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1

Aharonov–Bohm effects in magnetohydrodynamics  

NASA Astrophysics Data System (ADS)

It is shown that an Aharonov–Bohm (AB) effect exists in magnetohydrodynamics (MHD). This effect is best described in terms of the MHD variational variables (Kats, 2004; Yahalom and Lynden-Bell, 2008; Yahalom, 2010) [1,10,12]. If a MHD flow has a non-trivial topology some of the functions appearing in the MHD Lagrangian are non-single-valued. These functions have properties similar to the phases in the AB celebrated effect (Aharonov and Bohm, 1959; van Oudenaarden et al., 1998) [2,3]. While the manifestation of the quantum AB effect is in interference fringe patterns (Tonomura et al., 1982) [4], the manifestation of the MHD Aharonov–Bohm effects are through new dynamical conservation laws.

Yahalom, Asher

2013-10-01

2

The electric Aharonov-Bohm effect  

NASA Astrophysics Data System (ADS)

The seminal paper of Aharonov and Bohm [Phys. Rev. 115, 485 (1959)] is at the origin of a very extensive literature in some of the more fundamental issues in physics. They claimed that electromagnetic fields can act at a distance on charged particles even if they are identically zero in the region of space where the particles propagate, that the fundamental electromagnetic quantities in quantum physics are not only the electromagnetic fields but also the circulations of the electromagnetic potentials; what gives them a real physical significance. They proposed two experiments to verify their theoretical conclusions. The magnetic Aharonov-Bohm effect, where an electron is influenced by a magnetic field that is zero in the region of space accessible to the electron, and the electric Aharonov-Bohm effect where an electron is affected by a time-dependent electric potential that is constant in the region where the electron is propagating, i.e., such that the electric field vanishes along its trajectory. The Aharonov-Bohm effects imply such a strong departure from the physical intuition coming from classical physics that it is no wonder that they remain a highly controversial issue after more than fifty years, in spite of the fact that they are discussed in most of the text books in quantum mechanics. The magnetic case has been studied extensively. The experimental issues were settled by the remarkable experiments of Tonomura et al. [Phys. Rev. Lett. 48, 1443 (1982); Phys. Rev. Lett. 56, 792 (1986)] with toroidal magnets, that gave a strong evidence of the existence of the effect, and by the recent experiment of Caprez et al. [Phys. Rev. Lett. 99, 210401 (2007)] that shows that the results of the Tonomura et al. experiments cannot be explained by the action of a force. The theoretical issues were settled by Ballesteros and Weder [Commun. Math. Phys. 285, 345 (2009); J. Math. Phys. 50, 122108 (2009); Commun. Math. Phys. 303, 175 (2011)] who rigorously proved that quantum mechanics predicts the experimental results of Tonomura et al. and of Caprez et al. The electric Aharonov-Bohm effect has been much less studied. Actually, its existence, that has not been confirmed experimentally, is a very controversial issue. In their 1959 paper Aharonov and Bohm proposed an ansatz for the solution to the Schrödinger equation in regions where there is a time-dependent electric potential that is constant in space. It consists in multiplying the free evolution by a phase given by the integral in time of the potential. The validity of this ansatz predicts interference fringes between parts of a coherent electron beam that are subjected to different potentials. In this paper we prove that the exact solution to the Schrödinger equation is given by the Aharonov-Bohm ansatz up to an error bound in norm that is uniform in time and that decays as a constant divided by the velocity. Our results give, for the first time, a rigorous proof that quantum mechanics predicts the existence of the electric Aharonov-Bohm effect, under conditions that we provide. We hope that our results will stimulate the experimental research on the electric Aharonov-Bohm effect.

Weder, Ricardo

2011-05-01

3

The electric Aharonov-Bohm effect  

SciTech Connect

The seminal paper of Aharonov and Bohm [Phys. Rev. 115, 485 (1959)] is at the origin of a very extensive literature in some of the more fundamental issues in physics. They claimed that electromagnetic fields can act at a distance on charged particles even if they are identically zero in the region of space where the particles propagate, that the fundamental electromagnetic quantities in quantum physics are not only the electromagnetic fields but also the circulations of the electromagnetic potentials; what gives them a real physical significance. They proposed two experiments to verify their theoretical conclusions. The magnetic Aharonov-Bohm effect, where an electron is influenced by a magnetic field that is zero in the region of space accessible to the electron, and the electric Aharonov-Bohm effect where an electron is affected by a time-dependent electric potential that is constant in the region where the electron is propagating, i.e., such that the electric field vanishes along its trajectory. The Aharonov-Bohm effects imply such a strong departure from the physical intuition coming from classical physics that it is no wonder that they remain a highly controversial issue after more than fifty years, in spite of the fact that they are discussed in most of the text books in quantum mechanics. The magnetic case has been studied extensively. The experimental issues were settled by the remarkable experiments of Tonomura et al. [Phys. Rev. Lett. 48, 1443 (1982); Phys. Rev. Lett. 56, 792 (1986)] with toroidal magnets, that gave a strong evidence of the existence of the effect, and by the recent experiment of Caprez et al. [Phys. Rev. Lett. 99, 210401 (2007)] that shows that the results of the Tonomura et al. experiments cannot be explained by the action of a force. The theoretical issues were settled by Ballesteros and Weder [Commun. Math. Phys. 285, 345 (2009); J. Math. Phys. 50, 122108 (2009); Commun. Math. Phys. 303, 175 (2011)] who rigorously proved that quantum mechanics predicts the experimental results of Tonomura et al. and of Caprez et al. The electric Aharonov-Bohm effect has been much less studied. Actually, its existence, that has not been confirmed experimentally, is a very controversial issue. In their 1959 paper Aharonov and Bohm proposed an ansatz for the solution to the Schroedinger equation in regions where there is a time-dependent electric potential that is constant in space. It consists in multiplying the free evolution by a phase given by the integral in time of the potential. The validity of this ansatz predicts interference fringes between parts of a coherent electron beam that are subjected to different potentials. In this paper we prove that the exact solution to the Schroedinger equation is given by the Aharonov-Bohm ansatz up to an error bound in norm that is uniform in time and that decays as a constant divided by the velocity. Our results give, for the first time, a rigorous proof that quantum mechanics predicts the existence of the electric Aharonov-Bohm effect, under conditions that we provide. We hope that our results will stimulate the experimental research on the electric Aharonov-Bohm effect.

Weder, Ricardo [Departamento de Metodos Matematicos y Numericos, Instituto de Investigaciones en Matematicas Aplicadas y en Sistemas, Universidad Nacional Autonoma de Mexico, Apartado Postal 20-726, Mexico DF 01000 (Mexico)

2011-05-15

4

Quantum chaos in Aharonov-Bohm oscillations  

SciTech Connect

Aharonov-Bohm oscillations in a mesoscopic ballistic ring are considered under the influence of a resonant magnetic field with one and two frequencies. The authors investigate the oscillations of the time-averaged electron energy at zero temperature in the regime of an isolated quantum nonlinear resonance and at the transition to quantum chaos, when two quantum nonlinear resonances overlap. It is shown that the time-averaged energy exhibits resonant behavior as a function of the magnetic flux, and has a ``staircase`` dependence on the amplitude of the external field. The delocalization of the quasi-energy eigenfunctions is analyzed.

Berman, G.P. [Los Alamos National Lab., NM (United States). Theoretical Div.; Campbell, D.K. [Univ. of Illinois, Urbana, IL (United States). Dept. of Physics; Bulgakov, E.N. [Kirensky Inst. of Physics, Krasnoyarsk (Russian Federation); Krive, I.V. [Ukrainian Academy of Sciences, Kharkov (Ukraine). Inst. for Low Temperature Physics and Engineering

1995-10-01

5

Gauge invariance of the Aharonov-Bohm effect  

NASA Astrophysics Data System (ADS)

The phase-shift effect described by Aharonov and Bohm (1959) is investigated analytically for the case of a solenoid of finite length. The fundamental principles of EM potential theory are briefly reviewed; the equations for the finite solenoid are derived and analyzed; an idealized experiment with semicircular paths is described; the infinite-length solenoid is considered as a limiting case; and an experiment with rectilinear paths is discussed. The effect is shown to depend entirely on the transverse component of the vector potential and to be gauge invariant. The findings of gauge variance or nonexistence of the Aharonov-Bohm effect (Bocchieri et al., 1979) and its dependence on the B field (Roy, 1980; Home and Sengupta, 1983) are attributed to anomalous properties of the infinite-solenoid case.

Babiker, M.; Loudon, R.

1984-10-01

6

Nondispersive phase of the Aharonov-Bohm effect  

Microsoft Academic Search

An essential signature of the topological nature of all Aharonov-Bohm type phases is that they are nondispersive, i.e., independent of the velocity (wavelength) of the interfering particles. This implies that an Aharonov-Bohm phase shift can greatly exceed the usual limit given by the coherence length of the interfering beams. We report the results of a polarized neutron experiment demonstrating this

Gerald Badurek; Harald Weinfurter; Roland Gähler; Achim Kollmar; Stefan Wehinger; Anton Zeilinger

1993-01-01

7

Aharonov-Casher and scalar Aharonov-Bohm topological effects.  

PubMed

We reexamine the topological and nonlocal natures of the Aharonov-Casher and scalar Aharonov-Bohm phase effects. The underlying U(1) gauge structure is exhibited explicitly. And the conditions for developing topological Aharonov-Casher and scalar Aharonov-Bohm phases are clarified. We analyze the arguments of M. Peshkin and H.?J. Lipkin [Phys. Rev. Lett. 74, 2847 (1995)] in detail and show that they are based on the wrong Hamiltonian which yields their conclusion incorrect. PMID:22401183

Dulat, Sayipjamal; Ma, Kai

2012-02-17

8

Anomalous aharonov-bohm gap oscillations in carbon nanotubes.  

PubMed

The gap oscillations caused by a magnetic flux penetrating a carbon nanotube represent one of the most spectacular observations of the Aharonov-Bohm effect at the nanoscale. Our understanding of this effect is, however, based on the assumption that the electrons are strictly confined on the tube surface, on trajectories that are not modified by curvature effects. Using an ab initio approach based on density functional theory, we show that this assumption fails at the nanoscale inducing important corrections to the physics of the Aharonov-Bohm effect. Curvature effects and electronic density that is spilled out of the nanotube surface are shown to break the periodicity of the gap oscillations. We predict the key phenomenological features of this anomalous Aharonov-Bohm effect in semiconductive and metallic tubes and the existence of a large metallic phase in the low flux regime of multiwalled nanotubes, also suggesting possible experiments to validate our results. PMID:21805987

Sangalli, Davide; Marini, Andrea

2011-08-12

9

Aharonov-Bohm oscillations in a hydrogen atom  

NASA Astrophysics Data System (ADS)

We study both analytically and numerically the influence of a weak magnetic field on the hydrogen atom in a linearly polarized electromagnetic field. The interference pattern between two counter-rotating Trojan wavepackets exhibits an Aharonov-Bohm shift. A simple geometric interpretation is presented which shows the full analogy to the orthodox macroscopic Aharonov-Bohm interference. Long-time phase accumulation permits the observation of potentially arbitrary weak magnetic fields. The differential cross-section for delta-pulse ionization is also calculated and exhibits similar oscillations.

Kalinski, Maciej

1997-04-01

10

Group-theoretical derivation of Aharonov-Bohm phase shifts  

NASA Astrophysics Data System (ADS)

The phase shifts of the Aharonov-Bohm effect are generally determined by means of the partial wave decomposition of the underlying Schrödinger equation. It is shown here that they readily emerge from an o(2,1) calculation of the energy levels employing an added harmonic oscillator potential which discretizes the spectrum.

Hagen, C. R.

2013-02-01

11

Zero Modes in a System of Aharonov-Bohm Fluxes  

Microsoft Academic Search

We study zero modes of two-dimensional Pauli operators with Aharonov-Bohm fluxes in the case when the solenoids are arranged in periodic structures like chains or lattices. We also consider perturbations to such periodic systems which may be infinite and irregular but they are always supposed to be sufficiently scarce.

V. A. Geyler; P. Stovícek

2004-01-01

12

Aharonov-Bohm interactions of a vector unparticle  

NASA Astrophysics Data System (ADS)

Recently Georgi argued that a hypothetical conformally invariant hidden sector weakly interacting with ordinary particles will have unusual manifestations at low energies in terms of effective degrees of freedom called unparticles. In this paper we consider Aharonov-Bohm type of interactions due to the vector unparticle coupled to elementary fermions. We have found that the quantum mechanical phase shift is path dependent.

Kobakhidze, Archil

2007-11-01

13

Aharonov-Bohm effect for a relativistic Dirac electron  

NASA Astrophysics Data System (ADS)

We study the Aharonov-Bohm effect for a Dirac electron. We find that solutions to the Dirac equations are incompatible with the boundary conditions imposed by an impenetrable cylinder of finite radius. We also consider the problem of a magnetic flux shielded by a repulsive cylindrical potential barrier of finite height. Postal address: Carmelitas 4282, Caracas 1010-A, Venezuela.

Percoco, Umberto; Villalba, Víctor M.

1989-09-01

14

Interference of heavy holes in an Aharonov-Bohm ring  

NASA Astrophysics Data System (ADS)

We study the coherent transport of heavy holes through a one-dimensional ring in the presence of spin-orbit coupling. Spin-orbit interaction of holes, cubic in the in-plane components of momentum, gives rise to an angular momentum-dependent spin texture of the eigenstates and influences transport. We analyze the dependence of the resulting differential conductance of the ring on hole polarization of the leads and the signature of the textures in the Aharonov-Bohm oscillations when the ring is in a perpendicular magnetic field. We find that the polarization-resolved conductance reveals whether the dominant spin-orbit coupling is of Dresselhaus or Rashba type, and that the cubic spin-orbit coupling can be distinguished from the conventional linear coupling by observing the four-peak structure in the Aharonov-Bohm oscillations.

Stepanenko, Dimitrije; Lee, Minchul; Burkard, Guido; Loss, Daniel

2009-06-01

15

Observation of Aharonov-Bohm Effect by Electron Holography  

Microsoft Academic Search

In this experiment, an electron- and optical-holographic technique is employed with small toroidal ferromagnets each forming a magnetic-flux closure. The holographic interferometry proves that a phase difference between two electron beams having passed through the field-free regions agrees well with the fundamental relation known as the Aharonov-Bohm effect. It is also confirmed from the same hologram that flux leakage from

Akira Tonomura; Tsuyoshi Matsuda; Ryo Suzuki; Akira Fukuhara; Nobuyuki Osakabe; Hiroshi Umezaki; Junji Endo; Kohsei Shinagawa; Yutaka Sugita; Hideo Fujiwara

1982-01-01

16

Quantum anholonomies in time-dependent Aharonov-Bohm rings  

SciTech Connect

Anholonomies in eigenstates are studied through time-dependent variations of a magnetic flux in an Aharonov-Bohm ring. The anholonomies in the eigenenergy and the expectation values of eigenstates are shown to persist beyond the adiabatic regime. The choice of the gauge of the magnetic flux is shown to be crucial to clarify the relationship of these anholonomies to the eigenspace anholonomy, which is described by a non-Abelian connection in the adiabatic limit.

Tanaka, Atushi; Cheon, Taksu [Department of Physics, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397 (Japan); Laboratory of Physics, Kochi University of Technology, Tosa Yamada, Kochi 782-8502 (Japan)

2010-08-15

17

Quantum Phases: 50 years of the Aharonov--Bohm effect and 25 years of the Berry phase  

Microsoft Academic Search

This special issue celebrates the discovery of two of the most important aspects of quantum mechanics: the Aharonov–Bohm effect and the Berry phase. The issue includes work presented at two conferences, 50 Years of the Aharonov–Bohm Effect, 11–14 October 2009, Tel Aviv University, Israel, and the Aharonov–Bohm Effect and Berry Phase 50\\/25 Anniversary, 14–15 December 2009, Bristol University, UK.The Aharonov–Bohm

Mark Dennis; Sandu Popescu; Lev Vaidman

2010-01-01

18

Aharonov-Bohm effect in a singly connected point contact  

NASA Astrophysics Data System (ADS)

We report the discovery of an oscillation in the low-temperature magnetoresistance of a point contact in the two-dimensional electron gas of a GaAs-AlxGa1-xAs heterostructure. The oscillation is periodic in the magnetic field and is reminiscent of the Aharonov-Bohm effect in rings, although the geometry is singly connected. A possible mechanism for this quantum interference effect is tunneling between edge states across the point contact at the potential step at the entrance and the exit of the constriction.

van Loosdrecht, P. H. M.; Beenakker, C. W. J.; van Houten, H.; Williamson, J. G.; van Wees, B. J.; Mooij, J. E.; Foxon, C. T.; Harris, J. J.

1988-11-01

19

Aharonov-Bohm effect in the chiral Luttinger liquid  

NASA Astrophysics Data System (ADS)

Edge states of the quantum Hall fluid provide an almost unparalled opportunity to study mesoscopic effects in a highly correlated electron system. In this paper we develop a bosonization formalism for the finite-size edge state, as described by chiral Luttinger liquid theory, and use it to study the Aharonov-Bohm effect. The problem we address may be realized experimentally by measuring the tunneling current between two edge states through a third edge state formed around an antidot in the fractional quantum Hall effect regime. The finite size L of the antidot edge state introduces a temperature scale T0??v/?kBL, where v is the edge-state Fermi velocity. A renormalization group analysis reveals the existence of a two-parameter universal scaling function G~(X,Y) that describes the Aharonov-Bohm conductance resonances. We also show that the strong renormalization of the tunneling amplitudes that couple the antidot to the incident edge states, together with the nature of the Aharonov-Bohm interference process in a chiral system, prevent the occurrence of perfect resonances as the magnetic field is varied, even at zero temperature. In an experimentally realizable strong-antidot-coupling regime, where the source-to-drain transmission is weak, and at bulk filling factor g=1/q with q an odd integer, we predict the low-temperature (T<Aharonov-Bohm amplitude to vanish with temperature as T2q-2, in striking contrast to a Fermi liquid (q=1). Near T0, there is a pronounced maximum in the amplitude, also in contrast to a Fermi liquid. At high temperatures (T>>T0), however, we predict a crossover to a T2q-1e-qT/T0 temperature dependence, which is qualitatively similar to chiral Fermi liquid behavior. Careful measurements in the strong-antidot-coupling regime above T0 should be able to distinguish between a Fermi liquid and our predicted nearly Fermi liquid scaling. In addition, we predict an interesting high-temperature nonlinear response regime, where the voltage satisfies V>T>T0, which may also be used to distinguish between chiral Fermi liquid and chiral Luttinger liquid behavior. Finally, we predict mesoscopic edge-current oscillations, which are similar to the persistent current oscillations in a mesoscopic ring, except that they are not reduced in amplitude by weak disorder. In the fractional quantum Hall effects regime, these ``chiral persistent currents'' have a universal non-Fermi-liquid temperature dependence and may be another ideal system to observe a chiral Luttinger liquid.

Geller, Michael R.; Loss, Daniel

1997-10-01

20

Classical origins of the Aharonov-Bohm effect  

NASA Astrophysics Data System (ADS)

It is shown, in a large variety of manifestations, that the Aharonov—Bohm effect has classical counterparts in aspects concerning energy and momentum balance. No counterexamples are found in the cases considered, although whenever image charges shield the magnetic field region from the electric field of the passing electron the classical momentum effects, while present, would not be observable. Similarly, if the magnetic flux is maintained by superconductors, magnetic shielding will also render the classical energy effect unobservable. Partial shieldings of either type will reduce but not totally eliminate the corresponding observable classical manifestations of these effects.

Herman, R. M.

1992-05-01

21

Aharonov-Bohm quantum rings in high-Q microcavities  

NASA Astrophysics Data System (ADS)

A single-mode microcavity with an embedded Aharonov-Bohm quantum ring, which is pierced by a magnetic flux and subjected to a lateral electric field, is studied theoretically. It is shown that external electric and magnetic fields provide additional means of control of the emission spectrum of the system. In particular, when the magnetic flux through the quantum ring is equal to a half-integer number of the magnetic flux quantum, a small change in the lateral electric field allows tuning of the energy levels of the quantum ring into resonance with the microcavity mode providing an efficient way to control the quantum ring-microcavity coupling strength. Emission spectra of the system are calculated for several combinations of the applied magnetic and electric fields.

Alexeev, A. M.; Shelykh, I. A.; Portnoi, M. E.

2013-08-01

22

A Critical Reexamination of the Electrostatic Aharonov-Bohm Effect  

NASA Astrophysics Data System (ADS)

This paper undertakes a critical reexamination of the electrostatic version of the Aharonov-Bohm (“AB”) effect. The conclusions are as follows: 1. Aharonov and Bohm’s 1959 exposition is invalid because it does not consider the wavefunction of the entire system, including the source of electrostatic potential. 2. As originally proposed, the electrostatic AB effect does not exist. Perhaps surprisingly, this conclusion holds despite the relativistic covariance of the electromagnetic four-potential combined with the well-established magnetic AB effect. 3. Although the authors attempted, in a 1961 paper, to demonstrate that consideration of the entire system would not change their result, they inadvertently assumed the desired outcome in their analysis. 4. An oft-cited claim to have experimentally detected the electrostatic AB effect is mistaken, because the observed interference effect is clearly due to electric forces acting directly on charged particles.

Walstad, Allan

2010-11-01

23

Planar Massless Fermions in Coulomb and Aharonov-Bohm Potentials  

NASA Astrophysics Data System (ADS)

Solutions to the Dirac equation are constructed for a massless charged fermion in Coulomb and Aharonov-Bohm (AB) potentials in 2+1 dimensions. The Dirac Hamiltonian on this background is singular and needs a one-parameter self-adjoint extension, which can be given in terms of self-adjoint boundary conditions. We show that the virtual (quasistationary) bound states emerge in the presence of an attractive Coulomb potential when the so-called effective charges become overcritical and discuss a restructuring of the vacuum of the quantum electrodynamics when the virtual bound states emerge. We derive equations, which determine the energies and lifetimes of virtual bound states, find solutions of obtained equations for some values of parameters as well as analyze the local density of states (LDOS) as a function of energy in the presence of Coulomb and AB potentials.

Khalilov, V. R.; Lee, K. E.

2012-11-01

24

Aharonov-Bohm interferences from local deformations in graphene  

NASA Astrophysics Data System (ADS)

One of the most interesting aspects of graphene is the close relation between its structural and electronic properties. The observation of ripples both in free-standing graphene and in samples on a substrate has given rise to active investigation of the membrane-like properties of graphene, and the origin of the ripples remains one of the most interesting open problems concerning this system. The interplay of structural and electronic properties is successfully described by the modelling of curvature and elastic deformations by fictitious gauge fields. These fields have become an experimental reality after the observation of the Landau levels that can form in graphene due to strain. Here we propose a device to detect microstresses in graphene based on a scanning-tunnelling-microscopy set-up able to measure Aharonov-Bohm interferences at the nanometre scale. The predicted interferences in the local density of states are created by the fictitious magnetic field associated with elastic deformations of the sample.

de Juan, Fernando; Cortijo, Alberto; Vozmediano, María A. H.; Cano, Andrés

2011-10-01

25

Time-dependent transport in Aharonov-Bohm interferometers  

NASA Astrophysics Data System (ADS)

A numerical approach is employed to explain transport characteristics in realistic, quantum Hall-based Aharonov-Bohm (AB) interferometers. Firstly, the spatial distribution of incompressible strips, and thus the current channels, are obtained by applying a self-consistent Thomas-Fermi method to a realistic heterostructure under quantized Hall conditions. Secondly, the time-dependent Schrödinger equation is solved for electrons injected in the current channels. Distinctive AB oscillations are found as a function of the magnetic flux. The oscillation amplitude strongly depends on the mutual distance between the transport channels and on their width. At an optimal distance the amplitude and thus the interchannel transport is maximized, which determines the maximum visibility condition. On the other hand, the transport is fully suppressed at magnetic fields corresponding to half-integer flux quanta. The results confirm the applicability of realistic AB interferometers as controllable current switches.

Kotimäki, V.; Cicek, E.; Siddiki, A.; Räsänen, E.

2012-05-01

26

Aharonov-Bohm Effect in the Chiral Luttinger Liquid  

NASA Astrophysics Data System (ADS)

I will discuss recent work done with Daniel Loss and George Kirczenow on the Aharonov-Bohm effect in the fractional quantum Hall regime with chiral-Luttinger-liquid edge states.(M. R. Geller, D. Loss, and G. Kirczenow, Phys. Rev. Lett. 77), 5110 (1996). The problem we address is realized experimentally by measuring the tunneling current between two fractional edge states through a third edge state formed around an antidot. The finite size of the antidot edge state introduces a temperature scale T0 ? hbar v / ? kB L, where v is the edge-state Fermi velocity and L is the length of the antidot edge state. For example, v=10^6 cm/s and L=1 ? m yield T0 ? 25 mK. In an experimentally realizable strong-antidot-coupling regime, where the source-to-drain transmission is weak, and at bulk filling factor g = 1/q with q an odd integer, we predict the low-temperature (T << T_0) Aharonov-Bohm amplitude to vanish with temperature as T^2q-2, in striking contrast to a Fermi liquid (q=1). Near T_0, there is a pronounced maximum in the amplitude, also in contrast to a Fermi liquid. At high temperatures (T >> T_0), however, we predict a crossover to a T^2q-1 e^-q T/T0 temperature dependence, which is qualitatively similar to chiral Fermi liquid behavior. Careful measurements in the strong-antidot-coupling regime above T0 should be able to distinguish between a Fermi liquid and our predicted nearly Fermi-liquid scaling. In addition, we predict an interesting high-temperature nonlinear response regime, where the voltage satisfies V > T > T_0, which may also be used to distinguish between Fermi and Luttinger liquids. I will also discuss the tunneling in the weak-antidot-coupling case, which turns out to be considerably different than the weak tunneling regime of the related quantum-point-contact system.

Geller, Michael R.

1997-03-01

27

Spin-Polarized Fermions in AN Aharonov-Bohm Field  

NASA Astrophysics Data System (ADS)

The quantum-mechanical treatment of a fermion motion in an infinitely thin magnetic flux is given physically rigorous for a Dirac Hamiltonian with an Aharonov-Bohm potential in (2+1) dimensions. The Dirac Hamiltonian contains a parameter s, which can be applied to characterize two states of the fermion spin. The Hamiltonian on this background requires additional specification of a one-parameter self-adjoint extension, which can be given in terms of physically acceptable boundary conditions. It is shown that for some values of the parameter that labels the extensions there exists a bound state. Expressions for the scattering amplitudes and cross-sections are obtained and discussed for different values of the extension parameter. The scattering of spin-polarized electrons off a thin solenoid are studied in the plane perpendicular to the solenoid axis for three spatial dimensions. The scattering amplitudes and cross-sections for quantum transitions of spin-polarized electrons are determined and discussed.

Khalilov, V. R.; Lee, K. E.; Mamsurov, I. V.

2012-03-01

28

Quantum interference and Aharonov-Bohm oscillations in topological insulators  

NASA Astrophysics Data System (ADS)

Topological insulators (TIs) have an insulating bulk but a metallic surface. In the simplest case, the surface electronic structure of a three-dimensional (3D) TI is described by a single two-dimensional (2D) Dirac cone. A single 2D Dirac fermion cannot be realized in an isolated 2D system with time-reversal symmetry, but rather owes its existence to the topological properties of the 3D bulk wavefunctions. The transport properties of such a surface state are of considerable current interest; they have some similarities with graphene, which also realizes Dirac fermions, but have several unique features in their response to magnetic fields. In this review we give an overview of some of the main quantum transport properties of TI surfaces. We focus on the efforts to use quantum interference phenomena, such as weak anti-localization and the Aharonov-Bohm effect, to verify in a transport experiment the Dirac nature of the surface state and its defining properties. In addition to explaining the basic ideas and predictions of the theory, we provide a survey of recent experimental work.

Bardarson, Jens H.; Moore, Joel E.

2013-05-01

29

Dynamics of Non-Abelian Aharonov-Bohm Systems  

NASA Astrophysics Data System (ADS)

This thesis examines several examples of systems in which non-Abelian magnetic flux and non-Abelian forms of the Aharonov-Bohm effect play a role. We consider the dynamical consequences in these systems of some of the exotic phenomena associated with non-Abelian flux, such as Cheshire charge holonomy interactions and non-Abelian braid statistics. First, we use a mean-field approximation to study a model of U(2) non-Abelian anyons near its free -fermion limit. Some self-consistent states are constructed which show a small SU(2)-breaking charge density that vanishes in the fermionic limit. This is contrasted with the bosonic limit where the SU(2) asymmetry of the ground state can be maximal. Second, a global analogue of Cheshire charge is described, raising the possibility of observing Cheshire charge in condensed-matter systems. A potential realization in superfluid He-3 is discussed. Finally, we describe in some detail a method for numerically simulating the evolution of a network of non-Abelian (S_3 ) cosmic strings, keeping careful track of all magnetic fluxes and taking full account of their non-commutative nature. I present some preliminary results from this simulation, which is still in progress. The early results are suggestive of a qualitatively new, non-scaling behavior.

McGraw, Patrick Neal

1996-01-01

30

The Aharonov-Bohm effect in M"obius rings  

NASA Astrophysics Data System (ADS)

Electron transmission through finite-width 2D ring structures is calculated for cylindrical, flat (Aharonov-Bohm), and M"obius rings. In the presence of an external magnetic field, curves of constructive transmission display a pattern similar to that for a 1D ring. The periodicity in the magnetic flux, in units of h/e, is weakly broken on 2D rings of finite width, so that a description with a 1D-path is very acceptable. The unusual states with half-integer values of observed on M"obius rings, display a different characteristic in transmission. Such resonant states are in constructive interference for transmission at magnetic fields where the contribution from ordinary states with integer is in destructive interference, and vice versa. This leads to an alternating dominance of the set of half-integer states and the set of integer states in transport with increasing magnetic fields. We anticipate that M"obius rings would be synthesized with graphene ribbons in the near future.

Li, Zehao; Ramdas Ram-Mohan, L.

2013-03-01

31

Quantum phases of electric and magnetic dipoles as special cases of the Aharonov-Bohm phase  

NASA Astrophysics Data System (ADS)

It is shown that the vector potential of the Aharonov-Bohm effect is effectively the same as vector potentials of the quantum phases of electric and magnetic dipoles such as the Aharonov-Casher effect, when the Aharonov-Bohm solenoid is a straight cylinder with symmetric cross sections. With a circular cross section, the Aharonov-Bohm vector potential is effectively the same as the Aharonov-Casher vector potential, while with a rectangular cross section, it is effectively the same as the vector potential of the Casella phase. Therefore, we may say that the quantum phases of the dipoles belong to a subclass of the Aharonov-Bohm phase, and they must share the topological origin of the Aharonov-Bohm phase, even though their topological freedom is limited to the particle trajectories. However, the dipole phases have the extra relativistic effect that a magnetic (electric) dipole moving in an electric (magnetic) field feels an additional magnetic (electric) field, in its rest frame. This effect limits further the topological freedom of the dipole phases.

Lee, Tae-Yeon

2001-09-01

32

The Aharonov–Bohm Phase Shift and Boyer's Critical Considerations: New Experimental Result but Still an Open Subject?  

Microsoft Academic Search

The main experiments concerning the Aharonov–Bohm phase shifts, seen in an electron interference pattern, and their Boyer semiclassical explanations are reviewed. A new experiment is also presented which emphasizes the subtleties involved in the interpretations of the magnetic Aharonov–Bohm phase shift as a result of a non-dispersive or dispersive effect.

G. Matteucci; D. Iencinella; C. Beeli

2003-01-01

33

Photoionization cross section in a two-dimensional quantum ring: Aharonov-Bohm effect  

NASA Astrophysics Data System (ADS)

The photoionization cross section (PCS) of a quantum ring is investigated.The PCS of quantum rings is strongly affected by the radius-to-width ratio.The PCS of a quantum ring may occur Aharonov-Bohm oscillation even in a finite width.

Xie, Wenfang

2013-06-01

34

Gauge covariance of the Aharonov–Bohm phase in noncommutative quantum mechanics  

Microsoft Academic Search

The gauge covariance of the wave function phase factor in noncommutative quantum mechanics (NCQM) is discussed. We show that the naive path integral formulation and an approach where one shifts the coordinates of NCQM in the presence of a background vector potential leads to the gauge non-covariance of the phase factor. Due to this fact, the Aharonov–Bohm phase in NCQM

Masud Chaichian; Miklos Långvik; Shin Sasaki; Anca Tureanu

2008-01-01

35

Aharonov-Bohm Oscillations and Fano Resonance in a Mesoscopic Ring with a Side-Coupled Quantum Dot  

NASA Astrophysics Data System (ADS)

We calculate the transmission coefficient through an Aharonov-Bohm ring with a multi-level quantum dot side-coupled to one arm. Whenever a quantum dot level is tuned across the Fermi energy, the coupled arm is blocked for electron tunneling, namely anti-resonance. This leads to the suppression of the Aharonov-Bohm oscillations, accompanied by a phase jump of ? in the oscillations. The Aharonov-Bohm phase also changes sharply by ? in between neighboring anti-resonances due to the multi-level effect. The transmission has an expression of the generalized Fano form with a complex Fano parameter q in the presence of the Aharonov-Bohm flux.

Xiong, Yong-Jian; He, Zhou-Bo

36

Aharonov-Bohm Effect and High-Velocity Estimates of Solutions to the Schrödinger Equation  

NASA Astrophysics Data System (ADS)

The Aharonov-Bohm effect is a fundamental issue in physics that has been extensively studied in the literature and is discussed in most of the textbooks in quantum mechanics. The issues at stake are what are the fundamental electromagnetic quantities in quantum physics, if magnetic fields can act at a distance on charged particles and if the magnetic potentials have a real physical significance. The Aharonov-Bohm effect is a very controversial issue. From the experimental side the issues were settled by the remarkable experiments of Tonomura et al. (Phys Rev Lett 48:1443-1446, 1982; Phys Rev Lett 56:792-795, 1986) with toroidal magnets that gave a strong experimental evidence of the physical existence of the Aharonov-Bohm effect, and by the recent experiment of Caprez et al. (Phys Rev Lett 99:210401, 2007) that shows that the results of the Tonomura et al. experiments can not be explained by the action of a force. Aharonov and Bohm (Phys Rev 115:485-491, 1959) proposed an Ansatz for the solution to the Schrödinger equation in simply connected regions of space where there are no electromagnetic fields. It consists of multiplying the free evolution by the Dirac magnetic factor. The Aharonov-Bohm Ansatz predicts the results of the experiments of Tonomura et al. and of Caprez et al. Recently in Ballesteros and Weder (Math Phys 50:122108, 2009) we gave the first rigorous proof that the Aharonov-Bohm Ansatz is a good approximation to the exact solution for toroidal magnets under the conditions of the experiments of Tonomura et al. We provided a rigorous, simple, quantitative, error bound for the difference in norm between the exact solution and the Aharonov-Bohm Ansatz. In this paper we prove that these results do not depend on the particular geometry of the magnets and on the velocities of the incoming electrons used on the experiments, and on the gaussian shape of the wave packets used to obtain our quantitative error bound. We consider a general class of magnets that are a finite union of handlebodies. Each handlebody is diffeomorphic to a torus or a ball, and some of them can be patched though the boundary. We formulate the Aharonov-Bohm Ansatz that is appropriate to this general case and we prove that the exact solution to the Schrödinger equation is given by the Aharonov-Bohm Ansatz up to an error bound in norm that is uniform in time and that decays as a constant divided by v ? , 0 < ? < 1, with v the velocity. The results of Tonomura et al., of Caprez et al., our previous results and the results of this paper give a firm experimental and theoretical basis to the existence of the Aharonov-Bohm effect and to its quantum nature. Namely, that magnetic fields act at a distance on charged particles, and that this action at a distance is carried by the circulation of the magnetic potential which gives a real physical significance to magnetic potentials.

Ballesteros, Miguel; Weder, Ricardo

2011-04-01

37

The Aharonov-Bohm effect and Tonomura et al. experiments: Rigorous results  

SciTech Connect

The Aharonov-Bohm effect is a fundamental issue in physics. It describes the physically important electromagnetic quantities in quantum mechanics. Its experimental verification constitutes a test of the theory of quantum mechanics itself. The remarkable experiments of Tonomura et al. ['Observation of Aharonov-Bohm effect by electron holography', Phys. Rev. Lett 48, 1443 (1982) and 'Evidence for Aharonov-Bohm effect with magnetic field completely shielded from electron wave', Phys. Rev. Lett 56, 792 (1986)] are widely considered as the only experimental evidence of the physical existence of the Aharonov-Bohm effect. Here we give the first rigorous proof that the classical ansatz of Aharonov and Bohm of 1959 ['Significance of electromagnetic potentials in the quantum theory', Phys. Rev. 115, 485 (1959)], that was tested by Tonomura et al., is a good approximation to the exact solution to the Schroedinger equation. This also proves that the electron, that is, represented by the exact solution, is not accelerated, in agreement with the recent experiment of Caprez et al. in 2007 ['Macroscopic test of the Aharonov-Bohm effect', Phys. Rev. Lett. 99, 210401 (2007)], that shows that the results of the Tonomura et al. experiments can not be explained by the action of a force. Under the assumption that the incoming free electron is a Gaussian wave packet, we estimate the exact solution to the Schroedinger equation for all times. We provide a rigorous, quantitative error bound for the difference in norm between the exact solution and the Aharonov-Bohm Ansatz. Our bound is uniform in time. We also prove that on the Gaussian asymptotic state the scattering operator is given by a constant phase shift, up to a quantitative error bound that we provide. Our results show that for intermediate size electron wave packets, smaller than the ones used in the Tonomura et al. experiments, quantum mechanics predicts the results observed by Tonomura et al. with an error bound smaller than 10{sup -99}. It would be quite interesting to perform experiments with electron wave packets of intermediate size. Furthermore, we provide a physical interpretation of our error bound.

Ballesteros, Miguel; Weder, Ricardo [Projet POems, Domaine de Voluceau-Rocquencourt, Institut National de Recherche en Informatique et en Automatique Paris-Rocquencourt, BP 105, 78153 Le Chesnay Cedex France (France)

2009-12-15

38

Spin accumulation assisted by the Aharonov-Bohm-Fano effect of quantum dot structures  

PubMed Central

We investigate the spin accumulations of Aharonov-Bohm interferometers with embedded quantum dots by considering spin bias in the leads. It is found that regardless of the interferometer configurations, the spin accumulations are closely determined by their quantum interference features. This is mainly manifested in the dependence of spin accumulations on the threaded magnetic flux and the nonresonant transmission process. Namely, the Aharonov-Bohm-Fano effect is a necessary condition to achieve the spin accumulation in the quantum dot of the resonant channel. Further analysis showed that in the double-dot interferometer, the spin accumulation can be detailedly manipulated. The spin accumulation properties of such structures offer a new scheme of spin manipulation. When the intradot Coulomb interactions are taken into account, we find that the electron interactions are advantageous to the spin accumulation in the resonant channel.

2012-01-01

39

Gauge covariance of the Aharonov Bohm phase in noncommutative quantum mechanics  

NASA Astrophysics Data System (ADS)

The gauge covariance of the wave function phase factor in noncommutative quantum mechanics (NCQM) is discussed. We show that the naive path integral formulation and an approach where one shifts the coordinates of NCQM in the presence of a background vector potential leads to the gauge non-covariance of the phase factor. Due to this fact, the Aharonov Bohm phase in NCQM which is evaluated through the path-integral or by shifting the coordinates is neither gauge invariant nor gauge covariant. We show that the gauge covariant Aharonov Bohm effect should be described by using the noncommutative Wilson lines, what is consistent with the noncommutative Schrödinger equation. This approach can ultimately be used for deriving an analogue of the Dirac quantization condition for the magnetic monopole.

Chaichian, Masud; Långvik, Miklos; Sasaki, Shin; Tureanu, Anca

2008-08-01

40

Time-dependent Pauli equation in the presence of the Aharonov-Bohm effect  

SciTech Connect

We use the Lewis-Riesenfeld theory to determine the exact form of the wavefunctions of a two-dimensional Pauli equation of a charged spin 1/2 particle with time-dependent mass and frequency in the presence of the Aharonov-Bohm effect and a two-dimensional time-dependent harmonic oscillator. We find that the irregular solution at the origin as well as the regular one contributes to the phase of the wavefunction.

Bouguerra, Y. [Laboratoire de Physique Theorique, Faculte des Sciences, Universite de Jijel, BP 98, Ouled Aissa, Jijel 18000 (Algeria); Bounames, A. [Laboratoire de Physique Theorique, Faculte des Sciences, Universite de Jijel, BP 98, Ouled Aissa, Jijel 18000 (Algeria); Frankfurt Institute of Advanced Studies, Johann Wolfgang Goethe University, Ruth-Moufang-Str. 1, 60438 Frankfurt am Main (Germany); Maamache, M.; Saadi, Y. [Laboratoire de Physique Quantique et Systemes Dynamiques, Faculte des Sciences, Universite Ferhat Abbas de Setif, Setif 19000 (Algeria)

2008-04-15

41

Conductance Oscillations in an Aharonov-Bohm Ring Connected to Stubs  

NASA Astrophysics Data System (ADS)

In this paper one deals with some aspects concerning the quantum coherent transport through an one dimensional ballistic system. The system is an Aharonov-Bohm ring with a stub, coupled with two semi-infinite wires. The transmission probability through the mesoscopic structure is calculated using the quantum waveguide theory. This opens the way to describe the oscillations of the conductance versus magnetic flux.

Baltateanu, D. M.

2010-08-01

42

Scattering of spin 1/2 particles by the 2+1 dimensional noncommutative Aharonov-Bohm potential  

SciTech Connect

In this work we study modifications in the Aharonov-Bohm effect for relativistic spin 1/2 particles due to the noncommutativity of spacetime in 2+1 dimensions. The noncommutativity gives rise to a correction to the Aharonov-Bohm potential which is highly singular at the origin, producing divergences in a perturbative expansion around the usual solution of the free Dirac equation. This problem is surmounted by using a perturbative expansion around the exact solution of the commutative Aharonov-Bohm problem. We calculate, in this setting, the scattering amplitude and the corrections to the differential and total cross sections for a spin 1/2 particle, in the small-flux limit.

Ferrari, A. F.; Gomes, M.; Stechhahn, C. A. [Instituto de Fisica, Universidade de Sao Paulo, Caixa Postal 66318, 05315-970, Sao Paulo, SP (Brazil)

2007-10-15

43

A charged particle in a homogeneous magnetic field accelerated by a time-periodic Aharonov-Bohm flux  

SciTech Connect

We consider a nonrelativistic quantum charged particle moving on a plane under the influence of a uniform magnetic field and driven by a periodically time-dependent Aharonov-Bohm flux. We observe an acceleration effect in the case when the Aharonov-Bohm flux depends on time as a sinusoidal function whose frequency is in resonance with the cyclotron frequency. In particular, the energy of the particle increases linearly for large times. An explicit formula for the acceleration rate is derived with the aid of the quantum averaging method, and then it is checked against a numerical solution and a very good agreement is found. - Highlights: > A nonrelativistic quantum charged particle on a plane. > A homogeneous magnetic field and a periodically time-dependent Aharonov-Bohm flux. > The quantum averaging method applied to a time-dependent system. > A resonance of the AB flux with the cyclotron frequency. > An acceleration with linearly increasing energy; a formula for the acceleration rate.

Kalvoda, T. [Department of Theoretical Computer Science, Faculty of Information Technology, Czech Technical University in Prague, Kolejni 2, 160 00 Praha (Czech Republic); Stovicek, P., E-mail: stovicek@kmlinux.fjfi.cvut.cz [Department of Mathematics, Faculty of Nuclear Science, Czech Technical University in Prague, Trojanova 13, 120 00 Praha (Czech Republic)

2011-10-15

44

Bound states of the hydrogen atom in the presence of a magnetic monopole field and an Aharonov-Bohm potential  

NASA Astrophysics Data System (ADS)

In the present article we analyze the bound states of an electron in a Coulomb field when an Aharonov-Bohm field as well as a magnetic Dirac monopole are present. We solve, via separation of variables, the Schrödinger equation in spherical coordinates and we show how the hydrogen energy spectrum depends on the Aharonov-Bohm and the magnetic monopole strengths. The Klein-Gordon equation is also solved. Permanent address: Centro de Física, Instituto Venezolano de Investigaciones Científicas IVIC, Apartado 21827, Caracas 1020-A, Venezuela.

Villalba, Víctor M.

1994-10-01

45

Dephasing of electrons in the Aharonov-Bohm interferometer with a single-molecular vibrational junction.  

PubMed

Phase relaxation of electrons transferring through an electromechanical transistor is studied using the Aharonov-Bohm interferometer. Using the quantum master equation approach, the phase properties of an electron are numerically analyzed based on the interference fringes. The coherence of the electron is partially destroyed by its scattering on excited levels of the local nanomechanical oscillator. The transmission amplitudes with respect to two adjacent mechanical vibrational levels have a phase difference of ?. The character of the ? phase shift depends on the oscillator frequency only and is robust over a wide range of values of the applied voltage, tunneling length and damping rate of the mechanical oscillator. PMID:23615899

Lai, Wenxi; Xing, Yunhui; Ma, Zhongshui

2013-04-25

46

Aharonov-Bohm oscillations and weak antilocalization in topological insulator Sb2Te3 nanowires  

NASA Astrophysics Data System (ADS)

Recently, it has been theoretically predicted that Sb2Te3 and related materials are 3D topological insulators, a phase of matter that has a bulk bandgap and gapless electronic surface states protected by time-reversal symmetry. We report on low temperature magnetoresistance measurements on single crystalline Sb2Te3 nanowires with different cross sectional areas and high surface-to-volume ratios, synthesized via catalytic growth. The observation of Aharonov-Bohm oscillations and weak antilocalization indicates the presence of topological surface states.

Hamdou, Bacel; Gooth, Johannes; Dorn, August; Pippel, Eckhard; Nielsch, Kornelius

2013-06-01

47

Tunable Pseudogap Kondo Effect and Quantum Phase Transitions in Aharonov-Bohm Interferometers  

SciTech Connect

We study two quantum dots embedded in the arms of an Aharonov-Bohm ring threaded by a magnetic flux. This system can be described by an effective one-impurity Anderson model with an energy- and flux- dependent density of states. For specific values of the flux, this density of states vanishes at the Fermi energy, yielding a controlled realization of the pseudogap Kondo effect. The conductance and trans- mission phase shifts reflect a nontrivial interplay between wave interference and interactions, providing clear signatures of quantum phase transitions between Kondo and non-Kondo ground states.

Dias Da Silva, Luis G [ORNL; Sandler, Nancy [Ohio University; Simon, Pascal [Ohio University; Ingersent, Kevin [University of Florida; Ulloa, Sergio E [Ohio University, Athens

2009-01-01

48

Use of Aharonov-Bohm effect and chirality control in magnetic phase plates for transmission microscopy  

NASA Astrophysics Data System (ADS)

Initial holographic tests on thin rings of cobalt have demonstrated both onion (O) and vortex (V) states of magnetization, and show that the vortex state provides a uniform phase difference between inside and outside the ring as expected from the Aharonov-Bohm effect. Simple circular rings show a relatively small difference between the in-plane switching fields O?V and V?O and have unpredictable chirality (sense of flux rotation in the vortex mode). Simulations suggest that D-shaped rings provide both predictable chirality and a wider range between switching fields.

Edgcombe, C. J.; Loudon, J. C.

2012-07-01

49

Dephasing of electrons in the Aharonov-Bohm interferometer with a single-molecular vibrational junction  

NASA Astrophysics Data System (ADS)

Phase relaxation of electrons transferring through an electromechanical transistor is studied using the Aharonov-Bohm interferometer. Using the quantum master equation approach, the phase properties of an electron are numerically analyzed based on the interference fringes. The coherence of the electron is partially destroyed by its scattering on excited levels of the local nanomechanical oscillator. The transmission amplitudes with respect to two adjacent mechanical vibrational levels have a phase difference of ?. The character of the ? phase shift depends on the oscillator frequency only and is robust over a wide range of values of the applied voltage, tunneling length and damping rate of the mechanical oscillator.

Lai, Wenxi; Xing, Yunhui; Ma, Zhongshui

2013-05-01

50

Excitonic Aharonov-Bohm effect in a two-dimensional quantum ring  

SciTech Connect

We study theoretically the optical properties of an exciton in a two-dimensional ring threaded by a magnetic flux. We model the quantum ring by a confining potential that can be continuously tuned from strictly one-dimensional to truly two-dimensional with finite radius-to-width ratio. We present an analytic solution of the problem when the electron-hole interaction is short ranged. The oscillatory dependence of the oscillator strength as a function of the magnetic flux is attributed to the Aharonov-Bohm effect. The amplitude of the oscillations changes upon increasing the width of the quantum ring. We find that the Aharonov-Bohm oscillations of the ground state of the exciton decrease with increasing the width, but, remarkably, the amplitude remains finite down to radius-to-width ratios less than unity. We attribute this resilience of the excitonic oscillations to the nonsimple connectedness of our chosen confinement potential with its centrifugal core at the origin.

Gonzalez-Santander, C.; Dominguez-Adame, F. [Departamento de Fisica de Materiales, Universidad Complutense de Madrid, ES-28040 (Spain); Roemer, R. A. [Department of Physics and Centre for Scientific Computing, University of Warwick, Coventry, CV4 7AL (United Kingdom)

2011-12-15

51

Excitonic Aharonov-Bohm effect in a two-dimensional quantum ring  

NASA Astrophysics Data System (ADS)

We study theoretically the optical properties of an exciton in a two-dimensional ring threaded by a magnetic flux. We model the quantum ring by a confining potential that can be continuously tuned from strictly one-dimensional to truly two-dimensional with finite radius-to-width ratio. We present an analytic solution of the problem when the electron-hole interaction is short ranged. The oscillatory dependence of the oscillator strength as a function of the magnetic flux is attributed to the Aharonov-Bohm effect. The amplitude of the oscillations changes upon increasing the width of the quantum ring. We find that the Aharonov-Bohm oscillations of the ground state of the exciton decrease with increasing the width, but, remarkably, the amplitude remains finite down to radius-to-width ratios less than unity. We attribute this resilience of the excitonic oscillations to the nonsimple connectedness of our chosen confinement potential with its centrifugal core at the origin.

González-Santander, C.; Domínguez-Adame, F.; Römer, R. A.

2011-12-01

52

Triviality of the Aharonov-Bohm interaction in a spatially confining vacuum  

NASA Astrophysics Data System (ADS)

This paper explores long-range interactions between magnetically charged excitations of the vacuum of the dual Landau-Ginzburg theory (DLGT) and the dual Abrikosov vortices present in the same vacuum. We show that, in the London limit of DLGT, the corresponding Aharonov-Bohm-type interactions possess such a coupling that the interactions reduce to a trivial factor of e2 ?i×(integer). The same analysis is done in the SU( N c)-inspired [U(1)]^{Nc-1}-invariant DLGT, as well as in DLGT extended by a Chern-Simons term. It is furthermore explicitly shown that the Chern-Simons term leads to the appearance of knotted dual Abrikosov vortices.

Antonov, Dmitri

2012-05-01

53

Classical light analogue of the non-local Aharonov-Bohm effect  

NASA Astrophysics Data System (ADS)

We demonstrate the existence of a non-local geometric phase in the intensity-intensity correlations of classical incoherent light, that is not seen in the lower-order correlations. This two-photon Pancharatnam phase was observed and modulated in a Mach-Zehnder interferometer. Using acousto-optic interaction, independent phase noise was introduced to light in the two arms of the interferometer to create two independent incoherent classical sources from laser light. The experiment is the classical optical analogue of the multi-particle Aharonov-Bohm effect. As the trajectory of light over the Poincaré sphere introduces a phase shift observable only in the intensity-intensity correlation, it provides a means of deflecting the two-photon wavefront, while having no effect on single photons.

Satapathy, Nandan; Pandey, Deepak; Mehta, Poonam; Sinha, Supurna; Samuel, Joseph; Ramachandran, Hema

2012-03-01

54

An Elementary Aharonov-Bohm System in Three Space Dimensions: Quantum Attraction With No Classical Force  

SciTech Connect

As a consequence of the Aharonov-Bohm effect, there is a quantum-induced attraction between a charged particle and a rigid impenetrable hoop made from an arbitrarily thin tube containing a superconductor quantum of magnetic flux. This is remarkable because in classical physics there is no force between the two objects, and quantum-mechanical effects (associated with uncertainty-principle energy) generally are repulsive rather than attractive. For an incident spinless charged particle in a P wave, in a configuration with total angular momentum zero, we verify a resonance just above threshold using the Kohn variational principle in its S-matrix form. Even if optimistic choices of parameters describing a model system with these properties turned out to be feasible, the temperature required to observe the resonance would be far lower than has yet been attained in the laboratory.

Goldhaber, Alfred S.

2003-01-09

55

Elementary Aharonov-Bohm system in three space dimensions: Quantum attraction with no classical force  

SciTech Connect

As a consequence of the Aharonov-Bohm effect, there is a quantum-induced attraction between a charged particle and a rigid, impenetrable hoop made from an arbitrarily thin tube containing a superconductor quantum of magnetic flux. This is remarkable because in classical physics there is no force between the two objects, and quantum-mechanical effects (associated with uncertainty-principle energy) generally are repulsive rather than attractive. For an incident spinless charged particle in a P wave (in a configuration with total angular momentum zero) we verify a resonance just above threshold using the Kohn variational principle in its S-matrix form. Even if optimistic choices of parameters describing a model system with these properties were feasible, the temperature required to observe the resonance would be far lower than has yet been attained in the laboratory.

Goldhaber, Alfred Scharff [C. N. Yang Institute for Theoretical Physics and Department of Physics and Astronomy, State University of New York, Stony Brook, New York 11794-3840, USA (United States); Stanford Linear Accelerator Center, Menlo Park, California 94025, USA (United States); Requist, Ryan [C. N. Yang Institute for Theoretical Physics and Department of Physics and Astronomy, State University of New York, Stony Brook, New York 11794-3840, USA (United States)

2003-07-01

56

Interplay of Aharonov-Bohm and Berry phases in gate-defined graphene quantum dots  

NASA Astrophysics Data System (ADS)

We study the influence of a magnetic flux tube on the possibility to electrostatically confine electrons in a graphene quantum dot. Without a magnetic flux tube, the graphene pseudospin is responsible for a quantization of the total angular momentum to half-integer values. On the other hand, with a flux tube containing half a flux quantum, the Aharonov-Bohm phase and Berry phase precisely cancel, and we find a state at zero angular momentum that cannot be confined electrostatically. In this case, true bound states only exist in regular geometries for which states without zero-angular-momentum component exist, while nonintegrable geometries lack confinement. We support these arguments with a calculation of the two-terminal conductance of a gate-defined graphene quantum dot, which shows resonances for a disk-shaped geometry and for a stadium-shaped geometry without flux tube, but no resonances for a stadium-shaped quantum dot with a ?-flux tube.

Heinl, Julia; Schneider, Martin; Brouwer, Piet W.

2013-06-01

57

The role of internal degrees of freedom in Aharonov-Bohm-type interference phenomena  

NASA Astrophysics Data System (ADS)

We show that the pure Aharonov-Bohm (AB) effect, or its dual (DAB), depends only on the net electric, or magnetic charge of an interfering object, however many internal degrees of freedom that system may have. The reciprocal Aharonov-Casher (AC) and He-McKellar-Wilkens (HMW) effects, on the other hand, involve physical properties—the magnetic and electric polarization of the system—which couple a system’s internal degrees of freedom to its center-of-mass coordinate through the field. For composite systems this illustrates a fundamental difference between the two types of phenomenon, and one which could be important as the number of internal degrees of freedom become large. We show that, for a single internal degree of freedom, the result of this coupling is a transient loss of coherence in the observed interference of the center-of-mass coordinate.

Horsley, S. A. R.; Babiker, M.

2008-07-01

58

Aharonov-Bohm effect and giant magnetoresistance in graphene nanoribbon rings  

NASA Astrophysics Data System (ADS)

We report a numerical study on the Aharonov-Bohm (AB) effect and giant magnetoresistance in rectangular rings made of graphene nanoribbons (GNRs). We show that in the low-energy regime where only the first subband of contact GNRs contributes to the transport, the transmission probability can be strongly modulated, i.e., almost fully suppressed, when tuning a perpendicular magnetic field. On this basis, strong AB oscillations with giant negative magnetoresistance can be achieved at room temperature. The magnetoresistance reaches thousands of percent in perfect GNR rings and a few hundred percent with edge-disordered GNRs. The design rules to observe such strong effects are also discussed. Our study hence provides guidelines for further investigations of the AB interference and to obtain high magnetoresistance in graphene devices.

Nguyen, V. Hung; Niquet, Y. M.; Dollfus, P.

2013-07-01

59

Thermoelectric effect in an Aharonov-Bohm ring with an embedded quantum dot.  

PubMed

Thermoelectric effect is studied in an Aharonov-Bohm interferometer with an embedded quantum dot (QD) in the Coulomb blockade regime. The electrical conductance, electron thermal conductance, thermopower, and thermoelectric figure-of-merit are calculated by using the Keldysh Green's function method. It is found that the figure-of-merit ZT of the QD ring may be quite high due to the Fano effect originated from the quantum interference effect. Moreover, the thermoelectric efficiency is sensitive to the magnitude of the dot-lead and inter-lead coupling strengthes. The effect of intradot Coulomb repulsion on ZT is significant in the weak-coupling regime, and then large ZT values can be obtained at rather high temperature. PMID:22369454

Zheng, Jun; Chi, Feng; Lu, Xiao-Dong; Zhang, Kai-Cheng

2012-02-28

60

Thermoelectric effect in an Aharonov-Bohm ring with an embedded quantum dot  

PubMed Central

Thermoelectric effect is studied in an Aharonov-Bohm interferometer with an embedded quantum dot (QD) in the Coulomb blockade regime. The electrical conductance, electron thermal conductance, thermopower, and thermoelectric figure-of-merit are calculated by using the Keldysh Green's function method. It is found that the figure-of-merit ZT of the QD ring may be quite high due to the Fano effect originated from the quantum interference effect. Moreover, the thermoelectric efficiency is sensitive to the magnitude of the dot-lead and inter-lead coupling strengthes. The effect of intradot Coulomb repulsion on ZT is significant in the weak-coupling regime, and then large ZT values can be obtained at rather high temperature.

2012-01-01

61

Aharonov-Bohm oscillation of photoionization cross section in a quantum ring with a repulsive scattering center  

NASA Astrophysics Data System (ADS)

The photoionization cross section (PCS) associated with intersubband transitions in quantum rings which include a repulsive scattering centre is investigated for the case with the presence of an external magnetic field. Calculations are carried out by using the matrix diagonalization method of the Hamiltonian matrix within the effective-mass approximation. Our results show that both the magnetic field, the ring radius and the impurity can affect the PCS of quantum rings. In addition, we found that the resonant peak of the PCS shows the Aharonov-Bohm oscillation with changing the magnetic field and the ring radius. Moreover, the width of the ring can influence the Aharonov-Bohm oscillation in peak while the resonant peak value of the PCS decreases as the ring width increases in the same ring geometry.

Xie, Wenfang

2013-05-01

62

Aharonov-Bohm oscillations in the magnetic moment of multielectron randomly doped semiconductor cylindrical core-shell nanowires  

NASA Astrophysics Data System (ADS)

Energy spectra and the magnetic moments of semiconductor core-shell nanocylinders, subjected to a magnetic field, are theoretically studied for different numbers of electrons in the shell and different height-to-radius ratios of the cylinder. The electron-electron interaction is taken into account within the Hartree-Fock approximation. We focus on the perspectives to experimentally detect the Aharonov-Bohm oscillations in the magnetic moment of multielectron core-shell nanowires. Among the different factors that influence the shape and magnitude of these oscillations, the destructive effect due to the interaction of electrons with randomly distributed charged impurities appears most important. Nevertheless, Aharonov-Bohm oscillations of a sufficiently high magnitude survive when averaged over an assembly of nanowires with different impurity distributions.

Gladilin, V. N.; Tempere, J.; Devreese, J. T.; Koenraad, P. M.

2013-04-01

63

Aharonov-Bohm-like scattering, localization, and novel electronic states in hydrogenated graphene  

NASA Astrophysics Data System (ADS)

Metallic nature of transport in graphene, which is fairly robust with respect to varying amounts of disorder, changes in an unexpected way when vacancies are introduced in this material. At low energies, near the Dirac point, electron scattering on vacancies mimics scattering on Aharonov-Bohm solenoids carrying unit flux. This type of scattering results in a very narrow band of states at the Dirac point with properties resembling those of zeroth Landau level, which is positioned in the middle of a (pseudo)gap created by vacancies and resembling the cyclotron gap around zeroth Landau level. The fictitious magnetic field describing vacancies has opposite signs for the valleys K and K'. As a result of this, an externally applied magnetic field has opposite effects in the two valleys, suppressing (reinforcing) the gap in the K (K') valley. We show that this picture is in agreement with the behavior observed in a recent study [1] of electronic properties of graphene, which can be transformed from metallic state to insulating state by hydrogenation. [1] D. C. Elias, R. R. Nair, T. M. G. Mohiuddin, S. V. Morozov, P. Blake, M. P. Halsall, A. C. Ferrari, D. W. Boukhvalov, M. I. Katsnelson, A. K. Geim, K. S. Novoselov, arXiv:0810.4706

Shytov, Andrey; Abanin, Dmitry; Levitov, Leonid

2009-03-01

64

Creation of planar charged fermions in Coulomb and Aharonov-Bohm potentials  

NASA Astrophysics Data System (ADS)

The creation of charged fermions from the vacuum by a Coulomb field in the presence of an Aharonov-Bohm (AB) potential are studied in 2+1 dimensions. The process is governed by a (singular) Dirac Hamiltonian that requires the supplementary definition in order for it to be treated as a self-adjoint quantum-mechanical operator. By constructing a one-parameter self-adjoint extension of the Dirac Hamiltonian, specified by boundary conditions, we describe the (virtual bound) quasistationary states with "complex energy" emerging in an attractive Coulomb potential, derive for the first time, complex equations (depending upon the electron spin and the extension parameter) for the quasistationary state "complex energy". The constructed self-adjoint Dirac Hamiltonians in Coulomb and AB potentials are applied to provide a correct description to the low-energy electron excitations, as well as the creation of charged quasiparticles from the vacuum in graphene by the Coulomb impurity in the presence of AB potential. It is shown that the strong Coulomb field can create charged fermions for some range of the extension parameter.

Khalilov, V. R.

2013-08-01

65

Quantum nonlinear resonance and quantum chaos in Aharonov-Bohm oscillations in mesoscopic semiconductor rings  

SciTech Connect

We consider Aharonov-Bohm oscillations in a mesoscopic semiconductor ring threaded by both a constant magnetic flux and a time-dependent, resonant magnetic field with one or two frequencies. Working in the ballistic regime, we establish that the theory of {open_quotes}quantum nonlinear resonance{close_quotes} applies, and thus that this system represents a possible solid-state realization of {open_quotes}quantum nonlinear resonance{close_quotes} and {open_quotes}quantum chaos.{close_quotes} In particular, we investigate the behavior of the time-averaged electron energy at zero temperature in the regimes of (i) an isolated quantum nonlinear resonance and (ii) the transition to quantum chaos, when two quantum nonlinear resonances overlap. The time-averaged energy exhibits sharp resonant behavior as a function of the applied constant magnetic flux, and has a staircase dependence on the amplitude of the external time-dependent field. In the chaotic regime, the resonant behavior exhibits complex structure as a function of flux and frequency. We compare and contrast the quantum chaos expected in these mesoscopic {open_quotes}solid-state atoms{close_quotes} with that observed in Rydberg atoms in microwave fields, and discuss the prospects for experimental observation of the effects we predict. {copyright} {ital 1997} {ital The American Physical Society}

Berman, G.P. [Theoretical Division and Center for Nonlinear Studies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Bulgakov, E.N. [Kirensky Institute of Physics, 660036, Krasnoyarsk (Russia); Campbell, D.K. [Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801-3080 (United States); Krive, I.V. [Institute for Low Temperature Physics and Engineering, Ukrainian Academy of Sciences, 310164, Kharkov (Ukraine)

1997-10-01

66

Aharonov Bohm differential conductance modulation in defective metallic single-walled carbon nanotubes  

NASA Astrophysics Data System (ADS)

Using a perturbative approach, the effects of the energy gap induced by the Aharonov-Bohm (AB) flux on the transport properties of defective metallic single-walled carbon nanotubes (MSWCNTs) are investigated. The electronic waves scattered back and forth by a pair of impurities give rise to Fabry-Perot oscillations which constitutes a coherent backscattering interference pattern (CBSIP). It is shown that the CBSIP can be aperiodically modulated by applying a magnetic field parallel to the nanotube axis. In fact, the AB-flux brings this CBSIP under control by an additional phase shift. As a consequence, the extrema as well as zeros of the CBSIP are located at the irrational fractions of the quantity ?? = ?/?0, where ? is the flux piercing the nanotube cross section and ?0 = h/e is the magnetic quantum flux. Indeed, the spacing between two adjacent extrema in the magneto-differential conductance (MDC) profile is decreased with increasing magnetic field. The faster and higher and slower and shorter variations are then obtained by metallic zigzag and armchair nanotubes, respectively. Such results lead to the proposal that defective metallic nanotubes could be used as magneto-conductance switching devices based on the AB effect.

Bagheri, Mehran

2008-02-01

67

Transport properties of an Aharonov-Bohm ring with strong interdot Coulomb interaction.  

PubMed

Based on the Keldysh Green's function technique and the equation-of-motion method, we investigate theoretically the electronic transport properties of an Aharonov-Bohm ring with embedded coupled double quantum dots connected to two electrodes in a symmetrical parallel configuration in the presence of strong interdot Coulomb interaction. Special attention is paid to the effects of the interdot Coulomb interaction on the transport properties. It has been shown numerically that the interdot Coulomb interaction gives rise to four electronic states in the ring. The quantum interferences between two strongly coupled electronic states and two weakly coupled ones lead to two Breit-Wigner and two Fano resonances in the linear conductance spectrum with the magnetic flux switched on or the imbalance between the energy levels of two quantum dots. The positions and shapes of the four resonances can be controlled by adjusting the magnetic flux through the device or energy levels of the two quantum dots. When the Fermi energy levels in the leads sweep across the weakly coupled electronic states, the negative differential conductance (NDC) is developed in the current-voltage characteristics for the non-equilibrium case. PMID:21694045

Liu, Yu-Shen; Chen, Hao; Yang, Xi-Feng

2007-05-17

68

Aharonov-Bohm conductance of a disordered single-channel quantum ring  

NASA Astrophysics Data System (ADS)

We study the effect of weak disorder on tunneling conductance of a single-channel quantum ring threaded by magnetic flux. We assume that the temperature is higher than the level spacing in the ring and smaller than the Fermi energy. In the absence of disorder, the conductance shows sharp dips (antiresonances) as a function of magnetic flux. We discuss different types of disorder and find that the short-range disorder broadens antiresonances, while the long-range one leads to the appearance of additional resonant dips. We demonstrate that the resonant dips have essentially non-Lorentzian shape. The results are generalized to account for the spin-orbit interaction, which leads to splitting of the disorder-broadened resonant dips, and consequently, to coexisting of two types of oscillations (both having the form of sharp dips): Aharonov-Bohm oscillations with magnetic flux and Aharonov-Casher oscillations with the strength of the spin-orbit coupling. We also discuss the effect of the Zeeman coupling.

Shmakov, P. M.; Dmitriev, A. P.; Kachorovskii, V. Yu.

2013-06-01

69

Supercurrent and its Fano effect in a Josephson Aharonov-Bohm ring  

NASA Astrophysics Data System (ADS)

The Josephson current through an Aharonov-Bohm (AB) interferometer, in which a quantum dot (QD) is situated on one arm and a magnetic flux ? threads through the ring, has been investigated. In the presence of the magnetic flux, the relation between the Josephson current and the superconductor phase is complex, and the system can be adjusted to ? junction by either modulating the magnetic flux or the QD’s energy level ?d. Due to the electron-hole symmetry, the Josephson current I has the property I(?d,?)=I(-?d,?+?). The Josephson current exhibits a jump when a pair of Andreev bound states aligns with the Fermi energy. The condition for the current jump is given. Particularly, we find that the position of the current jump and the position of the maximum value of the critical current Ic are identical. Due to the interference between the two paths, the critical current Ic versus the QD’s level ?d shows a typical Fano shape, which is similar to the Fano effect in the corresponding normal device. However they also show some differences. For example, the critical current never reaches zero for any parameters, while the current in the normal device can reach zero at the destruction point.

Cheng, S.-G.; Xing, Y. X.; Xie, X. C.; Sun, Q.-F.

2009-02-01

70

Nonlocal phases of local quantum mechanical wavefunctions in static and time-dependent Aharonov-Bohm experiments  

NASA Astrophysics Data System (ADS)

We show that the standard Dirac phase factor is not the only solution of the usual gauge transformation equations. The full form of a general gauge function (that connects systems that move in different sets of scalar and vector potentials), apart from Dirac phases (spatial or temporal integrals over potentials), also contains terms of classical fields that act nonlocally (in spacetime) on the local solutions of the time-dependent Schrödinger equation. As a result, the phases of wavefunctions in the Schrödinger picture are affected nonlocally by spatially and temporally remote magnetic and electric fields, in specific ways that are fully explored. These contributions go beyond the usual Aharonov-Bohm effects (magnetic or electric). (i) Application to cases of particles passing through full static magnetic or electric fields leads to cancellations of Aharonov-Bohm phases at the observation point; these cancellations are linked to behaviors at the semiclassical level (i.e. the old Werner and Brill experimental observations, or their 'electric analogs'—or to more recent reports of Batelaan and Tonomura) but are shown to be far more general (true not only for narrow wavepackets but also for completely delocalized (spread-out) quantum states). By using these cancellations, certain previously unnoticed sign-errors in the literature are corrected. (ii) Application to time-dependent situations provides a remedy for erroneous results in the literature (concerning an uncritical use of Dirac phase factors) and leads to phases that contain an Aharonov-Bohm part and a field-nonlocal part: their competition is shown to recover relativistic causality in earlier 'paradoxes' (such as the van Kampen thought-experiment), while a more general consideration indicates that the temporal nonlocalities found here demonstrate in part a causal propagation of phases of quantum mechanical wavefunctions in the Schrödinger picture. This may open a new and direct way to address time-dependent double-slit experiments and the associated causal issues.

Moulopoulos, Konstantinos

2010-09-01

71

Aharonov-Bohm effect on AdS{sub 2} and nonlinear supersymmetry of reflectionless Poeschl-Teller system  

SciTech Connect

We explain the origin and the nature of a special nonlinear supersymmetry of a reflectionless Poeschl-Teller system by the Aharonov-Bohm effect for a non-relativistic particle on the AdS{sub 2}. A key role in the supersymmetric structure appearing after reduction by a compact generator of the AdS{sub 2} isometry is shown to be played by the discrete symmetries related to the space and time reflections in the ambient Minkowski space. We also observe that a correspondence between the two quantum non-relativistic systems is somewhat of the AdS/CFT holography nature.

Correa, Francisco [Departamento de Fisica, Universidad de Santiago de Chile, Casilla 307, Santiago 2 (Chile)], E-mail: fco.correa.s@gmail.com; Jakubsky, Vit [Departamento de Fisica, Universidad de Santiago de Chile, Casilla 307, Santiago 2 (Chile)], E-mail: v.jakubsky@gmail.com; Plyushchay, Mikhail S. [Departamento de Fisica, Universidad de Santiago de Chile, Casilla 307, Santiago 2 (Chile)], E-mail: mplyushc@lauca.usach.cl

2009-05-15

72

Aharonov-Bohm oscillations in a hydrogen atom in a radiation field through electron self-interference  

NASA Astrophysics Data System (ADS)

We study the influence of a weak magnetic field on time evolution of a quantum state that is a coherent superposition of two counter-rotating Trojan wave packets in a linearly polarized electromagnetic field. We demonstrate that both the interference pattern of the electron probability density and differential cross section for half-cycle pulse ionization exhibit periodic modulation as a function of magnetic flux cutting the plane of packet motion. The shift is proportional to the magnetic flux in a way characteristic for the Aharonov-Bohm effect.

Kalinski, Maciej

1998-03-01

73

Magnetoresistance of nanoscale molecular devices based on Aharonov-Bohm interferometry.  

PubMed

Control of conductance in molecular junctions is of key importance in the growing field of molecular electronics. The current in these junctions is often controlled by an electric gate designed to shift conductance peaks into the low bias regime. Magnetic fields, on the other hand, have rarely been used due to the small magnetic flux captured by molecular conductors (an exception is the Kondo effect in single-molecule transistors). This is in contrast to a related field, electronic transport through mesoscopic devices, where considerable activity with magnetic fields has led to a rich description of transport. The scarcity of experimental activity is due to the belief that significant magnetic response is obtained only when the magnetic flux is of the order of the quantum flux, while attaining such a flux for molecular and nanoscale devices requires unrealistic magnetic fields. Here we review recent theoretical work regarding the essential physical requirements necessary for the construction of nanometer-scale magnetoresistance devices based on an Aharonov-Bohm molecular interferometer. We show that control of the conductance properties using small fractions of a magnetic flux can be achieved by carefully adjusting the lifetime of the conducting electrons through a pre-selected single state that is well separated from other states due to quantum confinement effects. Using a simple analytical model and more elaborate atomistic calculations we demonstrate that magnetic fields which give rise to a magnetic flux comparable to 10(-3) of the quantum flux can be used to switch a class of different molecular and nanometer rings, ranging from quantum corrals, carbon nanotubes and even a molecular ring composed of polyconjugated aromatic materials. The unique characteristics of the magnetic field as a gate is further discussed and demonstrated in two different directions. First, a three-terminal molecular router devices that can function as a parallel logic gate, processing two logic operations simultaneously, is presented. Second, the role of inelastic effects arising from electron-phonon couplings on the magnetoresistance properties is analyzed. We show that a remarkable difference between electric and magnetic gating is also revealed when inelastic effects become significant. The inelastic broadening of response curves to electric gates is replaced by a narrowing of magnetoconductance peaks, thereby enhancing the sensitivity of the device. PMID:21693808

Hod, Oded; Baer, Roi; Rabani, Eran

2008-08-27

74

Role of spin-orbit interaction and Berry's phase in Aharonov-Bohm oscillations  

NASA Astrophysics Data System (ADS)

In this thesis we report the results of study on the role of spin-orbit (SO) interaction in Aharonov-Bohm (A-B) oscillations measured in (311)A GaAs two-dimensional (2D) holes, and the observed novel structures in the Fourier transform (FT) spectra of the A-B oscillations, which we interpret as manifestation of Berry's phase and interference of spin states. In the FT spectra of A-B oscillations measured in GaAs 2D holes, we observed novel structures, which are more complex than what is observed in the A-B measurements done in other materials (e.g., normal-metals and GaAs 2D electrons). To interpret the experimental data, we develop a simple model which considers A-B effect in a system with strong SO interaction. Using parameters such as spin-splitting energy (DeltaE), splitting of the Fermi wavevector (Deltak), and the effective magnetic field ( Beff), which characterize spin-related properties in GaAs 2D holes, we are able to obtain a qualitatively good agreement between simulations based on this model and experimental results. In addition, through further analysis of experimental data and careful comparison with simulated results, we demonstrate that observation of these novel features in GaAs 2D hole rings is indeed evidence for Berry's phase. Furthermore, it suggests that GaAs 2D hole is an excellent candidate for studying phenomena caused by spins. Moreover, the simple model mentioned above suggests a periodic evolution of A-B oscillations with Deltak, which can be tuned by changing the front gate voltage VFG. In the magnetoresistance of the ring, as VFG is tuned, we observe changes in the FT spectra. These changes can be systematically tracked in terms of simplicity and complexity in the FT structures as a function of V FG. Finally, to study the phase coherence of hole transport in our mesoscopic ring, we measured the temperature dependence of the A-B oscillations. We found that the average oscillation amplitude exhibits a temperature dependence of exp[-L/L?(T)], which represents the dephasing related to the phase coherence length L ? with L?(T) ˜ 1.5 T-1 mum.

Yau, Jeng-Bang

75

TOPICAL REVIEW: Magnetoresistance of nanoscale molecular devices based on Aharonov Bohm interferometry  

NASA Astrophysics Data System (ADS)

Control of conductance in molecular junctions is of key importance in the growing field of molecular electronics. The current in these junctions is often controlled by an electric gate designed to shift conductance peaks into the low bias regime. Magnetic fields, on the other hand, have rarely been used due to the small magnetic flux captured by molecular conductors (an exception is the Kondo effect in single-molecule transistors). This is in contrast to a related field, electronic transport through mesoscopic devices, where considerable activity with magnetic fields has led to a rich description of transport. The scarcity of experimental activity is due to the belief that significant magnetic response is obtained only when the magnetic flux is of the order of the quantum flux, while attaining such a flux for molecular and nanoscale devices requires unrealistic magnetic fields. Here we review recent theoretical work regarding the essential physical requirements necessary for the construction of nanometer-scale magnetoresistance devices based on an Aharonov-Bohm molecular interferometer. We show that control of the conductance properties using small fractions of a magnetic flux can be achieved by carefully adjusting the lifetime of the conducting electrons through a pre-selected single state that is well separated from other states due to quantum confinement effects. Using a simple analytical model and more elaborate atomistic calculations we demonstrate that magnetic fields which give rise to a magnetic flux comparable to 10-3 of the quantum flux can be used to switch a class of different molecular and nanometer rings, ranging from quantum corrals, carbon nanotubes and even a molecular ring composed of polyconjugated aromatic materials. The unique characteristics of the magnetic field as a gate is further discussed and demonstrated in two different directions. First, a three-terminal molecular router devices that can function as a parallel logic gate, processing two logic operations simultaneously, is presented. Second, the role of inelastic effects arising from electron-phonon couplings on the magnetoresistance properties is analyzed. We show that a remarkable difference between electric and magnetic gating is also revealed when inelastic effects become significant. The inelastic broadening of response curves to electric gates is replaced by a narrowing of magnetoconductance peaks, thereby enhancing the sensitivity of the device.

Hod, Oded; Baer, Roi; Rabani, Eran

2008-09-01

76

Aharonov-Bohm oscillations, quantum decoherence and amplitude modulation in mesoscopic InGaAs/InAlAs rings.  

PubMed

Low-temperature Aharonov-Bohm oscillations in the magnetoresistance of mesoscopic interferometric rings patterned on an InGaAs/InAlAs heterostructure are investigated for their dependence on excitation current and temperature. The rings have an average radius of 650 nm, and a lithographic arm width of 300 nm, yielding pronounced interference oscillations over a wide range of magnetic fields. Apart from a current and temperature dependence, the oscillation amplitude also shows a quasi-periodic modulation with applied magnetic field. The phase coherence length is extracted by analysis of the fundamental and higher Fourier components of the oscillations, and by direct analysis of the amplitude and its dependence on parameters. It is concluded that the Thouless energy forms the measure of excitation energies for quantum decoherence. The amplitude modulation finds an explanation in the effect of the magnetic flux threading the finite width of the interferometer arms. PMID:24096892

Ren, S L; Heremans, J J; Gaspe, C K; Vijeyaragunathan, S; Mishima, T D; Santos, M B

2013-10-04

77

Aharonov-Bohm oscillations, quantum decoherence and amplitude modulation in mesoscopic InGaAs/InAlAs rings  

NASA Astrophysics Data System (ADS)

Low-temperature Aharonov-Bohm oscillations in the magnetoresistance of mesoscopic interferometric rings patterned on an InGaAs/InAlAs heterostructure are investigated for their dependence on excitation current and temperature. The rings have an average radius of 650 nm, and a lithographic arm width of 300 nm, yielding pronounced interference oscillations over a wide range of magnetic fields. Apart from a current and temperature dependence, the oscillation amplitude also shows a quasi-periodic modulation with applied magnetic field. The phase coherence length is extracted by analysis of the fundamental and higher Fourier components of the oscillations, and by direct analysis of the amplitude and its dependence on parameters. It is concluded that the Thouless energy forms the measure of excitation energies for quantum decoherence. The amplitude modulation finds an explanation in the effect of the magnetic flux threading the finite width of the interferometer arms.

Ren, S. L.; Heremans, J. J.; Gaspe, C. K.; Vijeyaragunathan, S.; Mishima, T. D.; Santos, M. B.

2013-10-01

78

Bound Fermion States in a Vector 1/r and Aharonov-Bohm Potential in (2+1) Dimensions  

NASA Astrophysics Data System (ADS)

We construct systematically all the self-adjoint Dirac Hamiltonians with a vector 1/r and Aharonov-Bohm potential in (2+1) dimensions with taking into account the fermion spin. Then we find spectra of these self-adjoint Dirac Hamiltonians. There are one-parameter families of the self-adjoint Dirac Hamiltonians selected by physically acceptable boundary conditions. Equations determining spectra of the self-adjoint radial Dirac Hamiltonians are derived for various values of parameters. We show that the lowest fermion state in the considered potential becomes unstable when the effective charge is greater than the so-called critical charge, and that the effective charge is influenced by the magnetic flux and spin particle.

Khalilov, V. R.; Lee, K. E.

79

Distinguishability of stacks in ZnTe/ZnSe quantum dots via spectral analysis of Aharonov-Bohm oscillations  

NASA Astrophysics Data System (ADS)

A spectral analysis of the Aharonov-Bohm (AB) oscillations in photoluminescence intensity was performed for stacked type-II ZnTe/ZnSe quantum dots (QDs) fabricated within multilayered Zn-Se-Te system with sub-monolayer insertions of Te. Robust AB oscillations allowed for fine probing of distinguishable QDs stacks within the ensemble of QDs. The AB transition magnetic field, B AB , changed from the lower energy side to the higher energy side of the PL spectra revealing the presence of different sets of QDs stacks. The change occurs within the spectral range, where the contributing green and blue bands of the spectra overlapped. "Bundling" in lifetime measurements is seen at transition spectral regions confirming the results.

Roy, Bidisha; Ji, Haojie; Dhomkar, Siddharth; Cadieu, Fred J.; Peng, Le; Moug, Richard; Tamargo, Maria C.; Kuskovsky, Igor L.

2013-02-01

80

Quantum Geometric Phase in Majorana's Stellar Representation: Mapping onto a Many-Body Aharonov-Bohm Phase  

NASA Astrophysics Data System (ADS)

The (Berry-Aharonov-Anandan) geometric phase acquired during a cyclic quantum evolution of finite-dimensional quantum systems is studied. It is shown that a pure quantum state in a (2J+1)-dimensional Hilbert space (or, equivalently, of a spin-J system) can be mapped onto the partition function of a gas of independent Dirac strings moving on a sphere and subject to the Coulomb repulsion of 2J fixed test charges (the Majorana stars) characterizing the quantum state. The geometric phase may be viewed as the Aharonov-Bohm phase acquired by the Majorana stars as they move through the gas of Dirac strings. Expressions for the geometric connection and curvature, for the metric tensor, as well as for the multipole moments (dipole, quadrupole, etc.), are given in terms of the Majorana stars. Finally, the geometric formulation of the quantum dynamics is presented and its application to systems with exotic ordering such as spin nematics is outlined.

Bruno, Patrick

2012-06-01

81

Quantum geometric phase in Majorana's stellar representation: mapping onto a many-body Aharonov-Bohm phase.  

PubMed

The (Berry-Aharonov-Anandan) geometric phase acquired during a cyclic quantum evolution of finite-dimensional quantum systems is studied. It is shown that a pure quantum state in a (2J+1)-dimensional Hilbert space (or, equivalently, of a spin-J system) can be mapped onto the partition function of a gas of independent Dirac strings moving on a sphere and subject to the Coulomb repulsion of 2J fixed test charges (the Majorana stars) characterizing the quantum state. The geometric phase may be viewed as the Aharonov-Bohm phase acquired by the Majorana stars as they move through the gas of Dirac strings. Expressions for the geometric connection and curvature, for the metric tensor, as well as for the multipole moments (dipole, quadrupole, etc.), are given in terms of the Majorana stars. Finally, the geometric formulation of the quantum dynamics is presented and its application to systems with exotic ordering such as spin nematics is outlined. PMID:23004240

Bruno, Patrick

2012-06-11

82

Measurement of the second-order Zeeman effect on the sodium clock transition in the weak-magnetic-field region using the scalar Aharonov-Bohm phase  

SciTech Connect

The second-order Zeeman effect of the sodium clock transition in a weak magnetic field of less than 50 {mu}T was measured as the scalar Aharonov-Bohm phase by two-photon stimulated Raman atom interferometry. The ac Stark effect of the Raman pulse was canceled out by adopting an appropriate intensity ratio of two photons in the Raman pulse. The Ramsey fringes for the pulse separation of 7 ms were obtained with a phase uncertainty of {pi}/200 rad. The nondispersive feature of the scalar Aharonov-Bohm phase was clearly demonstrated through 18 fringes with constant amplitude. The Breit-Rabi formula of the sodium clock transition was verified to be {Delta}{nu}=(0.222{+-}0.003)x10{sup 12}xB{sup 1.998{+-}0.004} in a magnetic field of less than 50 {mu}T.

Numazaki, Kazuya; Imai, Hiromitsu; Morinaga, Atsuo [Department of Physics, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda-shi, Chiba 278-8510 (Japan)

2010-03-15

83

Flux-dependent effects in degenerate and symmetric double dot Aharonov-Bohm interferometer with and without interactions  

NASA Astrophysics Data System (ADS)

We study the steady-state characteristics and the transient behaviour of the non equilibrium double-dot Aharonov-Bohm interferometer using analytical tools and numerical simulations. Our simple setup includes non-interacting degenerate quantum dots that are coupled to two biased metallic leads at the same strength. A magnetic flux ? is piercing the set-up perpendicularly. As we tune the degenerate dots energies away from the symmetric point we observe four non trivial magnetic flux control effects: (i) flux dependency of the dots occupation, (ii) magnetic flux induced occupation difference between the dots, at degeneracy, (iii) the effect of ``phase-localization" of the dots coherence holds only at symmetric point, while in general both real and imaginary parts are non-zero, and (iv) coherent evolution survives even when the dephasing strength, introduced into our model using Buttiker probe, is large and comparable to the dots energies and the bias voltage. Moreover, not only finite dephasing strength does not destroy the coherence features, it can provide a new type of coherent oscillation. These four phenomena take place when the dot energies are gated, away from the symmetric point,demonstrating the delicate controllability over the dot occupation and coherence.

Bedkihal, Salil; Bandyopadhyay, Malay; Segal, Dvira

2013-03-01

84

Flux-dependent occupations and occupation difference in geometrically symmetric and energy degenerate double-dot Aharonov-Bohm interferometers  

NASA Astrophysics Data System (ADS)

We study the steady-state characteristics and the transient behavior of the nonequilibrium double-dot Aharonov-Bohm interferometer using analytical tools and numerical simulations. Our simple setup includes noninteracting degenerate quantum dots that are coupled to two biased metallic leads at the same strength. A magnetic flux ? pierces the interferometer perpendicularly. As we tune the degenerate dot energies away from the symmetric point, we observe four nontrivial magnetic flux-control effects: (i) flux dependency of the occupation of the dots, (ii) magnetic-flux-induced occupation difference between the dots, at degeneracy, (iii) the effect of “phase localization” of the dots’ coherence holds only at the symmetric point, while in general both real and imaginary parts of the coherence are nonzero, and (iv) coherent evolution survives even when the dephasing strength, introduced via Büttiker probes, is large and comparable to the dot energies and the bias voltage. In fact, finite dephasing can actually introduce new types of coherent oscillations into the system dynamics. These four phenomena take place when the dot energies are gated, to be positioned away from the symmetric point, demonstrating that the combination of bias voltage, magnetic flux, and gating field can provide delicate control over the occupation of each of the quantum dots and their coherence.

Bedkihal, Salil; Bandyopadhyay, Malay; Segal, Dvira

2013-01-01

85

The optical Aharonov-Bohm effect and magneto-optical properties in type-II quantum dots  

NASA Astrophysics Data System (ADS)

We present a detailed experimental study of the magneto-optical properties of type-II quantum dots (QDs) in: (1) ZnTe/ZnSe superlattices grown by Molecular Beam Epitaxy (MBE)---these Zn(SeTe) QDs evolve from Te-clustering in the ZnSe matrix during growth; and (2) diluted magnetic semiconductor, (ZnMn)Se, QDs in a ZnSe matrix produced by migration enhanced epitaxy. In case (1) the Zn(SeTe) QDs display large and robust (with temperature) oscillations as a function of magnetic field in both the photoluminescence energy and intensity as a result of the optical Aharonov-Bohm effect. The large strength of these oscillations is attributed to a combination of the type-II symmetry and the columnar geometry of the structures; the oscillations persist until 180K. The type-II diluted magnetic semiconductor, (ZnMn)Te quantum dots display similar oscillatory effects in the emission intensity. Interestingly, the coherence of the Aharonov-Bohm phase in these magnetic dots is strongly related to the spin polarization of the system due to the Mn-exciton exchange interaction as shown by the disappearance of the oscillations at low magnetic fields. The enhanced coherence at high fields, which leads to strong oscillations in intensity, is attributed to removal of magnetic disorder by the applied magnetic field. While the magnetic nature of the QDs is clear from the polarization measurements there is the seemingly contradictory behavior of a very small Zeeman shift for material that has a corresponding large Zeeman shift for the comparable composition of bulk (ZnMn)Te. More importantly, a red shift greater than 30 meV is observed in the peak energy of the PL as function of time after excitation with a picosecond pulse. These results can be explained by postulating formation of bound magnetic polarons in the QDs. The overall red shift is identified as the magnetic polaron binding energy, EMP; it is roughly independent of temperature, persisting up to 150K. The large MP binding energy is apparently contradictory to the small observed Zeeman splitting and the temperature dependence of the optical polarization in the steady state. These apparently contradictory properties are interpreted in terms of a model that explains the temperature dependence as well as the polarization and Zeeman energy splitting, while fully taking into account the polaron formation energy. The model is based on the hole-Mn and the Mn-Mn exchange coupling and their role in the magnetic polaron formation with a crucial aspect being the formation of an antiferromagnetically ordered state of the Mn spin system in each of the QDs in the absence of photoinjected holes.

Whiteside, Vincent Ryan

86

Effect of built-in electric field in stacked type-II ZnTe/ZnSe submonolayer quantum dots: enhancement and narrowing of Aharonov-Bohm oscillations  

NASA Astrophysics Data System (ADS)

Robust and narrow Aharonov-Bohm (AB) oscillations were observed in both intensity and energy of the mangeto-photoluminescence (PL) from stacked type-II ZnTe/ZnSe submonolayer quantum dots (QDs) grown via migration enhanced epitaxy. The narrowness and enhancement in the AB oscillations is a consequence of the built-in electric field in the system. Spectral analysis of cw magneto-PL and time-resolved PL suggest that the QD stacks size distribution is not large and thus broadening of the PL is possibly due to strong electron-phonon interaction as generally seen in bulk Zn-Se-Te systems.

Roy, Bidisha; Dhomkar, Siddharth; Ji, Haojie; Tamargo, Maria; Kuskovsky, Igor

2013-03-01

87

Excitonic Aharonov-Bohm effect in isotopically pure {sup 70}Ge/Si self-assembled type-II quantum dots  

SciTech Connect

We report on a magnetophotoluminescence study of isotopically pure {sup 70}Ge/Si self-assembled type-II quantum dots. Oscillatory behaviors attributed to the Aharonov-Bohm effect are simultaneously observed for the emission energy and intensity of excitons subject to an increasing magnetic field. When the magnetic flux penetrates through the ringlike trajectory of an electron moving around each quantum dot, the ground state of an exciton experiences a change in its angular momentum. Our results provide the experimental evidence for the phase coherence of localized electron wave functions in group-IV Ge/Si self-assembled quantum structures.

Miyamoto, Satoru; Ishikawa, Toyofumi; Eto, Mikio; Itoh, Kohei M. [School of Fundamental Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522 (Japan); Moutanabbir, Oussama [School of Fundamental Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522 (Japan); Max Planck Institute of Microstructure Physics, Weinberg 2, Halle (Saale), 06120 (Germany); Haller, Eugene E. [Lawrence Berkeley National Laboratory and UC Berkeley, 1 Cyclotron Road, Berkeley, California 94720 (United States); Sawano, Kentarou; Shiraki, Yasuhiro [Research Center for Silicon Nano-Science, Advanced Research Laboratories, Tokyo City University, 8-15-1 Todoroki, Setagaya-ku, Tokyo 158-0082 (Japan)

2010-08-15

88

Spin transfer in a ferromagnet-quantum dot and tunnel-barrier-coupled Aharonov-Bohm ring system with Rashba spin-orbit interactions.  

PubMed

The spin transfer effect in a ferromagnet-quantum dot (insulator)-ferromagnet Aharonov-Bohm (AB) ring system with Rashba spin-orbit (SO) interactions is investigated by means of the Keldysh nonequilibrium Green function method. It is found that both the magnitude and direction of the spin transfer torque (STT) acting on the right ferromagnet electrode can be effectively controlled by changing the magnetic flux threading the AB ring or the gate voltage on the quantum dot. The STT can be greatly augmented by matching a proper magnetic flux and an SO interaction at a cost of low electrical current. The STT, electrical current and spin current are uncovered to oscillate with the magnetic flux. The present results are expected to be useful for information storage in nanospintronics. PMID:21393698

Chen, Xi; Zheng, Qing-Rong; Su, Gang

2010-04-20

89

Electron transmission in the Aharonov-Bohm Interferometer with (and without) a spin impurity: Effect of finite width of quantum wires  

NASA Astrophysics Data System (ADS)

The Aharonov-Bohm interferometer (ABI) in a two-terminal configuration is a reliable tool to study electron transport in nanoscopic systems. Characterization of the ABI using the Griffith boundary conditions at the junctions of the leads and the ring reported earlier by Kumar and Sahoo (Inter. Jour. Mod. Phys. B 19, 3483 (2005)) are reanalyzed using improved boundary conditions recently proposed by Voo and Chen (Phys Rev B 73, 035307 (2006)). Transmittance (T) of electron as the electron momentum k is varied shows sharp localized peaks. The minimum of T as k is varied over a large range shows progressive increase with k and eventually saturates. Modification of T near the values of k corresponding to the resonances of the ring (without the leads) is not significant. However, noticeable changes do appear off the resonance positions. For the ABI with a spin half impurity-the problem investigated earlier by Joshi Sahoo and Jayannavar (Phys. Rev. B 64, 075320-1 (2001))-we find qualitative differences between large and small k behavior similar to the perfect ABI case. However, in the presence of magnetic flux, the interferometer becomes opaque to electrons for small k values. Our results suggest experiment tests not carried out so far to our knowledge.

Setty, Chandan; Senanayak, Satyaprasad P.; Sai, K. Vijay; Venkataramaniah, K.; Sahoo, Debendranath

2009-06-01

90

Tunable spin-dependent Andreev reflection in a four-terminal Aharonov-Bohm interferometer with coherent indirect coupling and Rashba spin-orbit interaction  

PubMed Central

Using the nonequilibrium Green’s function method, we theoretically study the Andreev reflection(AR) in a four-terminal Aharonov-Bohm interferometer containing a coupled double quantum dot with the Rashba spin-orbit interaction (RSOI) and the coherent indirect coupling via two ferromagnetic leads. When two ferromagnetic electrodes are in the parallel configuration, the spin-up conductance is equal to the spin-down conductance due to the absence of the RSOI. However, for the antiparallel alignment, the spin-polarized AR occurs resulting from the crossed AR (CAR) and the RSOI. The effects of the coherent indirect coupling, RSOI, and magnetic flux on the Andreev-reflected tunneling magnetoresistance are analyzed at length. The spin-related current is calculated, and a distinct swap effect emerges. Furthermore, the pure spin current can be generated due to the CAR when two ferromagnets become two half metals. It is found that the strong RSOI and the large indirect coupling are in favor of the CAR and the production of the strong spin current. The properties of the spin-related current are tunable in terms of the external parameters. Our results offer new ways to manipulate the spin-dependent transport.

2012-01-01

91

Curl-free vector potential observation on the macro-scale for charged particles in a magnetic field compared with that on the micro-scale: the Aharonov-Bohm effect  

NASA Astrophysics Data System (ADS)

The recently reported curl-free vector potential observation (Varma et al 2012 Eur. Phys. J. D 66 38) in relation to a system of charged particles in a magnetic field points to the existence of a new state of the electron—a quantum modulated state—which arises through a scattering-induced transition across Landau levels. This quantum modulated state has been shown to account for some very unusual effects on the macro-scale, which are distinct from the ones which can be understood in terms of a ‘classical electron’ and also from the ones which can be understood in terms of a ‘quantum electron’ on the micro-scale characterized by the Planck quantum. This quantum modulated state has been shown to account for the observation of a static curl-free vector potential on the macro-scale alluded to above, as well as other matter wave manifestations on the macro-scale. The macro-scale curl-free vector potential observation differs fundamentally from the corresponding micro-scale effect—the well-known Aharonov-Bohm effect. These two effects—on the macro-scale and the macro-scale—are compared and contrasted to each other here in their manner of detection of the static curl-free vector potential. Such a comparative study helps gain a deeper understanding of the nature of the quantum modulated state and the macro-scale matter wave it represents.

Varma, Ram K.

2012-10-01

92

Aharonov-Bohm problem for spin 1  

SciTech Connect

The basic AB {ital problem} is to determine how an unshielded tube of magnetic flux {Phi} affects arbitrarily long-wavelength charged particles impinging on it. For spin 1 at almost all {Phi} the particles do not penetrate the tube, so the interaction essentially is periodic in {Phi} (AB {ital effect}). Below-threshold bound states move freely only along the tube axis, and consequent induced vacuum currents supplement rather than screen {Phi}. For a pure magnetic interaction the tube must be broader than the particle Compton wavelength, i.e., only the nonrelativistic spin-1 AB problem exists. {copyright} {ital 1997} {ital The American Physical Society}

Horner, M.L.; Goldhaber, A.S. [Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Silver Street, Cambridge, CB3 9EW (United Kingdom)]|[Institute for Theoretical Physics, State University of New York, Stony Brook, New York 11794-3840 (United States)

1997-05-01

93

Bound states in twisted Aharonov-Bohm tubes  

SciTech Connect

Twisted tubes provide an excellent setting for the theoretical and experimental study of quantum mechanics in curved space. Here tubes with constant normal cross section are considered, for which the effect of twisting may be characterized in terms of the curvature and torsion of the curve which threads the twisted tube. When this tube is [open quotes]thin and slowly twisting[close quotes] it has been found, in various applications, that the lowest order effect of the tube's twisting is to introduce an attractive potential (along the curve) proportional to the square of the curvature. In this work, the authors study bound and scattered states of the Schroedinger equation in bent and twisted tubes of constant normal cross section threaded by whiskers of magnetic flux. 7 refs.

Dunne, G.; Jaffe, R.L. (Massachusetts Institute of Technology, Cambridge (United States))

1993-05-01

94

Aharonov-Bohm Eect and Quantum Chaos in Ballistic Systems  

Microsoft Academic Search

Acknowledgments I wish to express my gratitude to Prof. Katsuhiro Nakamura for continual guidance and encouragement during the course of the present work. I am also indebted to Prof. Tetsuo Ogawa (now at Tohoku Univ.) and Prof. Akira Terai for helpful discussions. A special acknowledgment is directed to Prof. Yoshitake Takane for critical but kind discussions re- garding the mesoscopic

Shiro Kawabata

1997-01-01

95

Aharonov-Bohm effect on Aharonov-Casher scattering  

SciTech Connect

The scattering of relativistic spin-1/2 neutral particles with a magnetic dipole moment by a long straight charged line and a magnetic flux line at the same position is studied. The scattering cross sections for unpolarized and polarized particles are obtained by solving the Dirac-Pauli equation. The results are in general the same as those for pure Aharonov-Casher scattering (by the charged line alone) as expected. However, in special cases when the incident energy, the line charge density, and the magnetic flux satisfy some relations, the cross section for polarized particles is dramatically changed. Relations between the polarization of incident particles and that of scattered ones are presented, both in the full relativistic case and the nonrelativistic limit. The characteristic difference between the general and special cases lies in the backward direction: in the general cases the incident particles are simply bounced while in the special cases their polarization is turned over simultaneously. For pure Aharonov-Casher scattering there exist cases where the helicities of all scattered particles are reversed. This seems to be remarkable but appears unnoticed previously. Two mathematical approaches are employed to deal with the singularity of the electric and magnetic field and it turns out that the physical results are essentially the same.

Lin Qionggui [School of Physics and Engineering, Sun Yat-Sen University, Guangzhou 510275 (China)

2010-01-15

96

Aharonov-Bohm effect in the presence of dissipative environments  

NASA Astrophysics Data System (ADS)

We study a particle on a ring in presence of various dissipative environments. We develop and solve a variational scheme assuming low-frequency dominance. Our solution produces a renormalization-group (RG) transformation to all orders in the inverse dissipation strength and, in particular, reproduces known two-loop results. Our RG leads to a weak dissipation parameter, for which a weak-coupling expansion for the position correlation function shows a 1/?2 decay in imaginary time.

Horovitz, Baruch; Le Doussal, Pierre

2010-10-01

97

Interplay of Coulomb blockade and Aharonov-Bohm resonances in a Luttinger liquid  

Microsoft Academic Search

We consider a ring of strongly interacting electrons connected to two external leads by tunnel junctions. By studying the positions of conductance resonances as a function of gate voltage and magnetic flux, the interaction parameter g can be determined experimentally. For a finite ring the minimum conductance is strongly influenced by device geometry and electron-electron interactions. In particular, if the

Jari M. Kinaret; Mats Jonson; Robert I. Shekhter; Sebastian Eggert

1998-01-01

98

Quantum mechanics of relativistic particles in multiply connected spaces and the Aharonov-Bohm effect.  

National Technical Information Service (NTIS)

We consider the motion of free relativistic particles in multiply connected spaces. We show that if one of the spatial dimensions has the topology of a circle then the D dimensional spacetime is compactified to D-1 dimensions and the particle mass increas...

J. Gamboa V. O. Rivelles

1990-01-01

99

Gravitational analogue of the Aharonov-Bohm effect in four and three dimensions  

SciTech Connect

Using the path-ordered products of the relevant affine connection we examine the effect of the parallel transport of vectors and spinors (three-dimensional case only) around closed paths (circles) in the field corresponding to the cylindrically symmetric cosmic string. We compute the solution for three-dimensional gravity also.

Bezerra, V.B.

1987-03-15

100

Scaling of Aharonov-Bohm couplings and the dynamical vacuum in gauge theories  

SciTech Connect

Recent results on the vacuum polarization induced by a thin string of magnetic flux lead us to suggest an analogue of the Copenhagen flux spaghetti'' QCD vacuum as a possible mechanism for avoiding the divergence of perturbative QED, thus permitting a consistent completion of the full, nonperturbative theory. The mechanism appears to operate for spinor, but not scalar, QED.

Goldhaber, A.S. (Intitute for Theoretical Physics, State University of New York, Stony Brook, New York 11794-3840 (United States)); Li, H. (Department of Physics, National Chung-Cheng University, Chia-Yi, Taiwan (Taiwan, Province of China)); Parwani, R.R. (Service de Physique Theorique, CE-Saclay, 91191 Gif-sur-Yvette (France))

1995-01-15

101

Compactness in the ? ¯ -Neumann problem, magnetic Schrödinger operators, and the Aharonov–Bohm effect  

Microsoft Academic Search

Compactness of the Neumann operator in the ?¯-Neumann problem is studied for weakly pseudoconvex bounded Hartogs domains in two dimensions. A nonsmooth domain is constructed for which condition (P) fails to hold, yet the Kohn Laplacian still has compact resolvent. The main result, in contrast, is that for smoothly bounded Hartogs domains, the well-known sufficient condition (P) is equivalent to

MICHAEL CHRIST; SIQI FU

2005-01-01

102

Evaluation of the Presence of Mutagenic Dyes in Sediments from Cristais River  

Microsoft Academic Search

Azo dyes are largely used by coloring textiles and can contaminate the aquatic environment, including the sediment, through their release through effluent discharges. In this work the presence of mutagenic azo dyes was evaluated using Thin Layer Chromatography in sediment samples of the Cristais River upstream and downstream of an azo dye processing plant discharge area. Mutagenicity of the sediment

Danielle Palma De Oliveira; Mônica Luisa Kuhlmann; Gisela De Aragão Umbuzeiro

2006-01-01

103

THE CONTRIBUTION OF AZO DYES TO THE MUTAGENIC ACTIVITY OF THE CRISTAIS RIVER  

EPA Science Inventory

To verify if compounds within the discharge of a dye processing plant were contributing to the mutagenicity repeatedly found in the Cristais River, Sao Paulo, Brazil, we chemically characterized the treated industrial effluent, raw and treated water, and the sludge produced by a ...

104

AZO DYES ARE MAJOR CONTRIBUTORS TO THE MUTAGENIC ACTIVITY DETECTED IN THE CRISTAIS RIVER WATERS  

EPA Science Inventory

To determine if compounds from a dye processing plant were contributing to the mutagenicity repeatedly found in the Cristais River, Sao Paulo, Brazil, we chemically characterized the treated industrial effluent, raw and treated water, and the sludge produced by a Drinking Water T...

105

Scalar Charged Particle in Presence of Magnetic and Aharonov-Bohm Fields Plus Scalar-Vector Killingbeck Potentials  

NASA Astrophysics Data System (ADS)

The generalized form of Killingbeck potential is an attractive Coulomb term plus a linear term and a harmonic oscillator term, i.e. - a/ r + br + ? r 2, which has a useful application in quarkonium spectroscopy. The ground state energy with the corresponding wave function are obtained for any arbitrary m-state in two-dimensional Klein-Gordon equation with equal mixture of scalar-vector Killingbeck potentials in the presence of constant magnetic and singular Ahoronov-Bohm flux fields perpendicular to the plane where the interacting charged particle is confined. The analytical exact iteration method is used in our solution. We obtain the energy eigensolutions for particle and antiparticle corresponding to S( r) = V( r) and S( r) = - V( r) cases, respectively. Some special cases like the Coulomb, harmonic oscillator potentials and the nonrelativistic limits are found in presence and absence of external fields.

Ikhdair, Sameer M.

2013-11-01

106

Influence of Coulomb interaction on the Aharonov-Bohm effect in an electronic Fabry-Pérot interferometer  

NASA Astrophysics Data System (ADS)

We study the role of Coulomb interaction in an electronic Fabry-Pérot interferometer (FPI) realized with chiral edge states in the integer quantum Hall regime in the limit of weak backscattering. Assuming that a compressible Coulomb island in a bulk region of the FPI is formed, we develop a capacitance model which explains the plethora of experimental data on the flux and gate periodicity of conductance oscillations. It is also shown that a suppression of finite-bias visibility stems from a combination of weak Coulomb blockade and a nonequilibrium dephasing by the quantum shot noise.

Ngo Dinh, Stéphane; Bagrets, Dmitry A.

2012-02-01

107

Two interacting charged particles in an Aharonov-Bohm ring: Bound state transitions, symmetry breaking, persistent currents, and Berry's phase  

SciTech Connect

By using a Green's function procedure we determine exactly the energy spectrum and the associated eigenstates of a system of two oppositely charged particles interacting through a contact potential and moving in a one-dimensional ring threaded by a magnetic flux. Critical interactions for the appearance of bound states are analytically determined and are viewed as limiting cases of many-body results from the area of interaction-induced metal-insulator transitions in charged quantal mixtures. Analytical expressions on one-body probability and charge current densities for this overall neutral system are derived and their single-valuedness leads to the possibility of states with broken symmetry, with possible experimental signatures in exciton spectra. Persistent currents are analytically determined and their properties investigated from the point of view of an interacting mesoscopic system. A cyclic adiabatic process on the interaction potential is also identified, with the associated Berry's phase directly linked to the electric (persistent) currents, the probability currents having no contribution for a neutral system.

Moulopoulos, Konstantinos; Constantinou, Martha [University of Cyprus, Department of Physics, P.O. Box 20537, 1678 Nicosia (Cyprus)

2004-12-15

108

The contribution of azo dyes to the mutagenic activity of the Cristais River.  

PubMed

To verify whether dyes emitted within the discharge of a dye processing plant were contributing to the mutagenicity repeatedly found in the Cristais River, Sao Paulo, Brazil, we chemically characterized the following mutagenic samples: the treated industrial effluent, raw and treated water, and the sludge produced by a Drinking Water Treatment Plant (DWTP) located approximately 6 km from the industrial discharge. Considering that 20% of the dyes used for coloring activities might be lost to wastewaters and knowing that several dyes have mutagenic activity, we decided to analyze the samples for the presence of dyes. Thin layer chromatographic analysis indicated the presence of three prevalent dyes in all samples, except for the drinking water. This combination of dyes corresponded to a commercial product used by the industry, and it tested positive in the Salmonella assay. The structures of the dye components were determined using proton magnetic resonance and mass spectrometric (MS) methods, and the dyes were tested for mutagenicity. The blue component was identified as the C.I. Disperse Blue 373, the violet as C.I. Disperse Violet 93, and the orange as C.I. Disperse Orange 37. The dyes showed mutagenic responses of 6300, 4600, and 280 revertants/microg for YG1041 with S9 respectively. A bioassay-directed fractionation/chemical analysis showed that the C.I. Disperse Blue 373 contributed 55% of the mutagenic activity of the DWTP sludge. We showed that these dyes contributed to the mutagenic activity found in the Cristais River environmental samples analyzed and are indirectly affecting the quality of the related drinking water. Therefore, we believe that this type of discharge should be more thoroughly characterized chemically and toxicologically. Additionally, human and ecological risks associated with the release of dye processing plant effluents should be more fully investigated, especially where the resultant water is taken for human consumption. PMID:15910902

de Aragão Umbuzeiro, Gisela; Freeman, Harold S; Warren, Sarah H; de Oliveira, Danielle Palma; Terao, Yoshiyasu; Watanabe, Tetsushi; Claxton, Larry D

2005-06-01

109

Estudos de termoluminescencia em alguns cristais naturais. (Thermoluminescence studies on some natural crystals).  

National Technical Information Service (NTIS)

A comparative study was performed on the minerals Amethyst, Calcite, Calamine, Spodumene, Feldspar, Rutile, and various types of Tourmaline, which can be used as thermoluminescent dosimeters. After the study and analysis of the thermoluminescent character...

M. C. P. Silva

1985-01-01

110

Inducao de cor, por irradiacao, em cristais de topazio. (Radiation induced color in topaz crystals).  

National Technical Information Service (NTIS)

The presence of defects and impurities in the crystal lattice alters the eletric field distribution within the crystal, allowing the electrons to occupy energy levels in the forbbiden band. Ionizing radiation supply the required energy to permit the elect...

A. C. Castagnet H. C. C. Rocca M. E. C. Rostilato

1989-01-01

111

Topology, Holes and Sources  

NASA Astrophysics Data System (ADS)

The Aharonov-Bohm effect is often called "topological." But it seems no more topological than magnetostatics, electrostatics or Newton-Poisson gravity (or just about any radiation, propagation from a source). I distinguish between two senses of "topological."

Afriat, Alexander

2013-03-01

112

Quantum interference, tunnel junctions and resonant tunneling interferometer  

Microsoft Academic Search

The quantum interference between two semiclassical trajectories was shown to be a great issue in mesoscopic systems with metallic conductivity. The effect persists also in the systems of tunnel junctions. It determines reproducible fluctuations of the I-V curve and Aharonov-Bohm effect in the system of two junctions. Quantum interference leads to quantization and discrete levels. To build a qualitative picture

Yuli V. Nazarov

1993-01-01

113

A theoretical study on orbital magnetism of mesoscopic ring systems  

Microsoft Academic Search

Spatial distribution of current and resultant magnetization of mesoscopic ring systems with finite width are investigated in various regimes of temperature and magnetic field based on the exactly solvable model. The Aharonov–Bohm (AB) oscillation is observed in low temperatures when electrons occupy only one Landau sublevel. When several Landau sublevels are occupied, the coherence of the AB oscillation is destroyed

Masako Saito; Takahiko Sasaki; Hidetoshi Fukuyama

2003-01-01

114

The structure of the electromagnetic field as derived from first principles  

Microsoft Academic Search

The physical origin of the coupling between the electromagnetic field and electrically charged particles is rooted in quantum physics, and is thus not directly accessible to classical electrodynamics. We provide a physical discussion of the electromagnetic potentials that bridges this gap. Starting from an examination of the Aharonov-Bohm effect, we recognize the fundamental role of the electromagnetic potentials in the

Frank Gronwald; J. Nitsch

2001-01-01

115

Domain-Wall Induced Phase Shifts in Spin Waves  

Microsoft Academic Search

We study the interaction between two important features of ferromagnetic nanoparticles: magnetic domain walls and spin waves. Micromagnetic simulations reveal that magnetostatic spin waves change their phase as they pass through domain walls. Similar to an Aharonov-Bohm experiment, we suggest to probe this effect by splitting the waves on different branches of a ring. The interference of merging waves depends

Riccardo Hertel; Wulf Wulfhekel; Jürgen Kirschner

2004-01-01

116

Circular quantum billiard with a singular magnetic flux line  

Microsoft Academic Search

We discuss the application of Gutzwiller's semiclassical theory to a circular billiard with a singular magnetic flux line added at its center. The Aharonov-Bohm effect manifests itself through the cancellation of periodic orbits for particular flux strengths. Diffraction phenomena affect the gross-shell structure of the level density and require corrections of higher order in h. The full quantization of the

S. M. Reimann; M. Brack; A. G. Magner; J. Blaschke; M. V. N. Murthy

1996-01-01

117

Experimental observation of time-delays associated with electric Matteucci-Pozzi phase shifts  

NASA Astrophysics Data System (ADS)

In 1985, Matteucci and Pozzi (1985 Phys. Rev. Lett. 54 2469) demonstrated the presence of a quantum mechanical phase shift for electrons passing a pair of oppositely charged biprism wires. For this experimental arrangement no forces deflect the electrons. Consequently, the result was reported as a non-local type-2 Aharonov-Bohm effect. Boyer (2002 Found. Phys. 32 41-50 1987 Nuovo Cimento B 100 685-701) showed theoretically that the Matteucci-Pozzi effect could be associated with a time delay caused by a classical force. We present experimental data that confirm the presence of a time delay. This result is in contrast to the situation for the original magnetic Aharonov-Bohm effect. On similar theoretical grounds, Boyer has also associated classical forces and time delays with the magnetic Aharonov-Bohm effect. Recently, we reported the absence of such observable time delays. The contrast with our current work illustrates the subtle nature of Aharonov-Bohm effects.

Hilbert, Shawn A.; Caprez, Adam; Batelaan, Herman

2011-09-01

118

Global Aspects of Gravitomagnetism  

Microsoft Academic Search

We consider global properties of gravitomagnetism by investigating the gravitomagnetic field of a rotating cosmic string. We show that although the gravitomagnetic field produced by such a configuration of matter vanishes locally, it can be detected globally. In this context we discuss the gravitational analogue of the Aharonov Bohm effect.

A. BARROS; V. B. BEZERRA; C. ROMERO

2003-01-01

119

Optically generated gauge potentials and their effects in cold atoms  

Microsoft Academic Search

Recent theoretical studies show the possibility of generating optical gauge potentials in neutral atoms using laser beams carrying orbital angular momentum. This is interesting not only because the gauge field is related to a variety of important quantum phenomena in physics, such as the Aharonov-Bohm effect, geometric phases, and the quantum Hall effect, but also due to the fact that

Jianjun Song

2008-01-01

120

Persistent current in an ordered-disordered separated cylinder  

NASA Astrophysics Data System (ADS)

The anomalous behavior of persistent current is examined in an ordered-disordered separated mesoscopic cylinder pierced by an Aharonov-Bohm (AB) flux J within a single-band non-interacting tight-binding framework. Our present analysis may be helpful for studying localization-delocalization transition in shell-doped nanotubes.

Dutta, Paramita; Maiti, Santanu K.; Karmakar, S. N.

2013-06-01

121

Quantum phase of an electric dipole moving in a magnetic dipole field  

NASA Astrophysics Data System (ADS)

It is shown that a neutral particle with an electric dipole moment acquires a quantum phase of Aharonov-Bohm type which is induced by a magnetic dipole field, in addition to the He-McKellar-Wilkens phase which requires a magnetic monopole field. Therefore this phase is measurable in principle. This phase is related to the Casella phase in the sense of the electromagnetic duality.

Lee, Tae-Yeon

2000-12-01

122

Dephasing and the Orthogonality Catastrophe in Tunneling through a Quantum Dot: The “Which Path?” Interferometer  

Microsoft Academic Search

The ``Which Path?'' interferometer consists of an Aharonov-Bohm ring with a\\u000aquantum dot (QD) built in one of its arms, and an additional quantum point\\u000acontact (QPC) located close to the QD. The transmission coefficient of the QPC\\u000adepends on the charge state of the QD. Hence the point contact causes\\u000acontrollable dephasing of transport through the QD, and acts

I. L. Aleiner; Ned S. Wingreen; Yigal Meir

1997-01-01

123

Adiabatic Tracking of a State: A New Route to Nonequilibrium Physics  

NASA Astrophysics Data System (ADS)

We present a novel numerical approach to track the response of a quantum system to an external perturbation that is progressively switched on. The method is applied, within the framework of the density matrix renormalization group technique, to track current-carrying states of interacting fermions in one dimension and in the presence of an Aharonov-Bohm magnetic flux. This protocol allows us to access highly excited states. We also discuss the connection with the entanglement entropy of these excited states.

Moliner, M.; Schmitteckert, P.

2013-09-01

124

Topological Raman band in the carbon nanohorn.  

PubMed

Raman spectroscopy has been used in chemistry and physics to investigate the fundamental process involving light and phonons. The carbon nanohorn introduces a new subject to Raman spectroscopy, namely topology. We show theoretically that a photoexcited carrier with a nonzero winding number activates a topological D Raman band through the Aharonov-Bohm effect. The topology-induced D Raman band can be distinguished from the ordinary D Raman band for a graphene edge by its peak position. PMID:24074113

Sasaki, Ken-Ichi; Sekine, Yoshiaki; Tateno, Kouta; Gotoh, Hideki

2013-09-10

125

The Effect of a Magnetic Flux Line in Quantum Theory  

Microsoft Academic Search

The nonlocal exchange of the conserved, gauge invariant quantity ei\\/ℏ(pk-e\\/cAk)Lk, Lk=const, k=1,2 between the charged particle and the magnetic flux line (in the k=3 direction) is responsible for the Aharonov-Bohm effect. This exchange occurs at a definite time, before the wave packets are brought together to interfere, and can be verified experimentally.

Y. Aharonov; T. Kaufherr

2004-01-01

126

Numerical simulations of a ballistic spin interferometer with Rashba spin-orbital interaction  

Microsoft Academic Search

We numerically investigate the transport behavior of a quasi-one-dimensional (1D) square loop device containing the Rashba spin-orbital interaction in the presence of a magnetic flux. The conductance versus the magnetic field shows the Al'tshuler-Aronov-Spivak (AAS) and Aharonov-Bohm (AB) oscillations. We focus on the oscillatory amplitudes, and find that both of them are strongly dependent on the spin precession angle (i.e.,

Zhenyue Zhu; Qing-Feng Sun; Bin Chen; X. C. Xie

2006-01-01

127

The quantum effects of electromagnetic fluxes  

Microsoft Academic Search

This paper is a review of the problem of the observable action of enclosed electromagnetic fluxes on the quantum-mechanical state of charged particles, known as the Aharonov-Bohm effect. The authors first describe the quantum effects of the fluxes in the quasiclassical approximation, and discuss their relation with basic quantum-mechanical principles. Then they examine the influence of modeling assumptions on the

S. Olariu; I. Iovitzu Popescu

1985-01-01

128

Quantum gates with topological phases  

SciTech Connect

We investigate two models for performing topological quantum gates with the Aharonov-Bohm (AB) and Aharonov-Casher (AC) effects. Topological one- and two-qubit Abelian phases can be enacted with the AB effect using charge qubits, whereas the AC effect can be used to perform all single-qubit gates (Abelian and non-Abelian) for spin qubits. Possible experimental setups suitable for a solid-state implementation are briefly discussed.

Ionicioiu, Radu [Institute for Scientific Interchange (ISI), Villa Gualino, Viale Settimio Severo 65, I-10133 Torino, (Italy)

2003-09-01

129

Topological Raman Band in the Carbon Nanohorn  

NASA Astrophysics Data System (ADS)

Raman spectroscopy has been used in chemistry and physics to investigate the fundamental process involving light and phonons. The carbon nanohorn introduces a new subject to Raman spectroscopy, namely topology. We show theoretically that a photoexcited carrier with a nonzero winding number activates a topological D Raman band through the Aharonov-Bohm effect. The topology-induced D Raman band can be distinguished from the ordinary D Raman band for a graphene edge by its peak position.

Sasaki, Ken-ichi; Sekine, Yoshiaki; Tateno, Kouta; Gotoh, Hideki

2013-09-01

130

Luttinger liquids and composite fermions in nanostructures: what is the nature of the edge states in the fractional quantum Hall regime?  

Microsoft Academic Search

We study the Aharonov-Bohm conductance oscillations of a constriction with an antidot in the fractional quantum Hall regime using a recently proposed composite-fermion Fermi liquid theory, and also using Wen's chiral Luttinger liquid theory extended to include mesoscopic effects. The predictions of the composite-fermion Fermi liquid theory are very similar to standard Fermi liquid theory and are consistent with recent

Michael R Geller; Daniel Loss; George Kirczenow

1997-01-01

131

Interference of two electrons entering a superconductor  

NASA Astrophysics Data System (ADS)

The subgap conductivity of a normal-superconductor (NS) tunnel junction is thought to be due to tunneling of two electrons. There is a strong interference between these two electrons, originating from the spatial phase coherence in the normal metal at a mesoscopic length scale and the intrinsic coherence of the superconductor. We evaluated the interference effect on the transport through an NS tunnel juction. We propose the layouts to observe drastic Aharonov-Bohm and Josephson effects.

Hekking, F. W. J.; Nazarov, Yu. V.

1993-09-01

132

Semiclassical quantization condition for magnetic energy levels of electrons in metals with band-contact lines  

Microsoft Academic Search

We refine the well-known quantization condition for magnetic energy levels of a semiclassical electron. The refined condition results in the energy shift of the levels when in k space the closed electron orbit links to the band-contact line (i.e., surrounds it). This effect is closely analogous to that of Aharonov–Bohm provided the band-contact line plays the role of the infinitely

G. P. Mikitik; Yu. V. Sharlai

1999-01-01

133

Magnetic field symmetries of nonlinear transport with elastic and inelastic scattering  

NASA Astrophysics Data System (ADS)

We study nonlinear electronic transport symmetries in Aharonov-Bohm interferometers subjected to inelastic-scattering effects and show that odd (even) conductance terms are even (odd) in the magnetic field when the junction is (left-right) spatially symmetric. This observation does not hold when spatial inversion symmetry is broken, as we show numerically. Under elastic dephasing effects, the Onsager-Casimir symmetry is maintained beyond linear response, irrespective of spatial asymmetries.

Bedkihal, Salil; Bandyopadhyay, Malay; Segal, Dvira

2013-10-01

134

On detecting discrete Cheshire charge  

NASA Astrophysics Data System (ADS)

We analyze the charges carried by loops of string in models with non-abelian local discrete symmetry. The charge on a loop has no localized source, but can be detected by means of the Aharonov-Bohm interaction of the loop with another string. We describe the process of charge detection, and the transfer of charge between point particles and string loops, in terms of gauge-invariant correlation functions.

Bucher, Martin; Lee, Kai-Ming; Preskill, John

1992-11-01

135

Atomic Stern-Gerlach interferences with time-dependent magnetic fields  

SciTech Connect

In atomic Stern-Gerlach (polarization) interferometry with time-dependent magnetic fields both the spatial and temporal parts of the atomic phase are generally affected. This leads to a total energy shift and to an inelastic momentum transfer. Some of the related effects are studied using a beam of metastable hydrogen atoms. In particular the scalar Aharonov-Bohm effect and its nondispersivity are considered, in addition to other phase shift effects occurring where the field gradient differs from zero.

Nic Chormaic, S.; Miniatura, C.; Gorceix, O.; Viaris de Lesegno, B.; Robert, J.; Feron, S.; Lorent, V.; Reinhardt, J.; Baudon, J.; Rubin, K. (Laboratoire de Physique des Lasers, Universite Paris-Nord, av. J.B. Clement, 93430-Villetaneuse (France))

1994-01-03

136

Haldane Gap and Fractional Oscillations in Gated Josephson Arrays  

NASA Astrophysics Data System (ADS)

An analogy between the twisted quantum xxz model and a gated Josephson junction array is used to predict sharp structure in the critical currents versus gate voltage, and fractional ac Josephson frequencies. We prove selection rules for level crossings which imply fractional periodicities of ground states with varying Aharonov-Bohm flux. Extrapolated numerical diagonalization on ladders indicates a Haldane gap at moderate easy-plane anisotropy, with vanishing superfluid stiffness. Physical parameters for experimental realization of these novel effects are proposed.

Altman, Ehud; Auerbach, Assa

1998-11-01

137

Quantum field theory of non-abelian strings and vortices  

NASA Astrophysics Data System (ADS)

We develop an operator formalism for investigating the properties of non-abelian cosmic strings (and vortices) in quantum field theory. Operators are constructed that introduce classical string sources and that create dynamical string loops. The operator construction in lattice gauge theory is explicitly described, and correlation functions are computed in the strong-coupling and weak-coupling limits. These correlation functions are used to study the long-range interactions of non-abelian strings, taking account of charge-screening effects due to virtual particles. Among the phenomena investigated are the Aharonov-Bohm interactions of strings with charged particles, holonomy interactions between string loops, string entanglement, the transfer of ``Cheshire charge'' to a string loop, and domain-wall decay via spontaneous string nucleation. We also anayze the Aharonov-Bohm interactions of magnetic monopoles with electric flux tubes in a confining gauge theory. We propose that the Aharonov-Bohm effect can be invoked to distinguish among various phases of a non-abelian gauge theory coupled to matter.

Alford, Mark G.; Kai-Ming, Lee; March-Russell, John; Preskill, John

1992-10-01

138

EM International. Volume 1  

SciTech Connect

It is the intent of EM International to describe the Office of Environmental Restoration and Waste Management`s (EM`s) various roles and responsibilities within the international community. Cooperative agreements and programs, descriptions of projects and technologies, and synopses of visits to international sites are all highlighted in this semiannual journal. Focus on EM programs in this issue is on international collaboration in vitrification projects. Technology highlights covers: in situ sealing for contaminated sites; and remote sensors for toxic pollutants. Section on profiles of countries includes: Arctic contamination by the former Soviet Union, and EM activities with Germany--cooperative arrangements.

Not Available

1993-07-01

139

Is EM dead?  

PubMed

Since electron microscopy (EM) first appeared in the 1930s, it has held centre stage as the primary tool for the exploration of biological structure. Yet, with the recent developments of light microscopy techniques that overcome the limitations imposed by the diffraction boundary, the question arises as to whether the importance of EM in on the wane. This Commentary describes some of the pioneering studies that have shaped our understanding of cell structure. These include the development of cryo-EM techniques that have given researchers the ability to capture images of native structures and at the molecular level. It also describes how a number of recent developments significantly increase the ability of EM to visualise biological systems across a range of length scales, and in 3D, ensuring that EM will remain at the forefront of biology research for the foreseeable future. PMID:24124192

Knott, Graham; Genoud, Christel

2013-10-15

140

Environmental Media Services (EMS)  

NSDL National Science Digital Library

Environmental Media Services (EMS) is a nonprofit communications clearinghouse committed to the expansion of media coverage on critical environmental and public health issues. True to their mission, EMS staff "build relationships with top scientists, physicians, and other experts to bring journalists the latest and most credible information." EMS's modest homepage is free of clutter but full of content. While several sections are under construction and updates (currently) appear irregular, a series of available articles provides useful summaries of important environmental news issues over the past six months. Current articles include "The impacts of global warming on the oceans" and "Cool companies," among others.

141

Gestão curricular em Matemática 1  

Microsoft Academic Search

Resumo. A gestão curricular realizada pelo professor implica uma (re)construção do currículo, tendo em conta os seus alunos e as suas condições de trabalho. Esta gestão curricular assenta, de modo central, em dois elementos. Um deles é a criação de tarefas, a partir das quais os alunos se possam envolver em actividades matematicamente ricas e produtivas. As tarefas podem ser

João Pedro da Ponte

142

by EM tomography  

Microsoft Academic Search

We have studied the in vitro reconstitution of sperm nuclei and small DNA templates to mitotic chroma- tin in Xenopus laevis egg extracts by three-dimensional (3D) electron microscopy (EM) tomography. Using specif- ically developed software, the reconstituted chromatin was interpreted in terms of nucleosomal patterns and the overall chromatin connectivity. The condensed chromatin formed

Peter König; Michael B. Braunfeld; John W. Sedat; David A. Agard

143

Second Encontro DA Sociedade Brasileira de Crescimento de Cristais (Second Meeting of the Brazilian Society for Crystal Growth).  

National Technical Information Service (NTIS)

The Meetings of the Brazilian Society for Crystal Growth aim at congregating all the active researchers in the country involved in some of the most diverse areas pertaining to the study of crystals, such as the growth, characterization, or applications of...

1995-01-01

144

Cloaking two-dimensional fermions  

SciTech Connect

A cloaking theory for a two-dimensional spin-(1/2) fermion is proposed. It is shown that the spinor of the two-dimensional fermion can be cloaked perfectly through controlling the fermion's energy and mass in a specific manner moving in an effective vector potential inside a cloaking shell. Different from the cloaking of three-dimensional fermions, the scaling function that determines the invisible region is uniquely determined by a nonlinear equation. It is also shown that the efficiency of the cloaking shell is unaltered under the Aharonov-Bohm effect.

Lin, De-Hone [Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan (China)

2011-09-15

145

Composite quasiparticles and the hidden quantum critical point in the topological transition scenario of high- Tc cuprates  

NASA Astrophysics Data System (ADS)

The quantum interference effects due to the Aharonov-Bohm-type phase factors are studied in the layered t-t'-t?-U-J strongly correlated system relevant for cuprates. Casting Coulomb interaction in terms of composite-fermions via the flux attachment facility, we argue that U(1) compact group instanton events labeled by a topological winding number are essential configurations of the phase field dual to the charge. The impact of these topological excitations is calculated for the phase diagram which displays the hidden quantum critical point.

Kope?, T. K.

2005-10-01

146

Magnetic and electronic properties of multiwall carbon nanotubes  

NASA Astrophysics Data System (ADS)

Multiwall carbon nanotubes were studied by dc magnetization and electron spin resonance (ESR) measurements. Hole doping is inferred from both the high-field dc susceptibility and ESR parameters complying favorably with the band model of two-dimensional graphite. Paramagnetic deviations are evinced on the diamagnetic susceptibility at weak fields and low temperatures, conforming qualitatively with the Aharonov-Bohm effect on the energy gap for magnetic field parallel to the tube axis. Comparison with theoretical predictions for ensembles of carbon nanotubes reveals appreciable differences, indicative of the diverse distribution of nanotubes as well as the presence of active doping.

Likodimos, V.; Glenis, S.; Guskos, N.; Lin, C. L.

2003-07-01

147

Landau quantization and curvature effects in a two-dimensional quantum dot  

NASA Astrophysics Data System (ADS)

In this work we have investigated the influence of topology in quantum dynamics in two-dimensional quantum dots in a conic surface. We analyze the quantum dynamics of particles in this dot when submitted to an external magnetic field and Aharonov-Bohm flux in the dot center. We obtain the eigenvalues and eigenfunctions exactly. We investigated the influence of geometry and topology on the magnetization, the Fermi energy, and the persistent currents. It is shown that the curvature of the space changes the oscillation pattern of those physical quantities.

Furtado, C.; Rosas, A.; Azevedo, S.

2007-09-01

148

Discrete gauge symmetry in continuum theories  

SciTech Connect

We point out that local symmetries can masquerade as discrete global symmetries to an observer equipped with only low-energy probes. The existence of the underlying local gauge invariance can, however, result in observable Aharonov-Bohm-type effects. Black holes can therefore carry discrete gauge charges: a form of nonclassical ''hair.'' Neither black-hole evaporation, wormholes, nor anything else can violate discrete gauge symmetries. In supersymmetric unified theories such discrete symmetries can forbid proton-decay amplitudes that might otherwise be catastrophic.

Krauss, L.M.; Wilczek, F.

1989-03-13

149

Pure phase decoherence in a ring geometry  

SciTech Connect

We study the dynamics of pure phase decoherence for a particle hopping around an N-site ring, coupled both to a spin bath and to an Aharonov-Bohm flux which threads the ring. Analytic results are found for the dynamics of the influence functional and of the reduced density matrix of the particle, both for initial single wave-packet states, and for states split initially into two separate wave packets moving at different velocities. We also give results for the dynamics of the current as a function of time.

Zhu, Z. [Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Rd., Vancouver, British Columbia, V6T 1Z1 (Canada); Aharony, A.; Entin-Wohlman, O. [Department of Physics and the Ilse Katz Center for Meso- and Nano-Scale Science and Technology, Ben Gurion University, Beer Sheva 84105 (Israel); Pacific Institute of Theoretical Physics, University of British Columbia, 6224 Agricultural Rd., Vancouver, British Columbia, V6T 1Z1 (Canada); Stamp, P. C. E. [Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Rd., Vancouver, British Columbia, V6T 1Z1 (Canada); Pacific Institute of Theoretical Physics, University of British Columbia, 6224 Agricultural Rd., Vancouver, British Columbia, V6T 1Z1 (Canada)

2010-06-15

150

Double-donor complex in vertically coupled quantum dots in a threading magnetic field  

PubMed Central

We consider a model of hydrogen-like artificial molecule formed by two vertically coupled quantum dots in the shape of axially symmetrical thin layers with on-axis single donor impurity in each of them and with the magnetic field directed along the symmetry axis. We present numerical results for energies of some low-lying levels as functions of the magnetic field applied along the symmetry axis for different quantum dot heights, radii, and separations between them. The evolution of the Aharonov-Bohm oscillations of the energy levels with the increase of the separation between dots is analyzed.

2012-01-01

151

The Aharonov-Casher and BERRY’S Phase Effects in Solids  

NASA Astrophysics Data System (ADS)

We consider the manifestations of charge-induced topological phase shift (Aharonov-Casher effect) in condensed matter physics. There will be an oscillating response to high voltage of the magnetic moment (persistent current) and conductivity, as well as a phase shift of the Aharonov-Bohm oscillation to a smaller voltage, for the normal metal ring threaded by a charged fiber. These oscillations shift in phase if the magnetic field vector rotates along the ring, as a consequence of the geometrical (Berry’s) phase associated with the electron spin.

Bogachek, E. N.; Krive, I. V.; Kulik, I. O.; Rozhavsky, A. S.

152

Noise-induced phase transition in the electronic Mach-Zehnder interferometer.  

PubMed

We consider dephasing in the electronic Mach-Zehnder interferometer strongly coupled to current noise created by a voltage biased quantum point contact (QPC). We find the visibility of Aharonov-Bohm oscillations as a function of voltage bias and express it via the cumulant generating function of noise. In the large-bias regime, high-order cumulants of current add up to cancel the dilution effect of a QPC. This leads to an abrupt change in the dependence of the visibility on voltage bias which occurs at the QPC's transparency T=1/2. Quantum fluctuations in the vicinity of this point smear out the sharp transition. PMID:19659304

Levkivskyi, Ivan P; Sukhorukov, Eugene V

2009-07-13

153

Observation of Spin-Orbit Berry’s Phase in Magnetoresistance of a Two-Dimensional Hole Anti-dot System  

NASA Astrophysics Data System (ADS)

We report a study of the Aharonov-Bohm (AB) type oscillation of weak field magnetoresistance in an anti-dot lattice (ADL) of a two-dimensional hole system in the presence of strong spin-orbit interaction. The Fourier transform of the oscillations reveals non-monotonic evolutions with the different range of harmonic component, which are indicative of the existence of additional phase factors. A simulation considering Berry’s phase and the phase arising from the spin-orbit shift in the momentum space shows qualitative agreement with the experiment.

Kang, Ning; Abe, Eisuke; Hashimoto, Yoshiaki; Iye, Yasuhiro; Katsumoto, Shingo

2007-08-01

154

Transport properties of topological insulators films and nanowires  

NASA Astrophysics Data System (ADS)

The last several years have witnessed the rapid developments in the study and understanding of topological insulators. In this review, after a brief summary of the history of topological insulators, we focus on the recent progress made in transport experiments on topological insulator films and nanowires. Some quantum phenomena, including the weak antilocalization, the Aharonov—Bohm effect, and the Shubnikov—de Haas oscillations, observed in these nanostructures are described. In addition, the electronic transport evidence of the superconducting proximity effect as well as an anomalous resistance enhancement in topological insulator/superconductor hybrid structures is included.

Liu, Yi; Ma, Zheng; Zhao, Yan-Fei; Meenakshi, Singh; Wang, Jian

2013-06-01

155

Magnetic nanostructures.  

PubMed

Characteristic results of magnetism in small particles, thin films and tunnel junctions are presented. As a consequence of the reduced atomic coordination in small clusters and thin films the electronic states and density of states are modified. Thus, magnetic moments and magnetization are affected. Generally, in clusters and thin films magnetic anisotropy plays a special role. In tunnel junctions the interplay of magnetism, spin currents and superconductivity are of particular interest. In ring-like mesoscopic systems Aharonov-Bohm-induced currents are studied. Results are given for single transition metal clusters, cluster ensembles, thin films, mesoscopic structures and tunnel systems. PMID:21393778

Bennemann, K

2010-06-02

156

Adiabatic tracking of a state: a new route to nonequilibrium physics.  

PubMed

We present a novel numerical approach to track the response of a quantum system to an external perturbation that is progressively switched on. The method is applied, within the framework of the density matrix renormalization group technique, to track current-carrying states of interacting fermions in one dimension and in the presence of an Aharonov-Bohm magnetic flux. This protocol allows us to access highly excited states. We also discuss the connection with the entanglement entropy of these excited states. PMID:24093238

Moliner, M; Schmitteckert, P

2013-09-17

157

Nonlocal Pancharatnam phase in two-photon interferometry  

NASA Astrophysics Data System (ADS)

We propose a polarized intensity interferometry experiment, which measures the nonlocal Pancharatnam phase acquired by a pair of Hanbury-Brown-Twiss photons. The setup involves two polarized thermal sources illuminating two polarized detectors. Varying the relative polarization angle of the detectors introduces a two-photon geometric phase. Local measurements at either detector do not reveal the effects of the phase, which is an optical analog of the multiparticle Aharonov-Bohm effect. The geometric phase sheds light on the three-slit experiment and suggests ways of tuning entanglement.

Mehta, Poonam; Samuel, Joseph; Sinha, Supurna

2010-09-01

158

NonAbelian cosmic string zero modes and SU(3)color Cheshire charge.  

NASA Astrophysics Data System (ADS)

The cosmic strings of certain GUT models can have a nonAbelian SU(3)color magnetic flux leading to a nonAbelian Aharonov-Bohm effect. We show that these strings behave as nonAbelian "Alice strings", with properties similar to the electromagnetic Alice strings discussed by A. S. Schwarz (1982). In particular, they can carry nonlocalizable colored Cheshire charge, with no apparent source. We discuss the quantization of the nonAbelian zero modes of these strings, and the physics of charge exchange with colored objects as well. An example of a realistic GUT model with such strings is given.

Bucher, M.; Goldhaber, A.

159

SO(10) cosmic strings and SU(3)color Cheshire charge  

NASA Astrophysics Data System (ADS)

Certain cosmic strings that occur in GUT models such as SO(10) can carry a magnetic flux which acts nontrivially on objects carrying SU(3)color quantum numbers. We show that such strings are non-Abelian Alice strings carrying nonlocalizable colored ``Cheshire'' charge. We examine claims made in the literature that SO(10) strings can have a long-range, topological Aharonov-Bohm interaction that turns quarks into leptons, and observe that such a process is impossible. We also discuss flux-flux scattering using a multisheeted formalism.

Bucher, Martin; Goldhaber, Alfred S.

1994-04-01

160

SO(10) cosmic strings and SU(3)[sub color] Cheshire charge  

SciTech Connect

Certain cosmic strings that occur in GUT models such as SO(10) can carry a magnetic flux which acts nontrivially on objects carrying SU(3)[sub color] quantum numbers. We show that such strings are non-Abelian Alice strings carrying nonlocalizable colored Cheshire'' charge. We examine claims made in the literature that SO(10) strings can have a long-range, topological Aharonov-Bohm interaction that turns quarks into leptons, and observe that such a process is impossible. We also discuss flux-flux scattering using a multisheeted formalism.

Bucher, M. (School of Natural Science, Institute for Advanced Study, Olden Lane, Princeton, New Jersey 08540 (United States) Institute for Theoretical Physics, State University of New York, Stony Brook, New York 11794-3840 (United States)); Goldhaber, A.S. (Institute for Theoretical Physics, State University of New York, Stony Brook, New York 11794-3840 (United States))

1994-04-15

161

Transport through quantum rings  

NASA Astrophysics Data System (ADS)

The transport of fermions through nanocircuits plays a major role in mesoscopic physics. Exploring the analogy with classical wave scattering, basic notions of nanoscale transport can be explained in a simple way, even at the level of undergraduate solid state physics courses, and more so if these explanations are supported by numerical simulations of these nanocircuits. This paper presents a simple tight-binding method for the study of the conductance of quantum nanorings connected to one-dimensional leads. We show how to address the effects of applied magnetic and electric fields and illustrate concepts such as Aharonov-Bohm conductance oscillations, resonant tunneling and destructive interference.

António, B. A. Z.; Lopes, A. A.; Dias, R. G.

2013-07-01

162

Cyclotron braid group structure for composite fermions  

NASA Astrophysics Data System (ADS)

Although they describe properties of 2D Hall systems in the fractional quantum regime well, composite fermions suffer from the unexplained character of the localized magnetic field flux-tubes attached to each particle in order to reproduce the Laughlin correlations via Aharonov-Bohm phase shifts. The identification of the cyclotron trajectories of 2D charged particles as accessible classical trajectories within the braid group approach at the magnetic field presence, allows, however, for the avoidance of the construction with fluxes. We introduce cyclotron braid subgroups for charged 2D systems at the fractional Landau-level filling associated in a more natural way with composite fermions without invoking field flux-tubes. The Aharonov-Bohm phase shifts caused by fluxes are replaced with the phase gain due to multi-loop cyclotron trajectories unavoidably occurring at the fractional filling of 1/p (p is an odd integer). Another approach to composite particles, using so-called vortices, is also discussed from the point of view of the cyclotron braid group description (for both odd and even p integers).

Jacak, J.; Jó?wiak, I.; Jacak, L.; Wieczorek, K.

2010-09-01

163

Macro-scale observation of curl-free vector potential: A manifestation of quantum modulation of the de Broglie wave  

NASA Astrophysics Data System (ADS)

Experimental results are presented here reporting the detection of a curl-free vector potential on the macro-scale as contrasted with the detection on the micro-scale à la Aharonov-Bohm. Such a detection is attributed to the `quantum modulation' of the plane wave state of the guiding centre motion of a charged particle in a magnetic field, which is generated concomitantly with the excitation of its Landau levels in a scattering episode, through the mechanism of quantum entanglement between the parallel and perpendicular degrees of freedom of the particle. Such a `quantum modulation' is also a matter wave, but on the macro-scale, and leads to the `sensing' of the curl-free vector potential on the macro-scale. Thus while the Aharonov-Bohm effect is attributed to the sensing of the curl-free vector potential by the de Broglie wave, its sensing on the macro-scale is attributed to the modulation of the de Broglie wave.

Varma, R. K.; Banerjee, S. B.; Ambastha, A.

2012-02-01

164

Transverse force on a vortex and vortex mass: Effects of free bulk and vortex-core bound quasiparticles  

NASA Astrophysics Data System (ADS)

The paper reassesses the old but still controversial problem of the transverse force on a vortex and the vortex mass. The transverse force from free bulk quasiparticles on the vortex, both in the Bose and the Fermi liquids, originates from the Aharonov-Bohm effect. However, in the Fermi liquid, one should take into account peculiarities of the Aharonov-Bohm effect for BCS quasiparticles described by two-component spinor wave functions. There is no connection between the transverse force (either from free bulk quasiparticles or from vortex-core bound quasiparticles) and the spectral flow in the vortex core in superfluid Fermi liquid, in contrast to widely known claims. In fact, there is no steady spectral flow in the core of the moving vortex, and the analogy with the Andreev bound states in the superconductor-normal-metal-superconductor junction, where the spectral flow is really possible, is not valid in this respect. The role of the backflow on the vortex mass is clarified. The backflow is an inevitable consequence of a mismatch between the currents inside and outside the vortex core and restores the conservation of the particle number (charge) violated by this mismatch. In the Fermi liquid, the backflow compensates the current through the core bound states, which is a source of the vortex mass (the Kopnin mass). This results in renormalization of the Kopnin vortex mass by a numerical factor.

Sonin, E. B.

2013-04-01

165

Project planning for EMS and SCADA systems  

Microsoft Academic Search

A typical supervisory control and data acquisition (SCADA) system or an energy management system (EMS) has an installed life of only 10 to 15 years. Because it can take five years or more to implement a new EMS or SCADA system, managing such projects is becoming a way of life for utilities. Project planning for EMS and SCADA systems is

Charles T. Lindeberg; Wayne R. Block

1993-01-01

166

Triple Jump Acceleration for the EM Algorithm  

Microsoft Academic Search

This paper presents the triple jump framework for ac- celerating the EM algorithm and other bound optimization methods. The idea is to extrapolate the third search point based on the previous two search points found by regu- lar EM. As the convergence rate of regular EM becomes slower, the distance of the triple jump will be longer, and thus provide

Han-shen Huang; Bou-ho Yang; Chun-nan Hsu

2005-01-01

167

Alveolar Echinococcosis: Characterization of Diagnostic Antigen Em18 and Serological Evaluation of Recombinant Em18  

PubMed Central

The Echinococcus multilocularis protein Em18 is one of the most promising antigens for use in serodiagnosis of alveolar echinococcosis in human patients. Here we identify an antigenic relationship between Em18 and a 65-kDa immunodominant E. multilocularis surface protein previously identified as either EM10 or EmII/3. The NH2-terminal sequence of native Em18 was determined, revealing it to be a fragment of EM10. Experiments were undertaken to investigate the effect of proteinase inhibitors on the degradation of EM10 in crude extracts of E. multilocularis protoscoleces. Em18 was found to be the product of degradation of EM10 by cysteine proteinase. A recombinant Em18 (RecEm18, derived from 349K to 508K of EM10) was successfully expressed by using Escherichia coli expression system and then evaluated for use in serodiagnosis of alveolar echinococcosis. RecEm18 was recognized by 27 (87.1%) and 28 (90.3%) of 31 serum samples from clinically and/or pathologically confirmed alveolar echinococcosis patients by enzyme-linked immunosorbent assay and immunoblotting, respectively. Of 33 serum samples from cystic echinococcosis patients, 1 was recorded as having a weak positive reaction to RecEm18; however, none of the serum samples which were tested from neurocysticercosis patients (n = 10) or healthy people (n = 15) showed positive reactions. RecEm18 has the potential for use in the differential serodiagnosis of alveolar echinococcosis.

Sako, Yasuhito; Nakao, Minoru; Nakaya, Kazuhiro; Yamasaki, Hiroshi; Gottstein, Bruno; Lightowers, Marshall W.; Schantz, Peter M.; Ito, Akira

2002-01-01

168

Risk Communication Within the EM Program  

Microsoft Academic Search

The U.S. Department of Energy Environmental Management program (EM) conducts the most extensive environmental remediation effort in the world. The annual EM budgets have exceeded $6,000,000,000 for approximately ten years and EM has assumed responsibility for the cleanup of the largest DOE reservations (i.e., at Hanford, Washington, Aiken, South Carolina, and Idaho Falls, Idaho) as well as the facilities at

Edelson

2003-01-01

169

Lietuvos teritorijos žem?s plutos deformacij? ir seismotektoninio potencialo ryšys  

NASA Astrophysics Data System (ADS)

Lietuvoje yra statini?, kelian?i? ekologinio pavojaus gr?sm? (Ignalinos atomin? elektrin?, Mažeiki? naftos perdirbimo ?mon?, chemijos gamyklos Jonavoje bei K?dainiuose ir pan.). Seisminiai ?vykiai gali sutrikdyti ši? ?moni? veikl? ir net lemti didel? pavoj? aplinkai, t. y. gali b?ti sukelta didel? aplinkos tarša chemin?mis bei radioaktyviosiomis medžiagomis. Seisminius ?vykius lemia teritorijos seismotektoninis potencialas. Seismotektoninis potencialas ir Žem?s plutos deformacijos yra tarpusavyje susij? rei\\vskiniai, kuriuos sukelia dažnai tie patys giluminiai procesai Žem?s gelm?se. Žem?s plutos deformacij? tyrimas yra vienas iš informacijos šaltini? prognozuojant teritorijos seismotektonin? aktyvum?. Straipsnyje nagrin?jamos Žem?s plutos horizontaliosios deformacijos, nustatomi Žem?s plutos ?tempi? poky?iai Lietuvos teritorijoje pagal GPS matavim? duomenis. Atlikus tyrimus pagal pateikiam? Žem?s plutos horizontali?j? deformacij? ir ?tempi? tyrimo metodik?, gauti nauji horizontali?j? deformacij? charakteristik? bei ?tempi? poky?i? rezultatai ir nustatytos j? s?sajos su seismotektoniniu potencialu.

Zakarevi?ius, Algimantas; Stanionis, Arminas; Levinskait?, Daiva

2010-01-01

170

DOE/EM Criticality Safety Needs Assessment  

SciTech Connect

The issue of nuclear criticality safety (NCS) in Department of Energy Environmental Management (DOE/EM) fissionable material operations presents challenges because of the large quantities of material present in the facilities and equipment that are committed to storage and/or material conditioning and dispositioning processes. Given the uncertainty associated with the material and conditions for many DOE/EM fissionable material operations, ensuring safety while maintaining operational efficiency requires the application of the most-effective criticality safety practices. In turn, more-efficient implementation of these practices can be achieved if the best NCS technologies are utilized. In 2002, DOE/EM-1 commissioned a survey of criticality safety technical needs at the major EM sites. These needs were documented in the report Analysis of Nuclear Criticality Safety Technology Supporting the Environmental Management Program, issued May 2002. Subsequent to this study, EM safety management personnel made a commitment to applying the best and latest criticality safety technology, as described by the DOE Nuclear Criticality Safety Program (NCSP). Over the past 7 years, this commitment has enabled the transfer of several new technologies to EM operations. In 2008, it was decided to broaden the basis of the EM NCS needs assessment to include not only current needs for technologies but also NCS operational areas with potential for improvements in controls, analysis, and regulations. A series of NCS workshops has been conducted over the past years, and needs have been identified and addressed by EM staff and contractor personnel. These workshops were organized and conducted by the EM Criticality Safety Program Manager with administrative and technical support by staff at Oak Ridge National Laboratory (ORNL). This report records the progress made in identifying the needs, determining the approaches for addressing these needs, and assimilating new NCS technologies into EM fissionable material operations. In addition, the report includes projections of future EM needs and associted recommendations.

Westfall, Robert Michael [ORNL; Hopper, Calvin Mitchell [ORNL

2011-02-01

171

Speech Modelling Using Subspace and EM Techniques  

Microsoft Academic Search

The speech waveform can be modelled as a piecewise-stationary linear stochastic state space system, and its parameters can be est imated using an expectation-maximisation (EM) algorithm. One problem is the ini- tialisation of the EM algorithm. Standard initialisation s chemes can lead to poor formant trajectories. But these trajectories howev er are impor- tant for vowel intelligibility. The aim of

Gavin Smith; João F. G. De Freitas; Tony Robinson; Mahesan Niranjan

1999-01-01

172

himu-em: The French Polynesian connection  

Microsoft Academic Search

himu, em i and em ii are three of the main geochemical mantle components that give rise to oceanic island basalts [1]. They represent the end members that produce the extreme isotopic compositions measured on intraplate volcanics. In French Polynesia, all three mantle components are represented in volcanic rocks. The characteristic himu signature is found in Tubuai, Mangaia and Rurutu,

Catherine Chauvel; Albrecht W. Hofmann; Philippe Vidal

1992-01-01

173

EM international activities. February 1997 highlights  

SciTech Connect

EM International Highlights is a brief summary of on-going international projects within the Department of Energy`s Office of Environmental Management (EM). This document contains sections on: Global Issues, activities in Western Europe, activities in central and Eastern Europe, activities in Russia, activities in Asia and the Pacific Rim, activities in South America, activities in North America, and International Organizations.

NONE

1997-02-01

174

National EMS Scope of Practice Model.  

National Technical Information Service (NTIS)

The National EMS Scope of Practice Model is a continuation of the commitment of the National Highway Traffic Safety Administration and the Health Resources and Services Administration to the implementation of the EMS Agenda for the Future. It is part of a...

2007-01-01

175

Abundâncias em estrelas de Bário  

NASA Astrophysics Data System (ADS)

Estrelas de Bário apresentam linhas intensas de elementos produzidos pelo processos (ex: Ba, Y, Sr, Zr) e bandas intensas de CN, C2 e CH. A hipótese mais aceita sobre a origem deste grupo peculiar é a de que essas estrelas façam parte de sistemas binários, tendo recebido material enriquecido em elementos pesados da companheira mais evoluída. Apresentamos neste trabalho uma análise detalhada de uma amostra de estrelas desta classe, incluindo determinação de parâmetros atmosféricos e cálculo de abundâncias. As temperaturas efetivas foram determinadas a partir de dados fotométricos obtidos com o Fotrap instalado no telescópio Zeiss do LNA (Laboratório Nacional de Astrofísica) (B-V, V-I, R-I, V-R), e coletados na literatura nos catálogos Hipparcos (B-V), 2MASS (Two Micron All Sky Survey) (V-K) e The General Catalogue Photometric Data (sistema Geneva). Obtivemos uma faixa de temperaturas de 4400 £ Tef £ 6500. As metalicidades foram determinadas a partir de linhas de Fe I e Fe II, estando os resultados no intervalo -1 £ [Fe/H] £ +0.1. O log g foi determinado pelo equilíbrio de ionização e pela relação com a magnitude bolométrica, a temperatura e a massa, sendo os resultados na faixa 1.5 £ log g £ 4.5. As distâncias utilizadas foram determinadas com o auxílio das paralaxes Hipparcos, e as massas determinadas por modelos de isócronas. Os espectros utilizados foram obtidos com o espectrógrafo FEROS no Telescópio de 1,5m do ESO (European Southern Observatory). As abundâncias foram calculadas por meio de síntese espectral de linhas individuais incluindo elementos alfa, pico do Fe, s e r. Encontramos um excesso de elementos pesados em relação ao Fe, como esperado para estrelas de Bário.

Allen, D. M.

2003-08-01

176

Manufacturing Methods of Multi-ingredient Compost with EM  

Microsoft Academic Search

This project is performed for increasing the integrated effect of EM by reasonable mixing of EM solution and multi-ingredient compost in agriculture. This compost has been manufactured by treating organic materials with EM and culturing other beneficial bacteria with high density, and by adding some minerals. The organic substrates were fermented by EM. There was a definite difference between organic

H. G. Ryang; M. S. Rim; Y. H. Rim; C. U. Chang; C. G. Kang; D. C. Yang

177

The error cause analysis in EM simulation of ship  

Microsoft Academic Search

To ensure validity and applicability of computation results, the EM characteristic of a ship must have a full embodiment in the simulation. In this paper, concerning EM environment, configuration feature and RF function requirements of a ship, illustrates EM characteristic and error cause from two aspects, i.e.EM simulation model, computation and analysis method. Aiming at a typical example, analyzes the

Wu Nan; Huang Song-gao; Wen Ding-e; Wang Chun

2008-01-01

178

Consumo e Fermentação Ruminal de Proteínas em Função de Suplementação Alimentar Energética e Protéica em Novilhos1  

Microsoft Academic Search

RESUMO - Objetivou-se analisar o efeito de suplementação energética sobre o consumo e a fermentação ruminal de proteínas em dois níveis de proteína dietética (6 e 20%). Quatro novilhos mestiços fistulados no rúmen foram utilizados em um quadrado latino e os tratamentos arranjados em um fatorial 2 × 2, em que as dietas testadas constituíram-se de: A. só feno; B.

Natália Guarino; Souza Barbosa; Rogério de Paula Lana; Gulab Newandram Jham; Arnaldo Chaer Borges; Antônio Bento Mâncio; José Carlos Pereira; Juliana Silva Oliveira

179

Marine EM Climatic Parameters. Annual Report.  

National Technical Information Service (NTIS)

Recently there has been increased interest within the U.S. Navy in the use of climatology-based products to support the planning and execution of military operations. Climatological databases of atmospheric features that impact electromagnetic (EM) propag...

A. E. Barrios P. A. Frederickson

2007-01-01

180

EMS offshore. A new horizon for paramedics.  

PubMed

The difficulty in getting medical aid to offshore drilling platforms can be a source of life-threatening delays. Recently, some companies have charted new waters by actually stationing EMS crews on their rigs. PMID:10116023

Mallard, A S

1991-10-01

181

Accelerated list-mode EM algorithm  

Microsoft Academic Search

List-mode data preserves all sampling information in three-dimensional (3-D) PET imaging and can reduce storage requirements for short-time frame acquisitions. List-mode expectation maximization-maximum likelihood (EM-ML), which has been implemented in a number of forms (such as the EM algorithm for list-mode maximum likelihood, the FAIR algorithm and COSEM), is an obvious choice to reconstruct from such data sets when the

A. J. Reader; R. Manavaki; S. Zhao; P. J. Julyan; D. L. Hastings; J. Zweit

2002-01-01

182

3D EM Characterization of Wafer Probes  

Microsoft Academic Search

The following paper describes a method to characterize wafer probes using a 3D EM simulator. Rather than following the traditional method of building a custom test fixture for different probe setups and measuring the S-parameters, this 3D EM characterization method yields multi-port S-parameters of a specific probe structure by utilizing simulations. For a standard characterization, the S-parameters can be a

Hanyi Ding; Randy Wolf; John Ferrario

2001-01-01

183

Condições físicas em galáxias HII  

NASA Astrophysics Data System (ADS)

Galáxias HII são galáxias anãs de baixa luminosidade que apresentam alta taxa de formação estelar. Seus espectros são dominados por intensas linhas de emissão devido à fotoionização pela presença de um grande número de estrelas do tipo O e B. Nós apresentamos um catálogo espectrofotométrico de 111 galáxias HII observadas no telescópio 1.52m do ESO com o espectrógrafo Boller & Chivens. Determinamos propriedades estatísticas da amostra e derivamos condições físicas (temperatura eletrônica, densidade eletrônica) e abundâncias químicas. Para algumas galáxias, fomos também capazes de resolver espacialmente regiões de formação estelar individuais e determinar propriedades espectroscópicas para estas regiões separadamente, o que nos permitiu avaliar as flutuações das condições físico-químicas dentro das galáxias HII. Em particular, vimos que apesar das galáxias HII apresentarem formação estelar espalhada ao longo do corpo da galáxia, são objetos quimicamente homogêneos. A fim de estudar a evolução temporal dos objetos durante o tempo de vida das estrelas ionizantes construimos também alguns diagramas relacionando razões de linhas de emissão com a largura equivalente de Hb (EW(Hb)). Para interpretar tais diagramas utilizamos modelos de fotoionização para populações estelares integradas. Concluímos que as galáxias HII não correspondem a simples idéia de um burst instantâneo envolvido por um gás opaco aos fótons ionizantes e com densidade constante. As relações observadas entre razões de linhas e EW(Hb) podem ser melhor compreendidas se as galáxias HII apresentarem populações estelares mais velhas, que contribuem para o contínuo óptico observado.

Kehrig, C.; Telles, E.; Cuisinier, F.

2003-08-01

184

SOFIS FTS EM test results  

NASA Astrophysics Data System (ADS)

The Solar Occultation FTS for Inclined-orbit Satellite (SOFIS) is a solar occultation Fourier transform spectrometer developed by the Ministry of the Environment (MOE) in Japan for the Global Change Observation Mission-A1 (GCOM-A1) satellite. GCOM-A1 will be placed in a 650 km non-sun-synchronous orbit, with an inclination angle of 69 degrees. ABB-Bomem is a sub-contractor of NTSpace (NEC-Toshiba Space) for the design and manufacturing of the FTS Engineering Model of SOFIS. SOFIS measures the vertical profile of the atmospheric constituents with 0.2 cm-1 spectral resolution for the spectral range covering 3-13 ?m. The atmospheric vertical resolution of SOFIS is 1 km. The target of SOFIS measurements is a global distribution of O3, HNO3, NO2, N2O, CH4, H2O, CO2, CFC-11, CFC-12, ClONO2, aerosol extinction, atmospheric pressure and temperature. NTSpace in Japan is the prime contractor of SOFIS. The spectrometer is an adapted version of the classical Michelson interferometer using an optimized optical layout and moving retro-reflectors. A solid-state laser diode operating at 1550 nm is used as metrology source of the interferometer. Its highly folded optical design results in a high performance instrument with a compact size. SOFIS FTS implements high performance control techniques to achieve outstanding speed stability of the moving mechanism. This paper describes the test activities of the SOFIS-FTS Engineering Model (EM) and preliminary results. The performances of the FTS are presented in terms of key parameters like signal-to-noise ratio, modulation efficiency and stability. Spectra acquired are shown and test methodology and analyses are presented. Lessons learned during assembly, integration and testing are described as well as improvements planned to be implemented in the Flight Model.

Soucy, Marc-Andre A.; Levesque, Luc E.; Tanii, Jun; Kawashima, Takahiro; Nakajima, Hideaki

2003-04-01

185

Tour of the Electromagnetic Spectrum (EMS) Videos  

NSDL National Science Digital Library

These videos introduce middle- and high school-age learners to the electromagnetic spectrum. The product consists of 8 animations including an introduction to electromagnetic waves and one animation for each wavelength of the EM spectrum (Radio, Microwave, Infrared, Visible, Ultraviolet, X-Rays and Gamma Rays). Each wavelength of the EM spectrum offers a construct to illustrate and teach about NASA sensors, missions, and science. Emphasis is placed on relevant science, such as lunar exploration, and hot science topics, such as climate change. The examples and narrative for each wavelength animation build on the learnersâ prior knowledge then introduces examples from NASA missions. These examples explore the use of spectral analysis and visualizations that help scientists make discoveries about the world around us using EM waves.

Benesch, Troy

2009-01-01

186

Risk Communication Within the EM Program  

SciTech Connect

The U.S. Department of Energy Environmental Management program (EM) conducts the most extensive environmental remediation effort in the world. The annual EM budgets have exceeded $6,000,000,000 for approximately ten years and EM has assumed responsibility for the cleanup of the largest DOE reservations (i.e., at Hanford, Washington, Aiken, South Carolina, and Idaho Falls, Idaho) as well as the facilities at Rocky Flats, Colorado and in Ohio. Each of these sites has areas of extensive radioactive and chemical contamination, numerous surplus facilities that require decontamination and removal, while some have special nuclear material that requires secure storage. The EM program has been criticized for being ineffective (1) and has been repeatedly reorganized to address perceived shortcomings. The most recent reorganization was announced in 2001 to become effective at the beginning of the 2003 Federal Fiscal Year (i.e., October 2002). It was preceded by a ''top to bottom'' review (TTBR) of the program (2) that identified several deficiencies that were to be corrected as a result of the reorganization. One prominent outcome of the TTBR was the identification of ''risk reduction'' as an organizing principle to prioritize the activities of the new EM program. The new program also sought to accelerate progress by identifying a set of critical activities at each site that could be accelerated and result in more rapid site closure, with attendant risk, cost, and schedule benefits. This paper investigates how the new emphasis on risk reduction in the EM program has been communicated to EM stakeholders and regulators. It focuses on the Rocky Flats Environmental Technology Site (RFETS) as a case study and finds that there is little evidence for a new emphasis on risk reduction in EM communications with RFETS stakeholders. Discussions between DOE and RFETS stakeholders often refer to ''risk,'' but the word serves as a placeholder for other concepts. Thus ''risk'' communication at RFETS is lively and involves important issues, but often does not inform participants about true ''risk reduction.''

Edelson, M.

2003-02-26

187

Experimental Realization of Strong Effective Magnetic Fields in an Optical Lattice  

SciTech Connect

We use Raman-assisted tunneling in an optical superlattice to generate large tunable effective magnetic fields for ultracold atoms. When hopping in the lattice, the accumulated phase shift by an atom is equivalent to the Aharonov-Bohm phase of a charged particle exposed to a staggered magnetic field of large magnitude, on the order of 1 flux quantum per plaquette. We study the ground state of this system and observe that the frustration induced by the magnetic field can lead to a degenerate ground state for noninteracting particles. We provide a measurement of the local phase acquired from Raman-induced tunneling, demonstrating time-reversal symmetry breaking of the underlying Hamiltonian. Furthermore, the quantum cyclotron orbit of single atoms in the lattice exposed to the magnetic field is directly revealed.

Aidelsburger, M.; Atala, M.; Trotzky, S.; Chen, Y.-A.; Bloch, I. [Fakultaet fuer Physik, Ludwig-Maximilians-Universitaet, Schellingstrasse 4, 80799 Muenchen (Germany); Max-Planck-Institut fuer Quantenoptik, Hans-Kopfermann-Strasse 1, 85748 Garching (Germany); Nascimbene, S. [Fakultaet fuer Physik, Ludwig-Maximilians-Universitaet, Schellingstrasse 4, 80799 Muenchen (Germany); Max-Planck-Institut fuer Quantenoptik, Hans-Kopfermann-Strasse 1, 85748 Garching (Germany); Laboratoire Kastler Brossel, CNRS, UPMC, Ecole Normale Superieure, 24 rue Lhomond, 75005 Paris (France)

2011-12-16

188

Correlated quantum transport of density wave electrons.  

PubMed

Recently observed Aharonov-Bohm quantum interference of the period h/2e in charge density wave rings strongly suggests that correlated density wave electron transport is a cooperative quantum phenomenon. The picture discussed here posits that quantum solitons nucleate and transport current above a Coulomb blockade threshold field. We propose a field-dependent tunneling matrix element and use the Schrödinger equation, viewed as an emergent classical equation as in Feynman's treatment of Josephson tunneling, to compute the evolving macrostate amplitudes, finding excellent quantitative agreement with voltage oscillations and current-voltage characteristics in NbSe(3). A proposed phase diagram shows the conditions favoring soliton nucleation versus classical depinning. PMID:22400766

Miller, J H; Wijesinghe, A I; Tang, Z; Guloy, A M

2012-01-18

189

(Research in the theory of condensed matter and elementary particles. ) Progress report  

SciTech Connect

Progress is summarized in these areas: a new formulation of two dimensional critical phenomena and string theory, supersymmetric critical phenomena and string compactification, conformal field theory on orbifolds, Gaussian models with twisted boundary conditions, modular invariance and supersymmetric critical phenomena, critical indices, conformal invariance, and current algebra, renormalization group fixed points and the string equation of motion, fermionic string field theory, N = 2 super Riemann surfaces, the spinor field in covariant superstring theory, covariant quantization of superstrings, models of aggregation, and quasi-supersymmetry in the BCS mechanism. Further work is proposed in the areas of two dimensional critical phenomena, two dimensional conformal field theory and string theory, the physics of computation, models of aggregation, and the many vortex Aharonov-Bohm problem. 57 refs. (LEW)

Not Available

1986-01-01

190

Coherent magneto-optical activity in a single chiral carbon nanotube  

NASA Astrophysics Data System (ADS)

We propose a theoretical framework and dynamical model for description of the natural optical activity and Faraday rotation in an individual chiral singlewalled carbon nanotube in the highly nonlinear coherent regime. The model is based on a discrete-level representation of the optically active states near the band edge. Chirality is modeled by a system Hamiltonian in a four-level basis corresponding to energy-level configurations, specific for each handedness, that are mirror reflections of each other. The axial magnetic field is introduced through the Aharonov-Bohm and Zeeman energy-level shifts. The time evolution of the quantum system, describing a single nanotube with defined chirality, under un ultrashort polarised pulse excitation is studied using the coupled coherent vector Maxwell-pseudospin equations [Ref.[34

Slavcheva, Gabriela; Roussignol, Philippe

191

Transport properties of two finite armchair graphene nanoribbons  

NASA Astrophysics Data System (ADS)

In this work, we present a theoretical study of the transport properties of two finite and parallel armchair graphene nanoribbons connected to two semi-infinite leads of the same material. Using a single ?-band tight binding Hamiltonian and based on Green's function formalisms within a real space renormalization techniques, we have calculated the density of states and the conductance of these systems considering the effects of the geometric confinement and the presence of a uniform magnetic field applied perpendicularly to the heterostructure. Our results exhibit a resonant tunneling behaviour and periodic modulations of the transport properties as a function of the geometry of the considered conductors and as a function of the magnetic flux that crosses the heterostructure. We have observed Aharonov-Bohm type of interference representing by periodic metal-semiconductor transitions in the DOS and conductance curves of the nanostructures.

Rosales, Luis; González, Jhon W.

2013-01-01

192

Defects and external field effects on the electronic properties of a carbon nanotube torus  

NASA Astrophysics Data System (ADS)

Electronic properties of toroidal carbon nanotubes are studied adopting a single ?-band tight binding Hamiltonian and following real-space renormalization techniques within the Green function formalism. The analysis is restricted to the achiral torus and the dependence of the toroidal energy spectra on its radius and thickness (tube radius) is inferred from the local density of states. The possibility of a metal-insulating transition occurrence in infinite single tubes and toroidal is investigated as functions of magnetic and electric fields applied in distinct configurations. As expected, periodical Aharonov-Bohm oscillations in the local density of states at the Fermi level of the nanostructures are found as a result of the annular symmetry. When substitutional impurities are taken into account such an oscillatory behavior is found to be preserved. Effects of vacancy defects on the electronic properties are also discussed.

Latgé, A.; Rocha, C. G.; Wanderley, L. A.; Pacheco, M.; Orellana, P.; Barticevic, Z.

2003-04-01

193

Quantum Computing through Quantum Networks  

NASA Astrophysics Data System (ADS)

Entanglement of two Aharonov-Bohm (AB) rings, or two artificial atoms, is similar to the entanglement of spins from two electrons. The directions of the angular momentum of two AB rings serve as the inputs for a basic two-bit computing in the quantum network. The question is whether the read-out is to be performed under a short and weak external perturbation? We found that a stronger entanglement than the situation needed for a quantum superposition combines with a strong external terminal connections is the only solution for robust classical readouts. A ``half-adder'' example will be presented. There has to be an inter-relation between internal and external coupling strengths. They are so adjusted for each other so that read-outs are possible.

Wu, Cheng

2013-03-01

194

Coulomb stability of the 4?-periodic Josephson effect of Majorana fermions  

NASA Astrophysics Data System (ADS)

The Josephson energy of two superconducting islands containing Majorana fermions is a 4?-periodic function of the superconducting phase difference. If the islands have a small capacitance, their ground state energy is governed by the competition of Josephson and charging energies. We calculate this ground-state energy in a ring geometry, as a function of the flux ? enclosed by the ring, and show that the dependence on the Aharonov-Bohm phase 2e?/? remains 4? periodic regardless of the ratio of charging and Josephson energies—provided that the entire ring is in a topologically nontrivial state. If part of the ring is topologically trivial, then the charging energy induces quantum phase slips that restore the usual 2? periodicity.

van Heck, B.; Hassler, F.; Akhmerov, A. R.; Beenakker, C. W. J.

2011-11-01

195

Low-dimensional nanostructures and a semiclassical approach for teaching Feynman's sum-over-paths quantum theory  

NASA Astrophysics Data System (ADS)

An introduction to quantum mechanics based on the sum-over-paths (SOP) method originated by Richard P Feynman and developed by E F Taylor and coworkers is presented. The Einstein-Brillouin-Keller (EBK) semiclassical quantization rules are obtained following the SOP approach for bounded systems, and a general approach to the calculation of propagation amplitude is discussed for unbounded systems. These semiclassical results are obtained when the SOP is limited to the trajectories classically allowed. EBK semiclassical quantization and the topological Maslov index are used to deduce the correct quantum mechanical results for systems which live in a two-dimensional world as quantum dots and quantum rings. In the latter systems, the semiclassical propagation amplitude is used to discuss the Aharonov-Bohm effect. The development involves only elementary calculus and also provides a theoretical introduction to the quantum nature of low-dimensional nanostructures.

Onorato, P.

2011-03-01

196

Quantum transport in topological insulator nanowires and thin films  

NASA Astrophysics Data System (ADS)

Topological insulators have an insulating bulk but a metallic surface. In the simplest case, the surface electronic structure of a 3D topological insulator is described by a single 2D Dirac cone. The transport properties of such a surface state are of considerable current interest; they have some similarities with graphene, which also realizes Dirac fermions, but have several unique features in their response to magnetic fields. In this talk, I give an overview of some of the main quantum transport properties of topological insulator surfaces. I focus on the efforts to use quantum interference phenomena, such as weak anti-localization and the Aharonov-Bohm effect, to verify in a transport experiment the Dirac nature of the surface state and its defining properties.

Bardarson, Jens H.

2013-03-01

197

Quantum operations: technical or fundamental challenge?  

NASA Astrophysics Data System (ADS)

A class of unitary operations generated by idealized, semiclassical fields is studied. The operations implemented by sharp potential kicks are revisited and the possibility of performing them by softly varying external fields is examined. The possibility of using the ion traps as ‘operation factories’ transforming quantum states is discussed. The non-perturbative algorithms indicate that the results of abstract ?-pulses of oscillator potentials can become real. Some of them, if empirically achieved, could be essential to examine certain atypical quantum ideas. In particular, simple dynamical manipulations might contribute to the Aharonov–Bohm criticism of the time–energy uncertainty principle, while some others may verify the existence of fundamental precision limits of the position measurements or the reality of ‘non-commutative geometries’.

Mielnik, Bogdan

2013-09-01

198

NRG study of the transmission phase shift through a two-level quantum dot with Kondo correlations  

NASA Astrophysics Data System (ADS)

The transmission phase shift through a Kondo quantum dot has been predicted to take the universal value ?/2 in the center of the Kondo valleyfootnotetextU. Gerland et al., Phys. Rev. Lett., 84, 3710 (2000).. Several experimental studies using a quantum dot embedded in an Aharonov-Bohm ring have aimed to check this prediction, which was finally verified in footnotetextM. Zaffalon et al., Phys. Rev. Lett., 100, 226601 (2008).. A recent experimentfootnotetextS. Takada et al., to be published (2012). has obtained particularly clean results for the transmission phase shift by eliminating the effect of backscattering. We provide a Numerical Renormalization Group study of a two-level quantum that shows very good qualitative agreement with these new experimental results. The effect of the second level, with width different from the first, is crucial for accounting for some of the observed experimental details.

Alex, Arne; Weichselbaum, Andreas; von Delft, Jan

2013-03-01

199

Giant Intrinsic Spin and Orbital Hall Effects in Sr2MO4 (M=Ru, Rh, Mo)  

NASA Astrophysics Data System (ADS)

We investigate the intrinsic spin Hall conductivity (SHC) and the d-orbital Hall conductivity (OHC) in metallic d-electron systems, by focusing on the t2g-orbital tight-binding model for Sr2MO4 (M=Ru, Rh, Mo). The conductivities obtained are one or 2 orders of magnitude larger than predicted values for p-type semiconductors with ˜5% hole doping. The origin of these giant Hall effects is the “effective Aharonov-Bohm phase” that is induced by the d-atomic angular momentum in connection with the spin-orbit interaction and the interorbital hopping integrals. The huge SHC and OHC generated by this mechanism are expected to be ubiquitous in multiorbital transition metal compounds, which opens the possibility of realizing spintronics as well as “orbitronics” devices.

Kontani, H.; Tanaka, T.; Hirashima, D. S.; Yamada, K.; Inoue, J.

2008-03-01

200

Study of Intrinsic Spin and Orbital Hall Effects in Pt Based on a (6s, 6p, 5d) Tight-Binding Model  

NASA Astrophysics Data System (ADS)

We study the origin of the intrinsic spin Hall conductivity (SHC) and the d-orbital Hall conductivity (OHC) in Pt based on a multiorbital tight-binding model with spin-orbit interaction. We find that the SHC exceeds 1000 \\hbar e-1\\cdot?-1 cm-1 when the resistivity ? is smaller than ˜10 {\\micro}? cm, whereas it decreases to 300 \\hbar e-1\\cdot?-1 cm-1 when ?˜ 100 {\\micro}? cm. In addition, the OHC is still larger than the SHC. The origin of the huge spin Hall effect (SHE) and d-orbital Hall effect (OHE) in Pt is the “effective Aharonov-Bohm phase” that is induced by the interorbital transition between dxy- and dx2-y2-orbitals with the aid of the strong spin-orbit interaction.

Kontani, Hiroshi; Naito, Masayuki; Hirashima, Dai S.; Yamada, Kosaku; Inoue, Jun-ichiro

2007-10-01

201

Point-contact spectroscopy of hopping transport : efffects of a magnetic field.  

SciTech Connect

The conductance of a point contact between two hopping insulators is expected to be dominated by the individual localized states in its vicinity. Here, we study the additional effects due to an external magnetic field. Combined with the measured conductance, the measured magnetoresistance provides detailed information on these states (e.g., their localization length, the energy difference, and the hopping distance between them). We also calculate the statistics of this magnetoresistance, which can be collected by changing the gate voltage in a single device. Since the conductance is dominated by the quantum interference of particular mesoscopic structures near the point contact, it is predicted to exhibit Aharonov-Bohm oscillations, which yield information on the geometry of these structures. These oscillations also depend on local spin accumulation and correlations, which can be modified by the external field. Finally, we also estimate the mesoscopic Hall voltage due to these structures.

Kozub, V. I.; Zyuzin, A. A.; Entin-Wohlman, O.; Aharony, A.; Galperin, Y. M.; Vinokur, V.; Materials Science Division; Russian Acad. Sci.; Ben Gurion Univ.; Univ. Oslo

2007-01-01

202

An experimental proposal to test dynamic quantum non-locality with single-atom interferometry  

NASA Astrophysics Data System (ADS)

Quantum non-locality based on the well-known Bell inequality is of kinematic nature. A different type of quantum non-locality, the non-locality of the quantum equation of motion, is recently put forward with connection to the Aharonov-Bohm effect (Popescu S., Nat. Phys., 6 (2010) 151). Evolution of the displacement operator provides an example to manifest such dynamic quantum non-locality. We propose an experiment using single-atom interferometry to test such dynamic quantum non-locality. We show how to measure evolution of the displacement operator with cold atoms in a spin-dependent optical lattice potential and discuss signature to identify dynamic quantum non-locality under a realistic experimental setting.

Zhu, Shi-Liang; Xue, Zheng-Yuan; Zhang, Dan-Wei; Duan, Lu-Ming

2011-06-01

203

The effects of electric and magnetic fields on charge density wave solitons: Possible collective quantum behavior  

NASA Astrophysics Data System (ADS)

Aharonov-Bohm oscillations of period h/2 e in the charge density wave (CDW) magneto-conductance of TaS3 rings strongly support the hypothesis that CDW electron transport is a cooperative quantum phenomenon. In the picture discussed here, droplets or aggregates of solitons and antisolitons quantum-mechanically nucleate and carry current above a Coulomb blockade threshold for CDW transport. The Schrödinger equation is treated as a "classical" description of emerging order parameters, as in Feynman's description of Josephson tunneling. However, one key distinction of the proposed CDW model is that both the amplitudes and relative phases of the soliton droplet order parameters can vary with time. This ability to vary both amplitudes and phases of wave-function-like order parameters may prove critical to any viable quantum information processing strategies robust against decoherence.

Miller, J. H.; Wijesinghe, A. I.

2013-07-01

204

Colloquium: Artificial gauge potentials for neutral atoms  

SciTech Connect

When a neutral atom moves in a properly designed laser field, its center-of-mass motion may mimic the dynamics of a charged particle in a magnetic field, with the emergence of a Lorentz-like force. In this Colloquium the physical principles at the basis of this artificial (synthetic) magnetism are presented. The corresponding Aharonov-Bohm phase is related to the Berry's phase that emerges when the atom adiabatically follows one of the dressed states of the atom-laser interaction. Some manifestations of artificial magnetism for a cold quantum gas, in particular, in terms of vortex nucleation are discussed. The analysis is then generalized to the simulation of non-Abelian gauge potentials and some striking consequences are presented, such as the emergence of an effective spin-orbit coupling. Both the cases of bulk gases and discrete systems, where atoms are trapped in an optical lattice, are addressed.

Dalibard, Jean; Gerbier, Fabrice; Juzeliunas, Gediminas; Oehberg, Patrik [Laboratoire Kastler Brossel, CNRS, UPMC, Ecole normale superieure, 24 rue Lhomond, 75005, Paris (France); Institute of Theoretical Physics and Astronomy, Vilnius University, A. Gostauto 12, Vilnius 01108 (Lithuania); SUPA, Department of Physics, Heriot-Watt University, Edinburgh, EH14 4AS (United Kingdom)

2011-10-01

205

Cylindric quantum wires in a threading magnetic field: A proposal of characterization based on zero bias electron transport  

NASA Astrophysics Data System (ADS)

We study the quantum transport properties of cylindrical shaped wires, with submicrometric diameters and large aspect ratio. The zero bias conductance as a function of temperature, magnetic field and disorder is calculated for different kinds of nano cylinders, from semiconductor quantum wires to carbon nanotubes. A comparison between our findings and the experimental results allows the understanding of the charge carriers' localization, in the external surface or in the core of the wires, by highlighting the basic mechanism of charge transport. We discuss how we can infer that in InAs quantum wires the carriers move in the core. We examine the Aharonov-Bohm oscillations and the quenching that should be observed in the measured magneto conductivity of InAs nano cylinders and carbon nanotubes emphasizing the role of the angle between field and tube.

Onorato, P.

2012-12-01

206

Scanning gate microscopy of quantum rings: effects of an external magnetic field and of charged defects.  

PubMed

We study scanning gate microscopy (SGM) in open quantum rings obtained from buried semiconductor InGaAs/InAlAs heterostructures. By performing a theoretical analysis based on the Keldysh-Green function approach we interpret the radial fringes observed in experiments as the effect of randomly distributed charged defects. We associate SGM conductance images with the local density of states (LDOS) of the system. We show that such an association cannot be made with the current density distribution. By varying an external magnetic field we are able to reproduce recursive quasi-classical orbits in LDOS and conductance images, which bear the same periodicity as the Aharonov-Bohm effect. PMID:19509453

Pala, M G; Baltazar, S; Martins, F; Hackens, B; Sellier, H; Ouisse, T; Bayot, V; Huant, S

2009-06-10

207

Exploring the magnetically induced field effect in carbon nanotube-based devices  

NASA Astrophysics Data System (ADS)

We report on the high magnetic field study of transport properties of gated small diameter (quasi)-metallic single wall carbon nanotubes (CNTs). We show that initially metallic CNT devices operate as CNT field-effect transistors under strong magnetic fields. This effect results from the Aharonov Bohm phenomena at the origin of a band gap opening in metallic nanotubes. Strong exponential magnetoresistance observed up to room temperature is the ultimate consequence of the linear increase of the band gap with a magnetic field. Finally, we show that intrinsic characteristics of a quasi-metallic CNT, such as the helical symmetry, as well as the parameters of the Schottky barriers formed at the contacts, can be deduced from temperature-dependent magnetoconductance measurements.

Fedorov, G.; Tselev, A.; Jimenez, D.; Latil, S.; Kalugin, N. G.; Barbara, P.; Smirnov, D.; Roche, S.

2008-03-01

208

Efficiency of three-terminal thermoelectric transport under broken time-reversal symmetry  

NASA Astrophysics Data System (ADS)

We investigate thermoelectric efficiency of systems with broken time-reversal symmetry under a three-terminal transport. Using a model of Aharonov-Bohm interferometer formed with three noninteracting quantum dots, we show that Carnot efficiency ?C can be achieved when the thermopower is a symmetric function of the applied magnetic field. On the other hand, the maximal value of the efficiency at maximum power is obtained for asymmetric thermopower. Indeed, we show that the Curzon-Ahlborn limit is exceeded within the linear response regime in our model. Moreover, we investigate thermoelectric efficiency for random Hamiltonians drawn from the Gaussian unitary ensemble and for a more abstract transmission model. In this latter model, we find that the efficiency is improved using sharp energy-dependent transmission functions.

Balachandran, Vinitha; Benenti, Giuliano; Casati, Giulio

2013-04-01

209

Ergodic versus diffusive decoherence in mesoscopic devices  

NASA Astrophysics Data System (ADS)

We report on the measurement of phase coherence length in a high-mobility two-dimensional electron gas patterned in two different geometries, a wire and a ring. The phase coherence length is extracted both from the weak localization correction in long wires and from the amplitude of the Aharonov-Bohm oscillations in a single ring, in a low-temperature regime when decoherence is dominated by electronic interactions. We show that these two measurements lead to different phase coherence lengths, namely L?wire?T-1/3 and L?ring?T-1/2. This difference reflects the fact that the electrons winding around the ring necessarily explore the whole sample (ergodic trajectories), while in a long wire the electrons lose their phase coherence before reaching the edges of the sample (diffusive regime).

Capron, Thibaut; Texier, Christophe; Montambaux, Gilles; Mailly, Dominique; Wieck, Andreas D.; Saminadayar, Laurent

2013-01-01

210

Influence of External Fields on the Killingbeck Potential: Quasi Exact Solution  

NASA Astrophysics Data System (ADS)

The Killingbeck potential consists of oscillator potential plus Cornell potential, i.e. ar2+ br - c/r, that it has received a great deal of attention in particle physics. In this paper, we study the energy levels and wave function for arbitrary m-state in two-dimensional (2D) Schrödinger equation (SE) with a Killingbeck potential under the influence of strong external uniform magnetic and Aharonov-Bohm (AB) flux fields perpendicular to the plane where the interacting particles are confined. We use the wave function ansatz method to solve the radial problem of the Schrödinger equation with Killingbeck potential. We obtain the energy levels in the absence of external fields and also find the energy levels of the familiar Coulomb and harmonic oscillator potentials.

Hamzavi, M.; Ikhdair, S. M.

2013-09-01

211

Black holes with quantum massive spin-2 hair  

SciTech Connect

We show that black holes can posses a long range quantum-mechanical hair associated with a massive spin-2 field, which can be detected by a stringy generalization of the Aharovon-Bohm effect, in which a string loop lassoes the black hole. The long distance effect persist for arbitrarily high mass of the spin-2 field. An analogous effect is exhibited by a massive antisymmetric two-form field. We make a close parallel between the two and the ordinary Aharonov-Bohm phenomenon, and also show that in the latter case the effect can be experienced even by the electrically-neutral particles, provided some boundary terms are added to the action.

Dvali, Gia [Center for Cosmology and Particle Physics, Department of Physics, New York University, New York, New York 10003 (United States)

2006-08-15

212

Monte Carlo study of particle renormalizations in the presence of dissipative environments  

NASA Astrophysics Data System (ADS)

We study the Aharonov-Bohm oscillations of a charged particle on a ring of radius R coupled to a dirty metal environment. With Monte Carlo methods we evaluate the curvature of these oscillations which has the form 1/M?R2 , where M? is an effective mass. We find that at low temperatures T the curvature approaches at large R>l an R independent M?>M , where l is the mean free path in the metal. This behavior is also consistent with perturbation theory in the particle-metal coupling parameter. At finite temperature T we identify dephasing lengths that scale as T-1 at R?l and as T-1/4 at R?l .

Kagalovsky, Victor; Horovitz, Baruch

2008-09-01

213

Geometric phase in Bohmian mechanics  

NASA Astrophysics Data System (ADS)

Using the quantum kinematic approach of Mukunda and Simon, we propose a geometric phase in Bohmian mechanics. A reparametrization and gauge invariant geometric phase is derived along an arbitrary path in configuration space. The single valuedness of the wave function implies that the geometric phase along a path must be equal to an integer multiple of 2?. The nonzero geometric phase indicates that we go through the branch cut of the action function from one Riemann sheet to another when we locally travel along the path. For stationary states, quantum vortices exhibiting the quantized circulation integral can be regarded as a manifestation of the geometric phase. The bound-state Aharonov-Bohm effect demonstrates that the geometric phase along a closed path contains not only the circulation integral term but also an additional term associated with the magnetic flux. In addition, it is shown that the geometric phase proposed previously from the ensemble theory is not gauge invariant.

Chou, Chia-Chun; Wyatt, Robert E.

2010-10-01

214

Photoionization cross section in a two-dimensional quantum ring with a donor impurity  

NASA Astrophysics Data System (ADS)

The transition energy, wave function and photoionization cross-section (PCS) in a Winternitz–Smorodinsky potential quantum ring (QR) with a donor impurity subjected to a uniform magnetic field along the z-axis have been investigated within the compact-density matrix approach. The dependence of these optical properties on the inner radius R1, the outer radius R2, and the magnetic field B is studied in detail. The results reveal that the transition energy, wave function and the PCS in a Winternitz–Smorodinsky potential QR have been strongly affected by these factors. In addition, it can be found that the resonant peak of the PCS presents the Aharonov–Bohm oscillation by changing the magnetic flux.

Jin, Mingge; Xie, Wenfang; Chen, Tairong

2013-10-01

215

Report of Feasibility Study. MAPA/HPCM EMS Project.  

National Technical Information Service (NTIS)

The first annual revision of the Comprehensive Plan for Areawide Emergency Medical Services (EMS) of the Health Planning Council of the Midlands, and a feasibility study regarding the establishment of an areawide EMS System are presented. The feasibility ...

1974-01-01

216

Rural and Frontier EMS Town Hall Meeting Summary.  

National Technical Information Service (NTIS)

Emergency Medical Services (EMS) struggle to meet the needs and demands of citizens in communities across the nation. For rural or frontier communities it is becoming even more challenging to meet the communitys needs for prehospital emergency care. EMS S...

2008-01-01

217

Sinopse dos marcos em matéria de segurança alimentar na ...  

Center for Food Safety and Applied Nutrition (CFSAN)

... 1995 Seafood Hazard Analysis Critical Control Point (Ponto de controle crítico para análise de risco em frutos do mar, HACCP na sigla em inglês ... More results from www.fda.gov/food/guidanceregulation/fsma

218

A emissão em 8mm e as bandas de Merrill-Sanford em estrelas carbonadas  

NASA Astrophysics Data System (ADS)

Estrelas carbonadas possuem bandas moleculares em absorção no visível e, no infravermelho (IR) as principais características espectrais se devem a emissão de grãos. Recentemente foi detectada a presença de bandas de SiC2 (Merrill-Sanford, MS) em emissão sendo atribuída à presença de um disco rico em poeira. Neste trabalho analisamos uma amostra de 14 estrelas carbonadas, observadas no telescópio de 1.52 m do ESO em 4 regiões espectrais diferentes, a fim de detectar as bandas de MS em emissão. Nossa amostra é composta de estrelas que apresentam além da emissão em 11.3 mm, outra em 8 mm. Esta última emissão, não usual nestes objetos, tem sido atribuída ou a moléculas de C2H2, ou a um composto sólido ainda indefinido. A detecção de emissões de MS e aquelas no IR, simultaneamente, revelaria um cenário mais complexo que o habitualmente esperado para os ventos destes objetos. No entanto como primeiro resultado, verificamos que as bandas de Merrill-Sanford encontram-se em absorção, não revelando nenhuma conexão com a emissão a 8 mm. Assim, temos duas hipóteses: (a) a emissão a 8 mm se deve à molécula C2H2 ou (b) essa emissão é resultado da emissão térmica de grãos. Testamos a segunda hipótese modelando a amostra com grãos não-homogêneos de SiC e quartzo, o qual emite em aproximadamente 8mm. Este grão seria produzido em uma fase evolutiva anterior a das carbonadas (estrelas S) e por terem uma estrutura cristalina são destruídos apenas na presença de campos de radiação ultravioleta muito intensos. Os modelos para os envoltórios utilizam o método de Monte Carlo para descrever o problema do transporte da radiação. As conclusões deste trabalho são: (1) as bandas de Merrill-Sanford se encontram em absorção, sugerindo um cenário usual para os ventos das estrelas da amostra; (2) neste cenário, a emissão em 8 mm seria resultado de grãos de quartzo com mantos de SiC, indicando que o quartzo poderia sobreviver a fase evolutiva S.

de Mello, A. B.; Lorenz-Martins, S.

2003-08-01

219

Do earthquakes generate EM signals?  

NASA Astrophysics Data System (ADS)

In recent years there has been significant interest in the seismoelectric effect which is the conversion of acoustic energy into electromagnetic energy. At the onset of the earthquake and at layer interfaces, it is postulated that the seismoelectric signal propagates at the speed of light and thus travels much faster than the acoustic wave. The focus has mainly been to use this method as a tool of predicting earthquakes. Our main objective is to study the possibility of using the seismoelectric effect to determine the origin time of an earthquake, establish an accurate velocity model and accurately locate microearthquakes. Another aspect of this research is to evaluate the possibility of detecting porous zones where seismic activity is postulated to generate fluid movement through porous medium. The displacement of pore fluid relative to the porous medium solid grains generates electromagnetic signals. The Institute of Earth Science and Engineering (IESE) has installed electromagnetic coils in 3 different areas to investigate the seismoelectric effect. Two of the research areas (Krafla in Iceland and Wairakei in New Zealand) are in active geothermal fields where high microearthquake activity has been recorded. The other area of research is at the site of the San Andreas Fault Observatory at Depth (SAFOD) at Parkfield area on the active San Andreas Fault which is associated with repeating earthquakes. In the Wairakei and Parkfield cases a single borehole electromagnetic coil close to borehole seismometers has been used whereas in the Krafla study area, 3 borehole electromagnetic coils coupled to borehole seismometers have been used. The technical difficulties of working in the borehole environment mean that some of these deployments had a short life span. Nevertheless in all cases data was gathered and is being analysed. At the SAFOD site, the electromagnetic coil recorded seismoelectric signals very close to a magnitude 2 earthquake. In the Wairakei and Krafla study areas, large swarms of earthquakes were located very close to the electromagnetic coils. This abstract focuses on the data from the Wairakei area. Preliminary data analysis has been carried out by band pass filtering and removing of the harmonics of the 50 Hz power line frequency. The initial results clearly show that electromagnetic signals accompany the seismic P and S waves (coseismic signal). Further data analysis involves the extraction of the seismoelectric signal generated at the onset of the earthquake and at interfaces from the coseismic signal and other ‘noise' sources. This processing step exhibits a major challenge in seismoelectric data processing. Unlike in other studies we measured the EM field and the seismic field at one location. Therefore the seismoelectric wave travelling at the speed of light cannot be determined as easily in the arrival times as when an array of coils is used. This makes the determination of the origin time much more difficult. Hence other processing techniques need to be explored.

Walter, Christina; Onacha, Stephen; Malin, Peter; Shalev, Eylon; Lucas, Alan

2010-05-01

220

Analysis of the EM Field Distribution in Smart Home  

Microsoft Academic Search

The purpose of this paper is to analyze the EM field distribution in U-home which is a smart home of Kun Shan University. It is apparent that wireless devices in U-home become EM field emitters. This paper states the measurement and the analysis of the EM field distribution generated by those devices. The measurements focus on some popular frequency bands,

Churng-Jou Tsai; Bo-Yuan Tsai; Jinn-Kwei Guo; Chun-Lin Lu; Chang-Fan Liu; Yu-Sheng Lin; Yeong-Her Wang

2010-01-01

221

On Convergence Properties of the EM Algorithm for Gaussian Mixtures  

Microsoft Academic Search

We build up the mathematical connection between the Expectation-Maximization (EM) algorithm and gradient-based approaches for maximum likelihood learning of finite gaussian mixtures. We show that the EM step in parameter space is obtained from the gradient via a projection matrix P, and we provide an explicit expression for the matrix. We then analyze the convergence of EM in terms of

Lei Xu; Michael I. Jordan

1996-01-01

222

Induced EM Field and Absorbed Power Density Inside Human Torsos by 1 to 500 MHZ EM Waves.  

National Technical Information Service (NTIS)

Presented are numerical results on the internal EM field and absorbed power density inside a human torso induced by EM waves of frequencies ranging from 1 to 500 MHz and of both vertical and horizontal polarizations.

B. S. Guru K. M. Chen

1976-01-01

223

Spectral and transport properties of quantum wires with bond disorder  

NASA Astrophysics Data System (ADS)

Systems with bond disorder are defined through lattice Hamiltonians that are of pure nearest neighbour hopping type, i.e., do not contain on-site contributions. They stand representative for the general family of disordered systems with chiral symmetries. Application of the Dorokhov-Mello-Pereyra-Kumar transfer matrix technique P.W. Brouwer et al. [Phys. Rev. Lett 81 (1998) 862; Phys. Rev. Lett. 84 (2000) 1913] has shown that both spectral and transport properties of quasi one-dimensional systems belonging to this category are highly unusual. Most notably, regimes with absence of exponential Anderson localization are observed, the single particle density of states exhibits singular structure in the vicinity of the band centre, and the manifestation of these phenomena depends in an apparently topological manner on the even- or oddness of the channel number. In this paper we re-consider the problem from the complementary perspective of the nonlinear /?-model. Relying on the standard analogy between one-dimensional statistical field theories and zero-dimensional quantum mechanics, we will relate the problem to the behaviour of a quantum point particle subject to an Aharonov-Bohm flux. We will build on this analogy to re-derive earlier DMPK results, identify a new class of even/odd staggering phenomena (now dependent on the total number of sites in the system) and trace back the anomalous behaviour of the bond disordered system to a simple physical mechanism, viz. the flux periodicity of the quantum Aharonov-Bohm system. We will also touch upon connections to the low energy physics of other lattice systems, notably disordered chiral systems in /0 and /2 dimensions and antiferromagnetic spin chains.

Altland, A.; Merkt, R.

2001-07-01

224

Visualization of Circuit Card EM Fields.  

National Technical Information Service (NTIS)

This is the final report for Air Force contract F(41608-96-CA)116: Visualization of Circuit Card EM Fields. Circuit cards (or circuit boards) of one type or another are used in nearly every electrical appliance used by the military or by commerce. This na...

D. Zwillinger

1998-01-01

225

EM algorithms for ML factor analysis  

Microsoft Academic Search

The details of EM algorithms for maximum likelihood factor analysis are presented for both the exploratory and confirmatory models. The algorithm is essentially the same for both cases and involves only simple least squares regression operations; the largest matrix inversion required is for aq ×q symmetric matrix whereq is the matrix of factors. The example that is used demonstrates that

Donald B. Rubin; Dorothy T. Thayer

1982-01-01

226

Áreas de Risco em Manaus: Inventário preliminar  

Microsoft Academic Search

O presente trabalho pautou-se em mapear as ocorrências registradas pela Defesa Civil Municipal (SEMDEC), nos anos de 2005 a 2008, com a finalidade de identificar as áreas mais afetadas por eventos adversos (alagação e deslizamento). Para tanto, foram utilizadas a base cartográfica Google Earth e QGIS. Uma das principais dificuldades foi a localização precisa dos eventos, pois as bases cartográficas

Denise Rodrigues Cruz; Karla R. Mendes Cassiano; Reinaldo Corrêa Costa

2009-01-01

227

EMS response to an airliner crash.  

PubMed

This report of an aircraft crash at a major airport in Kingston, Jamaica examines the response of the local Emergency Medical Services (EMS). Factors that impacted the response are discussed, and the need for more disaster simulation exercises is highlighted. The objective of this case report was to document the response of EMS personnel to the crash of American Airlines Flight 331, and to utilize the information to examine and improve the present protocol. While multiple errors can occur during a mass-casualty event, these can be reduced by frequent simulation exercises during which various personnel practice and learn designated roles. Efficient triage, proper communication, and knowledge of the roles are important in ensuring the best possible outcome. While the triage system and response of the EMS personnel were effective for this magnitude of catastrophe, more work is needed in order to meet predetermined standards. Ways in which this can be overcome include: (1) hosting more disaster simulation exercises; (2) encouraging more involvement with first responders; and (3) strengthening the links in the local EMS system. Vigorous public education must be instituted and maintained. PMID:22853919

Dasgupta, Shuvra; French, Simone; Williams-Johnson, Jean; Hutson, Rhonda; Hart, Nicole; Wong, Mark; Williams, Eric; Espinosa, Kurdell; Maycock, Celeste; Edwards, Romayne; McCartney, Trevor; Cawich, Shamir; Crandon, Ivor

2012-06-01

228

Mercury pollution in the Ems estuary  

NASA Astrophysics Data System (ADS)

From approximately 1960 to 1975 the Ems estuary received several tons of mercury per year from a chlor-alkali plant, a pesticide factory and some minor sources. The discharge has been reduced drastically from 1976 onwards. In 1975 and 1976 measurements were made on the distribution of mercury in the sediment. The horizontal distribution revealed a strong local enrichment of the sediment near the point of discharge. The vertical distribution was found to be in accordance with the local deposition rates. In the water phase no significant change in mercury content from 1975 to 1978/79 could be demonstrated. In 1978/79 a difference between Ems estuary and Dutch Wadden Sea was not significant. In 1978 mercury contents of eelpout Zoarces viviparus in the Ems estuary were about twice as high as in the Wadden Sea. In the Ems estuary a decrease of these contents was found between 1974/75 and 1978. A similar decline in the Wadden Sea may be related to a decreased mercury discharge by the River Rhine.

Essink, K.

1980-03-01

229

EM Topology: From Theory to Application  

Microsoft Academic Search

The paper presents the main principles of the Electromagnetic Topology theory and the way of adapting them in order to make possible efficient analysis of EM-Coupling problems. Particularly, a difference is made between a low frequency analysis for which an adaptation of the method is required and a high frequency analysis for which direct application of the method seems achievable.

J.-P. Parmantier; I. Junqua

2007-01-01

230

Marine EM in GOM: Advances and outlook  

NASA Astrophysics Data System (ADS)

Marine electromagnetic (EM) sounding methods provide valuable complementary information to conventional seismic exploration methods and success stories have been claimed by several oil companies: 1) as indicator of hydrocarbon presence derived from strong resistive anomalies 2) as complimentary tool in structural exploration. While 3D seismic identifies geological structures, it does not directly reveal the fluid content (hydrocarbons). Marine EM sounding exploits variations in electrical resistivity, and is directly sensitive to fluid saturation and thus resistive hydrocarbons. Under the right circumstances it can confirm the presence of hydrocarbons by identifying their resistive characteristics. This means that the possibility of drilling dry exploration wells is significantly reduced, as is the need for extensive appraisal drilling. EM data is used to resolve ambiguities in the structural interpretation of seismic data. For example, whereas the top of a diapiric salt body is often well constrained by seismic data, the position of the lower boundaries is often more elusive. Carbonate (or salt blankets, or resistive basalt) layers complicate the detection and characterization of deeper structure because of diffusive scattering in the layer. However, the resistivity contrast between these layers and the sediments below is an ideal target for EM sounding methods. Recently, two marine EM methods have become popular: The controlled source EM (CSEM) method and magnetotellurics (MT). The CSEM method uses an electric dipole source to transmit low frequency electromagnetic signals to an array of receivers that measure the electromagnetic field at the seafloor. Variation in amplitude and phase of the received signal as the source is towed through the receiver array yield the resistivity structure of the sub-surface to depths of several kilometers. The MT method uses naturally occurring electromagnetic source fields to determine the resistivity of the sub-surface. Thus, by studying the variation in response as a function of frequency, the variation in resistivity as a function of depth may be determined. These methods give complementary information about the resistivity structure of the sub-seafloor. Whereas CSEM data are primarily sensitive to resistive structures, and in particular to layers that are thin compared to their depth of burial, MT data can constrain larger scale conductive structure. By combining natural and controlled source methods better constraints on the geometry and properties of the seafloor can be gained than from either data type alone. Several case histories with large salt structures in the section illustrate that the techniques are useful for future exploration in the GOM. We see the technology moving from its present focus of deep water to include shallower water depths (where CSEM sounding is presently restricted). In addition, we envision the integration of complimentary EM techniques to get a better constrained resistivity image of the subsurface.

MacGregor, L. M.; Strack, K. M.

2005-05-01

231

The association between EMS workplace safety culture and safety outcomes  

PubMed Central

Objective Prior studies have highlighted wide variation in EMS workplace safety culture across agencies. We sought to determine the association between EMS workplace safety culture scores and patient or provider safety outcomes. Methods We administered a cross-sectional survey to EMS workers affiliated with a convenience sample of agencies. We recruited these agencies from a national EMS management organization. We used the EMS Safety Attitudes Questionnaire (EMS-SAQ) to measure workplace safety culture and the EMS Safety Inventory (EMS-SI), a tool developed to capture self-reported safety outcomes from EMS workers. The EMS-SAQ provides reliable and valid measures of six domains: safety climate, teamwork climate, perceptions of management, perceptions of working conditions, stress recognition, and job satisfaction. A panel of medical directors, paramedics, and occupational epidemiologists developed the EMS-SI to measure self-reported injury, medical errors and adverse events, and safety-compromising behaviors. We used hierarchical linear models to evaluate the association between EMS-SAQ scores and EMS-SI safety outcome measures. Results Sixteen percent of all respondents reported experiencing an injury in the past 3 months, four of every 10 respondents reported an error or adverse event (AE), and 90% reported safety-compromising behaviors. Respondents reporting injury scored lower on 5 of the 6 domains of safety culture. Respondents reporting an error or AE scored lower for 4 of the 6 domains, while respondents reporting safety-compromising behavior had lower safety culture scores for 5 of 6 domains. Conclusions Individual EMS worker perceptions of workplace safety culture are associated with composite measures of patient and provider safety outcomes. This study is preliminary evidence of the association between safety culture and patient or provider safety outcomes.

Weaver, Matthew D.; Wang, Henry E.; Fairbanks, Rollin J.; Patterson, Daniel

2012-01-01

232

Spacetime-based model of EM radiation  

NASA Astrophysics Data System (ADS)

A spacetime based model of an electric field and a photon is presented. The model assumes that 4 dimensional spacetime has vacuum fluctuations at all frequencies up to Planck frequency. Gravitational wave theory is used to give insights into electromagnetic (EM) radiation. From gravitational wave equations it is possible to derive the impedance of spacetime and quantify energy propagating in the medium of spacetime. EM radiation is shown to experience the same impedance as gravitational waves. This implies that photons also are waves in the medium of spacetime. The distortion of spacetime produced by a photon is calculated. Experiments are suggested including an experiment that may improve the sensitivity of experiments attempting to detect gravitational waves.

Macken, John A.

2013-10-01

233

Mercury pollution in the Ems estuary  

Microsoft Academic Search

From approximately 1960 to 1975 the Ems estuary received several tons of mercury per year from a chlor-alkali plant, a pesticide\\u000a factory and some minor sources. The discharge has been reduced drastically from 1976 onwards. In 1975 and 1976 measurements\\u000a were made on the distribution of mercury in the sediment. The horizontal distribution revealed a strong local enrichment of\\u000a the

K. Essink

1980-01-01

234

Topic-based language models using EM  

Microsoft Academic Search

In this paper, we propose a novel statistical language model to capture topic-related long-range dependencies. Topics are mod- eled in a latent variable framework in which we also derive an EM algorithm to perform a topic factor decomposition based on a segmented training corpus. The topic model is combined with a standard language model to be used for on-line word

Daniel Gildea; Thomas Hofmann

1999-01-01

235

Telescópio de patrulhamento solar em 12 GHz  

NASA Astrophysics Data System (ADS)

O telescópio de patrulhamento solar é um instrumento dedicado à observação de explosões solares com início de suas operações em janeiro de 2002, trabalhando próximo ao pico de emissão do espectro girossincrotrônico (12 GHz). Trata-se de um arranjo de três antenas concebido para a detecção de explosões e determinação em tempo real da localização da região emissora. Porém, desde sua implementação em uma montagem equatorial movimentada por um sistema de rotação constante (15 graus/hora) o rastreio apresentou pequenas variações de velocidade e folgas nas caixas de engrenagens. Assim, tornou-se necessária a construção de um sistema de correção automática do apontamento que era de fundamental importância para os objetivos do projeto. No segundo semestre de 2002 empreendemos uma série de tarefas com o objetivo de automatizar completamente o rastreio, a calibração, a aquisição de dados, controle de ganhos, offsets e transferência dos dados pela internet através de um projeto custeado pela FAPESP. O rastreio automático é realizado através de um inversor que controla a freqüência da rede de alimentação do motor de rastreio podendo fazer micro-correções na direção leste-oeste conforme os radiômetros desta direção detectem uma variação relativa do sinal. Foi adicionado também um motor na direção da declinação para correção automática da variação da direção norte-sul. Após a implementação deste sistema a precisão do rastreio melhorou para um desvio máximo de 30 segundos de arco, o que está muito bom para este projeto. O Telescópio se encontra em funcionamento automático desde março de 2003 e já conta com várias explosões observadas após a conclusão desta fase de automação. Estamos apresentando as explosões mais intensas do período e com as suas respectivas posições no disco solar.

Utsumi, F.; Costa, J. E. R.

2003-08-01

236

Generation and Identification of Arabidopsis EMS Mutants.  

PubMed

EMS mutant analysis is a routine experiment to identify new players in a specific biological process or signaling pathway using forward genetics. It begins with the generation of mutants by treating Arabidopsis seeds with EMS. A mutant with a phenotype of interest (mpi) is obtained by screening plants of the M2 generation under a specific condition. Once the phenotype of the mpi is confirmed in the next generation, map-based cloning is performed to locate the mpi mutation. During the map-based cloning, mpi plants (Arabidopsis Columbia-0 (Col-0) ecotype background) are first crossed with Arabidopsis Landsberg erecta (Ler) ecotype, and the presence or absence of the phenotype in the F1 hybrids indicates whether the mpi is recessive or dominant. F2 plants with phenotypes similar to the mpi, if the mpi is recessive, or those without the phenotype, if the mpi is dominant, are used as the mapping population. As few as 24 such plants are selected for rough mapping. After finding one marker (MA) linked to the mpi locus or mutant phenotype, more markers near MA are tested to identify recombinants. The recombinants indicate the interval in which the mpi is located. Additional recombinants and molecular markers are then required to narrow down the interval. This is an iterative process of narrowing down the mapping interval until no further recombinants or molecular markers are available. The genes in the mapping interval are then sequenced to look for the mutation. In the last step, the wild-type or mutated gene is cloned to generate binary constructs. Complementation or recapitulation provides the most convincing evidence in determining the mutation that causes the phenotype of the mpi. Here, we describe the procedures for generating mutants with EMS and analyzing EMS mutations by map-based cloning. PMID:24057369

Qu, Li-Jia; Qin, Genji

2014-01-01

237

Helicopter EMS: Research Endpoints and Potential Benefits  

PubMed Central

Patients, EMS systems, and healthcare regions benefit from Helicopter EMS (HEMS) utilization. This article discusses these benefits in terms of specific endpoints utilized in research projects. The endpoint of interest, be it primary, secondary, or surrogate, is important to understand in the deployment of HEMS resources or in planning further HEMS outcomes research. The most important outcomes are those which show potential benefits to the patients, such as functional survival, pain relief, and earlier ALS care. Case reports are also important “outcomes” publications. The benefits of HEMS in the rural setting is the ability to provide timely access to Level I or Level II trauma centers and in nontrauma, interfacility transport of cardiac, stroke, and even sepsis patients. Many HEMS crews have pharmacologic and procedural capabilities that bring a different level of care to a trauma scene or small referring hospital, especially in the rural setting. Regional healthcare and EMS system's benefit from HEMS by their capability to extend the advanced level of care throughout a region, provide a “backup” for areas with limited ALS coverage, minimize transport times, make available direct transport to specialized centers, and offer flexibility of transport in overloaded hospital systems.

Thomas, Stephen H.; Arthur, Annette O.

2012-01-01

238

Gradientes de abundâncias em galáxias espirais  

NASA Astrophysics Data System (ADS)

Gradientes de abundâncias obtidos através de observações de regiões H II têm um papel importante no estudo de formação e evolução de galáxias espirais. Determinações diretas de abundâncias somente são obtidas quando linhas de emissão sensíveis à temperatura eletrônica (e.g., [O III]l4363) são detectadas. Infelizmente estas linhas são fracas ou não observadas em regiões H II de baixa excitação. Nestes casos métodos empíricos são utilizados para estimar as abundâncias químicas. Entretanto, diferentes métodos têm produzido diferentes estimativas de gradientes de abundâncias. Neste trabalho, nós construímos modelos de fotoionização com o objetivo de descrever diagramas de diagnósticos construídos com dados publicados de algumas galáxias espirais normais e barradas. Comparações entre nossas estimativas de abundâncias e de outros métodos mostram que quando não há acordo entre eles, nossos modelos superestimam as abundâncias de O/H e N/H por um fator de 0.3 dex em relação a estimativas diretas de abundâncias, e por fator de 0.2 dex em relação a outros métodos empíricos. A origem da produção de nitrogênio nas galáxias estudadas é discutida.

Dors, O. L.., Jr.; Copetti, M. V. F.

2003-08-01

239

Activities of Effective Microorganism (EM) on the Nutrient Dynamics of Different Organic Materials Applied to Soil  

Microsoft Academic Search

A 56 days incubation study was set up to investigate the effects of combined application of effective microorganism (EM) with composted or fresh organic materials on soil nutrient dynamics. Treatments include; Water (W) as Control, EM, Kraal manure (KM) + W, KM + EM, Lawn clippings (LC) +W, LC+EM, Commercial compost (CC) + W and CC + EM. A CO

L. Ncube

240

Complete-data spaces and generalized EM algorithms  

Microsoft Academic Search

Expectation-maximization (EM) algorithms have been applied extensively for computing maximum-likelihood and penalized-likelihood parameter estimates in signal processing applications. Intrinsic to each EM algorithm is a complete-data space (CDS)-a hypothetical set of random variables that is related to the parameters more naturally than the measurements are. The authors describe two generalizations of the EM paradigm: (i) allowing the relationship between the

J. A. Fessler; A. O. Hero

1993-01-01

241

2. HI PAR (ACQUISITION RADAR) TOWER AND ENLISTED MEN (EM) ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

2. HI PAR (ACQUISITION RADAR) TOWER AND ENLISTED MEN (EM) BARRACKS WITH RADAR ATTACHED. - Nike Hercules Missile Battery Summit Site, Battery Control Administration & Barracks Building, Anchorage, Anchorage, AK

242

e/m Experiment Analysis Refinement  

NASA Astrophysics Data System (ADS)

Thomson's e/m experiment is widely popular in undergraduate courses to help gain an understanding of the properties of the electron. Our results using a standard apparatus, however, reveal significant systematic errors. We examine possible reasons for the discrepancy with the aim of modeling effects that were not included in the original analysis. We conclude that the energy loss of the electron beam as it travels through the helium and the distortion of the beam radius measurement by the curved glass of the tube are the two factors which dominate the discrepancy.

Harmon, Michael; Pruitt, Bryce; Velasquez, Kevin; Schelp, Rich

2011-10-01

243

Communication - An Effective Tool for Implementing ISO 14001/EMS  

SciTech Connect

The Idaho National Engineering and Environmental Laboratory (INEEL) received ISO 14001/EMS certification in June 2002. Communication played an effective role in implementing ISO 14001/EMS at the INEEL. This paper describes communication strategies used during the implementation and certification processes. The INEEL achieved Integrated Safety Management System (ISMS) and Voluntary Protection Program (VPP) Star status in 2001. ISMS implemented a formal process to plan and execute work. VPP facilitated worker involvement by establishing geographic units at various facilities with employee points of contact and management champions. The INEEL Environmental Management System (EMS) was developed to integrate the environmental functional area into its ISMS and VPP. Since the core functions of ISMS, VPP, and EMS are interchangeable, they were easy to integrate. Communication is essential to successfully implement an EMS. (According to ISO 14001 requirements, communication interacts with 12 other elements of the requirements.) We developed communication strategies that integrated ISMS, VPP, and EMS. For example, the ISMS, VPP, and EMS Web sites communicated messages to the work force, such as “VPP emphasizes the people side of doing business, ISMS emphasizes the system side of doing business, and EMS emphasizes the systems to protect the environment; but they all define work, identify and analyze hazards, and mitigate the hazards.” As a result of this integration, the work force supported and implemented the EMS. In addition, the INEEL established a cross-functional communication team to assist with implementing the EMS. The team included members from the Training and Communication organizations, VPP office, Pollution Prevention, Employee and Media Relations, a union representative, facility environmental support, and EMS staff. This crossfunctional team used various communication strategies to promote our EMS to all organization levels and successfully implemented EMS activities through VPP geographic units. In summary, the ISMS and VPP process at the INEEL provided the basic framework of management support and worker involvement to implement our EMS. A cross-functional communication team was established to facilitate the implementation with great success. Communication has been an effective tool for implementing an ISO 14001/EMS at the INEEL.

Rachel Damewood; Bowen Huntsman

2004-04-01

244

Convergence in Norm for Alternating Expectation-Maximization (EM) Type Algorithms  

Microsoft Academic Search

We provide a sufficient condition for convergence of a general class of alternating estimationmaximization(EM) type continuous-parameter estimation algorithms with respect to a given norm.This class includes EM, penalized EM, Green's OSL-EM, and other approximate EM algorithms.The convergence analysis can be extended to include alternating coordinate-maximization EM algorithmssuch as Meng and Rubin's ECM and Fessler and Hero's SAGE. The condition for

Alfred O. Hero; Jeffrey A. Fessler

1995-01-01

245

Recent development in open systems for EMS\\/SCADA  

Microsoft Academic Search

Based on the current situation and emerging trends of development of EMS\\/SCADA systems throughout the world, this report examines the `open system' concept from the viewpoints of users and suppliers. Current technologies for open distributed EMS\\/SCADAs and their possible future trends are described.

Yutaka Kokai; Fumio Masuda; Satoshi Horiike; Yasuji Sekine

1998-01-01

246

10 CFR Appendixes E-M to Part 52 - [Reserved  

Code of Federal Regulations, 2013 CFR

10 Energy 2 2013-01-01 2013-01-01 false [Reserved] E Appendixes E-M to Part 52 Energy NUCLEAR REGULATORY COMMISSION (CONTINUED) LICENSES, CERTIFICATIONS, AND APPROVALS FOR NUCLEAR POWER PLANTS Appendixes E-M to Part 52...

2013-01-01

247

A European Land Mobile Satellite System via EMS  

NASA Astrophysics Data System (ADS)

The paper analyzes the technical and market issues that influence the strategy of implementation of a Land Mobile Satellite System via the payload EMS (European Mobile System) embarked on ITALSAT F-2. The final goal is to determine services, network architecture, and added value chain that make LMSS via EMS profitable for a typical telecommunication company.

Ananasso, Fulvio; Mistretta, Ignazio

1991-10-01

248

Milho para Ensilagem Colhido em Diferentes Estádios de Maturidade1  

Microsoft Academic Search

4 Aluno de graduação em Agronomia - UNIFENAS 5 Aluno (a) de graduação em Zootecnia - UNIFENAS Abstract: This research work was conducted in the agricultural crop of 2005\\/2006 on the José do Rosário Vellano University farm in Alfenas\\/MG, with the purpose of evaluating the effect of the maturity stage of the corn for ensiling on the percentage of DM,

Adauton Vilela de Rezende; Hélio Henrique Vilela; Fabiana Ribeiro Caldara; André Ricardo da Silva; Geraldo Benedito de Souza Almeida; Simone Silvia Senedese

249

On-chip em-sensitive interconnect structures  

Microsoft Academic Search

Due to ever greater current densities in modern IC designs, electromigration (EM) in copper interconnects has become an important reliability factor. In this paper, we analyze current densities on bus and clock networks. We observe that under certain conditions, these networks may become sensitive to EM effects and prone to failure. We perform SPICE simulations on open source Wishbone bus

Di-an Li; Malgorzata Marek-Sadowska; Bill Lee

2010-01-01

250

Clustering Very Large Databases Using EM Mixture Models  

Microsoft Academic Search

Clustering very large databases is a challenge for traditional pattern recognition algorithms, e.g. the expectation-maximization (EM) algorithm for fitting mixture models, because of high memory and iteration requirements. Over large databases, the cost of the numerous scans required to converge and large memory requirement of the algorithm becomes prohibitive. We present a decomposition of the EM algorithm requiring a small

Paul S. Bradley; Cory Reina; Usama M. Fayyad

2000-01-01

251

Sobre o uso das séries de Puiseux em mecanica celeste  

NASA Astrophysics Data System (ADS)

Neste trabalho é apresentada uma demonstração do uso dos diferentes desenvolvimentos em séries para as equações de perturbação em Mecânica Celeste no marco Hamiltoniano. Em trabalhos clássicos como os de Poincaré (Poincaré, 1893) por exemplo, já esta planteado o uso de potências não inteiras no pequeno parâmetro, o que evidencia a não analiticidade das funções quando uma ressonância ocorre. Nestes trabalhos os desenvolvimentos são na raíz quadrada da massa de Júpiter (o pequeno parâmetro). Mais recentemente (Ferraz-Mello, 1985) outros tipos de desenvolvimentos foram aplicados modificando substancialmente as ordens de grandeza e a velocidade de convergência das séries. Com esta abordagem, os desenvolvimentos foram expressados em termos da raíz cúbica do pequeno parâmetro. Neste trabalho apresentamos um enfoque geral, onde os diferentes tipos de desenvolvimentos em séries de Puiseux (Valiron, 1950) são obtidos a partir da aplicação de Teorema de Preparação de Weierstrass (Goursat, 1916) considerando a equação de Hamilton-Jacobi como uma equação algébrica. Os resultados são aplicados ao problema restrito dos três corpos em ressonância de primeira ordem e, dependendo da grandeza da excentricidade do asteróide em relação à de Júpiter, obtemos os diferentes desenvolvimentos, em raíz quadrada ou raíz cúbica da massa de Júpiter.

Miloni, O. I.

2003-08-01

252

Optimal multiple source location estimation via the EM algorithm  

Microsoft Academic Search

We developed an algorithm for multiple source localization based on the Estimate-Maximize (EM) method. The EM method is an iterative algorithm that converges to the Maximum Likelihood (ML) estimate of the unknown parameters by exploiting the stochastic syctem under consideration. In our case the algorithm will converge to the exact ML estimates of the various sources location parameters, where each

M. Feder; E. Weinstein

1985-01-01

253

A Two-Round Variant of EM for Gaussian Mixtures  

Microsoft Academic Search

We show that, given data from a mixture of well-separated spherical Gaussians in , a sim- ple two-round variant of EM will, with high probability, learn the centers of the Gaussians to near-optimal precision, if the dimension is high ( ). We relate this to previous theoreti- cal and empirical work on the EM algorithm.

Sanjoy Dasgupta; Leonard J. Schulman

2000-01-01

254

Educational Program for EMS Systems Administration and Planning. Module B: EMS Systems in the United States - An Introductory Analysis.  

National Technical Information Service (NTIS)

An instructional module on emergency medical services (EMS) systems in the United States is presented as part of an educational program for EMS systems administration and planning. The program consists of 23 such modules, which can be adpated to a variety...

B. A. Cooper G. Gibson

1977-01-01

255

DOE EM industry programs robotics development  

SciTech Connect

The Office of Science and Technology (OST) manages an aggressive program for RD&D, as well as testing and evaluation for the U.S. Department of Energy`s (DOE) Environmental Management (EM) organization. The goal is to develop new and improved environmental restoration and waste management technologies to clean up the inventory of the DOE weapons complex faster, safer, and cheaper than is possible with currently available technologies. OST has organized technology management activities along focus teams for each major problem area. There are currently five focus areas: decontamination and decommissioning, tanks, subsurface contaminants, mixed waste, and plutonium. In addition, OST is pursuing research and development (R&D) that cuts across these focus areas by having applications in two or more focus areas. Currently, there are three cross-cutting programs: the robotics technology development; characterization, monitoring, and sensor technologies; and efficient separations and processing.

Staubly, R.; Kothari, V. [Dept. of Energy, Morgantown, WV (United States)

1997-12-01

256

Electromagnetic optimization of EMS-MAGLEV systems  

SciTech Connect

In EMS-MAGLEV high-speed transport systems, devices for propulsion, levitation and contactless on-board electric power transfer are combined in a single electromagnetic structure. The strong coupling among the windings affects the performance of each device and requires the utilization of numerical codes. The paper describes an overall optimization procedure, based on a suitable mathematical model of the system, which takes into account several items of the system performance. The parameters of the model are calculated by an automated sequence of FEM analyses of the configuration. Both the linear generator output characteristics and the propulsion force ripple are improved applying the procedure to a reference configuration. The results are compared with the results obtained by a sequence of partial optimizations operating separately on two different subsets of the geometric parameters.

Andriollo, M.; Martinelli, G.; Morini, A.; Tortella, A. [Univ. of Padova (Italy). Dept. of Electrical Engineering

1998-07-01

257

LAN based data communication in modern energy management systems (EMS)  

SciTech Connect

The use of energy management systems (EMS) demands high reliability, real-time behavior and more and more economical systems. The last demand requires use of inexpensive standard components, whenever possible. The following article discusses realization of EMS, especially system communication, with respect to these constraints. Problems due to conventional use of standardized communication protocols in distributed supervisory systems in general and highly-reliable systems in particular are shown. Multicast communication concepts are presented as solutions, using standardized protocols in a problem specific way. The presented concepts fulfill the necessity of using standard components as well as the specific demands towards EMS.

Dieterle, W.; Kochs, H.D. [Univ. of Duisburg (Germany). Dept. of Computer Science; Dittmar, E. [ABB Netzleittechnik Gmbh, Ladenburg (Germany)

1996-02-01

258

7 CFR 759.6 - EM to be made available.  

Code of Federal Regulations, 2013 CFR

...the FSA Administrator to make a determination that a natural disaster has occurred in a county, resulting in severe physical...If the FSA Administrator determines that such a natural disaster has occurred, then EM can be made available...

2013-01-01

259

E.M. and Hadronic Shower Simulation with FLUKA  

SciTech Connect

A description of the main features of e.m. and hadronic shower simulation models used in the FLUKA code is summarized and some recent applications are discussed. The general status of the FLUKA project is also reported.

Battistoni, G.; Fasso, A.; Ferrari, A.; Ranft, J.; Rubbia, A.; Sala, P.R.; /INFN, Milan /SLAC /CERN /Siegen U. /Zurich, ETH

2005-10-03

260

Superconducting Electromagnetic Suspension (EMS) System for Grumman Maglev Concept.  

National Technical Information Service (NTIS)

The Grumman developed Electromagnetic Suspension (EMS) Maglev system has the following key characteristics: a large operating airgap--40 mm; levitation at all speeds; both high speed and low speed applications; no deleterious effects on SC coils at low ve...

S. S. Kalsi

1994-01-01

261

Educational Program for EMS Systems Administration and Planning. Instructor's Manual.  

National Technical Information Service (NTIS)

An instructor's manual for the Emergency Medical Services (EMS) systems administration and planning educational program is presented. The program curriculum consists of 23 modules, which can be adapted to a variety of educational settings. Guidelines are ...

M. Howells B. A. Cooper

1977-01-01

262

Structure of Matter, Forces, EM Waves, Spectroscopy, Doppler Effect  

NSDL National Science Digital Library

These supplemental class notes cover the basic properties of matter, the nature of forces, the electromagnetic spectrum, and how astronomers exploit the properties of the EM spectrum to deduce the physical nature of distant objects.

O'Connell, Robert

2005-06-28

263

EM Telemetry Tool for Deep Well Drilling Applications. Final Report.  

National Technical Information Service (NTIS)

This final report discusses the successful development and testing of a deep operational electromagnetic (EM) telemetry system, produced under a cooperative agreement with the United States Department of Energy's National Energy Technology Laboratory. Thi...

J. M. Gabelmann

2005-01-01

264

7 CFR 1945.35 - Special EM loan training.  

Code of Federal Regulations, 2012 CFR

7 Agriculture 13 2012-01-01 2012-01-01 false Special EM...made for these additional travel funds: (1) Number of sessions. (2) Categories, by number, of personnel attending each session. (3) Estimated...

2012-01-01

265

Decentralized autonomous object-oriented EMS\\/SCADA system  

Microsoft Academic Search

Energy management systems\\/supervisory control and data acquisition (EMS\\/SCADA) systems are usually geographically distributed and have operational organizations. They are changing in accordance with the various and varying environments, and they should be flexible enough to adapt to those changes quickly. The paper proposes a new architecture called SCOPE (System Configuration of Power Control System) to realize flexible and reliable EMS\\/SCADA

Toshibumi. Seki; H. Sato; T. Tanaka; H. Watanabe

1997-01-01

266

Preliminary Experiment of EM Technology on Waste Water Treatment  

Microsoft Academic Search

The objective of the experiment was to investigate the effect of EM4 on improving the quality of waste water. The experiment was conducted in two locations of candy factory, viz Nestle and Trebor Companies in Jakarta. The EM4 was treated in laboratory condition to the effluent of waste water of non adjusted pH (pH 4.0) and adjusted pH (pH 7.44)

Gede Ngurah Wididana

267

Atlanta school system EMS yields eight-month payback  

Microsoft Academic Search

A $150,000 School Master energy management system (EMS) saved the Atlanta school system $250,000 and paid for itself in eight months by reducing electricity and gas consumption by 30% and 37%, respectively. The EMS includes a central processor and a remote stand-alone processor for each of 14 schools. A DOE matching grant cut the $303,000 cost in half. Monitors with

Warrock

1984-01-01

268

DOE-EM-45 PACKAGING OPERATIONS AND MAINTENANCE COURSE  

Microsoft Academic Search

Savannah River National Laboratory - Savannah River Packaging Technology (SRNL-SRPT) delivered the inaugural offering of the Packaging Operations and Maintenance Course for DOE-EM-45's Packaging Certification Program (PCP) at the University of South Carolina Aiken on September 1 and 2, 2009. Twenty-nine students registered, attended, and completed this training. The DOE-EM-45 Packaging Certification Program (PCP) sponsored the presentation of a new

R. Watkins; J. England

2010-01-01

269

EMS-Vision: a perceptual system for autonomous vehicles  

Microsoft Academic Search

The paper gives a survey on the new Expectation- based Multifocal Saccadic Vision (EMS-Vision) system for autonomous vehicle guidance developed at the Universität der Bundeswehr München (UBM). EMS-Vision is the third generation dynamic vision system following the 4-D approach. Its core element is a new camera arrangement, mounted on a high bandwidth pan-tilt head for active gaze control. Central knowledge

Rudolf Gregor; Michael Lützeler; Martin Pellkofer; K.-H. Siedersberger; Ernst Dieter Dickmanns

2002-01-01

270

Maximum likelihood noise cancellation using the EM algorithm  

Microsoft Academic Search

An approach to the two-microphone speech enhancement problem is discussed. Specifically, a maximum-likelihood (ML) problem is formulated for estimating the parameters needed for canceling the noise, and solved by the iterative EM (estimate-maximize) technique. The EM algorithm has been implemented for both a simplified and a more general scenario. The results improve upon those obtained with the classical least-squares approach

MEIR FEDER; ALAN V. OPPENHEIM; EHUD WEINSTEIN

1989-01-01

271

Reducing stress factors in EMS: report of a national survey.  

PubMed

The existence of stress, coping with stress, and the effects of stress in Emergency Medical Services (EMS) are highly current and hotly debated subjects. This article describes in part the results of a national survey of 25 EMS systems in 24 large metropolitan areas. The portion of the survey reported here focused on sources of stress and programs available to promote more effective coping with stres. Results are discussed generally and in terms of the services' organizational affiliations. PMID:10263702

Brownstone, J E; Shatoff, D K; Duckro, P N

1983-01-01

272

EM Telemetry Tool for Deep Well Drilling Applications  

SciTech Connect

This final report discusses the successful development and testing of a deep operational electromagnetic (EM) telemetry system, produced under a cooperative agreement with the United States Department of Energy's National Energy Technology Laboratory. This new electromagnetic telemetry system provides a wireless communication link between sensors deployed deep within oil and gas wells and data acquisition equipment located on the earth's surface. EM based wireless telemetry is a highly appropriate technology for oil and gas exploration in that it avoids the need for thousands of feet of wired connections. In order to achieve the project performance objectives, significant improvements over existing EM telemetry systems were made. These improvements included the development of new technologies that have improved the reliability of the communications link while extending operational depth. A key element of the new design is the incorporation of a data-fusion methodology which enhances the communication receiver's ability to extract very weak signals from large amounts of ambient environmental noise. This innovative data-fusion receiver based system adapts advanced technologies, not normally associated with low-frequency communications, and makes them work within the harsh drilling environments associated with the energy exploration market. Every element of a traditional EM telemetry system design, from power efficiency to reliability, has been addressed. The data fusion based EM telemetry system developed during this project is anticipated to provide an EM tool capability that will impact both onshore and offshore oil and gas exploration operations, for conventional and underbalanced drilling applications.

Jeffrey M. Gabelmann

2005-11-15

273

Electromagnetic divergence correction for 3D anisotropic EM modeling  

NASA Astrophysics Data System (ADS)

Until now, the application of divergence correction has been focusing on the electromagnetic (EM) isotropic modeling. However, in regions where the earth demonstrates strong electrical anisotropy due to lamina or faults saturated with water, the traditional divergence corrections may not be working for EM modeling. In this paper, based on the divergence-free property of the current density, we propose a divergence correction technique to speed up the EM modeling process for a 3D arbitrarily anisotropic earth. The volume current density weighting method is adopted for the discretization of divergence correction, so it can be applied to non-uniform grid model. By enforcing the constraints associated with the divergence-free property, the quasi-minimal residual (QMR) iterations and the total computational time for the EM modeling are largely reduced. Furthermore, we discuss how to divide the QMR process into sections and the influence of the number of iterations and the normalized residual on the solution process. We take a helicopter-borne EM system over a 3D earth with arbitrarily electrical anisotropy as an example to examine the effectiveness of our anisotropic divergence correction technique on the EM modelings.

Liu, Yun-He; Yin, Chang-Chun

2013-09-01

274

DOE EM industry programs robotics development  

SciTech Connect

The Office of Science and Technology (OST) manages an aggressive program for RD and D, as well as testing and evaluation for the Department of Energy`s (DOE`s) Environmental Management (EM) organization. The goal is to develop new and improved environmental restoration and waste management technologies to clean up the inventory of the DOE weapons complex faster, safer, and cheaper than is possible with currently available technologies. Robotic systems reduce worker exposure to the absolute minimum, while providing proven, cost-effective, and, for some applications, the only acceptable technique for addressing challenging problems. Development of robotic systems for remote operations occurs in three main categories: tank waste characterization and retrieval; decontamination and dismantlement; and characterization, mapping, and inspection systems. In addition, the Federal Energy Technology Center (FETC) has some other projects which fall under the heading of supporting R and D. The central objective of all FETC robotic projects is to make robotic systems more attractive by reducing costs and health risks associated with the deployment of robotic technologies in the cleanup of the nuclear weapons complex. This will be accomplished through development of robots that are cheaper, faster, safer, and more reliable, as well as more straightforward to modify/adapt and more intuitive to operate with autonomous capabilities and intelligent controls that prevent accidents and optimize task execution.

Staubly, R.; Kothari, V.

1998-12-31

275

Perfis de temperatura eletrônica em regiões HII  

NASA Astrophysics Data System (ADS)

As flutuações de temperatura eletrônica em regiões HII, inicialmente propostas para explicar as discrepâncias entre os valores de temperatura obtidos por diferentes métodos, têm sido apontadas como a causa mais provável das enormes diferenças encontradas entre as abundâncias químicas medidas através de linhas excitadas colisionalmente e de linhas de recombinação. Recentemente têm sido reportadas tentativas de detecção e quantificação diretas das flutuações de temperatura eletrônica através de medidas ponto a ponto, obtidas por meio de espectroscopia de fenda longa, das razões de linhas [OIII]l4263/l5007 e [NII]l5755/l6584, principais sensores de temperatura. Neste trabalho, utilizamos o código numérico de fotoionização Cloudy para avaliar a confiabilidade desse procedimento. Concluímos que, para valores de densidade eletrônica e de temperatura efetiva da estrela ionizante típicos das regiões HII, os perfis superficiais de temperatura obtidos via medidas do sensor [OIII]l4263/l5007 são bons traçadores dos gradientes internos de temperatura eletrônica. Já os perfis de temperatura eletrônica medidos por meio da razão [NII]l5755/l6584 não reproduzem os gradientes verdadeiros de temperatura.

Copetti, M. V. F.

2003-08-01

276

Image segmentation by EM-based adaptive pulse coupled neural networks in brain magnetic resonance imaging.  

PubMed

We propose an automatic hybrid image segmentation model that integrates the statistical expectation maximization (EM) model and the spatial pulse coupled neural network (PCNN) for brain magnetic resonance imaging (MRI) segmentation. In addition, an adaptive mechanism is developed to fine tune the PCNN parameters. The EM model serves two functions: evaluation of the PCNN image segmentation and adaptive adjustment of the PCNN parameters for optimal segmentation. To evaluate the performance of the adaptive EM-PCNN, we use it to segment MR brain image into gray matter (GM), white matter (WM) and cerebrospinal fluid (CSF). The performance of the adaptive EM-PCNN is compared with that of the non-adaptive EM-PCNN, EM, and Bias Corrected Fuzzy C-Means (BCFCM) algorithms. The result is four sets of boundaries for the GM and the brain parenchyma (GM+WM), the two regions of most interest in medical research and clinical applications. Each set of boundaries is compared with the golden standard to evaluate the segmentation performance. The adaptive EM-PCNN significantly outperforms the non-adaptive EM-PCNN, EM, and BCFCM algorithms in gray mater segmentation. In brain parenchyma segmentation, the adaptive EM-PCNN significantly outperforms the BCFCM only. However, the adaptive EM-PCNN is better than the non-adaptive EM-PCNN and EM on average. We conclude that of the three approaches, the adaptive EM-PCNN yields the best results for gray matter and brain parenchyma segmentation. PMID:20042313

Fu, J C; Chen, C C; Chai, J W; Wong, S T C; Li, I C

2009-12-29

277

The EM-POGO: A simple, absolute velocity profiler  

NASA Astrophysics Data System (ADS)

Electromagnetic current instrumentation has been added to the Bathy Systems, Inc. POGO transport sondes to produce a free-falling absolute velocity profiler called EM-POGO. The POGO is a free-fall profiler that measures a depth-averaged velocity using GPS fixes at the beginning and end of a round trip to the ocean floor (or a preset depth). The EM-POGO adds a velocity profile determined from measurements of motionally induced electric fields generated by the ocean current moving through the vertical component of the Earth's magnetic field. In addition to providing information about the vertical structure of the velocity, the depth-dependent measurements improve transport measurements by correcting for the non-constant fall-rate. Neglecting the variable fall rate results in errors O (1 cm s-1). The transition from POGO to EM-POGO included electrically isolating the POGO and electric-field-measuring circuits, installing a functional GPS receiver, finding a pressure case that provided an optimal balance among crush-depth, price and size, and incorporating the electrodes, electrode collar, and the circuitry required for the electric field measurement. The first EM-POGO sea-trial was in July 1999. In August 2006 a refurbished EM-POGO collected 15 absolute velocity profiles; relative and absolute velocity uncertainty was ˜1cms-1 and 0.5-5 cm s-1, respectively, at a vertical resolution of 25 m. Absolute velocity from the EM-POGO compared to shipboard ADCP measurements differed by ˜ 1-2 cm s-1, comparable to the uncertainty in absolute velocity from the ADCP. The EM-POGO is thus a low-cost, easy to deploy and recover, and accurate velocity profiler.

Terker, S. R.; Sanford, T. B.; Dunlap, J. H.; Girton, J. B.

2013-01-01

278

Electromagnetic multifrequency sounding device EMS, Prototype 2. Comparison with commercial tools.  

NASA Astrophysics Data System (ADS)

EMS was developped in ninetees in Institute of Geophysics, Russian Academy of sciences, Siberian branch. In 1996-2001 years the numerous works for hydrogeology, civil engineering and archaeology were performed using EMS. The last year the second prototybe has been compared with commercially available tools for EM prospection such as EM mapping, georadars and DC electrical resistivity tomography. In the comparison EMS feature good noise immunity, high sensibility and resolution. In some cases only EMS data shows the buried targets and it was proved immediately by excavation.

Abu Zeid, N.; Manstein, A.; Manstein, Y.; Morelli, G.; Santarato, G.

2003-04-01

279

Flutuações da temperatura eletrônica em NGC 2438 e NGC 2440  

NASA Astrophysics Data System (ADS)

Tradicionalmente, as abundâncias em nebulosas planetárias e regiões HII têm sido obtidas de linhas excitadas colisionalmente, as quais são fortemente dependentes da temperatura eletrônica. Alternativamente, as abundâncias químicas podem ser determinadas de linhas de recombinação, as quais são quase independententes da temperatura eletrônica. Entretanto, consideráveis diferenças têm sido encontradas entre estes dois métodos. Estas discrepâncias têm sido atribuídas às flutuações espaciais da temperatura eletrônica. Entretanto, as magnitudes necessárias de flutuações de temperatura eletrônica são consideravelmente mais altas do que aquelas preditas pelos modelos padrões de fotoionização e os mecânismos físicos que poderiam explicar as grandes flutuações de temperatura são desconhecidas. Desta forma, o estudo de variações da temperatura eletrônica em regiões HII e nebulosas planetárias tem ganho um renovado interesse. Neste trabalho apresentamos os resultados preliminares de um estudo observacional sobre variações internas da temperatura eletrônica nas nebulosas planetárias NGC 2440 e NGC 2438. Analisamos dados espectrofotométricos de fenda longa, com alta razão sinal-ruído, na faixa de 3300-6800 Å, com o espectrógrafo Cassegrain Boller & Chivens acoplado ao telescópio de 1.52 m do European Southern Observatory (ESO). Temperaturas eletrônicas foram derivadas da razão [OIII](l4959+l5007)/l4363 em diferentes posições em cada nebulosa planetária. Flutuações da temperatura eletrônica foram detectadas e suas magnitudes foram estimadas em NGC 2440 e NGC 2438.

Krabbe, A. C.; Copetti, M. V. F.

2003-08-01

280

Application of the EM algorithm to radiographic images.  

PubMed

The expectation maximization (EM) algorithm has received considerable attention in the area of positron emitted tomography (PET) as a restoration and reconstruction technique. In this paper, the restoration capabilities of the EM algorithm when applied to radiographic images is investigated. This application does not involve reconstruction. The performance of the EM algorithm is quantitatively evaluated using a "perceived" signal-to-noise ratio (SNR) as the image quality metric. This perceived SNR is based on statistical decision theory and includes both the observer's visual response function and a noise component internal to the eye-brain system. For a variety of processing parameters, the relative SNR (ratio of the processed SNR to the original SNR) is calculated and used as a metric to compare quantitatively the effects of the EM algorithm with two other image enhancement techniques: global contrast enhancement (windowing) and unsharp mask filtering. The results suggest that the EM algorithm's performance is superior when compared to unsharp mask filtering and global contrast enhancement for radiographic images which contain objects smaller than 4 mm. PMID:1435595

Brailean, J C; Little, D; Giger, M L; Chen, C T; Sullivan, B J

281

Analyses of Subnanometer Resolution Cryo-EM Density Maps  

PubMed Central

Today, electron cryomicroscopy (cryo-EM) can routinely achieve subnanometer resolutions of complex macromolecular assemblies. From a density map, one can extract key structural and functional information using a variety of computational analysis tools. At subnanometer resolution, these tools make it possible to isolate individual subunits, identify secondary structures, and accurately fit atomic models. With several cryo-EM studies achieving resolutions beyond 5 Å, computational modeling and feature recognition tools have been employed to construct backbone and atomic models of the protein components directly from a density map. In this chapter, we describe several common classes of computational tools that can be used to analyze and model subnanometer resolution reconstructions from cryo-EM. A general protocol for analyzing subnanometer resolution density maps is presented along with a full description of steps used in analyzing the 4.3 Å resolution structure of Mm-cpn.

Baker, Matthew L.; Baker, Mariah R.; Hryc, Corey F.; DiMaio, Frank

2011-01-01

282

Discos de acresção em sistemas Be-X  

NASA Astrophysics Data System (ADS)

Alguns fenômenos de outbursts em Be-X sugerem a existência, mesmo que temporária, de um disco de acresção quando da passagem do objeto compacto pelo periastro orbital. Neste trabalho avaliamos a possibilidade de formação do disco de acresção em sistemas Be+estrela de neutrons e Be+anã branca, e a influência da excentricidade orbital na ocorrência deste fenômeno. Utilizamos a expressão analítica para o momento angular específico da matéria constituinte de um meio em expansão lenta, como é o caso do disco circunstelar das estrelas Be, proposta por Wang(1981), sob a condição básica de que o raio de circularização deva ser maior do que o raio de Alfvén. Concluímos que existe um limite para o período orbital do sistema acima do qual não é possível a formação do disco de acresção, e que este valor aumenta para sistemas com excentricidade orbital maior.

Lopes de Oliveira, R.; Janot-Pacheco, E.

2003-08-01

283

EM-31 Alternative and Enhanced Chemical Cleaning Program  

SciTech Connect

King's introduction to his presentation made 5 important points: 1) Numerous SRS tanks scheduled for closure (contract commitments); 2) Cannot remove all sludge by mechanical means due to obstructions; 3) Chemical removal technology needed (likely oxalic acid); 4) Post - dissolution neutralization required prior to transfer to compliant tanks; 5) Sodium oxalate salts precipitate on neutralization and have negative downstream impacts. There were three SRS chemical cleaning programs in 2010: Baseline: 8wt percent OA batch contact, ECC: 1-3 wt. percent OA with oxalate destruction, and the Alternative/Enhanced Chemical Cleaning (EM-31). This talk is on the EM-31 program.

King, Bill (SRNL)

2010-11-01

284

EM-31 Alternative and Enhanced Chemical Cleaning Program  

ScienceCinema

King's introduction to his presentation made 5 important points: 1) Numerous SRS tanks scheduled for closure (contract commitments); 2) Cannot remove all sludge by mechanical means due to obstructions; 3) Chemical removal technology needed (likely oxalic acid); 4) Post - dissolution neutralization required prior to transfer to compliant tanks; 5) Sodium oxalate salts precipitate on neutralization and have negative downstream impacts. There were three SRS chemical cleaning programs in 2010: Baseline: 8wt percent OA batch contact, ECC: 1-3 wt. percent OA with oxalate destruction, and the Alternative/Enhanced Chemical Cleaning (EM-31). This talk is on the EM-31 program.

285

Transport quantique dans des nanostructures  

NASA Astrophysics Data System (ADS)

Quantum transport in nanostructures This work is devoted to the design, fabrication and magnetotransport investigations of mesoscopic devices. The sample are obtain by e-beam lithography and the measurements are performed at low temperature in a dilution refrigerator in the presence of a magnetic field. We have used MBE grown AlGaAs/GaAs heterojonctions as starting material to fabricate a bipartite tiling of rhombus called mathcal{T}3 lattice. We observe for the first time large amplitude h/e oscillations in this network as compared to the one measured in square lattices of similar size. These oscillations are the signature of a recently predited localization phenomenon induced by Aharonov-Bohm interferences on this peculiar topology. For particular values of the magnetic field the propagation of the electron wave function is bounded in a small number of cells, called Aharonov-Bohm cages. More strikingly, at high magnetic field, h/2e oscillations appear whose amplitude can be much higher than the fundamental period. Their temperature dependence is similar to that of the h/e signal. These observations withdraw a simple interpretation in terms of harmonics generation. The origin of this phenomenon is still unclear and needs more investigations. The influence electrical width of the wire defining the network and so the rule of the number of channels can be studied using a gate deposited over the lattice. In particular we have measured the amplitude dependence of the h/e and h/2e signal versus the gate voltage. Ce travail est consacré à la réalisation d'échantillons mésoscopiques à partir de la lithographie électronique ainsi qu'à leur caractérisation à très basse température en magnétotransport. Nous avons pour cela exploité le gaz bidimensionnel d'électrons situé à l'interface d'une hétérojonction AlGaAs/GaAs pour réaliser un réseau de boucle d'une géométrie particulière baptisée la géométrie mathcal{T}3. Nous avons observé sur cette structure des oscillations de conductance en fonction du flux du champ magnétique de période h/e dont l'amplitude est beaucoup plus importante que celle mesurée sur un réseau carré de même dimension. Cette différence constitue une signature d'un effet de localisation induit par le champ magnétique sur la topologie mathcal{T}3. Pour des valeurs spécifiques du champ magnétique, du fait des interférences destructives Aharonov-Bohm, la propagation des fonctions d'ondes est limitée à un ensemble fini de cellule du réseau appelé cage. De la dépendance en température des oscillations de période h/e mesurées sur le réseau mathcal{T}3 nous avons tiré une longueur caractéristique qui peut être rattachée au périmètre des cages. Un phénomène inattendu fut l'observation, pour des champs magnétiques plus importants, d'un doublement de fréquence des oscillations. Ces oscillations de période h/2e pouvant avoir une amplitude supérieure aux oscillations de période h/e, une interprétation en terme d'harmonique n'est pas possible. Enfin, l'influence de la largeur électrique des fils constituant le réseau et donc celle du nombre de canaux par brin a été étudiée en réalisant des grilles électrostatique. Les variations de l'amplitude des signaux en h/e et h/2e en fonction de la tension de grille ont été mesurés.

Naud, C.

2002-09-01

286

Rural Volunteer EMS: Reports from the Field. Final Report No. 99.  

National Technical Information Service (NTIS)

Prehospital emergency care services (EMS) are an essential component of a comprehensive health care system. Rural residents and those traveling through rural areas rely on EMS for treatment and transport in the event of an injury or other health emergency...

M. Hamon R. T. Slifkin S. Rutledge V. A. Freeman

2010-01-01

287

The Mediating Role Of EMS Teamwork As It Pertains To HR Factors And Perceived Environmental Performance  

Microsoft Academic Search

ABSTRACT Little management,theory or empirical results exist to guide managers,in maximizing,employee efforts to successfully implement Environmental Management Systems (EMS). In response, this study examines the relationship among,Human,Resource (HR) factors and employee perceptions of environmental,performance. Four hundred,thirty-seven (437) employees,were surveyed,in an organization with a well-developed EMS program,and ISO 14001 certification. Results suggest that management support for EMS, EMS training, employee empowerment,

Bonnie F. Daily; James W. Bishop; Robert Steiner

2007-01-01

288

Changes in the Microflora and Physiological - Biochemical Characteristics in the Culture of EM  

Microsoft Academic Search

Microflora of EM1 culture is converted from aerobic and neutral to anaerobic and acidic. Biochemical characteristics of EM1 changed according to change of microflora. pH, EC and content of organic acid of EM1 at the end of culture were 3 - 3.5, 0.6 - 0.9 s\\/m and 1.9 - 2.1 %, respectively. Antioxidation activity of EM1 increased in proportion to

C. M. Oh; S. B. Choi

289

EMS provider level does not impact use of air medical transport  

Microsoft Academic Search

Introduction: The local emergency medical services (EMS) provider level within a nearby EMS system changed from EMT-I to paramedic. This increase in level of care was expected to decrease utilization of air medical transport and increase acuity of patients flown. Setting: Semirural, mountainous area with an annual volume of 2800 transports. Methods: Retrospective review of the EMS database performed for

David E. Fosnocht; Eric R. Swanson; Elizabeth Middleton

2003-01-01

290

Convergence results for the EM approach to mixtures of experts architectures  

Microsoft Academic Search

The Expectation-Maximization (EM) algorithm is an iterative approach to maximum likelihood parameter estimation. Jordan and Jacobs recently proposed an EM algorithm for the mixture of experts architecture of Jacobs, Jordan, Nowlan and Hinton (1991) and the hierarchical mixture of experts architecture of Jordan and Jacobs (1992). They showed empirically that the EM algorithm for these architectures yields significantly faster convergence

Michael I. Jordan; Lei Xu

1995-01-01

291

Designing ergonomic interventions for EMS workers: Concept generation of patient-handling devices  

Microsoft Academic Search

Fire service personnel and private ambulance paramedics suffer musculoskeletal injuries as they lift and carry patients while performing emergency medical services (EMS). Engineering changes, such as the design of new EMS patient-handling devices, offer a potential intervention opportunity for combating this problem. The purpose of this qualitative descriptive study was to generate beginning ideas for the design of new EMS

Karen M. Conrad; Paul A. Reichelt; Steven A. Lavender; Jessica Gacki-Smith; Sally Hattle

2008-01-01

292

Multi-frequency electromagnetic sounding tool EMS. Archaeological discoveries. Case stories  

Microsoft Academic Search

EMS is the new patented tool for shallow-depth (up to 7 m) induction frequency sounding. The tool is developed in Institute of Geophysics, Siberian Branch of Russian Academy, Novosibirsk, RUSSIA. Few years of application of EMS prototypes in archaeological prospection gave us the well described picture of possibilities and limitations of EM sounding for archaeological purpose. We would like to

N. Abu Zeid; E. Balkov; M. Chemyakina; A. Manstein; Y. Manstein; G. Morelli; G. Santarato

2003-01-01

293

Achieving Environmental Excellence: An Environmental Management Systems (EMS) Handbook for Wastewater Utilities.  

National Technical Information Service (NTIS)

How this Handbook is Organized This Wastewater EMS Handbook guides you through EMS implementation based on the Plan-Do-Check-Act model of the ISO 14001 Environmental Management System. The Handbook is designed primarily for EMS implementers, so the heart ...

2004-01-01

294

Epiderme dos segmentos foliares de Mauritia flexuosa L. f. (Arecaceae) em três fases de desenvolvimento  

Microsoft Academic Search

RESUMO São apresentados os dados anatômicos da epiderme dos segmentos foliares de Mauritia flexuosa L. f. (Arecaceae) em três fases do desenvolvimento. Os segmentos foliares foram analisados em toda a extensão do limbo. As células intercostais da epiderme das faces adaxial e abaxial evidenciam-se com paredes sinuosas, retangulares e orientadas longitudinalmente em relação ao eixo do segmento foliar com acentuada

Mahedy Araújo Bastos Passos; Maria Sílvia de Mendonça

2006-01-01

295

HAMMONDIA HEYDORNI, NEOSPORA CANINUM E TOXOPLASMA GONDII EM CAPRINOS ABATIDOS NO ESTADO DA BAHIA, BRASIL  

Microsoft Academic Search

Resumo Hammondia heydorni, Neospora caninum e Toxoplasma gondii são protozoários coccídios que parasitam diferentes espécies animais domésticas e silvestres. E nquanto a infecção por H. heydorni parece ser assintomática, N. caninum e T. gondii podem provocar alterações reprodutivas em ruminantes. N. caninum é um importante causador de abortamentos em bovinos, ao passo que T. gondii induz a abortamentos em caprinos

R. S. UZÊDA; K. ABE-SANDES; L. F. P. GONDIM

296

ANÁLISE DAS ESTRATÉGIAS DE MARKETING EM UMA FECULARIA DA REGIÃO DE TUPÃ-SP  

Microsoft Academic Search

Nas últimas décadas, verificou-se uma mudança no comportamento do consumidor no sentido de adotar uma postura mais consciente em relação aos produtos que adquire. No setor alimentício, essa evolução é nítida, em função da busca por uma maior qualidade de vida, agregando à dieta questões de saúde, incluindo produtos com menor conteúdo de gorduras e calorias, rico em fibras, pobre

Joao Guilherme de Camargo Ferraz Machado; Timoteo Ramos Queiroz; Andrea Rossi Scalco

2008-01-01

297

Penalized maximum-likelihood image reconstruction using space-alternating generalized EM algorithms  

Microsoft Academic Search

Most expectation-maximization (EM) type algorithmsfor penalized maximum-likelihood image reconstructionconverge slowly, particularly when one incorporatesadditive background effects such as scatter, random coincidences,dark current, or cosmic radiation. In addition,regularizing smoothness penalties (or priors) introduce parametercoupling, rendering intractable the M-steps of mostEM-type algorithms. This paper presents space-alternatinggeneralized EM (SAGE) algorithms for image...

Jeffrey A. Fessler; Alfred O. Hero III

1995-01-01

298

Polyproline II structure is critical for the enzyme protective function of soybean Em (LEA1) conserved domains.  

PubMed

Group 1 late embryogenesis-abundant (LEA1) proteins protect enzyme activity from dehydration and are structurally conserved with three different 20 amino acid motifs in the N-terminal, middle and C-terminal domains. Three soybean Em (LEA1) domain peptides (Em-N, Em-2M and Em-C) covering these respective motifs were constructed and had differential protective ability on lactate dehydrogenase against freeze-thaw: Em-C > Em-2M > Em-N. CD spectroscopy revealed that Em-2M and Em-C contained both polyproline II (PII) helical structure and ?-helix, while Em-N had a high potential to form ?-helix but did not contain PII structure. The PII helical structure between the third and fifth glycine in the middle motif was shown, through site mutation, to be critical for the enzyme protective function of soybean Em (LEA1) conserved domain under freezing stress. PMID:21455835

Zou, Yongdong; Hong, Ruisha; He, Shuwen; Liu, Guobao; Huang, Zebo; Zheng, Yizhi

2011-04-01

299

EM Telemetry Tool for Deep Well Drilling Applications  

Microsoft Academic Search

This final report discusses the successful development and testing of a deep operational electromagnetic (EM) telemetry system, produced under a cooperative agreement with the United States Department of Energy's National Energy Technology Laboratory. This new electromagnetic telemetry system provides a wireless communication link between sensors deployed deep within oil and gas wells and data acquisition equipment located on the earth's

Jeffrey M. Gabelmann

2005-01-01

300

Communications technology guidelines for EMS\\/SCADA systems  

Microsoft Academic Search

The purpose of this Guideline Technical Paper is to provide a summary of the different communications technologies available for use or application with EMS\\/SCADA system projects. All of the various communication media are addressed with a brief description along with tables of the advantages and disadvantages of each and recommendations for choosing the most appropriate communication technology. The technologies discussed

Donald J. Marihart

2001-01-01

301

Texas Hold 'em Online Poker: A Further Examination  

ERIC Educational Resources Information Center

|Playing Texas Hold 'em Online Poker (THOP) is on the rise. However, there is relatively little research examining factors that contribute to problem gambling in poker players. The aim of this study was to extend the research findings of Hopley and Nicki (2010). The negative mood states of depression, anxiety and stress were found to be linked to…

Hopley, Anthony A. B.; Dempsey, Kevin; Nicki, Richard

2012-01-01

302

Preliminary study on the EMS of CRT display for computer  

Microsoft Academic Search

The Electromagnetic susceptibility (EMS) of cathode ray tube (CRT) display for computer was investigated preliminarily using the test method of bulk current injection (BCI). During the test, CW signals as electromagnetic interference (EMI) signals with different amplitude at a certain frequency were injected into the RGB, horizontal synchronization (HS) and vertical synchronization (VS) signal line of video graphics array (VGA)

Da Gang Xie; Nan Wu; Jing Yu; Xiang Song Yang; Dong Yun Hou

2010-01-01

303

Ultra-stiff, low mass, EM gun design  

Microsoft Academic Search

High performance in an electromagnetic (EM) gun implies high velocity with minimal transition from a solid to plasma armature. Factors that affect gun performance include armature integrity, bore straightness and bore stiffness. Experiences firing solid armature at CEM-UT since 1987 have shown that the lack of one or more of these three ingredients will result in less than desirable performance.

M. D. Werst; J. R. Kitzmiller; C. S. Hearn; G. A. Wedeking

2004-01-01

304

Analysis of composite EM scattering based on accurate geometry modeling  

Microsoft Academic Search

An approach to studying composite EM scattering from 2-D rough surface and half-buried 3-D target is proposed in this paper, from accurate geometry modeling to RCS analysis. First, two dimensional rough surface is simulated with spectral method, which then is converted into a continuous curved surface through inverse engineering. Target model and rough surface model are combined together to be

Jie Li; Qiong He; Lixin Guo; Bing Wei

2011-01-01

305

A Pilot Marine EM Study of Hydrate Ridge, Oregon  

Microsoft Academic Search

It has long been proposed (e.g. Nigel Edwards, U. Toronto) that EM methods may be able to detect and map gas hydrate, which is more resistive than host sediments and thus provides an electrical target. While the base of hydrates often produces a distinctive seismic signature (the bottom-simulating reflector, or BSR), the gradational upper surface is less well imaged using

K. Weitemeyer; S. Constable; J. Behrens

2004-01-01

306

Match'em: using fuzzy logic to profile criminals  

Microsoft Academic Search

This paper details research undertaken at Bournemouth University into the use of a fuzzy development system called Matcher to build an offender profiling system. A brief introduction is given on the background and uses for offender profiling and the Matcher tool used to build the Match'em system. A description of the design of the system and its evaluation is provided.

M. Lefly; V. Austin

1997-01-01

307

Detecção Cooperativa de Intrusões em Redes Carrier Ethernet  

Microsoft Academic Search

Resumo Hoje em dia os elementos de rede (NEs) da camada 2 do modelo OSI, bridges ou switches, são componentes complexos, com centenas de milhares de linhas de software, que podem ser vulneráveis a ataques, permitindo até a execução remota de código no seu CPU interno. Este trabalho apresenta um esquema para proteger infra-estruturas de rede Carrier Ethernet de ataques

Pan Jieke; João Redol; Miguel Correia

308

Sonar-Based Mapping With Mobile Robots Using EM  

Microsoft Academic Search

This paper presents an algorithms for learn- ing occupancy grid maps with mobile robots equipped with range finders, such as sonar sen- sors. Our approach employs the EM algorithm to solve the concurrent mapping and localization problem. To accommodate the spatial nature of range data, it relies on a two-layered representa- tion of maps, where global maps are composed from

Wolfram Burgard; Dieter Fox; Hauke Jans; Christian Matenar; Sebastian Thrun

309

Signs and Guides: Wayfinding Alternatives for the EMS Library.  

ERIC Educational Resources Information Center

|Concerned with increasing the accessibility of the collection of the Engineering/Math Sciences (EMS) Library at the University of California at Los Angeles through the use of self guidance systems, this practical study focused on the problem context, general library guides, and library signage in reviewing the literature, and conducted a survey…

Johnson, Johanna H.

310

An EM algorithm for wavelet-based image restoration  

Microsoft Academic Search

Abstract: This paper introduces an expectation--maximization(EM) algorithm for image restoration (deconvolution) based on apenalized likelihood formulated in the wavelet domain. Regularizationis achieved by promoting a reconstruction with low-complexity,expressed in the wavelet coefficients, taking advantage ofthe well known sparsity of wavelet representations. Previous workshave investigated wavelet-based restoration but, except for certainspecial cases, the resulting criteria are solved...

Mário A. T. Figueiredo; Robert D. Nowak

2003-01-01

311

Debris Avalanche Formation at Kick'em Jenny Submarine Volcano  

Microsoft Academic Search

Kick'em Jenny submarine volcano near Grenada is the most active volcanic center in the Lesser Antilles arc. Multibeam surveys of the volcano by NOAA in 2002 revealed an arcuate fault scarp east of the active cone, suggesting flank collapse. More extensive NOAA surveys in 2003 demonstrated the presence of an associated debris avalanche deposit, judging from their surface morphologic expression

H. Sigurdsson; S. N. Carey; D. Wilson

2005-01-01

312

Hierarchical mixtures of experts and the EM algorithm  

Microsoft Academic Search

We present a tree-structured architecture for supervised learning. The statistical model underlying the architecture is a hierarchical mixture model in which both the mixture coefficients and the mixture components are generalized linear models (GLIMs). Learning is treated as a maximum likelihood problem; in particular, we present an expectation-maximization (EM) algorithm for adjusting the parameters of the architecture. We also develop

Michael I. Jordan; Robert A. Jacobs

1993-01-01

313

Custo de bombas centrífugas funcionando como turbinas em microcentrais hidrelétricas  

Microsoft Academic Search

RESUMO: A implantação de microcentrais hidrelétricas é uma das alternativas para suprir com energia comunidades pequenas e isoladas, situadas normalmente na área rural. O aproveitamento de potenciais hidráulicos de pequeno porte é uma alternativa cada vez mais viável devido não só à falta de recursos financeiros para os grandes empreendimentos, mas também pelo imenso potencial de geração em centrais de

Carlos R. Balarim; Luiz A. Targa; Jorim S. Virgens Filho; Alceu G. Andrade Filho; Giovana K. Wiecheteck

2004-01-01

314

FFTF EM service pump design, application, and testing  

Microsoft Academic Search

During 1975, HEDL selected Atomics International to review the design of three classes of EM Pumps (L-30, L-100, L-200) and to fabricate a total of fifteen pumps. One of the L-100 pumps was shipped to the liquid Metal Engineering Center (LMEC) for sodium testing in the small components test loop (SCTL). The paper presents the HEDL design criteria, discusses the

G. Jacobson; E. H. Carter; G. J. Hallinan; R. L. Eichelberger

1977-01-01

315

Statistical Physics, Mixtures of Distributions, and the EM Algorithm  

Microsoft Academic Search

We show that there are strong relationships between approaches to optmization and learning based on statistical physics or mixtures of experts. In particular, the EM algorithm can be interpreted as converging either to a local maximum of the mixtures model or to a saddle point solution to the statistical physics system. An advantage of the statistical physics approach is that

Alan L. Yuille; Paul E. Stolorz; Joachim Utans

1994-01-01

316

EM Localization and Separation using Interaural Level and Phase Cues  

Microsoft Academic Search

We describe a system for localizing and separating multiple sound sources from a reverberant two-channel recording. It consists of a probabilistic model of interaural level and phase differences and an EM algorithm for finding the maximum likelihood parameters of this model. By assigning points in the interaural spectrogram probabilistically to sources with the best-fitting parameters and then estimating the parameters

Michael I. Mandel; Daniel P. W. Ellis

2007-01-01

317

Extending EMS capabilities to include online stability assessment  

Microsoft Academic Search

This paper describes the integration of stability assessment tools in the EMS. The main functions are the transient security and voltage security tools. They are invoked under several modes of operation to address the current state of the system as well as the immediate short-term planning horizons. Data exchange, preparation and output visualization are described in the context of distributed

Rene Avila-Rosales; Jay Giri; Rafael Lopez

2004-01-01

318

Síndrome da cabeça caída em doença do neurônio motor  

Microsoft Academic Search

RESUMO - A síndrome da cabeça caída é causada por diminuição de força nos músculos extensores do pescoço sendo encontrada em diversas doenças neuro m u s c u l a res, bem como, na esclerose lateral amiotrófica. D e s c revemos o caso de três mulheres com diagnóstico de doença do neurônio motor com quadro clínico de disfagia

Paulo José Lorenzoni; Marcos Christiano Lange; Cláudia S. K. Kay; Luiz G. M. P. de Almeida; Hélio A. G. Teive; Rosana H. Scola; Lineu C. Werneck

2006-01-01

319

A shape constrained MAP-EM algorithm for colorectal segmentation  

NASA Astrophysics Data System (ADS)

The task of effectively segmenting colon areas in CT images is an important area of interest in medical imaging field. The ability to distinguish the colon wall in an image from the background is a critical step in several approaches for achieving larger goals in automated computer-aided diagnosis (CAD). The related task of polyp detection, the ability to determine which objects or classes of polyps are present in a scene, also relies on colon wall segmentation. When modeling each tissue type as a conditionally independent Gaussian distribution, the tissue mixture fractions in each voxel via the modeled unobservable random processes of the underlying tissue types can be estimated by maximum a posteriori expectation-maximization (MAP-EM) algorithm in an iterative manner. This paper presents, based on the assumption that the partial volume effect (PVE) could be fully described by a tissue mixture model, a theoretical solution to the MAP-EM segmentation algorithm. However, the MAP-EM algorithm may miss some small regions which also belong to the colon wall. Combining with the shape constrained model, we present an improved algorithm which is able to merge similar regions and reserve fine structures. Experiment results show that the new approach can refine the jagged-like boundaries and achieve better results than merely exploited our previously presented MAP-EM algorithm.

Wang, Huafeng; Li, Lihong; Song, Bowen; Han, Fangfang; Liang, Zhengrong

2013-02-01

320

An EM algorithm for regression analysis with incomplete covariate information  

Microsoft Academic Search

Regression analysis is often challenged by the fact that some covariates are not completely observed. Among other approaches is a newly developed semiparametric maximum likelihood (SML) method that requires no parametric specification of the selection mechanism or the covariate distribution and that yields efficient inference, at least in some specific models. In this paper, we propose an EM algorithm for

Zhiwei Zhang; Howard E. Rockette

2007-01-01

321

GPS computer navigators to shorten EMS response and transport times.  

PubMed

GPS (global positioning satellite system to determine one's position on earth) units have become inexpensive and compact. The purpose of this study is to assess the effectiveness of a GPS enhanced computer street map navigator to improve the ability of EMS drivers in an urban setting to locate their destination and shorten response times. For part I, residential addresses in the city were randomly selected from a telephone directory. Two driver/navigator teams were assigned to drive to the address adhering to speed limits. One team used a standard street map, whereas the other team used a GPS computer navigator. The travel time and distance of the runs were compared. For part II, the computer GPS navigator was placed on an ambulance to supplement their normal methods of navigation to find the address requesting EMS. After the run was completed, EMS providers were interviewed to determine their opinion of whether the GPS navigator was helpful. For part I the results showed that in the 29 initial test runs, comparing the GPS team versus the standard map team, the mean distances traveled were 8.7 versus 9.0 kilometers (not significant) and the mean travel times were 13.5 versus 14.6 minutes (P=.02), respectively. The GPS team arrived faster in 72% runs. For part II the results showed that most EMS providers surveyed noted that the GPS computer navigator enhanced their ability to find the destination and all EMS providers acknowledged that it would enhance their ability to find a destination in an area in which they were unfamiliar. These results suggest that a portable GPS computer navigator system is helpful and can enhance the ability of prehospital care providers to locate their destination. Because these units are accurate and inexpensive, GPS computer navigators may be a valuable tool in reducing pre-hospital transport times. PMID:11326345

Ota, F S; Muramatsu, R S; Yoshida, B H; Yamamoto, L G

2001-05-01

322

An Evaluation of DOE-EM Public Participation Programs  

SciTech Connect

This report evaluates the scope and effectiveness of the public participation pr ograms, including Site-Specific Advisory Boards (SSABs), at seven U.S. Departmen t of Energy (DOE) sites: Fernald, Hanford, Los Alamos, Nevada, Oak Ridge, Paduc ah, and Savannah River. The primary purpose of the study is to assist both DOE Field and Headquarters managers in reviewing and understanding lessons learned o ver the past decade concerning public participation programs administered by the DOE Office of Environmental Management (EM). The evaluation provides a snapsh ot of selected EM public participation programs at a particular point of time. It is based on interviews and site visits conducted between January and June 200 2- a time of change within the program. The study focuses on public participati on programs that incorporate a variety of activities and address a wide range of individual site activities and decisions. It uses the Acceptability Diamond as an evaluative framework to answer questions about stakeholders' experiences wit h, and assessment of, DOE-EM's public participation programs. The Acceptability Diamond, which was developed by researchers from the Pacific Northwest National Laboratory in previous research, identifies four program dimensions - substanti ve issues, decision-making process, relationships, and accountability - that det ermine the effectiveness of an agency's interactions with local communities. Es sentially, a public participation program may be deemed effective to the extent that it provides for open disclosure and addresses all four acceptability dimens ions in ways that are appropriate and effective for a particular community and s ituation. This framework provides a guide for agencies to 1) set objectives, 2) design public participation and oversight programs, and 3) set criteria for eva luating program effectiveness. In the current study, where the framework is use d as a means of assessing program effectiveness, the focus is on stakeholders' p erspectives of public participation: on the nature of DOE-EM's public disclosure and the four interrelated dimensions of DOE-EM's interactions with its neighbor ing communities

Bradbury, Judith A.; Branch, Kristi M.; Malone, Elizabeth L.

2003-02-28

323

EM calibration based on Post OPC layout analysis  

NASA Astrophysics Data System (ADS)

Design for Manufacturability (DFM) involves changes to the design and CAD tools to help increase pattern printability and improve process control. Design for Reliability (DFR) performs the same to improve reliability of devices from failures such as Electromigration (EM), gate-oxide break down, hot carrier injection (HCI), Negative Bias Temperature Insatiability (NBTI) and mechanical stress effects. Electromigration (EM) occurs due to migration or displacement of atoms as a result of the movement of electrons through a conducting medium. The rate of migration determines the Mean Time to Failure (MTTF) which is modeled as a function of temperature and current density. The model itself is calibrated through failure analysis (FA) of parts that are deemed to have failed due to EM against design parameters such as linewidth. Reliability Verification (RV) of a design involves verifying that every conducting line in a design meets certain MTTF threshold. In order to perform RV, current density for each wire must be computed. Current itself is a function of the parasitics that are determined through RC extraction. The standard practice is to perform the RC extraction and current density calculation on drawn, pre-OPC layouts. If a wire fails to meet threshold for MTTF, it may be resized. Subsequently, mask preparation steps such as OPC and PSM introduce extra features such as SRAFs, jogs,hammerheads and serifs that change their resistance, capacitance and current density values. Hence, calibrating EM model based on pre-OPC layouts will lead to different results compared to post-OPC layouts. In this work, we compare EM model calibration and reliability check based on drawn layout versus predicted layout, where the drawn layout is pre-OPC layout and predicted layout is based on litho simulation of post-OPC layout. Results show significant divergence between these two approaches, making a case for methodology based on predicted layout.

Sreedhar, Aswin; Kundu, Sandip

2010-03-01

324

MAPEAMENTO DE GENES DE RESISTÊNCIA PARCIAL À FERRUGEM DA FOLHA EM CULTIVARES BRASILEIRAS DE TRIGO (Triticum aestivum L. em Thell)  

Microsoft Academic Search

Puccinia triticina Erikss. the causal agent of the leaf rust fungal disease common in southern Brazil, is the widest distributed and regularly occurring bread wheat (Triticum aestivum L. em Thell.) pathogen. The knowledge of resistance genes is fundamental for a more effective protection against the fungus. Due to the dinamic nature of cereal-fungus relationship, the resistance stability is difficult to

Sandra Patussi Brammer; Maria Irene; Baggio de Moraes; Amarílis L. Barcellos; Sandra Cristina; K. Milach; Antony Worland; Greg Penner

325

Composting of rice straw with effective microorganisms (EM) and its influence on compost quality  

PubMed Central

This study aims to assess the effect of EM application on the composting process of rice straw with goat manure and green waste and to evaluate the quality of both compost treatments. There are two treatment piles in this study, in which one pile was applied with EM and another pile without EM. Each treatment was replicated three times with 90 days of composting duration. The parameters for the temperature, pH, TOC and C/N ratio, show that decomposition of organic matter occurs during the 90-day period. The t-test conducted shows that there is a significant difference between compost with EM and compost without EM. The application of EM in compost increases the macro and micronutrient content. The following parameters support this conclusion: compost applied with EM has more N, P and K content (P?EM. Although the Fe in compost with EM is much higher (P?EM, for Zn and Cu, there is no significant difference between treatments. This study suggests that the application of EM is suitable to increase the mineralization in the composting process. The final resultant compost indicated that it was in the range of the matured level and can be used without any restriction.

2013-01-01

326

Composting of rice straw with effective microorganisms (EM) and its influence on compost quality.  

PubMed

This study aims to assess the effect of EM application on the composting process of rice straw with goat manure and green waste and to evaluate the quality of both compost treatments. There are two treatment piles in this study, in which one pile was applied with EM and another pile without EM. Each treatment was replicated three times with 90 days of composting duration. The parameters for the temperature, pH, TOC and C/N ratio, show that decomposition of organic matter occurs during the 90-day period. The t-test conducted shows that there is a significant difference between compost with EM and compost without EM. The application of EM in compost increases the macro and micronutrient content. The following parameters support this conclusion: compost applied with EM has more N, P and K content (P?EM. Although the Fe in compost with EM is much higher (P?EM, for Zn and Cu, there is no significant difference between treatments. This study suggests that the application of EM is suitable to increase the mineralization in the composting process. The final resultant compost indicated that it was in the range of the matured level and can be used without any restriction. PMID:23390930

Jusoh, Mohd Lokman Che; Manaf, Latifah Abd; Latiff, Puziah Abdul

2013-02-07

327

Efeito do gradiente de martensita induzida por deformação sobre o fenômeno de delayed cracking em aços inoxidáveis austeníticos  

Microsoft Academic Search

Resumo: O principal objetivo deste trabalho foi estudar o fenômeno de Delayed Cracking em aços inoxidáveis austeníticos quando foram severamente deformados em operações de estampagem. Durante a conformação, a austenita destes aços se transformou em martensita e a fração volumétrica desta fase apresentou variação em relação à altura da parede do copo e à composição química dos aços. O cobre

Marta Ribeiro dos Santos; Hélio José Batista Alves; Robson Guimarães Lopes; Berenice Mendonça Gonzalez

2007-01-01

328

Access to Emergency Medical Services in Rural Areas: The Supporting Role of State EMS Agencies. Working Paper Number 38.  

National Technical Information Service (NTIS)

The purpose of this study is to improve the limited knowledge about rural Emergency Medical Services (EMS) and the support of rural EMS by state EMS agencies. A telephone survey of state EMS directors was completed in early 2001 and collected information ...

A. Knott

2002-01-01

329

Conhecimento e inovação em sistemas locais de produção de revestimentos cerâmicos e os novos desafi os da concorrência internacional  

Microsoft Academic Search

RESUMO Este trabalho tem como objetivo contribuir para a compreensão das novas dinâmicas de geração de conhecimento e inovação em sistemas loc ais de produção a partir dos desafi os da concorrência internacional, por meio da realização de estudos em dois sistemas locais da indústria de cerâmica de revestimento no Brasil, um localizado em Santa Gertrudes\\/SP e outro em Criciúma\\/SC.

Gabriela Scur FEI; Renato Garcia EPUSP

2008-01-01

330

Em polypeptide and its messenger RNA levels are modulated by abscisic acid during embryogenesis in wheat.  

PubMed

The effect of abscisic acid (ABA) on the expression of the 'early-methionine-labeled' (Em) polypeptide was examined in cultured, immature wheat (Triticum aestivum, L.) embryos and in developing embryos in planta. A complementary DNA (cDNA) library was constructed from poly(A)-rich RNA from immature embryos cultured in the presence of ABA. ABA-enhanced sequences were first identified by differential colony-blot hybridization, and then verified using RNA slot-blot analysis. Dot-blot hybridization showed that one clone, p1015, was homologous to the previously isolated Em cDNA, pWG432. Electrophoretic analysis of the hybrid-select translation product of p1015 confirmed its identity as an Em sequence. Comparison of the p1015 cDNA insert size and the Em message size, from northern blot analysis, showed that p1015 contained about 87% of the Em sequence. RNA slot-blot analysis and protein electrophoresis showed that Em message, but not Em protein, accumulated at a low, basal level in immature embryos in the absence of ABA. Neither Em message nor Em protein was seen in three-day germinated seedlings. Steady-state levels of Em message and protein increased in immature embryos in the presence of ABA, both in culture and in planta. Regulation appeared to be primarily at the level of transcription or specific message stability. Regulation may also involve specific protein stability, since synthesis of Em protein continued in immature embryos in the absence of ABA, but Em protein did not accumulate in detectable amounts. We conclude that ABA specifically modulates Em message and protein levels in immature embryos, but is probably not responsible for the embryogenic specificity of Em expression. PMID:2932332

Williamson, J D; Quatrano, R S; Cuming, A C

1985-10-15

331

População nuclear e extranuclear em rádio-galáxias  

NASA Astrophysics Data System (ADS)

A natureza do contínuo UV/ótico em rádio-galáxias é muito importante para o seu entendimento. Em baixos redshifts existem evidências de que muitas delas são dominadas no ótico por luz de estrelas velhas, características de galáxias early-type e em altos redshifts a característica dominante é um excesso de luz no UV, freqüentemente associado com estruturas que estão alinhadas aos eixos das estruturas rádio em grande escala. Inicialmente esse excesso foi interpretado como devido a episódios intensos de formação estelar nas galáxias hospedeiras. Entretanto, as descobertas dos alinhamentos entre as estruturas UV e rádio modificaram essa idéia. Foi proposto que a formação estelar é iniciada pela passagem do jato rádio através do meio interestelar das galáxias hospedeiras. A natureza do excesso UV começou a ser compreendida em um estudo detalhado do continuo ótico da 3C321, onde se concluiu que o contínuo desta galáxia tem origem multicomponente, com contribuições de populações velhas e intermediárias, de luz espalhada oriunda de um quasar obscurecido e do contínuo nebular. No presente trabalho estudamos a população nuclear e extranuclear de uma amostra de 24 rádio-galáxias, utilizando espectros óticos de fenda longa, com alta razão sinal/ruído. Através do método de síntese espectral de populações estelares, foram estimadas as contribuições de populações estelares de diferentes idades (e de um contínuo tipo lei de potência devido a um AGN, FC) para a luz integrada das galáxias, em 4020Å. As principais conclusões deste trabalho são: apenas quatro dos objetos estudados têm contribuições significativas (maiores do que 10%) das populações de 100 milhões de anos ou mais jovens (ou de FC) ao longo da região espacial estudada (6 kpc centrais); nenhuma das rádio-galáxias de tipo FRI estudadas tem contribuição significativa destas populações ao longo desta região; duas (de oito) de tipo FRII tem contribuições significativas da luz que vem do AGN, na região nuclear; uma tem contribuição significativa das populações de 100 milhões de anos e mais jovens ao longo dos 4 kpc centrais, indicando claramente a presença de formação estelar recente. Comparando estes resultados com aqueles obtidos para uma amostra de galáxias não ativas de mesmo tipo de Hubble das rádio, encontramos que a principal diferença entre as duas amostras está na contribuição da população de 1 bilhão de anos, geralmente maior nas rádio-galáxias.

Raimann, D. I.; Storchi-Bergmann, T.; Quintana, H.; Alloin, D.; Hunstead, R.; Wisotzki, L.

2003-08-01

332

Magen David Adom--the EMS in Israel.  

PubMed

Israel is a small country with a population of around 7 million. The sole EMS provider for Israel is Magen David Adom (MDA) (translated as 'Red Shield of David'). MDA also carries out the functions of a National Society (similar to the Red Cross) and provides all the blood and blood product services for the country. Nationwide, the organisation responds to over 1000 emergency calls a day and uses doctors, paramedics, emergency medical technicians and volunteers. Local geopolitics has meant that MDA has to be prepared for anything from everyday emergency calls to suicide bombings and regional wars. MDA also prides itself in being able to rapidly assemble and dispatch mobile aid teams to scenes of international disasters. Such a broad range of activities is unusual for a single EMS organisation. PMID:17767990

Ellis, Daniel Y; Sorene, Eliot

2007-09-04

333

Long Term Monitoring of EM Signals Near Parkfield CA  

NASA Astrophysics Data System (ADS)

Fluctuations of resistivity and anomalous electromagnetic (EM) signals have often been reported as precursors to earthquakes. Most of these reports are based on anecdotal observations of unusual phenomena associated with distant earthquakes, with anomalous signals that are often orders of magnitude larger than expected based on laboratory measurements. In an attempt to assess the validity of these reports, and to understand how such signals might be generated, anomalous EM signals and resistivity have been monitored since 1995 using magnetotelluric (MT) instruments at the site of the focused earthquake prediction experiment at Parkfield, CA. This EM monitoring array was fully operational and producing high quality data when the long awaited 28 Sept Mw=6.0 Parkfield earthquake occured. The Parkfield MT site, consisting of three magnetic induction coils and replicated orthogonal electric dipoles, was situated within a few kilometers of the northwestern end of the surface rupture, providing unprecedented observations of EM signals at a well calibrated site in very close proximity to a moderate (M~6) earthquake. A second MT site near Hollister, CA was also functioning well before, during, and after the earthquake, providing a callibrated reference for cancellation of normal EM variations due to ionospheric and magnetospheric sources. Analysis of this data using a variety of techniques has not revealed any anomalous signals which were unambiguos precursors to the 28 September Earthquake. In particular, residual E and B fields computed in both the time and frequency domains over the year 2004 using the remote Hollister site for prediction have been analyzed statistically, revealing no long term trends or changes in anomalous EM signal or noise levels in the months to days preceeding the earthquake. Similarly, no anomalous bursts of EM activity are seen immediately preceeding the earthquake. Based on our analysis of these residuals we conclude that any anomalous magnetic signals would have to be at least 2-3 orders of magnitude weaker than those reported to preceed the Loma Prieta earthquake. A strong co-seismic signal was observed. Much of this signal can probably be explained by motion of the sensors in the Earth's main field, although local electrokinetic effects in the vicinity of the sensor may also have contributed to these signals. Statisitcal analysis has also been performed on variations of daily estimates of apparent resistivity and phase at Parkfield. Systematic variations in these parameters are observed, including slow seasonal modulations and more rapid changes on time scales of a few days. However, comparison to weather records suggest that these signals are most probably related to ground moisture and precipitation events, modifying near surface distortion of the electric fields. Multivariate statistical analysis, including principal components and canonical coherence analysis have also been applited to the data, allowing alternate views of temporal variations of signal and noise characteristics. Although there are some anomalous signals deserving more careful study, there is no evidence from this analysis for significant anomalous EM signals preceeding the Parkfield earthquake.

Kappler, K.; Morrison, H.; Egbert, G.

2005-12-01

334

Tenants' energy bill calculated by custom EMS and software  

SciTech Connect

A Dallas real estate company reduced energy bills by 25% by allocating costs among tenants more fairly. Xencom Inc. assembled an energy management system (EMS) and custom software for the company that monitors and bills tenants who override the EMS during off-hours. The 600-point system made up of components of a number of manufacturers was installed in two buildings. Payback should occur in 18 months. Tenants wishing to override the system between 7 p.m. and 7 a.m. weekdays and between Saturday noon and 7 a.m. Monday dial the computer on any touch phone to give their access and employee code, which identifies the office space for billing. The employee then identifies which building systems he needs.

Hines, V.

1985-08-19

335

Automatic Derivation of Statistical Algorithms: The EM Family and Beyond  

Microsoft Academic Search

Machine learning has reached a point where most probabilistic meth-ods can be understood as variations, extensions and combinations of a much smaller set of abstract themes, e. g., as different instances of the EM algorithm. This enables the systematic derivation of algorithms cus-tomized for different models. Here, we demonstrate the AUTOBAYES system which takes a high-level statistical model specification, uses

Alexander G. Gray; Bernd Fischer; Johann Schumann; Wray L. Buntine

2002-01-01

336

EM-Coffee: An Improvement of M-Coffee  

Microsoft Academic Search

Multiple sequence alignment is a basic of sequence analysis. In the development of multiple sequence alignment (MSA) approaches, M-Coffee [1] was proposed as a meta-method for assembling outputs from different individual multiple aligners into one single MSA to boost the accuracy. Authors showed that M-Coffee outperformed individual alignment methods. In this paper, we propose an improvement of M-coffee, called EM-Coffee,

Nguyen Ha Anh Tuan; Ha Tuan Cuong; Nguyen Hoang Dung; Le Sy Vinh; Tu Minh Phuong

2010-01-01

337

Demand-driven volume rendering of terascale EM data  

Microsoft Academic Search

In neuroscience, a very promising bottom-up approach to understanding how the brain works is built on acquiring and analyzing electron microscopy (EM) scans of brain tissue, an area known as Connectomics. This results in volume data of extremely high resolution of 3--5nm per pixel and 25--50nm slice thickness, overall leading to data sizes of many terabytes [Jeong et al. 2010].

Johanna Beyer; Markus Hadwiger; Won-Ki Jeong; Hanspeter Pfister; Jeff Lichtman

2011-01-01

338

DustEM: Dust extinction and emission modelling  

NASA Astrophysics Data System (ADS)

DustEM computes the extinction and the emission of interstellar dust grains heated by photons. It is written in Fortran 95 and is jointly developed by IAS and CESR. The dust emission is calculated in the optically thin limit (no radiative transfer) and the default spectral range is 40 to 108 nm. The code is designed so dust properties can easily be changed and mixed and to allow for the inclusion of new grain physics.

Compiègne, M.; Verstraete, L.; Jones, A.; Bernard, J.-P.; Boulanger, F.; Flagey, N.; Le Bourlot, J.; Paradis, D.; Ysard, N.

2013-07-01

339

Adaptive play in Texas Hold'em Poker  

Microsoft Academic Search

Abstract. We present a Texas Hold’em poker player for limit heads- up games. Our bot is designed to adapt automatically to the strategy of the opponent,and is not based on Nash equilibrium computation. The main idea is to design a bot that builds beliefs on his opponent’s hand. A forest of game,trees is generated according to those beliefs and the

Raphaël Maîtrepierre; Jérémie Mary; Rémi Munos

2008-01-01

340

Evolução temporal de discos circunstelares em estrelas Be  

NASA Astrophysics Data System (ADS)

A pesquisa do mecanismo que leva uma estrela do tipo Be a perder massa e formar um envelope circunstelar, nomeado como fenômeno Be, é uma questão em aberto, intrigante, e que adquire contornos interessantes em face às informações espectroscópicas de alta resolução. Nesta última década, consolida-se a idéia de que a forma destes envelopes é de tipo discóide, obedecendo a uma lei Kepleriana de velocidades, e mais ainda, recentemente há evidências de que a distribuição de matéria nestes discos pode assumir um caráter de anel. Medidas de algumas dimensões de discos circunstelares puderam ser obtidas pela análise de espectros de alta resolução e alta relação sinal-ruído para as estrelas Be: alpha Eri (HD 10144, B3Vpe), omicron And (HD 217675, B6IIIpe), e eta Cen (HD el972, B1.5Vne), no período dos anos de 1991 a 2001. Alguns modelos clássicos de envelope predizem uma distribuição de massa que decresce suavemente a partir da superfície estelar. Entretanto, considerando que a separação de picos de emissão em perfis de linhas do HeI e H-alpha, alargados por efeitos cinemáticos, é função do raio estelar e da velocidade rotacional projetada (vsini); nossos resultados sugerem a presença de um anel de matéria circunstelar, que aparece logo após a ejeção do material fotosférico, imediatamente acima da superfície estelar, e que se expande para raios maiores ao longo do tempo, eventualmente desconectando-se da superfície por uma região de densidade de matéria mínima. Tais interpretações revivem a idéia de que anéis de matéria circunstelar podem ser os responsáveis por algumas variabilidades em perfis de linhas de emissão, como as variações V/R.

Fernandes, M. V. M.; Leister, N. V.; Levenhagen, R. S.

2003-08-01

341

Parameter estimation of superimposed signals using the EM algorithm  

Microsoft Academic Search

A computationally efficient algorithm for parameter estimation of superimposed signals based on the two-step iterative EM (estimate-and-maximize, with an E step and an M step) algorithm is developed. The idea is to decompose the observed data into their signal components and then to estimate the parameters of each signal component separately. The algorithm iterates back and forth, using the current

MEIR FEDER; EHUD WEINSTEIN

1988-01-01

342

Single sensor active noise cancellation based on the EM algorithm  

Microsoft Academic Search

The authors develop an approach to active noise cancellation using a single microphone. The noise field is modelled as a stochastic process, and a time-adaptive algorithm based on a modification of the block-estimate-maximize (EM) algorithm is used to adaptively estimate the parameters of this process. Based on these parameter estimates a canceling signal is generated. The algorithm developed is evaluated

A. V. Oppenheim; E. Weinstein; K. C. Zangi; M. Feder; D. Gauger

1992-01-01

343

A Novel EM Gradiometric Surveying System for Geophysical Reconnaissance  

Microsoft Academic Search

Interferometric principles are widely used in precision physics experiments and\\/or in advanced laboratory-based phase measurement systems. Phase resolution of such systems is a few orders of magnitude higher compared to that of standard mixer-based quadrature demodulators or lock-in technique. The first attempt of applying interferometric signal processing to transmitter-target-receiver based electromagnetic (EM) surveying in geophysical prospecting is described. It is

Alexey V. Veryaskin; Francis A. Torres; Timo P. Vaalsta; Ju Li; David G. Blair

2011-01-01

344

Integrated EM & Thermal Simulations with Upgraded VORPAL Software  

Microsoft Academic Search

Nuclear physics accelerators are powered by microwaves which must travel in waveguides between room-temperature sources and the cryogenic accelerator structures. The ohmic heat load from the microwaves is affected by the temperature-dependent surface resistance and in turn affects the cryogenic thermal conduction problem. Integrated EM & thermal analysis of this difficult non-linear problem is now possible with the VORPAL finite-difference

D. N. Smithe; D. Karipides; P. Stoltz; G. Cheng; H. Wang

2011-01-01

345

Effect of the nuclear factors EmBP1 and viviparous1 on the transcription of the Em gene in HeLa nuclear extracts.  

PubMed Central

Templates constructed from the wheat Em and maize rab28 promoters are efficiently and accurately transcribed in the well-characterized cell-free transcription system prepared from HeLa nuclei. Deletion analysis of the Em promoter indicates that a G-box (CACGTG) element (Em1b) is required for transcription. USF, a Myc transcription factor in HeLa nuclear extracts, activates transcription by binding to Em1b, as shown by the ability of an antibody raised against USF to inhibit transcription and to interfere with Em1b complex formation in an electrophoretic mobility shift assay. The addition of the recombinant Viviparous1 protein from maize to HeLa nuclear extracts specifically stimulated transcription of the Em promoter but was dependent on the presence of USF in the extract. In USF-depleted extracts, the addition of recombinant EmBP1, a basic leucine zipper transcription factor from wheat, activated transcription through Em1b as well as from a similar G-box in the adenovirus major late promoter. Our study demonstrates that the basic transcriptional apparatus in HeLa nuclear extract supports transcription from plant promoters and can be used to assay the function of certain plant nuclear proteins, thereby helping to determine their effects on transcription.

Razik, M A; Quatrano, R S

1997-01-01

346

Estado nutricional em zinco e teste de acuidade do paladar em crianças de baixa estatura familiar Zinc nutritional status and taste acuity test in familial short stature children  

Microsoft Academic Search

Objetivos: Avaliar o estado nutricional em zinco e a percepção do paladar (salgado, doce, ácido e amargo) em crianças de baixa estatura familiar. Métodos: Estudo transversal de 30 crianças sem sinais de puberdade, pacientes do ambulatório de crescimento da Universidade Federal de São Paulo. A ingestão dietética foi avaliada pelo método do Registro Alimentar. Para o teste de acuidade do

Andréa G. Marques; Luiz A. Lopes; Olga M. S. Amancio

347

APLICAÇÃO DO DIAGRAMA DE CAUSA E EFEITO E DA ANÁLISE SWOT NA DEFINIÇÃO DE PRIORIDADES EM UMA PROPRIEDADE RURAL ESPECIALIZADA EM CRIA DE BOVINOS  

Microsoft Academic Search

Este artigo é resultante da utilização de duas ferramentas de gestão aplicadas a definição de problemas prioritários em uma propriedade rural especializada em cria de bovinos de corte. Contudo, este estudo foi composto de levantamento de dados e informações coletados a partir de entrevistas estruturadas aplicadas aos profissionais responsáveis pela produção, mercadologia, sistema de informações, finanças, gestão de pessoas e

Odilon Jose De Oliveira Neto; Jose Jeronimo de Lima; Vagner Antonio Maximo Cesar; Simone Oliveira Rezende; Reginaldo Santana Figueiredo

2008-01-01

348

EMS Providers and Exception From Informed Consent Research: Benefits, Ethics, and Community Consultation  

PubMed Central

As attention to, and motivation for, EMS-related research continues to grow, particularly exception from informed consent (EFIC) research, it is important to understand the thoughts, beliefs, and experiences of EMS providers who are actively engaged in the research. Study Objective We explored the attitudes, beliefs, and experiences of EMS providers regarding their involvement in prehospital emergency research, particularly EFIC research. Method Using a qualitative design, 24 participants were interviewed including Nationally Registered Paramedics and Virginia certified Emergency Medical Technicians employed at Richmond Ambulance Authority, the participating EMS agency. At the time of our interviews, the EMS agency was involved in an exception from informed consent trial. Transcribed interview data were coded and analyzed for themes. Findings were presented back to the EMS agency for validation. Results Overall, there appeared to be support for prehospital emergency research. Participants viewed research as necessary for the advancement of the field of EMS. Improvement in patient care was identified as one of the most important benefits. A number of ethical considerations were identified: individual risk versus public good and consent. EMS providers in our study were open to working with EMS researchers throughout the community consultation and public disclosure process. Conclusions EMS providers in our study value research and are willing to participate in studies. Support for research was balanced with concerns and challenges regarding the role of providers in the research process.

Ripley, Elizabeth; Ramsey, Cornelia; Prorock-Ernest, Amy; Foco, Rebecca; Luckett, Solomon; Ornato, Joseph P.

2013-01-01

349

Hydration-layer models for cryo-EM image simulation.  

PubMed

To compare cryo-EM images and 3D reconstructions with atomic structures in a quantitative way it is essential to model the electron scattering by solvent (water or ice) that surrounds protein assemblies. The most rigorous method for determining the density of solvating water atoms for this purpose has been to perform molecular-dynamics (MD) simulations of the protein-water system. In this paper we adapt the ideas of bulk-water modeling that are used in the refinement of X-ray crystal structures to the cryo-EM solvent-modeling problem. We present a continuum model for solvent density which matches MD-based results to within sampling errors. However, we also find that the simple binary-mask model of Jiang and Brünger (1994) performs nearly as well as the new model. We conclude that several methods are now available for rapid and accurate modeling of cryo-EM images and maps of solvated proteins. PMID:22609687

Shang, Zhiguo; Sigworth, Fred J

2012-05-17

350

Improving EM&V for Energy Efficiency Programs (Fact Sheet)  

SciTech Connect

This fact sheet describes the objectives of the U.S. Department of Energy Uniform Methods Project to bring consistency to energy savings calculations in U.S. energy efficiency programs. The U.S. Department of Energy (DOE) is developing a framework and a set of protocols for determining gross energy savings from energy efficiency measures and programs. The protocols represent a refinement of the body of knowledge supporting energy efficiency evaluation, measurement, and verification (EM&V) activities. They have been written by technical experts within the field and reviewed by industry experts. Current EM&V practice allows for multiple methods for calculating energy savings. These methods were developed to meet the needs of energy efficiency program administrators and regulators. Although they served their original objectives well, they have resulted in inconsistent and incomparable savings results - even for identical measures. The goal of the Uniform Methods Project is to strengthen the credibility of energy savings determinations by improving EM&V, increasing the consistency and transparency of how energy savings are determined.

Not Available

2012-07-01

351

EMS-Vision: combining on- and off-road driving  

NASA Astrophysics Data System (ADS)

In the past, work at the Universitat der Bundeswehr Muenchen (UBM) has been focused on autonomous road vehicles. During the last four years the Expectation-based Multi-focal Saccadic Vision (EMS-Vision) system has been developed and implemented. EMS-Vision is the 3rd generation dynamic vision system following the 4-D approach. The explicit representation of the own capabilities combined with a complex control and information flow allows the implementation of decision units for goal oriented activation of locomotion and perception. Due to this general approach and in contrast to former UBM systems that were specially designed and optimized for certain limited scenarios and domains, e.g., road following on Autobahnen, the EMS-Vision system can handle complex driving missions spanning multiple domains. It has been realized on a decentralized parallel hardware structure, exclusively built of commercial off-the-shelf components, in both UBM test vehicles VaMoRs and VaMP. Results from an autonomously performed mission on the UBM campus are discussed.

Gregor, Rudolf; Luetzeler, Michael; Dickmanns, Ernst D.

2001-09-01

352

International EMS. How demand is shifting around the world.  

PubMed

The panelists agreed that prehospital systems around the world might very well begin seeing higher demand and lower acuity. However, the unique aspects of each culture that create different prehospital concerns also create different solutions to these needs. U.S. providers must consider for-profit organizations when attempting to reduce fragmentation to gain one lobbying voice, while EMS providers in some nations, such as in Latin America and India, must consider integrating their treatments with local shamens to gain patient acceptance. In Franco-German systems, efficient doctor training has allowed placement of anesthesiologists on ambulances, while prehospital providers in Vietnam have basic concerns, such as whether prehospital care can be sustained in the hospital environment. The shift in EMS around the world will Sdepend more on the expectations and demands of the customers in each nation. It will also depend on the ability of its EMS leaders and administrators to come up with solutions that get customers the most appropriate care in the most affordable manner. To learn more, go to www.jems.com/2020vision. PMID:24159727

2013-06-01

353

GLLH EM Invisible Cloak With Novel Front Branching And Without Exceed Light Speed Violation  

Microsoft Academic Search

In this paper, we propose new Global and Local (GL) electromagnetic (EM) cloaks with distinctive class material a_{\\\\alpha \\\\beta}\\\\log ^\\\\alpha (b_{\\\\alpha \\\\beta}\\/h) h^\\\\beta (GLLH Cloak) without exceed light speed violation. The refractive index of the GLLH cloak material, $n(r)$, is large than one or equal to one. Our GLLH cloak is created by GL EM modeling and GL EM cloak

Ganquan Xieand; Jianhua Li; Lee Xie; Feng Xie

2010-01-01

354

Theoretical and experimental investigations of gravity modification by specially conditioned EM radiation  

NASA Astrophysics Data System (ADS)

Ordinary electromagnetic (em) fields do not couple significantly with those that underlie gravitation and give rise to inertia, and it is suggested that this is because they are of different field essence and form. It is also suggested that a much stronger electro-gravitic coupling might be accomplished for effective propulsion by conditioning ordinary em fields into configurations that are similar to those which underlie gravitation and give rise to inertia. This paper summarizes theoretical and experimental em field conditioning work. .

Froning, H. D.; Barrett, T. W.

2000-01-01

355

The Competitive EM Algorithm for Gaussian Mixtures with BYY Harmony Criterion  

Microsoft Academic Search

Gaussian mixture has been widely used for data modeling and analysis and the EM algorithm is generally employed for its parameter\\u000a learning. However, the EM algorithm may be trapped into a local maximum of the likelihood and even leads to a wrong result\\u000a if the number of components is not appropriately set. Recently, the competitive EM (CEM) algorithm for Gaussian

Hengyu Wang; Lei Li; Jinwen Ma

2008-01-01

356

EM-ANN models for microstrip vias and interconnects in dataset circuits  

Microsoft Academic Search

A novel approach for accurate and efficient modeling of monolithic microwave\\/millimeter wave integrated circuit (MMIC) components by using electromagnetically trained artificial neural network (EM-ANN) software modules is presented. Full-wave EM analysis is employed to characterize MMIC components. Structures for simulation are chosen using design of experiments (DOE) methodology. EM-ANN models are then trained using physical parameters as inputs and S-parameters

Paul M. Watson; Kuldip C. Gupta

1996-01-01

357

Detecção inesperada de efeitos de lentes fracas em grupos de galáxias pouco luminosos em raios-X  

NASA Astrophysics Data System (ADS)

Obtivemos, como parte do programa de verificação científica do GMOS Sul, imagens profundas de três grupos de galáxias: G97 e G102 (z~0,4) e G124 (z = 0,17). Esses alvos foram selecionados a partir do catálogo de fontes extensas de Vikhlinin (1998), por terem luminosidades em raios X menores que 3´1043 ergs s-1, valor cerca de uma ou duas ordens de grandeza inferior ao de aglomerados de galáxias. O objetivo primário dessas observações é o estudo da evolução de galáxias em grupos. Grupos são ambientes menos densos que aglomerados, contêm a grande maioria das galáxias do Universo mas que, até o momento, foram estudados detalhadamente apenas no Universo local (z~0). Com esses dados efetuamos uma análise estatística da distorção na forma das galáxias de fundo (lentes gravitacionais fracas) como forma de inferir o conteúdo e a distribuição de massa nesses grupos apesar de que, em princípio, esse efeito não deveria ser detectado uma vez que os critérios de seleção adotados previlegiam sistemas de baixa massa. De fato, para G124 obtivemos apenas um limite superior para sua massa que é compatível com sua luminosidade em raios X. De modo contrário e surpreendente, os objetos G102 e G097, aparentam ter massas que resultariam em dispersões de velocidade maiores que 1000 km s-1, muito maiores do que se espera para grupos de galáxias. Com efeito, para G097 obtivemos, a partir de dados do satélite XMM, uma estimativa para a temperatura do gás intragrupo de kT = 2,6 keV, que é tipica de sistemas com dispersões de velocidade de ~ 600 km s-1, bem característica de grupos. Essas contradições aparentes entre lentes fracas e raios X podem ser explicadas de dois modos: i) a massa obtida por lentes estaria sobreestimada devido à superposição de estruturas massivas ao longo da linha de visada ou ii) a temperatura do gás do meio intra-grupo reflete o potencial gravitacional de estruturas menores que estariam se fundindo para formar uma estrutura maior.

Carrasco, R.; Mendes de Oliveira, C.; Sodrã©, L., Jr.; Lima Neto, G. B.; Cypriano, E. S.; Lengruber, L. L.; Cuevas, H.; Ramirez, A.

2003-08-01

358

EM703, a new derivative of erythromycin, inhibits transforming growth factor-beta signaling in human lung fibroblasts.  

PubMed

Long-term, low-dose macrolide therapy has been proven to improve survival in patients with diffuse panbronchiolitis and cystic fibrosis, although the mechanisms by which it does so remain unknown. To elucidate the molecular mechanisms of the anti-inflammatory effects of macrolides, the authors examined the effects of erythromycin (EM-A) and new derivative EM703 on transforming growth factor (TGF)-beta /Smad signaling fibroblasts. EM-A and EM703 each inhibited fibroblast proliferation and the collagen production in human lung fibroblasts induced by TGF-beta. EM-A and EM703 inhibited the augmentation of Smad3 mRNA induced by TGF-beta. Smad7 mRNA was inhibited by TGF-beta, but augmented by coincubation with EM-A or EM703. EM-A and EM703 each inhibited p-Smad2/3 proteins induced by TGF-beta. Smad7 protein inhibited by TGF-beta restored beyond basal level by EM-A and EM703. These findings suggest that EM-A and EM703 inhibit TGF-beta signaling in human lung fibroblasts via inhibition of p-Smad2/3 through recovery of Smad7 level. PMID:18600500

Yu, ChangHe; Azuma, Arata; Li, YingJi; Wang, Chunyan; Abe, Sinji; Usuki, Jiro; Matsuda, Kuniko; Kudoh, Shoji; Sunazuka, Toshiaki; Omura, Satoshi

2008-08-01

359

Modeling of MHD edge containment in strip casting with ELEKTRA and CaPS-EM codes  

SciTech Connect

This paper presents modeling studies of magnetohydrodynamics analysis in twin-roll casting. Argonne National Laboratory (ANL) and ISPAT Inland Inc. (Inland), formerly Inland Steel Co., have worked together to develop a three-dimensional (3-D) computer model that can predict eddy currents, fluid flows, and liquid metal containment of an electromagnetic (EM) edge containment device. The model was verified by comparing predictions with experimental results of liquid metal containment and fluid flow in EM edge dams (EMDs) that were designed at Inland for twin-roll casting. This mathematical model can significantly shorten casting research on the use of EM fields for liquid metal containment and control. The model can optimize the EMD design so it is suitable for application, and minimize expensive time-consuming full-scale testing. Numerical simulation was performed by coupling a 3-D finite-element EM code (ELEKTRA) and a 3-D finite-difference fluids code (CaPS-EM) to solve heat transfer, fluid flow, and turbulence transport in a casting process that involves EM fields. ELEKTRA can predict the eddy-current distribution and the EM forces in complex geometries. CaPS-EM can model fluid flows with free surfaces. The computed 3-D magnetic fields and induced eddy currents in ELEKTRA are used as input to temperature- and flow-field computations in CaPS-EM. Results of the numerical simulation compared well with measurements obtained from both static and dynamic tests.

Chang, F. C.

2000-01-12

360

The characteristics of lithospheric origin ULF EM radiation in the lithosphere-atmosphere-ionosphere-magnetosphere system  

NASA Astrophysics Data System (ADS)

The penetration of ultra low frequency (0.01-100 s-1) electromagnetic (ULF EM) radiation throughout ionosphere are calculated numerically for source in the lithosphere and in the magnetosphere. The changes of perturbation area shape during propagation in the ionosphere are investigated for different <> types in the lithosphere which excite this EM radiation. The wave and spatial characteristics of penetrated into upper ionosphere ULF EM field are determined. The influence of altitude profile's main parameters of ionosphere plasma and geophysical condition onto the penetration effect of ULF EM radiation throughout is discussed.

Cheremnykh, O. K.; Grimalsky, V. V.; Kremenetsky, I.

361

Multi-frequency electromagnetic sounding tool EMS. Archaeological discoveries. Case stories.  

NASA Astrophysics Data System (ADS)

EMS is the new patented tool for shallow-depth (up to 7 m) induction frequency sounding. The tool is developed in Institute of Geophysics, Siberian Branch of Russian Academy, Novosibirsk, RUSSIA. Few years of application of EMS prototypes in archaeological prospection gave us the well described picture of possibilities and limitations of EM sounding for archaeological purpose. We would like to present several archaeological case stories including paleolitic, bronze and iron ages, antique and medieval targets discovery. The cases include complex geophysical works using GPR, Vertical DC sounding and magnetometry together with EM sounding. Archaeological proofs of geophysical prospection will be presented. The last September in Italy we have done the comparative work at few Italian archaeological sites. The second EMS prototype has been compared with commercially available tools for EM prospection such as EM mappers, georadars and DC electrical resistivity tomography. In the comparison EMS feature good noise immunity, high sensibility and resolution. In some cases only EMS data shows the buried targets and it was proved immediately by excavation. The researches were done with financial support of RFBR grant # 00-06-80421

Abu Zeid, N.; Balkov, E.; Chemyakina, M.; Manstein, A.; Manstein, Y.; Morelli, G.; Santarato, G.

2003-04-01

362

EM-21 Retrieval Knowledge Center: Waste Retrieval Challenges  

SciTech Connect

EM-21 is the Waste Processing Division of the Office of Engineering and Technology, within the U.S. Department of Energy’s (DOE) Office of Environmental Management (EM). In August of 2008, EM-21 began an initiative to develop a Retrieval Knowledge Center (RKC) to provide the DOE, high level waste retrieval operators, and technology developers with centralized and focused location to share knowledge and expertise that will be used to address retrieval challenges across the DOE complex. The RKC is also designed to facilitate information sharing across the DOE Waste Site Complex through workshops, and a searchable database of waste retrieval technology information. The database may be used to research effective technology approaches for specific retrieval tasks and to take advantage of the lessons learned from previous operations. It is also expected to be effective for remaining current with state-of-the-art of retrieval technologies and ongoing development within the DOE Complex. To encourage collaboration of DOE sites with waste retrieval issues, the RKC team is co-led by the Savannah River National Laboratory (SRNL) and the Pacific Northwest National Laboratory (PNNL). Two RKC workshops were held in the Fall of 2008. The purpose of these workshops was to define top level waste retrieval functional areas, exchange lessons learned, and develop a path forward to support a strategic business plan focused on technology needs for retrieval. The primary participants involved in these workshops included retrieval personnel and laboratory staff that are associated with Hanford and Savannah River Sites since the majority of remaining DOE waste tanks are located at these sites. This report summarizes and documents the results of the initial RKC workshops. Technology challenges identified from these workshops and presented here are expected to be a key component to defining future RKC-directed tasks designed to facilitate tank waste retrieval solutions.

Fellinger, Andrew P.; Rinker, Michael W.; Berglin, Eric J.; Minichan, Richard L.; Poirier, Micheal R.; Gauglitz, Phillip A.; Martin, Bruce A.; Hatchell, Brian K.; Saldivar, Eloy; Mullen, O Dennis; Chapman, Noel F.; Wells, Beric E.; Gibbons, Peter W.

2009-04-10

363

EM Modelling of RF Propagation Through Plasma Plumes  

NASA Astrophysics Data System (ADS)

Electric propulsion is a commercially attractive solution for attitude and position control of geostationary satellites. Hall-effect ion thrusters generate a localized plasma flow in the surrounding of the satellite, whose impact on the communication system needs to be qualitatively and quantitatively assessed. An electromagnetic modelling tool has been developed and integrated into the Antenna Design Framework- ElectroMagnetic Satellite (ADF-EMS). The system is able to guide the user from the plume definition phases through plume installation and simulation. A validation activity has been carried out and the system has been applied to the plume modulation analysis of SGEO/Hispasat mission.

Pandolfo, L.; Bandinelli, M.; Araque Quijano, J. L.; Vecchi, G.; Pawlak, H.; Marliani, F.

2012-05-01

364

SEI: Junior E&M Course Materials - Math Fundamentals  

NSDL National Science Digital Library

This is a collection of resources for teaching mathematical fundamentals of electro- and magnetostatics constructed over the course of four semesters of a transformed junior-level Electricity and Magnetism course. Included are homework questions, concept tests, and information about common student difficulties in the topic and ways to address these difficulties. This material was developed as part of a education research-based course transformation for junior level E&M. All of the resources developed for this course are available, sorted by individual topic and type, at http://www.compadre.org/psrc/items/Relations.cfm?ID=7891.

Pollock, Steven J.; Chasteen, Stephanie V.

2010-06-29

365

State of the Art in EM Field Computation  

SciTech Connect

This paper presents the advances in electromagnetic (EM) field computation that have been enabled by the US DOE SciDAC Accelerator Science and Technology project which supports the development and application of a suite of electromagnetic codes based on the higher-order finite element method. Implemented on distributed memory supercomputers, this state of the art simulation capability has produced results which are of great interest to accelerator designers and with realism previously not possible with standard codes. Examples from work on the International Linear Collider (ILC) project are described.

Ng, C.; Akcelik, V.; Candel, A.; Chen, S.; Folwell, N.; Ge, L.; Guetz, A.; Jiang, H.; Kabel, A.; Lee, L.-Q.; Li, Z.; Prudencio, E.; Schussman, G.; Uplenchwar, R.; Xiao, L.; Ko, K.; /SLAC

2006-09-25

366

Caucasicosides E-M, furostanol glycosides from Helleborus caucasicus.  

PubMed

Nine furostanol glycosides, namely caucasicosides E-M, were isolated from the MeOH extract of the leaves of Helleborus caucasicus, along with 11 known compounds including nine furostanol glycosides, a bufadienolide and an ecdysteroid. Their structures were established by the extensive use of 1D and 2D NMR experiments along with ESIMS(n) analyses. The steroidal composition of leaves of H. caucasicus shows as particular feature the occurrence of steroidal compounds belonging to the 5? series, unusual for Helleborus species, and in particular, caucasicosides F-H are based on a 5?-polyhydroxylated steroidal aglycon never reported before. PMID:21893324

Muzashvili, Tamar; Perrone, Angela; Napolitano, Assunta; Kemertelidze, Ether; Pizza, Cosimo; Piacente, Sonia

2011-09-03

367

8 EMS vendors now offer guaranteed savings plans  

SciTech Connect

At least eight companies now offer company-wide insurance policies guaranteeing the savings projections of energy-management system (EMS) dealers. The plans can guarantee either that energy costs will be lower than the lease payments or that the user will achieve a stated payback. The plan requires users to buy a maintenance contract with their system. Drawbacks are the disincentive for users to seek additional energy savings and the problem of how to measure the savings. Users can request a policy through an insurance company if they are hesitant about a company policy. Spokesmen for several companies offering the insurance option describe the highlights of their programs. (DCK)

Raymond, M.

1983-02-14

368

Effects of caffeine or EDTA post-treatment on EMS mutagenesis in soybean.  

PubMed

Seeds of soybean cultivar LD4 were mutagenically treated with EMS (0.3, 0.5, 0.6, 0.9, 1.5 and 1.8%) for 3 h only or plus caffeine (50 mM) or EDTA (1 mM) post-treatment for 5 h. The experimental results indicated that: (1) of the different concentrations of EMS treatment, the M2 mutation frequency induced with 0.6% EMS was the highest (9.7%). When the EMS concentration was over 0.9%, the mutation frequency decreased rapidly. (2) Of the EMS treatments plus caffeine or EDTA post-treatment, the mutagenic effect of 0.6% EMS was the best for inducing morphological variations. Caffeine post-treatment decreased notably the mutation frequency of EMS treatment; when concentrations of EMS were very high (1.5% and 1.8%), mutation frequencies of EDTA post-treatment were still 5.0% and 4.88%, but no mutants were found in EMS treatment or plus caffeine post-treatment. (3) In the M2 mutation spectrum, 11 kinds of mutant types were observed in EMS treatment or plus caffeine or EDTA post-treatment. Relative frequencies of some mutant types (growth period, plant height, grain size, leaf shape and sterility, etc.) were similar among the three treatments, but EDTA post-treatment could change the relative frequencies of yield characteristics (number of pods and grains, grain weight/plant) induced by EMS treatment only. PMID:7885367

Zhu, B; Gu, A; Deng, X; Geng, Y; Lu, Z

1995-04-01

369

Aristarchus's <em>On the Sizes and Distances of the Sun and the Moonem>: Greek and Arabic Texts  

NASA Astrophysics Data System (ADS)

In the 1920s, T. L. Heath pointed out that historians of mathematics have "given too little attention to Aristarchus". This is still true today. The Greek text of Aristarchus's On the Sizes and Distances of the Sun and the Moonem> has received little attention; the Arabic editions virtually none. Much of what this text has to tell us about ancient and medieval mathematics and the mathematical sciences has gone unnoticed. It should be taken as an important source for our understanding of the mathematical sciences of the early Hellenistic period.

Berggren, J. L.; Sidoli, N.

2007-05-01

370

ANÁLISE DOS INDICADORES DE HEMORRAGIA LETAL EM VÍTIMAS DE TRAUMA PENETRANTE DE TRONCO ADMITIDAS EM CHOQUE: UM MÉTODO OBJETIVO PARA SELECIONAR OS CANDIDATOS AO \\  

Microsoft Academic Search

RESUMO: Objetivo: Identificar os indicadores de hemorragia letal em vítimas de trauma penetrante de tronco, admitidas com hipotensão arterial sistêmica e analisar sua aplicabilidade na seleção dos candidatos ao \\

José Gustavo Parreira

371

Robust EM Continual Reassessment Method in Oncology Dose Finding  

PubMed Central

The continual reassessment method (CRM) is a commonly used dose-finding design for phase I clinical trials. Practical applications of this method have been restricted by two limitations: (1) the requirement that the toxicity outcome needs to be observed shortly after the initiation of the treatment; and (2) the potential sensitivity to the prespecified toxicity probability at each dose. To overcome these limitations, we naturally treat the unobserved toxicity outcomes as missing data, and use the expectation-maximization (EM) algorithm to estimate the dose toxicity probabilities based on the incomplete data to direct dose assignment. To enhance the robustness of the design, we propose prespecifying multiple sets of toxicity probabilities, each set corresponding to an individual CRM model. We carry out these multiple CRMs in parallel, across which model selection and model averaging procedures are used to make more robust inference. We evaluate the operating characteristics of the proposed robust EM-CRM designs through simulation studies and show that the proposed methods satisfactorily resolve both limitations of the CRM. Besides improving the MTD selection percentage, the new designs dramatically shorten the duration of the trial, and are robust to the prespecification of the toxicity probabilities.

Yuan, Ying; Yin, Guosheng

2012-01-01

372

Robust EM Continual Reassessment Method in Oncology Dose Finding.  

PubMed

The continual reassessment method (CRM) is a commonly used dose-finding design for phase I clinical trials. Practical applications of this method have been restricted by two limitations: (1) the requirement that the toxicity outcome needs to be observed shortly after the initiation of the treatment; and (2) the potential sensitivity to the prespecified toxicity probability at each dose. To overcome these limitations, we naturally treat the unobserved toxicity outcomes as missing data, and use the expectation-maximization (EM) algorithm to estimate the dose toxicity probabilities based on the incomplete data to direct dose assignment. To enhance the robustness of the design, we propose prespecifying multiple sets of toxicity probabilities, each set corresponding to an individual CRM model. We carry out these multiple CRMs in parallel, across which model selection and model averaging procedures are used to make more robust inference. We evaluate the operating characteristics of the proposed robust EM-CRM designs through simulation studies and show that the proposed methods satisfactorily resolve both limitations of the CRM. Besides improving the MTD selection percentage, the new designs dramatically shorten the duration of the trial, and are robust to the prespecification of the toxicity probabilities. PMID:22375092

Yuan, Ying; Yin, Guosheng

2011-09-01

373

Transmission phase shifts of Kondo impurities  

NASA Astrophysics Data System (ADS)

We study the coherent properties of transmission through Kondo impurities by considering an open Aharonov-Bohm ring with an embedded quantum dot. We develop a many-body scattering theory which enables us to calculate the conductance through the dot Gd, the transmission phase shift ?t, and the normalized visibility ? in terms of the single-particle T matrix. For the single-channel Kondo effect, we find at temperatures much below the Kondo temperature TK that ?t=?/2 without any corrections up to order (T/TK)2. The visibility has the form ?=1-(?T/TK)2. For the non-Fermi-liquid fixed point of the two-channel Kondo, we find that ?t=?/2 despite the fact that a scattering phase shift is not defined. The visibility is ?=1/2(1+4??T) with ?˜1/TK, thus, at zero temperature, exactly half of the conductance is carried by single-particle processes, and coherent transmission may actually increase with temperature. We explain that the spin summation masks the inherent scattering phases of the dot, which can be accessed only via a spin-resolved experiment. In addition, we calculate the effect of magnetic field and channel anisotropy, and generalize to the k-channel Kondo case.

Carmi, Assaf; Oreg, Yuval; Berkooz, Micha; Goldhaber-Gordon, David

2012-09-01

374

Topological Insulator Nanoribbons and Nanocrystals  

NASA Astrophysics Data System (ADS)

Following the discovery of two-dimensional topological insulator edge states in HgTe quantum wells at cryogenic temperatures, three dimensional (3D) topological insulators were recently discovered in Bismuth Selenide (Bi2Se3) and related compounds. Theoretical prediction and angle resolved photon emission spectroscopy studies show quantum spin Hall surface states in these 3D topological insulator materials. However, all the studies thus far have been on bulk size materials and it is challenging to observe directly the surface topological state conduction since its effects are masked by the residue bulk carrier. Here I present our study on topological insulator nanostructures, which can manifest the surface conduction states due their large surface-to-volume ratios. We show unambiguous transport evidence of topological surface states through periodic quantum interference effects in layered single-crystalline Bi2Se3 nanoribbons. Pronounced Aharonov-Bohm oscillations in the magnetoresistance clearly demonstrate the coverage of two-dimensional electrons on the entire surface. I will discuss our recent exciting study on topological insulator nanocrystals. Our results suggest that topological insulator nanoribbons and nanocrystals afford novel promising materials for future spintronic devices.

Cui, Yi

2010-03-01

375

Utilizing public scientific web lectures to teach contemporary physics at the high school level: A case study of learning  

NSDL National Science Digital Library

This paper describes a teaching experiment designed to examine the learning (i.e., retention of content and conceptual development) that takes place when public scientific web lectures delivered by scientists are utilized to present advanced ideas in physics to students with a high school background in physics. The students watched an exemplary public physics web lecture that was followed by a collaborative generic activity session. The collaborative session involved a guided critical reconstruction of the main arguments in the lecture, and a processing of the key analogical explanations. Then the students watched another exemplary web lecture on a different topic. The participants (N=14) were divided into two groups differing only in the order in which the lectures were presented. The studentsâ discussions during the activities show that they were able to reason and demonstrate conceptual progress, although the physics ideas in the lectures were far beyond their level in physics. The discussions during the collaborative session contributed significantly to the studentsâ understanding. We illustrate this point through an analysis of one of these discussions between two students on an analogical explanation of the Aharonov-Bohm effect that was presented in one of the lectures. The results from the tests that were administered to the participants several times during the intervention further support this contention.

Kapon, Shulamit; Ganiel, Uri; Eylon, Bat-Sheva

2013-05-28

376

Electron lifetime in Luttinger liquids  

NASA Astrophysics Data System (ADS)

We investigate the decoherence of the electron wave packet in purely ballistic one-dimensional systems described through the Luttinger liquid (LL). At a finite temperature T and long times t , we show that the electron Green’s function for a fixed wave vector close to one Fermi point decays as exp(-t/?F) —as opposed to the power-law behavior occurring at short times—and the emerging electron lifetime obeys ?F-1?T for spinful as well as spinless electrons. For strong interactions, (T?F)?1 , reflecting that the electron is not a good Landau quasiparticle in LL’s. We justify that fractionalization is the main source of electron decoherence for spinful as well as spinless electrons clarifying the peculiar electron mass renormalization close to the Fermi points. For spinless electrons and weak interactions, our intuition can be enriched through a diagrammatic approach or Fermi golden rule and through a Johnson-Nyquist noise picture. We stress that the electron lifetime (and the fractional quasiparticles) can be revealed from Aharonov-Bohm experiments or momentum resolved tunneling. We aim to compare the results with those of spin-incoherent and chiral LL’s.

Le Hur, Karyn

2006-10-01

377

Localized End States in Density Modulated Quantum Wires and Rings  

NASA Astrophysics Data System (ADS)

We study finite quantum wires and rings in the presence of a charge-density wave gap induced by a periodic modulation of the chemical potential. We show that the Tamm-Shockley bound states emerging at the ends of the wire are stable against weak disorder and interactions, for discrete open chains and for continuum systems. The low-energy physics can be mapped onto the Jackiw-Rebbi equations describing massive Dirac fermions and bound end states. We treat interactions via the continuum model and show that they increase the charge gap and further localize the end states. The electrons placed in the two localized states on the opposite ends of the wire can interact via exchange interactions and this setup can be used as a double quantum dot hosting spin qubits. The existence of these states could be experimentally detected through the presence of an unusual 4? Aharonov-Bohm periodicity in the spectrum and persistent current as a function of the external flux.

Gangadharaiah, Suhas; Trifunovic, Luka; Loss, Daniel

2012-03-01

378

Tailoring Fabry-Perot Interferometers for Fragile Fractional Quantum Hall States  

NASA Astrophysics Data System (ADS)

Depending on the relevance of Coulomb interactions, electronic Fabry-Perot interferometers can exhibit two qualitatively different types of interference, each of which can shed light on the unique physics of quantum Hall systems. Long observed in the integer quantum Hall (IQH) regime, the so-called ``Coulomb-dominated'' interference has only recently been confirmed in the fractional quantum Hall (FQH) regime, where its observation has remained limited to the simplest and most robust FQH states. Building on our recent observation and analysis of this type of interference at several fractional filling factors, we report on interferometer design improvements yielding greater visibility, most notably for weaker FQH states. We find that parameters such as the distance from the gates defining the interferometer to the 2DEG, gate layout, and wafer structure affect the visibility much more in the FQH regime than in the IQH regime. High sensitivity to such parameters is also a characteristic of the second type of interference, believed to arise from a pure Aharonov-Bohm effect, which has been clearly observed only in the IQH regime; we discuss efforts to observe this behavior in the FQH regime.

McClure, Douglas; Gallagher, Patrick; Marcus, Charles; Pfeiffer, Loren; West, Ken

2012-02-01

379

Unique spin-polarized transmission effects in a QD ring structure  

NASA Astrophysics Data System (ADS)

Spintronics is an emerging field in which the spin of the electron is used for switching purposes and to communicate information. In order to obtain spin-polarized electron transmission, the Zeeman effect is employed to produce spin-split energy states in quantum dots which are embedded in the arms of a mesoscopic Aharonov-Bohm (AB) ring heterostructure. The Zeeman splitting of the QD energy levels can be induced by a parallel magnetic field, or by a perpendicular field which also produces AB-effects. The combination of these effects on the transmission resonances of the structure is studied analytically and several parameter regimes are identified which produce a high degree of spin-polarized output. Contour and line plots of the weighted spin polarization as a function of electron energy and magnetic field are presented to visualize the degree of spin-polarization. Taking advantage of these unique parameter regimes shows the potential promise of such devices for producing spin-polarized currents.

Hedin, Eric; Joe, Yong

2010-10-01

380

Electrical control of a solid-state flying qubit.  

PubMed

Solid-state approaches to quantum information technology are attractive because they are scalable. The coherent transport of quantum information over large distances is a requirement for any practical quantum computer and has been demonstrated by coupling super-conducting qubits to photons. Single electrons have also been transferred between distant quantum dots in times shorter than their spin coherence time. However, until now, there have been no demonstrations of scalable 'flying qubit' architectures-systems in which it is possible to perform quantum operations on qubits while they are being coherently transferred-in solid-state systems. These architectures allow for control over qubit separation and for non-local entanglement, which makes them more amenable to integration and scaling than static qubit approaches. Here, we report the transport and manipulation of qubits over distances of 6 µm within 40 ps, in an Aharonov-Bohm ring connected to two-channel wires that have a tunable tunnel coupling between channels. The flying qubit state is defined by the presence of a travelling electron in either channel of the wire, and can be controlled without a magnetic field. Our device has shorter quantum gates (<1 µm), longer coherence lengths (?86 µm at 70 mK) and higher operating frequencies (?100 GHz) than other solid-state implementations of flying qubits. PMID:22426515

Yamamoto, Michihisa; Takada, Shintaro; Bäuerle, Christopher; Watanabe, Kenta; Wieck, Andreas D; Tarucha, Seigo

2012-03-18

381

Quantizations on the circle and coherent states  

NASA Astrophysics Data System (ADS)

We present a possible construction of coherent states on the unit circle as configuration space. Our approach is based on Borel quantizations on S1 including the Aharonov-Bohm-type quantum description. Coherent states are constructed by Perelomov’s method as group-related coherent states generated by Weyl operators on the quantum phase space {Z} \\times S^{1}. Because of the duality of canonical coordinates and momenta, i.e. the angular variable and the integers, this formulation can also be interpreted as coherent states over an infinite periodic chain. For the construction, we use the analogy with our quantization and coherent states over a finite periodic chain where the quantum phase space was {Z}_{M} \\times {Z}_{M}. The coherent states constructed in this work are shown to satisfy the resolution of unity. To compare them with canonical coherent states, some of their further properties are also studied demonstrating similarities as well as substantial differences. This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘Coherent states: mathematical and physical aspects’.

Chadzitaskos, G.; Luft, P.; Tolar, J.

2012-06-01

382

Quantum transport in electron Fabry-Perot interferometers  

NASA Astrophysics Data System (ADS)

We report experiments on Fabry-Perot electron interferometers in the integer quantum Hall regime. The GaAs/AlGaAs heterostructure devices consist of two constrictions defined by etch trenches in two-dimensional electron layer, enclosing an approximately circular island. The interferometer is formed by counterpropagating chiral edge channels coupled by tunneling in the two constrictions. Interference fringes are observed as conductance oscillations, similar to the Aharonov-Bohm effect. Front gates deposited in etch trenches allow us to fine tune the device and to change the constriction filling f relative to the bulk filling. Quantum-coherent conductance oscillations are observed on the f=1 4 plateaus. On plateau f , we observe f conductance oscillations per fundamental flux period h/e . This is attributed to the dominance of the electron-electron Coulomb interaction, effectively mixing Landau level occupation. On the other hand, the back-gate charge period is the same (one electron) on all plateaus, independent of filling. This is attributed to the self-consistent electrostatics in the large electron island. We also report dependence of the oscillation period on front-gate voltage for f=1 , 2, and 4 for three devices. We find a linear dependence, with the slope inversely proportional to f for f=1 and 2.

Camino, F. E.; Zhou, Wei; Goldman, V. J.

2007-10-01

383

Nonlocal momentum transfer in welcher Weg measurements  

NASA Astrophysics Data System (ADS)

A ``which-path'' (welcher Weg) measurement necessarily destroys the fringes in a double-slit interference experiment. We show that in all instances one may attribute this destruction to a disturbance of the particle's momentum by an amount equal to at least ??/2d, where d is the slit separation, in accordance with the uncertainty principle. However, this momentum transfer need not be local; that is, it need not act at either of the slits through which the particle passes. For well-known welcher Weg measurements such as Einstein's recoiling slit and Feynman's light microscope, the disturbance can be understood in terms of random classical momentum kicks that act locally. In some recent proposals, including that by Scully, Englert, and Walther [Nature (London) 351, 111 (1991)], the momentum transfer is of a peculiarly quantum, nonlocal nature. In this paper we introduce a formalism based on the Wigner function, as this describes both the local and nonlocal momentum transfer caused by any welcher Weg measurement. We show that for some examples, such as that of Scully, Englert, and Walther, there is no momentum disturbance at the slits even though the nonlocal momentum disturbance is sufficient to destroy the interference pattern. Finally, we discuss the experimental signatures of nonlocal versus local momentum transfer and demonstrate a strong similarity to the nonlocality of the Aharonov-Bohm effect.

Wiseman, H. M.; Harrison, F. E.; Collett, M. J.; Tan, S. M.; Walls, D. F.; Killip, R. B.

1997-07-01

384

The Aharanov-Bohm effect, magnetic monopoles and reversal in spin-ice lattices.  

PubMed

The proof of the Aharonov-Bohm (AB) effect has been one of the most important experiments of the last century and used as essential evidence for the theory of gauge fields. In this article, we look at its fundamental relation to the Dirac monopole and string. Despite the Dirac string being invisible to the AB effect, it can be used to study emergent quasiparticles in condensed matter settings that behave similar to the fundamental monopoles and strings between them. We utilize phase-imaging method based on the AB effect to study the ordering in a one-model system - that of frustrated spin ice - to understand the ordering processes that occur during a magnetic field reversal cycle. The reversal is linked to the propagation of monopole defects linked by flux channels, reminiscent of Dirac strings. Monopole interactions govern the defect densities within the lattice. Furthermore, we exploit these interactions to propose a new ordering method in which high degrees of ground-state ordering can be achieved in a frustrated system. PMID:23549453

Pollard, Shawn D; Zhu, Yimei

2013-04-02

385

Electrical transport studies of Topological Insulator Bi2Te3 Nanotubes  

NASA Astrophysics Data System (ADS)

We have studied electrical transport properties of candidate topological insulator Bismuth Telluride (Bi2Te3) nanotubes. Bi2Te3 nanotube samples were synthesized by solution phase method, with the outer diameters in the range of 70±5 nm and inner diameter 50±5 nm and the length of 3 to 10 um. Platinum contact leads were fabricated on the nanotubes by focusing ion beam assisted deposition. Electrical transport measurements were conducted at low temperatures and high magnetic fields (up to 9T). The nanotubes showed good insulating behavior in comparison with the thin films which are often metallic. Resistance oscillation as a function of magnetic field was observed when the magnetic field is applied parallel to the nanotubes. The periods range from 6000 Oe to 8350 Oe, which correspond to the diameter of 80 to 100 nm according to Aharonov-Bohm oscillation formula. This is close but slightly larger than the outer diameter of the nanotubes. The amplitude of the oscillations decays rapidly as field increases, possibly due to scattering. When the magnetic field was applied perpendicular to the nanotube, no resistance oscillation was observed. The possible origins of the oscillation effect will be discussed.

Du, Renzhong; Zhao, Weiwei; Wang, Jian; Yin, Yuewei; Dong, Sining; Li, Xiaoguang; Liu, Chaoxing; Chan, Moses; Li, Qi

2013-03-01

386

Transport measurements of the topological surface states in Bi2Te3 nanoribbon field effect devices  

NASA Astrophysics Data System (ADS)

We have grown nanoribbons (NRs) of Bi2Te3, a prototype topological insulator, by CVD and characterized them by TEM, Raman Spectroscopy and EDS. We fabricate backgated field effect devices where the chemical potential can be tuned and ambipolar field effect has been observed. The as-grown NRs are n-type and the 4-terminal resistance (R4p) versus temperature (T) shows a metallic behavior. Applying a sufficiently negative Vg, the R4p vs T displays an insulating behavior that saturates in a plateau at T < 100K, suggesting a metallic surface conduction dominant at low temperatures. Aharonov-Bohm (AB) oscillations of surface conducting carriers are observed in the magneto-resistance (MR) with a magnetic (B) field parallel to the NR axis. We have also measured the Shubnikov de Haas (SdH) oscillations with the B-field perpendicular to the NR axis at different carrier densities (n). The extrapolated Landau level crossing at 1/B = 0 is ˜0.5 and the extracted cyclotron mass from the T-dependence of the SdH oscillations is proportional to ?n, providing direct evidence of the Dirac fermion nature of the topological surface state. Gate-tunable weak anti-localization is observed and the extracted number of decoupled coherent conduction channels is 2 at the charge neutrality point.

Jauregui, Luis A.; Pettes, Michael T.; Shi, Li; Rokhinson, Leonid P.; Chen, Yong P.

2013-03-01

387

The Lorentz transformations of the vectors E, B, P, M and the external electric fields from a stationary superconducting wire with a steady current and from a stationary permanent magnet  

NASA Astrophysics Data System (ADS)

In the first part of this paper we review the fundamental difference between the usual transformations of the three-dimensional (3D) vectors of the electric field E, the magnetic field B, the polarization P, the magnetization M and the Lorentz transformations of the 4D geometric quantities, vectors E, B, P, M, with many additional explanations and several new results. In the second part, we have discussed the existence of the electric field vector E outside a stationary superconducting wire with a steady current and also different experiments for the detection of such electric fields. Furthermore, a fundamental prediction of the existence of the external electric field vector E from a stationary permanent magnet is considered. These electric fields are used for the resolution of the "charge-magnet paradox" with 4D geometric quantities for a qualitative explanation of the Aharonov-Bohm effect in terms of fields and not, as usual, in terms of the vector potential and for a qualitative explanation that the particle interference is not a test of a Lorentz-violating model of electrodynamics according to which a magnetic solenoid generates not only a static magnetic field but also a static electric field.

Ivezi?, Tomislav

2013-04-01

388

Fano-Rashba effect in thermoelectricity of a double quantum dot molecular junction.  

PubMed

We examine the relation between the phase-coherent processes and spin-dependent thermoelectric effects in an Aharonov-Bohm (AB) interferometer with a Rashba quantum dot (QD) in each of its arm by using the Green's function formalism and equation of motion (EOM) technique. Due to the interplay between quantum destructive interference and Rashba spin-orbit interaction (RSOI) in each QD, an asymmetrical transmission node splits into two spin-dependent asymmetrical transmission nodes in the transmission spectrum and, as a consequence, results in the enhancement of the spin-dependent thermoelectric effects near the spin-dependent asymmetrical transmission nodes. We also examine the evolution of spin-dependent thermoelectric effects from a symmetrical parallel geometry to a configuration in series. It is found that the spin-dependent thermoelectric effects can be enhanced by controlling the dot-electrode coupling strength. The simple analytical expressions are also derived to support our numerical results.PACS numbers: 73.63.Kv; 71.70.Ej; 72.20.Pa. PMID:22151740

Liu, Ys; Hong, Xk; Feng, Jf; Yang, Xf

2011-12-07

389

Classical Forces in Aharanov-Bohm Effects  

NASA Astrophysics Data System (ADS)

Our recent experimental and theoretical work will be reported on Aharanov-Bohm type effects [1]. This includes the experimental demonstration that the Matteucci-Pozzi phase shift is a result of a classical force [2], in contradiction to earlier claims that it is a Type-II Aharonov-Bohm effect [3]. This result is part of a larger discussion that is centered around a classical paradox. Aharonov and Rohrlich point out that this paradox is `` crucial for clarifying the entirely quantum interactions of `fluxons' and charges [4].'' Surprisingly, the Lorentz force acting on an infinite solenoid in the presence of an approaching charge is neglected [4]. Inclusion of the Lorentz force, along with the electromagnetic field momentum, leads to conservation of momentum. This motivates further investigation of the dual of the Aharanov- Bohm effect in which a neutral magnetic moment passes a charged wire. The question of sorting out which phase shifts are accompanied by classical force and which ones are not is still a topic of much debate and we report on our efforts to settle the argument. [4pt] [1] Batelaan H and Tonomura A 2009 Phys. Today 62 38--43[0pt] [2] Shawn A Hilbert et al 2011 New J. Phys. 13 093025[0pt] [3] Matteucci G and Pozzi G 1985 Phys. Rev. Lett. 54 2469[0pt] [4] Aharonov Y and Rohrlich D 2005 Quantum Paradoxes: Quantum Theory for the Perplexed (Weinheim: Wiley)

McGregor, Scot; Caprez, Adam; Batelaan, Herman; Hotovy, Ryan

2012-06-01

390

Coherent magneto-optical polarisation dynamics in a single chiral carbon nanotube  

NASA Astrophysics Data System (ADS)

We propose a theoretical framework and a dynamical model for the description of the natural optical activity and the Faraday rotation in an individual chiral single-walled carbon nanotube in the highly nonlinear coherent regime. The model is based on a discrete-level representation of the optically active states near the band edge. Chirality is modelled by a system Hamiltonian corresponding to energy-level configurations, specific for each handedness, that are mirror reflections of each other. An axial magnetic field is introduced through the Aharonov-Bohm and Zeeman energy-level shifts.The time evolution of the quantum system following an ultrafast circularly polarised optical excitation is studied using the coherent vector Maxwell pseudospin equations. Giant natural and magneto-optical gyrotropy, exceeding the one of the artificial photonic metamaterials, is numerically demonstrated for a single (5, 4) carbon nanotube and an estimate of the magnitude of the natural and magneto-chiral circular dichroism and specific optical rotatory power is obtained. The model provides a framework for the investigation of chirality and magnetic field dependence of the ultrafast nonlinear optical response of a single carbon nanotube.

Slavcheva, Gabriela; Roussignol, Philippe

2011-03-01

391

Finite temperature current densities and Bose-Einstein condensation in topologically nontrivial spaces  

NASA Astrophysics Data System (ADS)

We investigate the finite temperature expectation values of the charge and current densities for a complex scalar field with nonzero chemical potential in the background of a flat spacetime with spatial topology Rp×(S1)q. Along compact dimensions quasiperiodicity conditions with general phases are imposed on the field. In addition, we assume the presence of a constant gauge field which, due to the nontrivial topology of background space, leads to Aharonov-Bohm-like effects on the expectation values. By using the Abel-Plana-type summation formula and zeta function techniques, two different representations are provided for both the current and charge densities. The current density has nonzero components along the compact dimensions only and, in the absence of a gauge field, it vanishes for special cases of twisted and untwisted scalar fields. In the high-temperature limit, the current density and the topological part in the charge density are linear functions of the temperature. The Bose-Einstein condensation for a fixed value of the charge is discussed. The expression for the chemical potential is given in terms of the lengths of compact dimensions, temperature, and gauge field. It is shown that the parameters of the phase transition can be controlled by tuning the gauge field. The separate contributions to the charge and current densities coming from the Bose-Einstein condensate and from excited states are also investigated.

Bezerra de Mello, E. R.; Saharian, A. A.

2013-02-01

392

Intrinsic spin Hall effect and orbital Hall effect in 4d and 5d transition metals  

NASA Astrophysics Data System (ADS)

We study the intrinsic spin Hall conductivity (SHC) in various 5d transition metals (Ta, W, Re, Os, Ir, Pt, and Au) and 4d transition metals (Nb, Mo, Tc, Ru, Rh, Pd, and Ag) based on the Naval Research Laboratory tight-binding model, which enables us to perform quantitatively reliable analysis. In each metal, the obtained intrinsic SHC is independent of resistivity in the low resistive regime (?<50??cm) whereas it decreases in proportion to ?-2 in the high resistive regime. In the low resistive regime, the SHC takes a large positive value in Pt and Pd, both of which have approximately nine d electrons per ion (nd=9) . On the other hand, the SHC takes a large negative value in Ta, Nb, W, and Mo, where nd<5 . In transition metals, a conduction electron acquires the trajectory-dependent phase factor that originates from the atomic wave function. This phase factor, which is reminiscent of the Aharonov Bohm phase, is the origin of the SHC in paramagnetic metals and that of the anomalous Hall conductivity in ferromagnetic metals. Furthermore, each transition metal shows huge and positive d -orbital Hall conductivity (OHC), independent of the strength of the spin-orbit interaction. Since the OHC is much larger than the SHC, it will be possible to realize an orbitronics device made of transition metals.

Tanaka, T.; Kontani, H.; Naito, M.; Naito, T.; Hirashima, D. S.; Yamada, K.; Inoue, J.

2008-04-01

393

Superperiods in Interference of eÕ3 Laughlin Quasiparticles Encircling Filling 2/5 FractionalQuantum Hall Island  

SciTech Connect

We report experiments in a large, 2.5 {mu}m diameter Fabry-Perot quantum Hall interferometer with two tunneling constrictions. Interference fringes are observed as conductance oscillations as a function of applied magnetic field (the Aharonov-Bohm flux through the electron island) or a global backgate voltage (electronic charge in the island). Depletion is such that in the fractional quantum Hall regime, filling 1/3 current-carrying chiral edge channels pass through constrictions when the island filling is 2/5. The interferometer device is calibrated with fermionic electrons in the integer quantum Hall regime. In the fractional regime, we observe magnetic flux and charge periods 5h/e and 2e, respectively, corresponding to creation of ten e/5 Laughlin quasiparticles in the island. These results agree with our prior report of the superperiods in a much smaller interferometer device. The observed experimental periods are interpreted as imposed by anyonic statistical interaction of fractionally charged quasiparticles.

Lin, P.V.; Camino, F.; Goldman, V.J.

2009-12-01

394

Tuning the electronic states of carbon nanotube based devices under magnetic field  

NASA Astrophysics Data System (ADS)

Carbon nanotubes have already demonstrated their wide potential in nanoelectronics and optoelectronics. In our study, we demonstrate that an applied magnetic field, along with a control of the electrostatic doping, drastically modifies the electronic band structure of a carbon nanotube based transistor. Several examples will be addressed in this presentation. In a parallel configuration (B parallel to the tube axis), a quantum flux threading the tube induces a giant Aharonov-Bohm conductance modulation mediated by Schottky barriers which profile is magnetic field dependent. In the perpendicular configuration, the applied magnetic field breaks the revolution symmetry along the circumference and non conventional Landau states are expected in the high field regime. By playing with a carbon nanotube based electronic Fabry-Perot resonator, we bring evidence that the electronic transmission of the device can be modified by a transverse magnetic field. The field dependence of the resonant states of the cavity reveals the onset of the first landau state at zero energy. These experiments also enlighten the outstanding efficiency of magneto-conductance experiments to probe the electronic properties of carbon based nano-materials.

Nanot, Sebastien; Raquet, Bertrand; Escoffier, Walter; Broto, Jean-Marc; Avriller, Remi; Roche, Stephan

2009-03-01

395

Multi-terminal quantum transport through a single benzene molecule: Evidence of a molecular transistor  

NASA Astrophysics Data System (ADS)

We explore multi-terminal quantum transport through a benzene molecule threaded by an Aharonov-Bohm flux $\\phi$. A simple tight-binding model is used to describe the system and all the calculations are done based on the Green's function formalism. With a brief description of two-terminal quantum transport, we present a detailed study of three-terminal transport properties through the benzene molecule to reveal the actual mechanism of electron transport. Here we numerically compute the multi-terminal conductances, reflection probabilities and current-voltage characteristics in the aspects of molecular coupling strength and magnetic flux $\\phi$. Most significantly we observe that, the molecular system where the benzene molecule is attached to three terminals can be operated as a transistor, and we call it a molecular transistor. This aspect can be utilized in designing nano-electronic circuits and our investigation may provide a basic framework to study electron transport in any complicated multi-terminal quantum system.

Maiti, Santanu K.

2010-08-01

396

Supersymmetries of the spin-1/2 particle in the field of magnetic vortex, and anyons  

SciTech Connect

The quantum non-relativistic spin-1/2 planar systems in the presence of a perpendicular magnetic field are known to possess the N = 2 supersymmetry. We consider such a system in the field of a magnetic vortex, and find that there are just two self-adjoint extensions of the Hamiltonian that are compatible with the standard N = 2 supersymmetry. We show that only in these two cases one of the subsystems coincides with the original spinless Aharonov-Bohm model and comes accompanied by the super-partner Hamiltonian which allows a singular behavior of the wave functions. We find a family of additional, nonlocal integrals of motion and treat them together with local supercharges in the unifying framework of the tri-supersymmetry. The inclusion of the dynamical conformal symmetries leads to an infinitely generated superalgebra, that contains several representations of the superconformal osp(2 vertical bar 2) symmetry. We present the application of the results in the framework of the two-body model of identical anyons. The nontrivial contact interaction and the emerging N = 2 linear and nonlinear supersymmetries of the anyons are discussed.

Correa, Francisco, E-mail: correa@cecs.c [Centro de Estudios Cientificos (CECS), Valdivia (Chile); Falomir, Horacio, E-mail: falomir@fisica.unlp.edu.a [IFLP/CONICET - Departamento de Fisica, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, C.C. 67, (1900) La Plata (Argentina); Jakubsky, Vit, E-mail: v.jakubsky@gmail.co [Nuclear Physics Institute, ASCR, 250 68 Rez (Czech Republic); Plyushchay, Mikhail S., E-mail: mplyushc@lauca.usach.c [Departamento de Fisica, Universidad de Santiago de Chile, Casilla 307, Santiago 2 (Chile); Departamento de Fisica Teorica, Atomica y Optica, Universidad de Valladolid, 47071 Valladolid (Spain)

2010-12-15

397

Topological effects and particle physics analogies beyond the massless Dirac-Weyl fermion in graphene nanorings  

NASA Astrophysics Data System (ADS)

Armchair and zigzag edge terminations in planar hexagonal and trigonal graphene nanorings are shown to underlie one-dimensional topological states associated with distinctive energy gaps and patterns (e.g., linear dispersion of the energy of an hexagonal ring with an armchair termination versus parabolic dispersion for a zigzag terminated one) in the bands of the tight-binding spectra as a function of the magnetic field. A relativistic Dirac-Kronig-Penney model analysis of the tight-binding Aharonov-Bohm behavior reveals that the graphene quasiparticle in an armchair hexagonal ring is a condensed-matter realization of an ultrarelativistic fermion with a position-dependent mass term, akin to the zero-energy fermionic solitons with fractional charge familiar from quantum-field theory and from the theory of polyacetylene. The topological origins of the above behavior are highlighted by contrasting it with the case of a trigonal armchair ring, where we find that the quasiparticle excitations behave as familiar Dirac fermions with a constant mass. Furthermore, the spectra of a zigzag hexagonal ring correspond to the low-kinetic-energy nonrelativistic regime of a lepton-like massive fermion. A one-dimensional relativistic Lagrangian formalism coupling a fermionic and a scalar bosonic field via a Yukawa interaction, in conjunction with the breaking of the Z2 reflectional symmetry of the scalar field, is shown to unify the above dissimilar behaviors.

Romanovsky, Igor; Yannouleas, Constantine; Landman, Uzi

2013-04-01

398

Photoluminescence and magneto-optical properties of multilayered type-II ZnTe/ZnSe quantum dots  

NASA Astrophysics Data System (ADS)

Multilayered Zn-Se-Te structures grown by migration enhanced epitaxy are studied by temperature- and excitation-dependent photoluminescence (PL) as well as magneto-PL. The PL consists of two bands: a blue band, overlaid with band edge sharp lines, dominant at low temperatures and high excitation, and a green band, which appears at elevated temperature and low excitation. Upon varying excitation intensity by four orders of magnitude, the green band peak energy shifts by ˜60 meV, indicating recombination of excitons in type-II quantum dots (QDs); no significant shift is observed for the blue band. Therefore, the green emission is attributed to ZnTe/ZnSe type-II QDs, which co-exist with isoelectronic centers, responsible for the blue and band edge emissions. The existence of type-II ZnTe/ZnSe QDs is further confirmed by magneto-PL, for which the observed oscillations in the PL intensity as a function of magnetic field is explained in terms of the optical Aharonov-Bohm effect.

Kuskovsky, Igor L.; Gong, Y.; Neumark, G. F.; Tamargo, M. C.

2010-01-01

399

Snake orbits in graphene underneath an array of Ni0.80Fe0.20 nano-dots  

NASA Astrophysics Data System (ADS)

The existence of snake orbits in 2DEG formed at AlGaAs/GaAs heterojunction is theoretically predicted and experimentally demonstrated by creating a spatially inhomogeous magnetic field [1]. Due to its ambipolar nature, graphene opens up new possibilities to investigate snake orbits and other exotic phenomena by simply creating a p-n junction in a homogenous magnetic field. We have fabricated periodic arrays of Ni0.80Fe0.20 nano-dots on graphene with the dot diameter of 80 nm or 150 nm and the period of 160 nm or 300 nm, respectively. A quasi-periodic magneto-resistance oscillation is observed in the low-temperature magneto-transport measurement. We ascribe it to Aharonov-Bohm oscillations induced by snake orbits of carriers underneath the nano-dots. Due to the high work-function of Ni0.80Fe0.20, it is possible to generate local circular n-p and p--p junctions underneath the nanodots, which form the snake orbits of carriers in an external applied magnetic field. Dependence of these oscillations on temperature and carrier density and simulation work on snake orbits will be presented.[4pt] [1] J.E. Muller, Phys. Rev. Lett. 68, 385 (1992); P.D. Ye et al., Phys. Rev. Lett. 74, 3013 (1995).

Neal, Adam; Gu, Jiangjiang; Low, Tony; Ye, Peide

2011-03-01

400

Nonequilibrium transport through coupled quantum dots with electron phonon interaction  

NASA Astrophysics Data System (ADS)

We theoretically study transport properties of coupled quantum dots in parallel in the presence of electron phonon (e ph) interaction. Nonequilibrium transport under finite bias is calculated using the Keldysh Green function method. Firstly, we examine a double-dot interferometer with a penetrating magnetic flux (Aharonov Bohm phase phiv) between the two quantum dots. The differential conductance shows a sharp dip between double resonant peaks, as a function of energy levels in the quantum dots, when the two dots are equivalently coupled to external leads and 0 < phiv < ?. The e ph interaction significantly decreases the dip, reflecting an emission of phonons from one of the quantum dots. This dephasing effect is more prominent under larger bias voltage. Secondly, we study a T-shaped double-dot system in which one of the dots is connected to the external leads (dot 1) and the other is disconnected (dot 2). The differential conductance shows a dip between two resonant peaks, as in the double-dot interferometer. The dip is weakly reduced by an emission of phonons from dot 2. Phonon emission from dot 1 does not result in dephasing and hence does not influence the dip. Therefore the dip of the conductance is more robust against the e ph interaction in the T-shaped double-dot system than in the double-dot interferometer.

Ueda, Akiko; Eto, Mikio

2007-05-01

401

Cyclic hydrocarbons: nanoscopic (?)-SQUIDs?  

NASA Astrophysics Data System (ADS)

A nonperturbative method for calculating persistent currents in molecules and nanoscopic quantum rings is presented. Starting from the extended Hubbard model on a ring threaded by an Aharonov-Bohm flux, a feedback term through which the current can generate magnetic flux is added. Another extension of the Hamiltonian describes the energy stored in the internally generated field. This model is evaluated using exact diagonalization and an iterative scheme to find the minima of the free energy with respect to the current. The magnetic properties due to electron delocalization of conjugated hydrocarbons like benzene [magnetic anisotropy, magnetic susceptibility exaltation, nucleus-independent chemical shift (NICS)] — that have become important criteria for aromaticity — can be examined using this model. A possible novel mechanism for a permanent orbital magnetic moment in quantum rings analogous to the one in ?-SQUIDs is found in the framework of the proposed model. The quantum rings must satisfy two conditions to exhibit this kind of permanent orbital magnetic moment: a negative Drude weight and an inductivity above the critical level.

Himmerich, M.; van Dongen, P. G. J.; Noack, R. M.

2006-05-01

402

Fano-Rashba effect in thermoelectricity of a double quantum dot molecular junction  

PubMed Central

We examine the relation between the phase-coherent processes and spin-dependent thermoelectric effects in an Aharonov-Bohm (AB) interferometer with a Rashba quantum dot (QD) in each of its arm by using the Green's function formalism and equation of motion (EOM) technique. Due to the interplay between quantum destructive interference and Rashba spin-orbit interaction (RSOI) in each QD, an asymmetrical transmission node splits into two spin-dependent asymmetrical transmission nodes in the transmission spectrum and, as a consequence, results in the enhancement of the spin-dependent thermoelectric effects near the spin-dependent asymmetrical transmission nodes. We also examine the evolution of spin-dependent thermoelectric effects from a symmetrical parallel geometry to a configuration in series. It is found that the spin-dependent thermoelectric effects can be enhanced by controlling the dot-electrode coupling strength. The simple analytical expressions are also derived to support our numerical results. PACS numbers: 73.63.Kv; 71.70.Ej; 72.20.Pa

2011-01-01

403

Non-Abelian Discrete Gauge Theory.  

NASA Astrophysics Data System (ADS)

Gauge theory with a finite gauge group (or with a gauge group that has disconnected components) is systematically studied, with emphasis on the case of a non-Abelian gauge group. An operator formalism is developed, and an order parameter is constructed that can distinguish the various phases of a gauge theory. The non-Abelian Aharonov-Bohm interactions and holonomy interactions among cosmic string loops, vortices, and charged particles are analyzed; the detection of Cheshire charge and the transfer of charge between particles and string loops (or vortex pairs) are described. Non-Abelian gauge theory on a surface with non-trivial topology is also discussed. Interactions of vortices with "handles" on the surface are discussed in detail. The electric charge of the mouth of a "wormhole" and the magnetic flux "linked" by the wormhole are shown to be non-commuting observables. This observation is used to analyze the color electric field that results when a colored object traverses a wormhole.

Lee, Kai-Ming

404

Non-Abelian discrete gauge theory  

NASA Astrophysics Data System (ADS)

Gauge theory with a finite gauge group (or with a gauge group that has disconnected components) is systematically studied, with emphasis on the case of a non-Abelian gauge group. An operator formalism is developed, and an order parameter is constructed that can distinguish the various phases of a gauge theory. The non-Abelian Aharonov-Bohm interactions and holonomy interactions among cosmic string loops, vortices, and charged particles are analyzed; the detection of Cheshire charge and the transfer of charge between particles and string loops (or vortex pairs) are described. Non-Abelian gauge theory on a surface with non-trivial topology is also discussed. Interactions of vortices with "handles" on the surface are discussed in detail. The electric charge of the mouth of a "wormhole" and the magnetic flux "linked" by the wormhole are shown to be non-commuting observables. This observation is used to analyze the color electric field that results when a colored object traverses a wormhole.

Lee, Kai-Ming

405

Photon-assisted tunneling through open mesoscopic rings threaded by time-periodic magnetic fluxes  

NASA Astrophysics Data System (ADS)

Quantum waveguide theories have been successfully applied to various time-independent ballistic transports in mesoscopic structures, including typically the Aharonov-Bohm rings. Here, we consider the quantum transport along the one-dimensional electron structures driven by time-dependent external fields, typical the open mesoscopic rings threaded by time-periodic magnetic fluxes. Based on the well-known Floquet theorem we effectively separate the time and space variables in the transport equations. As a consequence, the time-dependence behaviors can be characterized by the so-called Floquet energies and the usual quantum waveguide theory (only involving with elastic scatterings) could be generalized to treat the situations with various inelastic scatterings between different Floquet energy sidebands. Our numerical results show clearly that, due to the interaction between the electrons and the applied oscillating fields (i.e., time-dependent fluxes), transmission resonances can be induced by means of photon emissions and absorptions. The influence of the amplitude of the additional static magnetic flux on these photon-assisted tunnelings are also investigated.

Yan, Cong Hua; Wei, Lian Fu

2010-01-01

406

Quantum network theory of computing with respect to entangled flux qubits and external perturbation  

NASA Astrophysics Data System (ADS)

In this work, we attempt to show the differences between traditional qubit-based spintronic methodology for quantum computation and the possible ballistic quantum network implementations. Flux qubits can be considered topologically similar to the persistent currents possessed as the angular momentum in Aharonov-Bohm loops, which can be coupled and thus entangled together. Since entanglement is guaranteed for coupled quantum networks, starting from a point-contacted situation, we first investigate how varying the degree of entanglement strength can affect the superposition of the four possible states for two isolated flux qubits being brought together. In general, the superposition is destroyed once the degree of entanglement is altered from the point-contact situation. However, we show that for a specific network with maximum entanglement, a Bell state situation can be produced. We then examine the effects of varying the external perturbation strength on the readout capability in quantum networks by changing the coupling strength through the cross-sectional area ratio. From the analysis of our results, we are persuaded to believe that two universally accepted components for quantum computing are not valid in the quantum network approach: the need of a weak perturbation for measurement of computational results and the requirement of fixed entanglement among qubits. We show there is an interplay between the strength of the entanglement and that of the external perturbation for high-fidelity classical readouts.

Cain, C. A.; Wu, C. H.

2013-04-01

407

An EM framework for segmentation of tissue mixtures from medical images  

Microsoft Academic Search

Image segmentation plays a major role in quantitative image analysis and computer aided detection (CAD) and diagnosis (CADx) for clinical applications. Conventional segmentation assigns a single label to each voxel, neglecting the partial volume (PV) effect. This work presents an EM (expectation maximization) framework for segmentation of tissue mixture in each voxel. Image data and tissue mixture models, EM algorithm

Zhengrong Liang; Xiang Li; Daria Eremina; Lihong Li

2003-01-01

408

The Greek EMS-SCADA: from the contractor to the user  

Microsoft Academic Search

The national electric utility of Greece has installed and put in operation a modern energy management system (EMS). This paper presents the evolution of the supervisory control and data acquisition (SCADA) system of the EMS during its two years of commercial operation. It classifies all the improvements implemented during this period in 3 areas: telecommunications, man-machine interface and core SCADA

D. T. Askounis; E. Kalfaoglou

2000-01-01

409

Comparison of EM and SEM Algorithms in Poisson Regression Models: A Simulation Study  

Microsoft Academic Search

In this work, we propose to compare two algorithms to compute maximum likelihood estimates for the parameters of a mixture Poisson regression model: the EM algorithm and the Stochastic EM algorithm. The comparison of the two procedures was done through a simulation study of the performance of these approaches on simulated data sets and real data sets. Simulation results show

Susana Faria; Gilda Soromenho

2012-01-01

410

Covariance Structure Model Fit Testing under Missing Data: An Application of the Supplemented EM Algorithm  

ERIC Educational Resources Information Center

|We apply the Supplemented EM algorithm (Meng & Rubin, 1991) to address a chronic problem with the "two-stage" fitting of covariance structure models in the presence of ignorable missing data: the lack of an asymptotically chi-square distributed goodness-of-fit statistic. We show that the Supplemented EM algorithm provides a convenient…

Cai, Li; Lee, Taehun

2009-01-01

411

Comparação entre o desempenho motor de homens e mulheres em séries múltiplas de exercícios com pesos  

Microsoft Academic Search

RESUMO A magnitude das respostas neuromusculares, metabólicas e morfológicas de homens e mulheres parece ser bastante diferen- ciada até mesmo quando esses sujeitos são submetidos a proto- colos de exercícios com pesos semelhantes. Todavia, as diferen- ças no desempenho motor entre homens e mulheres têm sido relatadas predominantemente em protocolos baseados em con- trações isométricas e isocinéticas. Assim, o objetivo

Emanuel Péricles Salvador; Edilson Serpeloni Cyrino; André Luiz Demantova Gurjão; Raphael Mendes Ritti Dias; Fábio Yuzo Nakamura; Arli Ramos de Oliveira

2005-01-01

412

Analysis of developing EM wave absorber for port logistics RFID system by using Amorphous metal powder  

Microsoft Academic Search

In this paper, we developed an EM wave absorber having the absorption ability of more than 15 dB for port logistics RFID system by using Amorphous Metal Powder. Firstly, we fabricated EM wave absorber by using Amorphous Metal Powder and CPE(Chlorinated Polyethylene) with different composition ratios 80 ? 20 wt.% and 85 ? 15 wt.%. Secondly, we designed the optimum

Dong Soo Choi; Dong Il Kim; Do Yeol Kim; Dong Han Choi

2011-01-01

413

Using the EM algorithm to train neural networks: misconceptions and a new algorithm for multiclass classification  

Microsoft Academic Search

The expectation-maximization (EM) algorithm has been of considerable interest in recent years as the basis for various algorithms in application areas of neural networks such as pattern recognition. However, there exists some misconceptions concerning its application to neural networks. In this paper, we clarify these misconceptions and consider how the EM algorithm can be adopted to train multilayer perceptron (MLP)

Shu-Kay Ng; Geoffrey John McLachlan

2004-01-01

414

Method for evaluating compatibility of commercial electromagnetic (EM) microsensor tracking systems with surgical and imaging tables  

NASA Astrophysics Data System (ADS)

Electromagnetic (EM) tracking systems have been successfully used for Surgical Navigation in ENT, cranial, and spine applications for several years. Catheter sized micro EM sensors have also been used in tightly controlled cardiac mapping and pulmonary applications. EM systems have the benefit over optical navigation systems of not requiring a line-of-sight between devices. Ferrous metals or conductive materials that are transient within the EM working volume may impact tracking performance. Effective methods for detecting and reporting EM field distortions are generally well known. Distortion compensation can be achieved for objects that have a static spatial relationship to a tracking sensor. New commercially available micro EM tracking systems offer opportunities for expanded image-guided navigation procedures. It is important to know and understand how well these systems perform with different surgical tables and ancillary equipment. By their design and intended use, micro EM sensors will be located at the distal tip of tracked devices and therefore be in closer proximity to the tables. Our goal was to define a simple and portable process that could be used to estimate the EM tracker accuracy, and to vet a large number of popular general surgery and imaging tables that are used in the United States and abroad.

Nafis, Christopher; Jensen, Vern; von Jako, Ron

2008-04-01

415

Effect of EM574 on Postprandial Pancreaticobiliary Secretion, Gastric Motor Activity, and Emptying in Conscious Dogs  

Microsoft Academic Search

EM574, an erythromycin derivative and a potentmotilin receptor agonist, is now under clinical trial asa gastroprokinetic drug. The aim of this study was toestimate the effect of EM574 on postprandial pancreaticobiliary secretion, gastric motoractivity, and emptying in conscious dogs. Five mongreldogs were prepared. Indwelling cannulas for bothinfusion of phenolsulfonphthalein and aspiration ofluminal samples were inserted into the proximal anddistal duodenum,

Toshiyuki Tanaka; Akiyoshi Mizumoto; Erito Mochiki; Hideki Suzuki; Zen Itoh; Satoshi Omura

1999-01-01

416

Mapping Coastal Wetlands Using EM and Airborne Lidar: a Texas Example  

Microsoft Academic Search

We combined EM induction and airborne lidar measurements with vegetation surveys along two transects across Mustang Island, a Texas barrier island, to examine whether EM and lidar can be used to map coastal wetlands and associated geomorphic environments. Lidar-derived elevations correlate well with National Wetland Inventory (NWI) upland, palustrine, estuarine, and marine units. Lidar can be used to map wetland

J. G. Paine; W. A. White; R. C. Smyth; J. R. Andrews; J. C. Gibeaut

2005-01-01

417

Educational Program for EMS Systems Administration and Planning. Module K: Legal Aspects of Emergency Medical Services.  

National Technical Information Service (NTIS)

An instructional module on the legal aspects of emergency medical services (EMS) is presented as part of an educational program on EMS systems administration and planning. The program consists of 23 such modules, which can be adapted to a variety of educa...

J. O. Page

1977-01-01

418

Effects of reinforced concrete walls on transmission of EM Wave in WLAN  

Microsoft Academic Search

In the condition of WLAN (wireless local area network), walls are the main obstacles in channel. Nowadays, many structures and buildings use reinforced concrete walls. These walls affect transmission of EM wave at some degree. This paper analyses the effects of some typical structural parameters of reinforced concrete walls on transmission of EM wave using a finite-difference time-domain (FDTD) solution

Liu Ping; Chen Gui; Long Yun-liang

2008-01-01

419

The mean field theory in EM procedures for blind Markov random field image restoration  

Microsoft Academic Search

A Markov random field (MRF) model-based EM (expectation-maximization) procedure for simultaneously estimating the degradation model and restoring the image is described. The MRF is a coupled one which provides continuity (inside regions of smooth gray tones) and discontinuity (at region boundaries) constraints for the restoration problem which is, in general, ill posed. The computational difficulty associated with the EM procedure

Jun Zhang

1993-01-01

420

Developing State and National Evaluation Infrastructures- Guidance for the Challenges and Opportunities of EM&V  

SciTech Connect

Evaluating the impacts and effectiveness of energy efficiency programs is likely to become increasingly important for state policymakers and program administrators given legislative mandates and regulatory goals and increasing reliance on energy efficiency as a resource. In this paper, we summarize three activities that the authors have conducted that highlight the expanded role of evaluation, measurement and verification (EM&V): a study that identified and analyzed challenges in improving and scaling up EM&V activities; a scoping study that identified issues involved in developing a national efficiency EM&V standard; and lessons learned from providing technical assistance on EM&V issues to states that are ramping up energy efficiency programs. The lessons learned are summarized in 13 EM&V issues that policy makers should address in each jurisdiction and which are listed and briefly described. The paper also discusses how improving the effectiveness and reliability of EM&V will require additional capacity building, better access to existing EM&V resources, new methods to address emerging issues and technologies, and perhaps foundational documents and approaches to improving the credibility and cross jurisdictional comparability of efficiency investments. Two of the potential foundational documents discussed are a national EM&V standard or resource guide and regional deemed savings and algorithm databases.

Schiller, Steven R.; Goldman, Charles A.

2011-06-24

421

Measurement and Analysis of L-Band (1535-1660 MHz) Electromagnetic (EM) Noise on Ships.  

National Technical Information Service (NTIS)

A program of L-band (1535-1660 MHz) electromagnetic (EM) noise measurements conducted on ships is described. The magnitude and duration of EM noise on ships is of particular significance in terms of potential radio frequency interference (RFI) to future M...

J. M. Clarke S. R. Cantor J. J. Winchus A. L. Caporale

1974-01-01

422

Características psicométricas do Maslach Burnout Inventory - Student Survey (MBI-SS) em estudantes universitários brasileiros  

Microsoft Academic Search

Resumo O Inventário de Burnout de Maslach (MBI-SS) foi projetado para avaliar a síndrome de burnout em estudantes. Este artigo analisa as características psicométricas (fidedignidade e validade de construto) do MBI-SS em uma amostra de 514 estudantes. A análise fatorial identificou três fatores correlatos às três dimensões originalmente identificadas no inventário: exaustão emocional, eficácia profissional e descrença, indicando que a

Mary Sandra Carlotto; Sheila Gonçalves Câmara

423

ANÁLISE ECONÔMICA DE SUCESSÕES DE CULTURAS PARA MILHO, COM NÍVEIS DE NITROGÊNIO EM COBERTURA  

Microsoft Academic Search

RESUMO - O milho é uma cultura presente em todas as regiões brasileiras; nos últimos anos, seus custos de produção aumentaram. Técnicas que proporcionem economia, sem perda de produtividade, podem incentivar seu cultivo, tão importante no sistema de rota- ção de culturas. Os adubos verdes são opções para a redução de custos, principalmente em relação ao nitrogênio. Utilizaram-se dados de

DENIS AUGUSTO DA SILVA; CARLOS FERREIRA DE SOUZA

424

Marginal maximum likelihood estimation of item parameters: Application of an EM algorithm  

Microsoft Academic Search

Maximum likelihood estimation of item parameters in the marginal distribution, integrating over the distribution of ability, becomes practical when computing procedures based on an EM algorithm are used. By characterizing the ability distribution empirically, arbitrary assumptions about its form are avoided. The Em procedure is shown to apply to general item-response models lacking simple sufficient statistics for ability. This includes

R. Darrell Bock; Murray Aitkin

1981-01-01

425

Estudo comparativo entre estrelas centrais de nebulosas planetárias deficientes em hidrogênio  

NASA Astrophysics Data System (ADS)

Apresentamos neste trabalho o resultado de um estudo das principais características espectrais das estrelas centrais de nebulosas planetárias (ECNP) deficientes em hidrogênio. A origem e a evolução dessas estrelas ainda constitui um problema em aberto na evolução estelar. Geralmente esses objetos são divididos em [WCE], [WCL] e [WELS]. Os tipos [WCE] e [WCL] apresentam um espectro típico de uma estrela Wolf-Rayet carbonada de população I e as [WELS] apresentam linhas fracas de carbono e oxigênio em emissão. Existem evidências que apontam a seguinte sequência evolutiva : [WCL] = > [WCE] = > [WELS] = > PG 1159 (pré anã-branca). No entanto, tal cenário apresenta falhas como por exemplo a falta de ECNP entre os tipos [WCL] e [WCE]. Baseados em uma amostra de 24 objetos obtida no telescópio de 1.52m em La Silla, Chile (acordo ESO/ON), ao longo do ano 2000, apresentamos os resultados da comparação das larguras equivalentes de diversas linhas relevantes entre os tipos [WCL], [WCE] e [WELS]. Verificamos que nossos dados estão de acordo com a sequência evolutiva. Baseado nas linhas de C IV, conseguimos dividir pela primeira vez as [WELS] em dois grupos principais. Além disso, os dados reforçam a afirmação de que as [WCE] são as estrelas que possuem a maior temperatura entre as ECNP deficientes em hidrogênio. Discutimos ainda, a escassez de dados disponíveis na literatura e a necessidade da obtenção de parametros físicos para estes objetos.

Marcolino, W. L. F.; de Araújo, F. X.

2003-08-01

426

Tumores experimentais do sistema nervoso central: padronização de modelo em roedores utilizando a linhagem 9L  

Microsoft Academic Search

RESUMO - Grande variedade de modelos experimentais foram estabelecidos em neuro-oncologia durante as últimas décadas, a fim de estudar a biologia tumoral e a eficiciência de novas drogas e novos tratamentos em gliomas malignos humanos. Embora estes modelos estejam bem caracterizados e sejam facilmente reproduzíveis e aplicáveis, há limitações quanto ao seu uso e à resposta obtida, principalmente quando utilizados

Custódio Michailowsky; Flavio Key Niura; Ângela C. do Valle; Shigueko Sonohara; Thales D'Alessandro Meneguin; Ana Maria C. Tsanaclis

2003-01-01

427

Global Convergence of the EM Algorithm for Unconstrained Latent Variable Models with Categorical Indicators  

ERIC Educational Resources Information Center

|Convergence of the expectation-maximization (EM) algorithm to a global optimum of the marginal log likelihood function for unconstrained latent variable models with categorical indicators is presented. The sufficient conditions under which global convergence of the EM algorithm is attainable are provided in an information-theoretic context by…

Weissman, Alexander

2013-01-01

428

Determining the ratio of charge to mass e\\/m for electrons by magnetic focusing  

Microsoft Academic Search

This paper describes an instrument based on Busch's method of determining e\\/m for electrons. A square-wave deflection voltage is used for deflecting an electron beam. With this instrument, one can more easily and more accurately determine e\\/m for the electron. A comparison is made experimentally and theoretically among several ways of deflecting an electron beam.

Yong-Kang Yang

1998-01-01

429

A Probabilistic Analysis of EM for Mixtures of Separated, Spherical Gaussians  

Microsoft Academic Search

We show that, given data from a mixture of k well-separated spherical Gaussians in Rd, a simple two-round variant of EM will, with high probability, learn the parameters of the Gaussians to near- optimal precision, if the dimension is high (d ln k). We relate this to previous theoretical and empirical work on the EM algorithm.

Sanjoy Dasgupta; Leonard J. Schulman

2007-01-01

430

Elogio do cotidiano: a confiança e a arte da vida social em uma comunidade amazônica  

Microsoft Academic Search

Como antropóloga (em vez de, por exemplo, filósofa)1 meu objetivo é compreender e desvelar as visões de mundo de outras pessoas, em parti- cular as dos povos indígenas da floresta tropical amazônica. A versão local que, por muitos anos, venho tentando entender pertence aos Pia- roa, um povo que vive ao longo de tributários do rio Orinoco, na Vene- zuela.

Joanna Overing

1999-01-01

431

Realce de Bordas em Imagens Digitais: Uma Abordagem por Números Fuzzy  

Microsoft Academic Search

O objetivo deste trabalho é apresentar uma nova abordagem para a extração de bordas em imagens em tons de cinza. A abordagem proposta é baseada na teoria de números fuzzy. Os números fuzzy são apropriados para lidar com incertezas, uma vez que quantificam matematica- mente termos lingüísticos do tipo \\

Inês Ap; Gasparotto Boaventura; Adilson Gonzaga

432

Simple and effective EM-based optimization procedure for microwave filters  

Microsoft Academic Search

A simple and effective computerized optimization procedure for microwave filters is discussed. The basic idea is to integrate a fast and accurate electromagnetic (EM) solver, a filter design strategy, and two different optimization algorithms. The structural parameters to be modified are then chosen with the objective of improving the interaction between the EM solver and the optimization process. A simple

J. T. Alos; M. Guglielmi

1997-01-01

433

Time-delay estimation for filtered Poisson processes using an EM-type algorithm  

Microsoft Academic Search

We develop a modified EM algorithm to estimate a nonrandom time shift parameter of an intensity associated with an inhomogeneous Poisson process Nt, whose points are only partially observed as a noise-contaminated output X of a linear time-invariant filter excited by a train of delta functions, a filtered Poisson process. The exact EM algorithm for computing the maximum likelihood time

Nikolaos Antoniadis; A. O. Hero

1994-01-01

434

Effect of Effective Microorganisms (EM®) on the Growth Parameters of Fayoumi and Horro Chicken  

Microsoft Academic Search

The study was conducted to determine growth promoter effects of Effective Microorganisms (EM) on Horro and Fayoumi chickens. This study was conducted at Agricultural Research Center and National Veterinary Institute (Debre Zeit). A total of 450 chickens (225 from each breed) were used in this study. Birds were grouped according to treatment groups: EM-treated (with feed, with water, with feed

E. wondmeneh; T. Getachew; D. Tadelle

2011-01-01

435

ITS and Transportation Safety: EMS System Data Integration to Improve Traffic Crash Emergency Response and Treatment - Phase III Report.  

National Technical Information Service (NTIS)

The transportation safety and Emergency Medical Services (EMS) literature has called for the development of better information system tools to support EMS to aid in reducing the human impact of medical emergencies. Building upon previous research by the r...

B. Hilton B. Schooley T. A. Horan

2011-01-01

436

NEW ISOTOPES OF EMANATION AND FRANCIUM: ²²³Em, ²²⁴Em, AND ²²⁴Fr  

Microsoft Academic Search

An examination of the products of the interaction of thorium with 230 ; Mev protons revealed evidence for the existence of the neutron-excess isotopes: ; Em²²³, Em²²⁴, and Fr²²⁴. The existence of these three new ; isotopes was confirmed by identification of their decay products: Ra²²³ and ; Ra²²⁴. (auth);

Bellido

1961-01-01

437

Cryo-EM modeling by the molecular dynamics flexible fitting method  

PubMed Central

The increasing power and popularity of cryo-electron (cryo-EM) microscopy in structural biology brought about the development of so-called hybrid methods, which permit the interpretation of cryo-EM density maps beyond their nominal resolution in terms of atomic models. The Cryo-EM Modeling Challenge 2010 is the first community effort to bring together developers of hybrid methods as well as cryo-EM experimentalists. Participating in the challenge, the molecular dynamics flexible fitting (MDFF) method was applied to a number of cryo-EM density maps. The results are described here with special emphasis on the use of symmetry-based restraints to improve the quality of atomic models derived from density maps of symmetric complexes; on a comparison of the stereochemical quality of atomic models resulting from different hybrid methods; and on application of MDFF to electron crystallography data.

Chan, Kwok-Yan; Trabuco, Leonardo G.; Schreiner, Eduard; Schulten, Klaus

2012-01-01

438

Fabrication and EM shielding properties of electrospining PANi/MWCNT/PEO fibrous membrane and its composite  

NASA Astrophysics Data System (ADS)

In this paper, Polyaniline-based fibrous membranes were fabricated with multi-walled carbon nanotubes and polyethylene oxide (PEO) by the electrospinning method. And then PANi/PEO/MWCNT fibrous membranes reinforced epoxy based nanocomposite was then fabricated. The morphology and electrical properties of PANi /MWCNT /PEO fibrous membrane was characterized by scanning electron microscope (SEM). The morphologies of the membranes indicate that the electrospining method can fabricate well nano structures fibrous membrane. The EM properties of the composite reinforced with the electrospining fibrous membrane were measured by vector network analyzer. The results show that the permittivity real, image parts and permeability real part of the composite increase by filling with PANI/PEO and PANI/CNT/PEO membrane. The EM shielding and absorb performance is base on the dielectric dissipation. And different membranes made of different materials show different EM parameter, and different EM shielding performance, which can be used to the EM shielding and stealth material design and fabrication.

Zhang, Zhichun; Jiang, Xueyong; Liu, Yanju; Leng, Jinsong

2012-03-01

439

A Generalized Fast Frequency Sweep Algorithm for Coupled Circuit-EM Simulations  

SciTech Connect

Frequency domain techniques are popular for analyzing electromagnetics (EM) and coupled circuit-EM problems. These techniques, such as the method of moments (MoM) and the finite element method (FEM), are used to determine the response of the EM portion of the problem at a single frequency. Since only one frequency is solved at a time, it may take a long time to calculate the parameters for wideband devices. In this paper, a fast frequency sweep based on the Asymptotic Wave Expansion (AWE) method is developed and applied to generalized mixed circuit-EM problems. The AWE method, which was originally developed for lumped-load circuit simulations, has recently been shown to be effective at quasi-static and low frequency full-wave simulations. Here it is applied to a full-wave MoM solver, capable of solving for metals, dielectrics, and coupled circuit-EM problems.

Rockway, J D; Champagne, N J; Sharpe, R M; Fasenfest, B

2004-01-14

440

Prevalence of Depression and Cognitive Impairment in Older Adult EMS Patients  

PubMed Central

Objectives To characterize the proportion of older adult ED patients with depression or cognitive impairment. To compare the prevalence of depression or cognitive impairment among ED patients arriving via EMS, as compared to other modes. Methods Community-dwelling older adults (age?60) presenting to an academic medical center ED were interviewed. Participants provided demographic and clinical information, and were evaluated for depression and cognitive impairment. Subjects arriving via EMS were compared to those arriving via other modes using the chi-square test, t-test, and the Wilcoxon rank sum test, where appropriate. Results Consent was obtained from 1342 eligible older adults; 695 (52%) arrived via EMS. The median age for those arriving via EMS was 74 (IQR 65, 82), 52% were female, 81% white. 15% of EMS patients had moderate or greater depression, as compared to 14% of patients arriving via other modes (p=0.52). 13% of EMS patients had cognitive impairment, as compared to 8% arriving via other modes (p<0.01). Depressed EMS patients frequently reported a history of depression (47%) and taking antidepressants (51%). Cognitively impaired EMS patients infrequently reported a history of dementia (16%) or taking medications for dementia (14%). Conclusions In this cohort of community-dwelling older adult ED patients depression and cognitive impairment were common. As compared to ED patients arriving by other transport means, patients arriving via EMS had similar prevalence of depression but an increased prevalence of cognitive impairment. Screening for depression and cognitive impairment by EMS providers may have value, but needs further investigation.

Shah, Manish N.; Jones, Courtney M. C.; Richardson, Thomas M.; Conwell, Yeates; Katz, Paul; Schneider, Sandra M.

2010-01-01

441

Perfil da automedicação em idosos participantes de grupos da terceira idade de uma cidade do sul do Brasil  

Microsoft Academic Search

Resumo Introdução: A automedicação tem sido objeto de muitas pesquisas e assume uma importância maior quando é realizada por idosos, pois geralmente representam um grupo polimedicado. Objetivo: Avaliar a automedicação em idosos participantes de grupos da terceira idade localizados em uma cidade do sul do Brasil. Métodos: Foi realizado um estudo transversal baseado em entrevistas com idosos participantes de grupos

Edézio Antunes Cascaes; Maria Luiza Falchetti; Dayani Galato

442

A Gentle Tutorial of the EM Algorithm and its Application to Parameter Estimation for Gaussian Mixture and Hidden Markov Models  

Microsoft Academic Search

We describe the maximum-likelihood parameter estimation problem and how the Expectation- Maximization (EM) algorithm can be used for its solution. We first describe the abstract form of the EM algorithm as it is often given in the literature. We then develop the EM pa- rameter estimation procedure for two applications: 1) finding the parameters of a mixture of Gaussian densities,

Jeff A. Bilmes

1997-01-01

443

Efeitos da monensina sobre a fermentação e sensibilidade de bactérias ruminais de bovinos sob dietas ricas em volumoso ou concentrado  

Microsoft Academic Search

RESUMO - Objetivou-se avaliar os efeitos da monensina sobre as mudanças nos padrões de fermentação e resistência à perda do potássio intracelular das bactérias ruminais provenientes de quatro bovinos recebendo dietas ricas em volumoso ou concentrado. As bactérias obtidas por centrifugação diferencial foram resuspensas em um meio pobre em potássio, no qual foi medida a perda do p otássio intracelular,

Rogério de Paula Lana; James B. Russell

2001-01-01

444

Making connections. Voice and data solutions for EMS.  

PubMed

Communications used to be so simple-1) grab the radio, 2) push and talk. Now we're besieged by a confusing assortment of technology and terms-wideband, broadband, VoIP, RoIP, ect.- and a constand thrumming imperative to achieve and improve and perfect some mystical state of full interoperability. Frankly, it can all be a bit much. With this supplement, we hope to clarify you options. We examine the importance of broadband for EMS, with its potential for larger data "pipes" between the hospital and the field; advances in the promising technologies of Voice over IP and Radio over IP; and how some systems are improving their interconnectedness and resulting operations. The jargon can be overwhelming, but the ideas are worth understanding. PMID:18814746

Careless, James; Erich, John

2008-08-01

445

Detecting particles in cryo-EM micrographs using learned features.  

PubMed

A new learning-based approach is presented for particle detection in cryo-electron micrographs using the Adaboost learning algorithm. The approach builds directly on the successful detectors developed for the domain of face detection. It is a discriminative algorithm which learns important features of the particle's appearance using a set of training examples of the particles and a set of images that do not contain particles. The algorithm is fast (10 s on a 1.3 GHz Pentium M processor), is generic, and is not limited to any particular shape or size of the particle to be detected. The method has been evaluated on a publicly available dataset of 82 cryoEM images of keyhole lympet hemocyanin (KLH). From 998 automatically extracted particle images, the 3-D structure of KLH has been reconstructed at a resolution of 23.2 A which is the same resolution as obtained using particles manually selected by a trained user. PMID:15065673

Mallick, Satya P; Zhu, Yuanxin; Kriegman, David

446

SEI: Junior E&M Course Materials - Tutorials  

NSDL National Science Digital Library

This collection of tutorials and tutorial pre-tests was constructed for a transformed junior-level Electricity and Magnetism course. These tutorials are weekly student sessions, modeled after research-validated curricula developed at the University of Washington. Using these materials in study/recitation sections, students work in small groups with the instructor as a learning coach. The materials are designed to target known student difficulties, to elicit and develop conceptual understanding and math/physics connections. They also help faculty listen to student reasoning, get a clearer sense of student ideas, and determine where they are struggling. This material was developed as part of a education research-based course transformation for junior level E&M. All of the resources developed for this course are available, sorted by individual topic and type, at http://www.compadre.org/psrc/items/Relations.cfm?ID=7891.

Pollock, Steven J.; Chasteen, Stephanie V.; Kinney, Edward; Dubson, Michael

2010-06-10

447

EM-based measurement fusion for HRR radar centroid processing  

NASA Astrophysics Data System (ADS)

This paper develops a new algorithm for high range resolution (HRR) radar centroid processing for scenarios where there are closely spaced objects. For range distributed targets with multiple discrete scatterers, HRR radars will receive detections across multiple range bins. When the resolution is very high, and the target has significant extent, then it is likely that the detections will not occur in adjacent bins. For target tracking purposes, the multiple detections must be grouped and fused to create a single object report and a range centroid estimate is computed since the detections are range distributed. With discrete scatterer separated by multiple range bins, then when closely spaced objects are present there is uncertainty about which detections should be grouped together for fusion. This paper applies the EM algorithm to form a recursive measurement fusion algorithm that segments the data into object clusters while simultaneously forming a range centroid estimate with refined bearing and elevation estimates.

Slocumb, Benjamin J.; Blair, W. Dale

2002-08-01

448

EM modeling of RF drive in DTL tank 4  

SciTech Connect

A 3-D MicroWave Studio model for the RF drive in the LANSCE DTL tank 4 has been built. Both eigensolver and time-domain modeling are used to evaluate maximal fields in the drive module and RF coupling. The LANSCE DTL tank 4 has recently been experiencing RF problems, which may or may not be related to its replaced RF coupler. This situation stimulated a request by Dan Rees to provide EM modeling of the RF drive in the DTL tank 4 (T4). Jim O'Hara provided a CAD model that was imported into the CST Microwave Studio (MWS) and after some modifications became a part of a simplified MWS model of the T4 RF drive. This technical note describes the model and presents simulation results.

Kurennoy, Sergey S. [Los Alamos National Laboratory

2012-06-19

449

Integrated EM & Thermal Simulations with Upgraded VORPAL Software  

SciTech Connect

Nuclear physics accelerators are powered by microwaves which must travel in waveguides between room-temperature sources and the cryogenic accelerator structures. The ohmic heat load from the microwaves is affected by the temperature-dependent surface resistance and in turn affects the cryogenic thermal conduction problem. Integrated EM & thermal analysis of this difficult non-linear problem is now possible with the VORPAL finite-difference time-domain simulation tool. We highlight thermal benchmarking work with a complex HOM feed-through geometry, done in collaboration with researchers at the Thomas Jefferson National Accelerator Laboratory, and discuss upcoming design studies with this emerging tool. This work is part of an effort to generalize the VORPAL framework to include generalized PDE capabilities, for wider multi-physics capabilities in the accelerator, vacuum electronics, plasma processing and fusion R&D fields, and we will also discuss user interface and algorithmic upgrades which facilitate this emerging multiphysics capability.

D.N. Smithe, D. Karipides, P. Stoltz, G. Cheng, H. Wang

2011-03-01

450

TrakEM2 Software for Neural Circuit Reconstruction  

PubMed Central

A key challenge in neuroscience is the expeditious reconstruction of neuronal circuits. For model systems such as Drosophila and C. elegans, the limiting step is no longer the acquisition of imagery but the extraction of the circuit from images. For this purpose, we designed a software application, TrakEM2, that addresses the systematic reconstruction of neuronal circuits from large electron microscopical and optical image volumes. We address the challenges of image volume composition from individual, deformed images; of the reconstruction of neuronal arbors and annotation of synapses with fast manual and semi-automatic methods; and the management of large collections of both images and annotations. The output is a neural circuit of 3d arbors and synapses, encoded in NeuroML and other formats, ready for analysis.

Cardona, Albert; Saalfeld, Stephan; Schindelin, Johannes; Arganda-Carreras, Ignacio; Preibisch, Stephan; Longair, Mark; Tomancak, Pavel; Hartenstein, Volker; Douglas, Rodney J.

2012-01-01

451

SEI: Junior E&M Course Materials - Homework  

NSDL National Science Digital Library

This homework question collection was constructed over the course of four semesters of a transformed junior-level Electricity and Magnetism course on electro- and magneto-statics. Many questions are related to textbook problems, but with added elements of explanation, sense-making, estimation or approximation, real-world connections, and multiple-representations. Not all these homework questions were used in the course design project. Some problems used include detailed instructor notes, including statistics on student performance on each homework problem assigned. The homework solutions are only available to instructors by writing the authors, Steven.Pollock@colorado.edu This material was developed as part of a education research-based course transformation for junior level E&M. All of the resources developed for this course are available, sorted by individual topic and type, at http://www.compadre.org/psrc/items/Relations.cfm?ID=7891.

Pollock, Steven J.; Chasteen, Stephanie V.

2010-06-10

452

OV-Wav: um novo pacote para análise multiescalar em astronomia  

NASA Astrophysics Data System (ADS)

Wavelets e outras formas de análise multiescalar têm sido amplamente empregadas em diversas áreas do conhecimento, sendo reconhecidamente superiores a técnicas mais tradicionais, como as análises de Fourier e de Gabor, em certas aplicações. Embora a teoria dos wavelets tenha começado a ser elaborada há quase trinta anos, seu impacto no estudo de imagens astronômicas tem sido pequeno até bem recentemente. Apresentamos um conjunto de programas desenvolvidos ao longo dos últimos três anos no Observatório do Valongo/UFRJ que possibilitam aplicar essa poderosa ferramenta a problemas comuns em astronomia, como a remoção de ruído, a detecção hierárquica de fontes e a modelagem de objetos com perfis de brilho arbitrários em condições não ideais. Este pacote, desenvolvido para execução em plataforma IDL, teve sua primeira versão concluída recentemente e está sendo disponibilizado à comunidade científica de forma aberta. Mostramos também resultados de testes controlados ao quais submetemos os programas, com a sua aplicação a imagens artificiais, com resultados satisfatórios. Algumas aplicações astrofísicas foram estudadas com o uso do pacote, em caráter experimental, incluindo a análise da componente de luz difusa em grupos compactos de galáxias de Hickson e o estudo de subestruturas de nebulosas planetárias no espaço multiescalar.

Pereira, D. N. E.; Rabaça, C. R.

2003-08-01

453

DOE-EM privatization and the 2006 Plan: Principles for procurement policies and risk management  

SciTech Connect

The Department of Energy`s Office of Environmental Remediation and Waste Management (EM) has recently set in place programs to restructure the strategic planning mechanism that will drive its clean-up schedule, The 2006 Plan, and to create a new set of business relationships with private contractors that will reduce costs--privatization. Taken together, the 2006 Plan and privatization will challenge EM to create new business practices to recast its risk management policies to support these initiatives while ensuring that its responsibilities toward the environment, human health, and worker safety (ES and H) are maintained. This paper argues that the 2006 Plan has transformed EM`s traditional, bottoms-up approach based on technical dictates to a top-down approach based on management goals--a transformation from an engineering problem to an economic problem. The 2006 Plan evolved from EM`s Ten-Year Plan, and seeks to convert the largely open-ended planning approach previously undertaken by EM to a plan bounded by time and dollars. The plan emphasizes making tradeoffs and choosing activities that deliver the most clean-up for the dollar. It also recognizes that each major player--stakeholders, DOE, OMB and Congress--has distinct interests that must be resolved if the process is to succeed. This, in turn, has created the need for a corresponding transformation in risk management practices from compliance-driven to benefit/cost-driven.

Bjornstad, D.J.; Jones, D.W.; Duemmer, C.L.

1997-08-01

454

Ondas de choque em jatos de quasares e objetos BL Lacertae  

NASA Astrophysics Data System (ADS)

Este trabalho é parte de um projeto que vem sendo realizado há dois anos no CRAAM, cujos objetivos principais são analisar e aplicar um modelo generalizado de ondas de choque em jatos relativísticos de plasma, presentes em quasares e objetos BL Lacertae, para explicar a variabilidade observada nestes objetos. O método consiste em uma decomposição de curvas de luz em séries de explosões similares, em várias freqüências, baseando-se em uma evolução espectro-temporal média das explosões. A partir da evolução média, um ajuste de cada explosão é feito com base em equações empíricas, modificando-se apenas parâmetros específicos de cada explosão. Inicialmente o modelo foi aplicado ajustando-se as curvas de luz a explosões delineadas por uma evolução do choque em três estágios, segundo a predominância do processo de emissão: síncrotron, Compton e adiabático. Entretanto, nesta nova fase de projeto, visando uma parametrização mais concisa, uma otimização do algoritmo de ajuste e uma convergência mais rápida, a formulação para cada evento foi assumida com uma evolução em apenas dois estágios: subida e descida. Isto possibilitou uma ótima delineação das curvas de luz das fontes OV236, OJ287, 3C273 e BL Lac, entre 1980 e 2000, nas freqüências 4.8, 8.0, 14.5 e 22 GHz, utilizando-se dados do Observatório da Universidade de Michigan, do Observatório do Itapetinga (Atibaia SP) e do Observatório Metsähovi. Como conclusões importantes, verificou-se que: os parâmetros ajustados descrevem o comportamento do jato; os valores do índice que descreve a expansão do jato sugerem que o mesmo se expande de uma forma não-cônica; o campo magnético é turbulento atrás da frente de choque; e as peculiaridades das explosões são devidas à influência de grandezas tais como o coeficiente da distribuição espectral de energia dos elétrons, a intensidade de campo magnético e o fator de feixe Doppler, no início do choque.

Melo, F. E.; Botti, L. C. L.

2003-08-01

455

Methodology for the development of a Canadian national EMS research agenda  

PubMed Central

Background Many health care disciplines use evidence-based decision making to improve patient care and system performance. While the amount and quality of emergency medical services (EMS) research in Canada has increased over the past two decades, there has not been a unified national plan to enable research, ensure efficient use of research resources, guide funding decisions and build capacity in EMS research. Other countries have used research agendas to identify barriers and opportunities in EMS research and define national research priorities. The objective of this project is to develop a national EMS research agenda for Canada that will: 1) explore what barriers to EMS research currently exist, 2) identify current strengths and opportunities that may be of benefit to advancing EMS research, 3) make recommendations to overcome barriers and capitalize on opportunities, and 4) identify national EMS research priorities. Methods/Design Paramedics, educators, EMS managers, medical directors, researchers and other key stakeholders from across Canada will be purposefully recruited to participate in this mixed methods study, which consists of three phases: 1) qualitative interviews with a selection of the study participants, who will be asked about their experience and opinions about the four study objectives, 2) a facilitated roundtable discussion, in which all participants will explore and discuss the study objectives, and 3) an online Delphi consensus survey, in which all participants will be asked to score the importance of each topic discovered during the interviews and roundtable as they relate to the study objectives. Results will be analyzed to determine the level of consensus achieved for each topic. Discussion A mixed methods approach will be used to address the four study objectives. We anticipate that the keys to success will be: 1) ensuring a representative sample of EMS stakeholders, 2) fostering an open and collaborative roundtable discussion, and 3) adhering to a predefined approach to measure consensus on each topic. Steps have been taken in the methodology to address each of these a priori concerns.

2011-01-01

456

Queda dos homic?dios em S?o Paulo, Brasil: uma an?lise descritiva  

PubMed Central

Objetivo Descrever a evolução da mortalidade por homicídios no Município de São Paulo segundo tipo de arma, sexo, raça ou cor, idade e áreas de exclusão/inclusão social entre 1996 e 2008. Métodos Estudo ecológico de série temporal. Os dados sobre óbitos ocorridos no Município foram coletados da base de dados do Programa de Aprimoramento das Informações sobre Mortalidade, seguindo a Classificação Internacional de Doenças, Décima Revisão (CID-10). Foram calculadas as taxas de mortalidade por homicídio (TMH) para a população total, por sexo, raça ou cor, faixa etária, tipo de arma e área de exclusão/inclusão social. As TMH foram padronizadas por idade pelo método direto. Foram calculados os percentuais de variação no período estudado. Para as áreas de exclusão/inclusão social foram calculados os riscos relativos de morte por homicídio. Resultados As TMH apresentaram queda de 73,7% entre 2001 e 2008. Foi observada redução da TMH em todos os grupos analisados, mais pronunciada em homens (?74,5%), jovens de 15 a 24 anos (?78,0%) e moradores de áreas de exclusão social extrema (?79,3%). A redução ocorreu, sobretudo, nos homicídios cometidos com armas de fogo (?74,1%). O risco relativo de morte por homicídio nas áreas de exclusão extrema (tendo como referência áreas com algum grau de exclusão social) foi de 2,77 em 1996, 3,9 em 2001 e 2,13 em 2008. Nas áreas de alta exclusão social, o risco relativo foi de 2,07 em 1996 e 1,96 em 2008. Conclusões Para compreender a redução dos homicídios no Município, é importante considerar macrodeterminantes que atingem todo o Município e todos os subgrupos populacionais e microdeterminantes que atuam localmente, influenciando de forma diferenciada os homicídios com armas de fogo e os homicídios na população jovem, no sexo masculino e em residentes em áreas de alta exclusão social.

Peres, Maria Fernanda Tourinho; Vicentin, Diego; Nery, Marcelo Batista; de Lima, Renato Sergio; de Souza, Edinilsa Ramos; Cerda, Magdalena; Cardia, Nancy; Adorno, e Sergio

2012-01-01

457

A row-action alternative to the EM algorithm for maximizing likelihoods in emission tomography  

SciTech Connect

The maximum likelihood (ML) approach to estimating the radioactive distribution in the body cross section has become very popular among researchers in emission computed tomography (ECT) since it has been shown to provide very good images compared to those produced with the conventional filtered backprojection (FBP) algorithm. The expectation maximization (EM) algorithm is an often-used iterative approach for maximizing the Poisson likelihood in ECT because of its attractive theoretical and practical properties. Its major disadvantage is that, due to its slow rate of convergence, a large amount of computation is often required to achieve an acceptable image. In this paper the authors present a row-action maximum likelihood algorithm (RAMLA) as an alterative to the EM algorithm for maximizing the Poisson likelihood in ECT. The authors deduce the convergence properties of this algorithm and demonstrate by way of computer simulations that the early iterates of RAMLA increase the Poisson likelihood in ECT at an order of magnitude faster than the standard EM algorithm. Specifically, they show that, from the point of view of measuring total radionuclide uptake in simulated brain phantoms, iterations 1, 2, 3, and 4 of RAMLA perform at least as well as iterations 45, 60, 70, and 80, respectively, of EM. Moreover, they show that iterations 1,2,3, and 4 of RAMLA achieve comparable likelihood values as iterations 45, 60, 70, and 80, respectively, of EM. They also present a modified version of a recent fast ordered subsets EM (OS-EM) algorithm and show that RAMLA is a special case of this modified OS-EM. Furthermore, they show that the modification converges to a ML solution whereas the standard OS-EM does not.

Browne, J. [Advanced Research and Applications Corp., Sunnyvale, CA (United States); Pierro, A.R. de [State Univ. of Campinas, Sao Paulo (Brazil). Dept. of Applied Mathematics

1996-10-01

458

Effects of integrated use of organic and inorganic nutrient sources with effective microorganisms (EM) on seed cotton yield in Pakistan.  

PubMed

A field experiment was conducted to determine the effects of integrated use of organic and inorganic nutrient sources with effective microorganisms on growth and yield of cotton. Treatments included: control; organic materials (OM); effective microorganisms (EM); OM+EM; mineral NPK (170:85:60 kg); 1/2 mineral NPK+EM; 1/2 mineral NPK+OM+EM and mineral NPK+OM+EM. OM and EM alone did not increase the yield and yield attributing components significantly but integrated use of both resulted in a 44% increase over control. Application of NPK in combination with OM and EM resulted in the highest seed cotton yield (2470 kg ha-1). Integrated use of OM+EM with 1/2 mineral NPK yielded 2091 kg ha-1, similar to the yield (2165 kg ha-1) obtained from full recommended NPK, indicating that this combination can substitute for 85 kg N ha-1. Combination of both N sources with EM also increased the concentrations of NPK in plants. Economic analysis suggested the use of 1/2 mineral NPK with EM+OM saves the mineral N fertilizer by almost 50% compared to a system with only mineral NPK application. This study indicated that application of EM increased the efficiency of both organic and mineral nutrient sources but alone was ineffective in increasing yield. PMID:16023343

Khaliq, Abdul; Abbasi, M Kaleem; Hussain, Tahir

2005-07-14

459

Effects of caffeine or EDTA post-treatment on EMS mutagenesis in soybean  

Microsoft Academic Search

Seeds of soybean cultivar LD4 were mutagenically treated with EMS (0.3, 0.5, 0.6, 0.9, 0.5 and 1.8%) for 3 h only or plus caffeine (50 mM) or EDTA (1 mM) post-treatment for 5 h. The experimental results indicated that: (1) of the different concentrations of EMS treatment, the M2 mutation frequency induced with 0.6% EMS was the highest (9.7%). When

Zhu Baoge; Gu Aiqiu; Deng Xiangdong; Deng Yuxuan; Lu Zixian

1995-01-01

460

EMS Provider Assessment of Vehicle Damage Compared to a Professional Crash Reconstructionist  

PubMed Central

Objective To determine the accuracy of EMS provider assessments of motor vehicle damage, when compared to measurements made by a professional crash reconstructionist. Methods EMS providers caring for adult patients injured during a motor vehicle crash and transported to the regional trauma center in a midsized community were interviewed upon ED arrival. The interview collected provider estimates of crash mechanism of injury. For crashes that met a preset severity threshold, the vehicle’s owner was asked to consent to having a crash reconstructionist assess their vehicle. The assessment included measuring intrusion and external auto deformity. Vehicle damage was used to calculate change in velocity. Paired t-test and correlation were used to compare EMS estimates and investigator derived values. Results 91 vehicles were enrolled; of these 58 were inspected and 33 were excluded because the vehicle was not accessible. 6 vehicles had multiple patients. Therefore, a total of 68 EMS estimates were compared to the inspection findings. Patients were 46% male, 28% admitted to hospital, and 1% died. Mean EMS estimated deformity was 18” and mean measured was 14”. Mean EMS estimated intrusion was 5” and mean measured was 4”. EMS providers and the reconstructionist had 67% agreement for determination of external auto deformity (kappa 0.26), and 88% agreement for determination of intrusion (kappa 0.27) when the 1999 Field Triage Decision Scheme Criteria were applied. Mean EMS estimated speed prior to the crash was 48 mph±13 and mean reconstructionist estimated change in velocity was 18 mph±12 (correlation -0.45). EMS determined that 19 vehicles had rolled over while the investigator identified 18 (kappa 0.96). In 55 cases EMS and the investigator agreed on seatbelt use, for the remaining 13 cases there was disagreement (5) or the investigator was unable to make a determination (8) (kappa 0.40). Conclusions This study found that EMS providers are good at estimating rollover. Vehicle intrusion, deformity, and seatbelt use appear to be more difficult to estimate with only fair agreement with the crash reconstructionist. As expected, the EMS provider estimated speed prior to the crash does not appear to be a reasonable proxy for change in velocity.

Lerner, E. Brooke; Cushman, Jeremy T.; Blatt, Alan; Lawrence, Richard; Shah, Manish N.; Swor, Robert; Brasel, Karen; Jurkovich, Gregory J.

2011-01-01

461

Vibrational symmetry classification and torsional tunneling splitting patterns in G6(EM), G12, and G36(EM) molecules  

NASA Astrophysics Data System (ADS)

It is shown that the torsional splitting patterns in methanol-like molecules, with the excitation of small amplitude vibrational modes in the methyl group, are determined by mechanisms that can be formulated in an almost identical fashion to that for ethane-like molecules. This is achieved by treating ethane-like molecules by the internal axis method (IAM) and methanol-like molecules by the principal axis method (PAM) or rho-axis method (RAM). Using the extended molecular groups G6(EM) or C6v(M) for methanol and G36(EM) for ethane, vibrations perpendicular to the internal rotation axis are conveniently described by modes of higher degeneracy (E for methanol and Gs for ethane) in the absence of coupling of top and frame. Head-tail coupling operators, except the cos-type barrier terms, lower the degeneracy, causing vibrational splittings. Coupled vibrational pairs with torsional splitting patterns that we call 'regular' (pure A1, A2 pairs for methanol and pure E1d, E2d pairs for ethane) or 'inverted' (pure B1, B2 pairs for methanol and pure E1s, E2s pairs for ethane) can be formed as limit cases. Actual splitting patterns occur between the above limits, and are basically determined by torsional Coriolis coupling, which can tune more or less to resonance pairs of uncoupled basis levels linked by specific head-tail coupling operators. The inversion of torsional splitting patterns, observed in perpendicular vibrational modes of the methyl group of methanol, can be predicted by these theoretical considerations. Similar considerations apply to molecules of G12 symmetry.

Lattanzi, F.; di Lauro, C.

462

Abscesso pulmonar de aspiração: dados diagnósticos e resultados terapêuticos em 241 casos Primary lung abscess: diagnostic findings and results of the treatment in 241 cases  

Microsoft Academic Search

SINOPSE São mostrados aspectos diagnósticos e terapêuticos do abscesso pulmonar de aspiração. No período de 1968 a 2002 foram reunidos e estudados 241 casos da doença - 199 em homens e 42 em mulheres, com média de idade de 41,3 anos. Em 69% dos pacientes esteve presente a ingestão de álcool e em 64% o hábito tabágico. Tosse, expectoração, febre

ÂNGELA P. ZIEGLER; José S. Moreira; Rua Carlos Von Koseritz

463

7. PHOTOCOPY, ELEVATIONS FOR E.M. BARRACKS, N.C.O. AND OFFICERS QUARTERS. ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

7. PHOTOCOPY, ELEVATIONS FOR E.M. BARRACKS, N.C.O. AND OFFICERS QUARTERS. - NIKE Missile Base SL-40, Barracks No. 1, North end of base, southest of Basketball Court & northwest of Barracks No. 2, Hecker, Monroe County, IL

464

Carbon Nanotube Fiber-Reinforced Composite Structures for EM and Lightning Strike Protection.  

National Technical Information Service (NTIS)

A method for repairing fiber-reinforced composite structures while maintaining original EM and lightning protection using carbon nanotubes, fibers, and thermoset resins is disclosed. According to one embodiment of the invention, the method comprises prepa...

D. H. Landis J. L. Conroy J. W. Piche P. J. Glatkowski

2005-01-01

465

Educational Program for EMS Systems Administration and Planning. Module Q: Personnel Management.  

National Technical Information Service (NTIS)

An instructional module on personnel management is presented as part of an educational program for emergency medical services (EMS) systems administration and planning. The program consists of 23 such modules, which can be adapted to a variety of educatio...

E. C. Murphy

1977-01-01

466