The role of ion optics modeling in the design and development of ion mobility spectrometers

NASA Astrophysics Data System (ADS)

Griffin, Matthew T.

2005-05-01

Detection of trace gases by ion mobility spectroscopy (IMS) has become common in recent years. In fact, IMS devices are the most commonly deployed military devices for the detection of classical chemical warfare agents (CWA). IMS devices are protecting the homeland by aiding first responders in the identification of toxic industrial chemicals (TICs) and providing explosive and narcotic screening systems. Spurred by the asymmetric threat posed by new threat agents and the ever expanding list of toxic chemicals, research in the development, improvement, and optimization of IMS systems has increased. Much of the research is focused on increasing the sensitivity and selectivity of IMS systems. Ion optics is a large area of study in the field of mass spectrometry, but has been mostly overlooked in the design and development of IMS systems. Ion optics provides insight into particle trajectories, duty cycle, and efficiency of these systems. This paper will outline the role that ion optics can have in the development of IMS systems and introduce the trade space for traditional IMS as well as differential mobility spectroscopy.

Theory of the stopping power of fast multicharged ions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yudin, G.L.

1991-12-01

The processes of Coulomb excitation and ionization of atoms by a fast charged particle moving along a classical trajectory are studied. The target electrons are described by the Dirac equation, while the field of the incident particle is described by the Lienard-Wiechert potential. The theory is formulated in the form most convenient for investigation of various characteristics of semiclassical atomic collisions. The theory of sudden perturbations, which is valid at high enough velocities for a high projectile charge, is employed to obtain probabilities and cross sections of the Coulomb excitation and ionization of atomic hydrogen by fast multiply charged ions.more » Based on the semiclassical sudden Born approximation, the ionization cross section and the average electronic energy loss of a fast ion in a single collision with an atom are investigated over a wide specific energy range from 500 keV/amu to 50 MeV/amu.« less

Nonsequential double ionization with mid-infrared laser fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Ying -Bin; Wang, Xu; Yu, Ben -Hai

Using a full-dimensional Monte Carlo classical ensemble method, we present a theoretical study of atomic nonsequential double ionization (NSDI) with mid-infrared laser fields, and compare with results from near-infrared laser fields. Unlike single-electron strong-field processes, double ionization shows complex and unexpected interplays between the returning electron and its parent ion core. As a result of these interplays, NSDI for mid-IR fields is dominated by second-returning electron trajectories, instead of first-returning trajectories for near-IR fields. Here, some complex NSDI channels commonly happen with near-IR fields, such as the recollision-excitation-with-subsequent-ionization (RESI) channel, are virtually shut down by mid-IR fields. Besides, the finalmore » energies of the two electrons can be extremely unequal, leading to novel e-e momentum correlation spectra that can be measured experimentally.« less

Nonsequential double ionization with mid-infrared laser fields

DOE PAGES

Li, Ying -Bin; Wang, Xu; Yu, Ben -Hai; ...

2016-11-18

Using a full-dimensional Monte Carlo classical ensemble method, we present a theoretical study of atomic nonsequential double ionization (NSDI) with mid-infrared laser fields, and compare with results from near-infrared laser fields. Unlike single-electron strong-field processes, double ionization shows complex and unexpected interplays between the returning electron and its parent ion core. As a result of these interplays, NSDI for mid-IR fields is dominated by second-returning electron trajectories, instead of first-returning trajectories for near-IR fields. Here, some complex NSDI channels commonly happen with near-IR fields, such as the recollision-excitation-with-subsequent-ionization (RESI) channel, are virtually shut down by mid-IR fields. Besides, the finalmore » energies of the two electrons can be extremely unequal, leading to novel e-e momentum correlation spectra that can be measured experimentally.« less

Fast Ion Mesurements in LAPD

NASA Astrophysics Data System (ADS)

Zhao, L.; Boehmer, H.; Edrich, D.; Heidbrink, W.; McWilliams, R.; Zimmerman, D.; Leneman, D.

2003-10-01

To study fast-ion transport, a 3-cm diameter, 17 MHZ, ˜80W, ˜3 mA argon source launches ˜500 eV ions in the LArge Plasma Device (LAPD). The beam is diagnosed with a gridded analyzer and, on a test stand at Irvine, laser-induced fluorescence (LIF). Neutral scattering is important near the source. The measured beam energy can be more than 100 eV larger than the accelerating voltage applied to the extraction grids. In LAPD the profile of the pulsed ion beam is measured at various axial locations between z=0.3-6.0 m from the source. When the beam velocity is parallel to the solenoidal field (0^o) evidence of peristaltic focusing, beam attenuation, and radial scattering is observed. At an angle of 22^o with respect to the field the beam follows the expected helical trajectory. Three meters axially from the source strong attenuation and elongation of the beam in the direction of the gyro-angle are observed. The data are compared with classical Coulomb and neutral scattering theory.

The Biharmonic Oscillator and Asymmetric Linear Potentials: From Classical Trajectories to Momentum-Space Probability Densities in the Extreme Quantum Limit

ERIC Educational Resources Information Center

Ruckle, L. J.; Belloni, M.; Robinett, R. W.

2012-01-01

The biharmonic oscillator and the asymmetric linear well are two confining power-law-type potentials for which complete bound-state solutions are possible in both classical and quantum mechanics. We examine these problems in detail, beginning with studies of their trajectories in position and momentum space, evaluation of the classical probability…

Theoretical Studies in Chemical Kinetics - Annual Report, 1970.

DOE R&D Accomplishments Database

Karplus, Martin

1970-10-01

The research performed includes (a) Alkali-Halide, Alkali-Halide (MX, M?X?) Exchange Reactions; (b) Inversion Problem; (c) Quantum Mechanics of Scattering Processes, (d) Transition State Analysis of Classical Trajectories, (e) Differential Cross Sections from Classical Trajectories; and (f) Other Studies.

Shortcuts to adiabaticity by counterdiabatic driving for trapped-ion displacement in phase space

PubMed Central

An, Shuoming; Lv, Dingshun; del Campo, Adolfo; Kim, Kihwan

2016-01-01

The application of adiabatic protocols in quantum technologies is severely limited by environmental sources of noise and decoherence. Shortcuts to adiabaticity by counterdiabatic driving constitute a powerful alternative that speed up time-evolution while mimicking adiabatic dynamics. Here we report the experimental implementation of counterdiabatic driving in a continuous variable system, a shortcut to the adiabatic transport of a trapped ion in phase space. The resulting dynamics is equivalent to a ‘fast-motion video' of the adiabatic trajectory. The robustness of this protocol is shown to surpass that of competing schemes based on classical local controls and Fourier optimization methods. Our results demonstrate that shortcuts to adiabaticity provide a robust speedup of quantum protocols of wide applicability in quantum technologies. PMID:27669897

Charge Transfer in Collisions of S^4+ with H.

NASA Astrophysics Data System (ADS)

Stancil, P. C.; Turner, A. R.; Cooper, D. L.; Schultz, D. R.; Rakovic, M. J.; Fritsch, W.; Zygelman, B.

2001-05-01

Charge transfer processes due to collisions of ground state S^4+ ions with atomic hydrogen were investigated for energies between 1 meV/u and 10 MeV/u using the quantum-mechanical molecular-orbital close-coupling (MOCC), atomic-orbital close-coupling, classical trajectory Monte Carlo (CTMC), and continuum distorted wave methods. The MOCC calculations utilized ab initio adiabatic potentials and nonadiabatic radial coupling matrix elements obtained with the spin-coupled valence-bond approach. A number of variants of the CTMC approach were explored, including different momentum and radial distributions for the initial state, as well as effective charge and quantum-defect models to determine the corresponding quantum state after capture into final partially-stripped S^3+ excited classical states. Hydrogen target isotope effects were explored and rate coefficients for temperatures between 100 and 10^6 K will be presented

Wigner phase space distribution via classical adiabatic switching

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bose, Amartya; Makri, Nancy; Department of Physics, University of Illinois, 1110 W. Green Street, Urbana, Illinois 61801

2015-09-21

Evaluation of the Wigner phase space density for systems of many degrees of freedom presents an extremely demanding task because of the oscillatory nature of the Fourier-type integral. We propose a simple and efficient, approximate procedure for generating the Wigner distribution that avoids the computational difficulties associated with the Wigner transform. Starting from a suitable zeroth-order Hamiltonian, for which the Wigner density is available (either analytically or numerically), the phase space distribution is propagated in time via classical trajectories, while the perturbation is gradually switched on. According to the classical adiabatic theorem, each trajectory maintains a constant action if themore » perturbation is switched on infinitely slowly. We show that the adiabatic switching procedure produces the exact Wigner density for harmonic oscillator eigenstates and also for eigenstates of anharmonic Hamiltonians within the Wentzel-Kramers-Brillouin (WKB) approximation. We generalize the approach to finite temperature by introducing a density rescaling factor that depends on the energy of each trajectory. Time-dependent properties are obtained simply by continuing the integration of each trajectory under the full target Hamiltonian. Further, by construction, the generated approximate Wigner distribution is invariant under classical propagation, and thus, thermodynamic properties are strictly preserved. Numerical tests on one-dimensional and dissipative systems indicate that the method produces results in very good agreement with those obtained by full quantum mechanical methods over a wide temperature range. The method is simple and efficient, as it requires no input besides the force fields required for classical trajectory integration, and is ideal for use in quasiclassical trajectory calculations.« less

Interpolating moving least-squares methods for fitting potential energy surfaces: using classical trajectories to explore configuration space.

PubMed

Dawes, Richard; Passalacqua, Alessio; Wagner, Albert F; Sewell, Thomas D; Minkoff, Michael; Thompson, Donald L

2009-04-14

We develop two approaches for growing a fitted potential energy surface (PES) by the interpolating moving least-squares (IMLS) technique using classical trajectories. We illustrate both approaches by calculating nitrous acid (HONO) cis-->trans isomerization trajectories under the control of ab initio forces from low-level HF/cc-pVDZ electronic structure calculations. In this illustrative example, as few as 300 ab initio energy/gradient calculations are required to converge the isomerization rate constant at a fixed energy to approximately 10%. Neither approach requires any preliminary electronic structure calculations or initial approximate representation of the PES (beyond information required for trajectory initial conditions). Hessians are not required. Both approaches rely on the fitting error estimation properties of IMLS fits. The first approach, called IMLS-accelerated direct dynamics, propagates individual trajectories directly with no preliminary exploratory trajectories. The PES is grown "on the fly" with the computation of new ab initio data only when a fitting error estimate exceeds a prescribed tight tolerance. The second approach, called dynamics-driven IMLS fitting, uses relatively inexpensive exploratory trajectories to both determine and fit the dynamically accessible configuration space. Once exploratory trajectories no longer find configurations with fitting error estimates higher than the designated accuracy, the IMLS fit is considered to be complete and usable in classical trajectory calculations or other applications.

Zero-point energy constraint in quasi-classical trajectory calculations.

PubMed

Xie, Zhen; Bowman, Joel M

2006-04-27

A method to constrain the zero-point energy in quasi-classical trajectory calculations is proposed and applied to the Henon-Heiles system. The main idea of this method is to smoothly eliminate the coupling terms in the Hamiltonian as the energy of any mode falls below a specified value.

Zero-Point Energy Constraint for Unimolecular Dissociation Reactions. Giving Trajectories Multiple Chances To Dissociate Correctly.

PubMed

Paul, Amit K; Hase, William L

2016-01-28

A zero-point energy (ZPE) constraint model is proposed for classical trajectory simulations of unimolecular decomposition and applied to CH4* → H + CH3 decomposition. With this model trajectories are not allowed to dissociate unless they have ZPE in the CH3 product. If not, they are returned to the CH4* region of phase space and, if necessary, given additional opportunities to dissociate with ZPE. The lifetime for dissociation of an individual trajectory is the time it takes to dissociate with ZPE in CH3, including multiple possible returns to CH4*. With this ZPE constraint the dissociation of CH4* is exponential in time as expected for intrinsic RRKM dynamics and the resulting rate constant is in good agreement with the harmonic quantum value of RRKM theory. In contrast, a model that discards trajectories without ZPE in the reaction products gives a CH4* → H + CH3 rate constant that agrees with the classical and not quantum RRKM value. The rate constant for the purely classical simulation indicates that anharmonicity may be important and the rate constant from the ZPE constrained classical trajectory simulation may not represent the complete anharmonicity of the RRKM quantum dynamics. The ZPE constraint model proposed here is compared with previous models for restricting ZPE flow in intramolecular dynamics, and connecting product and reactant/product quantum energy levels in chemical dynamics simulations.

Temperature-dependent kinetic measurements and quasi-classical trajectory studies for the OH(+) + H2/D2 → H2O(+)/HDO(+) + H/D reactions.

PubMed

Martinez, Oscar; Ard, Shaun G; Li, Anyang; Shuman, Nicholas S; Guo, Hua; Viggiano, Albert A

2015-09-21

We have measured the temperature-dependent kinetics for the reactions of OH(+) with H2 and D2 using a selected ion flow tube apparatus. Reaction occurs via atom abstraction to result in H2O(+)/HDO(+) + H/D. Room temperature rate coefficients are in agreement with prior measurements and resulting temperature dependences are T(0.11) for the hydrogen and T(0.25) for the deuterated reactions. This work is prompted in part by recent theoretical work that mapped a full-dimensional global potential energy surface of H3O(+) for the OH(+) + H2 → H + H2O(+) reaction [A. Li and H. Guo, J. Phys. Chem. A 118, 11168 (2014)], and reported results of quasi-classical trajectory calculations, which are extended to a wider temperature range and initial rotational state specification here. Our experimental results are in excellent agreement with these calculations which accurately predict the isotope effect in addition to an enhancement of the reaction rate constant due to the molecular rotation of OH(+). The title reaction is of high importance to astrophysical models, and the temperature dependence of the rate coefficients determined here should now allow for better understanding of this reaction at temperatures more relevant to the interstellar medium.

Electron capture in collisions of S4+ with atomic hydrogen

NASA Astrophysics Data System (ADS)

Stancil, P. C.; Turner, A. R.; Cooper, D. L.; Schultz, D. R.; Rakovic, M. J.; Fritsch, W.; Zygelman, B.

2001-06-01

Charge transfer processes due to collisions of ground state S4+(3s2 1S) ions with atomic hydrogen are investigated for energies between 1 meV u-1 and 10 MeV u-1 using the quantum mechanical molecular-orbital close-coupling (MOCC), atomic-orbital close-coupling, classical trajectory Monte Carlo (CTMC) and continuum distorted wave methods. The MOCC calculations utilize ab initio adiabatic potentials and nonadiabatic radial coupling matrix elements obtained with the spin-coupled valence-bond approach. A number of variants of the CTMC approach were explored, including different momentum and radial distributions for the initial state, as well as effective charge and quantum-defect models to determine the corresponding quantum state after capture into final partially stripped S3+ excited classical states. Hydrogen target isotope effects are explored and rate coefficients for temperatures between 100 and 106 K are also presented.

Dynamically biased statistical model for the ortho/para conversion in the H2 + H3+ → H3+ + H2 reaction.

PubMed

Gómez-Carrasco, Susana; González-Sánchez, Lola; Aguado, Alfredo; Sanz-Sanz, Cristina; Zanchet, Alexandre; Roncero, Octavio

2012-09-07

In this work we present a dynamically biased statistical model to describe the evolution of the title reaction from statistical to a more direct mechanism, using quasi-classical trajectories (QCT). The method is based on the one previously proposed by Park and Light [J. Chem. Phys. 126, 044305 (2007)]. A recent global potential energy surface is used here to calculate the capture probabilities, instead of the long-range ion-induced dipole interactions. The dynamical constraints are introduced by considering a scrambling matrix which depends on energy and determine the probability of the identity/hop/exchange mechanisms. These probabilities are calculated using QCT. It is found that the high zero-point energy of the fragments is transferred to the rest of the degrees of freedom, what shortens the lifetime of H(5)(+) complexes and, as a consequence, the exchange mechanism is produced with lower proportion. The zero-point energy (ZPE) is not properly described in quasi-classical trajectory calculations and an approximation is done in which the initial ZPE of the reactants is reduced in QCT calculations to obtain a new ZPE-biased scrambling matrix. This reduction of the ZPE is explained by the need of correcting the pure classical level number of the H(5)(+) complex, as done in classical simulations of unimolecular processes and to get equivalent quantum and classical rate constants using Rice-Ramsperger-Kassel-Marcus theory. This matrix allows to obtain a ratio of hop/exchange mechanisms, α(T), in rather good agreement with recent experimental results by Crabtree et al. [J. Chem. Phys. 134, 194311 (2011)] at room temperature. At lower temperatures, however, the present simulations predict too high ratios because the biased scrambling matrix is not statistical enough. This demonstrates the importance of applying quantum methods to simulate this reaction at the low temperatures of astrophysical interest.

Dynamically biased statistical model for the ortho/para conversion in the H2+H3+ --> H3++ H2 reaction

NASA Astrophysics Data System (ADS)

Gómez-Carrasco, Susana; González-Sánchez, Lola; Aguado, Alfredo; Sanz-Sanz, Cristina; Zanchet, Alexandre; Roncero, Octavio

2012-09-01

In this work we present a dynamically biased statistical model to describe the evolution of the title reaction from statistical to a more direct mechanism, using quasi-classical trajectories (QCT). The method is based on the one previously proposed by Park and Light [J. Chem. Phys. 126, 044305 (2007), 10.1063/1.2430711]. A recent global potential energy surface is used here to calculate the capture probabilities, instead of the long-range ion-induced dipole interactions. The dynamical constraints are introduced by considering a scrambling matrix which depends on energy and determine the probability of the identity/hop/exchange mechanisms. These probabilities are calculated using QCT. It is found that the high zero-point energy of the fragments is transferred to the rest of the degrees of freedom, what shortens the lifetime of H_5^+ complexes and, as a consequence, the exchange mechanism is produced with lower proportion. The zero-point energy (ZPE) is not properly described in quasi-classical trajectory calculations and an approximation is done in which the initial ZPE of the reactants is reduced in QCT calculations to obtain a new ZPE-biased scrambling matrix. This reduction of the ZPE is explained by the need of correcting the pure classical level number of the H_5^+ complex, as done in classical simulations of unimolecular processes and to get equivalent quantum and classical rate constants using Rice-Ramsperger-Kassel-Marcus theory. This matrix allows to obtain a ratio of hop/exchange mechanisms, α(T), in rather good agreement with recent experimental results by Crabtree et al. [J. Chem. Phys. 134, 194311 (2011), 10.1063/1.3587246] at room temperature. At lower temperatures, however, the present simulations predict too high ratios because the biased scrambling matrix is not statistical enough. This demonstrates the importance of applying quantum methods to simulate this reaction at the low temperatures of astrophysical interest.

Entangled trajectories Hamiltonian dynamics for treating quantum nuclear effects

NASA Astrophysics Data System (ADS)

Smith, Brendan; Akimov, Alexey V.

2018-04-01

A simple and robust methodology, dubbed Entangled Trajectories Hamiltonian Dynamics (ETHD), is developed to capture quantum nuclear effects such as tunneling and zero-point energy through the coupling of multiple classical trajectories. The approach reformulates the classically mapped second-order Quantized Hamiltonian Dynamics (QHD-2) in terms of coupled classical trajectories. The method partially enforces the uncertainty principle and facilitates tunneling. The applicability of the method is demonstrated by studying the dynamics in symmetric double well and cubic metastable state potentials. The methodology is validated using exact quantum simulations and is compared to QHD-2. We illustrate its relationship to the rigorous Bohmian quantum potential approach, from which ETHD can be derived. Our simulations show a remarkable agreement of the ETHD calculation with the quantum results, suggesting that ETHD may be a simple and inexpensive way of including quantum nuclear effects in molecular dynamics simulations.

Continuous quantum measurement and the quantum to classical transition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhattacharya, Tanmoy; Habib, Salman; Jacobs, Kurt

2003-04-01

While ultimately they are described by quantum mechanics, macroscopic mechanical systems are nevertheless observed to follow the trajectories predicted by classical mechanics. Hence, in the regime defining macroscopic physics, the trajectories of the correct classical motion must emerge from quantum mechanics, a process referred to as the quantum to classical transition. Extending previous work [Bhattacharya, Habib, and Jacobs, Phys. Rev. Lett. 85, 4852 (2000)], here we elucidate this transition in some detail, showing that once the measurement processes that affect all macroscopic systems are taken into account, quantum mechanics indeed predicts the emergence of classical motion. We derive inequalities thatmore » describe the parameter regime in which classical motion is obtained, and provide numerical examples. We also demonstrate two further important properties of the classical limit: first, that multiple observers all agree on the motion of an object, and second, that classical statistical inference may be used to correctly track the classical motion.« less

Vectorization of a classical trajectory code on a floating point systems, Inc. Model 164 attached processor.

PubMed

Kraus, Wayne A; Wagner, Albert F

1986-04-01

A triatomic classical trajectory code has been modified by extensive vectorization of the algorithms to achieve much improved performance on an FPS 164 attached processor. Extensive timings on both the FPS 164 and a VAX 11/780 with floating point accelerator are presented as a function of the number of trajectories simultaneously run. The timing tests involve a potential energy surface of the LEPS variety and trajectories with 1000 time steps. The results indicate that vectorization results in timing improvements on both the VAX and the FPS. For larger numbers of trajectories run simultaneously, up to a factor of 25 improvement in speed occurs between VAX and FPS vectorized code. Copyright © 1986 John Wiley & Sons, Inc.

Line mixing effects in isotropic Raman spectra of pure N{sub 2}: A classical trajectory study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ivanov, Sergey V., E-mail: serg.vict.ivanov@gmail.com; Boulet, Christian; Buzykin, Oleg G.

2014-11-14

Line mixing effects in the Q branch of pure N{sub 2} isotropic Raman scattering are studied at room temperature using a classical trajectory method. It is the first study using an extended modified version of Gordon's classical theory of impact broadening and shift of rovibrational lines. The whole relaxation matrix is calculated using an exact 3D classical trajectory method for binary collisions of rigid N{sub 2} molecules employing the most up-to-date intermolecular potential energy surface (PES). A simple symmetrizing procedure is employed to improve off-diagonal cross-sections to make them obeying exactly the principle of detailed balance. The adequacy of themore » results is confirmed by the sum rule. The comparison is made with available experimental data as well as with benchmark fully quantum close coupling [F. Thibault, C. Boulet, and Q. Ma, J. Chem. Phys. 140, 044303 (2014)] and refined semi-classical Robert-Bonamy [C. Boulet, Q. Ma, and F. Thibault, J. Chem. Phys. 140, 084310 (2014)] results. All calculations (classical, quantum, and semi-classical) were made using the same PES. The agreement between classical and quantum relaxation matrices is excellent, opening the way to the analysis of more complex molecular systems.« less

Direct Simulation Monte Carlo Application of the Three Dimensional Forced Harmonic Oscillator Model

DTIC Science & Technology

2017-12-07

quasi -classical scattering theory [3,4] or trajectory [5] calculations, semiclassical, as well as close-coupled [6,7] or full [8] quantum mechanical...the quasi -classical trajectory (QCT) calculations approach for ab initio modeling of collision processes. The DMS method builds on an earlier work...nu ar y 30 , 2 01 8 | h ttp :// ar c. ai aa .o rg | D O I: 1 0. 25 14 /1 .T 52 28 to directly use quasi -classical or quantum mechanic

An Angular Overlap Model for Cu(II) Ion in the AMOEBA Polarizable Force Field

PubMed Central

Xiang, Jin Yu; Ponder, Jay W.

2014-01-01

An extensible polarizable force field for transition metal ion was developed based on AMOEBA and the angular overlap model (AOM) with consistent treatment of electrostatics for all atoms. Parameters were obtained by fitting molecular mechanics (MM) energies to various ab initio gas-phase calculations. The results of parameterization were presented for copper (II) ion ligated to water and model fragments of amino acid residues involved in the copper binding sites of type 1 copper proteins. Molecular dynamics (MD) simulations were performed on aqueous copper (II) ion at various temperatures, as well as plastocyanin (1AG6) and azurin (1DYZ). Results demonstrated that the AMOEBA-AOM significantly improves the accuracy of classical MM in a number of test cases when compared to ab initio calculations. The Jahn-Teller distortion for hexa-aqua copper (II) complex was handled automatically without specifically designating axial and in-plane ligands. Analyses of MD trajectories resulted in a 6-coordination first solvation shell for aqueous copper (II) ion and a 1.8ns average residence time of water molecules. The ensemble average geometries of 1AG6 and 1DYZ copper binding sites were in general agreement with X-ray and previous computational studies. PMID:25045338

Charge Exchange X-Ray Emission due to Highly Charged Ion Collisions with H, He, and H2: Line Ratios for Heliospheric and Interstellar Applications

NASA Astrophysics Data System (ADS)

Cumbee, R. S.; Mullen, P. D.; Lyons, D.; Shelton, R. L.; Fogle, M.; Schultz, D. R.; Stancil, P. C.

2018-01-01

The fundamental collisional process of charge exchange (CX) has been established as a primary source of X-ray emission from the heliosphere, planetary exospheres, and supernova remnants. In this process, X-ray emission results from the capture of an electron by a highly charged ion from a neutral atom or molecule, to form a highly excited, high-charge state ion. As the captured electron cascades down to the lowest energy level, photons are emitted, including X-rays. To provide reliable CX-induced X-ray spectral models to realistically simulate these environments, line ratios and spectra are computed using theoretical CX cross sections obtained with the multi-channel Landau-Zener, atomic-orbital close-coupling, molecular-orbital close-coupling, and classical trajectory Monte Carlo methods for various collisional velocities relevant to astrophysics. X-ray spectra were computed for collisions of bare and H-like C to Al ions with H, He, and H2 with results compared to available experimental data. Using these line ratios, XSPEC models of CX emission in the northeast rim of the Cygnus Loop supernova remnant and the heliosphere are shown as examples with ion velocity dependence.

Fully differential cross sections for the single ionization of helium by fast ions: Classical model calculations

NASA Astrophysics Data System (ADS)

Sarkadi, L.

2018-04-01

Fully differential cross sections (FDCSs) have been calculated for the single ionization of helium by 1- and 3-MeV proton and 100-MeV/u C6 + ion impact using the classical trajectory Monte Carlo (CTMC) method in the nonrelativistic, three-body approximation. The calculations were made employing a Wigner-type model in which the quantum-mechanical position distribution of the electron is approximated by a weighted integral of the microcanonical distribution over a range of the binding energy of the electron. In the scattering plane, the model satisfactorily reproduces the observed shape of the binary peak. In the region of the peak the calculated FDCSs agree well with the results of continuum-distorted-wave calculations for all the investigated collisions. For 1-MeV proton impact the experimentally observed shift of the binary peak with respect to the first Born approximation is compared with the shifts obtained by different higher-order quantum-mechanical theories and the present CTMC method. The best result was achieved by CTMC, but still a large part of the shift remained unexplained. Furthermore, it was found that the classical theory failed to reproduce the shape of the recoil peak observed in the experiments, it predicts a much narrower peak. This indicates that the formation of the recoil peak is dominated by quantum-mechanical effects. For 100-MeV/u C6 + ion impact the present CTMC calculations confirmed the existence of the "double-peak" structure of the angular distribution of the electron in the plane perpendicular to the momentum transfer, in accordance with the observation, the prediction of an incoherent semiclassical model, and previous CTMC results. This finding together with wave-packet calculations suggests that the "C6 + puzzle" may be solved by considering the loss of the projectile coherence. Experiments to be conducted using ion beams of anisotropic coherence are proposed for a more differential investigation of the ionization dynamics.

Correlated multielectron dynamics in mid-infrared laser pulse interactions with neon atoms.

PubMed

Tang, Qingbin; Huang, Cheng; Zhou, Yueming; Lu, Peixiang

2013-09-09

The multielectron dynamics in nonsequential triple ionization (NSTI) of neon atoms driven by mid-infrared (MIR) laser pulses is investigated with the three-dimensional classical ensemble model. In consistent with the experimental result, our numerical result shows that in the MIR regime, the triply charged ion longitudinal momentum spectrum exhibits a pronounced double-hump structure at low laser intensity. Back analysis reveals that as the intensity increases, the responsible triple ionization channels transform from direct (e, 3e) channel to the various mixed channels. This transformation of the NSTI channels leads to the results that the shape of ion momentum spectra becomes narrow and the distinct maxima shift towards low momenta with the increase of the laser intensity. By tracing the triply ionized trajectories, the various ionization channels at different laser intensities are clearly identified and these results provide an insight into the complex dynamics of the correlated three electrons in NSTI.

Quantum-Classical Correspondence Principle for Work Distributions

NASA Astrophysics Data System (ADS)

Jarzynski, Christopher; Quan, H. T.; Rahav, Saar

2015-07-01

For closed quantum systems driven away from equilibrium, work is often defined in terms of projective measurements of initial and final energies. This definition leads to statistical distributions of work that satisfy nonequilibrium work and fluctuation relations. While this two-point measurement definition of quantum work can be justified heuristically by appeal to the first law of thermodynamics, its relationship to the classical definition of work has not been carefully examined. In this paper, we employ semiclassical methods, combined with numerical simulations of a driven quartic oscillator, to study the correspondence between classical and quantal definitions of work in systems with 1 degree of freedom. We find that a semiclassical work distribution, built from classical trajectories that connect the initial and final energies, provides an excellent approximation to the quantum work distribution when the trajectories are assigned suitable phases and are allowed to interfere. Neglecting the interferences between trajectories reduces the distribution to that of the corresponding classical process. Hence, in the semiclassical limit, the quantum work distribution converges to the classical distribution, decorated by a quantum interference pattern. We also derive the form of the quantum work distribution at the boundary between classically allowed and forbidden regions, where this distribution tunnels into the forbidden region. Our results clarify how the correspondence principle applies in the context of quantum and classical work distributions and contribute to the understanding of work and nonequilibrium work relations in the quantum regime.

Mapping quantum-classical Liouville equation: projectors and trajectories.

PubMed

Kelly, Aaron; van Zon, Ramses; Schofield, Jeremy; Kapral, Raymond

2012-02-28

The evolution of a mixed quantum-classical system is expressed in the mapping formalism where discrete quantum states are mapped onto oscillator states, resulting in a phase space description of the quantum degrees of freedom. By defining projection operators onto the mapping states corresponding to the physical quantum states, it is shown that the mapping quantum-classical Liouville operator commutes with the projection operator so that the dynamics is confined to the physical space. It is also shown that a trajectory-based solution of this equation can be constructed that requires the simulation of an ensemble of entangled trajectories. An approximation to this evolution equation which retains only the Poisson bracket contribution to the evolution operator does admit a solution in an ensemble of independent trajectories but it is shown that this operator does not commute with the projection operators and the dynamics may take the system outside the physical space. The dynamical instabilities, utility, and domain of validity of this approximate dynamics are discussed. The effects are illustrated by simulations on several quantum systems.

Superintegrability of the Fock-Darwin system

NASA Astrophysics Data System (ADS)

Drigho-Filho, E.; Kuru, Ş.; Negro, J.; Nieto, L. M.

2017-08-01

The Fock-Darwin system is analyzed from the point of view of its symmetry properties in the quantum and classical frameworks. The quantum Fock-Darwin system is known to have two sets of ladder operators, a fact which guarantees its solvability. We show that for rational values of the quotient of two relevant frequencies, this system is superintegrable, the quantum symmetries being responsible for the degeneracy of the energy levels. These symmetries are of higher order and close a polynomial algebra. In the classical case, the ladder operators are replaced by ladder functions and the symmetries by constants of motion. We also prove that the rational classical system is superintegrable and its trajectories are closed. The constants of motion are also generators of symmetry transformations in the phase space that have been integrated for some special cases. These transformations connect different trajectories with the same energy. The coherent states of the quantum superintegrable system are found and they reproduce the closed trajectories of the classical one.

Ultraviolet and Visible Emission Mechanisms in Astrophysics

NASA Technical Reports Server (NTRS)

Stancil, Phillip C.; Schultz, David R.

2003-01-01

The project involved the study of ultraviolet (UV) and visible emission mechanisms in astrophysical and atmospheric environments. In many situations, the emission is a direct consequence of a charge transferring collision of an ion with a neutral with capture of an electron to an excited state of the product ion. The process is also important in establishing the ionization and thermal balance of an astrophysical plasma. As little of the necessary collision data are available, the main thrust of the project was the calculation of total and state-selective charge transfer cross sections and rate coefficients for a very large number of collision systems. The data was computed using modern explicit techniques including the molecular-orbital close-coupling (MOCC), classical trajectory Monte Carlo (CTMC), and continuum distorted wave (CDW) methods. Estimates were also made in some instances using the multichannel Landau-Zener (MCLZ) and classical over-the-barrier (COB) models. Much of the data which has been computed has been formatted for inclusion in a charge transfer database on the World Wide Web (cfadc.phy.ornl.gov/astro/ps/data/). A considerable amount of data has been generated during the lifetime of the grant. Some of it has not been analyzed, but it will be as soon as possible, the data placed on our website, and papers ultimately written.

The Identification of the Mediterranean cyclones main classical trajectories towards Romania by using objective methods based on mathematical algorithms

NASA Astrophysics Data System (ADS)

Oana, Catrina; Parding, Kajsa Maria; Stefan, Sabina

2017-04-01

The importance of knowledge on the trajectories that Mediterranean cyclones follows toward Romania is fundamental because most of the times the weather phenomena that accompany them determine significant economic damage and not only. In the specialized literature, the principal classic trajectories on which the Mediterranean cyclones pass toward the south-east of Europe and by default toward Romania, causing in these areas a crucial weather conditions change in all aspects at any time during the year, have been determined in subjectively mode, many years ago, by C. Sorodoc (1962) E. I. Bordei (1983). Starting from the known 9 classic trajectories determined subjectively, in this study it was aimed and subsequently carried out their identification by this date, but objectively, using the method based on mathematic algorithms developed by Rasmus E. Benestad, Abdelkader Mezghani, and Kajsa M. Parding (2006). The study was carried out between January 2003 and December 2015, taking into account the fact that the presence of the Mediterranean cyclones may be established almost every month, these representing important links of the atmosphere movement over Europe. The data used by the daily review have contained values, in grid points, of the mean pressure field at sea level (MSLP), with spatial resolution of 0.75° x 0.75° and 6 hours temporal coverage, originating from ECMWF, ERA-Interim project (2006), and the chosen field of interest was between 15°W - 40°E and 30°N - 50°N. Of the total number of Mediterranean cyclones identified objectively, that followed trajectories toward Romania, were randomly selected only a few cases, which indicates the similarity between the paths of classic subjectively determined and those determined objectively. Validation of the results consisted in the first phase in a comparison between the trajectories identified with the classic trajectories determined subjectively, then was carried out a second validation, by analysis of the MSLP field, geopotential height and potential vorticity. As a conclusion, the results obtained highlights certainly reliability but especially the usefulness of the objective method used, in particular in carrying out the complex Mediterranean climatology studies and not only.

Scaling relationships for nonadiabatic energy relaxation times in warm dense matter: toward understanding the equation of state.

PubMed

Pradhan, Ekadashi; Magyar, Rudolph J; Akimov, Alexey V

2016-11-30

Understanding the dynamics of electron-ion energy transfer in warm dense (WD) matter is important to the measurement of equation of state (EOS) properties and for understanding the energy balance in dynamic simulations. In this work, we present a comprehensive investigation of nonadiabatic electron relaxation and thermal excitation dynamics in aluminum under high pressure and temperature. Using quantum-classical trajectory surface hopping approaches, we examine the role of nonadiabatic couplings and electronic decoherence in electron-nuclear energy transfer in WD aluminum. The computed timescales range from 400 fs to 4.0 ps and are consistent with existing experimental studies. We have derived general scaling relationships between macroscopic parameters of WD systems such as temperature or mass density and the timescales of energy redistribution between quantum and classical degrees of freedom. The scaling laws are supported by computational results. We show that electronic decoherence plays essential role and can change the functional dependencies qualitatively. The established scaling relationships can be of use in modelling of WD matter.

Quantum to classical transition in the Hořava-Lifshitz quantum cosmology

NASA Astrophysics Data System (ADS)

Bernardini, A. E.; Leal, P.; Bertolami, O.

2018-02-01

A quasi-Gaussian quantum superposition of Hořava-Lifshitz (HL) stationary states is built in order to describe the transition of the quantum cosmological problem to the related classical dynamics. The obtained HL phase-space superposed Wigner function and its associated Wigner currents describe the conditions for the matching between classical and quantum phase-space trajectories. The matching quantum superposition parameter is associated to the total energy of the classical trajectory which, at the same time, drives the engendered Wigner function to the classical stationary regime. Through the analysis of the Wigner flows, the quantum fluctuations that distort the classical regime can be quantified as a measure of (non)classicality. Finally, the modifications to the Wigner currents due to the inclusion of perturbative potentials are computed in the HL quantum cosmological context. In particular, the inclusion of a cosmological constant provides complementary information that allows for connecting the age of the Universe with the overall stiff matter density profile.

Mass-selective isolation of ions stored in a quadrupole ion trap. A simulation study

NASA Astrophysics Data System (ADS)

March, Raymond E.; Londry, Frank A.; Alfred, Roland L.; Franklin, Anthony M.; Todd, John F. J.

1992-01-01

Trajectories of single ions stored in the quadrupole ion trap have been calculated using a simulation program described as the specific program for quadrupolar resonance (SPQR). Previously, the program has been used for the investigation of quadrupolar resonance excitation of ions with a static working point (or co-ordinates) in the stability diagram. The program has been modified to accommodate continuous d.c. and/or r.f. voltage ramps so as to permit calculation of ion trajectories while the working point is being changed. The modified program has been applied to the calculation of ion trajectories during ion isolation, or mass-selective storage, in the ion trap. The quadrupolar resonance excitation aspect of SPQR was not used in this study. Trajectories are displayed as temporal variations of ion kinetic energy, and axial and radial excursions from the centre of the ion trap. The working points of three ion species (m/z 144, 146 and 148), located initially on the qz, axis with qz [approximate] 0.12, were moved to the vicinity of the upper apex by a combination of r.f. and d.c. voltages applied in succession. Stable trajectories were maintained only for the ion species of m/z 146 for which the working point lay within this apex; the other ion species were ejected either radially or axially. The d.c. voltage was then reduced to zero so as to restore the working point of the isolated ion species to the qz axis. The amplitude of the r.f voltage was reduced to its initial value so as to retrieve the initial working point for m/z 146. The process extended over a real time of 2.9 ms, and was collision-free. The trajectory of the isolated ion was stable during this process; the ion species with m/z value lower than that of the target ion, that is, m/z 144, was ejected axially at the [beta]z = 1 boundary, while that with higher m/z value, that is, m/z 148, was ejected radially at the [beta]r = 0 boundary, as expected. The moderating effects of buffer gas were not taken into consideration and ion kinetic energies during the sorting period were found to be sufficiently great that dissociative losses may be appreciable in a collisional system. A possible strategy for reducing kinetic energy during this process has been proposed.

Effects of convection electric field on upwelling and escape of ionospheric O(+)

NASA Technical Reports Server (NTRS)

Cladis, J. B.; Chiu, Yam T.; Peterson, William K.

1992-01-01

A Monte Carlo code is used to explore the full effects of the convection electric field on distributions of upflowing O(+) ions from the cusp/cleft ionosphere. Trajectories of individual ions/neutrals are computed as they undergo multiple charge-exchange collisions. In the ion state, the trajectories are computed in realistic models of the magnetic field and the convection, corotation, and ambipolar electric fields. The effects of ion-ion collisions are included, and the trajectories are computed with and without simultaneous stochastic heating perpendicular to the magnetic field by a realistic model of broadband, low frequency waves. In the neutral state, ballistic trajectories in the gravitational field are computed. The initial conditions of the ions, in addition to ambipolar electric field and the number densities and temperatures of O(+), H(+), and electrons as a function of height in the cusp/cleft region were obtained from the results of Gombosi and Killeen (1987), who used a hydrodynamic code to simulate the time-dependent frictional-heating effects in a magnetic tube during its motion though the convection throat. The distribution of the ion fluxes as a function of height are constructed from the case histories.

Large-scale atomistic calculations of clusters in intense x-ray pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ho, Phay J.; Knight, Chris

Here, we present the methodology of our recently developed Monte-Carlo/ Molecular-Dynamics method for studying the fundamental ultrafast dynamics induced by high-fluence, high-intensity x-ray free electron laser (XFEL) pulses in clusters. The quantum nature of the initiating ionization process is accounted for by a Monte Carlo method to calculate probabilities of electronic transitions, including photo absorption, inner-shell relaxation, photon scattering, electron collision and recombination dynamics, and thus track the transient electronic configurations explicitly. The freed electrons and ions are followed by classical particle trajectories using a molecular dynamics algorithm. These calculations reveal the surprising role of electron-ion recombination processes that leadmore » to the development of nonuniform spatial charge density profiles in x-ray excited clusters over femtosecond timescales. In the high-intensity limit, it is important to include the recombination dynamics in the calculated scattering response even for a 2- fs pulse. We also demonstrate that our numerical codes and algorithms can make e!cient use of the computational power of massively parallel supercomputers to investigate the intense-field dynamics in systems with increasing complexity and size at the ultrafast timescale and in non-linear x-ray interaction regimes. In particular, picosecond trajectories of XFEL clusters with attosecond time resolution containing millions of particles can be e!ciently computed on upwards of 262,144 processes.« less

Large-scale atomistic calculations of clusters in intense x-ray pulses

DOE PAGES

Ho, Phay J.; Knight, Chris

2017-04-28

Here, we present the methodology of our recently developed Monte-Carlo/ Molecular-Dynamics method for studying the fundamental ultrafast dynamics induced by high-fluence, high-intensity x-ray free electron laser (XFEL) pulses in clusters. The quantum nature of the initiating ionization process is accounted for by a Monte Carlo method to calculate probabilities of electronic transitions, including photo absorption, inner-shell relaxation, photon scattering, electron collision and recombination dynamics, and thus track the transient electronic configurations explicitly. The freed electrons and ions are followed by classical particle trajectories using a molecular dynamics algorithm. These calculations reveal the surprising role of electron-ion recombination processes that leadmore » to the development of nonuniform spatial charge density profiles in x-ray excited clusters over femtosecond timescales. In the high-intensity limit, it is important to include the recombination dynamics in the calculated scattering response even for a 2- fs pulse. We also demonstrate that our numerical codes and algorithms can make e!cient use of the computational power of massively parallel supercomputers to investigate the intense-field dynamics in systems with increasing complexity and size at the ultrafast timescale and in non-linear x-ray interaction regimes. In particular, picosecond trajectories of XFEL clusters with attosecond time resolution containing millions of particles can be e!ciently computed on upwards of 262,144 processes.« less

Direct observation and theory of trajectory-dependent electronic energy losses in medium-energy ion scattering.

PubMed

Hentz, A; Parkinson, G S; Quinn, P D; Muñoz-Márquez, M A; Woodruff, D P; Grande, P L; Schiwietz, G; Bailey, P; Noakes, T C Q

2009-03-06

The energy spectrum associated with scattering of 100 keV H+ ions from the outermost few atomic layers of Cu(111) in different scattering geometries provides direct evidence of trajectory-dependent electronic energy loss. Theoretical simulations, combining standard Monte Carlo calculations of the elastic scattering trajectories with coupled-channel calculations to describe inner-shell ionization and excitation as a function of impact parameter, reproduce the effects well and provide a means for far more complete analysis of medium-energy ion scattering data.

Chaotic scattering in an open vase-shaped cavity: Topological, numerical, and experimental results

NASA Astrophysics Data System (ADS)

Novick, Jaison Allen

We present a study of trajectories in a two-dimensional, open, vase-shaped cavity in the absence of forces The classical trajectories freely propagate between elastic collisions. Bound trajectories, regular scattering trajectories, and chaotic scattering trajectories are present in the vase. Most importantly, we find that classical trajectories passing through the vase's mouth escape without return. In our simulations, we propagate bursts of trajectories from point sources located along the vase walls. We record the time for escaping trajectories to pass through the vase's neck. Constructing a plot of escape time versus the initial launch angle for the chaotic trajectories reveals a vastly complicated recursive structure or a fractal. This fractal structure can be understood by a suitable coordinate transform. Reducing the dynamics to two dimensions reveals that the chaotic dynamics are organized by a homoclinic tangle, which is formed by the union of infinitely long, intersecting stable and unstable manifolds. This study is broken down into three major components. We first present a topological theory that extracts the essential topological information from a finite subset of the tangle and encodes this information in a set of symbolic dynamical equations. These equations can be used to predict a topologically forced minimal subset of the recursive structure seen in numerically computed escape time plots. We present three applications of the theory and compare these predictions to our simulations. The second component is a presentation of an experiment in which the vase was constructed from Teflon walls using an ultrasound transducer as a point source. We compare the escaping signal to a classical simulation and find agreement between the two. Finally, we present an approximate solution to the time independent Schrodinger Equation for escaping waves. We choose a set of points at which to evaluate the wave function and interpolate trajectories connecting the source point to each "detector point". We then construct the wave function directly from these classical trajectories using the two-dimensional WKB approximation. The wave function is Fourier Transformed using a Fast Fourier Transform algorithm resulting in a spectrum in which each peak corresponds to an interpolated trajectory. Our predictions are based on an imagined experiment that uses microwave propagation within an electromagnetic waveguide. Such an experiment exploits the fact that under suitable conditions both Maxwell's Equations and the Schrodinger Equation can be reduced to the Helmholtz Equation. Therefore, our predictions, while compared to the electromagnetic experiment, contain information about the quantum system. Identifying peaks in the transmission spectrum with chaotic trajectories will allow for an additional experimental verification of the intermediate recursive structure. Finally, we summarize our results and discuss possible extensions of this project.

Symmetrical windowing for quantum states in quasi-classical trajectory simulations: Application to electronically non-adiabatic processes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cotton, Stephen J.; Miller, William H., E-mail: millerwh@berkeley.edu

A recently described symmetrical windowing methodology [S. J. Cotton and W. H. Miller, J. Phys. Chem. A 117, 7190 (2013)] for quasi-classical trajectory simulations is applied here to the Meyer-Miller [H.-D. Meyer and W. H. Miller, J. Chem. Phys. 70, 3214 (1979)] model for the electronic degrees of freedom in electronically non-adiabatic dynamics. Results generated using this classical approach are observed to be in very good agreement with accurate quantum mechanical results for a variety of test applications, including problems where coherence effects are significant such as the challenging asymmetric spin-boson system.

Charge exchange collisions of slow C6 + with atomic and molecular H

NASA Astrophysics Data System (ADS)

Saha, Bidhan C.; Guevara, Nicolais L.; Sabin, John R.; Deumens, Erik; Öhrn, Yngve

2016-04-01

Charge exchange in collisions of C6+ ions with H and H2 is investigated theoretically at projectile energies 0.1 < E < 10 keV/amu, using electron nuclear dynamics (END) - a semi-classical approximation which not only includes electron translation factors for avoiding spurious couplings but also employs full dynamical trajectories to treat nuclear motions. Both the total and partial cross sections are reported for the collision of C6+ ions with atomic and molecular hydrogen. A comparison with other theoretical and experimental results shows, in general good agreement except at very low energy, considered here. For H2, the one- and two-electron charge exchange cross sections are calculated and compared with other theoretical and experimental results. Small but non-negligible isotope effects are found at the lowest energy studied in the charge transfer of C6+ with H. In low energy region, it is observed that H2 has larger isotope effects than H atom due to the polarizability effect which is larger than the mass effect.

Trajectory analysis of low-energy and hyperthermal ions scattered from Cu(110)

DOE Office of Scientific and Technical Information (OSTI.GOV)

McEachern, R. L.; Goodstein, D. M.; Cooper, B. H.

1989-05-15

We have investigated the trajectories of Na/sup +/ ions scattered from the Cu(110) surface in the <1/bar 1/0> and <001> azimuths for a range of incident energies from 56 eV to 4 keV. Our goal is to explain the trends observed in the energy spectra and determine what types of trajectories contribute to these spectra. Using the computer program SAFARI, we have performed simulations with trajectory analyses for 100-, 200-, and 400-eV scattering. We show results from the 100-eV simulations in both azimuths and compare them with the experimental data. The simulated energy spectra are in excellent agreement with themore » data. Ion trajectories and impact parameter plots from the simulations are used to determine the relative importance of different types of ion--surface-atom collisions. The simulations have shown that the striking differences observed in comparing the <1/bar 1/0> and <001> spectra are mostly due to ions which scatter from second-layer atoms. This system exhibits strong focusing onto the second-layer atoms by the first-layer rows, and the focusing is very sensitive to the spacing between the rows. At the lower beam energies, scattering from the second layer dominates the measured spectra.« less

Analysis of retarding field energy analyzer transmission by simulation of ion trajectories

NASA Astrophysics Data System (ADS)

van de Ven, T. H. M.; de Meijere, C. A.; van der Horst, R. M.; van Kampen, M.; Banine, V. Y.; Beckers, J.

2018-04-01

Retarding field energy analyzers (RFEAs) are used routinely for the measurement of ion energy distribution functions. By contrast, their ability to measure ion flux densities has been considered unreliable because of lack of knowledge about the effective transmission of the RFEA grids. In this work, we simulate the ion trajectories through a three-gridded RFEA using the simulation software SIMION. Using idealized test cases, it is shown that at high ion energy (i.e., >100 eV) the transmission is equal to the optical transmission rather than the product of the individual grid transparencies. Below 20 eV, ion trajectories are strongly influenced by the electric fields in between the grids. In this region, grid alignment and ion focusing effects contribute to fluctuations in transmission with ion energy. Subsequently the model has been used to simulate the transmission and energy resolution of an experimental RFEA probe. Grid misalignments reduce the transmission fluctuations at low energy. The model predicts the minimum energy resolution, which has been confirmed experimentally by irradiating the probe with a beam of ions with a small energy bandwidth.

Classical confinement and outward convection of impurity ions in the MST RFP

NASA Astrophysics Data System (ADS)

Kumar, S. T. A.; Den Hartog, D. J.; Mirnov, V. V.; Caspary, K. J.; Magee, R. M.; Brower, D. L.; Chapman, B. E.; Craig, D.; Ding, W. X.; Eilerman, S.; Fiksel, G.; Lin, L.; Nornberg, M.; Parke, E.; Reusch, J. A.; Sarff, J. S.

2012-05-01

Impurity ion dynamics measured with simultaneously high spatial and temporal resolution reveal classical ion transport in the reversed-field pinch. The boron, carbon, oxygen, and aluminum impurity ion density profiles are obtained in the Madison Symmetric Torus [R. N. Dexter et al., Fusion Technol. 19, 131 (1991)] using a fast, active charge-exchange-recombination-spectroscopy diagnostic. Measurements are made during improved-confinement plasmas obtained using inductive control of tearing instability to mitigate stochastic transport. At the onset of the transition to improved confinement, the impurity ion density profile becomes hollow, with a slow decay in the core region concurrent with an increase in the outer region, implying an outward convection of impurities. Impurity transport from Coulomb collisions in the reversed-field pinch is classical for all collisionality regimes, and analysis shows that the observed hollow profile and outward convection can be explained by the classical temperature screening mechanism. The profile agrees well with classical expectations. Experiments performed with impurity pellet injection provide further evidence for classical impurity ion confinement.

Galileo's Trajectory with Mild Resistance

ERIC Educational Resources Information Center

Groetsch, C. W.

2012-01-01

An aspect of Galileo's classical trajectory that persists in a simple resistance model is noted. The resistive model provides a case study for the classroom analysis of limiting behaviour of an implicitly defined function. (Contains 1 note.)

Ion-source modeling and improved performance of the CAMS high-intensity Cs-sputter ion source

NASA Astrophysics Data System (ADS)

Brown, T. A.; Roberts, M. L.; Southon, J. R.

2000-10-01

The interior of the high-intensity Cs-sputter source used in routine operations at the Center for Accelerator Mass Spectrometry (CAMS) has been computer modeled using the program NEDLab, with the aim of improving negative ion output. Space charge effects on ion trajectories within the source were modeled through a successive iteration process involving the calculation of ion trajectories through Poisson-equation-determined electric fields, followed by calculation of modified electric fields incorporating the charge distribution from the previously calculated ion trajectories. The program has several additional features that are useful in ion source modeling: (1) averaging of space charge distributions over successive iterations to suppress instabilities, (2) Child's Law modeling of space charge limited ion emission from surfaces, and (3) emission of particular ion groups with a thermal energy distribution and at randomized angles. The results of the modeling effort indicated that significant modification of the interior geometry of the source would double Cs + ion production from our spherical ionizer and produce a significant increase in negative ion output from the source. The results of the implementation of the new geometry were found to be consistent with the model results.

On the transition from the quantum to the classical regime for massive scalar particles: A spatiotemporal approach

NASA Astrophysics Data System (ADS)

Lusanna, Luca; Pauri, Massimo

2014-08-01

If the classical structure of space-time is assumed to define an a priori scenario for the formulation of quantum theory (QT), the coordinate representation of the solutions of the Schroedinger equation of a quantum system containing one ( N) massive scalar particle has a preferred status. Let us consider all of the solutions admitting a multipolar expansion of the probability density function (and more generally of the Wigner function) around a space-time trajectory to be properly selected. For every normalized solution there is a privileged trajectory implying the vanishing of the dipole moment of the multipolar expansion: it is given by the expectation value of the position operator . Then, the special subset of solutions which satisfy Ehrenfest's Theorem (named thereby Ehrenfest monopole wave functions (EMWF)), have the important property that this privileged classical trajectory is determined by a closed Newtonian equation of motion where the effective force is the Newtonian force plus non-Newtonian terms (of order ħ 2 or higher) depending on the higher multipoles of the probability distribution ρ. Note that the superposition of two EMWFs is not an EMWF, a result to be strongly hoped for, given the possible unwanted implications concerning classical spatial perception. These results can be extended to N-particle systems in such a way that, when N classical trajectories with all the dipole moments vanishing and satisfying Ehrenfest theorem are associated with the normalized wave functions of the N-body system, we get a natural transition from the 3 N-dimensional configuration space to the space-time. Moreover, these results can be extended to relativistic quantum mechanics. Consequently, in suitable states of N quantum particle which are EMWF, we get the "emergence" of corresponding "classical particles" following Newton-like trajectories in space-time. Note that all this holds true in the standard framework of quantum mechanics, i.e. assuming, in particular, the validity of Born's rule and the individual system interpretation of the wave function (no ensemble interpretation). These results are valid without any approximation (like ħ → 0, big quantum numbers, etc.). Moreover, we do not commit ourselves to any specific ontological interpretation of quantum theory (such as, e.g., the Bohmian one). We will argue that, in substantial agreement with Bohr's viewpoint, the macroscopic description of the preparation, certain intermediate steps and the detection of the final outcome of experiments involving massive particles are dominated by these classical "effective" trajectories. This approach can be applied to the point of view of de-coherence in the case of a diagonal reduced density matrix ρ red (an improper mixture) depending on the position variables of a massive particle and of a pointer. When both the particle and the pointer wave functions appearing in ρ red are EMWF, the expectation value of the particle and pointer position variables becomes a statistical average on a classical ensemble. In these cases an improper quantum mixture becomes a classical statistical one, thus providing a particular answer to an open problem of de-coherence about the emergence of classicality.

Liouville master equation for multielectron dynamics: Neutralization of highly charged ions near a LiF surface

NASA Astrophysics Data System (ADS)

Wirtz, Ludger; Reinhold, Carlos O.; Lemell, Christoph; Burgdörfer, Joachim

2003-01-01

We present a simulation of the neutralization of highly charged ions in front of a lithium fluoride surface including the close-collision regime above the surface. The present approach employs a Monte Carlo solution of the Liouville master equation for the joint probability density of the ionic motion and the electronic population of the projectile and the target surface. It includes single as well as double particle-hole (de)excitation processes and incorporates electron correlation effects through the conditional dynamics of population strings. The input in terms of elementary one- and two-electron transfer rates is determined from classical trajectory Monte Carlo calculations as well as quantum-mechanical Auger calculations. For slow projectiles and normal incidence, the ionic motion depends sensitively on the interplay between image acceleration towards the surface and repulsion by an ensemble of positive hole charges in the surface (“trampoline effect”). For Ne10+ we find that image acceleration is dominant and no collective backscattering high above the surface takes place. For grazing incidence, our simulation delineates the pathways to complete neutralization. In accordance with recent experimental observations, most ions are reflected as neutral or even as singly charged negative particles, irrespective of the charge state of the incoming ions.

Metal Ion Modeling Using Classical Mechanics

PubMed Central

2017-01-01

Metal ions play significant roles in numerous fields including chemistry, geochemistry, biochemistry, and materials science. With computational tools increasingly becoming important in chemical research, methods have emerged to effectively face the challenge of modeling metal ions in the gas, aqueous, and solid phases. Herein, we review both quantum and classical modeling strategies for metal ion-containing systems that have been developed over the past few decades. This Review focuses on classical metal ion modeling based on unpolarized models (including the nonbonded, bonded, cationic dummy atom, and combined models), polarizable models (e.g., the fluctuating charge, Drude oscillator, and the induced dipole models), the angular overlap model, and valence bond-based models. Quantum mechanical studies of metal ion-containing systems at the semiempirical, ab initio, and density functional levels of theory are reviewed as well with a particular focus on how these methods inform classical modeling efforts. Finally, conclusions and future prospects and directions are offered that will further enhance the classical modeling of metal ion-containing systems. PMID:28045509

Classical versus quantum dynamical chaos: Sensitivity to external perturbations, stability and reversibility

NASA Astrophysics Data System (ADS)

Sokolov, Valentin V.; Zhirov, Oleg V.; Kharkov, Yaroslav A.

The extraordinary complexity of classical trajectories of typical nonlinear systems that manifest stochastic behavior is intimately connected with exponential sensitivity to small variations of initial conditions and/or weak external perturbations. In rigorous terms, such classical systems are characterized by positive algorithmic complexity described by the Lyapunov exponent or, alternatively, by the Kolmogorov-Sinai entropy. The said implies that, in spite of the fact that, formally, any however complex trajectory of a perfectly isolated (closed) system is unique and differentiable for any certain initial conditions and the motion is perfectly reversible, it is impractical to treat that sort of classical systems as closed ones. Inevitably, arbitrary weak influence of an environment crucially impacts the dynamics. This influence, that can be considered as a noise, rapidly effaces the memory of initial conditions and turns the motion into an irreversible random process. In striking contrast, the quantum mechanics of the classically chaotic systems exhibit much weaker sensitivity and strong memory of the initial state. Qualitatively, this crucial difference could be expected in view of a much simpler structure of quantum states as compared to the extraordinary complexity of random and unpredictable classical trajectories. However the very notion of trajectories is absent in quantum mechanics so that the concept of exponential instability seems to be irrelevant in this case. The problem of a quantitative measure of complexity of a quantum state of motion, that is a very important and nontrivial issue of the theory of quantum dynamical chaos, is the one of our concern. With such a measure in hand, we quantitatively analyze the stability and reversibility of quantum dynamics in the presence of external noise. To solve this problem we point out that individual classical trajectories are of minor interest if the motion is chaotic. Properties of all of them are alike in this case and rather the behavior of their manifolds carries really valuable information. Therefore the phase-space methods and, correspondingly, the Liouville form of the classical mechanics become the most adequate. It is very important that, opposite to the classical trajectories, the classical phase space distribution and the Liouville equation have direct quantum analogs. Hence, the analogy and difference of classical and quantum dynamics can be traced by comparing the classical (W(c)(I,θ;t)) and quantum (Wigner function W(I,θ;t)) phase space distributions both expressed in identical phase-space variables but ruled by different(!) linear equations. The paramount property of the classical dynamical chaos is the exponentially fast structuring of the system's phase space on finer and finer scales. On the contrary, degree of structuring of the corresponding Wigner function is restricted by the quantization of the phase space. This makes Wigner function more coarse and relatively "simple" as compared to its classical counterpart. Fourier analysis affords quite suitable ground for analyzing complexity of a phase space distribution, that is equally valid in classical and quantum cases. We demonstrate that the typical number of Fourier harmonics is indeed a relevant measure of complexity of states of motion in both classical as well as quantum cases. This allowed us to investigate in detail and introduce a quantitative measure of sensitivity to an external noisy environment and formulate the conditions under which the quantum motion remains reversible. It turns out that while the mean number of harmonics of the classical phase-space distribution of a non-integrable system grows with time exponentially during the whole time of the motion, the time of exponential upgrowth of this number in the case of the corresponding quantum Wigner function is restricted only to the Ehrenfest interval 0 < t < tE - just the interval within which the Wigner function still satisfies the classical Liouville equation. We showed that the number of harmonics increases beyond this interval algebraically. This fact gains a crucial importance when the Ehrenfest time is so short that the exponential regime has no time to show up. Under this condition the quantum motion turns out to be quite stable and reversible.

Latent tracks and associated strain in Al2O3 irradiated with swift heavy ions

NASA Astrophysics Data System (ADS)

O'Connell, J. H.; Rymzhanov, R. A.; Skuratov, V. A.; Volkov, A. E.; Kirilkin, N. S.

2016-05-01

The morphology of latent ion tracks induced by high energy heavy ions in Al2O3 was investigated using a combination of high resolution transmission electron microscopy (HRTEM), exit wave reconstruction, geometric phase analysis and numerical simulations. Single crystal α-Al2O3 crystals were irradiated with 167 MeV Xe ions along the c-axis to fluences between 1 × 1010 and 1 × 1013 cm-2. Planar TEM lamella were prepared by focused ion beam (FIB) and geometrical phase analysis was performed on the phase image of the reconstructed complex electron wave at the specimen exit surface in order to estimate the latent strain around individual track cores. In addition to the experimental data, the material excitation in a SHI track was numerically simulated by combining Monte-Carlo code, describing the excitation of the electronic subsystem, with classical molecular dynamics of the lattice atoms. Experimental and simulation data both showed that the relaxation of the excess lattice energy results in the formation of a cylinder-like disordered region of about 4 nm in diameter consisting of an underdense core surrounded by an overdense shell. Modeling of the passage of a second ion in the vicinity of this disordered region revealed that this damaged area can be restored to a near damage free state. The estimation of a maximal effective distance of recrystallization between the ion trajectories yields values of about 6-6.5 nm which are of the same order of magnitude as those estimated from the saturation density of latent ion tracks detected by TEM.

Semi-analytical model for a static sheath including a weakly collisional presheath

NASA Astrophysics Data System (ADS)

Shirafuji, Tatsuru; Denpoh, Kazuki

2018-06-01

A semi-analytical static sheath (SASS) model can provide a spatial potential profile on a biased surface with microstructures, which can be used for predicting ion trajectories on the surface. However, two- or three-dimensional SASS models require a search procedure for a sheath edge equipotential profile, at which ions have the Bohm velocity, as the starting positions for calculating ion trajectories. This procedure can be troublesome when surface microstructures have complex structures. This difficulty is due to the fact that the SASS model cannot handle a presheath region. In this work, we propose a modified SASS model that can handle a presheath region. By using the modified SASS model, ion trajectories can be calculated from edges with arbitrary geometry without searching for the equipotential profile corresponding to sheath edges.

Mixed quantum/classical investigation of the photodissociation of NH3(Ã) and a practical method for maintaining zero-point energy in classical trajectories

NASA Astrophysics Data System (ADS)

Bonhommeau, David; Truhlar, Donald G.

2008-07-01

The photodissociation dynamics of ammonia upon excitation of the out-of-plane bending mode (mode ν2 with n2=0,…,6 quanta of vibration) in the à electronic state is investigated by means of several mixed quantum/classical methods, and the calculated final-state properties are compared to experiments. Five mixed quantum/classical methods are tested: one mean-field approach (the coherent switching with decay of mixing method), two surface-hopping methods [the fewest switches with time uncertainty (FSTU) and FSTU with stochastic decay (FSTU/SD) methods], and two surface-hopping methods with zero-point energy (ZPE) maintenance [the FSTU /SD+trajectory projection onto ZPE orbit (TRAPZ) and FSTU /SD+minimal TRAPZ (mTRAPZ) methods]. We found a qualitative difference between final NH2 internal energy distributions obtained for n2=0 and n2>1, as observed in experiments. Distributions obtained for n2=1 present an intermediate behavior between distributions obtained for smaller and larger n2 values. The dynamics is found to be highly electronically nonadiabatic with all these methods. NH2 internal energy distributions may have a negative energy tail when the ZPE is not maintained throughout the dynamics. The original TRAPZ method was designed to maintain ZPE in classical trajectories, but we find that it leads to unphysically high internal vibrational energies. The mTRAPZ method, which is new in this work and provides a general method for maintaining ZPE in either single-surface or multisurface trajectories, does not lead to unphysical results and is much less time consuming. The effect of maintaining ZPE in mixed quantum/classical dynamics is discussed in terms of agreement with experimental findings. The dynamics for n2=0 and n2=6 are also analyzed to reveal details not available from experiment, in particular, the time required for quenching of electronic excitation and the adiabatic energy gap and geometry at the time of quenching.

Mixed quantum/classical investigation of the photodissociation of NH3(A) and a practical method for maintaining zero-point energy in classical trajectories.

PubMed

Bonhommeau, David; Truhlar, Donald G

2008-07-07

The photodissociation dynamics of ammonia upon excitation of the out-of-plane bending mode (mode nu(2) with n(2)=0,[ellipsis (horizontal)],6 quanta of vibration) in the A electronic state is investigated by means of several mixed quantum/classical methods, and the calculated final-state properties are compared to experiments. Five mixed quantum/classical methods are tested: one mean-field approach (the coherent switching with decay of mixing method), two surface-hopping methods [the fewest switches with time uncertainty (FSTU) and FSTU with stochastic decay (FSTU/SD) methods], and two surface-hopping methods with zero-point energy (ZPE) maintenance [the FSTUSD+trajectory projection onto ZPE orbit (TRAPZ) and FSTUSD+minimal TRAPZ (mTRAPZ) methods]. We found a qualitative difference between final NH(2) internal energy distributions obtained for n(2)=0 and n(2)>1, as observed in experiments. Distributions obtained for n(2)=1 present an intermediate behavior between distributions obtained for smaller and larger n(2) values. The dynamics is found to be highly electronically nonadiabatic with all these methods. NH(2) internal energy distributions may have a negative energy tail when the ZPE is not maintained throughout the dynamics. The original TRAPZ method was designed to maintain ZPE in classical trajectories, but we find that it leads to unphysically high internal vibrational energies. The mTRAPZ method, which is new in this work and provides a general method for maintaining ZPE in either single-surface or multisurface trajectories, does not lead to unphysical results and is much less time consuming. The effect of maintaining ZPE in mixed quantum/classical dynamics is discussed in terms of agreement with experimental findings. The dynamics for n(2)=0 and n(2)=6 are also analyzed to reveal details not available from experiment, in particular, the time required for quenching of electronic excitation and the adiabatic energy gap and geometry at the time of quenching.

Trails of Kilovolt Ions Created by Subsurface Channeling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Redinger, Alex; Standop, Sebastian; Michely, Thomas

2010-02-19

Using scanning tunneling microscopy, we observe the damage trails produced by keV noble-gas ions incident at glancing angles onto Pt(111). Surface vacancies and adatoms aligned along the ion trajectory constitute the ion trails. Atomistic simulations reveal that these straight trails are produced by nuclear (elastic) collisions with surface layer atoms during subsurface channeling of the projectiles. In a small energy window around 5 keV, Xe{sup +} ions create vacancy grooves that mark the ion trajectory with atomic precision. The asymmetry of the adatom production on the two sides of the projectile path is traced back to the asymmetry of themore » ion's subsurface channel.« less

Autonomous quantum to classical transitions and the generalized imaging theorem

NASA Astrophysics Data System (ADS)

Briggs, John S.; Feagin, James M.

2016-03-01

The mechanism of the transition of a dynamical system from quantum to classical mechanics is of continuing interest. Practically it is of importance for the interpretation of multi-particle coincidence measurements performed at macroscopic distances from a microscopic reaction zone. Here we prove the generalized imaging theorem which shows that the spatial wave function of any multi-particle quantum system, propagating over distances and times large on an atomic scale but still microscopic, and subject to deterministic external fields and particle interactions, becomes proportional to the initial momentum wave function where the position and momentum coordinates define a classical trajectory. Currently, the quantum to classical transition is considered to occur via decoherence caused by stochastic interaction with an environment. The imaging theorem arises from unitary Schrödinger propagation and so is valid without any environmental interaction. It implies that a simultaneous measurement of both position and momentum will define a unique classical trajectory, whereas a less complete measurement of say position alone can lead to quantum interference effects.

Autonomous quantum to classical transitions and the generalized imaging theorem

DOE PAGES

Briggs, John S.; Feagin, James M.

2016-03-16

The mechanism of the transition of a dynamical system from quantum to classical mechanics is of continuing interest. Practically it is of importance for the interpretation of multi-particle coincidence measurements performed at macroscopic distances from a microscopic reaction zone. We prove the generalized imaging theorem which shows that the spatial wave function of any multi-particle quantum system, propagating over distances and times large on an atomic scale but still microscopic, and subject to deterministic external fields and particle interactions, becomes proportional to the initial momentum wave function where the position and momentum coordinates define a classical trajectory. Now, the quantummore » to classical transition is considered to occur via decoherence caused by stochastic interaction with an environment. The imaging theorem arises from unitary Schrödinger propagation and so is valid without any environmental interaction. It implies that a simultaneous measurement of both position and momentum will define a unique classical trajectory, whereas a less complete measurement of say position alone can lead to quantum interference effects.« less

Quantitative characterization of non-classic polarization of cations on clay aggregate stability.

PubMed

Hu, Feinan; Li, Hang; Liu, Xinmin; Li, Song; Ding, Wuquan; Xu, Chenyang; Li, Yue; Zhu, Longhui

2015-01-01

Soil particle interactions are strongly influenced by the concentration, valence and ion species and the pH of the bulk solution, which will also affect aggregate stability and particle transport. In this study, we investigated clay aggregate stability in the presence of different alkali ions (Li+, Na+, K+, and Cs+) at concentrations from10-5 to 10-1 mol L-1. Strong specific ion effects on clay aggregate stability were observed, and showed the order Cs+>K+>Na+>Li+. We found that it was not the effects of ion size, hydration, and dispersion forces in the cation-surface interactions but strong non-classic polarization of adsorbed cations that resulted in these specific effects. In this study, the non-classic dipole moments of each cation species resulting from the non-classic polarization were estimated. By comparing non-classic dipole moments with classic values, the observed dipole moments of adsorbed cations were up to 104 times larger than the classic values for the same cation. The observed non-classic dipole moments sharply increased with decreasing electrolyte concentration. We conclude that strong non-classic polarization could significantly suppress the thickness of the diffuse layer, thereby weakening the electric field near the clay surface and resulting in improved clay aggregate stability. Even though we only demonstrated specific ion effects on aggregate stability with several alkali ions, our results indicate that these effects could be universally important in soil aggregate stability.

Quantitative Characterization of Non-Classic Polarization of Cations on Clay Aggregate Stability

PubMed Central

Hu, Feinan; Li, Hang; Liu, Xinmin; Li, Song; Ding, Wuquan; Xu, Chenyang; Li, Yue; Zhu, Longhui

2015-01-01

Soil particle interactions are strongly influenced by the concentration, valence and ion species and the pH of the bulk solution, which will also affect aggregate stability and particle transport. In this study, we investigated clay aggregate stability in the presence of different alkali ions (Li+, Na+, K+, and Cs+) at concentrations from10−5 to 10−1 mol L−1. Strong specific ion effects on clay aggregate stability were observed, and showed the order Cs+>K+>Na+>Li+. We found that it was not the effects of ion size, hydration, and dispersion forces in the cation–surface interactions but strong non-classic polarization of adsorbed cations that resulted in these specific effects. In this study, the non-classic dipole moments of each cation species resulting from the non-classic polarization were estimated. By comparing non-classic dipole moments with classic values, the observed dipole moments of adsorbed cations were up to 104 times larger than the classic values for the same cation. The observed non-classic dipole moments sharply increased with decreasing electrolyte concentration. We conclude that strong non-classic polarization could significantly suppress the thickness of the diffuse layer, thereby weakening the electric field near the clay surface and resulting in improved clay aggregate stability. Even though we only demonstrated specific ion effects on aggregate stability with several alkali ions, our results indicate that these effects could be universally important in soil aggregate stability. PMID:25874864

Outer-Planet Mission Analysis Using Solar-Electric Ion Propulsion

NASA Technical Reports Server (NTRS)

Woo, Byoungsam; Coverstone, Victoria L.; Hartmann, John W.; Cupples, Michael

2003-01-01

Outer-planet mission analysis was performed using three next generation solar-electric ion thruster models. Optimal trajectories are presented that maximize the delivered mass to the designated outer planet. Trajectories to Saturn and Neptune with a single Venus gravity assist are investigated. For each thruster model, the delivered mass versus flight time curve was generated to obtain thruster model performance. The effects of power to the thrusters and resonance ratio of Venutian orbital periods to spacecraft period were also studied. Multiple locally optimal trajectories to Saturn and Neptune have been discovered in different regions of the parameter search space. The characteristics of each trajectory are noted.

Photodissociation of methyl formate: Conical intersections, roaming and triple fragmentation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, King-Chuen; Tsai, Po-Yu; Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan

2015-12-31

The photodissociation channels of methyl formate have been extensively investigated by two different advanced experimental techniques, ion imaging and Fourier-Transform-Infrared emission spectroscopy, combined with quantum chemical calculations and molecular dynamics simulations. Our aim is to characterize the role of alternative routes to the conventional transition-state mediated pathway: the roaming and the triple fragmentation processes. The photolysis experiments, carried out at a range of laser wavelengths in the vicinity of the triple fragmentation threshold, beside the simulation of large bunches of classical trajectories with different initial conditions, have shown that both mechanisms share a common path that involves a conical intersectionmore » during the relaxation process from the electronic excited state S{sub 1} to the ground state S{sub 0}.« less

Trajectory analysis of low-energy and hyperthermal ions scattered from Cu(110)

DOE Office of Scientific and Technical Information (OSTI.GOV)

McEachern, R.L.; Goodstein, D.M.; Cooper, B.H.

1989-05-15

Trajectories of Na{sup +} ions scattered from the Cu(110) surface in the <1 1bar 0> and <001> azimuths were studied for a range of incident energies from 56 eV to 4 keV. The goal is to explain the trends observed in the energy spectra and determine what types of trajectories contribute to these spectra. Using the computer program SAFARI, simulations were performed with trajectory analyses for 100-, 200-, and 400-eV scattering. We show results from the 100-eV simulations in both azimuths and compare them with the experimental data. The simulated energy spectra are in excellent agreement with the data. Ionmore » trajectories and impact parameter plots from the simulations are used to determine the relative importance of different types of ion-surface-atom collisions. The simulations have shown that the striking differences observed in comparing the <1 1bar 0> and <001> spectra are mostly due to ions which scatter from second-layer atoms. This system exhibits strong focusing onto the second-layer atoms by the first-layer rows, and the focusing is very sensitive to the spacing between the rows. At the lower beam energies, scattering from the second layer dominates the measured spectra.« less

Vibration-translation energy transfer in anharmonic diatomic molecules. 1: A critical evaluation of the semiclassical approximation

NASA Technical Reports Server (NTRS)

Mckenzie, R. L.

1974-01-01

The semiclassical approximation is applied to anharmonic diatomic oscillators in excited initial states. Multistate numerical solutions giving the vibrational transition probabilities for collinear collisions with an inert atom are compared with equivalent, exact quantum-mechanical calculations. Several symmetrization methods are shown to correlate accurately the predictions of both theories for all initial states, transitions, and molecular types tested, but only if coupling of the oscillator motion and the classical trajectory of the incident particle is considered. In anharmonic heteronuclear molecules, the customary semiclassical method of computing the classical trajectory independently leads to transition probabilities with anomalous low-energy resonances. Proper accounting of the effects of oscillator compression and recoil on the incident particle trajectory removes the anomalies and restores the applicability of the semiclassical approximation.

Advances in Heavy Ion Beam Probe Technology and Operation on MST

NASA Astrophysics Data System (ADS)

Demers, D. R.; Connor, K. A.; Schoch, P. M.; Radke, R. J.; Anderson, J. K.; Craig, D.; den Hartog, D. J.

2003-10-01

A technique to map the magnetic field of a plasma via spectral imaging is being developed with the Heavy Ion Beam Probe on the Madison Symmetric Torus. The technique will utilize two-dimensional images of the ion beam in the plasma, acquired by two CCD cameras, to generate a three-dimensional reconstruction of the beam trajectory. This trajectory, and the known beam ion mass, energy and charge-state, will be used to determine the magnetic field of the plasma. A suitable emission line has not yet been observed since radiation from the MST plasma is both broadband and intense. An effort to raise the emission intensity from the ion beam by increasing beam focus and current has been undertaken. Simulations of the accelerator ion optics and beam characteristics led to a technique, confirmed by experiment, that achieves a narrower beam and marked increase in ion current near the plasma surface. The improvements arising from these simulations will be discussed. Realization of the magnetic field mapping technique is contingent upon accurate reconstruction of the beam trajectory from the camera images. Simulations of two camera CCD images, including the interior of MST, its various landmarks and beam trajectories have been developed. These simulations accept user input such as camera locations, resolution via pixellization and noise. The quality of the images simulated with these and other variables will help guide the selection of viewing port pairs, image size and camera specifications. The results of these simulations will be presented.

Following the Ions through a Mass Spectrometer with Atmospheric Pressure Interface: Simulation of Complete Ion Trajectories from Ion Source to Mass Analyzer.

PubMed

Zhou, Xiaoyu; Ouyang, Zheng

2016-07-19

Ion trajectory simulation is an important and useful tool in instrumentation development for mass spectrometry. Accurate simulation of the ion motion through the mass spectrometer with atmospheric pressure ionization source has been extremely challenging, due to the complexity in gas hydrodynamic flow field across a wide pressure range as well as the computational burden. In this study, we developed a method of generating the gas flow field for an entire mass spectrometer with an atmospheric pressure interface. In combination with the electric force, for the first time simulation of ion trajectories from an atmospheric pressure ion source to a mass analyzer in vacuum has been enabled. A stage-by-stage ion repopulation method has also been implemented for the simulation, which helped to avoid an intolerable computational burden for simulations at high pressure regions while it allowed statistically meaningful results obtained for the mass analyzer. It has been demonstrated to be suitable to identify a joint point for combining the high and low pressure fields solved individually. Experimental characterization has also been done to validate the new method for simulation. Good agreement was obtained between simulated and experimental results for ion transfer though an atmospheric pressure interface with a curtain gas.

On the Relativistic Correction of Particles Trajectory in Tandem Type Electrostatic Accelerator

NASA Astrophysics Data System (ADS)

Minárik, Stanislav

2015-08-01

A constant potential is applied to the acceleration of the ion-beam in the tandem type electrostatic accelerator. However, not just one voltage is applied, but instead a number of applications can be made in succession by means of the tandem arrangement of high voltage tubes. This number of voltage applications, which is the number of so-called "stages" of a tandem accelerator, may be two, three, or four, depending on the chosen design. Electrostatic field with approximately constant intensity acts on ions in any stage. In general, non-relativistic dynamics is used for the description of the ion transport in tandem accelerator. Energies of accelerated ions are too low and relativistic effects cannot be commonly observed by standard experimental technique. Estimation of possible relativistic correction of ion trajectories is therefore only a matter of calculation. In this note, we briefly present such calculation. Our aim is to show how using the relativistic dynamics modifies the particles trajectory in tandem type accelerator and what parameters determine this modification.

Mean-trajectory approximation for electronic and vibrational-electronic nonlinear spectroscopy

NASA Astrophysics Data System (ADS)

Loring, Roger F.

2017-04-01

Mean-trajectory approximations permit the calculation of nonlinear vibrational spectra from semiclassically quantized trajectories on a single electronically adiabatic potential surface. By describing electronic degrees of freedom with classical phase-space variables and subjecting these to semiclassical quantization, mean-trajectory approximations may be extended to compute both nonlinear electronic spectra and vibrational-electronic spectra. A general mean-trajectory approximation for both electronic and nuclear degrees of freedom is presented, and the results for purely electronic and for vibrational-electronic four-wave mixing experiments are quantitatively assessed for harmonic surfaces with linear electronic-nuclear coupling.

A model for explaining fusion suppression using classical trajectory method

NASA Astrophysics Data System (ADS)

Phookan, C. K.; Kalita, K.

2015-01-01

We adopt a semi-classical approach for explanation of projectile breakup and above barrier fusion suppression for the reactions 6Li+152Sm and 6Li+144Sm. The cut-off impact parameter for fusion is determined by employing quantum mechanical ideas. Within this cut-off impact parameter for fusion, the fraction of projectiles undergoing breakup is determined using the method of classical trajectory in two-dimensions. For obtaining the initial conditions of the equations of motion, a simplified model of the 6Li nucleus has been proposed. We introduce a simple formula for explanation of fusion suppression. We find excellent agreement between the experimental and calculated fusion cross section. A slight modification of the above formula for fusion suppression is also proposed for a three-dimensional model.

Transition of recollision trajectories from linear to elliptical polarization

DOE PAGES

Li, Yingbin; Yu, Benhai; Tang, Qingbin; ...

2016-03-15

Using a classical ensemble method, we revisit the topic of recollision and nonsequential double ionization with elliptically polarized laser fields. We focus on how the recollision mechanism transitions from short trajectories with linear polarization to long trajectories with elliptical polarization. Furthermore, we propose how this transition can be observed by measuring the carrier-envelop-phase dependence of the correlated electron momentum spectra using currently available few-cycle laser pulses.

Measurements of C V flows from thermal charge-exchange excitation in divertor plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zaniol, B.; Isler, R. C.; Brooks, N. H.

2001-10-01

Certain transitions of C IV (C{sup 3+}) from n=7 to n=6 ({approx}7226 {angstrom}) and from n=6 to n=5 ({approx}4660 {angstrom}) sometimes appear much brighter in tokamak divertors than expected for electron-impact excitation from the ground state. This situation occurs because of charge exchange between C V (C{sup 4+}) and recycling thermal deuterium atoms in the n=2 level. As a result, it is possible to extend parallel flow measurements of carbon, which have previously been performed on C II--C IV ions using Doppler shift spectroscopy, to include flows of the He-like C V ions. The work described here includes modeling ofmore » the spectral features, correlation of state populations with classical Monte Carlo trajectory (CTMC) predictions, and applications to flow measurements in the DIII-D divertor [Plasma Physics Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159; Proceedings of the 18th IEEE/NPSS Symposium on Fusion Engineering, Albuquerque (Institute of Electrical and Electronic Engineers, Piscataway, 1999), p. 515].« less

Measurements of C V flows from thermal charge-exchange excitation in divertor plasmas

NASA Astrophysics Data System (ADS)

Zaniol, B.; Isler, R. C.; Brooks, N. H.; West, W. P.; Olson, R. E.

2001-10-01

Certain transitions of C IV (C3+) from n=7 to n=6 (≈7226 Å) and from n=6 to n=5 (≈4660 Å) sometimes appear much brighter in tokamak divertors than expected for electron-impact excitation from the ground state. This situation occurs because of charge exchange between C V (C4+) and recycling thermal deuterium atoms in the n=2 level. As a result, it is possible to extend parallel flow measurements of carbon, which have previously been performed on C II-C IV ions using Doppler shift spectroscopy, to include flows of the He-like C V ions. The work described here includes modeling of the spectral features, correlation of state populations with classical Monte Carlo trajectory (CTMC) predictions, and applications to flow measurements in the DIII-D divertor [Plasma Physics Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159; Proceedings of the 18th IEEE/NPSS Symposium on Fusion Engineering, Albuquerque (Institute of Electrical and Electronic Engineers, Piscataway, 1999), p. 515].

Composition and structure of surfaces by time-of-flight scattering and recoiling spectrometry (TOF-SARS)

NASA Astrophysics Data System (ADS)

Ahn, Jeongheon

1997-10-01

Time-of-flight scattering and recoiling spectrometry (TOF-SARS) was applied to characterize surface structures in order to understand the chemical and physical phenomena on various surfaces. The combination of TOF-SARS, LEED, and classical ion trajectory simulations has allowed characterization of the elemental composition in the outermost atomic layers, surface symmetry, and possible reconstruction or relaxation. The composition and structure of the CdS\\{0001\\}-(1 x 1) and CdS\\{000bar1\\}-(1 x 1) surfaces were investigated. The termination layer of each surface was determined by grazing incidence TOF-SARS. Both (1 x 1) surfaces are bulk-terminated without any reconstruction or relaxation detected by TOF-SARS. Each surface has two domains which are rotated by 60sp° from each other and there exist steps on both surfaces. The CdS\\{0001\\}-(1 x 1) surface is stabilized by O and H covering half a monolayer which are structurally ordered on the surface, while the O and H on the CdS\\{000bar1\\}-(1 x 1) stabilize the surface without ordering. The study of GaN\\{000bar1\\}-(1 x 1) shows the bulk-termination of the surface with no detectable reconstruction or relaxation. The surface is terminated in a N layer with Ga in the 2sp{nd}-layer. H atoms are bound to the outermost N atoms with a coverage of ˜3/4 monolayer and protrude outward from the surface. The surface termination, composition and structure of the Alsb2Osb3 (sapphire) were examined. The surface relaxation was studied quantitatively using classical ion trajectory simulations along with TOF-SARS. The surface undergoes 1sp{st}{-}2sp{nd}-layer relaxation as large as 0.5 A from the bulk value resulting in near coplanarity of Al and O atoms. The reconstruction of the Ni\\{100\\}-(2 x 2)-C surface was studied by TOF-SARS. The surface contained 80% of the (2 x 2)p4g phase and 20% of the unreconstructed (2 x 2) phase. The displacement of Ni atoms was determined by comparing the experimental and simulated results.

Quantum work in the Bohmian framework

NASA Astrophysics Data System (ADS)

Sampaio, R.; Suomela, S.; Ala-Nissila, T.; Anders, J.; Philbin, T. G.

2018-01-01

At nonzero temperature classical systems exhibit statistical fluctuations of thermodynamic quantities arising from the variation of the system's initial conditions and its interaction with the environment. The fluctuating work, for example, is characterized by the ensemble of system trajectories in phase space and, by including the probabilities for various trajectories to occur, a work distribution can be constructed. However, without phase-space trajectories, the task of constructing a work probability distribution in the quantum regime has proven elusive. Here we use quantum trajectories in phase space and define fluctuating work as power integrated along the trajectories, in complete analogy to classical statistical physics. The resulting work probability distribution is valid for any quantum evolution, including cases with coherences in the energy basis. We demonstrate the quantum work probability distribution and its properties with an exactly solvable example of a driven quantum harmonic oscillator. An important feature of the work distribution is its dependence on the initial statistical mixture of pure states, which is reflected in higher moments of the work. The proposed approach introduces a fundamentally different perspective on quantum thermodynamics, allowing full thermodynamic characterization of the dynamics of quantum systems, including the measurement process.

LSP simulations of fast ions slowing down in cool magnetized plasma

NASA Astrophysics Data System (ADS)

Evans, Eugene S.; Cohen, Samuel A.

2015-11-01

In MFE devices, rapid transport of fusion products, e.g., tritons and alpha particles, from the plasma core into the scrape-off layer (SOL) could perform the dual roles of energy and ash removal. Through these two processes in the SOL, the fast particle slowing-down time will have a major effect on the energy balance of a fusion reactor and its neutron emissions, topics of great importance. In small field-reversed configuration (FRC) devices, the first-orbit trajectories of most fusion products will traverse the SOL, potentially allowing those particles to deposit their energy in the SOL and eventually be exhausted along the open field lines. However, the dynamics of the fast-ion energy loss processes under conditions expected in the FRC SOL, where the Debye length is greater than the electron gyroradius, are not fully understood. What modifications to the classical slowing down rate are necessary? Will instabilities accelerate the energy loss? We use LSP, a 3D PIC code, to examine the effects of SOL plasma parameters (density, temperature and background magnetic field strength) on the slowing down time of fast ions in a cool plasma with parameters similar to those expected in the SOL of small FRC reactors. This work supported by DOE contract DE-AC02-09CH11466.

Estimation of key parameters in adaptive neuron model according to firing patterns based on improved particle swarm optimization algorithm

NASA Astrophysics Data System (ADS)

Yuan, Chunhua; Wang, Jiang; Yi, Guosheng

2017-03-01

Estimation of ion channel parameters is crucial to spike initiation of neurons. The biophysical neuron models have numerous ion channel parameters, but only a few of them play key roles in the firing patterns of the models. So we choose three parameters featuring the adaptation in the Ermentrout neuron model to be estimated. However, the traditional particle swarm optimization (PSO) algorithm is still easy to fall into local optimum and has the premature convergence phenomenon in the study of some problems. In this paper, we propose an improved method that uses a concave function and dynamic logistic chaotic mapping mixed to adjust the inertia weights of the fitness value, effectively improve the global convergence ability of the algorithm. The perfect predicting firing trajectories of the rebuilt model using the estimated parameters prove that only estimating a few important ion channel parameters can establish the model well and the proposed algorithm is effective. Estimations using two classic PSO algorithms are also compared to the improved PSO to verify that the algorithm proposed in this paper can avoid local optimum and quickly converge to the optimal value. The results provide important theoretical foundations for building biologically realistic neuron models.

Computational simulations of hydrogen circular migration in protonated acetylene induced by circularly polarized light

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shi, Xuetao; Li, Wen; Schlegel, H. Bernhard, E-mail: hbs@chem.wayne.edu

2016-08-28

The hydrogens in protonated acetylene are very mobile and can easily migrate around the C{sub 2} core by moving between classical and non-classical structures of the cation. The lowest energy structure is the T-shaped, non-classical cation with a hydrogen bridging the two carbons. Conversion to the classical H{sub 2}CCH{sup +} ion requires only 4 kcal/mol. The effect of circularly polarized light on the migration of hydrogens in oriented C{sub 2}H{sub 3}{sup +} has been simulated by Born-Oppenheimer molecular dynamics. Classical trajectory calculations were carried out with the M062X/6-311+G(3df,2pd) level of theory using linearly and circularly polarized 32 cycle 7 μmmore » cosine squared pulses with peak intensity of 5.6 × 10{sup 13} W/cm{sup 2} and 3.15 × 10{sup 13} W/cm{sup 2}, respectively. These linearly and circularly polarized pulses transfer similar amounts of energy and total angular momentum to C{sub 2}H{sub 3}{sup +}. The average angular momentum vectors of the three hydrogens show opposite directions of rotation for right and left circularly polarized light, but no directional preference for linearly polarized light. This difference results in an appreciable amount of angular displacement of the three hydrogens relative to the C{sub 2} core for circularly polarized light, but only an insignificant amount for linearly polarized light. Over the course of the simulation with circularly polarized light, this corresponds to a propeller-like motion of the three hydrogens around the C{sub 2} core of protonated acetylene.« less

Charge Transfer in Collisions of S^4+ with He.

NASA Astrophysics Data System (ADS)

Wang, J. G.; Stancil, P. C.; Turner, A. R.; Cooper, D. L.; Schultz, D. R.; Rakovic, M. J.; Fritsch, W.; Zygelman, B.

2001-05-01

Charge transfer processes due to collisions of ground state S^4+ ions with atomic helium were investigated for energies between 0.1 meV/u and 10 MeV/u. Total and state-selective cross sections and rate coefficients were obtained utilizing the quantum-mechanical molecular-orbital close-coupling (MOCC), atomic-orbital close-coupling, classical trajectory Monte Carlo (CTMC), and continuum distorted wave methods. The MOCC calculations utilized ab initio adiabatic potentials and nonadiabatic radial coupling matrix elements obtained with the spin-coupled valence-bond approach. A number of variants of the CTMC approach were also explored. Previous data are limited to an earlier Landau-Zener calculation of the total rate coefficient for which our results are two orders of magnitude larger. An observed multichannel interference effect in the MOCC results will also be discussed.

Radiative-emission analysis in charge-exchange collisions of O6 + with argon, water, and methane

NASA Astrophysics Data System (ADS)

Leung, Anthony C. K.; Kirchner, Tom

2017-04-01

Processes of electron capture followed by Auger and radiative decay were investigated in slow ion-atom and -molecule collisions. A quantum-mechanical analysis which utilizes the basis generator method within an independent electron model was carried out for collisions of O 6 + with Ar, H2O , and CH4 at impact energies of 1.17 and 2.33 keV/amu. At these impact energies, a closure approximation in the spectral representation of the Hamiltonian for molecules was found to be necessary to yield reliable results. Total single-, double-, and triple-electron-capture cross sections obtained show good agreement with previous measurements and calculations using the classical trajectory Monte Carlo method. The corresponding emission spectra from single capture for each collision system are in satisfactory agreement with previous calculations.

Rapid fixation of methylene chloride by a macrocyclic amine.

PubMed

Lee, Jung-Jae; Stanger, Keith J; Noll, Bruce C; Gonzalez, Carlos; Marquez, Manuel; Smith, Bradley D

2005-03-30

A simple macrocyclic amine is alkylated by methylene chloride to give a quaternary ammonium chloride salt. When methylene chloride is the solvent, the reaction exhibits pseudo-first-order kinetics, and the reaction half-life at 25.0 degrees C is 2.0 min. The reaction half-life for a structurally related, acyclic amine is approximately 50 000 times longer. Detailed calculations favor a mechanism where the methylene chloride associates with the macrocycle to form an activated prereaction complex. The macrocyclic nitrogen subsequently attacks the methylene chloride with a classic SN2 trajectory, and although the carbon-chlorine bond breaks, the chloride leaving group does not separate from the newly formed cationic macrocycle, such that the product is a tightly associated ion-pair. X-ray crystal structures of the starting amine and the product salt, as well as kinetic data, support this mechanism.

Trajectories and traversal times in quantum tunneling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Zhi Hong.

1989-01-01

The classical concepts of trajectories and traversal times applied to quantum tunneling are discussed. By using the Wentzel-Kramers-Brillouin approximation, it is found that in a forbidden region of a multidimensional space the wave function can be described by two sets of trajectories, or equivalently by two sets of wave fronts. The trajectories belonging to different sets are mutually orthogonal. An extended Huygens construction is proposed to determine these wave fronts and trajectories. In contrast to the classical results in the allowed region, these trajectories couple to each other. However, if the incident wave is normal to the turning surface, themore » trajectories are found to be independent and can be determined by Newton's equations of motion with inverted potential and energy. The multidimensional tunneling theory is then applied to the scanning tunneling microscope to calculate the current density distribution and to derive the expressions for the lateral resolution and the surface corrugation amplitude. The traversal time in quantum tunneling, i.e. tunneling time, is found to depend on model calculations and simulations. Computer simulation of a wave packet tunneling through a square barrier is performed. Several approaches, including the phase method, Larmor clock, and time-dependent barrier model, are investigated. For a square barrier, two characteristic times are found: One is equal to the barrier width divided by the magnitude of the imaginary velocity; the other is equal to the decay length divided by the incident velocity. It is believed that the tunneling time can only be defined operationally.« less

IBiSA_Tools: A Computational Toolkit for Ion-Binding State Analysis in Molecular Dynamics Trajectories of Ion Channels.

PubMed

Kasahara, Kota; Kinoshita, Kengo

2016-01-01

Ion conduction mechanisms of ion channels are a long-standing conundrum. Although the molecular dynamics (MD) method has been extensively used to simulate ion conduction dynamics at the atomic level, analysis and interpretation of MD results are not straightforward due to complexity of the dynamics. In our previous reports, we proposed an analytical method called ion-binding state analysis to scrutinize and summarize ion conduction mechanisms by taking advantage of a variety of analytical protocols, e.g., the complex network analysis, sequence alignment, and hierarchical clustering. This approach effectively revealed the ion conduction mechanisms and their dependence on the conditions, i.e., ion concentration and membrane voltage. Here, we present an easy-to-use computational toolkit for ion-binding state analysis, called IBiSA_tools. This toolkit consists of a C++ program and a series of Python and R scripts. From the trajectory file of MD simulations and a structure file, users can generate several images and statistics of ion conduction processes. A complex network named ion-binding state graph is generated in a standard graph format (graph modeling language; GML), which can be visualized by standard network analyzers such as Cytoscape. As a tutorial, a trajectory of a 50 ns MD simulation of the Kv1.2 channel is also distributed with the toolkit. Users can trace the entire process of ion-binding state analysis step by step. The novel method for analysis of ion conduction mechanisms of ion channels can be easily used by means of IBiSA_tools. This software is distributed under an open source license at the following URL: http://www.ritsumei.ac.jp/~ktkshr/ibisa_tools/.

State-specific tunneling lifetimes from classical trajectories: H-atom dissociation in electronically excited pyrrole

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, Weiwei; Domcke, Wolfgang; Farantos, Stavros C.

A trajectory method of calculating tunneling probabilities from phase integrals along straight line tunneling paths, originally suggested by Makri and Miller [J. Chem. Phys. 91, 4026 (1989)] and recently implemented by Truhlar and co-workers [Chem. Sci. 5, 2091 (2014)], is tested for one- and two-dimensional ab initio based potentials describing hydrogen dissociation in the {sup 1}B{sub 1} excited electronic state of pyrrole. The primary observables are the tunneling rates in a progression of bending vibrational states lying below the dissociation barrier and their isotope dependences. Several initial ensembles of classical trajectories have been considered, corresponding to the quasiclassical and themore » quantum mechanical samplings of the initial conditions. It is found that the sampling based on the fixed energy Wigner density gives the best agreement with the quantum mechanical dissociation rates.« less

Moyal dynamics and trajectories

NASA Astrophysics Data System (ADS)

Braunss, G.

2010-01-01

We give first an approximation of the operator δh: f → δhf := h*planckf - f*planckh in terms of planck2n, n >= 0, where h\\equiv h(p,q), (p,q)\\in {\\mathbb R}^{2 n} , is a Hamilton function and *planck denotes the star product. The operator, which is the generator of time translations in a *planck-algebra, can be considered as a canonical extension of the Liouville operator Lh: f → Lhf := {h, f}Poisson. Using this operator we investigate the dynamics and trajectories of some examples with a scheme that extends the Hamilton-Jacobi method for classical dynamics to Moyal dynamics. The examples we have chosen are Hamiltonians with a one-dimensional quartic potential and two-dimensional radially symmetric nonrelativistic and relativistic Coulomb potentials, and the Hamiltonian for a Schwarzschild metric. We further state a conjecture concerning an extension of the Bohr-Sommerfeld formula for the calculation of the exact eigenvalues for systems with classically periodic trajectories.

The ortho-to-para ratio of H2Cl+: Quasi-classical trajectory calculations and new simulations in light of new observations

NASA Astrophysics Data System (ADS)

Le Gal, R.; Xie, C.; Herbst, E.; Talbi, D.; Guo, H.; Muller, S.

2017-12-01

Multi-hydrogenated species with proper symmetry properties can present different spin configurations, and thus exist under different spin symmetry forms, labeled as para and ortho for two-hydrogen molecules. We investigated here the ortho-to-para ratio (OPR) of H2Cl+ in the light of new observations performed in the z = 0.89 absorber toward the lensed quasar PKS 1830-211 with the Atacama Large Millimeter/submillimeter Array (ALMA). Two independent lines of sight were observed, to the southwest (SW) and northeast (NE) images of the quasar, with OPR values found to be 3.15 ± 0.13 and 3.1 ± 0.5 in each region, respectively, in agreement with a spin statistical weight of 3:1. An OPR of 3:1 for a molecule containing two identical hydrogen nuclei can refer to either a statistical result or a high-temperature limit depending on the reaction mechanism leading to its formation. It is thus crucial to identify rigorously how OPRs are produced in order to constrain the information that these probes can provide. To understand the production of the H2Cl+ OPR, we undertook a careful theoretical study of the reaction mechanisms involved with the aid of quasi-classical trajectory calculations on a new global potential energy surface fit to a large number of high-level ab initio data. Our study shows that the major formation reaction for H2Cl+ produces this ion via a hydrogen abstraction rather than a scrambling mechanism. Such a mechanism leads to a 3:1 OPR, which is not changed by destruction and possible thermalization reactions for H2Cl+ and is thus likely to be the cause of observed 3:1 OPR ratios, contrary to the normal assumption of scrambling.

Wigner flow reveals topological order in quantum phase space dynamics.

PubMed

Steuernagel, Ole; Kakofengitis, Dimitris; Ritter, Georg

2013-01-18

The behavior of classical mechanical systems is characterized by their phase portraits, the collections of their trajectories. Heisenberg's uncertainty principle precludes the existence of sharply defined trajectories, which is why traditionally only the time evolution of wave functions is studied in quantum dynamics. These studies are quite insensitive to the underlying structure of quantum phase space dynamics. We identify the flow that is the quantum analog of classical particle flow along phase portrait lines. It reveals hidden features of quantum dynamics and extra complexity. Being constrained by conserved flow winding numbers, it also reveals fundamental topological order in quantum dynamics that has so far gone unnoticed.

Quantitative underwater 3D motion analysis using submerged video cameras: accuracy analysis and trajectory reconstruction.

PubMed

Silvatti, Amanda P; Cerveri, Pietro; Telles, Thiago; Dias, Fábio A S; Baroni, Guido; Barros, Ricardo M L

2013-01-01

In this study we aim at investigating the applicability of underwater 3D motion capture based on submerged video cameras in terms of 3D accuracy analysis and trajectory reconstruction. Static points with classical direct linear transform (DLT) solution, a moving wand with bundle adjustment and a moving 2D plate with Zhang's method were considered for camera calibration. As an example of the final application, we reconstructed the hand motion trajectories in different swimming styles and qualitatively compared this with Maglischo's model. Four highly trained male swimmers performed butterfly, breaststroke and freestyle tasks. The middle fingertip trajectories of both hands in the underwater phase were considered. The accuracy (mean absolute error) of the two calibration approaches (wand: 0.96 mm - 2D plate: 0.73 mm) was comparable to out of water results and highly superior to the classical DLT results (9.74 mm). Among all the swimmers, the hands' trajectories of the expert swimmer in the style were almost symmetric and in good agreement with Maglischo's model. The kinematic results highlight symmetry or asymmetry between the two hand sides, intra- and inter-subject variability in terms of the motion patterns and agreement or disagreement with the model. The two outcomes, calibration results and trajectory reconstruction, both move towards the quantitative 3D underwater motion analysis.

Multivalued classical mechanics arising from singularity loops in complex time

NASA Astrophysics Data System (ADS)

Koch, Werner; Tannor, David J.

2018-02-01

Complex-valued classical trajectories in complex time encounter singular times at which the momentum diverges. A closed time contour around such a singular time may result in final values for q and p that differ from their initial values. In this work, we develop a calculus for determining the exponent and prefactor of the asymptotic time dependence of p from the singularities of the potential as the singularity time is approached. We identify this exponent with the number of singularity loops giving distinct solutions to Hamilton's equations of motion. The theory is illustrated for the Eckart, Coulomb, Morse, and quartic potentials. Collectively, these potentials illustrate a wide variety of situations: poles and essential singularities at finite and infinite coordinate values. We demonstrate quantitative agreement between analytical and numerical exponents and prefactors, as well as the connection between the exponent and the time circuit count. This work provides the theoretical underpinnings for the choice of time contours described in the studies of Doll et al. [J. Chem. Phys. 58(4), 1343-1351 (1973)] and Petersen and Kay [J. Chem. Phys. 141(5), 054114 (2014)]. It also has implications for wavepacket reconstruction from complex classical trajectories when multiple branches of trajectories are involved.

Ion acceleration in a plasma focus

NASA Technical Reports Server (NTRS)

Gary, S. P.

1974-01-01

The electric and magnetic fields associated with anomalous diffusion to the axis of a linear plasma discharge are used to compute representative ion trajectories. Substantial axial acceleration of the ions is demonstrated.

Sperm chemotaxis in siphonophores. II. Calcium-dependent asymmetrical movement of spermatozoa induced by the attractant.

PubMed

Cosson, M P; Carré, D; Cosson, J

1984-06-01

Spermatozoa from siphonophores have been shown to be attracted towards an extracellular structure, the cupule, which covers the predetermined site of fertilization of the egg. Observations on sperm behaviour during the chemotactic response show that spermatozoa describe trajectories of large diameter (700-1000 micron) while far from the cupule, and of smaller diameter (200 micron) in the cupule area. The transition between the two types of swimming occurs progressively when spermatozoa cross a 3 mm wide area around the cupule. After a few minutes 99% of the spermatozoa keep swimming around the attractant source, following circular paths 150-200 micron in diameter. In the absence of the attractant, comparable modifications of sperm trajectories are observed in the presence of the ionophore A23187 and high calcium concentrations. In the presence of 10(-2) M calcium ions, A23187-treated spermatozoa describe trajectories 200 micron in diameter, which increase up to 800 micron at lower calcium concentrations (10(-6) M). In the absence of calcium ions, spermatozoa swim across the cupule area without modification of their trajectories and no sperm accumulation can be detected. This requirement of the chemotactic response for calcium ions is observed either with fresh cupules stuck on the eggs, with cupules separated from the eggs, or with cupule extracts. Moreover, a soluble component fractionated from the cupule induces, when diluted in sea water, a reduction in the size of the sperm trajectories and this also requires calcium ions. The present data show that the chemotactic response of siphonophore sperm, which requires millimolar concentrations of calcium ions, occurs through a non-transient induction of increased asymmetry of the flagellar waveform. It is proposed that the natural attractant operates to produce an increase in the intraaxonemal calcium concentration.

Fractional dynamics using an ensemble of classical trajectories

NASA Astrophysics Data System (ADS)

Sun, Zhaopeng; Dong, Hao; Zheng, Yujun

2018-01-01

A trajectory-based formulation for fractional dynamics is presented and the trajectories are generated deterministically. In this theoretical framework, we derive a new class of estimators in terms of confluent hypergeometric function (F11) to represent the Riesz fractional derivative. Using this method, the simulation of free and confined Lévy flight are in excellent agreement with the exact numerical and analytical results. In addition, the barrier crossing in a bistable potential driven by Lévy noise of index α is investigated. In phase space, the behavior of trajectories reveal the feature of Lévy flight in a better perspective.

Reactive trajectories of the Ru2+/3+ self-exchange reaction and the connection to Marcus' theory.

PubMed

Tiwari, Ambuj; Ensing, Bernd

2016-12-22

Outer sphere electron transfer between two ions in aqueous solution is a rare event on the time scale of first principles molecular dynamics simulations. We have used transition path sampling to generate an ensemble of reactive trajectories of the self-exchange reaction between a pair of Ru 2+ and Ru 3+ ions in water. To distinguish between the reactant and product states, we use as an order parameter the position of the maximally localised Wannier center associated with the transferring electron. This allows us to align the trajectories with respect to the moment of barrier crossing and compute statistical averages over the path ensemble. We compare our order parameter with two typical reaction coordinates used in applications of Marcus theory of electron transfer: the vertical gap energy and the solvent electrostatic potential at the ions.

Understanding the ion distributions near the boundaries of reconnection outflow region

NASA Astrophysics Data System (ADS)

Zhou, X.; Pan, D.; Angelopoulos, V.; Runov, A.; Zong, Q.; Pu, Z.

2016-12-01

An interesting signature observed shortly after the onset of magnetotail reconnection is the gradual appearance of a local peak of ion phase space density (PSD) in the duskward and downstream direction separated from the colder, nearly-isotropic ion population. Such characteristic ion distributions, well reproduced by a particle-tracing Liouville simulation, are found to appear only near the off-equatorial boundaries of the reconnection outflow region. Further analysis on ion trajectories suggests that the ions at the local peak and at the neighboring PSD cleft both belong to the outflowing population; they both meander across the neutral sheet to exhibit duskward velocities near the off-equatorial boundaries of their trajectories. The difference between them is that the local peak originates from ions previously constituting the pre-onset plasma sheet, whereas the cleft corresponds to the inflowing lobe ions before they are repelled in the downstream direction. As reconnection proceeds, the local PSD peak attenuates and then disappears, which indicates the eventual depletion of thermal ions in the pre-onset plasma sheet.

Study of In-Trap Ion Clouds by Ion Trajectory Simulations.

PubMed

Zhou, Xiaoyu; Liu, Xinwei; Cao, Wenbo; Wang, Xiao; Li, Ming; Qiao, Haoxue; Ouyang, Zheng

2018-02-01

Gaussian distribution has been utilized to describe the global number density distribution of ion cloud in the Paul trap, which is known as the thermal equilibrium theory and widely used in theoretical modeling of ion clouds in the ion traps. Using ion trajectory simulations, however, the ion clouds can now also be treated as a dynamic ion flow field and the location-dependent features could now be characterized. This study was carried out to better understand the in-trap ion cloud properties, such as the local particle velocity and temperature. The local ion number densities were found to be heterogeneously distributed in terms of mean and distribution width; the velocity and temperature of the ion flow varied with pressure depending on the flow type of the neutral molecules; and the "quasi-static" equilibrium status can only be achieved after a certain number of collisions, for which the time period is pressure-dependent. This work provides new insights of the ion clouds that are globally stable but subjected to local rf heating and collisional cooling. Graphical Abstract ᅟ.

Comparing Classical Water Models Using Molecular Dynamics to Find Bulk Properties

ERIC Educational Resources Information Center

Kinnaman, Laura J.; Roller, Rachel M.; Miller, Carrie S.

2018-01-01

A computational chemistry exercise for the undergraduate physical chemistry laboratory is described. In this exercise, students use the molecular dynamics package Amber to generate trajectories of bulk liquid water for 4 different water models (TIP3P, OPC, SPC/E, and TIP4Pew). Students then process the trajectory to calculate structural (radial…

On the Trajectories of Projectiles Depicted in Early Ballistic Woodcuts

ERIC Educational Resources Information Center

Stewart, Sean M.

2012-01-01

Motivated by quaint woodcut depictions often found in many late 16th and 17th century ballistic manuals of cannonballs fired in air, a comparison of their shapes with those calculated for the classic case of a projectile moving in a linear resisting medium is made. In considering the asymmetrical nature of such trajectories, the initial launch…

Optimal solar sail planetocentric trajectories

NASA Technical Reports Server (NTRS)

Sackett, L. L.

1977-01-01

The analysis of solar sail planetocentric optimal trajectory problem is described. A computer program was produced to calculate optimal trajectories for a limited performance analysis. A square sail model is included and some consideration is given to a heliogyro sail model. Orbit to a subescape point and orbit to orbit transfer are considered. Trajectories about the four inner planets can be calculated and shadowing, oblateness, and solar motion may be included. Equinoctial orbital elements are used to avoid the classical singularities, and the method of averaging is applied to increase computational speed. Solution of the two-point boundary value problem which arises from the application of optimization theory is accomplished with a Newton procedure. Time optimal trajectories are emphasized, but a penalty function has been considered to prevent trajectories which intersect a planet's surface.

Classical impurity ion confinement in a toroidal magnetized fusion plasma.

PubMed

Kumar, S T A; Den Hartog, D J; Caspary, K J; Magee, R M; Mirnov, V V; Chapman, B E; Craig, D; Fiksel, G; Sarff, J S

2012-03-23

High-resolution measurements of impurity ion dynamics provide first-time evidence of classical ion confinement in a toroidal, magnetically confined plasma. The density profile evolution of fully stripped carbon is measured in MST reversed-field pinch plasmas with reduced magnetic turbulence to assess Coulomb-collisional transport without the neoclassical enhancement from particle drift effects. The impurity density profile evolves to a hollow shape, consistent with the temperature screening mechanism of classical transport. Corroborating methane pellet injection experiments expose the sensitivity of the impurity particle confinement time to the residual magnetic fluctuation amplitude.

Supersaturated calcium carbonate solutions are classical

PubMed Central

Henzler, Katja; Fetisov, Evgenii O.; Galib, Mirza; Baer, Marcel D.; Legg, Benjamin A.; Borca, Camelia; Xto, Jacinta M.; Pin, Sonia; Fulton, John L.; Schenter, Gregory K.; Govind, Niranjan; Siepmann, J. Ilja; Mundy, Christopher J.; Huthwelker, Thomas; De Yoreo, James J.

2018-01-01

Mechanisms of CaCO3 nucleation from solutions that depend on multistage pathways and the existence of species far more complex than simple ions or ion pairs have recently been proposed. Herein, we provide a tightly coupled theoretical and experimental study on the pathways that precede the initial stages of CaCO3 nucleation. Starting from molecular simulations, we succeed in correctly predicting bulk thermodynamic quantities and experimental data, including equilibrium constants, titration curves, and detailed x-ray absorption spectra taken from the supersaturated CaCO3 solutions. The picture that emerges is in complete agreement with classical views of cluster populations in which ions and ion pairs dominate, with the concomitant free energy landscapes following classical nucleation theory. PMID:29387793

Supersaturated calcium carbonate solutions are classical.

PubMed

Henzler, Katja; Fetisov, Evgenii O; Galib, Mirza; Baer, Marcel D; Legg, Benjamin A; Borca, Camelia; Xto, Jacinta M; Pin, Sonia; Fulton, John L; Schenter, Gregory K; Govind, Niranjan; Siepmann, J Ilja; Mundy, Christopher J; Huthwelker, Thomas; De Yoreo, James J

2018-01-01

Mechanisms of CaCO 3 nucleation from solutions that depend on multistage pathways and the existence of species far more complex than simple ions or ion pairs have recently been proposed. Herein, we provide a tightly coupled theoretical and experimental study on the pathways that precede the initial stages of CaCO 3 nucleation. Starting from molecular simulations, we succeed in correctly predicting bulk thermodynamic quantities and experimental data, including equilibrium constants, titration curves, and detailed x-ray absorption spectra taken from the supersaturated CaCO 3 solutions. The picture that emerges is in complete agreement with classical views of cluster populations in which ions and ion pairs dominate, with the concomitant free energy landscapes following classical nucleation theory.

Trajectory Control and Optimization for Responsive Spacecraft

DTIC Science & Technology

2012-03-22

Orbital Elements and Local-Vertical-Local-Horizontal Frame 10 2.3 Equinoctial Frame with respect to ECI Frame [17] . . . . . . . . . 14 3.1...position and velocity, classical orbital elements , and equinoctial elements . These methods are detailed in the following sections. 2.1.1 Inertial Position...trajectory. However, if the singularities are unavoidable equinoctial orbital elements could be used. 2.1.3 Equinoctial Elements . Equinoctial

Trajectory study of supercollision relaxation in highly vibrationally excited pyrazine and CO2.

PubMed

Li, Ziman; Sansom, Rebecca; Bonella, Sara; Coker, David F; Mullin, Amy S

2005-09-01

Classical trajectory calculations were performed to simulate state-resolved energy transfer experiments of highly vibrationally excited pyrazine (E(vib) = 37,900 cm(-1)) and CO(2), which were conducted using a high-resolution transient infrared absorption spectrometer. The goal here is to use classical trajectories to simulate the supercollision energy transfer pathway wherein large amounts of energy are transferred in single collisions in order to compare with experimental results. In the trajectory calculations, Newton's laws of motion are used for the molecular motion, isolated molecules are treated as collections of harmonic oscillators, and intermolecular potentials are formed by pairwise Lennard-Jones potentials. The calculations qualitatively reproduce the observed energy partitioning in the scattered CO(2) molecules and show that the relative partitioning between bath rotation and translation is dependent on the moment of inertia of the bath molecule. The simulations show that the low-frequency modes of the vibrationally excited pyrazine contribute most to the strong collisions. The majority of collisions lead to small DeltaE values and primarily involve single encounters between the energy donor and acceptor. The large DeltaE exchanges result from both single impulsive encounters and chattering collisions that involve multiple encounters.

Stereodynamics in NO(X) + Ar inelastic collisions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brouard, M., E-mail: mark.brouard@chem.ox.ac.uk; Chadwick, H.; Gordon, S. D. S.

2016-06-14

The effect of orientation of the NO(X) bond axis prior to rotationally inelastic collisions with Ar has been investigated experimentally and theoretically. A modification to conventional velocity-map imaging ion optics is described, which allows the orientation of hexapole state-selected NO(X) using a static electric field, followed by velocity map imaging of the resonantly ionized scattered products. Bond orientation resolved differential cross sections are measured experimentally for a series of spin-orbit conserving transitions and compared with quantum mechanical calculations. The agreement between experimental results and those from quantum mechanical calculations is generally good. Parity pairs, which have previously been observed inmore » collisions of unpolarized NO with various rare gases, are not observed due to the coherent superposition of the two j = 1/2, Ω = 1/2 Λ-doublet levels in the orienting field. The normalized difference differential cross sections are found to depend predominantly on the final rotational state, and are not very sensitive to the final Λ-doublet level. The differential steric effect has also been investigated theoretically, by means of quantum mechanical and classical calculations. Classically, the differential steric effect can be understood by considering the steric requirement for different types of trajectories that contribute to different regions of the differential cross section. However, classical effects cannot account quantitatively for the differential steric asymmetry observed in NO(X) + Ar collisions, which reflects quantum interference from scattering at either end of the molecule. This quantum interference effect is dominated by the repulsive region of the potential.« less

Transport studies in high-performance field reversed configuration plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gupta, S., E-mail: sgupta@trialphaenergy.com; Barnes, D. C.; Dettrick, S. A.

2016-05-15

A significant improvement of field reversed configuration (FRC) lifetime and plasma confinement times in the C-2 plasma, called High Performance FRC regime, has been observed with neutral beam injection (NBI), improved edge stability, and better wall conditioning [Binderbauer et al., Phys. Plasmas 22, 056110 (2015)]. A Quasi-1D (Q1D) fluid transport code has been developed and employed to carry out transport analysis of such C-2 plasma conditions. The Q1D code is coupled to a Monte-Carlo code to incorporate the effect of fast ions, due to NBI, on the background FRC plasma. Numerically, the Q1D transport behavior with enhanced transport coefficients (butmore » with otherwise classical parametric dependencies) such as 5 times classical resistive diffusion, classical thermal ion conductivity, 20 times classical electron thermal conductivity, and classical fast ion behavior fit with the experimentally measured time evolution of the excluded flux radius, line-integrated density, and electron/ion temperature. The numerical study shows near sustainment of poloidal flux for nearly 1 ms in the presence of NBI.« less

Power-law distributions for a trapped ion interacting with a classical buffer gas.

PubMed

DeVoe, Ralph G

2009-02-13

Classical collisions with an ideal gas generate non-Maxwellian distribution functions for a single ion in a radio frequency ion trap. The distributions have power-law tails whose exponent depends on the ratio of buffer gas to ion mass. This provides a statistical explanation for the previously observed transition from cooling to heating. Monte Carlo results approximate a Tsallis distribution over a wide range of parameters and have ab initio agreement with experiment.

Influence of the interplanetary magnetic field orientation on polar cap ion trajectories - Energy gain and drift effects

NASA Technical Reports Server (NTRS)

Delcourt, D. C.; Horwitz, J. L.; Swinney, K. R.

1988-01-01

The influence of the interplanetary magnetic field (IMF) orientation on the transport of low-energy ions injected from the ionosphere is investigated using three-dimensional particle codes. It is shown that, unlike the auroral zone outflow, the ions originating from the polar cap region exhibit drastically different drift paths during southward and northward IMF. During southward IMF orientation, a 'two-cell' convection pattern prevails in the ionosphere, and three-dimensional simulations of ion trajectories indicate a preferential trapping of the light ions H(+) in the central plasma sheet, due to the wide azimuthal dispersion of the heavy ions, O(+). In contrast, for northward IMF orientation, the 'four-cell' potential distribution predicted in the ionosphere imposes a temporary ion drift toward higher L shells in the central polar cap. In this case, while the light ions can escape into the magnetotail, the heavy ions can remain trapped, featuring more intense acceleration (from a few electron volts up to the keV range) followed by precipitation at high invariant latitudes, as a consequence of their further travel into the tail.

Wisdom from Conservatory Faculty: Insights on Success in Classical Music Performance

ERIC Educational Resources Information Center

Jarvin, Linda; Subotnik, Rena F.

2010-01-01

What does it take to become a successful performer of Western classical music in the United States today? What factors, beyond technical proficiency and musicality, come into play? We started exploring these questions in a study of gatekeepers' (e.g., critics, artistic directors) views on key variables that contribute to the career trajectories of…

Dissipative quantum trajectories in complex space: Damped harmonic oscillator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chou, Chia-Chun, E-mail: ccchou@mx.nthu.edu.tw

Dissipative quantum trajectories in complex space are investigated in the framework of the logarithmic nonlinear Schrödinger equation. The logarithmic nonlinear Schrödinger equation provides a phenomenological description for dissipative quantum systems. Substituting the wave function expressed in terms of the complex action into the complex-extended logarithmic nonlinear Schrödinger equation, we derive the complex quantum Hamilton–Jacobi equation including the dissipative potential. It is shown that dissipative quantum trajectories satisfy a quantum Newtonian equation of motion in complex space with a friction force. Exact dissipative complex quantum trajectories are analyzed for the wave and solitonlike solutions to the logarithmic nonlinear Schrödinger equation formore » the damped harmonic oscillator. These trajectories converge to the equilibrium position as time evolves. It is indicated that dissipative complex quantum trajectories for the wave and solitonlike solutions are identical to dissipative complex classical trajectories for the damped harmonic oscillator. This study develops a theoretical framework for dissipative quantum trajectories in complex space.« less

Formation of stable inverse sheath in ion–ion plasma by strong negative ion emission

NASA Astrophysics Data System (ADS)

Zhang, Zhe; Wu, Bang; Yang, Shali; Zhang, Ya; Chen, Dezhi; Fan, Mingwu; Jiang, Wei

2018-06-01

The effect of strong charged particle emission on plasma–wall interactions is a classical, yet unresolved question in plasma physics. Previous studies on secondary electron emission have shown that with different emission coefficients, there are classical, space-charge-limited, and inverse sheaths. In this letter, we demonstrate that a stable ion–ion inverse sheath and ion–ion plasma are formed with strong surface emission of negative ions. The continuous space-charge-limited to inverse ion–ion sheath transition is observed, and the plasma near the surface consequently transforms into pure ion–ion plasma. The results may explain the long-puzzled experimental observation that the density of negative ions depends on only charge not mass in negative ion sources.

Revisiting Adiabatic Switching for Initial Conditions in Quasi-Classical Trajectory Calculations: Application to CH4.

PubMed

Qu, Chen; Bowman, Joel M

2016-07-14

Semiclassical quantization of vibrational energies, using adiabatic switching (AS), is applied to CH4 using a recent ab initio potential energy surface, for which exact quantum calculations of vibrational energies are available. Details of the present calculations, which employ a harmonic normal-mode zeroth-order Hamiltonian, emphasize the importance of transforming to the Eckart frame during the propagation of the adiabatically switched Hamiltonian. The AS energies for the zero-point, and fundamental excitations of two modes are in good agreement with the quantum ones. The use of AS in the context of quasi-classical trajectory calculations is revisited, following previous work reported in 1995, which did not recommend the procedure. We come to a different conclusion here.

Classical scattering calculations for diatomic molecules: A general procedure and application to the microwave spectrum O2

NASA Technical Reports Server (NTRS)

Mingelgrin, U.

1972-01-01

Many properties of gaseous systems such as electromagnetic absorption and emission, sound dispersion and absorption, may be elucidated if the nature of collisions between the particles in the system is understood. A procedure for the calculation of the classical trajectories of two interacting diatomic molecules is described. The dynamics of the collision will be assumed to be that of two rigid rotors moving in a specified potential. The actual outcome of a representative sample of many trajectories at 298K was computed, and the use of these values at any temperature for calculations of various molecular properties will be described. Calculations performed for the O2 microwave spectrum are given to demonstrate the use of the procedure described.

Lenard-Balescu calculations and classical molecular dynamics simulations of electrical and thermal conductivities of hydrogen plasmas

DOE PAGES

Whitley, Heather D.; Scullard, Christian R.; Benedict, Lorin X.; ...

2014-12-04

Here, we present a discussion of kinetic theory treatments of linear electrical and thermal transport in hydrogen plasmas, for a regime of interest to inertial confinement fusion applications. In order to assess the accuracy of one of the more involved of these approaches, classical Lenard-Balescu theory, we perform classical molecular dynamics simulations of hydrogen plasmas using 2-body quantum statistical potentials and compute both electrical and thermal conductivity from out particle trajectories using the Kubo approach. Our classical Lenard-Balescu results employing the identical statistical potentials agree well with the simulations.

Semiclassical relation between open trajectories and periodic orbits for the Wigner time delay.

PubMed

Kuipers, Jack; Sieber, Martin

2008-04-01

The Wigner time delay of a classically chaotic quantum system can be expressed semiclassically either in terms of pairs of scattering trajectories that enter and leave the system or in terms of the periodic orbits trapped inside the system. We show how these two pictures are related on the semiclassical level. We start from the semiclassical formula with the scattering trajectories and derive from it all terms in the periodic orbit formula for the time delay. The main ingredient in this calculation are correlations between scattering trajectories which are due to trajectories that approach the trapped periodic orbits closely. The equivalence between the two pictures is also demonstrated by considering correlation functions of the time delay. A corresponding calculation for the conductance gives no periodic orbit contributions in leading order.

Anharmonic quantum mechanical systems do not feature phase space trajectories

NASA Astrophysics Data System (ADS)

Oliva, Maxime; Kakofengitis, Dimitris; Steuernagel, Ole

2018-07-01

Phase space dynamics in classical mechanics is described by transport along trajectories. Anharmonic quantum mechanical systems do not allow for a trajectory-based description of their phase space dynamics. This invalidates some approaches to quantum phase space studies. We first demonstrate the absence of trajectories in general terms. We then give an explicit proof for all quantum phase space distributions with negative values: we show that the generation of coherences in anharmonic quantum mechanical systems is responsible for the occurrence of singularities in their phase space velocity fields, and vice versa. This explains numerical problems repeatedly reported in the literature, and provides deeper insight into the nature of quantum phase space dynamics.

Progress in the development of an H{sup −} ion source for cyclotrons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Etoh, H., E-mail: Hrh-Etoh@shi.co.jp; Aoki, Y.; Mitsubori, H.

2015-04-08

A multi-cusp DC H{sup −} ion source has been developed for cyclotrons in medical use. Beam optics of the H{sup −} ion beam is studied using a 2D beam trajectory code. The simulation results are compared with the experimental results obtained in the Mark I source, which has produced up to 16 mA H{sup −} ion beams. The optimum extraction voltages show good agreement between the calculation and the experimental results. A new ion source, Mark II source, is designed to achieve the next goal of producing an H{sup −} beam of 20 mA. The magnetic field configurations and the plasma electrodemore » design are optimized for Cs-seeded operation. Primary electron trajectory simulation shows that primary electrons are confined well and the magnetic filter prevents the primary electrons from entering into the extraction region.« less

Drift paths of ions composing multiple-nose spectral structures near the inner edge of the plasma sheet

NASA Astrophysics Data System (ADS)

Ferradas, C. P.; Zhang, J.-C.; Spence, H. E.; Kistler, L. M.; Larsen, B. A.; Reeves, G.; Skoug, R.; Funsten, H.

2016-11-01

We present a case study of the H+, He+, and O+ multiple-nose structures observed by the Helium, Oxygen, Proton, and Electron instrument on board Van Allen Probe A over one complete orbit on 28 September 2013. Nose structures are observed near the inner edge of the plasma sheet and constitute the signatures of ion drift in the highly dynamic environment of the inner magnetosphere. We find that the multiple noses are intrinsically associated with variations in the solar wind. Backward ion drift path tracings show new details of the drift trajectories of these ions; i.e., multiple noses are formed by ions with a short drift time from the assumed source location to the inner region and whose trajectories (1) encircle the Earth different number of times or (2) encircle the Earth equal number of times but with different drift time, before reaching the observation site.

Non-adiabatic dynamics around a conical intersection with surface-hopping coupled coherent states

DOE Office of Scientific and Technical Information (OSTI.GOV)

Humeniuk, Alexander; Mitrić, Roland, E-mail: roland.mitric@uni-wuerzburg.de

A surface-hopping extension of the coupled coherent states-method [D. Shalashilin and M. Child, Chem. Phys. 304, 103-120 (2004)] for simulating non-adiabatic dynamics with quantum effects of the nuclei is put forward. The time-dependent Schrödinger equation for the motion of the nuclei is solved in a moving basis set. The basis set is guided by classical trajectories, which can hop stochastically between different electronic potential energy surfaces. The non-adiabatic transitions are modelled by a modified version of Tully’s fewest switches algorithm. The trajectories consist of Gaussians in the phase space of the nuclei (coherent states) combined with amplitudes for an electronicmore » wave function. The time-dependent matrix elements between different coherent states determine the amplitude of each trajectory in the total multistate wave function; the diagonal matrix elements determine the hopping probabilities and gradients. In this way, both interference effects and non-adiabatic transitions can be described in a very compact fashion, leading to the exact solution if convergence with respect to the number of trajectories is achieved and the potential energy surfaces are known globally. The method is tested on a 2D model for a conical intersection [A. Ferretti, J. Chem. Phys. 104, 5517 (1996)], where a nuclear wavepacket encircles the point of degeneracy between two potential energy surfaces and interferes with itself. These interference effects are absent in classical trajectory-based molecular dynamics but can be fully incorpo rated if trajectories are replaced by surface hopping coupled coherent states.« less

Understanding the ion distributions near the boundaries of reconnection outflow region

NASA Astrophysics Data System (ADS)

Zhou, Xu-Zhi; Pan, Dong-Xiao; Angelopoulos, Vassilis; Runov, Andrei; Zong, Qiu-Gang; Pu, Zu-Yin

2016-10-01

An interesting signature observed shortly after the onset of magnetotail reconnection is the gradual appearance of a local peak of ion phase space density (PSD) in the duskward and downstream direction separated from the colder, nearly isotropic ion population. Such a characteristic ion distribution, served as a diagnostic signature of magnetotail reconnection and well reproduced by a particle-tracing Liouville simulation, are found to appear only near the off-equatorial boundaries of the reconnection outflow region. Further analysis on ion trajectories suggests that the ions within the local peak and within the neighboring PSD cleft both belong to the outflowing population; on top of their outflowing motion, they both meander across the neutral sheet to exhibit duskward velocities near the off-equatorial edges of their trajectories. The difference between them is that the local peak originates from ions previously constituting the preonset plasma sheet, whereas the cleft corresponds to the inflowing lobe ions before they are repelled in the downstream direction. As reconnection proceeds, the local PSD peak gradually attenuates and then disappears, which is a signature of reconnection flushing effect that depletes the ions in the preonset plasma sheet and eventually replaces them by lobe ions.

Self-consistent one dimension in space and three dimension in velocity kinetic trajectory simulation model of magnetized plasma-wall transition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chalise, Roshan, E-mail: plasma.roshan@gmail.com; Khanal, Raju

2015-11-15

We have developed a self-consistent 1d3v (one dimension in space and three dimension in velocity) Kinetic Trajectory Simulation (KTS) model, which can be used for modeling various situations of interest and yields results of high accuracy. Exact ion trajectories are followed, to calculate along them the ion distribution function, assuming an arbitrary injection ion distribution. The electrons, on the other hand, are assumed to have a cut-off Maxwellian velocity distribution at injection and their density distribution is obtained analytically. Starting from an initial guess, the potential profile is iterated towards the final time-independent self-consistent state. We have used it tomore » study plasma sheath region formed in presence of an oblique magnetic field. Our results agree well with previous works from other models, and hence, we expect our 1d3v KTS model to provide a basis for the studying of all types of magnetized plasmas, yielding more accurate results.« less

Remaining Useful Life Prediction for Lithium-Ion Batteries Based on Gaussian Processes Mixture

PubMed Central

Li, Lingling; Wang, Pengchong; Chao, Kuei-Hsiang; Zhou, Yatong; Xie, Yang

2016-01-01

The remaining useful life (RUL) prediction of Lithium-ion batteries is closely related to the capacity degeneration trajectories. Due to the self-charging and the capacity regeneration, the trajectories have the property of multimodality. Traditional prediction models such as the support vector machines (SVM) or the Gaussian Process regression (GPR) cannot accurately characterize this multimodality. This paper proposes a novel RUL prediction method based on the Gaussian Process Mixture (GPM). It can process multimodality by fitting different segments of trajectories with different GPR models separately, such that the tiny differences among these segments can be revealed. The method is demonstrated to be effective for prediction by the excellent predictive result of the experiments on the two commercial and chargeable Type 1850 Lithium-ion batteries, provided by NASA. The performance comparison among the models illustrates that the GPM is more accurate than the SVM and the GPR. In addition, GPM can yield the predictive confidence interval, which makes the prediction more reliable than that of traditional models. PMID:27632176

Squeezed coherent states of motion for ions confined in quadrupole and octupole ion traps

NASA Astrophysics Data System (ADS)

Mihalcea, Bogdan M.

2018-01-01

Quasiclassical dynamics of trapped ions is characterized by applying the time dependent variational principle (TDVP) on coherent state orbits, in case of quadrupole and octupole combined (Paul and Penning) or radiofrequency (RF) traps. A dequantization algorithm is proposed, by which the classical Hamilton (energy) function associated to the system results as the expectation value of the quantum Hamiltonian on squeezed coherent states. We develop such method and particularize the quantum Hamiltonian for both combined and RF nonlinear traps, that exhibit axial symmetry. We also build the classical Hamiltonian functions for the particular traps we considered, and find the classical equations of motion.

Modeling Magnetotail Ion Distributions with Global Magnetohydrodynamic and Ion Trajectory Calculations

NASA Technical Reports Server (NTRS)

El-Alaoui, M.; Ashour-Abdalla, M.; Raeder, J.; Peroomian, V.; Frank, L. A.; Paterson, W. R.; Bosqued, J. M.

1998-01-01

On February 9, 1995, the Comprehensive Plasma Instrumentation (CPI) on the Geotail spacecraft observed a complex, structured ion distribution function near the magnetotail midplane at x approximately -30 R(sub E). On this same day the Wind spacecraft observed a quiet solar wind and an interplanetary magnetic field (IMF) that was northward for more than five hours, and an IMF B(sub y) component with a magnitude comparable to that of the RAF B(sub z) component. In this study, we determined the sources of the ions in this distribution function by following approximately 90,000 ion trajectories backward in time, using the time-dependent electric and magnetic fields obtained from a global MHD simulation. The Wind observations were used as input for the MHD model. The ion distribution function observed by Geotail at 1347 UT was found to consist primarily of particles from the dawn side low latitude boundary layer (LLBL) and from the dusk side LLBL; fewer than 2% of the particles originated in the ionosphere.

A multi-state trajectory method for non-adiabatic dynamics simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tao, Guohua, E-mail: taogh@pkusz.edu.cn

2016-03-07

A multi-state trajectory approach is proposed to describe nuclear-electron coupled dynamics in nonadiabatic simulations. In this approach, each electronic state is associated with an individual trajectory, among which electronic transition occurs. The set of these individual trajectories constitutes a multi-state trajectory, and nuclear dynamics is described by one of these individual trajectories as the system is on the corresponding state. The total nuclear-electron coupled dynamics is obtained from the ensemble average of the multi-state trajectories. A variety of benchmark systems such as the spin-boson system have been tested and the results generated using the quasi-classical version of the method showmore » reasonably good agreement with the exact quantum calculations. Featured in a clear multi-state picture, high efficiency, and excellent numerical stability, the proposed method may have advantages in being implemented to realistic complex molecular systems, and it could be straightforwardly applied to general nonadiabatic dynamics involving multiple states.« less

An Investigation of Traveling-Wave Electrophoresis using a Trigonometric Potential

NASA Astrophysics Data System (ADS)

Vopal, James

Traveling-wave electrophoresis, a technique for microfluidic separations in lab-on-achip devices, is investigated using a trigonometric model that naturally incorporates the spatial periodicity of the device. Traveling-wave electrophoresis can be used to separate high-mobility ions from low-mobility ions in forensic and medical applications, with a separation threshold that can be tuned for specific applications by simply choosing the traveling wave frequency. Our simulations predict plateaus in the average ion velocity verses the mobility, plateaus that correspond to Farey fractions and yield Devil's staircases for non-zero discreteness values. The plateaus indicate that ions with different mobilities can travel with the same average velocity. To determine the conditions for chaos, Lyapunov exponents and contact maps are employed. Through the use of contact maps, the chaotic trajectories are determined to be either narrowband or broadband. Narrowband chaotic trajectories are exhibited in the plateaus of the average velocity, while broadband chaotic trajectories are exhibited where the average velocity varies nonmonotonically with the mobility. Narrowband chaos will be investigated in future work incorporating the role of diffusion. The results of this and future work can be used to develop new tools for electrophoretic separation.

Real time correlation function in a single phase space integral beyond the linearized semiclassical initial value representation.

PubMed

Liu, Jian; Miller, William H

2007-06-21

It is shown how quantum mechanical time correlation functions [defined, e.g., in Eq. (1.1)] can be expressed, without approximation, in the same form as the linearized approximation of the semiclassical initial value representation (LSC-IVR), or classical Wigner model, for the correlation function [cf. Eq. (2.1)], i.e., as a phase space average (over initial conditions for trajectories) of the Wigner functions corresponding to the two operators. The difference is that the trajectories involved in the LSC-IVR evolve classically, i.e., according to the classical equations of motion, while in the exact theory they evolve according to generalized equations of motion that are derived here. Approximations to the exact equations of motion are then introduced to achieve practical methods that are applicable to complex (i.e., large) molecular systems. Four such methods are proposed in the paper--the full Wigner dynamics (full WD) and the second order WD based on "Wigner trajectories" [H. W. Lee and M. D. Scully, J. Chem. Phys. 77, 4604 (1982)] and the full Donoso-Martens dynamics (full DMD) and the second order DMD based on "Donoso-Martens trajectories" [A. Donoso and C. C. Martens, Phys. Rev. Lett. 8722, 223202 (2001)]--all of which can be viewed as generalizations of the original LSC-IVR method. Numerical tests of the four versions of this new approach are made for two anharmonic model problems, and for each the momentum autocorrelation function (i.e., operators linear in coordinate or momentum operators) and the force autocorrelation function (nonlinear operators) have been calculated. These four new approximate treatments are indeed seen to be significant improvements to the original LSC-IVR approximation.

Zero-point energy conservation in classical trajectory simulations: Application to H2CO

NASA Astrophysics Data System (ADS)

Lee, Kin Long Kelvin; Quinn, Mitchell S.; Kolmann, Stephen J.; Kable, Scott H.; Jordan, Meredith J. T.

2018-05-01

A new approach for preventing zero-point energy (ZPE) violation in quasi-classical trajectory (QCT) simulations is presented and applied to H2CO "roaming" reactions. Zero-point energy may be problematic in roaming reactions because they occur at or near bond dissociation thresholds and these channels may be incorrectly open or closed depending on if, or how, ZPE has been treated. Here we run QCT simulations on a "ZPE-corrected" potential energy surface defined as the sum of the molecular potential energy surface (PES) and the global harmonic ZPE surface. Five different harmonic ZPE estimates are examined with four, on average, giving values within 4 kJ/mol—chemical accuracy—for H2CO. The local harmonic ZPE, at arbitrary molecular configurations, is subsequently defined in terms of "projected" Cartesian coordinates and a global ZPE "surface" is constructed using Shepard interpolation. This, combined with a second-order modified Shepard interpolated PES, V, allows us to construct a proof-of-concept ZPE-corrected PES for H2CO, Veff, at no additional computational cost to the PES itself. Both V and Veff are used to model product state distributions from the H + HCO → H2 + CO abstraction reaction, which are shown to reproduce the literature roaming product state distributions. Our ZPE-corrected PES allows all trajectories to be analysed, whereas, in previous simulations, a significant proportion was discarded because of ZPE violation. We find ZPE has little effect on product rotational distributions, validating previous QCT simulations. Running trajectories on V, however, shifts the product kinetic energy release to higher energy than on Veff and classical simulations of kinetic energy release should therefore be viewed with caution.

The envelope of ballistic trajectories and elliptic orbits

NASA Astrophysics Data System (ADS)

Butikov, Eugene I.

2015-11-01

Simple geometric derivations are given for the shape of the "safety domain" boundary for the family of Keplerian orbits of equal energy in a central gravitational field and for projectile trajectories in a uniform field. Examples of practical uses of the envelope of the family of orbits are discussed and illustrated by computer simulations. This material is appropriate for physics teachers and undergraduate students studying classical mechanics and orbital motions.

Negative ion generator

DOEpatents

Stinnett, R.W.

1984-05-08

A negative ion generator is formed from a magnetically insulated transmission line having a coating of graphite on the cathode for producing negative ions and a plurality of apertures on the opposed anode for the release of negative ions. Magnetic insulation keeps electrons from flowing from the cathode to the anode. A transverse magnetic field removes electrons which do escape through the apertures from the trajectory of the negative ions. 8 figs.

Negative ion generator

DOEpatents

Stinnett, Regan W.

1984-01-01

A negative ion generator is formed from a magnetically insulated transmission line having a coating of graphite on the cathode for producing negative ions and a plurality of apertures on the opposed anode for the release of negative ions. Magnetic insulation keeps electrons from flowing from the cathode to the anode. A transverse magnetic field removes electrons which do escape through the apertures from the trajectory of the negative ions.

KmL3D: a non-parametric algorithm for clustering joint trajectories.

PubMed

Genolini, C; Pingault, J B; Driss, T; Côté, S; Tremblay, R E; Vitaro, F; Arnaud, C; Falissard, B

2013-01-01

In cohort studies, variables are measured repeatedly and can be considered as trajectories. A classic way to work with trajectories is to cluster them in order to detect the existence of homogeneous patterns of evolution. Since cohort studies usually measure a large number of variables, it might be interesting to study the joint evolution of several variables (also called joint-variable trajectories). To date, the only way to cluster joint-trajectories is to cluster each trajectory independently, then to cross the partitions obtained. This approach is unsatisfactory because it does not take into account a possible co-evolution of variable-trajectories. KmL3D is an R package that implements a version of k-means dedicated to clustering joint-trajectories. It provides facilities for the management of missing values, offers several quality criteria and its graphic interface helps the user to select the best partition. KmL3D can work with any number of joint-variable trajectories. In the restricted case of two joint trajectories, it proposes 3D tools to visualize the partitioning and then export 3D dynamic rotating-graphs to PDF format. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.

Effect of ion velocity on creation of point defects halos of latent tracks in LiF

NASA Astrophysics Data System (ADS)

Volkov, A. E.; Schwartz, K.; Medvedev, N. A.; Trautmann, C.

2017-09-01

Parameters of point defects halos (F-color centers) created due to decays of self-trapped valence holes generated in nanometric vicinities of trajectories of gold ions of 275 MeV and 2187 MeV in LiF are estimated in absorption spectroscopy experiments. Such ions have approximately the same electronic stopping: 24.6 keV/nm and 22.9 keV/nm, respectively. In contrast to the usual concept of the velocity effect that a slower ion produces larger structure changes due to a higher density of the deposited energy, the opposite effect occurs for the defect halo revealing a larger radius and a larger defect concentration for an ion of the higher velocity realizing the same energy loss. Spatial spreading of generated valence holes before their self-trapping (500 fs) forms the size of the defect halos around the trajectories of the applied ions. Simulations with Monte-Carlo code TREKIS show no significant difference in the initial spatial distributions of these valence holes by the times of finishing of ionization cascades (∼10 fs after the projectile passage) within the radii of the defect halos deduced from the experiments. Using these distributions as initial conditions for spatial spreading of generated valence holes and taking into account the difference between the defect halo radii, the diffusion coefficients of these holes near the trajectories of 275 and 2187 MeV Au ions in LiF are estimated showing about six times larger value in tracks of the faster ion for irradiations at room temperatures. Presence of H-color centers changes considerably the kinetics of the created defect ensemble in the defect halo resulting in differences between the defect halo parameters in LiF crystals irradiated at 8 K vs. 300 K.

Effects of reactant rotational excitation on H + O2--> OH + O reaction rate constant: quantum wave packet, quasi-classical trajectory and phase space theory calculations.

PubMed

Lin, Shi Ying; Guo, Hua; Lendvay, György; Xie, Daiqian

2009-06-21

We examine the impact of initial rotational excitation on the reactivity of the H + O(2)--> OH + O reaction. Accurate Chebyshev wave packet calculations have been carried out for the upsilon(i) = 0, j(i) = 9 initial state of O(2) and the J = 50 partial wave. In addition, we present Gaussian-weighted quasi-classical trajectory and phase space theory calculations of the integral cross section and thermal rate constant for the title reaction. These theoretical results suggest that the initial rotational excitation significantly enhances reactivity with an amount comparable to the effect of initial vibrational state excitation. The inclusion of internally excited reactants is shown to improve the agreement with experimental rate constant.

Gaussian-based techniques for quantum propagation from the time-dependent variational principle: Formulation in terms of trajectories of coupled classical and quantum variables

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shalashilin, Dmitrii V.; Burghardt, Irene

2008-08-28

In this article, two coherent-state based methods of quantum propagation, namely, coupled coherent states (CCS) and Gaussian-based multiconfiguration time-dependent Hartree (G-MCTDH), are put on the same formal footing, using a derivation from a variational principle in Lagrangian form. By this approach, oscillations of the classical-like Gaussian parameters and oscillations of the quantum amplitudes are formally treated in an identical fashion. We also suggest a new approach denoted here as coupled coherent states trajectories (CCST), which completes the family of Gaussian-based methods. Using the same formalism for all related techniques allows their systematization and a straightforward comparison of their mathematical structuremore » and cost.« less

Fluctuating observation time ensembles in the thermodynamics of trajectories

NASA Astrophysics Data System (ADS)

Budini, Adrián A.; Turner, Robert M.; Garrahan, Juan P.

2014-03-01

The dynamics of stochastic systems, both classical and quantum, can be studied by analysing the statistical properties of dynamical trajectories. The properties of ensembles of such trajectories for long, but fixed, times are described by large-deviation (LD) rate functions. These LD functions play the role of dynamical free energies: they are cumulant generating functions for time-integrated observables, and their analytic structure encodes dynamical phase behaviour. This ‘thermodynamics of trajectories’ approach is to trajectories and dynamics what the equilibrium ensemble method of statistical mechanics is to configurations and statics. Here we show that, just like in the static case, there are a variety of alternative ensembles of trajectories, each defined by their global constraints, with that of trajectories of fixed total time being just one of these. We show how the LD functions that describe an ensemble of trajectories where some time-extensive quantity is constant (and large) but where total observation time fluctuates can be mapped to those of the fixed-time ensemble. We discuss how the correspondence between generalized ensembles can be exploited in path sampling schemes for generating rare dynamical trajectories.

Ion trajectory simulations of axial ac dipolar excitation in the Orbitrap

NASA Astrophysics Data System (ADS)

Wu, Guangxiang; Noll, Robert J.; Plass, Wolfgang R.; Hu, Qizhi; Perry, Richard H.; Cooks, R. Graham

2006-07-01

The newly developed version of the multi-particle ion trajectory simulation program, ITSIM 6.0, was applied to simulate ac dipolar excitation of ion axial motion in the Orbitrap. The Orbitrap inner and outer electrodes were generated in AutoCAD, a 3D drawing program. The electrode geometry was imported into the 3D field solver COMSOL; the field array was then imported into ITSIM 6.0. Ion trajectories were calculated by solving Newton's equations using Runge-Kutta integration methods. Compared to the analytical solution, calculated radial components of the field at the device's "equator" (z = 0) were within 0.5% and calculated axial components midway between the inner and outer electrodes were within 0.2%. The experiments simulated here involved the control of axial motion of ions in the Orbitrap by the application of dipolar ac signals to the split outer electrodes, as described in a recently published paper from this laboratory [Hu et al., J. Phys. Chem. A 110 (2006) 2682]. In these experiments, ac signal was applied at the axial resonant frequency of a selected ion. Axial excitation and eventual ion ejection resulted when the ac was in phase with, i.e., had 0° phase relative to ion axial motion. De-excitation of ion axial motion until the ions were at z = 0 and at rest with respect to the z-axis resulted if the applied ac was out of phase with ion motion, with re-excitation of ion axial motion occurring if the dipolar ac was continued beyond this point. Both de-excitation and re-excitation could be achieved mass-selectively and depended on the amplitude and duration (number of cycles) of the applied ac. The effects of ac amplitude, frequency, phase relative to ion motion, and bandwidth of applied waveform were simulated. All simulation results were compared directly with the experimental data and good agreement was observed. Such ion motion control experiments and their simulation provide the possibility to improve Orbitrap performance and to develop tandem mass spectrometry (MS/MS) capabilities inside the Orbitrap.

Calculated rate constants for the reaction ClO + O yields Cl + O2 between 220 and 1000 deg K. [molecular trajectories and stratospheric ozone

NASA Technical Reports Server (NTRS)

Jaffee, R. L.

1978-01-01

Classical trajectory calculations are presented for the reaction ClO + O yields Cl + O2, a reaction which is an important step in the chlorine-catalyzed destruction of ozone which is thought to occur in the 220 and 1000 K. The calculated rate constant is 4.36 x 10 to the minus 11th power exp (-191/T)cu cm molecule (-1)s(-1) and its value at 300 K is 2.3 plus or minus 10 to the 11th power cu cm molecule (-1)s(-1), about a factor of 2 lower than recent experimental data. The empirical potential energy surface used in the calculations was constructed to fit experimental data for ClO, O2 and ClOO molecules. Other important features of this potential surface, such as the barrier to reaction, were varied systematically and calculations were performed for a range of conditions to determine the best theoretical rate constants. Results demonstrate the utility of classical trajectory methods for determining activation energies and other kinetic data for important atmospheric reactions.

Few-body semiclassical approach to nucleon transfer and emission reactions

NASA Astrophysics Data System (ADS)

Sultanov, Renat A.; Guster, D.

2014-04-01

A three-body semiclassical model is proposed to describe the nucleon transfer and emission reactions in a heavy-ion collision. In this model the two heavy particles, i.e. nuclear cores A1(ZA1, MA1) and A2(ZA2, MA2), move along classical trajectories {{R}_1}( t ) and {{R}_2}( t ) respectively, while the dynamics of the lighter neutron (n) is considered from a quantum mechanical point of view. Here, Mi are the nucleon masses and Zi are the Coulomb charges of the heavy nuclei (i = 1, 2). A Faddeev-type semiclassical formulation using realistic paired nuclear-nuclear potentials is applied so that all three channels (elastic, rearrangement and break-up) are described in a unified manner. In order to solve the time-dependent equations the Faddeev components of the total three-body wave-function are expanded in terms of the input and output channel target eigenfunctions. In the special case, when the nuclear cores are identical (A1 ≡ A2) and also the two-level approximation in the expansion over the target (subsystem) functions is used, the time-dependent semiclassical Faddeev equations are resolved in an explicit way. To determine the realistic {{R}_1}( t ) and {{R}_2}( t ) trajectories of the nuclear cores, a self-consistent approach based on the Feynman path integral theory is applied.

Particle trajectories in seeds of Lactuca sativa and chromosome aberrations after exposure to cosmic heavy ions on cosmos biosatellites 8 and 9

NASA Astrophysics Data System (ADS)

Facius, R.; Scherer, K.; Reitz, G.; Bücker, H.; Nevzgodina, L. V.; Maximova, E. N.

1994-10-01

The potentially specific importance of the heavy ions of the galactic cosmic radiation for radiation protection in manned spaceflight continues to stimulate in situ, i.e., spaceflight experiments to investigate their radiobiological properties. Chromosome aberrations as an expression of a direct assault on the genome are of particular interest in view of cancerogenesis being the primary radiation risk for man in space. In such investigations the establishment of the geometrical correlation between heavy ions' trajectories and the location of radiation sensitive biological substructures is an essential task. The overall qualitative and quantitative precision achieved for the identification of particle trajectories in the order of 2~10 μm as well as the contributing sources of uncertainties are discussed. We describe how this was achieved for seeds of Lactuca sativa as biological test organisms, whose location and orientation had to be derived from contact photographies displaying their outlines and those of the holder plates only. The incidence of chromosome aberrations in cells exposed during the COSMOS 1887 (Biosatellite 8) and the COSMOS 2044 (Biosatellite 9) mission was determined for seeds hit by cosmic heavy ions. In those seeds the incidence of both single and multiple chromosome aberrations was enhanced. The results of the Biosatellite 9 experiment, however, are confounded by spaceflight effects unrelated to the passage of heavy ions.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seletskiy, S.; De Monte, V.; Di Lieto, A.

In the LEReC Cooling Section (CS) the RHIC ions are traveling together with and getting cooled by the LEReC electrons. The required cooling rate sets the limit of 150 urad on tolerable angles of the electrons in the CS. One of the components of overall electron angle is the angle of the e-beam trajectory with respect to the ion beam trajectory. We set the limit for electron trajectory angle to 100 urad. It is critical for preserving small trajectory angle to keep the transverse magnetic field inside the CS drifts within +/- 2.3 mG. The drifts in the CS mustmore » be shielded from the ambient magnetic fields of the RHIC tunnel, which can be as high as 0.5 G, to minimize the transverse field inside the CS vacuum chamber. In this paper we present the final design of the magnetic shielding of the LEReC CS and discuss the results of tests dedicated to studies of the shielding effectiveness.« less

Dynamics of alkali ions-neutral molecules reactions: Radio frequency-guided beam experimental cross-sections and direct quasiclassical trajectory studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aguilar, J.; Andres, J. de; Lucas, J. M.

2012-11-27

Different reactive processes taking place in collisions between alkali ions and neutral i-C{sub 3}H{sub 7}Cl molecules in the low (center of mass frame) energy range have been studied using an octopole radiofrequency guided-ion-beam apparatus developed in our laboratory. Cross-section energy dependences for all these reactions have been obtained in absolute units. Ab initio electronic structure calculations for those colliding systems evolving on the ground single potential surface have given relevant information on the main topological features of the surfaces. For some of the reactions a dynamic study by 'on the fly' trajectories has complemented the available experimental and electronic structuremore » information.« less

Signatures of the electron saddle swaps mechanism in the photon spectra following charge-exchange collisions

NASA Astrophysics Data System (ADS)

Otranto, Sebastian

2014-10-01

During the last few years, several experimental and theoretical studies have focused on state selective charge exchange processes between charged ions and alkali metals. These data are of particular importance for the tokamak nuclear fusion reactor program, since diagnostics on the plasma usually rely on charge-exchange spectroscopy. In this sense, alkali metals, have been proposed as potential alternatives to excited hydrogen/deuterium for which laboratory experiments are not feasible at present. In this talk, we present our recent work involving ion collisions with alkali metals. Oscillatory structures in the angular differential charge-exchange cross sections obtained using the MOTRIMS technique are correctly described by classical trajectory Monte Carlo simulations. These oscillations are found to originate from the number of swaps the electron undergoes around the projectile-target potential saddle before capture takes place and are very prominent at impact energies below 10 keV/amu. Moreover, cross sections of higher order of differentiability also indicate that the swaps leave distinctive signatures in the (n,l)-state selective cross sections and in the photon line emission cross sections. Oscillatory structures for the x-ray hardness ratio parameter are also predicted. In collaboration with Ronnie Hoekstra, Zernike Institute for Advanced Materials, University of Groningen and Ronald Olson, Department of Physics, Missouri University of Science and Technology.

Drift paths of ions composing multiple-nose spectral structures near the inner edge of the plasma sheet

DOE PAGES

Ferradas, C. P.; Zhang, J. -C.; Spence, H. E.; ...

2016-11-05

Here in this paper, we present a case study of the H +, He +, and O + multiple-nose structures observed by the Helium, Oxygen, Proton, and Electron instrument on board Van Allen Probe A over one complete orbit on 28 September 2013. Nose structures are observed near the inner edge of the plasma sheet and constitute the signatures of ion drift in the highly dynamic environment of the inner magnetosphere. We find that the multiple noses are intrinsically associated with variations in the solar wind. Backward ion drift path tracings show new details of the drift trajectories of thesemore » ions; i.e., multiple noses are formed by ions with a short drift time from the assumed source location to the inner region and whose trajectories (1) encircle the Earth different number of times or (2) encircle the Earth equal number of times but with different drift time, before reaching the observation site.« less

Drift paths of ions composing multiple-nose spectral structures near the inner edge of the plasma sheet

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ferradas, C. P.; Zhang, J. -C.; Spence, H. E.

Here in this paper, we present a case study of the H +, He +, and O + multiple-nose structures observed by the Helium, Oxygen, Proton, and Electron instrument on board Van Allen Probe A over one complete orbit on 28 September 2013. Nose structures are observed near the inner edge of the plasma sheet and constitute the signatures of ion drift in the highly dynamic environment of the inner magnetosphere. We find that the multiple noses are intrinsically associated with variations in the solar wind. Backward ion drift path tracings show new details of the drift trajectories of thesemore » ions; i.e., multiple noses are formed by ions with a short drift time from the assumed source location to the inner region and whose trajectories (1) encircle the Earth different number of times or (2) encircle the Earth equal number of times but with different drift time, before reaching the observation site.« less

Trajectory Optimization for Missions to Small Bodies with a Focus on Scientific Merit.

PubMed

Englander, Jacob A; Vavrina, Matthew A; Lim, Lucy F; McFadden, Lucy A; Rhoden, Alyssa R; Noll, Keith S

2017-01-01

Trajectory design for missions to small bodies is tightly coupled both with the selection of targets for a mission and with the choice of spacecraft power, propulsion, and other hardware. Traditional methods of trajectory optimization have focused on finding the optimal trajectory for an a priori selection of destinations and spacecraft parameters. Recent research has expanded the field of trajectory optimization to multidisciplinary systems optimization that includes spacecraft parameters. The logical next step is to extend the optimization process to include target selection based not only on engineering figures of merit but also scientific value. This paper presents a new technique to solve the multidisciplinary mission optimization problem for small-bodies missions, including classical trajectory design, the choice of spacecraft power and propulsion systems, and also the scientific value of the targets. This technique, when combined with modern parallel computers, enables a holistic view of the small body mission design process that previously required iteration among several different design processes.

Ehrenfest dynamics is purity non-preserving: A necessary ingredient for decoherence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alonso, J. L.; Instituto de Biocomputacion y Fisica de Sistemas Complejos; Unidad Asociada IQFR-BIFI, Universidad de Zaragoza, Mariano Esquillor s/n, E-50018 Zaragoza

2012-08-07

We discuss the evolution of purity in mixed quantum/classical approaches to electronic nonadiabatic dynamics in the context of the Ehrenfest model. As it is impossible to exactly determine initial conditions for a realistic system, we choose to work in the statistical Ehrenfest formalism that we introduced in Alonso et al. [J. Phys. A: Math. Theor. 44, 396004 (2011)]. From it, we develop a new framework to determine exactly the change in the purity of the quantum subsystem along with the evolution of a statistical Ehrenfest system. In a simple case, we verify how and to which extent Ehrenfest statistical dynamicsmore » makes a system with more than one classical trajectory, and an initial quantum pure state become a quantum mixed one. We prove this numerically showing how the evolution of purity depends on time, on the dimension of the quantum state space D, and on the number of classical trajectories N of the initial distribution. The results in this work open new perspectives for studying decoherence with Ehrenfest dynamics.« less

Representing and selecting vibrational angular momentum states for quasiclassical trajectory chemical dynamics simulations.

PubMed

Lourderaj, Upakarasamy; Martínez-Núñez, Emilio; Hase, William L

2007-10-18

Linear molecules with degenerate bending modes have states, which may be represented by the quantum numbers N and L. The former gives the total energy for these modes and the latter identifies their vibrational angular momentum jz. In this work, the classical mechanical analog of the N,L-quantum states is reviewed, and an algorithm is presented for selecting initial conditions for these states in quasiclassical trajectory chemical dynamics simulations. The algorithm is illustrated by choosing initial conditions for the N = 3 and L = 3 and 1 states of CO2. Applications of this algorithm are considered for initial conditions without and with zero-point energy (zpe) included in the vibrational angular momentum states and the C-O stretching modes. The O-atom motions in the x,y-plane are determined for these states from classical trajectories in Cartesian coordinates and are compared with the motion predicted by the normal-mode model. They are only in agreement for the N = L = 3 state without vibrational angular momentum zpe. For the remaining states, the Cartesian O-atom motions are considerably different from the elliptical motion predicted by the normal-mode model. This arises from bend-stretch coupling, including centrifugal distortion, in the Cartesian trajectories, which results in tubular instead of elliptical motion. Including zpe in the C-O stretch modes introduces considerable complexity into the O-atom motions for the vibrational angular momentum states. The short-time O-atom motions for these trajectories are highly irregular and do not appear to have any identifiable characteristics. However, the O-atom motions for trajectories integrated for substantially longer period of times acquire unique properties. With C-O stretch zpe included, the long-time O-atom motion becomes tubular for trajectories integrated to approximately 14 ps for the L = 3 states and to approximately 44 ps for the L = 1 states.

Experimental and theoretical kinetics for the H2O+ + H2/D2 → H3O+/H2DO+ + H/D reactions: observation of the rotational effect in the temperature dependence.

PubMed

Ard, Shaun G; Li, Anyang; Martinez, Oscar; Shuman, Nicholas S; Viggiano, Albert A; Guo, Hua

2014-12-11

Thermal rate coefficients for the title reactions computed using a quasi-classical trajectory method on an accurate global potential energy surface fitted to ∼81,000 high-level ab initio points are compared with experimental values measured between 100 and 600 K using a variable temperature selected ion flow tube instrument. Excellent agreement is found across the entire temperature range, showing a subtle, but unusual temperature dependence of the rate coefficients. For both reactions the temperature dependence has a maximum around 350 K, which is a result of H2O(+) rotations increasing the reactivity, while kinetic energy is decreasing the reactivity. A strong isotope effect is found, although the calculations slightly overestimate the kinetic isotope effect. The good experiment-theory agreement not only validates the accuracy of the potential energy surface but also provides more accurate kinetic data over a large temperature range.

Charge transfer and ionization in collisions of Si3+ with H from low to high energy

NASA Astrophysics Data System (ADS)

Wang, J. G.; He, B.; Ning, Y.; Liu, C. L.; Yan, J.; Stancil, P. C.; Schultz, D. R.

2006-11-01

Charge transfer processes due to collisions of ground state Si3+(3sS1) ions with atomic hydrogen are investigated using the quantum-mechanical molecular-orbital close-coupling (MOCC) and classical-trajectory Monte Carlo (CTMC) methods. The MOCC calculations utilize ab initio adiabatic potentials and nonadiabatic radial coupling matrix elements obtained from Herrero [J. Phys. B 29, 5583 (1996)] which were calculated with a full configuration-interaction method. Total and state-selective single-electron capture cross sections are obtained for collision energies from 0.01eV/u to 1MeV/u . Total and state-selective rate coefficients are also presented for temperatures from 2×103K to 107K . Comparison with existing data reveals that the total CTMC cross sections are in good agreement with the experimental measurements at the higher considered energies and that previous Landau-Zener calculations underestimate the total rate coefficients by a factor of up to two. The CTMC calculations of target ionization are presented for high energies.

Auroral particles

NASA Technical Reports Server (NTRS)

Evans, David S.

1987-01-01

The problems concerning the aurora posed prior to the war are now either solved in principle or were restated in a more fundamental form. The pre-war hypothesis concerning the nature of the auroral particles and their energies was fully confirmed, with the exception that helium and oxygen ions were identified as participating in the auroral particle precipitation in addition to the protons. The nature of the near-Earth energization processes affecting auroral particles was clarified. Charged particle trajectories in various electric field geometries were modeled. The physical problems have now moved from determining the nature and geometry of the electric fields, which accelerate charged particles near the Earth, to accounting for the existence of these electric fields as a natural consequence of the solar wind's interaction with Earth. Ultimately the reward in continuing the work in auroral and magnetospheric particle dynamics will be a deeper understanding of the subtleties of classical electricity and magnetism as applied to situations not blessed with well-defined and invariant geometries.

Temporal correlation and correlated momentum distribution in nonsequential double ionization of Mg by circularly polarized laser fields

NASA Astrophysics Data System (ADS)

Xu, Tong-Tong; Ben, Shuai; Guo, Pei-Ying; Song, Kai-Li; Zhang, Jun; Liu, Xue-Shen

2017-07-01

We use the classical ensemble method to investigate the nonsequential double ionization (NSDI) process of Mg atoms in circularly polarized laser fields at a lower laser intensity. We illustrate the temporal correlation of the ‘side-by-side’ and the ‘back-to-back emission’. It indicates that the two electrons are more likely to be emitted at the same time for the ‘side-by-side emission’. We demonstrate the electronic trajectories from recollision-induced ionization (RII) and recollision-induced excitation with subsequent ionization (RESI). The distribution of the angle between the two ionized directions of the two electrons and the ion momentum distribution show that the anticorrelation distribution is dominant in the RESI mechanism and correlation distribution is dominant in the RII mechanism. The momentum distributions of Mg atoms for the slow and the fast electrons present a similar structure to the experimental observation of Ar atoms by Liu et al 2014 (Phys. Rev. Lett. 112 013003).

Effects of the electron-hole pair in Auger and X-ray photoemission spectroscopy from surfaces of Fe-Si

NASA Astrophysics Data System (ADS)

Gervasoni, J. L.; Jenko, M.; Poniku, B.; Belič, I.; Juan, A.

2015-07-01

In this work, we investigate in detail the effects due to the interaction between an electron and a stationary positive ion (or atomic hole) in the neighborhood of a surface of Fe-Si, having a strong plasmon peak in their electron energy loss spectra, when it is excited with synchrotron radiation. We take into account the effects due to the sudden creation of an electron and the residual holes, one in the case of X-ray photoemission spectroscopy (XPS) and two in the case of Auger electron spectroscopy (AES). We use a semi classical dielectric formulation for the photoelectron trajectory, and we estimated the parameter rs, the radius of the sphere occupied by one electron in the solid, which is critical in order to define the electron density of the alloy. With the cited formulation, we have obtained a detailed behavior of the different contributions of the collective excitations in both processes.

Investigation of Kp- and Kd-atom formation and their collisional processes with hydrogen and deuterium targets by the classical-trajectory Monte Carlo method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Raeisi, G. M.; Department of Physics, Shahrekord University, Shahrekord 115; Kalantari, S. Z.

The classical-trajectory Monte Carlo method has been used to study the capture of negative kaons by hydrogen and deuterium atoms; subsequently, the elastic scattering, Stark mixing, and Coulomb deexcitation cross sections of Kp and Kd atoms have been determined. The results for kaonic atom formation confirm the initial conditions that have been parametrically applied by most atomic cascade models. Our results show that Coulomb deexcitation in Kp and Kd atoms with {Delta}n>1 is important in addition to n=1. We have shown that the contribution of molecular structure effects to the cross sections of the collisional processes is larger than themore » isotopic effects of the targets. We have also compared our results with the semiclassical approaches.« less

Classical trajectory studies of gas phase reaction dynamics and kinetics using ab initio potential energy surfaces

NASA Technical Reports Server (NTRS)

Jaffe, Richard L.; Pattengill, Merle D.; Schwenke, David W.

1989-01-01

Strategies for constructing global potential energy surfaces from a limited number of accurate ab initio electronic energy calculations are discussed. Generally, these data are concentrated in small regions of configuration space (e.g., in the vicinity of saddle points and energy minima) and difficulties arise in generating a potential function that is globally well-behaved. Efficient computer codes for carrying out classical trajectory calculations on vector and parallel processors are also described. Illustrations are given from recent work on the following chemical systems: Ca + HF yields CaF + H, H + H + H2 yields H2 + H2, N + O2 yields NO + O and O + N2 yields NO + N. The dynamics and kinetics of metathesis, dissociation, recombination, energy transfer and complex formation processes will be discussed.

Incidents Prediction in Road Junctions Using Artificial Neural Networks

NASA Astrophysics Data System (ADS)

Hajji, Tarik; Alami Hassani, Aicha; Ouazzani Jamil, Mohammed

2018-05-01

The implementation of an incident detection system (IDS) is an indispensable operation in the analysis of the road traffics. However the IDS may, in no case, represent an alternative to the classical monitoring system controlled by the human eye. The aim of this work is to increase detection and prediction probability of incidents in camera-monitored areas. Knowing that, these areas are monitored by multiple cameras and few supervisors. Our solution is to use Artificial Neural Networks (ANN) to analyze moving objects trajectories on captured images. We first propose a modelling of the trajectories and their characteristics, after we develop a learning database for valid and invalid trajectories, and then we carry out a comparative study to find the artificial neural network architecture that maximizes the rate of valid and invalid trajectories recognition.

Poincaré resonances and the limits of trajectory dynamics.

PubMed Central

Petrosky, T; Prigogine, I

1993-01-01

In previous papers we have shown that the elimination of the resonance divergences in large Poincare systems leads to complex irreducible spectral representations for the Liouville-von Neumann operator. Complex means that time symmetry is broken and irreducibility means that this representation is implementable only by statistical ensembles and not by trajectories. We consider in this paper classical potential scattering. Our theory applies to persistent scattering. Numerical simulations show quantitative agreement with our predictions. PMID:11607428

Formaldehyde roaming dynamics: Comparison of quasi-classical trajectory calculations and experiments.

PubMed

Houston, Paul L; Wang, Xiaohong; Ghosh, Aryya; Bowman, Joel M; Quinn, Mitchell S; Kable, Scott H

2017-07-07

The photodissociation dynamics of roaming in formaldehyde are studied by comparing quasi-classical trajectory calculations performed on a new potential energy surface (PES) to new and detailed experimental results detailing the CO + H 2 product state distributions and their correlations. The new PES proves to be a significant improvement over the past one, now more than a decade old. The new experiments probe both the CO and H 2 products of the formaldehyde dissociation. The experimental and trajectory data offer unprecedented detail about the correlations between internal states of the CO and H 2 dissociation products as well as information on how these distributions are different for the roaming and transition-state pathways. The data investigated include, for dissociation on the formaldehyde 2 1 4 3 band, (a) the speed distributions for individual vibrational/rotational states of the CO products, providing information about the correlated internal energy distributions of the H 2 product, and (b) the rotational and vibrational distributions for the CO and H 2 products as well as the contributions to each from both the transition state and roaming channels. The agreement between the trajectory and experimental data is quite satisfactory, although minor differences are noted. The general agreement provides support for future use of the experimental techniques and the new PES in understanding the dynamics of photodissociative processes.

Equivalence principle for quantum systems: dephasing and phase shift of free-falling particles

NASA Astrophysics Data System (ADS)

Anastopoulos, C.; Hu, B. L.

2018-02-01

We ask the question of how the (weak) equivalence principle established in classical gravitational physics should be reformulated and interpreted for massive quantum objects that may also have internal degrees of freedom (dof). This inquiry is necessary because even elementary concepts like a classical trajectory are not well defined in quantum physics—trajectories originating from quantum histories become viable entities only under stringent decoherence conditions. From this investigation we posit two logically and operationally distinct statements of the equivalence principle for quantum systems. Version A: the probability distribution of position for a free-falling particle is the same as the probability distribution of a free particle, modulo a mass-independent shift of its mean. Version B: any two particles with the same velocity wave-function behave identically in free fall, irrespective of their masses. Both statements apply to all quantum states, including those without a classical correspondence, and also for composite particles with quantum internal dof. We also investigate the consequences of the interaction between internal and external dof induced by free fall. For a class of initial states, we find dephasing occurs for the translational dof, namely, the suppression of the off-diagonal terms of the density matrix, in the position basis. We also find a gravitational phase shift in the reduced density matrix of the internal dof that does not depend on the particle’s mass. For classical states, the phase shift has a natural classical interpretation in terms of gravitational red-shift and special relativistic time-dilation.

Simulated electron beam trajectories toward a field ion microscopy specimen

NASA Astrophysics Data System (ADS)

Larson, D. J.; Camus, P. P.; Kelly, T. F.

1993-04-01

This article explores the conditions under which a directed electron beam originating nearly normal to the specimen axis can be made to impact the near-apex region of a field ion microscopy specimen in a high electric field. Electron trajectories were calculated using a modified Runge-Kutta numerical method. The results indicate that an electron beam can be directed to a specimen under typical field ion microscopy conditions using two methods: by varying initial beam tilt (less than 60 mrad) or by translating the initial beam position relative to the specimen apex (less than 5 mm). The net focusing effect of the high electric field on the electron beam can be treated, to first order, as an astigmatism and may be correctable by a post-lens deflection system.

Semiclassical propagator of the Wigner function.

PubMed

Dittrich, Thomas; Viviescas, Carlos; Sandoval, Luis

2006-02-24

Propagation of the Wigner function is studied on two levels of semiclassical propagation: one based on the Van Vleck propagator, the other on phase-space path integration. Leading quantum corrections to the classical Liouville propagator take the form of a time-dependent quantum spot. Its oscillatory structure depends on whether the underlying classical flow is elliptic or hyperbolic. It can be interpreted as the result of interference of a pair of classical trajectories, indicating how quantum coherences are to be propagated semiclassically in phase space. The phase-space path-integral approach allows for a finer resolution of the quantum spot in terms of Airy functions.

Ion energy balance in enhanced-confinement reversed-field pinch plasmas

NASA Astrophysics Data System (ADS)

Xing, Z. A.; Nornberg, M. D.; Boguski, J.; Craig, D.; den Hartog, D. J.; McCollam, K.

2017-10-01

Testing the applicability of collisional ion transport theory using tearing suppressed RFP plasma in MST achieved through Pulsed Poloidal Current Drive (PPCD), we find that the ion temperature dynamics in the core to be well-predicted by classical and collisional terms. Prior work demonstrated that impurity ion particle transport in PPCD plasmas is classical. Neoclassical effects on ions in the RFP are small and the stochastic transport is greatly suppressed during PPCD. Recent neutral modelling with DEGAS2 suggests higher core neutral temperatures than expected due to the preferential penetration of higher temperature neutrals generated by charge exchange. Further, investigations through equilibrium reconstruction point to the existence of an inward pinch flow associated with ExB drift. The heat balance model pulls together a wide range of diagnostic data to forward model Ti evolution in PPCD, which is then compared to charge exchange spectroscopy measurements of Ti. Ion power balance is mostly driven by classical effects including compressional heating, electron collisional heating, and charge exchange transport. This understanding provides a good baseline for investigations of anomalous heating in plasmas with tearing mode activity. This work is supported by US DOE.

Pitch Angle Dependence of Drift Resonant Ions Observed by the Van Allen Probes

NASA Astrophysics Data System (ADS)

Rankin, R.; Wang, C.; Wang, Y.; Zong, Q. G.; Zhou, X.

2017-12-01

Acceleration and modulation of ring current ions by poloidal mode ULF waves is investigated. A simplified MHD model of ULF waves in a dipole magnetic field is presented that includes phase mixing to perpendicular scales determined by the ionospheric Pedersen conductivity. The wave model is combined with a full Lorentz force test particle code to study drift and drift bounce resonance wave-particle interactions. Ion trajectories are traced backward-in-time to an assumed form of the distribution function, and Liouville's method is used to reconstruct the phase space density response (PSD) poloidal mode waves observed by the Van Allen Probes. In spite of its apparent simplicity, simulations using the wave and test particle models are able to explain the acceleration of ions and energy dispersion observed by the Van Allen Probes. The paper focuses on the pitch angle evolution of the initial PSD as it responds to the action of ULF waves. An interesting aspect of the study is the formation of butterfly ion distributions as ions make periodic radial oscillations across L. Ions become trapped in an effective potential well across a limited range of L and follow trajectories that cause them to surf along constant phase fronts. The impications of this new trapping mechanism for both ions and electrons is discussed.

Nuclear powered Mars cargo transport mission utilizing advanced ion propulsion

NASA Technical Reports Server (NTRS)

Galecki, Diane L.; Patterson, Michael J.

1987-01-01

Nuclear-powered ion propulsion technology was combined with detailed trajectory analysis to determine propulsion system and trajectory options for an unmanned cargo mission to Mars in support of manned Mars missions. A total of 96 mission scenarios were identified by combining two power levels, two propellants, four values of specific impulse per propellant, three starting altitudes, and two starting velocities. Sixty of these scenarios were selected for a detailed trajectory analysis; a complete propulsion system study was then conducted for 20 of these trajectories. Trip times ranged from 344 days for a xenon propulsion system operating at 300 kW total power and starting from lunar orbit with escape velocity, to 770 days for an argon propulsion system operating at 300 kW total power and starting from nuclear start orbit with circular velocity. Trip times for the 3 MW cases studied ranged from 356 to 413 days. Payload masses ranged from 5700 to 12,300 kg for the 300 kW power level, and from 72,200 to 81,500 kg for the 3 MW power level.

Tracking of Ball and Players in Beach Volleyball Videos

PubMed Central

Gomez, Gabriel; Herrera López, Patricia; Link, Daniel; Eskofier, Bjoern

2014-01-01

This paper presents methods for the determination of players' positions and contact time points by tracking the players and the ball in beach volleyball videos. Two player tracking methods are compared, a classical particle filter and a rigid grid integral histogram tracker. Due to mutual occlusion of the players and the camera perspective, results are best for the front players, with 74,6% and 82,6% of correctly tracked frames for the particle method and the integral histogram method, respectively. Results suggest an improved robustness against player confusion between different particle sets when tracking with a rigid grid approach. Faster processing and less player confusions make this method superior to the classical particle filter. Two different ball tracking methods are used that detect ball candidates from movement difference images using a background subtraction algorithm. Ball trajectories are estimated and interpolated from parabolic flight equations. The tracking accuracy of the ball is 54,2% for the trajectory growth method and 42,1% for the Hough line detection method. Tracking results of over 90% from the literature could not be confirmed. Ball contact frames were estimated from parabolic trajectory intersection, resulting in 48,9% of correctly estimated ball contact points. PMID:25426936

TEMPEST: Twin Electric Magnetospheric Probes Exploring on Spiral Trajectories--A Proposal to the Medium Class Explorer Program

NASA Technical Reports Server (NTRS)

1995-01-01

The objective of the Twin Electric Magnetospheric Probes Exploring on Spiral Trajectories (TEMPEST) mission is to understand the nature and causes of magnetic storm conditions in the magnetosphere whether they be manifested classically in the buildup of the ring current, or (as recently discovered) by storms of relativistic electrons that cause the deep dielectric charging responsible for disabling satellites in synchronous orbit, or by the release of energy into the auroral ionosphere and the plasma sheet during substorms.

Transferability of polarizable models for ion-water electrostatic interaction

NASA Astrophysics Data System (ADS)

Masia, Marco

2009-06-01

Studies of ion-water systems at condensed phase and at interfaces have pointed out that molecular and ionic polarization plays an important role for many phenomena ranging from hydrogen bond dynamics to water interfaces' structure. Classical and ab initio Molecular Dynamics simulations reveal that induced dipole moments at interfaces (e.g. air-water and water-protein) are usually high, hinting that polarizable models to be implemented in classical force fields should be very accurate in reproducing the electrostatic properties of the system. In this paper the electrostatic properties of three classical polarizable models for ion-water interaction are compared with ab initio results both at gas and condensed phase. For Li+- water and Cl--water dimers the reproducibility of total dipole moments obtained with high level quantum chemical calculations is studied; for the same ions in liquid water, Car-Parrinello Molecular Dynamics simulations are used to compute the time evolution of ionic and molecular dipole moments, which are compared with the classical models. The PD2-H2O model developed by the author and coworkers [Masia et al. J. Chem. Phys. 2004, 121, 7362] together with the gaussian intermolecular damping for ion-water interaction [Masia et al. J. Chem. Phys. 2005, 123, 164505] showed to be the fittest in reproducing the ab initio results from gas to condensed phase, allowing for force field transferability.

Molecular Dynamics Study of Twister Ribozyme: Role of Mg(2+) Ions and the Hydrogen-Bonding Network in the Active Site.

PubMed

Ucisik, Melek N; Bevilacqua, Philip C; Hammes-Schiffer, Sharon

2016-07-12

The recently discovered twister ribozyme is thought to utilize general acid-base catalysis in its self-cleavage mechanism, but the roles of nucleobases and metal ions in the mechanism are unclear. Herein, molecular dynamics simulations of the env22 twister ribozyme are performed to elucidate the structural and equilibrium dynamical properties, as well as to examine the role of Mg(2+) ions and possible candidates for the general base and acid in the self-cleavage mechanism. The active site region and the ends of the pseudoknots were found to be less mobile than other regions of the ribozyme, most likely providing structural stability and possibly facilitating catalysis. A purported catalytic Mg(2+) ion and the closest neighboring Mg(2+) ion remained chelated and relatively immobile throughout the microsecond trajectories, although removal of these Mg(2+) ions did not lead to any significant changes in the structure or equilibrium motions of the ribozyme on the microsecond time scale. In addition, a third metal ion, a Na(+) ion remained close to A1(O5'), the leaving group atom, during the majority of the microsecond trajectories, suggesting that it might stabilize the negative charge on A1(O5') during self-cleavage. The locations of these cations and their interactions with key nucleotides in the active site suggest that they may be catalytically relevant. The P1 stem is partially melted at its top and bottom in the crystal structure and further unwinds in the trajectories. The simulations also revealed an interconnected network comprised of hydrogen-bonding and π-stacking interactions that create a relatively rigid network around the self-cleavage site. The nucleotides involved in this network are among the highly conserved nucleotides in twister ribozymes, suggesting that this interaction network may be important to structure and function.

Atmospheric pressure ion focusing in a high-field asymmetric waveform ion mobility spectrometer

NASA Astrophysics Data System (ADS)

Guevremont, Roger; Purves, Randy W.

1999-02-01

The focusing of ions at atmospheric pressure and room temperature in a high-field asymmetric waveform ion mobility spectrometer (FAIMS) has been investigated. FAIMS operates with the application of a high-voltage, high-frequency asymmetric waveform across parallel plates. This establishes conditions wherein an ion migrates towards one of the plates because of a difference in the ion mobility at the low and high electric field conditions during application of the waveform. The migration can be stopped by applying a dc compensation voltage (CV) which serves to create a "balanced" condition wherein the ion experiences no net transverse motion. This method has also been called "transverse field compensation ion mobility spectrometry" and "field ion spectrometry®." If this experiment is conducted using a device with cylindrical geometry, rather than with flat plates, an ion focusing region can exist in the annular space between the two concentric cylinders. Ion trajectory modeling showed that the behavior of the ions in the cylindrical geometry FAIMS analyzer was unlike any previously described atmospheric pressure ion optics system. The ions appeared to be trapped, or focused by being caught between two opposing forces. Requirements for establishing this focus for a given ion were identified: the applied waveform must be asymmetric, the electric field must be sufficiently high that the mobility of the ion deviates from its low-field value during the high-voltage portion of the asymmetric waveform, and finally, the electric field must be nonuniform in space (e.g., cylindrical or spherical geometry). Experimental observations with a prototype FAIMS device, which was designed to measure the radial distribution of ions in the FAIMS analyzer region, have confirmed the results of ion trajectory modeling.

Comparison of cross sections from the quasi-classical trajectory method and the j(z)-conserving centrifugal sudden approximation with accurate quantum results for an atom-rigid nonlinear polyatomic collision

NASA Technical Reports Server (NTRS)

Schwenke, David W.

1993-01-01

We report the results of a series of calculations of state-to-state integral cross sections for collisions between O and nonvibrating H2O in the gas phase on a model nonreactive potential energy surface. The dynamical methods used include converged quantum mechanical scattering calculations, the j(z) conserving centrifugal sudden (j(z)-CCS) approximation, and quasi-classical trajectory (QCT) calculations. We consider three total energies 0.001, 0.002, and 0.005 E(h) and the nine initial states with rotational angular momentum less than or equal to 2 (h/2 pi). The j(z)-CCS approximation gives good results, while the QCT method can be quite unreliable for transitions to specific rotational sublevels. However, the QCT cross sections summed over final sublevels and averaged over initial sublevels are in better agreement with the quantum results.

On classical mechanical systems with non-linear constraints

NASA Astrophysics Data System (ADS)

Terra, Gláucio; Kobayashi, Marcelo H.

2004-03-01

In the present work, we analyze classical mechanical systems with non-linear constraints in the velocities. We prove that the d'Alembert-Chetaev trajectories of a constrained mechanical system satisfy both Gauss' principle of least constraint and Hölder's principle. In the case of a free mechanics, they also satisfy Hertz's principle of least curvature if the constraint manifold is a cone. We show that the Gibbs-Maggi-Appell (GMA) vector field (i.e. the second-order vector field which defines the d'Alembert-Chetaev trajectories) conserves energy for any potential energy if, and only if, the constraint is homogeneous (i.e. if the Liouville vector field is tangent to the constraint manifold). We introduce the Jacobi-Carathéodory metric tensor and prove Jacobi-Carathéodory's theorem assuming that the constraint manifold is a cone. Finally, we present a version of Liouville's theorem on the conservation of volume for the flow of the GMA vector field.

Optimal trajectories for aeroassisted orbital transfer

NASA Technical Reports Server (NTRS)

Miele, A.; Venkataraman, P.

1983-01-01

Consideration is given to classical and minimax problems involved in aeroassisted transfer from high earth orbit (HEO) to low earth orbit (LEO). The transfer is restricted to coplanar operation, with trajectory control effected by means of lift modulation. The performance of the maneuver is indexed to the energy expenditure or, alternatively, the time integral of the heating rate. Firist-order optimality conditions are defined for the classical approach, as are a sequential gradient-restoration algorithm and a combined gradient-restoration algorithm. Minimization techniques are presented for the aeroassisted transfer energy consumption and time-delay integral of the heating rate, as well as minimization of the pressure. It is shown that the eigenvalues of the Jacobian matrix of the differential system is both stiff and unstable, implying that the sequential gradient restoration algorithm in its present version is unsuitable. A new method, involving a multipoint approach to the two-poing boundary value problem, is recommended.

A Thomson-type mass and energy spectrometer for characterizing ion energy distributions in a coaxial plasma gun operating in a gas-puff mode

PubMed Central

Rieker, G. B.; Poehlmann, F. R.; Cappelli, M. A.

2013-01-01

Measurements of ion energy distribution are performed in the accelerated plasma of a coaxial electromagnetic plasma gun operating in a gas-puff mode at relatively low discharge energy (900 J) and discharge potential (4 kV). The measurements are made using a Thomson-type mass and energy spectrometer with a gated microchannel plate and phosphor screen as the ion sensor. The parabolic ion trajectories are captured from the sensor screen with an intensified charge-coupled detector camera. The spectrometer was designed and calibrated using the Geant4 toolkit, accounting for the effects on the ion trajectories of spatial non-uniformities in the spectrometer magnetic and electric fields. Results for hydrogen gas puffs indicate the existence of a class of accelerated protons with energies well above the coaxial discharge potential (up to 24 keV). The Thomson analyzer confirms the presence of impurities of copper and iron, also of relatively high energies, which are likely erosion or sputter products from plasma-electrode interactions. PMID:23983449

A Thomson-type mass and energy spectrometer for characterizing ion energy distributions in a coaxial plasma gun operating in a gas-puff mode

NASA Astrophysics Data System (ADS)

Rieker, G. B.; Poehlmann, F. R.; Cappelli, M. A.

2013-07-01

Measurements of ion energy distribution are performed in the accelerated plasma of a coaxial electromagnetic plasma gun operating in a gas-puff mode at relatively low discharge energy (900 J) and discharge potential (4 kV). The measurements are made using a Thomson-type mass and energy spectrometer with a gated microchannel plate and phosphor screen as the ion sensor. The parabolic ion trajectories are captured from the sensor screen with an intensified charge-coupled detector camera. The spectrometer was designed and calibrated using the Geant4 toolkit, accounting for the effects on the ion trajectories of spatial non-uniformities in the spectrometer magnetic and electric fields. Results for hydrogen gas puffs indicate the existence of a class of accelerated protons with energies well above the coaxial discharge potential (up to 24 keV). The Thomson analyzer confirms the presence of impurities of copper and iron, also of relatively high energies, which are likely erosion or sputter products from plasma-electrode interactions.

A Thomson-type mass and energy spectrometer for characterizing ion energy distributions in a coaxial plasma gun operating in a gas-puff mode.

PubMed

Rieker, G B; Poehlmann, F R; Cappelli, M A

2013-07-01

Measurements of ion energy distribution are performed in the accelerated plasma of a coaxial electromagnetic plasma gun operating in a gas-puff mode at relatively low discharge energy (900 J) and discharge potential (4 kV). The measurements are made using a Thomson-type mass and energy spectrometer with a gated microchannel plate and phosphor screen as the ion sensor. The parabolic ion trajectories are captured from the sensor screen with an intensified charge-coupled detector camera. The spectrometer was designed and calibrated using the Geant4 toolkit, accounting for the effects on the ion trajectories of spatial non-uniformities in the spectrometer magnetic and electric fields. Results for hydrogen gas puffs indicate the existence of a class of accelerated protons with energies well above the coaxial discharge potential (up to 24 keV). The Thomson analyzer confirms the presence of impurities of copper and iron, also of relatively high energies, which are likely erosion or sputter products from plasma-electrode interactions.

Relationship Between Precipitation Chemistry and Meteorological Parameters at a Urban Site in the North of Queretaro State

NASA Astrophysics Data System (ADS)

García Martínez, R.; Hernández, G.; Solis, S.; Torres, M. D.; Padilla, H.; Báez, A.

2010-12-01

A total of 50 wet precipitation samples were collected per event at the Juriquilla site from mid-May 2009 to the end of May 2010. The Juriquilla sampling site was located on the roof of the Geoscience Building, Universidad Nacional Autónoma de México, at the Juriquilla Campus in the city of Querétaro located at 20°41'58"N and 100°27'28" W, at 1920 meters above sea level (masl). Sampling was done in passive collectors that consisted of a high density polyethylene funnel connected to a 2-liter polyethylene bottle, supported by a rod 1.5 m above the roof. One of the collectors was used to take samples for trace metals. The analysis was done in soluble and insoluble fractions. Al, Ag, As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, V and Zn were analyzed by atomic absorption spectroscopy with a graphite furnace accessory. The other collector was used to measure pH and major ions (SO4-2, Cl-, NO3-, Ca2+, Mg2+, Na+, K+ and NH4+) in the soluble fractions, because it was assumed that these ions are completely soluble in rainwater. The major ions SO4-2, Cl-, and NO3-, were analyzed by a Varian Model 2010 ion chromatograph; Ca2+, Mg2+, Na+ and K+ were determined by flame atomic absorption spectrometry and NH4+ by a UV spectrophotometer. In this study, synoptic maps were used to analyze the transport of air masses before rainfall, enabling back trajectories to be used to estimate the source region of pollutants. To understand the variety of synoptic weather conditions, data were associated with the corresponding air mass back trajectories calculated by the NOAA HYSPLIT model (Hybrid Single-Particle Lagrangian Integrated Trajectory Model). Back trajectory models have very simple advection schemes to calculate the previous position of an air parcel by using estimated wind speed and direction for the time period prior to arrival at the selected site. In this study, the origin of the air mass for an event was evaluated by a three-day back-trajectory before arrival to Queretaro. Mass back trajectories were calculated for 1000 and 2000 meters above ground level (MAGL), because winds at these levels should be a good approximation to the mean transport wind, since this pressure level frequently lies near the center of the transport layer. Finally, trajectories were classified by eight different directions according to the directions of the air masses before rainfall.

Open Quantum Systems and Classical Trajectories

NASA Astrophysics Data System (ADS)

Rebolledo, Rolando

2004-09-01

A Quantum Markov Semigroup consists of a family { T} = ({ T}t)_{t ∈ B R+} of normal ω*- continuous completely positive maps on a von Neumann algebra 𝔐 which preserve the unit and satisfy the semigroup property. This class of semigroups has been extensively used to represent open quantum systems. This article is aimed at studying the existence of a { T} -invariant abelian subalgebra 𝔄 of 𝔐. When this happens, the restriction of { T}t to 𝔄 defines a classical Markov semigroup T = (Tt)t ∈ ∝ + say, associated to a classical Markov process X = (Xt)t ∈ ∝ +. The structure (𝔄, T, X) unravels the quantum Markov semigroup { T} , providing a bridge between open quantum systems and classical stochastic processes.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Ying-Jie, E-mail: yingjiezhang@qfnu.edu.cn; Han, Wei; Xia, Yun-Jie, E-mail: yjxia@qfnu.edu.cn

We propose a scheme of controlling entanglement dynamics of a quantum system by applying the external classical driving field for two atoms separately located in a single-mode photon cavity. It is shown that, with a judicious choice of the classical-driving strength and the atom–photon detuning, the effective atom–photon interaction Hamiltonian can be switched from Jaynes–Cummings model to anti-Jaynes–Cummings model. By tuning the controllable atom–photon interaction induced by the classical field, we illustrate that the evolution trajectory of the Bell-like entanglement states can be manipulated from entanglement-sudden-death to no-entanglement-sudden-death, from no-entanglement-invariant to entanglement-invariant. Furthermore, the robustness of the initial Bell-like entanglementmore » can be improved by the classical driving field in the leaky cavities. This classical-driving-assisted architecture can be easily extensible to multi-atom quantum system for scalability.« less

Generalized Gaussian wave packet dynamics: Integrable and chaotic systems.

PubMed

Pal, Harinder; Vyas, Manan; Tomsovic, Steven

2016-01-01

The ultimate semiclassical wave packet propagation technique is a complex, time-dependent Wentzel-Kramers-Brillouin method known as generalized Gaussian wave packet dynamics (GGWPD). It requires overcoming many technical difficulties in order to be carried out fully in practice. In its place roughly twenty years ago, linearized wave packet dynamics was generalized to methods that include sets of off-center, real trajectories for both classically integrable and chaotic dynamical systems that completely capture the dynamical transport. The connections between those methods and GGWPD are developed in a way that enables a far more practical implementation of GGWPD. The generally complex saddle-point trajectories at its foundation are found using a multidimensional Newton-Raphson root search method that begins with the set of off-center, real trajectories. This is possible because there is a one-to-one correspondence. The neighboring trajectories associated with each off-center, real trajectory form a path that crosses a unique saddle; there are exceptions that are straightforward to identify. The method is applied to the kicked rotor to demonstrate the accuracy improvement as a function of ℏ that comes with using the saddle-point trajectories.

Tsien's method for generating non-Keplerian trajectories. Part 2: The question of thrust to orbit a sphere and the restricted three-body problem

NASA Technical Reports Server (NTRS)

Murad, P. A.

1993-01-01

Tsien's method is extended to treat the orbital motion of a body undergoing accelerations and decelerations. A generalized solution is discussed for the generalized case where a body undergoes azimuthal and radial thrust and the problem is further simplified for azimuthal thrust alone. Judicious selection of thrust could generate either an elliptic or hyperbolic trajectory. This is unexpected especially when the body has only enough energy for a lower state trajectory. The methodology is extended treating the problem of vehicle thrust for orbiting a sphere and vehicle thrust within the classical restricted three-body problem. Results for the latter situation can produce hyperbolic trajectories through eigen value decomposition. Since eigen values for no-thrust can be imaginary, thrust can generate real eigen values to describe hyperbolic trajectories. Keplerian dynamics appears to represent but a small subset of a much larger non-Keplerian domain especially when thrust effects are considered. The need for high thrust long duration space-based propulsion systems for changing a trajectory's canonical form is clearly demonstrated.

From material science to avant-garde cuisine. The art of shaping liquids into spheres.

PubMed

Fu, Haohao; Liu, Yingzhe; Adrià, Ferran; Shao, Xueguang; Cai, Wensheng; Chipot, Christophe

2014-10-09

Employing avant-garde cuisine techniques, in particular sodium alginates, liquid food can be shaped into spheres, thereby conferring to the former original and sometimes unexpected forms and textures. To achieve this result, rational understanding of the science that underlies food physical chemistry is of paramount importance. In this contribution, the process of spherification is dissected for the first time at the atomic level by means of classical molecular dynamics simulations. Our results show that a thin membrane consisting of intertwined alginate chains forms in an aqueous solution containing calcium ions, thereby encapsulating in a sphere the aliment in its liquid state. They also show why the polysaccharide chains will not cohere into such a membrane in a solution of sodium ions. Analysis of the trajectories reveals the emergence of so-called egg-box spatial arrangements, which connect the alginate chains by means of repeated chelation of one calcium ion by two carboxylate groups. Free-energy calculations delineating the formation of these egg-box structures further illuminate the remarkable stability of such tridimensional organizations, which ensures at room temperature the spontaneous growth of the polysaccharide membrane. Spherification has been also examined for liquid aliments of different nature, modeled by charged, hydrophilic and hydrophobic compounds. The membrane-encapsulated food is shaped into robust and durable spheres, irrespective of the liquid core material. By reconciling the views of spherification at small and large scales, the present study lays the groundwork for the rational design of innovative cooking techniques relevant to avant-garde cuisine.

Transient chaos - a resolution of breakdown of quantum-classical correspondence in optomechanics.

PubMed

Wang, Guanglei; Lai, Ying-Cheng; Grebogi, Celso

2016-10-17

Recently, the phenomenon of quantum-classical correspondence breakdown was uncovered in optomechanics, where in the classical regime the system exhibits chaos but in the corresponding quantum regime the motion is regular - there appears to be no signature of classical chaos whatsoever in the corresponding quantum system, generating a paradox. We find that transient chaos, besides being a physically meaningful phenomenon by itself, provides a resolution. Using the method of quantum state diffusion to simulate the system dynamics subject to continuous homodyne detection, we uncover transient chaos associated with quantum trajectories. The transient behavior is consistent with chaos in the classical limit, while the long term evolution of the quantum system is regular. Transient chaos thus serves as a bridge for the quantum-classical transition (QCT). Strikingly, as the system transitions from the quantum to the classical regime, the average chaotic transient lifetime increases dramatically (faster than the Ehrenfest time characterizing the QCT for isolated quantum systems). We develop a physical theory to explain the scaling law.

Transient chaos - a resolution of breakdown of quantum-classical correspondence in optomechanics

PubMed Central

Wang, Guanglei; Lai, Ying-Cheng; Grebogi, Celso

2016-01-01

Recently, the phenomenon of quantum-classical correspondence breakdown was uncovered in optomechanics, where in the classical regime the system exhibits chaos but in the corresponding quantum regime the motion is regular - there appears to be no signature of classical chaos whatsoever in the corresponding quantum system, generating a paradox. We find that transient chaos, besides being a physically meaningful phenomenon by itself, provides a resolution. Using the method of quantum state diffusion to simulate the system dynamics subject to continuous homodyne detection, we uncover transient chaos associated with quantum trajectories. The transient behavior is consistent with chaos in the classical limit, while the long term evolution of the quantum system is regular. Transient chaos thus serves as a bridge for the quantum-classical transition (QCT). Strikingly, as the system transitions from the quantum to the classical regime, the average chaotic transient lifetime increases dramatically (faster than the Ehrenfest time characterizing the QCT for isolated quantum systems). We develop a physical theory to explain the scaling law. PMID:27748418

H- and He-like Charge-Exchange Induced X-ray Emission due to Ion Collisions with H, He, and H2

NASA Astrophysics Data System (ADS)

Cumbee, Renata; Mullen, Patrick; Miller, Ansley; Lyons, David; Shelton, Robin L.; Schultz, David R.; Stancil, Phillip C.; Leutenegger, Maurice A.

2017-08-01

When a hot plasma collides with a cold neutral gas interactions occur between the microscopic constituents including charge exchange (CX). CX is a process in which an electron can be transferred from a neutral atom or molecule into an excited energy level of an ion. Following this transfer, the excited electron relaxes to lower energy levels, emitting X-rays. This process has been established as a primary source of X-ray emission within our solar system, such as when the solar wind interacts with cometary and planetary atmospheres, and outside of our solar system, such as in the hot outflows of starburst galaxies.Since the CX X-ray emission spectrum varies greatly with collision velocity, it is critical that realistic CX data are included in X-ray spectral models of astrophysical environments in which CX might be significant in order to correctly estimate the ion abundance and plasma velocities. Here, line ratios and spectra are computed using theoretical CX cross sections obtained with the multi-channel Landau-Zener, atomic-orbital close-coupling, and classical-trajectory Monte Carlo methods for a variety of collision energies relevant to various astrophysical environments. Collisions of bare and H-like C, N, O, Ne, Mg, Al, Si, P, S, and Cl ions are shown with H, He, and H2 as the neutral collision targets. An X-ray model using line ratios for C-Si ions is then performed within XSPEC for a region of the Cygnus Loop supernova remnant for 8 collision energies in order to highlight the variation in CX spectral models with collision energy.R. Cumbee’s research was partially supported by an appointment to the NASA Postdoctoral Program at NASA GSFC, administered by Universities Space Research Association under contract with NASA. Work at UGA was partially supported by NASA grants NNX09AC46G and NNG09WF24I.

Quantum trajectory analysis of multimode subsystem-bath dynamics.

PubMed

Wyatt, Robert E; Na, Kyungsun

2002-01-01

The dynamics of a swarm of quantum trajectories is investigated for systems involving the interaction of an active mode (the subsystem) with an M-mode harmonic reservoir (the bath). Equations of motion for the position, velocity, and action function for elements of the probability fluid are integrated in the Lagrangian (moving with the fluid) picture of quantum hydrodynamics. These fluid elements are coupled through the Bohm quantum potential and as a result evolve as a correlated ensemble. Wave function synthesis along the trajectories permits an exact description of the quantum dynamics for the evolving probability fluid. The approach is fully quantum mechanical and does not involve classical or semiclassical approximations. Computational results are presented for three systems involving the interaction on an active mode with M=1, 10, and 15 bath modes. These results include configuration space trajectory evolution, flux analysis of the evolving ensemble, wave function synthesis along trajectories, and energy partitioning along specific trajectories. These results demonstrate the feasibility of using a small number of quantum trajectories to obtain accurate quantum results on some types of open quantum systems that are not amenable to standard quantum approaches involving basis set expansions or Eulerian space-fixed grids.

The OH + D2 --> HOD + D angle-velocity distribution: quasi-classical trajectory calculations on the YZCL2 and WSLFH potential energy surfaces and comparison with experiments at ET = 0.28 eV.

PubMed

Sierra, José Daniel; Martínez, Rodrigo; Hernando, Jordi; González, Miguel

2009-12-28

The angle-velocity distribution (HOD) of the OH + D(2) reaction at a relative translational energy of 0.28 eV has been calculated using the quasi-classical trajectory (QCT) method on the two most recent potential energy surfaces available (YZCL2 and WSLFH PESs), widely extending a previous investigation of our group. Comparison with the high resolution experiments of Davis and co-workers (Science, 2000, 290, 958) shows that the structures (peaks) found in the relative translational energy distributions of products could not be satisfactorily reproduced in the calculations, probably due to the classical nature of the QCT method and the importance of quantum effects. The calculations, however, worked quite well for other properties. Overall, both surfaces led to similar results, although the YZCL2 surface is more accurate to describe the H(3)O PES, as derived from comparison with high level ab initio results. The differences observed in the QCT calculations were interpreted considering the somewhat larger anisotropy of the YZCL2 PES when compared with the WSLFH PES.

SU-E-T-489: Quantum versus Classical Trajectory Monte Carlo Simulations of Low Energy Electron Transport.

PubMed

Thomson, R; Kawrakow, I

2012-06-01

Widely-used classical trajectory Monte Carlo simulations of low energy electron transport neglect the quantum nature of electrons; however, at sub-1 keV energies quantum effects have the potential to become significant. This work compares quantum and classical simulations within a simplified model of electron transport in water. Electron transport is modeled in water droplets using quantum mechanical (QM) and classical trajectory Monte Carlo (MC) methods. Water droplets are modeled as collections of point scatterers representing water molecules from which electrons may be isotropically scattered. The role of inelastic scattering is investigated by introducing absorption. QM calculations involve numerically solving a system of coupled equations for the electron wavefield incident on each scatterer. A minimum distance between scatterers is introduced to approximate structured water. The average QM water droplet incoherent cross section is compared with the MC cross section; a relative error (RE) on the MC results is computed. RE varies with electron energy, average and minimum distances between scatterers, and scattering amplitude. The mean free path is generally the relevant length scale for estimating RE. The introduction of a minimum distance between scatterers increases RE substantially (factors of 5 to 10), suggesting that the structure of water must be modeled for accurate simulations. Inelastic scattering does not improve agreement between QM and MC simulations: for the same magnitude of elastic scattering, the introduction of inelastic scattering increases RE. Droplet cross sections are sensitive to droplet size and shape; considerable variations in RE are observed with changing droplet size and shape. At sub-1 keV energies, quantum effects may become non-negligible for electron transport in condensed media. Electron transport is strongly affected by the structure of the medium. Inelastic scatter does not improve agreement between QM and MC simulations of low energy electron transport in condensed media. © 2012 American Association of Physicists in Medicine.

A high repetition deterministic single ion source

NASA Astrophysics Data System (ADS)

Sahin, C.; Geppert, P.; Müllers, A.; Ott, H.

2017-12-01

We report on a deterministic single ion source with high repetition rate and high fidelity. The source employs a magneto-optical trap, where ultracold rubidium atoms are photoionized. The electrons herald the creation of a corresponding ion, whose timing information is used to manipulate its trajectory in flight. We demonstrate an ion rate of up to 4× {10}4 {{{s}}}-1 and achieve a fidelity for single ion operation of 98%. The technique can be used for all atomic species, which can be laser-cooled, and opens up new applications in ion microscopy, ion implantation and surface spectroscopy.

Classical density functional theory and Monte Carlo simulation study of electric double layer in the vicinity of a cylindrical electrode

NASA Astrophysics Data System (ADS)

Zhou, Shiqi; Lamperski, Stanisław; Sokołowska, Marta

2017-07-01

We have performed extensive Monte-Carlo simulations and classical density functional theory (DFT) calculations of the electrical double layer (EDL) near a cylindrical electrode in a primitive model (PM) modified by incorporating interionic dispersion interactions. It is concluded that (i) in general, an unsophisticated use of the mean field (MF) approximation for the interionic dispersion interactions does not distinctly worsen the classical DFT performance, even if the salt ions considered are highly asymmetrical in size (3:1) and charge (5:1), the bulk molar concentration considered is high up to a total bulk ion packing fraction of 0.314, and the surface charge density of up to 0.5 C m-2. (ii) More specifically, considering the possible noises in the simulation, the local volume charge density profiles are the most accurately predicted by the classical DFT in all situations, and the co- and counter-ion singlet distributions are also rather accurately predicted; whereas the mean electrostatic potential profile is relatively less accurately predicted due to an integral amplification of minor inaccuracy of the singlet distributions. (iii) It is found that the layered structure of the co-ion distribution is abnormally possible only if the surface charge density is high enough (for example 0.5 C m-2) moreover, the co-ion valence abnormally influences the peak height of the first counter-ion layer, which decreases with the former. (iv) Even if both the simulation and DFT indicate an insignificant contribution of the interionic dispersion interaction to the above three ‘local’ quantities, it is clearly shown by the classical DFT that the interionic dispersion interaction does significantly influence a ‘global’ quantity like the cylinder surface-aqueous electrolyte interfacial tension, and this may imply the role of the interionic dispersion interaction in explaining the specific Hofmeister effects. We elucidate all of the above observations based on the arguments from the liquid state theory and at the molecular scale.

A model of curved saccade trajectories: spike rate adaptation in the brainstem as the cause of deviation away.

PubMed

Kruijne, Wouter; Van der Stigchel, Stefan; Meeter, Martijn

2014-03-01

The trajectory of saccades to a target is often affected whenever there is a distractor in the visual field. Distractors can cause a saccade to deviate towards their location or away from it. The oculomotor mechanisms that produce deviation towards distractors have been thoroughly explored in behavioral, neurophysiological and computational studies. The mechanisms underlying deviation away, on the other hand, remain unclear. Behavioral findings suggest a mechanism of spatially focused, top-down inhibition in a saccade map, and deviation away has become a tool to investigate such inhibition. However, this inhibition hypothesis has little neuroanatomical or neurophysiological support, and recent findings go against it. Here, we propose that deviation away results from an unbalanced saccade drive from the brainstem, caused by spike rate adaptation in brainstem long-lead burst neurons. Adaptation to stimulation in the direction of the distractor results in an unbalanced drive away from it. An existing model of the saccade system was extended with this theory. The resulting model simulates a wide range of findings on saccade trajectories, including findings that have classically been interpreted to support inhibition views. Furthermore, the model replicated the effect of saccade latency on deviation away, but predicted this effect would be absent with large (400 ms) distractor-target onset asynchrony. This prediction was confirmed in an experiment, which demonstrates that the theory both explains classical findings on saccade trajectories and predicts new findings. Copyright © 2014 Elsevier Inc. All rights reserved.

Quantum Dynamics with Short-Time Trajectories and Minimal Adaptive Basis Sets.

PubMed

Saller, Maximilian A C; Habershon, Scott

2017-07-11

Methods for solving the time-dependent Schrödinger equation via basis set expansion of the wave function can generally be categorized as having either static (time-independent) or dynamic (time-dependent) basis functions. We have recently introduced an alternative simulation approach which represents a middle road between these two extremes, employing dynamic (classical-like) trajectories to create a static basis set of Gaussian wavepackets in regions of phase-space relevant to future propagation of the wave function [J. Chem. Theory Comput., 11, 8 (2015)]. Here, we propose and test a modification of our methodology which aims to reduce the size of basis sets generated in our original scheme. In particular, we employ short-time classical trajectories to continuously generate new basis functions for short-time quantum propagation of the wave function; to avoid the continued growth of the basis set describing the time-dependent wave function, we employ Matching Pursuit to periodically minimize the number of basis functions required to accurately describe the wave function. Overall, this approach generates a basis set which is adapted to evolution of the wave function while also being as small as possible. In applications to challenging benchmark problems, namely a 4-dimensional model of photoexcited pyrazine and three different double-well tunnelling problems, we find that our new scheme enables accurate wave function propagation with basis sets which are around an order-of-magnitude smaller than our original trajectory-guided basis set methodology, highlighting the benefits of adaptive strategies for wave function propagation.

Mass Spectrometer Containing Multiple Fixed Collectors

NASA Technical Reports Server (NTRS)

Moskala, Robert; Celo, Alan; Voss, Guenter; Shaffer, Tom

2008-01-01

A miniature mass spectrometer that incorporates features not typically found in prior mass spectrometers is undergoing development. This mass spectrometer is designed to simultaneously measure the relative concentrations of five gases (H2, He, N2, O2, and Ar) in air, over the relative-concentration range from 10(exp -6) to 1, during a sampling time as short as 1 second. It is intended to serve as a prototype of a product line of easy-to-use, portable, lightweight, highspeed, relatively inexpensive instruments for measuring concentrations of multiple chemical species in such diverse applications as detecting explosive or toxic chemicals in air, monitoring and controlling industrial processes, measuring concentrations of deliberately introduced isotopes in medical and biological investigations, and general environmental monitoring. The heart of this mass spectrometer is an integral combination of a circular cycloidal mass analyzer, multiple fixed ion collectors, and two mass-selective ion sources. By circular cycloidal mass analyzer is meant an analyzer that includes (1) two concentric circular cylindrical electrodes for applying a radial electric field and (2) a magnet arranged to impose a magnetic flux aligned predominantly along the cylindrical axis, so that ions, once accelerated into the annulus between the electrodes, move along circular cycloidal trajectories. As in other mass analyzers, trajectory of each ion is determined by its mass-to-charge ratio, and so ions of different species can be collected simultaneously by collectors (Faraday cups) at different locations intersected by the corresponding trajectories (see figure). Unlike in other mass analyzers, the installation of additional collectors to detect additional species does not necessitate increasing the overall size of the analyzer assembly.

Riemann surfaces of complex classical trajectories and tunnelling splitting in one-dimensional systems

NASA Astrophysics Data System (ADS)

Harada, Hiromitsu; Mouchet, Amaury; Shudo, Akira

2017-10-01

The topology of complex classical paths is investigated to discuss quantum tunnelling splittings in one-dimensional systems. Here the Hamiltonian is assumed to be given as polynomial functions, so the fundamental group for the Riemann surface provides complete information on the topology of complex paths, which allows us to enumerate all the possible candidates contributing to the semiclassical sum formula for tunnelling splittings. This naturally leads to action relations among classically disjoined regions, revealing entirely non-local nature in the quantization condition. The importance of the proper treatment of Stokes phenomena is also discussed in Hamiltonians in the normal form.

Symmetrical Windowing for Quantum States in Quasi-Classical Trajectory Simulations

NASA Astrophysics Data System (ADS)

Cotton, Stephen Joshua

An approach has been developed for extracting approximate quantum state-to-state information from classical trajectory simulations which "quantizes" symmetrically both the initial and final classical actions associated with the degrees of freedom of interest using quantum number bins (or "window functions") which are significantly narrower than unit-width. This approach thus imposes a more stringent quantization condition on classical trajectory simulations than has been traditionally employed, while doing so in a manner that is time-symmetric and microscopically reversible. To demonstrate this "symmetric quasi-classical" (SQC) approach for a simple real system, collinear H + H2 reactive scattering calculations were performed [S.J. Cotton and W.H. Miller, J. Phys. Chem. A 117, 7190 (2013)] with SQC-quantization applied to the H 2 vibrational degree of freedom (DOF). It was seen that the use of window functions of approximately 1/2-unit width led to calculated reaction probabilities in very good agreement with quantum mechanical results over the threshold energy region, representing a significant improvement over what is obtained using the traditional quasi-classical procedure. The SQC approach was then applied [S.J. Cotton and W.H. Miller, J. Chem. Phys. 139, 234112 (2013)] to the much more interesting and challenging problem of incorporating non-adiabatic effects into what would otherwise be standard classical trajectory simulations. To do this, the classical Meyer-Miller (MM) Hamiltonian was used to model the electronic DOFs, with SQC-quantization applied to the classical "electronic" actions of the MM model---representing the occupations of the electronic states---in order to extract the electronic state population dynamics. It was demonstrated that if one ties the zero-point energy (ZPE) of the electronic DOFs to the SQC windowing function's width parameter this very simple SQC/MM approach is capable of quantitatively reproducing quantum mechanical results for a range of standard benchmark models of electronically non-adiabatic processes, including applications where "quantum" coherence effects are significant. Notably, among these benchmarks was the well-studied "spin-boson" model of condensed phase non-adiabatic dynamics, in both its symmetric and asymmetric forms---the latter of which many classical approaches fail to treat successfully. The SQC/MM approach to the treatment of non-adiabatic dynamics was next applied [S.J. Cotton, K. Igumenshchev, and W.H. Miller, J. Chem. Phys., 141, 084104 (2014)] to several recently proposed models of condensed phase electron transfer (ET) processes. For these problems, a flux-side correlation function framework modified for consistency with the SQC approach was developed for the calculation of thermal ET rate constants, and excellent accuracy was seen over wide ranges of non-adiabatic coupling strength and energetic bias/exothermicity. Significantly, the "inverted regime" in thermal rate constants (with increasing bias) known from Marcus Theory was reproduced quantitatively for these models---representing the successful treatment of another regime that classical approaches generally have difficulty in correctly describing. Relatedly, a model of photoinduced proton coupled electron transfer (PCET) was also addressed, and it was shown that the SQC/MM approach could reasonably model the explicit population dynamics of the photoexcited electron donor and acceptor states over the four parameter regimes considered. The potential utility of the SQC/MM technique lies in its stunning simplicity and the ease by which it may readily be incorporated into "ordinary" molecular dynamics (MD) simulations. In short, a typical MD simulation may be augmented to take non-adiabatic effects into account simply by introducing an auxiliary pair of classical "electronic" action-angle variables for each energetically viable Born-Oppenheimer surface, and time-evolving these auxiliary variables via Hamilton's equations (using the MM electronic Hamiltonian) in the same manner that the other classical variables---i.e., the coordinates of all the nuclei---are evolved forward in time. In a complex molecular system involving many hundreds or thousands of nuclear DOFs, the propagation of these extra "electronic" variables represents a modest increase in computational effort, and yet, the examples presented herein suggest that in many instances the SQC/MM approach will describe the true non-adiabatic quantum dynamics to a reasonable and useful degree of quantitative accuracy.

A study of quantum mechanical probabilities in the classical Hodgkin-Huxley model.

PubMed

Moradi, N; Scholkmann, F; Salari, V

2015-03-01

The Hodgkin-Huxley (HH) model is a powerful model to explain different aspects of spike generation in excitable cells. However, the HH model was proposed in 1952 when the real structure of the ion channel was unknown. It is now common knowledge that in many ion-channel proteins the flow of ions through the pore is governed by a gate, comprising a so-called "selectivity filter" inside the ion channel, which can be controlled by electrical interactions. The selectivity filter (SF) is believed to be responsible for the selection and fast conduction of particular ions across the membrane of an excitable cell. Other (generally larger) parts of the molecule such as the pore-domain gate control the access of ions to the channel protein. In fact, two types of gates are considered here for ion channels: the "external gate", which is the voltage sensitive gate, and the "internal gate" which is the selectivity filter gate (SFG). Some quantum effects are expected in the SFG due to its small dimensions, which may play an important role in the operation of an ion channel. Here, we examine parameters in a generalized model of HH to see whether any parameter affects the spike generation. Our results indicate that the previously suggested semi-quantum-classical equation proposed by Bernroider and Summhammer (BS) agrees strongly with the HH equation under different conditions and may even provide a better explanation in some cases. We conclude that the BS model can refine the classical HH model substantially.

Scalable implementation of boson sampling with trapped ions.

PubMed

Shen, C; Zhang, Z; Duan, L-M

2014-02-07

Boson sampling solves a classically intractable problem by sampling from a probability distribution given by matrix permanents. We propose a scalable implementation of boson sampling using local transverse phonon modes of trapped ions to encode the bosons. The proposed scheme allows deterministic preparation and high-efficiency readout of the bosons in the Fock states and universal mode mixing. With the state-of-the-art trapped ion technology, it is feasible to realize boson sampling with tens of bosons by this scheme, which would outperform the most powerful classical computers and constitute an effective disproof of the famous extended Church-Turing thesis.

Hydrogen adsorption site on the Ni?110?-p(1 × 2)-H surface from time-of-flight scattering and recoiling spectrometry (TOF-SARS)

NASA Astrophysics Data System (ADS)

Bu, H.; Roux, C. D.; Rabalais, J. W.

The adsorption site of hydrogen on the Ni{110}-p(1 × 2)-H surface resulting from saturation exposure to H 2 at ˜ 310-350 K has been investigated by time-of-flight scattering and recoiling spectrometry (TOF-SARS). The recoiled neutral plus ion hydrogen atom flux resulting from 2-5 keV Ar + or Ne + pulsed ion beams incident on the surface was monitored as a function of crystal azimuthal angle and beam incidence angle. From classical trajectory calculations and shadowing and blocking analyses, it is concluded that hydrogen atoms are localized at the pseudo-three-fold sites on the (1 × 2) missing-row (MR) reconstructed Ni{110} surface; the (1 × 2) MR reconstruction is induced by hydrogen adsorption shown elsewhere [Surf. Sci. 259 (1991) 253]. Only the pseudo-three-fold site is consistent with all of the experimental data. The coordinates of the hydrogen adsorption site with respect to the nickel lattice were determined. The lateral distance of hydrogen from the 1st-layer Ni <1 overline10> rows is 1.56 ± 0.12 Å and the vertical distance above the substrate is 0.21 ± 0.12 Å, providing NiH bond lengths of 2.0 Å to the two-layer Ni atoms and 1.5 Å to the 2nd-layer Ni atom.

Determining the composition of small features in atom probe: bcc Cu-rich precipitates in an Fe-rich matrix.

PubMed

Morley, A; Sha, G; Hirosawa, S; Cerezo, A; Smith, G D W

2009-04-01

Aberrations in the ion trajectories near the specimen surface are an important factor in the spatial resolution of the atom probe technique. Near the boundary between two phases with dissimilar evaporation fields, ion trajectory overlaps may occur, leading to a biased measurement of composition in the vicinity of this interface. In the case of very small second-phase precipitates, the region affected by trajectory overlaps may extend to the centre of the precipitate prohibiting a direct measurement of composition. A method of quantifying the aberrant matrix contribution and thus estimating the underlying composition is presented. This method is applied to the Fe-Cu-alloy system, where the precipitation of low-nanometre size Cu-rich precipitates is of considerable technical importance in a number of materials applications. It is shown definitively that there is a non-zero underlying level of Fe within precipitates formed upon thermal ageing, which is augmented and masked by trajectory overlaps. The concentration of Fe in the precipitate phase is shown to be a function of ageing temperature. An estimate of the underlying Fe level is made, which is at lower levels than commonly reported by atom probe investigations.

Study of beam optics and beam halo by integrated modeling of negative ion beams from plasma meniscus formation to beam acceleration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miyamoto, K.; Okuda, S.; Hatayama, A.

2013-01-14

To understand the physical mechanism of the beam halo formation in negative ion beams, a two-dimensional particle-in-cell code for simulating the trajectories of negative ions created via surface production has been developed. The simulation code reproduces a beam halo observed in an actual negative ion beam. The negative ions extracted from the periphery of the plasma meniscus (an electro-static lens in a source plasma) are over-focused in the extractor due to large curvature of the meniscus.

Characterizing quantum channels with non-separable states of classical light

NASA Astrophysics Data System (ADS)

Ndagano, Bienvenu; Perez-Garcia, Benjamin; Roux, Filippus S.; McLaren, Melanie; Rosales-Guzman, Carmelo; Zhang, Yingwen; Mouane, Othmane; Hernandez-Aranda, Raul I.; Konrad, Thomas; Forbes, Andrew

2017-04-01

High-dimensional entanglement with spatial modes of light promises increased security and information capacity over quantum channels. Unfortunately, entanglement decays due to perturbations, corrupting quantum links that cannot be repaired without performing quantum tomography on the channel. Paradoxically, the channel tomography itself is not possible without a working link. Here we overcome this problem with a robust approach to characterize quantum channels by means of classical light. Using free-space communication in a turbulent atmosphere as an example, we show that the state evolution of classically entangled degrees of freedom is equivalent to that of quantum entangled photons, thus providing new physical insights into the notion of classical entanglement. The analysis of quantum channels by means of classical light in real time unravels stochastic dynamics in terms of pure state trajectories, and thus enables precise quantum error correction in short- and long-haul optical communication, in both free space and fibre.

Quantum-classical analogies in waveguide arrays: From Fourier transforms to ion-laser interactions

NASA Astrophysics Data System (ADS)

Moya-Cessa, Héctor M.

2018-04-01

By using the fact that infinite and semi-infinite systems of differential equations may be casted as Schrödinger-like equations we show how quantum-classical analogies may be achieved. In particular we show how the analogies of ion-laser, functions of a phase operator and quantised-field-two-level-atom interactions may be emulated. We also show a realization of the fractional discrete Fourier transform.

Quasilinear analysis of ion Bernstein and lower hybrid waves synergy

NASA Astrophysics Data System (ADS)

Paoletti, F.; Cardinali, A.; Shoucri, M.; Shkarofsky, A.; Bernabei, S.; Ono, M.

1996-02-01

A quasilinear analysis of the absorption of Ion Bernstein Wave (IBW) by the electron population of the plasma is performed. It uses an analytical calculation of the amplitude of the electric field along the trajectory to obtain the quasilinear diffusion coefficient. A numerical integration of the Fokker-Planck equation is performed together with the dynamical evolution of the IBW and Lower Hybrid Wave (LHW) ray trajectories. The damping of IBW is calculated on the distorted distribution function generated by the previous application of Lower Hybrid Current Drive (LHCD) which has bridged the n∥-gap. This calculation is particularly relevant because of the IBW/LHW experiments on the Princeton Beta Experiment-Modified (PBX-M).

Static harmonization of dynamically harmonized Fourier transform ion cyclotron resonance cell.

PubMed

Zhdanova, Ekaterina; Kostyukevich, Yury; Nikolaev, Eugene

2017-08-01

Static harmonization in the Fourier transform ion cyclotron resonance cell improves the resolving power of the cell and prevents dephasing of the ion cloud in the case of any trajectory of the charged particle, not necessarily axisymmetric cyclotron (as opposed to dynamic harmonization). We reveal that the Fourier transform ion cyclotron resonance cell with dynamic harmonization (paracell) is proved to be statically harmonized. The volume of the statically harmonized potential distribution increases with an increase in the number of trap segments.

LORAKS Makes Better SENSE: Phase-Constrained Partial Fourier SENSE Reconstruction without Phase Calibration

PubMed Central

Kim, Tae Hyung; Setsompop, Kawin; Haldar, Justin P.

2016-01-01

Purpose Parallel imaging and partial Fourier acquisition are two classical approaches for accelerated MRI. Methods that combine these approaches often rely on prior knowledge of the image phase, but the need to obtain this prior information can place practical restrictions on the data acquisition strategy. In this work, we propose and evaluate SENSE-LORAKS, which enables combined parallel imaging and partial Fourier reconstruction without requiring prior phase information. Theory and Methods The proposed formulation is based on combining the classical SENSE model for parallel imaging data with the more recent LORAKS framework for MR image reconstruction using low-rank matrix modeling. Previous LORAKS-based methods have successfully enabled calibrationless partial Fourier parallel MRI reconstruction, but have been most successful with nonuniform sampling strategies that may be hard to implement for certain applications. By combining LORAKS with SENSE, we enable highly-accelerated partial Fourier MRI reconstruction for a broader range of sampling trajectories, including widely-used calibrationless uniformly-undersampled trajectories. Results Our empirical results with retrospectively undersampled datasets indicate that when SENSE-LORAKS reconstruction is combined with an appropriate k-space sampling trajectory, it can provide substantially better image quality at high-acceleration rates relative to existing state-of-the-art reconstruction approaches. Conclusion The SENSE-LORAKS framework provides promising new opportunities for highly-accelerated MRI. PMID:27037836

Effective dynamics of a classical point charge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Polonyi, Janos, E-mail: polonyi@iphc.cnrs.fr

2014-03-15

The effective Lagrangian of a point charge is derived by eliminating the electromagnetic field within the framework of the classical closed time path formalism. The short distance singularity of the electromagnetic field is regulated by an UV cutoff. The Abraham–Lorentz force is recovered and its similarity to quantum anomalies is underlined. The full cutoff-dependent linearized equation of motion is obtained, no runaway trajectories are found but the effective dynamics shows acausality if the cutoff is beyond the classical charge radius. The strength of the radiation reaction force displays a pole in its cutoff-dependence in a manner reminiscent of the Landau-polemore » of perturbative QED. Similarity between the dynamical breakdown of the time reversal invariance and dynamical symmetry breaking is pointed out. -- Highlights: •Extension of the classical action principle for dissipative systems. •New derivation of the Abraham–Lorentz force for a point charge. •Absence of a runaway solution of the Abraham–Lorentz force. •Acausality in classical electrodynamics. •Renormalization of classical electrodynamics of point charges.« less

Self-proton/ion radiography of laser-produced proton/ion beam from thin foil targets

NASA Astrophysics Data System (ADS)

Paudel, Y.; Renard-Le Galloudec, N.; Nicolai, Ph.; d'Humieres, E.; Ya. Faenov, A.; Kantsyrev, V. L.; Safronova, A. S.; Shrestha, I.; Osborne, G. C.; Shlyaptseva, V. V.; Sentoku, Y.

2012-12-01

Protons and multicharged ions generated from high-intensity laser interactions with thin foil targets have been studied with a 100 TW laser system. Protons/ions with energies up to 10 MeV are accelerated either from the front or the rear surface of the target material. We have observed for the first time that the protons/ions accelerated from the front surface of the target, in a direction opposite to the laser propagation direction, are turned around and pulled back to the rear surface, in the laser propagation direction. This proton/ion beam is able to create a self-radiograph of the target and glass stalk holding the target itself recorded through the radiochromic film stack. This unique result indicates strong long-living (ns time scale) magnetic fields present in the laser-produced plasma, which are extremely important in energy transport during the intense laser irradiation. The magnetic field from laser main pulse expands rapidly in the preformed plasma to rotate the laser produced protons. Radiation hydrodynamic simulations and ray tracing found that the magnetic field created by the amplified spontaneous emission prepulse is not sufficient to explain the particle trajectories, but the additional field created by the main pulse interaction estimated from particle-in-cell simulation is able to change the particle trajectories.

Fully adaptive propagation of the quantum-classical Liouville equation

NASA Astrophysics Data System (ADS)

Horenko, Illia; Weiser, Martin; Schmidt, Burkhard; Schütte, Christof

2004-05-01

In mixed quantum-classical molecular dynamics few but important degrees of freedom of a dynamical system are modeled quantum-mechanically while the remaining ones are treated within the classical approximation. Rothe methods established in the theory of partial differential equations are used to control both temporal and spatial discretization errors on grounds of a global tolerance criterion. The TRAIL (trapezoidal rule for adaptive integration of Liouville dynamics) scheme [I. Horenko and M. Weiser, J. Comput. Chem. 24, 1921 (2003)] has been extended to account for nonadiabatic effects in molecular dynamics described by the quantum-classical Liouville equation. In the context of particle methods, the quality of the spatial approximation of the phase-space distributions is maximized while the numerical condition of the least-squares problem for the parameters of particles is minimized. The resulting dynamical scheme is based on a simultaneous propagation of moving particles (Gaussian and Dirac deltalike trajectories) in phase space employing a fully adaptive strategy to upgrade Dirac to Gaussian particles and, vice versa, downgrading Gaussians to Dirac-type trajectories. This allows for the combination of Monte-Carlo-based strategies for the sampling of densities and coherences in multidimensional problems with deterministic treatment of nonadiabatic effects. Numerical examples demonstrate the application of the method to spin-boson systems in different dimensionality. Nonadiabatic effects occurring at conical intersections are treated in the diabatic representation. By decreasing the global tolerance, the numerical solution obtained from the TRAIL scheme are shown to converge towards exact results.

Fully adaptive propagation of the quantum-classical Liouville equation.

PubMed

Horenko, Illia; Weiser, Martin; Schmidt, Burkhard; Schütte, Christof

2004-05-15

In mixed quantum-classical molecular dynamics few but important degrees of freedom of a dynamical system are modeled quantum-mechanically while the remaining ones are treated within the classical approximation. Rothe methods established in the theory of partial differential equations are used to control both temporal and spatial discretization errors on grounds of a global tolerance criterion. The TRAIL (trapezoidal rule for adaptive integration of Liouville dynamics) scheme [I. Horenko and M. Weiser, J. Comput. Chem. 24, 1921 (2003)] has been extended to account for nonadiabatic effects in molecular dynamics described by the quantum-classical Liouville equation. In the context of particle methods, the quality of the spatial approximation of the phase-space distributions is maximized while the numerical condition of the least-squares problem for the parameters of particles is minimized. The resulting dynamical scheme is based on a simultaneous propagation of moving particles (Gaussian and Dirac deltalike trajectories) in phase space employing a fully adaptive strategy to upgrade Dirac to Gaussian particles and, vice versa, downgrading Gaussians to Dirac-type trajectories. This allows for the combination of Monte-Carlo-based strategies for the sampling of densities and coherences in multidimensional problems with deterministic treatment of nonadiabatic effects. Numerical examples demonstrate the application of the method to spin-boson systems in different dimensionality. Nonadiabatic effects occurring at conical intersections are treated in the diabatic representation. By decreasing the global tolerance, the numerical solution obtained from the TRAIL scheme are shown to converge towards exact results.

Student Support for Research in Hierarchical Control and Trajectory Planning

NASA Technical Reports Server (NTRS)

Martin, Clyde F.

1999-01-01

Generally, classical polynomial splines tend to exhibit unwanted undulations. In this work, we discuss a technique, based on control principles, for eliminating these undulations and increasing the smoothness properties of the spline interpolants. We give a generalization of the classical polynomial splines and show that this generalization is, in fact, a family of splines that covers the broad spectrum of polynomial, trigonometric and exponential splines. A particular element in this family is determined by the appropriate control data. It is shown that this technique is easy to implement. Several numerical and curve-fitting examples are given to illustrate the advantages of this technique over the classical approach. Finally, we discuss the convergence properties of the interpolant.

Study of geometric phase using classical coupled oscillators

NASA Astrophysics Data System (ADS)

Bhattacharjee, Sharba; Dey, Biprateep; Mohapatra, Ashok K.

2018-05-01

We illustrate the geometric phase associated with the cyclic dynamics of a classical system of coupled oscillators. We use an analogy between a classical coupled oscillator and a two-state quantum mechanical system to represent the evolution of the oscillator on an equivalent Hilbert space, which may be represented as a trajectory on the surface of a sphere. The cyclic evolution of the system leads to a change in phase, which consists of a dynamic phase along with an additional phase shift dependent on the geometry of the evolution. A simple experiment suitable for advanced undergraduate students is designed to study the geometric phase incurred during cyclic evolution of a coupled oscillator.

Charge Exchange: Velocity Dependent X-ray Emission Modeling

NASA Astrophysics Data System (ADS)

Cumbee, Renata

2017-06-01

Atomic collisions play a fundamental role in astrophysics, plasma physics, and fusion physics. Here, we focus on charge exchange (CX) between hot ions and neutral atoms and molecules. Even though charge exchange calculations can provide vital information, including neutral and ion density distributions, ion temperatures, elemental abundances, and ion charge state distributions in the environments considered, both theoretical calculations and laboratory studies of these processes lack the necessary reliability and/or coverage. In order to better understand the spectra we observe in astrophysical environments in which both hot plasma and neutral gas are present, including comets, the heliosphere, supernova remnants, galaxy clusters, star forming galaxies, the outflows of starburst galaxies, and cooling flows of hot gas in the intracluster medium, a thorough CX X-ray model is needed. Included in this model should be a complete set of X-ray line ratios for relevant ion and neutral interactions for a range of energies.In this work, theoretical charge exchange emission spectra are produced using cross sections calculated with widely applied approaches including the quantum mechanical molecular orbital close coupling (QMOCC), atomic orbital close coupling (AOCC), classical trajectory Monte Carlo (CTMC), and the multichannel Landau-Zener (MCLZ) methods. When possible, theoretical data are benchmarked to experiments. Using a comprehensive, but still far from complete, CX database, new models are performed for a variety of X-ray emitting environments. In an attempt to describe the excess emission in X-rays of the starburst galaxy M82, Ne X CX line ratios are compared to line ratios observed in the region. A more complete XSPEC X-ray emission model is produced for H-like and He-like C-Al ions colliding with H and He for a range of energies; 200 to 5000 eV/u. This model is applied to the northeast rim of the Cygnus Loop supernova remnant in an attempt to determine the contribution of CX within that region.This work was partially supported by NASA grants NNX09AC46G and NNG09WF24I and accomplished with the help of many collaborators including Phillip C. Stancil, David Lyons, Patrick Mullen, and Robin L. Shelton.

"Structure-making" ability of Na+ in dilute aqueous solution: an ONIOM-XS MD simulation study.

PubMed

Sripa, Pattrawan; Tongraar, Anan; Kerdcharoen, Teerakiat

2013-02-28

An ONIOM-XS MD simulation has been performed to characterize the "structure-making" ability of Na(+) in dilute aqueous solution. The region of most interest, i.e., a sphere that includes Na(+) and its surrounding water molecules, was treated at the HF level of accuracy using LANL2DZ and DZP basis sets for the ion and waters, respectively, whereas the rest of the system was described by classical pair potentials. Detailed analyzes of the ONIOM-XS MD trajectories clearly show that Na(+) is able to order the structure of waters in its surroundings, forming two prevalent Na(+)(H(2)O)(5) and Na(+)(H(2)O)(6) species. Interestingly, it is observed that these 5-fold and 6-fold coordinated complexes can convert back and forth with some degrees of flexibility, leading to frequent rearrangements of the Na(+) hydrates as well as numerous attempts of inner-shell water molecules to interchange with waters in the outer region. Such a phenomenon clearly demonstrates the weak "structure-making" ability of Na(+) in aqueous solution.

Electric Field Fluctuations in Water

NASA Astrophysics Data System (ADS)

Thorpe, Dayton; Limmer, David; Chandler, David

2013-03-01

Charge transfer in solution, such as autoionization and ion pair dissociation in water, is governed by rare electric field fluctuations of the solvent. Knowing the statistics of such fluctuations can help explain the dynamics of these rare events. Trajectories short enough to be tractable by computer simulation are virtually certain not to sample the large fluctuations that promote rare events. Here, we employ importance sampling techniques with classical molecular dynamics simulations of liquid water to study statistics of electric field fluctuations far from their means. We find that the distributions of electric fields located on individual water molecules are not in general gaussian. Near the mean this non-gaussianity is due to the internal charge distribution of the water molecule. Further from the mean, however, there is a previously unreported Bjerrum-like defect that stabilizes certain large fluctuations out of equilibrium. As expected, differences in electric fields acting between molecules are gaussian to a remarkable degree. By studying these differences, though, we are able to determine what configurations result not only in large electric fields, but also in electric fields with long spatial correlations that may be needed to promote charge separation.

Effect of nuclear shielding in collision of positive charged helium ions with helium atoms

NASA Astrophysics Data System (ADS)

Ghavaminia, Hoda; Ghavaminia, Shirin

2018-03-01

Differential in angle and absolute cross sections in energy of the scattered particles are obtained for single charge exchange in ^3He^+-^4He collisions by means of the four body boundary-corrected first Born approximation (CB1-4B). The quantum-mechanical post and prior transition amplitudes are derived in terms of two-dimensional real integrals in the case of the prior form and five-dimensional quadratures for the post form. The effect of the dynamic electron correlation through the complete perturbation potential and the nuclear-screening influence of the passive electrons on the electron capture process is investigated. The results obtained in the CB1-4B method are compared with the available experimental data. For differential cross sections, the present results are in better agreement with experimental data than other theoretical data at extreme forward scattering angles. The integral cross sections are in excellent agreement with the experiment. Also, total cross sections for single electron capture, has been investigated using the classical trajectory Monte Carlo method. The present calculated results are found to be in an excellent agreement with the experimental data.

Exploration of momentum evolution and three-dimensional localization in recombined electron wave packets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zeibel, J. G.; Jones, R. R.

2003-08-01

Picosecond ''half-cycle'' pulses (HCPs) have been used to produce electronic wave packets by recombining photoelectrons with their parent ions. The time-dependent momentum distributions of the bound wave packets are probed using a second HCP and the impulsive momentum retrieval (IMR) method. For a given delay between the initial photoionization event and the HCP recombination, classical trajectory simulations predict pronounced periodic wave packet motion for a restricted range of recombining HCP amplitudes. This motion is characterized by the repeated formation and collapse of a highly localized spike in the three-dimensional electron probability density at a large distance from the nucleus. Ourmore » experiments confirm that oscillatory wave packet motion occurs only for certain recombination ''kick'' strengths. Moreover, the measured time-dependent momentum distributions are consistent with the predicted formation of a highly localized electron packet. We demonstrate a variation of the IMR in which amplitude modulation of the HCP probe field is employed to suppress noise and allow for a more direct recovery of electron momentum from experimental ionization data.« less

Hexapole-selected supersonic beams of reactive radicals: CF3, SiF3, SH, CH, and C2H

NASA Astrophysics Data System (ADS)

Weibel, Michael A.; Hain, Toby D.; Curtiss, Thomas J.

1998-02-01

A supersonic corona discharge source was used to produce molecular beams of plasma particles. Neutral, polar components of the plasma mixture were selectively focused by an electrostatic hexapole, thereby "simplifying" the chemical and rotational state composition of the beam. Careful choice of a radical precursor, combined with control of discharge and hexapole voltage allowed the production of pure beams of CF3, SiF3, and SH (purity typically better than 90%), with no noticeable signal arising from undissociated precursor, ions, or other radicals. Focused beams from a hydrocarbon plasma contained a radical mixture of predominantly CH and C2H. Radical beams were characterized by rotationally and translationally cold temperatures (typically TR<20 K and TS<20 K, respectively) and high intensities (typically 1011-1012cm-2 s-1). Simulated focusing spectra using classical trajectory calculations showed generally good agreement with the experimental data, leading to the first experimental measurement of the permanent electric dipole moment of SiF3 (μ=1.2±0.1 D).

A Experimental Investigation of Fast Ion Confinement on the Isx-B Tokamak

NASA Astrophysics Data System (ADS)

Carnevali, Antonino

An experimental investigation of fast ion confinement was conducted on the ISX-B tokamak at the Oak Ridge National Laboratory to ascertain that the beam ion behavior is properly described by classical processes. Data were collected during tangential injection of H('0) beams (co-, counter -, and co- plus counter-) at power levels up to 1.9 MW in low plasma current (I(,p) = 80 to 215 kA) D('+) discharges. Experimental energy spectra of energetic charge-exchange neutrals along several sightlines in the torus equatorial plane are compared with the predictions of Fokker-Planck and orbit-following Monte Carlo calculations to verify the validity of classical theory. A further tool used in this investigation is the comparison of predicted and experimental beam-plasma neutron emission during injection of beams doped with 3% D('0). Both the fast neutral spectra and the beam-plasma neutron emission are in close agreement (within factors of <2) with the calculated values under a variety of plasma parameters, beam parameters, and injection geometries. Furthermore, measured decay rates of the beam-plasma neutron production following beam turn-off show that the beam slowing down --at energies close to the injection energy and in the plasma core-- is classical within a 30% uncertainty. These results demonstrate that classical theory describes well the behavior of the beam ions. Moreover, MHD activity is shown not to cause enhanced fast ion losses in the ISX-B. Also, beam additivity experiments indicate that the fast ion density in the plasma volume is proportional to the injected beam power P(,b). An unresolved issue is whether the central fast ion density is linear with P(,b). In addition, the analysis of charge-exchange spectra is critically evaluated. It is shown that the analysis need be integrated with a knowledge of the orbit topology to correctly interpret the spectra. Cases where the zero banana width, Fokker-Planck calculation is adequate/inadequate to predict fast neutral spectra and power deposited in the plasma are discussed.

Positive and negative ion beam merging system for neutral beam production

DOEpatents

Leung, Ka-Ngo; Reijonen, Jani

2005-12-13

The positive and negative ion beam merging system extracts positive and negative ions of the same species and of the same energy from two separate ion sources. The positive and negative ions from both sources pass through a bending magnetic field region between the pole faces of an electromagnet. Since the positive and negative ions come from mirror image positions on opposite sides of a beam axis, and the positive and negative ions are identical, the trajectories will be symmetrical and the positive and negative ion beams will merge into a single neutral beam as they leave the pole face of the electromagnet. The ion sources are preferably multicusp plasma ion sources. The ion sources may include a multi-aperture extraction system for increasing ion current from the sources.

Development and Tests of Elements of a Dust Telescope

NASA Astrophysics Data System (ADS)

Gruen, E.; Srama, R.; Rachev, M.; Srowig, A.; Sternovsky, Z.; Horanyi, M.; Amyx, K.; Auer, S.

2005-08-01

A dust telescope is a combination of a dust trajectory sensor together with an analyzer for the chemical composition of dust particles in space. Dust particles' trajectories are determined by the measurement of the electric signals that are induced when a charged grain flies through a position sensitive electrode system. The objective of the trajectory sensor is to measure dust charges in the range 10-16 to 10-13 C and dust speeds in the range 6 to 100 km/s. The trajectory sensor has four sensor planes consisting of about 16 wire electrodes each. Two adjacent planes have orthogonal wire direction. An ASIC charge sensitive amplifier has been developed with a RMS noise of about 1.5 10-17 C. The signals from 32 electrodes are digitized and sampled at 20 MHz rate by an ASIC transient recorder. First tests with a laboratory set-up have been performed and demonstrate a charge sensitivity corresponding to 100 electrons. The dust chemical analyzers shall have sufficient mass resolution in order to resolve ions with atomic mass number up to 100. The annular impact area of the mass analyzer will be > 0.1 m2. The mass spectrometer consists of the target area with an acceleration grid and the single-stage reflectron consisting of two grids and the central ion detector. Different field configurations have been found that have a mass resolution of M/Δ M > 150 for impacts onto the annular target between 100 and 240 mm from the center. An Ion Detector of 50 to 110 mm radius is necessary to collect all generated ions. A lab model has been constructed and first dust accelerator tests demonstrate a mass resolution (FWHM) of M/Δ M 250. Acknowledgements: This research is supported by NASA grant NAG5-11782 and by DLR grant 50OO0201.

Confinement degradation by Alfvén-eigenmode induced fast-ion transport in steady-state scenario discharges

DOE PAGES

Heidbrink, William W.; Ferron, John R.; Holcomb, Christopher T.; ...

2014-08-21

Here, analysis of neutron and fast-ion D α data from the DIII-D tokamak shows that Alfvén eigenmode activity degrades fast-ion confinement in many high β N, high q min, steady-state scenario discharges. (β N is the normalized plasma pressure and q min is the minimum value of the plasma safety factor.) Fast-ion diagnostics that are sensitive to the co-passing population exhibit the largest reduction relative to classical predictions. The increased fast-ion transport in discharges with strong AE activity accounts for the previously observed reduction in global confinement with increasing q min; however, not all high q min discharges show appreciablemore » degradation. Two relatively simple empirical quantities provide convenient monitors of these effects: (1) an 'AE amplitude' signal based on interferometer measurements and (2) the ratio of the neutron rate to a zero-dimensional classical prediction.« less

From transistor to trapped-ion computers for quantum chemistry.

PubMed

Yung, M-H; Casanova, J; Mezzacapo, A; McClean, J; Lamata, L; Aspuru-Guzik, A; Solano, E

2014-01-07

Over the last few decades, quantum chemistry has progressed through the development of computational methods based on modern digital computers. However, these methods can hardly fulfill the exponentially-growing resource requirements when applied to large quantum systems. As pointed out by Feynman, this restriction is intrinsic to all computational models based on classical physics. Recently, the rapid advancement of trapped-ion technologies has opened new possibilities for quantum control and quantum simulations. Here, we present an efficient toolkit that exploits both the internal and motional degrees of freedom of trapped ions for solving problems in quantum chemistry, including molecular electronic structure, molecular dynamics, and vibronic coupling. We focus on applications that go beyond the capacity of classical computers, but may be realizable on state-of-the-art trapped-ion systems. These results allow us to envision a new paradigm of quantum chemistry that shifts from the current transistor to a near-future trapped-ion-based technology.

From transistor to trapped-ion computers for quantum chemistry

PubMed Central

Yung, M.-H.; Casanova, J.; Mezzacapo, A.; McClean, J.; Lamata, L.; Aspuru-Guzik, A.; Solano, E.

2014-01-01

Over the last few decades, quantum chemistry has progressed through the development of computational methods based on modern digital computers. However, these methods can hardly fulfill the exponentially-growing resource requirements when applied to large quantum systems. As pointed out by Feynman, this restriction is intrinsic to all computational models based on classical physics. Recently, the rapid advancement of trapped-ion technologies has opened new possibilities for quantum control and quantum simulations. Here, we present an efficient toolkit that exploits both the internal and motional degrees of freedom of trapped ions for solving problems in quantum chemistry, including molecular electronic structure, molecular dynamics, and vibronic coupling. We focus on applications that go beyond the capacity of classical computers, but may be realizable on state-of-the-art trapped-ion systems. These results allow us to envision a new paradigm of quantum chemistry that shifts from the current transistor to a near-future trapped-ion-based technology. PMID:24395054

Fast ion beta limit measurements by collimated neutron detection in MST plasmas

NASA Astrophysics Data System (ADS)

Capecchi, William; Anderson, Jay; Bonofiglo, Phillip; Kim, Jungha; Sears, Stephanie

2015-11-01

Fast ion orbits in the reversed field pinch (RFP) are well ordered and classically confined despite magnetic field stochasticity generated by multiple tearing modes. Classical TRANSP modeling of a 1MW tangentially injected hydrogen neutral beam in MST deuterium plasmas predicts a core-localized fast ion density that can be up to 25% of the electron density and a fast ion beta of many times the local thermal beta. However, neutral particle analysis of an NBI-driven mode (presumably driven by a fast ion pressure gradient) shows mode-induced transport of core-localized fast ions and a saturated fast ion density. The TRANSP modeling is presumed valid until the onset of the beam-driven mode and gives an initial estimate of the volume-averaged fast ion beta of 1-2% (local core value up to 10%). A collimated neutron detector for fusion product profile measurements will be used to determine the spatial distribution of fast ions, allowing for a first measurement of the critical fast-ion pressure gradient required for mode destabilization. Testing/calibration data and initial fast-ion profiles will be presented. Characterization of both the local and global fast ion beta will be done for deuterium beam injection into deuterium plasmas for comparison to TRANSP predictions. Work supported by US DOE.

Stratification, School-Work Linkages and Vocational Education

ERIC Educational Resources Information Center

Ainsworth, James W.; Roscigno, Vincent J.

2005-01-01

Building on more classical status attainment and reproduction perspectives, this article examines the extent of class, race and gender inequality in high school vocational education, and the consequences for students' later educational and occupational trajectories. Analyses demonstrate significant class, race and gender disparities in vocational…

Weak-field few-femtosecond VUV photodissociation dynamics of water isotopologues

NASA Astrophysics Data System (ADS)

Baumann, Arne; Bazzi, Sophia; Rompotis, Dimitrios; Schepp, Oliver; Azima, Armin; Wieland, Marek; Popova-Gorelova, Daria; Vendrell, Oriol; Santra, Robin; Drescher, Markus

2017-07-01

We present a joint experimental and theoretical study of the VUV-induced dynamics of H2O and its deuterated isotopologues in the first excited state (A ˜1B1 ) utilizing a VUV-pump VUV-probe scheme combined with a b initio classical trajectory calculations. 16-fs VUV pulses centered at 161 nm created by fifth-order harmonic generation are employed for single-shot pump-probe measurements. Combined with a precise determination of the VUV pulses' temporal profile, they provide the necessary temporal resolution to elucidate sub-10-fs dissociation dynamics in the 1+1 photon ionization time window. Ionization with a single VUV photon complements established strong-field ionization schemes by disclosing the molecular dynamics under perturbative conditions. Kinetic isotope effects derived from the pump-probe experiment are found to be in agreement with our by ab initio classical trajectory calculations, taking into account photoionization cross sections for the ground and first excited state of the water cation.

Scalable digital hardware for a trapped ion quantum computer

NASA Astrophysics Data System (ADS)

Mount, Emily; Gaultney, Daniel; Vrijsen, Geert; Adams, Michael; Baek, So-Young; Hudek, Kai; Isabella, Louis; Crain, Stephen; van Rynbach, Andre; Maunz, Peter; Kim, Jungsang

2016-12-01

Many of the challenges of scaling quantum computer hardware lie at the interface between the qubits and the classical control signals used to manipulate them. Modular ion trap quantum computer architectures address scalability by constructing individual quantum processors interconnected via a network of quantum communication channels. Successful operation of such quantum hardware requires a fully programmable classical control system capable of frequency stabilizing the continuous wave lasers necessary for loading, cooling, initialization, and detection of the ion qubits, stabilizing the optical frequency combs used to drive logic gate operations on the ion qubits, providing a large number of analog voltage sources to drive the trap electrodes, and a scheme for maintaining phase coherence among all the controllers that manipulate the qubits. In this work, we describe scalable solutions to these hardware development challenges.

Uncertainty in predictions of oil spill trajectories in a coastal zone

NASA Astrophysics Data System (ADS)

Sebastião, P.; Guedes Soares, C.

2006-12-01

A method is introduced to determine the uncertainties in the predictions of oil spill trajectories using a classic oil spill model. The method considers the output of the oil spill model as a function of random variables, which are the input parameters, and calculates the standard deviation of the output results which provides a measure of the uncertainty of the model as a result of the uncertainties of the input parameters. In addition to a single trajectory that is calculated by the oil spill model using the mean values of the parameters, a band of trajectories can be defined when various simulations are done taking into account the uncertainties of the input parameters. This band of trajectories defines envelopes of the trajectories that are likely to be followed by the spill given the uncertainties of the input. The method was applied to an oil spill that occurred in 1989 near Sines in the southwestern coast of Portugal. This model represented well the distinction between a wind driven part that remained offshore, and a tide driven part that went ashore. For both parts, the method defined two trajectory envelopes, one calculated exclusively with the wind fields, and the other using wind and tidal currents. In both cases reasonable approximation to the observed results was obtained. The envelope of likely trajectories that is obtained with the uncertainty modelling proved to give a better interpretation of the trajectories that were simulated by the oil spill model.

Ups and downs of the expatriate experience? Understanding work adjustment trajectories and career outcomes.

PubMed

Zhu, Jing; Wanberg, Connie R; Harrison, David A; Diehn, Erica W

2016-04-01

We examine changes in work adjustment among 179 expatriates from 3 multinational organizations from predeparture through the first 9 months of a new international assignment. Our 10-wave results challenge classic U-shaped theories of expatriate adjustment (e.g., Torbiorn, 1982). Consistent with uncertainty reduction theory, our results instead suggest that expatriates typically experience a gradual increase in work adjustment over time. Two resources that expatriates bring to their assignments (previous culture-specific work experience and core self-evaluations) moderate the trajectory of work adjustment. Trajectory of adjustment predicts Month 9 career instrumentality and turnover intention, as well as career advancement (job promotion) 1.5 years further. Implications for theory, as well as for changes in expatriate management practices, are discussed. (c) 2016 APA, all rights reserved).

Electronic excitation and quenching of atoms at insulator surfaces

NASA Technical Reports Server (NTRS)

Swaminathan, P. K.; Garrett, Bruce C.; Murthy, C. S.

1988-01-01

A trajectory-based semiclassical method is used to study electronically inelastic collisions of gas atoms with insulator surfaces. The method provides for quantum-mechanical treatment of the internal electronic dynamics of a localized region involving the gas/surface collision, and a classical treatment of all the nuclear degrees of freedom (self-consistently and in terms of stochastic trajectories), and includes accurate simulation of the bath-temperature effects. The method is easy to implement and has a generality that holds promise for many practical applications. The problem of electronically inelastic dynamics is solved by computing a set of stochastic trajectories that on thermal averaging directly provide electronic transition probabilities at a given temperature. The theory is illustrated by a simple model of a two-state gas/surface interaction.

Hierarchical Control and Trajectory Planning

NASA Technical Reports Server (NTRS)

Martin, Clyde F.; Horn, P. W.

1994-01-01

Most of the time on this project was spent on the trajectory planning problem. The construction is equivalent to the classical spline construction in the case that the system matrix is nilpotent. If the dimension of the system is n then the spline of degree 2n-1 is constructed. This gives a new approach to the construction of splines that is more efficient than the usual construction and at the same time allows the construction of a much larger class of splines. All known classes of splines are reconstructed using the approach of linear control theory. As a numerical analysis tool control theory gives a very good tool for constructing splines. However, for the purposes of trajectory planning it is quite another story. Enclosed in this document are four reports done under this grant.

Superconformal Baryon-Meson Symmetry and Light-Front Holographic QCD

DOE PAGES

Dosch, Hans Guenter; de Teramond, Guy F.; Brodsky, Stanley J.

2015-04-10

We construct an effective QCD light-front Hamiltonian for both mesons and baryons in the chiral limit based on the generalized supercharges of a superconformal graded algebra. The superconformal construction is shown to be equivalent to a semi-classical approximation to light-front QCD and its embedding in AdS space. The specific breaking of conformal invariance inside the graded algebra uniquely determines the effective confinement potential. The generalized supercharges connect the baryon and meson spectra to each other in a remarkable manner. In particular, the π/b 1 Regge trajectory is identified as the superpartner of the nucleon trajectory. However, the lowest-lying state onmore » this trajectory, the π-meson is massless in the chiral limit and has no supersymmetric partner.« less

Communication: Note on detailed balance in symmetrical quasi-classical models for electronically non-adiabatic dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miller, William H., E-mail: millerwh@berkeley.edu; Cotton, Stephen J., E-mail: StephenJCotton47@gmail.com

2015-04-07

It is noted that the recently developed symmetrical quasi-classical (SQC) treatment of the Meyer-Miller (MM) model for the simulation of electronically non-adiabatic dynamics provides a good description of detailed balance, even though the dynamics which results from the classical MM Hamiltonian is “Ehrenfest dynamics” (i.e., the force on the nuclei is an instantaneous coherent average over all electronic states). This is seen to be a consequence of the SQC windowing methodology for “processing” the results of the trajectory calculation. For a particularly simple model discussed here, this is shown to be true regardless of the choice of windowing function employedmore » in the SQC model, and for a more realistic full classical molecular dynamics simulation, it is seen to be maintained correctly for very long time.« less

On understanding the relationship between structure in the potential surface and observables in classical dynamics: A functional sensitivity analysis approach

NASA Astrophysics Data System (ADS)

Judson, Richard S.; Rabitz, Herschel

1987-04-01

The relationship between structure in the potential surface and classical mechanical observables is examined by means of functional sensitivity analysis. Functional sensitivities provide maps of the potential surface, highlighting those regions that play the greatest role in determining the behavior of observables. A set of differential equations for the sensitivities of the trajectory components are derived. These are then solved using a Green's function method. It is found that the sensitivities become singular at the trajectory turning points with the singularities going as η-3/2, with η being the distance from the nearest turning point. The sensitivities are zero outside of the energetically and dynamically allowed region of phase space. A second set of equations is derived from which the sensitivities of observables can be directly calculated. An adjoint Green's function technique is employed, providing an efficient method for numerically calculating these quantities. Sensitivity maps are presented for a simple collinear atom-diatom inelastic scattering problem and for two Henon-Heiles type Hamiltonians modeling intramolecular processes. It is found that the positions of the trajectory caustics in the bound state problem determine regions of the highest potential surface sensitivities. In the scattering problem (which is impulsive, so that ``sticky'' collisions did not occur), the positions of the turning points of the individual trajectory components determine the regions of high sensitivity. In both cases, these lines of singularities are superimposed on a rich background structure. Most interesting is the appearance of classical interference effects. The interference features in the sensitivity maps occur most noticeably where two or more lines of turning points cross. The important practical motivation for calculating the sensitivities derives from the fact that the potential is a function, implying that any direct attempt to understand how local potential regions affect the behavior of the observables by repeatedly and systematically altering the potential will be prohibitively expensive. The functional sensitivity method enables one to perform this analysis at a fraction of the computational labor required for the direct method.

Modeling the hydration of mono-atomic anions from the gas phase to the bulk phase: the case of the halide ions F-, Cl-, and Br-.

PubMed

Trumm, Michael; Martínez, Yansel Omar Guerrero; Réal, Florent; Masella, Michel; Vallet, Valérie; Schimmelpfennig, Bernd

2012-01-28

In this work, we investigate the hydration of the halide ions fluoride, chloride, and bromide using classical molecular dynamics simulations at the 10 ns scale and based on a polarizable force-field approach, which treats explicitly the cooperative bond character of strong hydrogen bond networks. We have carried out a thorough analysis of the ab initio data at the MP2 or CCSD(T) level concerning anion/water clusters in gas phase to adjust the force-field parameters. In particular, we consider the anion static polarizabilities computed in gas phase using large atomic basis sets including additional diffuse functions. The information extracted from trajectories in solution shows well structured first hydration shells formed of 6.7, 7.0, and 7.6 water molecules at about 2.78 Å, 3.15 Å, and 3.36 Å for fluoride, chloride, and bromide, respectively. These results are in excellent agreement with the latest neutron- and x-ray diffraction studies. In addition, our model reproduces several other properties of halide ions in solution, such as diffusion coefficients, description of hydration processes, and exchange reactions. Moreover, it is also able to reproduce the electrostatic properties of the anions in solution (in terms of anion dipole moment) as reported by recent ab initio quantum simulations. All the results show the ability of the proposed model in predicting data, as well as the need of accounting explicitly for the cooperative character of strong hydrogen bonds to reproduce ab initio potential energy surfaces in a mean square sense and to build up a reliable force field. © 2012 American Institute of Physics

Behavior of light polarization in photon-scalar interaction

NASA Astrophysics Data System (ADS)

Azizi, Azizollah; Nasirimoghadam, Soudabe

2017-11-01

Quantum theories of gravity help us to improve our insight into the gravitational interactions. Motivated by the interesting effect of gravity on the photon trajectory, we treat a quantum recipe concluding a classical interaction of light and a massive object such as the sun. We use the linear quantum gravity to compute the classical potential of a photon interacting with a massive scalar. The leading terms have a traditional 1/r subordinate and demonstrate a polarization-dependent behavior. This result challenges the equivalence principle; attractive and/or repulsive interactions are admissible.

Above-Threshold Ionization by an Elliptically Polarized Field: Quantum Tunneling Interferences and Classical Dodging

NASA Astrophysics Data System (ADS)

Paulus, G. G.; Zacher, F.; Walther, H.; Lohr, A.; Becker, W.; Kleber, M.

1998-01-01

Measurements of above-threshold ionization electron spectra in an elliptically polarized field as a function of the ellipticity are presented. In the rescattering regime, electron yields quickly drop with increasing ellipticity. The yields of lower-energy electrons rise again when circular polarization is approached. A classical explanation for these effects is provided. Additional local maxima in the yields of lower-energy electrons can be interpreted as being due to interferences of electron trajectories that tunnel out at different times within one cycle of the field.

TH-EF-BRB-10: Dosimetric Validation of a Trajectory Based Cranial SRS Treatment Technique On a Varian TrueBeam Linac

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wilson, B; Vancouver Cancer Centre, Vancouver, BC; Gete, E

2016-06-15

Purpose: This work investigates the dosimetric accuracy of a trajectory based delivery technique in which an optimized radiation beam is delivered along a Couch-Gantry trajectory that is formed by simultaneous rotation of the linac gantry and the treatment couch. Methods: Nine trajectory based cranial SRS treatment plans were created using in-house optimization software. The plans were calculated for delivery on the TrueBeam STx linac with 6MV photon beam. Dose optimization was performed along a user-defined trajectory using MLC modulation, dose rate modulation and jaw tracking. The pre-defined trajectory chosen for this study is formed by a couch rotation through itsmore » full range of 180 degrees while the gantry makes four partial arc sweeps which are 170 degrees each. For final dose calculation, the trajectory based plans were exported to the Varian Eclipse Treatment Planning System. The plans were calculated on a homogeneous cube phantom measuring 18.2×18.2×18.2 cm3 with the analytical anisotropic algorithm (AAA) using a 1mm3 calculation voxel. The plans were delivered on the TrueBeam linac via the developer’s mode. Point dose measurements were performed on 9 patients with the IBA CC01 mini-chamber with a sensitive volume of 0.01 cc. Gafchromic film measurements along the sagittal and coronal planes were performed on three of the 9 treatment plans. Point dose values were compared with ion chamber measurements. Gamma analysis comparing film measurement and AAA calculations was performed using FilmQA Pro. Results: The AAA calculations and measurements were in good agreement. The point dose difference between AAA and ion chamber measurements were within 2.2%. Gamma analysis test pass rates (2%, 2mm passing criteria) for the Gafchromic film measurements were >95%. Conclusion: We have successfully tested TrueBeam’s ability to deliver accurate trajectory based treatments involving simultaneous gantry and couch rotation with MLC and dose rate modulation along the trajectory.« less

Direct measurements of classical and enhanced gradient-aligned cross-field ion flows in a helicon plasma source using laser-induced fluorescence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Siddiqui, M. Umair, E-mail: musiddiqui@mail.wvu.edu; Thompson, Derek S.; McIlvain, Julianne M.

2015-12-15

Direct laser induced fluorescence measurements are shown of cross-field ion flows normal to an absorbing boundary that is aligned parallel to the axial magnetic field in a helicon plasma. We show Langmuir and emissive probe measurements of local density and plasma potential in the same region, as well as floating probe spectra near the boundary. With these measurements, we investigate the influence of ion-neutral collisionality on radial ion transport by varying the ratio of the ion gyro-radius, ρ{sub i}, to the ion-neutral collision length, λ, over the range 0.34 ≤ ρ{sub i}λ{sup −1} ≤ 1.60. Classical drift-diffusion transport along density and potential gradients ismore » sufficient to describe flow profiles for most cases. For two parameter regimes (ρ{sub i}λ{sup −1} = 0.65 and 0.44), low-frequency electrostatic fluctuations (f < 10 kHz) and enhanced cross-field bulk ion flow to the boundary are observed.« less

On the neutralization in low energy ion scattering spectroscopy (leiss): He + ions on clean and oxygen covered Ni(001) surfaces

NASA Astrophysics Data System (ADS)

Preuss, E.

1981-10-01

A formula for the He + ion survival probability against neutralization is presented, which was derived from the fit of the azimuthal angular dependence of the Ni peak heights on clean and O covered Ni(001) surfaces observed in LEISS experiments and computer simulations. The formula contains a collision- and two Auger-type neutralization terms for the ion trajectories prolonged by multiple collisions above the "neutralization surface plane", which was assumed to be corrugated and shaped like muffin-tins.

Ca + HF - The anatomy of a chemical insertion reaction

NASA Technical Reports Server (NTRS)

Jaffe, R. L.; Pattengill, M. D.; Mascarello, F. G.; Zare, R. N.

1987-01-01

A comprehensive first-principles theoretical investigation of the gas phase reaction Ca + HF - CaF + H is reported. Ab initio potential energy calculations are first discussed, along with characteristics of the computed potential energy surface. Next, the fitting of the computed potential energy points to a suitable analytical functional form is described, and maps of the fitted potential surface are displayed. The methodology and results of a classical trajectory calculation utilizing the fitted potential surface are presented. Finally, the significance of the trajectory study results is discussed, and generalizations concerning dynamical aspects of Ca + HF scattering are drawn.

Rule-based navigation control design for autonomous flight

NASA Astrophysics Data System (ADS)

Contreras, Hugo; Bassi, Danilo

2008-04-01

This article depicts a navigation control system design that is based on a set of rules in order to follow a desired trajectory. The full control of the aircraft considered here comprises: a low level stability control loop, based on classic PID controller and the higher level navigation whose main job is to exercise lateral control (course) and altitude control, trying to follow a desired trajectory. The rules and PID gains were adjusted systematically according to the result of flight simulation. In spite of its simplicity, the rule-based navigation control proved to be robust, even with big perturbation, like crossing winds.

The dynamics of energy and charge transfer in low and hyperthermal energy ion-solid interactions

NASA Astrophysics Data System (ADS)

Ray, Matthew Preston

The energy and charge transfer dynamics for low and hyperthermal energy (10 eV to 2 keV) alkali and noble gas ions impacting noble metals as a function of incident energy, species and scattering geometry has been studied. The experiments were performed in an ultra-high vacuum scattering chamber attached to a low and hyperthermal energy beamline. The energy transfer was measured for K+ scattered from a Ag(001) surface along the [110] crystalline direction at a fixed laboratory angle of 90°. It was found that as the incident energy is reduced from 100 to 10 eV, the normalized scattered energy increased. Previous measurements have shown a decrease in the normalized energy as the incident ion energy is reduced due to an attractive image force. Trajectory analysis of the data using a classical scattering simulation revealed that instead of undergoing sequential binary collisions as in previous studies, the ion scatters from two surface atoms simultaneously leading to an increased normalized energy. Additionally, charge transfer measurements have been performed for Na + scattering from Ag(001) along the [110] crystalline direction at a fixed laboratory angle of 70°. It was found that over the range of energies used (10 eV to 2 keV), the neutralization probability of the scattered ions varied from ˜30% to ˜70% depending on the incident velocity, consistent with resonant charge transfer. A fully quantum mechanical model that treats electrons independently accurately reproduces the observed data. Measurements of electron-hole pair excitations were used to explore the pathways which a solid uses to dissipate the energy imparted by the incident ion beam. Ultrathin film (10 nm) metal-oxide-semiconductor (Au/SiO2/n-Si) devices were used to detect the electron-hole pairs for cases when the ion deposited all of its translational energy into the solid. The incident ions were incident at an angle normal to the surface of the device to maximize energy deposition and consequently electron-hole pair production. The rectifying metal-oxide-semiconductor device separates the electrons from the holes, allowing a current associated with electron-hole pair production to be measured. In these experiments a number of ion species (He+, Li+ , Ar+, K+) were made incident on multiple devices and the incident energy ranged from 100 eV to 2 keV. It was found that electron-hole pair production increased with incident ion velocity consistent with a kinetic electron excitation model where the electrons in the metal are partially confined to the surface.

Quantum trajectories in elastic atom-surface scattering: threshold and selective adsorption resonances.

PubMed

Sanz, A S; Miret-Artés, S

2005-01-01

The elastic resonant scattering of He atoms off the Cu(117) surface is fully described with the formalism of quantum trajectories provided by Bohmian mechanics. Within this theory of quantum motion, the concept of trapping is widely studied and discussed. Classically, atoms undergo impulsive collisions with the surface, and then the trapped motion takes place covering at least two consecutive unit cells. However, from a Bohmian viewpoint, atom trajectories can smoothly adjust to the equipotential energy surface profile in a sort of sliding motion; thus the trapping process could eventually occur within one single unit cell. In particular, both threshold and selective adsorption resonances are explained by means of this quantum trapping considering different space and time scales. Furthermore, a mapping between each region of the (initial) incoming plane wave and the different parts of the diffraction and resonance patterns can be easily established, an important issue only provided by a quantum trajectory formalism. (c) 2005 American Institute of Physics.

On-the-Fly ab Initio Semiclassical Calculation of Glycine Vibrational Spectrum

PubMed Central

2017-01-01

We present an on-the-fly ab initio semiclassical study of vibrational energy levels of glycine, calculated by Fourier transform of the wavepacket correlation function. It is based on a multiple coherent states approach integrated with monodromy matrix regularization for chaotic dynamics. All four lowest-energy glycine conformers are investigated by means of single-trajectory semiclassical spectra obtained upon classical evolution of on-the-fly trajectories with harmonic zero-point energy. For the most stable conformer I, direct dynamics trajectories are also run for each vibrational mode with energy equal to the first harmonic excitation. An analysis of trajectories evolved up to 50 000 atomic time units demonstrates that, in this time span, conformers II and III can be considered as isolated species, while conformers I and IV show a pretty facile interconversion. Therefore, previous perturbative studies based on the assumption of isolated conformers are often reliable but might be not completely appropriate in the case of conformer IV and conformer I for which interconversion occurs promptly. PMID:28489368

Ion dipole capture cross sections at low ion and rotational energies - Comparison of integrated capture cross sections with reaction cross sections for NH3 and H2O parent-ion collisions.

NASA Technical Reports Server (NTRS)

Dugan, J. V., Jr.; Canright, R. B., Jr.

1972-01-01

The numerical capture cross section is calculated from the capture ratio, defined as the fraction of trajectories reaching a prescribed minimum separation of 3 A. The calculated capture cross sections for a rotational temperature of 77 K suggest large reaction cross sections in 80 K experiments for the large dipole-moment target, methyl cyanide.

Ion mass separation modeling inside a plasma separator

NASA Astrophysics Data System (ADS)

Gavrikov, A. V.; Sidorov, V. S.; Smirnov, V. P.; Tarakanov, V. P.

2018-01-01

The results have been obtained in a continuation of the work for ion trajectories calculation in crossed electric and magnetic fields and also in a close alignment with the plasma separation study development. The main task was to calculate trajectories of ions of the substance imitating spent nuclear fuel in order to find a feasible plasma separator configuration. The three-dimensional modeling has been made with KARAT code in a single-particle approximation. The calculations have been performed under the following conditions. Magnetic field is produced by 2 coils of wire, the characteristic field strength in a uniform area is 1.4 kG. Electric field is produced by several electrodes (axial ones, anode shell and capacitor sheets) with electric potential up to 500 V. The characteristic linear size of the cylindrical separator area is ∼ 100 cm. The characteristic size of injection region is ∼ 1 cm. Spatial position of the injection region is inside the separator. The injection direction is along magnetic lines. Injected particles are single-charged ions with energies from 0 to 20 eV with atomic masses A = 150 and 240. Wide spreading angle range was investigated. As a result of simulation a feasible separator configuration was found. This configuration allows to achieve more than 10 cm spatial division distance for the separated ions and is fully compliant with and supplementary to the vacuum arc-based ion source research.

Quantum Dynamics and a Semiclassical Description of the Photon.

ERIC Educational Resources Information Center

Henderson, Giles

1980-01-01

Uses computer graphics and nonstationary, superposition wave functions to reveal the dynamic quantum trajectories of several molecular and electronic transitions. These methods are then coupled with classical electromagnetic theory to provide a conceptually clear picture of the emission process and emitted radiation localized in time and space.…

Re-Imagining a Christian University in a Secular Age

ERIC Educational Resources Information Center

Warner, Rob

2013-01-01

The contours of a secular age, as delineated by classical and contemporary sociologists of religion, have tended to result in secularising trajectories for church-founded institutions of Higher Education, some of which have migrated towards secular normativity. This article explores these trends and then proposes five characteristics of an…

Elucidating distinct ion channel populations on the surface of hippocampal neurons via single-particle tracking recurrence analysis

NASA Astrophysics Data System (ADS)

Sikora, Grzegorz; Wyłomańska, Agnieszka; Gajda, Janusz; Solé, Laura; Akin, Elizabeth J.; Tamkun, Michael M.; Krapf, Diego

2017-12-01

Protein and lipid nanodomains are prevalent on the surface of mammalian cells. In particular, it has been recently recognized that ion channels assemble into surface nanoclusters in the soma of cultured neurons. However, the interactions of these molecules with surface nanodomains display a considerable degree of heterogeneity. Here, we investigate this heterogeneity and develop statistical tools based on the recurrence of individual trajectories to identify subpopulations within ion channels in the neuronal surface. We specifically study the dynamics of the K+ channel Kv1.4 and the Na+ channel Nav1.6 on the surface of cultured hippocampal neurons at the single-molecule level. We find that both these molecules are expressed in two different forms with distinct kinetics with regards to surface interactions, emphasizing the complex proteomic landscape of the neuronal surface. Further, the tools presented in this work provide new methods for the analysis of membrane nanodomains, transient confinement, and identification of populations within single-particle trajectories.

A study of small impact parameter ion channeling effects in thin crystals

NASA Astrophysics Data System (ADS)

Motapothula, Mallikarjuna Rao; Breese, Mark B. H.

2018-03-01

We have recorded channeling patterns produced by 1-2 MeV protons aligned with ⟨1 1 1⟩ axes in 55 nm thick silicon crystals which exhibit characteristic angular structure for deflection angles up to and beyond the axial critical angle, ψ a . Such large angular deflections are produced by ions incident on atomic strings with small impact parameters, resulting in trajectories which pass through several radial rings of atomic strings before exiting the thin crystal. Each ring may focus, steer or scatter the channeled ions in the transverse direction and the resulting characteristic angular structure beyond 0.6 ψ a at different depths can be related to peaks and troughs in the nuclear encounter probability. Such "radial focusing" underlies other axial channeling phenomena in thin crystals including planar channeling of small impact parameter trajectories, peaks around the azimuthal distribution at small tilts and large shoulders in the nuclear encounter probability at tilts beyond ψ a .

[Application of classical isothermal adsorption models in heavy metal ions/ diatomite system and related problems].

PubMed

Zhu, Jian; Wu, Qing-Ding; Wang, Ping; Li, Ke-Lin; Lei, Ming-Jing; Zhang, Wei-Li

2013-11-01

In order to fully understand adsorption nature of Cu2+, Zn2+, Pb2+, Cd2+, Mn2+, Fe3+ onto natural diatomite, and to find problems of classical isothermal adsorption models' application in liquid/solid system, a series of isothermal adsorption tests were conducted. As results indicate, the most suitable isotherm models for describing adsorption of Pb2+, Cd2+, Cu2+, Zn2+, Mn2+, Fe3+ onto natural diatomite are Tenkin, Tenkin, Langmuir, Tenkin, Freundlich and Freundlich, respectively, the adsorption of each ion onto natural diatomite is mainly a physical process, and the adsorption reaction is favorable. It also can be found that, when using classical isothermal adsorption models to fit the experimental data in liquid/solid system, the equilibrium adsorption amount q(e) is not a single function of ion equilibrium concentration c(e), while is a function of two variables, namely c(e) and the adsorbent concentration W0, q(e) only depends on c(e)/W(0). Results also show that the classical isothermal adsorption models have a significant adsorbent effect, and their parameter values are unstable, the simulation values of parameter differ greatly from the measured values, which is unhelpful for practical use. The tests prove that four-adsorption-components model can be used for describing adsorption behavior of single ion in nature diatomite-liquid system, its parameters k and q(m) have constant values, which is favorable for practical quantitative calculation in a given system.

Generalized quantum theory of recollapsing homogeneous cosmologies

NASA Astrophysics Data System (ADS)

Craig, David; Hartle, James B.

2004-06-01

A sum-over-histories generalized quantum theory is developed for homogeneous minisuperspace type A Bianchi cosmological models, focusing on the particular example of the classically recollapsing Bianchi type-IX universe. The decoherence functional for such universes is exhibited. We show how the probabilities of decoherent sets of alternative, coarse-grained histories of these model universes can be calculated. We consider in particular the probabilities for classical evolution defined by a suitable coarse graining. For a restricted class of initial conditions and coarse grainings we exhibit the approximate decoherence of alternative histories in which the universe behaves classically and those in which it does not. For these situations we show that the probability is near unity for the universe to recontract classically if it expands classically. We also determine the relative probabilities of quasiclassical trajectories for initial states of WKB form, recovering for such states a precise form of the familiar heuristic “JṡdΣ” rule of quantum cosmology, as well as a generalization of this rule to generic initial states.

Smoothed quantum-classical states in time-irreversible hybrid dynamics

NASA Astrophysics Data System (ADS)

Budini, Adrián A.

2017-09-01

We consider a quantum system continuously monitored in time which in turn is coupled to an arbitrary dissipative classical system (diagonal reduced density matrix). The quantum and classical dynamics can modify each other, being described by an arbitrary time-irreversible hybrid Lindblad equation. Given a measurement trajectory, a conditional bipartite stochastic state can be inferred by taking into account all previous recording information (filtering). Here, we demonstrate that the joint quantum-classical state can also be inferred by taking into account both past and future measurement results (smoothing). The smoothed hybrid state is estimated without involving information from unobserved measurement channels. Its average over recording realizations recovers the joint time-irreversible behavior. As an application we consider a fluorescent system monitored by an inefficient photon detector. This feature is taken into account through a fictitious classical two-level system. The average purity of the smoothed quantum state increases over that of the (mixed) state obtained from the standard quantum jump approach.

LORAKS makes better SENSE: Phase-constrained partial fourier SENSE reconstruction without phase calibration.

PubMed

Kim, Tae Hyung; Setsompop, Kawin; Haldar, Justin P

2017-03-01

Parallel imaging and partial Fourier acquisition are two classical approaches for accelerated MRI. Methods that combine these approaches often rely on prior knowledge of the image phase, but the need to obtain this prior information can place practical restrictions on the data acquisition strategy. In this work, we propose and evaluate SENSE-LORAKS, which enables combined parallel imaging and partial Fourier reconstruction without requiring prior phase information. The proposed formulation is based on combining the classical SENSE model for parallel imaging data with the more recent LORAKS framework for MR image reconstruction using low-rank matrix modeling. Previous LORAKS-based methods have successfully enabled calibrationless partial Fourier parallel MRI reconstruction, but have been most successful with nonuniform sampling strategies that may be hard to implement for certain applications. By combining LORAKS with SENSE, we enable highly accelerated partial Fourier MRI reconstruction for a broader range of sampling trajectories, including widely used calibrationless uniformly undersampled trajectories. Our empirical results with retrospectively undersampled datasets indicate that when SENSE-LORAKS reconstruction is combined with an appropriate k-space sampling trajectory, it can provide substantially better image quality at high-acceleration rates relative to existing state-of-the-art reconstruction approaches. The SENSE-LORAKS framework provides promising new opportunities for highly accelerated MRI. Magn Reson Med 77:1021-1035, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

Quantum dynamics in phase space: Moyal trajectories 2

NASA Astrophysics Data System (ADS)

Braunss, G.

2013-01-01

Continuing a previous paper [G. Braunss, J. Phys. A: Math. Theor. 43, 025302 (2010), 10.1088/1751-8113/43/2/025302] where we had calculated ℏ2-approximations of quantum phase space viz. Moyal trajectories of examples with one and two degrees of freedom, we present in this paper the calculation of ℏ2-approximations for four examples: a two-dimensional Toda chain, the radially symmetric Schwarzschild field, and two examples with three degrees of freedom, the latter being the nonrelativistic spherically Coulomb potential and the relativistic cylinder symmetrical Coulomb potential with a magnetic field H. We show in particular that an ℏ2-approximation of the nonrelativistic Coulomb field has no singularity at the origin (r = 0) whereas the classical trajectories are singular at r = 0. In the third example, we show in particular that for an arbitrary function γ(H, z) the expression β ≡ pz + γ(H, z) is classically (ℏ = 0) a constant of motion, whereas for ℏ ≠ 0 this holds only if γ(H, z) is an arbitrary polynomial of second order in z. This statement is shown to extend correspondingly to a cylinder symmetrical Schwarzschild field with a magnetic field. We exhibit in detail a number of properties of the radially symmetric Schwarzschild field. We exhibit finally the problems of the nonintegrable Hénon-Heiles Hamiltonian and give a short review of the regular Hilbert space representation of Moyal operators.

Effect of ion clouds micromotion on measured signal in Fourier transform ion cyclotron resonance: Computer simulation.

PubMed

Vladimirov, Gleb; Kostyukevich, Yury; Kharybin, Oleg; Nikolaev, Eugene

2017-08-01

Particle-in-cell-based realistic simulation of Fourier transform ion cyclotron resonance experiments could be used to generate ion trajectories and a signal induced on the detection electrodes. It has been shown recently that there is a modulation of "reduced" cyclotron frequencies in ion cyclotron resonance signal caused by Coulomb interaction of ion clouds. In this work it was proposed to use this modulation in order to determine frequency difference between an ion of known m/z and all other ions generating signal in ion cyclotron resonance cell. It is shown that with an increase of number of ions in ion cyclotron resonance trap, the modulation index increases, which lead to a decrease in the accuracy of determination of peak intensities by super Fourier transform resolution methods such as filter diagonalization method.

Fluctuation theorems in feedback-controlled open quantum systems: Quantum coherence and absolute irreversibility

NASA Astrophysics Data System (ADS)

Murashita, Yûto; Gong, Zongping; Ashida, Yuto; Ueda, Masahito

2017-10-01

The thermodynamics of quantum coherence has attracted growing attention recently, where the thermodynamic advantage of quantum superposition is characterized in terms of quantum thermodynamics. We investigate the thermodynamic effects of quantum coherent driving in the context of the fluctuation theorem. We adopt a quantum-trajectory approach to investigate open quantum systems under feedback control. In these systems, the measurement backaction in the forward process plays a key role, and therefore the corresponding time-reversed quantum measurement and postselection must be considered in the backward process, in sharp contrast to the classical case. The state reduction associated with quantum measurement, in general, creates a zero-probability region in the space of quantum trajectories of the forward process, which causes singularly strong irreversibility with divergent entropy production (i.e., absolute irreversibility) and hence makes the ordinary fluctuation theorem break down. In the classical case, the error-free measurement ordinarily leads to absolute irreversibility, because the measurement restricts classical paths to the region compatible with the measurement outcome. In contrast, in open quantum systems, absolute irreversibility is suppressed even in the presence of the projective measurement due to those quantum rare events that go through the classically forbidden region with the aid of quantum coherent driving. This suppression of absolute irreversibility exemplifies the thermodynamic advantage of quantum coherent driving. Absolute irreversibility is shown to emerge in the absence of coherent driving after the measurement, especially in systems under time-delayed feedback control. We show that absolute irreversibility is mitigated by increasing the duration of quantum coherent driving or decreasing the delay time of feedback control.

Exploring the importance of quantum effects in nucleation: The archetypical Nen case

NASA Astrophysics Data System (ADS)

Unn-Toc, Wesley; Halberstadt, Nadine; Meier, Christoph; Mella, Massimo

2012-07-01

The effect of quantum mechanics (QM) on the details of the nucleation process is explored employing Ne clusters as test cases due to their semi-quantal nature. In particular, we investigate the impact of quantum mechanics on both condensation and dissociation rates in the framework of the microcanonical ensemble. Using both classical trajectories and two semi-quantal approaches (zero point averaged dynamics, ZPAD, and Gaussian-based time dependent Hartree, G-TDH) to model cluster and collision dynamics, we simulate the dissociation and monomer capture for Ne8 as a function of the cluster internal energy, impact parameter and collision speed. The results for the capture probability Ps(b) as a function of the impact parameter suggest that classical trajectories always underestimate capture probabilities with respect to ZPAD, albeit at most by 15%-20% in the cases we studied. They also do so in some important situations when using G-TDH. More interestingly, dissociation rates kdiss are grossly overestimated by classical mechanics, at least by one order of magnitude. We interpret both behaviours as mainly due to the reduced amount of kinetic energy available to a quantum cluster for a chosen total internal energy. We also find that the decrease in monomer dissociation energy due to zero point energy effects plays a key role in defining dissociation rates. In fact, semi-quantal and classical results for kdiss seem to follow a common "corresponding states" behaviour when the proper definition of internal and dissociation energies are used in a transition state model estimation of the evaporation rate constants.

Quantum Bohmian model for financial market

NASA Astrophysics Data System (ADS)

Choustova, Olga Al.

2007-01-01

We apply methods of quantum mechanics for mathematical modeling of price dynamics at the financial market. The Hamiltonian formalism on the price/price-change phase space describes the classical-like evolution of prices. This classical dynamics of prices is determined by “hard” conditions (natural resources, industrial production, services and so on). These conditions are mathematically described by the classical financial potential V(q), where q=(q1,…,qn) is the vector of prices of various shares. But the information exchange and market psychology play important (and sometimes determining) role in price dynamics. We propose to describe such behavioral financial factors by using the pilot wave (Bohmian) model of quantum mechanics. The theory of financial behavioral waves takes into account the market psychology. The real trajectories of prices are determined (through the financial analogue of the second Newton law) by two financial potentials: classical-like V(q) (“hard” market conditions) and quantum-like U(q) (behavioral market conditions).

Mixed quantum-classical simulations of the vibrational relaxation of photolyzed carbon monoxide in a hemoprotein

NASA Astrophysics Data System (ADS)

Schubert, Alexander; Falvo, Cyril; Meier, Christoph

2016-08-01

We present mixed quantum-classical simulations on relaxation and dephasing of vibrationally excited carbon monoxide within a protein environment. The methodology is based on a vibrational surface hopping approach treating the vibrational states of CO quantum mechanically, while all remaining degrees of freedom are described by means of classical molecular dynamics. The CO vibrational states form the "surfaces" for the classical trajectories of protein and solvent atoms. In return, environmentally induced non-adiabatic couplings between these states cause transitions describing the vibrational relaxation from first principles. The molecular dynamics simulation yields a detailed atomistic picture of the energy relaxation pathways, taking the molecular structure and dynamics of the protein and its solvent fully into account. Using the ultrafast photolysis of CO in the hemoprotein FixL as an example, we study the relaxation of vibrationally excited CO and evaluate the role of each of the FixL residues forming the heme pocket.

A stereoscopic imaging system for laser back scatter based trajectory measurement in ballistics: part 2

NASA Astrophysics Data System (ADS)

Chalupka, Uwe; Rothe, Hendrik

2012-03-01

The progress on a laser- and stereo-camera-based trajectory measurement system that we already proposed and described in recent publications is given. The system design was extended from one to two more powerful, DSP-controllable LASER systems. Experimental results of the extended system using different projectile-/weapon combinations will be shown and discussed. Automatic processing of acquired images using common 3DIP techniques was realized. Processing steps to extract trajectory segments from images as representative for the current application will be presented. Used algorithms for backward-calculation of the projectile trajectory will be shown. Verification of produced results is done against simulated trajectories, once in terms of detection robustness and once in terms of detection accuracy. Fields of use for the current system are within the ballistic domain. The first purpose is for trajectory measurement of small and middle caliber projectiles on a shooting range. Extension to big caliber projectiles as well as an application for sniper detection is imaginable, but would require further work. Beside classical RADAR, acoustic and optical projectile detection methods, the current system represents a further projectile location method under the new class of electro-optical methods that have been evolved in recent decades and that uses 3D imaging acquisition and processing techniques.

Ion trap simulation program, ITSIM: A powerful heuristic and predictive tool in ion trap mass spectrometry

NASA Astrophysics Data System (ADS)

Bui, Huy Anh

The multi-particle simulation program, ITSIM version 4.0, takes advantage of the enhanced performance of the Windows 95 and NT operating systems in areas such as memory management, user friendliness, flexibility of graphics and speed, to investigate the motion of ions in the quadrupole ion trap. The objective of this program is to use computer simulations based on mathematical models to improve the performance of the ion trap mass spectrometer. The simulation program can provide assistance in understanding fundamental aspects of ion trap mass spectrometry, precede and help to direct the course of experiments, as well as having didactic value in elucidating and allowing visualization of ion behavior under different experimental conditions. The program uses the improved Euler method to calculate ion trajectories as numerical solutions to the Mathieu differential equation. This Windows version can simultaneously simulate the trajectories of ions with a virtually unlimited number of different mass-to-charge ratios and hence allows realistic mass spectra, ion kinetic energy distributions and other experimentally measurable properties to be simulated. The large number of simulated ions allows examination of (i) the offsetting effects of mutual ion repulsion and collisional cooling in an ion trap and (ii) the effects of higher order fields. Field inhomogeneities arising from exit holes, electrode misalignment, imperfect electrode surfaces or new trap geometries can be simulated with the program. The simulated data are used to obtain mass spectra from mass-selective instability scans as well as by Fourier transformation of image currents induced by coherently moving ion clouds. Complete instruments, from an ion source through the ion trap mass analyzer to a detector, can now be simulated. Applications of the simulation program are presented and discussed. Comparisons are made between the simulations and experimental data. Fourier transformed experiments and a novel six-electrode ion trap mass spectrometer illustrate cases in which simulations precede new experiments. Broadband non-destructive ion detection based on induced image current measurements are described in the case of a quadrupole ion trap having cylindrical geometry.

Extended hamiltonian formalism and Lorentz-violating lagrangians

NASA Astrophysics Data System (ADS)

Colladay, Don

2017-09-01

A new perspective on the classical mechanical formulation of particle trajectories in Lorentz-violating theories is presented. Using the extended hamiltonian formalism, a Legendre Transformation between the associated covariant lagrangian and hamiltonian varieties is constructed. This approach enables calculation of trajectories using Hamilton's equations in momentum space and the Euler-Lagrange equations in velocity space away from certain singular points that arise in the theory. Singular points are naturally de-singularized by requiring the trajectories to be smooth functions of both velocity and momentum variables. In addition, it is possible to identify specific sheets of the dispersion relations that correspond to specific solutions for the lagrangian. Examples corresponding to bipartite Finsler functions are computed in detail. A direct connection between the lagrangians and the field-theoretic solutions to the Dirac equation is also established for a special case.

Quantum trajectories for high-order-harmonic generation from multiple rescattering events in the long-wavelength regime

NASA Astrophysics Data System (ADS)

He, Lixin; Li, Yang; Wang, Zhe; Zhang, Qingbin; Lan, Pengfei; Lu, Peixiang

2014-05-01

We have performed the quantum trajectory analysis for high-order-harmonic generation (HHG) with different driving laser wavelengths. By defining the ratio of HHG yields of the Nth and first rescattering events (YN/Y1), we quantitatively evaluate the HHG contributions from multiple rescatterings. The results show that the HHG yield ratio increases gradually with the increase of the laser wavelength, which demonstrates that high-order rescatterings provide ascendent contributions to HHG at longer wavelength. By calculating the classical electron trajectories, we find significant differences exist in the electron behaviors between the first and high-order rescatterings. Further investigations have demonstrated that the increasing HHG yield ratio is mainly attributed to the relatively smaller contributions from the short path of the first electron rescattering at longer laser wavelength.

igun - A program for the simulation of positive ion extraction including magnetic fields

NASA Astrophysics Data System (ADS)

Becker, R.; Herrmannsfeldt, W. B.

1992-04-01

igun is a program for the simulation of positive ion extraction from plasmas. It is based on the well known program egun for the calculation of electron and ion trajectories in electron guns and lenses. The mathematical treatment of the plasma sheath is based on a simple analytical model, which provides a numerically stable calculation of the sheath potentials. In contrast to other ion extraction programs, igun is able to determine the extracted ion current in succeeding cycles of iteration by itself. However, it is also possible to set values of current, plasma density, or ion current density. Either axisymmetric or rectangular coordinates can be used, including axisymmetric or transverse magnetic fields.

Nonresonant interaction of heavy ions with electromagnetic ion cyclotron waves

NASA Technical Reports Server (NTRS)

Berchem, J.; Gendrin, R.

1985-01-01

The motion of a heavy ion in the presence of an intense ultralow-frequency electromagnetic wave propagating along the dc magnetic field is analyzed. Starting from the basic equations of motion and from their associated two invariants, the heavy ion velocity-space trajectories are drawn. It is shown that after a certain time, particles whose initial phase angles are randomly distributed tend to bunch together, provided that the wave intensity b-sub-1 is sufficiently large. The importance of these results for the interpretation of the recently observed acceleration of singly charged He ions in conjunction with the occurrence of large-amplitude ion cyclotron waves in the equatorial magnetosphere is discussed.

LiquidLib: A comprehensive toolbox for analyzing classical and ab initio molecular dynamics simulations of liquids and liquid-like matter with applications to neutron scattering experiments

NASA Astrophysics Data System (ADS)

Walter, Nathan P.; Jaiswal, Abhishek; Cai, Zhikun; Zhang, Yang

2018-07-01

Neutron scattering is a powerful experimental technique for characterizing the structure and dynamics of materials on the atomic or molecular scale. However, the interpretation of experimental data from neutron scattering is oftentimes not trivial, partly because scattering methods probe ensemble-averaged information in the reciprocal space. Therefore, computer simulations, such as classical and ab initio molecular dynamics, are frequently used to unravel the time-dependent atomistic configurations that can reproduce the scattering patterns and thus assist in the understanding of the microscopic origin of certain properties of materials. LiquidLib is a post-processing package for analyzing the trajectory of atomistic simulations of liquids and liquid-like matter with application to neutron scattering experiments. From an atomistic simulation, LiquidLib provides the computation of various statistical quantities including the pair distribution function, the weighted and unweighted structure factors, the mean squared displacement, the non-Gaussian parameter, the four-point correlation function, the velocity auto correlation function, the self and collective van Hove correlation functions, the self and collective intermediate scattering functions, and the bond orientational order parameter. LiquidLib analyzes atomistic trajectories generated from packages such as LAMMPS, GROMACS, and VASP. It also offers an extendable platform to conveniently integrate new quantities into the library and integrate simulation trajectories of other file formats for analysis. Weighting the quantities by element-specific neutron-scattering lengths provides results directly comparable to neutron scattering measurements. Lastly, LiquidLib is independent of dimensionality, which allows analysis of trajectories in two, three, and higher dimensions. The code is beginning to find worldwide use.

Nuclear quantum effects in water exchange around lithium and fluoride ions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wilkins, David M.; Manolopoulos, David E.; Dang, Liem X.

2015-02-14

We employ classical and ring polymer molecular dynamics simulations to study the effect of nuclear quantum fluctuations on the structure and the water exchange dynamics of aqueous solutions of lithium and fluoride ions. While we obtain reasonably good agreement with experimental data for solutions of lithium by augmenting the Coulombic interactions between the ion and the water molecules with a standard Lennard-Jones ion-oxygen potential, the same is not true for solutions of fluoride, for which we find that a potential with a softer repulsive wall gives much better agreement. A small degree of destabilization of the first hydration shell ismore » found in quantum simulations of both ions when compared with classical simulations, with the shell becoming less sharply defined and the mean residence time of the water molecules in the shell decreasing. In line with these modest differences, we find that the mechanisms of the exchange processes are unaffected by quantization, so a classical description of these reactions gives qualitatively correct and quantitatively reasonable results. We also find that the quantum effects in solutions of lithium are larger than in solutions of fluoride. This is partly due to the stronger interaction of lithium with water molecules, partly due to the lighter mass of lithium and partly due to competing quantum effects in the hydration of fluoride, which are absent in the hydration of lithium.« less

Silver-Ion Solid Phase Extraction Separation of Classical, Aromatic, Oxidized, and Heteroatomic Naphthenic Acids from Oil Sands Process-Affected Water.

PubMed

Huang, Rongfu; Chen, Yuan; Gamal El-Din, Mohamed

2016-06-21

The separation of classical, aromatic, oxidized, and heteroatomic (sulfur-containing) naphthenic acid (NA) species from unprocessed and ozone-treated oil sands process-affected water (OSPW) was performed using silver-ion (Ag-ion) solid phase extraction (SPE) without the requirement of pre-methylation for NAs. OSPW samples before SPE and SPE fractions were characterized using ultra performance liquid chromatography ion mobility time-of-flight mass spectrometry (UPLC-IM-TOFMS) to corroborate the separation of distinct NA species. The mass spectrum identification applied a mass tolerance of ±1.5 mDa due to the mass errors of NAs were measured within this range, allowing the identification of O2S-NAs from O2-NAs. Moreover, separated NA species facilitated the tandem mass spectrometry (MS/MS) characterization of NA compounds due to the removal of matrix and a simplified composition. MS/MS results showed that classical, aromatic, oxidized, and sulfur-containing NA compounds were eluted into individual SPE fractions. Overall results indicated that the separation of NA species using Ag-ion SPE is a valuable method for extracting individual NA species that are of great interest for environmental toxicology and wastewater treatment research, to conduct species-specific studies. Furthermore, the separated NA species on the milligram level could be widely used as the standard materials for environmental monitoring of NAs from various contamination sites.

Influence of ion pairing in ionic liquids on electrical double layer structures and surface force using classical density functional approach.

PubMed

Ma, Ke; Forsman, Jan; Woodward, Clifford E

2015-05-07

We explore the influence of ion pairing in room temperature ionic liquids confined by planar electrode surfaces. Using a coarse-grained model for the aromatic ionic liquid [C4MIM(+)][BF4 (-)], we account for an ion pairing component as an equilibrium associating species within a classical density functional theory. We investigated the resulting structure of the electrical double layer as well as the ensuing surface forces and differential capacitance, as a function of the degree of ion association. We found that the short-range structure adjacent to surfaces was remarkably unaffected by the degree of ion pairing, up to several molecular diameters. This was even the case for 100% of ions being paired. The physical implications of ion pairing only become apparent in equilibrium properties that depend upon the long-range screening of charges, such as the asymptotic behaviour of surface forces and the differential capacitance, especially at low surface potential. The effect of ion pairing on capacitance is consistent with their invocation as a source of the anomalous temperature dependence of the latter. This work shows that ion pairing effects on equilibrium properties are subtle and may be difficult to extract directly from simulations.

Li+ solvation and kinetics of Li+-BF4-/PF6- ion pairs in ethylene carbonate. A molecular dynamics study with classical rate theories

NASA Astrophysics Data System (ADS)

Chang, Tsun-Mei; Dang, Liem X.

2017-10-01

Using our polarizable force-field models and employing classical rate theories of chemical reactions, we examine the ethylene carbonate (EC) exchange process between the first and second solvation shells around Li+ and the dissociation kinetics of ion pairs Li+-[BF4] and Li+-[PF6] in this solvent. We calculate the exchange rates using transition state theory and correct them with transmission coefficients computed by the reactive flux, Impey, Madden, and McDonald approaches, and Grote-Hynes theory. We found that the residence times of EC around Li+ ions varied from 60 to 450 ps, depending on the correction method used. We found that the relaxation times changed significantly from Li+-[BF4] to Li+-[PF6] ion pairs in EC. Our results also show that, in addition to affecting the free energy of dissociation in EC, the anion type also significantly influences the dissociation kinetics of ion pairing.

Trajectory design for an ion drive asteroids rendezvous mission launched into an Ariane geostationary transfer orbit

NASA Astrophysics Data System (ADS)

Pietrass, A. E.

1984-08-01

AMSAT has conceived an asteroid rendezvous mission which would consist of an Ariane-launched, 3-axis-stabilized, 350-kg spacecraft utilizing both mercury and solar electric ion propulsion. The spacecraft is to be equipped with a science instrument platform with a mass of approximately 30 to 50 kg. Practically uninterrupted earth departure opportunities are found for targets such as 4 Vesta, 8 Flora, and 19 Fortuna from 1986 through 1988. The 7 to 8 year mission would allow for a second rendezvous of 4 Vesta, and marginal additional fuel would make close flybys of targets feasible. Through the use of parameter optimization techniques, trajectories can be generated and the inclusion of constraints due to spacecraft techology, tour design, and navigation can be facilitated.

Treatment of Ion-Atom Collisions Using a Partial-Wave Expansion of the Projectile Wavefunction

ERIC Educational Resources Information Center

Wong, T. G.; Foster, M.; Colgan, J.; Madison, D. H.

2009-01-01

We present calculations of ion-atom collisions using a partial-wave expansion of the projectile wavefunction. Most calculations of ion-atom collisions have typically used classical or plane-wave approximations for the projectile wavefunction, since partial-wave expansions are expected to require prohibitively large numbers of terms to converge…

Inter-cusp Ion and Electron Transport in a Nstar-derivative Ion Thruster

NASA Technical Reports Server (NTRS)

Foster, John E.

2001-01-01

Diffusion of electrons and ions to anode surfaces between the magnetic cusps of a NASA Solar Electric Propulsion Technology Application Readiness ion thruster has been characterized. Ion flux measurements were made at the anode and at the screen grid electrode. The measurements indicated that the average ion current density at the anode and at the screen grid were approximately equal. Additionally, it was found that the electron flux to the anode between cusps is best described by the classical cross-field diffusion coefficient.

Ion and Electron Transport in an Nstar-derivative Ion Thruster. Revised

NASA Technical Reports Server (NTRS)

Foster, John E.

2001-01-01

Diffusion of electrons and ions to anode surfaces between the magnetic cusps of a NASA Solar Electric Propulsion Technology Application Readiness ion thruster has been characterized. Ion flux measurements were made at the anode and at the screen grid electrode. The measurements indicated that the average ion current density at the anode and at the screen grid were approximately equal. Additionally, it was found that the electron flux to the anode between cusps is best described by the classical cross-field diffusion coefficient.

Quantum treatment of the capture of an atom by a fast nucleus incident on a molecule

NASA Astrophysics Data System (ADS)

Shakeshaft, Robin; Spruch, Larry

1980-04-01

The classical double-scattering model of Thomas for the capture of electrons from atoms by fast ions yields a cross section σ which dominates over the single scattering contribution for sufficiently fast ions. The magnitude of the classical double-scattering σ differs, however, from its quantum-mechanical (second-Born) analog by an order of magnitude. Further, a "fast ion" means an ion of some MeV, and at those energies the cross sections are very low. On the other hand, as noted by Bates, Cook, and Smith, the double-scattering cross section for the capture of atoms from molecules by fast ions dominates over the single-scattering contribution for incident ions of very much lower energy; roughly, one must have the velocity of the incident projectile much larger than a characteristic internal velocity of the particles in the target. It follows that we are in the asymptotic domain not at about 10 MeV but at about 100 eV. For the reaction H+ + CH4-->H+2 + CH3 with incident proton energies of 70 to 150 eV, the peak in the angular distribution as determined experimentally is at almost precisely the value predicted by the classical model, but the theoretical total cross section is about 30 times too large. Using a quantum version of the classical model, which involves the same kinematics and therefore preserves the agreement with the angular distribution, we obtain somewhat better agreement with the experimental total cross section, by a factor of about 5. (To obtain very good agreement, one may have to perform a really accurate calculation of large-angle elastic scattering of protons and H atoms by CH3, and take into account interference effects.) In the center-of-mass frame, for sufficiently high incident energy, the first of the two scatterings involves the scattering of H+ by H through an angle of very close to 90°, and it follows that the nuclei of the emergent H+2 ion will almost all be in the singlet state. We have also calculated the cross section for the reaction D+ + CH4-->(HD)+ + CH3.

Trajectory dynamics study of the Ar + CH4 dissociation reaction at high temperatures: the importance of zero-point-energy effects.

PubMed

Marques, J M C; Martínez-Núñez, E; Fernandez-Ramos, A; Vazquez, S A

2005-06-23

Large-scale classical trajectory calculations have been performed to study the reaction Ar + CH4--> CH3 +H + Ar in the temperature range 2500 < or = T/K < or = 4500. The potential energy surface used for ArCH4 is the sum of the nonbonding pairwise potentials of Hase and collaborators (J. Chem. Phys. 2001, 114, 535) that models the intermolecular interaction and the CH4 intramolecular potential of Duchovic et al. (J. Phys. Chem. 1984, 88, 1339), which has been modified to account for the H-H repulsion at small bending angles. The thermal rate coefficient has been calculated, and the zero-point energy (ZPE) of the CH3 product molecule has been taken into account in the analysis of the results; also, two approaches have been applied for discarding predissociative trajectories. In both cases, good agreement is observed between the experimental and trajectory results after imposing the ZPE of CH3. The energy-transfer parameters have also been obtained from trajectory calculations and compared with available values estimated from experiment using the master equation formalism; in general, the agreement is good.

Molecular Growth Inside of Polycyclic Aromatic Hydrocarbon Clusters Induced by Ion Collisions.

PubMed

Delaunay, Rudy; Gatchell, Michael; Rousseau, Patrick; Domaracka, Alicja; Maclot, Sylvain; Wang, Yang; Stockett, Mark H; Chen, Tao; Adoui, Lamri; Alcamí, Manuel; Martín, Fernando; Zettergren, Henning; Cederquist, Henrik; Huber, Bernd A

2015-05-07

The present work combines experimental and theoretical studies of the collision between keV ion projectiles and clusters of pyrene, one of the simplest polycyclic aromatic hydrocarbons (PAHs). Intracluster growth processes induced by ion collisions lead to the formation of a wide range of new molecules with masses larger than that of the pyrene molecule. The efficiency of these processes is found to strongly depend on the mass and velocity of the incoming projectile. Classical molecular dynamics simulations of the entire collision process-from the ion impact (nuclear scattering) to the formation of new molecular species-reproduce the essential features of the measured molecular growth process and also yield estimates of the related absolute cross sections. More elaborate density functional tight binding calculations yield the same growth products as the classical simulations. The present results could be relevant to understand the physical chemistry of the PAH-rich upper atmosphere of Saturn's moon Titan.

Permeating disciplines: Overcoming barriers between molecular simulations and classical structure-function approaches in biological ion transport.

PubMed

Howard, Rebecca J; Carnevale, Vincenzo; Delemotte, Lucie; Hellmich, Ute A; Rothberg, Brad S

2018-04-01

Ion translocation across biological barriers is a fundamental requirement for life. In many cases, controlling this process-for example with neuroactive drugs-demands an understanding of rapid and reversible structural changes in membrane-embedded proteins, including ion channels and transporters. Classical approaches to electrophysiology and structural biology have provided valuable insights into several such proteins over macroscopic, often discontinuous scales of space and time. Integrating these observations into meaningful mechanistic models now relies increasingly on computational methods, particularly molecular dynamics simulations, while surfacing important challenges in data management and conceptual alignment. Here, we seek to provide contemporary context, concrete examples, and a look to the future for bridging disciplinary gaps in biological ion transport. This article is part of a Special Issue entitled: Beyond the Structure-Function Horizon of Membrane Proteins edited by Ute Hellmich, Rupak Doshi and Benjamin McIlwain. Copyright © 2017 Elsevier B.V. All rights reserved.

An analytical derivation of MC-SCF vibrational wave functions for the quantum dynamical simulation of multiple proton transfer reactions: Initial application to protonated water chains

NASA Astrophysics Data System (ADS)

Drukker, Karen; Hammes-Schiffer, Sharon

1997-07-01

This paper presents an analytical derivation of a multiconfigurational self-consistent-field (MC-SCF) solution of the time-independent Schrödinger equation for nuclear motion (i.e. vibrational modes). This variational MC-SCF method is designed for the mixed quantum/classical molecular dynamics simulation of multiple proton transfer reactions, where the transferring protons are treated quantum mechanically while the remaining degrees of freedom are treated classically. This paper presents a proof that the Hellmann-Feynman forces on the classical degrees of freedom are identical to the exact forces (i.e. the Pulay corrections vanish) when this MC-SCF method is used with an appropriate choice of basis functions. This new MC-SCF method is applied to multiple proton transfer in a protonated chain of three hydrogen-bonded water molecules. The ground state and the first three excited state energies and the ground state forces agree well with full configuration interaction calculations. Sample trajectories are obtained using adiabatic molecular dynamics methods, and nonadiabatic effects are found to be insignificant for these sample trajectories. The accuracy of the excited states will enable this MC-SCF method to be used in conjunction with nonadiabatic molecular dynamics methods. This application differs from previous work in that it is a real-time quantum dynamical nonequilibrium simulation of multiple proton transfer in a chain of water molecules.

Iterative reconstruction with boundary detection for carbon ion computed tomography

NASA Astrophysics Data System (ADS)

Shrestha, Deepak; Qin, Nan; Zhang, You; Kalantari, Faraz; Niu, Shanzhou; Jia, Xun; Pompos, Arnold; Jiang, Steve; Wang, Jing

2018-03-01

In heavy ion radiation therapy, improving the accuracy in range prediction of the ions inside the patient’s body has become essential. Accurate localization of the Bragg peak provides greater conformity of the tumor while sparing healthy tissues. We investigated the use of carbon ions directly for computed tomography (carbon CT) to create the relative stopping power map of a patient’s body. The Geant4 toolkit was used to perform a Monte Carlo simulation of the carbon ion trajectories, to study their lateral and angular deflections and the most likely paths, using a water phantom. Geant4 was used to create carbonCT projections of a contrast and spatial resolution phantom, with a cone beam of 430 MeV/u carbon ions. The contrast phantom consisted of cranial bone, lung material, and PMMA inserts while the spatial resolution phantom contained bone and lung material inserts with line pair (lp) densities ranging from 1.67 lp cm-1 through 5 lp cm-1. First, the positions of each carbon ion on the rear and front trackers were used for an approximate reconstruction of the phantom. The phantom boundary was extracted from this approximate reconstruction, by using the position as well as angle information from the four tracking detectors, resulting in the entry and exit locations of the individual ions on the phantom surface. Subsequent reconstruction was performed by the iterative algebraic reconstruction technique coupled with total variation minimization (ART-TV) assuming straight line trajectories for the ions inside the phantom. The influence of number of projections was studied with reconstruction from five different sets of projections: 15, 30, 45, 60 and 90. Additionally, the effect of number of ions on the image quality was investigated by reducing the number of ions/projection while keeping the total number of projections at 60. An estimation of carbon ion range using the carbonCT image resulted in improved range prediction compared to the range calculated using a calibration curve.

Transport implementation of the Bernstein-Vazirani algorithm with ion qubits

NASA Astrophysics Data System (ADS)

Fallek, S. D.; Herold, C. D.; McMahon, B. J.; Maller, K. M.; Brown, K. R.; Amini, J. M.

2016-08-01

Using trapped ion quantum bits in a scalable microfabricated surface trap, we perform the Bernstein-Vazirani algorithm. Our architecture takes advantage of the ion transport capabilities of such a trap. The algorithm is demonstrated using two- and three-ion chains. For three ions, an improvement is achieved compared to a classical system using the same number of oracle queries. For two ions and one query, we correctly determine an unknown bit string with probability 97.6(8)%. For three ions, we succeed with probability 80.9(3)%.

Emergent quantum mechanics without wavefunctions

NASA Astrophysics Data System (ADS)

Mesa Pascasio, J.; Fussy, S.; Schwabl, H.; Grössing, G.

2016-03-01

We present our model of an Emergent Quantum Mechanics which can be characterized by “realism without pre-determination”. This is illustrated by our analytic description and corresponding computer simulations of Bohmian-like “surreal” trajectories, which are obtained classically, i.e. without the use of any quantum mechanical tool such as wavefunctions. However, these trajectories do not necessarily represent ontological paths of particles but rather mappings of the probability density flux in a hydrodynamical sense. Modelling emergent quantum mechanics in a high-low intesity double slit scenario gives rise to the “quantum sweeper effect” with a characteristic intensity pattern. This phenomenon should be experimentally testable via weak measurement techniques.

Emergence of Global Shape Processing Continues through Adolescence

ERIC Educational Resources Information Center

Scherf, K. Suzanne; Behrmann, Marlene; Kimchi, Ruth; Luna, Beatriz

2009-01-01

The developmental trajectory of perceptual organization in humans is unclear. This study investigated perceptual grouping abilities across a wide age range (8-30 years) using a classic compound letter global/local (GL) task and a more fine-grained microgenetic prime paradigm (MPP) with both few- and many-element hierarchical displays. In the GL…

Classical Trajectory Study of Collision Energy Transfer between Ne and C2H2 on a Full Dimensional Accurate Potential Energy Surface.

PubMed

Liu, Yang; Huang, Yin; Ma, Jianyi; Li, Jun

2018-02-15

Collision energy transfer plays an important role in gas phase reaction kinetics and relaxation of excited molecules. However, empirical treatments are generally adopted for the collisional energy transfer in the master equation based approach. In this work, classical trajectory approach is employed to investigate the collision energy transfer dynamics in the C 2 H 2 -Ne system. The entire potential energy surface is described as the sum of the C 2 H 2 potential and interaction potential between C 2 H 2 and Ne. It is highlighted that both parts of the entire potential are highly accurate. In particular, the interaction potential is fit to ∼41 300 configurations determined at the level of CCSD(T)-F12a/cc-pCVTZ-F12 with the counterpoise correction. Collision energy transfer dynamics are then carried out on this benchmark potential and the widely used Lennard-Jones and Buckingham interaction potentials. Energy transfers and related probability densities at different collisional energies are reported and discussed.

Trajectory and System Analysis For Outer-Planet Solar-Electric Propulsion Missions

NASA Technical Reports Server (NTRS)

Cupples, Michael; Woo, Byoungsam; Coverstone, Victoria L.; Hartmann, John W.

2004-01-01

Outer-planet mission and systems analyses are performed using three next generation solar-electric ion thruster models. The impact of variations in thruster model, flight time, launch vehicle, propulsion and power systems characteristics is investigated. All presented trajectories have a single Venus gravity assist and maximize the delivered mass to Saturn or Neptune. The effect of revolution ratio - the ratio of Venusian orbital period to the flight time between launch and flyby dates - is also discussed.

Determining Iron Content in Foods by Spectrophotometry.

ERIC Educational Resources Information Center

Adams, Paul E.

1995-01-01

Describes a laboratory experiment for secondary school chemistry students utilizing the classic reaction between the iron(III) ion and the thiocyanate ion. The experiment also works very well in other chemistry courses as an experience in spectrophotometric analysis. (PVD)

Global Structure and Sodium Ion Dynamics in Mercury's Magnetosphere With the Offset Dipole

NASA Astrophysics Data System (ADS)

Yagi, M.; Seki, K.; Matsumoto, Y.; Delcourt, D. C.; Leblanc, F.

2017-11-01

We conducted global magnetohydrodynamics (MHD) simulation of Mercury's magnetosphere with the dipole offset, which was revealed by MESSENGER (Mercury Surface, Space Environment, Geochemistry, and Ranging) observations, in order to investigate its global structure under northward interplanetary magnetic field conditions. Sodium ion dynamics originating from the Mercury's exosphere is also investigated based on statistical trajectory tracing in the electric and magnetic fields obtained from the MHD simulations. The results reveal a north-south asymmetry characterized by open field lines around the southern polar region and northward deflection of the plasma sheet in the far tail. The asymmetry of magnetic field structure near the planet drastically affects trajectories of sodium ion and thus their pressure distributions and precipitation pattern onto the planet. Weaker magnetic field strength in the southern hemisphere than in the north increases ion loss by precipitation onto the planetary surface in the southern hemisphere. The "sodium ring," which is formed by high-energy sodium ions drifting around the planet, is also found in the vicinity of the planet. The sodium ring is almost circular under nominal solar wind conditions. The ring becomes partial under high solar wind density, because dayside magnetosphere is so compressed that there is no space for the sodium ions to drift around. In both cases, the sodium ring is formed by sodium ions that are picked up, accelerated in the magnetosheath just outside the magnetopause, and reentered into the magnetosphere due to combined effects of finite Larmor radius and convection electric field in the dawnside magnetosphere.

Lunar Ion Transport Near Magnetic Anomalies: Possible Implications for Swirl Formation

NASA Technical Reports Server (NTRS)

Keller, J. W.; Killen, R. M.; Stubbs, T. J.; Farrell, W. M.; Halekas, J. S.

2011-01-01

The bright swirling features on the lunar surface in areas around the Moon but most prominently at Reiner Gamma, have intrigued scientists for many years. After Apollo and later Lunar Prospector (LP} mapped the Lunar magnetic fields from orbit, it was observed that these features are generally associated with crustal magnetic anomalies. This led researchers to propose a number of explanations for the swirls that invoke these fields. Prominent among these include magnetic shielding in the form of a mini-magnetosphere which impedes space weathering by the solar wind, magnetically controlled dust transport, and cometary or asteroidal impacts that would result in shock magnetization with concomitant formation ofthe swirls. In this presentation, we will consider another possibility, that the ambient magnetic and electric fields can transport and channel secondary ions produced by micrometeorite or solar wind ion impacts. In this scenario, ions that are created in these impacts are under the influence of these fields and can drift for significant distances before encountering the magnetic anomalies when their trajectories are disrupted and concentrated onto nearby areas. These ions may then be responsible for chemical alteration of the surface leading either to a brightening effect or a disruption of space weathering processes. To test this hypothesis we have run ion trajectory simulations that show ions from regions about the magnetic anomalies can be channeled into very small areas near the anomalies and although questions remain as to nature of the mechanisms that could lead to brightening of the surface it appears that the channeling effect is consistent with the existence of the swirls.

Shear modulus of neutron star crust

NASA Astrophysics Data System (ADS)

Baiko, D. A.

2011-09-01

The shear modulus of solid neutron star crust is calculated by the thermodynamic perturbation theory, taking into account ion motion. At a given density, the crust is modelled as a body-centred cubic Coulomb crystal of fully ionized atomic nuclei of one type with a uniform charge-compensating electron background. Classic and quantum regimes of ion motion are considered. The calculations in the classic temperature range agree well with previous Monte Carlo simulations. At these temperatures, the shear modulus is given by the sum of a positive contribution due to the static lattice and a negative ∝ T contribution due to the ion motion. The quantum calculations are performed for the first time. The main result is that at low temperatures the contribution to the shear modulus due to the ion motion saturates at a constant value, associated with zero-point ion vibrations. Such behaviour is qualitatively similar to the zero-point ion motion contribution to the crystal energy. The quantum effects may be important for lighter elements at higher densities, where the ion plasma temperature is not entirely negligible compared to the typical Coulomb ion interaction energy. The results of numerical calculations are approximated by convenient fitting formulae. They should be used for precise neutron star oscillation modelling, a rapidly developing branch of stellar seismology.

Massive quantum regions for simulations on bio-nanomaterials: synthetic ferritin nanocages.

PubMed

Torras, Juan; Alemán, Carlos

2018-02-22

QM/MM molecular dynamics simulations on the 4His-ΔC* protein cage have been performed using multiple active zones (up to 86 quantum regions). The regulation and nanocage stability exerted by the divalent transition metal ions in the monomer-to-cage conversion have been understood by comparing high level quantum trajectories obtained using Cu 2+ and Ni 2+ coordination ions.

Free molecular collision cross section calculation methods for nanoparticles and complex ions with energy accommodation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Larriba, Carlos, E-mail: clarriba@umn.edu; Hogan, Christopher J.

2013-10-15

The structures of nanoparticles, macromolecules, and molecular clusters in gas phase environments are often studied via measurement of collision cross sections. To directly compare structure models to measurements, it is hence necessary to have computational techniques available to calculate the collision cross sections of structural models under conditions matching measurements. However, presently available collision cross section methods contain the underlying assumption that collision between gas molecules and structures are completely elastic (gas molecule translational energy conserving) and specular, while experimental evidence suggests that in the most commonly used background gases for measurements, air and molecular nitrogen, gas molecule reemission ismore » largely inelastic (with exchange of energy between vibrational, rotational, and translational modes) and should be treated as diffuse in computations with fixed structural models. In this work, we describe computational techniques to predict the free molecular collision cross sections for fixed structural models of gas phase entities where inelastic and non-specular gas molecule reemission rules can be invoked, and the long range ion-induced dipole (polarization) potential between gas molecules and a charged entity can be considered. Specifically, two calculation procedures are described detail: a diffuse hard sphere scattering (DHSS) method, in which structures are modeled as hard spheres and collision cross sections are calculated for rectilinear trajectories of gas molecules, and a diffuse trajectory method (DTM), in which the assumption of rectilinear trajectories is relaxed and the ion-induced dipole potential is considered. Collision cross section calculations using the DHSS and DTM methods are performed on spheres, models of quasifractal aggregates of varying fractal dimension, and fullerene like structures. Techniques to accelerate DTM calculations by assessing the contribution of grazing gas molecule collisions (gas molecules with altered trajectories by the potential interaction) without tracking grazing trajectories are further discussed. The presented calculation techniques should enable more accurate collision cross section predictions under experimentally relevant conditions than pre-existing approaches, and should enhance the ability of collision cross section measurement schemes to discern the structures of gas phase entities.« less

Observation of a high-energy tail in ion energy distribution in the cylindrical Hall thruster plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lim, Youbong; Kim, Holak; Choe, Wonho, E-mail: wchoe@kaist.ac.kr

2014-10-15

A novel method is presented to determine populations and ion energy distribution functions (IEDFs) of individual ion species having different charge states in an ion beam from the measured spectrum of an E × B probe. The inversion of the problem is performed by adopting the iterative Tikhonov regularization method with the characteristic matrices obtained from the calculated ion trajectories. In a cylindrical Hall thruster plasma, an excellent agreement is observed between the IEDFs by an E × B probe and those by a retarding potential analyzer. The existence of a high-energy tail in the IEDF is found to be mainly due to singlymore » charged Xe ions, and is interpreted in terms of non-linear ion acceleration.« less

Examples of Complete Solvability of 2D Classical Superintegrable Systems

NASA Astrophysics Data System (ADS)

Chen, Yuxuan; Kalnins, Ernie G.; Li, Qiushi; Miller, Willard, Jr.

2015-11-01

Classical (maximal) superintegrable systems in n dimensions are Hamiltonian systems with 2n-1 independent constants of the motion, globally defined, the maximum number possible. They are very special because they can be solved algebraically. In this paper we show explicitly, mostly through examples of 2nd order superintegrable systems in 2 dimensions, how the trajectories can be determined in detail using rather elementary algebraic, geometric and analytic methods applied to the closed quadratic algebra of symmetries of the system, without resorting to separation of variables techniques or trying to integrate Hamilton's equations. We treat a family of 2nd order degenerate systems: oscillator analogies on Darboux, nonzero constant curvature, and flat spaces, related to one another via contractions, and obeying Kepler's laws. Then we treat two 2nd order nondegenerate systems, an analogy of a caged Coulomb problem on the 2-sphere and its contraction to a Euclidean space caged Coulomb problem. In all cases the symmetry algebra structure provides detailed information about the trajectories, some of which are rather complicated. An interesting example is the occurrence of ''metronome orbits'', trajectories confined to an arc rather than a loop, which are indicated clearly from the structure equations but might be overlooked using more traditional methods. We also treat the Post-Winternitz system, an example of a classical 4th order superintegrable system that cannot be solved using separation of variables. Finally we treat a superintegrable system, related to the addition theorem for elliptic functions, whose constants of the motion are only rational in the momenta. It is a system of special interest because its constants of the motion generate a closed polynomial algebra. This paper contains many new results but we have tried to present most of the materials in a fashion that is easily accessible to nonexperts, in order to provide entrée to superintegrablity theory.

Anomalous Diffusion of Single Particles in Cytoplasm

PubMed Central

Regner, Benjamin M.; Vučinić, Dejan; Domnisoru, Cristina; Bartol, Thomas M.; Hetzer, Martin W.; Tartakovsky, Daniel M.; Sejnowski, Terrence J.

2013-01-01

The crowded intracellular environment poses a formidable challenge to experimental and theoretical analyses of intracellular transport mechanisms. Our measurements of single-particle trajectories in cytoplasm and their random-walk interpretations elucidate two of these mechanisms: molecular diffusion in crowded environments and cytoskeletal transport along microtubules. We employed acousto-optic deflector microscopy to map out the three-dimensional trajectories of microspheres migrating in the cytosolic fraction of a cellular extract. Classical Brownian motion (BM), continuous time random walk, and fractional BM were alternatively used to represent these trajectories. The comparison of the experimental and numerical data demonstrates that cytoskeletal transport along microtubules and diffusion in the cytosolic fraction exhibit anomalous (nonFickian) behavior and posses statistically distinct signatures. Among the three random-walk models used, continuous time random walk provides the best representation of diffusion, whereas microtubular transport is accurately modeled with fractional BM. PMID:23601312

Characteristic study of head-on collision of dust-ion acoustic solitons of opposite polarity with kappa distributed electrons

NASA Astrophysics Data System (ADS)

Parveen, Shahida; Mahmood, Shahzad; Adnan, Muhammad; Qamar, Anisa

2016-09-01

The head on collision between two dust ion acoustic (DIA) solitary waves, propagating in opposite directions, is studied in an unmagnetized plasma constituting adiabatic ions, static dust charged (positively/negatively) grains, and non-inertial kappa distributed electrons. In the linear limit, the dispersion relation of the dust ion acoustic (DIA) solitary wave is obtained using the Fourier analysis. For studying characteristic head-on collision of DIA solitons, the extended Poincaré-Lighthill-Kuo method is employed to obtain Korteweg-de Vries (KdV) equations with quadratic nonlinearities and investigated the phase shifts in their trajectories after the interaction. It is revealed that only compressive solitary waves can exist for the positive dust charged concentrations while for negative dust charge concentrations both the compressive and rarefactive solitons can propagate in such dusty plasma. It is found that for specific sets of plasma parameters, the coefficient of nonlinearity disappears in the KdV equation for the negative dust charged grains. Therefore, the modified Korteweg-de Vries (mKdV) equations with cubic nonlinearity coefficient, and their corresponding phase shift and trajectories, are also derived for negative dust charged grains plasma at critical composition. The effects of different plasma parameters such as superthermality, concentration of positively/negatively static dust charged grains, and ion to electron temperature ratio on the colliding soliton profiles and their corresponding phase shifts are parametrically examined.

Improvement of uniformity of the negative ion beams by tent-shaped magnetic field in the JT-60 negative ion source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoshida, Masafumi, E-mail: yoshida.masafumi@jaea.go.jp; Hanada, Masaya; Kojima, Atsushi

2014-02-15

Non-uniformity of the negative ion beams in the JT-60 negative ion source with the world-largest ion extraction area was improved by modifying the magnetic filter in the source from the plasma grid (PG) filter to a tent-shaped filter. The magnetic design via electron trajectory calculation showed that the tent-shaped filter was expected to suppress the localization of the primary electrons emitted from the filaments and created uniform plasma with positive ions and atoms of the parent particles for the negative ions. By modifying the magnetic filter to the tent-shaped filter, the uniformity defined as the deviation from the averaged beammore » intensity was reduced from 14% of the PG filter to ∼10% without a reduction of the negative ion production.« less

Double layers and double wells in arbitrary degenerate plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akbari-Moghanjoughi, M.

Using the generalized hydrodynamic model, the possibility of variety of large amplitude nonlinear excitations is examined in electron-ion plasma with arbitrary electron degeneracy considering also the ion temperature effect. A new energy-density relation is proposed for plasmas with arbitrary electron degeneracy which reduces to the classical Boltzmann and quantum Thomas-Fermi counterparts in the extreme limits. The pseudopotential method is employed to find the criteria for existence of nonlinear structures such as solitons, periodic nonlinear structures, and double-layers for different cases of adiabatic and isothermal ion fluids for a whole range of normalized electron chemical potential, η{sub 0}, ranging from dilutemore » classical to completely degenerate electron fluids. It is observed that there is a Mach-speed gap in which no large amplitude localized or periodic nonlinear excitations can propagate in the plasma under consideration. It is further revealed that the plasma under investigation supports propagation of double-wells and double-layers the chemical potential and Mach number ranges of which are studied in terms of other plasma parameters. The Mach number criteria for nonlinear waves are shown to significantly differ for cases of classical with η{sub 0} < 0 and quantum with η{sub 0} > 0 regimes. It is also shown that the localized structure propagation criteria possess significant dissimilarities for plasmas with adiabatic and isothermal ions. Current research may be generalized to study the nonlinear structures in plasma containing positrons, multiple ions with different charge states, and charged dust grains.« less

A walk through the approximations of ab initio multiple spawning

NASA Astrophysics Data System (ADS)

Mignolet, Benoit; Curchod, Basile F. E.

2018-04-01

Full multiple spawning offers an in principle exact framework for excited-state dynamics, where nuclear wavefunctions in different electronic states are represented by a set of coupled trajectory basis functions that follow classical trajectories. The couplings between trajectory basis functions can be approximated to treat molecular systems, leading to the ab initio multiple spawning method which has been successfully employed to study the photochemistry and photophysics of several molecules. However, a detailed investigation of its approximations and their consequences is currently missing in the literature. In this work, we simulate the explicit photoexcitation and subsequent excited-state dynamics of a simple system, LiH, and we analyze (i) the effect of the ab initio multiple spawning approximations on different observables and (ii) the convergence of the ab initio multiple spawning results towards numerically exact quantum dynamics upon a progressive relaxation of these approximations. We show that, despite the crude character of the approximations underlying ab initio multiple spawning for this low-dimensional system, the qualitative excited-state dynamics is adequately captured, and affordable corrections can further be applied to ameliorate the coupling between trajectory basis functions.

The control of electron quantum trajectories on the high-order harmonic generation of CO and N2 molecules in the presence of a low frequency field.

PubMed

Koushki, A M; Sadighi-Bonabi, R; Mohsen-Nia, M; Irani, E

2018-04-14

In the present work, an efficient method is theoretically investigated for extending high-order harmonics and ultrashort attosecond pulse generation in N 2 and CO molecules by using the time-dependent density functional theory approach. Our results show that by utilizing chirped laser field in the presence of a low frequency field, not only is the harmonic cutoff extended remarkably but also the single short quantum trajectory is selected to contribute to the harmonic spectra. When a low frequency field is added to the two-color chirped laser field, the long quantum trajectories are suppressed and only the short quantum trajectories contribute to the higher harmonic emission mechanism. As a result, the spectral modulation is significantly decreased and an intense ultrashort pulse can be generated from the supercontinuum region of high harmonics. With such a scheme, the isolated ultrashort attosecond pulses can be generated in length, velocity, and acceleration gauges. Furthermore, these results are explained by using the classical and quantum time-frequency analyses.

The control of electron quantum trajectories on the high-order harmonic generation of CO and N2 molecules in the presence of a low frequency field

NASA Astrophysics Data System (ADS)

Koushki, A. M.; Sadighi-Bonabi, R.; Mohsen-Nia, M.; Irani, E.

2018-04-01

In the present work, an efficient method is theoretically investigated for extending high-order harmonics and ultrashort attosecond pulse generation in N2 and CO molecules by using the time-dependent density functional theory approach. Our results show that by utilizing chirped laser field in the presence of a low frequency field, not only is the harmonic cutoff extended remarkably but also the single short quantum trajectory is selected to contribute to the harmonic spectra. When a low frequency field is added to the two-color chirped laser field, the long quantum trajectories are suppressed and only the short quantum trajectories contribute to the higher harmonic emission mechanism. As a result, the spectral modulation is significantly decreased and an intense ultrashort pulse can be generated from the supercontinuum region of high harmonics. With such a scheme, the isolated ultrashort attosecond pulses can be generated in length, velocity, and acceleration gauges. Furthermore, these results are explained by using the classical and quantum time-frequency analyses.

Non-statistical effects in bond fission reactions of 1,2-difluoroethane

NASA Astrophysics Data System (ADS)

Schranz, Harold W.; Raff, Lionel M.; Thompson, Donald L.

1991-08-01

A microcanonical, classical variational transition-state theory based on the use of the efficient microcanonical sampling (EMS) procedure is applied to simple bond fission in 1,2-difluoroethane. Comparison is made with results of trajectory calculations performed on the same global potential-energy surface. Agreement between the statistical theory and trajectory results for CC CF and CH bond fissions is poor with differences as large as a factor of 125. Most importantly, at the lower energy studied, 6.0 eV, the statistical calculations predict considerably slower rates than those computed from trajectories. We conclude from these results that the statistical assumptions inherent in the transition-state theory method are not valid for 1,2-difluoroethane in spite of the fact that the total intramolecular energy transfer rate out of CH and CC normal and local modes is large relative to the bond fission rates. The IVR rate is not globally rapid and the trajectories do not access all of the energetically available phase space uniformly on the timescale of the reactions.

A walk through the approximations of ab initio multiple spawning.

PubMed

Mignolet, Benoit; Curchod, Basile F E

2018-04-07

Full multiple spawning offers an in principle exact framework for excited-state dynamics, where nuclear wavefunctions in different electronic states are represented by a set of coupled trajectory basis functions that follow classical trajectories. The couplings between trajectory basis functions can be approximated to treat molecular systems, leading to the ab initio multiple spawning method which has been successfully employed to study the photochemistry and photophysics of several molecules. However, a detailed investigation of its approximations and their consequences is currently missing in the literature. In this work, we simulate the explicit photoexcitation and subsequent excited-state dynamics of a simple system, LiH, and we analyze (i) the effect of the ab initio multiple spawning approximations on different observables and (ii) the convergence of the ab initio multiple spawning results towards numerically exact quantum dynamics upon a progressive relaxation of these approximations. We show that, despite the crude character of the approximations underlying ab initio multiple spawning for this low-dimensional system, the qualitative excited-state dynamics is adequately captured, and affordable corrections can further be applied to ameliorate the coupling between trajectory basis functions.

Chemical characterization of fog and rain water collected at the eastern Andes cordillera

NASA Astrophysics Data System (ADS)

Beiderwieden, E.; Wrzesinsky, T.; Klemm, O.

2005-06-01

During a three month period in 2003 and 2004, the chemistry of fog and rainwater were studied at the "El Tiro" site in a tropical mountain forest ecosystem in Ecuador, South America. The fogwater samples were collected using a passive fog collector, and for the rain water, a standard rain sampler was employed. For all samples, electric conductivity, pH, and the concentrations of NH4+, K+, Na+, Ca2+, Mg2+, Cl-, NO3-, PO43-, and SO42-, were measured. For each fog sample, a 5 day back trajectory was calculated by the use of the HYSPLIT model. Two types of trajectories occurred. One type was characterized by advection of air masses from the East over the Amazonian basin, the other trajectory arrived one from the West after significant travel time over the Pacific Ocean. We found considerably higher ion concentrations in fogwater samples than in rain samples. Median pH values are 4.58 for fog water, and 5.26 for the rain samples, respectively. The median electric conductivity was 23 µS cm-1 for the fog and 6 µS cm-1 for the rain. The concentrations of all analysed ions were relatively low compared to other mountainous sites (Weathers et al., 1988; Elias et al., 1995; Schemenauer et al., 1995; Wrzesinsky and Klemm, 2000; Zimmermann and Zimmermann, 2002). The continent samples exhibit higher concentrations of most ions as compared to the pacific samples.

Properties of a planar electric double layer under extreme conditions investigated by classical density functional theory and Monte Carlo simulations.

PubMed

Zhou, Shiqi; Lamperski, Stanisław; Zydorczak, Maria

2014-08-14

Monte Carlo (MC) simulation and classical density functional theory (DFT) results are reported for the structural and electrostatic properties of a planar electric double layer containing ions having highly asymmetric diameters or valencies under extreme concentration condition. In the applied DFT, for the excess free energy contribution due to the hard sphere repulsion, a recently elaborated extended form of the fundamental measure functional is used, and coupling of Coulombic and short range hard-sphere repulsion is described by a traditional second-order functional perturbation expansion approximation. Comparison between the MC and DFT results indicates that validity interval of the traditional DFT approximation expands to high ion valences running up to 3 and size asymmetry high up to diameter ratio of 4 whether the high valence ions or the large size ion are co- or counter-ions; and to a high bulk electrolyte concentration being close to the upper limit of the electrolyte mole concentration the MC simulation can deal with well. The DFT accuracy dependence on the ion parameters can be self-consistently explained using arguments of liquid state theory, and new EDL phenomena such as overscreening effect due to monovalent counter-ions, extreme layering effect of counter-ions, and appearance of a depletion layer with almost no counter- and co-ions are observed.

Real-time observation of intramolecular proton transfer in the electronic ground state of chloromalonaldehyde: an ab initio study of time-resolved photoelectron spectra.

PubMed

do N Varella, Márcio T; Arasaki, Yasuki; Ushiyama, Hiroshi; Takatsuka, Kazuo; Wang, Kwanghsi; McKoy, Vincent

2007-02-07

The authors report on studies of time-resolved photoelectron spectra of intramolecular proton transfer in the ground state of chloromalonaldehyde, employing ab initio photoionization matrix elements and effective potential surfaces of reduced dimensionality, wherein the couplings of proton motion to the other molecular vibrational modes are embedded by averaging over classical trajectories. In the simulations, population is transferred from the vibrational ground state to vibrationally hot wave packets by pumping to an excited electronic state and dumping with a time-delayed pulse. These pump-dump-probe simulations demonstrate that the time-resolved photoelectron spectra track proton transfer in the electronic ground state well and, furthermore, that the geometry dependence of the matrix elements enhances the tracking compared with signals obtained with the Condon approximation. Photoelectron kinetic energy distributions arising from wave packets localized in different basins are also distinguishable and could be understood, as expected, on the basis of the strength of the optical couplings in different regions of the ground state potential surface and the Franck-Condon overlaps of the ground state wave packets with the vibrational eigenstates of the ion potential surface.

Electron capture in collisions of S4+ with helium

NASA Astrophysics Data System (ADS)

Wang, J. G.; Turner, A. R.; Cooper, D. L.; Schultz, D. R.; Rakovic, M. J.; Fritsch, W.; Stancil, P. C.; Zygelman, B.

2002-07-01

Charge transfer due to collisions of ground-state S4+(3s2 1S) ions with helium is investigated for energies between 0.1 meV u-1 and 10 MeV u-1. Total and state-selective single electron capture (SEC) cross sections and rate coefficients are obtained utilizing the quantum mechanical molecular-orbital close-coupling (MOCC), atomic-orbital close-coupling (AOCC), classical trajectory Monte Carlo (CTMC) and continuum distorted wave methods. The MOCC calculations utilize ab initio adiabatic potentials and nonadiabatic radial coupling matrix elements obtained with the spin-coupled valence-bond approach. Previous data are limited to a calculation of the total SEC rate coefficient using the Landau-Zener model that is, in comparison to the results presented here, three orders of magnitude smaller. The MOCC SEC cross sections at low energy reveal a multichannel interference effect. True double capture is also investigated with the AOCC and CTMC approaches while autoionizing double capture and transfer ionization (TI) is explored with CTMC. SEC is found to be the dominant process except for E>200 keV u-1 when TI becomes the primary capture channel. Astrophysical implications are briefly discussed.

Anomalous Growth Rate of Ag Nanocrystals Revealed by in situ STEM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ge, Mingyuan; Lu, Ming; Chu, Yong

In situ microscopy of colloidal nanocrystal growth offers a unique opportunity to acquire direct and straightforward data for assessing classical growth models. For this study, we observe the growth trajectories of individual Ag nanoparticles in solution using in situ scanning transmission electron microscopy. For the first time, we provide experimental evidence of growth rates of Ag nanoparticles in the presence of Pt in solution that are significantly faster than predicted by Lifshitz-Slyozov-Wagner theory. We attribute these observed anomalous growth rates to the synergistic effects of the catalytic properties of Pt and the electron beam itself. Transiently reduced Pt atoms servemore » as active sites for Ag ions to grow, thereby playing a key role in controlling the growth kinetics. Electron beam illumination greatly increases the local concentration of free radicals, thereby strongly influencing particle growth rate and the resulting particle morphology. Through a systematic investigation, we demonstrate the feasibility of utilizing these synergistic effects for controlling the growth rates and particle morphologies at the nanoscale. Our findings not only expand the current scope of crystal growth theory, but may also lead to a broader scientific application of nanocrystal synthesis.« less

Anomalous Growth Rate of Ag Nanocrystals Revealed by in situ STEM

DOE PAGES

Ge, Mingyuan; Lu, Ming; Chu, Yong; ...

2017-11-27

In situ microscopy of colloidal nanocrystal growth offers a unique opportunity to acquire direct and straightforward data for assessing classical growth models. For this study, we observe the growth trajectories of individual Ag nanoparticles in solution using in situ scanning transmission electron microscopy. For the first time, we provide experimental evidence of growth rates of Ag nanoparticles in the presence of Pt in solution that are significantly faster than predicted by Lifshitz-Slyozov-Wagner theory. We attribute these observed anomalous growth rates to the synergistic effects of the catalytic properties of Pt and the electron beam itself. Transiently reduced Pt atoms servemore » as active sites for Ag ions to grow, thereby playing a key role in controlling the growth kinetics. Electron beam illumination greatly increases the local concentration of free radicals, thereby strongly influencing particle growth rate and the resulting particle morphology. Through a systematic investigation, we demonstrate the feasibility of utilizing these synergistic effects for controlling the growth rates and particle morphologies at the nanoscale. Our findings not only expand the current scope of crystal growth theory, but may also lead to a broader scientific application of nanocrystal synthesis.« less

Communication: Two-step explosion processes of highly charged fullerene cations C{sub 60}{sup q+} (q = 20–60)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamazaki, Kaoru; Nakamura, Takashi; Kanno, Manabu

2014-09-28

To establish the fundamental understanding of the fragmentation dynamics of highly positive charged nano- and bio-materials, we carried out on-the-fly classical trajectory calculations on the fragmentation dynamics of C{sub 60}{sup q+} (q = 20–60). We used the UB3LYP/3-21G level of density functional theory and the self-consistent charge density-functional based tight-binding theory. For q ≥ 20, we found that a two-step explosion mechanism governs the fragmentation dynamics: C{sub 60}{sup q+} first ejects singly and multiply charged fast atomic cations C{sup z+} (z ≥ 1) via Coulomb explosions on a timescale of 10 fs to stabilize the remaining core cluster. Thermal evaporationsmore » of slow atomic and molecular fragments from the core cluster subsequently occur on a timescale of 100 fs to 1 ps. Increasing the charge q makes the fragments smaller. This two-step mechanism governs the fragmentation dynamics in the most likely case that the initial kinetic energy accumulated upon ionization to C{sub 60}{sup q+} by ion impact or X-ray free electron laser is larger than 100 eV.« less

Quantum synchronization of quantum van der Pol oscillators with trapped ions.

PubMed

Lee, Tony E; Sadeghpour, H R

2013-12-06

The van der Pol oscillator is the prototypical self-sustained oscillator and has been used to model nonlinear behavior in biological and other classical processes. We investigate how quantum fluctuations affect phase locking of one or many van der Pol oscillators. We find that phase locking is much more robust in the quantum model than in the equivalent classical model. Trapped-ion experiments are ideally suited to simulate van der Pol oscillators in the quantum regime via sideband heating and cooling of motional modes. We provide realistic experimental parameters for 171Yb+ achievable with current technology.

Ion manipulations in structures for lossless ion manipulations (SLIM): computational evaluation of a 90° turn and a switch

DOE PAGES

Garimella, Sandilya V. B.; Ibrahim, Yehia. M.; Webb, Ian K.; ...

2015-08-19

The process of redirecting ions through 90° turns and ‘tee’ switches utilizing Structures for Lossless Ion Manipulations (SLIM) was evaluated using theoretical and simulation methods at 4 Torr pressure. SIMION simulations were used to optimize and evaluate conditions for performing turns without loss of signal intensity or ion mobility resolving power. Fundamental considerations indicated that the “race track” effect during ion turns may incur only small losses to the ion mobility resolving power at 4 Torr pressure for the typical plume widths predicted in an optimized SLIM ‘tee’ switch design. The dynamic switching of ions into orthogonal channels was alsomore » evaluated using SIMION ion trajectory simulations, and achieved similar performance. Simulation results were in close agreement with experimental results and were used to refine SLIM designs and applied potentials for their use.« less

Centrifugal acceleration of ions in the polar magnetosphere

NASA Technical Reports Server (NTRS)

Swinney, Kenneth R.; Horwitz, James L.; Delcourt, D.

1987-01-01

The transport of ionospheric ions originating near the dayside cusp into the magnetotail is parametrically studied using a 3-D model of ion trajectories. It is shown that the centrifugal term in the guiding center parallel force equation dominates the parallel motion after about 4 Re geocentric distance. The dependence of the equatorial crossing distance on initial latitude, energy and convection electric field is presented for ions originating on the dayside ionosphere in the noon-midnight plane. It is also found that up to altitudes of about 5 Re, the motion is similar to that of a bead on a rotating rod, for which a simple analytical solution exists.

Comprehensive approach to fast ion measurements in the beam-driven FRC

NASA Astrophysics Data System (ADS)

Magee, Richard; Smirnov, Artem; Onofri, Marco; Dettrick, Sean; Korepanov, Sergey; Knapp, Kurt; the TAE Team

2015-11-01

The C-2U experiment combines tangential neutral beam injection, edge biasing, and advanced recycling control to explore the sustainment of field-reversed configuration (FRC) plasmas. To study fast ion confinement in such advanced, beam-driven FRCs, a synergetic technique was developed that relies on the measurements of the DD fusion reaction products and the hybrid code Q2D, which treats the plasma as a fluid and the fast ions kinetically. Data from calibrated neutron and proton detectors are used in a complementary fashion to constrain the simulations: neutron detectors measure the volume integrated fusion rate to constrain the total number of fast ions, while proton detectors with multiple lines of sight through the plasma constrain the axial profile of fast ions. One application of this technique is the diagnosis of fast ion energy transfer and pitch angle scattering. A parametric numerical study was conducted, in which additional ad hoc loss and scattering terms of varying strengths were introduced in the code and constrained with measurement. Initial results indicate that the energy transfer is predominantly classical, while, in some cases, non-classical pitch angle scattering can be observed.

"Roll of Thunder, Hear My Cry": A Culturally Specific, Subversive Concept of Child Agency.

ERIC Educational Resources Information Center

McDowell, Kelly

2002-01-01

Presents a critique of Mildred D. Taylor's "Roll of Thunder, Hear My Cry" with regard to its positioning of the child subject. Proposes that the novel contrasts classic works of children's fiction by following a trajectory of child agency, which is enabled through the novel's racial specificity. Discusses the role of historical…

Effect Sizes for Growth-Modeling Analysis for Controlled Clinical Trials in the Same Metric as for Classical Analysis

ERIC Educational Resources Information Center

Feingold, Alan

2009-01-01

The use of growth-modeling analysis (GMA)--including hierarchical linear models, latent growth models, and general estimating equations--to evaluate interventions in psychology, psychiatry, and prevention science has grown rapidly over the last decade. However, an effect size associated with the difference between the trajectories of the…

4D BADA-based Trajectory Generator and 3D Guidance Algorithm

NASA Technical Reports Server (NTRS)

Palacios, Eduardo Sepulveda; Johnson, Marcus A.

2013-01-01

This paper presents a hybrid integration between aerodynamic, airline procedures and other BADA-based (Base of Aircraft Data) coefficients with a classical aircraft dynamic model. This paper also describes a three-dimensional guidance algorithm implemented in order to produce commands for the aircraft to follow a flight plan. The software chosen for this work is MATLAB.

A Classical Trajectory Study of the Dissociation and Isomerization of C2H5

DTIC Science & Technology

2013-01-01

modifications are possible but would be sensible only in the context of systematic ab initio calculations to provide the basis for such changes. As the... Ciudad , T.; Ramírez, R.; Schulte, J.; Böhm, M. C. Anharmonic Effects on the Structural and Vibrational Properties of the Ethyl Radical: A Path Integral

Li + solvation and kinetics of Li +–BF 4 -/PF 6 - ion pairs in ethylene carbonate. A molecular dynamics study with classical rate theories

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, Tsun-Mei; Dang, Liem X.

Using our polarizable force-field models and employing classical rate theories of chemical reactions, we examine in this paper the ethylene carbonate (EC) exchange process between the first and second solvation shells around Li + and the dissociation kinetics of ion pairs Li +–[BF 4] and Li +–[PF 6] in this solvent. We calculate the exchange rates using transition state theory and correct them with transmission coefficients computed by the reactive flux, Impey, Madden, and McDonald approaches, and Grote-Hynes theory. We found that the residence times of EC around Li + ions varied from 60 to 450 ps, depending on themore » correction method used. We found that the relaxation times changed significantly from Li +–[BF 4] to Li +–[PF 6] ion pairs in EC. Finally, our results also show that, in addition to affecting the free energy of dissociation in EC, the anion type also significantly influences the dissociation kinetics of ion pairing.« less

Ab initio molecular dynamics simulation of LiBr association in water

NASA Astrophysics Data System (ADS)

Izvekov, Sergei; Philpott, Michael R.

2000-12-01

A computationally economical scheme which unifies the density functional description of an ionic solute and the classical description of a solvent was developed. The density functional part of the scheme comprises Car-Parrinello and related formalisms. The substantial saving in the computer time is achieved by performing the ab initio molecular dynamics of the solute electronic structure in a relatively small basis set constructed from lowest energy Kohn-Sham orbitals calculated for a single anion in vacuum, instead of using plane wave basis. The methodology permits simulation of an ionic solution for longer time scales while keeping accuracy in the prediction of the solute electronic structure. As an example the association of the Li+-Br- ion-pair system in water is studied. The results of the combined molecular dynamics simulation are compared with that obtained from the classical simulation with ion-ion interaction described by the pair potential of Born-Huggins-Mayer type. The comparison reveals an important role played by the polarization of the Br- ion in the dynamics of ion pair association.

Li + solvation and kinetics of Li +–BF 4 -/PF 6 - ion pairs in ethylene carbonate. A molecular dynamics study with classical rate theories

DOE PAGES

Chang, Tsun-Mei; Dang, Liem X.

2017-07-19

Using our polarizable force-field models and employing classical rate theories of chemical reactions, we examine in this paper the ethylene carbonate (EC) exchange process between the first and second solvation shells around Li + and the dissociation kinetics of ion pairs Li +–[BF 4] and Li +–[PF 6] in this solvent. We calculate the exchange rates using transition state theory and correct them with transmission coefficients computed by the reactive flux, Impey, Madden, and McDonald approaches, and Grote-Hynes theory. We found that the residence times of EC around Li + ions varied from 60 to 450 ps, depending on themore » correction method used. We found that the relaxation times changed significantly from Li +–[BF 4] to Li +–[PF 6] ion pairs in EC. Finally, our results also show that, in addition to affecting the free energy of dissociation in EC, the anion type also significantly influences the dissociation kinetics of ion pairing.« less

Dust trajectories and diagnostic applications beyond strongly coupled dusty plasmas

NASA Astrophysics Data System (ADS)

Wang, Zhehui; Ticoş, Cǎtǎlin M.; Wurden, Glen A.

2007-10-01

Plasma interaction with dust is of growing interest for a number of reasons. On the one hand, dusty plasma research has become one of the most vibrant branches of plasma science. On the other hand, substantially less is known about dust dynamics outside the laboratory strongly coupled dusty-plasma regime, which typically corresponds to 1015m-3 electron density with ions at room temperature. Dust dynamics is also important to magnetic fusion because of concerns about safety and potential dust contamination of the fusion core. Dust trajectories are measured under two plasma conditions, both of which have larger densities and hotter ions than in typical dusty plasmas. Plasma-flow drag force, dominating over other forces in flowing plasmas, can explain the dust motion. In addition, quantitative understanding of dust trajectories is the basis for diagnostic applications using dust. Observation of hypervelocity dust in laboratory enables dust as diagnostic tool (hypervelocity dust injection) in magnetic fusion. In colder plasmas (˜10eV or less), dust with known physical and chemical properties can be used as microparticle tracers to measure both the magnitude and directions of flows in plasmas with good spatial resolution as the microparticle tracer velocimetry.

High-Voltage, High-Impedance Ion Beam Production

DTIC Science & Technology

2009-06-01

the anode tube with a loosely-crumpled, thin aluminized- mylar foil. This spoils the virtual cathode and greatly reduces the neutron signal, as seen...ions follow ballistic (straight-line) trajectories in the drift tube (see Sec. VIII), then (except for the small displacement associated with bending...mTorr) ambient in the drift tube . Based on our previous experience, we would expect charge, but not necessarily current, neutralization of the beam

Coherent phase control of internal conversion in pyrazine

NASA Astrophysics Data System (ADS)

Gordon, Robert J.; Hu, Zhan; Seideman, Tamar; Singha, Sima; Sukharev, Maxim; Zhao, Youbo

2015-04-01

Shaped ultrafast laser pulses were used to study and control the ionization dynamics of electronically excited pyrazine in a pump and probe experiment. For pump pulses created without feedback from the product signal, the ion growth curve (the parent ion signal as a function of pump/probe delay) was described quantitatively by the classical rate equations for internal conversion of the S2 and S1 states. Very different, non-classical behavior was observed when a genetic algorithm (GA) employing phase-only modulation was used to minimize the ion signal at some pre-determined target time, T. Two qualitatively different control mechanisms were identified for early (T < 1.5 ps) and late (T > 1.5 ps) target times. In the former case, the ion signal was largely suppressed for t < T, while for t ≫ T, the ion signal produced by the GA-optimized pulse and a transform limited (TL) pulse coalesced. In contrast, for T > 1.5 ps, the ion growth curve followed the classical rate equations for t < T, while for t ≫ T, the quantum yield for the GA-optimized pulse was much smaller than for a TL pulse. We interpret the first type of behavior as an indication that the wave packet produced by the pump laser is localized in a region of the S2 potential energy surface where the vertical ionization energy exceeds the probe photon energy, whereas the second type of behavior may be described by a reduced absorption cross section for S0 → S2 followed by incoherent decay of the excited molecules. Amplitude modulation observed in the spectrum of the shaped pulse may have contributed to the control mechanism, although this possibility is mitigated by the very small focal volume of the probe laser.

Entangling spin-spin interactions of ions in individually controlled potential wells

NASA Astrophysics Data System (ADS)

Wilson, Andrew; Colombe, Yves; Brown, Kenton; Knill, Emanuel; Leibfried, Dietrich; Wineland, David

2014-03-01

Physical systems that cannot be modeled with classical computers appear in many different branches of science, including condensed-matter physics, statistical mechanics, high-energy physics, atomic physics and quantum chemistry. Despite impressive progress on the control and manipulation of various quantum systems, implementation of scalable devices for quantum simulation remains a formidable challenge. As one approach to scalability in simulation, here we demonstrate an elementary building-block of a configurable quantum simulator based on atomic ions. Two ions are trapped in separate potential wells that can individually be tailored to emulate a number of different spin-spin couplings mediated by the ions' Coulomb interaction together with classical laser and microwave fields. We demonstrate deterministic tuning of this interaction by independent control of the local wells and emulate a particular spin-spin interaction to entangle the internal states of the two ions with 0.81(2) fidelity. Extension of the building-block demonstrated here to a 2D-network, which ion-trap micro-fabrication processes enable, may provide a new quantum simulator architecture with broad flexibility in designing and scaling the arrangement of ions and their mutual interactions. This research was funded by the Office of the Director of National Intelligence (ODNI), Intelligence Advanced Research Projects Activity (IARPA), ONR, and the NIST Quantum Information Program.

Minimized state complexity of quantum-encoded cryptic processes

NASA Astrophysics Data System (ADS)

Riechers, Paul M.; Mahoney, John R.; Aghamohammadi, Cina; Crutchfield, James P.

2016-05-01

The predictive information required for proper trajectory sampling of a stochastic process can be more efficiently transmitted via a quantum channel than a classical one. This recent discovery allows quantum information processing to drastically reduce the memory necessary to simulate complex classical stochastic processes. It also points to a new perspective on the intrinsic complexity that nature must employ in generating the processes we observe. The quantum advantage increases with codeword length: the length of process sequences used in constructing the quantum communication scheme. In analogy with the classical complexity measure, statistical complexity, we use this reduced communication cost as an entropic measure of state complexity in the quantum representation. Previously difficult to compute, the quantum advantage is expressed here in closed form using spectral decomposition. This allows for efficient numerical computation of the quantum-reduced state complexity at all encoding lengths, including infinite. Additionally, it makes clear how finite-codeword reduction in state complexity is controlled by the classical process's cryptic order, and it allows asymptotic analysis of infinite-cryptic-order processes.

Mixed quantum-classical simulations of the vibrational relaxation of photolyzed carbon monoxide in a hemoprotein

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schubert, Alexander, E-mail: schubert@irsamc.ups-tlse.fr; Meier, Christoph; Falvo, Cyril

2016-08-07

We present mixed quantum-classical simulations on relaxation and dephasing of vibrationally excited carbon monoxide within a protein environment. The methodology is based on a vibrational surface hopping approach treating the vibrational states of CO quantum mechanically, while all remaining degrees of freedom are described by means of classical molecular dynamics. The CO vibrational states form the “surfaces” for the classical trajectories of protein and solvent atoms. In return, environmentally induced non-adiabatic couplings between these states cause transitions describing the vibrational relaxation from first principles. The molecular dynamics simulation yields a detailed atomistic picture of the energy relaxation pathways, taking themore » molecular structure and dynamics of the protein and its solvent fully into account. Using the ultrafast photolysis of CO in the hemoprotein FixL as an example, we study the relaxation of vibrationally excited CO and evaluate the role of each of the FixL residues forming the heme pocket.« less

Generalized Heisenberg Algebras, SUSYQM and Degeneracies: Infinite Well and Morse Potential

NASA Astrophysics Data System (ADS)

Hussin, Véronique; Marquette, Ian

2011-03-01

We consider classical and quantum one and two-dimensional systems with ladder operators that satisfy generalized Heisenberg algebras. In the classical case, this construction is related to the existence of closed trajectories. In particular, we apply these results to the infinite well and Morse potentials. We discuss how the degeneracies of the permutation symmetry of quantum two-dimensional systems can be explained using products of ladder operators. These products satisfy interesting commutation relations. The two-dimensional Morse quantum system is also related to a generalized two-dimensional Morse supersymmetric model. Arithmetical or accidental degeneracies of such system are shown to be associated to additional supersymmetry.

Electrical shielding box measurement of the negative hydrogen beam from Penning ion gauge ion source.

PubMed

Wang, T; Yang, Z; Dong, P; long, J D; He, X Z; Wang, X; Zhang, K Z; Zhang, L W

2012-06-01

The cold-cathode Penning ion gauge (PIG) type ion source has been used for generation of negative hydrogen (H(-)) ions as the internal ion source of a compact cyclotron. A novel method called electrical shielding box dc beam measurement is described in this paper, and the beam intensity was measured under dc extraction inside an electrical shielding box. The results of the trajectory simulation and dc H(-) beam extraction measurement were presented. The effect of gas flow rate, magnetic field strength, arc current, and extraction voltage were also discussed. In conclusion, the dc H(-) beam current of about 4 mA from the PIG ion source with the puller voltage of 40 kV and arc current of 1.31 A was extrapolated from the measurement at low extraction dc voltages.

Cherry-picking functionally relevant substates from long md trajectories using a stratified sampling approach.

PubMed

Chandramouli, Balasubramanian; Mancini, Giordano

2016-01-01

Classical Molecular Dynamics (MD) simulations can provide insights at the nanoscopic scale into protein dynamics. Currently, simulations of large proteins and complexes can be routinely carried out in the ns-μs time regime. Clustering of MD trajectories is often performed to identify selective conformations and to compare simulation and experimental data coming from different sources on closely related systems. However, clustering techniques are usually applied without a careful validation of results and benchmark studies involving the application of different algorithms to MD data often deal with relatively small peptides instead of average or large proteins; finally clustering is often applied as a means to analyze refined data and also as a way to simplify further analysis of trajectories. Herein, we propose a strategy to classify MD data while carefully benchmarking the performance of clustering algorithms and internal validation criteria for such methods. We demonstrate the method on two showcase systems with different features, and compare the classification of trajectories in real and PCA space. We posit that the prototype procedure adopted here could be highly fruitful in clustering large trajectories of multiple systems or that resulting especially from enhanced sampling techniques like replica exchange simulations. Copyright: © 2016 by Fabrizio Serra editore, Pisa · Roma.

The Wigner distribution and 2D classical maps

NASA Astrophysics Data System (ADS)

Sakhr, Jamal

2017-07-01

The Wigner spacing distribution has a long and illustrious history in nuclear physics and in the quantum mechanics of classically chaotic systems. In this paper, a novel connection between the Wigner distribution and 2D classical mechanics is introduced. Based on a well-known correspondence between the Wigner distribution and the 2D Poisson point process, the hypothesis that typical pseudo-trajectories of a 2D ergodic map have a Wignerian nearest-neighbor spacing distribution (NNSD) is put forward and numerically tested. The standard Euclidean metric is used to compute the interpoint spacings. In all test cases, the hypothesis is upheld, and the range of validity of the hypothesis appears to be robust in the sense that it is not affected by the presence or absence of: (i) mixing; (ii) time-reversal symmetry; and/or (iii) dissipation.

Molecular Studies of Complex Soil Organic Matter Interactions with Metal Ions and Mineral Surfaces using Classical Molecular Dynamics and Quantum Chemistry Methods

NASA Astrophysics Data System (ADS)

Andersen, A.; Govind, N.; Laskin, A.

2017-12-01

Mineral surfaces have been implicated as potential protectors of soil organic matter (SOM) against decomposition and ultimate mineralization to small molecules which can provide nutrients for plants and soil microbes and can also contribute to the Earth's elemental cycles. SOM is a complex mixture of organic molecules of biological origin at varying degrees of decomposition and can, itself, self-assemble in such a way as to expose some biomolecule types to biotic and abiotic attack while protecting other biomolecule types. The organization of SOM and SOM with mineral surfaces and solvated metal ions is driven by an interplay of van der Waals and electrostatic interactions leading to partitioning of hydrophilic (e.g. sugars) and hydrophobic (e.g., lipids) SOM components that can be bridged with amphiphilic molecules (e.g., proteins). Classical molecular dynamics simulations can shed light on assemblies of organic molecules alone or complexation with mineral surfaces. The role of chemical reactions is also an important consideration in potential chemical changes of the organic species such as oxidation/reduction, degradation, chemisorption to mineral surfaces, and complexation with solvated metal ions to form organometallic systems. For the study of chemical reactivity, quantum chemistry methods can be employed and combined with structural insight provided by classical MD simulations. Moreover, quantum chemistry can also simulate spectroscopic signatures based on chemical structure and is a valuable tool in interpreting spectra from, notably, x-ray absorption spectroscopy (XAS). In this presentation, we will discuss our classical MD and quantum chemistry findings on a model SOM system interacting with mineral surfaces and solvated metal ions.

Dynamics of a reconnection-driven runaway ion tail in a reversed field pinch plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderson, J. K., E-mail: jkanders@wisc.edu; Kim, J.; Bonofiglo, P. J.

2016-05-15

While reconnection-driven ion heating is common in laboratory and astrophysical plasmas, the underlying mechanisms for converting magnetic to kinetic energy remain not fully understood. Reversed field pinch discharges are often characterized by rapid ion heating during impulsive reconnection, generating an ion distribution with an enhanced bulk temperature, mainly perpendicular to magnetic field. In the Madison Symmetric Torus, a subset of discharges with the strongest reconnection events develop a very anisotropic, high energy tail parallel to magnetic field in addition to bulk perpendicular heating, which produces a fusion neutron flux orders of magnitude higher than that expected from a Maxwellian distribution.more » Here, we demonstrate that two factors in addition to a perpendicular bulk heating mechanism must be considered to explain this distribution. First, ion runaway can occur in the strong parallel-to-B electric field induced by a rapid equilibrium change triggered by reconnection-based relaxation; this effect is particularly strong on perpendicularly heated ions which experience a reduced frictional drag relative to bulk ions. Second, the confinement of ions varies dramatically as a function of velocity. Whereas thermal ions are governed by stochastic diffusion along tearing-altered field lines (and radial diffusion increases with parallel speed), sufficiently energetic ions are well confined, only weakly affected by a stochastic magnetic field. High energy ions traveling mainly in the direction of toroidal plasma current are nearly classically confined, while counter-propagating ions experience an intermediate confinement, greater than that of thermal ions but significantly less than classical expectations. The details of ion confinement tend to reinforce the asymmetric drive of the parallel electric field, resulting in a very asymmetric, anisotropic distribution.« less

Precise determination of water exchanges on a mineral surface

DOE PAGES

Stack, Andrew G.; Borreguero, Jose M.; Prisk, Timothy R.; ...

2016-10-03

Solvent exchanges on solid surfaces and dissolved ions are a fundamental property important for understanding chemical reactions, but the rates of fast exchanges are poorly constrained. In this paper, we probed the diffusional motions of water adsorbed onto nanoparticles of the mineral barite (BaSO 4) using quasi-elastic neutron scattering (QENS) and classical molecular dynamics (MD) to reveal the complex dynamics of water exchange along mineral surfaces. QENS data as a function of temperature and momentum transfer (Q) were fit using scattering functions derived from MD trajectories. The simulations reproduce the dynamics measured in the experiments at ambient temperatures, but asmore » temperature is lowered the simulations overestimate slower motions. Decomposition of the MD-computed QENS intensity into contributions from adsorbed and unbound water shows that the majority of the signal arises from adsorbed species, although the dynamics of unbound water cannot be dismissed. The mean residence times of water on each of the four surface sites present on the barite {001} were calculated using MD: at room temperature the low barium site is 194 ps, whereas the high barium site contains two distributions of motions at 84 and 2.5 ps. These contrast to 13 ps residence time on both sulfate sites, with an additional surface diffusion exchange of 66 ps. Surface exchanges are similar to those of the aqueous ions calculated using the same force field: Ba aq 2+ is 208 ps and SO 4aq 2- is 5.8 ps. Finally, this work demonstrates how MD can be a reliable method to deconvolute solvent exchange reactions when quantitatively validated by QENS measurements.« less

Atomic Scale Imaging of Nucleation and Growth Trajectories of an Interfacial Bismuth Nanodroplet.

PubMed

Li, Yingxuan; Bunes, Benjamin R; Zang, Ling; Zhao, Jie; Li, Yan; Zhu, Yunqing; Wang, Chuanyi

2016-02-23

Because of the lack of experimental evidence, much confusion still exists on the nucleation and growth dynamics of a nanostructure, particularly of metal. The situation is even worse for nanodroplets because it is more difficult to induce the formation of a nanodroplet while imaging the dynamic process with atomic resolution. Here, taking advantage of an electron beam to induce the growth of Bi nanodroplets on a SrBi2Ta2O9 platelet under a high resolution transmission electron microscope (HRTEM), we directly observed the detailed growth pathways of Bi nanodroplets from the earliest stage of nucleation that were previously inaccessible. Atomic scale imaging reveals that the dynamics of nucleation involves a much more complex trajectory than previously predicted based on classical nucleation theory (CNT). The monatomic Bi layer was first formed in the nucleation process, which induced the formation of the prenucleated clusters. Following that, critical nuclei for the nanodroplets formed both directly from the addition of atoms to the prenucleated clusters by the classical growth process and indirectly through transformation of an intermediate liquid film based on the Stranski-Krastanov growth mode, in which the liquid film was induced by the self-assembly of the prenucleated clusters. Finally, the growth of the Bi nanodroplets advanced through the classical pathway and sudden droplet coalescence. This study allows us to visualize the critical steps in the nucleation process of an interfacial nanodroplet, which suggests a revision of the perspective of CNT.

Influence of asymmetries in the magnetic draping pattern at Titan on the emission of energetic neutral atoms

NASA Astrophysics Data System (ADS)

Kabanovic, Slawa; Feyerabend, Moritz; Simon, Sven; Meeks, Zachary; Wulms, Veit

2018-03-01

We model the emission of energetic neutral atoms (ENAs) that are generated by the interaction between energetic ions from Saturn's magnetosphere and neutrals from the upper atmosphere of the giant planet's largest moon Titan. The trajectories of the parent ions and the resulting ENA emission morphology are highly sensitive to the electromagnetic field configuration near the moon. We therefore compare the ENA emission pattern for spatially homogeneous fields to the emission obtained from a magnetohydrodynamic (MHD) and a hybrid (kinetic ions, fluid electrons) model of Titan's magnetospheric interaction, by computing the trajectories of several billion energetic test particles. While the MHD model takes into account the draping of the magnetic field lines around Titan, the hybrid approach also considers the significant asymmetries in the electromagnetic fields due to the large gyroradii of pick-up ions from Titan's ionosphere. In all three models, the upstream parameters correspond to the conditions during Cassini's TA flyby of Titan. The shape, magnitude, and location of the ENA emission maxima vary considerably between these three field configurations. The magnetic pile-up region at Titan's ramside deflects a large number of the energetic parent ions, thereby reducing the ENA flux. However, the draped magnetic field lines in Titan's lobes rotate the gyration planes of the incident energetic ions, thereby facilitating the observable ENA production. Overall, the ENA flux calculated for the MHD model is weaker than the emission obtained for the electromagnetic fields from the hybrid code. In addition, we systematically investigate the dependency of the ENA emission morphology on the energy of the parent ions and on the upstream magnetic field strength.

Ion Kinetics in Silane Plasmas

DTIC Science & Technology

1988-02-01

stimulated emission. Rg2 + is then a classical excimer laser scheme which ought to apply generally to the homonuclear and heteronuclear rare- gas dimer...kinetics of ion formation by electron impact and subsequent reaction in silane:noble- gas mixtures have been examined using pulsed ion cyclotron reso...charge transfer reactions such as X + + SiH4 -- SiH + + X + (4 - n)(H, H2) where X+ is a rare- gas or s:licon-hydride ion. Room-temperature rate constants

Ion kinematics in a plasma focus.

NASA Technical Reports Server (NTRS)

Gary, S. P.; Hohl, F.

1973-01-01

The results of numerical integrations of three-dimensional equations of motion of ions subject to given electric and magnetic fields are presented. The fields represent those which may exist in the pinch phase of the plasma focus, although here they depend only on the radial coordinate. The ions initially have Maxwellian velocity distributions, and their trajectories are interpreted in terms of single-particle constants of the motion. Two models of the axial electric field Ez are considered. For strong Ez away from the axis, there is a cyclotron acceleration which leads to ion heating. For positive Ez on the axis, ions within a Larmor radius of the axis undergo very efficient acceleration; the results for this new model are in general agreement with experimental results.

Revealing dynamically-organized receptor ion channel clusters in live cells by a correlated electric recording and super-resolution single-molecule imaging approach.

PubMed

Yadav, Rajeev; Lu, H Peter

2018-03-28

The N-methyl-d-aspartate (NMDA) receptor ion-channel is activated by the binding of ligands, along with the application of action potential, important for synaptic transmission and memory functions. Despite substantial knowledge of the structure and function, the gating mechanism of the NMDA receptor ion channel for electric on-off signals is still a topic of debate. We investigate the NMDA receptor partition distribution and the associated channel's open-close electric signal trajectories using a combined approach of correlating single-molecule fluorescence photo-bleaching, single-molecule super-resolution imaging, and single-channel electric patch-clamp recording. Identifying the compositions of NMDA receptors, their spatial organization and distributions over live cell membranes, we observe that NMDA receptors are organized inhomogeneously: nearly half of the receptor proteins are individually dispersed; whereas others exist in heterogeneous clusters of around 50 nm in size as well as co-localized within the diffraction limited imaging area. We demonstrate that inhomogeneous interactions and partitions of the NMDA receptors can be a cause of the heterogeneous gating mechanism of NMDA receptors in living cells. Furthermore, comparing the imaging results with the ion-channel electric current recording, we propose that the clustered NMDA receptors may be responsible for the variation in the current amplitude observed in the on-off two-state ion-channel electric signal trajectories. Our findings shed new light on the fundamental structure-function mechanism of NMDA receptors and present a conceptual advancement of the ion-channel mechanism in living cells.

Preliminary Interpretation of Titan Plasma Interaction as Observed by the Cassini Plasma Spectrometer: Comparisons With Voyager 1

NASA Technical Reports Server (NTRS)

Hartle, R. E.; Sittler, E. C.; Johnson, R. E.; Simpson, D. G.; Smith, H. T.; Crary, F.; McComas, D. J.; Young, D. T.; Coates, A. J.; Neubauer, F. M.

2005-01-01

The Cassini Plasma Spectrometer (CAPS) instrument made measurements of Titan s plasma environment when the Cassini Orbiter flew through the moon s plasma wake October 26,2004 (flyby TA) and December 13,2004 (flyby TB). Preliminary CAPS ion and electron measurements from these encounters (1,2) are compared with measurements made by the Voyager I Plasma Science Instrument (PLS). The comparisons are used to evaluate previous interpretations and predictions of the Titan plasma environment that have been made using PLS measurements (3,4). The plasma wake trajectories of flybys TA, TB and Voyager 1 are similar because they occurred when Titan was near Saturn s local noon. These similarities make possible direct, meaningful comparisons between the various plasma wake measurements. The inquiries stimulated by the previous interpretations and predictions made using PLS data have produced the following results from the CAPS ion measurements: A) The major ambient ion components of Saturn s rotating magnetosphere in the vicinity of Titan are H+, H2+, and O+. B) Finite gyroradius effects are apparent in ambient 0 as the result of its interaction with Titan s atmosphere. C) The principal pickup ions are composed of H+, H2+, CH4+ and N2+. D) There is clear evidence of slowing down of the ambient plasma due to pickup ion mass loading; and, as the ionopause is approached, heavier pickup ions such as N2+ become dominant. The similarities and differences between the magnitudes and structures of the electron densities and temperatures along the three flyby trajectories are described

Changes in atmospheric chemical composition determined from ice core records in southwestern Siberia during the twentieth century

NASA Astrophysics Data System (ADS)

Joswiak, Daniel R.

The presented research includes analysis and interpretation of the upper 50 m of a deep ice core which was drilled at 49°48'22"N, 86°33'52" (4115 m.a.s.l.) on the Belukha Plateau, Altai, in southwestern Siberia. The main goal was to examine variability of geochemical records preserved in the ice in relation to climatic and environmental changes; and to determine the main aerosol sources using ground- and upper-level meteorological data. Ion chromatography was used to determine concentrations of anions (SO4, NO3, NO2, Cl), cations (NH4, Ca, K, Mg, Na), the carboxylic (organic) acids acetate (CH3COOH), formate (HCOOH), oxalate (C2O4), and methanesulfonic acid (CH3SO 3H). Major ion concentrations were dominated by sulfate (30.3%), nitrate (18.1%), formate (15.0%), and ammonium (12.4%). Highest concentrations were observed for sulfate; over 1460 ppb. Laser particle counting was used to determine size resolved number concentrations of particles ranging from 0.5 to 16.0 mum. Logarithmic distribution of particles was observed, with over 90% of the particle number concentration coming from particles less than 1.4 mum. Particle mass, calculated from the number concentration, revealed the greatest contribution (59%) to mass arrived with medium size particles (4.0-8.0 microm). Back-trajectories were modeled using NOAA's Hyplit model were modeled for the four days of maximum annual precipitation during a year of increased (1991) and decreased (1990) ion and particle concentrations. Principle components factor analysis was used to determine the main aerosol sources. The upper 50 m covers the time period from 1917 to 2002. Glacier flow models indicated the full depth of 170 m should provide over 1000 years of records. Insoluble particle concentrations preserved in the ice core were affected mainly by climatic conditions including precipitation regimes and wind speed variability. The small size particles (0.5-1.0 mm) are transported inter-continentally and associated with background atmospheric concentrations in the middle-troposphere. The large size particles (4.0-16.0 mum) are deposited from the atmosphere rapidly compared to small particles and were transported to high elevations from the central Asian desert sources. All size particles were found to be negatively correlated with average monthly temperatures indicating low temperatures during the dry particle deposition. During the first half of the 20th Century, soluble ions were dominated by organic acids; indicating mainly natural sources from vegetation and biomass burning. Ion profiles associated with human activities such as fuel combustion (SO4, NO3) significantly increased in concentration from the mid-1950s; coinciding with population growth in large industrialized cities upwind from the study location. Highest correlations between major ions and the ground and upper level wind speed were observed for SO4, indicating long-range transport of pollution to the Altai Mountains. Ion profiles associated with central Asian dust (Ca, Mg) and with sea salt aerosols (Na, Cl) were mainly influenced by climatic factors, and average concentrations did not significantly change during the 20th Century. Factor analysis revealed that ions typically associated with biomass burning (NH4, K) were not resolvable as indicators of separate aerosol source. The organic acid components better preserve forest fire signatures at this study location. The back-trajectories exhibited several notable differences in transport paths of air masses. The trajectories modeled for 1991 show a farther transport distance with significant time of transfer over heavily populated regions of Europe and Russia. The modeled back-trajectories over the Middle-East on two heaviest precipitation days in 1991 provided evidence of the large oil fires in Kuwait, appeared as increased concentrations in sulfate, nitrate, and organic acids. The modeled back-trajectories for 1990 show more localized transport paths or transport over sparsely populated Arctic and Polar Regions. Correlations were not found between the ice core geochemistry and the upper-level wind direction, illustrating the greater importance of the pathways of air masses arriving to the study location. Event-scale modeling of air mass back-trajectories showed a prospective method in determination of transport and source of pollutants preserved in snow and ice.

Trajectory Optimization of an Interstellar Mission Using Solar Electric Propulsion

NASA Technical Reports Server (NTRS)

Kluever, Craig A.

1996-01-01

This paper presents several mission designs for heliospheric boundary exploration using spacecraft with low-thrust ion engines as the primary mode of propulsion The mission design goal is to transfer a 200-kg spacecraft to the heliospheric boundary in minimum time. The mission design is a combined trajectory and propulsion system optimization problem. Trajectory design variables include launch date, launch energy, burn and coast arc switch times, thrust steering direction, and planetary flyby conditions. Propulsion system design parameters include input power and specific impulse. Both SEP and NEP spacecraft arc considered and a wide range of launch vehicle options are investigated. Numerical results are presented and comparisons with the all chemical heliospheric missions from Ref 9 are made.

Trajectory Design for the Lunar Polar Hydrogen Mapper Mission

NASA Technical Reports Server (NTRS)

Genova, Anthony L.; Dunham, David W.

2017-01-01

The presented trajectory was designed for the Lunar Polar Hydrogen Mapper (LunaH-Map) 6U CubeSat, which was awarded a ride on NASAs Space Launch System (SLS) with Exploration Mission 1 (EM-1) via NASAs 2015 SIMPLEX proposal call. After deployment from EM-1s upper stage (which is planned to enter heliocentric space via a lunar flyby), the LunaH-Map CubeSat will alter its trajectory via its low-thrust ion engine to target a lunar flyby that yields a Sun-Earth-Moon weak stability boundary transfer to set up a ballistic lunar capture. Finally, the orbit energy is lowered to reach the required quasi-frozen science orbit with periselene above the lunar south pole.

Nonlinear electronic stopping power of channeled slow light ions in ZnSe: Evidence of energy loss caused by formation and breaking of chemical bond

NASA Astrophysics Data System (ADS)

Li, Chang-kai; Wang, Feng; Gao, Cong-Zhang; Liao, Bin; Ouyang, Xiao-ping; Zhang, Feng-Shou

2018-07-01

Electronic stopping power of helium ions in a semiconductor material ZnSe has been investigated through non-adiabatic dynamics simulations at energies of a few keV under channeling condition. The stopping power is predicted to be proportional to velocity for the trajectory along middle axis of a 〈 1 1 0 〉 channel, as expected for the linear response theory accounts for election-hole pair creation. While for the off-center channeling trajectory, a counterintuitive of electronic stopping power versus velocity is observed. Our study, presented herein, finds a non-trivial connection between charge transfer and the force experienced by the projectile. Charge transfer can produce, throughout the collision process, additional force by continuously forming and breaking instantaneous chemical bonds between the projectile and the neighboring host atoms.

Charged particle tracking at Titan, and further applications

NASA Astrophysics Data System (ADS)

Bebesi, Zsofia; Erdos, Geza; Szego, Karoly

2016-04-01

We use the CAPS ion data of Cassini to investigate the dynamics and origin of Titan's atmospheric ions. We developed a 4th order Runge-Kutta method to calculate particle trajectories in a time reversed scenario. The test particle magnetic field environment imitates the curved magnetic environment in the vicinity of Titan. The minimum variance directions along the S/C trajectory have been calculated for all available Titan flybys, and we assumed a homogeneous field that is perpendicular to the minimum variance direction. Using this method the magnetic field lines have been calculated along the flyby orbits so we could select those observational intervals when Cassini and the upper atmosphere of Titan were magnetically connected. We have also taken the Kronian magnetodisc into consideration, and used different upstream magnetic field approximations depending on whether Titan was located inside of the magnetodisc current sheet, or in the lobe regions. We also discuss the code's applicability to comets.

Real-time evolution of non-Gaussian cumulants in the QCD critical regime

NASA Astrophysics Data System (ADS)

Mukherjee, Swagato; Venugopalan, Raju; Yin, Yi

2015-09-01

We derive a coupled set of equations that describe the nonequilibrium evolution of cumulants of critical fluctuations for spacetime trajectories on the crossover side of the QCD phase diagram. In particular, novel expressions are obtained for the nonequilibrium evolution of non-Gaussian skewness and kurtosis cumulants. UBy utilizing a simple model of the spacetime evolution of a heavy-ion collision, we demonstrate that, depending on the relaxation rate of critical fluctuations, skewness and kurtosis can differ significantly in magnitude as well as in sign from equilibrium expectations. Memory effects are important and shown to persist even for trajectories that skirt the edge of the critical regime. We use phenomenologically motivated parametrizations of freeze-out curves and of the beam-energy dependence of the net baryon chemical potential to explore the implications of our model study for the critical-point search in heavy-ion collisions.

Ion radial diffusion in an electrostatic impulse model for stormtime ring current formation

NASA Technical Reports Server (NTRS)

Chen, Margaret W.; Schulz, Michael; Lyons, Larry R.; Gorney, David J.

1992-01-01

Two refinements to the quasi-linear theory of ion radial diffusion are proposed and examined analytically with simulations of particle trajectories. The resonance-broadening correction by Dungey (1965) is applied to the quasi-linear diffusion theory by Faelthammar (1965) for an individual model storm. Quasi-linear theory is then applied to the mean diffusion coefficients resulting from simulations of particle trajectories in 20 model storms. The correction for drift-resonance broadening results in quasi-linear diffusion coefficients with discrepancies from the corresponding simulated values that are reduced by a factor of about 3. Further reductions in the discrepancies are noted following the averaging of the quasi-linear diffusion coefficients, the simulated coefficients, and the resonance-broadened coefficients for the 20 storms. Quasi-linear theory provides good descriptions of particle transport for a single storm but performs even better in conjunction with the present ensemble-averaging.

Real time evolution of non-Gaussian cumulants in the QCD critical regime

DOE PAGES

Mukherjee, Swagato; Venugopalan, Raju; Yin, Yi

2015-09-23

In this study, we derive a coupled set of equations that describe the nonequilibrium evolution of cumulants of critical fluctuations for spacetime trajectories on the crossover side of the QCD phase diagram. In particular, novel expressions are obtained for the nonequilibrium evolution of non-Gaussian skewness and kurtosis cumulants. UBy utilizing a simple model of the spacetime evolution of a heavy-ion collision, we demonstrate that, depending on the relaxation rate of critical fluctuations, skewness and kurtosis can differ significantly in magnitude as well as in sign from equilibrium expectations. Memory effects are important and shown to persist even for trajectories thatmore » skirt the edge of the critical regime. We use phenomenologically motivated parametrizations of freeze-out curves and of the beam-energy dependence of the net baryon chemical potential to explore the implications of our model study for the critical-point search in heavy-ion collisions.« less

EUROPA Multiple-Flyby Trajectory Design

NASA Technical Reports Server (NTRS)

Buffington, Brent; Campagnola, Stefano; Petropoulos, Anastassios

2012-01-01

As reinforced by the 2011 NRC Decadal Survey, Europa remains one of the most scientifically intriguing targets in planetary science due to its potential suitability for life. However, based on JEO cost estimates and current budgetary constraints, the Decadal Survey recommended-and later directed by NASA Headquarters-a more affordable pathway to Europa exploration be derived. In response, a flyby-only proof-of-concept trajectory has been developed to investigate Europa. The trajectory, enabled by employing a novel combination of new mission design techniques, successfully fulfills a set of Science Definition Team derived scientific objectives carried out by a notional payload including ice penetrating radar, topographic imaging, and short wavelength infrared observations, and ion neutral mass spectrometry in-situ measurements. The current baseline trajectory, referred to as 11-F5, consists of 34 Europa and 9 Ganymede flybys executed over the course of 2.4 years, reached a maximum inclination of 15 degrees, has a deterministic delta v of 157 m/s (post-PJR), and has a total ionizing dose of 2.06 Mrad (Si behind 100 mil Al, spherical shell). The 11-F5 trajectory and more generally speaking, flyby-only trajectories-exhibit a number of potential advantages over an Europa orbiter mission.

Nuclear quantum effects in water exchange around lithium and fluoride ions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wilkins, David M.; Manolopoulos, David; Dang, Liem X.

2015-02-14

We employ classical and ring polymer molecular dynamics simulations to study the effect of nuclear quantum fluctuations on the structure and the water exchange dynamics of aqueous solutions of lithium and fluoride ions. While we obtain reasonably good agreement with experimental data for solutions of lithium by augmenting the Coulombic interactions between the ion and the water molecules with a standard Lennard-Jones ion-oxygen potential, the same is not true for solutions of fluoride, for which we find that a potential with a softer repulsive wall gives much better agreement. A small degree of destabilization of the first hydration shell ismore » found in quantum simulations of both ions when compared with classical simulations, with the shell becoming less sharply defined and the mean residence time of the water molecules in the shell decreasing. In line with these modest differences, we find that the mechanisms of the water exchange reactions are unaffected by quantization, so a classical description of these reactions gives qualitatively correct and quantitatively reasonable results. We also find that the quantum effects in solutions of lithium are larger than in solutions of fluoride. This is partly due to the stronger interaction of lithium with water molecules, partly due to the lighter mass of lithium, and partly due to competing quantum effects in the hydration of fluoride, which are absent in the hydration of lithium. LXD was supported by US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences.« less

[Chemical characteristics of precipitation in South China Sea].

PubMed

Xiao, Hong-Wei; Long, Ai-Min; Xie, Lu-Hua; Xiao, Hua-Yun; Liu, Cong-Qiang

2014-02-01

Rainwater samples were collected in the summer on "Shiyan 3" during the 2012 South China Sea Sectional Scientific Survey. The concentrations of anion and cation, and pH in precipitation were determined and backward trajectories of air mass were simulated to analyze the chemical characteristics of ions and examine the source of ions. The results indicated that the mean pH value of precipitation was 6.3, with 5.6 of minimal value in summer in South China Sea. The order of anion and cation abundance was Cl(-) > S04(2-) > NO3(-) and Na(+) > Mg(2+) > Ca(2+) > K(+). Cl(-) was the major anion and Na(+) was the major cation, with concentrations of 2 637.5 microeq x L(-1) and 2095.5 microeq x L(-1), respectively, showing that they were the characteristics of marine atmospheric precipitation. There was a good linear relationship between each pair of 7 ions, with correlation coefficient above 0.9, suggesting that they may have a common source. However, the correlation coefficients were lower between NO3(-) and other ions than the others, suggesting that NO3(-) had more complex sources. The concentrations of Ca(2+) and K(+) in precipitation may be related to coral environment in South China Sea. The backward trajectories in 6 stations showed that the air mass was from south and southwest of South China Sea, without passing through above the continent. These results suggested that precipitation affected by human ion source can be ignored in summer in South China Sea.

Comparison of Molecular Dynamics with Classical Density Functional and Poisson–Boltzmann Theories of the Electric Double Layer in Nanochannels

PubMed Central

2012-01-01

Comparisons are made among Molecular Dynamics (MD), Classical Density Functional Theory (c-DFT), and Poisson–Boltzmann (PB) modeling of the electric double layer (EDL) for the nonprimitive three component model (3CM) in which the two ion species and solvent molecules are all of finite size. Unlike previous comparisons between c-DFT and Monte Carlo (MC), the present 3CM incorporates Lennard-Jones interactions rather than hard-sphere and hard-wall repulsions. c-DFT and MD results are compared over normalized surface charges ranging from 0.2 to 1.75 and bulk ion concentrations from 10 mM to 1 M. Agreement between the two, assessed by electric surface potential and ion density profiles, is found to be quite good. Wall potentials predicted by PB begin to depart significantly from c-DFT and MD for charge densities exceeding 0.3. Successive layers are observed to charge in a sequential manner such that the solvent becomes fully excluded from each layer before the onset of the next layer. Ultimately, this layer filling phenomenon results in fluid structures, Debye lengths, and electric surface potentials vastly different from the classical PB predictions. PMID:23316120

Thermodynamics of Small Alkali Metal Halide Cluster Ions: Comparison of Classical Molecular Simulations with Experiment and Quantum Chemistry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vlcek, Lukas; Uhlik, Filip; Moucka, Filip

We evaluate the ability of selected classical molecular models to describe the thermodynamic and structural aspects of gas-phase hydration of alkali halide ions and the formation of small water clusters. To understand the effect of many-body interactions (polarization) and charge penetration effects on the accuracy of a force field, we perform Monte Carlo simulations with three rigid water models using different functional forms to account for these effects: (i) point charge non-polarizable SPC/E, (ii) Drude point charge polarizable SWM4- DP, and (iii) Drude Gaussian charge polarizable BK3. Model predictions are compared with experimental Gibbs free energies and enthalpies of ionmore » hydration, and with microscopic structural properties obtained from quantum DFT calculations. We find that all three models provide comparable predictions for pure water clusters and cation hydration, but differ significantly in their description of anion hydration. None of the investigated classical force fields can consistently and quantitatively reproduce the experimental gas phase hydration thermodynamics. The outcome of this study highlights the relation between the functional form that describes the effective intermolecular interactions and the accuracy of the resulting ion hydration properties.« less

Ion extraction from a plasma

NASA Technical Reports Server (NTRS)

Aston, G.; Wilbur, P. J.

1981-01-01

The physical processes governing ion extraction from a plasma have been examined experimentally. The screen hole plasma sheath (the transition region wherein significant ion acceleration and complete electron retardation occurs) has been defined by equipotential plots for a variety of ion accelerator system geometries and operating conditions. It was found that the screen hole plasma sheath extends over a large distance, and influences ion and electron trajectories at least 15 Debye lengths within the discharge chamber. The electron density variation within the screen hole plasma sheath satisfied a Maxwell-Boltzmann density distribution at an effective electron temperature dependent on the discharge plasma primary-to-Maxwellian electron density ratio. Plasma ion flow up to and through the sheath was predominantly one-dimensional, and the ions entered the sheath region with a modified Bohm velocity. Low values of the screen grid thickness to screen hole diameter ratio were found to give good ion focusing and high extracted ion currents because of the effect of screen webbing on ion focusing.

Calibrating ion density profile measurements in ion thruster beam plasma

NASA Astrophysics Data System (ADS)

Zhang, Zun; Tang, Haibin; Ren, Junxue; Zhang, Zhe; Wang, Joseph

2016-11-01

The ion thruster beam plasma is characterized by high directed ion velocity (104 m/s) and low plasma density (1015 m-3). Interpretation of measurements of such a plasma based on classical Langmuir probe theory can yield a large experimental error. This paper presents an indirect method to calibrate ion density determination in an ion thruster beam plasma using a Faraday probe, a retarding potential analyzer, and a Langmuir probe. This new method is applied to determine the plasma emitted from a 20-cm-diameter Kaufman ion thruster. The results show that the ion density calibrated by the new method can be as much as 40% less than that without any ion current density and ion velocity calibration.

Historic disturbance regimes promote tree diversity only under low browsing regimes in eastern deciduous forest

Treesearch

Tim Nuttle; Alejandro A. Royo; Mary Beth Adams; Walter P. Carson

2013-01-01

Eastern deciduous forests are changing in species composition and diversity outside of classical successional trajectories. Three disturbance mechanisms appear central to this phenomenon: fire frequency is reduced, canopy gaps are smaller, and browsers are more abundant. Which factor is most responsible is a matter of great debate and remains unclear, at least partly...

Comparison of 3D Classical Trajectory and Transition-State Theory Reaction Cross Sections

DOE R&D Accomplishments Database

Koeppl, G. W.; Karplus, Martin

1970-10-01

Although there is excellent agreement for a system such as H+H{sub 2} --> H{sub 2}+H, in which both the potential and the particle masses are symmetric, significant deviations occur for more asymmetric reactions. A detailed analysis show that the calculated differences are from the violation of two assumptions of transition-state theory.

Lie-algebraic Approach to Dynamics of Closed Quantum Systems and Quantum-to-Classical Correspondence

NASA Astrophysics Data System (ADS)

Galitski, Victor

2012-02-01

I will briefly review our recent work on a Lie-algebraic approach to various non-equilibrium quantum-mechanical problems, which has been motivated by continuous experimental advances in the field of cold atoms. First, I will discuss non-equilibrium driven dynamics of a generic closed quantum system. It will be emphasized that mathematically a non-equilibrium Hamiltonian represents a trajectory in a Lie algebra, while the evolution operator is a trajectory in a Lie group generated by the underlying algebra via exponentiation. This turns out to be a constructive statement that establishes, in particular, the fact that classical and quantum unitary evolutions are two sides of the same coin determined uniquely by the same dynamic generators in the group. An equation for these generators - dubbed dual Schr"odinger-Bloch equation - will be derived and analyzed for a few of specific examples. This non-linear equation allows one to construct new exact non-linear solutions to quantum-dynamical systems. An experimentally-relevant example of a family of exact solutions to the many-body Landau-Zener problem will be presented. One practical application of the latter result includes dynamical means to optimize molecular production rate following a quench across the Feshbach resonance.

Effects of Solute Concentrations on Kinetic Pathways in Ni-Al-Cr Alloys

NASA Technical Reports Server (NTRS)

Booth-Morrison, Christopher; Weninger, Jessica; Sudbrack, Chantal K.; Mao, Zugang; Seidman, David N.; Noebe, Ronald D.

2008-01-01

The kinetic pathways resulting from the formation of coherent gamma'-precipitates from the gamma-matrix are studied for two Ni-Al-Cr alloys with similar gamma'-precipitate volume fractions at 873 K. The details of the phase decompositions of Ni-7.5Al-8.5Cr at.% and Ni-5.2Al-14.2Cr at.% for aging times from 1/6 to 1024 h are investigated by atom-probe tomography, and are found to differ significantly from a mean-field description of coarsening. The morphologies of the gamma'-precipitates of the alloys are similar, though the degrees of gamma'-precipitate coagulation and coalescence differ. Quantification within the framework of classical nucleation theory reveals that differences in the chemical driving forces for phase decomposition result in differences in the nucleation behavior of the two alloys. The temporal evolution of the gamma'-precipitate average radii and the gamma-matrix supersaturations follow the predictions of classical coarsening models. The compositional trajectories of the gamma-matrix phases of the alloys are found to follow approximately the equilibrium tie-lines, while the trajectories of the gamma'-precipitates do not, resulting in significant differences in the partitioning ratios of the solute elements.

Classical trajectory studies on the dynamics of one-photon double photionization of H2O

NASA Astrophysics Data System (ADS)

Streeter, Zachary; Yip, Frank; Reedy, Dylan P.; Landers, Allen; McCurdy, C. William

2017-04-01

Recent momentum imaging experiments at the Advanced Light Source have opened the possibility of measuring the complete triple differential cross section (TDCS) for one-photon double ionization of H2O in the molecular frame. The measurements depend on the complete breakup process, H2O + hν -> 2e-+ H+ + H+ +O. At the 57 eV photon energy of the experiment this process could proceed via any of the nine energetically accessible electronic states of H2O++. To discover which ionization channels contribute to the observed TDCS for the electrons measured in coincidence with different kinetic energy releases, we have carried out classical trajectory studies for breakup of the water dication on all nine potential surfaces, sampling from a Wigner phase space distribution for the vibrational ground state of H2O. The final momentum distributions of the protons and branching ratios between two- and three-body breakup are then analyzed and the results are compared with experiment to identify which ionization channels contribute to the TDCS observed in coincidence measurements of the ejected electrons. Office of Basic Energy Sciences, U.S. DOE.

Miniature Ion-Mobility Spectrometer

NASA Technical Reports Server (NTRS)

Hartley, Frank T.

2006-01-01

The figure depicts a proposed miniature ion-mobility spectrometer that would be fabricated by micromachining. Unlike prior ion-mobility spectrometers, the proposed instrument would not be based on a time-of-flight principle and, consequently, would not have some of the disadvantageous characteristics of prior time-of-flight ion-mobility spectrometers. For example, one of these characteristics is the need for a bulky carrier-gas-feeding subsystem that includes a shutter gate to provide short pulses of gas in order to generate short pulses of ions. For another example, there is need for a complex device to generate pulses of ions from the pulses of gas and the device is capable of ionizing only a fraction of the incoming gas molecules; these characteristics preclude miniaturization. In contrast, the proposed instrument would not require a carrier-gas-feeding subsystem and would include a simple, highly compact device that would ionize all the molecules passing through it. The ionization device in the proposed instrument would be a 0.1-micron-thick dielectric membrane with metal electrodes on both sides. Small conical holes would be micromachined through the membrane and electrodes. An electric potential of the order of a volt applied between the membrane electrodes would give rise to an electric field of the order of several megavolts per meter in the submicron gap between the electrodes. An electric field of this magnitude would be sufficient to ionize all the molecules that enter the holes. Ionization (but not avalanche arcing) would occur because the distance between the ionizing electrodes would be less than the mean free path of gas molecules at the operating pressure of instrument. An accelerating grid would be located inside the instrument, downstream from the ionizing membrane. The electric potential applied to this grid would be negative relative to the potential on the inside electrode of the ionizing membrane and would be of a magnitude sufficient to generate a moderate electric field. Positive ions leaving the membrane holes would be accelerated in this electric field. The resulting flux of ions away from the ionization membrane would create a partial vacuum that would draw more of the gas medium through the membrane. The figure depicts a filter electrode and detector electrodes located along the sides of a drift tube downstream from the accelerator electrode. These electrodes would apply a transverse AC electric field superimposed on a ramped DC electric field. The AC field would effect differential transverse dispersal of ions. At a given instant of time, the trajectories of most of the ions would be bent toward the electrodes, causing most of the ions to collide with the electrodes and thereby become neutralized. The DC field would partly counteract the dispersive effect of the AC field, straightening the trajectories of a selected species of ions; the selection would vary with the magnitude of the applied DC field. The straightening of the trajectories of the selected ions would enable them to pass into the region between the detector electrodes. Depending on the polarity of the voltage applied to the detector electrodes, the electric field between the detector electrodes would draw the selected ions to one of these electrodes. Hence, the current collected by one of the detector electrodes would be a measure of the abundance of ions of the selected species. The ramping of the filter- electrode DC voltage would sweep the selection of ions through the spectrum of ionic species.

Coupled forward-backward trajectory approach for nonequilibrium electron-ion dynamics

NASA Astrophysics Data System (ADS)

Sato, Shunsuke A.; Kelly, Aaron; Rubio, Angel

2018-04-01

We introduce a simple ansatz for the wave function of a many-body system based on coupled forward and backward propagating semiclassical trajectories. This method is primarily aimed at, but not limited to, treating nonequilibrium dynamics in electron-phonon systems. The time evolution of the system is obtained from the Euler-Lagrange variational principle, and we show that this ansatz yields Ehrenfest mean-field theory in the limit that the forward and backward trajectories are orthogonal, and in the limit that they coalesce. We investigate accuracy and performance of this method by simulating electronic relaxation in the spin-boson model and the Holstein model. Although this method involves only pairs of semiclassical trajectories, it shows a substantial improvement over mean-field theory, capturing quantum coherence of nuclear dynamics as well as electron-nuclear correlations. This improvement is particularly evident in nonadiabatic systems, where the accuracy of this coupled trajectory method extends well beyond the perturbative electron-phonon coupling regime. This approach thus provides an attractive route forward to the ab initio description of relaxation processes, such as thermalization, in condensed phase systems.

Formation of gyrotropic and non gyrotropic field-aligned beams in the Earth's quasi-perpendicular Ion Foreshock: Full-particle 2D simulation results

NASA Astrophysics Data System (ADS)

Savoini, P.; Lembege, B.

2013-12-01

The ion foreshock located upstream of the Earth's bow shock is populated with ions reflected back by the shock front with an high energy gain. In-situ spacecraft measurements have clearly established the existence of two distinct populations in the foreshock upstream of quasi-perpendicular shock region (i.e. for 45° ≤ ΘBn≤ 90°, where ΘBn is the angle between the shock normal and the upstream magnetostatic field): (i) field-aligned (';FAB') ion beams characterized by a gyrotropic distribution, and (ii) gyro-phase bunched (';GPB') ions characterized by a NON gyrotropic distribution, which exhibits a non-vanishing perpendicular bulk velocity. The purpose of the present work is to identify the possible sources of the different backstreaming ions and is based on the use of 2D PIC simulations of a curved shock, where full curvature effects, time of flight effects and both electrons and ions dynamics are fully described by a self consistent approach. Our analysis evidences that the two populations mentionned above may have different origins identified both in terms of interaction time and distance of penetration within the shock front. In particular, ours simulations evidence that "GPB" and ';FAB' populations are characterized by a short (Δinter= 1 to 2 tci) and much larger (Δinter= 1 to 10 tci) interaction time respectively, where τci is the ion upstream gyroperiod. In addition, a deeper statistical analysis of ion trajectories evidences that: (i) both populations can be discriminated in terms of injection angle into the shock front (i.e. defined between the local normal to the shock front and the gyration velocity vector at the time ions reach the front). Such a behavior explains how reflected ions can be splitted in the observed two populations "FAB" and "GPB". (ii) ion trajectories strongly differ between the "FAB" and "GPB" populations at the shock front. In particular, ';FAB' ions suffer multi-bounces whereas ';GPB '; ions make only one bounce. Such differences can explain why the ';FAB' population loses their gyro-phase coherency and become gyrotropic which is not the case for the "GPB". As evidenced by these simulations the origin of both populations can be associated directly to their interaction with the shock front itself and do not require any upstream instability which can be another source for such backstreaming ions.

Quantum dynamics in phase space: Moyal trajectories 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Braunss, G.

Continuing a previous paper [G. Braunss, J. Phys. A: Math. Theor. 43, 025302 (2010)] where we had calculated Planck-Constant-Over-Two-Pi {sup 2}-approximations of quantum phase space viz. Moyal trajectories of examples with one and two degrees of freedom, we present in this paper the calculation of Planck-Constant-Over-Two-Pi {sup 2}-approximations for four examples: a two-dimensional Toda chain, the radially symmetric Schwarzschild field, and two examples with three degrees of freedom, the latter being the nonrelativistic spherically Coulomb potential and the relativistic cylinder symmetrical Coulomb potential with a magnetic field H. We show in particular that an Planck-Constant-Over-Two-Pi {sup 2}-approximation of the nonrelativisticmore » Coulomb field has no singularity at the origin (r= 0) whereas the classical trajectories are singular at r= 0. In the third example, we show in particular that for an arbitrary function {gamma}(H, z) the expression {beta}{identical_to}p{sub z}+{gamma}(H, z) is classically ( Planck-Constant-Over-Two-Pi = 0) a constant of motion, whereas for Planck-Constant-Over-Two-Pi {ne} 0 this holds only if {gamma}(H, z) is an arbitrary polynomial of second order in z. This statement is shown to extend correspondingly to a cylinder symmetrical Schwarzschild field with a magnetic field. We exhibit in detail a number of properties of the radially symmetric Schwarzschild field. We exhibit finally the problems of the nonintegrable Henon-Heiles Hamiltonian and give a short review of the regular Hilbert space representation of Moyal operators.« less

Plasma electron hole kinematics. II. Hole tracking Particle-In-Cell simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, C.; Hutchinson, I. H.

The kinematics of a 1-D electron hole is studied using a novel Particle-In-Cell simulation code. A hole tracking technique enables us to follow the trajectory of a fast-moving solitary hole and study quantitatively hole acceleration and coupling to ions. We observe a transient at the initial stage of hole formation when the hole accelerates to several times the cold-ion sound speed. Artificially imposing slow ion speed changes on a fully formed hole causes its velocity to change even when the ion stream speed in the hole frame greatly exceeds the ion thermal speed, so there are no reflected ions. Themore » behavior that we observe in numerical simulations agrees very well with our analytic theory of hole momentum conservation and the effects of “jetting.”.« less

Controlling the Transport of an Ion: Classical and Quantum Mechanical Solutions

DTIC Science & Technology

2014-07-09

quantum systems: tools, achievements, and limitations Christiane P Koch Shortcuts to adiabaticity for an ion in a rotating radially- tight trap M Palmero...Keywords: coherent control, ion traps, quantum information, optimal control theory 1. Introduction Control methods are key enabling techniques in many...figure 6. 3.4. Feasibility analysis of quantum optimal control Numerical optimization of the wavepacket motion is expected to become necessary once

Toward understanding the roaming mechanism in H + MgH → Mg + HH reaction

DOE PAGES

Mauguiere, Frederic A. L.; Collins, Peter; Stamatiadis, Stamatis; ...

2016-02-26

The roaming mechanism in the reaction H + MgH →Mg + HH is investigated by classical and quantum dynamics employing an accurate ab initio threedimensional ground electronic state potential energy surface. The reaction dynamics are explored by running trajectories initialized on a four-dimensional dividing surface anchored on three-dimensional normally hyperbolic invariant manifold associated with a family of unstable orbiting periodic orbits in the entrance channel of the reaction (H + MgH). By locating periodic orbits localized in the HMgH well or involving H orbiting around the MgH diatom, and following their continuation with the total energy, regions in phase spacemore » where reactive or nonreactive trajectories may be trapped are found. In this way roaming reaction pathways are deduced in phase space. Patterns similar to periodic orbits projected into configuration space are found for the quantum bound and resonance eigenstates. Roaming is attributed to the capture of the trajectories in the neighborhood of certain periodic orbits. As a result, the complex forming trajectories in the HMgH well can either return to the radical channel or “roam” to the MgHH minimum from where the molecule may react.« less

A New Computational Technique for the Generation of Optimised Aircraft Trajectories

NASA Astrophysics Data System (ADS)

Chircop, Kenneth; Gardi, Alessandro; Zammit-Mangion, David; Sabatini, Roberto

2017-12-01

A new computational technique based on Pseudospectral Discretisation (PSD) and adaptive bisection ɛ-constraint methods is proposed to solve multi-objective aircraft trajectory optimisation problems formulated as nonlinear optimal control problems. This technique is applicable to a variety of next-generation avionics and Air Traffic Management (ATM) Decision Support Systems (DSS) for strategic and tactical replanning operations. These include the future Flight Management Systems (FMS) and the 4-Dimensional Trajectory (4DT) planning and intent negotiation/validation tools envisaged by SESAR and NextGen for a global implementation. In particular, after describing the PSD method, the adaptive bisection ɛ-constraint method is presented to allow an efficient solution of problems in which two or multiple performance indices are to be minimized simultaneously. Initial simulation case studies were performed adopting suitable aircraft dynamics models and addressing a classical vertical trajectory optimisation problem with two objectives simultaneously. Subsequently, a more advanced 4DT simulation case study is presented with a focus on representative ATM optimisation objectives in the Terminal Manoeuvring Area (TMA). The simulation results are analysed in-depth and corroborated by flight performance analysis, supporting the validity of the proposed computational techniques.

Spatial, seasonal trends and transboundary transport of PM2.5 inorganic ions in the Veneto region (Northeastern Italy)

NASA Astrophysics Data System (ADS)

Masiol, Mauro; Benetello, Francesca; Harrison, Roy M.; Formenton, Gianni; De Gaspari, Francesco; Pavoni, Bruno

2015-09-01

The Veneto region lies in the eastern part of the Po Valley (Italy). This is one of the hotspots in Europe for air quality, where efforts to meet the European standard for PM2.5 according to current and future legislation have been generally unsuccessful. Recent data indicating that ammonium, nitrate and sulphate account for about one third of total PM2.5 mass show that secondary inorganic aerosol (SIA) plays a key role in the exceedence of the standards. A sampling campaign for PM2.5 was carried out simultaneously in six major cities (2012-2013). The water soluble inorganic ions were quantified and data processed to: (1) investigate the seasonal trends and the spatial variations of the ionic component of aerosol; (2) identify chemical characteristics at the regional-scale and (3) assess the potential effects of long-range transport using back-trajectory cluster analysis and concentration-weighted trajectory (CWT) models. Results indicated that PM2.5 and SIA ions have an increasing gradient in concentrations from North (mountain) to South (lowland) and from East (coastal) to West (more continental), whereas K+ and Ca2+ levels are quite uniformly distributed. Similar seasonal trends in PM2.5 and ions are seen across the region. Simultaneous daily changes were observed and interpreted as a consequence of similar emission sources, secondary pollutant generation and accumulation/removal processes. Sulphate and nitrate were not directly related to the concentrations of their precursor gases and were generally largely, but not completely, neutralised by ammonium. The clustering of back-trajectories and CWT demonstrate that the long-range movement of the air masses has a major impact upon PM2.5 and ion concentrations: an area spreading from Eastern to Central Europe was identified as a main potential source for most ions. The valley sites are also heavily influenced by local emissions in slow moving northerly air masses. Finally, two episodes of high nitrate levels were investigated to explain why some sites are experiencing much higher concentrations than others. This study identifies some key features in the generation of SIA in the Po Valley, demonstrating that SIA generation is a regional pollution phenomenon and mitigation policies are required at regional, national and even European scales.

Semiclassical analysis of angular differential cross sections for single-electron capture in 250-eV H++H collisions

NASA Astrophysics Data System (ADS)

Frémont, F.

2015-05-01

A classical model based on the resolution of Hamilton equations of motion is used to determine the angular distribution of H projectiles following single-electron capture in H++H collisions at an incident projectile energy of 250 eV. At such low energies, the experimental charge-exchange probability and angular differential cross sections exhibit oscillatory structures that are classically related to the number of swaps the electron experiences between the target and the projectile during the collision. These oscillations are well reproduced by models based on quantum mechanics. In the present paper, the angular distribution of H projectiles is determined classically, at angles varying from 0.1° up to 7°. The variation in intensity due to interferences caused by the indiscernibility between different trajectories is calculated, and the role of these interferences is discussed.

Reproducing Quantum Probability Distributions at the Speed of Classical Dynamics: A New Approach for Developing Force-Field Functors.

PubMed

Sundar, Vikram; Gelbwaser-Klimovsky, David; Aspuru-Guzik, Alán

2018-04-05

Modeling nuclear quantum effects is required for accurate molecular dynamics (MD) simulations of molecules. The community has paid special attention to water and other biomolecules that show hydrogen bonding. Standard methods of modeling nuclear quantum effects like Ring Polymer Molecular Dynamics (RPMD) are computationally costlier than running classical trajectories. A force-field functor (FFF) is an alternative method that computes an effective force field that replicates quantum properties of the original force field. In this work, we propose an efficient method of computing FFF using the Wigner-Kirkwood expansion. As a test case, we calculate a range of thermodynamic properties of Neon, obtaining the same level of accuracy as RPMD, but with the shorter runtime of classical simulations. By modifying existing MD programs, the proposed method could be used in the future to increase the efficiency and accuracy of MD simulations involving water and proteins.

Microscopic dynamics of charge separation at the aqueous electrochemical interface.

PubMed

Kattirtzi, John A; Limmer, David T; Willard, Adam P

2017-12-19

We have used molecular simulation and methods of importance sampling to study the thermodynamics and kinetics of ionic charge separation at a liquid water-metal interface. We have considered this process using canonical examples of two different classes of ions: a simple alkali-halide pair, Na + I - , or classical ions, and the products of water autoionization, H 3 O + OH - , or water ions. We find that for both ion classes, the microscopic mechanism of charge separation, including water's collective role in the process, is conserved between the bulk liquid and the electrode interface. However, the thermodynamic and kinetic details of the process differ between these two environments in a way that depends on ion type. In the case of the classical ion pairs, a higher free-energy barrier to charge separation and a smaller flux over that barrier at the interface result in a rate of dissociation that is 40 times slower relative to the bulk. For water ions, a slightly higher free-energy barrier is offset by a higher flux over the barrier from longer lived hydrogen-bonding patterns at the interface, resulting in a rate of association that is similar both at and away from the interface. We find that these differences in rates and stabilities of charge separation are due to the altered ability of water to solvate and reorganize in the vicinity of the metal interface.

Microscopic dynamics of charge separation at the aqueous electrochemical interface

PubMed Central

Kattirtzi, John A.; Limmer, David T.; Willard, Adam P.

2017-01-01

We have used molecular simulation and methods of importance sampling to study the thermodynamics and kinetics of ionic charge separation at a liquid water–metal interface. We have considered this process using canonical examples of two different classes of ions: a simple alkali–halide pair, Na+I−, or classical ions, and the products of water autoionization, H3O+OH−, or water ions. We find that for both ion classes, the microscopic mechanism of charge separation, including water’s collective role in the process, is conserved between the bulk liquid and the electrode interface. However, the thermodynamic and kinetic details of the process differ between these two environments in a way that depends on ion type. In the case of the classical ion pairs, a higher free-energy barrier to charge separation and a smaller flux over that barrier at the interface result in a rate of dissociation that is 40 times slower relative to the bulk. For water ions, a slightly higher free-energy barrier is offset by a higher flux over the barrier from longer lived hydrogen-bonding patterns at the interface, resulting in a rate of association that is similar both at and away from the interface. We find that these differences in rates and stabilities of charge separation are due to the altered ability of water to solvate and reorganize in the vicinity of the metal interface. PMID:28698368

Quantum-classical correspondence for the inverted oscillator

NASA Astrophysics Data System (ADS)

Maamache, Mustapha; Ryeol Choi, Jeong

2017-11-01

While quantum-classical correspondence for a system is a very fundamental problem in modern physics, the understanding of its mechanism is often elusive, so the methods used and the results of detailed theoretical analysis have been accompanied by active debate. In this study, the differences and similarities between quantum and classical behavior for an inverted oscillator have been analyzed based on the description of a complete generalized Airy function-type quantum wave solution. The inverted oscillator model plays an important role in several branches of cosmology and particle physics. The quantum wave packet of the system is composed of many sub-packets that are localized at different positions with regular intervals between them. It is shown from illustrations of the probability density that, although the quantum trajectory of the wave propagation is somewhat different from the corresponding classical one, the difference becomes relatively small when the classical excitation is sufficiently high. We have confirmed that a quantum wave packet moving along a positive or negative direction accelerates over time like a classical wave. From these main interpretations and others in the text, we conclude that our theory exquisitely illustrates quantum and classical correspondence for the system, which is a crucial concept in quantum mechanics. Supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2016R1D1A1A09919503)

Neutral dynamics and ion energy transport in MST plasma

NASA Astrophysics Data System (ADS)

Xing, Zichuan; Nornberg, Mark; den Hartog, Daniel; Kumar, Santosh; Anderson, Jay

2015-11-01

Neutral dynamics can have a significant effect on ion energy transport through charge exchange collisions. Whereas previously charge exchange was considered a direct loss mechanism in MST plasmas, new analysis indicates that significant thermal charge exchange neutrals are reionized. Further, the temperatures of the neutral species in the core of the plasma are suspected to be much higher than room temperature, which has a large effect on ion energy losses due to charge exchange. The DEGAS2 Monte Carlo simulation code is applied to the MST reversed field pinch experiment to estimate the density and temperature profile of the neutral species. The result is then used to further examine the effect of the neutral species on ion energy transport in improved confinement plasmas. This enables the development of a model that accounts for collisional equilibration between species, classical convective and conductive energy transport, and energy loss due to charge exchange collisions. The goal is to quantify classical, stochastic, and anomalous ion heating and transport in RFP plasmas. Work supported by the US DOE. DEGAS2 is provided by PPPL and STRAHL is provided by Ralph Dux of the Max-Planck-Institut fur Plasmaphysik.

Reactive collisions for NO(2Π) + N(4S) at temperatures relevant to the hypersonic flight regime.

PubMed

Denis-Alpizar, Otoniel; Bemish, Raymond J; Meuwly, Markus

2017-01-18

The NO(X 2 Π) + N( 4 S) reaction which occurs entirely in the triplet manifold of N 2 O is investigated using quasiclassical trajectories and quantum simulations. Fully-dimensional potential energy surfaces for the 3 A' and 3 A'' states are computed at the MRCI+Q level of theory and are represented using a reproducing kernel Hilbert space. The N-exchange and N 2 -formation channels are followed by using the multi-state adiabatic reactive molecular dynamics method. Up to 5000 K these reactions occur predominantly on the N 2 O 3 A'' surface. However, for higher temperatures the contributions of the 3 A' and 3 A'' states are comparable and the final state distributions are far from thermal equilibrium. From the trajectory simulations a new set of thermal rate coefficients of up to 20 000 K is determined. Comparison of the quasiclassical trajectory and quantum simulations shows that a classical description is a good approximation as determined from the final state analysis.

Seagrass ecosystem trajectory depends on the relative timescales of resistance, recovery and disturbance.

PubMed

O'Brien, Katherine R; Waycott, Michelle; Maxwell, Paul; Kendrick, Gary A; Udy, James W; Ferguson, Angus J P; Kilminster, Kieryn; Scanes, Peter; McKenzie, Len J; McMahon, Kathryn; Adams, Matthew P; Samper-Villarreal, Jimena; Collier, Catherine; Lyons, Mitchell; Mumby, Peter J; Radke, Lynda; Christianen, Marjolijn J A; Dennison, William C

2017-09-18

Seagrass ecosystems are inherently dynamic, responding to environmental change across a range of scales. Habitat requirements of seagrass are well defined, but less is known about their ability to resist disturbance. Specific means of recovery after loss are particularly difficult to quantify. Here we assess the resistance and recovery capacity of 12 seagrass genera. We document four classic trajectories of degradation and recovery for seagrass ecosystems, illustrated with examples from around the world. Recovery can be rapid once conditions improve, but seagrass absence at landscape scales may persist for many decades, perpetuated by feedbacks and/or lack of seed or plant propagules to initiate recovery. It can be difficult to distinguish between slow recovery, recalcitrant degradation, and the need for a window of opportunity to trigger recovery. We propose a framework synthesizing how the spatial and temporal scales of both disturbance and seagrass response affect ecosystem trajectory and hence resilience. Copyright © 2017 Elsevier Ltd. All rights reserved.

A Reliability Comparison of Classical and Stochastic Thickness Margin Approaches to Address Material Property Uncertainties for the Orion Heat Shield

NASA Technical Reports Server (NTRS)

Sepka, Steve; Vander Kam, Jeremy; McGuire, Kathy

2018-01-01

The Orion Thermal Protection System (TPS) margin process uses a root-sum-square approach with branches addressing trajectory, aerothermodynamics, and material response uncertainties in ablator thickness design. The material response branch applies a bond line temperature reduction between the Avcoat ablator and EA9394 adhesive by 60 C (108 F) from its peak allowed value of 260 C (500 F). This process is known as the Bond Line Temperature Material Margin (BTMM) and is intended to cover material property and performance uncertainties. The value of 60 C (108 F) is a constant, applied at any spacecraft body location and for any trajectory. By varying only material properties in a random (monte carlo) manner, the perl-based script mcCHAR is used to investigate the confidence interval provided by the BTMM. In particular, this study will look at various locations on the Orion heat shield forebody for a guided and an abort (ballistic) trajectory.

A Reliability Comparison of Classical and Stochastic Thickness Margin Approaches to Address Material Property Uncertainties for the Orion Heat Shield

NASA Technical Reports Server (NTRS)

Sepka, Steven A.; McGuire, Mary Kathleen; Vander Kam, Jeremy C.

2018-01-01

The Orion Thermal Protection System (TPS) margin process uses a root-sum-square approach with branches addressing trajectory, aerothermodynamics, and material response uncertainties in ablator thickness design. The material response branch applies a bondline temperature reduction between the Avcoat ablator and EA9394 adhesive by 60 C (108 F) from its peak allowed value of 260 C (500 F). This process is known as the Bond Line Temperature Material Margin (BTMM) and is intended to cover material property and performance uncertainties. The value of 60 C (108 F) is a constant, applied at any spacecraft body location and for any trajectory. By varying only material properties in a random (monte carlo) manner, the perl-based script mcCHAR is used to investigate the confidence interval provided by the BTMM. In particular, this study will look at various locations on the Orion heat shield forebody for a guided and an abort (ballistic) trajectory.

Detailed classification of swimming paths in the Morris Water Maze: multiple strategies within one trial

PubMed Central

Gehring, Tiago V.; Luksys, Gediminas; Sandi, Carmen; Vasilaki, Eleni

2015-01-01

The Morris Water Maze is a widely used task in studies of spatial learning with rodents. Classical performance measures of animals in the Morris Water Maze include the escape latency, and the cumulative distance to the platform. Other methods focus on classifying trajectory patterns to stereotypical classes representing different animal strategies. However, these approaches typically consider trajectories as a whole, and as a consequence they assign one full trajectory to one class, whereas animals often switch between these strategies, and their corresponding classes, within a single trial. To this end, we take a different approach: we look for segments of diverse animal behaviour within one trial and employ a semi-automated classification method for identifying the various strategies exhibited by the animals within a trial. Our method allows us to reveal significant and systematic differences in the exploration strategies of two animal groups (stressed, non-stressed), that would be unobserved by earlier methods. PMID:26423140

Quantum-enhanced deliberation of learning agents using trapped ions

NASA Astrophysics Data System (ADS)

Dunjko, V.; Friis, N.; Briegel, H. J.

2015-02-01

A scheme that successfully employs quantum mechanics in the design of autonomous learning agents has recently been reported in the context of the projective simulation (PS) model for artificial intelligence. In that approach, the key feature of a PS agent, a specific type of memory which is explored via random walks, was shown to be amenable to quantization, allowing for a speed-up. In this work we propose an implementation of such classical and quantum agents in systems of trapped ions. We employ a generic construction by which the classical agents are ‘upgraded’ to their quantum counterparts by a nested process of adding coherent control, and we outline how this construction can be realized in ion traps. Our results provide a flexible modular architecture for the design of PS agents. Furthermore, we present numerical simulations of simple PS agents which analyze the robustness of our proposal under certain noise models.

Potential mapping with charged-particle beams

NASA Technical Reports Server (NTRS)

Robinson, J. W.; Tillery, D. G.

1979-01-01

Experimental methods of mapping the equipotential surfaces near some structure of interest rely on the detection of charged particles which have traversed the regions of interest and are detected remotely. One method is the measurement of ion energies for ions created at a point of interest and expelled from the region by the fields. The ion energy at the detector in eV corresponds to the potential where the ion was created. An ionizing beam forms the ions from background neutrals. The other method is to inject charged particles into the region of interest and to locate their exit points. A set of several trajectories becomes a data base for a systematic mapping technique. An iterative solution of a boundary value problem establishes concepts and limitations pertaining to the mapping problem.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, T.; Yang, Z.; Dong, P.

The cold-cathode Penning ion gauge (PIG) type ion source has been used for generation of negative hydrogen (H{sup -}) ions as the internal ion source of a compact cyclotron. A novel method called electrical shielding box dc beam measurement is described in this paper, and the beam intensity was measured under dc extraction inside an electrical shielding box. The results of the trajectory simulation and dc H{sup -} beam extraction measurement were presented. The effect of gas flow rate, magnetic field strength, arc current, and extraction voltage were also discussed. In conclusion, the dc H{sup -} beam current of aboutmore » 4 mA from the PIG ion source with the puller voltage of 40 kV and arc current of 1.31 A was extrapolated from the measurement at low extraction dc voltages.« less

Heavy ion beam probe operation in time varying equilibria of improved confinement reversed field pinch discharges.

PubMed

Demers, D R; Chen, X; Schoch, P M; Fimognari, P J

2010-10-01

Operation of a heavy ion beam probe (HIBP) on a reversed field pinch is unique from other toroidal applications because the magnetic field is more temporal and largely produced by plasma current. Improved confinement, produced through the transient application of a poloidal electric field which leads to a reduction of dynamo activity, exhibits gradual changes in equilibrium plasma quantities. A consequence of this is sweeping of the HIBP trajectories by the dynamic magnetic field, resulting in motion of the sample volume. In addition, the plasma potential evolves with the magnetic equilibrium. Measurement of the potential as a function of time is thus a combination of temporal changes of the equilibrium and motion of the sample volume. A frequent additional complication is a nonideal balance of ion current on the detectors resulting from changes in the beam trajectory (magnetic field) and energy (plasma potential). This necessitates use of data selection criteria. Nevertheless, the HIBP on the Madison Symmetric Torus has acquired measurements as a function of time throughout improved confinement. A technique developed to infer the potential in the improved confinement reversed field pinch from HIBP data in light of the time varying plasma equilibrium will be discussed.

High Power Electric Propulsion System for NEP: Propulsion and Trajectory Options

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koppel, Christophe R.; Duchemin, Olivier; Valentian, Dominique

Recent US initiatives in Nuclear Propulsion lend themselves naturally to raising the question of the assessment of various options and particularly to propose the High Power Electric Propulsion Subsystem (HPEPS) for the Nuclear Electric Propulsion (NEP). The purpose of this paper is to present the guidelines for the HPEPS with respect to the mission to Mars, for automatic probes as well as for manned missions. Among the various options, the technological options and the trajectory options are pointed out. The consequences of the increase of the electrical power of a thruster are first an increase of the thrust itself, butmore » also, as a general rule, an increase of the thruster performance due to its higher efficiency, particularly its specific impulse increase. The drawback is as a first parameter, the increase of the thruster's size, hence the so-called 'thrust density' shall be high enough or shall be drastically increased for ions thrusters. Due to the large mass of gas needed to perform the foreseen missions, the classical xenon rare gas is no more in competition, the total world production being limited to 20 -40 tons per year. Thus, the right selection of the propellant feeding the thruster is of prime importance. When choosing a propellant with lower molecular mass, the consequences at thruster level are an increase once more of the specific impulse, but at system level the dead mass may increase too, mainly because the increase of the mass of the propellant system tanks. Other alternatives, in rupture with respect to the current technologies, are presented in order to make the whole system more attractive. The paper presents a discussion on the thruster specific impulse increase that is sometime considered an increase of the main system performances parameter, but that induces for all electric propulsion systems drawbacks in the system power and mass design that are proportional to the thruster specific power increase (kW/N). The electric thruster specific impulse shall be optimized w.r.t. the mission. The trajectories taken into account in the paper are constrained by the allowable duration of the travel and the launcher size. The multi-arcs trajectories to Mars (using an optimized combination of chemical and Electric propulsion) are presented in detail. The compatibility with NEP systems that implies orbiting a sizeable nuclear reactor and a power generation system capable of converting thermal into electric power, with minimum mass and volumes fitting in with Ariane 5 or the Space Shuttle bay, is assessed.« less

Electron capture in collisions of Al2+ ions with He atoms at intermediate energies

NASA Astrophysics Data System (ADS)

Watanabe, A.; Sato, H.; Gu, J. P.; Hirsch, G.; Buenker, R. J.; Kimura, M.

2001-09-01

Electron capture resulting from collisions of Al2+ ions with He atoms from 0.15 to 1000 keV/u is investigated using a molecular-orbital representation within a semiclassical frame. Molecular electronic states and corresponding couplings are determined by the ALCHEMY program. Sixteen molecular states all connecting to single-electron-capture processes are included, and hence radial and rotational couplings among these channels are fully considered. The trajectory effect arising from the straight-line, Coulomb, and ground-state potential trajectories for electron-capture and excitation processes is carefully assessed. The electron-capture cross section by ground-state Al2+(2S) ions slowly increases before it reaches a maximum of 1.3×10-16 cm2 at 100 keV/u. Those for metastable Al2+(2P) ions sharply increase with increasing energy, and reach a peak at 1 keV/u with a value of 1.5×10-16 cm2. The earlier experimental data are found to be larger by an order of magnitude although their energy dependence is in good accord with the present result. Excitation cross sections for both the ground and metastable states are found to be much larger by a factor of 2-3 than corresponding capture cross sections above 1 keV/u although they become comparable below this energy.

Communication: Adiabatic and non-adiabatic electron-nuclear motion: Quantum and classical dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Albert, Julian; Kaiser, Dustin; Engel, Volker

2016-05-07

Using a model for coupled electronic-nuclear motion we investigate the range from negligible to strong non-adiabatic coupling. In the adiabatic case, the quantum dynamics proceeds in a single electronic state, whereas for strong coupling a complete transition between two adiabatic electronic states takes place. It is shown that in all coupling regimes the short-time wave-packet dynamics can be described using ensembles of classical trajectories in the phase space spanned by electronic and nuclear degrees of freedom. We thus provide an example which documents that the quantum concept of non-adiabatic transitions is not necessarily needed if electronic and nuclear motion ismore » treated on the same footing.« less

Quantization of the Szekeres system

NASA Astrophysics Data System (ADS)

Paliathanasis, A.; Zampeli, Adamantia; Christodoulakis, T.; Mustafa, M. T.

2018-06-01

We study the quantum corrections on the Szekeres system in the context of canonical quantization in the presence of symmetries. We start from an effective point-like Lagrangian with two integrals of motion, one corresponding to the Hamiltonian and the other to a second rank killing tensor. Imposing their quantum version on the wave function results to a solution which is then interpreted in the context of Bohmian mechanics. In this semiclassical approach, it is shown that there is no quantum corrections, thus the classical trajectories of the Szekeres system are not affected at this level. Finally, we define a probability function which shows that a stationary surface of the probability corresponds to a classical exact solution.

Developmental trajectories of offenders convicted of fraud: A follow-up to age 50 in a Dutch conviction cohort

PubMed Central

van der Geest, Victor R.; Weisburd, David; Blokland, Arjan A. J.

2016-01-01

This study describes the criminal careers of offenders convicted of fraud, distinguishing different career dimensions such as intermittency, versatility and specialization. Results indicate that most fraud offenders are versatile in the sense that they also have significant criminal records for other serious offending (that is, not fraud). At the same time they are also specialized in fraud. When we examine developmental trajectories of serious offending and next explore patterns of fraud for the groups identified, we find that offenders in our sample represent a heterogeneous group and that the classic divide between typical financial (for example, white-collar) offenders and common criminals does not apply to the majority of our sample. PMID:28989326

Chemical characterization of fog and rain water collected at the eastern Andes cordillera

NASA Astrophysics Data System (ADS)

Beiderwieden, E.; Wrzesinsky, T.; Klemm, O.

2005-09-01

During a three month period in 2003 and 2004, the chemistry of fog and rainwater were studied at the "El Tiro" site in a tropical mountain forest ecosystem in Ecuador, South America. The fogwater samples were collected using a passive fog collector, and for the rain water, a standard rain sampler was employed. For all samples, electric conductivity, pH, and the concentrations of NH4+, K+, Na+, Ca2+, Mg2+, Cl-, NO3-, PO43-, and SO42- were measured. For each fog sample, a 5 day back trajectory was calculated by the use of the HYSPLIT model. Two types of trajectories occurred. One type was characterized by advection of air masses from the East over the Amazonian basin, the other trajectory arrived one from the West after significant travel time over the Pacific Ocean. We found considerably higher ion concentrations in fogwater samples than in rain samples. Median pH values are 4.58 for fog water, and 5.26 for the rain samples, respectively. The median electric conductivity was 23 μS cm-1 for the fog and 6 μS cm-1 for the rain. The continent samples exhibit higher concentrations of most ions as compared to the pacific samples, but these differences could not be detected statistically.

Evaluation of the photoionization probability of H2+ by the trajectory semiclassical method

NASA Astrophysics Data System (ADS)

Arkhipov, D. N.; Astashkevich, S. A.; Mityureva, A. A.; Smirnov, V. V.

2018-07-01

The trajectory-based method for calculating the probabilities of transitions in the quantum system developed in our previous works and tested for atoms is applied to calculating the photoionization probability for the simplest molecule - hydrogen molecular ion. In a weak field it is established a good agreement between our photoionization cross section and the data obtained by other theoretical methods for photon energy in the range from one-photon ionization threshold up to 25 a.u. Photoionization cross section in the range 25 < ω ≤ 100 a.u. was calculated for the first time judging by the literature known to us. It is also confirmed that the trajectory method works in a wide range of the field magnitudes including superatomic values up to relativistic intensity.

Solar Electric Propulsion Triple-Satellite-Aided Capture With Mars Flyby

NASA Astrophysics Data System (ADS)

Patrick, Sean

Triple-Satellite-aided-capture sequences use gravity-assists at three of Jupiter's four massive Galilean moons to reduce the DeltaV required to enter into Jupiter orbit. A triple-satellite-aided capture at Callisto, Ganymede, and Io is proposed to capture a SEP spacecraft into Jupiter orbit from an interplanetary Earth-Jupiter trajectory that employs low-thrust maneuvers. The principal advantage of this method is that it combines the ISP efficiency of ion propulsion with nearly impulsive but propellant-free gravity assists. For this thesis, two main chapters are devoted to the exploration of low-thrust triple-flyby capture trajectories. Specifically, the design and optimization of these trajectories are explored heavily. The first chapter explores the design of two solar electric propulsion (SEP), low-thrust trajectories developed using the JPL's MALTO software. The two trajectories combined represent a full Earth to Jupiter capture split into a heliocentric Earth to Jupiter Sphere of Influence (SOI) trajectory and a Joviocentric capture trajectory. The Joviocentric trajectory makes use of gravity assist flybys of Callisto, Ganymede, and Io to capture into Jupiter orbit with a period of 106.3 days. Following this, in chapter two, three more SEP low-thrust trajectories were developed based upon those in chapter one. These trajectories, devised using the high-fidelity Mystic software, also developed by JPL, improve upon the original trajectories developed in chapter one. Here, the developed trajectories are each three separate, full Earth to Jupiter capture orbits. As in chapter one, a Mars gravity assist is used to augment the heliocentric trajectories. Gravity-assist flybys of Callisto, Ganymede, and Io or Europa are used to capture into Jupiter Orbit. With between 89.8 and 137.2-day periods, the orbits developed in chapters one and two are shorter than most Jupiter capture orbits achieved using low-thrust propulsion techniques. Finally, chapter 3 presents an original trajectory design for a Very-Long-Baseline Interferometry (VLBI) satellite constellation. The design was created for the 8th Global Trajectory Optimization Competition (GTOC8) in which participants are tasked with creating and optimizing low-thrust trajectories to place a series of three space craft into formation to map given radio sources.

Dielectric response in Bloch’s hydrodynamic model of an electron-ion plasma

NASA Astrophysics Data System (ADS)

Ishikawa, K.; Felderhof, B. U.

The linear response of an electron-ion plasma to an applied oscillating electric field is studied within the framework of Bloch’s classical hydrodynamic model. The ions are assumed to be fixed in space and distributed according to a known probability distribution. The linearized equations of motion for electron density and flow velocity are studied with the aid of a multiple scattering analysis and cluster expansion. This allows systematic reduction of the many-ion problem to a composition of few-ion problems, and shows how the longitudinal dielectric response function can in principle be calculated.

A multicolour graph as a complete topological invariant for \\Omega-stable flows without periodic trajectories on surfaces

NASA Astrophysics Data System (ADS)

Kruglov, V. E.; Malyshev, D. S.; Pochinka, O. V.

2018-01-01

Studying the dynamics of a flow on surfaces by partitioning the phase space into cells with the same limit behaviour of trajectories within a cell goes back to the classical papers of Andronov, Pontryagin, Leontovich and Maier. The types of cells (the number of which is finite) and how the cells adjoin one another completely determine the topological equivalence class of a flow with finitely many special trajectories. If one trajectory is chosen in every cell of a rough flow without periodic orbits, then the cells are partitioned into so-called triangular regions of the same type. A combinatorial description of such a partition gives rise to the three-colour Oshemkov-Sharko graph, the vertices of which correspond to the triangular regions, and the edges to separatrices connecting them. Oshemkov and Sharko proved that such flows are topologically equivalent if and only if the three-colour graphs of the flows are isomorphic, and described an algorithm of distinguishing three-colour graphs. But their algorithm is not efficient with respect to graph theory. In the present paper, we describe the dynamics of Ω-stable flows without periodic trajectories on surfaces in the language of four-colour graphs, present an efficient algorithm for distinguishing such graphs, and develop a realization of a flow from some abstract graph. Bibliography: 17 titles.

A scrutiny of the premise of the Rice-Ramsperger-Kassel-Marcus theory in isomerization reaction of an Ar7-type molecule

NASA Astrophysics Data System (ADS)

Takatsuka, Kazuo; Seko, Chihiro

1996-12-01

The validity of the physical premise of the Rice-Ramsperger-Kassel-Marcus (RRKM) theory is investigated in terms of the classical dynamics of isomerization reaction in Ar7-like molecules (clusters). The passage times of classical trajectories through the potential basins of isomers in the structural transitions are examined. In the high energy region corresponding to the so-called liquidlike phase, remarkable uniformity of the average passage times has been found. That is, the average passage time is characterized only by a basin through which a trajectory is currently passing and, hence, does not depend on the next visiting basins. This behavior is out of accord with the ordinary chemical law in that the ``reaction rates'' do not seem to depend on the height of the individual potential barriers. We ascribe this seemingly strange uniformity to the strong mixing (chaos) lying behind the rate process. That is, as soon as a classical path enters a basin, it gets involved into a chaotic zone in which many paths having different channels are entangled among each other, and effectively (in the statistical sense) loses its memory about which basin it came from and where it should visit next time. This model is verified by confirming that the populations of the lifetime of transition from one basin to others are expressed in exponential functions, which should have very similar exponents to each other in each passing-through basin. The inverse of the exponent is essentially proportional to the average passage time, and consequently brings about the uniformity. These populations set a foundation for the multichannel generalization of the RRKM theory. Two cases of the non-RRKM behaviors have been studied. One is a nonstatistical behavior in the low energy region such as the so-called coexistence phase. The other is the short-time behavior. It is well established [M. Berblinger and C. Schlier, J. Chem. Phys. 101, 4750 (1994)] that in a relatively simple and small system such as H+3, the so-called direct paths, which lead to dissociation before the phase-space mixing is completed, increase the probability of short-time passage. In contrast, we have found in our Ar7-like molecules that trajectories of short passage time are fewer than expected by the statistical theory. It is conceived that somewhat a long time in the initial stage of the isomerization is spent by a trajectory to find its ways out to the next basins.

Fast-ion transport in qmin>2, high- β steady-state scenarios on DIII-D

DOE PAGES

Holcomb, C. T.; Heidbrink, W. W.; Ferron, J. R.; ...

2015-05-22

The results from experiments on DIII-D [J. L. Luxon, Fusion Sci. Technol. 48, 828 (2005)] aimed at developing high β steady-state operating scenarios with high-qminqmin confirm that fast-ion transport is a critical issue for advanced tokamak development using neutral beam injection current drive. In DIII-D, greater than 11 MW of neutral beam heating power is applied with the intent of maximizing β N and the noninductive current drive. However, in scenarios with q min>2 that target the typical range of q 95= 5–7 used in next-step steady-state reactor models, Alfvén eigenmodes cause greater fast-ion transport than classical models predict. Thismore » enhanced transport reduces the absorbed neutral beam heating power and current drive and limits the achievable β N. Conversely similar plasmas except with q min just above 1 have approximately classical fast-ion transport. Experiments that take q min>3 plasmas to higher β P with q 95= 11–12 for testing long pulse operation exhibit regimes of better than expected thermal confinement. Compared to the standard high-q min scenario, the high β P cases have shorter slowing-down time and lower ∇β fast, and this reduces the drive for Alfvénic modes, yielding nearly classical fast-ion transport, high values of normalized confinement, β N, and noninductive current fraction. These results suggest DIII-D might obtain better performance in lower-q 95, high-q min plasmas using broader neutral beam heating profiles and increased direct electron heating power to lower the drive for Alfvén eigenmodes.« less

Fast-ion transport in q{sub min}>2, high-β steady-state scenarios on DIII-D

DOE Office of Scientific and Technical Information (OSTI.GOV)

Holcomb, C. T.; Heidbrink, W. W.; Collins, C.

2015-05-15

Results from experiments on DIII-D [J. L. Luxon, Fusion Sci. Technol. 48, 828 (2005)] aimed at developing high β steady-state operating scenarios with high-q{sub min} confirm that fast-ion transport is a critical issue for advanced tokamak development using neutral beam injection current drive. In DIII-D, greater than 11 MW of neutral beam heating power is applied with the intent of maximizing β{sub N} and the noninductive current drive. However, in scenarios with q{sub min}>2 that target the typical range of q{sub 95}= 5–7 used in next-step steady-state reactor models, Alfvén eigenmodes cause greater fast-ion transport than classical models predict. Thismore » enhanced transport reduces the absorbed neutral beam heating power and current drive and limits the achievable β{sub N}. In contrast, similar plasmas except with q{sub min} just above 1 have approximately classical fast-ion transport. Experiments that take q{sub min}>3 plasmas to higher β{sub P} with q{sub 95}= 11–12 for testing long pulse operation exhibit regimes of better than expected thermal confinement. Compared to the standard high-q{sub min} scenario, the high β{sub P} cases have shorter slowing-down time and lower ∇β{sub fast}, and this reduces the drive for Alfvénic modes, yielding nearly classical fast-ion transport, high values of normalized confinement, β{sub N}, and noninductive current fraction. These results suggest DIII-D might obtain better performance in lower-q{sub 95}, high-q{sub min} plasmas using broader neutral beam heating profiles and increased direct electron heating power to lower the drive for Alfvén eigenmodes.« less

Variability of FUV Emission Line in Classical T Tauri Stars as a Diagnostic for Disc Accretion

NASA Astrophysics Data System (ADS)

Ramkumar, B.; Johns-Krull, C. M.

2005-12-01

We present our results of FUV emission line variability studies done on four classical T Tauri stars. We have used the IUE Final Archive spectra of pre-main sequence stars to analyze the sample of four stars BP Tau, DR Tau, RU Lup and RY Tau where each of these low-resolution (R ˜6 Å) spectra was observed in the IUE short-wavelength band pass (1150--1980Å). Given a broad time line of multiple observations being available from the IUE Final archive, an intrinsic variability study has been possible with this sample. Our results indicate that the transition region lines \\ion{Si}{4} and \\ion{C}{4}, produced near the accretion shocks at ˜105 K, have a strong correlation between them in all four stars except DR Tau. We also observe a strong correlation between \\ion{C}{4} & \\ion{He}{2} on our entire sample with a correlation coefficient of 0.549 (false alarm probability = 7.9 x 10-2) or higher. In addition, \\ion{He}{2} correlates with the molecular hydrogen (1503Å) line in all but RU Lup. If the \\ion{He}{2} lines are produced because of X-ray ionization then the observed molecular hydrogen emission is indeed controlled by X-ray ionization and therefore \\ion{He}{2} could serve as an X-ray proxy for future studies. Also, our correlation results strengthen the fact that \\ion{C}{4} is a good predictor of \\ion{Si}{4} and have a common origin i.e. in accretion shocks in the star formation process.

Experimental and simulation-based investigation of He, Ne and Ar irradiation of polymers for ion microscopy

PubMed Central

Rzeznik, Lukasz; Fleming, Yves; Wirtz, Tom

2016-01-01

Summary Secondary ion mass spectrometry (SIMS) on the helium ion microscope (HIM) promises higher lateral resolution than on classical SIMS instruments. However, full advantage of this new technique can only be obtained when the interaction of He+ or Ne+ primary ions with the sample is fully controlled. In this work we investigate how He+ and Ne+ bombardment influences roughness formation and preferential sputtering for polymer samples and how they compare to Ar+ primary ions used in classical SIMS by combining experimental techniques with Molecular Dynamics (MD) simulations and SD_TRIM_SP modelling. The results show that diffusion coefficients for He, Ne and Ar in polymers are sufficiently high to prevent any accumulation of rare gas atoms in the polymers which could lead to some swelling and bubble formation. Roughness formation was also not observed. Preferential sputtering is more of a problem, with enrichment of carbon up to surface concentrations above 80%. In general, the preferential sputtering is largely depending on the primary ion species and the impact energies. For He+ bombardment, it is more of an issue for low keV impact energies and for the heavier primary ion species the preferential sputtering is sample dependent. For He+ steady state conditions are reached for fluences much higher than 1018 ions/cm2. For Ne+ and Ar+, the transient regime extends up to fluences of 1017–1018 ions/cm2. Hence, preferential sputtering needs to be taken into account when interpreting images recorded under He+ or Ne+ bombardment on the HIM. PMID:27547629

Reactive Collisions and Final State Analysis in Hypersonic Flight Regime

DTIC Science & Technology

2016-09-13

Kelvin.[7] The gas-phase, surface reactions and energy transfer at these tempera- tures are essentially uncharacterized and the experimental methodologies...high temperatures (1000 to 20000 K) and compared with results from experimentally derived thermodynamics quantities from the NASA CEA (NASA Chemical...with a reproducing kernel Hilbert space (RKHS) method[13] combined with Legendre polynomials; (2) quasi classical trajectory (QCT) calculations to study

Application of the comparison principle to analysis of nonlinear systems. [using Lipschitz condition and differential equations

NASA Technical Reports Server (NTRS)

Gunderson, R. W.

1975-01-01

A comparison principle based on a Kamke theorem and Lipschitz conditions is presented along with its possible applications and modifications. It is shown that the comparison lemma can be used in the study of such areas as classical stability theory, higher order trajectory derivatives, Liapunov functions, boundary value problems, approximate dynamic systems, linear and nonlinear systems, and bifurcation analysis.

Tracing the Transition from Study to a Contemporary Creative Working Life: The Trajectories of Professional Musicians

ERIC Educational Resources Information Center

Juuti, Sini; Littleton, Karen

2012-01-01

The classical music academy is a site dominated by traditional meanings of creative practice and an image of the professional creative career as solo performer that is fully available to only a very few students after graduating. The purpose of the study reported in this paper is to explore career-young professional pianists' talk about the…

Collapse of the soap-film bridge - Quasistatic description

NASA Astrophysics Data System (ADS)

Cryer, Steven A.; Steen, Paul H.

1992-11-01

Observations of the collapse of a soap-film bridge from a connected to a disconnected state are recorded. The equilibrium framework for this nonequilibrium event is classical. Experiments confirm predictions of stable and unstable equilibria. A quasistatic description is introduced for the dynamic states to extend the static theory. It is found to adequately describe the collapse trajectory while the bridge is still connected.

Collapse of the soap-film bridge - Quasistatic description

NASA Technical Reports Server (NTRS)

Cryer, Steven A.; Steen, Paul H.

1992-01-01

Observations of the collapse of a soap-film bridge from a connected to a disconnected state are recorded. The equilibrium framework for this nonequilibrium event is classical. Experiments confirm predictions of stable and unstable equilibria. A quasistatic description is introduced for the dynamic states to extend the static theory. It is found to adequately describe the collapse trajectory while the bridge is still connected.

Removing the barrier to the calculation of activation energies

DOE PAGES

Mesele, Oluwaseun O.; Thompson, Ward H.

2016-10-06

Approaches for directly calculating the activation energy for a chemical reaction from a simulation at a single temperature are explored with applications to both classical and quantum systems. The activation energy is obtained from a time correlation function that can be evaluated from the same molecular dynamics trajectories or quantum dynamics used to evaluate the rate constant itself and thus requires essentially no extra computational work.

The probability of false positives in zero-dimensional analyses of one-dimensional kinematic, force and EMG trajectories.

PubMed

Pataky, Todd C; Vanrenterghem, Jos; Robinson, Mark A

2016-06-14

A false positive is the mistake of inferring an effect when none exists, and although α controls the false positive (Type I error) rate in classical hypothesis testing, a given α value is accurate only if the underlying model of randomness appropriately reflects experimentally observed variance. Hypotheses pertaining to one-dimensional (1D) (e.g. time-varying) biomechanical trajectories are most often tested using a traditional zero-dimensional (0D) Gaussian model of randomness, but variance in these datasets is clearly 1D. The purpose of this study was to determine the likelihood that analyzing smooth 1D data with a 0D model of variance will produce false positives. We first used random field theory (RFT) to predict the probability of false positives in 0D analyses. We then validated RFT predictions via numerical simulations of smooth Gaussian 1D trajectories. Results showed that, across a range of public kinematic, force/moment and EMG datasets, the median false positive rate was 0.382 and not the assumed α=0.05, even for a simple two-sample t test involving N=10 trajectories per group. The median false positive rate for experiments involving three-component vector trajectories was p=0.764. This rate increased to p=0.945 for two three-component vector trajectories, and to p=0.999 for six three-component vectors. This implies that experiments involving vector trajectories have a high probability of yielding 0D statistical significance when there is, in fact, no 1D effect. Either (a) explicit a priori identification of 0D variables or (b) adoption of 1D methods can more tightly control α. Copyright © 2016 Elsevier Ltd. All rights reserved.

Simulation of Electric Potentials and Ion Motion in Planar Electrode Structures for Lossless Ion Manipulations (SLIM)

DOE PAGES

Garimella, Sandilya V. B; Ibrahim, Yehia M.; Webb, Ian K.; ...

2014-09-26

Here we report a conceptual study and computational evaluation of novel planar electrode Structures for Lossless Ion Manipulations (SLIM). Planar electrode SLIM devices were designed that allow for flexible ion confinement, transport and storage using a combination of RF and DC fields. Effective potentials can be generated that provide near ideal regions for confining ions in the presence of a gas. Ion trajectory simulations using SIMION 8.1 demonstrated the capability for lossless ion motion in these devices over a wide m/z range and a range of electric fields at low pressures (e.g. a few torr). More complex ion manipulations, e.g.more » turning ions by 90° and dynamically switching selected ion species into orthogonal channels, are also feasible. Lastly, the performance of SLIM devices at ~4 torr pressure for performing ion mobility based separations (IMS) is computationally evaluated and compared to initial experimental results, and both of which agree closely with experimental and theoretical IMS performance for a conventional drift tube design.« less

On non-autonomous dynamical systems

NASA Astrophysics Data System (ADS)

Anzaldo-Meneses, A.

2015-04-01

In usual realistic classical dynamical systems, the Hamiltonian depends explicitly on time. In this work, a class of classical systems with time dependent nonlinear Hamiltonians is analyzed. This type of problems allows to find invariants by a family of Veronese maps. The motivation to develop this method results from the observation that the Poisson-Lie algebra of monomials in the coordinates and momenta is clearly defined in terms of its brackets and leads naturally to an infinite linear set of differential equations, under certain circumstances. To perform explicit analytic and numerical calculations, two examples are presented to estimate the trajectories, the first given by a nonlinear problem and the second by a quadratic Hamiltonian with three time dependent parameters. In the nonlinear problem, the Veronese approach using jets is shown to be equivalent to a direct procedure using elliptic functions identities, and linear invariants are constructed. For the second example, linear and quadratic invariants as well as stability conditions are given. Explicit solutions are also obtained for stepwise constant forces. For the quadratic Hamiltonian, an appropriated set of coordinates relates the geometric setting to that of the three dimensional manifold of central conic sections. It is shown further that the quantum mechanical problem of scattering in a superlattice leads to mathematically equivalent equations for the wave function, if the classical time is replaced by the space coordinate along a superlattice. The mathematical method used to compute the trajectories for stepwise constant parameters can be applied to both problems. It is the standard method in quantum scattering calculations, as known for locally periodic systems including a space dependent effective mass.

Ion-Stockmayer clusters: Minima, classical thermodynamics, and variational ground state estimates of Li+(CH3NO2)n (n = 1-20)

NASA Astrophysics Data System (ADS)

Curotto, E.

2015-12-01

Structural optimizations, classical NVT ensemble, and variational Monte Carlo simulations of ion Stockmayer clusters parameterized to approximate the Li+(CH3NO2)n (n = 1-20) systems are performed. The Metropolis algorithm enhanced by the parallel tempering strategy is used to measure internal energies and heat capacities, and a parallel version of the genetic algorithm is employed to obtain the most important minima. The first solvation sheath is octahedral and this feature remains the dominant theme in the structure of clusters with n ≥ 6. The first "magic number" is identified using the adiabatic solvent dissociation energy, and it marks the completion of the second solvation layer for the lithium ion-nitromethane clusters. It corresponds to the n = 18 system, a solvated ion with the first sheath having octahedral symmetry, weakly bound to an eight-membered and a four-membered ring crowning a vertex of the octahedron. Variational Monte Carlo estimates of the adiabatic solvent dissociation energy reveal that quantum effects further enhance the stability of the n = 18 system relative to its neighbors.

Computer Modeling of High-Intensity Cs-Sputter Ion Sources

NASA Astrophysics Data System (ADS)

Brown, T. A.; Roberts, M. L.; Southon, J. R.

The grid-point mesh program NEDLab has been used to computer model the interior of the high-intensity Cs-sputter source used in routine operations at the Center for Accelerator Mass Spectrometry (CAMS), with the goal of improving negative ion output. NEDLab has several features that are important to realistic modeling of such sources. First, space-charge effects are incorporated in the calculations through an automated ion-trajectories/Poissonelectric-fields successive-iteration process. Second, space charge distributions can be averaged over successive iterations to suppress model instabilities. Third, space charge constraints on ion emission from surfaces can be incorporate under Child's Law based algorithms. Fourth, the energy of ions emitted from a surface can be randomly chosen from within a thermal energy distribution. And finally, ions can be emitted from a surface at randomized angles The results of our modeling effort indicate that significant modification of the interior geometry of the source will double Cs+ ion production from our spherical ionizer and produce a significant increase in negative ion output from the source.

Design of a Prototype Positive Ion Source with Slit Aperture Type Extraction System

NASA Astrophysics Data System (ADS)

Sharma, Sanjeev K.; Vattilli, Prahlad; Choksi, Bhargav; Punyapu, Bharathi; Sidibomma, Rambabu; Bonagiri, Sridhar; Aggrawal, Deepak; Baruah, Ujjwal K.

2017-04-01

The neutral beam injector group at IPR aims at developing an experimental positive ion source capable of delivering H+ ion beam having energy of 30 - 40 keV and carrying an ion beam current of 5 A. The slit aperture based extraction system is chosen for extracting and accelerating the ions so as to achieve low divergence of the ion beam (< 0.5°). For producing H+ ions a magnetic multi-pole bucket type plasma chamber is selected. We calculated the magnetic field due to cusp magnets and trajectories (orbits) of the primary electrons to investigate the two magnetic configurations i.e. line cusp and checker board. Numerical simulation is also carried out by using OPERA-3D to study the characteristic performance of the slit aperture type extraction-acceleration system. We report here the results of the studies carried out on various aspects of the design of the slit aperture type positive ion source.

Water-soluble main ions in precipitation over the southeastern Adriatic region: chemical composition and long-range transport.

PubMed

Dorđević, Dragana S; Tosić, Ivana; Unkasević, Miroslava; Durasković, Pavle

2010-11-01

Precipitation samples collected from 1995 to 2000 at meteorological station in the eastern outskirts of Herceg Novi (Montenegro) were analysed on Na(+), K(+), Mg(2+), Ca(2+), Cl(-), SO(4) (2-), NO(3)(-) and NH(4)(+). Four-day backward trajectory simulations were conducted during the precipitation period to investigate the regional transport of main ions and their deposition in the region of the southeastern Adriatic Sea. The air mass trajectories were classified into six trajectory categories by the origin and direction of their approach to Herceg Novi. A bottle and funnel with a small net between them was used for sampling at a height of 1.5 m above the ground. The concentrations of Cl(-), NO(3)(-), NH(4)(+) and SO(4)(2-) were determined spectrophotometrically, the concentrations of Na(+) and K(+) were determined by the FAES method and the concentrations of Mg(2+) and Ca(2+) by the FAAS method. The factor analysis technique (PCA analysis) based on the calculation of the factors was employed to differentiate the contribution of emission sources to the content of the main ions in the precipitation. The obtained data sets were processed using the SPSS 11.5 statistical program. The Hybrid Single-Particle Lagrangian Integrated Trajectory model was used to study the air origin for the city of Herceg Novi (42°27'N, 18°33'E), Montenegro. The following origins of the air masses were considered: northern Europe (NE), eastern Europe-northeastern Europe (EE-NE); eastern Mediterranean-southeastern Europe (EM-SE); Africa-Central Mediterranean (A-CM); western Mediterranean (WM); western Europe-Central Europe (WE-CE) and undefined. The heights and frequencies of precipitation coming by air masses from northern Europe and eastern-northeastern Europe are the lowest. On the contrary, the heights and frequencies of precipitation coming by air masses from the western Mediterranean (36.6%) and Africa and the Central Mediterranean (30.6%) are the highest. The sea salt components (Na(+), Cl(-), Mg(2+)) are significantly correlated, except for air masses originating from the northern and eastern European regions. Significant correlations between SO(4)(2-) and NO(3)(-) are found in air masses coming from the western Europe and North Africa, over the Mediterranean. The highest volume-weighted mean (VWM) of: SO(4)(2-), NH(4)(+) and Mg(2+) are for precipitation from EE-NE while the highest values of VWM of Cl(-) are from WM and of K(+) are from WE-CE. Long-range transport of Sahara dust is confirmed. For better estimation of origins of water-soluble ions in precipitation expanding list of analysis on anions of organic acids, such as HCOO(-), CH(3)COO(-), and C(2)H(2)COO(-), could be indicative of volatile organic compounds emitted by vegetation but also traffic. The chemical composition of precipitation together with a study of air backward trajectories is the proper tool for tracking the long-range transport of water-soluble ions and estimating transboundary pollution.

Relationship between wave energy and free energy from pickup ions in the Comet Halley environment

NASA Technical Reports Server (NTRS)

Huddleston, D. E.; Johnstone, A. D.

1992-01-01

The free energy available from the implanted heavy ion population at Comet Halley is calculated by assuming that the initial unstable velocity space ring distribution of the ions evolves toward a bispherical shell. Ultimately this free energy adds to the turbulence in the solar wind. Upstream and downstream free energies are obtained separately for the conditions observed along the Giotto spacecraft trajectory. The results indicate that the waves are mostly upstream propagating in the solar wind frame. The total free energy density always exceeds the measured wave energy density because, as expected in the nonlinear process of ion scattering, the available energy is not all immediately released. An estimate of the amount which has been released can be obtained from the measured oxygen ion distributions and again it exceeds that observed. The theoretical analysis is extended to calculate the k spectrum of the cometary-ion-generated turbulence.

Mass spectrometry and inhomogeneous ion optics

NASA Technical Reports Server (NTRS)

White, F. A.

1973-01-01

Work done in several areas to advance the state of the art of magnetic mass spectrometers is described. The calculations and data necessary for the design of inhomogeneous field mass spectrometers, and the calculation of ion trajectories through such fields are presented. The development and testing of solid state ion detection devices providing the capability of counting single ions is discussed. New techniques in the preparation and operation of thermal-ionization ion sources are described. Data obtained on the concentrations of copper in rainfall and uranium in air samples using the improved thermal ionization techniques are presented. The design of a closed system static mass spectrometer for isotopic analyses is discussed. A summary of instrumental aspects of a four-stage mass spectrometer comprising two electrostatic and two 90 deg. magnetic lenses with a 122-cm radius used to study the interaction of ions with solids is presented.

Computers and the design of ion beam optical systems

NASA Astrophysics Data System (ADS)

White, Nicholas R.

Advances in microcomputers have made it possible to maintain a library of advanced ion optical programs which can be used on inexpensive computer hardware, which are suitable for the design of a variety of ion beam systems including ion implanters, giving excellent results. This paper describes in outline the steps typically involved in designing a complete ion beam system for materials modification applications. Two computer programs are described which, although based largely on algorithms which have been in use for many years, make possible detailed beam optical calculations using microcomputers, specifically the IBM PC. OPTICIAN is an interactive first-order program for tracing beam envelopes through complex optical systems. SORCERY is a versatile program for solving Laplace's and Poisson's equations by finite difference methods using successive over-relaxation. Ion and electron trajectories can be traced through these potential fields, and plots of beam emittance obtained.

Compact injector with alternating phase focusing-interdigital H-mode linac and superconducting electron cyclotron resonance ion source for heavy ion cancer therapy

NASA Astrophysics Data System (ADS)

Hayashizaki, Noriyosu; Hattori, Toshiyuki; Matsui, Shinjiro; Tomizawa, Hiromitsu; Yoshida, Toru; Isokawa, Katsushi; Kitagawa, Atsushi; Muramatsu, Masayuki; Yamada, Satoru; Okamura, Masahiro

2000-02-01

We have researched a compact medical accelerator with low investment and running cost for the popularization of heavy ion cancer therapy. As the first step, the compact injector system has been investigated for a Heavy Ion Medical Accelerator in Chiba at National Institute of Radiological Sciences. The proposed new injector system consists of a 6 MeV/u interdigital H-mode (IH) linac of 3.1 m long and a 18 GHz superconducting electron cyclotron resonance (ECR) (SC-ECR) ion source. The IH linac with high power efficiency is appropriate to a medical and industrial injector system. Its beam trajectory was simulated and a prototype has been constructed. The SC-ECR ion source has been designed to realize lightweight and low power consumption and the mirror field distribution was estimated.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sakaki, H.; Fukuda, Y.; Nishiuchi, M.

A single-shot-imaging thin scintillator film was developed for an online Thomson parabola (TP) spectrometer and the first analysis of laser accelerated ions, using the online TP spectrometer, was demonstrated at the JAEA-Kansai Advanced Relativistic Engineering Laser System (J-KAREN). An energy spectrum of {approx}4.0 MeV protons is obtained using only this imaging film without the need of a microchannel plate that is typically utilized in online ion analyses. A general-purpose Monte Carlo particle and heavy ion-transport code system, which consists of various quantum dynamics models, was used for the prediction of the luminescent properties of the scintillator. The simulation can reasonablymore » predict not only the ion trajectories detected by the spectrometer, but also luminescence properties.« less

Influence of Chloride Ion and Temperature on the Corrosion Behavior of Ni-Fe-Cr Alloy 028

NASA Astrophysics Data System (ADS)

Zhang, L. N.; Dong, J. X.; Szpunar, J. A.; Zhang, M. C.; Basu, R.

Recently, the working condition of tubing systems used in oil and natural gas industries are severer than before with the increasing exploitation of acidic gas fields. The corrosion problems induced from the corrosive environment with chloride ion medium and high temperature have been much more concerned. The presence of chloride ion can accelerate the dissolution of metals. The corrosion performance is also sensitive to the operating temperature. Classic localized corrosions such as the pitting or the crevice type due to environmental temperature and chloride ion.

Ion distribution and selectivity of ionic liquids in microporous electrodes.

PubMed

Neal, Justin N; Wesolowski, David J; Henderson, Douglas; Wu, Jianzhong

2017-05-07

The energy density of an electric double layer capacitor, also known as supercapacitor, depends on ion distributions in the micropores of its electrodes. Herein we study ion selectivity and partitioning of symmetric, asymmetric, and mixed ionic liquids among different pores using the classical density functional theory. We find that a charged micropore in contact with mixed ions of the same valence is always selective to the smaller ions, and the ion selectivity, which is strongest when the pore size is comparable to the ion diameters, drastically falls as the pore size increases. The partitioning behavior in ionic liquids is fundamentally different from those corresponding to ion distributions in aqueous systems whereby the ion selectivity is dominated by the surface energy and entropic effects insensitive to the degree of confinement.

Water Lone Pair Delocalization in Classical and Quantum Descriptions of the Hydration of Model Ions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Remsing, Richard C.; Duignan, Timothy T.; Baer, Marcel D.

Understanding the nature of ionic hydration at a fundamental level has eluded scientists despite intense interest for nearly a century. In particular, the microscopic origins of the asymmetry of ion solvation thermodynamics with respect to the sign of the ionic charge remains a mystery. Here, we determine the response of accurate quantum mechanical water models to strong nanoscale solvation forces arising from excluded volumes and ionic electrostatic fields. This is compared to the predictions of two important limiting classes of classical models of water with fixed point changes, differing in their treatment of "lone-pair" electrons. Using the quantum water modelmore » as our standard of accuracy, we find that a single fixed classical treatment of lone pair electrons cannot accurately describe solvation of both apolar and cationic solutes, underlining the need for a more flexible description of local electronic effects in solvation processes. However, we explicitly show that all water models studied respond to weak long-ranged electrostatic perturbations in a manner that follows macroscopic dielectric continuum models, as would be expected. We emphasize the importance of these findings in the context of realistic ion models, using density functional theory and empirical models, and discuss the implications of our results for quantitatively accurate reduced descriptions of solvation in dielectric media.« less

Plasma sheath effects on ion collection by a pinhole

NASA Technical Reports Server (NTRS)

Herr, Joel L.; Snyder, David B.

1993-01-01

This work presents tables to assist in the evaluation of pinhole collection effects on spacecraft. These tables summarize results of a computer model which tracks particle trajectories through a simplified electric field in the plasma sheath. A technique is proposed to account for plasma sheath effects in the application of these results and scaling rules are proposed to apply the calculations to specific situations. This model is compared to ion current measurements obtained by another worker, and the agreement is very good.

Plasma Heating Simulation in the VASIMR System

NASA Technical Reports Server (NTRS)

Ilin, Andrew V.; ChangDiaz, Franklin R.; Squire, Jared P.; Carter, Mark D.

2005-01-01

The paper describes the recent development in the simulation of the ion-cyclotron acceleration of the plasma in the VASIMR experiment. The modeling is done using an improved EMIR code for RF field calculation together with particle trajectory code for plasma transport calculat ion. The simulation results correlate with experimental data on the p lasma loading and predict higher ICRH performance for a higher density plasma target. These simulations assist in optimizing the ICRF anten na so as to achieve higher VASIMR efficiency.

Heavy ion beam-ionosphere interactions - Electron acceleration

NASA Technical Reports Server (NTRS)

Kaufmann, R. L.; Arnoldy, R. L.; Moore, T. E.; Kintner, P. M.; Cahill, L. J., Jr.

1985-01-01

Moore et al. (1982) described a number of unexpected effects which were observed during the first Argon Release Controlled Study (ARCS 1, or rocket flight 29:014). The present paper provides a description of detailed analyses of the interaction of the argon beam with the ionosphere. An important feature of the considered test was that all detectors and the Ar(+) gun remained attached to the rocket throughout the flight. It is pointed out that the most dramatic effect of ion gun operation on ARCS 1 involved large changes in the fluxes of electrons with energies below about 600 eV. The observations are discussed, taking into account the distribution functions, azimuth dependence, and electron and ion trajectories. Attention is given to the perpendicular ion beam, the parallel ion beam, the acceleration of downgoing and upgoing electrons, and aspects of wave generation.

Nonlinear saturation of the slab ITG instability and zonal flow generation with fully kinetic ions

NASA Astrophysics Data System (ADS)

Miecnikowski, Matthew T.; Sturdevant, Benjamin J.; Chen, Yang; Parker, Scott E.

2018-05-01

Fully kinetic turbulence models are of interest for their potential to validate or replace gyrokinetic models in plasma regimes where the gyrokinetic expansion parameters are marginal. Here, we demonstrate fully kinetic ion capability by simulating the growth and nonlinear saturation of the ion-temperature-gradient instability in shearless slab geometry assuming adiabatic electrons and including zonal flow dynamics. The ion trajectories are integrated using the Lorentz force, and the cyclotron motion is fully resolved. Linear growth and nonlinear saturation characteristics show excellent agreement with analogous gyrokinetic simulations across a wide range of parameters. The fully kinetic simulation accurately reproduces the nonlinearly generated zonal flow. This work demonstrates nonlinear capability, resolution of weak gradient drive, and zonal flow physics, which are critical aspects of modeling plasma turbulence with full ion dynamics.

An electrostatic autoresonant ion trap mass spectrometer.

PubMed

Ermakov, A V; Hinch, B J

2010-01-01

A new method for ion extraction from an anharmonic electrostatic trap is introduced. Anharmonicity is a common feature of electrostatic traps which can be used for small scale spatial confinement of ions, and this feature is also necessary for autoresonant ion extraction. With the aid of ion trajectory simulations, novel autoresonant trap mass spectrometers (ART-MSs) have been designed based on these very simple principles. A mass resolution approximately 60 is demonstrated for the prototypes discussed here. We report also on the pressure dependencies, and the (mV) rf field strength dependencies of the ART-MS sensitivity. Importantly the new MS designs do not require heavy magnets, tight manufacturing tolerances, introduction of buffer gases, high power rf sources, nor complicated electronics. The designs described here are very inexpensive to implement relative to other instruments, and can be easily miniaturized. Possible applications are discussed.

X-ray emission from high temperature plasmas

NASA Technical Reports Server (NTRS)

Harries, W. L.

1977-01-01

The physical processes occurring in plasma focus devices were investigated with particular emphasis on X-ray emission. Topics discussed include: trajectories of high energy electrons; detection of ion trajectories; spatial distribution of neutron emission; space and time resolved emission of hard X-rays from a plasma focus; the staged plasma focus as a variation of the hypocloidal pinch; formation of current sheets in a staged plasma focus; and X-ray and neutron emission from a staged plasma focus. The possibility of operating dense plasma-focus type devices in multiple arrays beyond the scaling law for a single gun is discussed.

Jupiter Icy Moons Orbiter Mission design overview

NASA Technical Reports Server (NTRS)

Sims, Jon A.

2006-01-01

An overview of the design of a possible mission to three large moons of Jupiter (Callisto, Ganymede, and Europa) is presented. The potential Jupiter Icy Moons Orbiter (JIMO) mission uses ion thrusters powered by a nuclear reactor to transfer from Earth to Jupiter and enter a low-altitude science orbit around each of the moons. The combination of very limited control authority and significant multibody dynamics resulted in some aspects of the trajectory design being different than for any previous mission. The results of several key trades, innovative trajectory types and design processes, and remaining issues are presented.

Plasma IMS Composition Measurements for Europa and the Other Galilean Moons

NASA Technical Reports Server (NTRS)

Sittler, Edward; Cooper, John; Hartle, Richard; Lipatov, Alexander; Mahaffy, Paul; Paterson, William; Pachalidis, Nick; Coplan, Mike; Cassidy, Tim

2010-01-01

NASA and ESA are planning the joint Europa Jupiter System Mission (EJSM) to the Jupiter system with specific emphasis to Europa and Ganymede, respectively. The Japanese Space Agency is also planning an orbiter mission to explore Jupiter's magnetosphere and the Galilean satellites. For NASA's Jupiter Europa Orbiter (JEO) we are developing the 3D Ion Mass Spectrometer (IMS) with two main goals which can also be applied to the other Galilean moons, 1) measure the plasma interaction between Europa and Jupiter's magnetosphere and 2) infer the 4 pi surface composition to trace elemental and significant isotopic levels. The first goal supports the magnetometer (MAG) measurements, primarily directed at detection of Europa's sub-surface ocean, while the second gives information about transfer of material between the Galilean moons, and between the moon surfaces and subsurface layers putatively including oceans. The measurement of the interactions for all the Galilean moons can be used to trace the in situ ion measurements of pickup ions back to either Europa's or Ganymede's surface from the respectively orbiting spacecraft. The IMS instrument, being developed under NASA's Astrobiology Instrument Development Program, would maximally achieve plasma measurement requirements for JEO and EJSM while moving forward our knowledge of Jupiter system composition and source processes to far higher levels than previously envisaged. The composition of the global surfaces of Europa and Ganymede can be inferred from the measurement of ejected neutrals and pick-up ions using at minimum an in situ payload including MAG and IMS also fully capable of meeting Level 1 mission requirements for ocean detection and survey. Elemental and isotopic analysis of potentially extruded oceanic materials at the moon surfaces would further support the ocean objectives. These measurements should be made from a polar orbiting spacecraft about Europa or Ganymede at height 100 km. The ejecta produced by sputtering of the surfaces of Europa and Ganymede has been shown to be representative of the surface composition. Level 2 science on surface geology and composition can then be further enhanced by addition of the following: 3D Ion Neutral Mass Spectrometer (INNS), 3D plasma electron spectrometer (ELS), and hot plasma energetic particle instrument. The measurement approach is to alternate between times measuring pickup ions and times measuring plasma and magnetic field parameters along the spacecraft trajectory. By measuring the pickup ion energy, arrival direction and mass-per-charge, the ion can be traced back along the ejection trajectory to the approximate area of origin if the 3-D electric field and magnetic field are known. In situ observations of plasma flow velocities and vector magnetic fields can be used to determine the local convective electric field (E = -VXB) along the spacecraft trajectory. By combining this information with models of the magnetospheric interaction with Europa, one can generate 3D maps of the electric and magnetic field and compute the trajectories of the pickup ions back to the surface or exospheric points of origin. In the case of Ganymede there is the additional complexity of its own internal dipole magnetic field, while Io's volcanic activity introduces the complexity of a highly structured denser atmosphere. Callisto with its less globally extended exosphere will have a simpler interaction than for Europa (i.e., more like our moon). We will discuss these differences in light of the above proposed technique. Finally, the INNS observations and neutral exosphere models are needed to estimate production rates of pickup ions. The hot plasma measurements are needed to correct for sputtering rates which can be time dependent and electron plasma observations for electron impact ionization rates. Instrument characteristics, field-of-view requirements, modes of operation and effects of radiation on instrument functionality will be discussed.

Kinetic theory molecular dynamics and hot dense matter: theoretical foundations.

PubMed

Graziani, F R; Bauer, J D; Murillo, M S

2014-09-01

Electrons are weakly coupled in hot, dense matter that is created in high-energy-density experiments. They are also mildly quantum mechanical and the ions associated with them are classical and may be strongly coupled. In addition, the dynamical evolution of plasmas under these hot, dense matter conditions involve a variety of transport and energy exchange processes. Quantum kinetic theory is an ideal tool for treating the electrons but it is not adequate for treating the ions. Molecular dynamics is perfectly suited to describe the classical, strongly coupled ions but not the electrons. We develop a method that combines a Wigner kinetic treatment of the electrons with classical molecular dynamics for the ions. We refer to this hybrid method as "kinetic theory molecular dynamics," or KTMD. The purpose of this paper is to derive KTMD from first principles and place it on a firm theoretical foundation. The framework that KTMD provides for simulating plasmas in the hot, dense regime is particularly useful since current computational methods are generally limited by their inability to treat the dynamical quantum evolution of the electronic component. Using the N-body von Neumann equation for the electron-proton plasma, three variations of KTMD are obtained. Each variant is determined by the physical state of the plasma (e.g., collisional versus collisionless). The first variant of KTMD yields a closed set of equations consisting of a mean-field quantum kinetic equation for the electron one-particle distribution function coupled to a classical Liouville equation for the protons. The latter equation includes both proton-proton Coulombic interactions and an effective electron-proton interaction that involves the convolution of the electron density with the electron-proton Coulomb potential. The mean-field approach is then extended to incorporate equilibrium electron-proton correlations through the Singwi-Tosi-Land-Sjolander (STLS) ansatz. This is the second variant of KTMD. The STLS contribution produces an effective electron-proton interaction that involves the electron-proton structure factor, thereby extending the usual mean-field theory to correlated but near equilibrium systems. Finally, a third variant of KTMD is derived. It includes dynamical electrons and their correlations coupled to a MD description for the ions. A set of coupled equations for the one-particle electron Wigner function and the electron-electron and electron-proton correlation functions are coupled to a classical Liouville equation for the protons. This latter variation has both time and momentum dependent correlations.

Comparative analyses of plasma probe diagnostics techniques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Godyak, V. A.; Alexandrovich, B. M.

The subject of this paper is a comparative analysis of the plasma parameters inferred from the classical Langmuir probe procedure, from different theories of the ion current to the probe, and from measured electron energy distribution function (EEDF) obtained by double differentiation of the probe characteristic. We concluded that the plasma parameters inferred from the classical Langmuir procedure can be subjected to significant inaccuracy due to the non-Maxwellian EEDF, uncertainty of locating the plasma potential, and the arbitrariness of the ion current approximation. The plasma densities derived from the ion part of the probe characteristics diverge by as much asmore » an order of magnitude from the density calculated according to Langmuir procedure or calculated as corresponding integral of the measured EEDF. The electron temperature extracted from the ion part is always subjected to uncertainty. Such inaccuracy is attributed to modification of the EEDF for fast electrons due to inelastic electron collisions, and to deficiencies in the existing ion current theories; i.e., unrealistic assumptions about Maxwellian EEDFs, underestimation of the ion collisions and the ion ambipolar drift, and discounting deformation of the one-dimensional structure of the region perturbed by the probe. We concluded that EEDF measurement is the single reliable probe diagnostics for the basic research and industrial applications of highly non-equilibrium gas discharge plasmas. Examples of EEDF measurements point up importance of examining the probe current derivatives in real time and reiterate significance of the equipment technical characteristics, such as high energy resolution and wide dynamic range.« less

Restoring the consistency with the contact density theorem of a classical density functional theory of ions at a planar electrical double layer.

PubMed

Gillespie, Dirk

2014-11-01

Classical density functional theory (DFT) of fluids is a fast and efficient theory to compute the structure of the electrical double layer in the primitive model of ions where ions are modeled as charged, hard spheres in a background dielectric. While the hard-core repulsive component of this ion-ion interaction can be accurately computed using well-established DFTs, the electrostatic component is less accurate. Moreover, many electrostatic functionals fail to satisfy a basic theorem, the contact density theorem, that relates the bulk pressure, surface charge, and ion densities at their distances of closest approach for ions in equilibrium at a smooth, hard, planar wall. One popular electrostatic functional that fails to satisfy the contact density theorem is a perturbation approach developed by Kierlik and Rosinberg [Phys. Rev. A 44, 5025 (1991)PLRAAN1050-294710.1103/PhysRevA.44.5025] and Rosenfeld [J. Chem. Phys. 98, 8126 (1993)JCPSA60021-960610.1063/1.464569], where the full free-energy functional is Taylor-expanded around a bulk (homogeneous) reference fluid. Here, it is shown that this functional fails to satisfy the contact density theorem because it also fails to satisfy the known low-density limit. When the functional is corrected to satisfy this limit, a corrected bulk pressure is derived and it is shown that with this pressure both the contact density theorem and the Gibbs adsorption theorem are satisfied.

Comparative analyses of plasma probe diagnostics techniques

NASA Astrophysics Data System (ADS)

Godyak, V. A.; Alexandrovich, B. M.

2015-12-01

The subject of this paper is a comparative analysis of the plasma parameters inferred from the classical Langmuir probe procedure, from different theories of the ion current to the probe, and from measured electron energy distribution function (EEDF) obtained by double differentiation of the probe characteristic. We concluded that the plasma parameters inferred from the classical Langmuir procedure can be subjected to significant inaccuracy due to the non-Maxwellian EEDF, uncertainty of locating the plasma potential, and the arbitrariness of the ion current approximation. The plasma densities derived from the ion part of the probe characteristics diverge by as much as an order of magnitude from the density calculated according to Langmuir procedure or calculated as corresponding integral of the measured EEDF. The electron temperature extracted from the ion part is always subjected to uncertainty. Such inaccuracy is attributed to modification of the EEDF for fast electrons due to inelastic electron collisions, and to deficiencies in the existing ion current theories; i.e., unrealistic assumptions about Maxwellian EEDFs, underestimation of the ion collisions and the ion ambipolar drift, and discounting deformation of the one-dimensional structure of the region perturbed by the probe. We concluded that EEDF measurement is the single reliable probe diagnostics for the basic research and industrial applications of highly non-equilibrium gas discharge plasmas. Examples of EEDF measurements point up importance of examining the probe current derivatives in real time and reiterate significance of the equipment technical characteristics, such as high energy resolution and wide dynamic range.

The cooling of confined ions driven by laser beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reyna, L.G.; Sobehart, J.R.

1993-07-01

We finalize the dynamics of confined ions driven by a quantized radiation field. The ions can absorb photons from an incident laser beam and relax back to the ground state by either induced emissions or spontaneous emissions. Here we assume that the absorption of photons is immediately followed by spontaneous emissions, resulting in single-level ions perturbed by the exchange of momentum with the radiation field. The probability distribution of the ions is calculated using singular expansions in the low noise asymptotic limit. The present calculations reproduce the quantum results in the limit of heavy particles in static traps, and themore » classical results of ions in radio-frequency confining wells.« less

Bi-harmonic cantilever design for improved measurement sensitivity in tapping-mode atomic force microscopy.

PubMed

Loganathan, Muthukumaran; Bristow, Douglas A

2014-04-01

This paper presents a method and cantilever design for improving the mechanical measurement sensitivity in the atomic force microscopy (AFM) tapping mode. The method uses two harmonics in the drive signal to generate a bi-harmonic tapping trajectory. Mathematical analysis demonstrates that the wide-valley bi-harmonic tapping trajectory is as much as 70% more sensitive to changes in the sample topography than the standard single-harmonic trajectory typically used. Although standard AFM cantilevers can be driven in the bi-harmonic tapping trajectory, they require large forcing at the second harmonic. A design is presented for a bi-harmonic cantilever that has a second resonant mode at twice its first resonant mode, thereby capable of generating bi-harmonic trajectories with small forcing signals. Bi-harmonic cantilevers are fabricated by milling a small cantilever on the interior of a standard cantilever probe using a focused ion beam. Bi-harmonic drive signals are derived for standard cantilevers and bi-harmonic cantilevers. Experimental results demonstrate better than 30% improvement in measurement sensitivity using the bi-harmonic cantilever. Images obtained through bi-harmonic tapping exhibit improved sharpness and surface tracking, especially at high scan speeds and low force fields.

Numerical design of an EBIS collector to optimize electron collection and ion extraction

NASA Astrophysics Data System (ADS)

Dietrich, Jürgen

1990-12-01

For the Frankfurt EBIS (R. Becker et al., Nucl. Instr. and Meth. B24/25 (1987) 838, ref. [1]), a new collector was designed using the relativistic electron optics program EGUN (W.B. Herrmannsfeldt, SLAC-331 (1988), ref. [2]) and the magnetic field program INTMAG (R. Becker, Nucl. Instr. and Meth. B42 (1989) 303, ref. [3]). To model the fringing field of the main solenoid, a bucking coil and a cylindrical shim is provided. The current of the bucking coil and the position and shape of the shim are optimized with INTMAG for minimum fringing field to allow expansion of the electron beam by its space charge. The magnetic field data output from INTMAG is directly used as input for EGUN to calculate the electron and ion trajectories. The initial conditions for the trajectories were computed from the paraxial ray equation. Different operation modes of the collector are investigated including the behaviour of secondary electrons.

Simulation of Paramecium Chemotaxis Exposed to Calcium Gradients.

PubMed

Sarvestani, Ali N; Shamloo, Amir; Ahmadian, Mohammad Taghi

2016-06-01

Paramecium or other ciliates have the potential to be utilized for minimally invasive surgery systems, making internal body organs accessible. Paramecium shows interesting responses to changes in the concentration of specific ions such as K(+), Mg(2+), and Ca(2+) in the ambient fluid. Some specific responses are observed as, changes in beat pattern of cilia and swimming toward or apart from the ion source. Therefore developing a model for chemotactic motility of small organisms is necessary in order to control the directional movements of these microorganisms before testing them. In this article, we have developed a numerical model, investigating the effects of Ca(2+) on swimming trajectory of Paramecium. Results for Ca(2+)-dependent chemotactic motility show that calcium gradients are efficient actuators for controlling the Paramecium swimming trajectory. After applying a very low Ca(2+) gradient, a directional chemotaxis of swimming Paramecium is observable in this model. As a result, chemotaxis is shown to be an efficient method for controlling the propulsion of these small organisms.

Observation of bow shock protons at the lunar orbit. M.S. Thesis; [particle trajectory analysis of solar protons in the lunar atmosphere

NASA Technical Reports Server (NTRS)

Benson, J. L.

1974-01-01

Protons with energies ranging from about 500 eV to 3,500 eV were observed by the Suprathermal Ion Detector Experiment (SIDE) on both the dusk and dawn sides of the magnetosphere. On each lunation these particles appeared as a rather continuous phenomenon for 3 to 5 days after crossing from the dawn-side magnetosheath into the solar wind and for about 2 days prior to entering the dusk-side magnetosheath. Data from the SIDE and from the Explorer 35 lunar orbiting magnetometer were analyzed and these data indicated that the transverse ion flows observed by the SIDE in the pre and post bow shock crossing regions of the lunar orbit are due to these deviated solar wind particles. A computer model based on drift trajectories for particles leaving the shock was developed and synthetic particle data produced by this model are in good agreement with the observed data.

The physics, performance and predictions of the PEGASES ion-ion thruster

NASA Astrophysics Data System (ADS)

Aanesland, Ane

2014-10-01

Electric propulsion (EP) is now used systematically in space applications (due to the fuel and lifetime economy) to the extent that EP is now recognized as the next generation space technology. The uses of EP systems have though been limited to attitude control of GEO-stationary satellites and scientific missions. Now, the community envisages the use of EP for a variety of other applications as well; such as orbit transfer maneuvers, satellites in low altitudes, space debris removal, cube-sat control, challenging scientific missions close to and far from earth etc. For this we need a platform of EP systems providing much more variety in performance than what classical Hall and Gridded thrusters can provide alone. PEGASES is a gridded thruster that can be an alternative for some new applications in space, in particular for space debris removal. Unlike classical ion thrusters, here positive and negative ions are alternately accelerated to produce thrust. In this presentation we will look at the fundamental aspects of PEGASES. The emphasis will be put on our current understanding, obtained via analytical models, PIC simulations and experimental measurements, of the alternate extraction and acceleration process. We show that at low grid bias frequencies (10 s of kHz), the system can be described as a sequence of negative and positive ions accelerated as packets within a classical DC mode. Here secondary electrons created in the downstream chamber play an important role in the beam space charge compensation. At higher frequencies (100 s of kHz) the transit time of the ions in the grid gap becomes comparable to the bias period, leading to an ``AC acceleration mode.'' Here the beam is fully space charge compensated and the ion energy and current are functions of the applied frequency and waveform. A generalization of the Child-Langmuir space charge limited law is developed for pulsed voltages and allows evaluating the optimal parameter space and performance of PEGASES. This work received financial state aid managed by the Agence Nationale de la Recherche under the reference ANR-2011-BS09-40 (EPIC) and ANR-11-IDEX-0004-02 (Plas@Par).

Nothing to lose: why early career scientists make ideal entrepreneurs.

PubMed

Thon, Jonathan N

2014-12-01

An entrepreneurial movement within science strives to invert the classical trajectory of academic research careers by positioning trainees at the apex of burgeoning industries. Young scientists today have nothing to lose and everything to gain by pursuing this 'third road', and academic institutes and established companies only stand to benefit from supporting this emerging movement of discovery research with economic purpose. Copyright © 2014 Elsevier Ltd. All rights reserved.

Li + solvation and kinetics of Li +–BF 4 -/PF 6 - ion pairs in ethylene carbonate. A molecular dynamics study with classical rate theories

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, Tsun-Mei; Dang, Liem X.

Using our polarizable force-field models and employing classical rate theories of chemical reactions, we examine the ethylene carbonate (EC) exchange process between the first and second solvation shells around Li+ and the dissociation kinetics of ion pairs Li+-[BF4] and Li+-[PF6] in this solvent. We calculate the exchange rates using transition state theory and correct them with transmission coefficients computed by the reactive flux; Impey, Madden, and McDonald approaches; and Grote-Hynes theory. We found the residence times of EC around Li+ ions varied from 70 to 450 ps, depending on the correction method used. We found the relaxation times changed significantlymore » from Li+-[BF4] to Li+-[PF6] ion pairs in EC. Our results also show that, in addition to affecting the free energy of dissociation in EC, the anion type also significantly influence the dissociation kinetics of ion pairing. This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. The calculations were carried out using computer resources provided by the Office of Basic Energy Sciences.« less

Nonadiabatic nuclear dynamics of the ammonia cation studied by surface hopping classical trajectory calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Belyaev, Andrey K., E-mail: belyaev@herzen.spb.ru; Domcke, Wolfgang, E-mail: wolfgang.domcke@ch.tum.de; Lasser, Caroline, E-mail: classer@ma.tum.de

The Landau–Zener (LZ) type classical-trajectory surface-hopping algorithm is applied to the nonadiabatic nuclear dynamics of the ammonia cation after photoionization of the ground-state neutral molecule to the excited states of the cation. The algorithm employs a recently proposed formula for nonadiabatic LZ transition probabilities derived from the adiabatic potential energy surfaces. The evolution of the populations of the ground state and the two lowest excited adiabatic states is calculated up to 200 fs. The results agree well with quantum simulations available for the first 100 fs based on the same potential energy surfaces. Three different time scales are detected formore » the nuclear dynamics: Ultrafast Jahn–Teller dynamics between the excited states on a 5 fs time scale; fast transitions between the excited state and the ground state within a time scale of 20 fs; and relatively slow partial conversion of a first-excited-state population to the ground state within a time scale of 100 fs. Beyond 100 fs, the adiabatic electronic populations are nearly constant due to a dynamic equilibrium between the three states. The ultrafast nonradiative decay of the excited-state populations provides a qualitative explanation of the experimental evidence that the ammonia cation is nonfluorescent.« less

A quasi-classical study of energy transfer in collisions of hyperthermal H atoms with SO2 molecules.

PubMed

da Silva, Ramon S; Garrido, Juan D; Ballester, Maikel Y

2017-08-28

A deep understanding of energy transfer processes in molecular collisions is at central attention in physical chemistry. Particularly vibrational excitation of small molecules colliding with hot light atoms, via a metastable complex formation, has shown to be an efficient manner of enhancing reactivity. A quasi-classical trajectory study of translation-to-vibration energy transfer (T-V ET) in collisions of hyperthermal H( 2 S) atoms with SO 2 (X̃ 1 A ' ) molecules is presented here. For such a study, a double many-body expansion potential energy surface previously reported for HSO 2 ( 2 A) is used. This work was motivated by recent experiments by Ma et al. studying collisions of H + SO 2 at the translational energy of 59 kcal/mol [J. Ma et al., Phys. Rev. A 93, 040702 (2016)]. Calculations reproduce the experimental evidence that during majority of inelastic non-reactive collision processes, there is a metastable intermediate formation (HOSO or HSO 2 ). Nevertheless, the analysis of the trajectories shows that there are two distinct mechanisms in the T-V ET process: direct and indirect. Direct T-V processes are responsible for the high population of SO 2 with relatively low vibrational excitation energy, while indirect ones dominate the conversion from translational energy to high values of the vibrational counterpart.

Atomic photoionization processes under magnification

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lepine, F.; Bordas, Ch.; Nicole, C.

2004-09-01

Recently, classical simulations of threshold photoionization in the presence of an electric field have shown that a clear distinction between direct and indirect trajectories followed by the outgoing electron can be observed in the patterns of electron impacts on a two-dimensional detector. Subsequently, slow photoelectron imaging experiments have been reported where this distinction could be observed in atomic xenon. Furthermore, using a magnifying electrostatic lens to improve the velocity-map imaging technique, oscillatory patterns were observed modulating the classical envelope that was measured in the experiments of Nicole et al. [Phys. Rev. Lett. 88, 133001 (2002)]. This extension of slow photoelectronmore » imaging, called photoionization microscopy, relies on the existence of interferences between various trajectories by which the electron moves from the atom to the plane of observation. In this article we present the main experimental results obtained both in slow photoelectron imaging and in photoionization microscopy. The formation of the interference pattern is discussed in the framework of a semiclassical model that is described in detail elsewhere. The qualitative information that can be drawn from the experiments is discussed, and the potential applications of photoionization microscopy are considered. Particular attention is paid to the role of continuum Stark resonances that appear between the saddle point in the Coulomb+dc field potential and the field-free ionization limit.« less

Transfer matrix calculation for ion optical elements using real fields

NASA Astrophysics Data System (ADS)

Mishra, P. M.; Blaum, K.; George, S.; Grieser, M.; Wolf, A.

2018-03-01

With the increasing importance of ion storage rings and traps in low energy physics experiments, an efficient transport of ion species from the ion source area to the experimental setup becomes essential. Some available, powerful software packages rely on transfer matrix calculations in order to compute the ion trajectory through the ion-optical beamline systems of high complexity. With analytical approaches, so far the transfer matrices are documented only for a few ideal ion optical elements. Here we describe an approach (using beam tracking calculations) to determine the transfer matrix for any individual electrostatic or magnetostatic ion optical element. We verify the procedure by considering the well-known cases and then apply it to derive the transfer matrix of a 90-degree electrostatic quadrupole deflector including its realistic geometry and fringe fields. A transfer line consisting of a quadrupole deflector and a quadrupole doublet is considered, where the results from the standard first order transfer matrix based ion optical simulation program implementing the derived transfer matrix is compared with the real field beam tracking simulations.

Development of a beam ion velocity detector for the heavy ion beam probe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fimognari, P. J., E-mail: PJFimognari@XanthoTechnologies.com; Crowley, T. P.; Demers, D. R.

2016-11-15

In an axisymmetric plasma, the conservation of canonical angular momentum constrains heavy ion beam probe (HIBP) trajectories such that measurement of the toroidal velocity component of secondary ions provides a localized determination of the poloidal flux at the volume where they originated. We have developed a prototype detector which is designed to determine the beam angle in one dimension through the detection of ion current landing on two parallel planes of detecting elements. A set of apertures creates a pattern of ion current on wires in the first plane and solid metal plates behind them; the relative amounts detected bymore » the wires and plates determine the angle which beam ions enter the detector, which is used to infer the toroidal velocity component. The design evolved from a series of simulations within which we modeled ion beam velocity changes due to equilibrium and fluctuating magnetic fields, along with the ion beam profile and velocity dispersion, and studied how these and characteristics such as the size, cross section, and spacing of the detector elements affect performance.« less

A Study on Fast Gates for Large-Scale Quantum Simulation with Trapped Ions

PubMed Central

Taylor, Richard L.; Bentley, Christopher D. B.; Pedernales, Julen S.; Lamata, Lucas; Solano, Enrique; Carvalho, André R. R.; Hope, Joseph J.

2017-01-01

Large-scale digital quantum simulations require thousands of fundamental entangling gates to construct the simulated dynamics. Despite success in a variety of small-scale simulations, quantum information processing platforms have hitherto failed to demonstrate the combination of precise control and scalability required to systematically outmatch classical simulators. We analyse how fast gates could enable trapped-ion quantum processors to achieve the requisite scalability to outperform classical computers without error correction. We analyze the performance of a large-scale digital simulator, and find that fidelity of around 70% is realizable for π-pulse infidelities below 10−5 in traps subject to realistic rates of heating and dephasing. This scalability relies on fast gates: entangling gates faster than the trap period. PMID:28401945

A Study on Fast Gates for Large-Scale Quantum Simulation with Trapped Ions.

PubMed

Taylor, Richard L; Bentley, Christopher D B; Pedernales, Julen S; Lamata, Lucas; Solano, Enrique; Carvalho, André R R; Hope, Joseph J

2017-04-12

Large-scale digital quantum simulations require thousands of fundamental entangling gates to construct the simulated dynamics. Despite success in a variety of small-scale simulations, quantum information processing platforms have hitherto failed to demonstrate the combination of precise control and scalability required to systematically outmatch classical simulators. We analyse how fast gates could enable trapped-ion quantum processors to achieve the requisite scalability to outperform classical computers without error correction. We analyze the performance of a large-scale digital simulator, and find that fidelity of around 70% is realizable for π-pulse infidelities below 10 -5 in traps subject to realistic rates of heating and dephasing. This scalability relies on fast gates: entangling gates faster than the trap period.

Design and optimization of interplanetary spacecraft trajectories

NASA Astrophysics Data System (ADS)

McConaghy, Thomas Troy

Scientists involved in space exploration are always looking for ways to accomplish more with their limited budgets. Mission designers can decrease operational costs by crafting trajectories with low launch costs, short time-of-flight, or low propellant requirements. Gravity-assist maneuvers and low-thrust, high-efficiency ion propulsion can be of great help. This dissertation describes advances in methods to design and optimize interplanetary spacecraft trajectories. particularly for missions using gravity-assist maneuvers or low-thrust engines (or both). The first part of this dissertation describes a new, efficient, two-step methodology to design and optimize low-thrust gravity-assist trajectories. Models for the launch vehicle, solar arrays, and engines are introduced and several examples of optimized trajectories are presented. For example, a 3.7-year Earth-Venus-Earth-Mars-Jupiter flyby trajectory with maximized final mass is described. The way that the parameterization of the optimization problem affects convergence speed and reliability is also investigated. The choice of coordinate system is shown to make a significant difference. The second part of this dissertation describes a way to construct Earth-Mars cycler trajectories---periodic orbits that repeatedly encounter Earth and Mars, yet require little or no propellant. We find that well-known cyclers, such as the Aldrin cycler, are special cases of a much larger family of cyclers. In fact, so many new cyclers are found that a comprehensive naming system (nomenclature) is proposed. One particularly promising new cycler, the "ballistic S1L1 cycler" is analyzed in greater detail.

Old and new approaches to the interpretation of acid-base metabolism, starting from historical data applied to diabetic acidosis.

PubMed

Mioni, Roberto; Marega, Alessandra; Lo Cicero, Marco; Montanaro, Domenico

2016-11-01

The approach to acid-base chemistry in medicine includes several methods. Currently, the two most popular procedures are derived from Stewart's studies and from the bicarbonate/BE-based classical formulation. Another method, unfortunately little known, follows the Kildeberg theory applied to acid-base titration. By using the data produced by Dana Atchley in 1933, regarding electrolytes and blood gas analysis applied to diabetes, we compared the three aforementioned methods, in order to highlight their strengths and their weaknesses. The results obtained, by reprocessing the data of Atchley, have shown that Kildeberg's approach, unlike the other two methods, is consistent, rational and complete for describing the organ-physiological behavior of the hydrogen ion turnover in human organism. In contrast, the data obtained using the Stewart approach and the bicarbonate-based classical formulation are misleading and fail to specify which organs or systems are involved in causing or maintaining the diabetic acidosis. Stewart's approach, despite being considered 'quantitative', does not propose in any way the concept of 'an amount of acid' and becomes even more confusing, because it is not clear how to distinguish between 'strong' and 'weak' ions. As for Stewart's approach, the classical method makes no distinction between hydrogen ions managed by the intermediate metabolism and hydroxyl ions handled by the kidney, but, at least, it is based on the concept of titration (base-excess) and indirectly defines the concept of 'an amount of acid'. In conclusion, only Kildeberg's approach offers a complete understanding of the causes and remedies against any type of acid-base disturbance.

Evaluation of Adherence to Nutritional Intervention Through Trajectory Analysis.

PubMed

Sevilla-Villanueva, B; Gibert, K; Sanchez-Marre, M; Fito, M; Covas, M I

2017-05-01

Classical pre-post intervention studies are often analyzed using traditional statistics. Nevertheless, the nutritional interventions have small effects on the metabolism and traditional statistics are not enough to detect these subtle nutrient effects. Generally, this kind of studies assumes that the participants are adhered to the assigned dietary intervention and directly analyzes its effects over the target parameters. Thus, the evaluation of adherence is generally omitted. Although, sometimes, participants do not effectively adhere to the assigned dietary guidelines. For this reason, the trajectory map is proposed as a visual tool where dietary patterns of individuals can be followed during the intervention and can also be related with nutritional prescriptions. The trajectory analysis is also proposed allowing both analysis: 1) adherence to the intervention and 2) intervention effects. The analysis is made by projecting the differences of the target parameters over the resulting trajectories between states of different time-stamps which might be considered either individually or by groups. The proposal has been applied over a real nutritional study showing that some individuals adhere better than others and some individuals of the control group modify their habits during the intervention. In addition, the intervention effects are different depending on the type of individuals, even some subgroups have opposite response to the same intervention.

Negative-ion formation in the explosives RDX, PETN, and TNT by using the reversal electron attachment detection technique

NASA Technical Reports Server (NTRS)

Boumsellek, S.; Alajajian, S. H.; Chutjian, A.

1992-01-01

First results of a beam-beam, single-collision study of negative-ion mass spectra produced by attachment of zero-energy electrons to the molecules of the explosives RDX, PETN, and TNT are presented. The technique used is reversal electron attachment detection (READ) wherein the zero-energy electrons are produced by focusing an intense electron beam into a shaped electrostatic field which reverses the trajectory of electrons. The target beam is introduced at the reversal point, and attachment occurs because the electrons have essentially zero longitudinal and radial velocity. The READ technique is used to obtain the 'signature' of molecular ion formation and/or fragmentation for each explosive. Present data are compared with results from atmospheric-pressure ionization and negative-ion chemical ionization methods.

Ion Correlation Effects in Salt-Doped Block Copolymers

NASA Astrophysics Data System (ADS)

Brown, Jonathan R.; Seo, Youngmi; Hall, Lisa M.

2018-03-01

We apply classical density functional theory to study how salt changes the microphase morphology of diblock copolymers. Polymers are freely jointed and one monomer type favorably interacts with ions, to account for the selective solvation that arises from different dielectric constants of the microphases. By including correlations from liquid state theory of an unbound reference fluid, the theory can treat chain behavior, microphase separation, ion correlations, and preferential solvation, at the same coarse-grained level. We show good agreement with molecular dynamics simulations.

Network-based study of Lagrangian transport and mixing

NASA Astrophysics Data System (ADS)

Padberg-Gehle, Kathrin; Schneide, Christiane

2017-10-01

Transport and mixing processes in fluid flows are crucially influenced by coherent structures and the characterization of these Lagrangian objects is a topic of intense current research. While established mathematical approaches such as variational methods or transfer-operator-based schemes require full knowledge of the flow field or at least high-resolution trajectory data, this information may not be available in applications. Recently, different computational methods have been proposed to identify coherent behavior in flows directly from Lagrangian trajectory data, that is, numerical or measured time series of particle positions in a fluid flow. In this context, spatio-temporal clustering algorithms have been proven to be very effective for the extraction of coherent sets from sparse and possibly incomplete trajectory data. Inspired by these recent approaches, we consider an unweighted, undirected network, where Lagrangian particle trajectories serve as network nodes. A link is established between two nodes if the respective trajectories come close to each other at least once in the course of time. Classical graph concepts are then employed to analyze the resulting network. In particular, local network measures such as the node degree, the average degree of neighboring nodes, and the clustering coefficient serve as indicators of highly mixing regions, whereas spectral graph partitioning schemes allow us to extract coherent sets. The proposed methodology is very fast to run and we demonstrate its applicability in two geophysical flows - the Bickley jet as well as the Antarctic stratospheric polar vortex.

High charge state carbon and oxygen ions in Earth's equatorial quasi-trapping region

NASA Technical Reports Server (NTRS)

Christon, S. P.; Hamilton, D. C.; Gloeckler, G.; Eastmann, T. E.

1994-01-01

Observations of energetic (1.5 - 300 keV/e) medium-to-high charge state (+3 less than or equal to Q less than or equal to +7) solar wind origin C and O ions made in the quasi-trapping region (QTR) of Earth's magnetosphere are compared to ion trajectories calculated in model equatorial magnetospheric magnetic and electric fields. These comparisons indicate that solar wind ions entering the QTR on the nightside as an energetic component of the plasma sheet exit the region on the dayside, experiencing little or no charge exchange on the way. Measurements made by the CHarge Energy Mass (CHEM) ion spectrometer on board the Active Magnetospheric Particle Tracer Explorer/Charge Composition Explorer (AMPTE/CCE) spacecraft at 7 less than L less than 9 from September 1984 to January 1989 are the source of the new results contained herein: quantitative long-term determination of number densities, average energies, energy spectra, local time distributions, and their variation with geomagnetic disturbance level as indexed by Kp. Solar wind primaries (ions with charge states unchanged) and their secondaries (ions with generally lower charge states produced from primaries in the magnetosphere via charge exchange)are observed throughout the QTR and have distinctly different local time variations that persist over the entire 4-year analysis interval. During Kp larger than or equal to 3 deg intervals, primary ion (e.g., O(+6)) densities exhibit a pronounced predawn maximum with average energy minimum and a broad near-local-noon density minimum with average energy maximum. Secondary ion (e.g., O(+5)) densities do not have an identifiable predawn peak, rather they have a broad dayside maximum peaked in local morning and a nightside minimum. During Kp less than or equal to 2(-) intervals, primary ion density peaks are less intense, broader in local time extent, and centered near midnight, while secondary ion density local time variations diminish. The long-time-interval baseline helps to refine and extend previous observations; for example, we show that ionospheric contribution to O(+3)) is negligible. Through comparison with model ion trajectories, we interpret the lack of pronounced secondary ion density peaks colocated with the primary density peaks to indicate that: (1) negligible charge exchange occurs at L greater than 7, that is, solar wind secondaries are produced at L less than 7, and (2) solar wind secondaries do not form a significant portion of the plasma sheet population injected into the QTR. We conclude that little of the energetic solar wind secondary ion population is recirculated through the magnetosphere.

Angular Distributions of Differential Electron Capture Cross Sections in Collisions Between Low-Velocity Highly-Charged Ions and Neutral Targets.

NASA Astrophysics Data System (ADS)

Waggoner, William Tracy

1990-01-01

Experimental capture cross sections d sigma / dtheta versus theta , are presented for various ions incident on neutral targets. First, distributions are presented for Ar ^{rm 8+} ions incident on H_{rm 2}, D _{rm 2}, and Ar targets. Energy gain studies indicate that capture occurs to primarily a 5d,f final state of Ar^{rm 7+} with some contributions from transfer ionization (T.I.) channels. Angular distribution spectra for all three targets are similar, with spectra having a main peak located at forward angles which is attributed to single capture events, and a secondary structure occurring at large angles which is attributed to T.I. contributions. A series of Ar^{rm 8+} on Ar spectra were collected using a retarding grid system as a low resolution energy spectrometer to resolve single capture events from T.I. events. The resulting single capture and T.I. angular distributions are presented. Results are discussed in terms of a classical deflection function employing a simple two state curve crossing model. Angular distributions for electron capture from He by C, N, O, F, and Ne ions with charge states from 5 ^+-8^+ are presented for projectile energies between 1.2 and 2.0 kV. Distributions for the same charge state but different ion species are simlar, but not identical with distributions for the 5 ^+ and 7^+ ions being strongly forward peaked, the 6^+ distributions are much less forward peaked with the O^{6+} distributions showing structure, the Ne^{8+} ion distribution appears to be an intermediate case between forward peaking and large angle scattering. These results are discussed in terms of classical deflection functions which utilize two state Coulomb diabatic curve crossing models. Finally, angular distributions are presented for electron capture from He by Ar^{rm 6+} ions at energies between 1287 eV and 296 eV. At large projectile energies the distribution is broad. As the energy decreases below 523 eV, distributions shift to forward angles with a second peak appearing outside the Coulomb angle, theta_{c} = Q/2E, which continues to grow in magnitude as the projectile energy decreases further. Results are compared with a model calculation employing a two state diabatic Coulomb curve crossing model and the classical deflection function.

Oblique propagating electromagnetic ion - Cyclotron instability with A.C. field in outer magnetosphere

NASA Astrophysics Data System (ADS)

Pandey, R. S.; Singh, Vikrant; Rani, Anju; Varughese, George; Singh, K. M.

2018-05-01

In the present paper Oblique propagating electromagnetic ion-cyclotron wave has been analyzed for anisotropic multi ion plasma (H+, He+, O+ ions) in earth magnetosphere for the Dione shell of L=7 i.e., the outer radiation belt of the magnetosphere for Loss-cone distribution function with a spectral index j in the presence of A.C. electric field. Detail for particle trajectories and dispersion relation has been derived by using the method of characteristic solution on the basis of wave particle interaction and transformation of energy. Results for the growth rate have been calculated numerically for various parameters and have been compared for different ions present in magnetosphere. It has been found that for studying the wave over wider spectrum, anisotropy for different values of j should be taken. The effect of frequency of A.C. electric field and angle which propagation vector make with magnetic field, on growth rate has been explained.

Feasibility of a 90° electric sector energy analyzer for low energy ion beam characterization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mahinay, C. L. S., E-mail: cmahinay@nip.upd.edu.ph; Ramos, H. J.; Wada, M.

2015-02-15

A simple formula to calculate refocusing by locating the output slit at a specific distance away from the exit of 90° ion deflecting electric sector is given. Numerical analysis is also performed to calculate the ion beam trajectories for different values of the initial angular deviation of the beam. To validate the theory, a compact (90 mm × 5.5 mm × 32 mm) 90° sector ESA is fabricated which can fit through the inner diameter of a conflat 70 vacuum flange. Experimental results show that the dependence of resolution upon the distance between the sector exit and the Faraday cupmore » agrees with the theory. The fabricated 90° sector electrostatic energy analyzer was then used to measure the space resolved ion energy distribution functions of an ion beam with the energy as low as 600 eV.« less

A phenomenological approach to modeling chemical dynamics in nonlinear and two-dimensional spectroscopy.

PubMed

Ramasesha, Krupa; De Marco, Luigi; Horning, Andrew D; Mandal, Aritra; Tokmakoff, Andrei

2012-04-07

We present an approach for calculating nonlinear spectroscopic observables, which overcomes the approximations inherent to current phenomenological models without requiring the computational cost of performing molecular dynamics simulations. The trajectory mapping method uses the semi-classical approximation to linear and nonlinear response functions, and calculates spectra from trajectories of the system's transition frequencies and transition dipole moments. It rests on identifying dynamical variables important to the problem, treating the dynamics of these variables stochastically, and then generating correlated trajectories of spectroscopic quantities by mapping from the dynamical variables. This approach allows one to describe non-Gaussian dynamics, correlated dynamics between variables of the system, and nonlinear relationships between spectroscopic variables of the system and the bath such as non-Condon effects. We illustrate the approach by applying it to three examples that are often not adequately treated by existing analytical models--the non-Condon effect in the nonlinear infrared spectra of water, non-Gaussian dynamics inherent to strongly hydrogen bonded systems, and chemical exchange processes in barrier crossing reactions. The methods described are generally applicable to nonlinear spectroscopy throughout the optical, infrared and terahertz regions.

Optimum Climb to Cruise Noise Trajectories for the High Speed Civil Transport

NASA Technical Reports Server (NTRS)

Berton, Jeffrey J.

2003-01-01

By entraining large quantities of ambient air into advanced ejector nozzles, the jet noise of the proposed High Speed Civil Transport (HSCT) is expected to be reduced to levels acceptable for airport-vicinity noise certification. Away from the airport, however, this entrained air is shut off and the engines are powered up from their cutback levels to provide better thrust for the climb to cruise altitude. Unsuppressed jet noise levels propagating to the ground far from the airport are expected to be high. Complicating this problem is the HSCT's relative noise level with respect to the subsonic commercial fleet of 2010, which is expected to be much quieter than it is today after the retirement of older, louder, domestic stage II aircraft by the year 2000. In this study, the classic energy state approximation theory is extended to calculate trajectories that minimize the climb to cruise noise of the HSCT. The optimizer dynamically chooses the optimal altitude velocity trajectory, the engine power setting, and whether the ejector should be stowed or deployed with respect to practical aircraft climb constraints and noise limits.

Hyperbolic geometrical optics: Hyperbolic glass

NASA Astrophysics Data System (ADS)

De Micheli, Enrico; Scorza, Irene; Viano, Giovanni Alberto

2006-02-01

We study the geometrical optics generated by a refractive index of the form n (x,y)=1/y (y>0), where y is the coordinate of the vertical axis in an orthogonal reference frame in R2. We thus obtain what we call "hyperbolic geometrical optics" since the ray trajectories are geodesics in the Poincaré-Lobachevsky half-plane H2. Then we prove that the constant phase surface are horocycles and obtain the horocyclic waves, which are closely related to the classical Poisson kernel and are the analogs of the Euclidean plane waves. By studying the transport equation in the Beltrami pseudosphere, we prove (i) the conservation of the flow in the entire strip 0

Measuring the number of independent emitters in single-molecule fluorescence images and trajectories using coincident photons.

PubMed

Weston, Kenneth D; Dyck, Martina; Tinnefeld, Philip; Müller, Christian; Herten, Dirk P; Sauer, Markus

2002-10-15

A simple new approach is described and demonstrated for measuring the number of independent emitters along with the fluorescence intensity, lifetime, and emission wavelength for trajectories and images of single molecules and multichromophoric systems using a single PC plug-in card for time-correlated single-photon counting. The number of independent emitters present in the detection volume can be determined using the interphoton times in a manner similar to classical antibunching experiments. In contrast to traditional coincidence analysis based on pulsed laser excitation and direct measurement of coincident photon pairs using a time-to-amplitude converter, the interphoton distances are retrieved afterward by recording the absolute arrival time of each photon with nanosecond time resolution on two spectrally separated detectors. Intensity changes that result from fluctuations of a photophysical parameter can be distinguished from fluctuations due to changes in the number of emitters (e.g., photobleaching) in single chromophore and multichromophore intensity trajectories. This is the first report to demonstrate imaging with contrast based on the number of independently emitting species within the detection volume.

Extraction of highly charged ions from the Berlin Electron Beam Ion Trap for interactions with a gas target

DOE Office of Scientific and Technical Information (OSTI.GOV)

Allen, F.I.; Biedermann, C.; Radtke, R.

2006-03-15

Highly charged ions are extracted from the Berlin Electron Beam Ion Trap for investigations of charge exchange with a gas target. The classical over-the-barrier model for slow highly charged ions describes this process, whereby one or more electrons are captured from the target into Rydberg states of the ion. The excited state relaxes via a radiative cascade of the electron to ground energy. The cascade spectra are characteristic of the capture state. We investigate x-ray photons emitted as a result of interactions between Ar{sup 17+} ions at energies {<=}5q keV with Ar atoms. Of particular interest is the velocity dependencemore » of the angular momentum capture state l{sub c}.« less

Self-energy-modified Poisson-Nernst-Planck equations: WKB approximation and finite-difference approaches.

PubMed

Xu, Zhenli; Ma, Manman; Liu, Pei

2014-07-01

We propose a modified Poisson-Nernst-Planck (PNP) model to investigate charge transport in electrolytes of inhomogeneous dielectric environment. The model includes the ionic polarization due to the dielectric inhomogeneity and the ion-ion correlation. This is achieved by the self energy of test ions through solving a generalized Debye-Hückel (DH) equation. We develop numerical methods for the system composed of the PNP and DH equations. Particularly, toward the numerical challenge of solving the high-dimensional DH equation, we developed an analytical WKB approximation and a numerical approach based on the selective inversion of sparse matrices. The model and numerical methods are validated by simulating the charge diffusion in electrolytes between two electrodes, for which effects of dielectrics and correlation are investigated by comparing the results with the prediction by the classical PNP theory. We find that, at the length scale of the interface separation comparable to the Bjerrum length, the results of the modified equations are significantly different from the classical PNP predictions mostly due to the dielectric effect. It is also shown that when the ion self energy is in weak or mediate strength, the WKB approximation presents a high accuracy, compared to precise finite-difference results.

Ion-Stockmayer clusters: Minima, classical thermodynamics, and variational ground state estimates of Li{sup +}(CH{sub 3}NO{sub 2}){sub n} (n = 1–20)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Curotto, E., E-mail: curotto@arcadia.edu

2015-12-07

Structural optimizations, classical NVT ensemble, and variational Monte Carlo simulations of ion Stockmayer clusters parameterized to approximate the Li{sup +}(CH{sub 3}NO{sub 2}){sub n} (n = 1–20) systems are performed. The Metropolis algorithm enhanced by the parallel tempering strategy is used to measure internal energies and heat capacities, and a parallel version of the genetic algorithm is employed to obtain the most important minima. The first solvation sheath is octahedral and this feature remains the dominant theme in the structure of clusters with n ≥ 6. The first “magic number” is identified using the adiabatic solvent dissociation energy, and it marksmore » the completion of the second solvation layer for the lithium ion-nitromethane clusters. It corresponds to the n = 18 system, a solvated ion with the first sheath having octahedral symmetry, weakly bound to an eight-membered and a four-membered ring crowning a vertex of the octahedron. Variational Monte Carlo estimates of the adiabatic solvent dissociation energy reveal that quantum effects further enhance the stability of the n = 18 system relative to its neighbors.« less

Overview of MST Research

NASA Astrophysics Data System (ADS)

Sarff, J. S.; MST Team

2011-10-01

MST progress in advancing the RFP for (1) fusion plasma confinement with minimal external magnetization, (2) toroidal confinement physics, and (3) basic plasma physics is summarized. New tools and diagnostics are accessing physics barely studied in the RFP. Several diagnostic advances are important for ITER/burning plasma. A 1 MW neutral beam injector operates routinely for fast ion, heating, and transport investigations. Energetic ions are also created spontaneously by tearing mode reconnection, reminiscent of astrophysical plasmas. Classical confinement of impurity ions is measured in reduced-tearing plasmas. Fast ion slowing-down is also classical. Alfven-eigenmode-like activity occurs with NBI, but apparently not TAE. Stellarator-like helical structure appears in the core of high current plasmas, with improved confinement characteristics. FIR interferometry, Thomson scattering, and HIBP diagnostics are beginning to explore microturbulence scales, an opportunity to exploit the RFP's high beta and strong magnetic shear parameter space. A programmable power supply for the toroidal field flexibly explores scenarios from advanced inductive profile control to low current tokamak operation. A 1 MW 5.5 GHz source for electron Bernstein wave injection is nearly complete to investigate heating and current drive in over-dense plasmas. Supported by DOE and NSF.

Surface-hopping dynamics and decoherence with quantum equilibrium structure.

PubMed

Grunwald, Robbie; Kim, Hyojoon; Kapral, Raymond

2008-04-28

In open quantum systems, decoherence occurs through interaction of a quantum subsystem with its environment. The computation of expectation values requires a knowledge of the quantum dynamics of operators and sampling from initial states of the density matrix describing the subsystem and bath. We consider situations where the quantum evolution can be approximated by quantum-classical Liouville dynamics and examine the circumstances under which the evolution can be reduced to surface-hopping dynamics, where the evolution consists of trajectory segments exclusively evolving on single adiabatic surfaces, with probabilistic hops between these surfaces. The justification for the reduction depends on the validity of a Markovian approximation on a bath averaged memory kernel that accounts for quantum coherence in the system. We show that such a reduction is often possible when initial sampling is from either the quantum or classical bath initial distributions. If the average is taken only over the quantum dispersion that broadens the classical distribution, then such a reduction is not always possible.

Radiation of a nonrelativistic particle during its finite motion in a central field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karnakov, B. M., E-mail: karnak@theor.mephi.ru; Korneev, Ph. A., E-mail: korneev@theor.mephi.ru; Popruzhenko, S. V.

The spectrum and expressions for the intensity of dipole radiation lines are obtained for a classical nonrelativistic charged particle that executes a finite aperiodic motion in an arbitrary central field along a non-closed trajectory. It is shown that, in this case of a conditionally periodic motion, the radiaton spectrum consists of two series of equally spaced lines. It is pointed out that, according to the correspondence principle, the rise of two such series in the classical theory corresponds to the well-known selection rule |{delta}l = 1 for the dipole radiation in a central field in quantum theory, where l ismore » the orbital angular momentum of the particle. The results obtained can be applied to the description of the radiation and the absorption of a classical collisionless electron plasma in nanoparticles irradiated by an intense laser field. As an example, the rate of collisionless absorption of electromagnetic wave energy in equilibrium isotropic nanoplasma is calculated.« less

Stoichiometric network analysis and associated dimensionless kinetic equations. Application to a model of the Bray-Liebhafsky reaction.

PubMed

Schmitz, Guy; Kolar-Anić, Ljiljana Z; Anić, Slobodan R; Cupić, Zeljko D

2008-12-25

The stoichiometric network analysis (SNA) introduced by B. L. Clarke is applied to a simplified model of the complex oscillating Bray-Liebhafsky reaction under batch conditions, which was not examined by this method earlier. This powerful method for the analysis of steady-states stability is also used to transform the classical differential equations into dimensionless equations. This transformation is easy and leads to a form of the equations combining the advantages of classical dimensionless equations with the advantages of the SNA. The used dimensionless parameters have orders of magnitude given by the experimental information about concentrations and currents. This simplifies greatly the study of the slow manifold and shows which parameters are essential for controlling its shape and consequently have an important influence on the trajectories. The effectiveness of these equations is illustrated on two examples: the study of the bifurcations points and a simple sensitivity analysis, different from the classical one, more based on the chemistry of the studied system.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Valerio-Lizarraga, Cristhian A., E-mail: cristhian.alfonso.valerio.lizarraga@cern.ch; Departamento de Investigación en Física, Universidad de Sonora, Hermosillo; Lallement, Jean-Baptiste

The space charge effect of low energy, unbunched ion beams can be compensated by the trapping of ions or electrons into the beam potential. This has been studied for the 45 keV negative hydrogen ion beam in the CERN Linac4 Low Energy Beam Transport using the package IBSimu [T. Kalvas et al., Rev. Sci. Instrum. 81, 02B703 (2010)], which allows the space charge calculation of the particle trajectories. The results of the beam simulations will be compared to emittance measurements of an H{sup −} beam at the CERN Linac4 3 MeV test stand, where the injection of hydrogen gas directlymore » into the beam transport region has been used to modify the space charge compensation degree.« less

Quantum mechanical models for the Fermi shuttle

NASA Astrophysics Data System (ADS)

Sternberg, James; Ovchinnikov, S. Yu.; Macek, J. H.

2009-05-01

Although the Fermi shuttle was originally proposed as an explanation for highly energetic cosmic rays, it is also a mechanism for the production of high energy electrons in atomic collisions [1]. The Fermi shuttle is usually thought of as a classical effect and most models of this process rely on classical or semi-classical approximations. In this work we explore several quantum mechanical models for ion-atom collisions and examine the evidence for the Fermi shuttle in these models. [4pt] [1] B. Sulik, Cs. Koncz, K. Tok'esi, A. Orb'an, and D. Ber'enyi, Phys Rev. Lett. 88 073201 (2002)

Trajectory Optimization of a Bimodal Nuclear Powered Spacecraft to Mars

DTIC Science & Technology

1990-05-29

velocity M = initial mass of spacecraft o m= ion fuel expulsion rate (constant) 0 = thrust direction angle = gravitational constant of Sun AVto t...total velocity change possible for the impulsive engines AV1 = velocity change for Earth escape AV2 = velocity change for Mars capture AVto t = AV + AV

Charge exchange of solar wind ions in the Comet Halley coma

NASA Technical Reports Server (NTRS)

Shelley, E. G.; Ing-H. afgoldstein, B. E. AGGOLDSTEIN, R.; Ing-H. afgoldstein, B. E. AGGOLDSTEIN, R.

1986-01-01

The He(2+) and He(+) radial profiles measured by the Giotto mass spectrometer on the inbound trajectory to comet Halley are compared to a simple 1-dimensional charge exchange model. Results indicate that charge exchange alone cannot account for the observed radial profiles of He(2+) and He(+).

High order harmonic generation in rare gases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Budil, Kimberly Susan

1994-05-01

The process of high order harmonic generation in atomic gases has shown great promise as a method of generating extremely short wavelength radiation, extending far into the extreme ultraviolet (XUV). The process is conceptually simple. A very intense laser pulse (I ~10 13-10 14 W/cm 2) is focused into a dense (~10 17 particles/cm 3) atomic medium, causing the atoms to become polarized. These atomic dipoles are then coherently driven by the laser field and begin to radiate at odd harmonics of the laser field. This dissertation is a study of both the physical mechanism of harmonic generation as wellmore » as its development as a source of coherent XUV radiation. Recently, a semiclassical theory has been proposed which provides a simple, intuitive description of harmonic generation. In this picture the process is treated in two steps. The atom ionizes via tunneling after which its classical motion in the laser field is studied. Electron trajectories which return to the vicinity of the nucleus may recombine and emit a harmonic photon, while those which do not return will ionize. An experiment was performed to test the validity of this model wherein the trajectory of the electron as it orbits the nucleus or ion core is perturbed by driving the process with elliptically, rather than linearly, polarized laser radiation. The semiclassical theory predicts a rapid turn-off of harmonic production as the ellipticity of the driving field is increased. This decrease in harmonic production is observed experimentally and a simple quantum mechanical theory is used to model the data. The second major focus of this work was on development of the harmonic "source". A series of experiments were performed examining the spatial profiles of the harmonics. The quality of the spatial profile is crucial if the harmonics are to be used as the source for experiments, particularly if they must be refocused.« less

Structure evolution of mononuclear tungsten and molybdenum species in the protonation process: Insight from FPMD and DFT calculations

NASA Astrophysics Data System (ADS)

Zhang, Ning; Yi, Haibo; Zeng, Dewen; Zhao, Zhongwei; Wang, Wenlei; Costanzo, Francesca

2018-03-01

In this work, we apply static density functional theory (DFT) calculations, as well as classical and first-principles molecular dynamics (FPMD) simulations, using the free-energy perturbation method to study the protonation ability, active site and structures of W(VI) and Mo(VI) in acidic aqueous solution. Using FPMD simulations, utilizing the pKa's calculation technique, we concluded that the octahedral WO2(OH)2(H2O)2 is the true formula for tungstic acid (H2WO4), and the hydroxyl ligands are the acidic site. This aqueous structure of H2WO4 is analogous to the previously reported structure of molybdic acid (H2MoO4). The FPMD trajectories of the tungstic acid deprotonation show that the mono-protonated monotungstate ion (HWO4-) may partially exist as a five-coordinated WO3(OH)(H2O)- species except for the four-coordinated WO3(OH)- species. This result is supported by DFT calculations, with an isoenergetic point (ΔE = 1.9 kcal·mol-1) for the WO3(OH)(H2O)- and WO3(OH)- species, when explicit solvent molecules are taken into account. In contrast, for the H2MoO4 acid, FPMD trajectories during the deprotonation process show that two H2O ligands immediately escape from the first coordinated sphere of Mo(VI) to form the four-coordinated MoO3(OH)- species. This difference indicates that structural expansion of W(VI) began in the first protonated step, while that of Mo(VI) only occurs in the second step. In addition, our calculated first and second acid constants for tungstic acid are higher than previously reported values for molybdic acid. This result suggests that WO42- is more easily protonated than the MoO42- anion in the same acidic solution, which is further confirmed by DFT calculations of hydrated oxoanions and its protonated species, based upon the hydration energy.

Beam tracking simulation in the central region of a 13 MeV PET cyclotron

NASA Astrophysics Data System (ADS)

Anggraita, Pramudita; Santosa, Budi; Taufik, Mulyani, Emy; Diah, Frida Iswinning

2012-06-01

This paper reports the trajectories simulation of proton beam in the central region of a 13 MeV PET cyclotron, operating with negative proton beam (for easier beam extraction using a stripper foil), 40 kV peak accelerating dee voltage at fourth harmonic frequency of 77.88 MHz, and average magnetic field of 1.275 T. The central region covers fields of 240mm × 240mm × 30mm size at 1mm resolution. The calculation was also done at finer 0.25mm resolution covering fields of 30mm × 30mm × 4mm size to see the effects of 0.55mm horizontal width of the ion source window and the halted trajectories of positive proton beam. The simulations show up to 7 turns of orbital trajectories, reaching about 1 MeV of beam energy. The distribution of accelerating electric fields and magnetic fields inside the cyclotron were calculated in 3 dimension using Opera3D code and Tosca modules for static magnetic and electric fields. The trajectory simulation was carried out using Scilab 5.3.3 code.

Classical Calculations of Scattering Signatures from a Gravitational Singularity or the Scattering and Absorption Cross-Sections of a Black Hole

NASA Astrophysics Data System (ADS)

Difilippo, Felix C.

2012-09-01

Within the context of general relativity theory we calculate, analytically, scattering signatures around a gravitational singularity: angular and time distributions of scattered massive objects and photons and the time and space modulation of Doppler effects. Additionally, the scattering and absorption cross sections for the gravitational interactions are calculated. The results of numerical simulations of the trajectories are compared with the analytical results.

The design of electron and ion guns, beams, and collectors

NASA Astrophysics Data System (ADS)

Becker, Reinard; Herrmannsfeldt, William B.

2004-01-01

The well known `SLAC Electron Trajectory Program' (EGUN) has been ported to PCs and has been developed into a family of programs for the design and the optimization of particle optics devices including electron and ion guns, beam transport sections and collectors. We will discuss the application of these tools for the design and the optimization of the essential parts of EBIS/T devices. The discussion will include conditions in which restrictions in the reliability of simulations may occur due to the mathematical modeling and how to overcome them.

Has the QCD critical point been signaled by observations at the BNL relativistic heavy ion collider?

PubMed

Lacey, Roy A; Ajitanand, N N; Alexander, J M; Chung, P; Holzmann, W G; Issah, M; Taranenko, A; Danielewicz, P; Stöcker, Horst

2007-03-02

The shear viscosity to entropy ratio (eta/s) is estimated for the hot and dense QCD matter created in Au+Au collisions at BNL Relativistic Heavy Ion Collider (square root[s_{NN}]=200 GeV). A very low value is found; eta/s approximately 0.1, which is close to the conjectured lower bound (1/4pi). It is argued that such a low value is indicative of thermodynamic trajectories for the decaying matter which lie close to the QCD critical end point.

Monitoring Ion Activities In and Around Cells Using Ion-Selective Liquid-Membrane Microelectrodes

PubMed Central

Lee, Seong-Ki; Boron, Walter F.; Parker, Mark D.

2013-01-01

Determining the effective concentration (i.e., activity) of ions in and around living cells is important to our understanding of the contribution of those ions to cellular function. Moreover, monitoring changes in ion activities in and around cells is informative about the actions of the transporters and/or channels operating in the cell membrane. The activity of an ion can be measured using a glass microelectrode that includes in its tip a liquid-membrane doped with an ion-selective ionophore. Because these electrodes can be fabricated with tip diameters that are less than 1 μm, they can be used to impale single cells in order to monitor the activities of intracellular ions. This review summarizes the history, theory, and practice of ion-selective microelectrode use and brings together a number of classic and recent examples of their usefulness in the realm of physiological study. PMID:23322102

Ion-ion dynamic structure factor of warm dense mixtures

DOE PAGES

Gill, N. M.; Heinonen, R. A.; Starrett, C. E.; ...

2015-06-25

In this study, the ion-ion dynamic structure factor of warm dense matter is determined using the recently developed pseudoatom molecular dynamics method [Starrett et al., Phys. Rev. E 91, 013104 (2015)]. The method uses density functional theory to determine ion-ion pair interaction potentials that have no free parameters. These potentials are used in classical molecular dynamics simulations. This constitutes a computationally efficient and realistic model of dense plasmas. Comparison with recently published simulations of the ion-ion dynamic structure factor and sound speed of warm dense aluminum finds good to reasonable agreement. Using this method, we make predictions of the ion-ionmore » dynamical structure factor and sound speed of a warm dense mixture—equimolar carbon-hydrogen. This material is commonly used as an ablator in inertial confinement fusion capsules, and our results are amenable to direct experimental measurement.« less

A 2.5 kW advanced technology ion thruster

NASA Technical Reports Server (NTRS)

Poeschel, R. L.

1974-01-01

A program has been conducted in order to improve the performance characteristics of 30 cm thrusters. This program was divided into three distinct, but related tasks: (1) the discharge chamber and component design modifications proposed for inclusion in the engineering model thruster were evaluated and engineering specifications were verified; (2) thrust losses which result from the contributions of double charged ions and nonaxial ion trajectories to the ion beam current were measured and (3) the specification and verification of power processor and control requirements of the engineering model thruster design were demonstrated. Proven design modifications which provide improved efficiencies are incorporated into the engineering model thruster during a structural re-design without introducing additional delay in schedule or new risks. In addition, a considerable amount of data is generated on the relation of double ion production and beam divergence to thruster parameters. Overall thruster efficiency is increased from 68% to 71% at full power, including corrections for double ion and beam divergence thrust losses.

Characteristics of cometary picked-up ions in a global model of Giacobini-Zinner

NASA Astrophysics Data System (ADS)

Kimmel, C. D.; Luhmann, J. G.; Phillips, J. L.; Fedder, J. A.

1987-08-01

Energetic ions observed during the International Cometary Explorer (ICE) spacecraft flyby of comet Giacobini-Zinner provide information about both the constitution of comets and the plasma physical processes associated with their interaction with the solar wind. In this investigation the details of ion 'pickup,' in the limit where small-scale fluctuations in the plasma and magnetic field are neglected, are modeled by following the motion of a large number of initially cold, heavy (mass 18) ions in a global magnetohydrodynamic model of the local plasma and magnetic field. The results indicate how the background or macroscopic velocity and magnetic field structure of the comet can affect the average spatial and spectral characteristics of the observed cometary ions. These effects, which occur by virtue of forces associated with the compression and the curvature of the magnetic field in the presence of the stagnating plasma flow, can explain the double maxima in the time series of the energetic ion flux observed along the ICE trajectory.

Characteristics of cometary picked-up ions in a global model of Giacobini-Zinner

NASA Technical Reports Server (NTRS)

Kimmel, C. D.; Luhmann, J. G.; Phillips, J. L.; Fedder, J. A.

1987-01-01

Energetic ions observed during the International Cometary Explorer (ICE) spacecraft flyby of comet Giacobini-Zinner provide information about both the constitution of comets and the plasma physical processes associated with their interaction with the solar wind. In this investigation the details of ion 'pickup,' in the limit where small-scale fluctuations in the plasma and magnetic field are neglected, are modeled by following the motion of a large number of initially cold, heavy (mass 18) ions in a global magnetohydrodynamic model of the local plasma and magnetic field. The results indicate how the background or macroscopic velocity and magnetic field structure of the comet can affect the average spatial and spectral characteristics of the observed cometary ions. These effects, which occur by virtue of forces associated with the compression and the curvature of the magnetic field in the presence of the stagnating plasma flow, can explain the double maxima in the time series of the energetic ion flux observed along the ICE trajectory.