WorldWideScience

Sample records for anderson impurity model

  1. The completeness problem in the impurity Anderson model

    International Nuclear Information System (INIS)

    With the recent development of the nanoscopic technology, the impurity Anderson model (AIM) was experimentally realized in quantum dot devices, and there is renewed interest in the study of the Kondo physics of the AIM. Several Green's functions approximations by the equation of motion method (EOM), that incorporates the Kondo effect through a digamma function, have been presented in the literature as an adequate tool to describe, at least qualitatively, the Kondo effect. However, these approximations present several drawbacks: they are no longer valid as the temperature decreases below the Kondo temperature, because the logarithmic divergence of the digamma function makes the spectral density at the chemical potential to vanish, and the Friedel sum rule and the completeness in the occupation numbers are not fulfilled. In this work we present a critical discussion comparing the results of digamma approximations GF with the atomic approach, recently developed by some of us, that satisfy the completeness and the Friedel sum rule. We present results for the density of states, the Friedel sum rule and the completeness

  2. Electronic structure of vitamin B12 within the framework of the Haldane-Anderson impurity model

    Science.gov (United States)

    Kandemir, Zafer; Mayda, Selma; Bulut, Nejat

    2015-03-01

    We study the electronic structure of vitamin B12 (cyanocobalamine C63H88CoN14O14P) by using the framework of the multi-orbital single-impurity Haldane-Anderson model of a transition-metal impurity in a semiconductor host. Here, our purpose is to understand the many-body effects originating from the transition-metal impurity. In this approach, the cobalt 3 d orbitals are treated as the impurity states placed in a semiconductor host which consists of the rest of the molecule. The parameters of the resulting effective Haldane-Anderson model are obtained within the Hartree-Fock approximation for the electronic structure of the molecule. The quantum Monte Carlo technique is then used to calculate the one-electron and magnetic correlation functions of this effective Haldane-Anderson model for vitamin B12. We find that new states form inside the semiconductor gap due to the on-site Coulomb interaction at the impurity 3 d orbitals and that these states become the highest occupied molecular orbitals. In addition, we present results on the charge distribution and spin correlations around the Co atom. We compare the results of this approach with those obtained by the density-functional theory calculations.

  3. Magnetic field induced quantum phase transitions in the two-impurity Anderson model

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Lujun [Los Alamos National Laboratory; Zhu, Jian - Xin [Los Alamos National Laboratory

    2010-11-17

    In the two-impurity Anderson model, the inter-impurity spin exchange interaction favors a spin singlet state between two impurities leading to the localization of quasiparticles. We show that a local uniform magnetic field can delocalize the quasiparticies to restore the Kondo resonance. This transition is found to be continuous, accompanied by not only the divergence of the staggered (anti ferromagnetic) susceptibility, but also the divergence of the uniform spin susceptibility. This implies that the magnetic field induced quantum phase transitions in Kondo systems are in favor of the local critical type.

  4. Determinant method and quantum simulations of many-body effects in a single impurity Anderson model

    International Nuclear Information System (INIS)

    We present a short description of a quantum Monte Carlo technique that has proved useful for simulating many-body effects in systems of interacting fermins at finite temperatures. We then report our preliminary results using this technique on a single impurity Anderson model. Examples of such many-body effects as local moment formation, Kondo behavior, and mixed valence phenomena found in the simulations are shown

  5. Determinant method and quantum simulations of many-body effects in a single impurity Anderson model

    International Nuclear Information System (INIS)

    A short description is presented of a quantum Monte Carlo technique, often referred to as the determinant method, that has proved useful for simulating many-body effects in systems of interacting fermions at finite temperatures. Preliminary results using this technique on a single impurity Anderson model are reported. Examples of such many-body effects as local moment formation, Kondo behavior, and mixed valence phenomena found in the simulations are shown. 10 refs., 3 figs

  6. Electronic structure and correlations of vitamin B12 studied within the Haldane-Anderson impurity model

    Science.gov (United States)

    Kandemir, Zafer; Mayda, Selma; Bulut, Nejat

    2016-04-01

    We study the electronic structure and correlations of vitamin B12 (cyanocobalamine) by using the framework of the multi-orbital single-impurity Haldane-Anderson model of a transition-metal impurity in a semiconductor host. The parameters of the effective Haldane-Anderson model are obtained within the Hartree-Fock (HF) approximation. The quantum Monte Carlo (QMC) technique is then used to calculate the one-electron and magnetic correlation functions of this effective model. We observe that new states form inside the semiconductor gap found by HF due to the intra-orbital Coulomb interaction at the impurity 3d orbitals. In particular, the lowest unoccupied states correspond to an impurity bound state, which consists of states from mainly the CN axial ligand and the corrin ring as well as the Co eg-like orbitals. We also observe that the Co (3d) orbitals can develop antiferromagnetic correlations with the surrounding atoms depending on the filling of the impurity bound states. In addition, we make comparisons of the HF+QMC data with the density functional theory calculations. We also discuss the photoabsorption spectrum of cyanocobalamine.

  7. Ward identities for the Anderson impurity model: derivation via functional methods and the exact renormalization group

    International Nuclear Information System (INIS)

    Using functional methods and the exact renormalization group we derive Ward identities for the Anderson impurity model. In particular, we present a non-perturbative proof of the Yamada-Yosida identities relating certain coefficients in the low-energy expansion of the self-energy to the thermodynamic particle number and spin susceptibilities of the impurity. Our proof underlines the relation of the Yamada-Yosida identities to the U(1) x U(1) symmetry associated with the particle number and spin conservation in a magnetic field.

  8. Magnetic Moments of Chromium-Doped Gold Clusters: The Anderson Impurity Model in Finite Systems

    CERN Document Server

    Hirsch, K; Langenberg, A; Niemeyer, M; Langbehn, B; Möller, T; Terasaki, A; Issendorff, B v; Lau, J T

    2013-01-01

    The magnetic moment of a single impurity atom in a finite free electron gas is studied in a combined x-ray magnetic circular dichroism spectroscopy and density functional theory study of size-selected free chromium-doped gold clusters. The observed size-dependence of the local magnetic moment can essentially be understood in terms of the Anderson impurity model. Electronic shell closure in the host metal minimizes the interaction of localized impurity states with the confined free electron gas and preserves the full magnetic moment of $\\unit[5]{\\mu_B}$ in $\\mathrm{CrAu}_{2}^{+}$ and $\\mathrm{CrAu}_{6}^{+}$ clusters. Even for open-shell species, large local moments are observed that scale with the energy gap of the gold cluster. This indicates that an energy gap in the free electron gas generally stabilizes the local magnetic moment of the impurity.

  9. An alternative functional renormalization group approach to the single impurity Anderson model

    OpenAIRE

    Kinza, Michael; Ortloff, Jutta; Bauer, Johannes; Honerkamp, Carsten

    2012-01-01

    We present an alternative functional renormalization group (fRG) approach to the single-impurity Anderson model at finite temperatures. Starting with the exact self-energy and interaction vertex of a small system ('core') containing a correlated site, we switch on the hybridization with a non-interacting bath in the fRG-flow and calculate spectra of the correlated site. Different truncations of the RG-flow-equations and choices of the core are compared and discussed. Furthermore we calculate ...

  10. An Anderson Impurity Model for Efficient Sampling of Adiabatic Potential Energy Surfaces of Transition Metal Complexes

    CERN Document Server

    La Bute-Montiago X; Cox, D L

    2004-01-01

    We present a model intended for rapid sampling of ground and excited state potential energy surfaces for first-row transition metal active sites. The method is computationally inexpensive and is suited for dynamics simulations where (1) adiabatic states are required "on-the-fly" and (2) the primary source of the electronic coupling between the diabatic states is the perturbative spin-orbit interaction among the 3d electrons. The model Hamiltonian we develop is a variant of the Anderson impurity model and achieves efficiency through a physically motivated basis set reduction based on the large value of the d-d Coulomb interaction U_{d} and a Lanczos matrix diagonalization routine to solve for eigenvalues. The model parameters are constrained by fits to the partial density of states (PDOS) obtained from ab initio density functional theory calculations. For a particular application of our model we focus on electron-transfer occuring between cobalt ions solvated by ammonium, incorporating configuration interactio...

  11. Theory of the Anderson impurity model: The Schrieffer endash Wolff transformation reexamined

    International Nuclear Information System (INIS)

    We test the method of infinitesimal unitary transformations recently introduced by Wegner on the Anderson single impurity model. It is demonstrated that infinitesimal unitary transformations in contrast to the Schrieffer endash Wolff transformation allow the construction of an effective Kondo Hamiltonian consistent with the established results in this well understood model. The main reason for this is the intrinsic energy scale separation of Wegner close-quote s approach with respect to arbitrary energy differences coupled by matrix elements. This allows the construction of an effective Hamiltonian without facing a vanishing energy denominator problem. Similar energy denominator problems are troublesome in many models. Infinitesimal unitary transformations have the potential to provide a general framework for the systematic derivation of effective Hamiltonians without such problems. Copyright copyright 1996 Academic Press, Inc

  12. Buildup of the Kondo effect from real-time effective action for the Anderson impurity model

    Science.gov (United States)

    Bock, Sebastian; Liluashvili, Alexander; Gasenzer, Thomas

    2016-07-01

    The nonequilibrium time evolution of a quantum dot is studied by means of dynamic equations for time-dependent Green's functions derived from a two-particle-irreducible (2PI) effective action for the Anderson impurity model. Coupling the dot between two leads at different voltages, the dynamics of the current through the dot is investigated. We show that the 2PI approach is capable of describing the dynamical buildup of the Kondo effect, which shows up as a sharp resonance in the spectral function, with a width exponentially suppressed in the electron self-coupling on the dot. An external voltage applied to the dot is found to deteriorate the Kondo effect at the hybridization scale. The dynamic equations are evaluated within different nonperturbative resummation schemes, within the direct, particle-particle, and particle-hole channels, as well as their combination, and the results compared with those from other methods.

  13. Fermi-liquid theory for the single-impurity Anderson model

    Science.gov (United States)

    Mora, Christophe; Moca, Cǎtǎlin Paşcu; von Delft, Jan; Zaránd, Gergely

    2015-08-01

    We generalize Nozières' Fermi-liquid theory for the low-energy behavior of the Kondo model to that of the single-impurity Anderson model. In addition to the electrons' phase shift at the Fermi energy, the low-energy Fermi-liquid theory is characterized by four Fermi-liquid parameters: the two given by Nozières that enter to first order in the excitation energy, and two additional ones that enter to second order and are needed away from particle-hole symmetry. We express all four parameters in terms of zero-temperature physical observables, namely the local charge and spin susceptibilities and their derivatives with respect to the local level position. We determine these in terms of the bare parameters of the Anderson model using Bethe ansatz and numerical renormalization group (NRG) calculations. Our low-energy Fermi-liquid theory applies throughout the crossover from the strong-coupling Kondo regime via the mixed-valence regime to the empty-orbital regime. From the Fermi-liquid theory, we determine the conductance through a quantum dot symmetrically coupled to two leads in the regime of small magnetic field, low temperature, and small bias voltage, and compute the coefficients of the ˜B2 , ˜T2 , and ˜V2 terms exactly in terms of the Fermi-liquid parameters. The coefficients of T2, V2, and B2 are found to change sign during the Kondo to empty-orbital crossover. The crossover becomes universal in the limit that the local interaction is much larger than the level width. For completeness, we also compute the shot noise and discuss the resulting Fano factor.

  14. Non-equilibrium STLS approach to transport properties of single impurity Anderson model

    International Nuclear Information System (INIS)

    In this work, using the non-equilibrium Keldysh formalism, we study the effects of the electron–electron interaction and the electron-spin correlation on the non-equilibrium Kondo effect and the transport properties of the symmetric single impurity Anderson model (SIAM) at zero temperature by generalizing the self-consistent method of Singwi, Tosi, Land, and Sjolander (STLS) for a single-band tight-binding model with Hubbard type interaction to out of equilibrium steady-states. We at first determine in a self-consistent manner the non-equilibrium spin correlation function, the effective Hubbard interaction, and the double-occupancy at the impurity site. Then, using the non-equilibrium STLS spin polarization function in the non-equilibrium formalism of the iterative perturbation theory (IPT) of Yosida and Yamada, and Horvatic and Zlatic, we compute the spectral density, the current–voltage characteristics and the differential conductance as functions of the applied bias and the strength of on-site Hubbard interaction. We compare our spectral densities at zero bias with the results of numerical renormalization group (NRG) and depict the effects of the electron–electron interaction and electron-spin correlation at the impurity site on the aforementioned properties by comparing our numerical result with the order U2 IPT. Finally, we show that the obtained numerical results on the differential conductance have a quadratic universal scaling behavior and the resulting Kondo temperature shows an exponential behavior. -- Highlights: •We introduce for the first time the non-equilibrium method of STLS for Hubbard type models. •We determine the transport properties of SIAM using the non-equilibrium STLS method. •We compare our results with order-U2 IPT and NRG. •We show that non-equilibrium STLS, contrary to the GW and self-consistent RPA, produces the two Hubbard peaks in DOS. •We show that the method keeps the universal scaling behavior and correct

  15. Non-equilibrium STLS approach to transport properties of single impurity Anderson model

    Energy Technology Data Exchange (ETDEWEB)

    Rezai, Raheleh, E-mail: R_Rezai@sbu.ac.ir; Ebrahimi, Farshad, E-mail: Ebrahimi@sbu.ac.ir

    2014-04-15

    In this work, using the non-equilibrium Keldysh formalism, we study the effects of the electron–electron interaction and the electron-spin correlation on the non-equilibrium Kondo effect and the transport properties of the symmetric single impurity Anderson model (SIAM) at zero temperature by generalizing the self-consistent method of Singwi, Tosi, Land, and Sjolander (STLS) for a single-band tight-binding model with Hubbard type interaction to out of equilibrium steady-states. We at first determine in a self-consistent manner the non-equilibrium spin correlation function, the effective Hubbard interaction, and the double-occupancy at the impurity site. Then, using the non-equilibrium STLS spin polarization function in the non-equilibrium formalism of the iterative perturbation theory (IPT) of Yosida and Yamada, and Horvatic and Zlatic, we compute the spectral density, the current–voltage characteristics and the differential conductance as functions of the applied bias and the strength of on-site Hubbard interaction. We compare our spectral densities at zero bias with the results of numerical renormalization group (NRG) and depict the effects of the electron–electron interaction and electron-spin correlation at the impurity site on the aforementioned properties by comparing our numerical result with the order U{sup 2} IPT. Finally, we show that the obtained numerical results on the differential conductance have a quadratic universal scaling behavior and the resulting Kondo temperature shows an exponential behavior. -- Highlights: •We introduce for the first time the non-equilibrium method of STLS for Hubbard type models. •We determine the transport properties of SIAM using the non-equilibrium STLS method. •We compare our results with order-U2 IPT and NRG. •We show that non-equilibrium STLS, contrary to the GW and self-consistent RPA, produces the two Hubbard peaks in DOS. •We show that the method keeps the universal scaling behavior and correct

  16. A Functional Generalization of the Field-Theoretical Renormalization Group Approach for the Single-Impurity Anderson Model

    Science.gov (United States)

    Freire, Hermann; Corrêa, Eberth

    2012-02-01

    We apply a functional implementation of the field-theoretical renormalization group (RG) method up to two loops to the single-impurity Anderson model. To achieve this, we follow a RG strategy similar to that proposed by Vojta et al. (in Phys. Rev. Lett. 85:4940, 2000), which consists of defining a soft ultraviolet regulator in the space of Matsubara frequencies for the renormalized Green's function. Then we proceed to derive analytically and solve numerically integro-differential flow equations for the effective couplings and the quasiparticle weight of the present model, which fully treat the interplay of particle-particle and particle-hole parquet diagrams and the effect of the two-loop self-energy feedback into them. We show that our results correctly reproduce accurate numerical renormalization group data for weak to slightly moderate interactions. These results are in excellent agreement with other functional Wilsonian RG works available in the literature. Since the field-theoretical RG method turns out to be easier to implement at higher loops than the Wilsonian approach, higher-order calculations within the present approach could improve further the results for this model at stronger couplings. We argue that the present RG scheme could thus offer a possible alternative to other functional RG methods to describe electronic correlations within this model.

  17. Anderson impurity in a helical metal

    OpenAIRE

    Chen, WQ; Gao, JH; Zhang, FC; Feng, XY; Wang, QH

    2010-01-01

    We use a trial wave function to study the spin-1/2 Kondo effect of a helical metal on the surface of a three-dimensional topological insulator. While the impurity spin is quenched by conduction electrons, the spin-spin correlation of the conduction electron and impurity is strongly anisotropic in both spin and spatial spaces. As a result of strong spin-orbit coupling, the out-of-plane component of the impurity spin is found to be fully screened by the orbital angular momentum of the conductio...

  18. Spin susceptibility of Anderson impurities in arbitrary conduction bands

    Science.gov (United States)

    Fang, Tie-Feng; Tong, Ning-Hua; Cao, Zhan; Sun, Qing-Feng; Luo, Hong-Gang

    2015-10-01

    Spin susceptibility of Anderson impurities is a key quantity in understanding the physics of Kondo screening. Traditional numerical renormalization group (NRG) calculation of the impurity contribution χimp to susceptibility, defined originally by Wilson in a flat wide band, has been generalized before to structured conduction bands. The results brought about non-Fermi-liquid and diamagnetic Kondo behaviors in χimp, even when the bands are not gapped at the Fermi energy. Here, we use the full density-matrix (FDM) NRG to present high-quality data for the local susceptibility χloc and to compare them with χimp obtained by the traditional NRG. Our results indicate that those exotic behaviors observed in χimp are unphysical. Instead, the low-energy excitations of the impurity in arbitrary bands only without gap at the Fermi energy are still a Fermi liquid and paramagnetic. We also demonstrate that unlike the traditional NRG yielding χloc less accurate than χimp, the FDM method allows a high-precision dynamical calculation of χloc at much reduced computational cost, with an accuracy at least one order higher than χimp. Moreover, artifacts in the FDM algorithm to χimp and origins of the spurious non-Fermi-liquid and diamagnetic features are clarified. Our work provides an efficient high-precision algorithm to calculate the spin susceptibility of impurity for arbitrary structured bands, while negating the applicability of Wilson's definition to such cases.

  19. Anderson metal-insulator transitions with classical magnetic impurities

    Science.gov (United States)

    Jung, Daniel; Kettemann, Stefan; Slevin, Keith

    2016-04-01

    We study numerically the effects of classical magnetic impurities on the Anderson metal-insulator transition. We find that a small concentration of Heisenberg impurities enhances the critical disorder amplitude Wc with increasing exchange coupling strength J . The resulting scaling with J is analyzed which supports an anomalous scaling prediction by Wegner due to the combined breaking of time-reversal and spin-rotational symmetry. Moreover, we find that the presence of magnetic impurities lowers the critical correlation length exponent ν and enhances the multifractality parameter α0. The new value of ν improves the agreement with the value measured in experiments on the metal-insulator transition (MIT) in doped semiconductors like phosphor-doped silicon, where a finite density of magnetic moments is known to exist in the vicinity of the MIT. The results are obtained by a finite-size scaling analysis of the geometric mean of the local density of states which is calculated by means of the kernel polynomial method. We establish this combination of numerical techniques as a method to obtain critical properties of disordered systems quantitatively.

  20. Spectral density method to Anderson-Holstein model

    International Nuclear Information System (INIS)

    Two-parameter spectral density function of a magnetic impurity electron in a non-magnetic metal is calculated within the framework of the Anderson-Holstein model using the spectral density approximation method. The effect of electron-phonon interaction on the spectral function is investigated

  1. Superconductivity in Anderson lattice model

    International Nuclear Information System (INIS)

    We study the superconducting instabilities generated by the inclusion in the Anderson lattice model of a density-density attractive potential between correlated electrons on nearest-neighbouring sites. Using a description of the normal phase based on a perturbative expansion around the atomic limit, we treat the attractive potential in the broken symmetry Hartree-Fock scheme and analyze which of the possible symmetries of the superconducting order parameter leads to the highest possible transition temperature in the case of a two-dimensional square lattice. For values of the on-site f-repulsion large compared to the hopping amplitude, a suppression of any possible superconducting phase occurs, regardless of the of the symmetry of the order parameter. (author)

  2. Mean-field theory for the f2-f3 Anderson impurity

    International Nuclear Information System (INIS)

    A uranium impurity whose lovest ionic configurations are f2 and F3 is considered in a j j - coupling scheme in the limit of zero j.j coupling. A mean field theory to the f2-f3 Anderson - Coleman Hamiltonian is presented which is found to give useful results for ground state properties over whole range of f - occupations. (author)

  3. Multichannel Numerical Renormalization Group study of the Anderson Hamiltonian with multiple impurities

    Science.gov (United States)

    Stokes, James; Konik, Robert

    2014-03-01

    Using the Numerical Renormalization Group (NRG), the low energy sector of the Anderson Hamiltonian with two impurities in parallel has been previously argued to be consistent with an underscreened spin-1 Kondo effect (R. Zitko and J. Bonca, Phys. Rev. B 76, 241305 (2007); Logan et al., Phys. Rev. B 80, 125117 (2009)). Bethe Ansatz and slave boson calculations have given the ground state as a singlet (M. Kulkarni and R. M. Konik, Phys. Rev. B 83, 245121 (2011)). As an attempt to understand these differences, we have developed a modified NRG routine that takes into account the multiple channels arising from the logarithmic discretization of the Fermi sea. This could conceivably allow for more complicated screening processes suggested by the Bethe ansatz computations. Results of studies using this code for various numbers of impurities and channels will be presented and discussed in relationship to these conflicting views.

  4. Modelling static impurities

    OpenAIRE

    Correia, Sebastiao; Polonyi, Janos; Richert, Jean

    2000-01-01

    A simple model is presented for the calculation of the quenched average over impurities which are rendered static by setting their mass equal to infinity. The path integral formalism of the second quantized theory contains annealed averages only. The similarity with the Gaussian quenched potential model is discussed.

  5. Quasiparticle many-body dynamics of the Anderson model

    International Nuclear Information System (INIS)

    The paper addresses the many-body quasiparticle dynamics of the Anderson impurity model at finite temperatures in the framework of the equation-of-motion method. We find a new exact identity relating the one-particle and many-particle Green's Functions. Using this identity we present a consistent and general scheme for a construction of generalised mean fields (elastic scattering corrections) and self-energy (inelastic scattering) in terms of the Dyson equation. A new approach for the complex expansion for the single-particle propagator in terms of the Coulomb repulsion U and hybridization V is proposed. Using the exact identity, the essentially new many-body dynamical solution of SIAM has been derived. This approach offers a new way for the systematic construction of the approximative interpolating dynamical solutions of the strongly correlated electron systems. 47 refs

  6. Topological approximation of the nonlinear Anderson model

    Science.gov (United States)

    Milovanov, Alexander V.; Iomin, Alexander

    2014-06-01

    We study the phenomena of Anderson localization in the presence of nonlinear interaction on a lattice. A class of nonlinear Schrödinger models with arbitrary power nonlinearity is analyzed. We conceive the various regimes of behavior, depending on the topology of resonance overlap in phase space, ranging from a fully developed chaos involving Lévy flights to pseudochaotic dynamics at the onset of delocalization. It is demonstrated that the quadratic nonlinearity plays a dynamically very distinguished role in that it is the only type of power nonlinearity permitting an abrupt localization-delocalization transition with unlimited spreading already at the delocalization border. We describe this localization-delocalization transition as a percolation transition on the infinite Cayley tree (Bethe lattice). It is found in the vicinity of the criticality that the spreading of the wave field is subdiffusive in the limit t →+∞. The second moment of the associated probability distribution grows with time as a power law ∝ tα, with the exponent α =1/3 exactly. Also we find for superquadratic nonlinearity that the analog pseudochaotic regime at the edge of chaos is self-controlling in that it has feedback on the topology of the structure on which the transport processes concentrate. Then the system automatically (without tuning of parameters) develops its percolation point. We classify this type of behavior in terms of self-organized criticality dynamics in Hilbert space. For subquadratic nonlinearities, the behavior is shown to be sensitive to the details of definition of the nonlinear term. A transport model is proposed based on modified nonlinearity, using the idea of "stripes" propagating the wave process to large distances. Theoretical investigations, presented here, are the basis for consistency analysis of the different localization-delocalization patterns in systems with many coupled degrees of freedom in association with the asymptotic properties of the

  7. An Anderson-like model of the QCD chiral transition

    CERN Document Server

    Giordano, Matteo; Pittler, Ferenc

    2016-01-01

    We study the problems of chiral symmetry breaking and eigenmode localisation in finite-temperature QCD by looking at the lattice Dirac operator as a random Hamiltonian. We recast the staggered Dirac operator into an unconventional three-dimensional Anderson Hamiltonian ("Dirac-Anderson Hamiltonian") carrying internal degrees of freedom, with disorder provided by the fluctuations of the gauge links. In this framework, we identify the features relevant to chiral symmetry restoration and localisation of the low-lying Dirac eigenmodes in the ordering of the local Polyakov lines, and in the related correlation between spatial links across time slices, thus tying the two phenomena to the deconfinement transition. We then build a toy model based on QCD and on the Dirac-Anderson approach, replacing the Polyakov lines with spin variables and simplifying the dynamics of the spatial gauge links, but preserving the above-mentioned relevant dynamical features. Our toy model successfully reproduces the main features of the...

  8. Magnetic susceptibility of a two-channel Anderson model

    International Nuclear Information System (INIS)

    Temperature-dependent magnetic susceptibility is calculated for a two-channel Anderson model, by using the numerical renormalization group plus an interleaving procedure to recover the continuum of the conduction band. Fermi- and non-Fermi-liquid fixed points can be obtained in the low-temperature regime of the model susceptibility

  9. Magnetic susceptibility of a two-channel Anderson model

    Energy Technology Data Exchange (ETDEWEB)

    Ferreira, J.V.B.; Oliveira, L.N. de; Cox, D.L.; Libero, V.L. E-mail: valter@if.sc.usp.br

    2001-05-01

    Temperature-dependent magnetic susceptibility is calculated for a two-channel Anderson model, by using the numerical renormalization group plus an interleaving procedure to recover the continuum of the conduction band. Fermi- and non-Fermi-liquid fixed points can be obtained in the low-temperature regime of the model susceptibility.

  10. An Anderson-like model of the QCD chiral transition

    Science.gov (United States)

    Giordano, Matteo; Kovács, Tamás G.; Pittler, Ferenc

    2016-06-01

    We study the problems of chiral symmetry breaking and eigenmode localisation in finite-temperature QCD by looking at the lattice Dirac operator as a random Hamiltonian. We recast the staggered Dirac operator into an unconventional three-dimensional Anderson Hamiltonian ("Dirac-Anderson Hamiltonian") carrying internal degrees of freedom, with disorder provided by the fluctuations of the gauge links. In this framework, we identify the features relevant to chiral symmetry restoration and localisation of the low-lying Dirac eigenmodes in the ordering of the local Polyakov lines, and in the related correlation between spatial links across time slices, thus tying the two phenomena to the deconfinement transition. We then build a toy model based on QCD and on the Dirac-Anderson approach, replacing the Polyakov lines with spin variables and simplifying the dynamics of the spatial gauge links, but preserving the above-mentioned relevant dynamical features. Our toy model successfully reproduces the main features of the QCD spectrum and of the Dirac eigenmodes concerning chiral symmetry breaking and localisation, both in the ordered (deconfined) and disordered (confined) phases. Moreover, it allows us to study separately the roles played in the two phenomena by the diagonal and the off-diagonal terms of the Dirac-Anderson Hamiltonian. Our results support our expectation that chiral symmetry restoration and localisation of the low modes are closely related, and that both are triggered by the deconfinement transition.

  11. Spectra of Anderson Type Models with Decaying Randomness

    Indian Academy of Sciences (India)

    M Krishna; K B Sinha

    2001-05-01

    In this paper we consider some Anderson type models, with free parts having long range tails with the random perturbations decaying at different rates in different directions and prove that there is a.c. spectrum in the model which is pure. In addition, we show that there is pure point spectrum outside some interval. Our models include potentials decaying in all directions in which case absence of singular continuous spectrum is also shown.

  12. Numerical Renormalization Group Study of Probability Distributions for Local Fluctuations in the Anderson-Holstein and Holstein-Hubbard Models

    OpenAIRE

    Hewson, Alex C.; Bauer, Johannes

    2010-01-01

    We show that information on the probability density of local fluctuations can be obtained from a numerical renormalisation group calculation of a reduced density matrix. We apply this approach to the Anderson-Holstein impurity model to calculate the ground state probability density $\\rho(x)$ for the displacement $x$ of the local oscillator. From this density we can deduce an effective local potential for the oscillator and compare its form with that obtained from a semiclassical approximation...

  13. Smoothed universal correlations in the two-dimensional Anderson model

    OpenAIRE

    Uski, V.; Mehlig, B.; R.A. Romer; Schreiber, M.

    1998-01-01

    We report on calculations of smoothed spectral correlations in the two-dimensional Anderson model for weak disorder. As pointed out in (M. Wilkinson, J. Phys. A: Math. Gen. 21, 1173 (1988)), an analysis of the smoothing dependence of the correlation functions provides a sensitive means of establishing consistency with random matrix theory. We use a semiclassical approach to describe these fluctuations and offer a detailed comparison between numerical and analytical calculations for an exhaust...

  14. The parabolic Anderson model and long-range percolation

    OpenAIRE

    Erhard, Dirk

    2014-01-01

    This thesis has two parts. The first part deals with the parabolic Anderson model, which is a stochastic differential equation. It models the evolution of a field of particles performing independent simple random walks with binary branching. The focus of this work is on the exponential growth rate of the solution, where several basic properties are derived. The second part deals with two long-range percolation models. The occupied set of the first model is obtained by taking the union of a co...

  15. 1/(n-1) expansion for an Anderson impurity with N-fold degeneracy: a new large-N scheme based on a perturbation theory in U

    International Nuclear Information System (INIS)

    Full text: We describe a new large-N approach, which is referred to as 1/(N-1) expansion, to an N-fold degenerate Anderson impurity model with a finite Coulomb interaction U [1,2]. This approach is different from the usual 1/N expansion [3], non-crossing approximation [4], and recent developments [5,6] along the conventional large-N theory which is based on a perturbation expansion with respect to the tunneling matrix element v, between the impurity and conduction electrons, and on a scaling that takes Nv2 as a constant independent of N. In contrast, our formulation starts with the perturbation theory in U, for which a standard Feynman-diagrammatic analysis is applicable. Then, the perturbation series in U is reorganized as an expansion in powers of 1/(N-1), using the scaling that takes u=(N-1)U as an independent variable. The factor N-1 represents the number of interacting orbitals, excluding the one prohibited by the Pauli principle. This approach can be regarded as a fermionic analogue of an expansion scheme that was constructed for the bosonic N-component φ4 model for critical phenomena [7], and can be used to explore low-energy properties of quantum impurities and also lattice-fermion systems such as the Hubbard and periodic Anderson models. Our expansion scheme provides the Hartree-Fock (HF) approximation at zero order, where the limit N → ∞ is taken keeping u finite. Then, to leading order in 1/(N-1) it describes the Hartree-Fock random phase approximation (HF-RPA). The higher-order corrections, starting from order 1/(N-1)2 terms, describe systematically the fluctuations beyond the HF-RPA. We have calculated the renormalized parameters for the local-Fermi-liquid ground state up to terms of order 1/(N-1)2, and found that the results agree very closely with the exact numerical-renormalization-group results already at N=4, where the degeneracy is still not large. This ensures the reliability of our approach for N≥4. Note that the case for N=2 corresponds

  16. Quantum impurities in channel mixing baths

    Science.gov (United States)

    Liu, Jin-Guo; Wang, Da; Wang, Qiang-Hua

    2016-01-01

    We propose a versatile strategy for numerical renormalization group (NRG) solution of general channel-mixing Kondo and Anderson impurity models beyond previous reach. We illustrate the strategy by investigating the quantum phase transitions in models of Anderson impurities coupled to s - and d -wave superconducting baths. We discuss the effects of nontrivial channel-mixing in such models. Our strategy opens the door toward broad applications of NRG as impurity solver in cluster dynamical mean field theory for strongly correlated electron systems.

  17. Time-dependent Mott transition in the periodic Anderson model with nonlocal hybridization

    Science.gov (United States)

    Hofmann, Felix; Potthoff, Michael

    2016-08-01

    The time-dependent Mott transition in a periodic Anderson model with off-site, nearest-neighbor hybridization is studied within the framework of nonequilibrium self-energy functional theory. Using the two-site dynamical-impurity approximation, we compute the real-time dynamics of the optimal variational parameter and of different observables initiated by sudden quenches of the Hubbard-U and identify the critical interaction. The time-dependent transition is orbital selective, i.e., in the final state, reached in the long-time limit after the quench to the critical interaction, the Mott gap opens in the spectral function of the localized orbitals only. We discuss the dependence of the critical interaction and of the final-state effective temperature on the hybridization strength and point out the various similarities between the nonequilibrium and the equilibrium Mott transition. It is shown that these can also be smoothly connected to each other by increasing the duration of a U-ramp from a sudden quench to a quasi-static process. The physics found for the model with off-site hybridization is compared with the dynamical Mott transition in the single-orbital Hubbard model and with the dynamical crossover found for the real-time dynamics of the conventional Anderson lattice with on-site hybridization.

  18. A Holographic Two-Impurity Kondo Model

    CERN Document Server

    O'Bannon, Andy; Probst, Jonas

    2015-01-01

    We propose a model of a strongly-interacting two-impurity Kondo system based on the AdS/CFT correspondence, also known as holography. In a Landau Fermi Liquid, the single-impurity Kondo effect is the screening of an impurity spin at low temperature $T$. The two-impurity Kondo model then describes the competition between the Kondo interaction and the Heisenberg interaction between two impurity spins, also called the RKKY interaction. For spin-$1/2$ impurities, that competition leads to a quantum phase transition from a Kondo-screened phase to a phase in which the two impurity spins screen one another. Our holographic model is based on a $(1+1)$-dimensional CFT description of the two-impurity Kondo model, reliable for two impurities with negligible separation in space. We consider only impurity spins in a totally anti-symmetric representation of an $SU(N)$ spin symmetry. We employ a large-$N$ limit, in which both Kondo and RKKY couplings are double-trace, and both Kondo and inter-impurity screening appear as co...

  19. Classical mapping for Hubbard operators: Application to the double-Anderson model

    Energy Technology Data Exchange (ETDEWEB)

    Li, Bin; Miller, William H. [Department of Chemistry and Kenneth S. Pitzer Center for Theoretical Chemistry, University of California, and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Levy, Tal J.; Rabani, Eran [School of Chemistry, The Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978 (Israel)

    2014-05-28

    A classical Cartesian mapping for Hubbard operators is developed to describe the nonequilibrium transport of an open quantum system with many electrons. The mapping of the Hubbard operators representing the many-body Hamiltonian is derived by using analogies from classical mappings of boson creation and annihilation operators vis-à-vis a coherent state representation. The approach provides qualitative results for a double quantum dot array (double Anderson impurity model) coupled to fermionic leads for a range of bias voltages, Coulomb couplings, and hopping terms. While the width and height of the conduction peaks show deviations from the master equation approach considered to be accurate in the limit of weak system-leads couplings and high temperatures, the Hubbard mapping captures all transport channels involving transition between many electron states, some of which are not captured by approximate nonequilibrium Green function closures.

  20. Some Ergodic Theorems for a Parabolic Anderson Model

    Institute of Scientific and Technical Information of China (English)

    Yong LIU; Feng Xia YANG

    2012-01-01

    In this paper,we study some ergodic theorems of a class of linear systems of interacting diffusions,which is a parabolic Anderson model.First,under the assumption that the transition kernel a =(a(i,j))i,j∈s is doubly stochastic,we obtain the long-time convergence to an invariant probability measure Vh starting from a bounded a-harmonic function h based on self-duality property,and then we show the convergence to the invariant probability measure vh holds for a broad class of initial distributions.Second,if (a(i,j))i,j∈s is transient and symmetric,and the diffusion parameter c remains below a threshold,we are able to determine the set of extremal invariant probability measures with finite second moment.Finally,in the case that the transition kernel (a(i,j))i,j∈s is doubly stochastic and satisfies Case Ⅰ (see Case Ⅰ in [Shiga,T.:An interacting system in population genetics.J.Math.Kyoto Univ.,20,213-242 (1980)]),we show that this parabolic Anderson model locally dies out independent of the diffusion parameter c.

  1. Comparative study of many-body perturbation theory and time-dependent density functional theory in the out-of-equilibrium Anderson model

    OpenAIRE

    Uimonen, A. -M.; Khosravi, E.; Stan, A.; Stefanucci, Gianluca; Kurth, S.; Van Leeuwen, R; Gross, E. K. U.

    2011-01-01

    We study time-dependent electron transport through an Anderson model. The electronic interactions on the impurity site are included via the self-energy approximations at Hartree-Fock (HF), second Born (2B), GW, and T-matrix levels as well as within a time-dependent density functional (TDDFT) scheme based on the adiabatic Bethe-ansatz local density approximation (ABALDA) for the exchange-correlation potential. The Anderson model is driven out of equilibrium by applying a bias to the leads, and...

  2. The parabolic Anderson model random walk in random potential

    CERN Document Server

    König, Wolfgang

    2016-01-01

    This is a comprehensive survey on the research on the parabolic Anderson model – the heat equation with random potential or the random walk in random potential – of the years 1990 – 2015. The investigation of this model requires a combination of tools from probability (large deviations, extreme-value theory, e.g.) and analysis (spectral theory for the Laplace operator with potential, variational analysis, e.g.). We explain the background, the applications, the questions and the connections with other models and formulate the most relevant results on the long-time behavior of the solution, like quenched and annealed asymptotics for the total mass, intermittency, confinement and concentration properties and mass flow. Furthermore, we explain the most successful proof methods and give a list of open research problems. Proofs are not detailed, but concisely outlined and commented; the formulations of some theorems are slightly simplified for better comprehension.

  3. Lifshitz transitions in magnetic phases of the periodic Anderson model

    International Nuclear Information System (INIS)

    We investigate the reconstruction of a Fermi surface, which is called a Lifshitz transition, in magnetically ordered phases of the periodic Anderson model on a square lattice with a finite Coulomb interaction between f electrons. We apply the variational Monte Carlo method to the model by using the Gutzwiller wavefunctions for the paramagnetic, antiferromagnetic, ferromagnetic, and charge-density-wave states. We find that an antiferromagnetic phase is realized around half-filling and a ferromagnetic phase is realized when the system is far away from half-filling. In both magnetic phases, Lifshitz transitions take place. By analyzing the electronic states, we conclude that the Lifshitz transitions to large ordered-moment states can be regarded as itinerant-localized transitions of the f electrons. (author)

  4. Transport through an Anderson impurity: Current ringing, nonlinear magnetization, and a direct comparison of continuous-time quantum Monte Carlo and hierarchical quantum master equations

    Science.gov (United States)

    Härtle, R.; Cohen, G.; Reichman, D. R.; Millis, A. J.

    2015-08-01

    We give a detailed comparison of the hierarchical quantum master equation (HQME) method to a continuous-time quantum Monte Carlo (CT-QMC) approach, assessing the usability of these numerically exact schemes as impurity solvers in practical nonequilibrium calculations. We review the main characteristics of the methods and discuss the scaling of the associated numerical effort. We substantiate our discussion with explicit numerical results for the nonequilibrium transport properties of a single-site Anderson impurity. The numerical effort of the HQME scheme scales linearly with the simulation time but increases (at worst exponentially) with decreasing temperature. In contrast, CT-QMC is less restricted by temperature at short times, but in general the cost of going to longer times is also exponential. After establishing the numerical exactness of the HQME scheme, we use it to elucidate the influence of different ways to induce transport through the impurity on the initial dynamics, discuss the phenomenon of coherent current oscillations, known as current ringing, and explain the nonmonotonic temperature dependence of the steady-state magnetization as a result of competing broadening effects. We also elucidate the pronounced nonlinear magnetization dynamics, which appears on intermediate time scales in the presence of an asymmetric coupling to the electrodes.

  5. Attractive Hubbard model with disorder and the generalized Anderson theorem

    International Nuclear Information System (INIS)

    Using the generalized DMFT+Σ approach, we study the influence of disorder on single-particle properties of the normal phase and the superconducting transition temperature in the attractive Hubbard model. A wide range of attractive potentials U is studied, from the weak coupling region, where both the instability of the normal phase and superconductivity are well described by the BCS model, to the strong-coupling region, where the superconducting transition is due to Bose-Einstein condensation (BEC) of compact Cooper pairs, formed at temperatures much higher than the superconducting transition temperature. We study two typical models of the conduction band with semi-elliptic and flat densities of states, respectively appropriate for three-dimensional and two-dimensional systems. For the semi-elliptic density of states, the disorder influence on all single-particle properties (e.g., density of states) is universal for an arbitrary strength of electronic correlations and disorder and is due to only the general disorder widening of the conduction band. In the case of a flat density of states, universality is absent in the general case, but still the disorder influence is mainly due to band widening, and the universal behavior is restored for large enough disorder. Using the combination of DMFT+Σ and Nozieres-Schmitt-Rink approximations, we study the disorder influence on the superconducting transition temperature Tc for a range of characteristic values of U and disorder, including the BCS-BEC crossover region and the limit of strong-coupling. Disorder can either suppress Tc (in the weak-coupling region) or significantly increase Tc (in the strong-coupling region). However, in all cases, the generalized Anderson theorem is valid and all changes of the superconducting critical temperature are essentially due to only the general disorder widening of the conduction band

  6. DIVIMP Modeling of Impurity Transport in EAST

    International Nuclear Information System (INIS)

    Simulations of carbon impurity transport in SOL/divertor plasmas with Ohmic heating on EAST tokamak were performed using the two-dimensional (2D) Monte Carlo impurity transport code DIVIMP. The background plasmas for DIVIMP simulations were externally taken from B2.5/Eirene calculation. Besides the basic output of DIVIMP, the 2D density distributions of the carbon impurity with different ionization states and neutral carbon atoms were obtained, the 2D distributions of CII and CIII emissivities from C+1 and C+2 radiation respectively were also calculated. Comparison between the measured and calculated CIII emissivities showed favorable agreement, indicating that the impurity physics transport models, as implemented in the DIVIMP code, are suitable for the EAST tokamak plasma condition. (magnetically confined plasma)

  7. DIVIMP Modeling of Impurity Transport in EAST

    Science.gov (United States)

    Wang, Fuqiong; Chen, Yiping; Hu, Liqun

    2014-07-01

    Simulations of carbon impurity transport in SOL/divertor plasmas with Ohmic heating on EAST tokamak were performed using the two-dimensional (2D) Monte Carlo impurity transport code DIVIMP. The background plasmas for DIVIMP simulations were externally taken from B2.5/Eirene calculation. Besides the basic output of DIVIMP, the 2D density distributions of the carbon impurity with different ionization states and neutral carbon atoms were obtained, the 2D distributions of CII and CIII emissivities from C+1 and C+2 radiation respectively were also calculated. Comparison between the measured and calculated CIII emissivities showed favorable agreement, indicating that the impurity physics transport models, as implemented in the DIVIMP code, are suitable for the EAST tokamak plasma condition.

  8. Parabolic Anderson Model in a Dynamic Random Environment: Random Conductances

    Science.gov (United States)

    Erhard, D.; den Hollander, F.; Maillard, G.

    2016-06-01

    The parabolic Anderson model is defined as the partial differential equation ∂ u( x, t)/ ∂ t = κ Δ u( x, t) + ξ( x, t) u( x, t), x ∈ ℤ d , t ≥ 0, where κ ∈ [0, ∞) is the diffusion constant, Δ is the discrete Laplacian, and ξ is a dynamic random environment that drives the equation. The initial condition u( x, 0) = u 0( x), x ∈ ℤ d , is typically taken to be non-negative and bounded. The solution of the parabolic Anderson equation describes the evolution of a field of particles performing independent simple random walks with binary branching: particles jump at rate 2 d κ, split into two at rate ξ ∨ 0, and die at rate (- ξ) ∨ 0. In earlier work we looked at the Lyapunov exponents λ p(κ ) = limlimits _{tto ∞} 1/t log {E} ([u(0,t)]p)^{1/p}, quad p in {N} , qquad λ 0(κ ) = limlimits _{tto ∞} 1/2 log u(0,t). For the former we derived quantitative results on the κ-dependence for four choices of ξ : space-time white noise, independent simple random walks, the exclusion process and the voter model. For the latter we obtained qualitative results under certain space-time mixing conditions on ξ. In the present paper we investigate what happens when κΔ is replaced by Δ𝓚, where 𝓚 = {𝓚( x, y) : x, y ∈ ℤ d , x ˜ y} is a collection of random conductances between neighbouring sites replacing the constant conductances κ in the homogeneous model. We show that the associated annealed Lyapunov exponents λ p (𝓚), p ∈ ℕ, are given by the formula λ p({K} ) = {sup} {λ p(κ ) : κ in {Supp} ({K} )}, where, for a fixed realisation of 𝓚, Supp(𝓚) is the set of values taken by the 𝓚-field. We also show that for the associated quenched Lyapunov exponent λ 0(𝓚) this formula only provides a lower bound, and we conjecture that an upper bound holds when Supp(𝓚) is replaced by its convex hull. Our proof is valid for three classes of reversible ξ, and for all 𝓚

  9. Basic Properties of Conductivity and Normal Hall Effect in the Periodic Anderson Model

    Science.gov (United States)

    Watanabe, Shinji; Miyake, Kazumasa

    2016-04-01

    Exact formulas of diagonal conductivity σxx and Hall conductivity σxy are derived from the Kubo formula in hybridized two-orbital systems with arbitrary band dispersions. On the basis of the theoretical framework for the Fermi liquid based on these formulas, the ground-state properties of the periodic Anderson model with electron correlation and weak impurity scattering are studied on the square lattice. It is shown that imbalance of the mass-renormalization factors causes remarkable increase in σxx and σxy in the valence-fluctuation regime as the f level increases while the cancellation of the renormalization factors causes slight increase in σxx and σxy in the Kondo regime. The Hall coefficient RH shows almost constant behavior in both the regimes. Near half filling, RH is expressed by the total hole density as R{H} = 1/(bar{n}{hole}e) while RH approaches zero near quarter filling, which reflects the curvature of the Fermi surface. These results hold as far as the damping rate for f electrons is less than about 10% of the renormalized hybridization gap. From these results we discuss pressure dependence of residual resistivity and normal Hall effect in Ce- and Yb-based heavy electron systems.

  10. Quantum criticality of the two-channel pseudogap Anderson model: universal scaling in linear and non-linear conductance.

    Science.gov (United States)

    Wu, Tsan-Pei; Wang, Xiao-Qun; Guo, Guang-Yu; Anders, Frithjof; Chung, Chung-Hou

    2016-05-01

    The quantum criticality of the two-lead two-channel pseudogap Anderson impurity model is studied. Based on the non-crossing approximation (NCA) and numerical renormalization group (NRG) approaches, we calculate both the linear and nonlinear conductance of the model at finite temperatures with a voltage bias and a power-law vanishing conduction electron density of states, [Formula: see text] (0  conductances at the 2CK-LM quantum critical point are identified. Clear distinctions are found on the critical exponents between linear and non-linear conductance at criticality. The implications of these two distinct quantum critical properties for the non-equilibrium quantum criticality in general are discussed. PMID:27045815

  11. Microscopic models of impurities in silicon

    International Nuclear Information System (INIS)

    The study of electronic structure of insulated and complex puntual impurities in silicon responsible by the appearing of deep energy levels in the forbiden band of semiconductor, is presented. The molecular cluster model with the treatment of surface orbitals by Watson sphere within the formalism of Xα multiple scattering method, was used. The electronic structures of three clusters representative of perfect silicon crystal, which were used for the impurity studies, are presented. The method was applied to analyse insulated impurities of substitutional and interstitial hydrogen (Si:H and Si:Hi), subtitutional and interstitial iron in neutral and positive charge states (Si:Fe0,+, Si:Fe0,+) and substitutional gold in three charge states(Si,Au-,0,+). The thetraedic interstitial defect of silicon (Si:Sii) was also studied. The complex impurities: neighbour iron pair in the lattice (Si:Fe2), substitutional gold-interstitial iron pair (Si:AusFe) and substitutional boron-interstitial hydrogen pair (Si:BsHi), were analysed. (M.C.K.)

  12. Enhanced Wegner and Minami estimates and eigenvalue statistics of random Anderson models at spectral edges

    CERN Document Server

    Germinet, François

    2011-01-01

    We consider the discrete Anderson model and prove enhanced Wegner and Minami estimates where the interval length is replaced by the IDS computed on the interval. We use these estimates to improve on the description of finite volume eigenvalues and eigenfunctions obtained in a previous paper. As a consequence of the improved description of eigenvalues and eigenfunctions, we revisit a number of results on the spectral statistics in the localized regime and extend their domain of validity, namely : - the local spectral statistics for the unfolded eigenvalues; - the local asymptotic ergodicity of the unfolded eigenvalues; In dimension 1, for the standard Anderson model, the improvement enables us to obtain the local spectral statistics at band edge, that is in the Lifshitz tail regime. In higher dimensions, this works for modified Anderson models.

  13. Boundary quantum criticality in models of magnetic impurities coupled to bosonic baths

    International Nuclear Information System (INIS)

    We investigate quantum impurity problems, where a local magnetic moment is coupled to the spin density of a bosonic environment, leading to bosonic versions of the standard Kondo and Anderson impurity models. In a physical situation, these bosonic environments can correspond either to deconfined spinons in certain classes of Z2 frustrated antiferromagnets, or to particles in a multicomponent Bose gase (in which case the spin degree of freedom is attributed to hyperfine levels). Using renormalization group techniques, we establish that our impurity models, which feature an exchange interaction analogous to Kondo impurities in Fermi liquids, allow flow toward a stable strong-coupling state. Since the low-energy bosons exist around a single point in momentum space, and there is no Fermi surface, an impurity quantum phase transition occurs at intermediate coupling, separating screened and unscreened phases. This behavior is qualitatively different from previously studied spin-isotropic variants of the spin-boson model, which display stable intermediate-coupling fixed points and no screening

  14. Surface hopping with a manifold of electronic states. II. Application to the many-body Anderson-Holstein model

    International Nuclear Information System (INIS)

    We investigate a simple surface hopping (SH) approach for modeling a single impurity level coupled to a single phonon and an electronic (metal) bath (i.e., the Anderson-Holstein model). The phonon degree of freedom is treated classically with motion along–and hops between–diabatic potential energy surfaces. The hopping rate is determined by the dynamics of the electronic bath (which are treated implicitly). For the case of one electronic bath, in the limit of small coupling to the bath, SH recovers phonon relaxation to thermal equilibrium and yields the correct impurity electron population (as compared with numerical renormalization group). For the case of out of equilibrium dynamics, SH current-voltage (I-V) curve is compared with the quantum master equation (QME) over a range of parameters, spanning the quantum region to the classical region. In the limit of large temperature, SH and QME agree. Furthermore, we can show that, in the limit of low temperature, the QME agrees with real-time path integral calculations. As such, the simple procedure described here should be useful in many other contexts

  15. Quantum criticality of the two-channel pseudogap Anderson model: universal scaling in linear and non-linear conductance

    Science.gov (United States)

    Wu, Tsan-Pei; Wang, Xiao-Qun; Guo, Guang-Yu; Anders, Frithjof; Chung, Chung-Hou

    2016-05-01

    The quantum criticality of the two-lead two-channel pseudogap Anderson impurity model is studied. Based on the non-crossing approximation (NCA) and numerical renormalization group (NRG) approaches, we calculate both the linear and nonlinear conductance of the model at finite temperatures with a voltage bias and a power-law vanishing conduction electron density of states, {ρ\\text{c}}(ω )\\propto |ω -{μ\\text{F}}{{|}r} (0  energy {μ\\text{F}} . At a fixed lead-impurity hybridization, a quantum phase transition from the two-channel Kondo (2CK) to the local moment (LM) phase is observed with increasing r from r  =  0 to r={{r}\\text{c}}law scalings from the well-known \\sqrt{T} or \\sqrt{V} form is found. Moreover, novel power-law scalings in conductances at the 2CK-LM quantum critical point are identified. Clear distinctions are found on the critical exponents between linear and non-linear conductance at criticality. The implications of these two distinct quantum critical properties for the non-equilibrium quantum criticality in general are discussed.

  16. Spectral statistics for the discrete Anderson model in the localized regime

    CERN Document Server

    Germinet, François

    2010-01-01

    We report on recent results on the spectral statistics of the discrete Anderson model in the localized phase. Our results show, in particular, that, for the discrete Anderson Hamiltonian with smoothly distributed random potential at sufficiently large coupling, the limit of the level spacing distribution is that of i.i.d. random variables distributed according to the density of states of the random Hamiltonian. This text is a contribution to the proceedings of the conference "Spectra of Random Operators and Related Topics" held at Kyoto University, 02-04/12/09 organized by N. Minami and N. Ueki.

  17. Adaptive and self-averaging Thouless-Anderson-Palmer mean-field theory for probabilistic modeling

    DEFF Research Database (Denmark)

    Opper, Manfred; Winther, Ole

    2001-01-01

    We develop a generalization of the Thouless-Anderson-Palmer (TAP) mean-field approach of disorder physics. which makes the method applicable to the computation of approximate averages in probabilistic models for real data. In contrast to the conventional TAP approach, where the knowledge of the...

  18. Tractable approximations for probabilistic models: The adaptive Thouless-Anderson-Palmer mean field approach

    DEFF Research Database (Denmark)

    Opper, Manfred; Winther, Ole

    2001-01-01

    We develop an advanced mean held method for approximating averages in probabilistic data models that is based on the Thouless-Anderson-Palmer (TAP) approach of disorder physics. In contrast to conventional TAP. where the knowledge of the distribution of couplings between the random variables is...

  19. Tractable approximations for probabilistic models: The adaptive Thouless-Anderson-Palmer mean field approach

    OpenAIRE

    Opper, Manfred; Winther, Ole

    2001-01-01

    We develop an advanced mean held method for approximating averages in probabilistic data models that is based on the Thouless-Anderson-Palmer (TAP) approach of disorder physics. In contrast to conventional TAP. where the knowledge of the distribution of couplings between the random variables is required. our method adapts to the concrete couplings. We demonstrate the validity of our approach, which is so far restricted to models with nonglassy behavior? by replica calculations for a wide clas...

  20. Perturbation theory for Lyapunov exponents of an Anderson model on a strip

    CERN Document Server

    Schulz-Baldes, H

    2003-01-01

    It is proven that the localization length of an Anderson model on a strip of width $L$ is bounded above by $L/\\lambda^2$ for small values of the coupling constant $\\lambda$ of the disordered potential. For this purpose, a new formalism is developed in order to calculate the bottom Lyapunov exponent associated with random products of large symplectic matrices perturbatively in the coupling constant of the randomness.

  1. Interplay between magnetic correlation and evolution of Fermi liquid in the periodic Anderson model

    International Nuclear Information System (INIS)

    A simple effective scheme to improve the self energy obtained by the dynamical mean field theory is proposed, in which a feedback of magnetic fluctuations is taken into account. We demonstrate effectiveness of the scheme for the two-dimensional periodic Anderson model by investigating the effect of the magnetic fluctuation in the formation of heavy quasiparticles. It is found that the spectral intensity near the Fermi level is strongly suppressed by the antiferromagnetic fluctuation slightly above the magnetic instability.

  2. The exhaustion problem in the periodic Anderson model: An X-boson approach

    International Nuclear Information System (INIS)

    We study the thermodynamical properties of the periodic Anderson model (PAM), within the X-boson approach. The exhaustion problem is studied and we calculate the entropy and the specific heat for the heavy fermion Kondo regime (HF-K) of the PAM. We compute numerically the evolution of the Kondo lattice TKL and the Fermi liquid T* temperatures as function of the conduction electron occupation number nc. The results obtained are consistent with others reported in the literature for the Kondo lattice

  3. Entanglement in One-Dimensional Anderson Model with Long-Range Correlated Disorder

    Institute of Scientific and Technical Information of China (English)

    GUO Zi-Zheng

    2008-01-01

    @@ By using the measure of concurrence,the entanglement of the ground state in the one-dimensional Anderson model is studied with consideration of the long-range correlations. Three kinds of correlations are discussed.We compare the effects of the long-rang Gaussian and power-law correlations between the site energies on the concurrence,and demonstrate the existence of the band structure of the concurrence in the power-law case.

  4. The band-centre anomaly in the 1D Anderson model with correlated disorder

    International Nuclear Information System (INIS)

    We study the band-centre anomaly in the one-dimensional Anderson model with weak correlated disorder. Our analysis is based on the Hamiltonian map approach; the correspondence between the discrete model and its continuous counterpart is discussed in detail. We obtain analytical expressions of the localization length and of the invariant measure of the phase variable, valid for energies in a neighbourhood of the band centre. By applying these general results to specific forms of correlated disorder, we show how correlations can enhance or suppress the anomaly at the band centre. (paper)

  5. Anderson localization through Polyakov loops: Lattice evidence and random matrix model

    International Nuclear Information System (INIS)

    We investigate low-lying fermion modes in SU(2) gauge theory at temperatures above the phase transition. Both staggered and overlap spectra reveal transitions from chaotic (random matrix) to integrable (Poissonian) behavior accompanied by an increasing localization of the eigenmodes. We show that the latter are trapped by local Polyakov loop fluctuations. Islands of such ''wrong'' Polyakov loops can therefore be viewed as defects leading to Anderson localization in gauge theories. We find strong similarities in the spatial profile of these localized staggered and overlap eigenmodes. We discuss possible interpretations of this finding and present a sparse random matrix model that reproduces these features.

  6. Anderson localization through Polyakov loops: Lattice evidence and random matrix model

    Science.gov (United States)

    Bruckmann, Falk; Kovács, Tamás G.; Schierenberg, Sebastian

    2011-08-01

    We investigate low-lying fermion modes in SU(2) gauge theory at temperatures above the phase transition. Both staggered and overlap spectra reveal transitions from chaotic (random matrix) to integrable (Poissonian) behavior accompanied by an increasing localization of the eigenmodes. We show that the latter are trapped by local Polyakov loop fluctuations. Islands of such “wrong” Polyakov loops can therefore be viewed as defects leading to Anderson localization in gauge theories. We find strong similarities in the spatial profile of these localized staggered and overlap eigenmodes. We discuss possible interpretations of this finding and present a sparse random matrix model that reproduces these features.

  7. Anderson localization through Polyakov loops: lattice evidence and Random matrix model

    CERN Document Server

    Bruckmann, Falk; Schierenberg, Sebastian

    2011-01-01

    We investigate low-lying fermion modes in SU(2) gauge theory at temperatures above the phase transition. Both staggered and overlap spectra reveal transitions from chaotic (random matrix) to integrable (Poissonian) behavior accompanied by an increasing localization of the eigenmodes. We show that the latter are trapped by local Polyakov loop fluctuations. Islands of such "wrong" Polyakov loops can therefore be viewed as defects leading to Anderson localization in gauge theories. We find strong similarities in the spatial profile of these localized staggered and overlap eigenmodes. We discuss possible interpretations of this finding and present a sparse random matrix model that reproduces these features.

  8. Extending the Newns-Anderson model to molecules with floppy degrees of freedom. Validation by electronic structure calculations

    CERN Document Server

    Baldea, Ioan

    2012-01-01

    In cases where reorganization is important, present theoretical studies of molecular transport have inherently to resort to models. The Newns-Anderson model is ubiquitous for this purpose but, to author's knowledge, attempts to validate/challenge this model by microscopic calculations are missing in the literature. In this work, results of electronic structure calculations are presented, which demonstrate that the conventional Newns-Anderson model fails to describe redox-active tunneling junctions of recent experimental interest. For the case considered, the ($4, 4^\\prime$)-bipyridine molecule, the failure traces back to the floppy degree of freedom represented by the relative rotation of the two pyridine rings. Expressions that generalize the Newns-Anderson model are deduced, which include significant anharmonicities. These expressions can be straightforwardly utilized as input information in calculations of the partially coherent transport.

  9. Positivity of Lyapunov exponents for Anderson-type models on two coupled strings

    Directory of Open Access Journals (Sweden)

    Hakim Boumaza

    2007-03-01

    Full Text Available We study two models of Anderson-type random operators on two deterministically coupled continuous strings. Each model is associated with independent, identically distributed four-by-four symplectic transfer matrices, which describe the asymptotics of solutions. In each case we use a criterion by Gol'dsheid and Margulis (i.e. Zariski denseness of the group generated by the transfer matrices in the group of symplectic matrices to prove positivity of both leading Lyapunov exponents for most energies. In each case this implies almost sure absence of absolutely continuous spectrum (at all energies in the first model and for sufficiently large energies in the second model. The methods used allow for singularly distributed random parameters, including Bernoulli distributions.

  10. Decoherence-induced conductivity in the one-dimensional Anderson model

    Energy Technology Data Exchange (ETDEWEB)

    Stegmann, Thomas; Wolf, Dietrich E. [Department of Physics, University of Duisburg-Essen and CENIDE, 47048 Duisburg (Germany); Ujsághy, Orsolya [Department of Theoretical Physics, Budapest University of Technology and Economics, Budafoki út 8., H-1521 Budapest (Hungary)

    2014-08-20

    We study the effect of decoherence on the electron transport in the one-dimensional Anderson model by means of a statistical model [1, 2, 3, 4, 5]. In this model decoherence bonds are randomly distributed within the system, at which the electron phase is randomized completely. Afterwards, the transport quantity of interest (e.g. resistance or conductance) is ensemble averaged over the decoherence configurations. Averaging the resistance of the sample, the calculation can be performed analytically. In the thermodynamic limit, we find a decoherence-driven transition from the quantum-coherent localized regime to the Ohmic regime at a critical decoherence density, which is determined by the second-order generalized Lyapunov exponent (GLE) [4].

  11. Local moment approach as a quantum impurity solver for the Hubbard model

    Science.gov (United States)

    Barman, Himadri

    2016-07-01

    The local moment approach (LMA) has presented itself as a powerful semianalytical quantum impurity solver (QIS) in the context of the dynamical mean-field theory (DMFT) for the periodic Anderson model and it correctly captures the low-energy Kondo scale for the single impurity model, having excellent agreement with the Bethe ansatz and numerical renormalization group (NRG) results. However, the most common correlated lattice model, the Hubbard model, has not been explored well within the LMA+DMFT framework beyond the insulating phase. Here in our work, within the framework we complete the filling-interaction phase diagram of the single band Hubbard model at zero temperature. Our formalism is generic to any particle filling and can be extended to finite temperature. We contrast our results with another QIS, namely the iterated perturbation theory (IPT) and show that the second spectral moment sum rule improves better as the Hubbard interaction strength grows stronger in LMA, whereas it severely breaks down after the Mott transition in IPT. For the metallic case, the Fermi liquid (FL) scaling agreement with the NRG spectral density supports the fact that the FL scale emerges from the inherent Kondo physics of the impurity model. We also show that, in the metallic phase, the FL scaling of the spectral density leads to universality which extends to infinite frequency range at infinite correlation strength (strong coupling). At large interaction strength, the off half-filling spectral density forms a pseudogap near the Fermi level and filling-controlled Mott transition occurs as one approaches the half-filling. As a response property, we finally study the zero temperature optical conductivity and find universal features such as absorption peak position governed by the FL scale and a doping independent crossing point, often dubbed the isosbestic point in experiments.

  12. Full counting statistics for orbital-degenerate impurity Anderson model with Hund's rule exchange coupling.

    Science.gov (United States)

    Sakano, Rui; Nishikawa, Yunori; Oguri, Akira; Hewson, Alex C; Tarucha, Seigo

    2012-06-29

    We study nonequilibrium current fluctuations through a quantum dot, which includes a ferromagnetic Hund's rule coupling J, in the low-energy Fermi liquid regime using the renormalized perturbation theory. The resulting cumulant for the current distribution in the particle-hole symmetric case shows that spin-triplet and spin-singlet pairs of quasiparticles are formed in the current due to the Hund's rule coupling, and these pairs enhance the current fluctuations. In the fully screened higher-spin Kondo limit, the Fano factor takes a value F(b)=(9M+6)/(5M+4) determined by the orbital degeneracy M. We also investigate the crossover between the small and large J limits in the two-orbital case M=2, using the numerical renormalization group approach. PMID:23004997

  13. Anderson-Holstein model in two flavors of the noncrossing approximation

    Science.gov (United States)

    Chen, Hsing-Ta; Cohen, Guy; Millis, Andrew J.; Reichman, David R.

    2016-05-01

    The dynamical interplay between electron-electron interactions and electron-phonon coupling is investigated within the Anderson-Holstein model, a minimal model for open quantum systems that embody these effects. The influence of phonons on spectral and transport properties is explored in equilibrium, for nonequilibrium steady state and for transient dynamics after a quench. Both the particle-hole symmetric and the more generic particle-hole asymmetric cases are studied. The treatment is based on two complementary noncrossing approximations, the first of which is constructed around the weak-coupling limit and the second around the polaron limit. In general, the two methods disagree in nontrivial ways, indicating that more reliable approaches to the problem are needed. The frameworks used here can form the starting point for numerically exact methods based on bold-line continuous-time quantum Monte Carlo algorithms capable of treating open systems simultaneously coupled to multiple fermionic and bosonic baths.

  14. Delocalization and Sensitivity of Quantum Wavepacket in Coherently Perturbed Kicked Anderson Model

    Directory of Open Access Journals (Sweden)

    Hiroaki Yamada

    2004-03-01

    Full Text Available Abstract: We consider quantum diffusion of the initially localized wavepacket in one-dimensional kicked disordered system with classical coherent perturbation. The wavepacket localizes in the unperturbed kicked Anderson model. However, the wavepacket get delocalized even by coupling with monochromatic perturbation. We call the state "dynamically delocalized state". It is numerically shown that the delocalized wavepacket spread obeying diffusion law, and the perturbation strength dependence of the diffusion rate is given. The sensitivity of the delocalized state is also shown by the time-reversal experiment after random change in phase of the wavepacket. Moreover, it is found that the diffusion strongly depend on the initial phase of the perturbation. We discuss a relation between the "classicalization" of the quantum wave packet and the time-dependence of the initial phase dependence. The complex structure of the initial phase dependence is related to the entropy production in the quantum system.

  15. Efficient Localization Bounds in a Continuous N-Particle Anderson Model with Long-Range Interaction

    Science.gov (United States)

    Chulaevsky, Victor

    2016-04-01

    We establish strong dynamical and exponential spectral localization for a class of multi-particle Anderson models in a Euclidean space with an alloy-type random potential and a sub-exponentially decaying interaction of infinite range. For the first time in the mathematical literature, the uniform decay bounds on the eigenfunction correlators (EFCs) at low energies are proved, in the multi-particle continuous configuration space, in the (symmetrized) norm-distance, which is a natural distance in the multi-particle configuration space, and not in the Hausdorff distance. This results in uniform bounds on the EFCs in arbitrarily large but bounded domains in the physical configuration space, and not only in the actually infinite space, as in prior works on multi-particle localization in Euclidean spaces.

  16. Phase diagram and reentrance for the 3D Edwards–Anderson model using information theory

    International Nuclear Information System (INIS)

    Data compressor techniques are used to study the phase diagram of the generalized Edwards–Anderson model in three dimensions covering the full range of mixture between ferromagnetic (concentration 1−x) and antiferromagnetic interactions (concentration x). The recently proposed data compressor wlzip is used to recognize criticality by the maximum information content in the files storing the simulation processes. The method allows not only the characterization of the ferromagnetic to paramagnetic (FP) transition (x<0.22, or x>0.78) but also it equally well yields the spin-glass to paramagnetic (SP) transition (0.22Anderson model. • Ferromagnetic to paramagnetic and spin-glass to paramagnetic transitions are found. • A reentrant behavior is reported near the triple point. • Data compressor wlzip can operate for the full range of the phase diagram. • Results are robust with respect to equilibration and lattices size effects are small

  17. Pairwise entanglement in the XX model with a magnetic impurity

    International Nuclear Information System (INIS)

    For a three-qubit Heisenberg model in a uniform magnetic field, the pairwise thermal entanglement of any two sites is identical due to the exchange symmetry of sites. In this paper we consider the effect of a non-uniform magnetic field on the Heisenberg model, modelling a magnetic impurity on one site. Since pairwise entanglement is calculated by tracing out one of the three sites, the entanglement clearly depends on which site the impurity is located. When the impurity is located on the site which is traced out, that is, when it acts as an external field of the pair, the entanglement can be enhanced to the maximal value 1; while when the field acts on a site of the pair the corresponding concurrence can only be increased from 1/3 to 2/3. (author)

  18. Remotely screened electron-impurity scattering model for nanoscale MOSFETs

    International Nuclear Information System (INIS)

    The ionized impurities within the channel of nanoscale MOSFETs are shown to be strongly remotely screened by the close proximity of the highly doped, degenerate source and drain regions due to polarization charge effects. The position of the ionized impurity within the channel region controls the strength of the remote screening due to polarization charges induced in the source and drain, which increase heavily as the channel screening length exceeds the channel length. A remotely screened ionized impurity scattering potential is calculated based on an exact solution to Poisson's equation for a model system. This scattering potential includes the polarization charge effects from the source and the drain which may contribute separately or in combination depending on the position of the ionized impurity and the channel screening length. A scattering model is developed based on a simplified form of this scattering potential that is suitable for use in Monte Carlo simulations. The resulting scattering model is analysed and is shown to increase the ionized impurity mobility in the channel by a noticeable amount

  19. Non-Fermi liquid fixed points of a two-channel Anderson model

    International Nuclear Information System (INIS)

    A generalized two-channel Anderson Hamiltonian is diagonalized via the numerical renormalization group. The spectrum shows non-Fermi liquid fixed point for isotropic channel hybridization and normal Fermi liquid for the anisotropic case

  20. Non-Fermi liquid fixed points of a two-channel Anderson model

    Energy Technology Data Exchange (ETDEWEB)

    Ferreira, J.V.B.; Oliveira, L.N. de; Cox, D.L.; Libero, V.L. E-mail: valter@if.sc.usp.br

    2001-05-01

    A generalized two-channel Anderson Hamiltonian is diagonalized via the numerical renormalization group. The spectrum shows non-Fermi liquid fixed point for isotropic channel hybridization and normal Fermi liquid for the anisotropic case.

  1. Matrix product state calculations for one-dimensional quantum chains and quantum impurity models

    International Nuclear Information System (INIS)

    involving a Kondo exciton and population switching in quantum dots. It turns out that both phenomena rely on the various manifestations of Anderson orthogonality (AO), which describes the fact that the response of the Fermi sea to a quantum quench (i.e. an abrupt change of some property of the impurity or quantum dot) is a change of the scattering phase shifts of all the single-particle wave functions, therefore drastically changing the system. In this context, we demonstrate that NRG, a highly accurate method for quantum impurity models, allows for the calculation of all static and dynamic quantities related to AO and present an extensive NRG study for population switching in quantum dots. (orig.)

  2. Matrix product state calculations for one-dimensional quantum chains and quantum impurity models

    Energy Technology Data Exchange (ETDEWEB)

    Muender, Wolfgang

    2011-09-28

    involving a Kondo exciton and population switching in quantum dots. It turns out that both phenomena rely on the various manifestations of Anderson orthogonality (AO), which describes the fact that the response of the Fermi sea to a quantum quench (i.e. an abrupt change of some property of the impurity or quantum dot) is a change of the scattering phase shifts of all the single-particle wave functions, therefore drastically changing the system. In this context, we demonstrate that NRG, a highly accurate method for quantum impurity models, allows for the calculation of all static and dynamic quantities related to AO and present an extensive NRG study for population switching in quantum dots. (orig.)

  3. Slow dynamics in a two-dimensional Anderson-Hubbard model

    Science.gov (United States)

    Bar Lev, Yevgeny; Reichman, David R.

    2016-02-01

    We study the real-time dynamics of a two-dimensional Anderson-Hubbard model using nonequilibrium self-consistent perturbation theory within the second-Born approximation. When compared with exact diagonalization performed on small clusters, we demonstrate that for strong disorder this technique approaches the exact result on all available timescales, while for intermediate disorder, in the vicinity of the many-body localization transition, it produces quantitatively accurate results up to nontrivial times. Our method allows for the treatment of system sizes inaccessible by any numerically exact method and for the complete elimination of finite-size effects for the times considered. We show that for a sufficiently strong disorder the system becomes nonergodic, while for intermediate disorder strengths and for all accessible timescales transport in the system is strictly subdiffusive. We argue that these results are incompatible with a simple percolation picture, but are consistent with the heuristic random resistor network model where subdiffusion may be observed for long times until a crossover to diffusion occurs. The prediction of slow finite-time dynamics in a two-dimensional interacting and disordered system can be directly verified in future cold-atoms experiments.

  4. Characterizing and improving generalized belief propagation algorithms on the 2D Edwards–Anderson model

    International Nuclear Information System (INIS)

    We study the performance of different message passing algorithms in the two-dimensional Edwards–Anderson model. We show that the standard belief propagation (BP) algorithm converges only at high temperature to a paramagnetic solution. Then, we test a generalized belief propagation (GBP) algorithm, derived from a cluster variational method (CVM) at the plaquette level. We compare its performance with BP and with other algorithms derived under the same approximation: double loop (DL) and a two-way message passing algorithm (HAK). The plaquette-CVM approximation improves BP in at least three ways: the quality of the paramagnetic solution at high temperatures, a better estimate (lower) for the critical temperature, and the fact that the GBP message passing algorithm converges also to nonparamagnetic solutions. The lack of convergence of the standard GBP message passing algorithm at low temperatures seems to be related to the implementation details and not to the appearance of long range order. In fact, we prove that a gauge invariance of the constrained CVM free energy can be exploited to derive a new message passing algorithm which converges at even lower temperatures. In all its region of convergence this new algorithm is faster than HAK and DL by some orders of magnitude

  5. Nonequilibrium transport in the Anderson-Holstein model with interfacial screening

    Science.gov (United States)

    Perfetto, Enrico; Stefanucci, Gianluca

    Image charge effects in nanoscale junctions with strong electron-phonon coupling open the way to unexplored physical scenarios. Here we present a comprehensive study of the transport properties of the Anderson-Holstein model in the presence of dot-lead repulsion. We propose an accurate many-body approach to deal with the simultaneous occurrence of the Franck-Condon blockade and the screening-induced enhancement of the polaron mobility. Remarkably, we find that a novel mechanism of negative differential conductance origins from the competition between the charge blocking due to the electron-phonon interaction and the charge deblocking due to the image charges. An experimental setup to observe this phenomenon is discussed. References [1]E. Perfetto, G. Stefanucci and M. Cini, Phys. Rev. B 85, 165437 (2012). [2] E. Perfetto and G. Stefanucci, Phys. Rev. B 88, 245437 (2013). [3] E. Perfetto and G. Stefanucci, Journal of Computational Electronics 14, 352 (2015). E.P. and G.S. acknowledge funding by MIUR FIRB Grant No. RBFR12SW0J.

  6. Eigenfunction structure and scaling of two interacting particles in the one-dimensional Anderson model

    Science.gov (United States)

    Frahm, Klaus M.

    2016-04-01

    The localization properties of eigenfunctions for two interacting particles in the one-dimensional Anderson model are studied for system sizes up to N = 5000 sites corresponding to a Hilbert space of dimension ≈107 using the Green function Arnoldi method. The eigenfunction structure is illustrated in position, momentum and energy representation, the latter corresponding to an expansion in non-interacting product eigenfunctions. Different types of localization lengths are computed for parameter ranges in system size, disorder and interaction strengths inaccessible until now. We confirm that one-parameter scaling theory can be successfully applied provided that the condition of N being significantly larger than the one-particle localization length L1 is verified. The enhancement effect of the two-particle localization length L2 behaving as L2 ~ L21 is clearly confirmed for a certain quite large interval of optimal interactions strengths. Further new results for the interaction dependence in a very large interval, an energy value outside the band center, and different interaction ranges are obtained.

  7. Type-I integrable quantum impurities in the Heisenberg model

    CERN Document Server

    Doikou, Anastasia

    2013-01-01

    Type-I quantum impurities are investigated in the context of the integrable Heisenberg model. This type of defects is associated to the (q)-harmonic oscillator algebra. The transmission matrices associated to this particular type of defects are computed via the Bethe ansatz methodology for the XXX model, as well as for the critical and non-critical XXZ spin chain. In the attractive regime of the critical XXZ spin chain the transmission amplitudes for the breathers are also identified.

  8. Energy level statistics at the metal-insulator transition in the Anderson model of localization with anisotropic hopping

    OpenAIRE

    Milde, Frank; R{ö}mer, Rudolf A.

    1998-01-01

    Recently, a metal-insulator transition (MIT) was found in the anisotropic Anderson model of localization by transfer-matrix methods (TMM). This MIT has been also investigated by multifractal analysis (MFA) and the same critical disorders $W_c$ have been obtained within the accuracy of the data. We now employ energy level statistics (ELS) to further characterize the MIT. We find a crossover of the nearest-neighbor level spacing distribution $P(s)$ from GOE statistics at small disorder indicati...

  9. The physics of Kondo impurities in graphene.

    Science.gov (United States)

    Fritz, Lars; Vojta, Matthias

    2013-03-01

    This article summarizes our understanding of the Kondo effect in graphene, primarily from a theoretical perspective. We shall describe different ways to create magnetic moments in graphene, either by adatom deposition or via defects. For dilute moments, the theoretical description is in terms of effective Anderson or Kondo impurity models coupled to graphene's Dirac electrons. We shall discuss in detail the physics of these models, including their quantum phase transitions and the effect of carrier doping, and confront this with existing experimental data. Finally, we will point out connections to other quantum impurity problems, e.g., in unconventional superconductors, topological insulators, and quantum spin liquids. PMID:23411583

  10. The physics of Kondo impurities in graphene

    International Nuclear Information System (INIS)

    This article summarizes our understanding of the Kondo effect in graphene, primarily from a theoretical perspective. We shall describe different ways to create magnetic moments in graphene, either by adatom deposition or via defects. For dilute moments, the theoretical description is in terms of effective Anderson or Kondo impurity models coupled to graphene's Dirac electrons. We shall discuss in detail the physics of these models, including their quantum phase transitions and the effect of carrier doping, and confront this with existing experimental data. Finally, we will point out connections to other quantum impurity problems, e.g., in unconventional superconductors, topological insulators, and quantum spin liquids. (review article)

  11. Approaches to modeling of plasmas containing impurity at arbitrary concentration

    Science.gov (United States)

    Tokar, Mikhail Z.

    2016-02-01

    A new approximate method to modeling of two-ion-species plasmas with arbitrary concentration of impurity is developed. It based on the usage of equations for the electron density and the ratio of the ion species densities as new dependent variables. In contrast to motion equations for the ion mass velocities used normally, those for the new variables have a singularity at the Debye sheath only, as in the case of a one species plasma. Computations for the most critical situations of weak and intermediate friction between species due to Coulomb collisions reproduce nearly perfectly the results got by solving the original equations, however within a calculation time reduced by a factor of 102-103. In the case of strong friction, where ions’ velocities are very close each other, the normal procedure does not converge at all, but the new one, being precise in this limit, operates very reliably. Calculations are done for conditions typical in the linear device PSI-2, with deuterium plasmas seeded by neon impurity. For fixed electron and ion temperatures a critical density of impurity atoms is found, at which the electron density grows without limits. Such a catastrophic behavior does not occur if the electron and ion heat balances are taken into account to calculate the temperature profiles self-consistently.

  12. Anderson localization through Polyakov loops: lattice evidence and Random matrix model

    OpenAIRE

    Bruckmann, Falk; Kovács, Tamás G.; Schierenberg, Sebastian

    2011-01-01

    We investigate low-lying fermion modes in SU(2) gauge theory at temperatures above the phase transition. Both staggered and overlap spectra reveal transitions from chaotic (random matrix) to integrable (Poissonian) behavior accompanied by an increasing localization of the eigenmodes. We show that the latter are trapped by local Polyakov loop fluctuations. Islands of such "wrong" Polyakov loops can therefore be viewed as defects leading to Anderson localization in gauge theories. We find stron...

  13. Modeling Migration of Chemical Impurities in Drinking Water Supply Systems

    Science.gov (United States)

    Mercea, P.; Tosa, V.; Kovacs, Katalin; Piringer, O.

    2010-09-01

    A numerical method based on finite differences was developed to solve the problem of impurities' migration from a hollow core multilayer cylinder (pipe) filled with water. The numerical method is based on finite differences (FD) and the developed application is presented. The migration modeling is focused on the estimation of water contamination in a single household over a long period of time (up to 50 years). The input parameters for the FD algorithm are generated by Monte-Carlo sampling of a short term water consumption pattern in the household.

  14. A scaling limit theorem for the parabolic Anderson model with exponential potential

    CERN Document Server

    Lacoin, Hubert

    2010-01-01

    The parabolic Anderson problem is the Cauchy problem for the heat equation with random potential and localized initial condition. In this paper we consider potentials which are constant in time and independent exponentially distributed in space. We study the growth rate of the total mass of the solution in terms of weak and almost sure limit theorems, and the spatial spread of the mass in terms of a scaling limit theorem. The latter result shows that in this case, just like in the case of heavy tailed potentials, the mass gets trapped in a single relevant island with high probability.

  15. A one-dimensional plasma and impurity transport model for reversed field pinches

    International Nuclear Information System (INIS)

    In this thesis a one-dimensional (1-D) plasma and impurity transport model is developed to address issues related to impurity behavior in Reversed Field Pinch (RFP) fusion plasmas. A coronal non-equilibrium model is used for impurities. The impurity model is incorporated into an existing one dimensional plasma transport model creating a multi-species plasma transport model which treats the plasma and impurity evolution self-consistently. Neutral deuterium particles are treated using a one-dimensional (slab) model of neutral transport. The resulting mode, RFPBI, is then applied to existing RFP devices such as ZT-40M and MST, and also to examine steady state behavior of ZTH based on the design parameters. A parallel algorithm for the impurity transport equations is implemented and tested to determine speedup and efficiency

  16. Transport in the three-dimensional Anderson model: an analysis of the dynamics at scales below the localization length

    Energy Technology Data Exchange (ETDEWEB)

    Steinigeweg, Robin [Institut fuer Theoretische Physik, Technische Universitaet Braunschweig, Mendelsohnstrasse 3, D-38106 Braunschweig (Germany); Niemeyer, Hendrik; Gemmer, Jochen, E-mail: r.steinigeweg@tu-bs.d, E-mail: jgemmer@uos.d [Fachbereich Physik, Universitaet Osnabrueck, Barbarastrasse 7, D-49069 Osnabrueck (Germany)

    2010-11-15

    Single-particle transport in disordered potentials is investigated at scales below the localization length. The dynamics at those scales is concretely analyzed for the three-dimensional Anderson model with Gaussian on-site disorder. This analysis particularly includes the dependence of characteristic transport quantities on the amount of disorder and the energy interval, e.g. the mean free path that separates ballistic and diffusive transport regimes. For these regimes mean velocities and diffusion constants are quantitatively given. Using the Boltzmann equation in the limit of weak disorder, we reveal the known energy dependences of transport quantities. By the application of the time-convolutionless projection operator technique in the limit of strong disorder, we obtain evidence for much less pronounced energy dependences. All our results are partially confirmed by the numerically exact solution of the time-dependent Schroedinger equation or by approximative numerical integrators. A comparison with other findings in the literature is also provided.

  17. Effective cluster typical medium theory for the diagonal Anderson disorder model in one- and two-dimensions

    International Nuclear Information System (INIS)

    We develop a cluster typical medium theory to study localization in disordered electronic systems. Our formalism is able to incorporate non-local correlations beyond the local typical medium theory in a systematic way. The cluster typical medium theory utilizes the momentum-resolved typical density of states and hybridization function to characterize the localization transition. We apply the formalism to the Anderson model of localization in one- and two-dimensions. In one-dimension, we find that the critical disorder strength scales inversely with the linear cluster size with a power law, Wc ∼ (1/Lc)1/ν, whereas in two-dimensions, the critical disorder strength decreases logarithmically with the linear cluster size. Our results are consistent with previous numerical work and are in agreement with the one-parameter scaling theory. (paper)

  18. Modelling of turbulent impurity transport in fusion edge plasmas using measured and calculated ionization cross sections

    CERN Document Server

    Kendl, Alexander

    2014-01-01

    Turbulent transport of trace impurities impurities in the edge and scrape-off-layer of tokamak fusion plasmas is modelled by three dimensional electromagnetic gyrofluid computations including evolution of plasma profile gradients. The source function of impurity ions is dynamically computed from pre-determined measured and calculated electron impact ionization cross section data. The simulations describe the generation and further passive turbulent E-cross-B advection of the impurities by intermittent fluctuations and coherent filamentary structures (blobs) across the scrape-off-layer.

  19. DIVIMP modeling of impurity flows and screening in Alcator C-Mod

    International Nuclear Information System (INIS)

    We report on impurity transport modeling using the DIVIMP code which is able to qualitatively reproduce the poloidal variation of non-recycling impurity penetration factor (PFNR) found in C-Mod experiments: a lower PFNR is computed at the inboard (3.6%) and divertor target locations (0.7%) than at the outboard (11%). By artificially increasing the modeled inner SOL plasma flow to correspond to measured values, a better quantitative agreement between modeled and measured PFs is achieved. We have also roughly reproduced the observed penetration factor for recycling impurities both in time dependence and magnitude. The model has shown that under attached conditions, the majority of recycling impurity ions flow into the confined plasma through the outboard side separatrix. For detached conditions the impurity influx across the separatrix is more concentrated near the divertor

  20. Toward understanding and modeling of impurity gettering in silicon

    Energy Technology Data Exchange (ETDEWEB)

    Tan, Teh Y.; Gafiteanu, R.; Goesele, U.M. [Duke Univ., Durham, NC (United States)

    1995-08-01

    Gettering of harmful impurities away from the device active regions has already become an integral part of manufacturing integrated circuits (IC) using Czochralski (CZ) Si wafers, and is experiencing an increasing importance in Si solar cell fabrications for improving the cell efficiency. Gettering consists of (1) the creation of suitable gettering sites; and (2) the gettering processes of contaminants. Requirements for successful gettering differ between the IC and solar cell cases, because ICs are monolithic devices situated at the Si wafer surfaces while solar cells are bulk devices, and because the Si substrate materials used are different. For IC fabrications, the method used is that of intrinsic or internal gettering (IG) which utilizes oxygen precipitates and their associated defects in the CZ Si wafer bulk as gettering sites. Because of the bulk nature of IG sites, the scheme cannot be used also for solar cells. Only some kind of extrinsic or external gettering (EG) schemes with gettering sites located at the wafer surface regions can be used for solar cells. The gettering of the harmful contaminants, usually metals, to the gettering region involves the metal dissolution from precipitated state, the metal atom diffusion to and the stabilization at the gettering sites. A mathematical model of the gettering process is presented.

  1. Behaviors of impurity in ITER and DEMOs using BALDUR integrated predictive modeling code

    International Nuclear Information System (INIS)

    The behaviors of impurity are investigated using self-consistent modeling of 1.5D BALDUR integrated predictive modeling code, in which theory-based models are used for both core and edge region. In these simulations, a combination of NCLASS neoclassical transport and Multi-mode (MMM95) anomalous transport model is used to compute a core transport. The boundary is taken to be at the top of the pedestal, where the pedestal values are described using a theory-based pedestal model. This pedestal temperature model is based on a combination of magnetic and flow shear stabilization pedestal width scaling and an infinite-n ballooning pressure gradient model. The time evolution of plasma current, temperature and density profiles is carried out for ITER and DEMOs plasmas. As a result, the impurity behaviors such as impurity accumulation and impurity transport can be investigated. (author)

  2. Self-consistent modeling of plasma response to impurity spreading from intense localized source

    International Nuclear Information System (INIS)

    Non-hydrogen impurities unavoidably exist in hot plasmas of present fusion devices. They enter it intrinsically, due to plasma interaction with the wall of vacuum vessel, as well as are seeded for various purposes deliberately. Normally, the spots where injected particles enter the plasma are much smaller than its total surface. Under such conditions one has to expect a significant modification of local plasma parameters through various physical mechanisms, which, in turn, affect the impurity spreading. Self-consistent modeling of interaction between impurity and plasma is, therefore, not possible with linear approaches. A model based on the fluid description of electrons, main and impurity ions, and taking into account the plasma quasi-neutrality, Coulomb collisions of background and impurity charged particles, radiation losses, particle transport to bounding surfaces, is elaborated in this work. To describe the impurity spreading and the plasma response self-consistently, fluid equations for the particle, momentum and energy balances of various plasma components are solved by reducing them to ordinary differential equations for the time evolution of several parameters characterizing the solution in principal details: the magnitudes of plasma density and plasma temperatures in the regions of impurity localization and the spatial scales of these regions. The results of calculations for plasma conditions typical in tokamak experiments with impurity injection are presented. A new mechanism for the condensation phenomenon and formation of cold dense plasma structures is proposed.

  3. A Model of Irregular Impurity at the Surface of Nanoparticle and Catalytic Activity

    Institute of Scientific and Technical Information of China (English)

    I.V.Blinova; V.V.Gusarov; I.Yu.Popov

    2012-01-01

    A problem of nanocatalyst improvement is considered. The existence of irregularities at the surface of nanoparticle leads to the increasing of the surface/volume ratio and, correspondingly, to the improvement of the catalytic activity. But this impurity gives one an additional effect due to the change of the electronic density at the surface. We suggest simple model for the description of this effect. The model allows one to find the discrete spectrum of the Schrdinger operator for nanoparticle. Due to this impurity induced bound states the electron density increases near the surface. It leads to the increase of the catalytic activity of nanoparticles with surface impurities.

  4. Modeling of soluble impurities distribution in the steam generator secondary water

    Energy Technology Data Exchange (ETDEWEB)

    Matal, O.; Simo, T. [Energovyzkum s.r.o., Brno (Switzerland); Kucak, L.; Urban, F. [Slovak Technical Univ., Bratislava (Slovakia)

    1997-12-31

    A model was developed to compute concentration of impurities in the WWER 440 steam generator (SG) secondary water along the tube bundle. Calculated values were verified by concentration values obtained from secondary water sample chemical analysis. (orig.). 2 refs.

  5. Damage-spreading and out-of-equilibrium dynamics in the low-temperature regime of the two-dimensional ± J Edwards–Anderson model

    International Nuclear Information System (INIS)

    We present results showing the correlation between the out-of-equilibrium dynamics and the equilibrium damage-spreading process in the two-dimensional ± J Edwards–Anderson model at low temperatures. A key ingredient in our analysis is the projection of finite temperature spin configurations onto the ground state topology of the system. In particular, through numerical simulations we correlate ground state information with the out-of-equilibrium dynamics. We also analyse how the propagation of a small perturbation in equilibrated systems is related to the ground state topology. This damage-spreading study unveils the presence of rigid clusters of spins. We claim that these clusters give rise to the slow out-of-equilibrium dynamics observed in the temperature range between the glass temperature Tg = 0 of the two-dimensional ± J Edwards–Anderson model and the critical temperature Tc of the pure ferromagnetic Ising model

  6. Transmission resonance induced by a {delta}-like defect in the Fano-Anderson model with two Fano defects

    Energy Technology Data Exchange (ETDEWEB)

    Nguyen, Ba Phi; Kim, Kihong; Rotermund, Fabian [Department of Energy Systems Research, Ajou University, Suwon 443-749 (Korea, Republic of); Lim, Hanjo [Department of Electrical Engineering, Ajou University, Suwon 443-749 (Korea, Republic of)

    2012-09-15

    We study theoretically the propagation of waves in a discrete linear chain with two side-coupled Fano defects and one {delta}-like defect, using a modified Fano-Anderson model. Two separate cases, where the Fano defects are coupled to the chain by on-site coupling or by inter-site coupling, are considered. We find that the transmission behavior is very sensitive to whether the distance between the Fano defects and the {delta}-like defect, l, is even or odd. In the on-site coupling case, we find that for even values of l, the Fano-Feshbach resonance is sustained in the presence of a {delta}-like defect, but the position of the transmission peak is shifted and its shape becomes asymmetric. In the inter-site coupling case, the width of the asymmetric Fano resonance can be tuned by changing the coupling constants. When l is odd in the inter-site coupling case, we find that there exist two resonant transmissions in addition to the perfect reflection. In general, the {delta}-like defect strongly influences on the transmission resonance but does not alter the perfect reflection. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  7. Investigation of Anderson lattice behavior in Yb1-xLuxAl3

    International Nuclear Information System (INIS)

    Measurements of magnetic susceptibility χ(T), specific heat C(T), Hall coefficient RH(T), and Yb valence ν = 2 + nf [f-occupation number nf (T) determined from Yb L3 x-ray absorption measurements] were carried out on single crystals of Yb1-xLuxAl3. The low temperature anomalies observed in χ(T) and C(T) corresponding to an energy scale Tcoh ∼ 40 K in the intermediate valence, Kondo lattice compound YbAl3 are suppressed by Lu concentrations as small as 5% suggesting these low-T anomalies are extremely sensitive to disorder and, therefore, are a true coherence effect. By comparing the temperature dependence of various physical quantities to the predictions of the Anderson Impurity Model, the slow crossover behavior observed in YbAl3, in which the data evolve from a low-temperature coherent, Fermi-liquid regime to a high temperature local moment regime more gradually than predicted by the Anderson Impurity Model, appears to evolve to fast crossover behavior at x ∼ 0.7 where the evolution is more rapid than predicted. These two phenomena found in Yb1-xLuxAl3, i.e., the low-T anomalies and the slow/fast crossover behavior are discussed in relation to recent theories of the Anderson lattice

  8. Gyrokinetic modelling of stationary electron and impurity profiles in tokamaks

    CERN Document Server

    Skyman, Andreas; Tegnered, Daniel

    2014-01-01

    Particle transport due to Ion Temperature Gradient/Trapped Electron (ITG/TE) mode turbulence is investigated using the gyrokinetic code GENE. Both a reduced quasilinear (QL) treatment and nonlinear (NL) simulations are performed for typical tokamak parameters corresponding to ITG dominated turbulence. A selfconsistent treatment is used, where the stationary local profiles are calculated corresponding to zero particle flux simultaneously for electrons and trace impurities. The scaling of the stationary profiles with magnetic shear, safety factor, electron-to-ion temperature ratio, collisionality, toroidal sheared rotation, triangularity, and elongation is investigated. In addition, the effect of different main ion mass on the zero flux condition is discussed. The electron density gradient can significantly affect the stationary impurity profile scaling. It is therefore expected, that a selfconsistent treatment will yield results more comparable to experimental results for parameter scans where the stationary b...

  9. Comparison of impurity generation and penetration models with spectroscopy for the Tore Supra ergodic divertor

    International Nuclear Information System (INIS)

    Three-dimensional (3-D) simulations of impurity dynamics in the vicinity of a Tore Supra ergodic divertor neutralizer are presented and compared with spectroscopic observations for a medium density pulse in the high recycling regime. The numerical tool used for the description of impurity generation and transport is a version of the Monte Carlo code BBQ, while the geometry of the magnetic field lines is calculated by use of the MASTOC code. Substantial quantitative consistency is found between the experimental data and our simulations based on recent impurity generation and propagation models. For the given plasma conditions, physical sputtering induced by impact from deuterium ions is found to be the dominant mechanism leading to the carbon contamination of the edge plasma. Chemical sputtering releases a comparable number of carbon impurities from the surface interacting with the plasma but those particles are rapidly re-deposited or pumped away. We find the role of friction of the impurities with the background plasma to be of crucial importance for the determination of the impurity distribution close to the neutralizer. We further find that a flow reversal of the background plasma takes place at the leading edge of the neutralizer with a flow velocity of a few percent of the ion sound speed in the region that is just clear of the edge. (author)

  10. Functional Integrals and Free Energy in sine-Gordon-Thirring Model with Impurity Coupling

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The free energy at low temperature in ID sine-Gordon-Thirring model with impurity coupling is studied by means of functional integrals method. For massive free sine-Gordon-Thirring model, free energy is obtained from perturbation expansion of functional determinant. Moreover, the free energy of massive model is calculated by use of an auxiliary Bose Geld method.

  11. Mesoscopic Anderson Box: Connecting Weak to Strong Coupling

    Science.gov (United States)

    Liu, Dong E.; Burdin, Sebastien; Baranger, Harold U.; Ullmo, Denis

    2011-03-01

    Both the weakly coupled and strong coupling Anderson impurity problem are characterized by a Fermi-liquid theory with weakly interacting quasiparticles. In an Anderson box, mesoscopic fluctuations of the effective single particle properties will be large. We study how the statistical fluctuations in these two problems are connected. We use random matrix theory and the slave boson mean field approximation (SBMF, at low temperature) to address this question, obtaining the following results. First, for a resonant level model such as results from the SBMF approximation, we find the joint distribution of energy levels with and without the resonant level present. Second, if only energy levels within the Kondo resonance are considered, the distribution of perturbed levels collapse to one universal form for both GOE and GUE for all values of the coupling V. Finally, a purely Fermi liquid method is developed for calculating the perturbed levels within the Kondo resonance. Comparing the levels that result to those of the SBMF, we find remarkable agreement.

  12. Modeling of aluminum impurity entrainment in the PISCES-A He{sup +} plasma

    Energy Technology Data Exchange (ETDEWEB)

    Hajjar, R.J., E-mail: rhajjar@ucsd.edu [University of California at San Diego, La Jolla, CA 92093 (United States); Hollmann, E.M. [University of California at San Diego, La Jolla, CA 92093 (United States); Krasheninnikov, S.I. [University of California at San Diego, La Jolla, CA 92093 (United States); Nuclear Research National University, MEPhI, Moscow 115409 (Russian Federation); Doerner, R.P. [University of California at San Diego, La Jolla, CA 92093 (United States)

    2015-08-15

    A 1D theoretical model describing transport of Al impurities in a low temperature He{sup +} plasma is discussed. The model adopts a kinetic approach to describe impurity entrainment in a steady state He{sup +} plasma flow. Results of a 1D Monte Carlo simulation supporting this model are presented and compared to experimental data collected from PISCES-A linear experiment. Both simulation and experimental results confirm that impurities are quickly entrained by the background plasma and quickly acquire its flowing velocity. However, a major discrepancy is observed in the temporal width when comparing the simulation to the experimental Al{sup 2+} density profiles downstream the flow. Consideration of several potential effects suggests that background plasma velocity shear is the most likely cause for this discrepancy.

  13. Modeling of aluminum impurity entrainment in the PISCES-A He+ plasma

    International Nuclear Information System (INIS)

    A 1D theoretical model describing transport of Al impurities in a low temperature He+ plasma is discussed. The model adopts a kinetic approach to describe impurity entrainment in a steady state He+ plasma flow. Results of a 1D Monte Carlo simulation supporting this model are presented and compared to experimental data collected from PISCES-A linear experiment. Both simulation and experimental results confirm that impurities are quickly entrained by the background plasma and quickly acquire its flowing velocity. However, a major discrepancy is observed in the temporal width when comparing the simulation to the experimental Al2+ density profiles downstream the flow. Consideration of several potential effects suggests that background plasma velocity shear is the most likely cause for this discrepancy

  14. Renormalization group approach to the Fr\\"ohlich polaron model: application to impurity-BEC problem

    OpenAIRE

    Grusdt, F.; Shchadilova, Y. E.; Rubtsov, A.N.; Demler, E.

    2014-01-01

    When a mobile impurity interacts with a many-body system, such as a phonon bath, a polaron is formed. Despite the importance of the polaron problem for a wide range of physical systems, a unified theoretical description valid for arbitrary coupling strengths is still lacking. Here we develop a renormalization group approach for analyzing a paradigmatic model of polarons, the so-called Fröhlich model, and apply it to a problem of impurity atoms immersed in a Bose-Einstein condensate of ultra c...

  15. Quantum dissipative effects on non-equilibrium transport through a single-molecular transistor: The Anderson-Holstein-Caldeira-Leggett model

    Science.gov (United States)

    Raju, Ch. Narasimha; Chatterjee, Ashok

    2016-01-01

    The Anderson-Holstein model with Caldeira-Leggett coupling with environment is considered to describe the damping effect in a single molecular transistor (SMT) which comprises a molecular quantum dot (with electron-phonon interaction) mounted on a substrate (environment) and coupled to metallic electrodes. The electron-phonon interaction is first eliminated using the Lang-Firsov transformation and the spectral density function, charge current and differential conductance are then calculated using the non-equilibrium Keldysh Green function technique. The effects of damping rate, and electron-electron and electron-phonon interactions on the transport properties of SMT are studied at zero temperature.

  16. Hubbard Model for Atomic Impurities Bound by the Vortex Lattice of a Rotating Bose-Einstein Condensate.

    Science.gov (United States)

    Johnson, T H; Yuan, Y; Bao, W; Clark, S R; Foot, C; Jaksch, D

    2016-06-17

    We investigate cold bosonic impurity atoms trapped in a vortex lattice formed by condensed bosons of another species. We describe the dynamics of the impurities by a bosonic Hubbard model containing occupation-dependent parameters to capture the effects of strong impurity-impurity interactions. These include both a repulsive direct interaction and an attractive effective interaction mediated by the Bose-Einstein condensate. The occupation dependence of these two competing interactions drastically affects the Hubbard model phase diagram, including causing the disappearance of some Mott lobes. PMID:27367366

  17. Hubbard Model for Atomic Impurities Bound by the Vortex Lattice of a Rotating Bose-Einstein Condensate

    Science.gov (United States)

    Johnson, T. H.; Yuan, Y.; Bao, W.; Clark, S. R.; Foot, C.; Jaksch, D.

    2016-06-01

    We investigate cold bosonic impurity atoms trapped in a vortex lattice formed by condensed bosons of another species. We describe the dynamics of the impurities by a bosonic Hubbard model containing occupation-dependent parameters to capture the effects of strong impurity-impurity interactions. These include both a repulsive direct interaction and an attractive effective interaction mediated by the Bose-Einstein condensate. The occupation dependence of these two competing interactions drastically affects the Hubbard model phase diagram, including causing the disappearance of some Mott lobes.

  18. Experimental observations and model calculations of impurity radiation in a plasma gun compact torus experiment

    International Nuclear Information System (INIS)

    Several types of radiation measurements were performed on the Beta II compact forms experiment. Among these are time integrated spectra ranging in wavelength from the vuv to the uv, time resolved bolometer measurements of radiation from the x-ray to the infrared, and time and wavelength resolved measurements of certain spectral lines. It is difficult to relate any one of these measurements to plasma parameters of interest such as temperature, density, or impurity content. In this report we compare the results of these, and other measurements with two simple models of the power balance in the plasma in order to estimate the effect of carbon and oxygen impurities on plasma lifetime

  19. Persistence of energy-dependent localization in the Anderson-Hubbard model with increasing system size and doping.

    Science.gov (United States)

    Daley, P; Wortis, R

    2016-05-01

    Non-interacting systems with bounded disorder have been shown to exhibit sharp density of state peaks at the band edge which coincide with an energy range of abruptly suppressed localization. Recent work has shown that these features also occur in the presence of on-site interactions in ensembles of two-site Anderson-Hubbard systems at half filling. Here we demonstrate that this effect in interacting systems persists away from half filling, and moreover that energy regions with suppressed localization continue to appear in ensembles of larger systems despite a loss of sharp features in the density of states. PMID:27022884

  20. Effect of correlation energy on the stability of impurity spin models

    International Nuclear Information System (INIS)

    We apply density-functional theory to estimate the ground-state energy of the inhomogeneous Heisenberg model for nanoscale spin assemblies in the presence of boundaries or impurities. Correlations are shown to lift degeneracies present in the mean-field approximation

  1. Anderson transition in the three dimensional symplectic universality class

    OpenAIRE

    Asada, Yoichi; Slevin, Keith; Ohtsuki, Tomi

    2004-01-01

    We study the Anderson transition in the SU(2) model and the Ando model. We report a new precise estimate of the critical exponent for the symplectic universality class of the Anderson transition. We also report numerical estimation of the $\\beta$ function.

  2. Quantum-classical correspondence in multimensional nonlinear systems: Anderson localization and "superdiffusive" solitons

    KAUST Repository

    Brambila, Danilo

    2012-01-01

    We have theoretically studied Anderson localization in a 2D+1 nonlinear kicked rotor model. The system shows a very rich dynamical behavior, where the Anderson localization is suppressed and soliton wave-particles undergo a superdiffusive motion.

  3. Numerical study of the overlap Lee–Yang singularities in the three-dimensional Edwards–Anderson model

    International Nuclear Information System (INIS)

    We have characterized numerically, using the Janus computer, the Lee–Yang complex singularities related to the overlap in the 3D Ising spin-glass with binary couplings over a wide range of temperatures (both in the critical and in the spin-glass phase). Studying the behavior of the zeros at the critical point, we have obtained an accurate measurement of the anomalous dimension in very good agreement with the values quoted in the literature. In addition, by studying the density of the zeros we have been able to characterize the phase transition and to investigate the Edwards–Anderson order parameter in the spin-glass phase, finding agreement with the values obtained using more conventional techniques. (paper)

  4. Characterization and validation of an in silico toxicology model to predict the mutagenic potential of drug impurities*

    Energy Technology Data Exchange (ETDEWEB)

    Valerio, Luis G., E-mail: luis.valerio@fda.hhs.gov [Science and Research Staff, Office of Pharmaceutical Science, Center for Drug Evaluation and Research, U.S. Food and Drug Administration, 10903 New Hampshire Avenue, Silver Spring, MD 20993–0002 (United States); Cross, Kevin P. [Leadscope, Inc., 1393 Dublin Road, Columbus, OH, 43215–1084 (United States)

    2012-05-01

    Control and minimization of human exposure to potential genotoxic impurities found in drug substances and products is an important part of preclinical safety assessments of new drug products. The FDA's 2008 draft guidance on genotoxic and carcinogenic impurities in drug substances and products allows use of computational quantitative structure–activity relationships (QSAR) to identify structural alerts for known and expected impurities present at levels below qualified thresholds. This study provides the information necessary to establish the practical use of a new in silico toxicology model for predicting Salmonella t. mutagenicity (Ames assay outcome) of drug impurities and other chemicals. We describe the model's chemical content and toxicity fingerprint in terms of compound space, molecular and structural toxicophores, and have rigorously tested its predictive power using both cross-validation and external validation experiments, as well as case studies. Consistent with desired regulatory use, the model performs with high sensitivity (81%) and high negative predictivity (81%) based on external validation with 2368 compounds foreign to the model and having known mutagenicity. A database of drug impurities was created from proprietary FDA submissions and the public literature which found significant overlap between the structural features of drug impurities and training set chemicals in the QSAR model. Overall, the model's predictive performance was found to be acceptable for screening drug impurities for Salmonella mutagenicity. -- Highlights: ► We characterize a new in silico model to predict mutagenicity of drug impurities. ► The model predicts Salmonella mutagenicity and will be useful for safety assessment. ► We examine toxicity fingerprints and toxicophores of this Ames assay model. ► We compare these attributes to those found in drug impurities known to FDA/CDER. ► We validate the model and find it has a desired predictive

  5. Characterization and validation of an in silico toxicology model to predict the mutagenic potential of drug impurities*

    International Nuclear Information System (INIS)

    Control and minimization of human exposure to potential genotoxic impurities found in drug substances and products is an important part of preclinical safety assessments of new drug products. The FDA's 2008 draft guidance on genotoxic and carcinogenic impurities in drug substances and products allows use of computational quantitative structure–activity relationships (QSAR) to identify structural alerts for known and expected impurities present at levels below qualified thresholds. This study provides the information necessary to establish the practical use of a new in silico toxicology model for predicting Salmonella t. mutagenicity (Ames assay outcome) of drug impurities and other chemicals. We describe the model's chemical content and toxicity fingerprint in terms of compound space, molecular and structural toxicophores, and have rigorously tested its predictive power using both cross-validation and external validation experiments, as well as case studies. Consistent with desired regulatory use, the model performs with high sensitivity (81%) and high negative predictivity (81%) based on external validation with 2368 compounds foreign to the model and having known mutagenicity. A database of drug impurities was created from proprietary FDA submissions and the public literature which found significant overlap between the structural features of drug impurities and training set chemicals in the QSAR model. Overall, the model's predictive performance was found to be acceptable for screening drug impurities for Salmonella mutagenicity. -- Highlights: ► We characterize a new in silico model to predict mutagenicity of drug impurities. ► The model predicts Salmonella mutagenicity and will be useful for safety assessment. ► We examine toxicity fingerprints and toxicophores of this Ames assay model. ► We compare these attributes to those found in drug impurities known to FDA/CDER. ► We validate the model and find it has a desired predictive performance.

  6. The Anderson Current Loop

    Science.gov (United States)

    Anderson, Karl F.

    1994-01-01

    Four-wire-probe concept applied to electrical-resistance transducers. Anderson current loop is excitation-and-signal-conditioning circuit suitable for use with strain gauges, resistance thermometers, and other electrical-resistance transducers mounted in harsh environments. Used as alternative to Wheatstone bridge. Simplifies signal-conditioning problem, enabling precise measurement of small changes in resistance of transducer. Eliminates some uncertainties in Wheatstone-bridge resistance-change measurements in flight research. Current loop configuration makes effects of lead-wire and contact resistances insignificantly small. Also provides output voltage that varies linearly with change in gauge resistance, and does so at double sensitivity of Wheatstone bridge.

  7. STRATEGIES OF INTERNATIONAL FISCAL COMPETITION FOR FOREIGN DIRECT INVESTMENT IN A MODEL WITH IMPURE PUBLIC INPUTS

    OpenAIRE

    Sauer, Christoph; Schratzenstaller, Margit

    2002-01-01

    This paper concentrates on international fiscal competition for internationally mobile direct investment. We differentiate between multinational enterprises whose direct investments are internationally mobile and domestic enterprises whose investment activities are limited to their country of residence. In a model with impure public inputs we analyse strategies of tax competition and examine the effects of competition by government expenditures for public inputs under the assumption that pref...

  8. The calculational modeling of impurity mass transfer in NPP circuits with liquid metal coolant

    Energy Technology Data Exchange (ETDEWEB)

    Alexeev, V; Kozlov, F; Kumaev, V; Orlova, E; Klimanova, Yu; Torbenkova, I [SSC RF-IPPE (Russian Federation)], E-mail: alexeev@ippe.ru

    2008-02-15

    The authors create three levels of models (one-dimensional, two-dimensional and three-dimensional) for estimation of impurity mass transfer in sodium circuits units as well as applicable computational programs. In the one-dimensional model the flow path elements are simulated by annular channels. The Lagrange coordinate system is used in the mathematical description of processes in channels. The two-dimensional model is based on the porous body approximation and enables one to simulate global spatial distributions of coolant flow velocity fields, coolant and fuel rods temperatures, and concentration distribution of transferred substances. The mathematical description of passive multicomponent impurity transfer is carried out using the system of the differential equations with sources and impurity diffusion, written for each component. The equations are solved by the finite-difference method. The developed version of the three-dimensional code is based on a general approach of the spatial three-dimensional description of thermal-hydraulic and mass-transfer processes in fuel rod bundles. The determining system of finite-difference equations of hydrodynamics and heat exchange is obtained using the control volume approach. As a result of the performed calculations, valuable data on corrosion products transfer in the primary circuit of the BN-600 reactor are obtained.

  9. The calculational modeling of impurity mass transfer in NPP circuits with liquid metal coolant

    Science.gov (United States)

    Alexeev, V.; Kozlov, F.; Kumaev, V.; Orlova, E.; Klimanova, Yu; Torbenkova, I.

    2008-02-01

    The authors create three levels of models (one-dimensional, two-dimensional and three-dimensional) for estimation of impurity mass transfer in sodium circuits units as well as applicable computational programs. In the one-dimensional model the flow path elements are simulated by annular channels. The Lagrange coordinate system is used in the mathematical description of processes in channels. The two-dimensional model is based on the porous body approximation and enables one to simulate global spatial distributions of coolant flow velocity fields, coolant and fuel rods temperatures, and concentration distribution of transferred substances. The mathematical description of passive multicomponent impurity transfer is carried out using the system of the differential equations with sources and impurity diffusion, written for each component. The equations are solved by the finite-difference method. The developed version of the three-dimensional code is based on a general approach of the spatial three-dimensional description of thermal-hydraulic and mass-transfer processes in fuel rod bundles. The determining system of finite-difference equations of hydrodynamics and heat exchange is obtained using the control volume approach. As a result of the performed calculations, valuable data on corrosion products transfer in the primary circuit of the BN-600 reactor are obtained.

  10. Effect of coulomb interaction on Anderson localization

    International Nuclear Information System (INIS)

    We study the quantum mechanics of interacting particles in a disordered system, and in particular, what happens to Anderson localisation when interaction is taken into account. In the first part, one looks at the excited states of two particles in one dimension. For this model, it has been shown (Shepelyansky 1994) that a local repulsive interaction can partially destroy Anderson localisation. Here, we show that this model has similarities with the three-dimensional Anderson model at the metal-insulator transition. In particular, the maximum of rigidity obtained in the spectral statistics correspond to some intermediary statistics that cannot be described by random matrix theory neither by a Poisson statistics. The wave functions show a multifractal behaviour and the spreading of the center of mass of a wave packet is logarithmic in time. The second part deals with the ground state of a finite density of spinless fermions in two dimensions. After the scaling theory of localisation, it was commonly accepted that there was no metal in two dimensions. This idea has been challenged by the observation of a metal-insulator transition in low density electron gas (Kravchenko et al. 1994). We propose a scenario in which a metallic phase occurs between the Anderson insulator and the pinned Wigner crystal. This intermediate phase is characterized by an alignment of the local currents flowing in the system. (author)

  11. Modeling of impurity transport in high density plasma with highly enhanced radiation loss on JT-60U

    International Nuclear Information System (INIS)

    Impurity transport has been modeled using a 1-D transport code for the main plasma and a 2-D fluid code (UEDGE) for the divertor and scrape-off layer plasmas in the JT-60U high βp mode plasma with highly enhanced radiation by injecting seed impurity argon. The density profile of the seed impurity argon estimated from the soft x-ray profile was more peaked by a factor of 2 than the electron density profile. On the other hand, the density measurement of the fully ionized intrinsic impurity carbon indicated a flat carbon density profile. The radiation profile evaluated from these impurity density profiles was more peaked than the measurement in the main plasma. The divertor radiation calculated by the UEDGE code with the boundary condition of the argon density consistent with the 1-D transport analysis was localized around the strike points compared with the measurement. (author)

  12. Validation of gyrokinetic modelling of light impurity transport including rotation in ASDEX Upgrade

    CERN Document Server

    Casson, F J; Angioni, C; Camenen, Y; Dux, R; Fable, E; Fischer, R; Geiger, B; Manas, P; Menchero, L; Tardini, G

    2013-01-01

    Upgraded spectroscopic hardware and an improved impurity concentration calculation allow accurate determination of boron density in the ASDEX Upgrade tokamak. A database of boron measurements is compared to quasilinear and nonlinear gyrokinetic simulations including Coriolis and centrifugal rotational effects over a range of H-mode plasma regimes. The peaking of the measured boron profiles shows a strong anti-correlation with the plasma rotation gradient, via a relationship explained and reproduced by the theory. It is demonstrated that the rotodiffusive impurity flux driven by the rotation gradient is required for the modelling to reproduce the hollow boron profiles at higher rotation gradients. The nonlinear simulations validate the quasilinear approach, and, with the addition of perpendicular flow shear, demonstrate that each symmetry breaking mechanism that causes momentum transport also couples to rotodiffusion. At lower rotation gradients, the parallel compressive convection is required to match the mos...

  13. Entanglement of an impurity and conduction spins in the Kondo model

    OpenAIRE

    Oh, Sangchul; Kim, Jaewan

    2006-01-01

    Based on Yosida's ground state of the single-impurity Kondo Hamiltonian, we study three kinds of entanglement between an impurity and conduction electron spins. First, it is shown that the impurity spin is maximally entangled with all the conduction electrons. Second, a two-spin density matrix of the impurity spin and one conduction electron spin is given by a Werner state. We find that the impurity spin is not entangled with one conduction electron spin even within the Kondo screening length...

  14. Interleaved numerical renormalization group as an efficient multiband impurity solver

    Science.gov (United States)

    Stadler, K. M.; Mitchell, A. K.; von Delft, J.; Weichselbaum, A.

    2016-06-01

    Quantum impurity problems can be solved using the numerical renormalization group (NRG), which involves discretizing the free conduction electron system and mapping to a "Wilson chain." It was shown recently that Wilson chains for different electronic species can be interleaved by use of a modified discretization, dramatically increasing the numerical efficiency of the RG scheme [Phys. Rev. B 89, 121105(R) (2014), 10.1103/PhysRevB.89.121105]. Here we systematically examine the accuracy and efficiency of the "interleaved" NRG (iNRG) method in the context of the single impurity Anderson model, the two-channel Kondo model, and a three-channel Anderson-Hund model. The performance of iNRG is explicitly compared with "standard" NRG (sNRG): when the average number of states kept per iteration is the same in both calculations, the accuracy of iNRG is equivalent to that of sNRG but the computational costs are significantly lower in iNRG when the same symmetries are exploited. Although iNRG weakly breaks SU(N ) channel symmetry (if present), both accuracy and numerical cost are entirely competitive with sNRG exploiting full symmetries. iNRG is therefore shown to be a viable and technically simple alternative to sNRG for high-symmetry models. Moreover, iNRG can be used to solve a range of lower-symmetry multiband problems that are inaccessible to sNRG.

  15. Solution to the sign problem in a frustrated quantum impurity model

    CERN Document Server

    Hann, Connor T; Chandrasekharan, Shailesh

    2016-01-01

    In this work we solve the sign problem of a frustrated quantum impurity model consisting of three quantum spin-half chains interacting through an anti-ferromagnetic Heisenberg interaction at one end. We first map the model into a repulsive Hubbard model of spin-half fermions hopping on three independent one dimensional chains that interact through a triangular hopping at one end. We then convert the fermion model into an inhomogeneous one dimensional model and express the partition function as a weighted sum over fermion worldline configurations. By imposing a pairing of fermion worldlines in half the space we show that all negative weight configurations can be eliminated. This pairing naturally leads to the original frustrated quantum spin model at half filling and thus solves its sign problem.

  16. Model of diffusion of ion-implanted impurities, taking into account the effect of radiation defects created by ion implantation on the diffusion process

    International Nuclear Information System (INIS)

    Radiation defects created during implantation appreciably affect the process of redistribution of impurities during subsequent heat treatments. The development of models of diffusion of ion-implanted impurities, taking into account radiation defects, will substantially increase the adequacy of the modeling of doping processes at the design stage and at the stage of testing of modern semiconductor device and IMS technology. The authors propose such a model. For the model, the authors studied the diffusion of boron, gallium, arsenic, and antimony implanted in silicon. Thermal diffusion of these impurities is described under the assumption that the neutral and singly charged equilibrium vacancy-impurity complexes (VIC), formed correspondingly by singly charged and neutral vacancies and impurity atoms at the position of substitution, migrate. It is assumed that the different charge states of the vacancies and vacancy-impurity complexes as well as the impurity atoms, vacancies, and VIC are in local thermodynamic equilibrium

  17. Lithuania 1940 / Herbert Foster Anderson

    Index Scriptorium Estoniae

    Foster Anderson, Herbert

    2004-01-01

    Stseenid Leedu ennesõjaaegsest pealinnast Kaunasest briti ärimehe H. Foster Andersoni silme läbi 1940. aastal. Lühikokkuvõte raamatust: Foster Anderson, Herbert. Borderline Russia. London : Cresset press, 1942

  18. The Price-Anderson Act

    International Nuclear Information System (INIS)

    The Price-Anderson Act establishes nuclear liability law in the United States. First passed in 1957, it has influenced other nuclear liability legislation around the world. The insurer response the nuclear accident at Three Mile Island in 1979 demonstrates the application of the Act in a real life situation. The Price-Anderson Act is scheduled to be renewed in 2002, and the future use of commercial nuclear power in tge United States will be influenced by this renewal. (author)

  19. Bose-Hubbard model with random impurities: Multiband and nonlinear hopping effects

    Science.gov (United States)

    Stasińska, Julia; Łacki, Mateusz; Dutta, Omjyoti; Zakrzewski, Jakub; Lewenstein, Maciej

    2014-12-01

    We investigate the phase diagrams of theoretical models describing bosonic atoms in a lattice in the presence of randomly localized impurities. By including multiband and nonlinear hopping effects we enrich the standard model containing only the chemical-potential disorder with the site-dependent hopping term. We compare the extension of the MI and the BG phase in both models using a combination of the local mean-field method and a Hartree-Fock-like procedure, as well as the Gutzwiller-ansatz approach. We show analytical argument for the presence of triple points in the phase diagram of the model with chemical-potential disorder. These triple points, however, cease to exist after the addition of the hopping disorder.

  20. Finite Size Scaling Analysis of the Anderson Transition

    OpenAIRE

    Kramer, Bernhard; MacKinnon, Angus; Ohtsuki, Tomi; Slevin, Keith

    2010-01-01

    This chapter describes the progress made during the past three decades in the finite size scaling analysis of the critical phenomena of the Anderson transition. The scaling theory of localisation and the Anderson model of localisation are briefly sketched. The finite size scaling method is described. Recent results for the critical exponents of the different symmetry classes are summarised. The importance of corrections to scaling are emphasised. A comparison with experiment is made, and a di...

  1. Ferromagnetic order in the one-dimensional Anderson lattice

    International Nuclear Information System (INIS)

    Using bosonization an effective Hamiltonian is derived for the one-dimensional Anderson lattice model in the Toulouse limit. The effective Hamiltonian exhibits ferromagnetic ground state in the intermediate coupling regime. - Highlights: • 1D Anderson lattice is bosonized in the Toulouse limit. • The obtained effective Hamiltonian exhibits ferromagnetic order. • Ferromagnetism is due to a double-exchange mechanism. • The ferromagnetic transition has been identified to be an order–disorder transition

  2. Transverse Anderson localization of light: a tutorial review

    OpenAIRE

    Mafi, Arash

    2015-01-01

    This tutorial review gives an overview of the transverse Anderson localization of light in one and two transverse dimensions. A pedagogical approach is followed throughout the presentation, where many aspects of localization are illustrated by means of a few simple models. The tutorial starts with some basic aspects of random matrix theory, and light propagation through and reflection from a random stack of dielectric slabs. Transverse Anderson localization of light in one- and two-dimensiona...

  3. Modeling and data analysis of a palladium membrane reactor for tritiated impurities cleanup

    International Nuclear Information System (INIS)

    A Palladium Membrane Reactor (PMR) is under consideration for the tritium plant for the International Thermonuclear Experimental Reactor (ITER). The ITER reactor exhaust will contain tritiated impurities such as water and methane. Tritium will need to be recovered from these impurities for environmental and economic reasons. For this purpose a promising device, PMR, has been proposed. The PMR is a combined permeator and catalytic reactor. Shift catalysts are used to foster reactions such as water-gas shift, H2O + CO → H2 + CO2, and methane steam reforming, CH4 + H2O → 3H2 + CO. Due to thermodynamic limitations these reactions only proceed to partial completion. Thus, a Pd/Ag membrane, which is exclusively permeable to hydrogen isotopes, is incorporated into the reactor. By maintaining a vacuum on the permeate, product hydrogen isotopes are removed, enabling the reactions to proceed to completion. A model has been developed to study the complex interactions in a PMR so that the optimal design can be determined. The model accounts for the coupled effects of transport-limited permeation of hydrogen isotopes and chemical reactions. The permeation model is an extension of previous models that include the effects of temperature, wall thickness, reaction-side pressure, and permeate-side pressure. Reaction rates for methane steam reforming and the water-gas shift reaction are incorporated into the model along with the respective reverse reactions. The model is compared to PMR data and used to investigate the concentration and pressure profiles in the reactor. Due to the interactions of permeation and reaction complex profiles can be produced in a PMR. For example, the water concentration often increases after the inlet to the PMR to a maximum value, and then decreases to the low values expected with a PMR. Detailed information like this is required for the design and optimization of PMRs for the ITER tritium plant

  4. Ferromagnetism of magnetic impurities coupled indirectly via conduction electrons: Insights from various theoretical approaches

    Science.gov (United States)

    Titvinidze, Irakli; Schwabe, Andrej; Potthoff, Michael

    2014-07-01

    The magnetic ground-state properties of the periodic Anderson model with a regular depletion of the correlated sites are analyzed within different theoretical approaches. We consider the model on the one-dimensional chain and on the two-dimensional square lattice with hopping between nearest neighbors. At half-filling and with correlated impurities present at every second site, the depleted Anderson lattice is the most simple system where the indirect magnetic coupling mediated by the conduction electrons is ferromagnetic. We discuss the underlying electronic structure and the possible mechanisms that result in ferromagnetic long-range order. To this end, different numerical and analytical concepts are applied to the depleted Anderson and also to the related depleted Kondo lattice and are contrasted with each other. This includes numerical approaches, i.e., Hartree-Fock theory, density-matrix renormalization and dynamical mean-field theory, as well as analytical concepts, namely a variant of the Lieb-Mattis theorem and the concept of flat-band ferromagnetism, and, finally, perturbative approaches, i.e., the effective RKKY exchange in the limit of weak coupling and the "inverse indirect magnetic exchange" in the limit of strong coupling between the conduction band and the impurities.

  5. Measurements and modeling of impurity source distributions from the Tore Supra outboard pump limiter

    International Nuclear Information System (INIS)

    An experiment has been carried out to study impurity generation processes on an inertial limiter on Tore Supra. It is part of a plan to assemble a more detailed integrated picture of impurity generation at the inner wall, the outboard and vertical pump limiters, and the heating and current drive antennas. A system has been implemented to permit quantitative measurement of impurity sources from the outboard limiter in Tore Supra. Data are presented for a representative case in which the limiter is isolated as much as possible from connection with other Tore Supra plasma-facing components. The data are compared with results from the Monte-Carlo SOL impurity transport code BBQ, in an attempt to identify the mechanism for impurity release. Evidence of chemical sputtering as an important impurity source is seen

  6. Measurements and modeling of impurity source distributions from the Tore Supra outboard pump limiter

    International Nuclear Information System (INIS)

    An experiment has been carried out to study impurity generation processes on an inertial limiter on Tore Supra. It is part of a plan to assemble a more detailed integrated picture of impurity generation at the inner wall, the outboard and vertical pump limiters, and the heating and current drive antennas. A system has been implemented to permit quantitative measurement of impurity sources from the outboard limiter in Tore Supra. Data are presented for a representative case in which the limiter is isolated as much as possible from connection with other Tore Supra plasma-facing components. The data are compared with results from the Monte-Carlo SOL impurity transport code BBQ, in an attempt to identify the mechanism for impurity release. Evidence of chemical sputtering as an important impurity source is seen. (authors). 15 refs., 5 figs

  7. Renormalization group approach to the Fröhlich polaron model: application to impurity-BEC problem

    OpenAIRE

    Grusdt, F.; Shchadilova, Y. E.; Rubtsov, A.N.; Demler, E.

    2015-01-01

    When a mobile impurity interacts with a many-body system, such as a phonon bath, a polaron is formed. Despite the importance of the polaron problem for a wide range of physical systems, a unified theoretical description valid for arbitrary coupling strengths is still lacking. Here we develop a renormalization group approach for analyzing a paradigmatic model of polarons, the so-called Fröhlich model, and apply it to a problem of impurity atoms immersed in a Bose-Einstein condensate of ultra c...

  8. Experiments on the interactions between impurities and solitary waves in lattice model

    Institute of Scientific and Technical Information of China (English)

    朱逸斐; 陈伟中; 吕镭

    2003-01-01

    The interactions between solitary waves and impurities have been studied experimentally in a 1D nonlinear coupled pendulum chain under vertical excitation. The mass and the coupling are unique, except a single pendulum with length impurity in the chain. The experiment reveals: the long impurity repels breather and attracts kink while the short one attracts breather and repels kink under higher frequency driving, and the long impurity attracts breather and repels kink while the short one repels breather and attracts kink under the lower frequency driving. These results prove the current theoretical prediction based on continuum-limit approximation.

  9. Zeroth Order Phase Transition in a Holographic Superconductor with Single Impurity

    CERN Document Server

    Zeng, Hua Bi

    2014-01-01

    We studied the single normal impurity effect in superconductor by using the holographic method. When the size of impurity is much smaller compared to the host superconductor, we reproduced the Anderson theorem, which states that a conventional s-wave superconductor is robust to a normal (non-magnetic) impurity with small impurity strength or impurities with small concentration. While by increasing the size of impurity in a fixed host superconductor we also find a decrease $T_c$ of the host superconductor, the phase transition at the critical impurity strength is of zeroth order.

  10. 50 Years of Anderson Localization

    CERN Document Server

    Abrahams, Elihu

    2010-01-01

    In his groundbreaking paper Absence of diffusion in certain random lattices (1958), Philip W. Anderson originated, described and developed the physical principles underlying the phenomenon of the localization of quantum objects due to disorder. Anderson's 1977 Nobel Prize citation featured that paper, which was fundamental for many subsequent developments in condensed matter theory and technical applications. After more than a half century, the subject continues to be of fundamental importance. In particular, in the last 25 years, the phenomenon of localization has proved to be crucial for the

  11. Theoretical description of heavy impurity transport and its application to the modelling of tungsten in JET and ASDEX upgrade

    Czech Academy of Sciences Publication Activity Database

    Casson, F.J.; Angioni, C.; Belli, E.A.; Bilato, R.; Mantica, P.; Odstrčil, T.; Pütterich, T.; Valisa, M.; Garzotti, L.; Giroud, C.; Hobirk, J.; Maggi, C.F.; Mlynář, Jan; Reinke, M.L.

    2015-01-01

    Roč. 57, č. 1 (2015), 014031-014031. ISSN 0741-3335 Institutional support: RVO:61389021 Keywords : tokamak * impurity * transport * neoclassical * validation * modelling * tungsten Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 2.186, year: 2014 http://iopscience.iop.org/article/10.1088/0741-3335/57/1/014031/ meta

  12. Experimental Observation of Two-Dimensional Anderson Localization with the Atomic Kicked Rotor

    OpenAIRE

    Manai, Isam; Clément, Jean-François; Chicireanu, Radu; Hainaut, Clément; Garreau, Jean Claude; Szriftgiser, Pascal; Delande, Dominique

    2015-01-01

    Dimension 2 is expected to be the lower critical dimension for Anderson localization in a time-reversal-invariant disordered quantum system: the dynamics is generically localized in dimension lower than 2, while it presents a transition from a diffusive regime at weak disorder to a localized regime at strong disorder in dimension larger than 2. We use an atomic quasiperiodically kicked rotor – equivalent to a two-dimensional Anderson-like model – to experimentally study Anderson localization ...

  13. Triple point temperature of neon isotopes: Dependence on nitrogen impurity and sealed-cell model

    International Nuclear Information System (INIS)

    This paper illustrates a study conducted at INRIM, to further check how some quantities influence the value of the triple point temperature of the neon high-purity isotopes 20Ne and 22Ne. The influence of nitrogen as a chemical impurity in neon is critical with regard to the present best total uncertainty achieved in the measurement of these triple points, but only one determination is available in the literature. Checks are reported, performed on two different samples of 22Ne known to contain a N2 amount of 157⋅10−6, using two different models of sealed cells. The model of the cell can, in principle, have some effects on the shape of the melting plateau or on the triple point temperature observed for the sample sealed in it. This can be due to cell thermal parameters, or because the INRIM cell element mod. c contains many copper wires closely packed, which can, in principle, constrain the interface and induce a premelting-like effect. The reported results on a cell mod. Bter show no evident effect from the cell model and provide a value for the effect of N2 in Ne liquidus point of 8.6(1.9) μK ppm N2−1, only slightly different from the literature datum

  14. Determining impurities

    International Nuclear Information System (INIS)

    A method of determining the content of impurities in organic-origin natural fibrous materials, in which a specimen of said material is compacted to a surface density of from 0.05 to 50 g/cm2, whereupon it is exposed to the effect of a soft gamma-radiation, the mass attenuation coefficient (μ) is determined and the percentage content (Csub(A)) of impurities is assessed. The method has applications in the textile industry. (author)

  15. Model for impurity generation, transport and deposition in the complex CIEL environment

    Energy Technology Data Exchange (ETDEWEB)

    Hogan, J. [Fusion Energy Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States)]. E-mail: hoganjt@ornl.gov; Dufour, E. [DRFC, CEA-Cadarache, 13108 St. Paul lez Durance cedex (France); Lowry, C. [DRFC, CEA-Cadarache, 13108 St. Paul lez Durance cedex (France); Gunn, J. [DRFC, CEA-Cadarache, 13108 St. Paul lez Durance cedex (France); Corre, Y. [DRFC, CEA-Cadarache, 13108 St. Paul lez Durance cedex (France); Monier-Garbet, P. [DRFC, CEA-Cadarache, 13108 St. Paul lez Durance cedex (France); Mitteau, R. [DRFC, CEA-Cadarache, 13108 St. Paul lez Durance cedex (France); Tsitrone, E. [DRFC, CEA-Cadarache, 13108 St. Paul lez Durance cedex (France)

    2007-06-15

    We have re-examined the basic dependences of carbon generation due to physical (D{sup +} and C{sup n+}) sputtering and from thermally dependent sources (chemical erosion) by comparison with a spectroscopic database for carbon emission from localized regions of CIEL. To be able to compare with observations in this complex environment, a model for carbon generation and transport has been created to include contributions from the important, but non-ideal, processes of carbon generation from material in intra-tile gaps and from poorly adherent re-deposited layers. Consistency simulations have been carried out to assess the degree to which the spot observations represent local emission, due to possibly long mean free paths of high-energy emitted particles, or from impurities transported into the spectroscopic field of view from other areas. Model results are compared with the experimental trends in the ratio of CII and D{sub {alpha}} emission with power and edge parameters. In the course of the analysis a potentially important vector has been found for transport of re-deposited material to more remote locations and its significance discussed.

  16. Simulating graphene impurities

    OpenAIRE

    Marcin Szyniszewski

    2013-01-01

    We study a model of magnetic impurities deposited onto a graphene lattice, interacting via exchange of conduction electrons. Our objective is to look for the long-range ordering of the impurities, which would lead to drastic changes in the transport properties of graphene. Numerical simulations are performed and we indeed observe the ordered phase. We also estimate the critical temperature of a transition between disordered and ordered phases.

  17. Experimental Observation of Two-Dimensional Anderson Localization with the Atomic Kicked Rotor.

    Science.gov (United States)

    Manai, Isam; Clément, Jean-François; Chicireanu, Radu; Hainaut, Clément; Garreau, Jean Claude; Szriftgiser, Pascal; Delande, Dominique

    2015-12-11

    Dimension 2 is expected to be the lower critical dimension for Anderson localization in a time-reversal-invariant disordered quantum system. Using an atomic quasiperiodic kicked rotor-equivalent to a two-dimensional Anderson-like model-we experimentally study Anderson localization in dimension 2 and we observe localized wave function dynamics. We also show that the localization length depends exponentially on the disorder strength and anisotropy and is in quantitative agreement with the predictions of the self-consistent theory for the 2D Anderson localization. PMID:26705619

  18. Refined computational modeling of SOFCs degradation due to trace impurities in coal syngas

    Science.gov (United States)

    Sezer, Hayri

    The Solid Oxide Fuel Cell (SOFC) is a good alternative for clean and efficient power generation. These cells can be operated directly on a wide variety of fuels including biogas, hydrocarbon fuels and synthesized coal gas (syngas), which is a promising avenue for utilization of coal with much less environmental impact. One of the challenges in this technology is poisoning of SOFC anodes by trace impurities contained in coal syngas. One such impurity, phosphine is known to cause catastrophic failure of SOFC anode even at models are developed to predict the typical degradation behaviors observed in SOFC anode due to phosphine by extension of an in-house one-dimensional computational code. This model is first used to predict the effect of steam concentration on phosphine induced degradation in anode supported SOFCs. The model is refined based on the experimental observation, which indicate that the phosphine degradation is less severe in the absence of steam. Simulations results showed good agreement with experimental data. Then, a sensitivity analysis, using dual numbers automatic differentiation (DNAD) is performed to investigate the influence of empirical model parameters on model outputs, electrical potential, ohmic and polarization losses. Further, the refined one-dimensional model is extended to a three-dimensional model to study the phosphine induced performance degradation in relatively large planar cells operating on hydrogen fuel. The empirical model parameters are calibrated using button cell experiments and sensitivity analysis as a guide. These parameters are then used in planar cell simulations. The results from the three dimensional model show that the contaminant coverage of nickel and fuel distribution inside the anode is highly non-uniform. These non-uniform distributions are caused by the geometrical alignment of gas channels and current collectors, as well as the variation of gas concentration along the flow direction. The non-uniform deactivation

  19. Specific heat of a localized magnetic impurity in a non-magnetic host: A spectral density method for the Anderson–Holstein model

    International Nuclear Information System (INIS)

    The effect of electron–phonon interaction on the spectral function of a magnetic impurity in a non-magnetic host metal is studied within the framework of the Anderson–Holstein model using a spectral density method. The impurity contribution to the specific heat of the host metal is also calculated

  20. Thermodynamic model for forecasting of corrosion resistance of structural materials in liquid lithium and sodium, containing nonmetallic impurities

    International Nuclear Information System (INIS)

    Method for calculating the parameters of corrosion processes in liquid lithium and sodium, containing nonmetallic impurities, is proposed on the basis of a quasichemical model. A good agreement of the calculation results with the experimental data for Li-Fe-N, Li-Cr-N, Li-Ni-N, Na-Fe-O and Na-Ni-O systems allows one to recommend the given model for forecasting the structural material behaviour in other liquid-metal systems

  1. Anderson localization from classical trajectories

    OpenAIRE

    Brouwer, Piet W.; Altland, Alexander

    2008-01-01

    We show that Anderson localization in quasi-one dimensional conductors with ballistic electron dynamics, such as an array of ballistic chaotic cavities connected via ballistic contacts, can be understood in terms of classical electron trajectories only. At large length scales, an exponential proliferation of trajectories of nearly identical classical action generates an abundance of interference terms, which eventually leads to a suppression of transport coefficients. We quantitatively descri...

  2. Integrative Medicine Program- MD Anderson Cancer Center

    Directory of Open Access Journals (Sweden)

    Richard T Lee

    2012-06-01

    Full Text Available The Integrative Medicine Program at MD Anderson Cancer Center was first established in 1998.  Our mission is to empower patients with cancer and their families to become active partners in their own physical, psycho-spiritual, and social health through personalized education and evidenced-based clinical care to optimize health, quality of life, and clinical outcomes across the cancer continuum.  The program consists of three main components: clinical care, research, and education.  The Integrative Medicine Center provides clinical services to patients through individual and group programs.  The clinical philosophy of the center is to work collaboratively with the oncology teams to build comprehensive and integrative care plans that are personalized, evidence-based, and safe with the goal of improving clinical outcomes.  The individual services comprise of integrative oncology consultation, acupuncture, meditation, music therapy, nutrition, and oncology massage.  The center also provides a variety of group programs including meditation, yoga, tai chi, cooking classes and others.  Over the past 13 years, over 70,000 patients and families have participated in services and programs offered by the center.  The research portfolio focuses on three main areas: mind-body interventions, acupuncture, and meditation.  This lecture will focus on providing an overview of the Integrative Medicine Program at MD Anderson with a focus on the clinical services provided.  Participants will learn about the integrative clinical model and how this is applied to the care of cancer patients at MD Anderson Cancer Center.  Current and future research topics will be discussed as well as patient cases.

  3. Zeroth order phase transition in a holographic superconductor with single impurity

    Directory of Open Access Journals (Sweden)

    Hua Bi Zeng

    2015-08-01

    Full Text Available We investigate the single normal impurity effect in a superconductor by the holographic method. When the size of impurity is much smaller than the host superconductor, we can reproduce the Anderson theorem, which states that a conventional s-wave superconductor is robust to a normal (non-magnetic impurity with small impurity strength. However, by increasing the size of the impurity in a fixed-size host superconductor, we find a decreasing critical temperature Tc of the host superconductor, which agrees with the results in condensed matter literatures. More importantly, the phase transition at the critical impurity strength (or the critical temperature is of zeroth order.

  4. Lanczos transformation for quantum impurity problems in d-dimensional lattices: Application to graphene nanoribbons

    Science.gov (United States)

    Büsser, C. A.; Martins, G. B.; Feiguin, A. E.

    2013-12-01

    We present a completely unbiased and controlled numerical method to solve quantum impurity problems in d-dimensional lattices. This approach is based on a canonical transformation, of the Lanczos form, where the complete lattice Hamiltonian is exactly mapped onto an equivalent one-dimensional system, in the same spirit as Wilson's numerical renormalization, and Haydock's recursion method. We introduce many-body interactions in the form of a Kondo or Anderson impurity and we solve the low-dimensional problem using the density matrix renormalization group. The technique is particularly suited to study systems that are inhomogeneous, and/or have a boundary. The resulting dimensional reduction translates into a reduction of the scaling of the entanglement entropy by a factor Ld-1, where L is the linear dimension of the original d-dimensional lattice. This allows one to calculate the ground state of a magnetic impurity attached to an L×L square lattice and an L×L×L cubic lattice with L up to 140 sites. We also study the localized edge states in graphene nanoribbons by attaching a magnetic impurity to the edge or the center of the system. For armchair metallic nanoribbons we find a slow decay of the spin correlations as a consequence of the delocalized metallic states. In the case of zigzag ribbons, the decay of the spin correlations depends on the position of the impurity. If the impurity is situated in the bulk of the ribbon, the decay is slow as in the metallic case. On the other hand, if the adatom is attached to the edge, the decay is fast, within few sites of the impurity, as a consequence of the localized edge states, and the short correlation length. The mapping can be combined with ab initio band structure calculations to model the system, and to understand correlation effects in quantum impurity problems starting from first principles.

  5. Understanding impurity retention by divertors

    International Nuclear Information System (INIS)

    Simple, 1-D fluid model prescriptions are developed to predict under what circumstances impurities released at divertor targets would be expected to leak to the main plasma. The prescriptions are tested by comparison with results using the DIVIMP (divertor impurity) Monte Carlo code and are found to be well satisfied under strongly collisional conditions. The transition to collisionlessness degrades the agreement with the simple model. Usually, the simple model predicts a more-or-less catastrophic buildup of impurities outside the divertor. This, however, is an artificial result arising from the assumption of strictly one-dimensional, along B, motion; even weak cross-field transport can stop such impurity accumulation. ((orig.))

  6. Dimensional Dependence of Critical Exponent of the Anderson Transition in the Orthogonal Universality Class

    OpenAIRE

    Ueoka, Yoshiki; Slevin, Keith

    2014-01-01

    We report improved numerical estimates of the critical exponent of the Anderson transition in Anderson's model of localization in $d=4$ and $d=5$ dimensions. We also report a new Borel-Pad\\'e analysis of existing $\\epsilon$ expansion results that incorporates the asymptotic behaviour for $d\\to \\infty$ and gives better agreement with available numerical results.

  7. Modeling the Geochemical Impact of an Injection of CO2 and Associated Reactive Impurities into a Saline Reservoir

    OpenAIRE

    Andre, Laurent; Azaroual, Mohamed; Bernstone, Christian; Wittek, Andrea

    2012-01-01

    Numerical simulations performed with the TOUGHREACT code focus on the chemical reactivity of deep reservoir rock impacted by an injection of CO2 and associated reactive impurities (mainly SO2 and O2). A simplified two-dimensional radial geo-model representing the near wellbore domain of a saline reservoir enabled us to capture the global geochemical behaviour of this underground zone. Two ratios CO2/SO2 are investigated. The results of the numerical simulations highlight the high reactivity o...

  8. Holographic impurities and Kondo effect

    CERN Document Server

    Erdmenger, J; Hoyos, C; Newrzella, M-N; O'Bannon, A; Wu, J

    2015-01-01

    Magnetic impurities are responsible for many interesting phenomena in condensed matter systems, notably the Kondo effect and quantum phase transitions. Here we present a holographic model of a magnetic impurity that captures the main physical properties of the large-spin Kondo effect. We estimate the screening length of the Kondo cloud that forms around the impurity from a calculation of entanglement entropy and show that our results are consistent with the g-theorem.

  9. A novel QSAR model of Salmonella mutagenicity and its application in the safety assessment of drug impurities

    Energy Technology Data Exchange (ETDEWEB)

    Valencia, Antoni; Prous, Josep; Mora, Oscar [Prous Institute for Biomedical Research, Rambla de Catalunya, 135, 3-2, Barcelona 08008 (Spain); Sadrieh, Nakissa [Office of Pharmaceutical Science, Center for Drug Evaluation and Research, U.S. Food and Drug Administration, 10903 New Hampshire Avenue, Silver Spring, MD 20993-0002 (United States); Valerio, Luis G., E-mail: luis.valerio@fda.hhs.gov [Office of Pharmaceutical Science, Center for Drug Evaluation and Research, U.S. Food and Drug Administration, 10903 New Hampshire Avenue, Silver Spring, MD 20993-0002 (United States)

    2013-12-15

    As indicated in ICH M7 draft guidance, in silico predictive tools including statistically-based QSARs and expert analysis may be used as a computational assessment for bacterial mutagenicity for the qualification of impurities in pharmaceuticals. To address this need, we developed and validated a QSAR model to predict Salmonella t. mutagenicity (Ames assay outcome) of pharmaceutical impurities using Prous Institute's Symmetry℠, a new in silico solution for drug discovery and toxicity screening, and the Mold2 molecular descriptor package (FDA/NCTR). Data was sourced from public benchmark databases with known Ames assay mutagenicity outcomes for 7300 chemicals (57% mutagens). Of these data, 90% was used to train the model and the remaining 10% was set aside as a holdout set for validation. The model's applicability to drug impurities was tested using a FDA/CDER database of 951 structures, of which 94% were found within the model's applicability domain. The predictive performance of the model is acceptable for supporting regulatory decision-making with 84 ± 1% sensitivity, 81 ± 1% specificity, 83 ± 1% concordance and 79 ± 1% negative predictivity based on internal cross-validation, while the holdout dataset yielded 83% sensitivity, 77% specificity, 80% concordance and 78% negative predictivity. Given the importance of having confidence in negative predictions, an additional external validation of the model was also carried out, using marketed drugs known to be Ames-negative, and obtained 98% coverage and 81% specificity. Additionally, Ames mutagenicity data from FDA/CFSAN was used to create another data set of 1535 chemicals for external validation of the model, yielding 98% coverage, 73% sensitivity, 86% specificity, 81% concordance and 84% negative predictivity. - Highlights: • A new in silico QSAR model to predict Ames mutagenicity is described. • The model is extensively validated with chemicals from the FDA and the public domain.

  10. A novel QSAR model of Salmonella mutagenicity and its application in the safety assessment of drug impurities

    International Nuclear Information System (INIS)

    As indicated in ICH M7 draft guidance, in silico predictive tools including statistically-based QSARs and expert analysis may be used as a computational assessment for bacterial mutagenicity for the qualification of impurities in pharmaceuticals. To address this need, we developed and validated a QSAR model to predict Salmonella t. mutagenicity (Ames assay outcome) of pharmaceutical impurities using Prous Institute's Symmetry℠, a new in silico solution for drug discovery and toxicity screening, and the Mold2 molecular descriptor package (FDA/NCTR). Data was sourced from public benchmark databases with known Ames assay mutagenicity outcomes for 7300 chemicals (57% mutagens). Of these data, 90% was used to train the model and the remaining 10% was set aside as a holdout set for validation. The model's applicability to drug impurities was tested using a FDA/CDER database of 951 structures, of which 94% were found within the model's applicability domain. The predictive performance of the model is acceptable for supporting regulatory decision-making with 84 ± 1% sensitivity, 81 ± 1% specificity, 83 ± 1% concordance and 79 ± 1% negative predictivity based on internal cross-validation, while the holdout dataset yielded 83% sensitivity, 77% specificity, 80% concordance and 78% negative predictivity. Given the importance of having confidence in negative predictions, an additional external validation of the model was also carried out, using marketed drugs known to be Ames-negative, and obtained 98% coverage and 81% specificity. Additionally, Ames mutagenicity data from FDA/CFSAN was used to create another data set of 1535 chemicals for external validation of the model, yielding 98% coverage, 73% sensitivity, 86% specificity, 81% concordance and 84% negative predictivity. - Highlights: • A new in silico QSAR model to predict Ames mutagenicity is described. • The model is extensively validated with chemicals from the FDA and the public domain. • Validation tests

  11. Kolmogorov turbulence, Anderson localization and KAM integrability

    Science.gov (United States)

    Shepelyansky, D. L.

    2012-06-01

    The conditions for emergence of Kolmogorov turbulence, and related weak wave turbulence, in finite size systems are analyzed by analytical methods and numerical simulations of simple models. The analogy between Kolmogorov energy flow from large to small spacial scales and conductivity in disordered solid state systems is proposed. It is argued that the Anderson localization can stop such an energy flow. The effects of nonlinear wave interactions on such a localization are analyzed. The results obtained for finite size system models show the existence of an effective chaos border between the Kolmogorov-Arnold-Moser (KAM) integrability at weak nonlinearity, when energy does not flow to small scales, and developed chaos regime emerging above this border with the Kolmogorov turbulent energy flow from large to small scales.

  12. Anderson localization and momentum-space entanglement

    International Nuclear Information System (INIS)

    We consider Anderson localization and the associated metal–insulator transition for non-interacting fermions in D = 1, 2 space dimensions in the presence of spatially correlated on-site random potentials. To assess the nature of the wave function, we follow a recent proposal to study momentum-space entanglement. For a D = 1 model with long-range disorder correlations, both the entanglement spectrum and the entanglement entropy allow us to clearly distinguish between extended and localized states based upon a single realization of disorder. However, for other models, including the D = 2 case with long-range correlated disorder, we find that the method is not similarly successful. We analyze the reasons for its failure, concluding that the much desired generalization to higher dimensions may be problematic. (paper)

  13. EMC3-EIRENE modelling of edge impurity transport in the stochastic layer of the large helical device compared with extreme ultraviolet emission measurements

    Science.gov (United States)

    Dai, Shuyu; Kobayashi, M.; Kawamura, G.; Morita, S.; Zhang, H. M.; Oishi, T.; Feng, Y.; Wang, D. Z.; Suzuki, Y.; the LHD Experimental Group

    2016-06-01

    The transport properties and line emissions of carbon impurity in the stochastic layer of the Large Helical Device have been investigated with the 3D edge transport code EMC3-EIRENE. A parameter study has been performed to examine the sensitivity of the simulation results on each transport term in the impurity transport model and the impurity source characteristics, i.e. the source amount and the location. The modelling has revealed that in order to reproduce the experimental results of the emission distribution, the impurity perpendicular transport coefficient (D imp) and the first wall source play important roles, while changes to the ion thermal and the friction forces are rather irrelevant. The detailed study of flux tube tracing and magnetic field structure in the edge stochastic layer, in relation to impurity transport, has shown that the deeper penetration of impurity into the higher plasma density region due to the enhanced D imp and the first wall source is responsible for the change of emission pattern as well as the intensity. The analysis indicates that D imp might be larger than that of background plasma by a few factors and also that there probably exists a substantial amount of first wall impurity source.

  14. Benedict Andersons forestillede fællesskaber

    DEFF Research Database (Denmark)

    Ivarsson, Søren

    2007-01-01

    Artiklen diskuterer Benedict Andersons analyse af nationalismens opståen i en kolonial kontekst og den kritik som Partha Chatterjee har rejst mod denne. Udgivelsesdato: Januar 2008......Artiklen diskuterer Benedict Andersons analyse af nationalismens opståen i en kolonial kontekst og den kritik som Partha Chatterjee har rejst mod denne. Udgivelsesdato: Januar 2008...

  15. Anderson localization in nonlocal nonlinear media

    OpenAIRE

    Folli, Viola; Conti, Claudio

    2012-01-01

    The effect of focusing and defocusing nonlinearities on Anderson localization in highly nonlocal media is theoretically and numerically investigated. A perturbative approach is developed to solve the nonlocal nonlinear Schroedinger equation in the presence of a random potential, showing that nonlocality stabilizes Anderson states.

  16. Interplay of Anderson localization and strong interaction in disordered systems

    International Nuclear Information System (INIS)

    We study the interplay of disorder localization and strong local interactions within the Anderson-Hubbard model. Taking into account local Mott-Hubbard physics and static screening of the disorder potential, the system is mapped onto an effective single-particle Anderson model, which is studied within the self-consistent theory of electron localization. For fermions, we find rich nonmonotonic behavior of the localization length ξ, particularly in two-dimensional systems, including an interaction-induced exponential enhancement of ξ for small and intermediate disorders and a strong reduction of ξ due to hopping suppression by strong interactions. In three dimensions, we identify for half filling a Mott-Hubbard-assisted Anderson localized phase existing between the metallic and the Mott-Hubbard-gapped phases. For small U there is re-entrant behavior from the Anderson localized phase to the metallic phase. For bosons, the unrestricted particle occupation number per lattice site yields a monotonic enhancement of ξ as a function of decreasing interaction, which we assume to persist until the superfluid Bose-Einstein condensate phase is entered. Besides, we study cold atomic gases expanding, by a diffusion process, in a weak random potential. We show that the density-density correlation function of the expanding gas is strongly affected by disorder and we estimate the typical size of a speckle spot, i.e., a region of enhanced or depleted density. Both a Fermi gas and a Bose-Einstein condensate (in a mean-field approach) are considered. (orig.)

  17. Interplay of Anderson localization and strong interaction in disordered systems

    Energy Technology Data Exchange (ETDEWEB)

    Henseler, Peter

    2010-01-15

    We study the interplay of disorder localization and strong local interactions within the Anderson-Hubbard model. Taking into account local Mott-Hubbard physics and static screening of the disorder potential, the system is mapped onto an effective single-particle Anderson model, which is studied within the self-consistent theory of electron localization. For fermions, we find rich nonmonotonic behavior of the localization length {xi}, particularly in two-dimensional systems, including an interaction-induced exponential enhancement of {xi} for small and intermediate disorders and a strong reduction of {xi} due to hopping suppression by strong interactions. In three dimensions, we identify for half filling a Mott-Hubbard-assisted Anderson localized phase existing between the metallic and the Mott-Hubbard-gapped phases. For small U there is re-entrant behavior from the Anderson localized phase to the metallic phase. For bosons, the unrestricted particle occupation number per lattice site yields a monotonic enhancement of {xi} as a function of decreasing interaction, which we assume to persist until the superfluid Bose-Einstein condensate phase is entered. Besides, we study cold atomic gases expanding, by a diffusion process, in a weak random potential. We show that the density-density correlation function of the expanding gas is strongly affected by disorder and we estimate the typical size of a speckle spot, i.e., a region of enhanced or depleted density. Both a Fermi gas and a Bose-Einstein condensate (in a mean-field approach) are considered. (orig.)

  18. Interview with Philip W. Anderson

    International Nuclear Information System (INIS)

    Phil Anderson, Professor of Physics at Princeton University, has devoted his career to research in theoretical physics. He is a member of the National Academy of Science and the American Academy of Arts and Sciences, a foreign member of the Royal Society, and a foreign associate of the Accademia Lincei in Rome. The Americal Physical Society awarded him the Oliver E. Buckley Solid State Physics Prize in 1964. In 1977 he won the Nobel Prize in Physics with J.H. van Vleck and N.F. Mott. His work has encompassed a broad range of subjects: quantum theory of condensed matter, broken symmetry, transport theory and localization, random statistical systems, spectral line broadening, superfluidity in helium and neutron stars, magnetism, and superconductivity. His avocations include ''hiking, the game of GO, Romanesque architecture, and the human condition.'' In this interview he explains his RVB theory of the oxide superconductors and its historical context

  19. Dynamical impurity problems

    International Nuclear Information System (INIS)

    In the past few years there has been a resurgence of interest in dynamical impurity problems, as a result of developments in the theory of correlated electron systems. The general dynamical impurity problem is a set of conduction electrons interacting with an impurity which has internal degrees of freedom. The simplest and earliest example, the Kondo problem, has attracted interest since the mid-sixties not only because of its physical importance but also as an example of a model displaying logarithmic divergences order by order in perturbation theory. It provided one of the earliest applications of the renormalization group method, which is designed to deal with just such a situation. As we shall see, the antiferromagnetic Kondo model is controlled by a strong-coupling fixed point, and the essence of the renormalization group solution is to carry out the global renormalization numerically starting from the original (weak-coupling) Hamiltonian. In these lectures, we shall describe an alternative route in which we identify an exactly solvable model which renormalizes to the same fixed point as the original dynamical impurity problem. This approach is akin to determining the critical behavior at a second order phase transition point by solving any model in a given universality class

  20. Comparing models for the ground state energy of a trapped one-dimensional Fermi gas with a single impurity

    DEFF Research Database (Denmark)

    Loft, N. J. S.; Kristensen, Lasse Bjørn; Thomsen, Anders;

    2016-01-01

    We discuss the local density approximation approach to calculating the ground state energy of a one-dimensional Fermi gas containing a single impurity, and compare the results with exact numerical values that we have for up to 11 particles for general interaction strengths and up to 30 particles ...... the few-atom regime, yet it works surprisingly well for some models. Secondly, we find that the strong interaction theories quickly break down when the number of particles increase or the interaction strength decreases....

  1. Price-Anderson Law - reports on Price-Anderson issues

    International Nuclear Information System (INIS)

    Five of the six papers in this study are by experts outside the nuclear industry, and deal with fear, risk, and risk management as they apply to the review of the Price-Anderson Act. The purpose of the Act is to encourage private enterprise to develop a reliable source of electric power and to protect the public from the financial consequences of injury or damage that may occur during the process. The titles of the five papers are: (1) the effects of ionizing radiation on human health, (2) proof of causation through expert opinion evidence in low-level radiation cases, (3) a critical review of the probability of causation method, (4) the nuclear liability claims experience of the nuclear insurance pools, (5) review of nuclear liability compensation systems applicable to reactors outside the United States, and (6) the economic foundations of limited liability for nuclear reactor accidents. A separate abstract was prepared for each of the papers for EDB, EPA, and INS

  2. Modeling of limiter heat loads and impurity transport in Wendelstein 7-X startup plasmas

    Science.gov (United States)

    Effenberg, Florian; Feng, Y.; Frerichs, H.; Schmitz, O.; Hoelbe, H.; Koenig, R.; Krychowiak, M.; Pedersen, T. S.; Bozhenkov, S.; Reiter, D.

    2015-11-01

    The quasi-isodynamic stellarator Wendelstein 7-X starts plasma operation in a limiter configuration. The field consists of closed magnetic flux surfaces avoiding magnetic islands in the plasma boundary. Because of the small size of the limiters and the absence of wall-protecting elements in this phase, limiter heat loads and impurity generation due to plasma surface interaction become a concern. These issues are studied with the 3D fluid plasma edge and kinetic neutral transport code EMC3-Eirene. It is shown that the 3D SOL consists of three separate helical magnetic flux bundles of different field line connection lengths. A density scan at input power of 4MW reveals a strong modulation of the plasma paramters with the connection length. The limiter peak heat fluxes drop from 14 MWm-2 down to 10 MWm-2 with raising the density from 1 ×1018m-3 to 1.9 ×1019m-3, accompanied by an increase of the heat flux channel widths λq. Radiative power losses can help to avoid thermal overloads of the limiters at the upper margin of the heating power. The power removal feasibility of the intrinsic carbon and other extrinsic light impurities via active gas injection is discussed as a preparation of this method for island divertor operation. Work supported in part by start up funds of the Department of Engineering Physics at the University of Wisconsin - Madison, USA and by the U.S. Department of Energy under grant DE-SC0013911.

  3. Light focusing in the Anderson Regime

    CERN Document Server

    Leonetti, Marco; Mafi, Arash; Conti, Claudio

    2014-01-01

    Anderson localization is a regime in which diffusion is inhibited and waves (also electromagnetic waves) get localized. Here we exploit adaptive optics to achieve focusing in disordered optical fibers in the Anderson regime. By wavefront shaping and optimization, we observe the generation of a propagation invariant beam, where light is trapped transversally by disorder, and show that Anderson localizations can be also excited by extended speckled beams. We demonstrate that disordered fibers allow a more efficient focusing action with respect to standard fibers in a way independent of their length, because of the propagation invariant features and cooperative action of transverse localizations.

  4. The Anderson transition due to random spin-orbit coupling in two-dimension

    OpenAIRE

    Asada, Yoichi; Slevin, Keith; Ohtsuki, Tomi

    2003-01-01

    We report an analysis of the Anderson transition in an SU(2) model with chiral symmetry. Clear single parameter scaling behaviour is observed. We estimate the critical exponent for the divergence of the localization length to be $\

  5. Renormalization group approach to the Fröhlich polaron model: application to impurity-BEC problem

    Science.gov (United States)

    Grusdt, F.; Shchadilova, Y. E.; Rubtsov, A. N.; Demler, E.

    2015-07-01

    When a mobile impurity interacts with a many-body system, such as a phonon bath, a polaron is formed. Despite the importance of the polaron problem for a wide range of physical systems, a unified theoretical description valid for arbitrary coupling strengths is still lacking. Here we develop a renormalization group approach for analyzing a paradigmatic model of polarons, the so-called Fröhlich model, and apply it to a problem of impurity atoms immersed in a Bose-Einstein condensate of ultra cold atoms. Polaron energies obtained by our method are in excellent agreement with recent diagrammatic Monte Carlo calculations for a wide range of interaction strengths. They are found to be logarithmically divergent with the ultra-violet cut-off, but physically meaningful regularized polaron energies are also presented. Moreover, we calculate the effective mass of polarons and find a smooth crossover from weak to strong coupling regimes. Possible experimental tests of our results in current experiments with ultra cold atoms are discussed.

  6. Student trainee report of Walter L. Anderson

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — The following report is intended to summarize the activities of Walter L. Anderson, Student Trainee (Wildlife Biology) at Malheur National Wildlife Refuge during...

  7. Anderson localization in metallic nanoparticle arrays

    Science.gov (United States)

    Mai, Zhijie; Lin, Fang; Pang, Wei; Xu, Haitao; Tan, Suiyan; Fu, Shenhe; Li, Yongyao

    2016-06-01

    Anderson localization has been observed in various types of waves, such as matter waves, optical waves and acoustic waves. Here we reveal that the effect of Anderson localization can be also induced in metallic nonlinear nanoparticle arrays excited by a random electrically driving field. We find that the dipole-induced nonlinearity results in ballistic expansion of dipole intensity during evolution; while the randomness of the external driving field can suppress such an expansion. Increasing the strength of randomness above the threshold value, a localized pattern of dipole intensity can be generated in the metallic nanoparticle arrays. By means of statistics, the mean intensity distribution of the dipoles reveals the formation of Anderson localization. We further show that the generated Anderson localization is highly confined, with its size down to the scale of incident wavelength. The reported results might facilitate the manipulations of electromagnetic fields in the scale of wavelength.

  8. Anderson localization in metallic nanoparticle arrays

    CERN Document Server

    Mai, Zhijie; Pang, Wei; Xu, Haitao; Tan, Suiyan; Fu, Shenhe; Li, Yongyao

    2016-01-01

    Anderson localization has been observed in various types of waves, such as matter waves, optical waves and acoustic waves. Here we reveal that the effect of Anderson localization can be also induced in metallic nonlinear nanoparticle arrays excited by a random electrically driving field. We find that the dipole-induced nonlinearity results in ballistic expansion of dipole intensity during evolution; while the randomness of the external driving field can suppress such an expansion. Increasing the strength of randomness above the threshold value, a localized pattern of dipole intensity can be generated in the metallic nanoparticle arrays. By means of statistics, the mean intensity distribution of the dipoles reveals the formation of Anderson localization. We further show that the generated Anderson localization is highly confined, with its size down to the scale of incident wavelength. The reported results might facilitate the manipulations of electromagnetic fields in the scale of wavelength.

  9. A Thomas-Fermi model of localization of proton impurities in neutron matter

    International Nuclear Information System (INIS)

    We show that the proton impurity in a neutron matter can create an inhomogeneity in density which acts as a potential well localizing the proton's wave function. At low densities this inhomogeneity is a neutron bulge, whereas at high densities a neutron deficiency (bubble) occurs. We calculate variationally the proton's energy using a Gaussian wave function. The neutron background is treated in a Thomas-Fermi approximation. The Skyrme interactions are used. We find that the localized proton has lower energy than the plane wave proton for densities below the lower critical density n1 ≅ 0.3n0, and above the upper critical density nu ≅ 2.2n0, where n0 0.17 fm-3. We discuss some implications of the proton localization for magnetic properties of neutron matter containing a small admixture of protons. 23 refs., 10 figs. (author)

  10. Low Z impurity transport in tokamaks

    International Nuclear Information System (INIS)

    Low Z impurity transport in tokamaks was simulated with a one-dimensional impurity transport model including both neoclassical and anomalous transport. The neoclassical fluxes are due to collisions between the background plasma and impurity ions as well as collisions between the various ionization states. The evaluation of the neoclassical fluxes takes into account the different collisionality regimes of the background plasma and the impurity ions. A limiter scrapeoff model is used to define the boundary conditions for the impurity ions in the plasma periphery. In order to account for the spectroscopic measurements of power radiated by the lower ionization states, fluxes due to anomalous transport are included. The sensitivity of the results to uncertainties in rate coefficients and plasma parameters in the periphery are investigated. The implications of the transport model for spectroscopic evaluation of impurity concentrations, impurity fluxes, and radiated power from line emission measurements are discussed

  11. Perturbative Interpretation of Adaptive Thouless-Anderson-Palmer Free Energy

    OpenAIRE

    Yasuda, Muneki; Takahashi, Chako; Tanaka, Kazuyuki

    2016-01-01

    In conventional well-known derivation methods for the adaptive Thouless-Anderson-Palmer (TAP) free energy, special assumptions that are difficult to mathematically justify except in some mean-field models, must be made. Here, we present a new adaptive TAP free energy derivation method. Using this derivation technique, without any special assumptions, the adaptive TAP free energy can be simply obtained as a high-temperature expansion of the Gibbs free energy.

  12. Perturbative Interpretation of Adaptive Thouless-Anderson-Palmer Free Energy

    Science.gov (United States)

    Yasuda, Muneki; Takahashi, Chako; Tanaka, Kazuyuki

    2016-07-01

    In conventional well-known derivation methods for the adaptive Thouless-Anderson-Palmer (TAP) free energy, special assumptions that are difficult to mathematically justify except in some mean-field models, must be made. Here, we present a new adaptive TAP free energy derivation method. Using this derivation technique, without any special assumptions, the adaptive TAP free energy can be simply obtained as a high-temperature expansion of the Gibbs free energy.

  13. Random Magnetic Impurities and the $\\delta$ Impurity Problem

    OpenAIRE

    Desbois, Jean; Furtlehner, Cyril; Ouvry, Stéphane; Théorique, Division de Physique; IPN; Fr-91406, Orsay

    1994-01-01

    One considers the effect of disorder on the 2-dimensional density of states of an electron in a constant magnetic field superposed onto a Poissonnian random distribution of point vortices. If one restricts the electron Hilbert space to the lowest Landau level of the total average magnetic field, the random magnetic impurity problem is mapped onto a contact $\\delta$ impurity problem. A brownian motion analysis of the model, based on brownian probability distributions for arithmetic area windin...

  14. Modelling of impurity deposition in gaps of castellated structures in TEXTOR with the 3DGap code

    International Nuclear Information System (INIS)

    In fusion devices, fuel-rich redeposited layers are formed on plasma shadowed areas and especially in narrow gaps between surface tiles. The Monte-Carlo neutral transport code 3DGap has been developed to study impurity deposition in such gaps. Coupling with Particle-in-Cell simulations allows accounting for plasma penetration into the gaps. The code is applied to study carbon deposition in gaps of the ITER-like castellated test limiter (CTL) and between tiles of the toroidal belt limiter ALT-II of TEXTOR. In case of CTL, the deposition on gap sides can be quantitatively reproduced. However, certain discrepancies remain for the gap bottom. Similarly, deposition at side walls and at the bottom was observed in ALT-II gaps. In this experiment, boronization and normal plasma operation phases were alternated. Atomic ratio boron/carbon of about 3 in the deposit at the bottom in gaps was measured, while carbon dominates deposition near the gap entrance. This issue will be addressed together with the poloidal-toroidal asymmetry of carbon deposition in gaps.

  15. Transverse Anderson localization of light: a tutorial review

    CERN Document Server

    Mafi, Arash

    2015-01-01

    This tutorial review gives an overview of the transverse Anderson localization of light in one and two transverse dimensions. A pedagogical approach is followed throughout the presentation, where many aspects of localization are illustrated by means of a few simple models. The tutorial starts with some basic aspects of random matrix theory, and light propagation through and reflection from a random stack of dielectric slabs. Transverse Anderson localization of light in one- and two-dimensional coupled waveguide arrays is subsequently established and discussed. Recent experimental observations of localization and image transport in disordered optical fibers are discussed. More advanced topics, such as hyper-transport in longitudinally varying disordered waveguides, the impact of nonlinearity, and propagation of partially coherent and quantum light, are also examined.

  16. My Random Walks in Anderson's Garden

    CERN Document Server

    Baskaran, G

    2016-01-01

    Anderson's Garden is a drawing presented to Philip W. Anderson on the eve of his 60th birthday celebration, in 1983. This cartoon (Fig. 1), whose author is unknown, succinctly depicts some of Anderson's pre-1983 works, as a blooming garden. As an avid reader of Anderson's papers, random walk in Anderson's garden had become a part of my routine since graduate school days. This was of immense help and prepared me for a wonderful collaboration with the gardener himself, on the resonating valence bond (RVB) theory of High Tc cuprates and quantum spin liquids, at Princeton. The result was bountiful - the first (RVB mean field) theory for i) quantum spin liquids, ii) emergent fermi surfaces in Mott insulators and iii) superconductivity in doped Mott insulators. Beyond mean field theory - i) emergent gauge fields, ii) Ginzbuerg Landau theory with RVB gauge fields, iii) prediction of superconducting dome, iv) an early identification and study of a non-fermi liquid normal state of cuprates and so on. Here I narrate th...

  17. Magnetic Impurities in Graphene

    OpenAIRE

    Hu, F. M.; Ma, Tianxing; Lin, Hai-Qing; Gubernatis, J. E.

    2011-01-01

    We used a quantum Monte Carlo method to study the magnetic impurity adatoms on graphene. We found that by tuning the chemical potential we could switch the values of the impurity's local magnet moment between relatively large and small values. Our computations of the impurity's spectral density found its behavior to differ significantly from that of an impurity in a normal metal and our computations of the charge-charge and spin-spin correlations between the impurity and the conduction band e...

  18. Numerical renormalization group for impurity quantum phase transitions: structure of critical fixed points

    International Nuclear Information System (INIS)

    The numerical renormalization group method is used to investigate zero-temperature phase transitions in quantum impurity systems, in particular in the particle-hole symmetric soft-gap Anderson model. The model displays two stable phases whose fixed points can be built up of non-interacting single-particle states. In contrast, the quantum phase transitions turn out to be described by interacting fixed points, and their excitations cannot be described in terms of free particles. We show that the structure of the many-body spectrum of these critical fixed points can be understood using renormalized perturbation theory close to certain values of the bath exponents which play the role of critical dimensions. Contact is made with perturbative renormalization group calculations for the soft-gap Anderson and Kondo models. A complete description of the quantum critical many-particle spectra is achieved using suitable marginal operators; technically this can be understood as epsilon-expansion for full many-body spectra

  19. Numerical renormalization group for impurity quantum phase transitions: structure of critical fixed points

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Hyun-Jung [Theoretische Physik III, Elektronische Korrelationen und Magnetismus, Institut fuer Physik, Universitaet Augsburg, D-86135 Augsburg (Germany); Bulla, Ralf [Theoretische Physik III, Elektronische Korrelationen und Magnetismus, Institut fuer Physik, Universitaet Augsburg, D-86135 Augsburg (Germany); Vojta, Matthias [Institut fuer Theorie der Kondensierten Materie, Universitaet Karlsruhe, D-76128 Karlsruhe (Germany)

    2005-11-02

    The numerical renormalization group method is used to investigate zero-temperature phase transitions in quantum impurity systems, in particular in the particle-hole symmetric soft-gap Anderson model. The model displays two stable phases whose fixed points can be built up of non-interacting single-particle states. In contrast, the quantum phase transitions turn out to be described by interacting fixed points, and their excitations cannot be described in terms of free particles. We show that the structure of the many-body spectrum of these critical fixed points can be understood using renormalized perturbation theory close to certain values of the bath exponents which play the role of critical dimensions. Contact is made with perturbative renormalization group calculations for the soft-gap Anderson and Kondo models. A complete description of the quantum critical many-particle spectra is achieved using suitable marginal operators; technically this can be understood as epsilon-expansion for full many-body spectra.

  20. Random nanolasing in the Anderson localized regime

    DEFF Research Database (Denmark)

    Liu, Jin; Garcia, P. D.; Ek, Sara;

    2014-01-01

    multiple scattering. The applicability of random lasers has been limited due to multidirectional emission, lack of tunability, and strong mode competition with chaotic fluctuations due to a weak mode confinement. The regime of Anderson localization of light has been proposed for obtaining stable multimode...... random lasing, and initial work concerned macroscopic one-dimensional layered media. Here, we demonstrate on-chip random nanolasers where the cavity feedback is provided by the intrinsic disorder. The strong confinement achieved by Anderson localization reduces the spatial overlap between lasing modes...

  1. Charge Kondo anomalies in PbTe doped with Tl impurities

    OpenAIRE

    Costi, T. A.; Zlatic, V.

    2011-01-01

    We investigate the properties of PbTe doped with a small concentration $x$ of Tl impurities acting as acceptors and described by Anderson impurities with negative onsite correlation energy. We use the numerical renormalization group method to show that the resulting charge Kondo effect naturally accounts for the unusual low temperature and doping dependence of normal state properties, including the self-compensation effect in the carrier density and the non-magnetic Kondo anomaly in the resis...

  2. Topology dependent quantities at the Anderson transition

    OpenAIRE

    Slevin, Keith; Ohtsuki, Tomi; Kawarabayashi, Tohru

    2000-01-01

    The boundary condition dependence of the critical behavior for the three dimensional Anderson transition is investigated. A strong dependence of the scaling function and the critical conductance distribution on the boundary conditions is found, while the critical disorder and critical exponent are found to be independent of the boundary conditions.

  3. Corrections to scaling at the Anderson transition

    OpenAIRE

    Slevin, Keith; Ohtsuki, Tomi

    1998-01-01

    We report a numerical analysis of corrections to finite size scaling at the Anderson transition due to irrelevant scaling variables and non-linearities of the scaling variables. By taking proper account of these corrections, the universality of the critical exponent for the orthogonal universality class for three different distributions of the random potential is convincingly demonstrated.

  4. THE DISTRIBUTION MODELING OF IMPURITIES IN THE ATMOSPHERE WITH TAKING INTO ACCOUNT OF TERRAIN

    Directory of Open Access Journals (Sweden)

    P. B. Mashyhina

    2009-03-01

    Full Text Available The 2D numerical model to simulate the pollutant dispersion over complex terrain was proposed. The model is based on the equation of potential flow and the equation of admixture transfer. Results of the numerical experiment are presented.

  5. Preliminary Modelling of the Effect of Impurity in CO2 Streams on the Storage Capacity and the Plume Migration in Pohang Basin, Korea

    Science.gov (United States)

    Park, Yongchan; Choi, Byoungyoung; Shinn, Youngjae

    2015-04-01

    Captured CO2 streams contain various levels of impurities which vary depending on the combustion technology and CO2 sources such as a power plant and iron and steel production processes. Common impurities or contaminants are non-condensable gases like nitrogen, oxygen and hydrogen, and are also air pollutants like sulphur and nitrogen oxides. Specifically for geological storage, the non-condensable gases in CO2 streams are not favourable because they can decrease density of the injected CO2 stream and can affect buoyancy of the plume. However, separation of these impurities to obtain the CO2 purity higher than 99% would greatly increase the cost of capture. In 2010, the Korean Government announced a national framework to develop CCS, with the aim of developing two large scale integrated CCS projects by 2020. In order to achieve this goal, a small scale injection project into Pohang basin near shoreline has begun which is seeking the connection with a capture project, especially at a steel company. Any onshore sites that are suitable for the geological storage are not identified by this time so we turned to the shallow offshore Pohang basin where is close to a large-scale CO2 source. Currently, detailed site surveys are being undertaken and the collected data were used to establish a geological model of the basin. In this study, we performed preliminary modelling study on the effect of impurities on the geological storage using the geological model. Using a potential compositions of impurities in CO2 streams from the steel company, we firstly calculated density and viscosity of CO2 streams as a function of various pressure and temperature conditions with CMG-WINPROP and then investigated the effect of the non-condensable gases on storage capacity, injectivity and plume migrations with CMG-GEM. Further simulations to evaluate the areal and vertical sweep efficiencies by impurities were perform in a 2D vertical cross section as well as in a 3D simulation grid. Also

  6. Quantum criticality of a spin-1 XY model with easy-plane single-ion anisotropy via a two-time Green function approach avoiding the Anderson-Callen decoupling

    Science.gov (United States)

    Mercaldo, M. T.; Rabuffo, I.; De Cesare, L.; Caramico D'Auria, A.

    2016-04-01

    In this work we study the quantum phase transition, the phase diagram and the quantum criticality induced by the easy-plane single-ion anisotropy in a d-dimensional quantum spin-1 XY model in absence of an external longitudinal magnetic field. We employ the two-time Green function method by avoiding the Anderson-Callen decoupling of spin operators at the same sites which is of doubtful accuracy. Following the original Devlin procedure we treat exactly the higher order single-site anisotropy Green functions and use Tyablikov-like decouplings for the exchange higher order ones. The related self-consistent equations appear suitable for an analysis of the thermodynamic properties at and around second order phase transition points. Remarkably, the equivalence between the microscopic spin model and the continuous O(2) -vector model with transverse-Ising model (TIM)-like dynamics, characterized by a dynamic critical exponent z=1, emerges at low temperatures close to the quantum critical point with the single-ion anisotropy parameter D as the non-thermal control parameter. The zero-temperature critic anisotropy parameter Dc is obtained for dimensionalities d > 1 as a function of the microscopic exchange coupling parameter and the related numerical data for different lattices are found to be in reasonable agreement with those obtained by means of alternative analytical and numerical methods. For d > 2, and in particular for d=3, we determine the finite-temperature critical line ending in the quantum critical point and the related TIM-like shift exponent, consistently with recent renormalization group predictions. The main crossover lines between different asymptotic regimes around the quantum critical point are also estimated providing a global phase diagram and a quantum criticality very similar to the conventional ones.

  7. Subsurface impurities and vacancies in a three-dimensional topological insulator

    OpenAIRE

    Black-Schaffer, Annica M.; Balatsky, Alexander V.

    2012-01-01

    Using a three-dimensional microscopic lattice model of a strong topological insulator (TI) we study potential impurities and vacancies in surface and subsurface positions. For all impurity locations we find impurity-induced resonance states with energy proportional to the inverse of the impurity strength, although the impurity strength needed for a low-energy resonance state increases with the depth of the impurity. For strong impurities and vacancies as deep as 15 layers into the material, r...

  8. Integrals of motion for one-dimensional Anderson localized systems

    Science.gov (United States)

    Modak, Ranjan; Mukerjee, Subroto; Yuzbashyan, Emil A.; Shastry, B. Sriram

    2016-03-01

    Anderson localization is known to be inevitable in one-dimension for generic disordered models. Since localization leads to Poissonian energy level statistics, we ask if localized systems possess ‘additional’ integrals of motion as well, so as to enhance the analogy with quantum integrable systems. We answer this in the affirmative in the present work. We construct a set of nontrivial integrals of motion for Anderson localized models, in terms of the original creation and annihilation operators. These are found as a power series in the hopping parameter. The recently found Type-1 Hamiltonians, which are known to be quantum integrable in a precise sense, motivate our construction. We note that these models can be viewed as disordered electron models with infinite-range hopping, where a similar series truncates at the linear order. We show that despite the infinite range hopping, all states but one are localized. We also study the conservation laws for the disorder free Aubry-Andre model, where the states are either localized or extended, depending on the strength of a coupling constant. We formulate a specific procedure for averaging over disorder, in order to examine the convergence of the power series. Using this procedure in the Aubry-Andre model, we show that integrals of motion given by our construction are well-defined in localized phase, but not so in the extended phase. Finally, we also obtain the integrals of motion for a model with interactions to lowest order in the interaction.

  9. Impurity-induced divertor plasma oscillations

    International Nuclear Information System (INIS)

    Two different oscillatory plasma regimes induced by seeding the plasma with high- and low-Z impurities are found for ITER-like divertor plasmas, using computer modeling with the DUSTT/UEDGE and SOLPS4.3 plasma-impurity transport codes. The oscillations are characterized by significant variations of the impurity-radiated power and of the peak heat load on the divertor targets. Qualitative analysis of the divertor plasma oscillations reveals different mechanisms driving the oscillations in the cases of high- and low-Z impurity seeding. The oscillations caused by the high-Z impurities are excited near the X-point by an impurity-related instability of the radiation-condensation type, accompanied by parallel impurity ion transport affected by the thermal and plasma friction forces. The driving mechanism of the oscillations induced by the low-Z impurities is related to the cross-field transport of the impurity atoms, causing alteration between the high and low plasma temperature regimes in the plasma recycling region near the divertor targets. The implications of the impurity-induced plasma oscillations for divertor operation in the next generation tokamaks are also discussed

  10. Impurity-induced divertor plasma oscillations

    Energy Technology Data Exchange (ETDEWEB)

    Smirnov, R. D., E-mail: rsmirnov@ucsd.edu; Krasheninnikov, S. I.; Pigarov, A. Yu. [University of California, San Diego, La Jolla, California 92093 (United States); Kukushkin, A. S. [NRC “Kurchatov Institute”, Moscow 123182 (Russian Federation); National Research Nuclear University MEPhI, Moscow 115409 (Russian Federation); Rognlien, T. D. [Lawrence Livermore National Laboratory, Livermore, California 94551 (United States)

    2016-01-15

    Two different oscillatory plasma regimes induced by seeding the plasma with high- and low-Z impurities are found for ITER-like divertor plasmas, using computer modeling with the DUSTT/UEDGE and SOLPS4.3 plasma-impurity transport codes. The oscillations are characterized by significant variations of the impurity-radiated power and of the peak heat load on the divertor targets. Qualitative analysis of the divertor plasma oscillations reveals different mechanisms driving the oscillations in the cases of high- and low-Z impurity seeding. The oscillations caused by the high-Z impurities are excited near the X-point by an impurity-related instability of the radiation-condensation type, accompanied by parallel impurity ion transport affected by the thermal and plasma friction forces. The driving mechanism of the oscillations induced by the low-Z impurities is related to the cross-field transport of the impurity atoms, causing alteration between the high and low plasma temperature regimes in the plasma recycling region near the divertor targets. The implications of the impurity-induced plasma oscillations for divertor operation in the next generation tokamaks are also discussed.

  11. Coulomb impurity in graphene

    CERN Document Server

    Biswas, Rudro R; Son, Dam T

    2007-01-01

    We consider the problem of screening of an electrically charged impurity in a clean graphene sheet. When electron-electron interactions are neglected, the screening charge has a sign opposite to that of the impurity, and is localized near the impurity. Interactions between electrons smear out the induced charge density to give a large-distance tail that follows approximately, but not exactly, an r^{-2} behavior and with a sign which is the same as that of the impurity.

  12. Transversal Anderson localization of sound in acoustic waveguide arrays

    International Nuclear Information System (INIS)

    We present designs of one-dimensional acoustic waveguide arrays and investigate wave propagation inside. Under the condition of single identical waveguide mode and weak coupling, the acoustic wave motion in waveguide arrays can be modeled with a discrete mode-coupling theory. The coupling constants can be retrieved from simulations or experiments as the function of neighboring waveguide separations. Sound injected into periodic arrays gives rise to the discrete diffraction, exhibiting ballistic or extended transport in transversal direction. But sound injected into randomized waveguide arrays readily leads to Anderson localization transversally. The experimental results show good agreement with simulations and theoretical predictions. (paper)

  13. Non-Fermi liquid and Fermi liquid in two-channel anderson lattice model. Theory for PrA2Al20 (A = V, Ti) and PrIr2Zn20

    International Nuclear Information System (INIS)

    We theoretically investigate electronic states and physical properties in a two-channel Anderson lattice model to understand the non-Fermi liquid behaviors observed in PrV2Al20 and PrIr2Zn20, whose ground state of the crystalline electric field for a local f-electron is the Γ3 non-Kramers doublet of f2-configuration and whose excited state is the Γ7 Kramers doublet of f1-configuration. We use the expansion from the limit of the large degeneracy N of the ground state (1/N-expansion), with N being the spin–orbital degeneracy. The inclusion of the self-energy of conduction electrons up to the order of O(1/N) leads to heavy electrons with channel and spin–orbit degeneracies. We find that the electrical resistivity is proportional to the temperature T in the limit T → 0 and follows the √T-law in a wide temperature region, i.e., Tx < T < T0, where the typical values of Tx and T0 are Tx ∼ 10-3TK and T0 ∼ 10-2TK, respectively, TK being the Kondo temperature of the model. We also find non-Fermi liquid behaviors at T ≪ TK in a series of physical quantities; chemical potential, specific heat, and magnetic susceptibility, which explain the non-Fermi liquid behaviors observed in PrV2Al20 and PrIr2Zn20. At the same time, we find that the Fermi liquid behavior becomes prominent for the system with a small hybridization between f- and conduction electrons, explaining the Fermi liquid behaviors observed in PrTi2Al20. (author)

  14. Impurity penetration through the edge transport barrier

    Energy Technology Data Exchange (ETDEWEB)

    Belo, P [EURATOM/IST Fusion Association, Centro de Fusao Nuclear, Av. Rovisco Pais, 1049-001 Lisbon (Portugal); Parail, V [EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Corrigan, G [EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Heading, D [EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Houlberg, W [Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Monier-Garbet, P [Association Euratom-CEA, Cadarache 13108 Saint Paul Lez Durance (France); Ongena, J [Laboratoire de Physique des Plasmas-Laboratorium voor Plasmafysica, Association EURATOM-Belgian State, Ecole Royale Militaire-B-1000 Brussels, Koninklijke Militaire School (Belgium)

    2004-08-01

    The ELMs in H-mode plasmas manifest themselves as short bursts of increased edge transport, which expel energy and particles, including impurities from the plasma edge to the SOL and further towards target plates and limiters (Zohm H 1996 Plasma Phys. Control. Fusion 38 1213, Loarte A et al 2003 Plasma Phys. Control. Fusion 45 1549). ELMs are considered beneficial events with respect to impurities since they can prevent impurities from accumulating in the plasma core. JET has recently performed an experiment in which a controlled influx of noble gas impurities was successfully used in order to reduce the amplitude and frequency of type-I ELMs. An interesting correlation between the level of the main gas puffing and the radial redistribution of impurities has been found in this experiment: it was shown that impurities are contained near the separatrix in discharges with a relatively strong level of main gas puffing. Reduction of the puffing below a certain level leads to impurity accumulation in the core followed by thermal collapse. This paper describes the results of predictive modelling of impurity seeding experiments on JET using a coupling of the 1.5D core transport code JETTO (for the main ions) and 1D transport code SANCO (for impurities). Two sets of boundary conditions for the density and temperatures, which correspond to two different deuterium gas puffing rates, were used in the modelling. An explanation for the experimentally observed phenomenon is presented.

  15. Anderson introduces a new biomass baler

    Energy Technology Data Exchange (ETDEWEB)

    D' amour, L.; Lavoie, F. [Anderson Group Co., Chesterville, PQ (Canada)

    2010-07-01

    Canadian-based Anderson Group Company has developed an innovative round baler for harvesting a large variety of woody biomass. The baler was initially developed in 2005 in collaboration with the University Laval and Agriculture and Agri-Food Canada. The third generation BIOBALER{sup TM} is currently built, engineered and commercialized by Anderson. It can produce up to 40 bales/hr in short rotations woody crops such as willow and hybrid poplar. The unit can harvest brushes up to 125 mm in diameter. A standard tractor can pull the BIOBALER in fallow or abandoned land, under power transmission lines, and between planted trees. The patented BIOBALER includes a mulcher head attachment, a choice of long or short swivel tongue, a fixed chamber and an undercarriage frame.

  16. Effect of coulomb interaction on Anderson localization; Effet de l'interaction coulombienne sur la localisation d'Anderson dans des systemes de basses dimensions

    Energy Technology Data Exchange (ETDEWEB)

    Waintal, X

    1999-09-10

    We study the quantum mechanics of interacting particles in a disordered system, and in particular, what happens to Anderson localisation when interaction is taken into account. In the first part,one looks at the excited states of two particles in one dimension. For this model, it has been shown (Shepelyansky 1994) that a local repulsive interaction can partially destroy Anderson localisation. Here, we show that this model has similarities with the three-dimensional Anderson model at the metal-insulator transition. In particular, the maximum of rigidity obtained in the spectral statistics correspond to some intermediary statistics that cannot be described by random matrix theory neither by a Poisson statistics. The wave functions show a multifractal behaviour and the spreading of the center of mass of a wave packet is logarithmic in time. The second part deals with the ground state of a finite density of spinless fermions in two dimensions. After the scaling theory of localisation, it was commonly accepted that there was no metal in two dimensions. This idea has been challenged by the observation of a metal-insulator transition in low density electron gas (Kravchenko et al. 1994). We propose a scenario in which a metallic phase occurs between the Anderson insulator and the pinned Wigner crystal. This intermediate phase is characterized by an alignment of the local currents flowing in the system. (author)

  17. Integrative Medicine Program- MD Anderson Cancer Center

    OpenAIRE

    Lee, Richard T.

    2012-01-01

    The Integrative Medicine Program at MD Anderson Cancer Center was first established in 1998.  Our mission is to empower patients with cancer and their families to become active partners in their own physical, psycho-spiritual, and social health through personalized education and evidenced-based clinical care to optimize health, quality of life, and clinical outcomes across the cancer continuum.  The program consists of three main components: clinical care, research, and education.  The Integr...

  18. Universal mechanism for Anderson and weak localization.

    Science.gov (United States)

    Filoche, Marcel; Mayboroda, Svitlana

    2012-09-11

    Localization of stationary waves occurs in a large variety of vibrating systems, whether mechanical, acoustical, optical, or quantum. It is induced by the presence of an inhomogeneous medium, a complex geometry, or a quenched disorder. One of its most striking and famous manifestations is Anderson localization, responsible for instance for the metal-insulator transition in disordered alloys. Yet, despite an enormous body of related literature, a clear and unified picture of localization is still to be found, as well as the exact relationship between its many manifestations. In this paper, we demonstrate that both Anderson and weak localizations originate from the same universal mechanism, acting on any type of vibration, in any dimension, and for any domain shape. This mechanism partitions the system into weakly coupled subregions. The boundaries of these subregions correspond to the valleys of a hidden landscape that emerges from the interplay between the wave operator and the system geometry. The height of the landscape along its valleys determines the strength of the coupling between the subregions. The landscape and its impact on localization can be determined rigorously by solving one special boundary problem. This theory allows one to predict the localization properties, the confining regions, and to estimate the energy of the vibrational eigenmodes through the properties of one geometrical object. In particular, Anderson localization can be understood as a special case of weak localization in a very rough landscape. PMID:22927384

  19. Interaction-induced localization of mobile impurities in ultracold systems

    Science.gov (United States)

    Li, Jian; An, Jin; Ting, C. S.

    2013-11-01

    The impurities, introduced intentionally or accidentally into certain materials, can significantly modify their characteristics or reveal their intrinsic physical properties, and thus play an important role in solid-state physics. Different from those static impurities in a solid, the impurities realized in cold atomic systems are naturally mobile. Here we propose an effective theory for treating some unique behaviors exhibited by ultracold mobile impurities. Our theory reveals the interaction-induced transition between the extended and localized impurity states, and also explains the essential features obtained from several previous models in a unified way. Based on our theory, we predict many intriguing phenomena in ultracold systems associated with the extended and localized impurities, including the formation of the impurity-molecules and impurity-lattices. We hope this investigation can open up a new avenue for the future studies on ultracold mobile impurities.

  20. Dimensionality effects on spin-polarized quantum beats in ferromagnetic hosts with a pair of side-coupled impurities

    Energy Technology Data Exchange (ETDEWEB)

    Guessi, L.H.; Leandro, S.C.; Seridonio, A.C.; Siqueira, E.C. [Universidade Estadual Paulista Julio de Mesquita Filho (UNESP), Ilha Solteira, SP (Brazil). Dept. de Fisico Quimica; Souza, F.M.; Vernek, E. [Universidade Federal de Uberlandia (UFU), MG (Brazil). Inst. de Fisica; Yoshida, M. [Universidade Estadual Paulista Julio de Mesquita Filho (UNESP), Rio Claro, SP (Brazil); Figueira, M.S. [Universidade Federal Fluminense (UFF), Niteroi, RJ (Brazil). Inst. de Fisica

    2012-07-01

    Full text: In this work, we report a theoretical description of the differential conductance in the low bias regime, for a normal scanning tunneling microscope (STM) probe in the presence of ferromagnetic (FM) hosts with impurities. The hosts are treated as a spin-polarized electron gas hybridized to a pair of side-coupled impurities. Two setups of different dimensionalities are considered, a quantum wire (QW) and a metallic surface (MS). In order to deal with the non-interacting and the Coulomb blockade regimes of these systems, the analysis is done in the framework of the two-impurity Anderson model (TIAM) in combination with the equation of motion (EOM) approach for the Hamiltonian Green functions (GFs). The Fano effect appears in such setups, due to the quantum interference between the transport channels composed by the spin-polarized conduction bands and the electron tunneling into (or out of) the impurities. Thus the conductance of the STM reveals as a function of the probe position, a Fano interference strong dependent on the host dimensionality. It leads to the emergence of spin-polarized quantum beats in the Friedel oscillations for the conductance signal, which are uniform in the QW system in opposite to those found in the MS case, characterized by a long-range damped behavior. We remark that, the energy levels of the impurities and the Coulomb repulsion, modulate these beats. As a result, they establish a scenario where the interplay between the Coulomb blockade and the ferromagnetism of a metallic environment, can be useful for future quantum computation devices. (author)

  1. Anomalous electrical resistivity and Hall constant of Anderson lattice with finite f-band width

    CERN Document Server

    Panwar, S S

    2002-01-01

    We study here an extension of the periodic Anderson model by considering finite f-band width. A variational method is used to study the temperature dependence of electronic transport properties of Anderson lattice for different values of the f-band width. The electrical resistivity rho(T) and Hall constant R sub H (T) calculated show qualitatively the features experimentally observed in heavy fermion materials. We find that as f-band width increases, the low temperature peak in rho(T) disappears, while the low-temperature peak in R sub H (T) becomes sharper. (author)

  2. Anomalous electrical resistivity and Hall constant of Anderson lattice with finite f-band width

    International Nuclear Information System (INIS)

    We study here an extension of the periodic Anderson model by considering finite f-band width. A variational method is used to study the temperature dependence of electronic transport properties of Anderson lattice for different values of the f-band width. The electrical resistivity ρ(T) and Hall constant RH(T) calculated show qualitatively the features experimentally observed in heavy fermion materials. We find that as f-band width increases, the low temperature peak in ρ(T) disappears, while the low-temperature peak in RH(T) becomes sharper. (author)

  3. Chiral Condensate and Mott-Anderson Freeze-Out

    International Nuclear Information System (INIS)

    We present the idea of a Mott-Anderson freeze-out that suggests a key role of the localization of the hadron wave functions when traversing the hadronization transition. The extension of hadron wave functions in dense matter is governed by the behavior of the chiral quark condensate such that its melting at finite temperatures and chemical potentials entails an increase of the size of hadrons and thus their geometrical strong interaction cross sections. It is demonstrated within a schematic resonance gas model, that a kinetic freeze-out condition reveals a correlation with the reduction of the chiral condensate in the phase diagram up to 50% of its vacuum value. Generalizing the description of the chiral condensate by taking into account a full hadron resonance gas such correlation gets distorted. We discuss, that this may be due to our approximations in calculating the chiral condensate which disregard both, in-medium effects on hadron masses and hadron-hadron interactions. The latter, in particular due to quark exchange reactions, could lead to a delocalization of the hadron wave functions in accordance with the picture of a Mott-Anderson transition. (author)

  4. Evaluating the Anderson-Darling Distribution

    Directory of Open Access Journals (Sweden)

    George Marsaglia

    2004-02-01

    Full Text Available Except for n = 1, only the limit as n approaches infinity for the distribution of the Anderson-Darling test for uniformity has been found, and that in so complicated a form that published values for a few percentiles had to be determined by numerical integration, saddlepoint or other approximation methods. We give here our method for evaluating that asymptotic distribution to great accuracy--directly, via series with two-term recursions. We also give, for any particular n, a procedure for evaluating the distribution to the fourth digit, based on empirical CDF's from samples of size 1010 .

  5. Anderson localization of light with topological dislocations

    CERN Document Server

    Lobanov, Valery E; Vysloukh, Victor A; Torner, Lluis

    2013-01-01

    We predict Anderson localization of light with nested screw topological dislocations propagating in disordered two-dimensional arrays of hollow waveguides illuminated by vortex beams. The phenomenon manifests itself in the statistical presence of topological dislocations in ensemble-averaged output distributions accompanying standard disorder-induced localization of light spots. Remarkably, screw dislocations are captured by the light spots despite the fast and irregular transverse displacements and topological charge flipping undertaken by the dislocations due to the disorder. The statistical averaged modulus of the output local topological charge depends on the initial vorticity carried by the beam.

  6. Phil Anderson's Magnetic Ideas in Science

    CERN Document Server

    Coleman, Piers

    2016-01-01

    In Philip W. Anderson's research, magnetism has always played a special role, providing a prism through which other more complex forms of collective behavior and broken symmetry could be examined. I discuss his work on magnetism from the 1950s, where his early work on antiferromagnetism led to the pseudospin treatment of superconductivity - to the 70s and 80s, highlighting his contribution to the physics of local magnetic moments. Phil's interest in the mechanism of moment formation, and screening evolved into the modern theory of the Kondo effect and heavy fermions.

  7. Triaxially deformed relativistic point-coupling model for Λ hypernuclei: A quantitative analysis of the hyperon impurity effect on nuclear collective properties

    Science.gov (United States)

    Xue, W. X.; Yao, J. M.; Hagino, K.; Li, Z. P.; Mei, H.; Tanimura, Y.

    2015-02-01

    Background: The impurity effect of hyperons on atomic nuclei has received a renewed interest in nuclear physics since the first experimental observation of appreciable reduction of E 2 transition strength in low-lying states of the hypernucleus Λ7Li . Many more data on low-lying states of Λ hypernuclei will be measured soon for s d -shell nuclei, providing good opportunities to study the Λ impurity effect on nuclear low-energy excitations. Purpose: We carry out a quantitative analysis of the Λ hyperon impurity effect on the low-lying states of s d -shell nuclei at the beyond-mean-field level based on a relativistic point-coupling energy density functional (EDF), considering that the Λ hyperon is injected into the lowest positive-parity (Λs) and negative-parity (Λp) states. Method: We adopt a triaxially deformed relativistic mean-field (RMF) approach for hypernuclei and calculate the Λ binding energies of hypernuclei as well as the potential-energy surfaces (PESs) in the (β ,γ ) deformation plane. We also calculate the PESs for the Λ hypernuclei with good quantum numbers by using a microscopic particle rotor model (PRM) with the same relativistic EDF. The triaxially deformed RMF approach is further applied in order to determine the parameters of a five-dimensional collective Hamiltonian (5DCH) for the collective excitations of triaxially deformed core nuclei. Taking 25,27Mg Λ and Si31Λ as examples, we analyze the impurity effects of Λs and Λp on the low-lying states of the core nuclei. Results: We show that Λs increases the excitation energy of the 21+ state and decreases the E 2 transition strength from this state to the ground state by 12 %to17 % . On the other hand, Λp tends to develop pronounced energy minima with larger deformation, although it modifies the collective parameters in such a way that the collectivity of the core nucleus can be either increased or decreased. Conclusions: The quadrupole deformation significantly affects the

  8. Distribution of critical temperature at Anderson localization

    Science.gov (United States)

    Gammag, Rayda; Kim, Ki-Seok

    2016-05-01

    Based on a local mean-field theory approach at Anderson localization, we find a distribution function of critical temperature from that of disorder. An essential point of this local mean-field theory approach is that the information of the wave-function multifractality is introduced. The distribution function of the Kondo temperature (TK) shows a power-law tail in the limit of TK→0 regardless of the Kondo coupling constant. We also find that the distribution function of the ferromagnetic transition temperature (Tc) gives a power-law behavior in the limit of Tc→0 when an interaction parameter for ferromagnetic instability lies below a critical value. However, the Tc distribution function stops the power-law increasing behavior in the Tc→0 limit and vanishes beyond the critical interaction parameter inside the ferromagnetic phase. These results imply that the typical Kondo temperature given by a geometric average always vanishes due to finite density of the distribution function in the TK→0 limit while the typical ferromagnetic transition temperature shows a phase transition at the critical interaction parameter. We propose that the typical transition temperature serves a criterion for quantum Griffiths phenomena vs smeared transitions: Quantum Griffiths phenomena occur above the typical value of the critical temperature while smeared phase transitions result at low temperatures below the typical transition temperature. We speculate that the ferromagnetic transition at Anderson localization shows the evolution from quantum Griffiths phenomena to smeared transitions around the critical interaction parameter at low temperatures.

  9. SOURCES OF IMPURITIES: A REVIEW

    OpenAIRE

    Sapra Ashu; Kakkar Saloni; Narasimhan B.

    2012-01-01

    Impurity is defined as an entity of drug substance or drug product that is not chemical entity defined as drug substance, an excipient, or other additives to drug products. In Webster’s dictionary, impurity is “something that is impure or makes something else impure. In the pharmaceutical world, an impurity is generally considered as any other organic material besides the drug substance that arises out of the synthesis most of the time; inorganic contaminants are not considered as impurities ...

  10. Lattice path integral approach to the one-dimensional Kondo model

    International Nuclear Information System (INIS)

    An integrable Anderson-like impurity model in a correlated host is derived from a gl(2/1)-symmetric transfer matrix by means of the quantum-inverse-scattering-method (QISM). Using the quantum transfer matrix technique, free energy contributions of both the bulk and the impurity are calculated exactly. As a special case, the limit of a localized moment in a free bulk (Kondo limit) is performed in the Hamiltonian and in the free energy. In this case, high- and low-temperature scales are calculated with high accuracy

  11. Low Z impurity transport in tokamaks. [Neoclassical transport theory

    Energy Technology Data Exchange (ETDEWEB)

    Hawryluk, R.J.; Suckewer, S.; Hirshman, S.P.

    1978-10-01

    Low Z impurity transport in tokamaks was simulated with a one-dimensional impurity transport model including both neoclassical and anomalous transport. The neoclassical fluxes are due to collisions between the background plasma and impurity ions as well as collisions between the various ionization states. The evaluation of the neoclassical fluxes takes into account the different collisionality regimes of the background plasma and the impurity ions. A limiter scrapeoff model is used to define the boundary conditions for the impurity ions in the plasma periphery. In order to account for the spectroscopic measurements of power radiated by the lower ionization states, fluxes due to anomalous transport are included. The sensitivity of the results to uncertainties in rate coefficients and plasma parameters in the periphery are investigated. The implications of the transport model for spectroscopic evaluation of impurity concentrations, impurity fluxes, and radiated power from line emission measurements are discussed.

  12. Controlling Anderson localization in disordered photonic crystal waveguides

    DEFF Research Database (Denmark)

    Garcia-Fernández, David; Smolka, Stephan; Stobbe, Søren; Lodahl, Peter

    2010-01-01

    In most experiments on Anderson localization so far, only completely random systems without any long-range correlation between the scattering sites have been used, meaning that the Anderson localized modes cannot be controlled. Strongly confined modes were recently observed in the slow-light regime...

  13. Anderson Metal-Insulator Transitions With Classical Magnetic Impurities: Supplemental material

    OpenAIRE

    Jung, Daniel; Slevin, Keith; Kettemann, Stefan

    2015-01-01

    In the supplemental materials we justify our choice of the number of Chebychev moments used within the kernel polynomial method, show some preliminary results for the large coupling behavior, discuss possible correlation effects in the local density of states, estimate the spin relaxation length and introduce the goodness of fit probability that is used to assess the quality of the fits.

  14. Full counting statistics for current through each channel of orbital degenerate Anderson impurity with exchange interactions

    Science.gov (United States)

    Sakano, Rui; Oguri, Akira; Nisikawa, Yunori

    We study non-equilibrium currents, current fluctuations and cross-correlations of the currents through Kondo-correlated quantum dots at low applied bias-voltages, using full counting statistics. To elucidate impact of dot-site interaction to these current properties in crossover between noninteracting and some Kondo states, renormalized perturbation theory or local Fermi liquid theory are employed. The exact form of the cumulant generating function up to third order of bias-voltage is derived in term of renormalized parameters. Specifically, crossover behavior of the Fano factor (ratio between noise and current) and current crosscorrelations for two-fold orbital case is discussed with using computed renormalized parameters by numerical renormalization group.

  15. Simulated impurity transport in LHD from MIST

    Energy Technology Data Exchange (ETDEWEB)

    Rice, J.E. [National Inst. for Fusion Science, Toki, Gifu (Japan)

    1998-05-01

    The impurity transport code MIST and atomic physics package LINES are used to calculate the time evolution of charge state density profiles, individual line emissivity profiles and total radiated power profiles for impurities in LHD plasmas. Three model LHD plasmas are considered; a high density, low temperature case, a low density, high temperature case and the initial LHD start-up plasma (500 kW ECH), using impurity transport coefficient profiles from Heliotron E. The elements oxygen, neon, scandium, iron, nickel and molybdenum are considered, both injected and in steady state. (author)

  16. Simulated impurity transport in LHD from MIST

    International Nuclear Information System (INIS)

    The impurity transport code MIST and atomic physics package LINES are used to calculate the time evolution of charge state density profiles, individual line emissivity profiles and total radiated power profiles for impurities in LHD plasmas. Three model LHD plasmas are considered; a high density, low temperature case, a low density, high temperature case and the initial LHD start-up plasma (500 kW ECH), using impurity transport coefficient profiles from Heliotron E. The elements oxygen, neon, scandium, iron, nickel and molybdenum are considered, both injected and in steady state. (author)

  17. Controlling Anderson localization in disordered photonic crystal waveguides

    DEFF Research Database (Denmark)

    Garcia-Fernández, David; Smolka, Stephan; Stobbe, Søren;

    2010-01-01

    In most experiments on Anderson localization so far, only completely random systems without any long-range correlation between the scattering sites have been used, meaning that the Anderson localized modes cannot be controlled. Strongly confined modes were recently observed in the slow-light regime...... of a disordered photonic crystal waveguide and attributed to Anderson localization. We have tested this hypothesis by measuring the light localization length, ξloc, in a disordered photonic crystal waveguide and checked explicitly the criterion of one dimensional Anderson localization that ξloc is...... shorter than the waveguide length LS. Our measurements demonstrate for the first time the close relation between light localization and density of states, which can be used ultimately for controlling Anderson localized modes....

  18. Spectroscopic studies of impurity densities and impurity transport

    Science.gov (United States)

    Behringer, K.

    1992-06-01

    Spectrometers and spectra, mainly from JET, are discussed with respect to diagnostic potential and calibration problems. Spatial scan facilities or multichord diagnostics are essential for transport investigations, and several possibilities are shown. The interpretation of spectral line radiation usually requires the availability of impurity transport codes, which calculate the ionization balance in the presence of transport, the line emissivities and the total impurity radiation. Some atomic physics prerequisites of such codes are discussed. Theoretical and experimental approaches to the transport problem are investigated using ASDEX and JET results for anomalous transport. The occasional observation of neoclassical accumulation, for example after pellet injection, is presented and respective modeling is described. Some H mode transport phenomena are mentioned.

  19. Plea for European Price Anderson legislation

    International Nuclear Information System (INIS)

    The paper analyses the essential features and the basic differences in nuclear liability and coverage in the United States where the problem is governed by the Price-Anderson legislation, and the Member States of the European Community which adhere to the Paris Convention on Third Party Liability in the Field of Nuclear Energy. The paper undertakes to show that it is possible to introduce into the European Community certain elements of the American regime, in particular the solidarity of nuclear operators and the retroactive premium coverage without violating the basic principles of the Paris Convention. Consequently the paper advocates the adoption of such rules in Europe as a step towards harmonisation of nuclear coverage and safety and a means to reduce government interference. (author)

  20. Slow Relaxation in Anderson Critical Systems

    Science.gov (United States)

    Choi, Soonwon; Yao, Norman; Choi, Joonhee; Kucsko, Georg; Lukin, Mikhail

    2016-05-01

    We study the single particle dynamics in disordered systems with long range hopping, focusing on the critical cases, i.e., the hopping amplitude decays as 1 /rd in d-dimension. We show that with strong on-site potential disorder, the return probability of the particle decays as power-law in time. As on-site potential disorder decreases, the temporal profile smoothly changes from a simple power-law to the sum of multiple power-laws with exponents ranged from 0 to νmax. We analytically compute the decay exponents using a simple resonance counting argument, which quantitatively agrees with exact numerical results. Our result implies that the dynamics in Anderson Critical systems are dominated by resonances. Harvard-MIT CUA, Kwanjeong Educational Fellowship, AFOSR MURI, Samsung Scholarship.

  1. Local order dependent impurity levels in alloy semiconductors

    International Nuclear Information System (INIS)

    We develop a one band/may sites model for an isoelectronic impurity in a semiconductor alloy. The cluster-Bethe-lattice approximation is used to study the dependence of the impurity energy level upon the short range order (SRO) of the alloy. The Kikuchi parametrization is used to describe the latter. We take into account diagonal disorder only, with possible off-diagonal relaxation around the impurity site. All the inequivalent clusters of the impurity site and its first nearest neighbours are considered, thus including the important short range alloy potential fluctuations. Results are presented for the local density of impurity states, for different degrees of SRO in the alloy. (Author)

  2. Impurities in Bose-Einstein Condensates: From Polaron to Soliton.

    Science.gov (United States)

    Shadkhoo, Shahriar; Bruinsma, Robijn

    2015-09-25

    We propose that impurities in a Bose-Einstein condensate which is coupled to a transversely laser-pumped multimode cavity form an experimentally accessible and analytically tractable model system for the study of impurities solvated in correlated liquids and the breakdown of linear-response theory [corrected]. As the strength of the coupling constant between the impurity and the Bose-Einstein condensate is increased, which is possible through Feshbach resonance methods, the impurity passes from a large to a small polaron state, and then to an impurity-soliton state. This last transition marks the breakdown of linear-response theory. PMID:26451565

  3. Power radiated from ITER and CIT by impurities

    International Nuclear Information System (INIS)

    The MIST code has been used to model impurity radiation from the edge and core plasmas in ITER and CIT. A broad range of parameters have been varied, including Zeff, impurity species, impurity transport coefficients, and plasma temperature and density profiles, especially at the edge. For a set of these parameters representative of the baseline ITER ignition scenario, it is seen that impurity radiation, which is produced in roughly equal amounts by the edge and core regions, can make a major improvement in divertor operation without compromising core energy confinement. Scalings of impurity radiation with atomic number and machine size are also discussed. 22 refs., 16 figs

  4. Anderson Exploration Ltd. 1998 annual report

    International Nuclear Information System (INIS)

    In 1998, Anderson Exploration's undeveloped land inventory in the western provinces decreased 7% to 3,183,000 net acres largely due to lease expiries and drilling activity. The undeveloped land base is located 63% in Alberta, 19% in British Columbia, 17% in Saskatchewan, and 1% in Manitoba. During 1998, Anderson Exploration participated in drilling 446 wells for oil and gas vs. 669 for 1997. The average working interest in the wells was 63% vs. 64% in 1997. In 1998, the company spent $109 million on the construction of field gathering systems and production facilities vs. $123 million in 1997. In 1998, the company's gas sales increased to 555 million cubic feet per day from 549 million cubic feet per day in 1997. Crude oil sales averaged 29,808 barrels per day in 1998, an increase of 9% over the 1997 production. In 1998, the company replaced 148% of production with proven reserve additions, net of revisions, by spending 163% of cash flow from operations on capital spending. After a volatile year in 1 997, natural gas prices stabilized somewhat in 1998. A modest price increase was experienced in 1997. The company's average plant gate natural gas price increased modestly in 1998 to $1.94 per thousand cubic feet, marking the 3rd consecutive price increase. The company owns an average interest of 10.4% in two straddle plants at Empress, Alberta. The company operates and is a 50% owner of Federated Pipe Lines Ltd. The company is committed to protecting the health and safety of all employees and the public, as well as preserving the quality of the environment

  5. Phase growth in bistable systems with impurities

    OpenAIRE

    Echeverria, C.; Tucci, K.; Cosenza, M. G.

    2007-01-01

    A system of coupled chaotic bistable maps on a lattice with randomly distributed impurities is investigated as a model for studying the phenomenon of phase growth in nonuniform media. The statistical properties of the system are characterized by means of the average size of spatial domains of equivalent spin variables that define the phases. It is found that the rate at which phase domains grow becomes smaller when impurities are present and that the average size of the resulting domains in t...

  6. Description of the impurity transport code 'STRAHL'

    International Nuclear Information System (INIS)

    'STRAHL' is an interactive, stand-alone impurity transport code which is used on JET for the interpretation of spectroscopic measurements. It calculates the impurity ionisation balance on the basis of given plasma parameters and empirical transport models, using atomic physics data sets especially compiled for that purpose. The paper explains the basic ideas and formulas behind STRAHL in order to allow potential users to design their own special version. (U.K.)

  7. Imaging bolometers for visualization of plasma radiation and cross-validation of three dimensional impurity transport models for the Large Helical Device

    International Nuclear Information System (INIS)

    The InfraRed imaging Video Bolometer (IRVB) measures the radiation from the plasma in two dimensions, giving an image of the plasma radiation power loss. Using a geometry matrix calculated from a model of the LHD first wall, the IRVB sightline geometry and a three dimensional (3D) plasma grid, a synthetic instrument is developed using the 3D carbon impurity radiation results of the EMC3-EIRENE edge impurity transport code as an input. The output of the synthetic instrument are images of the plasma radiation at the IRVB foil due to the EMC3-EIRENE code, which are qualitatively compared with preliminary experimental images from the IRVB. Such a comparison for detached discharges in LHD in which an externally induced m/n = 1/1 magnetic island is applied shows that when the magnetic island is moved 36 degrees toroidally the enhanced radiation in the x-points of the magnetic island also moves as predicted by the EMC3-EIRENE code. (author)

  8. Quantum Hall criticality and localization in graphene with short-range impurities at the Dirac point.

    Science.gov (United States)

    Gattenlöhner, S; Hannes, W-R; Ostrovsky, P M; Gornyi, I V; Mirlin, A D; Titov, M

    2014-01-17

    We explore the longitudinal conductivity of graphene at the Dirac point in a strong magnetic field with two types of short-range scatterers: adatoms that mix the valleys and "scalar" impurities that do not mix them. A scattering theory for the Dirac equation is employed to express the conductance of a graphene sample as a function of impurity coordinates; an averaging over impurity positions is then performed numerically. The conductivity σ is equal to the ballistic value 4e2/πh for each disorder realization, provided the number of flux quanta considerably exceeds the number of impurities. For weaker fields, the conductivity in the presence of scalar impurities scales to the quantum-Hall critical point with σ≃4×0.4e2/h at half filling or to zero away from half filling due to the onset of Anderson localization. For adatoms, the localization behavior is also obtained at half filling due to splitting of the critical energy by intervalley scattering. Our results reveal a complex scaling flow governed by fixed points of different symmetry classes: remarkably, all key manifestations of Anderson localization and criticality in two dimensions are observed numerically in a single setup. PMID:24484036

  9. Numerical Studies of Impurities in Fusion Plasmas

    Science.gov (United States)

    Hulse, R. A.

    1982-09-01

    The coupled partial differential equations used to describe the behavior of impurity ions in magnetically confined controlled fusion plasmas require numerical solution for cases of practical interest. Computer codes developed for impurity modeling at the Princeton Plasma Physics Laboratory are used as examples of the types of codes employed for this purpose. These codes solve for the impurity ionization state densities and associated radiation rates using atomic physics appropriate for these low-density, high-temperature plasmas. The simpler codes solve local equations in zero spatial dimensions while more complex cases require codes which explicitly include transport of the impurity ions simultaneously with the atomic processes of ionization and recombination. Typical applications are discussed and computational results are presented for selected cases of interest.

  10. Motion of a Distinguishable Impurity in the Bose Gas: Arrested Expansion Without a Lattice and Impurity Snaking

    Science.gov (United States)

    Robinson, Neil J.; Caux, Jean-Sébastien; Konik, Robert M.

    2016-04-01

    We consider the real-time dynamics of an initially localized distinguishable impurity injected into the ground state of the Lieb-Liniger model. Focusing on the case where integrability is preserved, we numerically compute the time evolution of the impurity density operator in regimes far from analytically tractable limits. We find that the injected impurity undergoes a stuttering motion as it moves and expands. For an initially stationary impurity, the interaction-driven formation of a quasibound state with a hole in the background gas leads to arrested expansion—a period of quasistationary behavior. When the impurity is injected with a finite center-of-mass momentum, the impurity moves through the background gas in a snaking manner, arising from a quantum Newton's cradlelike scenario where momentum is exchanged back and forth between the impurity and the background gas.

  11. SOURCES OF IMPURITIES: A REVIEW

    Directory of Open Access Journals (Sweden)

    Sapra Ashu

    2012-01-01

    Full Text Available Impurity is defined as an entity of drug substance or drug product that is not chemical entity defined as drug substance, an excipient, or other additives to drug products. In Webster’s dictionary, impurity is “something that is impure or makes something else impure. In the pharmaceutical world, an impurity is generally considered as any other organic material besides the drug substance that arises out of the synthesis most of the time; inorganic contaminants are not considered as impurities unless they are toxic, such as heavy metals or arsenic. There are numerous sources of impurities and many different common terms are used for impurities such as Intermediates, Penultimate intermediates, Byproducts, Transformation products, Interaction products, related products and Degradation products. In this review, a description of different types of impurities in relation to ICH guidelines including specific examples, are presented.

  12. Impurity control in TFTR

    International Nuclear Information System (INIS)

    The control of impurities in TFTR will be a particularly difficult problem due to the large energy and particle fluxes expected in the device. As part of the TFTR Flexibility Modification (TEM) project, a program has been implemented to address this problem. Transport code simulations are used to infer an impurity limit criterion as a function of the impurity atomic number. The configurational designs of the limiters and associated protective plates are discussed along with the consideration of thermal and mechanical loads due to normal plasma operation, neutral beams, and plasma disruptions. A summary is given of the materials-related research, which has been a collaborative effort involving groups at Argonne National Laboratory, Sandia Laboratories, and Princeton Plasma Physics Laboratory. Conceptual designs are shown for getterng systems capable of regenerating absorbed tritium. Research on this topic by groups at the previously mentioned laboratories and SAES Research Laboratory is reviewed

  13. Sulfur Tolerant Solid Oxide Fuel Cell for Coal Syngas Application: Experimental Study on Diverse Impurity Effects and Fundamental Modeling of Electrode Kinetics

    Science.gov (United States)

    Gong, Mingyang

    With demand over green energy economy, fuel cells have been developed as a promising energy conversion technology with higher efficiency and less emission. Solid oxide fuel cells (SOFC) can utilize various fuels in addition to hydrogen including coal derived sygas, and thus are favored for future power generation due to dependence on coal in electrical industry. However impurities such as sulfur and phosphorous present in coal syngas in parts per million (p.p.m.) levels can severely poison SOFC anode typically made of Ni/yttria-stabilized-zirconia (Ni-YSZ) and limit SOFC applicability in economically derivable fuels. The focus of the research is to develop strategy for application of high performance SOFC in coal syngas with tolerance against trace impurities such as H2S and PH3. To realize the research goal, the experimental study on sulfur tolerant anode materials and examination of various fuel impurity effects on SOFC anode are combined with electrochemical modeling of SOFC cathode kinetics in order to benefit design of direct-coal-syngas SOFC. Tolerant strategy for SOFC anode against sulfur is studied by using alternative materials which can both mitigate sulfur poisoning and function as active anode components. The Ni-YSZ anode was modified by incorporation of lanthanum doped ceria (LDC) nano-coatings via impregnation. Cell test in coal syngas containing 20 ppm H2S indicated the impregnated LDC coatings inhibited on-set of sulfur poisoning by over 10hrs. Cell analysis via X-ray photon spectroscopy (XPS), X-ray diffraction (XRD) and electrochemistry revealed LDC coatings reacted with H2S via chemisorptions, resulting in less sulfur blocking triple--phase-boundary and minimized performance loss. Meanwhile the effects of PH3 impurity on SOFC anode is examined by using Ni-YSZ anode supported SOFC. Degradation of cell is found to be irreversible due to adsorption of PH3 on TPB and further reaction with Ni to form secondary phases with low melting point. The

  14. Numerical verification of universality for the Anderson transition

    OpenAIRE

    Slevin, Keith; Ohtsuki, Tomi

    2001-01-01

    We analyze the scaling behavior of the higher Lyapunov exponents at the Anderson transition. We estimate the critical exponent and verify its universality and that of the critical conductance distribution for box, Gaussian and Lorentzian distributions of the random potential.

  15. Controlling Anderson localization in disordered photonic crystal waveguides

    DEFF Research Database (Denmark)

    Garcia-Fernández, David; Smolka, Stephan; Stobbe, Søren;

    structures [1,2]. Originally proposed for electrons by P. W. Anderson [3], only completely random systems without any long-range correlation between the scattering sites have been used so far, meaning that the Anderson-localized modes cannot be controlled. In disordered photonic crystals, these modes are...... predicted to appear at frequencies in or near a band gap [4] providing a possible way to control Anderson-localized modes. We have tested this hypothesis by measuring the light localization length, ξ, in a disordered photonic crystal waveguide (PCW) as a function of the dispersive slowdown factor of light...... of the waveguide. Our measurements demonstrate for the first time the close relation between light localization and density of states [5], which can be used ultimately for controlling the extension and spectral position of Anderson-localized modes....

  16. Martin Anderson valis "Joonase lähetamise" / Priit Kuusk

    Index Scriptorium Estoniae

    Kuusk, Priit, 1938-

    2000-01-01

    M. Anderson kommenteeris ameerika muusikaajakirjas "Fanfare" viit talle kõige enam mõju avaldanud heliplaati, sh. R. Tobiase oratooriumi "Joonase lähetamine" CD-plaati (BIS). M. Andersoni huvist eesti muusika vastu

  17. Cavity quantum electrodynamics in the Anderson-localized regime

    DEFF Research Database (Denmark)

    Sapienza, Luca; Nielsen, Henri Thyrrestrup; Stobbe, Søren;

    2010-01-01

    We experimentally measure, by means of time-resolved photoluminescence spectroscopy, a 15-fold enhancement of the spontaneous emission decay rate of single semiconductor quantum dots coupled to disorder-induced Anderson-localized modes with efficiencies reaching 94%....

  18. 2011 South Carolina DNR Lidar: Tricounty (Anderson, Oconee, Pickens)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Towill Inc. collected LiDAR for over 3,500 square miles in York, Pickens, Anderson, and Oconee Counties in South Carolina. The nominal pulse spacing for this...

  19. Vacuum ultraviolet spectroscopic study of plasma impurities in the Tokapole II poloidal divertor experiment

    International Nuclear Information System (INIS)

    The main diagnostics were two vacuum ultraviolet spectrometers, which were used to identify impurities, observe impurity behavior, and measure the line radiated power. Impurity concentrations and the effects of impurities on gross plasma characteristics were determined with an impurity doping technique. The electron temperature was estimated by a time dependent coronal model describing the time history of the oxygen ions, and the ion temperature was obtaind from Doppler broadening measurements. Energy loss processes were studied with a power balance analysis

  20. Scaling of the conductance distribution near the Anderson transition

    OpenAIRE

    Slevin, Keith; Markoš, Peter; Ohtsuki, Tomi

    2002-01-01

    The single parameter scaling hypothesis is the foundation of our understanding of the Anderson transition. However, the conductance of a disordered system is a fluctuating quantity which does not obey a one parameter scaling law. It is essential to investigate the scaling of the full conductance distribution to establish the scaling hypothesis. We present a clear cut numerical demonstration that the conductance distribution indeed obeys one parameter scaling near the Anderson transition.

  1. The Anderson transition: time reversal symmetry and universality

    OpenAIRE

    Slevin, Keith; Ohtsuki, Tomi

    1997-01-01

    We report a finite size scaling study of the Anderson transition. Different scaling functions and different values for the critical exponent have been found, consistent with the existence of the orthogonal and unitary universality classes which occur in the field theory description of the transition. The critical conductance distribution at the Anderson transition has also been investigated and different distributions for the orthogonal and unitary classes obtained.

  2. Controlling Anderson localization in disordered photonic crystal waveguides

    DEFF Research Database (Denmark)

    Smolka, Stephan; Garcia, Pedro D.; Lodahl, Peter

    2010-01-01

    We prove Anderson localization in the slow-light regime of a photonic crystal waveguide by measuring the ensemble-averaged localization length which is controlled by the dispersion of the disordered photonic crystal waveguide.......We prove Anderson localization in the slow-light regime of a photonic crystal waveguide by measuring the ensemble-averaged localization length which is controlled by the dispersion of the disordered photonic crystal waveguide....

  3. Quantum entanglement investigation on impurity effects in the transverse Ising chain

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Xuchu [Key Laboratory of Functional Materials and Devices for Special Environments of CAS, Xinjiang Technical Institute of Physics & Chemistry of CAS, 40-1 South Beijing Road, Urumqi 830011 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Si, Tieyan [Harbin Institution of Technology, 92 West Dazhi Street, Nan Gang District, Harbin 150001 (China); Yang, Zhihua, E-mail: zhyang@ms.xjb.ac.cn [Key Laboratory of Functional Materials and Devices for Special Environments of CAS, Xinjiang Technical Institute of Physics & Chemistry of CAS, 40-1 South Beijing Road, Urumqi 830011 (China)

    2015-04-01

    The impurity effects of the transverse Ising spin model with a magnetic impurity are investigated via the correlation function and entanglement on the basis of an exact solution. The non-analytical transition point from an ordered phase to a disorder phase is significantly shifted by the impurity coupling with local host spins. The maximal entanglement point which usually appears around the critical point shows strong dependence on the impurity coupling strength with local host spin and the independent transverse field upon the impurity itself. Quantum entanglement in disordered spin phase is much stronger than that in ordered spin phase. The exact concurrence of impurity spin with local host spin suddenly increases to a large value from zero at a threshold value. The maximal entanglement point between impurity and local host spin increases as the impurity coupling strength increases. So the impurity coupling strength and local transverse field on the impurity can control position of critical point and maximal entanglement point.

  4. Quantum entanglement investigation on impurity effects in the transverse Ising chain

    International Nuclear Information System (INIS)

    The impurity effects of the transverse Ising spin model with a magnetic impurity are investigated via the correlation function and entanglement on the basis of an exact solution. The non-analytical transition point from an ordered phase to a disorder phase is significantly shifted by the impurity coupling with local host spins. The maximal entanglement point which usually appears around the critical point shows strong dependence on the impurity coupling strength with local host spin and the independent transverse field upon the impurity itself. Quantum entanglement in disordered spin phase is much stronger than that in ordered spin phase. The exact concurrence of impurity spin with local host spin suddenly increases to a large value from zero at a threshold value. The maximal entanglement point between impurity and local host spin increases as the impurity coupling strength increases. So the impurity coupling strength and local transverse field on the impurity can control position of critical point and maximal entanglement point

  5. Fractal growth in impurity-controlled solidification in lipid monolayers

    DEFF Research Database (Denmark)

    Fogedby, Hans C.; Sørensen, Erik Schwartz; Mouritsen, Ole G.

    1987-01-01

    A simple two-dimensional microscopic model is proposed to describe solidifcation processes in systems with impurities which are miscible only in the fluid phase. Computer simulation of the model shows that the resulting solids are fractal over a wide range of impurity concentrations and impurity...... diffusional constants. A fractal-forming mechanism is suggested for impurity-controlled solidification which is consistent with recent experimental observations of fractal growth of solid phospholipid domains in monolayers. The Journal of Chemical Physics is copyrighted by The American Institute of Physics....

  6. Modelling of surface roughness effects on impurity erosion and deposition in TEXTOR with a code package SURO/ERO/SDPIC

    International Nuclear Information System (INIS)

    The roughness-induced uneven erosion–deposition behaviour is widely observed on plasma-wetted surfaces in tokamaks. The three-dimensional (3D) angular distribution of background plasma and impurities is expected to have an impact on the local erosion–deposition characteristic on rough surfaces. The investigations of 13C deposition on rough surfaces in TEXTOR experiments have been re-visited by 3D treatment of surface morphology to evaluate the effect of 3D angular distribution and its connection with surface topography by the code package SURO/ERO/SDPIC. The simulation results show that the erosion/deposition patterns and evolution of surface topography are strongly affected by the azimuthal direction of incident flux. A reduced aspect ratio of rough surface leads to an increase in 13C deposition due to the enhanced trapping ability at surface recessions. The shadowing effect of rough surface has been revealed based on the relationship between 3D incident direction and surface topography properties. The more realistic surface structures used by 3D SURO can well reproduce the experimental results of the increase in the 13C deposition efficiency by a factor of 3–5 on a rough surface compared with a smooth one. The influence of sheath electric field on the local impact angle and resulting 13C deposition has been studied, which indicates that the difference in 13C deposition caused by sheath electric field can be alleviated by the use of more realistic surface structures. The difference in 13C deposition on smooth graphite and tungsten substrates has been specified by consideration of effects of kinetic reflection, enhanced physical sputtering and nucleation. (paper)

  7. Modelling of surface roughness effects on impurity erosion and deposition in TEXTOR with a code package SURO/ERO/SDPIC

    Science.gov (United States)

    Dai, Shuyu; Kirschner, A.; Sun, Jizhong; Tskhakaya, D.; Wang, Dezhen

    2014-12-01

    The roughness-induced uneven erosion-deposition behaviour is widely observed on plasma-wetted surfaces in tokamaks. The three-dimensional (3D) angular distribution of background plasma and impurities is expected to have an impact on the local erosion-deposition characteristic on rough surfaces. The investigations of 13C deposition on rough surfaces in TEXTOR experiments have been re-visited by 3D treatment of surface morphology to evaluate the effect of 3D angular distribution and its connection with surface topography by the code package SURO/ERO/SDPIC. The simulation results show that the erosion/deposition patterns and evolution of surface topography are strongly affected by the azimuthal direction of incident flux. A reduced aspect ratio of rough surface leads to an increase in 13C deposition due to the enhanced trapping ability at surface recessions. The shadowing effect of rough surface has been revealed based on the relationship between 3D incident direction and surface topography properties. The more realistic surface structures used by 3D SURO can well reproduce the experimental results of the increase in the 13C deposition efficiency by a factor of 3-5 on a rough surface compared with a smooth one. The influence of sheath electric field on the local impact angle and resulting 13C deposition has been studied, which indicates that the difference in 13C deposition caused by sheath electric field can be alleviated by the use of more realistic surface structures. The difference in 13C deposition on smooth graphite and tungsten substrates has been specified by consideration of effects of kinetic reflection, enhanced physical sputtering and nucleation.

  8. Impurity control in toroidal devices

    International Nuclear Information System (INIS)

    This summary report on the Technical Committee Meeting organized by the IAEA and held in Naka-Gun, Japan, 13-15 February 1989, provides an overview of the results presented. Of the twenty-three papers presented, sixteen were devoted to tokamak experiments. These presented data of plasma behavior in the scrape-off layer and divertor regions, as well as effects of impurities on the core plasma; these are summarized here. Other papers summarized deal with plasma-wall interactions, including wall material behavior. Still others deal with theoretical work on physics modelling in the edge region. Refs, figs and tabs

  9. Investigation of the impurity transport in the ASDEX tokamak by spectroscopical methods

    International Nuclear Information System (INIS)

    Plasma impurities: a central problem of controlled thermonuclear fusion; magnetic plasma confinement in a Tokamak; methods to the determination of plasma impurity transport coefficients - by temporally modulated gas admission; the transport equation for impurities; neoclassical and anomalous transport; harmonic analysis of time-dependent signals; solutions of the transport equation; experimental equipment and measurements; measuring results - consistency of simple transport models with radial phase measurements; linearity of the transport processes; plasma disturbance by impurity injection; determination of the diffusion coefficient by simplified transport models; comparison of transport models for impurities and background plasma; measurements of the impurity transport at the plasma edge by high modulation frequencies. (AH)

  10. Impurity injection by use of multiple-shell pellet

    International Nuclear Information System (INIS)

    A model of the three-layered multiple-shell pellet is studied in order to apply to the impurity injection experiment. The mass dependence of the ablation is examined by employing the neutral-cloud shielding model. The localization width of the impurity is estimated. (author)

  11. Tight-Binding Description of Impurity States in Semiconductors

    Science.gov (United States)

    Dominguez-Adame, F.

    2012-01-01

    Introductory textbooks in solid state physics usually present the hydrogenic impurity model to calculate the energy of carriers bound to donors or acceptors in semiconductors. This model treats the pure semiconductor as a homogeneous medium and the impurity is represented as a fixed point charge. This approach is only valid for shallow impurities…

  12. Impurity solitons with quadratic nonlinearities

    DEFF Research Database (Denmark)

    Clausen, Carl A. Balslev; Torres, Juan P-; Torner, Lluis

    We fmd families of solitary waves mediated by parametric mixing in quadratic nonlinear media that are localized at point-defect impurities. Solitons localized at attractive impurities are found to be dynamically stable. It is shown that localization at the impurity modifies strongly the soliton...

  13. Impurity solitons with quadratic nonlinearities

    DEFF Research Database (Denmark)

    Clausen, Carl A. Balslev; Torres, Juan P-; Torner, Lluis

    1998-01-01

    We fmd families of solitary waves mediated by parametric mixing in quadratic nonlinear media that are localized at point-defect impurities. Solitons localized at attractive impurities are found to be dynamically stable. It is shown that localization at the impurity modifies strongly the soliton...

  14. Unified description of perturbation theory and band center anomaly in one-dimensional Anderson localization

    International Nuclear Information System (INIS)

    We calculated numerically the localization length of one-dimensional Anderson model with diagonal disorder. For weak disorder, we showed that the localization length changes continuously as the energy changes from the band center to the boundary of the anomalous region near the band edge. We found that all the localization lengths for different disorder strengths and different energies collapse onto a single curve, which can be fitted by a simple equation. Thus the description of the perturbation theory and the band center anomaly were unified into this equation. -- Highlights: → We study the band center anomaly of one-dimensional Anderson localization. → We study numerically the Lyapunov exponent through a parametrization method of the transfer matrix. → We give a unified equation to describe the band center anomaly and perturbation theory.

  15. Fractional impurity moments in two-dimensional noncollinear magnets.

    Science.gov (United States)

    Wollny, Alexander; Fritz, Lars; Vojta, Matthias

    2011-09-23

    We study dilute magnetic impurities and vacancies in two-dimensional frustrated magnets with noncollinear order. Taking the triangular-lattice Heisenberg model as an example, we use quasiclassical methods to determine the impurity contributions to the magnetization and susceptibility. Most importantly, each impurity moment is not quantized but receives nonuniversal screening corrections due to local relief of frustration. At finite temperatures, where bulk long-range order is absent, this implies an impurity-induced magnetic response of Curie form, with a prefactor corresponding to a fractional moment per impurity. We also discuss the behavior in an applied magnetic field, where we find a singular linear-response limit for overcompensated impurities. PMID:22026900

  16. DEVELOPMENT OF A KINETIC REACTION RATE LIMITED STUDY ON DEGRADATION OF IMPURITY PROFILE FOR THE ESTIMATION OF ACETAMINOPHEN IN ACIDIC AQUEOUS SOLUTION FOR PHARMACEUTICAL DOSAGE FORM BY HIGH PERFORMANCES LIQUID CHROMATOGRAPHY.

    OpenAIRE

    Dilip Kumar Bevara*; Nageswara Rao Anipindi

    2013-01-01

    A reaction-limited model for impurity profile is developed for the acetaminophen which consists of degradation impurity as 4- Amino phenol including ten other potential impurities. As many ways of the synthetic routes for acetaminophen it has been identified the impurities are of eleven. Out of which many degrading impurities, 4-Amino phenol is one of the major degradant. And remaining Organic Impurities that may appear in acetaminophen preparations are process-related impurities. Impurity ev...

  17. Steady-state organization of binary mixtures by active impurities

    DEFF Research Database (Denmark)

    Sabra, Mads Christian; Gilhøj, Henriette; Mouritsen, Ole G.

    1998-01-01

    The structural reorganization of a phase-separated binary mixture in the presence of an annealed dilution of active impurities is studied by computer-simulation techniques via a simple two-dimensional lattice-gas model. The impurities, each of which has two internal states with different affinity...... for the two species, become active by an external driving of a transition between the two impurity states, leading to an energy flow from the impurities into the binary mixture. In steady state, the drive is found to break down the phase-separated state and lead to a new finite length scale controlled...

  18. Numerical Simulation of mobile BEC-impurity interaction

    Science.gov (United States)

    Lausch, Tobias; Grusdt, Fabian; Fleischhauer, Michael; Widera, Artur

    2016-05-01

    Cooling atoms to temperatures, where quantum effects become dominant, has become a standard in cold atom experiments. Especially interactions of quantum baths such as fermi gases and the implementation of impurities, which form fermi polarons, have been studied theoretically and experimentally in detail. However, detailed experiments on the bose polaron and the interaction between impurities and a bose gas are still elusive. We consider a model, where we immerse a single impurity into a BEC, which is described by Bogoliubov approximation. From the master equation, we derived the impurity's momentum resolved scattering and cooling dynamics for numerical simulations. Such cooling processes should enable momentum resolved radio-frequency spectroscopy of the BEC polaron.

  19. Anomalous diffusion, clustering, and pinch of impurities in plasma edge turbulence

    DEFF Research Database (Denmark)

    Priego, M.; Garcia, O.E.; Naulin, V.; Juul Rasmussen, J.

    2005-01-01

    The turbulent transport of impurity particles in plasma edge turbulence is investigated. The impurities are modeled as a passive fluid advected by the electric and polarization drifts, while the ambient plasma turbulence is modeled using the two-dimensional Hasegawa-Wakatani paradigm for resistive......-diffusion analysis of the evolution of impurity puffs. Additional effects appear for inertial impurities as a consequence of compressibility. First, the density of inertial impurities is found to correlate with the vorticity of the electric drift velocity, that is, impurities cluster in vortices of a precise...

  20. Addendum to impurity radiation from medium density plasmas

    International Nuclear Information System (INIS)

    A previous treatment of impurity radiation due to plasma contaminants is extended to include low-Z materials of the type anticipated for first walls in tokamak reactor designs. In addition, analytic fits are presented for the temperature dependence of the key quantities that enter into the modeling of tokamak impurity phenomena

  1. The Higgs Branch of Impurity Theories

    CERN Document Server

    Kapustin, A A; Kapustin, Anton; Sethi, Savdeep

    1998-01-01

    We consider supersymmetric gauge theories with impurities in various dimensions. These systems arise in the study of intersecting branes. Unlike conventional gauge theories, the Higgs branch of an impurity theory can have compact directions. For models with eight supercharges, the Higgs branch is a hyperKahler manifold given by the moduli space of solutions of certain differential equations. These equations are the dimensional reductions of self-duality equations with boundary conditions determined by the impurities. They can also be interpreted as Nahm transforms of self-duality equations on toroidally compactified spaces. We discuss the application of our results to the light-cone formulation of Yang-Mills theories and to the solution of certain N=2 d=4 gauge theories.

  2. Impurity screening studies in the ALCATOR C-Mod tokamak

    International Nuclear Information System (INIS)

    Screening experiments have been undertaken in both limited and diverted discharges with a range of gaseous impurities in ohmic discharges. Measurements have been made as a function of plasma density and of the poloidal position of gas injection. It has been found that for recycling impurities such as neon and argon the number of impurities in the core plasma is proportional to the number injected. For non-recycling impurities (carbon and nitrogen) the number in the core is a function of the rate of injection. For discharges limited on the inner wall the screening is a function of the poloidal position of injection, with the injection at the inner wall giving the poorest screening. In diverted discharges with recycling impurities the position of injection does not significantly affect the screening. For non-recycling impurities the screening is typically a factor of 3 better when impurities are injected from the divertor rather than from the outside midplane. However, the best screening occurs when the impurities are injected at the inner midplane. Screening is typically a factor of 10 better for diverted than for limited discharges. Impurity transport has been modelled using the Monte Carlo code DIVIMP with a background plasma derived from experimental measurements of plasma parameters at the target and in the scrape-off layer (SOL). It is found that the code can reproduce the experimental measurements within a factor of 2. (author). 12 refs, 3 figs

  3. Novel Bound States in Graphene with Impurities

    CERN Document Server

    Gupta, Kumar S

    2008-01-01

    We obtain a novel bound state spectrum of the low energy excitations near the Fermi points of graphene in the presence of a charge impurity. The effects of possible short range interactions induced by the impurity are modelled by suitable boundary conditions. The spectrum in the subcritical region of the effective Coulomb coupling is labelled by a parameter which characterizes the boundary conditions and determines the inequivalent quantizations of the system. In the supercritical region we obtain a renormalization group flow for the effective Coulomb coupling.

  4. Conductance fluctuations in a macroscopic 3-dimensional Anderson insulator

    International Nuclear Information System (INIS)

    We report magnetoconductance experiment on a amorphous Yx-Si1-x alloy (∼0.3). which is an Anderson insulator where spin-orbit scattering is strong. Two principal and new features emerge from the data: the first one is an halving of the localization length by the application of a magnetic field of about 2.5 Teslas. This effect is predicted by a new approach of transport in Anderson insulators where basic symetry considerations are the most important ingredient. The second one is the observation of reproducible conductance fluctuations at very low temperature in this macroscopic 3 D amorphous material

  5. Multiple-beam Propagation in an Anderson Localized Optical Fiber

    CERN Document Server

    Karbasi, Salman; Mafi, Arash

    2012-01-01

    We investigate the simultaneous propagation of multiple beams in a disordered Anderson localized optical fiber. The profiles of each beam fall off exponentially, enabling multiple channels at high-density. We examine the influence of fiber bends on the movement of the beam positions, which we refer to as drift. We investigate the extent of the drift of localized beams induced by macro-bending and show that it is possible to design Anderson localized optical fibers which can be used for practical beam-multiplexing applications.

  6. Absence of Anderson localization in certain random lattices

    OpenAIRE

    Choi, Wonjun; Yin, Cheng; Hooper, Ian R.; Bernes, William L.; Bertolotti, Jacopo

    2016-01-01

    We report on the transition between an Anderson localized regime and a conductive regime in a 1D scattering system with correlated disorder. We show experimentally that when long-range correlations, in the form of a power-law spectral density with power larger than 2, are introduced the localization length becomes much bigger than the sample size and the transmission peaks typical of an Anderson localized system merge into a pass band. As other forms of long-range correlations are known to ha...

  7. Controlling Anderson localization in disordered photonic crystal waveguides

    DEFF Research Database (Denmark)

    Garcia-Fernández, David; Smolka, Stephan; Stobbe, Søren; Lodahl, Peter

    Quantum optics and quantum information technologies require enhancement of light-matter interaction by, for example, confining light in a small volume. A very recently demonstrated route towards light confinement makes use of multiple scattering of light and wave interference in disordered photonic...... structures [1,2]. Originally proposed for electrons by P. W. Anderson [3], only completely random systems without any long-range correlation between the scattering sites have been used so far, meaning that the Anderson-localized modes cannot be controlled. In disordered photonic crystals, these modes are...

  8. Quasiparticle interference from magnetic impurities

    Science.gov (United States)

    Derry, Philip G.; Mitchell, Andrew K.; Logan, David E.

    2015-07-01

    Fourier transform scanning tunneling spectroscopy (FT-STS) measures the scattering of conduction electrons from impurities and defects, giving information about the electronic structure of both the host material and adsorbed impurities. We interpret such FT-STS measurements in terms of the quasiparticle interference (QPI), here investigating in detail the QPI due to single magnetic impurities adsorbed on a range of representative nonmagnetic host surfaces, and contrasting with the case of a simple scalar impurity or point defect. We demonstrate how the electronic correlations present for magnetic impurities markedly affect the QPI, showing, e.g., a large intensity enhancement due to the Kondo effect, and universality at low temperatures/scanning energies. The commonly used joint density of states interpretation of FT-STS measurements is also considered, and shown to be insufficient in many cases, including that of magnetic impurities.

  9. Modelling of wall and SOL processes and contamination of ITER plasma after impurity injection with the tokamak code TOKES

    International Nuclear Information System (INIS)

    In the future tokamak ITER the damage to the wall after the disruptions can be mitigated using preventive massive gas injection (MGI) of noble gases into confined plasma during the thermal quench. The gas gets ionized in the plasma, and then the ions dump into the scrape-off layer (SOL) and impact on the target. The contamination of core plasma results in fast loss of plasma energy by radiation. The radiation distributes rather homogeneously over the wall. However, enhanced radiation load in e.g. vicinity of gas jet entry is an issue for ITER design that can be addressed numerically. For the modelling the tokamak code TOKES is applied, after upgrading it with toroidally symmetric 2D plasma model. This allowed detailed radiation fluxes and the expansion of noble ions both across and along the magnetic surfaces. In the work one- and two-dimensional (2D) MGI models are evaluated. 2D model is preliminary compared with the tokamak DIII-D. Substantial discrepancies were explained, and then predictive simulations for ITER performed, with the conclusion that after the radiation flush in front of jet entry the wall temperature can exceed the beryllium melting point.

  10. Phase transitions and steady-state microstructures in a two-temperature lattice-gas model with mobile active impurities

    DEFF Research Database (Denmark)

    Henriksen, Jonas Rosager; Sabra, Mads Christian; Mouritsen, Ole G.

    2000-01-01

    . The properties of the model are calculated by Monte Carlo computer-simulation techniques. The two temperatures and the external drive on the system lead to a rich phase diagram including regions of microstructured phases in addition to macroscopically ordered (phase-separated) and disordered phases...

  11. Radiation effects on impurity diffusion in silicon

    International Nuclear Information System (INIS)

    Coherently combined experiments have been made in order to investigate certain parameters of the problem of diffusion under hydrogen irradiation. The physical basis of the problem (diffusion in semiconductors, particle irradiation, defect creation) is reviewed and the characterisation methods are then presented whilst laying emphasis on the way they restrict those experiments that are possible. The role of the parameters which are made to vary (temperature, current of the irradiation beam, irradiation time) is shown, using boron, arsenic or phosphorus as doping agent. The limitations of the single two-impurity model (one slow, one fast) is shown. It is also shown that with this model it is not possible to account integrally for the profiles obtained by ionic analysis. To complete the model, it was necessary to introduce defect precipitation as well as its effect on the diffusion length of the impurities. It was also possible to show the fundamental importance of the irradiation current parameter (and not of the total dose) and its interconnexion with the irradiation temperature parameter. With electric measurements an endeavour was also made to show the effect of residual defects on the conductivity and mobility of irradiated layers. The balancing of these layers led to studying the annealing of the defects and the experiments enabled the radiation enhanced to be oberved. The effect of the Fermi level position on the exo-diffusion of fast impurities was also shown, interpreted in terms of the formation and fast diffusion of a vacancy-impurity complex

  12. Anderson-Witting transport coefficients for flows in general relativity

    CERN Document Server

    Ambrus, Victor E

    2016-01-01

    The transport coefficients induced by the Anderson-Witting approximation of the collision term in the relativistic Boltzmann equation are derived for close to equilibrium flows in general relativity. Using the tetrad formalism, it is shown that the expression for these coefficients is the same as that obtained on flat space-time, in agreement with the generalized equivalence principle.

  13. Probing the statistical properties of Anderson localization with quantum emitters

    DEFF Research Database (Denmark)

    Smolka, Stephan; Nielsen, Henri Thyrrestrup; Sapienza, Luca;

    2011-01-01

    embedded in disordered photonic crystal waveguides as light sources. Anderson-localized modes are efficiently excited and the analysis of the photoluminescence spectra allows us to explore their statistical properties, for example the localization length and average loss length. With increasing the amount...

  14. Cavity quantum electrodynamics with Anderson-localized modes

    DEFF Research Database (Denmark)

    Sapienza, Luca; Nielsen, Henri Thyrrestrup; Stobbe, Søren;

    2010-01-01

    factor of 15 on resonance with the Anderson-localized mode, and 94% of the emitted single photons coupled to the mode. Disordered photonic media thus provide an efficient platform for quantum electrodynamics, offering an approach to inherently disorder-robust quantum information devices....

  15. Comparisons of physical and chemical sputtering in high density divertor plasmas with the Monte Carlo Impurity (MCI) transport model

    International Nuclear Information System (INIS)

    The MCI transport model was used to compare chemical and physical sputtering for a DIII-D divertor plasma near detachment. With physical sputtering alone the integrated carbon influx was 8.4 x 1019 neutral/s while physical plus chemical sputtering produced an integrated carbon influx of 1.7 x 1021 neutrals/s. The average carbon concentration in the computational volume increased from 0.012% with only physical sputtering to 0.182% with both chemical and physical sputtering. This increase in the carbon inventory produced more radiated power which is in better agreement with experimental measurements

  16. Interaction between dislocation and divalent impurity in KBr single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Ohgaku, T; Matsunaga, T, E-mail: ohgaku@kenroku.kanazawa-u.ac.jp [Graduate school of Natural Science and Technology, Kanazawa University, Kakumamachi, Kanazawa 920-1192 (Japan)

    2009-07-15

    Interaction between dislocation and divalent impurity has been investigated in KBr single crystals doped with various impurities by strain rate cycling tests under ultrasonic oscillation. The interaction energy between dislocation and impurity-vacancy dipole (I-V dipole) has been obtained by fitting Barnett model to experimental results. The interaction energies between dislocation and I-V dipole were determined to be 0.51, 0.30, 0.23 and 0.36eV for Ba{sup 2+}, Sr{sup 2+}, Ca{sup 2+} and Mg{sup 2+}, respectively. The energy increases with increasing ionic radius of divalent impurity except Mg{sup 2+}. This may be because the I-V dipole is made of a divalent impurity and a nearest vacancy for Ba{sup 2+}, Sr{sup 2+} and Ca{sup 2+} but of a divalent one and a next nearest vacancy for Mg{sup 2+}.

  17. Lattice dynamics of impurity clusters : application to pairs

    International Nuclear Information System (INIS)

    A general solution is obtained for the lattice dynamics of a cluster of n-impurity atoms using the double-time Green's function formalism. The cluster is characterized by n-mass defect and m-force constant change parameters. It is shown that this general solution for the Green's function for the n-impurity cluster can also be expressed in terms of the Green's function for the (n-1)-impurity cluster. As an application, the cluster impurity modes for a pair are calculated using the Debye model for the host lattice dynamics. The splitting of the high frequency local modes and nearly zero frequency resonant modes due to pairs show an oscillatory behaviour on varying the distance of separation between the two impurity atoms. These oscillations are most prominent for two similar impurities and get damped for two dissimilar impurities or if one of the impurities produces a force constant change. The predictions of the calculation provide qualitative explanation of the data obtained from the infrared measurements of the resonant modes in mixed crystal system of KBrsub(1-c)Clsub(c):Lisup(+) and KBrsub(1-c)Isub(c):Lisup(+). (author)

  18. Microscopic theory of impurity pumping

    International Nuclear Information System (INIS)

    Neoclassical transport coefficients for ion and impurity species in the plateau to Pfirsch--Schlueter regime are calculated using sources of particles and heat as driving forces. In the Pfirsch--Schlueter regime, such sources can lead to a reversal of the usual inward flux of impurities

  19. Neo-classical impurity transport

    International Nuclear Information System (INIS)

    The neo-classical theory for impurity transport in a toroidal plasma is outlined, and the results discussed. A general account is given of the impurity behaviour and its dependence on collisionality. The underlying physics is described with special attention to the role of the poloidal rotation

  20. Drug impurities: problems and regulations.

    Science.gov (United States)

    Pifferi, G; Mannucci, A

    1999-11-01

    The matter of impurities is a frequently debated issue, mainly focused on the validation of the analytical methods and on the toxicology of potential impurities. In the first part of the review, the classification, the source and the chemical aspects of impurities are briefly considered according to the current international regulations. A special attention is given to the analytical control, in both qualitative and quantitative terms, of unexpected impurities arising from changes in the manufacturing process or by degradation. The thresholds for identification and qualification of impurities in new drug substances and in new drug products are examined together with the safety studies, when required. Finally, the acceptance limits for four classes of residual solvents are also reported. PMID:10765465

  1. Critical exponent for the Anderson transition in the three-dimensional orthogonal universality class

    International Nuclear Information System (INIS)

    We report a careful finite size scaling study of the metal–insulator transition in Anderson's model of localization. We focus on the estimation of the critical exponent ν that describes the divergence of the localization length. We verify the universality of this critical exponent for three different distributions of the random potential: box, normal and Cauchy. Our results for the critical exponent are consistent with the measured values obtained in experiments on the dynamical localization transition in the quantum kicked rotor realized in a cold atomic gas. (paper)

  2. Divertor and gas blanket impurity control study

    International Nuclear Information System (INIS)

    A simple calculational model for the transport of particles across the scrap off region between the plasma and the wall in the presence of a divertor or a gas blanket has been developed. The model departs from previous work in including: (a) the entire impurity transport as well as its effect on the energy balance equations; (b) the recycling neutrals from the divertor, and (c) the reflected neutrals from the wall. Results obtained with this model show how the steady state impurity level in the plasma depends on the divertor parameters such as the neutral backflow from the divertor, the particle residence time and the scrape off thickness; and on the gas blanket parameters such as the neutral source strength and the gas blanket thickness. The variation of the divertor or gas blanket performance as a function of the heat and particle fluxes escaping from the plasma, the wall material and the cross field diffusion is examined and numerical examples are given

  3. : Community of Inquiry en E-learning : à propos du modèle de Garrison et d'Anderson

    OpenAIRE

    Jézégou, Annie

    2010-01-01

    This article is based on a constructively critical analysis of the model of community of inquiry developed by Garrison and Anderson (2003) as part of a research conducted in the area of e-learning. The authors claim that certain collaborative interactions create "distant presence" fostering the emergence of a community of inquiry which has a positive influence on individual and collective learning. More specifically, the article points out that until now, the model's theoretical foundations h...

  4. Community of Inquiry en E-learning : à propos du modèle de Garrison et d'Anderson

    OpenAIRE

    Jézégou, Annie

    2010-01-01

    This article is based on a constructively critical analysis of the model of Community of Inquiry developed by Garrison and Anderson (2003) as part of research conducted in the area of e-learning. The authors claim that certain collaborative interactions create “distant presence” fostering the emergence of a community of inquiry which has a positive influence on individual and collective learning. More specifically, the article points out that until now the model's theoretical foundations had ...

  5. Elastoresistivity of impurities in copper

    International Nuclear Information System (INIS)

    Among the numerous techniques used to observe impurities or defects in metals, elasto-resistivity has been relatively little used. Uniaxial elasto-resistivity due to substitutional impurities in copper, measured at 4.2 K, decreases when the impurity content increases. It is then possible to define a specific uniaxial elasto-resistivity of a given impurity in copper. Measurements have been extended to different temperatures, different rates of cold work (i.e. different dislocation concentrations) and different doses of irradiation (neutron irradiations at 20 K). The elasto-resistivity of pure copper at 4.2 K does not depend on the cold work performed at 300 K. A rule similar to Matthiessen's rule has been established when two types of defects are present. A correlation between our experiments of uniaxial elasto-resistivity and KONCZYKOWSKI'S measurements of hydrostatic piezoresistivity allows us to give a simple phenomenological description of the behavior of the impurities in the stress: the impurities get longer along the same direction as the elastic matrix. A simple evaluation shows that the elasto-resistivity and the thermo-electric power of an impurity are related

  6. Absence of Anderson localization in certain random lattices

    CERN Document Server

    Choi, Wonjun; Hooper, Ian R; Bernes, William L; Bertolotti, Jacopo

    2016-01-01

    We report on the transition between an Anderson localized regime and a conductive regime in a 1D scattering system with correlated disorder. We show experimentally that when long-range correlations, in the form of a power-law spectral density with power larger than 2, are introduced the localization length becomes much bigger than the sample size and the transmission peaks typical of an Anderson localized system merge into a pass band. As other forms of long-range correlations are known to have the opposite effect, i.e. to enhance localization, our results show that care is needed when discussing the effects of correlations, as different kinds of long-range correlations can give rise to very different behavior.

  7. Photon transport enhanced by transverse Anderson localization in disordered superlattices

    CERN Document Server

    Hsieh, Pin-Chun; McMillan, James; Tsai, Min-An; Lu, Ming; Panoiu, Nicolae; Wong, Chee Wei

    2014-01-01

    One of the daunting challenges in optical physics is to accurately control the flow of light at the subwavelength scale, by patterning the optical medium one can design anisotropic media. The light transport can also be significantly affected by Anderson localization, namely the wave localization in a disordered medium, a ubiquitous phenomenon in wave physics. Here we report the photon transport and collimation enhanced by transverse Anderson localization in chip-scale dispersion engineered anisotropic media. We demonstrate a new type of anisotropic photonic structure in which diffraction is nearly completely arrested by cascaded resonant tunneling through transverse guided resonances. By perturbing the shape of more than 4,000 scatterers in these superlattices we add structural disordered in a controlled manner and uncover the mechanism of disorder-induced transverse localization at the chip-scale. Arrested spatial divergence is captured in the power-law scaling, along with exponential asymmetric mode profil...

  8. Impurity screening in Tore Supra

    International Nuclear Information System (INIS)

    Ergodic divertor (ED) experiments in helium plasmas with carbonized and boronized wall conditions have been performed in Tore Supra. The intrinsic impurity decontamination effect (as well as the screening of purposely injected nitrogen impurities), previously observed in deuterium plasmas, has been confirmed also for conditions where the electron density in the confined (unperturbed) bulk plasma remains practically constant. Inward displacements of the plasma 0.10-0.15 m away from the ED modules result in the magnetic perturbation having little or no effect on impurities. (orig.)

  9. Mobile impurities in ferromagnetic liquids

    Science.gov (United States)

    Kantian, Adrian; Schollwoeck, Ulrich; Giamarchi, Thierry

    2011-03-01

    Recent work has shown that mobile impurities in one dimensional interacting systems may exhibit behaviour that differs strongly from that predicted by standard Tomonaga-Luttinger liquid theory, with the appearance of power-law divergences in the spectral function signifying sublinear diffusion of the impurity. Using time-dependent matrix product states, we investigate a range of cases of mobile impurities in systems beyond the analytically accessible examples to assess the existence of a new universality class of low-energy physics in one-dimensional systems. Correspondence: Adrian.Kantian@unige.ch This work was supported in part by the Swiss SNF under MaNEP and division II.

  10. Critical parameters from generalised multifractal analysis at the Anderson transition

    OpenAIRE

    Rodriguez, Alberto; Vasquez, Louella J.; Slevin, Keith; Römer, Rudolf A.

    2010-01-01

    We propose a generalization of multifractal analysis that is applicable to the critical regime of the Anderson localization-delocalization transition. The approach reveals that the behavior of the probability distribution of wavefunction amplitudes is sufficient to characterize the transition. In combination with finite-size scaling, this formalism permits the critical parameters to be estimated without the need for conductance or other transport measurements. Applying this method to high-pre...

  11. Quasiperiodic driving of Anderson localized waves in one dimension

    OpenAIRE

    Hatami, H.; Danieli, C.; Bodyfelt, J. D.; Flach, S

    2016-01-01

    We consider a quantum particle in a one-dimensional disordered lattice with Anderson localization, in the presence of multi-frequency perturbations of the onsite energies. Using the Floquet representation, we transform the eigenvalue problem into a Wannier-Stark basis. Each frequency component contributes either to a single channel or a multi-channel connectivity along the lattice, depending on the control parameters. The single channel regime is essentially equivalent to the undriven case. T...

  12. Many-body Anderson localization in one-dimensional systems

    Science.gov (United States)

    Delande, Dominique; Sacha, Krzysztof; Płodzień, Marcin; Avazbaev, Sanat K.; Zakrzewski, Jakub

    2013-04-01

    We show, using quasi-exact numerical simulations, that Anderson localization in a disordered one-dimensional potential survives in the presence of attractive interaction between particles. The localization length of the particles' center of mass—computed analytically for weak disorder—is in good agreement with the quasi-exact numerical observations using the time evolving block decimation algorithm. Our approach allows for simulation of the entire experiment including the final measurement of all atom positions.

  13. Experimental determination of critical exponents in Anderson localisation of light

    OpenAIRE

    Aegerter, Christof M.; Störzer, Martin; Maret, Georg

    2006-01-01

    Anderson localisation predicts a phase transition in transport, where the diffuse spread of particles comes to a halt with the introduction of a critical amount of disorder. This is due to constructive interference on closed multiple scattering loops which leads to a renormalisation of the diffusion coefficient. This can be described by a slowing-down of diffusion, where the diffusion coefficient decreases with time according to a power law with an exponent a. In the case of strong localisati...

  14. Non-random perturbations of the Anderson Hamiltonian

    CERN Document Server

    Molchanov, S

    2010-01-01

    The Anderson Hamiltonian $H_0=-\\Delta+V(x,\\omega)$ is considered, where $V$ is a random potential of Bernoulli type. The operator $H_0$ is perturbed by a non-random, continuous potential $-w(x) \\leq 0$, decaying at infinity. It will be shown that the borderline between finitely, and infinitely many negative eigenvalues of the perturbed operator, is achieved with a decay of $O(\\ln^{-2/d} |x|)$.

  15. Magnetic field nanosensor based on Mn impurities

    Directory of Open Access Journals (Sweden)

    Daniela ENCIU

    2014-06-01

    Full Text Available Nanosensors based on graphene nanoribbon, studied in the present work, could provide a special interest in (aero space applications. More specifically, the paper proposes the construction of a nanosensor based on Mn (Manganese impurities. Different spin configurations of the Mn atoms are considered. The mathematical model used to determine the spin transport is based on Kohn-Sham equations. The spin-dependent transmission functions are calculated using the formalism of the nonequilibrium Green’s functions. The implementation of the mathematical model is performed in the SIESTA package. The spin transport properties are determined using the first principle calculations using density functional theory. The graphene nanoribbon with transition metal impurities is based on active element – the system of spins – which is influenced by the external perturbation field. Such nanostructures may serve as spatial applications. The differences between different excited states are determined and it is established that the energy range overlaps the mid-infrared wavelengths.

  16. Analysis of Anderson Acceleration on a Simplified Neutronics/Thermal Hydraulics System

    Energy Technology Data Exchange (ETDEWEB)

    Toth, Alex [North Carolina State University (NCSU), Raleigh; Kelley, C. T. [North Carolina State University (NCSU), Raleigh; Slattery, Stuart R [ORNL; Hamilton, Steven P [ORNL; Clarno, Kevin T [ORNL; Pawlowski, R. P. P. [Sandia National Laboratories (SNL)

    2015-01-01

    ABSTRACT A standard method for solving coupled multiphysics problems in light water reactors is Picard iteration, which sequentially alternates between solving single physics applications. This solution approach is appealing due to simplicity of implementation and the ability to leverage existing software packages to accurately solve single physics applications. However, there are several drawbacks in the convergence behavior of this method; namely slow convergence and the necessity of heuristically chosen damping factors to achieve convergence in many cases. Anderson acceleration is a method that has been seen to be more robust and fast converging than Picard iteration for many problems, without significantly higher cost per iteration or complexity of implementation, though its effectiveness in the context of multiphysics coupling is not well explored. In this work, we develop a one-dimensional model simulating the coupling between the neutron distribution and fuel and coolant properties in a single fuel pin. We show that this model generally captures the convergence issues noted in Picard iterations which couple high-fidelity physics codes. We then use this model to gauge potential improvements with regard to rate of convergence and robustness from utilizing Anderson acceleration as an alternative to Picard iteration.

  17. Impurity states in two and three dimensional disordered system S

    International Nuclear Information System (INIS)

    We investigate the microscopic structure of the impurity states in two-and three-dimensional (2D and 3D) disordered system. A cluster model is outlined for the donor impurity density of states (DIDS) of doped semiconductors. It is shown that the impurity states are very sensitive to a change in the dimensionality of the system, i.e., from 3D to 2D system. It is found that all eigenstates become localized in 2D disordered system for a large range of concentration. (author)

  18. Impurity states in two - and three-dimensional disordered systems

    International Nuclear Information System (INIS)

    We investigate the microscopic structure of the impurity states in two-and three-dimensional (2D and 3d) disordered systems. A cluster model is outlined for the donor impurity density of states (DIDS) of doped semiconductors. It is shown that the impurity states are very sensitive to a change in the dimensionality of the system, i.e from 3D to 2D system. It is found that all eigenstates become localized in 2D disordered system for a large range of concentration. (Author)

  19. On impurity segregation on dislocations in metals

    OpenAIRE

    Netchaev, Yu.; Mukhina, L.

    1993-01-01

    Thermodynamic and crystallo-chemistry considerations are given about the possibility of existing linear distribution laws for some impurities in metals between bulk solution and near-dislocation segregation regions (NDSR) with composition and structure close to the corresponding intermetallic compound. The solutions of Fe in Al are considered. NDSR composition can be close to FeAl3. The experimental data on the solubilities are treated within the model developed to determine the effective bin...

  20. Impurity Influence on Nitride LEDs

    Directory of Open Access Journals (Sweden)

    O.I. Rabinovich

    2014-07-01

    Full Text Available Light emitting diodes (LEDs are widely used nowadays. They are used in major parts of our life. But it is still necessary to improve their characteristics. In this paper the impurity and Indium atoms influence on the LEDs characteristics is investigated by computer simulation. Simulation was carried out in Sim Windows. The program was improved for this purpose by creating new files for AlGaInN heterostructure and devices including more than 25 basic parameters. It was found that characteristics depend on impurity and indium atoms changes a lot. The optimum impurity concentration for doping barriers between quantum wells was achieved. By varying impurity and Indium concentration the distribution in AlGaInN heterostructure LEDs characteristics could be improved.

  1. Impurities confined in quantum structures

    CERN Document Server

    Holtz, Per Olof

    2004-01-01

    The introduction of impurities, even in very small concentrations, in a semiconductor can change its optical and electrical properties entirely. This attribute of the semiconductor is utilized in the manifoldness of their applications. In this book, the progress on elucidating the physical properties of impurities confined in quantum structures are reviewed with an emphasis on the experimental aspects. The major results of various kinds of characterization, such as infrared spectroscopy, Raman measurements, luminescence characterization, perturbation spectroscopy and dynamical studies of the confined impurities are reviewed, but also the theoretical basis to calculate the electronic structure of the confined donors and acceptors are presented. This monograph also describes more specific aspects of the confined impurities such as the properties in the high doping regime and the effects of hydrogen passivation.

  2. The impact of neutral impurity concentration on charge drift mobility in germanium

    CERN Document Server

    Mei, H; Wang, G -J; Yang, G

    2016-01-01

    We report a new result of the neutral impurity scattering of electrons and holes that has impact on the charge drift mobility in high purity germanium crystals at 77 Kelvin. The charge carrier concentration, mobility and resistivity are measured by Hall Effect system at 77 Kelvin. We investigated the contribution to the total charge drift mobility from ionized impurity scattering, lattice scattering, and neutral impurity scattering with the best theoretical models and experimental data. Several samples with measured Hall mobility from the grown crystals are used for this investigation. With the measured Hall mobility and ionized impurity concentration as well as the theoretical models, we calculated the neutral impurity concentration by the Matthiessen's rule. As a result, the distributions of the neutral impurity concentrations with respect to the radius of the crystals are obtained. Consequently, we demonstrate that neutral impurity scattering is a significant contribution to the charge drift mobility, whic...

  3. Efficient implementation of the continuous-time hybridization expansion quantum impurity solver

    Science.gov (United States)

    Hafermann, Hartmut; Werner, Philipp; Gull, Emanuel

    2013-04-01

    Strongly correlated quantum impurity problems appear in a wide variety of contexts ranging from nanoscience and surface physics to material science and the theory of strongly correlated lattice models, where they appear as auxiliary systems within dynamical mean-field theory. Accurate and unbiased solutions must usually be obtained numerically, and continuous-time quantum Monte Carlo algorithms, a family of algorithms based on the stochastic sampling of partition function expansions, perform well for such systems. With the present paper we provide an efficient and generic implementation of the hybridization expansion quantum impurity solver, based on the segment representation. We provide a complete implementation featuring most of the recently developed extensions and optimizations. Our implementation allows one to treat retarded interactions and provides generalized measurement routines based on improved estimators for the self-energy and for vertex functions. The solver is embedded in the ALPS-DMFT application package. Catalogue identifier: AEOL_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEOL_v1_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: Use of the hybridization expansion impurity solvers requires citation of this paper. Use of any ALPS program requires citation of the ALPS [1] paper. No. of lines in distributed program, including test data, etc.: 650044 No. of bytes in distributed program, including test data, etc.: 20553265 Distribution format: tar.gz Programming language: C++/Python. Computer: Desktop PC, high-performance computers. Operating system: Unix, Linux, OSX, Windows. Has the code been vectorized or parallelized?: Yes, MPI parallelized. RAM: 1 GB Classification: 7.3. External routines: ALPS [1, 2, 3], BLAS [4, 5], LAPACK [6], HDF5 [7] Nature of problem: Quantum impurity models were originally introduced to describe a magnetic transition metal ion in a non

  4. Modeling the geochemical impact of an injection of CO2 and associated reactive impurities (SO2 and O2) into a saline reservoir

    OpenAIRE

    Andre, Laurent; Azaroual, Mohamed; Bernstone, Christian; Wittek, Andrea

    2015-01-01

    Carbon dioxide storage in deep geological structures is a strategic technology to mitigate climate change and to promote green development. However, despite continuous efforts to develop cost effective capture processes to clean the CO2 stream before transportation and injection, traces of accessory gases cannot be entirely removed. Consequently, before any injection of these gas mixtures, the impact of impurities on the geochemical reactivity of the system must be evaluated. This paper descr...

  5. Triaxially deformed relativistic point-coupling model for $\\Lambda$ hypernuclei: a quantitative analysis of hyperon impurity effect on nuclear collective properties

    CERN Document Server

    Xue, W X; Hagino, K; Li, Z P; Mei, H; Tanimura, Y

    2014-01-01

    The impurity effect of hyperon on atomic nuclei has received a renewed interest in nuclear physics since the first experimental observation of appreciable reduction of $E2$ transition strength in low-lying states of hypernucleus $^{7}_\\Lambda$Li. Many more data on low-lying states of $\\Lambda$ hypernuclei will be measured soon for $sd$-shell nuclei, providing good opportunities to study the $\\Lambda$ impurity effect on nuclear low-energy excitations. We carry out a quantitative analysis of $\\Lambda$ hyperon impurity effect on the low-lying states of $sd$-shell nuclei at the beyond-mean-field level based on a relativistic point-coupling energy density functional (EDF), considering that the $\\Lambda$ hyperon is injected into the lowest positive-parity ($\\Lambda_s$) and negative-parity ($\\Lambda_p$) states. We adopt a triaxially deformed relativistic mean-field (RMF) approach for hypernuclei and calculate the $\\Lambda$ binding energies of hypernuclei as well as the potential energy surfaces (PESs) in $(\\beta, \\g...

  6. Parallel impurity dynamics in the TJ-II stellarator

    Science.gov (United States)

    Alonso, J. A.; Velasco, J. L.; Calvo, I.; Estrada, T.; Fontdecaba, J. M.; García-Regaña, J. M.; Geiger, J.; Landreman, M.; McCarthy, K. J.; Medina, F.; Van Milligen, B. Ph; Ochando, M. A.; Parra, F. I.; the TJ-II Team; the W7-X Team

    2016-07-01

    We review in a tutorial fashion some of the causes of impurity density variations along field lines and radial impurity transport in the moment approach framework. An explicit and compact form of the parallel inertia force valid for arbitrary toroidal geometry and magnetic coordinates is derived and shown to be non-negligible for typical TJ-II plasma conditions. In the second part of the article, we apply the fluid model including main ion-impurity friction and inertia to observations of asymmetric emissivity patterns in neutral beam heated plasmas of the TJ-II stellarator. The model is able to explain qualitatively several features of the radiation asymmetry, both in stationary and transient conditions, based on the calculated in-surface variations of the impurity density.

  7. Parallel impurity dynamics in the TJ-II stellarator

    CERN Document Server

    Alonso, J A; Estrada, T; Fontdecaba, J M; García-Regaña, J M; Geiger, J; Landreman, M; McCarthy, K J; Medina, F; Van Milligen, B Ph; Ochando, M A; Parra, F I; Velasco, J L

    2016-01-01

    We review in a tutorial fashion some of the causes of impurity density variations along field lines and radial impurity transport in the moment approach framework. An explicit and compact form of the parallel inertia force valid for arbitrary toroidal geometry and magnetic coordinates is derived and shown to be non-negligible for typical TJ-II plasma conditions. In the second part of the article, we apply the fluid model including main ion-impurity friction and inertia to observations of asymmetric emissivity patterns in neutral beam heated plasmas of the TJ-II stellarator. The model is able to explain qualitatively several features of the radiation asymmetry, both in stationary and transient conditions, based on the calculated in-surface variations of the impurity density.

  8. Nailing the Coffin Shut on Doubts that Violent Video Games Stimulate Aggression ∼Comment on Anderson et al. (2010).

    OpenAIRE

    Huesmann, L. Rowell

    2010-01-01

    Over the past half-century the mass media, including video games, have become important socializers of children. Observational learning theory has evolved into social-cognitive information processing models that explain that what a child observes in any venue has both short-term and long-term influences on the child's behaviors and cognitions. Anderson's (2010) extensive meta-analysis of the effects of violent video games confirms what these theories predict and what prior research about othe...

  9. Two independent pivotal statistics that test location and misspecification and add-up to the Anderson-Rubin statistic

    OpenAIRE

    Kleibergen, F.R.

    2002-01-01

    We extend the novel pivotal statistics for testing the parameters in the instrumental variables regression model. We show that these statistics result from a decomposition of the Anderson-Rubin statistic into two independent pivotal statistics. The first statistic is a score statistic that tests location and the second statistic tests misspecification. We obtain the conditional distribution of the likelihood ratio statistic that tests location in case of multiple parameters of interest. This ...

  10. Effects of Impurities in CO2 Spreading Model Development for Field Experiments in the Framework of the CO2QUEST Project

    Science.gov (United States)

    Rebscher, D.; Wolf, J. L.; Jung, B.; Bensabat, J.; Segev, R.; Niemi, A. P.

    2014-12-01

    The aim of the CO2QUEST project (Impact of the Quality of CO2 on Storage and Transport) is to investigate the effect of typical impurities in the CO2 stream captured from fossil fuel power plants on its safe and economic transportation and deep geologic storage. An important part of this EU funded project is to enhance the understanding of typical impurity effects in a CO2 stream regarding the performance of the storage. Based on the experimental site Heletz in Israel, where injection tests of water as well as of super-critical pure and impure CO2 will be conducted, numerical simulations are performed. These studies illustrate flow and transport of CO2 and brine as well as impurities induced chemical reactions in relation to changes in the reservoir, e.g. porosity, permeability, pH-value, and mineral composition. Using different THC codes (TOUGH2-ECO2N, TOUGHREACT, PFLOTRAN), the spatial distribution of CO2 and impurities, both in the supercritical and aqueous phases, are calculated. The equation of state (EOS) of above numerical codes are properly modified to deal with binary/tertiary gas mixtures (e.g. CO2-N2 or CO2-SO2). In addition, simulations for a push-pull test of about 10 days duration are performed, which will be validated against experimental field data. Preliminary results are as follows: (a) As expected, the injection of SO2 leads to a strong decrease in pH-value, hence, the total dissolution of carbonate minerals could be observed. (b) Due to the acidic attack on clay minerals , which is enhanced compared to a pure CO2 dissolution, a higher amount of metal ions are released, in particular Fe2+ and Mg2+ by a factor of 25 and 10, respectively. Whereas secondary precipitation occurs only for sulphur minerals, namely anhydrite and pyrite. (c) The co-injection of CO2 with N2 changes physical properties of the gas mixture. Increasing N2 contents induces density decrease of the gas mixture, resulting in faster and wider plume migration compared to the pure

  11. An impurity seeded radiative mantle for ITER

    International Nuclear Information System (INIS)

    Self-consistent, coupled transport/MHD/scrape-off layer (SOL) divertor calculations indicate that a stable, radiating mantle can be maintained just inside the separatrix by iron impurity injection into the SOL in an ITER EDA model. The power flux to the divertor plate is reduced thereby by an order of magnitude or more. This reduction of the power exhausted to the divertor is predicted to be achieved without significant deleterious effect on the core power balance, without producing significant changes in the current profile that might trigger a disruptive collapse of the current channel and without inducing an H to L mode transition. These results suggest that an impurity seeded radiative mantle should be considered as part of the solution to the divertor heat load problem in ITER and other future tokamaks. (author). 34 refs, 10 figs, 1 tab

  12. Impurities of oxygen in silicon

    International Nuclear Information System (INIS)

    The electronic structure of oxygen complex defects in silicon, using molecular cluster model with saturation by watson sphere into the formalism of Xα multiple scattering method is studied. A systematic study of the simulation of perfect silicon crystal and an analysis of the increasing of atom number in the clusters are done to choose the suitable cluster for the calculations. The divacancy in three charge states (Si:V2+, Si:V20, Si:V2-), of the oxygen pair (Si:O2) and the oxygen-vacancy pair (Si:O.V) neighbours in the silicon lattice, is studied. Distortions for the symmetry were included in the Si:V2+ and Si:O2 systems. The behavior of defect levels related to the cluster size of Si:V20 and Si:O2 systems, the insulated oxygen impurity of silicon in interstitial position (Si:Oi), and the complexes involving four oxygen atoms are analysed. (M.C.K.)

  13. A study of the impurity-induced phase transition in Ba sub x Sr sub 1 sub - sub x TiO sub 3 within the framework of the transverse-field Ising model

    CERN Document Server

    Wu Hua

    2003-01-01

    The transverse-field Ising model is successfully applied to the Ba sub x Sr sub 1 sub - sub x TiO sub 3 system. An impurity-induced paraelectric-ferroelectric phase transition is found for proper parameters. An explanation is offered for the results of the susceptibility chi(x, T), the transition temperature T sub m (x), the spontaneous polarization (P ) versus x and versus T, the field dependence of chi(x, T) and that of the polarization (P ) versus E for x, 0.2 <= x <= 0.95.

  14. Simulating the symmetron: domain walls and symmetry-restoring impurities

    CERN Document Server

    Pearson, Jonathan A

    2014-01-01

    In this paper we study the dynamics of relativistic domain walls in the presence of static symmetry-restoring impurities. The field theory is precisely the same as what is known to cosmologists as the "symmetron model", whereby the usual $\\mathbb{Z}_2$ symmetry breaking potential is appended with a space-varying mass-term (the space-variation is set by the profile of the impurity, which we take to be a "tanh"-function). After presenting the outcomes of a suite of different numerical experiments we have three main results: (1) domain walls pin to impurities, (2) domain wall necklaces can be energetically preferred configurations, and (3) impurities significantly modifies the usual ${N}_{\\rm dw}\\propto t^{-1}$ scaling law for random networks of domain walls.

  15. Study of impurity behaviour in non-coronal equilibrium state

    Institute of Scientific and Technical Information of China (English)

    Cheng Fa-Yin; Shi Bing-Ren

    2007-01-01

    A physical model of analysing the behaviour of impurities out of coronal equilibrium in tokamak plasmas has been proposed. Through solving the time-dependent rate equations including the effects of atomic processes and the particle transport losses, the ionization state distribution is obtained for a range of low Z impurities such as helium, carbon,oxygen and argon. By using the ionization state distribution of these impurities, the radiation rate coefficients and the mean charge state changing with plasma temperature are calculated. The results show that the mean charge stateis sensitively dependent on the parameter neτ, and this is the reason why the radiation power of impurities under non-coronal equilibrium conditions is several orders of magnitude higher than that under coronal equilibrium condition.

  16. Trace impurities in single crystals of hexagonal lithium iodate

    International Nuclear Information System (INIS)

    The purpose of this work was to investigate the combined entry of trace impurities into a single crystal of lithium iodate grown from an aqueous solution with additions of the radioactive isotopes 59Fe, 57Co, 54Mn, and 65Zn. The study made it possible to reveal considerable nonuniformity in the distribution of trace impurities, whose content is the crystal decreases over a range of several orders of magnitude. The isomorphous character of the entry of all the cationic trace impurities investigated into lithium iodate crystals was established. The adequacy of the mathematical model describing the chemical nonuniformity of single crystals grown from solutions by the method of isothermal evaporation was demonstrated experimentally. The experimental values of the distribution constants (as defined by Derner and Hoskins) of trace impurities of iron, manganese, cobalt, and zinc (when they are present together in the mother solutions) were obtained

  17. Forward approximation as a mean-field approximation for the Anderson and many-body localization transitions

    Science.gov (United States)

    Pietracaprina, Francesca; Ros, Valentina; Scardicchio, Antonello

    2016-02-01

    In this paper we analyze the predictions of the forward approximation in some models which exhibit an Anderson (single-body) or many-body localized phase. This approximation, which consists of summing over the amplitudes of only the shortest paths in the locator expansion, is known to overestimate the critical value of the disorder which determines the onset of the localized phase. Nevertheless, the results provided by the approximation become more and more accurate as the local coordination (dimensionality) of the graph, defined by the hopping matrix, is made larger. In this sense, the forward approximation can be regarded as a mean-field theory for the Anderson transition in infinite dimensions. The sum can be efficiently computed using transfer matrix techniques, and the results are compared with the most precise exact diagonalization results available. For the Anderson problem, we find a critical value of the disorder which is 0.9 % off the most precise available numerical value already in 5 spatial dimensions, while for the many-body localized phase of the Heisenberg model with random fields the critical disorder hc=4.0 ±0.3 is strikingly close to the most recent results obtained by exact diagonalization. In both cases we obtain a critical exponent ν =1 . In the Anderson case, the latter does not show dependence on the dimensionality, as it is common within mean-field approximations. We discuss the relevance of the correlations between the shortest paths for both the single- and many-body problems, and comment on the connections of our results with the problem of directed polymers in random medium.

  18. Density of states controls Anderson localization in disordered photonic crystal waveguides

    DEFF Research Database (Denmark)

    Garcia-Fernández, David; Smolka, Stephan; Stobbe, Søren;

    2010-01-01

    We prove Anderson localization in a disordered photonic crystal waveguide by measuring the ensemble-averaged extinction mean-free path, ℓe, which is controlled by the dispersion in the photon density of states (DOS) of the photonic crystal waveguide. Except for the very low DOS case, where out...... demonstrates the close relation between Anderson localization and the DOS in disordered photonic crystals, which opens a promising route to controlling and exploiting Anderson-localized modes for efficient light confinement....

  19. Impurity bubbles in a BEC

    Science.gov (United States)

    Timmermans, Eddy; Blinova, Alina; Boshier, Malcolm

    2013-05-01

    Polarons (particles that interact with the self-consistent deformation of the host medium that contains them) self-localize when strongly coupled. Dilute Bose-Einstein condensates (BECs) doped with neutral distinguishable atoms (impurities) and armed with a Feshbach-tuned impurity-boson interaction provide a unique laboratory to study self-localized polarons. In nature, self-localized polarons come in two flavors that exhibit qualitatively different behavior: In lattice systems, the deformation is slight and the particle is accompanied by a cloud of collective excitations as in the case of the Landau-Pekar polarons of electrons in a dielectric lattice. In natural fluids and gases, the strongly coupled particle radically alters the medium, e.g. by expelling the host medium as in the case of the electron bubbles in superfluid helium. We show that BEC-impurities can self-localize in a bubble, as well as in a Landau-Pekar polaron state. The BEC-impurity system is fully characterized by only two dimensionless coupling constants. In the corresponding phase diagram the bubble and Landau-Pekar polaron limits correspond to large islands separated by a cross-over region. The same BEC-impurity species can be adiabatically Feshbach steered from the Landau-Pekar to the bubble regime. This work was funded by the Los Alamos LDRD program.

  20. Spectroscopic measurement of impurity transport coefficients and penetration efficiencies in Alcator C-Mod plasmas

    Science.gov (United States)

    Graf, M. A.; Rice, J. E.; Terry, J. L.; Marmar, E. S.; Goetz, J. A.; McCracken, G. M.; Bombarda, F.; May, M. J.

    1995-01-01

    Impurity transport coefficients and the penetration efficiencies of intrinsic and injected impurities through the separatrix of diverted Alcator C-Mod discharges have been measured using x-ray and vacuum ultraviolet (VUV) spectroscopic diagnostics. The dominant low Z intrinsic impurity in C-Mod is carbon which is found to be present in concentrations of less than 0.5%. Molybdenum, from the plasma facing components, is the dominant high Z impurity and is typically found in concentrations of about 0.02%. Trace amounts of medium and high Z nonrecycling impurities can be injected at the midplane using the laser blow-off technique and calibrated amounts of recycling, gaseous impurities can be introduced through fast valves either at the midplane or at various locations in the divertor chamber. A five chord crystal x-ray spectrometer array with high spectral resolution is used to provide spatial profiles of high charge state impurities. An absolutely calibrated, grazing incidence VUV spectrograph with high time resolution and a broad spectral range allows for the simultaneous measurement of many impurity lines. Various filtered soft x-ray diode arrays allow for spatial reconstructions of plasma emissivity. The observed brightnesses and emissivities from a number of impurity lines are used together with the mist transport code and a collisional-radiative atomic physics model to determine charge state density profiles and impurity transport coefficients. Comparisons of the deduced impurity content with the measured Zeff and total radiated power of the plasma are made.

  1. Impurity entanglement in the J–J2–δ quantum spin chain

    International Nuclear Information System (INIS)

    The contribution to the entanglement of an impurity attached to one end of a J–J2–δ quantum spin chain (S = 1/2) is studied. Two different measures of the impurity contribution to the entanglement have been proposed: the impurity entanglement entropy Simp and the negativity N. The first, Simp, is based on a subtractive procedure where the entanglement entropy in the absence of the impurity is subtracted from results with the impurity present. The other, N, is the negativity of a part of the system separated from the impurity and the impurity itself. In this paper we compare the two measures and discuss their similarities and the differences between them. In the J–J2–δ model it is possible to perform very precise variational calculations close to the Majumdar–Ghosh point (J2 = J/2 and δ = 0) where the system is gapped with a dimerized ground state. We describe in detail how such calculations are done and how they can be used to calculate N as well as Simp for any impurity coupling JK. We then study the complete crossover in the impurity entanglement as JK is varied between 0 and 1 close to the Majumdar–Ghosh point. In particular, we study the impurity entanglement when a staggered nearest neighbour interaction proportional to δ is introduced. In this case we observe a very rapid reduction in the impurity entanglement as δ is increased

  2. Phase growth in bistable systems with impurities.

    Science.gov (United States)

    Echeverria, C; Tucci, K; Cosenza, M G

    2008-01-01

    A system of coupled chaotic bistable maps on a lattice with randomly distributed impurities is investigated as a model for studying the phenomenon of phase growth in nonuniform media. The statistical properties of the system are characterized by means of the average size of spatial domains of equivalent spin variables that define the phases. It is found that the rate at which phase domains grow becomes smaller when impurities are present and that the average size of the resulting domains in the inhomogeneous state of the system decreases when the density of impurities is increased. The phase diagram showing regions where homogeneous, heterogeneous, and chessboard patterns occur on the space of parameters of the system is obtained. A critical boundary that separates the regime of slow growth of domains from the regime of fast growth in the heterogeneous region of the phase diagram is calculated. The transition between these two growth regimes is explained in terms of the stability properties of the local phase configurations. Our results show that the inclusion of spatial inhomogeneities can be used as a control mechanism for the size and growth velocity of phase domains forming in spatiotemporal systems. PMID:18351923

  3. Price-Anderson Nuclear Safety Enforcement Program. 1996 Annual report

    International Nuclear Information System (INIS)

    This first annual report on DOE's Price Anderson Amendments Act enforcement program covers the activities, accomplishments, and planning for calendar year 1996. It also includes the infrastructure development activities of 1995. It encompasses the activities of the headquarters' Office of Enforcement in the Office of Environment, Safety and Health (EH) and Investigation and the coordinators and technical advisors in DOE's Field and Program Offices and other EH Offices. This report includes an overview of the enforcement program; noncompliances, investigations, and enforcement actions; summary of significant enforcement actions; examples where enforcement action was deferred; and changes and improvements to the program

  4. Note: Work function change measurement via improved Anderson method

    International Nuclear Information System (INIS)

    We propose the modification to the Anderson method of work function change (Δϕ) measurements. In this technique, the kinetic energy of the probing electrons is already low enough for non-destructive investigation of delicate molecular systems. However, in our implementation, all electrodes including filament of the electron gun are polarized positively. As a consequence, electron bombardment of any elements of experimental system is eliminated. Our modification improves cleanliness of the ultra-high vacuum system. As an illustration of the solution capabilities, we present Δϕ of the Ag(100) surface induced by cobalt phthalocyanine layers

  5. Note: Work function change measurement via improved Anderson method

    Energy Technology Data Exchange (ETDEWEB)

    Sabik, A., E-mail: sabik@ifd.uni.wroc.pl; Gołek, F.; Antczak, G. [Institute of Experimental Physics, University of Wrocław, Wrocław (Poland)

    2015-05-15

    We propose the modification to the Anderson method of work function change (Δϕ) measurements. In this technique, the kinetic energy of the probing electrons is already low enough for non-destructive investigation of delicate molecular systems. However, in our implementation, all electrodes including filament of the electron gun are polarized positively. As a consequence, electron bombardment of any elements of experimental system is eliminated. Our modification improves cleanliness of the ultra-high vacuum system. As an illustration of the solution capabilities, we present Δϕ of the Ag(100) surface induced by cobalt phthalocyanine layers.

  6. Implementation of legislation amending the Price--Anderson Act

    International Nuclear Information System (INIS)

    Proposed amendments for the implementation of the Price-Anderson Act require both persons licensed to possess plutonium in the amount of 5 kilograms or more and persons licensed to process plutonium in the amount of 1 kilogram or more for use in plutonium processing and fuel fabrication plants to maintain financial protection in the amount of $125 million. Indemnity coverage would be extended to such licensee at $5,000 per year. The Commission does not intend to extend separate coverage under the Act to transportation of nuclear materials. A proposed date of implementation is August 1977

  7. Quasiperiodic driving of Anderson localized waves in one dimension

    Science.gov (United States)

    Hatami, H.; Danieli, C.; Bodyfelt, J. D.; Flach, S.

    2016-06-01

    We consider a quantum particle in a one-dimensional disordered lattice with Anderson localization in the presence of multifrequency perturbations of the onsite energies. Using the Floquet representation, we transform the eigenvalue problem into a Wannier-Stark basis. Each frequency component contributes either to a single channel or a multichannel connectivity along the lattice, depending on the control parameters. The single-channel regime is essentially equivalent to the undriven case. The multichannel driving increases substantially the localization length for slow driving, showing two different scaling regimes of weak and strong driving, yet the localization length stays finite for a finite number of frequency components.

  8. Multi-Scale Jacobi Method for Anderson Localization

    Science.gov (United States)

    Imbrie, John Z.

    2015-11-01

    A new KAM-style proof of Anderson localization is obtained. A sequence of local rotations is defined, such that off-diagonal matrix elements of the Hamiltonian are driven rapidly to zero. This leads to the first proof via multi-scale analysis of exponential decay of the eigenfunction correlator (this implies strong dynamical localization). The method has been used in recent work on many-body localization (Imbrie in On many-body localization for quantum spin chains, arXiv:1403.7837 URL"/> , 2014).

  9. Signatures of Anderson localization excited by an optical frequency comb

    KAUST Repository

    Gentilini, S.

    2010-01-25

    We investigate Anderson localization of light as occurring in ultrashort excitations. A theory based on time dependent coupled-mode equations predicts universal features in the spectrum of the transmitted pulse. In particular, the process of strong localization of light is shown to correspond to the formation of peaks in both the amplitude and in the group delay of the transmitted pulse. Parallel ab initio simulations made with finite-difference time-domain codes and molecular dynamics confirm theoretical predictions, while showing that there exists an optimal degree of disorder for the strong localization. © 2010 The American Physical Society.

  10. Poloidal asymmetries of heavy impurities in the ASDEX upgrade plasma

    International Nuclear Information System (INIS)

    For heavy and highly charged impurities multiple mechanisms exist that produce non-constant impurities densities on the flux surfaces. As for neoclassical and turbulent transport models such an asymmetry is highly importance an effort is launched to experimentally characterize the asymmetries comparing them with theoretical expectations. In the ASDEX upgrade tokamak (AUG) is routinely observed increase of outboard tungsten density in fast rotating plasma. This asymmetry is caused by the centrifugal force pushing tungsten ions outward due to its high mass. Furthermore, the high charge makes heavy impurities sensitive to poloidal variations of the plasma potential. The variation can be generated by magnetic trapped ions heated by RF heating. In such a case, the presence of an inboard asymmetry or at least the absence of an outboard asymmetry due to the centrifugal force can be observed. Finally, ion-impurity friction enhanced by the large charge of the impurity ions may cause a relatively weak up-down asymmetry of the impurity density. The aim of this poster is to show first evidence of these asymmetries in the AUG plasmas, the description of the used methodology, and to compare with theoretical models based on the parallel force balance.

  11. Understanding the effects of dopant impurities on quaternary chalcogenide system properties by investigating and modeling local vibrational modes and Raman lineshapes

    Science.gov (United States)

    Sarswat, Prashant; Free, Michael

    2014-03-01

    Cu2ZnSnSxCZTSSe) has gained attention as a p-type absorber layer due to its attractive properties such as optimum band gap, high absorption coefficient, and use of low cost elements. However, impurities in CZTSSe produce detrimental effects, which limit the device performance. Phonon dispersion in most of the semiconductors is found to be susceptible to the pairing between atoms within the lattice. Hence, a change in phonon dispersion can be used to investigate the effects of foreign impurities on such pairing. Thus a series of experiments were conducted to investigate the effect of free holes on the optical phonons of doped CZTSSe system as well as to evaluate asymmetry in the Raman lineshape. When irradiated with photons, doped CZTS possibly produces a continuum of inter-valence band electronic excitations, which can envelop the Raman-active phonon energy. Such overlap between the electronic continuum and discrete state can cause interference effects in CZTSSe. It was observed that Raman lineshape becomes more asymmetric, wider, and shifts towards lower frequency when laser power density increased. All these observations were found for Raman A mode as well as E (TO, LO) mode for doped CZTSSe samples.

  12. Price-Anderson Act - the third decade. Report to Congress

    International Nuclear Information System (INIS)

    Subsection 170p. of the Atomic Energy Act of 1954, as amended, requires that the Commission submit to the Congress by August 1, 1983, a detailed report on the need for continuation or modification of Section 170 of the Act, the Price-Anderson provisions. The report is divided into four sections with detailed subject reports appended to the main report. Sections I through III include an examination of issues that the Commission was required by statute to study (i.e., condition of the nuclear industry, state of knowledge of nuclear safety, and availability of private insurance), and discussion of other issues of interest and importance to the Congress and to the public. The subjects covered are as follows: (1) overview of the Price-Anderson system; (2) the state of knowledge of nuclear safety; (3) availability of private insurance; (4) conditions of the nuclear industry; (5) causality and proof of damages; (6) limitation of liability and subsidy; and (7) a proposal that would provide for removal of the limitation of liability but with limited annual liability payments. Section IV of the report contains conclusions and recommendations. Section V contains a bibliography

  13. Dynamical Process of Dissociation of Excitons in Polymer Chains with Impurities

    Institute of Scientific and Technical Information of China (English)

    ZHAO Hong-Xia; ZHAO Hui; CHEN Yu-Guang

    2011-01-01

    @@ Within an extended Su-Schrieffer-Heeger model including impurity interactions,the dynamical process of exciton dissociation in the presence of an external electric field is investigated by using a non-adiabatic evolution method Under the action of impurities,the stability as well as the effective mass of the exciton is reduced.Our results show that the field required to dissociate the excitons depends sensitively on the strength of the impurity potential.As the impurity potential strength increases,the dissociation field decreases effectively.The theoretical results are expected to provide useful predictions concerning which polymers with properly impurity-assisted interactions are likely to be more suitable for use in organic solar cells.%Within an extended Su-Schrieffer-Heeger model including impurity interactions, the dynamical process ofexciton dissociation in the presence of an external electric field is investigated by using a non-adiabatic evolution method. Under the action of impurities, the stability as well as the effective mass of the exciton is reduced. Our results show that the field required to dissociate the excitons depends sensitively on the strength of the impurity potential. As the impurity potential strength increases, the dissociation field decreases effectively. The theoretical results are expected to provide useful predictions concerning which polymers with properly impurity-assisted interactions are likely to be more suitable for use in organic solar cells.

  14. Impurity doping processes in silicon

    CERN Document Server

    Wang, FFY

    1981-01-01

    This book introduces to non-experts several important processes of impurity doping in silicon and goes on to discuss the methods of determination of the concentration of dopants in silicon. The conventional method used is the discussion process, but, since it has been sufficiently covered in many texts, this work describes the double-diffusion method.

  15. Possible Anderson transition below two dimensions in disordered systems of noninteracting electrons

    OpenAIRE

    Asada, Yoichi; Slevin, Keith; Ohtsuki, Tomi

    2005-01-01

    We investigate the possibility of an Anderson transition below two dimensions in disordered systems of non-interacting electrons with symplectic symmetry. Numerical analysis of energy level statistics and conductance statistics on Sierpinski carpets with spin-orbit coupling indicates the occurrence of an Anderson transition below two dimensions.

  16. All-solid-state cavity QED using Anderson-localized modes in disordered photonic crystal waveguides

    DEFF Research Database (Denmark)

    Lodahl, Peter; Sapienza, Luca; Nielsen, Henri Thyrrestrup;

    2010-01-01

    We employ Anderson-localized modes in deliberately disordered photonic crystal waveguides to confine light and enhance the interaction with matter. A 15-fold enhancement of the decay rate of a single quantum dot is observed meaning that 94% of the emitted single photons are coupled to an Anderson...

  17. Classical impurities associated to high rank algebras

    International Nuclear Information System (INIS)

    Classical integrable impurities associated with high rank (glN) algebras are investigated. A particular prototype, i.e. the vector non-linear Schrödinger (NLS) model, is chosen as an example. A systematic construction of local integrals of motion as well as the time components of the corresponding Lax pairs is presented based on the underlying classical algebra. Suitable gluing conditions compatible with integrability are also extracted. The defect contribution is also examined in the case where non-trivial integrable conditions are implemented. It turns out that the integrable boundaries may drastically alter the bulk behavior, and in particular the defect contribution

  18. Numerical calculation of impurity charge state distributions

    Energy Technology Data Exchange (ETDEWEB)

    Crume, E. C.; Arnurius, D. E.

    1977-09-01

    The numerical calculation of impurity charge state distributions using the computer program IMPDYN is discussed. The time-dependent corona atomic physics model used in the calculations is reviewed, and general and specific treatments of electron impact ionization and recombination are referenced. The complete program and two examples relating to tokamak plasmas are given on a microfiche so that a user may verify that his version of the program is working properly. In the discussion of the examples, the corona steady-state approximation is shown to have significant defects when the plasma environment, particularly the electron temperature, is changing rapidly.

  19. Classical impurities associated to high rank algebras

    Energy Technology Data Exchange (ETDEWEB)

    Doikou, Anastasia, E-mail: A.Doikou@hw.ac.uk [Department of Mathematics, Heriot–Watt University, EH14 4AS, Edinburgh (United Kingdom); Department of Computer Engineering and Informatics, University of Patras, Patras GR-26500 (Greece)

    2014-07-15

    Classical integrable impurities associated with high rank (gl{sub N}) algebras are investigated. A particular prototype, i.e. the vector non-linear Schrödinger (NLS) model, is chosen as an example. A systematic construction of local integrals of motion as well as the time components of the corresponding Lax pairs is presented based on the underlying classical algebra. Suitable gluing conditions compatible with integrability are also extracted. The defect contribution is also examined in the case where non-trivial integrable conditions are implemented. It turns out that the integrable boundaries may drastically alter the bulk behavior, and in particular the defect contribution.

  20. Information Transmission and Anderson Localization in two-dimensional networks of firing-rate neurons

    Science.gov (United States)

    Natale, Joseph; Hentschel, George

    Firing-rate networks offer a coarse model of signal propagation in the brain. Here we analyze sparse, 2D planar firing-rate networks with no synapses beyond a certain cutoff distance. Additionally, we impose Dale's Principle to ensure that each neuron makes only or inhibitory outgoing connections. Using spectral methods, we find that the number of neurons participating in excitations of the network becomes insignificant whenever the connectivity cutoff is tuned to a value near or below the average interneuron separation. Further, neural activations exceeding a certain threshold stay confined to a small region of space. This behavior is an instance of Anderson localization, a disorder-induced phase transition by which an information channel is rendered unable to transmit signals. We discuss several potential implications of localization for both local and long-range computation in the brain. This work was supported in part by Grants JSMF/ 220020321 and NSF/IOS/1208126.

  1. Fundamental aspects of metallic impurities and impurity interactions in silicon during device processing

    Energy Technology Data Exchange (ETDEWEB)

    Graff, K. [TEMIC, TELEFUNKEN, Heilbronn (Germany)

    1995-08-01

    A review on the behavior of metallic impurities in silicon can be considerably simplified by a restriction on pure, dislocation-free, monocrystalline silicon. In this case interactions between different impurities and between impurities and grown-in lattice defects can be reduced. This restriction is observed in Chapter 1 for discussing the general behavior of metallic impurities in silicon.

  2. Anderson localisation of visible light on a nanophotonic chip

    CERN Document Server

    Crane, Tom; Sapienza, Luca

    2016-01-01

    Controlling the propagation of visible light on a chip is of tremendous interest in research areas such as energy harvesting, imaging, sensing and biology. Technological advances allow us to control light at the nanoscale and to strongly enhance the light-matter interaction in highly engineered devices. However, compared to state-of-the-art two-dimensional optical cavities operating at longer wavelengths, the quality factor of on-chip visible light confinement is several orders of magnitude lower. Our approach makes use of fabrication imperfections to trap light: we demonstrate, for the first time, Anderson localisation of visible light on a chip. Remarkably, compared to quality factors of engineered cavities, disorder-induced localisation proves to be more efficient in trapping light than highly engineered devices, thus reversing the trend observed so far. We measure light-confinement quality factors as high as 7600 and, by implementing a sensitive imaging technique, we directly visualise the localised modes...

  3. Anderson localization in metamaterials and other complex media

    CERN Document Server

    Gredeskul, Sergey A; Asatrian, Ara A; Bliokh, Konstantin Y; Bliokh, Yuri P; Freilikher, Valentin D; Shadrivov, Ilya V

    2012-01-01

    We review some recent (mostly ours) results on the Anderson localization of light and electron waves in complex disordered systems, including: (i) left-handed metamaterials, (ii) magneto-active optical structures, (iii) graphene superlattices, and (iv) nonlinear dielectric media. First, we demonstrate that left-handed metamaterials can significantly suppress localization of light and lead to an anomalously enhanced transmission. This suppression is essential at the long-wavelength limit in the case of normal incidence, at specific angles of oblique incidence (Brewster anomaly), and in the vicinity of the zero-epsilon or zero-mu frequencies for dispersive metamaterials. Remarkably, in disordered samples comprised of alternating normal and left-handed metamaterials, the reciprocal Lyapunov exponent and reciprocal transmittance increment can differ from each other. Second, we study magneto-active multilayered structures, which exhibit nonreciprocal localization of light depending on the direction of propagation ...

  4. Defect-controlled Anderson localization of light in photonic lattices

    International Nuclear Information System (INIS)

    The transverse localization of light in a disordered photonic lattice with a central defect is analyzed numerically. The effect of different input beam widths on various regimes of Anderson localization is investigated. The inclusion of a defect enhances the localization of both narrow and broad beams, as compared to the lattice with no defect. But, in the case of a broad beam a higher disorder level is needed to reach the same localization as for a narrow input beam. It is also investigated how the transverse localization of light in such geometries depends on both the strength of disorder and the strength of nonlinearity in the system. While in the linear regime the localization is most pronounced in the lattice with the defect, in the nonlinear regime this is not the case. (paper)

  5. Unconstitutionality of Section 170 (e) of the price Anderson Act

    International Nuclear Information System (INIS)

    Several environmental protection groups in the State of North Carolina have recently contested the conformity with the United States Constitution of Section 170 (e) of the Atomic Energy Act (Price-Anderson Act). The court seized of the question (the United States District Court for the western district of North Carolina, Charlotte Division) held in March 1977 that this Section and the other provisions of the Atomic Energy Act concerning implementation of the $560 million limitation of liability for nuclear damage were unconstitutional and unenforceable insofar as they applied to nuclear incidents occurring inside the United States. The defendants, the former United States Atomic Energy Commission and its then Commissioners as well as the Duke Power Company (the local electricity company) will appeal this decision. The note on case law analyses the arguments retained by the court. (NEA)

  6. Price-Anderson Nuclear Safety Enforcement Program. 1997 annual report

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1998-01-01

    This report summarizes activities in the Department of Energy's Price-Anderson Amendments Act (PAAA) Enforcement Program in calendar year 1997 and highlights improvements planned for 1998. The DOE Enforcement Program involves the Office of Enforcement and Investigation in the DOE Headquarters Office of Environment, Safety and Health, as well as numerous PAAA Coordinators and technical advisors in DOE Field and Program Offices. The DOE Enforcement Program issued 13 Notices of Violation (NOV`s) in 1997 for cases involving significant or potentially significant nuclear safety violations. Six of these included civil penalties totaling $440,000. Highlights of these actions include: (1) Brookhaven National Laboratory Radiological Control Violations / Associated Universities, Inc.; (2) Bioassay Program Violations at Mound / EG and G, Inc.; (3) Savannah River Crane Operator Uptake / Westinghouse Savannah River Company; (4) Waste Calciner Worker Uptake / Lockheed-Martin Idaho Technologies Company; and (5) Reactor Scram and Records Destruction at Sandia / Sandia Corporation (Lockheed-Martin).

  7. Price-Anderson Nuclear Safety Enforcement Program. 1997 annual report

    International Nuclear Information System (INIS)

    This report summarizes activities in the Department of Energy's Price-Anderson Amendments Act (PAAA) Enforcement Program in calendar year 1997 and highlights improvements planned for 1998. The DOE Enforcement Program involves the Office of Enforcement and Investigation in the DOE Headquarters Office of Environment, Safety and Health, as well as numerous PAAA Coordinators and technical advisors in DOE Field and Program Offices. The DOE Enforcement Program issued 13 Notices of Violation (NOV's) in 1997 for cases involving significant or potentially significant nuclear safety violations. Six of these included civil penalties totaling $440,000. Highlights of these actions include: (1) Brookhaven National Laboratory Radiological Control Violations / Associated Universities, Inc.; (2) Bioassay Program Violations at Mound / EG ampersand G, Inc.; (3) Savannah River Crane Operator Uptake / Westinghouse Savannah River Company; (4) Waste Calciner Worker Uptake / Lockheed-Martin Idaho Technologies Company; and (5) Reactor Scram and Records Destruction at Sandia / Sandia Corporation (Lockheed-Martin). Sandia / Sandia Corporation (Lockheed-Martin)

  8. Atomic Bose and Anderson Glasses in Optical Lattices

    Science.gov (United States)

    Damski, B.; Zakrzewski, J.; Santos, L.; Zoller, P.; Lewenstein, M.

    2003-08-01

    An ultracold atomic Bose gas in an optical lattice is shown to provide an ideal system for the controlled analysis of disordered Bose lattice gases. This goal may be easily achieved under the current experimental conditions by introducing a pseudorandom potential created by a second additional lattice or, alternatively, by placing a speckle pattern on the main lattice. We show that, for a noncommensurable filling factor, in the strong-interaction limit, a controlled growing of the disorder drives a dynamical transition from superfluid to Bose-glass phase. Similarly, in the weak interaction limit, a dynamical transition from superfluid to Anderson-glass phase may be observed. In both regimes, we show that even very low-intensity disorder-inducing lasers cause large modifications of the superfluid fraction of the system.

  9. Observation of impurity accumulation and concurrent impurity influx in PBX

    International Nuclear Information System (INIS)

    Impurity studies in L- and H-mode discharges in PBX have shown that both types of discharges can evolve into either an impurity accumulative or nonaccumulative case. In a typical accumulative discharge, Zeff peaks in the center to values of about 5. The central metallic densities can be high, n/sub met//n/sub e/ ≅ 0.01, resulting in central radiated power densities in excess of 1 W/cm3, consistent with bolometric estimates. The radial profiles of metals obtained independently from the line radiation in the soft x-ray and the VUV regions are very peaked. Concurrent with the peaking, an increase in the impurity influx coming from the edge of the plasma is observed. At the beginning of the accumulation phase the inward particle flux for titanium has values of 6 x 1010 and 10 x 1010 particles/cm2s at minor radii of 6 and 17 cm. At the end of the accumulation phase, this particle flux is strongly increased to values of 3 x 1012 and 1 x 1012 particles/cm2s. This increased flux is mainly due to influx from the edge of the plasma and to a lesser extent due to increased convective transport. Using the measured particle flux, an estimate of the diffusion coefficient D and the convective velocity v is obtained

  10. Multi-photon Rabi oscillations in high spin paramagnetic impurity

    International Nuclear Information System (INIS)

    We report on multiple photon monochromatic quantum oscillations (Rabi oscillations) observed by pulsed EPR (Electron Paramagnetic Resonance) of Mn2+ (S = 5/2) impurities in MgO. We find that when the microwave magnetic field is similar or large than the anisotropy splitting, the Rabi oscillations have a spectrum made of many frequencies not predicted by the S = l/2 Rabi model. We show that these new frequencies come from multiple photon coherent manipulation of the multi-level spin impurity. We develop a model based on the crystal field theory and the rotating frame approximation, describing the observed phenomenon with a very good agreement.

  11. Self-pumping impurity control

    Science.gov (United States)

    Brooks, J.N.; Mattas, R.F.

    1983-12-21

    It is an object of the present invention to provide an apparatus for removing impurities from the plasma in a fusion reactor without an external vacuum pumping system. It is also an object of the present invention to provide an apparatus for removing the helium ash from a fusion reactor. It is another object of the present invention to provide an apparatus which removes helium ash and minimizes tritium recycling and inventory.

  12. Impurity transport in ohmically heated TFTR plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Stratton, B.C.; Fonck, R.J.; Hulse, R.A.; Ramsey, A.T.; Timberlake, J.; Efthimion, P.C.; Fredrickson, E.; Grek, B.; Hill, K.W.; Johnson, D.W.

    1988-11-01

    Impurity transport in ohmically heated TFTR plasmas is studied by computer modeling of VUV line emissions from impurities injected using the laser-blowoff technique. The results are sensitive to uncertainties in the ionization and recombination rates used in the modeling; as a result, only a spatially averaged diffusion coefficient and parameterized convective velocity can be measured. Measurements of these transport parameters are presented for deuterium and helium discharges with I/sub p/ = 0.8-2.5 MA, /bar n/sub e// = 0.6-6.0/times/10/sup 19/ m/sup -3/, and Z/sub eff/ = 2-6. Diffusion coefficients are found to be in the 0.5-1.5 m/sup 2//s range, considerably larger than neoclassical values. Nonzero inward convective velocities are necessary to fit the data in most cases. No dependence of the diffusion coefficient on injected element, working gas species, or plasma current is found, but at a given current, the diffusion coefficient is smaller by approximately a factor of two in plasmas near the density limit than in discharges with /bar n/sub e//<3/times/10/sup 19/ m/sup -3/. 31 refs., 9 figs., 3 tabs.

  13. Impurity transport in ohmically heated TFTR plasmas

    International Nuclear Information System (INIS)

    Impurity transport in ohmically heated TFTR plasmas is studied by computer modeling of VUV line emissions from impurities injected using the laser-blowoff technique. The results are sensitive to uncertainties in the ionization and recombination rates used in the modeling; as a result, only a spatially averaged diffusion coefficient and parameterized convective velocity can be measured. Measurements of these transport parameters are presented for deuterium and helium discharges with I/sub p/ = 0.8-2.5 MA, /bar n/sub e// = 0.6-6.0/times/1019 m-3, and Z/sub eff/ = 2-6. Diffusion coefficients are found to be in the 0.5-1.5 m2/s range, considerably larger than neoclassical values. Nonzero inward convective velocities are necessary to fit the data in most cases. No dependence of the diffusion coefficient on injected element, working gas species, or plasma current is found, but at a given current, the diffusion coefficient is smaller by approximately a factor of two in plasmas near the density limit than in discharges with /bar n/sub e//19 m-3. 31 refs., 9 figs., 3 tabs

  14. Impurity diffusion in transition-metal oxides

    International Nuclear Information System (INIS)

    Intrinsic tracer impurity diffusion measurements in ceramic oxides have been primarily confined to CoO, NiO, and Fe3O4. Tracer impurity diffusion in these materials and TiO2, together with measurements of the effect of impurities on tracer diffusion (Co in NiO and Cr in CoO), are reviewed and discussed in terms of impurity-defect interactions and mechanisms of diffusion. Divalent impurities in divalent solvents seem to have a weak interaction with vacancies whereas trivalent impurities in divalent solvents strongly influence the vacancy concentrations and significantly reduce solvent jump frequencies near a trivalent impurity. Impurities with small ionic radii diffuse more slowly with a larger activation energy than impurities with larger ionic radii for all systems considered in this review. Cobalt ions (a moderate size impurity) diffuse rapidly along the open channels parallel to the c-axis in TiO2 whereas chromium ions (a smaller-sized impurity) do not. 60 references, 11 figures

  15. BWR water chemistry impurity studies

    International Nuclear Information System (INIS)

    Laboratory studies were made on the effect of water impurities on environmental cracking in simulated BWR water of stainless steel, low alloy steel and nickel-base alloys. Constant elongation rate tensile (CERT) tests were run in simulated normal water chemistry (NWC), hydrogen water chemistry (HWC), or start-up environment. Sulfate, chloride and copper with chloride added to the water at levels of a fraction of a ppM were found to be extremely deleterious to all kinds of materials except Type 316 NG. Other detrimental impurities were fluoride, silica and some organic acids, although acetic acid was beneficial. Nitrate and carbon dioxide were fairly inoccuous. Corrosion fatigue and constant load tests on compact tension specimens were run in simulated normal BWR water chemistry (NWC) or hydrogen water chemistry (HWC), without impurities or with added sulfate or carbon dioxide. For sensitized Type 304 SS in NWC, 0.1 ppM sulfate increased crack propagation rates in constant load tests by up to a factor of 100, and in fatigue tests up to a factor of 10. Also, cracking in Type 316 nuclear grade SS and Alloy 600 was enhanced, but to a smaller degree. Carbon dioxide was less detrimental than sulfate. 3 figs., 4 tabs

  16. Two-photon Anderson localization in a disordered quadratic waveguide array

    International Nuclear Information System (INIS)

    We theoretically investigate two-photon Anderson localization in a χ (2) waveguide array with off-diagonal disorder. The nonlinear parametric down-conversion process would enhance both the single-photon and the two-photon Anderson localization. In the strong disorder regime, the two-photon position correlation exhibits a bunching distribution around the pumped waveguides, which is independent of pumping conditions and geometrical structures of waveguide arrays. Quadratic nonlinearity can be supplied as a new ingredient for Anderson localization. Also, our results pave the way for engineering quantum states through nonlinear quantum walks. (paper)

  17. Quantum criticality at the Anderson transition: A typical medium theory perspective

    Science.gov (United States)

    Mahmoudian, Samiyeh; Tang, Shao; Dobrosavljević, Vladimir

    2015-10-01

    We present a complete analytical and numerical solution of the typical medium theory (TMT) for the Anderson metal-insulator transition. This approach self-consistently calculates the typical amplitude of the electronic wave functions, thus representing the conceptually simplest order-parameter theory for the Anderson transition. We identify all possible universality classes for the critical behavior, which can be found within such a mean-field approach. This provides insights into how interaction-induced renormalizations of the disorder potential may produce qualitative modifications of the critical behavior. We also formulate a simplified description of the leading critical behavior, thus obtaining an effective Landau theory for Anderson localization.

  18. Routes Towards Anderson-Like Localization of Bose-Einstein Condensates in Disordered Optical Lattices

    Science.gov (United States)

    Schulte, T.; Drenkelforth, S.; Kruse, J.; Ertmer, W.; Arlt, J.; Sacha, K.; Zakrzewski, J.; Lewenstein, M.

    2005-10-01

    We investigate, both experimentally and theoretically, possible routes towards Anderson-like localization of Bose-Einstein condensates in disordered potentials. The dependence of this quantum interference effect on the nonlinear interactions and the shape of the disorder potential is investigated. Experiments with an optical lattice and a superimposed disordered potential reveal the lack of Anderson localization. A theoretical analysis shows that this absence is due to the large length scale of the disorder potential as well as its screening by the nonlinear interactions. Further analysis shows that incommensurable superlattices should allow for the observation of the crossover from the nonlinear screening regime to the Anderson localized case within realistic experimental parameters.

  19. Routes Towards Anderson-Like Localization of Bose-Einstein Condensates in Disordered Optical Lattices

    International Nuclear Information System (INIS)

    We investigate, both experimentally and theoretically, possible routes towards Anderson-like localization of Bose-Einstein condensates in disordered potentials. The dependence of this quantum interference effect on the nonlinear interactions and the shape of the disorder potential is investigated. Experiments with an optical lattice and a superimposed disordered potential reveal the lack of Anderson localization. A theoretical analysis shows that this absence is due to the large length scale of the disorder potential as well as its screening by the nonlinear interactions. Further analysis shows that incommensurable superlattices should allow for the observation of the crossover from the nonlinear screening regime to the Anderson localized case within realistic experimental parameters

  20. Charge dependence of neoclassical and turbulent transport of light impurities on MAST

    Science.gov (United States)

    Henderson, S. S.; Garzotti, L.; Casson, F. J.; Dickinson, D.; O'Mullane, M.; Patel, A.; Roach, C. M.; Summers, H. P.; Tanabe, H.; Valovič, M.; the MAST Team

    2015-09-01

    Carbon and nitrogen impurity transport coefficients are determined from gas puff experiments carried out during repeat L-mode discharges on the Mega-Amp Spherical Tokamak (MAST) and compared against a previous analysis of helium impurity transport on MAST. The impurity density profiles are measured on the low-field side of the plasma, therefore this paper focuses on light impurities where the impact of poloidal asymmetries on impurity transport is predicted to be negligible. A weak screening of carbon and nitrogen is found in the plasma core, whereas the helium density profile is peaked over the entire plasma radius. Both carbon and nitrogen experience a diffusivity of the order of 10 m2s-1 and a strong inward convective velocity of ˜40 m s-1 near the plasma edge, and a region of outward convective velocity at mid-radius. The measured impurity transport coefficients are consistent with neoclassical Banana-Plateau predictions within ρ ≤slant 0.4 . Quasi-linear gyrokinetic predictions of the carbon and helium particle flux at two flux surfaces, ρ =0.6 and ρ =0.7 , suggest that trapped electron modes are responsible for the anomalous impurity transport observed in the outer regions of the plasma. The model, combining neoclassical transport with quasi-linear turbulence, is shown to provide reasonable estimates of the impurity transport coefficients and the impurity charge dependence.

  1. Internal transport barrier analysis including impurities in tokamak and helical reactor plasmas

    International Nuclear Information System (INIS)

    The operation with Internal Transport Barrier (ITB) is expected as a high performance operation. ITB is utilized to improve core plasma confinement in the reversed magnetic shear. It is considered that the changes of core plasma profile by the ITB cause changes of impurity transport. In a large fusion reactor, high-Z materials will be used as plasma facing components because high loads of heat and particles concentrate there. However, high-Z impurities from these components cause large radiation loss and dilute the fuel even if the amount of impurities is small. Therefore, in this study, firstly, the ITB formation which includes the effects of the magnetic shear and perturbed profiles by the pellet injection was simulated using the Toroidal Transport Analysis Linkage code TOTAL. Secondly, we analyzed transport of the tungsten impurities using an impurity model in TOTAL code, and compared the impurity profile in the case with ITB to the one without ITB in the tokamak reactor. The impurities decreased in the ITB formation region when ITB was formed, and the outward flux of total impurity density was observed there. It can be expected that outward flux of impurities is generated by the temperature and the density gradients. (author)

  2. Impurity transport in a collision-dominated rotating tokamak plasma

    International Nuclear Information System (INIS)

    The flux of heavy impurities is an axisymmetric, toroidal plasma with all particles in the collision-dominated regime is considered. Plasma rotation and charge-exchange with neutrals are taken into account. A hydrodynamic model employing Braginskii's transport equations is used. The theorry is extended to higher collision freqencies as compared to previous treatments. It is found that the Pfirsch-Schlueter flux is significantly reduced as compared to the value given by Rutherford and that it is of the same order of magnitude, or less, than the classical flux in all regimes considered. It is also shown that the impurity flux can be influenced by charge-exchange with neutrals. (author)

  3. Numerical study of impurity distribution in ultrasonic heat meter body

    Institute of Scientific and Technical Information of China (English)

    石硕; 孙建亭; 杜广生; 张敏

    2015-01-01

    Based on a discrete phase model, the numerical simulation is carried out for the flow fields of different size calcium carbo- nate suspensions in the ultrasonic heat meter body. The flow characteristics and the impurity distribution in the ultrasonic heat meter body are analyzed. The errors of the ultrasonic heat meter in measuring calcium carbonate suspensions of particles of 10 micrometers and the causes are analyzed by simulation and experiment. Results show the effects of the impurities on the value of the k coeffi- cient and the sound attenuation on the reflection path due to the particle distribution are the two main factors that influence the mea- surement accuracy.

  4. Electronic energy levels of nanorings with impurities and Aharonov-Bohm effects

    Science.gov (United States)

    Ramírez, S.

    2011-10-01

    By modeling impurities along a nanoring as general potential forms the Schrödinger equation for ballistic electrons is shown to separate in cylindrical coordinates. We find an analytical eigenvalue equation for N delta-function-barrier impurities in the presence of magnetic flux. Previous calculations of the electronic states of a one-dimensional (1D) and two-dimensional (2D) nanoring for only one or two impurities modeled by equal square barriers is explicitly extended to three and four different or equal impurities modeled as delta-barrier, square-barrier, or delta-well potential forms. This is shown to be generalizable to any number N. Effects on the energy spectra due to magnetic flux and different kinds and numbers of impurities are compared in 1D and 2D nanorings.

  5. Alpha particle diagnostics using impurity pellet injection

    International Nuclear Information System (INIS)

    We have proposed using impurity injection to measure the energy distribution of the fast confined alpha particles in a reacting plasma. The ablation cloud surrounding the injected pellet is thick enough that an equilibrium fraction Fo∞(E) of the incident alphas should be neutralized as they pass through the cloud. By observing neutrals created in the large spatial region of the cloud which is expected to be dominated by the helium-like ionization state, e.g., Li+ ions, we can determine the incident alpha distribution dnHe2+/dE from the measured energy distribution of neutral helium atoms. Initial experiments were performed on TEXT in which we compared pellet penetration with our impurity pellet ablation model, and measured the spatial distribution of various ionization states in carbon pellet clouds. Experiments have recently begun on TFTR with the goal of measuring the alpha particle energy distribution during D-T operation in 1993--94. A series of preliminary experiments are planned to test the diagnostic concept. The first experiments will observe neutrals from beam-injected deuterium ions and the high energy 3He tail produced during ICH minority heating on TFTR interacting with the cloud. We will also monitor by line radiation the charge state distributions in lithium, boron, and carbon clouds

  6. The Monte Carlo validation framework for the discriminant partial least squares model extended with variable selection methods applied to authenticity studies of Viagra® based on chromatographic impurity profiles.

    Science.gov (United States)

    Krakowska, B; Custers, D; Deconinck, E; Daszykowski, M

    2016-02-01

    The aim of this work was to develop a general framework for the validation of discriminant models based on the Monte Carlo approach that is used in the context of authenticity studies based on chromatographic impurity profiles. The performance of the validation approach was applied to evaluate the usefulness of the diagnostic logic rule obtained from the partial least squares discriminant model (PLS-DA) that was built to discriminate authentic Viagra® samples from counterfeits (a two-class problem). The major advantage of the proposed validation framework stems from the possibility of obtaining distributions for different figures of merit that describe the PLS-DA model such as, e.g., sensitivity, specificity, correct classification rate and area under the curve in a function of model complexity. Therefore, one can quickly evaluate their uncertainty estimates. Moreover, the Monte Carlo model validation allows balanced sets of training samples to be designed, which is required at the stage of the construction of PLS-DA and is recommended in order to obtain fair estimates that are based on an independent set of samples. In this study, as an illustrative example, 46 authentic Viagra® samples and 97 counterfeit samples were analyzed and described by their impurity profiles that were determined using high performance liquid chromatography with photodiode array detection and further discriminated using the PLS-DA approach. In addition, we demonstrated how to extend the Monte Carlo validation framework with four different variable selection schemes: the elimination of uninformative variables, the importance of a variable in projections, selectivity ratio and significance multivariate correlation. The best PLS-DA model was based on a subset of variables that were selected using the variable importance in the projection approach. For an independent test set, average estimates with the corresponding standard deviation (based on 1000 Monte Carlo runs) of the correct

  7. Price--Anderson Act: the insurance industry's view

    International Nuclear Information System (INIS)

    The insurance industry feels the expense of providing insurance coverage under the Price-Anderson Act is justified because it encouraged development of nuclear power and assured protection for the public in the event of an accident. Insurance pools have been instituted in about 20 countries in order to distribute the risk on a worldwide basis. Changes in the original Act allow an off-site claimant to get compensation with defense waived and provide for the transition of financial responsibility from the public to the private sector. To date the pools have refunded $9.7 of $12.7 million (73 percent) of the premiums to the insured and the remainder has grown into a $45 million fund, which reflects the success of the nuclear industry and the regulatory agencies in establishing a safe record. This record covers 60 power reactors, 50 research and development reactors, waste disposal sites, and about 50 nuclear facilities. With the exception of reactor operators and fuel reprocessors, the insurance is voluntary at premiums ranging from $1000 to $260,000. A total of $600,000 has been paid in claims

  8. Magnetic flux creep in HTSC and Anderson-Kim theory

    International Nuclear Information System (INIS)

    The theoretical and experimental data on flux creep in high-temperature superconductors (HTSC) were analyzed in the review paper. On the one hand, the main attention is paid to the most striking experimental results which have had a significant influence on the investigations of flux creep in HTSC. On the other hand, the analysis of theoretical studies is concentrated on the works, which explain the features of flux creep on the basis of the Anderson-Kim (AK) theory modifications, and received previously unsufficient attention. However, it turned out that the modified AK theory could explain a lot of features of flux creep in HTSC: the scaling behaviour of current-voltage curves of HTSC, the finite rate of flux creep at ultra low temperatures, the logarithmic dependence of effective pinning potential as a function of transport current and its decrease with temperature. The harmonic potential field which is used in this approach makes it possible to solve accurately the both problems: viscous vortex motion and flux creep in this field. Moreover the distribution of pinning potential and the interaction of vortices with each other are taken into account in the approach. Thus, the modification of the AK theory consists, essentially, in its detailed elaboration and approaching to real situations in superconductors

  9. What should the Price--Anderson Act accomplish

    International Nuclear Information System (INIS)

    A historical review of the Price-Anderson Act's goals is followed by recommendations for amendments to improve guarantees of public safety. Failures of the original Act are identified as its failure to cover some accident situations appropriately and to provide incentives for promoting public safety. Legislation should correct these problems and be extended to all energy areas. Legislation based on worst-case situations is not found to be meaningful in terms of increasing safety or estimating comprehensive compensation because it relies on invalidated assumptions, which are still useful in safety awareness. Legislation could take the direction of putting 1.5 percent of the reactor cost into a fund, with the vendor and licensee contributing equal parts. When an incident occurs at any reactor, another one percent is put in by every reactor plus a $1 million penalty proportioned among those responsible. The Federal government would cover amounts above the fund, which would have no limit. Compensation to public funds by the industry would be a social decision based on the social and economic impact

  10. Characterization of core impurity transport and accumulation in various operating regimes in DIII-D

    International Nuclear Information System (INIS)

    Impurity contaminants in the core plasma of future burning devices such as the International Thermonuclear Experimental Reactor (ITER) are inevitable and will undoubtedly have a deleterious effect on plasma performance. Unfortunately, because of the limited amount of information available, the models presently being used to predict ITER performance simply assume a flat concentration profile for all impurities with an ad hoc concentration chosen for each impurity. In an attempt to start closing the gap between present experimental data and these models, experiments have been conducted on DIII-D with particular emphasis placed on (1) characterizing the buildup of intrinsic impurities in the plasma core in various confinement and divertor regimes; (2) measuring the steady-state impurity density profiles in various operating regimes; and (3) determining whether impurity transport properties are dependent on the charge of the impurity. The primary focus of these studies has been on characterizing impurity buildup in a wide variety of operating conditions in ELMing H-mode plasmas. However, enhanced confinement regimes such as ELM-free H-mode, VH-mode, and the negative central shear (NCS) regime offer the potential of a more attractive reactor scenario. Since the degree of impurity accumulation will have a significant impact on the attractiveness of these regimes, studies have also been conducted to characterize impurity buildup in these regimes. In the present configuration of DIII-D in which graphite tiles cover ∼ 90% of the plasma facing surface, spectroscopic surveys show carbon to be the dominant impurity with the core carbon concentration typically between 1--3% of the electron density

  11. Impurity-induced moments in underdoped cuprates

    Energy Technology Data Exchange (ETDEWEB)

    Khaliullin, G. [Max-Planck-Institut fuer Physik komplexer Systeme, Noethnitzer Str. 38, D-01187 Dresden (Germany)]|[Kazan Physicotechnical Institute of the Russian Academy of Sciences, 420029 Kazan (Russia); Kilian, R. [Max-Planck-Institut fuer Physik komplexer Systeme, Noethnitzer Str. 38, D-01187 Dresden (Germany); Krivenko, S. [Kazan Physicotechnical Institute of the Russian Academy of Sciences, 420029 Kazan (Russia); Fulde, P. [Max-Planck-Institut fuer Physik komplexer Systeme, Noethnitzer Str. 38, D-01187 Dresden (Germany)

    1997-11-01

    We examine the effect of a nonmagnetic impurity in a two-dimensional spin liquid in the spin-gap phase, employing a drone-fermion representation of spin-1/2 operators. The properties of the local moment induced in the vicinity of the impurity are investigated and an expression for the nuclear-magnetic-resonance Knight shift is derived, which we compare with experimental results. Introducing a second impurity into the spin liquid an antiferromagnetic interaction between the moments is found when the two impurities are located on different sublattices. The presence of many impurities leads to a screening of this interaction as is shown by means of a coherent-potential approximation. Further, the Kondo screening of an impurity-induced local spin by charge carriers is discussed. {copyright} {ital 1997} {ital The American Physical Society}

  12. Impurity-induced moments in underdoped cuprates

    International Nuclear Information System (INIS)

    We examine the effect of a nonmagnetic impurity in a two-dimensional spin liquid in the spin-gap phase, employing a drone-fermion representation of spin-1/2 operators. The properties of the local moment induced in the vicinity of the impurity are investigated and an expression for the nuclear-magnetic-resonance Knight shift is derived, which we compare with experimental results. Introducing a second impurity into the spin liquid an antiferromagnetic interaction between the moments is found when the two impurities are located on different sublattices. The presence of many impurities leads to a screening of this interaction as is shown by means of a coherent-potential approximation. Further, the Kondo screening of an impurity-induced local spin by charge carriers is discussed. copyright 1997 The American Physical Society

  13. Moessbauer Studies of Implanted Impurities in Solids

    CERN Multimedia

    2002-01-01

    Moessbauer studies were performed on implanted radioactive impurities in semiconductors and metals. Radioactive isotopes (from the ISOLDE facility) decaying to a Moessbauer isotope were utilized to investigate electronic and vibrational properties of impurities and impurity-defect structures. This information is inferred from the measured impurity hyperfine interactions and Debye-Waller factor. In semiconductors isoelectronic, shallow and deep level impurities have been implanted. Complex impurity defects have been produced by the implantation process (correlated damage) or by recoil effects from the nuclear decay in both semiconductors and metals. Annealing mechanisms of the defects have been studied. \\\\ \\\\ In silicon amorphised implanted layers have been recrystallized epitaxially by rapid-thermal-annealing techniques yielding highly supersaturated, electrically-active donor concentrations. Their dissolution and migration mechanisms have been investigated in detail. The electronic configuration of Sb donors...

  14. Wyodak-Anderson clinker in the Powder River Basin, Wyoming and Montana (prbclkg.shp)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — This ArcView shapefile contains a polygon representation of the Wyodak-Anderson clinker in the Powder River Basin, Wyoming and Montana. This theme was created...

  15. Effect of impurities on kinetic transport processes in fusion plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Braun, Stefanie

    2010-12-10

    Within the framework of this thesis, different problems arising in connection with impurities have been investigated. Collisional damping of zonal flows in tokamaks: Since the Coulomb collision frequency increases with increasing ion charge, heavy, highly charged impurities play an important role in this process. The effect of such impurities on the linear response of the plasma to an external potential perturbation, as caused by zonal flows, is calculated with analytical methods. In comparison with a pure plasma, the damping of the flows occurs, as expected, considerably faster; for experimentally relevant parameters, the enhancement exceeds the effective charge Z{sub eff} of the plasma. Impurity transport driven by microturbulence in tokamaks: With regard to impurities, it is especially important whether the resulting flows are directed inwards or outwards, since they are deleterious for core energy confinement on the one hand, but on the other hand help protecting plasma-facing components from too high energy fluxes in the edge region. A semi-analytical model is presented describing the resulting impurity fluxes and the stability boundary of the underlying mode. The main goal is to bridge the gap between, on the one hand, costly numerical simulations, which are applicable to a broad range of problems but yield scarcely traceable results, and, on the other hand, analytical theory, which might ease the interpretation of the results but is so far rather rudimentary. The model is based on analytical formulae whenever possible but resorts to a numerical treatment when the approximations necessary for an analytical solution would lead to a substantial distortion of the results. Both the direction of the impurity flux and the stability boundary are found to depend sensitively on the plasma parameters such as the impurity density and the temperature gradient. Pfirsch-Schlueter transport in stellarators: Due to geometry effects, collisional transport plays a much more

  16. Effect of impurities on kinetic transport processes in fusion plasmas

    International Nuclear Information System (INIS)

    Within the framework of this thesis, different problems arising in connection with impurities have been investigated. Collisional damping of zonal flows in tokamaks: Since the Coulomb collision frequency increases with increasing ion charge, heavy, highly charged impurities play an important role in this process. The effect of such impurities on the linear response of the plasma to an external potential perturbation, as caused by zonal flows, is calculated with analytical methods. In comparison with a pure plasma, the damping of the flows occurs, as expected, considerably faster; for experimentally relevant parameters, the enhancement exceeds the effective charge Zeff of the plasma. Impurity transport driven by microturbulence in tokamaks: With regard to impurities, it is especially important whether the resulting flows are directed inwards or outwards, since they are deleterious for core energy confinement on the one hand, but on the other hand help protecting plasma-facing components from too high energy fluxes in the edge region. A semi-analytical model is presented describing the resulting impurity fluxes and the stability boundary of the underlying mode. The main goal is to bridge the gap between, on the one hand, costly numerical simulations, which are applicable to a broad range of problems but yield scarcely traceable results, and, on the other hand, analytical theory, which might ease the interpretation of the results but is so far rather rudimentary. The model is based on analytical formulae whenever possible but resorts to a numerical treatment when the approximations necessary for an analytical solution would lead to a substantial distortion of the results. Both the direction of the impurity flux and the stability boundary are found to depend sensitively on the plasma parameters such as the impurity density and the temperature gradient. Pfirsch-Schlueter transport in stellarators: Due to geometry effects, collisional transport plays a much more

  17. Impurity phases in beryllium oxide ceramic

    OpenAIRE

    Turnaev, S. K.; Bitsoev, G. D.; Kil'govatov, G. M.; Kiiko, V. S.

    2013-01-01

    An x-ray spectrographic method with an electron probe and a scanning electron microscope are used to study industrial ceramic specimen surface composition, distinguished by presence of a different color for both the main part, and impurity phases. BeO-ceramic specimens, having a visually differing color, are conditionally separated into three types. In reflected electron microphotographs impurities are distinguished qualitatively with respect to electrical conductivity. Iron impurity is invar...

  18. Trace organic impurities in gaseous helium

    Science.gov (United States)

    Schehl, T. A.

    1973-01-01

    A program to determine trace organic impurities present in helium has been initiated. The impurities were concentrated in a cryogenic trap to permit detection and identification by a gas chromatographic-mass spectrometric technique. Gaseous helium (GHe) exhibited 63 GC flame ionization response peaks. Relative GC peak heights and identifications of 25 major impurities by their mass spectra are given. As an aid to further investigation, identities are proposed for 16 other components, and their mass spectra are given.

  19. Impurity Effect on Spin Ladder System

    OpenAIRE

    Motome, Yukitoshi; Katoh, Nobuyuki; Furukawa, Nobuo; Imada, Masatoshi

    1996-01-01

    Effects of nonmagnetic impurity doping in a spin ladder system with a spin gap are investigated by the exact diagonalization as well as by the variational Monte Carlo calculations. Substantial changes in macroscopic properties such as enhancements in spin correlations and magnetic susceptibilities are observed in the low impurity concentration region, which are caused by the increase of low-energy states. These results suggest that small but finite amount of nonmagnetic impurity doping releva...

  20. Density Correlations of Magnetic Impurities and Disorder

    OpenAIRE

    Desbois, Jean; Furtlehner, Cyril; Ouvry, Stéphane

    1996-01-01

    We consider an electron coupled to a random distribution of point vortices in the plane (magnetic impurities). We analyze the effect of the magnetic impurities on the density of states of the test particle, when the magnetic impurities have a spatial probability distribution governed by Bose or Fermi statistic at a given temperature. Comparison is made with the Poisson distribution, showing that the zero temperature Fermi distribution corresponds to less disorder. A phase diagram describing i...

  1. Thomas Anderson Goudge and the introduction of symbolic logic at the University of Toronto

    OpenAIRE

    Anellis, Irving H.

    1997-01-01

    Thomas Anderson Goudge was the first member of the philosophy department faculty to teach a course in modern mathematical logic at the University of Toronto. We provide here a brief discussion of the origin of Goudge's interest in logic and of how he came to introduce symbolic logic courses into the philosophy department curriculum at the University of Toronto. Much of the information presented here is based upon John G. Slater's three-page essay "Thomas Anderson Goudge" pre...

  2. Analytical advances in pharmaceutical impurity profiling.

    Science.gov (United States)

    Holm, René; Elder, David P

    2016-05-25

    Impurities will be present in all drug substances and drug products, i.e. nothing is 100% pure if one looks in enough depth. The current regulatory guidance on impurities accepts this, and for drug products with a dose of less than 2g/day identification of impurities is set at 0.1% levels and above (ICH Q3B(R2), 2006). For some impurities, this is a simple undertaking as generally available analytical techniques can address the prevailing analytical challenges; whereas, for others this may be much more challenging requiring more sophisticated analytical approaches. The present review provides an insight into current development of analytical techniques to investigate and quantify impurities in drug substances and drug products providing discussion of progress particular within the field of chromatography to ensure separation of and quantification of those related impurities. Further, a section is devoted to the identification of classical impurities, but in addition, inorganic (metal residues) and solid state impurities are also discussed. Risk control strategies for pharmaceutical impurities aligned with several of the ICH guidelines, are also discussed. PMID:26690047

  3. Density correlations of magnetic impurities and disorder

    Energy Technology Data Exchange (ETDEWEB)

    Desbois, J.; Furtlehner, C.; Ouvry, S. [Paris-11 Univ., 91 - Orsay (France). Inst. de Physique Nucleaire

    1996-06-01

    An electron coupled to a random distribution of point vortices in the plane (magnetic impurities) is discussed. The effect of the magnetic impurities on the density of states of the test particle, when the magnetic impurities have a spatial probability distribution governed by Bose or Fermi statistic at a given temperature is analyzed. Comparison is made with the Poisson distribution, showing that the zero temperature Fermi distribution corresponds to less disorder. A phase diagram describing isolated impurities versus Landau level oscillations is proposed. (author). 6 refs.

  4. Density correlations of magnetic impurities and disorder

    International Nuclear Information System (INIS)

    An electron coupled to a random distribution of point vortices in the plane (magnetic impurities) is discussed. The effect of the magnetic impurities on the density of states of the test particle, when the magnetic impurities have a spatial probability distribution governed by Bose or Fermi statistic at a given temperature is analyzed. Comparison is made with the Poisson distribution, showing that the zero temperature Fermi distribution corresponds to less disorder. A phase diagram describing isolated impurities versus Landau level oscillations is proposed. (author)

  5. Distribution Fitting 2. Pearson-Fisher, Kolmogorov-Smirnov, Anderson-Darling, Wilks-Shapiro, Cramer-von-Misses and Jarque-Bera statistics

    OpenAIRE

    Jantschi, Lorentz; BOLBOACA, Sorana D.

    2009-01-01

    The methods measuring the departure between observation and the model were reviewed. The following statistics were applied on two experimental data sets: Chi-Squared, Kolmogorov-Smirnov, Anderson-Darling, Wilks-Shapiro, and Jarque-Bera. Both investigated sets proved not to be normal distributed. The Grubbs test identified one outlier and after its removal the normality of the set of 205 chemical active compounds was accepted. The second data set proved not to have any outliers. Kolmogorov-Smi...

  6. Transport and re-deposition of limiter-released metal impurities

    International Nuclear Information System (INIS)

    The transport parallel B-vector and re-deposition of limiter- (or divertor-target-)released metal impurities in a given counter-streaming scrape-off layer plasma is studied analytically by using a kinetic approach. Electron impact ionization, Coulomb collisions with the hydrogen ions, and impurity ion acceleration in a pre-sheath electric field are accounted for. The friction and electric-field forces provide the driving forces for impurity re-cycling in front of the limiter. Both hydrogen ion sputtering and self-sputtering are included (the latter for impurity emission perpendicular to the limiter surface). The analytical formulas are numerically evaluated for the example of sputtered iron impurities, assuming a simple model for a scrape-off layer plasma in contact with a stainless-steel poloidal ring limiter. (author)

  7. COMPARISONOF FACTORS AFFECTING THE DETECTION OF SMALL IMPURITIES IN BREAST CANCER USING EIT.

    Directory of Open Access Journals (Sweden)

    VIDYA SARODE

    2013-06-01

    Full Text Available Breast cancer is the second leading cause of cancer death after lung cancer among women. It is very essential to detect breast cancer at an early stage so as to cure it efficiently. This paper mainly focuses on detecting impurities of small dimensions in circular plastic phantom which relate small tumors in breast. Benign cancertumor is analogous to non conducting impurity while malignant tumor is analogous to conducting impurity. Electrical Impedance Tomography (EIT based conductivity images are obtained for both conducting as well as non conducting impurities using Electrical Impedance and Diffused Optical Reconstruction Software (EIDORS. Different factors affecting the shape and size of reconstructed impurity like frequency of current source, type of forward model, material of electrodes, are discussed and compared.

  8. Quasiparticle Properties of a Mobile Impurity in a Bose-Einstein Condensate.

    Science.gov (United States)

    Christensen, Rasmus Søgaard; Levinsen, Jesper; Bruun, Georg M

    2015-10-16

    We develop a systematic perturbation theory for the quasiparticle properties of a single impurity immersed in a Bose-Einstein condensate. Analytical results are derived for the impurity energy, effective mass, and residue to third order in the impurity-boson scattering length. The energy is shown to depend logarithmically on the scattering length to third order, whereas the residue and the effective mass are given by analytical power series. When the boson-boson scattering length equals the boson-impurity scattering length, the energy has the same structure as that of a weakly interacting Bose gas, including terms of the Lee-Huang-Yang and fourth order logarithmic form. Our results, which cannot be obtained within the canonical Fröhlich model of an impurity interacting with phonons, provide valuable benchmarks for many-body theories and for experiments. PMID:26550852

  9. Simulation of inertial and beam-driven effects on impurities in tokamak plasmas

    International Nuclear Information System (INIS)

    Experiments on beam-heated tokamak plasmas in the Impurity Study Experiment (ISX-B) indicate that counterinjection leads to enhanced accumulation of impurities and coinjection leads to reduced accumulation of impurities relative to ohmically heated plasmas. According to neoclassical theory, both inertial and beam-driven effects can modify impurity distributions in beam-heated plasmas. We have implemented treatments of these effects in our basic impurity transport simulation code, IMPTAR, in order to investigate whether these effects could account for the observations in ISX-B. We briefly review the neoclassical theory of these effects and infer various consequences. We then present simulation results for model coinjected and counterinjected ISX-B plasma with inertial and beam-driven effects treated both separately and together

  10. Effects of quenched impurities on surface diffusion, spreading, and ordering of O/W(110)

    DEFF Research Database (Denmark)

    Nikunen, P.; Vattulainen, Ilpo Tapio; Ala-Nissila, T.

    2002-01-01

    We study how quenched impurities affect the surface diffusion and ordering of strongly interacting adsorbate atoms on surfaces. To this end, we carry out Monte Carlo simulations for a lattice-gas model of O/W(110), including small concentrations of immobile impurities which block their adsorption...... sites. We examine the behavior of the diffusion coefficients and order parameters as a function of coverage corresponding to various ordered phases at low temperatures. The effects of impurities are examined under both equilibrium and nonequilibrium conditions, and the results are compared to recent...... studies on a completely clean surface. We find that even minute impurity concentrations affect the diffusion behavior considerably in equilibrium. The effects are strongest in ordered phases and close to phase boundaries, where quenched impurities lead to a reduction of order, which in turn leads to...

  11. Strain field due to transition metal impurities in Ni and Pd

    Indian Academy of Sciences (India)

    Hitesh Sharma; S Prakash

    2003-01-01

    The strain field due to body centered substitutional transition metal impurities in Ni and Pd metals are investigated. The calculations are carried out in the discrete lattice model of the metal using Kanzaki lattice static method. The effective ion–ion interaction potential due to Wills and Harrison is used to evaluate dynamical matrix and the impurity-induced forces. The results for atomic displacements due to 3d, 4d and 5d impurities (Fe, Co, Cu, Nb, Mo, Pd, Pt and Au) in Ni and (Fe, Co, Cu, Ni, Nb, Mo, Pt and Au) impurities in Pd are given up to 25 NN’s of impurity and these are compared with the available experimental data. The maximum displacements of 4.6% and 3.8% of 1NN distance are found for NiNb and PdNb alloys respectively, while the minimum displacements of 0.63% and 0.23% of 1NN distance are found for NiFe and PdFe alloys respectively. Except for Cu, the atomic displacements are found to be proportional to the core radii and d state radius. The relaxation energies for 3d impurities are found less than those for 4d and 5d impurities in Ni and Pd metals. Therefore, 3d impurities may easily be solvable in these metals.

  12. Effect of Nonmagnetic Impurity in Nearly Antiferromagnetic Fermi Liquid: Magnetic Correlations and Transport Phenomena

    Science.gov (United States)

    Kontani, Hiroshi; Ohno, Masanori

    2007-03-01

    In nearly AF metals such as high-Tc superconductors (HTSCs), heavy fermion systems and organic superconductors, a single nonmagnetic impurity frequently causes nontrivial widespread change of the electronic states. To elucidate this long-standing issue, we study a Hubbard model with a strong onsite impurity potential based on an improved fluctuation-exchange (FLEX) approximation, which we call the GV^I-FLEX method. We find that (i) both local and staggered susceptibilities are strongly enhanced around the impurity. By this reason, (ii) the quasiparticle lifetime as well as the local DOS are strongly suppressed in a wide area around the impurity (like a Swiss cheese hole), which causes the ``huge residual resistivity'' beyond the s-wave unitary scattering limit. We stress that the excess quasiparticle damping rate caused by impurities has strong momentum-dependence due to non-s-wave scatterings induced by many-body effects, so the structure of the ``hot spot/cold spot'' in the host system persists against impurity doping. This result could be examined by the ARPES measurements. In addition, (iii) only a few percent of impurities can causes a ``Kondo-like'' upturn of resistivity (dρ/dT<0) at low temperatures when the system is very close to the AF quantum critical point (QCP). We also discuss the impurity effect in the superconducting state.

  13. Numerical study of localized impurity in a Bose-Einstein condensate

    Science.gov (United States)

    Akram, Javed; Pelster, Axel

    2016-03-01

    Motivated by recent experiments, we investigate a single 133 Cs impurity in the center of a trapped 87 Rb Bose-Einstein condensate (BEC). Within a zero-temperature mean-field description we provide a one-dimensional physical intuitive model which involves two coupled differential equations for the condensate and the impurity wave function, which we solve numerically. With this we determine within the equilibrium phase diagram spanned by the intra- and interspecies coupling strength whether the impurity is localized at the trap center or expelled to the condensate border. In the former case we find that the impurity induces a bump or dip on the condensate for an attractive or a repulsive Rb-Cs interaction strength, respectively. Conversely, the condensate environment leads to an effective mass of the impurity which increases quadratically for small interspecies interaction strength. Afterwards, we investigate how the impurity imprint upon the condensate wave function evolves for two quench scenarios. At first we consider the case that the harmonic confinement is released. During the resulting time-of-flight expansion it turns out that the impurity-induced bump in the condensate wave function starts decaying marginally, whereas the dip decays with a characteristic time scale which decreases with increasing repulsive impurity-BEC interaction strength. Second, once the attractive or repulsive interspecies coupling constant is switched off, we find that white-shock waves or bisolitons emerge which both oscillate within the harmonic confinement with a characteristic frequency.

  14. Is the solvation parameter model or its adaptations adequate to account for ionic interactions when characterizing stationary phases for drug impurity profiling with supercritical fluid chromatography?

    Science.gov (United States)

    Galea, Charlene; West, Caroline; Mangelings, Debby; Vander Heyden, Yvan

    2016-06-14

    Nine commercially available polar and aromatic stationary phases were characterized under supercritical fluid chromatographic (SFC) conditions. Retention data of 64 pharmaceutical compounds was acquired to generate models based on the linear solvation energy relationship (LSER) approach. Previously, adaptation of the LSER model was done in liquid chromatography by the addition of two solute descriptors to describe the influence of positive (D(+)) and negative (D(-)) charges on the retention of ionized compounds. In this study, the LSER models, with and without the ionization terms for acidic and basic solutes, were compared. The improved fits obtained for the modified models support inclusion of the D(+) and D(-) terms for pharmaceutical compounds. Moreover, the statistical significance of the new terms in the models indicates the importance of ionic interactions in the retention of pharmaceutical compounds in SFC. However, unlike characterization through the retention profiles, characterization of the stationary phases by modelling never explains the retention variance completely and thus seems less appropriate. PMID:27181639

  15. Eliminating Impurity Traps in the Silane Process

    Science.gov (United States)

    Coleman, L. M.

    1982-01-01

    Redistribution reaction section of silane process progressively separates heavier parts of chlorosilane feedstock until light silane product is available for pyrolysis. Small amount of liquid containing impurities is withdrawn from processing stages in which trapping occurs and passed to earlier processing stage in which impurities tend to be removed via chemical reactions.

  16. Nonlinear screening of charge impurities in graphene

    OpenAIRE

    2006-01-01

    It is shown that a ``vacuum polarization'' induced by Coulomb potential in graphene leads to a strong suppression of electric charges even for undoped case (no charge carriers). A standard linear response theory is therefore not applicable to describe the screening of charge impurities in graphene. In particular, it overestimates essentially the contributions of charge impurities into the resistivity of graphene.

  17. Cryogenic Laser Calorimetry for Impurity Analysis

    Science.gov (United States)

    Swimm, R. T.

    1985-01-01

    The results of a one-year effort to determine the applicability of laser-calorimetric spectroscopy to the study of deep-level impurities in silicon are presented. Critical considerations for impurity analysis by laser-calorimetric spectroscopy are discussed, the design and performance of a cryogenic laser calorimeter is described, and measurements of background absorption in high-purity silicon are presented.

  18. Impurity transport in plasma edge turbulence

    OpenAIRE

    Naulin, Volker; Priego Wood, Martin; Juul Rasmussen, Jens

    2004-01-01

    The turbulent transport of minority species/impurities is investigated in 2D drift-wave turbulence as well as in 3D toroidal drift-Alfven edge turbulence. The full effects of perpendicular and -- in 3D -- parallel advection are kept for the impurity species. Anomalous pinch effects are recovered and explained in terms of Turbulent EquiPartition (TEP)

  19. Revealing the Degree of Magnetic Frustration by Non-Magnetic Impurities

    International Nuclear Information System (INIS)

    Imaging the magnetic fields around a non-magnetic impurity can provide a clear benchmark for quantifying the degree of magnetic frustration. Focusing on the strongly frustrated J1-J2 model and the spatially anisotropic J1a-J1b-J2 model, very distinct low energy behaviors reflect different levels of magnetic frustration. In the J1-J2 model, bound magnons appear trapped near the impurity in the ground state and strongly reduce the ordered moments for sites proximal to the impurity. In contrast, local moments in the J1a-J1b-J2 model are enhanced on the impurity neighboring sites. These theoretical predictions can be probed by experiments such as nuclear magnetic resonance and scanning tunneling microscopy, and the results can elucidate the role of frustration in antiferromagnets and help narrow the possible models to understand magnetism in the iron pnictdies.

  20. Effect of a nonmagnetic impurity in a nearly antiferromagnetic Fermi liquid: Magnetic correlations and transport phenomena

    Science.gov (United States)

    Kontani, Hiroshi; Ohno, Masanori

    2006-07-01

    In nearly antiferromagnetic (AF) metals such as high- Tc superconductors (HTSCs), a single nonmagnetic impurity frequently causes nontrivial widespread change of the electronic states. To elucidate this long-standing issue, we study a Hubbard model with a strong onsite impurity potential based on an improved fluctuation-exchange (FLEX) approximation, which we call the GVI -FLEX method. This model corresponds to the HTSC with dilute nonmagnetic impurity concentration. We find that (i) both local and staggered susceptibilities are strongly enhanced around the impurity. By this reason, (ii) the quasiparticle lifetime as well as the local density of states are strongly suppressed in a wide area around the impurity (like a Swiss cheese hole), which causes the “huge residual resistivity” beyond the s -wave unitary scattering limit. We stress that the excess quasiparticle damping rate caused by impurities has strong k -dependence due to non- s -wave scatterings induced by many-body effects, so the structure of the “hot spot/cold spot” in the host system persists against impurity doping. This result could be examined by the ARPES measurements. In addition, (iii) only a few percent of impurities can cause a “Kondo-like” upturn of resistivity (dρ/dT<0) at low T when the system is very close to the AF quantum critical point. The results (i)-(iii) obtained in the present study, which cannot be derived by the simple FLEX approximation, naturally explain the main impurity effects in HTSCs. We also discuss the impurity effect in heavy fermion systems and organic superconductors.

  1. Verification of Anderson Superexchange in MnO via Magnetic Pair Distribution Function Analysis and ab initio Theory

    Science.gov (United States)

    Frandsen, Benjamin A.; Brunelli, Michela; Page, Katharine; Uemura, Yasutomo J.; Staunton, Julie B.; Billinge, Simon J. L.

    2016-05-01

    We present a temperature-dependent atomic and magnetic pair distribution function (PDF) analysis of neutron total scattering measurements of antiferromagnetic MnO, an archetypal strongly correlated transition-metal oxide. The known antiferromagnetic ground-state structure fits the low-temperature data closely with refined parameters that agree with conventional techniques, confirming the reliability of the newly developed magnetic PDF method. The measurements performed in the paramagnetic phase reveal significant short-range magnetic correlations on a ˜1 nm length scale that differ substantially from the low-temperature long-range spin arrangement. Ab initio calculations using a self-interaction-corrected local spin density approximation of density functional theory predict magnetic interactions dominated by Anderson superexchange and reproduce the measured short-range magnetic correlations to a high degree of accuracy. Further calculations simulating an additional contribution from a direct exchange interaction show much worse agreement with the data. The Anderson superexchange model for MnO is thus verified by experimentation and confirmed by ab initio theory.

  2. Level repulsion exponent β for many-body localization transitions and for Anderson localization transitions via Dyson Brownian motion

    Science.gov (United States)

    Monthus, Cécile

    2016-03-01

    The generalization of the Dyson Brownian motion approach of random matrices to Anderson localization (AL) models (Chalker et al 1996 Phys. Rev. Lett. 77 554) and to many-body localization (MBL) Hamiltonians (Serbyn and Moore 2015 arXiv:1508.07293) is revisited to extract the level repulsion exponent β, where β =1 in the delocalized phase governed by the Wigner-Dyson statistics, β =0 , in the localized phase governed by the Poisson statistics, and 0 {{|}2} for the same eigenstate m  =  n and for consecutive eigenstates m  =  n  +  1. For the Anderson localization tight-binding Hamiltonian with random on-site energies h i , we find β =2{{Y}n,n+1}(N)/≤ft({{Y}n,n}(N)-{{Y}n,n+1}(N)\\right) in terms of the density correlation matrix {{Y}nm}(N)\\equiv {\\sum}i=1N| {{|}2}| {{|}2} for consecutive eigenstates m  =  n  +  1, while the diagonal element m  =  n corresponds to the inverse participation ratio {{Y}nn}(N)\\equiv {\\sum}i=1N| {{|}4} of the eigenstate |{φn}> .

  3. Verification of Anderson Superexchange in MnO via Magnetic Pair Distribution Function Analysis and ab initio Theory.

    Science.gov (United States)

    Frandsen, Benjamin A; Brunelli, Michela; Page, Katharine; Uemura, Yasutomo J; Staunton, Julie B; Billinge, Simon J L

    2016-05-13

    We present a temperature-dependent atomic and magnetic pair distribution function (PDF) analysis of neutron total scattering measurements of antiferromagnetic MnO, an archetypal strongly correlated transition-metal oxide. The known antiferromagnetic ground-state structure fits the low-temperature data closely with refined parameters that agree with conventional techniques, confirming the reliability of the newly developed magnetic PDF method. The measurements performed in the paramagnetic phase reveal significant short-range magnetic correlations on a ∼1  nm length scale that differ substantially from the low-temperature long-range spin arrangement. Ab initio calculations using a self-interaction-corrected local spin density approximation of density functional theory predict magnetic interactions dominated by Anderson superexchange and reproduce the measured short-range magnetic correlations to a high degree of accuracy. Further calculations simulating an additional contribution from a direct exchange interaction show much worse agreement with the data. The Anderson superexchange model for MnO is thus verified by experimentation and confirmed by ab initio theory. PMID:27232042

  4. Impurity radiation efficiency and retention in Tore Supra ergodic divertor experiments

    International Nuclear Information System (INIS)

    The screening effect of Ne and C in ergodic divertor plasmas is studied. Spectroscopic measurements show that the screening mechanism is not the same for the two impurities. A 2D model explains this difference by the longer penetration length of neutral Ne. 3D modelling of the plasma edge with the BBQ code confirms the brightness profile shape dependence on the edge Te. The 1D impurity transport code MIST coupled to BBQ interprets the screening effect as possibly due to strong impurity outfluxes coming out of the ergodic region. (author)

  5. Effect of Nitrogen Impurity on Electronic Properties of Boron Nanotubes

    Directory of Open Access Journals (Sweden)

    Sandeep Kumar Jain

    2014-01-01

    Full Text Available For the first time we present electronic band structure and density of states for nitrogen doped hexagonal ultrathin boron nanotubes in the framework of density functional theory. The considered models of nanotubes below 5 Å diameter are armchair (3,3, zigzag (5,0, and chiral (4,2. The impurity chosen for the study is nitrogen and concentration of impurity atoms is limited to two. The study reveals that (3,3 BNT retains its metallic nature after nitrogen doping. However, metallicity gets increased which is attributed by the excess electrons of nitrogen. Further, it also brings out that (5,0 BNT which is originally metal transforms into semiconductor after nitrogen interaction and the band gap at G point increases with the impurity. Moreover, the band gap of (4,2 BNT reduces significantly and turns into semimetal for nitrogen doping. Thus, the nitrogen impurity has the predominant effect on the electronic properties of BNTs and therefore can be regarded as suitable candidates for nanoelectronic and field emission devices.

  6. Commensurability effects in one-dimensional Anderson localization: Anomalies in eigenfunction statistics

    International Nuclear Information System (INIS)

    Highlights: → Statistics of normalized eigenfunctions in one-dimensional Anderson localization at E = 0 is studied. → Moments of inverse participation ratio are calculated. → Equation for generating function is derived at E = 0. → An exact solution for generating function at E = 0 is obtained. → Relation of the generating function to the phase distribution function is established. - Abstract: The one-dimensional (1d) Anderson model (AM), i.e. a tight-binding chain with random uncorrelated on-site energies, has statistical anomalies at any rational point f=(2a)/(λE) , where a is the lattice constant and λE is the de Broglie wavelength. We develop a regular approach to anomalous statistics of normalized eigenfunctions ψ(r) at such commensurability points. The approach is based on an exact integral transfer-matrix equation for a generating function Φr(u, φ) (u and φ have a meaning of the squared amplitude and phase of eigenfunctions, r is the position of the observation point). This generating function can be used to compute local statistics of eigenfunctions of 1d AM at any disorder and to address the problem of higher-order anomalies at f=p/q with q > 2. The descender of the generating function Pr(φ)≡Φr(u=0,φ) is shown to be the distribution function of phase which determines the Lyapunov exponent and the local density of states. In the leading order in the small disorder we derived a second-order partial differential equation for the r-independent ('zero-mode') component Φ(u, φ) at the E = 0 (f=1/2 ) anomaly. This equation is nonseparable in variables u and φ. Yet, we show that due to a hidden symmetry, it is integrable and we construct an exact solution for Φ(u, φ) explicitly in quadratures. Using this solution we computed moments Im = N2m> (m ≥ 1) for a chain of the length N → ∞ and found an essential difference between their m-behavior in the center-of-band anomaly and for energies outside this anomaly. Outside the anomaly the

  7. Finite-size corrections for ground states of Edwards-Anderson spin glasses

    Science.gov (United States)

    Boettcher, Stefan; Falkner, Stefan

    2012-05-01

    Extensive computations of ground-state energies of the Edwards-Anderson spin glass on bond-diluted, hypercubic lattices are conducted in dimensions d=3, ..., 7. Results are presented for bond densities exactly at the percolation threshold, p=pc, and deep within the glassy regime, p>pc, where finding ground states is one of the hardest combinatorial optimization problems. Finite-size corrections of the form 1/Nω are shown to be consistent throughout with the prediction ω=1-y/d, where y refers to the "stiffness" exponent that controls the formation of domain wall excitations at low temperatures. At p=pc, an extrapolation for d→∞ appears to match our mean-field results for these corrections. In the glassy phase, however, ω does not approach its anticipated mean-field value of 2/3, obtained from simulations of the Sherrington-Kirkpatrick spin glass on an N-clique graph. Instead, the value of ω reached at the upper critical dimension matches another type of mean-field spin glass models, namely those on sparse random networks of regular degree called Bethe lattices.

  8. Initiating tumor banking for translational research: MD Anderson and Liverpool experience.

    Science.gov (United States)

    Mishra, A; Pandey, A; Shaw, R

    2007-01-01

    The ultimate progress in the cancer diagnosis and therapy has only been possible with the ongoing translational research that is likely to play a very important role in future as well. Hence the importance of such translation from bedside to bench and vis versa cannot be over-emphasized. Accordingly it has become more important to collect tumor samples along with the clinical information in a systematic manner to perform a good basic science research in future. With a population of over a billion and a heavy burden of cancer, India has the 'biggest' potential to establish the 'largest' tumor bank across the globe. Establishing a tumor bank involves money and manpower that may not be feasible across most of the centers in India. Taking into the considering the model of tumor banking of the two leading institutions of the world (MD Anderson Cancer Center, USA and University Hospital Aintree, Liverpool UK), this article presents the salient tips for a center in India to get started with tumor banking with minimal investment. Furthermore a simplified form of ethical consent is presented for the centers to adapt unanimously. PMID:17401220

  9. Final Report - Effects of Impurities on Fuel Cell Performance and Durability

    Energy Technology Data Exchange (ETDEWEB)

    Trent Molter

    2012-08-18

    This program is focused on the experimental determination of the effects of key hydrogen side impurities on the performance of PEM fuel cells. Experimental data has been leveraged to create mathematical models that predict the performance of PEM fuel cells that are exposed to specific impurity streams. These models are validated through laboratory experimentation and utilized to develop novel technologies for mitigating the effects of contamination on fuel cell performance. Results are publicly disseminated through papers, conference presentations, and other means.

  10. Influence of iron impurities on defected graphene

    International Nuclear Information System (INIS)

    Highlights: • The interaction among a multivacancy graphene system and iron impurities is studied. • The studied iron impurities were single atom and tetrahedral and octahedral clusters. • DFT calculations using the VASP code were performed. • The embedding of Fe affects the structure and electronic behavior in the graphene. • Half metal or semimetal behavior can be obtained, depending on the Fe impurities. - Abstract: The aim of this work is to study the interaction of selected iron cluster impurities and a multivacancy graphene system, in terms of the structural distortion that the impurities cause as well as their magnetic response. While originally, the interaction has been limited to vacancies and isolated metallic atoms, in this case, we consider small iron clusters. This study was undertaken using Density Functional Theory (DFT) calculations. The influence of the iron impurities in the electronic structure of the vacant graphene system is discussed. The main conclusion of this work is that the presence of iron impurities acts lowering the magnetic signal due to the occurrence of spin pairing between carbon and iron, instead of enhancing the possible intrinsic carbon magnetism

  11. Influence of iron impurities on defected graphene

    Energy Technology Data Exchange (ETDEWEB)

    Faccio, Ricardo; Pardo, Helena [Centro NanoMat, Cryssmat-Lab, DETEMA, Polo Tecnológico de Pando, Facultad de Química, Universidad de la República, Cno. Saravia s/n, CP 91000 Pando (Uruguay); Centro Interdisciplinario en Nanotecnología, Química y Física de Materiales, Espacio Interdisciplinario, Universidad de la República, Montevideo (Uruguay); Araújo-Moreira, Fernando M. [Materials and Devices Group, Department of Physics, Universidade Federal de São Carlos, SP 13565-905 (Brazil); Mombrú, Alvaro W., E-mail: amombru@fq.edu.uy [Centro NanoMat, Cryssmat-Lab, DETEMA, Polo Tecnológico de Pando, Facultad de Química, Universidad de la República, Cno. Saravia s/n, CP 91000 Pando (Uruguay); Centro Interdisciplinario en Nanotecnología, Química y Física de Materiales, Espacio Interdisciplinario, Universidad de la República, Montevideo (Uruguay)

    2015-03-01

    Highlights: • The interaction among a multivacancy graphene system and iron impurities is studied. • The studied iron impurities were single atom and tetrahedral and octahedral clusters. • DFT calculations using the VASP code were performed. • The embedding of Fe affects the structure and electronic behavior in the graphene. • Half metal or semimetal behavior can be obtained, depending on the Fe impurities. - Abstract: The aim of this work is to study the interaction of selected iron cluster impurities and a multivacancy graphene system, in terms of the structural distortion that the impurities cause as well as their magnetic response. While originally, the interaction has been limited to vacancies and isolated metallic atoms, in this case, we consider small iron clusters. This study was undertaken using Density Functional Theory (DFT) calculations. The influence of the iron impurities in the electronic structure of the vacant graphene system is discussed. The main conclusion of this work is that the presence of iron impurities acts lowering the magnetic signal due to the occurrence of spin pairing between carbon and iron, instead of enhancing the possible intrinsic carbon magnetism.

  12. Tunneling spectroscopy of a phosphorus impurity atom on the Ge(111)-(2 × 1) surface

    Energy Technology Data Exchange (ETDEWEB)

    Savinov, S. V.; Oreshkin, A. I., E-mail: oreshkin@spmlab.phys.msu.su, E-mail: oreshkin@spmlab.ru [Moscow State University (Russian Federation); Oreshkin, S. I. [Moscow State University, Sternberg Astronomical Institute (Russian Federation); Haesendonck, C. van [Laboratorium voor Stoffysica en Magnetisme (Belgium)

    2015-06-15

    We numerically model the Ge(111)-(2 × 1) surface electronic properties in the vicinity of a P donor impurity atom located near the surface. We find a notable increase in the surface local density of states (LDOS) around the surface dopant near the bottom of the empty surface state band π*, which we call a split state due to its limited spatial extent and energetic position inside the band gap. We show that despite the well-established bulk donor impurity energy level position at the very bottom of the conduction band, a surface donor impurity on the Ge(111)-(2 × 1) surface might produce an energy level below the Fermi energy, depending on the impurity atom local environment. It is demonstrated that the impurity located in subsurface atomic layers is visible in a scanning tunneling microscope (STM) experiment on the Ge(111)-(2 × 1) surface. The quasi-1D character of the impurity image, observed in STM experiments, is confirmed by our computer simulations with a note that a few π-bonded dimer rows may be affected by the presence of the impurity atom. We elaborate a model that allows classifying atoms on the experimental low-temperature STM image. We show the presence of spatial oscillations of the LDOS by the density-functional theory method.

  13. Influence of the impurity-defect and impurity-impurity interactions on the crystalline silicon solar cells conversion efficiency

    International Nuclear Information System (INIS)

    This study aims at understanding the influence of the impurity - defect interaction on the silicon solar cell performances. We studied first the case of single-crystalline silicon. We combined numerical simulations and experimental data providing new knowledge concerning metal impurities in silicon, to quantify the evolution of the conversion efficiency with the impurity concentration. Mainly due to the gettering effects, iron appears to be quite well tolerated. It is not the case for gold, diffusing too slowly. Hydrogenation effects were limited. We transposed then this study toward multi-crystalline silicon. Iron seems rather well tolerated, due to the gettering effects but also due to the efficiency of the hydrogenation. When slow diffusers are present, multi crystalline silicon is sensitive to thermal degradation. n-type silicon could solve this problem, this material being less sensitive to metal impurities. (author)

  14. Impurity and quaternions in nonrelativistic scattering from a quantum memory

    International Nuclear Information System (INIS)

    Models of quantum computing rely on transformations of the states of a quantum memory. We study mathematical aspects of a model proposed by Wu in which the memory state is changed via the scattering of incoming particles. This operation causes the memory content to deviate from a pure state, i.e. induces impurity. For nonrelativistic particles scattered from a two-state memory and sufficiently general interaction potentials in (1+1) dimensions, we express impurity in terms of quaternionic commutators. In this context, pure memory states correspond to null hyperbolic quaternions. In the case with point interactions, the scattering process amounts to appropriate rotations of quaternions in the frequency domain. Our work complements previous analyses by Margetis and Myers (2006 J. Phys. A 39 11567)

  15. Image transport through a disordered optical fiber mediated by transverse Anderson localization

    CERN Document Server

    Karbasi, Salman; Koch, Karl W; Hawkins, Thomas; Ballato, John; Mafi, Arash

    2013-01-01

    Transverse Anderson localization of light allows localized optical-beam-transport through a transversely-disordered and longitudinally-invariant medium. Its successful implementation in disordered optical fibers recently resulted in the simultaneous propagation of multiple beams in a single strand of an optical fiber, suggesting potential applications for spatial beam multiplexing and image transport. We present what is, to the best of our knowledge, the first demonstration of optical image transport using transverse Anderson localization of light. The image transport quality obtained in the polymer disordered optical fiber is comparable with or better than some of the best commercially available multicore imaging fibers with less pixelation and higher contrast. A proof-of-concept glass version is also evaluated and further optimization is discussed. Our results open the way to device-level implementation of the transverse Anderson localization of light with potential applications in biological and medical im...

  16. John Anderson's development of (situational) realism and its bearing on psychology today.

    Science.gov (United States)

    Hibberd, Fiona J

    2009-10-01

    In 1927, the Scottish philosopher John Anderson arrived in Australia to take up the chair of Philosophy at the University of Sydney. By the late 1930s, the "macrostructure" of his realist system was in place. It includes a theory of process and a substantial metaphysics, one that opposes positivism, linguistic philosophy and all forms of idealism. However, beyond Australia it remains largely unknown, despite its bearing on a number of current issues in psychology and the social sciences generally. This article outlines Anderson's transition from Hegelian idealism to realism, describes aspects of his ontology and epistemology, compares some of Anderson's ideas with Dewey's pragmatism and explains their relevance to present-day psychology. PMID:20027696

  17. Transverse Anderson localization of light near Dirac points of photonic nanostructures

    CERN Document Server

    Deng, Hanying; Malomed, Boris A; Panoiu, Nicolae C; Ye, Fangwei

    2015-01-01

    We perform a comparative study of the Anderson localization of light beams in disordered layered photonic nanostructures that, in the limit of periodic layer distribution, possess either a Dirac point or a Bragg gap in the spectrum of the wavevectors. In particular, we demonstrate that the localization length of the Anderson modes increases when the width of the Bragg gap decreases, such that in the vanishingly small bandgap limit, namely when a Dirac point is formed, even extremely high levels of disorders are unable to localize the optical modes located near the Dirac point. A comparative analysis of the key features of the propagation of Anderson modes formed in the Bragg gap or near the Dirac point is also presented. Our findings could provide valuable guidelines in assessing the influence of structural disorder on the functionality of a broad array of optical nanodevices.

  18. Nuclear structure studies using the high resolution spectrometer at the Los Alamos Clinton P. Anderson Meson Physics Facility. Progress report

    International Nuclear Information System (INIS)

    This document constitutes a progress report (1984 to 1985) and renewal proposal for the ongoing medium energy nuclear physics research program. The research efforts were carried out with the High Resolution Spectrometer (HRS) at the Los Alamos Clinton P. Anderson Meson Physics Facility (LAMPF) and at Brookhaven National Laboratory. The LAMPF research includes (1) p+ nucleus scattering data for a test of nonrelativistic and relativistic models of medium energy interaction; (2) data for nuclear structure information; (3) proton + nucleon data for the study of the fundamental nucleon-nucleon interaction; and (4) development of the above models. The Brookhaven work is a study of the formation and use of hypernuclei as a tool for nuclear studies. Individual reports are indexed separately

  19. Simultaneous determination of impurities in nuclear grade uranium oxide by emission spectrography

    International Nuclear Information System (INIS)

    100 mg mixture of U3O8 containing standard impurities was excited (using DC arc) together with 1 mg Ga2O3 + 4 mg AgCl. The same condition of excitation was also carried out for samples. Intensities of each impurities was measured by calculating the difference between the contrast curve (Keiser model) of each element and the galium as an internal standard. A calibration curve was drawn using impurities as an ordinate and logarithma concentration as an absis. (author). 2 refs

  20. Effects of Solvent and Impurities on Crystal Morphology of Zinc Lactate Trihydrate

    Institute of Scientific and Technical Information of China (English)

    杨芗钰; 钱刚; 张相洋; 段学志; 周兴贵

    2014-01-01

    The crystal morphology of zinc lactate trihydrate in the absence or presence of impurities (viz. succinic acid, L-malic acid and D-malic acid) is investigated by molecular simulation based on surface docking model and COMPASS force field. Combing simulation results with our previous experimental results, it is found that the solvent mainly has an inhibition effect on the (0 0 2) surface, and succinic acid impurity will inhibit the growth of (0 0 2) and (0 1 1) surfaces while two enantiomers of malic acid impurity will inhibit the (0 0 2) and (1 0 0) surfaces, which are in good agreement with the experimental results.

  1. Magnetic impurities and materials design for semiconductor spintronics

    Czech Academy of Sciences Publication Activity Database

    Sato, K.; Dederichs, P. H.; Katayama-Yoshida, H.; Kudrnovský, Josef

    340-342, - (2003), s. 863-869. ISSN 0921-4526 R&D Projects: GA AV ČR IAA1010203 Grant ostatní: RTN1-1999(XE) 00145 Institutional research plan: CEZ:AV0Z1010914 Keywords : diluted magnetic semiconductors * Zener and double-exchange models * impurity bands * Curie temperature Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.908, year: 2003

  2. Modeling CO{sub 2}-Brine-Rock Interaction Including Mercury and H{sub 2}S Impurities in the Context of CO{sub 2} Geologic Storage

    Energy Technology Data Exchange (ETDEWEB)

    Spycher, N.; Oldenburg, C. M.

    2014-01-01

    This study uses modeling and simulation approaches to investigate the impacts on injectivity of trace amounts of mercury (Hg) in a carbon dioxide (CO{sub 2}) stream injected for geologic carbon sequestration in a sandstone reservoir at ~2.5 km depth. At the range of Hg concentrations expected (7-190 ppbV, or ~ 0.06-1.6 mg/std.m{sup 3}CO{sub 2}), the total volumetric plugging that could occur due to complete condensation of Hg, or due to complete precipitation of Hg as cinnabar, results in a very small porosity change. In addition, Hg concentration much higher than the concentrations considered here would be required for Hg condensation to even occur. Concentration of aqueous Hg by water evaporation into CO{sub 2} is also unlikely because the higher volatility of Hg relative to H{sub 2}O at reservoir conditions prevents the Hg concentration from increasing in groundwater as dry CO{sub 2} sweeps through, volatilizing both H{sub 2}O and Hg. Using a model-derived aqueous solution to represent the formation water, batch reactive geochemical modeling show that the reaction of the formation water with the CO{sub 2}-Hg mixture causes the pH to drop to about 4.7 and then become buffered near 5.2 upon reaction with the sediments, with a negligible net volume change from mineral dissolution and precipitation. Cinnabar (HgS(s)) is found to be thermodynamically stable as soon as the Hg-bearing CO{sub 2} reacts with the formation water which contains small amounts of dissolved sulfide. Liquid mercury (Hg(l)) is not found to be thermodynamically stable at any point during the simulation. Two-dimensional radial reactive transport simulations of CO{sub 2} injection at a rate of 14.8 kg/s into a 400 m-thick formation at isothermal conditions of 106°C and average pressure near 215 bar, with varying amounts of Hg and H{sub 2}S trace gases, show generally that porosity changes only by about ±0.05% (absolute, i.e., new porosity = initial porosity ±0.0005) with Hg predicted to readily

  3. Anderson localization of spinons in a spin-1/2 antiferromagnetic Heisenberg chain

    OpenAIRE

    Pan, B. Y.; Zhou, S. Y.; Hong, X. C.; Qiu, X; Li, S. Y.

    2012-01-01

    Anderson localization is a general phenomenon of wave physics, which stems from the interference between multiple scattering paths1,2. It was originally proposed for electrons in a crystal, but later was also observed for light3-5, microwaves6, ultrasound7,8, and ultracold atoms9-12. Actually, in a crystal, besides electrons there may exist other quasiparticles such as magnons and spinons. However the search for Anderson localization of these magnetic excitations is rare so far. Here we repor...

  4. Designed Assembly of Heterometallic Cluster Organic Frameworks Based on Anderson-Type Polyoxometalate Clusters.

    Science.gov (United States)

    Li, Xin-Xiong; Wang, Yang-Xin; Wang, Rui-Hu; Cui, Cai-Yan; Tian, Chong-Bin; Yang, Guo-Yu

    2016-05-23

    A new approach to prepare heterometallic cluster organic frameworks has been developed. The method was employed to link Anderson-type polyoxometalate (POM) clusters and transition-metal clusters by using a designed rigid tris(alkoxo) ligand containing a pyridyl group to form a three-fold interpenetrated anionic diamondoid structure and a 2D anionic layer, respectively. This technique facilitates the integration of the unique inherent properties of Anderson-type POM clusters and cuprous iodide clusters into one cluster organic framework. PMID:27061042

  5. Magnetic resonance peak and nonmagnetic impurities

    OpenAIRE

    Y. Sidis; Bourges, P.; Keimer, B.; Regnault, L. P.; Bossy, J.; Ivanov, A; Hennion, B.; Gautier-Picard, P.; Collin, G.

    2000-01-01

    Nonmagnetic Zn impurities are known to strongly suppress superconductivity. We review their effects on the spin excitation spectrum in $\\rm YBa_2Cu_3O_{7}$, as investigated by inelastic neutron scattering measurements.

  6. Nucleation of voids - the impurity effect

    International Nuclear Information System (INIS)

    Nucleation of voids under irradiation in multicomponent alloys remains an unsolved theoretical problem. Of particular interest are the effects of nonequilibrium solute segregation phenomena on the critical nucleus and the nucleation rate. The resolution of the multicomponent nucleation in a dissipative system also has broader implication to the field of irreversible thermodynamics. The present paper describes a recent study of solute segregation effects in void nucleation. We begin with a thermodynamic model for a nonequilibrium void with interfacial segregation. The thermodynamic model is coupled with kinetic considerations of solute/solvent diffusion under a bias, which is itself related to segregation by the coating effect, to assess the stability of void embryos. To determine nucleation rate, we develop a novel technique by extending the most probable path method in statistical mechanics for nonequilibrium steady state to simulate large fluctuation with nonlinear dissipation. The path of nucleation is determined by solving an analogous problem on particle trajectory in classical dynamics. The results of both the stability analysis and the fluctuation analysis establish the paramount significance of the impurity effect via the mechanism of nonequilibrium segregation. We conclude that over-segregation is probably the most general cause for the apparently low nucleation barriers that are responsible for nearly ubiquitous occurrence of void swelling in common metals

  7. Interactions between impurities and defects created by irradiation in iron

    International Nuclear Information System (INIS)

    Chapter 1 is a brief review of the most important properties of point defects: the author is particularly interested in radiation damage; the different models proposed until now to explain the five annealing stages are exposed. Chapter 2 describes the experimental processes insisting on how fruitful is the magnetic after-effect to investigate point-defects. In chapter 3, new experimental results are exposed and discussed. Owing to addition of impurities to iron, magnetic after effect, stored energy, resistivity and length measurements have allowed to establish that stage I is correctly explained by the Granato-Nilan model (90): only the last stage, IE, is related to the interstitial-vacancy annihilation after the interstitial have freely migrated into the network. Several models are discussed for stage II; though it is highly probable that di-interstitials have been observed after electron irradiation, after neutron irradiation none of the after-effect zones can be connected with them. Special phenomena are observed in irradiated iron containing such impurities as nickel, silicium (appearance of new after effect zones, their transformation); they show the successive complication of an elementary defect: iron interstitial associated with an impurity atom. In the last section, the author describes some experiments on iron-carbon alloy; these show that carbon atoms (having precipitated at a temperature lower than 300 deg. C return to solid solution when the alloy is heated above 330 deg. C. (author)

  8. A Model Approach to Flux-Pinning Properties of YBa2Cu 3O7-delta Thin Film Vortex States via Non-Superconducting Impurities

    Science.gov (United States)

    Gamble, Ronald S., Jr.

    Thin film YBa2Cu3O7--delta (YBCO) samples with added non-superconducting nanodot defects of CeO 2 and BaSnO2 are the focus of recent high-temperature superconductor studies. These nanodots allow magnetic flux to penetrate at these sites of the superconducting lattice thus creating a magnetic flux vortex state. Examining the structure shows that these quantized magnetic flux vortices arrange themselves in a self-assembled lattice. The nanodots, with non-superconducting properties, serve to present structural properties to restrict motion of these vorticies under a pinning-force and to enhance the critical current density. A formulation of a new model for the system by a variation in the electron pair velocity via the virtual work from the nanodot defects in accordance to the well-known Superconductivity theories is tested. A solution to the expression for the magnetic flux, zero net force and pair velocity will generate a setting for the optimal deposition parameters of number density, growth geometry and mass density of these nanodot structures. With a calculation of pair velocities from a similar work, a comparison is made between experimental and theoretical velocity calculations using growth geometry and chemical potential. This will yield insight into how the current density for a doped high-temperature superconductor will be modified and tuned based on the dynamics and density of the nanodots themselves.

  9. Parametrically Driven Nonlinear Oscillators with an Impurity

    Institute of Scientific and Technical Information of China (English)

    张卓; 唐翌

    2002-01-01

    By virtue of the method of multiple scales, we study a chain of parametrically driven nonlinear oscillators with a mass impurity. An equation is presented to describe the nonlinear wave of small amplitude in the chain.In our derivation, the equation is applicable to any eigenmode of coupled pendulum. Our result shows that a nonpropagation soliton emerges as the lowest or highest eigenmode of coupled pendulum is excited, and the impurity tends to pin the nonpropagation soliton excitation.

  10. Transport of Impurities in Tokamak Edge Turbulence

    Czech Academy of Sciences Publication Activity Database

    Seidl, Jakub; Papřok, Richard; Krlín, Ladislav

    Vol. P212. Roma: ENEA-Fusione, 2011. s. 88-88. [European Fusion Theory Conference(EFTC)/14./. 26.09.2011-29.09.2011, Frascati] R&D Projects: GA ČR GAP205/10/2055 Institutional research plan: CEZ:AV0Z20430508 Keywords : plasma turbulence * plasma impurities * impurity transport * drift waves Subject RIV: BL - Plasma and Gas Discharge Physics http://www.fusione.enea.it/EVENTS/EFTC14/upload/abstractsgiulia/JakubSeidl.pdf

  11. Achieving Improved Ohmic Confinement via impurity injection

    International Nuclear Information System (INIS)

    Improved Ohmic Confinement (IOC) was obtained in ASDEX after a modification of the divertors that allowed a larger (deuterium and impurity) backflow from the divertor chamber. The quality of IOC depended crucially on the wall conditions, i.e. IOC was best for uncovered stainless steel walls and vanished with boronization. Furthermore, IOC was found only in deuterium discharges. These circumstances led to the idea that IOC correlates with the content of light impurities in the plasma. To substantiate this working hypothesis, we present observations in deuterium discharges with boronized wall conditions into which various impurities have been injected with the aim to induce IOC conditions. The remainder of this contribution is organized according to the following lines: Firstly, the plasma behaviour in typical IOC discharges is characterized. Secondly, injection experiments with the low-Z impurities nitrogen and neon as well as with the high-Z impurities argon and krypton are discussed. Then, we concentrate on optimized neon puffing that yields the best confinement results which are similar to IOC conditions. Finally, these results are compared with experiments in other tokamaks and some conclusions are drawn about the effects of the impurity puffing on both, the central and the edge plasma behaviour. (author) 9 refs., 2 figs

  12. Achieving improved ohmic confinement via impurity injection

    International Nuclear Information System (INIS)

    Improved Ohmic Confinement (IOC) was obtained in ASDEX after a modification of the divertors that allowed a larger (deuterium and impurity) backflow from the divertor chamber. The quality of IOC depended crucially on the wall conditions, i.e. IOC was best for uncovered stainless steels walls and vanished with boronization. Furthermore, IOC was found only in deuterium discharges. These circumstances led to the idea that IOC correlates with the content of light impurities in the plasma. To substantiate this working hypothesis, we present observations in deuterium discharges with boronized wall conditions into which various impurities have been injected with the aim to induce IOC conditions. Firstly, the plasma behaviour in typical IOC discharges is characterized. Secondly, injection experiments with the low-Z impurities nitrogen and neon as well as with the high-Z impurities argon and krypton are discussed. Then, we concentrate on optimized neon puffing that yields the best confinement results which are similar to IOC conditions. Finally, these results are compared with eperiments in other tokamaks and some conclusions are drawn about the effects of the impurity puffing on both, the central and the edge plasma behaviour. (orig.)

  13. Texas Experimental Tokamak impurity injection system

    International Nuclear Information System (INIS)

    Summary investigation of impurity transport and measurements of ion temperature are facilitated by injecting controlled quantities of selected impurities into tokamaks as diagnostic probes. The impurity injector now in use on the Texas Experimental Tokamak (TEXT) was designed for reliable, automatic operation. In this system, a thin film of the desired impurity is placed near the edge of the plasma. The light pulse from a Q-switched ruby laser is directed to a preselected point on the target. A small part of the impurity film evaporates and drifts into the plasma. The laser beam may be scanned to many points on the target so that enough impurity pulses can be obtained from a single target to allow a full day's operation. The scanning assembly and associated electronics are designed to operate with minimum intervention and to facilitate rapid repair and modification. The system is fully automatic but also incorporates both remote and local manual control capabilities to permit system calibration and troubleshooting. In the event of component failure, its self-diagnostic capability can indicate the area for repair. The system is demonstrating its effectiveness and reliability in the support of three different experimental programs. Engineering aspects of the system are discussed in this paper

  14. Local chemistry of Al and P impurities in silica

    DEFF Research Database (Denmark)

    Lægsgaard, Jesper; Stokbro, Kurt

    2000-01-01

    The local structure around Al and P impurities in silica is investigated using density-functional theory. Two distinct cases are considered: impurities substituting for a Si atom in alpha quartz, and impurities implanted in a stoichiometric alpha-quartz crystal. Both impurity elements are found t...

  15. Isolation, Synthesis and Characterization of Rosiglitazone Maleate Impurities

    OpenAIRE

    Krishna, Singamsetty Radha; Brahmeshwar Rao, Mandava Venkata Naga; Raju, Tirmalaraju Satyanaryana; Himabindu, Vurimidi; Reddy, Ghanta Mahesh

    2008-01-01

    Three unknown impurities in rosiglitazone maleate 1 bulk drug at level below 0.1% (ranging from 0.05 to 0.1%) were detected by simple reverse phase high performance liquid chromatography. These impurities were preliminarily identified with LC-MS and characterized by the mass number of the impurities. Different experiments were conducted and finally synthesized and characterized the unknown impurities.

  16. A spectroscopic analysis of density-controlled impurity behavior in the DIII-D tokamak during H-mode

    International Nuclear Information System (INIS)

    With simultaneous spectral, temporal and chordal resolution, the STRS spectrometer was built to increase both the quality and quantity of spectroscopic impurity information available from tokamak discharges. The astigmatic properties of a grazing incidence spectrometer disperse spectra and provides angular resolution. STRS was installed at the DIII-D tokamak, and its data is compared to simulations to analyze impurity behavior. An unusual impurity behavior was discovered at DIII-D during H-mode with giant edge localized modes (ELMs): depending on the plasma current, impurities either accumulate in the plasma center, or are driven out from it. They also modulate at the ELM frequency. This behavior was found to depend on the electron density profile which oscillates between centrally peaked and hollow. Naturally occurring ELM phenomena produce electron density oscillations which cause impurity cycling and allow transport studies of intrinsic impurities. Particle flux is modeled with a constant anomalous diffusion coefficient and a convection coefficient which depends on electron density gradients. MIST impurity transport code simulation use time dependent electron density profiles, oscillating with giant ELMs, to show impurity concentrations follow the density peak as theoretically predicted. This reproduced the observations of intrinsic nickel spectra, and indicates that impurity transport in DIII-D h-mode is dominated by ion density gradients

  17. Simulating impurity production and transport for fusion edge plasmas

    Science.gov (United States)

    Gilmer, G.; Bringa, E.; Kubota, A.; Mundy, C.; Zepeda-Ruiz, L.; Rognlien, T. D.; Verboncoeur, J.

    2004-11-01

    A set of simulation models is under development to describe impurity production and transport, especially hydrocarbons, in tokamaks. The set is designed for use with either a developing kinetic code (see adjacent papers) or a fluid code for the main hydrogenic fuel ions and electrons. Three regions are treated: surface sputtering, near-surface transport and plasma chemistry, and whole edge transport. Regions are connected via interface data tables. Molecular dynamics sputtering simulations are performed to provide data and insight into the experimentally difficult low impact-energy regime where many-body effects must be included. Results are presented for proton and tritium bombardment at different incident angles and energies (10-300 eV) for graphite and amorphous hydrogenated carbon. Near-surface hydrocarbons are simulated with the XOOPIC particle code and CHEMKIN for initial chemistry understanding. The whole edge transport of impurities is described by the multi-species UEDGE transport code.

  18. Simulation of the impurity-vacancy clusters in Ni

    International Nuclear Information System (INIS)

    Formation energies and atomic configuration of impurity-vacancy, impurity-divacancy complexes are investigated using mathematical simulation method. Impurity introduction was simulated by changing the impurity atomic radius as compared to matrix atomic radius R0. It is shown, that if impurity radius exceeds 1.18 R0, impurity-divacancy complex transfers into a depleted configuration in which impurity atom is placed between the two vacancies. Possessing low activity and large capture radius, this complex may become an effective center of point defect recombination

  19. Simulation of impurity-vacancy clusters in Ni

    International Nuclear Information System (INIS)

    Formation energies and atomic configurations of impurity-vacancy, impurity-divacancy complexes have been investigated by computerized simulation. Impurity introduction is simulated by changing the atomic radius of the impurity in comparison with the atomic radius, R0, of the matrix. It is shown that with the impurity radius more than 1.18 R0 the impurity-divacancy complex transforms into the splitting configuration, in which the impurity atom is in the middle between two vacancies. This complex can become an effective centre of point defect recombination, when possessing light mobility and a large radius of capture

  20. Radiation Rates for Low Z Impurities in Edge Plasmas

    CERN Document Server

    Clark, R; Post, D

    1995-01-01

    The role of impurity radiation in the reduction of heat loads on divertor plates in present experiments such as DIII-D, JET, JT-60, ASDEX, and Alcator C-Mod, and in planned experiments such as ITER and TPX places a new degree of importance on the accuracy of impurity radiation emission rates for electron temperatures below 250 eV for ITER and below 150 eV for present experiments. We have calculated the radiated power loss using a collisional radiative model for Be, B, C, Ne and Ar using a multiple configuration interaction model which includes density dependent effects, as well as a very detailed treatment of the energy levels and meta-stable levels. The "collisional radiative" effects are very important for Be at temperatures below 10 eV. The same effects are present for higher Z impurities, but not as strongly. For some of the lower Z elements, the new rates are about a factor of two lower than those from a widely used, simpler average-ion package (ADPAK) developed for high Z ions and for higher temperature...

  1. Impurity Trapping of Positive Muons in Metals

    CERN Multimedia

    2002-01-01

    Polarized positive muons are implanted into metal samples. In an applied magnetic field the muon spin precession is studied. The line width in the precession frequency spectrum gives information about the static and dynamic properties of muons in a metal lattice. At temperatures where the muon is immobile within its lifetime the line width gives information about the site of location. At temperatures where the muon is mobile, the line width gives information on the diffusion process. It is known from experiments on quasi-elastic neutron scattering on hydrogen in niobium that interstitial impurities like nitrogen tend to act as traps for hydrogen. These trapping effects have now been studied systematically for muons in both f.c.c. metals (aluminium and copper) and b.c.c. metals (mainly niobium). Direct information on the trapping rates and the nature of the diffusion processes can be obtained since the muonic lifetime covers a time range where many of these processes occur.\\\\ \\\\ Mathematical models are set up ...

  2. 78 FR 41835 - Inflation Adjustments to the Price-Anderson Act Financial Protection Regulations

    Science.gov (United States)

    2013-07-12

    ... made the initial changes to the Price-Anderson Act amounts on October 27, 2005 (70 FR 61885), and the first periodic inflation adjustments on September 29, 2008 (73 FR 56451). This final rule makes the... Writing,'' published June 10, 1998 (63 FR 31883). X. Backfit Analysis and Issue Finality The NRC...

  3. Financial analysis of potential retrospective premium assessments under the Price-Anderson system

    International Nuclear Information System (INIS)

    Ten representative nuclear utilities have been analyzed over the period 1981 to 1983 to evaluate the effects of three levels of retrospective premiums on various financial indicators. This analysis continues and expands on earlier analyses prepared as background for deliberations by the US Congress for possible extension or modification of the Price-Anderson Act

  4. Single-ion-pair fluorescence ratios in ruby and Anderson localization

    Science.gov (United States)

    Chu, S.; Gibbs, H. M.; Passner, A.

    1981-12-01

    The experiment of Koo, Walker, and Geschwind (KWG) presenting evidence for a mobility edge separating localized and extended states has been repeated and extended. Although some of the features reported by KWG were seen, there are notable qualitative and quantitative differences in our work. We conclude that there is no compelling evidence for an Anderson transition in ruby.

  5. Ilu võitlus koleduse välja vastu / Rebekka Lotman ; kommenteerinud Mart Anderson

    Index Scriptorium Estoniae

    Lotman, Rebekka, 1978-

    2009-01-01

    Konkursside "25 kauneimat Eesti raamatut" ja "Viis kauneimat Eesti lasteraamatut" võidutööde näitus Eesti Rahvusraamatukogus. Võidutööde valikut kommenteerib žürii esimees Mart Anderson. Loetletud 2008. aasta 25 kaunimat raamatut. Nimekiri: 2008. aasta 25 kauneimat raamatut

  6. Ago Anderson pälvis Helmi Tohvelmani preemia / Karin Klaus

    Index Scriptorium Estoniae

    Klaus, Karin

    2009-01-01

    13. oktoobril anti Endla teatri näitlejale Ago Andersonile üle Helmi Tohvelmani auhind. Pidulik sündmus toimus Väätsa põhikoolis, Tohvelmani kodukohas. Anderson pälvis tunnustuse kui kerge kehakeelega näitleja

  7. 75 FR 34170 - Plastic Omnium Automotive Exteriors, LLC, Anderson, SC; Plastic Omnium Automotive Exteriors, LLC...

    Science.gov (United States)

    2010-06-16

    ..., South Carolina. The notice was published in the Federal Register April 23, 2010 (75 FR 21356). The... Employment and Training Administration Plastic Omnium Automotive Exteriors, LLC, Anderson, SC; Plastic Omnium Automotive Exteriors, LLC, Troy, MI; Amended Certification Regarding Eligibility To Apply for...

  8. Quantum resonance, Anderson localisation and selective rotational excitation in periodically kicked molecules

    Directory of Open Access Journals (Sweden)

    Averbukh I. Sh.

    2013-03-01

    Full Text Available We show that molecules kicked periodically by laser pulses currently used in molecular alignment experiments allow to observe effects of the periodically kicked quantum rotor in a real rotational system. Among these effects are Anderson localisation in angular momentum and the scaling of the quantum resonance. Based on this, we propose a new scheme for selective molecular rotational excitation.

  9. The Egg as a Symbol——Analysis of Sherwood Anderson's The Egg

    Institute of Scientific and Technical Information of China (English)

    孙慧春; 李伟

    2009-01-01

    @@ A naive narrator in Sherwood Anderson's The Egg leads the reader to witness the various experiences of his family related with eggs.The egg is a dominant theme in their living and an inseparable part of their family.The egg means something that he could only feel directly as a na(i)ve boy.

  10. An asymptotically normal G-estimate for the Anderson-Fisher discriminant function

    Energy Technology Data Exchange (ETDEWEB)

    Girko, V.L.; Pavlenko, T.V. [Kiev State Univ. (Ukraine)

    1994-06-05

    Conditions under which a G-estimate of the Anderson-Fisher discriminant function is asymptotically normal are investigated. This estimate decreases by an order of magnitude the quantity of observations needed for a given level of accuracy on the part of an estimate and is thus of significant interest for practical applications. 3 refs.

  11. Progress in nonmagnetic impurity doping studies on Fe-based superconductors

    Science.gov (United States)

    Li, Jun; Guo, Yan-Feng; Yang, Zhao-Rong; Yamaura, Kazunari; Takayama-Muromachi, Eiji; Wang, Hua-Bing; Wu, Pei-Heng

    2016-05-01

    We review the progress of nonmagnetic impurity doping studies on Fe-based superconductors. On the theoretical side, two highly promising candidates for the pairing symmetry order parameter, i.e. the multi-gap s ++ and s ± wave models, have been proposed but continuously debated. The debate arises because of the complex gap structure and exceptional magnetic and metallic behaviors of Fe-based superconductors, which may vary the influence of nonmagnetic defects in the chemical potential, impurity disorder, inter- and intra-band scattering strength, and electron localization. This creates difficulties in directly obtaining the most important information for understanding the symmetry order parameter. Experimentally, nonmagnetic impurity substitution studies have been widely carried out, which have provided very useful insights. We review herein the various nonmagnetic impurity doping experiments, including the controlled defects within the superconducting Fe2 X 2 planes through sample quality improvement, single impurity effects on the electronic state and local moment, the magnetic response of the Fe2 X 2 planes both on the macroscopic scale as the antiferromagnetic state and the local scale of moment, as well as the significant effect of modifying the transport properties. The experiments enable us to qualitatively analyze the nonmagnetic impurity effects on the superconducting state for many Fe-based superconductors. We also propose herein some strategies for nonmagnetic impurity doping study. As an important model for explaining the nonmagnetic impurity doping effects, the pair-breaking model is compared with various theoretical approaches via analysis of the pair-breaking rates of various Fe-superconductors.

  12. Nuclear-structure studies using the high-resolution spectrometer at the Los Alamos Clinton P. Anderson Meson Physics Facility. Progress report

    International Nuclear Information System (INIS)

    This document contains a description of the ongoing medium-energy nuclear-physics research program supported by the US Department of Energy with The University of Texas at Austin. A major part of the work is associated with research done using the High Resolution Spectrometer (HRS) at the Los Alamos Clinton P. Anderson Meson Physics Facility (LAMPF); this research focuses on: (1) providing data which test microscopic models of the medium - energy proton + nucleus interaction; (2) providing data which are to be analyzed to provide new nuclear-structure information (both ground state and excited state); and (3) developing and improving the models themselves. Publications are listed

  13. Multielemental segregation analysis of the thallium bromide impurities purified by repeated Bridgman technique

    Energy Technology Data Exchange (ETDEWEB)

    Santos, Robinson A. dos; Hamada, Margarida M., E-mail: rasantos@ipen.br, E-mail: mmhamada@ipen.br [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil); Costa, Fabio E. da; Gennari, Roseli F.; Martins, Joao F.T.; Marcondes, Renata M.; Mesquita, Carlos H. de [Universidade de Sao Paulo (IF/USP), Sao Paulo, SP (Brazil). Inst. de Fisica

    2011-07-01

    TlBr crystals were purified and grown by the repeated Bridgman method from two commercial TlBr salts and characterized to be used as radiation detectors. To evaluate the purification efficiency, measurements of the impurity concentration were made after each growth, analyzing the trace impurities by inductively coupled plasma mass spectroscopy (ICP-MS). A significant decrease of the impurity concentration resulting from the purification number was observed. To evaluate the crystal as a radiation semiconductor detector, measurements of its resistivity and gamma-ray spectroscopy were carried out. The radiation response depended on the crystal purity. The repeated Bridgman technique improved the TlBr crystal quality used as a radiation detector. A compartmental model was proposed to fit the impurity concentration as a function of the repetition number of the Bridgman growth. (author)

  14. Impurity effects on electrical conductivity of doped bilayer graphene in the presence of a bias voltage

    Institute of Scientific and Technical Information of China (English)

    E Lotfi; H Rezania; B Arghavaninia; M Yarmohammadi

    2016-01-01

    We address the electrical conductivity of bilayer graphene as a function of temperature, impurity concentration, and scattering strength in the presence of a finite bias voltage at finite doping, beginning with a description of the tight-binding model using the linear response theory and Green’s function approach. Our results show a linear behavior at high doping for the case of high bias voltage. The effects of electron doping on the electrical conductivity have been studied via changing the electronic chemical potential. We also discuss and analyze how the bias voltage affects the temperature behavior of the electrical conductivity. Finally, we study the behavior of the electrical conductivity as a function of the impurity concentration and scattering strength for different bias voltages and chemical potentials respectively. The electrical conductivity is found to be monotonically decreasing with impurity scattering strength due to the increased scattering among electrons at higher impurity scattering strength.

  15. Wildlife Protection, Mitigation, and Enhancement Plans, Anderson Ranch and Black Canyon Facilities: Final Report.

    Energy Technology Data Exchange (ETDEWEB)

    Meuleman, G. Allyn

    1987-06-01

    Under direction of the Pacific Northwest Electric Power Planning and Conservation Act of 1980, and the subsequent Northwest Power Planning Council's Columbia River Basin Fish and Wildlife Program, projects have been developed in Idaho to mitigate the impacts to wildlife habitat and production due to the development and operation of the Anderson Ranch and Black Canyon Facilities (i.e., dam, power plant, and reservoir areas). The Anderson Ranch Facility covered about 4812 acres of wildlife habitat while the Black Canyon Facility covered about 1115 acres. These acreages include dam and power plant staging areas. A separate mitigation plan has been developed for each facility. A modified Habitat Evaluation Procedure (HEP) was used to assess the benefits of the mitigation plans to wildlife. The interagency work group used the target species Habitat Units (HU's) lost at each facility as a guideline during the mitigation planning process, while considering the needs of wildlife in the areas. Totals of 9619 and 2238 target species HU's were estimated to be lost in the Anderson Ranch and Black Canyon Facility areas, respectively. Through a series of projects, the mitigation plans will provide benefits of 9620 target species HU's to replace Anderson Ranch wildlife impacts and benefits of 2195 target species HU's to replace Black Canyon wildlife impacts. Target species to be benefited by the Anderson Ranch and/or Black Canyon mitigation plans include the mallard, Canada goose, mink, yellow warbler, black-capped chickadee, ruffed grouse, mule deer, blue grouse, sharp-tailed grouse, ring-necked pheasant, and peregrine falcon.

  16. Rydberg Impurity Probes in Ultracold Gases

    Science.gov (United States)

    Mitchison, Mark; Johnson, Tomi; Plenio, Martin; Jaksch, Dieter

    2015-03-01

    Impurities immersed in ultracold gases can act as highly sensitive, tunable and potentially non-destructive probes of their environment. In this setting, we propose the use of an atomic impurity in a Rydberg state to measure density fluctuations via Ramsey interferometry. The rapid collisional dynamics of the light Rydberg electron interacting with the heavy gas particles, combined with the capability to quickly change the state of the impurity with optical pulses, make such a probe ideal for measuring local properties of ultracold gases. Our proposed device promises angle-resolved density measurements with sub-micron spatial resolution, and with no need to integrate over the line of sight. We outline how Rydberg impurity probes could be applied to study various interesting quantum states of current experimental relevance. We also discuss the possibility of using multiple Rydberg atoms to extract the spatial pair distribution function g (2) (r). Our work is placed in the context of other recently proposed impurity-based probes.

  17. Impurities in the Lithium Tokamak Experiment

    Science.gov (United States)

    Boyle, D. P.; Bell, R. E.; Kaita, R.; Majeski, R.; Biewer, T. M.; Gray, T. K.; Tritz, K.; Widmann, K.

    2014-10-01

    The Lithium Tokamak Experiment (LTX) is designed to study the low-recycling regime through the use of close-fitting, lithium-coated, heatable shell quadrants surrounding the plasma volume. Lithium coatings can getter and bury impurities, but they can also become covered by impurity compounds. Liquefied coatings can both dissolve impurity compounds and bring them to the surface, while sputtering and evaporation rates increase strongly with temperature. Here, we use spectroscopic measurements to assess the effects of varying wall conditions on plasma impurities, mainly Li, C, and O. A passive Doppler spectroscopy system measures toroidal and poloidal impurity profiles using fixed-wavelength and variable-wavelength visible spectrometers. In addition, survey and high-resolution extreme ultraviolet spectrometers detect emission from higher charge states. Preliminary results show that fresh Li coatings generally reduced C and O emission. C emission decreased sharply following the first solid Li coatings. Inverted toroidal profiles in a discharge with solid Li coatings show peaked Li III emissivity and temperature profiles. Recently, experiments with fresh liquid coatings led to especially strong O reduction. Results from these and additional experiments will be presented. Supported by US DOE Contracts DE-AC02-09CH11466 and DE-AC05-00OR22725.

  18. Gettering of metal impurities in silicon

    Energy Technology Data Exchange (ETDEWEB)

    Schroeter, W.; Spiecker, E.; Apel, M. [Universitaet Goettingen (Germany)

    1995-08-01

    Gettering means the removal of metallic impurities from the device-active area of the wafer by transport to a predesigned region-called gettering layer (GL). We introduce an interface at z = d{sub GL}, at which the effect of the gettering mechanism on the metal impurity distribution in the wafer is quantified, e.g. by specifying currents or by interfacial reactions of metal impurities, self interstitials etc. between GL and wafer. In response metal impurities will diffuse out of the wafer into the gettering layer. Following such a concept, in general three species of the metal impurity (M) are involved in gettering: M{sub p} {l_arrow} M{sub i} {l_arrow} M{sub GL}. M{sub p} denotes immobile species in the wafer, which are precipitated into suicides or segregated at extended defects or whose diffusivity is too small to contribute noticeably to transport during the gettering procedure - like many substitutional metal species.

  19. Theoretical study of impurity effects in iron-based superconductors

    Science.gov (United States)

    Navarro Gastiasoro, Maria; Hirschfeld, Peter; Andersen, Brian

    2013-03-01

    Several open questions remain unanswered for the iron-based superconductors (FeSC), including the importance of electronic correlations and the symmetry of the superconducting order parameter. Motivated by recent STM experiments which show a fascinating variety of resonant defect states in FeSC, we adopt a realistic five-band model including electronic Coulomb correlations to study local effects of disorder in the FeSC. In order to minimize the number of free parameters, we use the pairing interactions obtained from spin-fluctuation exchange to determine the homogeneous superconducting state. The ability of local impurity potentials to induce resonant states depends on their scattering strength Vimp; in addition, for appropriate Vimp, such states are associated with local orbital- and magnetic order. We investigate the density of states near such impurities and show how tunneling experiments may be used to probe local induced order. In the SDW phase, we show how C2 symmetry-breaking dimers are naturally formed around impurities which also form cigar-like (pi,pi) structures embedded in the (pi,0) magnetic bulk phase. Such electronic dimers have been shown to be candidates for explaining the so-called nematogens observed previously by QPI in Co-doped CaFe2As2.

  20. Impurity density derivation from bandpass soft x-ray tomography: applicability, perspectives and limitations

    International Nuclear Information System (INIS)

    Deriving impurity density from local soft x-ray (SXR) emissivity (reconstructed by background-subtracted tomography during trace injections) by line-emission modelling leads to uncertainties due to the unknown ionization balance, especially for medium-Z impurities. This paper proposes a paradigm shift in the way SXR tomography is used, from one that maximizes signal at the expense of uncertain modelling to one that relies on sharper spectral resolution used to better understand what exactly is being measured. It is indeed shown that the measured SXR emissivity of an impurity may be robust with respect to changes to its unknown ionization balance (i.e. with respect to impurity transport) under two conditions. First, the electron temperature must be above a certain threshold (typically 4–5 keV or higher for metals like Ni or Fe). Second, the spectral response of SXR detectors must have a tuneable band-pass and should focus on a specific spectral region for each considered impurity. Both these conditions aim at maximizing the Bremsstrahlung contribution, which has the weakest dependence on ion charge. Prospective applications for several impurities are discussed as well as practical limitations. Since this method offers diagnostics-designing potential, possible technological solutions are also discussed. (paper)

  1. Impurity and particle control for INTOR

    International Nuclear Information System (INIS)

    The INTOR impurity control system studies have been focused on the development of an impurity control system which would be able to provide the necessary heat removal and He pumping while satisfying the requirements for (1) minimum plasma contamination by impurities, (2) reasonable component lifetime (approx. 1 year), and (3) minimum size and cost. The major systems examined were poloidal divertors and pumped limiters. The poloidal divertor was chosen as the reference option since it offered the possibility of low sputtering rates due to the formation of a cool, dense plasma near the collector plates. Estimates of the sputtering rates associated with pumped limiters indicated that they would be too high for a reasonable system. Development of an engineering design concept was done for both the poloidal divertor and the pumped limiter

  2. On charged impurity structures in liquid helium

    International Nuclear Information System (INIS)

    The thermoluminescence spectra of impurity-helium condensates (IHC) submerged in superfluid helium have been observed for the first time. Thermoluminescence of impurity-helium condensates submerged in superfluid helium is explained by neutralization reactions occurring in impurity nanoclusters. Optical spectra of excited products of neutralization reactions between nitrogen cations and thermoactivated electrons were rather different from the spectra observed at higher temperatures, when the luminescence due to nitrogen atom recombination dominates. New results on current detection during the IHC destruction are presented. Two different mechanisms of nanocluster charging are proposed to describe the phenomena observed during preparation and warm-up of IHC samples in bulk superfluid helium, and destruction of IHC samples out of liquid helium.

  3. Triangular Ising antiferromagnets with quenched nonmagnetic impurities.

    Science.gov (United States)

    Tang, Huai-Lei; Zhu, Yi; Yang, Guo-Hong; Jiang, Ying

    2010-05-01

    In a random spin system, the cooperation of randomness and frustration will lead to a spin-glass phase. However, in geometrically frustrated spin systems, quenched nonmagnetic impurities lift frustration locally. This makes randomness and frustration in these systems as competitors rather than cooperators. By mapping the dilute triangular Ising antiferromagnetic system to elastic array of noncrossing strings, we find that the nonmagnetic impurities in the spin system play roles of pinning centers in the string system. Calculation shows that in the ground state of this system, the spin-glass correlation is power-law decayed, quite different from the standard behavior of spin glass in which spin-glass correlation between two spins at infinite distance tends to a finite value. This indicates that triangular Ising antiferromagnets with quenched nonmagnetic impurities cannot be a spin glass. Instead, in the ground states, they present properties of vortex glass. PMID:20866185

  4. Characteristics of impurity-induced pseudogap

    Science.gov (United States)

    Numata, Yoshinori; Uto, Tatsuro; Matuda, Azusa

    2016-05-01

    We have performed STM/STS measurements on a single crystal of Bi2.1Sr1.9Ca (Cu1-xCox) 2O8+δ (Co-Bi2212), to reveal impurity effects on the pseudogap in cuprate high-Tc superconductors. We report a drastic change in the temperature dependence of a pseudogap and in the density of states (DOS) modulation with a 4a period, in a certain doping range. In the Co 4% substituted samples, the pseudogap gradually closed like a gap of a BCS superconductor for slightly overdoped and overdoped regime, while their low temperature values were enhanced due to impurity. In addition, a disappearance of a 4a periodic modulation and a development of new modulation were observed in the DOS spatial distribution. These results indicate an intimate relation between the DOS modulation and the pseudogap, and qualitative difference in the impurity enhanced pseudogap and conventional one.

  5. Removal Of Volatile Impurities From Copper Concentrates

    Energy Technology Data Exchange (ETDEWEB)

    Winkel, L.; Schuler, A.; Frei, A.; Sturzenegger, M.

    2005-03-01

    To study the removal of volatile impurities from two different copper concentrates they have been heated on a thermo balance to temperatures between 900 and 1500 C. This sample treatment revealed that both concentrates undergo strong weight losses at 500 and 700 C. They were attributed to the removal of sulfur. Elemental analyses of the residues by ICP spectrometry have shown that the thermal treatment efficiently removes the volatile impurities. Already below 900 C most of the arsenic is removed by evaporation, the largest fraction of lead and zinc is removed in the temperature interval of 1300-1500 C. It was observed that quartz in the concentrate leads to the formation of a silicon-enriched phase besides a metal rich sulfide phase. The former is interpreted as an early stage of a silicate slag. Elemental analysis showed that the formation of this distinct slag phase does not hinder the efficient removal of volatile impurities. (author)

  6. Effect of impurity radiation on tokamak equilibrium

    International Nuclear Information System (INIS)

    The energy loss from a tokamak plasma due to the radiation from impurities is of great importance in the overall energy balance. Taking the temperature dependence of this loss for two impurities characteristic of those present in existing tokamak plasmas, the condition for radial power balance is derived. For the impurities considered (oxygen and iron) it is found that the radiation losses are concentrated in a thin outer layer of the plasma and the equilibrium condition places an upper limit on the plasma paraticle number density in this region. This limiting density scales with mean current density in the same manner as is experimentally observed for the peak number density of tokamak plasmas. The stability of such equilibria is also discussed. (author)

  7. Impurity transport and control in ASDEX Upgrade

    International Nuclear Information System (INIS)

    Impurity transport parameters of Si and Ne have been determined for H-mode and improved H-mode plasmas with and without central wave heating. The diffusion coefficient D is always anomalous in the edge region and about neoclassical in the centre, when central heating powers are low. Sufficient central wave heating increases the central D and leads also to a flattening of the central density profile. Accumulation of W has been studied in improved H-mode discharges. It strongly depends on the density peaking, and can become severe for purely NBI heated discharges with peaked density profiles, while for flat density profiles, which are achieved with sufficient central wave heating, the W concentrations are flat. Extrapolations of the found impurity behaviour were used to guide a case study of particle transport for the ITER-FEAT inductive operation reference scenario. It suggests sufficient anomalous transport and thus negligible impurity accumulation in the inner plasma region. (author)

  8. Correlations between locked modes and impurity influxes

    Energy Technology Data Exchange (ETDEWEB)

    Fishpool, G.M. [Commission of the European Communities, Abingdon (United Kingdom). JET Joint Undertaking; Lawson, K.D. [UKAEA Culham Lab., Abingdon (United Kingdom)

    1994-07-01

    An analysis of pulses that were disturbed by medium Z impurity influxes (Cl, Cr, Fe and Ni) recorded during the 91/92 JET operations, has demonstrated that such influxes can result in MHD modes which subsequently ``lock``. A correlation is found between the power radiated by the influx and the time difference between the start of the influx and the beginning of the locked mode. The growth in the amplitude of the locked mode itself can lead to further impurity influxes. A correlation is noted between intense influxes (superior to 10 MW) and the mode ``unlocking``. (authors). 4 refs., 4 figs.

  9. The electronic structure of impurities in semiconductors

    CERN Multimedia

    Nylandsted larsen, A; Svane, A

    2002-01-01

    The electronic structure of isolated substitutional or interstitial impurities in group IV, IV-IV, and III-V compound semiconductors will be studied. Mössbauer spectroscopy will be used to investigate the incorporation of the implanted isotopes on the proper lattice sites. The data can be directly compared to theoretical calculations using the LMTO scheme. Deep level transient spectroscopy will be used to identify the band gap levels introduced by metallic impurities, mainly in Si~and~Si$ _{x}$Ge$_{1-x}$. \\\\ \\\\

  10. Impurity diffusion of niobium in nickel

    International Nuclear Information System (INIS)

    Impurity diffusion of niobium in nickel has been studied employing sandwich type diffusion couples between pure nickel (99.99%) and Ni-4.6 at % Nb alloy, in the temperature range of 1200 to 1500 K. The concentration penetration profiles across the diffusion zone have been established by using electron probe micro analyser (EPMA). The chemical diffusion coefficients have been evaluated by employing Hall's analytical solution to Fick's law. The concentration dependence of these diffusion coefficients has been established and impurity diffusion coefficient of niobium in nickel DNb has been evaluated by extrapolating these values to zero mole fraction of niobium. (author). 11 refs., 2 figs

  11. Impurity radiation from medium density plasmas

    International Nuclear Information System (INIS)

    Impurity radiation from plasmas of densities typical of tokamaks and mirrors is examined for a variety of impurity species over a wide temperature range. Calculations indicate that radiative losses are enhanced during the early phase of the stripping process and that the radiation is much greater at temperatures characteristic of many electron atoms than had been generally recognized by the plasma physics community. These results are useful in the analysis of the energy balance in tokamaks and given important constraints on the choice of wall materials

  12. Plasma impurity-control studies in CTX

    International Nuclear Information System (INIS)

    In the past, magnetized coaxial gun generated Compact Toroids (CTs) have exhibited magnetic field and density lifetimes of about 250 to 350 μs and electron temperatures of about 10 eV. In recent experiments, after hydrogen discharge cleaning the gun and flux conserver surfaces, the lifetimes have been extended to 550 μs. This improvement in lifetime, together with spectroscopic and bolometric measurements, are consistent with the interpretation that the CT plasma losses are impurity dominated and that discharge cleaning is reducing the impurities. Details of these measurements are described as well as successful experiments which led to a more open flux conserver

  13. Influence of impurities on the crystallization of dextrose monohydrate

    Science.gov (United States)

    Markande, Abhay; Nezzal, Amale; Fitzpatrick, John; Aerts, Luc; Redl, Andreas

    2012-08-01

    The effects of impurities on dextrose monohydrate crystallization were investigated. Crystal nucleation and growth kinetics in the presence of impurities were studied using an in-line focused beam reflectance monitoring (FBRM) technique and an in-line process refractometer. Experimental data were obtained from runs carried out at different impurity levels between 4 and 11 wt% in the high dextrose equivalent (DE) syrup. It was found that impurities have no significant influence on the solubility of dextrose in water. However, impurities have a clear influence on the nucleation and growth kinetics of dextrose monohydrate crystallization. Nucleation and growth rate were favored by low levels of impurities in the syrup.

  14. Linear and Non-linear Rabi Oscillations of a Two-Level System Resonantly Coupled to an Anderson-Localized Mode

    CERN Document Server

    Bachelard, Nicolas; Sebbah, Patrick; Vanneste, Christian

    2014-01-01

    We use time-domain numerical simulations of a two-dimensional (2D) scattering system to study the interaction of a collection of emitters resonantly coupled to an Anderson-localized mode. For a small electric field intensity, we observe the strong coupling between the emitters and the mode, which is characterized by linear Rabi oscillations. Remarkably, a larger intensity induces non-linear interaction between the emitters and the mode, referred to as the dynamical Stark effect, resulting in non-linear Rabi oscillations. The transition between both regimes is observed and an analytical model is proposed which accurately describes our numerical observations.

  15. Startup impurity diagnostics in Wendelstein 7-X stellarator in the first operational phase

    Science.gov (United States)

    Thomsen, H.; Langenberg, A.; Zhang, D.; Bertschinger, G.; Biedermann, C.; Biel, W.; Burhenn, R.; Buttenschön, B.; Grosser, K.; König, R.; Kubkowska, M.; Marchuk, O.; Pablant, N.; Ryc, L.; Pedersen, T. S.; the W7-X Team

    2015-10-01

    An essential element for stationary stellarator operation is the understanding of the impurity transport behavior. Neoclassical theory predicts an impurity transport towards the plasma core for the standard ion root regime in stellarators [1,2]. The performance of a quasi-stationary device like Wendelstein 7-X stellarator (W7-X, presently in the commissioning phase in Greifswald, Germany) could be limited in case of strong impurity accumulation. Therefore, a set of plasma diagnostics is foreseen to obtain key experimental quantities for the neoclassical transport modeling as ion temperature profile, density gradients and impurity concentration [1]. The core impurity content is monitored by the High Efficiency eXtreme ultraviolet Overview Spectrometer system (HEXOS) [2], covering the wavelength range 2.5-160 nm (intermediate ionization states of all relevant heavy intrinsic impurity species) with high spectral resolution and a time resolution of 1 ms, adequate for transport analysis. Impurity radiation at shorter wave lengths (4 nm-0.06 nm) will be monitored with the SX pulse height analysis system (PHA) [3]. The ion temperature profile can be deduced from inversion of data from the High Resolution X-ray Imaging Spectrometer (HR-XIS), which measures the concentration and temperature of argon tracer gas in helium-like ionization stages [6,7,8]. A second X-ray Imaging Crystal Spectrometer (XICS), which will additionally provide the poloidal ion rotation velocity, is under preparation [8,9]. The total radiation will be measured by two bolometer cameras [10,11]. The status of the impurity diagnostics for the first operational phase in W7-X is summarized in this paper and an outlook for the next experimental campaign is given.

  16. Electron and impurity transport studies in the TCV Tokamak

    International Nuclear Information System (INIS)

    In this thesis electron and impurity transport are studied in the Tokamak à Configuration Variable (TCV) located at CRPP-EPFL in Lausanne. Understanding particle transport is primordial for future nuclear fusion power plants. Modeling of experiments in many specific plasma scenarios can help to understand the common elements of the physics at play and to interpret apparently contradictory experiments on the same machine and across different machines. The first part of this thesis deals with electron transport in TCV high confinement mode plasmas. It was observed that the electron density profile in these plasmas flatten when intense electron heating is applied, in contrast to observations on other machines where the increase of the profile peakedness was reported. It is shown with quasi-linear gyrokinetic simulations that this effect, usually interpreted as collisionality dependence, stems from the combined effect of many plasma parameters. The influence of the collisionality, electron to ion temperature ratio, the ratio of temperature gradients, and the Ware-pinch are studied with detailed parameter scans. It is shown that the complex interdependence of the various plasma parameters is greatly simplified when the simulation results are interpreted as a function of the average frequency of the main modes contributing to radial transport. In this way the model is able to explain the experimental results. It was also shown that the same basic understanding is at play in L-modes, H-modes and electron internal transport barriers. The second part of the thesis is devoted to impurity transport. A multi-purpose gas injection system is developed, commissioned and calibrated. It is shown that the system is capable of massive gas injections to provoke disruptions and delivering small puffs of gaseous impurities for perturbative transport experiments. This flexible tool is exploited in a series of impurity transport measurements with argon and neon injections. The impurities

  17. Impure Heisenberg systems with biquadratic interactions

    Science.gov (United States)

    Chakraborty, K. G.

    1980-08-01

    The purpose of the present paper is to study an impure Heisenberg ferromagnet governed by the Hamiltonian H=-Ji,Δ[S-->i.S-->i+Δ+α(S-->i.S-->i+Δ)2]-2J0Δ[S-->0.S-->Δ+α0(S-->0.S-->Δ)2], where J is the host-host bilinear exchange constant, 2(J+J0) is the host-impurity bilinear exchange constant, α and α0 being the corresponding biquadratic coupling parameters, and Δ, a nearest-neighbor vector. S--> and S-->0 are the host and the impurity spins, respectively. Through utilization of the Dyson transformation, it is shown that at low temperatures the effect of the biquadratic terms is simply to renormalize the bilinear exchange constants J and J0 by 1+2αS(S-1) and 1+α0(2SS0-S-S0), respectively. Some qualitative discussions on the scattering processes are presented. The method of Green's function is then employed to discuss the criteria for the existence of localized modes in the system. The situations appearing in KMnF3, RbMnF3, KNiF3, and MnF2 doped by impurities are critically examined. Some numerical estimates of the biquadratic parameters α and α0 are also made which are found to agree satisfactorily with those obtained by previous authors.

  18. Synthesis and Identification of Selected Impurities

    International Nuclear Information System (INIS)

    Non-active substances undesired, but often unavoidable compounds accompanying target active ingredients in various pesticide formulations have been synthesized for supporting product registration and evaluation of the total toxicological and physicochemical properties of formulated products. The synthesis and structural characterization of various impurities of pesticide active ingredients are described and illustrated by IR, NMR, GC and GC/MS data. (author)

  19. Liability coverage under the Price-Anderson Act for high level waste shipments and disposal

    International Nuclear Information System (INIS)

    The Price-Anderson Act provides the basis for a national system of liability protection for accidents arising out of nuclear activities. Private nuclear liability insurance and/or government indemnity is provided to certain Nuclear Regulatory Commission (NRC) licensees (principally operators of nuclear reactors) and certain Department of Energy (DOE) contractors (those whose activities DOE considers involve a risk of public liability for a substantial nuclear incident). As presently envisioned, both the coverage extended by the NRC to its licensees shipping spent fuel from reactors and the indemnity coverage extended by the DOE to its contractors operating a DOE repository under the Nuclear Waste Policy Act will be utilized to provide public liability protection for spent fuel shipments and disposal. Increased attention is being given to assuring a seamless web of protection provided under the Price-Anderson Act to Federal licensees and contractors

  20. Experimental observation of Anderson localization in laser-kicked molecular rotors

    CERN Document Server

    Bitter, Martin

    2016-01-01

    We observe and study the phenomenon of Anderson localization in a system of true quantum kicked rotors. Nitrogen molecules in a supersonic molecular jet are cooled down to 27~K and are rotationally excited by a periodic train of 24~high-intensity femtosecond pulses. Exponential distribution of the molecular angular momentum - the most unambiguous signature of Anderson localization - is measured directly by means of coherent Raman scattering. We demonstrate the suppressed growth of the molecular rotational energy with the number of laser kicks and study the dependence of the localization length on the kick strength. Both timing and amplitude noise in the pulse train is shown to destroy the localization and revive the diffusive growth of angular momentum.