Quantum theory of parametric excitation in plasmas with the driving field space dispersion

International Nuclear Information System (INIS)

Vo Hong Anh

1998-11-01

A development of the quantum theory of parametric wave excitation in plasmas is presented to take into account the effects of space dispersion of the driving external fields. The quantum equation of motion method with the use of appropriate matrix formalism leads to the system of dispersion equations for the eigenmodes of vibrations. Calculations show the enlargement of the excitable waves region both in wave number values and directions as compared to the case of dipole approximation considered earlier. (author)

Validation of missed space-group symmetry in X-ray powder diffraction structures with dispersion-corrected density functional theory

DEFF Research Database (Denmark)

Hempler, Daniela; Schmidt, Martin U.; Van De Streek, Jacco

2017-01-01

More than 600 molecular crystal structures with correct, incorrect and uncertain space-group symmetry were energy-minimized with dispersion-corrected density functional theory (DFT-D, PBE-D3). For the purpose of determining the correct space-group symmetry the required tolerance on the atomic...... with missed symmetry were investigated by dispersion-corrected density functional theory. In 98.5% of the cases the correct space group is found....

Theory of Nonlinear Dispersive Waves and Selection of the Ground State

International Nuclear Information System (INIS)

Soffer, A.; Weinstein, M.I.

2005-01-01

A theory of time-dependent nonlinear dispersive equations of the Schroedinger or Gross-Pitaevskii and Hartree type is developed. The short, intermediate and large time behavior is found, by deriving nonlinear master equations (NLME), governing the evolution of the mode powers, and by a novel multitime scale analysis of these equations. The scattering theory is developed and coherent resonance phenomena and associated lifetimes are derived. Applications include Bose-Einstein condensate large time dynamics and nonlinear optical systems. The theory reveals a nonlinear transition phenomenon, 'selection of the ground state', and NLME predicts the decay of excited state, with half its energy transferred to the ground state and half to radiation modes. Our results predict the recent experimental observations of Mandelik et al. in nonlinear optical waveguides

Rainbows without unicorns: metric structures in theories with modified dispersion relations

International Nuclear Information System (INIS)

Lobo, Iarley P.; Loret, Niccolo; Nettel, Francisco

2017-01-01

Rainbow metrics are a widely used approach to the metric formalism for theories with modified dispersion relations. They have had a huge success in the quantum gravity phenomenology literature, since they allow one to introduce momentum-dependent space-time metrics into the description of systems with a modified dispersion relation. In this paper, we introduce the reader to some realizations of this general idea: the original rainbow metrics proposal, the momentum-space-inspired metric and a Finsler geometry approach. As the main result of this work we also present an alternative definition of a four-velocity dependent metric which allows one to handle the massless limit. This paper aims to highlight some of their properties and how to properly describe their relativistic realizations. (orig.)

Rainbows without unicorns: metric structures in theories with modified dispersion relations

Science.gov (United States)

Lobo, Iarley P.; Loret, Niccoló; Nettel, Francisco

2017-07-01

Rainbow metrics are a widely used approach to the metric formalism for theories with modified dispersion relations. They have had a huge success in the quantum gravity phenomenology literature, since they allow one to introduce momentum-dependent space-time metrics into the description of systems with a modified dispersion relation. In this paper, we introduce the reader to some realizations of this general idea: the original rainbow metrics proposal, the momentum-space-inspired metric and a Finsler geometry approach. As the main result of this work we also present an alternative definition of a four-velocity dependent metric which allows one to handle the massless limit. This paper aims to highlight some of their properties and how to properly describe their relativistic realizations.

Rainbows without unicorns: metric structures in theories with modified dispersion relations

Energy Technology Data Exchange (ETDEWEB)

Lobo, Iarley P. [Universita ' ' La Sapienza' ' , Dipartimento di Fisica, Rome (Italy); ICRANet, Pescara (Italy); CAPES Foundation, Ministry of Education of Brazil, Brasilia (Brazil); Universidade Federal da Paraiba, Departamento de Fisica, Joao Pessoa, PB (Brazil); INFN Sezione Roma 1 (Italy); Loret, Niccolo [Ruder Boskovic Institute, Division of Theoretical Physics, Zagreb (Croatia); Nettel, Francisco [Universita ' ' La Sapienza' ' , Dipartimento di Fisica, Rome (Italy); Universidad Nacional Autonoma de Mexico, Instituto de Ciencias Nucleares, Mexico (Mexico); INFN Sezione Roma 1 (Italy)

2017-07-15

Rainbow metrics are a widely used approach to the metric formalism for theories with modified dispersion relations. They have had a huge success in the quantum gravity phenomenology literature, since they allow one to introduce momentum-dependent space-time metrics into the description of systems with a modified dispersion relation. In this paper, we introduce the reader to some realizations of this general idea: the original rainbow metrics proposal, the momentum-space-inspired metric and a Finsler geometry approach. As the main result of this work we also present an alternative definition of a four-velocity dependent metric which allows one to handle the massless limit. This paper aims to highlight some of their properties and how to properly describe their relativistic realizations. (orig.)

Combining a dispersal model with network theory to assess habitat connectivity.

Science.gov (United States)

Lookingbill, Todd R; Gardner, Robert H; Ferrari, Joseph R; Keller, Cherry E

2010-03-01

Assessing the potential for threatened species to persist and spread within fragmented landscapes requires the identification of core areas that can sustain resident populations and dispersal corridors that can link these core areas with isolated patches of remnant habitat. We developed a set of GIS tools, simulation methods, and network analysis procedures to assess potential landscape connectivity for the Delmarva fox squirrel (DFS; Sciurus niger cinereus), an endangered species inhabiting forested areas on the Delmarva Peninsula, USA. Information on the DFS's life history and dispersal characteristics, together with data on the composition and configuration of land cover on the peninsula, were used as input data for an individual-based model to simulate dispersal patterns of millions of squirrels. Simulation results were then assessed using methods from graph theory, which quantifies habitat attributes associated with local and global connectivity. Several bottlenecks to dispersal were identified that were not apparent from simple distance-based metrics, highlighting specific locations for landscape conservation, restoration, and/or squirrel translocations. Our approach links simulation models, network analysis, and available field data in an efficient and general manner, making these methods useful and appropriate for assessing the movement dynamics of threatened species within landscapes being altered by human and natural disturbances.

Calibration of Discrete Random Walk (DRW) Model via G.I Taylor's Dispersion Theory

Science.gov (United States)

Javaherchi, Teymour; Aliseda, Alberto

2012-11-01

Prediction of particle dispersion in turbulent flows is still an important challenge with many applications to environmental, as well as industrial, fluid mechanics. Several models of dispersion have been developed to predict particle trajectories and their relative velocities, in combination with a RANS-based simulation of the background flow. The interaction of the particles with the velocity fluctuations at different turbulent scales represents a significant difficulty in generalizing the models to the wide range of flows where they are used. We focus our attention on the Discrete Random Walk (DRW) model applied to flow in a channel, particularly to the selection of eddies lifetimes as realizations of a Poisson distribution with a mean value proportional to κ / ɛ . We present a general method to determine the constant of this proportionality by matching the DRW model dispersion predictions for fluid element and particle dispersion to G.I Taylor's classical dispersion theory. This model parameter is critical to the magnitude of predicted dispersion. A case study of its influence on sedimentation of suspended particles in a tidal channel with an array of Marine Hydrokinetic (MHK) turbines highlights the dependency of results on this time scale parameter. Support from US DOE through the Northwest National Marine Renewable Energy Center, a UW-OSU partnership.

Mathematical Theory of Dispersion-Managed Optical Solitons

CERN Document Server

Biswas, Anjan; Edwards, Matthew

2010-01-01

"Mathematical Theory of Dispersion-Managed Optical Solitons" discusses recent advances covering optical solitons, soliton perturbation, optical cross-talk, Gabitov-Turitsyn Equations, quasi-linear pulses, and higher order Gabitov-Turitsyn Equations. Focusing on a mathematical perspective, the book bridges the gap between concepts in engineering and mathematics, and gives an outlook to many new topics for further research. The book is intended for researchers and graduate students in applied mathematics, physics and engineering and also it will be of interest to those who are conducting research in nonlinear fiber optics. Dr. Anjan Biswas is an Associate Professor at the Department of Applied Mathematics & Theoretical Physics, Delaware State University, Dover, DE, USA; Dr. Daniela Milovic is an Associate Professor at the Department of Telecommunications, Faculty of Electronic Engineering, University of Nis, Serbia; Dr. Matthew Edwards is the Dean of the School of Arts and Sciences at Alabama A & M Univ...

Coupled-oscillator theory of dispersion and Casimir-Polder interactions

Energy Technology Data Exchange (ETDEWEB)

Berman, P. R.; Ford, G. W. [Physics Department, University of Michigan, 450 Church Street, Ann Arbor, Michigan 48109-1040 (United States); Milonni, P. W. [Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Department of Physics and Astronomy, University of Rochester, Rochester, New York 14627 (United States)

2014-10-28

We address the question of the applicability of the argument theorem (of complex variable theory) to the calculation of two distinct energies: (i) the first-order dispersion interaction energy of two separated oscillators, when one of the oscillators is excited initially and (ii) the Casimir-Polder interaction of a ground-state quantum oscillator near a perfectly conducting plane. We show that the argument theorem can be used to obtain the generally accepted equation for the first-order dispersion interaction energy, which is oscillatory and varies as the inverse power of the separation r of the oscillators for separations much greater than an optical wavelength. However, for such separations, the interaction energy cannot be transformed into an integral over the positive imaginary axis. If the argument theorem is used incorrectly to relate the interaction energy to an integral over the positive imaginary axis, the interaction energy is non-oscillatory and varies as r{sup −4}, a result found by several authors. Rather remarkably, this incorrect expression for the dispersion energy actually corresponds to the nonperturbative Casimir-Polder energy for a ground-state quantum oscillator near a perfectly conducting wall, as we show using the so-called “remarkable formula” for the free energy of an oscillator coupled to a heat bath [G. W. Ford, J. T. Lewis, and R. F. O’Connell, Phys. Rev. Lett. 55, 2273 (1985)]. A derivation of that formula from basic results of statistical mechanics and the independent oscillator model of a heat bath is presented.

Coupled-oscillator theory of dispersion and Casimir-Polder interactions

International Nuclear Information System (INIS)

Berman, P. R.; Ford, G. W.; Milonni, P. W.

2014-01-01

We address the question of the applicability of the argument theorem (of complex variable theory) to the calculation of two distinct energies: (i) the first-order dispersion interaction energy of two separated oscillators, when one of the oscillators is excited initially and (ii) the Casimir-Polder interaction of a ground-state quantum oscillator near a perfectly conducting plane. We show that the argument theorem can be used to obtain the generally accepted equation for the first-order dispersion interaction energy, which is oscillatory and varies as the inverse power of the separation r of the oscillators for separations much greater than an optical wavelength. However, for such separations, the interaction energy cannot be transformed into an integral over the positive imaginary axis. If the argument theorem is used incorrectly to relate the interaction energy to an integral over the positive imaginary axis, the interaction energy is non-oscillatory and varies as r −4 , a result found by several authors. Rather remarkably, this incorrect expression for the dispersion energy actually corresponds to the nonperturbative Casimir-Polder energy for a ground-state quantum oscillator near a perfectly conducting wall, as we show using the so-called “remarkable formula” for the free energy of an oscillator coupled to a heat bath [G. W. Ford, J. T. Lewis, and R. F. O’Connell, Phys. Rev. Lett. 55, 2273 (1985)]. A derivation of that formula from basic results of statistical mechanics and the independent oscillator model of a heat bath is presented

Wave-equation dispersion inversion

KAUST Repository

Li, Jing; Feng, Zongcai; Schuster, Gerard T.

2016-01-01

We present the theory for wave-equation inversion of dispersion curves, where the misfit function is the sum of the squared differences between the wavenumbers along the predicted and observed dispersion curves. The dispersion curves are obtained

On the spectral theory and dispersive estimates for a discrete Schroedinger equation in one dimension

International Nuclear Information System (INIS)

Pelinovsky, D. E.; Stefanov, A.

2008-01-01

Based on the recent work [Komech et al., 'Dispersive estimates for 1D discrete Schroedinger and Klein-Gordon equations', Appl. Anal. 85, 1487 (2006)] for compact potentials, we develop the spectral theory for the one-dimensional discrete Schroedinger operator, Hφ=(-Δ+V)φ=-(φ n+1 +φ n-1 -2φ n )+V n φ n . We show that under appropriate decay conditions on the general potential (and a nonresonance condition at the spectral edges), the spectrum of H consists of finitely many eigenvalues of finite multiplicities and the essential (absolutely continuous) spectrum, while the resolvent satisfies the limiting absorption principle and the Puiseux expansions near the edges. These properties imply the dispersive estimates parallel e itH P a.c. (H) parallel l σ 2 →l -σ 2 -3/2 for any fixed σ>(5/2) and any t>0, where P a.c. (H) denotes the spectral projection to the absolutely continuous spectrum of H. In addition, based on the scattering theory for the discrete Jost solutions and the previous results by Stefanov and Kevrekidis [''Asymptotic behaviour of small solutions for the discrete nonlinear Schroedinger and Klein-Gordon equations,'' Nonlinearity 18, 1841 (2005)], we find new dispersive estimates parallel e itH P a.c. (H) parallel l 1 →l ∞ -1/3 , which are sharp for the discrete Schroedinger operators even for V=0

Invariant Theory for Dispersed Transverse Isotropy: An Efficient Means for Modeling Fiber Splay

Science.gov (United States)

Freed, alan D.; Einstein, Daniel R.; Vesely, Ivan

2004-01-01

Most soft tissues possess an oriented architecture of collagen fiber bundles, conferring both anisotropy and nonlinearity to their elastic behavior. Transverse isotropy has often been assumed for a subset of these tissues that have a single macroscopically-identifiable preferred fiber direction. Micro-structural studies, however, suggest that, in some tissues, collagen fibers are approximately normally distributed about a mean preferred fiber direction. Structural constitutive equations that account for this dispersion of fibers have been shown to capture the mechanical complexity of these tissues quite well. Such descriptions, however, are computationally cumbersome for two-dimensional (2D) fiber distributions, let alone for fully three-dimensional (3D) fiber populations. In this paper, we develop a new constitutive law for such tissues, based on a novel invariant theory for dispersed transverse isotropy. The invariant theory is based on a novel closed-form splay invariant that can easily handle 3D fiber populations, and that only requires a single parameter in the 2D case. The model is polyconvex and fits biaxial data for aortic valve tissue as accurately as the standard structural model. Modification of the fiber stress-strain law requires no re-formulation of the constitutive tangent matrix, making the model flexible for different types of soft tissues. Most importantly, the model is computationally expedient in a finite-element analysis.

Validation of experimental molecular crystal structures with dispersion-corrected density functional theory calculations

International Nuclear Information System (INIS)

Streek, Jacco van de; Neumann, Marcus A.

2010-01-01

The accuracy of a dispersion-corrected density functional theory method is validated against 241 experimental organic crystal structures from Acta Cryst. Section E. This paper describes the validation of a dispersion-corrected density functional theory (d-DFT) method for the purpose of assessing the correctness of experimental organic crystal structures and enhancing the information content of purely experimental data. 241 experimental organic crystal structures from the August 2008 issue of Acta Cryst. Section E were energy-minimized in full, including unit-cell parameters. The differences between the experimental and the minimized crystal structures were subjected to statistical analysis. The r.m.s. Cartesian displacement excluding H atoms upon energy minimization with flexible unit-cell parameters is selected as a pertinent indicator of the correctness of a crystal structure. All 241 experimental crystal structures are reproduced very well: the average r.m.s. Cartesian displacement for the 241 crystal structures, including 16 disordered structures, is only 0.095 Å (0.084 Å for the 225 ordered structures). R.m.s. Cartesian displacements above 0.25 Å either indicate incorrect experimental crystal structures or reveal interesting structural features such as exceptionally large temperature effects, incorrectly modelled disorder or symmetry breaking H atoms. After validation, the method is applied to nine examples that are known to be ambiguous or subtly incorrect

Dispersion theory and sum rules for the non-minimum phase problem in optical spectroscopy

International Nuclear Information System (INIS)

Peiponen, Kai-Erik

2009-01-01

Dispersion relations and sum rules for integer powers of an optical response function are given in the case of the non-minimum phase problem. These relations were obtained using the concept of the Hilbert transform and Blaschke product. The theory presented in this paper is useful both in basic and applied studies of non-minimum phase functions in optics, and also other fields of physics such as high energy physics.

Validation of molecular crystal structures from powder diffraction data with dispersion-corrected density functional theory (DFT-D)

DEFF Research Database (Denmark)

van de Streek, Jacco; Neumann, Marcus A

2014-01-01

In 2010 we energy-minimized 225 high-quality single-crystal (SX) structures with dispersion-corrected density functional theory (DFT-D) to establish a quantitative benchmark. For the current paper, 215 organic crystal structures determined from X-ray powder diffraction (XRPD) data and published...

Theory of pairwise coupling embedded in more general local dispersion relations

International Nuclear Information System (INIS)

Fuchs, V.; Bers, A.; Harten, L.

1985-01-01

Earlier work on the mode conversion theory by Fuchs, Ko, and Bers is detailed and expanded upon, and its relation to energy conservation is discussed. Given a local dispersion relation, D(ω; k, z) = 0, describing stable waves excited at an externally imposed frequency ω, a pairwise mode-coupling event embedded therein is extracted by expanding D(k, z) around a contour k = k/sub c/(z) given by partialD/partialk = 0. The branch points of D(k, z) = 0 are the turning points of a second-order differential-equation representation. In obtaining the fraction of mode-converted energy, the connection formula and conservation of energy must be used together. Also, proper attention must be given to distinguish cases for which the coupling disappears or persists upon confluence of the branches, a property which is shown to depend on the forward (v/sub g/v/sub ph/>0) or backward (v/sub g/v/sub ph/<0) nature of the waves. Examples occurring in ion-cyclotron and lower-hybrid heating are presented, illustrating the use of the theory

Electrokinetic investigations on the system polystyrene/aqueous electrolyte solution : verification of model theories on dilute and concentrated dispersions

NARCIS (Netherlands)

Put, van der A.G.

1980-01-01

This thesis presents a systematic experimental and theoretical study on electrokinetic and electroconducting properties of disperse systems. The increasing interest in transport processes through charged porous systems has recently brought about a corresponding growth of models and theories since

Perturbation theory in Lagrangian hydrodynamics for a cosmological fluid with velocity dispersion

International Nuclear Information System (INIS)

Tatekawa, Takayuki; Suda, Momoko; Maeda, Kei-ichi; Morita, Masaaki; Anzai, Hiroki

2002-01-01

We extensively develop a perturbation theory for nonlinear cosmological dynamics, based on the Lagrangian description of hydrodynamics. We solve the hydrodynamic equations for a self-gravitating fluid with pressure, given by a polytropic equation of state, using a perturbation method up to second order. This perturbative approach is an extension of the usual Lagrangian perturbation theory for a pressureless fluid, in view of the inclusion of the pressure effect, which should be taken into account on the occurrence of velocity dispersion. We obtain the first-order solutions in generic background universes and the second-order solutions in a wider range of a polytropic index, whereas our previous work gives the first-order solutions only in the Einstein-de Sitter background and the second-order solutions for the polytropic index 4/3. Using the perturbation solutions, we present illustrative examples of our formulation in one- and two-dimensional systems, and discuss how the evolution of inhomogeneities changes for the variation of the polytropic index

ω→π0γ* and ϕ→π0γ* transition form factors in dispersion theory

Science.gov (United States)

Schneider, Sebastian P.; Kubis, Bastian; Niecknig, Franz

2012-09-01

We calculate the ω→π0γ* and ϕ→π0γ* electromagnetic transition form factors based on dispersion theory, relying solely on a previous dispersive analysis of the corresponding three-pion decays and the pion vector form factor. We compare our findings to recent measurements of the ω→π0μ+μ- decay spectrum by the NA60 collaboration, and strongly encourage experimental investigation of the Okubo-Zweig-Iizuka forbidden ϕ→π0ℓ+ℓ- decays in order to understand the strong deviations from vector-meson dominance found in these transition form factors.

Dispersion and damping of two-dimensional dust acoustic waves: theory and simulation

International Nuclear Information System (INIS)

Upadhyaya, Nitin; Miskovic, Z L; Hou, L-J

2010-01-01

A two-dimensional generalized hydrodynamics (GH) model is developed to study the full spectrum of both longitudinal and transverse dust acoustic waves (DAW) in strongly coupled complex (dusty) plasmas, with memory-function-formalism being implemented to enforce high-frequency sum rules. Results are compared with earlier theories (such as quasi-localized charge approximation and its extended version) and with a self-consistent Brownian dynamics simulation. It is found that the GH approach provides a good account, not only of dispersion relations, but also of damping rates of the DAW modes in a wide range of coupling strengths, an issue hitherto not fully addressed for dusty plasmas.

Dispersal of sticky particles

Science.gov (United States)

Reddy, Ramana; Kumar, Sanjeev

2007-12-01

In this paper, we show through simulations that when sticky particles are broken continually, particles are dispersed into fine dust only if they are present in a narrow range of volume fractions. The upper limit of this range is 0.20 in the 2D and 0.10 in the 3D space. An increase in the dimensionality of space reduces the upper limit nearly by a factor of two. This scaling holds for dispersal of particles in hyperdimensional space of dimensions up to ten, the maximum dimension studied in this work. The maximum values of volume fractions obtained are significantly lower than those required for close packing and random packing of discs in 2D and spheres in 3D space. These values are also smaller than those required for critical phenomena of cluster percolation. The results obtained are attributed to merger cascades of sticky particles, triggered by breakup events. A simple theory that incorporates this cascade is developed to quantitatively explain the observed scaling of the upper limit with the dimensionality of space. The theory also captures the dynamics of the dispersal process in the corresponding range of particle volume fractions. The theory suggests that cascades of order one and two predominantly decide the upper limit for complete dispersal of particles.

Dispersion self-energy of the electron

International Nuclear Information System (INIS)

Hawton, M.

1991-01-01

Electron mass renormalization and the Lamb shift have been investigated using the dispersion self-energy formalism. If shifts of both the electromagnetic field and quantum-mechanical transitions frequencies are considered, absorption from the electromagnetic field is canceled by emission due to atomic fluctuations. The frequencies of all modes are obtained from the self-consistency condition that the field seen by the electron is the same as the field produced by the expectation value of current. The radiation present can thus be viewed as arising from emission and subsequent reabsorption by matter. As developed here, the numerical predictions of dispersion theory are identical to those of quantum electrodynamics. The physical picture implied by dispersion theory is discussed in the context of semiclassical theories and quantum electrodynamics

Glass transition in soft-sphere dispersions

International Nuclear Information System (INIS)

RamIrez-Gonzalez, P E; Medina-Noyola, M

2009-01-01

The concept of dynamic equivalence among mono-disperse soft-sphere fluids is employed in the framework of the self-consistent generalized Langevin equation (SCGLE) theory of colloid dynamics to calculate the ideal glass transition phase diagram of model soft-sphere colloidal dispersions in the softness-concentration state space. The slow dynamics predicted by this theory near the glass transition is compared with available experimental data for the decay of the intermediate scattering function of colloidal dispersions of soft-microgel particles. Increasing deviations from this simple scheme occur for increasingly softer potentials, and this is studied here using the Rogers-Young static structure factor of the soft-sphere systems as the input of the SCGLE theory, without assuming a priori the validity of the equivalence principle above.

Analysis of the neutrons dispersion in a semi-infinite medium based in transport theory and the Monte Carlo method

International Nuclear Information System (INIS)

Arreola V, G.; Vazquez R, R.; Guzman A, J. R.

2012-10-01

In this work a comparative analysis of the results for the neutrons dispersion in a not multiplicative semi-infinite medium is presented. One of the frontiers of this medium is located in the origin of coordinates, where a neutrons source in beam form, i.e., μο=1 is also. The neutrons dispersion is studied on the statistical method of Monte Carlo and through the unidimensional transport theory and for an energy group. The application of transport theory gives a semi-analytic solution for this problem while the statistical solution for the flow was obtained applying the MCNPX code. The dispersion in light water and heavy water was studied. A first remarkable result is that both methods locate the maximum of the neutrons distribution to less than two mean free trajectories of transport for heavy water, while for the light water is less than ten mean free trajectories of transport; the differences between both methods is major for the light water case. A second remarkable result is that the tendency of both distributions is similar in small mean free trajectories, while in big mean free trajectories the transport theory spreads to an asymptote value and the solution in base statistical method spreads to zero. The existence of a neutron current of low energy and toward the source is demonstrated, in contrary sense to the neutron current of high energy coming from the own source. (Author)

Three-particle physics and dispersion relation theory

CERN Document Server

Anisovich, A V; Matveev, M A; Nikonov, V A; Nyiri, J; Sarantsev, A V

2013-01-01

The necessity of describing three-nucleon and three-quark systems have led to a constant interest in the problem of three particles. The question of including relativistic effects appeared together with the consideration of the decay amplitude in the framework of the dispersion technique. The relativistic dispersion description of amplitudes always takes into account processes connected with the investigated reaction by the unitarity condition or by virtual transitions; in the case of three-particle processes they are, as a rule, those where other many-particle states and resonances are produced. The description of these interconnected reactions and ways of handling them is the main subject of the book.

Giant magnon solution and dispersion relation in string theory in AdS3×S3×T4 with mixed flux

International Nuclear Information System (INIS)

Hoare, B.; Stepanchuk, A.; Tseytlin, A.A.

2014-01-01

We address the question of the exact form of the dispersion relation for light-cone string excitations in string theory in AdS 3 ×S 3 ×T 4 with mixed R–R and NS–NS 3-form fluxes. The analogy with string theory in AdS 5 ×S 5 suggests that in addition to the data provided by the perturbative near-BMN expansion and symmetry algebra considerations there is another source of information for the dispersion relation – the semiclassical giant magnon solution. In earlier work in (arXiv:1303.1037) and (arXiv:1304.4099) we found that the symmetry algebra constraints, which are consistent with a perturbative expansion, do not completely determine the form of the dispersion relation. The aim of the present paper is to fix the dispersion relation by constructing a generalisation of the known dyonic giant magnon soliton on S 3 to the presence of a non-zero NS–NS flux described by a WZ term in the string action (with coefficient q). We find that the angular momentum of this soliton gets shifted by a term linear in world-sheet momentum p. We also discuss the symmetry algebra of the string light-cone S-matrix and show that the exact dispersion relation, which should have the correct perturbative BMN and semiclassical giant magnon limits, should also contain such a linear momentum term. The simplicity of the resulting bound-state picture provides a strong argument in favour of this dispersion relation

Statistical Thermodynamics of Disperse Systems

DEFF Research Database (Denmark)

Shapiro, Alexander

1996-01-01

Principles of statistical physics are applied for the description of thermodynamic equilibrium in disperse systems. The cells of disperse systems are shown to possess a number of non-standard thermodynamic parameters. A random distribution of these parameters in the system is determined....... On the basis of this distribution, it is established that the disperse system has an additional degree of freedom called the macro-entropy. A large set of bounded ideal disperse systems allows exact evaluation of thermodynamic characteristics. The theory developed is applied to the description of equilibrium...

Geometry of physical dispersion relations

International Nuclear Information System (INIS)

Raetzel, Dennis; Rivera, Sergio; Schuller, Frederic P.

2011-01-01

To serve as a dispersion relation, a cotangent bundle function must satisfy three simple algebraic properties. These conditions are derived from the inescapable physical requirements that local matter field dynamics must be predictive and allow for an observer-independent notion of positive energy. Possible modifications of the standard relativistic dispersion relation are thereby severely restricted. For instance, the dispersion relations associated with popular deformations of Maxwell theory by Gambini-Pullin or Myers-Pospelov are not admissible. Dispersion relations passing the simple algebraic checks derived here correspond to physically admissible Finslerian refinements of Lorentzian geometry.

Dispersion Forces

CERN Document Server

Buhmann, Stefan Yoshi

2012-01-01

In this book, a modern unified theory of dispersion forces on atoms and bodies is presented which covers a broad range of advanced aspects and scenarios. Macroscopic quantum electrodynamics is shown to provide a powerful framework for dispersion forces which allows for discussing general properties like their non-additivity and the relation between microscopic and macroscopic interactions. It is demonstrated how the general results can be used to obtain dispersion forces on atoms in the presence of bodies of various shapes and materials. Starting with a brief recapitulation of volume I, this volume II deals especially with bodies of irregular shapes, universal scaling laws, dynamical forces on excited atoms, enhanced forces in cavity quantum electrodynamics, non-equilibrium forces in thermal environments and quantum friction. The book gives both the specialist and those new to the field a thorough overview over recent results in the field. It provides a toolbox for studying dispersion forces in various contex...

Generalization of the dispersion relations demonstration; Generalisation de la demonstration des relations de dispersion

Energy Technology Data Exchange (ETDEWEB)

Omnes, Roland [Commissariat a l' energie atomique et aux energies alternatives - CEA (France)

1960-07-01

A modification of the dispersion relations demonstration for two-particle collisions in field theory is indicated. The direct study of the holomorphy domain of the reaction amplitude, without any reference to a particular coordinate system, allows to demonstrate the dispersion relations with fixed pulse transfer for any input and output particle mass. Reprint of a paper published in Comptes rendus des seances de l'Academie des Sciences, t. 250, p. 1203-1205, sitting of 15 February 1960 [French] On indique une modification de la demonstration des relations de dispersion pour les collisions a deux particules en theorie des champs. En etudiant directement le domaine d'holomorphie de l'amplitude de reaction sans se referer a un systeme de coordonnees particulier, on demontre les relations de dispersion a transfert d'impulsion fixe dans le cas ou les masses des particules entrantes et sortantes sont quelconques. Reproduction d'un article publie dans les Comptes rendus des seances de l'Academie des Sciences, t. 250, p. 1203-1205, seance du 15 fevrier 1960.

Catchment Dispersion Mechanisms in an Urban Context

Science.gov (United States)

Gironas, J. A.; Mejia, A.; Rossel, F.; Rinaldo, A.; Rodriguez, F.

2014-12-01

Dispersion mechanisms have been examined in-depth in natural catchments in previous studies. However, these dispersion mechanisms have been studied little in urban catchments, where artificial transport elements and morphological arrangements are expected to modify travel times and mobilize excess rainfall from spatially distributed impervious sites. Thus, these features can modify the variance of the catchment's travel times and hence the total dispersion. This work quantifies the dispersion mechanisms in an urban catchment using the theory of transport by travel times as represented by the Urban Morpho-climatic Instantaneous Unit Hydrograph (U-McIUH) model. This model computes travel times based on kinematic wave theory and accounts explicitly for the path heterogeneities and altered connectivity patterns characteristic of an urban drainage network. The analysis is illustrated using the Aubinière urban catchment (France) as a case study. We found that kinematic dispersion is dominant for small rainfall intensities, whereas geomorphologic dispersion becomes more dominant for larger intensities. The total dispersion scales with the drainage area in a power law fashion. The kinematic dispersion is dominant across spatial scales up to a threshold of approximately 2-3 km2, after which the geomorphologic dispersion becomes more dominant. Overall, overland flow is responsible for most of the dispersion, while conduits tend to counteract the increase of the geomorphologic dispersion with a negative kinematic dispersion. Further studies with other catchments are needed to assess whether the latter is a general feature of urban drainage networks.

Optimal inequalities for the subtraction functions of the proton Compton scattering dispersion theory

International Nuclear Information System (INIS)

Caprini, I.

1982-06-01

Upper and lower bounds upon the subtraction functions required in the dispersion theory of the proton Compton process are derived in a framework wbich optimally exploits the gauge invariance, the fixed-t analyticity and the s-u crossing properties of the scattering amplitudes, together with the consequences of the s, u-channel unitarity. The bounds, which are expressed only in terms of measurable s, u-channel physical quantities, without any reference to model dependent annihilation channel contributions, appear to be quite restrictive for some values of the momentum transfer t. The results are significant for removing the sign ambiguity of the pion decay constant. Fsub(p) and for the estimation of the electromagnetic polarizabilities of the proton. (author)

Dispersion of acoustic surface waves by velocity gradients

Science.gov (United States)

Kwon, S. D.; Kim, H. C.

1987-10-01

The perturbation theory of Auld [Acoustic Fields and Waves in Solids (Wiley, New York, 1973), Vol. II, p. 294], which describes the effect of a subsurface gradient on the velocity dispersion of surface waves, has been modified to a simpler form by an approximation using a newly defined velocity gradient for the case of isotropic materials. The modified theory is applied to nitrogen implantation in AISI 4140 steel with a velocity gradient of Gaussian profile, and compared with dispersion data obtained by the ultrasonic right-angle technique in the frequency range from 2.4 to 14.8 MHz. The good agreement between experiments and our theory suggests that the compound layer in the subsurface region plays a dominant role in causing the dispersion of acoustic surface waves.

Trajectory and Relative Dispersion Case Studies and Statistics from the Green River Mesoscale Deformation, Dispersion, and Dissipation Program

Science.gov (United States)

Niemann, Brand Lee

A major field program to study beta-mesoscale transport and dispersion over complex mountainous terrain was conducted during 1969 with the cooperation of three government agencies at the White Sands Missile Range in central Utah. The purpose of the program was to measure simultaneously on a large number of days the synoptic and mesoscale wind fields, the relative dispersion between pairs of particle trajectories and the rate of small scale turbulence dissipation. The field program included measurements during more than 60 days in the months of March, June, and November. The large quantity of data generated from this program has been processed and analyzed to provide case studies and statistics to evaluate and refine Lagrangian variable trajectory models. The case studies selected to illustrate the complexities of mesoscale transport and dispersion over complex terrain include those with terrain blocking, lee waves, and stagnation, as well as those with large vertical wind shears and horizontal wind field deformation. The statistics of relative particle dispersion were computed and compared to the classical theories of Richardson and Batchelor and the more recent theories of Lin and Kao among others. The relative particle dispersion was generally found to increase with travel time in the alongwind and crosswind directions, but in a more oscillatory than sustained or even accelerated manner as predicted by most theories, unless substantial wind shears or finite vertical separations between particles were present. The relative particle dispersion in the vertical was generally found to be small and bounded even when substantial vertical motions due to lee waves were present because of the limiting effect of stable temperature stratification. The data show that velocity shears have a more significant effect than turbulence on relative particle dispersion and that sufficient turbulence may not always be present above the planetary boundary layer for "wind direction shear

The Theory of Adaptive Dispersion and Acoustic-phonetic Properties of Cross-language Lexical-tone Systems

Science.gov (United States)

Alexander, Jennifer Alexandra

Lexical-tone languages use fundamental frequency (F0/pitch) to convey word meaning. About 41.8% of the world's languages use lexical tone (Maddieson, 2008), yet those systems are under-studied. I aim to increase our understanding of speech-sound inventory organization by extending to tone-systems a model of vowel-system organization, the Theory of Adaptive Dispersion (TAD) (Liljencrants and Lindblom, 1972). This is a cross-language investigation of whether and how the size of a tonal inventory affects (A) acoustic tone-space size and (B) dispersion of tone categories within the tone-space. I compared five languages with very different tone inventories: Cantonese (3 contour, 3 level tones); Mandarin (3 contour, 1 level tone); Thai (2 contour, 3 level tones); Yoruba (3 level tones only); and Igbo (2 level tones only). Six native speakers (3 female) of each language produced 18 CV syllables in isolation, with each of his/her language's tones, six times. I measured tonal F0 across the vowel at onset, midpoint, and offglide. Tone-space size was the F0 difference in semitones (ST) between each language's highest and lowest tones. Tone dispersion was the F0 distance (ST) between two tones shared by multiple languages. Following the TAD, I predicted that languages with larger tone inventories would have larger tone-spaces. Against expectations, tone-space size was fixed across level-tone languages at midpoint and offglide, and across contour-tone languages (except Thai) at offglide. However, within each language type (level-tone vs. contour-tone), languages with smaller tone inventories had larger tone spaces at onset. Tone-dispersion results were also unexpected. The Cantonese mid-level tone was further dispersed from a tonal baseline than the Yoruba mid-level tone; Cantonese mid-level tone dispersion was therefore greater than theoretically necessary. The Cantonese high-level tone was also further dispersed from baseline than the Mandarin high-level tone -- at midpoint

Unifying Pore Network Modeling, Continuous Time Random Walk (CTRW) Theory and Experiment to Describe Impact of Spatial Heterogeneities on Solute Dispersion at Multiple Length-scales

Science.gov (United States)

Bijeljic, B.; Blunt, M. J.; Rhodes, M. E.

2009-04-01

This talk will describe and highlight the advantages offered by a novel methodology that unifies pore network modeling, CTRW theory and experiment in description of solute dispersion in porous media. Solute transport in a porous medium is characterized by the interplay of advection and diffusion (described by Peclet number, Pe) that cause dispersion of solute particles. Dispersion is traditionally described by dispersion coefficients, D, that are commonly calculated from the spatial moments of the plume. Using a pore-scale network model based on particle tracking, the rich Peclet-number dependence of dispersion coefficient is predicted from first principles and is shown to compare well with experimental data for restricted diffusion, transition, power-law and mechanical dispersion regimes in the asymptotic limit. In the asymptotic limit D is constant and can be used in an averaged advection-dispersion equation. However, it is highly important to recognize that, until the velocity field is fully sampled, the particle transport is non-Gaussian and D possesses temporal or spatial variation. Furthermore, temporal probability density functions (PDF) of tracer particles are studied in pore networks and an excellent agreement for the spectrum of transition times for particles from pore to pore is obtained between network model results and CTRW theory. Based on the truncated power-law interpretation of PDF-s, the physical origin of the power-law scaling of dispersion coefficient vs. Peclet number has been explained for unconsolidated porous media, sands and a number of sandstones, arriving at the same conclusion from numerical network modelling, analytic CTRW theory and experiment. The length traveled by solute plumes before Gaussian behaviour is reached increases with an increase in heterogeneity and/or Pe. This opens up the question on the nature of dispersion in natural systems where the heterogeneities at the larger scales will significantly increase the range of

Approximate method for treating dispersion in one-way quantum channels

International Nuclear Information System (INIS)

Stace, T. M.; Wiseman, H. M.

2006-01-01

Coupling the output of a source quantum system into a target quantum system is easily treated by cascaded systems theory if the intervening quantum channel is dispersionless. However, dispersion may be important in some transfer protocols, especially in solid-state systems. In this paper we show how to generalize cascaded systems theory to treat such dispersion, provided it is not too strong. We show that the technique also works for fermionic systems with a low flux, and can be extended to treat fermionic systems with large flux. To test our theory, we calculate the effect of dispersion on the fidelity of a simple protocol of quantum state transfer. We find good agreement with an approximate analytical theory that had been previously developed for this example

Audiovisual facilitation of clinical knowledge: a paradigm for dispersed student education based on Paivio's Dual Coding Theory.

Science.gov (United States)

Hartland, William; Biddle, Chuck; Fallacaro, Michael

2008-06-01

This article explores the application of Paivio's Dual Coding Theory (DCT) as a scientifically sound rationale for the effects of multimedia learning in programs of nurse anesthesia. We explore and highlight this theory as a practical infrastructure for programs that work with dispersed students (ie, distance education models). Exploring the work of Paivio and others, we are engaged in an ongoing outcome study using audiovisual teaching interventions (SBVTIs) that we have applied to a range of healthcare providers in a quasiexperimental model. The early results of that study are reported in this article. In addition, we have observed powerful and sustained learning in a wide range of healthcare providers with our SBVTIs and suggest that this is likely explained by DCT.

Dispersion corrected hartree-fock and density functional theory for organic crystal structure prediction.

Science.gov (United States)

Brandenburg, Jan Gerit; Grimme, Stefan

2014-01-01

We present and evaluate dispersion corrected Hartree-Fock (HF) and Density Functional Theory (DFT) based quantum chemical methods for organic crystal structure prediction. The necessity of correcting for missing long-range electron correlation, also known as van der Waals (vdW) interaction, is pointed out and some methodological issues such as inclusion of three-body dispersion terms are discussed. One of the most efficient and widely used methods is the semi-classical dispersion correction D3. Its applicability for the calculation of sublimation energies is investigated for the benchmark set X23 consisting of 23 small organic crystals. For PBE-D3 the mean absolute deviation (MAD) is below the estimated experimental uncertainty of 1.3 kcal/mol. For two larger π-systems, the equilibrium crystal geometry is investigated and very good agreement with experimental data is found. Since these calculations are carried out with huge plane-wave basis sets they are rather time consuming and routinely applicable only to systems with less than about 200 atoms in the unit cell. Aiming at crystal structure prediction, which involves screening of many structures, a pre-sorting with faster methods is mandatory. Small, atom-centered basis sets can speed up the computation significantly but they suffer greatly from basis set errors. We present the recently developed geometrical counterpoise correction gCP. It is a fast semi-empirical method which corrects for most of the inter- and intramolecular basis set superposition error. For HF calculations with nearly minimal basis sets, we additionally correct for short-range basis incompleteness. We combine all three terms in the HF-3c denoted scheme which performs very well for the X23 sublimation energies with an MAD of only 1.5 kcal/mol, which is close to the huge basis set DFT-D3 result.

Wave-equation dispersion inversion

KAUST Repository

Li, Jing

2016-12-08

We present the theory for wave-equation inversion of dispersion curves, where the misfit function is the sum of the squared differences between the wavenumbers along the predicted and observed dispersion curves. The dispersion curves are obtained from Rayleigh waves recorded by vertical-component geophones. Similar to wave-equation traveltime tomography, the complicated surface wave arrivals in traces are skeletonized as simpler data, namely the picked dispersion curves in the phase-velocity and frequency domains. Solutions to the elastic wave equation and an iterative optimization method are then used to invert these curves for 2-D or 3-D S-wave velocity models. This procedure, denoted as wave-equation dispersion inversion (WD), does not require the assumption of a layered model and is significantly less prone to the cycle-skipping problems of full waveform inversion. The synthetic and field data examples demonstrate that WD can approximately reconstruct the S-wave velocity distributions in laterally heterogeneous media if the dispersion curves can be identified and picked. The WD method is easily extended to anisotropic data and the inversion of dispersion curves associated with Love waves.

Skeletonized wave equation of surface wave dispersion inversion

KAUST Repository

Li, Jing; Schuster, Gerard T.

2016-01-01

We present the theory for wave equation inversion of dispersion curves, where the misfit function is the sum of the squared differences between the wavenumbers along the predicted and observed dispersion curves. Similar to wave-equation travel

Dispersion of Sound in Dilute Suspensions with Nonlinear Particle Relaxation

Science.gov (United States)

Kandula, Max

2010-01-01

The theory accounting for nonlinear particle relaxation (viscous and thermal) has been applied to the prediction of dispersion of sound in dilute suspensions. The results suggest that significant deviations exist for sound dispersion between the linear and nonlinear theories at large values of Omega(Tau)(sub d), where Omega is the circular frequency, and Tau(sub d) is the Stokesian particle relaxation time. It is revealed that the nonlinear effect on the dispersion coefficient due to viscous contribution is larger relative to that of thermal conduction

Application of London-type dispersion corrections to the solid-state density functional theory simulation of the terahertz spectra of crystalline pharmaceuticals.

Science.gov (United States)

King, Matthew D; Buchanan, William D; Korter, Timothy M

2011-03-14

The effects of applying an empirical dispersion correction to solid-state density functional theory methods were evaluated in the simulation of the crystal structure and low-frequency (10 to 90 cm(-1)) terahertz spectrum of the non-steroidal anti-inflammatory drug, naproxen. The naproxen molecular crystal is bound largely by weak London force interactions, as well as by more prominent interactions such as hydrogen bonding, and thus serves as a good model for the assessment of the pair-wise dispersion correction term in systems influenced by intermolecular interactions of various strengths. Modifications to the dispersion parameters were tested in both fully optimized unit cell dimensions and those determined by X-ray crystallography, with subsequent simulations of the THz spectrum being performed. Use of the unmodified PBE density functional leads to an unrealistic expansion of the unit cell volume and the poor representation of the THz spectrum. Inclusion of a modified dispersion correction enabled a high-quality simulation of the THz spectrum and crystal structure of naproxen to be achieved without the need for artificially constraining the unit cell dimensions.

Employment Effects of Dispersal Policies. Part I: Theory

DEFF Research Database (Denmark)

Damm, Anna Piil; Rosholm, Michael

2003-01-01

This paper formulates a partial search model in which unemployed individuals simultaneously search for job and location of residence. Most importantly, we show that, ceteris paribus, a decrease in current place utility increases the transition rate into a new location of residence and the transit...... are characterised by low average values of current place utility. Hence, the model predicts that dispersal policies increase the geographical mobility rates of refugees and, for a sufficiently large local reservation wage effect, decrease their job-finding rates....... and the transition rate into employment outside the local labour market, but decreases the transition rate into local employment. Thus, a decrease in current place utility decreases the overall job-finding rate if the local reservation wage effect dominates. We argue that dispersal policies on refugee immigrants...

The role of individual variation in marine larval dispersal

KAUST Repository

Nanninga, Gerrit B.

2014-12-08

The exchange of individuals among patchy habitats plays a central role in spatial ecology and metapopulation dynamics. Dispersal is frequently observed to vary non-randomly within populations (e.g., short vs. long), indicating that variability among individuals may shape heterogeneity in patterns of connectivity. The concept of context- and condition-dependent dispersal describes the balance between the costs and benefits of dispersal that arises from the interaction of temporal and spatial landscape heterogeneity (the context) with phenotypic variability among individuals (the condition). While this hypothesis is widely accepted in terrestrial theory, it remains questionable to what extent the concept of adaptive dispersal strategies may apply to marine larval dispersal, a process that is largely determined by stochastic forces. Yet, larvae of many taxa exhibit strong navigational capabilities and there is mounting evidence of widespread intra-specific variability in biological traits that are potentially correlated with dispersal potential. While so far there are few known examples of real larval dispersal polymorphisms, intra-specifically variable dispersal strategies may be common in marine systems. Whether adaptive or not, it is becoming apparent that inter-individual heterogeneity in morphology, behavior, condition, and life history traits may have critical effects on population-level heterogeneity in dispersal. Here, we explore the eco-evolutionary causes and consequences of intrinsic and extrinsic variability on larval dispersal by synthesizing the existing literature and drawing conceptual parallels from terrestrial theory. We emphasize the potential importance of larval dispersal polymorphisms in marine population dynamics.

Dispersive shock waves in nonlinear and atomic optics

Directory of Open Access Journals (Sweden)

Kamchatnov Anatoly

2017-01-01

Full Text Available A brief review is given of dispersive shock waves observed in nonlinear optics and dynamics of Bose-Einstein condensates. The theory of dispersive shock waves is developed on the basis of Whitham modulation theory for various situations taking place in these two fields. In particular, the full classification is established for types of wave structures evolving from initial discontinuities for propagation of long light pulses in fibers with account of steepening effect and for dynamics of the polarization mode in two-component Bose-Einstein condensates.

Gyro-viscosity and linear dispersion relations in pair-ion magnetized plasmas

Energy Technology Data Exchange (ETDEWEB)

Kono, M. [Faculty of Policy Studies, Chuo University, Tokyo 192-0393 (Japan); Vranjes, J. [Instituto de Astrofisica de Canarias, Tenerife E38205 (Spain); Departamento de Astrofisica, Universidad de La Laguna, Tenerife E38205 (Spain)

2015-11-15

A fluid theory has been developed by taking account of gyro-viscosity to study wave propagation characteristics in a homogeneous pair-ion magnetized plasma with a cylindrical symmetry. The exact dispersion relations derived by the Hankel-Fourier transformation are shown comparable with those observed in the experiment by Oohara and co-workers. The gyro-viscosity is responsible for the change in propagation characteristics of the ion cyclotron wave from forward to backward by suppressing the effect of the thermal pressure which normally causes the forward nature of dispersion. Although the experiment has been already explained by a kinetic theory by the present authors, the kinetic derivations are so involved because of exact particle orbits in phase space, finite Lamor radius effects, and higher order ion cyclotron resonances. The present fluid theory provides a simple and transparent structure to the dispersion relations since the gyro-viscosity is renormalized into the ion cyclotron frequency which itself indicates the backward nature of dispersion. The usual disadvantage of a fluid theory, which treats only fundamental modes of eigen-waves excited in a system and is not able to describe higher harmonics that a kinetic theory does, is compensated by simple derivations and clear picture based on the renormalization of the gyro-viscosity.

Statistical Physics of Colloidal Dispersions.

Science.gov (United States)

Canessa, E.

Available from UMI in association with The British Library. Requires signed TDF. This thesis is concerned with the equilibrium statistical mechanics of colloidal dispersions which represent useful model systems for the study of condensed matter physics; namely, charge stabilized colloidal dispersions and polymer stabilized colloidal dispersions. A one-component macroparticle approach is adopted in order to treat the macroscopic and microscopic properties of these systems in a simple and comprehensive manner. The thesis opens with the description of the nature of the colloidal state before reviewing some basic definitions and theory in Chapter II. In Chapter III a variational theory of phase equilibria based on the Gibbs-Bogolyobov inequality is applied to sterically stabilized colloidal dispersions. Hard spheres are chosen as the reference system for the disordered phases while an Einstein model is used for the ordered phases. The new choice of pair potential, taken for mathematical convenience, is a superposition of two Yukawa functions. By matching a double Yukawa potential to the van der Waals attractive potential at different temperatures and introducing a purely temperature dependent coefficient to the repulsive part, a rich variety of observed phase separation phenomena is qualitatively described. The behaviour of the potential is found to be consistent with a small decrease of the polymer layer thickness with increasing temperature. Using the same concept of a collapse transition the non-monotonic second virial coefficient is also explained and quantified. It is shown that a reduction of the effective macroparticle diameter with increasing temperature can only be partially examined from the point of view of a (binary-) polymer solution theory. This chapter concludes with the description of the observed, reversible, depletion flocculation behaviour. This is accomplished by using the variational formalism and by invoking the double Yukawa potential to allow

Neutron optical potential of 28Si derived from the dispersion relation

International Nuclear Information System (INIS)

Kitazawa, H.; Igarasi, S.; Katsuragi, D.; Harima, Y.

1992-01-01

Based upon the dispersion theory, an optical potential of 28 Si was determined at the neutron energies from the Fermi energy to 20 MeV. In particular, discussion was given on a characteristic behavior of the optical potential for low-energy neutrons. Moreover, the validity of the dispersion theory was investigated for neutron single-particle bound states in 29 Si. (orig.)

Dynamics of platicons due to third-order dispersion

Science.gov (United States)

Lobanov, Valery E.; Cherenkov, Artem V.; Shitikov, Artem E.; Bilenko, Igor A.; Gorodetsky, Michael L.

2017-07-01

Dynamics of platicons caused by the third-order dispersion is studied. It is shown that under the influence of the third-order dispersion platicons obtain angular velocity depending both on dispersion and on detuning value. A method of tuning of platicon associated optical frequency comb repetition rate is proposed. Contribution to the Topical Issue "Theory and Applications of the Lugiato-Lefever Equation", edited by Yanne K. Chembo, Damia Gomila, Mustapha Tlidi, Curtis R. Menyuk.

Limited dispersal in mobile hunter–gatherer Baka Pygmies

Science.gov (United States)

Verdu, Paul; Leblois, Raphaël; Froment, Alain; Théry, Sylvain; Bahuchet, Serge; Rousset, François; Heyer, Evelyne; Vitalis, Renaud

2010-01-01

Hunter–gatherer Pygmies from Central Africa are described as being extremely mobile. Using neutral genetic markers and population genetics theory, we explored the dispersal behaviour of the Baka Pygmies from Cameroon, one of the largest Pygmy populations in Central Africa. We found a strong correlation between genetic and geographical distances: a pattern of isolation by distance arising from limited parent–offspring dispersal. Our study suggests that mobile hunter–gatherers do not necessarily disperse over wide geographical areas. PMID:20427330

Spatial characterization of catchment dispersion mechanisms in an urban context

Science.gov (United States)

Rossel, Florian; Gironás, Jorge; Mejía, Alfonso; Rinaldo, Andrea; Rodriguez, Fabrice

2014-12-01

Previous studies have examined in-depth the dispersion mechanisms in natural catchments. In contrast, these dispersion mechanisms have been studied little in urban catchments, where artificial transport elements and morphological arrangements are expected to modify travel times and mobilize excess rainfall from spatially distributed impervious sites. This has the ability to modify the variance of the catchment's travel times and hence the total dispersion. This work quantifies the dispersion mechanisms in an urban catchment using the theory of transport by travel times as represented by the Urban Morpho-climatic Instantaneous Unit Hydrograph (U-McIUH) model. The U-McIUH computes travel times based on kinematic wave theory and accounts explicitly for the path heterogeneities and altered connectivity patterns characteristic of an urban drainage network. The analysis is illustrated using the Aubinière urban catchment in France as a case study. We found that kinematic dispersion is dominant for small rainfall intensities, whereas geomorphologic dispersion becomes more dominant for larger intensities. The total dispersion scales with the drainage area in a power law fashion. The kinematic dispersion is dominant across spatial scales up to a threshold of approximately 2-3 km2, after which the geomorphologic dispersion becomes more dominant. Overall, overland flow is responsible for most of the dispersion in the catchment, while conduits tend to counteract the increase of the geomorphologic dispersion with a negative kinematic dispersion. Further study with other catchments is needed to asses if the latter is a general feature of urban drainage networks.

Phase noise of dispersion-managed solitons

International Nuclear Information System (INIS)

Spiller, Elaine T.; Biondini, Gino

2009-01-01

We quantify noise-induced phase deviations of dispersion-managed solitons (DMS) in optical fiber communications and femtosecond lasers. We first develop a perturbation theory for the dispersion-managed nonlinear Schroedinger equation (DMNLSE) in order to compute the noise-induced mean and variance of the soliton parameters. We then use the analytical results to guide importance-sampled Monte Carlo simulations of the noise-driven DMNLSE. Comparison of these results with those from the original unaveraged governing equations confirms the validity of the DMNLSE as a model for many dispersion-managed systems and quantify the increased robustness of DMS with respect to noise-induced phase jitter.

Modelling of pollution dispersion in atmosphere

International Nuclear Information System (INIS)

Borysiewicz, M.; Stankiewicz, R.

1994-01-01

The paper contains the review of the mathematical foundation of atmospheric dispersion models. The atmospheric phenomena relevant to atmospheric dispersion model are discussed. In particular the parametrization of processes with time and space scales smaller than numerical grid size, limited by available computer power, is presented. The special attention was devoted to similarity theory and parametrization of boundary layer. The numerical methods are analysed and the drawbacks of the method are presented. (author). 99 refs, 15 figs, 3 tabs

Analysis of the neutrons dispersion in a semi-infinite medium based in transport theory and the Monte Carlo method; Analisis de la dispersion de neutrones en un medio semi-infinito en base a teoria de transporte y el metodo de Monte Carlo

Energy Technology Data Exchange (ETDEWEB)

Arreola V, G. [IPN, Escuela Superior de Fisica y Matematicas, Posgrado en Ciencias Fisicomatematicas, area en Ingenieria Nuclear, Unidad Profesional Adolfo Lopez Mateos, Edificio 9, Col. San Pedro Zacatenco, 07730 Mexico D. F. (Mexico); Vazquez R, R.; Guzman A, J. R., E-mail: energia.arreola.uam@gmail.com [Universidad Autonoma Metropolitana, Unidad Iztapalapa, Area de Ingenieria en Recursos Energeticos, Av. San Rafael Atlixco 186, Col. Vicentina, 09340 Mexico D. F. (Mexico)

2012-10-15

In this work a comparative analysis of the results for the neutrons dispersion in a not multiplicative semi-infinite medium is presented. One of the frontiers of this medium is located in the origin of coordinates, where a neutrons source in beam form, i.e., {mu}{omicron}=1 is also. The neutrons dispersion is studied on the statistical method of Monte Carlo and through the unidimensional transport theory and for an energy group. The application of transport theory gives a semi-analytic solution for this problem while the statistical solution for the flow was obtained applying the MCNPX code. The dispersion in light water and heavy water was studied. A first remarkable result is that both methods locate the maximum of the neutrons distribution to less than two mean free trajectories of transport for heavy water, while for the light water is less than ten mean free trajectories of transport; the differences between both methods is major for the light water case. A second remarkable result is that the tendency of both distributions is similar in small mean free trajectories, while in big mean free trajectories the transport theory spreads to an asymptote value and the solution in base statistical method spreads to zero. The existence of a neutron current of low energy and toward the source is demonstrated, in contrary sense to the neutron current of high energy coming from the own source. (Author)

Structure and stability of acrolein and allyl alcohol networks on Ag(111) from density functional theory based calculations with dispersion corrections

Science.gov (United States)

Ferullo, Ricardo M.; Branda, Maria Marta; Illas, Francesc

2013-11-01

The interaction of acrolein and allyl alcohol with the Ag(111) surface has been studied by means of periodic density functional theory based calculations including explicitly dispersion terms. Different coverage values have been explored going from isolated adsorbed molecules to isolated dimers, interacting dimers or ordered overlayers. The inclusion of the dispersion terms largely affects the calculated values of the adsorption energy and also the distance between adsorbed molecule and the metallic surface but much less the adsorbate-adsorbate interactions. Owing to the large dipole moment of acrolein, the present calculations predict that at high coverage this molecule forms a stable extensive two-dimensional network on the surface, caused by the alignment of the adsorbate dipoles. For the case of allyl alcohol, dimers and complex networks exhibit similar stability.

Introduction to nonlinear dispersive equations

CERN Document Server

Linares, Felipe

2015-01-01

This textbook introduces the well-posedness theory for initial-value problems of nonlinear, dispersive partial differential equations, with special focus on two key models, the Korteweg–de Vries equation and the nonlinear Schrödinger equation. A concise and self-contained treatment of background material (the Fourier transform, interpolation theory, Sobolev spaces, and the linear Schrödinger equation) prepares the reader to understand the main topics covered: the initial-value problem for the nonlinear Schrödinger equation and the generalized Korteweg–de Vries equation, properties of their solutions, and a survey of general classes of nonlinear dispersive equations of physical and mathematical significance. Each chapter ends with an expert account of recent developments and open problems, as well as exercises. The final chapter gives a detailed exposition of local well-posedness for the nonlinear Schrödinger equation, taking the reader to the forefront of recent research. The second edition of Introdu...

Magnetic effects in anomalous dispersion

International Nuclear Information System (INIS)

Blume, M.

1992-01-01

Spectacular enhancements of magnetic x-ray scattering have been predicted and observed experimentally. These effects are the result of resonant phenomena closely related to anomalous dispersion, and they are strongest at near-edge resonances. The theory of these resonances will be developed with particular attention to the symmetry properties of the scatterer. While the phenomena to be discussed concern magnetic properties the transitions are electric dipole or electric quadrupole in character and represent a subset of the usual anomalous dispersion phenomena. The polarization dependence of the scattering is also considered, and the polarization dependence for magnetic effects is related to that for charge scattering and to Templeton type anisotropic polarization phenomena. It has been found that the strongest effects occur in rare-earths and in actinides for M shell edges. In addition to the scattering properties the theory is applicable to ''forward scattering'' properties such as the Faraday effect and circular dichroism

Density-functional approaches to noncovalent interactions: a comparison of dispersion corrections (DFT-D), exchange-hole dipole moment (XDM) theory, and specialized functionals.

Science.gov (United States)

Burns, Lori A; Vázquez-Mayagoitia, Alvaro; Sumpter, Bobby G; Sherrill, C David

2011-02-28

A systematic study of techniques for treating noncovalent interactions within the computationally efficient density functional theory (DFT) framework is presented through comparison to benchmark-quality evaluations of binding strength compiled for molecular complexes of diverse size and nature. In particular, the efficacy of functionals deliberately crafted to encompass long-range forces, a posteriori DFT+dispersion corrections (DFT-D2 and DFT-D3), and exchange-hole dipole moment (XDM) theory is assessed against a large collection (469 energy points) of reference interaction energies at the CCSD(T) level of theory extrapolated to the estimated complete basis set limit. The established S22 [revised in J. Chem. Phys. 132, 144104 (2010)] and JSCH test sets of minimum-energy structures, as well as collections of dispersion-bound (NBC10) and hydrogen-bonded (HBC6) dissociation curves and a pairwise decomposition of a protein-ligand reaction site (HSG), comprise the chemical systems for this work. From evaluations of accuracy, consistency, and efficiency for PBE-D, BP86-D, B97-D, PBE0-D, B3LYP-D, B970-D, M05-2X, M06-2X, ωB97X-D, B2PLYP-D, XYG3, and B3LYP-XDM methodologies, it is concluded that distinct, often contrasting, groups of these elicit the best performance within the accessible double-ζ or robust triple-ζ basis set regimes and among hydrogen-bonded or dispersion-dominated complexes. For overall results, M05-2X, B97-D3, and B970-D2 yield superior values in conjunction with aug-cc-pVDZ, for a mean absolute deviation of 0.41 - 0.49 kcal/mol, and B3LYP-D3, B97-D3, ωB97X-D, and B2PLYP-D3 dominate with aug-cc-pVTZ, affording, together with XYG3/6-311+G(3df,2p), a mean absolute deviation of 0.33 - 0.38 kcal/mol.

Validation of molecular crystal structures from powder diffraction data with dispersion-corrected density functional theory (DFT-D)

International Nuclear Information System (INIS)

Streek, Jacco van de; Neumann, Marcus A.

2014-01-01

The accuracy of 215 experimental organic crystal structures from powder diffraction data is validated against a dispersion-corrected density functional theory method. In 2010 we energy-minimized 225 high-quality single-crystal (SX) structures with dispersion-corrected density functional theory (DFT-D) to establish a quantitative benchmark. For the current paper, 215 organic crystal structures determined from X-ray powder diffraction (XRPD) data and published in an IUCr journal were energy-minimized with DFT-D and compared to the SX benchmark. The on average slightly less accurate atomic coordinates of XRPD structures do lead to systematically higher root mean square Cartesian displacement (RMSCD) values upon energy minimization than for SX structures, but the RMSCD value is still a good indicator for the detection of structures that deserve a closer look. The upper RMSCD limit for a correct structure must be increased from 0.25 Å for SX structures to 0.35 Å for XRPD structures; the grey area must be extended from 0.30 to 0.40 Å. Based on the energy minimizations, three structures are re-refined to give more precise atomic coordinates. For six structures our calculations provide the missing positions for the H atoms, for five structures they provide corrected positions for some H atoms. Seven crystal structures showed a minor error for a non-H atom. For five structures the energy minimizations suggest a higher space-group symmetry. For the 225 SX structures, the only deviations observed upon energy minimization were three minor H-atom related issues. Preferred orientation is the most important cause of problems. A preferred-orientation correction is the only correction where the experimental data are modified to fit the model. We conclude that molecular crystal structures determined from powder diffraction data that are published in IUCr journals are of high quality, with less than 4% containing an error in a non-H atom

Planck-scale-modified dispersion relations in FRW spacetime

Science.gov (United States)

Rosati, Giacomo; Amelino-Camelia, Giovanni; Marcianò, Antonino; Matassa, Marco

2015-12-01

In recent years, Planck-scale modifications of the dispersion relation have been attracting increasing interest also from the viewpoint of possible applications in astrophysics and cosmology, where spacetime curvature cannot be neglected. Nonetheless, the interplay between Planck-scale effects and spacetime curvature is still poorly understood, particularly in cases where curvature is not constant. These challenges have been so far postponed by relying on an ansatz, first introduced by Jacob and Piran. We propose here a general strategy of analysis of the effects of modifications of the dispersion relation in Friedmann-Robertson-Walker spacetimes, applicable both to cases where the relativistic equivalence of frames is spoiled ("preferred-frame scenarios") and to the alternative possibility of "DSR-relativistic theories," theories that are fully relativistic but with relativistic laws deformed so that the modified dispersion relation is observer independent. We show that the Jacob-Piran ansatz implicitly assumes that spacetime translations are not affected by the Planck scale, while under rather general conditions, the same Planck-scale quantum-spacetime structures producing modifications of the dispersion relation also affect translations. Through the explicit analysis of one of the effects produced by modifications of the dispersion relation, an effect amounting to Planck-scale corrections to travel times, we show that our concerns are not merely conceptual but rather can have significant quantitative implications.

Noise figure of amplified dispersive Fourier transformation

International Nuclear Information System (INIS)

Goda, Keisuke; Jalali, Bahram

2010-01-01

Amplified dispersive Fourier transformation (ADFT) is a powerful tool for fast real-time spectroscopy as it overcomes the limitations of traditional optical spectrometers. ADFT maps the spectrum of an optical pulse into a temporal waveform using group-velocity dispersion and simultaneously amplifies it in the optical domain. It greatly simplifies spectroscopy by replacing the diffraction grating and detector array in the conventional spectrometer with a dispersive fiber and single-pixel photodetector, enabling ultrafast real-time spectroscopic measurements. Following our earlier work on the theory of ADFT, here we study the effect of noise on ADFT. We derive the noise figure of ADFT and discuss its dependence on various parameters.

Long-range dipolar order and dispersion forces in polar liquids

Science.gov (United States)

Besford, Quinn Alexander; Christofferson, Andrew Joseph; Liu, Maoyuan; Yarovsky, Irene

2017-11-01

Complex solvation phenomena, such as specific ion effects, occur in polar liquids. Interpretation of these effects in terms of structure and dispersion forces will lead to a greater understanding of solvation. Herein, using molecular dynamics, we probe the structure of polar liquids through specific dipolar pair correlation functions that contribute to the potential of mean force that is "felt" between thermally rotating dipole moments. It is shown that unique dipolar order exists at separations at least up to 20 Å for all liquids studied. When the structural order is compared with a dipolar dispersion force that arises from local co-operative enhancement of dipole moments, a strong agreement is found. Lifshitz theory of dispersion forces was compared with the structural order, where the theory is validated for all liquids that do not have significant local dipole correlations. For liquids that do have significant local dipole correlations, specifically liquid water, Lifshitz theory underestimates the dispersion force by a factor of 5-10, demonstrating that the force that leads to the increased structure in liquid water is missed by Lifshitz theory of van der Waals forces. We apply similar correlation functions to an ionic aqueous system, where long-range order between water's dipole moment and a single chloride ion is found to exist at 20 Å of separation, revealing a long-range perturbation of water's structure by an ion. Furthermore, we found that waters within the 1st, 2nd, and 3rd solvation shells of a chloride ion exhibit significantly enhanced dipolar interactions, particularly with waters at larger distances of separation. Our results provide a link between structures, dispersion forces, and specific ion effects, which may lead to a more robust understanding of solvation.

Dispersion- and Exchange-Corrected Density Functional Theory for Sodium Ion Hydration.

Science.gov (United States)

Soniat, Marielle; Rogers, David M; Rempe, Susan B

2015-07-14

A challenge in density functional theory is developing functionals that simultaneously describe intermolecular electron correlation and electron delocalization. Recent exchange-correlation functionals address those two issues by adding corrections important at long ranges: an atom-centered pairwise dispersion term to account for correlation and a modified long-range component of the electron exchange term to correct for delocalization. Here we investigate how those corrections influence the accuracy of binding free energy predictions for sodium-water clusters. We find that the dual-corrected ωB97X-D functional gives cluster binding energies closest to high-level ab initio methods (CCSD(T)). Binding energy decomposition shows that the ωB97X-D functional predicts the smallest ion-water (pairwise) interaction energy and larger multibody contributions for a four-water cluster than most other functionals - a trend consistent with CCSD(T) results. Also, ωB97X-D produces the smallest amounts of charge transfer and the least polarizable waters of the density functionals studied, which mimics the lower polarizability of CCSD. When compared with experimental binding free energies, however, the exchange-corrected CAM-B3LYP functional performs best (error <1 kcal/mol), possibly because of its parametrization to experimental formation enthalpies. For clusters containing more than four waters, "split-shell" coordination must be considered to obtain accurate free energies in comparison with experiment.

Relations de Dispersion et Diffusion des Glueballs et des Mesons dans la Theorie de Jauge U(1)(2+1) Compacte

Science.gov (United States)

Ahmed, Chaara El Mouez

Nous avons etudie les relations de dispersion et la diffusion des glueballs et des mesons dans le modele U(1)_{2+1} compact. Ce modele a ete souvent utilise comme un simple modele de la chromodynamique quantique (QCD), parce qu'il possede le confinement ainsi que les etats de glueballs. Par contre, sa structure mathematique est beaucoup plus simple que la QCD. Notre methode consiste a diagonaliser l'Hamiltonien de ce modele dans une base appropriee de graphes et sur reseau impulsion, afin de generer les relations de dispersion des glueballs et des mesons. Pour la diffusion, nous avons utilise la methode dependante du temps pour calculer la matrice S et la section efficace de diffusion des glueballs et des mesons. Les divers resultats obtenus semblent etre en accord avec les travaux anterieurs de Hakim, Alessandrini et al., Irving et al., qui eux, utilisent plutot la theorie des perturbations en couplage fort, et travaillent sur un reseau espace-temps.

A single hole tracer test to determine longitudinal dispersion

International Nuclear Information System (INIS)

Noy, D.J.; Holmes, D.C.

1986-03-01

The paper concerns a single hole tracer test to determine longitudinal dispersion, which is an important parameter in assessing the suitability of a site for radioactive waste disposal. The theory, equipment and procedure for measuring longitudinal dispersion in a single borehole is described. Results are presented for field trials conducted in an aquifer, where the technique produced good results. The measured value of longitudinal dispersion, from a single hole test, relates only to a limited volume of rock immediately adjacent to the borehole. (U.K.)

A Deformation Model of TRU Metal Dispersion Fuel Rod for HYPER

International Nuclear Information System (INIS)

Lee, Byoung Oon; Hwang, Woan; Park, Won S.

2002-01-01

Deformation analysis in fuel rod design is essential to assure adequate fuel performance and integrity under irradiation conditions. An in-reactor performance computer code for a dispersion fuel rod is being developed in the conceptual design stage of blanket fuel for HYPER. In this paper, a mechanistic deformation model was developed and the model was installed into the DIMAC program. The model was based on the elasto-plasticity theory and power-law creep theory. The preliminary deformation calculation results for (TRU-Zr)-Zr dispersion fuel predicted by DIMAC were compared with those of silicide dispersion fuel predicted by DIFAIR. It appeared that the deformation levels for (TRU-Zr)-Zr dispersion fuel were relatively higher than those of silicide fuel. Some experimental tests including in-pile and out-pile experiments are needed for verifying the predictive capability of the DIMAC code. An in-reactor performance analysis computer code for blanket fuel is being developed at the conceptual design stage of blanket fuel for HYPER. In this paper, a mechanistic deformation model was developed and the model was installed into the DIMAC program. The model was based on the elasto-plasticity theory and power-law creep theory. The preliminary deformation calculation results for (TRUZr)- Zr dispersion fuel predicted by DIMAC were compared with those of silicide dispersion fuel predicted by DIFAIR. It appears that the deformation by swelling within fuel meat is very large for both fuels, and the major deformation mechanism at cladding is creep. The swelling strain is almost constant within the fuel meat, and is assumed to be zero in the cladding made of HT9. It is estimated that the deformation levels for (TRU-Zr)-Zr dispersion fuel were relatively higher than those of silicide fuel, and the dispersion fuel performance may be limited by swelling. But the predicted volume change of the (TRU-Zr)-Zr dispersion fuel models is about 6.1% at 30 at.% burnup. The value of cladding

Nucleon form factors in dispersively improved chiral effective field theory. II. Electromagnetic form factors

Science.gov (United States)

Alarcón, J. M.; Weiss, C.

2018-05-01

We study the nucleon electromagnetic form factors (EM FFs) using a recently developed method combining chiral effective field theory (χ EFT ) and dispersion analysis. The spectral functions on the two-pion cut at t >4 Mπ2 are constructed using the elastic unitarity relation and an N /D representation. χ EFT is used to calculate the real functions J±1(t ) =f±1(t ) /Fπ(t ) (ratios of the complex π π →N N ¯ partial-wave amplitudes and the timelike pion FF), which are free of π π rescattering. Rescattering effects are included through the empirical timelike pion FF | Fπ(t) | 2 . The method allows us to compute the isovector EM spectral functions up to t ˜1 GeV2 with controlled accuracy (leading order, next-to-leading order, and partial next-to-next-to-leading order). With the spectral functions we calculate the isovector nucleon EM FFs and their derivatives at t =0 (EM radii, moments) using subtracted dispersion relations. We predict the values of higher FF derivatives, which are not affected by higher-order chiral corrections and are obtained almost parameter-free in our approach, and explain their collective behavior. We estimate the individual proton and neutron FFs by adding an empirical parametrization of the isoscalar sector. Excellent agreement with the present low-Q2 FF data is achieved up to ˜0.5 GeV2 for GE, and up to ˜0.2 GeV2 for GM. Our results can be used to guide the analysis of low-Q2 elastic scattering data and the extraction of the proton charge radius.

Dispersion relations for η '→ η π π

Science.gov (United States)

Isken, Tobias; Kubis, Bastian; Schneider, Sebastian P.; Stoffer, Peter

2017-07-01

We present a dispersive analysis of the decay amplitude for η '→ η π π that is based on the fundamental principles of analyticity and unitarity. In this framework, final-state interactions are fully taken into account. Our dispersive representation relies only on input for the {π π } and {π }η scattering phase shifts. Isospin symmetry allows us to describe both the charged and neutral decay channel in terms of the same function. The dispersion relation contains subtraction constants that cannot be fixed by unitarity. We determine these parameters by a fit to Dalitz-plot data from the VES and BES-III experiments. We study the prediction of a low-energy theorem and compare the dispersive fit to variants of chiral perturbation theory.

Dispersal similarly shapes both population genetics and community patterns in the marine realm

KAUST Repository

Chust, Guillem

2016-06-27

Dispersal plays a key role to connect populations and, if limited, is one of the main processes to maintain and generate regional biodiversity. According to neutral theories of molecular evolution and biodiversity, dispersal limitation of propagules and population stochasticity are integral to shaping both genetic and community structure. We conducted a parallel analysis of biological connectivity at genetic and community levels in marine groups with different dispersal traits. We compiled large data sets of population genetic structure (98 benthic macroinvertebrate and 35 planktonic species) and biogeographic data (2193 benthic macroinvertebrate and 734 planktonic species). We estimated dispersal distances from population genetic data (i.e., FST vs. geographic distance) and from β-diversity at the community level. Dispersal distances ranked the biological groups in the same order at both genetic and community levels, as predicted by organism dispersal ability and seascape connectivity: macrozoobenthic species without dispersing larvae, followed by macrozoobenthic species with dispersing larvae and plankton (phyto- and zooplankton). This ranking order is associated with constraints to the movement of macrozoobenthos within the seabed compared with the pelagic habitat. We showed that dispersal limitation similarly determines the connectivity degree of communities and populations, supporting the predictions of neutral theories in marine biodiversity patterns.

Dispersal similarly shapes both population genetics and community patterns in the marine realm

Science.gov (United States)

Chust, Guillem; Villarino, Ernesto; Chenuil, Anne; Irigoien, Xabier; Bizsel, Nihayet; Bode, Antonio; Broms, Cecilie; Claus, Simon; Fernández de Puelles, María L.; Fonda-Umani, Serena; Hoarau, Galice; Mazzocchi, Maria G.; Mozetič, Patricija; Vandepitte, Leen; Veríssimo, Helena; Zervoudaki, Soultana; Borja, Angel

2016-06-01

Dispersal plays a key role to connect populations and, if limited, is one of the main processes to maintain and generate regional biodiversity. According to neutral theories of molecular evolution and biodiversity, dispersal limitation of propagules and population stochasticity are integral to shaping both genetic and community structure. We conducted a parallel analysis of biological connectivity at genetic and community levels in marine groups with different dispersal traits. We compiled large data sets of population genetic structure (98 benthic macroinvertebrate and 35 planktonic species) and biogeographic data (2193 benthic macroinvertebrate and 734 planktonic species). We estimated dispersal distances from population genetic data (i.e., FST vs. geographic distance) and from β-diversity at the community level. Dispersal distances ranked the biological groups in the same order at both genetic and community levels, as predicted by organism dispersal ability and seascape connectivity: macrozoobenthic species without dispersing larvae, followed by macrozoobenthic species with dispersing larvae and plankton (phyto- and zooplankton). This ranking order is associated with constraints to the movement of macrozoobenthos within the seabed compared with the pelagic habitat. We showed that dispersal limitation similarly determines the connectivity degree of communities and populations, supporting the predictions of neutral theories in marine biodiversity patterns.

Dispersal similarly shapes both population genetics and community patterns in the marine realm

KAUST Repository

Chust, Guillem; Villarino, Ernesto; Chenuil, Anne; Irigoien, Xabier; Bizsel, Nihayet; Bode, Antonio; Broms, Cecilie; Claus, Simon; Ferná ndez de Puelles, Marí a L.; Fonda-Umani, Serena; Hoarau, Galice; Mazzocchi, Maria G.; Mozetič, Patricija; Vandepitte, Leen; Verí ssimo, Helena; Zervoudaki, Soultana; Borja, Angel

2016-01-01

Dispersal plays a key role to connect populations and, if limited, is one of the main processes to maintain and generate regional biodiversity. According to neutral theories of molecular evolution and biodiversity, dispersal limitation of propagules and population stochasticity are integral to shaping both genetic and community structure. We conducted a parallel analysis of biological connectivity at genetic and community levels in marine groups with different dispersal traits. We compiled large data sets of population genetic structure (98 benthic macroinvertebrate and 35 planktonic species) and biogeographic data (2193 benthic macroinvertebrate and 734 planktonic species). We estimated dispersal distances from population genetic data (i.e., FST vs. geographic distance) and from β-diversity at the community level. Dispersal distances ranked the biological groups in the same order at both genetic and community levels, as predicted by organism dispersal ability and seascape connectivity: macrozoobenthic species without dispersing larvae, followed by macrozoobenthic species with dispersing larvae and plankton (phyto- and zooplankton). This ranking order is associated with constraints to the movement of macrozoobenthos within the seabed compared with the pelagic habitat. We showed that dispersal limitation similarly determines the connectivity degree of communities and populations, supporting the predictions of neutral theories in marine biodiversity patterns.

Proposal of highly sensitive optofluidic sensors based on dispersive photonic crystal waveguides

DEFF Research Database (Denmark)

Xiao, Sanshui; Mortensen, Niels Asger

2007-01-01

Optofluidic sensors based on highly dispersive two-dimensional photonic crystal waveguides are studied theoretically. Results show that these structures are strongly sensitive to the refractive index of the infiltrated liquid (nl), which is used to tune dispersion of the photonic crystal waveguide....... The waveguide mode-gap edge shifts about 1.2 nm for δnl = 0.002. The shifts can be explained well by band structure theory combined with first-order perturbation theory. These devices are potentially interesting for chemical sensing applications....

Validation of experimental molecular crystal structures with dispersion-corrected density functional theory calculations.

Science.gov (United States)

van de Streek, Jacco; Neumann, Marcus A

2010-10-01

This paper describes the validation of a dispersion-corrected density functional theory (d-DFT) method for the purpose of assessing the correctness of experimental organic crystal structures and enhancing the information content of purely experimental data. 241 experimental organic crystal structures from the August 2008 issue of Acta Cryst. Section E were energy-minimized in full, including unit-cell parameters. The differences between the experimental and the minimized crystal structures were subjected to statistical analysis. The r.m.s. Cartesian displacement excluding H atoms upon energy minimization with flexible unit-cell parameters is selected as a pertinent indicator of the correctness of a crystal structure. All 241 experimental crystal structures are reproduced very well: the average r.m.s. Cartesian displacement for the 241 crystal structures, including 16 disordered structures, is only 0.095 Å (0.084 Å for the 225 ordered structures). R.m.s. Cartesian displacements above 0.25 A either indicate incorrect experimental crystal structures or reveal interesting structural features such as exceptionally large temperature effects, incorrectly modelled disorder or symmetry breaking H atoms. After validation, the method is applied to nine examples that are known to be ambiguous or subtly incorrect.

On the relativistic theory of electromagnetic dispersion relations and Poynting's theorem

International Nuclear Information System (INIS)

Lerche, I.

1975-01-01

Constitutive relations, and general dispersion relations, are derived for an arbitrary, anisotropic, dispersive and dissipative medium which is moving relative to an inertial observer. The constitutive relations are expressed in terms of the ''local'' dielectric tensor, magnetic permeability, etc., where ''local'' refers to the instantaneous rest frame of the medium. We also give the generalization of Poynting's theorem for power flow including the expression for the rate at which the moving medium does work on the radiation. In view of the current interest in radiation generated in, and passing through, pulsar magnetospheres, we believe that the general results presented here are, perhaps, not without some astrophysical import

Dispersion - does it degrade a pulse envelope

International Nuclear Information System (INIS)

Deighton, M.O.

1985-01-01

In hostile environments, transmitting information as ultrasonic Lamb wave pulses has advantages, since the stainless steel strip serving as a waveguide is very durable. Besides attenuation, velocity dispersion (inherent in Lamb waves) can be important even in fairly short guides. Theory shows that unlimited propagation of a pulsed r.f. envelope is possible, even with dispersion present. The constant group velocity needed would favour asub(o)-mode pulses over other modes, provided ordinary attenuation is small. An approximate formula indicates the useful range of a pulse, when group velocity does vary. (author)

Nonlocal homogenization theory in metamaterials: Effective electromagnetic spatial dispersion and artificial chirality

Science.gov (United States)

Ciattoni, Alessandro; Rizza, Carlo

2015-05-01

We develop, from first principles, a general and compact formalism for predicting the electromagnetic response of a metamaterial with nonmagnetic inclusions in the long-wavelength limit, including spatial dispersion up to the second order. Specifically, by resorting to a suitable multiscale technique, we show that the effective medium permittivity tensor and the first- and second-order tensors describing spatial dispersion can be evaluated by averaging suitable spatially rapidly varying fields, each satisfying electrostatic-like equations within the metamaterial unit cell. For metamaterials with negligible second-order spatial dispersion, we exploit the equivalence of first-order spatial dispersion and reciprocal bianisotropic electromagnetic response to deduce a simple expression for the metamaterial chirality tensor. Such an expression allows us to systematically analyze the effect of the composite spatial symmetry properties on electromagnetic chirality. We find that even if a metamaterial is geometrically achiral, i.e., it is indistinguishable from its mirror image, it shows pseudo-chiral-omega electromagnetic chirality if the rotation needed to restore the dielectric profile after the reflection is either a 0∘ or 90∘ rotation around an axis orthogonal to the reflection plane. These two symmetric situations encompass two-dimensional and one-dimensional metamaterials with chiral response. As an example admitting full analytical description, we discuss one-dimensional metamaterials whose single chirality parameter is shown to be directly related to the metamaterial dielectric profile by quadratures.

Covariant kinetic dispersion theory of linear transverse waves parallel propagating in magnetized plasmas with thermal anisotropy

International Nuclear Information System (INIS)

Lazar, M.; Schlickeiser, R.

2006-01-01

The properties of transverse waves parallel propagating in magnetized plasmas with arbitrary composition and thermally anisotropic, are investigated on the basis of relativistic Vlasov-Maxwell equations. The transverse dispersion relations for plasmas with arbitrary distribution functions are derived. These dispersion relations describe the linear response of the system to the initial perturbations and thus define all existing linear (transverse) plasma modes in the system. By analytic continuation the dispersion relations in the whole complex frequency plane are constructed. Further analysis is restricted to the important case of anisotropic bi-Maxwellian equilibrium plasma distribution functions. Explicit forms of the relativistically correct transverse dispersion relations are derived that hold for any values of the plasma temperatures and the temperature anisotropy. In the limit of nonrelativistic plasma temperatures the dispersion relations are expressed in terms of plasma dispersion function, however, the dependence on frequency and wave numbers is markedly different from the standard noncovariant nonrelativistic analysis. Only in the strictly unphysical formal limit of an infinitely large speed of light, c→∞, does the nonrelativistic dispersion relations reduce to the standard noncovariant dispersion relations

Getting super-excited with modified dispersion relations

Energy Technology Data Exchange (ETDEWEB)

Ashoorioon, Amjad; Casadio, Roberto [INFN—Sezione di Bologna, viale B. Pichat 6/2, I-40127 Bologna (Italy); Geshnizjani, Ghazal; Kim, Hyung J., E-mail: amjad.ashoorioon@bo.infn.it, E-mail: roberto.casadio@bo.infn.it, E-mail: ggeshniz@uwaterloo.ca, E-mail: h268kim@uwaterloo.ca [Department of Applied Mathematics, University of Waterloo Waterloo, Ontario, N2L 3G1 (Canada)

2017-09-01

We demonstrate that in some regions of parameter space, modified dispersion relations can lead to highly populated excited states, which we dub as 'super-excited' states. In order to prepare such super-excited states, we invoke dispersion relations that have negative slope in an interim sub-horizon phase at high momenta. This behaviour of quantum fluctuations can lead to large corrections relative to the Bunch-Davies power spectrum, which mimics highly excited initial conditions. We identify the Bogolyubov coefficients that can yield these power spectra. In the course of this computation, we also point out the shortcomings of the gluing method for evaluating the power spectrum and the Bogolyubov coefficients. As we discuss, there are other regions of parameter space, where the power spectrum does not get modified. Therefore, modified dispersion relations can also lead to so-called 'calm excited states'. We conclude by commenting on the possibility of obtaining these modified dispersion relations within the Effective Field Theory of Inflation.

The Whitham approach to dispersive shocks in systems with cubic–quintic nonlinearities

KAUST Repository

Crosta, M

2012-09-12

By employing a rigorous approach based on the Whitham modulation theory, we investigate dispersive shock waves arising in a high-order nonlinear Schrödinger equation with competing cubic and quintic nonlinear responses. This model finds important applications in both nonlinear optics and Bose–Einstein condensates. Our theory predicts the formation of dispersive shocks with totally controllable properties, encompassing both steering and compression effects. Numerical simulations confirm these results perfectly. Quite remarkably, shock tuning can be achieved in the regime of a very small high order, i.e. quintic, nonlinearity.

The Whitham approach to dispersive shocks in systems with cubic–quintic nonlinearities

KAUST Repository

Crosta, M; Trillo, S; Fratalocchi, Andrea

2012-01-01

By employing a rigorous approach based on the Whitham modulation theory, we investigate dispersive shock waves arising in a high-order nonlinear Schrödinger equation with competing cubic and quintic nonlinear responses. This model finds important applications in both nonlinear optics and Bose–Einstein condensates. Our theory predicts the formation of dispersive shocks with totally controllable properties, encompassing both steering and compression effects. Numerical simulations confirm these results perfectly. Quite remarkably, shock tuning can be achieved in the regime of a very small high order, i.e. quintic, nonlinearity.

Skeletonized wave equation of surface wave dispersion inversion

KAUST Repository

Li, Jing

2016-09-06

We present the theory for wave equation inversion of dispersion curves, where the misfit function is the sum of the squared differences between the wavenumbers along the predicted and observed dispersion curves. Similar to wave-equation travel-time inversion, the complicated surface-wave arrivals in traces are skeletonized as simpler data, namely the picked dispersion curves in the (kx,ω) domain. Solutions to the elastic wave equation and an iterative optimization method are then used to invert these curves for 2D or 3D velocity models. This procedure, denoted as wave equation dispersion inversion (WD), does not require the assumption of a layered model and is less prone to the cycle skipping problems of full waveform inversion (FWI). The synthetic and field data examples demonstrate that WD can accurately reconstruct the S-wave velocity distribution in laterally heterogeneous media.

A finite parallel zone model to interpret and extend Giddings' coupling theory for the eddy-dispersion in porous chromatographic media.

Science.gov (United States)

Desmet, Gert

2013-11-01

The finite length parallel zone (FPZ)-model is proposed as an alternative model for the axial- or eddy-dispersion caused by the occurrence of local velocity biases or flow heterogeneities in porous media such as those used in liquid chromatography columns. The mathematical plate height expression evolving from the model shows that the A- and C-term band broadening effects that can originate from a given velocity bias should be coupled in an exponentially decaying way instead of harmonically as proposed in Giddings' coupling theory. In the low and high velocity limit both models converge, while a 12% difference can be observed in the (practically most relevant) intermediate range of reduced velocities. Explicit expressions for the A- and C-constants appearing in the exponential decay-based plate height expression have been derived for each of the different possible velocity bias levels (single through-pore and particle level, multi-particle level and trans-column level). These expressions allow to directly relate the band broadening originating from these different levels to the local fundamental transport parameters, hence offering the possibility to include a velocity-dependent and, if, needed retention factor-dependent transversal dispersion coefficient. Having developed the mathematics for the general case wherein a difference in retention equilibrium establishes between the two parallel zones, the effect of any possible local variations in packing density and/or retention capacity on the eddy-dispersion can be explicitly accounted for as well. It is furthermore also shown that, whereas the lumped transport parameter model used in the basic variant of the FPZ-model only provides a first approximation of the true decay constant, the model can be extended by introducing a constant correction factor to correctly account for the continuous transversal dispersion transport in the velocity bias zones. Copyright © 2013 Elsevier B.V. All rights reserved.

Ab initio phonon dispersions of face centered cubic Pb: effects of spin-orbit coupling

International Nuclear Information System (INIS)

Dal Corso, Andrea

2008-01-01

I present the ab initio phonon dispersions of face centered cubic Pb calculated within the framework of density functional perturbation theory, with plane waves and a fully relativistic ultrasoft pseudopotential which includes spin-orbit coupling effects. I find that, within the local density approximation, the theory gives phonon frequencies close to the experimental inelastic neutron scattering data. Many of the anomalies present in these dispersions are well reproduced by the fully relativistic pseudopotential theory and can be shown to appear only for small values of the smearing parameter that controls the sharpness of the Fermi surface.

Holographic Fermions in Anisotropic Einstein-Maxwell-Dilaton-Axion Theory

International Nuclear Information System (INIS)

Kuang, Xiao-Mei; Fang, Li-Qing

2015-01-01

We investigate the properties of the holographic Fermionic system dual to an anisotropic charged black brane bulk in Einstein-Maxwell-Dilaton-Axion gravity theory. We consider the minimal coupling between the Dirac field and the gauge field in the bulk gravity theory and mainly explore the dispersion relation exponents of the Green functions of the dual Fermionic operators in the dual field theory. We find that along both the anisotropic and the isotropic directions the Fermi momentum will be effected by the anisotropy of the bulk theory. However, the anisotropy has influence on the dispersion relation which is almost linear for massless Fermions with charge q=2. The universal properties that the mass and the charge of the Fermi possibly correspond to nonlinear dispersion relation are also investigated

Should we stay or should we go: mechanisms and ecological consequences for biofilm dispersal.

Science.gov (United States)

McDougald, Diane; Rice, Scott A; Barraud, Nicolas; Steinberg, Peter D; Kjelleberg, Staffan

2011-11-28

In most environments, bacteria reside primarily in biofilms, which are social consortia of cells that are embedded in an extracellular matrix and undergo developmental programmes resulting in a predictable biofilm 'life cycle'. Recent research on many different bacterial species has now shown that the final stage in this life cycle includes the production and release of differentiated dispersal cells. The formation of these cells and their eventual dispersal is initiated through diverse and remarkably sophisticated mechanisms, suggesting that there are strong evolutionary pressures for dispersal from an otherwise largely sessile biofilm. The evolutionary aspect of biofilm dispersal is now being explored through the integration of molecular microbiology with eukaryotic ecological and evolutionary theory, which provides a broad conceptual framework for the diversity of specific mechanisms underlying biofilm dispersal. Here, we review recent progress in this emerging field and suggest that the merging of detailed molecular mechanisms with ecological theory will significantly advance our understanding of biofilm biology and ecology.

Compact dispersion relations for parametric instabilities of electromagnetic waves in magnetized plasmas

International Nuclear Information System (INIS)

Cohen, B.I.

1987-01-01

The existence of compact dispersion relations for parametric instabilities of coherent electromagnetic waves in magnetized plasmas is addressed here. In general, comprehensive dispersion relations for parametric instabilities in unmagnetized plasmas become more complicated in the presence of an applied time-independent magnetic field. This is demonstrated with a fluid perturbation theory. A compact dispersion relation for parametric instabilities in unmagnetized plasma is heuristically extended here to the case of a magnetized plasma. This dispersion relation gives the correct results in a variety of circumstances of interest in considering electron cyclotron heating applications

A simple and efficient dispersion correction to the Hartree-Fock theory (2): Incorporation of a geometrical correction for the basis set superposition error.

Science.gov (United States)

Yoshida, Tatsusada; Hayashi, Takahisa; Mashima, Akira; Chuman, Hiroshi

2015-10-01

One of the most challenging problems in computer-aided drug discovery is the accurate prediction of the binding energy between a ligand and a protein. For accurate estimation of net binding energy ΔEbind in the framework of the Hartree-Fock (HF) theory, it is necessary to estimate two additional energy terms; the dispersion interaction energy (Edisp) and the basis set superposition error (BSSE). We previously reported a simple and efficient dispersion correction, Edisp, to the Hartree-Fock theory (HF-Dtq). In the present study, an approximation procedure for estimating BSSE proposed by Kruse and Grimme, a geometrical counterpoise correction (gCP), was incorporated into HF-Dtq (HF-Dtq-gCP). The relative weights of the Edisp (Dtq) and BSSE (gCP) terms were determined to reproduce ΔEbind calculated with CCSD(T)/CBS or /aug-cc-pVTZ (HF-Dtq-gCP (scaled)). The performance of HF-Dtq-gCP (scaled) was compared with that of B3LYP-D3(BJ)-bCP (dispersion corrected B3LYP with the Boys and Bernadi counterpoise correction (bCP)), by taking ΔEbind (CCSD(T)-bCP) of small non-covalent complexes as 'a golden standard'. As a critical test, HF-Dtq-gCP (scaled)/6-31G(d) and B3LYP-D3(BJ)-bCP/6-31G(d) were applied to the complex model for HIV-1 protease and its potent inhibitor, KNI-10033. The present results demonstrate that HF-Dtq-gCP (scaled) is a useful and powerful remedy for accurately and promptly predicting ΔEbind between a ligand and a protein, albeit it is a simple correction procedure. Copyright © 2015 Elsevier Ltd. All rights reserved.

Anomalous acoustic dispersion in architected microlattice metamaterials

Science.gov (United States)

KröDel, Sebastian; Palermo, Antonio; Daraio, Chiara

The ability to control dispersion in acoustic metamaterials is crucial to realize acoustic filtering and rectification devices as well as perfect imaging using negative refractive index materials. Architected microlattice metamaterials immersed in fluid constitute a versatile platform for achieving such control. We investigate architected microlattice materials able to exploit locally resonant modes of their fundamental building blocks that couple with propagating acoustic waves. Using analytical, numerical and experimental methods we find that such lattice materials show a hybrid dispersion behavior governed by Biot's theory for long wavelengths and multiple scattering theory when wave frequency is close to the resonances of the building block. We identify the relevant geometric parameters to alter and control the group and phase velocities in this class of acoustic metamaterials. Furthermore, we fabricate small-scale acoustic metamaterial samples using high precision SLA additive manufacturing and test the resulting materials experimentally using a customized ultrasonic setup. This work paves the way for new acoustic devices based on microlattice metamaterials.

Interfacial phenomenon theory

International Nuclear Information System (INIS)

Kim, Jong Deuk

2000-02-01

This book is composed of 8 chapters. It tells what interfacial phenomenon is by showing interfacial energy, characteristic of interface and system of interface from chapter 1. It also introduces interfacial energy and structure theory, molecular structure and orientation theory, and interfacial electricity phenomenon theory in the following 3 chapters. It still goes on by introducing super molecule cluster, disequilibrium dispersion, and surface and film through 3 chapters. And the last chapter is about colloid and application of interface.

A hybrid plume model for local-scale dispersion

Energy Technology Data Exchange (ETDEWEB)

Nikmo, J.; Tuovinen, J.P.; Kukkonen, J.; Valkama, I.

1997-12-31

The report describes the contribution of the Finnish Meteorological Institute to the project `Dispersion from Strongly Buoyant Sources`, under the `Environment` programme of the European Union. The project addresses the atmospheric dispersion of gases and particles emitted from typical fires in warehouses and chemical stores. In the study only the `passive plume` regime, in which the influence of plume buoyancy is no longer important, is addressed. The mathematical model developed and its numerical testing is discussed. The model is based on atmospheric boundary-layer scaling theory. In the vicinity of the source, Gaussian equations are used in both the horizontal and vertical directions. After a specified transition distance, gradient transfer theory is applied in the vertical direction, while the horizontal dispersion is still assumed to be Gaussian. The dispersion parameters and eddy diffusivity are modelled in a form which facilitates the use of a meteorological pre-processor. Also a new model for the vertical eddy diffusivity (K{sub z}), which is a continuous function of height in the various atmospheric scaling regions is presented. The model includes a treatment of the dry deposition of gases and particulate matter, but wet deposition has been neglected. A numerical solver for the atmospheric diffusion equation (ADE) has been developed. The accuracy of the numerical model was analysed by comparing the model predictions with two analytical solutions of ADE. The numerical deviations of the model predictions from these analytic solutions were less than two per cent for the computational regime. The report gives numerical results for the vertical profiles of the eddy diffusivity and the dispersion parameters, and shows spatial concentration distributions in various atmospheric conditions 39 refs.

Large J expansion in ABJM theory revisited.

Science.gov (United States)

Dimov, H; Mladenov, S; Rashkov, R C

Recently there has been progress in the computation of the anomalous dimensions of gauge theory operators at strong coupling by making use of the AdS/CFT correspondence. On the string theory side they are given by dispersion relations in the semiclassical regime. We revisit the problem of a large-charge expansion of the dispersion relations for simple semiclassical strings in an [Formula: see text] background. We present the calculation of the corresponding anomalous dimensions of the gauge theory operators to an arbitrary order using three different methods. Although the results of the three methods look different, power series expansions show their consistency.

Computing modal dispersion characteristics of radially Asymmetric ...

African Journals Online (AJOL)

We developed a matrix theory that applies to with non-circular/circular but concentric layers fibers. And we compute the dispersion characteristics of radially unconventional fiber, known as Asymmetric Bragg fiber. An attempt has been made to determine how the modal characteristics change as circular Bragg fiber is ...

Progress in the axiomatic quantum field theory

International Nuclear Information System (INIS)

Vladimirov, V.S.; Polivanov, M.K.

1975-01-01

The authors consider the development of mathematical methods of solving quantum field theory problems from attempts of simple perfection of usual methods of quantum mechanics by elaborating the methods of perturbation theory and S-matrix, by working out the perturbation theory for quantum electrodynamics, and by applying dispersion relations and S-matrix for strong interactions. The method of dispersion relations results in the majority of radically new ways of describing the scattering amplitude. The grave disadvantage of all the methods is that they little define the dynamics of processes. The dynamic theory in the Heisenberg representation may be constructed on the basis of the axiomatic theory of S-matrix with the casuality condition. Another axiomatic direction has been recently developed; that is the so-called algebraic axiomatics which makes use of methods of Csup(*)-algebras

Quantum X waves with orbital angular momentum in nonlinear dispersive media

Science.gov (United States)

Ornigotti, Marco; Conti, Claudio; Szameit, Alexander

2018-06-01

We present a complete and consistent quantum theory of generalised X waves with orbital angular momentum in dispersive media. We show that the resulting quantised light pulses are affected by neither dispersion nor diffraction and are therefore resilient against external perturbations. The nonlinear interaction of quantised X waves in quadratic and Kerr nonlinear media is also presented and studied in detail.

Dispersion relations for η{sup '} → ηππ

Energy Technology Data Exchange (ETDEWEB)

Isken, Tobias; Kubis, Bastian; Schneider, Sebastian P. [Universitaet Bonn, Helmholtz-Institut fuer Strahlen- und Kernphysik and Bethe Center for Theoretical Physics, Bonn (Germany); Stoffer, Peter [Universitaet Bonn, Helmholtz-Institut fuer Strahlen- und Kernphysik and Bethe Center for Theoretical Physics, Bonn (Germany); University of California at San Diego, Department of Physics, La Jolla, CA (United States)

2017-07-15

We present a dispersive analysis of the decay amplitude for η{sup '} → ηππ that is based on the fundamental principles of analyticity and unitarity. In this framework, final-state interactions are fully taken into account. Our dispersive representation relies only on input for the ππ and πη scattering phase shifts. Isospin symmetry allows us to describe both the charged and neutral decay channel in terms of the same function. The dispersion relation contains subtraction constants that cannot be fixed by unitarity. We determine these parameters by a fit to Dalitz-plot data from the VES and BES-III experiments. We study the prediction of a low-energy theorem and compare the dispersive fit to variants of chiral perturbation theory. (orig.)

Dispersion of swimming algae in laminar and turbulent channel flows: consequences for photobioreactors.

Science.gov (United States)

Croze, Ottavio A; Sardina, Gaetano; Ahmed, Mansoor; Bees, Martin A; Brandt, Luca

2013-04-06

Shear flow significantly affects the transport of swimming algae in suspension. For example, viscous and gravitational torques bias bottom-heavy cells to swim towards regions of downwelling fluid (gyrotaxis). It is necessary to understand how such biases affect algal dispersion in natural and industrial flows, especially in view of growing interest in algal photobioreactors. Motivated by this, we here study the dispersion of gyrotactic algae in laminar and turbulent channel flows using direct numerical simulation (DNS) and a previously published analytical swimming dispersion theory. Time-resolved dispersion measures are evaluated as functions of the Péclet and Reynolds numbers in upwelling and downwelling flows. For laminar flows, DNS results are compared with theory using competing descriptions of biased swimming cells in shear flow. Excellent agreement is found for predictions that employ generalized Taylor dispersion. The results highlight peculiarities of gyrotactic swimmer dispersion relative to passive tracers. In laminar downwelling flow the cell distribution drifts in excess of the mean flow, increasing in magnitude with Péclet number. The cell effective axial diffusivity increases and decreases with Péclet number (for tracers it merely increases). In turbulent flows, gyrotactic effects are weaker, but discernable and manifested as non-zero drift. These results should have a significant impact on photobioreactor design.

Timing-jitter reduction in a dispersion-managed soliton system

International Nuclear Information System (INIS)

Mu, R.; Grigoryan, V.S.; Menyuk, C.R.; Golovchenko, E.A.; Pilipetskii, A.N.

1998-01-01

We found by using Monte Carlo simulations that the timing jitter in a dispersion-managed soliton system decreases as the strength of the dispersion management and hence the ratio of the pulse energy to the pulse bandwidth increases. The results are in qualitative but not quantitative agreement with earlier predictions that the decrease is inversely proportional to the square root of the pulse energy. Using an improved semi-analytical theory, we obtained quantitative agreement with the simulations. copyright 1998 Optical Society of America

Leonhard Euler's Wave Theory of Light

DEFF Research Database (Denmark)

Pedersen, Kurt Møller

2008-01-01

Euler's wave theory of light developed from a mere description of this notion based on an analogy between sound and light to a more and more mathematical elaboration on that notion. He was very successful in predicting the shape of achromatic lenses based on a new dispersion law that we now know...... of achromatic lenses, the explanation of colors of thin plates and of the opaque bodies as proof of his theory. When it came to the fundamental issues, the correctness of his dispersion law and the prediction of frequencies of light he was not at all successful. His wave theory degenerated, and it was not until...... is wrong. Most of his mathematical arguments were, however, guesswork without any solid physical reasoning. Guesswork is not always a bad thing in physics if it leads to new experiments or makes the theory coherent with other theories. And Euler tried to find such experiments. He saw the construction...

Defining the contributions of permanent electrostatics, Pauli repulsion, and dispersion in density functional theory calculations of intermolecular interaction energies

Energy Technology Data Exchange (ETDEWEB)

Horn, Paul R., E-mail: prhorn@berkeley.edu; Mao, Yuezhi; Head-Gordon, Martin, E-mail: mhg@cchem.berkeley.edu [Kenneth S. Pitzer Center for Theoretical Chemistry, Department of Chemistry, University of California, Berkeley, California 94720, USA and Chemical Sciences Division Lawrence Berkeley National Laboratory Berkeley, California 94720 (United States)

2016-03-21

In energy decomposition analysis of Kohn-Sham density functional theory calculations, the so-called frozen (or pre-polarization) interaction energy contains contributions from permanent electrostatics, dispersion, and Pauli repulsion. The standard classical approach to separate them suffers from several well-known limitations. We introduce an alternative scheme that employs valid antisymmetric electronic wavefunctions throughout and is based on the identification of individual fragment contributions to the initial supersystem wavefunction as determined by an energetic optimality criterion. The density deformations identified with individual fragments upon formation of the initial supersystem wavefunction are analyzed along with the distance dependence of the new and classical terms for test cases that include the neon dimer, ammonia borane, water-Na{sup +}, water-Cl{sup −}, and the naphthalene dimer.

A complex-polarization-propagator protocol for magneto-chiral axial dichroism and birefringence dispersion

DEFF Research Database (Denmark)

Cukras, Janusz; Kauczor, Joanna; Norman, Patrick

2016-01-01

A computational protocol for magneto-chiral dichroism and magneto-chiral birefringence dispersion is presented within the framework of damped response theory, also known as complex polarization propagator theory, at the level of time-dependent Hartree–Fock and time-dependent density functional th...

Dispersion of extensional waves in fluid-saturated porous cylinders at ultrasonic frequencies

International Nuclear Information System (INIS)

Berryman, J.G.

1983-01-01

Ultrasonic dispersion of extensional waves in fluid-saturated porous cylinders is studied by analyzing generalized Pochhammer equations derived using Biot's theory. Cases with open-pore surface and closed-pore surface boundary conditions are considered. For both cases, the dispersion of the fast extensional wave does not differ much qualitatively from the dispersion expected for extensional waves in isotropic elastic cylinders. A slow extensional wave propagates in the case with a closed-pore surface but not in the case with an open-pore surface. The propagating slow wave has very weak dispersion and its speed is always lower than, but close to, the bulk slow wave speed

Instabilities in passive dispersion oscillating fiber ring cavities

Science.gov (United States)

Copie, François; Conforti, Matteo; Kudlinski, Alexandre; Mussot, Arnaud; Biancalana, Fabio; Trillo, Stefano

2017-05-01

We investigate theoretically and experimentally the development of instabilities in passive ring cavities with stepwise longitudinal variation of the dispersion. We derive an extended version of the Lugiato-Lefever equation that permits to model dispersion oscillating cavities and we demonstrate that this equation is valid well beyond the mean field approximation. We review the theory of Turing (modulational) and Faraday (parametric) instability in inhomogeneous fiber cavities. We report the experimental demonstration of the generation of stable Turing and Faraday temporal patterns in the same device, which can be controlled by changing the detuning and/or the input power. Moreover, we experimentally record the round-trip-to-round-trip dynamics of the spectrum, which shows that Turing and Faraday instabilities not only differ by their characteristic frequency but also by their dynamical behavior. Contribution to the Topical Issue: "Theory and Applications of the Lugiato-Lefever Equation", edited by Yanne K. Chembo, Damia Gomila, Mustapha Tlidi, Curtis R. Menyuk.

Influence of prey dispersion on territory and group size of African lions: a test of the resource dispersion hypothesis.

Science.gov (United States)

Valeix, Marion; Loveridge, Andrew J; MacDonald, David W

2012-11-01

Empirical tests of the resource dispersion hypothesis (RDH), a theory to explain group living based on resource heterogeneity, have been complicated by the fact that resource patch dispersion and richness have proved difficult to define and measure in natural systems. Here, we studied the ecology of African lions Panthera leo in Hwange National Park, Zimbabwe, where waterholes are prey hotspots, and where dispersion of water sources and abundance of prey at these water sources are quantifiable. We combined a 10-year data set from GPS-collared lions for which information of group composition was available concurrently with data for herbivore abundance at waterholes. The distance between two neighboring waterholes was a strong determinant of lion home range size, which provides strong support for the RDH prediction that territory size increases as resource patches are more dispersed in the landscape. The mean number of herbivore herds using a waterhole, a good proxy of patch richness, determined the maximum lion group biomass an area can support. This finding suggests that patch richness sets a maximum ceiling on lion group size. This study demonstrates that landscape ecology is a major driver of ranging behavior and suggests that aspects of resource dispersion limit group sizes.

Progress in the axiomatic quantum field theory. [Review

Energy Technology Data Exchange (ETDEWEB)

Vladimirov, V S; Polivanov, M K

1975-01-01

The authors consider the development of mathematical methods of solving quantum field theory problems from attempts of simple perfection of usual methods of quantum mechanics by elaborating the methods of perturbation theory and S-matrix, by working out the perturbation theory for quantum electrodynamics, and by applying dispersion relations and S-matrix for strong interactions. The method of dispersion relations results in the majority of radically new ways of describing the scattering amplitude. The grave disadvantage of all the methods is that they little define the dynamics of processes. The dynamic theory in the Heisenberg representation may be constructed on the basis of the axiomatic theory of S-matrix with the casuality condition. Another axiomatic direction has been recently developed; that is the so-called algebraic axiomatics which makes use of methods of Csup(*)-algebras.

Inclusion of Dispersion Effects in Density Functional Theory

DEFF Research Database (Denmark)

Møgelhøj, Andreas

on fitting to high-level ab initio and experimental results. The fitting scheme, based on Baysian theory, focuses on the three aspects: a) model space, b) datasets, and c) model selection. The model space consists of a flexible expansion of the exchange enhancement factor in the generalized gradient......In this thesis, applications and development will be presented within the field of van der Waals interactions in density functional theory. The thesis is based on the three projects: i) van der Waals interactions effect on the structure of liquid water at ambient conditions, ii) development......-range van der Waals interactions is essential to describe the adsorption/desorption process and commonly used generalized gradient approximation functionals are seen to be incapable of this....

Effect of pore size distribution and flow segregation on dispersion in porous media

International Nuclear Information System (INIS)

Carbonell, R.G.

1978-11-01

In order to study the effect of the pore size distribution and flow segregation on dispersion in a porous media, the dispersion of solute in an array of parallel pores is considered. Equations are obtained for the dispersion coefficient in laminar and turbulent flow, as a function of the particle Peclet number. The theory fits quite well cumulative experimental data from various researchers in the Peclet number range from 10 -3 to 10 6 . The model also predicts some trends, backed by experimental data, regarding the effect of particle size, particle size distribution and fluid velocity on dispersion

Benchmarking of London Dispersion-Accounting Density Functional Theory Methods on Very Large Molecular Complexes.

Science.gov (United States)

Risthaus, Tobias; Grimme, Stefan

2013-03-12

A new test set (S12L) containing 12 supramolecular noncovalently bound complexes is presented and used to evaluate seven different methods to account for dispersion in DFT (DFT-D3, DFT-D2, DFT-NL, XDM, dDsC, TS-vdW, M06-L) at different basis set levels against experimental, back-corrected reference energies. This allows conclusions about the performance of each method in an explorative research setting on "real-life" problems. Most DFT methods show satisfactory performance but, due to the largeness of the complexes, almost always require an explicit correction for the nonadditive Axilrod-Teller-Muto three-body dispersion interaction to get accurate results. The necessity of using a method capable of accounting for dispersion is clearly demonstrated in that the two-body dispersion contributions are on the order of 20-150% of the total interaction energy. MP2 and some variants thereof are shown to be insufficient for this while a few tested D3-corrected semiempirical MO methods perform reasonably well. Overall, we suggest the use of this benchmark set as a "sanity check" against overfitting to too small molecular cases.

Use of multiple dispersal pathways facilitates amphibian persistence in stream networks

Science.gov (United States)

Campbell, Grant E.H.; Nichols, J.D.; Lowe, W.H.; Fagan, W.F.

2010-01-01

Although populations of amphibians are declining worldwide, there is no evidence that salamanders occupying small streams are experiencing enigmatic declines, and populations of these species seem stable. Theory predicts that dispersal through multiple pathways can stabilize populations, preventing extinction in habitat networks. However, empirical data to support this prediction are absent for most species, especially those at risk of decline. Our mark-recapture study of stream salamanders reveals both a strong upstream bias in dispersal and a surprisingly high rate of overland dispersal to adjacent headwater streams. This evidence of route-dependent variation in dispersal rates suggests a spatial mechanism for population stability in headwater-stream salamanders. Our results link the movement behavior of stream salamanders to network topology, and they underscore the importance of identifying and protecting critical dispersal pathways when addressing region-wide population declines.

Use of multiple dispersal pathways facilitates amphibian persistence in stream networks.

Science.gov (United States)

Campbell Grant, Evan H; Nichols, James D; Lowe, Winsor H; Fagan, William F

2010-04-13

Although populations of amphibians are declining worldwide, there is no evidence that salamanders occupying small streams are experiencing enigmatic declines, and populations of these species seem stable. Theory predicts that dispersal through multiple pathways can stabilize populations, preventing extinction in habitat networks. However, empirical data to support this prediction are absent for most species, especially those at risk of decline. Our mark-recapture study of stream salamanders reveals both a strong upstream bias in dispersal and a surprisingly high rate of overland dispersal to adjacent headwater streams. This evidence of route-dependent variation in dispersal rates suggests a spatial mechanism for population stability in headwater-stream salamanders. Our results link the movement behavior of stream salamanders to network topology, and they underscore the importance of identifying and protecting critical dispersal pathways when addressing region-wide population declines.

Validation of missed space-group symmetry in X-ray powder diffraction structures with dispersion-corrected density functional theory.

Science.gov (United States)

Hempler, Daniela; Schmidt, Martin U; van de Streek, Jacco

2017-08-01

More than 600 molecular crystal structures with correct, incorrect and uncertain space-group symmetry were energy-minimized with dispersion-corrected density functional theory (DFT-D, PBE-D3). For the purpose of determining the correct space-group symmetry the required tolerance on the atomic coordinates of all non-H atoms is established to be 0.2 Å. For 98.5% of 200 molecular crystal structures published with missed symmetry, the correct space group is identified; there are no false positives. Very small, very symmetrical molecules can end up in artificially high space groups upon energy minimization, although this is easily detected through visual inspection. If the space group of a crystal structure determined from powder diffraction data is ambiguous, energy minimization with DFT-D provides a fast and reliable method to select the correct space group.

Experimental research on dispersion parameters of ground water around the area of CIAE

International Nuclear Information System (INIS)

Yu Jun

1993-01-01

The dispersion are important parameters in modeling the migration of pollutant in the ground water. Due to the complexity of geological media, variant dispersion is expected according to the difference of the geological media. Three parts are included in physical simulation in the laboratory column, tracer experiment in the field and the prediction of dispersion using the stochastic model. Experimental results show that the dispersion obtained in the column are three orders of magnitude smaller than that obtained in the field. Using the field values of conductivity and stochastic theory, the calculated asymptotic longitudinal and lateral dispersion are 370 and 0.45 meters respectively and the correlation length is 400 meters approximately. Using the dispersion obtained from the formula in the paper can enhance the precision of the model prediction, the distance heeded to reach the Fick's dispersion is 6 km approximately

Approximate Stream Function wavemaker theory for highly non-linear waves in wave flumes

DEFF Research Database (Denmark)

Zhang, H.W.; Schäffer, Hemming Andreas

2007-01-01

An approximate Stream Function wavemaker theory for highly non-linear regular waves in flumes is presented. This theory is based on an ad hoe unified wave-generation method that combines linear fully dispersive wavemaker theory and wave generation for non-linear shallow water waves. This is done...... by applying a dispersion correction to the paddle position obtained for non-linear long waves. The method is validated by a number of wave flume experiments while comparing with results of linear wavemaker theory, second-order wavemaker theory and Cnoidal wavemaker theory within its range of application....

Noise-induced perturbations of dispersion-managed solitons

International Nuclear Information System (INIS)

Li, Jinglai; Spiller, Elaine; Biondini, Gino

2007-01-01

We study noise-induced perturbations of dispersion-managed solitons. We do so by first developing soliton perturbation theory for the dispersion-managed nonlinear Schroedinger (DMNLS) equation, which governs the long-term behavior of optical fiber transmission systems and certain kinds of femtosecond lasers. We show that the eigenmodes and generalized eigenmodes of the linearized DMNLS equation around traveling-wave solutions can be generated from the invariances of the DMNLS equations, we quantify the perturbation-induced parameter changes of the solution in terms of the eigenmodes and the adjoint eigenmodes, and we obtain evolution equations for the solution parameters. We then apply these results to guide importance-sampled Monte Carlo (MC) simulations and reconstruct the probability density functions of the solution parameters under the effect of noise, and we compare with standard MC simulations of the unaveraged system. The comparison further validates the use of the DMNLS equation as a model for dispersion-managed systems

Relationships of dispersive mass transport and stochastic convective flow through hydrologic systems

International Nuclear Information System (INIS)

Simmons, C.S.

1981-01-01

Uncertainty in water flow velocity appears to be a major factor in determining the magnitude of contaminant dispersion expected in a ground water system. This report discusses some concepts and mathematical methods relating dispersive contaminant transport to stochastic aspects of ground water flow. The theory developed should not be construed as absolutely rigorous mathematics, but is presented with the intention of clarifying the physical concepts

An introduction to effective field theory

International Nuclear Information System (INIS)

Donoghue, John F.

1999-01-01

In these lectures I describe the main ideas of effective field theory. These are first illustrated using QED and the linear sigma model as examples. Calculational techniques using both Feynman diagrams and dispersion relations are introduced. Within QCD, chiral perturbation theory is a complete effective field theory, and I give a guide to some calculations in the literature which illustrates key ideas. (author)

Dispersive effects in radiation transport and radiation hydrodynamics in matter at high density

International Nuclear Information System (INIS)

Crowley, B.J.B.

1983-01-01

In a recent research program (reported in AWRE 0 20/82) I have investigated the generalisation of the equations of radiation hydrodynamics when electromagnetic radiation is assumed to obey a linear-response dispersion relation of the form nω=kc where the refractive index n depends on the frequency ω and/or wave number k. From the application of the Boltzmann-Liouville transport theory to photons in the short-wavelength (geometrical optics) limit, I derive the energy and momentum equations which, when combined with a classical (Euler-Lagrange-Navier-Stokes) treatment of a fluid material medium in LTE, yield a complete dynamical theory of linear interactions (+ stimulated processes) between incoherent (thermal) radiation and dense, locally isotropic matter. The theory includes an account of pondero-motive forces and electro (magneto) striction. Moreover, it is apparently capable of being generalised to non-linear interactions in which the refractive index depends on the local specific intensity of the radiation field, and, to some extent, to the treatment of high-frequency coherent radiation. The generalisation of various approximated forms of radiation-transport theory (esp. diffusion) has been considered in detail. Some problems remain however. One such is the treatment of anomalous dispersion. Current research work is concentrating on the interesting atomic physics aspects of electromagnetic (esp. radiative) properties of a dispersive material medium

Theoretical Aspects of Phonon Dispersion Curves for Metals

International Nuclear Information System (INIS)

Cochran, W.

1965-01-01

Reasonably complete knowledge of the phonon dispersion curves for at least a dozen metallic elements and intermetallic compounds has now been obtained from neutron inelastic scattering experiments. The results have one feature in common: when analysed in terms of interatomic force constants they reveal the presence of comparatively long-range forces extending over several atomic spacings. The results for lead are particularly interesting; it did not prove possible to fit them by a force-constant model, but the dispersion curves for wave vectors in symmetry directions when analysed in terms of force constants between planes of atoms showed an oscillatory interatomic potential extending over distances of more than 20Å. This review is concerned with recent theoretical work which has a bearing on the calculation of phonon dispersion curves for metals and the explanation of the long range of the interatomic potential. The best hope at present for a general treatment of atomic interaction in metals appears to lie in the ''method of neutral pseudo-atoms'', (a description recently coined by Ziman). This approximate theory is outlined and its relevance to Kohn anomalies in phonon dispersion curves is discussed. Experimental data for sodium is consistent with the theory, and the interatomic potential in sodium varies periodically in a distance π/k F , where fik F is the Fermi momentum, as has already been demonstrated by Koenig in a different way. More exact calculations have been made for sodium by Toya and by Sham. The relationship between the different methods and other work of a more general character such as that of Harrison are discussed. (author) [fr

Ionic Liquid-Modified Thermosets and Their Nanocomposites: Dispersion, Exfoliation, Degradation, and Cure

Science.gov (United States)

Throckmorton, James A.

This dissertation explores the application of a room temperature ionic liquid (RTIL) to problems in the chemistry, processing, and modification of thermosetting polymers. In particular, the solution properties and reaction chemistry of 1-ethyl-3-methyl imidazolium dicyanamide (EMIM-DCN) are applied to problems of nanoparticle dispersion and processing, graphite exfoliation, cyanate ester (CE) cure, and the environmental degradation of CEs. Nanoparticle Dispersion: Nanocomposite processing can be simplified by using the same compound as both a nanoparticle solvent and an initiator for polymerization. This dual-function molecule can be designed both for solvent potential and reaction chemistry. EMIM-DCN, previously shown by our lab to act as an epoxy initiator, is used in the synthesis of silica and acid expanded graphite composites. These composites are then characterized for particle dispersion and physical properties. Individual particle dispersion of silica nanocomposites is shown, and silica nanocomposites at low loading show individual particle dispersion and improved modulus and fracture toughness. GNP nanocomposites show a 70% increase in modulus along with a 10-order of magnitude increase in electrical conductivity at 6.5 vol%, and an electrical percolation threshold of 1.7 vol%. Direct Graphite Exfoliation By Laminar Shear: This work presents a laminar-shear alternative to chemical processing and chaotic flow-fields for the direct exfoliation of graphite and the single-pot preparation of nanocomposites. Additionally, we develop the theory of laminar flow through a 3-roll mill, and apply that theory to the latest developments in the theory of graphite interlayer shear. The resulting nanocomposite shows low electrical percolation (0.5 vol%) and low thickness (1-3 layer) graphite/graphene flakes. Additionally, the effect of processing conditions by rheometry and comparison with solvent-free conditions reveal the interactions between processing and matrix

Glass-liquid-glass reentrance in mono-component colloidal dispersions

International Nuclear Information System (INIS)

Ramirez-Gonzalez, P E; Medina-Noyola, M; Vizcarra-Rendon, A; Guevara-Rodriguez, F de J

2008-01-01

The self-consistent generalized Langevin equation (SCGLE) theory of colloid dynamics is employed to describe the ergodic-non-ergodic transition in model mono-disperse colloidal dispersions whose particles interact through hard-sphere plus short-ranged attractive forces. The ergodic-non-ergodic phase diagram in the temperature-concentration state space is determined for the hard-sphere plus attractive Yukawa model within the mean spherical approximation for the static structure factor by solving a remarkably simple equation for the localization length of the colloidal particles. Finite real values of this property signals non-ergodicity and determines the non-ergodic parameters f(k) and f s (k). The resulting phase diagram for this system, which involves the existence of reentrant (repulsive and attractive) glass states, is compared with the corresponding prediction of mode coupling theory. Although both theories coincide in the general features of this phase diagram, there are also clear qualitative differences. One of the most relevant is the SCGLE prediction that the ergodic-attractive glass transition does not preempt the gas-liquid phase transition, but always intersects the corresponding spinodal curve on its high-concentration side. We also calculate the ergodic-non-ergodic phase diagram for the sticky hard-sphere model to illustrate the dependence of the predicted SCGLE dynamic phase diagram on the choice of one important constituent element of the SCGLE theory

Glass-liquid-glass reentrance in mono-component colloidal dispersions

Energy Technology Data Exchange (ETDEWEB)

Ramirez-Gonzalez, P E; Medina-Noyola, M [Instituto de Fisica ' Manuel Sandoval Vallarta' , Universidad Autonoma de San Luis Potosi, Alvaro Obregon 64, 78000 San Luis Potosi, SLP (Mexico); Vizcarra-Rendon, A [Unidad Academica de Fisica, Universidad Autonoma de Zacatecas, Paseo la Bufa y Calzada Solidaridad, 98600, Zacatecas, Zac. (Mexico); Guevara-Rodriguez, F de J [Coordinacion de IngenierIa Molecular, Instituto Mexicano del Petroleo, Eje Central Lazaro Cardenas 152, 07730 Mexico, DF (Mexico)

2008-05-21

The self-consistent generalized Langevin equation (SCGLE) theory of colloid dynamics is employed to describe the ergodic-non-ergodic transition in model mono-disperse colloidal dispersions whose particles interact through hard-sphere plus short-ranged attractive forces. The ergodic-non-ergodic phase diagram in the temperature-concentration state space is determined for the hard-sphere plus attractive Yukawa model within the mean spherical approximation for the static structure factor by solving a remarkably simple equation for the localization length of the colloidal particles. Finite real values of this property signals non-ergodicity and determines the non-ergodic parameters f(k) and f{sub s}(k). The resulting phase diagram for this system, which involves the existence of reentrant (repulsive and attractive) glass states, is compared with the corresponding prediction of mode coupling theory. Although both theories coincide in the general features of this phase diagram, there are also clear qualitative differences. One of the most relevant is the SCGLE prediction that the ergodic-attractive glass transition does not preempt the gas-liquid phase transition, but always intersects the corresponding spinodal curve on its high-concentration side. We also calculate the ergodic-non-ergodic phase diagram for the sticky hard-sphere model to illustrate the dependence of the predicted SCGLE dynamic phase diagram on the choice of one important constituent element of the SCGLE theory.

Regional zooplankton dispersal provides spatial insurance for ecosystem function.

Science.gov (United States)

Symons, Celia C; Arnott, Shelley E

2013-05-01

Changing environmental conditions are affecting diversity and ecosystem function globally. Theory suggests that dispersal from a regional species pool may buffer against changes in local community diversity and ecosystem function after a disturbance through the establishment of functionally redundant tolerant species. The spatial insurance provided by dispersal may decrease through time after environmental change as the local community monopolizes resources and reduces community invasibility. To test for evidence of the spatial insurance hypothesis and to determine the role dispersal timing plays in this response we conducted a field experiment using crustacean zooplankton communities in a subarctic region that is expected to be highly impacted by climate change - Churchill, Canada. Three experiments were conducted where nutrients, salt, and dispersal were manipulated. The three experiments differed in time-since-disturbance that the dispersers were added. We found that coarse measures of diversity (i.e. species richness, evenness, and Shannon-Weiner diversity) were generally resistant to large magnitude disturbances, and that dispersal had the most impact on diversity when dispersers were added shortly after disturbance. Ecosystem functioning (chl-a) was degraded in disturbed communities, but dispersal recovered ecosystem function to undisturbed levels. This spatial insurance for ecosystem function was mediated through changes in community composition and the relative abundance of functional groups. Results suggest that regional diversity and habitat connectivity will be important in the future to maintain ecosystem function by introducing functionally redundant species to promote compensatory dynamics. © 2012 Blackwell Publishing Ltd.

Dispersion relations in quantum electrodynamics on the noncommutative Minkowski space

Energy Technology Data Exchange (ETDEWEB)

Zahn, J.W.

2006-12-15

We study field theories on the noncommutative Minkowski space with noncommuting time. The focus lies on dispersion relations in quantized interacting models in the Yang-Feldman formalism. In particular, we compute the two-point correlation function of the field strength in noncommutative quantum electrodynamics to second order. At this, we take into account the covariant coordinates that allow the construction of local gauge invariant quantities (observables). It turns out that this does not remove the well-known severe infrared problem, as one might have hoped. Instead, things become worse, since nonlocal divergences appear. We also show that these cancel in a supersymmetric version of the theory if the covariant coordinates are adjusted accordingly. Furthermore, we study the {phi}{sup 3} and the Wess-Zumino model and show that the distortion of the dispersion relations is moderate for parameters typical for the Higgs field. We also discuss the formulation of gauge theories on noncommutative spaces and study classical electrodynamics on the noncommutative Minkowski space using covariant coordinates. In particular, we compute the change of the speed of light due to nonlinear effects in the presence of a background field. Finally, we examine the so-called twist approach to quantum field theory on the noncommutative Minkowski space and point out some conceptual problems of this approach. (orig.)

Dispersion relations in quantum electrodynamics on the noncommutative Minkowski space

International Nuclear Information System (INIS)

Zahn, J.W.

2006-12-01

We study field theories on the noncommutative Minkowski space with noncommuting time. The focus lies on dispersion relations in quantized interacting models in the Yang-Feldman formalism. In particular, we compute the two-point correlation function of the field strength in noncommutative quantum electrodynamics to second order. At this, we take into account the covariant coordinates that allow the construction of local gauge invariant quantities (observables). It turns out that this does not remove the well-known severe infrared problem, as one might have hoped. Instead, things become worse, since nonlocal divergences appear. We also show that these cancel in a supersymmetric version of the theory if the covariant coordinates are adjusted accordingly. Furthermore, we study the Φ 3 and the Wess-Zumino model and show that the distortion of the dispersion relations is moderate for parameters typical for the Higgs field. We also discuss the formulation of gauge theories on noncommutative spaces and study classical electrodynamics on the noncommutative Minkowski space using covariant coordinates. In particular, we compute the change of the speed of light due to nonlinear effects in the presence of a background field. Finally, we examine the so-called twist approach to quantum field theory on the noncommutative Minkowski space and point out some conceptual problems of this approach. (orig.)

A robust approach for analysing dispersion of elastic waves in an orthotropic cylindrical shell

Science.gov (United States)

Kaplunov, J.; Nobili, A.

2017-08-01

Dispersion of elastic waves in a thin orthotropic cylindrical shell is considered, within the framework of classical 2D Kirchhoff-Love theory. In contrast to direct multi-parametric analysis of the lowest propagating modes, an alternative robust approach is proposed that simply requires evaluation of the evanescent modes (quasi-static edge effect), which, at leading order, do not depend on vibration frequency. A shortened dispersion relation for the propagating modes is then derived by polynomial division and its accuracy is numerically tested against the full Kirchhoff-Love dispersion relation. It is shown that the same shortened relation may be also obtained from a refined dynamic version of the semi-membrane theory for cylindrical shells. The presented results may be relevant for modelling various types of nanotubes which, according to the latest experimental findings, possess strong material anisotropy.

Dispersion forces in a four-component density functional theory framework

OpenAIRE

Pilemalm, Robert

2009-01-01

The main purpose of this thesis is to implement the Gauss--Legendre quadrature for the dispersion coefficient. This has been done and can be now be made with different number of points. The calculations with this implementation has shown that the relativistic impact on helium, neon, argon and krypton is largest for krypton, that has the highest charge of its nucleus. It was also seen that the polarizability of neon as a function of the imaginary angular frequency decreases monotonically from ...

Parasite dispersal risk tolerance is mediated by its reproductive value.

Science.gov (United States)

Nolan, Maxcy P; Delaplane, Keith S

2017-10-01

Parasite dispersal theory draws heavily upon epidemiological SIR models in which host status (susceptible (S), infected (I), or recovered (R)) is used to study parasite dispersal evolution. In contrast to these extrinsically host-centric drivers, in this study we focus on an intrinsic driver, the parasite's reproductive value (predicted future offspring) as a regulator of the extent to which the individual will engage in risky dispersal behaviour. As a model system we use the honeybee Apis mellifera and its ectoparasite, the mite Varroa destructor . Mite reproduction happens exclusively inside cells of bee brood, and newly emerged fecund mites may parasitize either a homocolonial brood cell (low risk dispersal) or emigrate to a new bee colony via phoretic attachment to mature forager bees (high risk dispersal). In an empirical bioassay, prepartum mites (high reproductive value) and postpartum mites (low reproductive value) were offered a choice of newly emerged homocolonial worker bees (low risk), homocolonial pollen forager bees (high risk), or heterocolonial pollen foragers (high risk). A preference for newly emerged bees was earlier and more strongly sustained among prepartum mites. This suggests comparatively greater dispersal risk tolerance among postpartum mites with lower reproductive value. A dangerous bid for dispersal may be adaptive if the individual has already successfully reproduced and the rewards for successful dispersal are sufficiently large.

Dispersive approach to the axial anomaly and nonrenormalization theorem

International Nuclear Information System (INIS)

Pasechnik, R.S.; Teryaev, O.V.

2006-01-01

Anomalous triangle graphs for the divergence of the axial-vector current are studied using the dispersive approach generalized for the case of higher orders of perturbation theory. The validity of this procedure is proved up to the two-loop level. By direct calculation in the framework of dispersive approach we have obtained that the two-loop axial-vector-vector (AVV) amplitude is equal to zero. According to the Vainshtein's theorem, the transversal part of the anomalous triangle is not renormalized in the chiral limit. We generalize this theorem for the case of finite fermion mass in the triangle loop

Executive turnover: the influence of dispersion and other pay system characteristics.

Science.gov (United States)

Messersmith, Jake G; Guthrie, James P; Ji, Yong-Yeon; Lee, Jeong-Yeon

2011-05-01

Using tournament theory as a guiding theoretical framework, in this study, we assess the organizational implications of pay dispersion and other pay system characteristics on the likelihood of turnover among individual executives in organizational teams. Specifically, we estimate the effect of these pay system characteristics on executive turnover decisions. We use a multi-industry, multilevel data set composed of executives in publicly held firms to assess the effects of pay dispersion at the individual level. Consistent with previous findings, we find that pay dispersion is associated with an increased likelihood of executive turnover. In addition, we find that other pay characteristics also affect turnover, both directly and through a moderating effect on pay dispersion. Turnover is more likely when executives receive lower portions of overall top management team compensation and when they have more pay at risk. These conditions also moderate the relationship between pay dispersion and individual turnover decisions, as does receiving lower compensation relative to the market.

Nonrelativistic closed string theory

International Nuclear Information System (INIS)

Gomis, Jaume; Ooguri, Hirosi

2001-01-01

We construct a Galilean invariant nongravitational closed string theory whose excitations satisfy a nonrelativistic dispersion relation. This theory can be obtained by taking a consistent low energy limit of any of the conventional string theories, including the heterotic string. We give a finite first order worldsheet Hamiltonian for this theory and show that this string theory has a sensible perturbative expansion, interesting high energy behavior of scattering amplitudes and a Hagedorn transition of the thermal ensemble. The strong coupling duals of the Galilean superstring theories are considered and are shown to be described by an eleven-dimensional Galilean invariant theory of light membrane fluctuations. A new class of Galilean invariant nongravitational theories of light-brane excitations are obtained. We exhibit dual formulations of the strong coupling limits of these Galilean invariant theories and show that they exhibit many of the conventional dualities of M theory in a nonrelativistic setting

Dispersivity in heterogeneous permeable media

International Nuclear Information System (INIS)

Chesnut, D.A.

1994-01-01

When one fluid displaces another through a one-dimensional porous medium, the composition changes from pure displacing fluid at the inlet to pure displaced fluid some distance downstream. The distance over which an arbitrary percentage of this change occurs is defined as the mixing zone length, which increases with increasing average distance traveled by the displacement front. For continuous injection, the mixing zone size can be determined from a breakthrough curve as the time required for the effluent displacing fluid concentration to change from, say, 10% to 90%. In classical dispersion theory, the mixing zone grows in proportion to the square root of the mean distance traveled, or, equivalently, to the square root of the mean breakthrough time. In a multi-dimensional heterogeneous medium, especially at field scales, the size of the mixing zone grows almost linearly with mean distance or travel time. If an observed breakthrough curve is forced to fit the, clinical theory, the resulting effective dispersivity, instead of being constant, also increases almost linearly with the spatial or temporal scale of the problem. This occurs because the heterogeneity in flow properties creates a corresponding velocity distribution along the different flow pathways from the inlet to the outlet of the system. Mixing occurs mostly at the outlet, or wherever the fluid is sampled, rather than within the medium. In this paper, we consider the effects. of this behavior on radionuclide or other contaminant migration

Dispersivity in heterogeneous permeable media

International Nuclear Information System (INIS)

Chesnut, D.A.

1994-01-01

When one fluid displaces another through a one-dimensional porous medium, the composition changes from pure displacing fluid at the inlet to pure displaced fluid some distance downstream. The distance over which an arbitrary percentage (typically 80%) of this change occurs is defined as the mixing zone length, which increases with increasing average distance traveled by the displacement front. Alternatively, for continuous injection, the mixing zone size can be determined from a breakthrough curve as the time required for the effluent displacing fluid concentration to change from, say, 10% to 90%. In classical dispersion theory, the mixing zone grows in proportion to the square root of the mean distance traveled, or, equivalently, to the square root of the mean breakthrough time. In a multi-dimensional heterogeneous medium, especially at field scales, the size of the mixing zone grows almost linearly with mean distance or travel time. If an observed breakthrough curve is forced to fit the classical theory, the resulting effective dispersivity, instead of being constant, also increases almost linearly with the spatial or temporal scale of the problem. This occurs because the heterogeneity in flow properties creates a corresponding velocity distribution along the different flow pathways from the inlet to the outlet of the system. Mixing occurs mostly at the outlet, or wherever the fluid is sampled, rather than within the medium. In this paper, we consider the effects of this behavior on radionuclide or other contaminant migration

The neutral theory of biodiversity with random fission speciation

NARCIS (Netherlands)

Etienne, Rampal S.; Haegeman, Bart

The neutral theory of biodiversity and biogeography emphasizes the importance of dispersal and speciation to macro-ecological diversity patterns. While the influence of dispersal has been studied quite extensively, the effect of speciation has not received much attention, even though it was already

Measurements of dispersion forces between colloidal latex particles with the atomic force microscope and comparison with Lifshitz theory

Energy Technology Data Exchange (ETDEWEB)

Elzbieciak-Wodka, Magdalena; Ruiz-Cabello, F. Javier Montes; Trefalt, Gregor; Maroni, Plinio; Borkovec, Michal, E-mail: michal.borkovec@unige.ch [Department of Inorganic and Analytical Chemistry, University of Geneva, Sciences II, 30, Quai Ernest-Ansermet, 1205 Geneva (Switzerland); Popescu, Mihail N. [Ian Wark Research Institute, University of South Australia, Mawson Lakes, SA 5095 (Australia)

2014-03-14

Interaction forces between carboxylate colloidal latex particles of about 2 μm in diameter immersed in aqueous solutions of monovalent salts were measured with the colloidal probe technique, which is based on the atomic force microscope. We have systematically varied the ionic strength, the type of salt, and also the surface charge densities of the particles through changes in the solution pH. Based on these measurements, we have accurately measured the dispersion forces acting between the particles and estimated the apparent Hamaker constant to be (2.0 ± 0.5) × 10{sup −21} J at a separation distance of about 10 nm. This value is basically independent of the salt concentration and the type of salt. Good agreement with Lifshitz theory is found when roughness effects are taken into account. The combination of retardation and roughness effects reduces the value of the apparent Hamaker constant and its ionic strength dependence with respect to the case of ideally smooth surfaces.

Dispersive analysis of the pion transition form factor

Science.gov (United States)

Hoferichter, M.; Kubis, B.; Leupold, S.; Niecknig, F.; Schneider, S. P.

2014-11-01

We analyze the pion transition form factor using dispersion theory. We calculate the singly-virtual form factor in the time-like region based on data for the cross section, generalizing previous studies on decays and scattering, and verify our result by comparing to data. We perform the analytic continuation to the space-like region, predicting the poorly-constrained space-like transition form factor below , and extract the slope of the form factor at vanishing momentum transfer . We derive the dispersive formalism necessary for the extension of these results to the doubly-virtual case, as required for the pion-pole contribution to hadronic light-by-light scattering in the anomalous magnetic moment of the muon.

Controlling electrical percolation in multicomponent carbon nanotube dispersions.

Science.gov (United States)

Kyrylyuk, Andriy V; Hermant, Marie Claire; Schilling, Tanja; Klumperman, Bert; Koning, Cor E; van der Schoot, Paul

2011-04-10

Carbon nanotube reinforced polymeric composites can have favourable electrical properties, which make them useful for applications such as flat-panel displays and photovoltaic devices. However, using aqueous dispersions to fabricate composites with specific physical properties requires that the processing of the nanotube dispersion be understood and controlled while in the liquid phase. Here, using a combination of experiment and theory, we study the electrical percolation of carbon nanotubes introduced into a polymer matrix, and show that the percolation threshold can be substantially lowered by adding small quantities of a conductive polymer latex. Mixing colloidal particles of different sizes and shapes (in this case, spherical latex particles and rod-like nanotubes) introduces competing length scales that can strongly influence the formation of the system-spanning networks that are needed to produce electrically conductive composites. Interplay between the different species in the dispersions leads to synergetic or antagonistic percolation, depending on the ease of charge transport between the various conductive components.

An efficient method of reducing glass dispersion tolerance sensitivity

Science.gov (United States)

Sparrold, Scott W.; Shepard, R. Hamilton

2014-12-01

Constraining the Seidel aberrations of optical surfaces is a common technique for relaxing tolerance sensitivities in the optimization process. We offer an observation that a lens's Abbe number tolerance is directly related to the magnitude by which its longitudinal and transverse color are permitted to vary in production. Based on this observation, we propose a computationally efficient and easy-to-use merit function constraint for relaxing dispersion tolerance sensitivity. Using the relationship between an element's chromatic aberration and dispersion sensitivity, we derive a fundamental limit for lens scale and power that is capable of achieving high production yield for a given performance specification, which provides insight on the point at which lens splitting or melt fitting becomes necessary. The theory is validated by comparing its predictions to a formal tolerance analysis of a Cooke Triplet, and then applied to the design of a 1.5x visible linescan lens to illustrate optimization for reduced dispersion sensitivity. A selection of lenses in high volume production is then used to corroborate the proposed method of dispersion tolerance allocation.

Assessing photocatalytic power of g-C3N4 for solar fuel production: A first-principles study involving quasi-particle theory and dispersive forces.

Science.gov (United States)

Osorio-Guillén, J M; Espinosa-García, W F; Moyses Araujo, C

2015-09-07

First-principles quasi-particle theory has been employed to assess catalytic power of graphitic carbon nitride, g-C3N4, for solar fuel production. A comparative study between g-h-triazine and g-h-heptazine has been carried out taking also into account van der Waals dispersive forces. The band edge potentials have been calculated using a recently developed approach where quasi-particle effects are taken into account through the GW approximation. First, it was found that the description of ground state properties such as cohesive and surface formation energies requires the proper treatment of dispersive interaction. Furthermore, through the analysis of calculated band-edge potentials, it is shown that g-h-triazine has high reductive power reaching the potential to reduce CO2 to formic acid, coplanar g-h-heptazine displays the highest thermodynamics force toward H2O/O2 oxidation reaction, and corrugated g-h-heptazine exhibits a good capacity for both reactions. This rigorous theoretical study shows a route to further improve the catalytic performance of g-C3N4.

SAGE measurements of the stratospheric aerosol dispersion and loading from the Soufriere Volcano

Science.gov (United States)

Mccormick, M. P.; Kent, G. S.; Yue, G. K.; Cunnold, D. M.

1981-01-01

Explosions of the Soufriere volcano on the Caribbean Island of St. Vincent reduced two major stratospheric plumes which the stratospheric aerosol and gas experiment (SAGE) satellite tracked to West Africa and the North Atlantic Ocean. The total mass of the stratospheric ejecta measured is less than 0.5% of the global stratospheric aerosol burden. No significant temperature or climate perturbation is expected. It is found that the movement and dispersion of the plumes agree with those deduced from high altitude meteorological data and dispersion theory. The stratospheric aerosol dispersion and loading from the Soufrier volcano was measured.

Relativistic invariance of dispersion-relations and their associated wave-operators and Green-functions

International Nuclear Information System (INIS)

Censor, Dan

2010-01-01

Identifying invariance properties helps in simplifying calculations and consolidating concepts. Presently the Special Relativistic invariance of dispersion relations and their associated scalar wave operators is investigated for general dispersive homogeneous linear media. Invariance properties of the four-dimensional Fourier-transform integrals is demonstrated, from which the invariance of the scalar Green-function is inferred. Dispersion relations and the associated group velocities feature in Hamiltonian ray tracing theory. The derivation of group velocities for moving media from the dispersion relation for these media at rest is discussed. It is verified that the group velocity concept satisfies the relativistic velocity-addition formula. In this respect it is considered to be 'real', i.e., substantial, physically measurable, and not merely a mathematical artifact. Conversely, if we assume the group velocity to be substantial, it follows that the dispersion relation must be a relativistic invariant. (orig.)

Modelling of pollution dispersion in atmosphere; Modelowanie procesow propagacji skazen w atmosferze

Energy Technology Data Exchange (ETDEWEB)

Borysiewicz, M; Stankiewicz, R

1994-12-31

The paper contains the review of the mathematical foundation of atmospheric dispersion models. The atmospheric phenomena relevant to atmospheric dispersion model are discussed. In particular the parametrization of processes with time and space scales smaller than numerical grid size, limited by available computer power, is presented. The special attention was devoted to similarity theory and parametrization of boundary layer. The numerical methods are analysed and the drawbacks of the method are presented. (author). 99 refs, 15 figs, 3 tabs.

Dispersal and noise: Various modes of synchrony in ecological oscillators

KAUST Repository

Bressloff, Paul C.

2012-10-21

We use the theory of noise-induced phase synchronization to analyze the effects of dispersal on the synchronization of a pair of predator-prey systems within a fluctuating environment (Moran effect). Assuming that each isolated local population acts as a limit cycle oscillator in the deterministic limit, we use phase reduction and averaging methods to derive a Fokker-Planck equation describing the evolution of the probability density for pairwise phase differences between the oscillators. In the case of common environmental noise, the oscillators ultimately synchronize. However the approach to synchrony depends on whether or not dispersal in the absence of noise supports any stable asynchronous states. We also show how the combination of partially correlated noise with dispersal can lead to a multistable steady-state probability density. © 2012 Springer-Verlag Berlin Heidelberg.

Dispersal and noise: Various modes of synchrony in ecological oscillators

KAUST Repository

Bressloff, Paul C.; Lai, Yi Ming

2012-01-01

We use the theory of noise-induced phase synchronization to analyze the effects of dispersal on the synchronization of a pair of predator-prey systems within a fluctuating environment (Moran effect). Assuming that each isolated local population acts as a limit cycle oscillator in the deterministic limit, we use phase reduction and averaging methods to derive a Fokker-Planck equation describing the evolution of the probability density for pairwise phase differences between the oscillators. In the case of common environmental noise, the oscillators ultimately synchronize. However the approach to synchrony depends on whether or not dispersal in the absence of noise supports any stable asynchronous states. We also show how the combination of partially correlated noise with dispersal can lead to a multistable steady-state probability density. © 2012 Springer-Verlag Berlin Heidelberg.

Particle and surfactant interactions effected polar and dispersive components of interfacial energy in nanocolloids

Science.gov (United States)

Harikrishnan, A. R.; Das, Sarit K.; Agnihotri, Prabhat K.; Dhar, Purbarun

2017-08-01

We segregate and report experimentally for the first time the polar and dispersive interfacial energy components of complex nanocolloidal dispersions. In the present study, we introduce a novel inverse protocol for the classical Owens Wendt method to determine the constitutive polar and dispersive elements of surface tension in such multicomponent fluidic systems. The effect of nanoparticles alone and aqueous surfactants alone are studied independently to understand the role of the concentration of the dispersed phase in modulating the constitutive elements of surface energy in fluids. Surfactants are capable of altering the polar component, and the combined particle and surfactant nanodispersions are shown to be effective in modulating the polar and dispersive components of surface tension depending on the relative particle and surfactant concentrations as well as the morphological and electrostatic nature of the dispersed phases. We observe that the combined surfactant and particle colloid exhibits a similar behavior to that of the particle only case; however, the amount of modulation of the polar and dispersive constituents is found to be different from the particle alone case which brings to the forefront the mechanisms through which surfactants modulate interfacial energies in complex fluids. Accordingly, we are able to show that the observations can be merged into a form of quasi-universal trend in the trends of polar and dispersive components in spite of the non-universal character in the wetting behavior of the fluids. We analyze the different factors affecting the polar and dispersive interactions in such complex colloids, and the physics behind such complex interactions has been explained by appealing to the classical dispersion theories by London, Debye, and Keesom as well as by Derjaguin-Landau-Verwey-Overbeek theory. The findings shed light on the nature of wetting behavior of such complex fluids and help in predicting the wettability and the degree of

Chiral symmetry and dispersion relations: from $\\pi \\pi$ scattering to hadronic light-by-light.

CERN Multimedia

CERN. Geneva

2018-01-01

Chiral symmetry provides strong constraints on hadronic matrix elements at low energy, which are most efficiently derived with chiral perturbation theory. As an effective quantum field theory the latter also accounts for rescattering or unitarity effects, albeit only perturbatively, via the loop expansion. In cases where rescattering effects are important it becomes necessary to go beyond the perturbative expansion, e.g. by using dispersion relations. A matching between the chiral and the dispersive representation provides in several cases results of high precision. I will discuss this approach with the help of a few examples, like $\\pi \\pi$ scattering (which has been tested successfully by CERN experiments like NA48/2 and DIRAC), $\\eta \\to 3 \\pi$ and the hadronic light-by-light contribution to $(g-2)_\\mu$. For the latter quantity the implementation of the dispersive approach has opened up the way to a model-independent calculation and the concrete possibility to significantly reduce the theoretical uncertain...

Macroscopic QED in linearly responding media and a Lorentz-Force approach to dispersion forces

Energy Technology Data Exchange (ETDEWEB)

Raabe, Christian

2008-07-08

In this thesis, a very general quantization scheme for the macroscopic electromagnetic field in arbitrary linearly responding media is presented. It offers a unified approach to QED in such media. Applying the quantization scheme, a theory of the dispersion forces on the basis of the Lorentz force is developed. By regarding the dispersion force as the (ground-state or thermal-state) expectation value of the Lorentz force that acts on appropriately defined charge and current densities, Casimir, Casimir-Polder, and van der Waals forces are united in a very natural way that makes transparent their common physical basis. Application of the theory to planar structures yields generalizations of well-known Lifschitz and Casimir-type formulas. (orig.)

Macroscopic QED in linearly responding media and a Lorentz-Force approach to dispersion forces

International Nuclear Information System (INIS)

Raabe, Christian

2008-01-01

In this thesis, a very general quantization scheme for the macroscopic electromagnetic field in arbitrary linearly responding media is presented. It offers a unified approach to QED in such media. Applying the quantization scheme, a theory of the dispersion forces on the basis of the Lorentz force is developed. By regarding the dispersion force as the (ground-state or thermal-state) expectation value of the Lorentz force that acts on appropriately defined charge and current densities, Casimir, Casimir-Polder, and van der Waals forces are united in a very natural way that makes transparent their common physical basis. Application of the theory to planar structures yields generalizations of well-known Lifschitz and Casimir-type formulas. (orig.)

Structure and osmotic pressure of ionic microgel dispersions

Energy Technology Data Exchange (ETDEWEB)

Hedrick, Mary M. [Department of Physics, North Dakota State University, Fargo, North Dakota 58108-6050 (United States); Department of Chemistry and Biochemistry, North Dakota State University, Fargo, North Dakota 58108-6050 (United States); Chung, Jun Kyung; Denton, Alan R., E-mail: alan.denton@ndsu.edu [Department of Physics, North Dakota State University, Fargo, North Dakota 58108-6050 (United States)

2015-01-21

We investigate structural and thermodynamic properties of aqueous dispersions of ionic microgels—soft colloidal gel particles that exhibit unusual phase behavior. Starting from a coarse-grained model of microgel macroions as charged spheres that are permeable to microions, we perform simulations and theoretical calculations using two complementary implementations of Poisson-Boltzmann (PB) theory. Within a one-component model, based on a linear-screening approximation for effective electrostatic pair interactions, we perform molecular dynamics simulations to compute macroion-macroion radial distribution functions, static structure factors, and macroion contributions to the osmotic pressure. For the same model, using a variational approximation for the free energy, we compute both macroion and microion contributions to the osmotic pressure. Within a spherical cell model, which neglects macroion correlations, we solve the nonlinear PB equation to compute microion distributions and osmotic pressures. By comparing the one-component and cell model implementations of PB theory, we demonstrate that the linear-screening approximation is valid for moderately charged microgels. By further comparing cell model predictions with simulation data for osmotic pressure, we chart the cell model’s limits in predicting osmotic pressures of salty dispersions.

Structure and osmotic pressure of ionic microgel dispersions

International Nuclear Information System (INIS)

Hedrick, Mary M.; Chung, Jun Kyung; Denton, Alan R.

2015-01-01

We investigate structural and thermodynamic properties of aqueous dispersions of ionic microgels—soft colloidal gel particles that exhibit unusual phase behavior. Starting from a coarse-grained model of microgel macroions as charged spheres that are permeable to microions, we perform simulations and theoretical calculations using two complementary implementations of Poisson-Boltzmann (PB) theory. Within a one-component model, based on a linear-screening approximation for effective electrostatic pair interactions, we perform molecular dynamics simulations to compute macroion-macroion radial distribution functions, static structure factors, and macroion contributions to the osmotic pressure. For the same model, using a variational approximation for the free energy, we compute both macroion and microion contributions to the osmotic pressure. Within a spherical cell model, which neglects macroion correlations, we solve the nonlinear PB equation to compute microion distributions and osmotic pressures. By comparing the one-component and cell model implementations of PB theory, we demonstrate that the linear-screening approximation is valid for moderately charged microgels. By further comparing cell model predictions with simulation data for osmotic pressure, we chart the cell model’s limits in predicting osmotic pressures of salty dispersions

The Inward Dispersion of the Neutron Scattering Experiments in HTSC Cuprates

OpenAIRE

Dayan, Moshe

2016-01-01

The theory of the high temperature superconducting cuprates, which is based on the condensation of holes into strings in checker-board geometry, was successful to explain the elastically scattered Neutrons by spin waves. Here it is extended to analyze the inward dispersion curve of its inelastic counterpart, up to the resonance energy- . This extension is done by applying the perturbation theory of the linear response to the condensed strings. The approximated susceptibility is derived by mea...

Dispersion relations of elastic waves in one-dimensional piezoelectric/piezomagnetic phononic crystal with initial stresses.

Science.gov (United States)

Guo, Xiao; Wei, Peijun

2016-03-01

The dispersion relations of elastic waves in a one-dimensional phononic crystal formed by periodically repeating of a pre-stressed piezoelectric slab and a pre-stressed piezomagnetic slab are studied in this paper. The influences of initial stress on the dispersive relation are considered based on the incremental stress theory. First, the incremental stress theory of elastic solid is extended to the magneto-electro-elasto solid. The governing equations, constitutive equations, and boundary conditions of the incremental stresses in a magneto-electro-elasto solid are derived with consideration of the existence of initial stresses. Then, the transfer matrices of a pre-stressed piezoelectric slab and a pre-stressed piezomagnetic slab are formulated, respectively. The total transfer matrix of a single cell in the phononic crystal is obtained by the multiplication of two transfer matrixes related with two adjacent slabs. Furthermore, the Bloch theorem is used to obtain the dispersive equations of in-plane and anti-plane Bloch waves. The dispersive equations are solved numerically and the numerical results are shown graphically. The oblique propagation and the normal propagation situations are both considered. In the case of normal propagation of elastic waves, the analytical expressions of the dispersion equation are derived and compared with other literatures. The influences of initial stresses, including the normal initial stresses and shear initial stresses, on the dispersive relations are both discussed based on the numerical results. Copyright © 2015 Elsevier B.V. All rights reserved.

Species dispersal rates alter diversity and ecosystem stability in pond metacommunities.

Science.gov (United States)

Howeth, Jennifer G; Leibold, Mathew A

2010-09-01

Metacommunity theory suggests that relationships between diversity and ecosystem stability can be determined by the rate of species dispersal among local communities. The predicted relationships, however, may depend upon the relative strength of local environmental processes and disturbance. Here we evaluate the role of dispersal frequency and local predation perturbations in affecting patterns of diversity and stability in pond plankton metacommunities. Pond metacommunities were composed of three mesocosm communities: one of the three communities maintained constant "press" predation from a selective predator, bluegill sunfish (Lepomis macrochirus); the second community maintained "press" conditions without predation; and the third community experienced recurrent "pulsed" predation from bluegill sunfish. The triads of pond communities were connected at either no, low (0.7%/d), or high (20%/d) planktonic dispersal. Richness and composition of zooplankton and stability of plankton biomass and ecosystem productivity were measured at local and regional spatial scales. Dispersal significantly affected diversity such that local and regional biotas at the low dispersal rate maintained the greatest number of species. The unimodal local dispersal-diversity relationship was predator-dependent, however, as selective press predation excluded species regardless of dispersal. Further, there was no effect of dispersal on beta diversity because predation generated local conditions that selected for distinct community assemblages. Spatial and temporal ecosystem stability responded to dispersal frequency but not predation. Low dispersal destabilized the spatial stability of producer biomass but stabilized temporal ecosystem productivity. The results indicate that selective predation can prevent species augmentation from mass effects but has no apparent influence on stability. Dispersal rates, in contrast, can have significant effects on both species diversity and ecosystem

Quantum treatment of field propagation in a fiber near the zero dispersion wavelength

Science.gov (United States)

Safaei, A.; Bassi, A.; Bolorizadeh, M. A.

2018-05-01

In this report, we present a quantum theory describing the propagation of the electromagnetic radiation in a fiber in the presence of the third order dispersion coefficient. We obtained the quantum photon-polariton field, hence, we provide herein a coupled set of operator forms for the corresponding nonlinear Schrödinger equations when the third order dispersion coefficient is included. Coupled stochastic nonlinear Schrödinger equations were obtained by applying a positive P-representation that governs the propagation and interaction of quantum solitons in the presence of the third-order dispersion term. Finally, to reduce the fluctuations near solitons in the first approximation, we developed coupled stochastic linear equations.

A necessary condition for dispersal driven growth of populations with discrete patch dynamics.

Science.gov (United States)

Guiver, Chris; Packman, David; Townley, Stuart

2017-07-07

We revisit the question of when can dispersal-induced coupling between discrete sink populations cause overall population growth? Such a phenomenon is called dispersal driven growth and provides a simple explanation of how dispersal can allow populations to persist across discrete, spatially heterogeneous, environments even when individual patches are adverse or unfavourable. For two classes of mathematical models, one linear and one non-linear, we provide necessary conditions for dispersal driven growth in terms of the non-existence of a common linear Lyapunov function, which we describe. Our approach draws heavily upon the underlying positive dynamical systems structure. Our results apply to both discrete- and continuous-time models. The theory is illustrated with examples and both biological and mathematical conclusions are drawn. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

Dynamical theory of neutron diffraction

International Nuclear Information System (INIS)

Sears, V.F.

1978-01-01

We present a review of the dynamical theory of neutron diffraction by macroscopic bodies which provides the theoretical basis for the study of neutron optics. We consider both the theory of dispersion, in which it is shown that the coherent wave in the medium satisfies a macroscopic one-body Schroedinger equation, and the theory of reflection, refraction, and diffraction in which the above equation is solved for a number of special cases of interest. The theory is illustrated with the help of experimental results obtained over the past 10 years by a number of new techniques such as neutron gravity refractometry. Pendelloesung interference, and neutron interferometry. (author)

Temperature dependence of the electrical conductivity of vapor grown carbon nanofiber/epoxy composites with different filler dispersion levels

International Nuclear Information System (INIS)

Cardoso, P.; Silva, J.; Agostinho Moreira, J.; Klosterman, D.; Hattum, F.W.J. van; Simoes, R.; Lanceros-Mendez, S.

2012-01-01

The influence of the dispersion of vapor grown carbon nanofibers (VGCNF) on the electrical properties of VGCNF/epoxy composites has been studied. A homogeneous dispersion of the VGCNF does not imply better electrical properties. The presence of well distributed clusters appears to be a key factor for increasing composite conductivity. It is also shown that the main conduction mechanism has an ionic nature for concentrations below the percolation threshold, while above the percolation threshold it is dominated by hopping between the fillers. Finally, using the granular system theory it is possible to explain the origin of conduction at low temperatures. -- Highlights: ► The influence of dispersion of carbon nanofibers on epoxy is investigated. ► A homogeneous dispersion does not imply better electrical properties. ► The conduction mechanism has an ionic nature below the percolation threshold. ► Above the percolation threshold it is dominated by hopping between the fillers. ► The granular system theory allows explaining conduction at low temperatures.

Temperature dependence of the electrical conductivity of vapor grown carbon nanofiber/epoxy composites with different filler dispersion levels

Energy Technology Data Exchange (ETDEWEB)

Cardoso, P. [Center of Physics, University of Minho, Campus de Gualtar, 4710-057 Braga (Portugal); Silva, J. [Center of Physics, University of Minho, Campus de Gualtar, 4710-057 Braga (Portugal); Institute for Polymers and Composites IPC/I3N, University of Minho, Campus de Azurém, 4800-058 Guimares (Portugal); Agostinho Moreira, J. [IFIMUP and IN—Institute of Nanoscience and Nanotechnology, Department of Physics and Astronomy, Faculty of Science, University of Porto, Rua do Campo Alegre, 687, 4169-007 Porto (Portugal); Klosterman, D. [Chemical and Materials Engineering, University of Dayton, 300 College Park, Dayton, OH 45469-0246 (United States); Hattum, F.W.J. van [Institute for Polymers and Composites IPC/I3N, University of Minho, Campus de Azurém, 4800-058 Guimares (Portugal); Simoes, R. [Institute for Polymers and Composites IPC/I3N, University of Minho, Campus de Azurém, 4800-058 Guimares (Portugal); School of Technology, Polytechnic Institute of Cávado and Ave, Campus do IPCA, 4750-810 Barcelos (Portugal); Lanceros-Mendez, S., E-mail: lanceros@fisica.uminho.pt [Center of Physics, University of Minho, Campus de Gualtar, 4710-057 Braga (Portugal); INL—International Iberian Nanotechnology Laboratory, 4715-330 Braga (Portugal)

2012-10-01

The influence of the dispersion of vapor grown carbon nanofibers (VGCNF) on the electrical properties of VGCNF/epoxy composites has been studied. A homogeneous dispersion of the VGCNF does not imply better electrical properties. The presence of well distributed clusters appears to be a key factor for increasing composite conductivity. It is also shown that the main conduction mechanism has an ionic nature for concentrations below the percolation threshold, while above the percolation threshold it is dominated by hopping between the fillers. Finally, using the granular system theory it is possible to explain the origin of conduction at low temperatures. -- Highlights: ► The influence of dispersion of carbon nanofibers on epoxy is investigated. ► A homogeneous dispersion does not imply better electrical properties. ► The conduction mechanism has an ionic nature below the percolation threshold. ► Above the percolation threshold it is dominated by hopping between the fillers. ► The granular system theory allows explaining conduction at low temperatures.

Thermodynamic phase behavior of API/polymer solid dispersions.

Science.gov (United States)

Prudic, Anke; Ji, Yuanhui; Sadowski, Gabriele

2014-07-07

To improve the bioavailability of poorly soluble active pharmaceutical ingredients (APIs), these materials are often integrated into a polymer matrix that acts as a carrier. The resulting mixture is called a solid dispersion. In this work, the phase behaviors of solid dispersions were investigated as a function of the API as well as of the type and molecular weight of the carrier polymer. Specifically, the solubility of artemisinin and indomethacin was measured in different poly(ethylene glycol)s (PEG 400, PEG 6000, and PEG 35000). The measured solubility data and the solubility of sulfonamides in poly(vinylpyrrolidone) (PVP) K10 and PEG 35000 were modeled using the perturbed-chain statistical associating fluid theory (PC-SAFT). The results show that PC-SAFT predictions are in a good accordance with the experimental data, and PC-SAFT can be used to predict the whole phase diagram of an API/polymer solid dispersion as a function of the kind of API and polymer and of the polymer's molecular weight. This remarkably simplifies the screening process for suitable API/polymer combinations.

Effects of chemical dispersants on oil-brine interfacial tension and droplet formation

International Nuclear Information System (INIS)

Khelifa, A.; So, L.L.C.

2009-01-01

The dispersion of oil spilled in water is influenced by chemical dispersants via the modification of the interfacial properties of the oil, such as oil-brine interfacial tension (IFT). In this study, the physical properties and dispersion of oil were measured in order to determine the effects of chemical dispersants on IFT and oil viscosity and the effects on oil droplet formation. In theory, the maximum size of oil droplet that forms under turbulent mixing increases with IFT. Therefore, a reduction in IFT reduces the size distribution of oil droplets. This paper presented the results of an ongoing project aimed at providing quantitative understanding the influence that chemical dispersants have on the size distribution of oil droplets and oil dispersion. Findings showed that a valid approach is to separate the direct effects of chemical dispersants on oil properties, specifically oil-brine IFT and the effects of mixing on dispersion of chemically treated oil. Under constant mixing conditions, the reduction of the maximum oil droplet size that overcomes the breakage process is determined by the effects of chemical dispersant on oil properties. This correlates well with the dispersant-to-oil ratio (DOR) up to the critical micelle concentration (CMC). This good agreement can be attributed to the reduction of IFT with DOR. It was concluded that the reduction of IFT with dispersant concentration is an additional signature of oil composition on droplet formation, while mixing energy is an external parameter that is independent of oil properties. 17 refs., 3 tabs., 9 figs

Theory of dispersions and dampin.o of plasmons in electron liquid

International Nuclear Information System (INIS)

Monga, M.R.; Pathak, K.N.

1980-01-01

A general expression for the dynamical response function has been obtained using equation of motion method. The expression is exact upto second order in Coulomb potential as well as in wave vector q. The results correspond to taking into account the mechanism of damping of plasmons by excitation of two particles-two holes from the Fermi sea. The closed form expressions for the plasmon dispersion and damping have been obtained for the electron density parameter rsub(s) → 0. (author)

Coupled mode theory of periodic waveguides arrays

DEFF Research Database (Denmark)

Lavrinenko, Andrei; Chigrin, Dmitry N.

We apply the scalar coupled mode theory to the case of waveguides array consisting om two periodic waveguides. One of the waveguides is arbitrary shifted along another. A longitudinal shift acts as a parameter in the coupled mode theory. The proposed theory explains peculiarities of modes dispers...... dispersion and transmission in coupled periodic waveguides systems. Analytical results are compared with the numerical ones obtained by the plane wave expansion and FDTD methods....

Frequency doubling in poled polymers using anomalous dispersion phase-matching

Energy Technology Data Exchange (ETDEWEB)

Kowalczyk, T.C.; Singer, K.D. [Case Western Reserve Univ., Cleveland, OH (United States). Dept. of Physics; Cahill, P.A. [Sandia National Labs., Albuquerque, NM (United States)

1995-10-01

The authors report on a second harmonic generation in a poled polymer waveguide using anomalous dispersion phase-matching. Blue light ({lambda} = 407 nm) was produced by phase-matching the lowest order fundamental and harmonic modes over a distance of 32 {micro}m. The experimental conversion efficiency was {eta} = 1.2 {times} 10{sup {minus}4}, in agreement with theory. Additionally, they discuss a method of enhancing the conversion efficiency for second harmonic generation using anomalous dispersion phase-matching to optimize Cerenkov second harmonic generation. The modeling shows that a combination of phase-matching techniques creates larger conversion efficiencies and reduces critical fabrication requirements of the individual phase-matching techniques.

Reliability benefits of dispersed wind resource development

International Nuclear Information System (INIS)

Milligan, M.; Artig, R.

1998-05-01

Generating capacity that is available during the utility peak period is worth more than off-peak capacity. Wind power from a single location might not be available during enough of the peak period to provide sufficient value. However, if the wind power plant is developed over geographically disperse locations, the timing and availability of wind power from these multiple sources could provide a better match with the utility's peak load than a single site. There are other issues that arise when considering disperse wind plant development. Singular development can result in economies of scale and might reduce the costs of obtaining multiple permits and multiple interconnections. However, disperse development can result in cost efficiencies if interconnection can be accomplished at lower voltages or at locations closer to load centers. Several wind plants are in various stages of planning or development in the US. Although some of these are small-scale demonstration projects, significant wind capacity has been developed in Minnesota, with additional developments planned in Wyoming, Iowa and Texas. As these and other projects are planned and developed, there is a need to perform analysis of the value of geographically disperse sites on the reliability of the overall wind plant.This paper uses a production-cost/reliability model to analyze the reliability of several wind sites in the state of Minnesota. The analysis finds that the use of a model with traditional reliability measures does not produce consistent, robust results. An approach based on fuzzy set theory is applied in this paper, with improved results. Using such a model, the authors find that system reliability can be optimized with a mix of disperse wind sites

Improved pion pion scattering amplitude from dispersion relation formalism

International Nuclear Information System (INIS)

Cavalcante, I.P.; Coutinho, Y.A.; Borges, J. Sa

2005-01-01

Pion-pion scattering amplitude is obtained from Chiral Perturbation Theory at one- and two-loop approximations. Dispersion relation formalism provides a more economic method, which was proved to reproduce the analytical structure of that amplitude at both approximation levels. This work extends the use of the formalism in order to compute further unitarity corrections to partial waves, including the D-wave amplitude. (author)

Mechanics of dispersion of pollutants in coastal environment

International Nuclear Information System (INIS)

Jordaan, J.M. Jr.

1973-01-01

The relationships between energy dissipation (turbulence) and mixing and analogy with classical diffusion theory are reviewed. Typical solutions of the differential equations, for various initial and boundary conditions related to practical cases are presented. The natural processes that control the dispersion in the nearshore regions were studied in a wind-wave channel and in the field and interpretive conclusions are drawn on the practice of nearshore disposal of effluents

A laboratory dispersant effectiveness test which reflects dispersant efficiency in the field

International Nuclear Information System (INIS)

Lunel, T.; Wood, P.

1996-01-01

Oil dispersion efficiencies of surfactants, from laboratory dispersion tests and field data were compared and calibrated. Data from an oil spill, where dispersants were used as a major part of the response, was analysed. The data was accumulated through the monitoring of the dispersant operation of the Sea Empress spill incident, in which Forties Blend oil was spilled at sea. This detailed data set was used to calibrate existing laboratory dispersant tests, and to devise a new International Dispersant Effectiveness Test. The objective was to create a comprehensive guide to decision making on whether and when to start a dispersant spraying operation. The dispersion efficiencies obtained from the laboratory dispersant tests were compared with field data. Flume tests produced the highest percentage of dispersed oil for all the dispersal tests. However, it was emphasised that the total percentage of oil dispersed should not be the only measure of dispersant effectiveness, since it does not distinguish between the contribution of natural and chemically enhanced dispersion. 9 refs., 1 tab., 9 figs

Phonons and their dispersion in model ferroelastics Hg2Hal2

Science.gov (United States)

Roginskii, E. M.; Kvasov, A. A.; Markov, Yu. F.; Smirnov, M. B.

2012-05-01

Dispersion relations of the acoustic and optical phonon frequencies have been calculated and plotted, and the density of states of the phonon spectrum of Hg2Cl2 and Hg2Br2 crystals has been derived. The effect of hydrostatic pressure on the frequencies of acoustic and optical phonons and their dispersion has been theoretically analyzed. It has been found that an increase in the pressure leads to a strong softening of the slowest acoustic TA branch (the soft mode) at the X point of the Brillouin zone boundary, which is consistent with the phenomenological Landau theory and correlates with experiment.

Modes of speciation and the neutral theory of biodiversity

NARCIS (Netherlands)

Etienne, R.S.; Apol, M.E.F.; Olff, H.

2007-01-01

Hubbell's neutral theory of biodiversity has generated much debate over the need for niches to explain biodiversity patterns. Discussion of the theory has focused on its neutrality assumption, i.e. the functional equivalence of species in competition and dispersal. Almost no attention has been paid

Modes of speciation and the neutral theory of biodiversity

NARCIS (Netherlands)

Etienne, Rampal S.; Apol, M. Emile F.; Olff, Han; Weissing, Franz J.

Hubbell's neutral theory of biodiversity has generated much debate over the need for niches to explain biodiversity patterns. Discussion of the theory has focused on its neutrality assumption, i.e. the functional equivalence of species in competition and dispersal. Almost no attention has been paid

Measurement of chromatic dispersion of microstructured polymer fibers by white-light spectral interferometry

DEFF Research Database (Denmark)

Hlubina, Petr; Ciprian, Dalibor; Frosz, Michael Henoch

2009-01-01

We present a white-light spectral interferometric method for measuring the chromatic dispersion of microstructured fibers made of polymethyl methacrylate (PMMA). The method uses an unbalanced Mach-Zehnder interferometer with the fiber of known length placed in one of the interferometer arms...... of the method by measuring the wavelength dependence of the differential group refractive index of a pure silica fiber. We apply a five-term power series fit to the measured data and confirm by its differentiation that the chromatic dispersion of pure silica glass agrees well with theory. Second, we measure...... the chromatic dispersion for the fundamental mode supported by two different PMMA microstructured fibers, the multimode fiber and the large-mode area one....

Dispersion strengthening of aluminium-aluminium-oxide products

DEFF Research Database (Denmark)

Hansen, Niels

1970-01-01

The true stress-true strain curves at room temperature and at 400°C were determined for various types of aluminium-aluminium-oxide products containing from 0.2 to 4.7 weight per cent of aluminium oxide. The effect of particles on the initial flow stress and the flow stress for 0.2% offset at room...... temperature and at 400°C is in agreement with Orowan's theory. The increase in flow stress at room temperature for strain values below 3 per cent was related to the plastic strain by the equation σ-σoy=k1ε 1/2, where σoy is the initial flow stress and where k1 increases for increasing volume fraction...... and decreasing particle size of the dispersed particles. A general expression for k1 was derived for the relationship between the dislocation density and the strain in dispersion-strengthened products...

Acoustic and Seismic Dispersion in Complex Fluids and Solids

Science.gov (United States)

Goddard, Joe

2017-04-01

The first part of the present paper is the continuation of a previous work [3] on the effects of higher spatial gradients and temporal relaxation on stress and heat flux in complex fluids. In particular, the general linear theory is applied to acoustic dispersion, extending a simpler model proposed by Davis and Brenner [2]. The theory is applied to a linearized version of the Chapman-Enskog fluid [1] valid to terms of Burnett order and including Maxwell-Cataneo relaxation of stress and heat flux on relaxation time scales τ. For this model, the dispersion relation k(ω) giving spatial wave number k as function of temporal frequency ω is a cubic in k2, in contrast to the quadratic in k2 given by the classical model and the recently proposed modification [2]. The cubic terms are shown to be important only for ωτ = O(1) where Maxwell-Cataneo relaxation is also important. As a second part of the present work, it is shown how the above model can also be applied to isotropic solids, where both shear and pressure waves are important. Finally, consideration is given to hyperstress in micro- polar continua, including both graded and micro-morphic varieties. [1]S. Chapman and T. Cowling. The mathematical theory of non-uniform gases. Cambridge University Press, [Cambridge, UK], 1960. [2]A. M.J. Davis and H. Brenner. Thermal and viscous effects on sound waves: revised classical theory. J. Acoust. Soc. Am., 132(5):2963-9, 2012. [3] J.D. Goddard. On material velocities and non-locality in the thermo-mechanics of continua. Int. J. Eng. Sci., 48(11):1279-88, 2010.

Theory of a beam-induced electromagnetic mode in a magnetized plasma

International Nuclear Information System (INIS)

Baumgaertel, K.; Sauer, K.

1985-01-01

The theory of a recently discovered plasma wave mode is presented. In a non-Maxwellian high-beta plasma a new electromagnetic mode was detected containing a group of energetic field-aligned electrons. The theory uses the standard method for derivation of the dispersion relation, allowing non-Maxwellian electron distributions and right-hand polarization. The theoretical dispersion relation is compared with the empirical data. This comparison confirmes the existence of a right-hand circularly polarized mode propagating parallel to the external magnetic field. (D.Gy.)

Interphase and particle dispersion correlations in polymer nanocomposites

Science.gov (United States)

Senses, Erkan

Particle dispersion in polymer matrices is a major parameter governing the mechanical performance of polymer nanocomposites. Controlling particle dispersion and understanding aging of composites under large shear and temperature variations determine the processing conditions and lifetime of composites which are very important for diverse applications in biomedicine, highly reinforced materials and more importantly for the polymer composites with adaptive mechanical responses. This thesis investigates the role of interphase layers between particles and polymer matrices in two bulk systems where particle dispersion is altered upon deformation in repulsive composites, and good-dispersion of particles is retained after multiple oscillatory shearing and aging cycles in attractive composites. We demonstrate that chain desorption and re-adsorption processes in attractive composites under shear can effectively enhance the bulk microscopic mechanical properties, and long chains of adsorbed layers lead to a denser entangled interphase layer. We further designed experiments where particles are physically adsorbed with bimodal lengths of homopolymer chains to underpin the entanglement effect in interphases. Bimodal adsorbed chains are shown to improve the interfacial strength and used to modulate the elastic properties of composites without changing the particle loading, dispersion state or polymer conformation. Finally, the role of dynamic asymmetry (different mobilities in polymer blends) and chemical heterogeneity in the interphase layer are explored in systems of poly(methyl methacrylate) adsorbed silica nanoparticles dispersed in poly(ethylene oxide) matrix. Such nanocomposites are shown to exhibit unique thermal-stiffening behavior at temperatures above glass transitions of both polymers. These interesting findings suggest that the mobility of the surface-bound polymer is essential for reinforcement in polymer nanocomposites, contrary to existing glassy layer theories

A Stochastic Theory for Deep Bed Filtration Accounting for Dispersion and Size Distributions

DEFF Research Database (Denmark)

Shapiro, Alexander; Bedrikovetsky, P. G.

2010-01-01

We develop a stochastic theory for filtration of suspensions in porous media. The theory takes into account particle and pore size distributions, as well as the random character of the particle motion, which is described in the framework of the theory of continuous-time random walks (CTRW...

Numerical method for the dispersion relation of a hot and inhomogeneous plasma with an electron beam

International Nuclear Information System (INIS)

Devia, A.; Orrego, C.E.; Buitrago, G.

1990-01-01

A numerical method that is based in kinetic theory (Vlasov-Poison equations) was developed in order to calculate the dispersion relation for the interaction between a hot cylindrical and electron beam in any temperature and density. The plasma-beam system is located in a strong magnetic field. Many examples showing the effect of the temperatures and densities on the dispersion relation are given. (Author)

Can we trace biotic dispersals back in time? Introducing backward flow connectivity

Directory of Open Access Journals (Sweden)

Alessandro Ferrarini

2014-06-01

Full Text Available Connectivity in ecology deals with the problem of how species dispersal will happen given actual landscape and species presence/absence over such landscape. Hence it can be considered a forward (ahead in time scientific problem. I observe here that a backward theory of connectivity could be of deep interest as well: given the actual species presence/absence on the landscape, where with the highest probability such species is coming from? In other words, can we trace biotic dispersals back in time? Recently I have introduced a modelling and theoretical approach to ecological connectivity that is alternative to circuit theory and is able to fix the weak point of the "from-to" connectivity approach. The proposed approach holds also for mountain and hilly landscapes. In addition, it doesn't assume any intention for a species to go from source points to sink ones, because the expected path for the species is determined locally (pixel by pixel by landscape features. In this paper, I introduce a new theoretical and modelling approach called "backward flow connectivity". While flow connectivity predicts future species dispersal by minimizing at each step the potential energy due to fictional gravity over a frictional landscape, backward flow connectivity does exactly the opposite, i.e. maximizes potential energy at each step sending back the species to higher levels of potential energy due to fictional gravity on the frictional landscape. Using backward flow connectivity, one has at hand a new tool to revert timeline of species dispersal, hence being able to trace backward biotic dispersals. With few modifications, the applications of backward flow connectivity can be countless, for instance tracing back-in-time not only plants and animals but also ancient human migrations and viral paths.

Testing freshwater Lago Mare dispersal theory on the phylogeny relationships of iberian cyprinid genera Chondrostoma and Squalius (Cypriniformes, Cyprinidae

Directory of Open Access Journals (Sweden)

Carmona, José Ambrosio

2003-12-01

Full Text Available A phylogeny of the species in the genera Chondrostoma and Squalius was constructed based on the complete mitochondrial cytochrome b gene (1140pb. The molecular phylogeny was used to test the effect of the Mediterranean Lago Mare dispersal theory on the processes of divergence and speciation of European freshwater fishes. Phylogenetic relationships among Squalius samples and the molecular clock revealed that the ancestor of the current Iberian Squalius species inhabited a wide geographic area in the central and southwestern part of the former Iberian Peninsula during the Miocene before the Lago Mare phase. Similarly, the four main Iberian lineages of the genus Chondrostoma originated in the Middle-Upper Miocene. Hence, the Lago Mare phase of the Mediterranean Sea seems to have been a too recent paleogeographic event to have had any major impact on the dispersion of Squalius and Chondrostoma species. However, the reduction of the water-bodies during the Tortonian and Messinian may have intensified the isolation of populations. The Operational Biogeographic Units recovered from the Squalius and Chondrostoma phylogenies also reject the Lago Mare dispersal theory and support the idea that the differentiation processes were due to both the formation of the current hydrographical basin during the Plio-Pleistocene as well as to an earlier endorrheism event that occurred prior to hydrographical configuration.Realizamos una filogenia de los géneros Chondrostoma y Squalius mediante el estudio de la secuencia completa del gen mitocondrial citocromo b (1140pb. La filogenia molecular fue usada para comprobar el efecto que la teoría de dispersión del Mediterráneo Lago Mare ha tenido sobre los procesos de divergencia y especiación en los peces de agua dulce europeos. Las relaciones filogenéticas entre las muestras de Squalius y la aplicación del reloj molecular pusieron de manifiesto que el ancestro de las actuales especies ibéricas de Squalius habitaba

Study of phenomena of tracer transport and dispersion in fractured media

International Nuclear Information System (INIS)

Ippolito, Irene

1993-01-01

The objective of this research thesis is to present some transport phenomena according to two different approaches: firstly, the study of flows and tracing in a natural crack within a granitic site, and secondly, the study of flows of different geometries in model cracks, mainly by using techniques of tracer dispersion. The author first presents some properties of fractured media and elements of the theory of the phenomenon of dispersion. She notably discusses the reversibility of the Taylor dispersion which is the prevailing mechanism for simply connected geometries such as in the case of a flow between two continuous solid surfaces limiting a fracture. In the next chapters, the author reports the analysis of characteristics of local structures (mouths, roughnesses) of a single fracture by using echo dispersion. She reports experiments as well as Monte Carlo simulations performed on well defined geometries. In a parallel way, some characteristics measurements (rate-pressure, distribution of flows and tracing in transmission) and mechanical measurements of fracture deformation have been performed on a natural fracture in a granitic site [fr

Higher-order Cn dispersion coefficients for the alkali-metal atoms

International Nuclear Information System (INIS)

Mitroy, J.; Bromley, M.W.J.

2005-01-01

The van der Waals coefficients, from C 11 through to C 16 resulting from second-, third-, and fourth-order perturbation theory are estimated for the alkali-metal (Li, Na, K, and Rb) atoms. The dispersion coefficients are also computed for all possible combinations of the alkali-metal atoms and hydrogen. The parameters are determined from sum rules after diagonalizing a semiempirical fixed core Hamiltonian in a large basis. Comparisons of the radial dependence of the C n /r n potentials give guidance as to the radial regions in which the various higher-order terms can be neglected. It is seen that including terms up to C 10 /r 10 results in a dispersion interaction that is accurate to better than 1% whenever the inter-nuclear spacing is larger than 20a 0 . This level of accuracy is mainly achieved due to the fortuitous cancellation between the repulsive (C 11 ,C 13 ,C 15 ) and attractive (C 12 ,C 14 ,C 16 ) dispersion forces

Retention time variability as a mechanism for animal mediated long-distance dispersal.

Directory of Open Access Journals (Sweden)

Vishwesha Guttal

Full Text Available Long-distance dispersal (LDD events, although rare for most plant species, can strongly influence population and community dynamics. Animals function as a key biotic vector of seeds and thus, a mechanistic and quantitative understanding of how individual animal behaviors scale to dispersal patterns at different spatial scales is a question of critical importance from both basic and applied perspectives. Using a diffusion-theory based analytical approach for a wide range of animal movement and seed transportation patterns, we show that the scale (a measure of local dispersal of the seed dispersal kernel increases with the organisms' rate of movement and mean seed retention time. We reveal that variations in seed retention time is a key determinant of various measures of LDD such as kurtosis (or shape of the kernel, thinkness of tails and the absolute number of seeds falling beyond a threshold distance. Using empirical data sets of frugivores, we illustrate the importance of variability in retention times for predicting the key disperser species that influence LDD. Our study makes testable predictions linking animal movement behaviors and gut retention times to dispersal patterns and, more generally, highlights the potential importance of animal behavioral variability for the LDD of seeds.

Dispersion and Cluster Scales in the Ocean

Science.gov (United States)

Kirwan, A. D., Jr.; Chang, H.; Huntley, H.; Carlson, D. F.; Mensa, J. A.; Poje, A. C.; Fox-Kemper, B.

2017-12-01

Ocean flow space scales range from centimeters to thousands of kilometers. Because of their large Reynolds number these flows are considered turbulent. However, because of rotation and stratification constraints they do not conform to classical turbulence scaling theory. Mesoscale and large-scale motions are well described by geostrophic or "2D turbulence" theory, however extending this theory to submesoscales has proved to be problematic. One obvious reason is the difficulty in obtaining reliable data over many orders of magnitude of spatial scales in an ocean environment. The goal of this presentation is to provide a preliminary synopsis of two recent experiments that overcame these obstacles. The first experiment, the Grand LAgrangian Deployment (GLAD) was conducted during July 2012 in the eastern half of the Gulf of Mexico. Here approximately 300 GPS-tracked drifters were deployed with the primary goal to determine whether the relative dispersion of an initially densely clustered array was driven by processes acting at local pair separation scales or by straining imposed by mesoscale motions. The second experiment was a component of the LAgrangian Submesoscale Experiment (LASER) conducted during the winter of 2016. Here thousands of bamboo plates were tracked optically from an Aerostat. Together these two deployments provided an unprecedented data set on dispersion and clustering processes from 1 to 106 meter scales. Calculations of statistics such as two point separations, structure functions, and scale dependent relative diffusivities showed: inverse energy cascade as expected for scales above 10 km, a forward energy cascade at scales below 10 km with a possible energy input at Langmuir circulation scales. We also find evidence from structure function calculations for surface flow convergence at scales less than 10 km that account for material clustering at the ocean surface.

Barrier displacement on a neutral landscape: Towards a theory of continental biogeography

Science.gov (United States)

Albert, James S.; Schoolmaster, Donald; Tagliacollo, Victor; Duke-Sylvester, Scott M.

2017-01-01

Macroevolutionary theory posits three processes leading to lineage diversification and the formation of regional biotas: dispersal (species geographic range expansion), speciation (species lineage splitting), and extinction (species lineage termination). The Theory of Island Biogeography (TIB) predicts species richness values using just two of these processes; dispersal and extinction. Yet most species on Earth live on continents or continental shelves, and the dynamics of evolutionary diversification at regional and continental scales are qualitatively different from those that govern the formation of species richness on biogeographic islands. Certain geomorphological processes operating perennially on continental platforms displace barriers to gene flow and organismal dispersal, and affect all three terms of macroevolutionary diversification. For example, uplift of a dissected landscape and river capture both merge and separate portions of adjacent areas, allowing dispersal and larger geographic ranges, vicariant speciation and smaller geographic ranges, and extinction when range sizes are subdivided below a minimum persistence threshold.

The dispersion of the polariton frequencies in orthorhombic KNbO3

International Nuclear Information System (INIS)

Claus, R.; Winter, F.X.

1975-01-01

The dispersion of the polariton frequencies in all of the three main planes of an orthorhombic crystal has been studied at the example KNbO 3 for the first time. In this case pure transverse polar modes of the species A 1 , B 1 and B 2 occur. The investigations have been carried out with Raman scattering. The experimental data have been compared with dispersion curves, which have been calculated numerically on the basis of the general theory of polaritons. In each one of the main planes the pure transverse modes of one symmetry species are independent from the direction as predicted. (orig.) [de

Dispersion bias, dispersion effect, and the aerosol-cloud conundrum

International Nuclear Information System (INIS)

Liu Yangang; Daum, Peter H; Guo Huan; Peng Yiran

2008-01-01

This work examines the influences of relative dispersion (the ratio of the standard deviation to the mean radius of the cloud droplet size distribution) on cloud albedo and cloud radiative forcing, derives an analytical formulation that accounts explicitly for the contribution from droplet concentration and relative dispersion, and presents a new approach to parameterize relative dispersion in climate models. It is shown that inadequate representation of relative dispersion in climate models leads to an overestimation of cloud albedo, resulting in a negative bias of global mean shortwave cloud radiative forcing that can be comparable to the warming caused by doubling CO 2 in magnitude, and that this dispersion bias is likely near its maximum for ambient clouds. Relative dispersion is empirically expressed as a function of the quotient between cloud liquid water content and droplet concentration (i.e., water per droplet), yielding an analytical formulation for the first aerosol indirect effect. Further analysis of the new expression reveals that the dispersion effect not only offsets the cooling from the Twomey effect, but is also proportional to the Twomey effect in magnitude. These results suggest that unrealistic representation of relative dispersion in cloud parameterization in general, and evaluation of aerosol indirect effects in particular, is at least in part responsible for several outstanding puzzles of the aerosol-cloud conundrum: for example, overestimation of cloud radiative cooling by climate models compared to satellite observations; large uncertainty and discrepancy in estimates of the aerosol indirect effect; and the lack of interhemispheric difference in cloud albedo.

Modeling emerald ash borer dispersal using percolation theory: estimating the rate of range expansion in a fragmented landscape

Science.gov (United States)

Robin A. J. Taylor; Daniel A. Herms; Louis R. Iverson

2008-01-01

The dispersal of organisms is rarely random, although diffusion processes can be useful models for movement in approximately homogeneous environments. However, the environments through which all organisms disperse are far from uniform at all scales. The emerald ash borer (EAB), Agrilus planipennis, is obligate on ash (Fraxinus spp...

Linear theory of drift-tearing and interchange modes in a screw pinch

International Nuclear Information System (INIS)

Copenhaver, C.

1978-04-01

A drift dispersion relation, as applied to a resistive incompressible plasma in a screw pinch, is derived. This dispersion relation incorporates both drift-tearing and drift-interchange modes and is valid throughout the collisional regime by including kinetic theory factors. The dispersion relation reduces to the drift-tearing dispersion relation in the zero pressure gradient limit, and to the classical resistive dispersion relation in the zero drift limit. The electron temperature gradient instability is still present. Now, however, the introduction of the interchange-drift instability increases the growth rate further above the tearing-drift case. (orig.) [de

Dispersion, sorption and photodegradation of petroleum hydrocarbons in dispersant-seawater-sediment systems.

Science.gov (United States)

Zhao, Xiao; Liu, Wen; Fu, Jie; Cai, Zhengqing; O'Reilly, S E; Zhao, Dongye

2016-08-15

This work examined effects of model oil dispersants on dispersion, sorption and photodegradation of petroleum hydrocarbons in simulated marine systems. Three dispersants (Corexit 9500A, Corexit 9527A and SPC 1000) were used to prepare dispersed water accommodated oil (DWAO). While higher doses of dispersants dispersed more n-alkanes and PAHs, Corexit 9500A preferentially dispersed C11-C20 n-alkanes, whereas Corexit 9527A was more favorable for smaller alkanes (C10-C16), and SPC 1000 for C12-C28 n-alkanes. Sorption of petroleum hydrocarbons on sediment was proportional to TPH types/fractions in the DWAOs. Addition of 18mg/L of Corexit 9500A increased sediment uptake of 2-3 ring PAHs, while higher dispersant doses reduced the uptake, due to micelle-enhanced solubilization effects. Both dispersed n-alkanes and PAHs were susceptible to photodegradation under simulated sunlight. For PAHs, both photodegradation and photo-facilitated alkylation were concurrently taking place. The information can facilitate sounder assessment of fate and distribution of dispersed oil hydrocarbons in marine systems. Copyright © 2016 Elsevier Ltd. All rights reserved.

The cross-national pattern of happiness. Test of predictions implied in three theories of happiness

NARCIS (Netherlands)

R. Veenhoven (Ruut); J.J. Ehrhardt (Joop)

1995-01-01

textabstractABSTRACT. Predictions about level and dispersion of happiness in nations are derived from three theories of happiness: comparison-theory, folklore-theory and livability-theory. The predictions are tested on two cross national data-sets: a comparative survey among university students in

A general advection-diffusion model for radioactive substance dispersion released from nuclear power plants

International Nuclear Information System (INIS)

Buske, D.

2011-01-01

The present contribution focuses on the question of radioactive material dispersion after discharge from a nuclear power plant in the context of micro-meteorology, i.e. an atmospheric dispersion model. The advection-diffusion equation with Fickian closure for the turbulence is solved for the atmospheric boundary layer where the eddy diffusivity coefficients and the wind profile are assumed to be space dependent. The model is solved in closed form using integral transform and spectral theory. Convergence of the solution is discussed in terms of a convergence criterion using a new interpretation of the Cardinal Theorem of Interpolation theory and Parseval's theorem. The solution is compared to other methods and model adequacy is analyzed. Model validation is performed against experimental data from a controlled release of radioactive material at the Itaorna Beach (Angra dos Reis, Rio de Janeiro state, Brazil, 1985). (author)

Leonhard Euler's Wave Theory of Light

DEFF Research Database (Denmark)

Pedersen, Kurt Møller

2008-01-01

is wrong. Most of his mathematical arguments were, however, guesswork without any solid physical reasoning. Guesswork is not always a bad thing in physics if it leads to new experiments or makes the theory coherent with other theories. And Euler tried to find such experiments. He saw the construction......Euler's wave theory of light developed from a mere description of this notion based on an analogy between sound and light to a more and more mathematical elaboration on that notion. He was very successful in predicting the shape of achromatic lenses based on a new dispersion law that we now know...

Dispersion and current measurements

International Nuclear Information System (INIS)

Boelskifte, S.

1986-04-01

A model for the simulation of particle movements in water should incorporate the mutual distance dependent correlation. As long as reliable data are given accessible a model can be created of the dispersion in a given area from a statistical description of turbulence. Current measurements have been performed in an area north of the Swedish nuclear power plant Barsebaeck, and statistical time series analysis have made it possible to estimate multivariate autoregressive moving-average (ARMA) models for these data using the Box-Jenkins method. The correlation structure for the area has been investigated in detail. Transport and dispersion models for the marine environment are used in estimating doses to the population from the aquatic food chain. Some of these models are described with special emphasis on the time and length scales they cover. Furthermore, to illustrate the background of the simulation model, short introductuions are given to health physics, time series analysis, and turbulence theory. Analysis of the simulation model shows the relative importance of the different parameters. The model can be expanded to conditional simulation, where the current measurements are used directly to simulate the movement of one of the particles. Results from the model are also compared to results from a sampling of bioindicators (Fucus vesiculosus) along the Danish coast. The reliability of bioindicators in this kind of experiment is discussed. (author)

The Unified Neutral Theory of Biodiversity and Biogeography at Age Ten

NARCIS (Netherlands)

Rosindell, James; Hubbell, Stephen P.; Etienne, Rampal S.

A decade has now passed since Hubbell published The Unified Neutral Theory of Biodiversity and Biogeography. Neutral theory highlights the importance of dispersal limitation, speciation and ecological drift in the natural world and provides quantitative null models for assessing the role of

Effects of chemical dispersants on oil physical properties and dispersion. Volume 1

International Nuclear Information System (INIS)

Khelifa, A.; Fingas, M.; Hollebone, B.P.; Brown, C.E.; Pjontek, D.

2007-01-01

Laboratory and field testing have shown that the dispersion of oil spilled in water is influenced by chemical dispersants via the modification of the interfacial properties of the oil, such as oil-brine interfacial tension (IFT). This study focused on new laboratory experiments that measured the effects on the physical properties and dispersion of oil, with particular reference to the effects of chemical dispersants on IFT and oil viscosity and the subsequent effects on oil droplet formation. Experiments were conducted at 15 degrees C using Arabian Medium, Alaska North Slope and South Louisiana crude and Corexit 9500 and Corexit 9527 chemical dispersants. The dispersants were denser than the 3 oils. The effect of IFT reduction on oil dispersion was measured and showed substantial reduction in the size and enhancement of the concentration of oil droplets in the water column. It was shown that the brine-oil IFT associated with the 3 crudes reduced to less than 3.6 mN/m with the application of the chemical dispersants, even at a low dispersant-to-oil ratio (DOR) value of 1:200. The use of chemical dispersants increased the viscosity of the dispersant-oil mixture up to 40 per cent over the neat crude oil. It was shown that for each mixing condition, an optimum value of DOR exists that provides for maximal dispersant effectiveness. The IFT reaches maximum reduction at optimum DOR. It was suggested that oil spill modelling can be improved with further study of IFT reduction with DOR and variations of critical micelle concentration with the type and solubility of chemical dispersant, oil type and oil to water ratio. 13 refs., 3 tabs., 7 figs

The mechanisms of drug release from solid dispersions in water-soluble polymers.

Science.gov (United States)

Craig, Duncan Q M

2002-01-14

Solid dispersions in water-soluble carriers have attracted considerable interest as a means of improving the dissolution rate, and hence possibly bioavailability, of a range of hydrophobic drugs. However, despite the publication of numerous original papers and reviews on the subject, the mechanisms underpinning the observed improvements in dissolution rate are not yet understood. In this review the current consensus with regard to the solid-state structure and dissolution properties of solid dispersions is critically assessed. In particular the theories of carrier- and drug-controlled dissolution are highlighted. A model is proposed whereby the release behaviour from the dispersions may be understood in terms of the dissolution or otherwise of the drug into the concentrated aqueous polymer layer adjacent to the solid surface, including a derivation of an expression to describe the release of intact particles from the dispersions. The implications of a deeper understanding of the dissolution mechanisms are discussed, with particular emphasis on optimising the choice of carrier and manufacturing method and the prediction of stability problems.

Three-dimensional N=6 superconformal field theories and their membrane dynamics

International Nuclear Information System (INIS)

Berenstein, David; Trancanelli, Diego

2008-01-01

We analyze several aspects of the recent construction of three-dimensional conformal gauge theories by Aharony et al. in various regimes. We pay special attention to understanding how the M-theory geometry and interpretation can be extracted from the analysis of the field theory. We revisit the calculations of the moduli space of vacua and the complete characterization of chiral ring operators by analyzing the field theory compactified on a 2-sphere. We show that many of the states dual to these operators can be interpreted as D-brane states in the weak-coupling limit. Also, various features of the dual AdS geometry can be obtained by performing a strong coupling expansion around moduli space configurations, even though one is not taking the planar expansion. In particular, we show that at strong coupling the corresponding weak-coupling D-brane states of the chiral ring localize on particular submanifolds of the dual geometry that match the M-theory interpretation. We also study the massive spectrum of fields in the moduli space. We use this to investigate the dispersion relation of giant magnons from the field theory point of view. Our analysis predicts the exact functional form of the dispersion relation as a function of the world sheet momentum, independently of integrability assumptions, but not the exact form with respect to the 't Hooft coupling. We also get the dispersion relation of bound states of giant magnons from first principles, providing evidence for the full integrability of the corresponding spin chain model at strong 't Hooft coupling.

Granular controls on the dispersion of bed load tracers

Science.gov (United States)

Jerolmack, D. J.; Martin, R. L.; Phillips, C. B.

2014-12-01

Coarse particles are transported in a river as bed load, i.e., they move in frequent contact with and are supported by the granular bed. This movement is typically intermittent and may be described by a series of steps are rests, the distributions of which determine particle dispersion. Laboratory and field studies of bed load tracer dispersion have reported sub- and super-diffusive behavior, both of which have been successfully reproduced with stochastic transport models. Although researchers have invoked heavy-tailed step lengths as the cause of anomalous dispersion, most observations report thin-tailed distributions. Little attention has been paid to rest periods, and stochastic transport models have not been connected to the underlying mechanics of particle motion. Based on theoretical and experimental evidence, we argue that step lengths are thin-tailed and do not control the longterm dispersion of bed load tracers; they are determined by momentum balance between the fluid and solid. Using laboratory experiments with both marbles and natural sediments, we demonstrate that the rest time distribution is power law, and argue that this distribution controls asymptotic dispersion. Observed rest times far exceed any hydrodynamic timescale. Experiments reveal that rest times of deposited particles are governed by fluctuations in river bed elevation; in particular, the return time for the bed to scour to the base of a deposited particle. Stochastic fluctuations in bed elevation are describable by an Ornstein-Uhlenbeck (mean-reverting random walk) model that contains two parameters, which we show are directly related to the granular shear rate and range of bed elevation fluctuations, respectively. Combining these results with the theory of asymmetric random walks (particles only move downstream), we predict superdiffusive behavior that is in quantitative agreement with our observations of tracer dispersion in a natural river.

Breeding Dispersal by Birds in a Dynamic Urban Ecosystem.

Science.gov (United States)

Marzluff, John M; DeLap, Jack H; Oleyar, M David; Whittaker, Kara A; Gardner, Beth

2016-01-01

Changes in land cover during urbanization profoundly affect the diversity of bird communities, but the demographic mechanisms affecting diversity are poorly known. We advance such understanding by documenting how urbanization influences breeding dispersal-the annual movement of territorial adults-of six songbird species in the Seattle, WA, USA metropolitan area. We color-banded adults and mapped the centers of their annual breeding activities from 2000-2010 to obtain 504 consecutive movements by 337 adults. By comparing movements, annual reproduction, and mate fidelity among 10 developed, 5 reserved, and 11 changing (areas cleared and developed during our study) landscapes, we determined that adaptive breeding dispersal of sensitive forest species (Swainson's Thrush and Pacific wren), which involves shifting territory and mate after reproductive failure, was constrained by development. In changing lands, sensitive forest specialists dispersed from active development to nearby forested areas, but in so doing suffered low annual reproduction. Species tolerant of suburban lands (song sparrow, spotted towhee, dark-eyed junco, and Bewick's wren) dispersed adaptively in changing landscapes. Site fidelity ranged from 0% (Pacific wren in changing landscape) to 83% (Bewick's wren in forest reserve). Mate fidelity ranged from 25% (dark-eyed junco) to 100% (Bewick's wren). Variation in fidelity to mate and territory was consistent with theories positing an influence of territory quality, asynchronous return from migration, prior productivity, and reproductive benefits of retaining a familiar territory. Costly breeding dispersal, as well as reduced reproductive success and lowered survival cause some birds to decline in the face of urbanization. In contrast, the ability of species that utilize edges and early successional habitats to breed successfully, disperse to improve reproductive success after failure, and survive throughout the urban ecosystem enables them to maintain

Breeding Dispersal by Birds in a Dynamic Urban Ecosystem.

Directory of Open Access Journals (Sweden)

John M Marzluff

Full Text Available Changes in land cover during urbanization profoundly affect the diversity of bird communities, but the demographic mechanisms affecting diversity are poorly known. We advance such understanding by documenting how urbanization influences breeding dispersal-the annual movement of territorial adults-of six songbird species in the Seattle, WA, USA metropolitan area. We color-banded adults and mapped the centers of their annual breeding activities from 2000-2010 to obtain 504 consecutive movements by 337 adults. By comparing movements, annual reproduction, and mate fidelity among 10 developed, 5 reserved, and 11 changing (areas cleared and developed during our study landscapes, we determined that adaptive breeding dispersal of sensitive forest species (Swainson's Thrush and Pacific wren, which involves shifting territory and mate after reproductive failure, was constrained by development. In changing lands, sensitive forest specialists dispersed from active development to nearby forested areas, but in so doing suffered low annual reproduction. Species tolerant of suburban lands (song sparrow, spotted towhee, dark-eyed junco, and Bewick's wren dispersed adaptively in changing landscapes. Site fidelity ranged from 0% (Pacific wren in changing landscape to 83% (Bewick's wren in forest reserve. Mate fidelity ranged from 25% (dark-eyed junco to 100% (Bewick's wren. Variation in fidelity to mate and territory was consistent with theories positing an influence of territory quality, asynchronous return from migration, prior productivity, and reproductive benefits of retaining a familiar territory. Costly breeding dispersal, as well as reduced reproductive success and lowered survival cause some birds to decline in the face of urbanization. In contrast, the ability of species that utilize edges and early successional habitats to breed successfully, disperse to improve reproductive success after failure, and survive throughout the urban ecosystem enables them

Roles of survival and dispersal in reintroduction success of Griffon vulture (Gyps fulvus).

Science.gov (United States)

Le Gouar, Pascaline; Robert, Alexandre; Choisy, Jean-Pierre; Henriquet, Sylvain; Lecuyer, Philippe; Tessier, Christian; Sarrazin, François

2008-06-01

The success of reintroduction programs greatly depends on the amount of mortality and dispersal of the released individuals. Although local environmental pressures are likely to play an important role in these processes, they have rarely been investigated because of the lack of spatial replicates of reintroduction. In the present study, we analyzed a 25-year data set encompassing 272 individuals released in five reintroduction programs of Griffon Vultures (Gyps fulvus) in France to examine the respective roles of survival and dispersal in program successes and failures. We use recent developments in multi-strata capture-recapture models to take into account tag loss in survival estimates and to consider and estimate dispersal among release areas. We also examined the effects of sex, age, time, area, and release status on survival, and we tested whether dispersal patterns among release areas were consistent with habitat selection theories. Results indicated that the survival of released adults was reduced during the first year after release, with no difference between sexes. Taking into account local observations only, we found that early survival rates varied across sites. However when we distinguished dispersal from mortality, early survival rates became equal across release sites. It thus appears that among reintroduction programs difference in failure and success was due to differential dispersal among release sites. We revealed asymmetrical patterns of dispersal due to conspecific attraction: dispersers selected the closest and the largest population. We showed that mortality can be homogeneous from one program to another while, on the contrary, dispersal is highly dependent on the matrix of established populations. Dispersal behavior is thus of major interest for metapopulation restoration and should be taken into account in planning reintroduction designs.

Theory of multiwave mixing within the superconducting kinetic-inductance traveling-wave amplifier

Science.gov (United States)

Erickson, R. P.; Pappas, D. P.

2017-03-01

We present a theory of parametric mixing within the coplanar waveguide (CPW) of a superconducting nonlinear kinetic-inductance traveling-wave (KIT) amplifier engineered with periodic dispersion loadings. This is done by first developing a metamaterial band theory of the dispersion-engineered KIT using a Floquet-Bloch construction and then applying it to the description of mixing of the nonlinear RF traveling waves. Our theory allows us to calculate signal gain versus signal frequency in the presence of a frequency stop gap, based solely on loading design. We present results for both three-wave mixing (3WM), with applied dc bias, and four-wave mixing (4WM), without dc. Our theory predicts an intrinsic and deterministic origin to undulations of 4WM signal gain with signal frequency, apart from extrinsic sources, such as impedance mismatch, and shows that such undulations are absent from 3WM signal gain achievable with dc. Our theory is extensible to amplifiers based on Josephson junctions in a lumped LC-ladder transmission line (TWPA).

Removal of Disperse Blue 56 and Disperse Red 135 dyes from aqueous dispersions by modified montmorillonite nanoclay

Directory of Open Access Journals (Sweden)

Ahmadishoar Javad

2017-01-01

Full Text Available In this study modified montmorillonite was used as an adsorbent for the removal of two selected disperse dyes i.e., Disperse Blue 56 (DB and Disperse Red 135 (DR from dye dispersions. The adsorption equilibrium data of dyes adsorption were investigated by using Nernst, Freundlich and Langmuir isotherm models. The adsorption kinetics was analyzed by using different models including pseudo-first-order, pseudo-second-order, Elovich and Intraparticle diffusion model. The Freundlich isotherm was found to be the most appropriate model for describing the sorption of the dyes on modified nanoclay. The best fit to the experimental results was obtained by using the pseudo-second-order kinetic equation, which satisfactorily described the process of dye adsorption. Although different kinetic models may control the rate of the adsorption process, the results indicated that the main rate limiting step was the intraparticle diffusion. The results showed that the proposed modified montmorillonite could be used as an effective adsorbent for the removal of disperse dyes even from highly concentrated dispersions.

An experimental study of dielectric dispersion in porous media and its dependence on pore geometry

Energy Technology Data Exchange (ETDEWEB)

Haslund, E.

1996-12-31

Understanding water saturated composite media are important in the study of oil reservoirs. This doctoral thesis discusses measurements of the frequency dependent permittivity and conductivity of water saturated porous glass specimens. The experiments are designed to investigate the dispersion resulting from the geometrical properties of the pore space. Measurements are presented of the effective complex dielectric constant of water saturated porous glass specimens for frequencies below 13 MHz. The specimens are made from sintered glass spheres, and in some specimens thin plates are mixed in with the spheres. Low-conductivity water is used to saturate the pore space in order to scale the frequency range of the Maxwell-Wagner dispersion into the measurement range. The experiments are compared with two different effective medium approaches. One approach is the Mendelson and Cohen theory with randomly oriented spheroidal grains in addition to spherical grains, the other the Local porosity theory due to Hilfer. Both theories were found to be in good agreement with the experimental observations. 175 refs., 59 figs., 1 table

Dispersion and energy conservation relations of surface waves in semi-infinite plasma

International Nuclear Information System (INIS)

Atanassov, V.

1981-01-01

The hydrodynamic theory of surface wave propagation in semi-infinite homogeneous isotropic plasma is considered. Explicit linear surface wave solutions are given for the electric and magnetic fields, charge and current densities. These solutions are used to obtain the well-known dispersion relations and, together with the general energy conservation equation, to find appropriate definitions for the energy and the energy flow densities of surface waves. These densities are associated with the dispersion relation and the group velocity by formulae similar to those for bulk waves in infinite plasmas. Both cases of high-frequency (HF) and low-frequency (LF) surface waves are considered. (author)

Control of the hyperbolic dispersion of dielectrics by an ultrashort laser pulse

Science.gov (United States)

Zhang, Xiaoqin; Wang, Feng; Zhang, Fengshou; Yao, Yugui

2018-01-01

An idea of controlling hyperbolic dispersion of dielectric materials by an ultrashort laser pulse is proposed. Taking the diamond as a concrete example and using time-dependent density functional theory calculations, we show that the permittivity tensor of the material can be effectively tuned by an ultrashort laser pulse, serving as a transient hyperbolic medium with wide working frequency window. With easily tunable laser parameters, the material can even be switched by reversal of both elliptic and hyperbolic for a particular light frequency. Our result points out a route toward transient hyperbolic materials, and it offers methods to achieve tunable hyperbolic dispersion with great potential for ultrafast device applications.

Observation of Self-Cavitating Envelope Dispersive Shock Waves in Yttrium Iron Garnet Thin Films

Science.gov (United States)

Janantha, P. A. Praveen; Sprenger, Patrick; Hoefer, Mark A.; Wu, Mingzhong

2017-07-01

The formation and properties of envelope dispersive shock wave (DSW) excitations from repulsive nonlinear waves in a magnetic film are studied. Experiments involve the excitation of a spin wave step pulse in a low-loss magnetic Y3Fe5O12 thin film strip, in which the spin wave amplitude increases rapidly, realizing the canonical Riemann problem of shock theory. Under certain conditions, the envelope of the spin wave pulse evolves into a DSW that consists of an expanding train of nonlinear oscillations with amplitudes increasing from front to back, terminated by a black soliton. The onset of DSW self-cavitation, indicated by a point of zero power and a concomitant 180° phase jump, is observed for sufficiently large steps, indicative of the bidirectional dispersive hydrodynamic nature of the DSW. The experimental observations are interpreted with theory and simulations of the nonlinear Schrödinger equation.

Nanocomposites from Stable Dispersions of Carbon Nanotubes in Polymeric Matrices Using Dispersion Interaction

Science.gov (United States)

Wise, Kristopher Eric (Inventor); Park, Cheol (Inventor); Kang, Jin Ho (Inventor); Siochi, Emilie J. (Inventor); Harrison, Joycelyn S. (Inventor)

2016-01-01

Stable dispersions of carbon nanotubes (CNTs) in polymeric matrices include CNTs dispersed in a host polymer or copolymer whose monomers have delocalized electron orbitals, so that a dispersion interaction results between the host polymer or copolymer and the CNTs dispersed therein. Nanocomposite products, which are presented in bulk, or when fabricated as a film, fiber, foam, coating, adhesive, paste, or molding, are prepared by standard means from the present stable dispersions of CNTs in polymeric matrices, employing dispersion interactions, as presented hereinabove.

Synthesis of mono-dispersed nanofluids using solution plasma

Energy Technology Data Exchange (ETDEWEB)

Heo, Yong Kang, E-mail: yk@rd.numse.nagoya-u.ac.jp [Graduate School of Materials Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya (Japan); Bratescu, Maria Antoaneta, E-mail: maria@rd.numse.nagoya-u.ac.jp [Graduate School of Materials Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya (Japan); Knowledge Hub Aichi, Yakusa-cho, Nagakute-ku, Toyota (Japan); Ueno, Tomonaga, E-mail: tomo@rd.numse.nagoya-u.ac.jp [Graduate School of Materials Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya (Japan); Green Mobility Collaborative Research Center, Nagoya University, Furo-cho, Chikusa-ku, Nagoya (Japan); CREST, Japan Science and Technology Agency, Goban-cho, Chiyoda-ku, Tokyo (Japan); Saito, Nagahiro, E-mail: hiro@rd.numse.nagoya-u.ac.jp [Graduate School of Materials Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya (Japan); Knowledge Hub Aichi, Yakusa-cho, Nagakute-ku, Toyota (Japan); Green Mobility Collaborative Research Center, Nagoya University, Furo-cho, Chikusa-ku, Nagoya (Japan); CREST, Japan Science and Technology Agency, Goban-cho, Chiyoda-ku, Tokyo (Japan)

2014-07-14

Small-sized and well-dispersed gold nanoparticles (NPs) for nanofluidics have been synthesized by electrical discharge in liquid environment using termed solution plasma processing (SPP). Electrons and the hydrogen radicals are reducing the gold ions to the neutral form in plasma gas phase and liquid phase, respectively. The gold NPs have the smallest diameter of 4.9 nm when the solution temperature was kept at 20 °C. Nucleation and growth theory describe the evolution of the NP diameter right after the reduction reaction in function of the system temperature, NP surface energy, dispersion energy barrier, and nucleation rate. Negative charges on the NPs surface during and after SPP generate repulsive forces among the NPs avoiding their agglomeration in solution. Increasing the average energy in the SPP determines a decrease of the zeta potential and an increase of the NPs diameter. An important enhancement of the thermal conductivity of 9.4% was measured for the synthesized nanofluids containing NPs with the smallest size.

Dispersive analysis of the pion transition form factor

Energy Technology Data Exchange (ETDEWEB)

Hoferichter, M. [Technische Universitaet Darmstadt, Institut fuer Kernphysik, Darmstadt (Germany); GSI Helmholtzzentrum fuer Schwerionenforschung GmbH, ExtreMe Matter Institute EMMI, Darmstadt (Germany); University of Bern, Albert Einstein Center for Fundamental Physics, Institute for Theoretical Physics, Bern (Switzerland); Kubis, B.; Niecknig, F.; Schneider, S.P. [Universitaet Bonn, Helmholtz-Institut fuer Strahlen- und Kernphysik (Theorie) and Bethe Center for Theoretical Physics, Bonn (Germany); Leupold, S. [Uppsala Universitet, Institutionen foer fysik och astronomi, Box 516, Uppsala (Sweden)

2014-11-15

We analyze the pion transition form factor using dispersion theory. We calculate the singly-virtual form factor in the time-like region based on data for the e{sup +}e{sup -} → 3π cross section, generalizing previous studies on ω, φ → 3π decays and γπ → ππ scattering, and verify our result by comparing to e{sup +}e{sup -} → π{sup 0}γ data. We perform the analytic continuation to the space-like region, predicting the poorlyconstrained space-like transition form factor below 1 GeV, and extract the slope of the form factor at vanishing momentum transfer a{sub π} = (30.7 ± 0.6) x 10{sup -3}. We derive the dispersive formalism necessary for the extension of these results to the doubly-virtual case, as required for the pion-pole contribution to hadronic light-by-light scattering in the anomalous magnetic moment of the muon. (orig.)

Dispersion relation approach to sub-barrier heavy ion fusion reactions

International Nuclear Information System (INIS)

Franzin, V.L.M.; Hussein, M.S.

1986-07-01

With the aid of an inverse dispersion relation, which gives the imaginary part of the fusion inclusive polarization potential (IPP) in terms of the principal part integral involving the real part of the IPP, the sub-barrier fusion of heavy ions is discussed. The system 16 O+ A Sm is taken as an example. The reactive content of the extracted IPP is analysed within the coupled channels theory. (Author) [pt

Bands dispersion and charge transfer in β-BeH2

Science.gov (United States)

Trivedi, D. K.; Galav, K. L.; Joshi, K. B.

2018-04-01

Predictive capabilities of ab-initio method are utilised to explore bands dispersion and charge transfer in β-BeH2. Investigations are carried out using the linear combination of atomic orbitals method at the level of density functional theory. The crystal structure and related parameters are settled by coupling total energy calculations with the Murnaghan equation of state. Electronic bands dispersion from PBE-GGA is reported. The PBE-GGA, and PBE0 hybrid functional, show that β-BeH2 is a direct gap semiconductor with 1.18 and 2.40 eV band gap. The band gap slowly decreases with pressure and beyond l00 GPa overlap of conduction and valence bands at the r point is observed. Charge transfer is studied by means of Mullikan population analysis.

The Effects of Dispersal and Predator Density on Prey Survival in an Insect-Red Clover Metacommunity.

Science.gov (United States)

Stasek, David J; Radl, James N; Crist, Thomas O

2018-01-01

Trophic interactions are often studied within habitat patches, but among-patch dispersal of individuals may influence local patch dynamics. Metacommunity concepts incorporate the effects of dispersal on local and community dynamics. There are few experimental tests of metacommunity theory using insects compared to those conducted in microbial microcosms. Using connected experimental mesocosms, we varied the density of the leafhopper Agallia constricta Van Duzee (Homoptera: Cicadellidae) and a generalist insect predator, the damsel bug (Nabis spp., Heteroptera: Nabidae), to determine the effects of conspecific and predator density and varying the time available to dispersal among mesocosms on predation rates, dispersal rates, and leafhopper survival. Conspecific and damsel bug density did not affect dispersal rates in leafhoppers, but this may be due to leafhoppers' aversion to leaving the host plants or the connecting tubes between mesocosms hindering leafhopper movement. Leafhopper dispersal was higher in high-dispersal treatments. Survival rates of A. constricta were also lowest in treatments where dispersal was not limited. This is one of the first experimental studies to vary predator density and the time available to dispersal. Our results indicate that dispersal is the key to understanding short-term processes such as prey survival in predator-prey metacommunities. Further work is needed to determine how dispersal rates influence persistence of communities in multigenerational studies. © The Author(s) 2017. Published by Oxford University Press on behalf of Entomological Society of America.

Developments of BBG theory

International Nuclear Information System (INIS)

Koehler, H.S.

1979-01-01

A short review of the early developments due largely to K. A Brueckner is given. Special emphasis is given to insertions in hole and particle lines, dispersion-effects and healings, and how the quantitative effects of these are related to the nature of the force. The importance of higher-order insertions in hole and particle lines and its relation to the force is also emphasized. This is important in a quantitative comparison of BBG theory with variational theory. The inceased healing-distance due to the tensor force is also pointed out. This gives convergence problems. Experiment may leave room for a nuclear force with weaker tensor force than mostly used. (Auth.)

Calculations of the mean regional dispersion of a radioactive gas emitted from a continuous source

International Nuclear Information System (INIS)

Persson, C.

1974-10-01

The mean dispersion of a radioactive gas over distances of the order of 1000 kilometers is estimated with the aid of a statistical treatment of computed geostrophic trajectories and simplified vertical diffusion calculations based on the eddy diffusivity theory. (author)

Intramolecular BSSE and dispersion affect the structure of a dipeptide conformer

Science.gov (United States)

Hameed, Rabia; Khan, Afsar; van Mourik, Tanja

2018-05-01

B3LYP and MP2 calculations with the commonly-used 6-31+G(d) basis set predict qualitatively different structures for the Tyr-Gly conformer book1, which is the most stable conformer identified in a previous study. The structures differ mainly in the ψtyr Ramachandran angle (138° in the B3LYP structure and 120° in the MP2 structure). The causes for the discrepant structures are attributed to missing dispersion in the B3LYP calculations and large intramolecular BSSE in the MP2 calculations. The correct ψtyr value is estimated to be 130°. The MP2/6-31+G(d) profile identified an additional conformer, not present on the B3LYP surface, with a ψtyr value of 96° and a more folded structure. This minimum is, however, likely an artefact of large intramolecular BSSE values. We recommend the use of basis sets of at least quadruple-zeta quality in density functional theory (DFT), DFTaugmented with an empirical dispersion term (DFT-D) and second-order Møller-Plesset perturbation theory (MP2 ) calculations in cases where intramolecular BSSE is expected to be large.

Quantum theory of noncommutative fields

International Nuclear Information System (INIS)

Carmona, J.M.; Cortes, J.L.; Gamboa, J.; Mendez, F.

2003-01-01

Generalizing the noncommutative harmonic oscillator construction, we propose a new extension of quantum field theory based on the concept of 'noncommutative fields'. Our description permits to break the usual particle-antiparticle degeneracy at the dispersion relation level and introduces naturally an ultraviolet and an infrared cutoff. Phenomenological bounds for these new energy scales are given. (author)

Black hole radiation with modified dispersion relation in tunneling paradigm: free-fall frame

Energy Technology Data Exchange (ETDEWEB)

Wang, Peng; Yang, Haitang; Ying, Shuxuan [Sichuan University, Center for Theoretical Physics, College of Physical Science and Technology, Chengdu (China)

2016-01-15

Due to the exponential high gravitational red shift near the event horizon of a black hole, it might appear that the Hawking radiation would be highly sensitive to some unknown high energy physics. To study the effects of any unknown physics at the Planck scale on the Hawking radiation, the dispersive field theory models have been proposed, which are variations of Unruh's sonic black hole analogy. In this paper, we use the Hamilton-Jacobi method to investigate the dispersive field theory models. The preferred frame is the free-fall frame of the black hole. The dispersion relation adopted agrees with the relativistic one at low energy but is modified near the Planck mass m{sub p}. The corrections to the Hawking temperature are calculated for massive and charged particles to O(m{sub p}{sup -2}) and neutral and massless particles with λ = 0 to all orders. The Hawking temperature of radiation agrees with the standard one at the leading order. After the spectrum of radiation near the horizon is obtained, we use the brick wall model to compute the thermal entropy of a massless scalar field near the horizon of a 4D spherically symmetric black hole and a 2D one. Finally, the luminosity of a Schwarzschild black hole is calculated by using the geometric optics approximation. (orig.)

Accurate nonlocal theory for cascaded quadratic soliton compression

DEFF Research Database (Denmark)

Bache, Morten; Bang, Ole; Moses, Jeffrey

2007-01-01

We study soliton compression in bulk quadratic nonlinear materials at 800 nm, where group-velocity mismatch dominates. We develop a nonlocal theory showing that efficient compression depends strongly on characteristic nonlocal time scales related to pulse dispersion....

EXPERIMENTAL DETERMINATION OF WHISTLER WAVE DISPERSION RELATION IN THE SOLAR WIND

Energy Technology Data Exchange (ETDEWEB)

Stansby, D.; Horbury, T. S.; Chen, C. H. K.; Matteini, L., E-mail: david.stansby14@imperial.ac.uk [Department of Physics, Imperial College London, London SW7 2AZ (United Kingdom)

2016-09-20

The origins and properties of large-amplitude whistler wavepackets in the solar wind are still unclear. In this Letter, we utilize single spacecraft electric and magnetic field waveform measurements from the ARTEMIS mission to calculate the plasma frame frequency and wavevector of individual wavepackets over multiple intervals. This allows direct comparison of experimental measurements with theoretical dispersion relations to identify the observed waves as whistler waves. The whistlers are right-hand circularly polarized, travel anti-sunward, and are aligned with the background magnetic field. Their dispersion is strongly affected by the local electron parallel beta in agreement with linear theory. The properties measured are consistent with the electron heat flux instability acting in the solar wind to generate these waves.

Silicate Dispersion and Mechanical Reinforcement in Polysiloxane/Layered Silicate Nanocomposites

KAUST Repository

Schmidt, Daniel F.

2010-01-12

We report the first in-depth comparison of the mechanical properties and equilibrium solvent uptake of a range of polysiloxane nanocomposites based on treated and untreated montmorillonite and fumed silica nanofillers. We demonstrate the ability of equilibrium solvent uptake data (and, thus, overall physical and chemical cross-link density) to serve as a proxy for modulus (combining rubber elasticity and Flory-Rehner theory), hardness (via the theory of Boussinesq), and elongation at break, despite the nonideal nature of these networks. In contrast, we find that tensile and tear strength are not well-correlated with solvent uptake. Interfacial strength seems to dominate equilibrium solvent uptake and the mechanical properties it predicts. In the montmorillonite systems in particular, this results in the surprising consequence that equilibrium solvent uptake and mechanical properties are independent of dispersion state. We conclude that edge interactions play a more significant role than degree of exfoliation, a result unique in the field of polymer nanocomposites. This demonstrates that even a combination of polymer/nanofiller compatibility and thermodynamically stable nanofiller dispersion levels may not give rise to reinforcement. These findings provide an important caveat when attempting to connect structure and properties in polymer nanocomposites, and useful guidance in the design of optimized polymer/layered silicate nanocomposites in particular. © 2009 American Chemical Society.

Where does cosmological perturbation theory break down?

International Nuclear Information System (INIS)

Armendariz-Picon, Cristian; Fontanini, Michele; Penco, Riccardo; Trodden, Mark

2009-01-01

It is often assumed that initial conditions for the evolution of a cosmological mode should be set at the time its physical wavelength reaches a cut-off of the order of the Planck length. Beyond that scale, trans-Planckian corrections to the dispersion relation are supposed to become dominant, leading to the breakdown of cosmological perturbation theory. In this paper, we apply the effective field theory approach to the coupled metric-inflaton system in order to calculate the corrections to the power spectrum of scalar and tensor perturbations induced by higher-dimension operators at short wavelengths. These corrections can be interpreted as modifications of the dispersion relation, and thus open a window to probe the validity of cosmological perturbation theory. Both for scalars and tensors, the modifications become important when the Hubble parameter is of the order of the Planck mass, or when the physical wave number of a cosmological perturbation mode approaches the square of the Planck mass divided by the Hubble constant. Thus, the cut-off length at which such a breakdown occurs is finite, but much smaller than the Planck length.

Dispersion relation of Raman FEL with helical Wiggler and ion channel

International Nuclear Information System (INIS)

Hosseinalinezhad, M.; Bahmani, M.; Hasanbeigi, A.; Salehkoutahi, M.

2012-01-01

In this paper the theory of free electron laser with helical wiggler and ion channel guiding has been presented. The equations of motion for an electron have been analyzed. A formula for the dispersion relation is then derived in the low-gain-per-pass limit. The results of a numerical study of the growth rate enhancement due to the ion channel are presented and discussed.

Theoretical Aspects of Phonon Dispersion Curves for Metals; Aspects Theoriques des Courbes de Dispersion des Phonons pour les Metaux; Teoreticheskie aspekty fononnykh dispersionnykh krivykh dlya metallov; Aspectos Teoricos de las Curvas de Dispersion Fononica en Metales

Energy Technology Data Exchange (ETDEWEB)

Cochran, W. [Department of Natural Philosophy, University of Edinburgh, Scotland (United Kingdom)

1965-04-15

Reasonably complete knowledge of the phonon dispersion curves for at least a dozen metallic elements and intermetallic compounds has now been obtained from neutron inelastic scattering experiments. The results have one feature in common: when analysed in terms of interatomic force constants they reveal the presence of comparatively long-range forces extending over several atomic spacings. The results for lead are particularly interesting; it did not prove possible to fit them by a force-constant model, but the dispersion curves for wave vectors in symmetry directions when analysed in terms of force constants between planes of atoms showed an oscillatory interatomic potential extending over distances of more than 20A. This review is concerned with recent theoretical work which has a bearing on the calculation of phonon dispersion curves for metals and the explanation of the long range of the interatomic potential. The best hope at present for a general treatment of atomic interaction in metals appears to lie in the ''method of neutral pseudo-atoms'', (a description recently coined by Ziman). This approximate theory is outlined and its relevance to Kohn anomalies in phonon dispersion curves is discussed. Experimental data for sodium is consistent with the theory, and the interatomic potential in sodium varies periodically in a distance {pi}/k{sub F}, where fik{sub F} is the Fermi momentum, as has already been demonstrated by Koenig in a different way. More exact calculations have been made for sodium by Toya and by Sham. The relationship between the different methods and other work of a more general character such as that of Harrison are discussed. (author) [French] A la suite d'experiences de dispersion inelastique des neutrons, on a maintenant une connaissance assez complete des courbes de dispersion des phonons pour une douzaine de metaux et de composes intermetalliques au moins. Les resultats presentent le caractere commun suivant: si on les analyse en fonction

Ultrasonic absorption and velocity dispersion of binary mixture liquid crystal MBBA/EBBA

International Nuclear Information System (INIS)

Choi, K.

1979-01-01

The effect of phase transitions and the partial magnetic alignment for liquid crystal molecules on the ultrasonic absorption and velocity dispersion has been investigated. The binary mixture of Shiff base liquid crystals MBBA/EBBA (55:45 mole %) showed anomalous ultrasonic absorption and velocity dispersion at eutectic (Tsub(m) = -20 0 C) and clearing point (Tsub(c) = 50 0 C) at the frequency range of 5 MHz, 10MHz, 15MHz and 30 MHz. The experimental data were analyzed in terms of relaxation time and Fixman theory. The anisotropy of the propagation velocity due to the magnetic alignment was about 0.9% (the deviation between velocities propagating parallel and perpendicular to the applied field). (author)

Generalized Effective Medium Theory for Particulate Nanocomposite Materials

Directory of Open Access Journals (Sweden)

Muhammad Usama Siddiqui

2016-08-01

Full Text Available The thermal conductivity of particulate nanocomposites is strongly dependent on the size, shape, orientation and dispersion uniformity of the inclusions. To correctly estimate the effective thermal conductivity of the nanocomposite, all these factors should be included in the prediction model. In this paper, the formulation of a generalized effective medium theory for the determination of the effective thermal conductivity of particulate nanocomposites with multiple inclusions is presented. The formulated methodology takes into account all the factors mentioned above and can be used to model nanocomposites with multiple inclusions that are randomly oriented or aligned in a particular direction. The effect of inclusion dispersion non-uniformity is modeled using a two-scale approach. The applications of the formulated effective medium theory are demonstrated using previously published experimental and numerical results for several particulate nanocomposites.

Dispersion relation for long-wave neutrons and the possibility of its precise experimental verification

International Nuclear Information System (INIS)

Frank, A.I.; Nosov, V.G.

1995-01-01

Modern theoretical concepts concerning the dispersion relation for slow neutrons in matter are considered. The generally accepted optical-potential model is apparently not quite accurate and should be supplemented with some small corrections in the energy range attainable in experiments. For ultracold neutrons, these corrections are related to the proximity of the applicability boundary of the theory; for cold neutrons, these corrections are due to correlations in the positions of scatters. The accuracy of existing experiments is insufficient for confirmation or refutation these conclusions. A precision experiment is proposed to verify the dispersion relation for long-wave neutrons. 30 refs., 3 figs

Fractal and digital image processing to determine the degree of dispersion of carbon nanotubes

International Nuclear Information System (INIS)

Liang, Xiao-ning; Li, Wei

2016-01-01

The degree of dispersion is an important parameter to quantitatively study properties of carbon nanotube composites. Among the many methods for studying dispersion, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy are the most commonly used, intuitive, and convincing methods. However, they have the disadvantage of not being quantitative. To overcome this disadvantage, the fractal theory and digital image processing method can be used to provide a quantitative analysis of the morphology and properties of carbon nanotube composites. In this paper, the dispersion degree of carbon nanotubes was investigated using two fractal methods, namely, the box-counting method and the differential box-counting method. On the basis of the results, we propose a new method for the quantitative characterization of the degree of dispersion of carbon nanotubes. This hierarchical grid method can be used as a supplementary method, and can be combined with the fractal calculation method. Thus, the accuracy and effectiveness of the quantitative characterization of the dispersion degree of carbon nanotubes can be improved. (The outer diameter of the carbon nanotubes is about 50 nm; the length of the carbon nanotubes is 10–20 μm.)

Fractal and digital image processing to determine the degree of dispersion of carbon nanotubes

Energy Technology Data Exchange (ETDEWEB)

Liang, Xiao-ning, E-mail: xnliang0506@163.com; Li, Wei, E-mail: 1099006@mail.dhu.edu.cn, E-mail: liwei@dhu.edu.cn, E-mail: waiwentougao@outlook.com [Donghua University, College of Textiles (China)

2016-05-15

The degree of dispersion is an important parameter to quantitatively study properties of carbon nanotube composites. Among the many methods for studying dispersion, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy are the most commonly used, intuitive, and convincing methods. However, they have the disadvantage of not being quantitative. To overcome this disadvantage, the fractal theory and digital image processing method can be used to provide a quantitative analysis of the morphology and properties of carbon nanotube composites. In this paper, the dispersion degree of carbon nanotubes was investigated using two fractal methods, namely, the box-counting method and the differential box-counting method. On the basis of the results, we propose a new method for the quantitative characterization of the degree of dispersion of carbon nanotubes. This hierarchical grid method can be used as a supplementary method, and can be combined with the fractal calculation method. Thus, the accuracy and effectiveness of the quantitative characterization of the dispersion degree of carbon nanotubes can be improved. (The outer diameter of the carbon nanotubes is about 50 nm; the length of the carbon nanotubes is 10–20 μm.)

Basic scattering theory

International Nuclear Information System (INIS)

Queen, N.M.

1978-01-01

This series of lectures on basic scattering theory were given as part of a course for postgraduate high energy physicists and were designed to acquaint the student with some of the basic language and formalism used for the phenomenological description of nuclear reactions and decay processes used for the study of elementary particle interactions. Well established and model independent aspects of scattering theory, which are the basis of S-matrix theory, are considered. The subject is considered under the following headings; the S-matrix, cross sections and decay rates, phase space, relativistic kinematics, the Mandelstam variables, the flux factor, two-body phase space, Dalitz plots, other kinematic plots, two-particle reactions, unitarity, the partial-wave expansion, resonances (single-channel case), multi-channel resonances, analyticity and crossing, dispersion relations, the one-particle exchange model, the density matrix, mathematical properties of the density matrix, the density matrix in scattering processes, the density matrix in decay processes, and the helicity formalism. Some exercises for the students are included. (U.K.)

Importance of dispersion and electron correlation in ab initio protein folding.

Science.gov (United States)

He, Xiao; Fusti-Molnar, Laszlo; Cui, Guanglei; Merz, Kenneth M

2009-04-16

Dispersion is well-known to be important in biological systems, but the effect of electron correlation in such systems remains unclear. In order to assess the relationship between the structure of a protein and its electron correlation energy, we employed both full system Hartree-Fock (HF) and second-order Møller-Plesset perturbation (MP2) calculations in conjunction with the Polarizable Continuum Model (PCM) on the native structures of two proteins and their corresponding computer-generated decoy sets. Because of the expense of the MP2 calculation, we have utilized the fragment molecular orbital method (FMO) in this study. We show that the sum of the Hartree-Fock (HF) energy and force field (LJ6)-derived dispersion energy (HF + LJ6) is well correlated with the energies obtained using second-order Møller-Plesset perturbation (MP2) theory. In one of the two examples studied, the correlation energy as well as the empirical dispersive energy term was able to discriminate between native and decoy structures. On the other hand, for the second protein we studied, neither the correlation energy nor dispersion energy showed discrimination capabilities; however, the ab initio MP2 energy and the HF+LJ6 both ranked the native structure correctly. Furthermore, when we randomly scrambled the Lennard-Jones parameters, the correlation between the MP2 energy and the sum of the HF energy and dispersive energy (HF+LJ6) significantly drops, which indicates that the choice of Lennard-Jones parameters is important.

$K^{\\pm}n$ forward dispersion relations and the KN$\\Sigma$ coupling constant

CERN Document Server

Baillon, Paul; Ferro-Luzzi, M; Jenni, Peter; Perreau, J M; Tripp, R D; Ypsilantis, Thomas; Déclais, Y; Séguinot, Jacques

1976-01-01

Recent measurements of the K/sup -/n forward scattering amplitude at 1.2, 1.4, 2.6 GeV/c are used in a once-subtracted dispersion relation to determine the value of the KN Sigma coupling constant. The result is g/sub Sigma //sup 2/=1.9+or-3.2, in agreement with the prediction of the SU(3) theory.

Latitudinal phytoplankton distribution and the neutral theory of biodiversity

KAUST Repository

Chust, Guillem; Irigoien, Xabier; Chave, Jé rô me; Harris, Roger P.

2012-01-01

Recent studies have suggested that global diatom distributions are not limited by dispersal, in the case of both extant species and fossil species, but rather that environmental filtering explains their spatial patterns. Hubbell's neutral theory

Stereolithographic processing of ceramics: Photon diffusion in colloidal dispersion

Science.gov (United States)

Garg, Rajeev

The technique of ceramic stereolithography (CSL) has been developed for fabricating near net shape ceramic objects. In stereolithography, the three-dimensional computer design file of the object is sliced into thin layers. Each layer is physically fabricated by photocuring the surface of a liquid photo-polymerizable resin bath by raster scanning an ultra-violet laser across the surface of the resin. In CSL, the liquid resin is a high concentration colloidal dispersion in a solution of ultraviolet curable polymers. The ceramic green body fabricated by ceramic stereolithography technique is subjected to the post processing steps of drying, binder burnout and sintering to form a dense ceramic object. An aqueous alumina dispersion in photocuring polymers with particle volume fraction greater than 0.5 was formulated for CSL process. Low molecular weight solution polymers were found to be best suited for formulating ceramic resins due to their inherently low viscosity and favorable interactions with the ceramic dispersant. A hydroxyapatite ceramic resin was also developed for the use in the CSL technique. A model is developed to describe the photocuring process in concentrated ceramic dispersion. The curing profile in ceramic dispersion is governed by multiple scattering from the ceramic particles and absorption by the photocuring polymers. Diffusion theory of light transport is used to model the multiple scattering and absorption phenomena. It is found that diffusive transport adequately describes the phenomena of laser pulse propagation in highly concentrated colloidal dispersions. A model was developed to describe the absorption in highly concentrated ceramic dispersion. Various complex-shaped monolithic alumina and hydroxyapatite objects were fabricated by CSL and shown to possess uniform microstructure. The mechanical properties and sintering behavior of the parts fabricated by CSL are shown to be comparable to those fabricated by other ceramic processing technique

Dopant activation mechanism of Bi wire-δ-doping into Si crystal, investigated with wavelength dispersive fluorescence x-ray absorption fine structure and density functional theory.

Science.gov (United States)

Murata, Koichi; Kirkham, Christopher; Shimomura, Masaru; Nitta, Kiyofumi; Uruga, Tomoya; Terada, Yasuko; Nittoh, Koh-Ichi; Bowler, David R; Miki, Kazushi

2017-04-20

We successfully characterized the local structures of Bi atoms in a wire-δ-doped layer (1/8 ML) in a Si crystal, using wavelength dispersive fluorescence x-ray absorption fine structure at the beamline BL37XU, in SPring-8, with the help of density functional theory calculations. It was found that the burial of Bi nanolines on the Si(0 0 1) surface, via growth of Si capping layer at 400 °C by molecular beam epitaxy, reduced the Bi-Si bond length from [Formula: see text] to [Formula: see text] Å. We infer that following epitaxial growth the Bi-Bi dimers of the nanoline are broken, and the Bi atoms are located at substitutional sites within the Si crystal, leading to the shorter Bi-Si bond lengths.

Dispersal and individual quality in a long lived species

Science.gov (United States)

Cam, E.; Monnat, J.-Y.; Royle, J. Andrew

2004-01-01

The idea of differences in individual quality has been put forward in numerous long-term studies in long-lived species to explain differences in lifetime production among individuals. Despite the important role of individual heterogeneity in vital rates in demography, population dynamics and life history theory, the idea of 'individual quality' is elusive. It is sometimes assumed to be a static or dynamic individual characteristic. When considered as a dynamic trait, it is sometimes assumed to vary deterministically or stochastically, or to be confounded with the characteristics of the habitat. We addressed heterogeneity in reproductive performance among individuals established in higher-quality habitat in a long-lived seabird species. We used approaches to statistical inference based on individual random effects permitting quantification of heterogeneity in populations and assessment of individual variation from the population mean. We found evidence of heterogeneity in breeding probability, not success probability. We assessed the influence of dispersal on individual reproductive potential. Dispersal is likely to be destabilizing in species with high site and mate fidelity. We detected heterogeneity after dispersal, not before. Individuals may perform well regardless of quality before destabilization, including those that recruited in higher-quality habitat by chance, but only higher-quality individuals may be able to overcome the consequences of dispersal. Importantly, results differed when accounting for individual heterogeneity (an increase in mean breeding probability when individuals dispersed), or not (a decrease in mean breeding probability). In the latter case, the decrease in mean breeding probability may result from a substantial decrease in breeding probability in a few individuals and a slight increase in others. In other words, the pattern observed at the population mean level may not reflect what happens in the majority of individuals.

Calculation of the Green functions by the coupling constant dispersion relations

International Nuclear Information System (INIS)

Bogomalny, E.B.

1977-01-01

The discontinuities of the Green functions on the cut in the complex plane of the coupling constant are calculated by the steepest descent method. The saddle points are given by the solutions of the classical field equations at those values of the coupling constant for which the classical theory has no ground state. The Green functions at the physical values of the coupling constant are determined by dispersion relations. (Auth.)

Nonperturbative studies of quantum field theories on noncommutative spaces

International Nuclear Information System (INIS)

Volkholz, J.

2007-01-01

This work deals with three quantum field theories on spaces with noncommuting position operators. Noncommutative models occur in the study of string theories and quantum gravity. They usually elude treatment beyond the perturbative level. Due to the technique of dimensional reduction, however, we are able to investigate these theories nonperturbatively. This entails translating the action functionals into a matrix language, which is suitable for numerical simulations. First we explore the λφ 4 model on a noncommutative plane. We investigate the continuum limit at fixed noncommutativity, which is known as the double scaling limit. Here we focus especially on the fate of the striped phase, a phase peculiar to the noncommutative version of the regularized λφ 4 model. We find no evidence for its existence in the double scaling limit. Next we examine the U(1) gauge theory on a four-dimensional spacetime, where two spatial directions are noncommutative. We examine the phase structure and find a new phase with a spontaneously broken translation symmetry. In addition we demonstrate the existence of a finite double scaling limit which confirms the renormalizability of the theory. Furthermore we investigate the dispersion relation of the photon. In the weak coupling phase our results are consistent with an infrared instability predicted by perturbation theory. If the translational symmetry is broken, however, we find a dispersion relation corresponding to a massless particle. Finally, we investigate a supersymmetric theory on the fuzzy sphere, which features scalar neutral bosons and Majorana fermions. The supersymmetry is exact in the limit of infinitely large matrices. We investigate the phase structure of the model and find three distinct phases. Summarizing, we study noncommutative field theories beyond perturbation theory. Moreover, we simulate a supersymmetric theory on the fuzzy sphere, which might provide an alternative to attempted lattice formulations. (orig.)

Nonperturbative studies of quantum field theories on noncommutative spaces

Energy Technology Data Exchange (ETDEWEB)

Volkholz, J.

2007-11-16

This work deals with three quantum field theories on spaces with noncommuting position operators. Noncommutative models occur in the study of string theories and quantum gravity. They usually elude treatment beyond the perturbative level. Due to the technique of dimensional reduction, however, we are able to investigate these theories nonperturbatively. This entails translating the action functionals into a matrix language, which is suitable for numerical simulations. First we explore the {lambda}{phi}{sup 4} model on a noncommutative plane. We investigate the continuum limit at fixed noncommutativity, which is known as the double scaling limit. Here we focus especially on the fate of the striped phase, a phase peculiar to the noncommutative version of the regularized {lambda}{phi}{sup 4} model. We find no evidence for its existence in the double scaling limit. Next we examine the U(1) gauge theory on a four-dimensional spacetime, where two spatial directions are noncommutative. We examine the phase structure and find a new phase with a spontaneously broken translation symmetry. In addition we demonstrate the existence of a finite double scaling limit which confirms the renormalizability of the theory. Furthermore we investigate the dispersion relation of the photon. In the weak coupling phase our results are consistent with an infrared instability predicted by perturbation theory. If the translational symmetry is broken, however, we find a dispersion relation corresponding to a massless particle. Finally, we investigate a supersymmetric theory on the fuzzy sphere, which features scalar neutral bosons and Majorana fermions. The supersymmetry is exact in the limit of infinitely large matrices. We investigate the phase structure of the model and find three distinct phases. Summarizing, we study noncommutative field theories beyond perturbation theory. Moreover, we simulate a supersymmetric theory on the fuzzy sphere, which might provide an alternative to attempted

Cefuroxime axetil solid dispersions prepared using solution enhanced dispersion by supercritical fluids.

Science.gov (United States)

Jun, Seoung Wook; Kim, Min-Soo; Jo, Guk Hyun; Lee, Sibeum; Woo, Jong Soo; Park, Jeong-Sook; Hwang, Sung-Joo

2005-12-01

Cefuroxime axetil (CA) solid dispersions with HPMC 2910/PVP K-30 were prepared using solution enhanced dispersion by supercritical fluids (SEDS) in an effort to increase the dissolution rate of poorly water-soluble drugs. Their physicochemical properties in solid state were characterized by differential scanning calorimeter (DSC), powder X-ray diffraction (PXRD), Fourier transform infrared spectrometry (FT-IR) and scanning electron microscopy. No endothermic and characteristic diffraction peaks corresponding to CA were observed for the solid dispersions in DSC and PXRD. FTIR analysis demonstrated the presence of intermolecular hydrogen bonds between CA and HPMC 2910/PVP K-30 in solid dispersions, resulting in the formation of amorphous or non-crystalline CA. Dissolution studies indicated that the dissolution rates were remarkably increased in solid dispersions compared with those in the physical mixture and drug alone. In conclusion, an amorphous or non-crystalline CA solid dispersion prepared using SEDS could be very useful for the formulation of solid dosage forms.

IN-SYNC. II. VIRIAL STARS FROM SUBVIRIAL CORES—THE VELOCITY DISPERSION OF EMBEDDED PRE-MAIN-SEQUENCE STARS IN NGC 1333

International Nuclear Information System (INIS)

Foster, Jonathan B.; Cottaar, Michiel; Meyer, Michael R.; Covey, Kevin R.; Arce, Héctor G.; Nidever, David L.; Stassun, Keivan G.; Tan, Jonathan C.; Da Rio, Nicola; Chojnowski, S. Drew; Majewski, Steven R.; Skrutskie, Michael; Wilson, John C.; Flaherty, Kevin M.; Rebull, Luisa; Frinchaboy, Peter M.; Zasowski, Gail

2015-01-01

The initial velocity dispersion of newborn stars is a major unconstrained aspect of star formation theory. Using near-infrared spectra obtained with the APOGEE spectrograph, we show that the velocity dispersion of young (1-2 Myr) stars in NGC 1333 is 0.92 ± 0.12 km s –1 after correcting for measurement uncertainties and the effect of binaries. This velocity dispersion is consistent with the virial velocity of the region and the diffuse gas velocity dispersion, but significantly larger than the velocity dispersion of the dense, star-forming cores, which have a subvirial velocity dispersion of 0.5 km s –1 . Since the NGC 1333 cluster is dynamically young and deeply embedded, this measurement provides a strong constraint on the initial velocity dispersion of newly formed stars. We propose that the difference in velocity dispersion between stars and dense cores may be due to the influence of a 70 μG magnetic field acting on the dense cores or be the signature of a cluster with initial substructure undergoing global collapse

Application of the Lifshitz Theory to Poor Conductors

International Nuclear Information System (INIS)

Svetovoy, Vitaly B.

2008-01-01

The Lifshitz formula for dispersive forces is generalized to the materials, which cannot be described with the local dielectric response. The principal nonlocality of poor conductors is related to the finite screening length of the penetrating field and collisional relaxation; at low temperatures the role of collisions plays the Landau damping. Spatial dispersion makes the theory self-consistent. Our predictions are compared with the recent experiment. It is demonstrated that at low temperatures Casimir-Lifshitz entropy disappears as T in the case of degenerate plasma and as T 2 for the nondegenerate one

The scalar and electromagnetic form factors of the nucleon in dispersively improved Chiral EFT

Energy Technology Data Exchange (ETDEWEB)

Alarcon, Jose Manuel [Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)

2018-04-01

We present a method for calculating the nucleon form factors of G-parity-even operators. This method combines chiral effective field theory (χEFT) and dispersion theory. Through unitarity we factorize the imaginary part of the form factors into a perturbative part, calculable with χEFT, and a non-perturbative part, obtained through other methods. We consider the scalar and electromagnetic (EM) form factors of the nucleon. The results show an important improvement compared to standard chiral calculations, and can be used in analysis of the low-energy properties of the nucleon.

Testing the Neutral Theory of Biodiversity with Human Microbiome Datasets.

Science.gov (United States)

Li, Lianwei; Ma, Zhanshan Sam

2016-08-16

The human microbiome project (HMP) has made it possible to test important ecological theories for arguably the most important ecosystem to human health-the human microbiome. Existing limited number of studies have reported conflicting evidence in the case of the neutral theory; the present study aims to comprehensively test the neutral theory with extensive HMP datasets covering all five major body sites inhabited by the human microbiome. Utilizing 7437 datasets of bacterial community samples, we discovered that only 49 communities (less than 1%) satisfied the neutral theory, and concluded that human microbial communities are not neutral in general. The 49 positive cases, although only a tiny minority, do demonstrate the existence of neutral processes. We realize that the traditional doctrine of microbial biogeography "Everything is everywhere, but the environment selects" first proposed by Baas-Becking resolves the apparent contradiction. The first part of Baas-Becking doctrine states that microbes are not dispersal-limited and therefore are neutral prone, and the second part reiterates that the freely dispersed microbes must endure selection by the environment. Therefore, in most cases, it is the host environment that ultimately shapes the community assembly and tip the human microbiome to niche regime.

Seed dispersal in fens

NARCIS (Netherlands)

Middleton, Beth; van Diggelen, Rudy; Jensen, Kai

Question: How does seed dispersal reduce fen isolation and contribute to biodiversity? Location: European and North American fens. Methods: This paper reviews the literature on seed dispersal to fens. Results: Landscape fragmentation may reduce dispersal opportunities thereby isolating fens and

Analysis of environmental dispersion in a wetland flow under the effect of wind: Extended solution

Science.gov (United States)

Wang, Huilin; Huai, Wenxin

2018-02-01

The accurate analysis of the contaminant transport process in wetland flows is essential for environmental assessment. However, dispersivity assessment becomes complicated when the wind strength and direction are taken into consideration. Prior studies illustrating the wind effect on environmental dispersion in wetland flows simply focused on the mean longitudinal concentration distribution. Moreover, the results obtained by these analyses are not accurate when done on a smaller scale, namely, the initial stage of the contaminant transport process. By combining the concentration moments method (the Aris' method) and Gill's expansion theory, the previous researches on environmental dispersion in wetland flows with effect of wind have been extended. By adopting up to 4th-order moments, the wind effect-as illustrated by dimensionless parameters Er (wind force) and ω (wind direction)-on kurtosis and skewness is discussed, the up to 4th-order vertical concentration distribution is obtained, and the two-dimensional concentration distribution is illustrated. This work demonstrates that wind intensity and direction can significantly affect the contaminant dispersion. Moreover, the study presents a more accurate analytical solution of environmental dispersion in wetland flows under various wind conditions.

Partitioning of seed dispersal services between birds and bats in a fragment of the Brazilian Atlantic Forest

Directory of Open Access Journals (Sweden)

Raissa Sarmento

2014-06-01

Full Text Available Community-level network studies suggest that seed dispersal networks may share some universal properties with other complex systems. However, most of the datasets used so far in those studies have been strongly biased towards temperate birds, including not only dispersers, but also seed predators. Recent evidence from multi-taxon networks suggests that seed dispersal networks are not all alike and may be more complex than previously thought. Here, we used network theory to evaluate seed dispersal in a strongly impacted Atlantic Forest fragment in northeastern Brazil, where bats and birds are the only extant dispersers. We hypothesized that the seed dispersal network should be more modular then nested, and that the dispersers should segregate their services according to dispersal syndromes. Furthermore, we predicted that bat and bird species that are more specialized in frugivory would be more important for maintaining the network structure. The mixed network contained 56 plant species, 12 bat species, and eight bird species, and its structure was more modular (M = 0.58 then nested (NODF = 0.21 compared with another multi-taxon network and 21 single-taxon networks (with either bats or birds. All dispersed fruits had seeds smaller than 9 mm. Bats dispersed mainly green fruits, whereas birds dispersed fruits of various colors. The network contained eight modules: five with birds only, two with bats only, and one mixed. Most dispersers were peripheral, and only specialized frugivores acted as hubs or connectors. Our results strongly support recent studies, suggesting that seed dispersal networks are complex mosaics, where different taxa form separate modules with different properties, which in turn play complementary roles in the maintenance of the associated ecosystem functions and services.

Development of a theory of the spectral reflectance of minerals, part 3

Science.gov (United States)

Aronson, J. R.; Emslie, A. G.; Roach, L. H.; Smith, E. M.; Vonthuena, P. C.

1972-01-01

Significant refinements were made in the theory of the diffuse reflectance of particulate media. The theory predicts the opposite trends of reflectance with particle size in regions of the spectrum in which the particles are semi-transparent and those in which they are opaque. Enhanced absorption caused by wave-optical effects of small surface asperities and edges was used to improve the theory. The same mechanism remedies the theory to account for the data in spectral regions of anomalous dispersion.

String theory and water waves

International Nuclear Information System (INIS)

Iyer, Ramakrishnan; Johnson, Clifford V; Pennington, Jeffrey S

2011-01-01

We uncover a remarkable role that an infinite hierarchy of nonlinear differential equations plays in organizing and connecting certain c-hat <1 string theories non-perturbatively. We are able to embed the type 0A and 0B (A, A) minimal string theories into this single framework. The string theories arise as special limits of a rich system of equations underpinned by an integrable system known as the dispersive water wave hierarchy. We observe that there are several other string-like limits of the system, and conjecture that some of them are type IIA and IIB (A, D) minimal string backgrounds. We explain how these and several string-like special points arise and are connected. In some cases, the framework endows the theories with a non-perturbative definition for the first time. Notably, we discover that the Painleve IV equation plays a key role in organizing the string theory physics, joining its siblings, Painleve I and II, whose roles have previously been identified in this minimal string context.

Chemical countermeasures: Dispersants overview of dispersant use (including application) and research issues

International Nuclear Information System (INIS)

Butler, J.N.

1992-01-01

I will attempt in twenty minutes to summarize the state of research on oil spill dispersants as I perceive it. The expertise I bring to this task includes 20 years of experience with the fate and effects of petroleum in the marine environment, including participation in the 1973 and 1981 NRC studies and three years as chairman of the NRC committee on oil spill dispersants. I More recently I served on a committee of the International Maritime Organization which reviewed the open-quotes Impact of oil and related chemicals and wastes on the marine environment.close quotes That report will be published this year. However, my statements in this paper are not made as a representative of either NRC or IMO. They are my own interpretation of scientific literature cited in the above reviews. Dispersants are chemical formulations, which include surface active agents, designed to decrease the interfacial tension between oil and water. Because the first attempts to disperse oil on a large scale, at the Torrey Canyon spill of 1967, used highly toxic degreasing agents, dispersants have an undeserved reputation for toxicity. In fact, for twenty years dispersant formulations have been developed with an emphasis on reducing their toxicity to marine life. The dispersal of oil in water has been documented in the laboratory by dozens of papers (see references in NRC 1989, pp 70-79), and in the field by dozens of studies (NRC 1989, pp 165- 193). The toxicity of commercial dispersant formulations (NRC 1989, pp 81-123) and dispersed oil (NRC 1989, pp 123-147) has been tested on a wide variety of marine organisms ranging from algae to salmonid fishes. The NRC review has been updated by the IMO/GESAMP (1992) study, but the conclusions remain unchanged

Dispersing powders in liquids

CERN Document Server

Nelson, RD

1988-01-01

This book provides powder technologists with laboratory procedures for selecting dispersing agents and preparing stable dispersions that can then be used in particle size characterization instruments. Its broader goal is to introduce industrial chemists and engineers to the phenomena, terminology, physical principles, and chemical considerations involved in preparing and handling dispersions on a commercial scale. The book introduces novices to: - industrial problems due to improper degree of dispersion; - the nomenclature used in describing particles; - the basic physica

From the Neutral Theory to a Comprehensive and Multiscale Theory of Ecological Equivalence.

Science.gov (United States)

Munoz, François; Huneman, Philippe

2016-09-01

The neutral theory of biodiversity assumes that coexisting organisms are equally able to survive, reproduce, and disperse (ecological equivalence), but predicts that stochastic fluctuations of these abilities drive diversity dynamics. It predicts remarkably well many biodiversity patterns, although substantial evidence for the role of niche variation across organisms seems contradictory. Here, we discuss this apparent paradox by exploring the meaning and implications of ecological equivalence. We address the question whether neutral theory provides an explanation for biodiversity patterns and acknowledges causal processes. We underline that ecological equivalence, although central to neutral theory, can emerge at local and regional scales from niche-based processes through equalizing and stabilizing mechanisms. Such emerging equivalence corresponds to a weak conception of neutral theory, as opposed to the assumption of strict equivalence at the individual level in strong conception. We show that this duality is related to diverging views on hypothesis testing and modeling in ecology. In addition, the stochastic dynamics exposed in neutral theory are pervasive in ecological systems and, rather than a null hypothesis, ecological equivalence is best understood as a parsimonious baseline to address biodiversity dynamics at multiple scales.

Drawing theories apart the dispersion of Feynman diagrams in postwar physics

CERN Document Server

Kaiser, David

2005-01-01

Winner of the 2007 Pfizer Prize from the History of Science Society. Feynman diagrams have revolutionized nearly every aspect of theoretical physics since the middle of the twentieth century. Introduced by the American physicist Richard Feynman (1918-88) soon after World War II as a means of simplifying lengthy calculations in quantum electrodynamics, they soon gained adherents in many branches of the discipline. Yet as new physicists adopted the tiny line drawings, they also adapted the diagrams and introduced their own interpretations. Drawing Theories Apart traces how generations of young theorists learned to frame their research in terms of the diagrams—and how both the diagrams and their users were molded in the process.Drawing on rich archival materials, interviews, and more than five hundred scientific articles from the period, Drawing Theories Apart uses the Feynman diagrams as a means to explore the development of American postwar physics. By focusing on the ways young physicists learned new calcul...

An X-ray wave theory for heavily distorted crystals. 1

International Nuclear Information System (INIS)

Ohkawa, T.; Hashimoto, H.

1985-01-01

An X-ray diffraction theory is developed of monochromatic waves having spherical wave front, which is applicable to an interpretation of divergent X-ray diffraction images of crystals containing arbitral types of strain field. The theory is divided into two parts. In part I, Takagi's theory is expanded by introducing amplitude and phase correction functions and a new improved representation for the X-ray diffraction theory is given. In part II dispersion surfaces in heavily distorted crystals are discussed, and in the discussion the resonance shift functions are introduced. These formulations can lead to a complete understanding of the extinction phenomena. (author)

Seed dispersal in fens

Science.gov (United States)

Middleton, B.; Van Diggelen, R.; Jensen, K.

2006-01-01

Question: How does seed dispersal reduce fen isolation and contribute to biodiversity? Location: European and North American fens. Methods: This paper reviews the literature on seed dispersal to fens. Results: Landscape fragmentation may reduce dispersal opportunities thereby isolating fens and reducing genetic exchange. Species in fragmented wetlands may have lower reproductive success, which can lead to biodiversity loss. While fens may have always been relatively isolated from each other, they have become increasingly fragmented in modern times within agricultural and urban landscapes in both Europe and North America. Dispersal by water, animals and wind has been hampered by changes related to development in landscapes surrounding fens. Because the seeds of certain species are long-lived in the seed bank, frequent episodes of dispersal are not always necessary to maintain the biodiversity of fens. However, of particular concern to restoration is that some dominant species, such as the tussock sedge Carex stricta, may not disperse readily between fens. Conclusions: Knowledge of seed dispersal can be used to maintain and restore the biodiversity of fens in fragmented landscapes. Given that development has fragmented landscapes and that this situation is not likely to change, the dispersal of seeds might be enhanced by moving hay or cattle from fens to damaged sites, or by reestablishing lost hydrological connections. ?? IAVS; Opulus Press.

Non-unique factorizations algebraic, combinatorial and analytic theory

CERN Document Server

Geroldinger, Alfred

2006-01-01

From its origins in algebraic number theory, the theory of non-unique factorizations has emerged as an independent branch of algebra and number theory. Focused efforts over the past few decades have wrought a great number and variety of results. However, these remain dispersed throughout the vast literature. For the first time, Non-Unique Factorizations: Algebraic, Combinatorial, and Analytic Theory offers a look at the present state of the theory in a single, unified resource.Taking a broad look at the algebraic, combinatorial, and analytic fundamentals, this book derives factorization results and applies them in concrete arithmetical situations using appropriate transfer principles. It begins with a basic introduction that can be understood with knowledge of standard basic algebra. The authors then move to the algebraic theory of monoids, arithmetic theory of monoids, the structure of sets of lengths, additive group theory, arithmetical invariants, and the arithmetic of Krull monoids. They also provide a s...

Spurious dispersion effects at FLASH

International Nuclear Information System (INIS)

Prat, Eduard

2009-07-01

The performance of the Free-Electron Laser (FEL) process imposes stringent demands on the transverse trajectory and size of the electron beam. Since transverse dispersion changes off-energy particle trajectories and increases the effective beam size, dispersion must be controlled. This thesis treats the concept of dispersion in linacs, and analyses the impact of dispersion on the electron beam and on the FEL process. It presents generation mechanisms for spurious dispersion, quantifying its importance for FLASH (Free-electron Laser in Hamburg) and the XFEL (European X-ray Free-Electron Laser). A method for measuring and correcting dispersion and its implementation in FLASH is described. Experiments of dispersion e ects on the transverse beam quality and on the FEL performance are presented. (orig.)

Spurious dispersion effects at FLASH

Energy Technology Data Exchange (ETDEWEB)

Prat, Eduard

2009-07-15

The performance of the Free-Electron Laser (FEL) process imposes stringent demands on the transverse trajectory and size of the electron beam. Since transverse dispersion changes off-energy particle trajectories and increases the effective beam size, dispersion must be controlled. This thesis treats the concept of dispersion in linacs, and analyses the impact of dispersion on the electron beam and on the FEL process. It presents generation mechanisms for spurious dispersion, quantifying its importance for FLASH (Free-electron Laser in Hamburg) and the XFEL (European X-ray Free-Electron Laser). A method for measuring and correcting dispersion and its implementation in FLASH is described. Experiments of dispersion e ects on the transverse beam quality and on the FEL performance are presented. (orig.)

Application of sequential fragmentation/transport theory to deposits of 1723 and 1963-65 eruptions of Volcan Irazu, Costa Rica: positive dispersion case and fractal model

International Nuclear Information System (INIS)

Brenes, Jose; Alvarado, Guillermo E.

2013-01-01

The theory of Fragmentation and Sequential Transport (FST) was applied to the granulometric analyzes of the deposits from the eruptions of 1723 and 1963-65 of the Volcan Irazu. An appreciable number of cases of positive dispersion was showed, associated in the literature with aggregation processes. A new fractal dimension defined in research has shown to be the product of secondary fragmentation. The application of the new dimension is used in the analyses of the eruptions of 1723 and 1963-65. A fractal model of a volcanic activity is formulated for the first time. The Hurst coefficient and the exponent of the law of powers are incorporated. The existence of values of dissidence near zero have been indicators of an effusive process, as would be the lava pools. The results derived from the model were agreed with field observations. (author) [es

The Organizational Approach of Capability Theory: A Review Essay

OpenAIRE

Garzarelli, Giampaolo

2006-01-01

Richard Langlois, Tony Yu & Paul Robertson have assembled a collection of previously published papers that move beyond textbook production theory. This essay discusses work by Frank Knight and Hendrik Houthakker not reproduced in LYR in relation to the capability theory of economic organization. Knight identified the problem of organization as the search for and the coordination of different dispersed capabilities. Houthakker helps us to see more clearly that the benefits of specialization ar...

Metapopulation extinction risk: dispersal's duplicity.

Science.gov (United States)

Higgins, Kevin

2009-09-01

Metapopulation extinction risk is the probability that all local populations are simultaneously extinct during a fixed time frame. Dispersal may reduce a metapopulation's extinction risk by raising its average per-capita growth rate. By contrast, dispersal may raise a metapopulation's extinction risk by reducing its average population density. Which effect prevails is controlled by habitat fragmentation. Dispersal in mildly fragmented habitat reduces a metapopulation's extinction risk by raising its average per-capita growth rate without causing any appreciable drop in its average population density. By contrast, dispersal in severely fragmented habitat raises a metapopulation's extinction risk because the rise in its average per-capita growth rate is more than offset by the decline in its average population density. The metapopulation model used here shows several other interesting phenomena. Dispersal in sufficiently fragmented habitat reduces a metapopulation's extinction risk to that of a constant environment. Dispersal between habitat fragments reduces a metapopulation's extinction risk insofar as local environments are asynchronous. Grouped dispersal raises the effective habitat fragmentation level. Dispersal search barriers raise metapopulation extinction risk. Nonuniform dispersal may reduce the effective fraction of suitable habitat fragments below the extinction threshold. Nonuniform dispersal may make demographic stochasticity a more potent metapopulation extinction force than environmental stochasticity.

Sound dispersion in a spin-1 Ising system near the second-order phase transition point

International Nuclear Information System (INIS)

Erdem, Ryza; Keskin, Mustafa

2003-01-01

Sound dispersion relation is derived for a spin-1 Ising system and its behaviour near the second-order phase transition point or the critical point is analyzed. The method used is a combination of molecular field approximation and Onsager theory of irreversible thermodynamics. If we assume a linear coupling of sound wave with the order parameter fluctuations in the system, we find that the dispersion which is the relative sound velocity change with frequency behaves as ω 0 ε 0 , where ω is the sound frequency and ε the temperature distance from the critical point. In the ordered region, one also observes a frequency-dependent velocity or dispersion minimum which is shifted from the corresponding attenuation maxima. These phenomena are in good agreement with the calculations of sound velocity in other magnetic systems such as magnetic metals, magnetic insulators, and magnetic semiconductors

On the calculation of the structure of charge-stabilized colloidal dispersions using density-dependent potentials

International Nuclear Information System (INIS)

Castañeda-Priego, R; Lobaskin, V; Mixteco-Sánchez, J C; Rojas-Ochoa, L F; Linse, P

2012-01-01

The structure of charge-stabilized colloidal dispersions has been studied through a one-component model using a Yukawa potential with density-dependent parameters examined with integral equation theory and Monte Carlo simulations. Partial thermodynamic consistency was guaranteed by considering the osmotic pressure of the dispersion from the approximate mean-field renormalized jellium and Poisson-Boltzmann cell models. The colloidal structures could be accurately described by the Ornstein-Zernike equation with the Rogers-Young closure by using the osmotic pressure from the renormalized jellium model. Although we explicitly show that the correct effective pair-potential obtained from the inverse Monte Carlo method deviates from the Yukawa shape, the osmotic pressure constraint allows us to have a good description of the colloidal structure without losing information on the system thermodynamics. Our findings are corroborated by primitive model simulations of salt-free colloidal dispersions. (paper)

Wave dispersion characteristics of axially loaded magneto-electro-elastic nanobeams

Science.gov (United States)

Ebrahimi, Farzad; Barati, Mohammad Reza; Dabbagh, Ali

2016-11-01

The analysis of wave propagation behavior of a magneto-electro-elastic functionally graded (MEE-FG) nanobeam is performed in the framework of classical beam theory. To capture small-scale effects, the nonlocal elasticity theory of Eringen is applied. Furthermore, the material properties of nanobeam are assumed to vary gradually through the thickness based on power-law form. Nonlocal governing equations of MEE-FG nanobeam have been derived employing Hamilton's principle. The results of present research have been validated by comparing with those of previous investigations. An analytical solution of governing equations is utilized to obtain wave frequencies, phase velocities and escape frequencies. Effects of various parameters such as wave number, nonlocal parameter, gradient index, axial load, magnetic potential and electric voltage on wave dispersion characteristics of MEE-FG nanoscale beams are studied in detail.

Perturbation theory for plasmonic modulation and sensing

KAUST Repository

Raman, Aaswath

2011-05-25

We develop a general perturbation theory to treat small parameter changes in dispersive plasmonic nanostructures and metamaterials. We specifically apply it to dielectric refractive index and metallic plasma frequency modulation in metal-dielectric nanostructures. As a numerical demonstration, we verify the theory\\'s accuracy against direct calculations for a system of plasmonic rods in air where the metal is defined by a three-pole fit of silver\\'s dielectric function. We also discuss new optical behavior related to plasma frequency modulation in such systems. Our approach provides new physical insight for the design of plasmonic devices for biochemical sensing and optical modulation and future active metamaterial applications. © 2011 American Physical Society.

Halogen Bonding from Dispersion-Corrected Density-Functional Theory: The Role of Delocalization Error.

Science.gov (United States)

Otero-de-la-Roza, A; Johnson, Erin R; DiLabio, Gino A

2014-12-09

Halogen bonds are formed when a Lewis base interacts with a halogen atom in a different molecule, which acts as an electron acceptor. Due to its charge transfer component, halogen bonding is difficult to model using many common density-functional approximations because they spuriously overstabilize halogen-bonded dimers. It has been suggested that dispersion-corrected density functionals are inadequate to describe halogen bonding. In this work, we show that the exchange-hole dipole moment (XDM) dispersion correction coupled with functionals that minimize delocalization error (for instance, BH&HLYP, but also other half-and-half functionals) accurately model halogen-bonded interactions, with average errors similar to other noncovalent dimers with less charge-transfer effects. The performance of XDM is evaluated for three previously proposed benchmarks (XB18 and XB51 by Kozuch and Martin, and the set proposed by Bauzá et al.) spanning a range of binding energies up to ∼50 kcal/mol. The good performance of BH&HLYP-XDM is comparable to M06-2X, and extends to the "extreme" cases in the Bauzá set. This set contains anionic electron donors where charge transfer occurs even at infinite separation, as well as other charge transfer dimers belonging to the pnictogen and chalcogen bonding classes. We also show that functional delocalization error results in an overly delocalized electron density and exact-exchange hole. We propose intermolecular Bader delocalization indices as an indicator of both the donor-acceptor character of an intermolecular interaction and the delocalization error coming from the underlying functional.

Dispersion stability of thermal nanofluids

Directory of Open Access Journals (Sweden)

Fan Yu

2017-10-01

Full Text Available Thermal nanofluids, the engineered fluids with dispersed functional nanoparticles, have exhibited extraordinary thermophysical properties and added functionalities, and thus have enabled a broad range of important applications. The poor dispersion stability of thermal nanofluids, however, has been considered as a long-existing issue that limits their further development and practical application. This review overviews the recent efforts and progresses in improving the dispersion stability of thermal nanofluids such as mechanistic understanding of dispersion behavior of nanofluids, examples of both water-based and oil-based nanofluids, strategies to stabilize nanofluids, and characterization techniques for dispersion behavior of nanofluids. Finally, on-going research needs, and possible solutions to research challenges and future research directions in exploring stably dispersed thermal nanofluids are discussed. Keywords: Thermal nanofluids, Dispersion, Aggregation, Electrostatic stabilization, Steric stabilization

Hydrodynamic disperser

Energy Technology Data Exchange (ETDEWEB)

Bulatov, A.I.; Chernov, V.S.; Prokopov, L.I.; Proselkov, Yu.M.; Tikhonov, Yu.P.

1980-01-15

A hydrodynamic disperser is suggested which contains a housing, slit nozzles installed on a circular base arranged opposite from each other, resonators secured opposite the nozzle and outlet sleeve. In order to improve the effectiveness of dispersion by throttling the flow, each resonator is made in the form of a crimped plate with crimpings that decrease in height in a direction towards the nozzle.

Geometrical optimization of the transmission and dispersion properties of arrayed waveguide gratings using two stigmatic point mountings.

Science.gov (United States)

Muñoz, P; Pastor, D; Capmany, J; Martínez, A

2003-09-22

In this paper, the procedure to optimize flat-top Arrayed Waveguide Grating (AWG) devices in terms of transmission and dispersion properties is presented. The systematic procedure consists on the stigmatization and minimization of the Light Path Function (LPF) used in classic planar spectrograph theory. The resulting geometry arrangement for the Arrayed Waveguides (AW) and the Output Waveguides (OW) is not the classical Rowland mounting, but an arbitrary geometry arrangement. Simulation using previous published enhanced modeling show how this geometry reduces the passband ripple, asymmetry and dispersion, in a design example.

A new electrophoretic focusing principle: focusing of nonamphoteric weak ionogenic analytes using inverse electromigration dispersion profiles.

Science.gov (United States)

Gebauer, Petr; Malá, Zdena; Bocek, Petr

2010-03-01

This contribution introduces a new separation principle in CE which offers focusing of weak nonamphoteric ionogenic species and their inherent transport to the detector. The prerequisite condition for application of this principle is the existence of an inverse electromigration dispersion profile, i.e. a profile where pH is decreasing toward the anode or cathode for focusing of anionic or cationic weak analytes, respectively. The theory presented defines the principal conditions under which an analyte is focused on a profile of this type. Since electromigration dispersion profiles are migrating ones, the new principle offers inherent transport of focused analytes into the detection cell. The focusing principle described utilizes a mechanism different from both CZE (where separation is based on the difference in mobilities) and IEF (where separation is based on difference in pI), and hence, offers another separation dimension in CE. The new principle and its theory presented here are supplemented by convincing experiments as their proof.

Dispersal and metapopulation stability

Directory of Open Access Journals (Sweden)

Shaopeng Wang

2015-10-01

Full Text Available Metapopulation dynamics are jointly regulated by local and spatial factors. These factors may affect the dynamics of local populations and of the entire metapopulation differently. Previous studies have shown that dispersal can stabilize local populations; however, as dispersal also tends to increase spatial synchrony, its net effect on metapopulation stability has been controversial. Here we present a simple metapopulation model to study how dispersal, in interaction with other spatial and local processes, affects the temporal variability of metapopulations in a stochastic environment. Our results show that in homogeneous metapopulations, the local stabilizing and spatial synchronizing effects of dispersal cancel each other out, such that dispersal has no effect on metapopulation variability. This result is robust to moderate heterogeneities in local and spatial parameters. When local and spatial dynamics exhibit high heterogeneities, however, dispersal can either stabilize or destabilize metapopulation dynamics through various mechanisms. Our findings have important theoretical and practical implications. We show that dispersal functions as a form of spatial intraspecific mutualism in metapopulation dynamics and that its effect on metapopulation stability is opposite to that of interspecific competition on local community stability. Our results also suggest that conservation corridors should be designed with appreciation of spatial heterogeneities in population dynamics in order to maximize metapopulation stability.

Studies of Tracer Dispersion and Fluid Flow in Porous Media

Energy Technology Data Exchange (ETDEWEB)

Rage, T.

1996-12-31

This doctoral thesis explores the connection between the topology of a porous medium and its macroscopic transport properties and is based on computerized simulation. In porous media, both diffusion and convection contribute to the dispersion of a tracer and their combined effect is emphasized. The governing equations are solved numerically, using finite differences and Monte Carlo technique. The influence of finite Reynolds number on the outcome of echo-experiments is discussed. Comparing experiments and simulations it is found that nonlinear inertial forces lead to a visible deformation of a returned tracer at surprisingly small Reynolds numbers. In a study of tracer dispersion and fluid flow in periodic arrays of discs it is demonstrated that the mechanisms of mechanical dispersion in periodic media and in natural (non-periodic) porous media are essentially different. Measurements of the percolation probability distribution of a sandstone sample is presented. Local porosity theory predicts that this simple geometric function of a porous medium is of dominant importance for its macroscopic transport properties. It is demonstrated that many aspects of transport through fractures can be studied by using simple but realistic models and readily available computer resources. An example may be the transport of hydrocarbon fluids from the source rock to a reservoir. 165 refs., 44 figs., 1 table

Characterization of size, surface charge, and agglomeration state of nanoparticle dispersions for toxicological studies

International Nuclear Information System (INIS)

Jiang Jingkun; Oberdoerster, Guenter; Biswas, Pratim

2009-01-01

Characterizing the state of nanoparticles (such as size, surface charge, and degree of agglomeration) in aqueous suspensions and understanding the parameters that affect this state are imperative for toxicity investigations. In this study, the role of important factors such as solution ionic strength, pH, and particle surface chemistry that control nanoparticle dispersion was examined. The size and zeta potential of four TiO 2 and three quantum dot samples dispersed in different solutions (including one physiological medium) were characterized. For 15 nm TiO 2 dispersions, the increase of ionic strength from 0.001 M to 0.1 M led to a 50-fold increase in the hydrodynamic diameter, and the variation of pH resulted in significant change of particle surface charge and the hydrodynamic size. It was shown that both adsorbing multiply charged ions (e.g., pyrophosphate ions) onto the TiO 2 nanoparticle surface and coating quantum dot nanocrystals with polymers (e.g., polyethylene glycol) suppressed agglomeration and stabilized the dispersions. DLVO theory was used to qualitatively understand nanoparticle dispersion stability. A methodology using different ultrasonication techniques (bath and probe) was developed to distinguish agglomerates from aggregates (strong bonds), and to estimate the extent of particle agglomeration. Probe ultrasonication performed better than bath ultrasonication in dispersing TiO 2 agglomerates when the stabilizing agent sodium pyrophosphate was used. Commercially available Degussa P25 and in-house synthesized TiO 2 nanoparticles were used to demonstrate identification of aggregated and agglomerated samples.

Dispersion of multi-walled carbon nanotubes in biocompatible dispersants

International Nuclear Information System (INIS)

Piret, J.-P.; Detriche, S.; Vigneron, R.; Vankoningsloo, S.; Rolin, S.; Mejia Mendoza, J. H.; Masereel, B.; Lucas, S.; Delhalle, J.; Luizi, F.; Saout, C.; Toussaint, O.

2010-01-01

Owing to their phenomenal electrical and mechanical properties, carbon nanotubes (CNT) have been an area of intense research since their discovery in 1991. Different applications for these nanoparticles have been proposed, among others, in electronics and optics but also in the medical field. In parallel, emerging studies have suggested potential toxic effects of CNT while others did not, generating some conflicting outcomes. These discrepancies could be, in part, due to different suspension approaches used and to the agglomeration state of CNT in solution. In this study, we described a standardized protocol to obtain stable CNT suspensions, using two biocompatible dispersants (Pluronic F108 and hydroxypropylcellulose) and to estimate the concentration of CNT in solution. CNT appear to be greatly individualized in these two dispersants with no detection of remaining bundles or agglomerates after sonication and centrifugation. Moreover, CNT remained perfectly dispersed when added to culture medium used for in vitro cell experiments. We also showed that Pluronic F108 is a better dispersant than hydroxypropylcellulose. In conclusion, we have developed a standardized protocol using biocompatible surfactants to obtain reproducible and stable multi-walled carbon nanotubes suspensions which can be used for in vitro or in vivo toxicological studies.

On the Geocentric Nature of the Big Bang Theory

Science.gov (United States)

Wang, Ling Jun

2008-04-01

An expanding universe with all heavenly bodies moving isotropically away from the earth seems to suggest a geocentric theory which is evidently false. To defend the Big Bang Theory (BBT) from falling into a geocentric theory, it is argued that if the universe is expanding linearly from the singularity, the heavenly bodies would appear to be leaving away from each other with isotropic velocity distribution with respect to any observer. In this presentation we will prove rigorously with both classical and relativistic analysis that even strict linearity of Hubble's law would not save the Big Bang from falling into a geocentric theory. The key of the analysis rests on the two crucial necessary conditions for the raisin-pudding model: 1) The velocities and the positions of the earth and the galaxies must be measured simultaneously; 2) The velocity transformation between the reference frame of the earth and that of the singularity must be linear. The first condition can not be satisfied due to the speed limit of light; and the second condition can not be satisfied due to non linear velocity transformation of relativity. The whole problem is originated from the Doppler shift explanation of the red shift. Wang's Dispersive Extinction Theory (DET), however, interprets the red shift as being caused by the dispersive extinction of the star light by the space medium, and therefore does not lead to a geocentric universe. This lends a strong support to DET over BBT.

Low-energy theorems for Compton scattering up to order e/sup 4/. [Scattering amplitudes dispersion relations

Energy Technology Data Exchange (ETDEWEB)

Pippig, G

1975-01-01

Taking the Compton scattering of pions and deuterons as an example it is shown that low-energy theorems which are valid for the order e/sup 2/ are also valid for the next higher order of electromagnetic interactions. The imaginary component of the scattering amplitude was exactly calculated for the energy of incident photons in the order e/sup 4/ up to the desired one, whereas the real component was obtained from dispersion relations. It is proved that the results derived from the dispersion theory of strong interactions are equivalent to those obtained from quantum electrodynamics for spin 0 and spin 1, respectively.

Towards a dispersive determination of the pion transition form factor

Science.gov (United States)

Leupold, Stefan; Hoferichter, Martin; Kubis, Bastian; Niecknig, Franz; Schneider, Sebastian P.

2018-01-01

We start with a brief motivation why the pion transition form factor is interesting and, in particular, how it is related to the high-precision standard-model calculation of the gyromagnetic ratio of the muon. Then we report on the current status of our ongoing project to calculate the pion transition form factor using dispersion theory. Finally we present and discuss a wish list of experimental data that would help to improve the input for our calculations and/or to cross-check our results.

Towards a dispersive determination of the pion transition form factor

Directory of Open Access Journals (Sweden)

Leupold Stefan

2018-01-01

Full Text Available We start with a brief motivation why the pion transition form factor is interesting and, in particular, how it is related to the high-precision standard-model calculation of the gyromagnetic ratio of the muon. Then we report on the current status of our ongoing project to calculate the pion transition form factor using dispersion theory. Finally we present and discuss a wish list of experimental data that would help to improve the input for our calculations and/or to cross-check our results.

On the Optimum Dispersion of a Storage Ring for Electron Cooling with High Space Charge

CERN Document Server

Bosser, Jacques; Chanel, M; Marié, L; Möhl, D; Tranquille, G

2000-01-01

With the intense electron beams used for cooling, matching of the ion and electron velocity over the largest possible fraction of the beam profile becomes important. In this situation, a finite dispersion from the ring in the cooling section can lead to an appreciable gain in the transverse cooling speed. Based on a simple model of the cooling force, an expression for the "optimum" dispersion as a function of the electron beam intensity, the momentum spread and other properties of the ion beam will be derived. This simple theory will be compared to measurements made on the Low Energy Ion Ring (LEIR) at CERN during 1997.

Critical Dispersion-Theory Tests of Silicon's IR Refractive Index

Science.gov (United States)

Karstens, William; Smith, D. Y.

Silicon strongly absorbs both visible and UV light, but is highly transparent in the IR. Hence, it is a common choice for infrared windows and lenses. However, optical design is hindered by literature index values that disagree by up to 1%. In contrast optical-glass indices are known to 0.01% or better. The most widely available silicon IR indices are based on bulk measurements using either Snell's-Law refraction by a prism or channel-spectra interference of front- and backsurface reflections from a planar sample. To test the physical acceptability of these data, we have developed criteria based on a Taylor expansion of the Kramers-Kronig relation for the index at energies below strong inter-band transitions. These tests require that the coefficients of the series in powers of energy squared must be positive within the region of transparency. This is satisfied by essentially all prism measurements; their small scatter arises primarily from impurities and doping. In contrast, channel-spectra data fail in the second and third coefficients. A review of the experimental analysis indicates three problems besides purity: incorrect channel number arising from a channel-spectra model that neglects spectrum distortion by the weak lattice absorption; use of a series expansion of mixed parity in photon energy to describe the even-parity index; and use of an incorrect absorption energy in the Li-Sellmeier dispersion formula. Recommendations for IR index values for pure silicon will be discussed. Supported in part by the US Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC02-06CH11357.

Dispersion characteristics of two-dimensional unmagnetized dielectric plasma photonic crystal

International Nuclear Information System (INIS)

Li-Mei, Qi; Zi-Qiang, Yang; Feng, Lan; Xi, Gao; Da-Zhi, Li

2010-01-01

This paper studies dispersion characteristics of the transverse magnetic (TM) mode for two-dimensional unmagnetized dielectric plasma photonic crystal by a modified plane wave method. First, the cutoff behaviour is made clear by using the Maxwell–Garnett effective medium theory, and the influences of dielectric filling factor and dielectric constant on effective plasma frequency are analysed. Moreover, the occurence of large gaps in dielectric plasma photonic crystal is demonstrated by comparing the skin depth with the lattice constant, and the influence of plasma frequency on the first three gaps is also studied. Finally, by using the particle-in-cell simulation method, a transmission curve in the Γ – X direction is obtained in dielectric plasma photonic crystal, which is in accordance with the dispersion curves calculated by the modified plane wave method, and the large gap between the transmission points of 27 GHz and 47 GHz is explained by comparing the electric field patterns in particle-in-cell simulation

Selfing ability and dispersal are positively related, but not affected by range position: a multispecies study on southern African Asteraceae.

Science.gov (United States)

de Waal, C; Rodger, J G; Anderson, B; Ellis, A G

2014-05-01

Dispersal and breeding system traits are thought to affect colonization success. As species have attained their present distribution ranges through colonization, these traits may vary geographically. Although several theories predict associations between dispersal ability, selfing ability and the relative position of a population within its geographic range, there is little theoretical or empirical consensus on exactly how these three variables are related. We investigated relationships between dispersal ability, selfing ability and range position across 28 populations of 13 annual, wind-dispersed Asteraceae species from the Namaqualand region of South Africa. Controlling for phylogeny, relative dispersal ability--assessed from vertical fall time of fruits--was positively related to an index of autofertility--determined from hand-pollination experiments. These findings support the existence of two discrete syndromes: high selfing ability associated with good dispersal and obligate outcrossing associated with lower dispersal ability. This is consistent with the hypothesis that selection for colonization success drives the evolution of an association between these traits. However, no general effect of range position on dispersal or breeding system traits was evident. This suggests selection on both breeding system and dispersal traits acts consistently across distribution ranges. © 2014 The Authors. Journal of Evolutionary Biology © 2014 European Society For Evolutionary Biology.

Dynamical theory of neutron diffraction. [One-body Schroedinger equation, review

Energy Technology Data Exchange (ETDEWEB)

Sears, V F [Atomic Energy of Canada Ltd., Chalk River, Ontario. Chalk River Nuclear Labs.

1978-10-01

We present a review of the dynamical theory of neutron diffraction by macroscopic bodies which provides the theoretical basis for the study of neutron optics. We consider both the theory of dispersion, in which it is shown that the coherent wave in the medium satisfies a macroscopic one-body Schroedinger equation, and the theory of reflection, refraction, and diffraction in which the above equation is solved for a number of special cases of interest. The theory is illustrated with the help of experimental results obtained over the past 10 years by a number of new techniques such as neutron gravity refractometry. Pendelloesung interference, and neutron interferometry.

Tracer dispersion - experiment and CFD

International Nuclear Information System (INIS)

Zitny, R.

2004-01-01

Description of tracer distribution by means of dispersion models is a method successfully used in process engineering for fifty years. Application of dispersion models in reactor engineering for characterization of flows in column apparatus, heat exchangers, etc. is summarized and experimental tracer techniques as well as CFD methods for dispersion coefficients evaluation are discussed. Possible extensions of thermal axial dispersion model (ADM) and a core-wall ADM model suitable for description of tracer dispersion in laminar flows are suggested as well as CFD implementation as 1D finite elements. (author)

Acceleration, Energy Loss and Screening in Strongly-Coupled Gauge Theories

OpenAIRE

Chernicoff, Mariano; Guijosa, Alberto

2008-01-01

We explore various aspects of the motion of heavy quarks in strongly-coupled gauge theories, employing the AdS/CFT correspondence. Building on earlier work by Mikhailov, we study the dispersion relation and energy loss of an accelerating finite-mass quark in N=4 super-Yang-Mills, both in vacuum and in the presence of a thermal plasma. In the former case, we notice that the application of an external force modifies the dispersion relation. In the latter case, we find in particular that when a ...

Pigment dispersion and Artisan phakic intraocular lenses: crystalline lens rise as a safety criterion.

Science.gov (United States)

Baïkoff, Georges; Bourgeon, Grégoire; Jodai, Horacio Jitsuo; Fontaine, Aline; Lellis, Fernando Viera; Trinquet, Laure

2005-04-01

To validate the theory that crystalline lens rise can be used as a safety criterion to prevent pigment dispersion in eyes with an Artisan phakic intraocular lens (IOL) (Ophtec BV). Monticelli Clinic, Marseilles, France. A comparative analysis of crystalline lens rise in 9 eyes with pigment dispersion and 78 eyes without dispersion was performed. All eyes had previous implantation of an Artisan IOL. Anterior segment imaging was done using an anterior chamber optical coherence tomography (AC OCT) prototype. Crystalline lens rise was defined by the distance between the anterior pole of the crystalline lens and the horizontal plane joining the opposite iridocorneal recesses. The study confirmed that crystalline lens rise can be considered a safety criterion for implantation of Artisan-type phakic IOLs. The higher the crystalline lens rise, the greater the risk for developing pigment dispersion in the area of the pupil. This complication occurred more frequently in hyperopic eyes than in myopic eyes. Results indicate there is little or no risk for pigment dispersion if the rise is less than 600 microm; 67% of eyes with a rise of 600 microm or more developed pupillary pigment dispersion. In some cases in which the IOL was loosely fixated, there was no traction on the iris root and dispersion was prevented or delayed. Crystalline lens rise should be considered a new safety criterion for Artisan phakic IOL implantation and should also be applied to other types of phakic IOLs. The distance remaining between the crystalline lens rise and a 600 microm theoretical safety level allows one to calculate how long the IOL can safely remain in the eye.

Latitudinal phytoplankton distribution and the neutral theory of biodiversity

KAUST Repository

Chust, Guillem

2012-11-16

Recent studies have suggested that global diatom distributions are not limited by dispersal, in the case of both extant species and fossil species, but rather that environmental filtering explains their spatial patterns. Hubbell\\'s neutral theory of biodiversity provides a framework in which to test these alternatives. Our aim is to test whether the structure of marine phytoplankton (diatoms, dinoflagellates and coccolithophores) assemblages across the Atlantic agrees with neutral theory predictions. We asked: (1) whether intersite variance in phytoplankton diversity is explained predominantly by dispersal limitation or by environmental conditions; and (2) whether species abundance distributions are consistent with those expected by the neutral model. Location: Meridional transect of the Atlantic (50° N-50° S). Methods: We estimated the relative contributions of environmental factors and geographic distance to phytoplankton composition using similarity matrices, Mantel tests and variation partitioning of the species composition based upon canonical ordination methods. We compared the species abundance distribution of phytoplankton with the neutral model using Etienne\\'s maximum-likelihood inference method. Results: Phytoplankton communities are slightly more determined by niche segregation (24%), than by dispersal limitation and ecological drift (17%). In 60% of communities, the assumption of neutrality in species\\' abundance distributions could not be rejected. In tropical zones, where oceanic gyres enclose large stable water masses, most communities showed low species immigration rates; in contrast, we infer that communities in temperate areas, out of oligotrophic gyres, have higher rates of species immigration. Conclusions: Phytoplankton community structure is consistent with partial niche assembly and partial dispersal and drift assembly (neutral processes). The role of dispersal limitation is almost as important as habitat filtering, a fact that has been

Nuclear magnetic relaxation induced by exchange-mediated orientational randomization: longitudinal relaxation dispersion for spin I = 1.

Science.gov (United States)

Nilsson, Tomas; Halle, Bertil

2012-08-07

The frequency dependence of the longitudinal relaxation rate, known as the magnetic relaxation dispersion (MRD), can provide a frequency-resolved characterization of molecular motions in complex biological and colloidal systems on time scales ranging from 1 ns to 100 μs. The conformational dynamics of immobilized proteins and other biopolymers can thus be probed in vitro or in vivo by exploiting internal water molecules or labile hydrogens that exchange with a dominant bulk water pool. Numerous water (1)H and (2)H MRD studies of such systems have been reported, but the widely different theoretical models currently used to analyze the MRD data have resulted in divergent views of the underlying molecular motions. We have argued that the essential mechanism responsible for the main dispersion is the exchange-mediated orientational randomization (EMOR) of anisotropic nuclear (electric quadrupole or magnetic dipole) couplings when internal water molecules or labile hydrogens escape from orientationally confining macromolecular sites. In the EMOR model, the exchange process is thus not just a means of mixing spin populations but it is also the direct cause of spin relaxation. Although the EMOR theory has been used in several studies to analyze water (2)H MRD data from immobilized biopolymers, the fully developed theory has not been described. Here, we present a comprehensive account of a generalized version of the EMOR theory for spin I = 1 nuclides like (2)H. As compared to a previously described version of the EMOR theory, the present version incorporates three generalizations that are all essential in applications to experimental data: (i) a biaxial (residual) electric field gradient tensor, (ii) direct and indirect effects of internal motions, and (iii) multiple sites with different exchange rates. In addition, we describe and assess different approximations to the exact EMOR theory that are useful in various regimes. In particular, we consider the experimentally

Energy hyperspace for stacking interaction in AU/AU dinucleotide step: Dispersion-corrected density functional theory study.

Science.gov (United States)

Mukherjee, Sanchita; Kailasam, Senthilkumar; Bansal, Manju; Bhattacharyya, Dhananjay

2014-01-01

Double helical structures of DNA and RNA are mostly determined by base pair stacking interactions, which give them the base sequence-directed features, such as small roll values for the purine-pyrimidine steps. Earlier attempts to characterize stacking interactions were mostly restricted to calculations on fiber diffraction geometries or optimized structure using ab initio calculations lacking variation in geometry to comment on rather unusual large roll values observed in AU/AU base pair step in crystal structures of RNA double helices. We have generated stacking energy hyperspace by modeling geometries with variations along the important degrees of freedom, roll, and slide, which were chosen via statistical analysis as maximally sequence dependent. Corresponding energy contours were constructed by several quantum chemical methods including dispersion corrections. This analysis established the most suitable methods for stacked base pair systems despite the limitation imparted by number of atom in a base pair step to employ very high level of theory. All the methods predict negative roll value and near-zero slide to be most favorable for the purine-pyrimidine steps, in agreement with Calladine's steric clash based rule. Successive base pairs in RNA are always linked by sugar-phosphate backbone with C3'-endo sugars and this demands C1'-C1' distance of about 5.4 Å along the chains. Consideration of an energy penalty term for deviation of C1'-C1' distance from the mean value, to the recent DFT-D functionals, specifically ωB97X-D appears to predict reliable energy contour for AU/AU step. Such distance-based penalty improves energy contours for the other purine-pyrimidine sequences also. © 2013 Wiley Periodicals, Inc. Biopolymers 101: 107-120, 2014. Copyright © 2013 Wiley Periodicals, Inc.

Ultralow percolation threshold of single walled carbon nanotube-epoxy composites synthesized via an ionic liquid dispersant/initiator

Science.gov (United States)

Watters, Arianna L.; Palmese, Giuseppe R.

2014-09-01

Uniform dispersion of single walled carbon nanotubes (SWNTs) in an epoxy was achieved by a streamlined mechano-chemical processing method. SWNT-epoxy composites were synthesized using a room temperature ionic liquid (IL) with an imidazolium cation and dicyanamide anion. The novel approach of using ionic liquid that behaves as a dispersant for SWNTs and initiator for epoxy polymerization greatly simplifies nanocomposite synthesis. The material was processed using simple and scalable three roll milling. The SWNT dispersion of the resultant composite was evaluated by electron microscopy and electrical conductivity measurements in conjunction with percolation theory. Processing conditions were optimized to achieve the lowest possible percolation threshold, 4.29 × 10-5 volume fraction SWNTs. This percolation threshold is among the best reported in literature yet it was obtained using a streamlined method that greatly simplifies processing.

A computer model for dispersed fluid-solid turbulent flows

International Nuclear Information System (INIS)

Liu, C.H.; Tulig, T.J.

1985-01-01

A computer model is being developed to simulate two-phase turbulent flow phenomena in fluids containing finely dispersed solids. The model is based on a dual-continuum picture of the individual phases and an extension of a two-equation turbulence closure theory. The resulting set of nonlinear partial differential equations are solved using a finite difference procedure with special treatment to promote convergence. The model has been checked against a number of idealized flow problems with known solutions. The authors are currently comparing model predictions with measurements to determine a proper set of turbulence parameters needed for simulating two-phase turbulent flows

Anomalous behavior in the third harmonic generation z response through dispersion induced shape changes and matching χ(3)

Science.gov (United States)

Pillai, Rajesh S.; Brakenhoff, G. J.; Müller, M.

2006-09-01

The third harmonic generation (THG) axial response in the vicinity of an interface formed by two isotropic materials of normal dispersion is typically single peaked, with the maximum intensity at the interface position. Here it is shown experimentally that this THG z response may show anomalous behavior—being double peaked with a dip coinciding with the interface position—when the THG contributions from both materials are of similar magnitude. The observed anomalous behavior is explained, using paraxial Gaussian theory, by considering dispersion induced shape changes in the THG z response.

Strongly coupled dispersed two-phase flows; Ecoulements diphasiques disperses fortement couples

Energy Technology Data Exchange (ETDEWEB)

Zun, I.; Lance, M.; Ekiel-Jezewska, M.L.; Petrosyan, A.; Lecoq, N.; Anthore, R.; Bostel, F.; Feuillebois, F.; Nott, P.; Zenit, R.; Hunt, M.L.; Brennen, C.E.; Campbell, C.S.; Tong, P.; Lei, X.; Ackerson, B.J.; Asmolov, E.S.; Abade, G.; da Cunha, F.R.; Lhuillier, D.; Cartellier, A.; Ruzicka, M.C.; Drahos, J.; Thomas, N.H.; Talini, L.; Leblond, J.; Leshansky, A.M.; Lavrenteva, O.M.; Nir, A.; Teshukov, V.; Risso, F.; Ellinsen, K.; Crispel, S.; Dahlkild, A.; Vynnycky, M.; Davila, J.; Matas, J.P.; Guazelli, L.; Morris, J.; Ooms, G.; Poelma, C.; van Wijngaarden, L.; de Vries, A.; Elghobashi, S.; Huilier, D.; Peirano, E.; Minier, J.P.; Gavrilyuk, S.; Saurel, R.; Kashinsky, O.; Randin, V.; Colin, C.; Larue de Tournemine, A.; Roig, V.; Suzanne, C.; Bounhoure, C.; Brunet, Y.; Tanaka, A.T.; Noma, K.; Tsuji, Y.; Pascal-Ribot, S.; Le Gall, F.; Aliseda, A.; Hainaux, F.; Lasheras, J.; Didwania, A.; Costa, A.; Vallerin, W.; Mudde, R.F.; Van Den Akker, H.E.A.; Jaumouillie, P.; Larrarte, F.; Burgisser, A.; Bergantz, G.; Necker, F.; Hartel, C.; Kleiser, L.; Meiburg, E.; Michallet, H.; Mory, M.; Hutter, M.; Markov, A.A.; Dumoulin, F.X.; Suard, S.; Borghi, R.; Hong, M.; Hopfinger, E.; Laforgia, A.; Lawrence, C.J.; Hewitt, G.F.; Osiptsov, A.N.; Tsirkunov, Yu. M.; Volkov, A.N.

2003-07-01

This document gathers the abstracts of the Euromech 421 colloquium about strongly coupled dispersed two-phase flows. Behaviors specifically due to the two-phase character of the flow have been categorized as: suspensions, particle-induced agitation, microstructure and screening mechanisms; hydrodynamic interactions, dispersion and phase distribution; turbulence modulation by particles, droplets or bubbles in dense systems; collective effects in dispersed two-phase flows, clustering and phase distribution; large-scale instabilities and gravity driven dispersed flows; strongly coupled two-phase flows involving reacting flows or phase change. Topic l: suspensions particle-induced agitation microstructure and screening mechanisms hydrodynamic interactions between two very close spheres; normal stresses in sheared suspensions; a critical look at the rheological experiments of R.A. Bagnold; non-equilibrium particle configuration in sedimentation; unsteady screening of the long-range hydrodynamic interactions of settling particles; computer simulations of hydrodynamic interactions among a large collection of sedimenting poly-disperse particles; velocity fluctuations in a dilute suspension of rigid spheres sedimenting between vertical plates: the role of boundaries; screening and induced-agitation in dilute uniform bubbly flows at small and moderate particle Reynolds numbers: some experimental results. Topic 2: hydrodynamic interactions, dispersion and phase distribution: hydrodynamic interactions in a bubble array; A 'NMR scattering technique' for the determination of the structure in a dispersion of non-brownian settling particles; segregation and clustering during thermo-capillary migration of bubbles; kinetic modelling of bubbly flows; velocity fluctuations in a homogeneous dilute dispersion of high-Reynolds-number rising bubbles; an attempt to simulate screening effects at moderate particle Reynolds numbers using an hybrid formulation; modelling the two

Dispersion representations for hard exclusive processes. Beyond the born approximation

International Nuclear Information System (INIS)

Diehl, M.; Ivanov, D.Yu.

2007-07-01

Several hard exclusive scattering processes admit a description in terms of generalized parton distributions and perturbative hard-scattering kernels. Both the physical amplitude and the hard-scattering kernels fulfill dispersion relations. We give a detailed investigation of their consistency at all orders in perturbation theory. The results shed light on the information about generalized parton distributions that can be extracted from the real and imaginary parts of exclusive amplitudes. They also provide a practical consistency check for models of these distributions in which Lorentz invariance is not exactly satisfied. (orig.)

PARTICLE SCATTERING OFF OF RIGHT-HANDED DISPERSIVE WAVES

Energy Technology Data Exchange (ETDEWEB)

Schreiner, C.; Kilian, P.; Spanier, F., E-mail: cschreiner@astro.uni-wuerzburg.de [Centre for Space Research, North-West University, 2520 Potchefstroom (South Africa)

2017-01-10

Resonant scattering of fast particles off low frequency plasma waves is a major process determining transport characteristics of energetic particles in the heliosphere and contributing to their acceleration. Usually, only Alfvén waves are considered for this process, although dispersive waves are also present throughout the heliosphere. We investigate resonant interaction of energetic electrons with dispersive, right-handed waves. For the interaction of particles and a single wave a variable transformation into the rest frame of the wave can be performed. Here, well-established analytic models derived in the framework of magnetostatic quasi-linear theory can be used as a reference to validate simulation results. However, this approach fails as soon as several dispersive waves are involved. Based on analytic solutions modeling the scattering amplitude in the magnetostatic limit, we present an approach to modify these equations for use in the plasma frame. Thereby we aim at a description of particle scattering in the presence of several waves. A particle-in-cell code is employed to study wave–particle scattering on a micro-physically correct level and to test the modified model equations. We investigate the interactions of electrons at different energies (from 1 keV to 1 MeV) and right-handed waves with various amplitudes. Differences between model and simulation arise in the case of high amplitudes or several waves. Analyzing the trajectories of single particles we find no microscopic diffusion in the case of a single plasma wave, although a broadening of the particle distribution can be observed.

Spectral phase shift and residual angular dispersion of an accousto-optic programme dispersive filter

International Nuclear Information System (INIS)

Boerzsoenyi, A.; Meroe, M.

2010-01-01

Complete text of publication follows. There is an increasing demand for active and precise dispersion control of ultrashort laser pulses. In chirped pulse amplification (CPA) laser systems, the dispersion of the optical elements of the laser has to be compensated at least to the fourth order to obtain high temporal contrast compressed pulses. Nowadays the most convenient device for active and programmable control of spectral phase and amplitude of broadband laser pulses is the acousto-optic programmable dispersive filter (AOPDF), claimed to be able to adjust the spectral phase up to the fourth order. Although it has been widely used, surprisingly enough there has been only a single, low resolution measurement reported on the accuracy of the induced spectral phase shift of the device. In our paper we report on the first systematic experiment aiming at the precise characterization of an AOPDF device. In the experiment the spectral phase shift of the AOPDF device was measured by spectrally and spatially resolved interferometry, which is especially powerful tool to determine small dispersion values with high accuracy. Besides the spectral phase dispersion, we measured both the propagation direction angular dispersion (PDAD) and the phase front angular dispersion (PhFAD). Although the two quantities are equal for plane waves, there may be noticeable difference for Gaussian pulses. PDAD was determined simply by focusing the beam on the slit of an imaging spectrograph, while PhFAD was measured by the use of an inverted Mach-Zehnder interferometer and an imaging spectrograph. In the measurements, the spectral phase shift and both types of angular dispersion have been recorded upon the systematic change of all the accessible functions of the acousto-optic programmable dispersive filter. The measured values of group delay dispersion (GDD) and third order dispersion (TOD) have been found to agree with the preset values within the error of the measurement (1 fs 2 and 10 fs 3

The influence of the dispersion corrections on the performance of DFT method in modeling HNgY noble gas molecules and their complexes

Science.gov (United States)

Cukras, Janusz; Sadlej, Joanna

2018-01-01

The letter reports a comparative assessment of the usefulness of the two different Grimme's corrections for evaluating dispersion interaction (DFT-D3 and DFT-D3BJ) for the representative molecules of the family of noble-gas hydrides HXeY and their complexes with the HZ molecules, where Y and Z are F/Cl/OH/SH. with special regard to the dispersion term calculated by means of the symmetry-adapted perturbation theory (at the SAPT0 level). The results indicate that despite differences in the total interactions energy (DFT + corrections) versus SAPT0 results, the sequence of contributions of the individual dispersion terms is still maintained. Both dispersion corrections perform similarly and they improve the results suggesting that it is worthwhile to include them in calculations.

On the theory of wave packets

International Nuclear Information System (INIS)

Naumov, D.V.

2013-01-01

In this paper we discuss some aspects of the theory of wave packets. We consider a popular non-covariant Gaussian model used in various applications and show that it predicts too slow a longitudinal dispersion rate for relativistic particles. We revise this approach by considering a covariant model of Gaussian wave packets, and examine our results by inspecting a wave packet of an arbitrary form. A general formula for the time dependence of the dispersion of a wave packet of an arbitrary form is found. Finally, we give a transparent interpretation of the disappearance of the wave function over time due to the dispersion - a feature often considered undesirable, but which is unavoidable for wave packets. We find, starting with simple examples, proceeding with their generalizations and finally by considering the continuity equation, that the integral over time of both the flux and probability densities is asymptotically proportional to the factor 1/|x| 2 in the rest frame of the wave packet, just as in the case of an ensemble of classical particles

Continuous media theory for MR fluids in non-shearing flows

International Nuclear Information System (INIS)

Ruiz-López, J A; Hidalgo-Alvarez, R; Vicente, J de

2013-01-01

The enhanced mechanical response of magnetorheological fluids under slow compression has been investigated by means of experiments, theory and particle-level simulations. A wide range of magnetic field strengths (0–354 kA/m), dispersing medium viscosities (20–500 mPa·s) and particle concentrations (5–30 vol%) were investigated. Plastic media theory in compressive flow was in good agreement with experimental data. Slight deviations from the theory were associated to the so-called strengthening effect as the yield shear stress could increase during compression. Particle-level simulations were in good agreement with both experiments and simulations.

Quantum-optical input-output relations for dispersive and lossy multilayer dielectric plates

International Nuclear Information System (INIS)

Gruner, T.; Welsch, D.

1996-01-01

Using the Green-function approach to the problem of quantization of the phenomenological Maxwell theory, the propagation of quantized radiation through dispersive and absorptive multilayer dielectric plates is studied. Input-output relations are derived, with special emphasis on the determination of the quantum noise generators associated with the absorption of radiation inside the dielectric matter. The input-output relations are used to express arbitrary correlation functions of the outgoing field in terms of correlation functions of the incoming field and those of the noise generators. To illustrate the theory, photons at dielectric tunneling barriers are considered. It is shown that inclusion in the calculations of losses in the photonic band gaps may substantially change the barrier traversal times. copyright 1996 The American Physical Society

Design and development of a dust dispersion chamber to quantify the dispersibility of rock dust.

Science.gov (United States)

Perera, Inoka E; Sapko, Michael J; Harris, Marcia L; Zlochower, Isaac A; Weiss, Eric S

2016-01-01

Dispersible rock dust must be applied to the surfaces of entries in underground coal mines in order to inert the coal dust entrained or made airborne during an explosion and prevent propagating explosions. 30 CFR. 75.2 states that "… [rock dust particles] when wetted and dried will not cohere to form a cake which will not be dispersed into separate particles by a light blast of air …" However, a proper definition or quantification of "light blast of air" is not provided. The National Institute for Occupational Safety and Health (NIOSH) has, consequently, designed a dust dispersion chamber to conduct quantitative laboratory-scale dispersibility experiments as a screening tool for candidate rock dusts. A reproducible pulse of air is injected into the chamber and across a shallow tray of rock dust. The dust dispersed and carried downwind is monitored. The mass loss of the dust tray and the airborne dust measurements determine the relative dispersibility of the dust with respect to a Reference rock dust. This report describes the design and the methodology to evaluate the relative dispersibility of rock dusts with and without anti-caking agents. Further, the results of this study indicate that the dispersibility of rock dusts varies with particle size, type of anti-caking agent used, and with the untapped bulk density. Untreated rock dusts, when wetted and dried forming a cake that was much less dispersible than the reference rock dust used in supporting the 80% total incombustible content rule.

Nonlinear theory of the free-electron laser

International Nuclear Information System (INIS)

Chian, A.C.-L.; Padua Brito Serbeto, A. de.

1984-01-01

A theory of Raman free-electron laser using a circularly polarized electromagnetic pump is investigated. Coupled wave equations that describe both linear and nonlinear evolution of stimulated Raman scattering are derived. The dispersion relation and the growth rate for the parametric instability are obtained. Nonlinear processes that may lead to saturation of the free-electron laser are discussed. (Author) [pt

Polarization and switching properties of holographic polymer-dispersed liquid-crystal gratings. I. Theoretical model

Science.gov (United States)

Sutherland, Richard L.

2002-12-01

Polarization properties and electro-optical switching behavior of holographic polymer-dispersed liquid-crystal (HPDLC) reflection and transmission gratings are studied. A theoretical model is developed that combines anisotropic coupled-wave theory with an elongated liquid-crystal-droplet switching model and includes the effects of a statistical orientational distribution of droplet-symmetry axes. Angle- and polarization-dependent switching behaviors of HPDLC gratings are elucidated, and the effects on dynamic range are described. A new type of electro-optical switching not seen in ordinary polymer-dispersed liquid crystals, to the best of the author's knowledge, is presented and given a physical interpretation. The model provides valuable insight to the physics of these gratings and can be applied to the design of HPDLC holographic optical elements.

Density-functional approach to the three-body dispersion interaction based on the exchange dipole moment

Energy Technology Data Exchange (ETDEWEB)

Proynov, Emil; Wang, Matthew; Kong, Jing, E-mail: jing.kong@mtsu.edu [Department of Chemistry and Center for Computational Sciences, Middle Tennessee State University, Murfreesboro, Tennessee 37132 (United States); Liu, Fenglai [Department of Chemical and Biological Engineering, University at Buffalo, Buffalo, New York 14260 (United States); Gan, Zhengting [Q-Chem Inc., 5001 Baum Boulevard, Pittsburgh, Pennsylvania 15213 (United States)

2015-08-28

We implement and compute the density functional nonadditive three-body dispersion interaction using a combination of Tang-Karplus formalism and the exchange-dipole moment model of Becke and Johnson. The computation of the C{sub 9} dispersion coefficients is done in a non-empirical fashion. The obtained C{sub 9} values of a series of noble atom triplets agree well with highly accurate values in the literature. We also calculate the C{sub 9} values for a series of benzene trimers and find a good agreement with high-level ab initio values reported recently in the literature. For the question of damping of the three-body dispersion at short distances, we propose two damping schemes and optimize them based on the benzene trimers data, and the fitted analytic potentials of He{sub 3} and Ar{sub 3} trimers fitted to the results of high-level wavefunction theories available from the literature. Both damping schemes respond well to the optimization of two parameters.

Dispersal kernel estimation: A comparison of empirical and modelled particle dispersion in a coastal marine system

Science.gov (United States)

Hrycik, Janelle M.; Chassé, Joël; Ruddick, Barry R.; Taggart, Christopher T.

2013-11-01

Early life-stage dispersal influences recruitment and is of significance in explaining the distribution and connectivity of marine species. Motivations for quantifying dispersal range from biodiversity conservation to the design of marine reserves and the mitigation of species invasions. Here we compare estimates of real particle dispersion in a coastal marine environment with similar estimates provided by hydrodynamic modelling. We do so by using a system of magnetically attractive particles (MAPs) and a magnetic-collector array that provides measures of Lagrangian dispersion based on the time-integration of MAPs dispersing through the array. MAPs released as a point source in a coastal marine location dispersed through the collector array over a 5-7 d period. A virtual release and observed (real-time) environmental conditions were used in a high-resolution three-dimensional hydrodynamic model to estimate the dispersal of virtual particles (VPs). The number of MAPs captured throughout the collector array and the number of VPs that passed through each corresponding model location were enumerated and compared. Although VP dispersal reflected several aspects of the observed MAP dispersal, the comparisons demonstrated model sensitivity to the small-scale (random-walk) particle diffusivity parameter (Kp). The one-dimensional dispersal kernel for the MAPs had an e-folding scale estimate in the range of 5.19-11.44 km, while those from the model simulations were comparable at 1.89-6.52 km, and also demonstrated sensitivity to Kp. Variations among comparisons are related to the value of Kp used in modelling and are postulated to be related to MAP losses from the water column and (or) shear dispersion acting on the MAPs; a process that is constrained in the model. Our demonstration indicates a promising new way of 1) quantitatively and empirically estimating the dispersal kernel in aquatic systems, and 2) quantitatively assessing and (or) improving regional hydrodynamic

Unifying Pore Network Modeling, Continuous Time Random Walk Theory and Experiment - Accomplishments and Future Directions

Science.gov (United States)

Bijeljic, B.

2008-05-01

This talk will describe and highlight the advantages offered by a methodology that unifies pore network modeling, CTRW theory and experiment in description of solute dispersion in porous media. Solute transport in a porous medium is characterized by the interplay of advection and diffusion (described by Peclet number, Pe) that cause spreading of solute particles. This spreading is traditionally described by dispersion coefficients, D, defined by σ 2 = 2Dt, where σ 2 is the variance of the solute position and t is the time. Using a pore-scale network model based on particle tracking, the rich Peclet- number dependence of dispersion coefficient is predicted from first principles and is shown to compare well with experimental data for restricted diffusion, transition, power-law and mechanical dispersion regimes in the asymptotic limit. In the asymptotic limit D is constant and can be used in an averaged advection-dispersion equation. However, it is highly important to recognize that, until the velocity field is fully sampled, the particle transport is non-Gaussian and D possesses temporal or spatial variation. Furthermore, temporal probability density functions (PDF) of tracer particles are studied in pore networks and an excellent agreement for the spectrum of transition times for particles from pore to pore is obtained between network model results and CTRW theory. Based on the truncated power-law interpretation of PDF-s, the physical origin of the power-law scaling of dispersion coefficient vs. Peclet number has been explained for unconsolidated porous media, sands and a number of sandstones, arriving at the same conclusion from numerical network modelling, analytic CTRW theory and experiment. Future directions for further applications of the methodology presented are discussed in relation to the scale- dependent solute dispersion and reactive transport. Significance of pre-asymptotic dispersion in porous media is addressed from pore-scale upwards and the impact

Fractional quantum Hall systems near nematicity: Bimetric theory, composite fermions, and Dirac brackets

Science.gov (United States)

Nguyen, Dung Xuan; Gromov, Andrey; Son, Dam Thanh

2018-05-01

We perform a detailed comparison of the Dirac composite fermion and the recently proposed bimetric theory for a quantum Hall Jain states near half filling. By tuning the composite Fermi liquid to the vicinity of a nematic phase transition, we find that the two theories are equivalent to each other. We verify that the single mode approximation for the response functions and the static structure factor becomes reliable near the phase transition. We show that the dispersion relation of the nematic mode near the phase transition can be obtained from the Dirac brackets between the components of the nematic order parameter. The dispersion is quadratic at low momenta and has a magnetoroton minimum at a finite momentum, which is not related to any nearby inhomogeneous phase.

Laser control of natural disperse systems

Science.gov (United States)

Vlasova, Olga L.; Bezrukova, Alexandra G.

2003-10-01

Different water disperse systems were studied by integral (spectroturbidemetry) and differential light scattering method with a laser as a source of light. The investigation done concerns the state of kaolin dispersions at storage and under dilution as an example of mineral dispersion systems such as natural water. The role of some light scattering parameters for an optical analysis of water dispersions, like the dispersion of erythrocytes and bacterial cells -Escherichia coli is discussed. The results obtained can help to elaborate the methods for on-line optical control fo natural disperse systems (water, air) with mineral and biological particles.

Fluid analog model for boundary effects in field theory

International Nuclear Information System (INIS)

Ford, L. H.; Svaiter, N. F.

2009-01-01

Quantum fluctuations in the density of a fluid with a linear phonon dispersion relation are studied. In particular, we treat the changes in these fluctuations due to nonclassical states of phonons and to the presence of boundaries. These effects are analogous to similar effects in relativistic quantum field theory, and we argue that the case of the fluid is a useful analog model for effects in field theory. We further argue that the changes in the mean squared density are, in principle, observable by light scattering experiments.

Ultralow percolation threshold of single walled carbon nanotube-epoxy composites synthesized via an ionic liquid dispersant/initiator

International Nuclear Information System (INIS)

Watters, Arianna L; Palmese, Giuseppe R

2014-01-01

Uniform dispersion of single walled carbon nanotubes (SWNTs) in an epoxy was achieved by a streamlined mechano-chemical processing method. SWNT-epoxy composites were synthesized using a room temperature ionic liquid (IL) with an imidazolium cation and dicyanamide anion. The novel approach of using ionic liquid that behaves as a dispersant for SWNTs and initiator for epoxy polymerization greatly simplifies nanocomposite synthesis. The material was processed using simple and scalable three roll milling. The SWNT dispersion of the resultant composite was evaluated by electron microscopy and electrical conductivity measurements in conjunction with percolation theory. Processing conditions were optimized to achieve the lowest possible percolation threshold, 4.29 × 10 −5 volume fraction SWNTs. This percolation threshold is among the best reported in literature yet it was obtained using a streamlined method that greatly simplifies processing. (paper)

Transit time dispersion in pulmonary and systemic circulation: effects of cardiac output and solute diffusivity.

Science.gov (United States)

Weiss, Michael; Krejcie, Tom C; Avram, Michael J

2006-08-01

We present an in vivo method for analyzing the distribution kinetics of physiological markers into their respective distribution volumes utilizing information provided by the relative dispersion of transit times. Arterial concentration-time curves of markers of the vascular space [indocyanine green (ICG)], extracellular fluid (inulin), and total body water (antipyrine) measured in awake dogs under control conditions and during phenylephrine or isoproterenol infusion were analyzed by a recirculatory model to estimate the relative dispersions of transit times across the systemic and pulmonary circulation. The transit time dispersion in the systemic circulation was used to calculate the whole body distribution clearance, and an interpretation is given in terms of a lumped organ model of blood-tissue exchange. As predicted by theory, this relative dispersion increased linearly with cardiac output, with a slope that was inversely related to solute diffusivity. The relative dispersion of the flow-limited indicator antipyrine exceeded that of ICG (as a measure of intravascular mixing) only slightly and was consistent with a diffusional equilibration time in the extravascular space of approximately 10 min, except during phenylephrine infusion, which led to an anomalously high relative dispersion. A change in cardiac output did not alter the heterogeneity of capillary transit times of ICG. The results support the view that the relative dispersions of transit times in the systemic and pulmonary circulation estimated from solute disposition data in vivo are useful measures of whole body distribution kinetics of indicators and endogenous substances. This is the first model that explains the effect of flow and capillary permeability on whole body distribution of solutes without assuming well-mixed compartments.

Dispersion relation and growth in a two-stream free electron laser with helical wiggler and ion channel guiding

International Nuclear Information System (INIS)

Mehdian, Hassan; Abbasi, Negar

2008-01-01

A linear theory of two-stream free electron laser (FEL) with helical wiggler and ion channel guiding is presented. The dispersion relation is obtained with the help of fluid theory and the growth rate is analyzed through the numerical solutions. The considerable enhancement of the growth rate is demonstrated due to the two-stream instability and continuous tuning of peak growth rate ratio, two-stream FEL compared to single-stream FEL, in terms of varying the ion channel frequency is illustrated

Fickian dispersion is anomalous

Science.gov (United States)

Cushman, John H.; O'Malley, Dan

2015-12-01

The thesis put forward here is that the occurrence of Fickian dispersion in geophysical settings is a rare event and consequently should be labeled as anomalous. What people classically call anomalous is really the norm. In a Lagrangian setting, a process with mean square displacement which is proportional to time is generally labeled as Fickian dispersion. With a number of counter examples we show why this definition is fraught with difficulty. In a related discussion, we show an infinite second moment does not necessarily imply the process is super dispersive. By employing a rigorous mathematical definition of Fickian dispersion we illustrate why it is so hard to find a Fickian process. We go on to employ a number of renormalization group approaches to classify non-Fickian dispersive behavior. Scaling laws for the probability density function for a dispersive process, the distribution for the first passage times, the mean first passage time, and the finite-size Lyapunov exponent are presented for fixed points of both deterministic and stochastic renormalization group operators. The fixed points of the renormalization group operators are p-self-similar processes. A generalized renormalization group operator is introduced whose fixed points form a set of generalized self-similar processes. Power-law clocks are introduced to examine multi-scaling behavior. Several examples of these ideas are presented and discussed.

Interatomic methods for the dispersion energy derived from the adiabatic connection fluctuation-dissipation theorem

Science.gov (United States)

Tkatchenko, Alexandre; Ambrosetti, Alberto; DiStasio, Robert A.

2013-02-01

Interatomic pairwise methods are currently among the most popular and accurate ways to include dispersion energy in density functional theory calculations. However, when applied to more than two atoms, these methods are still frequently perceived to be based on ad hoc assumptions, rather than a rigorous derivation from quantum mechanics. Starting from the adiabatic connection fluctuation-dissipation (ACFD) theorem, an exact expression for the electronic exchange-correlation energy, we demonstrate that the pairwise interatomic dispersion energy for an arbitrary collection of isotropic polarizable dipoles emerges from the second-order expansion of the ACFD formula upon invoking the random-phase approximation (RPA) or the full-potential approximation. Moreover, for a system of quantum harmonic oscillators coupled through a dipole-dipole potential, we prove the equivalence between the full interaction energy obtained from the Hamiltonian diagonalization and the ACFD-RPA correlation energy. This property makes the Hamiltonian diagonalization an efficient method for the calculation of the many-body dispersion energy. In addition, we show that the switching function used to damp the dispersion interaction at short distances arises from a short-range screened Coulomb potential, whose role is to account for the spatial spread of the individual atomic dipole moments. By using the ACFD formula, we gain a deeper understanding of the approximations made in the interatomic pairwise approaches, providing a powerful formalism for further development of accurate and efficient methods for the calculation of the dispersion energy.

Does an ant-dispersed plant, Viola reichenbachiana, suffer from reduced seed dispersal under inundation disturbances?

NARCIS (Netherlands)

Prinzing, A.; Dauber, J.; Hammer, E.; Hammouti, N.; Bohning-Gaese, K.

2008-01-01

Many plant species use ants as seed dispersers. This dispersal mode is considered to be susceptible to disturbances, but the effect of natural, small-scale disturbances is still unknown. We investigated how small-scale disturbances due to inundation affect seed dispersal in Viola reichenbachiana, a

Clock synchronization and dispersion

International Nuclear Information System (INIS)

Giovannetti, Vittorio; Lloyd, Seth; Maccone, Lorenzo; Wong, Franco N C

2002-01-01

We present a method to defeat effects of dispersion of timing signals when synchronizing clocks. It is based on the recently proposed 'conveyor belt synchronization' scheme and on the quantum dispersion cancellation effect

Nozzle for electric dispersion reactor

Science.gov (United States)

Sisson, W.G.; Basaran, O.A.; Harris, M.T.

1995-11-07

A nozzle for an electric dispersion reactor includes two concentric electrodes, the inner one of the two delivering disperse phase fluid into a continuous phase fluid. A potential difference generated by a voltage source creates a dispersing electric field at the end of the inner electrode. 4 figs.

General theory of spontaneous emission near exceptional points.

Science.gov (United States)

Pick, Adi; Zhen, Bo; Miller, Owen D; Hsu, Chia W; Hernandez, Felipe; Rodriguez, Alejandro W; Soljačić, Marin; Johnson, Steven G

2017-05-29

We present a general theory of spontaneous emission at exceptional points (EPs)-exotic degeneracies in non-Hermitian systems. Our theory extends beyond spontaneous emission to any light-matter interaction described by the local density of states (e.g., absorption, thermal emission, and nonlinear frequency conversion). Whereas traditional spontaneous-emission theories imply infinite enhancement factors at EPs, we derive finite bounds on the enhancement, proving maximum enhancement of 4 in passive systems with second-order EPs and significantly larger enhancements (exceeding 400×) in gain-aided and higher-order EP systems. In contrast to non-degenerate resonances, which are typically associated with Lorentzian emission curves in systems with low losses, EPs are associated with non-Lorentzian lineshapes, leading to enhancements that scale nonlinearly with the resonance quality factor. Our theory can be applied to dispersive media, with proper normalization of the resonant modes.

Neutrality Versus Materiality: A Thermodynamic Theory of Neutral Surfaces

Directory of Open Access Journals (Sweden)

Rémi Tailleux

2016-09-01

Full Text Available In this paper, a theory for constructing quasi-neutral density variables γ directly in thermodynamic space is formulated, which is based on minimising the absolute value of a purely thermodynamic quantity J n . Physically, J n has a dual dynamic/thermodynamic interpretation as the quantity controlling the energy cost of adiabatic and isohaline parcel exchanges on material surfaces, as well as the dependence of in-situ density on spiciness, in a description of water masses based on γ, spiciness and pressure. Mathematically, minimising | J n | in thermodynamic space is showed to be equivalent to maximising neutrality in physical space. The physics of epineutral dispersion is also reviewed and discussed. It is argued, in particular, that epineutral dispersion is best understood as the aggregate effect of many individual non-neutral stirring events (being understood here as adiabatic and isohaline events with non-zero buoyancy, so that it is only the net displacement aggregated over many events that is approximately neutral. This new view resolves an apparent paradox between the focus in neutral density theory on zero-buoyancy motions and the overwhelming evidence that lateral dispersion in the ocean is primarily caused by non-zero buoyancy processes such as tides, residual currents and sheared internal waves. The efficiency by which a physical process contributes to lateral dispersion can be characterised by its energy signature, with those processes releasing available potential energy (negative energy cost being more efficient than purely neutral processes with zero energy cost. The latter mechanism occurs in the wedge of instability, and its source of energy is the coupling between baroclinicity, thermobaricity, and density compensated temperature/salinity anomalies. Such a mechanism, which can only exist in a salty ocean, is speculated to be important for dissipating spiciness anomalies and neutral helicity. The paper also discusses potential

Derivation of equations for scalar and fermion fields using properties of dispersion-codispersion operators

International Nuclear Information System (INIS)

Raoelina Andriambololona; Ranaivoson, R.T.R; Hanitriarivo, R.; Harison, V.

2014-01-01

We establish equations for scalar and fermion fields using results obtained from a study on a phase space representation of quantum theory that we have performed in a previous work. Our approaches are similar to the historical ones to obtain Klein-Gordon and Dirac equations but the main difference is that ours are based on the use of properties of operators called dispersion-codispersion operators. We begin with a brief recall about the dispersion-codispersion operators. Then, introducing a mass operator with its canonical conjugate coordinate and applying rules of quantization, based on the use of dispersion - codispersion operators , we deduce a second order differential operator relation from the relativistic expression relying energy, momentum and mass. Using Dirac matrices, we derive from this second order differential operator relation a first order one. The application of the second order differential operator relation on a scalar function gives the equation for the scalar field and the use of the first order differential operator relation leads to the equation for fermion field.

Analytical formulation of directly modulated OOFDM signals transmitted over an IM/DD dispersive link.

Science.gov (United States)

Sánchez, C; Ortega, B; Wei, J L; Tang, J; Capmany, J

2013-03-25

We provide an analytical study on the propagation effects of a directly modulated OOFDM signal through a dispersive fiber and subsequent photo-detection. The analysis includes the effects of the laser operation point and the interplay between chromatic dispersion and laser chirp. The final expression allows to understand the physics behind the transmission of a multi-carrier signal in the presence of residual frequency modulation and the description of the induced intermodulation distortion gives us a detailed insight into the diferent intermodulation products which impair the recovered signal at the receiver-end side. Numerical comparisons between transmission simulations results and those provided by evaluating the expression obtained are carried out for different laser operation points. Results obtained by changing the fiber length, laser parameters and using single mode fiber with negative and positive dispersion are calculated in order to demonstrate the validity and versatility of the theory provided in this paper. Therefore, a novel analytical formulation is presented as a versatile tool for the description and study of IM/DD OOFDM systems with variable design parameters.

A terahertz study of taurine: Dispersion correction and mode couplings

Science.gov (United States)

Dai, Zelin; Xu, Xiangdong; Gu, Yu; Li, Xinrong; Wang, Fu; Lian, Yuxiang; Fan, Kai; Cheng, Xiaomeng; Chen, Zhegeng; Sun, Minghui; Jiang, Yadong; Yang, Chun; Xu, Jimmy

2017-03-01

The low-frequency characteristics of polycrystalline taurine were studied experimentally by terahertz (THz) absorption spectroscopy and theoretically by ab initio density-functional simulations. Full optimizations with semi-empirical dispersion correction were performed in spectral computations and vibrational mode assignments. For comparison, partial optimizations with pure density functional theory were conducted in parallel. Results indicate that adding long-range dispersion correction to the standard DFT better reproduces the measured THz spectra than the popular partial optimizations. The main origins of the observed absorption features were also identified. Moreover, a coupled-oscillators model was proposed to explain the experimental observation of the unusual spectral blue-shift with the increase of temperature. Such coupled-oscillators model not only provides insights into the temperature dynamics of non-bonded interactions but also offers an opportunity to better understand the physical mechanisms behind the unusual THz spectral behaviors in taurine. Particularly, the simulation approach and novel coupled-oscillators model presented in this work are applicable to analyze the THz spectra of other molecular systems.

Do spatially-implicit estimates of neutral migration comply with seed dispersal data in tropical forests?

Directory of Open Access Journals (Sweden)

François Munoz

Full Text Available Neutral community models have shown that limited migration can have a pervasive influence on the taxonomic composition of local communities even when all individuals are assumed of equivalent ecological fitness. Notably, the spatially implicit neutral theory yields a single parameter I for the immigration-drift equilibrium in a local community. In the case of plants, seed dispersal is considered as a defining moment of the immigration process and has attracted empirical and theoretical work. In this paper, we consider a version of the immigration parameter I depending on dispersal limitation from the neighbourhood of a community. Seed dispersal distance is alternatively modelled using a distribution that decreases quickly in the tails (thin-tailed Gaussian kernel and another that enhances the chance of dispersal events over very long distances (heavily fat-tailed Cauchy kernel. Our analysis highlights two contrasting situations, where I is either mainly sensitive to community size (related to ecological drift under the heavily fat-tailed kernel or mainly sensitive to dispersal distance under the thin-tailed kernel. We review dispersal distances of rainforest trees from field studies and assess the consistency between published estimates of I based on spatially-implicit models and the predictions of the kernel-based model in tropical forest plots. Most estimates of I were derived from large plots (10-50 ha and were too large to be accounted for by a Cauchy kernel. Conversely, a fraction of the estimates based on multiple smaller plots (1 ha appeared too small to be consistent with reported ranges of dispersal distances in tropical forests. Very large estimates may reflect within-plot habitat heterogeneity or estimation problems, while the smallest estimates likely imply other factors inhibiting migration beyond dispersal limitation. Our study underscores the need for interpreting I as an integrative index of migration limitation which, besides

A simple theory of linear mode conversion

International Nuclear Information System (INIS)

Cairns, R.A.; Lashmore-Davies, C.N.; Woods, A.M.

1984-01-01

A summary is given of the basic theory of linear mode conversion involving the construction of differential equations for the mode amplitudes based on the properties of the dispersion relation in the neighbourhood of the mode conversion point. As an example the transmission coefficient for tunneling from the upper hybrid resonance through the evanescent region to the adjacent cut-off is treated. 7 refs, 3 figs

Theory of the spontaneous condensation of steam during expansion

International Nuclear Information System (INIS)

Kleitz, Alain

1978-01-01

When steam expands in a nozzle or turbine, it cools and, at a certain pressure level, the saturation limit is exceeded. The appearance of moisture does not comply with the simple laws of thermodynamic balance. The liquid phase appears only as from a certain sub-cooling of the steam, at which stage it forms suddenly as a finely dispersed mist. On the basis of the kinetic theory of gases and the critical radius concept, Oswatitch produced a theory on spontaneous condensation which was checked by tests in nozzles. On the other hand, this theory does not fully explain that which is observed in turbines or manifolds fed with fluids other than steam. Modifications have been made to the conventional theory in an endeavour to corroborate the experimental results [fr

3D Printed Prisms with Tunable Dispersion for the THz Frequency Range

Science.gov (United States)

Busch, Stefan F.; Castro-Camus, Enrique; Beltran-Mejia, Felipe; Balzer, Jan C.; Koch, Martin

2018-06-01

Here, we present a 3D printed prism for THz waves made out of an artificial dielectric material in which the dispersion can be tuned by external compression. The artificial material consists of thin dielectric layers with variable air spacings which has been produced using a fused deposition molding process. The material properties are carefully characterized and the functionality of the prisms is in a good agreement with the underlying theory. These prisms are durable, lightweight, inexpensive, and easy to produce.

3D Printed Prisms with Tunable Dispersion for the THz Frequency Range

Science.gov (United States)

Busch, Stefan F.; Castro-Camus, Enrique; Beltran-Mejia, Felipe; Balzer, Jan C.; Koch, Martin

2018-04-01

Here, we present a 3D printed prism for THz waves made out of an artificial dielectric material in which the dispersion can be tuned by external compression. The artificial material consists of thin dielectric layers with variable air spacings which has been produced using a fused deposition molding process. The material properties are carefully characterized and the functionality of the prisms is in a good agreement with the underlying theory. These prisms are durable, lightweight, inexpensive, and easy to produce.

Determination of dispersity of crushed granite

International Nuclear Information System (INIS)

Liu Dejun; Fan Xianhua; Zhang Yingjie; Yao Jun; Zhou Duo; Wang Yong

2004-01-01

The experimental crushed granite column breakthrough curves, using 99 Tc as spike tracer and 3 H as invariant tracer, are analyzed by different linear regression techniques. Dispersity of crushed granite and retardation factor of 99 TcO 4 - on the crushed granite are determined simultaneously by one linear regression technique. Dispersity of crushed granite is also obtained with 3 H as invariant tracer by the other linear regression technique. The dispersities found by spike source and invariant source methods are compared. The experimental results show that the dispersity found by spike source method is close to that found by invariant source method. It indicates that dispersity is only the characteristic of dispersion medium

Determination of dispersity of crushed granite

International Nuclear Information System (INIS)

Liu, D.J.; Fan, X.H.

2005-01-01

Experimental crushed granite column breakthrough curves, using 99 Tc as spike tracer and 3 H as invariant tracer, were analyzed by different linear regression techniques. Dispersity of crushed granite and the retardation factor of 99 TcO 4 - on the crushed granite were determined simultaneously by one linear regression. Dispersity of crushed granite was also obtained with 3 H as invariant tracer by the other linear regression. The dispersities found by spike source and invariant source methods are compared. Experimental results show that the dispersity found by the spike source method is close to that found by the invariant source method. This indicates that dispersity is only a characteristic of the dispersion medium. (author)

Towards an improved continuum theory for phase transformations

International Nuclear Information System (INIS)

Tijssens, M.G.A.; James, R.D.

2003-01-01

We develop a continuum theory for martensitic phase transformations in which explicit use is made of atomistic calculations based on density functional theory. Following the work of Rabe and coworkers, branches of the phonon-dispersion relation with imaginary frequencies are selected to construct a localized basis tailored to the symmetry of the crystal lattice. This so-called Wannier basis helps to construct an effective Hamiltonian of a particularly simple form. We extend the methodology by incorporating finite deformations and passing the effective Hamiltonian fully to continuum level. The developments so far are implemented on the shape memory material NiTi

Quantization of Space-like States in Lorentz-Violating Theories

Science.gov (United States)

Colladay, Don

2018-01-01

Lorentz violation frequently induces modified dispersion relations that can yield space-like states that impede the standard quantization procedures. In certain cases, an extended Hamiltonian formalism can be used to define observer-covariant normalization factors for field expansions and phase space integrals. These factors extend the theory to include non-concordant frames in which there are negative-energy states. This formalism provides a rigorous way to quantize certain theories containing space-like states and allows for the consistent computation of Cherenkov radiation rates in arbitrary frames and avoids singular expressions.

Dispersive shock waves in systems with nonlocal dispersion of Benjamin-Ono type

Science.gov (United States)

El, G. A.; Nguyen, L. T. K.; Smyth, N. F.

2018-04-01

We develop a general approach to the description of dispersive shock waves (DSWs) for a class of nonlinear wave equations with a nonlocal Benjamin-Ono type dispersion term involving the Hilbert transform. Integrability of the governing equation is not a pre-requisite for the application of this method which represents a modification of the DSW fitting method previously developed for dispersive-hydrodynamic systems of Korteweg-de Vries (KdV) type (i.e. reducible to the KdV equation in the weakly nonlinear, long wave, unidirectional approximation). The developed method is applied to the Calogero-Sutherland dispersive hydrodynamics for which the classification of all solution types arising from the Riemann step problem is constructed and the key physical parameters (DSW edge speeds, lead soliton amplitude, intermediate shelf level) of all but one solution type are obtained in terms of the initial step data. The analytical results are shown to be in excellent agreement with results of direct numerical simulations.

Meteorological perspective on intermediate range atmospheric dispersion

International Nuclear Information System (INIS)

Van der Hoven, I.

1981-01-01

The intermediate range of atmospheric transport and diffusion is defined as those dispersion processes which take place at downwind distances of 10 to 100 kilometers from pollutant sources. Meteorologists often define this range as the mesoscale. It is the range of distances where certain environmental assessments are of concern such as the determination of significant deterioration of visibility, the effect of effluent releases from tall stacks, and the effect of pollutant sources in rural settings upon the more distant urban centers. Atmospheric diffusion theory is based on steady state conditions and spatial homogeniety. Techniques must be developed to measure the inhomogenieties, models must be devised to account for the complexities, and a data base consisting of appropriate measured meteorological parameters concurrent with tracer gas concentrations should be collected

Optimizing optical pre-dispersion using transmit DSP for mitigation of Kerr nonlinearities in dispersion managed cables

Science.gov (United States)

Hopkins, James; Gaudette, Jamie; Mehta, Priyanth

2013-10-01

With the advent of digital signal processing (DSP) in optical transmitters and receivers, the ability to finely tune the ratio of pre and post dispersion compensation can be exploited to best mitigate the nonlinear penalties caused by the Kerr effect. A portion of the nonlinear penalty in optical communication channels has been explained by an increase in peak to average power ratio (PAPR) inherent in highly dispersed signals. The standard approach for minimizing these impairments applies 50% pre dispersion compensation and 50% post dispersion compensation, thereby decreasing average PAPR along the length of the cable, as compared with either 100% pre or post dispersion compensation. In this paper we demonstrate that simply considering the net accumulated dispersion, and applying 50/50 pre/post dispersion is not necessarily the best way to minimize PAPR and subsequent Kerr nonlinearities. Instead, we consider the cumulative dispersion along the entire length of the cable, and, taking into account this additional information, derive an analytic formula for the minimization of PAPR. Alignment with simulation and experimental measurements is presented using a commercially available 100Gb/s dual-polarization binary phase-shift-keying (DP-BPSK) coherent modem, with transmitter and receiver DSP. Measurements are provided from two different 5000km dispersion managed Submarine test-beds, as well as a 3800km terrestrial test-bed with a mixture of SMF-28 and TWRS optical fiber. This method is shown to deviate significantly from the conventional 50/50 method described above, in dispersion managed communications systems, and more closely aligns with results obtained from simulation and data collected from laboratory test-beds.

Existence and switching behavior of bright and dark Kerr solitons in whispering-gallery mode resonators with zero group-velocity dispersion

Science.gov (United States)

Talla Mbé, Jimmi H.; Milián, Carles; Chembo, Yanne K.

2017-07-01

We use the generalized Lugiato-Lefever model to investigate the phenomenon of Kerr optical frequency comb generation when group-velocity dispersion is null. In that case, the first dispersion term that plays a leading role is third-order dispersion. We show that this term is sufficient to allow for the existence of both bright and dark solitons. We identify the areas in the parameter space where both kind of solitons can be excited inside the resonator. We also unveil a phenomenon of hysteretic switching between these two types of solitons when the power of the pump laser is cyclically varied. Contribution to the Topical Issue "Theory and Applications of the Lugiato-Lefever Equation", edited by Yanne K. Chembo, Damia Gomila, Mustapha Tlidi, Curtis R. Menyuk.

Validation of molecular crystal structures from powder diffraction data with dispersion-corrected density functional theory (DFT-D).

Science.gov (United States)

van de Streek, Jacco; Neumann, Marcus A

2014-12-01

In 2010 we energy-minimized 225 high-quality single-crystal (SX) structures with dispersion-corrected density functional theory (DFT-D) to establish a quantitative benchmark. For the current paper, 215 organic crystal structures determined from X-ray powder diffraction (XRPD) data and published in an IUCr journal were energy-minimized with DFT-D and compared to the SX benchmark. The on average slightly less accurate atomic coordinates of XRPD structures do lead to systematically higher root mean square Cartesian displacement (RMSCD) values upon energy minimization than for SX structures, but the RMSCD value is still a good indicator for the detection of structures that deserve a closer look. The upper RMSCD limit for a correct structure must be increased from 0.25 Å for SX structures to 0.35 Å for XRPD structures; the grey area must be extended from 0.30 to 0.40 Å. Based on the energy minimizations, three structures are re-refined to give more precise atomic coordinates. For six structures our calculations provide the missing positions for the H atoms, for five structures they provide corrected positions for some H atoms. Seven crystal structures showed a minor error for a non-H atom. For five structures the energy minimizations suggest a higher space-group symmetry. For the 225 SX structures, the only deviations observed upon energy minimization were three minor H-atom related issues. Preferred orientation is the most important cause of problems. A preferred-orientation correction is the only correction where the experimental data are modified to fit the model. We conclude that molecular crystal structures determined from powder diffraction data that are published in IUCr journals are of high quality, with less than 4% containing an error in a non-H atom.

Increases of QT dispersion, corrected QT dispersion and QT interval in young healthy individuals during Ramadan fasting

Directory of Open Access Journals (Sweden)

Moradmand S

2003-06-01

Full Text Available Ramadan fasting is one of the most important religious duties of Muslims, that its effect on the heart has not been determined yet. Our objective was to evaluate the effect of Ramadan fasting on ventricular repolarization as assessed by QT interval, corrected QT interval, QT dispersion or corrected QT dispersion. Sixthy healthy subjects aged 20 to 35 years were dispersion included in this study. QT interval, corrected QT interval (QTc QT dispersion QTc dispersion, RR interval and QRS axis were measured in 12-lead surface electrocardiogram, once during fasting (10 to 11.5 hours of absolute fasting from food and liquid and another time, 15 tp 60 minutes after eating food at sunset, All of the subjects had been fasting 11 to 12 hours each day at least for 25 days during Ramadan. The study was performed at Amir Alam hospital in the year 2000. Maximal QT interval, mean QT interval and RR-interval, were longer during fasting (P<0.05, and both QT dispersion and QTc dispersion were increased (P<0.05. (QT dispersion: mean ±SD= 57.2±20.1 ms during fasting Vs 41.6±15.1 ms after meal, QTc dispersion=75.4±24.6 ms during fasting Vs 64.1±22.8 ms after meal. But mean QTc interval maximal QTc interval and QRS axis showed no significant difference. Prolongation of QT interval and RR interval during fasting, instead of no significant changes in corrected QT interval may primarily suggest that prolongation of RR-interval causes QTc interval not to have significant difference. But increases of QT dispersion and corrected QT dispersion (QTc dispersion during fasting -that are more reliable indicators of ventricular repolarization-support the idea that ventricular repolarization may be changed during Ramadan fasting. QT dispersion in cardiac patients is showed to increase from normal values of 30-40 to 64-138 ms, but in our study their increases did not reach critical value.

Investigation of Monodisperse Dendrimeric Polysaccharide Nanoparticle Dispersions Using Small Angle Neutron Scattering

Science.gov (United States)

Atkinson, John; Nickels, Jonathan; Papp-Szabo, Erzsi; Katsaras, John; Dutcher, John

2015-03-01

Phytoglycogen is a highly branched polysaccharide that is very similar to the energy storage molecule glycogen. We have isolated monodisperse phytoglycogen nanoparticles from corn and these particles are attractive for applications in the cosmetic, food and beverage, and biomedical industries. Many of these promising applications are due to the special interaction between the nanoparticles and water, which results in: (1) high solubility; (2) low viscosity and high stability in aqueous dispersions; and (3) a remarkable capacity to sequester and retain water. Our rheology measurements indicate that the nanoparticles behave like hard spheres in water, with the viscosity diverging for concentrations >25% (w/w). Because of this, aqueous suspensions of phytoglycogen provide an ideal platform for detailed testing of theories of colloidal glasses and jamming. To further explore the interaction of the phytoglycogen particles and water, we have performed small angle neutron scattering (SANS) measurements on the Extended Q-Range SANS (EQ-SANS) diffractometer at the Spallation Neutron Source at Oak Ridge National Laboratory. Measurements performed on phytoglycogen dispersions in mixtures of hydrogenated and deuterated water have allowed us to determine the particle size and average particle spacing as a function of the phytoglycogen concentration in the limits of dilute and concentrated dispersions.

Many-body dispersion effects in the binding of adsorbates on metal surfaces

Energy Technology Data Exchange (ETDEWEB)

Maurer, Reinhard J. [Department of Chemistry, Yale University, New Haven, Connecticut 06520 (United States); Ruiz, Victor G.; Tkatchenko, Alexandre [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin (Germany)

2015-09-14

A correct description of electronic exchange and correlation effects for molecules in contact with extended (metal) surfaces is a challenging task for first-principles modeling. In this work, we demonstrate the importance of collective van der Waals dispersion effects beyond the pairwise approximation for organic–inorganic systems on the example of atoms, molecules, and nanostructures adsorbed on metals. We use the recently developed many-body dispersion (MBD) approach in the context of density-functional theory [Tkatchenko et al., Phys. Rev. Lett. 108, 236402 (2012) and Ambrosetti et al., J. Chem. Phys. 140, 18A508 (2014)] and assess its ability to correctly describe the binding of adsorbates on metal surfaces. We briefly review the MBD method and highlight its similarities to quantum-chemical approaches to electron correlation in a quasiparticle picture. In particular, we study the binding properties of xenon, 3,4,9,10-perylene-tetracarboxylic acid, and a graphene sheet adsorbed on the Ag(111) surface. Accounting for MBD effects, we are able to describe changes in the anisotropic polarizability tensor, improve the description of adsorbate vibrations, and correctly capture the adsorbate–surface interaction screening. Comparison to other methods and experiment reveals that inclusion of MBD effects improves adsorption energies and geometries, by reducing the overbinding typically found in pairwise additive dispersion-correction approaches.

Real-time frequency-to-time mapping based on spectrally-discrete chromatic dispersion.

Science.gov (United States)

Dai, Yitang; Li, Jilong; Zhang, Ziping; Yin, Feifei; Li, Wangzhe; Xu, Kun

2017-07-10

Traditional photonics-assisted real-time Fourier transform (RTFT) usually suffers from limited chromatic dispersion, huge volume, or large time delay and attendant loss. In this paper we propose frequency-to-time mapping (FTM) by spectrally-discrete dispersion to increase frequency sensitivity greatly. The novel media has periodic ON/OFF intensity frequency response while quadratic phase distribution along disconnected channels, which de-chirps matched optical input to repeated Fourier-transform-limited output. Real-time FTM is then obtained within each period. Since only discrete phase retardation rather than continuously-changed true time delay is required, huge equivalent dispersion is then available by compact device. Such FTM is theoretically analyzed, and implementation by cascaded optical ring resonators is proposed. After a numerical example, our theory is demonstrated by a proof-of-concept experiment, where a single loop containing 0.5-meters-long fiber is used. FTM under 400-MHz unambiguous bandwidth and 25-MHz resolution is reported. Highly-sensitive and linear mapping is achieved with 6.25 ps/MHz, equivalent to ~4.6 × 10 4 -km standard single mode fiber. Extended instantaneous bandwidth is expected by ring cascading. Our proposal may provide a promising method for real-time, low-latency Fourier transform.

Dispersion Distance and the Matter Distribution of the Universe in Dispersion Space.

Science.gov (United States)

Masui, Kiyoshi Wesley; Sigurdson, Kris

2015-09-18

We propose that "standard pings," brief broadband radio impulses, can be used to study the three-dimensional clustering of matter in the Universe even in the absence of redshift information. The dispersion of radio waves as they travel through the intervening plasma can, like redshift, be used as a cosmological distance measure. Because of inhomogeneities in the electron density along the line of sight, dispersion is an imperfect proxy for radial distance and we show that this leads to calculable dispersion-space distortions in the apparent clustering of sources. Fast radio bursts (FRBs) are a new class of radio transients that are the prototypical standard ping and, due to their high observed dispersion, have been interpreted as originating at cosmological distances. The rate of fast radio bursts has been estimated to be several thousand over the whole sky per day and, if cosmological, the sources of these events should trace the large-scale structure of the Universe. We calculate the dispersion-space power spectra for a simple model where electrons and FRBs are biased tracers of the large-scale structure of the Universe, and we show that the clustering signal could be measured using as few as 10 000 events. Such a survey is in line with what may be achieved with upcoming wide-field radio telescopes.

Density fluctuation in a screened Coulombic colloid dispersion: comparison of the liquid and cubic phases of lipid A-diphosphate

International Nuclear Information System (INIS)

Brown, Helen; Ross, D. Keith; Paradies, Henrich H.

2004-01-01

Light-, small-angle X-ray and neutron scattering measurements of the dynamic structure factor S(Q,t) of strong interacting dispersions of lipid A-diphosphate were recorded and analysed applying existing models of liquid state theory. Lipid A-diphosphate ordering was observed at low volume fractions (phi=2.2x10 -4 ) and at very low ionic strength (I=10 -5 M). Upon increasing the particle number density of lipid A-diphosphate a transformation of the lattices of the colloidal crystals from a BCC lattice (a=36.20 nm) to a FCC lattice (a=57.30 nm) occurred. This strongly suggests a similarity in the preformed liquid structure and the cubic colloidal phase. The fit of both S eff (Q) and the principle peak I p (Q) with the effective particle charge supports of the main conclusions drawn from the SANS experiments and the liquid state theory indicating the presence of long-range order for the dispersions of lipid A-diphosphate

Normal-dispersion microresonator Kerr frequency combs

Directory of Open Access Journals (Sweden)

Xue Xiaoxiao

2016-06-01

Full Text Available Optical microresonator-based Kerr frequency comb generation has developed into a hot research area in the past decade. Microresonator combs are promising for portable applications due to their potential for chip-level integration and low power consumption. According to the group velocity dispersion of the microresonator employed, research in this field may be classified into two categories: the anomalous dispersion regime and the normal dispersion regime. In this paper, we discuss the physics of Kerr comb generation in the normal dispersion regime and review recent experimental advances. The potential advantages and future directions of normal dispersion combs are also discussed.

Dispersion modeling by kinematic simulation: Cloud dispersion model

International Nuclear Information System (INIS)

Fung, J C H; Perkins, R J

2008-01-01

A new technique has been developed to compute mean and fluctuating concentrations in complex turbulent flows (tidal current near a coast and deep ocean). An initial distribution of material is discretized into any small clouds which are advected by a combination of the mean flow and large scale turbulence. The turbulence can be simulated either by kinematic simulation (KS) or direct numerical simulation. The clouds also diffuse relative to their centroids; the statistics for this are obtained from a separate calculation of the growth of individual clouds in small scale turbulence, generated by KS. The ensemble of discrete clouds is periodically re-discretized, to limit the size of the small clouds and prevent overlapping. The model is illustrated with simulations of dispersion in uniform flow, and the results are compared with analytic, steady state solutions. The aim of this study is to understand how pollutants disperses in a turbulent flow through a numerical simulation of fluid particle motion in a random flow field generated by Fourier modes. Although this homogeneous turbulent is rather a 'simple' flow, it represents a building block toward understanding pollutant dispersion in more complex flow. The results presented here are preliminary in nature, but we expect that similar qualitative results should be observed in a genuine turbulent flow.

Hydrodynamic dispersion in a combined magnetohydrodynamic- electroosmotic-driven flow through a microchannel with slowly varying wall zeta potentials

Science.gov (United States)

Vargas, C.; Arcos, J.; Bautista, O.; Méndez, F.

2017-09-01

The effective dispersion coefficient of a neutral solute in the combined electroosmotic (EO) and magnetohydrodynamic (MHD)-driven flow of a Newtonian fluid through a parallel flat plate microchannel is studied. The walls of the microchannel are assumed to have modulated and low zeta potentials that vary slowly in the axial direction in a sinusoidal manner. The flow field required to obtain the dispersion coefficient is solved using the lubrication approximation theory. The solution of the electrical potential is based on the Debye-Hückel approximation for a symmetric (Z :Z ) electrolyte solution. The EO and MHD effects, together with the variations in the zeta potentials of the walls, are observed to notably modify the axial distribution of the effective dispersion coefficient. The problem is formulated for two cases of the zeta potential function. Note that the dispersion coefficient primarily depends on the Hartmann number, on the ratio of the half height of the microchannel to the Debye length, and on the assumed variation in the zeta potentials of the walls.

Energy dispersion of x-ray continua in the energy range 9kev to 19kev refraction on Si wafers

International Nuclear Information System (INIS)

Ebel, H.; Streli, C.; Pepponi, G.; Wobrauschek, P.

2000-01-01

Total reflection of x-rays in matter at given grazing incidence angle is characterized by the occurrence of an energy cut-off. Photons with energies greater than the cut-off energy penetrate into matter and are refracted according to a transition from the optically more dense to the optically less dense medium. Since the refractive index depends on photon energy, an energy dispersion of continuous x-radiation is observed. The present investigation is dedicated to the energy dispersion of continuous x-radiation (Mo, 45 kV) by Si wafers. Theory and experimental results are in excellent agreement. (author)

UV curable aqueous dispersions for wood coatings

International Nuclear Information System (INIS)

Peeters, S.; Bleus, J.P.; Wang, Z.J.; Arceneaux, J. A.; Hall, J.

1999-01-01

In this paper the characterisation of aqueous dispersions of UV curable resins is described. Two types of dispersions were used: dispersions that are tacky after water evaporation and tack - free before cure dispersions. The physical and rheological properties of these products have been determined and the performance of these dispersions in various formulations, especially for wood applications has been studied. With these dispersions, it is possible to produce coatings having a good cure speed, good surface hardness and good solvent -, chemical - and water resistance

Dispersion in cylindrical channels on the laminar flow at low Fourier numbers.

Science.gov (United States)

Kucza, Witold; Dąbrowa, Juliusz; Nawara, Katarzyna

2015-06-30

A numerical solution of the uniform dispersion model in cylindrical channels at low Fourier numbers is presented. The presented setup allowed to eliminate experimental non-idealities interfering the laminar flow. Double-humped responses measured in a flow injection system with impedance detection agreed with those predicted by theory. Simulated concentration profiles as well as flow injection analysis (FIA) responses show the predictive and descriptive power of the numerical approach. A strong dependence of peak shapes on Fourier numbers, at its low values, makes the approach suitable for determination of diffusion coefficients. In the work, the uniform dispersion model coupled with the Levenberg-Marquardt method of optimization allowed to determine the salt diffusion coefficient for KCl, NaCl, KMnO4 and CuSO4 in water. The determined values (1.83, 1.53, 1.57 and 0.90)×10(-9)m(2)s(-1), respectively, agree well with the literature data. Copyright © 2015 Elsevier B.V. All rights reserved.

Dispersive shock waves in Bose-Einstein condensates and nonlinear nano-oscillators in ferromagnetic thin films

Science.gov (United States)

Hoefer, Mark A.

This thesis examines nonlinear wave phenomena, in two physical systems: a Bose-Einstein condensate (BEC) and thin film ferromagnets where the magnetization dynamics are excited by the spin momentum transfer (SMT) effect. In the first system, shock waves generated by steep gradients in the BEC wavefunction are shown to be of the disperse type. Asymptotic and averaging methods are used to determine shock speeds and structure in one spatial dimension. These results are compared with multidimensional numerical simulations and experiment showing good, qualitative agreement. In the second system, a model of magnetization dynamics due to SMT is presented. Using this model, nonlinear oscillating modes---nano-oscillators---are found numerically and analytically using perturbative methods. These results compare well with experiment. A Bose-Einstein condensate (BEC) is a quantum fluid that gives rise to interesting shock wave nonlinear dynamics. Experiments depict a BEC that exhibits behavior similar to that of a shock wave in a compressible gas, e.g. traveling fronts with steep gradients. However, the governing Gross-Pitaevskii (GP) equation that describes the mean field of a BEC admits no dissipation hence classical dissipative shock solutions do not explain the phenomena. Instead, wave dynamics with small dispersion is considered and it is shown that this provides a mechanism for the generation of a dispersive shock wave (DSW). Computations with the GP equation are compared to experiment with excellent agreement. A comparison between a canonical 1D dissipative and dispersive shock problem shows significant differences in shock structure and shock front speed. Numerical results associated with laboratory experiments show that three and two-dimensional approximations are in excellent agreement and one dimensional approximations are in qualitative agreement. The interaction of two DSWs is investigated analytically and numerically. Using one dimensional DSW theory it is argued

Reactimeter dispersion equation

OpenAIRE

A.G. Yuferov

2016-01-01

The aim of this work is to derive and analyze a reactimeter metrological model in the form of the dispersion equation which connects reactimeter input/output signal dispersions with superimposed random noise at the inlet. It is proposed to standardize the reactimeter equation form, presenting the main reactimeter computing unit by a convolution equation. Hence, the reactimeter metrological characteristics are completely determined by this unit hardware function which represents a transient re...

Solitons in plasma and other dispersive media

International Nuclear Information System (INIS)

Ichikawa, Y.H.; Wadati, Miki.

1977-03-01

A review is given to recent development of extensive studies of nonlinear waves with purpose of showing methods of systematic analysis of nonlinear phenomena has been now established on the basis of new concept ''soliton''. Firstly, characteristic properties of various kinds of solitons are discussed with illustration of typical nonlinear evolution equations. Brief discussions are also given to basic mechanisms which ensure the remarkable stability and individuality of solitons. The reductive perturbation theory is a key method to reduce a given nonlinear system to a soliton system. Introductory survey is presented for an example of ionic mode in plasmas, although the method can be applied to any dispersive medium. Central subject of the present review is the analytical methods of solving nonlinear evolution equations. The inverse method, the Beacklund transformation and the conservation laws are discussed to emphasize that very firm analytical basis is now available to disentangle the nonlinear problems. Finally, a notion of ''dressed'' solitons is introduced on basis of the higher order analysis of the reductive perturbation theory. In spite of the fact that success is restricted so far only for the one dimensional system, the achievement of soliton physics encourages us to face dawn of nonlinear physics with a confident expectation for forthcoming break through in the field. (auth.)

Dispersal and biogeography of silica-scaled chrysophytes

DEFF Research Database (Denmark)

Kristiansen, Jørgen

2008-01-01

The silica-scaled chrysophytes—here mainly represented by the freshwater genera Mallomonas and Synura—have special problems in dispersal from one habitat to another because they cannot tolerate desiccation. Their dispersal is limited by the fragile construction and aquatic habit. Dispersal from one...... water body to another involves dangerous changes of the environment, and the ability to avoid desiccation during transport is crucial. So, air-borne and ectozoic dispersal by birds or mammals can only work at short distances. This danger may be avoided by endozoic dispersal of thick-walled cysts; as far....... The distribution of a species at a given time depends on several factors: dispersal capacity—available vectors—suitable available habitats—and most important: sufficient time for dispersal. It is remarkable that the chrysophytes—in spite of their fragile cell construction and apparently low dispersal capacity...

Nature of the Schwinger term in spinor electrodynamics. [Dispersion formulation,dimensions,green functions,c-number,linear unitarity condition

Energy Technology Data Exchange (ETDEWEB)

Nishijima, K; Sasaki, R [Tokyo Univ. (Japan). Dept. of Physics

1975-06-01

On the basis of the dispersion formulation of field theories the Schwinger term in spinor electrodynamics is shown to be a c-number. The essence of the proof consists in the dimensional argument and the characteristic features of the linear unitarity condition for a set of Green's functions involving the Schwinger term.

Primary assembly of soil communities: disentangling the effect of dispersal and local environment.

Science.gov (United States)

Ingimarsdóttir, María; Caruso, Tancredi; Ripa, Jörgen; Magnúsdóttir, Olöf Birna; Migliorini, Massimo; Hedlund, Katarina

2012-11-01

It has long been recognised that dispersal abilities and environmental factors are important in shaping invertebrate communities, but their relative importance for primary soil community assembly has not yet been disentangled. By studying soil communities along chronosequences on four recently emerged nunataks (ice-free land in glacial areas) in Iceland, we replicated environmental conditions spatially at various geographical distances. This allowed us to determine the underlying factors of primary community assembly with the help of metacommunity theories that predict different levels of dispersal constraints and effects of the local environment. Comparing community assembly of the nunataks with that of non-isolated deglaciated areas indicated that isolation of a few kilometres did not affect the colonisation of the soil invertebrates. When accounting for effects of geographical distances, soil age and plant richness explained a significant part of the variance observed in the distribution of the oribatid mites and collembola communities, respectively. Furthermore, null model analyses revealed less co-occurrence than expected by chance and also convergence in the body size ratio of co-occurring oribatids, which is consistent with species sorting. Geographical distances influenced species composition, indicating that the community is also assembled by dispersal, e.g. mass effect. When all the results are linked together, they demonstrate that local environmental factors are important in structuring the soil community assembly, but are accompanied with effects of dispersal that may "override" the visible effect of the local environment.

Dynamics of Dispersive Wave Generation in Gas-Filled Photonic Crystal Fiber with the Normal Dispersion

Directory of Open Access Journals (Sweden)

Zhixiang Deng

2017-01-01

Full Text Available The absence of Raman and unique pressure-tunable dispersion is the characteristic feature of gas-filled photonic crystal fiber (PCF, and its zero dispersion points can be extended to the near-infrared by increasing gas pressure. The generation of dispersive wave (DW in the normal group velocity dispersion (GVD region of PCF is investigated. It is demonstrated that considering the self-steepening (SS and introducing the chirp of the initial input pulse are two suitable means to control the DW generation. The SS enhances the relative average intensity of blue-shift DW while weakening that of red-shift DW. The required propagation distance of DW emission is markedly varied by introducing the frequency chirp. Manipulating DW generation in gas-filled PCF by the combined effects of either SS or chirp and three-order dispersion (TOD provides a method for a concentrated transfer of energy into the targeted wavelengths.

Oak Dispersal Syndromes: Do Red and White Oaks Exhibit Different Dispersal Srategies?

Science.gov (United States)

Michael Steele; Peter Smallwood; William B. Terzaghi; John E. Carlson; Thomas conteras; Amy McEuen

2004-01-01

We provide an overview of the ecological and evolutionary interactions between oaks and several of their dispersal agents, and review a series of studies that demonstrate how various acorn characteristics affect feeding and caching decisions of these animals, which in turn may influence oak dispersal and establishment. We demonstrate that acorns of red oak species show...

The dispersion of SWCNTs treated by coupling and dispersing agents in fiber reinforced polymer composities

Science.gov (United States)

Duan, Yuexin; Yuan, Lu; Zhao, Yan; Guan, Fengxia

2007-07-01

It is an obstacle issue for Carbon nanotubes (CNTs) applied in fiber reinforced polymer composites that CNTs is dispersed in nano-level, particularly for single-wall Carbon nanotubes (SWCNTs). In this paper, SWCNTs were treated by the coupling agent like volan and dispersing agent as BYK to improve the dispersion in the Glass Fiber/Epoxy composites. The result of dispersion of SWCNTs in composites was observed by Scanning electron microscopy (SEM). Then the Glass Transition Temperature (Tg) of these kinds of composites with treated and untreated SWCNTs were obtained by Dynamic Mechanical Thermal Analysis (DMTA). Moreover, the bending properties of these composites were tested.

Symmetry-adapted perturbation theory interaction energy decomposition for some noble gas complexes

Science.gov (United States)

Cukras, Janusz; Sadlej, Joanna

2008-06-01

This Letter contains a study of the interaction energy in HArF⋯N 2 and HArF⋯P 2 complexes. Symmetry-adapted perturbation theory (SAPT) has been applied to analyze the electrostatic, induction, dispersion and exchange contributions to the total interaction energy. The interaction energy has also been obtained by supermolecular method at the MP2, MP4, CCSD, CCSD(T) levels. The interaction energy for the studied complexes results from a partial cancelation of large attractive electrostatic, induction, dispersion terms by a strong repulsive exchange contribution. The induction and dispersion effects proved to be crucial in establishing the preference for the colinear HArF⋯N 2 and HArF⋯P 2 structures and shift direction of νHAr stretching vibrations.

The Mean and Scatter of the Velocity Dispersion-Optical Richness Relation for MaxBCG Galaxy Clusters

Energy Technology Data Exchange (ETDEWEB)

Becker, M.R.; McKay, T.A.; /Michigan U.; Koester, B.; /Chicago U., Astron. Astrophys. Ctr.; Wechsler, R.H.; /KIPAC, Menlo Park /SLAC /Stanford U., Phys. Dept.; Rozo, E.; /Ohio State U.; Evrard, A.; /Michigan U. /Michigan U., MCTP; Johnston, D.; /Caltech, JPL; Sheldon, E.; /New York U.; Annis, J.; /Fermilab; Lau, E.; /Chicago U., Astron. Astrophys. Ctr.; Nichol, R.; /Portsmouth U., ICG; Miller, C.; /Michigan U.

2007-06-05

The distribution of galaxies in position and velocity around the centers of galaxy clusters encodes important information about cluster mass and structure. Using the maxBCG galaxy cluster catalog identified from imaging data obtained in the Sloan Digital Sky Survey, we study the BCG--galaxy velocity correlation function. By modeling its non-Gaussianity, we measure the mean and scatter in velocity dispersion at fixed richness. The mean velocity dispersion increases from 202 {+-} 10 km s{sup -1} for small groups to more than 854 {+-} 102 km s{sup -1} for large clusters. We show the scatter to be at most 40.5{+-}3.5%, declining to 14.9{+-}9.4% in the richest bins. We test our methods in the C4 cluster catalog, a spectroscopic cluster catalog produced from the Sloan Digital Sky Survey DR2 spectroscopic sample, and in mock galaxy catalogs constructed from N-body simulations. Our methods are robust, measuring the scatter to well within one-sigma of the true value, and the mean to within 10%, in the mock catalogs. By convolving the scatter in velocity dispersion at fixed richness with the observed richness space density function, we measure the velocity dispersion function of the maxBCG galaxy clusters. Although velocity dispersion and richness do not form a true mass--observable relation, the relationship between velocity dispersion and mass is theoretically well characterized and has low scatter. Thus our results provide a key link between theory and observations up to the velocity bias between dark matter and galaxies.

Harmonization of French and German calculation procedures for atmospheric dispersion following accidental releases from nuclear power plants

International Nuclear Information System (INIS)

Crabol, B.; Romeo, E.; Nester, K.

1992-01-01

In case of an accident in a nuclear power plant near the French-German border different schemes for dispersion calculations in both countries will currently be applied. An intercomparison of these schemes initiated from the German-French Commission for the safety of nuclear installations (DFK) revealed in some meteorological situations large differences in the resulting concentrations for radionuclides. An ad hoc working group was installed by the DFK with the mandate to analyse the reasons for the different model results and also to consider new theoretical concepts. The working group has agreed to apply a Gaussian puff model for emergency response calculations. The results of the model based on turbulence parameterization via similarity approach or spectral theory - have been compared with tracer experiments for different emission heights and atmospheric stability regimes. As a reference the old modelling approaches have been included in the study. The simulations with the similarity approach and the spectral theory show a slightly better agreement to the measured concentration data than the schemes used in the past. Instead of diffusion categories both new approaches allow a continuous characterization of the atmospheric dispersion conditions. Because the spectral approach incorporates the sampling time of the meteorological data as an adjustable parameter thereby offering the possibility to adjust the dispersion model to different emission scenarios this turbulence parameterization scheme will be foreseen as the basis for a joint French-German puff model

Extragalactic dispersion measures of fast radio bursts

International Nuclear Information System (INIS)

Xu, Jun; Han, J. L.

2015-01-01

Fast radio bursts show large dispersion measures, much larger than the Galactic dispersion measure foreground. Therefore, they evidently have an extragalactic origin. We investigate possible contributions to the dispersion measure from host galaxies. We simulate the spatial distribution of fast radio bursts and calculate the dispersion measures along the sightlines from fast radio bursts to the edge of host galaxies by using the scaled NE2001 model for thermal electron density distributions. We find that contributions to the dispersion measure of fast radio bursts from the host galaxy follow a skew Gaussian distribution. The peak and the width at half maximum of the dispersion measure distribution increase with the inclination angle of a spiral galaxy, to large values when the inclination angle is over 70°. The largest dispersion measure produced by an edge-on spiral galaxy can reach a few thousand pc cm −3 , while the dispersion measures from dwarf galaxies and elliptical galaxies have a maximum of only a few tens of pc cm −3 . Notice, however, that additional dispersion measures of tens to hundreds of pc cm −3 can be produced by high density clumps in host galaxies. Simulations that include dispersion measure contributions from the Large Magellanic Cloud and the Andromeda Galaxy are shown as examples to demonstrate how to extract the dispersion measure from the intergalactic medium. (paper)

Assessing the performance of dispersionless and dispersion-accounting methods: helium interaction with cluster models of the TiO2(110) surface.

Science.gov (United States)

de Lara-Castells, María Pilar; Stoll, Hermann; Mitrushchenkov, Alexander O

2014-08-21

As a prototypical dispersion-dominated physisorption problem, we analyze here the performance of dispersionless and dispersion-accounting methodologies on the helium interaction with cluster models of the TiO2(110) surface. A special focus has been given to the dispersionless density functional dlDF and the dlDF+Das construction for the total interaction energy (K. Pernal, R. Podeswa, K. Patkowski, and K. Szalewicz, Phys. Rev. Lett. 2009, 109, 263201), where Das is an effective interatomic pairwise functional form for the dispersion. Likewise, the performance of symmetry-adapted perturbation theory (SAPT) method is evaluated, where the interacting monomers are described by density functional theory (DFT) with the dlDF, PBE, and PBE0 functionals. Our benchmarks include CCSD(T)-F12b calculations and comparative analysis on the nuclear bound states supported by the He-cluster potentials. Moreover, intra- and intermonomer correlation contributions to the physisorption interaction are analyzed through the method of increments (H. Stoll, J. Chem. Phys. 1992, 97, 8449) at the CCSD(T) level of theory. This method is further applied in conjunction with a partitioning of the Hartree-Fock interaction energy to estimate individual interaction energy components, comparing them with those obtained using the different SAPT(DFT) approaches. The cluster size evolution of dispersionless and dispersion-accounting energy components is then discussed, revealing the reduced role of the dispersionless interaction and intramonomer correlation when the extended nature of the surface is better accounted for. On the contrary, both post-Hartree-Fock and SAPT(DFT) results clearly demonstrate the high-transferability character of the effective pairwise dispersion interaction whatever the cluster model is. Our contribution also illustrates how the method of increments can be used as a valuable tool not only to achieve the accuracy of CCSD(T) calculations using large cluster models but also to

Angular dispersion and energy loss of H+ and He+ in metals

International Nuclear Information System (INIS)

Cantero, Esteban

2006-01-01

In this master thesis the effects produced when a light ion beam traverses a thin metallic film were studied.In particular, the interactions of low energy (E ≤ 10 keV) light ions (H + ,H 2 + , D + , He + ) with monocrystalline and also polycrystalline gold samples were investigated.In first place, the dependence of the stopping power with projectiles' velocity was studied, analyzing the threshold effect in the excitation of the 5d electrons in the channelling regime for energies between 0,4 and 9 keV.Next, the angular dispersion of ions in polycrystalline and monocrystalline films was measured and analyzed.Comparisons for different energies and projectiles were done, studying molecular and isotopic effects.Using Lindhard's channeling theory, a scale law for the angular dispersion of angles greater than the critical angle was found.Additionally, the angular dependence of the energy loss and the energy loss straggling of protons transmitted through monocrystals were measured.To explain the angular variations of these magnitudes a theoretical model based on the electronic density fluctuations inside the channel was developed [es

Dispersion of coupled mode-gap cavities

NARCIS (Netherlands)

Lian, Jin; Sokolov, Sergei; Yuce, E.; Combrie, S.; de Rossi, A.; Mosk, Allard

2015-01-01

The dispersion of a coupled resonator optical waveguide made of photonic crystal mode-gap cavities is pronouncedly asymmetric. This asymmetry cannot be explained by the standard tight binding model. We show that the fundamental cause of the asymmetric dispersion is the inherent dispersive cavity

Discrete dispersion models and their Tweedie asymptotics

DEFF Research Database (Denmark)

Jørgensen, Bent; Kokonendji, Célestin C.

2016-01-01

The paper introduce a class of two-parameter discrete dispersion models, obtained by combining convolution with a factorial tilting operation, similar to exponential dispersion models which combine convolution and exponential tilting. The equidispersed Poisson model has a special place in this ap......The paper introduce a class of two-parameter discrete dispersion models, obtained by combining convolution with a factorial tilting operation, similar to exponential dispersion models which combine convolution and exponential tilting. The equidispersed Poisson model has a special place...... in this approach, whereas several overdispersed discrete distributions, such as the Neyman Type A, Pólya-Aeppli, negative binomial and Poisson-inverse Gaussian, turn out to be Poisson-Tweedie factorial dispersion models with power dispersion functions, analogous to ordinary Tweedie exponential dispersion models...... with power variance functions. Using the factorial cumulant generating function as tool, we introduce a dilation operation as a discrete analogue of scaling, generalizing binomial thinning. The Poisson-Tweedie factorial dispersion models are closed under dilation, which in turn leads to a Poisson...

Structure factors and phonon dispersion in liquid Li0.61Na0.39 alloy

International Nuclear Information System (INIS)

Pratap, Arun; Lad, Kirit N.; Raval, K.G.

2004-01-01

The phonon spectra for liquid Li and Na have been computed through the phenomenological model of Bhatia and Singh for disordered systems like liquids and glasses and the obtained results have been compared with the available data obtained by inelastic neutron scattering (INS) and inelastic X-ray scattering (IXS) experiments. The effective pair potentials and their space derivatives are important ingredients in the computation of the dispersion curves. The pair potentials are obtained using the pseudo-potential theory. The empty core model proposed by Ashcroft is widely used for pseudo-potential calculations for alkali metals. But, it is thought to be unsuitable for Li because of its simple 1s electronic structure. However, it can be used with an additional term known as Born-Mayer (BM) core term. The influence of the BM core term on the phonon dispersion is discussed. The same pseudo-potential formalism has been employed to obtain the dispersion relation in liquid Li 0.61 Na 0.39 alloy. Apart from the phonon spectra, the Ashcroft-Langreth structure factors in the alloy are derived in the Percus-Yevick approximation. (author)

Unified theory of ballooning instabilities and temperature gradient driven trapped ion modes

International Nuclear Information System (INIS)

Xu, X.Q.

1990-08-01

A unified theory of temperature gradient driven trapped ion modes and ballooning instabilities is developed using kinetic theory in banana regimes. All known results, such as electrostatic and purely magnetic trapped particle modes and ideal MHD ballooning modes (or shear Alfven waves) are readily derived from our single general dispersion relation. Several new results from ion-ion collision and trapped particle modification of ballooning modes are derived and discussed and the interrelationship between those modes is established. 24 refs

Dispersion-theoretical analysis of the D + → K - π + π + Dalitz plot

Science.gov (United States)

Niecknig, Franz; Kubis, Bastian

2015-10-01

We study the Dalitz plot of the Cabibbo-favored charmed-meson decay D + → K -π+π+ using dispersion theory. The formalism respects all constraints from analyticity and unitarity, and consistently describes final-state interactions between all three decay products. We employ pion-pion and pion-kaon phase shifts as input, and fit the pertinent subtraction constants to Dalitz plot data by the CLEO and FOCUS collaborations. Phase motions of resonant as well as nonresonant amplitudes are discussed, which should provide crucial input for future studies of CP violation in similar three-body charm decays.

Characterisation of dispersion mechanisms in an urban catchment using a deterministic spatially distributed direct hydrograph travel time model

Science.gov (United States)

Rossel, F.; Gironas, J. A.

2012-12-01

The link between stream network structure and hydrologic response for natural basins has been extensively studied. It is well known that stream network organization and flow dynamics in the reaches combine to shape the hydrologic response of natural basins. Geomorphologic dispersion and hydrodynamic dispersion along with hillslope processes control to a large extent the overall variance of the hydrograph, particularly under the assumption of constant celerity throughout the basin. In addition, a third mechanism referred as to kinematic dispersion becomes relevant when considering spatial variations of celerity. On contrary, the link between the drainage network structure and overall urban terrain, and the hydrologic response in urban catchments has been much less studied. In particular, the characterization of the different dispersion mechanisms within urban areas remains to be better understood. In such areas artificial elements are expected to contribute to the total dispersion due to the variety of geometries and the spatial distribution of imperviousness. This work quantifies the different dispersion mechanisms in an urban catchment, focusing on their relevance and the spatial scales involved. For this purpose we use the Urban Morpho-climatic Instantaneous Unit Hydrograph model, a deterministic spatially distributed direct hydrograph travel time model, which computes travel times in hillslope, pipe, street and channel cells using formulations derived from kinematic wave theory. The model was applied to the Aubeniere catchment, located in Nantes, France. Unlike stochastic models, this deterministic model allows the quantification of dispersion mechanism at the local scale (i.e. the grid-cell). We found that kinematic dispersion is more relevant for small storm events, whereas geomorphologic dispersion becomes more significant for larger storms, as the mean celerity within the catchment increases. In addition, the total dispersion relates to the drainage area in

Modeling of dilute and dense dispersed fluid-particle flow

Energy Technology Data Exchange (ETDEWEB)

Laux, Harald

1998-08-01

A general two-fluid model is derived and applied in CFD computations to various test cases of important industrial multiphase flows. It is general in the sense of its applicability to dilute and dense dispersed fluid-particle flows. The model is limited to isothermal flow without mass transfer and only one particle phase is described. The instantaneous fluid phase equations, including the phase interaction terms, are derived from a volume averaging technique, and the instantaneous particle phase equations are derived from the kinetic theory of granular material. Whereas the averaging procedure, the treatment of the interaction terms, and the kinetic theory approach have been reported in literature prior to this work the combination of the approaches is new. The resulting equations are derived without ambiguity in the interpretation of the particle phase pressure (equation-of-state of particle phase). The basic modeling for the particle phase is improved in two steps. Because in the basic modeling only stresses due to kinetic and collisional interactions are included, a simple model for an effective viscosity is developed in order to allow also frictional stresses within the particle phase. Moreover, turbulent stresses and turbulent dispersion of particles play often an important role for the transport processes. Therefore in a second step, a two-equation turbulence model for both fluid and particle phase turbulence is derived by applying the phasic average to the instantaneous equations. The resulting k-{epsilon}-k{sup d}-{epsilon}{sup d} model is new. Mathematical closure is attempted such that the resulting set of equations is valid for both dilute arid dense flows. During the development of the closure relations a clear distinction is made between granular or ''viscous'' microscale fluctuations and turbulent macro scale fluctuations (true particle turbulence) within the particle phase. The set of governing equations is discretized by using a finite volume method

Modeling of dilute and dense dispersed fluid-particle flow

Energy Technology Data Exchange (ETDEWEB)

Laux, Harald

1998-08-01

A general two-fluid model is derived and applied in CFD computations to various test cases of important industrial multiphase flows. It is general in the sense of its applicability to dilute and dense dispersed fluid-particle flows. The model is limited to isothermal flow without mass transfer and only one particle phase is described. The instantaneous fluid phase equations, including the phase interaction terms, are derived from a volume averaging technique, and the instantaneous particle phase equations are derived from the kinetic theory of granular material. Whereas the averaging procedure, the treatment of the interaction terms, and the kinetic theory approach have been reported in literature prior to this work the combination of the approaches is new. The resulting equations are derived without ambiguity in the interpretation of the particle phase pressure (equation-of-state of particle phase). The basic modeling for the particle phase is improved in two steps. Because in the basic modeling only stresses due to kinetic and collisional interactions are included, a simple model for an effective viscosity is developed in order to allow also frictional stresses within the particle phase. Moreover, turbulent stresses and turbulent dispersion of particles play often an important role for the transport processes. Therefore in a second step, a two-equation turbulence model for both fluid and particle phase turbulence is derived by applying the phasic average to the instantaneous equations. The resulting k-{epsilon}-k{sup d}-{epsilon}{sup d} model is new. Mathematical closure is attempted such that the resulting set of equations is valid for both dilute arid dense flows. During the development of the closure relations a clear distinction is made between granular or ''viscous'' microscale fluctuations and turbulent macro scale fluctuations (true particle turbulence) within the particle phase. The set of governing equations is discretized by using a

Single-particle dispersion in compressible turbulence

Science.gov (United States)

Zhang, Qingqing; Xiao, Zuoli

2018-04-01

Single-particle dispersion statistics in compressible box turbulence are studied using direct numerical simulation. Focus is placed on the detailed discussion of effects of the particle Stokes number and turbulent Mach number, as well as the forcing type. When solenoidal forcing is adopted, it is found that the single-particle dispersion undergoes a transition from the ballistic regime at short times to the diffusive regime at long times, in agreement with Taylor's particle dispersion argument. The strongest dispersion of heavy particles is announced when the Stokes number is of order 1, which is similar to the scenario in incompressible turbulence. The dispersion tends to be suppressed as the Mach number increases. When hybrid solenoidal and compressive forcing at a ratio of 1/2 is employed, the flow field shows apparent anisotropic property, characterized by the appearance of large shock wave structures. Accordingly, the single-particle dispersion shows extremely different behavior from the solenoidal forcing case.

Effect of treatment temperature on the microstructure of asphalt binders: insights on the development of dispersed domains.

Science.gov (United States)

Menapace, I; Masad, E; Bhasin, A

2016-04-01

This paper offers important insights on the development of the microstructure in asphalt binders as a function of the treatment temperature. Different treatment temperatures are useful to understand how dispersed domains form when different driving energies for the mobility of molecular species are provided. Small and flat dispersed domains, with average diameter between 0.02 and 0.70 μm, were detected on the surface of two binders at room temperature, and these domains were observed to grow with an increase in treatment temperature (up to over 2 μm). Bee-like structures started to appear after treatment at or above 100°C. Moreover, the effect of the binder thickness on its microstructure at room temperature and at higher treatment temperatures was investigated and is discussed in this paper. At room temperature, the average size of the dispersed domains increased as the binder thickness decreased. A hypothesis that conciliates current theories on the origin and development of dispersed domains is proposed. Small dispersed domains (average diameter around 0.02 μm) are present in the bulk of the binder, whereas larger domains and bee-like structures develop on the surface, following heat treatment or mechanical disturbance that reduces the film thickness. Molecular mobility and association are the key factors in the development of binder microstructure. © 2015 The Authors Journal of Microscopy © 2015 Royal Microscopical Society.

Comparative toxicity of two oil dispersants, superdispersant-25 and corexit 9527, to a range of coastal species.

Science.gov (United States)

Scarlett, Alan; Galloway, Tamara S; Canty, Martin; Smith, Emma L; Nilsson, Johanna; Rowland, Steven J

2005-05-01

The acute toxicity of the oil dispersant Corexit 9527 reported in the literature is highly variable. No peer-reviewed data exist for Superdispersant-25 (SD-25). This study compares the toxicity of the two dispersants to a range of marine species representing different phyla occupying a wide range of niches: The marine sediment-dwelling amphipod Corophium volutator (Pallas), the common mussel Mytilus edulis (L.), the symbiotic snakelocks anemone Anemonia viridis (Forskål), and the seagrass Zostera marina (L.). Organisms were exposed to static dispersant concentrations for 48-h and median lethal concentration (LC50), median effect concentration (EC50), and lowest-observable-effect concentration (LOEC) values obtained. The sublethal effects of 48-h exposures and the ability of species to recover for up to 72 h after exposure were quantified relative to the 48-h endpoints. Results indicated that the anemone lethality test was the most sensitive with LOECs of 20 ppm followed by mussel feeding rate, seagrass photosynthetic index and amphipod lethality, with mussel lethality being the least sensitive with LOECs of 250 ppm for both dispersants. The results were consistent with current theory that dispersants act physically and irreversibly on the respiratory organs and reversibly, depending on exposure time, on the nervous system. Superdispersant-25 was found overall to be less toxic than Corexit 9527 and its sublethal effects more likely to be reversible following short-term exposure.

Nest-mediated seed dispersal

Science.gov (United States)

Robert J. Warren; Jason P. Love; Mark A. Bradford

2017-01-01

Many plant seeds travel on the wind and through animal ingestion or adhesion; however, an overlooked dispersal mode may lurk within those dispersal modes. Viable seeds may remain attached or embedded within materials birds gather for nest building. Our objective was to determine if birds inadvertently transport seeds when they forage for plant materials to...

Atmospheric dispersion of radioactive materials

International Nuclear Information System (INIS)

Chino, Masamichi

1988-01-01

The report describes currently available techniques for predicting the dispersion of accidentally released radioactive materials and techniques for visualization using computer graphics. A simulation study is also made on the dispersion of radioactive materials released from the Chernobyl plant. The simplest models include the Gauss plume model and the puff model, which cannot serve to analyze the effects of the topography, vertical wind shear, temperature inversion layer, etc. Numerical analysis methods using advection and dispersion equations are widely adopted for detailed evaluation of dispersion in an emergency. An objective analysis model or a hydrodynamical model is often used to calculate the air currents which are required to determine the advection. A small system based on the puff model is widely adopted in Europe, where the topography is considered to have only simple effects. A more sophisticated large-sized system is required in nuclear facilities located in an area with more complex topographic features. An emergency system for dispersion calculation should be equipped with a graphic display to serve for quick understanding of the radioactivity distribution. (Nogami, K.)

Effective description of higher-order scalar-tensor theories

Energy Technology Data Exchange (ETDEWEB)

Langlois, David [APC—Astroparticule et Cosmologie, Université Paris Diderot Paris 7, 75013 Paris (France); Mancarella, Michele; Vernizzi, Filippo [Institut de physique théorique, Université Paris Saclay, CEA, CNRS, 91191 Gif-sur-Yvette (France); Noui, Karim, E-mail: langlois@apc.univ-paris7.fr, E-mail: michele.mancarella@cea.fr, E-mail: karim.noui@lmpt.univ-tours.fr, E-mail: filippo.vernizzi@cea.fr [Laboratoire de Mathématiques et Physique Théorique, Université François Rabelais, Parc de Grandmont, 37200 Tours (France)

2017-05-01

Most existing theories of dark energy and/or modified gravity, involving a scalar degree of freedom, can be conveniently described within the framework of the Effective Theory of Dark Energy, based on the unitary gauge where the scalar field is uniform. We extend this effective approach by allowing the Lagrangian in unitary gauge to depend on the time derivative of the lapse function. Although this dependence generically signals the presence of an extra scalar degree of freedom, theories that contain only one propagating scalar degree of freedom, in addition to the usual tensor modes, can be constructed by requiring the initial Lagrangian to be degenerate. Starting from a general quadratic action, we derive the dispersion relations for the linear perturbations around Minkowski and a cosmological background. Our analysis directly applies to the recently introduced Degenerate Higher-Order Scalar-Tensor (DHOST) theories. For these theories, we find that one cannot recover a Poisson-like equation in the static linear regime except for the subclass that includes the Horndeski and so-called 'beyond Horndeski' theories. We also discuss Lorentz-breaking models inspired by Horava gravity.

Bimetric Theory of Fractional Quantum Hall States

Science.gov (United States)

Gromov, Andrey; Son, Dam Thanh

2017-10-01

We present a bimetric low-energy effective theory of fractional quantum Hall (FQH) states that describes the topological properties and a gapped collective excitation, known as the Girvin-Macdonald-Platzman (GMP) mode. The theory consists of a topological Chern-Simons action, coupled to a symmetric rank-2 tensor, and an action à la bimetric gravity, describing the gapped dynamics of a spin-2 mode. The theory is formulated in curved ambient space and is spatially covariant, which allows us to restrict the form of the effective action and the values of phenomenological coefficients. Using bimetric theory, we calculate the projected static structure factor up to the k6 order in the momentum expansion. To provide further support for the theory, we derive the long-wave limit of the GMP algebra, the dispersion relation of the GMP mode, and the Hall viscosity of FQH states. The particle-hole (PH) transformation of the theory takes a very simple form, making the duality between FQH states and their PH conjugates manifest. We also comment on the possible applications to fractional Chern insulators, where closely related structures arise. It is shown that the familiar FQH observables acquire a curious geometric interpretation within the bimetric formalism.

Bimetric Theory of Fractional Quantum Hall States

Directory of Open Access Journals (Sweden)

Andrey Gromov

2017-11-01

Full Text Available We present a bimetric low-energy effective theory of fractional quantum Hall (FQH states that describes the topological properties and a gapped collective excitation, known as the Girvin-Macdonald-Platzman (GMP mode. The theory consists of a topological Chern-Simons action, coupled to a symmetric rank-2 tensor, and an action à la bimetric gravity, describing the gapped dynamics of a spin-2 mode. The theory is formulated in curved ambient space and is spatially covariant, which allows us to restrict the form of the effective action and the values of phenomenological coefficients. Using bimetric theory, we calculate the projected static structure factor up to the k^{6} order in the momentum expansion. To provide further support for the theory, we derive the long-wave limit of the GMP algebra, the dispersion relation of the GMP mode, and the Hall viscosity of FQH states. The particle-hole (PH transformation of the theory takes a very simple form, making the duality between FQH states and their PH conjugates manifest. We also comment on the possible applications to fractional Chern insulators, where closely related structures arise. It is shown that the familiar FQH observables acquire a curious geometric interpretation within the bimetric formalism.

Dispersant affects the cellular influences of single-wall carbon nanotube: the role of CNT as carrier of dispersants.

Science.gov (United States)

Horie, Masanori; Stowe, Mayumi; Tabei, Miki; Kato, Haruhisa; Nakamura, Ayako; Endoh, Shigehisa; Morimoto, Yasuo; Fujita, Katsuhide

2013-06-01

The application of carbon nanotube (CNT) as a functional material to engineering and life sciences is advanced. In order to evaluate the cytotoxicity of CNT in vitro, some chemical and biological reagents are used for dispersants. In the present study, the cellular influences of six kinds of chemical or biological reagents used as dispersants were examined. Pluronic F-127, Pluronic F-68, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), pulmonary surfactant preparation Surfacten®, bovine serum albumin (BSA) and Tween 80 were used in the preparation of CNT-medium dispersants. The influences of each reagent on cell viability in human lung carcinoma A549 cells were small. However, Pluronic F-127, DPPC, Surfacten® and Tween 80 induced an increase of intracellular reactive oxygen species (ROS) level. Next, CNT-medium dispersions were prepared, using each reagent as a dispersant and applied to A549 cells. The cellular influences depended on the kind of dispersant. Cells exposed to CNT dispersion including Pluronic® F-127, Surfacten®, DPPC and Tween 80 showed LDH release to the culture supernatant. Induction of intracellular ROS level was observed in cells exposed to CNT dispersion including each reagent except BSA. These results suggest that the adsorbed dispersant reagents on the surface of the CNT affect its cellular influences, particularly the induction of oxidative stress.

Paradigm Lost: Ocean Acidification Will Overturn the Concept of Larval-Fish Biophysical Dispersal

Directory of Open Access Journals (Sweden)

Jeffrey M. Leis

2018-02-01

hedging and colonization of new locations will decrease. The biophysical dispersal paradigm will be lost in theory and in fact, which is predicted to result in lower recruitment and less bet hedging for demersal, perciform fishes. More research is required to determine if the larvae of other Orders will be effected in the same way, or if warm- and cold-water fish faunas will be similarly effected.

Pseudospectral modeling and dispersion analysis of Rayleigh waves in viscoelastic media

Science.gov (United States)

Zhang, K.; Luo, Y.; Xia, J.; Chen, C.

2011-01-01

Multichannel Analysis of Surface Waves (MASW) is one of the most widely used techniques in environmental and engineering geophysics to determine shear-wave velocities and dynamic properties, which is based on the elastic layered system theory. Wave propagation in the Earth, however, has been recognized as viscoelastic and the propagation of Rayleigh waves presents substantial differences in viscoelastic media as compared with elastic media. Therefore, it is necessary to carry out numerical simulation and dispersion analysis of Rayleigh waves in viscoelastic media to better understand Rayleigh-wave behaviors in the real world. We apply a pseudospectral method to the calculation of the spatial derivatives using a Chebyshev difference operator in the vertical direction and a Fourier difference operator in the horizontal direction based on the velocity-stress elastodynamic equations and relations of linear viscoelastic solids. This approach stretches the spatial discrete grid to have a minimum grid size near the free surface so that high accuracy and resolution are achieved at the free surface, which allows an effective incorporation of the free surface boundary conditions since the Chebyshev method is nonperiodic. We first use an elastic homogeneous half-space model to demonstrate the accuracy of the pseudospectral method comparing with the analytical solution, and verify the correctness of the numerical modeling results for a viscoelastic half-space comparing the phase velocities of Rayleigh wave between the theoretical values and the dispersive image generated by high-resolution linear Radon transform. We then simulate three types of two-layer models to analyze dispersive-energy characteristics for near-surface applications. Results demonstrate that the phase velocity of Rayleigh waves in viscoelastic media is relatively higher than in elastic media and the fundamental mode increases by 10-16% when the frequency is above 10. Hz due to the velocity dispersion of P

Elastic Dispersion and Attenuation in Fully Saturated Sandstones: Role of Mineral Content, Porosity, and Pressures

Science.gov (United States)

Pimienta, Lucas; Borgomano, Jan V. M.; Fortin, Jérôme; Guéguen, Yves

2017-12-01

Because measuring the frequency dependence of elastic properties in the laboratory is a technical challenge, not enough experimental data exist to test the existing theories. We report measurements of three fluid-saturated sandstones over a broad frequency band: Wilkenson, Berea, and Bentheim sandstones. Those sandstones samples, chosen for their variable porosities and mineral content, are saturated by fluids of varying viscosities. The samples elastic response (Young's modulus and Poisson's ratio) and hydraulic response (fluid flow out of the sample) are measured as a function of frequency. Large dispersion and attenuation phenomena are observed over the investigated frequency range. For all samples, the variation at lowest frequency relates to a large fluid flow directly measured out of the rock samples. These are the cause (i.e., fluid flow) and consequence (i.e., dispersion/attenuation) of the transition between drained and undrained regimes. Consistently, the characteristic frequency correlates with permeability for each sandstone. Beyond this frequency, a second variation is observed for all samples, but the rocks behave differently. For Berea sandstone, an onset of dispersion/attenuation is expected from both Young's modulus and Poisson's ratio at highest frequency. For Bentheim and Wilkenson sandstones, however, only Young's modulus shows dispersion/attenuation phenomena. For Wilkenson sandstone, the viscoelastic-like dispersion/attenuation response is interpreted as squirt flow. For Bentheim sandstone, the second effect does not fully follow such response, which could be due to a lower accuracy in the measured attenuation or to the occurence of another physical effect in this rock sample.

Effectiveness of dispersants on thick oil slicks

International Nuclear Information System (INIS)

Ross, S.; Belore, R.

1993-01-01

Experiments were conducted to determine the relationship between dispersant effectiveness and oil slick thickness, and thereby determine the optimum time for applying dispersant onto spilled oil at sea. Tests were completed at a lab-scale level by varying the three parameters of oil type, dispersant application, and oil thickness. The tests were intended to be comparative only. The primary oils used were Alberta sweet mix blend and Hibernia B-27 crude. The dispersant, Corexit 9527, was applied either premixed with the oil, dropwise in one application, or dropwise in multiple applications to simulate a multi-hit aircraft operation. The apparatus used in the experiment was an oscillating hoop tank, with oil-containing rings used to obtain and maintain uniform slick thickness. The results indicate that the effectiveness potential of a chemical dispersant does not decrease as slick thickness increases. In fact, results of the tests involving Hibernia oil suggest that oils that tend to herd easily would be treated more effectively if dispersant were applied when the oil was relatively thick (1 mm or greater) to avoid herding problems. The oil slicks premixed with dispersant did not disperse well in the thick oil tests, not because of dispersant-oil interaction problems but because of reduced mixing energy. 6 refs., 4 figs., 1 tab

Dispersal Timing: Emigration of Insects Living in Patchy Environments.

Directory of Open Access Journals (Sweden)

Milica Lakovic

Full Text Available Dispersal is a life-history trait affecting dynamics and persistence of populations; it evolves under various known selective pressures. Theoretical studies on dispersal typically assume 'natal dispersal', where individuals emigrate right after birth. But emigration may also occur during a later moment within a reproductive season ('breeding dispersal'. For example, some female butterflies first deposit eggs in their natal patch before migrating to other site(s to continue egg-laying there. How breeding compared to natal dispersal influences the evolution of dispersal has not been explored. To close this gap we used an individual-based simulation approach to analyze (i the evolution of timing of breeding dispersal in annual organisms, (ii its influence on dispersal (compared to natal dispersal. Furthermore, we tested (iii its performance in direct evolutionary contest with individuals following a natal dispersal strategy. Our results show that evolution should typically result in lower dispersal under breeding dispersal, especially when costs of dispersal are low and population size is small. By distributing offspring evenly across two patches, breeding dispersal allows reducing direct sibling competition in the next generation whereas natal dispersal can only reduce trans-generational kin competition by producing highly dispersive offspring in each generation. The added benefit of breeding dispersal is most prominent in patches with small population sizes. Finally, the evolutionary contests show that a breeding dispersal strategy would universally out-compete natal dispersal.

Partitioning of fresh crude oil between floating, dispersed and sediment phases: Effect of exposure order to dispersant and granular materials.

Science.gov (United States)

Boglaienko, Daria; Tansel, Berrin

2016-06-15

When three or more high and low energy substrates are mixed, wetting order can significantly affect the behavior of the mixture. We analyzed the phase distribution of fresh floating Louisiana crude oil into dispersed, settled and floating phases depending on the exposure sequence to Corexit 9500A (dispersant) and granular materials. In the experiments artificial sea water at salinity 34‰ was used. Limestone (2.00-0.300 mm) and quartz sand (0.300-0.075 mm) were used as the natural granular materials. Dispersant Corexit 9500A increased the amount of dispersed oil up to 33.76 ± 7.04%. Addition of granular materials after the dispersant increased dispersion of oil to 47.96 ± 1.96%. When solid particles were applied on the floating oil before the dispersant, oil was captured as oil-particle aggregates and removed from the floating layer. However, dispersant addition led to partial release of the captured oil, removing it from the aggregated form to the dispersed and floating phases. There was no visible oil aggregation with the granular materials when quartz or limestone was at the bottom of the flask before the addition of oil and dispersant. The results show that granular materials can be effective when applied from the surface for aggregating or dispersing oil. However, the granular materials in the sediments are not effective neither for aggregating nor dispersing floating oil. Copyright © 2016 Elsevier Ltd. All rights reserved.

Measuring short distance dispersal of Alliaria petiolata and determining potential long distance dispersal mechanisms

Directory of Open Access Journals (Sweden)

Christopher A. Loebach

2018-03-01

Full Text Available Introduction Alliaria petiolata, an herbaceous plant, has invaded woodlands in North America. Its ecology has been thoroughly studied, but an overlooked aspect of its biology is seed dispersal distances and mechanisms. We measured seed dispersal distances in the field and tested if epizoochory is a potential mechanism for long-distance seed dispersal. Methods Dispersal distances were measured by placing seed traps in a sector design around three seed point sources, which consisted of 15 second-year plants transplanted within a 0.25 m radius circle. Traps were placed at intervals ranging from 0.25–3.25 m from the point source. Traps remained in the field until a majority of seeds were dispersed. Eight probability density functions were fitted to seed trap counts via maximum likelihood. Epizoochory was tested as a potential seed dispersal mechanism for A. petiolata through a combination of field and laboratory experiments. To test if small mammals transport A. petiolata seeds in their fur, experimental blocks were placed around dense A. petiolata patches. Each block contained a mammal inclusion treatment (MIT and control. The MIT consisted of a wood-frame (31 × 61× 31 cm covered in wire mesh, except for the two 31 × 31 cm ends, placed over a germination tray filled with potting soil. A pan filled with bait was placed in the center of the tray. The control frame (11 × 31 × 61 cm was placed over a germination tray and completely covered in wire mesh to exclude animal activity. Treatments were in the field for peak seed dispersal. In March, trays were moved to a greenhouse and A. petiolata seedlings were counted and then compared between treatments. To determine if A. petiolata seeds attach to raccoon (Procyon lotor and white-tailed deer (Odocoileus virginianus fur, wet and dry seeds were dropped onto wet and dry fur. Furs were rotated 180 degrees and the seeds that remained attached were counted. To measure seed retention, seeds

Fundamentals of energy dispersive X-ray analysis

CERN Document Server

Russ, John C; Kiessling, R; Charles, J

1984-01-01

Fundamentals of Energy Dispersive X-ray Analysis provides an introduction to the fundamental principles of dispersive X-ray analysis. It presents descriptions, equations, and graphs to enable the users of these techniques to develop an intuitive and conceptual image of the physical processes involved in the generation and detection of X-rays. The book begins with a discussion of X-ray detection and measurement, which is accomplished by one of two types of X-ray spectrometer: energy dispersive or wavelength dispersive. The emphasis is on energy dispersive spectrometers, given their rather wid

Dispersed-phase catalysis in coal liquefaction

International Nuclear Information System (INIS)

Utz, B.R.; Cugini, A.V.; Frommell, E.A.

1990-01-01

This paper reports that the specific reaction (activation) conditions for the conversion of catalyst precursors to unsupported catalyst have a direct effect on the catalytic activity and dispersion. The importance of reaction intermediates in decomposition of ammonium heptamolybdate and ammonium tetrathiomolybdate, and the sensitivity of these intermediates to reaction conditions, were studied in coal liquefaction systems. Recent results indicate that optimization of activation conditions facilitates the formation of a highly dispersed and active form of molybdenum disulfide for coal liquefaction. The use of the catalyst precursors ammonium heptamolybdate, ammonium tetrathiomolybdate, and molybdenum trisulfide for the conversion of coal to soluble products will be discussed. The use of an unsupported dispersed-phase catalyst for direct coal liquefaction is not a novel concept and has been employed in may studies with varying success. Dispersed-phase catalysts soluble and oil-soluble salts, and as finely divided powders. While some methods of catalyst introduction give higher dispersion of the catalyst and greater activity for the liquefaction of coal, all of the techniques allow the formation of a finely dispersed inorganic phase

Magnon dispersion in thin magnetic films

International Nuclear Information System (INIS)

Balashov, T; Wulfhekel, W; Buczek, P; Sandratskii, L; Ernst, A

2014-01-01

Although the dispersion of magnons has been measured in many bulk materials, few studies deal with the changes in the dispersion when the material is in the form of a thin film, a system that is of interest for applications. Here we review inelastic tunneling spectroscopy studies of magnon dispersion in Mn/Cu 3 Au(1 0 0) and present new studies on Co and Ni thin films on Cu(1 0 0). The dispersion in Mn and Co films closely follows the dispersion of bulk samples with negligible dependence on thickness. The lifetime of magnons depends slightly on film thickness, and decreases considerably as the magnon energy increases. In Ni/Cu(1 0 0) films the thickness dependence of dispersion is much more pronounced. The measurements indicate a considerable mode softening for thinner films. Magnon lifetimes decrease dramatically near the edge of the Brillouin zone due to a close proximity of the Stoner continuum. The experimental study is supported by first-principles calculations. (paper)

Magnon dispersion in thin magnetic films.

Science.gov (United States)

Balashov, T; Buczek, P; Sandratskii, L; Ernst, A; Wulfhekel, W

2014-10-01

Although the dispersion of magnons has been measured in many bulk materials, few studies deal with the changes in the dispersion when the material is in the form of a thin film, a system that is of interest for applications. Here we review inelastic tunneling spectroscopy studies of magnon dispersion in Mn/Cu3Au(1 0 0) and present new studies on Co and Ni thin films on Cu(1 0 0). The dispersion in Mn and Co films closely follows the dispersion of bulk samples with negligible dependence on thickness. The lifetime of magnons depends slightly on film thickness, and decreases considerably as the magnon energy increases. In Ni/Cu(1 0 0) films the thickness dependence of dispersion is much more pronounced. The measurements indicate a considerable mode softening for thinner films. Magnon lifetimes decrease dramatically near the edge of the Brillouin zone due to a close proximity of the Stoner continuum. The experimental study is supported by first-principles calculations.

Generalized dispersive wave emission in nonlinear fiber optics.

Science.gov (United States)

Webb, K E; Xu, Y Q; Erkintalo, M; Murdoch, S G

2013-01-15

We show that the emission of dispersive waves in nonlinear fiber optics is not limited to soliton-like pulses propagating in the anomalous dispersion regime. We demonstrate, both numerically and experimentally, that pulses propagating in the normal dispersion regime can excite resonant dispersive radiation across the zero-dispersion wavelength into the anomalous regime.

Risk methodology for geologic disposal of radioactive waste: The distributed velocity method of solving the convective-dispersion equation

Energy Technology Data Exchange (ETDEWEB)

Campbell, James E; Longsine, Dennis E [Sandia National Laboratories, Albuquerque, New Mexico (United States); Reeves, Mark [INTERA Environmental Consultants, Inc. Houston, TX (United States)

1980-06-01

A new method is proposed for treating convective-dispersive transport. The motivation for developing this technique arises from the demands of performing a risk assessment for a nuclear waste repository. These demands include computational efficiency over a relatively large range of Peclet numbers and the ability to handle chains of decaying radionuclides with rather extreme contrasts in both solution velocities and half lives. To the extent it has been tested to date, the Distributed Velocity Method (DVM) appears to satisfy these demands. Included in this paper are the mathematical theory, numerical implementation, an error analysis employing statistical sampling and regression analysis techniques, and comparisons of DVM with other methods for convective-dispersive transport. (author)

Improved new generation dispersants

International Nuclear Information System (INIS)

Anon.

1993-01-01

The use of dispersants to combat oil spills has attracted controversy over the years, and there has been a number of accusations of the chemicals involved doing more harm than good. A new study by the International Petroleum Industry Environmental Conservation Association discusses the positive and the negatives of dispersant use to be considered when drawing up spill contingency plans. (author)

Dispersal of forest insects

Science.gov (United States)

Mcmanus, M. L.

1979-01-01

Dispersal flights of selected species of forest insects which are associated with periodic outbreaks of pests that occur over large contiguous forested areas are discussed. Gypsy moths, spruce budworms, and forest tent caterpillars were studied for their massive migrations in forested areas. Results indicate that large dispersals into forested areas are due to the females, except in the case of the gypsy moth.

Dense gas dispersion in the atmosphere

Energy Technology Data Exchange (ETDEWEB)

Nielsen, Morten

1998-09-01

Dense gas dispersion is characterized by buoyancy induced gravity currents and reduction of the vertical mixing. Liquefied gas releases from industrial accidents are cold because of the heat of evaporation which determines the density for a given concentration and physical properties. The temperature deficit is moderated by the heat flux from the ground, and this convection is an additional source of turbulence which affects the mixing. A simple model as the soil heat flux is used to estimate the ability of the ground to sustain the heat flux during release. The initial enthalpy, release rate, initial entrainment and momentum are discussed for generic source types and the interaction with obstacles is considered. In the MTH project BA experiments source with and without momentum were applied. The continuously released propane gas passed a two-dimensional removable obstacle perpendicular to the wind direction. Ground-level gas concentrations and vertical profiles of concentration, temperature, wind speed and turbulence were measured in front of and behind the obstacle. Ultrasonic anemometers providing fast velocity and concentration signals were mounted at three levels on the masts. The observed turbulence was influenced by the stability and the initial momentum of the jet releases. Additional information were taken from the `Dessert tortoise` ammonia jet releases, from the `Fladis` experiment with transition from dense to passive dispersion, and from the `Thorney Island` continuous releases of isothermal freon mixtures. The heat flux was found to moderate the negative buoyancy in both the propane and ammonia experiments. The heat flux measurements are compared to an estimate by analogy with surface layer theory. (au) 41 tabs., 146 ills., 189 refs.

Interspecific nematode signals regulate dispersal behavior.

Directory of Open Access Journals (Sweden)

Fatma Kaplan

Full Text Available Dispersal is an important nematode behavior. Upon crowding or food depletion, the free living bacteriovorus nematode Caenorhabditis elegans produces stress resistant dispersal larvae, called dauer, which are analogous to second stage juveniles (J2 of plant parasitic Meloidogyne spp. and infective juveniles (IJs of entomopathogenic nematodes (EPN, e.g., Steinernema feltiae. Regulation of dispersal behavior has not been thoroughly investigated for C. elegans or any other nematode species. Based on the fact that ascarosides regulate entry in dauer stage as well as multiple behaviors in C. elegans adults including mating, avoidance and aggregation, we hypothesized that ascarosides might also be involved in regulation of dispersal behavior in C. elegans and for other nematodes such as IJ of phylogenetically related EPNs.Liquid chromatography-mass spectrometry analysis of C. elegans dauer conditioned media, which shows strong dispersing activity, revealed four known ascarosides (ascr#2, ascr#3, ascr#8, icas#9. A synthetic blend of these ascarosides at physiologically relevant concentrations dispersed C. elegans dauer in the presence of food and also caused dispersion of IJs of S. feltiae and J2s of plant parasitic Meloidogyne spp. Assay guided fractionation revealed structural analogs as major active components of the S. feltiae (ascr#9 and C. elegans (ascr#2 dispersal blends. Further analysis revealed ascr#9 in all Steinernema spp. and Heterorhabditis spp. infected insect host cadavers.Ascaroside blends represent evolutionarily conserved, fundamentally important communication systems for nematodes from diverse habitats, and thus may provide sustainable means for control of parasitic nematodes.

The nonlinear effects on the characteristics of gravity wave packets: dispersion and polarization relations

Directory of Open Access Journals (Sweden)

S.-D. Zhang

2000-10-01

Full Text Available By analyzing the results of the numerical simulations of nonlinear propagation of three Gaussian gravity-wave packets in isothermal atmosphere individually, the nonlinear effects on the characteristics of gravity waves are studied quantitatively. The analyses show that during the nonlinear propagation of gravity wave packets the mean flows are accelerated and the vertical wavelengths show clear reduction due to nonlinearity. On the other hand, though nonlinear effects exist, the time variations of the frequencies of gravity wave packets are close to those derived from the dispersion relation and the amplitude and phase relations of wave-associated disturbance components are consistent with the predictions of the polarization relation of gravity waves. This indicates that the dispersion and polarization relations based on the linear gravity wave theory can be applied extensively in the nonlinear region.Key words: Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides

Operator approach to effective medium theory to overcome a breakdown of Maxwell Garnett approximation

DEFF Research Database (Denmark)

Popov, Vladislav; Lavrinenko, Andrei; Novitsky, Andrey

2016-01-01

that the zeroth-, first-, and second-order approximations of the operator effective medium theory correspond to electric dipoles, chirality, and magnetic dipoles plus electric quadrupoles, respectively. We discover that the spatially dispersive bianisotropic effective medium obtained in the second...

Dispersal of Engineered Male Aedes aegypti Mosquitoes.

Science.gov (United States)

Winskill, Peter; Carvalho, Danilo O; Capurro, Margareth L; Alphey, Luke; Donnelly, Christl A; McKemey, Andrew R

2015-11-01

Aedes aegypti, the principal vector of dengue fever, have been genetically engineered for use in a sterile insect control programme. To improve our understanding of the dispersal ecology of mosquitoes and to inform appropriate release strategies of 'genetically sterile' male Aedes aegypti detailed knowledge of the dispersal ability of the released insects is needed. The dispersal ability of released 'genetically sterile' male Aedes aegypti at a field site in Brazil has been estimated. Dispersal kernels embedded within a generalized linear model framework were used to analyse data collected from three large scale mark release recapture studies. The methodology has been applied to previously published dispersal data to compare the dispersal ability of 'genetically sterile' male Aedes aegypti in contrasting environments. We parameterised dispersal kernels and estimated the mean distance travelled for insects in Brazil: 52.8 m (95% CI: 49.9 m, 56.8 m) and Malaysia: 58.0 m (95% CI: 51.1 m, 71.0 m). Our results provide specific, detailed estimates of the dispersal characteristics of released 'genetically sterile' male Aedes aegypti in the field. The comparative analysis indicates that despite differing environments and recapture rates, key features of the insects' dispersal kernels are conserved across the two studies. The results can be used to inform both risk assessments and release programmes using 'genetically sterile' male Aedes aegypti.

Inertia: the discrepancy between individual and common good in dispersal and prospecting behaviour.

Science.gov (United States)

Delgado, María del Mar; Ratikainen, Irja I; Kokko, Hanna

2011-08-01

The group selection debate of the 1960s made it clear that evolution does not necessarily increase population performance. Individuals can be selected to have traits that diminish a common good and make population persistence difficult. At the extreme, the discrepancy between levels of selection is predicted to make traits evolve towards values at which a population can no longer persist (evolutionary suicide). Dispersal and prospecting are prime examples of traits that have a strong influence on population persistence under environmental and demographic stochasticity. Theory predicts that an 'optimal' dispersal strategy from a population point of view can differ considerably from that produced by individual-level selection. Because dispersal is frequently risky or otherwise costly, individuals are often predicted to disperse less than would be ideal for population performance (persistence or size). We define this discrepancy as 'inertia' and examine current knowledge of its occurrence and effects on population dynamics in nature. We argue that inertia is potentially widespread but that a framework is currently lacking for predicting precisely the extent to which it has a real influence on population persistence. The opposite of inertia, 'hypermobility' (more dispersal by individuals than would maximize population performance) remains a possibility: it is known that highest dispersal rates do not lead to best expected population performance, and examples of such high dispersal evolving exist at least in the theoretical literature. We also show, by considering prospecting behaviour, that similar issues arise in species with advanced cognitive and learning abilities. Individual prospecting strategies and the information acquired during dispersal are known to influence the decisions and therefore the fate of individuals and, as a corollary, populations. Again, the willingness of individuals to sample environments might evolve to levels that are not optimal for

Dispersion coefficients for H and He interactions with alkali-metal and alkaline-earth-metal atoms

International Nuclear Information System (INIS)

Mitroy, J.; Bromley, M.W.J.

2003-01-01

The van der Waals coefficients C 6 , C 8 , and C 10 for H and He interactions with the alkali-metal (Li, Na, K, and Rb) and alkaline-earth-metal (Be, Mg, Ca, and Sr) atoms are determined from oscillator strength sum rules. The oscillator strengths were computed using a combination of ab initio and semiempirical methods. The dispersion parameters generally agree with close to exact variational calculations for Li-H and Li-He at the 0.1% level of accuracy. For larger systems, there is agreement with relativistic many-body perturbation theory estimates of C 6 at the 1% level. These validations for selected systems attest to the reliability of the present dispersion parameters. About half the present parameters lie within the recommended bounds of the Standard and Certain compilation [J. Chem. Phys. 83, 3002 (1985)

Statistical problems of a galaxies formation theory

International Nuclear Information System (INIS)

Doroshkevich, A.G.; Shandarin, S.F.

1978-01-01

Some problems of galaxies and galaxy clusters formation from random adiabatic disturbances are discussed. Disturbances grow according to the nonlinear theory of gravitational instability. In this theory maxima of the largest characteristic values of a strain tensor have a particular significance as they are just the points of the formation of dense flattened structures - ''pancakes'' which then transform into galaxies and galaxy clusters. It is shown that parameters of a ''pancake'' such as time of the origin, mass, temperature etc. are determined by the lambda 11 largest characteristic value of the strain tensor in the centre of the ''pancake''. The lambda 11 distribution function the rate of mass condensation into ''pancakes'', the rate of production and the spatial density of ''pancakes'' are given. Some statistic properties of a single ''pancake'' such as a mean displacement and dispersion of a displacement in the vicinity of centre of a ''pancake'' were found. The possibility of connection between young galaxies and quasars is discussed in the framework of this theory

Proto-planetary disc evolution and dispersal

Science.gov (United States)

Rosotti, Giovanni Pietro

2015-05-01

Planets form from gas and dust discs in orbit around young stars. The timescale for planet formation is constrained by the lifetime of these discs. The properties of the formed planetary systems depend thus on the evolution and final dispersal of the discs, which is the main topic of this thesis. Observations reveal the existence of a class of discs called "transitional", which lack dust in their inner regions. They are thought to be the last stage before the complete disc dispersal, and hence they may provide the key to understanding the mechanisms behind disc evolution. X-ray photoevaporation and planet formation have been studied as possible physical mechanisms responsible for the final dispersal of discs. However up to now, these two phenomena have been studied separately, neglecting any possible feedback or interaction. In this thesis we have investigated what is the interplay between these two processes. We show that the presence of a giant planet in a photo-evaporating disc can significantly shorten its lifetime, by cutting the inner regions from the mass reservoir in the exterior of the disc. This mechanism produces transition discs that for a given mass accretion rate have larger holes than in models considering only X-ray photo-evaporation, constituting a possible route to the formation of accreting transition discs with large holes. These discs are found in observations and still constitute a puzzle for the theory. Inclusion of the phenomenon called "thermal sweeping", a violent instability that can destroy a whole disc in as little as 10 4 years, shows that the outer disc left can be very short-lived (depending on the X-ray luminosity of the star), possibly explaining why very few non accreting transition discs are observed. However the mechanism does not seem to be efficient enough to reconcile with observations. In this thesis we also show that X-ray photo-evaporation naturally explains the observed correlation between stellar masses and accretion

Dispersant effectiveness: Studies into the causes of effectiveness variations

International Nuclear Information System (INIS)

Fingas, M.F.; Kyle, D.; Tennyson, E.

1995-01-01

Effectiveness, a key issue of using dispersants, is affected by many interrelated factors. The principal factors involved are the oil composition, dispersant formulation, sea surface turbulence and dispersant quantity. Oil composition is a very strong determinant. Current dispersant formulation effectiveness correlates strongly with the amount of saturate component in the oil. The other components of the oil, the asphaltenes, resins or polars and aromatic fractions show a negative correlation with the dispersant effectiveness. Viscosity is also a predictor of dispersant effectiveness and may have an effect because it is in turn determined by oil composition. Dispersant composition is significant and interacts with oil composition. Dispersants show high effectiveness at HLB values near 10. Sea turbulence strongly affects dispersant effectiveness.Effectiveness rises with increasing turbulence to a maximum value. Effectiveness for current commercial dispersants is gaussian around a peak salinity value. Peak effectiveness is achieved at very high dispersant quantities--at a ratio of 1:5, dispersant-to-oil volume. Dispersant effectiveness for those oils tested and under the conditions measured, is approximately logarithmic with dispersant quantity and will reach about 50% of its peak value at a dispersant to oil ratio of about 1:20 and near zero at a ratio of about 1:50

Dispersive solitary wave solutions of Kadomtsev-Petviashvili and modified Kadomtsev-Petviashvili dynamical equations in unmagnetized dust plasma

Science.gov (United States)

Seadawy, A. R.; El-Rashidy, K.

2018-03-01

The Kadomtsev-Petviashvili (KP) and modified KP equations are two of the most universal models in nonlinear wave theory, which arises as a reduction of system with quadratic nonlinearity which admit weakly dispersive waves. The generalized extended tanh method and the F-expansion method are used to derive exact solitary waves solutions of KP and modified KP equations. The region of solutions are displayed graphically.

Dispersion properties of photonic crystal fibres

DEFF Research Database (Denmark)

Bjarklev, Anders Overgaard; Broeng, Jes; Dridi, Kim

1998-01-01

Approximate dispersion and bending properties of all-silica two-dimensional photonic crystal fibres are characterised by the combination of an effective-index model and classical analysis tools for optical fibres. We believe for the first time to have predicted the dispersion properties of photonic...... crystal fibres. The results strongly indicate that these fibres have potential applications as dispersion managing components...

Theory of electron cyclotron heating in the Constance II experiment

International Nuclear Information System (INIS)

Mauel, M.E.

1981-03-01

The bounce-averaged quasi-linear equation for a non-relativistic mirror-confined plasma interacting with electromagnetic waves is derived for use in the study of ECRH of the Constance II mirror experiment. The derivations follows the more formal examples given by Berk for electrostatic waves and Bernstein and Baxter for relativistic plasmas. The validity of the theory is discussed by examining individual particle orbits in an EM field. The local dispersion relation is found while deriving a self-consistent WKB theory which can be used to estimate the power transferred from the launching horn to the plasma

Generalized Lorentz-Dirac Equation for a Strongly Coupled Gauge Theory

Science.gov (United States)

Chernicoff, Mariano; García, J. Antonio; Güijosa, Alberto

2009-06-01

We derive a semiclassical equation of motion for a “composite” quark in strongly coupled large-Nc N=4 super Yang-Mills theory, making use of the anti-de Sitter space/conformal field theory correspondence. The resulting nonlinear equation incorporates radiation damping, and reduces to the standard Lorentz-Dirac equation for external forces that are small on the scale of the quark Compton wavelength, but has no self-accelerating or preaccelerating solutions. From this equation one can read off a nonstandard dispersion relation for the quark, as well as a Lorentz-covariant formula for its radiation rate.

Generalized Lorentz-Dirac Equation for a Strongly Coupled Gauge Theory

International Nuclear Information System (INIS)

Chernicoff, Mariano; Garcia, J. Antonio; Gueijosa, Alberto

2009-01-01

We derive a semiclassical equation of motion for a 'composite' quark in strongly coupled large-N c N=4 super Yang-Mills theory, making use of the anti-de Sitter space/conformal field theory correspondence. The resulting nonlinear equation incorporates radiation damping, and reduces to the standard Lorentz-Dirac equation for external forces that are small on the scale of the quark Compton wavelength, but has no self-accelerating or preaccelerating solutions. From this equation one can read off a nonstandard dispersion relation for the quark, as well as a Lorentz-covariant formula for its radiation rate.

Dispersion-engineered and highly-nonlinear microstructured polymer optical fibres

DEFF Research Database (Denmark)

Frosz, Michael Henoch; Nielsen, Kristian; Hlubina, Petr

2009-01-01

We demonstrate dispersion-engineering of microstructured polymer optical fibres (mPOFs) made of poly(methyl methacrylate) (PMMA). A significant shift of the total dispersion from the material dispersion is confirmed through measurement of the mPOF dispersion using white-light spectral interferome......We demonstrate dispersion-engineering of microstructured polymer optical fibres (mPOFs) made of poly(methyl methacrylate) (PMMA). A significant shift of the total dispersion from the material dispersion is confirmed through measurement of the mPOF dispersion using white-light spectral...

On the local field method with the account of spatial dispersion. Application to the optical activity theory

Science.gov (United States)

Tyu, N. S.; Ekhilevsky, S. G.

1992-07-01

For the perfect molecular crystals the equations of the local field method (LFM) with the account of spatial dispersion are formulated. They are used to derive the expression for the crystal polarizability tensor. For the first time within the framework of this method the formula for the gyrotropy tensor of an arbitrary optically active molecular crystal is obtained. This formula is analog of well known relationships of Lorentz-Lorenz.

The physiological effects of oil, dispersant and dispersed oil on the bay mussel, Mytilus trossulus, in Arctic/Subarctic conditions.

Science.gov (United States)

Counihan, Katrina L

2018-06-01

Increasing oil development around Alaska and other Arctic regions elevates the risk for another oil spill. Dispersants are used to mitigate the impact of an oil spill by accelerating natural degradation processes, but the reduced hydrophobicity of dispersed oil may increase its bioavailability to marine organisms. There is limited research on the effect of dispersed oil on cold water species and ecosystems. Therefore, spiked exposure tests were conducted with bay mussels (Mytilus trossulus) in seawater with non-dispersed oil, Corexit 9500 and oil dispersed with different concentrations of Corexit 9500. After three weeks of exposure, acute and chronic physiological impacts were determined. The majority of physiological responses occurred during the first seven days of exposure, with mussels exhibiting significant cytochrome P450 activity, superoxide dismutase activity and heat shock protein levels. Mussels exposed to non-dispersed oil also experienced immune suppression, reduced transcription and higher levels of mortality. After 21 days, mussels in all treatments exhibited evidence of genetic damage, tissue loss and a continued stress response. Bay mussels are useful as indicators of ecosystem health and recovery, and this study was an important step in understanding how non-dispersed oil, dispersant and dispersed oil affect the physiology of this sentinel species in Arctic/subarctic conditions. Copyright © 2018 Elsevier B.V. All rights reserved.

Analytical properties and behaviour of scattering amplitude at high energies in the localizable quantum field theory

International Nuclear Information System (INIS)

Lazur, V.Yu.; Khimich, I.V.

1977-01-01

Analytical properties of the elastic πN-scattering amplitude in in the cos THETA are proved in the Lehmann ellipse. The instrument for establishing analytical properties of the scattering amplitude in the cos THETA is the Jost-Lehmann-Dyson integral representation proved in terms of the localizable quantum field theory containing the strictly localizable theory and theory of moderate growth as particular cases. On this basis the Greenberg-Low restriction is obtained in frames of this class theories for the πN-scattering amplitude. This result gives a possibility to prove the ordinary dispersion relations with a finite number of subtraction in frames of the localizable quantum field theory

Experimental procedure for determination of dispersion coefficient in a column of porous medium using radiotracer; Procedimento experimental para determinacao do coeficiente de dispersao num meio poroso em coluna utilizando radiotracador

Energy Technology Data Exchange (ETDEWEB)

Souza, Roberto de [Universidade Federal, Rio de Janeiro, RJ (Brazil). Coordenacao dos Programas de Pos-graduacao de Engenharia; Heilbron Filho, Paulo Fernando Lavalle [Comissao Nacional de Energia Nuclear (CNEN), Rio de Janeiro, RJ (Brazil)

1997-12-31

The experimental procedures used for determination of parameters such as the molecular diffusion and the diffusion by mechanical convection, responsible for the dispersion in the porous medium, are presented. The experiments were conduct in a column, based on the theory of hydrodynamic dispersion. The radiotracer technique was employed to monitor the dispersion of the radioactive cloud through the porous medium. The radionuclide employed was the bromide 82 (Br{sup 82}), in the KBr chemical form 11 refs., 5 figs., 4 tabs.; e-mail: rs at serv.com.ufrj.br; paulo at cnen.gov.br

Progress in urban dispersion studies

DEFF Research Database (Denmark)

Batchvarova, E.; Gryning, Sven-Erik

2006-01-01

The present Study addresses recent achievements in better representation Of the urban area structure in meteorology and dispersion parameterisations. The setup and Main Outcome of several recent dispersion experiments in Urban areas and their use in model validation are discussed. The maximum con...

Coping with power dispersion?

DEFF Research Database (Denmark)

2014-01-01

The last decades have witnessed a significant shift in policy competences away from central governments in Europe. The reallocation of competences spans over three dimensions: upwards; sideways; and downwards. This collection takes the dispersion of powers as a starting point and seeks to assess...... how the actors involved cope with the new configurations. In this introduction, we discuss the conceptualization of power dispersion and highlight the ways in which the contributions add to this research agenda. We then outline some general conclusions and end by indicating future avenues of research....... Taken together, the collection contributes some answers to the challenge of defining and measuring – in a comparative way – the control and co-ordination mechanisms which power dispersion generates. It also explores the tension between political actors' quest for autonomy and the acknowledgement...

Pay Dispersion and Performance in Teams

Science.gov (United States)

Bucciol, Alessandro; Foss, Nicolai J.; Piovesan, Marco

2014-01-01

Extant research offers conflicting predictions about the effect of pay dispersion on team performance. We collected a unique dataset from the Italian soccer league to study the effect of intra-firm pay dispersion on team performance, under different definitions of what constitutes a “team”. This peculiarity of our dataset can explain the conflicting evidence. Indeed, we also find positive, null, and negative effects of pay dispersion on team performance, using the same data but different definitions of team. Our results show that when the team is considered to consist of only the members who directly contribute to the outcome, high pay dispersion has a detrimental impact on team performance. Enlarging the definition of the team causes this effect to disappear or even change direction. Finally, we find that the detrimental effect of pay dispersion is due to worse individual performance, rather than a reduction of team cooperation. PMID:25397615

Axial dispersion, holdup and slip velocity of dispersed phase in a pulsed sieve plate extraction column by radiotracer residence time distribution analysis.

Science.gov (United States)

Din, Ghiyas Ud; Chughtai, Imran Rafiq; Inayat, Mansoor Hameed; Khan, Iqbal Hussain

2008-12-01

Axial dispersion, holdup and slip velocity of dispersed phase have been investigated for a range of dispersed and continuous phase superficial velocities in a pulsed sieve plate extraction column using radiotracer residence time distribution (RTD) analysis. Axial dispersion model (ADM) was used to simulate the hydrodynamics of the system. It has been observed that increase in dispersed phase superficial velocity results in a decrease in its axial dispersion and increase in its slip velocity while its holdup increases till a maximum asymptotic value is achieved. An increase in superficial velocity of continuous phase increases the axial dispersion and holdup of dispersed phase until a maximum value is obtained, while slip velocity of dispersed phase is found to decrease in the beginning and then it increases with increase in superficial velocity of continuous phase.

Quantitative schemes in energy dispersive X-ray fluorescence implemented in AXIL

International Nuclear Information System (INIS)

Tchantchane, A.; Benamar, M.A.; Tobbeche, S.

1995-01-01

E.D.X.R.F (Energy Dispersive X-ray Fluorescence) has long been used for quantitative analysis of many types of samples including environment samples. the software package AXIL (Analysis of x-ray spectra by iterative least quares) is extensively used for the spectra analysis and the quantification of x-ray spectra. It includes several methods of quantitative schemes for evaluating element concentrations. We present the general theory behind each scheme implemented into the software package. The spectra of the performance of each of these quantitative schemes. We have also investigated their performance relative to the uncertainties in the experimental parameters and sample description

Larval fish dispersal in a coral-reef seascape

KAUST Repository

Almany, Glenn R.; Planes, Serge; Thorrold, Simon R.; Berumen, Michael L.; Bode, Michael; Saenz Agudelo, Pablo; Bonin, Mary C.; Frisch, Ashley J.; Harrison, Hugo B.; Messmer, Vanessa; Nanninga, Gerrit B.; Priest, Mark; Srinivasan, Maya; Sinclair-Taylor, Tane; Williamson, David H.; Jones, Geoffrey P.

2017-01-01

Larval dispersal is a critical yet enigmatic process in the persistence and productivity of marine metapopulations. Empirical data on larval dispersal remain scarce, hindering the use of spatial management tools in efforts to sustain ocean biodiversity and fisheries. Here we document dispersal among subpopulations of clownfish (Amphiprion percula) and butterflyfish (Chaetodon vagabundus) from eight sites across a large seascape (10,000 km2) in Papua New Guinea across 2 years. Dispersal of clownfish was consistent between years, with mean observed dispersal distances of 15 km and 10 km in 2009 and 2011, respectively. A Laplacian statistical distribution (the dispersal kernel) predicted a mean dispersal distance of 13–19 km, with 90% of settlement occurring within 31–43 km. Mean dispersal distances were considerably greater (43–64 km) for butterflyfish, with kernels declining only gradually from spawning locations. We demonstrate that dispersal can be measured on spatial scales sufficient to inform the design of and test the performance of marine reserve networks.

Larval fish dispersal in a coral-reef seascape

KAUST Repository

Almany, Glenn R.

2017-05-23

Larval dispersal is a critical yet enigmatic process in the persistence and productivity of marine metapopulations. Empirical data on larval dispersal remain scarce, hindering the use of spatial management tools in efforts to sustain ocean biodiversity and fisheries. Here we document dispersal among subpopulations of clownfish (Amphiprion percula) and butterflyfish (Chaetodon vagabundus) from eight sites across a large seascape (10,000 km2) in Papua New Guinea across 2 years. Dispersal of clownfish was consistent between years, with mean observed dispersal distances of 15 km and 10 km in 2009 and 2011, respectively. A Laplacian statistical distribution (the dispersal kernel) predicted a mean dispersal distance of 13–19 km, with 90% of settlement occurring within 31–43 km. Mean dispersal distances were considerably greater (43–64 km) for butterflyfish, with kernels declining only gradually from spawning locations. We demonstrate that dispersal can be measured on spatial scales sufficient to inform the design of and test the performance of marine reserve networks.

Velocity Dispersions Across Bulge Types

International Nuclear Information System (INIS)

Fabricius, Maximilian; Bender, Ralf; Hopp, Ulrich; Saglia, Roberto; Drory, Niv; Fisher, David

2010-01-01

We present first results from a long-slit spectroscopic survey of bulge kinematics in local spiral galaxies. Our optical spectra were obtained at the Hobby-Eberly Telescope with the LRS spectrograph and have a velocity resolution of 45 km/s (σ*), which allows us to resolve the velocity dispersions in the bulge regions of most objects in our sample. We find that the velocity dispersion profiles in morphological classical bulge galaxies are always centrally peaked while the velocity dispersion of morphologically disk-like bulges stays relatively flat towards the center--once strongly barred galaxies are discarded.

Effect of mechanical and chemical clay removals by hydrocyclone and dispersants on coal flotation

Energy Technology Data Exchange (ETDEWEB)

Oats, W.J.; Ozdemir, O.; Nguyen, A.V. [University of Queensland, Brisbane, Qld. (Australia). School of Chemical Engineering

2010-04-15

Fine minerals, mostly clays, are known to have a detrimental effect on coal flotation. This paper focuses on the effect of mechanical and chemical removals of fine minerals by hydrocyclone and dispersants on coal flotation. The experimental results showed that the flotation recovery slightly increased from medium acidic to medium alkaline ranges. The flotation experiments carried out with dispersants at different dosages showed that the dispersants did not enhance the flotation recovery significantly. However, the removal of the fine fraction from the feed using a hydrocyclone significantly increased the flotation recovery. The bubble-particle attachment tests also indicated that the attachment time between an air bubble and the coal particles increased in the presence of clay particles. These attachment time results clearly showed that the clay particles adversely affected the flotation of coal particles by covering the coal surfaces which reduced the efficiency of bubble-coal attachment. An analysis based on the colloid stability theory showed that the clay coating was governed by the van der Waals attraction and that the double-layer interaction played a secondary role. It was also concluded that the best way to increase the flotation recovery in the presence of clays was to remove these fine minerals by mechanical means such as hydrocylones.

A classical density functional theory of ionic liquids.

Science.gov (United States)

Forsman, Jan; Woodward, Clifford E; Trulsson, Martin

2011-04-28

We present a simple, classical density functional approach to the study of simple models of room temperature ionic liquids. Dispersion attractions as well as ion correlation effects and excluded volume packing are taken into account. The oligomeric structure, common to many ionic liquid molecules, is handled by a polymer density functional treatment. The theory is evaluated by comparisons with simulations, with an emphasis on the differential capacitance, an experimentally measurable quantity of significant practical interest.

Measurement of small dispersion values in optical components

DEFF Research Database (Denmark)

Peucheret, Christophe; Liu, Fenghai; Pedersen, Rune Johan Skullerud

1999-01-01

It is reported that small dispersion values in optical components can be measured using the RF modulation method originally restricted to large dispersions. Using a constant dispersion offset, arbitrarily small dispersion values can be measured with a resolution as good as 1.2 ps/nm....

Electroacoustic theory for concentrated colloids with overlapped DLs at arbitrary kappa alpha. I. Application to nanocolloids and nonaqueous colloids.

Science.gov (United States)

Shilov, V N; Borkovskaja, Y B; Dukhin, A S

2004-09-15

Existing theories of electroacoustic phenomena in concentrated colloids neglect the possibility of double layer overlap and are valid mostly for the "thin double layer," when the double layer thickness is much less than the particle size. In this paper we present a new electroacoustic theory which removes this restriction. This would make this new theory applicable to characterizing a variety of aqueous nanocolloids and of nonaqueous dispersions. There are two versions of the theory leading to the analytical solutions. The first version corresponds to strongly overlapped diffuse layers (so-called quasi-homogeneous model). It yields a simple analytical formula for colloid vibration current (CVI), which is valid for arbitrary ultrasound frequency, but for restricted kappa alpha range. This version of the theory, as well the Smoluchowski theory for microelectrophoresis, is independent of particle shape and polydispersity. This makes it very attractive for practical use, with the hope that it might be as useful as classical Smoluchowski theory. In order to determine the kappa alpha range of the quasi-homogeneous model validity we develop the second version that limits ultrasound frequency, but applies no restriction on kappa alpha. The ultrasound frequency should substantially exceed the Maxwell-Wagner relaxation frequency. This limitation makes active conductivity related current negligible compared to the passive dielectric displacement current. It is possible to derive an expression for CVI in the concentrated dispersion as formulae inhering definite integrals with integrands depending on equilibrium potential distribution. This second version allowed us to estimate the ranges of the applicability of the first, quasi-homogeneous version. It turns out that the quasi-homogeneous model works for kappa alpha values up to almost 1. For instance, at volume fraction 30%, the highest kappa alpha limit of the quasi-homogeneous model is 0.65. Therefore, this version of the

Observables and dispersion relations in κ-Minkowski spacetime

Science.gov (United States)

Aschieri, Paolo; Borowiec, Andrzej; Pachoł, Anna

2017-10-01

We revisit the notion of quantum Lie algebra of symmetries of a noncommutative spacetime, its elements are shown to be the generators of infinitesimal transformations and are naturally identified with physical observables. Wave equations on noncommutative spaces are derived from a quantum Hodge star operator. This general noncommutative geometry construction is then exemplified in the case of κ-Minkowski spacetime. The corresponding quantum Poincaré-Weyl Lie algebra of in-finitesimal translations, rotations and dilatations is obtained. The d'Alembert wave operator coincides with the quadratic Casimir of quantum translations and it is deformed as in Deformed Special Relativity theories. Also momenta (infinitesimal quantum translations) are deformed, and correspondingly the Einstein-Planck relation and the de Broglie one. The energy-momentum relations (dispersion relations) are consequently deduced. These results complement those of the phenomenological literature on the subject.

Model independent dispersion approach to proton Compton scattering

International Nuclear Information System (INIS)

Caprini, I.; Radescu, E.E.

1980-12-01

The proton Compton scattering at low and intermediate energies is studied by means of a dispersion framework which exploits in an optimal way the (fixed momentum transfer) analyticity properties of the amplitudes in conjunction with the consequences of the (s-channel) unitarity. The mathematical background of the work consists of methods specific to boundary value problems for analytic vector-valued functions and interpolation theory. In comparison with previous related work, the external problems to be solved now are much more difficult because of the inclusion of the photoproduction input and also lead to additional computational complications. The lower bounds on the differential cross-section, obtained without any reference to subtractions and annihilation channel contributions, appear sufficiently restrictive to evidentiate rigorously some inconsistencies between results of single pion photoproduction multipole extractions and proton Compton scattering data. (author)

Nonlinear Dispersive Elastic Waves in Solids: Exact, Approximate, and Numerical Solutions

Science.gov (United States)

Khajehtourian, Romik

Wave motion lies at the heart of many disciplines in the physical sciences and engineering. For example, problems and applications involving light, sound, heat, or fluid flow are all likely to involve wave dynamics at some level. A particular class of problems is concerned with the propagation of elastic waves in a solid medium, such as a fiber-reinforced composite material responding to vibratory excitations, or soil and rock admitting seismic waves moments after the onset of an earthquake, or phonon transport in a semiconducting crystal like silicon. Regardless of the type of wave, the dispersion relation provides a fundamental characterization of the elastodynamic properties of the medium. The first part of the dissertation examines the propagation of a large-amplitude elastic wave in a one-dimensional homogeneous medium with a focus on the effects of inherent nonlinearities on the dispersion relation. Considering a thin rod, where the thickness is small compared to the wavelength, an exact, closed-form formulation is presented for the treatment of two types of nonlinearity in the strain-displacement gradient relation: Green-Lagrange and Hencky. The derived relation is then verified by direct time-domain simulations, examining both instantaneous dispersion (by direct observation) and short-term, pre-breaking dispersion (by Fourier transformation). A high-order perturbation analysis is also conducted yielding an explicit analytical space-time solution, which is shown to be spectrally accurate. The results establish a perfect match between theory and simulation and reveal that regardless of the strength of the nonlinearity, the dispersion relation fully embodies all information pertaining to the nonlinear harmonic generation mechanism that unfolds as an arbitrary-profiled wave evolves in the medium. In the second part of the dissertation, the analysis is extended to a continuous periodic thin rod exhibiting multiple phases or embedded local resonators. The

Analysis of site-specific dispersion conditions

International Nuclear Information System (INIS)

Paesler-Sauer, J.

1989-03-01

This report presents an analysis of atmospheric dispersion conditions in the environs of nuclear power stations in the Federal Republic of Germany. The analysis is based on meteorological data measured on the power station sites (KFUe = nuclear reactor remote control records) and by neighbouring stations operated by the German Weather Service. The data are series of hourly mean values of wind and temperature gradient or stability class over the period of one or more years. The aim of the data analysis is to find types of dispersion conditions characterized by the flow field and stratification, and to assess the feasibility of calculating these quantities in the case of an emergency. Influences of terrain structures in the environs of the site are considered. The annual frequencies of types of dispersion situations are assessed, the capability to recognize the dispersion situation from meteorological data measured on the site and the applicability of dispersion models are discussed. (orig.) [de

Lattice instability and martensitic transformation in LaAg predicted from first-principles theory

DEFF Research Database (Denmark)

Vaitheeswaran, G.; Kanchana, V.; Zhang, X.

2012-01-01

The electronic structure, elastic constants and lattice dynamics of the B2 type intermetallic compound LaAg are studied by means of density functional theory calculations with the generalized gradient approximation for exchange and correlation. The calculated equilibrium properties and elastic......, calculated using density functional perturbation theory, are in good agreement with available inelastic neutron scattering data. Under pressure, the phonon dispersions develop imaginary frequencies, starting at around 2.3 GPa, in good accordance with the martensitic instability observed above 3.4 GPa...

Canine goniodysgenesis-related glaucoma: a morphologic review of 100 cases looking at inflammation and pigment dispersion.

Science.gov (United States)

Reilly, Christopher M; Morris, Rebecca; Dubielzig, Richard R

2005-01-01

To investigate the role of pigment dispersion and inflammation in the pathogenesis of goniodysgenesis-related glaucoma (GDRG). Cases of GDRG were selected when the duration of the disease was specified and there was not any confounding pathology. Cases were grouped into 7-day (chronic) durations, based on the time required to effect end-stage retinal damage. Acute cases were further divided into pigment dispersion: segmental loss of posterior iris pigment epithelium, clumping of posterior iris pigment epithelium, pigmented cells in the trabecular meshwork or anterior chamber and preferential settling of pigmented cells in the ventral aspect of the iridocorneal angle. Slides were also evaluated for the presence of neutrophils and/or lymphoplasmacytic cells in the trabecular meshwork (TM). Differences between groups were analyzed statistically. Of 100 cases evaluated, 34 were 7-days (chronic) in duration. Of all globes examined, 96% had at least one sign of pigment dispersion, with no significant difference between groups. Two or more signs of pigment dispersion were present in 76% of all globes. The 4-7-day group was significantly more likely than the 7-day groups. Neutrophils were present in the TM of 86% of 7-day cases to have neutrophils in the TM, with 65% and 17% [corrected] positive cases, respectively. Lymphoplasmacytic inflammation was present in 53% of all cases, with no significant difference between groups. Cases in the 7-day cases to have both types of inflammation. Our results indicate that both acute inflammation and pigment dispersion may be key factors in the pathogenesis of GDRG. Pigment dispersion is prevalent at all time points and increases during the first 7 days. The finding of iris pigment epithelial loss supports the theory that pupillary block associated with iris-lens touching may be important in the pathogenesis of GDRG.

Transoceanic Dispersal and Plate Tectonics Shaped Global Cockroach Distributions: Evidence from Mitochondrial Phylogenomics.

Science.gov (United States)

Bourguignon, Thomas; Tang, Qian; Ho, Simon Y W; Juna, Frantisek; Wang, Zongqing; Arab, Daej A; Cameron, Stephen L; Walker, James; Rentz, David; Evans, Theodore A; Lo, Nathan

2017-04-01

Following the acceptance of plate tectonics theory in the latter half of the 20th century, vicariance became the dominant explanation for the distributions of many plant and animal groups. In recent years, however, molecular-clock analyses have challenged a number of well-accepted hypotheses of vicariance. As a widespread group of insects with a fossil record dating back 300 My, cockroaches provide an ideal model for testing hypotheses of vicariance through plate tectonics versus transoceanic dispersal. However, their evolutionary history remains poorly understood, in part due to unresolved relationships among the nine recognized families. Here, we present a phylogenetic estimate of all extant cockroach families, as well as a timescale for their evolution, based on the complete mitochondrial genomes of 119 cockroach species. Divergence dating analyses indicated that the last common ancestor of all extant cockroaches appeared ∼235 Ma, ∼95 My prior to the appearance of fossils that can be assigned to extant families, and before the breakup of Pangaea began. We reconstructed the geographic ranges of ancestral cockroaches and found tentative support for vicariance through plate tectonics within and between several major lineages. We also found evidence of transoceanic dispersal in lineages found across the Australian, Indo-Malayan, African, and Madagascan regions. Our analyses provide evidence that both vicariance and dispersal have played important roles in shaping the distribution and diversity of these insects.

GSpecDisp: A matlab GUI package for phase-velocity dispersion measurements from ambient-noise correlations

Science.gov (United States)

Sadeghisorkhani, Hamzeh; Gudmundsson, Ólafur; Tryggvason, Ari

2018-01-01

We present a graphical user interface (GUI) package to facilitate phase-velocity dispersion measurements of surface waves in noise-correlation traces. The package, called GSpecDisp, provides an interactive environment for the measurements and presentation of the results. The selection of a dispersion curve can be done automatically or manually within the package. The data are time-domain cross-correlations in SAC format, but GSpecDisp measures phase velocity in the spectral domain. Two types of phase-velocity dispersion measurements can be carried out with GSpecDisp; (1) average velocity of a region, and (2) single-pair phase velocity. Both measurements are done by matching the real part of the cross-correlation spectrum with the appropriate Bessel function. Advantages of these two types of measurements are that no prior knowledge about surface-wave dispersion in the region is needed, and that phase velocity can be measured up to that period for which the inter-station distance corresponds to one wavelength. GSpecDisp can measure the phase velocity of Rayleigh and Love waves from all possible components of the noise correlation tensor. First, we briefly present the theory behind the methods that are used, and then describe different modules of the package. Finally, we validate the developed algorithms by applying them to synthetic and real data, and by comparison with other methods. The source code of GSpecDisp can be downloaded from: https://github.com/Hamzeh-Sadeghi/GSpecDisp

Rheological Behavior of Bentonite-Polyester Dispersions

Science.gov (United States)

Abu-Jdayil, Basim; Al-Omari, Salah Addin

2013-07-01

The rheological behavior of a bentonite clay dispersed in unsaturated polyester was investigated. The effects of the solid content and particle size on the steady and transient rheological properties of the dispersions were studied. In addition, two types of bentonite with different Na+/Ca+2 ratio were used in this study. The Herschel-Bulkley and the Weltman models were used to describe the apparent viscosity of the bentonite-polyester composite in relation to the shear rate and shearing time. The bentonite-polyester dispersions were found to exhibit both Newtonian and non-Newtonian behavior. The transition from a Newtonian to a Bingham plastic and then to a shear-thinning material with a yield stress was found to depend on the solid concentration, the particle size, and the type of bentonite. At a low solid content, the apparent viscosity of the bentonite dispersion increased linearly with solid concentration. But a dramatic increase in the apparent viscosity beyond a solid content of 20 wt.% was observed. On the other hand, a thixotropic behavior was detected in bentonite-polyester dispersions with a high solid content and a low particle size. However, this behavior was more pronounced in dispersions with a high Na+/Ca+2 ratio.

Relation of wave energy and momentum with the plasma dispersion relation in an inhomogeneous plasma

International Nuclear Information System (INIS)

Berk, H.L.; Pfirsch, D.

1988-01-01

The expressions for wave energy and angular momentum commonly used in homogeneous and near-homogeneous media is generalized to inhomogeneous media governed by a nonlocal conductivity tensor. The expression for wave energy applies to linear excitations in an arbitrary three-dimensional equilibrium, while the expression for angular momentum applies to linear excitations of azimuthally symmetric equilibria. The wave energy E-script/sub wave/ is interpreted as the energy transferred from linear external sources to the plasma if there is no dissipation. With dissipation, such a simple interpretation is lacking as energy is also thermally absorbed. However, for azimuthally symmetric equilibria, the expression for the wave energy in a frame rotating with a frequency ω can be unambiguously separated from thermal energy. This expression is given by E-script/sub wave/ -ωL/sub wave/ l, where L/sub wave/ is the wave angular momentum defined in the text and l the azimuthal wavenumber and it is closely related to the real part of a dispersion relation for marginal stability. The imaginary part of the dispersion is closely related to the energy input into a system. Another useful quantity discussed is the impedance form, which can be used for three-dimensional equilibrium without an ignorable coordinate and the expression is closely related to the wave impedance used in antenna theory. Applications to stability theory are also discussed

THEORY OF DISPERSED FIXED-DELAY INTERFEROMETRY FOR RADIAL VELOCITY EXOPLANET SEARCHES

International Nuclear Information System (INIS)

Van Eyken, Julian C.; Ge Jian; Mahadevan, Suvrath

2010-01-01

The dispersed fixed-delay interferometer (DFDI) represents a new instrument concept for high-precision radial velocity (RV) surveys for extrasolar planets. A combination of a Michelson interferometer and a medium-resolution spectrograph, it has the potential for performing multi-object surveys, where most previous RV techniques have been limited to observing only one target at a time. Because of the large sample of extrasolar planets needed to better understand planetary formation, evolution, and prevalence, this new technique represents a logical next step in instrumentation for RV extrasolar planet searches, and has been proven with the single-object Exoplanet Tracker (ET) at Kitt Peak National Observatory, and the multi-object W. M. Keck/MARVELS Exoplanet Tracker at Apache Point Observatory. The development of the ET instruments has necessitated fleshing out a detailed understanding of the physical principles of the DFDI technique. Here we summarize the fundamental theoretical material needed to understand the technique and provide an overview of the physics underlying the instrument's working. We also derive some useful analytical formulae that can be used to estimate the level of various sources of error generic to the technique, such as photon shot noise when using a fiducial reference spectrum, contamination by secondary spectra (e.g., crowded sources, spectroscopic binaries, or moonlight contamination), residual interferometer comb, and reference cross-talk error. Following this, we show that the use of a traditional gas absorption fiducial reference with a DFDI can incur significant systematic errors that must be taken into account at the precision levels required to detect extrasolar planets.

The Braer incident: Dispersion in action

International Nuclear Information System (INIS)

Thomas, D.

1993-01-01

In January 1993, the tanker Braer foundered in the Shetland Islands and pollution from the cargo of 85,000 tonnes of Gullfaks crude oil was reported almost immediately. The tanker was battered by storm winds and finally broke up, spilling the remainder of its cargo into the bay at Garth's Ness. Dispersants were applied to the oil plumes, assisting the significant natural dispersion. Shoreline protection and cleanup activities included construction of spade dams and sorbent barriers. Oil concentrations in water, air, sediment, and fish were monitored. The sampling program undertaken during the spill period is described. Measured hydrocarbon concentrations in salmon farm areas were not observed to rise above 4 ppM. The high rates of dispersion make the Braer incident worthy of detailed study both in terms of understanding the mechanism of the dispersion process and also in assessing the environmental effects following high dispersed oil concentrations. Estimates of the spill's mass balance are provided for the bay at Garth's Ness, where the highest oil concentrations were observed, and along the 26 km of coastline which received the most significant concentrations of dispersed oil. Contrary to laboratory experiments which showed that the Gullfaks crude would emulsify at the high sea states prevailing at the time, the Braer spill did not emulsify and most of the oil released was dispersed naturally into the water column. It appears that it is most appropriate to model the Braer spill as a spillage of floating or dissolved chemical. 4 refs., 4 figs., 6 tabs

The comparative effects of oil dispersants and oil/dispersant conjugates on germination of the marine macroalga Phyllospora comosa (Fucales: Phaeophyta)