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The periodicity effect in the two-centre Dirac problem is here analyzed from a physicist's point of view. Some usual physical interpretations and natural assumptions are introduced which collectively lead to the idea that the e/su...
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The periodicity effect in the two-centre Dirac problem is here analyzed from a physicist's point of view. Some usual physical interpretations and natural assumptions are introduced which collectively lead to the idea that the e/sup +/ e/sup -/ pair creation in heavy ion collisions is a heated vacuum de-excitation process. (Atomindex citation 20:023812)
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The recombination dynamics of geminate cation-electron pairs in liquid hexane was studied by combining picosecond optical excitation with sensitive photoconductivity measurements. The experiments monitor the generation of free cha...
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The recombination dynamics of geminate cation-electron pairs in liquid hexane was studied by combining picosecond optical excitation with sensitive photoconductivity measurements. The experiments monitor the generation of free charge carriers by photoassisted geminate pair dissociation. The charge-pair survival probability is given approximately by the photoconductivity signals measured as a function of the delay time between photoionization and infrared photodissociation. The time course of the charge pair annihilation is compared with transient solutions of the Smoluchowski equation governing diffusive recombination in a Coulomb well. Agreement between theory and experiment can only be reached by allowing for a distribution of charge pair separation. Theoretical work relevant to the generation of free electrons and holes (or anions and cations) in electron donor-acceptor materials has been completed. The lowest charge-transfer excited state (CT sub 1 ) of electron donor-acceptor crystals or polymers is demonstrated to be a plausible precursor of free charge carriers when such materials are photoexcited. Rate constants for the dissociation of charge-transfer states are formulated for two approximate descriptions of CT sub 1 : classical ion pair and Wannier exciton. The electric field dependence of the dissociation rate constant is postulated to be given by Onsager's 1934 theory (0-34) of ion pair dissociation. (ERA citation 09:020564)
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The true muon pairs production is experimentally associated with a background of random combinations originating mainly from uncorrelated decays of mesons (pi) and K into muons. Several methods for determining the background have ...
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The true muon pairs production is experimentally associated with a background of random combinations originating mainly from uncorrelated decays of mesons (pi) and K into muons. Several methods for determining the background have been proposed in the past years. The non trivial errors that has to be associated with the 're-combinatorial method' which is the principal focus of this study are estimated. For the sake of comparison the other method currently used in the NA38 experiment, which derives from the same framework, will also be considered. (K.A.). 13 refs. (Atomindex citation 29:006386)
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The prospect of new colliding-beam accelerators capable of producing collisions of highly stripped high-Z ions, at fixed-target energies per nucleon up to 20 TeV or more, has motivated much interest in lepton-pair production from ...
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The prospect of new colliding-beam accelerators capable of producing collisions of highly stripped high-Z ions, at fixed-target energies per nucleon up to 20 TeV or more, has motivated much interest in lepton-pair production from the QED vacuum. The time-dependent and essentially classical electromagnetic fields involved in such collisions contain larger Fourier components which give rise to sizable lepton-pair production in addition to many other exotic particles. The process of electron-positron production with electron capture is a principal beam-loss mechanism for highly charged ions in a storage ring. In this process, the electron is created in a bound state of one of the participant heavy ions (most likely the 1s state), thus changing the ion's charge state and causing it to be deflected out of the beam. There is a long and sometimes controversial history concerning the use of perturbative methods in studying electromagnetic lepton-pair production; however, reliable perturbative calculations have been used as input into design models for the Relativistic Heavy-Ion Collider (RHIC). Applying perturbation theory to these processes at high energies and small impact parameters results in probabilities which violate unitarity, and cross sections which violate the Froissart bound. This evidence, along with the initial nonperturbative studies, suggests that higher-order QED effects will be important for extreme relativistic collisions. Clearly, large nonperturbative effects in electron-pair production with capture would have important implications for RHIC. In this paper, the authors briefly discuss recent progress in nonperturbative studies of the capture problem. In Section 2, they state the Dirac equation for a lepton in the time-dependent external field of a heavy ion which must be solved to compute lepton-capture probabilities. Section 4 surveys results from recent applications of coupled-channel and lattice techniques to the lepton-capture problem.
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The dynamics of how a solvent responds to a solute still remains an unsolved, butcritically important, scientific problem. The prospects for understanding solvation dynamics at a molecular level have increased dramatically recentl...
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The dynamics of how a solvent responds to a solute still remains an unsolved, butcritically important, scientific problem. The prospects for understanding solvation dynamics at a molecular level have increased dramatically recently with experimental refinements in ultrafast spectroscopy of liquids, as well as improvements in computational techniques for the modeling of these processes. In this project we studied the solvation dynamics associated with ion pairs in solution using the relatively new technique of femtosecond terahertz time domain transmission spectroscopy coupled with a theoretical approach based on molecular dynamics simulations. The objective of this proposal was to probe, on a molecular and intermolecular scale both experimentally and theoretically, the mechanisms and timescales involved in both the formation and dynamic behavior of ion pairs in solution. To accomplish this goal we further developed the technique of femtosecond terahertz time domain transmission spectroscopy for the study of dynamic molecular interactions in liquids, closely coupling the spectroscopic results obtained to molecular dynamics calculations. Our results validate terahertz spectroscopy as a technique for the investigation of the solvation dynamics in electrolytic solutions of technological importance.
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The dynamics of how a solvent responds to a solute still remains an unsolved, but critically important, scientific problem. The prospects for understanding solvation dynamics at a molecular level have increased dramatically recent...
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The dynamics of how a solvent responds to a solute still remains an unsolved, but critically important, scientific problem. The prospects for understanding solvation dynamics at a molecular level have increased dramatically recently with experimental refinements in ultrafast spectroscopy of liquids, as well as improvements in computational techniques for the modeling of these processes. In this project we studied the solvation dynamics associated with ion pairs in solution using the relatively new technique of femtosecond terahertz time domain transmission spectroscopy coupled with a theoretical approach based on molecular dynamics simulations. The objective of this proposal was to probe, on a molecular and intermolecular scale both experimentally and theoretically, the mechanisms and timescales involved in both the formation and dynamic behavior of ion pairs in solution. To accomplish this goal we further developed the technique of femtosecond terahertz time domain transmission spectroscopy for the study of dynamic molecular interactions in liquids, closely coupling the spectroscopic results obtained to molecular dynamics calculations. Our results validate terahertz spectroscopy as a technique for the investigation of the solvation dynamics in electrolytic solutions of technological importance.
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We present a description of an experiment which can be used to search for effects of strong electromagnetic fields on the production of e(sup +)e(sup (minus)) pairs in the elastic scattering of two heavy ions at RHIC. A very brief...
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We present a description of an experiment which can be used to search for effects of strong electromagnetic fields on the production of e(sup +)e(sup (minus)) pairs in the elastic scattering of two heavy ions at RHIC. A very brief discussion of other possible studies of electromagnetic phenomena at RHIC is also presented.
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The prospect of new colliding-beam accelerators capable of producing collisions of highly stripped high-Z ions, at fixed-target energies per nucleon up to 20 TeV or more, has motivated much interest in lepton-pair production from ...
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The prospect of new colliding-beam accelerators capable of producing collisions of highly stripped high-Z ions, at fixed-target energies per nucleon up to 20 TeV or more, has motivated much interest in lepton-pair production from the QED vacuum. The time-dependent and essentially classical electromagnetic fields involved in such collisions contain larger Fourier components which give rise to sizable lepton-pair production in addition to many other exotic particles. The process of electron-positron production with electron capture is a principal beam-loss mechanism for highly charged ions in a storage ring. In this process, the electron is created in a bound state of one of the participant heavy ions (most likely the 1s state), thus changing the ion's charge state and causing it to be deflected out of the beam. There is a long and sometimes controversial history concerning the use of perturbative methods in studying electromagnetic lepton-pair production; however, reliable perturbative calculations have been used as input into design models for the Relativistic Heavy-Ion Collider (RHIC). Applying perturbation theory to these processes at high energies and small impact parameters results in probabilities which violate unitarity, and cross sections which violate the Froissart bound. This evidence, along with the initial nonperturbative studies, suggests that higher-order QED effects will be important for extreme relativistic collisions. Clearly, large nonperturbative effects in electron-pair production with capture would have important implications for RHIC. In this paper, the authors briefly discuss recent progress in nonperturbative studies of the capture problem. In Section 2, they state the Dirac equation for a lepton in the time-dependent external field of a heavy ion which must be solved to compute lepton-capture probabilities. Section 4 surveys results from recent applications of coupled-channel and lattice techniques to the lepton-capture problem.
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Electron and positron production in relativistic ion-atom collisions is discussed within the context of the time-dependent Dirac-Hartree approximation to a fully relativistic field theory of the collision. The time-dependent field...
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Electron and positron production in relativistic ion-atom collisions is discussed within the context of the time-dependent Dirac-Hartree approximation to a fully relativistic field theory of the collision. The time-dependent fields are treated classically, and the numerical methods employing basis splines are discussed in detail and contrasted with results obtained from the case of non-relativistic velocities. The results of a one-dimensional model are presented and show a moderately large probability for pair production followed by electron capture. 8 refs., 16 figs. (ERA citation 11:049384)
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