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1

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

2

Molecular beam studies of free-radical processes: photodissociation, inelastic and reactive collisions  

Microsoft Academic Search

In this review, the production and detection of a wide range of unstable free-radical species under molecular beam conditions are described. The use of such molecular beam methods to study the photodissociation and inelastic and reactive scattering of free radicals in recent years is reviewed. A selection of the many experiments on the photodissociation of radicals that have been performed

J. Christopher Whitehead

1996-01-01

3

Molecular orbital model of atomic collisions  

Microsoft Academic Search

Molecular orbitals and their behavior under promotion are important concepts introduced by Robert Mulliken. A molecular analysis of atomic collisions uses these concepts in a modified form. Such an analysis works well within the limits of its validity, namely, in slow atomic collisions involving excitaton of inner-shell electrons by MO promotion, with subsequent coupling between a few states. To succeed

William Lichten

1980-01-01

4

Tight-binding molecular-dynamics simulation of buckyball collisions  

SciTech Connect

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 specific energies and orientations produce interesting novel molecules, such as small baby cages, caps, and even a Russian-Doll molecule in which a small cage is trapped in a bigger one. 28 refs., 5 figs., 2 tabs.

Zhang, B.L.; Wang, C.Z.; Chan, C.T.; Ho, K.M. (Iowa State Univ., Ames (United States))

1993-04-01

5

Energy transfer in diatom/diatom molecular collisions  

SciTech Connect

In a collision of two molecules, the translational energy of the collision may be redistributed into internal energy of rotation, vibration, or electron motion, in one or both of the colliding partners. In addition, internal energy in one or more of these modes may be [open quotes]quenched[close quotes] into translation, leading to a superelastic collision. Such energy transfer may take place by a number of mechanisms. This energy transfer is of fundamental importance in understanding chemical reaction dynamics. Nearly all chemical reactions take place through a bimolecular collision process (or multiple bimolecular collisions) and the quantum state specificity of the reaction can have a major role in determining the kinetics of the reaction, In particular, the author has investigated vibrational energy transfer in collisions between two diatomic molecules. In addition to serving as models for all molecular collision process, gas phase collisions of these species are ubiquitous in atmospheric phenomena which are of critical importance in answering the current questions about the human induced degradation of the earth's atmospheric. Classical trajectory methods have been used to explore the excitation of vibrations in gas-phase collisions of the nitrogen molecular ion with its parent molecule. The near symmetry of the reactants is shown to result in a high probability that the two molecules are excited by an equal amount of energy. This provides a possible explanation of the molecular beam measurements which show that the total number of vibrational energy quanta excited in the collision is, with a high probability that the two molecules are excited by an equal amount of energy. This provides a possible explanation of the molecular beam measurements which show that the total number of vibrational energy quanta excited in the collision is, with a high probability, even.

Sohlberg, K.W.

1992-01-01

6

Aligned molecular collisions and a stereodynamical mechanism for selective chirality  

Microsoft Academic Search

Investigations of the stereodynamics of elementary processes provide the background for perspective demonstration of the manifestation\\u000a of chiral effects in molecular collisions. Advances in experimental vacuum technology allow the generation of molecular beams\\u000a containing oriented molecules. Here, we focus on collisional alignment, a molecular polarization phenomenon occurring in supersonic\\u000a expansions of gaseous mixtures. The underlying physical mechanisms, relevant gas-phase experiments

Vincenzo Aquilanti; Gaia Grossi; Andrea Lombardi; Glauciete S. Maciel; Federico Palazzetti

2011-01-01

7

Ultracold molecular collisions in combined electric and magnetic fields  

NASA Astrophysics Data System (ADS)

We consider collisions of electric and magnetic polar molecules, taking the OH radical as an example, subject to combined electric and magnetic static fields. We show that the relative orientation of the fields has an important effect on the collision processes for different fields' magnitudes at different collision energies. This is due to the way the molecules polarize in the combined electric and magnetic fields and hence the way the electric dipole-dipole interaction rises. If OH molecules are confined in magnetic quadrupole traps and if an electric field is applied, molecular collisions will strongly depend on the position as well as the velocity of the molecules. Consequences on the molecular dynamics are discussed.

Quéméner, Goulven; Bohn, John L.

2013-07-01

8

Theoretical Studies of Molecular Collisions.  

National Technical Information Service (NTIS)

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 ap...

D. J. Kouri

1991-01-01

9

Molecular Wave Functions and Inelastic Atomic Collisions  

Microsoft Academic Search

A theoretical interpretation is given of inelastic atomic collisions, especially violent cases where the atomic electron shells deeply interpenetrate. The basis set consists of a product of single-particle, hydrogen-molecular-ion orbital wave functions. The occurrence of large energy losses at critical internuclear distances can be seen as a result of the promotion of inner-shell electrons predicted by molecular-orbital (MO) theory. Energy

William Lichten

1967-01-01

10

Radiative Transitions for Molecular Collisions in an Intense Laser Field.  

National Technical Information Service (NTIS)

Quantum mechanical and semiclassical approaches are discussed for the study of molecular collisions in an intense laser field. Both a coherent state and Fock state representation of the photon field are investigated. The collision dynamics is described in...

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

1976-01-01

11

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

12

Quantum molecular dynamics and particle production in heavy ion collisions  

NASA Astrophysics Data System (ADS)

The production of photons, kaons, antikaons and antiprotons in heavy-ion collisions is calculated in the framework of ``quantum'' molecular dynamics (QMD). The Skyrme potentials, with parameters chosen to generate the soft and hard nuclear equations of state(EOS), are used in the propagation of nucleons within QMD. The sensitivity of the production of each type of particle to the EOS is discussed. The mechanisms of production processes are studied. The theoretical results are compared with the available experimental data.

Huang, S. W.; Faessler, A.; Li, G. Q.; Khoa, D. T.; Lehmann, E.; Matin, M. A.; Ohtsuka, N.; Puri, R. K.

13

Description of ionization in the molecular approach to atomic collisions  

SciTech Connect

Molecular treatments of atomic collisions have traditionally been restricted to low nuclear velocities because of their failure to reproduce the fall of the capture cross sections at higher velocities. The limitation has recently been seen to be due to their description of ionizing processes. This feature is shown here to be a general one for multicharged ion-atom collisions. Its origin and characteristics are described and illustrated for the prototypical Li{sup 3+}+H(1s) reaction. Ionization appears as a result of the inertia of the electron cloud to adiabatically follow the nuclear motion. This gives rise to nonadiabatic transitions, which represent an ionizing flux whenever the nuclear velocity is high enough that the energy of the traveling molecular orbitals involved is positive in both moving atomic reference frames. Two strongly connected mechanisms appear, corresponding to the relative translational and rotational nuclear motions. Because of the finiteness of the basis, these mechanisms terminate with unphysical trapping effects. While interesting {ital per se}, knowledge of these features is also useful with respect to improving molecular treatments of atomic collisions with the addition of pseudostates. {copyright} {ital 1996} {ital The American Physical Society}

Harel, C.; Jouin, H.; Pons, B. [Laboratoire des Collisions Atomiques, Centre de Physique Theorique et Modelisation, URA 1537 du CNRS, Universite de Bordeaux I, 351 Cours de Liberation, 33405 Talence Cedex (France); Errea, L.F.; Mendez, L.; Riera, A. [Departamento de Quimica, C-IX, Universidad Autonoma de Madrid, Cantoblanco, E-28049 Madrid (Spain)

1997-01-01

14

Coherent optical transient study of molecular collisions: Theory and observations  

Microsoft Academic Search

It has been shown recently that molecular gas samples excited with coherent light can display a variety of transient phenomena, similar to those found in nuclear magnetic resonance. This article elucidates how these coherence effects can be used to isolate or unfold molecular collision mechanisms that normally remain hidden within the optical line shape. Elastic collisions, for example, are easily

Paul R. Berman; J. M. Levy; Richard G. Brewer

1975-01-01

15

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.

16

Interference effects in collisions between heavy ions and molecular targets  

NASA Astrophysics Data System (ADS)

The transfer-excitation process in O8+ + H2 collisions is studied at high impact energies using an independent event model. The transfer-excitation probability is expressed as a product of a capture probability from H2 (PC), leaving the H2+ in its ground state, and an excitation probability (PE) of the residual target to a dissociative state, PC is evaluated in the Continuum Distorted Wave-Eikonal Final State (CDW-EFS) model and PE is calculated in the first Born approximation (FBA). The differential cross-sections are studied as a function of the molecular orientation and the interference patterns obtained are compared with the available experimental data.

Corchs, S. E.; Busnengo, H. F.; Rivarola, R. D.; McGuire, J. H.

1996-08-01

17

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

18

Molecular dynamics mass spectrometric study of the collision-induced dissociation of CS2+ ions at low and intermediate collision energies  

NASA Astrophysics Data System (ADS)

The dynamics of the collision-induced dissociation of CS2+ molecular ions to CS and S+ fragment ions has been investigated using a crossed-beam tandem hybrid mass spectrometer at collision energies ranging from near threshold to 34.5 eV in the center-of-mass (CM) reference frame. The results show that small impact parameter impulsive collisions are involved in the collisional activation process, resulting in extensive scattering of fragment ions with intensity maxima at non-zero angles. The dissociation of CS2+ to S+ proceeds via a mechanism mainly involving the transfer of the minimum amount of energy required to dissociate the parent ion into S+ (4S) and CS (X1 [Sigma]+) at all collision energies. However, the mechanism for the formation of CS+ depends strongly on the collision energy. Energy transfer is very efficient for this process and a large fraction of the CM collision energy is converted to internal excitation of the colliding CS2+ ions up to a maximum of nearly 16 eV (at 34.5 eV collision energy). At the lowest collision energy we have investigated, 6.5 eV, the lowest energy reaction path to form CS+ (X2 [Sigma]+) and S (3P) is followed exclusively. However, as the collision energy is increased, several additional dissociation channels contribute towards the total dissociation. These results are rationalized by the efficient electronic excitation of the colliding CS2+ ions at these collision energies.

Shukla, A. K.; Tosh, R. E.; Chen, Y. B.; Futrell, J. H.

1995-08-01

19

Resonant electron-CF collision processes  

SciTech Connect

Electronic structure methods are combined with variationalfixed-nuclei electron scattering calculations and nuclear dynamicsstudies to characterize resonant vibrational excitation and electronattachment processes in collisions between low-energy electrons and CFradicals. Several low-lying negative ion states are found which give riseto strong vibrational excitation and which are expected to dominate thelow-energy electron scattering cross sections. We have also studiedseveral processes which could lead to production of negative ions (F- andC-), However, in contrast to other recent predictions, we do not find CFin itsground state to be a significant source of negative ion productionwhen interacting with thermal electrons.

Trevisan, Cynthia S.; Orel, Ann E.; Rescigno, Thomas N.

2005-03-18

20

Rovibrational analysis of molecular collisions using coherent states  

NASA Astrophysics Data System (ADS)

A generalization of the Prony method, which fits a set of complex exponentials to a time dependent signal, is presented. This generalized Prony method is applied to analyze rovibrational dynamics of products in a theoretical treatment of molecular collisions. Employing suitable coherent states an a posteriori quantum analysis can be performed on molecular trajectories with classical nuclei obtained with electron nuclear dynamics theory. Illustrative calculations are presented for state resolved cross sections of proton collisions with water molecules and compared to results from crossed beam experiments.

Blass, Anatol; Deumens, Erik; Öhrn, Yngve

2001-11-01

21

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

22

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

23

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

24

Nucleon Molecular Orbitals and the Transition Mechanism Between Molecular Orbitals in Nucleus-Nucleus Collisions.  

National Technical Information Service (NTIS)

The molecular orbitals of the nucleon(s) in nucleus-nucleus collisions are dynamically defined as a linear combination of nucleon single-particle orbits (LCNO) in a rotating frame by using the coupled-reaction-channel (CRC) theory. Nucleon molecular orbit...

B. Imanishi S. Misono W. von Oertzen H. Voit

1988-01-01

25

Atomic collision processes in dense plasmas  

SciTech Connect

A detailed investigation of various atomic collision processes important to the determination of the structure and evolution of dense plasmas is presented. Volume 1 studies general collisional processes in dense plasmas, while Volume 2 studies specific mechanism by which energy is transferred among the constituents of a dense plasma. Specifically, in chapter I, attention is focused upon ion-ion recombination processes in dense plasmas, which involves the full set of multicomponent BBGKY equations appropriate for a three component gas composed of positive and negative ions, and neutral particles. This yields a set of coupled Boltzmann-type equations to be solved for the full phase space evolution of the plasma, valid for arbitrary neutral gas density. In chapters III, IV of volume 2 the electron-impact excitation of excited hydrogen and helium atoms, respectively, are studied via the multichannel eikonal theory (MET) of Flannery and McCann. The MET is modified to account, asymptotically, for the strong dipole couplings present between the excited station of hydrogen and helium, thereby allowing accurate computation of differential and integral cross sections and the relevant orientation and alignment parameters.

Mansky, E.J. II

1985-01-01

26

Transport description of intermediate processes in heavy ion collisions  

SciTech Connect

An extension of the diffusion model is proposed in order to describe the intermediate processes and the compound nucleus formation in heavy ion collisions. The model describes the intermediate processes and fusion in terms of the formation and the evolution of a long-lived dinuclear molecular complex (DMC) and its subsequent decay by fragmentation. The colliding ions can be trapped into the pocket of the entrance channel nucleus-nucleus potential and a DMC is formed. This DMC acts as a doorway state towards formation of a completely equilibrated compound nucleus (CN). It evolves through the exchange of nucleons to different dinuclear configurations. At each stage of its evolution, there is a finite probability for direct fragmentation into outgoing channels by thermal penetration over the barrier. The doorway states that do not fragment relax into a CN configuration and are identified as the fusion yield. 8 refs.

Ayik, S.; Shivakumar, B.; Shapira, D.

1986-01-01

27

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

28

Collision physics in the atomic and molecular universe  

NASA Astrophysics Data System (ADS)

The wavelength range and high resolution of the space instruments Chandra, Newton, SOHO, Suzaku, Herschel, Spitzer, and the upcoming ASTRO-H and James Webb Space Telescope have increased the need for laboratory collision-physics measurements to interpret astrophysical phenomena. A review will be given of charge exchange of highly-charged ions with neutral comet and planet atmospheres; and the formation of complex molecules in stellar regions. These space observations are linked to laboratory measurements of absolute charge-exchange cross sections; and molecular formation of species such as CO2, CH3OH, and CH3CH2OH involving fast H- and O-atom collisions with abundant interstellar molecules adsorbed on dust-grain analogues.

Chutjian, A.; Simcic, J.; Madzunkov, S. M.; MacAskill, J. A.; Mawhorter, R. J.; Tsikata, E.

2012-11-01

29

Atomic Collision Processes in Dense Plasmas  

NASA Astrophysics Data System (ADS)

In the present work a detailed investigation of various atomic collision processes important to the determination of the structure and evolution of dense plasmas is presented. In volume 1 a study of general collisional processes in dense plasmas is given, while in volume 2 specific mechanisms by which energy is transferred among the constituents of a dense plasma is studied. Specifically, in chapter I, attention will be focused upon ion-ion recombination processes in dense plasmas, which involves the full set of multicomponent BBGKY equations appropriate for a three component gas composed of positive and negative ions, and neutral particles. This yields a set of coupled Boltzmann-type equations to be solved for the full phase-space evolution of the plasma, valid for arbitrary neutral gas density. In the limit of low (neutral) gas densities the theory in chapter I naturally tends to the exact quasi-equilibrium treatment of ion-ion recombination of Bates and Moffett, and Bates and Flannery. It also provides a firm basis for developing a fully general theory of recombination in dense plasmas subject to external electromagnetic fields as well as for dense plasmas with arbitrary ion densities. In chapter II symmetric resonance charge transfer processes Rg('+) + Rg (--->) Rg + Rg('+) for Rg = Ne, Ar, Kr, and Xe are studied via a quantal phase shift analysis. Accurate ab-initio and density functional potentials for the Rg(,2)('+), dimer are to be used, with the effects of spin-orbit coupling included, in order to compute elastic, charge-transfer, diffusion, and viscosity cross sections in the thermal energy region. In chapters III, IV of volume 2 the electron-impact excitation of excited hydrogen and helium atoms, respectively, are studied via the multichannel eikonal theory (MET) of Flannery and McCann. The MET is modified to account, asymptotically, for the strong dipole couplings present between the excited states of hydrogen and helium, thereby allowing accurate computation of differential and integral cross sections and the relevant orientation and alignment parameters.

Mansky, Edmund Jacob, II

30

State-to-state collision dynamics of molecular free radicals  

SciTech Connect

State-to-state collision dynamics of molecular radicals were investigated by the laser-induced fluorescence technique in a pulsed, crossed-beam apparatus. Dramatically different product state distributions were observed for two prototypical radicals, NCO({tilde X}{sup 2}{product}) and CH(X{sup 2}{product}). Based on a quantum scattering formalism and general considerations of the potential energy surfaces these observations were interpreted as generic features for the inelastic scattering of {sup 2}{product} radicals. The differences observed for NCO and CH are the results of well-known Hund's coupling classification of linear molecules.

Macdonald, R.G.; Liu, K.

1992-01-01

31

State-to-state collision dynamics of molecular free radicals  

SciTech Connect

State-to-state collision dynamics of molecular radicals were investigated by the laser-induced fluorescence technique in a pulsed, crossed-beam apparatus. Dramatically different product state distributions were observed for two prototypical radicals, NCO({tilde X}{sup 2}{product}) and CH(X{sup 2}{product}). Based on a quantum scattering formalism and general considerations of the potential energy surfaces these observations were interpreted as generic features for the inelastic scattering of {sup 2}{product} radicals. The differences observed for NCO and CH are the results of well-known Hund`s coupling classification of linear molecules.

Macdonald, R.G.; Liu, K.

1992-02-01

32

Near-Threshold Inelastic Collisions Using Molecular Beams with a Tunable Velocity  

Microsoft Academic Search

Molecular scattering behavior has generally proven difficult to study at low collision energies. We formed a molecular beam of OH radicals with a narrow velocity distribution and a tunable absolute velocity by passing the beam through a Stark decelerator. The transition probabilities for inelastic scattering of the OH radicals with Xe atoms were measured as a function of the collision

Joop J. Gilijamse; Steven Hoekstra; Sebastiaan Y. T. van de Meerakker; Gerrit C. Groenenboom; Gerard Meijer

2006-01-01

33

Multiple-electron processes in fast ion-atom collisions  

SciTech Connect

Research in atomic physics at the Lawrence Berkeley Laboratory Super-HILAC and Bevalac accelerators on multiple-electron processes in fast ion-atom collisions is described. Experiments have studied various aspects of the charge-transfer, ionization, and excitation processes. Examples of processes in which electron correlation plays a role are resonant transfer and excitation and Auger-electron emission. Processes in which electron behavior can generally be described as uncorrelated include ionization and charge transfer in high-energy ion-atom collisions. A variety of experiments and results for energies from 1 MeV/u to 420 MeV/u are presented. 20 refs., 15 figs.

Schlachter, A.S.

1989-03-01

34

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

35

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

36

Attosecond timing the ultrafast charge-transfer process in atomic collisions  

SciTech Connect

By solving the three-dimensional, time-dependent Schroedinger equation, we have demonstrated that the ultrafast charge-transfer process in ion-atom collisions can be mapped out with attosecond extreme uv (xuv) pulses. During the dynamic-charge transfer from the target atom to the projectile ion, the electron coherently populates the two sites of both nuclei, which can be viewed as a 'short-lived' molecular state. A probing attosecond xuv pulse can instantly unleash the delocalized electron from such a ''transient molecule,'' so that the resulting photoelectron may exhibit a ''double-slit'' interference. On the contrary, either reduced or no photoelectron interference will occur if the attosecond xuv pulse strikes well before or after the collision. Therefore, by monitoring the photoelectron interference visibility, one can precisely time the ultrafast charge-transfer process in atomic collisions with time-delayed attosecond xuv pulses.

Hu, S. X. [Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623 (United States)

2011-04-15

37

Collisions of alkali negative ions with atomic and molecular targets  

SciTech Connect

Ion-beam measurements are presented for the total cross section sigma/sub e/(E) for electron detachment of Na/sup -/, K/sup -/. and Cs/sup -/ in low-energy (E/sub lab/ < 300 eV) collisions with atomic and molecular targets. The data for the Cs/sup -/ projectile is previously unreported and extends our recent study of Na/sup -/ and K/sup -/. The motivation for this work is due in part to the observation that these alkali-metal anions (denoted M/sup -/) are similar to H/sup -/ in that they have two s-electrons outside a closed shell. In particular, it is of interest to determine whether the energy dependence of sigma/sub e/(E) for M/sup -/ is similar to that observed for H/sup -/. 21 refs., 5 figs.

Champion, R.; Scott, D.; Hug, M.S.; Doverspike, L.

1986-01-01

38

Multichannel quantum defect theory for cold molecular collisions  

SciTech Connect

Multichannel quantum defect theory (MQDT) is shown to be capable of producing quantitatively accurate results for low-energy atom-molecule scattering calculations. With a suitable choice of reference potential and short-range matching distance, it is possible to define a matrix that encapsulates the short-range collision dynamics and is only weakly dependent on energy and magnetic field. Once this has been produced, calculations at additional energies and fields can be performed at a computational cost that is proportional to the number of channels N and not to N{sup 3}. MQDT thus provides a promising method for carrying out low-energy molecular scattering calculations on systems where full exploration of the energy dependence and the field dependence is currently impractical.

Croft, James F. E.; Wallis, Alisdair O. G.; Hutson, Jeremy M.; Julienne, Paul S. [Department of Chemistry, Durham University, South Road, Durham DH1 3LE (United Kingdom); Joint Quantum Institute, NIST and the University of Maryland, Gaithersburg, Maryland 20899-8423 (United States)

2011-10-15

39

Particle dynamics description of “BGK collisions” as a Poisson process  

NASA Astrophysics Data System (ADS)

The Gordeyev integral for plasma particles colliding with neutrals is obtained using a particle dynamics formalism in which the collisions are modeled as a discrete Poisson process. The result leads to an electron density fluctuation spectrum model for partially ionized plasmas which is identical with the spectral model obtained from BGK plasma kinetic equations. This isomorphism between the Poisson process and the BGK operator is analogous to a similar relation between the Brownian motion process and the Fokker-Planck operator with constant coefficients. We take advantage of this analogy to derive a collisional ISR spectrum model that takes into account collisions with both neutrals and charged species.

Milla, Marco; Kudeki, Erhan

2009-07-01

40

Effects of molecular orientation on electron-transfer collisions  

SciTech Connect

K{sup +} ions have been detected from the intersection of a beam of K atoms (5-30 eV) with beams of various simple molecules, such as CH{sub 3}Br and CF{sub 3}Br, which had been oriented prior to the collision. Production of ions in the collision is found to be highly dependent on orientation. The effect is most pronounced near threshold ({approx}5 eV) and almost disappears at higher (30 eV) energies. Attack at the reactive halogen end produces the most ions, regardless of the polarity of that end. For each molecule, the reactive end seems to have the lower threshold energy. These observations may be a result of the electron being transferred to a specific end of the molecule, but the experiments measure only the net result of an electron transfer followed by the separation of the ions. Whether or not electron jump per se depends on orientation is still an open question, but the authors are able to qualitatively interpret the experimental results as being due to interactions between the ions as they separate in the exit channel. Most of the negative molecular ions dissociate, ejecting a halogen X{sup {minus}} in the direction of the (oriented) molecular axis. If the X end is oriented away from the incoming K atom, the ejected X{sup {minus}} will travel in the same direction as the K{sup +}, making the electron more likely to return to the K{sup +} ion and reducing the K{sup +} signal in this unfavorable orientation.

Harland, P.W.; Carman, H.S. Jr.; Phillips, L.F.; Brooks, P.R. (Rice Univ., Houston, TX (United States))

1991-10-17

41

Collisional and dissociative processes involving molecular free radicals  

Microsoft Academic Search

A collaborative experimental and theoretical study of a number of elementary collisional processes involving small molecular free radicals of importance in combustion and in the decomposition of propellants has been carried out. These have involved chemical reactions and photodissociation, as well as nonreactive collision-induced rotational and electronic transitions. Information on non-bonding interactions involving free radicals was also obtained from analysis

Paul J. Dagdigian; Millard H. Alexander

1995-01-01

42

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

43

Fermion Molecular Dynamics for Rearrangement Collisions with Simple Molecules  

NASA Astrophysics Data System (ADS)

The Fermion Molecular Dynamics (FMD) method enables an all-electron treatment of reactive scattering using quasiclassical theory.(J.S. Cohen, Phys. Rev. A 54), 573 (1996); 56, 3583 (1997). It has previously been applied to ion-atom collisions and to atoms in strong laser fields. Here it is extended to molecular targets. A simple effective potential is found to provide a useful quasiclassical description of the hydrogen molecule. In particular, it is applied to capture of negative particles (barp and ?^-) by the hydrogen molecule. In contrast to the case with the same atomic targets, strong effects of the target isotope and projectile mass have been found. Negative particles having kinetic energies up to 100 eV are captured while the atomic capture cross sections cut off rapidly above 14 eV (in the c.m. system). The difference is due to the influence of ro-vibrational excitation, in addition to the electronic excitation also possible for atomic targets. Angular scattering distributions, needed for designing a proposed experiment, have been evaluated.

Cohen, J. S.

1998-05-01

44

Molecular collision studies with Stark-decelerated beams  

NASA Astrophysics Data System (ADS)

Molecular scattering behaviour has generally proven difficult to study at low collision energies. We formed a molecular beam of OH radicals with a narrow velocity distribution and a tunable velocity by passing the beam through a Stark decelerator [1]. The transition probabilities for inelastic scattering of the OH radicals with Xe atoms were measured as a function of the collision energy in the range of 50 to 400 wavenumbers. The behaviour of the cross-sections for inelastic scattering near the energetic thresholds was accurately measured, and excellent agreement was obtained with cross-sections derived from coupled- channel calculations on ab initio computed potential energy surfaces [2]. For collision studies at lower energies, the decelerated beams of molecules can be loaded into a variety of traps. In these traps, electric fields are used to keep the molecules confined in a region of space where they can be studied in complete isolation from the (hot) environment. Typically, 10^5 state- selected molecules can be trapped for times up to several seconds at a density of 10^7 mol/cm^3 and at a temperature of several tens of mK [3]. The long interaction time afforded by the trap has been exploited to measure the infrared radiative lifetime of vibrationally excited OH radicals, for instance, as well as to study the far-infrared optical pumping of these polar molecules due to blackbody radiation [4]. As an alternative to these traps, we have demonstrated an electrostatic storage ring for neutral molecules. In its simplest form, a storage ring is a trap in which the molecules - rather than having a minimum potential energy at a single location in space - have a minimum potential energy on a circle. To fully exploit the possibilities offered by a ring structure, it is imperative that the molecules remain in a bunch as they revolve around the ring. This ensures a high density of stored molecules, moreover, this makes it possible to inject multiple - either co-linear or counter propagating - packets into the ring without affecting the packet(s) already stored. We have recently demonstrated a prototype molecular synchrotron, which will be used as a low-energy collider for neutral molecules in the future [5].[1] H.L. Bethlem, G. Berden, and G. Meijer, Phys. Rev. Lett. 83, (1999) 1558-1561.[2] J.J. Gilijamse, S. Hoekstra, S.Y.T. van de Meerakker, G.C. Groenenboom, and G. Meijer, Science 313, (2006) 1617-1620.[3] S.Y.T. van de Meerakker, P.H.M. Smeets, N. Vanhaecke, R.T. Jongma, and G. Meijer, Phys. Rev. Lett. 94, (2005) Artn. 023004.[4] S. Hoekstra, J.J. Gilijamse, B. Sartakov, N. Vanhaecke, L. Scharfenberg, S.Y.T. van de Meerakker, and G. Meijer, Phys. Rev. Lett. 98, (2007) Artn. 133001.[5] C.E. Heiner, D. Carty, G. Meijer, and H.L. Bethlem, Nature Physics 3, (2007) 115-118.

Meijer, Gerard

2008-03-01

45

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

46

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

47

Wall-collision line broadening of molecular oxygen within nanoporous materials  

SciTech Connect

Wall-collision broadening of near-infrared absorption lines of molecular oxygen confined in nanoporous zirconia is studied by employing high-resolution diode-laser spectroscopy. The broadening is studied for pores of different sizes under a range of pressures, providing new insights on how wall collisions and intermolecular collisions influence the total spectroscopic line profile. The pressure series show that wall-collision broadening is relatively more prominent under reduced pressures, enabling sensitive means to probe pore sizes of porous materials. In addition, we show that the total wall-collision-broadened profile strongly deviates from a Voigt profile and that wall-collision broadening exhibits an additive-like behavior to the pressure and Doppler broadening.

Xu, Can T.; Lewander, Maerta; Andersson-Engels, Stefan; Svensson, Tomas; Svanberg, Sune [Department of Physics, Lund University, P. O. Box 118, SE-221 00 Lund (Sweden); Adolfsson, Erik [Ceramic Materials, SWEREA IVF, Box 104, SE-431 22 Moelndal (Sweden)

2011-10-15

48

Elastic Cross Sections for Electron Collisions with Molecules Relevant to Plasma Processing  

SciTech Connect

Absolute electron-impact cross sections for molecular targets, including their radicals, are important in developing plasma reactors and testing various plasma processing gases. Low-energy electron collision data for these gases are sparse and only the limited cross section data are available. In this report, elastic cross sections for electron-polyatomic molecule collisions are compiled and reviewed for 17 molecules relevant to plasma processing. Elastic cross sections are essential for the absolute scale conversion of inelastic cross sections, as well as for testing computational methods. Data are collected and reviewed for elastic differential, integral, and momentum transfer cross sections and, for each molecule, the recommended values of the cross section are presented. The literature has been surveyed through early 2010.

Yoon, J.-S.; Song, M.-Y.; Kato, H.; Hoshino, M.; Tanaka, H.; Brunger, M. J.; Buckman, S. J.; Cho, H. [National Fusion Research Institute, Gwahangno 113, Yuseong-gu, Daejeon 305-333 (Korea, Republic of); Department of Material and Life Sciences, Sophia University, Tokyo 102-8554 (Japan); ARC Centre for Antimatter-Matter Studies, School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide, South Australia 5001 (Australia); ARC Centre for Antimatter-Matter Studies, Research School of Physics and Engineering, Australian National University, Canberra, Australian Capital Territory 0200 (Australia); Physics Department, Chungnam National University, Daejeon 305-764 (Korea, Republic of)

2010-09-15

49

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

NASA Astrophysics Data System (ADS)

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; Hogan, Christopher J.

2013-10-01

50

Quantum Mechanical Theory of Molecular Collisions in a Laser Field.  

National Technical Information Service (NTIS)

The effect of a radiation field on (ion) atom- (di) atom collison systems is considered. A detailed derivation is presented for the modified coupled equations that result from adding the field to the coupled channel formalism for nonreactive collisions. A...

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

1976-01-01

51

Collisional and dissociative processes involving molecular free radicals  

NASA Astrophysics Data System (ADS)

A collaborative experimental and theoretical study of a number of elementary collisional processes involving small molecular free radicals of importance in combustion and in the decomposition of propellants has been carried out. These have involved chemical reactions and photodissociation, as well as nonreactive collision-induced rotational and electronic transitions. Information on non-bonding interactions involving free radicals was also obtained from analysis of the electronic spectrum of van der Waals complexes of these species.

Dagdigian, Paul J.; Alexander, Millard H.

1995-04-01

52

Isolating Quantum Mechanical Processes in Billiard Ball Collisions  

NASA Astrophysics Data System (ADS)

The few-body problem remains an important unsolved Physics problem. In atomic collisions, while the interactions are well understood, the problem is still not solvable. However, at intermediate or high energies, the contributions to ionization from binary collisions may be isolated and studied directly. Final-state interactions between the charged projectile and the ejected electron following ionization have been calculated to give cusp-like structures in the differential ionization cross section when the projectile and ejected electron emerge in the same direction with the same speed.(See for example, M.W. Lucas, K.F. Man and W. Steckelmacher, in Lecture Notes in Physics vol. 213, ed K.O. Groeneveld, W. Meckbach and I. Sellin (Berlin: Springer), p1 (1984).) These processes are known as ``capture to the continuum" for a positive projectile and "anticapture to the continuum" for a negative projectile.(L.H. Thomas, Proc. Roy. Soc. A114 561 (1927).)^,(See J.S. Briggs, Comments At. Mol. Phys. 23, 175 (1989), for more recent work.) The projectile can transfer significant momentum in these collisions and two or more outgoing particles can significant velocity after the collision which cannot be accounted for theoretically. Therefor experimental measurements can provide guidance for further theoretical development. We have reported the first experimental evidence of electron anticapture to the continuum at about 45^circ in e^- - Ar scattering at 1000 eV. This double-binary collision mechanism (the electron scattering analogue of the Thomas forward peak in ion-atom scattering) has been isolated by studying correlated projectile and ejected electrons traveling in the same direction following e^--Ar collisions. The cross section for this process rises as 45^circ is approached, but drops precipitously at about 45^circ. This dip is the signature of anticapture to the continuum for negative projectiles and corresponds to a zero Coulomb density of states factor at 45^circ. In addition, a significant departure from the Rutherford formula have been found for the one-electron differential cross section at large scattering angles.

Golden, D. E.

1997-10-01

53

Molecular dynamics simulation of energy exchanges during hydrogen collision with graphite sheets  

SciTech Connect

Experiments show that the energy of particles incident on divertor plates in fusion devices seldom exceeds 100 eV. Trim code and its variants are not suitable to predict the sputtering yield of carbon-based divertor plates for this energy range and, therefore, a dynamic model, taking into account the C-H bond formation and breaking, and the structure of carbon, is needed. In this paper, the molecular dynamics method is employed to investigate collision processes between incident hydrogen atoms and a graphene sheet. The simulation results demonstrate that the collision processes cannot be adequately described by a simple binary approximation. The energy transfer from the projectile to the graphite sheet exhibits a very complicated behavior when the kinetic energy of the incident hydrogen atom is below 30 eV, strongly depending on the impact position. When its kinetic energy is lower than 0.35 eV, the incident hydrogen is always reflected back from the single, perfect graphite sheet; when its kinetic energy is higher than 0.35 eV, then whether the incident particle penetrates the graphite sheet, is reflected back or is adsorbed depends on the impact position. In certain areas of the graphite sheet, either adsorption or reflection of an incident hydrogen atom can occur in two different energy ranges.

Sun Jizhong; Li Shouyang; Wang Dezhen [Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Ministry of Education), School of Physics and Optoelectronic Technology and College of Advanced Science and Technology, Dalian University of Technology, Dalian 116024 (China); Stirner, Thomas [University of Applied Sciences Deggendorf, Edlmairstr. 6-8, D-94469 Deggendorf (Germany); Chen Junlin [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China)

2010-06-15

54

Iterative approach to the Schwinger variational principle applied to electron--molecular-ion collisions  

SciTech Connect

We present a study of electron--molecular-ion collisions. The scattering equations are solved using an iterative approach to the Schwinger variational principle. These equations are formulated using the Coulomb Green's function to properly treat the long-range Coulomb tail of the molecular-ion potential. We apply this approach to electron--hydrogen-molecular-ion collisions in the static-exchange approximation. We obtain elastic differential cross sections, and also use the continuum states from these calculations to compute the photoionization cross section of the hydrogen molecule. The iterative method used here converged rapidly in all calculations performed.

Lucchese, R.R.; McKoy, V.

1981-08-01

55

Cold electron collisions with atomic and molecular ions in merged beams: high-resolution collision spectroscopy in storage rings  

NASA Astrophysics Data System (ADS)

Down to the lowest collision energies, free electrons efficiently react with atomic and molecular cations. Atomic ions can bind the colliding electrons by the emission of photons (radiative and dielectronic recombination), while molecular ions are efficiently broken up by slow free electrons without an energy barrier (dissociative recombination). For most atomic and molecular species, the cross sections for recombination and other inelastic cross sections show important resonances reflecting the energetic positions as well as the autoionization and pre-dissociation of quasibound intermediate states formed in the electron collision. High resolution experiments revealing such resonances as well as the underlying atomic and molecular properties and the rich dynamics are performed with merged beams of ions and electrons in ion storage rings, using event-by event counting and imaging methods. Recently, monochromatic electron impact energies down into the few-meV range have been realized by intense and cold merged electron beams from photocathode sources. Ion beam storage controls the internal vibrational and, to some extent, rotational state of the cation. Fast-beam multiparticle imaging is used to reconstruct the molecular fragmentation events and to monitor the initial ionic ro-vibrational state. Examples of recent measurements with multicharged atomic ions and with smaller molecules, from the hydrogen ions to di- and triatomic heavier species (such as CF^+ and CH2^+) are presented.

Wolf, Andreas

2008-10-01

56

Dynamic processes in heavy-ion collisions at intermediate energies  

NASA Astrophysics Data System (ADS)

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. The 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 of the CsI(Tl)-Wall (CIW) covering the backward hemisphere and, located at mid-rapidity, the central trigger detector (CTD), a gas chamber with microstrip read-out backed by 48 plastic scintillators. The forward region is covered by 16 of the plastic scintillators of the CTD and by the MUR, a time-of-flight wall consisting of 96 plastic scintillator sheets. In earlier experiments only fragments with atomic number, Z, greater then two could be identifled in the CTD. Therefore, an investigation was done into the properties of different drift gases. The use of freon (CF4) in the drift chamber, combined with an increase of the gas pressure to 150 mbar, makes it possible to identify all particles with Z ? 2. Under these conditions particles with Z = 1 can only be identifled to approximately 25 AMeV. The Isospin Quantum Molecular Dynamics (IQMD) model has been used, to interpret the measured data. This model gives a microscopical description of heavy-ion collisions and simulates collisions on an event by event basis. In IQMD all protons and neutrons are represented as individual Gaussian wave packets. After initialisation the path of each nucleon is calculated for 200 fm/c, after which the simulation is stopped. At this time, nucleons which are close in space are clustered into fragments. The events generated by IQMD can then be processed by a GEANT detector simulation. This calculation takes into account the effects of the detector on the incoming particles. By using the GEANT simulation it is possible to give a direct comparison between the results of IQMD and the experimental data. The impact-parameter selection procedure, based on the charged-particle multiplicity, was studied using IQMD events and the GEANT detector simulation. This showed that indeed an impact-parameter selection can be made with this method. However, the accuracy of this selection for these small systems is not very good. In particular the central-event selection is heavily polluted by mid-central events. Only mid-central events have been studied for 24Mg+27A1 at 45 and 95 AMeV. In order to study the collective flow in heavy-ion collisions, first the event plane has to be reconstructed. Again IQMD events and the GEANT detector simulation were used to investigate the effectiveness of several different event-plane reconstruction methods. It was found that an event plane can be reconstructed. The azimuthal-correlation method gives marginally the best result. With this method to reconstruct the reaction plane, the directed in-plane fiow was studied. The experimental data showed a strongly reduced flow at 95 AMeV compared to 45 AMeV, in accordance with a balancing energy of 114 ± 10 AMeV as derived from literature. Finally, the reaction dynamics were studied using the azimuthal correlations and the polar-angle distributions of intermediate-mass fragments (IMFs) emitted at midrapidity, both of which do not require an event-plane reconstructioh. The azimuthal correlations for the two energies are quite similar, whereas the directed in-plane flow is substantially higher at 45 AMeV than at 95 AMeV. This shows that the azimuthal correlations are insensitive to the magnitude of the directed in-plane flow. At both energies, the azimuthal-correlation functions for the various IMFs show absolute maxima at 180°, which can not be explained by a mid-rapidity source emitting fragments mdependently. However, the distributions are described by IQMD. The maxima are either caused target-projectile correlations (as in IQMD) or by momentum conservation. To describe the momentum-conservation scenario, a second model was introduced, which simulates the prompt multifragmentation of

Prendergast, E. P.

1999-03-01

57

Universal Four-Boson States in Ultracold Molecular Gases: Resonant Effects in Dimer-Dimer Collisions  

SciTech Connect

We study the manifestations of universal four-body physics in ultracold dimer-dimer collisions. We show that resonant features associated with three-body Efimov physics and dimer-dimer scattering lengths are universally related. The emergence of universal four-boson states allows for the tunability of the dimer-dimer interaction, thus enabling the future study of ultracold molecular gases with both attractive and repulsive interactions. Moreover, our study of the interconversion between dimers and Efimov trimers shows that B{sub 2}+B{sub 2}->B{sub 3}+B rearrangement reactions can provide an efficient trimer formation mechanism. Our analysis of the temperature dependence of this reaction provides an interpretation of the available experimental data and sheds light on the possible experimental realization of rearrangement processes in ultracold gases.

D'Incao, J. P. [Department of Physics and JILA, University of Colorado, Boulder, Colorado 80309-0440 (United States); Institut fuer Quantenoptik und Quanteninformation, Oesterreichische Akademie der Wissenschaften, 6020 Innsbruck (Austria); Stecher, J. von; Greene, Chris H. [Department of Physics and JILA, University of Colorado, Boulder, Colorado 80309-0440 (United States)

2009-07-17

58

Non-equilibrium fission processes in intermediate energy nuclear collisions  

SciTech Connect

We have measured the target fragment yields, angular and energy distributions for the interaction of 12-16 MeV/A/sup 32/S with /sup 165/Ho and /sup 197/Au and for the interaction of 32 and 44 MeV/A /sup 40/Ar with /sup 197/Au. The Au fission fragments associated with the peripheral collision peak in the folding angle distribution originate in a normal, ''slow'' fission process in which statistical equilibrium has been established. At the two lowest projectile energies, the Au fission fragments associated with the central collision peak in the folding angle distribution originate in part from ''fast'' (/tau//approximately//sup /minus/23/s), non-equilibrium processes. Most of the Ho fission fragments originate in non- equilibrium processes. The fast, non-equilibrium process giving rise to these fragments has many of the characteristics of ''fast fission'', but the cross sections associated with these fragments are larger than one would expect from current theories of ''fast fission. '' 14 refs., 8 figs.

Loveland, W.; Casey, C.; Xu, Z.; Seaborg, G.T.; Aleklett, K.; Sihver, L.

1989-04-01

59

Measurements of scattering processes in negative ion-atom collisions  

SciTech Connect

This Technical Progress Report describes the progress made on the research objectives during the past twelve months. This research project is designed to provide measurements of various scattering processes which occur in H{sup {minus}} collisions with atomic (specifically, noble gas and atomic hydrogen) targets at intermediate energies. 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 in progress will provide either experimentally-determined cross sections or set upper limits to those cross sections. In either case, these measurements will be stringent tests of our understanding in energetic negative ion-atom collisions. This series of experiments required the construction of a new facility and the initial ion beam was accelerated through the apparatus in April 1991.

Kvale, T.J.

1992-01-01

60

Collision dynamics in electron-capture processes with excitation  

SciTech Connect

We have measured the projectile scattering-angle dependency for various electronic final states for single-electron capture in p+He and {sup 3}He{sup +}+He collisions at incident energies between 60 and 630 keV/u. We find pronounced peak structures in the scattering-angle dependence of some of the ratios of different capture channels. We interpret this as experimental evidence that an excitation process of the target is caused by a transverse momentum transfer that leads to an additional projectile deflection.

Schoeffler, M. S. [Institut fuer Kernphysik, University Frankfurt, Max-von-Laue-Str. 1, 60438 Frankfurt (Germany); Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Titze, J. N.; Schmidt, L. Ph. H.; Jahnke, T.; Jagutzki, O.; Schmidt-Boecking, H.; Doerner, R. [Institut fuer Kernphysik, University Frankfurt, Max-von-Laue-Str. 1, 60438 Frankfurt (Germany)

2009-10-15

61

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

62

Millikelvin Reactive Collisions between Sympathetically Cooled Molecular Ions and Laser-Cooled Atoms in an Ion-Atom Hybrid Trap  

NASA Astrophysics Data System (ADS)

We report on a study of cold reactive collisions between sympathetically cooled molecular ions and laser-cooled atoms in an ion-atom hybrid trap. Chemical reactions were studied at average collision energies ?Ecoll?/kB?20mK, about 2 orders of magnitude lower than has been achieved in previous experiments with molecular ions. Choosing N2++Rb as a prototypical system, we find that the reaction rate is independent of the collision energy within the range studied, but strongly dependent on the internal state of Rb. Highly efficient charge exchange four times faster than the Langevin rate was observed with Rb in the excited (5p) P3/22 state. This observation is rationalized by a capture process dominated by the charge-quadrupole interaction and a near resonance between the entrance and exit channels of the system. Our results provide a test of classical models for reactions of molecular ions at the lowest energies reached thus far.

Hall, Felix H. J.; Willitsch, Stefan

2012-12-01

63

Generalization of the Hartree-Fock approach to collision processes  

SciTech Connect

The conventional Hartree and Hartree-Fock approaches for bound states are generalized to treat atomic collision processes. All the single-particle orbitals, for both bound and scattering states, are determined simultaneously by requiring full self-consistency. This generalization is achieved by introducing two {ital Ans{umlt a}tze}: (a) the weak asymptotic boundary condition, which maintains the correct scattering energy and target orbitals with correct number of nodes, and (b) square integrable amputated scattering functions to generate self-consistent field (SCF) potentials for the target orbitals. The exact initial target and final-state asymptotic wave functions are not required and thus need not be specified {ital a priori}, as they are determined simultaneously by the SCF iterations. To check the asymptotic behavior of the solution, the theory is applied to elastic electron-hydrogen scattering at low energies. The solution is found to be stable and the weak asymptotic condition is sufficient to produce the correct scattering amplitudes. The SCF potential for the target orbital shows the strong penetration by the projectile electron during the collision, but the exchange term tends to restore the original form. Potential applicabilities of this extension are discussed, including the treatment of ionization and shake-off processes. {copyright} {ital 1997} {ital The American Physical Society}

Hahn, Y. [Department of Physics, University of Connecticut, Storrs, Connecticut 06269 (United States)]|[TRG, 49 Timber Drive, Storrs, Connecticut 06268 (United States)

1997-06-01

64

Calculations of fast ion collisions with multi-center molecular targets  

NASA Astrophysics Data System (ADS)

The theoretical treatment of ion-molecule collisions is challenging for several reasons: the systems have many degrees of freedom, a rather complex geometry, and the electron dynamics might be nonperturbative and involve electron-electron interaction effects. However, the interest in accurate calculations has been growing recently. An important reason for this development is the relevance of ion-molecule collisions for a number of fields, such as atmospheric science, and the understanding of radiation damage of biological tissue. We have developed a new approach to meet these challenges [1]. It disregards rovibrational motion, but it does address the multi-center geometry of the system and the generally nonperturbative nature of the electron dynamics. The key ingredients are an expansion of the initially populated molecular orbitals in terms of a single-center basis and a spectral representation of the molecular Hamiltonian. This facilitates a separation of molecular geometry and collision dynamics and makes it possible to use well-established ion-atom methods with relatively minor modifications. We have extended our basis generator method to deal with the collision dynamics and report on results for ionization and fragmentation of water molecules by proton and He^+ ion impact over wide ranges of collision energies. For the case of He^+ impact this will include a discussion of effects due to the presence of the projectile electron. [4pt] [1] H. J. Lüdde et al., Phys. Rev. A 80, 060702(R) (2009)

Kirchner, Tom

2011-06-01

65

Electron-Driven Processes: From Single Collision Experiments to High-Pressure Discharge Plasmas  

NASA Astrophysics Data System (ADS)

Plasmas are complex systems which consist of various groups of interacting particles (neutral atoms and molecules in their ground states and in excite states, electrons, and positive and negative ions). In principle, one needs to understand and describe all interactions between these particles in order to model the properties of the plasma and to predict its behavior. However, two-body interactions are often the only processes of relevance and only a subset of all possible collisional interactions are important. The focus of this talk is on collisional and radiative processes in low-temperature plasmas, both at low and high pressures. We will limit the discussion (i) to ionization and dissociation processes in molecular low-pressure plasmas and (ii) to collisional and radiative processes in high-pressure plasmas in rare gases and mixtures of rare gases and N2, O2, and H2. Electron-impact dissociation processes can be divided into dissociative excitation and dissociation into neutral ground-state fragments. Neutral molecular dissociation has only recently received attention from experimentalists and theorists because of the serious difficulties associated with the investigation of these processes. Collisional and radiative processes in high-pressure plasmas provide a fertile environment to the study of interactions that go beyond binary collisions involving ground-state species. Step-wise processes and three-body collisions begin to dominate the behavior of such plasmas. We will discuss examples of such processes as they relate to high-pressure rare gas discharge plasmas. Work supported by NSF, DOE, DARPA, NASA, and ABA Inc.

Becker, Kurt

2001-10-01

66

Dynamic molecular collision (DMC) model for rarefied gas flow simulations by the DSMC method  

Microsoft Academic Search

The Dynamic Molecular Collision (DMC) model is constructed for accurate and realistic simulations of rarefied gas flows of nonpolar diatomic molecules by the Direct Simulation Monte Carlo (DSMC) method. This model is applicable for moderate temperatures (up to a few hundred K for nitrogen), where most molecules are in the vibrational ground state and the vibrational degree of freedom can

T. Tokumasu; Y. Matsumoto

1999-01-01

67

Gas-Phase Studies of Collisions of Small Molecular Free Radical Species  

Microsoft Academic Search

The spectroscopy of several small molecular free radicals and the collision dynamics of reactions of such species has been investigated in a series of laser fluorescence experiments carried out with molecular beams and in a cell. The spectroscopic studies include observation of a number of new NCO ~ A^2Sigma ^+ - ~ X^2Pi (0,v _2,0) - (v _1,v_2,v_3 ) vibronic

Dipti Patel-Misra

1992-01-01

68

Collision-induced vibrational absorption in molecular hydrogens  

SciTech Connect

Collision induced absorption (CIA) spectra of the first overtone bands of H{sub 2}, D{sub 2}, and HD have been recorded for gas densities up to 500 amagat at 77-300 K. Analyses of these spectra reveal that (1) contrary to the observations in the fundamental bands, the contribution of the isotropic overlap interaction to the first overtone bands is negligible, (2) the squares of the matrix elements B{sub 32}(R)/ea{sub o} [= {lambda}{sub 32} exp(-(R-{sigma})/{rho}{sub 32}) + 3 (R/a{sub o}){sup -4}] where the subscripts 3 and 2 represent L and {lambda}, respectively, account for the absorption intensity of the bands and (3) the mixed term, 2,3 {lambda}{sub 32} exp (-(R-{sigma})/{rho}{sub 32}) <{vert_bar}Q{vert_bar}> <{alpha}> (R/a){sup -4}, gives a negative contribution. In the CIA spectra of H{sub 2} in its second overtone region recorded at 77, 201 and 298 K for gas densities up to 1000 amagat, a dip in the Q branch with characteristic Q{sub p} and Q{sub R} components has been observed. The analysis of the absorption profiles reveals, in addition to the previously known effects, the occurrence of the triple-collision transitions of H{sub 2} of the type Q{sub 1}(J) + Q{sub 1}(J) + Q{sub 1}(J) for the first time. From the profile analysis the absorption coefficient of these transitions is obtained.

Reddy, S.P.

1993-05-01

69

Single and multiple electron removal processes in proton-water-molecule collisions  

NASA Astrophysics Data System (ADS)

Charge-state correlated cross sections for single- and multiple-electron removal processes (capture and ionization) in proton-H2O collisions are calculated by using the nonperturbative basis generator method adapted for ion-molecule collisions [Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.80.060702 80, 060702(R) (2009)]. The results are compared with experimental data for a wide range of impact energies spanning from 20 keV to several MeV. Single-electron removal probabilities in each molecular orbital are evaluated using the inclusive-probability formalism to predict the yields of charged fragments (H2O+, OH+, H+, O+) according to branching ratios that are valid at high impact energies. At intermediate and low energies, we calculate improved fragmentation cross sections that include the effects of multiple-electron removal processes. The resulting fragmentation yields agree with experiments at the 20%-30% level even below 100 keV impact energy.

Murakami, Mitsuko; Kirchner, Tom; Horbatsch, Marko; Lüdde, Hans Jürgen

2012-05-01

70

Near-threshold inelastic collisions using molecular beams with a tunable velocity.  

PubMed

Molecular scattering behavior has generally proven difficult to study at low collision energies. We formed a molecular beam of OH radicals with a narrow velocity distribution and a tunable absolute velocity by passing the beam through a Stark decelerator. The transition probabilities for inelastic scattering of the OH radicals with Xe atoms were measured as a function of the collision energy in the range of 50 to 400 wavenumbers, with an overall energy resolution of about 13 wavenumbers. The behavior of the cross-sections for inelastic scattering near the energetic thresholds was accurately measured, and excellent agreement was obtained with cross-sections derived from coupled-channel calculations on ab initio computed potential energy surfaces. PMID:16973875

Gilijamse, Joop J; Hoekstra, Steven; van de Meerakker, Sebastiaan Y T; Groenenboom, Gerrit C; Meijer, Gerard

2006-09-15

71

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

72

Validity of the work–energy theorem in molecular dynamics simulations for nanodroplets collisions  

Microsoft Academic Search

Work–energy theorem is examined for nanodroplets collisions in molecular dynamics simulations. Work term and energy term in the work–energy theorem are separately calculated and the equality between them is checked. The terms are based on different microscopic variables. A serious mismatch between them is observed. Therefore, we have to pay attention to calculating some physical quantities related to the work–energy

Sangrak Kim

2012-01-01

73

Present-day views on atomic collision processes at intermediate and high impact velocities  

Microsoft Academic Search

Present day views on atomic collision processes at intermediate and high nonrelativistic impact velocities are introduced. Powerful accelerators of highly charged particles could be a tool to confirm the views definitely and for new investigations in those ranges of impact velocities. In the study of a collision of two heavy particles A and B (atoms, ions or molecules), the knowledge

Gayet

1983-01-01

74

Trap-induced resonances in controlled atomic collisions for quantum information processing  

Microsoft Academic Search

Controlled collisions of ultracold atoms in optical lattices provide new avenues for quantum control and quantum information processing. The ability to precisely vary lattice parameters and the rich internal structure of trapped atoms allow for novel state manipulation. In this research, we investigate and develop new methods for analyzing and designing coherent controlled collisions of ultracold atoms in separated traps.

Rene Stock

2005-01-01

75

a Time-Dependent Molecular Orbital Approach to Ion-Solid Surface Collisions  

NASA Astrophysics Data System (ADS)

A time-dependent molecular orbital method has been developed to study charge transfer in collisions of ions with metal surfaces at energies between 1 au and 170 au. A set of localized basis functions, consisting of generalized Wannier functions for the surface and s- and p-atomic functions for the ion, is used to separate the system into primary and secondary regions. An effective Hamiltonian and time-dependent equations for the electron density matrix are obtained in the primary region, where most charge transfer occurs. The equations for the electron density matrix are solved with a linearization scheme. The method is suitable to study atomic orbital polarization for collisions of ions and surfaces. A model calculation for Na^+ + W(110) collisions with a prescribed trajectory is presented. The interaction potentials between the W(110) surface and Na 3s and 3p orbitals are calculated from a Na pseudopotential and a step potential for W(110). Results show that the yield of neutralized atoms oscillates with the collision energy as the result of the near-resonance charge transfer mechanism. The time-dependence of the density matrix provides insight on the dynamics of electron transfer along the atomic trajectory.

Feng, Eric Quinn

1991-02-01

76

Estimates of Collisional Cooling and Quenching Rates for Atomic and Molecular Ion Collisions with Ultracold Atoms.  

NASA Astrophysics Data System (ADS)

Translational cross sections and rate coefficients for cold ion-neutral elastic and charge-exchange collisions (either atomic or molecular) are >> larger (˜10^6 a.u.) than neutral-neutral collisions at the same CM energy. This is due to the long range polarization potential V(R) = -C4/R^4, where C4 is proportional to the polarizability of the neutral partner. Thus collisions between ultracold alkali atoms (trapped in a magneto-optic trap or MOT) and low-energy ions can be used for sympathetic cooling experiments. We are building a prototype hybrid-trap apparatus [1] that applies these principles to collisions of Ca^+ ions (which can be laser pre-cooled) with MOT-trapped ultracold Na atoms. Some calculations on this system and other related ion-neutral systems have been published [2] and some initial experiments on other ion-neutral species have begun [3]. Estimates of cooling and quenching rates in the low K-mK CM energy range for Ca+ on Na and other cases will be presented and possible experiments described. [1] Winthrop W. Smith, Oleg P. Makarov and Jian Lin, J. Modern Optics 52, 2253 (2005). [2] R. Côt'e and A. Dalgarno, Phys. Rev. A 62, 012709 (2000); R. Côt'e, Phys. Rev. Lett. 85, 5316 (2000). [3] A. Grier, M. Cetina, F.Orucevic, and V. Vuletic, ArXiv atom-ph/0808.3620.

Smith, Winthrop; Wells, James

2009-05-01

77

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

78

(Collision processes of interest in MFE plasama research): Progress report  

SciTech Connect

Research on this grant is devoted to the calculation of heavy particle collision cross sections needed for diagnostics studies of magnetic fusion plasmas. This work requires the development and testing of new theoretical techniques, and the implementation of benchmarked methods to collisions pertinent to fusion reactors. On the last context, we have provided the cross sections for modeling the beam penetration in an ERT plasma, charge exchange recombination values for impurity ion diagnostic studies, and those for assessing the feasibility of using a high efficiency plasma neutralizer for 0.5 to 1.0 MeV/u D/sup /minus// beams. We have also extended our theoretical understanding to H/sup +/, He/sup + +/ + He collisions in order to be prepared for the modeling of helium and transport in the next generation of reactors.

Not Available

1989-01-01

79

1978 Bibliography of Atomic and Molecular Processes.  

National Technical Information Service (NTIS)

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 at...

1980-01-01

80

The Atomic and Molecular Universe: Collisions in Hot Plasmas to the Building Blocks of Life  

NASA Astrophysics Data System (ADS)

Basic atomic and molecular collision phenomena are operative at the core of an enormous range of astrophysical plasmas, including the interstellar medium (ISM), protostellar regions, stars, our Sun, and planetary atmospheres, ionospheres, & magnetospheres. Laboratory measurements of cross sections and lifetimes are needed to establish plasma charge-state distributions. A required database includes absolute electron- impact excitation, ionization, and recombination cross sections in highly-charged ions (HCIs); photoionization cross sections; and absolute single- and multiple charge-exchange cross sections between a neutral target and an HCI, as when a solar/stellar wind meets a circumstellar cloud or passing comet to generate X- rays via charge exchange. Since satellites and spacecraft often detect photons from the astronomical object, the infrared-to-X- ray emissions are governed by a balance between collisional excitation and radiative decay, so that accurate lifetimes, branching fractions, and Einstein A and B coefficients are also needed. On yet another level, observations in the infrared-to- millimeter wave region from, for example, the Green Bank Telescope, Spitzer, Sofia, Herschel, and the James Webb Telescope provide information on molecular formation in the ISM and protostellar regions. Over 144 atomic, molecular, and ionic species have been identified to date. Recent laboratory results will be given on formation of some of these polyatomic molecules in superthermal, ground-state H- and O-atom collisions with simple, grain-adsorbed species, and results compared to the impressive array of space spectroscopic data.

Chutjian, Ara

2010-03-01

81

Nuclear imaging of molecular processes in cancer  

Microsoft Academic Search

Molecular imaging using radionuclides has brought about the possibility to image a wide range of molecular processes using\\u000a radiotracers injected into the body at very low concentrations that should not perturb the processes being studied. Examples\\u000a include specific peptide receptor expression, angiogenesis, multi drug resistance, hypoxia, glucose metabolism, and many others.\\u000a This article presents an overview, aimed at the non-specialist

Rafael Torres Martin de Rosales; Erik Årstad; Philip J. Blower

2009-01-01

82

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

83

Study of the freeze-out process in heavy ion collisions at relativistic energies  

NASA Astrophysics Data System (ADS)

In this work, we investigate the freeze-out process in heavy ion collisions at different relativistic energies. We present a study of standard blast-wave fits and Tsallis blast-wave fits performed to the transverse momentum spectra obtained in Au+Au collisions at RHIC energies. In addition, comparisons with simulated heavy ion collisions data using the UrQMD code will be presented to provide more detailed insight into the properties of the space-time evolution such as collective dynamics of the dense matter.

Ristea, O.; Jipa, A.; Ristea, C.; Esanu, T.; Calin, M.; Barzu, A.; Scurtu, A.; Abu-Quoad, I.

2013-03-01

84

ATOMIC AND MOLECULAR PHYSICS: Lie Algebraic Approach to Energy Transfer for Collinear Collision of Two Anharmonic Diatomic Molecules  

NASA Astrophysics Data System (ADS)

An anharmonic oscillator algebra model is used to study the collinear collisions of two diatomic molecules. The transition probability for vibration-vibration energy transfer is presented. For an application of the method, we talk about the collision of N2+CO, N2+O2, and N2+N2. Through long time averaging, the transition probability changes to the function of total energy of the system. Comparing the results with the quantum results, we can see that the dynamical Lie algebraic method is useful for describing the anharmonic diatomic molecular collision.

Wang, Xiao-Yan; Wang, Peng-Cheng; Qiu, Jian-Feng; Wang, Jin-Xi; Hou, Li-Xia; Xie, Jin-Dong Ding, Shi-Liang

2010-02-01

85

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.

86

A measurement of absolute cross sections for multielectron processes in slow collisions between highly charged ions and atoms  

Microsoft Academic Search

In this experiment absolute cross sections for single and multielectron processes in slow collisions, Aq+ + B --> Ar+ + Bs+ +(t + s - q)e-, have been measured. By means of a coincidence time-of-flight technique, the charge state of the projectile before and after the collision and the charge state of the target after the collision are determined. The

H. Cederquist; G. Astner; A. Bárány; H. Danared; A. Johnson; L. Liljeby; K.-G. Rensfelt; S. Huldt; P. Hvelplund; H. Knudsen

1987-01-01

87

First evidence of hard scattering processes in single tagged ?? collisions  

Microsoft Academic Search

For the first time, multihadronic production from single tagged ?? collisions has been studied, where one of the scattered leptons was tagged at very low virtual photon absolute mass squared (?Q2? = 0.06 (GeV\\/c2)2). Data collected during 1991 and 1992 in the DELPHI experiment at LEP are shown to agree well with predictions which included the non-perturbative vector meson dominance

P. Abreu; W. Adam; T. Adye; E. Agasi; I. Ajinenko; R. Aleksan; G. D. Alekseev; P. P. Allport; S. Almehed; F. M. L. Almeida; S. J. Alvsvaag; U. Amaldi; A. Andreazza; M. L. Andrieux; P. Antilogus; W. D. Apel; Y. Arnoud; B. Åsman; J. E. Augustin; A. Augustinus; P. Baillon; P. Bambade; F. Barao; R. Barate; G. Barbiellini; D. Y. Bardin; G. J. Barker; A. Baroncelli; O. Barring; J. A. Barrio; W. Bartl; M. J. Bates; M. Battaglia; M. Baubillier; J. Baudot; K. H. Becks; M. Begalli; P. Beilliere; P. Beltran; A. C. Benvenuti; M. Berggren; D. Bertrand; F. Bianchi; M. Bigi; M. S. Bilenky; P. Billoir; J. Bjarne; D. Bloch; 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; J. M. Brunet; L. Bugge; T. Buran; A. Buys; M. Caccia; M. Calvi; A. J. Camacho Rozas; T. Camporesi; V. Canale; M. Canepa; K. Cankocak; F. Cao; F. Carena; P. Carrilho; L. Carroll; C. Caso; V. Cassio; M. V. Castillo Gimenez; A. Cattai; F. R. Cavallo; L. Cerrito; V. Chabaud; A. Chan; Ph. Charpentier; L. Chaussard; J. Chauveau; P. Checchia; G. A. Chelkov; 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; W. Da Silva; C. Defoix; P. Delpierre; N. Demaria; A. De Angelis; H. De Boeck; W. De Boer; S. De Brabandere; C. De Clercq; M. D. M. De Fez Laso; C. De La Vaissiere; B. De Lotto; A. De Min; L. De Paula; C. De Saint-Jean; H. Dijkstra; L. Di Ciaccio; F. Djama; J. Dolbeau; M. Donszelmann; K. Doroba; M. Dracos; J. Drees; M. Dris; Y. Dufour; F. Dupont; D. Edsall; R. Ehret; T. Ekelof; G. Ekspong; M. Elsing; J. P. Engel; N. Ershaidat; M. Espirito Santo; D. Fassouliotis; M. Feindt; A. Ferrer; T. A. Filippas; A. Firestone; H. Foeth; E. Fokitis; F. Fontanelli; F. Formenti; J. L. Fousset; B. Franek; P. Frenkiel; D. C. Fries; A. G. Frodesen; R. Fruhwirth; F. Fulda-Quenzer; H. Furstenau; J. Fuster; D. Gamba; M. Gandelman; C. Garcia; J. Garcia; C. Gaspar; U. Gasparini; Ph. Gavillet; E. N. Gazis; D. Gele; J. P. Gerber; D. Gillespie; R. Gokieli; B. Golob; V. M. Golovatyuk; J. J. Gomez Y Cadenas; G. Gopal; L. Gorn; M. Gorski; V. Gracco; F. Grard; E. Graziani; G. Grosdidier; P. Gunnarsson; J. Guy; U. Haedinger; F. Hahn; M. Hahn; S. Hahn; S. Haider; Z. Hajduk; A. Hakansson; A. Hallgren; K. Hamacher; W. Hao; F. J. Harris; V. Hedberg; R. Henriques; J. J. Hernandez; J. A. Hernando; P. Herquet; H. Herr; T. L. Hessing; E. Higon; H. J. Hilke; T. S. Hill; S. O. Holmgren; P. J. Holt; D. Holthuizen; P. F. Honore; M. Houlden; J. Hrubec; 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; L. Jonsson; P. Juillot; M. Kaiser; G. Kalmus; F. Kapusta; M. Karlsson; E. Karvelas; A. Katargin; 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; C. Kreuter; J. Krolikowski; I. Kronkvist; W. Krupinski; K. Kulka; K. Kurvinen; C. Lacasta; I. Laktineh; C. Lambropoulos; J. W. Lamsa; L. Lanceri; P. Langefeld; V. Lapin; I. Last; J. P. Laugier; R. Lauhakangas; G. Leder; F. Ledroit; R. Leitner; Y. Lemoigne; J. Lemonne; G. Lenzen; V. Lepeltier; T. Lesiak; J. M. Levy; E. Lieb; D. Liko; 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. Mc Cubbin; R. Mc Kay; R. Mc Nulty; J. Medbo; C. Meroni; W. T. Meyer; A. Miagkov; 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; S. Navas; P. Negri; S. Nemecek; W. Neumann; N. Neumeister; R. Nicolaidou; B. S. Nielsen; V. Nikolaenko; P. Niss; A. Nomerotski; A. Normand; V. Obraztsov; A. G. Olshevski; R. Orava; K. Osterberg; A. Ouraou; P. Paganini; M. Paganoni; R. Pain; H. Palka; Th. D. Papadopoulou; L. Pape; F. Parodi; A. Passeri; M. Pegoraro

1995-01-01

88

Diffractive processes in electron-proton and proton-proton collisions  

SciTech Connect

In this paper we give a brief description of diffractive processes. We focus on ep collisions at HERA and outline key features of exclusive diffraction in hadron-hadron collision. We discuss respectively: diffractive parton distributions of the proton obtained from DGLAP fits to HERA data, including the twist-4 contribution, afterwards diffractive charm production from dipole model and at the end shortly exclusive production of a Higgs boson in pp scattering.

Luszczak, A. [Institute of Nuclear Physics, Polish Academy of Sciences, Cracow (Poland)

2009-04-20

89

Electron collisions with the BeH+ molecular ion in the R-matrix approach  

NASA Astrophysics Data System (ADS)

The R-matrix method is used to study electron collisions with the BeH+ molecular ion. The diatomic version of the UK Molecular R-matrix codes is used and a configuration-interaction calculation is first performed for the BeH+ target to obtain its potential energy curves for 19 lowest singlet and triplet states. Scattering calculations are then done to yield excitation and rotational excitation cross sections in the energy range 0 - 14 eV. Additionally we also obtain bound states of BeH and their quantum defects at the BeH equilibrium bond length 2.5369 a 0. Resonance positions and widths for Feshbach resonances in the e-BeH+ system are also obtained and presented at the equilibrium bond length 2.5369 a 0.

Chakrabarti, K.; Tennyson, J.

2012-01-01

90

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

91

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

92

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

93

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

NASA Astrophysics Data System (ADS)

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 torch of meteorite impact and have continued in an impact crater in the case of the arising of the simplest life form. It is generally accepted that planets are the optimal place for the origin and evolution of life. In the process of forming the planetary systems the meteorites, space bodies feeding planet growth, appear around stars. In the process of Earth's formation, meteorite sizes ranged from hundreds and thousands of kilometres. These space bodies consisted mostly of the planetesimals and comet nucleus. During acceleration in Earth's gravitational field they reached hypervelocity and, hitting the surface of planet, generated powerful blowouts of hot plasma in the form of a torch. They also created giant-size craters and dense dust clouds. These bodies were composed of all elements needed for the synthesis of organic compounds, with the content of carbon being up to 5%-15%. A new idea of possible synthesis of the complex organic compounds in the hypervelocity impact-generated plasma torch was proposed and experimentally confirmed. A previously unknown and experimentally corroborated feature of the impact-generated plasma torch allowed a new concept of the prehistory of life to be developed. According to this concept the intensive synthesis of complex organic compounds arose during meteoritic bombardment in the first 0.5 billion years at the stage of the planet's formation. This most powerful and destructive action in Earth's history could have played a key role and prepared conditions for the origin of life. In the interstellar gas-dust clouds, the synthesis of simple organic matter could have been explained by an identical process occurring in the plasma torch of hypervelocity collisions between submicron size dust particles. It is assumed that the processes occurred in the highly unbalanced hot plasma simultaneously with the synthesis of simple and complicated organic compounds, thereby ensuring their ordering and assembly. Bona fide experimental evidence presented below indicates that the physical fields generated in the plasma environment in the process of the formation and expansion of the torch meet the main requirements toward “true” local chiral fields. These fields were very likely to be capable to trigger the initial, weak breaking of enantiomer symmetry and determine the “sign” of the asymmetry of the bioorganic world. These fields could have worked as “trapping” fields influencing spontaneous processes occurring in highly overheated and nonequilibrium plasma in the state that is far from the thermodynamical branch of equilibrium and may have contributed to the formation of an environment needed for the synthesis of homochiral molecular structures, which, in turn, were needed for the emergence of the primary forms of living matter. It has been shown experimentally that the plasma-chemical processes in the torch have high catalytic properties and assure the rise of the chemical reaction rates by 10-100 million times. In the process of the plasma flyaway this in turn can assure the fast formation of simple and complicated organic compounds, including hyper-branched polymers. It is possible to assume that predominantly inorganic substances from meteorites were used for the synthesis of complicated organic compounds on early Earth. A laboratory experiment with hypervelocity impact plasma torch modelling by a laser with a Q-switch mode has shown the possibility of high-molecular organic compound synthesis, with mass of approximately 5000 a.m.u. by meteorite impact with an effective diameter of 100 mkm. The target contained only H, C, N and O elements in inorganic forms. The approximation of the curve received in these experimen

Managadze, G.

2010-07-01

94

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

95

Bibliography of atomic and molecular processes, 1983  

SciTech Connect

This annotated bibliography includes papers on atomic and molecular processes published during 1983. 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.)

1984-10-01

96

The conference on the dynamics of molecular collisions held at Snowbird, Utah on 14-19 July 1985  

NASA Astrophysics Data System (ADS)

The research discussed at the conference included: reactive scattering studies with state selection and aligned reactants; reactive and nonreactive resonances; reactions of transition metal ions; reactive close coupling calculations and the distorted wave and quantal transition state theories of reactive scattering; potential energy surfaces; experimental studies of vibrational and rotational energy transfer collisions in the vapor and condensed phases, in ions in flow tubes, and at surfaces; collision-free energy transfer; infrared and visible fluorescence, theory and experiment for collisions of open-shell and electronically excited molecules; collisional interactions of molecules with surfaces; desorption; helium beam diffraction; and photodissociation. The plenary discussions following the lectures were exceptionally vital and provided a strong indication of the current excitement in this field. The posters covered an even broader spectrum of work on the dynamics of molecular collisions.

Truhlar, D. G.

1985-07-01

97

Four-body charge transfer processes in heavy particle collisions  

NASA Astrophysics Data System (ADS)

Fully differential cross sections (FDCS) for proton + helium single capture and transfer-excitation collisions are presented using the Four-Body Transfer-Excitation (4BTE) model. This is a first order perturbative model that allows for any two-particle interaction to be studied. For single capture, the effect of the projectile-nuclear term in the perturbation is examined. It is shown that inclusion of this term results in an unphysical minimum in the FDCS, but is required to correctly predict the magnitude of the experimental results. For transfer-excitation, the role of electron correlation in the target helium atom is studied, and shown to be unimportant in the calculation of the FDCS.

Harris, A. L.; Peacher, J. L.; Schulz, M.; Madison, D. H.

2010-02-01

98

Multiple electron transfer processes in collisions of N6+ and O7+ with methane  

NASA Astrophysics Data System (ADS)

Recent experiments on collision processes of O7+ and N6+ 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 N6+ and O7+ 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 N6+ is slightly larger, but that the O7+ leaves the methane in a higher charged state with higher probability, leading to more fragmentation in the collisions with O7+ .

Guevara, N. L.; Teixeira, E.; Hall, B.; Deumens, E.; Öhrn, Y.; Sabin, J. R.

2009-12-01

99

Molecular processes in the early Universe  

NASA Astrophysics Data System (ADS)

Molecular processes first took place in the Universe in the recombination era as the expanding Universe cooled adiabatically and recombined when the cooling radiation field ran out of photons energetic enough to cause photoionization. The formation of neutral helium heralded the dawn of chemistry as the neutral atoms participated in processes of radiative association to form molecular ions. Dissociative recombination of the molecular ions produced neutral atoms and accelerated the conversion of the ionized plasma into a neutral gas. The subsequent chemistry involved hydrogen, deuterium, helium and lithium created earlier in a brief period of nucleosynthesis. With the continued expansion the Universe became cold and dark and chemistry came to a temporary end until the formation and gravitational collapse of the first distinct cosmological objects. Heavy elements were made, a new source of radiation - starlight - appeared and a richer chemistry was initiated.

Dalgarno, A.

2005-01-01

100

Spin-flip processes in low-energy Fe[sup 17+] + He collisions  

SciTech Connect

Spin-nonconserving electron transfer processes violating the Wigner rule'' have been studied for slow multiply charged ion-atom collisions. Experimentally a strong population of highly metastable sodium-like quartet states in low energy Fe[sup 17+] + He single collision events has been observed. The possibility of double-electron capture plus spin-flip mechanisms has been discussed experimentally and theoretically, Our theoretical model using time dependent perturbation theory predicts that spin-flip processes are as likely as no spin flip under the conditions of our experiment.

Bruch, R.; Altick, P.L.; Rauscher, E.; Wang, H. (Department of Physics, University of Nevada, Reno, Reno, Nevada 89557 (United States)); Schneider, D. (High Temperature Physics Division, Lawrence Livermore National Laboratory, Livermore, California 94550 (United States))

1993-06-05

101

Molecular sieving silica membrane fabrication process  

DOEpatents

A process 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.

Raman, Narayan K. (400 Maple St. SE., Apartment 112, Albuquerque, NM 87106); Brinker, Charles Jeffrey (14 Eagle Nest Dr., NE., Albuquerque, NM 87122)

1998-01-01

102

Molecular sieving silica membrane fabrication process  

DOEpatents

A process 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.

Raman, Narayan K. (Monroeville, PA); Brinker, Charles Jeffrey (Albuquerque, NM)

1999-01-01

103

MOLECULAR PROCESSES IN CELLULAR ARSENIC METABOLISM  

EPA Science Inventory

Elucidating molecular processes that underlie accumulation, metabolism, and binding of iAs and its methylated metabolites provides a basis for understanding the modes of action by which iAs acts as a toxin and a carcinogen. One approach to this problem is to construct a conceptu...

104

Geodynamic processes of Taiwan arc–continent collision and comparison with analogs in Timor, Papua New Guinea, Urals and Corsica  

Microsoft Academic Search

The Taiwan arc–continent collision involves four geodynamic processes: intra-oceanic subduction; initial arc–continent collision; advanced arc–continent collision; and arc collapse\\/subduction. These processes now occur simultaneously in 19–24°30?N but have operated sequentially southward since the Late Miocene. Although the geological and geophysical features appear to change progressively from north to south across the island, they are distinct within individual tectonic regimes. Using

Chi-Yue Huang; Peter B Yuan; Ching-Weei Lin; Tan K Wang; Chung-Pai Chang

2000-01-01

105

Multichannel quantum defect theory for cold molecular collisions with a strongly anisotropic potential energy surface  

NASA Astrophysics Data System (ADS)

We show that multichannel quantum defect theory (MQDT) can be applied successfully as an efficient computational method for cold molecular collisions in Li+NH, which has a deep and strongly anisotropic interaction potential. In this strongly coupled system, closed-channel poles restrict the range over which the MQDT Y can be interpolated. We present an improved procedure to transform the MQDT reference functions so that the poles are removed from the energy range of interest. Effects due to very-long-range spin dipolar couplings are outside the scope of MQDT, but can be added perturbatively. This procedure makes it possible to calculate the elastic and inelastic cross sections, over the entire range of energies and fields needed to evaluate the feasibility of sympathetic cooling of NH by Li, using coupled-channel calculations at only five combinations of energy and field.

Croft, James F. E.; Hutson, Jeremy M.

2013-03-01

106

Numerical simulation by the molecular collision theory of two-phase mixture explosion characteristics in closed or vented vessels  

Microsoft Academic Search

The aim of this work consists in presenting a simple modelling (the molecular collision theory), easily usable in an industrial environment in order to predict the evolution of thermodynamical characteristics of the combustion of two-phase mixtures in a closed or a vented vessel. Basic characteristics of the modelling have been developed for ignition and combustion of propulsive powders and adapted

J. M. Pascaud; J. Brossard; J. M. Lombard

1999-01-01

107

Quasi-molecular processes in dense plasmas  

NASA Astrophysics Data System (ADS)

Quasi-molecular phenomena occur in dense plasmas when the interatomic spacing is comparable to the characteristic wavelength of the electrons. If the electronic states are bound, covalent orbitals arise with different excitation energies, radiative rates, and collisional rates than for isolated ions. For continuum electrons, charge localization near transient clusters of nuclei can influence many scattering and transport processes. Several consequences of quasi-molecular phenomena in plasmas were identified and a possible explanation of high energy features associated with helium-like emissions lines observed in recent inertial fusion experiments was given.

Younger, S. M.

108

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

109

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

110

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

111

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

112

Convoy electrons from atomic and molecular heavy ion collisions with solids  

NASA Astrophysics Data System (ADS)

Energy distributions of convoy electrons have been measured for different projectiles ( 0203 MeV/u < Ep/Mp < 2.7 MeV/u) traversing thin carbon foils ( 2 ?g/cm2 < px < 20 ?g/cm2 ). The motivation of our study is to elucidate the mechanisms of convoy electron production in ion-solid collisions. The analysis of the convoy peak's shape and yield dependence on dwell time td, velocity vp, incident charge state qi and atomic number zp of the projectile shows significant deviations from theories of ECC and ELC in single collision systems. In non-equilibrium of the projectile charge ( td < 2 fs ) the convoy electron yield Yc of atomic heavy ions depends strongly on qi and exhibits an exponential dependence on the dwell time. Here the ELC process prevails. In the higher dwell time regime ( td > 2 fs ) the convoy electron yield Yc is described by Yc zp 3.2Ep -1.3. In comparison to free isotachic electrons the convoy electrons have an effective mean free path about two up to ten times higher. The value depends on the velocity vp and the nuclear charge zp and suggests a strong correlation between the convoy electron and the traversing ion. We discuss the observed convoy production and their strong dwell time dependence ( td < 30 fs ).

Koschar, P.; Latz, R.; Kemmler, J.; Burkhard, M.; Frischkorn, H. J.; Hofmann, D.; Schader, J.; Schramm, R.; Groeneveld, K. O.; Brenig, M.; Elston, S.; Sellin, I. A.; Meckbach, W.

113

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

114

Measurement of the jet width in ?? collisions and in e+e- annihilation process at TRISTAN  

NASA Astrophysics Data System (ADS)

The shape of jets produced in (quasi-) real photon-photon collisions as well as in e+e- annihilation process has been studied with a cone jet finding algorithm, using the data taken with the TOPAZ detector at the TRISTAN e+e- collider at an average center-of-mass energy (see) of 58 GeV. The results are presented in terms of the jet width as a function of the jet transverse energy (ETjet) as well as a scaled transverse jet energy, xT (=2ETjet/sqrt(s)). The jet width narrows as EjetT increases; however, at the same value of ETjet the jet width in ?? collisions at TRISTAN is significantly narrower than that in ?p collisions at HERA. By comparing our results with the data in other reactions, it has been shown that the jet width in ??, ?p, pp¯ collisions as well as the e+e- annihilation process has an approximate scaling behavior as a function of xT.

Topaz Collaboration; Adachi, K.; Hayashii, H.; Miyabayashi, K.; Noguchi, S.; Miyamoto, A.; Tauchi, T.; Abe, K.; Abe, T.; Adachi, I.; Aoki, M.; Aoki, M.; Enomoto, R.; Emi, K.; Fujii, H.; Fujii, K.; Fujii, T.; Fujimoto, J.; Fujiwara, N.; Hirano, H.; Howell, B.; Iida, N.; Ikeda, H.; Inoue, Y.; Itami, S.; Itoh, R.; Iwasaki, H.; Iwasaki, M.; Kajikawa, R.; Kaneyuki, K.; Kato, S.; Kawabata, S.; Kichimi, H.; Kobayashi, M.; Koltick, D.; Levine, I.; Mamada, H.; Muramatsu, K.; Nagai, K.; Nakabayashi, K.; Nakamura, M.; Nakano, E.; Nitoh, O.; Ochi, A.; Ochiai, F.; Ohishi, N.; Ohnishi, Y.; Ohshima, Y.; Okuno, H.; Okusawa, T.; Shibata, E.; Sugiyama, A.; Sugiyama, H.; Suzuki, S.; Takahashi, K.; Takahashi, T.; Tanimori, T.; Teramoto, Y.; Tomoto, M.; Tsukamoto, T.; Tsumura, T.; Uno, S.; Watanabe, Y.; Yamamoto, A.; Yamauchi, M.

1999-04-01

115

The Theory of High Energy Collision Processes - Final Report DOE/ER/40158-1  

SciTech Connect

In 1984, DOE awarded Harvard University a new Grant DE-FG02-84ER40158 to continue their support of Tai Tsun Wu as Principal Investigator of research on the theory of high energy collision processes. This Grant was renewed and remained active continuously from June 1, 1984 through November 30, 2007. Topics of interest during the 23-year duration of this Grant include: the theory and phenomenology of collision and production processes at ever higher energies; helicity methods of QED and QCD; neutrino oscillations and masses; Yang-Mills gauge theory; Beamstrahlung; Fermi pseudopotentials; magnetic monopoles and dyons; cosmology; classical confinement; mass relations; Bose-Einstein condensation; and large-momentum-transfer scattering processes. This Final Report describes the research carried out on Grant DE-FG02-84ER40158 for the period June 1, 1984 through November 30, 2007. Two books resulted from this project and a total of 125 publications.

Wu, Tai, T.

2011-09-15

116

Two-Electron Transfers and Molecular X-Ray Radiation During Heavy Ion Collisions Zwei-Elektronenuebergaenge und Molekulare Roentgenstrahlung bei Schwerionenkollisionen.  

National Technical Information Service (NTIS)

Continuous X-ray emission spectra in heavy ion collisions are attributed to quasi-molecular transfer. Comparisons of single spectrum measurements for Al-Al, Ca-Ca, Cl-Ni, Fe-Ni, Ni-Fe, Ni-Ni, and Ag-Ag collisions agree well with theoretical predictions.

C. Stoller

1976-01-01

117

Collisions between Tunable Halo Dimers: Exploring an Elementary Four-Body Process with Identical Bosons  

SciTech Connect

We study inelastic collisions in a pure, trapped sample of Feshbach molecules made of bosonic cesium atoms in the quantum halo regime. We measure the relaxation rate coefficient for decay to lower-lying molecular states and study the dependence on scattering length and temperature. We identify a pronounced loss minimum with varying scattering length along with a further suppression of loss with decreasing temperature. Our observations provide insight into the physics of a few-body quantum system that consists of four identical bosons at large values of the two-body scattering length.

Ferlaino, F.; Knoop, S.; Mark, M.; Berninger, M.; Schoebel, H.; Naegerl, H.-C. [Institut fuer Experimentalphysik and Zentrum fuer Quantenphysik, Universitaet Innsbruck, 6020 Innsbruck (Austria); Grimm, R. [Institut fuer Experimentalphysik and Zentrum fuer Quantenphysik, Universitaet Innsbruck, 6020 Innsbruck (Austria); Institut fuer Quantenoptik und Quanteninformation, Oesterreichische Akademie der Wissenschaften, 6020 Innsbruck (Austria)

2008-07-11

118

Electron Transfer Processes to Continuum in Near-Relativistic Ion-Atom Collisions  

SciTech Connect

Theories for electron transfer to the continuum have encountered considerable difficulties to take into account the intrinsic many-electron processes in the capture channel. This may partially be attributed to large momentum transfers involved and thus collision systems are mostly not in the realm of first order perturbation theories. For this reason we have studied collision systems where simultaneously distinct competing electron transfer processes are found to be active, like radiative (RECC) and non-radiative electron capture to continuum (ECC) in the relativistic domain where one or two even active electrons are involved; here another, though distinct, transfer process, the projectile electron loss to continuum (ELC), permits additionally to study the dynamics of ionization very close to threshold. We have studied these electron transfer processes simultaneously in forward electron emission in two systems of different projectile Compton profile, U{sup 88+}+N{sub 2} and Sn{sup 47+}+N{sub 2} collisions using the forward electron spectrometer at the supersonic jet-target of the ESR storage ring. We report first results and compare with theory.

Hagmann, S. [Institut fuer Kernphysik, Univ. Frankfurt (Germany); GSI, Darmstadt (Germany); Stoehlker, Th.; Fritzsche, S. [GSI, Darmstadt (Germany); Physik Institut, Univ. Heidelberg (Germany); Surzhykov, A. [Max Planck Institut fuer Kernphysik, Heidelberg (Germany); Physik Institut, Univ. Heidelberg (Germany); Jakubassa-Amundsen, D. [Mathemat. Inst., LMU-Muenchen (Germany); Najjari, B.; Voitkiv, A.; Ullrich, J.; Moshammer, R. [Max Planck Institut fuer Kernphysik, Heidelberg (Germany); Kozhuharov, C.; Gumberidze, A.; Spillmann, U.; Reuschl, R.; Hess, S.; Trotsenko, S.; Bosch, F.; Liesen, D. [GSI, Darmstadt (Germany); Nofal, M. [GSI, Darmstadt (Germany); Max Planck Institut fuer Kernphysik, Heidelberg (Germany); Doerner, R. [Institut fuer Kernphysik, Univ. Frankfurt (Germany); Rothard, H. [CIRIL-Ganil, Caen (France)] (and others)

2009-03-10

119

Three-dimensional analysis of the collision process of a bead on a granular packing.  

PubMed

We present results of the collision process of a bead onto a static granular packing. We provide, in particular, a three-dimensional (3D) extensive characterization of this process from a model experiment that allows us to propel a spherical bead onto a granular packing with a well-controlled velocity and impact angle. A collision typically produces a high-energy particle (rebound particle) and several low-energy grains (ejected particles). The collision process is recorded by means of two fast video cameras. The sequence of images from both cameras are then analyzed via image processing and the trajectories of all particles are reconstructed in 3D space. We show that the incident particle does not remain in the vertical incident plane after the rebound and that the deviation angle increases with increasing impact angle. Concerning the ejected particles, we demonstrated that the ejection angle (measured with respect to the horizontal plane) is surprisingly independent of both the impact angle and velocity of the incident particle, and is very close to 60 degrees . The horizontal component of the ejection speed of the splashed particles is found to be weakly dependent on the incident speed and impact angle, and is relatively isotropic (no particular horizontal direction is favored). This last feature suggests that the bead packing acts as a perfect diffusive medium with respect to energy propagation. PMID:19391737

Ammi, Madani; Oger, Luc; Beladjine, Djaoued; Valance, Alexandre

2009-02-18

120

Three-dimensional analysis of the collision process of a bead on a granular packing  

NASA Astrophysics Data System (ADS)

We present results of the collision process of a bead onto a static granular packing. We provide, in particular, a three-dimensional (3D) extensive characterization of this process from a model experiment that allows us to propel a spherical bead onto a granular packing with a well-controlled velocity and impact angle. A collision typically produces a high-energy particle (rebound particle) and several low-energy grains (ejected particles). The collision process is recorded by means of two fast video cameras. The sequence of images from both cameras are then analyzed via image processing and the trajectories of all particles are reconstructed in 3D space. We show that the incident particle does not remain in the vertical incident plane after the rebound and that the deviation angle increases with increasing impact angle. Concerning the ejected particles, we demonstrated that the ejection angle (measured with respect to the horizontal plane) is surprisingly independent of both the impact angle and velocity of the incident particle, and is very close to 60°. The horizontal component of the ejection speed of the splashed particles is found to be weakly dependent on the incident speed and impact angle, and is relatively isotropic (no particular horizontal direction is favored). This last feature suggests that the bead packing acts as a perfect diffusive medium with respect to energy propagation.

Ammi, Madani; Oger, Luc; Beladjine, Djaoued; Valance, Alexandre

2009-02-01

121

Absorption measurements of alkali-metal resonance lines broadened by He and molecular hydrogen collisions  

NASA Astrophysics Data System (ADS)

The optical and near-infrared spectroscopic observations of cool brown dwarfs exhibit very prominent signatures of sodium and potassium resonance lines. The atmospheres of these objects are mainly composed of molecular hydrogen and helium and the collisions of these species with the alkali-metal atoms induce broadening of the K and Na resonance lines by as much as 100 nm either side of the line core. Particularly important are the far line wings, where satellite features which are usually very temperature-sensitive may appear due to extrema in the difference potentials. These features are highly sensitive to pressure and temperature, whereas their position and shape depend critically on the details in the interaction potentials. Accurate line profiles can serve as valuable diagnostics of the physical characteristics of brown dwarfs and extrasolar giant planets. Experimental determinations of the far wings are indispensable in validating the theoretical models. We report here our measurements of the absorption coefficients for pressure broadening in the far wings of the 4s-4p and 4s-5p doublet lines of potassium atoms in the presence of helium and hydrogen gas at temperatures around 900 K. Supported in part by NASA grant NNG06GF06G.

Shindo, F.; Babb, J.; Kirby, K.

2007-06-01

122

Tensorial slip theory for gas flows and comparison with molecular dynamics simulations using an anisotropic gas-wall collision mechanism  

NASA Astrophysics Data System (ADS)

In this paper we examine the anisotropic slip theory for gas flows based on tangential accommodation coefficients and compare it with molecular dynamics (MD) results. A special gas-wall boundary condition is employed within MD simulations to mimic the anisotropic gas-wall collision mechanism. Results from MD simulations with different surface orientations show good agreement with the slip quantification proposed in this work.

Pham, Thanh Tung; To, Quy Dong; Lauriat, Guy; Léonard, Céline

2013-05-01

123

Drell-Yan Process in p-p Collisions from a Holographic Model  

NASA Astrophysics Data System (ADS)

We study Drell-Yan process in proton-proton collisions through the exchange of vector mesons using the holographic hard wall model to describe the dynamics and interactions of vector mesons and baryons. We estimate the angular parameters ?, ?, ? of the produced dileptons in a region of {qT^2 << Q2}, where the effective coupling of perturbative QCD is large due to logarithm corrections.

Ballon-Bayona, Carlos A.; Boschi-Filho, Henrique; Braga, Nelson R. F.

2012-05-01

124

One and two-electron processes in collisions between hydrogen molecules and slow highly charged ions  

Microsoft Academic Search

A coincidence time-of-flight technique coupled with projectile charge state analysis was used to study electron capture in collisions between slow highly charged ions and hydrogen molecules. We found single electron capture with no target excitation to be the dominant process for both C6+ projectiles at a velocity of 0.8 atomic units and Ar11+ projectiles at v=0.63a.u. Double electron capture and

E. Wells; K. D. Carnes; H. Tawara; R. Ali; Emil Y. Sidky; Clara Illescas; I. Ben-Itzhak

2005-01-01

125

Investigation of the transfer ionization process in collisions of partially stripped ions on He  

Microsoft Academic Search

In this paper a projectile ion-recoil ion coincidence technique is used to investigate the transfer ionization processes in collisions of 0.22-6.30 MeV Cq+ ions and 0.25-6.35 MeV Oq+ ions (q = 1, 2, 3, 4) with the He atom separately. The cross section ratio f of transfer ionization to single electron transfer is measured, and the dependence of f on

Hui-Ping Liu; Xi-Meng Chen; Xiao-Ping Ouyang; Fa-Yuan Xi; Guang-Hui Su

2010-01-01

126

Inelastic processes in e-HCl collisions in the energy range including the dissociation threshold  

Microsoft Academic Search

Inelastic processes in low-energy collisions of electrons with HCl molecules are considered. We present results of calculations of vibrational excitation cross sections from the ground state and vibrationally excited states, dissociative attachment cross sections, and electron-impact dissociation cross sections near threshold. Our approach is based on the resonance R-matrix theory with the quasiclassical treatment of the nuclear motion. We use

I. I. Fabrikant; S. A. Kalin; A. K. Kazansky

1991-01-01

127

Quantum mechanical close coupling approach to molecular collisions. jz -conserving coupled states approximation  

Microsoft Academic Search

New coupled equations describing collisions of an atom and a diatomic molecule are derived in this paper. By utilizing a description of the collision in terms of rotating coordinates, all coupling in the z component of angular momentum is isolated into purely kinematic effects. By neglecting these couplings, one is led to approximate equations for which the jz component of

Paul McGuire; Donald J. Kouri

1974-01-01

128

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

129

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

130

Intermolecular Collision Scheme of DSMC Taking Molecular Locations within a Cell into Account  

NASA Astrophysics Data System (ADS)

The intermolecular collision scheme is developed to obtain an excellent result even if cells are lengthened (more than the local mean free path) in the DSMC calculation. In the new scheme, the velocity of one molecule of a collision pair is modified before and after the substantial collision calculation (the core of the collision calculation), assuming that velocity distributions in all flowfield are in local equilibrium with some temperature and flow velocity (local Maxwellian distribution). The DSMC calculation should be repeated two or more times by using a coarse cell network. That is, the first calculation is done by the conventional collision scheme, and the second (or more) calculation is repeated by the new collision scheme using local Maxwellian velocity distributions that are obtained by the first (or earlier) calculation. The new collision scheme is applied to a one-dimensional normal shock wave, a two-dimensional vortex in a square cavity, an axisymmetric supersonic free jet, and a three-dimensional supersonic jet, respectively, and its effect on them is confirmed. In the axisymmetric problem and the three-dimensional problem, however, it turns out that a complete modification of velocities of molecules in the new scheme might produce distortions of flowfield and, consequently, the velocity modifications might be limited to 50 or 60% of their full effect.

Usami, Masaru; Nakayama, Tsutomu

2003-05-01

131

Collision tectonics  

SciTech Connect

The motions of lithospheric plates have produced most existing mountain ranges, but structures produced as a result of, and following the collision of continental plates need to be distinguished from those produced before by subduction. If subduction is normally only stopped when collision occurs, then most geologically ancient fold belts must be collisional, so it is essential to recognize and understand the effects of the collision process. This book consists of papers that review collision tectonics, covering tectonics, structure, geochemistry, paleomagnetism, metamorphism, and magmatism.

Coward, M.P.; Ries, A.C.

1985-01-01

132

Transdifferentiation: a cell and molecular reprogramming process.  

PubMed

Evidence has emerged recently indicating that differentiation is not entirely a one-way process, and that it is possible to convert one cell type to another, both in vitro and in vivo. This phenomenon is called transdifferentiation, and is generally defined as the stable switch of one cell type to another. Transdifferentiation plays critical roles during development and in regeneration pathways in nature. Although this phenomenon occurs rarely in nature, recent studies have been focused on transdifferentiation and the reprogramming ability of cells to produce specific cells with new phenotypes for use in cell therapy and regenerative medicine. Thus, understanding the principles and the mechanism of this process is important for producing desired cell types. Here some well-documented examples of transdifferentiation, and their significance in development and regeneration are reviewed. In addition, transdifferentiation pathways are considered and their potential molecular mechanisms, especially the role of master switch genes, are considered. Finally, the significance of transdifferentiation in regenerative medicine is discussed. PMID:22526624

Sisakhtnezhad, Sajjad; Matin, Maryam M

2012-04-25

133

Effect of molecular weight on polymer processability  

Microsoft Academic Search

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

Karg

1983-01-01

134

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

135

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

136

Two-electron processes in ionization of molecular hydrogen  

Microsoft Academic Search

Cross sections for double ionization and ionization plus excitation of H2 by high-energy charged particles are calculated as a function of the orientation of the H2 internuclear axis. The contributions of the double-collision process, and the shake-off or shake-up processes have been considered. The results are compared with the data of Edwards et al. [Phys. Rev. A 42 (1990) 1367,

L. Nagy; L. Vegh

1994-01-01

137

Statistical kinetics of processive molecular motors  

NASA Astrophysics Data System (ADS)

We describe new theoretical and experimental tools for studying biological motor proteins at the single molecule scale. These tools enable measurements of molecular fuel economies, thereby providing insight into the pathways for conversion of biochemical energy into mechanical work. Kinesin is an ATP-dependent motor that moves processively along microtubules in discrete steps of 8 nm. How many molecules of ATP are hydrolysed per step? To determine this coupling ratio, we develop a fluctuation analysis, which relates the variance in records of mechanical displacement to the number of rate-limiting biochemical transitions in the engine cycle. Using fluctuation analysis and optical trapping interferometry, we determine that near zero load, single molecules of kinesin hydrolyse one ATP nucleotide per 8-nm step. To study kinesin behavior under load, we use a molecular force clamp, capable of maintaining constant loads on single kinesin motors moving processively. Analysis of records of motion under variable ATP concentrations and loads reveals that kinesin is a `tightly- coupled' motor, maintaining the 1:1 coupling ratio up to loads of ~ 5 pN. Moreover, a Michaelis-Menten analysis of velocity shows that the kinesin cycle contains at least two load- dependent transitions. The rate of one of these transitions affects ATP affinity, while the other does not. Therefore, the kinesin stall force must depend on the ATP concentration, as is demonstrated experimentally. These findings rule out existing theoretical models of kinesin motility. We develop a simple theoretical formalism describing a tightly-coupled mechanism for movement. This `energy-landscape' formalism quantitatively accounts for motile properties of RNA polymerase (RNAP), the enzyme that transcribes DNA into RNA. The shapes of RNAP force-velocity curves indicate that biochemical steps limiting transcription rates at low loads do not generate movement. Modeling suggests that high loads may halt RNAP by promoting a structural change which moves all or part of the enzyme backwards along the DNA through a distance of 5-10 base pairs. Using the energy landscape formalism, we also propose a model for kinesin. The model incorporates both the ATP-dependent and the ATP-independent mechanical transitions in the motor cycle and explains experimental measurements of kinesin velocity.

Schnitzer, Mark Jacob

1999-10-01

138

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

139

Relativistic calculations of inner-shell atomic processes in low-energy ion-atom collisions  

NASA Astrophysics Data System (ADS)

Relativistic calculations of inner-shell atomic processes in low-energy Ne-F8+(1s) and Xe-Xe53+(1s) collisions are performed. The method of calculation exploits the active-electron approximation and is based on the coupled-channel approach with atomic-like Dirac-Sturm-Fock orbitals, localized at the ions (atoms). The screening density-functional theory is applied for description of the interaction with passive electrons. The role of relativistic effects is analyzed.

Kozhedub, Yury S.; Tupitsyn, Ilya I.; Shabaev, Vladimir M.; Hagmann, Siegbert; Plunien, Günter; Stöhlker, Thomas

2013-09-01

140

Theoretical investigations of inelastic processes in slow to fast ion-atom collisions  

NASA Astrophysics Data System (ADS)

Within the close-coupling formalism, we have studied the inelastic processes of a variety of ion-atom collision systems in a wide range of impact energies. Semiclassical approximation has been used for intermediate- to high-energy collisions. As for the low-energy collisions, quantum mechanical approach is applied. We have performed an extensive semiclassical two-electron two-center atomic orbital close-coupling (TCAOCC2e) calculation to study the single ionization cross sections in p + He(1s2) collisions. The stabilities of the ionization probability and cross sections are examined with respect to the choice of the basis sets. Below 40 keV, our cross sections are slightly higher than the Force Impulse Method. They disagree with the existing experimental data, and therefore we conclude that a new measurement is needed. A combination of the Eikonal approximation and a one-electron TCAOCC was utilized to study the state-selective differential charge transfer cross sections for Na+ + Rb(5s,5p) at E = 2, 5 and 7 keV. The theoretical results are in good agreement when compared to the recent measurements obtained with Rb targets cooled in a magnetic optical trap (MOTRIMS). Despite the fine resolution offered by MOTRIMS, the experimental angular differential cross sections do not exhibit the oscillatory structure shown in the theory. Using the Hyperspherical method, we searched for bound rotational states of helium trimer by solving the Schrodinger equation in the adiabatic representation. From the resulting repulsive potential curves for non-zero angular momenta, we showed that there are no bound rotational states in any of the isotopes of the He trimer. A conjoint technique of Hyperspherical Coordinate, Smooth Variable Discretization (SVD) and R -matrix propagation methods was used to study the slow 20 eV--2 keV H+ + D(1s) collisions. This quantum mechanical approach is free from ambiguities associated with the conventional Born-Oppenheimer (BO) method. We showed that the cross sections for excitation and charge transfer to 2p states are essentially identical over the whole energy range and stay relatively independent of energy from 2 keV down to 150 eV. Below 150 keV, the cross sections decrease precipitously with decreasing energy. The rapid drop of cross sections was explained with the aid of hyperspherical potential curves.

Lee, Teck Ghee

141

Disintegration of argon clusters in collisions with highly vibrationally excited SF6 molecules in crossed molecular and cluster beams  

NASA Astrophysics Data System (ADS)

It has been found that collisions of highly vibrationally excited SF6 molecules (with the vibrational energy E vib ? 0.5-2.0 eV) with Ar N clusters (where N ? 30-40 is the number of atoms in a cluster) in crossed molecular and cluster beams result in capture of molecules followed by complete disintegration of the clusters. Possible applications of the effect for selective doping of clusters with molecules, laser separation of isotopes, and selective transport of molecules to the surface are discussed.

Makarov, G. N.; Petin, A. N.

2013-03-01

142

Double Electron Processes in Low Energy Isotope Bare Ions 13C6+ with Helium Collisions  

NASA Astrophysics Data System (ADS)

The isotopic bare ion 13C6+ was employed to collide with helium at 4.15-11.08 keV/u. The relative partial cross sections were measured by position-sensitive and time-of-flight coincident techniques. It is shown that the direct-ionization (DI) process can be completely ignored in this region, the transfer ionization (TI) process is the most important double-electron channel, and the probability of the pure double-electron capture (DC) process is quite small. The cross-section ratio of the total double-electron (DE) process (i.e. DC+TI) to the single-electron capture (SC) process is experimentally determined to be approximately a constant of 0.09±0.03 in this region, and this value is obviously smaller than the predictions of the classical over-barrier models and the semi-empirical scaling laws. It is found that the cross-section ratio of pure DC to DE decreases obviously as the projectile velocity increases. Because the pure DC process only comes from the radiation de-excitation following the DC process and are competed by the TI process (comes from the auto-ionization following the DC process), this implies that the population of the two captured electrons depends distinctly on the collision velocity. Comparison with works on Ar16+-He by Wu et al. [Phys. Rev. A 48 (1993) 3617] reveals that the strong projectile-dependent character of the pure DC process exists.

Yu, De-Yang; Cai, Xiao-Hong; Lu, Rong-Chun; Shao, Cao-Jie; Lu, Jun; Ruan, Fang-Fang; Zhang, Hong-Qiang; Cui, Ying; Xu, Xu; Shao, Jian-Xiong; Ding, Bao-Wei; Yang, Zhi-Hu; Chen, Xi-Meng

2005-06-01

143

Matter-Wave Entanglement and Teleportation by Molecular Dissociation and Collisions  

Microsoft Academic Search

We propose dissociation of cold diatomic molecules as a source of atom pairs with highly correlated (entangled) positions and momenta, approximating the original quantum state introduced by Einstein, Podolsky, and Rosen (EPR) [Phys. Rev. 47, 777 (1935)]. Wave packet teleportation is shown to be achievable by its collision with one of the EPR correlated atoms and manipulation of the other

T. Opatrný; G. Kurizki

2001-01-01

144

Matter-Wave Entanglement and Teleportation by Molecular Dissociation and Collisions  

NASA Astrophysics Data System (ADS)

We propose dissociation of cold diatomic molecules as a source of atom pairs with highly correlated (entangled) positions and momenta, approximating the original quantum state introduced by Einstein, Podolsky, and Rosen (EPR) [Phys. Rev. 47, 777 (1935)]. Wave packet teleportation is shown to be achievable by its collision with one of the EPR correlated atoms and manipulation of the other atom in the pair.

Opatrný, T.; Kurizki, G.

2001-04-01

145

Cross sections for ionization of rare gas excimers by electron impact and atomic and molecular processes in excimer lasers. Final report 1 Apr 78-30 Sep 79  

SciTech Connect

Theoretical cross sections for ionization of metastable excimers - helium, neon, argon, krypton and xenon - and of metastable mercury are presented. Systematic trends in inelastic form factors and Born cross sections for collisional transitions between excited neighboring levels of atoms are discovered and discussed. Key cycles of atomic and molecular collision processes in excimer lasers are delineated and discussed.

Flannery, M.R.; McCann, K.J.

1980-03-01

146

Inelastic processes in e --HCl collisions in the energy range including the dissociation threshold  

SciTech Connect

Inelastic processes in low-energy collisions of electrons with HCl molecules are considered. We present results of calculations of vibrational excitation cross sections from the ground state and vibrationally excited states, dissociative attachment cross sections, and electron-impact dissociation cross sections near threshold. Our approach is based on the resonance {ital R}-matrix theory with the quasiclassical treatment of the nuclear motion. We use a rigorous procedure for the inclusion of the vibrational continuum. This allows for calculations of the cross sections in the energy range including dissociation threshold. The results for the dissociation cross sections are analyzed from the point of view of the threshold law for the three-particle break-up process.

Fabrikant, I.I.; Kalin, S.A.; Kazansky, A.K. (Department of Physics and Astronomy, University of Nebraska, Lincoln, Nebraska (USA))

1991-10-01

147

CROSS SECTIONS FOR COLLISION PROCESSES OF Li ATOMS INTERACTING WITH ELECTRONS, PROTONS, MULTIPLY CHARGED IONS, AND HYDROGEN MOLECULES  

Microsoft Academic Search

The available experimental and theoretical cross section data for collision processes of Li atoms in the ground state and excited (up ton= 3) states with electrons, protons, and multiply charged ions have been collected and critically assessed. The electron-impact processes include excitation from the ground state, transitions between excited states withn= 2, 3, and ionization from all states considered. The

D. Wutte; R. K. JANEV; F. Aumayr; M. Schneider; J. Schweinzer; J. J. Smith; H. P. WINTER

1997-01-01

148

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

149

Single- and Multiple-Electron Removal Processes in Proton-Water Vapor Collisions  

NASA Astrophysics Data System (ADS)

Charge-state correlated cross sections for single- and multiple-electron removal processes due to capture and ionization in proton-H2O collisions are calculated by using the non-perturbative basis generator method adapted for ion-molecule collisions [1]. Orbital-specific cross sections for vacancy production are evaluated using this method to predict the yields of charged fragments (H2O^+, OH^+, H^+, O^+) according to branching ratios known to be valid at high impact energies. At intermediate and low energies, we obtain fragmentation results on the basis of predicted multi-electron removal cross sections, and explain most of the available experimental data [2]. The cross sections for charge transfer and for ionization are also compared with recent multi-center classical-trajectory Monte Carlo calculations [3] for impact energies from 20keV to several MeV. [4pt] [1] H.J. L"udde et al, Phys. Rev. A 80, 060702(R) (2009)[0pt] [2] M. Murakami et al, to be submitted to Phys. Rev. A (2012)[0pt] [3] C. Illescas et al, Phys. Rev. A 83, 052704 (2011)

Murakami, Mitsuko; Kirchner, Tom; Horbatsch, Marko; Jürgen Lüdde, Hans

2012-06-01

150

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

151

ATOMIC AND MOLECULAR PHYSICS: Collision-Induced Coherence Effect on Coherent Population Transfer  

NASA Astrophysics Data System (ADS)

We investigate the effect of collision-induced coherence on coherent population transfer with the stimulated Raman adiabatic passage technique in a double A-type four-level system with a widely separated excited doublet. It is shown that when the two pulsed lasers with Rabi frequencies nearly comparable to the energy separation of the doublet are tuned to the particular frequency where the condition for quantum interference is satisfied, the very low transfer efficiency due to the nonadiabatic coupling between the two degenerate adiabatic states could be enhanced significantly with the increase of the collisional decay rates in a moderate range. The enhanced transfer efficiency results from the weakening of the nonadiabatic coupling between the two degenerate adiabatic states realized through collision-induced destructive quantum interference.

Yang, Xi-Hua; Zhang, Jun; Zhang, Hui-Fang; Yan, Xiao-Na

2009-07-01

152

Matter-wave entanglement and teleportation by molecular dissociation and collisions.  

PubMed

We propose dissociation of cold diatomic molecules as a source of atom pairs with highly correlated (entangled) positions and momenta, approximating the original quantum state introduced by Einstein, Podolsky, and Rosen (EPR) [Phys. Rev. 47, 777 (1935)]. Wave packet teleportation is shown to be achievable by its collision with one of the EPR correlated atoms and manipulation of the other atom in the pair. PMID:11290137

Opatrný, T; Kurizki, G

2001-04-01

153

Charge transfer in collisions of C{sup 2+} carbon ions with CO and OH targets  

SciTech Connect

The charge transfer in collisions of C{sup 2+} ions with the CO molecule and the OH radical has been studied theoretically by means of ab initio quantum chemistry molecular methods followed by a semiclassical dynamical treatment in the keV collision energy range. The comparison of the cross sections calculated for these two collision systems exhibits interesting features with regard to the anisotropy of these processes and the influence of the vibration of the molecular target.

Bene, E. [Institute of Nuclear Research, Hungarian Academy of Sciences, P.O. Box 51, H-4001 Debrecen (Hungary); Martinez, P. [Departamento de Quimica, Laboratorio Asociado al CIEMAT de Fisica Atomica y Molecular en Plasmas de Fusion, Universidad Autonoma de Madrid, Madrid 28049 (Spain); Halsaz, G. J. [Department of Information Technology, University of Debrecen, P.O. Box 12, H-4010 Debrecen (Hungary); Vibok, A. [Department of Theoretical Physics, University of Debrecen, P.O. Box 5, H-4010 Debrecen (Hungary); Bacchus-Montabonel, M. C. [Laboratoire de Spectrometrie Ionique et Moleculaire, CNRS et Universite de Lyon, 43 Boulevard du 11 Novembre 1918, 69622 Villeurbanne Cedex (France)

2009-07-15

154

One- and two-electron processes in collisions between hydrogen molecules and slow highly charged ions  

NASA Astrophysics Data System (ADS)

A coincidence time-of-flight technique coupled with projectile charge state analysis was used to study electron capture in collisions between slow highly charged ions and hydrogen molecules. We found single electron capture with no target excitation to be the dominant process for both C6+ projectiles at a velocity of 0.8 atomic units and Ar11+ projectiles at v = 0.63 a.u. Double electron capture and transfer excitation, however, were found to be comparable and occur about 30% of the time relative to single capture. Most projectiles (96%) auto-ionize quickly following double capture into doubly excited states. The data are compared to classical and quantum mechanical model calculations.

Wells, E.; Carnes, K. D.; Tawara, H.; Ali, R.; Sidky, Emil Y.; Illescas, Clara; Ben-Itzhak, I.

2005-12-01

155

Nonstatistical fluctuations for deep inelastic processes in {sup 27}Al+{sup 27}Al collisions  

SciTech Connect

The excitation functions (EFs) for different fragments produced in the {sup 27}Al+{sup 27}Al dissipative collisions have been measured in steps of 250 keV in the incident energy range 122-132 MeV. Deep inelastic processes have been selected by integrating events on a total kinetic energy loss window of 12 MeV between 20 and 32 MeV. Large fluctuations are observed in all the studied EFs. Large-channel cross-correlation coefficients confirm the nonstatistical origin of these fluctuations. The energy autocorrelation function (EAF) shows damped oscillation structure as expected when a dinuclear system with a lifetime [{tau}=(5.1{+-}2.1){center_dot}10{sup -21}s], similar with its revolution period (T=4.9{center_dot}10{sup -21}sec), is formed. From the periodicity of the EAF oscillations, information on the deformation of the {sup 27}Al+{sup 27}Al dinucleus is inferred.

Berceanu, I.; Duma, M.; Moisa, D.; Petrovici, M.; Pop, A.; Simion, V. [National Institute of Physics and Nuclear Engineering, P.O. Box MG-6, H-76900 Bucharest (Romania); Zoppo, A. Del [Istituto Nazionale di Fisica Nucleare, Laboratorio Nazionale del Sud, v. S. Sofia 44, I-95100, Catania (Italy); D'Erasmo, G. [Istituto Nazionale di Fisica Nucleare, Sezione di Bari, v. Amendola 173, I-70126 Bari (Italy); Dipartimento di Fisica, Universita di Bari, V. Amendola 173, I-70126, Bari (Italy); Imme, G.; Lanzano, G.; Pagano, A. [Istituto Nazionale di Fisica Nucleare and Dipartimento di Fisica, I-95129 Catania (Italy); Pantaleo, A. [Istituto Nazionale di Fisica Nucleare, Sezione di Bari, v. Amendola 173, I-70126 Bari (Italy); Raciti, G. [Istituto Nazionale di Fisica Nucleare, Laboratorio Nazionale del Sud, v. S. Sofia 44, I-95100, Catania (Italy); Dipartimento di Fisica, Universita di Catania, I-95129 Catania (Italy)

2006-08-15

156

Nuclear de-excitation processes following medium energy heavy ion collisions  

SciTech Connect

As heavy ion reaction studies have progressed from beam energies below 10 MeV/nucleon to higher energies, many non-equilibrium reaction phenomena have been observed. Among these are nucleon emission with velocities in excess of the beam velocity, incomplete momentum transfer to evaporation residue and fission-like fragments, ..gamma..-rays with energies in excess of 100 MeV, and ..pi../sup 0/ production when beam energies are below the threshold for production by the nucleon-nucleon collision mechanism. Additionally, prefission neutrons have been observed in excess of numbers expected from equilibrium models. A few of the approaches which have been applied to these phenomena are as follows: Intranuclear cascade: two body collisions are assumed to mediate the equilibration. The geometry and momentum space is followed semiclassically. The approach has many successes though it may suffer in a few applications is not following holes; TDHF considers one body processes only; in the energy regime of interest, two body processes are important so that this may not be a viable approach; Boltzmann-Uehling-Uhlenbeck or Vlasov-Uehling-Uhlenbeck (BUU/VUU) equations combine both one body and two body dynamics. The spatial and momentum evolution of the reactions are followed in a mean field. These should be the Cadillacs of the models. They are computationally tedious, and sometimes significant approximations are made in order to achieve computational tract ability; models of collective deceleration. A very simple model approach is discussed to interpret these phenomena, the Boltzmann master equation (BME). The hybrid model was the first to be applied to the question of heavy ion precompound decay, and the BME second. 26 refs., 5 figs., 2 tabs.

Blann, M.

1986-09-01

157

Effect of hyperfine interactions on ultracold molecular collisions: NH(3?-) with Mg(1S) in magnetic fields  

NASA Astrophysics Data System (ADS)

We investigate the effect of hyperfine interactions on ultracold molecular collisions in magnetic fields, using 24Mg(1S)+14NH(3?-) as a prototype system. We explore the energy and magnetic-field dependence of the cross sections, comparing the results with previous calculations that neglected hyperfine interactions [A.O.G. Wallis and J. M. Hutson, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.103.183201 103, 183201 (2009)]. The main effect of hyperfine interactions for spin relaxation cross sections is that the kinetic energy release of the dominant outgoing channels does not reduce to zero at low fields. This results in reduced centrifugal suppression of the cross sections and increased inelastic cross sections at low energy and low field. We also analyze state-to-state cross sections, for various initial states, and show that hyperfine interactions introduce additional mechanisms for spin relaxation. In particular, there are hyperfine-mediated collisions to outgoing channels that are not centrifugally suppressed. However, for Mg+NH these unsuppressed channels make only small contributions to the total cross sections. We consider the implications of our results for sympathetic cooling of NH by Mg and conclude that the ratio of elastic to inelastic cross sections remains high enough for sympathetic cooling to proceed.

González-Martínez, Maykel L.; Hutson, Jeremy M.

2011-11-01

158

Collision processes involving heavy many-electron ions interacting with neutral atoms  

NASA Astrophysics Data System (ADS)

An overview of experimental data and theoretical computational methods is given for effective cross sections of charge exchange (electron capture) and electron loss (projectile ionization) processes involving heavy many-electron ions (like Xe ^{q+}, Pb ^{q+}, W ^{q+}, U ^{q+}) colliding with neutral atoms (H, He, N, Ne, Ar, Kr, Xe) in the E \\approx 10 keV/u - 10 Gev/u energy range, i.e., from low up to relativistic energies. These charge-changing processes can occur with a high probability, reaching 10^{-14} - 10^{-16} cm ^2 cross-section values and, therefore, they play a key role in the kinetics of laboratory and astrophysical plasmas and influence the lifetimes of ion beams in accelerator facilities. Multielectron capture and loss processes are considered, as well, since their importance in the case of heavy atomic projectiles strongly increases, and a contribution to the total cross sections reaches more than 50%. An important aspect of the overview is a consideration of the influence of the inner-shell electrons of two colliding systems and a role of isotope effects in electron capture by very slow ions ( E \\approx 10 - 100 eV/u) from hydrogen isotopes H, D, and T. A short description of the corresponding computer codes is given for the calculation of cross sections of electron capture and electron loss processes for complex atoms and ions over a wide collision energy range.

Tolstikhina, Inga Yu; Shevelko, Vyacheslav P.

2013-03-01

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

Split-Bin Correlation Functions for Multi-Particle Processes in PP Collisions at 400 GeV/c  

NASA Astrophysics Data System (ADS)

The pseudorapidity and azimuthal angle distributions for charged particle produced in pp collisions at 400 GeV/c have been measured by using the LEBC films offered by CERN NA27 collaboration. The split-bin correlation functions have been calculated. The results show that the correlations are produced by resonance-like processes.

Wang, Shaoshun; Zhang, Jie; Xiao, Chenguo; Xiong, Weijun; Kou, Jinchun; Xia, Xiaojuan; Zhong, Yu

1993-07-01

161

Dynamics of DNA-Obstacle Collisions  

NASA Astrophysics Data System (ADS)

Understanding polyelectrolyte-obstacle collisions is crucial in order to improve DNA electrophoretic separations in microfluidic devices containing rigid obstacles (Doyle et. al. Science 295 (2237), 2002). Additionally, the polymer collisions play an important role in the rheology of entangled systems. Here we present data from the observation of single DNA molecules in electrophoretic motion colliding with single microfabricated obstacles. Large DNA fragments (48.5-168.9 kbp) are fluorescently dyed with TOTO-1 for microscopic observation. The time evolution of the center of mass velocity is followed under a microscope and tracked using custom software routines to quantitatively analyze the collision process. This data leads to a distribution of unhooking times for each size DNA molecule at a given electric field strength and shows the importance of molecular elasticity in providing separation of DNA. The data from strong electric field collisions are compared to previous simulations and collision models.

Doyle, Patrick; Randall, Greg

2003-03-01

162

Collisional and Dissociative Processes Involving Molecular Free Radicals.  

National Technical Information Service (NTIS)

A collaborative experimental and theoretical study of a number of elementary collisional processes involving small molecular free radicals of importance in combustion and in the decomposition of propellants has been carried out. These have involved chemic...

P. J. Dagdigian M. H. Alexander

1995-01-01

163

R-matrix approach with proper boundary conditions for dissipative and nondissipative collision processes  

SciTech Connect

We develop an R-matrix approach to treating collision processes which explicitly takes into account, by means of a simple energy-dependent analytic function, the out-of-phase oscillations of the incident and scattered standing waves in the interior region. Thereby we avoid the use of the Bloch operator. In place of the Bloch operator the incident wave provides the source term in an inhomogeneous equation for the scattered wave. We take those subchannels not treated exactly into account via the optical potential, which is generally non-Hermitian due to dissipation at the boundary. The optical potential is constructed on a real analytic basis using a resolvent that satisfies outgoing-wave boundary conditions. The use of an analytic basis together with the direct determination of the K matrix, rather than the R matrix, at the boundary (this is done by matching the interior wave function to the nearly exact analytic solution beyond the boundary) makes the method particularly well suited to the treatment of ultracold collisions. We have tested our method by applying it to one-photon single-ionization of (He1s{sup 2}) accompanied by excitation to He{sup +}(2s) or He{sup +}(2p) for photon energies above the complete breakup threshold, where the optical potential is non-Hermitian. Excellent agreement with experiment is obtained for the cross sections for photoionization to both He{sup +} (n=1) and to He{sup +} (n=2). The 2s-to-2p branching ratio is strongly influenced by both the optical potential and, at photon energies less than a few tens of eV above the breakup threshold, the nonadiabatic dipole mixing of the 2s and 2p states.

Xu Hao; Shakeshaft, Robin [Physics Department, University of Southern California, Los Angeles, California 90089-0484 (United States)

2011-01-15

164

On the diabatic separate-atom limit of molecular orbitals in atomic collisions  

Microsoft Academic Search

The authors examine the possibility of establishing a one to one correlation between molecular orbitals and the separate-atom orbitals corresponding to substates with a given principal quantum number. They consider the specific case of the 3 sigma and 4 sigma molecular orbitals for various asymmetric diatomic systems. They discuss the influence of the ionisation state of the system on this

C. Falcon; A. Macias; A. Riera; A. Salin

1981-01-01

165

Processing of Collision Data to Support Efficient Diagnosis of Concussion in Sports Athletes  

Microsoft Academic Search

Collision\\/Contact sports persons, particularly football and hockey players are involved in very high impact collisions during play. The player may be subjected to Concussion a medical term related to the disturbance in the brain function following a blow to head or a violent impact. This Concussion may result in to Mild Traumatic Brain Injury (MTBI). Often it is difficult to

Dayananda Suratkal

2012-01-01

166

Measurement of the weak mixing angle with the Drell-Yan process in proton-proton collisions at the LHC  

NASA Astrophysics Data System (ADS)

A multivariate likelihood method to measure electroweak couplings with the Drell-Yan process at the LHC is presented. The process is described by the dilepton rapidity, invariant mass, and decay angle distributions. The decay angle ambiguity due to the unknown assignment of the scattered constituent quark and antiquark to the two protons in a collision is resolved statistically using correlations between the observables. The method is applied to a sample of dimuon events from proton-proton collisions at s=7TeV collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 1.1fb-1. From the dominant uu¯, dd¯??*/Z??-?+ process, the effective weak mixing angle parameter is measured to be sin?2?eff=0.2287±0.0020(stat.)±0.0025(syst.). This result is consistent with measurements from other processes, as expected within the standard model.

Chatrchyan, S.; Khachatryan, V.; Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Bergauer, T.; Dragicevic, M.; Erö, J.; Fabjan, C.; Friedl, M.; Frühwirth, R.; Ghete, V. M.; Hammer, J.; Hänsel, S.; Hoch, M.; Hörmann, N.; Hrubec, J.; Jeitler, M.; Kiesenhofer, W.; Krammer, M.; Liko, D.; Mikulec, I.; Pernicka, M.; Rahbaran, B.; Rohringer, H.; Schöfbeck, R.; Strauss, J.; Taurok, A.; Teischinger, F.; Trauner, C.; Wagner, P.; Waltenberger, W.; Walzel, G.; Widl, E.; Wulz, C.-E.; Mossolov, V.; Shumeiko, N.; Suarez Gonzalez, J.; Bansal, S.; Benucci, L.; de Wolf, E. A.; Janssen, X.; Luyckx, S.; Maes, T.; Mucibello, L.; Ochesanu, S.; Roland, B.; Rougny, R.; Selvaggi, M.; van Haevermaet, H.; van Mechelen, P.; van Remortel, N.; Blekman, F.; Blyweert, S.; D'Hondt, J.; Gonzalez Suarez, R.; Kalogeropoulos, A.; Maes, M.; Olbrechts, A.; van Doninck, W.; van Mulders, P.; van Onsem, G. P.; Villella, I.; Charaf, O.; Clerbaux, B.; de Lentdecker, G.; Dero, V.; Gay, A. P. R.; Hammad, G. H.; Hreus, T.; Marage, P. E.; Raval, A.; Thomas, L.; Vander Marcken, G.; Vander Velde, C.; Vanlaer, P.; Adler, V.; Cimmino, A.; Costantini, S.; Grunewald, M.; Klein, B.; Lellouch, J.; Marinov, A.; McCartin, J.; Ryckbosch, D.; Thyssen, F.; Tytgat, M.; Vanelderen, L.; Verwilligen, P.; Walsh, S.; Zaganidis, N.; Basegmez, S.; Bruno, G.; Caudron, J.; Ceard, L.; Cortina Gil, E.; de Favereau de Jeneret, J.; Delaere, C.; Favart, D.; Forthomme, L.; Giammanco, A.; Grégoire, G.; Hollar, J.; Lemaitre, V.; Liao, J.; Militaru, O.; Nuttens, C.; Ovyn, S.; Pagano, D.; Pin, A.; Piotrzkowski, K.; Schul, N.; Beliy, N.; Caebergs, T.; Daubie, E.; Alves, G. A.; Brito, L.; de Jesus Damiao, D.; Pol, M. E.; Souza, M. H. G.; Aldá Júnior, W. L.; Carvalho, W.; da Costa, E. M.; de Oliveira Martins, C.; Fonseca de Souza, S.; Matos Figueiredo, D.; Mundim, L.; Nogima, H.; Oguri, V.; Prado da Silva, W. L.; Santoro, A.; Silva Do Amaral, S. M.; Sznajder, A.; Anjos, T. S.; Bernardes, C. A.; Dias, F. A.; Fernandez Perez Tomei, T. R.; Gregores, E. M.; Lagana, C.; Marinho, F.; Mercadante, P. G.; Novaes, S. F.; Padula, Sandra S.; Darmenov, N.; Genchev, V.; Iaydjiev, P.; Piperov, S.; Rodozov, M.; Stoykova, S.; Sultanov, G.; Tcholakov, V.; Trayanov, R.; Vutova, M.; Dimitrov, A.; Hadjiiska, R.; Karadzhinova, A.; Kozhuharov, V.; Litov, L.; Mateev, M.; Pavlov, B.; Petkov, P.; Bian, J. G.; Chen, G. M.; Chen, H. S.; Jiang, C. H.; Liang, D.; Liang, S.; Meng, X.; Tao, J.; Wang, J.; Wang, J.; Wang, X.; Wang, Z.; Xiao, H.; Xu, M.; Zang, J.; Zhang, Z.; Ban, Y.; Guo, S.; Guo, Y.; Li, W.; Mao, Y.; Qian, S. J.; Teng, H.; Zhu, B.; Zou, W.; Cabrera, A.; Gomez Moreno, B.; Ocampo Rios, A. A.; Osorio Oliveros, A. F.; Sanabria, J. C.; Godinovic, N.; Lelas, D.; Lelas, K.; Plestina, R.; Polic, D.; Puljak, I.; Antunovic, Z.; Dzelalija, M.; Kovac, M.; Brigljevic, V.; Duric, S.; Kadija, K.; Luetic, J.; Morovic, S.; Attikis, A.; Galanti, M.; Mousa, J.; Nicolaou, C.; Ptochos, F.; Razis, P. A.; Finger, M.; Finger, M., Jr.; Assran, Y.; Ellithi Kamel, A.; Khalil, S.; Mahmoud, M. A.; Radi, A.; Hektor, A.; Kadastik, M.; Müntel, M.; Raidal, M.; Rebane, L.; Tiko, A.; Azzolini, V.; Eerola, P.; Fedi, G.; Voutilainen, M.; Czellar, S.; Härkönen, J.; Heikkinen, A.; Karimäki, V.; Kinnunen, R.; Kortelainen, M. J.; Lampén, T.; Lassila-Perini, K.; Lehti, S.; Lindén, T.; Luukka, P.; Mäenpää, T.; Tuominen, E.; Tuominiemi, J.; Tuovinen, E.; Ungaro, D.; Wendland, L.; Banzuzi, K.; Karjalainen, A.; Korpela, A.; Tuuva, T.; Sillou, D.; Besancon, M.; Choudhury, S.; Dejardin, M.; Denegri, D.; Fabbro, B.; Faure, J. L.; Ferri, F.; Ganjour, S.; Givernaud, A.; Gras, P.; Hamel de Monchenault, G.; Jarry, P.; Locci, E.; Malcles, J.; Marionneau, M.; Millischer, L.; Rander, J.; Rosowsky, A.; Shreyber, I.; Titov, M.; Baffioni, S.; Beaudette, F.; Benhabib, L.; Bianchini, L.; Bluj, M.; Broutin, C.; Busson, P.; Charlot, C.; Dahms, T.; Dobrzynski, L.; Elgammal, S.; Granier de Cassagnac, R.; Haguenauer, M.; Miné, P.; Mironov, C.; Ochando, C.; Paganini, P.; Sabes, D.; Salerno, R.; Sirois, Y.; Thiebaux, C.; Veelken, C.; Zabi, A.; Agram, J.-L.; Andrea, J.; Bloch, D.; Bodin, D.; Brom, J.-M.; Cardaci, M.; Chabert, E. C.; Collard, C.; Conte, E.; Drouhin, F.; Ferro, C.; Fontaine, J.-C.; Gelé, D.; Goerlach, U.; Greder, S.; Juillot, P.; Karim, M.; Le Bihan, A.-C.; Mikami, Y.; van Hove, P.; Fassi, F.; Mercier, D.; Baty, C.; Beauceron, S.; Beaupere, N.; Bedjidian, M.; Bondu, O.; Boudoul, G.; Boumediene, D.; Brun, H.; Chasserat, J.; Chierici, R.; Contardo, D.; Depasse, P.; El Mamouni, H.; Fay, J.; Gascon, S.; Ille, B.; Kurca, T.; Le Grand, T.; Lethuillier, M.; Mirabito, L.; Perries, S.; Sordini, V.; Tosi, S.; Tschudi, Y.; Verdier, P.; Viret, S.; Lomidze, D.; Anagnostou, G.; Beranek, S.; Edelhoff, M.; Feld, L.; Heracleous, N.; Hindrichs, O.; Jussen, R.

2011-12-01

167

3D ejection behavior of different sized particles in the grain-bed collision process  

NASA Astrophysics Data System (ADS)

The impact-ejection process on a mixed-grain-size bed with granular packing was simulated with the discrete element method in order to understand the interaction between different sized grains in natural aeolian sand transport. In this model, the granular bed was formed by settling the randomly generated two-sized particles under gravity, and then a foreign particle was shot onto the granular bed at different speeds and angles. The recorded speed, direction and number of the ejected particles were then analyzed. It was found that the probability distributions of the ejection speed and angle for different sized particles are all identical to those for the single size grain-bed collision process, the mean ejection speeds of different sized particles are nearly equal, and the mean ejection angles of different sized particles are all equal to a constant of 60°. The average number of each size of ejected particles grows linearly with the increasing impact speed but remains invariant for various impact angles. Moreover, the smaller particles are preferentially ejected and the ratio between the mean numbers of different sized particles is independent of both the impact speed and angle. Additionally, the ejected particles were found to move in a 3D space, they become distributed symmetrically around the incident plane and jump not only forward but also backward. These results are critical to understanding the grain size-induced inhomogeneity in aeolian sand transport.

Xing, Mao; He, Caiyun

2013-04-01

168

A non-adiabatic wavepacket dynamical study of the low energy charge transfer process in the S3+ + H collision  

NASA Astrophysics Data System (ADS)

The collisional system S3+ + H ? S2+ + H+ has been studied using a time-dependent wavepacket methodology in two-dimensions. Using available potential energy surfaces and coupling matrix elements obtained from multireference ab initio calculations, five non-adiabatically coupled electronic states of 1? symmetry have been included in the dynamical simulations. The collision has been studied in the low energy regime of 1-10 eV. The wavepacket treatment accounts for the description of the collision including all possible impact parameters simultaneously in all spatial directions of the considered plane. The molecular movie of the scattered products arising from charge transfer yields the angular distribution and the total charge transfer probability vs. initial kinetic energy of the projectile. A detailed analysis of the forward, sideways, and backward scattering mechanisms showing different patterns is presented.

?abuda, Marta; González-Vázquez, Jesús; Martín, Fernando; González, Leticia

2012-05-01

169

Molecular-dynamics-based study of the collisions of hyperthermal atomic oxygen with graphene using the ReaxFF reactive force field.  

PubMed

In this work, we have investigated the hyperthermal collisions of atomic oxygens with graphene through molecular dynamics simulations using the ReaxFF reactive force field. First, following Paci et al. (J. Phys. Chem. A 2009, 113, 4677 - 4685), 5-eV energetic collisions of atomic oxygen with a 24-atom pristine graphene sheet and a sheet with a single vacancy defect, both functionalized with oxygen atoms in the form of epoxides, were studied. We found that the removal of an O(2) molecule from the surface of the graphene sheet occurs predominantly through an Eley-Rideal-type reaction mechanism. Our results, in terms of the number of occurrences of various reactive events, compared well with those reported by Paci et al. Subsequently, energetic collisions of atomic oxygen with a 25-times-expanded pristine sheet were investigated. The steady-state oxygen coverage was found to be more than one atom per three surface carbon atoms. Under an oxygen impact, the graphene sheet was always found to buckle along its diagonal. In addition, the larger sheet exhibited trampoline-like behavior, as a result of which we observed a much larger number of inelastic scattering events than those reported by Paci et al. for the smaller system. Removal of O(2) from the larger sheet occurred strictly through an Eley-Rideal-type reaction. Investigation of the events leading to the breakup of a pristine unfunctionalized graphene sheet and the effects of the presence of a second layer beneath the graphene sheet in an AB arrangement was done through successive impacts with energetic oxygen atoms on the structures. Breakup of a graphene sheet was found to occur in two stages: epoxide formation, followed by the creation and growth of defects. Events leading to the breakup of a two-layer graphene stack included epoxide formation, transformation from an AB to an AA arrangement as a result of interlayer bonding, defect formation and expansion in the top layer, and finally erosion of the bottom layer. We observed that the breakup of the two-layer stack occurred through a sequential, layer-by-layer, erosion process. PMID:21942282

Srinivasan, Sriram Goverapet; van Duin, Adri C T

2011-10-25

170

Modeling tribochemical processes using a combined molecular and hydrodynamic approach  

Microsoft Academic Search

A recently developed molecular-hydrodynamic approach to modeling tribochemical processes is applied to the prediction of the effects of pressure and temperature on fluid phase dissociation and surface decomposition reactions. The theoretical approach combines molecular statistical thermodynamics and continuum viscoeleastic hydrodynamics. The systems modeled include the dissociation of Cl2 in the fluid phase, and the decomposition of Cl2 and diphenyldisulfide C6H5-S-S-C6H5

Dor Ben-Amotz; Ilya Kudish

1999-01-01

171

Revisiting the Reactivity of Uracil During Collision Induced Dissociation: Tautomerism and Charge-Directed Processes  

NASA Astrophysics Data System (ADS)

In our recent work towards the nontarget identification of products of nucleic acid (NA) damage in urine, we have found previous work describing the dissociation of NA bases not adequate to fully explain their observed reactivity. Here we revisit the gas-phase chemistry of protonated uracil (U) during collision induced dissociation (CID) using two modern tandem mass spectrometry techniques; quadrupole ion trap (QIT) and quadrupole time of flight (Q-TOF). We present detailed mechanistic proposals that account for all observed products of our experiments and from previous isotope labeling data, and that are supported by previous ion spectroscopy results and theoretical work. The diverse product-ions of U cannot be explained adequately by only considering the lowest energy form of protonated U as a precursor. The tautomers adopted by U during collisional excitation make it possible to relate the complex reactivity observed to reasonable mechanistic proposals and feasible product-ion structures for this small highly conjugated heterocycle. These reactions proceed from four different stable tautomers, which are excited to a specific activated precursor from which dissociation can occur via a charge-directed process through a favorable transition state to give a stabilized product. Understanding the chemistry of uracil at this level will facilitate the identification of new modified uracil derivatives in biological samples based solely on their reactivity during CID. Our integrated approach to describing ion dissociation is widely applicable to other NA bases and similar classes of biomolecules.

Beach, Daniel G.; Gabryelski, Wojciech

2012-05-01

172

Multielectron processes in close collisions of slow Neq+ (q=1-9) ions with Ar atoms  

NASA Astrophysics Data System (ADS)

We have studied the multielectron processes in close collisions between slow Neq+ ions ( q=1-9 , energies of 5 and 14keV ) and Ar atoms through measurements of the charge-state correlations between 27° scattered and 70° recoiling ions. At the selected scattering angle, the internuclear distance of the closest approach at 35keV is comparable to the L -shell radius of Ar atoms. A drastic difference between low-charged (q=1-3) and highly charged (q=7-9) Ne ions was found. For example, the most probable channel for the Ne7+ projectile is three-electron capture accompanied with two-electron loss whereas for the Ne+ projectile pure double ionization was found most probable. As a general trend, the mean charges of the both ions and the mean number of captured electrons increase almost linearly with incident charge q , while the mean number of ejected electrons from the system is independent of q at both 5 and 14keV . We also measured the charge state distributions of the Ar recoil ions as function of the Neq+ ( q=3 , 5, and 7) energies between 5 and 63keV , which corresponds to distances of closest approach between 0.6a.u. and 0.17a.u. We found that the charge of the Ar ions increases at internuclear distances less than 0.32a.u.

Hoshino, Masamitsu; Kambara, Tadashi; Kanai, Yasuyuki; Schuch, Reinhold; Yamazaki, Yasunori

2007-03-01

173

Theory of Low-Energy Electron-Atom Collisions and Related Processes.  

National Technical Information Service (NTIS)

Imaginative new approaches to the theoretical treatment of low-energy electron-atom collisions are being proposed and tested by investigations. This paper reviews current activity, citing successes and problem areas, giving a characterization of the statu...

J. N. Bardsley

1975-01-01

174

Coulomb-influenced collisions in aerosols and dusty plasmas.  

PubMed

In aerosol and dusty plasma systems, the behavior of suspended particles (grains) is often strongly influenced by collisions occurring between ions and particles, as well as between particles themselves. In determining the collision kernel or collision rate coefficient for such charged entities, complications arise in that the collision process can be completely described neither by continuum transport mechanics nor by free molecular (ballistic) mechanics; that is, collisions are transition regime processes. Further, both the thermal energy and the potential energy between colliding entities can strongly influence the collision rate and must be considered. Flux-matching theory, originally developed by Fuchs, is frequently applied for calculation of collision rate coefficients under these circumstances. However, recent work suggests that crucial assumptions in flux-matching theory are not appropriate to describe transition regime collisions in the presence of potential interactions. Here, we combine dimensional analysis and mean first passage time calculations to infer the collision kernel between dilute charged entities suspended in a light background gas at thermal equilibrium. The motion of colliding entities is described by a Langevin equation, and Coulombic interactions are considered. It is found that the dimensionless collision kernel for these conditions, H, is a function of the diffusive Knudsen number, Kn(D) (in contrast to the traditional Knudsen number), and the potential energy to thermal energy ratio, ?(E). For small and large Kn(D), it is found that the dimensionless collision kernels inferred from mean first passage time calculations collapse to the appropriate continuum and free molecular limiting forms, respectively. Further, for repulsive collisions (?(E) negative) or attractive collisions with ?(E)<0.5, calculated results are in excellent agreement with flux-matching theory predictions, and the dimensionless collision kernel can be determined conveniently via use of the H(Kn(D)) relationship found for hard-sphere collisions with modified definitions of H and Kn(D) to account for potential energy. However, for ?(E)>0.5, it is found that flux-matching theory predictions substantially underestimate the collision kernel. We find that the collision process in this regime is governed by the minimum of Kn(D) and Kn(?) (Kn(?) = 3Kn(D)/2?(E)), and based on calculations, propose a function H(Kn(D), Kn(?)) for collision kernel evaluation. The situations for which ?(E)>0.5 apply to singly charged nanoparticles and multiply charged submicrometer and supermicrometer particles, and are thus prevalent in both aerosol and dusty plasma environments. PMID:22463340

Gopalakrishnan, Ranganathan; Hogan, Christopher J

2012-02-27

175

Coulomb-influenced collisions in aerosols and dusty plasmas  

NASA Astrophysics Data System (ADS)

In aerosol and dusty plasma systems, the behavior of suspended particles (grains) is often strongly influenced by collisions occurring between ions and particles, as well as between particles themselves. In determining the collision kernel or collision rate coefficient for such charged entities, complications arise in that the collision process can be completely described neither by continuum transport mechanics nor by free molecular (ballistic) mechanics; that is, collisions are transition regime processes. Further, both the thermal energy and the potential energy between colliding entities can strongly influence the collision rate and must be considered. Flux-matching theory, originally developed by Fuchs, is frequently applied for calculation of collision rate coefficients under these circumstances. However, recent work suggests that crucial assumptions in flux-matching theory are not appropriate to describe transition regime collisions in the presence of potential interactions. Here, we combine dimensional analysis and mean first passage time calculations to infer the collision kernel between dilute charged entities suspended in a light background gas at thermal equilibrium. The motion of colliding entities is described by a Langevin equation, and Coulombic interactions are considered. It is found that the dimensionless collision kernel for these conditions, H, is a function of the diffusive Knudsen number, KnD (in contrast to the traditional Knudsen number), and the potential energy to thermal energy ratio, ?E. For small and large KnD, it is found that the dimensionless collision kernels inferred from mean first passage time calculations collapse to the appropriate continuum and free molecular limiting forms, respectively. Further, for repulsive collisions (?E negative) or attractive collisions with ?E<0.5, calculated results are in excellent agreement with flux-matching theory predictions, and the dimensionless collision kernel can be determined conveniently via use of the H(KnD) relationship found for hard-sphere collisions with modified definitions of H and KnD to account for potential energy. However, for ?E>0.5, it is found that flux-matching theory predictions substantially underestimate the collision kernel. We find that the collision process in this regime is governed by the minimum of KnD and Kn? (Kn?=3KnD/2?E), and based on calculations, propose a function H(KnD, Kn?) for collision kernel evaluation. The situations for which ?E>0.5 apply to singly charged nanoparticles and multiply charged submicrometer and supermicrometer particles, and are thus prevalent in both aerosol and dusty plasma environments.

Gopalakrishnan, Ranganathan; Hogan, Christopher J., Jr.

2012-02-01

176

Dielectronic processes producing radiative stabilization in slow Ne{sup 10+}+He collisions  

Microsoft Academic Search

Different contributions to radiative stabilization in Ne{sup 10+}+He collisions at projectile energies of 10 and 150 keV are studied. For both energies, radiative stabilization is found to be equal to â0.3 when referred to the total double capture. In Ne{sup 10+}+He collisions doubly excited states 3{ital lnl}{sup â²} and 4{ital lnl}{sup â²} ({ital n}â¥4) are either produced by uncorrelated two-electron

J. Chesnel; H. Merabet; F. Fremont; G. Cremer; X. Husson; D. Lecler; G. Rieger; A. Spieler; M. Grether; N. Stolterfoht

1996-01-01

177

Dielectronic processes producing radiative stabilization in slow Ne10++He collisions  

Microsoft Academic Search

Different contributions to radiative stabilization in Ne10++He collisions at projectile energies of 10 and 150 keV are studied. For both energies, radiative stabilization is found to be equal to ~=0.3 when referred to the total double capture. In Ne10++He collisions doubly excited states 3lnl' and 4lnl' (n>=4) are either produced by uncorrelated two-electron transitions or by dielectronic mechanisms due to

J.-Y. Chesnel; H. Merabet; F. Frémont; G. Cremer; X. Husson; D. Lecler; G. Rieger; A. Spieler; M. Grether; N. Stolterfoht

1996-01-01

178

Photochemical processes in a two-component molecular contaminant film  

NASA Astrophysics Data System (ADS)

Previously, significant laboratory work has been performed on the photochemical deposition and darkening of molecular contaminant films. Much of this work addresses single, purified molecular species to understand fundamental photochemical processes. However, some of this work disagrees with other studies involving mixed, real spacecraft materials. There are also points of disagreement with contaminated returned optics from the Hubble Space Telescope where mixed contaminants were found. In this paper, we describe a method for vacuum depositing a controlled, reproducible contaminant film containing two molecular species: tetramethyl-tetraphenyl trisiloxane (DC 704) and dioctyl phthalate (DOP). We use this film to show differences in photochemical processes compared to a pure film of DC 704. We show that some photopolymerization processes occur more slowly in a two-component, mixed film during accelerated exposure to vacuum ultraviolet (VUV) radiation.

Luey, Kenneth T.; Coleman, Dianne J.

2008-08-01

179

Charge transfer processes in collisions of slow highly charged ions with polar molecules CO and C3H8  

Microsoft Academic Search

Charge transfer processes resulting from low energy collisions of polar molecules CO and C3H8 with highly charged Be2+ and B2+ ions have been investigated experimentally and theoretically. The potential for the one-electron exchange interaction between a polar molecule and highly charged atomic ion were obtained in closed analytical form in the framework of a semiclassical approach. Obtained results were used

M. V. Khoma; Makoto Imai; O. M. Karbovanets; Y. Kikuchi; M. Saito; Y. Haruyama; M. I. Karbovanets; I. Yu Kretinin; A. Itoh; R. J. Buenker

2009-01-01

180

Numerical simulation by the molecular collision theory of two-phase mixture explosion characteristics in closed or vented vessels  

NASA Astrophysics Data System (ADS)

The aim of this work consists in presenting a simple modelling (the molecular collision theory), easily usable in an industrial environment in order to predict the evolution of thermodynamical characteristics of the combustion of two-phase mixtures in a closed or a vented vessel. Basic characteristics of the modelling have been developed for ignition and combustion of propulsive powders and adapted with appropriate parameters linked to simplified kinetics. A simple representation of the combustion phenomena based on energy transfers and the action of specific molecules is presented. The model is generalized to various mixtures such as dust suspensions, liquid fuel drops and hybrid mixtures composed of dust and a gaseous supply such as methane or propane in the general case of vented explosions. The pressure venting due to the vent breaking is calculated from thermodynamical characteristics given by the model and taking into account, the mass rate of discharge of the different products deduced from the standard orifice equations. The application conditions determine the fuel ratio of the used mixtures, the nature of the chemical kinetics and the calculation of a universal set of parameters. The model allows to study the influence of the fuel concentration and the supply of gaseous additives, the influence of the vessel volume (2400ell leq V_bleq 250 000ell) and the influence of the venting pressure or the vent area. The first results have been compared with various experimental works available for two phase mixtures and indicate quite correct predictions.

Pascaud, J. M.; Brossard, J.; Lombard, J. M.

1999-09-01

181

Observation of anisotropic interactions and molecular orbitals of CO upon collision with He*(23S) atoms by two-dimensional Penning ionization electron spectroscopy  

Microsoft Academic Search

By collision-energy\\/electron-energy-resolved 2D Penning ionization electron spectroscopy as well as by theoretical calculations of the collisional ionization dynamics, the outer shape of molecular orbitals for ionization to X(2?+) and A(2?) states of CO+ was sensitively probed, and the anisotropy of the interaction between He*(23S) and CO was determined. Ionization to the B(2?+) state of CO+ was assigned to autoionization from

N Kishimoto; M Yamazaki; Y Hanzawa; T Horio; K Ohno

2007-01-01

182

Subduction and collision processes in the Central Andes constrained by converted seismic phases.  

PubMed

The Central Andes are the Earth's highest mountain belt formed by ocean-continent collision. Most of this uplift is thought to have occurred in the past 20 Myr, owing mainly to thickening of the continental crust, dominated by tectonic shortening. Here we use P-to-S (compressional-to-shear) converted teleseismic waves observed on several temporary networks in the Central Andes to image the deep structure associated with these tectonic processes. We find that the Moho (the Mohorovici? discontinuity--generally thought to separate crust from mantle) ranges from a depth of 75 km under the Altiplano plateau to 50 km beneath the 4-km-high Puna plateau. This relatively thin crust below such a high-elevation region indicates that thinning of the lithospheric mantle may have contributed to the uplift of the Puna plateau. We have also imaged the subducted crust of the Nazca oceanic plate down to 120 km depth, where it becomes invisible to converted teleseismic waves, probably owing to completion of the gabbro-eclogite transformation; this is direct evidence for the presence of kinetically delayed metamorphic reactions in subducting plates. Most of the intermediate-depth seismicity in the subducting plate stops at 120 km depth as well, suggesting a relation with this transformation. We see an intracrustal low-velocity zone, 10-20 km thick, below the entire Altiplano and Puna plateaux, which we interpret as a zone of continuing metamorphism and partial melting that decouples upper-crustal imbrication from lower-crustal thickening. PMID:11140679

Yuan, X; Sobolev, S V; Kind, R; Oncken, O; Bock, G; Asch, G; Schurr, B; Graeber, F; Rudloff, A; Hanka, W; Wylegalla, K; Tibi, R; Haberland, C; Rietbrock, A; Giese, P; Wigger, P; Röwer, P; Zandt, G; Beck, S; Wallace, T; Pardo, M; Comte, D

183

Energy- and angle-resolved spectroscopy of electrons from ion-atom collisions  

NASA Astrophysics Data System (ADS)

We report on an experimental setup for measurements of double differential cross sections of electron capture processes in collisions of slow, highly charged ions with atomic and molecular gas targets.

Holste, K.; Ricz, S.; Schippers, S.; Müller, A.

2012-11-01

184

A sustainable process for catalytic oxidative bromination with molecular oxygen.  

PubMed

Workin' in a bromine: A palladium-polyoxometalate amphiphilic hybrid material serves as catalyst for oxidative brominations. The emulsion-based process avoids the use of toxic and corrosive bromination agents such as Br2 or HBr, and uses molecular oxygen as oxidant. The only side product is water, which is also the reaction medium. The catalyst offers good recoverability and recyclability. PMID:23776057

Huang, Zhijun; Li, Fengbo; Chen, Bingfeng; Lu, Tao; Yuan, Yin; Yuan, Guoqing

2013-06-14

185

Molecular dynamics simulation on the dissociation process of methane hydrates  

Microsoft Academic Search

The dissociation process of methane hydrate is simulated at P = 30 bar and T = 315, 320 and 325 K, using NPT molecular dynamics (MD) method. An eight unit-cell methane hydrate is employed as a model system. A series of analytical results concerned with the dissociation process are used to exhibit the continuous changes of methane hydrate from crystal to liquid. As a result,

L. Y. Ding; C. Y. Geng; Y. H. Zhao; H. Wen

2007-01-01

186

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

187

Influence of nuclear exchange on nonadiabatic electron processes in H{sup +}+H{sub 2} collisions  

SciTech Connect

H{sup +}+H{sub 2} collisions are studied by means of a semiclassical approach that explicitly accounts for nuclear rearrangement channels in nonadiabatic electron processes. A set of classical trajectories is used to describe the nuclear motion, while the electronic degrees of freedom are treated quantum mechanically in terms of a three-state expansion of the collision wavefunction. We describe electron capture and vibrational excitation, which can also involve nuclear exchange and dissociation, in the E= 2-1000 eV impact energy range. We compare dynamical results obtained with two parametrizations of the potential energy surface of H{sub 3}{sup +} ground electronic state. Total cross sections for E > 10 eV agree with previous results using a vibronic close-coupling expansion, and with experimental data for E < 10 eV. Additionally, some prototypical features of both nuclear and electron dynamics at low E are discussed.

Errea, L. F.; Illescas, Clara; Macias, A.; Mendez, L.; Rabadan, I.; Riera, A. [Laboratorio Asociado al CIEMAT de Fisica Atomica y Molecular en Plasmas de Fusion, Departamento de Quimica, Universidad Autonoma de Madrid, Madrid-28049 (Spain); Pons, B. [Centre Lasers Intenses et Applications, Universite de Bordeaux-I-UMR 5107 CNRS-CEA, 351 Cours de la Liberation, 33405 Talence (France)

2010-12-28

188

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

189

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

190

Quantum Resonance Effects in Electronic-to-Vibrational Energy Transfer in Molecular Collisions.  

National Technical Information Service (NTIS)

Quantum mechanical calculations are carried out for the collinear process X(2P3/2) + H2 yields X(2P1/2) + H2 where X is the halogen atom F or Br. With two model, nonreactive, adiabatic potential energy surfaces, each correlating asymptotically to a spin-o...

I. H. Zimmerman T. F. George

1974-01-01

191

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

Microsoft Academic Search

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

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

2007-01-01

192

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

193

Projectile charge dependence of multi-electron transfer processes in highly charged ion-atom collisions  

Microsoft Academic Search

We have measured the absolute multi-electron transfer cross sections and branching ratios for the decay of multiply excited Rydberg ions in slow Iq+-Xe, Ar (10 <= q <= 20) collisions combining the initial growth rate method with coincidence method. We report the incident ion charge dependence of transfer cross sections and branching ratios.

H. A. Sakaue; H. Tawara; I. Yamada; K. Hosaka; F. Krok; F. J. Currell; N. Nakamura; S. Ohtani; H. Watanabe; A. Danjo; M. Kimura; A. Matsumoto; M. Sakurai; M. Yoshino

1997-01-01

194

Exclusive processes in electron-ion collisions in the dipole formalism  

NASA Astrophysics Data System (ADS)

We compare the predictions of two saturation models for production of vector mesons and of photons in electron-ion collisions. The models considered are the b-CGC and the rcBK. The calculations were made in the kinematical range of the LHeC and of the future eRHIC.

Cazaroto, E. R.; Navarra, F. S.; Carvalho, F.; Gonçalves, V. P.

2013-03-01

195

Parton energy loss and modified beam quark distribution functions in Drell-Yan process in p+A collisions  

NASA Astrophysics Data System (ADS)

Within the framework of generalized collinear factorization in perturbative QCD (pQCD), we study the effect of initial multiple parton scattering and induced parton energy loss in Drell-Yan (DY) process in proton-nucleus collisions. We express the contribution from multiple parton scattering and induced gluon radiation to the DY dilepton spectra in terms of nuclear modified effective beam quark distribution functions. The modification depends on the quark transport parameter in nuclear medium. This is similar to the final-state multiple parton scattering in deeply inelastic scattering (DIS) off large nuclei and leads to the suppression of the Drell-Yan cross section in p+A relative to p+p collisions. With the value of quark transport parameter determined from the nuclear modification of single-inclusive DIS hadron spectra as measured by the HERMES experiment, we calculate DY spectra in p+A collisions and find the nuclear suppression due to beam parton energy loss negligible at the Fermilab energy Elab=800 GeV in the kinematic region as covered by the E866 experiment. Most of the observed nuclear suppression of DY spectra in E866 experiment can be described well by parton shadowing in target nuclei as given by the EPS08 parameterization. The effect of beam parton energy loss, however, becomes significant for DY lepton pairs with large beam parton momentum fraction x? or small target parton momentum fraction x. We also predict the DY cross section in p+A collisions at lower beam proton energy Elab=120 GeV and show significant suppression due to initial state parton energy loss at moderately large x? where the effect of parton shadowing is very small.

Xing, Hongxi; Guo, Yun; Wang, Enke; Wang, Xin-Nian

2012-04-01

196

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

197

Measurements of scattering processes in negative ion-atom collisions. Technical progress report, 1 September 1991--31 August 1992  

SciTech Connect

This Technical Progress Report describes the progress made on the research objectives during the past twelve months. This research project is designed to provide measurements of various scattering processes which occur in H{sup {minus}} collisions with atomic (specifically, noble gas and atomic hydrogen) targets at intermediate energies. 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 in progress will provide either experimentally-determined cross sections or set upper limits to those cross sections. In either case, these measurements will be stringent tests of our understanding in energetic negative ion-atom collisions. This series of experiments required the construction of a new facility and the initial ion beam was accelerated through the apparatus in April 1991.

Kvale, T.J.

1992-04-01

198

Accelerating molecular dynamic simulation on graphics processing units.  

PubMed

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. PMID:19191337

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

2009-04-30

199

Coordinate space translation technique for simulation of electronic process in the ion-atom collision.  

PubMed

Recently we developed a theoretical model of ion-atom collisions, which was made on the basis of a time-dependent density functional theory description of the electron dynamics and a classical treatment of the heavy particle motion. Taking advantage of the real-space grid method, we introduce a "coordinate space translation" technique to allow one to focus on a certain space of interest such as the region around the projectile or the target. Benchmark calculations are given for collisions between proton and oxygen over a wide range of impact energy. To extract the probability of charge transfer, the formulation of Lu?dde and Dreizler [J. Phys. B 16, 3973 (1983)] has been generalized to ensemble-averaging application in the particular case of O((3)P). Charge transfer total cross sections are calculated, showing fairly good agreements between experimental data and present theoretical results. PMID:21513388

Wang, Feng; Hong, Xuhai; Wang, Jian; Kim, Kwang S

2011-04-21

200

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

201

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

Microsoft Academic Search

The production of multihadronic states in ?? 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 highpT have been selected under the requirement that no scattered electron or positron is

P. Abreu; W. Adam; T. Adye; E. Agasi; R. Aleksan; G. D. Alekseev; P. Allport; S. Almehed; F. M. L. Almeida Junior; S. J. Alvsvaag; U. Amaldi; A. Andreazza; P. Antilogus; W.-D. Apel; R. J. Apsimon; Y. Arnoud; B. Åsman; J.-E. Augustin; A. Augustinus; P. Baillon; P. Bambade; F. Barao; R. Barate; G. Barbiellini; D. Y. Bardin; G. J. Barker; A. Baroncelli; O. Barring; J. A. Barrio; W. Bartl; M. J. Bates; M. Battaglia; M. Baubillier; K.-H. Becks; M. Begalli; P. Beilliere; Yu. Belokopytov; P. Beltran; A. 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; G. Darbo; 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; L. Di Ciaccio; F. Djama; J. Dolbeau; M. Donszelmann; K. Doroba; M. Dracos; J. Drees; M. Dris; Y. Dufour; F. Dupont; D. 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. Firestone; H. Foeth; E. Fokitis; F. Fontanelli; K. A. J. Forbes; F. Formenti; J.-L. Fousset; S. Francon; B. Franek; P. Frenkiel; D. C. Fries; A. G. Frodesen; R. Fruhwirth; F. Fulda-Quenzer; H. Furstenau; J. 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; G. Gopal; L. Gorn; M. Gorski; V. 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; R. Leitner; Y. Lemoigne; J. Lemonne; G. Lenzen; V. Lepeltier; J. M. Levy; 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; B. S. Nielsen; V. Nikolaenko

1994-01-01

202

First evidence of hard scattering processes in single tagged gammagamma collisions  

Microsoft Academic Search

For the first time, multihadronic production from single tagged gammagamma collisions has been studied, where one of the scattered leptons was tagged at very low virtual photon absolute mass squared ( = 0.06GeV\\/(c2))2 ). Data collected during 1991 and 1992 in the DELPHI experiment at LEP are shown to agree well with predictions which included the non-perturbative vector meson dominance

P. Abreu; W. Adam; T. Adye; E. Agasi; I. Ajinenko; R. Aleksan; G. D. Alekseev; P. P. Allport; S. Almehed; F. M. L. Almeida; S. J. Alvsvaag; U. Amaldi; A. Andreazza; M. L. Andrieux; P. Antilogus; W.-D. Apel; Y. Arnoud; B. Åsman; J.-E. Augustin; A. Augustinus; P. Baillon; P. Bambade; F. Barao; R. Barate; G. Barbiellini; D. Y. Bardin; G. J. Barker; A. Baroncelli; O. Barring; J. A. Barrio; W. Bartl; M. J. Bates; M. Battaglia; M. Baubillier; J. Baudot; K.-H. Becks; M. Begalli; P. Beilliere; P. Beltran; A. C. Benvenuti; M. Berggren; D. Bertrand; F. Bianchi; M. Bigi; M. S. Bilenky; P. Billoir; J. Bjarne; D. Bloch; 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; J.-M. Brunet; L. Bugge; T. Buran; A. Buys; M. Caccia; M. Calvi; A. J. Camacho Rozas; T. Camporesi; V. Canale; M. Canepa; K. Cankocak; F. Cao; F. Carena; P. Carrilho; L. Carroll; C. Caso; V. Cassio; M. V. Castillo Gimenez; A. Cattai; F. R. Cavallo; L. Cerrito; V. Chabaud; A. Chan; Ph. Charpentier; L. Chaussard; J. Chauveau; P. Checchia; G. A. Chelkov; 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; W. da Silva; C. Defoix; P. Delpierre; N. Demaria; A. de Angelis; H. de Boeck; W. de Boer; S. de Brabandere; C. de Clercq; M. D. M. de Fez Laso; C. de La Vaissiere; B. de Lotto; A. de Min; L. de Paula; C. de Saint-Jean; H. Dijkstra; L. di Ciaccio; F. Djama; J. Dolbeau; M. Donszelmann; K. Doroba; M. Dracos; J. Drees; M. Dris; Y. Dufour; F. Dupont; D. Edsall; R. Ehret; T. Ekelof; G. Ekspong; M. Elsing; J.-P. Engel; N. Ershaidat; M. Espirito Santo; D. Fassouliotis; M. Feindt; A. Ferrer; T. A. Filippas; A. Firestone; H. Foeth; E. Fokitis; F. Fontanelli; F. Formenti; J.-L. Fousset; B. Franek; P. Frenkiel; D. C. Fries; A. G. Frodesen; R. Fruhwirth; F. Fulda-Quenzer; H. Furstenau; J. Fuster; D. Gamba; M. Gandelman; C. Garcia; J. Garcia; C. Gaspar; U. Gasparini; Ph. Gavillet; E. N. Gazis; D. Gele; J.-P. Gerber; D. Gillespie; R. Gokieli; B. Golob; V. M. Golovatyuk; J. J. Gomez Y Cadenas; G. Gopal; L. Gorn; M. Gorski; V. Gracco; F. Grard; E. Graziani; G. Grosdidier; P. Gunnarsson; J. Guy; U. Haedinger; F. Hahn; M. Hahn; S. Hahn; S. Haider; Z. Hajduk; A. Hakansson; A. Hallgren; K. Hamacher; W. Hao; F. J. Harris; V. Hedberg; R. Henriques; J. J. Hernandez; J. A. Hernando; P. Herquet; H. Herr; T. L. Hessing; E. Higon; H. J. Hilke; T. S. Hill; S.-O. Holmgren; P. J. Holt; D. Holthuizen; P. F. Honore; M. Houlden; J. Hrubec; 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; L. Jonsson; P. Juillot; M. Kaiser; G. Kalmus; F. Kapusta; M. Karlsson; E. Karvelas; A. Katargin; 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; C. Kreuter; J. Krolikowski; I. Kronkvist; W. Krupinski; K. Kulka; K. Kurvinen; C. Lacasta; I. Laktineh; C. Lambropoulos; J. W. Lamsa; L. Lanceri; P. Langefeld; V. Lapin; I. Last; J.-P. Laugier; R. Lauhakangas; G. Leder; F. Ledroit; R. Leitner; Y. Lemoigne; J. Lemonne; G. Lenzen; V. Lepeltier; T. Lesiak; J. M. Levy; E. Lieb; D. Liko; 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. Mc Cubbin; R. Mc Kay; R. Mc Nulty; J. Medbo; C. Meroni; W. T. Meyer; A. Miagkov; 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; S. Navas; P. Negri; S. Nemecek; W. Neumann; N. Neumeister; R. Nicolaidou; B. S. Nielsen; V. Nikolaenko; P. Niss; A. Nomerotski; A. Normand; V. Obraztsov; A. G. Olshevski; R. Orava; K. Osterberg; A. Ouraou; P. Paganini; M. Paganoni; R. Pain; H. Palka; Th. D. Papadopoulou; L. Pape; F. Parodi; A. Passeri; M. Pegoraro

1995-01-01

203

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

204

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

205

Myosin-V stepping kinetics: A molecular model for processivity  

PubMed Central

Myosin-V is a molecular motor that moves processively along its actin track. We have used a feedback-enhanced optical trap to examine the stepping kinetics of this movement. By analyzing the distribution of time periods separating discrete ?36-nm mechanical steps, we characterize the number and duration of rate-limiting biochemical transitions preceding each such step. These data show that myosin-V is a tightly coupled motor whose cycle time is limited by ADP release. On the basis of these results, we propose a model for myosin-V processivity.

Rief, Matthias; Rock, Ronald S.; Mehta, Amit D.; Mooseker, Mark S.; Cheney, Richard E.; Spudich, James A.

2000-01-01

206

Four-body charge transfer processes in proton-helium collisions  

NASA Astrophysics Data System (ADS)

Recent advancements in experimental techniques now allow for the study of fully differential cross sections (FDCS) for four-body collisions. The simplest four-body problem is a charged particle collision with a helium atom, in which both atomic electrons change state. This type of collision can result in many different outcomes, such as double excitation, excitation ionization, double ionization, transfer excitation, transfer ionization and double charge transfer. In this paper, we compare absolute experimental proton-helium FDCS for transfer excitation with the fully quantum mechanical 4BTTE (four-body transfer with target excitation) model. This model was previously used to study TTE for proton energies between 25 and 75 keV and reasonable agreement was found with the experimental data for large scattering angles, but not small angles. Since this is a first-order model, which contains contributions from all higher order terms, one would expect improved agreement with increasing energy and the purpose of this work was to look at higher energies. We found that the agreement with the magnitude of the experimental data became worse with increasing energy while the agreement with the shape of the data was reasonably good. Consequently, we conclude that the model contains the physical effects that determine the shape but not the magnitude of the cross section.

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

2012-02-01

207

Semiclassical Theory of Electronic Transitions in Molecular Collisions: Combined Effects of Tunneling and Energetically In-Accessible Electronic States.  

National Technical Information Service (NTIS)

The semiclassical theory of collision-induced electronic transitions is extended to describe tunneling and the effect of energetically inaccessible states. The powerful technique of analytic continuation is utilized to yield very good agreement with exact...

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

1976-01-01

208

Charge transfer processes in collisions of slow highly charged ions with polar molecules CO and C3H8  

NASA Astrophysics Data System (ADS)

Charge transfer processes resulting from low energy collisions of polar molecules CO and C3H8 with highly charged Be2+ and B2+ ions have been investigated experimentally and theoretically. The potential for the one-electron exchange interaction between a polar molecule and highly charged atomic ion were obtained in closed analytical form in the framework of a semiclassical approach. Obtained results were used for close-coupling calculations of total cross sections for single electron transfer in the studied reactions.

Khoma, M. V.; Imai, Makoto; Karbovanets, O. M.; Kikuchi, Y.; Saito, M.; Haruyama, Y.; Karbovanets, M. I.; Kretinin, I. Yu; Itoh, A.; Buenker, R. J.

2009-04-01

209

Photonic, Electronic and Atomic Collisions  

NASA Astrophysics Data System (ADS)

Plenary. Electron collisions - past, present and future / J. W. McConkey. Collisions of slow highly charged ions with surfaces / J. Burgdörfer ... [et al.]. Atomic collisions studied with "reaction-microscopes" / R. Moshammer ... [et al.]. Rydberg atoms: a microscale laboratory for studying electron-molecule tnteractions / F. B. Dunning -- Collisions involvintg photons. Quantum control of photochemical reaction dynamics and molecular functions / M. Yamaki ... [et al.]. Manipulating and viewing Rydberg wavepackets / R. R. Jones. Angle-resolved photoelectrons as a probe of strong-field interactions / M. Vrakking. Ultracold Rydberg atoms in a structured environment / I. C. H. Liu and J. M. Rost. Synchrotron-radiation-based recoil ion momentum spectroscopy of laser cooled and trapped cesium atoms / L. H. Coutinho. Reconstruction of attosecond pulse trains / Y. Mairesse ... [et al.]. Selective excitation of metastable atomic states by Femto- and attosecond laser pulses / A. D. Kondorskiy. Accurate calculations of triple differential cross sections for double photoionization of the hygrogen molecule / W. Vanroose ... [et al.]. Double and triple photoionization of Li and Be / J. Colgan, M. S. Pindzola and F. Robicheaux. Few/many body dynamics in strong laser fields / J. Zanghellini and T. Brabec. Rescattering-induced effects in electron-atom scattering in the presence of a circularly polarized laser field / A. V. Flegel ... [et al.]. Multidimensional photoelectron spectroscopy / P. Lablanquie ... [et al.]. Few photon and strongly driven transitions in the XUV and beyond / P. Lambropoulos, L. A. A. Nikolopoulos and S. I. Themelis. Ionization dynamics of atomic clusters in intense laser pulses / U. Saalmann and J. M. Rost. On the second order autocorrelation of an XUV attosecond pulse train / E. P. Benis ... [et al.]. Evidence for rescattering in molecular dissociation / I. D. Williams ... [et al.]. Photoionizing ions using synchrotron radiation / R. Phaneuf. Photo double ionization of fixed in space deuterium molecules / T. Weber ... [et al.]. Coherence and intramolecular scattering in molecular photoionization / U. Becker. Experimental observation of interatomic coulombic decay in neon dimers / T. Jahnke ... [et al.]. Ionization by short UV laser pulses: secondary ATI peaks of the electron spectrum / V. D. Rodríguez, E. Cormier and R. Gayet. Molecular frame photoemission in photoionization of H[symbol] and D[symbol]: the role of dissociation on autoionization of the Q[symbol] and Q[symbol] doubly excited states / D. Dowek, M. Lebech and J. C. Houver. 3p photoemission of 3d transition metals - atoms, molecules and clusters / M. Martins -- Collisions involving electrons. Spin-resolved collisions of electrons with atoms and molecules / G. F. Hanne. Calculation of ionization and excitation processes using the convergent close-coupling method / D. V. Fursa, I. Bray and A. T. Stelbovics. The B-spline R-matrix method for electron and photon collisions with atoms and ions / O. Zatsarinny and K. Bartschat. Absolute angle-differential cross sections for excitation of neon atoms electrons of energy 16.6-19.2 eV / M. Allan ... [et al.]. Studies of QED and nuclear size effects with highly charged ions in an EBIT / J. R. Crespo López-Urrutia ... [et al.]. Recombination of astrophysically relevant ions: Be-like C, N, and O / M. Fogle ... [et al.]. Dissociation and excitation of molecules and molecular ions by electron impact / A. E. Orel and J. Royal state-selective X-ray study of the radiative recombination of U[symbol] ions with cooling electrons / M. Pajek ... [et al.]. Electron collisions with trapped, metastable helium / L. J. Uhlmann ... [et al.]. Non-dipole effects in electron and photon impact ionization / N. L. S. Martin. Electron driven processes in atmospheric behaviour / L. Campbell, M. J. Brunger and P. J. 0. Teubner. Calculation of excitation and ionization for electron-molecule collisions at intermediate energies / J. D. Gorfinkiel. Absolute total cross sections for electron-CH[symbol] scattering at intermediate en

Fainstein, Pablo D.; Lima, Marco Aurelio P.; Miraglia, Jorge E.; Montenegro, Eduardo C.; Rivarola, Roberto D.

2006-11-01

210

Two Molecular Information Processing Systems Based on Catalytic Nucleic Acids  

NASA Astrophysics Data System (ADS)

Mixtures of molecules are capable of powerful information processing [1]. This statement is in the following way self-evident: it is a hierarchically organized complex mixture of molecules that is formulating it to other similarly organized mixtures of molecules. By making such a statement I am not endorsing the extreme forms of reductionism; rather, I am making what I think is a small first step towards harnessing information processing prowess of molecules and, hopefully, overcoming some limitations of more traditional computing paradigms. There are different ideas on how to understand and use molecular information processing abilities and I will list some below. My list is far from inclusive, and delineations are far from clear-cut; whenever available, I will provide examples from our research efforts. I should stress, for a computer science audience that I am a chemist. Thus, my approach may have much different focus and mathematical rigor, then if it would be taken by a computer scientist.

Stojanovic, Milan

211

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

212

Selective-state charge transfer in a collision between a Li sup 3+ ion and a ground-state Li atom: A molecular-state approach (US)  

SciTech Connect

The semiclassical, impact-parameter method, based on a 15-state molecular-orbital expansion, is employed to calculate the cross sections for charge transfer in Li{sup 3+}-Li collisions. Electron-translation effects have been taken into account. In addition to total capture, cross sections for capture into individual states have also been calculated. The present results show qualitative agreement with the other available theory; details, however, are different. It is found that this reaction, through state-selective capture into the {ital n}=4 manifold of Li{sup 2+}, may provide a useful mechanism to achieve population inversion necessary for short-wavelength lasers.

Kumar, A.; Lane, N.F. (Department of Physics, Rice Quantum Institute, Rice University, Houston, Texas 77251 (USA)); Kimura, M. (Argonne National Laboratory, Argonne, Illinois 60439 (USA) Department of Physics, Rice Quantum Institute, Rice University, Houston, Texas 77251 (USA))

1991-01-01

213

Hydrogen Atom Collision Processes in Cool Stellar Atmospheres: Effects on Spectral Line Strengths and Measured Chemical Abundances in Old Stars  

NASA Astrophysics Data System (ADS)

The precise measurement of the chemical composition of stars is a fundamental problem relevant to many areas of astrophysics. State-of-the-art approaches attempt to unite accurate descriptions of microphysics, non-local thermodynamic equilibrium (non-LTE) line formation and 3D hydrodynamical model atmospheres. In this paper I review progress in understanding inelastic collisions of hydrogen atoms with other species and their influence on spectral line formation and derived abundances in stellar atmospheres. These collisions are a major source of uncertainty in non-LTE modelling of spectral lines and abundance determinations, especially for old, metal-poor stars, which are unique tracers of the early evolution of our galaxy. Full quantum scattering calculations of direct excitation processes X(nl) + H leftrightarrow X(n'l') + H and charge transfer processes X(nl) + H leftrightarrow X+ + H- have been done for Li, Na and Mg [1,2,3] based on detailed quantum chemical data, e.g. [4]. Rate coefficients have been calculated and applied to non-LTE modelling of spectral lines in stellar atmospheres [5,6,7,8,9]. In all cases we find that charge transfer processes from the first excited S-state are very important, and the processes affect measured abundances for Li, Na and Mg in some stars by as much as 60%. Effects vary with stellar parameters (e.g. temperature, luminosity, metal content) and so these processes are important not only for accurate absolute abundances, but also for relative abundances among dissimilar stars.

Barklem, Paul S.

2012-12-01

214

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

215

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

2003-04-15

216

Studies of fluctuation processes in nuclear collisions. [Dept. of Physics, Tennessee Technological Univ. , Cookeville, Tennessee  

SciTech Connect

Investigations of various aspects of heavy-ion collisions were carried out in the framework of the Boltzmann-Langevin Model (BLM). In a previous work, by projection the BLM onto a collective space, a memory-dependent collective transport model was reduced. This model was applied to thermal fission to investigate the influence of the memory effects on the fission dynamics. Some results of the calculations are presented. In addition a reduction of the relativistic BLM to a two-fluid model was carried out, and transport coefficients associated with fluid dynamical variables was carried out. Then this model was applied to investigate equilabration and fluctuation properties in a counter-streaming nuclear fluid.

Ayik, S.

1993-02-01

217

Studies of fluctuation processes in nuclear collisions. Progress report, March 1, 1992--February 28, 1993  

SciTech Connect

Investigations of various aspects of heavy-ion collisions were carried out in the framework of the Boltzmann-Langevin Model (BLM). In a previous work, by projection the BLM onto a collective space, a memory-dependent collective transport model was reduced. This model was applied to thermal fission to investigate the influence of the memory effects on the fission dynamics. Some results of the calculations are presented. In addition a reduction of the relativistic BLM to a two-fluid model was carried out, and transport coefficients associated with fluid dynamical variables was carried out. Then this model was applied to investigate equilabration and fluctuation properties in a counter-streaming nuclear fluid.

Ayik, S.

1993-02-01

218

Single- and double-electron processes in collisions of Xe{sup 23+} ions with helium  

SciTech Connect

We report the measurements of relative cross sections for single capture (SC), double capture (DC), single ionization (SI), double ionization (DI), and transfer ionization (TI) in collisions of Xe{sup 23+} ions with helium atoms in the velocity range of 0.65-1.32 a.u. The relative cross sections show a weak velocity dependence. The cross-section ratio of double- (DE) to single-electron (SE) removal from He, {sigma}{sub DE}/{sigma}{sub SE}, is about 0.45. Single capture is the dominant reaction channel which is followed by transfer ionization, while only very small probabilities are found for pure ionization and double capture. The present experimental data are in satisfactory agreement with the estimations by the extended classical over-barrier (ECB) model.

Ding Baowei; Wan Chengliang; Chen Shangwen [School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000 (China); Yu Deyang; Ruan Fangfang; Lu Rongchun; Cai Xiaohong [Institute of Modern Physics, Chinese Academy of Science, Lanzhou 730000 (China); Shao Caojie [Institute of Modern Physics, Chinese Academy of Science, Lanzhou 730000 (China); Graduate School of the Chinese Academy of Sciences, Beijing 100049 (China)

2010-09-15

219

Low-energy single-electron capture cross sections in C{sup 6+}/C{sup 4+} - Na(3s) and N{sup 7+}/N{sup 5+} - Na(3s) collisions: Molecular state approach  

SciTech Connect

The low-energy state-selective capture cross sections for single-electron transfer from the ground state of Na(3s) atoms by fully (C{sup 6+} and N{sup 7+}) and partially stripped (C{sup 4+} and N{sup 5+}) ions have been calculated using the semiclassical approximation in the molecular orbital formulation augmented with the proper electron translation factor. The method of pseudopotential is invoked to account for the interaction of the active electron with the moving nuclei, whose relative motion is considered via a straight-line trajectory. Although both C{sup 4+} and N{sup 5+} have identical He-like structure, their roles reveal very different collision dynamics. The projectile C{sup 4+} exhibits a distinctive role due to its finite core; a low-energy structure in the total capture cross section for C{sup 4+} -Na(3s) collisions is observed and explained. For bare projectiles (C{sup 6+} and N{sup 7+}) there remains an increasing tendency of the Stark mixing to characterize the electron transfer processes; it enhances the population of the higher {ell} states. The {ell} distribution of the charge-transfer cross section for various projectile is also discussed.

Saha, B.C.; Kuman, A.

1999-12-01

220

One Dimensional Collision Model  

NSDL National Science Digital Library

The One Dimensional Collision model allows the user to collide two objects and investigate whether momentum and/or kinetic energy are conserved in the collision process. To keep things simple, we'll confine ourselves to collisions along a single line. Special cases include the completely inelastic case, in which the objects stick together after the collision, as well as the completely elastic case, in which kinetic energy is conserved. The One Dimensional Collision was created using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_bu_Collisions1D.jar file will run the program if Java is installed.

Duffy, Andrew

2010-04-28

221

Molecular Tracking, through Processing, of Campylobacter Strains Colonizing Broiler Flocks?  

PubMed Central

Many of the poultry flocks produced in the United Kingdom are colonized with Campylobacter, and the intensive nature of poultry processing usually results in contaminated carcasses. In this study, a previously reported molecular oligonucleotide probe method was used to track a specific flock-colonizing strain(s) on broiler carcasses during processing in two United Kingdom commercial poultry processing plants. Five Campylobacter-positive flocks were sampled at four points along the processing line, postbleed, postpluck, prechill, and postchill, and two Campylobacter-negative flocks processed immediately after positive flocks were sampled prechill. flaA was sequenced from Campylobacter strains isolated from these flocks, and strain-specific probes were synthesized. Skin and cecal samples were plated onto selective agar to give individual colonies, which were transferred onto membranes. These were then hybridized with the strain- and genus-specific probes. For all the 5 positive flocks, there was a significant reduction in campylobacters postbleed compared to postpluck but no subsequent fall on sampling pre- and postchill, and the strain(s) predominating on the carcasses throughout processing came from the flock being processed. This indicates that strains from the abattoir environment were not a significant cause of carcass contamination in flocks with well-established campylobacter colonization. However, negative flocks that were preceded by positive flocks were contaminated by strains that did not generally originate from the predominating strains recovered from the ceca of the previous positive flocks. This suggests that the abattoir environment has a significant role in the contamination of carcasses from negative but not fully colonized flocks.

Elvers, Karen T.; Morris, Victoria K.; Newell, Diane G.; Allen, Vivien M.

2011-01-01

222

Atomic and molecular surface and volume processes in the analysis of negative hydrogen discharges  

SciTech Connect

The principal source of negative ion generation in hydrogen discharges is now recognized to be low-energy electron attachment to H/sub 2/(/nu//prime//prime/) molecules excited to the middle portion of the vibrational spectrum. Electron excitation processes are generally taken to be the principal source of H/sub 2/(/nu//prime//prime/) generation, with high-energy excitations through the singlet spectrum being the principal excitation process populating the active portion of the vibrational spectrum. A description of the collisional re-excitation from level /nu//prime//prime/, to level /nu//prime//prime/, requires 15 /times/ 15 matrix of cross sections linking all initial and final levels. These cross sections have been evaluated and incorporated into the modelling code. An additional source of vibrational excitation may be derived from recombination of H/sub 2//sup +/ and H/sub 3//sup +/ ions on the surfaces of the discharge. In this case the molecular ions will impinge with kinetic energies given by the plasma potential, 1--10 eV. In this paper we report the evaluation of H/sub 2/(/nu//prime//prime/) resulting from the surface recombination process. The use of low-work-function materials for the discharge surfaces makes possible two additional source of negative ions: the direct formation of negative ions by hydrogen atoms rebounding from the surface, and the dissociation of H/sub 2//sup /minus// ions formed in the surface selvage. A recent paper has demonstrated the efficacy of Ba surfaces as an active medium for H/sup /minus// formation. Here we shall extend our discussion to H/sub 2//sup +/, H/sub 3//sup +/ collisions on Ba surfaces and inventory the generation of H, H/sub 2/(/nu//prime//prime/), and H/sup /minus// rebounding from these surfaces. 16 refs., 4 figs.

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

1989-07-03

223

Rydberg state population due to multicapture processes in Kr[sup q+] (q=17-18) on Kr collisions  

SciTech Connect

Initial population distributions in principal quantum numbers n of excited states were obtained in multicapture processes for Kr[sup q+] (q=17-18) on Kr collisions at low energy ([approx]5 keV/u). Radiative decay curves of Rydberg transitions of the projectivle ions have been measured by shifting the target gas jet along the projectile beam, i.e. perpendicularly to the observation axis. As a result for Kr[sup 18+] projectiles, we have found that an Kr[sup 16+] constant initial population from n=14 to n=19 allows the observed Kr XVII 14--15 radiative decay curve to reproduce relatively well. In addition to this, coincidence time of flight spectroscopy between recoil ion photons and recoil ions have been performed in order to determine the decay curves of recoil ion transitions. We found an initial population distribution centered around n=20 for the 7i--8k transition of Kr VII recoil ion.

Martin, S.; Denis, A.; Delon, A.; Desesquelles, J. (LASIM Universite Lyon 1, Campus de la Doua, F-69622 Villeurbanne Cedex (France)); Ouerdane, Y. (TSI Universite de Saint-Etienne, 23 rue du Dr Paul Michelon, F-4202, Saint-Etienne (France))

1993-06-05

224

Strong Alignment Observed for the Time-Reversed Photoionization Process Studied in Relativistic Collisions with Bare Uranium Ions  

SciTech Connect

In high-energy atomic collisions between bare high-Z projectiles and low-Z target atoms, an electron may be captured radiatively into an excited projectile state which subsequently decays by x-ray emission. This process is the inverse of two-photon{endash}one-electron ionization, in which the first photon resonantly excites an electron from the hydrogenic 1s{sub 1/2} ground state and a second photon ionizes the excited electron. We present an experimental and theoretical study of the angular distribution of the Ly-{alpha}{sub 1} (2p{sub 3/2}{r_arrow}1s{sub 1/2} ) x rays following radiative electron capture. From the observed anisotropic emission pattern a significant alignment of the intermediate 2p{sub 3/2} state is deduced. {copyright} {ital 1997} {ital The American Physical Society}

Stoehlker, T. [Institut fuer Kernphysik, University of Frankfurt, 60486 Frankfurt (Germany); Stoehlker, T.; Bosch, F.; Gallus, A.; Kozhuharov, C.; Menzel, G.; Mokler, P.H.; Prinz, H.T. [Gesellschaft fuer Schwerionenforschung, 64220 Darmstadt (Germany); Eichler, J.; Eichler, J. [Fachbereich Physik, Freie Universitaet Berlin, 14195 Berlin (Germany); Ichihara, A.; Shirai, T. [Japan Atomic Energy Research Institute, Tokai-mura, Ibaraki 319-11 (Japan); Dunford, R.W. [Physics Divison, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Ludziejewski, T.; Rymuza, P. [Institute for Nuclear Studies, 05-400 Swierk (Poland); Stachura, Z. [Institute of Nuclear Physics, 31-342 Cracow (Poland); Swiat, P.; Warczak, A. [Institute of Physics, Jagiellonian University, 30-059 Cracow, Poland] [Wayne State University, Detroit, Michigan 48202 (United States)

1997-10-01

225

The B-spline R-matrix method for atomic processes: application to atomic structure, electron collisions and photoionization  

NASA Astrophysics Data System (ADS)

The basic ideas of the B-spline R-matrix (BSR) approach are reviewed, and the use of the method is illustrated with a variety of applications to atomic structure, electron-atom collisions and photo-induced processes. Special emphasis is placed on complex, open-shell targets, for which the method has proven very successful in reproducing, for example, a wealth of near-threshold resonance structures. Recent extensions to a fully relativistic framework and intermediate energies have allowed for an accurate treatment of heavy targets as well as a fully nonperturbative scheme for electron-impact ionization. Finally, field-free BSR Hamiltonian and electric dipole matrices can be employed in the time-dependent treatment of intense short-pulse laser-atom interactions.

Zatsarinny, Oleg; Bartschat, Klaus

2013-06-01

226

Inelastic processes in K+-He collisions in energy range 0.7–10 keV  

NASA Astrophysics Data System (ADS)

Absolute cross sections for charge exchange, ionization, stripping, and excitation in K+-He collisions were measured in the ion energy range 0.7–10 keV. The experimental data and the schematic correlation diagrams are used to analyze and determine the mechanisms for these processes. The increase of the excitation probability of inelastic channels with the angle of scattering is revealed. An exceptionally highly excited state of He is observed and a peculiarity for the excitation function of the resonance line is explained. The intensity ratio for the excitation of the K II ?=60.1 nm and ?=61.2 nm lines is 5:1, which indicates the high probability for excitation of the singlet resonance level 1P1 compared to the triplet level 3P1. The similarity of the population of the 4p state of the potassium ion and atom as well as the anomalously small values of the excitation cross sections are explained.

Lomsadze, R. A.; Gochitashvili, M. R.; Kezerashvili, R. Ya.; Mosulishvili, N. O.; Phaneuf, R.

2013-04-01

227

Procesos cuasi-moleculares en enanas blancas frías  

NASA Astrophysics Data System (ADS)

We show that the radiation emitted by very cool white dwarf stars (Teff ~< 3000 K) with pure hydrogen atmospheres, is fully formed by radiative processes induced by atomic and molecular collisions. FULL TEXT IN SPANISH

Rohrmann, R. D.; Althaus, L. G.; Kepler, S. O.

228

Solution processed molecular floating gate for flexible flash memories.  

PubMed

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. PMID:24172758

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

2013-10-31

229

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

230

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

231

ATOMIC AND MOLECULAR PHYSICS: Influence of Isotope Substitution Helium Atom on Partial Cross Sections in He-HF Collisions  

NASA Astrophysics Data System (ADS)

Close-coupling equation and anisotropic potential developed in our previous research are applied to HF-3He (4He, 6He, 8He, 10He) collision system, and partial cross sections (PCSs) at the incident energy of 40 meV are calculated. By analyzing the differences of these PCSs, change rules of PCSs with the increase of partial wave number, and with the change of the mass of isotope substitution helium atom are obtained. The results show that excitation PCSs converge faster than elastic PCSs for collision energy and each of systems considered here. Also excitation PCSs converge more rapidly for high-excited states. Tail effect is present only in elastic scattering and low-excited states but not in high-excited states. With the increase of the mass of isotope substitution helium atom, converging speed of elastic, total inelastic, and state-to-state excitation PCS slows down, and the maxima of these PCSs undergoes a regular change.

Yu, Chun-Ri; Zhang, Jie; Chen, Li; Jiang, Gui-Sheng; Huang, Guo-Dong

2009-11-01

232

Collision limited reaction rates for arbitrarily shaped particles across the entire diffusive Knudsen number range.  

PubMed

Aerosol particle reactions with vapor molecules and molecular clusters are often collision rate limited, hence determination of particle-vapor molecule and particle-molecular cluster collision rates are of fundamental importance. These collisions typically occur in the mass transfer transition regime, wherein the collision kernel (collision rate coefficient) is dependent upon the diffusive Knudsen number, Kn(D). While this alone prohibits analytical determination of the collision kernel, aerosol particle- vapor molecule collisions are further complicated when particles are non-spherical, as is often the case for particles formed in high temperature processes (combustion). Recently, through a combination of mean first passage time simulations and dimensional analysis, it was shown that the collision kernel for spherical particles and vapor molecules could be expressed as a dimensionless number, H, which is solely a function of Kn(D). In this work, it is shown through similar mean first passage times and redefinitions of H and Kn(D) that the H(Kn(D)) relationship found for spherical particles applies for particles of arbitrary shape, including commonly encountered agglomerate particles. Specifically, it is shown that to appropriately define H and Kn(D), two geometric descriptors for a particle are necessary: its Smoluchowski radius, which defines the collision kernel in the continuum regime (Kn(D)?0) and its orientationally averaged projected area, which defines the collision kernel in the free molecular regime (Kn(D)??). With these two parameters, as well as the properties of the colliding vapor molecule (mass and diffusion coefficient), the particle-vapor molecule collision kernel in the continuum, transition, and free molecular regimes can be simply calculated using the H(Kn(D)) relationship. PMID:21823695

Gopalakrishnan, Ranganathan; Thajudeen, Thaseem; Hogan, Christopher J

2011-08-01

233

Parton radiative processes and pressure isotropization in relativistic heavy ion collisions  

NASA Astrophysics Data System (ADS)

The impact of radiative processes on kinetic equilibration is studied via a radiative transport model. The 2?3 processes can significantly increase the level of thermalization. These processes lead to an approximate coupling constant scaling of the evolution of the pressure anisotropy qualitatively different from the case with only 2?2 partonic processes. Furthermore, thermal and Color Glass Condensate motivated initial conditions are shown to share the same asymptotic evolution when 2?3 processes are included. This emphasizes the unique role of radiative processes in Quark-Gluon Plasma thermalization.

Zhang, Bin; Wortman, Warner A.

2010-09-01

234

New geometry for the quasi-binary incident electron centre of mass collision in (e, 3e) process on He  

NASA Astrophysics Data System (ADS)

We present in this paper the results of our calculation of five-fold differential cross sections (FDCS) in a new geometrical arrangement (constant theta-12-phi-12 mode) for the study of the quasi-binary incident electron-centre of mass collision in the (e, 3e) process on He in a better way. In this geometrical arrangement, we restrict the momentum of the centre of mass of the ejected electrons to lie in the scattering plane, defined by the momenta of the incident and scattered electrons, even though the momenta of the ejected electrons are not in the scattering plane. This geometrical mode has a greater potential to study the quasi-binary collision than the earlier study of FDCS (Choubisa et al 2003a Pramana J. Phys. 60 1187, 2003b J. Phys. B: At. Mol. Opt. Phys. 36 1731, Lahmam-Bennani et al 2002 J. Phys. B: At. Mol. Opt. Phys. 35 L215) in the coplanar constant theta-12 mode which has a limited application due to the restriction on the momenta of all the outgoing electrons to lie in the scattering plane whereas the new geometrical mode can be used for any direction of ejected electrons as long as the momentum of the centre of mass is in the scattering plane. We present our first and second Born results in the 3 C wave approach and compare our results with the available experimental data and the first Born CCC theory to check the consistency of our theoretical model and it is found to be satisfactory qualitatively. The results of our calculation of FDCS in the first as well as the second Born approximation on the He atom in the proposed geometrical mode reveal some interesting features about the quasi-binary incident electron-centre of mass collision, its dependence on the geometrical arrangement of the momenta of the ejected electrons as well as on the first- and the second-order projectile-target interaction. We are of the opinion that this geometrical arrangement may serve as a useful guideline for future (e, 3e) experimentations.

Choubisa, Rakesh; Sud, K. K.

2008-02-01

235

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

236

Inelastic and ballistic processes resulting from CsF--Ar collisions  

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. While the calculated results show no significant dependence on the initial relative velocity or on the initial vibrational quantum number of CsF, they do show a systematic variation with the initial rotational quantum number---the ballistic effect is more pronounced than that observed experimentally for initial quantum rotational numbers less than 30 and is not pronounced enough for rotational quantum numbers more than 100. Two mechanisms give rise to the ballistic peak. The first one is dominant when the laboratory scattering angle is equal, or nearly equal, to the laboratory angle of the centroid velocity. This mechanism transfers almost all of the relative translational energy into the internal energy of the diatom and magnifies the center-of-mass (c.m.) differential cross section almost a million times. This is due to a singularity in the Jacobian at very small c.m. recoil velocities, which physically means that a small solid angle in the laboratory frame can collect the signal from all 4[pi] steradians in the c.m. frame.

Sharma, R.D. (Phillips Laboratory, Optical Environment Division (GPOS), Hanscom Air Force Base, Massachusetts 01731-5000 (United States)); Sindoni, J.M. (Yap Analytics Inc., Lexington, Massachusetts 02173 (United States))

1993-01-15

237

Molecular epidemiology biomarkers--sample collection and processing considerations.  

PubMed

Biomarker studies require processing and storage of numerous biological samples with the goals of obtaining a large amount of information and minimizing future research costs. An efficient study design includes provisions for processing of the original samples, such as cryopreservation, DNA isolation, and preparation of specimens for exposure assessment. Use of standard, two-dimensional and nanobarcodes and customized electronic databases assure efficient management of large sample collections and tracking results of data analyses. Standard operating procedures and quality control plans help to protect sample quality and to assure validity of the biomarker data. 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. Appropriate informed consent must be obtained from the study subjects prior to sample collection and confidentiality of results maintained. Finally, examples of three biorepositories of different scale (European Cancer Study, National Cancer Institute and School of Public Health Biorepository, University of California, Berkeley) are used to illustrate challenges faced by investigators and the ways to overcome them. New software and biorepository technologies are being developed by many companies that will help to bring biological banking to a new level required by molecular epidemiology of the 21st century. PMID:15967217

Holland, Nina T; Pfleger, Laura; Berger, Eileen; Ho, Alan; Bastaki, Maria

2005-08-01

238

Investigation of ionization processes in subthermal collisions of rubidium n{sup 2}P atoms with one another and with the ground-state Rb atoms  

SciTech Connect

The chemoionization processes in Rydberg-Rydberg and Rydberg-ground-state rubidium collisions at 60 K were investigated for the principal quantum number n=11. The ratio of the rate constant k{sub 2} for atomic ion formation in Rydberg-Rydberg collisions to the rate constant k{sub 1} for associative ionization in Rydberg-ground-state atomic collisions was measured. The value k{sub 2}=(1.5 {plus_minus} 0.4) X 10{sup -8} cm{sup 3} s{sup -1} was determined using the literature data for k{sub 1}. The value obtained coincides to a factor of two with that calculated within the Katsuura-Smirnov model. 16 refs., 4 figs.

Borodin, V.M.; Dobrolezh, B.V.; Klyucharev, A.N.; Tsyganov, A.B. [St. Petersburg State Univ., Peterhof (Russian Federation)

1995-01-01

239

Interplay between computer simulation and transport theory in the analysis of ion-beam-induced collision processes in solids  

Microsoft Academic Search

A brief summary is given of recent work on five loosely connected topics within atomic collisions in solids: (i) preferential recoil implantation in multicomponent targets, (ii) pronounced nonlinear behavior of atomic collision sequences induced by keV heavy ions, (iii) linear and nonlinear effects induced by cluster bombardment, (iv) round robin computer simulation of ejection probability in sputtering, and (v) depth

Peter Sigmund

1989-01-01

240

Onland signatures of the Palawan microcontinental block and Philippine mobile belt collision and crustal growth process: A review  

Microsoft Academic Search

The collision of the Palawan microcontinental block with the Philippine mobile belt had significantly influenced the geological evolution of the Philippines. Multiple collisions involving several fragments, through space and time, resulted into the collage of terranes of varying origin exposed in this part of central Philippines. Cusping of the overriding plate, volcanic arc gap, ophiolite emplacement, incipient back-arc rifting, island

Graciano P. Yumul; Carla B. Dimalanta; Edanjarlo J. Marquez; Karlo L. Queaño

2009-01-01

241

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

242

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

243

New semiclassical decoupling scheme for electronic transitions in molecular collisions: Application to vibrational-to-electronic energy transfer  

SciTech Connect

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.; Lam, K.S.; DeVries, P.L.; George, T.F.

1980-07-01

244

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

245

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

246

Conversion process of aromatic hydrocarbon from low molecular paraffin hydrocarbon  

SciTech Connect

This patent describes a process for conversion of low molecular paraffin hydrocarbon to aromatic hydrocarbon which comprises bringing the low molecular paraffin hydrocarbons into contact with a metallo-silicate catalyst (Si/Me) wherein the atomic ratio of Si/Me is 25-3200, and Me is one selected from the group consisting of Al, Ga, Ti, Zr, Ge, La, Mn, Cr, Sc, V, Fe, W, Mo and Ni, which is impregnated or ion-exchanged with 0.25-1.5% by weight of platinum or gallium, based on the catalyst, or a gallium-silicate cataylst. The atomic ratio of Si/Ga is 20-3200. The catalyst is prepared by the following steps; a first step of preparing solutions of (A), (B), and (C), the (A) being an aqueous solution containing (a) a quaternary lower alkylammonium cation R, (b) an alkaline metal of sodium or potassium, and (c) an aqueous solution of a water soluble salt of a metal Me selected from the group consisting of Al, Ga, Ti, Zr, Ge, La, Mn, Cr, Sc, V, Fe, W, Mo and Ni; (B) an aqueous silicate solution, and (C) an aqueous solution of an ion modifier. Add the solution (A) and solution (B) to the solution (C) at a constant speed until a gelly mixture having a pH of around 10. Then grind the resulting gel mixture. Heat the gel mixture to a temperature of 150/sup 0/-190/sup 0/C at a constant speed followed by heating to 190/sup 0/-200/sup 0/C at a constant speed or an exponential speed to obtain a precourser synthetic metallosilicate having the following chemical composition in molar ratio: Si/Me: 25-3200 OH-SiO/sub 2/: 0.3-1.0 H/sub 2/O/SiO/sub 2/: 30-100 R/R+alkalimetal: 0.05-0.15 NaCl/H/sub 2/O: 0.01-0.06 wherein R is a quaternary alkylammonium cation, the alkali metal is sodium or potassium and Me is Al, Ga, Ti, Zr, Ge, La, Mn, Cr, Sc, V, Fe, W, Mo or Ni and fourth step of calcining the precourser.

Inui, T.

1987-11-03

247

New Insights Into the Fission Process by the Study of Relativistic Nuclear Collisions  

SciTech Connect

An experimental and theoretical campaign dedicated to a better understanding of the fission process has been started at GSI several years ago. The waste amount of data measured at GSI gave new information on different aspects of the nuclear-fission process, such as nuclear viscosity at small deformation, transient effects, influence of shell effects on mass- and charge-division in fission, pairing correlations. All this lead to a development of a model, which proved successful in describing fragment formation in spallation and fragmentation reactions.

Kelic, Aleksandra; Schmidt, Karl-Heinz [GSI, Planckstr. 1, Darmstadt, D-64291 (Germany)

2007-05-22

248

Particle in cell analysis of a laser-cluster interaction including collision and ionization processes.  

PubMed

A new particle-in-cell (PIC) code which includes collisional and ionization processes has been developed to study laser-plasma interaction. Using the new code, the dynamics of a cluster plasma in a strong laser field has been analyzed and the threshold intensity of the resonant heating, which was previously predicted is accurately evaluated. The angular dependence of ion energy spectrum has also been simulated. As a result, it is found that the anisotropic energy spectrum depends strongly on the presence or absence of collisional processes. PMID:20174069

Taguchi, Toshihiro; Antonsen, Thomas M; Palastro, John; Milchberg, Howard; Mima, Kunioki

2010-02-01

249

Mountain building processes during continent–continent collision in the Uralides  

Microsoft Academic Search

Since the early 1990's the Paleozoic Uralide Orogen of Russia has been the target of a significant research initiative as part of EUROPROBE and GEODE, both European Science Foundation programmes. One of the main objectives of these research programmes was the determination of the tectonic processes that went into the formation of the orogen. In this review paper we focus

D. Brown; C. Juhlin; C. Ayala; A. Tryggvason; F. Bea; J. Alvarezmarron; R. Carbonell; D. Seward; U. Glasmacher; V. Puchkov; A. Perez-Estaun

2008-01-01

250

From subduction to collision: Control of deep processes on the evolution of convergent plate boundary  

Microsoft Academic Search

Using laboratory experiments, we investigate the dynamics of the collisional process that follows the closure of an oceanic basin. The evolution of these experiments systematically shows four successive episodes of deformation, which correspond to (1) the initiation of oceanic subduction, (2) a mature period of oceanic subduction, (3) an episode of continental subduction, during which the trench absorbs all the

Vincent Regard; Claudio Faccenna; Joseph Martinod; Olivier Bellier; Jean-Charles Thomas

2003-01-01

251

ATOMIC AND MOLECULAR PHYSICS: Relativistic Distorted-Wave Collision Strengths of Ni-, Cu- and Zn-like Au Ions  

NASA Astrophysics Data System (ADS)

Excitation energies and electron impact excitation strengths from the ground states of Ni-, Cu- and Zn-like Au ions are calculated. The collision strengths are computed by a 213-levels expansion for the Ni-like Au ion, 405-levels expansion for the Cu-like Au ion and 229-levels expansion for the Zn-like Au ion. Configuration interactions are taken into account for all levels included. The target state wavefunctions are calculated by using the Grasp92 code. The continuum orbits are computed in the distorted-wave approximation, in which the direct and exchange potentials among all the electrons are included. Excellent agreement is found when the results are compared with previous calculations and recent measurements.

Yang, Ning-Xuan; Dong, Chen-Zhong; Jiang, Jun

2009-05-01

252

Cold collisions between boson or fermion molecules  

SciTech Connect

We theoretically investigate collisions between electrostatically trapped cold polar molecules and compare boson and fermion isotopes. Evaporative cooling seems possible for fermion molecules as the ratio of the collision loss cross section to the elastic collision cross section (R) gets smaller as the molecular temperature T lowers. With boson molecules, R gets larger as T lowers, which makes evaporative cooling difficult. The elastic collision cross section between fermion molecules can be larger than that for boson molecules with certain conditions.

Kajita, Masatoshi [Communications Research Laboratory, 4-2-1, Nukui-Kitamachi, Koganei, Tokyo 184-8795 (Japan)

2004-01-01

253

Atomic collisions: Heavy-particle projectiles  

Microsoft Academic Search

The objective of this paper was a review of the text `Atomic Collisions: Heavy-Particle Projectiles` by McDaniel, Mitchell, and Rudd. The text discusses a number of theoretical treatments of atomic collisions. Similarly, the text introduces and compares several experimental methods. Topics include: elastic\\/inelastic\\/reactive collisions, ionization and charge transfer, molecular dissociation, and electron\\/ion transport. Collision energies are limited to those in

Earl W. Mcdaniel; J. B. A. Mitchell; M. Eugene Rudd

1993-01-01

254

Head shock versus Mach cone: Azimuthal correlations from 2?3 parton processes in relativistic heavy-ion collisions  

NASA Astrophysics Data System (ADS)

We study the energy momentum deposited by fast moving partons within a medium using linearized viscous hydrodynamics. The particle distribution produced by this energy momentum is computed using the Cooper-Frye formalism. We show that, for the conditions arising in heavy-ion collisions, energy momentum is preferentially deposited along the head shock of the fast moving partons. We also show that the double hump in the away-side of azimuthal correlations can be produced by two (instead of one) away-side partons that deposit their energy momentum along their directions of motion. These partons originate in the in-medium hard scattering in 2?3 processes. We compare the results of the analysis to azimuthal angular correlations from PHENIX and show that the calculation reproduces the data systematics of a decreasing away-side correlation when the momentum of the associated hadron becomes closer to the momentum of the leading hadron. This scenario seems to avoid the shortcomings of the Mach cone as the origin of the double-hump structure in the away-side.

Ayala, Alejandro; Dominguez, Isabel; Tejeda-Yeomans, Maria Elena

2013-08-01

255

Atomic Processes in the Solar Wind: EUV and X-ray Emission Induced by Charge-Transfer Collisions  

NASA Astrophysics Data System (ADS)

The atomic processes associated with the interaction of the Solar Wind (SW) ions with neutral interstellar, planetary, and cometary gases are briefly reviewed. The charge-exchange mechanism of X-ray and Extreme Ultraviolet (EUV) emission of the highly charged SW ions is described in detail. The unique spectra of cascading photons arising in collisions between heavy SW ions and neutral atoms or molecules are demonstrated. Emission spectra of individual SW ions are computed using results of recent laboratory measurements and quantal calculations. The synthetic spectra of the charge-transfer EUV and X-ray emission are constructed for the slow and fast solar wind interacting with the cometary and interstellar gases. Results of spectral modeling are compared with observational data from ROSAT, EUVE, FUSE and Chandra X-ray telescopes. The contribution of the charge-exchange mechanism to diffuse X-ray background is evaluated. A remote diagnostic of the SW plasma and interstellar gas based on analysis of the charge-transfer emission is discussed.

Kharchenko, V.

2004-09-01

256

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

257

Multielectron Processes in Heavy Ion{endash}Atom Collisions at Intermediate Velocity  

SciTech Connect

Using high resolution x-ray spectroscopy, we have measured projectile electron single and multiple cross sections when a two-electron Ar{sup 16+} ion collides with neutral target atoms. For a fixed impact velocity (v{sub p}=23 a.u. ) , but using various targets from He to Xe, a range from the perturbative regime to the strong interaction regime has been investigated. Double excitation cross sections are found to be well reproduced by an independent electron model. First measurements of capture-ionization cross sections are also reported and show the importance of this often-neglected process. {copyright} {ital 1997} {ital The American Physical Society}

Vernhet, D.; Rozet, J.P.; Wohrer, K.; Chetioui, A. [GPS (CNRS UMR 75-88), Universites Paris 7 et 6, 2 Place Jussieu, 75251 Paris Cedex 05 (France); Adoui, L.; Cassimi, A.; Grandin, J.P.; Ramillon, J.M. [CIRIL (UMR N11 CEA/CNRS), Rue Claude Bloch, B.P.5133, 14070 Caen Cedex 5 (France); Cornille, M. [DARC, Observatoire de Paris Meudon, Place Jansen, 92195 Meudon Cedex (France); Stephan, C. [NIM, IPN, Universite Paris 11, B.P.N1, 91405 Orsay Cedex (France)

1997-11-01

258

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

259

High-speed collision  

Microsoft Academic Search

This paper reviews the theoretical and experimental studies performed at the A.M. Lavrent'ev Hydrodynamics Institute of the Academy of Sciences of the USSR in high-speed collision processes and the high-speed interactions of materials with various barriers. Collisions with semi-infinite and finite-thickness obstacles were modeled and the protective properties of a thin screen were evaluated. Impact and shock deformation and crater

L. A. Merzhievskii; V. M. Titov

1988-01-01

260

Limits on a lepton number violating process in e/sup +/e/sup -/ collisions  

SciTech Connect

If a new hypothetical particle induces a lepton number violating process, it could also affect e/sup +/e/sup -/ ..-->.. ..mu../sup +/..mu../sup -/ and /tau//sup +//tau//sup -/ through its t-channel exchange. A fit of the measured cross sections and forward-backward asymmetries at PEP and PETRA yields the 90% CL limits on the coupling of the particle: G/sub e..mu../ < 0.119G/sub F/ and G/sub er/ < 0.085G/sub F/, where G/sub F/ is the Fermi coupling constant. These limits exclude certain regions of couplings allowed by other lepton number violation searches. 6 refs., 2 figs., 1 tab.

Gan, K.K.

1988-10-01

261

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

SciTech Connect

The energy and angular dependence of double differential cross sections d{sup 2{sigma}}/d{Omega}dE were measured for p,d,t, {sup 3,4,6}He, {sup 6,7,8}Li, {sup 7,9,10}Be, {sup 10,11}B, 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 {approx}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 d{sup 2{sigma}}/d{Omega}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.; Kistryn, M.; Kliczewski, St.; Kozik, E. [H. Niewodniczanski Institute of Nuclear Physics PAN, Radzikowskiego 152, PL-31342 Krakow (Poland); Fidelus, M.; Jarczyk, L.; Kamys, B.; Kistryn, St.; Kowalczyk, A.; Magiera, A.; Rudy, Z.; Wojciechowski, M. [M. Smoluchowski Institute of Physics, Jagellonian University, Reymonta 4, PL-30059 Krakow (Poland); Filges, D.; Goldenbaum, F.; Machner, H. [Institut fuer Kernphysik, Forschungszentrum Juelich, D-52425 Juelich (Germany); Hodde, H. [Institut fuer Strahlen- und Kernphysik, Bonn University, D-53121 Bonn (Germany); Kulessa, P.; Pysz, K.; Siudak, R. [H. Niewodniczanski Institute of Nuclear Physics PAN, Radzikowskiego 152, PL-31342 Krakow (Poland); Institut fuer Kernphysik, Forschungszentrum Juelich, D-52425 Juelich (Germany); Piskor-Ignatowicz, B. [M. Smoluchowski Institute of Physics, Jagellonian University, Reymonta 4, PL-30059 Krakow (Poland); Institut fuer Kernphysik, Forschungszentrum Juelich, D-52425 Juelich (Germany)

2010-09-15

262

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

263

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

264

The Johari-Goldstein Process of a Model Diatomic Molecular System in the Supercooled State  

Microsoft Academic Search

Combining the intermediate scattering function of the center of mass and that of individual atoms obtained by molecular dynamics simulation, we devise a method of analyzing the contribution of the internal motion in the relaxation process. We apply the analysis to the relaxation process of a model diatomic molecular system in the supercooled state and show that the rotational motion

Mariko Higuchi; Takashi Odagaki

2002-01-01

265

Study of ab initio molecular data for inelastic and reactive collisions involving the H{sub 3}{sup +} quasimolecule  

SciTech Connect

The lowest two ab initio potential energy surfaces (PES), and the corresponding nonadiabatic couplings between them, have been obtained for the H{sub 3}{sup +} system; the molecular data are compared to those calculated with the diatomic in molecules (DIM) method. The form of the couplings is discussed in terms of the topology of the molecular structure of the triatomic. The method of Baer is employed to generate 'diabatic' states and the residual nonadiabatic couplings are calculated. The ab initio results for these are markedly different from the corresponding DIM data, and show the need to consider the third PES.

Barragan, P.; Errea, L.F.; Macias, A.; Mendez, L.; Rabadan, I.; Riera, A.; Lucas, J.M.; Aguilar, A. [Laboratorio Asociado al CIEMAT de Fisica Atomica y Molecular en Plasmas de Fusion, Departamento de Quimica, Universidad Autonoma de Madrid, 28049-Madrid (Spain); Departament de Quimica Fisica, Universitat de Barcelona, CeRQT-PCB. C/ Marti i Franques, 1. 08028-Barcelona (Spain)

2004-12-15

266

Shell effect on stabilization processes following multi-electron transfer in slow Ar q +–Ar ( q = 6–9, 11) collisions  

Microsoft Academic Search

We experimentally investigate the shell effect on the stabilization processes following the multi-electron transfer in slow collisions of Arq+–Ar (q=6–9, 11). The relative cross-section ratios of multi-electron transfer and of the subsequent stabilization with respect to single-electron capture are measured meanwhile compared with the theoretical results predicted by the classical over-barrier model. Our result indicates that the multi-electron transfer is

Rongchun Lu; Deyang Yu; Caojie Shao; Fangfang Ruan; Yingli Xue; Xiaohong Cai

2010-01-01

267

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 (1 MeV/amu) over a range of projectile charge states (q = 1-9,14,20). Preliminary results indicate that for a highly charged F{sup 9+} projectile the DI/SI and IE/SI ratios are 6.8% and 24.7%, respectively, a large increase from the ratios of 0.13% and 1.95%, respectively, for H{sup +} projectiles. For low charge states, the DI/SI is negligible relative to the IE/SI ratio, while for more highly charged projectiles the DI/SI ratio becomes comparable to the IE/SI ratio. This indicates that double-ionization increases much more rapidly with projectile charge than ionization-excitation.

Wells, E.; Ben-Itzhak, I.; Carnes, K.D.; Krishnamurthi, V.

1996-05-01

268

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

269

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

270

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

271

Control of ultracold atomic collisions with resonant light  

NASA Astrophysics Data System (ADS)

We present a detailed semianalytic theory of cold atom collisions in the presence of one or more laser fields tuned near molecular resonances. This theory expands upon a previous development(J. L. Bohn and P. S. Julienne, Phys. Rev. A 54), R4367 (1996). by accounting explicitly for light-induced shifts and line broadenings apparent at high laser intensities. We use this theory to determine realistic laser settings for guiding the outcome of cold collision processes. One aspect of such control is the production of ensembles of ultracold molecules, which can then be trapped in FORT experiments.

Bohn, John L.; Julienne, Paul S.

1997-04-01

272

The freezing process of small lipid vesicles at molecular resolution  

Microsoft Academic Search

At present very little is known about the kinetic barriers which a small vesicle will face during the transformation from the liquid-crystalline to the gel phase, and what the structure of frozen vesicles looks like at the molecular level. The formation of gel domains in the strongly curved bilayer of a small vesicle seems almost paradoxical and is expected to

H. Jelger Risselada; Siewert J. Marrink

2009-01-01

273

Radiative Collisions between Molecular and Electron Beams, V. Angular Momentum Distributions of CH* Separating from Simple Organic Molecules  

Microsoft Academic Search

Observations have been done of electron bombardments of the C2H2, CH2O and CH3OH molecular jets in vacuum. The free radical CH*(B2Sigma-) always shows a normal distribution of angular momentum. This experimental result is entirely different from the previous reports on the free radical OH*(2Sigma+) splitting from H2O or H2O2. For instance, the distribution curve for CH* from C2H2 shows its

Tadao Horie; Takayuki Nagura; Masamoto Otsuka

1960-01-01

274

Energy transfer, scattering and dissociation in ion atom collisions: CO2+/Ar  

NASA Astrophysics Data System (ADS)

Collision-induced dissociation (CID) and nondissociative scattering of CO2+ ions following collision with a supersonic molecular beam of argon has been studied at low collision energies by crossed-beam tandem mass spectrometry. The center-of-mass (c.m.) velocity contour diagram at 23.8 eV collision energy showed that the scattering of CO2+ ions have two energetically distinct components: elastic collisions at smaller angles in which momentum exchange apparently involves Ar/O repulsive interactions and inelastic collisions at larger angles in which internally excited CO2+ ions recoil from the two-body CO2+/Ar c.m. The most probable energy transfer in the inelastic process is 4.8+/-0.5 eV, just below the lowest dissociation threshold. The CID processes at the same collision energy leading to fragment ions, CO+ and O+, show similar characteristics. CID occurs via both spectator knock-out and two-body collisions that result into two distinct scattering patterns. The energy transfers for the two pathways for O+ fragment ions are 4.7+/-0.5 eV for knock-out collisions and 7.6+/-0.5 eV for the two-body inelastic recoil collision mechanism. It is suggested that CID for O+ via the latter process must involve an electronic state higher than the C state and proceed via curve crossing. Energy transfers for CO+ fragment ions via the two corresponding processes are 5.7+/-0.5 eV and 7.6+/-0.5 eV, respectively, clearly suggesting similar mechanisms for energy transfer and dissociation for this CID process also. It is suggested that the bent geometry of the CO2+ ions may be an important factor in promoting two distinct mechanisms.

Tosh, Ronald E.; Shukla, Anil K.; Futrell, Jean H.

2001-02-01

275

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.

2013-10-01

276

Molecular mechanisms of olfactory processing in the mammalian olfactory epithelium.  

PubMed

In humans the sense of smell plays an important role in protecting the organism from external hazards like fire, gas or spoiled food, in the consumption of food and in chemical communication with one another. Increasingly, the study of human olfaction is relevant to a number of medical problems connected with olfactory dysfunction, i.e. neurodegenerative diseases which are also manifested in the olfactory epithelium. Although much is known about behavioral aspects and neuronal activities elicited by odorants, we still cannot clearly describe the molecular mechanisms by which odor stimuli are transformed into an electrical cell signal. Here recent progress in our knowledge about the molecular elements of the transduction machinery are reviewed. It can help to understand the general principles underlying our sense of smell. PMID:8883103

Hatt, H

277

Molecular Ion Dissociation Processes in a Partially Cooled Electrostatic Trap  

SciTech Connect

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 Randy [ORNL; Bannister, Mark E [ORNL; Deng, Shihu [ORNL; FogleJr, Michael R [Auburn University, Auburn, Alabama; Thomas, R. D. [Stockholm University, Stockholm, Sweden

2011-01-01

278

The determinants of the molecular substitution process in turtles.  

PubMed

Neutral rates of molecular evolution vary across species, and this variation has been shown to be related to biological traits. One of the first patterns to be observed in vertebrates has been an inverse relationship between body mass (BM) and substitution rates. The effects of three major life-history traits (LHT) that covary with BM - metabolic rate, generation time and longevity (LON) - have been invoked to explain this relationship. However, most of the theoretical and empirical evidence supporting this relationship comes from endothermic vertebrates, that is, mammals and birds, in which the environmental conditions, especially temperature, do not have a direct impact on cellular and molecular biology. We analysed the variations in mitochondrial and nuclear rates of synonymous substitution across 224 turtle species and examined their correlation with two LHT (LON and BM) and two environmental variables [latitude (LAT) and habitat]. Our analyses indicate that in turtles, neutral rates of molecular evolution are hardly correlated with LON or BM. Rather, both the mitochondrial and nuclear substitution rates are significantly correlated with LAT - faster evolution in the tropics - and especially so for aquatic species. These results question the generality of the relationships reported in mammals and birds and suggest that environmental factors might be the strongest determinants of the mutation rate in ectotherms. PMID:23176666

Lourenço, J M; Glémin, S; Chiari, Y; Galtier, N

2012-11-23

279

Projectile angular-differential cross sections for electron transfer processes in ion-helium collisions: Evidence for the applicability of the independent electron model  

SciTech Connect

The electron dynamics in p-He and He{sup 2+}-He collisions have been investigated on the level of the independent electron model by using the two-center basis generator method. Projectile angular-differential cross sections for various one- and two-electron processes involving electron transfer have been calculated with the eikonal approximation. Overall, the calculated cross sections are in good agreement with the most recent experimental cold target recoil ion momentum spectroscopy data taken at impact energies in the range from 40 to 630 keV/amu. This demonstrates, somewhat surprisingly, that electron correlations play but a minor role for the processes and the energies considered.

Zapukhlyak, Myroslav; Kirchner, Tom [Max Planck Institute for the Physics of Complex Systems, D-01187 Dresden (Germany); Department of Physics and Astronomy, York University, Toronto, Ontario, M3J 1P3 (Canada)

2009-12-15

280

Characterization of molecular change of heavy oil under mild thermal processing using FT-IR spectroscopy  

Microsoft Academic Search

In order to quickly and economically obtain the information of molecular changes occurring in heavy oils during thermal processing, simulated mixtures of heavy oils and their pyrolyzed products were prepared from four model compounds, i.e., naphthalene, tetralin, decalin, and n-heptane. FT-IR absorption characteristics and average molecular parameters of the mixtures were correlated; the molecular parameters included the number ratio of

Ai-jun GUO; Zhi-hui REN; Ling-yan TIAN; Zong-xian WANG

2007-01-01

281

Molecular beam studies of reaction dynamics  

Microsoft Academic Search

The major thrust of this research project is to elucidate detailed dynamics of simple reactions that are theoretically important and to unravel the mechanism of complex chemical reactions or photochemical processes that play important roles in many macroscopic processes. Molecular beams of reactants are used to study individual reactive encounters between molecules or to monitor photodissociation events in a collision-free

1990-01-01

282

Designing of Photochemical Hole Burning Materials: Burning Process in Hydrogen Bonding and Proton Transfer Molecular System  

Microsoft Academic Search

The burning process of persistent spectral holes in quinizarin and its hydroxy derivatives is investigated from the viewpoint of hydrogen bonding and proton transfer molecular systems. Correlations among molecular structure, electronic structure and hole forming ability are substantial. A possible underlying mechanism involving diabatic crossing of the ground state is proposed and a close comparison to that in free-base porphyrin

Toshiro Tani; Youichi Sakakibara

1992-01-01

283

Dehydrogenation Processes and Molecular Clusters in Mass Spectra of Organometallic and Coordination Compounds  

Microsoft Academic Search

A method for the calculation of components from the complex molecular pattern is proposed. The modelling of molecular ion region in mass spectrum is applied to cases where for detection of the dehydrogenation processes effects such as losses of protons, hydrogen radicals or hydrogen molecules may occur. The parts of (M?H) and (M?2H) bands are determined as components of the

Andrzej J. Goraczko; Jacek A. Szymura

2000-01-01

284

Thermodynamics of irreversible processes and derivation of a system of differential equations for molecular transfer  

Microsoft Academic Search

On the basis of the linear laws of the thermodynamics of irreversible processes and the law of conservation of matter, a system of differential equations is derived for molecular transfer in the presence of n interrelated flows of generalized charges.

P. V. Tsoi

1965-01-01

285

Bibliography of Atomic and Molecular Processes. Volume 1, 1978-1981.  

National Technical Information Service (NTIS)

This annotated bibliography lists 10,676 works on atomic and molecular processes reported in publications dated 1978-1981. Sources include scientific journals, conference proceedings, and books. Each entry is designated by one or more of the 114 categorie...

C. F. Barnett D. H. Crandall B. J. Farmer

1982-01-01

286

Ultrafast molecular processes mapped by femtosecond x-ray diffraction  

NASA Astrophysics Data System (ADS)

X-ray diffraction with a femtosecond time resolution allows for mapping photoinduced structural dynamics on the length scale of a chemical bond and in the time domain of atomic and molecular motion. In a pump-probe approach, a femtosecond excitation pulse induces structural changes which are probed by diffracting a femtosecond hard x-ray pulse from the excited sample. The transient angular positions and intensities of diffraction peaks give insight into the momentary atomic or molecular positions and into the distribution of electronic charge density. The simultaneous measurement of changes on different diffraction peaks is essential for determining atom positions and charge density maps with high accuracy. Recent progress in the generation of ultrashort hard x-ray pulses (Cu K?, wavelength ?=0.154 nm) in laser-driven plasma sources has led to the implementation of the powder diffraction and the rotating crystal method with a time resolution of 100 fs. In this contribution, we report new results from powder diffraction studies of molecular materials. A first series of experiments gives evidence of a so far unknown concerted transfer of electrons and protons in ammonium sulfate [(NH4)2SO4], a centrosymmetric structure. Charge transfer from the sulfate groups results in the sub-100 fs generation of a confined electron channel along the c-axis of the unit cell which is stabilized by transferring protons from the adjacent ammonium groups into the channel. Time-dependent charge density maps display a periodic modulation of the channel's charge density by low-frequency lattice motions with a concerted electron and proton motion between the channel and the initial proton binding site. A second study addresses atomic rearrangements and charge dislocations in the non-centrosymmetric potassium dihydrogen phosphate [KH2PO4, KDP]. Photoexcitation generates coherent low-frequency motions along the LO and TO phonon coordinates, leaving the average atomic positions unchanged. The time-dependent maps of electron density demonstrate a concomitant oscillatory relocation of electronic charge with a spatial amplitude of the order of a chemical bond length, two orders of magnitude larger than the vibrational amplitudes. The coherent phonon motions drive the charge relocation, similar to a soft mode driven phase transition between the ferro- and paraelectric phase of KDP.

Elsaesser, Thomas

2012-02-01

287

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

288

Ab initio molecular dynamics simulation on the formation process of He@C?? synthesized by explosion.  

PubMed

The applications of endohedral non-metallic fullerenes are limited by their low production rate. Recently, an explosive method developed in our group shows promise to prepare He@C?? at fairly high yield, but the mechanism of He inserting into C?? cage at explosive conditions was not clear. Here, ab initio molecular dynamics analysis has been used to simulate the collision between C?? molecules at high-temperature and high-pressure induced by explosion. The results show that defects formed on the fullerene cage by collidsion can effectively decrease the reaction barrier for the insertion of He into C??, and the self-healing capability of the defects was also observed. PMID:23296568

Li, Jian-Ying; Liu, Li-Min; Jin, Bo; Liang, Hua; Yu, Hai-Jun; Zhang, Hong-Chang; Chu, Shi-Jin; Peng, Ru-Fang

2013-01-08

289

Electron-Driven Molecular Processes Induced in Biological Systems by Electromagnetic and Other Ionizing Sources  

NASA Astrophysics Data System (ADS)

We describe, and analyse in some detail, a selection of the most recent theoretical and computational models which attempt to explain, at the molecular level, the dynamics of metastable negative ion formation from biological molecules in the gas-phase. Such Transient Negative Ions (TNIs) are related to the nanoscopic nuclear dynamics presiding over the occurrence of irreversible damage in the biosystems through the many possible pathways leading to dissociative attachment decay of the initial TNI. We will review the theoretical approach we adopted to study electron-molecule collision as applied to systems of biological interest. The connection between the spatial symmetry of the metastable anion and its role during the dissociative electron attachment event is also discussed and analysed through several examples.

Baccarelli, I.; Gianturco, F. A.; Grandi, A.; Lucchese, R. R.; Sanna, N.

290

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.

291

The influence of electron-electron interaction on inner-shell excitation processes in heavy-ion collisions  

Microsoft Academic Search

The authors present calculations of electron excitation rates in heavy-ion collisions, in which the electron-electron interaction is treated within a relativistic self-consistent field approach. In comparison with earlier calculations neglecting electron shielding, the authors obtain increased probabilities for K-hole and delta -electron production, whereas the total positron yield decreases. Computed probabilities are compared with available experimental data.

T. H. J. de Reus; J. Reinhardt; B. Muller; W. Greiner; G. Soff; U. Muller

1984-01-01

292

Experimental test of higher-order electron-capture processes in collisions of fast protons with atomic hydrogen  

NASA Astrophysics Data System (ADS)

We present measurements of the angular distribution of fast hydrogen atoms formed by electron capture of 2.8- and 5.0-MeV protons in atomic hydrogen. In the angular region of the Thomas peak (0.47 mrad) the experimental results obtained with this pure three-body collision system are in reasonable agreement with a strong potential Born calculation and the impulse approximation, but not with other higher-order theories.

Vogt, H.; Schuch, R.; Justiniano, E.; Schulz, M.; Schwab, W.

1986-11-01

293

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

294

Protein Molecular Structures, Protein SubFractions, and Protein Availability Affected by Heat Processing: A Review  

SciTech Connect

The utilization and availability of protein depended on the types of protein and their specific susceptibility to enzymatic hydrolysis (inhibitory activities) in the gastrointestine and was highly associated with protein molecular structures. Studying internal protein structure and protein subfraction profiles leaded to an understanding of the components that make up a whole protein. An understanding of the molecular structure of the whole protein was often vital to understanding its digestive behavior and nutritive value in animals. In this review, recently obtained information on protein molecular structural effects of heat processing was reviewed, in relation to protein characteristics affecting digestive behavior and nutrient utilization and availability. The emphasis of this review was on (1) using the newly advanced synchrotron technology (S-FTIR) as a novel approach to reveal protein molecular chemistry affected by heat processing within intact plant tissues; (2) revealing the effects of heat processing on the profile changes of protein subfractions associated with digestive behaviors and kinetics manipulated by heat processing; (3) prediction of the changes of protein availability and supply after heat processing, using the advanced DVE/OEB and NRC-2001 models, and (4) obtaining information on optimal processing conditions of protein as intestinal protein source to achieve target values for potential high net absorbable protein in the small intestine. The information described in this article may give better insight in the mechanisms involved and the intrinsic protein molecular structural changes occurring upon processing.

Yu,P.

2007-01-01

295

Collisions Between Laser-Cooled Atoms  

Microsoft Academic Search

Collisions between laser-cooled atoms have a number of remarkable features. The exceptionally low temperature in laser-cooled clouds (<100 muK) means that the collision dynamics are not only sensitive to very long-range interatomic forces (even as modified by tiny hyperfine interactions), but also strongly depend on multiple light emission and absorption processes during the course of the collision. The light-induced collision

Thad Walker

1997-01-01

296

Electronic quenching of OH A 2?+ radicals in single collision events with molecular hydrogen: Quantum state distribution of the OH X 2? products  

NASA Astrophysics Data System (ADS)

We report a combined experimental and theoretical investigation of the nonreactive quenching channel resulting from electronic quenching of OH A 2?+ by molecular hydrogen. The experiments utilize a pump-probe scheme to determine the OH X 2? population distribution following collisional quenching in a pulsed supersonic expansion. The pump laser excites OH A 2?+ (?'=0, N'=0), which has a significantly reduced fluorescence lifetime due to quenching by H2. The probe laser monitors the OH X 2? (?'', N'') population via laser-induced fluorescence on various A-X transitions under single collision conditions. The experiments reveal a high degree of rotational excitation (N'') of the quenched OH X 2? products observed in ?''=1 and 2 as well as a pronounced propensity for quenching into the ?(A') ?-doublet level. These experiments have been supplemented by extensive multireference, configuration-interaction calculations aimed at exploring the topology of the relevant potential energy surfaces. Electronic quenching of OH A 2?+ by H2 proceeds through conical intersections between two potentials of A' reflection symmetry (in planar geometry) that correlate with the electronically excited A 2?+ and ground X 2? states of OH. The conical intersections occur in high-symmetry geometries, in which the O side of OH points toward H2. Corroborating and extending earlier work of Hoffman and Yarkony [J. Chem. Phys. 113, 10091 (2000)], these calculations reveal a steep gradient away from the OH-H2 conical intersection as a function of both the OH orientation and interfragment distance. The former will give rise to a high degree of OH rotational excitation, as observed for the quenched OH X 2? products.

Cleary, Patricia A.; Dempsey, Logan P.; Murray, Craig; Lester, Marsha I.; K?os, Jacek; Alexander, Millard H.

2007-05-01

297

Electron-Biomolecule Collision Studies Using the Schwinger Multichannel Method  

NASA Astrophysics Data System (ADS)

We review applications of the Schwinger multichannel method to low-energy electron collisions with polyatomic molecules of biological interest. After briefly describing the method, its implementation, and its strengths and limitations, we turn to a discussion of specific molecular systems, with an emphasis on studies related to radiation damage to DNA mediated by secondary electrons. Throughout, we situate our results in the context of calculated and experimental data on electron scattering, dissociative attachment, and other relevant processes.

Winstead, Carl; McKoy, Vincent

298

Final Report, "Molecular Design of Hydrocarbon Oxidation Catalytic Processes"  

SciTech Connect

The main goal of this project had been to use model systems to correlate selectivities in partial oxidation catalysis with the presence of specific sites on the surface of the catalyst. Extensive work was performed this year on characterizing oxygen-treated nickel surfaces by chemical means. Specifically, the surface chemistry of ammonia coadsorbed with atomic oxygen on Ni(110) single-crystal surfaces was studied by temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). It was determined that at intermediate oxygen coverages direct ammonia adsorption on nickel sites is suppressed, but a new high-temperature reaction regime is generated at 400 K where NHx surface fragments are rehydrogenated concurrently with the production of water and molecular hydrogen. The extensive isotope scrambling and hydrogen transfer seen from nitrogen- to oxygen-containing surface intermediates, and the optimum yields seen for this 400 K state at intermediate oxygen coverages, strongly suggest the direct interaction of the adsorbed ammonia with oxygen atoms at the end of the –Ni–O- rows that form upon reconstruction of the surface. Hydrogen transfer between ammonia and oxygen appears to take place directly via hydrogen bonding, and to be reversible but biased towards water formation. An equilibrium is reached between the produced water and the reacting surface oxygen and hydrogen. The strong influence of the OH surface groups on the thermal chemistry of the adsorbed ammonia was interpreted in terms of the adsorbing geometry of the OH groups on the surface, and of hydrogen bonding between adsorbed OH and NH3 species. In terms of alcohol reactivity, the adsorption of 2-iodoethanol, a precursor for the preparation of 2-hydroxyethyl and oxametallacycle surface species, was found to lead to two configurations involving either just the iodine atom or both iodine and hydroxyl ends of the molecule. A complex chemical behavior starts around 140 K with the production of small amounts of ethylene and water, most likely via the concerted decomposition or disproportionation of the adsorbed molecular species. The bulk of the 2-iodoethanol decomposes at about 150 K via an initial carbon-iodine scission to form –O(H)CH2CH2– (~80%) and 2-hydroxyethyl (~20%) intermediates. Two competing reactions are involved with the subsequent conversion of the 2-hydroxyethyl species around 160 K, a reductive elimination with surface hydrogen to yield ethanol, and a ?-H elimination to surface vinyl alcohol. The –O(H)CH2CH2–, on the other hand, dehydrogenates to a –OCH2CH2– oxametallacycle species about the same temperature. Both 2-hydroxyethyl and oxametallacycle species tautomerize to acetaldehyde, around 210 K and above 250 K, respectively, and some of that acetaldehyde desorbs while the rest decomposes to hydrogen and carbon monoxide. We contend that a better understanding of the surface chemistry of oxygen-containing surfaces can lead to better selectivities in catalysis. This is arguably the most important issue in the field of catalysis in the near future, and one that impacts several technologies of interest to DOE such as the manufacturing of speciality chemicals and the control and removal of pollutants. Additional work was performed on the characterization of the chemistry of methyl and methylene adsorbed species on oxygen-treated nickel surfaces. Complex chemistry was observed involving not only hydrogenation and dehydrogenation steps, but also C-C couplings and methylene insertions to produce heavier hydrocarbons, and oxygen insertion reactions that yield oxygenates. Finally, a dual titration technique employing xenon and a chemically sensitive probe was developed to identify minority catalytic sites on oxide surfaces. In the case of oxygen-treated Ni(110) single crystals, it was found that both hydrogen transfer with adsorbed water or ammonia and certain hydrocarbon hydrogenation reactions take place at the end of the –Ni–O rows that form in this system. Carbon and nitrogen oxides, on the other hand, display no pre

Professor Francisco Zaera

2007-08-09

299

Multiple electron transfer in slow collisions of highly charged ions and atoms  

NASA Astrophysics Data System (ADS)

Multi-electron transfer processes in slow collisions Arq++Ar (/q=5,...,10) have been studied theoretically by means of a molecular dynamics approach. We discuss the electron transfer dynamics, in particular with respect to the assumptions made in overbarrier models. Furthermore, absolute cross-sections are defined and compared to experimental data.

Zarour, Bilel; Saalmann, Ulf

2003-05-01

300

Multiple electron transfer in slow collisions of highly charged ions and atoms  

Microsoft Academic Search

Multi-electron transfer processes in slow collisions Arq++Ar (q=5,…,10) have been studied theoretically by means of a molecular dynamics approach. We discuss the electron transfer dynamics, in particular with respect to the assumptions made in overbarrier models. Furthermore, absolute cross-sections are defined and compared to experimental data.

Bilel Zarour; Ulf Saalmann

2003-01-01

301

Theory of atomic collisions at ultracold temperatures  

SciTech Connect

This paper outlines key problems in the theory of atomic collisions at ultracold temperatures. Features associated with the unusual energy time and distance scales encountered in ultracold collisions are described. The molecular physics of excited plus ground state alkali dimers is examined. A quasistatic model is developed to describe collision rates between normal and ultracold temperatures. Mechanisms are proposed for the very different associative ionization rates observed in an optical trap and in optical molasses. (AIP)

Julienne, P.S.; Heather, R. (Molecular Physics Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)); Vigue, J. (Laboratoire de Spectroscopie Hertzienne de l'Ecole Normale Superieure (France) Laboratoire Associe au Centre National de la Recherche Scientifique et a l'Universite Pierre et Marie Curie (France))

1991-08-05

302

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

2001-02-14

303

Real-time investigation of nucleic acids phosphorylation process using molecular beacons  

Microsoft Academic Search

Phosphorylation of nucleic acids is an indispensable process to repair strand interruption of nucleic acids. We have studied the process of phosphoryla- tion using molecular beacon (MB) DNA probes in real-time and with high selectivity. The MB employed in this method is devised to sense the product of a 'phosphorylation-ligation' coupled enzyme reaction. Compared with the current assays, this novel

Zhiwen Tang; Kemin Wang; Weihong Tan; Changbei Ma; Jun Li; Lingfeng Liu; Qiuping Guo; Xiangxian Meng

2005-01-01

304

Ultrasmall volume molecular isothermal amplification in microfluidic chip with advanced surface processing  

Microsoft Academic Search

In this paper, we developed a metal micro-fluidic chip with advanced surface processing for ultra-small volume molecular isothermal amplification. This method takes advantages of the nucleic acid amplification with good stability and consistency, high sensitivity about 31 genomic DNA copies and bacteria specific gene identification. Based on the advanced surface processing, the bioreaction assays of nucleic acid amplification was dropped

Guoliang Huang; Li Ma; Xiaoyong Yang; Xu Yang

2011-01-01

305

Nitrite transport to the chloroplast in Chlamydomonas reinhardtii: molecular evidence for a regulated process  

Microsoft Academic Search

Nitrite transport to the chloroplast is not a well documented process in spite of being a central step in the nitrate assimilation pathway. The lack of molecular evidence, as well as the easy diffusion of nitrite through biological membranes, have made this physiological process difficult to understand in plant nutrition. The aim of this review is to illustrate that nitrite

Aurora Galvan; Jesus Rexach; Vicente Mariscal; Emilio Fernandez

2010-01-01

306

Antihydrogen - Hydrogen Collisions  

NASA Astrophysics Data System (ADS)

Recently, both the ATRAP (G. Gabrielse et al., PRL 89 213404, (2002)) and ATHENA (M. Amoretti et al., Nature 419 (2002)) experiments at the CERN anti-proton decelerator have successfully created and detected low temperature antihydrogen atoms in the laboratory. Present efforts are directed toward the goal of trapping and cooling the antihydrogen into the ultra-cold regime in order to enable tests, of unprecedented accuracy, for some of the most fundamental symmetries of matter and anti-matter. Several methods for cooling have been proposed. Here we discuss the feasibility of cooling antihydrogen via its contact with ultra-cold matter, in particular hydrogen. The cooling efficiency is determined by the collision properties of this system. Annihilation of the leptons, the proton and antiproton, as well as re-arrangements into protonium and positronium during a collision conspire to limit the utility of sympathetic cooling. In this talk we will discuss the various collision processes and present calculated collision data in order to assess the viability of sympathetic cooling of antimatter in contact with matter. We will also discuss properties of the novel, unstable, exotic molecule (B. Zygelman et al., PRA 69, 042715 (2004)) that has been predicted as a possible by-product in a collision of antihydrogen with an hydrogen atom. Collaborators in this study include, A. Dalgarno, P. Froelich, S. Jonsell and A. Saenz. Partial support was provided by an NSF grant to the Harvard-MIT CUA where the author was a Visiting Scientist.

Zygelman, Bernard

2005-05-01

307

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

308

FAST TRACK COMMUNICATION: Oscillation structures in elastic and electron capture cross sections for H+-H collisions in Debye plasmas  

NASA Astrophysics Data System (ADS)

We find that the number of vibrational states in the ground potential of a H2+ molecular ion embedded in the Debye plasma and the number of Regge oscillations in the resonant charge transfer cross section of the H+ + H collision system in the plasma are quasi-conserved when the Debye radius D is larger than 1.4a0. The elastic and resonant charge transfer processes in the H+ + H collision have been studied in the 0.1 meV-100 eV collision energy range for a wide range of Debye radii using a highly accurate calculation based on the modified ab initio multireference configuration interaction code. Remarkable plasma screening effects have been found in both the molecular structure and the collision dynamics of this system. Shape resonances, Regge and glory oscillations have been found in the integral cross sections in the considered energy range even for strong interaction screening, showing their ubiquitous nature.

Wu, Y.; Wang, J. G.; Krstic, P. S.; Janev, R. K.

2010-10-01

309

Vibrationally resolved charge transfer for proton collisions with CO and H collisions with CO{sup +}  

SciTech Connect

Electron capture by protons following collisions with carbon monoxide, and the reverse process, is studied with a quantal molecular-orbital coupled-channel method utilizing the infinite order sudden approximation for collision energies between 0.5 and 1000 eV/u. The potential surfaces and couplings, computed with the multireference single- and double-excitation method for a range of H{sup +}-CO orientation angles and C-O separations, are adopted in the scattering calculations. Results including vibrationally resolved and orientation-angle-dependent cross sections are presented for a range of CO and CO{sup +} vibrational levels. Comparison with experiment is made where possible and the relevance of the reaction in astrophysics and atmospheric physics is discussed.

Lin, C. Y.; Stancil, P. C.; Li, Y.; Gu, J. P.; Liebermann, H. P.; Buenker, R. J.; Kimura, M. [Department of Physics and Astronomy and the Center for Simulational Physics, University of Georgia, Athens, Georgia 30602-2451 (United States); Fachbereich C-Mathematik und Naturwissenschaften, Bergische Universitaet Wuppertal, D-42097 Wuppertal (Germany); Graduate School of Sciences, Kyushu University, Fukuoka 812-8581 (Japan)

2007-07-15

310

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

311

Stochastic molecular dynamics study of trans-gauche isomerization processes in simple chain molecules  

NASA Astrophysics Data System (ADS)

Trans-gauche isomerization rates for n-butane, n-pentane, and n-decane are determined from a stochastic molecular dynamics calculation of the reactive fluxes. Analysis of the deviations of these rates from the transition state theory predictions shows that the transmission coefficients differ markedly from unity for all physically realizable conditions. The dependence of the transmission coefficient on the collision frequency or friction constant parameterizing the stochastic element is discussed. A comparison between the stochastic dynamics and a true Newtonian molecular dynamics simulation of n-butane in a simple liquid solvent indicates that the reactive flux correlation function is significantly different than would be predicted by the high friction noninertial theory first discussed long ago by Kramers. For longer chain molecules, the isomerization rates depend upon which particular torsional angle is considered, and upon the configurational state of the neighboring angles. This dependence is analyzed. Finally, calculations are presented which address certain questions concerning the use of holonomic constraints in the dynamics of alkane chains.

Montgomery, John A.; Holmgren, Stephen L.; Chandler, David

1980-10-01

312

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

313

Computational approaches to shed light on molecular mechanisms in biological processes  

PubMed Central

Computational approaches based on Molecular Dynamics simulations, Quantum Mechanical methods and 3D Quantitative Structure-Activity Relationships were employed by computational chemistry groups at the University of Milano-Bicocca to study biological processes at the molecular level. The paper reports the methodologies adopted and the results obtained on Aryl hydrocarbon Receptor and homologous PAS proteins mechanisms, the properties of prion protein peptides, the reaction pathway of hydrogenase and peroxidase enzymes and the defibrillogenic activity of tetracyclines.

Bonati, Laura; Bruschi, Maurizio; Cosentino, Ugo; De Gioia, Luca; Fantucci, Pier Carlo; Pandini, Alessandro; Papaleo, Elena; Pitea, Demetrio; Saracino, Gloria A.A.; Zampella, Giuseppe

2011-01-01

314

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

315

Collisional studies of gaseous molecular lasers. Technical report  

Microsoft Academic Search

Molecular collision studies at Princeton are reviewed. The areas of research involved are CO laser kinetics, global collision theory; quantum number scaling and the analysis of spectral line shapes; stochastic theory of molecular collisions; and vibration-rotation relaxation in molecular collisions.

Rabitz

1977-01-01

316

Shell effect on stabilization processes following multi-electron transfer in slow Arq+-Ar (q = 6-9, 11) collisions  

NASA Astrophysics Data System (ADS)

We experimentally investigate the shell effect on the stabilization processes following the multi-electron transfer in slow collisions of Arq+-Ar (q = 6-9, 11). The relative cross-section ratios of multi-electron transfer and of the subsequent stabilization with respect to single-electron capture are measured meanwhile compared with the theoretical results predicted by the classical over-barrier model. Our result indicates that the multi-electron transfer is dominant when the projectile charge is large and the subsequent stabilization shows a dramatic variation if the projectile L-shell configuration becomes open. It shows that the subsequent stabilization processes of multiply excited scattering ions have a strong dependence on the projectile shell.

Lu, Rongchun; Yu, Deyang; Shao, Caojie; Ruan, Fangfang; Xue, Yingli; Cai, Xiaohong

2010-09-01

317

Polarization and collision velocity dependence of associative ionization in cold Na(3 p)-Na(3 p) collisions  

NASA Astrophysics Data System (ADS)

We studied the polarization dependence of the associative ionization (AI) process Na(3 p) + Na(3 p) ? Na{2/+} at collision velocities between 100 and 700 m/s (5 and 200 K), using linearly and circularly polarized light for the excitation. We found that the polarization dependence varies strongly in the collision velocity range under study. At the high end of our scale preparation of both collision partners in the | m j |=1/2 substates yields the highest AI-rate, but at low velocities this ceases being so: the polarization dependence becomes less pronounced and at the low end of our scale the preparation | m j 2|, | m j 2|=3/2, 1/2 is most effective. All cross sections increase strongly at lower velocities. Combined with previous work this maps the detailed polarization dependence from 100 2400 m/s (5-2500 K). From these total results it is concluded that at collision velocities ?500 m/s mainly one molecular potential curve leads to AI, but that this changes considerably at lower collision velocities. The findings are compared with recent theoretical results by Geltman, and we find large discrepancies.

Meijer, H. A. J.

1990-12-01

318

Invisible Collisions  

NSDL National Science Digital Library

This activity relates an elastic collision to the change in a satelliteâs or spacecraftâs speed and direction resulting from a planetary fly-by, often called a âgravity assistâ maneuver. Both hands-on and online interactive methods are used to explore these topics.

Hallau, Keri

2009-01-01

319

Continental collision  

NASA Astrophysics Data System (ADS)

Many models have been put forward to explain how the on-going collision between India and Asia has yielded the world's highest mountains and most expansive plateau, the Tibetan plateau. Now scientists from Dalhousie University in Halifax, Nova Scotia, Canada, writing in the journal Nature, propose a new solution:

320

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

321

Bibliography of atomic and molecular processes. Volume 1, 1978-1981  

SciTech Connect

This annotated bibliography lists 10,676 works on atomic and molecular processes reported in publications dated 1978-1981. 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 county 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.; Farmer, B.J. (comps.)

1982-10-01

322

Comparative molecular-orbital and atomic-orbital study of electron transfer and excitation in He sup + +Na(3 s ) collisions at energies of 0. 05 to 20 keV/amu  

SciTech Connect

Electron transfer and excitation in 0.05- to 20-keV/amu He{sup +}+Na(3{ital s}) collisions is studied theoretically within the close-coupling method with two-electron molecular- and atomic-orbital expansion basis sets. Results agree with the trend of other information on this system. Remaining discrepancies that are larger than those in similar contemporary studies of one-electron systems are discussed with reference to the convergence of this two-electron study. Results for the integral alignment parameter {ital A}{sub 20} are also presented as a guideline for future experimental study.

Fritsch, W. (Bereich Kern- und Strahlenphysik, Hahn-Meitner-Institut Berlin, D-1000 Berlin 39, West Germany (DE) Department of Physics, Rice University, Houston, Texas 77251 (USA)); Kimura, M. (Argonne National Laboratory, Argonne, Illinois 60439 Department of Physics, Rice University, Houston, Texas 77251 (USA)); Lane, N.F. (Department of Physics and Rice Quantum Institute, Rice University, Houston, Texas 77251 (USA))

1990-01-01

323

3D imaging of molecular-ion dissociation following slow impact with atomic targets  

NASA Astrophysics Data System (ADS)

Collisions between few keV molecular ions and atoms result primarily in collision-induced dissociation (CID) and dissociative capture (DC). The CID process can be a result of vibrational excitation; however, previous experimental efforts were unable to resolve the vibrational process from the competing electronic excitation, complicating comparison with theory. Employing coincidence 3D momentum imaging of the ion beam fragments and recoil ions, we are able to experimentally separate the vibrational (vCID) and electronic (eCID) processes, giving new insight into the vibrational mechanism. We investigate the influence of alignment and orientation of the molecule on eCID and vCID as well as other collision channels. In addition, we address the fate of the target atom following these collisions. A sample of results exploring CID and other processes occurring in such collisions will be presented.

Berry, Ben; Johnson, Nora G.; Wolff, Wania; Sayler, A. Max; Hathiramani, Dag; Maseberg, Jack W.; Fahrenholtz, Sam; Carnes, K. D.; Ben-Itzhak, I.

2012-06-01

324

On the fundamental processes in molecular electrical doping of organic semiconductors  

NASA Astrophysics Data System (ADS)

Integer electron transfer between organic semiconductors (OSCs) and strong donor/acceptor molecules has been regarded as the fundamental mechanism of molecular electrical doping. However, this process entails a number of consequences that are in conflict with well-established concepts of organic-semiconductor physics such as the charge-induced appearance of polaronic states within the fundamental gap of the OSC. Here, from the results of (time-dependent) density-functional theory calculations on prototypical OSC/dopant pairs, we derive a new and different picture for the mechanism of molecular electrical doping, which resolves these inconsistencies. Common doping-related observations are rationalized through intermolecular hybridization of OSC and dopant frontier molecular orbitals. Controlling the degree of this hybridization thus naturally emerges as a strategy for the design of improved molecular dopants in future high-performance organic electronic devices.

Heimel, Georg; Salzmann, Ingo; Koch, Norbert

2012-06-01

325

L-italic- and n-italic-changing processes in the Rydberg states of Li induced by thermal collisions with H/sub 2/, N/sub 2/, CO, and D/sub 2/  

SciTech Connect

Collisional transfers induced in the n-italic = 6--13 Li Rydberg states by H/sub 2/, N/sub 2/, and CO molecules have been experimentally studied in a heat-pipe oven. The l-italic-mixing cross sections have been deduced from the fast component of the population relaxations following pulsed laser excitation. The order of magnitude of these cross sections (10/sup 3/ A-circle/sup 2/) is well predicted by the existing theories. For large n-italic, the cross sections stay approximately constant. This can be partly explained by the influence of inelastic processes such as n-italic changing. In the particular case of H/sub 2/, n-italic-changing collisions have been identified by the fluorescence starting from the n-italic' = n-italic +- 1, n-italic-2 levels. Cross sections of the order of 10 A-circle/sup 2/ have been measured. The systematic study of the n-italic-changing cross sections as a function of the transferred energy shows some evidence of resonance phenomena corresponding to an energy exchange between the Rydberg electron and the molecular rotation. This effect is also observed when H/sub 2/ is replaced by D/sub 2/. These resonances are well described by the theory of Petitjean and Gounand based on the e-italic-quadrupolar interaction.

Dubreuil, B.; Harnafi, M.

1986-08-01

326

Nanoparticle collisions in the gas phase in the presence of singular contact potentials.  

PubMed

Collisional growth and ionization is commonplace for gas phase nanoparticles (i.e., in aerosols). Nanoparticle collisions in atmospheric pressure environments occur in the mass transfer transition regime, and further attractive singular contact potentials (which arise when modeling nanoparticles as condensed matter and for which the potential energy approaches -? when two entities contact) often have a non-negligible influence on collision processes. For these reasons collision rate calculations for nanoparticles in the gas phase are not straightforward. We use mean first passage time calculations to develop a simple relationship to determine the collision rate in the gas phase, accounting for the influences of both the transition regime and singular contact potentials (specifically the non-retarded van der Waals and image potentials). In the presented analysis, methods to determine the degree of enhancement in collision rate due to attractive singular potentials in the continuum (diffusive) regime, ?(C), and the degree of enhancement in the free molecular (ballistic) regime, ?(FM), are first reviewed. Accounting for these enhancement factors, with mean first passage time calculations it is found that the collision rate for gas phase nanoparticles with other gas phase entities can be determined from a relationship between the dimensionless collision rate coefficient, H, and the diffusive Knudsen number, Kn(D), i.e., the ratio of the mean collision persistence distance to the collision length scale. This coincides with the H(Kn(D)) relationship found to appropriately describe collisions between entities interacting via a hard-sphere potential, but with ?(C) and ?(FM) incorporated into the definitions of both H and Kn(D), respectively. The H(Kn(D)) relationship is compared to the predictions of flux matching theory, used prevalently in prior work for collision rate calculation, and through this comparison it is found that at high potential energy to thermal energy ratios, flux matching theory predictions underestimate the true collision rate. Finally, a series of experimental measurements of nanoparticle-nanoparticle collision rates are compared to the determined H(Kn(D)) expression, considering that nanoparticles interact via non-retarded van der Waals potentials. Very good agreement is found with collision rates inferred from experiments, with almost all measured values from four separate studies within 25% of model predictions. PMID:22897282

Ouyang, Hui; Gopalakrishnan, Ranganathan; Hogan, Christopher J

2012-08-14

327

Inelastic titanium-titanium collisions  

SciTech Connect

We have measured cold inelastic collisions between neutral ground-state titanium atoms: collisions that cause transitions between the different magnetic sublevels of the [3d{sup 2}4s{sup 2}]{sup 3}F{sub 2} ground state of {sup 50}Ti, as well as collisions that cause transitions between the fine-structure levels of the [3d{sup 2}4s{sup 2}]{sup 3}F{sub J} electronic ground state. Both processes occur with large rate coefficients, as would be expected from titanium's anisotropic electronic potential.

Lu, M.-J.; Singh, Vijay; Weinstein, Jonathan D. [Department of Physics, University of Nevada, Reno, Nevada 89557 (United States)

2009-05-15

328

Molecular dynamics simulation study of the ? - and ? -relaxation processes in a realistic model polymer  

NASA Astrophysics Data System (ADS)

Molecular dynamics simulations of a melt of freely rotating chains of 1,4-polybutadiene (FRC-PBD) have been performed over a wide range of temperature. Removal of the dihedral barriers in FRC-PBD allows for complete resolution of the Johari-Goldstein ? process from the primary ? process in the simulation time window. We find that relaxation in the ? regime occurs as the result of large-angle excursions of all backbone dihedrals. While during the ? process each dihedral visits all available states, the complete relaxation of torsional autocorrelation function ( ? process) occurs only when the polymer matrix shows significant motion and each dihedral populates all states with equilibrium probability.

Bedrov, Dmitry; Smith, Grant D.

2005-05-01

329

Molecular-Level Processes Governing the Interaction of Contaminants with Iron and Manganese Oxides - Final Report  

Microsoft Academic Search

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 structurally and compositionally well-defined mineral surfaces will lead to: (i) improved models of contaminant fate and transport in geochemical systems,

G. E. Brown Jr; S. A. Chambers

1999-01-01

330

Molecular photocatalytic processes. I. Kinetic description and conversion efficiency of light energy  

SciTech Connect

This paper investigates the kinetic models of photocatalytic processes. The efficiency and productivity of systems for converting solar energy my molecular photocatalytic systems are analyzed within the framework of a kinetic approach. Equations have been obtained which relate the energy conversion and productivity factors of the systems to the intensity of the light flux being absorbed and the concentrations of electron donors and acceptors.

Varfolomeev, S.D.

1985-11-01

331

Purification process of octacosanol extracts from rice bran wax by molecular distillation  

Microsoft Academic Search

Molecular distillation (MD) was used to increase the purity of octacosanol extracts from transesterified rice bran wax (RBW), and the effects of MD parameters on the purification process and efficiency were studied. The octacosanol content, triacontanol content and the ratio of octacosanol content (Co) to triacontanol content (Ct) in distillates and residues, the yields of distillates and residues, and split

Fang Chen; Zhengfu Wang; Guanghua Zhao; Xiaojun Liao; Tongyi Cai; Linyu Guo; Xiaosong Hu

2007-01-01

332

Processes for converting methane to higher molecular weight hydrocarbons via sulfur-containing intermediates  

SciTech Connect

This patent describes a process for converting methane to higher molecular weight hydrocarbons. The process comprising the steps of contacting methane with carbonyl sulfide in the presence of UV light under conditions sufficient to generate Ch/sub 3/SH; and contacting CH/sub 3/SH with a catalyst under conditions sufficient to produce hydrogen sulfide and a mixture of hydrocarbons having at least two carbon atoms.

Han, S.; Palermo, R.E.

1989-09-05

333

Using neural networks to construct models of the molecular beam epitaxy process  

Microsoft Academic Search

This paper presents the systematic characterization of the molecular beam epitaxy (MBE) process to quantitatively model the effects of process conditions on film qualities. A five-layer, undoped AlGaAs and InGaAs single quantum well structure grown on a GaAs substrate is designed and fabricated. Six input factors (time and temperature for oxide removal, substrate temperatures for AlGaAs and InGaAs layer growth,

Kyeong K. Lee; Terence Brown; Georgianna Dagnall; Robert Bicknell-Tassius; April Brown; Gary S. May

2000-01-01

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

2012-12-11

335

Chemodiversity and molecular plasticity: recognition processes as explored by property spaces.  

PubMed

In the last few years, a need to account for molecular flexibility in drug-design methodologies has emerged, even if the dynamic behavior of molecular properties is seldom made explicit. For a flexible molecule, it is indeed possible to compute different values for a given conformation-dependent property and the ensemble of such values defines a property space that can be used to describe its molecular variability; a most representative case is the lipophilicity space. In this review, a number of applications of lipophilicity space and other property spaces are presented, showing that this concept can be fruitfully exploited: to investigate the constraints exerted by media of different levels of structural organization, to examine processes of molecular recognition and binding at an atomic level, to derive informative descriptors to be included in quantitative structure--activity relationships and to analyze protein simulations extracting the relevant information. Much molecular information is neglected in the descriptors used by medicinal chemists, while the concept of property space can fill this gap by accounting for the often-disregarded dynamic behavior of both small ligands and biomacromolecules. Property space also introduces some innovative concepts such as molecular sensitivity and plasticity, which appear best suited to explore the ability of a molecule to adapt itself to the environment variously modulating its property and conformational profiles. Globally, such concepts can enhance our understanding of biological phenomena providing fruitful descriptors in drug-design and pharmaceutical sciences. PMID:21707401

Vistoli, Giulio; Pedretti, Alessandro; Testa, Bernard

2011-06-01

336

Higher-order processes in the electromagnetic production of electron-positron pairs in relativistic heavy-ion collisions  

SciTech Connect

We study higher-order effects in the electromagnetic production of electron-positron pairs in relativistic heavy-ion collisions. Treating the field of the heavy ions as an external field and neglecting the interaction among electrons and positrons, we show that the [ital N]-pair creation amplitude is the antisymmetrized product of [ital N] one-pair creation amplitudes and the vacuum amplitude. Neglecting contributions coming from exchange terms, we show that the total probability for [ital N] pairs is approximately a Poisson distribution. We investigate further the structure of the reduced one-pair amplitude, concentrating especially on multiple-particle corrections. We calculate the first of these corrections in second-order Magnus theory based on our previous result [Phys. Rev. A 49, 1584 (1994)] in the second-order Born approximation for impact parameter [ital b] zero. Explicit calculations show that the total probability is increased up to 10% by this correction for realistic collider parameters. The calculations can also be used to confirm the use of the Poisson distribution for the total probability.

Hencken, K.; Trautmann, D. (Institut fuer Theoretische Physik der Universitaet Basel, Klingelbergstrasse 82, 4056 Basel (Switzerland)); Baur, G. (Institut fuer Kernphysik (Theorie), Forschungszentrum Juelich, 52425 Juelich (Germany))

1995-02-01

337

Graphene hydrogenation by molecular hydrogen in the process of graphene oxide thermal reduction  

NASA Astrophysics Data System (ADS)

Thermal reduction in molecular hydrogen of the graphene oxide films has been studied by X-ray photoelectron spectroscopy using synchrotron radiation. The restoration process was revealed to be accompanied by hydrogenation due to collisionally induced interaction of molecular hydrogen with carbon atoms. One side hydrogenated graphene films consisting of 20 ?m one monolayer flakes were fabricated on SiO2/Si surface with hydrogen concentration as far as 40 at. %, at which the 0.3 eV bandgap opening was observed. It was shown that both H-coverage and bandgap width of the films can be controlled by varying the temperature of the heat treatment.

Mikoushkin, V. M.; Nikonov, S. Yu.; Dideykin, A. T.; Vul', A. Ya.; Sakseev, D. A.; Baidakova, M. V.; Vilkov, O. Yu.; Nelyubov, A. V.

2013-02-01

338

Low Energy Electron Molecule Collisions  

Microsoft Academic Search

Low energy electron molecule collisions are important in many technological, environmental and biological processes. Electrons are known to be the `drivers' of technological processes based around gas discharges, from lights and lamps to surface processing plasmas. In such environments electrons are responsible for much of the vibrational and electronic excitation that results in photon emissions, for the formation of long-lived

Stephen Buckman

2007-01-01

339

Method of bioluminescence imaging for molecular imaging of physiological and pathological processes.  

PubMed

Molecular imaging has emerged as a powerful tool in basic, pre-clinical and clinical research for monitoring a variety of molecular and cellular processes in living organisms. Optical imaging techniques, mainly bioluminescence imaging, have extensively been used to study biological processes because of their exquisite sensitivity and high signal-to noise ratio. However, current applications have mainly been limited to small animals due to attenuation and scattering of light by tissues but efforts are ongoing to overcome these hurdles. Here, we focus on bioluminescence imaging by giving a brief overview of recent advances in instrumentation, current available reporter gene-reporter probe systems and applications such as cell trafficking, protein-protein interactions and imaging endogenous processes. PMID:19324090

Gheysens, Olivier; Mottaghy, Felix M

2009-03-24

340

Theoretical model for motility and processivity of two-headed molecular motors  

NASA Astrophysics Data System (ADS)

The processive motion of two-headed molecular motors is studied theoretically by introducing a model that takes into account the coordinated motion of the constituent heads and the detachment process of heads from linear molecular tracks. The mean velocity, the mean run length, and the mean run time of the motor along the track are calculated numerically based on the Langevin equation. It turns out that the model, with appropriate choice of model parameters, can explain qualitatively the dependence of these quantities on the external load and adenosin triphosphate concentration observed experimentally for kinesin motors. Furthermore, we discuss how the motility and processivity of the motor are affected by various model parameters, which may be tested by experiments.

Kanada, Ryo; Sasaki, Kazuo

2003-06-01

341

Steady-state balance conditions for molecular motor cycles and stochastic nonequilibrium processes  

NASA Astrophysics Data System (ADS)

Molecular motors and nanomachines are considered that are coupled to exergonic processes which provide energy input to these motors and allow them to perform work. The motor dynamics is described by continuous-time Markov processes on a discrete state space, which can contain an arbitrary number of cycles consisting of two dicycles with opposite orientation. For the steady state of such a motor, the statistical entropy produced during the completion of each dicycle is expressed in terms of its transition rates. Identifying this statistical entropy with the heat released by the motor and using the first law of thermodynamics, we derive steady-state balance conditions that generalize the well-known detailed balance conditions in equilibrium. Our derivation is rather general and applies to any nonequilibrium system described as a Markov process. For molecular motors, these balance conditions depend on the external load force and can be decomposed into a zero-force and a force-dependent part.

Liepelt, S.; Lipowsky, R.

2007-03-01

342

New trends in collision detection performance  

Microsoft Academic Search

Collision detection on industrial digital mock-up is one of the challenging problems for real- time interaction in virtual reality applications. The fast increase of graphics hardware performance, multiplication of cores number and recent improvements on their programmability, bring new directions to the optimisation of collision detection algorithms. Since few years methods appear handling General-Purpose Processing on Graphics Processing Unit (GPGPU)

Quentin Avril; Valérie Gouranton; Bruno Arnaldi

343

Molecular dynamics study of nonequilibrium processes of evaporation and condensation at a vapor-liquid interface  

NASA Astrophysics Data System (ADS)

Nonequilibrium processes of evaporation and condensation at a vapor-liquid interface are studied by molecular dynamics simulations, which is devised to be free from any artificial constraints on molecular motions in the vicinity of the interface. To decrease statistical fluctuations on the results, the dynamics of a vapor-liquid two-phase system of almost 0.3 million Lennard-Jones molecules is simulated for more than 107 steps. The system with a steady evaporation or condensation mass flux can be realized by driving two vapor regions on the both sides of a planar liquid film, and thus the simulation is free from artificial controls of molecular motions in the liquid film and in the neighborhood of the interfaces. This enables us to evaluate the mass, momentum, and energy fluxes, which are relevant to the velocity distribution of molecules leaving the interface when the nonequilibrium evaporation or condensation occurs there.

Yano, Takeru

2012-11-01

344

Dynamics of charge transfer and chemical reactions of doubly-charged ions at low collision energies  

Microsoft Academic Search

Results of beam scattering studies on the dynamics of single charge transfer and chemical reactions of doubly-charged ions carried out in Prague are reviewed. Investigation of several atomic ion-atom charge transfer processes at collision energies 0·1-10 eV provides data on differential and relative total cross-sections of state-to-state processes. Populations of electronic and vibrational states of molecular product ions are obtained

Zdenek Herman

1996-01-01

345

The triplet “molecular processes–product–process” engineering: the future of chemical engineering ?  

Microsoft Academic Search

Today chemical engineering has to answer to the changing needs of the chemical and related process industries and to meet the market demands. Being a key to survival in globalization of trade and competition, the evolution of chemical engineering is thus necessary. Its ability to cope with the scientific and technological problems encountered will be appraised in this paper. To

Jean-Claude Charpentier

2002-01-01

346

Magnetic diffusion and ionization fractions in dense molecular clouds - The role of charged grains  

Microsoft Academic Search

The physics of magnetic diffusion in dense molecular clouds is examined, with particular attention given to the role of charged grains in controlling the process. The ionization fraction of dense molecular clouds in the presence of grains is determined from considerations of charge exchange, dissociative recombination, radiative recombination and collisions between grains and charged species, and it is found that

B. G. Elmegreen

1979-01-01

347

An overview of atomic and molecular processes in critical velocity ionization  

SciTech Connect

Alfven's critical ionization velocity (CIV) is a multistep process involving plasma physics and plasma chemistry. The authors present an overview of the time development of some atomic and molecular processes in CIV. In the pre-onset stage, metastable states play an important role: They provide an energy pooling mechanism allowing low energy electrons to participate in the ionization processes; they may explain the low energy threshold as well as the fast time scale in the onset of CIV. For a sustaining CIV to occur, Townsend's criterion has to be satisfied. The kinetic energies of the neutrals are transformed to plasma wave energies via beam-plasma instabilities, and the plasma waves that heat the electrons result in a tail formation. Excitation of neutrals with subsequent radiation is an important energy loss mechanism. Finite beam size also limits the instability growth rate. In the propagation of CIV, ion-molecule reactions and molecular dissociative recombination are important. Ion-molecule reactions change the temporal chemical composition in a CIV process and help explain some results in CIV experiments. Molecular dissociative recombination reduces the plasma density, lowers the effective neutral mass, and loses energy via excitation and radiation; it tends to quench the propagation of CIV. Depending on various parameters, oscillatory behavior of CIV may occur.

Lai, S.T.; Murad, E.; McNeil, W.J.

1989-04-01

348

Bond Rearrangement Following Collisions Between Fast Ions and Ammonia or Methane  

NASA Astrophysics Data System (ADS)

The production of H2+ and H3+ fragments upon dissociation of ammonia and methane molecules following collisions with fast ions involves rearrangements of the molecular bonds. By examining the relative probabilities for bond rearrangement in collisions between 1 MeV/amu F7+ ions or 4 MeV protons and NH3, ND3, CH4, and CD4, we are able to investigate the rearrangement process as a function of the initial target geometry and search for isotopic effects that could give clues about the rearrangement mechanism. Technical aspects of the experiment due to the use of the heavier isotopes or the highly-charged projectiles are also discussed.

Wells, E.; Parke, E.; Doshier, Laura; Lueking, Amy; Jochim, Bethany; Carey, Sharayah; Leonard, Mat; Carnes, K. D.; Ben-Itzhak, I.

2009-03-01

349

Subthreshold K+ production in 1GeV/u 197Au + 197Au collisions  

NASA Astrophysics Data System (ADS)

We calculate the K+-production cross section in 197Au+197Au collisions at 1 GeV/u in the framework of quantum molecular dynamics (QMD). The Skyrme potentials, with parameters chosen to generate the soft and hard nuclear equations of state, are used in the propagation of nucleons within QMD. Our calculations show that the kaons are produced from an earlier stage of the collisions and mainly through a two-step process. Theoretical predictions with the soft equation of state are in good agreement with the experimental data from SIS at GSI. The results for soft and hard equations of state differ by approximately a factor 2 to 3.

Huang, S. W.; Faessler, Amand; Li, G. Q.; Puri, Rajeev K.; Lehmann, E.; Khoa, Dao T.; Matin, M. A.

1993-01-01

350

Computing molecular fluctuations in biochemical reaction systems based on a mechanistic, statistical theory of irreversible processes.  

PubMed

We discuss the quantification of molecular fluctuations in the biochemical reaction systems within the context of intracellular processes associated with gene expression. We take the molecular reactions pertaining to circadian rhythms to develop models of molecular fluctuations in this chapter. There are a significant number of studies on stochastic fluctuations in intracellular genetic regulatory networks based on single cell-level experiments. In order to understand the fluctuations associated with the gene expression in circadian rhythm networks, it is important to model the interactions of transcriptional factors with the E-boxes in the promoter regions of some of the genes. The pertinent aspects of a near-equilibrium theory that would integrate the thermodynamical and particle dynamic characteristics of intracellular molecular fluctuations would be discussed, and the theory is extended by using the theory of stochastic differential equations. We then model the fluctuations associated with the promoter regions using general mathematical settings. We implemented ubiquitous Gillespie's algorithms, which are used to simulate stochasticity in biochemical networks, for each of the motifs. Both the theory and the Gillespie's algorithms gave the same results in terms of the time evolution of means and variances of molecular numbers. As biochemical reactions occur far away from equilibrium-hence the use of the Gillespie algorithm-these results suggest that the near-equilibrium theory should be a good approximation for some of the biochemical reactions. PMID:21187228

Kulasiri, Don

2011-01-01

351

Molecular control of electron and hole transfer processes: Theory and applications  

SciTech Connect

Recent decades have seen remarkable advances in microscopic understanding of electron transfer (ET) processes in widely ranging contexts, including solid-state, liquid solution, and complex biological assemblies. The primary goal of this chapter is to report recent advances in the modeling, calculation, and analysis of electronic coupling in complex molecular aggregates, thereby allowing an assessment of current progress toward the goal of molecular-level control and design. The control of electron transfer kinetics (i.e., enhancing desired processes, while inhibiting others) involves, of course, system energetics (especially activation and reorganization energies) as well as electronic coupling, which is most directly relevant only after the system has reached the appropriate point (or region) along the reaction coordinate. Nevertheless, to focus the discussion in this chapter, the authors will consider such energetics, and the associated molecular and solvent coordinates which control then, only to the extent that they bear on the analysis of the electronic coupling. In the following sections they first discuss the formulation of basic ET models, including the definition of initial and final states, the role of orbitals and 1-particle models in a many-electron context, the utility of various effective Hamiltonians, and the role of vibronic as well as purely electronic effects. With these theoretical tools in hand, they then examine very recent applications to complex molecular systems using the techniques of computational quantum chemistry, followed by detailed analysis of the numerical results. They then conclude with some comments regarding the current ``state of the art`` and remaining challenges.

Newton, M.D. [Brookhaven National Lab., Upton, NY (United States). Dept. of Chemistry; Cave, R.J. [Harvey Mudd Coll., Claremont, CA (United States). Dept. of Chemistry

1996-02-01

352

Ultrasmall volume molecular isothermal amplification in microfluidic chip with advanced surface processing  

NASA Astrophysics Data System (ADS)

In this paper, we developed a metal micro-fluidic chip with advanced surface processing for ultra-small volume molecular isothermal amplification. This method takes advantages of the nucleic acid amplification with good stability and consistency, high sensitivity about 31 genomic DNA copies and bacteria specific gene identification. Based on the advanced surface processing, the bioreaction assays of nucleic acid amplification was dropped about 392nl in volume. A high numerical aperture confocal optical detection system was advanced to sensitively monitor the DNA amplification with low noise and high power collecting fluorescence near to the optical diffraction limit. A speedy nucleic acid isothermal amplification was performed in the ultra-small volume microfluidic chip, where the time at the inflexions of second derivative to DNA exponential amplified curves was brought forward and the sensitivity was improved about 65 folds to that of in current 25?l Ep-tube amplified reaction, which indicates a promising clinic molecular diagnostics in the droplet amplification.

Huang, Guoliang; Ma, Li; Yang, Xiaoyong; Yang, Xu

2011-01-01

353

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

354

An emerging molecular and cellular framework for memory processing by the hippocampus  

Microsoft Academic Search

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

Gayle M. Wittenberg; Joe Z. Tsien

2002-01-01

355

Molecular simulation evidence for processive motion of Trichoderma reesei Cel7A during cellulose depolymerization  

Microsoft Academic Search

We present free energy calculations for the Trichoderma reesei Cel7A (cellobiohydrolase I) linker peptide from molecular dynamics simulations directed towards understanding the linker role in cellulose hydrolysis. The calculations predict an energy storage mechanism of the linker under stretching\\/compression that is consistent with processive depolymerization. The linker exhibits two stable states at lengths of 2.5nm and 5.5nm during extension\\/compression, with

Xiongce Zhao; Tauna R. Rignall; Clare McCabe; William S. Adney; Michael E. Himmel

2008-01-01

356

4B4Rate determining processes for the production of radiation in high power molecular lasers  

Microsoft Academic Search

The excitation mechanisms and relaxation processes will be described for a closed molecular gas laser of 240 cm length and 2.3 cm diameter filled with 1 torr carbon dioxide, 2.5 torr nitrogen, and 7.2 torr helium; the influence of adding 0.2 torr water vapor is discussed. When all the four components are present, an output of 103 watts is reached

W. Witteman

1966-01-01

357

Isolation and Identification of Listeria monocytogenes in Processed Meat by a Combined Cultural-molecular Method  

Microsoft Academic Search

The isolation and identification of Listeria monocytogenes in processed meat samples by a combined cultural-molecular method is described. It allows the identification of Listeria strains by means of a hybridization technique with a specific DNA probe directed to the listerial internalin gene. The specificity of this method was found to be 100% and sensitivity was as low as 1 CFU\\/2.5

Angela Ingianni; Marta Quartuccio; Maria Antonietta Madeddu; Adriana Sanna; Sandro Dessi; Raffaello Pompei

2007-01-01

358

Dislocation processes in the deformation of nanocrystalline aluminium by molecular-dynamics simulation  

Microsoft Academic Search

The mechanical behaviour of nanocrystalline materials (that is, polycrystals with a grain size of less than 100 nm) remains controversial. Although it is commonly accepted that the intrinsic deformation behaviour of these materials arises from the interplay between dislocation and grain-boundary processes, little is known about the specific deformation mechanisms. Here we use large-scale molecular-dynamics simulations to elucidate this intricate

Vesselin Yamakov; Dieter Wolf; Simon R. Phillpot; Amiya K. Mukherjee; Herbert Gleiter; Forschungszentrum Karlsruhe

2002-01-01

359

Deformation processes in [ 1 1 2 ¯ 0 ] -textured nanocrystalline Mg by molecular dynamics simulation  

Microsoft Academic Search

Plastic deformation of nanocrystalline Mg is studied using molecular dynamics simulation. In a [112¯0]-textured structure, slip and twinning behaviors are observed during tensile loading. Various twinning and slip process are identified, with basal slip and tensile {101¯2}?101¯1? twinning being dominant. For grain sizes larger than ?30nm, basal slip occurs at a lower strain than twinning; for smaller grain sizes, twinning

D.-H. Kim; M. V. Manuel; F. Ebrahimi; J. S. Tulenko; S. R. Phillpot

2010-01-01

360

Puck collisions  

NASA Astrophysics Data System (ADS)

Collisions between two ice hockey pucks sliding on frictionless ice are studied, with both inelasticity and frictional contact between the colliding surfaces of the two pucks taken into account. The latter couples translational and rotational motion. The full solution depends on the sign and magnitude of the initial mismatch between the surface velocities at the point of contact. The initial state defines two physically distinct regimes for the friction coefficient. To illustrate the complexities, we discuss at length the typical situation (well known from curling) when puck number 1 is initially at rest, and is hit by puck number 2 with an arbitrary impact parameter, velocity and angular velocity. We find that the total outgoing angle between the pucks exceeds \\frac{1}{2}\\pi if and only if the collision leads to a net increase in the translational part of the kinetic energy. The conditions for this to happen are scrutinized, and the results are presented both analytically and numerically by a set of representative curves. This paper is written with an ambitious undergraduate, and her teacher, in mind.

Hauge, E. H.

2012-09-01

361

Molecular-Level Processes Governing the Interaction of Contaminants with Iron and Manganese Oxides - Final Report  

SciTech Connect

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 structurally and compositionally well-defined mineral surfaces will lead to: (i) improved models of contaminant fate and transport in geochemical systems, and (ii) optimized manipulation of these processes for remediation purposes. To contribute to this understanding, we will study, both experimentally and theoretically, redox processes involving three important contaminants - chromate ion, carbon tetrachloride, and trichloroethene TCE, on the following iron and manganese oxides - hematite, magnetite, maghemite, and pyrolusite. These oxides and their hydroxylated analogs commonly occur as coatings on minerals or as interfaces in the subsurface environment. Single-crystal surfaces of these oxides will be synthesized in carefully controlled fashion by molecular beam epitaxy. These surfaces, as well as high surface are powdered samples of these oxides, will be used in spectroscopic and kinetic experiments in both aqueous and gas phases. Our goal is to identify products and to determine the kinetics and mechanisms of surface-catalyzed redox reaction of Cr(VI) and CR(III), and the reductive dechlorination of carbon tetrachloride and TCE. The combination of theory and experiment will provide the base information needed to scale from the molecular level to the microscopic grain level minerals.

Brown Jr., G. E.; Chambers, S. A.

1999-10-31

362

Formation, molecular structure, and morphology of humins in biomass conversion: influence of feedstock and processing conditions.  

PubMed

Neither the routes through which humin byproducts are formed, nor their molecular structure have yet been unequivocally established. A better understanding of the formation and physicochemical properties of humins, however, would aid in making biomass conversion processes more efficient. Here, an extensive multiple-technique-based study of the formation, molecular structure, and morphology of humins is presented as a function of sugar feed, the presence of additives (e.g., 1,2,4-trihydroxybenzene), and the applied processing conditions. Elemental analyses indicate that humins are formed through a dehydration pathway, with humin formation and levulinic acid yields strongly depending on the processing parameters. The addition of implied intermediates to the feedstocks showed that furan and phenol compounds formed during the acid-catalyzed dehydration of sugars are indeed included in the humin structure. IR spectra, sheared sum projections of solid-state 2DPASS (13) C?NMR spectra, and pyrolysis GC-MS data indicate that humins consist of a furan-rich polymer network containing different oxygen functional groups. The structure is furthermore found to strongly depend on the type of feedstock. A model for the molecular structure of humins is proposed based on the data presented. PMID:23836679

van Zandvoort, Ilona; Wang, Yuehu; Rasrendra, Carolus B; van Eck, Ernst R H; Bruijnincx, Pieter C A; Heeres, Hero J; Weckhuysen, Bert M

2013-07-08

363

Linking molecular and population processes in mathematical models of quorum sensing.  

PubMed

Many bacteria alter their behaviors as a function of population density, via a process known as quorum sensing (QS). QS is achieved by the synthesis and detection of diffusible signal molecules, often involving complex signal transduction pathways and regulatory networks. Mathematical models have been developed to investigate a number of aspects of QS, resulting in a wide range of model structures; many have focused on either the molecular or the population scale. In this paper, I show that many published models fail to satisfy physical constraints (such as conservation of matter) or rely on a priori assumptions that may not be valid. I present new, simple models of canonical Gram-negative and Gram-positive QS systems, in both well-mixed and biofilm populations, focusing on the interaction between molecular and population processes. I show that this interaction may be crucial for several important features of QS, including bistability and the localization of QS in space. The results highlight the need to link molecular and population processes carefully in QS models, provide a general framework for understanding the behavior of complex system-specific models, and suggest new directions for both theoretical and experimental work. PMID:23892934

Brown, David

2013-07-27

364

Simultaneous optical excitation of Na electronic and CF{sub 4} vibrational modes in Na+CF{sub 4} collisions  

SciTech Connect

We report on the ultraviolet excitation of Na(3s)+CF{sub 4} collision pairs in a crossed molecular beam experiment. We observe Na(3d) collision products originating from the process Na(3s)+CF{sub 4}({nu}{sub 3}=0)+h{nu}{yields}Na(3d)+CF{sub 4}({nu}{sub 3}=1). The spectral intensity distribution of the collision products and the prevailing small angle scattering confirm a previously proposed long range dipole-dipole mechanism. We report velocity-resolved spectra and a comparison to preliminary numerical results based on collisional broadening theory. Polarization experiments suggest future potential for the observation of collision geometries.

Alekseev, V. A. [Department of Physics, St. Petersburg State University, Peterhof 198504 (Russian Federation); Grosser, J.; Hoffmann, O. [Institut fuer Gravitationsphysik, Leibniz Universitaet Hannover, 30167 Hannover (Germany); Rebentrost, F. [Max-Planck-Institut fuer Quantenoptik, 85748 Garching (Germany)

2008-11-28

365

Termolecular association and laser-assisted electron-(excited) atom collisions. Annual report, 1 Jul 90-30 Jun 91  

SciTech Connect

The objective of the present research is to formulate, develop and implement new theoretical descriptions of the following atomic and molecular processes: Laser-Assisted Collisions: A new theory of laser-assisted electron-(excited) atom collisions, in which the dressed states of the atom A in the laser field are closely coupled and the Volkov states of the projectile electron in the laser field are included; Termolecular Recombination: The transport-collisional set of Master equations for Termolecular Recombination, A + B + M yields AB + M as a function of gas density has been developed by M. R. Flannery. Angular Momentum Changes in Collisions with excited atoms: Work is progressing on the cross sections for angular momentum changes, in heavy-particle and electron-atom (e-B) collisions where the target atom is initially in an excited state.

Flannery, M.R.

1991-08-23

366

On the Tolerance to Manufacturing Defects in Molecular QCA Tiles for Processing-by-wire  

Microsoft Academic Search

Among emerging technologies, Quantum-dot Cellular Automata (QCA) relies on innovative computational paradigms. For nano-scale\\u000a implementation, the so-called processing-by-wire (PBW) paradigm in QCA is very effective as processing takes place, while\\u000a signal communication is accomplished. This paper analyzes the defect tolerance properties of PBW for manufacturing tiles by\\u000a molecular QCA cells. Based on a 3?×?3 grid and various input\\/output arrangements in

Jing Huang; Mariam Momenzadeh; Fabrizio Lombardi

2007-01-01

367

Collision Scenarios and Probabilistic Collision Damage  

Microsoft Academic Search

This paper examines the influence of collision scenario random variables on the extent of predicted damage in ship collisions. Struck and striking ship speed, collision angle, striking ship type and striking ship displacement are treated as independent random variables. Other striking ship characteristics are treated as dependent variables derived from the independent variables based on relationships developed from worldwide ship

Alan J. Brown

2001-01-01

368

Collision scenarios and probabilistic collision damage  

Microsoft Academic Search

This paper examines the influence of collision scenario random variables on the extent of predicted damage in ship collisions. Struck and striking ship speed, collision angle, striking ship type and striking ship displacement are treated as independent random variables. Other striking ship characteristics are treated as dependent variables derived from the independent variables based on relationships developed from worldwide ship

A. J. Brown

2002-01-01

369

Utilization of efficient gradient and Hessian computations in the force field optimization process of molecular simulations  

NASA Astrophysics Data System (ADS)

Computer simulations of chemical systems, especially systems of condensed matter, are highly important for both scientific and industrial applications. Thereby, molecular interactions are modeled on a microscopic level in order to study their impact on macroscopic phenomena. To be capable of predicting physical properties quantitatively, accurate molecular models are indispensable. Molecular interactions are described mathematically by force fields, which have to be parameterized. Recently, an automated gradient-based optimization procedure was published by the authors based on the minimization of a loss function between simulated and experimental physical properties. The applicability of gradient-based procedures is not trivial at all because of two reasons: firstly, simulation data are affected by statistical noise, and secondly, the molecular simulations required for the loss function evaluations are extremely time-consuming. Within the optimization process, gradients and Hessians were approximated by finite differences so that additional simulations for the respective modified parameter sets were required. Hence, a more efficient approach to computing gradients and Hessians is presented in this work. The method developed here is based on directional instead of partial derivatives. It is compared with the classical computations with respect to computation time. Firstly, molecular simulations are replaced by fit functions that define a functional dependence between specific physical observables and force field parameters. The goal of these simulated simulations is to assess the new methodology without much computational effort. Secondly, it is applied to real molecular simulations of the three chemical substances phosgene, methanol and ethylene oxide. It is shown that up to 75% of the simulations can be avoided using the new algorithm.

Hülsmann, Marco; Kopp, Sonja; Huber, Markus; Reith, Dirk

2013-01-01

370

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

371

Deformation Mechanism and Punch Taper Effects on Nanoimprint Process by Molecular Dynamics  

NASA Astrophysics Data System (ADS)

A molecular dynamics analysis model is proposed to study the effects of parameters on the nanoimprint process, for example, taper angle, imprint depth and spring back. The nanoimprint process comprises one punch and one specimen at an isothermal state of 400 K, while the deformed material is a copper fcc single crystal and the punch material is a nickel fcc single crystal. There were a total of 10,080 atoms in copper measuring 12.02 nm and 5.72 nm in length and height, respectively. There were a total of 4,200 atoms in nickel with a typical length and depth in a punch tooth of 6.24 nm and 3.52 nm, respectively. Computer simulation codes based on Hamiltonian dynamics, periodical boundary conditions and the Morse potential function were used to simulate the nanoimprint process. By varying the punch taper angle and the imprint depth, useful information about the nanoimprint process was obtained.

Hsu, Quang-Cherng; Wu, Chen-Da; Fang, Te-Hua

2004-11-01

372

Studies on Deformation Mechanism and Punch Taper Effects on Nanoimprint Processes by Molecular Dynamics  

NASA Astrophysics Data System (ADS)

A molecular dynamics analysis model is proposed to study the effects of parameters on nanoimprint process, for example: taper angle, imprint depth and spring back. The nanoimprint process comprises one punch and one specimen at an isothermal state of 400K, while the deformed material is a copper FCC single crystal and the punch material is a nickel FCC single crystal. There were a total of 10,080 atoms in copper measuring 12.02 nm × 5.72 nm in length and height, respectively. There were a total of 4,200 atoms in nickel where the typical length and depth in punch tooth are 6.24 nm × 3.52 nm, respectively. Computer simulation codes based on Hamiltonian dynamics, periodical boundary conditions and Morse potential function were used to simulate the nanoimprint processes. By varying the punch taper angle and the imprinting depth, useful information for nanoimprint process has been obtained.

Hsu, Quang-Cherng; Wu, Chen-Da; Fang, Te-Hua

2004-06-01

373

Molecular Processes of Inhibition and Stimulation of ATP Synthase Caused by the Phytotoxin Tentoxin*S?  

PubMed Central

F1-ATPase is the smallest mechanical motor known. Tentoxin, a cyclic peptide produced by phytopathogenic fungi, inactivates the F1 motor in sensitive plants at nanomolar to micromolar concentrations, whereas higher concentrations surpass the natural activity of the enzyme. Single molecule studies now have clarified the molecular steps involved in both processes. Inactivation delays the dwell time of a single step in the complete 360° turn and results in an asymmetric rotation of the central rotor subunit. In contrast, rotation in the stimulated F1 particle is smooth and accompanied by strongly reduced ADP inhibition. Our study provides for the first time the direct observation of a noncompetitively inhibited state of the enzyme and directly visualizes the regulation of the molecular motor by an external natural compound. In addition, the ADP release step during catalysis was revealed by analysis of the single molecule rotation behavior. Hence, tentoxin is a sophisticated molecular tool to mark and control certain catalytic steps within the reaction pathway of the molecular F1 motor.

Meiss, Erik; Konno, Hiroki; Groth, Georg; Hisabori, Toru

2008-01-01

374

Molecular processes of inhibition and stimulation of ATP synthase caused by the phytotoxin tentoxin.  

PubMed

F1-ATPase is the smallest mechanical motor known. Tentoxin, a cyclic peptide produced by phytopathogenic fungi, inactivates the F1 motor in sensitive plants at nanomolar to micromolar concentrations, whereas higher concentrations surpass the natural activity of the enzyme. Single molecule studies now have clarified the molecular steps involved in both processes. Inactivation delays the dwell time of a single step in the complete 360 degrees turn and results in an asymmetric rotation of the central rotor subunit. In contrast, rotation in the stimulated F1 particle is smooth and accompanied by strongly reduced ADP inhibition. Our study provides for the first time the direct observation of a noncompetitively inhibited state of the enzyme and directly visualizes the regulation of the molecular motor by an external natural compound. In addition, the ADP release step during catalysis was revealed by analysis of the single molecule rotation behavior. Hence, tentoxin is a sophisticated molecular tool to mark and control certain catalytic steps within the reaction pathway of the molecular F1 motor. PMID:18579520

Meiss, Erik; Konno, Hiroki; Groth, Georg; Hisabori, Toru

2008-06-25

375

Ultrarelativistic quantum molecular dynamics calculations of two-pion Hanbury-Brown-Twiss correlations in central Pb-Pb collisions at sNN=2.76 TeV  

NASA Astrophysics Data System (ADS)

Two-pion Hanbury-Brown-Twiss (HBT) correlations for central Pb-Pb collisions at the Large-Hadron-Collider (LHC) energy of sNN=2.76 TeV are investigated with the microscopic transport model ultrarelativistic quantum molecular dynamics. The transverse momentum dependence of the Pratt-Bertsch HBT radii is extracted from a three-dimensional Gaussian fit to the correlator in the longitudinal comoving system. Qualitative agreement with the ALICE data is obtained, however Rout is overpredicted by nearly 50%. The LHC results are also compared to data from the STAR experiment at RHIC. For both energies we find that the calculated RO:RS ratio is always larger than data, indicating that the emission in the model is less explosive than observed in the data.

Li, Qingfeng; Gräf, G.; Bleicher, Marcus

2012-03-01

376

3? end mRNA processing: molecular mechanisms and implications for health and disease  

PubMed Central

Recent advances in the understanding of the molecular mechanism of mRNA 3? end processing have uncovered a previously unanticipated integrated network of transcriptional and RNA-processing mechanisms. A variety of human diseases impressively reflect the importance of the precision of the complex 3? end-processing machinery and gene specific deregulation of 3? end processing can result from mutations of RNA sequence elements that bind key specific processing factors. Interestingly, more general deregulation of 3? end processing can be caused either by mutations of these processing factors or by the disturbance of the well-coordinated equilibrium between these factors. From a medical perspective, both loss of function and gain of function can be functionally relevant, and an increasing number of different disease entities exemplifies that inappropriate 3? end formation of human mRNAs can have a tremendous impact on health and disease. Here, we review the mechanistic hallmarks of mRNA 3? end processing, highlight the medical relevance of deregulation of this important step of mRNA maturation and illustrate the implications for diagnostic and therapeutic strategies.

Danckwardt, Sven; Hentze, Matthias W; Kulozik, Andreas E

2008-01-01

377

Time dependences in energy transfer process induced by collision between two 3P-excited sodium atoms  

Microsoft Academic Search

High density of Na(3P) atoms has been achieved by means of laser excitation. Effective lifetimes of atomic states populated by the collisional process involving excited atoms have been measured. Dependence of these effective lifetimes on the effective lifetime of the 3 2P state has been observed as a function of vapor density.

A. Kopystynska; P. Kowalczyk

1978-01-01

378

Collisions and Langmuir waves in nonideal plasmas  

Microsoft Academic Search

Langmuir waves and particle-particle collisions in an equilibrium two-component plasma consisting of nondegenerate electrons\\u000a and singly charged ions are studied by molecular dynamics simulation. Dispersion of frequency and damping rate is determined\\u000a for Langmuir waves. A method is outlined for extending the theory of Langmuir waves developed for ideal plasmas to nonideal\\u000a plasmas. Conductivity and dynamic collision frequency are determined

I. V. Morozov; G. E. Norman

2005-01-01

379

Dual inhibition of chaperoning process by taxifolin: molecular dynamics simulation study.  

PubMed

Hsp90 (heat shock protein 90), a molecular chaperone, stabilizes more than 200 mutated and over expressed oncogenic proteins in cancer development. Cdc37 (cell division cycle protein 37), a co-chaperone of Hsp90, has been found to facilitate the maturation of protein kinases by acting as an adaptor and load these kinases onto the Hsp90 complex. Taxifolin (a natural phytochemical) was found to bind at ATP-binding site of Hsp90 and stabilized the inactive "open" or "lid-up" conformation as evidenced by molecular dynamic simulation. Furthermore, taxifolin was found to bind to interface of Hsp90 and Cdc37 complex and disrupt the interaction of residues of both proteins which were essential for the formation of active super-chaperone complex. Thus, taxifolin was found to act as an inhibitor of chaperoning process and may play a potential role in the cancer chemotherapeutics. PMID:22609743

Verma, Sharad; Singh, Amit; Mishra, Abha

2012-04-23

380

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

381

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

382

Collision Density of Hot Atoms. II  

Microsoft Academic Search

Analytical and stochastic methods are used to investigate hot-atom reactions for relatively low-energy hot atoms such as those produced by photochemical processes. Collision densities for hot atoms are presented for several reactive systems in which the reaction probability and the threshold energy are varied. Solutions for the collision density obtained by analytical methods and independently by stochastic methods were in

D. M. Chapin; M. D. Kostin

1967-01-01

383

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

384

Stimulated formation of ultracold ground (NaCa)^+ molecular ions  

Microsoft Academic Search

Ultracold atomic systems in which electric charges play an important role are of particular interest. Futhermore, the recently proposed possibility of sympathetic cooling of ions by cold neutral atoms in the same trap has opened the way to new fundamental collision process studies [1]. We theoretically study the possibility of forming ultracold ground (NaCa)^+ molecular ions starting with a Ca^+

Philippe Pellegrini; Harvey Michels; Winthrop Smith; Robin Coté

2006-01-01

385

Close-coupling calculations of low-energy inelastic and elastic processes in 4He collisions with H2: A comparative study of two potential energy surfaces  

NASA Astrophysics Data System (ADS)

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(?=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(?=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 (?=10,j=0) and (?=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.

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

386

The forward glory effect in the differential cross sections measured below Elab = 50 eV for the one-electron capture process in N5+-He collisions  

NASA Astrophysics Data System (ADS)

A crossed-beam apparatus was used to measure the relative state-selective differential cross sections for the one-electron capture process in the N5+-He system from ?lab = -3° to 21° at Elab = 27.5 and 47.5 eV. The main reaction channel was found to be N5+ (1s2 1S) + He ? N4+ (1s23s 2S) + He+ + 16.8 eV. The differential cross section for this channel is pronounced at ?cm = 0, and it shows another peak at a certain angle that depends on the collision energy. The O5+-He system at Elab = 47.5 eV was measured for comparison. The differential cross section for the main reaction channel O5+ (1s22s 2S) + He ? O4+ (1s22s3p 1,3P) + He+ + 17 eV is zero at ?cm = 0, and it shows only a single peak at ?cm = 0.314 rad. The structures observed in the N5+-He system were analysed using the classical deflection function based on ab initio potentials. The peak observed at ?cm = 0 is assigned to the forward glory effect and the second peak to the inelastic rainbow effect.

Itoh, Yoh

2011-09-01

387

Demonstration of momentum and kinetic energy during an entire collision  

NASA Astrophysics Data System (ADS)

A collision is a physical phenomenon commonly occurring in our daily life. In the classroom, the instructor usually demonstrates collision to enhance students' conceptual understanding of momentum conservation and kinetic energy conservation in collisions.1-3 The results of such demonstrations illustrate that the total linear momentum and the kinetic energy for elastic collisions in a system are similar both before and after the collision.4 Demonstrating the momentum and kinetic energy while the two objects are in the process of colliding can provide greater insight into these concepts. Such demonstration results during the collision are rarely described, however, because the time during the collision process is very brief, making the determination of the velocity or momentum of each object very difficult.5 In this paper, we intend to present an interactive demonstration6 proposed to illustrate the results of momentum conservation and kinetic energy conservation simultaneously for the entire collision.

Sawadthaisong, Nattakit; Chitaree, Ratchapak; Barufaldi, James P.

2011-01-01

388

Use of Molecular Typing Methods To Trace the Dissemination ofListeria monocytogenesin a Shrimp Processing Plant  

Microsoft Academic Search

Molecular typing of bacteria has been widely used in epidemiological studies but not as extensively for tracing the transmission of pathogenic bacteria in food plants. This study was conducted to examine the potential use of two molecular typing methods, random amplified polymorphic DNA (RAPD) analysis and pulsed-field gel electrophoresis (PFGE), to traceListeria monocytogenescontamination in a shrimp processing plant. Ribotyping and

M. T. DESTRO; M. F. F. LEITAO; M. FARBER

1996-01-01

389

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

390

Stark mixing by ion-Rydberg atom (molecule) collisions  

NASA Astrophysics Data System (ADS)

Classical molecular dynamics simulations are performed to cover Stark mixing transitions (nl-->nl') in Rydberg atoms by collision with slow ionsE Accuracy is tested by comparison with the exact analytical classical probabilities previously obtained when the ion-atom potential is taken as the long-range ion-dipole interaction. The results are provided not only for the ion-dipole interaction but also for the full electrostatic interaction. It is shown, by comparison, that the ion-dipole potential alone provides reliable probabilities. The method is highly accurate and is very amenable to ready inclusion of other processes competing with Stark mixing.

Balaraman, G. S.; Flannery, M. R.

2009-02-01

391

Simulating Picosecond X-ray Diffraction from shocked crystals by Post-processing Molecular Dynamics Calculations  

SciTech Connect

Calculations of the x-ray diffraction patterns from shocked crystals derived from the results of Non-Equilibrium-Molecular-Dynamics (NEMD) simulations are presented. The atomic coordinates predicted by the NEMD simulations combined with atomic form factors are used to generate a discrete distribution of electron density. A Fast-Fourier-Transform (FFT) of this distribution provides an image of the crystal in reciprocal space, which can be further processed to produce quantitative simulated data for direct comparison with experiments that employ picosecond x-ray diffraction from laser-irradiated crystalline targets.

Kimminau, G; Nagler, B; Higginbotham, A; Murphy, W; Park, N; Hawreliak, J; Kadau, K; Germann, T C; Bringa, E M; Kalantar, D; Lorenzana, H; Remington, B; Wark, J

2008-06-19

392

Excitonic processes in aromatic molecular crystals of strong exciton-phonon coupling  

NASA Astrophysics Data System (ADS)

We overview our experimental work on exciton self-trapping in simple organic molecular crystals. First we show pressure-induced change in the exciton-phonon interaction, indicating that the interaction depends strongly on the intermolecular distance, and then we demonstrate the experimental results and compare them with theoretical results on the exciton-phonon coupling constants, presence of the self-trapping barrier, intermediate self-trapped exciton states, the radiative annihilation of excitons at the exit of the self-trapping path. Most of this paper is devoted to show exciton relaxation processes visualized in time-resolved luminescence in Pyrene.

Matsui, Atsuo H.

1995-02-01

393

Growth processes in molecular beam expitaxy of single-crystal Al layers on AlAs  

Microsoft Academic Search

The molecular beam epitaxial growth processes of Al single-crystal layers deposited at room temperature on As-stabilized and on Al-stabilized AlAs surfaces are investigated insitu using reflection high-energy electron diffraction (RHEED). The epitaxy relationship of Al with the underlying AlAs is (011)[100]Al\\/\\/(001)[110]AlAs irrespective of the surface stoichiometry of AlAs. Detailed RHEED investigation suggests that the initially deposited two one-monolayer-thick Al layers

Hiroaki Nakahara; Hirofumi Matuhata; Yasumasa Okada; Tateki Kurosu; Masamori Iida; Takafumi Yao

1991-01-01

394

Competition of coalescence and 'fireball' processes in nonequilibrium emission of light charged particles from p+Au collisions  

SciTech Connect

The energy and angular dependence of the double differential cross sections d{sup 2}{sigma}/d{omega}dE were measured for p,d,t,{sup 3,4,6}He, {sup 6,7,8,9}Li, {sup 7,9,10}Be, and {sup 10,11,12}B 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 {sup 3}He 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.; Kistryn, M.; Kliczewski, St.; Kozik, E. [H. Niewodniczanski Institute of Nuclear Physics PAN, Radzikowskiego 152, PL-31342 Krakow (Poland); Fidelus, M.; Jarczyk, L.; Kamys, B.; Kistryn, St.; Kowalczyk, A.; Magiera, A.; Rudy, Z.; Wojciechowski, M. [M. Smoluchowski Institute of Physics, Jagellonian University, Reymonta 4, PL-30059 Krakow (Poland); Filges, D.; Goldenbaum, F.; Machner, H. [Institut fuer Kernphysik, Forschungszentrum Juelich, D-52425 Juelich (Germany); Hodde, H. [Institut fuer Strahlen- und Kernphysik, Bonn University, D-53121 Bonn (Germany); Kulessa, P.; Pysz, K.; Siudak, R. [H. Niewodniczanski Institute of Nuclear Physics PAN, Radzikowskiego 152, PL-31342 Krakow (Poland); Institut fuer Kernphysik, Forschungszentrum Juelich, D-52425 Juelich (Germany); Piskor-Ignatowicz, B. [M. Smoluchowski Institute of Physics, Jagellonian University, Reymonta 4, PL-30059 Krakow (Poland); Institut fuer Kernphysik, Forschungszentrum Juelich, D-52425 Juelich (Germany)

2008-08-15

395

MZmine 2: Modular framework for processing, visualizing, and analyzing mass spectrometry-based molecular profile data  

PubMed Central

Background Mass spectrometry (MS) coupled with online separation methods is commonly applied for differential and quantitative profiling of biological samples in metabolomic as well as proteomic research. Such approaches are used for systems biology, functional genomics, and biomarker discovery, among others. An ongoing challenge of these molecular profiling approaches, however, is the development of better data processing methods. Here we introduce a new generation of a popular open-source data processing toolbox, MZmine 2. Results A key concept of the MZmine 2 software design is the strict separation of core functionality and data processing modules, with emphasis on easy usability and support for high-resolution spectra processing. Data processing modules take advantage of embedded visualization tools, allowing for immediate previews of parameter settings. Newly introduced functionality includes the identification of peaks using online databases, MSn data support, improved isotope pattern support, scatter plot visualization, and a new method for peak list alignment based on the random sample consensus (RANSAC) algorithm. The performance of the RANSAC alignment was evaluated using synthetic datasets as well as actual experimental data, and the results were compared to those obtained using other alignment algorithms. Conclusions MZmine 2 is freely available under a GNU GPL license and can be obtained from the project website at: http://mzmine.sourceforge.net/. The current version of MZmine 2 is suitable for processing large batches of data and has been applied to both targeted and non-targeted metabolomic analyses.

2010-01-01

396

Asymptotic expansions for three-body continuum and bound states relevant for ion-atom collision processes  

NASA Astrophysics Data System (ADS)

The continuum and bound states of a target electron in the field of a projectile ion are derived within the continuum distorted wave (CDW) approach. Unlike the CDW approximation of Cheshire, in addition we take into account a three-body coupling between the electron-target and electron-projectile subsystems to the first order in a small parameter O(1/R) where R is internuclear separation. It is found that the derived wave functions satisfy the Schrödinger equation up to terms of the second order O(1/R2), and as a consequence, give a better account of the interaction zone. These analytical functions can be used to investigate numerically the first-order (and partially higher-order) three-body coupling effects in the processes of excitation, ionization and charge transfer of an atom by ion impact.

Kunikeev, Sh. D.

1999-06-01

397

Convergent-close-coupling calculations for excitation and ionization processes of electron-hydrogen collisions in Debye plasmas  

SciTech Connect

Electron-hydrogen scattering in weakly coupled hot-dense plasmas has been investigated using the convergent-close-coupling method. The Yukawa-type Debye-Hueckel potential has been used to describe the plasma screening effects. The target structure, excitation dynamics, and ionization process change dramatically as the screening is increased. Excitation cross sections for the 1s{yields}2s,2p,3s,3p,3d and 2s{yields}2p,3s,3p,3d transitions and total and total ionization cross sections for the scattering from the 1s and 2s states are presented. Calculations cover the energy range from thresholds to high energies (250 eV) for various Debye lengths. We find that as the screening increases, the excitation and total cross sections decrease, while the total ionization cross sections increase.

Zammit, Mark C.; Fursa, Dmitry V.; Bray, Igor [Australian Research Council Centre for Antimatter-Matter Studies, Curtin University of Technology, GPO Box U1987, Perth, Western Australia 6845 (Australia)

2010-11-15

398

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

399

Infrared absorption by molecular gases as a probe of nanoporous silica xerogel and molecule-surface collisions: Low-pressure results  

NASA Astrophysics Data System (ADS)

Transmission spectra of gases confined (but not adsorbed) within the pores of a 1.4-cm-thick silica xerogel sample have been recorded between 2.5 and 5 ?m using a high-resolution Fourier transform spectrometer. This was done for pure CO, CO2, N2O, H2O, and CH4 at room temperature and pressures of a few hectopascals. Least-squares fits of measured absorption lines provide the optical-path lengths within the confined (LC) and free (LF) gas inside the absorption cell and the half width at half maximum ?C of the lines of the confined gases. The values of LC and LF retrieved using numerous transitions of all studied species are very consistent. Furthermore, LC is in satisfactory agreement with values obtained from independent measurements, thus showing that reliable information on the open porosity volume can be retrieved from an optical experiment. The values of ?C, here resulting from collisions of the molecules with the inner surfaces of the xerogel pores, are practically independent of the line for each gas and inversely proportional to the square root of the probed-molecule molar mass. This is a strong indication that, for the studied transitions, a single collision of a molecule with a pore surface is sufficient to change its rotational state. A previously proposed simple model, used for the prediction of the line shape, leads to satisfactory agreement with the observations. It also enables a determination of the average pore size, bringing information complementary to that obtained from nitrogen adsorption porosimetry.

Vander Auwera, J.; Ngo, N. H.; El Hamzaoui, H.; Capoen, B.; Bouazaoui, M.; Ausset, P.; Boulet, C.; Hartmann, J.-M.

2013-10-01

400

Dynamic plasma screening effects on electron capture process in hydrogenic ion{endash}fully stripped ion collisions in dense plasmas  

SciTech Connect

In dense plasmas, dynamic plasma screening effects are investigated on electron capture from hydrogenic ions by past fully stripped ions. The classical Bohr{endash}Lindhard model has been applied to obtain the electron capture probability. The interaction potential in dense plasmas is represented in terms of the longitudinal dielectric function. The classical straight-line trajectory approximation is applied to the motion of the projectile ion in order to visualize the electron capture probability as a function of the impact parameter, projectile energy, and plasma parameters. The electron capture probability including the dynamic plasma screening effect is always greater than that including the static plasma screening effect. When the projectile velocity is smaller than the electron thermal velocity, the dynamic polarization screening effect becomes the static plasma screening effect. When the projectile velocity is greater than the plasma electron thermal velocity, the interaction potential is almost unshielded. The difference between the dynamic and static plasma screening effects is more significant for low energy projectiles. It is found that the static screening formula obtained by the Debye{endash}H{umlt u}ckel model overestimates the plasma screening effects on the electron capture processes in dense plasmas. {copyright} {ital 1997 American Institute of Physics.}

Jung, Y. [Department of Physics, Hanyang University, Ansan, Kyunggi-Do 425-791, South (Korea)

1997-07-01

401

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

2012-12-31

402

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

403

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

404

Atomic collision cascades in solids  

Microsoft Academic Search

The nature of atomic collision cascades is of importance in a fundamental scientific sense for these events occur widely in nature. They are also important in a technological sense for in solids they initiate the processes of radiation damage, sputtering and ion implantation.Theoretical models of cascades have been developed which depend upon data gathered in diverse experiments in which matter

M. W Thompson

2002-01-01

405

Low Energy Electron Molecule Collisions  

NASA Astrophysics Data System (ADS)

Low energy electron molecule collisions are important in many technological, environmental and biological processes. Electrons are known to be the `drivers' of technological processes based around gas discharges, from lights and lamps to surface processing plasmas. In such environments electrons are responsible for much of the vibrational and electronic excitation that results in photon emissions, for the formation of long-lived metastable species, and for the production of highly reactive free radicals through processes such as dissociative attachment. Electron collisions also play an important role in our atmosphere and those of all planets and stars. In recent years low energy electrons have also been shown to play a vital role in cell and tissue damage caused by ionizing radiation. One of the key goals for collision physics, both experiment and theory, is to provide accurate, absolute cross sections for such low energy charged particle collisions - elastic scattering, vibrational excitation, near-threshold electronic excitation. This talk will focus on some recent advances in these areas. This work is done in collaboration with James Sullivan, Violaine Vizcaino, Stan Newman, Julian Lower, Subhendu Mondal, Chris Colyer, Michael Brunger, Todd Maddern and Leigh Hargreaves.

Buckman, Stephen

2007-06-01

406

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

407

Matter & Interactions Practice Problems: Collisions  

NSDL National Science Digital Library

This web page contains problems to supplement the introductory textbook Matter and Interactions, by Ruth Chabay and Bruce Sherwood. These problems are designed for use with Volume 1, Chapter 9 on collisions. Topics include elastic, inelastic, and head-on collisions. Each problem can be viewed separately, with solutions, or downloaded as a pdf file. The site includes videos showing solutions to many of the problems. These can be followed with RSS or as podcasts from iTunes. Instructors are encouraged to submit their own problems and solutions. Problems should be submitted in LaTeX; ample support is provided for this process on the web site.

Titus, Aaron

2010-01-11

408

Immunohistochemistry of tissue prepared by a molecular-friendly fixation and processing system.  

PubMed

A recently introduced histologic fixative (Universal Molecular Fixative [UMFIX]) has been shown to preserve macromolecules in tissue at ambient temperature. When UMFIX-exposed tissues are processed by a formalin-free, microwave-assisted rapid processing system, the resulting paraffin blocks retain good histomorphology and intact nucleic acids suitable for expression microarray analysis. Because UMFIX may be used as an alternative to formalin, the authors set out to study the effect of this new fixation and processing system on immunohistochemistry (IHC) by analyzing a range of human neoplastic and non-neoplastic specimens. Parallel slices from surgically removed specimens were fixed in formalin and UMFIX and processed in a rapid microwave-assisted tissue processor. IHC was performed following routine procedures. The staining for those antibodies that normally required antigen retrieval was carried out with and without that step. The intensity and pattern of reactions were compared in 144 tissue samples fixed by the two methods using 70 monoclonal and polyclonal antibodies. The intensity of IHC reactions for most cytoplasmic antigens was generally equal or stronger in UMFIX tissues. This was particularly true with intermediate filaments and HercepTest, where the antigen retrieval step became unnecessary. Conversely, there was a decrease in the intensity of reactions for HepPar1, bcl-2, and three nuclear antigens (Ki-67, TTF-1, and estrogen receptor). Increasing their exposure times optimized the sensitivity of the latter four antibodies. The study shows that IHC staining results of tissues fixed in UMFIX and processed by the microwave-assisted system are comparable to those obtained on formalin-fixed, similarly processed specimens. There is an enhancement of the sensitivity of few antibodies in UMFIX-exposed tissue, rendering antigen retrieval unnecessary. This increased sensitivity may be due to the effect of eliminating formalin from fixation and processing or the microwave energy. PMID:16082256

Nadji, M; Nassiri, M; Vincek, V; Kanhoush, R; Morales, A R

2005-09-01

409

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

410

Ab initio study of charge-transfer dynamics in collisions of C{sup 2+} ions with hydrogen chloride  

SciTech Connect

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 C{sup 2+} 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.

Rozsalyi, E.; Vibok, A. [Department of Theoretical Physics, University of Debrecen, P.O. Box 5, H-4010 Debrecen (Hungary); Bene, E. [Institute of Nuclear Research, Hungarian Academy of Sciences, P.O. Box 51, H-4001 Debrecen (Hungary); Halasz, G. J. [Department of Information Technology, University of Debrecen, P.O. Box 12, H-4010 Debrecen (Hungary); Bacchus-Montabonel, M. C. [Laboratoire de Spectrometrie Ionique et Moleculaire, Universite de Lyon (Lyon I), CNRS-UMR5579, 43 Bd. du 11 Novembre 1918, F-69622 Villeurbanne Cedex (France)

2011-05-15

411

ATOMIC AND MOLECULAR PHYSICS: Interference Angle on Quantum Rotational Energy Transfer in Na + Na2 (A1 ?+u, v = 8 ~ b3?0u, v = 14) Molecular Collision System  

NASA Astrophysics Data System (ADS)

In order to study the collisional quantum interference (CQI) on rotational energy transfer in atom-diatom system, we have studied the relation of the integral interference angle and differential interference angle in Na + Na2 (A1 ?+u, v = 8 ~ b3?0u, v = 14) collision system. In this paper, based on the first-Born approximation of time-dependent perturbation theory and taking into accounts the anisotropic effect of Lennard-Jones interaction potentials, we present a theoretical model of collisional quantum interference in intramolecular rotational energy transfer, and a relationship between differential and integral interference angles.

Wang, Wei-Li; Miao, Gang; Li, Jian; Ma, Feng-Cai

2009-12-01

412

The early molecular processes underlying the neurological manifestations of an animal model of Wilson's disease.  

PubMed

The Long-Evans Cinnamon (LEC) rat shows age-dependent hepatic manifestations that are similar to those of Wilson's disease (WD). The pathogenic process in the brain has, however, not been evaluated in detail due to the rarity of the neurological symptoms. However, copper accumulation is noted in LEC rat brain tissue from 24 weeks of age, which results in oxidative injuries. The current study investigated the gene expression profiles of LEC rat brains at 24 weeks of age in order to identify the important early molecular changes that underlie the development of neurological symptoms in WD. Biological ontology-based analysis revealed diverse altered expressions of the genes related to copper accumulation. Of particular interest, we found altered expression of genes connected to mitochondrial respiration (Sdhaf2 and Ndufb7), calcineurin-mediated cellular processes (Ppp3ca, Ppp3cb, and Camk2a), amyloid precursor protein (Anks1b and A2m) and alpha-synuclein (Snca). In addition to copper-related changes, compensatory upregulations of Cp and Hamp reflect iron-mediated neurotoxicity. Of note, reciprocal expression of Asmt and Bhmt is an important clue that altered S-adenosylhomocysteine metabolism underlies brain injury in WD, which is directly correlated to the decreased expression of S-adenosylhomocysteine hydrolase in hepatic tissue in LEC rats. In conclusion, our study indicates that diverse molecular changes, both variable and complex, underlie the development of neurological manifestations in WD. Copper-related injuries were found to be the principal pathogenic process, but Fe- or adenosylhomocysteine-related injuries were also implicated. Investigations using other animal models or accessible human samples will be required to confirm our observations. PMID:23519153

Lee, Beom Hee; Kim, Joo Hyun; Kim, Jae-Min; Heo, Sun Hee; Kang, Minji; Kim, Gu-Hwan; Choi, Jin-Ho; Yoo, Han-Wook

2013-03-21

413

The problems of solar-terrestrial coupling and new processes introduced to the physics of the ionosphere from the physics of atomic collisions  

NASA Astrophysics Data System (ADS)

Further progress in research of solar-terrestrial coupling requires better understanding of solar variability influence on the ionosphere. The most powerful manifestations of solar variability are solar flares and geomagnetic storms. During a flare EUV/X-ray irradiations are completely absorbed in the ionosphere producing SID. During geomagnetic storms precipitations of electrons with energy of several keV (and to a lesser extent protons precipitations) from radiation belts and geomagnetosphere produce additional ionization and low latitude auroras. Considering the physics of ionosphere during the last several decades we have been taking into account three novel processes well known in the physics of atomic collisions. These are Auger effect [S. V. Avakyan, The consideration of Auger processes in the upper atmosphere of Earth. In Abstracts of paper presented at the Tenth scien. and techn. Conf. of young specialists of S.I. Vavilov State Optical Institute, 1974, 29-31.], multiple photoionization of upper, valence shell [S.V. Avakyan, The source of O++ ions in the upper atmosphere, 1979, Cosmic Res, 17, 942 - 943] and Rydberg excitation of all the components of upper atmosphere [S.V. Avakyan, The new factor in the physics of solar - terrestrial relations - Rydberg atomic and molecules states. Conf. on Physics of solar-terrestrial relationships, 1994, Almaty, 3 - 5]. In the present paper the results of bringing these new processes in the ionospheric physics are discussed and also its possible role in the physics of solar-terrestrial coupling is considered. Involving these processes to the model estimations allowed us for the first time to come to the following important conclusions: - Auger electrons play the determinant role at the formation of energy spectrum of photoelectrons and secondary auroral electrons at the range above 150 eV; - double photoionization of the outer shell of the oxygen atom (by a single photon) plays a dominant role in the formation of ionospheric doubly charged positive ions, and Auger effect mainly determines the formation of double- and triple charged ions in the low ionosphere of planets and also comets; - transitions in the Rydberg excited ionospheric atoms and molecules play the main role in generation of new type of upper atmospheric emission - microwave characteristic radiation. The ionospheric O++ ions fill the magnetosphere after geomagnetic storms. These ions scatter the solar radiation in one of the most intense lines with a wavelength of 30.4 nm (He+) and also in the 50.7-, 70.3-, 83.3-83.5-nm lines in geocorona to the nocturnal side, giving rise to additional ionization and optical excitation in the F-region. The first calculations of the excitation rate of Rydberg states by photoelectrons and by auroral electrons (including Auger electrons) were carried out. It was shown that such process can generate the microwave ionospheric radioemission. Such emissions were observed during solar flares and in auroras. We suggest that Rydberg microwave radioemissions which take place during ionospheric disturbances produced by the solar flares and geomagnetic storms can be considered as an agent of influence of solar-geomagnetic activity on the biosphere and also as a factor of Sun-weather-climate links All these results obtained experimental confirmation in space investigations and in some ground-based measurements carried out with radiophysical and optical methods. The new processes which we introduced to the physics of upper atmosphere and ionosphere are now widely used in the ionospheric science for interpretation of spacecraft measurement data (the spacecrafts ISIS, GEOS-1, IMAGE, the satellites DE-1,-B, EXOS-D (AKEBOHO), FAST, Intercosmos-19, -24, -25, the orbital stations "Salut", "Mir"). There is a Russian patent on the method of remote registration of radioactive atmospheric clouds and nuclear weapon tests over the atmosphere by means of optical fluorescence which is based on Auger processes.

Avakyan, Sergei

2010-05-01

414

Collision time-correlation functions in the semiclassical limit. II. Vibrational-rotational energy transfer in molecule-molecule collisions  

Microsoft Academic Search

A semiclassical limit of collisional time-correlation functions is applied to energy transfer in collisions between two molecules. The internal degrees of freedom (vibration and rotation) are treated quantum mechanically while the relative motion is described by classical trajectories for fixed molecular orientations. Hence the theory is well-suited to the analysis of energy and angular distributions in collisions governed by general

Eduardo Vilallonga; David A. Micha

1987-01-01

415

Processing of meteoritic organic materials as a possible analog of early molecular evolution in planetary environments.  

PubMed

The composition of the Sutter's Mill meteorite insoluble organic material was studied both in toto by solid-state NMR spectroscopy of the powders and by gas chromatography-mass spectrometry analyses of compounds released upon their hydrothermal treatment. Results were compared with those obtained for other meteorites of diverse classifications (Murray, GRA 95229, Murchison, Orgueil, and Tagish Lake) and found to be so far unique in regard to the molecular species released. These include, in addition to O-containing aromatic compounds, complex polyether- and ester-containing alkyl molecules of prebiotic appeal and never detected in meteorites before. The Sutter's Mill fragments we analyzed had likely been altered by heat, and the hydrothermal conditions of the experiments realistically mimic early Earth settings, such as near volcanic activity or impact craters. On this basis, the data suggest a far larger availability of meteoritic organic materials for planetary environments than previously assumed and that molecular evolution on the early Earth could have benefited from accretion of carbonaceous meteorites both directly with soluble compounds and, for a more protracted time, through alteration, processing, and release from their insoluble organic materials. PMID:24019471

Pizzarello, Sandra; Davidowski, Stephen K; Holland, Gregory P; Williams, Lynda B

2013-09-09

416

Molecular dynamic simulation of dicarboxylic acid coated aqueous aerosol: structure and processing of water vapor.  

PubMed

Organic monolayers at the surfaces of aqueous aerosols play an important role in determining the mass, heat transfer rate and surface reactivity of atmospheric aerosols. They can potentially contribute to the formation of cloud condensation nuclei (CCN) and are involved in a series of chemical reactions occurring in atmosphere. Recent studies even suggest that organic-coated interfaces could have played some role in prebiotic biochemistry and the origin of life. However, creating reproducible, well-characterized aqueous aerosol particles coated with organic films is an experimental challenge. This opens the opportunity for computer simulations and modeling of these complex structures. In this work, molecular dynamics simulation was used to probe the structure and the interfacial properties of the dicarboxylic acid coated aqueous aerosol. Low molecular weight dicarboxylic acids of various chain lengths and water solubility were chosen to coat a water droplet consisting of 2440 water molecules. For malonic acid coated aerosol, the surface acid molecules dissolved into the water core and formed an ordered structure due to the hydrophobic interactions. The acid and the water are separated inside the aerosol. For other nanoaerosols coated with low solubility acids, phase separation between water and acid molecules was observed on the surface of the particle. To study the water processing of the coated aerosols, the water vapor accommodation factors were calculated. PMID:21479309

Ma, Xiaofei; Chakraborty, Purnendu; Henz, Brian J; Zachariah, Michael R

2011-04-09

417

Annihilation of nematic point defects: pre-collision and post-collision evolution.  

PubMed

The annihilation of the nematic hedgehog and anti-hedgehog within an infinite cylinder of radius R is studied. The semi-microscopic lattice-type model and Brownian molecular dynamics are used. We distinguish among the i) early pre-collision, ii) late pre-collision, iii) early post-collision, and iv) late post-collision stages. In the pre-collision stage our results agree qualitatively with the existing experimental observations and also continuum-type simulations. The core of each defect exhibits a ring-like structure, where the ring axis is set perpendicular to the cylinder symmetry axis. For xi(0)d/(2R) > 1 the interaction between defects is negligible, where xi(0)d describes the initial separation of defects. Consequently, the defects annihilate within the simulation time window for xi(0)d/(2R) < 1. For close enough defects their separation scales as xi(d) [see text] (t(c)- t)(0.4+/-0.1), where t(c) stands for the collision time. In elastically aniso