered and, as a basic result, it is shown that the Heinz density operator (which has been used to develope a gauge covariant kinetic theory) is a particular solution for the (Klein-Gordon and Dirac) density-matrix equation.

  9. Interaction picture density matrix quantum Monte Carlo.

    PubMed

    Malone, Fionn D; Blunt, N S; Shepherd, James J; Lee, D K K; Spencer, J S; Foulkes, W M C

    2015-07-28

    The recently developed density matrix quantum Monte Carlo (DMQMC) algorithm stochastically samples the N-body thermal density matrix and hence provides access to exact properties of many-particle quantum systems at arbitrary temperatures. We demonstrate that moving to the interaction picture provides substantial benefits when applying DMQMC to interacting fermions. In this first study, we focus on a system of much recent interest: the uniform electron gas in the warm dense regime. The basis set incompleteness error at finite temperature is investigated and extrapolated via a simple Monte Carlo sampling procedure. Finally, we provide benchmark calculations for a four-electron system, comparing our results to previous work where possible. PMID:26233116

  10. Transition matrices and orbitals from reduced density matrix theory

    NASA Astrophysics Data System (ADS)

    Etienne, Thibaud

    2015-06-01

    In this contribution, we report two different methodologies for characterizing the electronic structure reorganization occurring when a chromophore undergoes an electronic transition. For the first method, we start by setting the theoretical background necessary to the reinterpretation through simple tensor analysis of (i) the transition density matrix and (ii) the natural transition orbitals in the scope of reduced density matrix theory. This novel interpretation is made more clear thanks to a short compendium of the one-particle reduced density matrix theory in a Fock space. The formalism is further applied to two different classes of excited states calculation methods, both requiring a single-determinant reference, that express an excited state as a hole-particle mono-excited configurations expansion, to which particle-hole correlation is coupled (time-dependent Hartree-Fock/time-dependent density functional theory) or not (configuration interaction single/Tamm-Dancoff approximation). For the second methodology presented in this paper, we introduce a novel and complementary concept related to electronic transitions with the canonical transition density matrix and the canonical transition orbitals. Their expression actually reflects the electronic cloud polarisation in the orbital space with a decomposition based on the actual contribution of one-particle excitations from occupied canonical orbitals to virtual ones. This approach validates our novel interpretation of the transition density matrix elements in terms of the Euclidean norm of elementary transition vectors in a linear tensor space. A proper use of these new concepts leads to the conclusion that despite the different principles underlying their construction, they provide two equivalent excited states topological analyses. This connexion is evidenced through simple illustrations of (in)organic dyes electronic transitions analysis.

  11. Transition matrices and orbitals from reduced density matrix theory

    SciTech Connect

    Etienne, Thibaud

    2015-06-28

    In this contribution, we report two different methodologies for characterizing the electronic structure reorganization occurring when a chromophore undergoes an electronic transition. For the first method, we start by setting the theoretical background necessary to the reinterpretation through simple tensor analysis of (i) the transition density matrix and (ii) the natural transition orbitals in the scope of reduced density matrix theory. This novel interpretation is made more clear thanks to a short compendium of the one-particle reduced density matrix theory in a Fock space. The formalism is further applied to two different classes of excited states calculation methods, both requiring a single-determinant reference, that express an excited state as a hole-particle mono-excited configurations expansion, to which particle-hole correlation is coupled (time-dependent Hartree-Fock/time-dependent density functional theory) or not (configuration interaction single/Tamm-Dancoff approximation). For the second methodology presented in this paper, we introduce a novel and complementary concept related to electronic transitions with the canonical transition density matrix and the canonical transition orbitals. Their expression actually reflects the electronic cloud polarisation in the orbital space with a decomposition based on the actual contribution of one-particle excitations from occupied canonical orbitals to virtual ones. This approach validates our novel interpretation of the transition density matrix elements in terms of the Euclidean norm of elementary transition vectors in a linear tensor space. A proper use of these new concepts leads to the conclusion that despite the different principles underlying their construction, they provide two equivalent excited states topological analyses. This connexion is evidenced through simple illustrations of (in)organic dyes electronic transitions analysis.

  12. Effective potential in density matrix functional theory.

    PubMed

    Nagy, A; Amovilli, C

    2004-10-01

    In the previous paper it was shown that in the ground state the diagonal of the spin independent second-order density matrix n can be determined by solving a single auxiliary equation of a two-particle problem. Thus the problem of an arbitrary system with even electrons can be reduced to a two-particle problem. The effective potential of the two-particle equation contains a term v(p) of completely kinetic origin. Virial theorem and hierarchy of equations are derived for v(p) and simple approximations are proposed. A relationship between the effective potential u(p) of the shape function equation and the potential v(p) is established.

  13. Effective potential in density matrix functional theory.

    PubMed

    Nagy, A; Amovilli, C

    2004-10-01

    In the previous paper it was shown that in the ground state the diagonal of the spin independent second-order density matrix n can be determined by solving a single auxiliary equation of a two-particle problem. Thus the problem of an arbitrary system with even electrons can be reduced to a two-particle problem. The effective potential of the two-particle equation contains a term v(p) of completely kinetic origin. Virial theorem and hierarchy of equations are derived for v(p) and simple approximations are proposed. A relationship between the effective potential u(p) of the shape function equation and the potential v(p) is established. PMID:15473719

  14. Localized density matrix minimization and linear-scaling algorithms

    NASA Astrophysics Data System (ADS)

    Lai, Rongjie; Lu, Jianfeng

    2016-06-01

    We propose a convex variational approach to compute localized density matrices for both zero temperature and finite temperature cases, by adding an entry-wise ℓ1 regularization to the free energy of the quantum system. Based on the fact that the density matrix decays exponentially away from the diagonal for insulating systems or systems at finite temperature, the proposed ℓ1 regularized variational method provides an effective way to approximate the original quantum system. We provide theoretical analysis of the approximation behavior and also design convergence guaranteed numerical algorithms based on Bregman iteration. More importantly, the ℓ1 regularized system naturally leads to localized density matrices with banded structure, which enables us to develop approximating algorithms to find the localized density matrices with computation cost linearly dependent on the problem size.

  15. Matrix product operators, matrix product states, and ab initio density matrix renormalization group algorithms

    NASA Astrophysics Data System (ADS)

    Chan, Garnet Kin-Lic; Keselman, Anna; Nakatani, Naoki; Li, Zhendong; White, Steven R.

    2016-07-01

    Current descriptions of the ab initio density matrix renormalization group (DMRG) algorithm use two superficially different languages: an older language of the renormalization group and renormalized operators, and a more recent language of matrix product states and matrix product operators. The same algorithm can appear dramatically different when written in the two different vocabularies. In this work, we carefully describe the translation between the two languages in several contexts. First, we describe how to efficiently implement the ab initio DMRG sweep using a matrix product operator based code, and the equivalence to the original renormalized operator implementation. Next we describe how to implement the general matrix product operator/matrix product state algebra within a pure renormalized operator-based DMRG code. Finally, we discuss two improvements of the ab initio DMRG sweep algorithm motivated by matrix product operator language: Hamiltonian compression, and a sum over operators representation that allows for perfect computational parallelism. The connections and correspondences described here serve to link the future developments with the past and are important in the efficient implementation of continuing advances in ab initio DMRG and related algorithms.

  16. Matrix product operators, matrix product states, and ab initio density matrix renormalization group algorithms.

    PubMed

    Chan, Garnet Kin-Lic; Keselman, Anna; Nakatani, Naoki; Li, Zhendong; White, Steven R

    2016-07-01

    Current descriptions of the ab initio density matrix renormalization group (DMRG) algorithm use two superficially different languages: an older language of the renormalization group and renormalized operators, and a more recent language of matrix product states and matrix product operators. The same algorithm can appear dramatically different when written in the two different vocabularies. In this work, we carefully describe the translation between the two languages in several contexts. First, we describe how to efficiently implement the ab initio DMRG sweep using a matrix product operator based code, and the equivalence to the original renormalized operator implementation. Next we describe how to implement the general matrix product operator/matrix product state algebra within a pure renormalized operator-based DMRG code. Finally, we discuss two improvements of the ab initio DMRG sweep algorithm motivated by matrix product operator language: Hamiltonian compression, and a sum over operators representation that allows for perfect computational parallelism. The connections and correspondences described here serve to link the future developments with the past and are important in the efficient implementation of continuing advances in ab initio DMRG and related algorithms.

  17. Matrix product operators, matrix product states, and ab initio density matrix renormalization group algorithms.

    PubMed

    Chan, Garnet Kin-Lic; Keselman, Anna; Nakatani, Naoki; Li, Zhendong; White, Steven R

    2016-07-01

    Current descriptions of the ab initio density matrix renormalization group (DMRG) algorithm use two superficially different languages: an older language of the renormalization group and renormalized operators, and a more recent language of matrix product states and matrix product operators. The same algorithm can appear dramatically different when written in the two different vocabularies. In this work, we carefully describe the translation between the two languages in several contexts. First, we describe how to efficiently implement the ab initio DMRG sweep using a matrix product operator based code, and the equivalence to the original renormalized operator implementation. Next we describe how to implement the general matrix product operator/matrix product state algebra within a pure renormalized operator-based DMRG code. Finally, we discuss two improvements of the ab initio DMRG sweep algorithm motivated by matrix product operator language: Hamiltonian compression, and a sum over operators representation that allows for perfect computational parallelism. The connections and correspondences described here serve to link the future developments with the past and are important in the efficient implementation of continuing advances in ab initio DMRG and related algorithms. PMID:27394094

  18. Correlation density matrices for one-dimensional quantum chains based on the density matrix renormalization group

    NASA Astrophysics Data System (ADS)

    Münder, W.; Weichselbaum, A.; Holzner, A.; von Delft, Jan; Henley, C. L.

    2010-07-01

    A useful concept for finding numerically the dominant correlations of a given ground state in an interacting quantum lattice system in an unbiased way is the correlation density matrix (CDM). For two disjoint, separated clusters, it is defined to be the density matrix of their union minus the direct product of their individual density matrices and contains all the correlations between the two clusters. We show how to extract from the CDM a survey of the relative strengths of the system's correlations in different symmetry sectors and the nature of their decay with distance (power law or exponential), as well as detailed information on the operators carrying long-range correlations and the spatial dependence of their correlation functions. To achieve this goal, we introduce a new method of analysing the CDM, termed the dominant operator basis (DOB) method, which identifies in an unbiased fashion a small set of operators for each cluster that serve as a basis for the dominant correlations of the system. We illustrate this method by analysing the CDM for a spinless extended Hubbard model that features a competition between charge density correlations and pairing correlations, and show that the DOB method successfully identifies their relative strengths and dominant correlators. To calculate the ground state of this model, we use the density matrix renormalization group, formulated in terms of a variational matrix product state (MPS) approach within which subsequent determination of the CDM is very straightforward. In an extended appendix, we give a detailed tutorial introduction to our variational MPS approach for ground state calculations for one-dimensional quantum chain models. We present in detail how MPSs overcome the problem of large Hilbert space dimensions in these models and describe all the techniques needed for handling them in practice.

  19. Matrix model approach to cosmology

    NASA Astrophysics Data System (ADS)

    Chaney, A.; Lu, Lei; Stern, A.

    2016-03-01

    We perform a systematic search for rotationally invariant cosmological solutions to toy matrix models. These models correspond to the bosonic sector of Lorentzian Ishibashi, Kawai, Kitazawa and Tsuchiya (IKKT)-type matrix models in dimensions d less than ten, specifically d =3 and d =5 . After taking a continuum (or commutative) limit they yield d -1 dimensional Poisson manifolds. The manifolds have a Lorentzian induced metric which can be associated with closed, open, or static space-times. For d =3 , we obtain recursion relations from which it is possible to generate rotationally invariant matrix solutions which yield open universes in the continuum limit. Specific examples of matrix solutions have also been found which are associated with closed and static two-dimensional space-times in the continuum limit. The solutions provide for a resolution of cosmological singularities, at least within the context of the toy matrix models. The commutative limit reveals other desirable features, such as a solution describing a smooth transition from an initial inflation to a noninflationary era. Many of the d =3 solutions have analogues in higher dimensions. The case of d =5 , in particular, has the potential for yielding realistic four-dimensional cosmologies in the continuum limit. We find four-dimensional de Sitter d S4 or anti-de Sitter AdS4 solutions when a totally antisymmetric term is included in the matrix action. A nontrivial Poisson structure is attached to these manifolds which represents the lowest order effect of noncommutativity. For the case of AdS4 , we find one particular limit where the lowest order noncommutativity vanishes at the boundary, but not in the interior.

  20. Density matrix embedding theory for interacting electron-phonon systems

    NASA Astrophysics Data System (ADS)

    Sandhoefer, Barbara; Chan, Garnet Kin-Lic

    2016-08-01

    We describe the extension of the density matrix embedding theory framework to coupled interacting fermion-boson systems. This provides a frequency-independent, entanglement embedding formalism to treat bulk fermion-boson problems. We illustrate the concepts within the context of the one-dimensional Hubbard-Holstein model, where the phonon bath states are obtained from the Schmidt decomposition of a self-consistently adjusted coherent state. We benchmark our results against accurate density matrix renormalization group calculations.

  1. Communication: Wigner functions in action-angle variables, Bohr-Sommerfeld quantization, the Heisenberg correspondence principle, and a symmetrical quasi-classical approach to the full electronic density matrix.

    PubMed

    Miller, William H; Cotton, Stephen J

    2016-08-28

    It is pointed out that the classical phase space distribution in action-angle (a-a) variables obtained from a Wigner function depends on how the calculation is carried out: if one computes the standard Wigner function in Cartesian variables (p, x), and then replaces p and x by their expressions in terms of a-a variables, one obtains a different result than if the Wigner function is computed directly in terms of the a-a variables. Furthermore, the latter procedure gives a result more consistent with classical and semiclassical theory-e.g., by incorporating the Bohr-Sommerfeld quantization condition (quantum states defined by integer values of the action variable) as well as the Heisenberg correspondence principle for matrix elements of an operator between such states-and has also been shown to be more accurate when applied to electronically non-adiabatic applications as implemented within the recently developed symmetrical quasi-classical (SQC) Meyer-Miller (MM) approach. Moreover, use of the Wigner function (obtained directly) in a-a variables shows how our standard SQC/MM approach can be used to obtain off-diagonal elements of the electronic density matrix by processing in a different way the same set of trajectories already used (in the SQC/MM methodology) to obtain the diagonal elements. PMID:27586896

  2. Communication: Wigner functions in action-angle variables, Bohr-Sommerfeld quantization, the Heisenberg correspondence principle, and a symmetrical quasi-classical approach to the full electronic density matrix.

    PubMed

    Miller, William H; Cotton, Stephen J

    2016-08-28

    It is pointed out that the classical phase space distribution in action-angle (a-a) variables obtained from a Wigner function depends on how the calculation is carried out: if one computes the standard Wigner function in Cartesian variables (p, x), and then replaces p and x by their expressions in terms of a-a variables, one obtains a different result than if the Wigner function is computed directly in terms of the a-a variables. Furthermore, the latter procedure gives a result more consistent with classical and semiclassical theory-e.g., by incorporating the Bohr-Sommerfeld quantization condition (quantum states defined by integer values of the action variable) as well as the Heisenberg correspondence principle for matrix elements of an operator between such states-and has also been shown to be more accurate when applied to electronically non-adiabatic applications as implemented within the recently developed symmetrical quasi-classical (SQC) Meyer-Miller (MM) approach. Moreover, use of the Wigner function (obtained directly) in a-a variables shows how our standard SQC/MM approach can be used to obtain off-diagonal elements of the electronic density matrix by processing in a different way the same set of trajectories already used (in the SQC/MM methodology) to obtain the diagonal elements.

  3. Communication: Wigner functions in action-angle variables, Bohr-Sommerfeld quantization, the Heisenberg correspondence principle, and a symmetrical quasi-classical approach to the full electronic density matrix

    NASA Astrophysics Data System (ADS)

    Miller, William H.; Cotton, Stephen J.

    2016-08-01

    It is pointed out that the classical phase space distribution in action-angle (a-a) variables obtained from a Wigner function depends on how the calculation is carried out: if one computes the standard Wigner function in Cartesian variables (p, x), and then replaces p and x by their expressions in terms of a-a variables, one obtains a different result than if the Wigner function is computed directly in terms of the a-a variables. Furthermore, the latter procedure gives a result more consistent with classical and semiclassical theory—e.g., by incorporating the Bohr-Sommerfeld quantization condition (quantum states defined by integer values of the action variable) as well as the Heisenberg correspondence principle for matrix elements of an operator between such states—and has also been shown to be more accurate when applied to electronically non-adiabatic applications as implemented within the recently developed symmetrical quasi-classical (SQC) Meyer-Miller (MM) approach. Moreover, use of the Wigner function (obtained directly) in a-a variables shows how our standard SQC/MM approach can be used to obtain off-diagonal elements of the electronic density matrix by processing in a different way the same set of trajectories already used (in the SQC/MM methodology) to obtain the diagonal elements.

  4. Density matrix renormalization group with efficient dynamical electron correlation through range separation

    SciTech Connect

    Hedegård, Erik Donovan Knecht, Stefan; Reiher, Markus; Kielberg, Jesper Skau; Jensen, Hans Jørgen Aagaard

    2015-06-14

    We present a new hybrid multiconfigurational method based on the concept of range-separation that combines the density matrix renormalization group approach with density functional theory. This new method is designed for the simultaneous description of dynamical and static electron-correlation effects in multiconfigurational electronic structure problems.

  5. Convergence of Density-Matrix Expansions for Nuclear Interactions

    SciTech Connect

    Carlsson, B. G.; Dobaczewski, J.

    2010-09-17

    We extend density-matrix expansions in nuclei to higher orders in derivatives of densities and test their convergence properties. The expansions allow for converting the interaction energies characteristic to finite- and short-range nuclear effective forces into quasilocal density functionals. We also propose a new type of expansion that has excellent convergence properties when benchmarked against the binding energies obtained for the Gogny interaction.

  6. The ab-initio density matrix renormalization group in practice

    SciTech Connect

    Olivares-Amaya, Roberto; Hu, Weifeng; Sharma, Sandeep; Yang, Jun; Chan, Garnet Kin-Lic; Nakatani, Naoki

    2015-01-21

    The ab-initio density matrix renormalization group (DMRG) is a tool that can be applied to a wide variety of interesting problems in quantum chemistry. Here, we examine the density matrix renormalization group from the vantage point of the quantum chemistry user. What kinds of problems is the DMRG well-suited to? What are the largest systems that can be treated at practical cost? What sort of accuracies can be obtained, and how do we reason about the computational difficulty in different molecules? By examining a diverse benchmark set of molecules: π-electron systems, benchmark main-group and transition metal dimers, and the Mn-oxo-salen and Fe-porphine organometallic compounds, we provide some answers to these questions, and show how the density matrix renormalization group is used in practice.

  7. The ab-initio density matrix renormalization group in practice

    NASA Astrophysics Data System (ADS)

    Olivares-Amaya, Roberto; Hu, Weifeng; Nakatani, Naoki; Sharma, Sandeep; Yang, Jun; Chan, Garnet Kin-Lic

    2015-01-01

    The ab-initio density matrix renormalization group (DMRG) is a tool that can be applied to a wide variety of interesting problems in quantum chemistry. Here, we examine the density matrix renormalization group from the vantage point of the quantum chemistry user. What kinds of problems is the DMRG well-suited to? What are the largest systems that can be treated at practical cost? What sort of accuracies can be obtained, and how do we reason about the computational difficulty in different molecules? By examining a diverse benchmark set of molecules: π-electron systems, benchmark main-group and transition metal dimers, and the Mn-oxo-salen and Fe-porphine organometallic compounds, we provide some answers to these questions, and show how the density matrix renormalization group is used in practice.

  8. Combining density-functional theory and density-matrix-functional theory

    SciTech Connect

    Rohr, Daniel R.; Pernal, Katarzyna; Toulouse, Julien

    2010-11-15

    We combine density-functional theory with density-matrix-functional theory to draw the best from both worlds. This is achieved by range separation of the electronic interaction which permits one to rigorously combine a short-range density functional with a long-range density-matrix functional. The short-range density functional is approximated by the short-range version of the Perdew-Burke-Ernzerhof functional (srPBE). The long-range density-matrix functional is approximated by the long-range version of the Buijse-Baerends functional (lrBB). The obtained srPBE+lrBB method accurately describes both the static and dynamic electron correlation at a computational cost similar to that of standard density-functional approximations. This is shown for the dissociation curves of the H{sub 2}, LiH, BH, and HF molecules.

  9. A matrix approach for assessing biosolids stability

    SciTech Connect

    Switzenbaum, M.S.; Moss, L.H.; Epstein, E.; Pincince, A.B.; Donovan, J.F.

    1998-07-01

    Stability assessment of biosolids must be made on the basis of the stabilization process used and the intended use of the manufactured biosolids. In this manner, a matrix based on technology and use was developed as an approach for assessing biosolids stability. Specific tests were recommended as to the most useful methods of stability assessment for each of the stabilization technologies examined.

  10. Communication: Four-component density matrix renormalization group

    SciTech Connect

    Knecht, Stefan Reiher, Markus; Legeza, Örs

    2014-01-28

    We present the first implementation of the relativistic quantum chemical two- and four-component density matrix renormalization group algorithm that includes a variational description of scalar-relativistic effects and spin–orbit coupling. Numerical results based on the four-component Dirac–Coulomb Hamiltonian are presented for the standard reference molecule for correlated relativistic benchmarks: thallium hydride.

  11. Matrix Methods for Estimating the Coherence Functions from Estimates of the Cross-Spectral Density Matrix

    DOE PAGESBeta

    Smallwood, D. O.

    1996-01-01

    It is shown that the usual method for estimating the coherence functions (ordinary, partial, and multiple) for a general multiple-input! multiple-output problem can be expressed as a modified form of Cholesky decomposition of the cross-spectral density matrix of the input and output records. The results can be equivalently obtained using singular value decomposition (SVD) of the cross-spectral density matrix. Using SVD suggests a new form of fractional coherence. The formulation as a SVD problem also suggests a way to order the inputs when a natural physical order of the inputs is absent.

  12. Effect of vibrational relaxation on DIET: a density matrix treatment

    NASA Astrophysics Data System (ADS)

    Guo, H.; Ma, G.

    2000-04-01

    The influence of substrate-induced vibrational relaxation on desorption induced by electronic transitions (DIET) is studied using a density matrix formulation. The one-dimensional model describing the DIET dynamics of NO consists of two electronic states. Relaxation in both electronic and vibrational modes is simulated with dissipative Liouvillians of the Lindblad form. As expected, vibrational relaxation results in a smaller desorption yield and lower product translational temperature.

  13. Random matrix approach to categorical data analysis

    NASA Astrophysics Data System (ADS)

    Patil, Aashay; Santhanam, M. S.

    2015-09-01

    Correlation and similarity measures are widely used in all the areas of sciences and social sciences. Often the variables are not numbers but are instead qualitative descriptors called categorical data. We define and study similarity matrix, as a measure of similarity, for the case of categorical data. This is of interest due to a deluge of categorical data, such as movie ratings, top-10 rankings, and data from social media, in the public domain that require analysis. We show that the statistical properties of the spectra of similarity matrices, constructed from categorical data, follow random matrix predictions with the dominant eigenvalue being an exception. We demonstrate this approach by applying it to the data for Indian general elections and sea level pressures in the North Atlantic ocean.

  14. Graph-based simulation of quantum computation in the density matrix representation

    NASA Astrophysics Data System (ADS)

    Viamontes, George F.; Markov, Igor L.; Hayes, John P.

    2004-08-01

    Quantum-mechanical phenomena are playing an increasing role in information processing, as transistor sizes approach the nanometer level, and quantum circuits and data encoding methods appear in the securest forms of communication. Simulating such phenomena efficiently is exceedingly difficult because of the vast size of the quantum state space involved. A major complication is caused by errors (noise) due to unwanted interactions between the quantum states and the environment. Consequently, simulating quantum circuits and their associated errors using the density matrix representation is potentially significant in many applications, but is well beyond the computational abilities of most classical simulation techniques in both time and memory resources. The size of a density matrix grows exponentially with the number of qubits simulated, rendering array-based simulation techniques that explicitly store the density matrix intractable. In this work, we propose a new technique aimed at efficiently simulating quantum circuits that are subject to errors. In particular, we describe new graph-based algorithms implemented in the simulator QuIDDPro/D. While previously reported graph-based simulators operate in terms of the state-vector representation, these new algorithms use the density matrix representation. To gauge the improvements offered by QuIDDPro/D, we compare its simulation performance with an optimized array-based simulator called QCSim. Empirical results, generated by both simulators on a set of quantum circuit benchmarks involving error correction, reversible logic, communication, and quantum search, show that the graph-based approach far outperforms the array-based approach.

  15. Shrinkage covariance matrix approach for microarray data

    NASA Astrophysics Data System (ADS)

    Karjanto, Suryaefiza; Aripin, Rasimah

    2013-04-01

    Microarray technology was developed for the purpose of monitoring the expression levels of thousands of genes. A microarray data set typically consists of tens of thousands of genes (variables) from just dozens of samples due to various constraints including the high cost of producing microarray chips. As a result, the widely used standard covariance estimator is not appropriate for this purpose. One such technique is the Hotelling's T2 statistic which is a multivariate test statistic for comparing means between two groups. It requires that the number of observations (n) exceeds the number of genes (p) in the set but in microarray studies it is common that n < p. This leads to a biased estimate of the covariance matrix. In this study, the Hotelling's T2 statistic with the shrinkage approach is proposed to estimate the covariance matrix for testing differential gene expression. The performance of this approach is then compared with other commonly used multivariate tests using a widely analysed diabetes data set as illustrations. The results across the methods are consistent, implying that this approach provides an alternative to existing techniques.

  16. Density matrix renormalization group numerical study of the kagome antiferromagnet.

    PubMed

    Jiang, H C; Weng, Z Y; Sheng, D N

    2008-09-12

    We numerically study the spin-1/2 antiferromagnetic Heisenberg model on the kagome lattice using the density-matrix renormalization group method. We find that the ground state is a magnetically disordered spin liquid, characterized by an exponential decay of spin-spin correlation function in real space and a magnetic structure factor showing system-size independent peaks at commensurate magnetic wave vectors. We obtain a spin triplet excitation gap DeltaE(S=1)=0.055+/-0.005 by extrapolation based on the large size results, and confirm the presence of gapless singlet excitations. The physical nature of such an exotic spin liquid is also discussed.

  17. Fractional spin in reduced density-matrix functional theory.

    PubMed

    Helbig, N; Theodorakopoulos, G; Lathiotakis, N N

    2011-08-01

    We study the behavior of different functionals of the one-body reduced density matrix (1RDM) for systems with fractional z-component of the total spin. We define these systems as ensembles of integer spin states. It is shown that, similarly to density functional theory, the error in the dissociation of diatomic molecules is directly related to the deviation from constancy of the atomic total energies as functions of the fractional spin. However, several functionals of the 1RDM show a size inconsistency which leads to additional errors. We also investigate the difference between a direct evaluation of the energy of an ensemble of integer-spin systems and a direct minimization of the energy of a fractional-spin system.

  18. The problem of the universal density functional and the density matrix functional theory

    SciTech Connect

    Bobrov, V. B. Trigger, S. A.

    2013-04-15

    The analysis in this paper shows that the Hohenberg-Kohn theorem is the constellation of two statements: (i) the mathematically rigorous Hohenberg-Kohn lemma, which demonstrates that the same ground-state density cannot correspond to two different potentials of an external field, and (ii) the hypothesis of the existence of the universal density functional. Based on the obtained explicit expression for the nonrel-ativistic particle energy in a local external field, we prove that the energy of the system of more than two non-interacting electrons cannot be a functional of the inhomogeneous density. This result is generalized to the system of interacting electrons. It means that the Hohenberg-Kohn lemma cannot provide justification of the universal density functional for fermions. At the same time, statements of the density functional theory remain valid when considering any number of noninteracting ground-state bosons due to the Bose condensation effect. In the framework of the density matrix functional theory, the hypothesis of the existence of the universal density matrix functional corresponds to the cases of noninteracting particles and to interaction in the Hartree-Fock approximation.

  19. Generalized Pauli constraints in reduced density matrix functional theory

    NASA Astrophysics Data System (ADS)

    Theophilou, Iris; Lathiotakis, Nektarios N.; Marques, Miguel A. L.; Helbig, Nicole

    2015-04-01

    Functionals of the one-body reduced density matrix (1-RDM) are routinely minimized under Coleman's ensemble N-representability conditions. Recently, the topic of pure-state N-representability conditions, also known as generalized Pauli constraints, received increased attention following the discovery of a systematic way to derive them for any number of electrons and any finite dimensionality of the Hilbert space. The target of this work is to assess the potential impact of the enforcement of the pure-state conditions on the results of reduced density-matrix functional theory calculations. In particular, we examine whether the standard minimization of typical 1-RDM functionals under the ensemble N-representability conditions violates the pure-state conditions for prototype 3-electron systems. We also enforce the pure-state conditions, in addition to the ensemble ones, for the same systems and functionals and compare the correlation energies and optimal occupation numbers with those obtained by the enforcement of the ensemble conditions alone.

  20. Generalized Pauli constraints in reduced density matrix functional theory

    SciTech Connect

    Theophilou, Iris; Helbig, Nicole; Lathiotakis, Nektarios N.; Marques, Miguel A. L.

    2015-04-21

    Functionals of the one-body reduced density matrix (1-RDM) are routinely minimized under Coleman’s ensemble N-representability conditions. Recently, the topic of pure-state N-representability conditions, also known as generalized Pauli constraints, received increased attention following the discovery of a systematic way to derive them for any number of electrons and any finite dimensionality of the Hilbert space. The target of this work is to assess the potential impact of the enforcement of the pure-state conditions on the results of reduced density-matrix functional theory calculations. In particular, we examine whether the standard minimization of typical 1-RDM functionals under the ensemble N-representability conditions violates the pure-state conditions for prototype 3-electron systems. We also enforce the pure-state conditions, in addition to the ensemble ones, for the same systems and functionals and compare the correlation energies and optimal occupation numbers with those obtained by the enforcement of the ensemble conditions alone.

  1. Density matrix embedding in an antisymmetrized geminal power bath

    SciTech Connect

    Tsuchimochi, Takashi; Welborn, Matthew; Van Voorhis, Troy

    2015-07-14

    Density matrix embedding theory (DMET) has emerged as a powerful tool for performing wave function-in-wave function embedding for strongly correlated systems. In traditional DMET, an accurate calculation is performed on a small impurity embedded in a mean field bath. Here, we extend the original DMET equations to account for correlation in the bath via an antisymmetrized geminal power (AGP) wave function. The resulting formalism has a number of advantages. First, it allows one to properly treat the weak correlation limit of independent pairs, which DMET is unable to do with a mean-field bath. Second, it associates a size extensive correlation energy with a given density matrix (for the models tested), which AGP by itself is incapable of providing. Third, it provides a reasonable description of charge redistribution in strongly correlated but non-periodic systems. Thus, AGP-DMET appears to be a good starting point for describing electron correlation in molecules, which are aperiodic and possess both strong and weak electron correlation.

  2. Watching excitons move: the time-dependent transition density matrix

    NASA Astrophysics Data System (ADS)

    Ullrich, Carsten

    2012-02-01

    Time-dependent density-functional theory allows one to calculate excitation energies and the associated transition densities in principle exactly. The transition density matrix (TDM) provides additional information on electron-hole localization and coherence of specific excitations of the many-body system. We have extended the TDM concept into the real-time domain in order to visualize the excited-state dynamics in conjugated molecules. The time-dependent TDM is defined as an implicit density functional, and can be approximately obtained from the time-dependent Kohn-Sham orbitals. The quality of this approximation is assessed in simple model systems. A computational scheme for real molecular systems is presented: the time-dependent Kohn-Sham equations are solved with the OCTOPUS code and the time-dependent Kohn-Sham TDM is calculated using a spatial partitioning scheme. The method is applied to show in real time how locally created electron-hole pairs spread out over neighboring conjugated molecular chains. The coupling mechanism, electron-hole coherence, and the possibility of charge separation are discussed.

  3. A random matrix approach to language acquisition

    NASA Astrophysics Data System (ADS)

    Nicolaidis, A.; Kosmidis, Kosmas; Argyrakis, Panos

    2009-12-01

    Since language is tied to cognition, we expect the linguistic structures to reflect patterns that we encounter in nature and are analyzed by physics. Within this realm we investigate the process of lexicon acquisition, using analytical and tractable methods developed within physics. A lexicon is a mapping between sounds and referents of the perceived world. This mapping is represented by a matrix and the linguistic interaction among individuals is described by a random matrix model. There are two essential parameters in our approach. The strength of the linguistic interaction β, which is considered as a genetically determined ability, and the number N of sounds employed (the lexicon size). Our model of linguistic interaction is analytically studied using methods of statistical physics and simulated by Monte Carlo techniques. The analysis reveals an intricate relationship between the innate propensity for language acquisition β and the lexicon size N, N~exp(β). Thus a small increase of the genetically determined β may lead to an incredible lexical explosion. Our approximate scheme offers an explanation for the biological affinity of different species and their simultaneous linguistic disparity.

  4. Advanced density matrix renormalization group method for nuclear structure calculations

    NASA Astrophysics Data System (ADS)

    Legeza, Ã.-.; Veis, L.; Poves, A.; Dukelsky, J.

    2015-11-01

    We present an efficient implementation of the Density Matrix Renormalization Group (DMRG) algorithm that includes an optimal ordering of the proton and neutron orbitals and an efficient expansion of the active space utilizing various concepts of quantum information theory. We first show how this new DMRG methodology could solve a previous 400 keV discrepancy in the ground state energy of 56Ni. We then report the first DMRG results in the p f +g 9 /2 shell model space for the ground 0+ and first 2+ states of 64Ge which are benchmarked with reference data obtained from a Monte Carlo shell model. The corresponding correlation structure among the proton and neutron orbitals is determined in terms of two-orbital mutual information. Based on such correlation graphs we propose several further algorithmic improvement possibilities that can be utilized in a new generation of tensor network based algorithms.

  5. Thouless theorem for matrix product states and subsequent post density matrix renormalization group methods

    NASA Astrophysics Data System (ADS)

    Wouters, Sebastian; Nakatani, Naoki; Van Neck, Dimitri; Chan, Garnet Kin-Lic

    2013-08-01

    The similarities between Hartree-Fock (HF) theory and the density matrix renormalization group (DMRG) are explored. Both methods can be formulated as the variational optimization of a wave-function Ansatz. Linearization of the time-dependent variational principle near a variational minimum allows to derive the random phase approximation (RPA). We show that the nonredundant parameterization of the matrix product state (MPS) tangent space [J. Haegeman, J. I. Cirac, T. J. Osborne, I. Pižorn, H. Verschelde, and F. Verstraete, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.107.070601 107, 070601 (2011)] leads to the Thouless theorem for MPS, i.e., an explicit nonredundant parameterization of the entire MPS manifold, starting from a specific MPS reference. Excitation operators are identified, which extends the analogy between HF and DMRG to the Tamm-Dancoff approximation (TDA), the configuration interaction (CI) expansion, and coupled cluster theory. For a small one-dimensional Hubbard chain, we use a CI-MPS Ansatz with single and double excitations to improve on the ground state and to calculate low-lying excitation energies. For a symmetry-broken ground state of this model, we show that RPA-MPS allows to retrieve the Goldstone mode. We also discuss calculations of the RPA-MPS correlation energy. With the long-range quantum chemical Pariser-Parr-Pople Hamiltonian, low-lying TDA-MPS and RPA-MPS excitation energies for polyenes are obtained.

  6. Density matrix reconstruction of a large angular momentum

    NASA Astrophysics Data System (ADS)

    Klose, Gerd

    2001-10-01

    A complete description of the quantum state of a physical system is the fundamental knowledge necessary to statistically predict the outcome of measurements. In turning this statement around, Wolfgang Pauli raised already in 1933 the question, whether an unknown quantum state could be uniquely determined by appropriate measurements-a problem that has gained new relevance in recent years. In order to harness the prospects of quantum computing, secure communication, teleportation, and the like, the development of techniques to accurately control and measure quantum states has now become a matter of practical as well as fundamental interest. However, there is no general answer to Pauli's very basic question, and quantum state reconstruction algorithms have been developed and experimentally demonstrated only for a few systems so far. This thesis presents a novel experimental method to measure the unknown and generally mixed quantum state for an angular momentum of arbitrary magnitude. The (2F + 1) x (2F + 1) density matrix describing the quantum state is hereby completely determined from a set of Stern-Gerlach measurements with (4F + 1) different orientations of the quantization axis. This protocol is implemented for laser cooled Cesium atoms in the 6S1/2(F = 4) hyperfine ground state manifold, and is applied to a number of test states prepared by optical pumping and Larmor precession. A comparison of the input and the measured states shows successful reconstructions with fidelities of about 0.95.

  7. Reduced density-matrix functional theory: Correlation and spectroscopy

    SciTech Connect

    Di Sabatino, S.; Romaniello, P.; Berger, J. A.; Reining, L.

    2015-07-14

    In this work, we explore the performance of approximations to electron correlation in reduced density-matrix functional theory (RDMFT) and of approximations to the observables calculated within this theory. Our analysis focuses on the calculation of total energies, occupation numbers, removal/addition energies, and spectral functions. We use the exactly solvable Hubbard dimer at 1/4 and 1/2 fillings as test systems. This allows us to analyze the underlying physics and to elucidate the origin of the observed trends. For comparison, we also report the results of the GW approximation, where the self-energy functional is approximated, but no further hypothesis is made concerning the approximations of the observables. In particular, we focus on the atomic limit, where the two sites of the dimer are pulled apart and electrons localize on either site with equal probability, unless a small perturbation is present: this is the regime of strong electron correlation. In this limit, using the Hubbard dimer at 1/2 filling with or without a spin-symmetry-broken ground state allows us to explore how degeneracies and spin-symmetry breaking are treated in RDMFT. We find that, within the used approximations, neither in RDMFT nor in GW, the signature of strong correlation is present, when looking at the removal/addition energies and spectral function from the spin-singlet ground state, whereas both give the exact result for the spin-symmetry broken case. Moreover, we show how the spectroscopic properties change from one spin structure to the other.

  8. The origin of linear scaling Fock matrix calculation with density prescreening

    NASA Astrophysics Data System (ADS)

    Mitin, Alexander V.

    2015-12-01

    A theorem was proven, which reads that the number of nonzero two-electron integrals scales linearly with respect to the number of basis functions for large molecular systems. This permits to show that linear scaling property of the Fock matrix calculation with using density prescreening arises due to linear scaling properties of the number of nonzero two-electron integrals and the number of leading matrix elements of density matrix. This property is reinforced by employing the density prescreening technique. The use of the density difference prescreening further improves the linear scaling property of the Fock matrix calculation method. As a result, the linear scaling regime of the Fock matrix calculation can begin from the number of basis functions of 2000-3000 in dependence on the basis function type in molecular calculations. It was also shown that the conventional algorithm of Fock matrix calculation from stored nonzero two-electron integrals with density prescreening possesses linear scaling property.

  9. The origin of linear scaling Fock matrix calculation with density prescreening

    SciTech Connect

    Mitin, Alexander V.

    2015-12-31

    A theorem was proven, which reads that the number of nonzero two-electron integrals scales linearly with respect to the number of basis functions for large molecular systems. This permits to show that linear scaling property of the Fock matrix calculation with using density prescreening arises due to linear scaling properties of the number of nonzero two-electron integrals and the number of leading matrix elements of density matrix. This property is reinforced by employing the density prescreening technique. The use of the density difference prescreening further improves the linear scaling property of the Fock matrix calculation method. As a result, the linear scaling regime of the Fock matrix calculation can begin from the number of basis functions of 2000–3000 in dependence on the basis function type in molecular calculations. It was also shown that the conventional algorithm of Fock matrix calculation from stored nonzero two-electron integrals with density prescreening possesses linear scaling property.

  10. Performance of the density matrix functional theory in the quantum theory of atoms in molecules.

    PubMed

    García-Revilla, Marco; Francisco, E; Costales, A; Martín Pendás, A

    2012-02-01

    The generalization to arbitrary molecular geometries of the energetic partitioning provided by the atomic virial theorem of the quantum theory of atoms in molecules (QTAIM) leads to an exact and chemically intuitive energy partitioning scheme, the interacting quantum atoms (IQA) approach, that depends on the availability of second-order reduced density matrices (2-RDMs). This work explores the performance of this approach in particular and of the QTAIM in general with approximate 2-RDMs obtained from the density matrix functional theory (DMFT), which rests on the natural expansion (natural orbitals and their corresponding occupation numbers) of the first-order reduced density matrix (1-RDM). A number of these functionals have been implemented in the promolden code and used to perform QTAIM and IQA analyses on several representative molecules and model chemical reactions. Total energies, covalent intra- and interbasin exchange-correlation interactions, as well as localization and delocalization indices have been determined with these functionals from 1-RDMs obtained at different levels of theory. Results are compared to the values computed from the exact 2-RDMs, whenever possible.

  11. Performance of the density matrix functional theory in the quantum theory of atoms in molecules.

    PubMed

    García-Revilla, Marco; Francisco, E; Costales, A; Martín Pendás, A

    2012-02-01

    The generalization to arbitrary molecular geometries of the energetic partitioning provided by the atomic virial theorem of the quantum theory of atoms in molecules (QTAIM) leads to an exact and chemically intuitive energy partitioning scheme, the interacting quantum atoms (IQA) approach, that depends on the availability of second-order reduced density matrices (2-RDMs). This work explores the performance of this approach in particular and of the QTAIM in general with approximate 2-RDMs obtained from the density matrix functional theory (DMFT), which rests on the natural expansion (natural orbitals and their corresponding occupation numbers) of the first-order reduced density matrix (1-RDM). A number of these functionals have been implemented in the promolden code and used to perform QTAIM and IQA analyses on several representative molecules and model chemical reactions. Total energies, covalent intra- and interbasin exchange-correlation interactions, as well as localization and delocalization indices have been determined with these functionals from 1-RDMs obtained at different levels of theory. Results are compared to the values computed from the exact 2-RDMs, whenever possible. PMID:21943031

  12. Density-matrix operatorial solution of the non-Markovian master equation for quantum Brownian motion

    SciTech Connect

    Intravaia, F.; Maniscalco, S.; Messina, A.

    2003-04-01

    An original method to exactly solve the non-Markovian master equation describing the interaction of a single harmonic oscillator with a quantum environment in the weak-coupling limit is reported. By using a superoperatorial approach, we succeed in deriving the operatorial solution for the density matrix of the system. Our method is independent of the physical properties of the environment. We show the usefulness of our solution deriving explicit expressions for the dissipative time evolution of some observables of physical interest for the system, such as, for example, its mean energy.

  13. Statistical approach to nuclear level density

    SciTech Connect

    Sen'kov, R. A.; Horoi, M.; Zelevinsky, V. G.

    2014-10-15

    We discuss the level density in a finite many-body system with strong interaction between the constituents. Our primary object of applications is the atomic nucleus but the same techniques can be applied to other mesoscopic systems. We calculate and compare nuclear level densities for given quantum numbers obtained by different methods, such as nuclear shell model (the most successful microscopic approach), our main instrument - moments method (statistical approach), and Fermi-gas model; the calculation with the moments method can use any shell-model Hamiltonian excluding the spurious states of the center-of-mass motion. Our goal is to investigate statistical properties of nuclear level density, define its phenomenological parameters, and offer an affordable and reliable way of calculation.

  14. Nuclear level density: Shell-model approach

    NASA Astrophysics Data System (ADS)

    Sen'kov, Roman; Zelevinsky, Vladimir

    2016-06-01

    Knowledge of the nuclear level density is necessary for understanding various reactions, including those in the stellar environment. Usually the combinatorics of a Fermi gas plus pairing is used for finding the level density. Recently a practical algorithm avoiding diagonalization of huge matrices was developed for calculating the density of many-body nuclear energy levels with certain quantum numbers for a full shell-model Hamiltonian. The underlying physics is that of quantum chaos and intrinsic thermalization in a closed system of interacting particles. We briefly explain this algorithm and, when possible, demonstrate the agreement of the results with those derived from exact diagonalization. The resulting level density is much smoother than that coming from conventional mean-field combinatorics. We study the role of various components of residual interactions in the process of thermalization, stressing the influence of incoherent collision-like processes. The shell-model results for the traditionally used parameters are also compared with standard phenomenological approaches.

  15. A random matrix approach to credit risk.

    PubMed

    Münnix, Michael C; Schäfer, Rudi; Guhr, Thomas

    2014-01-01

    We estimate generic statistical properties of a structural credit risk model by considering an ensemble of correlation matrices. This ensemble is set up by Random Matrix Theory. We demonstrate analytically that the presence of correlations severely limits the effect of diversification in a credit portfolio if the correlations are not identically zero. The existence of correlations alters the tails of the loss distribution considerably, even if their average is zero. Under the assumption of randomly fluctuating correlations, a lower bound for the estimation of the loss distribution is provided.

  16. A Random Matrix Approach to Credit Risk

    PubMed Central

    Guhr, Thomas

    2014-01-01

    We estimate generic statistical properties of a structural credit risk model by considering an ensemble of correlation matrices. This ensemble is set up by Random Matrix Theory. We demonstrate analytically that the presence of correlations severely limits the effect of diversification in a credit portfolio if the correlations are not identically zero. The existence of correlations alters the tails of the loss distribution considerably, even if their average is zero. Under the assumption of randomly fluctuating correlations, a lower bound for the estimation of the loss distribution is provided. PMID:24853864

  17. Energy density matrix formalism for interacting quantum systems: Quantum Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Krogel, Jaron T.; Kim, Jeongnim; Reboredo, Fernando A.

    2014-07-01

    We develop an energy density matrix that parallels the one-body reduced density matrix (1RDM) for many-body quantum systems. Just as the density matrix gives access to the number density and occupation numbers, the energy density matrix yields the energy density and orbital occupation energies. The eigenvectors of the matrix provide a natural orbital partitioning of the energy density while the eigenvalues comprise a single-particle energy spectrum obeying a total energy sum rule. For mean-field systems the energy density matrix recovers the exact spectrum. When correlation becomes important, the occupation energies resemble quasiparticle energies in some respects. We explore the occupation energy spectrum for the finite 3D homogeneous electron gas in the metallic regime and an isolated oxygen atom with ground-state quantum Monte Carlo techniques implemented in the qmcpack simulation code. The occupation energy spectrum for the homogeneous electron gas can be described by an effective mass below the Fermi level. Above the Fermi level evanescent behavior in the occupation energies is observed in similar fashion to the occupation numbers of the 1RDM. A direct comparison with total energy differences shows a quantitative connection between the occupation energies and electron addition and removal energies for the electron gas. For the oxygen atom, the association between the ground-state occupation energies and particle addition and removal energies becomes only qualitative. The energy density matrix provides an avenue for describing energetics with quantum Monte Carlo methods which have traditionally been limited to total energies.

  18. Time-dependent occupation numbers in reduced-density-matrix-functional theory: Application to an interacting Landau-Zener model

    SciTech Connect

    Requist, Ryan; Pankratov, Oleg

    2011-05-15

    We prove that if the two-body terms in the equation of motion for the one-body reduced density matrix are approximated by ground-state functionals, the eigenvalues of the one-body reduced density matrix (occupation numbers) remain constant in time. This deficiency is related to the inability of such an approximation to account for relative phases in the two-body reduced density matrix. We derive an exact differential equation giving the functional dependence of these phases in an interacting Landau-Zener model and study their behavior in short- and long-time regimes. The phases undergo resonances whenever the occupation numbers approach the boundaries of the interval [0,1]. In the long-time regime, the occupation numbers display correlation-induced oscillations and the memory dependence of the functionals assumes a simple form.

  19. Reduced-density-matrix description for pump-probe optical phenomena in moving atomic systems

    NASA Astrophysics Data System (ADS)

    Jacobs, V. L.

    2014-09-01

    Linear and nonlinear (especially coherent) electromagnetic interactions of moving many-electron atoms are investigated using a reduced-density-matrix description, which is applied to electromagnetically induced transparency and related resonant pump-probe optical phenomena. External magnetic fields are included on an equal footing with the electromagnetic fields and spin-Zeeman interactions are taken into account. Complimentary time-domain (equation-of-motion) and frequency-domain (resolvent-operator) formulations of the reduced-density-matrix description are self-consistently developed. The general nonperturbative and non-Markovian formulations provide a fundamental framework for systematic evaluations of corrections to the standard Born (lowest-order-perturbation) and Markov (short-memory-time) approximations. The macroscopic electromagnetic response is described semiclassically, employing a perturbation expansion of the reduced-density operator in powers of the classical electromagnetic field. Our primary results are compact Liouville-space operator expressions for the linear and general (nth-order) nonlinear macroscopic electromagnetic-response tensors, which can be evaluated for nonlocal and nonstationary optical media described by multilevel atomic-system representations. Interactions among atoms and with environmental photons are treated as line-broadening effects by means of a general Liouville-space self-energy operator, for which the tetradic-matrix elements are explicitly evaluated in the diagonal, lowest-order, and Markov approximations. The compact Liouville-space operator expressions that are derived for the macroscopic electromagnetic-response tensors are introduced into the dynamical description of the electromagnetic-field propagation. It is pointed out that a quantized-electromagnetic-field approach will be required for a fully self-consistent quantum-mechanical treatment of local-field effects and radiative corrections.

  20. Iterative linearized density matrix propagation for modeling coherent excitation energy transfer in photosynthetic light harvesting.

    PubMed

    Huo, P; Coker, D F

    2010-11-14

    Rather than incoherent hopping between chromophores, experimental evidence suggests that the excitation energy transfer in some biological light harvesting systems initially occurs coherently, and involves coherent superposition states in which excitation spreads over multiple chromophores separated by several nanometers. Treating such delocalized coherent superposition states in the presence of decoherence and dissipation arising from coupling to an environment is a significant challenge for conventional theoretical tools that either use a perturbative approach or make the Markovian approximation. In this paper, we extend the recently developed iterative linearized density matrix (ILDM) propagation scheme [E. R. Dunkel et al., J. Chem. Phys. 129, 114106 (2008)] to study coherent excitation energy transfer in a model of the Fenna-Matthews-Olsen light harvesting complex from green sulfur bacteria. This approach is nonperturbative and uses a discrete path integral description employing a short time approximation to the density matrix propagator that accounts for interference between forward and backward paths of the quantum excitonic system while linearizing the phase in the difference between the forward and backward paths of the environmental degrees of freedom resulting in a classical-like treatment of these variables. The approach avoids making the Markovian approximation and we demonstrate that it successfully describes the coherent beating of the site populations on different chromophores and gives good agreement with other methods that have been developed recently for going beyond the usual approximations, thus providing a new reliable theoretical tool to study coherent exciton transfer in light harvesting systems. We conclude with a discussion of decoherence in independent bilinearly coupled harmonic chromophore baths. The ILDM propagation approach in principle can be applied to more general descriptions of the environment.

  1. Modeling for Matrix Multicracking Evolution of Cross-ply Ceramic-Matrix Composites Using Energy Balance Approach

    NASA Astrophysics Data System (ADS)

    Longbiao, Li

    2015-12-01

    The matrix multicracking evolution of cross-ply ceramic-matrix composites (CMCs) has been investigated using energy balance approach. The multicracking of cross-ply CMCs was classified into five modes, i.e., (1) mode 1: transverse multicracking; (2) mode 2: transverse multicracking and matrix multicracking with perfect fiber/matrix interface bonding; (3) mode 3: transverse multicracking and matrix multicracking with fiber/matrix interface debonding; (4) mode 4: matrix multicracking with perfect fiber/matrix interface bonding; and (5) mode 5: matrix multicracking with fiber/matrix interface debonding. The stress distributions of four cracking modes, i.e., mode 1, mode 2, mode 3 and mode 5, are analysed using shear-lag model. The matrix multicracking evolution of mode 1, mode 2, mode 3 and mode 5, has been determined using energy balance approach. The effects of ply thickness and fiber volume fraction on matrix multicracking evolution of cross-ply CMCs have been investigated.

  2. A Problem-Centered Approach to Canonical Matrix Forms

    ERIC Educational Resources Information Center

    Sylvestre, Jeremy

    2014-01-01

    This article outlines a problem-centered approach to the topic of canonical matrix forms in a second linear algebra course. In this approach, abstract theory, including such topics as eigenvalues, generalized eigenspaces, invariant subspaces, independent subspaces, nilpotency, and cyclic spaces, is developed in response to the patterns discovered…

  3. The transfer matrix approach to circular graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Chau Nguyen, H.; Nguyen, Nhung T. T.; Nguyen, V. Lien

    2016-07-01

    We adapt the transfer matrix (T-matrix) method originally designed for one-dimensional quantum mechanical problems to solve the circularly symmetric two-dimensional problem of graphene quantum dots. Similar to one-dimensional problems, we show that the generalized T-matrix contains rich information about the physical properties of these quantum dots. In particular, it is shown that the spectral equations for bound states as well as quasi-bound states of a circular graphene quantum dot and related quantities such as the local density of states and the scattering coefficients are all expressed exactly in terms of the T-matrix for the radial confinement potential. As an example, we use the developed formalism to analyse physical aspects of a graphene quantum dot induced by a trapezoidal radial potential. Among the obtained results, it is in particular suggested that the thermal fluctuations and electrostatic disorders may appear as an obstacle to controlling the valley polarization of Dirac electrons.

  4. A state interaction spin-orbit coupling density matrix renormalization group method.

    PubMed

    Sayfutyarova, Elvira R; Chan, Garnet Kin-Lic

    2016-06-21

    We describe a state interaction spin-orbit (SISO) coupling method using density matrix renormalization group (DMRG) wavefunctions and the spin-orbit mean-field (SOMF) operator. We implement our DMRG-SISO scheme using a spin-adapted algorithm that computes transition density matrices between arbitrary matrix product states. To demonstrate the potential of the DMRG-SISO scheme we present accurate benchmark calculations for the zero-field splitting of the copper and gold atoms, comparing to earlier complete active space self-consistent-field and second-order complete active space perturbation theory results in the same basis. We also compute the effects of spin-orbit coupling on the spin-ladder of the iron-sulfur dimer complex [Fe2S2(SCH3)4](3-), determining the splitting of the lowest quartet and sextet states. We find that the magnitude of the zero-field splitting for the higher quartet and sextet states approaches a significant fraction of the Heisenberg exchange parameter. PMID:27334156

  5. Density matrix perturbation theory for magneto-optical response of periodic insulators

    NASA Astrophysics Data System (ADS)

    Lebedeva, Irina; Tokatly, Ilya; Rubio, Angel

    2015-03-01

    Density matrix perturbation theory offers an ideal theoretical framework for the description of response of solids to arbitrary electromagnetic fields. In particular, it allows to consider perturbations introduced by uniform electric and magnetic fields under periodic boundary conditions, though the corresponding potentials break the translational invariance of the Hamiltonian. We have implemented the density matrix perturbation theory in the open-source Octopus code on the basis of the efficient Sternheimer approach. The procedures for responses of different order to electromagnetic fields, including electric polarizability, orbital magnetic susceptibility and magneto-optical response, have been developed and tested by comparison with the results for finite systems and for wavefunction-based perturbation theory, which is already available in the code. Additional analysis of the orbital magneto-optical response is performed on the basis of analytical models. Symmetry limitations to observation of the magneto-optical response are discussed. The financial support from the Marie Curie Fellowship PIIF-GA-2012-326435 (RespSpatDisp) is gratefully acknowledged.

  6. A state interaction spin-orbit coupling density matrix renormalization group method

    NASA Astrophysics Data System (ADS)

    Sayfutyarova, Elvira R.; Chan, Garnet Kin-Lic

    2016-06-01

    We describe a state interaction spin-orbit (SISO) coupling method using density matrix renormalization group (DMRG) wavefunctions and the spin-orbit mean-field (SOMF) operator. We implement our DMRG-SISO scheme using a spin-adapted algorithm that computes transition density matrices between arbitrary matrix product states. To demonstrate the potential of the DMRG-SISO scheme we present accurate benchmark calculations for the zero-field splitting of the copper and gold atoms, comparing to earlier complete active space self-consistent-field and second-order complete active space perturbation theory results in the same basis. We also compute the effects of spin-orbit coupling on the spin-ladder of the iron-sulfur dimer complex [Fe2S2(SCH3)4]3-, determining the splitting of the lowest quartet and sextet states. We find that the magnitude of the zero-field splitting for the higher quartet and sextet states approaches a significant fraction of the Heisenberg exchange parameter.

  7. A state interaction spin-orbit coupling density matrix renormalization group method.

    PubMed

    Sayfutyarova, Elvira R; Chan, Garnet Kin-Lic

    2016-06-21

    We describe a state interaction spin-orbit (SISO) coupling method using density matrix renormalization group (DMRG) wavefunctions and the spin-orbit mean-field (SOMF) operator. We implement our DMRG-SISO scheme using a spin-adapted algorithm that computes transition density matrices between arbitrary matrix product states. To demonstrate the potential of the DMRG-SISO scheme we present accurate benchmark calculations for the zero-field splitting of the copper and gold atoms, comparing to earlier complete active space self-consistent-field and second-order complete active space perturbation theory results in the same basis. We also compute the effects of spin-orbit coupling on the spin-ladder of the iron-sulfur dimer complex [Fe2S2(SCH3)4](3-), determining the splitting of the lowest quartet and sextet states. We find that the magnitude of the zero-field splitting for the higher quartet and sextet states approaches a significant fraction of the Heisenberg exchange parameter.

  8. Development of edge effects around experimental ecosystem hotspots is affected by edge density and matrix type

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Ecological edge effects are sensitive to landscape context. In particular, edge effects can be altered by matrix type and by the presence of other nearby edges. We experimentally altered patch configurations in an African savanna to determine how edge density and matrix type influence edge effect de...

  9. Structure of icosahedral quasicrystals and density-matrix functional theory for correlation effects

    NASA Astrophysics Data System (ADS)

    Hennig, Richard Georg

    In the first part of this work, the atomic and electronic structure as well as the energetics of the icosahedral TiZrNi quasicrystal and the 1/1 approximant W-TiZrNi were determined. An atomic decoration model for the quasicrystal was developed invoking similarities to the structure of the 1/1 approximant. The structure of the quasicrystal was refined using a combined approach of diffraction refinement and ab initio calculations. The ternary ground state phase diagram was calculated using density-functional calculations. It was found that the TiZrNi quasicrystal is lower in energy than the competing phases indicating that it is a ground state quasicrystal. The electronic density of states of the quasicrystals shows a pseudogap. The hydrogen site energy distribution of the approximant was calculated and it was shown that a determination of the distribution by chemical potential measurements is impossible due to its complexity and the strong temperature and concentration dependent hydrogen-hydrogen interactions. In the second part of this work a density-matrix functional for isolated impurities was developed. The density-matrix functional for the electron interaction energy, was based on two theorems proved in this work. It was shown that the second-moment approximation yields the exact ground state for a dimer molecule with arbitrary on-site and inter-site Coulomb interactions. The second-moment approximation is implemented as a variational method. By comparison to results from exact diagonalization and the Hartree-Fock method it was shown that the functional was accurate in the case of isolated impurities. The combined effect of disorder and electron interactions for the model of an Anderson impurity in a random alloy were investigated and unexpected crossover behavior in the effects of disorder and electron interactions on the spin fluctuations was found. As a first application of the second-moment approximation, the electronic structure of dangling-bond defects

  10. Hybrid-Space Density Matrix Renormalization Group Study of the Two-Dimensional Hubbard Model

    NASA Astrophysics Data System (ADS)

    Ehlers, Georg; Noack, Reinhard M.

    We investigate the ground state of the two-dimensional Hubbard model on a cylinder geometry at intermediate coupling and weak doping. We study properties such as the behavior of the ground-state energy, pair-field correlations, and the appearance of stripes. We find striped ground states generically, with the width of the stripes depending on the filling, the boundary conditions, and the circumference of the cylinder. Furthermore, we analyse the interplay between the different stripe configurations and the decay of the pairing correlations. Our analysis is based on a hybrid-space density matrix renormalization group (DMRG) approach, which uses a momentum-space representation in the transverse and a real-space representation in the longitudinal direction. Exploiting the transverse momentum quantum number makes significant speedup and memory savings compared to the real-space DMRG possible. In particular, we obtain computational costs that are independent of the cylinder width for fixed size of the truncated Hilbert space.

  11. Symmetry-conserving purification of quantum states within the density matrix renormalization group

    NASA Astrophysics Data System (ADS)

    Nocera, A.; Alvarez, G.

    2016-01-01

    The density matrix renormalization group (DMRG) algorithm was originally designed to efficiently compute the zero-temperature or ground-state properties of one-dimensional strongly correlated quantum systems. The development of the algorithm at finite temperature has been a topic of much interest, because of the usefulness of thermodynamics quantities in understanding the physics of condensed matter systems, and because of the increased complexity associated with efficiently computing temperature-dependent properties. The ancilla method is a DMRG technique that enables the computation of these thermodynamic quantities. In this paper, we review the ancilla method, and improve its performance by working on reduced Hilbert spaces and using canonical approaches. We furthermore explore its applicability beyond spins systems to t -J and Hubbard models.

  12. Symmetry-conserving purification of quantum states within the density matrix renormalization group

    DOE PAGESBeta

    Nocera, Alberto; Alvarez, Gonzalo

    2016-01-28

    The density matrix renormalization group (DMRG) algorithm was originally designed to efficiently compute the zero-temperature or ground-state properties of one-dimensional strongly correlated quantum systems. The development of the algorithm at finite temperature has been a topic of much interest, because of the usefulness of thermodynamics quantities in understanding the physics of condensed matter systems, and because of the increased complexity associated with efficiently computing temperature-dependent properties. The ancilla method is a DMRG technique that enables the computation of these thermodynamic quantities. In this paper, we review the ancilla method, and improve its performance by working on reduced Hilbert spaces andmore » using canonical approaches. Furthermore we explore its applicability beyond spins systems to t-J and Hubbard models.« less

  13. Construct order parameters from the reduced density matrix spectra

    SciTech Connect

    Gu, Shi-Jian; Yu, Wing Chi; Lin, Hai-Qing

    2013-09-15

    In this paper, we try to establish a connection between a quantum information concept, i.e., the mutual information, and the conventional order parameter in condensed matter physics. We show that non-vanishing mutual information between two subsystems separated by a long distance means the existence of long-range orders in the system. By analyzing the spectra of the reduced density matrices that are used to calculate the mutual information, we show how to derive the local order operators that identify various ordered phases in condensed matter physics. -- Highlights: •Discussed the relation between long-range order and the mutual information (MI). •Pointed out how to check the existence of long-range order from MI. •Proposed a scheme to derive the diagonal and off-diagonal order parameter. •Gave three examples to show the effectiveness of the scheme.

  14. Evaluation of a Matrix Management Approach to School Organizations.

    ERIC Educational Resources Information Center

    Gogolin, Marilyn T.; Martois, John S.

    The Management Responsibility Guidance (MRG) process is a matrix management program designed to clarify roles and improve staff integration, decision-making, effectiveness, and productivity. In 1976-77, Los Angeles County (California) used this approach in four pilot special education schools. As part of the MRG process, each staff member…

  15. Matrix density effects on the mechanical properties of SiC fiber-reinforced silicon nitride matrix properties

    NASA Technical Reports Server (NTRS)

    Bhatt, Ramakrishna T.; Kiser, Lames D.

    1990-01-01

    The room temperature mechanical properties were measured for SiC fiber reinforced reaction-bonded silicon nitride composites (SiC/RBSN) of different densities. The composites consisted of approx. 30 vol percent uniaxially aligned 142 micron diameter SiC fibers (Textron SCS-6) in a reaction-bonded Si3N4 matrix. The composite density was varied by changing the consolidation pressure during RBSN processing and by hot isostatically pressing the SiC/RBSN composites. Results indicate that as the consolidation pressure was increased from 27 to 138 MPa, the average pore size of the nitrided composites decreased from 0.04 to 0.02 microns and the composite density increased from 2.07 to 2.45 gm/cc. Nonetheless, these improvements resulted in only small increases in the first matrix cracking stress, primary elastic modulus, and ultimate tensile strength values of the composites. In contrast, HIP consolidation of SiC/RBSN resulted in a fully dense material whose first matrix cracking stress and elastic modulus were approx. 15 and 50 percent higher, respectively, and ultimate tensile strength values were approx. 40 percent lower than those for unHIPed SiC/RBSN composites. The modulus behavior for all specimens can be explained by simple rule-of-mixture theory. Also, the loss in ultimate strength for the HIPed composites appears to be related to a degradation in fiber strength at the HIP temperature. However, the density effect on matrix fracture strength was much less than would be expected based on typical monolithic Si3N4 behavior, suggesting that composite theory is indeed operating. Possible practical implications of these observations are discussed.

  16. A Surrogate Measure of Cortical Bone Matrix Density by Long T2 -Suppressed MRI.

    PubMed

    Seifert, Alan C; Li, Cheng; Wehrli, Suzanne L; Wehrli, Felix W

    2015-12-01

    Magnetic resonance has the potential to image and quantify two pools of water within bone: free water within the Haversian pore system (transverse relaxation time, T2 > 1 ms), and water hydrogen-bonded to matrix collagen (T2 ∼ 300 to 400 μs). Although total bone water concentration quantified by MRI has been shown to scale with porosity, greater insight into bone matrix density and porosity may be gained by relaxation-based separation of bound and pore water fractions. The objective of this study was to evaluate a recently developed surrogate measurement for matrix density, single adiabatic inversion recovery (SIR) zero echo-time (ZTE) MRI, in human bone. Specimens of tibial cortical bone from 15 donors (aged 27 to 97 years; 8 female and 7 male) were examined at 9.4T field strength using two methods: (1) (1)H ZTE MRI, to capture total (1)H signal, and (2) (1)H SIR-ZTE MRI, to selectively image matrix-associated (1)H signal. Total water, bone matrix, and bone mineral densities were also quantified gravimetrically, and porosity was measured by micro-CT. ZTE apparent total water (1)H concentration was 32.7 ± 3.2 M (range 28.5 to 40.3 M), and was correlated positively with porosity (R(2) = 0.80) and negatively with matrix and mineral densities (R(2) =  0.90 and 0.82, respectively). SIR-ZTE apparent bound water (1)H concentration was 32.9 ± 3.9 M (range 24.4 to 39.8 M), and its correlations were opposite to those of apparent total water: negative with porosity (R(2) = 0.73) and positive with matrix density (R(2) = 0.74) and mineral density (R(2) = 0.72). Porosity was strongly correlated with gravimetric matrix density (R(2) = 0.91, negative) and total water density (R(2) = 0.92, positive). The strong correlations of SIR-ZTE-derived apparent bound water (1)H concentration with ground-truth measurements suggest that this quantitative solid-state MRI method provides a nondestructive surrogate measure of bone matrix density

  17. Density-matrix based determination of low-energy model Hamiltonians from ab initio wavefunctions

    SciTech Connect

    Changlani, Hitesh J.; Zheng, Huihuo; Wagner, Lucas K.

    2015-09-14

    We propose a way of obtaining effective low energy Hubbard-like model Hamiltonians from ab initio quantum Monte Carlo calculations for molecular and extended systems. The Hamiltonian parameters are fit to best match the ab initio two-body density matrices and energies of the ground and excited states, and thus we refer to the method as ab initio density matrix based downfolding. For benzene (a finite system), we find good agreement with experimentally available energy gaps without using any experimental inputs. For graphene, a two dimensional solid (extended system) with periodic boundary conditions, we find the effective on-site Hubbard U{sup ∗}/t to be 1.3 ± 0.2, comparable to a recent estimate based on the constrained random phase approximation. For molecules, such parameterizations enable calculation of excited states that are usually not accessible within ground state approaches. For solids, the effective Hamiltonian enables large-scale calculations using techniques designed for lattice models.

  18. Density-matrix based determination of low-energy model Hamiltonians from ab initio wavefunctions.

    PubMed

    Changlani, Hitesh J; Zheng, Huihuo; Wagner, Lucas K

    2015-09-14

    We propose a way of obtaining effective low energy Hubbard-like model Hamiltonians from ab initio quantum Monte Carlo calculations for molecular and extended systems. The Hamiltonian parameters are fit to best match the ab initio two-body density matrices and energies of the ground and excited states, and thus we refer to the method as ab initio density matrix based downfolding. For benzene (a finite system), we find good agreement with experimentally available energy gaps without using any experimental inputs. For graphene, a two dimensional solid (extended system) with periodic boundary conditions, we find the effective on-site Hubbard U(∗)/t to be 1.3 ± 0.2, comparable to a recent estimate based on the constrained random phase approximation. For molecules, such parameterizations enable calculation of excited states that are usually not accessible within ground state approaches. For solids, the effective Hamiltonian enables large-scale calculations using techniques designed for lattice models. PMID:26374007

  19. Systematic construction of density functionals based on matrix product state computations

    NASA Astrophysics Data System (ADS)

    Lubasch, Michael; Fuks, Johanna I.; Appel, Heiko; Rubio, Angel; Cirac, J. Ignacio; Bañuls, Mari-Carmen

    2016-08-01

    We propose a systematic procedure for the approximation of density functionals in density functional theory that consists of two parts. First, for the efficient approximation of a general density functional, we introduce an efficient ansatz whose non-locality can be increased systematically. Second, we present a fitting strategy that is based on systematically increasing a reasonably chosen set of training densities. We investigate our procedure in the context of strongly correlated fermions on a one-dimensional lattice in which we compute accurate training densities with the help of matrix product states. Focusing on the exchange-correlation energy, we demonstrate how an efficient approximation can be found that includes and systematically improves beyond the local density approximation. Importantly, this systematic improvement is shown for target densities that are quite different from the training densities.

  20. The Density Matrix Renormalization Group for Strongly Correlated Electron Systems: A Generic Implementation

    SciTech Connect

    Alvarez, Gonzalo

    2009-01-01

    The purpose of this paper is (1) to present a generic and fully functional implementation of the density-matrix renormalization group (DMRG) algorithm, and (2) to describe how to write additional strongly-correlated electron models and geometries by using templated classes. Besides considering general models and geometries, the code implements Hamiltonian symmetries in a generic way and parallelization over symmetry-related matrix blocks.

  1. Prevention of accidental exposure in radiotherapy: the risk matrix approach.

    PubMed

    Vilaragut, J J; Duménigo, C; Delgado, J M; Morales, J; McDonnell, J D; Ferro, R; Ortiz López, P; Ramírez, M L; Pérez Mulas, A; Papadopulos, S; Gonçalves, M; López Morones, R; Sánchez Cayuela, C; Cascajo Castresana, A; Somoano, F; Álvarez, C; Guillén, A; Rodríguez, M; Pereira, P P; Nader, A

    2013-02-01

    Knowledge and lessons from past accidental exposures in radiotherapy are very helpful in finding safety provisions to prevent recurrence. Disseminating lessons is necessary but not sufficient. There may be additional latent risks for other accidental exposures, which have not been reported or have not occurred, but are possible and may occur in the future if not identified, analyzed, and prevented by safety provisions. Proactive methods are available for anticipating and quantifying risk from potential event sequences. In this work, proactive methods, successfully used in industry, have been adapted and used in radiotherapy. Risk matrix is a tool that can be used in individual hospitals to classify event sequences in levels of risk. As with any anticipative method, the risk matrix involves a systematic search for potential risks; that is, any situation that can cause an accidental exposure. The method contributes new insights: The application of the risk matrix approach has identified that another group of less catastrophic but still severe single-patient events may have a higher probability, resulting in higher risk. The use of the risk matrix approach for safety assessment in individual hospitals would provide an opportunity for self-evaluation and managing the safety measures that are most suitable to the hospital's own conditions. PMID:23274816

  2. Matrix sublimation method for the formation of high-density amorphous ice

    NASA Astrophysics Data System (ADS)

    Kouchi, A.; Hama, T.; Kimura, Y.; Hidaka, H.; Escribano, R.; Watanabe, N.

    2016-08-01

    A novel method for the formation of amorphous ice involving matrix sublimation has been developed. A CO-rich CO:H2O mixed ice was deposited at 8-10 K under ultra-high vacuum condition, which was then allowed to warm. After the sublimation of matrix CO at 35 K, amorphous ice remained. The amorphous ice formed exhibits a highly porous microscale texture; however, it also rather exhibits a density similar to that of high-density amorphous ice formed under high pressure. Furthermore, unlike conventional vapor-deposited amorphous ice, the amorphous ice is stable up to 140 K, where it transforms directly to cubic ice Ic.

  3. Time-dependent renormalized Redfield theory II for off-diagonal transition in reduced density matrix

    NASA Astrophysics Data System (ADS)

    Kimura, Akihiro

    2016-09-01

    In our previous letter (Kimura, 2016), we constructed time-dependent renormalized Redfield theory (TRRT) only for diagonal transition in a reduced density matrix. In this letter, we formulate the general expression for off-diagonal transition in the reduced density matrix. We discuss the applicability of TRRT by numerically comparing the dependencies on the energy gap of the exciton relaxation rate by using the TRRT and the modified Redfield theory (MRT). In particular, we roughly show that TRRT improves MRT for the detailed balance about the excitation energy transfer reaction.

  4. Alternative Approaches to High Energy Density Fusion

    NASA Astrophysics Data System (ADS)

    Hammer, J.

    2016-10-01

    This paper explores selected approaches to High Energy Density (HED) fusion, beginning with discussion of ignition requirements at the National Ignition Facility (NIF). The needed improvements to achieve ignition are closely tied to the ability to concentrate energy in the implosion, manifested in the stagnation pressure, Pstag. The energy that must be assembled in the imploded state to ignite varies roughly as Pstag-2, so among other requirements, there is a premium on reaching higher Pstag to achieve ignition with the available laser energy. The U.S. inertial confinement fusion program (ICF) is pursuing higher Pstag on NIF through improvements to capsule stability and symmetry. One can argue that recent experiments place an approximate upper bound on the ultimate ignition energy requirement. Scaling the implosions consistently in spatial, temporal and energy scales shows that implosions of the demonstrated quality ignite robustly at 9-15 times the current energy of NIF. While lasers are unlikely to reach that bounding energy, it appears that pulsed-power sources could plausibly do so, giving a range of paths forward for ICF depending on success in improving energy concentration. In this paper, I show the scaling arguments then discuss topics from my own involvement in HED fusion. The recent Viewfactor experiments at NIF have shed light on both the observed capsule drive deficit and errors in the detailed modelling of hohlraums. The latter could be important factors in the inability to achieve the needed symmetry and energy concentration. The paper then recounts earlier work in Fast Ignition and the uses of pulsed-power for HED and fusion applications. It concludes with a description of a method for improving pulsed-power driven hohlraums that could potentially provide a factor of 10 in energy at NTF-like drive conditions and reach the energy bound for indirect drive ICF.

  5. Alternative Approaches to High Energy Density Fusion

    NASA Astrophysics Data System (ADS)

    Hammer, J.

    2016-03-01

    This paper explores selected approaches to High Energy Density (HED) fusion, beginning with discussion of ignition requirements at the National Ignition Facility (NIF). The needed improvements to achieve ignition are closely tied to the ability to concentrate energy in the implosion, manifested in the stagnation pressure, Pstag . The energy that must be assembled in the imploded state to ignite varies roughly as Pstag -2, so among other requirements, there is a premium on reaching higher Pstag to achieve ignition with the available laser energy. The U.S. inertial confinement fusion program (ICF) is pursuing higher Pstag on NIF through improvements to capsule stability and symmetry. One can argue that recent experiments place an approximate upper bound on the ultimate ignition energy requirement. Scaling the implosions consistently in spatial, temporal and energy scales shows that implosions of the demonstrated quality ignite robustly at 9-15 times the current energy of NIF. While lasers are unlikely to reach that bounding energy, it appears that pulsed-power sources could plausibly do so, giving a range of paths forward for ICF depending on success in improving energy concentration. In this paper, I show the scaling arguments then discuss topics from my own involvement in HED fusion. The recent Viewfactor experiments at NIF have shed light on both the observed capsule drive deficit and errors in the detailed modelling of hohlraums. The latter could be important factors in the inability to achieve the needed symmetry and energy concentration. The paper then recounts earlier work in Fast Ignition and the uses of pulsed- power for HED and fusion applications. It concludes with a description of a method for improving pulsed-power driven hohlraums that could potentially provide a factor of 10 in energy at NIF-like drive conditions and reach the energy bound for indirect drive ICF.

  6. Computing the Density Matrix in Electronic Structure Theory on Graphics Processing Units.

    PubMed

    Cawkwell, M J; Sanville, E J; Mniszewski, S M; Niklasson, Anders M N

    2012-11-13

    The self-consistent solution of a Schrödinger-like equation for the density matrix is a critical and computationally demanding step in quantum-based models of interatomic bonding. This step was tackled historically via the diagonalization of the Hamiltonian. We have investigated the performance and accuracy of the second-order spectral projection (SP2) algorithm for the computation of the density matrix via a recursive expansion of the Fermi operator in a series of generalized matrix-matrix multiplications. We demonstrate that owing to its simplicity, the SP2 algorithm [Niklasson, A. M. N. Phys. Rev. B2002, 66, 155115] is exceptionally well suited to implementation on graphics processing units (GPUs). The performance in double and single precision arithmetic of a hybrid GPU/central processing unit (CPU) and full GPU implementation of the SP2 algorithm exceed those of a CPU-only implementation of the SP2 algorithm and traditional matrix diagonalization when the dimensions of the matrices exceed about 2000 × 2000. Padding schemes for arrays allocated in the GPU memory that optimize the performance of the CUBLAS implementations of the level 3 BLAS DGEMM and SGEMM subroutines for generalized matrix-matrix multiplications are described in detail. The analysis of the relative performance of the hybrid CPU/GPU and full GPU implementations indicate that the transfer of arrays between the GPU and CPU constitutes only a small fraction of the total computation time. The errors measured in the self-consistent density matrices computed using the SP2 algorithm are generally smaller than those measured in matrices computed via diagonalization. Furthermore, the errors in the density matrices computed using the SP2 algorithm do not exhibit any dependence of system size, whereas the errors increase linearly with the number of orbitals when diagonalization is employed.

  7. Kinetic equations for a density matrix describing nonlinear effects in spectral line wings

    SciTech Connect

    Parkhomenko, A. I. Shalagin, A. M.

    2011-11-15

    Kinetic quantum equations are derived for a density matrix with collision integrals describing nonlinear effects in spectra line wings. These equations take into account the earlier established inequality of the spectral densities of Einstein coefficients for absorption and stimulated radiation emission by a two-level quantum system in the far wing of a spectral line in the case of frequent collisions. The relationship of the absorption and stimulated emission probabilities with the characteristics of radiation and an elementary scattering event is found.

  8. Hydrogen transfer in vibrationally relaxing benzoic acid dimers: Time-dependent density matrix dynamics and infrared spectra

    NASA Astrophysics Data System (ADS)

    Scheurer, Christoph; Saalfrank, Peter

    1996-02-01

    We employ time-dependent density matrix theory to characterize the concerted double-hydrogen transfer in benzoic acid dimers—the ``system''—embedded in their crystalline environment—the ``bath.'' The Liouville-von Neumann equation for the time evolution of the reduced nuclear density matrix is solved numerically, employing one- and two-dimensional models [R. Meyer and R. R. Ernst, J. Chem. Phys. 93, 5528 (1990)], the state representation for all operators and a matrix propagator based on Newton's polynomials [M. Berman, R. Kosloff, and H. Tal-Ezer, J. Phys. A 25, 1283 (1992)]. Dissipative processes such as environment-induced vibrational energy and phase relaxation, are accounted for within the Lindblad dynamical semigroup approach. The calculation of temperature-dependent relaxation matrix elements is based on a microscopic, perturbative theory proposed earlier [R. Meyer and R. R. Ernst, J. Chem. Phys. 93, 5528 (1990)]. For the evaluation of the dissipative system dynamics, we compute (i) time-dependent state populations, (ii) energy and entropy flow between system and bath, (iii) expectation values for the hydrogen transfer coordinate, (iv) characteristic dephasing times and (v) temperature-dependent infrared spectra, determined with a recently proposed method by Neugebauer et al. Various ``pure'' and ``thermal'' nonequilibrium initial states are considered, and their equilibration with the bath followed in time.

  9. A transition matrix approach to the Davenport gryo calibration scheme

    NASA Technical Reports Server (NTRS)

    Natanson, G. A.

    1998-01-01

    The in-flight gyro calibration scheme commonly used by NASA Goddard Space Flight Center (GSFC) attitude ground support teams closely follows an original version of the Davenport algorithm developed in the late seventies. Its basic idea is to minimize the least-squares differences between attitudes gyro- propagated over the course of a maneuver and those determined using post- maneuver sensor measurements. The paper represents the scheme in a recursive form by combining necessary partials into a rectangular matrix, which is propagated in exactly the same way as a Kalman filters square transition matrix. The nontrivial structure of the propagation matrix arises from the fact that attitude errors are not included in the state vector, and therefore their derivatives with respect to estimated a parameters do not appear in the transition matrix gyro defined in the conventional way. In cases when the required accuracy can be achieved by a single iteration, representation of the Davenport gyro calibration scheme in a recursive form allows one to discard each gyro measurement immediately after it was used to propagate the attitude and state transition matrix. Another advantage of the new approach is that it utilizes the same expression for the error sensitivity matrix as that used by the Kalman filter. As a result the suggested modification of the Davenport algorithm made it possible to reuse software modules implemented in the Kalman filter estimator, where both attitude errors and gyro calibration parameters are included in the state vector. The new approach has been implemented in the ground calibration utilities used to support the Tropical Rainfall Measuring Mission (TRMM). The paper analyzes some preliminary results of gyro calibration performed by the TRMM ground attitude support team. It is demonstrated that an effect of the second iteration on estimated values of calibration parameters is negligibly small, and therefore there is no need to store processed gyro data

  10. Analysis of the segmented contraction of basis functions using density matrix theory.

    PubMed

    Custodio, Rogério; Gomes, André Severo Pereira; Sensato, Fabrício Ronil; Trevas, Júlio Murilo Dos Santos

    2006-11-30

    A particular formulation based on density matrix (DM) theory at the Hartree-Fock level of theory and the description of the atomic orbitals as integral transforms is introduced. This formulation leads to a continuous representation of the density matrices as functions of a generator coordinate and to the possibility of plotting either the continuous or discrete density matrices as functions of the exponents of primitive Gaussian basis functions. The analysis of these diagrams provides useful information allowing: (a) the determination of the most important primitives for a given orbital, (b) the core-valence separation, and (c) support for the development of contracted basis sets by the segmented method.

  11. Density-matrix renormalization group algorithm with multi-level active space.

    PubMed

    Ma, Yingjin; Wen, Jing; Ma, Haibo

    2015-07-21

    The density-matrix renormalization group (DMRG) method, which can deal with a large active space composed of tens of orbitals, is nowadays widely used as an efficient addition to traditional complete active space (CAS)-based approaches. In this paper, we present the DMRG algorithm with a multi-level (ML) control of the active space based on chemical intuition-based hierarchical orbital ordering, which is called as ML-DMRG with its self-consistent field (SCF) variant ML-DMRG-SCF. Ground and excited state calculations of H2O, N2, indole, and Cr2 with comparisons to DMRG references using fixed number of kept states (M) illustrate that ML-type DMRG calculations can obtain noticeable efficiency gains. It is also shown that the orbital re-ordering based on hierarchical multiple active subspaces may be beneficial for reducing computational time for not only ML-DMRG calculations but also DMRG ones with fixed M values. PMID:26203012

  12. Infections on Temporal Networks—A Matrix-Based Approach

    PubMed Central

    Koher, Andreas; Lentz, Hartmut H. K.; Hövel, Philipp; Sokolov, Igor M.

    2016-01-01

    We extend the concept of accessibility in temporal networks to model infections with a finite infectious period such as the susceptible-infected-recovered (SIR) model. This approach is entirely based on elementary matrix operations and unifies the disease and network dynamics within one algebraic framework. We demonstrate the potential of this formalism for three examples of networks with high temporal resolution: networks of social contacts, sexual contacts, and livestock-trade. Our investigations provide a new methodological framework that can be used, for instance, to estimate the epidemic threshold, a quantity that determines disease parameters, for which a large-scale outbreak can be expected. PMID:27035128

  13. Infections on Temporal Networks--A Matrix-Based Approach.

    PubMed

    Koher, Andreas; Lentz, Hartmut H K; Hövel, Philipp; Sokolov, Igor M

    2016-01-01

    We extend the concept of accessibility in temporal networks to model infections with a finite infectious period such as the susceptible-infected-recovered (SIR) model. This approach is entirely based on elementary matrix operations and unifies the disease and network dynamics within one algebraic framework. We demonstrate the potential of this formalism for three examples of networks with high temporal resolution: networks of social contacts, sexual contacts, and livestock-trade. Our investigations provide a new methodological framework that can be used, for instance, to estimate the epidemic threshold, a quantity that determines disease parameters, for which a large-scale outbreak can be expected. PMID:27035128

  14. Electronic quasiparticles in the quantum dimer model: Density matrix renormalization group results

    NASA Astrophysics Data System (ADS)

    Lee, Junhyun; Sachdev, Subir; White, Steven R.

    2016-09-01

    We study a recently proposed quantum dimer model for the pseudogap metal state of the cuprates. The model contains bosonic dimers, representing a spin-singlet valence bond between a pair of electrons, and fermionic dimers, representing a quasiparticle with spin-1/2 and charge +e . By density matrix renormalization group calculations on a long but finite cylinder, we obtain the ground-state density distribution of the fermionic dimers for a number of different total densities. From the Friedel oscillations at open boundaries, we deduce that the Fermi surface consists of small hole pockets near (π /2 ,π /2 ) , and this feature persists up to a doping density of 1/16. We also compute the entanglement entropy and find that it closely matches the sum of the entanglement entropies of a critical boson and a low density of free fermions. Our results support the existence of a fractionalized Fermi liquid in this model.

  15. Momentum density and spatial form of correlated density matrix in model two-electron atoms with harmonic confinement

    SciTech Connect

    Akbari, Ali; Rubio, Angel; March, Norman H.

    2007-09-15

    The detailed nature of the correlated first-order density matrix for the model atoms in the title for arbitrary interparticle interaction u(r{sub 12}) is studied. One representation with contracted information is first explored by constructing the momentum density {rho}(p) in terms of the wave function of the relative motion, say {psi}{sub R}(r{sub 12}), which naturally depends on the choice of u(r{sub 12}). For u(r{sub 12})=e{sup 2}/r{sub 12}, the so-called Hookean atom, and for the inverse square law u(r{sub 12})={lambda}/r{sub 12}{sup 2}, plots are presented of the above density {rho}(p) in momentum space. The correlated kinetic energy is recovered from averaging p{sup 2}/2m, m denoting the electron mass, with respect to {rho}(p). The second method developed is in coordinate space and expands the density matrix {gamma}(r{sub 1},r{sub 2}) in Legendre polynomials, using relative coordinate r{sub 1}-r{sub 2}, center-of-mass coordinate (r{sub 1}+r{sub 2})/2 and the angle, {theta} say, between these two vectors. For the Moshinsky atom in which u(r{sub 12})=(1/2)kr{sub 12}{sup 2} only the s term (l=0) contributes to the Legendre polynomial expansion. The specific example we present of the inverse square law model is shown to be characterized by the low-order terms (s+d) of the Legendre expansion. The Wigner function is finally calculated analytically for both Moshinsky and inverse square law models.

  16. Momentum density and spatial form of correlated density matrix in model two-electron atoms with harmonic confinement

    NASA Astrophysics Data System (ADS)

    Akbari, Ali; March, Norman H.; Rubio, Angel

    2007-09-01

    The detailed nature of the correlated first-order density matrix for the model atoms in the title for arbitrary interparticle interaction u(r12) is studied. One representation with contracted information is first explored by constructing the momentum density ρ(p) in terms of the wave function of the relative motion, say ΨR(r12) , which naturally depends on the choice of u(r12) . For u(r12)=e2/r12 , the so-called Hookean atom, and for the inverse square law u(r12)=λ/r122 , plots are presented of the above density ρ(p) in momentum space. The correlated kinetic energy is recovered from averaging p2/2m , m denoting the electron mass, with respect to ρ(p) . The second method developed is in coordinate space and expands the density matrix γ(r1,r2) in Legendre polynomials, using relative coordinate r1-r2 , center-of-mass coordinate (r1+r2)/2 and the angle, θ say, between these two vectors. For the Moshinsky atom in which u(r12)=(1)/(2)kr122 only the s term (l=0) contributes to the Legendre polynomial expansion. The specific example we present of the inverse square law model is shown to be characterized by the low-order terms (s+d) of the Legendre expansion. The Wigner function is finally calculated analytically for both Moshinsky and inverse square law models.

  17. Coherent nonlinear optical studies of elementary processes in biological complexes: diagrammatic techniques based on the wave function versus the density matrix

    PubMed Central

    Biggs, Jason D.; Voll, Judith A.; Mukamel, Shaul

    2012-01-01

    Two types of diagrammatic approaches for the design and simulation of nonlinear optical experiments (closed-time path loops based on the wave function and double-sided Feynman diagrams for the density matrix) are presented and compared. We give guidelines for the assignment of relevant pathways and provide rules for the interpretation of existing nonlinear experiments in carotenoids. PMID:22753822

  18. Obtaining Hartree-Fock and density functional theory doubly excited states with Car-Parrinello density matrix search

    NASA Astrophysics Data System (ADS)

    Liang, Wenkel; Isborn, Christine M.; Li, Xiaosong

    2009-11-01

    The calculation of doubly excited states is one of the major problems plaguing the modern day excited state workhorse methodology of linear response time dependent Hartree-Fock (TDHF) and density function theory (TDDFT). We have previously shown that the use of a resonantly tuned field within real-time TDHF and TDDFT is able to simultaneously excite both the α and β electrons to achieve the two-electron excited states of minimal basis H2 and HeH+ [C. M. Isborn and X. Li, J. Chem. Phys. 129, 204107 (2008)]. We now extend this method to many electron systems with the use of our Car-Parrinello density matrix search (CP-DMS) with a first-principles fictitious mass method for wave function optimization [X. Li, C. L. Moss, W. Liang, and Y. Feng, J. Chem. Phys. 130, 234115 (2009)]. Real-time TDHF/TDDFT is used during the application of the laser field perturbation, driving the electron density toward the doubly excited state. The CP-DMS method then converges the density to the nearest stationary state. We present these stationary state doubly excited state energies and properties at the HF and DFT levels for H2, HeH+, lithium hydride, ethylene, and butadiene.

  19. Multireference quantum chemistry through a joint density matrix renormalization group and canonical transformation theory.

    PubMed

    Yanai, Takeshi; Kurashige, Yuki; Neuscamman, Eric; Chan, Garnet Kin-Lic

    2010-01-14

    We describe the joint application of the density matrix renormalization group and canonical transformation theory to multireference quantum chemistry. The density matrix renormalization group provides the ability to describe static correlation in large active spaces, while the canonical transformation theory provides a high-order description of the dynamic correlation effects. We demonstrate the joint theory in two benchmark systems designed to test the dynamic and static correlation capabilities of the methods, namely, (i) total correlation energies in long polyenes and (ii) the isomerization curve of the [Cu(2)O(2)](2+) core. The largest complete active spaces and atomic orbital basis sets treated by the joint DMRG-CT theory in these systems correspond to a (24e,24o) active space and 268 atomic orbitals in the polyenes and a (28e,32o) active space and 278 atomic orbitals in [Cu(2)O(2)](2+). PMID:20095661

  20. Conditions for Describing Triplet States in Reduced Density Matrix Functional Theory.

    PubMed

    Theophilou, Iris; Lathiotakis, Nektarios N; Helbig, Nicole

    2016-06-14

    We consider necessary conditions for the one-body reduced density matrix (1RDM) to correspond to a triplet wave function of a two-electron system. The conditions concern the occupation numbers and are different for the high spin projections, Sz = ±1, and the Sz = 0 projection. Hence, they can be used to test if an approximate 1RDM functional yields the same energies for both projections. We employ these conditions in reduced density matrix functional theory calculations for the triplet excitations of two-electron systems. In addition, we propose that these conditions can be used in the calculation of triplet states of systems with more than two electrons by restricting the active space. We assess this procedure in calculations for a few atomic and molecular systems. We show that the quality of the optimal 1RDMs improves by applying the conditions in all the cases we studied. PMID:27171683

  1. Density-matrix method applied to mode coupling in lenslike fibers

    NASA Astrophysics Data System (ADS)

    Maeda, K.; Hamasaki, J.

    1980-04-01

    Mode conversion due to random refractive-index fluctuations of a lossless multimode waveguide is considered. An equation of motion for an average density matrix, which describes wave phenomena in statistically identical waveguides is derived. This equation includes the coupled power equation given by Marcuse, and also describes evolution of correlations between propagating modes. Using this equation, mode-conversion characteristics among degenerate modes in a lenslike fiber are obtained for several correlation lengths and variances of the refractive-index fluctuations.

  2. Matrix density effects on the mechanical properties of SiC/RBSN composites

    NASA Technical Reports Server (NTRS)

    Bhatt, Ramakrishna T.; Kiser, James D.

    1990-01-01

    The room temperature mechanical properties were measured for SiC fiber reinforced reaction-bonded silicon nitride composites (SiC/RBSN) of different densities. The composites consisted of approx. 30 vol percent uniaxially aligned 142 micron diameter SiC fibers (Textron SCS-6) in a reaction-bonded Si3N4 matrix. The composite density was varied by changing the consolidation pressure during RBSN processing and by hot isostatically pressing the SiC/RBSN composites. Results indicate that as the consolidation pressure was increased from 27 to 138 MPa, the average pore size of the nitrided composites decreased from 0.04 to 0.02 microns and the composite density increased from 2.07 to 2.45 gm/cc. Nonetheless, these improvements resulted in only small increases in the first matrix cracking stress, primary elastic modulus, and ultimate tensile strength values of the composites. In contrast, HIP consolidation of SiC/RBSN resulted in a fully dense material whose first matrix cracking stress and elastic modulus were approx. 15 and 50 percent higher, respectively, and ultimate tensile strength values were approx. 40 percent lower than those for unHIPed SiC/RBSN composites. The modulus behavior for all specimens can be explained by simple rule-of-mixture theory. Also, the loss in ultimate strength for the HIPed composites appears to be related to a degradation in fiber strength at the HIP temperature. However, the density effect on matrix fracture strength was much less than would be expected based on typical monolithic Si3N4 behavior, suggesting that composite theory is indeed operating. Possible practical implications of these observations are discussed.

  3. Derivation of the density matrix of a single photon produced in parametric down-conversion

    SciTech Connect

    Kolenderski, Piotr; Wasilewski, Wojciech

    2009-07-15

    We discuss an effective numerical method of density matrix determination of fiber coupled single photon generated in process of spontaneous parametric down conversion in type I noncollinear configuration. The presented theory has been successfully applied in case of source utilized to demonstrate the experimental characterization of spectral state of single photon, what was reported in Wasilewski, Kolenderski, and Frankowski [Phys. Rev. Lett. 99, 123601 (2007)].

  4. Liquid cooled approaches for high density avionics

    NASA Astrophysics Data System (ADS)

    Levasseur, Robert

    Next-generation aircraft will require avionics that provide greater system performance in a smaller volume, a process that requires highly developed thermal management techniques. To meet this need, a liquid-cooled approach has been developed to replace the conventional air-cooled approach for high-power applications. Liquid-cooled chassis and flow-through modules have been developed to limit junction temperatures to acceptable levels. Liquid cooling also permits emergency operation after loss of coolant for longer time intervals, which is desirable for flight-critical airborne applications. Activity to date has emphasized the development of chassis and modules that support the US Department of Defense's (DoD) two-level maintenance initiative as governed by the Joint Integrated Avionics Working Group (JIAWG).

  5. Density-matrix formalism for the photoion-electron entanglement in atomic photoionization

    SciTech Connect

    Radtke, T.; Fritzsche, S.; Surzhykov, A.

    2006-09-15

    The density-matrix theory, based on Dirac's relativistic equation, is applied for studying the entanglement between the photoelectron and residual ion in the course of the photoionization of atoms and ions. In particular, emphasis is placed on deriving the final-state density matrix of the overall system 'photoion+electron', including interelectronic effects and the higher multipoles of the radiation field. This final-state density matrix enables one immediately to analyze the change of entanglement as a function of the energy, angle and the polarization of the incoming light. Detailed computations have been carried out for the 5s photoionization of neutral strontium, leading to a photoion in a 5s {sup 2}S J{sub f}=1/2 level. It is found that the photoion-electron entanglement decreases significantly near the ionization threshold and that, in general, it depends on both the photon energy and angle. The possibility to extract photoion-electron pairs with a well-defined degree of entanglement may have far-reaching consequences for quantum information and elsewhere.

  6. A density-matrix model of photosynthetic electron transfer with microscopically estimated vibrational relaxation times

    NASA Astrophysics Data System (ADS)

    Parson, William W.; Warshel, Arieh

    2004-01-01

    The dispersed-polaron (spin-boson) model is reviewed briefly and then used to develop a density-matrix model for studies of electron transfer in condensed phases. The frequencies and Franck-Condon factors for solvent vibrational modes that are coupled to electron transfer are obtained from molecular dynamics (MD) simulations by the dispersed-polaron treatment. Microscopic rate constants for vibrational relaxations, dephasing and coherence transfer between the solvent modes are obtained by fitting the time dependence of the solvent coordinates in the density-matrix treatment to the corresponding time dependence obtained from molecular-dynamics simulations with a classical linear-response approximation. This is done by adjusting a single parameter, the time constant for thermal equilibration of the two lowest levels of a solvent mode ( T10). The model thus focuses on the coupling between solvent modes, rather than on the more widely studied coupling of solute modes by the thermal bath. The resulting density-matrix model is used to examine vibronic coupling in the initial electron-transfer step in photosynthetic bacterial reaction centers. Values of T10 in the range of 1-2 ps are consistent with molecular-dynamics simulations of the time-dependent energy gap between the reactant and product states (P* and P +B -), and also with the damping of coherent vibrational motions that are seen experimentally after excitation of reaction centers with a short pulse of light. In both the density-matrix model and the MD simulations, the autocorrelation function of the energy gap also has a decay component with a time constant of about 50 fs, which we ascribe to the group dephasing of oscillatory motions at many different frequencies. This component is insensitive to vibrational relaxations and is largely irrelevant to the electron-transfer dynamics. Using values of T10 in the range of 1-2 ps, a model with five vibrational modes reproduces the main features of electron transfer

  7. Matrix model approach to minimal Liouville gravity revisited

    NASA Astrophysics Data System (ADS)

    Belavin, V.; Rud, Yu

    2015-05-01

    Using the connection with the Frobenius manifold (FM) structure, we study the matrix model description of minimal Liouville gravity (MLG) based on the Douglas String equation. Our goal is to find an exact discrete formulation of the (q,p) MLG model that intrinsically contains information about the conformal selection rules. We discuss how to modify the FM structure appropriately for this purposes. We propose a modification of the construction for Lee-Yang series involving the {{A}p-1} algebra instead of the previously used A1 algebra. With the new prescription, we calculate correlators on the sphere up to four points and find full agreement with the continuous approach without using resonance transformations.

  8. Two functions of the density matrix and their relation to the chemical bond

    NASA Astrophysics Data System (ADS)

    Schmider, Hartmut L.; Becke, Axel D.

    2002-02-01

    We examine and compare two previously introduced functions of the one-particle density matrix that are suitable to represent its off-diagonal structure in a condensed form and that have illustrative connections to the nature of the chemical bond. One of them, the Localized-Orbital Locator (LOL) [J. Molec. Struct. (THEOCHEM) 527, 51 (2000)], is based only on the noninteracting kinetic-energy density τ and the charge density ρ at a point, and gives an intuitive measure of the relative speed of electrons in its vicinity. Alternatively, LOL focuses on regions that are dominated by single localized orbitals. The other one, the Parity Function P [J. Chem. Phys. 105, 11134 (1996)], is a section through the Wigner phase-space function at zero momentum, and contains information about the phase of the interference of atomiclike orbital contributions from bound centers. In this paper, we discuss the way in which these functions condense information in the density matrix, and illustrate on a variety of examples of unusual chemical bonds how they can help to understand the nature of "covalence."

  9. Density hysteresis of heavy water confined in a nanoporous silica matrix

    PubMed Central

    Zhang, Yang; Faraone, Antonio; Kamitakahara, William A.; Liu, Kao-Hsiang; Mou, Chung-Yuan; Leão, Juscelino B.; Chang, Sung; Chen, Sow-Hsin

    2011-01-01

    A neutron scattering technique was developed to measure the density of heavy water confined in a nanoporous silica matrix in a temperature-pressure range, from 300 to 130 K and from 1 to 2,900 bars, where bulk water will crystalize. We observed a prominent hysteresis phenomenon in the measured density profiles between warming and cooling scans above 1,000 bars. We interpret this hysteresis phenomenon as support (although not a proof) of the hypothetical existence of a first-order liquid–liquid phase transition of water that would exist in the macroscopic system if crystallization could be avoided in the relevant phase region. Moreover, the density data we obtained for the confined heavy water under these conditions are valuable to large communities in biology and earth and planetary sciences interested in phenomena in which nanometer-sized water layers are involved. PMID:21746898

  10. Density hysteresis of heavy water confined in a nanoporous silica matrix

    SciTech Connect

    Zhang, Yang; Faraone, Antonio; Kamitakahara, William; Liu, Kao-Hsiang; Mou, Chung-Yuan; Leao, Juscelino B; Chang, Sung C; Chen, Sow-hsin H

    2011-01-01

    A neutron scattering technique was developed to measure the density of heavy water confined in a nanoporous silica matrix in a temperature-pressure range, from 300 to 130 K and from 1 to 2,900 bars, where bulk water will crystalize. We observed a prominent hysteresis phenomenon in the measured density profiles between warming and cooling scans above 1,000 bars. We inter- pret this hysteresis phenomenon as support (although not a proof) of the hypothetical existence of a first-order liquid liquid phase transition of water that would exist in the macroscopic system if crystallization could be avoided in the relevant phase region. Moreover, the density data we obtained for the confined heavy water under these conditions are valuable to large communities in biology and earth and planetary sciences interested in phenomena in which nanometer-sized water layers are involved.

  11. The Chondrule-Matrix Complementarity, a Big Data Approach

    NASA Astrophysics Data System (ADS)

    Harak, M.; Hezel, D. C.

    2016-08-01

    We compiled >3500 chondrule and matrix data from 80 literature sources. We developed an algorithm to automatically search this database, and identified a large number of complementary element relationships between chondrules and matrix.

  12. Spin orbit coupling for molecular ab initio density matrix renormalization group calculations: Application to g-tensors

    SciTech Connect

    Roemelt, Michael

    2015-07-28

    Spin Orbit Coupling (SOC) is introduced to molecular ab initio density matrix renormalization group (DMRG) calculations. In the presented scheme, one first approximates the electronic ground state and a number of excited states of the Born-Oppenheimer (BO) Hamiltonian with the aid of the DMRG algorithm. Owing to the spin-adaptation of the algorithm, the total spin S is a good quantum number for these states. After the non-relativistic DMRG calculation is finished, all magnetic sublevels of the calculated states are constructed explicitly, and the SOC operator is expanded in the resulting basis. To this end, spin orbit coupled energies and wavefunctions are obtained as eigenvalues and eigenfunctions of the full Hamiltonian matrix which is composed of the SOC operator matrix and the BO Hamiltonian matrix. This treatment corresponds to a quasi-degenerate perturbation theory approach and can be regarded as the molecular equivalent to atomic Russell-Saunders coupling. For the evaluation of SOC matrix elements, the full Breit-Pauli SOC Hamiltonian is approximated by the widely used spin-orbit mean field operator. This operator allows for an efficient use of the second quantized triplet replacement operators that are readily generated during the non-relativistic DMRG algorithm, together with the Wigner-Eckart theorem. With a set of spin-orbit coupled wavefunctions at hand, the molecular g-tensors are calculated following the scheme proposed by Gerloch and McMeeking. It interprets the effective molecular g-values as the slope of the energy difference between the lowest Kramers pair with respect to the strength of the applied magnetic field. Test calculations on a chemically relevant Mo complex demonstrate the capabilities of the presented method.

  13. Extending the range of real time density matrix renormalization group simulations

    NASA Astrophysics Data System (ADS)

    Kennes, D. M.; Karrasch, C.

    2016-03-01

    We discuss a few simple modifications to time-dependent density matrix renormalization group (DMRG) algorithms which allow to access larger time scales. We specifically aim at beginners and present practical aspects of how to implement these modifications within any standard matrix product state (MPS) based formulation of the method. Most importantly, we show how to 'combine' the Schrödinger and Heisenberg time evolutions of arbitrary pure states | ψ > and operators A in the evaluation of ψ(t) = < ψ | A(t) | ψ > . This includes quantum quenches. The generalization to (non-)thermal mixed state dynamics ρ(t) =Tr [ ρA(t) ] induced by an initial density matrix ρ is straightforward. In the context of linear response (ground state or finite temperature T > 0) correlation functions, one can extend the simulation time by a factor of two by 'exploiting time translation invariance', which is efficiently implementable within MPS DMRG. We present a simple analytic argument for why a recently-introduced disentangler succeeds in reducing the effort of time-dependent simulations at T > 0. Finally, we advocate the python programming language as an elegant option for beginners to set up a DMRG code.

  14. Efficient parallel linear scaling construction of the density matrix for Born-Oppenheimer molecular dynamics.

    PubMed

    Mniszewski, S M; Cawkwell, M J; Wall, M E; Mohd-Yusof, J; Bock, N; Germann, T C; Niklasson, A M N

    2015-10-13

    We present an algorithm for the calculation of the density matrix that for insulators scales linearly with system size and parallelizes efficiently on multicore, shared memory platforms with small and controllable numerical errors. The algorithm is based on an implementation of the second-order spectral projection (SP2) algorithm [ Niklasson, A. M. N. Phys. Rev. B 2002 , 66 , 155115 ] in sparse matrix algebra with the ELLPACK-R data format. We illustrate the performance of the algorithm within self-consistent tight binding theory by total energy calculations of gas phase poly(ethylene) molecules and periodic liquid water systems containing up to 15,000 atoms on up to 16 CPU cores. We consider algorithm-specific performance aspects, such as local vs nonlocal memory access and the degree of matrix sparsity. Comparisons to sparse matrix algebra implementations using off-the-shelf libraries on multicore CPUs, graphics processing units (GPUs), and the Intel many integrated core (MIC) architecture are also presented. The accuracy and stability of the algorithm are illustrated with long duration Born-Oppenheimer molecular dynamics simulations of 1000 water molecules and a 303 atom Trp cage protein solvated by 2682 water molecules.

  15. Efficient parallel linear scaling construction of the density matrix for Born-Oppenheimer molecular dynamics.

    PubMed

    Mniszewski, S M; Cawkwell, M J; Wall, M E; Mohd-Yusof, J; Bock, N; Germann, T C; Niklasson, A M N

    2015-10-13

    We present an algorithm for the calculation of the density matrix that for insulators scales linearly with system size and parallelizes efficiently on multicore, shared memory platforms with small and controllable numerical errors. The algorithm is based on an implementation of the second-order spectral projection (SP2) algorithm [ Niklasson, A. M. N. Phys. Rev. B 2002 , 66 , 155115 ] in sparse matrix algebra with the ELLPACK-R data format. We illustrate the performance of the algorithm within self-consistent tight binding theory by total energy calculations of gas phase poly(ethylene) molecules and periodic liquid water systems containing up to 15,000 atoms on up to 16 CPU cores. We consider algorithm-specific performance aspects, such as local vs nonlocal memory access and the degree of matrix sparsity. Comparisons to sparse matrix algebra implementations using off-the-shelf libraries on multicore CPUs, graphics processing units (GPUs), and the Intel many integrated core (MIC) architecture are also presented. The accuracy and stability of the algorithm are illustrated with long duration Born-Oppenheimer molecular dynamics simulations of 1000 water molecules and a 303 atom Trp cage protein solvated by 2682 water molecules. PMID:26574255

  16. Internal one-particle density matrix for Bose-Einstein condensates with finite number of particles in a harmonic potential

    SciTech Connect

    Yamada, Taiichi; Funaki, Yasuro; Horiuchi, Hisashi; Roepke, Gerd; Schuck, Peter; Tohsaki, Akihiro

    2009-05-15

    Investigations on the internal one-particle density matrix in the case of Bose-Einstein condensates with a finite number (N) of particles in a harmonic potential are performed. We solve the eigenvalue problem of the Pethick-Pitaevskii-type internal density matrix and find a fragmented condensate. On the contrary the condensate Jacobi-type internal density matrix gives complete condensation into a single state. The internal one-particle density matrix is, therefore, shown to be different in general for different choices of the internal coordinate system. We propose two physically motivated criteria for the choice of the adequate coordinate systems that give us a unique answer for the internal one-particle density matrix. One criterion is that in the infinite particle number limit (N={infinity}) the internal one-particle density matrix should have the same eigenvalues and eigenfunctions as those of the corresponding ideal Bose-Einstein condensate in the laboratory frame. The other criterion is that the coordinate of the internal one-particle density matrix should be orthogonal to the remaining (N-2) internal coordinates, though the (N-2) coordinates, in general, do not need to be mutually orthogonal. This second criterion is shown to imply the first criterion. It is shown that the internal Jacobi coordinate system satisfies these two criteria while the internal coordinate system adopted by Pethick and Pitaevskii for the construction of the internal one-particle density matrix does not. It is demonstrated that these two criteria uniquely determine the internal one-particle density matrix that is identical to that calculated with the Jacobi coordinates. The relevance of this work concerning {alpha}-particle condensates in nuclei, as well as bosonic atoms in traps, is pointed out.

  17. An approach to fast fits of the unintegrated gluon density

    SciTech Connect

    Knutsson, Albert; Bacchetta, Alessandro; Kutak, Krzyzstof; Jung, Hannes

    2009-01-01

    An approach to fast fits of the unintegrated gluon density has been developed and used to determine the unintegrated gluon density by fits to deep inelastic scatting di-jet data from HERA. The fitting method is based on the determination of the parameter dependence by help of interpolating between grid points in the parameter-observable space before the actual fit is performed.

  18. Control-matrix approach to stellarator design and control

    SciTech Connect

    Mynick, H.E.; Pomphrey, N.

    2000-02-09

    The full space Z always equal to {l{underscore}brace}Zj=1,..Nz{r{underscore}brace} of independent variables defining a stellarator configuration is large. To find attractive design points in this space, or to understand operational flexibility about a given design point, one needs insight into the topography in Z-space of the physics figures of merit Pi which characterize the machine performance, and means of determining those directions in Z-space which give one independent control over the Pi, as well as those which affect none of them, and so are available for design flexibility. The control matrix (CM) approach described here provides a mathematical means of obtaining these. In this work, the authors describe the CM approach and use it in studying some candidate Quasi-Axisymmetric (QA) stellarator configurations the NCSX design group has been considering. In the process of the analysis, a first exploration of the topography of the configuration space in the vicinity of these candidate systems has been performed, whose character is discussed.

  19. Computation of the Density Matrix in Electronic Structure Theory in Parallel on Multiple Graphics Processing Units.

    PubMed

    Cawkwell, M J; Wood, M A; Niklasson, Anders M N; Mniszewski, S M

    2014-12-01

    The algorithm developed in Cawkwell, M. J. et al. J. Chem. Theory Comput. 2012 , 8 , 4094 for the computation of the density matrix in electronic structure theory on a graphics processing unit (GPU) using the second-order spectral projection (SP2) method [ Niklasson, A. M. N. Phys. Rev. B 2002 , 66 , 155115 ] has been efficiently parallelized over multiple GPUs on a single compute node. The parallel implementation provides significant speed-ups with respect to the single GPU version with no loss of accuracy. The performance and accuracy of the parallel GPU-based algorithm is compared with the performance of the SP2 algorithm and traditional matrix diagonalization methods on a multicore central processing unit (CPU).

  20. Density matrix treatment of non-adiabatic photoinduced electron transfer at a semiconductor surface.

    PubMed

    Micha, David A

    2012-12-14

    Photoinduced electron transfer at a nanostructured surface leads to localized transitions and involves three different types of non-adiabatic couplings: vertical electronic transitions induced by light absorption emission, coupling of electronic states by the momentum of atomic motions, and their coupling due to interactions with electronic density fluctuations and vibrational motions in the substrate. These phenomena are described in a unified way by a reduced density matrix (RDM) satisfying an equation of motion that contains dissipative rates. The RDM treatment is used here to distinguish non-adiabatic phenomena that are localized from those due to interaction with a medium. The fast decay of localized state populations due to electronic density fluctuations in the medium has been treated within the Lindblad formulation of rates. The formulation is developed introducing vibronic states constructed from electron orbitals available from density functional calculations, and from vibrational states describing local atomic displacements. Related ab initio molecular dynamics calculations have provided diabatic momentum couplings between excited electronic states. This has been done in detail for an indirect photoexcitation mechanism of the surface Ag(3)Si(111):H, which leads to long lasting electronic charge separation. The resulting coupled density matrix equations are solved numerically to obtain the population of the final charge-separated state as it changes over time, for several values of the diabatic momentum coupling. New insight and unexpected results are presented here which can be understood in terms of photoinduced non-adiabatic transitions involving many vibronic states. It is found that the population of long lasting charge separation states is larger for smaller momentum coupling, and that their population grows faster for smaller coupling.

  1. The rigorous stochastic matrix multiplication scheme for the calculations of reduced equilibrium density matrices of open multilevel quantum systems

    SciTech Connect

    Chen, Xin

    2014-04-21

    Understanding the roles of the temporary and spatial structures of quantum functional noise in open multilevel quantum molecular systems attracts a lot of theoretical interests. I want to establish a rigorous and general framework for functional quantum noises from the constructive and computational perspectives, i.e., how to generate the random trajectories to reproduce the kernel and path ordering of the influence functional with effective Monte Carlo methods for arbitrary spectral densities. This construction approach aims to unify the existing stochastic models to rigorously describe the temporary and spatial structure of Gaussian quantum noises. In this paper, I review the Euclidean imaginary time influence functional and propose the stochastic matrix multiplication scheme to calculate reduced equilibrium density matrices (REDM). In addition, I review and discuss the Feynman-Vernon influence functional according to the Gaussian quadratic integral, particularly its imaginary part which is critical to the rigorous description of the quantum detailed balance. As a result, I establish the conditions under which the influence functional can be interpreted as the average of exponential functional operator over real-valued Gaussian processes for open multilevel quantum systems. I also show the difference between the local and nonlocal phonons within this framework. With the stochastic matrix multiplication scheme, I compare the normalized REDM with the Boltzmann equilibrium distribution for open multilevel quantum systems.

  2. A practical guide to density matrix embedding theory in quantum chemistry

    DOE PAGESBeta

    Wouters, Sebastian; Jimenez-Hoyos, Carlos A.; Sun, Qiming; Chan, Garnet K.-L.

    2016-05-09

    Density matrix embedding theory (DMET) (Knizia, G.; Chan, G. K.-L. Phys. Rev. Lett. 2012, 109, 186404) provides a theoretical framework to treat finite fragments in the presence of a surrounding molecular or bulk environment, even when there is significant correlation or entanglement between the two. In this work, we give a practically oriented and explicit description of the numerical and theoretical formulation of DMET. We also describe in detail how to perform self-consistent DMET optimizations. Furthermore, we explore different embedding strategies with and without a self-consistency condition in hydrogen rings, beryllium rings, and a sample SN2 reaction.

  3. Self-consistent calculation of dephasing in quantum cascade structures within a density matrix method

    NASA Astrophysics Data System (ADS)

    Freeman, Will

    2016-05-01

    Dephasing in terahertz quantum cascade structures is studied within a density matrix formalism. We self-consistently calculate the pure dephasing time from the intrasubband interactions within the upper and lower lasing states. Interface roughness and ionized impurity scattering interactions are included in the calculation. Dephasing times are shown to be consistent with measured spontaneous emission spectra, and the lattice temperature dependence of the device output power is consistent with experiment. The importance of including multiple optical transitions when a lower miniband continuum is present and the resulting multi-longitudinal modes within the waveguide resonant cavity are also shown.

  4. Magic frequencies in atom-light interaction for precision probing of the density matrix.

    PubMed

    Givon, Menachem; Margalit, Yair; Waxman, Amir; David, Tal; Groswasser, David; Japha, Yonathan; Folman, Ron

    2013-08-01

    We analyze theoretically and experimentally the existence of a magic frequency for which the absorption of a linearly polarized light beam by a vapor of alkali-metal atoms is independent of the population distribution among the Zeeman sublevels and the angle between the beam and a magnetic field. The phenomenon originates from a peculiar cancellation of the contributions of higher moments of the atomic density matrix, and is described using the Wigner-Eckart theorem and inherent properties of Clebsch-Gordan coefficients. One important application is the robust measurement of the hyperfine population.

  5. Communication: Active space decomposition with multiple sites: Density matrix renormalization group algorithm

    SciTech Connect

    Parker, Shane M.; Shiozaki, Toru

    2014-12-07

    We extend the active space decomposition method, recently developed by us, to more than two active sites using the density matrix renormalization group algorithm. The fragment wave functions are described by complete or restricted active-space wave functions. Numerical results are shown on a benzene pentamer and a perylene diimide trimer. It is found that the truncation errors in our method decrease almost exponentially with respect to the number of renormalization states M, allowing for numerically exact calculations (to a few μE{sub h} or less) with M = 128 in both cases. This rapid convergence is because the renormalization steps are used only for the interfragment electron correlation.

  6. Differential cross sections and spin density matrix elements for the reaction gamma p -> p omega

    SciTech Connect

    M. Williams, D. Applegate, M. Bellis, C.A. Meyer

    2009-12-01

    High-statistics differential cross sections and spin density matrix elements for the reaction gamma p -> p omega have been measured using the CLAS at Jefferson Lab for center-of-mass (CM) energies from threshold up to 2.84 GeV. Results are reported in 112 10-MeV wide CM energy bins, each subdivided into cos(theta_CM) bins of width 0.1. These are the most precise and extensive omega photoproduction measurements to date. A number of prominent structures are clearly present in the data. Many of these have not previously been observed due to limited statistics in earlier measurements.

  7. Highly linear high-density vector quantiser and vector-matrix multiplier

    NASA Astrophysics Data System (ADS)

    Pedroni, V. A.

    1994-06-01

    Simplicity is a key factor in the development of high-density systems. The authors discuss a balanced, four-quadrant, fully-analogue vector-matrix multiplier (VMM) and a vector quantiser (VQ) which require very small silicon area for their implementations, while presenting high linearity, a totally flexible input dynamic range, a symmetric power consumption behaviour, and are inherently suitable for parallel operation. The circuits require only four transistors per synapse in the VMM and two in the VQ, plus two (small) refresh transistors.

  8. A new approach for estimating the density of liquids

    NASA Astrophysics Data System (ADS)

    Sakagami, T.; Fuchizaki, K.; Ohara, K.

    2016-10-01

    We propose a novel approach with which to estimate the density of liquids. The approach is based on the assumption that the systems would be structurally similar when viewed at around the length scale (inverse wavenumber) of the first peak of the structure factor, unless their thermodynamic states differ significantly. The assumption was implemented via a similarity transformation to the radial distribution function to extract the density from the structure factor of a reference state with a known density. The method was first tested using two model liquids, and could predict the densities within an error of several percent unless the state in question differed significantly from the reference state. The method was then applied to related real liquids, and satisfactory results were obtained for predicted densities. The possibility of applying the method to amorphous materials is discussed.

  9. A new approach for estimating the density of liquids.

    PubMed

    Sakagami, T; Fuchizaki, K; Ohara, K

    2016-10-01

    We propose a novel approach with which to estimate the density of liquids. The approach is based on the assumption that the systems would be structurally similar when viewed at around the length scale (inverse wavenumber) of the first peak of the structure factor, unless their thermodynamic states differ significantly. The assumption was implemented via a similarity transformation to the radial distribution function to extract the density from the structure factor of a reference state with a known density. The method was first tested using two model liquids, and could predict the densities within an error of several percent unless the state in question differed significantly from the reference state. The method was then applied to related real liquids, and satisfactory results were obtained for predicted densities. The possibility of applying the method to amorphous materials is discussed. PMID:27494268

  10. Large-Scale Variational Two-Electron Reduced-Density-Matrix-Driven Complete Active Space Self-Consistent Field Methods.

    PubMed

    Fosso-Tande, Jacob; Nguyen, Truong-Son; Gidofalvi, Gergely; DePrince, A Eugene

    2016-05-10

    A large-scale implementation of the complete active space self-consistent field (CASSCF) method is presented. The active space is described using the variational two-electron reduced-density-matrix (v2RDM) approach, and the algorithm is applicable to much larger active spaces than can be treated using configuration-interaction-driven methods. Density fitting or Cholesky decomposition approximations to the electron repulsion integral tensor allow for the simultaneous optimization of large numbers of external orbitals. We have tested the implementation by evaluating singlet-triplet energy gaps in the linear polyacene series and two dinitrene biradical compounds. For the acene series, we report computations that involve active spaces consisting of as many as 50 electrons in 50 orbitals and the simultaneous optimization of 1892 orbitals. For the dinitrene compounds, we find that the singlet-triplet gaps obtained from v2RDM-driven CASSCF with partial three-electron N-representability conditions agree with those obtained from configuration-interaction-driven approaches to within one-third of 1 kcal mol(-1). When enforcing only the two-electron N-representability conditions, v2RDM-driven CASSCF yields less accurate singlet-triplet energy gaps in these systems, but the quality of the results is still far superior to those obtained from standard single-reference approaches. PMID:27065086

  11. Separability Criterion for Arbitrary Multipartite Pure State Based on the Rank of Reduced Density Matrix

    NASA Astrophysics Data System (ADS)

    Zhao, Chao; Yang, Guo-wu; Li, Xiao-yu

    2016-09-01

    Nowadays, there are plenty of separability criteria which are used to detect entanglement. Many of them are limited to apply for some cases. In this paper, we propose a separability criterion for arbitrary multipartite pure state which is based on the rank of reduced density matrix. It is proved that the rank of reduced density matrices of a multipartite state is closely related to entanglement. In fact it can be used to characterize entanglement. Our separability criterion is a necessary and sufficient condition for detecting entanglement. Furthermore, it is able to help us find the completely separable form of a multipartite pure state according to some explicit examples. Finally it demonstrates that our method are more suitable for some specific case. Our separability criterion are simple to understand and it is operational.

  12. Cell density modulates growth, extracellular matrix, and protein synthesis of cultured rat mesangial cells.

    PubMed

    Wolthuis, A; Boes, A; Grond, J

    1993-10-01

    Mesangial cell (MC) hyperplasia and accumulation of extracellular matrix are hallmarks of chronic glomerular disease. The present in vitro study examined the effects of cell density on growth, extracellular matrix formation, and protein synthesis of cultured rat MCs. A negative linear relationship was found between initial plating density and DNA synthesis per cell after 24 hours incubation in medium with 10% fetal calf serum (range: 1 x 10(3) to 7 x 10(5) MCs/2cm2, r = 0.996, P < 0.001). Enzyme-linked immunosorbent assay of the amount of fibronectin in the conditioned medium after 72 hours showed a negative relationship with increasing cell density. In contrast, the amount of cell-associated fibronectin increased to maximal values in confluent cultures, and no further increase was seen at supraconfluency. The relative collagen synthesis in the conditioned medium and cell layer--assessed by collagenase digestion after 5 hours [3H]proline pulse labeling--showed a similar pattern. Secreted collagen decreased with increasing cell density from 3.4% to 0.2% of total protein synthesis. In contrast, cell-associated collagen increased from 1.1% to 11.8% of newly synthesized protein until confluency followed by a decrease to 4.2% at supraconfluency. Specific immunoprecipitation of collagen types I, III, and IV revealed a significant (twofold) increase in collagen I synthesis per cell at confluency. Collagen III and IV synthesis was not affected by cell density. Specific protein expression in both the medium and cell layer were analyzed by two-dimensional polyacrylamide gel electrophoresis (150 to 20 kd, pI 5.0 to 7.0) after 20 hours steady-state metabolic labeling with [35S]methionine. Supraconfluent MCs displayed overexpression of 10, underexpression of four, new expression of five, and changed mobility of three different intracellular proteins. Of interest was the overexpression of two proteins (89 kd, pI 5.31 and 72 kd, pI 5.32) that were identified by immunoblotting as

  13. A cantilever-free approach to dot-matrix nanoprinting

    PubMed Central

    Brown, Keith A.; Eichelsdoerfer, Daniel J.; Shim, Wooyoung; Rasin, Boris; Radha, Boya; Liao, Xing; Schmucker, Abrin L.; Liu, Guoliang; Mirkin, Chad A.

    2013-01-01

    Scanning probe lithography (SPL) is a promising candidate approach for desktop nanofabrication, but trade-offs in throughput, cost, and resolution have limited its application. The recent development of cantilever-free scanning probe arrays has allowed researchers to define nanoscale patterns in a low-cost and high-resolution format, but with the limitation that these are duplication tools where each probe in the array creates a copy of a single pattern. Here, we report a cantilever-free SPL architecture that can generate 100 nanometer-scale molecular features using a 2D array of independently actuated probes. To physically actuate a probe, local heating is used to thermally expand the elastomeric film beneath a single probe, bringing it into contact with the patterning surface. Not only is this architecture simple and scalable, but it addresses fundamental limitations of 2D SPL by allowing one to compensate for unavoidable imperfections in the system. This cantilever-free dot-matrix nanoprinting will enable the construction of surfaces with chemical functionality that is tuned across the nano- and macroscales. PMID:23861495

  14. Leptogenesis with heavy neutrino flavours: from density matrix to Boltzmann equations

    SciTech Connect

    Blanchet, Steve; Bari, Pasquale Di; Jones, David A.; Marzola, Luca E-mail: pdb1d08@soton.ac.uk E-mail: daj1g08@soton.ac.uk

    2013-01-01

    Leptogenesis with heavy neutrino flavours is discussed within a density matrix formalism. We write the density matrix equation, describing the generation of the matter-antimatter asymmetry, for an arbitrary choice of the right-handed (RH) neutrino masses. For hierarchical RH neutrino masses lying in the fully flavoured regimes, this reduces to multiple-stage Boltzmann equations. In this case we recover and extend results previously derived within a quantum state collapse description. We confirm the generic existence of phantom terms. However, taking into account the effect of gauge interactions, we show that they are washed out at the production with a wash-out rate that is halved compared to that one acting on the total asymmetry. In the N{sub 1}-dominated scenario they cancel without contributing to the final baryon asymmetry. In other scenarios they do not in general and they have to be taken into account. We also confirm that there is a (orthogonal) component in the asymmetry produced by the heavier RH neutrinos which completely escapes the washout from the lighter RH neutrinos and show that phantom terms additionally contribute to it. The other (parallel) component is washed out with the usual exponential factor, even for weak washout. Finally, as an illustration, we study the two RH neutrino model in the light of the above findings, showing that phantom terms can contribute to the final asymmetry also in this case.

  15. Sodium hydrosulfide prevents myocardial dysfunction through modulation of extracellular matrix accumulation and vascular density.

    PubMed

    Pan, Li-Long; Wang, Xian-Li; Wang, Xi-Ling; Zhu, Yi-Zhun

    2014-12-12

    The aim was to examine the role of exogenous hydrogen sulfide (H2S) on cardiac remodeling in post-myocardial infarction (MI) rats. MI was induced in rats by ligation of coronary artery. After treatment with sodium hydrosulfide (NaHS, an exogenous H2S donor, 56 μM/kg·day) for 42 days, the effects of NaHS on left ventricular morphometric features, echocardiographic parameters, heme oxygenase-1 (HO-1), matrix metalloproteinases-9 (MMP-9), type I and type III collagen, vascular endothelial growth factor (VEGF), CD34, and α-smooth muscle actin (α-SMA) in the border zone of infarct area were analyzed to elucidate the protective mechanisms of exogenous H2S on cardiac function and fibrosis. Forty-two days post MI, NaHS-treatment resulted in a decrease in myocardial fibrotic area in association with decreased levels of type I, type III collagen and MMP-9 and improved cardiac function. Meanwhile, NaHS administration significantly increased cystathionine γ-lyase (CSE), HO-1, α-SMA, and VEGF expression. This effect was accompanied by an increase in vascular density in the border zone of infarcted myocardium. Our results provided the strong evidences that exogenous H2S prevented cardiac remodeling, at least in part, through inhibition of extracellular matrix accumulation and increase in vascular density.

  16. Leptogenesis with heavy neutrino flavours: from density matrix to Boltzmann equations

    NASA Astrophysics Data System (ADS)

    Blanchet, Steve; Di Bari, Pasquale; Jones, David A.; Marzola, Luca

    2013-01-01

    Leptogenesis with heavy neutrino flavours is discussed within a density matrix formalism. We write the density matrix equation, describing the generation of the matter-antimatter asymmetry, for an arbitrary choice of the right-handed (RH) neutrino masses. For hierarchical RH neutrino masses lying in the fully flavoured regimes, this reduces to multiple-stage Boltzmann equations. In this case we recover and extend results previously derived within a quantum state collapse description. We confirm the generic existence of phantom terms. However, taking into account the effect of gauge interactions, we show that they are washed out at the production with a wash-out rate that is halved compared to that one acting on the total asymmetry. In the N1-dominated scenario they cancel without contributing to the final baryon asymmetry. In other scenarios they do not in general and they have to be taken into account. We also confirm that there is a (orthogonal) component in the asymmetry produced by the heavier RH neutrinos which completely escapes the washout from the lighter RH neutrinos and show that phantom terms additionally contribute to it. The other (parallel) component is washed out with the usual exponential factor, even for weak washout. Finally, as an illustration, we study the two RH neutrino model in the light of the above findings, showing that phantom terms can contribute to the final asymmetry also in this case.

  17. Unraveling multi-spin effects in rotational resonance nuclear magnetic resonance using effective reduced density matrix theory.

    PubMed

    SivaRanjan, Uppala; Ramachandran, Ramesh

    2014-02-01

    A quantum-mechanical model integrating the concepts of reduced density matrix and effective Hamiltonians is proposed to explain the multi-spin effects observed in rotational resonance (R(2)) nuclear magnetic resonance (NMR) experiments. Employing this approach, the spin system of interest is described in a reduced subspace inclusive of its coupling to the surroundings. Through suitable model systems, the utility of our theory is demonstrated and verified with simulations emerging from both analytic and numerical methods. The analytic results presented in this article provide an accurate description/interpretation of R(2) experimental results and could serve as a test-bed for distinguishing coherent/incoherent effects in solid-state NMR.

  18. Density-matrix-spectroscopic algorithm for excited-state adiabatic surfaces and molecular dynamics of a protonated Schiff base

    NASA Astrophysics Data System (ADS)

    Tsiper, E. V.; Chernyak, V.; Tretiak, S.; Mukamel, S.

    1999-05-01

    Excited-state potentials of a short protonated Schiff base cation which serves as a model for the photoisomerization of retinal are computed by combining a semi-empirical ground-state adiabatic surface with excitation energies obtained using the time-dependent coupled electronic oscillator (CEO) approach. Excited-state molecular dynamic simulation of the in-plane motion of cis-C5H6NH2+ following impulsive optical excitation reveals a dominating 1754 cm-1 π-conjugation mode. A new molecular dynamics algorithm is proposed which resembles the Car-Parinello ground-state technique and is based on the adiabatic propagation of the ground-state single-electron density matrix and the collective electronic modes along the trajectory.

  19. Unraveling multi-spin effects in rotational resonance nuclear magnetic resonance using effective reduced density matrix theory

    SciTech Connect

    SivaRanjan, Uppala; Ramachandran, Ramesh

    2014-02-07

    A quantum-mechanical model integrating the concepts of reduced density matrix and effective Hamiltonians is proposed to explain the multi-spin effects observed in rotational resonance (R{sup 2}) nuclear magnetic resonance (NMR) experiments. Employing this approach, the spin system of interest is described in a reduced subspace inclusive of its coupling to the surroundings. Through suitable model systems, the utility of our theory is demonstrated and verified with simulations emerging from both analytic and numerical methods. The analytic results presented in this article provide an accurate description/interpretation of R{sup 2} experimental results and could serve as a test-bed for distinguishing coherent/incoherent effects in solid-state NMR.

  20. Spin-adapted density matrix renormalization group algorithms for quantum chemistry

    NASA Astrophysics Data System (ADS)

    Sharma, Sandeep; Chan, Garnet Kin-Lic

    2012-03-01

    We extend the spin-adapted density matrix renormalization group (DMRG) algorithm of McCulloch and Gulacsi [Europhys. Lett. 57, 852 (2002)], 10.1209/epl/i2002-00393-0 to quantum chemical Hamiltonians. This involves using a quasi-density matrix, to ensure that the renormalized DMRG states are eigenfunctions of hat{S}^2, and the Wigner-Eckart theorem, to reduce overall storage and computational costs. We argue that the spin-adapted DMRG algorithm is most advantageous for low spin states. Consequently, we also implement a singlet-embedding strategy due to Tatsuaki [Phys. Rev. E 61, 3199 (2000)], 10.1103/PhysRevE.61.3199 where we target high spin states as a component of a larger fictitious singlet system. Finally, we present an efficient algorithm to calculate one- and two-body reduced density matrices from the spin-adapted wavefunctions. We evaluate our developments with benchmark calculations on transition metal system active space models. These include the Fe2S2, [Fe2S2(SCH3)4]2-, and Cr2 systems. In the case of Fe2S2, the spin-ladder spacing is on the microHartree scale, and here we show that we can target such very closely spaced states. In [Fe2S2(SCH3)4]2-, we calculate particle and spin correlation functions, to examine the role of sulfur bridging orbitals in the electronic structure. In Cr2 we demonstrate that spin-adaptation with the Wigner-Eckart theorem and using singlet embedding can yield up to an order of magnitude increase in computational efficiency. Overall, these calculations demonstrate the potential of using spin-adaptation to extend the range of DMRG calculations in complex transition metal problems.

  1. Defining specificities, genes, antigens, and antibodies- A matrix approach.

    PubMed

    Wohlgemuth, A

    1978-12-01

    We study the consequences of assigning single letter symbols to operationally defined entities such as genes, antigens, specificities, and antibodies. If this is to be done and if reagents are not specific in recognizing the products of single genes or single antigens, then these entities must be defined by a 'definition matrix' to avoid mislabeling a matrix of data. A method is given whereby for a given matrix of data all possible definition matrices consistent with this data can be obtained. In particular, all the ways of labeling by the complex-complex code of Hirschfeld can be so obtained.

  2. Simple Approach to Renormalize the Cabibbo-Kobayashi-Maskawa Matrix

    SciTech Connect

    Kniehl, Bernd A.; Sirlin, Alberto

    2006-12-01

    We present an on-shell scheme to renormalize the Cabibbo-Kobayashi-Maskawa (CKM) matrix. It is based on a novel procedure to separate the external-leg mixing corrections into gauge-independent self-mass and gauge-dependent wave function renormalization contributions, and to implement the on-shell renormalization of the former with nondiagonal mass counterterm matrices. Diagonalization of the complete mass matrix leads to an explicit CKM counterterm matrix, which automatically satisfies all the following important properties: it is gauge independent, preserves unitarity, and leads to renormalized amplitudes that are nonsingular in the limit in which any two fermions become mass degenerate.

  3. Approach to inherently stable interfaces for ceramic matrix composites

    SciTech Connect

    Besmann, T.M.; Kupp, E.R.; Stinton, D.P.; Shanmugham, S.

    1996-09-01

    Virtually all ceramic matrix composites require and interface coating between the fibers and matrix to achieve the desired mechanical performance. To date, the most effective interface materials for non- oxide matrix composites have been carbon and boron nitride. They are, however, susceptible to oxidation at elevated temperatures, and thus under many envisioned operating environments they will fail, possibly allowing oxidation of the fibers as well, adversely affecting mechanical behavior. Current efforts are directed toward developing stable interface coating, which include oxides and silicon carbide with appropriate thermomechanical properties.

  4. Validity of power functionals for a homogeneous electron gas in reduced-density-matrix-functional theory

    NASA Astrophysics Data System (ADS)

    Putaja, A.; Eich, F. G.; Baldsiefen, T.; Räsänen, E.

    2016-03-01

    Physically valid and numerically efficient approximations for the exchange and correlation energy are critical for reduced-density-matrix-functional theory to become a widely used method in electronic structure calculations. Here we examine the physical limits of power functionals of the form f (n ,n') =(nn')α for the scaling function in the exchange-correlation energy. To this end we obtain numerically the minimizing momentum distributions for the three- and two-dimensional homogeneous electron gas, respectively. In particular, we examine the limiting values for the power α to yield physically sound solutions that satisfy the Lieb-Oxford lower bound for the exchange-correlation energy and exclude pinned states with the condition n (k )<1 for all wave vectors k . The results refine the constraints previously obtained from trial momentum distributions. We also compute the values for α that yield the exact correlation energy and its kinetic part for both the three- and two-dimensional electron gas. In both systems, narrow regimes of validity and accuracy are found at α ≳0.6 and at rs≳10 for the density parameter, corresponding to relatively low densities.

  5. Random matrix theory for portfolio optimization: a stability approach

    NASA Astrophysics Data System (ADS)

    Sharifi, S.; Crane, M.; Shamaie, A.; Ruskin, H.

    2004-04-01

    We apply random matrix theory (RMT) to an empirically measured financial correlation matrix, C, and show that this matrix contains a large amount of noise. In order to determine the sensitivity of the spectral properties of a random matrix to noise, we simulate a set of data and add different volumes of random noise. Having ascertained that the eigenspectrum is independent of the standard deviation of added noise, we use RMT to determine the noise percentage in a correlation matrix based on real data from S&P500. Eigenvalue and eigenvector analyses are applied and the experimental results for each of them are presented to identify qualitatively and quantitatively different spectral properties of the empirical correlation matrix to a random counterpart. Finally, we attempt to separate the noisy part from the non-noisy part of C. We apply an existing technique to cleaning C and then discuss its associated problems. We propose a technique of filtering C that has many advantages, from the stability point of view, over the existing method of cleaning.

  6. Quantum phase transition by employing trace distance along with the density matrix renormalization group

    SciTech Connect

    Luo, Da-Wei; Xu, Jing-Bo

    2015-03-15

    We use an alternative method to investigate the quantum criticality at zero and finite temperature using trace distance along with the density matrix renormalization group. It is shown that the average correlation measured by the trace distance between the system block and environment block in a DMRG sweep is able to detect the critical points of quantum phase transitions at finite temperature. As illustrative examples, we study spin-1 XXZ chains with uniaxial single-ion-type anisotropy and the Heisenberg spin chain with staggered coupling and external magnetic field. It is found that the trace distance shows discontinuity at the critical points of quantum phase transition and can be used as an indicator of QPTs.

  7. Quasi-particle energy spectra in local reduced density matrix functional theory.

    PubMed

    Lathiotakis, Nektarios N; Helbig, Nicole; Rubio, Angel; Gidopoulos, Nikitas I

    2014-10-28

    Recently, we introduced [N. N. Lathiotakis, N. Helbig, A. Rubio, and N. I. Gidopoulos, Phys. Rev. A 90, 032511 (2014)] local reduced density matrix functional theory (local RDMFT), a theoretical scheme capable of incorporating static correlation effects in Kohn-Sham equations. Here, we apply local RDMFT to molecular systems of relatively large size, as a demonstration of its computational efficiency and its accuracy in predicting single-electron properties from the eigenvalue spectrum of the single-particle Hamiltonian with a local effective potential. We present encouraging results on the photoelectron spectrum of molecular systems and the relative stability of C20 isotopes. In addition, we propose a modelling of the fractional occupancies as functions of the orbital energies that further improves the efficiency of the method useful in applications to large systems and solids. PMID:25362285

  8. Density matrix renormalization group study of triangular Kitaev-Heisenberg model

    NASA Astrophysics Data System (ADS)

    Sota, Shigetoshi; Sjinjo, Kazuya; Shirakawa, Tomonori; Tohyama, Takami; Yunoki, Seiji

    2015-03-01

    Topological insulator has been one of the most active subjects in the current condensed matter physics. For most of topological insulators electron correlations are considered to be not essential. However, in the case where electron correlations are strong, novel phases such as a spin liquid phase can emerge in competition with a spin-orbit coupling. Here, using the density matrix renormalization group method, we investigate magnetic phase of a triangular Kitaev-Heisenberg (quantum compass) model that contains a spin-orbital interaction and spin frustration in the antiferromagnetic region. The triangular Kitaev-Heisenberg model is regarded as a dual model of the honeycomb Kitaev-Heisenberg model that is usually employed to discuss A2CuO3 (A=Na, K). Systematically calculating ground state energy, entanglement entropy, entanglement spectrum, and spin-spin correlation functions, we discuss the duality between the triangular and the honeycomb Kitaev-Heisenberg model as well as the ground state magnetic phases.

  9. A Practical Guide to Density Matrix Embedding Theory in Quantum Chemistry.

    PubMed

    Wouters, Sebastian; Jiménez-Hoyos, Carlos A; Sun, Qiming; Chan, Garnet K-L

    2016-06-14

    Density matrix embedding theory (DMET) (Knizia, G.; Chan, G. K.-L. Phys. Rev. Lett. 2012, 109, 186404) provides a theoretical framework to treat finite fragments in the presence of a surrounding molecular or bulk environment, even when there is significant correlation or entanglement between the two. In this work, we give a practically oriented and explicit description of the numerical and theoretical formulation of DMET. We also describe in detail how to perform self-consistent DMET optimizations. We explore different embedding strategies with and without a self-consistency condition in hydrogen rings, beryllium rings, and a sample SN2 reaction. The source code for the calculations in this work can be obtained from https://github.com/sebwouters/qc-dmet .

  10. Reduced Density Matrix and Entanglement Entropy of Permutationally Invariant Quantum Many-Body Systems

    NASA Astrophysics Data System (ADS)

    Popkov, Vladislav; Salerno, Mario

    2013-06-01

    In this paper we discuss the properties of the reduced density matrix of quantum many body systems with permutational symmetry and present basic quantification of the entanglement in terms of the von Neumann (VNE), Renyi and Tsallis entropies. In particular, we show, on the specific example of the spin 1/2 Heisenberg model, how the RDM acquires a block diagonal form with respect to the quantum number k fixing the polarization in the subsystem conservation of Sz and with respect to the irreducible representations of the Sn group. Analytical expression for the RDM elements and for the RDM spectrum are derived for states of arbitrary permutational symmetry and for arbitrary polarizations. The temperature dependence and scaling of the VNE across a finite temperature phase transition is discussed and the RDM moments and the Rényi and Tsallis entropies calculated both for symmetric ground states of the Heisenberg chain and for maximally mixed states.

  11. Reduced Density Matrix and Entanglement Entropy of Permutationally Invariant Quantum Many-Body Systems

    NASA Astrophysics Data System (ADS)

    Popkov, Vladislav; Salerno, Mario

    2012-11-01

    In this paper we discuss the properties of the reduced density matrix of quantum many body systems with permutational symmetry and present basic quantification of the entanglement in terms of the von Neumann (VNE), Renyi and Tsallis entropies. In particular, we show, on the specific example of the spin 1/2 Heisenberg model, how the RDM acquires a block diagonal form with respect to the quantum number k fixing the polarization in the subsystem conservation of Sz and with respect to the irreducible representations of the Sn group. Analytical expression for the RDM elements and for the RDM spectrum are derived for states of arbitrary permutational symmetry and for arbitrary polarizations. The temperature dependence and scaling of the VNE across a finite temperature phase transition is discussed and the RDM moments and the Rényi and Tsallis entropies calculated both for symmetric ground states of the Heisenberg chain and for maximally mixed states.

  12. Quasi-particle energy spectra in local reduced density matrix functional theory

    SciTech Connect

    Lathiotakis, Nektarios N.; Helbig, Nicole; Rubio, Angel

    2014-10-28

    Recently, we introduced [N. N. Lathiotakis, N. Helbig, A. Rubio, and N. I. Gidopoulos, Phys. Rev. A 90, 032511 (2014)] local reduced density matrix functional theory (local RDMFT), a theoretical scheme capable of incorporating static correlation effects in Kohn-Sham equations. Here, we apply local RDMFT to molecular systems of relatively large size, as a demonstration of its computational efficiency and its accuracy in predicting single-electron properties from the eigenvalue spectrum of the single-particle Hamiltonian with a local effective potential. We present encouraging results on the photoelectron spectrum of molecular systems and the relative stability of C{sub 20} isotopes. In addition, we propose a modelling of the fractional occupancies as functions of the orbital energies that further improves the efficiency of the method useful in applications to large systems and solids.

  13. Low-density, high-strength intermetallic matrix composites by XD (trademark) synthesis

    NASA Technical Reports Server (NTRS)

    Kumar, K. S.; Dipietro, M. S.; Brown, S. A.; Whittenberger, J. D.

    1991-01-01

    A feasibility study was conducted to evaluate the potential of particulate composites based on low-density, L1(sub 2) trialuminide matrices for high-temperature applications. The compounds evaluated included Al22Fe3Ti8 (as a multiphase matrix), Al67Ti25Cr8, and Al66Ti25Mn9. The reinforcement consisted of TiB2 particulates. The TiB2 composites were processed by ingot and powder metallurgy techniques. Microstructural characterization and mechanical testing were performed in the hot-pressed and hot-isostatic-pressed condition. The casting were sectioned and isothermally forged into pancakes. All the materials were tested in compression as a function of temperature, and at high temperatures as a function of strain rate. The test results are discussed.

  14. Density-matrix renormalization-group study of current and activity fluctuations near nonequilibrium phase transitions.

    PubMed

    Gorissen, Mieke; Hooyberghs, Jef; Vanderzande, Carlo

    2009-02-01

    Cumulants of a fluctuating current can be obtained from a free-energy-like generating function, which for Markov processes equals the largest eigenvalue of a generalized generator. We determine this eigenvalue with the density-matrix renormalization group for stochastic systems. We calculate the variance of the current in the different phases, and at the phase transitions, of the totally asymmetric exclusion process. Our results can be described in the terms of a scaling ansatz that involves the dynamical exponent z . We also calculate the generating function of the dynamical activity (total number of configuration changes) near the absorbing-state transition of the contact process. Its scaling properties can be expressed in terms of known critical exponents. PMID:19391693

  15. Differential cross sections and spin density matrix elements for the reaction γp→pω

    NASA Astrophysics Data System (ADS)

    Williams, M.; Applegate, D.; Bellis, M.; Meyer, C. A.; Adhikari, K. P.; Anghinolfi, M.; Baghdasaryan, H.; Ball, J.; Battaglieri, M.; Bedlinskiy, I.; Berman, B. L.; Biselli, A. S.; Bookwalter, C.; Briscoe, W. J.; Brooks, W. K.; Burkert, V. D.; Careccia, S. L.; Carman, D. S.; Cole, P. L.; Collins, P.; Crede, V.; D'Angelo, A.; Daniel, A.; Vita, R. De; Sanctis, E. De; Deur, A.; Dey, B.; Dhamija, S.; Dickson, R.; Djalali, C.; Dodge, G. E.; Doughty, D.; Dugger, M.; Dupre, R.; Alaoui, A. El; Elouadrhiri, L.; Eugenio, P.; Fedotov, G.; Fegan, S.; Fradi, A.; Gabrielyan, M. Y.; Garçon, M.; Gevorgyan, N.; Gilfoyle, G. P.; Giovanetti, K. L.; Girod, F. X.; Gohn, W.; Golovatch, E.; Gothe, R. W.; Griffioen, K. A.; Guidal, M.; Guo, L.; Hafidi, K.; Hakobyan, H.; Hanretty, C.; Hassall, N.; Hicks, K.; Holtrop, M.; Ilieva, Y.; Ireland, D. G.; Ishkhanov, B. S.; Isupov, E. L.; Jawalkar, S. S.; Jo, H. S.; Johnstone, J. R.; Joo, K.; Keller, D.; Khandaker, M.; Khetarpal, P.; Kim, W.; Klein, A.; Klein, F. J.; Krahn, Z.; Kubarovsky, V.; Kuleshov, S. V.; Kuznetsov, V.; Livingston, K.; Lu, H. Y.; Mayer, M.; McAndrew, J.; McCracken, M. E.; McKinnon, B.; Mikhailov, K.; Mirazita, M.; Mokeev, V.; Moreno, B.; Moriya, K.; Morrison, B.; Moutarde, H.; Munevar, E.; Nadel-Turonski, P.; Nepali, C. S.; Niccolai, S.; Niculescu, G.; Niculescu, I.; Niroula, M. R.; Niyazov, R. A.; Osipenko, M.; Ostrovidov, A. I.; Paris, M.; Park, K.; Park, S.; Pasyuk, E.; Pereira, S. Anefalos; Perrin, Y.; Pisano, S.; Pogorelko, O.; Pozdniakov, S.; Price, J. W.; Procureur, S.; Protopopescu, D.; Raue, B. A.; Ricco, G.; Ripani, M.; Ritchie, B. G.; Rosner, G.; Rossi, P.; Sabatié, F.; Saini, M. S.; Salamanca, J.; Salgado, C.; Schott, D.; Schumacher, R. A.; Seraydaryan, H.; Sharabian, Y. G.; Smith, E. S.; Sober, D. I.; Sokhan, D.; Stepanyan, S. S.; Stoler, P.; Strakovsky, I. I.; Strauch, S.; Taiuti, M.; Tedeschi, D. J.; Tkachenko, S.; Ungaro, M.; Vineyard, M. F.; Voutier, E.; Watts, D. P.; Weinstein, L. B.; Weygand, D. P.; Wood, M. H.; Zhang, J.; Zhao, B.

    2009-12-01

    High-statistics differential cross sections and spin-density matrix elements for the reaction γp→pω have been measured using the CEBAF large acceptance spectrometer (CLAS) at Jefferson Lab for center-of-mass (c.m.) energies from threshold up to 2.84 GeV. Results are reported in 11210-MeV wide c.m. energy bins, each subdivided into cosθc.m.ω bins of width 0.1. These are the most precise and extensive ω photoproduction measurements to date. A number of prominent structures are clearly present in the data. Many of these have not previously been observed due to limited statistics in earlier measurements.

  16. A Practical Guide to Density Matrix Embedding Theory in Quantum Chemistry.

    PubMed

    Wouters, Sebastian; Jiménez-Hoyos, Carlos A; Sun, Qiming; Chan, Garnet K-L

    2016-06-14

    Density matrix embedding theory (DMET) (Knizia, G.; Chan, G. K.-L. Phys. Rev. Lett. 2012, 109, 186404) provides a theoretical framework to treat finite fragments in the presence of a surrounding molecular or bulk environment, even when there is significant correlation or entanglement between the two. In this work, we give a practically oriented and explicit description of the numerical and theoretical formulation of DMET. We also describe in detail how to perform self-consistent DMET optimizations. We explore different embedding strategies with and without a self-consistency condition in hydrogen rings, beryllium rings, and a sample SN2 reaction. The source code for the calculations in this work can be obtained from https://github.com/sebwouters/qc-dmet . PMID:27159268

  17. Generalized information (entanglement) entropies depending on the probability (density matrix), (modified gravity)

    NASA Astrophysics Data System (ADS)

    Obregón, Octavio; Cabo Bizet, Nana Geraldine

    2016-03-01

    Generalized information (entanglement) entropy(ies) that depend only on the probability (the density matrix) will be exhibited. It will be shown that these generalized information entropy(ies) are obtained by means of the superstatistics proposal and they correspond to generalized entanglement entropy(ies) that are at the same time a consequence of generalizing the Replica trick. Following the entropic force formulation, these generalized entropy(ies) provide a modified Newtońs law of gravitation. We discuss the difficulties to get an associated theory of gravity. Moreover, our results show corrections to the von Neumann entropy S0 that are larger than the usual UV ones and also than the corrections to the length dependent AdS3 entropy which result comparable to the UV ones. The correction terms due to the new entropy would modify the Ryu-Takayanagi identification between the CFT and the gravitational AdS3 entropies.

  18. Transfer and reconstruction of the density matrix in off-axis electron holography.

    PubMed

    Röder, Falk; Lubk, Axel

    2014-11-01

    The reduced density matrix completely describes the quantum state of an electron scattered by an object in transmission electron microscopy. However, the detection process restricts access to the diagonal elements only. The off-diagonal elements, determining the coherence of the scattered electron, may be obtained from electron holography. In order to extract the influence of the object from the off-diagonals, however, a rigorous consideration of the electron microscope influences like aberrations of the objective lens and the Möllenstedt biprism in the presence of partial coherence is required. Here, we derive a holographic transfer theory based on the generalization of the transmission cross-coefficient including all known holographic phenomena. We furthermore apply a particular simplification of the theory to the experimental analysis of aloof beam electrons scattered by plane silicon surfaces.

  19. Magnitude and significance of the higher-order reduced density matrix cumulants

    NASA Astrophysics Data System (ADS)

    Herbert, John M.

    Using full configuration interaction wave functions for Be and LiH, in both minimal and extended basis sets, we examine the absolute magnitude and energetic significance of various contributions to the three-electron reduced density matrix (3-RDM) and its connected (size-consistent) component, the 3-RDM cumulant (3-RDMC). Minimal basis sets are shown to suppress the magnitude of the 3-RDMC in an artificial manner, whereas in extended basis sets, 3-RDMC matrix elements are often comparable in magnitude to the corresponding 3-RDM elements, even in cases where this result is not required by spin angular momentum coupling. Formal considerations suggest that these observations should generalize to higher-order p-RDMs and p-RDMCs (p > 3). This result is discussed within the context of electronic structure methods based on the contracted Schrödinger equation (CSE), as solution of the CSE relies on 3- and 4-RDM ?reconstruction functionals? that neglect the 3-RDMC, the 4-RDMC, or both. Although the 3-RDMC is responsible for at most 0.2% of the total electronic energy in Be and LiH, it accounts for up to 70% of the correlation energy, raising questions regarding whether (and how) the CSE can offer a useful computational methodology.

  20. Linear response theory for the density matrix renormalization group: Efficient algorithms for strongly correlated excited states

    NASA Astrophysics Data System (ADS)

    Nakatani, Naoki; Wouters, Sebastian; Van Neck, Dimitri; Chan, Garnet Kin-Lic

    2014-01-01

    Linear response theory for the density matrix renormalization group (DMRG-LRT) was first presented in terms of the DMRG renormalization projectors [J. J. Dorando, J. Hachmann, and G. K.-L. Chan, J. Chem. Phys. 130, 184111 (2009)]. Later, with an understanding of the manifold structure of the matrix product state (MPS) ansatz, which lies at the basis of the DMRG algorithm, a way was found to construct the linear response space for general choices of the MPS gauge in terms of the tangent space vectors [J. Haegeman, J. I. Cirac, T. J. Osborne, I. Pižorn, H. Verschelde, and F. Verstraete, Phys. Rev. Lett. 107, 070601 (2011)]. These two developments led to the formulation of the Tamm-Dancoff and random phase approximations (TDA and RPA) for MPS. This work describes how these LRTs may be efficiently implemented through minor modifications of the DMRG sweep algorithm, at a computational cost which scales the same as the ground-state DMRG algorithm. In fact, the mixed canonical MPS form implicit to the DMRG sweep is essential for efficient implementation of the RPA, due to the structure of the second-order tangent space. We present ab initio DMRG-TDA results for excited states of polyenes, the water molecule, and a [2Fe-2S] iron-sulfur cluster.

  1. One plus two-body random matrix ensembles with parity: Density of states and parity ratios

    SciTech Connect

    Vyas, Manan; Srivastava, P. C.; Kota, V. K. B.

    2011-06-15

    One plus two-body embedded Gaussian orthogonal ensemble of random matrices with parity [EGOE(1+2)-{pi}] generated by a random two-body interaction (modeled by GOE in two-particle spaces) in the presence of a mean field for spinless identical fermion systems is defined, generalizing the two-body ensemble with parity analyzed by Papenbrock and Weidenmueller [Phys. Rev. C 78, 054305 (2008)], in terms of two mixing parameters and a gap between the positive ({pi}=+) and negative ({pi}=-) parity single-particle (sp) states. Numerical calculations are used to demonstrate, using realistic values of the mixing parameters appropriate for some nuclei, that the EGOE(1+2)-{pi} ensemble generates Gaussian form (with corrections) for fixed parity eigenvalue densities (i.e., state densities). The random matrix model also generates many features in parity ratios of state densities that are similar to those predicted by a method based on the Fermi-gas model for nuclei. We have also obtained, by applying the formulation due to Chang et al. [Ann. Phys. (NY) 66, 137 (1971)], a simple formula for the spectral variances defined over fixed-(m{sub 1},m{sub 2}) spaces, where m{sub 1} is the number of fermions in the positive parity sp states and m{sub 2} is the number of fermions in the negative parity sp states. Similarly, using the binary correlation approximation, in the dilute limit, we have derived expressions for the lowest two-shape parameters. The smoothed densities generated by the sum of fixed-(m{sub 1},m{sub 2}) Gaussians with lowest two-shape corrections describe the numerical results in many situations. The model also generates preponderance of positive parity ground states for small values of the mixing parameters, and this is a feature seen in nuclear shell-model results.

  2. An infrastructureless approach to estimate vehicular density in urban environments.

    PubMed

    Sanguesa, Julio A; Fogue, Manuel; Garrido, Piedad; Martinez, Francisco J; Cano, Juan-Carlos; Calafate, Carlos T; Manzoni, Pietro

    2013-01-01

    In Vehicular Networks, communication success usually depends on the density of vehicles, since a higher density allows having shorter and more reliable wireless links. Thus, knowing the density of vehicles in a vehicular communications environment is important, as better opportunities for wireless communication can show up. However, vehicle density is highly variable in time and space. This paper deals with the importance of predicting the density of vehicles in vehicular environments to take decisions for enhancing the dissemination of warning messages between vehicles. We propose a novel mechanism to estimate the vehicular density in urban environments. Our mechanism uses as input parameters the number of beacons received per vehicle, and the topological characteristics of the environment where the vehicles are located. Simulation results indicate that, unlike previous proposals solely based on the number of beacons received, our approach is able to accurately estimate the vehicular density, and therefore it could support more efficient dissemination protocols for vehicular environments, as well as improve previously proposed schemes. PMID:23435054

  3. Probing intrinsic anisotropies of fluorescence: Mueller matrix approach.

    PubMed

    Saha, Sudipta; Soni, Jalpa; Chandel, Shubham; Kumar, Uday; Ghosh, Nirmalya

    2015-08-01

    We demonstrate that information on “intrinsic” anisotropies of fluorescence originating from preferential orientation/organization of fluorophore molecules can be probed using a Mueller matrix of fluorescence. For this purpose, we have developed a simplified model to decouple and separately quantify the depolarization property and the intrinsic anisotropy properties of fluorescence from the experimentally measured fluorescence Mueller matrix. Unlike the traditionally defined fluorescence anisotropy parameter, the Mueller matrix-derived fluorescence polarization metrics, namely, fluorescence diattenuation and polarizance parameters, exclusively deal with the intrinsic anisotropies of fluorescence. The utility of these newly derived fluorescence polarimetry parameters is demonstrated on model systems exhibiting multiple polarimetry effects, and an interesting example is illustrated on biomedically important fluorophores, collagen. PMID:26301796

  4. Full density-matrix numerical renormalization group calculation of impurity susceptibility and specific heat of the Anderson impurity model

    NASA Astrophysics Data System (ADS)

    Merker, L.; Weichselbaum, A.; Costi, T. A.

    2012-08-01

    Recent developments in the numerical renormalization group (NRG) allow the construction of the full density matrix (FDM) of quantum impurity models [see A. Weichselbaum and J. von Delft, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.99.076402 99, 076402 (2007)] by using the completeness of the eliminated states introduced by F. B. Anders and A. Schiller [F. B. Anders and A. Schiller, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.95.196801 95, 196801 (2005)]. While these developments prove particularly useful in the calculation of transient response and finite-temperature Green's functions of quantum impurity models, they may also be used to calculate thermodynamic properties. In this paper, we assess the FDM approach to thermodynamic properties by applying it to the Anderson impurity model. We compare the results for the susceptibility and specific heat to both the conventional approach within NRG and to exact Bethe ansatz results. We also point out a subtlety in the calculation of the susceptibility (in a uniform field) within the FDM approach. Finally, we show numerically that for the Anderson model, the susceptibilities in response to a local and a uniform magnetic field coincide in the wide-band limit, in accordance with the Clogston-Anderson compensation theorem.

  5. Random matrix approach to the distribution of genomic distance.

    PubMed

    Alexeev, Nikita; Zograf, Peter

    2014-08-01

    The cycle graph introduced by Bafna and Pevzner is an important tool for evaluating the distance between two genomes, that is, the minimal number of rearrangements needed to transform one genome into another. We interpret this distance in topological terms and relate it to the random matrix theory. Namely, the number of genomes at a given 2-break distance from a fixed one (the Hultman number) is represented by a coefficient in the genus expansion of a matrix integral over the space of complex matrices with the Gaussian measure. We study generating functions for the Hultman numbers and prove that the two-break distance distribution is asymptotically normal.

  6. Random Matrix Approach to the Distribution of Genomic Distance

    PubMed Central

    Alexeev, Nikita

    2014-01-01

    Abstract The cycle graph introduced by Bafna and Pevzner is an important tool for evaluating the distance between two genomes, that is, the minimal number of rearrangements needed to transform one genome into another. We interpret this distance in topological terms and relate it to the random matrix theory. Namely, the number of genomes at a given 2-break distance from a fixed one (the Hultman number) is represented by a coefficient in the genus expansion of a matrix integral over the space of complex matrices with the Gaussian measure. We study generating functions for the Hultman numbers and prove that the two-break distance distribution is asymptotically normal. PMID:24650202

  7. Random matrix approach to the distribution of genomic distance.

    PubMed

    Alexeev, Nikita; Zograf, Peter

    2014-08-01

    The cycle graph introduced by Bafna and Pevzner is an important tool for evaluating the distance between two genomes, that is, the minimal number of rearrangements needed to transform one genome into another. We interpret this distance in topological terms and relate it to the random matrix theory. Namely, the number of genomes at a given 2-break distance from a fixed one (the Hultman number) is represented by a coefficient in the genus expansion of a matrix integral over the space of complex matrices with the Gaussian measure. We study generating functions for the Hultman numbers and prove that the two-break distance distribution is asymptotically normal. PMID:24650202

  8. Density matrix reconstruction of three-level atoms via Rydberg electromagnetically induced transparency

    NASA Astrophysics Data System (ADS)

    Gavryusev, V.; Signoles, A.; Ferreira-Cao, M.; Zürn, G.; Hofmann, C. S.; Günter, G.; Schempp, H.; Robert-de-Saint-Vincent, M.; Whitlock, S.; Weidemüller, M.

    2016-08-01

    We present combined measurements of the spatially resolved optical spectrum and the total excited-atom number in an ultracold gas of three-level atoms under electromagnetically induced transparency conditions involving high-lying Rydberg states. The observed optical transmission of a weak probe laser at the center of the coupling region exhibits a double peaked spectrum as a function of detuning, while the Rydberg atom number shows a comparatively narrow single resonance. By imaging the transmitted light onto a charge-coupled-device camera, we record hundreds of spectra in parallel, which are used to map out the spatial profile of Rabi frequencies of the coupling laser. Using all the information available we can reconstruct the full one-body density matrix of the three-level system, which provides the optical susceptibility and the Rydberg density as a function of spatial position. These results help elucidate the connection between three-level interference phenomena, including the interplay of matter and light degrees of freedom and will facilitate new studies of many-body effects in optically driven Rydberg gases.

  9. Exploring multicollinearity using a random matrix theory approach.

    PubMed

    Feher, Kristen; Whelan, James; Müller, Samuel

    2012-01-01

    Clustering of gene expression data is often done with the latent aim of dimension reduction, by finding groups of genes that have a common response to potentially unknown stimuli. However, what is poorly understood to date is the behaviour of a low dimensional signal embedded in high dimensions. This paper introduces a multicollinear model which is based on random matrix theory results, and shows potential for the characterisation of a gene cluster's correlation matrix. This model projects a one dimensional signal into many dimensions and is based on the spiked covariance model, but rather characterises the behaviour of the corresponding correlation matrix. The eigenspectrum of the correlation matrix is empirically examined by simulation, under the addition of noise to the original signal. The simulation results are then used to propose a dimension estimation procedure of clusters from data. Moreover, the simulation results warn against considering pairwise correlations in isolation, as the model provides a mechanism whereby a pair of genes with `low' correlation may simply be due to the interaction of high dimension and noise. Instead, collective information about all the variables is given by the eigenspectrum.

  10. A novel approach for FE-SEM imaging of wood-matrix polymer interface in a biocomposite.

    PubMed

    Singh, Adya P; Anderson, Ross; Park, Byung-Dae; Nuryawan, Arif

    2013-01-01

    Understanding the interface between polymer and biomass in composite products is important for developing high performance products, as the quality of adhesion at the interface determines composite properties. For example, with greater stiffness compared to polymer matrix, such as that of high density polyethylene, the wood component enhances stiffness of wood-polymer composites, provided there is good adhesion between composite components. However, in composites made from wood flour (wood particles) and synthetic resins it is often difficult to clearly resolve particle-matrix interfaces in the conventionally employed microscopy method that involves SEM examination of fractured faces of composites. We developed a novel approach, where composites made from high density polyethylene and wood flour were examined and imaged with a FE-SEM (field emission scanning electron microscope) in transverse sections cut through the composites. Improved definition of the interface was achieved using this approach, which enabled a more thorough comparison to be made of the features of the interface between wood particles and the matrix in composites with and without a coupling agent, as it was possible to clearly resolve the interfaces for particles of all sizes, from large particles consisting of many cells down to tiny cell wall fragments, particularly in composites that did not incorporate the coupling agent used to enhance particle adhesion with the matrix polymer. The method developed would be suitable particularly for high definition SEM imaging of a wide range of composites made combining wood and agricultural residues with synthetic polymers.

  11. A novel approach for FE-SEM imaging of wood-matrix polymer interface in a biocomposite.

    PubMed

    Singh, Adya P; Anderson, Ross; Park, Byung-Dae; Nuryawan, Arif

    2013-01-01

    Understanding the interface between polymer and biomass in composite products is important for developing high performance products, as the quality of adhesion at the interface determines composite properties. For example, with greater stiffness compared to polymer matrix, such as that of high density polyethylene, the wood component enhances stiffness of wood-polymer composites, provided there is good adhesion between composite components. However, in composites made from wood flour (wood particles) and synthetic resins it is often difficult to clearly resolve particle-matrix interfaces in the conventionally employed microscopy method that involves SEM examination of fractured faces of composites. We developed a novel approach, where composites made from high density polyethylene and wood flour were examined and imaged with a FE-SEM (field emission scanning electron microscope) in transverse sections cut through the composites. Improved definition of the interface was achieved using this approach, which enabled a more thorough comparison to be made of the features of the interface between wood particles and the matrix in composites with and without a coupling agent, as it was possible to clearly resolve the interfaces for particles of all sizes, from large particles consisting of many cells down to tiny cell wall fragments, particularly in composites that did not incorporate the coupling agent used to enhance particle adhesion with the matrix polymer. The method developed would be suitable particularly for high definition SEM imaging of a wide range of composites made combining wood and agricultural residues with synthetic polymers. PMID:24063951

  12. A novel gastro-floating multiparticulate system for dipyridamole (DIP) based on a porous and low-density matrix core: in vitro and in vivo evaluation.

    PubMed

    Li, Zhao; Xu, Heming; Li, Shujuan; Li, Qijun; Zhang, Wenji; Ye, Tiantian; Yang, Xinggang; Pan, Weisan

    2014-01-30

    The study was aimed to develop a novel gastro-floating multiparticulate system based on a porous and low-density matrix core with excellent floatability. The gastro-floating pellets (GFP) were composed of a porous matrix core, a drug loaded layer (DIP and HPMC), a sub-coating layer (HPMC) and a retarding layer (Eudragit(®) NE 30D). The porous matrix cores were evaluated in specific. EC was chosen as the matrix membrane for its rigidity and minimal expansion to large extent. The porous matrix core was achieved by the complete release of the bulk water soluble excipient from the EC coated beads, and mannitol was selected as the optimal water soluble excipient. SEM photomicrographs confirmed the structure of porous matrix cores. The compositions of GFP were investigated and optimized by orthogonal array design. The optimized formulation could sustain the drug release for 12h and float on the dissolution medium for at least 12h without lag time to float. The pharmacokinetic study was conducted in beagle dogs, and the relative bioavailability of the test preparation was 193.11±3.43%. In conclusion, the novel gastro-floating pellets can be developed as a promising approach for the gastro-retentive drug delivery systems. PMID:24368104

  13. A novel gastro-floating multiparticulate system for dipyridamole (DIP) based on a porous and low-density matrix core: in vitro and in vivo evaluation.

    PubMed

    Li, Zhao; Xu, Heming; Li, Shujuan; Li, Qijun; Zhang, Wenji; Ye, Tiantian; Yang, Xinggang; Pan, Weisan

    2014-01-30

    The study was aimed to develop a novel gastro-floating multiparticulate system based on a porous and low-density matrix core with excellent floatability. The gastro-floating pellets (GFP) were composed of a porous matrix core, a drug loaded layer (DIP and HPMC), a sub-coating layer (HPMC) and a retarding layer (Eudragit(®) NE 30D). The porous matrix cores were evaluated in specific. EC was chosen as the matrix membrane for its rigidity and minimal expansion to large extent. The porous matrix core was achieved by the complete release of the bulk water soluble excipient from the EC coated beads, and mannitol was selected as the optimal water soluble excipient. SEM photomicrographs confirmed the structure of porous matrix cores. The compositions of GFP were investigated and optimized by orthogonal array design. The optimized formulation could sustain the drug release for 12h and float on the dissolution medium for at least 12h without lag time to float. The pharmacokinetic study was conducted in beagle dogs, and the relative bioavailability of the test preparation was 193.11±3.43%. In conclusion, the novel gastro-floating pellets can be developed as a promising approach for the gastro-retentive drug delivery systems.

  14. An equivalent roughness model for seabed backscattering at very high frequencies using a band-matrix approach.

    PubMed

    Wendelboe, Gorm; Jacobsen, Finn; Bell, Judith M

    2007-02-01

    This work concerns modeling of very high frequency (>100 kHz) sonar images obtained from a sandy seabed. The seabed is divided into a discrete number of ID height profiles. For each height profile the backscattered pressure is computed by an integral equation method for interface scattering between two homogeneous media as formulated by Chan [IEEE Trans. Antennas Propag. 46, 142-149 (1998)]. However, the seabed is inhomogeneous, and volume scattering is a major contributor to backscattering. The SAX99 experiments revealed that the density in the unconsolidated sediment within the first 5 mm exhibits a high spatial variation. For that reason, additional roughness is introduced: For each surface point a stochastic realization of the density along the vertical is generated, and the sediment depth at which the density has its maximum value will constitute the new height field value. The matrix of the full integral equation is reduced to a band matrix as the interaction between the point sources on the seabed is neglected from a certain range; this allows computations on long height profiles with lengths up to approximately 25 m (at 300 kHz). The equivalent roughness approach, combined with the band-matrix approach, agrees with SAX99 data at 300 kHz.

  15. Floquet topological systems in the vicinity of level crossings: Reservoir induced coherence of the Floquet density matrix and steady-state entropy production

    NASA Astrophysics Data System (ADS)

    Dehghani, Hossein; Mitra, Aditi

    Results are presented for a Floquet topological system for the case where the separation between quasi-energy levels becomes small, and in particular, comparable to the coupling strength to an external reservoir. For this case, even at steady-state, the reduced density matrix in the Floquet basis has non-zero off-diagonal elements, with the strength of the off-diagonal elements increasing as one approaches the level crossings. The steady-state reduced density matrix has oscillations at integer multiples of the periodic drive, and a Fourier decomposition allows the extraction of the occupation of the Floquet quasi-energy levels, which also depends on the coupling to the reservoir. The lack of detailed balance is quantified in terms of an entropy production rate. Supported by US Department of Energy, Office of Science, Basic Energy Sciences, under Award No. DE-SC0010821.

  16. High-density collagen gel tubes as a matrix for primary human bladder smooth muscle cells.

    PubMed

    Micol, Lionel A; Ananta, Michael; Engelhardt, Eva-Maria; Mudera, Vivek C; Brown, Robert A; Hubbell, Jeffrey A; Frey, Peter

    2011-02-01

    Tissue-engineered grafts for the urinary tract are being investigated for the potential treatment of several urologic diseases. These grafts, predominantly tubular-shaped, usually require in vitro culture prior to implantation to allow cell engraftment on initially cell-free scaffolds. We have developed a method to produce tubular-shaped collagen scaffolds based on plastic compression. Our approach produces a ready cell-seeded graft that does not need further in vitro culture prior to implantation. The tubular collagen scaffolds were in particular investigated for their structural, mechanical and biological properties. The resulting construct showed an especially high collagen density, and was characterized by favorable mechanical properties assessed by axial extension and radial dilation. Young modulus in particular was greater than non-compressed collagen tubes. Seeding densities affected proliferation rate of primary human bladder smooth muscle cells. An optimal seeding density of 10(6) cells per construct resulted in a 25-fold increase in Alamar blue-based fluorescence after 2 wk in culture. These high-density collagen gel tubes, ready seeded with smooth muscle cells could be further seeded with urothelial cells, drastically shortening the production time of graft for urinary tract regeneration.

  17. Decoherence in chaotic and integrable systems: a random matrix approach

    NASA Astrophysics Data System (ADS)

    Gorin, T.; Seligman, T. H.

    2003-03-01

    We study the influence of chaos and order on entanglement and decoherence. In view of applications in quantum computing and teleportation which should be able to work with arbitrarily complicated states, we pay particular attention to the behavior of random states. While studies with coherent states indicate that chaos accelerates decoherence and entanglement, we find that there is practically no difference between the chaotic and the integrable case, as far as random states are concerned. In the present studies we use unitary time evolution of the total system, and partial traces to emulate decoherence. Random matrix models are a natural choice to describe the dynamics of random states. The invariant aspects of chaos and order are then reflected in the different spectral statistics. We develop random matrix models for the evolution of entanglement for a large variety of situations, discussing the strong coupling case in full detail.

  18. A reduced-scaling density matrix-based method for the computation of the vibrational Hessian matrix at the self-consistent field level

    SciTech Connect

    Kussmann, Jörg; Luenser, Arne; Beer, Matthias; Ochsenfeld, Christian

    2015-03-07

    An analytical method to calculate the molecular vibrational Hessian matrix at the self-consistent field level is presented. By analysis of the multipole expansions of the relevant derivatives of Coulomb-type two-electron integral contractions, we show that the effect of the perturbation on the electronic structure due to the displacement of nuclei decays at least as r{sup −2} instead of r{sup −1}. The perturbation is asymptotically local, and the computation of the Hessian matrix can, in principle, be performed with O(N) complexity. Our implementation exhibits linear scaling in all time-determining steps, with some rapid but quadratic-complexity steps remaining. Sample calculations illustrate linear or near-linear scaling in the construction of the complete nuclear Hessian matrix for sparse systems. For more demanding systems, scaling is still considerably sub-quadratic to quadratic, depending on the density of the underlying electronic structure.

  19. Assessment of a three-dimensional line-of-response probability density function system matrix for PET.

    PubMed

    Yao, Rutao; Ramachandra, Ranjith M; Mahajan, Neeraj; Rathod, Vinay; Gunasekar, Noel; Panse, Ashish; Ma, Tianyu; Jian, Yiqiang; Yan, Jianhua; Carson, Richard E

    2012-11-01

    To achieve optimal PET image reconstruction through better system modeling, we developed a system matrix that is based on the probability density function for each line of response (LOR-PDF). The LOR-PDFs are grouped by LOR-to-detector incident angles to form a highly compact system matrix. The system matrix was implemented in the MOLAR list mode reconstruction algorithm for a small animal PET scanner. The impact of LOR-PDF on reconstructed image quality was assessed qualitatively as well as quantitatively in terms of contrast recovery coefficient (CRC) and coefficient of variance (COV), and its performance was compared with a fixed Gaussian (iso-Gaussian) line spread function. The LOR-PDFs of three coincidence signal emitting sources, (1) ideal positron emitter that emits perfect back-to-back γ rays (γγ) in air; (2) fluorine-18 (¹⁸F) nuclide in water; and (3) oxygen-15 (¹⁵O) nuclide in water, were derived, and assessed with simulated and experimental phantom data. The derived LOR-PDFs showed anisotropic and asymmetric characteristics dependent on LOR-detector angle, coincidence emitting source, and the medium, consistent with common PET physical principles. The comparison of the iso-Gaussian function and LOR-PDF showed that: (1) without positron range and acollinearity effects, the LOR-PDF achieved better or similar trade-offs of contrast recovery and noise for objects of 4 mm radius or larger, and this advantage extended to smaller objects (e.g. 2 mm radius sphere, 0.6 mm radius hot-rods) at higher iteration numbers; and (2) with positron range and acollinearity effects, the iso-Gaussian achieved similar or better resolution recovery depending on the significance of positron range effect. We conclude that the 3D LOR-PDF approach is an effective method to generate an accurate and compact system matrix. However, when used directly in expectation-maximization based list-mode iterative reconstruction algorithms such as MOLAR, its superiority is not clear

  20. Matrix Structure Exploitation in Generalized Eigenproblems Arising in Density Functional Theory

    SciTech Connect

    Di Napoli, Edoardo; Bientinesi, Paolo

    2010-09-30

    In this short paper, the authors report a new computational approach in the context of Density Functional Theory (DFT). It is shown how it is possible to speed up the self-consistent cycle (iteration) characterizing one of the most well-known DFT implementations: FLAPW. Generating the Hamiltonian and overlap matrices and solving the associated generalized eigenproblems Ax = {lambda}Bx constitute the two most time-consuming fractions of each iteration. Two promising directions, implementing the new methodology, are presented that will ultimately improve the performance of the generalized eigensolver and save computational time.

  1. Many-body localization and transition by density matrix renormalization group and exact diagonalization studies

    NASA Astrophysics Data System (ADS)

    Lim, S. P.; Sheng, D. N.

    2016-07-01

    A many-body localized (MBL) state is a new state of matter emerging in a disordered interacting system at high-energy densities through a disorder-driven dynamic phase transition. The nature of the phase transition and the evolution of the MBL phase near the transition are the focus of intense theoretical studies with open issues in the field. We develop an entanglement density matrix renormalization group (En-DMRG) algorithm to accurately target highly excited states for MBL systems. By studying the one-dimensional Heisenberg spin chain in a random field, we demonstrate the accuracy of the method in obtaining energy eigenstates and the corresponding statistical results of quantum states in the MBL phase. Based on large system simulations by En-DMRG for excited states, we demonstrate some interesting features in the entanglement entropy distribution function, which is characterized by two peaks: one at zero and another one at the quantized entropy S =ln2 with an exponential decay tail on the S >ln2 side. Combining En-DMRG with exact diagonalization simulations, we demonstrate that the transition from the MBL phase to the delocalized ergodic phase is driven by rare events where the locally entangled spin pairs develop power-law correlations. The corresponding phase diagram contains an intermediate or crossover regime, which has power-law spin-z correlations resulting from contributions of the rare events. We discuss the physical picture for the numerical observations in this regime, where various distribution functions are distinctly different from results deep in the ergodic and MBL phases for finite-size systems. Our results may provide new insights for understanding the phase transition in such systems.

  2. Ray-transfer-matrix approach to unstable resonator analysis.

    PubMed

    Ewanizky, T F

    1979-03-01

    A parametric analysis of unstable resonators is described. The resonator is mathematically represented by an appropriate ray-transfer-matrix, and changes in Gaussian beam parameters are calculated after propagation through the optical structure. The results highlight an inherent selective property that presents an effective loss mechanism for divergent radiation. This selective property is shown to be dependent on the resonator parameters of optical magnification and confocal length error. The analysis concludes that the initially backward-propagating radiation during the prelasing period is important in establishing low threshold and good beam quality in confocal unstable-resonator lasers. PMID:20208805

  3. Particles, holes, and solitons: a matrix product state approach.

    PubMed

    Draxler, Damian; Haegeman, Jutho; Osborne, Tobias J; Stojevic, Vid; Vanderstraeten, Laurens; Verstraete, Frank

    2013-07-12

    We introduce a variational method for calculating dispersion relations of translation invariant (1+1)-dimensional quantum field theories. The method is based on continuous matrix product states and can be implemented efficiently. We study the critical Lieb-Liniger model as a benchmark and excellent agreement with the exact solution is found. Additionally, we observe solitonic signatures of Lieb's type II excitation. In addition, a nonintegrable model is introduced where a U(1)-symmetry breaking term is added to the Lieb-Liniger Hamiltonian. For this model we find evidence of a nontrivial bound-state excitation in the dispersion relation.

  4. Spin Density Matrix Elements in Exclusive Production of Omega Mesons at HERMES

    NASA Astrophysics Data System (ADS)

    Marukyan, Hrachya

    2016-02-01

    Exclusive electroproduction of ω mesons on unpolarized hydrogen and deuterium targets is studied at HERMES in the kinematic region of Q2 > 1.0GeV2, 3.0GeV < W < 6.3GeV, and ‑ t‧ < 0.2GeV2. The data were accumulated during the 1996-2007 running period using the 27.6GeV longitudinally polarized electron or positron beams at HERA. The determination of the virtual-photon longitudinal-to-transverse cross-section ratio shows that a considerable part of the cross section arises from transversely polarized photons. Spin density matrix elements are derived and presented in projections of Q2 or ‑ t‧. Violation of s-channel helicity conservation is observed for some of these elements. A sizable contribution from unnatural-parity-exchange amplitudes is found and the phase shift between those amplitudes that describe transverse ω production by longitudinal and transverse virtual photons is determined for the first time. Good agreement is found between the HERMES proton data and results of a pQCD-inspired phenomenological model that includes pion-pole contributions.

  5. Random Matrix Approach to Quantum Adiabatic Evolution Algorithms

    NASA Technical Reports Server (NTRS)

    Boulatov, Alexei; Smelyanskiy, Vadier N.

    2004-01-01

    We analyze the power of quantum adiabatic evolution algorithms (Q-QA) for solving random NP-hard optimization problems within a theoretical framework based on the random matrix theory (RMT). We present two types of the driven RMT models. In the first model, the driving Hamiltonian is represented by Brownian motion in the matrix space. We use the Brownian motion model to obtain a description of multiple avoided crossing phenomena. We show that the failure mechanism of the QAA is due to the interaction of the ground state with the "cloud" formed by all the excited states, confirming that in the driven RMT models. the Landau-Zener mechanism of dissipation is not important. We show that the QAEA has a finite probability of success in a certain range of parameters. implying the polynomial complexity of the algorithm. The second model corresponds to the standard QAEA with the problem Hamiltonian taken from the Gaussian Unitary RMT ensemble (GUE). We show that the level dynamics in this model can be mapped onto the dynamics in the Brownian motion model. However, the driven RMT model always leads to the exponential complexity of the algorithm due to the presence of the long-range intertemporal correlations of the eigenvalues. Our results indicate that the weakness of effective transitions is the leading effect that can make the Markovian type QAEA successful.

  6. Random-matrix approach to RPA equations. I

    NASA Astrophysics Data System (ADS)

    Barillier-Pertuisel, X.; Bohigas, O.; Weidenmüller, H. A.

    2009-09-01

    We study the RPA equations in their most general form by taking the matrix elements appearing in the RPA equations as random. This yields either a unitary or an orthogonally invariant random-matrix model that does not appear in the Altland-Zirnbauer classification. The average spectrum of the model is studied with the help of a generalized Pastur equation. Two independent parameters govern the behaviour of the system: the strength α2 of the coupling between positive- and negative-energy states and the distance between the origin and the centers of the two semicircles that describe the average spectrum for α2 = 0, the latter measured in units of the equal radii of the two semicircles. With increasing α2, positive- and negative-energy states become mixed and ever more of the spectral strength of the positive-energy states is transferred to those at negative energy, and vice versa. The two semicircles are deformed and pulled toward each other. As they begin to overlap, the RPA equations yield non-real eigenvalues: The system becomes unstable. We determine analytically the critical value of the strength for the instability to occur. Several features of the model are illustrated numerically.

  7. Random-matrix approach to RPA equations. I

    SciTech Connect

    Barillier-Pertuisel, X. Bohigas, O.; Weidenmueller, H.A.

    2009-09-15

    We study the RPA equations in their most general form by taking the matrix elements appearing in the RPA equations as random. This yields either a unitary or an orthogonally invariant random-matrix model that does not appear in the Altland-Zirnbauer classification. The average spectrum of the model is studied with the help of a generalized Pastur equation. Two independent parameters govern the behaviour of the system: the strength {alpha}{sup 2} of the coupling between positive- and negative-energy states and the distance between the origin and the centers of the two semicircles that describe the average spectrum for {alpha}{sup 2} = 0, the latter measured in units of the equal radii of the two semicircles. With increasing {alpha}{sup 2}, positive- and negative-energy states become mixed and ever more of the spectral strength of the positive-energy states is transferred to those at negative energy, and vice versa. The two semicircles are deformed and pulled toward each other. As they begin to overlap, the RPA equations yield non-real eigenvalues: The system becomes unstable. We determine analytically the critical value of the strength for the instability to occur. Several features of the model are illustrated numerically.

  8. Exact and quasi-classical density matrix and Wigner functions for a particle in the box and half space

    NASA Technical Reports Server (NTRS)

    Akhundova, E. A.; Dodonov, V. V.; Manko, V. I.

    1993-01-01

    The exact expressions for density matrix and Wigner functions of quantum systems are known only in special cases. Corresponding Hamiltonians are quadratic forms of Euclidean coordinates and momenta. In this paper we consider the problem of one-dimensional free particle movement in the bounded region 0 is less than x is less than a (including the case a = infinity).

  9. Random matrix approach to quantum adiabatic evolution algorithms

    SciTech Connect

    Boulatov, A.; Smelyanskiy, V.N.

    2005-05-15

    We analyze the power of the quantum adiabatic evolution algorithm (QAA) for solving random computationally hard optimization problems within a theoretical framework based on random matrix theory (RMT). We present two types of driven RMT models. In the first model, the driving Hamiltonian is represented by Brownian motion in the matrix space. We use the Brownian motion model to obtain a description of multiple avoided crossing phenomena. We show that nonadiabatic corrections in the QAA are due to the interaction of the ground state with the 'cloud' formed by most of the excited states, confirming that in driven RMT models, the Landau-Zener scenario of pairwise level repulsions is not relevant for the description of nonadiabatic corrections. We show that the QAA has a finite probability of success in a certain range of parameters, implying a polynomial complexity of the algorithm. The second model corresponds to the standard QAA with the problem Hamiltonian taken from the RMT Gaussian unitary ensemble (GUE). We show that the level dynamics in this model can be mapped onto the dynamics in the Brownian motion model. For this reason, the driven GUE model can also lead to polynomial complexity of the QAA. The main contribution to the failure probability of the QAA comes from the nonadiabatic corrections to the eigenstates, which only depend on the absolute values of the transition amplitudes. Due to the mapping between the two models, these absolute values are the same in both cases. Our results indicate that this 'phase irrelevance' is the leading effect that can make both the Markovian- and GUE-type QAAs successful.

  10. Random matrix approach to the dynamics of stock inventory variations

    NASA Astrophysics Data System (ADS)

    Zhou, Wei-Xing; Mu, Guo-Hua; Kertész, János

    2012-09-01

    It is well accepted that investors can be classified into groups owing to distinct trading strategies, which forms the basic assumption of many agent-based models for financial markets when agents are not zero-intelligent. However, empirical tests of these assumptions are still very rare due to the lack of order flow data. Here we adopt the order flow data of Chinese stocks to tackle this problem by investigating the dynamics of inventory variations for individual and institutional investors that contain rich information about the trading behavior of investors and have a crucial influence on price fluctuations. We find that the distributions of cross-correlation coefficient Cij have power-law forms in the bulk that are followed by exponential tails, and there are more positive coefficients than negative ones. In addition, it is more likely that two individuals or two institutions have a stronger inventory variation correlation than one individual and one institution. We find that the largest and the second largest eigenvalues (λ1 and λ2) of the correlation matrix cannot be explained by random matrix theory and the projections of investors' inventory variations on the first eigenvector u(λ1) are linearly correlated with stock returns, where individual investors play a dominating role. The investors are classified into three categories based on the cross-correlation coefficients CV R between inventory variations and stock returns. A strong Granger causality is unveiled from stock returns to inventory variations, which means that a large proportion of individuals hold the reversing trading strategy and a small part of individuals hold the trending strategy. Our empirical findings have scientific significance in the understanding of investors' trading behavior and in the construction of agent-based models for emerging stock markets.

  11. Random matrix approach to cross correlations in financial data

    NASA Astrophysics Data System (ADS)

    Plerou, Vasiliki; Gopikrishnan, Parameswaran; Rosenow, Bernd; Amaral, Luís A.; Guhr, Thomas; Stanley, H. Eugene

    2002-06-01

    We analyze cross correlations between price fluctuations of different stocks using methods of random matrix theory (RMT). Using two large databases, we calculate cross-correlation matrices C of returns constructed from (i) 30-min returns of 1000 US stocks for the 2-yr period 1994-1995, (ii) 30-min returns of 881 US stocks for the 2-yr period 1996-1997, and (iii) 1-day returns of 422 US stocks for the 35-yr period 1962-1996. We test the statistics of the eigenvalues λi of C against a ``null hypothesis'' - a random correlation matrix constructed from mutually uncorrelated time series. We find that a majority of the eigenvalues of C fall within the RMT bounds [λ-,λ+] for the eigenvalues of random correlation matrices. We test the eigenvalues of C within the RMT bound for universal properties of random matrices and find good agreement with the results for the Gaussian orthogonal ensemble of random matrices-implying a large degree of randomness in the measured cross-correlation coefficients. Further, we find that the distribution of eigenvector components for the eigenvectors corresponding to the eigenvalues outside the RMT bound display systematic deviations from the RMT prediction. In addition, we find that these ``deviating eigenvectors'' are stable in time. We analyze the components of the deviating eigenvectors and find that the largest eigenvalue corresponds to an influence common to all stocks. Our analysis of the remaining deviating eigenvectors shows distinct groups, whose identities correspond to conventionally identified business sectors. Finally, we discuss applications to the construction of portfolios of stocks that have a stable ratio of risk to return.

  12. The density matrix renormalization group for strongly correlated electron systems: A generic implementation

    NASA Astrophysics Data System (ADS)

    Alvarez, G.

    2009-09-01

    The purpose of this paper is (i) to present a generic and fully functional implementation of the density-matrix renormalization group (DMRG) algorithm, and (ii) to describe how to write additional strongly-correlated electron models and geometries by using templated classes. Besides considering general models and geometries, the code implements Hamiltonian symmetries in a generic way and parallelization over symmetry-related matrix blocks. Program summaryProgram title: DMRG++ Catalogue identifier: AEDJ_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEDJ_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: See file LICENSE No. of lines in distributed program, including test data, etc.: 15 795 No. of bytes in distributed program, including test data, etc.: 83 454 Distribution format: tar.gz Programming language: C++, MPI Computer: PC, HP cluster Operating system: Any, tested on Linux Has the code been vectorized or parallelized?: Yes RAM: 1 GB (256 MB is enough to run included test) Classification: 23 External routines: BLAS and LAPACK Nature of problem: Strongly correlated electrons systems, display a broad range of important phenomena, and their study is a major area of research in condensed matter physics. In this context, model Hamiltonians are used to simulate the relevant interactions of a given compound, and the relevant degrees of freedom. These studies rely on the use of tight-binding lattice models that consider electron localization, where states on one site can be labeled by spin and orbital degrees of freedom. The calculation of properties from these Hamiltonians is a computational intensive problem, since the Hilbert space over which these Hamiltonians act grows exponentially with the number of sites on the lattice. Solution method: The DMRG is a numerical variational technique to study quantum many body Hamiltonians. For one-dimensional and quasi one-dimensional systems, the

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

    PubMed

    Chen, Zhenhua; Chen, Xun; Wu, Wei

    2013-04-28

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

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

    NASA Astrophysics Data System (ADS)

    Chen, Zhenhua; Chen, Xun; Wu, Wei

    2013-04-01

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

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

    PubMed

    Chen, Zhenhua; Chen, Xun; Wu, Wei

    2013-04-28

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

  16. Density-Matrix Calculations of the 1.5 T Citrate Signal Acquired with Volume-Localized STEAM Sequences

    NASA Astrophysics Data System (ADS)

    Mulkern, R. V.; Bowers, J. L.; Peled, S.; Williamson, D. S.

    1996-03-01

    Citrate detection and quantitation with proton spectroscopic methods are of current interest as potential tools in the diagnosis and staging of prostate cancer. Thestimulatedechoacquisitionmode (STEAM) sequence is a commonly used volume-localization method for detecting citrate signal. Since the1H citrate resonance at clinically available field strengths arises from a strongly coupled two-spin system, the 90° RF pulses and localizing gradients used in STEAM sequences result in a complicated dependence of signal intensity on timing intervals and gradient amplitudes. The density-matrix formalism has been applied to arrive at a general solution to this problem. Citrate-signal properties at 1.5 T for different gradient localization schemes are examined with the solution. Optimal interpulse delays, deleterious gradient balances, zero-quantum oscillations with mixing time, and a low-frequency, large-amplitude oscillation with echo time are identified for signals acquired with the standard disposition of gradients in STEAM. The generality of the solution also allows for an examination of nonstandard gradient disposition schemes for enhancing citrate signal and for quantifying the sensitivity of such approaches to both field inhomogeneities and off-resonance effects.

  17. Exploiting the spatial locality of electron correlation within the parametric two-electron reduced-density-matrix method

    NASA Astrophysics Data System (ADS)

    DePrince, A. Eugene; Mazziotti, David A.

    2010-01-01

    The parametric variational two-electron reduced-density-matrix (2-RDM) method is applied to computing electronic correlation energies of medium-to-large molecular systems by exploiting the spatial locality of electron correlation within the framework of the cluster-in-molecule (CIM) approximation [S. Li et al., J. Comput. Chem. 23, 238 (2002); J. Chem. Phys. 125, 074109 (2006)]. The 2-RDMs of individual molecular fragments within a molecule are determined, and selected portions of these 2-RDMs are recombined to yield an accurate approximation to the correlation energy of the entire molecule. In addition to extending CIM to the parametric 2-RDM method, we (i) suggest a more systematic selection of atomic-orbital domains than that presented in previous CIM studies and (ii) generalize the CIM method for open-shell quantum systems. The resulting method is tested with a series of polyacetylene molecules, water clusters, and diazobenzene derivatives in minimal and nonminimal basis sets. Calculations show that the computational cost of the method scales linearly with system size. We also compute hydrogen-abstraction energies for a series of hydroxyurea derivatives. Abstraction of hydrogen from hydroxyurea is thought to be a key step in its treatment of sickle cell anemia; the design of hydroxyurea derivatives that oxidize more rapidly is one approach to devising more effective treatments.

  18. Ab initio density matrix renormalization group study of magnetic coupling in dinuclear iron and chromium complexes

    SciTech Connect

    Harris, Travis V.; Morokuma, Keiji; Kurashige, Yuki; Yanai, Takeshi

    2014-02-07

    The applicability of ab initio multireference wavefunction-based methods to the study of magnetic complexes has been restricted by the quickly rising active-space requirements of oligonuclear systems and dinuclear complexes with S > 1 spin centers. Ab initio density matrix renormalization group (DMRG) methods built upon an efficient parameterization of the correlation network enable the use of much larger active spaces, and therefore may offer a way forward. Here, we apply DMRG-CASSCF to the dinuclear complexes [Fe{sub 2}OCl{sub 6}]{sup 2−} and [Cr{sub 2}O(NH{sub 3}){sub 10}]{sup 4+}. After developing the methodology through systematic basis set and DMRG M testing, we explore the effects of extended active spaces that are beyond the limit of conventional methods. We find that DMRG-CASSCF with active spaces including the metal d orbitals, occupied bridging-ligand orbitals, and their virtual double shells already capture a major portion of the dynamic correlation effects, accurately reproducing the experimental magnetic coupling constant (J) of [Fe{sub 2}OCl{sub 6}]{sup 2−} with (16e,26o), and considerably improving the smaller active space results for [Cr{sub 2}O(NH{sub 3}){sub 10}]{sup 4+} with (12e,32o). For comparison, we perform conventional MRCI+Q calculations and find the J values to be consistent with those from DMRG-CASSCF. In contrast to previous studies, the higher spin states of the two systems show similar deviations from the Heisenberg spectrum, regardless of the computational method.

  19. Density matrix embedding theory studies of the two-dimensional Hubbard model

    NASA Astrophysics Data System (ADS)

    Zheng, Bo-Xiao

    Density matrix embedding theory (DMET) provides a quantum embedding framework to compute the electronic structure in strongly correlated lattice systems. It has been applied to various model Hamiltonians and ab initio systems. In this talk, I will review the results obtained in the two-dimensional one-band Hubbard model using DMET. Over the last years, we mapped a calibrated ground-state phase diagram of the two-dimensional Hubbard model, concerning magnetic, superconducting and various inhomogeneous phases. Based on the results from this work, as well as the consistent data from other numerical methods, we are able to conclude that many parts of the Hubbard phase diagram is already settled up to an accurate energy scale of 0.001t. Recently, by using large-scale auxiliary-field quantum Monte Carlo (AFQMC) in the impurity problem, we are able to treat much larger embedded clusters at half-filling (and with the constrained path approximation at non-half-filling), which provides a deeper understanding on the finite-size effects of energy and observables in both quantum embedding and finite cluster numerical methods. Finally, we systematically investigated the putative inhomogeneous phases in the underdoped, strong coupling Hubbard model, proposing new inhomogeneous patterns as strong candidates for the ground state. Reference: [1] Bo-Xiao Zheng, Garnet K.-L. Chan, arXiv:1504.01784 [2] J.P.F. Leblanc, Andrey E. Antipov, et al., arXiv:1505.02290 We acknowledge funding from the US Department of Energy, Office of Science, through DE-SC0008624 and DE-SC0010530. This work was also performed as part of the Simons Collaboration on the Many Electron Problem, sponsored by the Simons Foundation.

  20. Two-dimensional density-matrix topological fermionic phases: topological Uhlmann numbers.

    PubMed

    Viyuela, O; Rivas, A; Martin-Delgado, M A

    2014-08-15

    We construct a topological invariant that classifies density matrices of symmetry-protected topological orders in two-dimensional fermionic systems. As it is constructed out of the previously introduced Uhlmann phase, we refer to it as the topological Uhlmann number n_{U}. With it, we study thermal topological phases in several two-dimensional models of topological insulators and superconductors, computing phase diagrams where the temperature T is on an equal footing with the coupling constants in the Hamiltonian. Moreover, we find novel thermal-topological transitions between two nontrivial phases in a model with high Chern numbers. At small temperatures we recover the standard topological phases as the Uhlmann number approaches to the Chern number.

  1. Increased extracellular matrix density decreases MCF10A breast cell acinus formation in 3D culture conditions.

    PubMed

    Lance, Amanda; Yang, Chih-Chao; Swamydas, Muthulekha; Dean, Delphine; Deitch, Sandy; Burg, Karen J L; Dréau, Didier

    2016-01-01

    The extracellular matrix (ECM) contributes to the generation and dynamic of normal breast tissue, in particular to the generation of polarized acinar and ductal structures. In vitro 3D culture conditions, including variations in the composition of the ECM, have been shown to directly influence the formation and organization of acinus-like and duct-like structures. Furthermore, the density of the ECM appears to also play a role in the normal mammary tissue and tumour formation. Here we show that the density of the ECM directly influences the number, organization and function of breast acini. Briefly, non-malignant human breast MCF10A cells were incubated in increasing densities of a Matrigel®-collagen I matrix. Elastic moduli near and distant to the acinus structures were measured by atomic force microscopy, and the number of acinus structures was determined. Immunochemistry was used to investigate the expression levels of E-cadherin, laminin, matrix metalloproteinase-14 and ß-casein in MCF10A cells. The modulus of the ECM was significantly increased near the acinus structures and the number of acinus structures decreased with the increase in Matrigel-collagen I density. As evaluated by the expression of laminin, the organization of the acinus structures present was altered as the density of the ECM increased. Increases in both E-cadherin and MMP14 expression by MCF10A cells as ECM density increased were also observed. In contrast, MCF10A cells expressed lower ß-casein levels as the ECM density increased. Taken together, these observations highlight the key role of ECM density in modulating the number, organization and function of breast acini.

  2. Simulation of sprays using a Lagrangian filtered density function approach

    NASA Astrophysics Data System (ADS)

    Liu, Wanjiao; Garrick, Sean

    2013-11-01

    Sprays and atomization have wide applications in industry, including combustion/engines, pharmaceutics and agricultural spraying. Due to the complexity of the underlying processes, much of the underlying phenomena are not fully understood. Numerical simulation may provide ways to investigate atomization and spray dynamics. Large eddy simulation (LES) is a practical approach to flow simulation as it resolves only the large-scale structures while modeling the sub-grid scale (SGS) effects. We combine a filtered density function (FDF) based approach with a Lagrangian volume-of-fluid method to perform LES. This resulting methodology is advantageous in that it has no diffusive or dissipative numerical errors, and the highly non-linear surface tension force appears in closed form thus the modeling of the SGS surface tension is not needed when simulating turbulent, multiphase flows. We present the methodology and some results for the simulation of multiphase jets.

  3. Floating matrix tablets based on low density foam powder: effects of formulation and processing parameters on drug release.

    PubMed

    Streubel, A; Siepmann, J; Bodmeier, R

    2003-01-01

    The aim of this study was to develop and physicochemically characterize single unit, floating controlled drug delivery systems consisting of (i). polypropylene foam powder, (ii). matrix-forming polymer(s), (iii). drug, and (iv). filler (optional). The highly porous foam powder provided low density and, thus, excellent in vitro floating behavior of the tablets. All foam powder-containing tablets remained floating for at least 8 h in 0.1 N HCl at 37 degrees C. Different types of matrix-forming polymers were studied: hydroxypropyl methylcellulose (HPMC), polyacrylates, sodium alginate, corn starch, carrageenan, gum guar and gum arabic. The tablets eroded upon contact with the release medium, and the relative importance of drug diffusion, polymer swelling and tablet erosion for the resulting release patterns varied significantly with the type of matrix former. The release rate could effectively be modified by varying the "matrix-forming polymer/foam powder" ratio, the initial drug loading, the tablet geometry (radius and height), the type of matrix-forming polymer, the use of polymer blends and the addition of water-soluble or water-insoluble fillers (such as lactose or microcrystalline cellulose). The floating behavior of the low density drug delivery systems could successfully be combined with accurate control of the drug release patterns.

  4. A Wigner Monte Carlo approach to density functional theory

    SciTech Connect

    Sellier, J.M. Dimov, I.

    2014-08-01

    In order to simulate quantum N-body systems, stationary and time-dependent density functional theories rely on the capacity of calculating the single-electron wave-functions of a system from which one obtains the total electron density (Kohn–Sham systems). In this paper, we introduce the use of the Wigner Monte Carlo method in ab-initio calculations. This approach allows time-dependent simulations of chemical systems in the presence of reflective and absorbing boundary conditions. It also enables an intuitive comprehension of chemical systems in terms of the Wigner formalism based on the concept of phase-space. Finally, being based on a Monte Carlo method, it scales very well on parallel machines paving the way towards the time-dependent simulation of very complex molecules. A validation is performed by studying the electron distribution of three different systems, a Lithium atom, a Boron atom and a hydrogenic molecule. For the sake of simplicity, we start from initial conditions not too far from equilibrium and show that the systems reach a stationary regime, as expected (despite no restriction is imposed in the choice of the initial conditions). We also show a good agreement with the standard density functional theory for the hydrogenic molecule. These results demonstrate that the combination of the Wigner Monte Carlo method and Kohn–Sham systems provides a reliable computational tool which could, eventually, be applied to more sophisticated problems.

  5. Approaches to 100 Gbit/sq. in. recording density

    NASA Technical Reports Server (NTRS)

    Kryder, Mark H.

    1994-01-01

    A recording density of 10 Gbit/sq. in. is being pursued by a number of companies and universities in the National Storage Industry Consortium. It is widely accepted that this goal will be achieved in the laboratory within a few years. In this paper approaches to achieving 100 Gbit/sq. in. storage densities are considered. A major obstacle to continued scaling of magnetic recording to higher densities is that as the bit size is reduced, the grain size in the magnetic media must be reduced in order that media noise does not become so large that the signal to noise ratio (SNR) degrades sufficiently to make detection impossible. At 100 Gbit/sq. in., the bit size is only 0.006 square micrometers, which, in order to achieve 30 dB SNR, requires a grain size of about 2.5 nm. Such small grains are subject to thermal instability, and the recorded information will degrade over time unless the magnetic anisotropy of the materials used is increased significantly, or the media thickness is made much larger than expected on the basis of scaling today's longitudinal media thickness.

  6. Semivariational approach to QCD at finite temperature and baryon density

    SciTech Connect

    Palumbo, Fabrizio

    2008-07-01

    Recently a new bosonization method has been used to derive, at zero fermion density, an effective action for relativistic field theories whose partition function is dominated by fermionic composites, chiral mesons in the case of QCD. This approach shares two important features with variational methods: the restriction to the subspace of the composites, and the determination of their structure functions by a variational calculation. But unlike standard variational methods it treats excited states on the same footing as the ground state. I show that this bosonization method is an approximation of an exact procedure in which composites are introduced in the presence of fermionic states with the quantum numbers of the constituents (quasiparticles). This procedure consists of an independent Bogoliubov transformation at each time slice. The time-dependent parameters of the transformation are then associated with composite fields. In this way states of nonvanishing fermion (baryon) number (neglected in the bosonization approach) are retained. By the exact procedure I derive an effective action for QCD at finite temperature and baryon density. I test the result on a four-fermion interaction model.

  7. Fragment approach to constrained density functional theory calculations using Daubechies wavelets

    SciTech Connect

    Ratcliff, Laura E.; Genovese, Luigi; Mohr, Stephan; Deutsch, Thierry

    2015-06-21

    In a recent paper, we presented a linear scaling Kohn-Sham density functional theory (DFT) code based on Daubechies wavelets, where a minimal set of localized support functions are optimized in situ and therefore adapted to the chemical properties of the molecular system. Thanks to the systematically controllable accuracy of the underlying basis set, this approach is able to provide an optimal contracted basis for a given system: accuracies for ground state energies and atomic forces are of the same quality as an uncontracted, cubic scaling approach. This basis set offers, by construction, a natural subset where the density matrix of the system can be projected. In this paper, we demonstrate the flexibility of this minimal basis formalism in providing a basis set that can be reused as-is, i.e., without reoptimization, for charge-constrained DFT calculations within a fragment approach. Support functions, represented in the underlying wavelet grid, of the template fragments are roto-translated with high numerical precision to the required positions and used as projectors for the charge weight function. We demonstrate the interest of this approach to express highly precise and efficient calculations for preparing diabatic states and for the computational setup of systems in complex environments.

  8. Fragment approach to constrained density functional theory calculations using Daubechies wavelets.

    PubMed

    Ratcliff, Laura E; Genovese, Luigi; Mohr, Stephan; Deutsch, Thierry

    2015-06-21

    In a recent paper, we presented a linear scaling Kohn-Sham density functional theory (DFT) code based on Daubechies wavelets, where a minimal set of localized support functions are optimized in situ and therefore adapted to the chemical properties of the molecular system. Thanks to the systematically controllable accuracy of the underlying basis set, this approach is able to provide an optimal contracted basis for a given system: accuracies for ground state energies and atomic forces are of the same quality as an uncontracted, cubic scaling approach. This basis set offers, by construction, a natural subset where the density matrix of the system can be projected. In this paper, we demonstrate the flexibility of this minimal basis formalism in providing a basis set that can be reused as-is, i.e., without reoptimization, for charge-constrained DFT calculations within a fragment approach. Support functions, represented in the underlying wavelet grid, of the template fragments are roto-translated with high numerical precision to the required positions and used as projectors for the charge weight function. We demonstrate the interest of this approach to express highly precise and efficient calculations for preparing diabatic states and for the computational setup of systems in complex environments. PMID:26093548

  9. Efficient tree tensor network states (TTNS) for quantum chemistry: Generalizations of the density matrix renormalization group algorithm

    NASA Astrophysics Data System (ADS)

    Nakatani, Naoki; Chan, Garnet Kin-Lic

    2013-04-01

    We investigate tree tensor network states for quantum chemistry. Tree tensor network states represent one of the simplest generalizations of matrix product states and the density matrix renormalization group. While matrix product states encode a one-dimensional entanglement structure, tree tensor network states encode a tree entanglement structure, allowing for a more flexible description of general molecules. We describe an optimal tree tensor network state algorithm for quantum chemistry. We introduce the concept of half-renormalization which greatly improves the efficiency of the calculations. Using our efficient formulation we demonstrate the strengths and weaknesses of tree tensor network states versus matrix product states. We carry out benchmark calculations both on tree systems (hydrogen trees and π-conjugated dendrimers) as well as non-tree molecules (hydrogen chains, nitrogen dimer, and chromium dimer). In general, tree tensor network states require much fewer renormalized states to achieve the same accuracy as matrix product states. In non-tree molecules, whether this translates into a computational savings is system dependent, due to the higher prefactor and computational scaling associated with tree algorithms. In tree like molecules, tree network states are easily superior to matrix product states. As an illustration, our largest dendrimer calculation with tree tensor network states correlates 110 electrons in 110 active orbitals.

  10. Efficient tree tensor network states (TTNS) for quantum chemistry: generalizations of the density matrix renormalization group algorithm.

    PubMed

    Nakatani, Naoki; Chan, Garnet Kin-Lic

    2013-04-01

    We investigate tree tensor network states for quantum chemistry. Tree tensor network states represent one of the simplest generalizations of matrix product states and the density matrix renormalization group. While matrix product states encode a one-dimensional entanglement structure, tree tensor network states encode a tree entanglement structure, allowing for a more flexible description of general molecules. We describe an optimal tree tensor network state algorithm for quantum chemistry. We introduce the concept of half-renormalization which greatly improves the efficiency of the calculations. Using our efficient formulation we demonstrate the strengths and weaknesses of tree tensor network states versus matrix product states. We carry out benchmark calculations both on tree systems (hydrogen trees and π-conjugated dendrimers) as well as non-tree molecules (hydrogen chains, nitrogen dimer, and chromium dimer). In general, tree tensor network states require much fewer renormalized states to achieve the same accuracy as matrix product states. In non-tree molecules, whether this translates into a computational savings is system dependent, due to the higher prefactor and computational scaling associated with tree algorithms. In tree like molecules, tree network states are easily superior to matrix product states. As an illustration, our largest dendrimer calculation with tree tensor network states correlates 110 electrons in 110 active orbitals.

  11. The matrix approach to mental health care: Experiences in Florianopolis, Brazil.

    PubMed

    Soares, Susana; de Oliveira, Walter Ferreira

    2016-03-01

    This article reports on the experience of a matrix approach to mental health in primary health care. Professionals who work in the Family Health Support Nuclei, Núcleos de Apoio à Saúde da Família, pointed to challenges of this approach, especially regarding the difficulties of introducing pedagogic actions in the health field and problems related to work relationships. As the matrix approach and its practice are new aspects of the Brazilian Unified Health System, the academic knowledge must walk hand in hand with everyday professional practice to help improve the quality of the services offered in this context. PMID:26987828

  12. Modeling State-Space Aeroelastic Systems Using a Simple Matrix Polynomial Approach for the Unsteady Aerodynamics

    NASA Technical Reports Server (NTRS)

    Pototzky, Anthony S.

    2008-01-01

    A simple matrix polynomial approach is introduced for approximating unsteady aerodynamics in the s-plane and ultimately, after combining matrix polynomial coefficients with matrices defining the structure, a matrix polynomial of the flutter equations of motion (EOM) is formed. A technique of recasting the matrix-polynomial form of the flutter EOM into a first order form is also presented that can be used to determine the eigenvalues near the origin and everywhere on the complex plane. An aeroservoelastic (ASE) EOM have been generalized to include the gust terms on the right-hand side. The reasons for developing the new matrix polynomial approach are also presented, which are the following: first, the "workhorse" methods such as the NASTRAN flutter analysis lack the capability to consistently find roots near the origin, along the real axis or accurately find roots farther away from the imaginary axis of the complex plane; and, second, the existing s-plane methods, such as the Roger s s-plane approximation method as implemented in ISAC, do not always give suitable fits of some tabular data of the unsteady aerodynamics. A method available in MATLAB is introduced that will accurately fit generalized aerodynamic force (GAF) coefficients in a tabular data form into the coefficients of a matrix polynomial form. The root-locus results from the NASTRAN pknl flutter analysis, the ISAC-Roger's s-plane method and the present matrix polynomial method are presented and compared for accuracy and for the number and locations of roots.

  13. Matrix RGD ligand density and L1CAM-mediated Schwann cell interactions synergistically enhance neurite outgrowth.

    PubMed

    Romano, Nicole H; Madl, Christopher M; Heilshorn, Sarah C

    2015-01-01

    The innate biological response to peripheral nerve injury involves a complex interplay of multiple molecular cues to guide neurites across the injury gap. Many current strategies to stimulate regeneration take inspiration from this biological response. However, little is known about the balance of cell-matrix and Schwann cell-neurite dynamics required for regeneration of neural architectures. We present an engineered extracellular matrix (eECM) microenvironment with tailored cell-matrix and cell-cell interactions to study their individual and combined effects on neurite outgrowth. This eECM regulates cell-matrix interactions by presenting integrin-binding RGD (Arg-Gly-Asp) ligands at specified densities. Simultaneously, the addition or exclusion of nerve growth factor (NGF) is used to modulate L1CAM-mediated Schwann cell-neurite interactions. Individually, increasing the RGD ligand density from 0.16 to 3.2mM resulted in increasing neurite lengths. In matrices presenting higher RGD ligand densities, neurite outgrowth was synergistically enhanced in the presence of soluble NGF. Analysis of Schwann cell migration and co-localization with neurites revealed that NGF enhanced cooperative outgrowth between the two cell types. Interestingly, neurites in NGF-supplemented conditions were unable to extend on the surrounding eECM without the assistance of Schwann cells. Blocking studies revealed that L1CAM is primarily responsible for these Schwann cell-neurite interactions. Without NGF supplementation, neurite outgrowth was unaffected by L1CAM blocking or the depletion of Schwann cells. These results underscore the synergistic interplay between cell-matrix and cell-cell interactions in enhancing neurite outgrowth for peripheral nerve regeneration. PMID:25308870

  14. Methods for directly determining the two-electron reduced density matrix with applications to quantum phase transitions and chemical reactions

    NASA Astrophysics Data System (ADS)

    Schwerdtfeger, Christine Ann

    An N-particle system can be described without approximation using a two-particle reduced density matrix (2-RDM) if the particles are indistinguishable and interact pairwise. If a 2-RDM is determined without using an N-particle wavefunction, the computational advantage of using a two-particle representation is realized. Directly minimizing the energy as a functional of the 2-RDM, however, does not yield a 2-RDM that describes an N -particle system (N-representable). In this thesis we discuss two approaches for determining approximately N-representable 2-RDMS without using wavefunctions. In the first approach, known as the variational 2-RDM method, we minimize the energy as a function of the 2-RDM while explicitly enforcing a subset of N-representability conditions on the 2-RDM to obtain a lower bound to the exact energy. We apply this approach to the strongly correlated quantum phase transition in the 1D transverse Ising model and demonstrate that compared to the exact solution, the variational 2-RDM method provides an accurate description of the Ising lattice and is an alternative tool for locating a quantum phase transition using only the ground electronic state. The second approach used in this work is the parametric 2-RDM method. The 2-RDM is parameterized using a reference 2-RDM and a subset of N-representability conditions. We apply the method to several isomerization reactions including those of oxywater, ammonia oxide, carbonic acid and diazene. Results obtained using the parametric 2-RDM method reproduce experimental results in predicting the equilibrium ratio of cis- to trans-carbonic acid isomers and describe the multireference transition state in the isomerization of diazene as well as multireference wavefunction methods. We extend the 2-RDM parameterization to describe electronic systems in arbitrary spin states and demonstrate similar accuracy at equilibrium and nonequilibrium geometries as was seen in describing singlet electronic states. Lastly, we

  15. Time-dependent transition density matrix for visualizing charge-transfer excitations in photoexcited organic donor-acceptor systems

    NASA Astrophysics Data System (ADS)

    Li, Yonghui; Ullrich, Carsten

    2013-03-01

    The time-dependent transition density matrix (TDM) is a useful tool to visualize and interpret the induced charges and electron-hole coherences of excitonic processes in large molecules. Combined with time-dependent density functional theory on a real-space grid (as implemented in the octopus code), the TDM is a computationally viable visualization tool for optical excitation processes in molecules. It provides real-time maps of particles and holes which gives information on excitations, in particular those that have charge-transfer character, that cannot be obtained from the density alone. Some illustration of the TDM and comparison with standard density difference plots will be shown for photoexcited organic donor-acceptor molecules. This work is supported by NSF Grant DMR-1005651

  16. A new approach to calculate the transport matrix in RF cavities

    SciTech Connect

    Eidelman, Yu.; Mokhov, N.; Nagaitsev, S.; Solyak, N.; /Fermilab

    2011-03-01

    A realistic approach to calculate the transport matrix in RF cavities is developed. It is based on joint solution of equations of longitudinal and transverse motion of a charged particle in an electromagnetic field of the linac. This field is a given by distribution (measured or calculated) of the component of the longitudinal electric field on the axis of the linac. New approach is compared with other matrix methods to solve the same problem. The comparison with code ASTRA has been carried out. Complete agreement for tracking results for a TESLA-type cavity is achieved. A corresponding algorithm will be implemented into the MARS15 code. A realistic approach to calculate the transport matrix in RF cavities is developed. Complete agreement for tracking results with existed code ASTRA is achieved. New algorithm will be implemented into MARS15 code.

  17. Path integral molecular dynamics method based on a pair density matrix approximation: An algorithm for distinguishable and identical particle systems

    NASA Astrophysics Data System (ADS)

    Miura, Shinichi; Okazaki, Susumu

    2001-09-01

    In this paper, the path integral molecular dynamics (PIMD) method has been extended to employ an efficient approximation of the path action referred to as the pair density matrix approximation. Configurations of the isomorphic classical systems were dynamically sampled by introducing fictitious momenta as in the PIMD based on the standard primitive approximation. The indistinguishability of the particles was handled by a pseudopotential of particle permutation that is an extension of our previous one [J. Chem. Phys. 112, 10 116 (2000)]. As a test of our methodology for Boltzmann statistics, calculations have been performed for liquid helium-4 at 4 K. We found that the PIMD with the pair density matrix approximation dramatically reduced the computational cost to obtain the structural as well as dynamical (using the centroid molecular dynamics approximation) properties at the same level of accuracy as that with the primitive approximation. With respect to the identical particles, we performed the calculation of a bosonic triatomic cluster. Unlike the primitive approximation, the pseudopotential scheme based on the pair density matrix approximation described well the bosonic correlation among the interacting atoms. Convergence with a small number of discretization of the path achieved by this approximation enables us to construct a method of avoiding the problem of the vanishing pseudopotential encountered in the calculations by the primitive approximation.

  18. Oxidized low-density lipoprotein alters the effect of matrix stiffness on the formation of endothelial networks and capillary lumens

    PubMed Central

    2013-01-01

    Abstract Formation of new blood vessels is essential for vascular repair and remodeling, and it is known that biomechanical properties of extracellular matrix play a major role in this process. Our earlier studies have also shown that exposing endothelial cells to oxidized modification of low-density lipoproteins (oxLDL) increases endothelial stiffness and facilitates their ability to form cellular networks, suggesting that it facilitates endothelial angiogenic potential. The goal of this study, therefore, was to test the interrelationship between matrix stiffness and oxLDL in the regulation of angiogenesis. Our results show that, as expected, an increase in matrix stiffness inhibited endothelial network formation and that exposure to oxLDL significantly facilitated this process. We also show, however, that oxLDL-induced facilitation of endothelial networks was observed only in stiff (3 mg/mL) but not in soft (1 mg/mL) collagen gels, resulting in blunting the effect of matrix stiffness. Also unexpectedly, we show that an increase in matrix stiffness results in a significant increase in the number of capillary lumens that are formed by single cells or pairs of cells, suggesting that while endothelial connectivity is impaired, formation of single-cell lumens is facilitated. oxLDL facilitates lumen formation, but this effect is also matrix dependent and is observed only in soft gels and not in stiff gels. Finally, an increase in both matrix stiffness and oxLDL exposure results in changes in capillary morphology, with the formation of larger capillary lumens. Overall, our study suggests that oxLDL plays an important role in formation of new capillaries and their morphology and that this effect is critically dependent on the extracellular environment’s compliance, thereby underlining the importance of the interdependence of these parameters. PMID:24618546

  19. Oxidized low-density lipoprotein alters the effect of matrix stiffness on the formation of endothelial networks and capillary lumens.

    PubMed

    Gundavaram, Madhu S; Shentu, Tzu Pin; Kowalsky, Gregory B; Volkov, Suncica; Schraufnagel, Dean E; Levitan, Irena

    2013-09-01

    Abstract Formation of new blood vessels is essential for vascular repair and remodeling, and it is known that biomechanical properties of extracellular matrix play a major role in this process. Our earlier studies have also shown that exposing endothelial cells to oxidized modification of low-density lipoproteins (oxLDL) increases endothelial stiffness and facilitates their ability to form cellular networks, suggesting that it facilitates endothelial angiogenic potential. The goal of this study, therefore, was to test the interrelationship between matrix stiffness and oxLDL in the regulation of angiogenesis. Our results show that, as expected, an increase in matrix stiffness inhibited endothelial network formation and that exposure to oxLDL significantly facilitated this process. We also show, however, that oxLDL-induced facilitation of endothelial networks was observed only in stiff (3 mg/mL) but not in soft (1 mg/mL) collagen gels, resulting in blunting the effect of matrix stiffness. Also unexpectedly, we show that an increase in matrix stiffness results in a significant increase in the number of capillary lumens that are formed by single cells or pairs of cells, suggesting that while endothelial connectivity is impaired, formation of single-cell lumens is facilitated. oxLDL facilitates lumen formation, but this effect is also matrix dependent and is observed only in soft gels and not in stiff gels. Finally, an increase in both matrix stiffness and oxLDL exposure results in changes in capillary morphology, with the formation of larger capillary lumens. Overall, our study suggests that oxLDL plays an important role in formation of new capillaries and their morphology and that this effect is critically dependent on the extracellular environment's compliance, thereby underlining the importance of the interdependence of these parameters.

  20. Electronic coupling matrix elements from charge constrained density functional theory calculations using a plane wave basis set

    NASA Astrophysics Data System (ADS)

    Oberhofer, Harald; Blumberger, Jochen

    2010-12-01

    We present a plane wave basis set implementation for the calculation of electronic coupling matrix elements of electron transfer reactions within the framework of constrained density functional theory (CDFT). Following the work of Wu and Van Voorhis [J. Chem. Phys. 125, 164105 (2006)], the diabatic wavefunctions are approximated by the Kohn-Sham determinants obtained from CDFT calculations, and the coupling matrix element calculated by an efficient integration scheme. Our results for intermolecular electron transfer in small systems agree very well with high-level ab initio calculations based on generalized Mulliken-Hush theory, and with previous local basis set CDFT calculations. The effect of thermal fluctuations on the coupling matrix element is demonstrated for intramolecular electron transfer in the tetrathiafulvalene-diquinone (Q-TTF-Q-) anion. Sampling the electronic coupling along density functional based molecular dynamics trajectories, we find that thermal fluctuations, in particular the slow bending motion of the molecule, can lead to changes in the instantaneous electron transfer rate by more than an order of magnitude. The thermal average, ( {< {| {H_ab } |^2 } > } )^{1/2} = 6.7 {mH}, is significantly higher than the value obtained for the minimum energy structure, | {H_ab } | = 3.8 {mH}. While CDFT in combination with generalized gradient approximation (GGA) functionals describes the intermolecular electron transfer in the studied systems well, exact exchange is required for Q-TTF-Q- in order to obtain coupling matrix elements in agreement with experiment (3.9 mH). The implementation presented opens up the possibility to compute electronic coupling matrix elements for extended systems where donor, acceptor, and the environment are treated at the quantum mechanical (QM) level.

  1. Manifestly Hermitian semiclassical expansion for the one-particle density matrix of a two-dimensional Fermi gas

    NASA Astrophysics Data System (ADS)

    Bencheikh, K.; van Zyl, B. P.; Berkane, K.

    2016-08-01

    The semiclassical ℏ expansion of the one-particle density matrix for a two-dimensional Fermi gas is calculated within the Wigner transform method of B. Grammaticos and A. Voros [Ann. Phys. (N.Y.) 123, 359 (1979), 10.1016/0003-4916(79)90343-9], originally developed in the context of nuclear physics. The method of Grammaticos and Voros has the virtue of preserving both the Hermiticity and idempotency of the density matrix to all orders in the ℏ expansion. As a topical application, we use our semiclassical expansion to go beyond the local-density approximation for the construction of the total dipole-dipole interaction energy functional of a two-dimensional, spin-polarized dipolar Fermi gas. We find a finite, second-order gradient correction to the Hartree-Fock energy, which takes the form ɛ (∇ρ ) 2/√{ρ } , with ɛ being small (|ɛ |≪1 ) and negative. We test the quality of the corrected energy by comparing it with the exact results available for harmonic confinement. Even for small particle numbers, the gradient correction to the dipole-dipole energy provides a significant improvement over the local-density approximation.

  2. Linear-scaling density-functional simulations of charged point defects in Al2O3 using hierarchical sparse matrix algebra.

    PubMed

    Hine, N D M; Haynes, P D; Mostofi, A A; Payne, M C

    2010-09-21

    We present calculations of formation energies of defects in an ionic solid (Al(2)O(3)) extrapolated to the dilute limit, corresponding to a simulation cell of infinite size. The large-scale calculations required for this extrapolation are enabled by developments in the approach to parallel sparse matrix algebra operations, which are central to linear-scaling density-functional theory calculations. The computational cost of manipulating sparse matrices, whose sizes are determined by the large number of basis functions present, is greatly improved with this new approach. We present details of the sparse algebra scheme implemented in the ONETEP code using hierarchical sparsity patterns, and demonstrate its use in calculations on a wide range of systems, involving thousands of atoms on hundreds to thousands of parallel processes.

  3. A Synthetic Approach to the Transfer Matrix Method in Classical and Quantum Physics

    ERIC Educational Resources Information Center

    Pujol, O.; Perez, J. P.

    2007-01-01

    The aim of this paper is to propose a synthetic approach to the transfer matrix method in classical and quantum physics. This method is an efficient tool to deal with complicated physical systems of practical importance in geometrical light or charged particle optics, classical electronics, mechanics, electromagnetics and quantum physics. Teaching…

  4. Filtered density function approach for reactive transport in groundwater

    NASA Astrophysics Data System (ADS)

    Suciu, Nicolae; Schüler, Lennart; Attinger, Sabine; Knabner, Peter

    2016-04-01

    Spatial filtering may be used in coarse-grained simulations (CGS) of reactive transport in groundwater, similar to the large eddy simulations (LES) in turbulence. The filtered density function (FDF), stochastically equivalent to a probability density function (PDF), provides a statistical description of the sub-grid, unresolved, variability of the concentration field. Besides closing the chemical source terms in the transport equation for the mean concentration, like in LES-FDF methods, the CGS-FDF approach aims at quantifying the uncertainty over the whole hierarchy of heterogeneity scales exhibited by natural porous media. Practically, that means estimating concentration PDFs on coarse grids, at affordable computational costs. To cope with the high dimensionality of the problem in case of multi-component reactive transport and to reduce the numerical diffusion, FDF equations are solved by particle methods. But, while trajectories of computational particles are modeled as stochastic processes indexed by time, the concentration's heterogeneity is modeled as a random field, with multi-dimensional, spatio-temporal sets of indices. To overcome this conceptual inconsistency, we consider FDFs/PDFs of random species concentrations weighted by conserved scalars and we show that their evolution equations can be formulated as Fokker-Planck equations describing stochastically equivalent processes in concentration-position spaces. Numerical solutions can then be approximated by the density in the concentration-position space of an ensemble of computational particles governed by the associated Itô equations. Instead of sequential particle methods we use a global random walk (GRW) algorithm, which is stable, free of numerical diffusion, and practically insensitive to the increase of the number of particles. We illustrate the general FDF approach and the GRW numerical solution for a reduced complexity problem consisting of the transport of a single scalar in groundwater

  5. Very high cell density perfusion of CHO cells anchored in a non-woven matrix-based bioreactor.

    PubMed

    Zhang, Ye; Stobbe, Per; Silvander, Christian Orrego; Chotteau, Véronique

    2015-11-10

    Recombinant Chinese Hamster Ovary (CHO) cells producing IgG monoclonal antibody were cultivated in a novel perfusion culture system CellTank, integrating the bioreactor and the cell retention function. In this system, the cells were harbored in a non-woven polyester matrix perfused by the culture medium and immersed in a reservoir. Although adapted to suspension, the CHO cells stayed entrapped in the matrix. The cell-free medium was efficiently circulated from the reservoir into- and through the matrix by a centrifugal pump placed at the bottom of the bioreactor resulting in highly homogenous concentrations of the nutrients and metabolites in the whole system as confirmed by measurements from different sampling locations. A real-time biomass sensor using the dielectric properties of living cells was used to measure the cell density. The performances of the CellTank were studied in three perfusion runs. A very high cell density measured as 200 pF/cm (where 1 pF/cm is equivalent to 1 × 10(6)viable cells/mL) was achieved at a perfusion rate of 10 reactor volumes per day (RV/day) in the first run. In the second run, the effect of cell growth arrest by hypothermia at temperatures lowered gradually from 37 °C to 29 °C was studied during 13 days at cell densities above 100 pF/cm. Finally a production run was performed at high cell densities, where a temperature shift to 31 °C was applied at cell density 100 pF/cm during a production period of 14 days in minimized feeding conditions. The IgG concentrations were comparable in the matrix and in the harvest line in all the runs, indicating no retention of the product of interest. The cell specific productivity was comparable or higher than in Erlenmeyer flask batch culture. During the production run, the final harvested IgG production was 35 times higher in the CellTank compared to a repeated batch culture in the same vessel volume during the same time period.

  6. An entropy-driven matrix completion (E-MC) approach to complex network mapping

    NASA Astrophysics Data System (ADS)

    Koochakzadeh, Ali; Pal, Piya

    2016-05-01

    Mapping the topology of a complex network in a resource-efficient manner is a challenging problem with applications in internet mapping, social network inference, and so forth. We propose a new entropy driven algorithm leveraging ideas from matrix completion, to map the network using monitors (or sensors) which, when placed on judiciously selected nodes, are capable of discovering their immediate neighbors. The main challenge is to maximize the portion of discovered network using only a limited number of available monitors. To this end, (i) a new measure of entropy or uncertainty is associated with each node, in terms of the currently discovered edges incident on that node, and (ii) a greedy algorithm is developed to select a candidate node for monitor placement based on its entropy. Utilizing the fact that many complex networks of interest (such as social networks), have a low-rank adjacency matrix, a matrix completion algorithm, namely 1-bit matrix completion, is combined with the greedy algorithm to further boost its performance. The low rank property of the network adjacency matrix can be used to extrapolate a portion of missing edges, and consequently update the node entropies, so as to efficiently guide the network discovery algorithm towards placing monitors on the nodes that can turn out to be more informative. Simulations performed on a variety of real world networks such as social networks and peer networks demonstrate the superior performance of the matrix-completion guided approach in discovering the network topology.

  7. Tests on the extracted current density of negative hydrogen ions from a single element of the matrix source

    SciTech Connect

    Lishev, St.; Yordanov, D. Shivarova, A.

    2015-04-08

    Concepts for the extraction of volume-produced negative hydrogen ions from a rf matrix source (a matrix of small-radius discharges with a planar-coil inductive driving) are presented and discussed based on experimental results for the current densities of the extracted ions and the co-extracted electrons. The experiment has been carried out in a single discharge of the source: a rf discharge with a radius of 2.25 cm inductively driven by a 3.5-turn planar coil. The length of the discharge tube, the area of the reference electrode inserted in the discharge volume, the discharge modes, the magnetic filter and its position along the discharge length, the position of the permanent magnets for the separation of the co-extracted electrons from the extracted ions in the extraction device and the bias applied to its first electrode are considered as factors influencing the extracted currents of negative ions.

  8. A physical-space approach for the probability hypothesis density and cardinalized probability hypothesis density filters

    NASA Astrophysics Data System (ADS)

    Erdinc, Ozgur; Willett, Peter; Bar-Shalom, Yaakov

    2006-05-01

    The probability hypothesis density (PHD) filter, an automatically track-managed multi-target tracker, is attracting increasing but cautious attention. Its derivation is elegant and mathematical, and thus of course many engineers fear it; perhaps that is currently limiting the number of researchers working on the subject. In this paper, we explore a physical-space approach - a bin model - which leads us to arrive the same filter equations as the PHD. Unlike the original derivation of the PHD filter, the concepts used are the familiar ones of conditional probability. The original PHD suffers from a "target-death" problem in which even a single missed detection can lead to the apparent disappearance of a target. To obviate this, PHD originator Mahler has recently developed a new "cardinalized" version of PHD (CPHD). We are able to extend our physical-space derivation to the CPHD case as well. We stress that the original derivations are mathematically correct, and need no embellishment from us; our contribution here is to offer an alternative derivation, one that we find appealing.

  9. Energy-density field approach for low- and medium-frequency vibroacoustic analysis of complex structures using a statistical computational model

    NASA Astrophysics Data System (ADS)

    Kassem, M.; Soize, C.; Gagliardini, L.

    2009-06-01

    In this paper, an energy-density field approach applied to the vibroacoustic analysis of complex industrial structures in the low- and medium-frequency ranges is presented. This approach uses a statistical computational model. The analyzed system consists of an automotive vehicle structure coupled with its internal acoustic cavity. The objective of this paper is to make use of the statistical properties of the frequency response functions of the vibroacoustic system observed from previous experimental and numerical work. The frequency response functions are expressed in terms of a dimensionless matrix which is estimated using the proposed energy approach. Using this dimensionless matrix, a simplified vibroacoustic model is proposed.

  10. Taming the pion condensation in QCD at finite baryon density: a numerical test in a random matrix model

    NASA Astrophysics Data System (ADS)

    Aoki, Sinya; Hanada, Masanori; Nakamura, Atsushi

    2015-05-01

    In the Monte Carlo study of QCD at finite baryon density based upon the phase reweighting method, the pion condensation in the phase-quenched theory and associated zero-mode prevent us from going to the low-temperature high-density region. We propose a method to circumvent them by a simple modification of the density of state method. We first argue that the standard version of the density of state method, which is invented to solve the overlapping problem, is effective only for a certain `good' class of observables. We then modify it so as to solve the overlap problem for `bad' observables as well. While, in the standard version of the density of state method, we usually constrain an observable we are interested in, we fix a different observable in our new method which has a sharp peak at some particular value characterizing the correct vacuum of the target theory. In the finite-density QCD, such an observable is the pion condensate. The average phase becomes vanishingly small as the value of the pion condensate becomes large, hence it is enough to consider configurations with π+ ≃ 0, where the zero mode does not appear. We demonstrate an effectiveness of our method by using a toy model (the chiral random matrix theory) which captures the properties of finite-density QCD qualitatively. We also argue how to apply our method to other theories including finite-density QCD. Although the example we study numerically is based on the phase reweighting method, the same idea can be applied to more general reweighting methods and we show how this idea can be applied to find a possible QCD critical point.

  11. A Delphi-matrix approach to SEA and its application within the tourism sector in Taiwan

    SciTech Connect

    Kuo, N.-W. . E-mail: ibis@ntcn.edu.tw; Hsiao, T.-Y.; Yu, Y.-H.

    2005-04-15

    Strategic Environmental Assessment (SEA) is a procedural tool and within the framework of SEA, several different types of analytical methods can be used in the assessment. However, the impact matrix used currently in Taiwan has some disadvantages. Hence, a Delphi-matrix approach to SEA is proposed here to improve the performance of Taiwan's SEA. This new approach is based on the impact matrix combination with indicators of sustainability, and then the Delphi method is employed to collect experts' opinions. In addition, the assessment of National Floriculture Park Plan and Taiwan Flora 2008 Program is taken as an example to examine this new method. Although international exhibition is one of the important tourism (economic) activities, SEA is seldom about tourism sector. Finally, the Delphi-matrix approach to SEA for tourism development plan is established containing eight assessment topics and 26 corresponding categories. In summary, three major types of impacts: resources' usages, pollution emissions, and local cultures change are found. Resources' usages, such as water, electricity, and natural gas demand, are calculated on a per capita basis. Various forms of pollution resulting from this plan, such as air, water, soil, waste, and noise, are also identified.

  12. Collision frequencies in density-matrix kinetic equations describing nonlinear effects in the wings of spectral lines

    SciTech Connect

    Parkhomenko, A I; Shalagin, Anatolii M

    2011-11-30

    Using the eikonal approximation, we have calculated effective collision frequencies in density-matrix kinetic equations describing nonlinear effects in the wings of spectral lines. We have established the relation between the probabilities of absorption and stimulated emission and the characteristics of the radiation and elementary scattering event. The example of the power interaction potential shows that quantum mechanical calculation of the collision frequencies in the eikonal approximation and previously known spectral line wing theory give similar results for the probability of radiation absorption.

  13. A New Approach of Designing Superalloys for Low Density

    NASA Technical Reports Server (NTRS)

    MacKay, Rebecca A.; Gabb, Timothy P.; Smialek, James L.; Nathal, Michael V.

    2010-01-01

    New low-density single-crystal (LDS) alloy, have bee. developed for turbine blade applications, which have the potential for significant improvements in the thrust-to-weight ratio over current production superalloys. An innovative alloying strategy was wed to achieve alloy density reductions, high-temperature creep resistance, microstructural stability, and cyclic oxidation resistance. The alloy design relies on molybdenum as a potent. lower-density solid-solution strengthener in the nickel-based superalloy. Low alloy density was also achieved with modest rhenium levels tmd the absence of tungsten. Microstructural, physical mechanical, and environmental testing demonstrated the feasibility of this new LDS superalloy design.

  14. Influence of Hemp Fibers Pre-processing on Low Density Polyethylene Matrix Composites Properties

    NASA Astrophysics Data System (ADS)

    Kukle, S.; Vidzickis, R.; Zelca, Z.; Belakova, D.; Kajaks, J.

    2016-04-01

    In present research with short hemp fibres reinforced LLDPE matrix composites with fibres content in a range from 30 to 50 wt% subjected to four different pre-processing technologies were produced and such their properties as tensile strength and elongation at break, tensile modulus, melt flow index, micro hardness and water absorption dynamics were investigated. Capillary viscosimetry was used for fluidity evaluation and melt flow index (MFI) evaluated for all variants. MFI of fibres of two pre-processing variants were high enough to increase hemp fibres content from 30 to 50 wt% with moderate increase of water sorption capability.

  15. Predicting Fish Densities in Lotic Systems: a Simple Modeling Approach

    EPA Science Inventory

    Fish density models are essential tools for fish ecologists and fisheries managers. However, applying these models can be difficult because of high levels of model complexity and the large number of parameters that must be estimated. We designed a simple fish density model and te...

  16. Communication: Novel quantum states of electron spins in polycarbenes from ab initio density matrix renormalization group calculations.

    PubMed

    Mizukami, Wataru; Kurashige, Yuki; Yanai, Takeshi

    2010-09-01

    An investigation into spin structures of poly(m-phenylenecarbene), a prototype of magnetic organic molecules, is presented using the ab initio density matrix renormalization group method. It is revealed by achieving large-scale multireference calculations that the energy differences between high-spin and low-spin states (spin-gaps) of polycarbenes decrease with increasing the number of carbene sites. This size-dependency of the spin-gaps strikingly contradicts the predictions with single-reference methods including density functional theory. The wave function analysis shows that the low-spin states are beyond the classical spin picture, namely, much of multireference character, and thus are manifested as strongly correlated quantum states. The size dependence of the spin-gaps involves an odd-even oscillation, which cannot be explained by the integer-spin Heisenberg model with a single magnetic-coupling constant.

  17. t-Jz ladder: Density-matrix renormalization group and series expansion calculations of the phase diagram

    NASA Astrophysics Data System (ADS)

    Weisse, A.; Bursill, R. J.; Hamer, C. J.; Weihong, Zheng

    2006-04-01

    The phase diagram of the two-leg t-Jz ladder is explored, using the density-matrix renormalization group method. Results are obtained for energy gaps, electron density profiles, and correlation functions for the half filled and quarter filled cases. The effective Lagrangian velocity parameter vρ is shown to vanish at half filling. The behavior of the one-hole gap in the Nagaoka limit is investigated, and found to disagree with theoretical predictions. A tentative phase diagram is presented, which is quite similar to the full t-J ladder, but scaled up by a factor of about 2 in coupling. Near half filling a Luther-Emery phase is found, which may be expected to show superconducting correlations, while near quarter filling the system appears to be in a Tomonaga-Luttinger phase.

  18. Computation of Raman Spectra from Density Matrix Linear Response Theory in Extended Lagrangian Born-Oppenheimer Molecular Dynamics

    NASA Astrophysics Data System (ADS)

    Niklasson, Anders; Coe, Joshua; Cawkwell, Marc

    2011-06-01

    Linear response calculations based on density matrix perturbation theory [A. M. N. Niklasson and M. Challacombe, Phys. Rev. Lett. 92, 193001 (2004)] have been developed within a self-consistent tight-binding method for extended Lagrangian Born-Oppenheimer molecular dynamics [A. M. N. Niklasson, Phys. Rev. Lett., 100, 123004 (2008)]. Besides the nuclear coordinates, extended auxiliary electronic degrees of freedom are added to the regular Born-Oppenheimer Lagrangian, both for the electronic ground state and response densities. This formalism enables highly efficient, on-the-fly, analytic computations of the polarizability autocorrelation functions and the Raman spectra during energy conserving Born-Oppenheimer molecular dynamics trajectories. We will illustrate these capabilities via time-resolved Raman spectra computed during explicit, reactive molecular dynamics simulations of the shock compression of methane, benzene, tert-butylacetylene. Comparisons will be made with experimental results where possible.

  19. Combating matrix effects in LC/ESI/MS: the extrapolative dilution approach.

    PubMed

    Kruve, Anneli; Leito, Ivo; Herodes, Koit

    2009-09-28

    Liquid chromatography electrospray mass spectrometry--LC/ESI/MS--a primary tool for analysis of low volatility compounds in difficult matrices--suffers from the matrix effects in the ESI ionization. It is well known that matrix effects can be reduced by sample dilution. However, the efficiency of simple sample dilution is often limited, in particular by the limit of detection of the method, and can strongly vary from sample to sample. In this study matrix effect is investigated as the function of dilution. It is demonstrated that in some cases dilution can eliminate matrix effect, but often it is just reduced. Based on these findings we propose a new quantitation method based on consecutive dilutions of the sample and extrapolation of the analyte content to the infinite dilution, i.e. to matrix-free solution. The method was validated for LC/ESI/MS analysis of five pesticides (methomyl, thiabendazole, aldicarb, imazalil, methiocarb) in five matrices (tomato, cucumber, apple, rye and garlic) at two concentration levels (0.5 and 5.0 mg kg(-1)). Agreement between the analyzed and spiked concentrations was found for all samples. It was demonstrated that in terms of accuracy of the obtained results the proposed extrapolative dilution approach works distinctly better than simple sample dilution. The main use of this approach is envisaged for (a) method development/validation to determine the extent of matrix effects and the ways of overcoming them and (b) as a second step of analysis in the case of samples having analyte contents near the maximum residue limits (MRL). PMID:19733738

  20. Combinational effect of matrix elasticity and alendronate density on differentiation of rat mesenchymal stem cells.

    PubMed

    Jiang, Pengfei; Mao, Zhengwei; Gao, Changyou

    2015-06-01

    Differentiation of mesenchymal stem cells (MSCs) is regulated by multivariate physical and chemical signals in a complicated microenvironment. In this study, polymerizable double bonds (GelMA) and osteo-inductive alendronate (Aln) (Aln-GelMA) were sequentially grafted onto gelatin molecules. The biocompatible hydrogels with defined stiffness in the range of 4-40 kPa were prepared by using polyethylene glycol diacrylate (PEGDA) as additional crosslinker. The Aln density was adjusted from 0 to 4 μM by controlling the ratio between the GelMA and Aln-GelMA. The combinational effects of stiffness and Aln density on osteogenic differentiation of MSCs were then studied in terms of ALP activity, collagen type I and osteocalcin expression, and calcium deposition. The results indicated that the stiffness and Aln density could synergistically improve the expression of all these osteogenesis markers. Their osteo-inductive effects are comparable to some extent, and high Aln density could be more effective than the stiffness.

  1. Shrinkage covariance matrix approach based on robust trimmed mean in gene sets detection

    NASA Astrophysics Data System (ADS)

    Karjanto, Suryaefiza; Ramli, Norazan Mohamed; Ghani, Nor Azura Md; Aripin, Rasimah; Yusop, Noorezatty Mohd

    2015-02-01

    Microarray involves of placing an orderly arrangement of thousands of gene sequences in a grid on a suitable surface. The technology has made a novelty discovery since its development and obtained an increasing attention among researchers. The widespread of microarray technology is largely due to its ability to perform simultaneous analysis of thousands of genes in a massively parallel manner in one experiment. Hence, it provides valuable knowledge on gene interaction and function. The microarray data set typically consists of tens of thousands of genes (variables) from just dozens of samples due to various constraints. Therefore, the sample covariance matrix in Hotelling's T2 statistic is not positive definite and become singular, thus it cannot be inverted. In this research, the Hotelling's T2 statistic is combined with a shrinkage approach as an alternative estimation to estimate the covariance matrix to detect significant gene sets. The use of shrinkage covariance matrix overcomes the singularity problem by converting an unbiased to an improved biased estimator of covariance matrix. Robust trimmed mean is integrated into the shrinkage matrix to reduce the influence of outliers and consequently increases its efficiency. The performance of the proposed method is measured using several simulation designs. The results are expected to outperform existing techniques in many tested conditions.

  2. Response calculations based on an independent particle system with the exact one-particle density matrix: Polarizabilities

    SciTech Connect

    Giesbertz, K. J. H.; Gritsenko, O. V.; Baerends, E. J.

    2014-05-14

    Recently, we have demonstrated that the problems finding a suitable adiabatic approximation in time-dependent one-body reduced density matrix functional theory can be remedied by introducing an additional degree of freedom to describe the system: the phase of the natural orbitals [K. J. H. Giesbertz, O. V. Gritsenko, and E. J. Baerends, Phys. Rev. Lett. 105, 013002 (2010); K. J. H. Giesbertz, O. V. Gritsenko, and E. J. Baerends, J. Chem. Phys. 133, 174119 (2010)]. In this article we will show in detail how the frequency-dependent response equations give the proper static limit (ω → 0), including the perturbation in the chemical potential, which is required in static response theory to ensure the correct number of particles. Additionally we show results for the polarizability for H{sub 2} and compare the performance of two different two-electron functionals: the phase-including Löwdin–Shull functional and the density matrix form of the Löwdin–Shull functional.

  3. Enhancement in field emission current density of Ni nanoparticles embedded in thin silica matrix by swift heavy ion irradiation

    SciTech Connect

    Sarker, Debalaya; Patra, Rajkumar; Srivastava, P.; Ghosh, S.; Kumar, H.; Kabiraj, D.; Avasthi, D. K.; Vayalil, Sarathlal K.; Roth, S. V.

    2014-05-07

    The field emission (FE) properties of nickel nanoparticles embedded in thin silica matrix irradiated with 100 MeV Au{sup +7} ions at various fluences are studied here. A large increase in FE current density is observed in the irradiated films as compared to their as deposited counterpart. The dependence of FE properties on irradiation fluence is correlated with surface roughness, density of states of valence band and size distribution of nanoparticles as examined with atomic force microscope, X-ray photoelectron spectroscopy, and grazing incidence small angle x-ray scattering. A current density as high as 0.48 mA/cm{sup 2} at an applied field 15 V/μm has been found for the first time for planar field emitters in the film irradiated with fluence of 5.0 × 10{sup 13} ions/cm{sup 2}. This significant enhancement in the current density is attributed to an optimized size distribution along with highest surface roughness of the same. This new member of field emission family meets most of the requirements of cold cathodes for vacuum micro/nanoelectronic devices.

  4. Increasing the power density when using inert matrix fuels to reduce production of transuranics

    SciTech Connect

    Recktenwald, G.D.; Deinert, M.R.

    2013-07-01

    Reducing the production of transuranics is a goal of most advanced nuclear fuel cycles. One way to do this is to recycle the transuranics into the same reactors that are currently producing them using an inert matrix fuel. In previous work we have modeled such a reactor where 72%, of the core is comprised of standard enriched uranium fuel pins, with the remaining 28% fuel made from Yttria stabilized zirconium, in which transuranics are loaded. A key feature of this core is that all of the transuranics produced by the uranium fuel assemblies are later burned in inert matrix fuel assemblies. It has been shown that this system can achieve reductions in transuranic waste of more than 86%. The disadvantage of such a system is that the core power rating must be significantly lower than a standard pressurized water reactor. One reason for the lower power is that high burnup of the uranium fuel precludes a critical level of reactivity at the end of the campaign. Increasing the uranium enrichment and changing the pin pitch are two ways to increase burnup while maintaining criticality. In this paper we use MCNPX and a linear reactivity model to quantify the effect of these two parameters on the end of campaign reactivity. Importantly, we show that in the region of our proposed reactor, enrichment increases core reactivity by 0.02 per percent uranium 235 and pin pitch increases reactivity by 0.02 per mm. Reactivity is lost at a rate of 0.005 per MWd/kgIHM uranium burnup. (authors)

  5. Spin alignment and density matrix measurement in sup 28 Si + sup 12 C orbiting reaction

    SciTech Connect

    Ray, A.; Shapira, D.; Halbert, M.L.; Gomez del Campo, J.; Kim, H.J. ); Sullivan, J.P. . Cyclotron Inst.); Shivakumar, B.; Mitchell, J. . Wright Nuclear Structure Lab.)

    1990-01-01

    Gamma-ray angular correlations have been measured for the strongly damped reactions {sup 12}C({sup 28}Si,{sup 12}C){sup 28}Si between {theta}{sub cm} = (120{degree} {minus} 160{degree}) for E{sub cm} = 43.5 and 48 MeV. We find that the density matrices for the {sup 12}C(2{sub 1}{sup +}) and {sup 28}Si states are almost diagonal with respect to the direction of motion of the outgoing particle. The measured density matrices and spin alignments are consistent with the picture of formation of a long-lived dinuclear complex undergoing orbiting, bending and wriggling motions, but not with those obtained from statistical compound nucleus or sticking model calculations. 17 refs., 2 figs., 1 tab.

  6. Density matrix description of laser-induced hot electron mediated photodesorption of NO from Pt(111)

    NASA Astrophysics Data System (ADS)

    Saalfrank, Peter; Baer, Roi; Kosloff, Ronnie

    1994-12-01

    Based on the numerical solution of the Liouville-von Neumann equation for dissipative systems, the photodesorption dynamics of NO/Pt(111) are studied. Dissipative terms are used to describe the quenching of electronically excited states on the metal, electronic dephasing and the indirect (hot-electron mediated) excitation processes in the DIMET and DIET limits. Norm and energy flow, desorption probabilities and density time-of-flight spectra are computed.

  7. Association weight matrix: a network-based approach towards functional genome-wide association studies.

    PubMed

    Reverter, Antonio; Fortes, Marina R S

    2013-01-01

    In this chapter we describe the Association Weight Matrix (AWM), a novel procedure to exploit the results from genome-wide association studies (GWAS) and, in combination with network inference algorithms, generate gene networks with regulatory and functional significance. In simple terms, the AWM is a matrix with rows represented by genes and columns represented by phenotypes. Individual {i, j}th elements in the AWM correspond to the association of the SNP in the ith gene to the jth phenotype. While our main objective is to provide a recipe-like tutorial on how to build and use AWM, we also take the opportunity to briefly reason the logic behind each step in the process. To conclude, we discuss the impact on AWM of issues like the number of phenotypes under scrutiny, the density of the SNP chip and the choice of contrast upon which to infer the cause-effect regulatory interactions. PMID:23756904

  8. On the GPI approach with unknown inertia matrix in robot manipulators

    NASA Astrophysics Data System (ADS)

    Arteaga-Pérez, Marco A.; Gutiérrez-Giles, Alejandro

    2014-04-01

    This article discusses the design of generalised proportional integral observers for the tracking control of robot manipulators. The unknown, possibly state-dependent, additive nonlinearity influencing the input-output description, in terms of the tracking error dynamics is modelled for observer construction purposes, as an absolutely bounded, additive, unknown time-varying perturbation input signal. A disadvantage of the approach lies in the fact that the system inertia matrix is usually required for implementation. In this work, it is shown how the approach can be modified to avoid the use of the inertia matrix when it is unknown. A set of experiments with three different test beds is carried out to show the good performance of the proposed algorithm.

  9. A multivariate approach to filling gaps in large ecological data sets using probabilistic matrix factorization techniques

    NASA Astrophysics Data System (ADS)

    Schrodt, F. I.; Shan, H.; Kattge, J.; Reich, P.; Banerjee, A.; Reichstein, M.

    2012-12-01

    With the advent of remotely sensed data and coordinated efforts to create global databases, the ecological community has progressively become more data-intensive. However, in contrast to other disciplines, statistical ways of handling these large data sets, especially the gaps which are inherent to them, are lacking. Widely used theoretical approaches, for example model averaging based on Akaike's information criterion (AIC), are sensitive to missing values. Yet, the most common way of handling sparse matrices - the deletion of cases with missing data (complete case analysis) - is known to severely reduce statistical power as well as inducing biased parameter estimates. In order to address these issues, we present novel approaches to gap filling in large ecological data sets using matrix factorization techniques. Factorization based matrix completion was developed in a recommender system context and has since been widely used to impute missing data in fields outside the ecological community. Here, we evaluate the effectiveness of probabilistic matrix factorization techniques for imputing missing data in ecological matrices using two imputation techniques. Hierarchical Probabilistic Matrix Factorization (HPMF) effectively incorporates hierarchical phylogenetic information (phylogenetic group, family, genus, species and individual plant) into the trait imputation. Kernelized Probabilistic Matrix Factorization (KPMF) on the other hand includes environmental information (climate and soils) into the matrix factorization through kernel matrices over rows and columns. We test the accuracy and effectiveness of HPMF and KPMF in filling sparse matrices, using the TRY database of plant functional traits (http://www.try-db.org). TRY is one of the largest global compilations of plant trait databases (750 traits of 1 million plants), encompassing data on morphological, anatomical, biochemical, phenological and physiological features of plants. However, despite of unprecedented

  10. Water clusters in an argon matrix: infrared spectra from molecular dynamics simulations with a self-consistent charge density functional-based tight binding/force-field potential.

    PubMed

    Simon, Aude; Iftner, Christophe; Mascetti, Joëlle; Spiegelman, Fernand

    2015-03-19

    The present theoretical study aims at investigating the effects of an argon matrix on the structures, energetics, dynamics, and infrared (IR) spectra of small water clusters (H2O)n (n = 1-6). The potential energy surface is obtained from a hybrid self-consistent charge density functional-based tight binding/force-field approach (SCC-DFTB/FF) in which the water clusters are treated at the SCC-DFTB level and the matrix is modeled at the FF level by a cluster consisting of ∼340 Ar atoms with a face centered cubic (fcc) structure, namely (H2O)n/Ar. With respect to a pure FF scheme, this allows a quantum description of the molecular system embedded in the matrix, along with all-atom geometry optimization and molecular dynamics (MD) simulations of the (H2O)n/Ar system. Finite-temperature IR spectra are derived from the MD simulations. The SCC-DFTB/FF scheme is first benchmarked on (H2O)Arn clusters against correlated wave function results and DFT calculations performed in the present work, and against FF data available in the literature. Regarding (H2O)n/Ar systems, the geometries of the water clusters are found to adapt to the fcc environment, possibly leading to intermolecular distortion and matrix perturbation. Several energetical quantities are estimated to characterize the water clusters in the matrix. In the particular case of the water hexamer, substitution and insertion energies for the prism, bag, and cage are found to be lower than that for the 6-member ring isomer. Finite-temperature MD simulations show that the water monomer has a quasifree rotation motion at 13 K, in agreement with experimental data. In the case of the water dimer, the only large-amplitude motion is a distortion-rotation intermolecular motion, whereas only vibration motions around the nuclei equilibrium positions are observed for clusters with larger sizes. Regarding the IR spectra, we find that the matrix environment leads to redshifts of the stretching modes and almost no shift of the

  11. Water clusters in an argon matrix: infrared spectra from molecular dynamics simulations with a self-consistent charge density functional-based tight binding/force-field potential.

    PubMed

    Simon, Aude; Iftner, Christophe; Mascetti, Joëlle; Spiegelman, Fernand

    2015-03-19

    The present theoretical study aims at investigating the effects of an argon matrix on the structures, energetics, dynamics, and infrared (IR) spectra of small water clusters (H2O)n (n = 1-6). The potential energy surface is obtained from a hybrid self-consistent charge density functional-based tight binding/force-field approach (SCC-DFTB/FF) in which the water clusters are treated at the SCC-DFTB level and the matrix is modeled at the FF level by a cluster consisting of ∼340 Ar atoms with a face centered cubic (fcc) structure, namely (H2O)n/Ar. With respect to a pure FF scheme, this allows a quantum description of the molecular system embedded in the matrix, along with all-atom geometry optimization and molecular dynamics (MD) simulations of the (H2O)n/Ar system. Finite-temperature IR spectra are derived from the MD simulations. The SCC-DFTB/FF scheme is first benchmarked on (H2O)Arn clusters against correlated wave function results and DFT calculations performed in the present work, and against FF data available in the literature. Regarding (H2O)n/Ar systems, the geometries of the water clusters are found to adapt to the fcc environment, possibly leading to intermolecular distortion and matrix perturbation. Several energetical quantities are estimated to characterize the water clusters in the matrix. In the particular case of the water hexamer, substitution and insertion energies for the prism, bag, and cage are found to be lower than that for the 6-member ring isomer. Finite-temperature MD simulations show that the water monomer has a quasifree rotation motion at 13 K, in agreement with experimental data. In the case of the water dimer, the only large-amplitude motion is a distortion-rotation intermolecular motion, whereas only vibration motions around the nuclei equilibrium positions are observed for clusters with larger sizes. Regarding the IR spectra, we find that the matrix environment leads to redshifts of the stretching modes and almost no shift of the

  12. A distance difference matrix approach to identifying transcription factors that regulate differential gene expression

    PubMed Central

    De Bleser, Pieter; Hooghe, Bart; Vlieghe, Dominique; van Roy, Frans

    2007-01-01

    We introduce a method that considers target genes of a transcription factor, and searches for transcription factor binding sites (TFBSs) of secondary factors responsible for differential responses among these targets. Based on the distance difference matrix concept, the method simultaneously integrates statistical overrepresentation and co-occurrence of TFBSs. Our approach is validated on datasets of differentially regulated human genes and is shown to be highly effective in detecting TFBSs responsible for the observed differential gene expression. PMID:17504544

  13. Transfer matrix approach to propagation of angular plane wave spectra through metamaterial multilayer structures

    NASA Astrophysics Data System (ADS)

    Banerjee, Partha P.; Li, Han; Aylo, Rola; Nehmetallah, Georges

    2011-10-01

    The development of electromagnetic (EM) metamaterials for perfect lensing and optical cloaking has given rise to novel multilayer bandgap structures using stacks of positive and negative index materials. Propagation of a collection of TE or TM plane waves, comprising the angular plane wave spectrum, through such structures is analyzed by using the transfer matrix method (TMM) on every plane wave component. Results obtained from this TMM approach for a Gaussian spectrum are compared with those using standard FEM techniques.

  14. Positron accumulation effect in particles embedded in a low-density matrix

    SciTech Connect

    Dryzek, Jerzy; Siemek, Krzysztof

    2015-02-07

    Systematic studies of the so-called positron accumulation effect for samples with particles embedded in a matrix are reported. This effect is related to energetic positrons which penetrate inhomogeneous medium. Due to differences in the linear absorption coefficient, different amounts of positrons are accumulated and annihilate in the identical volume of both materials. Positron lifetime spectroscopy and Doppler broadening of the annihilation line using Na-22 positrons were applied to the studies of the epoxy resin samples with embedded micro-sized particles of transition metals, i.e., Ni, Sn, Mo, W, and nonmetal particles, i.e., Si and NaF. The significant difference between the determined fraction of positrons annihilating in the particles and the particle volume fraction indicates the positron accumulation effect. The simple phenomenological model and Monte Carlo simulations are able to describe the main features of the obtained dependencies. The aluminum alloy with embedded Sn nanoparticles is also considered for demonstration differences between the accumulation and another related effect, i.e., the positron affinity.

  15. Effects of spin-orbit interactions in disordered conductors: A random-matrix approach

    NASA Astrophysics Data System (ADS)

    Macêdo, A. M. S.; Chalker, J. T.

    1992-12-01

    A description in terms of random matrices is used to study the effects of strong spin-orbit coupling in disordered conductors. It is shown that the ensemble of transfer matrices can be conveniently parametrized using quaternions. A diffusion equation is derived for the evolution, with sample length, of the transfer-matrix distribution. In the insulating regime, a uniform density of Lyapunov exponents is obtained, and the expected universal multiplication factors in the localization length are derived when time-reversal symmetry is broken. Weak antilocalization, backscattering depletion, and universal conductance fluctuations are obtained in the metallic regime.

  16. An information theory approach to the density of the earth

    NASA Technical Reports Server (NTRS)

    Graber, M. A.

    1977-01-01

    Information theory can develop a technique which takes experimentally determined numbers and produces a uniquely specified best density model satisfying those numbers. A model was generated using five numerical parameters: the mass of the earth, its moment of inertia, three zero-node torsional normal modes (L = 2, 8, 26). In order to determine the stability of the solution, six additional densities were generated, in each of which the period of one of the three normal modes was increased or decreased by one standard deviation. The superposition of the seven models is shown. It indicates that current knowledge of the torsional modes is sufficient to specify the density in the upper mantle but that the lower mantle and core will require smaller standard deviations before they can be accurately specified.

  17. Teaching the extracellular matrix and introducing online databases within a multidisciplinary course with i-cell-MATRIX: A student-centered approach.

    PubMed

    Sousa, João Carlos; Costa, Manuel João; Palha, Joana Almeida

    2010-03-01

    The biochemistry and molecular biology of the extracellular matrix (ECM) is difficult to convey to students in a classroom setting in ways that capture their interest. The understanding of the matrix's roles in physiological and pathological conditions study will presumably be hampered by insufficient knowledge of its molecular structure. Internet-available resources can bridge the division between the molecular details and ECM's biological properties and associated processes. This article presents an approach to teach the ECM developed for first year medical undergraduates who, working in teams: (i) Explore a specific molecular component of the matrix, (ii) identify a disease in which the component is implicated, (iii) investigate how the component's structure/function contributes to ECM' supramolecular organization in physiological and in pathological conditions, and (iv) share their findings with colleagues. The approach-designated i-cell-MATRIX-is focused on the contribution of individual components to the overall organization and biological functions of the ECM. i-cell-MATRIX is student centered and uses 5 hours of class time. Summary of results and take home message: A "1-minute paper" has been used to gather student feedback on the impact of i-cell-MATRIX. Qualitative analysis of student feedback gathered in three consecutive years revealed that students appreciate the approach's reliance on self-directed learning, the interactivity embedded and the demand for deeper insights on the ECM. Learning how to use internet biomedical resources is another positive outcome. Ninety percent of students recommend the activity for subsequent years. i-cell-MATRIX is adaptable by other medical schools which may be looking for an approach that achieves higher student engagement with the ECM.

  18. Transfer-matrix approach for finite-difference time-domain simulation of periodic structures.

    PubMed

    Deinega, Alexei; Belousov, Sergei; Valuev, Ilya

    2013-11-01

    Optical properties of periodic structures can be calculated using the transfer-matrix approach, which establishes a relation between amplitudes of the wave incident on a structure with transmitted or reflected waves. The transfer matrix can be used to obtain transmittance and reflectance spectra of finite periodic structures as well as eigenmodes of infinite structures. Traditionally, calculation of the transfer matrix is performed in the frequency domain and involves linear algebra. In this work, we present a technique for calculation of the transfer matrix using the finite-difference time-domain (FDTD) method and show the way of its implementation in FDTD code. To illustrate the performance of our technique we calculate the transmittance spectra for opal photonic crystal slabs consisting of multiple layers of spherical scatterers. Our technique can be used for photonic band structure calculations. It can also be combined with existing FDTD methods for the analysis of periodic structures at an oblique incidence, as well as for modeling point sources in a periodic environment. PMID:24329377

  19. Establishing conservation laws in pair-correlated many-body theories: T-matrix approaches

    NASA Astrophysics Data System (ADS)

    He, Yan; Levin, K.

    2014-01-01

    We address conservation laws associated with current, momentum, and energy and show how they can be satisfied within many body theories which focus on pair correlations. Of interest are two well known T-matrix theories which represent many body theories which incorporate pairing in the normal state. The first of these is associated with the Nozieres Schmitt-Rink theory, while the second involves the T matrix of a BCS-Leggett-like state as identified by Kadanoff and Martin. T-matrix theories begin with an ansatz for the single particle self energy and are to be distinguished from Φ-derivable theories which introduce an ansatz for a particular contribution to the thermodynamical potential. Conservation laws are equivalent to Ward identities which we address in some detail here. Although Φ-derivable theories are often referred to as "conserving theories," a consequence of this work is the demonstration that these two T-matrix approaches similarly can be made to obey all conservation laws. When simplifying approximations are made in Φ-derivable or other theories, one has to take care that the end results are not incompatible with conservation.

  20. Transfer-matrix approach for finite-difference time-domain simulation of periodic structures.

    PubMed

    Deinega, Alexei; Belousov, Sergei; Valuev, Ilya

    2013-11-01

    Optical properties of periodic structures can be calculated using the transfer-matrix approach, which establishes a relation between amplitudes of the wave incident on a structure with transmitted or reflected waves. The transfer matrix can be used to obtain transmittance and reflectance spectra of finite periodic structures as well as eigenmodes of infinite structures. Traditionally, calculation of the transfer matrix is performed in the frequency domain and involves linear algebra. In this work, we present a technique for calculation of the transfer matrix using the finite-difference time-domain (FDTD) method and show the way of its implementation in FDTD code. To illustrate the performance of our technique we calculate the transmittance spectra for opal photonic crystal slabs consisting of multiple layers of spherical scatterers. Our technique can be used for photonic band structure calculations. It can also be combined with existing FDTD methods for the analysis of periodic structures at an oblique incidence, as well as for modeling point sources in a periodic environment.

  1. Invertibility of retarded response functions for Laplace transformable potentials: Application to one-body reduced density matrix functional theory.

    PubMed

    Giesbertz, K J H

    2015-08-01

    A theorem for the invertibility of arbitrary response functions is presented under the following conditions: the time dependence of the potentials should be Laplace transformable and the initial state should be a ground state, though it might be degenerate. This theorem provides a rigorous foundation for all density-functional-like theories in the time-dependent linear response regime. Especially for time-dependent one-body reduced density matrix (1RDM) functional theory, this is an important step forward, since a solid foundation has currently been lacking. The theorem is equally valid for static response functions in the non-degenerate case, so can be used to characterize the uniqueness of the potential in the ground state version of the corresponding density-functional-like theory. Such a classification of the uniqueness of the non-local potential in ground state 1RDM functional theory has been lacking for decades. With the aid of presented invertibility theorem presented here, a complete classification of the non-uniqueness of the non-local potential in 1RDM functional theory can be given for the first time.

  2. The nutrient density approach to healthy eating: challenges and opportunities

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The term 'nutrient density' for foods/beverages has been used loosely to promote the Dietary Guidelines for Americans. The 2010 Dietary Guidelines for Americans defined 'all vegetables, fruits, whole grains, fat-free or low-fat milk and milk products, seafood, lean meats and poultry, eggs, beans and...

  3. Assessing students approaches to learning using a matrix framework in a Malaysian public university.

    PubMed

    Teoh, Hee Chong; Abdullah, Maria Chong; Roslan, Samsilah; Mohd Daud, Shaffe

    2014-01-01

    This study aims to evaluate the learning characteristics of students using a matrix framework of learning approaches (MFLA) in a Malaysian public university. A survey form based on Biggs's study process questionnaire (SPQ) was distributed to a total of 350 students. This study employed a descriptive correlation research design to address the research objectives. The findings revealed that Malaysian students are prone to applying the achieving approach in their studies. The achieving approach is the most preferable learning characteristic. The results also indicated that four of the nine hypothetical learning approaches exist, two of which are positive in nature. As a result, a proposed teaching method based on the MFLA was introduced to suit the needs of these major learning characteristics among students.

  4. Differential cross sections and spin density matrix elements for the reaction {gamma}p{yields}p{omega}

    SciTech Connect

    Williams, M.; Applegate, D.; Bellis, M.; Meyer, C. A.; Dey, B.; Dickson, R.; Krahn, Z.; McCracken, M. E.; Moriya, K.; Schumacher, R. A.; Adhikari, K. P.; Careccia, S. L.; Dodge, G. E.; Klein, A.; Mayer, M.; Nepali, C. S.; Niroula, M. R.; Seraydaryan, H.; Tkachenko, S.; Weinstein, L. B.

    2009-12-15

    High-statistics differential cross sections and spin-density matrix elements for the reaction {gamma}p{yields}p{omega} have been measured using the CEBAF large acceptance spectrometer (CLAS) at Jefferson Lab for center-of-mass (c.m.) energies from threshold up to 2.84 GeV. Results are reported in 112 10-MeV wide c.m. energy bins, each subdivided into cos{theta}{sub c.m.}{sup {omega}} bins of width 0.1. These are the most precise and extensive {omega} photoproduction measurements to date. A number of prominent structures are clearly present in the data. Many of these have not previously been observed due to limited statistics in earlier measurements.

  5. Pressure-Induced Amorphization and a New High Density Amorphous Metallic Phase in Matrix-Free Ge Nanoparticles.

    PubMed

    Corsini, Niccolo R C; Zhang, Yuanpeng; Little, William R; Karatutlu, Ali; Ersoy, Osman; Haynes, Peter D; Molteni, Carla; Hine, Nicholas D M; Hernandez, Ignacio; Gonzalez, Jesus; Rodriguez, Fernando; Brazhkin, Vadim V; Sapelkin, Andrei

    2015-11-11

    Over the last two decades, it has been demonstrated that size effects have significant consequences for the atomic arrangements and phase behavior of matter under extreme pressure. Furthermore, it has been shown that an understanding of how size affects critical pressure-temperature conditions provides vital guidance in the search for materials with novel properties. Here, we report on the remarkable behavior of small (under ~5 nm) matrix-free Ge nanoparticles under hydrostatic compression that is drastically different from both larger nanoparticles and bulk Ge. We discover that the application of pressure drives surface-induced amorphization leading to Ge-Ge bond overcompression and eventually to a polyamorphic semiconductor-to-metal transformation. A combination of spectroscopic techniques together with ab initio simulations were employed to reveal the details of the transformation mechanism into a new high density phase-amorphous metallic Ge.

  6. The tensor hypercontracted parametric reduced density matrix algorithm: coupled-cluster accuracy with O(r(4)) scaling.

    PubMed

    Shenvi, Neil; van Aggelen, Helen; Yang, Yang; Yang, Weitao; Schwerdtfeger, Christine; Mazziotti, David

    2013-08-01

    Tensor hypercontraction is a method that allows the representation of a high-rank tensor as a product of lower-rank tensors. In this paper, we show how tensor hypercontraction can be applied to both the electron repulsion integral tensor and the two-particle excitation amplitudes used in the parametric 2-electron reduced density matrix (p2RDM) algorithm. Because only O(r) auxiliary functions are needed in both of these approximations, our overall algorithm can be shown to scale as O(r(4)), where r is the number of single-particle basis functions. We apply our algorithm to several small molecules, hydrogen chains, and alkanes to demonstrate its low formal scaling and practical utility. Provided we use enough auxiliary functions, we obtain accuracy similar to that of the standard p2RDM algorithm, somewhere between that of CCSD and CCSD(T).

  7. The tensor hypercontracted parametric reduced density matrix algorithm: coupled-cluster accuracy with O(r(4)) scaling.

    PubMed

    Shenvi, Neil; van Aggelen, Helen; Yang, Yang; Yang, Weitao; Schwerdtfeger, Christine; Mazziotti, David

    2013-08-01

    Tensor hypercontraction is a method that allows the representation of a high-rank tensor as a product of lower-rank tensors. In this paper, we show how tensor hypercontraction can be applied to both the electron repulsion integral tensor and the two-particle excitation amplitudes used in the parametric 2-electron reduced density matrix (p2RDM) algorithm. Because only O(r) auxiliary functions are needed in both of these approximations, our overall algorithm can be shown to scale as O(r(4)), where r is the number of single-particle basis functions. We apply our algorithm to several small molecules, hydrogen chains, and alkanes to demonstrate its low formal scaling and practical utility. Provided we use enough auxiliary functions, we obtain accuracy similar to that of the standard p2RDM algorithm, somewhere between that of CCSD and CCSD(T). PMID:23927246

  8. Low-lying excited states in armchair polyacene within Pariser-Parr-Pople model: A density matrix renormalization group study

    SciTech Connect

    Das, Mousumi

    2014-03-28

    We studied the nature of the ground state and low-lying excited states of armchair polyacene oligomers (Polyphenanthrene) within long-range Pariser-Parr-Pople model Hamiltonian with up to 14 monomers using symmetrized density matrix renormalization group technique. The ground state of all armchair polyacenes studied is found to be singlet. The results show that lowest singlet dipole allowed excited state has higher energy for armchair polyacenes as compared to linear fused polyacenes. Moreover, unlike linear fused polyacenes, the lowest singlet excited state of these oligomers is always found to lie below the lowest dipole forbidden two-photon state indicating that these armchair polyacene oligomers strongly fluoresce. The calculations of low-lying excitations on singly and triply electron doped armchair polyacene oligomers show a low energy band with strong transition dipole moment that coupled to charge conductivity. This implies armchair polyacene posses novel field-effect transistor properties.

  9. The calculation of generalized oscillator strength densities of Argon by using an eigenchannel R-matrix method

    NASA Astrophysics Data System (ADS)

    Gao, X.; Li, J. M.

    2012-06-01

    Understanding the detailed dynamics of electron-ion interactions is of fundamental importance to various plasma applications in the fields of astrophysics, fusion energy researches and so on. Theoretical computations should play indispensable role to satisfy needs. Using our modified R-matrix code R-Eigen, we can directly calculate the short-range scattering matrices with good analytical properties in the whole energy regions, from which we can obtain all energy levels and the related scattering cross sections with accuracies comparable with spectroscopic precision. With the corresponding high-quality eigenchannel wavefunctions, various transition matrix elements can be readily calculated, such as the generalized oscillator strength densities (GOSD). The GOSD is directly related with the high-energy electron impact excitation cross sections. In eigenchannel representation, the GOSD curves of the excited states in an eigenchannel form a surface, which is a smooth function of the momentum transfers and the excitation energies. From such smooth GOSDs, we can obtain the generalized oscillator strength of any specific excited state through multichannel quantum defect theory, e.g. infinite Rydberg(including strongly perturbed one), autoionization and continuum states. As an example, we will present our recent calculation results of Ar, which are in good agreement with available benchmark experiments.

  10. Matrix operator approach to the quantum evolution operator and the geometric phase

    NASA Astrophysics Data System (ADS)

    Kim, Sang Pyo; Kim, Jewan; Soh, Kwang Sup

    2013-11-01

    The Moody-Shapere-Wilczek's adiabatic effective Hamiltonian and Lagrangian method is developed further into the matrix effective Hamiltonian (MEH) and Lagrangian (MEL) approach to a parameter-dependent quantum system. The matrix-operator approach formulated in the product integral (PI) provides not only a method to find the wave function efficiently in the MEH approach but also higher order corrections to the effective action systematically in the MEL approach, a la the Magnus expansion and the Kubo cumulant expansion. A coupled quantum system of a light particle of a harmonic oscillator is worked out, and as a by-product, a new kind of gauge potential (Berry's connection) is found even for nondegenerate cases (real eigenfunctions). Moreover, in the PI formulation the holonomy of the induced gauge potential is related to Schlesinger's exact formula for the gauge field tensor. A superadiabatic expansion is also constructed, and a generalized Dykhne formula, depending on the contour integrals of the homotopy class of complex degenerate points, is rephrased in the PI formulation.

  11. The nutrient density approach to healthy eating: challenges and opportunities.

    PubMed

    Nicklas, Theresa A; Drewnowski, Adam; O'Neil, Carol E

    2014-12-01

    The term 'nutrient density' for foods/beverages has been used loosely to promote the Dietary Guidelines for Americans. The 2010 Dietary Guidelines for Americans defined 'all vegetables, fruits, whole grains, fat-free or low-fat milk and milk products, seafood, lean meats and poultry, eggs, beans and peas (legumes), and nuts and seeds that are prepared without added solid fats, added sugars, and sodium' as nutrient dense. The 2010 Dietary Guidelines for Americans further states that nutrient-dense foods and beverages provide vitamins, minerals and other substances that may have positive health effects with relatively few (kilo)calories or kilojoules. Finally, the definition states nutrients and other beneficial substances have not been 'diluted' by the addition of energy from added solid fats, added sugars or by the solid fats naturally present in the food. However, the Dietary Guidelines Advisory Committee and other scientists have failed to clearly define 'nutrient density' or to provide criteria or indices that specify cut-offs for foods that are nutrient dense. Today, 'nutrient density' is a ubiquitous term used in the scientific literature, policy documents, marketing strategies and consumer messaging. However, the term remains ambiguous without a definitive or universal definition. Classifying or ranking foods according to their nutritional content is known as nutrient profiling. The goal of the present commentary is to address the research gaps that still exist before there can be a consensus on how best to define nutrient density, highlight the situation in the USA and relate this to wider, international efforts in nutrient profiling.

  12. Density matrix treatment of combined instantaneous and delayed dissipation for an electronically excited adsorbate on a solid surface

    NASA Astrophysics Data System (ADS)

    Leathers, Andrew S.; Micha, David A.; Kilin, Dmitri S.

    2009-10-01

    The interaction of an excited adsorbate with a medium undergoing electronic and vibrational transitions leads to fast dissipation due to electronic energy relaxation and slow (or delayed) dissipation from vibrational energy relaxation. A theoretical and computational treatment of these phenomena has been done in terms of a reduced density matrix satisfying a generalized Liouville-von Neumann equation, with instantaneous dissipation constructed from state-to-state transition rates, and delayed dissipation given by a memory term derived from the time-correlation function (TCF) of atomic displacements in the medium. Two representative applications are presented here, where electronic excitation may enhance vibrational relaxation of an adsorbate. They involve femtosecond excitation of (a) a CO molecule adsorbed on the Cu(001) metal surface and (b) a metal cluster on a semiconductor surface, Ag3Si(111):H, both electronically excited by visible light and undergoing electron transfer and dissipative dynamics by electronic and vibrational relaxations. Models have been parametrized in both cases from electronic structure calculations and known TCFs for the medium, which are slowly decaying in case (a) and fast decaying in case (b). This requires different numerical procedures in the solution of the integrodifferential equations for the reduced density matrix, which have been solved with an extension of the Runge-Kutta algorithm. Results for the populations of vibronic states versus time show that they oscillate due to vibrational coupling through dissipative interaction with the substrate and show quantum coherence. The total population of electronic states is, however, little affected by vibrational motions. Vibrational relaxation is important only at very long times to establish thermal equilibrium.

  13. Parametric hierarchical matrix approach for the wideband optical response of large-scale molecular aggregates

    NASA Astrophysics Data System (ADS)

    Ansari-Oghol-Beig, Davood; Rostami, Masoud; Chernobrovkina, Ekaterina; Saikin, Semion K.; Valleau, Stéphanie; Mosallaei, Hossein; Aspuru-Guzik, Alán

    2013-10-01

    Fast and efficient calculations of optical responses using electromagnetic models require computational acceleration and compression techniques. A hierarchical matrix approach is adopted for this purpose. In order to model large-scale molecular structures, these methods should be applied over wide frequency spectra. Here, we introduce a novel parametric hierarchical matrix method that allows one for a rapid construction of a wideband system representation and enables an efficient wideband solution. We apply the developed method to the modeling of the optical response of bacteriochlorophyll tubular aggregates as found in green photosynthetic bacteria. We show that the parametric method can provide one with the frequency and time-domain solutions for structures of the size of 100 000 molecules, which is comparable to the size of the whole antenna complex in a bacterium. The absorption spectrum is calculated and the significance of electrodynamic retardation effects for relatively large structures, i.e., with respect to the wavelength of light, is briefly studied.

  14. Efficient matrix approach to optical wave propagation and Linear Canonical Transforms.

    PubMed

    Shakir, Sami A; Fried, David L; Pease, Edwin A; Brennan, Terry J; Dolash, Thomas M

    2015-10-01

    The Fresnel diffraction integral form of optical wave propagation and the more general Linear Canonical Transforms (LCT) are cast into a matrix transformation form. Taking advantage of recent efficient matrix multiply algorithms, this approach promises an efficient computational and analytical tool that is competitive with FFT based methods but offers better behavior in terms of aliasing, transparent boundary condition, and flexibility in number of sampling points and computational window sizes of the input and output planes being independent. This flexibility makes the method significantly faster than FFT based propagators when only a single point, as in Strehl metrics, or a limited number of points, as in power-in-the-bucket metrics, are needed in the output observation plane. PMID:26480196

  15. Efficient matrix approach to optical wave propagation and Linear Canonical Transforms.

    PubMed

    Shakir, Sami A; Fried, David L; Pease, Edwin A; Brennan, Terry J; Dolash, Thomas M

    2015-10-01

    The Fresnel diffraction integral form of optical wave propagation and the more general Linear Canonical Transforms (LCT) are cast into a matrix transformation form. Taking advantage of recent efficient matrix multiply algorithms, this approach promises an efficient computational and analytical tool that is competitive with FFT based methods but offers better behavior in terms of aliasing, transparent boundary condition, and flexibility in number of sampling points and computational window sizes of the input and output planes being independent. This flexibility makes the method significantly faster than FFT based propagators when only a single point, as in Strehl metrics, or a limited number of points, as in power-in-the-bucket metrics, are needed in the output observation plane.

  16. Modeling limit languages via limit adjacency matrix and Yusof-Goode approaches

    NASA Astrophysics Data System (ADS)

    Lim, Wen Li, Yusof, Yuhani

    2015-05-01

    Limit language was introduced by Goode and Pixton in 2004 under the framework of formal language theory. It is a subset of splicing languages which is restricted to the molecules that will be presented in the splicing system after the reaction of biochemical has run to its completion. In this paper, limit adjacency matrix will be introduced to model the existence of limit languages from splicing languages. Besides, it can be used to characterize the splicing language in terms of active persistent, adult/inert and transient properties based on Yusof-Goode splicing system. In this paper, some examples and theorems that have been formulated via limit adjacency matrix approach will be presented too.

  17. Efficient density matrix renormalization group algorithm to study Y junctions with integer and half-integer spin

    NASA Astrophysics Data System (ADS)

    Kumar, Manoranjan; Parvej, Aslam; Thomas, Simil; Ramasesha, S.; Soos, Z. G.

    2016-02-01

    An efficient density matrix renormalization group (DMRG) algorithm is presented and applied to Y junctions, systems with three arms of n sites that meet at a central site. The accuracy is comparable to DMRG of chains. As in chains, new sites are always bonded to the most recently added sites and the superblock Hamiltonian contains only new or once renormalized operators. Junctions of up to N =3 n +1 ≈500 sites are studied with antiferromagnetic (AF) Heisenberg exchange J between nearest-neighbor spins S or electron transfer t between nearest neighbors in half-filled Hubbard models. Exchange or electron transfer is exclusively between sites in two sublattices with NA≠NB . The ground state (GS) and spin densities ρr= at site r are quite different for junctions with S =1 /2 , 1, 3/2, and 2. The GS has finite total spin SG=2 S (S ) for even (odd) N and for MG=SG in the SG spin manifold, ρr>0 (<0 ) at sites of the larger (smaller) sublattice. S =1 /2 junctions have delocalized states and decreasing spin densities with increasing N . S =1 junctions have four localized Sz=1 /2 states at the end of each arm and centered on the junction, consistent with localized states in S =1 chains with finite Haldane gap. The GS of S =3 /2 or 2 junctions of up to 500 spins is a spin density wave with increased amplitude at the ends of arms or near the junction. Quantum fluctuations completely suppress AF order in S =1 /2 or 1 junctions, as well as in half-filled Hubbard junctions, but reduce rather than suppress AF order in S =3 /2 or 2 junctions.

  18. New quadrature approach based on operational matrix for solving a class of fractional variational problems

    NASA Astrophysics Data System (ADS)

    Ezz-Eldien, S. S.

    2016-07-01

    This manuscript presents a new numerical approach to approximate the solution of a class of fractional variational problems. The presented approach is consisting of using the shifted Legendre orthonormal polynomials as basis functions of the operational matrix of fractional derivatives (described in the Caputo sense) and that of fractional integrals (described in the sense of Riemann-Liouville) with the help of the Legendre-Gauss quadrature formula together with the Lagrange multipliers method for converting such fractional variational problems into easier problems that consist of solving an algebraic system in the unknown coefficients. The convergence of the proposed method is analyzed. Finally, in order to demonstrate the accuracy of the present method, some test problems are introduced with their approximate solutions and comparisons with other numerical approaches.

  19. Nuclear clustering in the energy density functional approach

    SciTech Connect

    Ebran, J.-P.; Khan, E.; Nikšić, T.; Vretenar, D.

    2015-10-15

    Nuclear Energy Density Functionals (EDFs) are a microscopic tool of choice extensively used over the whole chart to successfully describe the properties of atomic nuclei ensuing from their quantum liquid nature. In the last decade, they also have proved their ability to deal with the cluster phenomenon, shedding a new light on its fundamental understanding by treating on an equal footing both quantum liquid and cluster aspects of nuclei. Such a unified microscopic description based on nucleonic degrees of freedom enables to tackle the question pertaining to the origin of the cluster phenomenon and emphasizes intrinsic mechanisms leading to the emergence of clusters in nuclei.

  20. A new approach to mass spectrometer measurements of thermospheric density

    NASA Technical Reports Server (NTRS)

    Melfi, L. T., Jr.; Brock, F. J.; Brown, C. A., Jr.

    1974-01-01

    The gas sampling problem in satellite and high velocity probes was investigated by applying the theory of a drifting Maxwellian gas. A lens system using a free stream ion source was developed and experimentally evaluated over the pressure range of 0.00001 to 0.01 N/m sq (approx. 10 to the minus 7th power to 0.0001 torr). The source has high beam transparency, which minimizes gas-surface collisions within, or near, the ionization volume. It is shown that for high ion energy (60 eV), the extracted ion beam has an on-axis energy spread of less than 4 eV, and that 90 percent of the ions are within 2.5 deg of the beam axis. It is concluded that the molecular beam mass spectrometer concept, developed for gas density measurements in the upper atmosphere, substantially reduces gas-surface scattering and gas-surface reactions in the sample, and preserves the integrity of the gas sample during the analysis process. Studies show that both the Scout and Delta launch vehicles have adequate volume, control, velocity, and data acquisition capability necessary to obtain thermospheric number density in real time.

  1. Ignitor and the High Density Approach for Fusion*

    NASA Astrophysics Data System (ADS)

    Bombarda, F.; Coppi, B.

    2010-11-01

    The high plasma density regimes discovered by high magnetic field toroidal experiments have both outstanding confinement characteristics and degree of purity, and are at the basis of the Ignitor design. The main purpose of the Ignitor experiment is, in fact, that of establishing the reactor physics in regimes close to ignition, where the thermonuclear instability can set in with all its associated non linear effects. ``Extended limiter'' and double X-point configurations have been analyzed and relevant transport simulations show that similar burning plasma conditions can be attained with both, by Ohmic heating only or with modest amounts of ICRH auxiliary heating. The driving factor for the machine design (R01.32 m, a xb0.47x0.83 m^2, BT<=13 T, Ip<=11 MA) is the poloidal field pressure that can contain, under macroscopically stable conditions, the peak plasma pressures corresponding to ignition. Objectives other than ignition can be envisioned for the relatively near term, for example that of high flux neutron sources for material testing involving compact, high density fusion machines. This has been one of the incentives that have led the Ignitor Project to adopt magnesium diboride (MgB2) superconducting cables in the machine design, a first in fusion research. Accordingly, the largest coils (about 5 m diameter) of the machine will be made entirely of MgB2 cables. *Sponsored in part by ENEA of Italy and by the U.S. D.O.E.

  2. Matrix approach to discrete fractional calculus II: Partial fractional differential equations

    NASA Astrophysics Data System (ADS)

    Podlubny, Igor; Chechkin, Aleksei; Skovranek, Tomas; Chen, YangQuan; Vinagre Jara, Blas M.

    2009-05-01

    A new method that enables easy and convenient discretization of partial differential equations with derivatives of arbitrary real order (so-called fractional derivatives) and delays is presented and illustrated on numerical solution of various types of fractional diffusion equation. The suggested method is the development of Podlubny's matrix approach [I. Podlubny, Matrix approach to discrete fractional calculus, Fractional Calculus and Applied Analysis 3 (4) (2000) 359-386]. Four examples of numerical solution of fractional diffusion equation with various combinations of time-/space-fractional derivatives (integer/integer, fractional/integer, integer/fractional, and fractional/fractional) with respect to time and to the spatial variable are provided in order to illustrate how simple and general is the suggested approach. The fifth example illustrates that the method can be equally simply used for fractional differential equations with delays. A set of MATLAB routines for the implementation of the method as well as sample code used to solve the examples have been developed.

  3. Suspension parameter estimation in the frequency domain using a matrix inversion approach

    NASA Astrophysics Data System (ADS)

    Thite, A. N.; Banvidi, S.; Ibicek, T.; Bennett, L.

    2011-12-01

    The dynamic lumped parameter models used to optimise the ride and handling of a vehicle require base values of the suspension parameters. These parameters are generally experimentally identified. The accuracy of identified parameters can depend on the measurement noise and the validity of the model used. The existing publications on suspension parameter identification are generally based on the time domain and use a limited degree of freedom. Further, the data used are either from a simulated 'experiment' or from a laboratory test on an idealised quarter or a half-car model. In this paper, a method is developed in the frequency domain which effectively accounts for the measurement noise. Additional dynamic constraining equations are incorporated and the proposed formulation results in a matrix inversion approach. The nonlinearities in damping are estimated, however, using a time-domain approach. Full-scale 4-post rig test data of a vehicle are used. The variations in the results are discussed using the modal resonant behaviour. Further, a method is implemented to show how the results can be improved when the matrix inverted is ill-conditioned. The case study shows a good agreement between the estimates based on the proposed frequency-domain approach and measurable physical parameters.

  4. Equivalence of the channel-corrected-T-matrix and anomalous-propagator approaches to condensation

    SciTech Connect

    Morawetz, K.

    2010-09-01

    Any many-body approximation corrected for unphysical repeated collisions in a given condensation channel is shown to provide the same set of equations as they appear by using anomalous propagators. The ad hoc assumption in the latter theory about nonconservation of particle numbers can be released. In this way, the widespread used anomalous-propagator approach is given another physical interpretation. A generalized Soven equation follows which improves a chosen approximation in the same way as the coherent-potential approximation improves the averaged T matrix for impurity scattering.

  5. A Sparse Matrix Approach for Simultaneous Quantification of Nystagmus and Saccade

    NASA Technical Reports Server (NTRS)

    Kukreja, Sunil L.; Stone, Lee; Boyle, Richard D.

    2012-01-01

    The vestibulo-ocular reflex (VOR) consists of two intermingled non-linear subsystems; namely, nystagmus and saccade. Typically, nystagmus is analysed using a single sufficiently long signal or a concatenation of them. Saccade information is not analysed and discarded due to insufficient data length to provide consistent and minimum variance estimates. This paper presents a novel sparse matrix approach to system identification of the VOR. It allows for the simultaneous estimation of both nystagmus and saccade signals. We show via simulation of the VOR that our technique provides consistent and unbiased estimates in the presence of output additive noise.

  6. Transfer matrix method-based approach to study the bi-gyrotropic magnetic materials

    NASA Astrophysics Data System (ADS)

    Zamani, Mehdi; Hajesmaeili, Hamidreza Nezhad; Zandi, Mohammad Hossein

    2016-08-01

    Optical and magneto-optical (MO) responses in magnetic multilayer systems are calculated by transfer matrix method (TMM). In a bi-gyrotropic medium, electric permittivity (ε) and magnetic permeability (μ) coefficients are in the form of non-diagonal tensors, synchronously, which their non-diagonal elements refer to the existence of anisotropy in such medium. In the present study, in addition to present a TMM based-approach for bi-gyrotropic medium, numerical simulations for studying the amount of optical and MO parameters of the bi-gyrotropic Yttrium Iron Garnet (YIG) material, in both transmission and reflection configurations, have been done.

  7. Progress in many-body theory with the equation of motion method: Time-dependent density matrix meets self-consistent RPA and applications to solvable models

    NASA Astrophysics Data System (ADS)

    Schuck, Peter; Tohyama, Mitsuru

    2016-04-01

    The Bogoliubov-Born-Green-Kirkwood-Yvon or time-dependent density matrix (TDDM) hierarchy of equations for higher density matrices is truncated at the three-body level in approximating the three-body correlation function by a quadratic form of two-body ones, closing the equations in this way. The procedure is discussed in detail and it is shown in nontrivial model cases that the approximate inclusion of three-body correlation functions is very important to obtain precise results. A small amplitude approximation of this time-dependent nonlinear equation for the two-body correlation function is performed (STDDM*-b) and it is shown that the one-body sector of this generalized nonlinear second random phase approximation (RPA) equation is equivalent to the self-consistent RPA (SCRPA) approach which had been derived previously by different techniques. It is discussed in which way SCRPA also contains the three-body correlations. TDDM and SCRPA are tested versus exactly solvable model cases.

  8. Correlation and volatility in an Indian stock market: A random matrix approach

    NASA Astrophysics Data System (ADS)

    Kulkarni, Varsha; Deo, Nivedita

    2007-11-01

    We examine the volatility of an Indian stock market in terms of correlation of stocks and quantify the volatility using the random matrix approach. First we discuss trends observed in the pattern of stock prices in the Bombay Stock Exchange for the three-year period 2000 2002. Random matrix analysis is then applied to study the relationship between the coupling of stocks and volatility. The study uses daily returns of 70 stocks for successive time windows of length 85 days for the year 2001. We compare the properties of matrix C of correlations between price fluctuations in time regimes characterized by different volatilities. Our analyses reveal that (i) the largest (deviating) eigenvalue of C correlates highly with the volatility of the index, (ii) there is a shift in the distribution of the components of the eigenvector corresponding to the largest eigenvalue across regimes of different volatilities, (iii) the inverse participation ratio for this eigenvector anti-correlates significantly with the market fluctuations and finally, (iv) this eigenvector of C can be used to set up a Correlation Index, CI whose temporal evolution is significantly correlated with the volatility of the overall market index.

  9. Combinatorial theory of the semiclassical evaluation of transport moments. I. Equivalence with the random matrix approach

    SciTech Connect

    Berkolaiko, G.; Kuipers, J.

    2013-11-15

    To study electronic transport through chaotic quantum dots, there are two main theoretical approaches. One involves substituting the quantum system with a random scattering matrix and performing appropriate ensemble averaging. The other treats the transport in the semiclassical approximation and studies correlations among sets of classical trajectories. There are established evaluation procedures within the semiclassical evaluation that, for several linear and nonlinear transport moments to which they were applied, have always resulted in the agreement with random matrix predictions. We prove that this agreement is universal: any semiclassical evaluation within the accepted procedures is equivalent to the evaluation within random matrix theory. The equivalence is shown by developing a combinatorial interpretation of the trajectory sets as ribbon graphs (maps) with certain properties and exhibiting systematic cancellations among their contributions. Remaining trajectory sets can be identified with primitive (palindromic) factorisations whose number gives the coefficients in the corresponding expansion of the moments of random matrices. The equivalence is proved for systems with and without time reversal symmetry.

  10. Energy density and stress: A new approach to teaching electromagnetism

    NASA Astrophysics Data System (ADS)

    Herrmann, F.

    1989-08-01

    By introducing the electromagnetic field in the customary way, ideas are promoted that do not correspond to those of contemporary physics: on the one hand, ideas that stem from pre-Maxwellian times when interactions were still conceived as actions at a distance and, on the other hand, ideas that can be understood only from the point of view that the electromagnetic field is carried by a medium. A part of a course in electromagnetism is sketched in which, from the beginning, the electromagnetic field is presented as a system in its own right and the local quantities energy density and stress are put into the foreground. In this way, justice is done to the views of modern physics and, moreover, the field becomes conceptually simpler.

  11. A Density Functional Approach to Polarizable Models: A Kim-Gordon-Response Density Interaction Potential for Molecular Simulations

    SciTech Connect

    Tabacchi, G; Hutter, J; Mundy, C

    2005-04-07

    A combined linear response--frozen electron density model has been implemented in a molecular dynamics scheme derived from an extended Lagrangian formalism. This approach is based on a partition of the electronic charge distribution into a frozen region described by Kim-Gordon theory, and a response contribution determined by the instaneous ionic configuration of the system. The method is free from empirical pair-potentials and the parameterization protocol involves only calculations on properly chosen subsystems. They apply this method to a series of alkali halides in different physical phases and are able to reproduce experimental structural and thermodynamic properties with an accuracy comparable to Kohn-Sham density functional calculations.

  12. Density evolution in systems with slow approach to equilibrium

    NASA Astrophysics Data System (ADS)

    Nelson, Kevin Taylor

    This dissertation investigates the evolution of probability densities under the Frobenius-Perron operator U in chaotic iterated-map systems that are slow to reach equilibrium. It first concentrates on one-dimensional maps that are slow to reach equilibrium because they feature intermittent chaos due to the presence of a marginal fixed point. Using the method of shift states and coherent states under U, certain results are obtained concerning the spectrum of U in various functional spaces, using as the main example the cusp map f( x) = 1 - ∣1-2x . Those results are applied to obtain corrections to the well-known leading 1/t form of the x-x autocorrelation function C(t). The symbolic dynamics of one-dimensional maps are then investigated, with particular emphasis on the implications of the existence of intermittent chaos and with applications to topological conjugation. Next, the statistics of extreme values in one-dimensional maps are investigated. Fn(x) is defined as the probability that a point chosen from an initial probability distribution and its first n - 1 iterates under a particular map are all less than x; the properties of F n(x) are derived analytically for a wide variety of one-dimensional maps, and the conclusions are confirmed numerically. Finally, higher-dimensional area-preserving maps are investigated. The technique of local spectral decomposition for U, in which approximate right and left eigenstates for U are constructed localized on unstable periodic points, is used to study density evolution and correlation of observables over time.

  13. A novel approach for the fabrication of all-inorganic nanocrystal solids: Semiconductor matrix encapsulated nanocrystal arrays

    NASA Astrophysics Data System (ADS)

    Moroz, Pavel

    Growing fossil fuels consumption compels researchers to find new alternative pathways to produce energy. Along with new materials for the conversion of different types of energy into electricity innovative methods for efficient processing of energy sources are also introduced. The main criteria for the success of such materials and methods are the low cost and compelling performance. Among different types of materials semiconductor nanocrystals are considered as promising candidates for the role of the efficient and cheap absorbers for solar energy applications. In addition to the anticipated cost reduction, the integration of nanocrystals (NC) into device architectures is inspired by the possibility of tuning the energy of electrical charges in NCs via nanoparticle size. However, the stability of nanocrystals in photovoltaic devices is limited by the stability of organic ligands which passivate the surface of semiconductors to preserve quantum confinement. The present work introduces a new strategy for low-temperature processing of colloidal nanocrystals into all-inorganic films: semiconductor matrix encapsulated nanocrystal arrays (SMENA). This methodology goes beyond the traditional ligand-interlinking scheme and relies on the encapsulation of morphologically-defined nanocrystal arrays into a matrix of a wide-band gap semiconductor, which preserves optoelectronic properties of individual nanoparticles. Fabricated solids exhibit excellent thermal stability, which is attributed to the heteroepitaxial structure of nanocrystal-matrix interfaces. The main characteristics and properties of these solids were investigated and compared with ones of traditionally fabricated nanocrystal films using standard spectroscopic, optoelectronic and electronic techniques. As a proof of concept, we. We also characterized electron transport phenomena in different types of nanocrystal films using all-optical approach. By measuring excited carrier lifetimes in either ligand-linked or

  14. Stochastic wave packet vs. direct density matrix solution of Liouville-von Neumann equations for photodesorption problems

    NASA Astrophysics Data System (ADS)

    Saalfrank, Peter

    1996-11-01

    The performance of stochastic wave packet approaches is contrasted with a direct method to numerically solve quantum open system Liouville-von Neumann equations for photodesorption problems. As a test case a simple one-dimensional two-state state model representative for NO/Pt(111) is adopted. Both desorption induced by electronic transitions (DIET) treated by a single-dissipative channel model, and desorption induced by multiple electronic transitions (DIMET) treated by a double-dissipative channel model, are considered. It is found that stochastic wave packets are a memory-saving alternative to direct matrix propagation schemes. However, if statistically rare events as for example the bond breaking in NO/Pt(111) are of interest, the former converges only slowly to the exact results. We also find that - in the case of coordinate-independent rates - Gadzuk's "jumping wave packet and weighted average" procedure frequently employed to describe DIET dynamics, is a rapidly converging variant of the stochastic wave packet approach, and therefore rigorously equivalent to the exact solution of a Liouville-von Neumann equation. The usual stochastic (Monte Carlo) wave packet approach, however, is more generally applicable, and allows for example to quantify the notion of "multiple" in DIMET processes.

  15. A multireference density functional approach to the calculation of the excited states of uranium ions

    NASA Astrophysics Data System (ADS)

    Beck, Eric V.

    the hybrid method used 100% Hartree-Fock (HF) exchange and an electron correlation-only density functional as the basis for a modified Graphical Unitary Group Approach (GUGA) based CI calculation. The CI algorithm was modified to exponentially scale the off-diagonal matrix elements of the CI Hamiltonian in order to reduce the double counting of electronic correlation computed by both the DFT correlation functional and the CI calculation. The scaling applied to the interaction between states in the CI calculation exponentially decreased to zero as the energy difference between states grew. This algorithm left interactions between degenerate or nearly degenerate states unsealed, while rapidly scaling to zero interactions between states widely separated in energy. The two empirical parameters which controlled this off diagonal matrix element scaling were determined through the use of a training set of light atoms and molecules consisting of H2, He, Li, Be, B, C, N, O, F, Ne, and Be2. The average DFT/MRCI errors with respect to exact Full Configuration Interaction (FCI) results on this training set was 9.0559 milli Hartrees (mH) over 11 atomic and molecular systems. CI expansion length tailoring through virtual orbital freezing. Consistently favorable results were obtained when virtual orbitals 30-40 electron Volts (eV) above the highest occupied molecular orbital were frozen, providing the best trade off between method accuracy and reduction in CI expansion length. Using this approach to paring the CI expansion length, reductions in the size of the CI expansions of a factor of 25-64 were achieved. The values of the two off diagonal scaling parameters were determined by minimizing the average absolute error between the DFT/MRCI and exact FCI calculations for all test atoms and molecules combined. The values of the parameters obtained for the 100% HF exchange and Perdew Burke and Ernzerhof (PBE) 1996 Generalized Gradient Approximation (GGA) correlation functional

  16. First measurements of the {rho}{sup 3} spin density matrix elements in {gamma}p --> p {omega} using CLAS at JLAB

    SciTech Connect

    Vernarsky, Brian J.

    2014-01-01

    In an effort towards a ''complete'' experiment for the ω meson, we present studies from an experiment with an unpolarized target and a circularly polarized photon beam (g1c), carried out using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. The experiment was analyzed using an extended maximum likelihood fit with partial wave amplitudes. New likelihood functions were calculated to account for the polarization of the photon beam. Both circular and linear polarizations are explored. The results of these fits are then used to project out the spin density matrix for the {omega}. First measurements of the {rho}{sup 3} spin density matrix elements will be presented using this method.

  17. Two approaches to the model drug immobilization into conjugated polymer matrix.

    PubMed

    Krukiewicz, Katarzyna; Stokfisz, Anna; Zak, Jerzy K

    2015-09-01

    The purpose of this study is to develop biocompatible and conducting coating being carrier of biologically active compounds with the potential use in neuroprosthetics. Conducting polypyrrole matrix has been used to immobilize and release model drugs, quercetin and ciprofloxacin. Two routes of immobilization are described: drugs have been incorporated in the polymer matrix in the course of the electropolymerization process or after polymerization, in the course of polymer oxidation. Using UV/Vis spectroscopic detection we demonstrate that both immobilization approaches display different drug-loading efficiencies. In the case of ciprofloxacin, drug incorporation following synthesis is a more efficient immobilization approach (final drug concentration: 43.3 (±9.5) μM/cm(2)), while for quercetin the highest loading is accomplished by drug incorporation during synthesis (final drug concentration: 29.1 (±5.9) μM/cm(2)). The process of drug incorporation results in the variation of surface morphology with respect to the method of immobilization as well as the choice of drug. The results prove that electrochemical methods are efficient procedures for making multifunctional polymer matrices which might be perspective bioactive coatings for implantable neuroprosthetic devices.

  18. Evaluation of bioprosthetic heart valve failure using a matrix-fibril shear stress transfer approach.

    PubMed

    Anssari-Benam, Afshin; Barber, Asa H; Bucchi, Andrea

    2016-02-01

    A matrix-fibril shear stress transfer approach is devised and developed in this paper to analyse the primary biomechanical factors which initiate the structural degeneration of the bioprosthetic heart valves (BHVs). Using this approach, the critical length of the collagen fibrils l c and the interface shear acting on the fibrils in both BHV and natural aortic valve (AV) tissues under physiological loading conditions are calculated and presented. It is shown that the required critical fibril length to provide effective reinforcement to the natural AV and the BHV tissue is l c  = 25.36 µm and l c  = 66.81 µm, respectively. Furthermore, the magnitude of the required shear force acting on fibril interface to break a cross-linked fibril in the BHV tissue is shown to be 38 µN, while the required interfacial force to break the bonds between the fibril and the surrounding extracellular matrix is 31 µN. Direct correlations are underpinned between these values and the ultimate failure strength and the failure mode of the BHV tissue compared with the natural AV, and are verified against the existing experimental data. The analyses presented in this paper explain the role of fibril interface shear and critical length in regulating the biomechanics of the structural failure of the BHVs, for the first time. This insight facilitates further understanding into the underlying causes of the structural degeneration of the BHVs in vivo. PMID:26715134

  19. Evaluation of bioprosthetic heart valve failure using a matrix-fibril shear stress transfer approach.

    PubMed

    Anssari-Benam, Afshin; Barber, Asa H; Bucchi, Andrea

    2016-02-01

    A matrix-fibril shear stress transfer approach is devised and developed in this paper to analyse the primary biomechanical factors which initiate the structural degeneration of the bioprosthetic heart valves (BHVs). Using this approach, the critical length of the collagen fibrils l c and the interface shear acting on the fibrils in both BHV and natural aortic valve (AV) tissues under physiological loading conditions are calculated and presented. It is shown that the required critical fibril length to provide effective reinforcement to the natural AV and the BHV tissue is l c  = 25.36 µm and l c  = 66.81 µm, respectively. Furthermore, the magnitude of the required shear force acting on fibril interface to break a cross-linked fibril in the BHV tissue is shown to be 38 µN, while the required interfacial force to break the bonds between the fibril and the surrounding extracellular matrix is 31 µN. Direct correlations are underpinned between these values and the ultimate failure strength and the failure mode of the BHV tissue compared with the natural AV, and are verified against the existing experimental data. The analyses presented in this paper explain the role of fibril interface shear and critical length in regulating the biomechanics of the structural failure of the BHVs, for the first time. This insight facilitates further understanding into the underlying causes of the structural degeneration of the BHVs in vivo.

  20. A matrix approach for optical detection and imaging through highly scattering media (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Badon, Amaury; Li, Dayan; Lerosey, Geoffroy; Boccara, Claude; Fink, Mathias; Aubry, Alexandre

    2016-03-01

    Our approach first consists in measuring a time-gated reflection matrix associated to a scattering medium using a spatial light modulator at the input and a CCD camera at the output. An interferometric arm allows to discriminate the scattered photons as a function of their time of flight. Inspired by previous works in acoustics, a random matrix approach then allows to get rid of multiple scattering. This improves by far the detection and imaging of targets embedded in or hidden behind a highly scattering medium. As proof of concept, we tackle with the issue of imaging ZnO micrometric beads across a highly scattering paper sheet whose optical thickness is of 12.5 ls, with ls the scattering mean free path. This experimental situation is particularly extreme, even almost desperate for imaging. The ballistic wave has to go through 25 ls back and forth, thus undergoing an attenuation of 10^-11 in intensity. For an incident plane wave, 1 scattered photon over 1000 billions is associated to the target beads. In optical coherence tomography, the single-to-multiple scattering ratio is of 5×10^-4 which prevents from any target detection and imaging. On the contrary, our approach allows to get rid of most of the multiple scattering contribution in this extreme situation. By means of the time-reversal operator, the ballistic echoes associated to each bead are extracted and allow to reconstruct a satisfying image of the targets. The perspective of this work is to apply this promising approach to in-depth imaging of biological tissues.

  1. Bottom-up and top-down solid-state NMR approaches for bacterial biofilm matrix composition

    NASA Astrophysics Data System (ADS)

    Cegelski, Lynette

    2015-04-01

    The genomics and proteomics revolutions have been enormously successful in providing crucial "parts lists" for biological systems. Yet, formidable challenges exist in generating complete descriptions of how the parts function and assemble into macromolecular complexes and whole-cell assemblies. Bacterial biofilms are complex multicellular bacterial communities protected by a slime-like extracellular matrix that confers protection to environmental stress and enhances resistance to antibiotics and host defenses. As a non-crystalline, insoluble, heterogeneous assembly, the biofilm extracellular matrix poses a challenge to compositional analysis by conventional methods. In this perspective, bottom-up and top-down solid-state NMR approaches are described for defining chemical composition in complex macrosystems. The "sum-of-the-parts" bottom-up approach was introduced to examine the amyloid-integrated biofilms formed by Escherichia coli and permitted the first determination of the composition of the intact extracellular matrix from a bacterial biofilm. An alternative top-down approach was developed to define composition in Vibrio cholerae biofilms and relied on an extensive panel of NMR measurements to tease out specific carbon pools from a single sample of the intact extracellular matrix. These two approaches are widely applicable to other heterogeneous assemblies. For bacterial biofilms, quantitative parameters of matrix composition are needed to understand how biofilms are assembled, to improve the development of biofilm inhibitors, and to dissect inhibitor modes of action. Solid-state NMR approaches will also be invaluable in obtaining parameters of matrix architecture.

  2. Bottom-up and top-down solid-state NMR approaches for bacterial biofilm matrix composition.

    PubMed

    Cegelski, Lynette

    2015-04-01

    The genomics and proteomics revolutions have been enormously successful in providing crucial "parts lists" for biological systems. Yet, formidable challenges exist in generating complete descriptions of how the parts function and assemble into macromolecular complexes and whole-cell assemblies. Bacterial biofilms are complex multicellular bacterial communities protected by a slime-like extracellular matrix that confers protection to environmental stress and enhances resistance to antibiotics and host defenses. As a non-crystalline, insoluble, heterogeneous assembly, the biofilm extracellular matrix poses a challenge to compositional analysis by conventional methods. In this perspective, bottom-up and top-down solid-state NMR approaches are described for defining chemical composition in complex macrosystems. The "sum-of-the-parts" bottom-up approach was introduced to examine the amyloid-integrated biofilms formed by Escherichia coli and permitted the first determination of the composition of the intact extracellular matrix from a bacterial biofilm. An alternative top-down approach was developed to define composition in Vibrio cholerae biofilms and relied on an extensive panel of NMR measurements to tease out specific carbon pools from a single sample of the intact extracellular matrix. These two approaches are widely applicable to other heterogeneous assemblies. For bacterial biofilms, quantitative parameters of matrix composition are needed to understand how biofilms are assembled, to improve the development of biofilm inhibitors, and to dissect inhibitor modes of action. Solid-state NMR approaches will also be invaluable in obtaining parameters of matrix architecture. PMID:25797008

  3. Bottom-Up and Top-Down Solid-State NMR Approaches for Bacterial Biofilm Matrix Composition

    PubMed Central

    Cegelski, Lynette

    2015-01-01

    The genomics and proteomics revolutions have been enormously successful in providing crucial “parts lists” for biological systems. Yet, formidable challenges exist in generating complete descriptions of how the parts function and assemble into macromolecular complexes and whole-cell assemblies. Bacterial biofilms are complex multicellular bacterial communities protected by a slime-like extracellular matrix that confers protection to environmental stress and enhances resistance to antibiotics and host defenses. As a non-crystalline, insoluble, heterogeneous assembly, the biofilm extracellular matrix poses a challenge to compositional analysis by conventional methods. In this Perspective, bottom-up and top-down solid-state NMR approaches are described for defining chemical composition in complex macrosystems. The “sum-of-theparts” bottom-up approach was introduced to examine the amyloid-integrated biofilms formed by E. coli and permitted the first determination of the composition of the intact extracellular matrix from a bacterial biofilm. An alternative top-down approach was developed to define composition in V. cholerae biofilms and relied on an extensive panel of NMR measurements to tease out specific carbon pools from a single sample of the intact extracellular matrix. These two approaches are widely applicable to other heterogeneous assemblies. For bacterial biofilms, quantitative parameters of matrix composition are needed to understand how biofilms are assembled, to improve the development of biofilm inhibitors, and to dissect inhibitor modes of action. Solid-state NMR approaches will also be invaluable in obtaining parameters of matrix architecture. PMID:25797008

  4. A transversal approach for patch-based label fusion via matrix completion.

    PubMed

    Sanroma, Gerard; Wu, Guorong; Gao, Yaozong; Thung, Kim-Han; Guo, Yanrong; Shen, Dinggang

    2015-08-01

    Recently, multi-atlas patch-based label fusion has received an increasing interest in the medical image segmentation field. After warping the anatomical labels from the atlas images to the target image by registration, label fusion is the key step to determine the latent label for each target image point. Two popular types of patch-based label fusion approaches are (1) reconstruction-based approaches that compute the target labels as a weighted average of atlas labels, where the weights are derived by reconstructing the target image patch using the atlas image patches; and (2) classification-based approaches that determine the target label as a mapping of the target image patch, where the mapping function is often learned using the atlas image patches and their corresponding labels. Both approaches have their advantages and limitations. In this paper, we propose a novel patch-based label fusion method to combine the above two types of approaches via matrix completion (and hence, we call it transversal). As we will show, our method overcomes the individual limitations of both reconstruction-based and classification-based approaches. Since the labeling confidences may vary across the target image points, we further propose a sequential labeling framework that first labels the highly confident points and then gradually labels more challenging points in an iterative manner, guided by the label information determined in the previous iterations. We demonstrate the performance of our novel label fusion method in segmenting the hippocampus in the ADNI dataset, subcortical and limbic structures in the LONI dataset, and mid-brain structures in the SATA dataset. We achieve more accurate segmentation results than both reconstruction-based and classification-based approaches. Our label fusion method is also ranked 1st in the online SATA Multi-Atlas Segmentation Challenge. PMID:26160394

  5. A transversal approach for patch-based label fusion via matrix completion

    PubMed Central

    Sanroma, Gerard; Wu, Guorong; Gao, Yaozong; Thung, Kim-Han; Guo, Yanrong; Shen, Dinggang

    2015-01-01

    Recently, multi-atlas patch-based label fusion has received an increasing interest in the medical image segmentation field. After warping the anatomical labels from the atlas images to the target image by registration, label fusion is the key step to determine the latent label for each target image point. Two popular types of patch-based label fusion approaches are (1) reconstruction-based approaches that compute the target labels as a weighted average of atlas labels, where the weights are derived by reconstructing the target image patch using the atlas image patches; and (2) classification-based approaches that determine the target label as a mapping of the target image patch, where the mapping function is often learned using the atlas image patches and their corresponding labels. Both approaches have their advantages and limitations. In this paper, we propose a novel patch-based label fusion method to combine the above two types of approaches via matrix completion (and hence, we call it transversal). As we will show, our method overcomes the individual limitations of both reconstruction-based and classification-based approaches. Since the labeling confidences may vary across the target image points, we further propose a sequential labeling framework that first labels the highly confident points and then gradually labels more challenging points in an iterative manner, guided by the label information determined in the previous iterations. We demonstrate the performance of our novel label fusion method in segmenting the hippocampus in the ADNI dataset, subcortical and limbic structures in the LONI dataset, and mid-brain structures in the SATA dataset. We achieve more accurate segmentation results than both reconstruction-based and classification-based approaches. Our label fusion method is also ranked 1st in the online SATA Multi-Atlas Segmentation Challenge. PMID:26160394

  6. Effects of ultrasound on estradiol level, bone mineral density, bone biomechanics and matrix metalloproteinase-13 expression in ovariectomized rabbits

    PubMed Central

    XIA, LU; HE, HONGCHEN; GUO, HUA; QING, YUXI; HE, CHENG-QI

    2015-01-01

    The aim of the present study was to observe the effect of ultrasound (US) on estradiol level, bone mineral density (BMD), bone biomechanics and matrix metalloproteinase-13 (MMP-13) expression in ovariectomized (OVX) rabbits. A total of 28 virgin New Zealand white rabbits were randomly assigned into the following groups: Control (control group), ovariectomy (OVX group), ovariectomy with ultrasound therapy (US group) and ovariectomy with estrogen replacement therapy group (ERT group). At 8 weeks after ovariectomy, the US group received ultrasound treatment while the ERT group were orally treated with conjugated estrogens, and the control and OVX groups remained untreated. The estradiol level, BMD and bone biomechanics, cartilage histology and the MMP-13 expression were analyzed after the intervention. The results indicate that the US treatment increased estradiol level, BMD and bone biomechanical function. Furthermore, the US treatment appeared to improve the recovery of cartilage morphology and decreased the expression of MMP-13 in OVX models. Furthermore, the results suggest that 10 days of US therapy was sufficient to prevent the reduction of estradiol, BMD and bone biomechanical function, to protect osteoarthritis cartilage structure, and to reduce MMP-13 transcription and expression in OVX rabbits. Therefore, US treatment may be a potential treatment for postmenopausal osteoarthritis and osteoporosis. PMID:26622502

  7. Treating molecules in arbitrary spin states using the parametric two-electron reduced-density-matrix method

    NASA Astrophysics Data System (ADS)

    Schwerdtfeger, Christine A.; Mazziotti, David A.

    2012-07-01

    Minimizing the electronic energy with respect to a parameterized two-electron reduced density matrix (2-RDM) is known as a parametric variational 2-RDM method. The parametric 2-RDM method with the M 2-RDM parametrization [D. A. Mazziotti, Phys. Rev. Lett. 101, 253002 (2008)], 10.1103/PhysRevLett.101.253002 is extended to treat molecules in arbitrary spin states. Like its singlet counterpart, the M parametric 2-RDM method for arbitrary spin states is derived using approximate N-representability conditions, which allow it to capture more correlation energy than coupled cluster with single and double excitations at a lower computational cost. We present energies, optimized bond lengths, potential energy curves, and occupation numbers for a set of molecules in a variety of spin states using the M and K parametric 2-RDM methods as well as several wavefunction methods. We show that the M parametric 2-RDM method can describe bond breaking of open-shell molecules like triplet {B_2} and singlet and triplet {OH^+} even in the presence of strong correlation. Finally, the computed 2-RDMs are shown to be nearly N-representable at both equilibrium and non-equilibrium geometries.

  8. Transfer-matrix study of a hard-square lattice gas with two kinds of particles and density anomaly.

    PubMed

    Oliveira, Tiago J; Stilck, Jürgen F

    2015-09-01

    Using transfer matrix and finite-size scaling methods, we study the thermodynamic behavior of a lattice gas with two kinds of particles on the square lattice. Only excluded volume interactions are considered, so that the model is athermal. Large particles exclude the site they occupy and its four first neighbors, while small particles exclude only their site. Two thermodynamic phases are found: a disordered phase where large particles occupy both sublattices with the same probability and an ordered phase where one of the two sublattices is preferentially occupied by them. The transition between these phases is continuous at small concentrations of the small particles and discontinuous at larger concentrations, both transitions are separated by a tricritical point. Estimates of the central charge suggest that the critical line is in the Ising universality class, while the tricritical point has tricritical Ising (Blume-Emery-Griffiths) exponents. The isobaric curves of the total density as functions of the fugacity of small or large particles display a minimum in the disordered phase.

  9. Matrix shaped pulsed laser deposition: New approach to large area and homogeneous deposition

    NASA Astrophysics Data System (ADS)

    Akkan, C. K.; May, A.; Hammadeh, M.; Abdul-Khaliq, H.; Aktas, O. C.

    2014-05-01

    Pulsed laser deposition (PLD) is one of the well-established physical vapor deposition methods used for synthesis of ultra-thin layers. Especially PLD is suitable for the preparation of thin films of complex alloys and ceramics where the conservation of the stoichiometry is critical. Beside several advantages of PLD, inhomogeneity in thickness limits use of PLD in some applications. There are several approaches such as rotation of the substrate or scanning of the laser beam over the target to achieve homogenous layers. On the other hand movement and transition create further complexity in process parameters. Here we present a new approach which we call Matrix Shaped PLD to control the thickness and homogeneity of deposited layers precisely. This new approach is based on shaping of the incoming laser beam by a microlens array and a Fourier lens. The beam is split into much smaller multi-beam array over the target and this leads to a homogenous plasma formation. The uniform intensity distribution over the target yields a very uniform deposit on the substrate. This approach is used to deposit carbide and oxide thin films for biomedical applications. As a case study coating of a stent which has a complex geometry is presented briefly.

  10. Lateral density variations in elastic Earth models from an extended minimum energy approach

    NASA Technical Reports Server (NTRS)

    Sanchez, B. V.

    1980-01-01

    Kaula's minimum energy approach was extended to include the nonhydrostatic gravitational potential energy and the density perturbation field was obtained to degree and order eight. The depth profiles for the density perturbation show a stratification with density excesses and deficiencies alternating with depth. The addition of the gravitational potential energy in the minimization process does not change significantly the conclusions based on results for the minimum shear strain energy case, concerning the inability of the mantle to withstand the lateral loading elastically.

  11. A practical approach to lake water density from electrical conductivity and temperature

    NASA Astrophysics Data System (ADS)

    Moreira, Santiago; Schultze, Martin; Rahn, Karsten; Boehrer, Bertram

    2016-07-01

    Density calculations are essential to study stratification, circulation patterns, internal wave formation and other aspects of hydrodynamics in lakes and reservoirs. Currently, the most common procedure is the use of CTD (conductivity, temperature and depth) profilers and the conversion of measurements of temperature and electrical conductivity into density. In limnic waters, such approaches are of limited accuracy if they do not consider lake-specific composition of solutes, as we show. A new approach is presented to correlate density and electrical conductivity, using only two specific coefficients based on the composition of solutes. First, it is necessary to evaluate the lake-specific coefficients connecting electrical conductivity with density. Once these coefficients have been obtained, density can easily be calculated based on CTD data. The new method has been tested against measured values and the most common equations used in the calculation of density in limnic and ocean conditions. The results show that our new approach can reproduce the density contribution of solutes with a relative error of less than 10 % in lake waters from very low to very high concentrations as well as in lakes of very particular water chemistry, which is better than all commonly implemented density calculations in lakes. Finally, a web link is provided for downloading the corresponding density calculator.

  12. Block Lanczos density-matrix renormalization group method for general Anderson impurity models: Application to magnetic impurity problems in graphene

    NASA Astrophysics Data System (ADS)

    Shirakawa, Tomonori; Yunoki, Seiji

    2014-11-01

    We introduce a block Lanczos (BL) recursive technique to construct quasi-one-dimensional models, suitable for density-matrix renormalization group (DMRG) calculations, from single- as well as multiple-impurity Anderson models in any spatial dimensions. This new scheme, named BL-DMRG method, allows us to calculate not only local but also spatially dependent static and dynamical quantities of the ground state for general Anderson impurity models without losing elaborate geometrical information of the lattice. We show that the BL-DMRG method can be easily extended to treat a multiorbital Anderson impurity model where not only inter- and intraorbital Coulomb interactions but also Hund's coupling and pair hopping interactions are included. We also show that the symmetry adapted BL bases can be utilized, when it is appropriate, to reduce the computational cost. As a demonstration, we apply the BL-DMRG method to three different models for graphene with a structural defect and with a single hydrogen or fluorine absorbed, where a single Anderson impurity is coupled to conduction electrons in the honeycomb lattice. These models include (i) a single adatom on the honeycomb lattice, (ii) a substitutional impurity in the honeycomb lattice, and (iii) an effective model for a single carbon vacancy in graphene. Our analysis of the local dynamical magnetic susceptibility and the local density of states at the impurity site reveals that, for the particle-hole symmetric case at half-filling of electron density, the ground state of model (i) behaves as an isolated magnetic impurity with no Kondo screening, while the ground state of the other two models forms a spin-singlet state where the impurity moment is screened by the conduction electrons. We also calculate the real-space dependence of the spin-spin correlation functions between the impurity site and the conduction sites for these three models. Our results clearly show that, reflecting the presence or absence of unscreened

  13. Global financial indices and twitter sentiment: A random matrix theory approach

    NASA Astrophysics Data System (ADS)

    García, A.

    2016-11-01

    We use Random Matrix Theory (RMT) approach to analyze the correlation matrix structure of a collection of public tweets and the corresponding return time series associated to 20 global financial indices along 7 trading months of 2014. In order to quantify the collection of tweets, we constructed daily polarity time series from public tweets via sentiment analysis. The results from RMT analysis support the fact of the existence of true correlations between financial indices, polarities, and the mixture of them. Moreover, we found a good agreement between the temporal behavior of the extreme eigenvalues of both empirical data, and similar results were found when computing the inverse participation ratio, which provides an evidence about the emergence of common factors in global financial information whether we use the return or polarity data as a source. In addition, we found a very strong presumption that polarity Granger causes returns of an Indonesian index for a long range of lag trading days, whereas for Israel, South Korea, Australia, and Japan, the predictive information of returns is also presented but with less presumption. Our results suggest that incorporating polarity as a financial indicator may open up new insights to understand the collective and even individual behavior of global financial indices.

  14. A random matrix theory of decoherence

    NASA Astrophysics Data System (ADS)

    Gorin, T.; Pineda, C.; Kohler, H.; Seligman, T. H.

    2008-11-01

    Random matrix theory is used to represent generic loss of coherence of a fixed central system coupled to a quantum-chaotic environment, represented by a random matrix ensemble, via random interactions. We study the average density matrix arising from the ensemble induced, in contrast to previous studies where the average values of purity, concurrence and entropy were considered; we further discuss when one or the other approach is relevant. The two approaches agree in the limit of large environments. Analytic results for the average density matrix and its purity are presented in linear response approximation. The two-qubit system is analysed, mainly numerically, in more detail.

  15. Thermal analysis of high intensity organic light-emitting diodes based on a transmission matrix approach

    NASA Astrophysics Data System (ADS)

    Qi, Xiangfei; Forrest, Stephen R.

    2011-12-01

    We use a general transmission matrix formalism to determine the thermal response of organic light-emitting diodes (OLEDs) under high currents normally encountered in ultra-bright illumination conditions. This approach, based on Laplace transforms, facilitates the calculation of transient coupled heat transfer in a multi-layer composite characteristic of OLEDs. Model calculations are compared with experimental data on 5 cm × 5 cm green and red-emitting electrophosphorescent OLEDs under various current drive conditions. This model can be extended to study other complex optoelectronic structures under a wide variety of conditions that include heat removal via conduction, radiation, and convection. We apply the model to understand the effects of using high-thermal- conductivity substrates, and the transient thermal response under pulsed-current operation.

  16. Vibration localization in mono- and bi-coupled bladed disks - A transfer matrix approach

    NASA Technical Reports Server (NTRS)

    Ottarsson, Gisli; Pierre, Christophe

    1993-01-01

    A transfer matrix approach to the analysis of the dynamics of mistuned bladed disks is presented. The study focuses on mono-coupled systems, in which each blade is coupled to its two neighboring blades, and bi-coupled systems, where each blade is coupled to its four nearest neighbors. Transfer matrices yield the free dynamics, both the characteristic free wave and the normal modes - in closed form for the tuned assemblies. Mistuned assemblies are represented by random transfer matrices and an examination of the effect of mistuning on harmonic wave propagation yields the localization factor - the average rate of spatial wave amplitude decay per blade - in the mono-coupled assembly. Based on a comparison of the wave propagation characteristics of the mono- and bi-coupled assemblies, important conclusions are drawn about the effect of the additional coupling coordinate on the sensitivity to mistuning and the strength of mode localization predicted by a mono-coupled analysis.

  17. Application of Transfer Matrix Approach to Modeling and Decentralized Control of Lattice-Based Structures

    NASA Technical Reports Server (NTRS)

    Cramer, Nick; Swei, Sean Shan-Min; Cheung, Kenny; Teodorescu, Mircea

    2015-01-01

    This paper presents a modeling and control of aerostructure developed by lattice-based cellular materials/components. The proposed aerostructure concept leverages a building block strategy for lattice-based components which provide great adaptability to varying ight scenarios, the needs of which are essential for in- ight wing shaping control. A decentralized structural control design is proposed that utilizes discrete-time lumped mass transfer matrix method (DT-LM-TMM). The objective is to develop an e ective reduced order model through DT-LM-TMM that can be used to design a decentralized controller for the structural control of a wing. The proposed approach developed in this paper shows that, as far as the performance of overall structural system is concerned, the reduced order model can be as e ective as the full order model in designing an optimal stabilizing controller.

  18. Uncovering fermionic zero-energy modes through a boundary-matrix approach

    NASA Astrophysics Data System (ADS)

    Alase, Abhijeet; Cobanera, Emilio; Ortiz, Gerardo; Viola, Lorenza

    Given a non-interacting fermionic lattice system with arbitrary boundary conditions, we show how the problem of diagonalizing the single-particle Hamiltonian can be split into suitably defined bulk and boundary problems. Following this exact separation, a boundary matrix may be constructed, which contains complete information about the emergence and nature of zero-energy modes, even in the thermodynamic limit. Our approach is applicable to model Hamiltonians in arbitrary space dimensions of relevance to topological quantum matter. As a concrete illustration, we show how to correctly describe the zero-energy Majorana modes of a time-reversal-invariant two-band s-wave topological superconductor in a Josephson ring configuration, and also provide physical insight into the predicted unconventional Josephson effect.

  19. The Role of Extracellular Matrix in Glioma Invasion: A Cellular Potts Model Approach

    PubMed Central

    Rubenstein, Brenda M.; Kaufman, Laura J.

    2008-01-01

    In this work, a cellular Potts model based on the differential adhesion hypothesis is employed to analyze the relative importance of select cell-cell and cell-extracellular matrix (ECM) contacts in glioma invasion. To perform these simulations, three types of cells and two ECM components are included. The inclusion of explicit ECM with an inhomogeneous fibrous component and a homogeneously dispersed afibrous component allows exploration of the importance of relative energies of cell-cell and cell-ECM contacts in a variety of environments relevant to in vitro and in vivo experimental investigations of glioma invasion. Simulations performed here focus chiefly on reproducing findings of in vitro experiments on glioma spheroids embedded in collagen I gels. For a given range and set ordering of energies associated with key cell-cell and cell-ECM interactions, our model qualitatively reproduces the dispersed glioma invasion patterns found for most glioma cell lines embedded as spheroids in collagen I gels of moderate concentration. In our model, we find that invasion is maximized at intermediate collagen concentrations, as occurs experimentally. This effect is seen more strongly in model gels composed of short collagen fibers than in those composed of long fibers, which retain significant connectivity even at low density. Additional simulations in aligned model matrices further elucidate how matrix structure dictates invasive patterns. Finally, simulations that allow invading cells to both dissolve and deposit ECM components demonstrate how Q-Potts models may be elaborated to allow active cell alteration of their surroundings. The model employed here provides a quantitative framework with which to bound the relative values of cell-cell and cell-ECM interactions and investigate how varying the magnitude and type of these interactions, as well as ECM structure, could potentially curtail glioma invasion. PMID:18835895

  20. Stratified quantization approach to dissipative quantum systems: Derivation of the Hamiltonian and kinetic equations for reduced density matrices

    SciTech Connect

    Richardson, W.H. . E-mail: whr@stanford.edu

    2006-06-15

    A technique for describing dissipative quantum systems that utilizes a fundamental Hamiltonian, which is composed of intrinsic operators of the system, is presented. The specific system considered is a capacitor (or free particle) that is coupled to a resistor (or dissipative medium). The microscopic mechanisms that lead to dissipation are represented by the standard Hamiltonian. Now dissipation is really a collective phenomenon of entities that comprise a macroscopic or mesoscopic object. Hence operators that describe the collective features of the dissipative medium are utilized to construct the Hamiltonian that represents the coupled resistor and capacitor. Quantization of the spatial gauge function is introduced. The magnetic energy part of the coupled Hamiltonian is written in terms of that quantized gauge function and the current density of the dissipative medium. A detailed derivation of the kinetic equation that represents the capacitor or free particle is presented. The partial spectral densities and functions related to spectral densities, which enter the kinetic equations as coefficients of commutators, are evaluated. Explicit expressions for the nonMarkoffian contribution in terms of products of spectral densities and related functions are given. The influence of all two-time correlation functions are considered. Also stated is a remainder term that is a product of partial spectral densities and which is due to higher order terms in the correlation density matrix. The Markoffian part of the kinetic equation is compared with the Master equation that is obtained using the standard generator in the axiomatic approach. A detailed derivation of the Master equation that represents the dissipative medium is also presented. The dynamical equation for the resistor depends on the spatial wavevector, and the influence of the free particle on the diagonal elements (in wavevector space) is stated.

  1. Large eigenvalue of the cumulant part of the two-electron reduced density matrix as a measure of off-diagonal long-range order

    NASA Astrophysics Data System (ADS)

    Raeber, Alexandra; Mazziotti, David A.

    2015-11-01

    Off-diagonal long-range order (ODLRO) in the two-electron reduced density matrix (2-RDM) has long been recognized as a mathematical characteristic of conventional superconductors. The large eigenvalue of the 2-RDM has been shown to be a useful measure of this long-range order. The 2-RDM can be represented as the sum of a connected (cumulant) piece and an unconnected piece. In this work, we show that the cumulant 2-RDM also has a large eigenvalue in the limit of ODLRO. The largest eigenvalue of the cumulant 2-RDM, we prove, is bounded from above by N . In the limit of extreme pairing, such as Cooper pairing, the largest eigenvalue and the trace of the cumulant 2-RDM approach their extreme values of N and -N , respectively. While the trace of the cumulant 2-RDM, which is computable from only a knowledge of the 1-RDM, can reflect ODLRO, it alone does not appear to be a sufficient criterion. The large eigenvalue of the cumulant 2-RDM, we show, implies the large eigenvalue of the 2-RDM and, hence, is a natural measure of ODLRO that vanishes in the mean-field limit.

  2. Density-matrix theory for the ground state of spin-compensated harmonically confined two-electron model atoms with general interparticle repulsion

    NASA Astrophysics Data System (ADS)

    Akbari, Ali; March, Norman H.; Rubio, Angel

    2009-09-01

    For model two-electron atoms with harmonic confinement, the correlated first-order density matrix can be expressed in terms of the relative motion wave function ΨR(r) . Here we demonstrate that the probability density P(r) associated with this wave function is directly related to the x-ray scattering factor f(G) . This latter quantity, in turn, is determined by the ground-state electron density n(r) . The Euler-Lagrange equation of the resulting density-matrix theory is thereby shown to take the form of a third-order integro-differential equation for n(r) in which the probability density P(r)=ΨR2(r) also appears. For two specific choices of the interaction between the two fermions under consideration, the above integro-differential equation derived here is shown to lead back to known linear homogeneous differential equations for the electron density. Finally, it is emphasized that specific equations summarized here will apply directly to theoretical study of the nonrelativistic ground-state electron density n(r,Z) in the He-like ions with atomic number Z .

  3. S-matrix decomposition, natural reaction channels, and the quantum transition state approach to reactive scattering.

    PubMed

    Manthe, Uwe; Ellerbrock, Roman

    2016-05-28

    A new approach for the quantum-state resolved analysis of polyatomic reactions is introduced. Based on the singular value decomposition of the S-matrix, energy-dependent natural reaction channels and natural reaction probabilities are defined. It is shown that the natural reaction probabilities are equal to the eigenvalues of the reaction probability operator [U. Manthe and W. H. Miller, J. Chem. Phys. 99, 3411 (1993)]. Consequently, the natural reaction channels can be interpreted as uniquely defined pathways through the transition state of the reaction. The analysis can efficiently be combined with reactive scattering calculations based on the propagation of thermal flux eigenstates. In contrast to a decomposition based straightforwardly on thermal flux eigenstates, it does not depend on the choice of the dividing surface separating reactants from products. The new approach is illustrated studying a prototypical example, the H + CH4 → H2 + CH3 reaction. The natural reaction probabilities and the contributions of the different vibrational states of the methyl product to the natural reaction channels are calculated and discussed. The relation between the thermal flux eigenstates and the natural reaction channels is studied in detail.

  4. A general non-Abelian density matrix renormalization group algorithm with application to the C{sub 2} dimer

    SciTech Connect

    Sharma, Sandeep

    2015-01-14

    We extend our previous work [S. Sharma and G. K.-L. Chan, J. Chem. Phys. 136, 124121 (2012)], which described a spin-adapted (SU(2) symmetry) density matrix renormalization group algorithm, to additionally utilize general non-Abelian point group symmetries. A key strength of the present formulation is that the requisite tensor operators are not hard-coded for each symmetry group, but are instead generated on the fly using the appropriate Clebsch-Gordan coefficients. This allows our single implementation to easily enable (or disable) any non-Abelian point group symmetry (including SU(2) spin symmetry). We use our implementation to compute the ground state potential energy curve of the C{sub 2} dimer in the cc-pVQZ basis set (with a frozen-core), corresponding to a Hilbert space dimension of 10{sup 12} many-body states. While our calculated energy lies within the 0.3 mE{sub h} error bound of previous initiator full configuration interaction quantum Monte Carlo and correlation energy extrapolation by intrinsic scaling calculations, our estimated residual error is only 0.01 mE{sub h}, much more accurate than these previous estimates. Due to the additional efficiency afforded by the algorithm, the excitation energies (T{sub e}) of eight lowest lying excited states: a{sup 3}Π{sub u}, b{sup 3}Σ{sub g}{sup −}, A{sup 1}Π{sub u}, c{sup 3}Σ{sub u}{sup +}, B{sup 1}Δ{sub g}, B{sup ′1}Σ{sub g}{sup +}, d{sup 3}Π{sub g}, and C{sup 1}Π{sub g} are calculated, which agree with experimentally derived values to better than 0.06 eV. In addition, we also compute the potential energy curves of twelve states: the three lowest levels for each of the irreducible representations {sup 1}Σ{sub g}{sup +}, {sup 1}Σ{sub u}{sup +}, {sup 1}Σ{sub g}{sup −}, and {sup 1}Σ{sub u}{sup −}, to an estimated accuracy of 0.1 mE{sub h} of the exact result in this basis.

  5. Convex-set description of quantum phase transitions in the transverse Ising model using reduced-density-matrix theory.

    PubMed

    Schwerdtfeger, Christine A; Mazziotti, David A

    2009-06-14

    Quantum phase transitions in N-particle systems can be identified and characterized by the movement of the two-particle reduced density matrix (2-RDM) along the boundary of its N-representable convex set as a function of the Hamiltonian parameter controlling the phase transition [G. Gidofalvi and D. A. Mazziotti, Phys. Rev. A 74, 012501 (2006)]. For the one-dimensional transverse Ising model quantum phase transitions as well as their finite-lattice analogs are computed and characterized by the 2-RDM movement with respect to the transverse magnetic field strength g. The definition of a 2-RDM "speed" quantifies the movement of the 2-RDM per unit of g, which reaches its maximum at the critical point of the phase transition. For the infinite lattice the convex set of 2-RDMs and the 2-RDM speed are computed from the exact solution of the 2-RDM in the thermodynamic limit of infinite N [P. Pfeuty, Ann. Phys. 57, 79 (1970)]. For the finite lattices we compute the 2-RDM convex set and its speed by the variational 2-RDM method [D. A. Mazziotti, Phys. Rev. Lett. 93, 213001 (2004)] in which approximate ground-state 2-RDMs are calculated without N-particle wave functions by using constraints, known as N-representability conditions, to restrict the 2-RDMs to represent quantum system of N fermions. Advantages of the method include: (i) rigorous lower bounds on the ground-state energies, (ii) polynomial scaling of the calculation with N, and (iii) independence of the N-representability conditions from a reference wave function, which enables the modeling of multiple quantum phases. Comparing the 2-RDM convex sets for the finite- and infinite-site lattices reveals that the variational 2-RDM method accurately captures the shape of the convex set and the signature of the phase transition in the 2-RDM movement. From the 2-RDM all one- and two-particle expectation values (or order parameters) of the quantum Ising model can also be computed including the pair correlation function, which

  6. A unifying probabilistic Bayesian approach to derive electron density from MRI for radiation therapy treatment planning

    NASA Astrophysics Data System (ADS)

    Sudhan Reddy Gudur, Madhu; Hara, Wendy; Le, Quynh-Thu; Wang, Lei; Xing, Lei; Li, Ruijiang

    2014-11-01

    MRI significantly improves the accuracy and reliability of target delineation in radiation therapy for certain tumors due to its superior soft tissue contrast compared to CT. A treatment planning process with MRI as the sole imaging modality will eliminate systematic CT/MRI co-registration errors, reduce cost and radiation exposure, and simplify clinical workflow. However, MRI lacks the key electron density information necessary for accurate dose calculation and generating reference images for patient setup. The purpose of this work is to develop a unifying method to derive electron density from standard T1-weighted MRI. We propose to combine both intensity and geometry information into a unifying probabilistic Bayesian framework for electron density mapping. For each voxel, we compute two conditional probability density functions (PDFs) of electron density given its: (1) T1-weighted MRI intensity, and (2) geometry in a reference anatomy, obtained by deformable image registration between the MRI of the atlas and test patient. The two conditional PDFs containing intensity and geometry information are combined into a unifying posterior PDF, whose mean value corresponds to the optimal electron density value under the mean-square error criterion. We evaluated the algorithm’s accuracy of electron density mapping and its ability to detect bone in the head for eight patients, using an additional patient as the atlas or template. Mean absolute HU error between the estimated and true CT, as well as receiver operating characteristics for bone detection (HU > 200) were calculated. The performance was compared with a global intensity approach based on T1 and no density correction (set whole head to water). The proposed technique significantly reduced the errors in electron density estimation, with a mean absolute HU error of 126, compared with 139 for deformable registration (p = 2  ×  10-4), 283 for the intensity approach (p = 2  ×  10-6) and 282 without density

  7. A unifying probabilistic Bayesian approach to derive electron density from MRI for radiation therapy treatment planning.

    PubMed

    Gudur, Madhu Sudhan Reddy; Hara, Wendy; Le, Quynh-Thu; Wang, Lei; Xing, Lei; Li, Ruijiang

    2014-11-01

    MRI significantly improves the accuracy and reliability of target delineation in radiation therapy for certain tumors due to its superior soft tissue contrast compared to CT. A treatment planning process with MRI as the sole imaging modality will eliminate systematic CT/MRI co-registration errors, reduce cost and radiation exposure, and simplify clinical workflow. However, MRI lacks the key electron density information necessary for accurate dose calculation and generating reference images for patient setup. The purpose of this work is to develop a unifying method to derive electron density from standard T1-weighted MRI. We propose to combine both intensity and geometry information into a unifying probabilistic Bayesian framework for electron density mapping. For each voxel, we compute two conditional probability density functions (PDFs) of electron density given its: (1) T1-weighted MRI intensity, and (2) geometry in a reference anatomy, obtained by deformable image registration between the MRI of the atlas and test patient. The two conditional PDFs containing intensity and geometry information are combined into a unifying posterior PDF, whose mean value corresponds to the optimal electron density value under the mean-square error criterion. We evaluated the algorithm's accuracy of electron density mapping and its ability to detect bone in the head for eight patients, using an additional patient as the atlas or template. Mean absolute HU error between the estimated and true CT, as well as receiver operating characteristics for bone detection (HU > 200) were calculated. The performance was compared with a global intensity approach based on T1 and no density correction (set whole head to water). The proposed technique significantly reduced the errors in electron density estimation, with a mean absolute HU error of 126, compared with 139 for deformable registration (p = 2  ×  10(-4)), 283 for the intensity approach (p = 2  ×  10(-6)) and 282 without density

  8. Approach for computing 1D fracture density: application to fracture corridor characterization

    NASA Astrophysics Data System (ADS)

    Viseur, Sophie; Chatelée, Sebastien; Akriche, Clement; Lamarche, Juliette

    2016-04-01

    Fracture density is an important parameter for characterizing fractured reservoirs. Many stochastic simulation algorithms that generate fracture networks indeed rely on the determination of a fracture density on volumes (P30) to populate the reservoir zones with individual fracture surfaces. However, only 1D fracture density (P10) are available from subsurface data and it is then important to be able to accurately estimate this entity. In this paper, a novel approach is proposed to estimate fracture density from scan-line or well data. This method relies on regression, hypothesis testing and clustering techniques. The objective of the proposed approach is to highlight zones where fracture density are statistically very different or similar. This technique has been applied on both synthetic and real case studies. These studies concern fracture corridors, which are particular tectonic features that are generally difficult to characterize from subsurface data. These tectonic features are still not well known and studies must be conducted to better understand their internal spatial organization and variability. The presented synthetic cases aim at showing the ability of the approach to extract known features. The real case study illustrates how this approach allows the internal spatial organization of fracture corridors to be characterized.

  9. Evaluating the B-cell density with various activation functions using White Noise Path Integral Approach

    NASA Astrophysics Data System (ADS)

    Aban, C. J. G.; Bacolod, R. O.; Confesor, M. N. P.

    2015-06-01

    A The White Noise Path Integral Approach is used in evaluating the B-cell density or the number of B-cell per unit volume for a basic type of immune system response based on the modeling done by Perelson and Wiegel. From the scaling principles of Perelson [1], the B- cell density is obtained where antigens and antibodies mutates and activation function f(|S-SA|) is defined describing the interaction between a specific antigen and a B-cell. If the activation function f(|S-SA|) is held constant, the major form of the B-cell density evaluated using white noise analysis is similar to the form of the B-cell density obtained by Perelson and Wiegel using a differential approach.A piecewise linear functionis also used to describe the activation f(|S-SA|). If f(|S-SA|) is zero, the density decreases exponentially. If f(|S-SA|) = S-SA-SB, the B- cell density increases exponentially until it reaches a certain maximum value. For f(|S-SA|) = 2SA-SB-S, the behavior of B-cell density is oscillating and remains to be in small values.

  10. Bone mineral (31)P and matrix-bound water densities measured by solid-state (31)P and (1)H MRI.

    PubMed

    Seifert, Alan C; Li, Cheng; Rajapakse, Chamith S; Bashoor-Zadeh, Mahdieh; Bhagat, Yusuf A; Wright, Alexander C; Zemel, Babette S; Zavaliangos, Antonios; Wehrli, Felix W

    2014-07-01

    Bone is a composite material consisting of mineral and hydrated collagen fractions. MRI of bone is challenging because of extremely short transverse relaxation times, but solid-state imaging sequences exist that can acquire the short-lived signal from bone tissue. Previous work to quantify bone density via MRI used powerful experimental scanners. This work seeks to establish the feasibility of MRI-based measurement on clinical scanners of bone mineral and collagen-bound water densities, the latter as a surrogate of matrix density, and to examine the associations of these parameters with porosity and donors' age. Mineral and matrix-bound water images of reference phantoms and cortical bone from 16 human donors, aged 27-97 years, were acquired by zero-echo-time 31-phosphorus ((31)P) and 1-hydrogen ((1)H) MRI on whole body 7T and 3T scanners, respectively. Images were corrected for relaxation and RF inhomogeneity to obtain density maps. Cortical porosity was measured by micro-computed tomography (μCT), and apparent mineral density by peripheral quantitative CT (pQCT). MRI-derived densities were compared to X-ray-based measurements by least-squares regression. Mean bone mineral (31)P density was 6.74 ± 1.22 mol/l (corresponding to 1129 ± 204 mg/cc mineral), and mean bound water (1)H density was 31.3 ± 4.2 mol/l (corresponding to 28.3 ± 3.7 %v/v). Both (31)P and bound water (BW) densities were correlated negatively with porosity ((31)P: R(2) = 0.32, p < 0.005; BW: R(2) = 0.63, p < 0.0005) and age ((31)P: R(2) = 0.39, p < 0.05; BW: R(2) = 0.70, p < 0.0001), and positively with pQCT density ((31)P: R(2) = 0.46, p < 0.05; BW: R(2) = 0.50, p < 0.005). In contrast, the bone mineralization ratio (expressed here as the ratio of (31)P density to bound water density), which is proportional to true bone mineralization, was found to be uncorrelated with porosity, age or pQCT density. This work establishes the feasibility of image-based quantification of bone mineral and bound

  11. Modeling the potential energy field caused by mass density distribution with Eton approach

    NASA Astrophysics Data System (ADS)

    Alkahtani, Badr Saad T.; Atangana, Abdon

    2016-04-01

    A new approach for modeling real world problems called the "Eton Approach" was presented in this paper. The "Eton approach" combines both the concept of the variable order derivative together with Atangana derivative with memory derivative. The Atangana derivative with memory is used to account for the memory and fractional derivative for its filter effect. The approach was used to describe the potential energy field that is caused by a given charge or mass density distribution.We solve the modified model numerically and present supporting numerical simulations.

  12. Matrix compatible solid phase microextraction coating, a greener approach to sample preparation in vegetable matrices.

    PubMed

    Naccarato, Attilio; Pawliszyn, Janusz

    2016-09-01

    This work proposes the novel PDMS/DVB/PDMS fiber as a greener strategy for analysis by direct immersion solid phase microextraction (SPME) in vegetables. SPME is an established sample preparation approach that has not yet been adequately explored for food analysis in direct immersion mode due to the limitations of the available commercial coatings. The robustness and endurance of this new coating were investigated by direct immersion extractions in raw blended vegetables without any further sample preparation steps. The PDMS/DVB/PDMS coating exhibited superior features related to the capability of the external PDMS layer to protect the commercial coating, and showed improvements in terms of extraction capability and in the cleanability of the coating surface. In addition to having contributed to the recognition of the superior features of this new fiber concept before commercialization, the outcomes of this work serve to confirm advancements in the matrix compatibility of the PDMS-modified fiber, and open new prospects for the development of greener high-throughput analytical methods in food analysis using solid phase microextraction in the near future.

  13. On matrix-model approach to simplified Khovanov-Rozansky calculus

    NASA Astrophysics Data System (ADS)

    Morozov, A.; Morozov, And.; Popolitov, A.

    2015-10-01

    Wilson-loop averages in Chern-Simons theory (HOMFLY polynomials) can be evaluated in different ways - the most difficult, but most interesting of them is the hypercube calculus, the only one applicable to virtual knots and used also for categorification (higher-dimensional extension) of the theory. We continue the study of quantum dimensions, associated with hypercube vertices, in the drastically simplified version of this approach to knot polynomials. At q = 1 the problem is reformulated in terms of fat (ribbon) graphs, where Seifert cycles play the role of vertices. Ward identities in associated matrix model provide a set of recursions between classical dimensions. For q ≠ 1 most of these relations are broken (i.e. deformed in a still uncontrollable way), and only few are protected by Reidemeister invariance of Chern-Simons theory. Still they are helpful for systematic evaluation of entire series of quantum dimensions, including negative ones, which are relevant for virtual link diagrams. To illustrate the effectiveness of developed formalism we derive explicit expressions for the 2-cabled HOMFLY of virtual trefoil and virtual 3.2 knot, which involve respectively 12 and 14 intersections - far beyond any dreams with alternative methods. As a more conceptual application, we describe a relation between the genus of fat graph and Turaev genus of original link diagram, which is currently the most effective tool for the search of thin knots.

  14. Global asymptotic stability analysis for delayed neural networks using a matrix-based quadratic convex approach.

    PubMed

    Zhang, Xian-Ming; Han, Qing-Long

    2014-06-01

    This paper is concerned with global asymptotic stability for a class of generalized neural networks with interval time-varying delays by constructing a new Lyapunov-Krasovskii functional which includes some integral terms in the form of ∫(t-h)(t)(h-t-s)(j)ẋ(T)(s)Rjẋ(s)ds(j=1,2,3). Some useful integral inequalities are established for the derivatives of those integral terms introduced in the Lyapunov-Krasovskii functional. A matrix-based quadratic convex approach is introduced to prove not only the negative definiteness of the derivative of the Lyapunov-Krasovskii functional, but also the positive definiteness of the Lyapunov-Krasovskii functional. Some novel stability criteria are formulated in two cases, respectively, where the time-varying delay is continuous uniformly bounded and where the time-varying delay is differentiable uniformly bounded with its time-derivative bounded by constant lower and upper bounds. These criteria are applicable to both static neural networks and local field neural networks. The effectiveness of the proposed method is demonstrated by two numerical examples.

  15. A novel variable selection approach that iteratively optimizes variable space using weighted binary matrix sampling.

    PubMed

    Deng, Bai-chuan; Yun, Yong-huan; Liang, Yi-zeng; Yi, Lun-zhao

    2014-10-01

    In this study, a new optimization algorithm called the Variable Iterative Space Shrinkage Approach (VISSA) that is based on the idea of model population analysis (MPA) is proposed for variable selection. Unlike most of the existing optimization methods for variable selection, VISSA statistically evaluates the performance of variable space in each step of optimization. Weighted binary matrix sampling (WBMS) is proposed to generate sub-models that span the variable subspace. Two rules are highlighted during the optimization procedure. First, the variable space shrinks in each step. Second, the new variable space outperforms the previous one. The second rule, which is rarely satisfied in most of the existing methods, is the core of the VISSA strategy. Compared with some promising variable selection methods such as competitive adaptive reweighted sampling (CARS), Monte Carlo uninformative variable elimination (MCUVE) and iteratively retaining informative variables (IRIV), VISSA showed better prediction ability for the calibration of NIR data. In addition, VISSA is user-friendly; only a few insensitive parameters are needed, and the program terminates automatically without any additional conditions. The Matlab codes for implementing VISSA are freely available on the website: https://sourceforge.net/projects/multivariateanalysis/files/VISSA/.

  16. Multispin correlations and pseudo-thermalization of the transient density matrix in solid-state NMR: free induction decay and magic echo.

    PubMed

    Morgan, Steven W; Oganesyan, Vadim; Boutis, Gregory S

    2012-12-14

    Quantum unitary evolution typically leads to thermalization of generic interacting many-body systems. There are very few known general methods for reversing this process, and we focus on the magic echo, a radio-frequency pulse sequence known to approximately "rewind" the time evolution of dipolar coupled homonuclear spin systems in a large magnetic field. By combining analytic, numerical, and experimental results we systematically investigate factors leading to the degradation of magic echoes, as observed in reduced revival of mean transverse magnetization. Going beyond the conventional analysis based on mean magnetization we use a phase encoding technique to measure the growth of spin correlations in the density matrix at different points in time following magic echoes of varied durations and compare the results to those obtained during a free induction decay (FID). While considerable differences are documented at short times, the long-time behavior of the density matrix appears to be remarkably universal among the types of initial states considered - simple low order multispin correlations are observed to decay exponentially at the same rate, seeding the onset of increasingly complex high order correlations. This manifestly athermal process is constrained by conservation of the second moment of the spectrum of the density matrix and proceeds indefinitely, assuming unitary dynamics. PMID:23710125

  17. Density matrix renormalization group study in energy space for a single-impurity Anderson model and an impurity quantum phase transition

    NASA Astrophysics Data System (ADS)

    Shirakawa, Tomonori; Yunoki, Seiji

    2016-05-01

    The density matrix renormalization group method is introduced in energy space to study Anderson impurity models. The method allows for calculations in the thermodynamic limit and is advantageous for studying not only the dynamical properties, but also the quantum entanglement of the ground state at the vicinity of an impurity quantum phase transition. This method is applied to obtain numerically exactly the ground-state phase diagram of the single-impurity Anderson model on the honeycomb lattice at half-filling. The calculation of local static quantities shows that the phase diagram contains two distinct phases, the local moment (LM) phase and the asymmetric strong coupling (ASC) phase, but no Kondo screening phase. These results are supported by the local spin and charge excitation spectra, which exhibit qualitatively different behavior in these two phases and also reveal the existence of the valence fluctuating point at the phase boundary. For comparison, we also study the low-energy effective pseudogap Anderson model using the method introduced here. Although the high-energy excitations are obviously different, we find that the ground-state phase diagram and the asymptotically low-energy excitations are in good quantitative agreement with those for the single-impurity Anderson model on the honeycomb lattice, thus providing a quantitative justification for the previous studies based on low-energy approximate approaches. Furthermore, we find that the lowest entanglement level is doubly degenerate for the LM phase, whereas it is singlet for the ASC phase and is accidentally threefold degenerate at the valence fluctuating point. This should be contrasted with the degeneracy of the energy spectrum because the ground state is found to be always singlet. Our results therefore clearly demonstrate that the low-lying entanglement spectrum can be used to determine with high accuracy the phase boundary of the impurity quantum phase transition.

  18. An Efficient Computational Approach for the Calculation of the Vibrational Density of States.

    PubMed

    Aieta, Chiara; Gabas, Fabio; Ceotto, Michele

    2016-07-14

    We present an optimized approach for the calculation of the density of fully coupled vibrational states in high-dimensional systems. This task is of paramount importance, because partition functions and several thermodynamic properties can be accurately estimated once the density of states is known. A new code, called paradensum, based on the implementation of the Wang-Landau Monte Carlo algorithm for parallel architectures is described and applied to real complex systems. We test the accuracy of paradensum on several molecular systems, including some benchmarks for which an exact evaluation of the vibrational density of states is doable by direct counting. In addition, we find a significant computational speedup with respect to standard approaches when applying our code to molecules up to 66 degrees of freedom. The new code can easily handle 150 degrees of freedom. These features make paradensum a very promising tool for future calculations of thermodynamic properties and thermal rate constants of complex systems. PMID:26840098

  19. Direct Density Derivative Estimation.

    PubMed

    Sasaki, Hiroaki; Noh, Yung-Kyun; Niu, Gang; Sugiyama, Masashi

    2016-06-01

    Estimating the derivatives of probability density functions is an essential step in statistical data analysis. A naive approach to estimate the derivatives is to first perform density estimation and then compute its derivatives. However, this approach can be unreliable because a good density estimator does not necessarily mean a good density derivative estimator. To cope with this problem, in this letter, we propose a novel method that directly estimates density derivatives without going through density estimation. The proposed method provides computationally efficient estimation for the derivatives of any order on multidimensional data with a hyperparameter tuning method and achieves the optimal parametric convergence rate. We further discuss an extension of the proposed method by applying regularized multitask learning and a general framework for density derivative estimation based on Bregman divergences. Applications of the proposed method to nonparametric Kullback-Leibler divergence approximation and bandwidth matrix selection in kernel density estimation are also explored. PMID:27140943

  20. Eulerian Mapping Closure Approach for Probability Density Function of Concentration in Shear Flows

    NASA Technical Reports Server (NTRS)

    He, Guowei; Bushnell, Dennis M. (Technical Monitor)

    2002-01-01

    The Eulerian mapping closure approach is developed for uncertainty propagation in computational fluid mechanics. The approach is used to study the Probability Density Function (PDF) for the concentration of species advected by a random shear flow. An analytical argument shows that fluctuation of the concentration field at one point in space is non-Gaussian and exhibits stretched exponential form. An Eulerian mapping approach provides an appropriate approximation to both convection and diffusion terms and leads to a closed mapping equation. The results obtained describe the evolution of the initial Gaussian field, which is in agreement with direct numerical simulations.

  1. Assessing REDD+ performance of countries with low monitoring capacities: the matrix approach

    NASA Astrophysics Data System (ADS)

    Bucki, M.; Cuypers, D.; Mayaux, P.; Achard, F.; Estreguil, C.; Grassi, G.

    2012-03-01

    Estimating emissions from deforestation and degradation of forests in many developing countries is so uncertain that the effects of changes in forest management could remain within error ranges (i.e. undetectable) for several years. Meanwhile UNFCCC Parties need consistent time series of meaningful performance indicators to set credible benchmarks and allocate REDD+ incentives to the countries, programs and activities that actually reduce emissions, while providing social and environmental benefits. Introducing widespread measuring of carbon in forest land (which would be required to estimate more accurately changes in emissions from degradation and forest management) will take time and considerable resources. To ensure the overall credibility and effectiveness of REDD+, parties must consider the design of cost-effective systems which can provide reliable and comparable data on anthropogenic forest emissions. Remote sensing can provide consistent time series of land cover maps for most non-Annex-I countries, retrospectively. These maps can be analyzed to identify the forests that are intact (i.e. beyond significant human influence), and whose fragmentation could be a proxy for degradation. This binary stratification of forests biomes (intact/non-intact), a transition matrix and the use of default carbon stock change factors can then be used to provide initial estimates of trends in emission changes. A proof-of-concept is provided for one biome of the Democratic Republic of the Congo over a virtual commitment period (2005-2010). This approach could allow assessment of the performance of the five REDD+ activities (deforestation, degradation, conservation, management and enhancement of forest carbon stocks) in a spatially explicit, verifiable manner. Incentives could then be tailored to prioritize activities depending on the national context and objectives.

  2. Financial Distress Prediction Using Discrete-time Hazard Model and Rating Transition Matrix Approach

    NASA Astrophysics Data System (ADS)

    Tsai, Bi-Huei; Chang, Chih-Huei

    2009-08-01

    Previous studies used constant cut-off indicator to distinguish distressed firms from non-distressed ones in the one-stage prediction models. However, distressed cut-off indicator must shift according to economic prosperity, rather than remains fixed all the time. This study focuses on Taiwanese listed firms and develops financial distress prediction models based upon the two-stage method. First, this study employs the firm-specific financial ratio and market factors to measure the probability of financial distress based on the discrete-time hazard models. Second, this paper further focuses on macroeconomic factors and applies rating transition matrix approach to determine the distressed cut-off indicator. The prediction models are developed by using the training sample from 1987 to 2004, and their levels of accuracy are compared with the test sample from 2005 to 2007. As for the one-stage prediction model, the model in incorporation with macroeconomic factors does not perform better than that without macroeconomic factors. This suggests that the accuracy is not improved for one-stage models which pool the firm-specific and macroeconomic factors together. In regards to the two stage models, the negative credit cycle index implies the worse economic status during the test period, so the distressed cut-off point is adjusted to increase based on such negative credit cycle index. After the two-stage models employ such adjusted cut-off point to discriminate the distressed firms from non-distressed ones, their error of misclassification becomes lower than that of one-stage ones. The two-stage models presented in this paper have incremental usefulness in predicting financial distress.

  3. Experimental and theoretical approach for the clustering of globally coupled density oscillators based on phase response.

    PubMed

    Horie, Masanobu; Sakurai, Tatsunari; Kitahata, Hiroyuki

    2016-01-01

    We investigated the phase-response curve of a coupled system of density oscillators with an analytical approach. The behaviors of two-, three-, and four-coupled systems seen in the experiments were reproduced by the model considering the phase-response curve. Especially in a four-coupled system, the clustering state and its incidence rate as functions of the coupling strength are well reproduced with this approach. Moreover, we confirmed that the shape of the phase-response curve we obtained analytically was close to that observed in the experiment where a perturbation is added to a single-density oscillator. We expect that this approach to obtaining the phase-response curve is general in the sense that it could be applied to coupled systems of other oscillators such as electrical-circuit oscillators, metronomes, and so on.

  4. Hyperon-nucleus folding potentials in the complex G-matrix approach

    NASA Astrophysics Data System (ADS)

    Furumoto, T.; Sakuragi, Y.; Yamamoto, Y.

    2010-04-01

    We have constructed the hyperon-nucleus optical potential based on the complex G-matrix folding model. The complex G-matrix interactions are derived from the extended-soft core (ESC) model interactions, ESC04a and ESC08. The elastic cross sections and analyzing powers are calculated using the folding-model potentials (FMPs) based on the complex G-matrix interactions. The strength functions for the ( π, K) reaction are also obtained using the FMPs and are compared with the result calculated with a phenomenological repulsive optical potential. The ESC08 interaction gives a better result than does ESC04a.

  5. Internal state variable approach for predicting stiffness reductions in fibrous laminated composites with matrix cracks

    NASA Technical Reports Server (NTRS)

    Lee, Jong-Won; Allen, D. H.; Harris, C. E.

    1989-01-01

    A mathematical model utilizing the internal state variable concept is proposed for predicting the upper bound of the reduced axial stiffnesses in cross-ply laminates with matrix cracks. The axial crack opening displacement is explicitly expressed in terms of the observable axial strain and the undamaged material properties. A crack parameter representing the effect of matrix cracks on the observable axial Young's modulus is calculated for glass/epoxy and graphite/epoxy material systems. The results show that the matrix crack opening displacement and the effective Young's modulus depend not on the crack length, but on its ratio to the crack spacing.

  6. Microstructural Characterization of a Mg Matrix U-Mo Dispersion Fuel Plate Irradiated in the Advanced Test Reactor to High Fission Density: SEM Results

    NASA Astrophysics Data System (ADS)

    Keiser, Dennis D.; Jue, Jan-Fong; Miller, Brandon D.; Gan, Jian; Robinson, Adam B.; Medvedev, Pavel G.; Madden, James W.; Moore, Glenn A.

    2016-06-01

    Low-enriched (U-235 <20 pct) U-Mo dispersion fuel is being developed for use in research and test reactors. In most cases, fuel plates with Al or Al-Si alloy matrices have been tested in the Advanced Test Reactor to support this development. In addition, fuel plates with Mg as the matrix have also been tested. The benefit of using Mg as the matrix is that it potentially will not chemically interact with the U-Mo fuel particles during fabrication or irradiation, whereas with Al and Al-Si alloys such interactions will occur. Fuel plate R9R010 is a Mg matrix fuel plate that was aggressively irradiated in ATR. This fuel plate was irradiated as part of the RERTR-8 experiment at high temperature, high fission rate, and high power, up to high fission density. This paper describes the results of the scanning electron microscopy (SEM) analysis of an irradiated fuel plate using polished samples and those produced with a focused ion beam. A follow-up paper will discuss the results of transmission electron microscopy (TEM) analysis. Using SEM, it was observed that even at very aggressive irradiation conditions, negligible chemical interaction occurred between the irradiated U-7Mo fuel particles and Mg matrix; no interconnection of fission gas bubbles from fuel particle to fuel particle was observed; the interconnected fission gas bubbles that were observed in the irradiated U-7Mo particles resulted in some transport of solid fission products to the U-7Mo/Mg interface; the presence of microstructural pathways in some U-9.1 Mo particles that could allow for transport of fission gases did not result in the apparent presence of large porosity at the U-7Mo/Mg interface; and, the Mg-Al interaction layers that were present at the Mg matrix/Al 6061 cladding interface exhibited good radiation stability, i.e. no large pores.

  7. A comprehensive approach for the assessment of in-situ pavement density using GPR technique

    NASA Astrophysics Data System (ADS)

    Plati, Christina; Georgiou, Panos; Loizos, Andreas

    2013-04-01

    electromagnetic mixing (EM) theory, through the utilization of proper models. These models enable the prediction of asphalt mixture density dependent on its bulk dielectric constant as measured by the GPR, the dielectric properties of the asphalt mix materials, as well as other material information. The goal of the present study is to attempt to verify the prediction performance of various density models. To accomplish this goal GPR surveys were carried out in the field during asphalt pavement construction to evaluate the density results due to different compaction modes. The GPR data was analyzed to calculate the appropriate asphalt mix dielectric properties needed for the activation of the considered density prediction models. Predicted densities were compared with densities of the field cores extracted from the as-built asphalt pavement prior to trafficking. It was found that the predicted density values were significantly lower when compared to the ground truth data. A further investigation of the effect of temperature on GPR readings showed that GPR seems to overestimate the in-situ density. However, this approach could be used effectively to evaluate the performance of different compaction methods and set up the compaction pattern that is needed to achieve the desired asphalt pavement density.

  8. Matrix continued fraction approach to the relativistic quantum mechanical spin-zero Feshbach-Villars equations

    NASA Astrophysics Data System (ADS)

    Brown, Natalie

    In this thesis we solve the Feshbach-Villars equations for spin-zero particles through use of matrix continued fractions. The Feshbach-Villars equations are derived from the Klein-Gordon equation and admit, for the Coulomb potential on an appropriate basis, a Hamiltonian form that has infinite symmetric band-matrix structure. The corresponding representation of the Green's operator of such a matrix can be given as a matrix continued fraction. Furthermore, we propose a finite dimensional representation for the potential operator such that it retains some information about the whole Hilbert space. Combining these two techniques, we are able to solve relativistic quantum mechanical problems of a spin-zero particle in a Coulomb-like potential with a high level of accuracy.

  9. Thomas-Fermi approach to density functional theory: binding energy for atomic systems

    NASA Astrophysics Data System (ADS)

    Di Rocco, H. O.; Lanzini, F.; Aguiar, J. C.

    2016-11-01

    In this work, we re-examine the Thomas-Fermi formalism as an approach to the calculation of atomic binding energies. We focus on the concept of electron density as the central magnitude, and the way in which the different contributions to the total energy can be evaluated from it. Total energies of simple atoms (Z = 2 to 10) are calculated using three different analytical approximations for the electronic density, and the results are compared with those obtained within the Hartree-Fock model.

  10. Scattering of electromagnetic waves by spheroidal particles: a novel approach exploiting the scr(T) matrix computed in spheroidal coordinates

    SciTech Connect

    Schulz, F. Michael; Stamnes, Knut Stamnes, Jakob A.

    1998-11-01

    A method other than the extended-boundary-condition method (EBCM) to compute the {ital T} matrix for electromagnetic scattering is presented. The separation-of-variables method (SVM) is used to solve the electromagnetic scattering problem for a spheroidal particle and to derive its scr(T) matrix in spheroidal coordinates. A transformation is developed for transforming the scr(T) matrix in spheroidal coordinates into the corresponding T matrix in spherical coordinates. The T matrix so obtained can be used for analytical calculation of the optical properties of ensembles of randomly oriented spheroids of arbitrary shape by use of an existing method to average over orientational angles. The optical properties obtained with the SVM and the EBCM are compared for different test cases. For mildly aspherical particles the two methods yield indistinguishable results. Small differences appear for highly aspherical particles. The new approach can be used to compute optical properties for arbitrary values of the aspect ratio. To test the accuracy of the expansion coefficients of the spheroidal functions for arbitrary arguments, a new testing method based on the completeness relation of the spheroidal functions is developed. {copyright} 1998 Optical Society of America

  11. The effect of oxygen tension on human articular chondrocyte matrix synthesis: integration of experimental and computational approaches.

    PubMed

    Li, S; Oreffo, R O C; Sengers, B G; Tare, R S

    2014-09-01

    Significant oxygen gradients occur within tissue engineered cartilaginous constructs. Although oxygen tension is an important limiting parameter in the development of new cartilage matrix, its precise role in matrix formation by chondrocytes remains controversial, primarily due to discrepancies in the experimental setup applied in different studies. In this study, the specific effects of oxygen tension on the synthesis of cartilaginous matrix by human articular chondrocytes were studied using a combined experimental-computational approach in a "scaffold-free" 3D pellet culture model. Key parameters including cellular oxygen uptake rate were determined experimentally and used in conjunction with a mathematical model to estimate oxygen tension profiles in 21-day cartilaginous pellets. A threshold oxygen tension (pO2 ≈ 8% atmospheric pressure) for human articular chondrocytes was estimated from these inferred oxygen profiles and histological analysis of pellet sections. Human articular chondrocytes that experienced oxygen tension below this threshold demonstrated enhanced proteoglycan deposition. Conversely, oxygen tension higher than the threshold favored collagen synthesis. This study has demonstrated a close relationship between oxygen tension and matrix synthesis by human articular chondrocytes in a "scaffold-free" 3D pellet culture model, providing valuable insight into the understanding and optimization of cartilage bioengineering approaches.

  12. Assessment of Content-Based Image Retrieval Approaches for Mammography Based on Breast Density Patterns.

    PubMed

    Purwadi, Nabila Sabatini; Atay, Hüseyin Tanzer; Kurt, Kenan Kaan; Turkeli, Serkan

    2016-01-01

    This study is trying to assess methods commonly used in content-based image retrieval (CBIR) for screening mammography analysis. A database consists of 12 different BI-RADS classes related to breast density patterns of mammogram patches which are taken from IRMA database is used in this study. Three feature extraction methods, namely grey-level co-occurrence matrix (GLCM), principal component analysis (PCA), and scale-invariant feature transform (SIFT) are being investigated and compared with prior studies. Two retrieval methods are also used in this study, namely k-nearest neighbor (KNN) and mutual information (MI) to measure the similarity between query image and images in database. The result will be evaluated using positive count rate in each query for each class. The result of this study is expected to contribute more towards better Computed-Aided Diagnosis (CADx) and specifically screening mammography analysis in clinical cases. PMID:27577481

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

    PubMed

    Chen, Zhenhua; Chen, Xun; Wu, Wei

    2013-04-28

    In this paper, by applying the reduced density matrix (RDM) approach for nonorthogonal orbitals developed in the first paper of this series, efficient algorithms for matrix elements between VB structures and energy gradients in valence bond self-consistent field (VBSCF) method were presented. Both algorithms scale only as nm(4) for integral transformation and d(2)n(β)(2) for VB matrix elements and 3-RDM evaluation, while the computational costs of other procedures are negligible, where n, m, d, and n(β )are the numbers of variable occupied active orbitals, basis functions, determinants, and active β electrons, respectively. Using tensor properties of the energy gradients with respect to the orbital coefficients presented in the first paper of this series, a partial orthogonal auxiliary orbital set was introduced to reduce the computational cost of VBSCF calculation in which orbitals are flexibly defined. Test calculations on the Diels-Alder reaction of butadiene and ethylene have shown that the novel algorithm is very efficient for VBSCF calculations. PMID:23635124

  14. The effect of dynamic changes in soil bulk density on hydraulic properties: modeling approaches

    NASA Astrophysics Data System (ADS)

    Assouline, Shmuel

    2014-05-01

    Natural and artificial processes, like rainfall-induced soil surface sealing or mechanical compaction, disturb the soil structure and enhance dynamic changes of the related pore size distribution. These changes may influence many aspects of the soil-water-plant-atmosphere system. One of the easiest measurable variables is the soil bulk density. Approaches are suggested that could model the effect of the change in soil bulk density on soil permeability, water retention curve (WRC) and unsaturated hydraulic conductivity function (HCF). The resulting expressions were calibrated and validated against experimental data corresponding to different soil types at various levels of compaction, and enable a relatively good prediction of the effect of bulk density on the soil hydraulic properties. These models allow estimating the impact of such changes on flow processes and on transport properties of heterogeneous soil profiles.

  15. Density functional theory approach for calculation of dielectric properties of warm dense matter

    NASA Astrophysics Data System (ADS)

    Saitov, Ilnur

    2015-06-01

    The reflectivity of shocked xenon was measured in the experiments of Mintsev and Zaporoghets for wavelength 1064 nm. But there is no adequate theoretical explanation of these reflectivity results in the framework of the standard methods of nonideal plasma theory. The assumption of significant width to the shock front gives a good agreement with the experimental data. However, there are no evidences of this effect in the experiment. Reflectivity of shocked compressed xenon plasma is calculated in the framework of the density functional theory approach as in. Dependencies on the frequency of incident radiation and on the plasma density are analyzed. The Fresnel formula for the reflectivity is used. The longitudinal expression in the long wavelength limit is applied for the calculation of the imaginary part of the dielectric function. The real part of the dielectric function is calculated by means of the Kramers-Kronig transformation. The approach for the calculation of plasma frequency is developed.

  16. A new approach for analyzing bird densities from variable circular-plot counts

    USGS Publications Warehouse

    Fancy, S.G.

    1997-01-01

    An approach for calculating bird densities from variable circular-plot counts is described. The approach differs from previous methods in that data from several surveys are pooled and detection distances are adjusted as if all distances were recorded by a single observer under a given set of field conditions. Adjustments for covariates that affect detection distances such as observer, weather, time of day, and vegetation type are made using coefficients calculated by multiple linear regression. The effective area surveyed under standard conditions is calculated from the pooled data set and then used to determine the effective area surveyed at each sampling station under the actual conditions when the station was sampled. The method was validated in two field studies where the density of birds could be determined by independent methods. Computer software for entering and analyzing data by this method is described.

  17. Properties of the single-site reduced density matrix in the Bose-Bose resonance model in the ground state and in quantum quenches

    NASA Astrophysics Data System (ADS)

    Dorfner, F.; Heidrich-Meisner, F.

    2016-06-01

    We study properties of the single-site reduced density matrix in the Bose-Bose resonance model as a function of system parameters. This model describes a single-component Bose gas with a resonant coupling to a diatomic molecular state, here defined on a lattice. A main goal is to demonstrate that the eigenstates of the single-site reduced density matrix have structures that are characteristic for the various quantum phases of this system. Since the Hamiltonian conserves only the global particle number but not the number of bosons and molecules individually, these eigenstates, referred to as optimal modes, can be nontrivial linear combinations of bare eigenstates of the molecular and boson particle number. We numerically analyze the optimal modes and their weights, the latter giving the importance of the corresponding state, in the ground state of the Bose-Bose resonance model. We find that the single-site von Neumann entropy is sensitive to the location of the phase boundaries. We explain the structure of the optimal modes and their weight spectra using perturbation theory and via a comparison to results for the single-component Bose-Hubbard model. We further study the dynamical evolution of the optimal modes and of the single-site entanglement entropy in two quantum quenches that cross phase boundaries of the model and show that these quantities are thermal in the steady state. For our numerical calculations, we use the density-matrix renormalization group method for ground-state calculations and time evolution in a Krylov subspace for the quench dynamics as well as exact diagonalization.

  18. Unified matrix approach to the description of phase-space rotators.

    PubMed

    Gitin, Andrey V

    2016-03-01

    In optics, the rotation of a phase-space can be realized via light propagation through both an inhomogeneous medium with a radial gradient of refractive index and two special kinds of mirror-symmetrical optical systems suggested by Lohmann. Although light propagation through Lohmann's systems is described in terms of matrix optics, light propagation through the gradient-index medium is traditionally described as a solution of the wave equation. The difference in these descriptions hinders the understanding of the phase-space rotators. Fortunately, there is a matrix description of light propagation through a gradient-index medium too. A general description of the phase-space rotators is presented, which can be used to treat light propagation through both Lohmann's systems and the gradient-index medium in a unified matrix manner.

  19. A matrix safety frame approach to robot safety for space applications. Thesis

    NASA Technical Reports Server (NTRS)

    Montgomery, T. D.; Lauderbaugh, L. Ken

    1988-01-01

    The planned use of autonomous robots in space applications has generated many new safety problems. This thesis assesses safety of autonomous robot systems through the structure of a proposed three-dimensional matrix safety frame. By identifying the common points of accidents and fatalities involving terrestrial robots, reviewing terrestrial robot safety standards, and modifying and extending these results to space applications, hazards are identified and their associated risks assessed. Three components of the safeguarding dimension of the matrix safety frame, safeguarding through design and operation for intrinsic safety, and incorporation of add-on safety systems are explained through examples for both terrestrial and space robots. A space robot hazard identification checklist, a qualitative tool for robot systems designers, is developed using the structure imparted by the matrix safety frame. The development of an expert system from the contents of the checklist is discussed.

  20. Comparison of Conjugate Gradient Density Matrix Search and Chebyshev Expansion Methods for Avoiding Diagonalization in Large-Scale Electronic Structure Calculations

    NASA Technical Reports Server (NTRS)

    Bates, Kevin R.; Daniels, Andrew D.; Scuseria, Gustavo E.

    1998-01-01

    We report a comparison of two linear-scaling methods which avoid the diagonalization bottleneck of traditional electronic structure algorithms. The Chebyshev expansion method (CEM) is implemented for carbon tight-binding calculations of large systems and its memory and timing requirements compared to those of our previously implemented conjugate gradient density matrix search (CG-DMS). Benchmark calculations are carried out on icosahedral fullerenes from C60 to C8640 and the linear scaling memory and CPU requirements of the CEM demonstrated. We show that the CPU requisites of the CEM and CG-DMS are similar for calculations with comparable accuracy.

  1. Intercomparison of the GOS approach, superposition T-matrix method, and laboratory measurements for black carbon optical properties during aging

    NASA Astrophysics Data System (ADS)

    He, Cenlin; Takano, Yoshi; Liou, Kuo-Nan; Yang, Ping; Li, Qinbin; Mackowski, Daniel W.

    2016-11-01

    We perform a comprehensive intercomparison of the geometric-optics surface-wave (GOS) approach, the superposition T-matrix method, and laboratory measurements for optical properties of fresh and coated/aged black carbon (BC) particles with complex structures. GOS and T-matrix calculations capture the measured optical (i.e., extinction, absorption, and scattering) cross sections of fresh BC aggregates, with 5-20% differences depending on particle size. We find that the T-matrix results tend to be lower than the measurements, due to uncertainty in theoretical approximations of realistic BC structures, particle property measurements, and numerical computations in the method. On the contrary, the GOS results are higher than the measurements (hence the T-matrix results) for BC radii <100 nm, because of computational uncertainty for small particles, while the discrepancy substantially reduces to 10% for radii >100 nm. We find good agreement (differences <5%) between the two methods in asymmetry factors for various BC sizes and aggregating structures. For aged BC particles coated with sulfuric acid, GOS and T-matrix results closely match laboratory measurements of optical cross sections. Sensitivity calculations show that differences between the two methods in optical cross sections vary with coating structures for radii <100 nm, while differences decrease to 10% for radii >100 nm. We find small deviations (≤10%) in asymmetry factors computed from the two methods for most BC coating structures and sizes, but several complex structures have 10-30% differences. This study provides the foundation for downstream application of the GOS approach in radiative transfer and climate studies.

  2. Determination of pharmaceuticals in sewage sludge and biochar from hydrothermal carbonization using different quantification approaches and matrix effect studies.

    PubMed

    Vom Eyser, C; Palmu, K; Otterpohl, R; Schmidt, T C; Tuerk, J

    2015-01-01

    Producing valuable biochar from waste materials using thermal processes like hydrothermal carbonization (HTC) has gained attention in recent years. However, the fate of micropollutants present in these waste sources have been neglected, although they might entail the risk of environmental pollution. Thus, an HPLC-MS/MS method was developed for 12 pharmaceuticals to determine the micropollutant load of biochar, which was made from sewage sludge via HTC within 4 h at 210 °C. Pressurized liquid extraction was applied to extract the compounds. Because of the high load of co-extracted matter, matrix effects in HPLC-MS/MS were investigated using matrix effect profiles. Interfering compounds suppressed 50% of the phenazone signal in sewage sludge and 70% in biochar, for example. The quantification approaches external calibration, internal standard analysis, and standard addition were compared considering recovery rates, standard deviations, and measurement uncertainties. The external analysis resulted in decreased or enhanced recovery rates. Spiking before LC-MS/MS compensated instrumental matrix effects. Still, recovery rates remained below 70% for most compounds because this approach neglects sample losses during the extraction. Internal standards compensated for the matrix effects sufficiently for up to five compounds. The standard addition over the whole procedure proved to compensate for the matrix effects for 11 compounds and achieved recovery rates between 85 and 125%. Additionally, results showed good reproducibility and validity. Only sulfamethoxazole recovery rate remained below 70% in sewage sludge. Real sample analysis showed that three pharmaceuticals were detected in the biochar, while the corresponding sewage sludge source contained 8 of the investigated compounds. PMID:25098418

  3. Simulated one-pass list-mode: an approach to on-the-fly system matrix calculation.

    PubMed

    Gillam, J E; Solevi, P; Oliver, J F; Rafecas, M

    2013-04-01

    In the development of prototype systems for positron emission tomography a valid and robust image reconstruction algorithm is required. However, prototypes often employ novel detector and system geometries which may change rapidly under optimization. In addition, developing systems generally produce highly granular, or possibly continuous detection domains which require some level of on-the-fly calculation for retention of measurement precision. In this investigation a new method of on-the-fly system matrix calculation is proposed that provides advantages in application to such list-mode systems in terms of flexibility in system modeling. The new method is easily adaptable to complicated system geometries and available computational resources. Detection uncertainty models are used as random number generators to produce ensembles of possible photon trajectories at image reconstruction time for each datum in the measurement list. However, the result of this approach is that the system matrix elements change at each iteration in a non-repetitive manner. The resulting algorithm is considered the simulation of a one-pass list (SOPL) which is generated and the list traversed during image reconstruction. SOPL alters the system matrix in use at each iteration and so behavior within the maximum likelihood-expectation maximization algorithm was investigated. A two-pixel system and a small two dimensional imaging model are used to illustrate the process and quantify aspects of the algorithm. The two-dimensional imaging system showed that, while incurring a penalty in image resolution, in comparison to a non-random equal-computation counterpart, SOPL provides much enhanced noise properties. In addition, enhancement in system matrix quality is straightforward (by increasing the number of samples in the ensemble) so that the resolution penalty can be recovered when desired while retaining improvement in noise properties. Finally the approach is tested and validated against a

  4. Determination of pharmaceuticals in sewage sludge and biochar from hydrothermal carbonization using different quantification approaches and matrix effect studies.

    PubMed

    Vom Eyser, C; Palmu, K; Otterpohl, R; Schmidt, T C; Tuerk, J

    2015-01-01

    Producing valuable biochar from waste materials using thermal processes like hydrothermal carbonization (HTC) has gained attention in recent years. However, the fate of micropollutants present in these waste sources have been neglected, although they might entail the risk of environmental pollution. Thus, an HPLC-MS/MS method was developed for 12 pharmaceuticals to determine the micropollutant load of biochar, which was made from sewage sludge via HTC within 4 h at 210 °C. Pressurized liquid extraction was applied to extract the compounds. Because of the high load of co-extracted matter, matrix effects in HPLC-MS/MS were investigated using matrix effect profiles. Interfering compounds suppressed 50% of the phenazone signal in sewage sludge and 70% in biochar, for example. The quantification approaches external calibration, internal standard analysis, and standard addition were compared considering recovery rates, standard deviations, and measurement uncertainties. The external analysis resulted in decreased or enhanced recovery rates. Spiking before LC-MS/MS compensated instrumental matrix effects. Still, recovery rates remained below 70% for most compounds because this approach neglects sample losses during the extraction. Internal standards compensated for the matrix effects sufficiently for up to five compounds. The standard addition over the whole procedure proved to compensate for the matrix effects for 11 compounds and achieved recovery rates between 85 and 125%. Additionally, results showed good reproducibility and validity. Only sulfamethoxazole recovery rate remained below 70% in sewage sludge. Real sample analysis showed that three pharmaceuticals were detected in the biochar, while the corresponding sewage sludge source contained 8 of the investigated compounds.

  5. An Approach to Calculate Mineralś Bulk Moduli KS from Chemical Composition and Density ρ

    NASA Astrophysics Data System (ADS)

    Breuer, S.; Schilling, F. R.; Mueller, B.; Drüppel, K.

    2015-12-01

    The elastic properties of minerals are fundamental parameters for technical and geotechnical applications and an important research topic towards a better understanding of the Earth's interior. Published elastic properties, chemical composition, and density data of 86 minerals (total of 258 data including properties of minerals at various p, T conditions) were collected into a database. It was used to test different hypotheses about relationships between these properties (e.g. water content in minerals and their Poisson's ratio). Furthermore, a scheme to model the average elastic properties, i.e. the bulk modulus KS, based on mineral density and composition was developed. Birch's law, a linearity between density ρ and wave velocity (e.g. vp.), is frequently used in seismic and seismology to derive density of the Earth's interior from seismic velocities. Applying the compiled mineral data contradicts the use of a simple velocity-density relation (e.g. Gardneŕs relation, 1974). The presented model-approach to estimate the mineralś bulk moduli Ks (as Voigt-Reuss-Hill average) is based on the idea of pressure-temperature (p-T) dependent ionś bulk moduli. Using a multi-exponential regression to ascertain the ionś bulk moduli and by applying an exponential scaling with density ρ, their bulk moduli could be modelled. As a result, > 88 % of the 258 bulk moduli data are predicted with an uncertainty of < 20 % compared to published values. Compared to other models (e.g. Anderson et al. 1970 and Anderson & Nafe 1965), the here presented approach to model the bulk moduli only requires the density ρ and chemical composition of the mineral and is not limited to a specific group of minerals, composition, or structure. In addition to this, by using the pressure and temperature dependent density ρ(p, T), it is possible to predict bulk moduli for varying p-T conditions. References:Gardner, G.H.F, Gardner, L.W. and Gregory, A.R. (1974). Geophysics, 39, No. 6, 770

  6. A Transfer Learning Approach for Applying Matrix Factorization to Small ITS Datasets

    ERIC Educational Resources Information Center

    Voß, Lydia; Schatten, Carlotta; Mazziotti, Claudia; Schmidt-Thieme, Lars

    2015-01-01

    Machine Learning methods for Performance Prediction in Intelligent Tutoring Systems (ITS) have proven their efficacy; specific methods, e.g. Matrix Factorization (MF), however suffer from the lack of available information about new tasks or new students. In this paper we show how this problem could be solved by applying Transfer Learning (TL),…

  7. Information Architecture for the Web: The IA Matrix Approach to Designing Children's Portals.

    ERIC Educational Resources Information Center

    Large, Andrew; Beheshti, Jamshid; Cole, Charles

    2002-01-01

    Presents a matrix that can serve as a tool for designing the information architecture of a Web portal in a logical and systematic manner. Highlights include interfaces; metaphors; navigation; interaction; information retrieval; and an example of a children's Web portal to provide access to museum information. (Author/LRW)

  8. Phase-separated ferromagnetism in a spin-imbalanced system of Fermi atoms loaded in an optical ladder: A density-matrix renormalization-group study

    SciTech Connect

    Okumura, M.; Yamada, S.; Machida, M.; Aoki, H.

    2011-03-15

    We consider repulsively interacting, cold fermionic atoms loaded on an optical ladder lattice in a trapping potential. The density-matrix renormalization-group method is used to numerically calculate the ground state for systematically varied values of interaction U and spin imbalance p in the Hubbard model on the ladder. The system exhibits rich structures, where a fully spin-polarized phase, spatially separated from other domains in the trapping potential, appears for large enough U and p. The phase-separated ferromagnetism can be captured as a real-space image of the energy gap between the ferromagnetic and other states arising from the combined effect of the Nagaoka ferromagnetism extended to the ladder and the density dependence of the energy separation between competing states. We also predict how to maximize the ferromagnetic region.

  9. Dynamic impact response of high-density square honeycombs made of TRIP steel and TRIP matrix composite material

    NASA Astrophysics Data System (ADS)

    Ehinger, D.; Krüger, L.; Krause, S.; Martin, U.; Weigelt, C.; Aneziris, C. G.

    2012-08-01

    Two designs of square-celled metallic honeycomb structures fabricated by a modified extrusion technology based on a powder feedstock were investigated. The strength and ductility of these cellular materials are achieved by an austenitic CrNi (AISI 304) steel matrix particle reinforced by an MgO partially-stabilized zirconia building up their cell wall microstructure. Similar to the mechanical behaviour of the bulk materials, the strengthening mechanism and the martensitic phase transformations in the cell walls are affected by the deformation temperature and the nominal strain rate. The microstructure evolution during quasi-static and dynamic impact compression up to high strain rates of 103 1/s influences the buckling and failure behaviour of the honeycomb structures. In contrast to bending-dominated quasi-isotropic networks like open-celled metal foams, axial compressive loading to the honeycomb's channels causes membrane stretching as well as crushing of the vertical cell node elements and cell walls. The presented honeycomb materials differ geometrically in their cell wall thickness-to-cell size-ratio. Therefore, the failure behaviour is predominantly controlled by global buckling and torsional-flexural buckling, respectively, accompanied by plastic matrix flow and strengthening of the cell wall microstructure.

  10. Network trending; leadership, followership and neutrality among companies: A random matrix approach

    NASA Astrophysics Data System (ADS)

    Mobarhan, N. S. Safavi; Saeedi, A.; Roodposhti, F. Rahnamay; Jafari, G. R.

    2016-11-01

    In this article, we analyze the cross-correlation between returns of different stocks to answer the following important questions. The first one is: If there exists collective behavior in a financial market, how could we detect it? And the second question is: Is there a particular company among the companies of a market as the leader of the collective behavior? Or is there no specified leadership governing the system similar to some complex systems? We use the method of random matrix theory to answer the mentioned questions. Cross-correlation matrix of index returns of four different markets is analyzed. The participation ratio quantity related to each matrices' eigenvectors and the eigenvalue spectrum is calculated. We introduce shuffled-matrix created of cross correlation matrix in such a way that the elements of the later one are displaced randomly. Comparing the participation ratio quantities obtained from a correlation matrix of a market and its related shuffled-one, on the bulk distribution region of the eigenvalues, we detect a meaningful deviation between the mentioned quantities indicating the collective behavior of the companies forming the market. By calculating the relative deviation of participation ratios, we obtain a measure to compare the markets according to their collective behavior. Answering the second question, we show there are three groups of companies: The first group having higher impact on the market trend called leaders, the second group is followers and the third one is the companies who have not a considerable role in the trend. The results can be utilized in portfolio construction.

  11. Hybrid elastin-like polypeptide-polyethylene glycol (ELP-PEG) hydrogels with improved transparency and independent control of matrix mechanics and cell ligand density.

    PubMed

    Wang, Huiyuan; Cai, Lei; Paul, Alexandra; Enejder, Annika; Heilshorn, Sarah C

    2014-09-01

    Hydrogels have been developed as extracellular matrix (ECM) mimics both for therapeutic applications and basic biological studies. In particular, elastin-like polypeptide (ELP) hydrogels, which can be tuned to mimic several biochemical and physical characteristics of native ECM, have been constructed to encapsulate various types of cells to create in vitro mimics of in vivo tissues. However, ELP hydrogels become opaque at body temperature because of ELP's lower critical solution temperature behavior. This opacity obstructs light-based observation of the morphology and behavior of encapsulated cells. In order to improve the transparency of ELP hydrogels for better imaging, we have designed a hybrid ELP-polyethylene glycol (PEG) hydrogel system that rapidly cross-links with tris(hydroxymethyl) phosphine (THP) in aqueous solution via Mannich-type condensation. As expected, addition of the hydrophilic PEG component significantly improves the light transmittance. Coherent anti-Stokes Raman scattering (CARS) microscopy reveals that the hybrid ELP-PEG hydrogels have smaller hydrophobic ELP aggregates at 37 °C. Importantly, this hydrogel platform enables independent tuning of adhesion ligand density and matrix stiffness, which is desirable for studies of cell-matrix interactions. Human fibroblasts encapsulated in these hydrogels show high viability (>98%) after 7 days of culture. High-resolution confocal microscopy of encapsulated fibroblasts reveals that the cells adopt a more spread morphology in response to higher RGD ligand concentrations and softer gel mechanics.

  12. Hybrid Elastin-like Polypeptide–Polyethylene Glycol (ELP-PEG) Hydrogels with Improved Transparency and Independent Control of Matrix Mechanics and Cell Ligand Density

    PubMed Central

    2015-01-01

    Hydrogels have been developed as extracellular matrix (ECM) mimics both for therapeutic applications and basic biological studies. In particular, elastin-like polypeptide (ELP) hydrogels, which can be tuned to mimic several biochemical and physical characteristics of native ECM, have been constructed to encapsulate various types of cells to create in vitro mimics of in vivo tissues. However, ELP hydrogels become opaque at body temperature because of ELP’s lower critical solution temperature behavior. This opacity obstructs light-based observation of the morphology and behavior of encapsulated cells. In order to improve the transparency of ELP hydrogels for better imaging, we have designed a hybrid ELP-polyethylene glycol (PEG) hydrogel system that rapidly cross-links with tris(hydroxymethyl) phosphine (THP) in aqueous solution via Mannich-type condensation. As expected, addition of the hydrophilic PEG component significantly improves the light transmittance. Coherent anti-Stokes Raman scattering (CARS) microscopy reveals that the hybrid ELP-PEG hydrogels have smaller hydrophobic ELP aggregates at 37 °C. Importantly, this hydrogel platform enables independent tuning of adhesion ligand density and matrix stiffness, which is desirable for studies of cell–matrix interactions. Human fibroblasts encapsulated in these hydrogels show high viability (>98%) after 7 days of culture. High-resolution confocal microscopy of encapsulated fibroblasts reveals that the cells adopt a more spread morphology in response to higher RGD ligand concentrations and softer gel mechanics. PMID:25111283

  13. Ionic Asymmetry and Solvent Excluded Volume Effects on Spherical Electric Double Layers: A Density Functional Approach

    SciTech Connect

    Medasani, Bharat; Ovanesyan, Zaven; Thomas, Dennis G.; Sushko, Maria L.; Marucho, Marcelo

    2014-05-29

    In this article we present a classical density functional theory for electrical double layers of spherical macroions that extends the capabilities of conventional approaches by accounting for electrostatic ion correlations, size asymmetry and excluded volume effects. The approach is based on a recent approximation introduced by Hansen-Goos and Roth for the hard sphere excess free energy of inhomogeneous fluids (J. Chem. Phys. 124, 154506). It accounts for the proper and efficient description of the effects of ionic asymmetry and solvent excluded volume, especially at high ion concentrations and size asymmetry ratios including those observed in experimental studies. Additionally, we utilize a leading functional Taylor expansion approximation of the ion density profiles. In addition, we use the Mean Spherical Approximation for multi-component charged hard sphere fluids to account for the electrostatic ion correlation effects. These approximations are implemented in our theoretical formulation into a suitable decomposition of the excess free energy which plays a key role in capturing the complex interplay between charge correlations and excluded volume effects. We perform Monte Carlo simulations in various scenarios to validate the proposed approach, obtaining a good compromise between accuracy and computational cost. We use the proposed computational approach to study the effects of ion size, ion size asymmetry and solvent excluded volume on the ion profiles, integrated charge, mean electrostatic potential, and ionic coordination number around spherical macroions in various electrolyte mixtures. Our results show that both solvent hard sphere diameter and density play a dominant role in the distribution of ions around spherical macroions, mainly for experimental water molarity and size values where the counterion distribution is characterized by a tight binding to the macroion, similar to that predicted by the Stern model.

  14. Ionic asymmetry and solvent excluded volume effects on spherical electric double layers: A density functional approach

    NASA Astrophysics Data System (ADS)

    Medasani, Bharat; Ovanesyan, Zaven; Thomas, Dennis G.; Sushko, Maria L.; Marucho, Marcelo

    2014-05-01

    In this article, we present a classical density functional theory for electrical double layers of spherical macroions that extends the capabilities of conventional approaches by accounting for electrostatic ion correlations, size asymmetry, and excluded volume effects. The approach is based on a recent approximation introduced by Hansen-Goos and Roth for the hard sphere excess free energy of inhomogeneous fluids [J. Chem. Phys. 124, 154506 (2006); Hansen-Goos and Roth, J. Phys.: Condens. Matter 18, 8413 (2006)]. It accounts for the proper and efficient description of the effects of ionic asymmetry and solvent excluded volume, especially at high ion concentrations and size asymmetry ratios including those observed in experimental studies. Additionally, we utilize a leading functional Taylor expansion approximation of the ion density profiles. In addition, we use the mean spherical approximation for multi-component charged hard sphere fluids to account for the electrostatic ion correlation effects. These approximations are implemented in our theoretical formulation into a suitable decomposition of the excess free energy which plays a key role in capturing the complex interplay between charge correlations and excluded volume effects. We perform Monte Carlo simulations in various scenarios to validate the proposed approach, obtaining a good compromise between accuracy and computational cost. We use the proposed computational approach to study the effects of ion size, ion size asymmetry, and solvent excluded volume on the ion profiles, integrated charge, mean electrostatic potential, and ionic coordination number around spherical macroions in various electrolyte mixtures. Our results show that both solvent hard sphere diameter and density play a dominant role in the distribution of ions around spherical macroions, mainly for experimental water molarity and size values where the counterion distribution is characterized by a tight binding to the macroion, similar to that

  15. Ionic asymmetry and solvent excluded volume effects on spherical electric double layers: a density functional approach.

    PubMed

    Medasani, Bharat; Ovanesyan, Zaven; Thomas, Dennis G; Sushko, Maria L; Marucho, Marcelo

    2014-05-28

    In this article, we present a classical density functional theory for electrical double layers of spherical macroions that extends the capabilities of conventional approaches by accounting for electrostatic ion correlations, size asymmetry, and excluded volume effects. The approach is based on a recent approximation introduced by Hansen-Goos and Roth for the hard sphere excess free energy of inhomogeneous fluids [J. Chem. Phys. 124, 154506 (2006); Hansen-Goos and Roth, J. Phys.: Condens. Matter 18, 8413 (2006)]. It accounts for the proper and efficient description of the effects of ionic asymmetry and solvent excluded volume, especially at high ion concentrations and size asymmetry ratios including those observed in experimental studies. Additionally, we utilize a leading functional Taylor expansion approximation of the ion density profiles. In addition, we use the mean spherical approximation for multi-component charged hard sphere fluids to account for the electrostatic ion correlation effects. These approximations are implemented in our theoretical formulation into a suitable decomposition of the excess free energy which plays a key role in capturing the complex interplay between charge correlations and excluded volume effects. We perform Monte Carlo simulations in various scenarios to validate the proposed approach, obtaining a good compromise between accuracy and computational cost. We use the proposed computational approach to study the effects of ion size, ion size asymmetry, and solvent excluded volume on the ion profiles, integrated charge, mean electrostatic potential, and ionic coordination number around spherical macroions in various electrolyte mixtures. Our results show that both solvent hard sphere diameter and density play a dominant role in the distribution of ions around spherical macroions, mainly for experimental water molarity and size values where the counterion distribution is characterized by a tight binding to the macroion, similar to that

  16. Ionic asymmetry and solvent excluded volume effects on spherical electric double layers: a density functional approach.

    PubMed

    Medasani, Bharat; Ovanesyan, Zaven; Thomas, Dennis G; Sushko, Maria L; Marucho, Marcelo

    2014-05-28

    In this article, we present a classical density functional theory for electrical double layers of spherical macroions that extends the capabilities of conventional approaches by accounting for electrostatic ion correlations, size asymmetry, and excluded volume effects. The approach is based on a recent approximation introduced by Hansen-Goos and Roth for the hard sphere excess free energy of inhomogeneous fluids [J. Chem. Phys. 124, 154506 (2006); Hansen-Goos and Roth, J. Phys.: Condens. Matter 18, 8413 (2006)]. It accounts for the proper and efficient description of the effects of ionic asymmetry and solvent excluded volume, especially at high ion concentrations and size asymmetry ratios including those observed in experimental studies. Additionally, we utilize a leading functional Taylor expansion approximation of the ion density profiles. In addition, we use the mean spherical approximation for multi-component charged hard sphere fluids to account for the electrostatic ion correlation effects. These approximations are implemented in our theoretical formulation into a suitable decomposition of the excess free energy which plays a key role in capturing the complex interplay between charge correlations and excluded volume effects. We perform Monte Carlo simulations in various scenarios to validate the proposed approach, obtaining a good compromise between accuracy and computational cost. We use the proposed computational approach to study the effects of ion size, ion size asymmetry, and solvent excluded volume on the ion profiles, integrated charge, mean electrostatic potential, and ionic coordination number around spherical macroions in various electrolyte mixtures. Our results show that both solvent hard sphere diameter and density play a dominant role in the distribution of ions around spherical macroions, mainly for experimental water molarity and size values where the counterion distribution is characterized by a tight binding to the macroion, similar to that

  17. Cumulant Approximated Second-Order Perturbation Theory Based on the Density Matrix Renormalization Group for Transition Metal Complexes: A Benchmark Study.

    PubMed

    Phung, Quan Manh; Wouters, Sebastian; Pierloot, Kristine

    2016-09-13

    The complete active space second order perturbation theory (CASPT2) can be extended to larger active spaces by using the density matrix renormalization group (DMRG) as solver. Two variants are commonly used: the costly DMRG-CASPT2 with exact 4-particle reduced density matrix (4-RDM) and the cheaper DMRG-cu(4)-CASPT2 in which the 4-cumulant is discarded. To assess the accuracy and limitations of the latter variant DMRG-cu(4)-CASPT2 we study the spin state energetics of iron porphyrin Fe(P) and its model compound FeL2, a model for the active center of NiFe hydrogenase, and manganese-oxo porphyrin MnO(P)(+); a series of excited states of chromium hexacarbonyl Cr(CO)6; and the interconversion of two Cu2O2(2+) isomers. Our results clearly show that PT2 on top of DMRG is essential in order to obtain quantitative results for transition metal complexes. Good results were obtained with DMRG-cu(4)-CASPT2 as compared to full CASPT2 and DMRG-CASPT2 in calculations with small- and medium-sized active spaces. In calculations with large-sized active spaces (∼30 active orbitals), the performance of DMRG-cu(4)-CASPT2 is less impressive due to the errors originating from both the finite number of renormalized states m and the 4-RDM approximation. PMID:27547847

  18. A new approach to the solution of large, full matrix equations: A two-dimensional potential flow feasibility study

    NASA Technical Reports Server (NTRS)

    James, R. M.; Clark, R. W.

    1979-01-01

    An approach to the solution of matrix problems resulting from integral equations of mathematical physics is presented. Based on the inherent smoothness in such equations, the problem is reformulated using a set of orthogonal basis vectors, leading to an equivalent coefficient problem which can be of lower order without significantly impairing the accuracy of the solution. This approach was evaluated using a two-dimensional Neumann problem describing the inviscid, incompressible flow over an airfoil. Two different kinds of mode functions were investigated, namely eigenfunction series and Fourier series. The method using Fourier series was found preferable. It uses all of the coefficients from a Fast Fourier Transform algorithm in an approximate method which exploits the known structure of the transformed coefficient matrix and very promising results for the flow over a realistic airfoil are obtained. On the basis of the results presented here, an order of magnitude reduction in this computer time can be expected for such problems as compared with the time for a direct matrix solution.

  19. Circuit theory and full counting statistics of charge transfer through mesoscopic systems: A random-matrix approach

    NASA Astrophysics Data System (ADS)

    Duarte-Filho, G. C.; Macedo-Junior, A. F.; Macêdo, A. M. S.

    2007-08-01

    We introduce a random-matrix description of full counting statistics of charge transfer through a quantum mesoscopic system at finite temperature in the presence two nonideal contacts. Using the exact map between random-matrix theory and the supersymmetric nonlinear σ model, we demonstrate, via explicit calculations, that the saddle-point equation, derived by applying the variational principle to the supersymmetric action, can be cast in the form of the two-terminal version of Nazarov’s circuit theory, thus giving it the status of a controlled approximation. For the case in which the mesoscopic system is a quantum dot at zero temperature, this circuit theory has recently been shown [A. L. R. Barbosa and A. M. S. Macêdo, Phys. Rev. B 71, 235307 (2005)] to reproduce exactly the asymptotic semiclassical limit of the Poisson kernel in perfect agreement with a diagrammatic approach for averaging over the unitary group. We report applications of our formalism to the description of charge transfer through a quantum dot, a quantum chain, and a quantum wire. We also discuss the role of different symmetry classes (orthogonal, unitary, and symplectic) and show how to use known exact connections between the supersymmetric nonlinear σ model and random scattering matrix theories to perform both perturbative and nonperturbative calculations. We believe that our results will help unify the various approaches being currently used in mesoscopic physics of hybrid devices within a single physically sound and mathematically rigorous theoretical scheme.

  20. Size dependence of yield strength simulated by a dislocation-density function dynamics approach

    NASA Astrophysics Data System (ADS)

    Leung, P. S. S.; Leung, H. S.; Cheng, B.; Ngan, A. H. W.

    2015-04-01

    The size dependence of the strength of nano- and micron-sized crystals is studied using a new simulation approach in which the dynamics of the density functions of dislocations are modeled. Since any quantity of dislocations can be represented by a density, this approach can handle large systems containing large quantities of dislocations, which may handicap discrete dislocation dynamics schemes due to the excessive computation time involved. For this reason, pillar sizes spanning a large range, from the sub-micron to micron regimes, can be simulated. The simulation results reveal the power-law relationship between strength and specimen size up to a certain size, beyond which the strength varies much more slowly with size. For specimens smaller than ∼4000b, their strength is found to be controlled by the dislocation depletion condition, in which the total dislocation density remains almost constant throughout the loading process. In specimens larger than ∼4000b, the initial dislocation distribution is of critical importance since the presence of dislocation entanglements is found to obstruct deformation in the neighboring regions within a distance of ∼2000b. This length scale suggests that the effects of dense dislocation clusters are greater in intermediate-sized specimens (e.g. 4000b and 8000b) than in larger specimens (e.g. 16 000b), according to the weakest-link concept.

  1. Random matrix approach to group correlations in development country financial market

    NASA Astrophysics Data System (ADS)

    Qohar, Ulin Nuha Abdul; Lim, Kyuseong; Kim, Soo Yong; Liong, The Houw; Purqon, Acep

    2015-12-01

    Financial market is a borderless economic activity, everyone in this world has the right to participate in stock transactions. The movement of stocks is interesting to be discussed in various sciences, ranging from economists to mathe-maticians try to explain and predict the stock movement. Econophysics, as a discipline that studies the economic behavior using one of the methods in particle physics to explain stock movement. Stocks tend to be unpredictable probabilistic regarded as a probabilistic particle. Random Matrix Theory is one method used to analyze probabilistic particle is used to analyze the characteristics of the movement in the stock collection of developing country stock market shares of the correlation matrix. To obtain the characteristics of the developing country stock market and use characteristics of stock markets of developed countries as a parameter for comparison. The result shows market wide effect is not happened in Philipine market and weak in Indonesia market. Contrary, developed country (US) has strong market wide effect.

  2. A reduced rank approach for covariance matrix estimation in EEG signal classification.

    PubMed

    Tomida, Naoki; Yamagishi, Masao; Yamada, Isao; Tanaka, Toshihisa

    2014-01-01

    Common Spatial Pattern (CSP) methods are widely used to extract the brain activity for brain machine interfacing (BMI) based on electroencephalogram (EEG). For each mental task, CSP methods estimate a covariance matrix of EEG signals and adopt the uniform average of the sample covariance matrices over trials. However, the uniform average is sensitive to outliers caused by e.g. unrelated brain activity. In this paper, we propose an improvement of the estimated covariance matrix utilized in CSP methods by reducing the influence of the outliers as well as guaranteeing positive definiteness. More precisely, our estimation is the projection of the uniform average onto the intersection of two convex sets: the first set is a special reduced dimensional subspace which alleviates the influence of the outliers; the second is the positive definite cone. A numerical experiment supports the effectiveness of the proposed technique.

  3. An explicit matrix formulation of the dynamical equations for flexible multibody systems - A recursive approach

    NASA Astrophysics Data System (ADS)

    Amirouche, F. M. L.; Xie, M.

    1993-01-01

    The dynamic simulation of complex rigid/flexible multibody systems relies greatly on the presentation and development of the equations of motion. To achieve computational speed in the execution and to further develop the control algorithms, the expressions involved in the kinematics and the subsequent coefficients associated with the equations of motion must be clearly defined. The intention of this paper is to develop a recursive formulation based on finite element method where all terms are presented in a matrix form. The methodology permits one to identify the coupling between rigid and flexible body motion, and build the necessary arrays for the application at hand. The equations of motion are based on Kane's equation and the general matrix representation for n bodies of its partial velocities and partial angular velocities. The algorithm developed is applied to a single two-link robot manipulator and the subsequent explicit equations of motion are presented.

  4. Quantum-statistical T-matrix approach to line broadening of hydrogen in dense plasmas

    SciTech Connect

    Lorenzen, Sonja; Wierling, August; Roepke, Gerd; Reinholz, Heidi; Zammit, Mark C.; Fursa, Dmitry V.; Bray, Igor

    2010-10-29

    The electronic self-energy {Sigma}{sup e} is an important input in a quantum-statistical theory for spectral line profile calculations. It describes the influence of plasma electrons on bound state properties. In dense plasmas, the effect of strong, i.e. close, electron-emitter collisions can be considered by three-particle T-matrix diagrams. These digrams are approximated with the help of an effective two-particle T-matrix, which is obtained from convergent close-coupling calculations with Debye screening. A comparison with other theories is carried out for the 2p level of hydrogen at k{sub B}T = 1 eV and n{sub e} = 2{center_dot}10{sup 23} m{sup -3}, and results are given for n{sub e} = 1{center_dot}10{sup 25} m{sup -3}.

  5. Exploring Eddy-Covariance Measurements Using a Spatial Approach: The Eddy Matrix

    NASA Astrophysics Data System (ADS)

    Engelmann, Christian; Bernhofer, Christian

    2016-10-01

    Taylor's frozen turbulence hypothesis states that "standard" eddy-covariance measurements of fluxes at a fixed location can replace a spatial ensemble of instantaneous values at multiple locations. For testing this hypothesis, a unique turbulence measurement set-up was used for two measurement campaigns over desert (Namibia) and grassland (Germany) in 2012. This "Eddy Matrix" combined nine ultrasonic anemometer-thermometers and 17 thermocouples in a 10 m × 10 m regular grid with 2.5-m grid distance. The instantaneous buoyancy flux derived from the spatial eddy covariance of the Eddy Matrix was highly variable in time (from -0.3 to 1 m K s^{-1}). However, the 10-min average reflected 83 % of the reference eddy-covariance flux with a good correlation. By introducing a combined eddy-covariance method (the spatial eddy covariance plus the additional flux of the temporal eddy covariance of the spatial mean values), the mean flux increases by 9 % relative to the eddy-covariance reference. Considering the typical underestimation of fluxes by the standard eddy-covariance method, this is seen as an improvement. Within the limits of the Eddy Matrix, Taylor's hypothesis is supported by the results.

  6. Correlated R-matrix theory of electron scattering: A coupled-cluster approach

    NASA Astrophysics Data System (ADS)

    Sur, Chiranjib; Pradhan, Anil; Sadayappan, P.

    2007-06-01

    Study of electron scattering from heavy atoms/ions not only demands high speed computing machines but also improved theoretical descriptions of the relativistic and correlation effects for the target atoms/ions as well. We will give an outline of the coupled-cluster R-matrix (CCRM) theory to incorporate the effect of electron correlation through coupled-cluster theory (CCT), the size extensive and one of the most accurate many body theories which is equivalant to an all-order many-body perturbation theory (MBPT). General theoretical formulation of CCRM and the computational implementation using the high level Mathematica style language compiler known as Tensor Contraction Engine (TCE) will be presented. Electronic structure calculations using CCT involve large collections of tensor contractions (generalized matrix multiplications). TCE searches for an optimal implementation of these tensor contraction expressions and generates high performance FORTRAN code for CCT. We will also comment on the interfacing of TCE generated code with the Breit-Pauli R-matrix code to make a next generation CCRM software package. This theoretical formulation and the new sets of codes can be used to study electron scattering / photoionization in heavy atomic systems where relativistic and electron correlation effects are very important.

  7. A sublinear-scaling approach to density-functional-theory analysis of crystal defects

    NASA Astrophysics Data System (ADS)

    Ponga, M.; Bhattacharya, K.; Ortiz, M.

    2016-10-01

    We develop a sublinear-scaling method, referred to as MacroDFT, for the study of crystal defects using ab-initio Density Functional Theory (DFT). The sublinear scaling is achieved using a combination of the Linear Scaling Spectral Gauss Quadrature method (LSSGQ) and a Coarse-Graining approach (CG) based on the quasi-continuum method. LSSGQ reformulates DFT and evaluates the electron density without computing individual orbitals. This direct evaluation is possible by recourse to Gaussian quadrature over the spectrum of the linearized Hamiltonian operator. Furthermore, the nodes and weights of the quadrature can be computed independently for each point in the domain. This property is exploited in CG, where fields of interest are computed at selected nodes and interpolated elsewhere. In this paper, we present the MacroDFT method, its parallel implementation and an assessment of convergence and performance by means of test cases concerned with point defects in magnesium.

  8. Innovative User Defined Density Profile Approach To FSW Of Aluminium Foam

    SciTech Connect

    Contorno, Dorotea; Fratini, Livan; Filice, Luigino; Gagliardi, Francesco; Umbrello, Domenico; Shivpuri, Rajiv

    2007-04-07

    Metallic foams are one of the most exciting materials in the world of mechanical industry due to their reduced mass and the good mechanical, thermal and acoustic characteristics. Consequently, their application, is increasing day by day even with the important drawbacks that reduce their suitability and diffusion such as high manufacturing cost and difficulty in processing. An innovative approach is outlined in this paper that enables the production of complex shapes taking advantage of deformation processing and friction stir welding (FSW). The aim is to create customized tailored manufactured parts. The cellular construction of foams makes this approach rather challenging as the cell walls are extremely thin and deform unpredictably especially in the presence of rotating and moving hard tool. In this paper, an integrated approach to overcome some of the above challenges is proposed. The initial density is modified by using simple deformation processes, in order to obtained the desired 'crushed density', customized for the intended application. Then, the panels are joined to specially designed solid blocks by using FSW process with a proper set-up. Finally, the obtained specimens are evaluated for mechanical performance and the quality of the joint.

  9. Chromium liquid waste inertization in an inorganic alkali activated matrix: leaching and NMR multinuclear approach.

    PubMed

    Ponzoni, Chiara; Lancellotti, Isabella; Barbieri, Luisa; Spinella, Alberto; Saladino, Maria Luisa; Martino, Delia Chillura; Caponetti, Eugenio; Armetta, Francesco; Leonelli, Cristina

    2015-04-01

    A class of inorganic binders, also known as geopolymers, can be obtained by alkali activation of aluminosilicate powders at room temperature. The process is affected by many parameters (curing time, curing temperature, relative humidity etc.) and leads to a resistant matrix usable for inertization of hazardous waste. In this study an industrial liquid waste containing a high amount of chromium (≈ 2.3 wt%) in the form of metalorganic salts is inertized into a metakaolin based geopolymer matrix. One of the innovative aspects is the exploitation of the water contained in the waste for the geopolymerization process. This avoided any drying treatment, a common step in the management of liquid hazardous waste. The evolution of the process--from the precursor dissolution to the final geopolymer matrix hardening--of different geopolymers containing a waste amount ranging from 3 to 20%wt and their capability to inertize chromium cations were studied by: i) the leaching tests, according to the EN 12,457 regulation, at different curing times (15, 28, 90 and 540 days) monitoring releases of chromium ions (Cr(III) and Cr(VI)) and the cations constituting the aluminosilicate matrix (Na, Si, Al); ii) the humidity variation for different curing times (15 and 540 days); iii) SEM characterization at different curing times (28 and 540 days); iv) the trend of the solution conductivity and pH during the leaching test; v) the characterization of the short-range ordering in terms of TOT bonds (where T is Al or Si) by (29)Si and (27)Al solid state magic-angle spinning nuclear magnetic resonance (ss MAS NMR) for geopolymers containing high amounts of waste (10-20%wt). The results show the formation of a stable matrix after only 15 days independently on the waste amount introduced; the longer curing times increase the matrices stabilities and their ability to immobilize chromium cations. The maximum amount of waste that can be inertized is around 10 wt% after a curing time of 28 days.

  10. Complex-energy approach to sum rules within nuclear density functional theory

    NASA Astrophysics Data System (ADS)

    Hinohara, Nobuo; Kortelainen, Markus; Nazarewicz, Witold; Olsen, Erik

    2015-04-01

    Background: The linear response of the nucleus to an external field contains unique information about the effective interaction, the correlations governing the behavior of the many-body system, and the properties of its excited states. To characterize the response, it is useful to use its energy-weighted moments, or sum rules. By comparing computed sum rules with experimental values, the information content of the response can be utilized in the optimization process of the nuclear Hamiltonian or the nuclear energy density functional (EDF). But the additional information comes at a price: compared to the ground state, computation of excited states is more demanding. Purpose: To establish an efficient framework to compute energy-weighted sum rules of the response that is adaptable to the optimization of the nuclear EDF and large-scale surveys of collective strength, we have developed a new technique within the complex-energy finite-amplitude method (FAM) based on the quasiparticle random-phase approximation (QRPA). Methods: To compute sum rules, we carry out contour integration of the response function in the complex-energy plane. We benchmark our results against the conventional matrix formulation of the QRPA theory, the Thouless theorem for the energy-weighted sum rule, and the dielectric theorem for the inverse-energy-weighted sum rule. Results: We derive the sum-rule expressions from the contour integration of the complex-energy FAM. We demonstrate that calculated sum-rule values agree with those obtained from the matrix formulation of the QRPA. We also discuss the applicability of both the Thouless theorem about the energy-weighted sum rule and the dielectric theorem for the inverse-energy-weighted sum rule to nuclear density functional theory in cases when the EDF is not based on a Hamiltonian. Conclusions: The proposed sum-rule technique based on the complex-energy FAM is a tool of choice when optimizing effective interactions or energy functionals. The method

  11. Asymptotic analysis of the density of states in random matrix models associated with a slowly decaying weight

    NASA Astrophysics Data System (ADS)

    Kuijlaars, A. B. J.

    2001-08-01

    The asymptotic behavior of polynomials that are orthogonal with respect to a slowly decaying weight is very different from the asymptotic behavior of polynomials that are orthogonal with respect to a Freud-type weight. While the latter has been extensively studied, much less is known about the former. Following an earlier investigation into the zero behavior, we study here the asymptotics of the density of states in a unitary ensemble of random matrices with a slowly decaying weight. This measure is also naturally connected with the orthogonal polynomials. It is shown that, after suitable rescaling, the weak limit is the same as the weak limit of the rescaled zeros.

  12. Development of tough, low-density titanium-based bulk metallic glass matrix composites with tensile ductility

    PubMed Central

    Hofmann, Douglas C.; Suh, Jin-Yoo; Wiest, Aaron; Lind, Mary-Laura; Demetriou, Marios D.; Johnson, William L.

    2008-01-01

    The mechanical properties of bulk metallic glasses (BMGs) and their composites have been under intense investigation for many years, owing to their unique combination of high strength and elastic limit. However, because of their highly localized deformation mechanism, BMGs are typically considered to be brittle materials and are not suitable for structural applications. Recently, highly-toughened BMG composites have been created in a Zr–Ti-based system with mechanical properties comparable with high-performance crystalline alloys. In this work, we present a series of low-density, Ti-based BMG composites with combinations of high strength, tensile ductility, and excellent fracture toughness. PMID:19074287

  13. A MinMax self-consistent-field approach for auxiliary density functional theory.

    PubMed

    Köster, Andreas M; Del Campo, Jorge M; Janetzko, Florian; Zuniga-Gutierrez, Bernardo

    2009-03-21

    A MinMax self-consistent-field (SCF) approach is derived in the framework of auxiliary density functional theory. It is shown that the SCF convergence can be guided by the fitting coefficients that arise from the variational fitting of the Coulomb potential. An in-core direct inversion of the iterative subspace (DIIS) algorithm is presented. Due to its reduced memory demand this new in-core DIIS method can be applied without overhead to very large systems with tens of thousands of basis and auxiliary functions. Due to the new DIIS error definition systems with fractional occupation numbers can be treated, too.

  14. A Dynamic Density Functional Theory Approach to Diffusion in White Dwarfs and Neutron Star Envelopes

    NASA Astrophysics Data System (ADS)

    Diaw, A.; Murillo, M. S.

    2016-09-01

    We develop a multicomponent hydrodynamic model based on moments of the Born-Bogolyubov-Green-Kirkwood-Yvon hierarchy equations for physical conditions relevant to astrophysical plasmas. These equations incorporate strong correlations through a density functional theory closure, while transport enters through a relaxation approximation. This approach enables the introduction of Coulomb coupling correction terms into the standard Burgers equations. The diffusive currents for these strongly coupled plasmas is self-consistently derived. The settling of impurities and its impact on cooling can be greatly affected by strong Coulomb coupling, which we show can be quantified using the direct correlation function.

  15. A self-assembling peptide matrix used to control stiffness and binding site density supports the formation of microvascular networks in three dimensions

    PubMed Central

    Stevenson, M.D.; Piristine, H.; Hogrebe, N.J.; Nocera, T.M.; Boehm, M.W.; Reen, R.K.; Koelling, K.W.; Agarwal, G.; Sarang-Sieminski, A.L.; Gooch, K.J.

    2015-01-01

    A three-dimensional (3-D) cell culture system that allows control of both substrate stiffness and integrin binding density was created and characterized. This system consisted of two self-assembling peptide (SAP) sequences that were mixed in different ratios to achieve the desired gel stiffness and adhesiveness. The specific peptides used were KFE ((acetyl)-FKFEFKFE-CONH2), which has previously been reported not to support cell adhesion or MVN formation, and KFE-RGD ((acetyl)-GRGDSP-GG-FKFEFKFE-CONH2), which is a similar sequence that incorporates the RGD integrin binding site. Storage modulus for these gels ranged from ~60 to 6000 Pa, depending on their composition and concentration. Atomic force microscopy revealed ECM-like fiber microarchitecture of gels consisting of both pure KFE and pure KFE-RGD as well as mixtures of the two peptides. This system was used to study the contributions of both matrix stiffness and adhesiveness on microvascular network (MVN) formation of endothelial cells and the morphology of human mesenchymal stem cells (hMSC). When endothelial cells were encapsulated within 3-D gel matrices without binding sites, little cell elongation and no network formation occurred, regardless of the stiffness. In contrast, matrices containing the RGD binding site facilitated robust MVN formation, and the extent of this MVN formation was inversely proportional to matrix stiffness. Compared with a matrix of the same stiffness with no binding sites, a matrix containing RGD-functionalized peptides resulted in a ~2.5-fold increase in the average length of network structure, which was used as a quantitative measure of MVN formation. Matrices with hMSC facilitated an increased number and length of cellular projections at higher stiffness when RGD was present, but induced a round morphology at every stiffness when RGD was absent. Taken together, these results demonstrate the ability to control both substrate stiffness and binding site density within 3-D cell

  16. An alternative approach for assessment of liquid chromatography-mass spectrometry matrix effects using auto-sampler programmed co-injection.

    PubMed

    Rogers, Caitlyn A; Stockham, Peter C; Nash, Christine M; Martin, Sheridan M; Kostakis, Chris; Lenehan, Claire E

    2016-03-01

    We report the use of auto-sampler programmable functions to co-inject analyte standard solution and matrix extract to assess ion enhancement and suppression (matrix effects) in LC-MS. This is effectively an automated post-extraction addition (APEA) procedure, emulating the manual post-extraction addition (PEA) approach widely adopted for assessment of matrix effects. To verify that APEA was comparable to the conventional PEA approach, matrix effects were determined using both methods for a selection of 31 illicit and pharmaceutical drugs in 10 different human urine extracts. Matrix effects measured using APEA were statistically indistinguishable from manual PEA methodology for 27 of the 31 drugs. Of the four drugs that showed significant differences using the two methods, three differed by less than 2 %, which is within the expected accuracy limits required for matrix effect determinations. The remaining analyte, trimeprazine, was found to degrade in the spiked PEA matrix extract, accounting for the difference between matrix effects measured by the PEA and APEA approaches. APEA enables a single matrix extract to be assessed at multiple analyte concentrations, resulting in a considerable reduction in sample preparation time. In addition, APEA can reduce the quantity of analyte-free sample matrix required for matrix effect assessment, which is an important consideration in certain analytical and bioanalytical fields. This work shows that APEA may be considered as an acceptable alternative to PEA for the assessment of matrix effects in LC-MS method validation and may be applicable to a variety of matrices such as environmental samples.

  17. Teaching the Extracellular Matrix and Introducing Online Databases within a Multidisciplinary Course with i-Cell-MATRIX: A Student-Centered Approach

    ERIC Educational Resources Information Center

    Sousa, Joao Carlos; Costa, Manuel Joao; Palha, Joana Almeida

    2010-01-01

    The biochemistry and molecular biology of the extracellular matrix (ECM) is difficult to convey to students in a classroom setting in ways that capture their interest. The understanding of the matrix's roles in physiological and pathological conditions study will presumably be hampered by insufficient knowledge of its molecular structure.…

  18. Disposable polymeric high-density nanovial arrays for matrix assisted laser desorption/ionization-time of flight-mass spectrometry: I. Microstructure development and manufacturing.

    PubMed

    Marko-Varga, G; Ekstrom, S; Heildin, G; Nilsson, J; Laureli, T

    2001-10-01

    In order to meet the expected enormous demand for mass spectrometry (MS) throughput as a result of the current efforts to completely map the human proteome, this paper presents a new concept for low-cost high-throughput protein identification by matrix assisted laser desorption/ionization-time of flight-(MALDI-TOF)-MS peptide mapping using disposable polymeric high-density nanovial MALDI target plates. By means of microfabrication technology precision engineered nanovial arrays are fabricated in polymer substrates such as polymethylmethacrylate (PMMA) and polycarbonate (PC). The target plate fabrication processes investigated were precision micromilling, cold embossing and injection moulding (work in progress). Nanovial dimensions were 300, 400 or 500 microm. Typical array densities were 165 nanovials/cm2, which corresponds to 3,300 vials on a full Applied Biosystems MALDI target plate. Obtained MALDI data displayed equal mass resolution, accuracy, signal intensity for peptide standards as compared to high-density silicon nanovial arrays previously reported by our group [7], as well as conventional stainless steel or gold targets. PMID:11700729

  19. Activation of Yes-Associated Protein in Low-Grade Meningiomas Is Regulated by Merlin, Cell Density, and Extracellular Matrix Stiffness.

    PubMed

    Tanahashi, Kuniaki; Natsume, Atsushi; Ohka, Fumiharu; Motomura, Kazuya; Alim, Adiljan; Tanaka, Ichidai; Senga, Takeshi; Harada, Ichiro; Fukuyama, Ryuichi; Sumiyoshi, Naoyuki; Sekido, Yoshitaka; Wakabayashi, Toshihiko

    2015-07-01

    The NF2 gene product Merlin is a protein containing ezrin, radixin, and moesin domains; it is a member of the 4.1 protein superfamily associated with the membrane cytoskeleton and also interacts with cell surface molecules. The mammalian Hippo cascade, a downstream signaling cascade of merlin, inactivates the Yes-associated protein (YAP). Yes-associated protein is activated by loss of the NF2 gene and functions as an oncogene in meningioma cells; however, the factors controlling YAP expression, phosphorylation, and subcellular localization in meningiomas have not been fully elucidated. Here, we demonstrate that merlin expression is heterogeneous in 1 NF2 gene-negative and 3 NF2 gene-positive World Health Organization grade I meningiomas. In the NF2 gene-positive meningiomas, regions with low levels of merlin (tumor rims) had greater numbers of cells with nuclear YAP versus regions with high merlin levels (tumor cores). Merlin expression and YAP phosphorylation were also affected by cell density in the IOMM-Lee and HKBMM human meningioma cell lines; nuclear localization of YAP was regulated by cell density and extracellular matrix (ECM) stiffness in IOMM-Lee cells. These results suggest that cell density and ECM stiffness may contribute to the heterogeneous loss of merlin and increased nuclear YAP expression in human meningiomas.

  20. Applications of a Novel Clustering Approach Using Non-Negative Matrix Factorization to Environmental Research in Public Health

    PubMed Central

    Fogel, Paul; Gaston-Mathé, Yann; Hawkins, Douglas; Fogel, Fajwel; Luta, George; Young, S. Stanley

    2016-01-01

    Often data can be represented as a matrix, e.g., observations as rows and variables as columns, or as a doubly classified contingency table. Researchers may be interested in clustering the observations, the variables, or both. If the data is non-negative, then Non-negative Matrix Factorization (NMF) can be used to perform the clustering. By its nature, NMF-based clustering is focused on the large values. If the data is normalized by subtracting the row/column means, it becomes of mixed signs and the original NMF cannot be used. Our idea is to split and then concatenate the positive and negative parts of the matrix, after taking the absolute value of the negative elements. NMF applied to the concatenated data, which we call PosNegNMF, offers the advantages of the original NMF approach, while giving equal weight to large and small values. We use two public health datasets to illustrate the new method and compare it with alternative clustering methods, such as K-means and clustering methods based on the Singular Value Decomposition (SVD) or Principal Component Analysis (PCA). With the exception of situations where a reasonably accurate factorization can be achieved using the first SVD component, we recommend that the epidemiologists and environmental scientists use the new method to obtain clusters with improved quality and interpretability. PMID:27213413

  1. Comparing Tehran STOCK Exchange as AN Emerging Market with a Mature Market by Random Matrix Approach

    NASA Astrophysics Data System (ADS)

    Namaki, A.; Raei, R.; Jafari, G. R.

    We analyze cross-correlation between return fluctuations of stocks of an emerging market by using random matrix theory (RMT). We test the statistics of eigenvalues of cross-correlation (C) between stocks of the Tehran Price Index (TEPIX) as an emerging market and compare these with a mature market (US market). According to the "null hypothesis," a random correlation matrix constructed from mutually uncorrelated time series, the deviation from the Gaussian orthogonal ensemble of RTM is a good criterion. We find that a majority of the eigenvalues of C fall within the bulk (RMT bounds between λ+ and λ-) for the eigenvalues of the random correlation matrices. Further, we find that the distribution of eigenvector components for the eigenvectors corresponding to the largest deviating eigenvalues, display systematic deviations from the RMT prediction. Analyzing the components of the deviating eigenvectors by Inverse Participation Ratio, leads us to know that the largest eigenvalue corresponds to an influence common to the whole market. Our analysis of the other deviating eigenvectors shows distinct industries, whose identities corresponds to the structure of the Iran business environment.

  2. Approach to kinetic energy density functionals: Nonlocal terms with the structure of the von Weizsaecker functional

    SciTech Connect

    Garcia-Aldea, David; Alvarellos, J. E.

    2008-02-15

    We propose a kinetic energy density functional scheme with nonlocal terms based on the von Weizsaecker functional, instead of the more traditional approach where the nonlocal terms have the structure of the Thomas-Fermi functional. The proposed functionals recover the exact kinetic energy and reproduce the linear response function of homogeneous electron systems. In order to assess their quality, we have tested the total kinetic energies as well as the kinetic energy density for atoms. The results show that these nonlocal functionals give as good results as the most sophisticated functionals in the literature. The proposed scheme for constructing the functionals means a step ahead in the field of fully nonlocal kinetic energy functionals, because they are capable of giving better local behavior than the semilocal functionals, yielding at the same time accurate results for total kinetic energies. Moreover, the functionals enjoy the possibility of being evaluated as a single integral in momentum space if an adequate reference density is defined, and then quasilinear scaling for the computational cost can be achieved.

  3. Neural network approach to quantum-chemistry data: Accurate prediction of density functional theory energies

    NASA Astrophysics Data System (ADS)

    Balabin, Roman M.; Lomakina, Ekaterina I.

    2009-08-01

    Artificial neural network (ANN) approach has been applied to estimate the density functional theory (DFT) energy with large basis set using lower-level energy values and molecular descriptors. A total of 208 different molecules were used for the ANN training, cross validation, and testing by applying BLYP, B3LYP, and BMK density functionals. Hartree-Fock results were reported for comparison. Furthermore, constitutional molecular descriptor (CD) and quantum-chemical molecular descriptor (QD) were used for building the calibration model. The neural network structure optimization, leading to four to five hidden neurons, was also carried out. The usage of several low-level energy values was found to greatly reduce the prediction error. An expected error, mean absolute deviation, for ANN approximation to DFT energies was 0.6±0.2 kcal mol-1. In addition, the comparison of the different density functionals with the basis sets and the comparison of multiple linear regression results were also provided. The CDs were found to overcome limitation of the QD. Furthermore, the effective ANN model for DFT/6-311G(3df,3pd) and DFT/6-311G(2df,2pd) energy estimation was developed, and the benchmark results were provided.

  4. Likelihood approaches for the invariant density ratio model with biased-sampling data

    PubMed Central

    Shen, Yu; Ning, Jing; Qin, Jing

    2012-01-01

    The full likelihood approach in statistical analysis is regarded as the most efficient means for estimation and inference. For complex length-biased failure time data, computational algorithms and theoretical properties are not readily available, especially when a likelihood function involves infinite-dimensional parameters. Relying on the invariance property of length-biased failure time data under the semiparametric density ratio model, we present two likelihood approaches for the estimation and assessment of the difference between two survival distributions. The most efficient maximum likelihood estimators are obtained by the em algorithm and profile likelihood. We also provide a simple numerical method for estimation and inference based on conditional likelihood, which can be generalized to k-arm settings. Unlike conventional survival data, the mean of the population failure times can be consistently estimated given right-censored length-biased data under mild regularity conditions. To check the semiparametric density ratio model assumption, we use a test statistic based on the area between two survival distributions. Simulation studies confirm that the full likelihood estimators are more efficient than the conditional likelihood estimators. We analyse an epidemiological study to illustrate the proposed methods. PMID:23843663

  5. The local projection in the density functional theory plus U approach: A critical assessment

    NASA Astrophysics Data System (ADS)

    Wang, Yue-Chao; Chen, Ze-Hua; Jiang, Hong

    2016-04-01

    Density-functional theory plus the Hubbard U correction (DFT + U) method is widely used in first-principles studies of strongly correlated systems, as it can give qualitatively (and sometimes, semi-quantitatively) correct description of energetic and structural properties of many strongly correlated systems with similar computational cost as local density approximation or generalized gradient approximation. On the other hand, the DFT + U approach is limited both theoretically and practically in several important aspects. In particular, the results of DFT + U often depend on the choice of local orbitals (the local projection) defining the subspace in which the Hubbard U correction is applied. In this work we have systematically investigated the issue of the local projection by considering typical transition metal oxides, β-MnO2 and MnO, and comparing the results obtained from different implementations of DFT + U. We found that the choice of the local projection has significant effects on the DFT + U results, which are more significant for systems with stronger covalent bonding (e.g., MnO2) than those with more ionic bonding (e.g., MnO). These findings can help to clarify some confusion arising from the practical use of DFT + U and may also provide insights for the development of new first-principles approaches beyond DFT + U.

  6. The local projection in the density functional theory plus U approach: A critical assessment.

    PubMed

    Wang, Yue-Chao; Chen, Ze-Hua; Jiang, Hong

    2016-04-14

    Density-functional theory plus the Hubbard U correction (DFT + U) method is widely used in first-principles studies of strongly correlated systems, as it can give qualitatively (and sometimes, semi-quantitatively) correct description of energetic and structural properties of many strongly correlated systems with similar computational cost as local density approximation or generalized gradient approximation. On the other hand, the DFT + U approach is limited both theoretically and practically in several important aspects. In particular, the results of DFT + U often depend on the choice of local orbitals (the local projection) defining the subspace in which the Hubbard U correction is applied. In this work we have systematically investigated the issue of the local projection by considering typical transition metal oxides, β-MnO2 and MnO, and comparing the results obtained from different implementations of DFT + U. We found that the choice of the local projection has significant effects on the DFT + U results, which are more significant for systems with stronger covalent bonding (e.g., MnO2) than those with more ionic bonding (e.g., MnO). These findings can help to clarify some confusion arising from the practical use of DFT + U and may also provide insights for the development of new first-principles approaches beyond DFT + U. PMID:27083707

  7. A kinetic approach to modeling the manufacture of high density strucutral foam: Foaming and polymerization

    SciTech Connect

    Rao, Rekha R.; Mondy, Lisa Ann; Noble, David R.; Brunini, Victor; Roberts, Christine Cardinal; Long, Kevin Nicholas; Soehnel, Melissa Marie; Celina, Mathias C.; Wyatt, Nicholas B.; Thompson, Kyle R.; Tinsley, James

    2015-09-01

    We are studying PMDI polyurethane with a fast catalyst, such that filling and polymerization occur simultaneously. The foam is over-packed to tw ice or more of its free rise density to reach the density of interest. Our approach is to co mbine model development closely with experiments to discover new physics, to parameterize models and to validate the models once they have been developed. The model must be able to repres ent the expansion, filling, curing, and final foam properties. PMDI is chemically blown foam, wh ere carbon dioxide is pr oduced via the reaction of water and isocyanate. The isocyanate also re acts with polyol in a competing reaction, which produces the polymer. A new kinetic model is developed and implemented, which follows a simplified mathematical formalism that decouple s these two reactions. The model predicts the polymerization reaction via condensation chemis try, where vitrification and glass transition temperature evolution must be included to correctly predict this quantity. The foam gas generation kinetics are determined by tracking the molar concentration of both water and carbon dioxide. Understanding the therma l history and loads on the foam due to exothermicity and oven heating is very important to the results, since the kinetics and ma terial properties are all very sensitive to temperature. The conservation eq uations, including the e quations of motion, an energy balance, and thr ee rate equations are solved via a stabilized finite element method. We assume generalized-Newtonian rheology that is dependent on the cure, gas fraction, and temperature. The conservation equations are comb ined with a level set method to determine the location of the free surface over time. Results from the model are compared to experimental flow visualization data and post-te st CT data for the density. Seve ral geometries are investigated including a mock encapsulation part, two configur ations of a mock stru ctural part, and a bar geometry to

  8. Towards a filtered density function approach for reactive transport in groundwater

    NASA Astrophysics Data System (ADS)

    Suciu, N.; Schüler, L.; Attinger, S.; Knabner, P.

    2016-04-01

    Evolution equations for probability density functions (PDFs) and filtered density functions (FDFs) of random species concentrations weighted by conserved scalars are formulated as Fokker-Planck equations describing stochastically equivalent processes in concentration-position spaces. This approach provides consistent numerical PDF/FDF solutions, given by the density in the concentration-position space of an ensemble of computational particles governed by the associated Itô equations. The solutions are obtained by a global random walk (GRW) algorithm, which is stable, free of numerical diffusion, and practically insensitive to the increase of the number of particles. The general FDF approach and the GRW numerical solution are illustrated for a reduced complexity problem consisting of the transport of a single scalar in groundwater. Randomness is induced by the stochastic parameterization of the hydraulic conductivity, characterized by short range correlations and small variance. The objective is to infer the statistics of the random concentration sampled at the plume center of mass, integrated over the transverse dimension of a two-dimensional spatial domain. The PDF/FDF problem can therefore be formulated in a two-dimensional domain as well, a spatial dimension and one in the concentration space. The upscaled drift and diffusion coefficients describing the PDF transport in the physical space are estimated on single-trajectories of diffusion in velocity fields with short-range correlations, owing to their self-averaging property. The mixing coefficients describing the PDF transport in concentration spaces are parameterized by the trend and the noise inferred from the statistical analysis of an ensemble of simulated concentration time series, as well as by classical mixing models. A Gaussian spatial filter applied to a Kraichnan velocity field generator is used to construct coarse-grained simulations (CGS) for FDF problems. The purposes of the CGS simulations are

  9. Enhanced Constraints for Accurate Lower Bounds on Many-Electron Quantum Energies from Variational Two-Electron Reduced Density Matrix Theory

    NASA Astrophysics Data System (ADS)

    Mazziotti, David A.

    2016-10-01

    A central challenge of physics is the computation of strongly correlated quantum systems. The past ten years have witnessed the development and application of the variational calculation of the two-electron reduced density matrix (2-RDM) without the wave function. In this Letter we present an orders-of-magnitude improvement in the accuracy of 2-RDM calculations without an increase in their computational cost. The advance is based on a low-rank, dual formulation of an important constraint on the 2-RDM, the T 2 condition. Calculations are presented for metallic chains and a cadmium-selenide dimer. The low-scaling T 2 condition will have significant applications in atomic and molecular, condensed-matter, and nuclear physics.

  10. Optical properties of crystalline and amorphous silicon slabs with adsorbed metal clusters and with dopants: A combined ab-initio electronic structure and density matrix treatment

    NASA Astrophysics Data System (ADS)

    Kilin, Dimitri; Micha, David; Ramirez, Jessica

    2011-03-01

    The optical absorbance and surface photovoltage of slabs of Si with varying number of layers have been calculated starting from their atomic structure. Results have been obtained for nanostructured surfaces with adsorbed metal clusters and for group III and V dopants, from ab initio DFT with periodic boundary conditions for extended systems, and from time-dependent DFT for supercells. Density matrix equations of motion (EOM) have been parametrized in a basis set of Kohn-Sham orbitals, for both crystalline and amorphous Si slabs. Results for properties and from electronic charge distributions provide insight on slab confinement effects for electronically excited states and for particle-hole creation. In addition, the integrodifferential EOMs have been solved for an initial femtosecond pulse excitation to analyze the nature of electron transfer at the surfaces, relevant to photovoltaics. Work supported by the NSF and by the Dreyfus Foundation to DM.

  11. Biomaterials approaches to modeling macrophage-extracellular matrix interactions in the tumor microenvironment.

    PubMed

    Springer, Nora L; Fischbach, Claudia

    2016-08-01

    Tumors are characterized by aberrant extracellular matrix (ECM) remodeling and chronic inflammation. While advances in biomaterials and tissue engineering strategies have led to important new insights regarding the role of ECM composition, structure, and mechanical properties in cancer in general, the functional link between these parameters and macrophage phenotype is poorly understood. Nevertheless, increasing experimental evidence suggests that macrophage behavior is similarly controlled by physicochemical properties of the ECM and consequential changes in mechanosignaling. Here, we will summarize the current knowledge of macrophage biology and ECM-mediated differences in mechanotransduction and discuss future opportunities of biomaterials and tissue engineering platforms to interrogate the functional relationship between these parameters and their relevance to cancer. PMID:26921768

  12. Transfer matrix approach for the Kerr and Faraday rotation in layered nanostructures

    NASA Astrophysics Data System (ADS)

    Széchenyi, Gábor; Vigh, Máté; Kormányos, Andor; Cserti, József

    2016-09-01

    To study the optical rotation of the polarization of light incident on multilayer systems consisting of atomically thin conductors and dielectric multilayers we present a general method based on transfer matrices. The transfer matrix of the atomically thin conducting layer is obtained using the Maxwell equations. We derive expressions for the Kerr (Faraday) rotation angle and for the ellipticity of the reflected (transmitted) light as a function of the incident angle and polarization of the light. The method is demonstrated by calculating the Kerr (Faraday) angle for bilayer graphene in the quantum anomalous Hall state placed on the top of dielectric multilayers. The optical conductivity of the bilayer graphene is calculated in the framework of a four-band model.

  13. Biomaterials approaches to modeling macrophage-extracellular matrix interactions in the tumor microenvironment.

    PubMed

    Springer, Nora L; Fischbach, Claudia

    2016-08-01

    Tumors are characterized by aberrant extracellular matrix (ECM) remodeling and chronic inflammation. While advances in biomaterials and tissue engineering strategies have led to important new insights regarding the role of ECM composition, structure, and mechanical properties in cancer in general, the functional link between these parameters and macrophage phenotype is poorly understood. Nevertheless, increasing experimental evidence suggests that macrophage behavior is similarly controlled by physicochemical properties of the ECM and consequential changes in mechanosignaling. Here, we will summarize the current knowledge of macrophage biology and ECM-mediated differences in mechanotransduction and discuss future opportunities of biomaterials and tissue engineering platforms to interrogate the functional relationship between these parameters and their relevance to cancer.

  14. An inner-outer nonlinear programming approach for constrained quadratic matrix model updating

    NASA Astrophysics Data System (ADS)

    Andretta, M.; Birgin, E. G.; Raydan, M.

    2016-01-01

    The Quadratic Finite Element Model Updating Problem (QFEMUP) concerns with updating a symmetric second-order finite element model so that it remains symmetric and the updated model reproduces a given set of desired eigenvalues and eigenvectors by replacing the corresponding ones from the original model. Taking advantage of the special structure of the constraint set, it is first shown that the QFEMUP can be formulated as a suitable constrained nonlinear programming problem. Using this formulation, a method based on successive optimizations is then proposed and analyzed. To avoid that spurious modes (eigenvectors) appear in the frequency range of interest (eigenvalues) after the model has been updated, additional constraints based on a quadratic Rayleigh quotient are dynamically included in the constraint set. A distinct practical feature of the proposed method is that it can be implemented by computing only a few eigenvalues and eigenvectors of the associated quadratic matrix pencil.

  15. An NDE approach for characterizing quality problems in polymer matrix composites

    NASA Technical Reports Server (NTRS)

    Roth, Don J.; Baaklini, George Y.; Sutter, James K.; Bodis, James R.; Leonhardt, Todd A.; Crane, Elizabeth A.

    1994-01-01

    Polymer matrix composite (PMC) materials are periodically identified appearing optically uniform but containing a higher than normal level of global nonuniformity as indicated from preliminary ultrasonic scanning. One such panel was thoroughly examined by nondestructive (NDE) and destructive methods to quantitatively characterize the nonuniformity. The NDE analysis of the panel was complicated by the fact that the panel was not uniformly thick. Mapping of ultrasonic velocity across a region of the panel in conjunction with an error analysis was necessary to (1) characterize properly the porosity gradient that was discovered during destructive analyses and (2) account for the thickness variation effects. Based on this study, a plan for future NDE characterization of PMC's is presented to the PMC community.

  16. A micro to macro approach to polymer matrix composites damage modeling : final LDRD report.

    SciTech Connect

    English, Shawn Allen; Brown, Arthur A.; Briggs, Timothy M.

    2013-12-01

    Capabilities are developed, verified and validated to generate constitutive responses using material and geometric measurements with representative volume elements (RVE). The geometrically accurate RVEs are used for determining elastic properties and damage initiation and propagation analysis. Finite element modeling of the meso-structure over the distribution of characterizing measurements is automated and various boundary conditions are applied. Plain and harness weave composites are investigated. Continuum yarn damage, softening behavior and an elastic-plastic matrix are combined with known materials and geometries in order to estimate the macroscopic response as characterized by a set of orthotropic material parameters. Damage mechanics and coupling effects are investigated and macroscopic material models are demonstrated and discussed. Prediction of the elastic, damage, and failure behavior of woven composites will aid in macroscopic constitutive characterization for modeling and optimizing advanced composite systems.

  17. Transfer matrix approach for the Kerr and Faraday rotation in layered nanostructures.

    PubMed

    Széchenyi, Gábor; Vigh, Máté; Kormányos, Andor; Cserti, József

    2016-09-21

    To study the optical rotation of the polarization of light incident on multilayer systems consisting of atomically thin conductors and dielectric multilayers we present a general method based on transfer matrices. The transfer matrix of the atomically thin conducting layer is obtained using the Maxwell equations. We derive expressions for the Kerr (Faraday) rotation angle and for the ellipticity of the reflected (transmitted) light as a function of the incident angle and polarization of the light. The method is demonstrated by calculating the Kerr (Faraday) angle for bilayer graphene in the quantum anomalous Hall state placed on the top of dielectric multilayers. The optical conductivity of the bilayer graphene is calculated in the framework of a four-band model.

  18. Predicting critical temperatures of iron(II) spin crossover materials: density functional theory plus U approach.

    PubMed

    Zhang, Yachao

    2014-12-01

    A first-principles study of critical temperatures (T(c)) of spin crossover (SCO) materials requires accurate description of the strongly correlated 3d electrons as well as much computational effort. This task is still a challenge for the widely used local density or generalized gradient approximations (LDA/GGA) and hybrid functionals. One remedy, termed density functional theory plus U (DFT+U) approach, introduces a Hubbard U term to deal with the localized electrons at marginal computational cost, while treats the delocalized electrons with LDA/GGA. Here, we employ the DFT+U approach to investigate the T(c) of a pair of iron(II) SCO molecular crystals (α and β phase), where identical constituent molecules are packed in different ways. We first calculate the adiabatic high spin-low spin energy splitting ΔE(HL) and molecular vibrational frequencies in both spin states, then obtain the temperature dependent enthalpy and entropy changes (ΔH and ΔS), and finally extract T(c) by exploiting the ΔH/T - T and ΔS - T relationships. The results are in agreement with experiment. Analysis of geometries and electronic structures shows that the local ligand field in the α phase is slightly weakened by the H-bondings involving the ligand atoms and the specific crystal packing style. We find that this effect is largely responsible for the difference in T(c) of the two phases. This study shows the applicability of the DFT+U approach for predicting T(c) of SCO materials, and provides a clear insight into the subtle influence of the crystal packing effects on SCO behavior.

  19. Predicting critical temperatures of iron(II) spin crossover materials: Density functional theory plus U approach

    SciTech Connect

    Zhang, Yachao

    2014-12-07

    A first-principles study of critical temperatures (T{sub c}) of spin crossover (SCO) materials requires accurate description of the strongly correlated 3d electrons as well as much computational effort. This task is still a challenge for the widely used local density or generalized gradient approximations (LDA/GGA) and hybrid functionals. One remedy, termed density functional theory plus U (DFT+U) approach, introduces a Hubbard U term to deal with the localized electrons at marginal computational cost, while treats the delocalized electrons with LDA/GGA. Here, we employ the DFT+U approach to investigate the T{sub c} of a pair of iron(II) SCO molecular crystals (α and β phase), where identical constituent molecules are packed in different ways. We first calculate the adiabatic high spin-low spin energy splitting ΔE{sub HL} and molecular vibrational frequencies in both spin states, then obtain the temperature dependent enthalpy and entropy changes (ΔH and ΔS), and finally extract T{sub c} by exploiting the ΔH/T − T and ΔS − T relationships. The results are in agreement with experiment. Analysis of geometries and electronic structures shows that the local ligand field in the α phase is slightly weakened by the H-bondings involving the ligand atoms and the specific crystal packing style. We find that this effect is largely responsible for the difference in T{sub c} of the two phases. This study shows the applicability of the DFT+U approach for predicting T{sub c} of SCO materials, and provides a clear insight into the subtle influence of the crystal packing effects on SCO behavior.

  20. Recursive mass matrix factorization and inversion: An operator approach to open- and closed-chain multibody dynamics

    NASA Technical Reports Server (NTRS)

    Rodriguez, G.; Kreutz, K.

    1988-01-01

    This report advances a linear operator approach for analyzing the dynamics of systems of joint-connected rigid bodies.It is established that the mass matrix M for such a system can be factored as M=(I+H phi L)D(I+H phi L) sup T. This yields an immediate inversion M sup -1=(I-H psi L) sup T D sup -1 (I-H psi L), where H and phi are given by known link geometric parameters, and L, psi and D are obtained recursively by a spatial discrete-step Kalman filter and by the corresponding Riccati equation associated with this filter. The factors (I+H phi L) and (I-H psi L) are lower triangular matrices which are inverses of each other, and D is a diagonal matrix. This factorization and inversion of the mass matrix leads to recursive algortihms for forward dynamics based on spatially recursive filtering and smoothing. The primary motivation for advancing the operator approach is to provide a better means to formulate, analyze and understand spatial recursions in multibody dynamics. This is achieved because the linear operator notation allows manipulation of the equations of motion using a very high-level analytical framework (a spatial operator algebra) that is easy to understand and use. Detailed lower-level recursive algorithms can readily be obtained for inspection from the expressions involving spatial operators. The report consists of two main sections. In Part 1, the problem of serial chain manipulators is analyzed and solved. Extensions to a closed-chain system formed by multiple manipulators moving a common task object are contained in Part 2. To retain ease of exposition in the report, only these two types of multibody systems are considered. However, the same methods can be easily applied to arbitrary multibody systems formed by a collection of joint-connected regid bodies.

  1. Authorship matrix: a rational approach to quantify individual contributions and responsibilities in multi-author scientific articles.

    PubMed

    Clement, T Prabhakar

    2014-06-01

    We propose a rational method for addressing an important question-who deserves to be an author of a scientific article? We review various contentious issues associated with this question and recommend that the scientific community should view authorship in terms of contributions and responsibilities, rather than credits. We propose a new paradigm that conceptually divides a scientific article into four basic elements: ideas, work, writing, and stewardship. We employ these four fundamental elements to modify the well-known International Committee of Medical Journal Editors (ICMJE) authorship guidelines. The modified ICMJE guidelines are then used as the basis to develop an approach to quantify individual contributions and responsibilities in multi-author articles. The outcome of the approach is an authorship matrix, which can be used to answer several nagging questions related to authorship.

  2. A signal processing approach for enhanced Acoustic Emission data analysis in high activity systems: Application to organic matrix composites

    NASA Astrophysics Data System (ADS)

    Kharrat, M.; Ramasso, E.; Placet, V.; Boubakar, M. L.

    2016-03-01

    Structural elements made of Organic Matrix Composites (OMC) under complex loading may suffer from high Acoustic Emission (AE) activity caused by the emergence of different emission sources at high rates with high noise level, which finally engender continuous emissions. The detection of hits in this situation becomes a challenge particularly during fatigue tests. This work suggests an approach based on the Discrete Wavelet Transform (DWT) denoising applied on signal segments. A particular attention is paid to the adjustment of the denoising parameters based on pencil lead breaks and their influence on the quality of the denoised AE signals. The validation of the proposed approach is performed on a ring-shaped Carbon Fiber Reinforced Plastics (CFRP) under in-service-like conditions involving continuous emissions with superimposed damage-related transients. It is demonstrated that errors in hit detection are greatly reduced leading to a better identification of the natural damage scenario based on AE signals.

  3. Nanofiber–microsphere (nano-micro) matrices for bone regenerative engineering: a convergence approach toward matrix design

    PubMed Central

    Nelson, Clarke; Khan, Yusuf; Laurencin, Cato T.

    2014-01-01

    Bone is an essential organ for health and quality of life. Due to current shortfalls in therapy for bone tissue engineering, scientists have sought the application of synthetic materials as bone graft substitutes. As a composite organic/inorganic material with significant extra cellular matrix (ECM), one way to improve bone graft substitutes may be to engineer a synthetic matrix that is influenced by the physical appearance of natural ECM networks. In this work, the authors evaluate composite, hybrid scaffolds for bone tissue engineering based on composite ceramic/polymer microsphere scaffolds with synthetic ECM-mimetic networks in their pore spaces. Using thermally induced phase separation, nanoscale fibers were deposited in the pore spaces of structurally sound microsphere-based scaffold with a density proportionate to the initial polymer concentration. Porosimetry and mechanical testing indicated no significant changes in overall pore characteristics or mechanical integrity as a result of the fiber deposition process. These scaffolds displayed adequate mechanical integrity on the scale of human trabecular bone and supported the adhesion and proliferation of cultured mouse calvarial osteoblasts. Drawing from natural cues, these scaffolds may represent a new avenue forward for advanced bone tissue engineering scaffolds. PMID:26816620

  4. Statistical Analysis of the Figure of Merit of a Two-Level Thermoelectric System: A Random Matrix Approach

    NASA Astrophysics Data System (ADS)

    Abbout, Adel; Ouerdane, Henni; Goupil, Christophe

    2016-09-01

    Using the tools of random matrix theory we develop a statistical analysis of the transport properties of thermoelectric low-dimensional systems made of two electron reservoirs set at different temperatures and chemical potentials, and connected through a low-density-of-states two-level quantum dot that acts as a conducting chaotic cavity. Our exact treatment of the chaotic behavior in such devices lies on the scattering matrix formalism and yields analytical expressions for the joint probability distribution functions of the Seebeck coefficient and the transmission profile, as well as the marginal distributions, at arbitrary Fermi energy. The scattering matrices belong to circular ensembles which we sample to numerically compute the transmission function, the Seebeck coefficient, and their relationship. The exact transport coefficients probability distributions are found to be highly non-Gaussian for small numbers of conduction modes, and the analytical and numerical results are in excellent agreement. The system performance is also studied, and we find that the optimum performance is obtained for half-transparent quantum dots; further, this optimum may be enhanced for systems with few conduction modes.

  5. A mixed basis density functional approach for one-dimensional systems with B-splines

    NASA Astrophysics Data System (ADS)

    Ren, Chung-Yuan; Chang, Yia-Chung; Hsue, Chen-Shiung

    2016-05-01

    A mixed basis approach based on density functional theory is extended to one-dimensional (1D) systems. The basis functions here are taken to be the localized B-splines for the two finite non-periodic dimensions and the plane waves for the third periodic direction. This approach will significantly reduce the number of the basis and therefore is computationally efficient for the diagonalization of the Kohn-Sham Hamiltonian. For 1D systems, B-spline polynomials are particularly useful and efficient in two-dimensional spatial integrations involved in the calculations because of their absolute localization. Moreover, B-splines are not associated with atomic positions when the geometry structure is optimized, making the geometry optimization easy to implement. With such a basis set we can directly calculate the total energy of the isolated system instead of using the conventional supercell model with artificial vacuum regions among the replicas along the two non-periodic directions. The spurious Coulomb interaction between the charged defect and its repeated images by the supercell approach for charged systems can also be avoided. A rigorous formalism for the long-range Coulomb potential of both neutral and charged 1D systems under the mixed basis scheme will be derived. To test the present method, we apply it to study the infinite carbon-dimer chain, graphene nanoribbon, carbon nanotube and positively-charged carbon-dimer chain. The resulting electronic structures are presented and discussed in detail.

  6. Gauge cooling for the singular-drift problem in the complex Langevin method — a test in Random Matrix Theory for finite density QCD

    NASA Astrophysics Data System (ADS)

    Nagata, Keitaro; Nishimura, Jun; Shimasaki, Shinji

    2016-07-01

    Recently, the complex Langevin method has been applied successfully to finite density QCD either in the deconfinement phase or in the heavy dense limit with the aid of a new technique called the gauge cooling. In the confinement phase with light quarks, however, convergence to wrong limits occurs due to the singularity in the drift term caused by small eigenvalues of the Dirac operator including the mass term. We propose that this singular-drift problem should also be overcome by the gauge cooling with different criteria for choosing the complexified gauge transformation. The idea is tested in chiral Random Matrix Theory for finite density QCD, where exact results are reproduced at zero temperature with light quarks. It is shown that the gauge cooling indeed changes drastically the eigenvalue distribution of the Dirac operator measured during the Langevin process. Despite its non-holomorphic nature, this eigenvalue distribution has a universal diverging behavior at the origin in the chiral limit due to a generalized Banks-Casher relation as we confirm explicitly.

  7. Toward Reliable Prediction of Hyperfine Coupling Constants Using Ab Initio Density Matrix Renormalization Group Method: Diatomic (2)Σ and Vinyl Radicals as Test Cases.

    PubMed

    Lan, Tran Nguyen; Kurashige, Yuki; Yanai, Takeshi

    2014-05-13

    The density matrix renormalization group (DMRG) method is used in conjunction with the complete active space (CAS) procedure, the CAS configuration interaction (CASCI), and the CAS self-consistent field (CASSCF) to evaluate hyperfine coupling constants (HFCCs) for a series of diatomic (2)Σ radicals (BO, CO(+), CN, and AlO) and vinyl (C2H3) radical. The electron correlation effects on the computed HFCC values were systematically investigated using various levels of active space, which were increasingly extended from single valence space to large-size model space entailing double valence and at least single polarization shells. In addition, the core correlation was treated by including the core orbitals in active space. Reasonably accurate results were obtained by the DMRG-CASSCF method involving orbital optimization, while DMRG-CASCI calculations with Hartree-Fock orbitals provided poor agreement of the HFCCs with the experimental values. To achieve further insights into the accuracy of HFCC calculations, the orbital contributions to the total spin density were analyzed at a given nucleus, which is directly related to the FC term and is numerically sensitive to the level of correlation treatment and basis sets. The convergence of calculated HFCCs with an increasing number of renormalized states was also assessed. This work serves as the first study on the performance of the ab initio DMRG method for HFCC prediction.

  8. SURVEY DESIGN FOR SPECTRAL ENERGY DISTRIBUTION FITTING: A FISHER MATRIX APPROACH

    SciTech Connect

    Acquaviva, Viviana; Gawiser, Eric; Bickerton, Steven J.; Grogin, Norman A.; Guo Yicheng; Lee, Seong-Kook

    2012-04-10

    The spectral energy distribution (SED) of a galaxy contains information on the galaxy's physical properties, and multi-wavelength observations are needed in order to measure these properties via SED fitting. In planning these surveys, optimization of the resources is essential. The Fisher Matrix (FM) formalism can be used to quickly determine the best possible experimental setup to achieve the desired constraints on the SED-fitting parameters. However, because it relies on the assumption of a Gaussian likelihood function, it is in general less accurate than other slower techniques that reconstruct the probability distribution function (PDF) from the direct comparison between models and data. We compare the uncertainties on SED-fitting parameters predicted by the FM to the ones obtained using the more thorough PDF-fitting techniques. We use both simulated spectra and real data, and consider a large variety of target galaxies differing in redshift, mass, age, star formation history, dust content, and wavelength coverage. We find that the uncertainties reported by the two methods agree within a factor of two in the vast majority ({approx}90%) of cases. If the age determination is uncertain, the top-hat prior in age used in PDF fitting to prevent each galaxy from being older than the universe needs to be incorporated in the FM, at least approximately, before the two methods can be properly compared. We conclude that the FM is a useful tool for astronomical survey design.

  9. Nanoscale viscoelasticity of extracellular matrix proteins in soft tissues: A multiscale approach.

    PubMed

    Miri, Amir K; Heris, Hossein K; Mongeau, Luc; Javid, Farhad

    2014-02-01

    It is hypothesized that the bulk viscoelasticity of soft tissues is determined by two length-scale-dependent mechanisms: the time-dependent response of the extracellular matrix (ECM) proteins at the nanometer scale and the biophysical interactions between the ECM solid structure and interstitial fluid at the micrometer scale. The latter is governed by poroelasticity theory assuming free motion of the interstitial fluid within the porous ECM structure. In a recent study (Heris, H.K., Miri, A.K., Tripathy, U., Barthelat, F., Mongeau, L., 2013. J. Mech. Behav. Biomed. Mater.), atomic force microscopy was used to measure the response of porcine vocal folds to a creep loading and a 50-nm sinusoidal oscillation. A constitutive model was calibrated and verified using a finite element model to accurately predict the nanoscale viscoelastic moduli of ECM. A generally good correlation was obtained between the predicted variation of the viscoelastic moduli with depth and that of hyaluronic acids in vocal fold tissue. We conclude that hyaluronic acids may regulate vocal fold viscoelasticity. The proposed methodology offers a characterization tool for biomaterials used in vocal fold augmentations.

  10. A Density Functional Approach to Para-hydrogen at Zero Temperature

    NASA Astrophysics Data System (ADS)

    Ancilotto, Francesco; Barranco, Manuel; Navarro, Jesús; Pi, Marti

    2016-10-01

    We have developed a density functional (DF) built so as to reproduce either the metastable liquid or the solid equation of state of bulk para-hydrogen, as derived from quantum Monte Carlo zero temperature calculations. As an application, we have used it to study the structure and energetics of small para-hydrogen clusters made of up to N=40 molecules. We compare our results for liquid clusters with diffusion Monte Carlo (DMC) calculations and find a fair agreement between them. In particular, the transition found within DMC between hollow-core structures for small N values and center-filled structures at higher N values is reproduced. The present DF approach yields results for (pH_2)_N clusters indicating that for small N values a liquid-like character of the clusters prevails, while solid-like clusters are instead energetically favored for N ≥ 15.

  11. Mixtures of ions and amphiphilic molecules in slit-like pores: A density functional approach

    SciTech Connect

    Pizio, O.; Rżysko, W. Sokołowski, S.; Sokołowska, Z.

    2015-04-28

    We investigate microscopic structure and thermodynamic properties of a mixture that contains amphiphilic molecules and charged hard spheres confined in slit-like pores with uncharged hard walls. The model and the density functional approach are the same as described in details in our previous work [Pizio et al., J. Chem. Phys. 140, 174706 (2014)]. Our principal focus is in exploring the effects brought by the presence of ions on the structure of confined amphiphilic particles. We have found that for some cases of anisotropic interactions, the change of the structure of confined fluids occurs via the first-order transitions. Moreover, if anions and cations are attracted by different hemispheres of amphiphiles, a charge at the walls appears at the zero value of the wall electrostatic potential. For a given thermodynamic state, this charge is an oscillating function of the pore width.

  12. Affinity Density: a novel genomic approach to the identification of transcription factor regulatory targets

    PubMed Central

    Hazelett, Dennis J.; Lakeland, Daniel L.; Weiss, Joseph B.

    2009-01-01

    Methods: A new method was developed for identifying novel transcription factor regulatory targets based on calculating Local Affinity Density. Techniques from the signal-processing field were used, in particular the Hann digital filter, to calculate the relative binding affinity of different regions based on previously published in vitro binding data. To illustrate this approach, the complete genomes of Drosophila melanogaster and D.pseudoobscura were analyzed for binding sites of the homeodomain proteinc Tinman, an essential heart development gene in both Drosophila and Mouse. The significant binding regions were identified relative to genomic background and assigned to putative target genes. Valid candidates common to both species of Drosophila were selected as a test of conservation. Results: The new method was more sensitive than cluster searches for conserved binding motifs with respect to positive identification of known Tinman targets. Our Local Affinity Density method also identified a significantly greater proportion of Tinman-coexpressed genes than equivalent, optimized cluster searching. In addition, this new method predicted a significantly greater than expected number of genes with previously published RNAi phenotypes in the heart. Availability: Algorithms were implemented in Python, LISP, R and maxima, using MySQL to access locally mirrored sequence data from Ensembl (D.melanogaster release 4.3) and flybase (D.pseudoobscura). All code is licensed under GPL and freely available at http://www.ohsu.edu/cellbio/dev_biol_prog/affinitydensity/. Contact: hazelett@ohsu.edu PMID:19401399

  13. Fully Internally Contracted Multireference Configuration Interaction Theory Using Density Matrix Renormalization Group: A Reduced-Scaling Implementation Derived by Computer-Aided Tensor Factorization.

    PubMed

    Saitow, Masaaki; Kurashige, Yuki; Yanai, Takeshi

    2015-11-10

    We present an extended implementation of the multireference configuration interaction (MRCI) method combined with the quantum-chemical density matrix renormalization group (DMRG). In the previous study, we introduced the combined theory, referred to as DMRGMRCI, as a method to calculate high-level dynamic electron correlation on top of the DMRG wave function that accounts for active-space (or strong) correlation using a large number of active orbitals. The DMRG-MRCI method is built on the full internal-contraction scheme for the compact reference treatment and on the cumulant approximation for the treatment of the four-particle rank reduced density matrix (4-RDM). The previous implementation achieved the MRCI calculations with the active space (24e,24o), which are deemed the record largest, whereas the inherent Nact 8 × N complexity of computation was found a hindrance to using further large active space. In this study, an extended optimization of the tensor contractions is developed by explicitly incorporating the rank reduction of the decomposed form of the cumulant-approximated 4-RDM into the factorization. It reduces the computational scaling (to Nact7 × N) as well as the cache-miss penalty associated with direct evaluation of complex cumulant reconstruction. The present scheme, however, faces the increased complexity of factorization patterns for optimally implementing the tensor contraction terms involving the decomposed 4-RDM objects. We address this complexity using the enhanced symbolic manipulation computer program for deriving and coding programmable equations. The new DMRG-MRCI implementation is applied to the determination of the stability of the iron(IV)-oxo porphyrin relative to the iron(V) electronic isomer (electromer) using the active space (29e,29o) (including four second d-shell orbitals of iron) with triple-ζ-quality atomic orbital basis sets. The DMRG-cu(4)-MRCI+Q model is shown to favor the triradicaloid iron(IV)-oxo state as the lowest

  14. Efficient Parallel All-Electron Four-Component Dirac-Kohn-Sham Program Using a Distributed Matrix Approach II.

    PubMed

    Storchi, Loriano; Rampino, Sergio; Belpassi, Leonardo; Tarantelli, Francesco; Quiney, Harry M

    2013-12-10

    We propose a new complete memory-distributed algorithm, which significantly improves the parallel implementation of the all-electron four-component Dirac-Kohn-Sham (DKS) module of BERTHA (J. Chem. Theory Comput. 2010, 6, 384). We devised an original procedure for mapping the DKS matrix between an efficient integral-driven distribution, guided by the structure of specific G-spinor basis sets and by density fitting algorithms, and the two-dimensional block-cyclic distribution scheme required by the ScaLAPACK library employed for the linear algebra operations. This implementation, because of the efficiency in the memory distribution, represents a leap forward in the applicability of the DKS procedure to arbitrarily large molecular systems and its porting on last-generation massively parallel systems. The performance of the code is illustrated by some test calculations on several gold clusters of increasing size. The DKS self-consistent procedure has been explicitly converged for two representative clusters, namely Au20 and Au34, for which the density of electronic states is reported and discussed. The largest gold cluster uses more than 39k basis functions and DKS matrices of the order of 23 GB. PMID:26592273

  15. Biomaterial arrays with defined adhesion ligand densities and matrix stiffness identify distinct phenotypes for tumorigenic and nontumorigenic human mesenchymal cell types

    PubMed Central

    Le, Ngoc Nhi; Nguyen, Eric H.; Zorn, Stefan; Parlato, Matthew; Loveland, Samuel G.; Schwartz, Michael P.; Murphy, William L.

    2014-01-01

    Here, we aimed to investigate migration of a model tumor cell line (HT-1080 fibrosarcoma cells, HT-1080s) using synthetic biomaterials to systematically vary peptide ligand density and substrate stiffness. A range of substrate elastic moduli were investigated by using poly(ethylene glycol) (PEG) hydrogel arrays (0.34 - 17 kPa) and self-assembled monolayer (SAM) arrays (~0.1-1 GPa), while cell adhesion was tuned by varying the presentation of Arg-Gly-Asp (RGD)-containing peptides. HT-1080 motility was insensitive to cell adhesion ligand density on RGD-SAMs, as they migrated with similar speed and directionality for a wide range of RGD densities (0.2-5% mol fraction RGD). Similarly, HT-1080 migration speed was weakly dependent on adhesion on 0.34 kPa PEG surfaces. On 13 kPa surfaces, a sharp initial increase in cell speed was observed at low RGD concentration, with no further changes observed as RGD concentration was increased further. An increase in cell speed ~ two-fold for the 13 kPa relative to the 0.34 kPa PEG surface suggested an important role for substrate stiffness in mediating motility, which was confirmed for HT-1080s migrating on variable modulus PEG hydrogels with constant RGD concentration. Notably, despite ~ two-fold changes in cell speed over a wide range of moduli, HT-1080s adopted rounded morphologies on all surfaces investigated, which contrasted with well spread primary human mesenchymal stem cells (hMSCs). Taken together, our results demonstrate that HT-1080s are morphologically distinct from primary mesenchymal cells (hMSCs) and migrate with minimal dependence on cell adhesion for surfaces within a wide range of moduli, whereas motility is strongly influenced by matrix mechanical properties. PMID:25386339

  16. Biomaterial arrays with defined adhesion ligand densities and matrix stiffness identify distinct phenotypes for tumorigenic and nontumorigenic human mesenchymal cell types.

    PubMed

    Hansen, Tyler D; Koepsel, Justin T; Le, Ngoc Nhi; Nguyen, Eric H; Zorn, Stefan; Parlato, Matthew; Loveland, Samuel G; Schwartz, Michael P; Murphy, William L

    2014-05-01

    Here, we aimed to investigate migration of a model tumor cell line (HT-1080 fibrosarcoma cells, HT-1080s) using synthetic biomaterials to systematically vary peptide ligand density and substrate stiffness. A range of substrate elastic moduli were investigated by using poly(ethylene glycol) (PEG) hydrogel arrays (0.34 - 17 kPa) and self-assembled monolayer (SAM) arrays (~0.1-1 GPa), while cell adhesion was tuned by varying the presentation of Arg-Gly-Asp (RGD)-containing peptides. HT-1080 motility was insensitive to cell adhesion ligand density on RGD-SAMs, as they migrated with similar speed and directionality for a wide range of RGD densities (0.2-5% mol fraction RGD). Similarly, HT-1080 migration speed was weakly dependent on adhesion on 0.34 kPa PEG surfaces. On 13 kPa surfaces, a sharp initial increase in cell speed was observed at low RGD concentration, with no further changes observed as RGD concentration was increased further. An increase in cell speed ~ two-fold for the 13 kPa relative to the 0.34 kPa PEG surface suggested an important role for substrate stiffness in mediating motility, which was confirmed for HT-1080s migrating on variable modulus PEG hydrogels with constant RGD concentration. Notably, despite ~ two-fold changes in cell speed over a wide range of moduli, HT-1080s adopted rounded morphologies on all surfaces investigated, which contrasted with well spread primary human mesenchymal stem cells (hMSCs). Taken together, our results demonstrate that HT-1080s are morphologically distinct from primary mesenchymal cells (hMSCs) and migrate with minimal dependence on cell adhesion for surfaces within a wide range of moduli, whereas motility is strongly influenced by matrix mechanical properties.

  17. Semisolid matrix filled capsules: an approach to improve dissolution stability of phenytoin sodium formulation.

    PubMed

    El Massik, M A; Abdallah, O Y; Galal, S; Daabis, N A

    2003-05-01

    Seven semisolid fill bases were selected for the formulation of 24 capsule formulations, each containing 100 mg of phenytoin sodium. The fill materials were selected based on the water absorption capacity of their mixtures with phenytoin sodium. The fill matrices included lipophilic bases (castor oil, soya oil, and Gelucire (G) 33/01), amphiphilic bases (G 44/14 and Suppocire BP), and water-soluble bases (PEG 4000 and PEG 6000). The drug:base ratio was 1:2. Excipients such as lecithin, docusate sodium, and poloxamer 188 were added to some formulations. The dissolution rate study indicated that formulations containing lipophilic and amphiphilic bases showed the best release profiles. These are F4 (castor oil-1% docusate sodium); F10 (castor oil-3% poloxamer 188); F14 (G33/01-10% lecithin); F17 (G33/01-1% docusate sodium), and F20 (Suppocire BP). Further, the dissolution stability of the five formulations above was assessed by an accelerated stability study at 30 degrees C and 75% RH using standard Epanutin capsules for comparison. The study included the test and standard capsules either packed in the container of marketed Epanutin capsules (packed) or removed from their outer pack (unpacked). Release data indicated superior release rates of castor oil based formulations (F4 and F10) relative to standard capsules in both the unpacked and packed forms. For instance, the extent of drug release at 30 min after 1 month was 91% for F4 and F10 and 20% for standard capsules. Drug release from packed capsules after 6 months storage was 88% for both formulations F4 and F10 and 35% for standard capsules. In conclusion, the pharmaceutical quality of phenytoin sodium capsules can be improved by using a semisolid lipophilic matrix filled in hard gelatin capsules. PMID:12779283

  18. Density functional theory approach to gold-ligand interactions: Separating true effects from artifacts

    NASA Astrophysics Data System (ADS)

    Koppen, Jessica V.; Hapka, Michał; Modrzejewski, Marcin; Szcześniak, Małgorzata M.; Chałasiński, Grzegorz

    2014-06-01

    Donor-acceptor interactions are notoriously difficult and unpredictable for conventional density functional theory (DFT) methodologies. This work presents a reliable computational treatment of gold-ligand interactions of the donor-acceptor type within DFT. These interactions require a proper account of the ionization potential of the electron donor and electron affinity of the electron acceptor. This is accomplished in the Generalized Kohn Sham framework that allows one to relate these properties to the frontier orbitals in DFT via the tuning of range-separated functionals. A donor and an acceptor typically require different tuning schemes. This poses a problem when the binding energies are calculated using the supermolecular method. A two-parameter tuning for the monomer properties ensures that a common functional, optimal for both the donor and the acceptor, is found. A reliable DFT approach for these interactions also takes into account the dispersion contribution. The approach is validated using the water dimer and the (HAuPH3)2 aurophilic complex. Binding energies are computed for Au4 interacting with the following ligands: SCN-, benzenethiol, benzenethiolate anion, pyridine, and trimethylphosphine. The results agree for the right reasons with coupled-cluster reference values.

  19. A numerical spectral approach to solve the dislocation density transport equation

    NASA Astrophysics Data System (ADS)

    Djaka, K. S.; Taupin, V.; Berbenni, S.; Fressengeas, C.

    2015-09-01

    A numerical spectral approach is developed to solve in a fast, stable and accurate fashion, the quasi-linear hyperbolic transport equation governing the spatio-temporal evolution of the dislocation density tensor in the mechanics of dislocation fields. The approach relies on using the Fast Fourier Transform algorithm. Low-pass spectral filters are employed to control both the high frequency Gibbs oscillations inherent to the Fourier method and the fast-growing numerical instabilities resulting from the hyperbolic nature of the transport equation. The numerical scheme is validated by comparison with an exact solution in the 1D case corresponding to dislocation dipole annihilation. The expansion and annihilation of dislocation loops in 2D and 3D settings are also produced and compared with finite element approximations. The spectral solutions are shown to be stable, more accurate for low Courant numbers and much less computation time-consuming than the finite element technique based on an explicit Galerkin-least squares scheme.

  20. Consumption of palatable food primes food approach behavior by rapidly increasing synaptic density in the VTA.

    PubMed

    Liu, Shuai; Globa, Andrea K; Mills, Fergil; Naef, Lindsay; Qiao, Min; Bamji, Shernaz X; Borgland, Stephanie L

    2016-03-01

    In an environment with easy access to highly palatable and energy-dense food, food-related cues drive food-seeking regardless of satiety, an effect that can lead to obesity. The ventral tegmental area (VTA) and its mesolimbic projections are critical structures involved in the learning of environmental cues used to predict motivationally relevant outcomes. Priming effects of food-related advertising and consumption of palatable food can drive food intake. However, the mechanism by which this effect occurs, and whether these priming effects last days after consumption, is unknown. Here, we demonstrate that short-term consumption of palatable food can prime future food approach behaviors and food intake. This effect is mediated by the strengthening of excitatory synaptic transmission onto dopamine neurons that is initially offset by a transient increase in endocannabinoid tone, but lasts days after an initial 24-h exposure to sweetened high-fat food (SHF). This enhanced synaptic strength is mediated by a long-lasting increase in excitatory synaptic density onto VTA dopamine neurons. Administration of insulin into the VTA, which suppresses excitatory synaptic transmission onto dopamine neurons, can abolish food approach behaviors and food intake observed days after 24-h access to SHF. These results suggest that even a short-term exposure to palatable foods can drive future feeding behavior by "rewiring" mesolimbic dopamine neurons. PMID:26884159

  1. Consumption of palatable food primes food approach behavior by rapidly increasing synaptic density in the VTA

    PubMed Central

    Liu, Shuai; Globa, Andrea K.; Mills, Fergil; Naef, Lindsay; Qiao, Min; Bamji, Shernaz X.; Borgland, Stephanie L.

    2016-01-01

    In an environment with easy access to highly palatable and energy-dense food, food-related cues drive food-seeking regardless of satiety, an effect that can lead to obesity. The ventral tegmental area (VTA) and its mesolimbic projections are critical structures involved in the learning of environmental cues used to predict motivationally relevant outcomes. Priming effects of food-related advertising and consumption of palatable food can drive food intake. However, the mechanism by which this effect occurs, and whether these priming effects last days after consumption, is unknown. Here, we demonstrate that short-term consumption of palatable food can prime future food approach behaviors and food intake. This effect is mediated by the strengthening of excitatory synaptic transmission onto dopamine neurons that is initially offset by a transient increase in endocannabinoid tone, but lasts days after an initial 24-h exposure to sweetened high-fat food (SHF). This enhanced synaptic strength is mediated by a long-lasting increase in excitatory synaptic density onto VTA dopamine neurons. Administration of insulin into the VTA, which suppresses excitatory synaptic transmission onto dopamine neurons, can abolish food approach behaviors and food intake observed days after 24-h access to SHF. These results suggest that even a short-term exposure to palatable foods can drive future feeding behavior by “rewiring” mesolimbic dopamine neurons. PMID:26884159

  2. A low-rank matrix recovery approach for energy efficient EEG acquisition for a wireless body area network.

    PubMed

    Majumdar, Angshul; Gogna, Anupriya; Ward, Rabab

    2014-01-01

    We address the problem of acquiring and transmitting EEG signals in Wireless Body Area Networks (WBAN) in an energy efficient fashion. In WBANs, the energy is consumed by three operations: sensing (sampling), processing and transmission. Previous studies only addressed the problem of reducing the transmission energy. For the first time, in this work, we propose a technique to reduce sensing and processing energy as well: this is achieved by randomly under-sampling the EEG signal. We depart from previous Compressed Sensing based approaches and formulate signal recovery (from under-sampled measurements) as a matrix completion problem. A new algorithm to solve the matrix completion problem is derived here. We test our proposed method and find that the reconstruction accuracy of our method is significantly better than state-of-the-art techniques; and we achieve this while saving sensing, processing and transmission energy. Simple power analysis shows that our proposed methodology consumes considerably less power compared to previous CS based techniques. PMID:25157551

  3. Scattering matrix approach to the dissociative recombination of HCO{sup +} and N{sub 2}H{sup +}

    SciTech Connect

    Fonseca dos Santos, S.; Douguet, N.; Orel, A. E.; Kokoouline, V.

    2014-04-28

    We present a theoretical study of the indirect dissociative recombination of linear polyatomic ions at low collisional energies. The approach is based on the computation of the scattering matrix just above the ionization threshold and enables the explicit determination of all diabatic electronic couplings responsible for dissociative recombination. In addition, we use the multi-channel quantum-defect theory to demonstrate the precision of the scattering matrix by reproducing accurately ab initio Rydberg state energies of the neutral molecule. We consider the molecular ions N{sub 2}H{sup +} and HCO{sup +} as benchmark systems of astrophysical interest and improve former theoretical studies, which had repeatedly produced smaller cross sections than experimentally measured. Specifically, we demonstrate the crucial role of the previously overlooked stretching modes for linear polyatomic ions with large permanent dipole moment. The theoretical cross sections for both ions agree well with experimental data over a wide energy range. Finally, we consider the potential role of the HOC{sup +} isomer in the experimental cross sections of HCO{sup +} at energies below 10 meV.

  4. Enhanced performance of mixed-matrix membranes through a graft copolymer-directed interface and interaction tuning approach.

    PubMed

    Chi, Won Seok; Kim, Sang Jin; Lee, Seung-Joon; Bae, Youn-Sang; Kim, Jong Hak

    2015-02-01

    Herein, a high performance mixed-matrix membrane (MMM) is reported with simultaneously large improvements in the CO2 permeability by 880 % from 70.2 to 687.7 Barrer (1 Barrer=1×10(-10)  cm(3)  cm cm(-2)  s(-1)  cmHg(-1) ) and CO2 /N2 selectivity by 14.4 % from 30.5 to 34.9. These findings represent one of the most dramatic improvements ever reported for MMMs. These improvements are obtained through an interface and interaction tuning approach based on an amphiphilic grafted copolymer. Poly(vinyl chloride)-g-poly(oxyethylene methacrylate) (PVC-g-POEM) graft copolymer plays a key role as a soft organic matrix to provide good permeation properties, uniform distribution of zeolite imidazole frameworks-8 (ZIF-8), and better interfacial contact with inorganic compounds. In particular, the CO2 /C3 H8 and CO2 /C3 H6 selectivities reached 10.5 and 42.7, respectively, for PVC-g-POEM/ZIF (40 %) MMMs; this indicates that it could be a promising membrane material for the purification of C3 hydrocarbons. PMID:25393936

  5. A Low-Rank Matrix Recovery Approach for Energy Efficient EEG Acquisition for a Wireless Body Area Network

    PubMed Central

    Majumdar, Angshul; Gogna, Anupriya; Ward, Rabab

    2014-01-01

    We address the problem of acquiring and transmitting EEG signals in Wireless Body Area Networks (WBAN) in an energy efficient fashion. In WBANs, the energy is consumed by three operations: sensing (sampling), processing and transmission. Previous studies only addressed the problem of reducing the transmission energy. For the first time, in this work, we propose a technique to reduce sensing and processing energy as well: this is achieved by randomly under-sampling the EEG signal. We depart from previous Compressed Sensing based approaches and formulate signal recovery (from under-sampled measurements) as a matrix completion problem. A new algorithm to solve the matrix completion problem is derived here. We test our proposed method and find that the reconstruction accuracy of our method is significantly better than state-of-the-art techniques; and we achieve this while saving sensing, processing and transmission energy. Simple power analysis shows that our proposed methodology consumes considerably less power compared to previous CS based techniques. PMID:25157551

  6. TH-A-BRF-01: A Probabilistic Bayesian Approach to Derive Electron Density From MRI for Radiation Therapy Treatment Planning

    SciTech Connect

    Gudur, M; Hara, W; Wang, L; Xing, L; Li, R

    2014-06-15

    Purpose: MRI significantly improves the accuracy and reliability of target delineation for patient simulation and treatment planning in radiation therapy, due to its superior soft tissue contrast as compared to CT. An MRI based simulation will reduce cost and simplify clinical workflow with zero ionizing radiation. However, MRI lacks the key electron density information. The purpose of this work is to develop a reliable method to derive electron density from MRI. Methods: We adopt a probabilistic Bayesian approach for electron density mapping based on T1-weighted head MRI. For each voxel, we compute conditional probability of electron densities given its: (1) T1 intensity and (2) geometry in a reference anatomy, obtained by deformable image registration between the MRI of test patient and atlas. Intensity and geometry information are combined into a unifying posterior probability density function whose mean gives the electron density. Mean absolute HU error between the estimated and true CT, as well as ROC's for bone detection (HU>200) were calculated for 8 patients. The performance was compared with a global intensity approach based on T1 and no density correction (set whole head to water). Results: The proposed technique significantly reduced the errors in electron density estimation, with a mean absolute HU error of 132, compared with 139 for deformable registration (p=10{sup −3}), 371 for the intensity approach (p=10{sup −5}) and 282 without density correction (p=2×10{sup −4}). For 90% sensitivity in bone detection, the proposed method had a specificity of 85% and that for deformable registration, intensity and without density correction are 80%, 24% and 10% respectively. Conclusion: The proposed unifying method provides accurate electron density estimation and bone detection from MRI of the head with highly heterogeneous regions. This paves the way for accurate dose calculation and generating reference images for patient setup in MRI-based treatment

  7. Detecting Cracks in Ceramic Matrix Composites by Electrical Resistance

    NASA Technical Reports Server (NTRS)

    Smith, Craig; Gyekenyesi, Andrew

    2011-01-01

    The majority of damage in SiC/SiC ceramic matrix composites subjected to monotonic tensile loads is in the form of distributed matrix cracks. These cracks initiate near stress concentrations, such as 90o fiber tows or large matrix pores and continue to accumulate with additional stress until matrix crack saturation is achieved. Such damage is difficult to detect with conventional nondestructive evaluation techniques (immersion ultrasonics, x-ray, etc.). Monitoring a specimen.s electrical resistance change provides an indirect approach for monitoring matrix crack density. Sylramic-iBN fiber- reinforced SiC composites with a melt infiltrated (MI) matrix were tensile tested at room temperature. Results showed an increase in resistance of more than 500% prior to fracture, which can be detected either in situ or post-damage. A relationship between resistance change and matrix crack density was also determined.

  8. Detecting Damage in Ceramic Matrix Composites Using Electrical Resistance

    NASA Technical Reports Server (NTRS)

    Smith, Craig E.; Gyekenyesi, Andrew

    2011-01-01

    The majority of damage in SiC/SiC ceramic matrix composites subjected to monotonic tensile loads is in the form of distributed matrix cracks. These cracks initiate near stress concentrations, such as 90 deg fiber tows or large matrix pores and continue to accumulate with additional stress until matrix crack saturation is achieved. Such damage is difficult to detect with conventional nondestructive evaluation techniques (immersion ultrasonics, x-ray, etc.). Monitoring a specimen.s electrical resistance change provides an indirect approach for monitoring matrix crack density. Sylramic-iBN fiber- reinforced SiC composites with a melt infiltrated (MI) matrix were tensile tested at room temperature. Results showed an increase in resistance of more than 500% prior to fracture, which can be detected either in situ or post-damage. A relationship between resistance change and matrix crack density was also determined.

  9. CheMPS2: A free open-source spin-adapted implementation of the density matrix renormalization group for ab initio quantum chemistry

    NASA Astrophysics Data System (ADS)

    Wouters, Sebastian; Poelmans, Ward; Ayers, Paul W.; Van Neck, Dimitri

    2014-06-01

    The density matrix renormalization group (DMRG) has become an indispensable numerical tool to find exact eigenstates of finite-size quantum systems with strong correlation. In the fields of condensed matter, nuclear structure and molecular electronic structure, it has significantly extended the system sizes that can be handled compared to full configuration interaction, without losing numerical accuracy. For quantum chemistry (QC), the most efficient implementations of DMRG require the incorporation of particle number, spin and point group symmetries in the underlying matrix product state (MPS) ansatz, as well as the use of so-called complementary operators. The symmetries introduce a sparse block structure in the MPS ansatz and in the intermediary contracted tensors. If a symmetry is non-abelian, the Wigner-Eckart theorem allows to factorize a tensor into a Clebsch-Gordan coefficient and a reduced tensor. In addition, the fermion signs have to be carefully tracked. Because of these challenges, implementing DMRG efficiently for QC is not straightforward. Efficient and freely available implementations are therefore highly desired. In this work we present CheMPS2, our free open-source spin-adapted implementation of DMRG for ab initio QC. Around CheMPS2, we have implemented the augmented Hessian Newton-Raphson complete active space self-consistent field method, with exact Hessian. The bond dissociation curves of the 12 lowest states of the carbon dimer were obtained at the DMRG(28 orbitals, 12 electrons, DSU(2) = 2500)/cc-pVDZ level of theory. The contribution of 1 s core correlation to the X1Σg+ bond dissociation curve of the carbon dimer was estimated by comparing energies at the DMRG(36o, 12e, DSU(2) = 2500)/cc-pCVDZ and DMRG-SCF(34o, 8e, DSU(2) = 2500)/cc-pCVDZ levels of theory.

  10. Matrix approach for modeling of emission from multilayer spin-polarized light-emitting diodes and lasers

    NASA Astrophysics Data System (ADS)

    Fördös, Tibor; Postava, Kamil; Jaffrès, Henri; Pištora, Jaromír

    2014-06-01

    Spin-polarized light sources such as the spin-polarized light-emitting diodes (spin-LEDs) and spin-polarized lasers (spin-lasers) are prospective devices in which the radiative recombination of spin-polarized carriers results in emission of circularly polarized photons. The main goal of this article is to model emitted radiation and its polarization properties from spin-LED and spin-controlled vertical-cavity surface-emitting laser (spin-VCSEL) solid-state structures. A novel approach based on 4 × 4 transfer matrix formalism is derived for modeling of the interaction of light with matter in active media of resonant multilayer anisotropic structure and enables magneto-optical effects. Quantum transitions, which result in photon emission, are described using general Jones source vectors.

  11. Differential cross sections, charge production asymmetry, and spin-density matrix elements for D ∗±(2010) produced in 500 GeV/ cπ--nucleon interactions

    NASA Astrophysics Data System (ADS)

    Aitala, E. M.; Amato, S.; Anjos, J. C.; Appel, J. A.; Ashery, D.; Banerjee, S.; Bediaga, I.; Blaylock, G.; Bracker, S. B.; Burchat, P. R.; Burnstein, R. A.; Carter, T.; Carvalho, H. S.; Copty, N. K.; Cremaldi, L. M.; Darling, C.; Denisenko, K.; Devmal, S.; Fernandez, A.; Fox, G. F.; Gagnon, P.; Gobel, C.; Gounder, K.; Halling, A. M.; Herrera, G.; Hurvits, G.; James, C.; Kasper, P. A.; Kwan, S.; Langs, D. C.; Leslie, J.; Lundberg, B.; Magnin, J.; Massafferri, A.; MayTal-Beck, S.; Meadows, B.; de Mello Neto, J. R. T.; Mihalcea, D.; Milburn, R. H.; de Miranda, J. M.; Napier, A.; Nguyen, A.; d'Oliveira, A. B.; O'Shaughnessy, K.; Peng, K. C.; Perera, L. P.; Purohit, M. V.; Quinn, B.; Radeztsky, S.; Rafatian, A.; Reay, N. W.; Reidy, J. J.; dos Reis, A. C.; Rubin, H. A.; Sanders, D. A.; Santha, A. K. S.; Santoro, A. F. S.; Schwartz, A. J.; Sheaff, M.; Sidwell, R. A.; Slaughter, A. J.; Sokoloff, M. D.; Solano Salinas, C. J.; Stanton, N. R.; Stefanski, R. J.; Stenson, K.; Summers, D. J.; Takach, S.; Thorne, K.; Tripathi, A. K.; Watanabe, S.; Weiss-Babai, R.; Wiener, J.; Witchey, N.; Wolin, E.; Yang, S. M.; Yi, D.; Yoshida, S.; Zaliznyak, R.; Zhang, C.; Fermilab E791 Collaboration

    2002-07-01

    We report differential cross sections for the production of D ∗±(2010) produced in 500 GeV/ cπ--nucleon interactions from experiment E791 at Fermilab, as functions of Feynman- x ( xF) and transverse momentum squared ( pT2). We also report the D ∗± charge asymmetry and spin-density matrix elements as functions of these variables. Investigation of the spin-density matrix elements shows no evidence of polarization. The average values of the spin alignment are < η>=0.01±0.02 and -0.01±0.02 for leading and non-leading particles, respectively.

  12. Reducing Complexity: A Regularized Non-negative Matrix Approximation (NNMA) Approach to X-ray Spectromicroscopy Analysis

    NASA Astrophysics Data System (ADS)

    Mak, Rachel Y. C.

    2014-09-01

    X-ray absorption spectromicroscopy combines microscopy and spectroscopy to provide rich information about the chemical organization of materials down to the nanoscale. But with richness also comes complexity: natural materials such as biological or environmental science specimens can be composed of complex spectroscopic mixtures of different materials. The challenge becomes how we could meaningfully simplify and interpret this information. Approaches such as principal component analysis and cluster analysis have been used in previous studies, but with some limitations that we will describe. This leads us to develop a new approach based on a development of non-negative matrix approximation (NNMA) analysis with both sparseness and spectra similarity regularizations. We apply this new technique to simulated spectromicroscopy datasets as well as a preliminary study of the large-scale biochemical organization of a human sperm cell. NNMA analysis is able to select major features of the sperm cell without the physically erroneous negative weightings or thicknesses in the calculated image which appeared in previous approaches.

  13. The Decision Support Matrix (DSM) Approach to Reducing Risk of Flooding and Water Pollution in Farmed Landscapes

    NASA Astrophysics Data System (ADS)

    Hewett, Caspar J. M.; Quinn, Paul; Wilkinson, Mark

    2014-05-01

    Intense farming plays a key role in contributing to problems such as increased flood risk, soil erosion and poor water quality. This means that there is great potential for agricultural practitioners to play a major part in reducing multiple risks through better land-use management. Greater understanding by farmers, land managers, practitioners and policy-makers of the ways in which farmed landscapes contribute to risks and the ways in which those risks might be mitigated can be an essential component in improving practice. The Decision Support Matrix (DSM) approach involves the development of a range of visualization and communication tools to help compare the risks associated with different farming practices and explore options to manage runoff. DSMs are simple decision support systems intended for use by the non-expert which combine expert hydrological evidence with local knowledge of runoff patterns. They are developed through direct engagement with stakeholders, ensuring that the examples and language used makes sense to end-users. A key element of the tools is that they show the current conditions of the land and describe extremes of land-use management within a hydrological and agricultural land-management context. The tools include conceptual models of a series of pre-determined runoff scenarios, providing the end-user with a variety of potential land management practices and runoff management options. Visual examples of different farming practices are used to illustrate the impact of good and bad practice on specific problems such as nutrient export or risk of flooding. These show both how current conditions cause problems downstream and how systems are vulnerable to changes in climate and land-use intensification. The level of risk associated with a particular land management option is represented by a mapping on a two- or three-dimensional matrix. Interactive spreadsheet-based tools are developed in which multiple questions allow the user to explore

  14. A New Approach to Minimize Acellular Dermal Matrix Use in Prosthesis-based Breast Reconstruction

    PubMed Central

    Hadad, Ivan; Liu, Allen S.

    2015-01-01

    Background: Acellular dermal matrices (ADMs) are often used to improve lower-pole contour, as well as allow for single-stage reconstruction, but numerous studies have shown an increased complication rate using ADM. As such, our group has developed a minimal-ADM-use technique to lower complications while effectively recreating lower-pole contour. Methods: A total of 380 postmastectomy prosthesis-based breast reconstructions were performed in 265 patients by a single surgeon. One hundred eight reconstructions were performed using the traditional ADM technique, with a large piece of ADM along the entire inferior and lateral borders. Two hundred twenty-five reconstructions were performed with the minimal-use technique, patching only the lateral area of the reconstruction. Thirty-five reconstructions were performed without the use of any ADM for high-risk reconstructions, most often in morbidly obese patients. Results: Comparing the traditional technique with the minimal-use technique, the seroma rate dropped from 3% to 0%. The rate of infection and reconstruction loss fell from 9% to 1%. Upon greatly reducing or eliminating the use of ADM use in obese patients, the seroma rate decreased from 15.4% to 5.7%, and the reconstruction loss rate decreased from 38% to 9%. Conclusions: This article describes a new surgical approach to minimize the amount of ADM necessary to create an aesthetically pleasing breast reconstruction. We believe that this approach helps avoid the complications of seroma, infection, and loss of the reconstruction. In certain obese patients, total avoidance of ADM may be the better choice. PMID:26301161

  15. A New Approach to Modeling Densities and Equilibria of Ice and Gas Hydrate Phases

    NASA Astrophysics Data System (ADS)

    Zyvoloski, G.; Lucia, A.; Lewis, K. C.

    2011-12-01

    , and NaCl in permafrost conditions are presented to illustrate the predictive capabilities of the multi-scale GHC equation. In particular, we show that the GHC equation correctly predicts 1) The density of 1h ice and methane hydrate to within 1%. 2) The melting curve for hexagonal ice. 3) The hydrate-gas phase co-existence curve. 4) Various phase equilibrium involving ice and hydrate phases. We also show that the GHC equation approach can be readily incorporated into subsurface flow simulation programs like FEHM to predict the behavior of permafrost and other reservoirs where ice and/or hydrates are present. Many geometric illustrations are used to elucidate key concepts. References A. Lucia, A Multi-Scale Gibbs Helmholtz Constrained Cubic Equation of State. J. Thermodynamics: Special Issue on Advances in Gas Hydrate Thermodynamics and Transport Properties. Available on-line [doi:10.1155/2010/238365]. A. Lucia, B.M. Bonk, A. Roy and R.R. Waterman, A Multi-Scale Framework for Multi-Phase Equilibrium Flash. Comput. Chem. Engng. In press.

  16. A regularized matrix factorization approach to induce structured sparse-low-rank solutions in the EEG inverse problem

    NASA Astrophysics Data System (ADS)

    Montoya-Martínez, Jair; Artés-Rodríguez, Antonio; Pontil, Massimiliano; Hansen, Lars Kai

    2014-12-01

    We consider the estimation of the Brain Electrical Sources (BES) matrix from noisy electroencephalographic (EEG) measurements, commonly named as the EEG inverse problem. We propose a new method to induce neurophysiological meaningful solutions, which takes into account the smoothness, structured sparsity, and low rank of the BES matrix. The method is based on the factorization of the BES matrix as a product of a sparse coding matrix and a dense latent source matrix. The structured sparse-low-rank structure is enforced by minimizing a regularized functional that includes the ℓ 21-norm of the coding matrix and the squared Frobenius norm of the latent source matrix. We develop an alternating optimization algorithm to solve the resulting nonsmooth-nonconvex minimization problem. We analyze the convergence of the optimization procedure, and we compare, under different synthetic scenarios, the performance of our method with respect to the Group Lasso and Trace Norm regularizers when they are applied directly to the target matrix.

  17. Energies and structures in biradical chemistry from the parametric two-electron reduced-density matrix method: applications to the benzene and cyclobutadiene biradicals.

    PubMed

    McManus, Alison L; Hoy, Erik P; Mazziotti, David A

    2015-05-21

    The treatment of biradical chemistry presents a challenge for electronic structure theory, especially single-reference methods, as it requires the description of varying degrees and kinds of electron correlation. In this work we assess the ability of the parametric two-electron reduced-density matrix (p2-RDM) method to describe biradical chemistry through application to the benzene and cyclobutadiene biradicals. The relative energy of o- and m-benzynes predicted by the p2-RDM method is consistent with Wenthold et al.'s experimental determinations, while the more difficult relative energy prediction of the more multi-referenced p-benzyne is within 1.4 kcal mol(-1) of the experimental value [P. G. Wenthold et al., J. Am. Chem. Soc., 1998, 120, 5279], which is significantly better than traditional single-reference methods. We observe that the degree of multireference correlation in the biradicals depends upon the distance between their radical centers, with the largest radical separation displaying the largest degree of multireference correlation. In addition to relative and absolute electronic energies, we report molecular geometries, natural orbitals, and natural-orbital occupations for the benzene and cyclobutadiene biradicals.

  18. Accurate prediction of diradical chemistry from a single-reference density-matrix method: Model application to the bicyclobutane to gauche-1,3-butadiene isomerization

    SciTech Connect

    Bertels, Luke W.; Mazziotti, David A.

    2014-07-28

    Multireference correlation in diradical molecules can be captured by a single-reference 2-electron reduced-density-matrix (2-RDM) calculation with only single and double excitations in the 2-RDM parametrization. The 2-RDM parametrization is determined by N-representability conditions that are non-perturbative in their treatment of the electron correlation. Conventional single-reference wave function methods cannot describe the entanglement within diradical molecules without employing triple- and potentially even higher-order excitations of the mean-field determinant. In the isomerization of bicyclobutane to gauche-1,3-butadiene the parametric 2-RDM (p2-RDM) method predicts that the diradical disrotatory transition state is 58.9 kcal/mol above bicyclobutane. This barrier is in agreement with previous multireference calculations as well as recent Monte Carlo and higher-order coupled cluster calculations. The p2-RDM method predicts the Nth natural-orbital occupation number of the transition state to be 0.635, revealing its diradical character. The optimized geometry from the p2-RDM method differs in important details from the complete-active-space self-consistent-field geometry used in many previous studies including the Monte Carlo calculation.

  19. Ionization and fragmentation of complex molecules studied with a density functional theory based approach

    NASA Astrophysics Data System (ADS)

    Kirchner, Tom

    2013-05-01

    Ion-impact induced ionization and fragmentation of complex molecules have important applications in many branches of science. If the molecule is H2O an obvious topic to address is the radiobiological relevance of these processes, e.g. in the context of hadron therapy, to name just one example. From a more fundamental physics viewpoint ion-molecule collision systems constitute interesting many-body systems, whose analysis poses challenges to both experimentalists and theorists. This talk will describe a theoretical approach to ion-molecule collisions, which is based on density functional theory to describe the nonperturbative electron dynamics. The basis generator method applied in the past successfully to ion-atom collisions is adapted to deal with the multi-center problem one faces when one considers molecular targets. Cross sections for single- and multiple-electron processes (capture and transfer to the continuum) are obtained directly from solving time-dependent Kohn-Sham-type orbital equations and using a Slater determinant based analysis. Fragmentation yields are predicted on the basis of a semi-phenomenological model which uses the calculated cross sections as input. Results will be presented for various ions impacting on water molecules in the energy range of 10-5000 keV/amu and compared with experimental data and previous theoretical calculations where available. First applications of the model to collisions involving CH4 molecules will also be discussed. This work has been supported by SHARCNET and NSERC Canada.

  20. Modeling solvation effects in real-space and real-time within density functional approaches

    SciTech Connect

    Delgado, Alain; Corni, Stefano; Pittalis, Stefano; Rozzi, Carlo Andrea

    2015-10-14

    The Polarizable Continuum Model (PCM) can be used in conjunction with Density Functional Theory (DFT) and its time-dependent extension (TDDFT) to simulate the electronic and optical properties of molecules and nanoparticles immersed in a dielectric environment, typically liquid solvents. In this contribution, we develop a methodology to account for solvation effects in real-space (and real-time) (TD)DFT calculations. The boundary elements method is used to calculate the solvent reaction potential in terms of the apparent charges that spread over the van der Waals solute surface. In a real-space representation, this potential may exhibit a Coulomb singularity at grid points that are close to the cavity surface. We propose a simple approach to regularize such singularity by using a set of spherical Gaussian functions to distribute the apparent charges. We have implemented the proposed method in the OCTOPUS code and present results for the solvation free energies and solvatochromic shifts for a representative set of organic molecules in water.

  1. Modeling solvation effects in real-space and real-time within density functional approaches

    NASA Astrophysics Data System (ADS)

    Delgado, Alain; Corni, Stefano; Pittalis, Stefano; Rozzi, Carlo Andrea

    2015-10-01

    The Polarizable Continuum Model (PCM) can be used in conjunction with Density Functional Theory (DFT) and its time-dependent extension (TDDFT) to simulate the electronic and optical properties of molecules and nanoparticles immersed in a dielectric environment, typically liquid solvents. In this contribution, we develop a methodology to account for solvation effects in real-space (and real-time) (TD)DFT calculations. The boundary elements method is used to calculate the solvent reaction potential in terms of the apparent charges that spread over the van der Waals solute surface. In a real-space representation, this potential may exhibit a Coulomb singularity at grid points that are close to the cavity surface. We propose a simple approach to regularize such singularity by using a set of spherical Gaussian functions to distribute the apparent charges. We have implemented the proposed method in the Octopus code and present results for the solvation free energies and solvatochromic shifts for a representative set of organic molecules in water.

  2. Advanced Ginzburg-Landau theory of freezing: A density-functional approach

    NASA Astrophysics Data System (ADS)

    Tóth, Gyula I.; Provatas, Nikolas

    2014-09-01

    This paper revisits the weakly fourth-order anisotropic Ginzburg-Landau (GL) theory of freezing (also known as the Landau-Brazowskii model or theory of weak crystallization) by comparing it to a recent density functional approach, the phase-field crystal (PFC) model. First we study the critical behavior of a generalized PFC model and show that (i) the so-called one-mode approximation is exact in the leading order, and (ii) the direct correlation function has no contribution to the phase diagram near the critical point. Next, we calculate the anisotropy of the crystal-liquid interfacial free energy in the phase-field crystal (PFC) model analytically. For comparison, we also determine the anisotropy numerically and show that no range of parameters can be found for which the phase-field crystal equation can quantitatively model anisotropy for metallic materials. Finally, we derive the leading order PFC amplitude model and show that it coincides with the weakly fourth-order anisotropic GL theory, as a consequence of the assumptions of the GL theory being inherent in the PFC model. We also propose a way to calibrate the anisotropy in the Ginzburg-Landau theory via a generalized gradient operator emerging from the direct correlation function appearing in the generating PFC free energy functional.

  3. Modeling solvation effects in real-space and real-time within density functional approaches.

    PubMed

    Delgado, Alain; Corni, Stefano; Pittalis, Stefano; Rozzi, Carlo Andrea

    2015-10-14

    The Polarizable Continuum Model (PCM) can be used in conjunction with Density Functional Theory (DFT) and its time-dependent extension (TDDFT) to simulate the electronic and optical properties of molecules and nanoparticles immersed in a dielectric environment, typically liquid solvents. In this contribution, we develop a methodology to account for solvation effects in real-space (and real-time) (TD)DFT calculations. The boundary elements method is used to calculate the solvent reaction potential in terms of the apparent charges that spread over the van der Waals solute surface. In a real-space representation, this potential may exhibit a Coulomb singularity at grid points that are close to the cavity surface. We propose a simple approach to regularize such singularity by using a set of spherical Gaussian functions to distribute the apparent charges. We have implemented the proposed method in the Octopus code and present results for the solvation free energies and solvatochromic shifts for a representative set of organic molecules in water. PMID:26472367

  4. Detection of soft tissue densities from digital breast tomosynthesis: comparison of conventional and deep learning approaches

    NASA Astrophysics Data System (ADS)

    Fotin, Sergei V.; Yin, Yin; Haldankar, Hrishikesh; Hoffmeister, Jeffrey W.; Periaswamy, Senthil

    2016-03-01

    Computer-aided detection (CAD) has been used in screening mammography for many years and is likely to be utilized for digital breast tomosynthesis (DBT). Higher detection performance is desirable as it may have an impact on radiologist's decisions and clinical outcomes. Recently the algorithms based on deep convolutional architectures have been shown to achieve state of the art performance in object classification and detection. Similarly, we trained a deep convolutional neural network directly on patches sampled from two-dimensional mammography and reconstructed DBT volumes and compared its performance to a conventional CAD algorithm that is based on computation and classification of hand-engineered features. The detection performance was evaluated on the independent test set of 344 DBT reconstructions (GE SenoClaire 3D, iterative reconstruction algorithm) containing 328 suspicious and 115 malignant soft tissue densities including masses and architectural distortions. Detection sensitivity was measured on a region of interest (ROI) basis at the rate of five detection marks per volume. Moving from conventional to deep learning approach resulted in increase of ROI sensitivity from 0:832 +/- 0:040 to 0:893 +/- 0:033 for suspicious ROIs; and from 0:852 +/- 0:065 to 0:930 +/- 0:046 for malignant ROIs. These results indicate the high utility of deep feature learning in the analysis of DBT data and high potential of the method for broader medical image analysis tasks.

  5. Two-electron R-matrix approach to calculations of potential-energy curves of long-range Rydberg molecules

    NASA Astrophysics Data System (ADS)

    Tarana, Michal; Čurík, Roman

    2016-05-01

    We introduce a computational method developed for study of long-range molecular Rydberg states of such systems that can be approximated by two electrons in a model potential of the atomic cores. The method is based on a two-electron R-matrix approach inside a sphere centered on one of the atoms. The wave function is then connected to a Coulomb region outside the sphere via a multichannel version of the Coulomb Green's function. This approach is applied to a study of Rydberg states of Rb2 for internuclear separations R from 40 to 320 bohrs and energies corresponding to n from 7 to 30. We report bound states associated with the low-lying 3Po resonance and with the virtual state of the rubidium atom that turn into ion-pair-like bound states in the Coulomb potential of the atomic Rydberg core. The results are compared with previous calculations based on single-electron models employing a zero-range contact-potential and short-range modele potential. Czech Science Foundation (Project No. P208/14-15989P).

  6. Phase-space densities and effects of resonance decays in a hydrodynamic approach to heavy ion collisions

    SciTech Connect

    Akkelin, S.V.; Sinyukov, Yu.M.

    2004-12-01

    A method allowing analysis of the overpopulation of phase space in heavy ion collisions in a model-independent way is proposed within the hydrodynamic approach. It makes it possible to extract a chemical potential of thermal pions at freeze-out, irrespective of the form of freeze-out (isothermal) hypersurface in Minkowski space and transverse flows on it. The contributions of resonance (with masses up to 2 GeV) decays to spectra, interferometry volumes, and phase-space densities are calculated and discussed in detail. The estimates of average phase-space densities and chemical potentials of thermal pions are obtained for SPS and RHIC energies. They demonstrate that multibosonic phenomena at those energies might be considered as a correction factor rather than as a significant physical effect. The analysis of the evolution of the pion average phase-space density in chemically frozen hadron systems shows that it is almost constant or slightly increases with time while the particle density and phase-space density at each space point decreases rapidly during the system's expansion. We found that, unlike the particle density, the average phase-space density has no direct link to the freeze-out criterion and final thermodynamic parameters, being connected rather to the initial phase-space density of hadronic matter formed in relativistic nucleus-nucleus collisions.

  7. Spike train statistics and dynamics with synaptic input from any renewal process: a population density approach.

    PubMed

    Ly, Cheng; Tranchina, Daniel

    2009-02-01

    In the probability density function (PDF) approach to neural network modeling, a common simplifying assumption is that the arrival times of elementary postsynaptic events are governed by a Poisson process. This assumption ignores temporal correlations in the input that sometimes have important physiological consequences. We extend PDF methods to models with synaptic event times governed by any modulated renewal process. We focus on the integrate-and-fire neuron with instantaneous synaptic kinetics and a random elementary excitatory postsynaptic potential (EPSP), A. Between presynaptic events, the membrane voltage, v, decays exponentially toward rest, while s, the time since the last synaptic input event, evolves with unit velocity. When a synaptic event arrives, v jumps by A, and s is reset to zero. If v crosses the threshold voltage, an action potential occurs, and v is reset to v(reset). The probability per unit time of a synaptic event at time t, given the elapsed time s since the last event, h(s, t), depends on specifics of the renewal process. We study how regularity of the train of synaptic input events affects output spike rate, PDF and coefficient of variation (CV) of the interspike interval, and the autocorrelation function of the output spike train. In the limit of a deterministic, clocklike train of input events, the PDF of the interspike interval converges to a sum of delta functions, with coefficients determined by the PDF for A. The limiting autocorrelation function of the output spike train is a sum of delta functions whose coefficients fall under a damped oscillatory envelope. When the EPSP CV, sigma A/mu A, is equal to 0.45, a CV for the intersynaptic event interval, sigma T/mu T = 0.35, is functionally equivalent to a deterministic periodic train of synaptic input events (CV = 0) with respect to spike statistics. We discuss the relevance to neural network simulations. PMID:19431264

  8. Approach to diagnosing celiac disease in patients with low bone mineral density or fragility fractures

    PubMed Central

    Rios, Lorena P.; Khan, Aliya; Sultan, Muhammad; McAssey, Karen; Fouda, Mona A.; Armstrong, David

    2013-01-01

    Abstract Objective To provide clinicians with an update on the diagnosis of celiac disease (CD) and to make recommendations on the indications to screen for CD in patients presenting with low bone mineral density (BMD) or fragility fractures. Quality of evidence A multidisciplinary task force developed clinically relevant questions related to the diagnosis of CD as the basis for a literature search of the MEDLINE, EMBASE, and CENTRAL databases (January 2000 to January 2009) using the key words celiac disease, osteoporosis, osteopenia, low bone mass, and fracture. The existing literature consists of level I and II studies. Main message The estimated prevalence of asymptomatic CD is 2% to 3% in individuals with low BMD. Routine screening for CD is not justified in patients with low BMD. However, targeted screening for CD is recommended for patients who have T-scores of −1.0 or less at the spine or hip, or a history of fragility fractures in association with any CD-related symptoms or conditions; family history of CD; or low urinary calcium levels, vitamin D insufficiency, and raised parathyroid hormone levels despite adequate intake of calcium and vitamin D. Celiac disease testing should be performed while the subject is consuming a gluten-containing diet; initial screening should be performed with human recombinant immunoglobulin (Ig) A tissue transglutaminase or other IgA tissue transglutaminase assays, in association with IgA endomysial antibody immunofluorescence. Duodenal biopsy is necessary to confirm the diagnosis of CD. Human leukocyte antigen typing might assist in confirming or ruling out the diagnosis of CD in cases where serology and histology are discordant. Definitive diagnosis is based on clinical, serologic, and histologic features, combined with a positive response to a gluten-free diet. Conclusion Current evidence does not support routine screening for CD in all patients with low BMD. A targeted case-finding approach is appropriate for patients

  9. Broken symmetry approach to density functional calculation of zero field splittings including anisotropic exchange interactions

    SciTech Connect

    Kessler, Eva M. V.; Schmitt, Sebastian; Wüllen, Christoph van

    2013-11-14

    The broken symmetry approach to the calculation of zero field splittings (or magnetic anisotropies) of multinuclear transition metal complexes is further developed. A procedure is suggested how to extract spin Hamiltonian parameters for anisotropic exchange from a set of broken symmetry density functional calculations. For isotropic exchange coupling constants J{sub ij}, the established procedure is retrieved, and anisotropic (or pseudodipolar) exchange coupling tensors D{sub ij} are obtained analogously. This procedure only yields the sum of the individual single-ion zero field splitting tensors D{sub i}. Therefore, a procedure based on localized orbitals has been developed to extract the individual single-ion contributions. With spin Hamiltonian parameters at hand, the zero field splittings of the individual spin multiplets are calculated by an exact diagonalization of the isotropic part, followed by a spin projection done numerically. The method is applied to the binuclear cation [LCr(OH){sub 3}CrL]{sup 3+} (L = 1,4,7-trimethyl-1,4,7-triazanonane) for which experimental zero field splittings for all low-energy spin states are known, and to the single-molecule magnet [Fe{sub 4}(CH{sub 3}C(CH{sub 2}O){sub 3}){sub 2}(dpm){sub 6}] (Hdpm = 2,2,6,6-tetramethylheptane-3,5-dione). In both these 3d compounds, the single-ion tensors mainly come from the spin-orbit interaction. Anisotropic exchange is dominated by the spin-dipolar interaction only for the chromium compound. Despite the rather small isotropic exchange couplings in the iron compound, spin-orbit and spin-dipolar contributions to anisotropic exchange are of similar size here.

  10. Effects of thermal cycling on density, elastic modulus, and vibrational damping in an alumina particulate reinforced aluminum metal matrix composite (Al{sub 2}O{sub 3p}/2014 Al)

    SciTech Connect

    Wolfenden, A.; Tang, H.H.; Chawla, K.; Hermel, T.

    1999-07-01

    The effects of thermal cycling on the mechanical and physical properties, namely, the density, dynamic elastic modulus and vibrational damping, were measured for a particular reinforced metal matrix composite (MMC). The material was made by Duralcan. Specimens were exposed to up thermal cycles from room temperature to 300 C. The density of the material was measured by the Archimedes technique. The dynamic Young`s Modulus and vibrational damping of the material were determined by the piezoelectric ultrasonic composite oscillator technique (PUCOT). The results showed that the density and elastic modulus of the material increased only slightly due to the thermal cycling while the damping increased significantly. An increase in dislocation concentration near the particle/matrix interfaces caused by the thermal cycling could account for the measured results.

  11. Data analysis techniques, differential cross sections, and spin density matrix elements for the reaction γp → Φp

    DOE PAGESBeta

    Dey, B.; Meyer, C. A.; Bellis, M.; Williams, M.; Adhikari, K. P.; Adikaram, D.; Aghasyan, M.; Amaryan, M. J.; Anderson, M. D.; Anefalos Pereira, S.; et al

    2014-05-27

    High-statistics measurements of differential cross sections and spin density matrix elements for the reaction γ p → Φp have been made using the CLAS detector at Jefferson Lab. We cover center-of-mass energies (√s) from 1.97 to 2.84 GeV, with an extensive coverage in the Φ production angle. The high statistics of the data sample made it necessary to carefully account for the interplay between the Φ natural lineshape and effects of the detector resolution, that are found to be comparable in magnitude. We study both the charged- (Φ → K⁺K⁻) and neutral- (Φ → K0SK0L)more » $$K\\bar{K}$$ decay modes of the Φ. Further, for the charged mode, we differentiate between the cases where the final K⁻ track is directly detected or its momentum reconstructed as the total missing momentum in the event. The two charged-mode topologies and the neutral-mode have different resolutions and are calibrated against each other. Extensive usage is made of kinematic fitting to improve the reconstructed Φ mass resolution. Our final results are reported in 10- and mostly 30-MeV-wide √s bins for the charged- and the neutral-mode, respectively. Possible effects from K⁺Λ* channels with p$$K\\bar{K}$$ final-states are discussed. These present results constitute the most precise and extensive Φ photoproduction measurements to date and in conjunction with the ω photoproduction results recently published by CLAS, will greatly improve our understanding of low energy vector meson photoproduction.« less

  12. Magnetic properties and pairing tendencies of the iron-based superconducting ladder BaFe2S3: Combined ab initio and density matrix renormalization group study

    DOE PAGESBeta

    Patel, Niravkumar D.; Nocera, Alberto; Alvarez, Gonzalo; Arita, Ryotaro; Moreo, Adriana; Dagotto, Elbio

    2016-08-10

    The recent discovery of superconductivity under high pressure in the two-leg ladder compound BaFe2S3 [H. Takahashi et al., Nat. Mater. 14, 1008 (2015)] opens a broad avenue of research, because it represents the first report of pairing tendencies in a quasi-one-dimensional iron-based high-critical-temperature superconductor. Similarly, as in the case of the cuprates, ladders and chains can be far more accurately studied using many-body techniques and model Hamiltonians than their layered counterparts, particularly if several orbitals are active. In this publication, we derive a two-orbital Hubbard model from first principles that describes individual ladders of BaFe2S3. The model is studied withmore » the density matrix renormalization group. These first reported results are exciting for two reasons: (i) at half-filling, ferromagnetic order emerges as the dominant magnetic pattern along the rungs of the ladder, and antiferromagnetic order along the legs, in excellent agreement with neutron experiments; and (ii) with hole doping, pairs form in the strong coupling regime, as found by studying the binding energy of two holes doped on the half-filled system. In addition, orbital selective Mott phase characteristics develop with doping, with only oneWannier orbital receiving the hole carriers while the other remains half-filled. Lastly, these results suggest that the analysis of models for iron-based two-leg ladders could clarify the origin of pairing tendencies and other exotic properties of iron-based high-critical-temperature superconductors in general.« less

  13. Magnetic properties and pairing tendencies of the iron-based superconducting ladder BaFe2S3 : Combined ab initio and density matrix renormalization group study

    NASA Astrophysics Data System (ADS)

    Patel, Niravkumar D.; Nocera, Alberto; Alvarez, Gonzalo; Arita, Ryotaro; Moreo, Adriana; Dagotto, Elbio

    2016-08-01

    The recent discovery of superconductivity under high pressure in the two-leg ladder compound BaFe2S3 [H. Takahashi et al., Nat. Mater. 14, 1008 (2015), 10.1038/nmat4351] opens a broad avenue of research, because it represents the first report of pairing tendencies in a quasi-one-dimensional iron-based high-critical-temperature superconductor. Similarly, as in the case of the cuprates, ladders and chains can be far more accurately studied using many-body techniques and model Hamiltonians than their layered counterparts, particularly if several orbitals are active. In this publication, we derive a two-orbital Hubbard model from first principles that describes individual ladders of BaFe2S3 . The model is studied with the density matrix renormalization group. These first reported results are exciting for two reasons: (i) at half-filling, ferromagnetic order emerges as the dominant magnetic pattern along the rungs of the ladder, and antiferromagnetic order along the legs, in excellent agreement with neutron experiments; and (ii) with hole doping, pairs form in the strong coupling regime, as found by studying the binding energy of two holes doped on the half-filled system. In addition, orbital selective Mott phase characteristics develop with doping, with only one Wannier orbital receiving the hole carriers while the other remains half-filled. These results suggest that the analysis of models for iron-based two-leg ladders could clarify the origin of pairing tendencies and other exotic properties of iron-based high-critical-temperature superconductors in general.

  14. Parametrization of the two-electron reduced density matrix for its direct calculation without the many-electron wave function: Generalizations and applications

    SciTech Connect

    Mazziotti, David A.

    2010-06-15

    An improved parametrization of the two-electron reduced density matrix (2-RDM) [D. A. Mazziotti, Phys. Rev. Lett. 101, 253002 (2008)] was recently shown to yield energies and properties that are markedly better than those calculated by traditional ab initio methods of similar computational scaling. In this paper a family of such energy functionals, generalizing the ones obtained previously, is derived through the use of (i) p-particle contraction relations based on the contraction of the cumulant expansions of p-particle RDMs and (ii) Cauchy-Schwarz relations that arise from an important set of N-representability constraints known as the two-positivity conditions. The 2-RDMs are explicitly parameterized in terms of the first-order part of the cumulant 2-RDM and, for the inclusion of single excitations, a second-order part of the 1-RDM. In contrast to earlier formulations based on the coefficients from configuration interaction with single and double excitations (CISD), the cumulant-based parametric 2-RDM methods, from the properties of cumulants, are rigorously size extensive. We also show that writing the energy functionals in terms of correlated 1-RDMs and cumulant 2-RDMs reduces the computational cost of the parametric 2-RDM methods to that of CISD. Applications are made to ground-state energies of several molecules, equilibrium bond distances, and frequencies of HF, F{sub 2}, and CO, the relative energy of the cis and trans isomers of HO{sub 3}{sup -}, and the HCN-HNC isomerization reaction. For bond breaking in hydrogen fluoride the improved and more efficient parametric 2-RDM methods yield energies with similar accuracies at both equilibrium and nonequilibrium geometries in 6-31G** and polarized valence quadruple-{zeta} basis sets. Computed 2-RDMs very nearly satisfy well-known N-representability conditions.

  15. Intermolecular forces and nonbonded interactions: Superoperator nonlinear time-dependent density-functional-theory response approach

    SciTech Connect

    Harbola, Upendra; Mukamel, Shaul

    2004-11-01

    Electrostatic and dispersive interactions of polarizable molecules are expressed in terms of generalized (nonretarded) charge-density response functions of the isolated molecules, which in turn are expanded using the collective electronic oscillator (CEO) eigenmodes of linearized time-dependent density-functional theory. Closed expressions for the intermolecular energy are derived to sixth order in charge fluctuation amplitudes.

  16. Promoting 6th Graders' Understanding of Density: A Computer Modeling Approach. Technical Report 86-5.

    ERIC Educational Resources Information Center

    Smith, Carol; And Others

    The concept of the density of a material has an important role in elementary and secondary school science curricula, but it is a difficult concept to grasp. This project explores why this should be and whether there are some simpler, more accessible notions which can serve as the basis for building a concept of density in students' minds during…

  17. Semiempirical Molecular Dynamics (SEMD) I: Midpoint-Based Parallel Sparse Matrix-Matrix Multiplication Algorithm for Matrices with Decay.

    PubMed

    Weber, Valéry; Laino, Teodoro; Pozdneev, Alexander; Fedulova, Irina; Curioni, Alessandro

    2015-07-14

    In this paper, we present a novel, highly efficient, and massively parallel implementation of the sparse matrix-matrix multiplication algorithm inspired by the midpoint method that is suitable for matrices with decay. Compared with the state of the art in sparse matrix-matrix multiplications, the new algorithm heavily exploits data locality, yielding better performance and scalability, approaching a perfect linear scaling up to a process box size equal to a characteristic length that is intrinsic to the matrices. Moreover, the method is able to scale linearly with system size reaching constant time with proportional resources, also regarding memory consumption. We demonstrate how the proposed method can be effectively used for the construction of the density matrix in electronic structure theory, such as Hartree-Fock, density functional theory, and semiempirical Hamiltonians. We present the details of the implementation together with a performance analysis up to 185,193 processes, employing a Hamiltonian matrix generated from a semiempirical NDDO scheme.

  18. Density measurements as a condition monitoring approach for following the aging of nuclear power plant cable materials

    NASA Astrophysics Data System (ADS)

    Gillen, K. T.; Celina, M.; Clough, R. L.

    1999-10-01

    Monitoring changes in material density has been suggested as a potentially useful condition monitoring (CM) method for following the aging of cable jacket and insulation materials in nuclear power plants. In this study, we compare density measurements and ultimate tensile elongation results versus aging time for most of the important generic types of commercial nuclear power plant cable materials. Aging conditions, which include thermal-only, as well as combined radiation plus thermal, were chosen such that potentially anomalous effects caused by diffusion-limited oxidation (DLO) are unimportant. The results show that easily measurable density increases occur in most important cable materials. For some materials and environments, the density change occurs at a fairly constant rate throughout the mechanical property lifetime. For cases involving so-called induction-time behavior, density increases are slow to moderate until after the induction time, at which point they begin to increase dramatically. In other instances, density increases rapidly at first, then slows down. The results offer strong evidence that density measurements, which reflect property changes under both radiation and thermal conditions, could represent a very useful CM approach.

  19. A Coordinated Approach to Curricular Review and Development in Undergraduate Geoscience Programs: Using a Matrix to Identify and Track Skills and Skill Development

    NASA Astrophysics Data System (ADS)

    MacDonald, R.; Savina, M. E.

    2003-12-01

    One approach to curriculum review and development is to construct a matrix of the desired skills versus courses in the departmental curriculum. The matrix approach requires faculty to articulate their goals, identify specific skills, and assess where in the curriculum students will learn and practice these skills and where there are major skills gaps. Faculty members in the Geology Department at Carleton College developed a matrix of skills covered in geology courses with the following objectives: 1) Geology majors should begin their "senior integrative exercise" having practiced multiple times all of the formal steps in the research process (recognizing problems, writing proposals, carrying out a project, reporting a project in several ways); 2) Geology majors should learn and practice a variety of professional and life skills life (e.g. computer skills, field skills, lab skills, and interpretive skills).The matrix was used to identify where in the curriculum various research methods and skills were addressed and to map potential student experiences to the objectives. In Carleton's non-hierarchical curriculum, the matrix was used to verify that students have many opportunities to practice research and life skills regardless of the path they take to completion of the major. In William and Mary's more structured curriculum, the matrix was used to ensure that skills build upon each other from course to course. Faculty members in the Geology Department at the College of William and Mary first used this approach to focus on teaching quantitative skills across the geology curriculum, and later used it in terms of teaching research, communication, and information literacy skills. After articulating goals and skills, faculty members in both departments developed more specific skill lists within each category of skills, then described the current assignments and activities in each course relative to the specific components of the matrix and discussed whether to add

  20. THE COLUMN DENSITY VARIANCE IN TURBULENT INTERSTELLAR MEDIA: A FRACTAL MODEL APPROACH

    SciTech Connect

    Seon, Kwang-Il

    2012-12-20

    Fractional Brownian motion structures are used to investigate the dependency of column density variance ({sigma}{sup 2}{sub lnN}) in the turbulent interstellar medium on the variance of three-dimensional density ({sigma}{sup 2}{sub ln{rho}}) and the power-law slope of the density power spectrum. We provide quantitative expressions to infer the three-dimensional density variance, which is not directly observable, from the observable column density variance and spectral slope. We also investigate the relationship between the column density variance and sonic Mach number (M{sub s}) in the hydrodynamic (HD) regime by assuming the spectral slope and density variance to be functions of sonic Mach number, as obtained from the HD turbulence simulations. They are related by the expression {sigma}{sup 2}{sub lnN} = A{sigma}{sub ln{rho}} {sup 2} = Aln (1 + b {sup 2} M{sup 2}{sub s}), suggested by Burkhart and Lazarian for the magnetohydrodynamic case. The proportional constant A varies from Almost-Equal-To 0.2 to Almost-Equal-To 0.4 in the HD regime as the turbulence forcing parameter b increases from 1/3 (purely solenoidal forcing) to 1 (purely compressive forcing). It is also discussed that the parameter A is lowered in the presence of a magnetic field.