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1

Semiclassical theory of electronically nonadiabatic transitions in molecular collision processes  

NASA Technical Reports Server (NTRS)

An introductory account of the semiclassical theory of the S-matrix for molecular collision processes is presented, with special emphasis on electronically nonadiabatic transitions. This theory is based on the incorporation of classical mechanics with quantum superposition, and in practice makes use of the analytic continuation of classical mechanics into the complex space of time domain. The relevant concepts of molecular scattering theory and related dynamical models are described and the formalism is developed and illustrated with simple examples - collinear collision of the A+BC type. The theory is then extended to include the effects of laser-induced nonadiabatic transitions. Two bound continuum processes collisional ionization and collision-induced emission also amenable to the same general semiclassical treatment are discussed.

Lam, K. S.; George, T. F.

1979-01-01

2

Molecular collision processes in the presence of picosecond laser pulses  

NASA Technical Reports Server (NTRS)

Radiative transitions in molecular collision processes taking place in the presence of picosecond pulses are studied within a semiclassical formalism. An expression for adiabatic potential surfaces in the electronic-field representation is obtained, which directly leads to the evaluation of transition probabilities. Calculations with a Landau-Zener-type model indicate that picosecond pulses can be much more effective in inducing transitions than a single long pulse of the same intensity and the same total energy, if the intensity is sufficiently high that the perturbation treatment is not valid.

Lee, H. W.; George, T. F.

1979-01-01

3

Inelastic Collision Processes of Methane and Ethane Molecules at a Pt(111) Surface Studied by Molecular Beam Scattering Techniques  

NASA Astrophysics Data System (ADS)

Despite distinct differences in molecular structures andchemical bonds of various alkanes, the inelastic collision processesof CH4 and C2H6 on a Pt(111) surface have been found tobe very similar. Both processes can be explained qualitatively by asimple classical binary collision model. Angular intensitydistributions of reflected molecules of both species indicate thatdirect inelastic collision is primarily governed by the molecularmass, the incident kinetic energy of the molecule and the surfacetemperature of the Pt(111). Other factors such as the molecularstructure and chemical bond play minor roles in the process. However,the degree of inelastic collision, that is, the energy transfer rateper collision, increases with the molecular mass. Helium atomscattering has revealed that the dissociation process on the surfaceis identical for both molecules depending on the incident energy andthe surface temperature, as methyl moiety, ethylidyne moiety andcomplete decomposition into carbon and hydrogen atoms,successively. At elevated surface temperatures, however, thermallyassisted hydrogen tunneling appears to dominate ethane dissociation.

Yagyu, Shinjiro; Kino, Yasunobu; Ikeuchi, Toshiyuki; Hiraoka, Tomomi; Kondo, Takahiro; Yamamoto, Shigehiko

1999-12-01

4

TOPICAL REVIEW: The time-dependent close-coupling method for atomic and molecular collision processes  

Microsoft Academic Search

We review the development of the time-dependent close-coupling method to study atomic and molecular few body dynamics. Applications include electron and photon collisions with atoms, molecules, and their ions.

M. S. Pindzola; F. Robicheaux; S. D. Loch; J. C. Berengut; T. Topcu; J. Colgan; M. Foster; D. C. Griffin; C. P. Ballance; D. R. Schultz; T. Minami; N. R. Badnell; M. C. Witthoeft; D. R. Plante; D. M. Mitnik; J. A. Ludlow; U. Kleiman

2007-01-01

5

Accelerating spectral atomic and molecular collisions methods with graphics processing units  

NASA Astrophysics Data System (ADS)

We present a computation method to accelerate the calculation of the Hamiltonian of a three-body time independent Schrödinger equation for collisions. The Hamiltonian is constructed with one dimensional (basis overlaps) and two dimensional (interparticle interaction) integrals that are mapped into a computational grid in a Graphics Processing Unit (GPU). We illustrate the method for the case of an electron impact single ionization of a two electron atom. This proposal makes use of a Generalized Sturmian Basis set for each electron, which are obtained numerically on a quadrature grid that is used to compute the integrals in the GPU. The optimal computation is more than twenty times faster in the GPU than the calculation in CPU. The method can be easily scaled to computers with several Graphics Processing Units or clusters.

Colavecchia, F. D.

2014-07-01

6

Theoretical studies of molecular collisions  

NASA Technical Reports Server (NTRS)

The following subject areas are covered: (1) total integral reactive cross sections and vibrationally resolved reaction probabilities for F + H2 = HF + H; (2) a theoretical study of inelastic O + N2 collisions; (3) body frame close coupling wave packet approach to gas phase atom-rigit rotor inelastic collisions; (4) wave packet study of gas phase atom-rigit motor scattering; (5) the application of optical potentials for reactive scattering; (6) time dependent, three dimensional body frame quantal wave packet treatment of the H + H2 exchange reaction; (7) a time dependent wave packet approach to atom-diatom reactive collision probabilities; (8) time dependent wave packet for the complete determination of s-matrix elements for reactive molecular collisions in three dimensions; (9) a comparison of three time dependent wave packet methods for calculating electron-atom elastic scattering cross sections; and (10) a numerically exact full wave packet approach to molecule-surface scattering.

Kouri, Donald J.

1991-01-01

7

Energy transfer in molecular collisions  

NASA Astrophysics Data System (ADS)

Vibrational and rotational energy transfer in hyperthermal molecular collisions are investigated by means of time correlation function methods. Within this approach, the collisional differential cross section is expressed as the Fourier transform of the time correlation function of the transition operator, which evolves in time in accordance with the internal motions of the noninteracting molecules. The approach used allows the systematic introduction of approximations to the transition operator, which are based on models of the intermolecular forces and of the collision dynamics, the resulting correlation functions are readily evaluated for most polyatomics without need of internal state or partial wave expansions. The multicenter representation of the intermolecular potential is investigated, and multicenter surfaces are developed for ther interaction of Li(+) with CO and with CO2. Combining these developments, differential cross sections for the vibrational and rotational excitation of N2, CO and CO2 in collisions with hyperthermal Li(+) ions are calculated.

Vilallonga, E. F.

1981-08-01

8

Ion-Ion Collision Processes: Experiment  

SciTech Connect

Collisions between ions belong to the elementary processes occurring in all plasmas. Experimental data, measured by the crossed beams technique, for charge transfer in ion-ion collisions at keV energies are reviewed. One-electron and quasi-one-electron collision systems are discussed, which provide an ideal testing ground for theory. First ever measurements of angular differential as well as state selective electron capture cross sections are presented. Data on homo-nuclear collisions between heavy ions are also shown, as they are relevant to beam intensity losses in modern accelerator and storage rings. Finally, current studies involving molecular ions are reviewed.

Braeuning, H.; Salzborn, E. [Institut fuer Atom- und Molekuelphysik, Universitaet Giessen, D-35392 Giessen (Germany)

2005-05-27

9

Vibrational Excitation in Molecular Collisions  

NASA Astrophysics Data System (ADS)

The collision energy dependence of the total cross sections for state resolved translation to vibration energy transfer was measured for several neutral systems. Measurements were made for vibrationally inelastic collisions of iodine with helium, neon, and hydrogen isotopes, as well as collisions of aniline and paradifluorobenzene with helium, all in the thermal energy range. Our new experimental technique uses pulsed supersonic molecular beams for initial state selection, crossed at a variable intersection angle for kinematic, continuously tunable collision energy selection. The scattered products are state-selectively detected in the intersection region by laser induced fluoroscence. The iodine cross section energy dependences are approximately linear, quadratic, and cubic for v = 0 to 1, 2, and 3 excitations respectively, as expected from a classical-quantal correspondence principle model. Extreme mode specificity was observed in the polyatoms as only 3 of about 20 energetically accessible vibrations were observed to be collisionally excited. In aniline, the 2 lowest frequency modes were excited. The cross section for single quantum excitations of the inversion mode of the amine group is a strongly decreasing function over the 20 to 250 meV collision energy range. The other observed mode, an out-of-plane bend of the amine group shows a linear onset at threshold for single quantum excitations. The only vibration excited in paradifluorobenzene was the lowest frequency, out-of-plane fluorine bend. Excitation of 1 and 2 quanta was observed. The cross sections both have approximately linear onset at threshold.

Hall, Gregory

10

Tight-binding molecular-dynamics simulation of buckyball collisions  

Microsoft Academic Search

The collisions between C[sub 60] molecules are studied by tight-binding molecular-dynamics simulations. We observe three different regimes of behavior as the collisions become more and more energetic: bouncing, fusion, and fragmentation. The critical energies for fusion and fragmentation as well as details of the energy transfer during the collision process for the bouncing regime are investigated. The collisions at several

B. L. Zhang; C. Z. Wang; C. T. Chan; K. M. Ho

1993-01-01

11

Ab Initio Molecular Dynamics Simulations of Molecular Collisions of Nitromethane  

Microsoft Academic Search

Ab initio molecular dynamics simulations of bimolecular collisions of nitromethane, and collisions of one nitromethane molecule into a cluster of 12 nitromethane molecules have been performed. For the bimolecular simulations we have examined a variety of collision orientations and collision velocities between 6.5 and 12.0 km\\/s. The lowest dissociation threshold velocity found was 7.0 km\\/s for an anti-parallel collision orientation.

Dongqing Wei; Fan Zhang; Tom K. Woo

2002-01-01

12

Electron capture processes in the collision between rubidium ions and sodium neutral atoms by crossed molecular beams  

Microsoft Academic Search

Electron capture processes in the collision between rubidium ions and sodium metal atoms, leading to Rb(5 2P12,32) and Rb(6 2P12,32), have been studied by measuring the fluorescent emission of the excited species formed in a crossed beam experiment. Total cross sections have been determined in the 0.35–5.0 keV energy range. The [Rb(5 2P12,32) ? Rb(5 2S12)] electronic transition has been

T. Romero; J. de Andrés; M. Albertí; J. M. Lucas; A. Aguilar

1997-01-01

13

Cross Sections and Related Data for Electron Collisions with Hydrogen Molecules and Molecular Ions  

Microsoft Academic Search

Data are compiled and evaluated for collision processes of excitation, dissociation, ionization, attachment, and recombination of hydrogen molecules and molecular ions (H+2, H+3) by electron impact as well as for properties of their collision products.

H. Tawara; Y. Itikawa; H. Nishimura; M. Yoshino

1990-01-01

14

Scattering angle dependence of double-collision processes  

NASA Astrophysics Data System (ADS)

In solid targets projectile and target K vacancies or 1s? molecular orbital (MO) X-rays may be created by a double-collision process where a projectile L or K vacancy is formed in one-collision then transfer to the K shell or radiates a MO X-ray in a second collision. The scattering-angle dependence of the probability for this process to occur is calculated. The projectile scattering in the first collision can influence the observed scattering-angle dependence in several ways: (1) the MO X-ray production probability falls off faster with decreasing angle, (2) the azimuthal angular distribution of MO X-ray emission is smeared out, and (3) predicted oscillations in the MO X ray spectrum for fixed impact parameter in the second collision are probably not observable in solid targets.

Anholt, R.

1982-07-01

15

Long-lived complexes and chaos in ultracold molecular collisions  

NASA Astrophysics Data System (ADS)

Estimates for the lifetime of collision complexes formed during ultracold molecular collisions based on density-of-states arguments are shown to be consistent with similar estimates based on classical trajectory calculations. In the classical version, these collisions are shown to exhibit chaos and their fractal dimension is calculated versus collision energy. From these results, a picture emerges that ultracold collisions are likely classically ergodic, justifying the density-of-states estimates for lifetimes. These results point the way toward using the techniques of classical and quantum chaos to interpret molecular collisions in the ultracold regime.

Croft, James F. E.; Bohn, John L.

2014-01-01

16

Division XII / Commission 14 / Working Group Collision Processes  

NASA Astrophysics Data System (ADS)

Research in atomic and molecular collision processes and spectral line broadening has been very active since our last report, Peach, Dimitrijevi? & Stancil 2009. Given the large volume of the published literature and the limited space available, we have attempted to identify work most relevant to astrophysics. Since our report can not be comprehensive, additional publications can be found in the databases at the web addresses listed in the final section. Elastic and inelastic collisions among electrons, atoms, ions, and molecules are included and charge transfer can be very important in collisions between heavy particles.

Peach, Gillian; Dimitrijevic, Milan S.

2012-04-01

17

Division XII / Commission 14 / Working Group Collision Processes  

NASA Astrophysics Data System (ADS)

Research in atomic and molecular collision processes and spectral line broadening has been very active since our last report (Schultz & Stancil 2007, Allard & Peach 2007). Given the large volume of the published literature and the limited space available, we have attempted to identify work most relevant to astrophysics. Since our report is not comprehensive, additional publications can be found in the databases at the web addresses listed in the final section. Elastic and inelastic collisions among electrons, atoms, ions, and molecules are included and reactive processes are also considered, but except for charge exchange, they receive only sparse coverage.

Peach, Gillian; Dimitrijevic, Milan S.; Stancil, Phillip C.

18

Molecular processes in comets  

NASA Technical Reports Server (NTRS)

Classical trajectory calculations of the cross sections for vibrational and rotational energy exchange in direct and reactive collisions of hydrogen atoms and hydrogen molecules have been carried out. To test the sensitivity, three potential energy surfaces have been used. For the exchange transitions which occur at small internuclear distances, the rate coefficients for the three surfaces agree quite well. For the direct transitions, there are significant differences for the pure rotational transitions from j=0 to 2 and from j=1 to j=3 in which there is no change in vibration. For higher j the differences tend to disappear, suggesting that the rotational angular momentum can couple to the orbital angular momentum to overcome the centrifugal barrier. Complete numerically exact quantum mechanical calculations for the process in which vJ changes have been performed. Dr. M. A'Hearn has provided data on the fluorescent population of the NH rotational and fine-structure levels from which we should be able to predict accurate photodissociation lifetimes. The distribution rate of C2 is being investigated. A review of H3(+) in terrestrial and extraterrestrial environments was prepared for a volume of Advances in Atomic, Molecular and Optical Physics.

Dalgarno, A.

1993-01-01

19

Analysis of the formation of CH+ in collision of C2+ ions with molecular hydrogen  

NASA Astrophysics Data System (ADS)

A theoretical treatment of the different processes involved in the collision of C2+ ions with molecular hydrogen is developed with consideration of charge transfer and formation of the CH+ molecular ion. Calculations of the potential energy surfaces and couplings are performed by means of ab initio quantum chemistry methods. Analysis of the different routes is detailed.

Bacchus-Montabonel, Marie-Christine; Wiesenfeld, Laurent

2013-09-01

20

Molecular vibrational states during a collision  

NASA Technical Reports Server (NTRS)

Alternative algebraic techniques to approximate a given Hamiltonian by a harmonic oscillator are described both for time-independent and time-dependent systems. We apply them to the description of a one dimensional atom-diatom collision. From the resulting evolution operator, we evaluate vibrational transition probabilities as well as other time-dependent properties. As expected, the ground vibrational state becomes a squeezed state during the collision.

Recamier, Jose A.; Jauregui, Rocio

1995-01-01

21

FOREWORD: Collision Processes of Metallic Ions in Fusion Plasmas  

NASA Astrophysics Data System (ADS)

On May 16-18, 1990, an Advisory Group Meeting on "Atomic and Molecular Data for Metallic Impurities in Fusion Plasmas" was organized by the Atomic and Molecular Data Unit of the International Atomic Energy Agency and held in Vienna, Austria. The objectives of the Meeting were to review the status of atomic collision data for the most important fusion plasma metallic impurities (Ti, Cr, Fe and Ni), to identify the gaps in the database in relation to the data needs of the current fusion research and reactor design work, and to report on recent original cross section calculations and measurements for the collision processes of these ions. The scope of the meeting included the following collision processes: (a) Electron collisions with Tiq+, Crq+, Feq+ and Niq+ ions (excitation, ionization, radiative and dielectronic recombination); (b) Collisions of Tiq+, Crq+, Feq+ and Niq+ ions with H, H2, and He (total and state-selective electron capture, excitation, ionization and dissociative processes with H2). The meeting was attended by fifteen participants covering almost uniformly the various collision processes, energy ranges and research methods (theoretical and experimental). In the area of electron-ion collision processes, extensive reviews of the current research and cross section data situation have been presented by Y Hahn (on radiative and dielectronic recombination), D Gregory (on excitation) and A Muller (on ionization). Contributions regarding the cross sections and/or reaction rates of many specific processes were given by N Badnell, K Berrington, M Bitter, R E H Clark, A Muller and V P Shevelko. V A Abramov provided a comparison of the electron-impact excitation data, evaluated by several groups, and demonstrated their consistency in the majority of analyzed cases. In the area of heavy-particle collision processes, the research and database situation was reviewed by H B Gilbody. Original cross section information for specific heavy-particle collision processes was presented by H Cederquist, W Fritsch, R E Olson, K Katsonis and G L Yudin. The present Topical Issue of Physica Scripta contains the contributions presented at the meeting with the exception of the presentation of V A Abramov. The reports of the Working Groups, established at the meeting to critically evaluate the available data and to identify the gaps in the database, are also included in this volume. An appropriate introductory comment by the Guest Editor on the impurity sources and the role of impurity collision processes in fusion plasmas is also added. On behalf of the International Atomic Energy Agency, I take this opportunity to thank the participants of the Advisory Group Meeting for their dedicated work and valuable contribution to this international endeavour and for their co-operativeness in the course of preparation of this volume.

Janev, R. K.

1991-01-01

22

Colliding molecular clouds in head-on galaxy collisions  

Microsoft Academic Search

We present further observations of molecular gas in head-on collisions of spiral galaxies, this time of the CO(J=1-> 0) and CO(J=2-> 1) lines in the UGC 813 - UGC 816 system. UGC 813\\/6 are only the second known example of head-on spiral-spiral collisions, the first example being the UGC 12914\\/5 pair. Strong CO emission is present in the bridge between

J. Braine; U. Lisenfeld; P.-A. Duc; E. Brinks; V. Charmandaris; S. Leon

2004-01-01

23

The "Collisions Cube" Molecular Dynamics Simulator.  

ERIC Educational Resources Information Center

Describes a molecular dynamics simulator that employs ping-pong balls as the atoms or molecules and is suitable for either large lecture halls or small classrooms. Discusses its use in illustrating many of the fundamental concepts related to molecular motion and dynamics and providing a three-dimensional perspective of molecular motion. (JRH)

Nash, John J.; Smith, Paul E.

1995-01-01

24

Electromagnetic processes in relativistic heavy ion collisions  

NASA Astrophysics Data System (ADS)

Electromagnetic effects in relativistic heavy ion collisions with impact parameter larger than the sum of the nuclear radii are studied using the virtual photon method. With increasing value of the relativistic parameter ? the hardness of the virtual photon spectrum increases. This leads to interesting new effects which will also have to be considered in the design of future relativistic heavy ion machines and experiments. The excitation of high-lying giant E1 and E2 multipole resonances is calculated as well as electromagnetic pion production. Coulomb bremsstrahlung is calculated and compared to the bremsstrahlung emitted in the more violent central nuclear collisions. K-shell ionization and electron-positron pair production is studied. The latter process has a very large cross section for heavy ions and contributes significantly to the stopping power of relativistic heavy ions in a dense medium.

Bertulani, C. A.; Baur, G.

1986-10-01

25

Factorization of scattering information in molecular collision theory  

Microsoft Academic Search

In several important approximate treatments in molecular collision theory, the S- and T-matrices are local in some subset of coordinates. Linear factorization relations and consistency conditions are derived for the matrix elements of such local operator and sometimes for the appropriately averaged square of the magnitude of these matrix elements. The coefficients in these relations and conditions are spectroscopic (i.e.,

Chan

1983-01-01

26

Reactive Molecular Dynamics of Hypervelocity Collisions of PETN Molecules  

Microsoft Academic Search

Born-Oppenheimer direct dynamics classical trajectory simulations of bimolecular collisions of PETN molecules have been performed to investigate the fundamental mechanisms of hypervelocity chemistry relevant to initiating reactions immediately behind the shock wavefront in energetic molecular crystals. The solid-state environment specifies the initial orientations of colliding molecules. The threshold velocities for initiating chemistry for a variety of crystallographic orientations were correlated

A. C. Landerville; I. I. Oleynik; C. T. White

2009-01-01

27

Long-range forces and the collisions of free-molecular and transition regime aerosols  

SciTech Connect

An aerosol here is understood to be a two-component system comprised of gaseous and condensed phases with the characteristic that the condensed phase is not an equilibrium subsystem. In contrast to the usual definitions based upon geometrical or mechanical variables, this quasi-thermodynamic formulation is framed to emphasize the dynamical behavior of aerosols by allowing for coagulation and other aerosol evolutionary processes as natural consequences of the interactions and state variables appropriate to the system. As will become clear later, it also provides a point of departure for distinguishing aerosol particles from unstable gas-phase cluster systems. The question of accommodation in particle collisions must be addressed as a prelude to the discussion of the role of long-range forces. Microscopic reversibility is frequently assumed for molecular collisions with either molecules or solid surfaces. In the case of aerosol collisions, the implication of this assumption is that collisions are elastic, which is contrary to the evidence from coagulation experiments and the conventional operational assumption of sticking upon collision. Gay and Berne have performed computer simulations of the collision of two clusters consisting of a total of 135 molecules interacting via Lennard-Jones potentials. That work showed that complete accommodation, accompanied by overall heating of the unified cluster, occurred. Since heating represents an irreversible degradation of the kinetic energy of the collision, the hamiltonian of the two-cluster system should be considered as dissipative and therefore microscopic reversibility does not apply.

Marlow, W.H.

1988-12-31

28

Molecular Processes in Comets  

NASA Technical Reports Server (NTRS)

The research focused on molecular hydrogen and its response to ultraviolet radiation, photoelectron impact excitation and X-ray radiation and on the interpretation of the ultraviolet spectra of the Jupiter dayglow and auroras. A systematic effort was made to obtain reliable rate coefficients for rovibrational energy transfer of H2, particularly in collisions with hydrogen atoms. We carried out elaborate quantum-mechanical calculations of the scattering of H and H2 on what had been characterized as a reliable potential energy surface of the H3 molecular system. These calculations took into account reactive channels and rate coefficients for ortho-para transitions were obtained. Quantal calculations are too complex to be applied to all the possible rovibrational transitions and we turned to a semi-classical method. With it we calculated rate coefficients for transitions, reactive and non-reactive, for all the rovibrational levels. We carried out the calculations for three of the available H3 potential energy surfaces. We discovered an unexpected sensitivity of the rate coefficients for the non-reactive channels to the potential energy surface. This discovery stimulated more thorough investigations of the potential energy surface elsewhere and to the construction of a new surface. We have used it in further semi-classical calculations in work that will shortly be 2 completed and which, together with new quantum-mechanical calculations should comprise a set of reliable rate coefficients that can be used in discussions of H2 on the Jovian planets. We carried out a detailed study of the Jovian ultraviolet dayglow. There has been a long-running argument about the dayglow on Jupiter. There are two sources of excitation: fluorescence and photoelectron impact excitation. It had been argued that a third source "the electron glow" was needed to bring theory and observation into agreement. We believe we have shown conclusively that the third source is unnecessary. We have achieved a close quantitative agreement between the predicted spectrum arising from fluorescence and photoelectrons and the measured spectrum. We also demonstrated a method by which the presence of HD could be established observationary. Similar calculations were carried out of the ultraviolet spectra of the Jovian auroras. We again found close agreement. Indeed, the agreement was so detailed we were able to derive the temperature of the atmosphere. We found, contrary to the standard model of the time, a high temperature between 400 K and 600 K and established the presence of a significant temperature gradient. A large temperature gradient was indeed found by direct sampling with the Jupiter probe.

Dalgarno, A.

1998-01-01

29

Reactive molecular dynamics of hypervelocity collisions of PETN molecules.  

PubMed

Born-Oppenheimer direct dynamics classical trajectory simulations of bimolecular collisions of PETN molecules have been performed to investigate the fundamental mechanisms of hypervelocity chemistry relevant to initiating reactions immediately behind the shock wavefront in energetic molecular crystals. The solid-state environment specifies the initial orientations of colliding molecules. The threshold velocities for initiating chemistry for a variety of crystallographic orientations were correlated with available experimental data on anisotropic shock sensitivity of PETN. Collisions normal to the planes (001) and (110) were found to be most sensitive with threshold velocities on the order of characteristic particle velocities in detonating PETN. The production of NO2 is the dominant reaction pathway in most of the reactive cases. The simulations show that the reactive chemistry, driven by dynamics rather than temperature during hypervelocity collisions, can occur at a very short time scale (10(-13) s) under highly nonequilibrium conditions. PMID:19817467

Landerville, A C; Oleynik, I I; White, C T

2009-11-01

30

Reactive Molecular Dynamics of Hypervelocity Collisions of PETN Molecules  

NASA Astrophysics Data System (ADS)

Born-Oppenheimer direct dynamics classical trajectory simulations of bimolecular collisions of PETN molecules have been performed to investigate the fundamental mechanisms of hypervelocity chemistry relevant to initiating reactions immediately behind the shock wavefront in energetic molecular crystals. The solid-state environment specifies the initial orientations of colliding molecules. The threshold velocities for initiating chemistry for a variety of crystallographic orientations were correlated with available experimental data on anisotropic shock sensitivity of PETN. Collisions normal to the planes (001) and (110) were found to be most sensitive with threshold velocities on the order of characteristic particle velocities in detonating PETN. The production of NO2 is the dominant reaction pathway in most of the reactive cases. The simulations show that the reactive chemistry, driven by dynamics rather than temperature during hypervelocity collisions, can occur at a very short time scale (10-13 s) under highly nonequilibrium conditions.

Landerville, A. C.; Oleynik, I. I.; White, C. T.

2009-10-01

31

Maxwell molecular collision model in kinetic theory of gases  

NASA Astrophysics Data System (ADS)

Classical and quantum properties of the Maxwell molecular collision model are considered. An almost classical kinetic equation is derived, in which the scattering for small angles from 0 to theta(0) is described with the help of quantum cross sections and represented by the Landau-type collision integral. The rest of the collision operator, accounting for the scattering from theta(0) to pi, has the conventional Boltzmann form with a natural angle cut-off theta(0). The Bobylev (1975) and Krooh and Wu (1977) solution satisfies this equation and at the same time shows that the exact value of the angle theta(0) does not affect the solution of this equation. An analytical expression for the Maxwell model cross section is also obtained.

Memnonov, V. P.

32

Optimal separable bases and molecular collisions  

SciTech Connect

A new methodology is proposed for the efficient determination of Green`s functions and eigenstates for quantum systems of two or more dimensions. For a given Hamiltonian, the best possible separable approximation is obtained from the set of all Hilbert space operators. It is shown that this determination itself, as well as the solution of the resultant approximation, are problems of reduced dimensionality for most systems of physical interest. Moreover, the approximate eigenstates constitute the optimal separable basis, in the sense of self-consistent field theory. These distorted waves give rise to a Born series with optimized convergence properties. Analytical results are presented for an application of the method to the two-dimensional shifted harmonic oscillator system. The primary interest however, is quantum reactive scattering in molecular systems. For numerical calculations, the use of distorted waves corresponds to numerical preconditioning. The new methodology therefore gives rise to an optimized preconditioning scheme for the efficient calculation of reactive and inelastic scattering amplitudes, especially at intermediate energies. This scheme is particularly suited to discrete variable representations (DVR`s) and iterative sparse matrix methods commonly employed in such calculations. State to state and cumulative reactive scattering results obtained via the optimized preconditioner are presented for the two-dimensional collinear H + H{sub 2} {yields} H{sub 2} + H system. Computational time and memory requirements for this system are drastically reduced in comparison with other methods, and results are obtained for previously prohibitive energy regimes.

Poirier, L.W. [Univ. of California, Berkeley, CA (United States)]|[Lawrence Berkeley National Lab., CA (United States)

1997-12-01

33

Time-of-flight spectroscopy of molecular structure, collision processes, and gas-surface interactions. Final technical report 15 Jun 75-14 Jun 80  

Microsoft Academic Search

Progress in molecular physics research using time-of-flight techniques to measure velocity distributions of fragments from dissociating molecules is reported. Electron bombardment at energies between 20 and 100 eV was used to dissociate the molecules, and only fragments with kinetic energies greater than about 1 eV were detected. Both metastable hydrogen atoms and one-, two-, and three-atom hydrogenic charged fragments were

W. E. Jr Lamb; L. C. Jr McIntyre

1980-01-01

34

Charge-transfer processes in F2+ +H--> F+ + H+ collisions and the reverse process at low-keV energies  

Microsoft Academic Search

Theoretical investigations on single charge-transfer processes in collisions of F2++H-->F++H+ and its reverse process have been carried out at collision energies from 20eV\\/uto10keV\\/u . The molecular orbital expansion method within the semiclassical impact parameter formalism has been employed for the scattering dynamics, while the ab initio multireference single- and double-excitation configuration interaction (MRD-CI) method was adopted for determination of molecular

C. M. Dutta; J. P. Gu; G. Hirsch; R. J. Buenker; P. Nordlander; M. Kimura

2005-01-01

35

Observation of collision induced processes in rubidium-ethane vapour  

NASA Astrophysics Data System (ADS)

The collision-induced stimulated resonant emission on 5 2P1/2-5 2S1/2 transition in rubidium vapour in the presence of ethane as a buffer gas is measured. This effect is investigated experimentally and analyzed theoretically in the small gain approximation. Within this approximation, the main differences between the generation of collision induced amplified spontaneous emission (ASE) signal in cesium-ethane, rubidium-ethane and sodium-ethane mixture were estimated. The dependencies of the ASE intensity on the energy of the laser pump and ethane pressure are measured and the efficiency of the ASE signal generation as a function of the exciting energy is given. The model of longitudinally pumped alkali metal-molecular gas amplifier was developed in order to explain the unusual behaviour of the dependence of the efficiency of the ASE signal generation in the rubidium-ethane mixture on the Gaussian pump beam exciting energy. Some analogies with erbium and ytterbium doped fiber amplification processes are given.

Konefa? , Z.

1999-06-01

36

Accuracy of molecular data in the understanding of ultracold collisions  

SciTech Connect

We show through close-coupled quantum-scattering calculations that the cross section for fine-structure-changing collisions between excited [sup 2][ital P][sub 3/2] and ground [sup 2][ital S][sub 1/2] [ital A] atoms of the same species, where [ital A]=Rb or Cs, is very sensitive to the molecular potentials and spin-orbit matrix elements of the alkali-metal-dimer species. Spectroscopic studies of these species are needed to extract accurate parameters. New high-resolution photoassociation spectroscopy of trapped atoms could be used for this purpose.

Dulieu, O. (Laboratoire des Collisions Atomiques et Moleculaires, Batiment 351, Universite Paris-Sud, 91405 Orsay Cedex (France)); Julienne, P. (Molecular Physics Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)); Weiner, J. (Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742 (United States))

1994-01-01

37

A collision process responsible for widespread formation of H anions  

NASA Astrophysics Data System (ADS)

The hydride ion H? is widely understood to play a major role in many processes important for physics, cosmology, astrophysics and chemistry. Here we report that H- ions can be formed by collision-induced fragmentation of molecules containing hydrogen and heavier nuclei. We observed H? emission from OH+ + Ar and OH+ + acetone collisions at the energy of 7 keV. Our data reveal a process of electron-grabbing by fast hydrogen fragments emitted in hard collisions with large momentum transfer between atomic cores.

Juhász, Zoltán; Sulik, Béla; Kovács, Sándor T. S.; Lattouf, Elie; Rangama, Jimmy; Bene, Erika; Huber, Bernd; Frémont, François; Méry, Aiain; Poully, Jean-Christophe; Rousseau, Patrick; Herczku, Péter; Chesnel, Jean-Yves

2014-04-01

38

Low-energy collision process of sodium cluster ions  

NASA Astrophysics Data System (ADS)

Dissociation dynamics of a size-selected sodium cluster ion, Na9+, in collision with a series of rare-gas atoms, He, Ne, Ar, Kr and Xe, was investigated by measuring the absolute cross sections by use of a tandem mass-spectrometer. The dominant processes for the dissociation are Na and Na2 release from the parent cluster ion. Total cross sections for the dissociation except for the Xe collision is explained in a scheme of classical collision. In the Xe collision, it was found that the cross sections observed were smaller than the cross sections predicted by the classical collision scheme, probably because of long range interaction between the cluster ion and Xe atom. On the other hand, the branching fractions for the Na and the Na2 release are predicted well by the orbital correlation diagrams for the dissociation systems.

Tanaka, Hideki; Hanmura, Tetsu; Nonose, Shinji; Kondow, Tamotsu

1997-06-01

39

Calculation of total cross sections for charge exchange in molecular collisions  

NASA Technical Reports Server (NTRS)

Areas of investigation summarized include nitrogen ion-nitrogen molecule collisions; molecular collisions with surfaces; molecular identification from analysis of cracking patterns of selected gases; computer modelling of a quadrupole mass spectrometer; study of space charge in a quadrupole; transmission of the 127 deg cylindrical electrostatic analyzer; and mass spectrometer data deconvolution.

Ioup, J.

1979-01-01

40

Laser-enhanced dynamics in molecular rate processes  

NASA Technical Reports Server (NTRS)

The present discussion deals with some theoretical aspects associated with the description of molecular rate processes in the presence of intense laser radiation, where the radiation actually interacts with the molecular dynamics. Whereas for weak and even moderately intense radiation, the absorption and stimulated emission of photons by a molecular system can be described by perturbative methods, for intense radiation, perturbation theory is usually not adequate. Limiting the analysis to the gas phase, an attempt is made to describe nonperturbative approaches applicable to the description of such processes (in the presence of intense laser radiation) as electronic energy transfer in molecular (in particular atom-atom) collisions; collision-induced ionization and emission; and unimolecular dissociation.

George, T. F.; Zimmerman, I. H.; Devries, P. L.; Yuan, J.-M.; Lam, K.-S.; Bellum, J. C.; Lee, H.-W.; Slutsky, M. S.

1978-01-01

41

Molecular dynamics based chemistry models of hypervelocity collisions of O(3P) + SO2(X, 1A1) in DSMC.  

PubMed

A significant process in the formation of the unique atmosphere of Io, a Jovian moon, is collision-induced dissociation of sulfur dioxide. The direct simulation Monte Carlo method (DSMC) is used to model the rarefied gas dynamics of the Ionian atmosphere. However, there is a lack of reliable reaction and collision cross sections needed for hypervelocity conditions. In this work, collisions between SO(2) and O were studied using molecular dynamics/quasi-classical trajectories methods with the potential of Murrell and a force field for reactive systems (ReaxFF). Dissociation to SO was found to be the significant reacting process, but at higher collision energies, complete atomization of SO(2) was found to frequently occur. In contrast, dissociation to O(2) was found to be mostly negligible and formation of SO(3) occurred only at low impact velocities. The chemistry and collision models developed from the Murrell and ReaxFF methods were implemented in DSMC simulations and compared to the baseline DSMC collision and reaction models. It was found that the selection of both the dissociation reaction cross section and the non-reactive collision model has a significant effect on the counterflow, shock gas dynamic structure. PMID:23387593

Parsons, Neal; Levin, Deborah A; van Duin, Adri C T

2013-01-28

42

Molecular dynamics based chemistry models of hypervelocity collisions of O(3P) + SO2(X, 1A1) in DSMC  

NASA Astrophysics Data System (ADS)

A significant process in the formation of the unique atmosphere of Io, a Jovian moon, is collision-induced dissociation of sulfur dioxide. The direct simulation Monte Carlo method (DSMC) is used to model the rarefied gas dynamics of the Ionian atmosphere. However, there is a lack of reliable reaction and collision cross sections needed for hypervelocity conditions. In this work, collisions between SO2 and O were studied using molecular dynamics/quasi-classical trajectories methods with the potential of Murrell and a force field for reactive systems (ReaxFF). Dissociation to SO was found to be the significant reacting process, but at higher collision energies, complete atomization of SO2 was found to frequently occur. In contrast, dissociation to O2 was found to be mostly negligible and formation of SO3 occurred only at low impact velocities. The chemistry and collision models developed from the Murrell and ReaxFF methods were implemented in DSMC simulations and compared to the baseline DSMC collision and reaction models. It was found that the selection of both the dissociation reaction cross section and the non-reactive collision model has a significant effect on the counterflow, shock gas dynamic structure.

Parsons, Neal; Levin, Deborah A.; van Duin, Adri C. T.

2013-01-01

43

Effect of laser frequency on a collision-induced radiative process  

NASA Technical Reports Server (NTRS)

A review is presented of the principles of collision induced radiative processes, followed by an examination of the effects of laser frequencies on these processes. A one-dimensional problem involving two electron states is considered, and it is found that the Hamiltonian of the radiation field is dominated by electric-dipole interaction which couples states of different parity. Transitions are noted to be dependent on collisions, and the complexities of three-dimensional systems are expressed as considerations of the angular momentum of the photon, the necessity of treating different states simultaneously, and the fact that a radiation field destroys rotational invariance. Changing the radiation frequency alters the crossing point and offers opportunities to study the interplay of potential surfaces with molecular dynamics. Experiments on Na+A systems are outlined for several collision energies and various laser frequencies. Multiple crossings were obtained, although the total cross-section, at all energies, decreased at 18,350/cm.

Devries, P. L.; George, T. F.

1981-01-01

44

Applications of cross sections for electron-molecule collision processes  

SciTech Connect

The role of electron-molecule collision cross sections is discussed for the study of the ionospheric and auroral processes in planetary atmospheres and of discharge-pumped lasers. These two areas emphasize the importance of further theoretical and experimental studies concerning electron-impact processes. 13 refs., 3 figs., 2 tabs. (WRF)

Cartwright, D.C.

1985-01-01

45

Charge-transfer processes in F{sup 2+}+HâF{sup +}+H{sup +} collisions and the reverse process at low-keV energies  

Microsoft Academic Search

Theoretical investigations on single charge-transfer processes in collisions of F{sup 2+}+HâF{sup +}+H{sup +} and its reverse process have been carried out at collision energies from 20 eV\\/u to 10 keV\\/u. The molecular orbital expansion method within the semiclassical impact parameter formalism has been employed for the scattering dynamics, while the ab initio multireference single- and double-excitation configuration interaction (MRD-CI) method

C. M. Dutta; P. Nordlander; J. P. Gu; G. Hirsch; R. J. Buenker; M. Kimura

2005-01-01

46

Importance of post collision interactions for charge transfer process  

NASA Astrophysics Data System (ADS)

Recently experimental fully differential cross sections (FDCS) have been reported for double capture, single capture and transfer excitation in proton helium collisions. In case of double capture, the proton captures both of the electrons from helium and leaves the collision as a H- ion. For single capture, the proton captures one electron from helium and leaves the other electron in the ground state. Transfer excitation is similar to single capture except the target is excited to an excited state. Recently experiments performed for proton energies ranging from 25keV to 300keV. We introduce here a theoretical model for charge transfer processes which is fully quantum mechanical and takes all post collision interactions (PCI) between the particles into account exactly. Numerically, this requires a full nine-dimensional integral which is computationally expensive. The theoretical results will be compared with absolute experimental measurements.

Chowdhury, Uttam; Harris, Allison; Peacher, Jerry; Madison, Don

2012-06-01

47

Theory of Molecular Collisions in the Presence of a Laser Field.  

National Technical Information Service (NTIS)

The reaction dynamics and mechanism of energy transfer in a gas-phase molecular collision system can be dramatically affected by an intense, external laser field. A rigorous theoretical treatment must consider explicitly the interaction of the field with ...

T. F. George J. R. Laing J. M. Yuan I. H. Zimmerman

1976-01-01

48

Bibliography of Molecular Dissociation in Heavy Particle Collisions, 1950--75.  

National Technical Information Service (NTIS)

This annotated bibliography lists published work on molecular dissociation in heavy particle collisions for the period 1950 to 1975. Sources include scientific journals, abstract compilations, conference proceedings, books, and reports. The bibliography i...

E. W. McDaniel C. F. Barnett D. H. Crandall H. B. Gilbody M. I. Kirkpatrick

1979-01-01

49

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

SciTech Connect

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 is 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.

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

2013-10-15

50

Charge transfer rate coefficients in collision of C 2+ ions with CO and N 2 molecular targets  

NASA Astrophysics Data System (ADS)

An ab initio molecular treatment of the charge transfer process in collision of C 2+ ions with the isoelectronic CO and N 2 targets has been performed. The corresponding rate coefficients in the 400-50 000 K temperature range are compared to recent measurements of Gao and Kwong at Tequiv = 1.17 × 10 4 K. A global satisfactory agreement is observed and some general behaviour may be deduced.

Bacchus-Montabonel, M. C.; Tergiman, Y. S.

2010-09-01

51

FORMATION OF MASSIVE MOLECULAR CLOUD CORES BY CLOUD-CLOUD COLLISION  

SciTech Connect

Recent observations of molecular clouds around rich massive star clusters including NGC 3603, Westerlund 2, and M20 revealed that the formation of massive stars could be triggered by a cloud-cloud collision. By using three-dimensional, isothermal, magnetohydrodynamics simulations with the effect of self-gravity, we demonstrate that massive, gravitationally unstable, molecular cloud cores are formed behind the strong shock waves induced by cloud-cloud collision. We find that the massive molecular cloud cores have large effective Jeans mass owing to the enhancement of the magnetic field strength by shock compression and turbulence in the compressed layer. Our results predict that massive molecular cloud cores formed by the cloud-cloud collision are filamentary and threaded by magnetic fields perpendicular to the filament.

Inoue, Tsuyoshi [Department of Physics and Mathematics, Aoyama Gakuin University, Sagamihara, Kanagawa 252-5258 (Japan); Fukui, Yasuo, E-mail: inouety@phys.aoyama.ac.jp [Department of Physics, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602 (Japan)

2013-09-10

52

Metastability of isoformyl ions in collisions with helium and hydrogen. [in interstellar molecular clouds  

NASA Technical Reports Server (NTRS)

The stability of HOC(+) ions under conditions in interstellar molecular clouds is considered. In particular, the possibility that collisions with helium or hydrogen will induce isomerization to the stable HCO(+) form is examined theoretically. Portions of the electronic potential energy surfaces for interaction with He and H atoms are obtained from standard quantum mechanical calculations. Collisions with He atoms are found to be totally ineffective for inducing isomerization. Collisions with H atoms are found to be ineffective at low interstellar temperatures owing to a small (about 500 K) barrier in the entrance channel; at higher temperatures where this barrier can be overcome, however, collisions with hydrogen atoms do result in conversion to the stable HCO(+) form. Although detailed calculations are not presented, it is argued that low-energy collisions with H2 molecules are also ineffective in destroying the metastable ion.

Green, S.

1984-01-01

53

Desorption induced by atomic and molecular ion collisions on LiF  

NASA Astrophysics Data System (ADS)

Atomic and molecular nitrogen ion beams, produced by the PUC-Rio Van de Graaff accelerator, were used to bombard lithium fluoride thin films. Desorption of secondary ions was measured by means of a time-of-flight mass spectrometer equipped with a double grid acceleration system. The outputs of the experiment are the axial kinetic energy distribution and the desorption yield of the emitted ions. This information allowed determination of the relative contribution to desorption due to collision cascades (nuclear sputtering) and to electronic excitation (electronic sputtering). It was observed that F- ions are desorbed as a result of collision cascades and that the F- ion yields depends linearly on the number of constuents in the projectile, i.e., Y(N2+)=2Y(N+). The emission of clusters such as (LiF)Li+ was found to be caused by electronic excitation and the (LiF)Li+ yield revealed a nonlinear dependence: Y(N2+)>2Y(N+). Both processes were found to contribute to Li+ desorption. These effects are discussed in terms of the density of deposited energy which depends on the projectile velocity and on the electronic stopping power.

Pereira, J. A. M.; da Silveira, E. F.

1999-06-01

54

Rototranslational collision-induced absorption and collision-induced light scattering spectra of molecular hydrogen using isotropic intermolecular potentials  

NASA Astrophysics Data System (ADS)

Quantum mechanical lineshapes of collision-induced absorption (CIA) at different temperatures and of collision-induced light scattering (CILS) at room temperature are computed for gaseous molecular hydrogen using theoretical values for induced dipole moments and pair-polarizability trace and anisotropy as input. Comparison with measured spectra of absorption, isotropic and anisotropic light scattering shows satisfactory agreement, for which the uncertainty in measurement of its spectral moments is seen to be large. Empirical models of the dipole moment and pair-polarizability trace and anisotropy which reproduce the experimental spectra and the first three spectral moments more closely than the fundamental theory are also given. Good agreement between computed and experimental lineshapes of both absorption and scattering is obtained when potential models which are constructed from the thermophysical, transport, total scattering cross-section and spectroscopic properties are used. Also, the use of the new potential in lattice dynamic calculations yields good results for several properties of solid hydrogen.

El-Kader, M. S. A.; Maroulis, G.; Bich, E.

2012-07-01

55

Collision dynamics of methyl radicals and highly vibrationally excited molecules using crossed molecular beams  

SciTech Connect

The vibrational to translational (V{yields}T) energy transfer in collisions between large highly vibrationally excited polyatomics and rare gases was investigated by time-of-flight techniques. Two different methods, UV excitation followed by intemal conversion and infrared multiphoton excitation (IRMPE), were used to form vibrationally excited molecular beams of hexafluorobenzene and sulfur hexafluoride, respectively. The product translational energy was found to be independent of the vibrational excitation. These results indicate that the probability distribution function for V{yields}T energy transfer is peaked at zero. The collisional relaxation of large polyatomic molecules with rare gases most likely occurs through a rotationally mediated process. Photodissociation of nitrobenzene in a molecular beam was studied at 266 nm. Two primary dissociation channels were identified including simple bond rupture to produce nitrogen dioxide and phenyl radical and isomerization to form nitric oxide and phenoxy radical. The time-of-flight spectra indicate that simple bond rupture and isomerization occurs via two different mechanisms. Secondary dissociation of the phenoxy radicals to carbon monoxide and cyclopentadienyl radicals was observed as well as secondary photodissociation of phenyl radical to give H atom and benzyne. A supersonic methyl radical beam source is developed. The beam source configuration and conditions were optimized for CH{sub 3} production from the thermal decomposition of azomethane. Elastic scattering of methyl radical and neon was used to differentiate between the methyl radicals and the residual azomethane in the molecular beam.

Chu, P.M.Y.

1991-10-01

56

Molecular cooling via Sisyphus processes  

NASA Astrophysics Data System (ADS)

We present a study of Sisyphus cooling of molecules: The scattering of a single photon removes a substantial amount of the molecular kinetic energy and an optical pumping step allows one to repeat the process. A review of the produced cold molecules so far indicates that the method can be implemented for most of them, making it a promising method able to produce a large sample of molecules at sub-mK temperatures. Considerations of the required experimental parameters, for instance the laser power and linewidth or the trap anisotropy and dimensionality, are given. Rate equations, as well as scattering and dipolar forces, are solved using kinetic Monte Carlo methods for several lasers and several levels. For NH molecules, such detailed simulation predicts a 1000-fold temperature reduction and an increase of the phase-space density by a factor of 107. Even in the case of molecules with both low Franck-Condon coefficients and a nonclosed pumping scheme, 60% of trapped molecules can be cooled from 100 mK to sub-mK temperatures in a few seconds. Additionally, these methods can be applied to continuously decelerate and cool a molecular beam.

Comparat, Daniel

2014-04-01

57

Mass-independent isotopic fractionation in nonadiabatic molecular collisions  

NASA Astrophysics Data System (ADS)

The conditions under which nonadiabatic collisions should induce mass-independent isotopic fractionation are considered, and the consequences of such fractionation are discussed. It is shown that mass-independent isotopic fractionation in the UV photolysis of ozone is but one example of a general class of such fractionations that should be associated with nonadiabatic collisions. It is demonstrated that nonadiabatic effects may be the source of the equal O-17 and O-18 isotopic enrichment in meteoritic material observed by Clayton et al. (1973) as well as the equal O-17 and O-18 enrichments produced by Heidenreich and Thiemens using electrical discharges in oxygen-containing gas samples. The effect of oxygen isotopic fractionation in the UV photolysis of ozone on the isotope distributions among oxygen-containing species in the atmosphere is considered.

Valentini, James J.

1987-06-01

58

Momentum Transfer Approximation for the Calculation of Molecular Transition Probabilities in High Temperature Gas Kinetic Collisions.  

National Technical Information Service (NTIS)

A straightforward method, the momentum transfer approximation, is proposed for the determination of the probabilities of inelastic (non-electronic) processes in high temperature gas kinetic collisions. The approximation is applicable to polyatomic as well...

A. P. Proudian

1965-01-01

59

To what extent do molecular collisions arising from water vapour efflux impede stomatal O3 influx?  

PubMed

Pre-requisite for reliable O(3) risk assessment for plants is determination of stomatal O(3) uptake. One unaddressed uncertainty in this context relates to transpiration-induced molecular collisions impeding stomatal O(3) influx. This study quantifies, through physical modelling, the error made when estimating stomatal O(3) flux without accounting for molecular collisions arising from transpiratory mass flow of gas out of the leaf. The analysis demonstrates that the error increases with increasing leaf-to-air water vapour mole fraction difference (?w), being zero in water vapour saturated air and 4.2% overestimation at ?w of 0.05. Overestimation is approximately twice as large in empirical studies quantifying stomatal O(3) flux from measured leaf or canopy water flux, if neglecting both water vapour-dry air collisions (causing overestimation of leaf conductance) and collisions involving O(3). Correction for transpiration-induced molecular collisions is thus relevant for both empirical research and for large-scale modelling of stomatal O(3) flux across strong spatial ?w gradients. PMID:22763329

Uddling, Johan; Matyssek, Rainer; Pettersson, Jan B C; Wieser, Gerhard

2012-11-01

60

Cloud-cloud collision in the Sgr B2 molecular cloud complex  

NASA Astrophysics Data System (ADS)

We present results from a high-resolution wide-field imaging observation of the central molecular zone (CMZ) in H13CO+ J = (1 - 0) and SiO v=0, J = (2-1) emission lines by using the Nobeyama 45-m telescope in order to depict the high-density molecular gas mass distribution and explore molecular gas affected by interstellar shocks. We found a candidate for ongoing cloud-cloud collision in the Sgr B2 complex. This is identified as a hollow paraboloid-like structure in the l-b-v data cube of both emission lines. The central part of the feature is denser and warmer than the outer envelope and contains a vast amount of shocked molecular gas. These properties are consistent with those expected from simulations of cloud-cloud collisions in the CMZ.

Tsuboi, Masato; Miyazaki, Atsushi; Handa, Toshihiro

2014-05-01

61

Molecular effects observed in auger transitions from H + AND H 2+ collisions with solid, molecular and atomic targets  

NASA Astrophysics Data System (ADS)

The molecular effect is measured by the ratio R = {Y A( H2+) }/{Y A( H+) } of H 2+- and (1 MeV/u) H +-i For carbon foil surfaces Rsolid?1.3 resulting from the high energy region of the Auger peak, is caused mostly by the projectile electron interacting with the target atoms. In collisions with CH 4, C 4H 10 and Ar targets, Rgas? 0.75 is attributed to screeni under single collision conditions. The Auger line shapes and R values resulting from solid and gaseous targets are discussed.

Burkhard, M.; Koschar, P.; Heil, O.; Kemmler, J.; Kövér, A.; Szabó, Gy.; Berényi, D.; Groeneveld, K. O.

1987-04-01

62

Broadening and shifts of the lines of molecular ions by collisions with neutral perturbers  

Microsoft Academic Search

We present a theoretical model for studying the shape of the rotational lines of molecular ions perturbed by collisions with neutral species. This model shows that the interaction between the ionic monopole and the multipole moments of the perturber has no role in the collisional relaxation of the lines. The effect of the ionic monopole is restricted to that of

G. Buffa; O. Tarrini; G. Cazzoli; L. Dore

1994-01-01

63

Many-electron aspects of molecular promotion in ion-atom collisions - Production of core-excited states of Li in Li/+/-He collisions  

NASA Technical Reports Server (NTRS)

Production of core-excited autoionizing states of neutral Li having configurations of the form 1snln(prime)l(prime) has been observed over the impact-energy range from 10-50 keV. Although the results for production of all such states is remarkably consistent with a quasi-molecular-excitation model proposed by Stolterfoht and Leithaeuser (1976), production of individual lines in the observed spectra exhibits collision-velocity dependencies indicative of considerably more complex processes, including processes which appear to be inherently two-electron in nature. Excitation functions are presented for (1s2s/2/)/2/S, 1s(2s2p/3/P)/2/P, 1s(2s2p/1/P)/2/P, and (1s2p/2/)/2/D core-excited state of Li and for total core excitation.

Elston, S. B.; Vane, C. R.; Schumann, S.

1979-01-01

64

Molecular-orbital X-rays and their anisotropies in heavy-ion collisions in solids and gases  

NASA Astrophysics Data System (ADS)

Molecular-orbital spectra and anisotropies were measured in Cl+NaCl, Cl+KCl, Cl +Ti, and Cl+Ar collisions at bombarding energies between 0.5 and 2.6MeV/a.m.u. The results suggest that at low bombarding energies MO x-rays in the KCl and NaCl targets are partly produced by a two-collision process. Qualitative differences between the anisotropies of gas- and solid-target induced MO x-ray spectra underline this result. Also, new information on the bombarding-energy dependency of anisotropies at higher projectile velocities has been obtained, confirming previous observations in low- Z systems.

Stoller, Ch; Anholt, R.; Meyerhof, W. E.

1981-06-01

65

Stratospheric measurements of collision-induced absorption by molecular oxygen  

NASA Technical Reports Server (NTRS)

High-resolution stratospheric solar absorption spectra recorded at sunset with a balloon-borne interferometer, from an altitude of 33 km, are used in a study of collision-induced absorption by the fundamental vibration-rotation band of O2, whose continuum has been identified in the 1400-1700/cm region in spectra obtained at tangent altitudes below 22 km. It is found that transmittance measurements in intervals free of atmospheric line absorption agree with values calculated with the O2 absorption coefficients of Timofeyev and Tonkov (1978), and that the measurements indicate a 20% upper limit for the uncertainty of the available O2 absorption coefficients at lower stratospheric temperatures, on the order of 220 K.

Rinsland, C. P.; Smith, M. A. H.; Seals, R. K., Jr.; Goldman, A.; Murcray, F. J.; Murcray, D. G.; Larsen, J. C.; Rarig, P. L.

1982-01-01

66

Vibrational relaxation in H/sub 2/ molecules by wall collisions: applications to negative ion source processes  

SciTech Connect

In the volume of a hydrogen discharge, H/sub 2/ molecules, excited to high vibrational levels (v'' > 6), are formed either by fast-electron collisions or from H/sub 2//sup +/ ions that are accelerated across the discharge-wall potential that undergo Auger neutralization prior to impact with the discharge chamber wall. We have used computer molecular dynamics to study the de-excitation and re-excitation of vibrationally-excited H/sub 2/ molecules undergoing repeated wall collisions. The initial translational energies range from thermal to 100 eV and the initial vibrational states range from v'' = 2 to v'' = 12. The average loss or gain of vibrational, rotational, translational, and total molecular energies and the survival rates of the molecules have been evaluated. At thermal energies vibrational de-excitation is the predominant process, and a consistent picture emerges of rapid energy redistribution into all the molecular degrees of freedom and a slower rate of loss of total molecular energy to the wall. At higher translational energies (1 to 100 eV) a substantial fraction of the molecules survive with large (v'' > 6) vibrational energy. This vibrational population provides a contribution to the total excited vibrational population comparable to that from the fast-electron collision process.

Karo, A.M.; Hiskes, J.R.; Hardy, R.J.

1984-10-01

67

Molecular processes in a high temperature shock layer  

NASA Technical Reports Server (NTRS)

Models of the shock layer encountered by an Aeroassisted Orbital Transfer Vehicle require as input accurate cross sections and rate constants for the atomic and molecular processes that characterize the shock radiation. From the estimated atomic and molecular densities in the shock layer and the expected residence time of 1 m/s, it can be expected that electron-ion collision processes will be important in the shock model. Electron capture by molecular ions followed by dissociation, e.g., O2(+) + e(-) yields 0 + 0, can be expected to be of major importance since these processes are known to have high rates (e.g., 10 to the -7th power cu/cm/sec) at room temperature. However, there have been no experimental measurements of dissociative recombination (DR) at temperatures ( 12000K) that are expected to characterize the shock layer. Indeed, even at room temperature, it is often difficult to perform experiments that determine the dependence of the translational energy and quantum yields of the product atoms on the electronic and vibrational state of the reactant molecular ions. Presented are ab initio quantum chemical studies of DR for molecular ions that are likely to be important in the atmospheric shock layer.

Guberman, S. L.

1984-01-01

68

Indene formation under single-collision conditions from the reaction of phenyl radicals with allene and methylacetylene--a crossed molecular beam and ab initio study.  

PubMed

Polycyclic aromatic hydrocarbons (PAHs) are regarded as key intermediates in the molecular growth process that forms soot from incomplete fossil fuel combustion. Although heavily researched, the reaction mechanisms for PAH formation have only been investigated through bulk experiments; therefore, current models remain conjectural. We report the first observation of a directed synthesis of a PAH under single-collision conditions. By using a crossed-molecular-beam apparatus, phenyl radicals react with C(3)H(4) isomers, methylacetylene and allene, to form indene at collision energies of 45 kJ mol(-1). The reaction dynamics supported by theoretical calculations show that both isomers decay through the same collision complex, are indirect, have long lifetimes, and form indene in high yields. Through the use of deuterium-substituted reactants, we were able to identify the reaction pathway to indene. PMID:21956874

Parker, Dorian S N; Zhang, Fangtong; Kaiser, Ralf I; Kislov, Vadim V; Mebel, Alexander M

2011-11-01

69

Effect of molecular weight on polymer processability  

SciTech Connect

Differences in rheological behavior due to the polymer molecular weight and molecular weight distribution have been shown with the MPT. SBR polymers having high molecular weight fractions develop higher stress relaxation time values due to the higher degree of polymer entanglements. Tests conducted at increasing temperatures show the diminishing influence of the polymer entanglements upon stress relaxation time. EPDM polymers show stress relaxation time and head pressure behavior which correlates with mill processability. As anticipated, compounded stock of EPDM have broad molecular weight distribution has higher stress relaxation time values than EPDM compounds with narrow molecular weight distribution.

Karg, R.F.

1983-01-01

70

Laser and isotope effects in charge transfer processes in atomic collisions  

NASA Astrophysics Data System (ADS)

Charge transfer processes are fundamental to the understanding of matter neutralization in atomic and molecular processes. Due to the polarizability of the material, charge transfer can be enhanced or suppressed during the interaction with electromagnetic radiation. Furthermore, charge transfer has different contributions arising from the radial and rotational regions of the potential interaction in the collision, which depend on the mass of the target and projectile. Since these effects appear in a very short time (femtoseconds), the dynamics must be carried out outside the Born-Oppenheimer approximation. In this work, we present charge transfer results for He2+ ions colliding with atomic hydrogen and tritium atoms for collision energies from 100 eV/amu up to 1.5 keV/amu, assisted by a fast, short laser pulses of intensity 3.5×1012 W/cm2 and wave length of 790 nm by means of an electron-nuclear dynamic treatment. We find large isotope effects in the low-energy region up to one order of magnitude in the charge transfer cross-section in the absence of the laser pulse. In the presence of the laser pulse, the isotope effect is negligible and the charge transfer cross-section is enhanced up to two orders of magnitude in the low-energy region.

Cabrera-Trujillo, R.

71

Molecular dynamics simulations for CO2 spectra. II. The far infrared collision-induced absorption band  

Microsoft Academic Search

Classical molecular dynamics simulations have been carried out for gaseous CO2 starting from various anisotropic intermolecular potential energy surfaces. Through calculations for a large number of molecules treated as rigid rotors, the time evolution of the interaction-induced electric dipole vector is obtained and the Laplace transform of its autocorrelation function gives the collision-induced absorption rototranslational spectrum. The results are successfully

J.-M. Hartmann; C. Boulet; D. Jacquemart

2011-01-01

72

Gas-Phase Molecular Dynamics: High Resolution Spectroscopy and Collision Dynamics of Transient Species  

SciTech Connect

This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. High-resolution spectroscopy, augmented by theoretical and computational methods, is used to investigate the structure and collision dynamics of chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry. Applications and methods development are equally important experimental components of this work.

Hall,G.E.; Sears, T.J.

2009-04-03

73

Resonant Ion Pair Formation in Electron Collisions with Ground State Molecular Ions  

Microsoft Academic Search

Resonant ion pair formation from collisions of electrons with ground state diatomic molecular ions has been observed and absolute cross sections measured. The cross section for HD+ is characterized by an abrupt threshold at 1.9 eV and 14 resolved peaks in the range of energies 0<=E<=14 eV. The dominant mechanism responsible for the structures appears to be resonant capture and

W. Zong; G. H. Dunn; N. Djuric; M. Larsson; C. H. Greene; A. Al-Khalili; A. Neau; A. M. Derkatch; L. Vikor; W. Shi; A. Le Padellec; S. Rosén; H. Danared; M. Af Ugglas

1999-01-01

74

Star Formation in Disk Galaxies. I. Formation and Evolution of Giant Molecular Clouds via Gravitational Instability and Cloud Collisions  

NASA Astrophysics Data System (ADS)

We investigate the formation and evolution of giant molecular clouds (GMCs) in a Milky-Way-like disk galaxy with a flat rotation curve. We perform a series of three-dimensional adaptive mesh refinement numerical simulations that follow both the global evolution on scales of ~20 kpc and resolve down to scales lsim10 pc with a multiphase atomic interstellar medium. In this first study, we omit star formation and feedback, and focus on the processes of gravitational instability and cloud collisions and interactions. We define clouds as regions with n H >= 100 cm-3 and track the evolution of individual clouds as they orbit through the galaxy from their birth to their eventual destruction via merger or via destructive collision with another cloud. After ~140 Myr a large fraction of the gas in the disk has fragmented into clouds with masses ~106 M sun and a mass spectrum similar to that of Galactic GMCs. The disk settles into a quasi-steady-state in which gravitational scattering of clouds keeps the disk near the threshold of global gravitational instability. The cloud collision time is found to be a small fraction, ~1/5, of the orbital time, and this is an efficient mechanism to inject turbulence into the clouds. This helps to keep clouds only moderately gravitationally bound, with virial parameters of order unity. Many other observed GMC properties, such as mass surface density, angular momentum, velocity dispersion, and vertical distribution, can be accounted for in this simple model with no stellar feedback.

Tasker, Elizabeth J.; Tan, Jonathan C.

2009-07-01

75

Electron capture and deprotonation processes observed in collisions between Xe8+ and multiply protonated cytochrome-C  

NASA Astrophysics Data System (ADS)

Electron-transfer processes in interaction between highly charged ions and multiply protonated proteins have been studied. Collisions between Xe8+ at 96 keV and protonated cytochrome-C at selected charge state (q from 15+ to 19+) result in mass spectra composed mainly of intact molecular ions. From the spectra, single and double electron capture processes by Xe8+ from the protonated molecular ions were identified and the relative cross sections were measured. An unexpected process, the deprotonation process, was also observed. It is tentatively attributed to the loss of a proton induced by the strong electric field carried by the projectile ion in long-distance collisions. Upon charge variation of the molecular target from 15 to 19, the single and double electron capture cross sections remain nearly constant, while the relative cross section of the deprotonation process increases dramatically from 0.8% (±0.1%) to 17% (±1%). This strong charge dependency is explained by the decrease of the proton affinities with the charge. This proton removal process has not been observed previously. It seems to be specific to the long-distance Coulomb interactions between protons bound along the protein chain and the highly charged atomic ions.

Martin, S.; Ortega, C.; Chen, L.; Brédy, R.; Vernier, A.; Dugourd, P.; Antoine, R.; Bernard, J.; Reitsma, G.; Gonzalez-Magaña, O.; Hoekstra, R.; Schlathölter, T.

2014-01-01

76

Description of ionization in the molecular approach to atomic collisions. II  

NASA Astrophysics Data System (ADS)

We complement a previous article [Harel et al., Phys. Rev. A 55, 287 (1997)] that studied the characteristics of the description of ionization by the molecular approach to atomic collisions, by comparing the wave functions with accurate counterparts. We show how the failure of the basis to describe the phase of the ionizing wave function results in a trapping of the corresponding population in some molecular channels. The time evolution of the molecular wave function then departs from the exact one and the ionization and capture mechanisms appear as interlocked. We thus elucidate the question of the ``natural'' boundary of the molecular approach and draw further consequences as to the choice of pseudostates and the use of translation factors.

Errea, L. F.; Harel, C.; Jouin, H.; Méndez, L.; Pons, B.; Riera, A.; Sevila, I.

2002-02-01

77

The rate coefficients of the chemi-ionization processes in slow Li*(n) + Na collisions  

Microsoft Academic Search

The semi-classical method for determining the rate coefficients of the chemi-ionization processes in slow non-symmetric atom-Rydberg atom collisions is applied to the Li*(n) + Na case. Calculated rate coefficients are compared with the existing experimental data from the literature. Obtained results have confirmed that resonant mechanism of non-elastic processes in atom-Rydberg atom collisions are fully applicable to non-symmetric chemi-ionization processes.

Lj M. Ignjatovic; A. A. Mihajlov; A. N. Klyucharev

2008-01-01

78

The rate coefficients of the chemi-ionization processes in slow Li*(n) + Na collisions  

Microsoft Academic Search

The semi-classical method for determining the rate coefficients of the chemi-ionization processes in slow non-symmetric atom–Rydberg atom collisions is applied to the Li*(n) + Na case. Calculated rate coefficients are compared with the existing experimental data from the literature. Obtained results have confirmed that resonant mechanism of non-elastic processes in atom–Rydberg atom collisions are fully applicable to non-symmetric chemi-ionization processes.

Lj M Ignjatovi?; A A Mihajlov; A N Klyucharev

2008-01-01

79

Gas phase atomic and molecular processes  

NASA Astrophysics Data System (ADS)

We perform fully quantum mechanical calculations of the lithium 2 p -2 s and sodium 3 p -3 s resonance lines pressure broadened by collisions with helium atoms. Using carefully constructed potential energy surfaces and transition dipole moments, we have obtained the emission and absorption coefficients at temperatures from 200 to 3000 K at wavelengths between 500 and 1000 nm for lithium and at temperatures from 158 to 3000 K at wavelengths between 500 and 760 nm for sodium. Contributions from quasi-bound levels are included. Our results are in good agreement with experiment. These broadened line profiles are important in developing effective diagnostics on the temperatures, densities, albedos and composition of the atmospheres of brown dwarfs and extrasolar giant planets. We compute the diffusion coefficients of ground and excited-state lithium and sodium atoms in a helium gas. They are valuable in predicting the sign and magnitude of the light-induced drift for the gas mixture. We calculate the dispersion coefficients of the long range interactions of alkali-metal atoms with molecular hydrogen and helium atoms. The uncertainties in our results are less than 2%. We study the relaxation of the v = 1 vibrational level of carbon monoxide induced by collisions with helium three atoms in ultracold temperatures. We confirm the Wigner's threshold law which states that in the zero temperature limit the inelastic quenching cross sections are inversely proportional to the velocity of the incident atom. Our calculations agree well with experiment and we find enhanced rate coefficients as compared to those for 4 He-CO. We study the chemistry of hydrogen fluoride in the interstellar medium. We consider fine-structure collisions and find that most fluorine atoms reside in the ground 2 P 3/ 2 state. We calculate the rate coefficients for the reaction of F( 2 P 3/2 ) atoms in collisions with H 2 . Our results agree well with experiment. We confirm the conclusions of Neufeld et al. that in interstellar clouds HF is the major form of gas phase fluorine.

Zhu, Cheng

80

Single- and double-electron capture processes in low-energy collisions of N3+ with He  

NASA Astrophysics Data System (ADS)

Single-electron capture (SEC) and double-electron capture (DEC) processes in collisions of ground state N3+ (2s21S) ions with He are investigated by using the quantum-mechanical molecular-orbital close-coupling (QMOCC) method. The ab initio adiabatic potentials, radial and rotational coupling matrices utilized in QMOCC calculations, are obtained from the multireference single- and double-excitation configuration interaction approach. Total and state-selective SEC and DEC cross sections are presented in the low-energy range from 0.1 eV to 15 keV (i.e., 0.007 eV/u -1.07 keV/u) and rate coefficients in the temperature range from 104 to 107 K. Our results indicate that the SEC dominates the charge-transfer process in the considered energy region of this collision system and the SEC cross sections are nearly constant in the relatively high-collision energy region, while the DEC cross sections are about 2 orders of magnitude smaller. It is found that, for the SEC processes, in the dominant mechanisms, electrons are captured to exoergic channels N2+ (2s2p22D,2S), and for the DEC processes, they are captured to N+ (2s22p21D,1S). Our calculations also reveal that rotational couplings become important at E > 10 eV/u for SEC and E > 200 eV/u for DEC processes.

Liu, X. J.; Wang, J. G.; Qu, Y. Z.; Buenker, R. J.

2011-10-01

81

Molecular dynamics study of particle particle collisions between hydrogen-passivated silicon nanoparticles  

NASA Astrophysics Data System (ADS)

One of the significant challenges in the use of nanoparticles is the control of primary particle size and extent of agglomeration when grown from the gas phase. In this paper we evaluate a possible strategy of surface passivation. Here the particle particle interaction of hydrogen-surface-terminated silicon nanoparticles has been evaluated using molecular dynamics simulation. Nanoparticles of the size between 200 and 6400 silicon atoms at 300 1800 K were studied with a reparametrized Kohen-Tully-Stillinger empirical interatomic potential. A hydrogen monolayer is shown to prevent coalescence between particles under thermal collision conditions. The critical approach energy for coalescence was found to increase with increasing particle size but decreases with increasing temperature. Both solid and liquid droplets were seen to bounce at thermal energies, and in some cases, “superelastic” collisions are observed, where the rebound kinetic energy of the droplet is higher than the approach energy. These results suggest that surface coatings can significantly retard nanoaerosol growth.

Hawa, T.; Zachariah, M. R.

2004-01-01

82

Analyzing collision processes with the smartphone acceleration sensor  

NASA Astrophysics Data System (ADS)

It has been illustrated several times how the built-in acceleration sensors of smartphones can be used gainfully for quantitative experiments in school and university settings (see the overview in Ref. 1). The physical issues in that case are manifold and apply, for example, to free fall,2 radial acceleration,3 several pendula,4,5 or the exploitation of everyday contexts.6 This paper supplements these applications and presents an experiment to study elastic and inelastic collisions. In addition to the masses of the two impact partners, their velocities before and after the collision are of importance, and these velocities can be determined by numerical integration of the measured acceleration profile.

Vogt, Patrik; Kuhn, Jochen

2014-02-01

83

Modeling electron and energy transfer processes in collisions between ions and Polycyclic Aromatic Hydrocarbon molecules  

NASA Astrophysics Data System (ADS)

In this work we study collisions between ions and Polycyclic Aromatic Hydrocarbons with the aid of a novel over-the-barrier model and well-established models for nuclear and electronic stopping processes.

Chen, Tao; Alexander, John; Forsberg, Björn; Pettersson, Alf; Gatchell, Michael; Cederquist, Henrik; Zettergren, Henning

2014-04-01

84

Overview on collision processes of highly charged ions with atoms present status and problems  

SciTech Connect

This paper provides a brief discussion on the present status of the collision physics of highly charged ions with atoms. The emphasis is on the main achievements in understanding and describing the most important collision processes, and as charge transfer, ionization and Auger-type processes, and even more on those open problems which, due either to their scientific or practical importance, represent challenges to current research in this field. The paper concentrates on general ideas and problems whose development and solutions have advanced or will advance our basic understanding of the collision dynamics of multiply charged ions with atoms.

Janev, R.K.

1983-05-01

85

Solar spot influence on Earth's molecular processes  

NASA Astrophysics Data System (ADS)

The paper considers the two-century-old problem of how solar spots influence biological objects on the Earth. It describes the modern state of the kT-problem, which for a long time has been the most difficult obstacle in explaining solar activity effects. Based on recent advances in spin chemistry and magnetoplasticity physics, it is shown that a `molecular target' sensitive to weak electromagnetic fields is spins in non-equilibrial states of the molecular system. A way of how solar spots can influence Earth's molecular, including biological, processes through a `transparency window' in the Earth's atmosphere is proposed.

Evstafyev, Vladimir K.

2013-01-01

86

Collision-induced electronic transitions in complexes between benzene and molecular oxygen  

NASA Astrophysics Data System (ADS)

The collision-induced electric dipole transition moments for the O 2 + C 6H 6 complex have been investigated by the multi-configurational self-consistent field linear response method. Cooperative simultaneous transitions, ( 1? g, 3B 1 u) ? ( 3? g-1, A 1 g) and ( 1? g, 3E 1 u) ? ( 3? g-1, A 1 g) , as well as singlet-triplet and singlet-singlet transitions in each molecule have been studied in gas phase and in solvent phase as modelled by a self-consistent reaction field method. Strong intensity enhancement, respectively, reduction is predicted for the 3B 1 u ? 1A 1 gand1E 1 u ? 1A 1 g transitions in benzene colliding with oxygen in gas or solvent environments. We find that transitions involving singlet molecular oxygen are greatly enhanced at intermolecular distances easily reached at normal temperature conditions; the b1?g+ - a1?g, a1?g - X3?g- and b1?g+ - X3?g- transition probabilities are predicted to become enhanced approximately by 10 5, 10 3 and 10 0 times in O 2 + C 6H 6 collisions. The enhancement is of such a magnitude that singlet molecular oxygen should be easy to detect by absorption and emission experiments tuned to the particular frequencies. It is argued that the benzene molecule is the most efficient choice among a set of organic colliders for promoting intensity of the Herzberg III band in molecular oxygen.

Minaev, Boris F.; Mikkelsen, Kurt V.; Ågren, Hans

1997-07-01

87

Molecular Dynamics Simulation of Defect Production in Collision Cascades in Zircon  

SciTech Connect

Defect production in collision cascades in zircon has been examined by molecular dynamics simulations using a partial charge model combined with the Ziegler-Biersack-Littmark potential. U, Zr, Si and O recoils with energies ranging from 250 eV to 5 keV were simulated in the NVE ensemble. To obtain good statistics, 5-10 cascades in randomly chosen directions were simulated for each ion and energy. The damage consists of mainly Si and O Frenkel pairs, a smaller number of Zr Frenkel pairs, and Zr on Si antisite defects. Defect production, interstitial clustering, ion beam mixing and Si-O-Si polymerization increase with PKA mass and energy.

Devanathan, Ram; Corrales, Louis R.; Weber, William J.; Chartier, Alain; Meis, Constantin

2005-01-01

88

Comparison of binary collision approximation and molecular dynamics for displacement cascades in GaAs.  

SciTech Connect

The predictions of binary collision approximation (BCA) and molecular dynamics (MD) simulations of displacement cascades in GaAs are compared. There are three issues addressed in this work. The first is the optimal choice of the effective displacement threshold to use in the BCA calculations to obtain the best agreement with MD results. Second, the spatial correlations of point defects are compared. This is related to the level of clustering that occurs for different types of radiation. Finally, the size and structure of amorphous zones seen in the MD simulations is summarized. BCA simulations are not able to predict the formation of amorphous material.

Foiles, Stephen Martin

2011-10-01

89

Resonant Ion Pair Formation in Electron Collisions with Ground State Molecular Ions  

SciTech Connect

Resonant ion pair formation from collisions of electrons with ground state diatomic molecular ions has been observed and absolute cross sections measured. The cross section for HD{sup +} is characterized by an abrupt threshold at 1.9thinspthinspeV and 14 resolved peaks in the range of energies 0{le}E{le}14 eV . The dominant mechanism responsible for the structures appears to be resonant capture and stabilization, modified by two-channel quantum interference. Data on HF{sup +} show structure correlated with photoionization of HF and with dissociative recombination of electrons with this ion. {copyright} {ital 1999} {ital The American Physical Society }

Zong, W.; Dunn, G.H.; Djuric, N.; Greene, C.H.; Neau, A. [JILA and Department of Physics, University of Colorado and National Institute of Standards and Technology, Boulder, Colorado 80309-0440 (United States)] [JILA and Department of Physics, University of Colorado and National Institute of Standards and Technology, Boulder, Colorado 80309-0440 (United States); Zong, W.; Larsson, M.; Al-Khalili, A.; Neau, A.; Derkatch, A.M.; Vikor, L.; Shi, W.; Rosen, S. [Department of Molecular Physics, Stockholm University, Box 6730 S-113 85 Stockholm (Sweden)] [Department of Molecular Physics, Stockholm University, Box 6730 S-113 85 Stockholm (Sweden); Le Padellec, A. [Universite Catholique de Louvain, Institut de Physique, Chemin du cyclotron, 2-B1348 Louvain-la-Neuve (Belgium)] [Universite Catholique de Louvain, Institut de Physique, Chemin du cyclotron, 2-B1348 Louvain-la-Neuve (Belgium); Danared, H.; af Ugglas, M. [Manne Siegbahn Laboratory, S-104 05 Stockholm (Sweden)] [Manne Siegbahn Laboratory, S-104 05 Stockholm (Sweden)

1999-08-01

90

Theory of High-Energy Inelastic Collisions between Molecular Systems. Dissociation of H+2 on Collision with H2  

Microsoft Academic Search

Inelastic collisions between the hydrogen molecule ion (H+2) and the hydrogen molecule are investigated theoretically within the framework of the first Born approximation. The possibility that H+2 may be in an excited vibrational state before the collision takes place is given special consideration. Appropriate sums of the theoretical cross sections are identified with the experimental measurements of the cross section

James M. Peek; Thomas A. Green; W. H. Weihofen

1967-01-01

91

1982 bibliography of atomic and molecular processes  

SciTech Connect

This annotated bibliography includes papers on atomic and molecular processes published during 1982. Sources include scientific journals, conference proceedings, and books. Each entry is designated by one or more of the 114 categories of atomic and molecular processes used by the Controlled Fusion Atomic Data Center, Oak Ridge National Laboratory to classify data. Also indicated is whether the work was experimental or theoretical, what energy range was covered, what reactants were investigated, and the country of origin of the first author. Following the bibliographical listing, the entries are indexed according to the categories and according to reactants within each subcategory.

Barnett, C.F.; Crandall, D.H.; Gilbody, H.B.; Gregory, D.C.; Kirkpatrick, M.I.; McDaniel, E.W.; McKnight, R.H.; Meyer, F.W.; Morgan, T.J.; Phaneuf, R.A. (comps.)

1984-05-01

92

1985 bibliography of atomic and molecular processes  

SciTech Connect

This annotated bibliography includes papers on atomic and molecular processes published during 1985. Sources include scientific journals, conference proceedings, and books. Each entry is designated by one or more of the 114 categories of atomic and molecular processes used by the Controlled Fusion Atomic Data Center, Oak Ridge National Laboratory to classify data. Also indicated is whether the work was experimental or theoretical, what energy range was covered, what reactants were investigated, and the country of origin of the first author. Following the bibliographical listing, the entries are indexed according to the categories and according to reactants within each subcategory.

Barnett, C.F.; Gilbody, H.B.; Gregory, D.C.; Griffin, P.M.; Havener, C.C.; Howald, A.M.; Kirkpatrick, M.I.; McDaniel, E.W.; Meyer, F.W.; Morgan, T.J. (comps.)

1986-06-01

93

Multielectronic close-coupling treatment of atomic and molecular collisions: applications to H+-Li collisions in the keV energy range  

NASA Astrophysics Data System (ADS)

We present a new approach to describe electronic processes occurring in ion-atom and ion-molecule collisions at impact energies ranging from 50 eV.u?1 to 1 MeV.u?1. The treatment is based on the semiclassical approximation in which the time-dependent Schrödinger equation is solved non perturbatively, taking into account all the electrons of the collision system. This allows to describe exactly multielectronic processes and also, at the same footing, processes involving valence and inner shell electrons. We apply this model to describe electron transfer in a genuine three-electron system, H+-Li.

Labaigt, Gabriel; Dubois, Alain

2014-04-01

94

Charge Transfer Processes in Collisions of Si4+ Ions with He Atoms at Intermediate Energies  

NASA Astrophysics Data System (ADS)

Charge transfer in collisions of Si4+ ions with He atoms below 100 keV/u is studied by using a molecular orbital representation within both the semiclassical and quantal representations. Single transfer reaction Si4++He ?Si3++He+ has been studied by a number of theoretical investigations. In addition to the reaction (1), the first semiclassical MOCC calculations are performed for the double transfer channel Si4++HE?Si2++He2+ Nine molecular states that connect both with single and double electron transfer processes are considered in the present model. Electronic states and corresponding couplings are determined by the multireference single- and double- excitation configuration interaction method. The present cross sections tie well with the earlier calculations of Stancil et al., Phys. Rev. A 55, 1064 (1997) at lower energies, but show a rather different magnitude from those of Bacchus-Montabonel and Ceyzeriat, Phys. Rev. A 58, 1162 (1998). The present rate constant is found to be significantly different from the experimental finding of Fang and Kwong, Phys. Rev. A 59, 342 (1996) at 4,600 K, and hence does not support the experiment.

Suzuki, R.; Watanabe, A.; Sato, H.; Gu, J. P.; Hirsch, G.; Buenker, R. J.; Kimura, M.; Stancil, P. C.

95

Dynamic processes in heavy-ion collisions at intermediate energies  

Microsoft Academic Search

This thesis describes the study of the reaction dynamics in heavy-ion collisions of small nuclear systems at intermediate energies. For this, experiments were performed of 24Mg+27A1 at 45 and 95 AMeV. \\u000aThe experiments described in this thesis were performed at the GANIL accelerator facility in Caeri (France) using the Huygens detectors in conjunction with the ‘MUR’. The Huygens detectors consist

E. P. Prendergast

1999-01-01

96

Half-Collision Dynamics of Excited Metal Atom Quenching Processes  

NASA Astrophysics Data System (ADS)

Half-collision studies of the quenching of excited states of Zn by Xe and Cd by H_2, CH_4 and i-C_4H _{10} have been undertaken and have provided information concerning the role of alignment of the excited metal atom p-orbital as well as other dynamical information and details about the potential energy surfaces (curves) involved in the quenching process. Van der Waals complexes of a single metal atom with a rare gas atom or quencher molecule are prepared using a supersonic expansion of the metal vapor, carrier gas and quencher gas. To provide a more detailed understanding of van der Waals bonding involving closed shell metal atoms, spectroscopic investigations of the MgcdotNe, Zncdot Ar and ZncdotKr C ^1Pi_1 and X^1 Sigma_0^+ states as well as the ZncdotXe D^1Sigma _0^+ and X^1Sigma _0^+ states via laser induced fluorescence have also been performed. No fluorescence is observed from the Zn cdotXe C^1Pi_1 state which predissociates to Zn(4s4p^3 P_{rm J}) + Xe, permitting the C state to be characterized via a Zn(4s4p^3P_2) "action spectrum." Modeling of the deeply bound C state and the shallow D state using Morse potentials suggests that the long range tail of the C state curve crosses the inner wall of the D state curve. For the CdcdotCH _4 and CdcdotC _4H_{10} complexes, fluorescence is not observed from either the C or D states. However, Cd(5s5p^3P _{rm J}) action spectra are obtained for C and D state excitation. A Cd(5s5p ^3P_0) action spectrum is observed as a result of CdcdotCH _4 A and B state excitation. Rotational structure is observed in the vibrational bands and has permitted characterization of the Cdcdot CH_4 X and A states within a pseudodiatomic approximation and provided evidence for hindered rotation of the methane molecule. When CdcdotH_2 or CdcdotD_2 is excited to the red of the Cd(5s5p^1 P_1 >=ts 5s5s^1S_0) atomic transition, fluorescence is again absent while Cd(5s5p ^3P_{rm J}) action spectra are observed. The observation in the spectra of vibrational structure, which is superimposed on a continuum, suggests that two processes lead to predissociation. The vibrational structure observed is not consistent with an excited state bound solely by van der Waals forces. It is proposed that the vibrational motion in this state results from the coupling of symmetric stretch and bending vibrations in a C_{rm 2v} geometry.

Wallace, Ingvar Axel, II

97

Molecular sieving silica membrane fabrication process  

DOEpatents

A process is described for producing a molecular sieve silica membrane comprising depositing a hybrid organic-inorganic polymer comprising at least one organic constituent and at least one inorganic constituent on a porous substrate material and removing at least a portion of the at least one organic constituent of the hybrid organic-inorganic polymer, forming a porous film. 11 figs.

Raman, N.K.; Brinker, C.J.

1999-08-10

98

Fragmentation process of size-selected aluminum cluster anions in collision with a silicon surface  

Microsoft Academic Search

Dynamical processes involved in the collision of aluminum cluster anions, Al?N (4?N?25), with a silicon surface were investigated. Intact and fragment cluster anions, Al?n (n?N), were produced upon the collision. The surf02ace-tangent and surface-normal recoil velocity components of these product a0n0ions were determined. The tangential recoil velocities of the fragment cluster anions were considerably slow, ranging from 5% to 30%

Akira Terasaki; Tatsuya Tsukuda; Hisato Yasumatsu; Toshiki Sugai; Tamotsu Kondow

1996-01-01

99

Collision-induced dissociation processes of Nb/sup +//sub 4/ and Fe/sup +//sub 4/: Fission vs evaporation  

SciTech Connect

Collision-induced dissociation (CID) of Nb/sup +//sub 4/ and Fe/sup +//sub 4/ with Xe has been studied over an energy range of 0--20 eV with a new instrument designed to study cold cluster ions. The energy dependences of the cross sections are presented. It is found that the lowest energy pathway for Nb/sup +//sub 4/ CID is fragmentation into molecular ions, or fission. Analysis of this process yields D/sup 0/(Nb/sup +//sub 2/--Nb/sub 2/) = 4.3 +- 0.3 eV. Fe/sup +//sub 4/, on the other hand, fragments only by sequential loss of Fe. Analysis of the lowest energy process gives D/sup 0/(Fe/sup +//sub 3/--Fe) = 1.8 +- 0.2 eV. No evidence for molecular Fe/sub n/ fragments is observed.

Loh, S.K.; Lian, L.; Hales, D.A.; Armentrout, P.B.

1988-07-01

100

Electron Capture in Low Energy Collisions of N^2+ with Molecular Hydrogen.  

NASA Astrophysics Data System (ADS)

Ab initio CI adiabatic potentials and dipole moment matrix elements for the triatomic dication NH^2+2 in the collinear, asymmetric arrangement have been calculated. A diabatic description of the collision process is obtained by a unitary transformation in a representation that diagonalizes the dipole moment matrix.(H.-J. Werner and W. Meyer, J. Chem. Phys. 74), 5802 (1981). Neglecting H2 orientation and rotation, cross sections for the charge transfer process N^2+ + H_2(v=0) ? N^+ + H^+_2(v^') are determined with a close-coupled quantal method. Results will be compared to recent measurements.(Z. Fang and V. H. S. Kwong, private communication (1996).)

Stancil, P. C.; Zygelman, B.; Kirby, K.

1996-05-01

101

Computation of Collision-Induced Absorption by Simple Molecular Complexes, for Astrophysical Applications  

NASA Astrophysics Data System (ADS)

The interaction-induced absorption by collisional pairs of H{_2} molecules is an important opacity source in the atmospheres of various types of planets and cool stars, such as late stars, low-mass stars, brown dwarfs, cool white dwarf stars, the ambers of the smaller, burnt out main sequence stars, exoplanets, etc., and therefore of special astronomical interest The emission spectra of cool white dwarf stars differ significantly in the infrared from the expected blackbody spectra of their cores, which is largely due to absorption by collisional H{_2}-H{_2}, H{_2}-He, and H{_2}-H complexes in the stellar atmospheres. Using quantum-chemical methods we compute the atmospheric absorption from hundreds to thousands of kelvin. Laboratory measurements of interaction-induced absorption spectra by H{_2} pairs exist only at room temperature and below. We show that our results reproduce these measurements closely, so that our computational data permit reliable modeling of stellar atmosphere opacities even for the higher temperatures. First results for H_2-He complexes have already been applied to astrophysical models have shown great improvements in these models. L. Frommhold, Collision-Induced Absorption in Gases, Cambridge University Press, Cambridge, New York, 1993 and 2006 X. Li, K. L. C. Hunt, F. Wang, M. Abel, and L. Frommhold, Collision-Induced Infrared Absorption by Molecular Hydrogen Pairs at Thousands of Kelvin, Int. J. of Spect., vol. 2010, Article ID 371201, 11 pages, 2010. doi: 10.1155/2010/371201 M. Abel, L. Frommhold, X. Li, and K. L. C. Hunt, Collision-induced absorption by H{_2} pairs: From hundreds to thousands of Kelvin, J. Phys. Chem. A, 115, 6805-6812, 2011} L. Frommhold, M. Abel, F. Wang, M. Gustafsson, X. Li, and K. L. C. Hunt, "Infrared atmospheric emission and absorption by simple molecular complexes, from first principles", Mol. Phys. 108, 2265, 2010 M. Abel, L. Frommhold, X. Li, and K. L. C. Hunt, Infrared absorption by collisional H_2-He complexes at temperatures up to 9000 K and frequencies from 0 to 20000 cm-1, J. Chem. Phys., 136, 044319, 2012 D. Saumon, M. S. Marley, M. Abel, L. Frommhold, and R. S. Freedman, New H_2 collision-induced absorption and NH_3 opacity and the spectra of the coolest brown dwarfs, Astrophysical Journal, 2012

Abel, Martin; Frommhold, Lothar; Li, Xiaoping; Hunt, Katharine L. C.

2012-06-01

102

Application of molecular modeling to biological processing  

NASA Astrophysics Data System (ADS)

Detailed understanding of the molecular basis for biological processes is now available through computational modeling techniques. Advances in computational algorithms and technology allow applications to large biological macromolecules and permits the study of such problems as binding mechanisms, chemical reactivity, structural and conformational effects, and simulations of molecular motions. Recent crystallographic data provides access to detailed structural information that allows analysis and comparison of various computational techniques. Preliminary semiempirical studies on N-acetylneuraminic acid are presented as an example of computational studies on binding mechanisms. N-acetylneuraminic acid is a substituted carbohydrate, which is a recognition site for binding of proteins (i.e., cholera toxin). These calculations provide some insight into electronic effects on bin in a crystal complex and the effect of the molecular charge on hydrogen bonding the crystal complex.

Lowrey, Alfred H.; Famini, George R.; Wick, Charles

1993-07-01

103

Formation of giant molecular clouds in global spiral structures: The role of orbital dynamics and cloud-cloud collisions  

NASA Technical Reports Server (NTRS)

The different roles played by orbital dynamics and dissipative cloud-cloud collisions in the formation of giant molecular clouds (GMCs) in a global spiral structure are investigated. The interstellar medium (ISM) is simulated by a system of particles, representing clouds, which orbit in a spiral-perturbed, galactic gravitational field. The overall magnitude and width of the global cloud density distribution in spiral arms is very similar in the collisional and collisionless simulations. The results suggest that the assumed number density and size distribution of clouds and the details of individual cloud-cloud collisions have relatively little effect on these features. Dissipative cloud-cloud collisions play an important steadying role for the cloud system's global spiral structure. Dissipative cloud-cloud collisions also damp the relative velocity dispersion of clouds in massive associations and thereby aid in the effective assembling of GMC-like complexes.

Roberts, W. W., Jr.; Stewart, G. R.

1987-01-01

104

Plasma and collision processes of hypervelocity meteorite impact in the prehistory of life  

Microsoft Academic Search

A new concept is proposed, according to which the plasma and collision processes accompanying hypervelocity impacts of meteorites can contribute to the arising of the conditions on early Earth, which are necessary for the appearance of primary forms of living matter. It was shown that the processes necessary for the emergence of living matter could have started in a plasma

G. Managadze

2010-01-01

105

Molecular structure and orientation in processed polymers  

Microsoft Academic Search

We characterize the orientation distribution function (ODF) of molecular-scale structure in a set of solution- and melt-spun fibers of a liquid crystalline polyester in order to assess the role of processing in these fibers. The polyester is composed of 40% 1,4-hydroxybenzoic acid, 30% isophthalic acid, and 30% hydroquinone. Crystallinity is measured by both wide angle X-ray scattering (WAXS) and differential

D. C. Oda; G. C. Rutledge

1999-01-01

106

Molecular structure and orientation in processed polymers  

Microsoft Academic Search

We present a method for analyzing the molecular scale orientation and structure of processed polymers using wide angle X-ray scattering data (WAXS). The technique is applied to the analysis of solution-spun fibers of a liquid crystalline polyester comprised of 1,4-hydroxybenzoic acid, isophthalic acid, and hydroquinone. The orientation distribution function (ODF) of the non-crystalline component of the polyester is constructed using

D. C Oda; G. C Rutledge

1999-01-01

107

Atomic collisions with relativistic heavy ions. VI. Radiative processes  

NASA Astrophysics Data System (ADS)

Besides characteristic target and projectile x rays, x-ray continua and radiative-electron-capture photons are seen in collisions with relativistic heavy ions ranging in energy from 82 to 422 MeV/amu and in atomic number from Xe to U. The angular distribution, centroid energy, cross section, and line shape of the broad radiative-electron-capture lines are analyzed. The observed continua are due to primary- and secondary-electron bremsstrahlung. In the projectile frame, primary bremsstrahlung is the radiative scattering of incident target electrons from the projectile nucleus. The continuum cross sections and angular distributions are calculated, and are compared with experiment. Secondary-electron bremsstrahlung, due to the radiative scattering of ionized target electrons from other target nuclei, is target-thickness dependent, and the cross section increases roughly with the square of the target atomic number. The calculated primary-electron bremsstrahlung cross sections are lower than experiment.

Anholt, R.; Stoller, Ch.; Molitoris, J. D.; Spooner, D. W.; Morenzoni, E.; Andriamonje, S. A.; Meyerhof, W. E.; Bowman, H.; Xu, J.-S.; Xu, Z.-Z.; Rasmussen, J. O.; Hoffmann, D. H. H.

1986-04-01

108

Phase-index problem in the semiclassical description of molecular collisions  

NASA Astrophysics Data System (ADS)

Semiclassical approaches of molecular collisions as proposed by Miller and Marcus involve phase indices, related to focal and turning points along trajectories contributing to S matrix elements. The main purpose of the work is to revisit the previous approaches in the case of two degrees of freedom rotationally inelastic collisions so as to make phase indices explicitly appear from first principles. Classical S matrix theory (CSMT) and three semiclassical initial value representation (SCIVR) treatments, respectively involving simple, double, and triple integrals, are considered. The phase index is either the Maslov index of the classical configuration space Green function (CSMT and the first two SCIVR methods), or the Maslov index of the Van Vleck-Gutzwiller space-time propagator (third SCIVR method). In order to assess the validity of the four previous approaches, their predictions are compared with exact quantum scattering results for interaction potentials leading to strong quantum interferences. The Gaussian weighting procedure, recently introduced in the quasiclassical trajectory method, is used here for practical CSMT calculations. We finally discuss the standard application of CSMT in the light of the previous developments and results.

Bonnet, L.; Crespos, C.

2008-12-01

109

Charge Transfer in Collisions between Molecular Ions and Atomic Hydrogen/Deuterium^1  

NASA Astrophysics Data System (ADS)

Using the Oak Ridge National Laboratory ion--atom merged--beams apparatus, absolute cross sections of direct and dissociative charge transfer (CT) between H/D and different molecular ions (D2^+, CO^+, and O2^+) are measured from 20 eV/u to 2 keV/u collision energies. Toward high energy where the differences in Q-value of the reaction can be neglected and the rovibrational modes can be considered as frozen, the measured cross sections for the diatomic ions all converge to (7 ± 0.5) x 10-16 cm^2 at 2 keV/u and are consistent with a rovibrational frozen (H2^+, H) calculation (Physical Review A 84, 062716, 2011). Below one keV/u collision energy, the measured cross sections exhibit trends which are compared to previous merged-beams measurements of CT with H for atomic ions with a variety of electrons on the core. [4pt] ^1Research supported by the NASA Solar & Heliospheric Physics Program NNH07ZDA001N, the Office of Fusion Energy Sciences and the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences of the U.S. Department of Energy, the National Science Foundation through Grant No. PHY-106887.

Andrianarijaona, V. M.; Draganic, I. N.; Seely, D. G.; Havener, C. C.

2012-06-01

110

Theory of molecular rate processes in the presence of intense laser radiation  

NASA Technical Reports Server (NTRS)

The present paper deals with the influence of intense laser radiation on gas-phase molecular rate processes. Representations of the radiation field, the particle system, and the interaction involving these two entities are discussed from a general rather than abstract point of view. The theoretical methods applied are outlined, and the formalism employed is illustrated by application to a variety of specific processes. Quantum mechanical and semiclassical treatments of representative atom-atom and atom-diatom collision processes in the presence of a field are examined, and examples of bound-continuum processes and heterogeneous catalysis are discussed within the framework of both quantum-mechanical and semiclassical theories.

George, T. F.; Zimmerman, I. H.; Devries, P. L.; Yuan, J.-M.; Lam, K.-S.; Bellum, J. C.; Lee, H.-W.; Slutsky, M. S.; Lin, J.-T.

1979-01-01

111

Anion production in high-velocity cluster-atom collisions; the electron capture process revisited  

NASA Astrophysics Data System (ADS)

Anion production cross sections in collisions between Cn+, Cn carbon clusters (n ? 5) and helium atoms have been measured in high-velocity collisions (v = 2.25 and 2.6 au). This paper focuses on two of the three processes responsible for the Cn- production, namely double electron capture (DEC) onto Cn+ cations and single electron capture onto neutral (SECN) Cn. They were experimentally distinguished from a gaseous thickness dependence study. Dissociative and non-dissociative cross sections were measured and, in the case of DEC, all dissociative branching ratios measured; for these small systems, the C2- fragment was found magical. Data concerning electron capture in neutral-neutral collisions are extremely rare, especially at high velocity. Introduction of this measured process in the independent atom and electron (IAE) model allowed us to revisit and satisfactorily reproduce the so-far unexplained size evolution of single electron capture (SEC) cross sections in 2.6 au Cn+-He (n ? 10) collisions (Chabot et al 2006 J. Phys. B: At. Mol. Opt. Phys. 39 2593-603). IAE calculations for DEC cross sections and their comparison with experiment suggest a loss of electron in anionic Cn- species after the collision, competing with fragmentation and depending on the size.

Béroff, K.; Chabot, M.; Martinet, G.; Pino, T.; Bouneau, S.; Le Padellec, A.; Féraud, G.; Do Thi, N.; Calvo, F.; Bordas, C.; Lépine, F.

2013-01-01

112

Spectroscopic Studies of Atomic and Molecular Processes in the Edge Region of Magnetically Confined Fusion Plasmas  

NASA Astrophysics Data System (ADS)

Edge plasma studies are of vital importance for understanding plasma-wall interactions in magnetically confined fusion devices. These interactions determine the transport of neutrals into the plasma, and the properties of the plasma discharge. This presentation deals with optical spectroscopic studies of the plasma boundary, and their rôle in elucidating the prevailing physical conditions. Recorded spectra are of four types: emission spectra of ions and atoms, produced by electron impact excitation and by charge-exchange recombination, atomic spectra arising from electron impact-induced molecular dissociation and ionisation, visible spectra of molecular hydrogen and its isotopic combinations, and laser-induced fluorescence (LIF) spectra. The atomic spectra are strongly influenced by the confining magnetic field (Zeeman and Paschen-Back effects), which produces characteristic features useful for species identification, temperature determination by Doppler broadening, and studies of chemical and physical sputtering. Detailed analysis of the Zeeman components in both optical and LIF spectra shows that atomic hydrogen is produced in various velocity classes, some related to the relevant molecular Franck-Condon energies. The latter reflect the dominant electron collision processes responsible for production of atoms from molecules. This assignment has been verified by gas-puffing experiments through special test limiters. The higher-energy flanks of hydrogen line profiles probably also show the influence of charge-exchange reactions with molecular ions accelerated in the plasma sheath (`scrape-off layer') separating limiter surfaces from the edge plasma, in analogy to acceleration in the cathode-fall region of gas discharges. While electron collisions play a vital rôle in generating the spectra, ion collisions with excited atomic radiators act through re-distribution of population among the atomic fine-structure sublevels, and momentum transfer to the atomic nuclei via ion-induced dipole collisions with the bound electrons. The ions are thus important in randomising and equilibrating the velocity distribution of atomic products of molecular dissociation.

Hey, J. D.; Brezinsek, S.; Mertens, Ph.; Unterberg, B.

2006-12-01

113

Gas-Phase Molecular Dynamics: High Resolution Spectroscopy and Collision Dynamics of Transient Species  

SciTech Connect

This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. Chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry are investigated by high resolution spectroscopic tools. Production, reaction, and energy transfer processes are investigated by transient, double resonance, polarization and saturation spectroscopies, with an emphasis on technique development and connection with theory, as well as specific molecular properties.

Hall, G.E.

2011-05-31

114

Gas-Phase Molecular Dynamics: High Resolution Spectroscopy and Collision Dynamics of Transient Species  

SciTech Connect

This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. Chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry are investigated by high resolution spectroscopic tools. Production, reaction, and energy transfer processes are investigated by transient, double resonance, polarization and saturation spectroscopies, with an emphasis on technique development and connection with theory, as well as specific molecular properties.

Hall G. E.; Goncharov, V.

2012-05-29

115

Dynamics of transfer ionization process in p-He collisions at intermediate energies  

NASA Astrophysics Data System (ADS)

Using the reaction microscope technique, we have performed a kinematically complete experiment on transfer ionization in 50 to 100 keV proton-helium collisions. A careful inspect on the momentum balance provides insight into the dynamics of the transfer ionization process.

Guo, D. L.; Ma, X.; Zhang, S. F.; Zhu, X. L.; Feng, W. T.; Zhang, R. T.; Li, B.; Liu, H. P.; Yan, S.; Zhang, P.

2014-04-01

116

Studies of fluctuation processes in nuclear collisions. Progress report, March 1, 1995--March 31, 1996  

SciTech Connect

This progress report studies of fluctuation processes in nuclear collisions discusses the following topics: quantal effects on growth of instabilities in nuclear matter; collisional damping of giant resonances in a non-Markovian approach; and medium-modified interaction induced by fluctuations.

Ayik, S.

1996-03-01

117

Non-radiative inelastic processes in lithium-helium ion-atom collisions  

NASA Astrophysics Data System (ADS)

Aims: The aims are to estimate efficiencies of non-radiative inelastic processes in lithium-helium ion-atom collisions and to compare them to those for radiative processes. Methods: Non-radiative inelastic cross-sections and rate coefficients for different lithium-helium ion-atom collisions are estimated by means of the recently proposed branching probability current method, which is based on the accurate ab initio adiabatic Born-Oppenheimer potentials that have been recently calculated for the low-lying 1,3?+ and 1,3? states of the LiHe+ ion. Results: It is shown that at low temperatures the radiative depopulation in Li+ + He and Li + He+ collisions dominates over the non-radiative processes, while in Li+ + He(2s 3S) collisions the non-radiative processes dominate over the radiative association at temperatures above 3000 K, which can be expected to have some influence on depopulations of metastable He in high temperature astrophysical environments.

Belyaev, Andrey K.; Augustovi?ová, Lucie; Soldán, Pavel; Kraemer, Wolfgang P.

2014-05-01

118

Hard processes in p-A collisions with MC generator HARDPING 3.0  

NASA Astrophysics Data System (ADS)

Hard processes in p-A collisions at high energies with MC (Monte Carlo) generator HARDPING (HARD Probe IN-teraction Generator) are discussed. Such effects as energy loss and multiple rescattering initial and produced hadrons and their constituents are implemented into the HARDPING. It provides a reasonably good description of hadron production in p-A collisions at 400 GeV (Cronin effect). Predictions by the HARPING 3.0 for lepton pairs production in p-A at proton beam energy 120 GeV ( s=15.08 GeV) at Fermilab Tevatron Booster and s=5.02 TeV at CERN LHC are presented.

Berdnikov, Ya. A.; Ivanov, A. E.; Kim, V. T.; Murzin, V. A.; Suetin, D. P.

2013-12-01

119

Non-adiabatic interactions in charge transfer collisions  

NASA Astrophysics Data System (ADS)

An analysis of the charge transfer mechanism in the collision of multiply charged ions with molecular and biomolecular targets is performed, considering the non-adiabatic interactions between the molecular states involved. Collisions of doubly charged C 2+ ions on small molecular targets, CO and OH, have been investigated, together with the analysis of charge transfer between C 4+ ions on uracil and halouracil biomolecular targets. The process is studied theoretically by means of ab-initio molecular calculations followed by a semi-classical treatment of the collision dynamics. The influence of rotational couplings is discussed with regard to the collision energy. Strong anisotropic and vibration effects are pointed out.

Bacchus-Montabonel, Marie-Christine; Rozsályi, Emese; Bene, Erika; Halász, Gábor J.; Vibók, Ágnes

2013-09-01

120

Single-electron capture collisions of ground and metastable Ne2+ ions with molecular gases  

NASA Astrophysics Data System (ADS)

Using the translational energy-gain spectroscopy technique, we have measured the energy-gain spectra and absolute total cross sections for single-electron capture in collisions of Ne2+ with N2, CO2 and H2O at laboratory impact energies between 50 and 400 eV and 0° scattering angles. In all the collision systems studied here, reaction channels have been observed which indicate the presence of the long-lived metastable states of (2s2 2p4?1D and 1S) in the Ne2+ incident beam. These measurements also indicate that capture from the metastable states into excited states of the projectile product ions is the most important inelastic process. Contributions from capture accompanied by the excitation and ionization of the target product are also detected. In addition, the energy dependence of the total single-electron capture cross sections is studied and found to slowly increase with increasing impact energy. The present data are compared with the theoretical calculations of the classical over the barrier, extended classical over the barrier and Landau-Zener models.

Hasan, A.; Abu-Haija, O.; Harris, J.; Elkafrawy, T.; Kayani, A.; Kamber, E. Y.

2013-09-01

121

Nuclear collision processes around the Bragg peak in proton therapy  

Microsoft Academic Search

In the physical processes of proton interaction in bio-materials, most of the proton energy is transferred to electrons. Ionization\\u000a and excitation occur most frequently around the Bragg peak region, where nuclear reactions also exist. In this study, we investigated\\u000a the processes of energy deposition by considering interactions including the nuclear reactions between protons and water molecules\\u000a by a Monte Carlo

Yuka Matsuzaki; Hiroyuki Date; Kenneth Lee Sutherland; Yoshiaki Kiyanagi

2010-01-01

122

Optimizing rotary processes in synthetic molecular motors  

PubMed Central

We deal with the issue of quantifying and optimizing the rotation dynamics of synthetic molecular motors. For this purpose, the continuous four-stage rotation behavior of a typical light-activated molecular motor was measured in detail. All reaction constants were determined empirically. Next, we developed a Markov model that describes the full motor dynamics mathematically. We derived expressions for a set of characteristic quantities, i.e., the average rate of quarter rotations or “velocity,” V, the spread in the average number of quarter rotations, D, and the dimensionless Péclet number, Pe = V/D. Furthermore, we determined the rate of full, four-step rotations (?eff), from which we derived another dimensionless quantity, the “rotational excess,” r.e. This quantity, defined as the relative difference between total forward (?+) and backward (??) full rotations, is a good measure of the unidirectionality of the rotation process. Our model provides a pragmatic tool to optimize motor performance. We demonstrate this by calculating V, D, Pe, ?eff, and r.e. for different rates of thermal versus photochemical energy input. We find that for a given light intensity, an optimal temperature range exists in which the motor exhibits excellent efficiency and unidirectional behavior, above or below which motor performance decreases.

Geertsema, Edzard M.; van der Molen, Sense Jan; Martens, Marco; Feringa, Ben L.

2009-01-01

123

Molecular dynamics simulations for CO2 spectra. II. The far infrared collision-induced absorption band  

NASA Astrophysics Data System (ADS)

Classical molecular dynamics simulations have been carried out for gaseous CO2 starting from various anisotropic intermolecular potential energy surfaces. Through calculations for a large number of molecules treated as rigid rotors, the time evolution of the interaction-induced electric dipole vector is obtained and the Laplace transform of its autocorrelation function gives the collision-induced absorption rototranslational spectrum. The results are successfully compared with those of previous similar calculations before studies of the influences of the intermolecular potential and induced-dipole components are made. The calculated spectra show a significant sensitivity to anisotropic forces consistently with previous analyses limited to the spectral moments. The present results also demonstrate the importance of vibrational and back-induction contributions to the induced dipole. Comparisons between measured far infrared (0-250 cm-1) spectra at different temperatures and results calculated without the use of any adjustable parameter are made. When the best and more complete input data are used, the quality of our predictions is similar to that obtained by Gruszka et al. [Mol. Phys. 93, 1007 (1998)] after the introduction of ad hoc short-range overlap contributions. Our results thus largely obviate the need for such contributions the magnitudes of which remain questioned. Nevertheless, problems remain since, whereas good agreements with measurements are obtained above 50 cm-1, the calculations significantly underestimate the absorption below, a problem which is discussed in terms of various possible error sources.

Hartmann, J.-M.; Boulet, C.; Jacquemart, D.

2011-03-01

124

Molecular dynamics simulations for CO2 spectra. II. The far infrared collision-induced absorption band.  

PubMed

Classical molecular dynamics simulations have been carried out for gaseous CO(2) starting from various anisotropic intermolecular potential energy surfaces. Through calculations for a large number of molecules treated as rigid rotors, the time evolution of the interaction-induced electric dipole vector is obtained and the Laplace transform of its autocorrelation function gives the collision-induced absorption rototranslational spectrum. The results are successfully compared with those of previous similar calculations before studies of the influences of the intermolecular potential and induced-dipole components are made. The calculated spectra show a significant sensitivity to anisotropic forces consistently with previous analyses limited to the spectral moments. The present results also demonstrate the importance of vibrational and back-induction contributions to the induced dipole. Comparisons between measured far infrared (0-250 cm(-1)) spectra at different temperatures and results calculated without the use of any adjustable parameter are made. When the best and more complete input data are used, the quality of our predictions is similar to that obtained by Gruszka et al. [Mol. Phys. 93, 1007 (1998)] after the introduction of ad hoc short-range overlap contributions. Our results thus largely obviate the need for such contributions the magnitudes of which remain questioned. Nevertheless, problems remain since, whereas good agreements with measurements are obtained above 50 cm(-1), the calculations significantly underestimate the absorption below, a problem which is discussed in terms of various possible error sources. PMID:21384978

Hartmann, J-M; Boulet, C; Jacquemart, D

2011-03-01

125

Comparison of molecular dynamics and binary collision approximation simulations for atom displacement analysis  

NASA Astrophysics Data System (ADS)

Molecular dynamics (MD) and binary collision approximation (BCA) computer simulations are employed to study surface damage by single ion impacts. The predictions of BCA and MD simulations of displacement cascades in amorphous and crystalline silicon and BCC tungsten by 1 keV Ar+ ion bombardment are compared. Single ion impacts are studied at angles of 50°, 60° and 80° from normal incidence. Four parameters for BCA simulations have been optimized to obtain the best agreement of the results with MD. For the conditions reported here, BCA agrees with MD simulation results at displacements larger than 5 Å for amorphous Si, whereas at small displacements a difference between BCA and MD arises due to a material flow component observed in MD simulations but absent from a regular BCA approach due to the algorithm limitations. MD and BCA simulation results for crystalline W are found to be in a good agreement even at small displacements, while in crystalline Si there is some difference due to displacements in amorphous pockets.

Bukonte, L.; Djurabekova, F.; Samela, J.; Nordlund, K.; Norris, S. A.; Aziz, M. J.

2013-02-01

126

Charge Transfer Process During Collision of Riming Graupel Pellet with Small Ice Crystals within a Thundercloud  

NASA Technical Reports Server (NTRS)

A charge transfer process during the collision of a riming graupel pellet and an ice-crystal at low temperature is proposed. During riming, the surface structure of graupel deviates from perfect crystalline structure. A concept of quasi-solid layer (QSL) formation on the surface is introduced. This QSL contains defects formed during riming. In absence of impurities, positively charged X-defect abundance is considered in the outer layer. These defects are assumed to be the charge carriers during the charge transfer process. Some part of the QSL is stripped off by the colliding ice crystals, which thereby gain some positive charge, leaving the graupel pellet negatively charged. With the proposed model, fC to pC of charge transfer is observed per collision. A transition temperature between -10 C to -15 C is also noted beyond which the QSL concept does not hold. This transition temperature is dependent on the bulk liquid water content of the cloud.

Datta, Saswati; De, Utpal K.; Goswami, K.; Jones, Linwood

1999-01-01

127

PROGRESS IN THE APPLICATION OF CLASSICAL S-MATRIX THEORY TO INELASTIC COLLISION PROCESSES  

SciTech Connect

Methods are described which effectively solve two of the technical difficulties associated with applying classical S?matrix theory to inelastic/reactive scattering. Specifically, it is shown that rather standard numerical methods can be used to solve the ’’root search’’ problem (i.e., the nonlinear boundary value problem necessary to impose semiclassical quantum conditions at the beginning and the end of the classical trajectories) and also how complex classical trajectories, which are necessary to describe classically forbidden (i.e., tunneling) processes, can be computed in a numerically stable way. Application is made to vibrational relaxation of H{sub 2} by collision with He (within the helicity conserving approximation). The only remaining problem with regard to applying classical S?matrix theory to complex collision processes has to do with the availability of multidimensional uniform asymptotic formulas for interpolating the ’’primitive’’ semiclassical expressions between their various regions of validity.

McCurdy, C.William; Miller, William H.

1980-05-01

128

Spin-Flip and Elastic Processes in Slow Collisions of Mesic Atoms  

Microsoft Academic Search

The reduced adiabatic hyperspherical (RAHS) basis suggested previously is used for the calculation of elastic and spin-flip\\u000a cross sections in the processes (a?)\\u000a F\\u000a + a ? (a?)\\u000a F? + a, a = (p, \\u000a d, \\u000a t), for collision energies 10?3 ? ? ? 102 eV. The rapid convergence of the method is demonstrated. A comparison of the obtained results with

D. I. Abramov; V. V. Gusev; L. I. Ponomarev

2001-01-01

129

Electron-ion collisions. [Basic physics of inelastic processes of excitation, ionization, and recombination  

SciTech Connect

This discussion concentrates on basic physics aspects of inelastic processes of excitation, ionization, and recombination that occur during electron-ion collisions. Except for cases of illustration along isoelectronic sequences, only multicharged (at least +2) ions will be specifically discussed with some emphasis of unique physics aspects associated with ionic charge. The material presented will be discussed from a primarily experimental viewpoint with most attention to electron-ion interacting beams experiments.

Crandall, D.H.

1982-01-01

130

Effects of collision processes between laser-ablated fragments and ambient gases  

Microsoft Academic Search

Time and space resolved photo-emission measurements of Cu and CuO have been done to understand collisions and oxidation processes during laser ablation of YBaCuO superconducting targets under various pressures or oxygen and argon. It has been reported that the oxygen atmosphere is necessary to compensate the oxygen deficiency during the flight of laser ablated fragments for obtaining YBaCuO superconducting thin

Kohzoh Masuda; Osamu Eryu; Kenji Yamaoka; Kouichi Murakami

1993-01-01

131

LETTER TO THE EDITOR: Post-collision interaction in double Auger processes  

Microsoft Academic Search

A post-collision interaction (PCI) in the inner-shell photoionization followed by a double Auger decay is considered. The general analytical expressions for an amplitude and a cross section of the process under consideration are obtained. These formulae allow for the PCI distortion and are valid for a wide range of velocities of the photoelectron except a near-threshold region. The possibility of

S. A. Sheinerman

1998-01-01

132

Angle and energy resolved studies of the collision-induced dissociation of polyatomic molecular ions: Baseline studies of CH[sub 4][sup +] and C[sub 3]H[sub 8][sup +  

SciTech Connect

A deeper fundamental understanding of the collision process and subsequent dissociation for polyatomic ions is essential to optimize future studies of collision induced dissociation (CID). An instrument was developed with an unique system of electrostatic lenses that allows CID to be observed in the energy range from a few tenths of an eV to several thousand eV. The instrument permits daughter ion distributions to be mapped in angle and energy. The CID spectra of methane and propane were investigated at keV energies using a commercial tandem mass spectrometer. The relative abundances of the daughter ions, the energy deposition, and kinetic energy release were determined as a function of collision gas was also investigated and interpreted in terms of center of mass (CM) collision energy and the Massey adiabatic criterion most probable energy deposition. The daughter ion abundance, kinetic energy transfer, and kinetic energy release were observed as a function of collision gas, CM collision energy and attenuation of the primary ion beam. A simple model is proposed to describe the effect of multiple collisions on the CID process. Propane molecular ion CID was investigated with the new instrument at laboratory energies ranging from 18 eV to 1 keV and CM collision energies ranging from 1.5 eV to 450 eV. The daughter ion distributions obtained from these experiments show that there is no change in mechanism between CID observed in quadrupole instruments at eV energies and CID observed in sector instruments at keV lab energies. The energy and angular distribution of CID daughter ions is close to the CM with large CM scattering angles at low energy and shifts to near the elastic scattering circle and small CM scattering angles at high lab energies.

Anderson, S.G.

1992-01-01

133

A wind tunnel study of the effects of collision processes on the shape and oscillation for moderate-size raindrops  

NASA Astrophysics Data System (ADS)

Drop–drop collision experiments were carried out at the Mainz vertical wind tunnel. Water drops of 2.5 mm diameter were freely floated at their terminal velocities in a vertical air stream and collided with 0.5 mm diameter droplets. The collisions were recorded with a high speed digital video camera at a frame rate of 1000 per second. Altogether 116 collision events were observed, 75 of which ended with coalescence, and the rest with filament type breakup. The coalescence efficiency and its dependence on the Weber number and on the eccentricity of the colliding drops showed good agreement with earlier numerical studies. Thirty-six recorded collisions were further analyzed in order to characterize the oscillation behavior of large drops after a collisional excitation. Besides the introduction of the experimental method for studying the raindrop collisions, the study primarily focused on the characterization of the average value and the amplitude of the axis ratio variation, the active oscillation modes and their frequencies, and the decay of the oscillations excited by the collision. In spite of the fact that the amplitude of the axis ratio variation increased up to 4 to 6 times of its value before collision – depending on whether the collision ended with coalescence or breakup –, the average axis ratios increased by less than 1%. Since the sizes of largest drops after collision remained practically unchanged during the collision process, the frequencies of the active fundamental (n = 2) oscillation modes of the drops did not change significantly either. Instantaneously after collision the transverse oscillation mode and the whole body rotation dominated, while at a later instant the oblate–prolate mode determined again the drop shape alteration. It was further found that the damping of the oscillation after collision can be adequately described by the viscous decay of a liquid spherical drop.

Szakáll, Miklós; Kessler, Simon; Diehl, Karoline; Mitra, Subir K.; Borrmann, Stephan

2014-06-01

134

Electron Capture and Loss Processes in Forward Electron Emission in Fast Ion-atom Collisions  

NASA Astrophysics Data System (ADS)

Forward-going continuum electron emission has been investigated in 0.4-2 MeV/u O7+ and O8++He collisions. The one and two-electron processes of electron capture to the continuum (ECC), electron loss to the continuum (ELC), and transfer ionization (TI) have been separated by detecting cusp electrons in coincidence with the outgoing charge states of the projectile ions. The data are compared to earlier results of Zhu et al. for the O7++Ar collision system [1]. The relative importance of the different contributions to forward electron emission and the role of the electron-electron interaction are discussed. The relationships of these results to recent studies of radiative-electron-capture-to-the continuum (RECC) are discussed.

Tóth, G.; Závodszky, P. A.; Tanis, J. A.

2009-03-01

135

Electromagnetic processes in nucleus-nucleus collisions relating to space radiation research  

NASA Technical Reports Server (NTRS)

Most of the papers within this report deal with electromagnetic processes in nucleus-nucleus collisions which are of concern in the space radiation program. In particular, the removal of one and two nucleons via both electromagnetic and strong interaction processes has been extensively investigated. The theory of relativistic Coulomb fission has also been developed. Several papers on quark models also appear. Finally, note that the theoretical methods developed in this work have been directly applied to the task of radiation protection of astronauts. This has been done by parameterizing the theoretical formalism in such a fashion that it can be used in cosmic ray transport codes.

Norbury, John W.

1992-01-01

136

Molecular Processing of Polymers with Cyclodextrins  

NASA Astrophysics Data System (ADS)

We summarize our recent studies employing the cyclic starch derivatives called cyclodextrins (CDs) to both nanostructure and functionalize polymers. Two important structural characteristics of CDs are taken advantage of to achieve these goals. First the ability of CDs to form noncovalent inclusion complexes (ICs) with a variety of guest molecules, including many polymers, by threading and inclusion into their relatively hydrophobic interior cavities, which are roughly cylindrical with diameters of ˜ 0.5 - 1.0 nm. ?-, ?-, and ?-CD contain six, seven, and eight ?-1,4-linked glucose units, respectively. Warm water washing of polymer-CD-ICs containing polymer guests insoluble in water or treatment with amylase enzymes serves to remove the host CDs and results in the coalescence of the guest polymers into solid samples. When guest polymers are coalesced from the CD-ICs by removing their host CDs, they are observed to solidify with structures, morphologies, and even conformations that are distinct from bulk samples made from their solutions and melts. Molecularly mixed, intimate blends of two or more polymers that are normally immiscible can be obtained from their common CD-ICs, and the phase segregation of incompatible blocks can be controlled (suppressed or increased) in CD-IC coalesced block copolymers. In addition, additives may be more effectively delivered to polymers in the form of their crystalline CD-ICs or soluble CD-rotaxanes. Secondly, the many hydroxyl groups attached to the exterior rims of CDs, in addition to conferring water solubility, provide an opportunity to covalently bond them to polymers either during their syntheses or via postpolymerization reactions. Polymers containing CDs in their backbones or attached to their side chains are observed to more readily accept and retain additives, such as dyes and fragrances. Processing with CDs can serve to both nanostructure and functionalize polymers, leading to greater understanding of their behaviors and to new properties and applications.

Tonelli, Alan E.

137

Ion-Neutral Collisions in the Interstellar Medium: Wave Damping and Elimination of Collisionless Processes  

NASA Astrophysics Data System (ADS)

Most phases of the interstellar medium contain neutral atoms in addition to ions and electrons. This introduces differences in plasma physics processes in those media relative to the solar corona and the solar wind at a heliocentric distance of 1 astronomical unit. In this paper, we consider two well-diagnosed, partially-ionized interstellar plasmas. The first is the Warm Ionized Medium (WIM) which is probably the most extensive phase in terms of volume. The second is the gas of the Local Clouds of the Very Local Interstellar Medium (VLISM). Ion-neutral interactions seem to be important in both media. In the WIM, ion-neutral collisions are relatively rare, but sufficiently frequent to damp magnetohydrodynamic (MHD) waves (as well as propagating MHD eddies) within less than a parsec of the site of generation. This result raises interesting questions about the sources of turbulence in the WIM. In the case of the VLISM, the ion-neutral collision frequency is higher than that in the WIM, because the hydrogen is partially neutral rather than fully ionized. We present results showing that prominent features of coronal and solar wind turbulence seem to be absent in VLISM turbulence. For example, ion temperature does not depend on ion mass. This difference may be due to ion-neutral collisions, which distribute power from more effectively heated massive ions such as iron to other ion species and neutral atoms.

Spangler, Steven R.; Savage, Allison H.; Redfield, Seth

2011-09-01

138

Ion-Neutral Collisions in the Interstellar Medium: Wave Damping and Elimination of Collisionless Processes  

SciTech Connect

Most phases of the interstellar medium contain neutral atoms in addition to ions and electrons. This introduces differences in plasma physics processes in those media relative to the solar corona and the solar wind at a heliocentric distance of 1 astronomical unit. In this paper, we consider two well-diagnosed, partially-ionized interstellar plasmas. The first is the Warm Ionized Medium (WIM) which is probably the most extensive phase in terms of volume. The second is the gas of the Local Clouds of the Very Local Interstellar Medium (VLISM). Ion-neutral interactions seem to be important in both media. In the WIM, ion-neutral collisions are relatively rare, but sufficiently frequent to damp magnetohydrodynamic (MHD) waves (as well as propagating MHD eddies) within less than a parsec of the site of generation. This result raises interesting questions about the sources of turbulence in the WIM. In the case of the VLISM, the ion-neutral collision frequency is higher than that in the WIM, because the hydrogen is partially neutral rather than fully ionized. We present results showing that prominent features of coronal and solar wind turbulence seem to be absent in VLISM turbulence. For example, ion temperature does not depend on ion mass. This difference may be due to ion-neutral collisions, which distribute power from more effectively heated massive ions such as iron to other ion species and neutral atoms.

Spangler, Steven R.; Savage, Allison H. [Department of Physics and Astronomy, University of Iowa (United States); Redfield, Seth [Department of Astronomy and Van Vleck Observatory, Wesleyan University (United States)

2011-09-21

139

A model for energy transfer in inelastic molecular collisions applicable at steady state or non-steady state and for an arbitrary distribution of collision energies  

Microsoft Academic Search

A new model for energy exchange between translational and internal degrees of freedom in atom-molecule collisions has been\\u000a developed. It is suitable for both steady state conditions (e.g., a large number of collisions with thermal kinetic energies)\\u000a and non-steady state conditions with an arbitrary distribution of collision energies (e.g., single high-energy collisions).\\u000a In particular, it does not require that the

Wolfgang R. Plass; R. Graham Cooks

2003-01-01

140

H(D) ? D(H) + Cu(111) collision system: molecular dynamics study of surface temperature effects.  

PubMed

All the channels of the reaction dynamics of gas-phase H (or D) atoms with D (or H) atoms adsorbed onto a Cu(111) surface have been studied by quasiclassical constant energy molecular dynamics simulations. The surface is flexible and is prepared at different temperature values, such as 30 K, 94 K, and 160 K. The adsorbates were distributed randomly on the surface to create 0.18 ML, 0.28 ML, and 0.50 ML of coverages. The multi-layer slab is mimicked by a many-body embedded-atom potential energy function. The slab atoms can move according to the exerted external forces. Treating the slab atoms non-rigid has an important effect on the dynamics of the projectile atom and adsorbates. Significant energy transfer from the projectile atom to the surface lattice atoms takes place especially during the first impact that modifies significantly the details of the dynamics of the collisions. Effects of the different temperatures of the slab are investigated in this study. Interaction between the surface atoms and the adsorbates is modeled by a modified London-Eyring-Polanyi-Sato (LEPS) function. The LEPS parameters are determined by using the total energy values which were calculated by a density functional theory and a generalized gradient approximation for an exchange-correlation energy for many different orientations, and locations of one- and two-hydrogen atoms on the Cu(111) surface. The rms value of the fitting procedure is about 0.16 eV. Many different channels of the processes on the surface have been examined, such as inelastic reflection of the incident hydrogen, subsurface penetration of the incident projectile and adsorbates, sticking of the incident atom on the surface. In addition, hot-atom and Eley-Rideal direct processes are investigated. The hot-atom process is found to be more significant than the Eley-Rideal process. Furthermore, the rate of subsurface penetration is larger than the sticking rate on the surface. In addition, these results are compared and analyzed as a function of the surface temperatures. PMID:21528959

Vurdu, Can D; Güvenç, Ziya B

2011-04-28

141

H(D) -> D(H) + Cu(111) collision system: Molecular dynamics study of surface temperature effects  

PubMed Central

All the channels of the reaction dynamics of gas-phase H (or D) atoms with D (or H) atoms adsorbed onto a Cu(111) surface have been studied by quasiclassical constant energy molecular dynamics simulations. The surface is flexible and is prepared at different temperature values, such as 30 K, 94 K, and 160 K. The adsorbates were distributed randomly on the surface to create 0.18 ML, 0.28 ML, and 0.50 ML of coverages. The multi-layer slab is mimicked by a many-body embedded-atom potential energy function. The slab atoms can move according to the exerted external forces. Treating the slab atoms non-rigid has an important effect on the dynamics of the projectile atom and adsorbates. Significant energy transfer from the projectile atom to the surface lattice atoms takes place especially during the first impact that modifies significantly the details of the dynamics of the collisions. Effects of the different temperatures of the slab are investigated in this study. Interaction between the surface atoms and the adsorbates is modeled by a modified London–Eyring–Polanyi–Sato (LEPS) function. The LEPS parameters are determined by using the total energy values which were calculated by a density functional theory and a generalized gradient approximation for an exchange-correlation energy for many different orientations, and locations of one- and two-hydrogen atoms on the Cu(111) surface. The rms value of the fitting procedure is about 0.16 eV. Many different channels of the processes on the surface have been examined, such as inelastic reflection of the incident hydrogen, subsurface penetration of the incident projectile and adsorbates, sticking of the incident atom on the surface. In addition, hot-atom and Eley-Rideal direct processes are investigated. The hot-atom process is found to be more significant than the Eley-Rideal process. Furthermore, the rate of subsurface penetration is larger than the sticking rate on the surface. In addition, these results are compared and analyzed as a function of the surface temperatures.

Vurdu, Can D.; Guvenc, Ziya B.

2011-01-01

142

Hydrodynamical processes in the Draco molecular cloud  

Microsoft Academic Search

IRAS 100 micron images of the Draco cloud show several cloud components with cometary plumes of material extending 7-10 pc. The brightest plumes are very uniform in thickness but often terminate in large amorphous regions. The structure is consistent with low Reynolds number hydrodynamics and is suggestive of a molecular cloud shedding material in a plume as it falls onto

Sten F. Odenwald; Lee J. Rickard

1987-01-01

143

Continental Collision, Oceanic Subduction and Related Geodynamical Processes: a Numerical Modeling Perspective  

NASA Astrophysics Data System (ADS)

Collisional and subduction zones are sites on the Earth surface where two continents collide or an oceanic plate descends into the mantle, respectively. Aside these gross scale phenomena, a wide variety of other small scale geological processes take place at the same time. The study of these processes is crucial for the understanding of the subduction/collision history and for the interpretation of geophysical data that, in turn, give informations about the present day structure of these areas. In the recent years, coupled petrological-thermomechanical numerical models have been used to study processes occurring at collision/subduction settings. We use I2VIS code with realistic visco-plastic rheologies (Gerya and Yuen, 2003) to model subduction zones characterized by an early oceanic subduction followed by continental collision. Collision between two continents includes mountain chains building, continental crust recycling in the mantle and exhumation of HP-UHP metamorphic rocks. In case of plate decoupling, asthenospheric mantle wedges between the continents triggering the retreating and delamination of the converging continental plate. In order to investigate hydration and subsequent dehydration of the slab, we also performed 2D numerical models of a spontaneously bending oceanic plate using I2ELVIS code that account for visco-elasto-plastic rheologies (Gerya and Yuen, 2007). At the outer rise, bending-related slab faulting occurs and provides a pathway for water percolation in the slab. Faults generally deep trenchward, but antithetic faults are also common. As the slab subducts, serpentinized faults acquire a sub-vertical position; on the other hand, pressure and temperature increase so that hydrous phases become unstable and elevated pore fluid pressure build up allowing to brittle deformation at big depths. Results are consistent with intermediate-depth earthquakes distribution and confirm the now well accepted theory that dehydration of the slab as the main trigger mechanism for earthquakes with deep hypocenters. We also found that the anisotropy measured above subduction zones seems to be related to the spatial distribution of the serpentinized faults in the slab.

Faccenda, M.; Gerya, T.; Burlini, L.; Chakraborty, S.

2008-05-01

144

Molecular theory of K-vacancy production in heavy-ion-atom collisions at small impact parameters  

NASA Astrophysics Data System (ADS)

1 s? vacancy production is calculated by approximating the 1 s? molecular wave function with an atomic 1 s wave function for a charge Z(R) centered at a distance h(R) from the heavier nucleus. h(R) and Z(R) are determined by minimizing the 1 s? electronic energy. Previous calculations with the atomic semi-classical approximation ( h=0, Z(R)= Z 2, the target atomic number) showed that the probability of making Cu K vacancies in 0.5- to 2-MeV/a.m.u. H+, D+, and He++Cu collisions can be written as P(?)=A(1+ Bcos ?), where ? is the scattering angle and A and B are constants for ??10°. Although the recoil and dipole excitation contributions to P(?) (which interfere destructively in the atomic theory) are independently smaller in the molecular calculations, similar B values are obtained.

Anholt, R.

1980-09-01

145

Time-of-Flight Experiments in Molecular Motion and Electron-Atom Collision Kinematics  

ERIC Educational Resources Information Center

Describes a set of experiments for an undergraduate laboratory which demonstrates the relationship between velocity, mass, and temperature in a gas. The experimental method involves time-of-flight measurements on atoms excited to metastable states by electron impact. Effects resulting from recoil in the electron-atom collision can also be…

Donnelly, Denis P.; And Others

1971-01-01

146

Atomic and molecular sciences  

SciTech Connect

The theoretical atomic and molecular physics program at Rice University addresses basic questions about the collision dynamics of electrons, atoms, ions and molecules, emphasizing processes related to possible new energy technologies and other applications. The program focuses on inelastic collision processes that are important in understanding energy and ionization balance in disturbed gases and plasmas. Emphasis is placed on systems and processes where some experimental information is available or where theoretical results may be expected to stimulate new measurements. Examples of current projects include: excitation and charge-transfer processes; orientation and alignment of excited states following collisions; Rydberg atom collisions with atoms and molecules; Penning ionization and ion-pair formation in atom-atom collisions; electron-impact ionization in dense, high-temperature plasmas; electron-molecule collisions; and related topics.

Lane, N.F.

1989-12-11

147

Sub-lithospheric small scale convection - a process for continental collision magmatism  

NASA Astrophysics Data System (ADS)

We have studied the role of sub-lithospheric small scale convection in the generation of collision zone magmatism, using combined geodynamic-petrological models. We compare the results with the collisional magmatism of the Turkish-Iranian plateau, where a number of randomly (in both space and time) distributed volcanic centres on has been produced by the active Arabia-Eurasia collision since initial plate collision at ~27-35 Ma. These volcanic rocks have a highly variable geochemical signature, but commonly point to a lithospheric mantle or asthenospheric source. Major and trace element characteristics span the range from OIB-like, to calc-alkali, shoshonitic and even ultrapotassic. We suggest these spatially, temporally and chemically diverse patterns of volcanism are caused by sub-lithospheric small scale convection (SSC), manifested as small (50 to 300 km) convection cells at the lithosphere-asthenosphere boundary and dripping of the lithospheric mantle into the asthenosphere. SSC is activated by the increased amount of water in the lithospheric and asthenospheric mantle and its rheological weakening effect. The increase in water content is caused by the subduction prior to the collision and/or continental subduction during collision. The mantle convection code CitCom, together with a parameterized melting model, is used to model the SSC process. We relate the water content to the mantle solidus and viscosity, and the amount of depletion to the viscosity and buoyancy of the mantle material. We measure the amount of magmatism taking place by assuming direct and instantaneous percolation of mantle melts to the surface. We mimic the dislocation creep mechanism with a diffusion creep mechanism using low activation energy--either one is needed for the SSC to take place under realistic conditions. Results show that SSC is able to produce small degrees (0-2 %) of melting of the mantle through dripping lithosphere, decompression melting, erosion of the overlying lithosphere, and advection of hot material into contact with the cold lithosphere. The degree of melting might be strongly controlled by the lithosphere thickness and the extent of its hydration during the past Tethyan subduction. Mantle melting leaves behind depleted, more viscous and more buoyant layers at the lithosphere-asthenosphere boundary which may take millions of years before sinking back to deeper mantle. Average volcanic layer thicknesses of hundreds of meters can be reached via the SSC process, corresponding to observations from the Turkish-Iranian plateau. By its random nature, SSC can explain why the continental collision magmatism on the Turkish-Iranian plateau does not seem to have clearly recognisable spatial or temporal patterns. The potential of the SSC to effectively mix the asthenosphere-lithosphere close to their boundary appears to offer an explanation for the geochemical heterogeneity of the observed volcanism. SSC may be related to whole mantle delamination (offering zones of weaknesses for its initiation) or slab break-off (SSC being enhanced by the break-off), but neither is a prerequisite for SSC magmatism.

Kaislaniemi, Lars; van Hunen, Jeroen; Allen, Mark; Neill, Iain

2014-05-01

148

Sub-lithospheric small scale convection - a process for continental collision magmatism  

NASA Astrophysics Data System (ADS)

We have studied the role of sub-lithospheric small scale convection in the generation of collision zone magmatism, using combined geodynamic-petrological models. We compare the results with the collisional magmatism of the Turkish-Iranian plateau, where a number of randomly (in both space and time) distributed volcanic centres on has been produced by the active Arabia-Eurasia collision since initial plate collision at ~27-35 Ma. These volcanic rocks have a highly variable geochemical signature, but commonly point to a lithospheric mantle or asthenospheric source. Major and trace element characteristics span the range from OIB-like, to calc-alkali, shoshonitic and even ultrapotassic. We suggest these spatially, temporally and chemically diverse patterns of volcanism are caused by sub-lithospheric small scale convection (SSC), manifested as small (50 to 300 km) convection cells at the lithosphere-asthenosphere boundary and dripping of the lithospheric mantle into the asthenosphere. SSC is activated by the increased amount of water in the lithospheric and asthenospheric mantle and its rheological weakening effect. The increase in water content is caused by the subduction prior to the collision and/or continental subduction during collision. The mantle convection code CitCom, together with a parameterized melting model, is used to model the SSC process. We relate the water content to the mantle solidus and viscosity, and the amount of depletion to the viscosity and buoyancy of the mantle material. We measure the amount of magmatism taking place by assuming direct and instantaneous percolation of mantle melts to the surface. We mimic the dislocation creep mechanism with a diffusion creep mechanism using low activation energy--either one is needed for the SSC to take place under realistic conditions. Results show that SSC is able to produce small degrees (0-2 %) of melting of the mantle through dripping lithosphere, decompression melting, erosion of the overlying lithosphere, and advection of hot material into contact with the cold lithosphere. The degree of melting might be strongly controlled by the lithosphere thickness and the extent of its hydration during the past Tethyan subduction. Mantle melting leaves behind depleted, more viscous and more buoyant layers at the lithosphere-asthenosphere boundary which may take millions of years before sinking back to deeper mantle. Average volcanic layer thicknesses of hundreds of meters can be reached via the SSC process, corresponding to observations from the Turkish-Iranian plateau. By its random nature, SSC can explain why the continental collision magmatism on the Turkish-Iranian plateau does not seem to have clearly recognisable spatial or temporal patterns. The potential of the SSC to effectively mix the asthenosphere-lithosphere close to their boundary appears to offer an explanation for the geochemical heterogeneity of the observed volcanism. SSC may be related to whole mantle delamination (offering zones of weaknesses for its initiation) or slab break-off (SSC being enhanced by the break-off), but neither is a prerequisite for SSC magmatism.

Kaislaniemi, L.; Van Hunen, J.; Allen, M. B.; Neill, I.

2013-12-01

149

Molecular Basis for the Photosynthetic Primary Process  

PubMed Central

In this paper, the molecular details for the primary reaction in photosynthesis are deduced from several recent critical experimental observations. A symmetrical structure is proposed for the basic unit of the reaction center in plant photosynthesis. A mathematical consequence of the symmetrical arrangement is the creation of an anomalously long-lived trap state, which makes possible the summation of a reaction-center triplet excitation and an antenna chlorophyll singlet excitation to bring the photoactive chlorophylls to a charge-transfer state prior to entering into a primary photochemical reaction.

Fong, Francis K.

1974-01-01

150

Hydrodynamical processes in the Draco molecular cloud  

SciTech Connect

IRAS 100 micron images of the Draco cloud show several cloud components with cometary plumes of material extending 7-10 pc. The brightest plumes are very uniform in thickness but often terminate in large amorphous regions. The structure is consistent with low Reynolds number hydrodynamics and is suggestive of a molecular cloud shedding material in a plume as it falls onto the galactic plane from the halo region. A subsequent study of the 100 micron images from the entire IRAS survey has revealed a total of 14 additional cometlike objects with /b II/ greater then 15 deg. 42 references.

Odenwald, S.F.; Rickard, L.J.

1987-07-01

151

The influence of surface processes in modulating the deformation of the deep lithosphere during collision  

NASA Astrophysics Data System (ADS)

The importance of climate-controlled surface processes (erosion and deposition) in influencing the tectonics of plate collision and orogenesis has been well recognized for crustal-scale tectonics. We consider the geodynamics of coupled crust and mantle processes during such collisional events to consider how the surface processes modify the deformation of the deeper parts of the plate and lithosphere as a whole. The geodynamics are explored quantitatively using high resolution 2D thermal-mechanical numerical experiments. The model has a free surface, prescribed erosional laws (e.g., empirically derived relief- and slope-dependent erosion), and sediment deposition dependent on the amount of material eroded make up the top boundary of the model domain and allow topography to develop self consistently with the underlying tectonics. The models reveal that during the early stages of continental plate collision, the altered of crustal mass flux by surface erosion can modify the stress regime within the crust and at the crust-mantle interface and subsequently the behaviour of the underlying mantle lithosphere. For example with active surface erosion stable subduction-like plate consumption is maintained. In the absence of erosion, subduction is inhibited by accumulating crust causing the convergent plates to steepen dip, detach, and reverse consumption polarity. We also isolate the influence of sediment deposition in the collisional models. In very different ways, the surface transport and deposition of the eroded material can have a significant effect on modulating the dynamics of the whole lithosphere between various modes of deformation. Overall, the models reveal the sensitivity of the near-surface and deep continental plate boundary evolution to surface processes.

Pysklywec, Russell; Gray, Robert

2014-05-01

152

New process observed in collisions between highly charged protonated protein and Xe8+ Xe5+ He2+ ions  

NASA Astrophysics Data System (ADS)

Electron multicapture processes have been studied in collisions between cytochrome C protein and highly charged Xe and He projectile at keV kinetic energy range. In competition with single and double electron capture, a new and unexpected channel attributed to deprotonation process of the protein has been observed.

Martin, S.; Chen, L.; Brédy, R.; Vernier, A.; Dugourd, P.; Antoine, R.; Ortéga, C.; Ji, M.; Bernard, J.; Gonzalez Maganad, O.; Reitsma, G.; Schlathölter, T.

2014-04-01

153

Modeling of collision and coalescence of droplets during microgravity processing of Zn-Bi immiscible alloys  

NASA Technical Reports Server (NTRS)

A population balance model is presented for the coarsening of the dispersed phase of liquid-liquid two-phase mixtures in microgravity due to gravity sedimentation and Marangoni migration, which lead to the collision and coalescence of droplets. The model is used to predict the evolution of the size distribution of the dispersed phase in a liquid-phase miscibility gap system, Zn-Bi, which has been used in a number of experimental microgravity processing studies in which significant phase segregation has been observed. The analysis shows that increasing the temperature gradient, gravity level, volume fraction of the dispersed phase, initial average drop radius, initial standard deviation of droplet radii, or the temperature coefficient of the interfacial tension leads to an increase in the rate of droplet growth due to collision and coalescence. Comparison of the distribution evolutions for unimodal and bimodal initial distributions shows that the latter yield significantly more rapid droplet growth. Finally, it is shown that droplet growth can be dramatically reduced with antiparallel orientation of the gravity vector and the temperature gradient, provided that the relative magnitude of these two vectors is properly chosen.

Davis, R. H.; Rogers, J. R.

1990-01-01

154

Methods for Processing and Interpretation of AIS Signals Corrupted by Noise and Packet Collisions  

NASA Astrophysics Data System (ADS)

The authors deal with the operation of Automatic Identification System (AIS) used in the marine traffic monitoring to broadcast messages containing information about the vessel: id, payload, size, speed, destination etc., meant primarily for avoidance of ship collisions. To extend the radius of AIS operation, it is envisaged to dispose its receivers on satellites. However, in space, due to a large coverage area, interfering factors are especially pronounced - such as packet collision, Doppler's shift and noise impact on AIS message receiving, pre-processing and decoding. To assess the quality of an AIS receiver's operation, a test was carried out in which, varying automatically frequency, amplitude, noise, and other parameters, the data on the ability of the receiver's ability to decode AIS signals are collected. In the work, both hardware- and software-based AIS decoders were tested. As a result, quite satisfactory statistics has been gathered - both on the common and the differing features of such decoders when operating in space. To obtain reliable data on the software-defined radio AIS receivers, further research is envisaged.

Po?evskis, J.; Krasti?š, M.; Kor?ts, G.; Skorodumovs, A.; Trokšs, J.

2012-01-01

155

Multiple electron transfer processes in collisions of N{sup 6+} and O{sup 7+} with methane  

SciTech Connect

Recent experiments on collision processes of O{sup 7+} and N{sup 6+} ions colliding with methane at the same velocity show unexpected differences in the fragmentation cross sections of the methane. Despite the expected similarity of these two processes, as both projectiles are hydrogenic, the mechanisms of electron transfer are different and lead to different fragmentation cross sections. In the present work, the collisions between N{sup 6+} and O{sup 7+} ions and methane are investigated theoretically at equal velocities corresponding to projectile energies of 30 and 35 keV, respectively. Electron-nuclear dynamics is used to study multiple electron transfer processes occurring in these collisions. Several multiple charge transfer probabilities are calculated and results, averaged over various orientations of the methane molecule, are reported. The collisions proceed in two stages: a fast stage of electron transfer from methane to the ion, and a much slower stage of breakup of the methane. We find and explain the intuitively unexpected result that the total charge transfer cross section for N{sup 6+} is slightly larger, but that the O{sup 7+} leaves the methane in a higher charged state with higher probability, leading to more fragmentation in the collisions with O{sup 7+}.

Guevara, N. L.; Teixeira, E.; Hall, B.; Deumens, E.; Oehrn, Y.; Sabin, J. R. [Quantum Theory Project, Department of Chemistry and Physics, University of Florida, Gainesville, Florida 32611-8435 (United States)

2009-12-15

156

Near-threshold photoionization of hydrogenlike uranium studied in ion-atom collisions via the time-reversed process.  

PubMed

Radiative electron capture, the time-reversed photoionization process occurring in ion-atom collisions, provides presently the only access to photoionization studies for very highly charged ions. By applying the deceleration mode of the ESR storage ring, we studied this process in low-energy collisions of bare uranium ions with low- Z target atoms. This technique allows us to extend the current information about photoionization to much lower energies than those accessible for neutral heavy elements in the direct reaction channel. The results prove that for high- Z systems, higher-order multipole contributions and magnetic corrections persist even at energies close to the threshold. PMID:11177990

Stöhlker, T; Ma, X; Ludziejewski, T; Beyer, H F; Bosch, F; Brinzanescu, O; Dunford, R W; Eichler, J; Hagmann, S; Ichihara, A; Kozhuharov, C; Krämer, A; Liesen, D; Mokler, P H; Stachura, Z; Swiat, P; Warczak, A

2001-02-01

157

Electron emission and electron transfer processes in proton-naphthalene collisions at intermediate velocities  

NASA Astrophysics Data System (ADS)

We investigate the fragmentation and ionization of naphthalene by protons at intermediate velocities (between 1.41 and 2.68 a.u.). Relative cross sections for electron capture (EC), electron emission (EE), and capture ionization are measured. The EC cross sections decrease rapidly over the energy range under consideration (50-150 keV) and are lower than EE cross sections. The EE cross sections, on the other hand, change very slowly in this energy range. The energetics of interactions is quantified by comparing the mass spectra with the photodissociation breakdown curves from literature. In the case of single capture, resonant electron transfer to n = 1 state in H+ is seen to dominate the interaction but is shown to be accompanied by a small amount of electronic energy loss. In the EE mode, two mechanisms are shown to be active in the collision process: large impact parameter plasmon excitation mode, and closer encounters with higher amounts of electronic energy loss.

Mishra, P. M.; Rajput, J.; Safvan, C. P.; Vig, S.; Kadhane, U.

2013-11-01

158

A molecular-beam study of the collision dynamics of methane and ethane upon a graphitic monolayer on Pt(111)  

NASA Astrophysics Data System (ADS)

Utilizing a supersonic molecular-beam scattering technique, the angular intensity distributions of alkane molecules (CH4 and C2H6) have been measured, which are scattered from a chemically inert and highly oriented monolayer graphite (MG) on Pt(111). A MG which covers the Pt(111) surface with a full monolayer is found to induce a large energy loss of alkanes during collision with the surface by phonon creation due to the large mass ratio of an alkane molecule with respect to MG. Based on the classical cube model, only applicable to the molecules without internal mode excitation, the effective masses of MG of 76 (six atoms of carbon) and Pt(111) of 585 (three atoms of platinum) are determined from rare-gas atom scattering data. Despite the difference in the degree of freedom between CH4 and rare-gas atoms, CH4 scattering is found to be well described by the simple hard-cube model as a result of the high symmetry of the CH4 structure. With the recently developed ellipsoid-washboard model, an extension of the hard-cube model to include some internal mode excitation of impinging molecules in addition to the surface corrugation, it is found that unlike CH4 the cartwheel rotation mode of C2H6 is significantly excited during collision, while the helicopter mode excitation is negligible on a flat MG surface.

Kondo, Takahiro; Mori, Daisuke; Okada, Ryuta; Sasaki, Masahiro; Yamamoto, Shigehiko

2005-09-01

159

Collision Processes of Highly Charged Ions with Electrons Studied with an Electron Beam Ion Trap  

SciTech Connect

The electron beam ion trap in Tokyo (Tokyo-EBIT)is suitable for studying relativistic effects in the collisions of highly charged heavy ions with electrons because it can produce and trap very highly charged heavy ions which interact with a mono-energetic and unidirectional relativistic electron beam with an energy of up to 200 keV. Recently, we have been studying resonant processes in ionization and recombination by measuring the charge abundance inside the EBIT at the equilibrium. The abundance ratio between adjacent charge states varies slowly with the electron energy when there is no resonant process. However, when the electron energy coincides with the resonant energy at which ionization or recombination is enhanced, the abundance ratio can drastically change. Thus, the resonant processes can be studied by measuring the abundance ratio between adjacent ions as a function of electron beam energy. In this talk, recent progress for heavy ions with very high charge states up to He-like Bi{sup 81+}, is presented. For such ions, relativistic effects significantly affect the resonant processes. For example, the generalized Breit interaction (GBI) effect, which treats the retardation in the exchange of single virtual photon between the free and orbital electrons, has been clearly observed in the DR resonant strength in Li-like Bi{sup 80+}. Recently we have also found that the GBI effect plays an important role in the interference between non-resonant and resonant recombinations. Experimental results are presented in comparison with theoretical calculations.

Nakamura, Nobuyuki; Watanabe, Tsutomu; Ohtani, Shunsuke [Inst. for Laser Science, University of Electro-Communications, Tokyo 182-8585 (Japan); Kavanagh, Anthony P.; Currell, Fred J. [Queen's University Belfast, Belfast BT7 1NN (United Kingdom); Watanabe, Hirofumi [Chubu University, Aichi 487-8501 (Japan); Sakaue, Hiroyuki A.; Kato, Daiji [National Institute for Fusion Science, Toki, Gifu 509-5292 (Japan); Li Yueming [Institute of Applied Physics and Computational Mathematics, P.O.Box 8009, Beijing 100088 (China); Tong Xiaoming [Center for Computational Sciences, University of Tsukuba, Ibaraki 305-8577 (Japan)

2009-09-10

160

Collision Processes of Highly Charged Ions with Electrons Studied with an Electron Beam Ion Trap  

NASA Astrophysics Data System (ADS)

The electron beam ion trap in Tokyo (Tokyo-EBIT)[1] is suitable for studying relativistic effects in the collisions of highly charged heavy ions with electrons because it can produce and trap very highly charged heavy ions which interact with a mono-energetic and unidirectional relativistic electron beam with an energy of up to 200 keV. Recently, we have been studying resonant processes in ionization[2] and recombination[3] by measuring the charge abundance inside the EBIT at the equilibrium. The abundance ratio between adjacent charge states varies slowly with the electron energy when there is no resonant process. However, when the electron energy coincides with the resonant energy at which ionization or recombination is enhanced, the abundance ratio can drastically change. Thus, the resonant processes can be studied by measuring the abundance ratio between adjacent ions as a function of electron beam energy[4]. In this talk, recent progress for heavy ions with very high charge states up to He-like Bi81+, is presented. For such ions, relativistic effects significantly affect the resonant processes. For example, the generalized Breit interaction (GBI) effect, which treats the retardation in the exchange of single virtual photon between the free and orbital electrons, has been clearly observed in the DR resonant strength in Li-like Bi80+ [5]. Recently we have also found that the GBI effect plays an important role in the interference between non-resonant and resonant recombinations. Experimental results are presented in comparison with theoretical calculations.

Nakamura, Nobuyuki; Kavanagh, Anthony P.; Watanabe, Hirofumi; Sakaue, Hiroyuki A.; Li, Yueming; Kato, Daiji; Currell, Fred J.; Tong, Xiao-Ming; Watanabe, Tsutomu; Ohtani, Shunsuke

2009-09-01

161

Accelerating molecular dynamics simulations using Graphics Processing Units with CUDA  

Microsoft Academic Search

Molecular dynamics is an important computational tool to simulate and understand biochemical processes at the atomic level. However, accurate simulation of processes such as protein folding requires a large number of both atoms and time steps. This in turn leads to huge runtime requirements. Hence, finding fast solutions is of highest importance to research. In this paper we present a

Weiguo Liu; Bertil Schmidt; Gerrit Voss; Wolfgang Müller-Wittig

2008-01-01

162

Femtosecond laser field induced modifications of electron-transfer processes in Ne{sup +}-He collisions  

SciTech Connect

We demonstrate the presence of femtosecond laser induced charge transfer in Ne{sup +}-He collisions. Electron transfer in ion-atom collisions is considerably modified when the collision is embedded in a strong laser field with the laser intensity of {approx}10{sup 15} W/cm{sup 2}. The observed anisotropy of the He{sup +} angular distribution confirms the prediction of early work that the capture probability varies significantly with the laser polarization angle.

Lu Zhenzhong; Chen Deying; Fan Rongwei; Xia Yuanqin

2012-01-02

163

One and two electron processes in collisions of highly charged ions with He at velocities around 1 a.u  

Microsoft Academic Search

We have studied one and two electron processes in collisions of Ar16+ and O8+ ions with He atoms at velocities between 0.23 and 1.67 a.u. These processes were identified by measuring the final charges of the projectile and recoil ions in coincidence. Single electron capture (SC) is the dominant process at all our velocities. Transfer ionization (TI), where the He

J. P. Giese; W. Wu; I. Ben-Itzhak; C. L. Cocke; R. Ali; P. Richard; M. Stoeckli; H. Schoene

1993-01-01

164

Dewaxing catalysts and processes employing non-zeolitic molecular sieves  

Microsoft Academic Search

This patent describes the process for dewaxing a hydrocarbon feedstock to reduce its pour point. It comprises: contacting the hydrocarbon feedstock at effective dewaxing conditions with a dewaxing catalyst comprising an effective amount of at lest one non-zeolitic molecular sieve selected from the group consisting of SAPO, ELAPSO, MeAPO, FeAPO, TiAPO, and ELAPO molecular sieves, and characterized in its calcined

R. J. Pellet; J. A. Rabo; G. N. Long; F. P. Gortsema; A. R. Springer

1990-01-01

165

Unified description of transverse momentum spectrums contributed by soft and hard processes in high-energy nuclear collisions  

NASA Astrophysics Data System (ADS)

The transverse momentum spectrums of ? -, ? +, K -, K +, , and p produced in p-Pb collisions at ? s NN = 502 TeV measured by the CMS Collaboration and in Pb-Pb collisions at ? s NN = 2.76 TeV measured by the ALICE Collaboration are described by a two-component Erlang distribution. The first component corresponds to "soft" excitation process and contributes in the low transverse momentum region, which is contributed by 2-5 partons (sea quarks and gluons) with strong interactions. The second component corresponds to "hard" scattering process and contributes in the high transverse momentum region, which is contributed by 2 partons (valent quarks) with violent head-on collision. Each parton source contributes an exponential transverse momentum spectrum. Both the soft and hard processes result in an Erlang distribution. The transverse momentum spectrums of final-state charged particles are then described by the two-component Erlang distribution. The contribution ratio (30-40%) of the hard process extracted from nuclear collisions at the Large Hadron Collider is consistent with that (17-46%) obtained from other methods.

Liu, Fu-Hu; Gao, Ya-Qin; Tian, Tian; Li, Bao-Chun

2014-06-01

166

A molecular dynamics simulation of the destruction of explosive molecules at high-velocity collisions  

Microsoft Academic Search

The infrared spectra and the energies of dissociation of R-NO2 bonds (R?C, N, and O) were calculated for explosive molecules (trinitrotoluene, hexogen, octogen, pentaerythrityl tetranitrate,\\u000a triaminotrinitrobenzene, and nitromethane). The time of kinetic energy redistribution over intramolecular vibrational modes\\u000a for these molecules (the V-V relaxation time) was calculated by the molecular dynamics simulation method. Molecular dynamics simulations were also used\\u000a to

A. A. Selezenev; A. Yu. Aleinikov; I. V. Briginas

2008-01-01

167

Reaction of formaldehyde cation with molecular hydrogen: Effects of collision energy and H2CO+ vibrations  

NASA Astrophysics Data System (ADS)

The effects on the title reaction of collision energy (Ecol) and five H2CO+ vibrational modes have been studied over a center-of-mass Ecol range from 0.1 to 2.3 eV. Electronic structure and Rice-Ramsperger-Kassel-Marcus calculations were used to examine properties of various complexes and transition states that might be important. Only the hydrogen abstraction (HA) product channel is observed, and despite being exoergic, HA has an appearance energy of ~0.4 eV, consistent with a transition state found in the electronic structure calculations. A precursor complex-mediated mechanism might possibly be involved at very low Ecol, but the dominant mechanism is direct over the entire Ecol range. The magnitude of the HA cross section is strongly, and mode specifically affected by H2CO+ vibrational excitation, however, vibrational energy has no effect on the appearance energy.

Liu, Jianbo; Anderson, Scott L.

2004-05-01

168

Fundamental processes in low energy collisions of alkali anions and atoms  

SciTech Connect

A summary of observations of collisions of alkali ions with atoms and molecules and collisions of H/sup -/ and D/sup -/ with alkali atoms is presented. The energy range of the experiments was 5

Champion, R.L.; Doverspike, L.D.; Scott, D.M.; Wang, Y.

1987-07-30

169

1978 bibliography of atomic and molecular processes. [Bibliography  

SciTech Connect

This annotated bibliography lists 2557 works on atomic and molecular processes reported in publications dated 1978. Sources include scientific journals, conference proceedings, and books. Each entry is designated by one or more of the 114 categories of atomic and molecular processes used by the Controlled Fusion Atomic Data Center to classify data. Also indicated is whether the work was experimental or theoretical, what energy range was covered, what reactants were investigated, and the country of origin of the first author. Following the bibliographical listing are indexes of reactants and authors.

Not Available

1980-03-01

170

1979 bibliography of atomic and molecular processes. [Bibliography  

SciTech Connect

This annotated bibliography lists 2146 works on atomic and molecular processes reported in publications dated 1979. Sources include scientific journals, conference proceedings, and books. Each entry is designated by one or more of the 114 categories of atomic and molecular processes used by the Controlled Fusion Atomic Data Center, Oak Ridge National Laboratory, to classify data. Also indicated is whether the work was experimental or theoretical, what energy range was covered, what reactants were investigated, and the country of origin of the first author. Following the bibliographical listing are indexes of reactants and authors.

None

1980-08-01

171

Atomic collision effects during PLD processes: nonstoichiometry control in transparent superconductors  

NASA Astrophysics Data System (ADS)

The pulsed laser deposition (PLD) growth processes of spinel lithium titanates, Li4Ti5O12 and LiTi2O4, on MgAl2O4 (111) substrates are investigated. Although a Li4Ti5O12 target was used for the depositions, the Li/Ti atomic ratio of the species arriving at the substrate during deposition was only ~0.5, enabling high quality LiTi2O4 films to be prepared with a rocking curve full-width at half-maximum of ~0.05°. The LiTi2O4 epitaxial thin films exhibited high conductivity at room temperature (~3.0 × 103 ?-1cm-1) and a superconducting transition temperature of ~13.3 K. These values are the highest recorded for epitaxial thin films. Moreover, the effect of collisions between the atoms in a plume were studied quantitatively. These results demonstrate the importance of the target composition, providing further insight into Licontaining metal-oxide deposition processes using PLD.

Hitosugi, Taro; Packwood, D.; Shiraki, S.

2014-03-01

172

Velocity dependence of one- and two-electron processes in intermediate-velocity Ar16++He collisions  

Microsoft Academic Search

We report investigations of one- and two-electron processes in the collisions of 0.9-keV\\/u to 60-keV\\/u (vp=0.19-1.55 a.u.) Ar16+ ions with He targets. The cross sections for these processes were measured by observing the final charges of the Ar ions and the recoiling target ions in coincidence. The average Q values for the capture channels were determined by measuring the longitudinal

W. Wu; J. P. Giese; I. Ben-Itzhak; C. L. Cocke; P. Richard; M. Stockli; R. Ali; H. Schoene; R. E. Olson

1993-01-01

173

Molecular dynamics study of particle particle collisions between hydrogen-passivated silicon nanoparticles  

Microsoft Academic Search

One of the significant challenges in the use of nanoparticles is the control of primary particle size and extent of agglomeration when grown from the gas phase. In this paper we evaluate a possible strategy of surface passivation. Here the particle particle interaction of hydrogen-surface-terminated silicon nanoparticles has been evaluated using molecular dynamics simulation. Nanoparticles of the size between 200

T. Hawa; M. R. Zachariah

2004-01-01

174

Molecular-beam studies of primary photochemical processes  

SciTech Connect

Application of the method of molecular-beam photofragmentation translational spectroscopy to the investigation of primary photochemical processes of polyatomic molecules is described. Examples will be given to illustrate how information concerning the energetics, dynamics, and mechanism of dissociation processes can be obtained from the precise measurements of angular and velocity distributions of products in an experiment in which a well-defined beam of molecules is crossed with a laser.

Lee, Y.T.

1982-12-01

175

Stopping powers and cross sections due to two-photon processes in relativistic nucleus-nucleus collision  

NASA Technical Reports Server (NTRS)

The radiation dose received from high energy galactic cosmic rays (GCR) is a limiting factor in the design of long duration space flights and the building of lunar and martian habitats. It is of vital importance to have an accurate understanding of the interactions of GCR in order to assess the radiation environment that the astronauts will be exposed to. Although previous studies have concentrated on the strong interaction process in GCR, there are also very large effects due to electromagnetic (EM) interactions. In this report we describe our first efforts at understanding these EM production processes due to two-photon collisions. More specifically, we shall consider particle production processes in relativistic heavy ion collisions (RHICs) through two-photon exchange.

Cheung, Wang K.; Norbury, John W.

1992-01-01

176

Implementation of exterior complex scaling in B-splines to solve atomic and molecular collision problems  

SciTech Connect

B-spline methods are now well established as widely applicable tools for the evaluation of atomic and molecular continuum states. The mathematical technique of exterior complex scaling has been shown, in a variety of other implementations, to be a powerful method with which to solve atomic and molecular scattering problems, because it allows the correct imposition of continuum boundary conditions without their explicit analytic application. In this paper, an implementation of exterior complex scaling in B-splines is described that can bring the well-developed technology of B-splines to bear on new problems, including multiple ionization and breakup problems, in a straightforward way. The approach is demonstrated for examples involving the continuum motion of nuclei in diatomic molecules as well as electronic continua. For problems involving electrons, a method based on Poisson's equation is presented for computing two-electron integrals over B-splines under exterior complex scaling.

McCurdy, C. William; Martin, Fernando

2003-11-18

177

Stability of nuclei in peripheral collisions in the JAERI quantum molecular dynamics model  

SciTech Connect

The JAERI quantum molecular dynamics (JQMD) model has been successfully used for a long time now to describe many different aspects of nuclear reactions in a unified way. In some cases, however, the JQMD model cannot produce consistent results: First, it lacks a fully relativistically covariant approach to the problem of molecular dynamics; second, the quantum-mechanical ground state of nuclei cannot be faithfully reproduced in a semiclassical framework. Therefore, we introduce R-JQMD, an improved version of JQMD that also features a new ground-state initialization algorithm for nuclei. We compare the structure of the two codes and discuss whether R-JQMD can be adjusted to improve JQMD's agreement with measured heavy-ion fragmentation cross sections.

Mancusi, Davide; Niita, Koji; Maruyama, Tomoyuki; Sihver, Lembit [Nuclear Engineering, Applied Physics, Chalmers University of Technology, Gothenburg (Sweden); Research Organization for Information Science and Technology, Tokai-mura (Japan); College of Bioresource, Nihon Unniversity, Fujisawa (Japan); Nuclear Engineering, Applied Physics, Chalmers University of Technology, Gothenburg, Sweden and Department of Mathematics, Computer Science and Physics, Roanoke College, Salem, Virginia (United States)

2009-01-15

178

Multiple ionization and excitation processes in single ion-atom collisions  

SciTech Connect

Several experimental methods are discussed, which, by relying on intentionally imposed restrictions such as coincidence requirements and/or special detection geometries, permit measurements differential in several important collision parameters. Such multiply differential measurements are necessary for the isolation of particular excitation and ionization mechanisms and provide much more stringent tests of existing theories. Emphasis is on single collision phenomena involving primarily heavy ions at velocities comparable to K-shell velocities. (GHT)

Elston, S.B.

1980-01-01

179

Mesoscopic Properties of Molecular Folding and Aggregation Processes  

NASA Astrophysics Data System (ADS)

Protein folding, peptide aggregation and crystallization, as well as adsorption of molecules on soft or solid substrates have an essential feature in common: In all these processes, structure formation is guided by a collective, cooperative behavior of the molecular subunits lining up to build chainlike macromolecules. Proteins experience conformational transitions related to thermodynamic phase transitions. For chains of finite length, an important difference of crossovers between conformational (pseudo)phases is, however, that these transitions are typically rather smooth processes, i.e., thermodynamic activity is not necessarily signalized by strong entropic or energetic fluctuations. Nonetheless, in order to understand generic properties of molecular structure-formation processes, the analysis of mesoscopic models from a statistical physics point of view enables first insights into the nature of conformational transitions in small systems. Here, we review recent results obtained by means of sophisticated generalized-ensemble computer simulations of minimalistic coarse-grained models.

Bachmann, Michael; Janke, Wolfhard

2008-11-01

180

Young-type interference in collisions between Helium and molecular Hydrogen ions  

NASA Astrophysics Data System (ADS)

The dissociative electron transfer from He into slow diatomic molecular ions was measured in a kinematically complete experiment by using cold target recoil ion momentum spectroscopy (COLTRIMS) in combination with a high resolution molecular fragment imaging technique. The electron transfer leads to neutral molecules in highly excited electronic states which dissociate in a second step of the reaction. With COLTRIMS we determine the energy which is taken from the motion of the projectile and transferred to internal degrees of freedom of the molecule. Furthermore we are able to determine the kinetic energy release (KER) of the dissociation as well as the spatial orientation of the molecular break up. When using H2^+ as projectiles this enables us to select the direct population of the lowest dissociative state of H2 b^3?^+u from the measured data. This reaction channel was analyzed in an inverse kinematics scheme where the molecule is regarded as two closely lying scattering centers at which an incoming He wave scatters. The orientation and the distance of these two scattering centers are obtained by detecting the fragments after the reaction, as the internuclear vector can be determined using the reflection as well as the axial recoil approximation. We find a striking double slit interference pattern in the transverse momentum transfer between the He atom and the molecule which we can modulate by selecting different internuclear distances (i.e. KERs) in our offline analysis. Compared to an optical double slit, the interference's minima and maxima are swapped. The latter is the result of a phase shift in the electronic part of the wave function.

Schmidt, Lothar

2009-05-01

181

Experimental separation of the Thomas charge-transfer process in high-velocity p-He collisions  

SciTech Connect

We present differential cross sections of electron capture in 7.5 MeV and 12.5 MeV proton-helium collisions. Complete experimental separations of the Thomas and the kinematic single electron capture processes in the two-dimensional He{sup +} momentum distribution in the plane perpendicular to the fast ion beam have been achieved. We compare the resulting projectile angular differential cross section with the two most recent theoretical calculations and expose significant deviations.

Fischer, D.; Stoechkel, K.; Cederquist, H.; Zettergren, H.; Reinhed, P.; Schuch, R.; Schmidt, H. T. [Department of Physics, Stockholm University, S-10691 Stockholm (Sweden); Kaellberg, A.; Simonsson, A. [Manne Siegbahn Laboratory, Stockholm University, S-10405 Stockholm (Sweden)

2006-05-15

182

Multiple-electron capture processes in 70keV 15N7++Ar collisions: A triple-coincidence study  

Microsoft Academic Search

Double- through quintuple-electron capture processes in the 70-keV 15N7++Ar collision system have been investigated by means of time-of-flight triple-coincidence measurements of Auger electrons, scattered projectile, and target recoil ions. Subpartial Auger-electron spectra corresponding to specific pairs of final projectile and recoil-ion charge states have been obtained and discussed within the framework of the extended classical overbarrier model [A. Niehaus, J.

E. D. Emmons; A. A. Hasan; R. Ali

1999-01-01

183

Triple-Coincidence Investigations of Multi-Electron Processes in 60 keV C^6++Ar Collisions  

Microsoft Academic Search

Multi-electron processes in 60 keV C^6++Ar collisions have been investigated by means of time-of-flight triple-coincidence measurements of Auger electrons, recoil ions and scattered projectiles. The measurements have been performed at the UNR 14 GHz ECR ion source research facility. Partial Auger spectra corresponding to specific recoil ion charge states, and sub-partial Auger spectra corresponding to specific final projectile and recoil

H. Merabet; R. Ali; H. Cakmak; A. A. Hasan; T. Osipov; R. A. Phaneuf

1998-01-01

184

Stopping powers and cross sections due to two-photon processes in relativistic nucleus-nucleus collisions  

NASA Technical Reports Server (NTRS)

The effects of electromagnetic-production processes due to two-photon exchange in nucleus-nucleus collisions are discussed. Feynman diagrams for two-photon exchange are evaluated using quantum electrodynamics. The total cross section and stopping power for projectile and target nuclei of identical charge are found to be significant for heavy nuclei above a few GeV per nucleon-incident energy.

Cheung, Wang K.; Norbury, John W.

1994-01-01

185

Positron emission tomography provides molecular imaging of biological processes  

PubMed Central

Diseases are biological processes, and molecular imaging with positron emission tomography (PET) is sensitive to and informative of these processes. This is illustrated by detection of biological abnormalities in neurological disorders with no computed tomography or MRI anatomic changes, as well as even before symptoms are expressed. PET whole body imaging in cancer provides the means to (i) identify early disease, (ii) differentiate benign from malignant lesions, (iii) examine all organs for metastases, and (iv) determine therapeutic effectiveness. Diagnostic accuracy of PET is 8–43% higher than conventional procedures and changes treatment in 20–40% of the patients, depending on the clinical question, in lung and colorectal cancers, melanoma, and lymphoma, with similar findings in breast, ovarian, head and neck, and renal cancers. A microPET scanner for mice, in concert with human PET systems, provides a novel technology for molecular imaging assays of metabolism and signal transduction to gene expression, from mice to patients: e.g., PET reporter gene assays are used to trace the location and temporal level of expression of therapeutic and endogenous genes. PET probes and drugs are being developed together—in low mass amounts, as molecular imaging probes to image the function of targets without disturbing them, and in mass amounts to modify the target's function as a drug. Molecular imaging by PET, optical technologies, magnetic resonance imaging, single photon emission tomography, and other technologies are assisting in moving research findings from in vitro biology to in vivo integrative mammalian biology of disease.

Phelps, Michael E.

2000-01-01

186

Accelerating Molecular Dynamic Simulation on Graphics Processing Units  

PubMed Central

We describe a complete implementation of all-atom protein molecular dynamics running entirely on a graphics processing unit (GPU), including all standard force field terms, integration, constraints, and implicit solvent. We discuss the design of our algorithms and important optimizations needed to fully take advantage of a GPU. We evaluate its performance, and show that it can be more than 700 times faster than a conventional implementation running on a single CPU core.

Friedrichs, Mark S.; Eastman, Peter; Vaidyanathan, Vishal; Houston, Mike; Legrand, Scott; Beberg, Adam L.; Ensign, Daniel L.; Bruns, Christopher M.; Pande, Vijay S.

2009-01-01

187

Subduction/obduction processes prior to collision: records from the Tavsanli zone (western Turkey)  

NASA Astrophysics Data System (ADS)

The tectono-metamorphic evolution of the ~80Ma high-pressure low-temperature (HP-LT) Tavsanli zone (Western Anatolia, Izmir-Ankara suture zone) is herein reappraised to highlight processes occurring along a fossil subduction interface, from initial intra-oceanic subduction to continental subduction and soft collision. Structural and petrological data allow in particular (i) to constrain the nature, internal structure and PT conditions of the oceanic accreted oceanic unit sandwiched between the continental Orhaneli unit and the non-metamorphic obducted ophiolite on top; (ii) to revaluate the peak-pressure conditions for the subducted northern margin of the Anatolide-Tauride Block (the Orhaneli unit). In the ocean slices, two distinct, extensive oceanic complexes (OC1 and OC2) are recognised on top of one another, incipient HP-LT imprint (OC1) to blueschist facies conditions (OC2). Based on the first occurrence of Fe-Mg carpholite and on pseudosection calculations, PT estimates of 250-350°C and 11-13 kbar are inferred for OC2. The internal structure of the accretionary complex points to the underplating of kilometre-scale units at different depths along the plate interface and to contrasting dynamics with respect to both the underlying continental unit and the ophiolite. PT conditions for the continental Orhaneli unit are reappraised at 22 kbar and 500°C using both Raman spectroscopy on carbonaceous matter and pseudosection modelling and are similar to PT conditions known for the leading edge of the continental Arabian margin in Oman. Inter-plate mechanical coupling within the Tavsanli zone is finally compared to the Oman case to shed light on regional scale tectonics, accretionary dynamics and (rapid) thermal reequilibration of the subduction interface.

Plunder, A.; Agard, P.; Chopin, C.; Okay, A. I.

2013-12-01

188

Inelastic collisions of excited lithium molecules  

Microsoft Academic Search

Energy transfer and reactions during molecular collisions are fundamental processes in astronomy and chemistry. The H2 + H system has been well studied, and theoretical calculations are now becoming feasible for an excited lithium dimer colliding with a ground state lithium atom, increasing interest in corresponding experimental measurements. Our laboratory observes laser-induced fluorescence spectra from lithium vapor in a heat

Mark Rosenberry; Ramesh Marhatta; Brian Stewart

2010-01-01

189

Study of a hydrogen-bombardment process for molecular cross-linking within thin films  

SciTech Connect

A low-energy hydrogen bombardment method, without using any chemical additives, has been designed for fine tuning both physical and chemical properties of molecular thin films through selectively cleaving C-H bonds and keeping other bonds intact. In the hydrogen bombardment process, carbon radicals are generated during collisions between C-H bonds and hydrogen molecules carrying {approx}10 eV kinetic energy. These carbon radicals induce cross-linking of neighboring molecular chains. In this work, we focus on the effect of hydrogen bombardment on dotriacontane (C{sub 32}H{sub 66}) thin films as growing on native SiO{sub 2} surfaces. After the hydrogen bombardment, XPS results indirectly explain that cross-linking has occurred among C{sub 32}H{sub 66} molecules, where the major chemical elements have been preserved even though the bombarded thin film is washed by organic solution such as hexane. AFM results show the height of the perpendicular phase in the thin film decreases due to the bombardment. Intriguingly, Young's modulus of the bombarded thin films can be increased up to {approx}6.5 GPa, about five times of elasticity of the virgin films. The surface roughness of the thin films can be kept as smooth as the virgin film surface after thorough bombardment. Therefore, the hydrogen bombardment method shows a great potential in the modification of morphological, mechanical, and tribological properties of organic thin films for a broad range of applications, especially in an aggressive environment.

Liu, Y.; Yang, J. [Department of Mechanical and Materials Engineering, University of Western Ontario, London, Ontario (Canada); Yang, D. Q.; Nie, H.-Y.; Lau, W. M. [Surface Science Western, University of Western Ontario, London, Ontario (Canada)

2011-02-21

190

Molecular and dust scattering processes in astrophysical environments  

NASA Astrophysics Data System (ADS)

Understanding the formation and evolution of structure in the universe requires knowledge of the stellar energy output and its processing by gas and dust, evaluating the abundances of atomic and molecular species, and constraining thermodynamic parameters. Molecules, with molecular hydrogen and carbon monoxide being the most abundant, are a major component of the interstellar medium, and play an essential role in structure formation, by participating in gas cooling. Molecular fluorescence studies aim to provide a better interpretation of far-ultraviolet observations, constraining the molecular abundances and their interaction with the radiation field. The fluorescent emission lines offer a set of diagnostics for molecules complementary to absorption line spectroscopy and to observations at infrared and radio wavelengths, but are often poorly reproduced by models. In this work, I have developed and expanded fluorescence models for molecular hydrogen and carbon monoxide, and employed them in determining the spatial distribution of CO in cometary comae, in characterizing the effects of partial frequency redistribution for emission line scattering in planetary atmospheres and reflection nebulae, and in abundance determinations from Bowen fluorescence lines of H 2 in planetary nebulae. Follow-up optical and infrared observations were used in addition to UV data to diagnose molecular excitation, temperature, and spatial distribution in planetary nebula M27. Knowledge of the spectral energy distribution of the exciting stars in the far- ultraviolet is essential in constraining both the fluorescence models and understanding the scattering properties of nebular gas and dust. Sounding rocket observations of the Trifid and Orion nebulae, performed as part of this work, provided the necessary dynamic range and spatial resolution to measure simultaneously the nebular scattered light and the spectral energy distribution of the illuminating stars. These low extinction sight lines offered a unique view of the intrinsic stellar output below 1200 Å, and an excellent proving ground for the instrument performance. The analysis of these observations using fluorescence and dust scattering models is underway.

Lupu, Roxana-Elena

2009-06-01

191

Large scale molecular dynamics modeling of materials fabrication processes  

SciTech Connect

An atomistic molecular dynamics model of materials fabrication processes is presented. Several material removal processes are shown to be within the domain of this simulation method. Results are presented for orthogonal cutting of copper and silicon and for crack propagation in silica glass. Both copper and silicon show ductile behavior, but the atomistic mechanisms that allow this behavior are significantly different in the two cases. The copper chip remains crystalline while the silicon chip transforms into an amorphous state. The critical stress for crack propagation in silica glass was found to be in reasonable agreement with experiment and a novel stick-slip phenomenon was observed.

Belak, J.; Glosli, J.N.; Boercker, D.B.; Stowers, I.F.

1994-02-01

192

Single- and double-electron-capture processes in the collisions of C4+ ions with He  

NASA Astrophysics Data System (ADS)

The nonradiative single-electron-capture (SEC) and double-electron-capture (DEC) processes for C4+(1s2) colliding with He atoms are investigated by using the quantum-mechanical molecular-orbital close-coupling method. Total and state-selective electron-capture cross sections are calculated in the energy range of 10-6-6 keV/amu. For energies less than 2 keV/amu, the DEC dominates the electron-capture processes. As the energy increases, the SEC cross sections increase while the DEC cross sections decrease; when E > 2 keV/amu, the SEC process becomes the dominant mechanism. It is found that the SEC processes mainly result from the electron capture to n = 3 channels of C3+ ion for energy below 0.7 keV/amu and from n = 2 channels for E>0.7 keV/amu. Compared with the available theoretical calculations, better agreement is achieved between the present results and the available measurements for total DEC and SEC cross sections. For state-resolved cross sections, excellent agreement is obtained for two-electron capture to C2+(2s2), C2+(2s2p), and C2+(2p2) and one-electron capture to C3+(2s) and C3+(2p) between the present calculations and the available theoretical and experimental results.

Yan, L. L.; Wu, Y.; Qu, Y. Z.; Wang, J. G.; Buenker, R. J.

2013-08-01

193

Interstellar Processes Leading to Molecular Deuterium Enrichment and Their Detection  

NASA Technical Reports Server (NTRS)

Large deuterium (D) enrichments in meteoritic materials indicate that interstellar organic materials survived incorporation into parent bodies within the forming Solar System. These enrichments are likelier due to one or more of four distinct astrochemical processes. These are (1) low temperature gas phase ion-molecule reactions; (2) low temperature gas-grain reactions; (3) gas phase unimolecular photodissociation, and (4) ultraviolet photolysis in D-enriched ice mantles. Each of these processes should be associated with molecular carriers having, distinct regiochemical signatures (D placement on the product molecules, correlation with specific chemical functionalities, etc.). These processes are reviewed and specific spectroscopic signatures for the detection of these processes in space are identified and described.

Sandford, Scott A.; Kliss, Mark (Technical Monitor)

2001-01-01

194

Galaxy collisions.  

NASA Astrophysics Data System (ADS)

Theories of how galaxies, the fundamental constituents of large-scale structure, form and evolve have undergone a dramatic paradigm shift in the last few decades. Earlier views were of rapid, early collapse and formation of basic structures, followed by slow evolution of the stellar populations and steady buildup of the chemical elements. Current theories emphasize hierarchical buildup via recurrent collisions and mergers, separated by long periods of relaxation and secular restructuring. Thus, collisions between galaxies are now seen as a primary process in their evolution. This article begins with a brief history of how this once peripheral subject found its way to center stage. The author then tours parts of the vast array of collisional forms that have been discovered to date. Many examples are provided to illustrate how detailed numerical models and multiwaveband observations have allowed the general chronological sequence of collisional morphologies to be deciphered, and how these forms are produced by the processes of tidal kinematics, hypersonic gas dynamics, collective dynamical friction and violent relaxation. Galaxy collisions may trigger the formation of a large fraction of all the stars ever formed, and play a key role in fueling active galactic nuclei. Current understanding of the processes involved is reviewed. The last decade has seen exciting new discoveries about how collisions are orchestrated by their environment, how collisional processes depend on environment, and how these environments depend on redshift or cosmological time. These discoveries and prospects for the future are summarized in the final sections.

Struck, C.

195

Cosmic Collision  

NSDL National Science Digital Library

This Hubblesite website provides two movies about galaxy collisions. The first movie called "Cosmic Collision" details the collision of the Milky Way and the Andromeda galaxy. The second movie, "Striking Encounters", discusses the dynamics of galaxy collisions.

Space Telescope Science Institute, Formal E.; Administration, National A.

2005-04-27

196

Numerical simulation for polymer solutions based on a hybrid computation of multi-particle collision dynamics and coarse-grained molecular dynamics  

NASA Astrophysics Data System (ADS)

Numerical simulation of the flow-induced structure of complex fluids is an important issue in the flow analysis of complex fluids. Several schemes have been proposed for coupling the macro flow computation and the micro simulation of the inner structure of complex fluids. The present study proposed a numerical model based on a hybrid computation of multi particle collision dynamics (MPCD) and coarse-grained molecular dynamics (MD). The present model can easily treat hydrodynamic interactions among polymers, which play an important role in the dynamics of polymers in non-dilute solutions. In the MPCD, a solvent is represented by point-like particles (solvent particles) that move with a continuous distribution of velocities. The MPCD algorithm consists of a streaming step and a collision step. A scheme based on the MPC-AT+a algorithm for the collision step was adopted in the present simulation. Furthermore polymers were modeled by elastic dumbbells. The movement of beads of the dumbbells was computed using a coarse-grained MD, and the interaction among beads and solvent particles were considered in the collision step. Numerical simulations of shear flows were performed to analyze the dynamics of linear polymers. The numerical results agree well with both experimental results and predictions by other numerical methods.

Yamamoto, Takehiro; Masaoka, Norichika

2014-05-01

197

Study of hard scattering processes in multihadron production from gammagamma collisions at LEP  

Microsoft Academic Search

The production of multihadronic states in gammagamma collisions at LEP has been studied with the DELPHI detector. The analyzed data correspond to an integrated luminosity of about 32pb-1, collected in the LEP runs of 1990 1992. Minimum bias data and a sample of events with jets at high p T have been selected under the requirement that no scattered electron

P. Abreu; Apeldoorn van G. W; T. Adye; E. E. Agasi; Roy Aleksan; G. D. Alekseev; P. Allport; S. Almehed; F. M. L. Almeida Junior; S. J. Alvsvaag; Ugo Amaldi; A. Andreazza; P. Antilogus; W.-D. Apel; R. J. Apsimon; Y. Arnoud; B. Åsman; J.-E. Augustin; A. Augustinus; Paul Baillon; P. Bambade; F. Barao; R. Barate; Guido Barbiellini; Dimitri Yuri Bardin; G. J. Barker; A. Baroncelli; O. Barring; J. A. Barrio; Walter Bartl; M. J. Bates; Marco Battaglia; M. Baubillier; K.-H. Becks; M. Begalli; P. Beilliere; Yu A Belokopytov; P. Beltran; Alberto C Benvenuti; M. Berggren; D. Bertrand; F. Bianchi; M. Bigi; M. S. Bilenky; P. Billoir; J. Bjarne; D. Bloch; J. Blocki; S. Blyth; V. Bocci; P. N. Bogolubov; T. Bolognese; M. Bonesini; W. Bonivento; P. S. L. Booth; G. Borisov; C. Bosio; B. Bostjancic; S. Bosworth; O. Botner; B. Bouquet; C. Bourdarios; T. J. V. Bowcock; M. Bozzo; S. Braibant; P. Branchini; K. D. Brand; R. A. Brenner; H. Briand; C. Bricman; L. Brillault; R. C. A. Brown; P. Bruckman; J.-M. Brunet; A. Budziak; L. Bugge; T. Buran; A. Buys; J. A. M. A. Buytaert; M. Caccia; M. Calvi; A. J. Camacho Rozas; R. Campion; T. Bamporesi; V. Canale; K. Cankocak; F. Cao; F. Carena; P. Carrilho; L. Carroll; R. Cases; M. V. Castillo Gimenez; A. Cattai; F. R. Cavallo; L. Cerrito; V. Chabaud; A. Chan; M. Chapkin; Ph. Charpentier; J. Chauveau; P. Checchia; G. A. Chelkov; L. Chevalier; P. Chliapnikov; V. Chorowicz; J. T. M. Chrin; V. Cindro; P. Collins; J. L. Contreras; R. Contri; E. Cortina; G. Cosme; F. Couchot; H. B. Crawley; D. Crennell; G. Crosetti; J. Cuevas Maestro; S. Czellar; E. Dahl-Jensen; J. Dahm; B. Dalmagne; M. Dam; G. Damgaard; E. Daubie; A. Daum; P. D. Dauncey; M. Davenport; J. Davies; J. da Silva; C. Defoix; P. Delpierre; N. Demaria; A. de Angelis; H. de Boeck; W. de Boer; S. de Brabandere; C. de Clerq; M. D. M. de Fez Laso; C. de La Vaissiere; B. de Lotto; A. de Min; L. de Paula; H. Dijkstra; Lucia Di Ciaccio; F. Djama; J. Dolbeau; M. Donszelmann; K. Doroba; M. Dracos; J. Drees; M. Dris; Y. Dufour; F. Dupont; D M Edsall; L.-O. Eek; R. Ehret; T. Ekelof; G. Ekspong; A. Elliot Peisert; M. Elsing; J.-P. Engel; N. Ershaidat; M. Espirito Santo; D. Fassouliotis; M. Feindt; A. Fenyuk; A. Ferrer; T. A. Filippas; A Filippas-Tassos; H. Foeth; E. Fokitis; F. Fontanelli; K. A. J. Forbes; F. Formenti; J.-L. Fousset; S. Francon; B J Franek; P. Frenkiel; D E C Fries; A. G. Frodesen; R. Fruhwirth; F. Fulda-Quenzer; H. Furstenau; J A Fuster; D. Gamba; M. Gandelman; C. Garcia; J. Garcia; C. Gaspar; U. Gasparini; Ph. Gavillet; E. N. Gazis; J.-P. Gerber; P. Giacomelli; D. Gillespie; R. Gokieli; B. Golob; V. M. Golovatyuk; J. J. Gomez Y Cadenas; Gian P Gopal; L. Gorn; M. Gorski; Valerio Gracco; F. Grard; E. Graziani; G. Grosdidier; B. Grossetete; P. Gunnarsson; J. Guy; U. Haedinger; F. Hahn; M. Hahn; S. Hahn; S. Haider; Z. Hajduk; A. Hakansson; A. Hallgren; U. Hamacher; G. Hamel de Monchenault; W. Hao; F. J. Harris; V. Hedberg; R. Henriques; J. J. Hernandez; J. A. Hernando; P. Herquet; H. Herr; T. L. Hessing; C. O. Higgins; E. Higon; H. J. Hilke; T. S. Hill; S. D. Hodgson; T. Hofmokl; S.-O. Holmgren; P. J. Holt; D. Holthuizen; P. F. Honore; M. Houlden; K. Huet; K. Hultqvist; P. Ioannou; P.-S. Iversen; J. N. Jackson; R. Jacobsson; P. Jalocha; G. Jarlskog; P. Jarry; B. Jean-Marie; E. K. Johansson; M. Jonker; L. Jonsson; P. Juillot; M. Kaiser; G. Kalkanis; G. Kalmus; F. Kapusta; M. Karlsson; E. Karvelas; S. Katsanevas; E. C. Katsoufis; R. Keranen; B. A. Khomenko; N. N. Khovanski; B. King; N. J. Kjaer; H. Klein; A. Klovning; P. Kluit; A. Koch-Mehrin; J. H. Koehne; B. Koene; P. Kokkinias; M. Koratzinos; K. Korcyl; A. V. Korytov; V. Kostioukhine; C. Kourkoumelis; O. Kouznetsov; P. H. Kramer; M. Krammer; C. Kreuter; J. Krolikowski; I. Kronkvist; W. Krupinski; W. Kucewicz; K. Kulka; K. Kurvinen; C. Lacasta; C. Lambropoulos; J. W. Lamsa; L. Lanceri; P. Langefeld; V. Lapin; I. Last; J.-P. Laugier; R. Lauhakangas; G. Leder; F. Ledroit; Y. Lemoigne; J. Lemonne; G. Lenzen; V. Lepeltier; E. Lieb; D. Liko; J. Lindgren; R. Lindner; A. Lipniacka; I. Lippi; B. Loerstad; M. Lokajicek; J. G. Loken; A. Lopez-Fernandez; M. A. Lopez Aguera; M. Los; D. Loukas; J. J. Lozano; P. Lutz; L. Lyons; G. Maehlum; J. Maillard; A. Maio; A. Maltezos; F. Mandl; J. Marco; B. Marechal; M. Margoni; J.-C. Marin; C. Mariotti; A. Markou; T. Maron; S. Marti; C. Martinez-Rivero; F. Martinez-Vidal; F. Matorras; C. Matteuzzi; G. Matthiae; M. Mazzucato; M. McCubbin; R. McKay; R. McNulty; J. Medbo; C. Meroni; W. T. Meyer; M. Michelotto; E. Migliore; I. Mikulec; L. Mirabito; W. A. Mitaroff; G. V. Mitselmakher; U. Mjoernmark; T. Moa; R. Moeller; K. Moenig; M. R. Monge; P. Morettini; H. Mueller; W. J. Murray; B. Muryn; G. Myatt; F. Naraghi; F. L. Navarria; P. Negri; S. Nemecek; W. Neumann; N. Neumeister; R. Nicolaidou

1994-01-01

198

Measuring Hard Processes in RHIC A+A Collisions Through Leading Particles in PHENIX  

NASA Astrophysics Data System (ADS)

Understanding how single quarks and gluons propagate through high-temperature, high-density nuclear matter is of fundamental interest to both high-energy and nuclear physics. This propagation can be studied by observing the destinies of high-PT quarks and gluons created in initial parton-parton collisions within a high-energy nucleus-nucleus collision. Several theories predict that the effect of energy loss on a parton traveling through a deconfined QGP could dramatically impact the final jet PT spectrum in a RHIC A+A collision. While jet measurement through the traditional cone-energy-content method is problematic in the RHIC A+A environment, high-PT partons can be studied through the alternative of measuring leading particles, namely single high-PT hadrons and photons. The PHENIX experiment at RHIC has an excellent capability for studying --- i.e. reconstructing, identifying, and triggering on --- high-PT particles and so will be able to address hard scattering in RHIC A+A collisions in detail. A proposed program of jet-related measurements in PHENIX will be presented, and the parton-propagation physics they address will be discussed.

Stankus, Paul

1998-04-01

199

Process for attaching molecular wires and devices to carbon nanotubes and compositions thereof  

NASA Technical Reports Server (NTRS)

The present invention is directed towards processes for covalently attaching molecular wires and molecular electronic devices to carbon nanotubes and compositions thereof. Such processes utilize diazonium chemistry to bring about this marriage of wire-like nanotubes with molecular wires and molecular electronic devices.

Tour, James M. (Inventor); Bahr, Jeffrey L. (Inventor); Yang, Jiping (Inventor)

2008-01-01

200

Band structure and accumulation point in the spectrum of quantum collision operator in a one-dimensional molecular chain  

NASA Astrophysics Data System (ADS)

We consider the eigenvalue problem of a kinetic collision operator for a quantum Brownian particle interacting with a one-dimensional chain. The quantum nature of the system gives rise to a difference operator. For the one-dimensional case, the momentum space separates into infinite sets of disjoint subspaces dynamically independent of one another. The eigenvalue problem of the collision operator is solved with the continued fraction method. The spectrum is non-negative, possesses an accumulation point, and exhibits a band structure. We also construct the eigenvectors of the collision operator and establish their completeness and orthogonality relations in each momentum subspaces.

Tay, B. A.; Kanki, Kazuki; Tanaka, Satoshi; Petrosky, Tomio

2011-02-01

201

Mise en evidence d'un mecanisme simultane de production de fragments dans les collisions centrales du systeme (sup 86)Kr + (sup 197)Au a 60 MeV par nucleon. (Detection of simultaneous processes leading to multifragmentation in central collisions of the system (sup 86)Kr + (sup 197)Au, at 60 MeV per nucleon).  

National Technical Information Service (NTIS)

Multi-fragments production in intermediate-energy heavy ion collisions is the most important deexcitation process for hot nuclei produced in small impact-parameter collisions (central collisions). The study of the 60 A.MeV Kr+Au system, performed at GANIL...

O. Lopez

1993-01-01

202

Inhibition Of Molecular And Biological Processes Using Modified Oligonucleotides  

DOEpatents

A method of inhibiting at least one molecular process in a sample, comprising administering to the sample an oligonucleotide or polynucleotide containing at least one monomeric unit having formula (I): wherein A is an organic moiety, n is at least 1, and each X is independently selected from the group consisting of --NRCOCONu, --NHCOCR.sub.2 CR.sub.2 CONu, --NHCOCR.dbd.CRCONu, and --NHCOSSCONu, wherein each R independently represents H or a substituted or unsubstituted alkyl group, and Nu represents a nucleophile, or a salt of the compound.

Kozyavkin, Sergei A. (Germantown, MD) [Germantown, MD; Malykh, Andrei G. (Germantown, MD) [Germantown, MD; Polouchine, Nikolai N. (Montgomery Village, MD) [Montgomery Village, MD; Slesarev, Alexei I. (Germantown, MD) [Germantown, MD

2003-04-15

203

Fundamental processes in low energy collisions of alkali anions and atoms  

SciTech Connect

Negative ion sources often employ alkali metal atoms in one way or another in order to increase their yield. Models which describe equilibrium conditions or the nature of energy transport within these sources require, among other things, information about the two-body cross sections for various scattering channels which involve either alkali negative ions or alkali atoms. The purpose of this report is to provide a brief summary of recent experimental observations in which collisions of alkali anions (M/sup -/) with various atoms and molecules and collisions of H/sup -/ and D/sup -/ with alkali atoms (M) have been investigated. The energy range of the experiments, 5 < E < 500 eV, includes those kinetics energies often found in discharge-type ion sources. The specific experiments which will be discussed focus upon measurements of total cross sections for collisional electron detachment and charge transfer of negative ions. 16 refs., 7 figs.

Champion, R.L.; Doverspike, L.D.; Scott, D.M.; Wang, Y.

1986-01-01

204

Collision damage processes due to energetic heavy ions in silver chloride  

Microsoft Academic Search

The optical absorption band induced by energetic heavy ions implanted into AgCl single crystals at 77°K must be connected with the formation of silver colloids. The experimental (primitization and E.P.R. spectra) and theoretical study, makes it possible to obtain an approximate value of cluster radius. The colloid concentration is correlated with nuclear stopping power. It is shown that the collision

Ch. Diaine; J. L. Gisclon; J. Dupuy

1980-01-01

205

Measurements of scattering processes in negative ion: Atom collisions. Technical progress report, 1 September 1991--31 December 1994  

SciTech Connect

This report describes the progress made on the research objectives during the past three years of the grant. This research project is designed to study various scattering processes which occur in H{sup {minus}} collisions with atomic (specifically, noble gas and atomic hydrogen) targets in the intermediate energy region. These processes include: elastic scattering, single- and double-electron detachment, and target excitation/ionization. For the elastic and target inelastic processes where H{sup {minus}} is scattered intact, the experimental technique of Ion Energy-Loss Spectroscopy (IELS) will be employed to identify the final target state(s). In most of the above processes, cross sections are unknown both experimentally and theoretically. The measurements will provide total cross sections (TCS) initially, and once the angular positioning apparatus is installed, will provide angular differential cross sections (ADCS).

Kvale, T.J.

1994-09-27

206

Charge transfer processes: the role of optimized molecular orbitals.  

PubMed

The influence of the molecular orbitals on charge transfer (CT) reactions is analyzed through wave function-based calculations. Characteristic CT processes in the organic radical 2,5-di-tert-butyl-6-oxophenalenoxyl linked with tetrathiafulvalene and the inorganic crystalline material LaMnO3 show that changes in the inner shells must be explicitly taken into account. Such electronic reorganization can lead to a reduction of the CT vertical transition energy up to 66%. A state-specific approach accessible through an adapted CASSCF (complete active space self-consistent field) methodology is capable of reaching good agreement with the experimental spectroscopy of CT processes. A partitioning of the relaxation energy in terms of valence- and inner-shells is offered and sheds light on their relative importance. This work paves the way to the intimate description of redox reactions using quantum chemistry methods. PMID:24781811

Meyer, Benjamin; Domingo, Alex; Krah, Tim; Robert, Vincent

2014-08-01

207

Finding Novel Molecular Connections between Developmental Processes and Disease  

PubMed Central

Identifying molecular connections between developmental processes and disease can lead to new hypotheses about health risks at all stages of life. Here we introduce a new approach to identifying significant connections between gene sets and disease genes, and apply it to several gene sets related to human development. To overcome the limits of incomplete and imperfect information linking genes to disease, we pool genes within disease subtrees in the MeSH taxonomy, and we demonstrate that such pooling improves the power and accuracy of our approach. Significance is assessed through permutation. We created a web-based visualization tool to facilitate multi-scale exploration of this large collection of significant connections (http://gda.cs.tufts.edu/development). High-level analysis of the results reveals expected connections between tissue-specific developmental processes and diseases linked to those tissues, and widespread connections to developmental disorders and cancers. Yet interesting new hypotheses may be derived from examining the unexpected connections. We highlight and discuss the implications of three such connections, linking dementia with bone development, polycystic ovary syndrome with cardiovascular development, and retinopathy of prematurity with lung development. Our results provide additional evidence that plays a key role in the early pathogenesis of polycystic ovary syndrome. Our evidence also suggests that the VEGF pathway and downstream NFKB signaling may explain the complex relationship between bronchopulmonary dysplasia and retinopathy of prematurity, and may form a bridge between two currently-competing hypotheses about the molecular origins of bronchopulmonary dysplasia. Further data exploration and similar queries about other gene sets may generate a variety of new information about the molecular relationships between additional diseases.

Park, Jisoo; Wick, Heather C.; Kee, Daniel E.; Noto, Keith; Maron, Jill L.; Slonim, Donna K.

2014-01-01

208

Finding novel molecular connections between developmental processes and disease.  

PubMed

Identifying molecular connections between developmental processes and disease can lead to new hypotheses about health risks at all stages of life. Here we introduce a new approach to identifying significant connections between gene sets and disease genes, and apply it to several gene sets related to human development. To overcome the limits of incomplete and imperfect information linking genes to disease, we pool genes within disease subtrees in the MeSH taxonomy, and we demonstrate that such pooling improves the power and accuracy of our approach. Significance is assessed through permutation. We created a web-based visualization tool to facilitate multi-scale exploration of this large collection of significant connections (http://gda.cs.tufts.edu/development). High-level analysis of the results reveals expected connections between tissue-specific developmental processes and diseases linked to those tissues, and widespread connections to developmental disorders and cancers. Yet interesting new hypotheses may be derived from examining the unexpected connections. We highlight and discuss the implications of three such connections, linking dementia with bone development, polycystic ovary syndrome with cardiovascular development, and retinopathy of prematurity with lung development. Our results provide additional evidence that TGFB lays a key role in the early pathogenesis of polycystic ovary syndrome. Our evidence also suggests that the VEGF pathway and downstream NFKB signaling may explain the complex relationship between bronchopulmonary dysplasia and retinopathy of prematurity, and may form a bridge between two currently-competing hypotheses about the molecular origins of bronchopulmonary dysplasia. Further data exploration and similar queries about other gene sets may generate a variety of new information about the molecular relationships between additional diseases. PMID:24874013

Park, Jisoo; Wick, Heather C; Kee, Daniel E; Noto, Keith; Maron, Jill L; Slonim, Donna K

2014-05-01

209

The quasi-molecular absorption bands in UV region caused by the non-symmetric ion-atom radiative processes in the solar photosphere  

NASA Astrophysics Data System (ADS)

The aim of this research is to show that the radiative processes in strongly non- symmetric ion- atom collisions significantly influence on the opacity of the solar photosphere in UV region. Within this work only the He+H+ and H+A+ ion-atom systems, where A is the atom of one of the metal (Mg, Si and Al), are taken in to account. It is caused by the fact that the needed characteristics of the corresponding molecular ions, i.e. molecular potential curves and dipole matrix elements, have been determined by now. Here the non-symmetric radiative processes are considered under the conditions characterizing the non-LTE standard model of the solar atmosphere (Vernazza J, Avrett E and Loser R 1981 ApJS 45 635), which gives the possibility to perform all needed calculations and determined the corresponding spectral absorption coefficients. It is shown that the examined processes generate rather wide quasi-molecular absorption bands in the UV and VUV regions, whose intensity is comparable and sometimes even larger than the intensity of known one's caused by the H+H+ radiative collision processes, which are included now in the solar atmosphere models. Consequently, the presented results suggest that the non-symmetric ion-atom absorption processes have to be also included in standard models of the solar atmosphere.

Mihajlov, A. A.; Sre?kovi?, V. A.; Ignjatovi?, L. J. M.; Dimitrijevi?, M. S.; Metropoulos, A.

2012-12-01

210

Half-Collision Studies of Excited Metal Atom - Molecule Interactions  

Microsoft Academic Search

We report on state-resolved studies of excited state molecular dynamics, including both reactive and nonreactive (energy transfer) processes using half-collision techniques. Scattering state spectroscopy is used to investigate electronic orbital alignment effects on the reactive quenching of excited p-state alkali and alkaline earth metal atoms in collisions with hydrogen and methane. These experiments give information about the shape of the

P. D. Kleiber; J. Chen; T. H. Wong

1998-01-01

211

MOLECULAR CLOUDS IN THE TRIFID NEBULA M20: POSSIBLE EVIDENCE FOR A CLOUD-CLOUD COLLISION IN TRIGGERING THE FORMATION OF THE FIRST GENERATION STARS  

SciTech Connect

A large-scale study of the molecular clouds toward the Trifid Nebula, M20, has been made in the J = 2-1 and J = 1-0 transitions of {sup 12}CO and {sup 13}CO. M20 is ionized predominantly by an O7.5 star HD164492. The study has revealed that there are two molecular components at separate velocities peaked toward the center of M20 and that their temperatures-30-50 K as derived by a large velocity gradient analysis-are significantly higher than the 10 K of their surroundings. We identify the two clouds as the parent clouds of the first generation stars in M20. The mass of each cloud is estimated to be {approx}10{sup 3} M{sub sun} and their separation velocity is {approx}8 km s{sup -1} over {approx}1-2 pc. We find that the total mass of stars and molecular gas in M20 is less than {approx}3.2 x 10{sup 3} M{sub sun}, which is too small by an order of magnitude to gravitationally bind the system. We argue that the formation of the first generation stars, including the main ionizing O7.5 star, was triggered by the collision between the two clouds in a short timescale of {approx}1 Myr, a second example alongside Westerlund 2, where a super-star cluster may have been formed due to cloud-cloud collision triggering.

Torii, K.; Enokiya, R.; Sano, H.; Yoshiike, S.; Hanaoka, N.; Ohama, A.; Furukawa, N.; Dawson, J. R.; Moribe, N.; Oishi, K.; Nakashima, Y.; Okuda, T.; Yamamoto, H.; Kawamura, A.; Mizuno, N.; Onishi, T.; Fukui, Y. [Department of Physics and Astrophysics, Nagoya University, Chikusa-ku, Nagoya, Aichi 464-8601 (Japan); Maezawa, H. [Department of Astrophysics, Graduate School of Science, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531 (Japan); Mizuno, A., E-mail: torii@a.phys.nagoya-u.ac.jp [Solar-Terrestrial Environment Laboratory, Nagoya University, Chikusa-ku, Nagoya, Aichi 464-8601 (Japan)

2011-09-01

212

Atomic Realization of the Young Single Electron Interference Process in Individual Autoionization Collisions  

NASA Astrophysics Data System (ADS)

Young's double-slit demonstration, applied to the interference of single electrons, is considered to be one of the most beautiful experiments in Physics. This "gedanken" experiment proposed by R. Feynman in 1963, was achieved quite recently. Of course, the diffraction of electrons by atomic arrays had already been studied many decades before, but the novelty in these experiments was that one electron at a time collides with a single two-slit arrangement. Here we propose a novel atomic realization of a Young interference experiment, where a single electron source and a two-center scatterer are prepared in each collision event.

Barrachina, R. O.; Žitnik, M.

2006-11-01

213

Inelastic and ballistic processes resulting from CsF-Ar collisions. (Reannouncement with new availability information)  

SciTech Connect

This paper continues the study of inelastic and ballistic collisions for the CsF-Ar system using the impulse approximation (IA). The IA expresses the atom-diatom potential as the sum of the two atom-atom potentials. The atom-atom interaction is approximated by a hard core potential, and the laboratory differential cross sections are calculated for an initial relative translational energy of 1.0 eV as a function of the laboratory recoil velocity of CsF. The calculated differential cross sections are in excellent agreement with the experimental measurements for all eight laboratory scattering angles for which the data are available.

Sharma, R.D.; Sindoni, J.M.

1993-01-15

214

Reply to ‘Comment on “Four-body charge transfer processes in proton helium collisions”’  

NASA Astrophysics Data System (ADS)

Houamer and Popov have performed a first Born approximation calculation (FBA) for TTE (charge transfer with target excitation) for 300 keV proton-helium collisions. Their results are in reasonable agreement with the absolute measurements of Schöffler (2006 PhD thesis, University of Frankfurt am Main) whereas our FBA results yielded the shape of the experimental data reasonably well (except for small scattering angles) but with a magnitude that was a factor of 144 larger than experiment. Consequently, Houamer and Popov conclude that our results must have huge numerical errors. We have extensively tested our codes and we do not find any evidence to support this claim.

Chowdhury, U.; Harris, A. L.; Peacher, J. L.; Madison, D. H.

2013-01-01

215

Molecular chaperone GroEL/ES: unfolding and refolding processes.  

PubMed

Molecular chaperones are a special class of heat shock proteins (Hsp) that assist the folding and formation of the quaternary structure of other proteins both in vivo and in vitro. However, some chaperones are complex oligomeric proteins, and one of the intriguing questions is how the chaperones fold. The representatives of the Escherichia coli chaperone system GroEL (Hsp60) and GroES (Hsp10) have been studied most intensively. GroEL consists of 14 identical subunits combined into two interacting ring-like structures of seven subunits each, while the co-chaperone GroES interacting with GroEL consists of seven identical subunits combined into a dome-like oligomeric structure. In spite of their complex quaternary structure, GroEL and GroES fold well both in vivo and in vitro. However, the specific oligomerization of GroEL subunits is dependent on ligands and external conditions. This review analyzes the literature and our own data on the study of unfolding (denaturation) and refolding (renaturation) processes of these molecular chaperones and the effect of ligands and solvent composition. Such analysis seems to be useful for understanding the folding mechanism not only of the GroEL/GroES complex, but also of other oligomeric protein complexes. PMID:24490731

Ryabova, N A; Marchenkov, V V; Marchenkova, S Yu; Kotova, N V; Semisotnov, G V

2013-12-01

216

Solution processed molecular floating gate for flexible flash memories  

PubMed Central

Solution processed fullerene (C60) molecular floating gate layer has been employed in low voltage nonvolatile memory device on flexible substrates. We systematically studied the charge trapping mechanism of the fullerene floating gate for both p-type pentacene and n-type copper hexadecafluorophthalocyanine (F16CuPc) semiconductor in a transistor based flash memory architecture. The devices based on pentacene as semiconductor exhibited both hole and electron trapping ability, whereas devices with F16CuPc trapped electrons alone due to abundant electron density. All the devices exhibited large memory window, long charge retention time, good endurance property and excellent flexibility. The obtained results have great potential for application in large area flexible electronic devices.

Zhou, Ye; Han, Su-Ting; Yan, Yan; Huang, Long-Biao; Zhou, Li; Huang, Jing; Roy, V. A. L.

2013-01-01

217

Graphics processing units accelerated semiclassical initial value representation molecular dynamics  

NASA Astrophysics Data System (ADS)

This paper presents a Graphics Processing Units (GPUs) implementation of the Semiclassical Initial Value Representation (SC-IVR) propagator for vibrational molecular spectroscopy calculations. The time-averaging formulation of the SC-IVR for power spectrum calculations is employed. Details about the GPU implementation of the semiclassical code are provided. Four molecules with an increasing number of atoms are considered and the GPU-calculated vibrational frequencies perfectly match the benchmark values. The computational time scaling of two GPUs (NVIDIA Tesla C2075 and Kepler K20), respectively, versus two CPUs (Intel Core i5 and Intel Xeon E5-2687W) and the critical issues related to the GPU implementation are discussed. The resulting reduction in computational time and power consumption is significant and semiclassical GPU calculations are shown to be environment friendly.

Tamascelli, Dario; Dambrosio, Francesco Saverio; Conte, Riccardo; Ceotto, Michele

2014-05-01

218

Graphics processing units accelerated semiclassical initial value representation molecular dynamics.  

PubMed

This paper presents a Graphics Processing Units (GPUs) implementation of the Semiclassical Initial Value Representation (SC-IVR) propagator for vibrational molecular spectroscopy calculations. The time-averaging formulation of the SC-IVR for power spectrum calculations is employed. Details about the GPU implementation of the semiclassical code are provided. Four molecules with an increasing number of atoms are considered and the GPU-calculated vibrational frequencies perfectly match the benchmark values. The computational time scaling of two GPUs (NVIDIA Tesla C2075 and Kepler K20), respectively, versus two CPUs (Intel Core i5 and Intel Xeon E5-2687W) and the critical issues related to the GPU implementation are discussed. The resulting reduction in computational time and power consumption is significant and semiclassical GPU calculations are shown to be environment friendly. PMID:24811627

Tamascelli, Dario; Dambrosio, Francesco Saverio; Conte, Riccardo; Ceotto, Michele

2014-05-01

219

Genomic Signal Processing: Predicting Basic Molecular Biological Principles  

NASA Astrophysics Data System (ADS)

Advances in high-throughput technologies enable acquisition of different types of molecular biological data, monitoring the flow of biological information as DNA is transcribed to RNA, and RNA is translated to proteins, on a genomic scale. Future discovery in biology and medicine will come from the mathematical modeling of these data, which hold the key to fundamental understanding of life on the molecular level, as well as answers to questions regarding diagnosis, treatment and drug development. Recently we described data-driven models for genome-scale molecular biological data, which use singular value decomposition (SVD) and the comparative generalized SVD (GSVD). Now we describe an integrative data-driven model, which uses pseudoinverse projection (1). We also demonstrate the predictive power of these matrix algebra models (2). The integrative pseudoinverse projection model formulates any number of genome-scale molecular biological data sets in terms of one chosen set of data samples, or of profiles extracted mathematically from data samples, designated the ``basis'' set. The mathematical variables of this integrative model, the pseudoinverse correlation patterns that are uncovered in the data, represent independent processes and corresponding cellular states (such as observed genome-wide effects of known regulators or transcription factors, the biological components of the cellular machinery that generate the genomic signals, and measured samples in which these regulators or transcription factors are over- or underactive). Reconstruction of the data in the basis simulates experimental observation of only the cellular states manifest in the data that correspond to those of the basis. Classification of the data samples according to their reconstruction in the basis, rather than their overall measured profiles, maps the cellular states of the data onto those of the basis, and gives a global picture of the correlations and possibly also causal coordination of these two sets of states. Mapping genome-scale protein binding data using pseudoinverse projection onto patterns of RNA expression data that had been extracted by SVD and GSVD, a novel correlation between DNA replication initiation and RNA transcription during the cell cycle in yeast, that might be due to a previously unknown mechanism of regulation, is predicted. (1) Alter & Golub, Proc. Natl. Acad. Sci. USA 101, 16577 (2004). (2) Alter, Golub, Brown & Botstein, Miami Nat. Biotechnol. Winter Symp. 2004 (www.med.miami.edu/mnbws/alter-.pdf)

Alter, Orly

2005-03-01

220

Earthquake processes of the Himalayan collision zone in eastern Nepal and the southern Tibetan Plateau  

NASA Astrophysics Data System (ADS)

Focal mechanisms determined from moment tensor inversion and first motion polarities of the Himalayan Nepal Tibet Seismic Experiment (HIMNT) coupled with previously published solutions show the Himalayan continental collision zone near eastern Nepal is deforming by a variety of styles of deformation. These styles include strike-slip, thrust and normal faulting in the upper and lower crust, but mostly strike-slip faulting near or below the crust-mantle boundary (Moho). One normal faulting earthquake from this experiment accommodates east-west extension beneath the Main Himalayan Thrust of the Lesser Himalaya while three upper crustal normal events on the southern Tibetan Plateau are consistent with east-west extension of the Tibetan crust. Strike-slip earthquakes near the Himalayan Moho at depths >60 km also absorb this continental collision. Shallow plunging P-axes and shallow plunging EW trending T-axes, proxies for the predominant strain orientations, show active shearing at focal depths ~60-90 km beneath the High Himalaya and southern Tibetan Plateau. Beneath the southern Tibetan Plateau the plunge of the P-axes shift from vertical in the upper crust to mostly horizontal near the crust-mantle boundary, indicating that body forces may play larger role at shallower depths than at deeper depths where plate boundary forces may dominate.

de la Torre, T. L.; Monsalve, G.; Sheehan, A. F.; Sapkota, S.; Wu, F.

2007-11-01

221

An intestinal surgery simulator: real-time collision processing and visualization.  

PubMed

This research work is aimed toward the development of a VR-based trainer for colon cancer removal. It enables the surgeons to interactively view and manipulate the concerned virtual organs as during a real surgery. First, we present a method for animating the small intestine and the mesentery (the tissue that connects it to the main vessels) in real-time, thus enabling user interaction through virtual surgical tools during the simulation. We present a stochastic approach for fast collision detection in highly deformable, self-colliding objects. A simple and efficient response to collisions is also introduced in order to reduce the overall animation complexity. Second, we describe a new method based on generalized cylinders for fast rendering of the intestine. An efficient curvature detection method, along with an adaptive sampling algorithm, is presented. This approach, while providing improved tessellation without the classical self-intersection problem, also allows for high-performance rendering thanks to the new 3D skinning feature available in recent GPUs. The rendering algorithm is also designed to ensure a guaranteed frame rate. Finally, we present the quantitative results of the simulations and describe the qualitative feedback obtained from the surgeons. PMID:15527052

Raghupathi, Laks; Grisoni, Laurent; Faure, François; Marchal, Damien; Cani, Marie-Paule; Chaillou, Christophe

2004-01-01

222

Biological sample collection and processing for molecular epidemiological studies.  

PubMed

Molecular epidemiology uses biomarkers and advanced technology to refine the investigation of the relationship between environmental exposures and diseases in humans. It requires careful handling and storage of precious biological samples with the goals of obtaining a large amount of information from limited samples, and minimizing future research costs by use of banked samples. Many factors, such as tissue type, time of collection, containers used, preservatives and other additives, transport means and length of transit time, affect the quality of the samples and the stability of biomarkers and must be considered at the initial collection stage. An efficient study design includes provisions for further processing of the original samples, such as cryopreservation of isolated cells, purification of DNA and RNA, and preparation of specimens for cytogenetic, immunological and biochemical analyses. Given the multiple uses of the samples in molecular epidemiology studies, appropriate informed consent must be obtained from the study subjects prior to sample collection. Use of barcoding and electronic databases allow more efficient management of large sample banks. Development of standard operating procedures and quality control plans is a safeguard of the samples' quality and of the validity of the analyses results. Finally, specific state, federal and international regulations are in place regarding research with human samples, governing areas including custody, safety of handling, and transport of human samples, as well as communication of study results.Here, we focus on the factors affecting the quality and the potential future use of biological samples and some of the provisions that must be made during collection, processing, and storage of samples, based on our experience in the Superfund Basic Research Program and Children's Environmental Health Center, at the University of California, Berkeley. PMID:12787814

Holland, Nina T; Smith, Martyn T; Eskenazi, Brenda; Bastaki, Maria

2003-06-01

223

A molecular dynamics model of the orthogonal cutting process  

SciTech Connect

Material removal, as found in the cutting and grinding processes, is important in many areas of fabrication technology. Examples include high-speed machining by single point turning, surface milling and drilling. An idealized model that contains the essential physics of these processes is the two-dimensional orthogonal cutting geometry. Following the work of Shaw, an attempt is made to obtain a fundamental understanding of the commonly observed phenomena in the chip forming process: the atomistic mechanisms of plastic deformation within the primary shear zone and the observed shear angle ({phi}); the resultant energy flow from the tool doing work; the stress, strain and material flow fields; the morphology of the chip (smooth, segmented, crystalline or amorphous); the role of different depths of cut (t), rake angles ({alpha}), and clearance angles ({theta}); and the role of the tool tip radius, roughness (friction), and wear. The molecular dynamics computer simulation method is an ideal tool for the study of the atomistic mechanisms of these deformation processes. Simulations are performed for a model of copper at room temperature using 10{sup 3}--10{sup 6} atoms, depths of cut in the range l--50nm. and cutting speeds of 1--2500 meters per second (m/s). These simulations are strictly two dimensional (plane strain). Here, focus is on the chip forming process, the atomistic mechanisms of plastic deformation, the flow of energy into the chip and workpiece, and the material flow and stress fields for the orthogonal geometry ({alpha} = 0), sharp tools, and shallow depths of cut (t {approx} 5 nm). 5 refs., 3 figs.

Belak, J.F.; Stowers, I.F.

1990-07-16

224

Angular distributions of collision induced dissociation: Dependence on kinetic energy release  

Microsoft Academic Search

Collisions between molecular-ion projectiles and atomic targets at energies of a few keV\\/amu lead predominantly to dissociative capture (DC) and collision-induced dissociation (CID). The CID process can be driven by electronic or vibrational excitation. The angular distribution of electronic CID, defined as the dissociation yield versus the angle between the molecular dissociation axis and the beam direction, is predicted by

Kevin Carnes; Ben Berry; Wania Wolff; Nora G. Johnson; A. Max Sayler; Bishwanath Gaire; Mohammad Zohrabi; Jarlath McKenna; Itzik Ben-Itzhak

2010-01-01

225

Molecular solution processing of metal chalcogenide thin film solar cells  

NASA Astrophysics Data System (ADS)

The barrier to utilize solar generated electricity mainly comes from their higher cost relative to fossil fuels. However, innovations with new materials and processing techniques can potentially make cost effective photovoltaics. One such strategy is to develop solution processed photovoltaics which avoid the expensive vacuum processing required by traditional solar cells. The dissertation is mainly focused on two absorber material system for thin film solar cells: chalcopyrite CuIn(S,Se)2 (CISS) and kesterite Cu2ZnSn(S,Se) 4 organized in chronological order. Chalcopyrite CISS is a very promising material. It has been demonstrated to achieve the highest efficiency among thin film solar cells. Scaled-up industry production at present has reached the giga-watt per year level. The process however mainly relies on vacuum systems which account for a significant percentage of the manufacturing cost. In the first section of this dissertation, hydrazine based solution processed CISS has been explored. The focus of the research involves the procedures to fabricate devices from solution. The topics covered in Chapter 2 include: precursor solution synthesis with a focus on understanding the solution chemistry, CISS absorber formation from precursor, properties modification toward favorable device performance, and device structure innovation toward tandem device. For photovoltaics to have a significant impact toward meeting energy demands, the annual production capability needs to be on TW-level. On such a level, raw materials supply of rare elements (indium for CIS or tellurium for CdTe) will be the bottleneck limiting the scalability. Replacing indium with zinc and tin, earth abundant kesterite CZTS exhibits great potential to reach the goal of TW-level with no limitations on raw material availability. Chapter 3 shows pioneering work towards solution processing of CZTS film at low temperature. The solution processed devices show performances which rival vacuum-based techniques and is partially attributed to the ease in controlling composition and CZTS phase through this technique. Based on this platform, comprehensive characterization on CZTS devices is carried out including solar cells and transistors. Especially defects properties are exploited in Chapter 4 targeting to identify the limiting factors for further improvement on CZTS solar cells efficiency. Finally, molecular structures and precursor solution stability have been explored, potentially to provide a universal approach to process multinary compounds.

Yang, Wenbing

226

In vivo optical molecular imaging: principles and signal processing issues  

Microsoft Academic Search

In vivo optical molecular imaging involves the use of light emitting tracers combined with sophisticated sensing modalities to perform in vivo imaging of genetic and molecular information. In contrast to the classical diagnostic imaging tools which image the end effects of the diseases, optical molecular imaging could enhance our knowledge of biological phenomena, monitor genetic expression and the alteration of

Jong Chul Ye; Kevin Webb; Rick Millane; Charles Bouman

2005-01-01

227

Electron Capture Process in Collisions of Proton with Excited State of Helium  

NASA Astrophysics Data System (ADS)

Total and state-selective cross sections for single electron capture (SEC) from then = 2 excited state of helium colliding by protons are calculated in the energy range of 1.0-100.0keV/u by using the two-center atomic orbital close-coupling method. The interaction of the active electron with helium ion is represented by a model potential. Total SEC cross sections show a monotonic decreasing trend with increasing collision energy, and display a different behavior compared with the case from the ground state of helium. It is also found that the dominant reaction channel is captured to the H(2p) state up to 40keV/u, and then the capture to the H(1s) or H(2s) state becomes more pronounced. Moreover, the alignment dependence on the initial states is obtained for the electron capture from He(2p0) and He (2p1).

Wang, Xue-Rong; Liu, Ling; Wang, Jian-Guo

2010-12-01

228

Digital detection and processing of laser beacon signals for aircraft collision hazard warning  

NASA Technical Reports Server (NTRS)

A low-cost collision hazard warning system suitable for implementation in both general and commercial aviation is presented. Laser beacon systems are used as sources of accurate relative position information that are not dependent on communication between aircraft or with the ground. The beacon system consists of a rotating low-power laser beacon, detector arrays with special optics for wide angle acceptance and filtering of solar background light, microprocessors for proximity and relative trajectory computation, and pilot displays of potential hazards. The laser beacon system provides direct measurements of relative aircraft positions; using optimal nonlinear estimation theory, the measurements resulting from the current beacon sweep are combined with previous data to provide the best estimate of aircraft proximity, heading, minimium passing distance, and time to closest approach.

Sweet, L. M.; Miles, R. B.; Russell, G. F.; Tomeh, M. G.; Webb, S. G.; Wong, E. Y.

1981-01-01

229

The Role of Atomic and Molecular Processes in Magnetic Fusion Plasmas  

SciTech Connect

Plasma edge physics (plasmas with temperatures in the 1 to 100 eV range, near solid surfaces) has become a key issue in controlled nuclear fusion research. As for the physics of the fully ionized hot plasma core, appropriate dimensionless parameters have been identified: present fusion research acts like wind-channel experiments on downsized models, with respect to future fusion reactors. This is not longer possible for the plasma edge region due to dominant effects from atomic and surface processes. Integrated computational models comprising the physics of the plasma flow near boundaries, the atomic and molecular processes and the particle-surface interactions are the only tool to evaluate present experimental results (LHD, JT60, Tore Supra, JET,...) with respect to their relevance for future fusion power experiments (ITER) or a reactor.In particular proton and electron collisions with the hydrogenic molecules H2, O2, T2, DT, and their ions, play a key role in cooling and attenuating the magnetically confined plasma, before it hits exposed target surfaces. The surface released molecules travel in a bath of electrons and hydrogenic ions, with plasma temperatures (in the relevant region) in the 1 to 20 eV range, and typical (plasma) scale lengths are in the 1 to 10 cm range.Sample calculations with current fusion plasma edge codes, as e.g. used by the international design team for the ITER prototypical fusion reactor, applied to the tokamak with the highest divertor collisionality today (Alcator-C-Mod), are used to demonstrate these issues.

Reiter, Detlev; Baeva, Margarita; Marchuk, Oleksandr; Janev, Ratko K. [Institut fuer Plasmaphysik, Forschungszentrum Juelich GmbH, EURATOM Association, Trilateral Euregio Cluster, D-52425 Juelich (Germany)

2005-05-27

230

The Role of Atomic and Molecular Processes in Magnetic Fusion Plasmas  

NASA Astrophysics Data System (ADS)

Plasma edge physics (plasmas with temperatures in the 1 to 100 eV range, near solid surfaces) has become a key issue in controlled nuclear fusion research. As for the physics of the fully ionized hot plasma core, appropriate dimensionless parameters have been identified: present fusion research acts like wind-channel experiments on downsized models, with respect to future fusion reactors. This is not longer possible for the plasma edge region due to dominant effects from atomic and surface processes. Integrated computational models comprising the physics of the plasma flow near boundaries, the atomic and molecular processes and the particle-surface interactions are the only tool to evaluate present experimental results (LHD, JT60, Tore Supra, JET,...) with respect to their relevance for future fusion power experiments (ITER) or a reactor. In particular proton and electron collisions with the hydrogenic molecules H2, O2, T2, DT, and their ions, play a key role in cooling and attenuating the magnetically confined plasma, before it hits exposed target surfaces. The surface released molecules travel in a bath of electrons and hydrogenic ions, with plasma temperatures (in the relevant region) in the 1 to 20 eV range, and typical (plasma) scale lengths are in the 1 to 10 cm range. Sample calculations with current fusion plasma edge codes, as e.g. used by the international design team for the ITER prototypical fusion reactor, applied to the tokamak with the highest divertor collisionality today (Alcator-C-Mod), are used to demonstrate these issues.

Reiter, Detlev; Baeva, Margarita; Marchuk, Oleksandr; Janev, Ratko K.

2005-05-01

231

Molecular beam epitaxy for advanced gate stack materials and processes  

NASA Astrophysics Data System (ADS)

The material requirements for future CMOS generations - as given by the ITRS roadmap - are very challenging. This includes a high K dielectric without a low K interfacial layer, a high mobility channel and the appropriate metal gate. With the help of two projects INVEST and ET4US, we are building up a molecular beam epitaxy (MBE) infrastructure to grow this material set on large area wafers that can be further processed into small scale devices. In the INVEST project, we have developed an MBE system for the growth of complex oxides on semiconductors. The system follows the overall design of a production tool and is equipped with an RF atomic oxygen source, effusion cells, e-beam evaporators and a differential pumping stage. The oxide growth process starts with desorbing the initial surface oxide on the Si wafers in ultra-high vacuum and high temperature to create a clean reconstructed 2x1 surface. Using the atomic oxygen it is possible to oxidize the surface in a well controlled manner at low temperature and to grow very thin and dense SiOx layers, followed by the growth of 2-6 nm amorphous high K dielectrics. The process parameters permit to tune the interface layer from a SiOx rich to a silicide rich interface with a significant impact on the capacitance and the leakage. Initial focus is on developing an optimized growth recipe for high quality amorphous HfO2 and LaHfO3.5 films. This recipe was subsequently used to make wafers for a transistor batch that gave us the first N short channel MBE MOSFET's (100 nm) using an etched gate process flow. Some highlights of the first batch for 3nm HfO2 MOSFET are a high mobility (> 270 cm^2/Vs) with a corresponding low leakage current of 2 mA/cm^2). While there were some process issues for LaHfO3.5, the 3 nm MOSFET showed very low leakage currents below 10-6 A/cm^2. Interestingly all the LaHFO3.5 MOSFETs showed very low threshold voltage instabilities. In collaboration with C. Marchiori, M. Sousa, A.Guiller, H. Siegwart, D. Caimi, J. Fompeyrine, D. J Webb, C. Rossel, R. Germann of IBM Research GmbH Zurich Switzerland; L. Pantisano, M. Claes, T. Conard, M. Demand, W. Deweerd, S. DeGendt, M. Heyns, M. Houssa, M. Aoulaiche, G. Lujan, L. Ragnarsson, E. Rohr, T. Schram of IMEC Leuven Belgium; J. Hooker, Z.M Rittersma, Y. Furukawa of Philips Research Leuven Belgium and J. W. Seo of EPFL Lausanne Switzerland.

Locquet, Jean-Pierre

2005-03-01

232

Molecular Specificity of Multiple Hippocampal Processes Governing Fear Extinction  

PubMed Central

SYNOPSIS Over many years, fear extinction has been conceptualized as one dominant process, new inhibitory learning, which serves to dampen previously acquired fear. Here we present an alternative view, that brain region-specific processing of representations, expectations and emotional attributes of the fear-provoking event, recruits unique mechanisms that interdependently contribute to the conditioning and extinction of fear. The co-occurrence of these mechanisms within the fear circuit can thus be tracked and differentiated at a molecular and cellular level. Among others, the transcriptional regulators cFos, cAMP-dependent response element binding protein (CREB), Zif268, and extracellular signal-regulated kinases (Erk) stand out as hippocampal nuclear markers signaling novelty, arousal, retrieval, and prediction error, respectively. Consistent with evidence from human studies, these findings indicate that, beyond inhibitory learning, fear extinction requires modification of the emotional attributes and expectations that define the threatening context. Given the likely dysregulation of one or more of these processes in anxiety disorders, a key research challenge for the future is the identification and enhancement of individual extinction mechanisms to target the specific components of fear. Environmental stimuli lacking affective properties (conditioned stimuli, CS) rapidly become threatening if presented with stressful events (unconditioned stimuli, US). Consequently, based on a CS-US association, the presentation of the CS triggers species-specific fear responses until the US consistently stops occurring. At that point, new learning takes place and the fear response declines, a phenomenon termed extinction. The view that extinction occurs because a new, inhibitory CS-noUS association gains control over behavior 106, has remained dominant in the field (reviewed by 20,33,35,100). The implications of impaired fear regulation in the development of anxiety disorders have stimulate-d intense research in this area. Rodent studies identified the circuits involved in the conditioning and extinction of fear of salient cues 99,98,85,93,150, generating data that were confirmed in humans with brain imaging approaches 114,130. Nevertheless, research with experimental animals has not fully taken advantage of human data in order to better interpret extinction mechanisms in the framework of learning, expectation and emotion governing fear-motivated behavior. The present article aims to summarize recent molecular evidence on fear extinction, focusing on hippocampal mechanisms and experimental models of contextual fear, and compare the results with other relevant fear paradigms and human imaging studies. Instead of conceptualizing extinction learning as one process, such as CS-noUS association or inhibitory learning 19,26,96, we propose that fear extinction reflects the behavioral output of several region-specific learning processes that modify different components of the conditioning memory. The significance of these findings is discussed in the framework of fear regulation and anxiety disorders.

Radulovic, Jelena; Tronson, Natalie C.

2010-01-01

233

Electron transfer and spin-flip processes in atom-atom collisions from variationally improved time-dependent Hartree-Fock results  

Microsoft Academic Search

A variational functional for transition amplitudes is applied to atom-atom collisions using a time-dependent formalism. The transition amplitude is a functional of two independent trial wave functions with specified initial and final conditions, respectively. Transition probabilities are obtained by evaluating the functional in terms of standard time-dependent Hartree-Fock (TDHF) trial functions. The TDHF method is implemented by expanding the molecular

Bela Gazdy; David A. Micha

1987-01-01

234

Detailed seismic velocity structure beneath the Hokkaido corner, NE Japan: Collision process of the forearc sliver  

NASA Astrophysics Data System (ADS)

1. Introduction In south-eastern Hokkaido, the Kuril forearc sliver is colliding with the northeastern Japan arc due to the oblique subduction of the Pacific plate. This collision causes the formation of the Hidaka mountain range since the late Miocene (Kimura, 1986) and delamination of the lower-crust materials of the Kuril forearc sliver, which would be expected to descend into the mantle wedge below (e.g., Ito 2000; Ito and Iwasaki, 2002). In this study, we precisely investigated the three-dimensional seismic velocity structure beneath the Hokkaido corner to examine the collision of two forearcs in this area by using both of data from a dense temporary seismic network deployed in this area (Katsumata et al. [2006]) and those from the Kiban observation network, which covers the entire Japanese Islands with a station separation of 15-20 km. 2. Data and method The double-difference tomography method (Zhang and Thurber, 2003; 2006) was applied to a large number of arrival time data of 201,527 for P-waves and 150,963 for S-waves that were recorded at 125 stations from 10,971 earthquakes that occurred from 1999 to 2010. Grid intervals were set at 10 km in the along-arc direction, 12.5 km perpendicular to it, and 5-10 km in the vertical direction. 3. Results and discussion Inhomogeneous seismic velocity structure was clearly imaged in the Hokkaido corner at depths of 0-120 km. A high-velocity anomaly of P- and S- waves with a volume of 20 km x 90 km x 35km was detected just beneath the main zone of the Hidaka metamorphic belt at depths of 0-35 km. This high-velocity anomaly is continuously distributed from the depths of the mantle wedge to the surface. The western edge of the anomaly exactly corresponds to the Hidaka main thrust (HMT) at the surface. The highest velocity value in the anomaly corresponds to those of the uppermost mantle material (e.g. peridotite). The location of them at depths of 0-35km is also consistent with that of the Horoman-Peridotite belt, which is located at the southwestern edge of the main zone of the Hidaka metamorphic belt.On the other hand, a low-velocity anomaly of P- and S- waves with a volume of 80 km x 100 km x 50 km is distributed to the west of the Hidaka metamorphic belt at depths of 35-90km. This low-velocity anomaly seems to be continuously distributed from the continental crust of the NE Japan forearc. The velocity values of this low-V anomaly correspond to those of crustal materials, which is consistent with results of the tomographic study of Kita et al. [2010, EPSL] and Takanami et al. [1982]. Comparison with the results of seismic reflection surveys of Ito [2000] shows that the boundary between anomalous high-velocity mantle materials and low-velocity continental crustal materials just beneath the Hidaka main thrust (HMT) presently obtained is exactly consistent with the locations of reflection planes of their study. Moreover, our study also suggests that the anomalous low-velocity crustal materials at the mantle wedge depth appears to belong to the NE Japan forearc crust, which does not support the expectation of the previous studies that the delaminated lower-crust materials of the Kuril forearc sliver descends into the mantle wedge due to the collision.

Kita, S.; Hasegawa, A.; Okada, T.; Nakajima, J.; Matsuzawa, T.; Katsumata, K.

2010-12-01

235

Molecular Dynamics. VI. Free-Path Distributions and Collision Rates for Hard-Sphere and Square-Well Molecules  

Microsoft Academic Search

Free-path distributions and collision rates for systems of hard-sphere and square-well molecules are computed and compared to simple models. Mean free paths for solids and dense fluids are found to be within 2% of those predicted by dividing the kinetic-theory mean free path by the relative probability of two molecules in contact. These mean free paths are much smaller than

T. Einwohner; B. J. Alder

1968-01-01

236

Free-free quasi-molecular absorption and satellites in Lyman-alpha due to collisions with H and H^+^.  

NASA Astrophysics Data System (ADS)

We present new theoretical calculations of the total line profiles of Lyman ? including both red and blue far wings. All the transitions involved due to H-H and H-H^+^ collisions are taken into account and weighted by their dipole transition moments. The resulting profile shows a number of satellite features, at least two of which have been observed in ultraviolet spectra of hydrogen-rich white dwarfs.

Allard, N. F.; Koester, D.; Feautrier, N.; Spielfiedel, A.

1994-12-01

237

Quasiclassical R -matrix theory of inelastic processes in collisions of electrons with HCl molecules  

SciTech Connect

The {ital R}-matrix theory for the vibrational excitation and dissociative attachment in {ital e}-HCl collisions is developed. Only one pole in the {ital R}-matrix expansion is included. This allows for making a connection between the {ital R}-matrix and the nonlocal-complex-potential theories, and for obtaining the expression for the dissociative-attachment cross section without using the {ital R}-matrix radius in the internuclear coordinate. All matrix elements in the equation for the vibrational-excitation and dissociative-attachment amplitudes are calculated using the quasiclassical approach. We study how the results depend on the number of vibrational levels of the neutral molecule included in the theory and show how to exclude the vibrational continuum by a modification of the nonlocal-complex potential. The results for the vibrational-excitation cross sections are extremely sensitive to the behavior of the {ital R}-matrix potential curve near the point of crossing this curve with the potential curve of the neutral molecule. Particularly in some cases the cross section at the threshold peak exhibits the boomerang oscillations earlier found for HCl by Domcke (in {ital Aspects} {ital of} {ital Electron}{minus}{ital Molecule} {ital Scattering} {ital and} {ital Photoionization}, edited by A. Herzenberg (AIP, New Haven, 1989), p. 169). The dissociative-attachment cross sections are in reasonable agreement with experiment and with other theories.

Fabrikant, I.I. (Department of Physics and Astronomy, University of Nebraska, Lincoln, Nebraska 68588-0111 (US))

1991-04-01

238

Molecularly imprinted polymers in the drug discovery process  

Microsoft Academic Search

Since molecularly imprinted polymers (MIPs) are designed to have a memory for their molecular templates it is easy to draw parallels with the affinity between biological receptors and their substrates. Could MIPs take the place of natural receptors in the selection of potential drug molecules from synthetic compound libraries? To answer that question this review discusses the results of MIP

Daniel L. Rathbone

2005-01-01

239

Computer-aided molecular design of solvents for separation processes  

SciTech Connect

The search for potential solvents for liquid extraction and extractive distillation is carried out through a group contribution molecular design of solvents (MOLDES) approach. A set of submolecular groups (UNIFAC) is used for the synthesis of molecular structures with desired solvent properties. Submolecular group combination (linking) properties are characterized to ensure the chemical feasibility of the MOLDES generated molecular structures. The size of the combinatorial problem posed by the molecular synthesis procedure is reduced by group selection and by imposing physical and molecular constraints at different stages. Criteria are developed for solvent evaluation and the reliability of the VLE and the LLE UNIFAC parameter tables for solvent screening are compared with experimental data for the recovery of oxychemical by liquid extraction from dilute aqueous solutions.

Pretel, E.J.; Lopez, P.A.; Bottini, S.B.; Brignole, E.A. (UNS-CONICET, Bahia Blanca (Argentina))

1994-08-01

240

Tectonic significance of the Eratosthenes Seamount: a continental fragment in the process of collision with a subduction zone in the eastern Mediterranean (Ocean Drilling Program Leg 160)  

Microsoft Academic Search

One of the objectives of ODP Leg 160 in the eastern Mediterranean Sea (April–May, 1995) was concerned with the study of processes of genesis and incipient collision of an inferred crustal fragment, the Eratosthenes Seamount, with the active margin of the Eurasian plate to the north, represented by southern Cyprus. The upper part of the Eratosthenes Seamount (i.e. upper several

Alastair H. F Robertson

1998-01-01

241

Charge transfer, electronic quantum processes, and dissociation dynamics in molecule-surface collisions  

Microsoft Academic Search

In this paper some fundamental processes in molecule-surface dynamics are addressed; charge transfer from a metal surface to an incident or adsorbed particle, non-adiabatic electronic processes, and bond breaking dynamics. These processes are illustrated and discussed by referring to two recent experiments and the associated theories.The first example is Cl2 molecules impinging on a clean potassium surface [L. Hellberg, J.

Bengt Kasemo

1996-01-01

242

Molecular-orbital study of late-fission times in deep-inelastic 238U+238U collisions  

NASA Astrophysics Data System (ADS)

The U-like K-vacancy production probability in 7.5-MeV/nucleon deep-inelastic 238U+238U collisions has been measured for no-fission, single-fission, and double-fission exit channels. The results are interpreted using quasimolecular orbital correlations for diatomic and triatomic configurations. This leads to the determination of lower limits for the time scale for late fission of U-like products (>=8 and >=4 as) and their probability (>=77% and >=52%), at mean initial-excitation energies of ~40 and ~105 MeV, respectively.

Molitoris, J. D.; Meyerhof, W. E.; Stoller, Ch.; Anholt, R.; Spooner, D. W.; Moretto, L. G.; Sobotka, L. G.; McDonald, R. J.; Wozniak, G. J.; McMahan, M. A.; Blumenfeld, L.; Colonna, N.; Nessi, M.; Morenzoni, E.

1993-02-01

243

A new semiclassical decoupling scheme for electronic transitions in molecular collisions - Application to vibrational-to-electronic energy transfer  

NASA Technical Reports Server (NTRS)

A new semiclassical decoupling scheme (the trajectory-based decoupling scheme) is introduced in a computational study of vibrational-to-electronic energy transfer for a simple model system that simulates collinear atom-diatom collisions. The probability of energy transfer (P) is calculated quasiclassically using the new scheme as well as quantum mechanically as a function of the atomic electronic-energy separation (lambda), with overall good agreement between the two sets of results. Classical mechanics with the new decoupling scheme is found to be capable of predicting resonance behavior whereas an earlier decoupling scheme (the coordinate-based decoupling scheme) failed. Interference effects are not exhibited in P vs lambda results.

Lee, H.-W.; Lam, K. S.; Devries, P. L.; George, T. F.

1980-01-01

244

Tectonic processes during oblique collision: Insights from the St. Elias orogen, northern North American Cordillera  

USGS Publications Warehouse

Oblique convergence in the St. Elias orogen of southern Alaska and northwestern Canada has constructed the world's highest coastal mountain range and is the principal driver constructing all of the high topography in northern North America. The orogen originated when the Yakutat terrane was excised from the Cordilleran margin and was transported along margin-parallel strike-slip faults into the subduction-transform transition at the eastern end of the Aleutian trench. We examine the last 3 m.y. of this collision through an analysis of Euler poles for motion of the Yakutat microplate with respect to North America and the Pacific. This analysis indicates a Yakutat-Pacific pole near the present southern triple junction of the microplate and' predicts convergence to dextral-oblique convergence across the offshore Transition fault, onland structures adjacent to the Yakutat foreland, or both, with plate speeds increasing from 10 to 30 mm/yr from southeast to northwest. Reconstructions based on these poles show that NNW transport of the collided block into the NE trending subduction zone forced contraction of EW line elements as the collided block was driven into the subduction-transform transition. This suggests the collided block was constricted as it was driven into the transition. Constriction provides an explanation for observed vertical axis refolding of both earlier formed fold-thrust systems and the collisional suture at the top of the fold-thrust stack. We also suggest that this motion was partially accommodated by lateral extrusion of the western portion of the orogen toward the Aleutian trench. Important questions remain regarding which structures accommodated parts of this motion. The Transition fault may have accommodated much of the Yakutat-Pacific convergence on the basis of our analysis and previous interpretations of GPS-based geodetic data. Nonetheless, it is locally overlapped by up to 800 m of undeformed sediment, yet elsewhere shows evidence of young deformation. This contradiction could be produced if the overlapping sediments are too young to have accumulated significant deformation, or GPS motions may be deflected by transient strains or strains from poorly understood fault interactions. In either case, more data are needed to resolve the paradox. Copyright 2004 by the American Geophysical Union.

Pavlis, T. L.; Picornell, C.; Serpa, L.; Bruhn, R. L.; Plafker, G.

2004-01-01

245

Tectonic processes during oblique collision: Insights from the St. Elias orogen, northern North American Cordillera  

NASA Astrophysics Data System (ADS)

Oblique convergence in the St. Elias orogen of southern Alaska and northwestern Canada has constructed the world's highest coastal mountain range and is the principal driver constructing all of the high topography in northern North America. The orogen originated when the Yakutat terrane was excised from the Cordilleran margin and was transported along margin-parallel strike-slip faults into the subduction-transform transition at the eastern end of the Aleutian trench. We examine the last 3 m.y. of this collision through an analysis of Euler poles for motion of the Yakutat microplate with respect to North America and the Pacific. This analysis indicates a Yakutat-Pacific pole near the present southern triple junction of the microplate and predicts convergence to dextral-oblique convergence across the offshore Transition fault, onland structures adjacent to the Yakutat foreland, or both, with plate speeds increasing from 10 to 30 mm/yr from southeast to northwest. Reconstructions based on these poles show that NNW transport of the collided block into the NE trending subduction zone forced contraction of EW line elements as the collided block was driven into the subduction-transform transition. This suggests the collided block was constricted as it was driven into the transition. Constriction provides an explanation for observed vertical axis refolding of both earlier formed fold-thrust systems and the collisional suture at the top of the fold-thrust stack. We also suggest that this motion was partially accommodated by lateral extrusion of the western portion of the orogen toward the Aleutian trench. Important questions remain regarding which structures accommodated parts of this motion. The Transition fault may have accommodated much of the Yakutat-Pacific convergence on the basis of our analysis and previous interpretations of GPS-based geodetic data. Nonetheless, it is locally overlapped by up to 800 m of undeformed sediment, yet elsewhere shows evidence of young deformation. This contradiction could be produced if the overlapping sediments are too young to have accumulated significant deformation, or GPS motions may be deflected by transient strains or strains from poorly understood fault interactions. In either case, more data are needed to resolve the paradox.

Pavlis, Terry L.; Picornell, Carlos; Serpa, Laura; Bruhn, Ronald L.; Plafker, George

2004-06-01

246

Angular distribution of [delta] electrons emitted in collisions of 1. 0-MeV/u F[sup [ital q]+] ([ital q]=4,6,8,9) with molecular hydrogen  

SciTech Connect

The angular distribution, as well as the energy distribution of [delta] electrons produced in collisions of 1.0-MeV/u F[sup [ital q]+] ([ital q]=4,6,8,9) ions with molecular hydrogen, have been studied for laboratory observation angles ([theta][sub [ital L

Liao, C.; Richard, P.; Grabbe, S.R.; Bhalla, C.P.; Zouros, T.J.M.; Hagmann, S. (J.R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, Kansas 66506-2604 (United States))

1994-08-01

247

PTtD evolution of continental crust during subduction-collision processes : example of the Briançonnais domain (Western Alps, France).  

NASA Astrophysics Data System (ADS)

Understanding exhumation processes of high to ultra-high pressure (HP to UHP) terrains during plate convergence is a major challenge for the comprehension of plate convergence processes and mountain building. Contemporaneous contraction and extension coupled with erosion are frequently proposed to drive the exhumation process. In the internal alpine belt, HP and UHP metamorphism are recorded both in the Piemont oceanic unit and in the continental units such as the Internal Crystalline Massifs and the Briançonnais zone. In the western Alps, the consensus is to relate the top to NW then W directed D1 thrusting phase to nappe stacking and exhumation of the HP to UHP units within a subduction channel. Although there is an agreement on the occurrence of a top to the east D2 tectonic phase, its significance in terms of shortening or extensional deformation is controversial. On one hand, top to the east D2 shear zones and associated folds are interpreted as backthrusts or backfolds active during the Oligocene syn-collisional shortening phase, post-dating the exhumation of the HP units. On the other hand, D2 structures are interpreted as top the east normal faults that are active during the exhumation of the HP unit within a subduction channel. To decipher between these two different interpretations, we conducted a combined structural, petrological and geochronological study of the Modane-Aussois area in order to build a PTtD path of the Briançonnais zone. The current construction of a high velocity railway tunnel between the Maurienne and Susa valleys provides the opportunity to gather a large amount of geological data in the internal Western Alps and to extend surface observation at depth. We provide a structural analysis on ductile and brittle domains. New PT estimates are obtained using pseudosection and multiequilibra methods. Ar/Ar step heating on phengite provide time constraint on tectonic phases. Then, in light of our data and available literature, we focus on the significance of the D2 structures in the internal Western Alps. Results indicate that polyphased tectonic occurs during exhumation. The first deformation phase (D1) is characterized by nappe stacking in a context of top to the NW shearing, between 37 and 35 Ma deformation occurs between 1.0 and 0.5 GPa and 360-350°C. Top to the East deformation phase (D2) is associated with decompression up to 0.1 GPa and cooling down to 280°C. D2 deformations end at 31Ma. Following these phases of ductile deformation, two successive brittle deformation phases are evidenced: the first one is characterized by a N-S direction of extension and produce the overall tilting toward the south of the studied zone. The second one is characterized by E-W direction of extension. In the Internal Alps, the transition between Oceanic-continental subduction and continental collision occurred at 32Ma. In this context, D1 deformations that are dated between 37 and 35 Ma are clearly related to continental subduction. In the same way, brittle deformation phases are the expression of continental collision. The D2 tectonic phase took place at the transition between subduction and collision. Its attribution to one of these two processes remains ambiguous and will be discussed at the light of these new results.

Strzerzynski, P.; Guillot, S.; Leloup, P. H.; Arnaud, N.; Vidal, O.; Ledru, P.; Courrioux, G.; Darmendrail, X.

2009-04-01

248

and Two-Electron Processes in the Collisions of Multiply Charged Ions with Helium from Low to High Velocities  

Microsoft Academic Search

Ionization and electron capture in collisions of multiply charged ions with He from low to high velocities are investigated using novel coincident recoil momentum spectroscopy. The cross-over between dominance of capture and ionization is observed for highly charged ions. Strong onset of target direct ionization (SI) is observed at collision velocities around 1.5 a.u. This effective \\

Wuchun Wu

1994-01-01

249

Monte Carlo simulation in molecular gas dynamics  

Microsoft Academic Search

In the Monte Carlo simulation in the molecular gas dynamics, the behaviors of molecules are probabilistically simulated based on the Boltzmann equation assumptions, i.e., binary molecular collisions, molecular chaos, and vanishingly short time and small physical space for molecular collisions; the simulated molecules are probabilistically followed using random numbers on a computer through the molecular motions the molecular collisions, and

K. Koura

1983-01-01

250

A Hybrid approach to molecular continuum processes combiningGaussian basis functions and the discrete variable representation  

SciTech Connect

Gaussian basis functions, routinely employed in molecular electronic structure calculations, can be combined with numerical grid-based functions in a discrete variable representation to provide an efficient method for computing molecular continuum wave functions. This approach, combined with exterior complex scaling, obviates the need for slowly convergent single-center expansions, and allows one to study a variety of electron-molecule collision problems. The method is illustrated by computation of various bound and continuum properties of H2+.

Rescigno, Thomas N.; Horner, Daniel A.; Yip, Frank L.; McCurdy,C. William

2005-08-29

251

Comparison of nonequilibrium processes in p+Ni and p+Au collisions at GeV energies  

NASA Astrophysics Data System (ADS)

The energy and angular dependence of double differential cross sections d2?/d?dE were measured for p,d,t, He3,4,6, Li6,7,8, Be7,9,10, B10,11, and C produced in collisions of 1.2, 1.9, and 2.5 GeV protons with a Ni target. The shape of the spectra and angular distributions almost does not change whereas the absolute value of the cross sections increases by a factor ~1.7 for all ejectiles in this beam energy range. It was found that energy and angular dependencies of the cross sections cannot be reproduced by microscopic models of intranuclear cascade including coalescence of nucleons coupled to statistical model for evaporation of particles from excited, equilibrated residual nuclei. The inclusion of nonequilibrium processes, described by a phenomenological model of the emission from fast and hot moving sources, resulting from break up of the target nucleus, leads to very good reproduction of data. Cross sections of these processes are quite large, exhausting approximately half of the total production cross sections. Due to good reproduction of energy and angular dependencies of d2?/d?dE it was possible to determine total production cross sections for all studied ejectiles. Results obtained in this work point to the analogous reaction mechanism for proton induced reactions on Ni target as that observed previously for Au target in the same beam energy range.

Budzanowski, A.; Fidelus, M.; Filges, D.; Goldenbaum, F.; Hodde, H.; Jarczyk, L.; Kamys, B.; Kistryn, M.; Kistryn, St.; Kliczewski, St.; Kowalczyk, A.; Kozik, E.; Kulessa, P.; Machner, H.; Magiera, A.; Piskor-Ignatowicz, B.; Pysz, K.; Rudy, Z.; Siudak, R.; Wojciechowski, M.

2010-09-01

252

Gain control in molecular information processing: lessons from neuroscience  

NASA Astrophysics Data System (ADS)

Statistical properties of environments experienced by biological signaling systems in the real world change, which necessitates adaptive responses to achieve high fidelity information transmission. One form of such adaptive response is gain control. Here, we argue that a certain simple mechanism of gain control, understood well in the context of systems neuroscience, also works for molecular signaling. The mechanism allows us to transmit more than 1 bit (on or off) of information about the signal independent of the signal variance. It does not require additional molecular circuitry beyond that already present in many molecular systems, and in particular, it does not depend on existence of feedback loops. The mechanism provides a potential explanation for abundance of ultrasensitive response curves in biological regulatory networks.

Nemenman, Ilya

2012-04-01

253

Charged Higgs and neutral Higgs pair production of the weak gauge boson fusion process in electron-positron collisions  

NASA Astrophysics Data System (ADS)

Pair production of the neutral and charged Higgs bosons is a unique process that is a signature of the two-Higgs-doublet model. In this paper, we study the pair production and decays of the Higgses in the neutrinophilic two-Higgs-doublet model. The pair production occurs through the W and Z gauge boson fusion process. In the neutrinophilic model, the vacuum expectation value (VEV) of the second Higgs doublet is small and is proportional to the neutrino mass. The smallness of VEV is associated with the approximate global U(1) symmetry, which is slightly broken. Therefore, there is a suppression factor for the U(1) charge breaking process. The second Higgs doublet has U(1) charge; its single production from gauge boson fusion violates the U(1) charge conservation and is strongly suppressed. In contrast to the single production, the pair production of the Higgses conserves U(1) charge and the approximate symmetry does not forbid it. To search for the pair productions in a collider experiment, we study the production cross section of a pair of charged Higgs and neutral Higgs bosons in e^+ e^- collisions with a center of energy from 600 GeV to 2000 GeV. The total cross section varies from 10^{-4} fb to 10^{-3} fb for the degenerate (200 GeV) charged and neutral Higgs mass case. The background process to the signal is the gauge boson pair W^+ + Z production and their decays. We show that the signal over background ratio is about 2-3% by combining the cross section ratio with ratios of branching fractions.

Morozumi, Takuya; Tamai, Kotaro

2013-09-01

254

Driving ordering processes in molecular-dynamics simulations.  

PubMed

Self-organized criticality describes the emergence of complexity in dynamical nonequilibrium systems. In this paper we introduce a unique approach whereby a driven energy conversion is utilized as a sampling bias for ordered arrangements in molecular dynamics simulations of atomic and molecular fluids. This approach gives rise to dramatically accelerated nucleation rates, by as much as 30 orders of magnitude, without the need of predefined order parameters, which commonly employed rare-event sampling methods rely on. The measured heat fluxes suggest how the approach can be generalized. PMID:24877946

Dittmar, Harro; Kusalik, Peter G

2014-05-16

255

Driving Ordering Processes in Molecular-Dynamics Simulations  

NASA Astrophysics Data System (ADS)

Self-organized criticality describes the emergence of complexity in dynamical nonequilibrium systems. In this paper we introduce a unique approach whereby a driven energy conversion is utilized as a sampling bias for ordered arrangements in molecular dynamics simulations of atomic and molecular fluids. This approach gives rise to dramatically accelerated nucleation rates, by as much as 30 orders of magnitude, without the need of predefined order parameters, which commonly employed rare-event sampling methods rely on. The measured heat fluxes suggest how the approach can be generalized.

Dittmar, Harro; Kusalik, Peter G.

2014-05-01

256

Collision Energy Dependence of Defect Formation in Graphene  

SciTech Connect

Molecular dynamics simulations are performed using an empirical potential to simulate the collision process of an energetic carbon atom hitting a graphene sheet. According to the different impact locations within the graphene sheet, the incident threshold energies of different defects caused by the collision are determined to be 22 eV for a single vacancy, 36 eV for a divacancy, 60 eV for a Stone-Wales defect, and 65 eV for a hexavacancy. Study of the evolution and stability of the defects formed by these collisions suggests that the single vacancy reconstructs into a pentagon pair and the divacancy transforms into a pentagon-octagon-pentagon configuration. The displacement threshold energy in graphene is investigated by using the dynamical method, and a reasonable value 22.42 eV is clarified by eliminating the heating effect induced by the collision.

Mao, Fei [Beijing Normal University; Zhang, Chao [Beijing Normal University; Zhang, Yanwen [ORNL; Zhang, Fenf-Shou [Beijing Normal University

2012-01-01

257

Collision Energy Dependence of Defect Formation in Graphene  

NASA Astrophysics Data System (ADS)

Molecular dynamics simulations are performed using an empirical potential to simulate the collision process of an energetic carbon atom hitting a graphene sheet. According to the different impact locations within the graphene sheet, the incident threshold energies of different defects caused by the collision are determined to be 22 eV for a single vacancy, 36 eV for a divacancy, 60 eV for a Stone-Wales defect, and 65 eV for a hexavacancy. Study of the evolution and stability of the defects formed by these collisions suggests that the single vacancy reconstructs into a pentagon pair and the divacancy transforms into a pentagon-octagon-pentagon configuration. The displacement threshold energy in graphene is investigated by using the dynamical method, and a reasonable value 22.42 eV is clarified by eliminating the heating effect induced by the collision.

Mao, Fei; Zhang, Chao; Zhang, Yan-Wen; Zhang, Feng-Shou

2012-07-01

258

A Study of Energy Transfer Processes in Molecular Lasers.  

National Technical Information Service (NTIS)

A very brief summary is presented on the following research: Close coupling codes for the calculation of cross sections of interest to the molecular lasers N2, N2O, CO2, and CO; Extension of an existing computer program for the vibrational population dist...

A. J. Glass

1970-01-01

259

Molecular Structure and Diffusional Processes Across Intact Epidermis.  

National Technical Information Service (NTIS)

The penetration rate for small molecular weight alcohols is approximately given by the expression: Js = Kp Km dCs, where Kp = 0.001-3 cm/hr. is essentially the permeability constant for water in the membrane, Km is the membrane-water partition coefficient...

R. J. Scheuplein

1965-01-01

260

Collision Lab  

NSDL National Science Digital Library

Use an air hockey table to investigate simple collisions in 1D and more complex collisions in 2D. Experiment with the number of discs, masses, and initial conditions. Vary the elasticity and see how the total momentum and kinetic energy changes during collisions.

Simulations, Phet I.; Dubson, Mike; Loeblein, Trish; Perkins, Kathy; Gratny, Mindy; Olson, Jon

2010-10-01

261

Effect of Processing on the Molecular Structure, Rheology, Crystallization, Morphology and Physical Properties of Polyethylenes  

NASA Astrophysics Data System (ADS)

To develop an understanding of the physical properties of polyolefins, the basic thermodynamic, rheological and molecular structural features that characterize the melt and the crystalline state must be understood. The molecular structure; which includes molecular weight (MW), molecular weight distribution (MWD), short and long chain branching and the state of entanglement; strongly influence the processing and the physical properties of polyethylenes. In this presnetation we will focus on the role of long chain branching (LCB) and state of entanglement on the processing and properties of the linear polyethylenes (HDPE), high pressure branched polyethylenes (LDPE) and alpha-olefin copolymers (LLDPE).

Prasad, A.

1997-03-01

262

Collision-Induced Absorption Spectra of Binary Mixtures of Molecular Hydrogen with Molecular Deuterium and Argon and of Pure Hydrogen, D  

NASA Astrophysics Data System (ADS)

In the present research project a systematic study of the collision-induced infrared absorption (CIA) spectra of the binary mixtures of H_2 - D_2 in the region of the double fundamental vibrations of H_2 and D_2, and H_2 - Ar in the fundamental band of H_2, and of pure HD in its fundamental and first overtone regions was undertaken. The experiments were carried out with a 2.0 m high-pressure low-temperature transmission-type absorption cell at 77, 201 and 296 K at total gas densities up to 550 amagat. Infrared prism and grating spectrometers equipped with a microprocessor -controlled stepping motor were used to record the spectra. All the experimental results obtained represent first-time observations in collision-induced absorption. Collision-induced infrared absorption spectra of the double transitions of H_2(v=1>=ts 0) and D_2(v=1>=ts 0) have been observed at 77 and 201 K in the spectral region 7000-8000 cm^{-1} for total gas densities up to 550 amagat with a partial gas density ratio of 1:1 of H_2 and D_2. The observed spectra are interpreted in terms of the transitions, Q_1(J) of H_2+Q_1(J) of D _2, Q_1(J) of H_2+S _1(J) of D_2, S_1(J) of H_2 + Q_1(J) of D_2, and S_1(J) of H_2 + S_1(J) of D_2 for J = 0 and 1 for H _2 and J = 0, 1, and 2 for D_2. Analysis of the experimental absorption profiles was carried out using appropriate lineshape functions. The absorption coefficients, lineshape parameters, etc., are obtained from the analysis. Collision-induced enhancement absorption spectra of the fundamental band of H_2 in H_2 - Ar mixtures were recorded at room temperature for a base density of 72 amagat of H_2 for several partial densities of Ar up to 440 amagat. Hexadecapole-induced U transitions, U_1(1), U_1(2), Q_1(0)+U _0(1), and Q_1(1) + U_0(1) have been identified in the spectral region 5400 -6200 cm^{-1}. A "cage" model has been proposed to account for the double transitions of H_2 - H_2 in the H _2 - Ar enhancement spectra. From the analysis of the absorption profiles, the lineshape parameters and the absorption coefficients have been determined. The collision-induced absorption spectrum of the first overtone band of HD in the pure gas was observed at 77 K for gas densities up to 320 amagat. In addition to the allowed transitions P_2(1), R_2(0), and R_2(1), the CIA transitions Q_2(J)+Q_0(J), Q_1(J)+Q_1(J), Q_2(J)+S _0(J), S_2(J)+Q_0(J), Q _1(J)+S_1(J), S_2(J)+S_0(J), and S_1(J)+S_1(J) have been observed. An analysis of the observed absorption profiles has been completed. It is found that the isotropic overlap induction mechanism does not contribute to the intensity of the band and that negative contribution to the intensity of the band comes from the mixed term (2 sqrt{3}lambda_{32}exp [-(R - sigma)/rho_{32 }]times < vJmid Qmid v^' J^'>(R/a _0)^{-4}. The fundamental band of HD has been investigated at 77 K for gas densities in the range 40-310 amagat. For the first time the collision -induced transitions of the type T_1(1) + Q_0(J), Q_1(J) + T_0(1), U_1(0) + Q_0(J), Q_1(J) + U_0(0), V_1(0) + Q_0(J), and Q _1(J) + V_0(0) for HD have been identified. Here T, U, and V transitions correspond to DeltaJ = 3, 4, and 5, respectively.

Hsieh, Chang-Tsang William

263

Molecular Clouds toward the Super Star Cluster NGC 3603 Possible Evidence for a Cloud-Cloud Collision in Triggering the Cluster Formation  

NASA Astrophysics Data System (ADS)

We present new large field observations of molecular clouds with NANTEN2 toward the super star cluster NGC 3603 in the transitions 12CO(J = 2-1, J = 1-0) and 13CO(J = 2-1, J = 1-0). We suggest that two molecular clouds at 13 km s-1 and 28 km s-1 are associated with NGC 3603 as evidenced by higher temperatures toward the H II region, as well as morphological correspondence. The mass of the clouds is too small to gravitationally bind them, given their relative motion of ~20 km s-1. We suggest that the two clouds collided with each other 1 Myr ago to trigger the formation of the super star cluster. This scenario is able to explain the origin of the highest mass stellar population in the cluster, which is as young as 1 Myr and is segregated within the central sub-pc of the cluster. This is the second super star cluster along with Westerlund 2 where formation may have been triggered by a cloud-cloud collision.

Fukui, Y.; Ohama, A.; Hanaoka, N.; Furukawa, N.; Torii, K.; Dawson, J. R.; Mizuno, N.; Hasegawa, K.; Fukuda, T.; Soga, S.; Moribe, N.; Kuroda, Y.; Hayakawa, T.; Kawamura, A.; Kuwahara, T.; Yamamoto, H.; Okuda, T.; Onishi, T.; Maezawa, H.; Mizuno, A.

2014-01-01

264

Experimental impact cratering provides ground truth data for understanding planetary-scale collision processes  

NASA Astrophysics Data System (ADS)

Impact cratering is generally accepted as one of the primary processes that shape planetary surfaces in the solar system. While post-impact analysis of craters by remote sensing or field work gives many insights into this process, impact cratering experiments have several advantages for impact research: 1) excavation and ejection processes can be directly observed, 2) physical parameters of the experiment are defined and can be varied, and 3) cratered target material can be analyzed post-impact in an unaltered, uneroded state. The main goal of the MEMIN project is to comprehensively quantify impact processes by conducting a stringently controlled experimental impact cratering campaign on the meso-scale with a multidisciplinary analytical approach. As a unique feature we use two-stage light gas guns capable of producing impact craters in the decimeter size-range in solid rocks that, in turn, allow detailed spatial analysis of petrophysical, structural, and geochemical changes in target rocks and ejecta. In total, we have carried out 24 experiments at the facilities of the Fraunhofer EMI, Freiburg - Germany. Steel, aluminum, and iron meteorite projectiles ranging in diameter from 2.5 to 12 mm were accelerated to velocities ranging from 2.5 to 7.8 km/s. Targets were solid rocks, namely sandstone, quartzite and tuff that were either dry or saturated with water. In the experimental setup, high speed framing cameras monitored the impact process, ultrasound sensors were attached to the target to record the passage of the shock wave, and special particle catchers were positioned opposite of the target surface to capture the ejected target and projectile material. In addition to the cratering experiments, planar shock recovery experiments were performed on the target material, and numerical models of the cratering process were developed. The experiments resulted in craters with diameters up to 40 cm, which is unique in laboratory cratering research. Target porosity exponentially reduces crater volumes and cratering efficiency relative to non-porous rocks, and also yields less steep ejecta angles. Microstructural analysis of the subsurface shows a zone of pervasive grain crushing and pore space reduction. This is in good agreement with new mesoscale numerical models, which are able to quantify localized shock pressure behavior in the target's pore space. Planar shock recovery experiments confirm these local pressure excursions, based on microanalysis of shock metamorphic features in quartz. Saturation of porous target rocks with water counteracts many of the effects of porosity. Post-impact analysis of projectile remnants shows that during mixing of projectile and target melts, the Fe of the projectile is preferentially partitioned into target melt to a greater degree than Ni and Co. We plan to continue evaluating the experimental results in combination with numerical models. These models help to quantify and evaluate cratering processes, while experimental data serve as benchmarks to validate the improved numerical models, thus helping to "bridge the gap" between experiments and nature. The results confirm and expand current crater scaling laws, and make an application to craters on planetary surfaces possible.

Poelchau, Michael H.; Deutsch, Alex; Kenkmann, Thomas

2013-04-01

265

Molecular Ion Dissociation Processes in a Partially Cooled Electrostatic Trap  

NASA Astrophysics Data System (ADS)

An experimental capability being developed at the Oak Ridge National Laboratory Multi-Charged Ion Research Facility (ORNL MIRF) is described that enables stored cooling and state characterization of atomic and molecular ions of essentially any mass. Ions selected from a variety of available (hot and cold) sources are injected into a 1.5 meter long electrostatic mirror trap, in which excited internal states decay by radiative cooling. Ion lifetime studies or direct measurements of 'in-trap' interactions of molecular ions with electrons or atomic targets are accomplished with either a crossed electron beam or atomic beam (with recoil ion detection) located in the field-free region of the ion-trap, coupled with product velocity imaging. Similarly, extraction of trap-cooled ions can be used 'out-of-trap' for near state-specific electron capture (EC) and dissociative charge exchange (DCE) studies employing higher resolution COLTRIMS techniques coupled with fragment imaging.

Vane, C. R.; Bannister, M. E.; Deng, S.; Fogle, M.; Thomas, R. D.

2011-07-01

266

Molecular and genetic diversity in the metastatic process of melanoma.  

PubMed

Diversity between metastatic melanoma tumours in individual patients is known; however, the molecular and genetic differences remain unclear. To examine the molecular and genetic differences between metastatic tumours, we performed gene-expression profiling of 63 melanoma tumours obtained from 28 patients (two or three tumours/patient), followed by analysis of their mutational landscape, using targeted deep sequencing of 1697 cancer genes and DNA copy number analysis. Gene-expression signatures revealed discordant phenotypes between tumour lesions within a patient in 50% of the cases. In 18 of 22 patients (where matched normal tissue was available), we found that the multiple lesions within a patient were genetically divergent, with one or more melanoma tumours harbouring 'private' somatic mutations. In one case, the distant subcutaneous metastasis of one patient occurring 3?months after an earlier regional lymph node metastasis had acquired 37 new coding sequence mutations, including mutations in PTEN and CDH1. However, BRAF and NRAS mutations, when present in the first metastasis, were always preserved in subsequent metastases. The patterns of nucleotide substitutions found in this study indicate an influence of UV radiation but possibly also DNA alkylating agents. Our results clearly demonstrate that metastatic melanoma is a molecularly highly heterogeneous disease that continues to progress throughout its clinical course. The private aberrations observed on a background of shared aberrations within a patient provide evidence of continued evolution of individual tumours following divergence from a common parental clone, and might have implications for personalized medicine strategies in melanoma treatment. PMID:24399611

Harbst, Katja; Lauss, Martin; Cirenajwis, Helena; Winter, Christof; Howlin, Jillian; Törngren, Therese; Kvist, Anders; Nodin, Björn; Olsson, Eleonor; Häkkinen, Jari; Jirström, Karin; Staaf, Johan; Lundgren, Lotta; Olsson, Håkan; Ingvar, Christian; Gruvberger-Saal, Sofia K; Saal, Lao H; Jönsson, Göran

2014-05-01

267

A comparison of the charge transfer and collisional activation processes in collisions between keV He + and CO 2  

Microsoft Academic Search

A commercial mass spectrometer coupled with a spectrograph and charge-coupled device (CCD) was used to obtain the collision-induced emission (CIE) spectra (190–1020nm) from 4 to 8keV collisions between projectile He+ ions and CO2 target gas (He+\\/CO2). The observed emissions were from the A2?u+ and B2?u+ states of CO2+, excited states of He, along with excited fragments. The relative vibrational population

Yawei Lin; Paul M. Mayer

2010-01-01

268

Evaluation of the Influence of Amino Acid Composition on the Propensity for Collision-Induced Dissociation of Model Peptides Using Molecular Dynamics Simulations  

SciTech Connect

The dynamical behavior of model peptides was evaluated with respect to their ability to form internal proton donor-acceptor pairs using molecular dynamics simulations. The proton donor-acceptor pairs are postulated to be prerequisites for peptide bond cleavage resulting in formation of b and y ions during low energy collision-induced dissociation in tandem mass spectrometry (MS/MS). The simulations for the polyalanine pentamer Ala5H+ were compared to experimental data from collision energy-resolved surface induced dissociation (SID) studies. The results of the simulation are insightful into the events that likely lead up to the fragmentation of peptides. 9-mer polyalanine-based model peptides were used to examine the dynamical effect of each of the 20 common amino acids on the probability to form donor-acceptor pairs at labile peptide bonds. A continuous range of probabilities was observed as a function of the substituted amino acid. However, the location of the peptide bond involved in the donor-acceptor pair plays a critical role in the dynamical behavior. This influence of position on the probability of forming a donor-acceptor pair would be hard to predict from statistical analyses on experimental spectra of aggregate, diverse peptides. In addition, the inclusion of basic side chains in the model peptides alters the probability of forming donor-acceptor pairs across the entire backbone. In this case there are still more ionizing protons than basic residues, but the side chains of the basic amino acids form stable hydrogen bond networks with the peptide carbonyl oxygens and thus act to prevent free access of “mobile protons” to labile peptide bonds. It is clear from the work that the identification of peptides from low-energy CID using automated computational methods should consider the location of the fragmenting bond as well as the amino acid composition.

Cannon, William R.; Taasevigen, Danny J.; Baxter, Douglas J.; Laskin, Julia

2007-09-01

269

Corresponding aspects of strong-field multiquantum processes and ion-atom collisions  

NASA Astrophysics Data System (ADS)

An approximate correspondence between collisional processes and the interaction of atoms with intense short pulses of radiation yields simple relations connecting the parameters governing these two classes of phenomena. This correspondence can be visualized by the consideration of suitable constructed trajectories representing the radiative (multiphoton) and collisional interactions. Comparisons of spectral data in the extreme ultraviolet region for Ne, Ar, Kr, and Xe produced by collisional excitation and subpicosecond ultraviolet laser irradiation indicate approximate conformance with the expectations stemming from this analysis. These results suggest that, for ultraviolet radiation, this approach may be useful in understanding the gross features of the strong-field multiquantum interaction over the range of intensity spanning from about 10 to the 16th W/sq cm to about 10 to the 21st W/sq cm.

Boyer, K.; Gibson, G.; Jara, H.; Luk, T. S.; McIntyre, I. A.

1988-10-01

270

Hot gas, Masers, and Cloud Collisions: The extreme properties of molecular gas at the heart of the Milky Way Galaxy  

NASA Astrophysics Data System (ADS)

Molecular gas properties in the central 500 parsecs of the Galaxy are markedly different from those in the Galactic disk. Galactic center gas clouds are characterized by large, turbulent line widths, high temperatures, and substantial densities-\\ however, existing constraints on the extremes of these properties are poor. We present new results from surveys of Galactic center molecular gas with the Karl G. Jansky VLA and the Robert C. Byrd GBT which probe the Galactic center ISM at higher resolutions and higher energies than any previous work. Our surveys, primarily using the ammonia molecule, present new limits on the turbulence, temperature, and density in these molecular clouds. This poster focuses in the M0.25+0.01 cloud, a massive and apparently starless cloud which is the focus of numerous recent studies. Results include the detection of an extremely hot (T˜400-500 K) molecular gas component, and new masers, including unexpectedly abundant Class I methanol maser emission which appears to trace large-scale shock structure.

Mills, Elisabeth A. C.; Morris, Mark R.; Lang, Cornelia C.; Butterfield, Natalie; Ludovici, Dominic; Schmitz, Susan; Ott, Juergen

2013-07-01

271

Performance of an Arc-Heated Supersonic Molecular Beam and Its Application to Molecule-Molecule Collision Studies.  

National Technical Information Service (NTIS)

Bases for designs of the several components of an intermediate-energy high-intensity molecular beam are presented. Intermediate energies and high intensities are realized as a consequence of heating the beam gas in an electric arc and then converting the ...

E. L. Knuth N. M. Kuluva

1967-01-01

272

The role of orbital dynamics and cloud-cloud collisions in the formation of giant molecular clouds in global spiral structures  

NASA Technical Reports Server (NTRS)

The role of orbit crowding and cloud-cloud collisions in the formation of GMCs and their organization in global spiral structure is investigated. Both N-body simulations of the cloud system and a detailed analysis of individual particle orbits are used to develop a conceptual understanding of how individual clouds participate in the collective density response. Detailed comparisons are made between a representative cloud-particle simulation in which the cloud particles collide inelastically with one another and give birth to and subsequently interact with young star associations and stripped down simulations in which the cloud particles are allowed to follow ballistic orbits in the absence of cloud-cloud collisions or any star formation processes. Orbit crowding is then related to the behavior of individual particle trajectories in the galactic potential field. The conceptual picture of how GMCs are formed in the clumpy ISMs of spiral galaxies is formulated, and the results are compared in detail with those published by other authors.

Roberts, William W., Jr.; Stewart, Glen R.

1987-01-01

273

Transfer-excitation processes in collisions of N{sup 3+} ions with H{sub 2}, He, Ne, and Ar targets  

SciTech Connect

High-resolution translational energy-gain spectra for single-electron capture by N{sup 3+} ions from H{sub 2}, He, Ne, and Ar have been measured experimentally at laboratory impact energies of 6, 9, 12, and 15 keV. For N{sup 3+}-He and Ne collisions, transfer excitation into the 2{ital s}2{ital p}{sup 2} state of N{sup 2+} is significantly populated, while in N{sup 3+}-H{sub 2} collisions, transfer excitation into the 2{ital s}2{ital p}{sup 2}{sup 2}{ital P} state dominates at low energies. In N{sup 3+}-Ar collisions, pure single-electron capture into 3{ital s} is selectively populated. In all the collision systems studied here, contributions from processes commencing with a long-lived metastable state of N{sup 3+}{bold (}2{ital s}({sup 2}{ital S})2{ital p}{sup 3}{ital P}{bold )} are detected. The translational energy-gain spectra are interpreted qualitatively in terms of the reaction windows, which are calculated using the single-crossing Landau-Zener model and the extended version of the classical over-the-barrier model. Total cross sections for single-electron capture for N{sup 3+} ions colliding with He and H{sub 2} are also measured and compared with available measurements and theoretical calculations. {copyright} {ital 1996 The American Physical Society.}

Kamber, E.Y.; Akguengoer, K. [Department of Physics, Western Michigan University, Kalamazoo, Michigan 49008-5151 (United States)] [Department of Physics, Western Michigan University, Kalamazoo, Michigan 49008-5151 (United States); Leather, C.; Brenton, A.G. [Mass Spectrometry Research Unit, University of Wales Swansea, Swansea SA28PP (United Kingdom)] [Mass Spectrometry Research Unit, University of Wales Swansea, Swansea SA28PP (United Kingdom)

1996-08-01

274

Charge dependence of one and two electron processes in collisions between hydrogen molecules and fast projectiles  

SciTech Connect

The ratio of double to single ionization (DI/SI) as well as the ratio of ionization-excitation to single ionization (IE/SI) in hydrogen molecules was studied by examining the effect of the projectile charge on these processes. The DI/SI and IE/SI ratios were measured using the coincidence time of flight technique at a fixed velocity (corresponding to 1 MeV/amu) over a range of projectile charge states (q=1-9,14,20). The results for a highly charged Cu{sup 20+} projectile, for example, indicate that the DI/SI and IE/SI ratios are 11{percent} and 45{percent}, respectively, a large increase from the ratios of 0.13{percent} and 1.95{percent}, respectively, for H{sup +} projectiles. The DI/SI ratio increases much more rapidly with projectile charge than the IE/SI ratio. In addition, the results show that the rate of increase of both these ratios decreases for highly charged projectiles. {copyright} {ital 1997 American Institute of Physics.}

Wells, E.; Ben-Itzhak, I.; Carnes, K.D. [James R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, Kansas 66506-2604 (United States); Krishnamurthi, V. [James R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, Kansas 66506-2604 (United States)]|[Etec Systems Inc., 26460 Corporate Ave., Hayward, California 94545 (United States)

1997-02-01

275

Entropy and chemical change. 1: Characterization of product (and reactant) energy distributions in reactive molecular collisions: Information and enthropy deficiency  

NASA Technical Reports Server (NTRS)

Optimal means of characterizing the distribution of product energy states resulting from reactive collisions of molecules with restricted distributions of initial states are considered, along with those for characterizing the particular reactant state distribution which yields a given set of product states at a specified total energy. It is suggested to represent the energy-dependence of global-type results in the form of square-faced bar plots, and of data for specific-type experiments as triangular-faced prismatic plots. The essential parameters defining the internal state distribution are isolated, and the information content of such a distribution is put on a quantitative basis. The relationship between the information content, the surprisal, and the entropy of the continuous distribution is established. The concept of an entropy deficiency, which characterizes the specificity of product state formation, is suggested as a useful measure of the deviance from statistical behavior. The degradation of information by experimental averaging is considered, leading to bounds on the entropy deficiency.

Bernstein, R. B.; Levine, R. D.

1972-01-01

276

Heavy particle atomic collisions in astrophysics: Beyond H and He targets  

SciTech Connect

The physical conditions relating to the emission of x-rays from Jovian and cometary atmospheres and to supernova ejecta are briefly described. Emphasis is placed on elucidating the relevance and importance of atomic collision processes, the availability of data, and the outstanding data needs for modeling these environments. Some preliminary theoretical studies of electron capture for important collisions systems, involving molecular and atomic metal targets, are presented. {copyright} {ital 1998 American Institute of Physics.}

Stancil, P.C.; Krstic, P.S.; Schultz, D.R. [Physics Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831-6372 (United States)

1998-09-01

277

Heavy particle atomic collisions in astrophysics: Beyond H and He targets  

SciTech Connect

The physical conditions relating to the emission of x-rays from Jovian and cometary atmospheres and to supernova ejecta are briefly described. Emphasis is placed on elucidating the relevance and importance of atomic collision processes, the availability of data, and the outstanding data needs for modeling these environments. Some preliminary theoretical studies of electron capture for important collisions systems, involving molecular and atomic metal targets, are presented.

Stancil, P.C.; Krstic, P.S.; Schultz, D.R.

1998-06-01

278

Nonperturbative treatment of multielectron processes in ion-molecule scattering: Application to He{sup 2+}-H{sub 2} collisions  

SciTech Connect

We present a nonperturbative theory to describe multielectronic processes occurring in the course of collisions between an ion and a molecule. The approach is based on the expansion of the electronic scattering wave function onto asymptotic mono- or multicenter states with proper translational conditions and includes both static and dynamical electronic correlations. Therefore, it has a wide application range around intermediate impact velocities v{approx_equal}v{sub e}, where v{sub e} is the averaged electron velocity in the initial state. As a first application, we report results on single- and double-electron capture processes in He{sup 2+}-H{sub 2} collisions for impact energies ranging from 0.01 to 25 keV/u. Special emphasis on the prediction of cross sections for double-electron capture into doubly excited states of helium is addressed.

Sisourat, Nicolas; Dubois, Alain [Laboratoire de Chimie Physique - Matiere et Rayonnement, UMR 7614, UPMC Universite Paris 6, 11 rue Pierre et Marie Curie, F-75231 Paris Cedex 05 (France); LCPMR, UMR 7614, CNRS, F-75005 Paris (France); Pilskog, Ingjald [Laboratoire de Chimie Physique - Matiere et Rayonnement, UMR 7614, UPMC Universite Paris 6, 11 rue Pierre et Marie Curie, F-75231 Paris Cedex 05 (France); Department of Physics and Technology, University of Bergen, N-5007 Bergen (Norway)

2011-11-15

279

Molecular connections between nuclear and ciliary import processes  

PubMed Central

As an organelle, the cilium contains a unique complement of protein and lipid. Recent work has begun to shed light on the mechanisms that regulate entry of ciliary proteins into the compartment. Here, we focus on the mechanisms that regulate ciliary entry of cytosolic molecules. Studies have revealed a size exclusion mechanism for ciliary entry that is similar to the barrier to nuclear entry. Active import into the ciliary compartment involves nuclear trafficking components including importins, a Ran-guanosine triphosphate gradient, and nucleoporins. Together, this work indicates that nuclei and cilia share molecular, structural and mechanistic components that regulate import into the compartments.

2013-01-01

280

The model of interaction of charged particle and plasma fluxed with metallic part surface under the combined processing taking into account collision thermo-physical, thermo-elastic, diffusive and thermo-chemical processes  

Microsoft Academic Search

The investigations of erosion coefficients was performed on the basis of the model of interaction of a charged particle and plasma with a metallic target, taking into consideration the collision, thermo-physical, thermo-chemical, diffusive, thermo-elastic, thermoplastic, thermo-fatigue and plasma-chemical processes

G. I. Kostyuk; E. Voliak

2000-01-01

281

Soft x-ray and Auger electron spectroscopy of single and double electron capture processes in slow Ne{sup 8+}+He collisions  

SciTech Connect

We have performed high resolution extreme ultraviolet (EUV) photon and Auger electron measurements to elucidate single and double capture processes in Ne{sup 8+}+He single collisions at 80 keV impact energy. Numerous new transitions both in the Auger and the EUV spectra have been identified by means of extensive theoretical calculations and correlation diagrams. These data are of importance for the modeling of impurities in plasma and for future plasma diagnostics. {copyright} {ital 1997 American Institute of Physics.}

Bliman, S.; Cornille, M. [Universite de Marne la Valle (France)] [Universite de Marne la Valle (France); Langereis, A.; Nordgren, J. [Department of Physics, University of Uppsala (Sweden)] [Department of Physics, University of Uppsala (Sweden); Bruch, R.; Phaneuf, R.; Swenson, J. [Department of Physics, Univerity of Nevada, Reno, Nevada 89557 (United States)] [Department of Physics, Univerity of Nevada, Reno, Nevada 89557 (United States); Schneider, D. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)] [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)

1997-01-01

282

Large molecular dynamics simulations of collision cascades in single-crystal, bi-crystal, and poly-crystal UO 2  

Microsoft Academic Search

Classical molecular dynamics simulations have been carried out to study the primary damage due to ?-decay self-irradiations in single-, bi-, and poly-crystal UO2 matrices. In all the cases no amorphization has been found, only the creation of few point defects is observed. However, in all grain boundary systems numerous point defects are created along the interfaces. Furthermore, cascade morphologies depend

L. Van Brutzel; E. Vincent-Aublant; J.-M. Delaye

2009-01-01

283

Large molecular dynamics simulations of collision cascades in single-crystal, bi-crystal, and poly-crystal UO2  

Microsoft Academic Search

Classical molecular dynamics simulations have been carried out to study the primary damage due to alpha-decay self-irradiations in single-, bi-, and poly-crystal UO2 matrices. In all the cases no amorphization has been found, only the creation of few point defects is observed. However, in all grain boundary systems numerous point defects are created along the interfaces. Furthermore, cascade morphologies depend

L. van Brutzel; E. Vincent-Aublant; J.-M. Delaye

2009-01-01

284

Optical Probes for Molecular Processes in Live Cells  

NASA Astrophysics Data System (ADS)

In this review, I summarize the development over the past several years of fluorescent and/or bioluminescent indicators to pinpoint cellular processes in living cells. These processes involve second messengers, protein phosphorylations, protein-protein interactions, protein-ligand interactions, nuclear receptor-coregulator interactions, nucleocytoplasmic trafficking of functional proteins, and protein localization.

Umezawa, Yoshio

2008-07-01

285

Applying CLIPS to control of molecular beam epitaxy processing  

NASA Technical Reports Server (NTRS)

A key element of U.S. industrial competitiveness in the 1990's will be the exploitation of advanced technologies which involve low-volume, high-profit manufacturing. The demands of such manufacture limit participation to a few major entities in the U.S. and elsewhere, and offset the lower manufacturing costs of other countries which have, for example, captured much of the consumer electronics market. One such technology is thin-film epitaxy, a technology which encompasses several techniques such as Molecular Beam Epitaxy (MBE), Chemical Beam Epitaxy (CBE), and Vapor-Phase Epitaxy (VPE). Molecular Beam Epitaxy (MBE) is a technology for creating a variety of electronic and electro-optical materials. Compared to standard microelectronic production techniques (including gaseous diffusion, ion implantation, and chemical vapor deposition), MBE is much more exact, though much slower. Although newer than the standard technologies, MBE is the technology of choice for fabrication of ultraprecise materials for cutting-edge microelectronic devices and for research into the properties of new materials.

Rabeau, Arthur A.; Bensaoula, Abdelhak; Jamison, Keith D.; Horton, Charles; Ignatiev, Alex; Glover, John R.

1990-01-01

286

Reducing Si population in the ISM by charge exchange collisions with He+: a quantum modelling of the process  

NASA Astrophysics Data System (ADS)

The possible losses of silicon atom population during star-forming evolution and in the (photon-dominated region) PDR environments of the interstellar medium (ISM) can have different origins, one being the charge exchange (CE) encounter with the helium cations (Si + He+) one of the most abundant species in those environments. This work investigates the different features of the likely interaction potentials leading to asymptotic partners like Si, Si+, Si++ and He or He+, in order to determine the influence of more accurate cross-sections on the chemical evolution of the ISM. We analyse the behaviour of interacting Si and He atoms by using ab initio quantum molecular methods. To obtain the corresponding transition probabilities, we employ a simple sequential grouping of single-crossing Landau-Zener events, and the time-dependent rate coefficients for the CE processes involved are obtained over a broad range of the gas temperatures. The results are seen to differ substantially from an earlier Langevin-type modelling of such process and further suggest a much more complex variety of possible molecular evolution mechanisms. We find, in fact, the unexpected presence of electron shake-off effects leading to Si++ generation yielding to emission of an electron, which has never been considered before and that, although with markedly smaller cross-sections, can indeed contribute to Si losses after the primary CE event. The consequences of these novel findings are tested on evolutionary model calculations and the results discussed in detail.

Satta, M.; Grassi, T.; Gianturco, F. A.; Yakovleva, S. A.; Belyaev, A. K.

2013-12-01

287

A comparison of the charge transfer and collisional activation processes in collisions between keV He + and CO 2  

NASA Astrophysics Data System (ADS)

A commercial mass spectrometer coupled with a spectrograph and charge-coupled device (CCD) was used to obtain the collision-induced emission (CIE) spectra (190-1020 nm) from 4 to 8 keV collisions between projectile He + rad ions and CO 2 target gas (He + rad /CO 2). The observed emissions were from the A2?u+ and B2?u+ states of CO2+rad , excited states of He, along with excited fragments. The relative vibrational population of the A2?u+ state were estimated and compared with our previous CO2+rad /He studies. The results indicate that charge transfer ionization of CO 2 in He + rad /CO 2 collisions is similar to that of photoexcitation, while in the case of CO2+rad /He, the population is more evenly distributed due to intramolecular vibrational redistribution (IVR) after the collision. Adiabatic potential energy surfaces calculated at the CISD/6-311+g(2df) level of theory for CO2+rad /He collisions, show the curve crossing of the CO2+rad A2?u+ and CO2+rad B2?u+ states, in agreement with our observation.

Lin, Yawei; Mayer, Paul M.

2010-12-01

288

Molecular Modeling of Environmentally Important Processes: Reduction Potentials  

ERIC Educational Resources Information Center

The increasing use of computational quantum chemistry in the modeling of environmentally important processes is described. The employment of computational quantum mechanics for the prediction of oxidation-reduction potential for solutes in an aqueous medium is discussed.

Lewis, Anne; Bumpus, John A.; Truhlar, Donald G.; Cramer, Christopher J.

2004-01-01

289

Atmospheric processes on ice nanoparticles in molecular beams  

PubMed Central

This review summarizes some recent experiments with ice nanoparticles (large water clusters) in molecular beams and outlines their atmospheric relevance: (1) Investigation of mixed water–nitric acid particles by means of the electron ionization and sodium doping combined with photoionization revealed the prominent role of HNO3 molecule as the condensation nuclei. (2) The uptake of atmospheric molecules by water ice nanoparticles has been studied, and the pickup cross sections for some molecules exceed significantly the geometrical sizes of the ice nanoparticles. (3) Photodissociation of hydrogen halides on water ice particles has been shown to proceed via excitation of acidically dissociated ion pair and subsequent biradical generation and H3O dissociation. The photodissociation of CF2Cl2 molecules in clusters is also mentioned. Possible atmospheric consequences of all these results are briefly discussed.

Farnik, Michal; Poterya, Viktoriya

2014-01-01

290

Angular distribution of ? electrons emitted in collisions of 1.0-MeV/u Fq+ (q=4,6,8,9) with molecular hydrogen  

NASA Astrophysics Data System (ADS)

The angular distribution, as well as the energy distribution of ? electrons produced in collisions of 1.0-MeV/u Fq+ (q=4,6,8,9) ions with molecular hydrogen, have been studied for laboratory observation angles (?L) from 0° to 70° with respect to the beam direction. The measurements are in fair agreement with the impulse approximation calculations which use the quantal elastic electron-ion differential scattering cross sections folded with the Compton profile of the target electrons. We observe that the energy of the centroid of the binary-encounter-electron (BEE) peak is projectile charge state, q, and laboratory angle, ?L, dependent. Moreover, at 0°, an enhancement of the ratio of the observed double differential cross section for nonbare projectiles to that for the bare ion projectiles, ?(q+)/?(9+), is observed, contrary to the q2 scaling predicted by a first Born calculation for ionization. This ratio ?(q+)/?(9+) decreases nonotonically with increasing ?L, and becomes smaller than one for ?L>=30°.

Liao, C.; Richard, P.; Grabbe, S. R.; Bhalla, C. P.; Zouros, T. J. M.; Hagmann, S.

1994-08-01

291

Collinear Collision Chemistry: 1. A Simple Model for Inelastic and Reactive Collision Dynamics  

ERIC Educational Resources Information Center

Discusses a model for the collinear collision of an atom with a diatomic molecule on a simple potential surface. Indicates that the model can provide a framework for thinking about molecular collisions and reveal many factors which affect the dynamics of reactive and inelastic collisions. (CC)

Mahan, Bruce H.

1974-01-01

292

Molecular processes in astrophysics: Calculations of hydrogen + hydrogen gas excitation, de-excitation, and cooling  

NASA Astrophysics Data System (ADS)

The implications of H+H2 cooling in astrophysics is important to several applications. One of the most significant and pure applications is its role in cooling in the early universe. Other applications would include molecular dynamics in nebulae and their collapse into stars and astrophysical shocks. Shortly after the big bang, the universe was a hot primordial gas of photons, electrons, and nuclei among other ingredients. By far the most dominant nuclei in the early universe was hydrogen. In fact, in the early universe the matter density was 90 percent hydrogen and only 10 percent helium with small amounts of lithium and deuterium. In order for structure to form in the universe, this primordial gas must form atoms and cool. One of the significant cooling mechanisms is the collision of neutral atomic hydrogen with a neutral diatomic hydrogen molecule. This work performs calculations to determine collisional cooling rates of hydrogen using two potential surfaces.

Kelley, Matthew Thomas

293

Molecular processes in a high temperature shock layer  

NASA Technical Reports Server (NTRS)

The development of techniques for the calculation of electron capture widths, electronic wave functions, cross sections and rates needed for the description of the dissociative recombination (DR) of molecular ions with electrons were described. The cross sections and rates were calculated by using harmonic oscillator wave functions for the ion and a delta function approximation for the continuum vibrational wave function in the repulsive dissociative channel. In order to obtain DR cross sections of quantitative accuracy, a computer program which solves the one dimensional nuclear motion wave equation was revised to calculate the cross sections and rates. The program and the new results are described. Included is a discussion of large windows found in the dissociative recombination cross sections from excited ion vibrational levels. These windows have not been previously reported in the literature. The magnitude of the DR cross sections for several dissociative routes are sensitive to the location of the crossing of the neutral and ion potential curves. Studies of the effects of basis set and CI wave function size on vertical excitation energies are described. Preliminary studies on N2 and O2 using large scale wave functions are also reported.

Guberman, S. L.

1985-01-01

294

GR@PPA 2.8: Initial-state jet matching for weak-boson production processes at hadron collisions  

NASA Astrophysics Data System (ADS)

The initial-state jet matching method introduced in our previous studies has been applied to the event generation of single W and Z production processes and diboson (WW, WZ and ZZ) production processes at hadron collisions in the framework of the GR@PPA event generator. The generated events reproduce the transverse momentum spectra of weak bosons continuously in the entire kinematical region. The matrix elements (ME) for hard interactions are still at the tree level. As in previous versions, the decays of weak bosons are included in the matrix elements. Therefore, spin correlations and phase-space effects in the decay of weak bosons are exact at the tree level. The program package includes custom-made parton shower programs as well as ME-based hard interaction generators in order to achieve self-consistent jet matching. The generated events can be passed to general-purpose event generators to make the simulation proceed down to the hadron level. Program summaryProgram title: GR@PPA 2.8 Catalogue identifier: ADRH_v3_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADRH_v3_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 112 146 No. of bytes in distributed program, including test data, etc.: 596 667 Distribution format: tar.gz Programming language: Fortran; with some included libraries coded in C and C++ Computer: All Operating system: Any UNIX-like system RAM: 1.6 Mega bytes at minimum Classification: 11.2 Catalogue identifier of previous version: ADRH_v2_0 Journal reference of previous version: Comput. Phys. Comm. 175 (2006) 665 External routines: Bash and Perl for the setup, and CERNLIB, ROOT, LHAPDF, PYTHIA according to the user's choice. Does the new version supersede the previous version?: No, this version supports only a part of the processes included in the previous versions. Nature of problem: We need to combine those processes including 0 jet and 1 jet in the matrix elements using an appropriate matching method, in order to simulate weak-boson production processes in the entire kinematical region. Solution method: The leading logarithmic components to be included in parton distribution functions and parton showers are subtracted from 1-jet matrix elements. Custom-made parton shower programs are provided to ensure satisfactory performance of the matching method. Reasons for new version: An initial-state jet matching method has been implemented. Summary of revisions: Weak-boson production processes associated with 0 jet and 1 jet can be consistently merged using the matching method. Restrictions: The built-in parton showers are not compatible with the PYTHIA new PS and the HERWIG PS. Unusual features: A large number of particles may be produced by the parton showers and passed to general-purpose event generators. Running time: About 10 min for initialization plus 25 s for every 1k-event generation for W production in the LHC condition, on a 3.0-GHz Intel Xeon processor with the default setting.

Odaka, Shigeru; Kurihara, Yoshimasa

2012-04-01

295

Young stellar disks formed by the collision of a molecular cloud with a circumnuclear disk at the Galactic center  

NASA Astrophysics Data System (ADS)

We suggest a new formation mechanism for the inclined, sub-parsec scale and counterrotating stellar disks observed around the central black hole in the Milky Way Galactic center. The simulation of a single molecular cloud crashing into a circumnuclear ring of gas leads to the inflow of multiple streams of gas towards the central parsec region. The time delayed arrival of those streams forms multiple, sub-parsec scale accretion disks, with angular momentum depending on the ratio of cloud and circumnuclear ring material. These accretion disks could then be the progenitors which fragmented into the observed stellar disks. A similar event might have also led to the creation of the so-called minispiral in the Galactic center.

Alig, C.; Schartmann, M.; Burkert, A.; Dolag, K.

2014-05-01

296

Collision Dynamics of Decimeter Bodies  

NASA Astrophysics Data System (ADS)

The collision dynamics of decimeter bodies are important for the early phase of planet formation. Planets form by accretion of km-sized objects, the so called planetesimals. These planetesimals evolve from small grains, but their formation process is not yet understood entirely. Two groups of models try to explain the formation process. Decimeter bodies and their collision behavior play a vital role in both groups. The threshold between bouncing and fragmentation is especially interesting for coagulation models, as decimeter bodies are the direct precursors to meter sized bodies. But the collision dynamics are also relevant for the models, which describe planetesimal formation by gravitational collapse in dense regions of the protoplanetary disk. We will present preliminary results of our collision experiments. Previous experiments on mutual collisions of decimeter dust agglomerates showed that the threshold between bouncing and fragmentation lies at a collision velocity of 16.2 cm/s, which corresponds to a specific kinetic energy of 5 mJ/kg. We expand these experiments to investigate the conditions for “catastrophic disruption” of decimeter dust bodies. Here, “catastrophic disruption” means that the largest fragment of a collision partner has only half the mass of the original body. Furthermore, we extend the parameter range to ice aggregates. We will present first experimental results of collisions of ice aggregates in the decimeter range. In these first experiments we will analyze the threshold conditions for solid ice. We will investigate the collision dynamics for both central and non-central collisions.

Deckers, Johannes; Teiser, J.

2013-10-01

297

Molecular basis of processing wheat gluten toward biobased materials.  

PubMed

The unique properties of the wheat grain reside primarily in the gluten-forming storage proteins of its endosperm. Wheat gluten's structural and functional properties have led to an expanding diversity of applications in food products. However, its viscoelastic properties and low water solubility also are very interesting features for nonfood applications. Moreover, gluten is annually renewable and perfectly biodegradable. In the processing and setting of gluten containing products, temperature plays a very important role. In this review, the structure and reactivity of gluten are discussed and the importance of sulfhydryl (SH) and disulfide (SS) groups is demonstrated. Wheat gluten aggregation upon thermosetting proceeds through direct covalent cross-linking in and between its protein groups, glutenin and gliadin. Predominant reactions include SH oxidation and SH/SS interchange reactions leading to the formation of SS cross-links. Additionally, thermal treatment of gluten can result in the formation of other than SS covalent bonds. We here review two main technological approaches to make gluten-based materials: wet processes resulting in thin films and dry processes, such as extrusion or compression molding, exploiting the thermoplastic properties of proteins under low moisture conditions and potentially resulting in very useful materials. Gluten bioplastics can also be reinforced with natural fibers, resulting in biocomposites. Although a lot of progress has been made the past decade, the current gluten materials are still outperformed by their synthetic polymer counterparts. PMID:20141101

Lagrain, Bert; Goderis, Bart; Brijs, Kristof; Delcour, Jan A

2010-03-01

298

Modeling droplet collision and coalescence in an icing wind tunnel and the influence of these processes on droplet size distribution  

Microsoft Academic Search

A theoretical model of a two-phase air\\/dispersed water spray flow in an icing wind tunnel is presented here. The mutual interactions taking place within the dispersed phase known as binary droplet collisions, as well as gravitational sedimentation are considered. Where large droplets and low air stream velocities are concerned, the effect of gravity on droplet dynamics is considerable. Gravity causes

László E. Kollár; Masoud Farzaneh; Anatolij R. Karev

2005-01-01

299

Collision Animations  

NSDL National Science Digital Library

This series of interactive Flash animation explores all aspects of the India-Eurasian continental collision. Animations show the motion of the two continents, the growth of the Himalayas, earthquakes resulting from their collision, and the incredible rate of erosion of the newly formed mountains.

Environment, University O.

300

Spatially Resolved Atomic and Molecular Spectroscopy in Microelectronics Processing Plasmas  

SciTech Connect

Plasma processing of microelectronic materials is strongly dependent on the generation and control of neutral radial and ion species generated in a plasma. For example, process uniformity across a #er is drken by a combination of plasma charged particle and neutral uniformity. Due to extensive rexarch and engineering the current generation of commercial plasma reactors can generate very radially uniform ion distributions, usually better than ~ 2 perwnt as determined by ion saturation measurements. Due in part to the difficulty associated with determining the neutral radial distributions, control of the neutral radical uniformity is less well developed. This abstract will review our recent measurements of the spatial distribution of severaI important atomic and molecukw species in inductively coupled plasmas through C12 / BCIJ / Ar containing gas mixtures. Measured species include the ground state Cl and BC1 densities as well as the metastable argon density. The fbeus of this review will be on the experimental techniques and results. In addition to assisting in the development of a fbndarnental understanding of the important pkunna physics, these measurements have been used to benchmark multi dimensional plasma discharge codes.

Hebner, G.A.

1998-10-14

301

Molecular structure, processing, and tissue distribution of matrilin-4.  

PubMed

Matrilin-4 is the most recently identified member of the matrilin family of von Willebrand factor A-like domain containing extracellular matrix adapter proteins. Full-length matrilin-4 was expressed in 293-EBNA cells, purified using affinity tags, and subjected to biochemical characterization. The largest oligomeric form of recombinantly expressed full-length matrilin-4 is a trimer as shown by electron microscopy, SDS-polyacrylamide gel electrophoresis, and mass spectrometry. Proteolytically processed matrilin-4 species were also detected. The cleavage occurs in the short linker region between the second von Willebrand factor A-like domain and the coiled-coil domain leading to the release of large fragments and the formation of dimers and monomers of intact subunits still containing a trimeric coiled-coil. In immunoblots of calvaria extracts similar degradation products could be detected, indicating that a related proteolytic processing occurs in vivo. Matrilin-4 was first observed at day 7.5 post-coitum in mouse embryos. Affinity-purified antibodies detect a broad expression in dense and loose connective tissue, bone, cartilage, central and peripheral nervous systems and in association with basement membranes. In the matrix formed by cultured primary embryonic fibroblasts, matrilin-4 is found in a filamentous network connecting individual cells. PMID:11279097

Klatt, A R; Nitsche, D P; Kobbe, B; Macht, M; Paulsson, M; Wagener, R

2001-05-18

302

Advancing polymer process understanding in package and board applications through molecular modeling  

Microsoft Academic Search

In this paper we will discuss two molecular modeling methods which have been developed and applied at Honeywell to help predict material behavior from the process engineer's standpoint. Both stress cycling and process analyses have been used to trend the probable behavior of material types in order to provide advanced intelligence on possible failure mechanisms. For instance, we have found

N. E. Iwamoto

2000-01-01

303

Molecular epidemiology and disinfectant susceptibility of Listeria monocytogenes from meat processing plants and human infections  

Microsoft Academic Search

We have investigated the molecular epidemiology of Listeria monocytogenes from the meat processing industry producing cold cuts and from cases of human listeriosis by discriminative pulsed-field gel electrophoresis (PFGE). A subset of the isolates was also investigated for susceptibility to a disinfectant based on quaternary ammonium compounds (QAC) frequently used in the meat processing industry. The purpose of this investigation

Even Heir; Bjørn-Arne Lindstedt; Ole-Johan Røtterud; Traute Vardund; Georg Kapperud; Truls Nesbakken

2004-01-01

304

Dewaxing catalysts and processes employing titanoaluminosilicate molecular sieves  

SciTech Connect

This patent describes a process for dewaxing a hydrocarbon feedstock comprising contacting the hydrocarbon feedstock with a dewaxing catalyst comprising at least one titanoaluminosilicate (TASO) characterized in its calcined form by an adsorption of isobutane of at least 2 percent by weight at a pressure of 500 torr and a temperature of 20/sup 0/C and further characterized in its calcined form by an adsorption of triethylamine of less than 5 percent by weight at a pressure of 2.6 torr and a temperature of 22/sup 0/C, the amount of the TASO in the catalyst and the condition of the contacting being effective to cause dewaxing of the hydrocarbon feedstock.

Pellet, R.J.; Gortsema, F.P.; Long, G.N.; Rabo, J.

1987-08-11

305

K Vacancy Production in Medium-Z Heavy Ion Collisions.  

National Technical Information Service (NTIS)

During slow encounters between projectile and target atoms, the electronic atomic wave functions of the two collision partners distort and form molecular orbitals (MOs). K vacancy formation in slow heavy-ion collisions, which occur when electrons are exci...

R. Anholt

1975-01-01

306

Cluster Matter Formation in Cluster Collisions  

NASA Astrophysics Data System (ADS)

By using the tight-binding molecular dynamics simulations in cluster collisions, we give some evidences of the structures of (Na9)2 cluster dimer and (Na4)4 cluster tetramer from the dynamical point of view. We show that the (Na9)2 and (Na4)4 cluster matter may exist as intermediate states and finally decay to compact structure in real collision process. With a technique called "sharp cooling", the stable cluster structures (Na9)2 and (Na4)4 are brought into being to end. The eigen-mode frequencies of these clusters are obtained with Fourier transform of the velocity auto-correlation function which can characterize their structure properties.

Wang, Z. P.; Zhang, F. S.; Zeng, X. H.; Wang, F.; Zhang, S. F.; Zhang, Y. P.

307

The Henry Ford Production System: LEAN Process Redesign Improves Service in the Molecular Diagnostic Laboratory  

PubMed Central

Accurate and timely molecular test results play an important role in patient management; consequently, there is a customer expectation of short testing turnaround times. Baseline data analysis revealed that the greatest challenge to timely result generation occurred in the preanalytic phase of specimen collection and transport. Here, we describe our efforts to improve molecular testing turnaround times by focusing primarily on redesign of preanalytic processes using the principles of LEAN production. Our goal was to complete greater than 90% of the molecular tests in less than 3 days. The project required cooperation from different laboratory disciplines as well as individuals outside of the laboratory. The redesigned processes involved defining and standardizing the protocols and approaching blood and tissue specimens as analytes for molecular testing. The LEAN process resulted in fewer steps, approaching the ideal of a one-piece flow for specimens through collection/retrieval, transport, and different aspects of the testing process. The outcome of introducing the LEAN process has been a 44% reduction in molecular test turnaround time for tissue specimens, from an average of 2.7 to 1.5 days. In addition, extending LEAN work principles to the clinician suppliers has resulted in a markedly increased number of properly collected and shipped blood specimens (from 50 to 87%). These continuous quality improvements were accomplished by empowered workers in a blame-free environment and are now being sustained with minimal management involvement.

Cankovic, Milena; Varney, Ruan C.; Whiteley, Lisa; Brown, Ron; D'Angelo, Rita; Chitale, Dhananjay; Zarbo, Richard J.

2009-01-01

308

Molden: a pre- and post-processing program for molecular and electronic structures  

Microsoft Academic Search

Molden is a software package for pre- and postprocessing of computational chemistry program data. Interfacing to the ab initio programs Gamess-US\\/UK and Gaussian and to the semi-empirical package MOPAC is provided. The emphasis is on computation and visualization of electronic and molecular properties but, e.g., reaction pathways can be simulated as well. Some molecular properties of interest are processed directly

G. Schaftenaar; J. H. Noordik

2000-01-01

309

Molecular Insights into Poly(ADP-ribose) Recognition and Processing  

PubMed Central

Poly(ADP-ribosyl)ation is a post-translational protein modification involved in the regulation of important cellular functions including DNA repair, transcription, mitosis and apoptosis. The amount of poly(ADP-ribosyl)ation (PAR) in cells reflects the balance of synthesis, mediated by the PARP protein family, and degradation, which is catalyzed by a glycohydrolase, PARG. Many of the proteins mediating PAR metabolism possess specialised high affinity PAR-binding modules that allow the efficient sensing or processing of the PAR signal. The identification of four such PAR-binding modules and the characterization of a number of proteins utilising these elements during the last decade has provided important insights into how PAR regulates different cellular activities. The macrodomain represents a unique PAR-binding module which is, in some instances, known to possess enzymatic activity on ADP-ribose derivatives (in addition to PAR-binding). The most recently discovered example for this is the PARG protein, and several available PARG structures have provided an understanding into how the PARG macrodomain evolved into a major enzyme that maintains PAR homeostasis in living cells.

Zaja, Roko; Mikoc, Andreja; Barkauskaite, Eva; Ahel, Ivan

2012-01-01

310

Towards a molecular-level theory of carbohydrate processivity in glycoside hydrolases.  

PubMed

Polysaccharide depolymerization in nature is primarily accomplished by processive glycoside hydrolases (GHs), which abstract single carbohydrate chains from polymer crystals and cleave glycosidic linkages without dissociating after each catalytic event. Understanding the molecular-level features and structural aspects of processivity is of importance due to the prevalence of processive GHs in biomass-degrading enzyme cocktails. Here, we describe recent advances towards the development of a molecular-level theory of processivity for cellulolytic and chitinolytic enzymes, including the development of novel methods for measuring rates of key steps in processive action and insights gained from structural and computational studies. Overall, we present a framework for developing structure-function relationships in processive GHs and outline additional progress towards developing a fundamental understanding of these industrially important enzymes. PMID:24863902

Beckham, Gregg T; Ståhlberg, Jerry; Knott, Brandon C; Himmel, Michael E; Crowley, Michael F; Sandgren, Mats; Sørlie, Morten; Payne, Christina M

2014-06-01

311

Symmetric and asymmetric collision effects on the formation of singly and doubly-charged ions in sputtering process  

NASA Astrophysics Data System (ADS)

Measurements of Si2+ and Si+ ions sputtered due to bombardment of 3-5 keV Ar+ ions on silicon substrate have been performed for understanding exact charge-state formation mechanisms. Examination on the penetration depth dependence of incident particle on secondary ion formation has been performed. A closure look at the energetics of the secondary ions from their kinetic energy distributions suggests that Si+ ions are predominantly formed in the upper surface layer and Si2+ ions are produced due to target-target symmetric collision-induced Si 2 p shell vacancy creation following the Auger electron emission. Furthermore, the increase in the oxygen-induced impurity in the silicon substrate enables us to explore the gradual transition from the dominating symmetric to asymmetric collision channel for production of Si2+ ions.

Mondal, S.; Gnaser, H.; Chakraborty, P.

2012-07-01

312

Efficient integration of optimal solvent and process design using molecular clustering  

Microsoft Academic Search

We present a molecular clustering approach for the efficient incorporation of solvent design information into process synthesis in the integrated design of solvent\\/process systems. The approach is to be used in conjunction with an integrated solvent\\/process design approach where the solvent design stage utilises multi-objective optimisation in order to identify Pareto optimal solvent candidates that are subsequently evaluated in a

Athanasios I. Papadopoulos; Patrick Linke

2006-01-01

313

Peripheral processes 2 {yields} 3 and 2 {yields} 4 in QED and QCD in p-p-bar high-energy collisions  

SciTech Connect

Differential cross sections of processes with high-energy p(-p)p collisions-creation of a scalar, a pseudoscalar and a lepton pair-are considered in the Weizsacker-Williams approximation in QED in the QCD framework, processes with conversion of the initial proton (antiproton) to fermionic jets accompanied with one gluon jet and the state of two gluons and a quark-antiquark pair (without a rapidity gap) are considered in the framework of the effective Regge action of Lipatov's theory. The process of creation of a Higgs boson accompanied with two fermionic jets is considered. The azimuthal correlation in the process of two gluon jets separated by a rapidity gap is investigated. The gluon Reggeization effects are taken into account. Some distributions are illustrated by numerical calculations.

Ahmadov, A. I., E-mail: ahmadov@theor.jinr.ru; Bystritskiy, Yu. M., E-mail: bystr@theor.jinr.ru; Kuraev, E. A., E-mail: kuraev@theor.jinr.ru [Joint Institute for Nuclear Research (Russian Federation)

2011-10-15

314

Correlating molecular spectroscopy and molecular chemometrics to explore carbohydrate functional groups and utilization of coproducts from biofuel and biobrewing processing.  

PubMed

Dried distillers grains with solubles (DDGS) was coproducts from bioethanol and biobrewing industry. It was an excellent resource of protein and energy feedstuff in China. Conventional studies often focus on traditional nutritional profiles. To data, there is little research on molecular structure-nutrition interaction of carbohydrate in coproducts. In this study, five kinds of corn-grain based DDGS and two kinds of barley-grain based DDGS were collected from different manufactures in the north of China. They were coded as "1, 2, 3, 4, 5, 6, and 7", respectively. The primary purposes of this project were to investigate the molecular structure-nutrition interaction of carbohydrate in coproducts, in terms of (1) carbohydrate-related chemical composition and nutrient profiles, (2) predicted values for energy in coproducts for animal, and (3) in situ digestion of dry matter. The result showed that acid detergent fiber content in corn DDGS and barley DDGS had negative correlation with structural carbohydrate peak area, cellulose compounds, and carbohydrate component peaks (first, second, and total peak area), which were measured with molecular spectroscopy. The correlation between carbohydrate peak area (second and total) and digestible fiber (tdNDF) were negative. There were no correlation between carbohydrate spectral intensities and energy values, carbohydrate subfractions partitioned by CNCPS system, and in situ rumen degradation. The results indicate that carbohydrate spectral profiles (functional groups) are associated with the carbohydrate nutritive values in coproducts from biofuel and biobrewing processing. PMID:24738876

Chen, Limei; Zhang, Xuewei; Yu, Peiqiang

2014-06-01

315

Monte Carlo simulation of molecular flux on simple spacecraft surfaces due to self- and ambient-scatter of outgassing molecules  

Microsoft Academic Search

A computer program was developed for the Monte Carlo simulation of molecular flux impingement on simple spacecraft surfaces due to self- and ambient-scatter of outgassing molecules. The molecules are assumed to be elastic spheres with a Maxwellian velocity distribution. Binary elastic collision processes were adopted in a hard-sphere collision model. A Test Particle Monte Carlo (TPMC) methodology was used for

Chien Fan; Clifford Gee; Michael Fong

1993-01-01

316

Cosmic Collisions  

NSDL National Science Digital Library

This Web site, created to complement the Museum's Cosmic Collisions space show, takes a look at the hypersonic impacts that drive the dynamic and continuing evolution of the universe. The site includes a one-minute QuickTime preview of the space show, a collection of 26 scientific simulations and visualizations, a look at the fusion of cutting-edge astrophysics research and state-of-the-art science visualization expertise that went into creating Cosmic Collisions and other information.

317

Quantum Chemical Molecular Dynamics Studies on the Chemical Mechanical Polishing Process of Cu Surface  

NASA Astrophysics Data System (ADS)

The dynamic behavior of the oxidation reaction of the Cu surface during the Cu chemical-mechanical polishing (CMP) process was investigated by a novel tight-binding quantum chemical molecular dynamics method. We confirmed that our tight-binding quantum chemical molecular dynamics method with first-principles parameterization can calculate the structures, and electronic states of various molecules and solids related to the Cu-CMP process as accurately as the density functional calculations, while the CPU time of the new method is around 5,000 times faster than that of the first-principles molecular dynamics calculations. We employed hydrogen peroxide solution as a slurry and the Cu surface as a substrate to simulate the Cu-CMP process by using our accelerated quantum chemical molecular dynamics method. Three types of models were constructed to analyze the effect of the pH of the slurry and Miller plane of the Cu surface on the dynamic behaviors of the oxidation process of the Cu surface. We indicate that the pH of the slurry strongly affects the oxidation process of Cu surface. Moreover, we clarified that the oxidation mechanism depends on the Miller plane of the Cu surfaces.

Yokosuka, Toshiyuki; Sasata, Katsumi; Kurokawa, Hitoshi; Takami, Seiichi; Kubo, Momoji; Imamura, Akira; Miyamoto, Akira

2003-04-01

318

Charge Transfer in Collisions of S^4+ with He  

Microsoft Academic Search

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

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

2001-01-01

319

Electron capture in collisions of S4+ with atomic hydrogen  

Microsoft Academic Search

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

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

2001-01-01

320

Electron capture in collisions of S4+ with atomic hydrogen  

Microsoft Academic Search

Charge transfer processes due to collisions of ground state S4+(3s21S) 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

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

2001-01-01

321

Charge Transfer in Collisions of S^4+ with H  

Microsoft Academic Search

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

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

2001-01-01

322

Photoinitiated collisions between cold Cs Rydberg atoms  

SciTech Connect

Experimental studies of a photoinitiated collision in an ultracold Cs Rydberg gas are presented. The process is characterized by measuring the laser intensity dependence of the absorption, the number of particles leaving each collision, and the recoil velocity of the collision fragments. The results of the experiment are compared to ab initio Rydberg pair interaction potentials.

Overstreet, K. Richard; Schwettmann, Arne; Tallant, Jonathan; Shaffer, James P. [University of Oklahoma, Homer L. Dodge Department of Physics and Astronomy, 440 West Brooks Street, Norman, Oklahoma 73019 (United States)

2007-07-15

323

Magnitude of long-term non-lithostatic pressure variations in lithospheric processes: insight from thermo-mechanical subduction/collision models  

NASA Astrophysics Data System (ADS)

On the one hand, the principle of lithostatic pressure is habitually used in metamorphic geology to calculate paleo-depths of metamorphism from mineralogical pressure estimates given by geobarometry. On the other hand, it is obvious that this lithostatic (hydrostatic) pressure principle should only be valid for an ideal case of negligible deviatoric stresses during the long-term development of the entire tectono-metamorphic system - the situation, which newer comes to existence in natural lithospheric processes. The question is therefore not "Do non-lithostatic pressure variations exist?" but " What is the magnitude of long-term non-lithostatic pressure variations in various lithospheric processes, which can be recorded by mineral equilibria of respective metamorphic rocks?". The later question is, in particular, relevant for various types of high-pressure (HP) and ultrahigh-pressure (UHP) rocks, which are often produced in convergent plate boundary settings (e.g., Hacker and Gerya, 2013). This question, can, in particular, be answered with the use of thermo-mechanical models of subduction/collision processes employing realistic P-T-stress-dependent visco-elasto-brittle/plastic rheology of rocks. These models suggest that magnitudes of pressure deviations from lithostatic values can range >50% underpressure to >100% overpressure, mainly in the regions of bending of rheologically strong mantle lithosphere (Burg and Gerya, 2005; Li et al., 2010). In particular, strong undepresures along normal faults forming within outer rise regions of subducting plates can be responsible for downward water suction and deep hydration of oceanic slabs (Faccenda et al., 2009). Weaker HP and UHP rocks of subduction/collision channels are typically subjected to lesser non-lithostatic pressure variations with characteristic magnitudes ranging within 10-20% from the lithostatic values (Burg and Gerya, 2005; Li et al., 2010). The strength of subducted crustal rocks and the degree of confinement of the subduction/collision channel are the key factors controlling this magnitude (Burg and Gerya, 2005; Li et al., 2010). High-temperature (>700 C) UHP rocks formed by continental crust subduction typically demonstrate negligible non-lithostatic pressure variations at peak metamorphic conditions, although these variations can be larger at the prograde stage (Gerya et al., 2008; Li et al., 2010). However, the variability of tectonic mechanisms by which UHP rocks can form (e.g., Sizova et al., 2012; Hacker and Gerya, 2013) precludes generalization of this result for all types of UHP-complexes. References Burg, J.-P., Gerya, T.V. (2005) Viscous heating and thermal doming in orogenic metamorphism: numerical modeling and geological implications. J. Metamorph. Geol., 23, 75-95. Faccenda, M., Gerya, T.V., Burlini, L. (2009) Deep slab hydration induced by bending related variations in tectonic pressure. Nature Geoscience, 2, 790-793. Gerya T.V., Perchuk, L.L., Burg J.-P. (2008) Transient hot channels: perpetrating and regurgitating ultrahigh-pressure, high temperature crust-mantle associations in collision belts. Lithos, 103, 236-256. Hacker, B., Gerya, T.V. (2013) Paradigms, new and old, for ultrahigh-pressure tectonism. Tectonophysics, 603, 79-88. Li, Z., Gerya, T.V., Burg, J.P. (2010) Influence of tectonic overpressure on P-T paths of HP-UHP rocks in continental collision zones: Thermomechanical modelling. J. Metamorphic Geol., 28, 227-247. Sizova, E., Gerya, T., Brown M. (2012) Exhumation mechanisms of melt-bearing ultrahigh pressure crustal rocks during collision of spontaneously moving plates. Journal of Metamorphic Geology, 30, 927-955.

Gerya, Taras

2014-05-01

324

Electron reemission processes following photoelectron recapture due to post-collision interaction in inner-shell photoionization of water molecules.  

PubMed

Electron reemission following photoelectron recapture due to post-collision interaction has been studied at 0.7 eV the inner-shell photoionization threshold of water molecules, using a multi-electron coincidence method. Electron reemissions after single Auger decay occur from O and OH fragments which are produced by the dissociations of high-n Rydberg H2O(+) states populated through photoelectron recapture. In addition, electron reemissions after double Auger decay are identified in triple coincidence events, where autoionization lines from O and O(+) fragments are observed. PMID:23758372

Hikosaka, Y; Sawa, M; Nakano, M; Soejima, K; Lablanquie, P; Penent, F; Ito, K

2013-06-01

325

Electron reemission processes following photoelectron recapture due to post-collision interaction in inner-shell photoionization of water molecules  

NASA Astrophysics Data System (ADS)

Electron reemission following photoelectron recapture due to post-collision interaction has been studied at 0.7 eV the inner-shell photoionization threshold of water molecules, using a multi-electron coincidence method. Electron reemissions after single Auger decay occur from O and OH fragments which are produced by the dissociations of high-n Rydberg H2O+ states populated through photoelectron recapture. In addition, electron reemissions after double Auger decay are identified in triple coincidence events, where autoionization lines from O and O+ fragments are observed.

Hikosaka, Y.; Sawa, M.; Nakano, M.; Soejima, K.; Lablanquie, P.; Penent, F.; Ito, K.

2013-06-01

326

Molecular architecture of the human pre-mRNA 3? processing complex  

PubMed Central

SUMMARY Pre-mRNA 3?-end formation is an essential step in eukaryotic gene expression. Over half of human genes produce alternatively polyadenylated mRNAs, suggesting that regulated polyadenylation is an important mechanism for post-transcriptional gene control. Although a number of mammalian mRNA 3? processing factors have been identified, the full protein composition of the 3? processing machinery has not been determined, and its structure is unknown. Here we report the purification and subsequent proteomic and structural characterization of human mRNA 3? processing complexes. Remarkably, the purified 3? processing complex contains ~85 proteins, including known and new core 3? processing factors and over 50 proteins that may mediate crosstalk with other processes. Electron microscopic analyses show that the core 3? processing complex has a distinct “kidney” shape and is ~250 Å in length. Together, our data has revealed the complexity and molecular architecture of the pre-mRNA 3? processing complex.

Shi, Yongsheng; Di Giammartino, Dafne Campigli; Taylor, Derek; Sarkeshik, Ali; Rice, William J.; Yates, John R.; Frank, Joachim; Manley, James L.

2010-01-01

327

Towards understanding the molecular mechanism of the endocytosis-like process in the bacterium Gemmata obscuriglobus.  

PubMed

An endocytosis-like process of protein uptake in the planctomycete Gemmata obscuriglobus is a recently discovered process unprecedented in the bacterial world. The molecular mechanisms underlying this process are not yet characterized. A homolog of the MC (membrane-coating) proteins of eukaryotes has been proposed to be involved in the mechanism of this process, but its relationship to eukaryote proteins is controversial. However, a number of other proteins of G. obscuriglobus with domains homologous to those involved in endocytosis in eukaryotes can also be identified. Here we critically evaluate current bioinformatic knowledge, and suggest practical experimental steps to overcome the limits of bioinformatics in elucidating the molecular mechanism of endocytosis in bacteria. This article is part of a Special Issue entitled: Protein trafficking and secretion in bacteria. Guest Editors: Anastassios Economou and Ross Dalbey. PMID:24144586

Fuerst, John A; Sagulenko, Evgeny

2014-08-01

328

Experimental Study of Molecular Processes in Liquids at High Pressures by Acoustic Means.  

National Technical Information Service (NTIS)

The report concerns the experimental study of molecular processes in liquids at high pressures by acoustic means and summarizes the over-all goals and activities of the work involved and presents a list of the personnel and published results of the projec...

G. Holton

1969-01-01

329

MOLECULAR-LEVEL PROCESS GOVERNING THE INTERACTION OF CONTAMINANTS WITH IRON AND MANGANESE OXIDES  

EPA Science Inventory

Many of the inorganic and organic contaminants present in sediments at DOE sites can be altered or destroyed by reduction and oxidation (redox) reactions occurring at mineral surfaces. A fundamental understanding of such redox processes provided by molecular-level studies on stru...

330

Enhanced mechanical properties of graphene/copper nanocomposites using a molecular-level mixing process.  

PubMed

RGO flakes are homogeneously dispersed in a Cu matrix through a molecular-level mixing process. This novel fabrication process prevents the agglomeration of the RGO and enhances adhesion between the RGO and the Cu. The yield strength of the 2.5 vol% RGO/Cu nanocomposite is 1.8 times higher than that of pure Cu. The strengthening mechanism of the RGO is investigated by a double cantilever beam test using the graphene/Cu model structure. PMID:23983045

Hwang, Jaewon; Yoon, Taeshik; Jin, Sung Hwan; Lee, Jinsup; Kim, Taek-Soo; Hong, Soon Hyung; Jeon, Seokwoo

2013-12-10

331

Atom-Molecule Collisions in an Optically Trapped Gas  

Microsoft Academic Search

Cold inelastic collisions between confined cesium (Cs) atoms and Cs2 molecules are investigated inside a CO2 laser dipole trap. Inelastic atom-molecule collisions can be observed and measured with a rate coefficient of ˜2.6×10-11cm3s-1, mainly independent of the molecular rovibrational state populated. Lifetimes of purely atomic and molecular samples are essentially limited by rest gas collisions. The pure molecular trap lifetime

Nassim Zahzam; Thibault Vogt; Marcel Mudrich; Daniel Comparat; Pierre Pillet

2006-01-01

332

Reversible Simulations of Elastic Collisions  

SciTech Connect

Consider a system of N identical hard spherical particles moving in a d-dimensional box and undergoing elastic, possibly multi-particle, collisions. We develop a new algorithm that recovers the pre-collision state from the post-collision state of the system, across a series of consecutive collisions, \\textit{with essentially no memory overhead}. The challenge in achieving reversibility for an n-particle collision (where, in general, n<< N) arises from the presence of nd-d-1 degrees of freedom (arbitrary angles) during each collision, as well as from the complex geometrical constraints placed on the colliding particles. To reverse the collisions in a traditional simulation setting, all of the particular realizations of these degrees of freedom (angles) during the forward simulation must be tracked. This requires memory proportional to the number of collisions, which grows very fast with N and d, thereby severely limiting the \\textit{de facto} applicability of the scheme. This limitation is addressed here by first performing a pseudo-randomization of angles, which ensures determinism in the reverse path for any values of n and d. To address the more difficult problem of geometrical and dynamic constraints, a new approach is developed which correctly samples the constrained phase space. Upon combining the pseudo-randomization with correct phase space sampling, perfect reversibility of collisions is achieved, as illustrated for n<=3, d=2, and n=2, d=3. This result enables, for the first time, reversible simulations of elastic collisions with essentially zero memory accumulation. In principle, the approach presented here could be generalized to larger values of n, which would be of definite interest for molecular dynamics simulations at high densities.

Perumalla, Kalyan S [ORNL; Protopopescu, Vladimir A [ORNL

2013-01-01

333

Molden: a pre- and post-processing program for molecular and electronic structures.  

PubMed

Molden is a software package for pre- and postprocessing of computational chemistry program data. Interfacing to the ab initio programs Games-US/UK and Gaussian and to the semi-empirical package MOPAC is provided. The emphasis is on computation and visualization of electronic and molecular properties but, e.g., reaction pathways can be simulated as well. Some molecular properties of interest are processed directly from the output of the computational chemistry programs, others are calculated in MOLDEN before display. The package features different options to display MOLecular electronic DENsity, each focusing on a different structural aspect: molecular orbitals, electron density, molecular minus atomic density and the Laplacian of the electron density. To display difference density, either the spherically averaged atomic density or the oriented ground state atomic density can be used for a number of standard basis sets. The quantum mechanical electrostatic potential or a distributed multiple expansion derived electrostatic potential can be calculated and atomic charges can be fitted to these potentials calculated on Connolly surface(s). Reaction pathways and molecular vibrations can be visualized. Input structures can be generated with a Z-matrix editor. A variety of graphics languages is supported: XWindows, postscript, VRML and Povray format. PMID:10721501

Schaftenaar, G; Noordik, J H

2000-02-01

334

Molecular dynamics studies of fluid/oil interfaces for improved oil recovery processes.  

PubMed

In our paper, we study the interface wettability, diffusivity, and molecular orientation between crude oil and different fluids for applications in improved oil recovery (IOR) processes through atomistic molecular dynamics (MD). The salt concentration, temperature, and pressure effects on the physical chemistry properties of different interfaces between IOR agents [brine (H(2)O + % NaCl), CO(2), N(2), and CH(4)] and crude oil have been determined. From the interfacial density profiles, an accumulation of aromatic molecules near the interface has been observed. In the case of brine interfaced with crude oil, our calculations indicate an increase in the interfacial tension with increasing pressure and salt concentration, which favors oil displacement. On the other hand, with the other fluids studied (CO(2), N(2), and CH(4)), the interfacial tension decreases with increasing pressure and temperature. With interfacial tension reduction, an increase in fluid diffusivity in the oil phase is observed. We also studied the molecular orientation properties of the hydrocarbon and fluids molecules in the interface region. We perceived that the molecular orientation could be affected by changes in the interfacial tension and diffusivity of the molecules in the interface region with the increased pressure and temperature: pressure (increasing) ? interfacial tension (decreasing) ? diffusion (increasing) ? molecular ordering. From a molecular point of view, the combination of low interfacial tension and high diffusion of molecules in the oil phase gives the CO(2) molecules unique properties as an IOR fluid compared with other fluids studied here. PMID:23163479

de Lara, Lucas S; Michelon, Mateus F; Miranda, Caetano R

2012-12-20

335

Theoretical atomic collision physics  

SciTech Connect

The theoretical atomic physics at Rice University focuses on obtaining a better understanding of the mechanisms that control inelastic collisions between excited atoms and atoms, molecules and ions. Particular attention is given to systems and processes that are of potential importance to advanced energy technologies. In the current year, significant progress has been made in quantitative studies of: quenching of low-Rydberg Na atoms in thermal energy collisions with He, Ne and Ar atoms; selective excitation resulting from charge transfer in collisions of highly stripped ions of He, Li, C, and with Li, Na and He atoms and H{sub 2} molecules at keV energies; differential elastic and single, and double electron transfer in He{sup ++} collisions with He at keV energies; inelastic electron-transfer in ultra-low-energy-energy (T=8 to 80K) collisions between {sup 3}He{sup +} and {sup 4}He and {sup 4}He{sup +} and {sup 3}He; a formalism for ionization by electron impact of ions in dense, high temperature plasmas.

Lane, N.F. (Rice Univ., Houston, TX (USA) Rice Univ., Houston, TX (USA). Quantum Inst.)

1990-01-01

336

Merging Galaxies, Cosmic Collisions  

NASA Technical Reports Server (NTRS)

Exciting Hubble Space Telescope images of more than a dozen very distant colliding galaxies indicate that, at least in some cases, big massive galaxies form through collisions between smaller ones, in a generation after generation never-ending story. The Hubble image shows the paired galaxies very close together with streams of stars being pulled out of the galaxies. The colliding 'parent' galaxies lose their shape and smoother galaxies are formed. The whole merging process can take less than a billion years. The Hubble Space Telescope imaged 81 galaxies in the galaxy cluster 8 billion light-years away. Astronomers say the collisions have never been observed before at this frequency. Many of the collisions involve very massive galaxies, and the end result will be even more massive galaxies.

1999-01-01

337

Simultaneous detection of Raman- and collision-induced molecular rotations of O2 and N2 via femtosecond multi-pulses in combination with quartz-enhanced photoacoustic spectroscopy  

NASA Astrophysics Data System (ADS)

Molecular rotational states of nitrogen and oxygen molecules at room temperature and atmospheric pressure are excited by femtosecond double- and multi-pulses with variable temporal pulse distances, and quartz-enhanced photoacoustic spectroscopy is used for their detection. A simple extrapolation of measured double-pulse data is presented, which predicts form and position of Raman-excited spectral features and thus enables us to distinguish between spectral lines caused by Raman-scattering- and collision-induced absorption both appearing when excitation by pulse trains is used.

Schippers, W.; Köhring, M.; Böttger, S.; Willer, U.; Flachenecker, G.; Schade, W.

2013-09-01

338

Smallest artificial molecular neural-net for collective and emergent information processing  

NASA Astrophysics Data System (ADS)

While exploring the random diffusion of 2 bit molecular switches (we define as molecular neuron) on an atomic flat Au (111) substrate, we have found that at least four molecules are required to construct a functional neural net. Surface electron density wave enables communication of one to many molecules at a time-a prerequisite for the parallel processing. Here we have shown that in a neural net of several molecules, some of them could dynamically store information as memory and consistently replicate the fundamental relationship that is found only in a collective and emergent computing system like our brain.

Bandyopadhyay, Anirban; Sahu, Satyajit; Fujita, Daisuke

2009-09-01

339

Rotationally Inelastic Collisions of c2 with ORTHO-H2 and PARA-H2  

NASA Astrophysics Data System (ADS)

Close-coupled and coupled states cross-sections for rotational transitions in C2 on collision with ortho- and pa ra-H2 have been calculated using a potential energy surface based on the ab initio calculations of Lavendy et al. The coupled states approximation is found to be qualitatively accurate. The H2 molecule is well represented by its rotational ground state (j =0 or j = 1) at collision energies below its rotational excitation threshold. Rate coefficients for excitation of C2 by collision with H2 are derived from the calculated collision cross-sections, and are found to be higher than earlier estimates. Key words: molecular processes - ISM: molecules.

Phillips, T. R.

1994-12-01

340

Quantum-state resolved bimolecular collisions of velocity-controlled OH with NO radicals.  

PubMed

Whereas atom-molecule collisions have been studied with complete quantum-state resolution, interactions between two state-selected molecules have proven much harder to probe. Here, we report the measurement of state-resolved inelastic scattering cross sections for collisions between two open-shell molecules that are both prepared in a single quantum state. Stark-decelerated hydroxyl (OH) radicals were scattered with hexapole-focused nitric oxide (NO) radicals in a crossed-beam configuration. Rotationally and spin-orbit inelastic scattering cross sections were measured on an absolute scale for collision energies between 70 and 300 cm(-1). These cross sections show fair agreement with quantum coupled-channels calculations using a set of coupled model potential energy surfaces based on ab initio calculations for the long-range nonadiabatic interactions and a simplistic short-range interaction. This comparison reveals the crucial role of electrostatic forces in complex molecular collision processes. PMID:23180857

Kirste, Moritz; Wang, Xingan; Schewe, H Christian; Meijer, Gerard; Liu, Kopin; van der Avoird, Ad; Janssen, Liesbeth M C; Gubbels, Koos B; Groenenboom, Gerrit C; van de Meerakker, Sebastiaan Y T

2012-11-23

341

Fragmentation studies of CF^+ and HF^+ ions in collisions with cold electrons  

NASA Astrophysics Data System (ADS)

The fundamental molecules composed of atoms from the second row of the periodic table (C,N,O,F) have a rich structure of excited potential curves that can be probed at high energy resolution by observing fragmentation processes following collisions with quasi-monochromatic electrons. Experiments of this type are performed in merged electron and ion beams at the ion storage ring TSR in Heidelberg, Germany. Using a cold, photocathode-produced electron beam, experiments on the system CF^+ yield rich structure in the collision energy dependence of both dissociative recombination (DR) and excitation (DE). The fragment-imaging technique shows a strong collision energy dependence of final ground and excited states of DR products. Moreover, an angular anisotropy of DR is observed for elevated collision energies. DR of HF^+ displays extremely low kinetic energy release of neutral fragments yielding resolution on initial rotational states of the ions. This predestines HF^+ to be used as ``molecular thermometer.''

Novotny, Oldrich; Altevogt, S.; Berg, M. H.; Bing, D.; Buhr, H.; Fadil, H.; Froese, M.; Hoffmann, J.; Jordon-Thaden, B.; Krantz, C.; Lange, M.; Lestinsky, M.; Mendes, M.; Novotny, S.; Orlov, D. A.; Petrignani, A.; Shornikov, A.; Sorg, T.; Stuetzel, J.; Wolf, A.; Jaroshevich, A. S.

2008-10-01

342

Efficient representations of continuum states for photoionization processes from atomic and molecular targets  

NASA Astrophysics Data System (ADS)

The investigation of single and double photoionization effects in small atoms and molecules provides a means to probe fundamental quantum mechanical phenomena concerning electron correlation and interference effects. To consider these concepts accurately from first principles requires the construction of the exact final continuum states of a many body problem in atomic double photoionization and of the complicated continuum states in molecular single photoionization. Methods designed for incorporating exterior complex scaling (ECS) have proven very successful towards accomplishing these goals, providing a rigorous framework for describing continuum states involving any number of outgoing electrons with numerical exactness. Furthermore, such methods render solutions that can be interrogated to extract the full richness of information about the photoionization process from the wave function. This work aims to demonstrate the use of exterior complex scaling by first exactly solving the three-body breakup problem of the atomic hydride anion. H-- is the simplest atomic system and is most sensitive to electron correlation effects. The application of ECS with an efficient finite-element discrete variable representation proves quite capable and well-suited for this atomic Coulomb breakup problem. The evolution of this framework to treat molecular problems efficiently with exactness is furthered by the design of a hybrid basis method. The incorporation of analytic Gaussian basis sets ubiquitous in bound state molecular descriptions seems natural for considering molecular continuum states. The hybrid method is described in full detail and applied to completely describe photoionization of molecular H+2 and Li+2 . Photoionization of simple molecular systems offers significantly more complexity in the resulting angular distributions of the ejected electron as the target geometry becomes less atomic-like, i.e., as the internuclear separation increases. In this regard, investigation of photoejection from Li+2 provides a molecular environment ideal for considering the role of internuclear distance in molecular continuum states. With its relatively long equilibrium bond length of R = 5.86 bohr, the extreme target geometry of Li+2 offers the possibility of investigating interference effects caused by the photoelectron de Broglie wavelength becoming comparable with the bond length at relatively low photoejection energies. The aid of the hybrid basis in treating this problem proves substantial, providing an intuitive and robust framework for complete solution of processes involving continuum states of molecular targets.

Yip, Frank L.

343

Adaptive binary splitting for efficient RFID tag anti-collision  

Microsoft Academic Search

Tag collision arbitration for passive RFID tags is a significant issue for fast tag identification. This letter presents a novel tag anti-collision scheme called adaptive binary splitting (ABS). For reducing collisions, ABS assigns distinct timeslots to tags by using information obtained from the last identification process. Our performance evaluation shows that ABS outperforms other tree based tag anti-collision protocols.

Jihoon Myung; Wonjun Lee; J. Srivastava

2006-01-01

344

Association between Higher Order Visual Processing Abilities and a History of Motor Vehicle Collision Involvement by Drivers Ages 70 and Over  

PubMed Central

Purpose. To examine in a population-based sample of 2000 drivers aged 70 years and older, the independent association between higher order visual processing impairment and motor vehicle collision (MVC) rate during the prior 5 years. Methods. Three higher order visual processing screening tests were administered since previous research found associations between impaired performance on these screens and MVC involvement. They included an estimate of visual processing speed under divided attention conditions (useful field of view [UFOV] subset 2); Trails B, a paper and pencil test of visual processing speed also involving problem solving, executive function, and working memory; and the visual closure subtest of the Motor Free Visual Perception Test (MVPT) examining the ability to recognize objects only partially visible. Potentially confounding variables were also assessed including demographics, general cognitive status, visual acuity, and contrast sensitivity. MVC involvement was determined by accident reports from the Alabama Department of Public Safety, and driving exposure was estimated from the Driving Habits Questionnaire. Results. MVC rates (for at fault and all MVCs) were significantly higher for those older drivers with impairments in any of the three visual processing screening tests. After adjustment for potentially confounding influences, the association between MVC rate and Trails B remained significant, whereas the association with MVPT and UFOV did not. Conclusions. This population-based study of drivers aged 70 years and older suggests that a paper and pencil test assessing higher order visual processing skills is independently associated with a recent history of MVC involvement.

Friedman, Carly; McGwin, Gerald; Ball, Karlene K.; Owsley, Cynthia

2013-01-01

345

Charge-transfer processes in collisions of H+ ions with H2, D2, CO, and CO2 molecules in the energy range 0.2-4.0 keV  

NASA Astrophysics Data System (ADS)

Charge-transfer processes resulting from collisions of H+ ions with H2, D2, CO, and CO2 molecules have been experimentally investigated in the energy range of 0.2-4.0 keV by using the initial growth-rate method. Theoretical analysis based on a molecular-orbital expansion method for H2 and CO targets was also carried out. The observed cross sections are compared with previous experimental and theoretical data. The present results for H2 are found to be in excellent accord with the recommended data by Barnett [Oak Ridge National Laboratory Report No. ORNL-6086 (1990)], and hence, confirm the accuracy of the recommended data. But, at 0.2 keV, the present data for D2 are found to be smaller than those for H2. For the CO molecule, the present data qualitatively agree well with most previous measurements, but show the stronger energy dependence, while the present theory shows a pronounced structure at around 0.25 keV and ties well with other low-energy measurements below 0.1 keV. For the CO2 molecule, the present results are in excellent accord with other measurements above 1 keV, while they show some differences below this energy where our experimental result displays the stronger energy dependence. These data are useful for various applications.

Kusakabe, Toshio; Asahina, Kensuke; Gu, Jiang P.; Hirsch, Gerhard; Buenker, Robert J.; Kimura, Mineo; Tawara, Hiroyuki; Nakai, Yohta

2000-12-01

346

Galaxy collisions  

Microsoft Academic Search

Theories of how galaxies, the fundamental constituents of large-scale structure, form and evolve have undergone a dramatic paradigm shift in the last few decades. Earlier views were of rapid, early collapse and formation of basic structures, followed by slow evolution of the stellar populations and steady buildup of the chemical elements. Current theories emphasize hierarchical buildup via recurrent collisions and

Curtis Struck

1999-01-01

347

Effect of vacuum processing on outgassing within an orbiting molecular shield  

NASA Technical Reports Server (NTRS)

The limiting hydrogen number density in an orbiting molecular shield is highly dependent on the outgassing rates from the materials of construction for the shield, experimental apparatus, and other hardware contained within the shield. Ordinary degassing temperatures used for ultrahigh vacuum studies (less than 450 C) are not sufficient to process metals so that the contribution to the number density within the shield due to outgassing is less than the theoretically attainable level (approximately 200 per cu. cm). Pure aluminum and type 347 stainless steel were studied as candidate shield materials. Measurements of their hydrogen concentration and diffusion coefficients were made, and the effects of high temperature vacuum processing (greater than 600 C) on their resulting outgassing rates was determined. The densities in a molecular shield due to the outgassing from either metal were substantially less ( 0.003) than the density due to the ambient atomic hydrogen flux at an orbital altitude of 500 km.

Outlaw, R. A.

1982-01-01

348

Molecular Basis of a Million-Fold Affinity Maturation Process in a Protein-Protein Interaction  

SciTech Connect

Protein engineering is becoming increasingly important for pharmaceutical applications where controlling the specificity and affinity of engineered proteins is required to create targeted protein therapeutics. Affinity increases of several thousand-fold are now routine for a variety of protein engineering approaches, and the structural and energetic bases of affinity maturation have been investigated in a number of such cases. Previously, a 3-million-fold affinity maturation process was achieved in a protein-protein interaction composed of a variant T-cell receptor fragment and a bacterial superantigen. Here, we present the molecular basis of this affinity increase. Using X-ray crystallography, shotgun reversion/replacement scanning mutagenesis, and computational analysis, we describe, in molecular detail, a process by which extrainterfacial regions of a protein complex can be rationally manipulated to significantly improve protein engineering outcomes.

D Bonsor; S Postel; B Pierce; N Wang; P Zhu; R Buonpane; Z Weng; D Kranz; E Sundberg

2011-12-31

349

Molecular basis of a million-fold affinity maturation process in a protein-protein interaction  

PubMed Central

Protein engineering is increasingly important for pharmaceutical applications where controlling the specificity and affinity of engineered proteins is required to create targeted protein therapeutics. Affinity increases of several thousand-fold are now routine for a variety of protein engineering approaches and the structural and energetic bases of affinity maturation have been investigated in a number of such cases. Previously, a 3 million-fold affinity maturation process was achieved in a protein-protein interaction comprised of a variant T cell receptor fragment and a bacterial superantigen. Here, we present the molecular basis of this affinity increase. Using X-ray crystallography, shotgun reversion/replacement-scanning mutagenesis and computational analysis we describe, in molecular detail, a process by which extra-interfacial regions of a protein complex can be rationally manipulated to significantly improve protein engineering outcomes.

Bonsor, Daniel A.; Postel, Sandra; Pierce, Brian G.; Wang, Ningyan; Zhu, Penny; Buonpane, Rebecca A.; Weng, Zhiping; Kranz, David M.; Sundberg, Eric J.

2011-01-01

350

Power Factor Enhancement in Solution-Processed Organic n-Type Thermoelectrics Through Molecular Design.  

PubMed

A new class of high-performance n-type organic thermoelectric materials, self-doping perylene diimide derivatives with modified side chains, is reported. These materials achieve the highest n-type thermoelectric performance of solution-processed organic materials reported to date, with power factors as high as 1.4 ?W/mK(2) . These results demonstrate that molecular design is a promising strategy for enhancing organic thermoelectric performance. PMID:24633973

Russ, Boris; Robb, Maxwell J; Brunetti, Fulvio G; Miller, P Levi; Perry, Erin E; Patel, Shrayesh N; Ho, Victor; Chang, William B; Urban, Jeffrey J; Chabinyc, Michael L; Hawker, Craig J; Segalman, Rachel A

2014-06-01

351

Direct molecular-level Monte Carlo simulation of Joule-Thomson processes  

Microsoft Academic Search

We present an application of the recently developed constant enthalpy-constant pressure Monte Carlo method [Smith, W. R., and Lísal, M., 2002, Phys. Rev. E, 66, 01114] for the direct simulation of Joule-Thomson expansion processes using a molecular-level system model. For the alternative refrigerant HFC-32 (CH2F2), we perform direct simulations of the isenthalpic integral Joule-Thomson effect (temperature drop) resulting from Joule-Thomson

Martin Lísal; William R. Smith; Karel Aim

2003-01-01

352

Cross Sections for Positive-Ion and Electron Production in Collisions of 1-25 KeV Hydrogen Atoms with Atomic and Molecular Gases.  

National Technical Information Service (NTIS)

Cross sections are reported for production of positive ions and electrons in collisions of hydrogen atoms in the energy range 1-25 keV with He, Ne, A, Kr, Xe, H2, and O2. Slow, positive ions are produced by capture of an electron by the fast atom from the...

R. J. McNeal D. C. Clark R. A. Klingberg

1970-01-01

353

All-dry processible and PAG-attached molecular glasses for improved lithographic performance  

NASA Astrophysics Data System (ADS)

As the semiconductor industry moves forward, resolution limits are being pushed to the sub-30 nm regime. In order to meet these demands, radical new resist design and processes must be explored. We have developed a molecular glass system for all-dry processing conditions. Physical vapor deposition (PVD) has been used for film formation onto silicon wafers. PVD deposits a uniform film of controlled thickness free from impurities that are often introduced by casting solvents used in traditional spin coating methods. Thermal development is used as an alternative to processing in solvents in order to prevent resist swelling and pattern collapse by capillary forces. The deposited molecule is designed to crosslink upon E-beam irradiation without additives, and therefore form a homogeneous, single component film. PAG-attached molecular glasses have been synthesized in order to promote film homogeneity as well. By tethering PAG directly to the molecular glass core, issues such as PAG aggregation can be remedied. Acid migration, which increases blur and LER, can also be hindered.

Krysak, Marie; Kolb, Tristan; Neuber, Christian; Schmidt, Hans-Werner; Ober, Christopher K.

2010-03-01

354

Molecular dynamics model of ultraviolet matrix-assisted laser desorption/ionization including ionization processes.  

PubMed

A molecular dynamics model of UV-MALDI including ionization processes is presented. In addition to the previously described breathing sphere approach developed for simulation of laser ablation/desorption of molecular systems, it includes radiative and nonradiative decay, exciton hopping, two pooling processes, and electron capture. The results confirm the main conclusions of the continuum model of Knochenmuss, Anal. Chem. 2003, 75, 2199, but provide a much more detailed description of the interaction between ablation/desorption and ionization processes in the critical early time regime. Both desorption and ablation regimes generate free ions, and yields are in accordance with experiment. The first molecular ions are emitted at high velocities shortly before neutral desorption begins, because of surface charging caused by electron escape from the top of the sample. Later ions are entrained and thermalized in the plume of neutral molecules and clusters. Clusters are found to be stable on a nanosecond time scale, so the ions in them will be released only slowly, if at all. Exciton hopping rate and the mean radius for ion recombination are shown to be key parameters that can have a significant effect on net ion yield. PMID:16853990

Knochenmuss, Richard; Zhigilei, Leonid V

2005-12-01

355

Geochemical Interpretation of Collision Volcanism  

NASA Astrophysics Data System (ADS)

Collision volcanism can be defined as volcanism that takes place during an orogeny from the moment that continental subduction starts to the end of orogenic collapse. Its importance in the Geological Record is greatly underestimated as collision volcanics are easily misinterpreted as being of volcanic arc, extensional or mantle plume origin. There are many types of collision volcanic province: continent-island arc collision (e.g. Banda arc); continent-active margin collision (e.g. Tibet, Turkey-Iran); continent-rear-arc collision (e.g. Bolivia); continent-continent collision (e.g. Tuscany); and island arc-island arc collision (e.g. Taiwan). Superimposed on this variability is the fact that every orogeny is different in detail. Nonetheless, there is a general theme of cyclicity on different time scales. This starts with syn-collision volcanism resulting from the subduction of an ocean-continent transition and continental lithosphere, and continues through post-collision volcanism. The latter can be subdivided into orogenic volcanism, which is related to thickened crust, and post-orogenic, which is related to orogenic collapse. Typically, but not always, collision volcanism is preceded by normal arc volcanism and followed by normal intraplate volcanism. Identification and interpretation of collision volcanism in the Geologic Record is greatly facilitated if a dated stratigraphic sequence is present so that the petrogenic evolution can be traced. In any case, the basis of fingerprinting collision terranes is to use geochemical proxies for mantle and subduction fluxes, slab temperatures, and depths and degrees of melting. For example, syn-collision volcanism is characterized by a high subduction flux relative to mantle flux because of the high input flux of fusible sediment and crust coupled with limited mantle flow, and because of high slab temperatures resulting from the decrease in subduction rate. The resulting geochemical patterns are similar regardless of collision type with extreme LILE and significant HFSE enrichment relative to MORB and with large negative Nb-Ta and Ti anomalies. Post-collision volcanism is usually ascribed to combinations of slab detachment, delamination, and slab roll back (orogenic) and extension (post-orogenic). The magma source is typically conductively-heated, sub-continental mantle lithosphere with composition and depth of melting depending on the nature and evolution of the collision zone in question. Geochemical patterns may be similar to those of syn-collision basalts or of intraplate, continental basalts - or transitional between these. This variability in space and time, though problematic for geochemical fingerprinting, can give clues to the polarity and development of the collision zone, for example by highlighting the distribution of subduction-modified mantle lithosphere and hence of pre-collision subduction zones. One characteristic common to this setting is a high crustal input resulting from the presence of a hot, thick 'crustal chemical filter' which is evident on geochemical projections that highlight AFC-type processes. Using this, and other, geochemical features it is possible to develop methodologies to at least partly see through the complexity of collision terranes.

Pearce, Julian

2014-05-01

356

Simulation of collisions between buckyballs and graphene sheets  

Microsoft Academic Search

The phenomena of buckyball–graphene collisions were investigated by classical molecular dynamics (MD) simulation using the empirical Tersoff potential. Three cases were investigated: collisions between a buckyball and a single-layer graphene; collisions between a nano-onion (a double-layer concentric spherical nanostructure: a C60 in a C320) and a single-layer graphene; collisions between a nano-onion and a double-layer graphene. The impact velocity of

Zhen Zhang; Xianqiao Wang; Jiaoyan Li

2011-01-01

357

Simulation of collisions between buckyballs and graphene sheets  

Microsoft Academic Search

The phenomena of buckyball–graphene collisions were investigated by classical molecular dynamics (MD) simulation using the empirical Tersoff potential. Three cases were investigated: collisions between a buckyball and a single-layer graphene; collisions between a nano-onion (a double-layer concentric spherical nanostructure: a C60 in a C320) and a single-layer graphene; collisions between a nano-onion and a double-layer graphene. The impact velocity of

Zhen Zhang; Xianqiao Wang; Jiaoyan Li

2012-01-01

358

Molecularly mediated processing and assembly of nanoparticles: exploring the interparticle interactions and structures.  

PubMed

The harnessing of the nanoscale properties of nanoparticles in most technological applications requires the abilities of controlled processing and assembly, which has been an important challenge because of the difficulty in manipulating interparticle properties. Molecularly mediated processing and assembly of nanoparticles have emerged as an important strategy for addressing this challenge. The capability of this strategy in manipulating size, shape, composition, and interparticle properties has significant implications for designing sensing, biosensing, nanoprobing, and many other functional nanostructures. This Account highlights some of the important findings in investigating both interparticle and collective properties as a forum for discussing new opportunities in exploiting nanoparticle-based designs and applications. The concept of mediator-template assembly of nanoparticles explores the combination of the forces from a mediator and a templating molecule for designing and controlling the interparticle interactions. The manipulation of the interparticle interaction properties and the detection of the molecular signatures are two of the key elements in this concept. A series of well-defined molecular mediators ranging from inorganic, organic, supramolecular, to biological molecules have been explored to ascertain how these two elements can be achieved in nanoparticle assemblies. The emphasis is the fundamental understanding of interparticle molecular interactions, such as covalent, electrostatic, hydrogen bonding, multidentate coordination, pi-pi interactions, etc. Each of these molecular interactions has been examined using specific molecules, such as multifunctional ligands, tunable sizes, shapes, or charges, well-defined molecular rigidity and chirality, or spectroscopic signatures, such as fluorescence and Raman scattering. Examples included thiols, thioethers, carboxylic acids, fullerenes, dyes, homocysteines, cysteines, glutathiones, proteins, and DNAs as molecular mediators for the assembly of gold, alloy, and magnetic nanoparticles. The understanding of these systems provided insights into how the unique electrical, optical, magnetic, and spectroscopic properties of the nanoparticle assemblies can be exploited for potential applications. This Account also highlights a few examples in chemical sensing and bioprobing to illustrate the importance of interparticle interactions and structures in exploiting these properties. One example involves thin-film assemblies of metal nanoparticles as biomimetic ion channels or chemiresistor sensing arrays by exploiting the nanostructured ligand framework interactions. Other examples explore the surface-enhanced Raman scattering signature as nanoprobes for the detection of protein binding or the enzyme-based cutting of interparticle DNAs. The detailed understanding of the design and control parameters in these and other systems should have a profound impact on the exploration of nanoparticles in a wide range of technological applications. PMID:19378982

Lim, Stephanie I; Zhong, Chuan-Jian

2009-06-16

359

Theoretical atomic and molecular physics: Progress report, July 1, 1988 through June 30, 1989  

Microsoft Academic Search

The theoretical atomic and molecular physics program at Rice University emphasizes fundamental questions regarding the structure and collision dynamics of various atomic and molecular systems with some attention given to atomic processes at surfaces. Our activities have been centered on continuing the projects initiated last year as well as beginning some new studies. These include: differential elastic and charge-transfer scattering

1989-01-01

360

Molecular characterization of a vacuolar processing enzyme related to a putative cysteine proteinase of Schistosoma mansoni.  

PubMed Central

Proproteins of various vacuolar proteins are post-translationally processed into mature forms by the action of a unique vacuolar processing enzyme. If such a processing enzyme is transported to vacuoles together with proprotein substrates, the enzyme must be a latent form. Immunocytochemical localization of a vacuolar processing enzyme, a 37-kD cysteine proteinase, in the endosperm of maturing castor bean seeds places the enzyme in the vacuolar matrix, where a variety of proproteins is also present. To characterize a molecular structure of vacuolar processing enzyme, we isolated a cDNA for the enzyme. Deduced primary structure of a 55-kD precursor is 33% identical to a putative cysteine proteinase of the human parasite Schistosoma mansoni. The precursor is composed of a signal peptide, a 37-kD active processing enzyme domain, and a propeptide fragment. Although the precursor expressed in Escherichia coli has no vacuolar processing activity, a 36-kD immunopositive protein expressed in E. coli is active. These results suggest that the activation of the vacuolar processing enzyme requires proteolytic cleavage of a 14-kD C-terminal propeptide fragment of the precursor.

Hara-Nishimura, I; Takeuchi, Y; Nishimura, M

1993-01-01

361

Molecular processes leading to aberrant androgen receptor signaling and castration resistance in prostate cancer  

PubMed Central

Hormone therapies targeting androgen receptor signaling are the mainstay of treatment for patients with advanced prostate cancer. The length of clinical remission induced by hormone therapies varies substantially among treated patients. Why some patients progress rapidly after treatment while others benefit with prolonged remission is a question that remains unsolved. The androgen receptor signaling pathway is the key molecular determinant of castration resistance, and a key target for prostate cancer drug design. Recent advances in characterizing molecular processes leading to the development of castration-resistant prostate cancer, including the discovery of multiple androgen receptor splicing variants, offer opportunities for rational development of new clinical tools or approaches to predict, monitor or control/prevent prostate cancer progression in the castrate setting.

Hu, Rong; Denmeade, Samuel R; Luo, Jun

2011-01-01

362

Processes of DNA condensation induced by multivalent cations: Approximate annealing experiments and molecular dynamics simulations  

NASA Astrophysics Data System (ADS)

The condensation of DNA induced by spermine is studied by atomic force microscopy (AFM) and molecular dynamics (MD) simulation in this paper. In our experiments, an equivalent amount of multivalent cations is added to the DNA solutions in different numbers of steps, and we find that the process of DNA condensation strongly depends on the speed of adding cations. That is, the slower the spermine cations are added, the slower the DNA aggregates. The MD and steered molecular dynamics (SMD) simulation results agree well with the experimental results, and the simulation data also show that the more steps of adding multivalent cations there are, the more compact the condensed DNA structure will be. This investigation can help us to control DNA condensation and understand the complicated structures of DNA—cation complexes.

Chai, Ai-Hua; Ran, Shi-Yong; Zhang, Dong; Jiang, Yang-Wei; Yang, Guang-Can; Zhang, Lin-Xi

2013-09-01

363

Chemi-ionization Processes. Alkali-metal Geocosmical Plasmas  

SciTech Connect

Chemi-ionization processes, leading to formation of molecular ions, can play an essential role in the sequence of ion-molecular reactions on surfaces of solid particles or in associative processes of the binary collisions leading to surprising variety of molecular formations in interstellar gas and geocosmical plasmas. The presented results may be recommended for the interpretation of experimental data and for theoretical research of geocosmical plasmas, first of all the the volcanic gases on Io.

Klyucharev, Andrey N.; Bezuglov, Nikolay N.; Matveev, Andrey A. [V.A. Fock Institute of Physics, Saint-Petersburg State University, Ulianovskaya 1, 198504, St. Petersburg, Petrodvorets (Russian Federation); Mihajlov, Anatolij A.; Ignjatovic, Ljubinko M. [Institute of Physics, P.O. Box 57, 11001 Belgrade (Serbia); Dimitrijevic, Milan S. [Astronomical Observatory, Volgina 7, 11160 Belgrade 74 (Serbia)

2007-09-28

364

Molecular processes during fat cell development revealed by gene expression profiling and functional annotation  

PubMed Central

Background Large-scale transcription profiling of cell models and model organisms can identify novel molecular components involved in fat cell development. Detailed characterization of the sequences of identified gene products has not been done and global mechanisms have not been investigated. We evaluated the extent to which molecular processes can be revealed by expression profiling and functional annotation of genes that are differentially expressed during fat cell development. Results Mouse microarrays with more than 27,000 elements were developed, and transcriptional profiles of 3T3-L1 cells (pre-adipocyte cells) were monitored during differentiation. In total, 780 differentially expressed expressed sequence tags (ESTs) were subjected to in-depth bioinformatics analyses. The analysis of 3'-untranslated region sequences from 395 ESTs showed that 71% of the differentially expressed genes could be regulated by microRNAs. A molecular atlas of fat cell development was then constructed by de novo functional annotation on a sequence segment/domain-wise basis of 659 protein sequences, and subsequent mapping onto known pathways, possible cellular roles, and subcellular localizations. Key enzymes in 27 out of 36 investigated metabolic pathways were regulated at the transcriptional level, typically at the rate-limiting steps in these pathways. Also, coexpressed genes rarely shared consensus transcription-factor binding sites, and were typically not clustered in adjacent chromosomal regions, but were instead widely dispersed throughout the genome. Conclusions Large-scale transcription profiling in conjunction with sophisticated bioinformatics analyses can provide not only a list of novel players in a particular setting but also a global view on biological processes and molecular networks.

Hackl, Hubert; Burkard, Thomas Rainer; Sturn, Alexander; Rubio, Renee; Schleiffer, Alexander; Tian, Sun; Quackenbush, John; Eisenhaber, Frank; Trajanoski, Zlatko

2005-01-01

365

Reactive Molecular Dynamics of Detonating Petn  

Microsoft Academic Search

We investigate the initial chemical events sustaining a detonation in shock-compressed PETN resulting from intermolecular collisions behind the shock wave using first-principles reactive molecular dynamics. The reaction dynamics of bimolecular collisions was studied as a function of collision velocities and crystallographic orientations. For each orientation, threshold collision velocities of reaction, and products of decomposition were determined. The timescale of reaction

A. C. Landerville; I. I. Oleynik; C. T. White

2009-01-01

366

REACTIVE MOLECULAR DYNAMICS OF DETONATING PETN  

Microsoft Academic Search

We investigate the initial chemical events sustaining a detonation in shock-compressed PETN resulting from intermolecular collisions behind the shock wave using first-principles reactive molecular dynamics. The reaction dynamics of bimolecular collisions was studied as a function of collision velocities and crystallographic orientations. For each orientation, threshold collision velocities of reaction, and products of decomposition were determined. The timescale of reaction

A. C. Landerville; I. I. Oleynik; C. T. White

2009-01-01

367

Collision Risk Evaluation Based on Deceleration for Collision Avoidance  

NASA Astrophysics Data System (ADS)

Our previous paper proposed a deceleration for collision avoidance (DCA) as an index to evaluate the collision risk against a forward obstacle. In order to reduce the calculation amount, the calculation process of the DCA assumed that the following vehicle performed an uniform motion within a constant reaction time. However, the assumption would yield underestimation of the collision risk when the following vehicle accelerates and overestimation when it decelerates. Therefore, in this manuscript, the DCA was calculated on the assumption that the following vehicle kept the uniformly-accelerated motion within the reaction time and the numerical simulation was performed to show that the improved DCA could evaluate the collision risk properly compared to the conventional DCA.

Hiraoka, Toshihiro; Takada, Shota

368

Lifshitz-van der Waals forces in aerosol particle collisions. I - Introduction: Water droplets  

Microsoft Academic Search

The role of van der Waals forces in bringing about collisions between aerosol particles in the free-molecular, transition and continuum regimes of flow is assessed for the case of two water particles. Droplet collision rates are computed according to an expression for free-molecular collisions between aerosol particles with a singular, attractive contact potential and the extension of this expression to

W. H. Marlow

1980-01-01

369

Abinitio study of charge-transfer dynamics in collisions of C2+ ions with hydrogen chloride  

NASA Astrophysics Data System (ADS)

Ab initio quantum chemistry molecular calculations followed by a semiclassical dynamical treatment in the keV collision energy range have been developed for the study of the charge-transfer process in collisions of C2+ ions with hydrogen chloride. The mechanism has been investigated in detail in connection with avoided crossings between states involved in the reaction. A simple mechanism driven by a strong nonadiabatic coupling matrix element has been pointed out for this process. A comparative analysis with the halogen fluoride target corresponding to a similar electronic configuration shows a quite different charge-transfer mechanism leading to a very different behavior of the cross sections. Such behavior may be correlated to specific nonadiabatic interactions observed in these collision systems.

Rozsályi, E.; Bene, E.; Halász, G. J.; Vibók, Á.; Bacchus-Montabonel, M. C.

2011-05-01

370

MOLECULAR SIEVES AS CATALYSTS FOR METHANOL DEHYDRATION IN THE LPDMEtm PROCESS  

SciTech Connect

Several classes of molecular sieves were investigated as methanol dehydration catalysts for the LPDME{trademark} (liquid-phase dimethyl ether) process. Molecular sieves offer a number of attractive features as potential catalysts for the conversion of methanol to DME. These include (1) a wide range of acid strengths, (2) diverse architectures and channel connectivities that provide latitude for steric control, (3) high active site density, (4) well-investigated syntheses and characterization, and (5) commercial availability in some cases. We directed our work in two areas: (1) a general exploration of the catalytic behavior of various classes of molecular sieves in the LPDME{trademark} system and (2) a focused effort to prepare and test zeolites with predominantly Lewis acidity. In our general exploration, we looked at such diverse materials as chabazites, mordenites, pentasils, SAPOs, and ALPOs. Our work with Lewis acidity sought to exploit the structural advantages of zeolites without the interfering effects of deleterious Broensted sites. We used zeolite Ultrastable Y (USY) as our base material because it possesses a high proportion of Lewis acid sites. This work was extended by modifying the USY through ion exchange to try to neutralize residual Broensted acidity.

Andrew W. Wang

2002-04-01

371

Study of applied magnetic field magnetoplasmadynamic thrusters with particle-in-cell code with Monte Carlo collision. I. Computation methods and physical processes  

SciTech Connect

A two-dimensional axisymmetric electromagnetic particle-in-cell code with Monte Carlo collision conditions has been developed for an applied-field magnetoplasmadynamic thruster simulation. This theoretical approach establishes a particle acceleration model to investigate the microscopic and macroscopic characteristics of particles. This new simulation code was used to study the physical processes associated with applied magnetic fields. In this paper (I), detail of the computation procedure and results of predictions of local plasma and field properties are presented. The numerical model was applied to the configuration of a NASA Lewis Research Center 100-kW magnetoplasmadynamic thruster which has well documented experimental results. The applied magnetic field strength was varied from 0 to 0.12 T, and the effects on thrust were calculated as a basis for verification of the theoretical approach. With this confirmation, the changes in the distributions of ion density, velocity, and temperature throughout the acceleration region related to the applied magnetic fields were investigated. Using these results, the effects of applied field on physical processes in the thruster discharge region could be represented in detail, and those results are reported.

Tang Haibin; Cheng Jiao; Liu Chang [School of Astronautics, Beijing University of Aeronautics and Astronautics, Beijing 100191 (China); York, Thomas M. [Ohio State University, Columbus, Ohio 43235 (United States)

2012-07-15

372

Enhanced light-assisted-collision rate via excitation to the long-lived 5S{sub 1/2}-5D{sub 5/2} molecular potential in an {sup 85}Rb magneto-optical trap  

SciTech Connect

We report measurements of a significant increase in the two-body loss rate in an {sup 85}Rb magneto-optic trap (MOT) caused by the addition of light resonant with the 5P{sub 3/2}-to-5D{sub 5/2} transition (776 nm) in Rb. Exposure to the additional light resulted in up to a factor of 5 decrease in the steady-state number of atoms in the MOT. This loss is attributed to more than an order of magnitude increase in the light-assisted collision rate brought about by the 776-nm light. By measuring the intensity dependence of the loss rate, the loss channel was identified to be the relatively long-lived 5S{sub 1/2}-5D{sub 5/2} molecular potential.

Wilson, Truman M.; Roberts, Jacob L. [Department of Physics, Colorado State University, Fort Collins, Colorado 80523 (United States)

2011-03-15

373

Laser modification of ultracold atomic collisions: Theory  

Microsoft Academic Search

Specific molecular mechanisms are proposed for associative ionization collisions of ultracold sodium atoms in a hybrid optical trap. When an intense, strongly detuned optical trap laser is on, the ionization rate is modulated by molecular bound-state resonances which are strongly affected by field dressing. When the weak, slightly detuned optical molasses lasers are on to provide cooling, an excitation mechanism

Paul S. Julienne; Robert Heather

1991-01-01

374

Signal processing for molecular and cellular biological physics: an emerging field  

PubMed Central

Recent advances in our ability to watch the molecular and cellular processes of life in action—such as atomic force microscopy, optical tweezers and Forster fluorescence resonance energy transfer—raise challenges for digital signal processing (DSP) of the resulting experimental data. This article explores the unique properties of such biophysical time series that set them apart from other signals, such as the prevalence of abrupt jumps and steps, multi-modal distributions and autocorrelated noise. It exposes the problems with classical linear DSP algorithms applied to this kind of data, and describes new nonlinear and non-Gaussian algorithms that are able to extract information that is of direct relevance to biological physicists. It is argued that these new methods applied in this context typify the nascent field of biophysical DSP. Practical experimental examples are supplied.

Little, Max A.; Jones, Nick S.

2013-01-01

375

Observation of the amorphous zinc oxide recrystalline process by molecular dynamics simulation  

PubMed Central

The detailed structural variations of amorphous zinc oxide (ZnO) as well as wurtzite (B4) and zinc blende (B3) crystal structures during the temperature elevation process were observed by molecular dynamics simulation. The amorphous ZnO structure was first predicted through the simulated-annealing basin-hopping algorithm with the criterion to search for the least stable structure. The density and X-ray diffraction profiles of amorphous ZnO of the structure were in agreement with previous reports. The local structural transformation among different local structures and the recrystalline process of amorphous ZnO at higher temperatures are observed and can explain the structural transformation and recrystalline mechanism in a corresponding experiment [Bruncko et al., Thin Solid Films 520, 866-870 (2011)].

Lin, Ken-Huang; Sun, Shih-Jye; Ju, Shin-Pon; Tsai, Jen-Yu; Chen, Hsin-Tsung; Hsieh, Jin-Yuan

2013-01-01

376

Femtosecond laser processing of germanium: an ab initio molecular dynamics study  

NASA Astrophysics Data System (ADS)

An ab initio molecular dynamics study of femtosecond laser processing of germanium is presented in this paper. The method based on the finite temperature density functional theory is adopted to probe the structural change, thermal motion of the atoms, dynamic property of the velocity autocorrelation, and the vibrational density of states. Starting from a cubic system at room temperature (300 K) containing 64 germanium atoms with an ordered arrangement of 1.132 nm in each dimension, the femtosecond laser processing is simulated by applying a Nosé-Hoover thermostat to the electronic subsystem for ˜100 fs and continuing with a microcanonical ensemble simulation of ˜200 fs. The simulation results show solid, liquid and gas phases of germanium under adjusted intensities of the femtosecond laser irradiation. We find that the irradiated germanium is distinguishable from the usual germanium crystal by analysing their melting and dynamic properties.

Ji, Pengfei; Zhang, Yuwen

2013-12-01

377

Acceleration of Early-Photon Fluorescence Molecular Tomography with Graphics Processing Units  

PubMed Central

Fluorescence molecular tomography (FMT) with early-photons can improve the spatial resolution and fidelity of the reconstructed results. However, its computing scale is always large which limits its applications. In this paper, we introduced an acceleration strategy for the early-photon FMT with graphics processing units (GPUs). According to the procedure, the whole solution of FMT was divided into several modules and the time consumption for each module is studied. In this strategy, two most time consuming modules (Gd and W modules) were accelerated with GPU, respectively, while the other modules remained coded in the Matlab. Several simulation studies with a heterogeneous digital mouse atlas were performed to confirm the performance of the acceleration strategy. The results confirmed the feasibility of the strategy and showed that the processing speed was improved significantly.

Wang, Xin; Zhang, Bin; Cao, Xu; Liu, Fei; Luo, Jianwen; Bai, Jing

2013-01-01

378

Signal processing for molecular and cellular biological physics: an emerging field.  

PubMed

Recent advances in our ability to watch the molecular and cellular processes of life in action--such as atomic force microscopy, optical tweezers and Forster fluorescence resonance energy transfer--raise challenges for digital signal processing (DSP) of the resulting experimental data. This article explores the unique properties of such biophysical time series that set them apart from other signals, such as the prevalence of abrupt jumps and steps, multi-modal distributions and autocorrelated noise. It exposes the problems with classical linear DSP algorithms applied to this kind of data, and describes new nonlinear and non-Gaussian algorithms that are able to extract information that is of direct relevance to biological physicists. It is argued that these new methods applied in this context typify the nascent field of biophysical DSP. Practical experimental examples are supplied. PMID:23277603

Little, Max A; Jones, Nick S

2013-02-13

379

An emerging molecular and cellular framework for memory processing by the hippocampus.  

PubMed

The hippocampus plays a central role in memory consolidation, a process for converting short-term memory into cortically stored, long-lasting memory in the mammalian brain. Here, we review recent data and discuss the 'synaptic re-entry reinforcement' (SRR) hypothesis, which can account for the role of the hippocampus in memory consolidation at both the molecular and systems levels. The central idea of the SRR hypothesis is that reactivation of neural ensembles in the hippocampus during the consolidation period results in multiple rounds of NMDA-receptor-dependent synaptic reinforcement of the hippocampal memory traces created during initial learning. In addition, such reactivation and reinforcement processes permit the hippocampus to act as a 'coincidence regenerator', providing coordinated input that drives the coherent reactivation of cortical neurons, resulting in the progressive strengthening of cortical memory traces through reactivation of cortical NMDA receptors. PMID:12220877

Wittenberg, Gayle M; Tsien, Joe Z

2002-10-01

380

Observation of the amorphous zinc oxide recrystalline process by molecular dynamics simulation  

NASA Astrophysics Data System (ADS)

The detailed structural variations of amorphous zinc oxide (ZnO) as well as wurtzite (B4) and zinc blende (B3) crystal structures during the temperature elevation process were observed by molecular dynamics simulation. The amorphous ZnO structure was first predicted through the simulated-annealing basin-hopping algorithm with the criterion to search for the least stable structure. The density and X-ray diffraction profiles of amorphous ZnO of the structure were in agreement with previous reports. The local structural transformation among different local structures and the recrystalline process of amorphous ZnO at higher temperatures are observed and can explain the structural transformation and recrystalline mechanism in a corresponding experiment [Bruncko et al., Thin Solid Films 520, 866-870 (2011)].

Lin, Ken-Huang; Sun, Shih-Jye; Ju, Shin-Pon; Tsai, Jen-Yu; Chen, Hsin-Tsung; Hsieh, Jin-Yuan

2013-02-01

381

Urea transporters in kidney: molecular analysis and contribution to the urinary concentrating process1.  

PubMed

Facilitated urea transporters (UTs) are responsible for urea accumulation in the renal inner medulla of the mammalian kidney and therefore play a central role in the urinary concentrating process. Recently, the cDNAs encoding three members of the UT family, UT1, UT2, and UT3 have been cloned. These transporters are expressed in different structures of the mammalian kidney. In rat, UT1 resides in the apical membrane of terminal inner medullary collecting ducts, where it mediates vasopressin-regulated urea reabsorption. UT2 and UT3 are located in descending thin limbs of Henle's loop and descending vasa recta, respectively, and participate in urinary recycling processes, which minimize urea escape from the inner medulla. UT1 and UT2 are regulated independently and respond differently to changes in dietary protein content and hydration state. Identification and characterization of these urea transporters advances our understanding of the molecular basis and regulation of the urinary concentrating mechanism. PMID:9729501

Tsukaguchi, H; Shayakul, C; Berger, U V; Hediger, M A

1998-09-01

382

Model approach for low-energy inelastic atomic collisions and application to Al+H and Al++H-  

NASA Astrophysics Data System (ADS)

A model approach is derived for estimates of cross sections and rate coefficients in low-energy inelastic collisions of hydrogen atoms and negative ions with other atoms and positive ions, which are of astrophysical interests. The approach is based on the asymptotic method for electronic molecular structure determination and on the branching probability current method for a nonadiabatic nuclear dynamical treatment. The derived approach is applied to low-energy Al + H and Al+ + H- inelastic collisions. It is shown that the processes with the largest values of cross sections and rates are the excitation and de-excitation ones between the Al(3d) and Al(4p) states in collisions with H, as well as the ion-pair formation and the mutual neutralization processes between these states and the ionic state; the second largest cross sections correspond to the similar processes involving the Al(4s) state. The mechanisms of the processes are discussed in detail.

Belyaev, Andrey K.

2013-11-01

383

Structure of a simple molecular dynamics FORTRAN program optimized for CRAY vector processing computers  

NASA Astrophysics Data System (ADS)

A program structure for efficient vectorization of molecular dynamics FORTRAN programs on CRAY vector processing computers is described. Though coded for a very simple pure atomic fluid in a cubic cell with periodic boundary conditions the program can easily be modified to handle more complicated systems. A detailed analysis shows that the present program is faster by 36% for N = 256 particles and faster by more than a factor of 3 for N = 2048 compared with a fully vectorized molecular dynamics program written for the CYBER 205 vector processing machine. In comparison with a link cell MD program also written for a CRAY the program described here runs three times faster for a large particle number N = 6912. This factor increases with decreasing N to 6.3 for N = 1372. The speedup is achieved by i) long vectors in inner loops wherever possible; ii) limiting the number of arithmetic operations in inevitably short loops as much as possible; iii) appropriate library routines; iv) integer index vector neighbour lists.

Schoen, Martin

1989-01-01

384

Study the sensitivity of molecular functional groups to bioethanol processing in lipid biopolymer of co-products using DRIFT molecular spectroscopy  

NASA Astrophysics Data System (ADS)

To date, there is no study on bioethanol processing-induced changes in molecular structural profiles mainly related to lipid biopolymer. The objectives of this study were to: (1) determine molecular structural changes of lipid related functional groups in the co-products that occurred during bioethanol processing; (2) relatively quantify the antisymmetric CH 3 and CH 2 (ca. 2959 and 2928 cm -1, respectively), symmetric CH 3 and CH 2 (ca. 2871 and 2954 cm -1, respectively) functional groups, carbonyl C dbnd O ester (ca. 1745 cm -1) and unsaturated groups (CH attached to C dbnd C) (ca. 3007 cm -1) spectral intensities as well as their ratios of antisymmetric CH 3 to antisymmetric CH 2, and (3) illustrate the molecular spectral analyses as a research tool to detect for the sensitivity of individual moleculars to the bioethanol processing in a complex plant-based feed and food system without spectral parameterization. The hypothesis of this study was that bioethanol processing changed the molecular structure profiles in the co-products as opposed to original cereal grains. These changes could be detected by infrared molecular spectroscopy and will be related to nutrient utilization. The results showed that bioethanol processing had effects on the functional groups spectral profiles in the co-products. It was found that the CH 3-antisymmetric to CH 2-antisymmetric stretching intensity ratio was changed. The spectral features of carbonyl C dbnd O ester group and unsaturated group were also different. Since the different types of cereal grains (wheat vs. corn) had different sensitivity to the bioethanol processing, the spectral patterns and band component profiles differed between their co-products (wheat DDGS vs. corn DDGS). The multivariate molecular spectral analyses, cluster analysis and principal component analysis of original spectra (without spectral parameterization), distinguished the structural differences between the wheat and wheat DDGS and between the corn and corn DDGS in the antisymmetric and symmetric CH 3 and CH 2 spectral region (ca. 2994-2800 cm -1) and unsaturated group band region (3025-2996 cm -1). Further study is needed to quantify molecular structural changes in relation to nutrient utilization of lipid biopolymer.

Yu, Peiqiang

2011-11-01

385

Board-invited review: Sensitivity and responses of functional groups to feed processing methods on a molecular basis  

PubMed Central

In complex feed structures, there exist main chemical functional groups which are associated with nutrient utilization and availability and functionality. Each functional group has unique molecular structure therefore produce unique molecular vibration spectral profile. Feed processing has been used to improve nutrient utilization for many years. However, to date, there was little study on processing-induced changes of feed intrinsic structure and functional groups on a molecular basis within intact tissue. This is because limited research technique is available to study inherent structure on a molecular basis. Recently bioanalytical techniques: such as Synchrotron Infrared Microspectroscopy as well as Diffuse Reflectance Infrared Fourier Transform molecular spectroscopy have been developed. These techniques enable to detect molecular structure change within intact tissues. These techniques can prevent destruction or alteration of the intrinsic protein structures during processing for analysis. However, these techniques have not been used in animal feed and nutrition research. The objective of this review was show that with the advanced technique, sensitivity and responses of functional groups to feed processing on a molecular basis could be detected in my research team. These functional groups are highly associated with nutrient utilization in animals.

2012-01-01

386

Close-coupling calculations of low-energy inelastic and elastic processes in 4He collisions with H2: A comparative study of two potential energy surfaces.  

PubMed

The two most recently published potential energy surfaces (PESs) for the HeH2 complex, the so-called MR (Muchnick and Russek) and BMP (Boothroyd, Martin, and Peterson) surfaces, are quantitatively evaluated and compared through the investigation of atom-diatom collision processes. The BMP surface is expected to be an improvement, approaching chemical accuracy, over all conformations of the PES compared to that of the MR surface. We found significant differences in inelastic rovibrational cross sections computed on the two surfaces for processes dominated by large changes in target rotational angular momentum. In particular, the H2(nu=1,j=0) total quenching cross section computed using the BMP potential was found to be a factor of 1000 larger than that obtained with the MR surface. A lesser discrepancy persists over a large range of energies from the ultracold to thermal and occurs for other low-lying initial rovibrational levels. The MR surface was used in previous calculations of the H2(nu=1,j=0) quenching rate coefficient and gave results in close agreement with the experimental data of Audibert et al. which were obtained for temperatures between 50 and 300 K. Examination of the rovibronic coupling matrix elements, which are obtained following a Legendre expansion of the PES, suggests that the magnitude of the anisotropy of the BMP potential is too large in the interaction region. However, cross sections for elastic and pure rotational processes obtained from the two PESs differ typically by less than a factor of 2. The small differences may be ascribed to the long-range and anharmonic components of the PESs. Exceptions occur for (nu=10,j=0) and (nu=11,j=1) where significant enhancements have been found for the low-energy quenching and elastic cross sections due to zero-energy resonances in the BMP PES which are not present in the MR potential. PMID:15638586

Lee, Teck-Ghee; Rochow, C; Martin, R; Clark, T K; Forrey, R C; Balakrishnan, N; Stancil, P C; Schultz, D R; Dalgarno, A; Ferland, Gary J

2005-01-01

387

Particle-in-cell/Monte Carlo collision simulation of the ionization process of surface-wave plasma discharges resonantly excited by surface plasmon polaritons  

SciTech Connect

Although surface-wave plasma (SWP) sources have many industrial applications, the ionization process for SWP discharges is not yet well understood. The resonant excitation of surface plasmon polaritons (SPPs) has recently been proposed to produce SWP efficiently, and this work presents a numerical study of the mechanism to produce SWP sources. Specifically, SWP resonantly excited by SPPs at low pressure (0.25 Torr) are modeled using a two-dimensional in the working space and three-dimensional in the velocity space particle-in-cell with the Monte Carlo collision method. Simulation results are sampled at different time steps, in which the detailed information about the distribution of electrons and electromagnetic fields is obtained. Results show that the mode conversion between surface waves of SPPs and electron plasma waves (EPWs) occurs efficiently at the location where the plasma density is higher than 3.57 Multiplication-Sign 10{sup 17} m{sup -3}. Due to the effect of the locally enhanced electric field of SPPs, the mode conversion between the surface waves of SPPs and EPWs is very strong, which plays a significant role in efficiently heating SWP to the overdense state.

Chen Zhaoquan [College of Electrical and Information Engineering, Anhui University of Science and Technology, Huainan, Anhui 232001 (China); State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian, Liaoning 116024 (China); State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China); Ye Qiubo [College of Electrical and Information Engineering, Anhui University of Science and Technology, Huainan, Anhui 232001 (China); Communications Research Centre, 3701 Carling Ave., Ottawa K2H 8S2 (Canada); Xia Guangqing [State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian, Liaoning 116024 (China); Hong Lingli; Hu Yelin; Zheng Xiaoliang; Li Ping [College of Electrical and Information Engineering, Anhui University of Science and Technology, Huainan, Anhui 232001 (China); Zhou Qiyan [College of Electrical and Information Engineering, Anhui University of Science and Technology, Huainan, Anhui 232001 (China); State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China); Hu Xiwei; Liu Minghai [State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China)

2013-03-15

388

Isotopic Composition as a Signature for Different Processes Leading to Fragment Production in Midperipheral Ni+Al, Ni, Ag Collisions at 30 MeV/Nucleon  

NASA Astrophysics Data System (ADS)

The results of experiments performed to investigate the Ni+Al, Ni+Ni, Ni+Ag reactions at 30 MeV/nucleon are presented. From the study of dissipative midperipheral collisions, it has been possible to detect events in which Intermediate Mass Fragments (IMF) production takes place. The decay of a quasi-projectile has been identified; its excitation energy leads to a multifragmentation totally described in terms of a statistical disassembly of a thermalized system (T?4 MeV, E* ?4 MeV/nucleon). Moreover, for the systems Ni+Ni, Ni+Ag, in the same nuclear reaction, a source with velocity intermediate between that of the quasi-projectile and that of the quasi-target, emitting IMF, is observed. The fragments produced by this source are more neutron rich than the average matter of the overall system, and have a charge distribution different, with respect to those statistically emitted from the quasi-projectile. The above features suggest that this production comes from material which is "surface-like" (since it originates from the overlap of the two nuclei). To investigate the neutron content in both processes the 4He and 6He experimental yields were studied.

Milazzo, P. M.; Margagliotti, G. V.; Rui, R.; Vannini, G.; Colonna, N.; Gramegna, F.; Mastinu, P. F.; Agodi, C.; Alba, R.; Bellia, G.; Coniglione, R.; Del Zoppo, A.; Finocchiaro, P.; Maiolino, C.; Migneco, E.; Piattelli, P.; Santonocito, D.; Sapienza, P.; Iori, I.; Moroni, A.

2007-01-01

389

Molecular dissection of novel trafficking and processing of the T. gondii rhoptry metalloprotease Toxolysin-1  

PubMed Central

Toxoplasma gondii utilizes specialized secretory organelles called rhoptries to invade and hijack its host cell. Many rhoptry proteins are proteolytically processed at a highly conserved S?XE site to remove organellar targeting sequences that may also affect protein activity. We have studied the trafficking and biogenesis of a secreted rhoptry metalloprotease with homology to insulysin that we named Toxolysin-1 (TLN1). Through genetic ablation and molecular dissection of TLN1 we have identified the smallest rhoptry targeting domain yet reported and expanded the consensus sequence of the rhopty pro-domain cleavage site. In addition to removal of its pro-domain, Toxolysin-1 undergoes a C-terminal cleavage event that occurs at a processing site not previously seen in Toxoplasma rhoptry proteins. While pro-domain cleavage occurs in the nascent rhoptries, processing of the C-terminal region precedes commitment to rhoptry targeting, suggesting that it is mediated by a different maturase, and we have identified residues critical for proteolysis. We have additionally shown that both pieces of TLN1 associate in a detergent resistant complex, formation of which is necessary for trafficking of the C-terminal portion to the rhoptries. Together, these studies reveal novel processing and trafficking events that are present in the protein constituents of this unusual secretory organelle.

Hajagos, Bettina E.; Turetzky, Jay M.; Peng, Eric D.; Cheng, Stephen J.; Ryan, Christopher M.; Souda, Puneet; Whitelegge, Julian P.; Lebrun, Maryse; Dubremetz, Jean-Francois; Bradley, Peter J.

2012-01-01

390

Enhancement of the neutral-beam stopping cross section in fusion plasmas due to multistep collision processes  

SciTech Connect

Multistep processes involving excited atomic states are found to produce a substantial increase in the stopping cross section for a neutral hydrogen beam injected into a plasma, and thus to reduce the beam penetration. For typical plasma and beam parameters of current large tokamak experiments, the stopping cross-sectional enhancement is found to vary from 25% to 50% depending on the beam energy, plasma density, and impurity level. For neutral hydrogen beams with energies greater than or equal to 500 keV, envisioned in tokamak amd mirror reactor designs, the enhancement can be as large as 80 to 90%.

Boley, C.D.; Janev, R.K.; Post, D.E.

1983-10-01

391

Mechanical properties and biocompatibility of melt processed, self-reinforced ultrahigh molecular weight polyethylene.  

PubMed

The low efficiency of fabrication of ultrahigh molecular weight polyethylene (UHMWPE)-based artificial knee joint implants is a bottleneck problem because of its extremely high melt viscosity. We prepared melt processable UHMWPE (MP-UHMWPE) by addition of 9.8 wt% ultralow molecular weight polyethylene (ULMWPE) as a flow accelerator. More importantly, an intense shear flow was applied during injection molding of MP-UHMWPE, which on one hand, promoted the self-diffusion of UHMWPE chains, thus effectively reducing the structural defects; on the other hand, increased the overall crystallinity and induced the formation of self-reinforcing superstructure, i.e., interlocked shish-kebabs and oriented lamellae. Aside from the good biocompatibility, and the superior fatigue and wear resistance to the compression-molded UHMWPE, the injection-molded MP-UHMWPE exhibits a noteworthy enhancement in tensile properties and impact strength, where the yield strength increases to 46.3 ± 4.4 MPa with an increment of 128.0%, the ultimate tensile strength and Young's modulus rise remarkably up to 65.5 ± 5.0 MPa and 1248.7 ± 45.3 MPa, respectively, and the impact strength reaches 90.6 kJ/m(2). These results suggested such melt processed and self-reinforced UHMWPE parts hold a great application promise for use of knee joint implants, particularly for younger and more active patients. Our work sets up a new method to fabricate high-performance UHMWPE implants by tailoring the superstructure during thermoplastic processing. PMID:24835044

Huang, Yan-Fei; Xu, Jia-Zhuang; Li, Jian-Shu; He, Ben-Xiang; Xu, Ling; Li, Zhong-Ming

2014-08-01

392

Collision broadening in two-photon spectroscopy  

Microsoft Academic Search

Collision-broadening theory is used to obtain a general expression for the steady-state rate of two-photon simultaneous absorption as a function of their sum energies and momenta in gases, under conditions where both homogeneous (collision) and inhomogeneous (Doppler) broadening take place. Effects of molecular motion on the line-broadening parameters are discussed, as well as extensions to bands of overlapping lines, inclusion

Abraham Ben-Reuven; Joshua Jortner; Lewis Klein; Shaul Mukamel

1976-01-01

393

Inelastic vector soliton collisions: a lattice-based quantum representation: One contribution of 21 to a Theme 'Connecting scales: micro, meso and macro processes'  

Microsoft Academic Search

Lattice-based quantum algorithms are developed for vector soliton collisions in the completely integrable Manakov equations, a system of coupled nonlinear Schrödinger (coupled-NLS) equations that describe the propagation of pulses in a birefringent fibre of unity cross-phase modulation factor. Under appropriate conditions the exact 2-soliton vector solutions yield inelastic soliton collisions, in agreement with the theoretical predictions of Radhakrishnan et al.

George Vahala; Linda Vahala; Jeffrey Yepez

2004-01-01

394

Competition of coalescence and ``fireball'' processes in nonequilibrium emission of light charged particles from p+Au collisions  

NASA Astrophysics Data System (ADS)

The energy and angular dependence of the double differential cross sections d2?/d?dE were measured for p,d,t,He3,4,6, Li6,7,8,9, Be7,9,10, and B10,11,12 isotopes produced in reactions of 1.2- and 1.9-GeV protons on a Au target. The beam energy dependence of the data, supplemented by the cross sections from a previous experiment at 2.5 GeV, is very smooth. The shape of the spectra and angular distributions do not change significantly in the beam energy range from 1.2 to 2.5 GeV. However, the absolute value of the cross sections increases for all ejectiles. The intermediate mass fragment spectra and their angular distributions are very well reproduced by a phenomenological model of two emitting, moving sources, with parameters smoothly varying with energy. The double differential cross sections for light charged particles were analyzed in the framework of the microscopic model calculations of intranuclear cascade, including the coalescence of nucleons and a statistical model for evaporation of particles from excited residual nuclei. However, the energy and angular dependencies of the data agree with neither predictions of the microscopic intranuclear cascade calculations for protons nor the coalescence calculations for other light charged particles. A very good description of the data is achieved by the phenomenological inclusion of the emission of light charged particles from a “fireball” (i.e., a fast and hot moving source). It was found that the nonequilibrium processes are very important for the production of light charged particles. They exhaust 40% 80% of the total cross section—depending on the emitted particles. Coalescence and fireball emission yield comparable contributions to the cross sections with the exception of the He3 data where coalescence clearly dominates. For all light charged particles, the ratio of nonequilibrium processes to processes proceeding through a phase of statistical equilibrium does not change significantly between the beam energies of 1.2 and 2.5 GeV.

Budzanowski, A.; Fidelus, M.; Filges, D.; Goldenbaum, F.; Hodde, H.; Jarczyk, L.; Kamys, B.; Kistryn, M.; Kistryn, St.; Kliczewski, St.; Kowalczyk, A.; Kozik, E.; Kulessa, P.; Machner, H.; Magiera, A.; Piskor-Ignatowicz, B.; Pysz, K.; Rudy, Z.; Siudak, R.; Wojciechowski, M.

2008-08-01

395

Time-dependent wave-packet method for the complete determination of S-matrix elements for reactive molecular collisions in three dimensions  

NASA Technical Reports Server (NTRS)

An alternative time-dependent wave-packet method for treating three-dimensional gas phase reactive atom-diatom collisions is presented. The method employs a nonreactive body-frame wave packet propagation procedure, made possible by judicious use of absorbing optical potentials, a novel scheme for interpolating the wave function from coordinates in one arrangement to those in another and the fact that the time-dependent Schroedinger equation is an initial-value problem. The last feature makes possible a computationally viable and accurate procedure for changing from one arrangement's coordinates to another. In addition, the method allows the determination of S-matrix elements over a wide range of energies from a single wave-packet propagation. The method is illustrated by carrying out detailed calculations of inelastic and reactive scattering in the H + H2 system using the Liu-Siegbahn-Truhlar-Horowitz potential surface.

Judson, Richard S.; Kouri, Donald J.; Neuhauser, Daniel; Baer, Michael

1990-01-01

396

Molecular dynamics studies of the process of amyloid aggregation of peptide fragments of transthyretin.  

PubMed

It has been shown recently that an 11-residue peptide fragment of transthyretin, TTR(105-115), can form amyloid fibrils in vitro by adopting an extended beta-strand conformation. We used molecular dynamics simulations on systems of TTR(105-115) peptides, for a total length of about 5 micros, to explore the process of self-assembly and the structures of the resulting aggregates. Our results suggest that an antiparallel association of the beta-strands is more probable than a parallel one and that the central residues (T106-L111) in a beta-strand have a high propensity to form inter-peptide hydrogen bonds. The study of the dynamics of self-association indicated that, for this peptide, trajectories leading to conformations with high alpha-helical content are off-pathway from those leading to aggregates with high beta-structure content. We also show that the diverse oligomeric structures that form spontaneously in the molecular dynamics simulations are, to a large extent, compatible with solid-state NMR experimental measurements, including chemical shifts, on fully formed fibrils. The strategy that we present may therefore be used in the design of new experiments to determine the structure of amyloid fibrils, such as those involving site-specific isotope labelling schemes to measure key inter-atomic distances. PMID:15210354

Paci, Emanuele; Gsponer, Jörg; Salvatella, Xavier; Vendruscolo, Michele

2004-07-01

397

A novel "correlated ion and neutral time of flight" method: Event-by-event detection of neutral and charged fragments in collision induced dissociation of mass selected ions  

NASA Astrophysics Data System (ADS)

A new tandem mass spectrometry (MS/MS) method based on time of flight measurements performed on an event-by-event detection technique is presented. This "correlated ion and neutral time of flight" method allows to explore Collision Induced Dissociation (CID) fragmentation processes by directly identifying not only all ions and neutral fragments produced but also their arrival time correlations within each single fragmentation event from a dissociating molecular ion. This constitutes a new step in the characterization of molecular ions. The method will be illustrated here for a prototypical case involving CID of protonated water clusters H+(H2O)n = 1-5 upon collisions with argon atoms.

Teyssier, C.; Fillol, R.; Abdoul-Carime, H.; Farizon, B.; Farizon, M.; Märk, T. D.

2014-01-01

398

SHOCK WAVES IN COLLISION-FREE PLASMAS  

Microsoft Academic Search

Investigations of shock-wave structures provide an excellent opportunity ; for studying the dissipation processes in collision-free plasntas. The thickness ; of collision-free shock waves was previously obtained from measurements of the ; light emitted by the plasma in a magnetic annular shock tube. The magnitude of ; the shock thickness, and its Mach number and density dependence were in agreement

M. Camac; A. R. Kantrowitz; M. M. Litvak; R. M. Patrick; H. E. Petschek

1961-01-01

399

Modelling of high pressure binary droplet collisions  

Microsoft Academic Search

Droplet collision efficiency is a rather uncharted area for real hydrocarbon systems under non-atmospheric conditions. It is also of great interest in many industrial applications. In this work binary head-on droplet collisions at high pressure have been simulated using the lattice Boltzmann method. A model that captures the physics of the coalescence process is used where no external criterion for

Pablo M. Dupuy; Yi Lin; Maria Fernandino; Hugo A. Jakobsen; Hallvard F. Svendsen

2011-01-01

400

Numerical simulation of binary liquid droplet collision  

NASA Astrophysics Data System (ADS)

A numerical investigation of binary droplet collision has been conducted. The complete process of the collision of two liquid droplets is dynamically simulated by solving the incompressible Navier-Stokes equations coupled with the convective equation of the level set function that captures the interface between the liquid and the gas phases. The simulations cover four major regimes of binary collision: bouncing, coalescence, reflexive separation, and stretching separation. For water droplets in air, the numerical results are compared with the experiments by and Ashgriz and Poo [J. Fluid Mech. 221, 183 (1990)] on collision consequences. For hydrocarbon (C14H30) droplets in nitrogen gas, the simulated results are compared in detail with the time-resolved photographic images of the collision processes obtained by Qian and Law [J. Fluid Mech. 331, 59 (1997)] in every collision regime. The present numerical results suggest that the mechanism of a bouncing collision is governed by the macroscopic dynamics. However, the fact that the present macroscopic numerical model is unable to capture the collision regime of coalescence after minor deformation supports the speculation that its mechanism is related to the microscopic dynamics. Furthermore, the transition from bouncing to coalescence collisions has been predicted and agrees well with the analytical model. The mechanism of satellite droplet formation for head-on collision and stretching separation collision is also studied based on the detailed time-resolved dynamic simulation results. It is then confirmed that end pinching is the main cause of satellite formation in head-on collisions whereas the capillary-wave instability becomes dominant in large impact parameter cases. In the case of an intermediate impact parameter, the effects of twisting and stretching due to the angular momentum and the inertia of the colliding droplets are significant for the satellite formation.

Pan, Yu; Suga, Kazuhiko

2005-08-01

401

Low temperature conversion of molecular species via a hybrid plasma discharge -- catalytic process  

NASA Astrophysics Data System (ADS)

Various avenues are being perused towards developing more sustainable energy sources to meet current and future energy requirements. Central to these energy surety related concerns is the efficiency of a given processes (chemical reaction) employed for synthesis of these fuels or energy sources. We present results from our preliminary studies on using low-temperature non-equilibrium discharges, coupled to active surfaces as a means of efficiently dissociating key molecular species that may be used towards fuel synthesis. Specifically, we focus on dissociating carbon dioxide to form carbon monoxide which is used in conjunction with hydrogen to generate syngas and higher hydrocarbons. While studies have been performed using various plasma sources, we primarily use a ``hybrid'' plasmas with tuned E/N that has been demonstrated to efficiently dissociate carbon dioxide[1]. [1] S. N. Andreev et. al, Spectrochimica Acta A 60, 3361 (2004).

Barnat, Ed

2008-10-01

402

On the use of graphics processing units (GPUs) for molecular dynamics simulation of spherical particles  

NASA Astrophysics Data System (ADS)

General-purpose computation on Graphics Processing Units (GPU) on personal computers has recently become an attractive alternative to parallel computing on clusters and supercomputers. We present the GPU-implementation of an accurate molecular dynamics algorithm for a system of spheres. The new hybrid CPU-GPU implementation takes into account all the degrees of freedom, including the quaternion representation of 3D rotations. For additional versatility, the contact interaction between particles is defined using a force law of enhanced generality, which accounts for the elastic and dissipative interactions, and the hard-sphere interaction parameters are translated to the soft-sphere parameter set. We prove that the algorithm complies with the statistical mechanical laws by examining the homogeneous cooling of a granular gas with rotation. The results are in excellent agreement with well established mean-field theories for low-density hard sphere systems. This GPU technique dramatically reduces user waiting time, compared with a traditional CPU implementation.

Hidalgo, R. C.; Kanzaki, T.; Alonso-Marroquin, F.; Luding, S.

2013-06-01

403

Many-body processes in atomic and molecular physics. Progress report  

SciTech Connect

A proposal is presented for theoretical efforts towards the following projects: (1) carry out rotational predissociation lifetime calculations of several van der Waals molecules for which accurate potential energy surfaces were obtained recently by van der Waals molecular spectroscopic methods; (2) development and extension of the complex coordinate - coupled channel formalism to vibrational predissociation studies; (3) Floquet theory study of the quantum dynamics of multiphoton excitation of vibrational-rotational states of small molecules by laser light; (4) development and extension of the method of complex quasi-vibrational energy formalism to the study of intense field multiphoton dissociation of diatomic molecules and to photodissociation process in the presence of shape resonances; (5) investigation of the external field effects in multiphoton excitation and dissociation of small molecules. Depending on time and resources, several other projects may also be pursued. A detailed discussion covering these proposed projects is presented.

Chu, S.I.

1981-01-01

404

Electron spin resonance studies on reduction process of nitroxyl spin radicals used in molecular imaging  

NASA Astrophysics Data System (ADS)

The Electron spin resonance studies on the reduction process of nitroxyl spin probes were carried out for 1mM 14N labeled nitroxyl radicals in pure water and 1 mM concentration of ascorbic acid as a function of time. The electron spin resonance parameters such as signal intensity ratio, line width, g-value, hyperfine coupling constant and rotational correlation time were determined. The half life time was estimated for 1mM 14N labeled nitroxyl radicals in 1 mM concentration of ascorbic acid. The ESR study reveals that the TEMPONE has narrowest line width and fast tumbling motion compared with TEMPO and TEMPOL. From the results, TEMPONE has long half life time and high stability compared with TEMPO and TEMPOL radical. Therefore, this study reveals that the TEMPONE radical can act as a good redox sensitive spin probe for molecular imaging.

Dhas, M. Kumara; Jawahar, A.; Benial, A. Milton Franklin

2014-04-01

405

Planarization process of single crystalline silicon asperity under abrasive rolling effect studied by molecular dynamics simulation  

NASA Astrophysics Data System (ADS)

In the chemical mechanical polishing (CMP) process, the complex behaviors of abrasive particles play important roles in the planarization of wafer surface. Particles embedded in the pad remove materials by ploughing, while particles immersed in the slurry by rolling across the wafer surface. In this paper, processes of the particle rolling across a silicon surface with an asperity under various down forces and external driving forces were studied using molecular dynamics (MD) simulation method. The simulations clarified the asperity shape evolution during the rolling process and analyzed the energy changes of the simulation system and the interaction forces acted on the silica particle. It was shown that both the down force and the driving force had important influences on the amount of the material removed. With relatively small down forces and driving forces applied on the particle, the material removal occurred mainly in the front end of the asperity; when the down forces and driving forces were large enough, e.g., 100 nN, the material removal could take place at the whole top part of the asperity. The analysis of energy changes and interaction forces provided favorable explanations to the simulation results.

Si, Lina; Guo, Dan; Luo, Jianbin; Xie, Guoxin

2012-10-01

406

Identification of molecular processes needed for vascular formation through transcriptome analysis of different vascular systems  

PubMed Central

Background Vascular system formation has been studied through molecular and genetic approaches in Arabidopsis, a herbaceous dicot that is used as a model system. Different vascular systems have developed in other plants such as crops and trees. Uncovering shared mechanisms underlying vascular development by transcriptome analysis of different vascular systems may help to transfer knowledge acquired from Arabidopsis to other economically important species. Results Conserved vascular genes and biological processes fundamental to vascular development were explored across various plants. Through comparative transcriptome analysis, 226 genes from Arabidopsis, 217 genes from poplar and 281 genes from rice were identified as constituting 107 conserved vascular gene groups. These gene groups are expressed mainly in vascular tissues and form a complex coexpression network with multiple functional connections. To date, only half of the groups have been experimentally investigated. The conserved vascular gene groups were classified into 9 essential processes for vascular development. 18 groups (17%) lack of annotations were classified as having unknown functions. Conclusion The study provides a map of fundamental biological processes conserved across different vascular systems. It identifies gaps in the experimental investigation of pathways active in vascular formation, which if explored, could lead to a more complete understanding of vascular development.

2013-01-01

407

Understanding the role of London dispersion forces in molecular surface processes  

NASA Astrophysics Data System (ADS)

The interactions and dynamics of molecules at surfaces and within pores are essential to many chemical processes, ranging from molecular storage to catalysis and self-assembly. A molecular level understanding of molecule-surface interactions is crucial for tuning surface/pore selectivity and reactivity. While it is clear that strong chemisorption bonds facilitate these interactions, the role of weaker van der Waals (vdW) forces, which include London dispersion and ?-? stacking interactions, are often unknown or overlooked. Recent advances in density functional theory (DFT) have now made it possible to reliably account for London dispersion interactions. In this paper, I will discuss the use of one such technique, the Rutgers-Chalmers vdW non-local correlation functional,ootnotetextM. Dion, H. Rydberg, E. Schr"oder, B. I. Lundqvist and D. C. Langreth, Phys. Rev. Lett., 92, 246401 (2004)^,ootnotetextT. Thonhauser, V. R. Cooper, S. Li, A. Puzder, P. Hyldgaard, and David C. Langreth, Phys. Rev. B, 76, 125112 (2007) to demonstrate how the inclusion of London dispersion forces is critical for a truly first principles understanding of processes sensitive to molecule-surface interactions, such as the loading of H2 within porous materials and the chemisorption of organic molecules at surfaces. These works highlight the fundamental importance of London dispersion interactions in the broader context of chemical physics. This work was supported by the Department of Energy, BES, Materials Sciences and Engineering Division.ootnotetextCollaborators: Guo Li, Isaac Tamblyn, Yungok Ihm, Jun-Hyung Cho, Shixuan Du, Jeffrey B. Neaton, Hong-Jun Gao, Zhenyu Zhang, James R. Morris

Cooper, Valentino R.

2012-02-01

408

Biogeochemical Processes in Late Archean Marine Biosphere Revealed by Isotopic and Molecular Records  

NASA Astrophysics Data System (ADS)

The presence of shallow-marine oxygen oases and associated aerobic ecosystems in an otherwise anoxic and anaerobic world has been proposed by researchers to explain the anomalous 40 permil spread in organic-carbon isotope values during the late Archean. To test this hypothesis, we studied isotopic, molecular, and lithologic records of 2.7-2.5 Ga rocks of different depositional facies from the Hamersley Province, Western Australia. Kerogen carbon-isotopic compositions indicate that extreme 13C-depletion (more than -45 permil) was associated with shallow-marine-carbonate environments at 2.72 Ga and with deepwater environments thereafter. Moreover, kerogen-carbon-isotope values associated with carbonate environments became enriched by more than 10 permil over 100-150 Ma. These observations suggest that microbial processes responsible for extreme 13C-depletion became less significant in shallow carbonate environments, but remained important in deeper settings. Molecular biomarker ratios determined for associated bitumens: 1) strongly correlate to kerogen carbon-isotope values and other biomarker ratios, and, 2) show relationships with depositional facies and dolomite abundance giving credence to a syngenetic relationship with host rocks. The biomarker data confirm aerobic methanotrophs in the Late Archean biosphere, but not in strong association with extreme 13C-depletion. Biomarker patterns reflect a greater association of aerobic respiration and oxygenic photosynthesis in shallow carbonate environments compared to deeper settings. Collectively, the data record dramatic changes in carbon cycling associated with environmental partitioning of microbial processes and ecosystems over 100-150 Ma. Most likely, this represents increased bioavailability of strong electron acceptors with the expansion of oxidant-rich oases prior to rise in atmospheric oxygen.

Eigenbrode, J. L.; Freeman, K. H.; Summons, R. E.

2004-12-01

409

Theoretical study of charge transfer dynamics in collisions of C6+ carbon ions with pyrimidine nucleobases  

NASA Astrophysics Data System (ADS)

A theoretical approach of the charge transfer dynamics induced by collision of C6+ ions with biological targets has been performed in a wide collision energy range by means of ab-initio quantum chemistry molecular methods. The process has been investigated for the target series thymine, uracil and 5-halouracil corresponding to similar molecules with different substituent on carbon C5. Such a study may be related to hadrontherapy treatments by C6+carbon ions and may provide, in particular, information on the radio-sensitivity of the different bases with regard to ion-induced radiation damage. The results have been compared to a previous analysis concerning the collision of C4+ carbon ions with the same biomolecular targets and significant charge effects have been pointed out.

Bacchus-Montabonel, M. C.

2012-07-01

410

Hints on the deformation penetration induced by subductions and collision processes: Seismic anisotropy beneath the Adria region (Central Mediterranean)  

NASA Astrophysics Data System (ADS)

is a small region surrounded by three mountain belts: the Alps, the Apennines, and the Dinarides, built up by long evolution of subduction and collisional systems. We present 253 shear wave splitting measurements obtained by studying more than 100 teleseismic events for 12 stations. SKS splitting measurements show 3-D complexity and quite strong upper mantle deformation. We carefully analyzed results in terms of back azimuthal coverage and interpret measurements as related to Adria rotation and to subductions evolution. In the northern part of Adria, the anisotropy pattern follows the arcuate shape of the Alps; the same pattern, parallel to the mountains, occurs along the Apennines, but fast directions show a sudden change in the Adria foreland. This lateral variation has been analyzed to isolate a distinct Adria mantle anisotropic pattern, which is identified as NE-SW fast direction along the western microplate boundary and as N-S fast direction at Trieste. This pattern might be induced by drag effect of the counterclockwise rotation of Adria lithosphere that behaves as an independent microplate as identified by GPS data. Our measurements suggest that the geodynamic process that generated the Alps is more efficient deforming a larger volume of mantle than its Apennine counterpart. Moreover, the mantle circulation we hypothesize looking at the regional-scale patterns of anisotropy requires the existence of an escape route beneath the Alps-Apennines transition, through which the mantle flows and feed circulation in the Tyrrhenian mantle system as suggested by previous geodynamic models and as seen by some tomographic studies.

Salimbeni, Simone; Pondrelli, Silvia; Margheriti, Lucia

2013-11-01

411

Quaternary post-collision alkaline volcanism NW of Ahar (NW Iran): geochemical constraints of fractional crystallization process  

NASA Astrophysics Data System (ADS)

Major and trace elements and Sr-Nd isotopic data are presented for the Quaternary alkaline volcanism NW of Ahar (NW Iran). The exposed rocks mainly consist of alkali basalts, trachybasalts, basaltic trachyandesites and trachyandesites. Alkali basalts and trachybasalts display microlithic porphyritic texture with phenocrysts of olivine, clinopyroxene, and plagioclase in microlithic groundmass. In the more evolved rocks (basaltic trachyandesites and trachyandesites), amphibole and biotite have appeared. Major and trace element abundances vary along continuous trends of decreasing MgO, TiO2, Fe2O3*, CaO, Co, Cr, V and Zn, and increasing K2O, Al2O3, Ba and Th with increasing SiO2. The Sr and Nd isotopic ratios vary from 0.704463 to 0.704921 and from 0.512649 to 0.512774, respectively. Alkali basalts with high 143Nd/144Nd ratio, low 87Sr/86Sr ratio and high MgO, Ni and Cr contents indicate that they were generated from relatively primitive magmas. Ba, Cr and La/Sm ratios versus Rb suggest that fractional crystallization of alkali basalts could have played a significant role in the formation of evolved rocks. Assimilation and fractional crystallization modelling, as well as Rb/Zr, Th/Yb and Ta/Yb ratios clearly indicate that crustal contamination accompanied by the fractional crystallization played an important role in petrogenesis of the trachyandesites. The small compositional differences between magma types, isotopic composition, mineralogy and nonlinear trends on Harker diagrams also indicate that magma mixing was not an essential process in the evolution of the Ahar magmas. Petrogenetic modelling has been used to constrain sources. Trace element ratio plots and REE modelling indicate that the alkali basalts were generated from a spinel-peridotite source via small degrees (~2.5%) of fractional melting.

Dabiri, Rahim; Emami, Mohamad Hashem; Mollaei, Habib; Chen, Bin; Abedini, Mansor Vosogi; Omran, Nematallah Rashidnejad; Ghaffari, Mitra

2011-12-01

412

The collision cross sections for excitation energy transfer in Rb*(5 P 3\\/2) + K(4 S 1\\/2) --> Rb(5 S 1\\/2) + K*(4 P J ) processes  

Microsoft Academic Search

The collisional excitation transfer for the processes Rb*(5 P 3\\/2)+K(4 S 1\\/2) --> Rb(5 S 1\\/2)+K*(4 P J ), J=1\\/2, 3\\/2, was investigated using two-photon laser excitation technique with a thermionic heat-pipe diode as a detector. The population densities of the K 4 P J levels induced by collisions with excited Rb atoms as well as those produced by direct

V. Horvatic; C. Vadla; M. Movre

1993-01-01

413

Calculation of the Trubnikov and Nanbu Collision Kernels: Implications for Numerical Modeling of Coulomb Collisions  

SciTech Connect

We investigate the accuracy of and assumptions underlying the numerical binary Monte-Carlo collision operator due to Nanbu [K. Nanbu, Phys. Rev. E 55 (1997)]. The numerical experiments that resulted in the parameterization of the collision kernel used in Nanbu's operator are argued to be an approximate realization of the Coulomb-Lorentz pitch-angle scattering process, for which an analytical solution for the collision kernel is available. It is demonstrated empirically that Nanbu's collision operator quite accurately recovers the effects of Coulomb-Lorentz pitch-angle collisions, or processes that approximate these (such interspecies Coulomb collisions with very small mass ratio) even for very large values of the collisional time step. An investigation of the analytical solution shows that Nanbu's parameterized kernel is highly accurate for small values of the normalized collision time step, but loses some of its accuracy for larger values of the time step. Careful numerical and analytical investigations are presented, which show that the time dependence of the relaxation of a temperature anisotropy by Coulomb-Lorentz collisions has a richer structure than previously thought, and is not accurately represented by an exponential decay with a single decay rate. Finally, a practical collision algorithm is proposed that for small-mass-ratio interspecies Coulomb collisions improves on the accuracy of Nanbu's algorithm.

Dimits, A M; Wang, C; Caflisch, R; Cohen, B I; Huang, Y

2008-08-06

414

Organic Semiconductors: A Molecular Picture of the Charge-Transport and Energy-Transport Processes.  

NASA Astrophysics Data System (ADS)

Conjugated organic oligomer and polymer materials are being increasingly considered for their incorporation as the active semiconductor elements in devices such as photo-voltaic cells, light-emitting diodes, or field-effects transistors. In the operation of these devices, electron-transfer and energy-transfer processes play a key role, for instance in the form of charge transport (in the bulk or across interfaces), energy transport, charge separation, or charge recombination [1]. Here, we provide a theoretical description of electron-transfer phenomena based on electron-transfer theory, which allows us to provide a molecular, chemically-oriented understanding. In this presentation, we focus on the parameters that impact the mobility of charge carriers [2], that is the electronic coupling within chains and between adjacent chains and the reorganization energy of the chains upon ionization. Materials under study include conjugated oligomers such as oligoacenes, oligothiophene-acenes, oligothiophenes, and oligothienacenes. [1] J.L. Br'edas, D. Beljonne, V. Coropceanu, and J. Cornil, ``Charge-Transfer and Energy-Transfer Processes in pi-Conjugated Oligomers and Polymers'', Chemical Reviews, 104, 4971-5004 (2004). [2] V. Coropceanu, J. Cornil, D.A. da Silva Filho, Y. Olivier, R. Silbey, and J.L. Br'edas, ``Charge Transport in Organic Semiconductors'', Chemical Reviews, 107, xxx (2007).

Brédas, Jean-Luc

2007-03-01

415

The crystallization process of liquid vanadium studied by ab initio molecular dynamics  

NASA Astrophysics Data System (ADS)

We present a study of the crystallization process in liquid vanadium over a temperature range from 3000?K down to 1500?K using ab initio molecular dynamics simulations. Short-range order evolution during solidification is studied using various structural analysis methods. We show that the icosahedral-like short-range order is detected in the stable liquid phase and grows upon supercooling. The system undergoes a first-order phase transition (from a liquid to a solid state) at a temperature of about 1600?K. The crystal nucleation process is further studied using the time–temperature transformation mechanism by annealing the system at 1650?K. The nucleation is examined using bond-orientational order and density fluctuation analysis. Our finding is that various precursors appear in the region of high bond-orientational order with the majority having body-centered cubic (bcc)-like symmetry. This bcc-like region grows on annealing via thermal fluctuations. Our results reveal that the bond-orientational order precedes the density fluctuation, and is the main driving factor for nucleation.

Debela, T. T.; Wang, X. D.; Cao, Q. P.; Zhang, D. X.; Jiang, J. Z.